To see the other types of publications on this topic, follow the link: Chemomechanical.
Dissertations / Theses on the topic 'Chemomechanical'
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the top 40 dissertations / theses for your research on the topic 'Chemomechanical.'
Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.
You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.
Browse dissertations / theses on a wide variety of disciplines and organise your bibliography correctly.
1
Spencer, C. I. "Chemomechanical coupling in skeletal muscle." Thesis, Open University, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.383710.
Full text
2
Stolic, Nicole. "Does chemomechanical caries removal affect restoration survival?" Thesis, Malmö högskola, Odontologiska fakulteten (OD), 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:mau:diva-19614.
Full textAbstract:
SyfteDenna systematiska översiktsstudie gjordes i syfte att sammanställa randomiserade kontrollerade studier som jämför fyllningsöverlevnaden där kaviteten preparerats med Carisolv, borr och/eller hand exkavering. Studien gjordes också för att kunna användas till fortsatta studier inom området.Material & MetodDatabassökning i PubMed och Cochrane gjordes. Alla titlar och sammanfattningar lästes, de som var relevanta för denna studie lästes sedan i fulltext. Totalt 9 artiklar inkluderades och varje artikel granskades m h a GRADE modellen för att bestämma studiernas evidensstyrka.Resultat913 tänder behandlades med en av metoderna. Studierna undersökte fyllningsöverlevnaden vid olika uppföljningstillfällen, mellan 6 månader och 2 år. Resultaten visar inga statistiskt signifikanta skillnader för fyllningsöverlevnad mellan de olika metoderna.SlutsatsResultaten visar ingen statistisk skillnad i fyllningsöverlevnad mellan Carisolv och andra metoder för att avlägsna karies. Resultaten kan stödja karies exkavering med Carisolv, eftersom metoden dessutom kan användas för karies exkavering på barn och tandvårdsrädda patienter då metoden är mindre obehaglig och patienten behöver således inte lokalanestesi lika ofta. Dock är studierna inom detta område få samt att de har låg evidensstyrka vilket gör att det behövs fler studier på området med högre evidensstyrka.AimThis systematic review aimed to summarize randomized controlled trials (RCTs) that evaluate the survival rates of restorations, comparing the Carisolv system to hand excavation and/or the conventional drilling method. The aim was also to collect all data in one place to be used for further research.Materials & MethodsA database screening of PubMed and the Cochrane library was performed. One reviewer read all titles and abstracts, those considered of interest were fully scrutinized. A total of 9 articles were included and each was evaluated using the GRADE-system. The studies were appraised to have a low level of evidence.ResultsA total 913 teeth received treatment either with Carisolv, hand excavation and/or drilling. The studies evaluated the success rate of dental restorations at follow-ups between 6 months to two years. The results showed no significant difference in success rate of restorations made either by Carisolv, bur or hand excavation.ConclusionsThe results showed as high success rates for caries removal with Carisolv as with other methods, in terms of restoration survival, and that there was no statistically significant difference between the test group and control group. These results are encouraging for caries removal with Carisolv since it also can be used as an alternative treatment for children and patients with dental fear due to the less painful experience and lesser need for local anesthesia. The present studies on this subject are few and have limited evidence, thus underlining the need for more studies on the subject and studies with higher evidence for further research.
3
Hamama, Hamdi Hosni Hamdan Eldesouki. "Influence of chemomechanical caries removal methods on dentine." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2014. http://hdl.handle.net/10722/202369.
Full textAbstract:
Chemomechanical caries excavation is an excellent example of conservative caries removal methods due to its ability to reliably preserve a greater thickness of caries-affected dentine (CAD). Chemomechanical caries removal (CMCR) agents dissolve the denatured collagen fibrils leaving the sound and partially degraded fibrils intact. Also, one of the main advantages of the CMCR method is its characteristic visual excavation end point sign, after this point, the solution fails to become turbid. Chemomechanical caries removal agents are classified based on their chemistry into sodium hypochlorite (NaOCl)- or enzyme-based CMCR agents.
The aim of this project was to evaluate the efficacy of currently available chemomechanical caries removal methods and their effects on tooth substrate, residual bacteria, and bonding to dentine with either resin- or resin-modified glass ionomer (RM-GIC)-based adhesives. The current project was designed to answer five research questions. The first research question aimed to compare the caries excavation time between CMCR and rotary caries removal methods. According to the outcome of this study, the NaOCl-based CMCR method is more time consuming compared with the enzyme-based CMCR method. Furthermore, no significant difference in caries excavation time was found between the enzymebased CMCR and the caries-detector guided rotary caries excavation method.
The second research question investigated the effects of CMCR methods on surface topography, hardness and chemical structure of dentine. The morphological analysis showed that there was no smear layer formed following enzyme-based CMCR; while it was partially absent after the NaOCl-based CMCR method. Also, the Vickers hardness of residual dentine following both CMCR methods was lower than the hardness of dentine following the rotary caries removal method. Moreover, the outcome of this study also revealed that the CMCR methods investigated had no adverse effect on the chemical structure of dentine.
The third research question was regarding the evaluation of the antibacterial effects of CMCR agents. Accordingly, a study was conducted on coronal cariesfree dentine discs using a modified non-invasive protocol. This confocal laser scanning microscopy study reported that the enzyme-based CMCR agent (Papacarie) showed an antimicrobial effect similar to 2% chlorhexidine gluconate solution (gold standard antibacterial solution). The NaOCl-based CMCR agent (Carisolv) showed a weak antibacterial activity, which could be improved by subsequent application of a silver diamine fluoride and potassium iodide agent.
The ‘adhesion studies section’ of this project consists of three studies and was conducted to answer the fourth and fifth research questions of this project. The outcomes of the first and second studies showed that surface treatment of dentine with 37% phosphoric acid for 5 seconds had no adverse effect on bonding of RMGIC adhesives to both sound and caries-affected dentine, which addressed the fourth research question.
The purpose of the last research question was to evaluate the effect of CMCR method on bonding of MDP-containing self-etch and RM-GIC adhesives to residual caries-affected dentine. It was concluded that CMCR methods had no adverse effects on bonding to dentine and both adhesive systems showed good bond strengths to caries-affected dentine.published_or_final_version
Dentistry
Doctoral
Doctor of Philosophy
4
Lee, Michael V. "Development of chemomechanical functionalization and nanografting on silicon surfaces /." Diss., CLICK HERE for online access, 2007. http://contentdm.lib.byu.edu/ETD/image/etd2023.pdf.
Full text
5
Coy, David Laughlin. "The activation and chemomechanical stoichiometry of cargo-loaded kinesin /." Thesis, Connect to this title online; UW restricted, 1998. http://hdl.handle.net/1773/10530.
Full text
6
Lee, Michael Vernon. "Development of Chemomechanical Functionalization and Nanografting on Silicon Surfaces." BYU ScholarsArchive, 2007. https://scholarsarchive.byu.edu/etd/1435.
Full textAbstract:
Progress in chemomechanical functionalization was made by investigating the binding of molecules and surface coverage on the silicon surface, demonstrating functionalization of silicon with gases by chemomechanical means, analyzing atomic force microscopy probe tip wear in atomic force microscopy (AFM) chemomechanical nanografting, combining chemomechanical functionalization and nanografting to pattern silicon with an atomic force microscope, and extending chemomechanical nanografting to silicon dioxide. Molecular mechanics of alkenes and alkynes bound to Si(001)-2x1 as a model of chemomechanically functionalized surfaces indicated that complete coverage is energetically favorable and becomes more favorable for longer chain species. Scribing a silicon surface in the presence of ethylene and acetylene demonstrated chemomechanical functionalization with gaseous reagents, which simplifies sample cleanup and adds a range of reagents to those possible for chemomechanical functionalization. Thermal desorption spectroscopy was performed on chemomechanically functionalized samples and demonstrated the similarity in binding of molecules to the scribed silicon surface and to the common Si(001)-2x1 and Si(111)-7x7 surfaces. The wearing of atomic force microscope probe tips during chemomechanical functionalization was investigated by correlating change over time and force with widths of created lines to illustrate the detrimental effect of tip wear on mechanically-driven nanopatterning methods. In order to have a starting surface more stable than hydrogen-terminated silicon, silicon reacted with 1-octene was used as a starting surface for AFM chemomechanical functionalization, producing chemomechanical nanografting. Chemomechanical nanografting was then demonstrated on silicon dioxide using silane molecules; the initial passivating layer reduced the tip friction on the surface to allow only partial nanografting of the silane molecules. These studies broadened the scope and understanding of chemomechanical functionalization and nanografting.
7
Cho, Hansohl. "Atomistic simulations of chemomechanical processes in nanomaterials under extreme environments." Thesis, Massachusetts Institute of Technology, 2009. http://hdl.handle.net/1721.1/57788.
Full textAbstract:
Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2009.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 142-146).
The complex chemomechanical behavior of nanomaterials under extreme thermal and mechanical environments is of interest for a range of basic science and defense applications. By the limitation of experimental approaches for objects of nanometer, novel computational methods have been developed to investigate such phenomena in nanomaterials under extreme environments. In this thesis, novel continuum and atomistic mechanical modeling and simulations are implemented and constructed for the analysis of the chemomechanical behavior of the dissimilar nano-scale metals, Nickel and Aluminum under a variety of thermal and mechanical stimuli. These studies form the basis of preliminary research on the predictive design principles for reactive polymer nanocomposites.
by Hansohl Cho.
S.M.
8
Cannon, Bennion Rhead. "Design and Analysis of End-Effector Systems for Scribing on Silicon." BYU ScholarsArchive, 2003. https://scholarsarchive.byu.edu/etd/95.
Full textAbstract:
This thesis investigates end-effector systems used in a chemomechanical scribing process. Chemomechanical scribing is a method of patterning silicon to selectively deposit a monolayer of material on the surface of the silicon. This thesis details the development of a unique end-effector for chemomechanical scribing using a compliant mechanism solution. The end-effector is developed to scribe lines that have uniform geometry and produce less chipping on the surface of the silicon. The resulting scribing mechanism is passively controlled, has high lateral stiffness, and low axial stiffness. The mechanism is analyzed using the pseudo-rigid-body model and linear-elastic beam method to determine the axial stiffness, finite element methods to determine the lateral stiffness, and fatigue analysis to determine mechanism cycle life. This thesis also investigates the significance of mechanical factors on the chemomechanical scribing process using the compliant end-effector. The factors examined are scribing force, scribing speed, tip geometry, wafer orientation, and wetting liquid. The factors are analyzed using a two-step approach: first, an analysis of the influence of the mechanical factors on line characteristics and second, an analysis of the influence of line characteristics on line performance.
9
Bierbaum, Veronika. "Chemomechanical coupling and motor cycles of the molecular motor myosin V." Phd thesis, Universität Potsdam, 2011. http://opus.kobv.de/ubp/volltexte/2011/5361/.
Full textAbstract:
In the living cell, the organization of the complex internal structure relies to a large extent on molecular motors. Molecular motors are proteins that are able to convert chemical energy from the hydrolysis of adenosine triphosphate (ATP) into mechanical work. Being about 10 to 100 nanometers in size, the molecules act on a length scale, for which thermal collisions have a considerable impact onto their motion. In this way, they constitute paradigmatic examples of thermodynamic machines out of equilibrium.
This study develops a theoretical description for the energy conversion by the molecular motor myosin V, using many different aspects of theoretical physics. Myosin V has been studied extensively in both bulk and single molecule experiments. Its stepping velocity has been characterized as a function of external control parameters such as nucleotide concentration and applied forces. In addition, numerous kinetic rates involved in the enzymatic reaction of the molecule have been determined. For forces that exceed the stall force of the motor, myosin V exhibits a 'ratcheting' behaviour: For loads in the direction of forward stepping, the velocity depends on the concentration of ATP, while for backward loads there is no such influence.
Based on the chemical states of the motor, we construct a general network theory that incorporates experimental observations about the stepping behaviour of myosin V. The motor's motion is captured through the network description supplemented by a Markov process to describe the motor dynamics. This approach has the advantage of directly addressing the chemical kinetics of the molecule, and treating the mechanical and chemical processes on equal grounds. We utilize constraints arising from nonequilibrium thermodynamics to determine motor parameters and demonstrate that the motor behaviour is governed by several chemomechanical motor cycles. In addition, we investigate the functional dependence of stepping rates on force by deducing the motor's response to external loads via an appropriate Fokker-Planck equation. For substall forces, the dominant pathway of the motor network is profoundly different from the one for superstall forces, which leads to a stepping behaviour that is in agreement with the experimental observations.
The extension of our analysis to Markov processes with absorbing boundaries allows for the calculation of the motor's dwell time distributions. These reveal aspects of the coordination of the motor's heads and contain direct information about the backsteps of the motor.
Our theory provides a unified description for the myosin V motor as studied in single motor experiments.Die hier vorgelegte Arbeit entwickelt unter Verwendung vieler verschiedener Aspekte der statistischen Physik eine Theorie der chemomechanischen Kopplung für den Energieumsatz des molekularen Motors Myosin V. Das Myosin V ist sowohl in chemokinetischen wie in Einzelmolekülexperimenten grundlegend untersucht worden. Seine Schrittgeschwindigkeit ist in Abhängigkeit verschiedener externer Parameter, wie der Nukleotidkonzentration und einer äußeren Kraft, experimentell bestimmt. Darüber hinaus ist eine große Anzahl verschiedener chemokinetischer Raten, die an der enzymatischen Reaktion des Moleküls beteiligt sind, quantitativ erfasst. Unter der Wirkung externer Kräfte, die seine Anhaltekraft überschreiten, verhält sich der Motor wie eine Ratsche: Für Kräfte, die entlang der Schrittbewegung des Motors wirken, hängt seine Geschwindigkeit von der ATP-Konzentration ab, für rückwärts angreifende Kräfte jedoch ist die Bewegung des Motors unabhängig von ATP. Auf der Grundlage der chemischen Zustände des Motors wird eine Netzwerktheorie aufgebaut, die die experimentellen Beobachtungen des Schrittverhaltens für Myosin V einschließt. Diese Netzwerkbeschreibung dient als Grundlage für einen Markovprozess, der die Dynamik des Motors beschreibt. Die Verwendung diskreter Zustände bietet den Vorteil der direkten Erfassung der chemischen Kinetik des Moleküls. Darüber hinaus werden chemische und mechanische Eigenschaften des Motors in gleichem Maße im Modell berücksichtigt. Durch die Erfassung der Enzymkinetik mittels eines stochastischen Prozesses lässt sich die Motordynamik mit Hilfe des stationären Zustands der Netzwerkdarstellung beschreiben. Um diesen zu bestimmen, verwenden wir eine graphentheoretische Methode, die auf Kirchhoff zurückgreift. Wir zeigen in Einklang mit den Gesetzen der Thermodynamik für Nichtgleichgewichtssysteme, dass das Schrittverhalten des Motors von mehreren chemomechanischen Zyklen beeinflusst wird. Weiterhin untersuchen wir das funktionale Verhalten mechanischer Schrittraten in Abhängigkeit der äußeren Kraft unter Verwendung einer geeigneten Fokker-Planck-Gleichung. Hierfür wird auf die Theorie einer kontinuierlichen Beschreibung von molekularen Methoden zurückgegriffen. Wir berechnen Größen wie die mittlere Schrittgeschwindigkeit, das Verhältnis von Vorwärts- und Rückwärtsschritten, und die Lauflänge des Motors in Abhängigkeit einer äußeren angreifenden Kraft sowie der Nukleotidkonzentration, und vergleichen diese mit experimentellen Daten. Für Kräfte, die kleiner als die Anhaltekraft des Motors sind, unterscheidet sich der chemomechanische Zyklus grundlegend von demjenigen, der für große Kräfte dominiert. Diese Eigenschaft resultiert in einem Schrittverhalten, das mit den experimentellen Beobachtungen übereinstimmt. Es ermöglicht weiterhin die Zerlegung des Netzwerks in einzelne Zyklen, die die Bewegung des Motors für verschiedene Bereiche externer Kräfte erfassen. Durch die Erweiterung unseres Modells auf Markovprozesse mit absorbierenden Zuständen können so die Wartezeitenverteilungen für einzelne Zyklen des Motors analytisch berechnet werden. Sie erteilen Aufschluss über die Koordination des Motors und enthalten zudem direkte Informationen über seine Rückwärtsschritte, die experimentell nicht erfasst sind. Für das gesamte Netzwerk werden die Wartezeitenverteilungen mit Hilfe eines Gillespie-Algorithmus bestimmt. Unsere Theorie liefert eine einheitliche Beschreibung der Eigenschaften von Myosin V, die in Einzelmolekülexperimenten erfasst werden können.
10
Nicol, Irene. "Etching and chemomechanical polishing of compound semiconductors using halogen-based reagents." Thesis, University of Glasgow, 1996. http://theses.gla.ac.uk/1631/.
Full textAbstract:
The reactions of dichlorine and dibromine on compound semiconductors follow a pattern of halogenation of the substrate surface, followed by solvation of the halogenated products and removal of the secondary products in the etchant solutions. The reactions of hypochlorite and hydrogen peroxide follow a similar pattern, beginning with oxidation of the substrate surface, followed by subsequent hydration in the etchant solution and final product removal. The solubility of the products and the action of the polishing pad and abrasive are all critical to the passivation of the surface and the production of a polished substrate. The pH dependence of sodium hypochlorite is explained in terms of its composition. At low pH (<8) the main component of the etchant solution is dichlorine. At high pH (>8) the main component of the etchant solution is hypochlorite anion. Thus hypochlorite solution may be considered as a parallel to dibromine at low pH, but is more consistent with the behaviour of hydrogen peroxide at high pH. Thus, aqueous sodium hypochlorite solution may be formulated as part of the series O-O, O-X, X-X, where X represents a halogen. The General Model for Chemomechanical Polishing is formulated on the basis of the three stages of reaction observed for all the reagents examined: Oxidation of the substrate; solvation/hydration of the oxidation products; removal of the products from the substrate surface. Novel bromine-based organic reagents have been designed, synthesised and used to etch and polish gallium arsenide and cadmium telluride substrates. These compounds have shown that properties such as stock removal rate, pH dependence and selectivity may be predicted and even designed into etchants to produce the optimum conditions for polishing a given substrate.
11
Maragh, Janille Maria. "A multiscale framework for the chemomechanical characterization of ancient heterogeneous materials." Thesis, Massachusetts Institute of Technology, 2021. https://hdl.handle.net/1721.1/130820.
Full textAbstract:
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Civil and Environmental Engineering, February, 2021Cataloged from the official PDF of thesis.
Includes bibliographical references (pages 167-188).
Over the course of hundreds--or sometimes even thousands--of years, ancient building materials have survived environmental exposure, modifications, and restorations, often to an extreme degree. These processes, which have occurred from antiquity all the way to the present, have resulted in materials that are poorly understood both chemically and mechanically. This increases the difficulty of designing conservation, preservation, and restoration strategies to ensure that future generations have access to the same ancient marvels that are accessible today. This is further complicated by the inherent value of cultural heritage materials, which makes it challenging and impractical to obtain this information using large samples.
In this work, a minimally invasive multiscale chemomechanical framework for the study and homogenization of heterogeneous composite materials of unknown composition is presented, with the ultimate goal being the chemomechanical characterization of ancient Roman mortar. First, advanced chemical characterization methods are used with computational techniques to better understand the phases present in a sample, and the application of these techniques to the study of ancient Roman mortar is presented. It is then demonstrated how the techniques developed for this study may be used for other applications, for example in the determination of ancient production technologies and in the understanding of the underlying mechanisms responsible for the durability and time resilience of ancient materials.
In a chemical characterization study of a fragment of the Temple Scroll, the longest and most visually striking of the Dead Sea Scrolls, evaporitic sulfate salts that point to a unique production process are identified. The second half of this thesis demonstrates how chemistry is interfaced with mechanics in the chemomechanical homogenization framework. Instead of directly using ancient Roman concrete, which is of immense cultural value, the homogenization framework is tested on a series of modern mortars produced using ordinary Portland cement, which bear numerous similarities to ancient Roman mortars but are more readily accessible and more easily produced. First, scanning electron microscopy energy dispersive X-ray spectroscopy (SEM-EDS) is used with data clustering algorithms to identify the distribution of phases in each sample.
Next, microindentation is used to assign mechanical properties to each of the chemically distinct phases identified, allowing for the generation of large-area high-resolution maps of mechanical properties. In the final stage of the framework, computational homogenization is performed: the chemomechanical maps are converted to finite element models, which are subjected to uniaxial compression and pure shear simulations to obtain estimates of the effective elastic properties of the samples, which are validated using laboratory compression testing data. Finally, the framework is applied to an ancient mortar sample using phase properties from the literature to estimate its effective elastic properties.
by Janille Maria Maragh.
Ph. D.
Ph.D. Massachusetts Institute of Technology, Department of Civil and Environmental Engineering
12
Paradise, Ranjani Krishnan. "Chemomechanical regulation of integrin activation and cellular processes in acidic extracellular pH." Thesis, Massachusetts Institute of Technology, 2012. http://hdl.handle.net/1721.1/75840.
Full textAbstract:
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Biological Engineering, 2012.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student submitted PDF version of thesis.
Includes bibliographical references (p. 162-176).
It is well established that extracellular pH (pHe) becomes acidic in several important physiological and pathological contexts, including the tumor and wound microenvironments. Although it is known that acidic pHe can have profound effects on cell adhesion and migration processes integral to tumor progression and wound healing, the molecular mechanisms underlying the cellular responses to acidic pHe are largely unknown. Transmembrane integrin receptors form a physical linkage between cells and the extracellular matrix, and are thus capable of modulating cell adhesion and migration in response to extracellular conditions. In this thesis, computational and experimental approaches are used to investigate the role of acidic extracellular pH in regulating activation and binding of integrin [alpha]v[beta]3, and to characterize the consequences for downstream subcellular- and cellular-scale processes. Molecular dynamics simulations demonstrate that opening of the integrin [alpha]v[beta]3 headpiece occurs more frequently in acidic pHe than in normal pHe, and that this increased headpiece opening can be partially attributed to protonation of ASP[beta]127 in acidic pHe. These computational data indicate that acidic pHe can promote activation of integrin [alpha]v[beta]3. This is consistent with flow cytometry and atomic force microscope-enabled molecular force spectroscopy experiments, which demonstrate that there are more activated [alpha]v[beta]3 receptors on live [alpha]v[beta]3 CHO-B2 cell surfaces at acidic pHe than at normal pHe 7.4. Put together, these atomistic- and molecular-level data suggest a novel mechanism of outside-in integrin activation regulation by acidic extracellular pH. Next, the consequences of acid-induced integrin activation for subcellular- and cellular-scale processes are investigated. Kymography experiments show that [alpha]v[beta]3 CHO-B2 cell membrane protrusion lifetime is increased and protrusion velocity is decreased for cells in pHe 6.5, compared to cells in pHe 7.4. Furthermore, [alpha]v[beta]3 CHO-B2 cells in pHe 6.5 form more actin-integrin adhesion complexes than cells in pHe 7.4, and acidic extracellular pH results in increased cell area and decreased cell circularity. Cell migration measurements demonstrate that [alpha]v[beta]3 CHO-B2 cells in pHe 6.5 migrate slower than cells in pHe 7.4, and that the fibronectin ligand density required for peak migration speed is lower for cells in pHe 6.5. Together, these data show that acidic pHe affects subcellular- and cellular-scale processes in a manner that is consistent with increased integrin activation in this condition. Finally, the migration behavior of [alpha]v[beta]3 CHO-B2 cells, bovine retinal microvascular endothelial cells, and NIH-3T3 fibroblasts in an extracellular pH gradient is investigated. Results demonstrate that NIH-3T3 fibroblasts do not exhibit directional preferences in the pHe gradient, but that [alpha]v[beta]3 CHO-B2 cells and bovine retinal microvascular endothelial cells migrate preferentially toward the acidic end of the gradient. These data suggest that acidic extracellular pH may serve as a cue that directs migration of angiogenic endothelial cells to poorly vascularized regions of tumors and wounds. Overall, this thesis research results in multiscale, in-depth understanding of extracellular pH as a critical regulator of cell function, with associated implications for tumor growth, wound healing, and the role of proton pumps in cell migration.
by Ranjani Krishnan Paradise.
Ph.D.
13
Sundaresan, Vishnu Baba. "Biological Ion Transporters as Gating Devices for Chemomechanical and Chemoelectrical Energy Conversion." Diss., Virginia Tech, 2007. http://hdl.handle.net/10919/27891.
Full textAbstract:
This dissertation presents a new class of engineered devices, fabricated from synthetic materials and protein transporters extracted from cell membranes of plants, that use chemomechanical and chemoelectrical energy conversion processes to perform mechanical and electrical work.
The chemomechanical energy conversion concept is implemented in a protein based actuator. The chemical energy is applied as an electrochemical gradient of protons across a membrane assembly formed from phospholipids and SUT4 -a proton-sucrose cotransporter. The membrane assembly forms a physical barrier between two chambers in the actuator. The SUT4 proteins in the membrane assembly balances the applied electrochemical gradient by a concentration gradient of sucrose across the membrane. The sucrose gradient simultaneously generates an osmotic flow which deforms a flexible wall in a constrained chamber of the actuator, thus exhibiting mechanical strain. The sucrose concentration balanced by the protein transporter is used as the control variable for fluid flow through the membrane. The transport properties of the membrane assembly has been characterized for the control variable in the system. The reaction kinetics based model for solute transport through the cotransporter is modified to compute the equilibrium constant for solute binding and fluid translocation rate through the membrane. The maximum initial flux rate through the membrane is computed to be 2.51+/-0.6 ul/ug.cm^2.min for an applied pH4.0/pH7.0 concentration gradient across the membrane. The flux rate can be modulated by varying the sucrose concentration in the actuator. The prototype actuator has been fabricated using the characterized membrane assembly. A maximum deformation of 60microns at steady state is developed by the actuator for 20 mM sucrose concentration in the system.
The chemoelectrical energy conversion concept is based on the electrogenic proton pumps in plasma and vacuolar membranes of a plant cell. A prototype device referred to as a BioCell demonstrates the chemoelectric energy conversion using V-type ATPase extracted from plant cell membranes. The enzyme in the bilayer lipid membrane hydrolyzes ATP and converts the chemical energy from the reaction into a charge gradient across the membrane. Silver-silver chloride electrodes on both the sides of the membrane convert the charge established by the proton pumps into cell voltage. The redox reactions at the surface of the electrodes result in a current through the external load connected to the terminals of the BioCell. The single cell behaves like a constant current power source and has an internal resistance of 10-22kOhms. The specific power from the cell of the membrane assembly is estimated to be around 2microwatts/sq/cm. The demonstration of chemoelectrical energy conversion shows the possibility to use ATP as an alternative source of electrical power to design novel chemo-electro-mechanical devices.Ph. D.
14
Schmidt, Matthias [Verfasser], Jan [Akademischer Betreuer] Kierfeld, and Ute [Gutachter] Löw. "Chemomechanical simulation of microtubule dynamics / Matthias Schmidt ; Gutachter: Ute Löw ; Betreuer: Jan Kierfeld." Dortmund : Universitätsbibliothek Dortmund, 2020. http://d-nb.info/1232075248/34.
Full text
15
Abuhaikal, Muhannad (Muhannad A. R. ). "Nano-ChemoMechanical assessment of Rice Husk Ash cement by wavelength dispersive spectroscopy and nanoindentation." Thesis, Massachusetts Institute of Technology, 2011. http://hdl.handle.net/1721.1/66856.
Full textAbstract:
Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2011.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 188-195).
Cement global production stands at 3 Giga tons making concrete the most consumed structural mateial worldwide. This massively produced material comes with a heavy environmental footprint rendering the cement industry contributing about 5% to global CO₂ emission. Rice Husk Ash (RHA) among many other silicious materials, has the potential to partially replace cement and enhance the properties of the final product. The goal of this thesis is an investigation of the fundamental properties of RHA cement. For a set of RHA cement paste samples, we investigate at the nano-scale the effect of RHA incorporation on chemical and mechanical properties of cement. RHA is found to have high pozzolanic properties through its reaction with portlandite to form different types of calcium silicate hydrate (C-S-H). It is found that C-S-H in RHA cement has lower Ca/Si ratios compared to pure ordinary portland cement (OPC) samples prepared under the same conditions. Incorporation of RHA has minor effect on the mechanical properties of cement paste at the nano scale for low water-to-binder ratios while significant improvement in mechanical properties is found at high water-to-binder ratios. We arrive at these conclusions as a result of a dual chemical-mechanical analysis at the nanoscale in which electron probe microanalysis (EPMA) and nanoindentations are employed.
by Muhannad Abuhaikal.
S.M.
16
Silva, Emílio César Cavalcante Melo da. "Effects of water on chemomechanical instabilities in amorphous silica : nanoscale experiments and molecular simulation." Thesis, Massachusetts Institute of Technology, 2007. http://hdl.handle.net/1721.1/42221.
Full textAbstract:
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2007.Includes bibliographical references (leaves 95-103).
We elucidate the tensile failure mechanism of amorphous silica and the effects of water on the process, combining: (a) atomic force microscope (AFM) bending tests, (b) molecular dynamics (MD) simulation and (c) molecular orbital (MO) simulation. Bending tests of silica nanowires provide validation for the predictions of the simulations, in which we study the failure of dry silica using MD and define a representative system to be studied with the more chemically accurate MO method. We used the AFM to perform bending tests on silica nanowires of diameter D < 1 [mu]m, which have very high surface-to-volume ratio and no microscopic flaws. No size effects on elastic modulus were observed down to 130 nm. For 500 nm wires, water reduces the strength from 10.5 GPa in air to 6.5 GPa in water, results comparable to those reported for micrometer-scale fibers. By probing the strength of silica at this scale, we bring experiments to the length scales accessible to atomistic simulation. Using classical MD, we found that crystalline silica fails globally by crack nucleation, but amorphous silica displays plastic deformation due to the formation of local defects, which cascade into larger compound defects. We extend to amorphous systems the instability criterion for material failure and use the Lanczos iteration method to isolate unstable modes. Failure of these modes create local defects, which are used to define a simpler representative system. We studied the water effect on these defects using a semi-empirical MO method, showing first that a water dimer is sufficient to lower the strength of a single Si-O-Si bond. Next, we use a representative system to describe the failure mechanism near instability.
(cont.) We found that water reduces the tensile strength by both reducing the athermal failure strain and the energy barrier for failure. In summary, we demonstrate experimentally that the tensile strength of amorphous silica is governed by the nanoscale crack initiation event, after which the system fails in a brittle manner. Using a multiscale approach, we describe the nanoscale mechanism through MD simulation and the effect of water through MO simulation, bridging the gap between breaking a single bond and breaking a macroscopic body in tension.
by Emílio César Cavalcante Melo da Silva.
Ph.D.
17
Thompson, Michael Todd. "Quantifying effects of substrata chemomechanical properties on eukaryotic and prokaryotic cell adhesion and morphology." Thesis, Massachusetts Institute of Technology, 2008. http://hdl.handle.net/1721.1/45915.
Full textAbstract:
Thesis (Ph. D.)--Harvard-MIT Division of Health Sciences and Technology, 2008.Includes bibliographical references (p. 193-201).
It is now widely accepted that cells are capable of processing both mechanical and chemical signals from the extracellular environment. Exactly how these two factors affect the cell biology in the context of physiological circumstances is an area of intense interest that has given rise to an entire field of study called cell mechanotransduction. The unambiguous decoupling of mechanical and chemical properties that stimulate cell development and phenotypic change is challenging from an experimental standpoint. This thesis describes some of the first studies of chemomechanical coupling arising from anchorage-dependent forces between cells and a versatile class of chemically and mechanically tunable polymer thin films, termed polyelectrolyte multilayers. Specifically, investigation of the effects of extracellular chemomechanical stimulation on cell morphology and adhesion in the eukaryotic cells such as vascular endothelial cells and fibroblasts; and the adhesion of prokaryotic cells S. epidermidis and E. coli are presented. Endothelial cells (EC) comprise a major portion of the cell population in the human body. Because of the extensive distribution of endothelial cells in various tissues, they function across a broad range of mechanical and chemical environments. Furthermore, a general understanding of how mechanical forces contribute to the development of cellular function is an important aspect in the development of therapeutic techniques and materials capable of addressing a wide spectrum of human diseases and injuries. Cell adhesion to extracellular matrices and tissues can be indicative of underlying molecular processes in both healthy and disease states.
(cont.) Through the use of a mechanically tunable class of polymer thin films called polyelectrolyte multilayers (PEMs) developed by Rubner et al., we have demonstrated that the adhesion and morphology of human microvascular endothelial cells depend directly on the mechanical stiffness of these synthetic substrates, as quantified by the nominal elastic modulus E. Characterization of the mechanical properties and surface features of PEMs is attained via scanning probe microscopy (SPM) and SPM-enabled nanoindentation. Typical cellular response to increased substrata stiffness includes increased number of cells adhered per unit substratum area. We have further demonstrated that the chemical and mechanical signals imposed at the cell-substrata interface can be decoupled, thereby providing two independent parameters capable of controlling cell behavior. This capacity of the cell to sense and/or exert chemical and mechanical forces, in addition to initiating a sustained molecular response, is termed the chemomechanical response element. Finally, adhesion dependent mechanosensation in bacteria is explored, with respect to the chemomechanical response elements common to eukaryotic and prokaryotic cells. Potential applications towards the development of therapeutic materials and compounds for treatment of various disease states are discussed, with particular attention to limiting hospital acquired infections.
by Michael Todd Thompson.
Ph.D.
18
Kelby, Timothy Simon. "Smart brushes on flexible substrates : probing the chemomechanical properties of stimulus-responsive polymer brushes." Thesis, University of Cambridge, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.610331.
Full text
19
Bierbaum, Veronika Verfasser], and Reinhard [Akademischer Betreuer] [Lipowsky. "Chemomechanical coupling and motor cycles of the molecular motor myosin V / Veronika Bierbaum. Betreuer: Reinhard Lipowsky." Potsdam : Universitätsbibliothek der Universität Potsdam, 2011. http://d-nb.info/1015077870/34.
Full text
20
Bierbaum, Veronika [Verfasser], and Reinhard [Akademischer Betreuer] Lipowsky. "Chemomechanical coupling and motor cycles of the molecular motor myosin V / Veronika Bierbaum. Betreuer: Reinhard Lipowsky." Potsdam : Universitätsbibliothek der Universität Potsdam, 2011. http://d-nb.info/1015077870/34.
Full text
21
Khadka, Suraj. "A Numerical Study of the Coupled Geomechanical Processes in Sinkholes." University of Toledo / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1532970968316002.
Full text
22
Jagannathan, Deepak. "Calcium-Silicate-Hydrate in cementitious systems : chemomechanical correlations, extreme temperature behavior, and kinetics and morphology of in-situ formation." Thesis, Massachusetts Institute of Technology, 2013. http://hdl.handle.net/1721.1/92651.
Full textAbstract:
Thesis: S.M., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2013.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 96-102).
Concrete, the second most used material on the planet, is a multi-scale heterogeneous material. A fundamental component known as Calcium-Silicate-Hydrate which forms from the reaction between cement and water is the binding phase in concrete. Curiously, this is the least understood component of concrete because of its porous amorphous structure. Further, beyond mere scientific curiosity, cementS̆s industry large carbon footprint due to its volume of usage sets up a practical context to seek improvements in concrete performance and equip concrete with additional functionalities. It is our contention that we can better understand the least known and crucial component of concrete, Calcium-Silicate-Hydrate, to inform the design of next generation of high performance concrete. With this broad theme, this thesis presents three different aspects of properties of Calcium Silicate Hydrate: chemomechanical correlations, behavior under extreme temperature and pressures, and kinetics and nanostructure of in-situ formation. Calcium Silicate Hydrate (C-S-H) formed in-situ in concrete is believed to have a layered structure with silicate chains similar to crystal structures of Tobermorite and Jennite. Its chemical composition, characterized by Ca/Si ratio, must therefore influence its silicate chain structure and thus its mechanical properties. We explore the correlation between CS- H composition and its mechanical properties. By varying chemical composition of cement clinkers and supplementary cementitious materials, water/cement ratios, and hydration temperatures, we prepare cement pastes with different C-S-H of different C/S ratios. We use nanoindentation and X-ray spectroscopy to respectively measure the mechanical properties and composition of C-S-H. We then study the mechanical performance of C-S-H at elevated temperatures. This is relevant in the design of infrastructure that can sustain extreme events such as blasts and high velocity impacts. As a starting point for concrete that would enable such infrastructure, we use ultra high performance concrete (UHPC). We use nanoindentation and X-ray spectroscopy to respectively measure mechanical properties and composition of individual components of UHPC. We compare the composition and properties of C-S-H found in UHPC to that found in ordinary cement pastes (OPC). Our grid nanoindentation experiments also reveal an artifacts created by the incorporation of steel fiber reinforcements in UHPC. We find that steel fiber reinforcements disrupt the perfect packing of constituent materials in UHPC to create capillary porosity at microscale. Further, we study the mechanical properties of C-S-H in concrete specimens subjected to high temperatures of 400°C and 1000°C. As a product of the reaction between cement and water, the properties of C-S-H are ultimately controlled by the reaction. To obtain quantitative kinetics, we use time-lapse optical microscopy to study hydration of micron sized monoclinic C₃S particles with in droplets of water of 50 [mu]m. Using Raman spectroscopy, we characterize the hydration product growing inside these droplets.
by Deepak Jagannathan.
S.M.
23
Panthi, Sadrish. "Exploring a Distinct Element Method Approach for Coupled Chemo-Mechanical Mechanisms in Geomaterials." University of Toledo / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1388742157.
Full text
24
Zhang, Kuan. "Chemomagnetooptically controlled nanomotors for (bio)contaminant removal in water." Doctoral thesis, Universitat Autònoma de Barcelona, 2019. http://hdl.handle.net/10803/668667.
Full textAbstract:
El objetivo de la tesis es desarrollar nanomotores autónomos de silicio/metal activados fotoelectroquímicamente, explorar y comprender los mecanismos involucrados en el proceso de propulsión y analizar su posible aplicación en la eliminación de (bio)contaminantes en el agua a través de la generación in situ de especies reactivas de oxígeno. Básicamente se ha centrado en nanomotores de Si/Pt, que pueden autopropulsarse a partir de la descomposición fotoquímica del H2O2 bajo luz blanca y también con capacidades para ser activados por luz NIR.
Se ha desarrollado un método fácil para fabricar nanoestructuras de silicio a gran escala como núcleo de los nanomotores utilizando litografía coloidal conjuntamente con corrosión química asistida por metal. Se lograron nanoestructuras de silicio con diferentes dimensiones, morfologías superficiales y porosidades.
La actuación fotoquímica de los nanomotores de Si/Pt se evaluó en función del factor de rugosidad del catalizador de Pt. Las nanoestructuras de Si/Pt con bajo factor de rugosidad en el metal exhibieron escaso movimiento, mientras que las nanoestructuras de Si/Pt con alto factor de rugosidad en el metal mostraron un movimiento direccional sustancial pero insensible a la modulación de la luz. La evaluación del desempeño del nanomotor de Si/Pt en la degradación de contaminantes orgánicos en agua proporcionó indicios de dos vías químicas competitivas en la descomposición del H2O2, que finalmente dictaminaron el mecanismo de propulsión dominante. Este resultado se respaldó comparando el rendimiento nanomotor con el de sus contrapartes inmovilizadas, es decir, bombas de Si/Pt con diferentes factores de rugosidad de Pt. Se demostró que existen dos mecanismos de propulsión competitivos en los motores de Pt/Si en presencia de luz dependiendo de la ruta de descomposición del H2O2. Uno es un proceso electro-osmótico que emerge de reacciones redox fotoactivadas mediadas por el Si como ánodo y el Pt como cátodo y que ocurre preferentemente cuando el Pt tiene baja rugosidad. La otra es la difusio-ósmosis que es insensible a la luz y se desencadena por la descomposición redox del H2O2 exclusivamente en la superficie rugosa de Pt. Por lo tanto, se puede mostrar que el mecanismo de actuación de los motores Pt/Si puede cambiarse desde un mecanismo electrocinético controlado por luz a difusio-ósmosis insensible a la luz aumentando la rugosidad de la superficie del metal. Además, el aumento de la rugosidad en Pt redujo en gran medida la generación de especies reactivas de oxígeno en el motor, las cuales ocurren cuando el peróxido de hidrógeno se descompone por reacciones redox foctoactivadas en lugares distintos del motor (en el Si como ánodo y en el Pt como cátodo). Esto hizo que disminuyese la capacidad del motor como agente de degradación de contaminantes.
En la parte final del trabajo de tesis, se logró desarrollar un motor con control fotoquímico en base a un microdiodo de silicio/Au con uniones p-n. Este sistema ayudó a establecer los criterios para desarrollar micro/nanomotores eficientes sensibles a luz en base a silicio. La unión n-p ayuda a maximizar las reacciones fotoredox entre el Si y el metal noble mediante el campo eléctrico auto-generado en la unión y que favorece la separación agujero/electrón. Además, se llegó a la conclusión de que el perímetro de la interfaz debería ser lo suficientemente grande y la superficie del metal noble debería presentar bajos factores de rugosidad.
Finalmente, se desarrolló un nanomotor basado en Si/ Fe de valencia cero que resultó muy prometedor para la degradación de contaminantes orgánicos bajo luz visible. Este nanosistema proporcionó una importante contribución de especies reactivas de oxígeno mediante el efecto fotocatalítico, aparte de la contribución proporcionada por la reacciones Fenton producidas por el hierro mismo.
Esta tesis ha logrado un progreso relevante en la comprensión de micro/nanomotores fotocatalíticos basados en silicio y ha demostrado que estos sistemas tienen un gran potencial para futuras aplicaciones prácticas. Sin embargo, todavía se necesita mucho trabajo para seguir mejorando y optimizando el motor, lo que garantiza la continuación de esta línea de investigación.The goal of the thesis is to develop photoelectrochemically activated silicon/metal autonomous nanomotors, to explore and understand the mechanisms involved in the propulsion process, and to analyse their potential application in (bio) contaminant removal in water through their in-situ generation of reactive oxygen species. We have basically focused on Si/Pt nanomotors which can self-propel from the photochemical decomposition of H2O2 triggered by white light illumination and with also capabilities to be activated by NIR light. We have developed a facile method to fabricate large scale of silicon nanostructures as core of the nanomotors using colloidal lithography in conjunction with metal-assisted etching. Silicon nanostructures with different dimensions, surface morphologies, and porosities were accomplished. We have evaluated the photochemical actuation of Si/Pt nanomotors with different roughness factors at the Pt catalyst. Si/Pt nanostructures with low metal roughness factor hardly moved but Si/Pt nanostructures with high metal roughness factor exhibited a substantial directional motion but insensitive to light modulation. Evaluation of the Si/Pt nanomotor performance for degradation of benzene based pollutants in water provided hints of two competing chemical pathways in H2O2 decomposition, which finally dictate the dominant propulsion mechanism. Such finding was supported by comparing the nanomotor performance with the one of their immobilized counterparts Si/Pt pumps with different Pt roughness factors. It was demonstrated that there are two competing propulsion mechanisms at the Pt/Si motors under light illumination depending on the H2O2 decomposition pathway. One is an electro-osmotic process which stemmed from a separated photoactivation redox reaction mediated by Si as anode and smooth Pt as cathode. The other is diffusion-osmosis and not light responsive and is triggered by the redox decomposition of H2O2 exclusively at the rough Pt surface. Therefore we could show that the actuation mechanism of the Pt/Si motors can be switched from light-controlled electrokinetics to light-insensitive diffusio-osmosis by only increasing the metal surface roughness. Moreover the increased roughness in Pt greatly decreased the motor generation of reactive oxygen species, which are expected to take place from a photochemical separated redox reaction at anode and cathode, and hence decreasing the motor capability as pollutant degradation agent. In the final part of the thesis work, we have successfully achieved a photochemical-controlled silicon/Au microdiode with p-n heterojunctions which has aided to settle the criteria to build up optimized light sensitive silicon based micro/nanomotors. The n-p junction helps to maximize separated photoredox reactions between Si and noble metal by the built-in electric field which favours the hole/electron separation. Moreover, it was concluded that the perimeter of the interface should be large enough and the surface of noble metal should exhibit low roughness factors. Finally we have found a promising nanomotor based on Si/zero-valent iron (ZVI) for relevant organic degradation performance under visible light illumination through the generation of reactive oxygen species. This nanosystem has provided an important contribution of the photocatalytic effect for the overall generation of ROS apart from the contribution provided by the iron Fenton reaction. This thesis has accomplished a relevant progress in understanding silicon based photocatalytic micro-/nanomotors and it has shown that these systems hold great potential for future practical applications. However, much work is still needed to continue improving and optimizing the engine, which guarantees the continuation of this line of research.
25
Chen, Irene Chou. "Chemomechanics of self-oscillating gels." Thesis, Massachusetts Institute of Technology, 2013. http://hdl.handle.net/1721.1/81678.
Full textAbstract:
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 2013.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 167-173).
Biological materials such as cardiac and skin tissue exhibit the unique capacity to transduce mechanical stimuli into propagating electrical and chemical signals throughout the body. Few synthetic materials have been engineered to produce communicative chemical signals in response to mechanical input, though such synthetic material analogues could enable devices that mimic biological tissues and pressure sensitive processes whereby molecular mechanoreceptors enable rapid and localized transmission of chemical signals. In this thesis, self-oscillating polymer gels comprising N-isopropylacrylamideco- Ru(bpy) 3 are synthesized in order to elucidate chemical and mechanical (chemomechanical) coupling in synthetic, stimuli-responsive materials, and to design mechanically induced, oscillatory signaling systems. N-isopropylacrylamide-co-Ru(bpy) 3 gels represent a unique class of polymeric materials known as BZ gels, that are capable of undergoing the Belousov- Zhabotinsky (BZ) self-oscillating reaction. When submerged in stagnant solution containing chemical reactants, and in the absence of continuously applied external perturbation, the BZ gels exhibit sustained, colorful oscillations due to the changing oxidation state of Ru(bpy)3 transition metal complex. By measuring temperature profiles of the BZ gel, we showed that the swelling behavior and hydrophobicity of the gel depend on the oxidation state of covalently bound Ru(bpy) 3 . Using timelapse microscopy, we recorded the BZ oscillations and tracked the far from equilibrium chemical behavior exhibited by the gels. At constant system temperature, the BZ reaction induced cyclic changes in the osmotic pressure of the gel, resulting in periodic gel swelling and shrinking. Such volumetric changes, driven by the BZ reaction, are largest (22 %) when the edge length of the gel is relatively short (0.6 mm), and pattern formation is dominated by slow kinetics. Therefore, by quantifying the chemomechanical behavior of BZ gels, we demonstrated that the gels convert chemical oscillations into mechanical actuation. Next, we sought to design novel stimuli-responsive behavior in BZ gels by devising methods for mechanically triggering oscillations in quiescent gels. When sufficient macroscopic compressive stress was applied to submerged, non-oscillating gels, BZ oscillations were triggered and persisted until the stress was removed. To our knowledge, BZ gels represent the first synthetic hydrogel capable of producing oscillations in response to mechanical stimuli. To establish the conditions conducive to mechanical triggering, we quantified the chemical regimes for which BZ gels spontaneously oscillate or fail to oscillate. In doing so, we demonstrated that such regimes are governed by the ratio of inhibitor to activator species, which are both intermediate species that are produced throughout the reaction, providing negative and positive chemical feedback, respectively. Mechanically triggerable conditions corresponded to an intermediate ratio of reactant to inhibitor species, such that mechanical compression enabled transitions near the boundary dividing the non-oscillatory and oscillatory regimes. By varying the crosslinking density of the material, we also showed that both the required stress and strain for inducing oscillations in BZ gels increased with decreasing polymer volume fraction. Application of macroscopic, compressive stress to BZ gels caused a decrease in overall gel volume and an increase in the concentration of Ru(bpy) 3 , and oscillations were triggered at a critical concentration of Ru(bpy)3. In demonstrating that BZ gels can sense mechanical pressure and respond by transducing such energy into chemical oscillations, we have opened up new avenues of research based on mechanical sensing in BZ gels. Finally, we explore the mechanisms of synthetic "communication" in which discrete BZ gels sense mechanical stress and transmit chemical signals to neighboring gels. Specifically, we designed arrays of closely spaced gels (0.2 mm gap distance) that communicate via diffusion of activator species. We demonstrated that mechanical triggering can induce wave directionality to a set of gels that would otherwise exhibit disorder, and can propagate signals that change directions by migrating around bends without decay in signal amplitude. By introducing a node to a set of BZ gels, we showed that the BZ signal can split without attenuation, effectively doubling the system output. Last, we quantified the collision of two mechanically induced signals to show that wave collision occurs without amplification, and results in signal extinction. Taken altogether, these studies of signal propagation in BZ gels demonstrate that the underlying mechanism of BZ gel communication is governed by the diffusion of activator species. In addition to demonstrating for the first time a synthetic hydrogel that is capable of generating oscillations in response to mechanical compression, we have shown that BZ gels can propagate mechanically induced signals over long ranges and complex trajectories. Our results can be used to facilitate understanding of complex biological phenomena involving chemomechanical coupling and mechanotransduction, or to design advanced, functional materials that act as pulsating chemical or pressure sensors.
by Irene Chou Chen.
Ph.D.
26
Maloney, John Mapes. "Chemomechanics of attached and suspended cells." Thesis, Massachusetts Institute of Technology, 2012. http://hdl.handle.net/1721.1/75846.
Full textAbstract:
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2012.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student submitted PDF version of thesis.
Includes bibliographical references (p. 173-184).
Chemomechanical coupling in single eukaryotic animal cells is investigated in the con- text of the attached (substratum-adhered) and the suspended (free-floating) states. These dichotomous configurations determine behavioral differences and commonalities relevant to therapeutic reimplantation of stem cells and to our general under- standing of the cell as an animate material. Analytical, simulation, and experimental techniques are applied to key questions including: (1) How deep can mechanosensitive attached cells "feel" into the adjacent environment? (2) In what manner do suspended cells deform, absent the prominent actomyosin stress fibers that arise upon attachment to a rigid substratum? (3) What explains the remarkable mechanical heterogeney among single cells within a population? (4) Can we leverage putative mechanical markers of useful stem cells to sort them before reimplantation in tissue generation therapies? Attached cells are found to barely detect an underlying rigid base more than 10 micrometers below the surface of a compliant coating. This conclusion, based on ex- tensions to the Boussinesq problem of elasticity theory, is validated by observations of cell morphology on compliant polyacrylamide coatings in a range of thicknesses. Analytical equations are developed for estimating the effective stiffness sensed by a cell atop a compliant layer. We also identify and consider conceptualizations of a "critical thickness," representing the minimum suitable thickness for a specific application. This parameter depends on the cell behavior of interest; the particular case of stem cell culture for paracrine extraction is presented as a case study. Suspended cells are found to exhibit no single characteristic time scale during de- formation; rather, they behave as power-law (or "soft glassy") materials. Here, optical stretching is used as a non-contact technique to show that stress fibers and probe-cell contact are not critical in enabling power-law rheological behavior of cells. Further- more, suspended cell fluidity, as characterized by both the hysteresivity of complex modulus and the power-law exponent of creep compliance, is found to be unaffected by adenosine triphosphate (ATP) depletion, showing that ATP hydrolysis is not the origin of fluidity in cells during deformation. However, ATP depletion does reduce the natural variation in hysteresivity values among cells. This finding, and the finding that changes in the power-law exponent and stiffness of single cells are correlated upon repeated loading, motivates study of how and why these parameters are coupled. To further explore this coupling, chemomechanical cues are applied to cell populations to elucidate the origin of the wide, right-skewed distribution of stiffness values that is consistently observed. The distribution and width are found to be not detectably dependent on cell-probe contact, cell lineage, cell cycle, mechanical perturbation, or fixation by chemical crosslinking. However, ATP depletion again reduces heterogeneity, now in the case of cell stiffness values. It is further found analytically that a postulated Gaussian distribution of power-law exponent values leads naturally to the log-normal distribution of cell stiffness values that is widely observed. Based on these connections, a framework is presented to improve our understanding of the appearance of mechanical heterogeneity in successively more complex assemblies of cell components. Two case studies are described to explore the implications of unavoidable intrinsic variation of cell stiffness in diagnostic and therapeutic applications. Finally, all the single-cell mechanical parameters studied so far (stiffness during creep and recovery, stiffness heterogeneity among cells, and power-law exponents in creep and recovery) are characterized in mesenchymal stem cells during twenty population doublings with the aim of developing a high-throughput sorting tool. How- ever, mechanical and structural changes that are observed in the attached state during this culture time are not observed after cell detachment from the substratum. The absence in the suspended state of these alterations indicates that they manifest themselves through stress fiber arrangement rather than cortical network arrangement. While optical stretching under the present approach does not detect mechanical markers of extended passaging that are correlated with decreased differentiation propensity, the technique is nevertheless found capable of investigating another structural transition: mechanical stiffening over tens of minutes after adherent cells are suspended. This previously unquantified transition is correlated with membrane resorption and reattachment to the cortex as the cell "remodels" after substratum detachment. Together, these quantitative studies and models of attached and suspended cells de- fine the extremes of the extracellular environment while probing mechanisms that con- tribute to cellular chemomechanical response. An integration of the results described above shows that no one existing model can describe cell chemomechanics. However, the cell can be usefully described as a material -- one in which animate mechanisms such as active contraction will generally, but not invariably, need to be considered as augmenting existing viscoelastic theories of inanimate matter.
by John Mapes Maloney.
Ph.D.
27
Corrêa, Fernanda Nahás Pires. ""Avaliação da dentina remanescente após remoção de cárie com instrumento cortante rotatório e métodos químico-mecânicos, utilizando análise de microdureza, fluorescência laser e MEV"." Universidade de São Paulo, 2006. http://www.teses.usp.br/teses/disponiveis/23/23132/tde-06032006-124318/.
Full textAbstract:
Este trabalho in vitro teve objetivo de avaliar a superfície dentinária remanescente após remoção de tecido dentinário cariado, com instrumento cortante rotatório em baixa rotação e dois métodos químico-mecânicos (Papacárie® e Carisolv®) através da fluorescência laser (DIAGNOdent), microdureza e microscopia eletrônica de varredura. Na primeira fase do estudo, trinta incisivos decíduos com lesão de cárie em uma das faces proximais provenientes do Banco de Dentes Humanos da FOUSP foram avaliados antes e após a remoção do tecido cariado, pela fluorescência laser, sendo posteriormente preparados avaliação da microdureza . O teste de microdureza foi realizado em diferentes distâncias abaixo da dentina tratada após remoção do tecido cariado (50, 100, 150, 200, 300, 400 e 500µm) e do lado hígido (100, 150, 200, 300, 400, 500, 1000 e 1500 µm). Posteriormente, mais 30 dentes decíduos cariados foram divididos em três grupos de acordo com os diferentes tipos de tratamento para análise em MEV, sendo 15 dentes para análise do substrato e 15 dentes para observação de réplicas. Para obtenção destas, os dentes foram restaurados com o adesivo Single Bond (3M) e resina Filtek Z100 (3M) para avaliação de tags (15). Concluiu-se que houve diferença estatisticamente significante nos valores de fluorescência laser da dentina cariada e da dentina após a remoção do tecido cariado, não havendo influência dos tipos de tratamento utilizados. A análise estatística da microdureza mostrou que a dureza da dentina remanescente após remoção do tecido cariado foi menor que aquela obtida do lado hígido, não havendo diferença entre os grupos tratados: Instrumento cortante rotatório, Papacárie® e Carisolv®. Na análise em MEV pode-se observar com uso do Papacárie® e Carisolv® presença de uma camada amorfa semelhante a smear layer e poucas áreas com túbulos dentinários expostos; e no grupo do instrumento rotatório constatou-se superfície uniforme e lisa com smear layer característica e exposição de túbulos dentinários. Todos os grupos apresentaram acentuada formação de tagsThe purpose of this in vitro study was to analyze the residual dentinal surfaces following caries removal using rotatory instruments and two chemomechanical methods (Papacárie® and Carisolv®), by laser fluorescence (DIAGNOdent), microhardness test and scanning electron microscopy (SEM). Thirty primary incisives, from the Human Bank Teeth of FOUSP, with carious cavities on one of the proximal surfaces were evaluated, before and after caries removal, by laser fluorescence, and then, prepared for the microhardness test. Microhardness was measured in different distances bellow the carious cavity side (50, 100, 150, 200, 300, 400 e 500µm) and on sound dentine of the other proximal side (100, 150, 200, 300, 400, 500, 1000 e 1500 µm). Next, other 30 primary incisives were divided in three groups, according to the caries removal method used, and their residual dentine was examined under SEM (15). After caries removal, 15 of these teeth were restored with Single Bond (3M) adhesive system and Z100 Filtek composite resin (3M). The tags of the replicas were observed under SEM. In conclusion, the laser fluorescence measurements observed before and after caries removal showed statistically significant difference in all groups; however, there was no difference among the caries removal methods used. The microhardness values of the residual dentinal surfaces were significantly lower than the ones found on sound dentine. No difference was found among the three caries removal methods regarding the microhardness values of residual dentine. Under SEM, the chemomechanical caries removal methods (Papacárie® and Carisolv®) formed an amorphous layer, similar to the smear layer and few exposed dentinal tubules; the conventional caries removal method produced a smooth and regular dentinal surface, with typical smear layer and exposed dentinal tubules. All groups showed abundant tag formation
28
Caccin, Marco. "Oxide chemomechanics by hybrid atomistic machine learning methods." Thesis, King's College London (University of London), 2017. https://kclpure.kcl.ac.uk/portal/en/theses/oxide-chemomechanics-by-hybrid-atomistic-machine-learning-methods(e69ed02a-5b80-4353-aa55-e5186e8cc36f).html.
Full textAbstract:
Atomic scale phenomena concurring to atomic bond ruptures at a crack tip determine the chemomechanical properties of oxide materials, thus a better understanding of them is instrumental in addressing engineering issues related to the brittleness of oxides. In a fracturing material, the macroscopic stress field couples with the chemical reactions occurring at the crack tip in a bidirectional interplay requiring a concurrent multiscale (QM/MM) computational approach. Due to long range electrostatic interactions, the dynamics of chemically accurate description of the neighbourhood of a breaking bond requires ab initio calculations on several hundred atoms on a timescale of picoseconds. First, to make these prohibitively demanding calculations tractable I developed an ensemble parallel QM/MM computational strategy comprising a novel graph partitioning method for optimal load balancing that is able to efficiently parallellise the workload over hundreds of thousands of cores on supercomputing facilities. Secondly, I present a computational study of crack propagation in two–dimensional silica systems that have recently been experimentally synthesized, which provide ideal and physically observed structures that are key to the understanding of atomic scale phenomena in fracture events in oxides. The atomic structure, either crystalline or amorphous, and the emerging set of free energy barriers to crack advance are the basis to understand the fundamental difference in the crack dynamics observed at a larger scale. Finally, I explored different pathways to make efficient use of the information produced by ab initio calculations by studying machine learning methods capable of predicting local physical observables as a function of the local atomic environment. This includes a machine learning–augmented method to obtain free energy barriers of hybrid accuracy that only require DFT calculations on just a small fraction of the sampled atomic configurations.
29
Swallow, Jessica G. "Chemomechanics of non-stoichiometric oxide films for energy conversion." Thesis, Massachusetts Institute of Technology, 2018. http://hdl.handle.net/1721.1/115606.
Full textAbstract:
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2018.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references.
Electrochemical energy conversion and storage devices including solid oxide fuel cells (SOFCs) and lithium ion batteries (LIBs) are enabled by materials known as "non-stoichiometric oxides" that contain large concentrations of point defects such as oxygen or lithium vacancies. While this non-stoichiometry provides the essential functional properties of ionic conductivity or reactivity that make these materials useful, it also tends to couple to material volume through the effect of chemical expansion. Chemical expansion, or volume coupled to defect concentration, is in turn tied to mechanical variables including stress, strain, and elastic constants. This electrochemomechanical coupling, or interaction between functional properties, defect chemistry, and mechanical variables, can have important consequences for devices operated in extreme environments, where unexpected stress may lead to fracture, or well-engineered strain may enhance device efficiency. Such effects are particularly important in thin film devices, where strain engineering is within reach, undesired fracture can devastate performance, and defect chemistry and related properties can differ from bulk systems. In this thesis, we present a concerted investigation of chemomechanical coupling, including interactions between material chemistry, environmental conditions, stress, strain, and mechanical properties, for films of the model material PrxCe1-xO2-[delta] (PCO) that is a fluorite-structured oxide relevant to SOFC applications. PCO is an excellent model system because of its well-established defect chemistry model and known thermal and chemical expansion coefficients. The thesis begins by first characterizing key chemomechanical effects in PCO, including electrochemically induced high temperature actuation and nonstoichiometry- dependent mechanical properties that are modulated by environmental conditions including temperature and oxygen partial pressure. We then explore the mechanisms and microstructural contributions to these effects via computational modeling and high temperature transmission electron microscopy, identifying ways in which chemomechanical effects in thin film non-stoichiometric oxides differ from those in bulk. Finally, we extend the experimental and computational methods developed in the thesis to characterizing similar effects in Li-storage materials, demonstrating the broad applicability of results across the classes of non-stoichiometric oxides. We first describe an experimental study in which we developed a novel method of detecting chemical expansion on short time scales in the model system PCO and characterized material deformation for a range of conditions of temperature and effective oxygen partial pressure (pO2). In this method, electrically-stimulated chemical expansion caused mechanical deflection of a substrate, an effect that for PCO was enhanced for elevated temperatures or reducing conditions ...
by Jessica G. Swallow.
Ph. D.
30
Hori, Yêska Braga. "Análise in vivo da atividade antimicrobiana do Endo-PTC leve associado ao hipoclorito de sódio 1%." Universidade de São Paulo, 2018. http://www.teses.usp.br/teses/disponiveis/23/23156/tde-12062018-104726/.
Full textAbstract:
Durante o preparo químico-cirúrgico são utilizados instrumentos e substâncias químicas, que constituem um binômio indivisível e necessário para alcançar a modelagem e a sanificação dos canais radiculares. Assim, propõe-se com este trabalho avaliar in vivo, por meio de método molecular de PCR quantitativo, baseado em DNA (qPCR), a eficiência do preparo químico-cirúrgico empregando como agente de irrigação o Hipoclorito de Sódio (NaOCL) a 2,5% ou o Gel de Endo PTC associado ao Hipoclorito de Sódio a 1,0% na redução bacteriana de canais radiculares de dentes portadores de periodontite apical primária. Foram selecionados 30 pacientes portadores de infecção endodôntica primária, totalizando 30 dentes, com rarefação óssea periapical visível na radiografia, sem tratamento endodôntico prévio. Os pacientes foram divididos de forma randomizada em dois grupos distintos, de acordo com a substância química auxiliar utilizada durante a instrumentação, NaOCL 1% + Endo-PTC leve ou NaOCL 2,5%. Em todos os casos empregou-se instrumentos Reciproc R40 ou R50 e as coletas foram realizadas antes (S1) e após o prepare químico-cirúrgico (S2). A análise de aderência foi realizada por meio do teste de Kolmogorov-Smirnov, as análises intragrupo foram realizadas com teste de Wilcoxon para amostras relacionadas e as comparações entre os dois grupos foram realizadas com o teste de Mann-Whitney, para a análise quantitativa de bactérias. Em ambos os grupos, houve diminuição significativa no número de bactérias entre S1 e S2 (p<0,05). No grupo NaOCL 1% + Endo-PTC leve, houve redução de 3,7x105(S1) para 5,7x104 (S2). No grupo NaOCl 2,5%, redução de 1,3x105 (S1) para 1,1x104(S2). Na comparação entre grupos, o NaOCL a 2,5% (91,62%) promoveu maior redução bacteriana do que o grupo NaOCL 1% + Endo-PTC (84,60%) (p<0,05).During the chemomechanical preparation, instruments and chemical substances are used, which constitute an indivisible and necessary binomial to achieve modeling and sanification. Knowing the auxiliary chemical substances, understanding their mechanisms of action, being able to use them efficiently, is fundamental, so that the chemical-surgical preparation is well performed by the clinician. Thus, the purpose of this study is to evaluate in vivo, the efficiency of the chemomechanical preparation using as the irrigant agent 2,5% sodium hypochlorite and Endo-PTC gel, associated to 1% sodium hypochlorite, to assess the bacterial reduction of root canals of teeth with primary apical periodontitis, using a molecular quantitative method DNA-based - polymerase chain reaction (qPCR). Were selected 30 patients with primary infection totaling 30 teeth, with visible periapical bone rarefaction on the radiography, without previous endodontic treatment. Patients were randomly divided into two distinct groups according to the auxiliary chemical substances used during the instrumentation, 1% sodium hypochlorite associated with Endo-PTC gel or 2,5% sodium hypochlorite. In all cases, reciproc instruments R40 or R50 were used and the samples were taken before (S1) and after chemical surgical preparation (S2). The adherence analysis was performed using the Kolmogorov-Smirnov test, intragroup analysis were performed with Wilcoxon test for related samples and comparisions between the two groups were performed with the Mann-Whitney test for the quantitative analysis of bacteria. In the both groups, there was a significant decrease in the number of bacteria between S1 and S2 (p<0,05), the inicial sample (S1) of the group Endo-PTC, the median 3,7x105, reduced to 5,7x104. In the other group of NaOCl, the median in S1 was 1,3x105 that reduced to 1,1x104 . In the comparision between groups, the 2,5% NaOCl promoted a greater microbial reduction of 91,62%, than the Endo-PTC associated with 1% NaOCl (p<0,05) 84,60%.
31
Zeiger, Adam Scott. "Chemomechanics at cell-cell and cell-matrix interfaces critical to angiogenesis." Thesis, Massachusetts Institute of Technology, 2013. http://hdl.handle.net/1721.1/88378.
Full textAbstract:
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, February 2014.Cataloged from PDF version of thesis. "February 2014."
Includes bibliographical references.
The ability to characterize and control cellular responses in vitro has far reaching implications for basic science and applied medical research. For well over 125 years, researchers have studied the behavior of biological cells under in vitro conditions where rigid glass or plastic Petri dishes and defined media in the laboratory replace the compliant solids and crowded fluids of the human body in vivo. While these tools have enabled several important advances in understanding cell functions and pathological mechanisms, the behavior of tissue cells in vitro can differ remarkably from those observed in in vivo tissue microenvironments. It is becoming increasingly appreciated that there is a close coupling between the chemical and mechanical microenvironments of the cell (i.e., the chemomechanical niche). Therefore, the biochemical reactions and conditions responsible for generating mechanical stresses and attendant cell behaviors may not be well represented in typical in vitro assays. In several key respects, particularly in terms of cell proliferation, adhesion, migration and phenotypic metabolism, in vitro assays often misrepresent the major characteristics of these behaviors in vivo. Most physiological processes are defined in part by mechanical force, mechanical microenvironment, and chemical stimuli (e.g., in angiogenesis or regulation of stern cell differentation), and therefore require an updated methodology to studying cellular mechanics and behavior. This thesis aims to address the molecular- to cellular-level chemical and mechanical environments that modulate cell function in vivo at the cell-cell and cell-matrix interfaces, while aiming to more accurately reproduce these cell responses in vitro. The experiments and analyses described in this work investigate two key questions at the heart of angiogenesis. First, how does the protein dense nature of tissue nicroenvironments affect extracellular matrix organization and, in turn, direct cell-matrix guided functions and cytoskeletal organization? This will be addressed by the addition of inert crowders which artificially enhance the effective concentration of relevant macromolecules and proteins in vitro. Second, how do the mechanically couplings and biochemical signals between adjacent, dissimilar cell types in the microvasculature coordinate and guide angiogenesis? Multiple types of deformable substrata will be used to investigate the mechanical strain and soluble growth factors generated by perivascular cells and the response of microvascular endothelial cells to those cues. This includes the development of a novel uniaxial strain-generating device and tissue culture surfaces for endothelial cells. Atomic force microscopy enabled imaging and nanoindentation, mechanically and chemically defined substrata, immunocyto-chemistry, and novel quanitification and analysis techniques are used concomitantly to answer these questions. Ultimately, this thesis aims to close the gap between in vitro cell culture and in vivo cell physiology, especially in directing and characterizing chemomechanical cues implicated in angiogenesis, and to inform the design of future experiments and microenvironments with non-dilute culture media and deformable substrata.
by Adam Scott Zeiger.
Ph. D.
32
Gil, Ludovic. "A general continuum theory of finite strain chemoporomechanics with application to subcutaneous injections." Thesis, Institut polytechnique de Paris, 2020. http://www.theses.fr/2020IPPAX080.
Full textAbstract:
L'administration de traitements par voie sous-cutanée se fait par l'injection d'un fluide dans les tissus adipeux (couche de graisse située entre le derme et le muscle). L'objectif de cette thèse est d'identifier les phénomènes physiques associés à ce problème bio-mécanique, puis de développer un cadre cohérent de mécanique des milieux continus permettant de modéliser les injections sous-cutanées. A plus long terme, un tel modèle permettrait de développer des outils numériques offrant les capacités d'analyser et de contrôler les paramètres d'injection afin d'optimiser le compromis entre efficacité et confort de l'injection pour les patients, tout en réduisant le recours aux expérimentations in-vivo couteuses.Nous adoptons un point de vue macroscopique où un fluide visqueux et composé d'espèces chimiques en solutions (pouvant porter des charges électriques) est injecté dans une matrice solide visco-élastique, prenant en compte le drainage du fluide injecté par les réseaux sanguins et lymphatiques. Les problèmes d'ingénierie similaires sont nombreux, cependant, l'état de l'art pouvant s'appliquer à ce sujet peut présenter certaines incohérences. Les théories existantes, souvent basées sur la théorie des mélanges de fluides ou les approches bi-phasiques en poro-mécanique, nécessitent l'introduction de variables d'interaction et mélangent des raisonnements macroscopiques et microscopiques pour inclure certains phénomènes comme la tortuosité. Cela peut mener à des résultats en contradiction avec le principe d'objectivité.Nous utilisons les principes de la thermodynamique des processus irréversibles pour proposer un modèle général sans hypothèse superflue en distinguant le régime où la vitesse du fluide est constitutive, de celui où elle est considérée comme variable cinématique. Les résultats sont appliqués à la modélisation des injections et le système d'équations est résolu numériquement par la méthode des éléments finis, avec une discrétisation spatiale suivant la procédure de Galerkin et un schéma temporel d'Euler explicite, prenant en compte le mauvais conditionnement du problème. Ce schéma numérique permet la simulation de problèmes aux limites représentatifs des injectionsThe term subcutaneous injection refers to the delivery of medication into the adipose tissue, which corresponds to the fat layer embedded between the dermis and the muscle. The approach of this investigation is first to understand the physics involved in this complex biomechanical problem and to develop a consistent continuum mechanics model for the associated boundary value problem. The goal of this work is to develop the tools to better analyze and then control the parameters of the injection to optimize for effectiveness and patient acceptability of pain, while reducing the need for costly animal experimentation.A continuum mechanics description of the boundary value problem is hereby adopted which involves finite strain poroelasticity, where a viscous fluid, containing different electrically charged species (medication), is injected into a highly deformable, porous viscoelastic matrix, accounting for absorption of chemical species by blood and lymph vessels. Even though a vast literature exists on poromechanics, motivated by various engineering and physics applications, the state of the art applicable to subcutaneous injection modeling presents several inconsistencies and unnecessary complexities. Existing models, often based on mixture theory, require a long list of difficult-to-identify constitutive interaction parameters, and often mix continuum with micromechanical considerations to include certain phenomena (such as tortuosity) and can violate the objectivity principle.Using the tools of thermodynamics of nonequilibrium processes, a consistent continuum theory for finite strain chemoporomechanics is hereby derived with the least number of variables and phenomenological hypotheses. Two cases are distinguished, according to whether the fluid velocity is a constitutive or an independent kinematic variable, the latter case being required for taking complex effects such as tortuosity into account. The obtained results are subsequently used to identify appropriate constitutive laws for the various components and their interactions involved in subcutaneous injections (skeleton, carrying fluid, chemical species, etc). A numerical scheme is proposed for the solution of the corresponding boundary value problems based on a Galerkin FEM procedure for the spatial discretization and a straightforward forward Euler scheme for time. Special algorithmic attention is needed to avoid stiff systems, due to the simultaneous presence of variables differing by large orders of magnitude. The resulting numerical scheme is subsequently applied to the solution of different injection process boundary value problems
33
Bullara, Domenico. "Nonlinear reactive processes in constrained media." Doctoral thesis, Universite Libre de Bruxelles, 2015. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/209073.
Full textAbstract:
In this thesis we show how reactive processes can be affected by the presence of different types of spatial constraints, so much so that their nonlinear dynamics can be qualitatively altered or that new and unexpected behaviors can be produced. To understand how this interplay can occur in general terms, we theoretically investigate four very different examples of this situation. The first system we study is a reversible trimolecular chemical reaction which is taking place in closed one-dimensional lattices. We show that the low dimensionality may or may not prevent the reaction from reaching its equilibrium state, depending on the microscopic properties of the molecular reactive mechanism.
The second reactive process we consider is a network of biological interactions between pigment cells on the skin of zebrafish. We show that the combination of short-range and long-range contact-mediated feedbacks can promote a Turing instability which gives rise to stationary patterns in space with intrinsic wavelength, without the need of any kind of motion.
Then we investigate the behavior of a typical chemical oscillator (the Brusselator) when it is constrained in a finite space. We show that molecular crowding can in such cases promote new nonlinear dynamical behaviors, affect the usual ones or even destroy them.
Finally we look at the situation where the constraint is given by the presence of a solid porous matrix that can react with a perfect gas in an exothermic way. We show on one hand that the interplay between reaction, heat flux and mass transport can give rise to the propagation of adsorption waves, and on the other hand that the coupling between the chemical reaction and the changes in the structural properties of the matrix can produce sustained chemomechanical oscillations.
These results show that spatial constraints can affect the kinetics of reactions, and are able to produce otherwise absent nonlinear dynamical behaviors. As a consequence of this, the usual understanding of the nonlinear dynamics of reactive systems can be put into question or even disproved. In order to have a better understanding of these systems we must acknowledge that mechanical and structural feedbacks can be important components of many reactive systems, and that they can be the very source of complex and fascinating phenomena.
Doctorat en Sciences
info:eu-repo/semantics/nonPublished
34
Lee, Sunyoung Ph D. Massachusetts Institute of Technology. "Chemomechanics at the cell-material interface : measurements and implications of forced molecular unbinding." Thesis, Massachusetts Institute of Technology, 2009. http://hdl.handle.net/1721.1/53246.
Full textAbstract:
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2009.Cataloged from PDF version of thesis.
Includes bibliographical references.
The main goal of this thesis is to study the coupled interactions between chemically and mechanically characterized materials and cells that are relevant to microvascular physiology and pathology. In particular, the mechanical characterization of cell surface structure and force generation are realized via various atomic force microscopy (AFM) imaging techniques including AFM cell force spectroscopy and functionalized force imaging. In these approaches, the recognition of mechanical responses of cells or mapping of cell surface receptors is mediated by chemomechanically characterized AFM cantilevers. The high spatial and force resolution of AFM imaging techniques and force spectroscopy enabled investigation of mechanical interaction at the cell-cell or cell-material interfaces. This interaction was studied via the mapping of specific receptors on endothelial cell surfaces and the detection of pN-scale force transmission through ligand-receptor pairs on the plasma membrane with biophysical interpretation of cellular force generation. This thesis consists of four major chapters: the recognition of vascular endothelial growth factor receptors and of anti-angiogenic oligopeptide receptors on endothelial cell surfaces, mechanical interaction between endothelial cells and pericytes that encompass capillary blood vessels; cell-matrix contact via focal complexes; and leukemia cells rolling on endothelial cell surfaces and P-selectin-conjugated glass substrata.
(cont.) This thesis also includes appendices that detail the effect of force transducer stiffness on the measurement of unbinding force, nerve cell imaging to I observe the connection between axons and dendrites, and chemomechanical characterization of polyelectrolyte multilayers, biodegradable hydrogels, and biological glues. In Chapter 2, transmembrane receptors on endothelial cell surfaces are mapped and associated binding kinetics/thermodynamics of ligand-receptor pairs are quantified via AFM functionalized force imaging or single-molecule recognition imaging. Functionalized force imaging is then used to identify unknown receptors, receptors for an oligopeptide isolated from tissue inhibitor of metalloproteinase-2, called Loop 6. In Chapter 3, mechanical stress by pericytes that envelop capillary blood vessels is quantified, demonstrating that pericytes exert significant mechanical strain on the extracellular environment. In Chapter 4, picoNewton-scale force dynamics at fibroblasts' focal complexes, measured in real-time through cell force spectroscopy, demonstrates that cells exert mechanical force that can speed the rupture of ligand-receptor pairs in focal complexes during migration and adhesion to underlying substrata. The last part of this thesis, Chapter 5, discusses the role of actin-mediated force in leukemia cell rolling on endothelial cell surfaces. The measurement of picoNewton-scale force dynamics using cell force spectroscopy suggests that, in addition to drag force exerted by blood flow, cytoskeletal force dynamics contribute to the cell rolling process.
(cont.) Together, these studies from the single-molecule to whole-cell level detail the strong coupling between mechanical force and ligand-receptor reaction kinetics.
by Sunyoung Lee.
Ph.D.
35
Tweedie, Catherine Anne. "Multiscale chemomechanics of polymer deformation under contact : predicting structure-property correlations from the bulk to the interphase." Thesis, Massachusetts Institute of Technology, 2008. http://hdl.handle.net/1721.1/44684.
Full textAbstract:
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2008.Includes bibliographical references.
The development of nanoscale polymeric materials for mechanical applications necessitates advances in small-volume experimental techniques and analyses that reflect the viscoelastoplastic behavior of such materials. In this thesis, the time-dependence and response of homogeneous engineering polymers under confined contact loading are characterized as a function of polymer physical and structural properties. The validity of the time-independent metric indentation hardness Hi is evaluated through the combination of nanoindentation and atomic force microscopy imaging. In addition, the classic, time-dependent metric creep compliance J(t) is used to establish the experimental conditions necessary for linear elastic behavior for a set of thermoplastic and thermoset materials. For large indentations (hmax > 1 um), properties are tacitly assumed to reflect the properties of bulk polymer; however, this assumption does not hold within 100 nm of a free surface or interface of amorphous polymers such as polystyrene and polycarbonate. The contact deformation mechanism near an amorphous polymer surface is found to scale with the surface area of contact, suggesting the dynamic formation of a structural interphase region. Chemical probe functionalization experiments are developed to explore the effects of probe surface charge on the probe-polymer interface and contribute to the understanding of the interphase that dominates nanocomposite material response. A technique to rapidly screen mechanical response of combinatorial polymer libraries is presented, to establish structure-property-processing relationships of such chemomechanically defined interfaces before nanoscale deformation mechanisms in confined polymers are fully understood.
(cont.) Finally, material design for elastic, viscoelastic, and viscoelastoplastic mechanical properties is discussed in terms of polymer physical length and time scales.
by Catherine Anne Tweedie.
Ph.D.
36
Heukamp, Franz H. (Franz Hoyte) 1973. "Chemomechanics of calcium leaching of cement-based materials at different scales : the role of CH-dissolution and C-S-H degradation on strength and durability performance of materials and structures." Thesis, Massachusetts Institute of Technology, 2003. http://hdl.handle.net/1721.1/29282.
Full textAbstract:
Thesis (Ph. D .)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2003.Includes bibliographical references (p. 327-341).
Calcium leaching is a durability threat for cement-based materials employed in critical infrastructures, such as Nuclear Waste Storage Systems. This thesis presents a comprehensive study of the material and structural consequences of calcium leaching on the strength and deformation behavior of cementitious materials. Starting from a three-level microstructural division of the heterogeneous microstructure of cement-based materials, a series of experimental and theoretical investigations is conducted leading to the development of a novel constitutive model and model-based simulations of the long-term mechanical performance of concrete structures subjected to calcium leaching. A chemically accelerated leaching device is developed using an ammonium nitrate solution to obtain asymptotically leached specimens in short times. An acceleration rate of 300 compared to natural leaching is obtained. The strength domain of leached cement pastes and mortars is evaluated through triaxial compression tests and uniaxial tension tests, revealing an important strength loss and an increased pressure sensitivity of the materials at failure, associated with leaching. A micromechanical approach for the homogenization of the elastic properties and the strength properties based on the three microstructural levels is developed. These developments allow estimating the relations between the microstructural changes and poroelastic properties including Biot-coefficient and Biot-modulus. In addition, upscaling schemes for the cohesion and friction properties on different levels of cement-based materials are developed.
(cont.) Through this the influence of the Interfacial Transition Zone on the strength of intact and leached materials is evaluated. The micromechanical elements of the analysis are combined in a chemoporoplastic constitutive model. The porosity created by calcium dissolution (chemical porosity) is identified as a state variable, relating dissolution process and mechanical properties. The model is implemented in a commercial finite-element program, and model-based simulations show the predictive capability of the developed approach to improve the durability design of concrete structures subjected to calcium leaching.
by Franz H. Heukamp.
Ph.D .
37
Lin, Chih-Peng, and 林志朋. "A Study on the Chemomechanical Polishing(CMP) Properties of Marble." Thesis, 1997. http://ndltd.ncl.edu.tw/handle/85961426723126535872.
Full textAbstract:
碩士國立成功大學
資源工程學系
85
ABSTRACT Chemomechanical polishing (CMP) for planarization has become one of the most rapidly growing segments of the semiconductor manufacturing market.Application of CMP for the planarization of interlayer dielectric as well as polysilicon and tungsten metal studs was pioneered by IBM and had been used in the fabrication of very large scale integrated circuits since 1985.CMP is carried out by pressing a rotating wafer against a moving polishing pad on which a suitable slurry is dispensed. For oxide polishing, the slurry consists of silica particles dispersed in an aqueous solution. The oxide surface is chemically modified and this modified layer can be removed by mechanical action. The speed of the marble surface reaction to acid is very fast. We can observe the marble surface before and after acid etching and polishing process by means of infrared spectroscope. Under the acid circumstance, the oxalic acid will react with the marble surface and produces fine calcite particles attached on the surface. After a long time of polishing, this reaction will cause etching pores. In mechanical polishing condition, oxalic acid solution has the function of erosion and can remove the scraps. CMP under alkaline condition, sodium silicate solution has the function of gelation, and forms a film on the marble surface which filling the pores and cracks on the marble surface, instead of planarization. α-serum is a kind of Na- Si organic substance co-precipitated from oxalic acid and sodium silicate. This serum is formed in the range of pH from 1.43 to 3.50 and the particle''s size is distributed between 5μm ~100μ m.. It can dissolve in water, but can''t dissolve in alcohol. α- serum will offer a chemical reaction in the polishing of marble under acid condition. By means of mechanical polishing, it can promote the function of planarization, in the mean time, the chemical reaction can also remove the scraps caused by mechanical polishing. For polishing of the white marble, the largest brightness after mechanical polishing is only 82, but the brightness after CMP of α-serum is above 95. It can also shorten the duration of polishing time. In the polishing experiment, the infusion of chemical polishing after the initial period of mechanical polishing will change the abrasion rate and appear the difference between mechanical polishing and chemical polishing. The variation of line regression rate of brightness can explain the quantity of both mechanical and chemical polishing.
38
Flamenbaum, Michael Hal. "Chemomechanical vs. traditional caries removal in children operator and child perspective : a thesis submitted in the partial fulfillment ... for the degree of Master of Science in Pediatric Dentistry ... /." 2002. http://catalog.hathitrust.org/api/volumes/oclc/68962492.html.
Full text
39
Teixeira, Olivier Silva. "Métodos alternativos ao uso dos instrumentos rotativos no tratamento de cáries." Master's thesis, 2017. http://hdl.handle.net/10284/6141.
Full textAbstract:
Introdução: Nos últimos anos, tem surgido na Medicina Dentária novas técnicas e materiais,
que têm sido melhorados de modo a permitir o conforto do paciente e a preservação da
estrutura dentária sadia através do conceito de medicina dentária minimamente invasiva. Este
conceito é de grande importância na clinica de odontopediatria, isto pois o tratamento
restaurador com o uso de instrumentos rotativos gera muita ansiedade e medo nas crianças.
Objectivo: O objectivo do presente trabalho consiste na elaboração de uma revisão
bibliográfica da eficiência e eficácia dos métodos alternativos aos instrumentos rotativos,
sendo este o principal propósito da motivação do autor: a de conseguir quebrar o receio, medo
e fobia que muitas crianças têm aos instrumentos rotativos, proporcionando-lhes estas
abordagens mais conservadoras e menos dolorosas, não só em termos físicos mas também
psicológicos.
Metodologia: A pesquisa bibliográfica foi efetuada nos motores de pesquisa da
MEDLINE/Pubmed, ScienceDirect e SCOPUS, no período compreendido entre novembro de
2016 e fevereiro de 2017, com as seguintes palavras-chave isoladas e combinadas entre elas:
chemomechanical caries removal, Carisolv, Papacárie, air abrasion, caries removal,
bioactiveglass, laser caries removal e laser Er:YAG.
Conclusão: Existem alternativas viáveis aos instrumentos rotativos, não comprometendo o
sucesso do tratamento da doença de cárie, visto que alguns métodos são tão eficazes como os
instrumentos rotativos. Estes métodos alternativos são de grande importância, pois permitem
ao Médico Dentista uma alternativa aquando necessário tratamentos envolvendo pacientes
com necessidades especiais. Quanto ás técnicas apresentadas é necessário que o profissional
respeites as indicações e contraindicações e a sua aplicabilidade deve ser analisada
individualmente em cada caso a fim de escolher o melhor método.Introduction: In recent years new techniques and materials have arisen in dental medicine that have been improved to allow patient comfort and preservation of healthy tooth structure through the concept of minimally invasive dental medicine. This concept is of great importance in the pediatric dentistry clinic, since the restorative treatment with the use of rotating instruments generates a lot of anxiety and fear in the children. Objective: The objective of the present work is the elaboration of a bibliographical review of the efficiency and effectiveness of alternative methods to rotary instruments, this being the main purpose of the motivation of the author: to be able to break the fear, fear and phobia that many children have to rotary instruments , Giving them these more conservative and less painful approaches, not only in physical but also psychological terms. Methodology: The literature search was carried out in the MEDLINE / Pubmed, ScienceDirect and SCOPUS search engines, from November 2016 to February 2017, with the following keywords isolated and combined: chemomechanical caries removal, Carisolv, Papacari, Air abrasion, caries removal, bioactiveglass, laser caries removal and Er: YAG laser. Conclusion: There are viable alternatives to rotating instruments, not compromising the success of caries disease treatment, since some methods are as effective as rotary instruments. These alternative methods are of great importance as they allow the Dentist an alternative when necessary treatments involving patients with special needs. Regarding the techniques presented, it is necessary that the professional respect the indications and contraindications and their applicability should be analyzed individually in each case in order to choose the best method.
40
Pini, Cesare. "Microfluidic Systems based on Chemical Volume-Phase-Transition Stimuli-Responsive Hydrogels." 2017. https://tud.qucosa.de/id/qucosa%3A32755.
Full textAbstract:
Microfluidics is an expanding research field that lies at the interface of engineering, physics, chemistry and biology and offers promises in the development in a wide range of applications from point-of-care (POC) diagnostics to regenerative medicine, from drug testing to DNA sequencing. The number of publications in the field has been steadily growing in the last two decades and the trend does not show any sign of slowing down. On top of that, the market value generated by microfluidics is expected to quadruple in the time spam from 2013 to 2023: from 1.59 billion dollars in 2013, it is expected to grow to 8.64 billion dollars in 2023. There are however a series of limitations which prevent the full development of microfluidic technology. As it has already been pointed out in many publications in the last decade, the lack of a killer application capable of really making the difference out of the research labs and the academic playgrounds around the world is an impeding factor to the full-scale development of microfluidcs at an industrial level, also due to the lack of industrial standards. A number of authors, though, are of the opinion that the actual concept itself needs to challanged and that a complete re-thinking of the current technological platform should be done in order to make the breakthrough advance allowing a long-standing promising field to finally realise itself.In this work a completely new concept, based on volume-phase-transition smart-hydrogels, is presented and the foundations for a transistor-like technological platform are laid. A strong focus is therefore based on the basic element itself, i.e. volume-phase-transition smart-hydrogels, and on the possible ways that it might be integrated in microfluidic systems. Furthermore, basic circuits that lay the foundations for a logic system are presented together with other applications that replicate some elementary functions in microelectronics, such as oscillators. Finally, integration of logic gates as well as basic circuits is presented, in order to lay the foundations for chemical integrated microfluidic circuits.