Dissertations / Theses: 'Chemical mechanics'

1

Lai, Jiun-Yu. "Mechanics, mechanisms, and modeling of the chemical mechanical polishing process." Thesis, Massachusetts Institute of Technology, 2001. http://hdl.handle.net/1721.1/8860.

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Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2001.
Includes bibliographical references.
The ever-increasing demand for high-performance microelectronic devices has motivated the semiconductor industry to design and manufacture Ultra-Large-Scale Integrated (ULSI) circuits with smaller feature size, higher resolution, denser packing, and multi-layer interconnects. The ULSI technology places stringent demands on global planarity of the Interlevel Dielectric (ILD) layers. Compared with other planarization techniques, the Chemical Mechanical Polishing (CMP) process produces excellent local and global planarization at low cost. It is thus widely adopted for planarizing inter-level dielectric (silicon dioxide) layers. Moreover, CMP is a critical process for fabricating the Cu damascene patterns, low-k dielectrics, and shallow isolated trenches. The wide range of materials to be polished concurrently or sequentially, however, increases the complexity of CMP and necessitates an understanding of the process fundamentals for optimal process design. This thesis establishes a theoretical framework to relate the process parameters to the different wafer/pad contact modes to study the behavior of wafer-scale polishing. Several models of polishing - microcutting, brittle fracture, surface melting and burnishing - are reviewed. Blanket wafers coated with a wide range of materials are polished to verify the models. Plastic deformation is identified as the dominant mechanism of material removal in fine abrasive polishing.
(cont.) Additionally, contact mechanics models, which relate the pressure distribution to the pattern geometry and pad elastic properties, explain the die-scale variation of material removal rate (MRR) on pattern geometry. The pad displacement into low features of submicron lines is less than 0.1 nm. Hence the applied load is only carried by the high features, and the pressure on high features increases with the area fraction of interconnects. Experiments study the effects of pattern geometry on the rates of pattern planarization, oxide overpolishing and Cu dishing. It was observed that Cu dishing of submicron features is less than 20 nm and contributes less to surface non-uniformity than does oxide overpolishing. Finally, a novel in situ detection technique, based on the change of the reflectance of the patterned surface at different polishing stages, is developed to detect the process endpoint and minimize overpolishing. Models that employ light scattering theory and statistical treatment correlate the sampled reflectance with the surface topography and Cu area fraction for detecting the process regime and endpoint. The experimental results agree well with the endpoint detection schemes predicted by the models.
by Jiun-Yu Lai.
Ph.D.

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2

Levert, Joseph Albert. "Interface mechanics of chemical mechanical polishing for integrated circuit planarization." Diss., Georgia Institute of Technology, 1997. http://hdl.handle.net/1853/15914.

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3

Baxter, John. "Mechanics of granular heaps." Thesis, University of Surrey, 1998. http://epubs.surrey.ac.uk/843468/.

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The formation and evolution of heaps of granular material has in recent years received ever-increasing research attention. As with other aspects of the granular physics field, much of this attention has focused on the use of numerical simulations, including the discrete element modelling technique. Before advancements in computing technology made numerical methods a viable option, assemblies of granular materials were typically rather poorly characterised by a limited range of bulk properties, such as the angle of repose of a heap. Such properties were found to be rather insensitive to the characteristics of the individual particles and as such were of limited practical use as the basis for process design. Consequently, problems in granular materials storage, handling and flow were typically tackled using semi-empirical approaches relying on long experience of similar process situations. The availability of computing resources has resulted in the spawning of a widely diverse range of numerical simulation approaches for the solution of bulk solids handling problems. However, this development in itself has given rise to further problems. The poor characterisation of assemblies by bulk properties has made experimental confirmation of numerical simulation techniques difficult, and this is perhaps partly responsible for the injudicious use of inappropriate numerical techniques within the research community. By a systematic study of the mechanics of granular heaps using the discrete element technique, this dissertation establishes that the choice of mathematical model and model parameters at the heart of any numerical method is of crucial importance for the realistic simulation of granular assemblies. The angle of repose is established as being rather insensitive to most single particle properties. The dissertation establishes the usefulness of the granular dynamics simulation method by demonstrating how internal 'microstructural' properties of granular heaps can be computed, and examines how simulation can complement relatively new non-invasive techniques for measuring such properties experimentally. Simulation and experiment are also used as the basis for a tentative mathematical model for the kinetics of segregation and stratification processes in poured heaps.

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Tang, Shengchang Ph D. Massachusetts Institute of Technology. "Dynamics and mechanics of associating polymer networks." Thesis, Massachusetts Institute of Technology, 2016. http://hdl.handle.net/1721.1/107874.

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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Chemical Engineering, 2016.
Cataloged from PDF version of thesis.
Includes bibliographical references.
Associating polymers have attracted much interest in a variety of applications such as selfhealing materials, biomaterials, rheological modifiers, and actuators. The interplay of polymer topology and sticker chemistry presents significant challenges in understanding the physics of associating polymers across a wide range of time and length scales. This thesis aims to provide new insights into the structure-dynamics-mechanics relationships of associating polymer networks. This thesis first examines diffusion of various types of associating polymers in the gel state through a combination of experiment and theory. By using forced Rayleigh scattering (FRS), phenomenological super-diffusion is revealed as a general feature in associating networks. Experimental findings are quantitatively explained by a simple two-state model that accounts for the interplay of chain diffusion and the dynamic association-dissociation equilibrium of polymer chains with surrounding network. Furthermore, hindered self-diffusion is shown to directly correlate with a deviation from the Maxwellian behavior in materials rheological response on the long time scale. To further understand how sticker dynamics affects the network mechanical properties, a new method referred to as "sticker diffusion and dissociation spectrometry" is developed to quantify the dissociation rate of stickers in the network junctions. It is demonstrated that sticker dissociation is a prerequisite step for sticker exchange that leads to macroscopic stress relaxation. Finally, this thesis explores the use of fluorescence recovery after photobleaching (FRAP) to measure self-diffusion of associating polymers, and a mathematical framework is established. The second part of this thesis focuses on the development of new methods of controlling the mechanical properties of associating networks through engineering the molecular structure of polymer chains. Specifically, topological entanglement is introduced into the network through extending the polymer chains to reach beyond their entanglement threshold. This strategy drastically enhances material's toughness, extensibility, creep resistance and stability in solutions. Various types of coupling chemistries are then explored to fine tune the extent of entanglement. The entanglement effect and the long-time relaxation of materials can be further controlled by introducing branching points into the macromolecules.
by Shengchang Tang.
Ph. D.

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Martin, John Daniel Ph D. Massachusetts Institute of Technology. "Modulating tissue mechanics to increase oxygen delivery to tumors." Thesis, Massachusetts Institute of Technology, 2015. http://hdl.handle.net/1721.1/98158.

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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Chemical Engineering, 2015.
Cataloged from PDF version of thesis.
Includes bibliographical references.
Solid tumors have low oxygen tension - hypoxia - that fuels disease progression and treatment resistance. Thus, strategies for alleviating hypoxia are needed. Two factors affect tissue oxygen levels: oxygen supply via blood vessels and oxygen consumption by cells. I focused on improving supply to combat hypoxia. Two vessel abnormalities limit supply. Compression decreases the density of perfused vessels supplying tumors. Excessive leakiness slows blood flow partly by reducing the intravascular pressure drop. Strategies to repair leakiness towards decreasing hypoxia exist, so I developed approaches for overcoming compression. In order to understand the origin of vessel compression, we developed the first ex vivo technique to estimate compressive solid stresses held in tumors. We made measurements of this residual solid stress in numerous tumor types from patients and mice to confirm that elevated stress is conserved across tumors. We then identified structural components within tumors that contribute to stress. Since cancer cells were known to compress vessels, we found that depleting them reduced stress, as did depleting fibroblasts, collagen, and hyaluronan. Depleting these components decompressed blood and lymphatic vessels. After identifying targets to reduce stress, we sought to decrease stress therapeutically to improve treatment outcomes. First, we demonstrated that losartan, an FDA-approved therapy indicated for hypertension, decreases the activation of fibroblasts and the production and maintenance of collagen and hyaluronan. As a result, losartan decompressed vessels, restored perfusion, decreased hypoxia, and potentiated chemotherapy. These results provide a rationale for retrospective analyses demonstrating losartan's benefit and for future clinical trials, one of which is currently underway (NCT01821729). To understand how reversing compression modulates both individual vessels and the vascular network to improve oxygen delivery, we developed a technique using multiphoton phosphorescence quenching microscopy to map oxygenation to perfused blood vessels in live tissues. This technique allowed us to compare the effects of reversing compression to the effects of repairing leakiness on individual vessels and vascular network geometry. In comparing and contrasting these two strategies, we showed how each of these strategies could be improved to increase oxygen delivery. This work also has implications for optimally combining both treatment strategies to increase oxygen delivery to tumors.
by John Daniel Martin.
Ph. D.

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6

Bielenberg, James R. (James Ronald) 1976. "The ramifications of diffusive volume transport in classical fluid mechanics." Thesis, Massachusetts Institute of Technology, 2004. http://hdl.handle.net/1721.1/30061.

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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 2004.
Includes bibliographical references (leaves 160-166).
The thesis that follows consists of a collection of work supporting and extending a novel reformulation of fluid mechanics, wherein the linear momentum per unit mass in a fluid continuum, m, is supposed equal to the volume velocity v[sub]v. The latter differs from the barycentric velocity V[sub]m by the vector field j[sub]v, where j[sub]v = v[sub]v - v[sub]m represents the heretofore largely ignored diffusive transport of volume. We will begin by giving a motivating discussion containing example problems which point to the possible need for a change in the constitutive choice for in. This will be followed by a brief outline of the kinematic concepts necessary to understand and utilize volume transport, including a general expression for j[sub]v. We will conclude by presenting the modified governing equations that result from the constitutive choice m = v[sub]v. Upon completing the required overview of existing ideas, a detailed linear irreversible thermodynamic study of the modified governing equations which result from the choice m = v[sub]v is presented. This analysis yields, inter alia, an expression for the entropy production per unit volume in the fluid which requires that the deviatoric stress tensor be expressed in terms of the volume velocity. Furthermore, an expression for the diffusive flux of internal energy is derived that differs from classical results by a term proportional to the diffusive flux of volume. This change in the internal energy flux stems from the explicit recognition of a diffusive volume flux, and precedes any specific choice of constitutive expression for the molecular flux of heat or species.
(cont.) The remainder of the thesis, which constitutes the bulk of the work performed, focuses on testing the proposed equation set against known experimental data. Each of the physically measurable phenomena treated herein was previously believed outside the realm of classical continuum fluid dynamics. We begin by considering the thermophoretic and diffusiophoretic motion of particles suspended in gases or liquids. We continue by studying the thermo-molecular pressure drop which results from applying a temperature gradient across the ends of a closed capillary. We conclude by presenting a hydrodynamic/Brownian motion model of thermal diffusion in liquids, wherein theoretical predictions for the Soret coefficient in a binary liquid system are presented that may be evaluated from readily available physicochemical data. It is shown, in each case, that the predictions of our modified theory are in agreement with experimental data. The final chapter of this dissertation is dedicated to utilizing the results derived in the previous chapters to comment on the veracity of the claim that the specific linear momentum in a fluid is given by the volume, rather than the barycentric, velocity. General arguments supporting this claim are presented and then followed by a list of questions which remain to be answered. Finally, a list of proposed experiments are detailed which could further test the predictions made herein.
by James R. Bielenberg.
Ph.D.

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7

Bergström, Per. "Modelling Mechanics of Fibre Network using Discrete Element Method." Licentiate thesis, Mittuniversitetet, Avdelningen för kemiteknik, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:miun:diva-34640.

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Low-density fibre networks are a fundamental structural framework of everyday hygiene products, such as baby diapers, incontinence and feminine care products, bathroom tissue and kitchen towels. These networks are a random assembly of fibres, loosely bonded and oriented in the plane direction. Designing such a complex network structure for better performance, better use of materials and lower cost is a constant challenge for product designers, requiring in-depth knowledge and understanding of the structure and properties on the particle (fibre) level. This thesis concerns the development of a computational design platform that will generate low-density fibre networks and test their properties, seamlessly, with the aim to deepening the fundamental understanding of the micromechanics of this class of fibre networks. To achieve this goal, we have used a particle-based method, the Discrete Element Method (DEM), to model the fibres and fibre networks. A fibre is modelled as a series of linked beads, so that one can consider both its axial properties (stretching and bending) and transverse properties (shearing,twisting and transverse compression). For manufacturing simulations, we developed the models for depositing fibres to form a fibre network, consolidating the fibre network, compressing to make a 3D-structured network, and creating creping. For testing the end-use performance, we have developed two models and investigated the micromechanics of the fibre network in uniaxial compression in the thickness direction (ZD) and in uniaxial tension in the in-plane direction. In the ZD-uniaxial compression of entangled (unbonded) fibrenetworks, the compression stress exhibits a power-law relationship with density, with a threshold density. During compression, the fibre deformation mode changed from fibre bending to the transverse compression of fibre. Accordingly, the transverse properties of the fibreshad a large impact on the constitutive relation. By considering a realistic value for the transverse fibre property, we were able to predict the valuesof the exponent widely observed in the experimental literature. We havefound that the deviation of the experimental values from those predictions by the earlier theoretical studies is due to the neglect of the transverse fibre property. For tensile properties of bonded networks, we have investigated scaling of network strength with density and fibre–fibre bond strength. The network strength showed beautiful scaling behaviour with both density and bond strength, with exponents 1.88 and 1.08 respectively. The elastic modulus of the network, on the other hand, showed a changing exponent(from 2.16 to 1.69) with density in accordance with previous results in the literature. We have also reconfirmed that, with increasing density, the deformation mode changes from bending to stretching. The predicted results for both elastic modulus and strength agreed very well with experimental data of fibre networks of varying densities reported in the literature. We have developed a computational platform, based on DEM, for accurately modelling a fibre network from its manufacturing process to product properties. This is a tool that allows a versatile design of materials and products used for hygiene products, providing a promising venue for exploring the parameter space of new material and process design.

Vid tidpunkten för framläggningen av avhandlingen var följande delarbeten opublicerade: delarbete 2 och 3 (manuskript).

At the time of the defence the following papers were unpublished: paper 2 and 3 (manuscript).

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8

Dasi, Lakshmi Prasad. "Statistical characteristics of turbulent chemical plumes." Thesis, Georgia Institute of Technology, 2000. http://hdl.handle.net/1853/21256.

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9

Glassman, Matthew James. "Synthesis, nanostructure, and mechanics of thermoresponsively tough biomaterials from artificial polypeptides." Thesis, Massachusetts Institute of Technology, 2015. http://hdl.handle.net/1721.1/101505.

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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Chemical Engineering, 2015.
Cataloged from PDF version of thesis.
Includes bibliographical references.
Artificial protein hydrogels have attracted interest as injectable fillers and scaffolds for tissue engineering and regeneration, but the same features that enable minimally-invasive implantation of these biomaterials typically make them susceptible to mechanical degradation in the tissue environment. Achieving a rapid and sufficiently large increase in gel toughness post-injection is a crucial challenge for developing load-bearing injectable implants that persist for the needed lifetime of the implant. To address these complex goals, the objective of this thesis has been to engineer physical hydrogels that shear-thin at low temperatures but responsively assemble into a nanostructured, reinforced state at body temperature. For this purpose, the thermoresponsive aggregation of poly(N-isopropylacrylamide) (PNIPAM) and elastin-like polypeptides (ELPs) was leveraged to assemble nanostructured hydrogels from dual-associative block copolymers. Hybrid protein-polymers or protein fusions were formed by fusing PNIPAM or ELPs to the termini of a soluble artificial polypeptide decorated with self-associating [alpha]-helical domains. In cold solutions, these polypeptide block copolymers formed weak, injectable gels due to helix-associations alone; upon heating to physiological temperatures, the endblocks aggregated to form a reinforcing network of close-packed micelles throughout the gel, leading to over a 10-fold increase in elastic modulus and over 10³-fold increase in the longest stress relaxation time. Micelle packing and morphology could be tuned by endblock chemistry and block architecture, allowing for orthogonal control of gel viscoelasticity over timescales separated by four orders of magnitude. Furthermore, through the discovery of a new gelation mechanism for ELPs, simple but tough hydrogels were engineered and explored as biocompatible substrates for tissue engineering. Unlike solutions of other ELPs that have been studied extensively for decades, ELPs that have an alanine mutation in the third position of the repeat unit (i.e. VPAVG) were found to undergo arrested phase separation upon heating when formulated above a critical concentration. Solidification resulted in a bicontinuous, nanoscale network that could be manipulated by ELP design. Critically, this reversible mechanism produced extremely stiff physical gels with a relaxation time greater than 10³ seconds and shear moduli almost 10 MPa, nearly that of natural rubber despite consisting of 70% water. These ELPs were chain-extended via reversible coupling of terminal cysteine residues, leading to oxidatively-responsive increases in gel extensibility and overall toughness. Biofunctionalized gels maintained the viability of mesenchymal stem cells and chondrocytes in 2D and 3D, respectively, making these simple gel formulations a promising platform for biomedical applications. Ultimately, through controlled macromolecular synthesis and functionalization, combined with a fundamental understanding of the structure and mechanics of these new materials, this thesis has led to the development of responsively tough biomaterials that are promising for long-term performance under physiological conditions.
by Matthew James Glassman.
Ph. D.

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10

Holmvall, Martin. "Nip Mechanics, Hydrodynamics and Print Quality in Flexo Post-Printing." Doctoral thesis, Mittuniversitetet, Institutionen för naturvetenskap, teknik och matematik, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:miun:diva-11347.

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11

Shan, Lei. "Mechanical interactions at the interface of chemical mechanical polishing." Diss., Georgia Institute of Technology, 2000. http://hdl.handle.net/1853/17774.

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Matek, Christian C. A. "Statistical mechanics of nucleic acids under mechanical stress." Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:ce44cf50-2001-4f54-8e57-d1757f709fd6.

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In this thesis, the response of DNA and RNA to linear and torsional mechanical stress is studied using coarse-grained models. Inspired by single-molecule assays developed over the last two decades, the end-to-end extension, buckling and torque response behaviour of the stressed molecules is probed under conditions similar to experimentally used setups. Direct comparison with experimental data yields excellent agreement for many conditions. Results from coarse-grained simulations are also compared to the predictions of continuum models of linear polymer elasticity. A state diagram for supercoiled DNA as a function of twist and tension is determined. A novel confomational state of mechanically stressed DNA is proposed, consisting of a plectonemic structure with a denaturation bubble localized in its end-loop. The interconversion between this novel state and other, known structural motifs of supercoiled DNA is studied in detail. In particular, the influence of sequence properties on the novel state is investigated. Several possible implications for supercoiled DNA structures in vivo are discussed. Furthermore, the dynamical consequences of coupled denaturation and writhing are studied, and used to explain observations from recent single molecule experiments of DNA strand dynamics. Finally, the denaturation behaviour, topology and dynamics of short DNA minicircles is studies using coarse-grained simulations. Long-range interactions in the denaturation behaviour of the system are observed. These are induced by the topology of the system, and are consistent with results from recent molecular imaging studies. The results from coarse-grained simulations are related to modelling of the same system in all-atom simulations and a local denaturation model of DNA, yielding insight into the applicability of these different modelling approaches to study different processes in nucleic acids.

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Kent, Anthony Clifford. "The mechanics of abrasion relating to household cleaning." Thesis, University of Birmingham, 2016. http://etheses.bham.ac.uk//id/eprint/6954/.

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Abrasion of polymer surface films or coatings in an everyday occurrence, whether in the home, work or industry. As a result a wide variety of polymer films can be found on surfaces. Despite the numerous applications, three body thin film abrasion appears a niche area of study and as a result under-researched. This investigation focuses on identifying, characterising and quantifying the abrasive wear of a baked dehydrated castor oil deposit formed on stainless steel. The primary aim of this project is to understand how the fundamental properties of the liquid abrasive cleaning system contribute to the material removal. Investigations have primarily been carried out using a reciprocating linear tribometer for the cleaning and a profilometer to measure the wear. The wear of the baked oil film was found to largely follow the established Archard wear equation of sliding distance and load, despite the fact it was derived to describe two body and not three body wear. However the wear rate was not inversely proportional to hardness and there were significant effects when parameters not in the Archard equation are considered. IN particular changing the speed, viscosity, particle size and distribution all had an impact on the wear.

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Samudrala, Niveditha. "Colloidal particles at fluid interfaces| Adsorption, assembly, and mechanics." Thesis, Yale University, 2017. http://pqdtopen.proquest.com/#viewpdf?dispub=10633262.

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Mechanics of emulsion droplets is crucial in applications where the encapsulated payload needs to be released under mechanical stimulus. This dissertation explores dumbbell nanoparticles as emulsifiers with focus on the emergent mechanical stability of the particle assembly at interfaces. Using a combination of freeze fracture shadow casting cryo-scanning electron microscopy and analytical modelling, I first investigate the complex adsorption behavior of individual dumbbells and discuss the corresponding implications for particle assembly at the interface. I then investigate the onset of mechanical instabilities in droplets stabilized by dumbbells using micropipette aspiration. I compare my findings to the control experiments of bare droplets and droplets stabilized with molecular surfactant under aspiration. In all three cases, the magnitude of the critical pressure for the onset of instabilities is set by the fluid surface tension. While particles have a dramatic impact on the mechanism of failure, the mechanical strength of the droplets is only modestly increased. This work provides experimental handles that can be tuned to aid the mechanical stability of emulsion droplets. The findings also inform advances in the mechanics of highly bendable sheets.

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15

Rauenzahn, Rick Meier. "Analysis of rock mechanics and gas dynamics of flame-jet thermal spallation drilling." Thesis, Massachusetts Institute of Technology, 1986. http://hdl.handle.net/1721.1/14884.

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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 1986.
MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE
Bibliography: v.2, leaves 574-583.
by Rick Meier Rauenzahn.
Ph.D.

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Reding, Derek James. "Shock induced chemical reactions in energetic structural materials." Diss., Atlanta, Ga. : Georgia Institute of Technology, 2009. http://hdl.handle.net/1853/28174.

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Thesis (M. S.)--Aerospace Engineering, Georgia Institute of Technology, 2009.
Committee Chair: Hanagud, Sathya; Committee Member: Kardomateas, George; Committee Member: McDowell, David; Committee Member: Ruzzene, Massimo; Committee Member: Thadhani, Naresh.

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McKissic, Kelley S. "Understanding the Role of Energy in Chemical Reactions from Mechanics to Photochemistry." University of Cincinnati / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1439562321.

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Eberhardt, Oliver, and Thomas Wallmersperger. "Analysis of the mechanical behavior of single wall carbon nanotubes by a modified molecular structural mechanics model incorporating an advanced chemical force field." SPIE, 2018. https://tud.qucosa.de/id/qucosa%3A35173.

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The outstanding properties of carbon nanotubes (CNTs) keep attracting the attention of researchers from different fields. CNTs are promising candidates for applications e.g. in lightweight construction but also in electronics, medicine and many more. The basis for the realization of the manifold applications is a detailed knowledge of the material properties of the carbon nanotubes. In particular for applications in lightweight constructions or in composites, the knowledge of the mechanical behavior of the CNTs is of vital interest. Hence, a lot of effort is put into the experimental and theoretical determination of the mechanical material properties of CNTs. Due to their small size, special techniques have to be applied. In this research, a modified molecular structural mechanics model for the numerical determination of the mechanical behavior of carbon nanotubes is presented. It uses an advanced approach for the geometrical representation of the CNT structure while the covalent bonds in the CNTs are represented by beam elements. Furthermore, the model is specifically designed to overcome major drawbacks in existing molecular structural mechanics models. This includes energetic consistency with the underlying chemical force field. The model is developed further to enable the application of a more advanced chemical force field representation. The developed model is able to predict, inter alia, the lateral and radial stiffness properties of the CNTs. The results for the lateral stiffness are given and discussed in order to emphasize the progress made with the presented approach.

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Henn, Julian. "The electron density a bridge between exact quantum mechanics and fuzzy chemical concepts /." Doctoral thesis, [S.l. : s.n.], 2004. http://deposit.ddb.de/cgi-bin/dokserv?idn=971615535.

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Nadim, Ali. "Transport and statistical mechanics of flexible chains and clusters of Brownian particles in quiescent viscous fluids." Thesis, Massachusetts Institute of Technology, 1986. http://hdl.handle.net/1721.1/15051.

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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 1986.
MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE.
Bibliography: leaves 156-158.
by Ali Nadim.
Ph.D.

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21

Brousseau, Patrick. "Numerical study of extrudate swell in circular and annular dies." Thesis, McGill University, 1990. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=60439.

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Extrudate swell is an important phenomenon in polymer extrusion, affecting many polymer processes. The ability of predicting swell, using rheological properties of the resin, would help the design and operation of plastics processing equipment. Different techniques for predicting swell are reviewed.
A computer program has been written to predict steady-state, isothermal extrudate swell in annular and circular dies. The equations of motion and continuity have been solved along with selected constitutive relations. Newtonian, power-law and the viscoelastic Maxwell and Giesekus rheological models were chosen. The Galerkin formulation of the Finite Element Method has been used to solve the system of differential equations.
The predictions for Newtonian, power-law and Maxwell models have been verified with existing experimental or numerical results when available. The results for the swell of Maxwell and Giesekus fluids have been compared at the same levels of elasticity. The effects of inertia and gravity on extrudate position and swell have been studied. Different geometries of an annular die (converging, diverging) were also examined.

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van, Heiningen Jan Adam. "Optical tweezers electrophoresis with applications to micro-fluidic velocimetry, nano-tube bending mechanics, and polymer adsorption dynamics." Thesis, McGill University, 2011. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=96677.

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Polymer adsorption and desorption onto micro-spheres, and the micromechanics of single polymeric nanotubes were investigated using optical tweezers.In parallel-plate micro-channels, frequency-dependent apparent micro-sphere electrophoretic mobilities were measured in various sodium chloride and calcium chloride electrolytes, and channel gap ocations. The apparent electrophoretic mobility reflects anomalous electro-osmotic flow (EOF) dynamics, which are present in compliant parallel-plate micro-channels. At limiting high and low frequencies, the EOF dynamics are those of an open and closed channel, respectively.Using optical tweezers electrophoresis (OTE), electrophoretic mobilities of single silica micro-spheres were measured during poly(ethylene oxide) adsorption and desorption. For neutral polymers, the electrophoretic mobility is a sensitive measure of adsorbed polymer hydrodynamic layer thickness. However, at the position of zero-EOF in closed parallel-plate channels, transient EOF artifacts are observed when polymers adsorb on channel walls. Such artifacts are reduced when polymers flow parallel to the electric field in parallel-plate micro-channels. In this polymer-flow configuration, low-frequency apparent electrophoretic mobilities reflect intrinsic particle mobility dynamics. Polymer hydrodynamic layer thickness and adsorbed amounts were calculated from electrophoretic mobilities using electrokinetic models and calculated equilibrium layer profiles. The growth of the hydrodynamic layer thickness reflects polymer reptation and diffusion through initially adsorbed layers, limited by polymer reconformation dynamics. Desorption kinetics were faster than expected by local equilibrium models.The bending of polymer composite nanotubes was investigated in various transverse hydrodynamic flows using multiple optical tweezers. Directed assembly of latex beads to a single nanotube was undertaken, and two of these beads were used as handles for the nanotube bending experiments. The calculated nanotube Young's moduli were in agreement with macroscale continuum models for the bulk materials.
L'adsorption et la désorption de polymères sur des micro-sphères, ainsi que la micromécanique de nanotubes polymériques uniques, ont été étudiées à l'aide de pinces optiques.Dans les canaux à plaques parallèles, d'apparentes mobilités électrophoretiques de micro-sphères, dépendantes de la fréquence, ont été mesurées dans diverses concentrations d'électrolytes de chlorure de sodium et de chlorure de calcium, ainsi que dans divers sites d'instercices de canaux. La mobilité électrophorétique apparente reflète une dynamique d'écoulement électro-osmotique (EOF) anormale, laquelle est présente dans les micro-canaux à plaques parallèles souples. Aux limites de fréquences élevées et basses, les dynamiques d'EOF sont celles de canaux ouverts et fermés, respectivement. Les mobilités électrophorétiques des particules simples de silice ont été mesurées pendant l'adsorption et la désorption de poly(oxyde d'éthylène) en utilisant l'électrophorèse avec pinces optiques (OTE). Pour les polymères neutres, la mobilité électrophorétique est une mesure sensible à l'épaisseur hydrodynamique de couches de polymères adsorbés. Cependant, à la position de zéro-EOF dans les canaux fermés à plaques parallèles, on observe des artefacts d'EOF lorsque les polymères adsorbent aux murs des canaux. Ces artefacts sont réduits lorsque les polymères coulent parallèlement au champ électrique dans les micro-canaux à plaques parallèles. Dans cette configuration de l'écoulement de polymères, les mobilités électrophorétiques de basse fréquence apparentes reflètent des dynamiques de mobilité de particules intrinsèques. L'épaisseur hydrodynamique des couches de polymères et les montants adsorbés ont été calculés à partir des mobilités électrophorétiques à l'aide de modèles électrokinétiques et des profils de couches d'équilibre calculés. La croissance de l'épaisseur hydrodynamique des couches reflète la reptation et la diffusion des polymères au travers des couches initialement adsorbées, limitées par la dynamique de reconformation de polymères. La cinétique de désorption était plus rapide que celle prévue par les modèles d'équilibre local. Le recourbement des nanotubes de polymères composés a été étudié dans divers écoulements hydrodynamiques transversaux à l'aide de pinces optiques multiples. Le rassemblement des perles de latex dirigé à un simple nanotube a été entrepris, et deux de ces perles ont été employées en tant que poignées pour les expériences de recourbement de nanotubes. Les modules de Young calculés des nanotubes étaient en accord avec les modèles de continuum macroscopiques pour les matériaux en vrac.

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Jantan, Mohd Dahlan. "Chemical preservation of some refractory timber species of Malaysia." Thesis, University of Portsmouth, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.310381.

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The treatability of six Malaysian timbers namely Red Balau (Shorea guiso), Kapur (Dryobafanops aromatica), Kasai (Pometia pinnata), Kulim (Scorodocarpus borneensis), Kempas (Koompassia malaccensis) and Keruing (Dipterocarpus grandiflorus) using the applied pressure processes (oscillating pressure, conventional Bethell and a modified Bethell process) was investigated. Treatments were carried out with a commercial water-borne copper-chromearsenic (CCA) preservative, known as Celcure-AP. The conventional Bethell process was the most effective method of wood treatment followed by the modified Bethell and the oscillating pressure process. While sufficient preservative retention and absorption was achieved in Kempas and Keruing to meet the Malaysian Standard MS 386 : 1986 specifications for exterior timber used in ground contact, the other four timbers - Red Balau, Kapur, Kasai and Kulim did not fulfil this requirement, even when treated at the most extreme treatment conditions. Using the three pressure processes, seasoning period and treatment time were found to have significant effects on preservative retention and penetration in all timber species. Investigations into the effect of three pretreatment procedures - steaming, incising and ponding to improve the treatability of the six timber species were carried out. Incising was the most effective pretreatment procedure in enhancing the treatability of these timbers. However, at the highest incising density employed (4,500 incisions/m2), it was still not possible to treat Red Balau, Kapur, Kasai and Kulim timber to achieve satisfactory target preservative retention and penetration. The less effective incising procedure was due mainly to the low incising density used. The possibility of improving the treatability of these four timber species further using higher incising densities and other methods of inCising pretreatment is discussed. Steaming, incising and ponding pretreatments had a pronounced effect on the strength properties of timbers based on reduction of their modulus of elasticity (M.D. E.), modulus of rupture (M.O.A.), compressive strength and hardness. The highest strength losses were observed in timbers that had been ponded for 6 months. Significant strength losses were also observed in incised and steamed timbers, but the magnitudes were lower than the 6 month ponding regime. This was attributed to low incising density and the short steaming period. The performance of Celcure-AP in the six timber species was evaluated in laboratory and field tests. In addition, a copper-azole formulation (Tanalith-3485) was also evaluated on Kempas timber. Laboratory tests involved exposure of treated wood blocks to five decay fungi - Pycnoporus sanguineus, Trametes versicolor, Coniophora puteana, Gloeophyllum trabeum and Oligoporus placenta. The less durable timbers - Kempas and Keruing needed a higher loading of Celcure-AP in order to give equal performance compared to the more durable timbers - Red Balau, Kapur, Kasai and Kulim. Based on copper retention in treated samples, a higher loading of Tanalith-3485 was required in Kempas to achieve comparable results to Celcure-AP treated samples. However, the concentration levels of Tanalith-3485 used in the present study were sufficient to afford protection to Kempas stakes exposed for 36 months in the field test. A longer exposure period is however, recommended for a full evaluation of timber/preservative combinations against wood deteriorating organisms under Malaysian conditions. In the field test, soft rot fungi were the main causal organisms in the attack of timbers in test site A (fungal test bed), while in test site B stake failure was due mainly to termite attack.

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Wigenstam, Elisabeth. "Pathogenesis and treatment of chemical-induced lung injury." Doctoral thesis, Umeå universitet, Institutionen för folkhälsa och klinisk medicin, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-52738.

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Inhalation of chemical substances can cause irritation to airways and in high doses acute airway injury. When mice are exposed to the alkylating nitrogen mustard analogue melphalan they develop an acute airway inflammation with a rapid influx of neutrophils to the lungs. The acute phase is followed by long-term respiratory complications characterized by bronchitis, lung fibrosis, and airway hyperreactivity. In this thesis, a mouse model for chemical airway inflammation was established and the effects on the lungs in a time span from 6 hours up to 3 months were investigated in order to study both acute effects and possible chronic injury. We find that treatment with corticosteroids, e.g. dexamethasone, effectively blocks the inflammatory reaction in several ways: Neutrophil influx to the lungs is diminished, the expression of the proinflammatory cytokines interleukin (IL) -6 and IL-1b is decreased and edema formation as well as development of lung fibrosis is mitigated. In acute airway inflammation we show that the antioxidant vitamin E can be used as a possible complement to corticosteroids but not as a replacement since it causes insufficient downregulation of the inflammatory response. We show the importance of the T lymphocytes as they play a prominent role in the pathogenesis of long-term lung injuries caused by melphalan. Especially the minor gd T cell subset is of major importance orchestrating a number of responses including the acute cytokine and neutrophil response and late-phase lung fibrosis. In order to find the critical time for dexamethasone treatment, mice were exposed to melphalan, treated with dexamethasone at specific time points and lung physiology and airway reactivity was measured in anaesthetized, tracheostomized mice using a small animal ventilator. From these results we conclude that an early treatment, i.e. within one hour after exposure, with dexamethasone is needed to prevent chronic lung injury. This thesis was undertaken with the main goal to better understand the pathogenesis of melphalan-induced airway inflammation. We believe that our findings have shed new light in this area of research and hope that this increased knowledge may be of future clinical use.

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25

Chen, Guizhong. "A study of wellbore stability in shales including poroelastic, chemical, and thermal effects." Access restricted to users with UT Austin EID Full text (PDF) from UMI/Dissertation Abstracts International, 2001. http://wwwlib.umi.com/cr/utexas/fullcit?p3025005.

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26

Phillips, Cynthia Michelle. "Model-based design optimization of heterogeneous micro-reactors and chemical sensors." Thesis, Georgia Institute of Technology, 2002. http://hdl.handle.net/1853/18390.

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27

Durlofsky, Louis J. "Topics in fluid mechanics : I. flow between finite rotating disks II. simulation of hydrodynamically interacting particles in stokes flow." Thesis, Massachusetts Institute of Technology, 1986. http://hdl.handle.net/1721.1/15049.

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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 1986.
MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE.
Includes bibliographies.
by Louis J. Durlofsky.
I. Flow between finite rotating disks II. Simulation of hydrodynamically interacting particles in stokes flow.
Ph.D.

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28

Ivancic, William Daniel. "Effect of Surface Oxidation on the Mechanics of Carbon Nanotube Laden Interfaces." Cleveland State University / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=csu1513462892789772.

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29

Cardias, Maria de Fatima Castro. "The protection of wood against fungal decay by isocyanate chemical modification." Thesis, Bangor University, 1992. https://research.bangor.ac.uk/portal/en/theses/the-protection-of-wood-against-fungal-decay-by-isocyanate-chemical-modification(0e432d60-3e1c-4a5d-977f-09a7330f378c).html.

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The purpose of this study was to assess the bioprotectant performance of chemical modification wi th three different isocyanates (n-butyl, hexyl and l,6-diisocyanatohexane, BuNCO, HeNCO and HOI respectively) in Corsican pine (Pinus nigra Schneid) sapwood. Wood-isocyanate bond formation was verified by the increase in sample weight, volume and by infrared spectroscopy. Basidiomycete (Coniophora puteana, Gloeophyllum trabeum, Coriolus versicolor, Pycnoporus sanguineus) decay tests demonstrated protection by chemical modification. The relationships of fungal species, weight percent gain (WPG), decay induced weight loss and moisture content were examined. One of the brown rot fungi, ~. puteana, showed higher threshold protection values than the other fungi tested and the di isocyanate showed better perf ormance. Scanning Electron Microscopy and enzyme detection tests (cellulase and phenol oxidases) have been carried out in an attempt to gain a better understanding of the treatment performance. Chemical characteristics of the sound and brown rotted wood (~. puteana) have been examined using sulphuric acid, sodium chlori te and high performance liquid chromatography-HPLC (gel permeation chromatography-GPC) procedures to clarify the principles which govern isocyanate modifications and restrict fungal decay. A number of parameters were examined including lignin and holocellulose contents, holocellulose molecular weight and degree of polymerisation (OP and dispersity). These demonstrated that chemical modification changed the configuration of the original wood polymers. Al though preferential modification occurred at lower weight percent gains in the lignin fraction appreciable wood protection against C. puteana only occurred when the holocellulose fraction showed substantial changes due to chemical modification. To examine further the effect of moisture and loading of substituent groups within the outer layers of wood after chemical modification (BuNCO & HOI), tensile strength resistance to surface colonisation by soft rot fungi was undertaken utilizing thin wood strips after unsterile soil tests. Less modification was necessary to achieve protection against soft rot in this test.

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Mwasame, P. Masafu. "Multiscale Investigation of Fundamental Rheological Phenomena in Particulate Suspensions Based on Flow-Microstructure Interactions." Thesis, University of Delaware, 2018. http://pqdtopen.proquest.com/#viewpdf?dispub=10680885.

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Suspensions and dispersions are an important class of complex fluids frequently encountered in a variety of industrial processes and are prominent in many consumer products such as beauty creams and food dressing. The extensive use of suspensions can be partly attributed to their unique rheological properties such as shear-induced normal stresses, yield stress, time-dependent viscosity and shear thinning. These rheological properties are a direct result of the interplay between the suspension microstructure and flow and have consequences for material processing. The quantitative understanding of suspension rheology so far has been dominated by empirical models. However, such models are either very specialized to particular flows, involve numerous/unphysical parameters, or are inadequate to describe rheological phenomena such as normal stresses. Alternatively, microscopic approaches have primarily been successful in addressing idealized cases and/or small length/time scales. Therefore, the goal of this thesis is to develop new and improved classes of continuum models that clearly connect the suspension microstructure under flow to the observed macroscopic rheology.

In this thesis, new, generally multiscale methods are applied towards developing robust constitutive models for suspension rheology. Two primary modeling approaches are employed to advance the modeling of suspension rheology in this thesis. First is a bottom-up approach that starts from a microscopic description of the suspension microstructure (e.g., the evolving aggregate size distribution) that is then coupled to an empirical/phenomenological equation to allow for the evaluation of the shear stress. The shortcoming of using a phenomenological stress expression is counterbalanced by the accurate microstructure picture provided by a microscopic framework. The second technique is a top-down approach that starts from a macroscopic description of the system through the use of state variables whose dynamic equations are developed within the Hamiltonian-enhanced Non-Equilibrium Thermodynamics framework. The key benefit of this latter approach is that the expressions for the stress tensor and microstructure, with the latter represented by a second rank tensor, emerge self-consistently from the framework. Moreover, the generated equations are applicable to general flows. The multiscale nature of suspension microstructure implies that depending on the phenomena of interest, one or the other or a combination of the two approaches may be favored. Regardless of the approach taken, a recurrent theme in this work is the clear association of the observed macroscopic rheological behavior with an underlying microscopic picture. Finally, for all the suspensions emphasized in this thesis i.e., thixotropic, polydisperse, noncolloidal and emulsions, the corresponding rheological models developed are validated against experimental/simulation data revealing their predictive capability.

A number of important specific accomplishments are achieved in this thesis. To begin with, a population balance-based constitutive model for thixotropic suspensions is developed. Unlike alternative phenomenological models currently in use, a population balance-based model incorporates parameters with clear physical meaning. As a result, the resultant model holds promise for inverse design of thixotropic materials such as pastes that are used in many industrial processes. Next, the use of a conformation tensor as an internal variable to represent changes in suspension microstructure during material deformation is also demonstrated. For the first time, a comprehensive conformation tensor-based framework for suspensions, with a rigor approaching that performed previously for polymeric system, is realized. When applied to dilute emulsions, the conformation tensor-based rheological model that results is in exact agreement with existing asymptotic microscopic theory. In the same emulsion system, effects of microinertia and Ostwald ripening have also been included within a conformation tensor-based model for the first time. In concentrated suspensions, the conformation based theory has been shown to be capable of describing emerging secondary structure in the particle configuration leading to first and second normal stress differences that are both negative. Additional advances have also been made to develop self-consistent approximations for polydisperse suspension viscosity and testing them against prototype experiments. On a broader level, this work provides a number of methodologies for systematic constitutive model development in complex fluids. From an engineering perspective, the results of this thesis can be used to improve upon existing numerical tools, e.g., computational fluid dynamics, to allow for accurate simulation of industrial processes such as extrusion and screen printing of thixotropic pastes, suspensions and emulsions.

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Al-Awad, Musaed Naser J. "Physico-chemical analysis of shale-drilling fluid interaction and its application in borehole stability studies." Thesis, Heriot-Watt University, 1994. http://hdl.handle.net/10399/1368.

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Shale is often the most difficult of all formations to maintain a stable wellbore in when drillincr ::> for oil and gas. Time and money spent overcoming this problem during drilling, together with overall reduced profit margins. has led the oil industry to devote considerable time and effort to solve the problem of unstable boreholes in shales. It has long been established that the moisture adsorption (or desorption) of shale rocks can be controlled by the salinity of drilling fluid. When compacted shale (under constant compaction stress) adsorbs moisture, its total volume increases and swelling strains develop. Developed swelling strains then become an integral part of the effective radial stress acting on the shale formation contributing to borehole failure. A mathematical model has been developed for predicting the swelling behaviour of shale when placed in contact with water under moderate pressures and the effect of the swelling on borehole (in)stability. The model is based on thermodynamic theory which suggests that fluid movement into or out of a shale is driven by an imbalance in the partial molar free energy of the shale and the contacting fluid. Conversion of the free energy of each system (fluid and shale) into "total swelling pressure" made it possible to model transient pressures and strains generated in shale. The analytical solution of the radial diffusivity equation is reduced to a simpler form for the model. The model was validated using equipment and experimental techniques which allow continuous monitoring of shale swelling as function of time and distance from the wetting end. It was found that increasing the compaction stress acting on the shale reduced the rate of swelling, and increasing the hydraulic pressure of the fluid on the shale's wetted surface increased the rate of swelling. This behaviour was adequately described by the model which therefore represents a new method for predicting shale swelling as function of time and radial distance under different environments. Swelling strains are then used to predict related changes in shale mechanical properties (failure criteria) and well (in)stability. Several well-site index tests have been developed to study shale-drilling fluid interaction at wellsite. These index tests can provide input data for the mathematical model. Drilling fluids can be screened for their ability to control shale swelling, thus minimising the risk of well bore instability.

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Rossich, Molina Estefanía. "Addressing the reactivity of biomolecules in the gas phase : coupling tandem mass spectrometry with chemical dynamics simulations." Thesis, Université Paris-Saclay (ComUE), 2016. http://www.theses.fr/2016SACLE043.

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Durant cette thèse, nous avons abordé l'étude de la réactivité en phase gazeuse des biomolécules. L’avènement des techniques d’ionisation douces telle que l’ionisation par éléctronébulisation, a rendu possible ces dernières années, la formation d'ions en phase gazeuse sans dégrader la biomolécule étudiée.La Dissociation Induite par Collision (CID) est un cas particulier de spectrométrie de masse en tandem, que nous avons utilisée durant ce travail. Le principe du CID est d'activer les modes rovibrationnelles d’un système moléculaire ionique par collision avec un gaz inerte, ce qui augmente la probabilité de fragmentation de l'ion. Bien qu'étant une technique très utile d'un point de vue analytique, la spectrométrie de masse en tandem ne donne pas d'informations sur les mécanismes des réactions se produisant dans la cellule de collision; afin d’obtenir ces informations, les simulations de dynamique chimiques apparaissent comme un outil satisfaisant. En effet, en utilisant la dynamique directe, nous évitons ainsi d'explorer la totalité de la surface d'énergie potentielle, qui devient compliquée lors de l’étude d’édifices moléculaires de grande taille. Etant donné que les simulations de dynamique chimiques sont limitées à de courtes échelles, de l’ordre de la dizaine de picosecondes, nous avons également employé la théorie unimoléculaire RRKM (Rice-Ramsperger-Kassel-Marcus) pour étudier la réactivité à des temps plus longs, en vue de comprendre les processus réactionnels se produisant à l’issue du processus de relaxation vibrationnelle intramoléculaire (IVR). Durant ce travail de thèse, nous avons choisi d'étudier comme système modèle de base nucléique la molécule d'uracile. Par ailleurs,nous avons aussi étudié la réactivité en phase gazeuse de sucres (cellobiose, maltose et gentiobiose), qui ont été au préalable dérivatisés afin de localiser la charge sur la molécule et ainsi simplifier l’étude théorique associée
In the present thesis, we address the study of the reactivity of biomolecules in the gasphase.The advent of soft ionization techniques such as electrospray ionization, made possible, in the last years, the gentle formation of ions in the gas phase without breaking the molecule understudy.Collision Induced Dissociation (CID) is aparticular case of tandem mass spectrometrydynamics simulations are pointed like asatisfactory tool. Using direct dynamics weavoid exploring the whole potential energysurface, which becomes really complicatedwhen dealing with big molecules.Since chemical dynamics simulations arerestricted to the short time scale reactivity,typically ~10ps, we make use of the Rice–Ramsperger–Kassel–Marcus (RRKM)unimolecular theory to study the reactivity atUniversité Paris-SaclayEspace Technologique / Immeuble DiscoveryRoute de l’Orme aux Merisiers RD 128 / 91190 Saint-Aubin, Francethat we use in the present thesis. The aim of CIDis to activate the rovibrational modes of an ionicmolecular system by collisions with an inert gas,increasing the probability of the ion of beingfragmented.Despite being a really useful technique, tandemmass spectrometry does not give informationabout the mechanisms of the reactions takingplace in the collision cell; in order to obtain suchinformation, chemicallonger time scales to understand reaction pathsthat take place after intramolecular vibrationrelaxation (IVR).In the present thesis we have chosen to study asmodel system of nucleobase the uracil molecule.Furthermore, we also studied the gas-phase reactivity of carbohydrates (cellobiose, maltose and gentiobiose), which were preliminarily derivatized in order to simplify the charge localization, and consequently the theoretical study

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Sergentu, Dumitru-Claudiu. "Géométries, electronic structures, and physico-chemical porperties of astatine species : an application of relativistic quantum mechanics." Thesis, Nantes, 2016. http://www.theses.fr/2016NANT4024/document.

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Les tentatives menées pour détruire des cellules cancéreuses avec les agents radiothérapeutiques à base de 211 At qui ont été synthétisés jusqu’à présent ne sont pas encore pleinement satisfaisantes car elles sont entachées par une deastatination in vivo. Étant donné que ce problème est lié aux connaissances actuelles qui sont limitées concernant la chimie de base de l’astate et de ses espèces, des recherches fondamentales combinant des expériences à l’échelle des ultra-traces et des études théoriques ont été lancées. Dans cette thèse, une étude théorique de plusieurs espèces de l’astate est réalisée au moyen de méthodes relativistes basées sur la théorie de la fonctionnelle de la densité ou des méthodes à basées sur la fonction d’onde. Tout d'abord, les méthodes qui peuvent être utilisées pour faire des prédictions pertinentes sont établies. A l’aide de ces approches, nous rationaliserons les structures électroniques, géométries et propriétés physicochimiques des différents systèmes d'intérêt théorique ou expérimental, en particulier les espèces AtF3 et AtO+. Finalement, nous identifierons formellement une nouvelle espèce de l’astate à l’aide de résultats expérimentaux et de calculs, ce qui non seulement complète le diagramme de Pourbaix de l’astate en milieu aqueux non complexant, mais aussi donne des informations cruciales pour identifier des conditions expérimentales pour rendre le plus « réactif » possible le précurseur At−, qui est de nos jours impliqué dans la synthèse d’agents radiothérapeutiques innovants
Trials to destroy cancer cells with currently synthesized 211 At-based radiotherapeutic agents are not yet fully satisfactorily since they resume to in vivo deastatination. Since this issue is related to the limited knowledge of the basic chemistry of At and its species, fundamental researches combining ultra-trace experiments and computational studies have been initiated. In this thesis, a computational study of several At species is performed, by means of relativistic density functional theory and wave-function-based calculations. First, the quantum mechanical approaches that can safely be used to make adequate predictions are established. Using these approaches, we attempt to rationalize the electronic structures, geometries, and physico-chemical properties of various systems of theoretical and/or experimental interest, in particular the AtF3 and AtO+ ones. By the end, we firmly identify a new At species by combining outcomes of experiments and calculations. This new species not only completes the Pourbaix diagram of At in aqueous and non-complexing media, but also gives clues of identifying experimental conditions to make best reactive the At– precursor, which is currently involved in the synthesis of promising radiotherapeutic agents

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Stewart, Gregory D. "Numerical simulation of titania deposition in a cold-walled impinging jet type APCVD reactor." Ohio : Ohio University, 1995. http://www.ohiolink.edu/etd/view.cgi?ohiou1178908165.

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Kamali-Asl, Arash. "Coupled Thermal-Hydrological-Mechanical-Chemical Processes In Geothermal And Shale Energy Developments." ScholarWorks @ UVM, 2019. https://scholarworks.uvm.edu/graddis/1031.

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Coupled Thermal-Hydrological-Mechanical-Chemical (THMC) processes that exist in the development of different geo-resources (e.g. deep geothermal and shale gas) affect the fracture response (i.e. aperture and permeability), which in turn influences the reservoir production. The main goal of this study was to experimentally evaluate the impact of THMC processes on the response of rock specimens relevant for deep geothermal and shale gas formations. The effects of THMC processes were investigated on: (i) success of the hydraulic fracturing/hydro-shearing mechanism during stimulation stage, and (ii) closure of the created network of fractures during production stage. The elastic, cyclic, creep, and failure characteristics of different intact reservoir rocks in both short- and long-term were investigated to evaluate their response in stimulation stage. In addition, a series of flow tests on fractured reservoir cores were conducted to evaluate how THMC processes affect fracture response subjected to different stress levels, temperatures, composition of injected fluid, and injection rate. Moreover, the sensitivity of ultrasonic signatures (i.e. velocity, amplitude, attenuation, and time-frequency content) to (i) microstructural changes in the intact rocks, and (ii) flow-induced alterations of aperture/permeability in the fractured rocks were investigated. Analysis of hydraulic data, chemical composition of the effluent, ultrasonic signatures, and X-Ray micro-CT and SEM images, provided invaluable information that facilitated interpretation of the effects of coupled THMC processes on fracture response.

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Zhang, Ziyang. "The application of modified linear elastic fracture mechanics (LEFM) and its implication for tear strength development of fibrous materials." Miami University / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=miami1604416361486942.

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Al-Badairy, Hameed Hussein S. "The mechanical and chemical failure of alumina scales formed on Fe-Cr-Al based alloys." Thesis, University of Liverpool, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.367056.

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Kayes, A. P. "The influence of chemical pre-treatment on the occurrence of filiform corrosion in aluminium alloys." Thesis, Cranfield University, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.323842.

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Collings, Ines Emily. "Structure-property relationships in framework materials : anomalous mechanics by design." Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:92efee44-d428-4907-8f99-716f4e0cfee7.

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Framework materials that contain molecular bridging ligands between metal nodes—as seen in coordination polymers—not only give rise to enhanced structural diversity, but also to a range of useful and unusual mechanical properties. This thesis demonstrates the general structure–property relationships that are developed for coordination polymers in order to enable prediction and design of their mechanical properties, and hence structural flexibility. Variable-temperature and -pressure diffraction experiments are employed for the determination of their mechanical properties, namely by calculating thermal expansion and compressibility coefficients. The anomalous and varied mechanical responses observed are rationalised by the important structural features, or the so-called mechanical building units (XBUs), of the coordination polymers. The XBUs are considered within the setting of framework topology, geometry, and composition in order to establish general design principles for targeting different degrees of flexibility within coordination polymers. The XBUs are identified first in silver(I) 2-methylimidazolate, Ag(mim), a framework which is comprised of structural motifs of varying strength, namely argentophilic interactions, hinge points and metal–ligand bonding. The anomalous mechanical responses in Ag(mim) are shown to be rationalised entirely by the XBUs present in the structure. The XBU abstraction is then applied to a range of other coordination polymers and shown to correspond directly with the anomalous responses known in these materials. The metal–ligand–metal linker XBU is investigated further in both cadmium imidazolate, Cd(im)₂, and zinc cyanide, Zn(CN)₂. Here, the linker chemistries are completely different between the two frameworks, but the diamondoid arrangement of the linkers, and thus the topology, is the same. The structural responses of the two frameworks are examined to unravel the extent of topology- and chemistry-driven mechanics. It is found that the topology dominates the atomic displacements of both frameworks, indicating the existence of common soft-mode dynamics which are likely to extend to other coordination polymers with the same topology. The three-dimensional framework-hinging XBUs in zinc isonicotinate, Zn(ISN)₂, and indium deuterium terephthalate, InD(BDC)₂, are considered next. These frameworks have the same topology but contrasting framework geometries, evident from the differing c/a-lattice parameter ratios. In this case, a geometric formalism is derived which can predict the direction of framework mechanical anisotropy in Zn(ISN)₂ and InD(BDC)₂ and other uniaxial coordination polymers. Finally, a family of ABX₃-type transition metal(II) formates are investigated, where both the B-site and A-site cations are varied. The chemical modifications give rise to variations in B- or A-site cation sizes, which are found to correlate with the magnitude of mechanical responses. These structure–mechanical property relationships—based upon framework topology, geometry and composition—are presented in separate chapters, and in each case generalised so that they can be applied to a range of coordination polymers. Hence the design principles determined here can provide the materials science community with an intuition on the type and magnitude of responses possible in these materials under different external stimuli.

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40

Federici, Justin Alexander. "Catalytic kinetics and thermal management in microchemical systems for distributed energy and portable power generation." Access to citation, abstract and download form provided by ProQuest Information and Learning Company; downloadable PDF file, 252 p, 2009. http://proquest.umi.com/pqdweb?did=1885675121&sid=4&Fmt=2&clientId=8331&RQT=309&VName=PQD.

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Patel, R. "Fluid mechanics of direct gravure roll coating : coat thickness and uniformity in direct gravure roll coating and their relation to operating conditions; an experimental and theoretical study." Thesis, University of Bradford, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.329261.

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Franz, David, and University of Lethbridge Faculty of Arts and Science. "Turing patterns in linear chemical reaction systems with nonlinear cross diffusion." Thesis, Lethbridge, Alta. : University of Lethbridge, Faculty of Arts and Science, 2007, 2007. http://hdl.handle.net/10133/659.

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Turing patterns have been studied for over 50 years as a pattern forming mechanism. To date the current focus has been on the reaction mechanism, with little to no emphasis on the diffusion terms. This work focuses on combining the simplest reaction mechanism possible and the use of nonlinear cross diffusion to form Turing patterns. We start by using two methods of bifurcation analysis to show that our model can form a Turing instability. A diffusion model (along with some variants) is then presented along with the results of numerical simulations. Various tests on both the numerical methods and the model are done to ensure the accuracy of the results. Finally an additional model that is closed to mass flow is introduced along with preliminary results.
vi, 55 leaves : ill. ; 29 cm.

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Baker, Matthew J. "CFD simulation of flow through packed beds using the finite volume technique." Thesis, University of Exeter, 2011. http://hdl.handle.net/10036/3396.

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When a disordered packed bed, or any heterogeneous media is studied using computational fluid dynamics, the tortuous task of generating a domain and creating a workable mesh presents a challenging issue to Engineers and Scientists. In this Thesis these challenges are addressed in the form of three studies in which both traditional and novel techniques are used to generate packed beds of spheres and cylinders for analysis using computational fluid dynamics, more specifically, the finite volume method. The first study uses a Monte-Carlo method to generate random particle locations for use with a traditional CADbased meshing approach. Computational studies are performed and compared in detail with experimental equivalent beds. In the second study, where there is a need for actual, physical beds to be studied, magnetic-resonance-imaging is used coupled with a novel approach known as image based meshing. In parallel experimental studies are performed on the experimental bed and compared with computational data. In the third study, to overcome fidelity issues with the previous approaches, a physical packed bed is manufactured which is 100% geometrically faithful to its computational counterpart to provide a direct comparison. All three computational studies have shown promising results in comparison with the experimental data described in this Thesis, with the data of Reichelt (1972) and the semi-empirical correlation of Eisfeld & Schnitzlein (2001). All experiments and computational models were carried out by the author unless otherwise stated.

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Shen, Yubin. "The chemical and mechanical behaviors of polymer / reactive metal systems under high strain rates." Diss., Georgia Institute of Technology, 2012. http://hdl.handle.net/1853/45804.

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As one category of energetic materials, impact-initiated reactive materials are able to release a high amount of stored chemical energy under high strain rate impact loading, and are used extensively in civil and military applications. In general, polymers are introduced as binder materials to trap the reactive metal powders inside, and also act as an oxidizing agent for the metal ingredient. Since critical attention has been paid on the metal / metal reaction, only a few types of polymer / reactive metal interactions have been studied in the literature. With the higher requirement of materials resistant to different thermal and mechanical environments, the understanding and characterization of polymer / reactive metal interactions are in great demand. In this study, PTFE (Polytetrafluoroethylene) 7A / Ti (Titanium) composites were studied under high strain rates by utilizing the Taylor impact and SHPB tests. Taylor impact tests with different impact velocities, sample dimensions and sample configurations were conducted on the composite, equipped with a high-speed camera for tracking transient images during the sudden process. SHPB and Instron tests were carried out to obtain the stress vs. strain curves of the composite under a wide range of strain rates, the result of which were also utilized for fitting the constitutive relations of the composite based on the modified Johnson-Cook strength model. Thermal analyses by DTA tests under different flow rates accompanied with XRD identification were conducted to study the reaction mechanism between PTFE 7A and Ti when only heat was provided. Numerical simulations on Taylor impact tests and microstructural deformations were also performed to validate the constitutive model built for the composite system, and to investigate the possible reaction mechanism between two components. The results obtained from the high strain rate tests, thermal analyses and numerical simulations were combined to provide a systematic study on the reaction mechanism between PTFE and Ti in the composite systems, which will be instructive for future energetic studies on other polymer / reactive metal systems.

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Tchernook, Ivan. "Strategies for Computational Investigation of Reaction Mechanisms in Organic and Polymer Chemistry Using Static Quantum Mechanics." Doctoral thesis, Universitätsbibliothek Chemnitz, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:ch1-qucosa-198756.

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This thesis presents computational studies of problems in the organic and polymer chemistry. The state-of-the art quantum chemical methods are used to gain further insight into the origin and the nature of the reactions in three different organic and polymer systems. The research questions are conceptually approached by identifying the key aspects. Then an appropriate strategy for the quantum chemical modeling is developed. In the scope of the polymer chemistry, the novel synthesis technique of nanostructured materials, the so-called twin polymerization, is investigated. Using three model systems of increasing complexity the influence of the anion (trifluoroacetate) in the reaction system is investigated. The effect of the solvent polarity as well as the effect of the entropic contributions are also considered. The rearrangement reaction of the volatile cyanotritylcarbenes is another topic. These carbenes readily rearrange to ethene main products, however also small amount of the unexpected heptafulvenes is formed. This unprecedented heptafulvene formation is modeled in detail and the energetics is systematically evaluated to identify most reasonable rearrangement pathways of the probable multiple alternative routes. Computational investigation of other tritylcarbenes with varying spectator substituents results in sophisticated data base for experimental investigations. At last, some controversial observations in experimental studies concerning the kinetics of the electrophilic alkylation of the barbiturate anion are studied. To interpret the kinetic measurements, different alkylation pathways are analyzed with respect to their energetics. Further, the influence of microsolvation is demonstrated.

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Matito, i. Gras Eduard. "Development, implementation and application of electronic structural descriptors to the analysis of the chemical bonding, aromaticity and chemical reactivity." Doctoral thesis, Universitat de Girona, 2006. http://hdl.handle.net/10803/7940.

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En la literatura sobre mecànica quàntica és freqüent trobar descriptors basats en la densitat de parells o la densitat electrònica, amb un èxit divers segons les aplicacions que atenyin. Per tal de que tingui sentit químic un descriptor ha de donar la definició d'un àtom en una molècula, o ésser capaç d'identificar regions de l'espai molecular associades amb algun concepte químic (com pot ser un parell solitari o zona d'enllaç, entre d'altres). En aquesta línia, s'han proposat diversos esquemes de partició: la teoria d'àtoms en molècules (AIM), la funció de localització electrònica (ELF), les cel·les de Voroni, els àtoms de Hirshfeld, els àtoms difusos, etc.
L'objectiu d'aquesta tesi és explorar descriptors de la densitat basats en particions de l'espai molecular del tipus AIM, ELF o àtoms difusos, analitzar els descriptors existents amb diferents nivells de teoria, proposar nous descriptors d'aromaticitat, així com estudiar l'habilitat de totes aquestes eines per discernir entre diferents mecanismes de reacció.
In the literature, several electronic descriptors based in the pair density or the density have been proposed with more or less success in their pratical applications. In order to be chemically meaningful the descriptor must give a definition of an "atom" in a molecule, or instead be able to identify some chemical interesting regions (such as lone pair, bonding region, among others). In this line, several molecular partition schemes have been put forward: atoms in molecules (AIM), electron localization function (ELF), Voronoi cells, Hirshfeld atoms, fuzzy atoms, etc.
The goal of this thesis is to explore the density descriptors based on the molecular partitions of AIM, ELF and fuzzy atom, analyze the existing decriptors at several levels of theory, propose new aromaticity descriptors, and study its ability to discern between different mechanisms of reaction.

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True, Aaron Conway. "Ecological engines: Finescale hydrodynamic and chemical cues, zooplankton behavior, and implications for nearshore marine ecosystems." Diss., Georgia Institute of Technology, 2014. http://hdl.handle.net/1853/54019.

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Ephemeral patches of hydrodynamic and chemical sensory cues at fine scales are fundamentally important to the life success of plankton populations and thus the overall health and vitality of nearshore marine ecosystems. We employed various tools from experimental fluid mechanics to create ecologically-relevant hydrodynamic and chemical conditions in a recirculating flume system for zooplankton behavioral assays. The goal was to quantify and correlate changes in zooplankton behavior with coincident sensory cues. A laminar, planar free jet (the Bickley jet) was used to create finescale, free shear layers with targeted hydrodynamic characteristics as well as finescale, sharp-edged layers of both beneficial and toxic ("red tide") phytoplankton species. Planar particle image velocimetry (PIV) and laser-induced fluorescence (LIF) were used to quantify the flow and concentration fields, respectively. Behavioral assays with a variety of crustacean zooplankton species including Antarctic krill (Euphausia superba), estuarine crab larvae (Panopeus herbstii), and calanoid copepods (Temora longicornis and Acartia tonsa), each unique in its ecology, morphology, and life history, show clear and statistically-significant behavioral responses to relevant hydrodynamic and chemical cues. Estuarine crab larvae optimize short term and long term behavioral needs (foraging and habitat selection) by sensing and exploiting the information contained in multi-directional free shear flows. In the presence of thin layers of toxic algal exudates (Karenia brevis), T. longicornis and A. tonsa exhibit explicit avoidance behaviors through significant increases in swimming speed and overall behavioral variability resulting in a conspicuous hydrodynamic signature in a risk/benefit behavioral response. Finally, Antarctic krill exploit the hydrodynamic cues contained in a free shear layer to modify swimming behaviors and ultimately graze in a thin phytoplankton layer (Tetraselmis spp.). Each species is able to sense and exploit the information contained in coherent hydrodynamic and chemical sensory cues to change swimming kinematics and alter macroscale trajectory characteristics. Quantifying changes in zooplankton behavior in response to ecologically-relevant sensory cues is a crucial step towards modeling (e.g. via biophysically-coupled individual-based ecosystem models) and managing sustainable marine fisheries.

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Berg, Jan-Erik. "Wood and fibre mechanics related to the thermomechanical pulping process." Doctoral thesis, Mittuniversitetet, Institutionen för naturvetenskap, teknik och matematik, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:miun:diva-6725.

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The main objective of this thesis was to improve the understanding of some aspects on wood and fibre mechanics related to conditions in the thermomechanical pulping process. Another objective was to measure the power distribution between the rotating plates in a refiner. The thesis comprises the following parts: –A literature review aimed at describing fracture in wood and fibres as related to the thermomechanical pulping process –An experimental study of fracture in wood under compression, at conditions similar to those in feeding of chips into preheaters and chip refiners –An experimental study of the effect of impact velocity on the fracture of wood, related to conditions of fibre separation in the breaker bar zone in a chip refiner –A micromechanical model of the deterioration of wood fibres, related to the development of fibre properties during the intense treatment in the small gap in the refining zone –Measurements of the power distribution in a refiner. The fracture in wood under compression was investigated by use of acoustic emission monitoring. The wood was compressed in both lateral and longitudinal directions to predict preferred modes of deformation in order to achieve desired irreversible changes in the wood structure. It was concluded that the most efficient compression direction in this respect is longitudinal. Preferable temperature at which the compression should be carried out and specific energy input needed in order to achieve substantial changes in the wood structure were also given. The fibre separation step and specifically the effect of impact velocity on the fracture energy were studied by use of a falling weight impact tester. The fracture surfaces were also examined under a microscope. An increase in impact velocity resulted in an increase in fracture energy. In the thermomechanical pulping process the fibres are subjected to lateral compression, tension and shear which causes the creation of microcracks in the fibre wall. This damage reduces the fibre wall stiffness. A simplified analytical model is presented for the prediction of the stiffness degradation due to the damage state in a wood fibre, loaded in uni-axial tension or shear. The model was based on an assumed displacement field together with the minimum total potential energy theorem. For the damage development an energy criterion was employed. The model was applied to calculate the relevant stiffness coefficients as a function of the damage state. The energy consumption in order to achieve a certain damage state in a softwood fibre by uniaxial tension or shear load was also calculated. The energy consumption was found to be dependent on the microfibril angle in the middle secondary wall, the loading case, the thicknesses of the fibre cell wall layers, and conditions such as moisture content and temperature. At conditions, prevailing at the entrance of the gap between the plates in a refiner and at relative high damage states, more energy was needed to create cracks at higher microfibril angles. The energy consumption was lower for earlywood compared to latewood fibres. For low microfibril angles, the energy consumption was lower for loading in shear compared to tension for both earlywood and latewood fibres. Material parameters, such as initial damage state and specific fracture energy, were determined by fitting of input parameters to experimental data. Only a part of the electrical energy demand in the thermomechanical pulping process is considered to be effective in fibre separation and developing fibre properties. Therefore it is important to improve the understanding of how this energy is distributed along the refining zone. Investigations have been carried out in a laboratory single-disc refiner. It was found that a new developed force sensor is an effective way of measuring the power distribution within the refining zone. The collected data show that the tangential force per area and consequently also the power per unit area increased with radial position. The results in this thesis improve the understanding of the influence of some process parameters in thermomechanical pulping related wood and fibre mechanics such as loading rate, loading direction, moisture content and temperature to separate the fibres from the wood and to achieve desired irreversible changes in the fibre structure. Further, the thesis gives an insight of the spatial energy distribution in a refiner during thermomechanical pulping.

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Li, Ji. "INVESTIGATION OF THE FRACTURE RESISTANCE OF PAPER UTILIZING A MODIFIED LINEAR ELASTIC FRACTURE MECHANICS MODEL." Miami University / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=miami1438342461.

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Angellier, Hélène. "Nanocristaux d'amidon de maïs cireux pour applications composites." Phd thesis, Université Joseph Fourier (Grenoble), 2005. http://tel.archives-ouvertes.fr/tel-00010699.

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Une suspension aqueuse de nanocristaux d'amidon de maïs cireux est obtenue par hydrolyse acide de grains d'amidon (longueur:40-60nm, largeur:15-30nm, épaisseur:5-7nm). Le premier objectif de la thèse est l'optimisation de la préparation de ces nanocristaux par la mise en place d'un plan d'expériences. Leur structure moléculaire est ensuite étudiée par dégradation enzymatique, et leur modification chimique de surface est envisagée. Le deuxième objectif est l'utilisation de ces nanocristaux comme charge de renfort dans une matrice polymère. Deux polymères naturels ont été choisis: le latex de caoutchouc naturel et l'amidon thermopalstique. Les nanocomposites, mis en oeuvre par casting, sont caractérisés en termes de propriétés morphologiques, structurales, barrière et mécaniques.

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Dissertations / Theses on the topic 'Chemical mechanics'

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