Academic literature on the topic 'Octahedral configuration'

Structural charge arises on the surfaces of soil mineral particles in which either cation vacancies or isomorphic substitutions of cations by cations of lower valence occur. The principal minerals bearing structural charge are therefore the micas (Section 2.2), the 2:1 clay minerals (Section 2.3), or the Mn(IV) oxide, birnessite (Section 2.4). These three classes of mineral are all layer type and the cleavage surface on which their structural charge is manifest is a plane of O ions. The plane of O ions on the cleavage surface of a layer-type aluminosilicate is called a siloxane surface.This plane is characterized by hexagonal symmetry in the configuration of its constituent O ions, as shown at the top of Fig. 2.3 and, more explicitly, on the right side of Fig. 2.4, where a portion of the siloxane surface of the micas is depicted. Reactive molecular units on the surfaces of soil particles are termed surface functional groups. The functional group associated with the siloxane surface is the roughly hexagonal (strictly speaking, ditrigonalbecause the hexagonal symmetry is distorted when the tetrahedral sheet is fused to an octahedral sheet to form a layer) cavity formed by six corner-sharing silica tetrahedra. This cavity has a diameter of about 0.26 nm. The reactivity of the siloxane cavity depends on the nature of the electronic charge distribution in the layer structure. If there are no nearby isomorphic cations substitutions to create a negative charge, the O ions bordering the siloxane cavity function as an electron cloud donor that can bind molecules weakly through the van der Waals interaction. These interactions are akin to those underlying the hydrophobic interaction, discussed in Section 3.5, because the O in the siloxane surface can form only very weak hydrogen bonds with water molecules. Therefore, uncharged patches on siloxane surfaces may be considered hydrophobic regions to a certain degree, with, accordingly, an attraction for hydrophobic organic molecules. However, if isomorphic substitution of Al3+ by either Fe2+ or Mg2+ occurs in the octahedral sheet, the resulting structural charge is manifest on the siloxane cavities, as discussed in Section 2.3.

The abundant presence of aluminum (Al) in the environment, its commercial importance, and the potential toxic effects of dissolved forms of Al on living organisms have brought about extensive studies of Al hydrolysis products that originate from natural processes and industrial activities. A recent review of past studies of hydroxyaluminum (hydroxy-Al) solutions illustrates the complexity of aluminum hydrolysis. Because of the need to identify and quantify individual Al ion species, initial investigations of concentrated solutions of hydroly/ed aluminum salts using 27A1 nuclear magnetic resonance (NMR) spectrometry began more than 20 years ago in the United Kingdom with continuous-wave instrumentation. Since then, groups in Switzerland, France, and the United States as well as in the UK, involved with geochemical and pharmacological investigations, have applied pulse NMR instruments to conduct research mostly with concentrated Al hydrolysates. In NMR spectrometry, shapes and positions of spectral peaks indicate aluminum nuclei in different chemical environments, and the peak areas are proportional to the number of nuclei in each given symmetry. Figures 8.1 (a) and (b) and 8.2(a) and (b) illustrate liquid-state 27A1 NMR spectra of aluminum hydrolysis products. The well-defined peak at 62.5ppm, downfield from the Oppm reference position for Al(H2O)3+6, has been attributed to the tetrahedrally coordinated aluminum ion within the highly symmetrical configuration of the [AlO4Al12(OH)24(H2O)12]7+ species or “Al13” polyion in aqueous solution. This geometrical arrangement, also termed the “Keggin” structure, was originally deduced from X-ray diffraction studies of aluminum hydroxysulfate and hydroxyselenate salts precipitated from heated concentrated aluminum solutions after being partly neutralized with base. The Al13 structural unit that was postulated has 12 Al ions octahedrally coordinated with OH ions enclosing the central tetrahedral Al ion which is bonded to four of the octahedral ions through bridging by O2− ions. For a given sample specimen, broad NMR spectral peaks indicate the existence of (1) chemical-exchange processes and (2) species having less symmetry and larger electric field gradients than those which give rise to narrower peaks. Mildly acidic solutions of aluminum hydrolysis products exhibit a broad peak downfield from 0ppm centered at ~1 to ~2ppm.

Transition metal oxides (TMOs) have gained enormous heed in the last decades with their ability to deliver high capacitance. Importunity of futuristic, economical, and eco-friendly energy storage devices with more power/energy densities have increased outstanding interest in inventing new materials that boost performance to fulfill the energy requirements of modern society. Spinel Cobaltite (AB2O4), A, and B for tetrahedral and octahedral configurations of oxygen to form a closed packing of the cubic lattice. Spinel Structure of Cobaltites The physical and chemical properties of cobaltites depend upon their chemical composition and microstructural characteristics, which further depend on the synthesis methods with which they have been synthesized. The methods often include solgel, hydrothermal, electrospinning, and chemical processes. The different cobaltites with different chemical compositions are Co3O4[Tricobalt tetra oxide(CCO)], FeCo2O4[Iron cobaltite(FCO)], CuCo2O4[Copper cobaltite(CuCO)], NiCo2O4[Nickel cobaltite(NCO)], and ZnCo2O4[Zinc Cobaltite(ZCO)]. The Iron Cobaltite was found to exhibit ferromagnetic behavior at room temperature. The Co3O4 nanorods exhibit ultra capacitance of 281 Fg-1 . The FeCo2O4 microspheres nanosheets, nanoflakes, and nanofibers, exhibit ultra capacitance of 231.5 Fg-1 , 339 Fg-1 , 433 Fg-1 , 165 Fg-1 respectively. Also, the ZnCo2O4 nanowires show a value of about 1400 Fg-1 . The nickel cobaltite nanosheets and Copper cobaltite show the most prominent supercapacitive behavior having values of 2282 Fg-1 and 3080 Fg

Abstract The geometric characteristics of three well-known movable octahedral 6R mechanisms are described and then, by matrix algebra method, we derive their general displacement closed-form solutions for further investigation and analysis. Based on the fundamentals of three dimensional analytical coordinate geometry, a systematic approach is offered to generate the configuration of movable octahedral 6R mechanism with the help of computer graphics. In addition, a user-friendly computer aided program implementing the process of generation synthesis can be developed in Autolisp, a Lisp language interpreter within autoCAD. The numerical results for every generation and their constrained motion are confirmed by the derived analytical solutions. The physical models of these synthesized mechanisms are also built respectively.

Silicate minerals have been found to improve physical and mechanical properties of polymers significantly through clay/polymer nanocomposites. This class of materials uses smectite-type clays, such as hectorite, montmorillonite, magadiite, and synthetic mica, as fillers to enhance the properties of polymers. One of the most important properties of smectite-type clays is their layered structure, in which each layer is constructed from tetrahedrally coordinated Si atoms fused into an edge-shared octahedral plane of either Al(OH)3 or Mg(OH)2. The layers exhibit excellent mechanical properties parallel to the layer direction due to the nature of the bonding between these atoms. It has been found that Young’s modulus in the layer direction is 50 to 400 times higher than that of a typical polymer [1–5]. The layers have a high aspect ratio and each one is approximately 1 nm thick, while the diameter may vary from 30 nm to several microns or larger. Hundreds or thousands of these layers are stacked together with weak van der Waals forces to form a clay particle. With such a configuration, it is possible to tailor clays into various different structures in polymer [1,6,7].

The development of variable-stiffness systems is key to the advance of compact engineering solutions in a number of fields. Rigidizable structures exhibit variable-stiffness based on external stimuli. This function is necessary for deployable structures, such as inflatable space antennas, where the deployed structure is semi-permanent. Rigidization is also useful for a wide range of applications, such as prosthetics and exoskeletons, to help support external loads. In general, variable-stiffness designs suffer from a tradeoff between the magnitude of stiffness change and the ability of the structure to resist mechanical failure at any stiffness state. This paper presents the design, analysis, and fabrication of a rigidizable structure based on inflatable octet-truss cells. An octet-truss is a lattice-like configuration of elements, traditionally beams, arranged in a geometry reminiscent of that of the FCC lattice found in many metals; namely, the truss elements are arranged to form a single interior octahedral cell surrounded by eight tetrahedral cells. The interior octahedral cell is the core of the octet-truss unit cell, and is used as the main structure for examining the mechanics of the unit as a whole. In this work, the elements of the inflatable octet truss are pneumatic air muscles, also called McKibben actuators. Generalized McKibben actuators are a type of tubular pneumatic actuator that possess the ability to either contract or expand axially due to an applied pressure. Their unique kinematics are achieved by using a fiber wrap around an isotropic elastomeric shell. Under normal conditions, pressurizing the isotropic shell causes expansion in all directions, like a balloon. The fiber wrap constrains the ability of the shell to freely expand, due to the fiber stiffness. The wrap geometry thus guides the extensile/contractile motion of the actuator by controlling its kinematics. It is their ability to contract under pressure that makes McKibben actuators unique, and consequently they are of great interest presently to the robotics community due to their similitude to organic muscles. Kinematic analysis from constrained maximization of the shell volume during pressurization is used to obtain relations between the input work due to applied pressure and the resulting shape change due to strain energy. Analytical results are presented to describe the truss stiffness as a function of the McKibben geometry at varying pressures.

Energy absorption capability of structures with embedded pores depends upon the amount of voids present and their configurations/distributions. In this study, the energy absorption of acrylonitrile butadiene styrene (ABS) and polylactic acid (PLA) structures with varying pore shapes and sizes are investigated. The research was performed by two teams comprised of High School/Middle School teachers and undergraduate students as part of National Science Foundation (NSF) sponsored Research Experience for Teacher (RET)/Research Experience for Undergraduates (REU) teams. ABS samples were fabricated by Team 1 and utilized cubic unit cells with octahedral pores while Team 2 fabricated PLA samples that utilized unit cells with spherical pores. Eight sets of samples with dimensions 25mm × 25mm × 20mm were fabricated using a Makerbot Replicator 2X for ABS samples and a Lulzbot TAZ 5 for PLA samples. Each sample incorporated a 5 × 5 × 4 array of pores. All the samples were tested in compression and energy absorption per unit material volume of all the samples up to a particular maximum load was calculated from load-deflection curves. It is observed that the specific energy absorption of PLA and ABS porous structures greatly increases with increased porosity.

Abstract Although Stewart platforms have been applied in the designs of aricraft and vehicle simulators and parallel robots in many years, their closed-form solution of direct (forward) position analysis has not been completely solved. Up to the present time, only the relatively simple Stewart platforms have been analyzed. Examples are the octahedral Stewart and the 4-4 Stewart platforms, in which two pairs of both upper and lower joint centers are coincident. The former results in in an eighth degree polynomial and the latter results in an eighth and a twelfth degree polynomials for different cases. The single unknown variable is in the form of square of a tan-half-angle. This paper further extends the direct position analysis to a more genearl case of the Stewart platform, the 4-6 Stewart platforms, in which two pairs of upper joint centers of adjacent limbs are coincident. The result is a sixteenth degree polynomial in the square of a tan-half-angle, which indicates that a maximum of 32 configurations may be obtained. It is also shown that the previously derived solutions of 4-4 and and 3-6 Stewart platforms can be easily deduced from the sixteenth degree polynomial by setting some geometric parameters be equal to 1 or 0.

While cancers have no known cure, some of them can be successfully treated with the combination of surgery and systematic therapy. In general, systemic/widespread chemotherapy is usually injected into the bloodstream to attempt to target cancer cells. Such procedure often imparts devastating side effects because cancer drugs are nonspecific in activity, and transporting them throughout the bloodstream further reduces their ability to target the right region. This means that they kill both healthy and unhealthy cells. It has been observed that the physiological conditions of the fluids around living cells can be characterized by pH, and the magnitude of pH around a living cell is different from cancerous cells. Moreover, a multiscale anatomy of carcinoma will reveal that the microstructure of cancer cells contains some characteristic elements such as specific biomarker receptors and DNA molecules that exclusively differentiate them from healthy cells. If these cancer specific ligands can be intercalated by some functional molecules supplied from an implantable patch, then the patch can be envisioned to serve as a complementary technology with current systemic therapy to enhance localized treatment efficiency, minimize excess injections/surgeries, and prevent tumor recurrence. The broader objective of our current research is to capture some fundamental insights of such drug delivery patch system. It is envisioned that the essential components of the device is nanodiamonds (ND), parylene buffer layer and doxorubicin (DOX) drugs. In its simplest form, self-assembled nanodiamonds - functionalized or pristine, and DOX molecules are contained inside parylene capsule. The efficient functioning of the device is characterized by its ability to precisely detect targets (cancer cells) and then to release drugs at a controlled manner. The fundamental science issues concerning the development of the ND-based device include: 1. A precise identification of the equilibrium structure and self assembled morphology of nanodiamonds, 2. Fundamental understanding of the drug adsorption and desorption process to and from NDs, and 3. The rate of drug release through the parylene buffers. The structure of the nanodiamond (ND) is crucial to the adsorption and desorption of drug molecules because it not only changes the self-assembly configuration but also alters the surface electrostatics. To date, the structure and electrostatics of NDs are not yet well understood. A density functional tight binding theory (DFTB) study on smaller [2] NDs suggests a facet dependent charge distributions on ND surfaces. These charges are estimated by Mulliken Analysis [1]. Using the charges for smaller NDs (∼valid for 1–3.3 nm dia ND) we first projected surface charges for larger (4–10 nm) truncated octahedral nanodiamonds (TOND), and it has been found that the [100] face and the [111] face contain positively and negatively charged atoms, respectively. These projected charges are then utilized to obtain the self assembled structure of pristine TONDs from Molecular Dynamics (MD) simulations [4] as shown in Fig. 1. The opposite charges on the [100] and [111] face invoked electrostatic attractions among the initially isolated NDs and a network of nanodiamond agglutinates are formed as evidenced in Fig. 1(b). This study confirms why as manufactured NDs are found in agglomerated form. The study also suggests that a large fraction of ND surfaces become unavailable for drug absorption as many of the [100] faces are coherently connected to [111] faces. As a result, it can be perceived that effective area for drug adsorption on ND surfaces will be less compared to theoretical prediction which suggests that a 4nm TOND may contain as high 360 drug molecules on its surface [5]. It has been observed that as manufactured NDs may contain a variety of functional groups, and currently, we are studying the mechanism of self-assembly for functionalized nanodiamonds so that we understand the role of functional groups. The next phase of calculation involves binding of the DOX to the NDs. Essentially, the understanding of drug absorption and desorption profile at a controlled rate to and from NDs is the most critical part of the device design. Some recent quantum calculation suggests that part of NDs and drug molecules contain opposite charges at their surfaces; it has been a natural interpretation that interactions between ND and drug molecules should be straight-forward — NDs should attract to drugs as soon as they come closure. Recent experiments [6], however, suggest that NDs usually do not interact with drug molecules in the presence of neutral solutions. Addition of NaCl in the solution improves the interaction dramatically. In the first part of the study, we [3–5] have studied the interaction of single DOX molecules with TOND surfaces via MD simulation. As shown in Fig. 2, this study suggests that DOX molecules first arrange them around the preferential sites on nanodiamonds (e.g. around the [111] face) and then spontaneously attach on the surface. It is also observed that only DOX molecule is attached per facets of TONDs. It can be noted that each TOND has 6 [100] face and 8 [111] faces. Figure 3 shows the energy minimization process during the DOX-ND interaction. It can be noted that these simulations have been performed in vacuum environment. In order to see how DOX interacts in solution media, another set of simulations have been conducted where “vacuum” environment have been replaced with solution media of different pH. Moreover, functionalization on the ND surfaces will create a different environment for the DOX molecules. Research is underway to capture the fundamental physics on the DOX loading and release to and from functionalized nanodiamonds. Once we understand the essential physics of drug loading and unloading, in the future we plan to model diffusion controlled drug release through ND coated film device by incorporating the multiscale science learned from the current study. Results from this study will provide fundamental insight on the definitive targeting of infected cells and high resolution controlling of drug molecules.