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Articles 1 - 26 of 26

Full-Text Articles in Physics

Numerical Simulation Of Nonlinear Vibrations Of Discrete Mass With Harmonic Force Perturbation, M. Yusupov, B. A. Akhmedov, Olga Karpova Dec 2020

Numerical Simulation Of Nonlinear Vibrations Of Discrete Mass With Harmonic Force Perturbation, M. Yusupov, B. A. Akhmedov, Olga Karpova

Acta of Turin Polytechnic University in Tashkent

The problem of vibration of a single-mass system under the force excitation of vibration associated with a fixed base by a weightless nonlinear viscoelastic spring is considered. To take into account the rheological properties of the spring material, the Boltzmann-Volterra principle was used. Mathematical models of the problem under consideration are obtained, which are described by integro-differential equations. A solution method based on the use of quadrature formulas has been developed and a computer program has been compiled on its basis, the results obtained are presented in the form of graphs. The influence of nonlinear and rheological properties of a ...


The Conundrum Of Relaxation Volumes In First-Principles Calculations Of Charged Defects In Uo₂, Anuj Goyal, Kiran Mathew, Richard G. Hennig, Aleksandr V. Chernatynskiy Dec 2019

The Conundrum Of Relaxation Volumes In First-Principles Calculations Of Charged Defects In Uo₂, Anuj Goyal, Kiran Mathew, Richard G. Hennig, Aleksandr V. Chernatynskiy

Physics Faculty Research & Creative Works

The defect relaxation volumes obtained from density-functional theory (DFT) calculations of charged vacancies and interstitials are much larger than their neutral counterparts, seemingly unphysically large. We focus on UO2 as our primary material of interest, but also consider Si and GaAs to reveal the generality of our results. In this work, we investigate the possible reasons for this and revisit the methods that address the calculation of charged defects in periodic DFT. We probe the dependence of the proposed energy corrections to charged defect formation energies on relaxation volumes and find that corrections such as potential alignment remain ambiguous with ...


Geometry, Growth And Pattern Formation In Thin Elastic Structures, Salem Al-Mosleh Oct 2018

Geometry, Growth And Pattern Formation In Thin Elastic Structures, Salem Al-Mosleh

Doctoral Dissertations

Thin shells are abundant in nature and industry, from atomic to planetary scales. The mechanical behavior of a thin shell depends crucially on its geometry and embedding in 3 dimensions (3D). In fact, the behavior of extremely thin shells becomes scale independent and only depends on geometry. That is why the crumpling of graphene will have similarities to the crumpling of paper. In this thesis, we start by discussing the static behavior of thin shells, highlighting the role of asymptotic curves (curves with zero normal curvature) in determining the possible deformations and in controlling the folding patterns. In particular, we ...


Curvature-Induced Stiffness And The Spatial Variation Of Wavelength In Wrinkled Sheets, Joseph Paulsen, Evan Hohlfeld, Hunter King, Jiangshui Huang, Zhanglong Qiu, Thomas P. Russell, Narayanan Menon, Dominic Vella, Benny Davidovitch Jan 2016

Curvature-Induced Stiffness And The Spatial Variation Of Wavelength In Wrinkled Sheets, Joseph Paulsen, Evan Hohlfeld, Hunter King, Jiangshui Huang, Zhanglong Qiu, Thomas P. Russell, Narayanan Menon, Dominic Vella, Benny Davidovitch

Physics

Wrinkle patterns in compressed thin sheets are ubiquitous in nature and technology, from the furrows on our foreheads to crinkly plant leaves, from ripples on plastic-wrapped objects to the protein film on milk. The current understanding of an elementary descriptor of wrinkles—their wavelength—is restricted to deformations that are parallel, spatially uniform, and nearly planar. However, most naturally occurring wrinkles do not satisfy these stipulations. Here we present a scheme that quantitatively explains the wrinkle wavelength beyond such idealized situations. We propose a local law that incorporates both mechanical and geometrical effects on the spatial variation of wrinkle wavelength ...


Unearthing The Anticrystal: Criticality In The Linear Response Of Disordered Solids, Carl Peter Goodrich Jan 2015

Unearthing The Anticrystal: Criticality In The Linear Response Of Disordered Solids, Carl Peter Goodrich

Publicly Accessible Penn Dissertations

The fact that a disordered material is not constrained in its properties in the same way as a crystalline one presents significant and yet largely untapped potential for novel material design. However, unlike their crystalline counterparts, disordered solids are not well understood. Though currently the focus of intense research, one of the primary obstacles is the lack of a theoretical framework for thinking about disorder and its relation to mechanical properties. To this end, we study a highly idealized system composed of frictionless soft spheres at zero temperature that, when compressed, undergos a jamming phase transition with diverging length scales ...


Elasticity Of Differentiated And Undifferentiated Human Neuroblastoma Cells Characterized By Atomic Force Microscopy, Shijia Zhao, Alexander B. Stamm, Jeong Soon Lee, Alexei Gruverman, Jung Yul Lim, Linxia Gu Jan 2015

Elasticity Of Differentiated And Undifferentiated Human Neuroblastoma Cells Characterized By Atomic Force Microscopy, Shijia Zhao, Alexander B. Stamm, Jeong Soon Lee, Alexei Gruverman, Jung Yul Lim, Linxia Gu

Mechanical & Materials Engineering Faculty Publications

Human neuroblastoma (SH-SY5Y) cells, with its ability to differentiate into neurons, have been widely used as the in vitro cell culture model for neuroscience research, especially in studying the pathogenesis of Parkinson’s disease (PD) and developing therapeutic strategies. Cellular elasticity could potentially serve as a biomarker to quantitatively distinguish undifferentiated and differentiated SH-SY5Y cells. The goal of this work is to characterize the retinoic acid (RA) induced alternations of elastic properties of SH-SY5Y cells using atomic force microscopy (AFM). The elasticity was measured at multiple points of a single cell. Results have shown that the differentiation of SH-SY5Y cell ...


Rhombohedral Magnetostriction In Dilute Iron (Co) Alloys, Nicholas J. Jones, Gabriela Petculescu, Marilyn Wun-Fogle, James B. Restorff, Arthur E. Clark, Kristi B. Hathaway, Deborah L. Schlagel, Thomas A. Lograsso Jan 2015

Rhombohedral Magnetostriction In Dilute Iron (Co) Alloys, Nicholas J. Jones, Gabriela Petculescu, Marilyn Wun-Fogle, James B. Restorff, Arthur E. Clark, Kristi B. Hathaway, Deborah L. Schlagel, Thomas A. Lograsso

Ames Laboratory Publications

Iron is a well-utilized material in structural and magnetic applications. This does not mean, however, that it is well understood, especially in the field of magnetostriction. In particular, the rhombohedral magnetostriction of iron, λ111 , is anomalous in two respects: it is negative in sign, in disagreement with the prediction of first principles theory, and its magnitude decreases with increasing temperature much too rapidly to be explained by a power law dependence on magnetization. These behaviors could arise from the location of the Fermi level, which leaves a small region of the majority 3d t2g states unfilled, possibly favoring small internal ...


On The Crumpling Of Thin Sheets, Anne Dominique Cambou Nov 2014

On The Crumpling Of Thin Sheets, Anne Dominique Cambou

Doctoral Dissertations

The inner walls of mitochondria, cabbage leaves, and even the Himalayas are all examples of thin sheets: objects with a thickness much smaller than their length and width. Despite their differences in size and in material composition, similar patterns emerge when sheets are crumpled or forced into a small three-dimensional space. As the compaction progresses, the deformations focus into increasingly sharper features that look like the network of peaks and creases found on the surface of a balled up piece of paper. In this regime, external forces are straining the membrane, causing the elastic energy to localize while leaving most ...


Structure And Elasticity Of Lipid Membranes With Genistein And Daidzein Bioflavinoids Using X-Ray Scattering And Md Simulations., Mohit Raghunathan, Yuriy Zubovski, Richard Venable, Richard Pastor, John Nagle, Stephanie Tristram-Nagle Aug 2014

Structure And Elasticity Of Lipid Membranes With Genistein And Daidzein Bioflavinoids Using X-Ray Scattering And Md Simulations., Mohit Raghunathan, Yuriy Zubovski, Richard Venable, Richard Pastor, John Nagle, Stephanie Tristram-Nagle

Prof. Stephanie Tristram-Nagle Ph.D.

This work reports the effects of the bioflavinoids genistein and daidzein on lipid bilayers as determined by volume measurements, X-ray scattering, and molecular dynamics simulations. The experimental and simulated total molecular volumes were found to be in outstanding agreement with each other before the addition of genistein and daidzein and also after their addition. Both bioflavinoids inserted into the hydrocarbon region of both DOPC and diphytanoylPC near the carbonyls of the lipids and both decreased the bilayer thicknesses. The long axes of both bioflavinoids were oriented nearly parallel to the plane of the bilayer with their carbonyl groups preferentially pointed ...


Swelling And Folding As Mechanisms Of 3d Shape Formation In Thin Elastic Sheets, Marcelo A. Dias Sep 2012

Swelling And Folding As Mechanisms Of 3d Shape Formation In Thin Elastic Sheets, Marcelo A. Dias

Open Access Dissertations

We work with two different mechanisms to generate geometric frustration on thin elastic sheets; isotropic differential growth and folding. We describe how controlled growth and prescribing folding patterns are useful tools for designing three-dimensional objects from information printed in two dimensions. The first mechanism is inspired by the possibility to control shapes by swelling polymer films, where we propose a solution for the problem of shape formation by asking the question, ``what 2D metric should be prescribed to achieve a given 3D shape?'', namely the reverse problem. We choose two different types of initial configurations of sheets, disk-like with one ...


Geometries In Soft Matter, Zhenwei Yao May 2012

Geometries In Soft Matter, Zhenwei Yao

Physics - Dissertations

No abstract provided.


A Locking-Free Hp Dpg Method For Linear Elasticity With Symmetric Stresses, Jamie Bramwell, Leszek Demkowicz, Jay Gopalakrishnan, Weifeng Qiu Jan 2012

A Locking-Free Hp Dpg Method For Linear Elasticity With Symmetric Stresses, Jamie Bramwell, Leszek Demkowicz, Jay Gopalakrishnan, Weifeng Qiu

Mathematics and Statistics Faculty Publications and Presentations

We present two new methods for linear elasticity that simultaneously yield stress and displacement approximations of optimal accuracy in both the mesh size h and polynomial degree p. This is achieved within the recently developed discontinuous Petrov- Galerkin (DPG) framework. In this framework, both the stress and the displacement ap- proximations are discontinuous across element interfaces. We study locking-free convergence properties and the interrelationships between the two DPG methods.


Exploring Bacterial Nanowires: From Properties To Functions And Implications, Kar Man Leung Aug 2011

Exploring Bacterial Nanowires: From Properties To Functions And Implications, Kar Man Leung

Electronic Thesis and Dissertation Repository

The discovery of electrically conductive bacterial nanowires from a broad range of microbes provides completely new insights into microbial physiology. Shewanella oneidensis strain MR-1, a dissimilatory metal-reducing bacterium, produces extracellular bacterial nanowires up to tens of micrometers long, with a lateral dimension of ~10 nm. The Shewanella bacterial nanowires are efficient electrical conductors as revealed by scanning probe techniques such as CP-AFM and STM.

Direct electrical transport measurements along Shewanella nanowires reveal a measured nanowire resistivity on the order of 1 Ω∙cm. With electron transport rates up to 109/s at 100 mV, bacterial nanowires can serve as ...


Magnetostriction, Elasticity, And D03 Phase Stability In Fe–Ga And Fe–Ga–Ge Alloys, G. Petculescu, K. L. Ledet, Mianliang Huang, Thomas A. Lograsso, Y. N. Zhang, R. Q. Wu, M. Wun-Fogle, J. B. Restorff, A. E. Clark, K. B. Hathaway Mar 2011

Magnetostriction, Elasticity, And D03 Phase Stability In Fe–Ga And Fe–Ga–Ge Alloys, G. Petculescu, K. L. Ledet, Mianliang Huang, Thomas A. Lograsso, Y. N. Zhang, R. Q. Wu, M. Wun-Fogle, J. B. Restorff, A. E. Clark, K. B. Hathaway

Ames Laboratory Conference Papers, Posters, and Presentations

The contrast between the saturation tetragonal magnetostriction, λγ,2 = (3/2)λ100, of Fe1−xGax and Fe1−yGey, at compositions where both alloys exhibit D03 cubic symmetry (second peak region), was investigated. This region corresponds to x = 28 at. % Ga and y = 18 at. % Ge or, in terms of e/a = 2 x + 3 y + 1, to an e/a value of ∼1.55 for each of the alloys. Single crystal, slow-cooled, ternary Fe1−xy GaxGey alloys with e/a ∼1.55 and gradually increasing y ...


Elastic And Magnetic Properties Of Tb6fe(Sb,Bi)2 Using Resonant Ultrasound Spectroscopy., David Michael Mccarthy Aug 2010

Elastic And Magnetic Properties Of Tb6fe(Sb,Bi)2 Using Resonant Ultrasound Spectroscopy., David Michael Mccarthy

Masters Theses

Tb6FeSb2 and Tb6FeBi2 are novel rare earth compounds with little prior research. These compounds show high and variable curie temperatures for rare-earth compounds. This has lead to a literature review which includes the discussion of: elasticity, resonance, and magnetism. This review is used to discuss the theory and methodology which can relate these various properties to each other. Furthermore, synthesis, x-ray analysis, and RUS sample preparation of Tb6FeSb2 and Tb6FeBi2 were completed.

Resonant Ultrasound Spectroscopy (RUS) elastic studies were taken for Tb6FeSb2 and Tb6FeBi2 as a function temperature from 5-300K, in various magnetic fields ranging from 0-9T. Tb6FeSb2’s and ...


Wrinkling, Folding, And Snapping Instabilities In Polymer Films, Douglas Peter Holmes Sep 2009

Wrinkling, Folding, And Snapping Instabilities In Polymer Films, Douglas Peter Holmes

Open Access Dissertations

This work focuses on understanding deformation mechanisms and responsiveness associated with the wrinkling, folding, and snapping of thin polymer films. We demonstrated the use of elastic instabilities in confined regimes, such as the crumpling and snapping of surface attached sheets. We gained fundamental insight into a thin film's ability to localize strain. By taking advantage of geometric strain localization we were able to develop new strategies for responsive surfaces that will have a broad impact on adhesive, optical, and patterning applications. Using the rapid closure of the Venus flytrap's leafets as dictated by the onset of a snap ...


Viscoelastic Flow In Rotating Curved Pipes, Yitung Chen, Huajun Chen, Jinsuo Zhang, Benzhao Zhang Aug 2006

Viscoelastic Flow In Rotating Curved Pipes, Yitung Chen, Huajun Chen, Jinsuo Zhang, Benzhao Zhang

Mechanical Engineering Faculty Publications

Fully developed viscoelastic flows in rotating curved pipes with circular cross section are investigated theoretically and numerically employing the Oldroyd-B fluid model. Based on Dean’s approximation, a perturbation solution up to the secondary order is obtained. The governing equations are also solved numerically by the finite volume method. The theoretical and numerical solutions agree with each other very well. The results indicate that the rotation, as well as the curvature and elasticity, plays an important role in affecting the friction factor, the secondary flow pattern and intensity. The co-rotation enhances effects of curvature and elasticity on the secondary flow ...


Large Magnetically Induced Strains In Ni50mn28.7ga21.3 Driven With Collinear Field And Stress, A. Malla, M. J. Dapino, Thomas A. Lograsso, Deborah L. Schlagel Mar 2006

Large Magnetically Induced Strains In Ni50mn28.7ga21.3 Driven With Collinear Field And Stress, A. Malla, M. J. Dapino, Thomas A. Lograsso, Deborah L. Schlagel

Ames Laboratory Publications

Despite the huge magnetic-field-induced strain (MFIS) of up to 9.5% exhibited by certain Ni–Mn–Ga alloys, their usefulness in applications is severely hindered by the electromagnet device needed for driving the alloys with a magnetic field and orthogonal loading stress. In this paper we present macroscopic measurements obtained from a single crystal of Ni50Mn28.7Ga21.3 which demonstrate a large reversible MFIS of −4100 ppm when the alloy is driven with quasistatic magnetic fields and fixed compressive stresses applied collinearly along the [001] axis. This collinear configuration marks a fundamental difference with prior ...


Dislocation-Indenter Interaction In Nanoindentation, M. Ravi Shankar, Alexander H. King, Srinivasan Chandrasekar Jan 2005

Dislocation-Indenter Interaction In Nanoindentation, M. Ravi Shankar, Alexander H. King, Srinivasan Chandrasekar

Alexander H. King

A formulation of dislocation-indenter interaction in two-dimensional, isotropic elasticity is presented. A significant dislocation-indenter interaction is predicted when dislocations are nucleated very close to the indenter. This interaction is expected to have an important influence on dislocation motion and multiplication. Upon nucleation close to the indenter, the dislocations are shown to modify the load, load distribution, and moment acting on the indenter. This effect is seen to vary with the indentation contact length. Further away from the indenter, the indenter-dislocation interaction is shown to be negligible.


Protonium Formation In The P̅-H Collision At Low Energies By A Diabatic Approach, M. Hesse, Anh-Thu Le, C. D. Lin May 2004

Protonium Formation In The P̅-H Collision At Low Energies By A Diabatic Approach, M. Hesse, Anh-Thu Le, C. D. Lin

Physics Faculty Research & Creative Works

We present a diabatization technique in combination with the recently developed hyperspherical close coupling (HSCC) method. In contrast to the strict diabatization, our simple diabatization procedure transforms only sharp avoided crossings in the adiabatic hyperspherical potential curves into real crossings. With this approach, the weak collision channels can be removed from the close-coupling calculations. This method is used to study the antiproton-hydrogen collision at low energies. In the case of a scaled down (anti)proton mass, we show that a 10-channel calculation is enough to obtain converged cross sections at low energies. The results also indicate that protonium formation occurs ...


Tunable Local Polariton Modes In Semiconductors, Michael G. Foygel, Alexey Yamilov, Lev I. Deych, Alexander A. Lisyansky Sep 2001

Tunable Local Polariton Modes In Semiconductors, Michael G. Foygel, Alexey Yamilov, Lev I. Deych, Alexander A. Lisyansky

Physics Faculty Research & Creative Works

We study the local states within the polariton band gap that arise due to deep defect centers with strong electron-phonon coupling. Electron transitions involving deep levels may result in alteration of local elastic constants. In this case, substantial reversible transformations of the impurity polariton density of states occur, which include the appearance/disappearance of the polariton impurity band, and its shift and/or the modification of its shape. These changes can be induced by thermo- and photoexcitation of the localized electron states or by trapping of injected charge carriers. We develop a simple model, which is applied to the O ...


Vanishing Elasticity For Wet Foams: Equivalence With Emulsions And Role Of Polydispersity, A. Saint-James, Douglas J. Durian Jan 1999

Vanishing Elasticity For Wet Foams: Equivalence With Emulsions And Role Of Polydispersity, A. Saint-James, Douglas J. Durian

Department of Physics Papers

We present an experimental study of the rheology of polydisperse aqueous foams of different gas volume fractions φ. With oscillatory deformation at fixed frequency, we determine the behavior of the maximum stress as a function of the strain amplitude. At low strain, the maximum stress increases linearly, defining a shear modulus G.G. At progressively higher strains, the response eventually becomes nonlinear, defining the yield strain and the yield stress. While φ decreases toward φc=0.635±0.01,φc=0.635±0.01, GG goes to zero, and the yield stress decreases by many orders of magnitude with a ...


Recent Developments In Modeling Of The Stress Derivative Of Magnetization In Ferromagnetic Materials, David C. Jiles, Michael K. Devine Nov 1994

Recent Developments In Modeling Of The Stress Derivative Of Magnetization In Ferromagnetic Materials, David C. Jiles, Michael K. Devine

Ames Laboratory Publications

The effect of changing stress on the magnetization of ferromagnetic materials leads to behavior in which the magnetization may increase, or decrease, when exposed to the same stress under the same external conditions. A simple empirical law seems to govern the behavior when the magnetization begins from a major hysteresis loop. The application of the law of approach, in which the derivative of the magnetization with respect to the elastic energy supplied dM/dW is proportional to the magnetization displacement M anM, is discussed.


Magnetic And Crystallographic Order In Α‐Manganese, A. C. Lawson, Allen C. Larson, M. C. Aronson, S. Johnson, Z. Fisk, Paul C. Canfield, J. D. Thompson, R. B. Von Dreele Jan 1994

Magnetic And Crystallographic Order In Α‐Manganese, A. C. Lawson, Allen C. Larson, M. C. Aronson, S. Johnson, Z. Fisk, Paul C. Canfield, J. D. Thompson, R. B. Von Dreele

Paul C. Canfield

We have made time‐of‐flight neutron diffractionmeasurements on α‐manganese metal. Powder diffraction measurements were made at 14 temperatures between 15 and 305 K, and single crystalmeasurements were made at 15 and 300 K. We found that the crystal structure of α‐Mn is tetragonal below its Néel point of 100 K, with crystal symmetryI4̄2m and magnetic (Shubnikov) symmetry P I 4̄21 c. In agreement with the earlier results of Yamada et al., there are six independent magnetic atoms, and we found that their moments are weakly temperature dependent. The onset of magnetic order causes slight changes ...


Single Crystalline Elastic Constants Of C15-Type Mal2 Intermetallic Compounds , Raymond John Schiltz Jan 1972

Single Crystalline Elastic Constants Of C15-Type Mal2 Intermetallic Compounds , Raymond John Schiltz

Retrospective Theses and Dissertations

No abstract provided.


The Debye Temperatures Of Copper-Rich, Cu-Au Alloys , William Henry Cullen Jr. Jan 1971

The Debye Temperatures Of Copper-Rich, Cu-Au Alloys , William Henry Cullen Jr.

Retrospective Theses and Dissertations

No abstract provided.