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Temperature and composition dependent screw dislocation mobility in austenitic stainless steels from large-scale molecular dynamics

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npj Computational Materials 2020年第1期6卷 176-185页

作者： Kevin Chu Michael E.Foster Ryan B.Sills Xiaowang Zhou Ting Zhu david l.mcdowell School of Materials Science and Engineering Georgia Institute of Technology AtlantaAtlantaGA 30332USA Sandia National laboratories LivermoreCA 94550USA Department of Materials Science and Engineering Rutgers UniversityPiscatawayNJ 08854USA Woodruff School of Mechanical Engineering Georgia Institute of TechnologyAtlantaGA 30332USA

Extensive molecular dynamics simulations are performed to determine screw dislocation mobility in austenitic Fe_(0.7)NixCr_(0.3-x) stainless steels as a function of temperature ranging from 100 to 1300 K,resolved shear stress from 30 to 140 MPa,and Ni composition from 0.0 to 30.0 at%.These mobility data are fitted to a linear mobility law with a nonzero stress offset,referred to as the threshold *** find that both the linear drag coefficient and the threshold stress increase with Ni *** drag coefficient increases with temperature,whereas the threshold stress decreases with *** on these calculations,we determine fitting functions for the linear solute drag coefficient as a function of temperature and *** mobility laws determined in this study may serve to inform dislocation dynamics simulations pertinent to dislocation network evolution at elevated temperatures for a wide composition range of austenitic stainless steels.

关键词： austenitic dislocation dynamics

On the mechanistic origins of maximum strength in nanocrystalline metals

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npj Computational Materials 2020年第1期6卷 393-404页

作者： Ankit Gupta Jacob Gruber Satish S.Rajaram Gregory B.Thompson david l.mcdowell Garritt J.Tucker Colorado School of Mines Mechanical EngineeringGoldenCO 80401USA Department of Mechanical Engineering Drexel UniversityPhiladelphiaPA 19104USA Department of Metallurgical and Materials Engineering University of AlabamaTuscaloosaAL 35487USA Department of Mechanical Engineering Georgia Institute of TechnologyAtlantaGA 30332USA

The maximum strength of polycrystalline metals/alloys has been suggested to occur at nanoscale grain sizes where the governing deformation mechanism transitions from dislocation plasticity to grain boundary mediated *** tremendous progress recently uncovering links between transitions in nanoscale mechanisms and peak strength,the scientific literature is mostly devoid of any quantitative support,owing to the difficulty in measuring the resolved contribution of individual mechanisms to microstructural strain *** this study,the contribution of individual nanoscale mechanisms to the overall deformation of nanocrystalline Ni is calculated from atomistic simulations leveraging continuum-based kinematic metrics to compute mechanistic contributions to microstructural strain.

关键词： strength deformation grain

Silk-based nerve guidance conduits with macroscopic holes modulate the vascularization of regenerating rat sciatic nerve

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Neural Regeneration Research 2025年第6期20卷 1789-1800页

作者： Carina Hromada Patrick Heimel Markus Kerbl lászlóGál Sylvia Nürnberger Barbara Schaedl James Ferguson Nicole Swiadek Xavier Monforte Johannes C.Heinzel Antal Nógrádi Andreas H.Teuschl-Woller david Hercher Department life Science Engineering University of Applied Sciences Technikum WienViennaAustria Austrian Cluster for Tissue Regeneration ViennaAustria ludwig Boltzmann Institute for Traumatology The Research Center in Cooperation with AUVAViennaAustria University Clinic of Dentistry Medical University of ViennaViennaAustria Department of Plastic Reconstructive and Aesthetic SurgeryLandesklinikum Wiener Neustadt2700 Wiener NeustadtAustria Department of Anatomy Histology and EmbryologyAlbert Szent-Györgyi Medical SchoolUniversity of SzegedSzegedHungary Medical University of Vienna Department of Orthopedics and Trauma SurgeryDevision of Trauma SurgeryViennaAustria Department of Hand- PlasticReconstructive and Burn SurgeryBG Unfallklinik TuebingenUniversity of TuebingenTuebingenGermany

Peripheral nerve injuries induce a severe motor and sensory deficit. Since the availability of autologous nerve transplants for nerve repair is very limited, alternative treatment strategies are sought, including the use of tubular nerve guidance conduits(tNGCs). However, the use of tNGCs results in poor functional recovery and central necrosis of the regenerating tissue, which limits their application to short nerve lesion defects(typically shorter than 3 cm). Given the importance of vascularization in nerve regeneration, we hypothesized that enabling the growth of blood vessels from the surrounding tissue into the regenerating nerve within the tNGC would help eliminate necrotic processes and lead to improved regeneration. In this study, we reported the application of macroscopic holes into the tubular walls of silk-based tNGCs and compared the various features of these improved silk^(+) tNGCs with the tubes without holes(silk^(–) tNGCs) and autologous nerve transplants in an 8-mm sciatic nerve defect in rats. Using a combination of micro-computed tomography and histological analyses, we were able to prove that the use of silk^(+) tNGCs induced the growth of blood vessels from the adjacent tissue to the intraluminal neovascular formation. A significantly higher number of blood vessels in the silk^(+) group was found compared with autologous nerve transplants and silk^(–), accompanied by improved axon regeneration at the distal coaptation point compared with the silk^(–) tNGCs at 7 weeks postoperatively. In the 15-mm(critical size) sciatic nerve defect model, we again observed a distinct ingrowth of blood vessels through the tubular walls of silk^(+) tNGCs, but without improved functional recovery at 12 weeks postoperatively. Our data proves that macroporous tNGCs increase the vascular supply of regenerating nerves and facilitate improved axonal regeneration in a short-defect model but not in a critical-size defect model. This study suggests that further optimizatio

关键词： axon regeneration blood vessel functional recovery macroporous nerve lesion peripheral nerve repair sciatic nerve silk-based nerve guidance conduit vascularization

Sequential slip transfer of mixed-character dislocations across Σ3 coherent twin boundary in FCC metals: a concurrent atomistic-continuum study

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npj Computational Materials 2016年第1期2卷 247-255页

作者： Shuozhi Xu liming Xiong Youping Chen david l.mcdowell Woodruff School of Mechanical Engineering Georgia Institute of TechnologyAtlantaGAUSA Department of Aerospace Engineering Iowa State UniversityAmesIAUSA Department of Mechanical and Aerospace Engineering University of FloridaGainesvilleFLUSA School of Materials Science and Engineering Georgia Institute of TechnologyAtlantaGAUSA

Sequential slip transfer across grain boundaries(GB)has an important role in size-dependent propagation of plastic deformation in polycrystalline *** example,the Hall–Petch effect,which states that a smaller average grain size results in a higher yield stress,can be rationalised in terms of dislocation pile-ups against *** spite of extensive studies in modelling individual phases and grains using atomistic simulations,well-accepted criteria of slip transfer across GBs are still lacking,as well as models of predicting irreversible GB structure *** transfer is inherently multiscale since both the atomic structure of the boundary and the long-range fields of the dislocation pile-up come into *** this work,concurrent atomistic-continuum simulations are performed to study sequential slip transfer of a series of curved dislocations from a given pile-up onΣ3 coherent twin boundary(CTB)in Cu and Al,with dominant leading screw character at the site of interaction.A Frank-Read source is employed to nucleate dislocations *** is found that subject to a shear stress of 1.2 GPa,screw dislocations transfer into the twinned grain in Cu,but glide on the twin boundary plane in ***,four dislocation/CTB interaction modes are identified in Al,which are affected by(1)applied shear stress,(2)dislocation line length,and(3)dislocation line *** results elucidate the discrepancies between atomistic simulations and experimental observations of dislocation-GB reactions and highlight the importance of directly modeling sequential dislocation slip transfer reactions using fully 3D models.

关键词： grain boundary transfer

Complement-dependent neuroinflammation in spinal cord injury:from pathology to therapeutic implications

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Neural Regeneration Research 2025年第5期20卷 1324-1335页

作者： Hassan Saad Bachar El Baba Ali Tfaily Firas Kobeissy Juanmarco Gutierrez Gonzalez Daniel Refai Gerald R.Rodts Christian Mustroph david Gimbel Jonathan Grossberg Daniel l.Barrow Matthew F.Gary Ali M.Alawieh Department of Neurosurgery Emory University School of MedicineAtlantaGAUSA Department of Neurology Yale UniversityNew HavenCTUSA Center for Neurotrauma Multiomics&Biomarkers(CNMB)Morehouse School of MedicineAtlantaGAUSA

Spinal cord injury remains a major cause of disability in young adults,and beyond acute decompression and rehabilitation,there are no pharmacological treatments to limit the progression of injury and optimize recovery in this *** the thorough investigation of the complement system in triggering and propagating cerebral neuroinflammation,a similar role for complement in spinal neuroinflammation is a focus of ongoing *** this work,we survey the current literature investigating the role of complement in spinal cord injury including the sources of complement proteins,triggers of complement activation,and role of effector functions in the *** study relevant data demonstrating the different triggers of complement activation after spinal cord injury including direct binding to cellular debris,and or activation via antibody binding to damage-associated molecular *** effector functions of complement have been implicated in spinal cord injury,and we critically evaluate recent studies on the dual role of complement anaphylatoxins in spinal cord injury while emphasizing the lack of pathophysiological understanding of the role of opsonins in spinal cord *** this pathophysiological review,we systematically review the different translational approaches used in preclinical models of spinal cord injury and discuss the challenges for future translation into human *** review emphasizes the need for future studies to dissect the roles of different complement pathways in the pathology of spinal cord injury,to evaluate the phases of involvement of opsonins and anaphylatoxins,and to study the role of complement in white matter degeneration and regeneration using translational strategies to supplement genetic models.

关键词： complement neuroinflammation neuroplasticity regeneration spinal cord injury targeted therapy

TOPOlOGY AND CASCADING lINE OUTAGES IN POWER GRIDS

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Journal of Systems Science and Systems Engineering 2007年第2期16卷 202-221页

作者： david l. PEPYNE University of Massachusetts Amherst MA USA

Motivated by the small world network research of Watts ＆ Strogatz, this paper studies relationships between topology and cascading line outages in electric power grids. Cascading line outages are a type of cascading collapse that can occur in power grids when the transmission network is congested. It is characterized by a self-sustaining sequence of line outages followed by grid breakup, which generally leads to widespread blackout. The main findings of this work are twofold： On one hand, the work suggests that topologies with more disorder in their interconnection topology tend to be robust with respect to cascading line outages in the sense of being able to support greater generation and demand levels than more regularly interconnected topologies. On the other hand, the work suggests that topologies with more disorder tend to be more fragile in that should a cascade get started, they tend to break apart after fewer outages than more regularly interconnected topologies. Thus, as has been observed in other complex networks, there appears to be a tradeoff between robustness and fragility. These results were established using synthetically generated power grid topologies and verified using the IEEE 57 bus and 188 bus power grid test cases.

关键词： Power grid blackout cascading line failure complex networks robust yet fragile

OPTIMAl INVERSE lQG CONTROl FOR CERTAIN ODE AND PDE STATIONARY PROCESSES

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Journal of Systems Science & Complexity 2010年第3期23卷 584-599页

作者： david l.RUSSEll Department of Mathematics Virginia Tech

Following work carried out earlier on linear-quadratic optimal control for linear finitedimensional stationary systems we report,in this article,on extension of some of those results to certaininfinite dimensional systems;in particular a class of PDE systems of elliptic *** systems arestudied in the now familiar framework developed by *** and ***,specialized to asubclass of such systems important in a variety of *** an extended example this paperstudies an optimal redistribution problem in a groundwater flow system governed by Darcy's equation,presenting both analytic and computational work related to such problems.

关键词： Elliptic PDE linear feedback control stationary system.

Dislocation Creep Accommodated by Grain Boundary Sliding in Dunite

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Journal of Earth Science 2010年第5期21卷 541-554页

作者： Yonghong Zhao david l Kohlstedt School of Earth and Space Sciences Peking University Department of Geology and Geophysics University of Minnesota

To investigate the role of grain boundary sliding during dislocation creep of dunite, a series of deformation experiments were carried out under anhydrous conditions on fine-grained （-15 μm） samples synthesized from powdered San Carlos olivine and powdered San Carlos olivine＋1.5 vol.% MORB. Triaxial compressive creep tests were conducted at a temperature of 1 473 K and confining pressures of 200 and 400 MPa using a high-resolution, gas-medium deformation apparatus. Each sample was deformed at several levels of differential stress between 100 and 250 MPa to yield strain rates in the range of 10^-6 to 10^-4 s^-1. Under these conditions, the dominant creep mechanism involves the motion of dislocations, largely on the easy slip system （010）[100], accommodated by grain boundary sliding （gbs）. This grain size-sensitive creep regime is characterized by a stress exponent of n=3.4±0.2 and a grain size exponent of p=2.0±0.2. The activation volume for this gbs-accommodated dislocation creep regime is V＊=（26±3）×10^-6 m2·mol^-1. Comparison of our flow law for gbs-accommodated dislocation creep with those for diffusion creep and for dislocation creep reveals that the present flow law is important for the flow of mantle rocks with grain sizes of 〈100μm at differential stresses 〉20 MPa. Hence, gbs-accommodated dislocation creep is likely to be an important deformation mechanism in deep-rooted, highly localized shear zones in the lithospheric upper mantle.

关键词： grain boundary sliding creep olivine flow law.

MEMS-in-the-lens architecture for a miniature high-NA laser scanning microscope

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light(Science & Applications) 2019年第1期8卷 665-675页

作者： Tianbo liu Milind Rajadhyaksha david l.Dickensheets Electrical and Computer Engineering Department Montana State UniversityBozemanMT 59715USA Dermatology Department Memorial Sloan Kettering Cancer CenterNew YorkNY 10022USA

laser scanning microscopes can be miniaturized for in vivo imaging by substituting optical microelectromechanical system(MEMS)devices in place of larger *** emergence of multifunctional active optical devices can support further miniaturization beyond direct component replacement because those active devices enable diffraction-limited performance using simpler optical system *** this paper,we propose a catadioptric microscope objective lens that features an integrated MEMS device for performing biaxial scanning,axial focus adjustment,and control of spherical *** MEMS-in-the-lens architecture incorporates a reflective MEMS scanner between a low-numerical-aperture back lens group and an aplanatic hyperhemisphere front refractive element to support high-numerical-aperture *** implemented this new optical system using a recently developed hybrid polymer/silicon MEMS three-dimensional scan mirror that features an annular aperture that allows it to be coaxially aligned within the objective lens without the need for a beam *** optical performance of the active catadioptric system is simulated and imaging of hard targets and human cheek cells is demonstrated with a confocal microscope that is based on the new objective lens design.

关键词： scanning scanner mirror