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JUMPING INSTABILITIES IN THE POST-BUCKLING OF A BEAM ON A PArTIAL NONLINEAr FOUNDATION

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Acta Mechanica Solida Sinica 2013年第5期26卷 500-513页

作者： Yin Zhang kevin D murphy State Key Laboratory of Nonlinear Mechanics (LNM) Institute of Mechanics Chinese Academy of Sciences Department of Mechanical Engineering University of Connecticut

Mode jumping is an instability phenomenon in the post-buckling region, which causes a sudden change in the equilibrium configuration and is thus harmful to structure. The con- figuration of a partial elastic foundation can directly induce mode coupling from the buckling stage and through the whole post-buckling region. The mode coupling effect due to the configuration of partial foundation on mode jumping is investigated and demonstrated to be an important factor of determining mode jumping. By properly choosing the partial elastic foundation configuration, mode jumping can be avoided.

关键词： instability mode jumping tertiary jumping buckling beam elastic foundation

Tensionless contact of a finite circular plate

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Acta Mechanica Sinica 2012年第5期28卷 1374-1381页

作者： Yin Zhang kevin D.murphy State Key Laboratory of Nonlinear Mechanics(LNM) Institute of MechanicsChinese Academy of Sciences Department of Mechanical Engineering the University of Connecticut

A general formulation is developed for the contact behavior of a finite circular plate with a tensionless elastic foundation. The gap distance between the plate and elastic foundation is incorporated as an important parameter. Unlike the previous models with zero gap distance and large/infinite plate radius, which assumes the lift-off/separation of a flexural plate from its supporting elastic foundation, this study shows that lift-off may not occur. The results show how the contact area varies with the plate radius, boundary conditions and gap distance. When the plate radius becomes large enough and the gap distance is reduced to zero, the converged contact radius close to the previous ones is obtained.

关键词： Tensionless contact Elastic foundation Plate Lift-off

Tensionless contact of a finite beam:Concentrated load inside and outside the contact zone

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Acta Mechanica Sinica 2013年第6期29卷 836-839页

作者： Yin Zhang kevin D.murphy State Key Laboratory of Nonlinear Mechanics Institute of MechanicsChinese Academy of Sciences Department of Mechanical Engineering University of ConnecticutStorrsCT 06268USA

For a finite beam with a nonzero gap distance, an asymmetric concentrated load can be either inside or outside of the contact zone. A new governing equation is given for the case of a concentrated load outside the contact zone. By numerically solving the left-side and right-side contact lengths of the beam, a criterion is established to determine whether the concentrated load is inside or outside the contact zone. A more general approach on the tensionless contact of a beam is thus presented.

关键词： Tensionless contact Lift-off Beam

CrACK PrOPAGATION IN STrUCTUrES SUBJECTED TO PErIODIC EXCITATION

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Acta Mechanica Solida Sinica 2007年第3期20卷 236-246页

作者： Zhang Yin murphy kevin D. State Key Laboratory of Nonlinear Mechanics （LNM） Institute of Mechanics Chinese Academy of Sciences Beijing 100080 China Department of Mechanical Engineering University of Connecticut CT 06269-3139 USA

In the present paper, asimple mechanical modelis developed to predict thedynamic response of a cracked structure subjected to periodic excitation, which has been used to identify the physical mechanisms in leading the growth or arrest of cracking. The structure under consideration consists of a beam with a crack along the axis, and thus, the crack may open in Mode I and in the axial direction propagate when the beam vibrates. In this paper, the system is modeled as a cantilever beam lying on a partial elastic foundation, where the portion of the beam on the foundation represents the intact portion of the beam. Modal analysis is employed to obtain a closed form solution for the structural response. Crack propagation is studied by allowing the elastic foundation to shorten （mimicking crack growth） if a displacement criterion, based on the material toughness, is met. As the crack propagates, the structural model is updated using the new foundation length and the response continues. From this work, two mechanisms for crack arrest are identified. It is also shown that the crack propagation is strongly influenced by the transient response of the structure.

关键词： crack propagation/arrest elastic foundation modal analysis vibration natural frequency

Nonlinear dynamic response of beam and its application in nanomechanical resonator

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Acta Mechanica Sinica 2012年第1期28卷 190-200页

作者： Yin Zhang Yun Liu kevin D.murphy State Key Laboratory of Nonlinear Mechanics Institute of MechanicsChinese Academy of Sciences100190 BeijingChina Faculty of Information and Automation Kunming University of Science and Technology650051 KunmingChina Department of Mechanical Engineering The University of ConnecticutStorrsCT 06269USA

Nonlinear dynamic response of nanomechanical resonator is of very important characteristics in its application. Two categories of the tension-dominant and curvaturedominant nonlinearities are analyzed. The dynamic nonlinearity of four beam structures of nanomechanical resonator is quantitatively studied via a dimensional analysis approach. The dimensional analysis shows that for the nanomechanical resonator of tension-dominant nonlinearity, its dynamic nonlinearity decreases monotonically with increasing axial loading and increases monotonically with the increasing aspect ratio of length to thickness; the dynamic nonlinearity can only result in the hardening effects. However, for the nanomechanical resonator of the curvature-dominant nonlinearity, its dynamic nonlinearity is only dependent on axial loading. Compared with the tension-dominant nonlinearity, the curvature-dominant nonlinearity increases monotonically with increasing axial loading; its dynamic nonlinearity

关键词： resonator. Dynamic response. Dynamic nonlinearity - Dimensional analysis

BUCKLING LOADS AND EIGENFrEQUENCIES OF A BrACED BEAM rESTING ON AN ELASTIC FOUNDATION

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Acta Mechanica Solida Sinica 2011年第6期24卷 510-518页

作者： Yin Zhang Yun Liu Peng Chen kevin D murphy State Key Laboratory of-Nonlinear Mechanics （LN M） Institute of Mechanics Chinese Academy of Sciences Beijing 100190 China Faculty of Information and Automation Kunming University of Science and Technology Kunming 650051 China Department of Civil Engineerning Guangdong Technical College of Water Resources and Electric Engineering Guangzhou 510635 China Department of Mechanical Engineering University of Connecticut Storrs CT 06269 USA

The eigenvalue problems of the buckling loads and natural frequencies of a braced beam on an elastic foundation are investigated. sented. The eigenvalues vary with the different The exact solutions for the eigenvalues are preparameters and are especially sensitive to the brace location. As the beam of a continuous system has infinite eigenvalues and these eigenvalues are influenced differently by a brace, the eigenvalues show rich variation patterns. Because these eigenvalues physically correspond to the structure buckling loads and natural frequencies, the study on the eigenvalues variation patterns can offer a design guidance of using a lateral brace of translation spring to strengthen the structure.

关键词： beam elastic foundation buckling eigenfrequency curve crossing curve veering

Inflammasome links traumatic brain injury, chronic traumatic encephalopathy, and Alzheimer's disease

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Neural regeneration research 2025年第6期20卷 1644-1664页

作者： Gabriela Seplovich Yazan Bouchi Juan Pablo de rivero Vaccari Jennifer C.Munoz Pareja Andrew reisner Laura Blackwell Yehia Mechref kevin K.Wang J.Adrian Tyndall Binu Tharakan Firas Kobeissy Department of Surgery Morehouse School of MedicineAtlantaGAUSA Department of Neurobiology Center for NeurotraumaMultiomics&Biomarkers(CNMB)Neuroscience InstituteMorehouse School of MedicineAtlantaGAUSA Department of Neurological Surgery and the Miami Project to Cure Paralysis University of Miami Miller School of MedicineMiamiFLUSA Division of Pediatric Critical Care Department of PediatricsUniversity of Miami Miller School of MedicineMiamiFLUSA Department of Pediatrics Emory UniversityAtlantaGAUSA Department of Neurosurgery Children’s Healthcare of AtlantaAtlantaGAUSA Department of Chemistry and Biochemistry Texas Tech UniversityLubbockTXUSA Morehouse School of Medicine AtlantaGAUSA

Traumatic brain injury, chronic traumatic encephalopathy, and Alzheimer's disease are three distinct neurological disorders that share common pathophysiological mechanisms involving neuroinflammation. One sequela of neuroinflammation includes the pathologic hyperphosphorylation of tau protein, an endogenous microtubule-associated protein that protects the integrity of neuronal cytoskeletons. Tau hyperphosphorylation results in protein misfolding and subsequent accumulation of tau tangles forming neurotoxic aggregates. These misfolded proteins are characteristic of traumatic brain injury, chronic traumatic encephalopathy, and Alzheimer's disease and can lead to downstream neuroinflammatory processes, including assembly and activation of the inflammasome complex. Inflammasomes refer to a family of multimeric protein units that, upon activation, release a cascade of signaling molecules resulting in caspase-induced cell death and inflammation mediated by the release of interleukin-1β cytokine. One specific inflammasome, the NOD-like receptor protein 3, has been proposed to be a key regulator of tau phosphorylation where it has been shown that prolonged NOD-like receptor protein 3 activation acts as a causal factor in pathological tau accumulation and spreading. This review begins by describing the epidemiology and pathophysiology of traumatic brain injury, chronic traumatic encephalopathy, and Alzheimer's disease. Next, we highlight neuroinflammation as an overriding theme and discuss the role of the NOD-like receptor protein 3 inflammasome in the formation of tau deposits and how such tauopathic entities spread throughout the brain. We then propose a novel framework linking traumatic brain injury, chronic traumatic encephalopathy, and Alzheimer's disease as inflammasomedependent pathologies that exist along a temporal continuum. Finally, we discuss potential therapeutic targets that may intercept this pathway and ultimately minimize long-term neurological decline.

关键词： Alzheimer's disease caspase-1 chronic traumatic encephalopathy inflammasomes neurodegeneration neuroinflammation NLrP1 NLrP3 pyroptosis tauopathy traumatic brain injury

Use of sensory substitution devices as a model system for investigating cross-modal neuroplasticity in humans

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Neural regeneration research 2015年第11期10卷 1717-1719页

作者： Amy C.Nau Matthew C.murphy kevin C.Chan UPMC Eye Center Ophthalmology and Visual Science Research Center Department of Ophthalmology School of Medicine University of Pittsburgh Mc Gowan Institute for regenerative Medicine University of Pittsburgh Louis J.Fox Center for Vision restoration University of Pittsburgh Department of Bioengineering Swanson School of Engineering University of Pittsburgh McGowan Institute for regenerative Medicine University of Pittsburgh Center for the Neural Basis of Cognition University of Pittsburgh Carnegie Mellon University

Blindness provides an unparalleled opportunity to study plasticity of the nervous system in *** work in this area examined the often dramatic modifications to the visual cortex that result when visual input is completely absent from birth or very early in life（Kupers and Ptito,2014）.More recent studies explored what happens to the visual pathways in the context of acquired *** is particularly relevant as the majority of diseases that cause vision loss occur in the elderly.

关键词： Use of sensory substitution devices as a model system for investigating cross-modal neuroplasticity in humans BOLD

Effect of abutment modeling on the seismic response ofbridge structures

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Earthquake Engineering and Engineering Vibration 2008年第4期7卷 395-402页

作者： Ady Aviram kevin r.Mackie Bozidar Stojadinovic Department of Civil and Environmental Engineering University of CaliforniaBerkeley Department of Civil and Environmental Engineering University of Central Florida

Abutment behavior significantly influences the seismic response of certain bridge structures. Specifically in the case of short bridges with relatively stiff superstructures typical of highway overpasses, embankment mobilization and inelastic behavior of the soil material under high shear deformation levels dominate the response of the bridge and its column bents. This paper investigates the sensitivity of bridge seismic response with respect to three different abutment modeling approaches. The abutment modeling approaches are based on three increasing levels of complexity that attempt to capture the critical components and modes of abutment response without the need to generate continuum models of the embankment, approach, and abutment foundations. Six existing reinforced concrete bridge structures, typical of Ordinary Bridges in California, are selected for the analysis. Nonlinear models of the bridges are developed in OpenSees. Three abutment model types of increasing complexity are developed for each bridge, denoted as roller, simplified, and spring abutments. The roller model contains only single-point constraints. The spring model contains discrete representations of backfill, bearing pad, shear key, and back wall behavior. The simplified model is a compromise between the efficient roller model and the comprehensive spring model. Modal, pushover, and nonlinear dynamic time history analyses are conducted for the six bridges using the three abutment models for each bridge. Comparisons of the analysis results show major differences in mode shapes and periods, ultimate base shear strength, as well as peak displacements of the column top obtained due to dynamic excitation. The adequacy of the three abutment models used in the study to realistically represent all major resistance mechanisms and components of the abutments, including an accurate estimation of their mass, stiffness, and nonlinear hysteretic behavior, is evaluated. recommendations for abutment modeling

关键词： embankment backfill shear keys bearing pads nonlinear analysis