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  • 1
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    On the failure load and mechanism of polycrystalline graphene by nanoindentation (2014)
    Springer Nature
    Details
    Publication Date: 2014-12-12
    Description: Nanoindentation has been recently used to measure the mechanical properties of polycrystalline graphene. However, the measured failure loads are found to be scattered widely and vary from lab to lab. We perform molecular dynamics simulations of nanoindentation on polycrystalline graphene at different sites including grain center, grain boundary (GB), GB triple junction, and holes. Depending on the relative position between the indenter tip and defects, significant scattering in failure load is observed. This scattering is found to arise from a combination of the non-uniform stress state, varied and weakened strengths of different defects, and the relative location between the indenter tip and the defects in polycrystalline graphene. Consequently, the failure behavior of polycrystalline graphene by nanoindentation is critically dependent on the indentation site, and is thus distinct from uniaxial tensile loading. Our work highlights the importance of the interaction between the indentation tip and defects, and the need to explicitly consider the defect characteristics at and near the indentation site in polycrystalline graphene during nanoindentation. Scientific Reports 4 doi: 10.1038/srep07437
    Electronic ISSN: 2045-2322
    Topics: Natural Sciences in General
    Published by Springer Nature
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  • 2
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    Inverse Pseudo Hall-Petch Relation in Polycrystalline Graphene (2014)
    Springer Nature
    Details
    Publication Date: 2014-08-09
    Description: Understanding the grain size-dependent failure behavior of polycrystalline graphene is important for its applications both structurally and functionally. Here we perform molecular dynamics simulations to study the failure behavior of polycrystalline graphene by varying both grain size and distribution. We show that polycrystalline graphene fails in a brittle mode and grain boundary junctions serve as the crack nucleation sites. We also show that its breaking strength and average grain size follow an inverse pseudo Hall-Petch relation, in agreement with experimental measurements. Further, we find that this inverse pseudo Hall-Petch relation can be naturally rationalized by the weakest-link model, which describes the failure behavior of brittle materials. Our present work reveals insights into controlling the mechanical properties of polycrystalline graphene and provides guidelines for the applications of polycrystalline graphene in flexible electronics and nano-electronic-mechanical devices. Scientific Reports 4 doi: 10.1038/srep05991
    Electronic ISSN: 2045-2322
    Topics: Natural Sciences in General
    Published by Springer Nature
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  • 3
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    Anomalous spiral motion of steps near dislocations on silicon surfaces (2006)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 2006-09-02
    Description: We have used low-energy electron microscopy to measure step motion on Si(111) and Si(001) near dislocations during growth and sublimation. Steps on Si(111) exhibit the classic rotating Archimedean spiral motion, as predicted by Burton, Cabrera, and Frank. Steps on Si(001), however, move in a strikingly different manner. The strain-relieving anomalous behavior can be understood in detail by considering how the local step velocity is affected by the nonuniform strain field arising from the dislocation. We show how the dynamic step-flow pattern is related to the dislocation slip system.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Hannon, J B -- Shenoy, V B -- Schwarz, K W -- New York, N.Y. -- Science. 2006 Sep 1;313(5791):1266-9.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉IBM Research Division, T. J. Watson Research Center, Yorktown Heights, NY 10598, USA. jbhannon@us.ibm.com〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/16946065" target="_blank"〉PubMed〈/a〉
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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  • 4
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    Anomalous strength characteristics of tilt grain boundaries in graphene (2010)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 2010-11-13
    Description: Graphene in its pristine form is one of the strongest materials tested, but defects influence its strength. Using atomistic calculations, we find that, counter to standard reasoning, graphene sheets with large-angle tilt boundaries that have a high density of defects are as strong as the pristine material and, unexpectedly, are much stronger than those with low-angle boundaries having fewer defects. We show that this trend is not explained by continuum fracture models but can be understood by considering the critical bonds in the strained seven-membered carbon rings that lead to failure; the large-angle boundaries are stronger because they are able to better accommodate these strained rings. Our results provide guidelines for designing growth methods to obtain sheets with strengths close to that of pristine graphene.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Grantab, Rassin -- Shenoy, Vivek B -- Ruoff, Rodney S -- New York, N.Y. -- Science. 2010 Nov 12;330(6006):946-8. doi: 10.1126/science.1196893.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉School of Engineering, Brown University, Providence, RI 02906, USA.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/21071664" target="_blank"〉PubMed〈/a〉
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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  • 5
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    Detyrosinated microtubules buckle and bear load in contracting cardiomyocytes (2016)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 2016-04-23
    Description: The microtubule (MT) cytoskeleton can transmit mechanical signals and resist compression in contracting cardiomyocytes. How MTs perform these roles remains unclear because of difficulties in observing MTs during the rapid contractile cycle. Here, we used high spatial and temporal resolution imaging to characterize MT behavior in beating mouse myocytes. MTs deformed under contractile load into sinusoidal buckles, a behavior dependent on posttranslational "detyrosination" of alpha-tubulin. Detyrosinated MTs associated with desmin at force-generating sarcomeres. When detyrosination was reduced, MTs uncoupled from sarcomeres and buckled less during contraction, which allowed sarcomeres to shorten and stretch with less resistance. Conversely, increased detyrosination promoted MT buckling, stiffened the myocyte, and correlated with impaired function in cardiomyopathy. Thus, detyrosinated MTs represent tunable, compression-resistant elements that may impair cardiac function in disease.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Robison, Patrick -- Caporizzo, Matthew A -- Ahmadzadeh, Hossein -- Bogush, Alexey I -- Chen, Christina Yingxian -- Margulies, Kenneth B -- Shenoy, Vivek B -- Prosser, Benjamin L -- HL089847/HL/NHLBI NIH HHS/ -- HL105993/HL/NHLBI NIH HHS/ -- R00-HL114879/HL/NHLBI NIH HHS/ -- R01EB017753/EB/NIBIB NIH HHS/ -- T32AR053461-09/AR/NIAMS NIH HHS/ -- T32HL007954/HL/NHLBI NIH HHS/ -- New York, N.Y. -- Science. 2016 Apr 22;352(6284):aaf0659. doi: 10.1126/science.aaf0659.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Physiology, Pennsylvania Muscle Institute, University of Pennsylvania Perelman School of Medicine, Philadelphia, PA 19104, USA. ; Department of Materials Science and Engineering, University of Pennsylvania School of Engineering and Applied Science, Philadelphia, PA 19104, USA. ; Department of Medicine, University of Pennsylvania Perelman School of Medicine, Philadelphia, PA 19104, USA. ; Department of Physiology, Pennsylvania Muscle Institute, University of Pennsylvania Perelman School of Medicine, Philadelphia, PA 19104, USA. bpros@mail.med.upenn.edu.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/27102488" target="_blank"〉PubMed〈/a〉
    Keywords: Animals ; Desmin/metabolism ; Elasticity ; Heart Failure/metabolism/physiopathology ; Humans ; Male ; Mice ; Microtubules/*metabolism ; Models, Biological ; *Myocardial Contraction ; Myocytes, Cardiac/metabolism/*physiology ; Peptide Synthases/genetics/metabolism ; *Protein Processing, Post-Translational ; RNA, Small Interfering/genetics ; Rats ; Rats, Sprague-Dawley ; Sarcomeres/metabolism ; Tubulin/*metabolism ; Tyrosine/*metabolism
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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  • 6
    Electronic Resource
    Electronic Resource
    Strain induced stabilization of stepped Si and Ge surfaces near (001) (2002)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 81 (2002), S. 364-366 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report on calculations of the formation energies of several [100] and [110] oriented step structures on biaxially stressed Si and Ge (001) surfaces. It is shown that a novel rebonded [100] oriented single-height step is strongly stabilized by compressive strain compared to most well-known step structures. We propose that the side walls of "hut"-shaped quantum dots observed in recent experiments on SiGe/Si films are made up of these steps. Our calculations provide an explanation for the nucleationless growth of shallow mounds, with steps along the [100] and [110] directions in low- and high-misfit films, respectively, and for the stability of the (105) facets under compressive strain. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1491611
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  • 7
    Electronic Resource
    Electronic Resource
    A methodology for computing nonlinear fracture parameters for a bulging crack in a pressurised aircraft fuselage (1994)
    Springer
    Computational mechanics 14 (1994), S. 529-548 
    Details
    ISSN: 1432-0924
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract A computational methodology for obtaining nonlinear fracture parameters which account for the effects of plasticity at the tips of a bulging crack in a pressurised aircraft fuselage is developed. The methodology involves a hierarchical three stage analysis (global, intermediate, and local) of the cracked fuselage, with the crack incorporated into the model at each stage. The global analysis is performed using a linear elastic shell finite element model in which the stiffeners are treated as beam elements. The geometrically nonlinear nature of the bulging phenomenon is emulated in the intermediate analysis using a geometrically nonlinear shell finite element model. The local analysis is a three-dimensional solid finite element model of the cracked skin using a hypoelastic-plastic rate formulation. Kinematic boundary conditions for each stage are obtained from the preceding stage in the hierarchy using a general mesh independent mechanism. The T *integral, which accounts for both large deformations and plasticity, is taken to be the fracture parameter characterising the severity of the conditions at the crack tip, and is evaluated from the local analysis using the Equivalent Domain Integral (EDI) method. The implementation of the EDI technique for finite deformations in shell space is also outlined. The methodology is applied to a number of example problems for which correction factors relating the nonlinear T * values to those obtained from a linear elastic stiffened shell analysis are computed. The issue of flapping is addressed by investigating the behaviour of the longitudinal stress parallel to the crack for various cases.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00350836
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  • 8
    Electronic Resource
    Electronic Resource
    Biochemical and molecular analysis of plants derived from embryogenic tissue cultures of napier grass (Pennisetum purpureum K. Schum) (1992)
    Springer
    Theoretical and applied genetics 83 (1992), S. 947-955 
    Details
    ISSN: 1432-2242
    Keywords: Gramineae ; napier grass ; Somatic embryo genesis ; Variation ; Pennisetum purpureum
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary We have investigated the extent of biochemical and molecular variation in 63 plants of napier grass (Pennisetum purpureum K. Schum.) regenerated from 3- to 24-week-old embryogenic callus cultures. The calli were derived from cultured basal segments of young leaves and immature inflorescences obtained from a single fieldgrown donor plant. The entire population was analyzed for the activity of 14 isozyme systems, but no qualitative variation was found at any of the loci examined. Similarly, no restriction fragment length polymorphisms (RFLPs) were detected in the mitochondrial, plastid and nuclear genomes in a representative sample of regenerated plants. Our results confirm earlier reports of the genetic uniformity of plants derived from somatic embryos and highlight their value both for clonal propagation and for genetic transformation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00232955
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  • 9
    Electronic Resource
    Electronic Resource
    Dispersion forces in wetting (1995)
    Springer
    Journal of low temperature physics 101 (1995), S. 361-366 
    Details
    ISSN: 1573-7357
    Keywords: 68.45.-v ; 68.45.Gd ; 68.10.Cr
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract tA simple, analytically tractable, model is used to obtain wetting phase diagrams for insulators on insulating and metallic substrates. The phase diagrams are consistent with the general rule that if the vapor phases of A and B are dilute and dispersion forces allow wetting of A on B then, wetting of B on A is not allowed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00753321
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  • 10
    Electronic Resource
    Electronic Resource
    The Hydrodynamic Equations of Superfluid Mixtures in Magnetic Traps (1998)
    Springer
    Journal of low temperature physics 111 (1998), S. 937-952 
    Details
    ISSN: 1573-7357
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The hydrodynamics equations of binary mixtures of Bose gases, Fermi gases, and mixtures of Bose and Fermi gases in the presence of external potentials are derived. These equations can be applied to current experiments on mixtures of atomic gases confined in magnetic traps.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1022285510305
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