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Articles 61 - 90 of 94
Full-Text Articles in Engineering
The Montana Mule: A Case Study In Interdisciplinary Capstone Design, Brock J. Lameres, Ahsan Mian, Hunter Lloyd, Robb Larson
The Montana Mule: A Case Study In Interdisciplinary Capstone Design, Brock J. Lameres, Ahsan Mian, Hunter Lloyd, Robb Larson
Mechanical and Materials Engineering Faculty Publications
The Montana MULE: A Case Study in Interdisciplinary Capstone Design In May of 2010, NASA held the 1st annual Lunabotics Mining Competition at theKennedy Space Center in Florida. In this competition, 22 teams from across the nationbuilt remote-controlled, robotic excavators to mine lunar regolith simulant. The winnerof the competition was the team who could successfully deposit the most regolith into acollector in 15 minutes. The goal of this competition was to encourage multidisciplinarycapstone design projects. Of the 22 teams that participated in the competition, the“Montana MULE” from Montana State University (MSU) was the only robot tosuccessfully mine the qualifying weight …
The Relationship Between Induced Fluid Structure And Boundary Slip In Nanoscale Polymer Films, Nikolai V. Priezjev
The Relationship Between Induced Fluid Structure And Boundary Slip In Nanoscale Polymer Films, Nikolai V. Priezjev
Mechanical and Materials Engineering Faculty Publications
The molecular mechanism of slip at the interface between polymer melts and weakly attractive smooth surfaces is investigated using molecular dynamics simulations. In agreement with our previous studies on slip flow of shear-thinning fluids, it is shown that the slip length passes through a local minimum at low shear rates and then increases rapidly at higher shear rates. We found that at sufficiently high shear rates, the slip flow over atomically flat crystalline surfaces is anisotropic. It is demonstrated numerically that the friction coefficient at the liquid-solid interface (the ratio of viscosity and slip length) undergoes a transition from a …
Slip Boundary Conditions For The Moving Contact Line In Molecular Dynamics And Continuum Simulations, Nikolai V. Priezjev, Anoosheh Niavarani
Slip Boundary Conditions For The Moving Contact Line In Molecular Dynamics And Continuum Simulations, Nikolai V. Priezjev, Anoosheh Niavarani
Mechanical and Materials Engineering Faculty Publications
The problem of the moving contact line between two immiscible fluids on a smooth surface is revisited using molecular dynamics (MD) and continuum simulations. In MD simulations a finite slip is allowed by choosing incommensurate wall-fluid densities and weak wall-fluid interaction energies. The shear stresses and velocity fields are extracted carefully in the bulk fluid region as well as near the moving contact line. In agreement with previous studies, we found slowly decaying partial slip region away from the contact line. In steady-state shear flows we extract the friction coefficient along the liquid-solid interface, the local slip length, and the …
Modeling The Combined Effect Of Surface Roughness And Shear Rate On Slip Flow Of Simple Fluids, Nikolai V. Priezjev, Anoosheh Niavarani
Modeling The Combined Effect Of Surface Roughness And Shear Rate On Slip Flow Of Simple Fluids, Nikolai V. Priezjev, Anoosheh Niavarani
Mechanical and Materials Engineering Faculty Publications
Molecular dynamics (MD) and continuum simulations are carried out to investigate the influence of shear rate and surface roughness on slip flow of a Newtonian fluid. For weak wall-fluid interaction energy, the nonlinear shear-rate dependence of the intrinsic slip length in the flow over an atomically flat surface is computed by MD simulations. We describe laminar flow away from a curved boundary by means of the effective slip length defined with respect to the mean height of the surface roughness. Both the magnitude of the effective slip length and the slope of its rate-dependence are significantly reduced in the presence …
Shear Rate Threshold For The Boundary Slip In Dense Polymer Films, Nikolai V. Priezjev
Shear Rate Threshold For The Boundary Slip In Dense Polymer Films, Nikolai V. Priezjev
Mechanical and Materials Engineering Faculty Publications
The shear rate dependence of the slip length in thin polymer films confined between atomically flat surfaces is investigated by molecular dynamics simulations. The polymer melt is described by the bead-spring model of linear flexible chains. We found that at low shear rates the velocity profiles acquire a pronounced curvature near the wall and the absolute value of the negative slip length is approximately equal to thickness of the viscous interfacial layer. At higher shear rates, the velocity profiles become linear and the slip length increases rapidly as a function of shear rate. The gradual transition from no-slip to steady-state …
The Effective Slip Length And Vortex Formation In Laminar Flow Over A Rough Surface, Anoosheh Niavarani, Nikolai V. Priezjev
The Effective Slip Length And Vortex Formation In Laminar Flow Over A Rough Surface, Anoosheh Niavarani, Nikolai V. Priezjev
Mechanical and Materials Engineering Faculty Publications
The flow of viscous incompressible fluid over a periodically corrugated surface is investigated numerically by solving the Navier–Stokes equation with the local slip and no-slip boundary conditions. We consider the effective slip length which is defined with respect to the level of the mean height of the surface roughness. With increasing corrugation amplitude the effective no-slip boundary plane is shifted toward the bulk of the fluid, which implies a negative effective slip length. The analysis of the wall shear stress indicates that a flow circulation is developed in the grooves of the rough surface provided that the local boundary condition …
Rheological Study Of Polymer Flow Past Rough Surfaces With Slip Boundary Conditions, Anoosheh Niavarani, Nikolai V. Priezjev
Rheological Study Of Polymer Flow Past Rough Surfaces With Slip Boundary Conditions, Anoosheh Niavarani, Nikolai V. Priezjev
Mechanical and Materials Engineering Faculty Publications
The slip phenomena in thin polymer films confined by either flat or periodically corrugated surfaces are investigated by molecular dynamics and continuum simulations. For atomically flat surfaces and weak wall-fluid interactions, the shear rate dependence of the slip length has a distinct local minimum which is followed by a rapid increase at higher shear rates. For corrugated surfaces with wavelength larger than the radius of gyration of polymer chains, the effective slip length decays monotonically with increasing corrugation amplitude. At small amplitudes, this decay is reproduced accurately by the numerical solution of the Stokes equation with constant and rate-dependent local …
Slip Boundary Conditions For Shear Flow Of Polymer Melts Past Atomically Flat Surfaces, Anoosheh Niavarani, Nikolai V. Priezjev
Slip Boundary Conditions For Shear Flow Of Polymer Melts Past Atomically Flat Surfaces, Anoosheh Niavarani, Nikolai V. Priezjev
Mechanical and Materials Engineering Faculty Publications
Molecular dynamics simulations are carried out to investigate the dynamic behavior of the slip length in thin polymer films confined between atomically smooth thermal surfaces. For weak wall-fluid interactions, the shear rate dependence of the slip length acquires a distinct local minimum followed by a rapid growth at higher shear rates. With increasing fluid density, the position of the local minimum is shifted to lower shear rates. We found that the ratio of the shear viscosity to the slip length, which defines the friction coefficient at the liquid/solid interface, undergoes a transition from a nearly constant value to the power …
Effect Of Surface Roughness On Rate-Dependent Slip In Simple Fluids, Nikolai V. Priezjev
Effect Of Surface Roughness On Rate-Dependent Slip In Simple Fluids, Nikolai V. Priezjev
Mechanical and Materials Engineering Faculty Publications
Molecular dynamics simulations are used to investigate the influence of molecular-scale surface roughness on the slip behavior in thin liquid films. The slip length increases almost linearly with the shear rate for atomically smooth rigid walls and incommensurate structures of the liquid/solid interface. The thermal fluctuations of the wall atoms lead to an effective surface roughness, which makes the slip length weakly dependent on the shear rate. With increasing the elastic stiffness of the wall, the surface roughness smoothes out and the strong rate dependence is restored again. Both periodically and randomly corrugated rigid surfaces reduce the slip length and …
Rate-Dependent Slip Boundary Conditions For Simple Fluids, Nikolai V. Priezjev
Rate-Dependent Slip Boundary Conditions For Simple Fluids, Nikolai V. Priezjev
Mechanical and Materials Engineering Faculty Publications
The dynamic behavior of the slip length in a fluid flow confined between atomically smooth surfaces is investigated using molecular dynamics simulations. At weak wall-fluid interactions, the slip length increases nonlinearly with the shear rate provided that the liquid/solid interface forms incommensurable structures. A gradual transition to the linear rate-dependence is observed upon increasing the wall-fluid interaction. We found that the slip length can be well described by a function of a single variable that in turn depends on the in-plane structure factor, contact density and temperature of the first fluid layer near the solid wall. Extensive simulations show that …
Titanium Alloyed With Boron, Seshacharyulu Tamirisakandala, Daniel B. Miracle, Raghavan Srinivasan, Jay S. Gunasekera
Titanium Alloyed With Boron, Seshacharyulu Tamirisakandala, Daniel B. Miracle, Raghavan Srinivasan, Jay S. Gunasekera
Mechanical and Materials Engineering Faculty Publications
Small additions of boron to conventional titanium alloys have been found to produce significant changes to the microstructures and associated properties. Grain refinement and improved strength and stiffness are first-order effects, which lead to possibilities for developing novel and affordable processing methodologies and to enhance performance over conventional titanium alloys. In this article, we introduce this new class of titanium alloys and describe unique formability benefits achieved via engineering microstructures.
X-Ray Photoelectron Spectroscopic Studies Of Dolomite Surfaces Exposed To Undersaturated And Supersaturated Aqueous Solutions, Xiaoming Hu, Pratik Joshi, Sharmila M. Mukhopadhyay, Steven R. Higgins
X-Ray Photoelectron Spectroscopic Studies Of Dolomite Surfaces Exposed To Undersaturated And Supersaturated Aqueous Solutions, Xiaoming Hu, Pratik Joshi, Sharmila M. Mukhopadhyay, Steven R. Higgins
Mechanical and Materials Engineering Faculty Publications
Cleaved surfaces of dolomite were studied using ex-situ X-ray photoelectron spectroscopy (XPS) following exposure of the surfaces to various experimental conditions. Dolomite samples exposed to air, to a highly undersaturated solution (0.1 M NaCl, pH = 9), and to solution with a supersaturation (-Delta mu/kT) of 5.5 (pH = 9) were investigated with semiquantitative methods of analysis to ascertain the degree of non-stoichiometry resulting at the dolomite surface from reactive conditions. It was found that the dolomite cleavage surface in undersaturated solution was not altered significantly from the stoichiometric surface termination. The composition of the cleaved surface after exposure to …
Method Of Reducing Internal Stress In Materials, Maher S. Amer, John F. Maguire
Method Of Reducing Internal Stress In Materials, Maher S. Amer, John F. Maguire
Mechanical and Materials Engineering Faculty Publications
Methods are provided for adjusting and controlling the stress between layers of material in a multilayer structure. A first stress is configured in a region of stress on the substrate material. A second material is then deposited over the substrate. A second stress results between the substrate and the second material such that a net stress results where the net stress is a function of said first and second stresses. As such, the first stress can be configured to achieve a predetermined, desired net stress. For example, the first stress can be configured to cancel out the second stress such …
Slip Behavior In Liquid Films On Surfaces Of Patterned Wettability: Comparison Between Continuum And Molecular Dynamics Simulations, Nikolai V. Priezjev, Anton A. Darhuber, Sandra M. Troian
Slip Behavior In Liquid Films On Surfaces Of Patterned Wettability: Comparison Between Continuum And Molecular Dynamics Simulations, Nikolai V. Priezjev, Anton A. Darhuber, Sandra M. Troian
Mechanical and Materials Engineering Faculty Publications
We investigate the behavior of the slip length in Newtonian liquids subject to planar shear bounded by substrates with mixed boundary conditions. The upper wall, consisting of a homogenous surface of finite or vanishing slip, moves at a constant speed parallel to a lower stationary wall, whose surface is patterned with an array of stripes representing alternating regions of no shear and finite or no slip. Velocity fields and effective slip lengths are computed both from molecular dynamics (MD) simulations and solution of the Stokes equation for flow configurations either parallel or perpendicular to the stripes. Excellent agreement between the …
Unsteady Tip Leakage, Bow Shock, Igv Wake Interaction In A Compressor, Xuedong Zhou, J. Mitch Wolff
Unsteady Tip Leakage, Bow Shock, Igv Wake Interaction In A Compressor, Xuedong Zhou, J. Mitch Wolff
Mechanical and Materials Engineering Faculty Publications
Unsteady aerodynamic analysis of Inlet Guide Vane (IGV)/rotor interaction is conducted with a commercial CFD solver, STAR-CD. 12% and 26% IGV axial chord IGV/Rotor spacing configurations were examined for 100% corrected speed at choke, peak efficiency and near stall conditions to investigate bow shock/tip leakage interaction within blade rows. Comparison with IGV surface unsteady pressure experimental data indicates good agreement at the IGV trailing edge across the span for both spacing configurations; therefore, validating the modeling of the high speed, highly loaded transonic compressor. The strongest effect on the tip clearance flow physics was caused by decreasing the axial spacing. …
Vibrational Behavior Of The MN+1AxN Phases From First-Order Raman Scattering (M=Ti,V,Cr, A=Si, X=C,N), Jonathan E. Spanier, Surojit Gupta, Maher S. Amer, Michel W. Barsoum
Vibrational Behavior Of The MN+1AxN Phases From First-Order Raman Scattering (M=Ti,V,Cr, A=Si, X=C,N), Jonathan E. Spanier, Surojit Gupta, Maher S. Amer, Michel W. Barsoum
Mechanical and Materials Engineering Faculty Publications
We report on the Raman spectra of Ti3SiC2 (312), M2AlC(211) (M=Ti, V, Cr, and Nb) and Ti4AlN3 (413), as representative compounds from the family of Mn+1AXn phases. Intense and narrow first-order Raman peaks are observed, and we present an analysis of the spectra based on symmetry considerations and from results of first-principles calculations of phonon frequencies. The agreement between experimental and calculated mode energies is excellent. The identification of the modes enables application of Raman scattering as a diagnostic tool for the detailed study of the structural and physical properties of this family of compounds and their …
Studies On Yba2nbo6 And Yba2cu3-Xnbxoy Buffer Layers, S. Sathiraju, R. Wheeler, Paul N. Barnes, T. L. Peterson, Iman Maartense, A. L. Campbell, N. A. Yust, T. J. Haugan, Q. Jia, Paul Arendt, Sharmila M. Mukhopadhyay, S. Vemulakonda
Studies On Yba2nbo6 And Yba2cu3-Xnbxoy Buffer Layers, S. Sathiraju, R. Wheeler, Paul N. Barnes, T. L. Peterson, Iman Maartense, A. L. Campbell, N. A. Yust, T. J. Haugan, Q. Jia, Paul Arendt, Sharmila M. Mukhopadhyay, S. Vemulakonda
Mechanical and Materials Engineering Faculty Publications
No abstract provided.
Cfd Analysis Of Unsteady Separated Transonic Oscillation Cascade Aerodynamics, Xuedong Zhou, J. Mitch Wolff
Cfd Analysis Of Unsteady Separated Transonic Oscillation Cascade Aerodynamics, Xuedong Zhou, J. Mitch Wolff
Mechanical and Materials Engineering Faculty Publications
With an improved algebraic mesh-deforming algorithm, STAR-CD, a commercial computational fluid dynamics (CFD) solver is employed for the numerical analysis of a transonic oscillating linear cascade of advanced design blades. The center blade oscillates 0.6-degrees about the middle cord. The numerical simulation is conducted for a frequency range from 200 Hz to 500 Hz. A hybrid grid, which utilizes a structured O-grid around the airfoil and an unstructured grid everywhere else is employed. The Spalart-Allmaras (S-A), one equation turbulence model, along with other two equation k-ε models, are also utilized for the steady state simulation. The S-A turbulence …
Joining Challenges In The Packaging Of Biomems, Hans Herfurth, Reiner Witte, S. Heinemann, Golam Newaz, Ahsan Mian, Daniel Georgiev, Greg Auner
Joining Challenges In The Packaging Of Biomems, Hans Herfurth, Reiner Witte, S. Heinemann, Golam Newaz, Ahsan Mian, Daniel Georgiev, Greg Auner
Mechanical and Materials Engineering Faculty Publications
Micro-joining and hermetic sealing of dissimilar and biocompatible materials is a critical issue for a broad spectrum of products such as micro -electronical, micro -optical and biomedical products and devices. Novel implantable microsystems currently under development will include functions such as localized sensing of temperature and pressure, electrical stimulation of neural tissue and the delivery of drugs. These devices are designed to be long-term implants that are remotely powered and controlled. The development of new, biocompatible materials and manufacturing processes that ensure long-lasting functionality and reliability are critical challenges. Important factors in the assembly of such systems are the small …
External And Intrinsic Anchoring In Nematic Liquid Crystals: A Monte Carlo Study, Nikolai V. Priezjev, G. Skacej, R. A. Pelcovits, S. Zumer
External And Intrinsic Anchoring In Nematic Liquid Crystals: A Monte Carlo Study, Nikolai V. Priezjev, G. Skacej, R. A. Pelcovits, S. Zumer
Mechanical and Materials Engineering Faculty Publications
We present a Monte Carlo study of external surface anchoring in nematic cells with partially disordered solid substrates, as well as of intrinsic anchoring at free nematic interfaces. The simulations are based on the simple hexagonal lattice model with a spatially anisotropic intermolecular potential. We estimate the corresponding extrapolation length b by imposing an elastic deformation in a hybrid cell-like nematic sample. Our estimates for b increase with increasing surface disorder and are essentially temperature independent. Experimental values of b are approached only when both the coupling of nematic molecules with the substrate and the anisotropy of nematic-nematic interactions are …
Optomechanical Properties Of Stretched Polymer Dispersed Liquid Crystal Films For Scattering Polarizer Applications, Iciro Amimori, Nikolai V. Priezjev, Robert A. Pelcovits, Gregory P. Crawford
Optomechanical Properties Of Stretched Polymer Dispersed Liquid Crystal Films For Scattering Polarizer Applications, Iciro Amimori, Nikolai V. Priezjev, Robert A. Pelcovits, Gregory P. Crawford
Mechanical and Materials Engineering Faculty Publications
A scattering polarizer is created by subjecting a polymer dispersed liquid crystal (PDLC) film to tensile strain. The optomechanical properties of the film are investigated by simultaneously measuring the stress-strain and polarization dependent optical transmission characteristics. The correlation between transmittances of two orthogonal polarizations and the stress-strain curve reveals that the polymer orientation as well as the droplet shape anisotropy influences the liquid crystal alignment within the droplets. A Monte-Carlo simulation based on the Lebwohl-Lasher model is used to explain the subtle influence of polymer orientation on liquid crystal alignment.
Coarsening Dynamics Of Biaxial Nematic Liquid Crystals, Nikolai V. Priezjev, Robert A. Pelcovits
Coarsening Dynamics Of Biaxial Nematic Liquid Crystals, Nikolai V. Priezjev, Robert A. Pelcovits
Mechanical and Materials Engineering Faculty Publications
We study the coarsening dynamics of two- and three-dimensional biaxial nematic liquid crystals, using Langevin dynamics. Unlike previous work, we use a model with no a priori relationship among the three elastic constants associated with director deformations. Biaxial nematics possess four topologically distinct classes of defects, three of which have half-integer charge, while the fourth, which plays a minor role in coarsening, is of integer charge. We find a rich variety of coarsening behavior, including the presence of one, two, or three of the half-integer classes at late times, depending on the relative values of the elastic constants and the …
Virtual Surfaces, Director Domains And The Freedericksz Transition In Polymer Stabilized Nematic Liquid Crystals, Pavel A. Kossyrev, Jun Qi, Nikolai V. Priezjev, Robert A. Pelcovits, Gregory P. Crawford
Virtual Surfaces, Director Domains And The Freedericksz Transition In Polymer Stabilized Nematic Liquid Crystals, Pavel A. Kossyrev, Jun Qi, Nikolai V. Priezjev, Robert A. Pelcovits, Gregory P. Crawford
Mechanical and Materials Engineering Faculty Publications
The critical field of the Freedericksz transition and switching dynamics are investigated for polymer stabilized nematic liquid crystals as a function of polymer concentration. A simple phenomenological model is proposed to describe the observed critical field and dynamic response time behaviors as a function of concentration. In this model the polymer fibrils form director domains, which are bounded by virtual surfaces with a finite anchoring energy. The Freedericksz transition occurs independently within each of these domains.
Correlation Between The Xps Peak Shapes Of Y1bu2cu3o7-X And Film Quality, Paul N. Barnes, Sharmila M. Mukhopadhyay, Timothy J. Haugan, Swaminathan Krishnaswami, Justin C. Tolliver, Iman Maartense
Correlation Between The Xps Peak Shapes Of Y1bu2cu3o7-X And Film Quality, Paul N. Barnes, Sharmila M. Mukhopadhyay, Timothy J. Haugan, Swaminathan Krishnaswami, Justin C. Tolliver, Iman Maartense
Mechanical and Materials Engineering Faculty Publications
X-ray photoelectron spectroscopy (XPS) depth profiling was used to investigate the compositional and chemical profile of a typical YBCO coated conductor architecture. Results of the process revealed that the Y(3d) photoelectronic peak shape in these films is very different from bulk YBCO. To investigate this, several samples of Y i Ba2Cu307_„ thin films were intentionally created of varying quality. The films were deposited on LaA10 3 by pulsed laser deposition with ./c. values ranging from poorly conducting up to several MA/cm2. Initial results indicated a potential correlation between the Y(3d) XPS peak shape (full-width-half-maximum) of the YBCO and the film …
Simulations Of Nematic Liquid Crystals: Confined Geometries, Phase Transitions And Topological Defects, Nikolai V. Priezjev
Simulations Of Nematic Liquid Crystals: Confined Geometries, Phase Transitions And Topological Defects, Nikolai V. Priezjev
Mechanical and Materials Engineering Faculty Publications
The physics of liquid crystals is an exciting field of research with important practical applications. In this dissertation we present the results of simulation studies of nematic liquid crystals using Monte Carlo and molecular dynamic techniques. In our first project we performed Monte Carlo Simulations of the Lebwohl-Lasher (LL) model of nematic liquid crystals confined to cylindrical cavities with perpendicular anchoring. In this particular geometry one has an interesting interplay between bulk and surface energies, which results in different director configurations inside the cylinder. Our work reconciled the apparent contradictions between the results of earlier simulations and approximate analytics theories. …
Strongly Screened Vortex Lattice Model With Disorder, C. Giardina', Nikolai V. Priezjev, J. M. Kosterlitz
Strongly Screened Vortex Lattice Model With Disorder, C. Giardina', Nikolai V. Priezjev, J. M. Kosterlitz
Mechanical and Materials Engineering Faculty Publications
The three dimensional XY model with quenched random disorder and finite screening is studied. We argue that the system scales to model with λ≃0≃T and the resulting effective model is studied numerically by defect energy scaling. In zero external field we find that there exists a true superconducting phase with a stiffness exponent θ≃+1.0 for weak disorder. For low magnetic field and weak disorder, there is also a superconducting phase with θ≃+1.0 which we conjecture is a Bragg glass. For larger disorder or applied field, there is a non superconducting phase with θ≃−1.0. We estimate the critical external field whose …
Disclination Loop Behavior Near The Nematic-Isotropic Transition, Nikolai V. Priezjev, Robert A. Pelcovits
Disclination Loop Behavior Near The Nematic-Isotropic Transition, Nikolai V. Priezjev, Robert A. Pelcovits
Mechanical and Materials Engineering Faculty Publications
We investigate the behavior of disclination loops in the vicinity of the first-order nematic-isotropic transition in the Lebwohl-Lasher and related models. We find that two independent measures of the transition temperature, the free energy, and the distribution of disclination line segments, give essentially identical values. We also calculate the distribution function D(p) of disclination loops of perimeter p and fit it to a quasiexponential form. Below the transition, D(p) falls off exponentially, while in the neighborhood of the transition, it decays with a power-law exponent approximately equal to 2.5, consistent with a “blowout” of loops at the transition. In a …
Cluster Monte Carlo Simulations Of The Nematic--Isotropic Transition, Nikolai V. Priezjev, Robert A. Pelcovits
Cluster Monte Carlo Simulations Of The Nematic--Isotropic Transition, Nikolai V. Priezjev, Robert A. Pelcovits
Mechanical and Materials Engineering Faculty Publications
We report the results of simulations of the three-dimensional Lebwohl-Lasher model of the nematic-isotropic transition using a single cluster Monte Carlo algorithm. The algorithm, first introduced by Kunz and Zumbach to study two-dimensional nematics, is a modification of the Wolff algorithm for spin systems, and greatly reduces critical slowing down. We calculate the free energy in the neighborhood of the transition for systems up to linear size 70. We find a double well structure with a barrier that grows with increasing system size. We thus obtain an upper estimate of the value of the transition temperature in the thermodynamic limit.
Surface Extrapolation Length And Director Structures In Confined Nematics, Nikolai V. Priezjev, Robert A. Pelcovits
Surface Extrapolation Length And Director Structures In Confined Nematics, Nikolai V. Priezjev, Robert A. Pelcovits
Mechanical and Materials Engineering Faculty Publications
We report the results of Monte Carlo simulations of the Lebwohl-Lasher model of nematic liquid crystals confined to cylindrical cavities with homeotropic anchoring. We show that the ratio of the bulk to surface couplings is not in general equal to the corresponding parameter K/W used in elastic theory (where K is the Frank elastic constant in the one-constant approximation and W is the surface anchoring strength). By measuring the temperature dependence of K/W (which is equivalent to the surface extrapolation length) we are able to reconcile the results of our simulations as well as others with the predictions of elastic …
Three-Dimensional Dynamic Analysis Of Wheelchair Propulsion, Mary M. Rodgers, Srinivas Tummarakota, Junghsen Lieh
Three-Dimensional Dynamic Analysis Of Wheelchair Propulsion, Mary M. Rodgers, Srinivas Tummarakota, Junghsen Lieh
Mechanical and Materials Engineering Faculty Publications
A three-dimensional (3-D) inverse dynamic model of wheelchair propulsion was developed using the Newton-Euler method based on body coordinate systems. With this model, the arm was assumed to be three rigid segments (hand, forearm, and upper arm) connected by the wrist, elbow, and shoulder joints. A symbolic method was adopted to generate the equations of motion. The model was used to compute the joint forces and moments based on the inputs obtained from a 3-D motion analysis system, which included an instrumented wheelchair, video cameras, and a data acquisition system. The linear displacements of markers placed on the joints were …