A heuristic model on the role of plasticity in adaptive evolution: plasticity increases adaptation, population viability and genetic variation.

PubMed

Gomez-Mestre, Ivan; Jovani, Roger

2013-11-22

An ongoing new synthesis in evolutionary theory is expanding our view of the sources of heritable variation beyond point mutations of fixed phenotypic effects to include environmentally sensitive changes in gene regulation. This expansion of the paradigm is necessary given ample evidence for a heritable ability to alter gene expression in response to environmental cues. In consequence, single genotypes are often capable of adaptively expressing different phenotypes in different environments, i.e. are adaptively plastic. We present an individual-based heuristic model to compare the adaptive dynamics of populations composed of plastic or non-plastic genotypes under a wide range of scenarios where we modify environmental variation, mutation rate and costs of plasticity. The model shows that adaptive plasticity contributes to the maintenance of genetic variation within populations, reduces bottlenecks when facing rapid environmental changes and confers an overall faster rate of adaptation. In fluctuating environments, plasticity is favoured by selection and maintained in the population. However, if the environment stabilizes and costs of plasticity are high, plasticity is reduced by selection, leading to genetic assimilation, which could result in species diversification. More broadly, our model shows that adaptive plasticity is a common consequence of selection under environmental heterogeneity, and hence a potentially common phenomenon in nature. Thus, taking adaptive plasticity into account substantially extends our view of adaptive evolution.

Emerging Applications of Bedside 3D Printing in Plastic Surgery

PubMed Central

Chae, Michael P.; Rozen, Warren M.; McMenamin, Paul G.; Findlay, Michael W.; Spychal, Robert T.; Hunter-Smith, David J.

2015-01-01

Modern imaging techniques are an essential component of preoperative planning in plastic and reconstructive surgery. However, conventional modalities, including three-dimensional (3D) reconstructions, are limited by their representation on 2D workstations. 3D printing, also known as rapid prototyping or additive manufacturing, was once the province of industry to fabricate models from a computer-aided design (CAD) in a layer-by-layer manner. The early adopters in clinical practice have embraced the medical imaging-guided 3D-printed biomodels for their ability to provide tactile feedback and a superior appreciation of visuospatial relationship between anatomical structures. With increasing accessibility, investigators are able to convert standard imaging data into a CAD file using various 3D reconstruction softwares and ultimately fabricate 3D models using 3D printing techniques, such as stereolithography, multijet modeling, selective laser sintering, binder jet technique, and fused deposition modeling. However, many clinicians have questioned whether the cost-to-benefit ratio justifies its ongoing use. The cost and size of 3D printers have rapidly decreased over the past decade in parallel with the expiration of key 3D printing patents. Significant improvements in clinical imaging and user-friendly 3D software have permitted computer-aided 3D modeling of anatomical structures and implants without outsourcing in many cases. These developments offer immense potential for the application of 3D printing at the bedside for a variety of clinical applications. In this review, existing uses of 3D printing in plastic surgery practice spanning the spectrum from templates for facial transplantation surgery through to the formation of bespoke craniofacial implants to optimize post-operative esthetics are described. Furthermore, we discuss the potential of 3D printing to become an essential office-based tool in plastic surgery to assist in preoperative planning, developing intraoperative guidance tools, teaching patients and surgical trainees, and producing patient-specific prosthetics in everyday surgical practice. PMID:26137465

Emerging Applications of Bedside 3D Printing in Plastic Surgery.

PubMed

Chae, Michael P; Rozen, Warren M; McMenamin, Paul G; Findlay, Michael W; Spychal, Robert T; Hunter-Smith, David J

2015-01-01

Modern imaging techniques are an essential component of preoperative planning in plastic and reconstructive surgery. However, conventional modalities, including three-dimensional (3D) reconstructions, are limited by their representation on 2D workstations. 3D printing, also known as rapid prototyping or additive manufacturing, was once the province of industry to fabricate models from a computer-aided design (CAD) in a layer-by-layer manner. The early adopters in clinical practice have embraced the medical imaging-guided 3D-printed biomodels for their ability to provide tactile feedback and a superior appreciation of visuospatial relationship between anatomical structures. With increasing accessibility, investigators are able to convert standard imaging data into a CAD file using various 3D reconstruction softwares and ultimately fabricate 3D models using 3D printing techniques, such as stereolithography, multijet modeling, selective laser sintering, binder jet technique, and fused deposition modeling. However, many clinicians have questioned whether the cost-to-benefit ratio justifies its ongoing use. The cost and size of 3D printers have rapidly decreased over the past decade in parallel with the expiration of key 3D printing patents. Significant improvements in clinical imaging and user-friendly 3D software have permitted computer-aided 3D modeling of anatomical structures and implants without outsourcing in many cases. These developments offer immense potential for the application of 3D printing at the bedside for a variety of clinical applications. In this review, existing uses of 3D printing in plastic surgery practice spanning the spectrum from templates for facial transplantation surgery through to the formation of bespoke craniofacial implants to optimize post-operative esthetics are described. Furthermore, we discuss the potential of 3D printing to become an essential office-based tool in plastic surgery to assist in preoperative planning, developing intraoperative guidance tools, teaching patients and surgical trainees, and producing patient-specific prosthetics in everyday surgical practice.

Structural Chemistry of Human RNA Methyltransferases.

PubMed

Schapira, Matthieu

2016-03-18

RNA methyltransferases (RNMTs) play important roles in RNA stability, splicing, and epigenetic mechanisms. They constitute a promising target class that is underexplored by the medicinal chemistry community. Information of relevance to drug design can be extracted from the rich structural coverage of human RNMTs. In this work, the structural chemistry of this protein family is analyzed in depth. Unlike most methyltransferases, RNMTs generally feature a substrate-binding site that is largely open on the cofactor-binding pocket, favoring the design of bisubstrate inhibitors. Substrate purine or pyrimidines are often sandwiched between hydrophobic walls that can accommodate planar ring systems. When the substrate base is laying on a shallow surface, a 5' flanking base is sometimes anchored in a druggable cavity. The cofactor-binding site is structurally more diverse than in protein methyltransferases and more druggable in SPOUT than in Rossman-fold enzymes. Finally, conformational plasticity observed both at the substrate and cofactor binding sites may be a challenge for structure-based drug design. The landscape drawn here may inform ongoing efforts toward the discovery of the first human RNMT inhibitors.

How environment and genes shape the adolescent brain.

PubMed

Paus, Tomáš

2013-07-01

This article is part of a Special Issue "Puberty and Adolescence". This review provides a conceptual framework for the study of factors--in our genes and environment--that shape the adolescent brain. I start by pointing out that brain phenotypes obtained with magnetic resonance imaging are complex traits reflecting the interplay of genes and the environment. In some cases, variations in the structural phenotypes observed during adolescence have their origin in the pre-natal or early post-natal periods. I then emphasize the bidirectional nature of brain-behavior relationships observed during this period of human development, where function may be more likely to influence structure rather than vice versa. In the main part of this article, I review our ongoing work on the influence of gonadal hormones on the adolescent brain. I also discuss the importance of social context and brain plasticity on shaping the relevant neural circuits. Copyright © 2013 Elsevier Inc. All rights reserved.

A Dynamic Connectome Supports the Emergence of Stable Computational Function of Neural Circuits through Reward-Based Learning.

PubMed

Kappel, David; Legenstein, Robert; Habenschuss, Stefan; Hsieh, Michael; Maass, Wolfgang

2018-01-01

Synaptic connections between neurons in the brain are dynamic because of continuously ongoing spine dynamics, axonal sprouting, and other processes. In fact, it was recently shown that the spontaneous synapse-autonomous component of spine dynamics is at least as large as the component that depends on the history of pre- and postsynaptic neural activity. These data are inconsistent with common models for network plasticity and raise the following questions: how can neural circuits maintain a stable computational function in spite of these continuously ongoing processes, and what could be functional uses of these ongoing processes? Here, we present a rigorous theoretical framework for these seemingly stochastic spine dynamics and rewiring processes in the context of reward-based learning tasks. We show that spontaneous synapse-autonomous processes, in combination with reward signals such as dopamine, can explain the capability of networks of neurons in the brain to configure themselves for specific computational tasks, and to compensate automatically for later changes in the network or task. Furthermore, we show theoretically and through computer simulations that stable computational performance is compatible with continuously ongoing synapse-autonomous changes. After reaching good computational performance it causes primarily a slow drift of network architecture and dynamics in task-irrelevant dimensions, as observed for neural activity in motor cortex and other areas. On the more abstract level of reinforcement learning the resulting model gives rise to an understanding of reward-driven network plasticity as continuous sampling of network configurations.

A Dynamic Connectome Supports the Emergence of Stable Computational Function of Neural Circuits through Reward-Based Learning

PubMed Central

Habenschuss, Stefan; Hsieh, Michael

2018-01-01

Synaptic connections between neurons in the brain are dynamic because of continuously ongoing spine dynamics, axonal sprouting, and other processes. In fact, it was recently shown that the spontaneous synapse-autonomous component of spine dynamics is at least as large as the component that depends on the history of pre- and postsynaptic neural activity. These data are inconsistent with common models for network plasticity and raise the following questions: how can neural circuits maintain a stable computational function in spite of these continuously ongoing processes, and what could be functional uses of these ongoing processes? Here, we present a rigorous theoretical framework for these seemingly stochastic spine dynamics and rewiring processes in the context of reward-based learning tasks. We show that spontaneous synapse-autonomous processes, in combination with reward signals such as dopamine, can explain the capability of networks of neurons in the brain to configure themselves for specific computational tasks, and to compensate automatically for later changes in the network or task. Furthermore, we show theoretically and through computer simulations that stable computational performance is compatible with continuously ongoing synapse-autonomous changes. After reaching good computational performance it causes primarily a slow drift of network architecture and dynamics in task-irrelevant dimensions, as observed for neural activity in motor cortex and other areas. On the more abstract level of reinforcement learning the resulting model gives rise to an understanding of reward-driven network plasticity as continuous sampling of network configurations. PMID:29696150

Initial Mechanical Testing of Superalloy Lattice Block Structures Conducted

NASA Technical Reports Server (NTRS)

Krause, David L.; Whittenberger, J. Daniel

2002-01-01

The first mechanical tests of superalloy lattice block structures produced promising results for this exciting new lightweight material system. The testing was performed in-house at NASA Glenn Research Center's Structural Benchmark Test Facility, where small subelement-sized compression and beam specimens were loaded to observe elastic and plastic behavior, component strength levels, and fatigue resistance for hundreds of thousands of load cycles. Current lattice block construction produces a flat panel composed of thin ligaments arranged in a three-dimensional triangulated trusslike structure. Investment casting of lattice block panels has been developed and greatly expands opportunities for using this unique architecture in today's high-performance structures. In addition, advances made in NASA's Ultra-Efficient Engine Technology Program have extended the lattice block concept to superalloy materials. After a series of casting iterations, the nickel-based superalloy Inconel 718 (IN 718, Inco Alloys International, Inc., Huntington, WV) was successfully cast into lattice block panels; this combination offers light weight combined with high strength, high stiffness, and elevated-temperature durability. For tests to evaluate casting quality and configuration merit, small structural compression and bend test specimens were machined from the 5- by 12- by 0.5-in. panels. Linear elastic finite element analyses were completed for several specimen layouts to predict material stresses and deflections under proposed test conditions. The structural specimens were then subjected to room-temperature static and cyclic loads in Glenn's Life Prediction Branch's material test machine. Surprisingly, the test results exceeded analytical predictions: plastic strains greater than 5 percent were obtained, and fatigue lives did not depreciate relative to the base material. These assets were due to the formation of plastic hinges and the redundancies inherent in lattice block construction, which were not considered in the simplified computer models. The fatigue testing proved the value of redundancies since specimen strength was maintained even after the fracture of one or two ligaments. This ongoing test program is planned to continue through high-temperature testing. Also scheduled for testing are IN 718 lattice block panels with integral face sheets, as well as specimens cast from a higher temperature alloy. The initial testing suggests the value of this technology for large panels under low and moderate pressure loadings and for high-risk, damage-tolerant structures. Potential aeropropulsion uses for lattice blocks include turbine-engine actuated panels, exhaust nozzle flaps, and side panel structures.

Using the virtual brain to reveal the role of oscillations and plasticity in shaping brain's dynamical landscape.

PubMed

Roy, Dipanjan; Sigala, Rodrigo; Breakspear, Michael; McIntosh, Anthony Randal; Jirsa, Viktor K; Deco, Gustavo; Ritter, Petra

2014-12-01

Spontaneous brain activity, that is, activity in the absence of controlled stimulus input or an explicit active task, is topologically organized in multiple functional networks (FNs) maintaining a high degree of coherence. These "resting state networks" are constrained by the underlying anatomical connectivity between brain areas. They are also influenced by the history of task-related activation. The precise rules that link plastic changes and ongoing dynamics of resting-state functional connectivity (rs-FC) remain unclear. Using the framework of the open source neuroinformatics platform "The Virtual Brain," we identify potential computational mechanisms that alter the dynamical landscape, leading to reconfigurations of FNs. Using a spiking neuron model, we first demonstrate that network activity in the absence of plasticity is characterized by irregular oscillations between low-amplitude asynchronous states and high-amplitude synchronous states. We then demonstrate the capability of spike-timing-dependent plasticity (STDP) combined with intrinsic alpha (8-12 Hz) oscillations to efficiently influence learning. Further, we show how alpha-state-dependent STDP alters the local area dynamics from an irregular to a highly periodic alpha-like state. This is an important finding, as the cortical input from the thalamus is at the rate of alpha. We demonstrate how resulting rhythmic cortical output in this frequency range acts as a neuronal tuner and, hence, leads to synchronization or de-synchronization between brain areas. Finally, we demonstrate that locally restricted structural connectivity changes influence local as well as global dynamics and lead to altered rs-FC.

Removal of area CA3 from hippocampal slices induces postsynaptic plasticity at Schaffer collateral synapses that normalizes CA1 pyramidal cell discharge.

PubMed

Dumas, Theodore C; Uttaro, Michael R; Barriga, Carolina; Brinkley, Tiffany; Halavi, Maryam; Wright, Susan N; Ferrante, Michele; Evans, Rebekah C; Hawes, Sarah L; Sanders, Erin M

2018-06-21

Neural networks that undergo acute insults display remarkable reorganization. This injury related plasticity is thought to permit recovery of function in the face of damage that cannot be reversed. Previously, an increase in the transmission strength at Schaffer collateral to CA1 pyramidal cell synapses was observed after long-term activity reduction in organotypic hippocampal slices. Here we report that, following acute preparation of adult rat hippocampal slices and surgical removal of area CA3, input to area CA1 was reduced and Schaffer collateral synapses underwent functional strengthening. This increase in synaptic strength was limited to Schaffer collateral inputs (no alteration to temporoammonic synapses) and acted to normalize postsynaptic discharge, supporting a homeostatic or compensatory response. Short-term plasticity was not altered, but an increase in immunohistochemical labeling of GluA1 subunits was observed in the stratum radiatum (but not stratum moleculare), suggesting increased numbers of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors and a postsynaptic locus of expression. Combined, these data support the idea that, in response to the reduction in presynaptic activity caused by removal of area CA3, Schaffer collateral synapses undergo a relatively rapid increase in functional efficacy likely supported by insertion of more AMPARs, which maintains postsynaptic excitability in CA1 pyramidal neurons. This novel fast compensatory plasticity exhibits properties that would allow it to maintain optimal network activity levels in the hippocampus, a brain structure lauded for its ongoing experience-dependent malleability. Copyright © 2018 Elsevier B.V. All rights reserved.

Synaptic Plasticity, Dementia and Alzheimer Disease.

PubMed

Skaper, Stephen D; Facci, Laura; Zusso, Morena; Giusti, Pietro

2017-01-01

Neuroplasticity is not only shaped by learning and memory but is also a mediator of responses to neuron attrition and injury (compensatory plasticity). As an ongoing process it reacts to neuronal cell activity and injury, death, and genesis, which encompasses the modulation of structural and functional processes of axons, dendrites, and synapses. The range of structural elements that comprise plasticity includes long-term potentiation (a cellular correlate of learning and memory), synaptic efficacy and remodelling, synaptogenesis, axonal sprouting and dendritic remodelling, and neurogenesis and recruitment. Degenerative diseases of the human brain continue to pose one of biomedicine's most intractable problems. Research on human neurodegeneration is now moving from descriptive to mechanistic analyses. At the same time, it is increasing apparently that morphological lesions traditionally used by neuropathologists to confirm post-mortem clinical diagnosis might furnish us with an experimentally tractable handle to understand causative pathways. Consider the aging-dependent neurodegenerative disorder Alzheimer's disease (AD) which is characterised at the neuropathological level by deposits of insoluble amyloid β-peptide (Aβ) in extracellular plaques and aggregated tau protein, which is found largely in the intracellular neurofibrillary tangles. We now appreciate that mild cognitive impairment in early AD may be due to synaptic dysfunction caused by accumulation of non-fibrillar, oligomeric Aβ, occurring well in advance of evident widespread synaptic loss and neurodegeneration. Soluble Aβ oligomers can adversely affect synaptic structure and plasticity at extremely low concentrations, although the molecular substrates by which synaptic memory mechanisms are disrupted remain to be fully elucidated. The dendritic spine constitutes a primary locus of excitatory synaptic transmission in the mammalian central nervous system. These structures protruding from dendritic shafts undergo dynamic changes in number, size and shape in response to variations in hormonal status, developmental stage, and changes in afferent input. It is perhaps not unexpected that loss of spine density may be linked to cognitive and memory impairment in AD, although the underlying mechanism(s) remain uncertain. This article aims to present a critical overview of current knowledge on the bases of synaptic dysfunction in neurodegenerative diseases, with a focus on AD, and will cover amyloid- and nonamyloid- driven mechanisms. We will consider also emerging data dealing with potential therapeutic approaches for ameliorating the cognitive and memory deficits associated with these disorders. Copyright© Bentham Science Publishers; For any queries, please email at epub@benthamscience.org.

Lizards fail to plastically adjust nesting behavior or thermal tolerance as needed to buffer populations from climate warming.

PubMed

Telemeco, Rory S; Fletcher, Brooke; Levy, Ofir; Riley, Angela; Rodriguez-Sanchez, Yesenia; Smith, Colton; Teague, Collin; Waters, Amanda; Angilletta, Michael J; Buckley, Lauren B

2017-03-01

Although observations suggest the potential for phenotypic plasticity to allow adaptive responses to climate change, few experiments have assessed that potential. Modeling suggests that Sceloporus tristichus lizards will need increased nest depth, shade cover, or embryonic thermal tolerance to avoid reproductive failure resulting from climate change. To test for such plasticity, we experimentally examined how maternal temperatures affect nesting behavior and embryonic thermal sensitivity. The temperature regime that females experienced while gravid did not affect nesting behavior, but warmer temperatures at the time of nesting reduced nest depth. Additionally, embryos from heat-stressed mothers displayed increased sensitivity to high-temperature exposure. Simulations suggest that critically low temperatures, rather than high temperatures, historically limit development of our study population. Thus, the plasticity needed to buffer this population has not been under selection. Plasticity will likely fail to compensate for ongoing climate change when such change results in novel stressors. © 2016 John Wiley & Sons Ltd.

Tests of a Fast Plastic Scintillator for High-Precision Half-Life Measurements

NASA Astrophysics Data System (ADS)

Laffoley, A. T.; Dunlop, R.; Finlay, P.; Leach, K. G.; Michetti-Wilson, J.; Rand, E. T.; Svensson, C. E.; Grinyer, G. F.; Thomas, J. C.; Ball, G.; Garnsworthy, A. B.; Hackman, G.; Orce, J. N.; Triambak, S.; Williams, S. J.; Andreoiu, C.; Cross, D.

2013-03-01

A fast plastic scintillator detector is evaluated for possible use in an ongoing program of high-precision half-life measurements of short lived β emitters. Using data taken at TRI-UMF's Isotope Separator and Accelerator Facility with a radioactive 26Na beam, a detailed investigation of potential systematic effects with this new detector setup is being performed. The technique will then be applied to other β-decay half-life measurements including the superallowed Fermi β emitters 10C, 14O, and T = 1/2 decay of 15O.

Sleep, Plasticity and the Pathophysiology of Neurodevelopmental Disorders: The Potential Roles of Protein Synthesis and Other Cellular Processes

PubMed Central

Picchioni, Dante; Reith, R. Michelle; Nadel, Jeffrey L.; Smith, Carolyn B.

2014-01-01

Sleep is important for neural plasticity, and plasticity underlies sleep-dependent memory consolidation. It is widely appreciated that protein synthesis plays an essential role in neural plasticity. Studies of sleep-dependent memory and sleep-dependent plasticity have begun to examine alterations in these functions in populations with neurological and psychiatric disorders. Such an approach acknowledges that disordered sleep may have functional consequences during wakefulness. Although neurodevelopmental disorders are not considered to be sleep disorders per se, recent data has revealed that sleep abnormalities are among the most prevalent and common symptoms and may contribute to the progression of these disorders. The main goal of this review is to highlight the role of disordered sleep in the pathology of neurodevelopmental disorders and to examine some potential mechanisms by which sleep-dependent plasticity may be altered. We will also briefly attempt to extend the same logic to the other end of the developmental spectrum and describe a potential role of disordered sleep in the pathology of neurodegenerative diseases. We conclude by discussing ongoing studies that might provide a more integrative approach to the study of sleep, plasticity, and neurodevelopmental disorders. PMID:24839550

Striking Plasticity of CRISPR-Cas9 and Key Role of Non-target DNA, as Revealed by Molecular Simulations.

PubMed

Palermo, Giulia; Miao, Yinglong; Walker, Ross C; Jinek, Martin; McCammon, J Andrew

2016-10-26

The CRISPR (clustered regularly interspaced short palindromic repeats)-Cas9 system recently emerged as a transformative genome-editing technology that is innovating basic bioscience and applied medicine and biotechnology. The endonuclease Cas9 associates with a guide RNA to match and cleave complementary sequences in double stranded DNA, forming an RNA:DNA hybrid and a displaced non-target DNA strand. Although extensive structural studies are ongoing, the conformational dynamics of Cas9 and its interplay with the nucleic acids during association and DNA cleavage are largely unclear. Here, by employing multi-microsecond time scale molecular dynamics, we reveal the conformational plasticity of Cas9 and identify key determinants that allow its large-scale conformational changes during nucleic acid binding and processing. We show how the "closure" of the protein, which accompanies nucleic acid binding, fundamentally relies on highly coupled and specific motions of the protein domains, collectively initiating the prominent conformational changes needed for nucleic acid association. We further reveal a key role of the non-target DNA during the process of activation of the nuclease HNH domain, showing how the nontarget DNA positioning triggers local conformational changes that favor the formation of a catalytically competent Cas9. Finally, a remarkable conformational plasticity is identified as an intrinsic property of the HNH domain, constituting a necessary element that allows for the HNH repositioning. These novel findings constitute a reference for future experimental studies aimed at a full characterization of the dynamic features of the CRISPR-Cas9 system, and-more importantly-call for novel structure engineering efforts that are of fundamental importance for the rational design of new genome-engineering applications.

33 CFR 151.63 - Shipboard control of garbage.

Code of Federal Regulations, 2014 CFR

2014-07-01

... (CONTINUED) POLLUTION VESSELS CARRYING OIL, NOXIOUS LIQUID SUBSTANCES, GARBAGE, MUNICIPAL OR COMMERCIAL WASTE... Antarctic Treaty as it Pertains to Pollution from Ships Garbage Pollution and Sewage § 151.63 Shipboard... plastics in ship stores. (6) Ongoing educational programs to train shipboard personnel of garbage handling...

33 CFR 151.63 - Shipboard control of garbage.

Code of Federal Regulations, 2010 CFR

2010-07-01

... (CONTINUED) POLLUTION VESSELS CARRYING OIL, NOXIOUS LIQUID SUBSTANCES, GARBAGE, MUNICIPAL OR COMMERCIAL WASTE... Antarctic Treaty as it Pertains to Pollution from Ships Garbage Pollution and Sewage § 151.63 Shipboard... plastics in ship stores. (6) Ongoing educational programs to train shipboard personnel of garbage handling...

33 CFR 151.63 - Shipboard control of garbage.

Code of Federal Regulations, 2011 CFR

2011-07-01

... (CONTINUED) POLLUTION VESSELS CARRYING OIL, NOXIOUS LIQUID SUBSTANCES, GARBAGE, MUNICIPAL OR COMMERCIAL WASTE... Antarctic Treaty as it Pertains to Pollution from Ships Garbage Pollution and Sewage § 151.63 Shipboard... plastics in ship stores. (6) Ongoing educational programs to train shipboard personnel of garbage handling...

33 CFR 151.63 - Shipboard control of garbage.

Code of Federal Regulations, 2013 CFR

2013-07-01

... (CONTINUED) POLLUTION VESSELS CARRYING OIL, NOXIOUS LIQUID SUBSTANCES, GARBAGE, MUNICIPAL OR COMMERCIAL WASTE... Antarctic Treaty as it Pertains to Pollution from Ships Garbage Pollution and Sewage § 151.63 Shipboard... plastics in ship stores. (6) Ongoing educational programs to train shipboard personnel of garbage handling...

33 CFR 151.63 - Shipboard control of garbage.

Code of Federal Regulations, 2012 CFR

2012-07-01

... (CONTINUED) POLLUTION VESSELS CARRYING OIL, NOXIOUS LIQUID SUBSTANCES, GARBAGE, MUNICIPAL OR COMMERCIAL WASTE... Antarctic Treaty as it Pertains to Pollution from Ships Garbage Pollution and Sewage § 151.63 Shipboard... plastics in ship stores. (6) Ongoing educational programs to train shipboard personnel of garbage handling...

Structural Synaptic Plasticity Has High Memory Capacity and Can Explain Graded Amnesia, Catastrophic Forgetting, and the Spacing Effect

PubMed Central

Knoblauch, Andreas; Körner, Edgar; Körner, Ursula; Sommer, Friedrich T.

2014-01-01

Although already William James and, more explicitly, Donald Hebb's theory of cell assemblies have suggested that activity-dependent rewiring of neuronal networks is the substrate of learning and memory, over the last six decades most theoretical work on memory has focused on plasticity of existing synapses in prewired networks. Research in the last decade has emphasized that structural modification of synaptic connectivity is common in the adult brain and tightly correlated with learning and memory. Here we present a parsimonious computational model for learning by structural plasticity. The basic modeling units are “potential synapses” defined as locations in the network where synapses can potentially grow to connect two neurons. This model generalizes well-known previous models for associative learning based on weight plasticity. Therefore, existing theory can be applied to analyze how many memories and how much information structural plasticity can store in a synapse. Surprisingly, we find that structural plasticity largely outperforms weight plasticity and can achieve a much higher storage capacity per synapse. The effect of structural plasticity on the structure of sparsely connected networks is quite intuitive: Structural plasticity increases the “effectual network connectivity”, that is, the network wiring that specifically supports storage and recall of the memories. Further, this model of structural plasticity produces gradients of effectual connectivity in the course of learning, thereby explaining various cognitive phenomena including graded amnesia, catastrophic forgetting, and the spacing effect. PMID:24858841

Secretory products of macrophages: twenty-five years on.

PubMed

Nathan, Carl

2012-04-01

No longer do scientists look down on macrophages as "garbage men" that act "nonspecifically." Last fall's Nobel Prizes honored two of the few scientists who studied macrophages three decades ago. Now perhaps thousands do, and the subtypes they describe reflect ongoing discoveries of macrophages' extraordinary plasticity.

76 FR 175 - Continental Structural Plastics Including On-Site Leased Workers From Kelly Services and Time...

Federal Register 2010, 2011, 2012, 2013, 2014

2011-01-03

... Plastics Including On-Site Leased Workers From Kelly Services and Time Staffing; North Baltimore, OH... Adjustment Assistance on December 31, 2008, applicable to workers of Continental Structural Plastics, North... Baltimore, Ohio location of Continental Structural Plastics. The Department has determined that these...

Managing cover crops on strawberry furrow bottoms

USDA-ARS?s Scientific Manuscript database

Bare furrows in strawberry fields with plastic mulch covered beds can lead to lots of soil erosion and runoff during winter rainy periods. This article describes how growers can plant and manage cover crops in these furrows to minimize runoff and soil erosion. This is based on on-going research at...

Cell-Autonomous Regulation of Dendritic Spine Density by PirB.

PubMed

Vidal, George S; Djurisic, Maja; Brown, Kiana; Sapp, Richard W; Shatz, Carla J

2016-01-01

Synapse density on cortical pyramidal neurons is modulated by experience. This process is highest during developmental critical periods, when mechanisms of synaptic plasticity are fully engaged. In mouse visual cortex, the critical period for ocular dominance (OD) plasticity coincides with the developmental pruning of synapses. At this time, mice lacking paired Ig-like receptor B (PirB) have excess numbers of dendritic spines on L5 neurons; these spines persist and are thought to underlie the juvenile-like OD plasticity observed in adulthood. Here we examine whether PirB is required specifically in excitatory neurons to exert its effect on dendritic spine and synapse density during the critical period. In mice with a conditional allele of PirB (PirB fl/fl ), PirB was deleted only from L2/3 cortical pyramidal neurons in vivo by timed in utero electroporation of Cre recombinase. Sparse mosaic expression of Cre produced neurons lacking PirB in a sea of wild-type neurons and glia. These neurons had significantly elevated dendritic spine density, as well as increased frequency of miniature EPSCs, suggesting that they receive a greater number of synaptic inputs relative to Cre - neighbors. The effect of cell-specific PirB deletion on dendritic spine density was not accompanied by changes in dendritic branching complexity or axonal bouton density. Together, results imply a neuron-specific, cell-autonomous action of PirB on synaptic density in L2/3 pyramidal cells of visual cortex. Moreover, they are consistent with the idea that PirB functions normally to corepress spine density and synaptic plasticity, thereby maintaining headroom for cells to encode ongoing experience-dependent structural change throughout life.

76 FR 13227 - Continental Structural Plastics, Including On-Site Leased Workers From Kelly Services and Doepker...

Federal Register 2010, 2011, 2012, 2013, 2014

2011-03-10

... Plastics, Including On-Site Leased Workers From Kelly Services and Doepker Group, Inc., Formerly Known As... Continental Structural Plastics, North Baltimore, Ohio. The workers produce exterior body panels and under... to TA-W-64,458 is hereby issued as follows: All workers of Continental Structural Plastics, including...

Study of an athermal quasi static plastic deformation in a 2D granular material

NASA Astrophysics Data System (ADS)

Zhang, Jie; Zheng, Jie

In crystalline materials, the plasticity has been well understood in terms of dynamics of dislocation, i.e. flow defects in the crystals where the flow defects can be directly visualized under a microscope. In a contrast, the plasticity in amorphous materials, i.e. glass, is still poorly understood due to the disordered nature of the materials. In this talk, I will discuss the recent results we have obtained in our ongoing research of the plasticity of a 2D glass in the athermal quasi static limit where the 2D glass is made of bi-disperse granular disks with very low friction. Starting from a densely packed homogeneous and isotropic initial state, we apply pure shear deformation to the system. For a sufficiently small strain, the response of the system is linear and elastic like; when the strain is large enough, the plasticity of the system gradually develops and eventually the shear bands are fully developed. In this study, we are particularly interested in how to relate the local plastic deformation to the macroscopic response of the system and also in the development of the shear bands.

Study of an athermal quasi static plastic deformation in a 2D granular material

NASA Astrophysics Data System (ADS)

Zhang, Jie; Zheng, Jie

2016-11-01

In crystalline materials, the plasticity has been well understood in terms of dynamics of dislocation, i.e. flow defects in the crystals where the flow defects can be directly visualized under a microscope. In a contrast, the plasticity in amorphous materials, i.e. glass, is still poorly understood due to the disordered nature of the materials. In this talk, I will discuss the recent results we have obtained in our ongoing research of the plasticity of a 2D glass in the athermal quasi static limit where the 2D glass is made of bi-disperse granular disks with very low friction. Starting from a densely packed homogeneous and isotropic initial state, we apply pure shear deformation to the system. For a sufficiently small strain, the response of the system is linear and elastic like; when the strain is large enough, the plasticity of the system gradually develops and eventually the shear bands are fully developed. In this study, we are particularly interested in how to relate the local plastic deformation to the macroscopic response of the system and also in the development of the shear bands.

Study of an athermal quasi static plastic deformation in a 2D granular material

NASA Astrophysics Data System (ADS)

Zhang, Jie

2017-11-01

In crystalline materials, the plasticity has been well understood in terms of dynamics of dislocation, i.e. flow defects in the crystals where the flow defects can be directly visualized under a microscope. In a contrast, the plasticity in amorphous materials, i.e. glass, is still poorly understood due to the disordered nature of the materials. In this talk, I will discuss the recent results we have obtained in our ongoing research of the plasticity of a 2D glass in the athermal quasi static limit where the 2D glass is made of bi-disperse granular disks with very low friction. Starting from a densely packed homogeneous and isotropic initial state, we apply pure shear deformation to the system. For a sufficiently small strain, the response of the system is linear and elastic like; when the strain is large enough, the plasticity of the system gradually develops and eventually the shear bands are fully developed. In this study, we are particularly interested in how to relate the local plastic deformation to the macroscopic response of the system and also in the development of the shear bands.

Plastics and Environmental Health: The Road Ahead

PubMed Central

North, Emily J.; Halden, Rolf U.

2013-01-01

Plastics continue to benefit society in innumerable ways, even though recent public focus on plastics has centered mostly on human health and environmental concerns, including endocrine-disrupting properties and long-term pollution. The benefits of plastics are particularly apparent in medicine and public health. Plastics are versatile, cost-effective, require less energy to produce than alternative materials – such as metal or glass – and can be manufactured to have many different properties. Due to these characteristics, polymers are used in diverse health applications, such as disposable syringes and intravenous bags, sterile packaging for medical instruments as well as in joint replacements, tissue engineering, etc. However, not all current uses of plastics are prudent and sustainable, as illustrated by widespread, unwanted human exposure to endocrine-disrupting bisphenol-A (BPA) and di-(2-ethylhexyl)phthalate (DEHP), problems arising from the large quantities of plastic being disposed of, and depletion of non-renewable petroleum resources as a result of ever increasing mass-production of plastic consumer articles. By example of the healthcare sector, this review concentrates on benefits and downsides of plastics and identities opportunities to change the composition and disposal practices of these invaluable polymers for a more sustainable future consumption. It highlights ongoing efforts to phase out DEHP and BPA in the healthcare and food industry, and discusses biodegradable options for plastic packaging, opportunities for reducing plastic medical waste, and recycling in medical facilities in the quest to reap a maximum of benefits from polymers without compromising human health or the environment in the process. PMID:23337043

Plastics and environmental health: the road ahead.

PubMed

North, Emily J; Halden, Rolf U

2013-01-01

Plastics continue to benefit society in innumerable ways, even though recent public focus on plastics has centered mostly on human health and environmental concerns, including their endocrine-disrupting properties and the long-term pollution they represent. The benefits of plastics are particularly apparent in medicine and public health. Plastics are versatile, cost-effective, require less energy to produce than alternative materials like metal or glass, and can be manufactured to have many different properties. Due to these characteristics, polymers are used in diverse health applications like disposable syringes and intravenous bags, sterile packaging for medical instruments as well as in joint replacements, tissue engineering, etc. However, not all current uses of plastics are prudent and sustainable, as illustrated by the widespread, unwanted human exposure to endocrine-disrupting bisphenol A (BPA) and di-(2-ethylhexyl)phthalate (DEHP), problems arising from the large quantities of plastic being disposed of, and depletion of non-renewable petroleum resources as a result of the ever-increasing mass production of plastic consumer articles. Using the health-care sector as example, this review concentrates on the benefits and downsides of plastics and identifies opportunities to change the composition and disposal practices of these invaluable polymers for a more sustainable future consumption. It highlights ongoing efforts to phase out DEHP and BPA in the health-care and food industry and discusses biodegradable options for plastic packaging, opportunities for reducing plastic medical waste, and recycling in medical facilities in the quest to reap a maximum of benefits from polymers without compromising human health or the environment in the process.

Hierarchical structure and physicochemical properties of plasticized chitosan.

PubMed

Meng, Qingkai; Heuzey, Marie-Claude; Carreau, Pierre J

2014-04-14

Plasticized chitosan with hierarchical structure, including multiple length scale structural units, was prepared by a "melt"-based method, that is, thermomechanical mixing, as opposed to the usual casting-evaporation procedure. Chitosan was successfully plasticized by thermomechanical mixing in the presence of concentrated lactic acid and glycerol using a batch mixer. Different plasticization formulations were compared in this study, in which concentrated lactic acid was used as protonation agent as well as plasticizer. The microstructure of thermomechanically plasticized chitosan was investigated by X-ray diffraction, scanning electron microscopy, and optical microscopy. With increasing amount of additional plasticizers (glycerol or water), the crystallinity of the plasticized chitosan decreased from 63.7% for the original chitosan powder to almost zero for the sample plasticized with additional water. Salt linkage between lactic acid molecules and amino side chains of chitosan was confirmed by FTIR spectroscopy: the lactic acid molecules expanded the space between the chitosan molecules of the crystalline phase. In the presence of other plasticizers (glycerol and water), various levels of structural units including an amorphous phase, nanofibrils, nanofibril clusters, and microfibers were produced under mechanical shear and thermal energy and identified for the first time. The thermal and thermomechanical properties of the plasticized chitosan were measured by thermogravimetric analysis, differential scanning calorimetric, and DMA. These properties were correlated with the different levels of microstructure, including multiple structural units.

Secretory products of macrophages: twenty-five years on

PubMed Central

Nathan, Carl

2012-01-01

No longer do scientists look down on macrophages as “garbage men” that act “nonspecifically.” Last fall’s Nobel Prizes honored two of the few scientists who studied macrophages three decades ago. Now perhaps thousands do, and the subtypes they describe reflect ongoing discoveries of macrophages’ extraordinary plasticity. PMID:22570864

In vivo Visuotopic Brain Mapping with Manganese-Enhanced MRI and Resting-State Functional Connectivity MRI

PubMed Central

Chan, Kevin C.; Fan, Shu-Juan; Chan, Russell W.; Cheng, Joe S.; Zhou, Iris Y.; Wu, Ed X.

2014-01-01

The rodents are an increasingly important model for understanding the mechanisms of development, plasticity, functional specialization and disease in the visual system. However, limited tools have been available for assessing the structural and functional connectivity of the visual brain network globally, in vivo and longitudinally. There are also ongoing debates on whether functional brain connectivity directly reflects structural brain connectivity. In this study, we explored the feasibility of manganese-enhanced MRI (MEMRI) via 3 different routes of Mn2+ administration for visuotopic brain mapping and understanding of physiological transport in normal and visually deprived adult rats. In addition, resting-state functional connectivity MRI (RSfcMRI) was performed to evaluate the intrinsic functional network and structural-functional relationships in the corresponding anatomical visual brain connections traced by MEMRI. Upon intravitreal, subcortical, and intracortical Mn2+ injection, different topographic and layer-specific Mn enhancement patterns could be revealed in the visual cortex and subcortical visual nuclei along retinal, callosal, cortico-subcortical, transsynaptic and intracortical horizontal connections. Loss of visual input upon monocular enucleation to adult rats appeared to reduce interhemispheric polysynaptic Mn2+ transfer but not intra- or inter-hemispheric monosynaptic Mn2+ transport after Mn2+ injection into visual cortex. In normal adults, both structural and functional connectivity by MEMRI and RSfcMRI was stronger interhemispherically between bilateral primary/secondary visual cortex (V1/V2) transition zones (TZ) than between V1/V2 TZ and other cortical nuclei. Intrahemispherically, structural and functional connectivity was stronger between visual cortex and subcortical visual nuclei than between visual cortex and other subcortical nuclei. The current results demonstrated the sensitivity of MEMRI and RSfcMRI for assessing the neuroarchitecture, neurophysiology and structural-functional relationships of the visual brains in vivo. These may possess great potentials for effective monitoring and understanding of the basic anatomical and functional connections in the visual system during development, plasticity, disease, pharmacological interventions and genetic modifications in future studies. PMID:24394694

Plastic and Large-Deflection Analysis of Nonlinear Structures

NASA Technical Reports Server (NTRS)

Thomson, R. G.; Hayduk, R. J.; Robinson, M. P.; Durling, B. J.; Pifko, A.; Levine, H. S.; Armen, H. J.; Levy, A.; Ogilvie, P.

1982-01-01

Plastic and Large Deflection Analysis of Nonlinear Structures (PLANS) system is collection of five computer programs for finite-element static-plastic and large deflection analysis of variety of nonlinear structures. System considers bending and membrane stresses, general three-dimensional bodies, and laminated composites.

Plastic particles in coastal pelagic ecosystems of the Northeast Pacific ocean.

PubMed

Doyle, Miriam J; Watson, William; Bowlin, Noelle M; Sheavly, Seba B

2011-02-01

The purpose of this study was to examine the distribution, abundance and characteristics of plastic particles in plankton samples collected routinely in Northeast Pacific ecosystems, and to contribute to the development of ideas for future research into the occurrence and impact of small plastic debris in marine pelagic ecosystems. Plastic debris particles were assessed from zooplankton samples collected as part of the National Oceanic and Atmospheric Administration's (NOAA) ongoing ecosystem surveys during two research cruises in the Southeast Bering Sea in the spring and fall of 2006 and four research cruises off the U.S. west coast (primarily off southern California) in spring, summer and fall of 2006, and in January of 2007. Nets with 0.505 mm mesh were used to collect surface samples during all cruises, and sub-surface samples during the four cruises off the west coast. The 595 plankton samples processed indicate that plastic particles are widely distributed in surface waters. The proportion of surface samples from each cruise that contained particles of plastic ranged from 8.75 to 84.0%, whereas particles were recorded in sub-surface samples from only one cruise (in 28.2% of the January 2007 samples). Spatial and temporal variability was apparent in the abundance and distribution of the plastic particles and mean standardized quantities varied among cruises with ranges of 0.004-0.19 particles/m³, and 0.014-0.209 mg dry mass/m³. Off southern California, quantities for the winter cruise were significantly higher, and for the spring cruise significantly lower than for the summer and fall surveys (surface data). Differences between surface particle concentrations and mass for the Bering Sea and California coast surveys were significant for pair-wise comparisons of the spring but not the fall cruises. The particles were assigned to three plastic product types: product fragments, fishing net and line fibers, and industrial pellets; and five size categories: <1 mm, 1-2.5 mm, >2.5-5 mm, >5-10 mm, and >10 mm. Product fragments accounted for the majority of the particles, and most were less than 2.5 mm in size. The ubiquity of such particles in the survey areas and predominance of sizes <2.5 mm implies persistence in these pelagic ecosystems as a result of continuous breakdown from larger plastic debris fragments, and widespread distribution by ocean currents. Detailed investigations of the trophic ecology of individual zooplankton species, and their encounter rates with various size ranges of plastic particles in the marine pelagic environment, are required in order to understand the potential for ingestion of such debris particles by these organisms. Ongoing plankton sampling programs by marine research institutes in large marine ecosystems are good potential sources of data for continued assessment of the abundance, distribution and potential impact of small plastic debris in productive coastal pelagic zones. © 2010 Elsevier Ltd. All rights reserved.

Hebbian Wiring Plasticity Generates Efficient Network Structures for Robust Inference with Synaptic Weight Plasticity

PubMed Central

Hiratani, Naoki; Fukai, Tomoki

2016-01-01

In the adult mammalian cortex, a small fraction of spines are created and eliminated every day, and the resultant synaptic connection structure is highly nonrandom, even in local circuits. However, it remains unknown whether a particular synaptic connection structure is functionally advantageous in local circuits, and why creation and elimination of synaptic connections is necessary in addition to rich synaptic weight plasticity. To answer these questions, we studied an inference task model through theoretical and numerical analyses. We demonstrate that a robustly beneficial network structure naturally emerges by combining Hebbian-type synaptic weight plasticity and wiring plasticity. Especially in a sparsely connected network, wiring plasticity achieves reliable computation by enabling efficient information transmission. Furthermore, the proposed rule reproduces experimental observed correlation between spine dynamics and task performance. PMID:27303271

Structural Crashworthiness and Failure

DTIC Science & Technology

1993-04-16

body motion occurs. This rigid -plastic idealization for dynamically loaded structures is based upon the fact that the plastic deformation of a...in general, for any tensor variable x, i represents the convective derivative. It should be noted that the rigid body rotation is included in the...clamped, impulsively loaded, rigid - plastic beam.’ (a) First phase of motion with stationary transverse plastic hinges at A and E and stationary plastic

In-situ atomic force microscopy observation revealing gel-like plasticity on a metallic glass surface

NASA Astrophysics Data System (ADS)

Lu, Y. M.; Zeng, J. F.; Huang, J. C.; Kuan, S. Y.; Nieh, T. G.; Wang, W. H.; Pan, M. X.; Liu, C. T.; Yang, Y.

2017-03-01

It has been decade-long and enduring efforts to decipher the structural mechanism of plasticity in metallic glasses; however, it still remains a challenge to directly reveal the structural change, if any, that precedes; and dominant plastics flow in them. Here, by using the dynamic atomic force microscope as an "imaging" as well as a "forcing" tool, we unfold a real-time sequence of structural evolution occurring on the surface of an Au-Si thin film metallic glass. In sharp contrast to the common notion that plasticity comes along with mechanical softening in bulk metallic glasses, our experimental results directly reveal three types of nano-sized surface regions, which undergo plasticity but exhibit different characters of structural evolution following the local plasticity events, including stochastic structural rearrangement, unusual local relaxation and rejuvenation. As such, yielding on the metallic-glass surface manifests as a dynamic equilibrium between local relaxation and rejuvenation as opposed to shear instability in bulk metallic-glasses. Our finding demonstrates that plasticity on the metallic glass surface of Au-Si metallic glass bears much resemblance to that of the colloidal gels, of which nonlinear rheology rather than shear instability governs the constitutive behavior of plasticity.

Medical Specialty Society Sponsored Data Registries – Opportunities in Plastic Surgery

PubMed Central

Hume, Keith M.; Crotty, Catherine A.; Simmons, Christopher J.; Neumeister, Michael W.; Chung, Kevin C.

2014-01-01

Clinical data registries are commonly used worldwide and are implemented for a variety of purposes ranging from physician or facility clinic logs for tracking patients, collecting outcomes data, to measuring quality improvement or safety of medical devices. In the United States, the Food and Drug Administration has used data collected through registries to facilitate the drug and device regulatory process, ongoing surveillance during the product life-cycle, and for disease appraisals. Furthermore, the Centers for Medicare and Medicaid Services, in certain instances, base registry participation and submitting data to registries as factors for reimbursement decisions. The purpose of this article is to discuss the use of clinical data registries, the role that medical specialty societies, in particular the American Society of Plastic Surgeons and The Plastic Surgery Foundation, can have in the development and management of registries, and the opportunities for registry use in Plastic Surgery. As outcomes data are becoming essential measures of quality healthcare delivery, participating in registry development and centralized data collection has become a critical effort for Plastic Surgery to engage in to proactively participate in the national quality and performance measurement agenda. PMID:23806935

Variation in adult stress resistance does not explain vulnerability to climate change in copper butterflies.

PubMed

Klockmann, Michael; Wallmeyer, Leonard; Fischer, Klaus

2017-03-15

Ongoing climate change is a major threat to biodiversity. However, although many species clearly suffer from ongoing climate change, others benefit from it, for example, by showing range expansions. However, which specific features determine a species' vulnerability to climate change? Phenotypic plasticity, which has been described as the first line of defence against environmental change, may be of utmost importance here. Against this background, we here compare plasticity in stress tolerance in 3 copper butterfly species, which differ arguably in their vulnerability to climate change. Specifically, we investigated heat, cold and desiccation resistance after acclimatization to different temperatures in the adult stage. We demonstrate that acclimation at a higher temperature increased heat but decreased cold tolerance and desiccation resistance. Contrary to our predictions, species did not show pronounced variation in stress resistance, though plastic capacities in temperature stress resistance did vary across species. Overall, our results seemed to reflect population-rather than species-specific patterns. We conclude that the geographical origin of the populations used should be considered even in comparative studies. However, our results suggest that, in the 3 species studied here, vulnerability to climate change is not in the first place determined by stress resistance in the adult stage. As entomological studies focus all too often on adults only, we argue that more research effort should be dedicated to other developmental stages when trying to understand insect responses to environmental change. © 2017 Institute of Zoology, Chinese Academy of Sciences.

Persistent Angiogenesis in the Autism Brain: An Immunocytochemical Study of Postmortem Cortex, Brainstem and Cerebellum

ERIC Educational Resources Information Center

Azmitia, E. C.; Saccomano, Z. T.; Alzoobaee, M. F.; Boldrini, M.; Whitaker-Azmitia, P. M.

2016-01-01

In the current work, we conducted an immunocytochemical search for markers of ongoing neurogenesis (e.g. nestin) in auditory cortex from postmortem sections of autism spectrum disorder (ASD) and age-matched control donors. We found nestin labeling in cells of the vascular system, indicating blood vessels plasticity. Evidence of angiogenesis was…

Castable plastic mold with electroplatable base

DOEpatents

Domeier, Linda A.; Morales, Alfredo M.; Gonzales, Marcela G.; Keifer, Patrick M.

2004-01-20

A sacrificial plastic mold having an electroplatable backing is provided as are methods of making such a mold via the infusion of a castable liquid formulation through a porous metal substrate (sheet, screen, mesh or foam) and into the features of a micro-scale master mold. Upon casting and demolding, the porous metal substrate is embedded within the cast formulation and projects a plastic structure with features determined by the mold tool. The plastic structure provides a sacrificial plastic mold mechanically bonded to the porous metal substrate, which provides a conducting support suitable for electroplating either contiguous or non-contiguous metal replicates. After electroplating and lapping, the sacrificial plastic can be dissolved, leaving the desired metal structure bonded to the porous metal substrate. Optionally, the electroplated structures may be debonded from the porous substrate by selective dissolution of the porous substrate or a coating thereon.

The effects of hormones and physical exercise on hippocampal structural plasticity.

PubMed

Triviño-Paredes, Juan; Patten, Anna R; Gil-Mohapel, Joana; Christie, Brian R

2016-04-01

The hippocampus plays an integral role in certain aspects of cognition. Hippocampal structural plasticity and in particular adult hippocampal neurogenesis can be influenced by several intrinsic and extrinsic factors. Here we review how hormones (i.e., intrinsic modulators) and physical exercise (i.e., an extrinsic modulator) can differentially modulate hippocampal plasticity in general and adult hippocampal neurogenesis in particular. Specifically, we provide an overview of the effects of sex hormones, stress hormones, and metabolic hormones on hippocampal structural plasticity and adult hippocampal neurogenesis. In addition, we also discuss how physical exercise modulates these forms of hippocampal plasticity, giving particular emphasis on how this modulation can be affected by variables such as exercise regime, duration, and intensity. Understanding the neurobiological mechanisms underlying the modulation of hippocampal structural plasticity by intrinsic and extrinsic factors will impact the design of new therapeutic approaches aimed at restoring hippocampal plasticity following brain injury or neurodegeneration. Copyright © 2016 Elsevier Inc. All rights reserved.

Multispectral brain morphometry in Tourette syndrome persisting into adulthood

PubMed Central

Martino, Davide; Cavanna, Andrea E.; Hutton, Chloe; Orth, Michael; Robertson, Mary M.; Critchley, Hugo D.; Frackowiak, Richard S.

2010-01-01

Tourette syndrome is a childhood-onset neuropsychiatric disorder with a high prevalence of attention deficit hyperactivity and obsessive-compulsive disorder co-morbidities. Structural changes have been found in frontal cortex and striatum in children and adolescents. A limited number of morphometric studies in Tourette syndrome persisting into adulthood suggest ongoing structural alterations affecting frontostriatal circuits. Using cortical thickness estimation and voxel-based analysis of T1- and diffusion-weighted structural magnetic resonance images, we examined 40 adults with Tourette syndrome in comparison with 40 age- and gender-matched healthy controls. Patients with Tourette syndrome showed relative grey matter volume reduction in orbitofrontal, anterior cingulate and ventrolateral prefrontal cortices bilaterally. Cortical thinning extended into the limbic mesial temporal lobe. The grey matter changes were modulated additionally by the presence of co-morbidities and symptom severity. Prefrontal cortical thickness reduction correlated negatively with tic severity, while volume increase in primary somatosensory cortex depended on the intensity of premonitory sensations. Orbitofrontal cortex volume changes were further associated with abnormal water diffusivity within grey matter. White matter analysis revealed changes in fibre coherence in patients with Tourette syndrome within anterior parts of the corpus callosum. The severity of motor tics and premonitory urges had an impact on the integrity of tracts corresponding to cortico-cortical and cortico-subcortical connections. Our results provide empirical support for a patho-aetiological model of Tourette syndrome based on developmental abnormalities, with perturbation of compensatory systems marking persistence of symptoms into adulthood. We interpret the symptom severity related grey matter volume increase in distinct functional brain areas as evidence of ongoing structural plasticity. The convergence of evidence from volume and water diffusivity imaging strengthens the validity of our findings and attests to the value of a novel multimodal combination of volume and cortical thickness estimations that provides unique and complementary information by exploiting their differential sensitivity to structural change. PMID:21071387

Sacrificial plastic mold with electroplatable base

DOEpatents

Domeier, Linda A.; Hruby, Jill M.; Morales, Alfredo M.

2002-01-01

A sacrificial plastic mold having an electroplatable backing is provided. One embodiment consists of the infusion of a softened or molten thermoplastic through a porous metal substrate (sheet, screen, mesh or foam) and into the features of a micro-scale molding tool contacting the porous metal substrate. Upon demolding, the porous metal substrate will be embedded within the thermoplastic and will project a plastic structure with features determined by the mold tool. This plastic structure, in turn, provides a sacrificial plastic mold mechanically bonded to the porous metal substrate which provides a conducting support suitable for electroplating either contiguous or non-contiguous metal replicates. After electroplating and lapping, the sacrificial plastic can be dissolved to leave the desired metal structure bonded to the porous metal substrate. Optionally, the electroplated structures may be debonded from the porous substrate by selective dissolution of the porous substrate or a coating thereon.

Sacrificial Plastic Mold With Electroplatable Base

DOEpatents

Domeier, Linda A.; Hruby, Jill M.; Morales, Alfredo M.

2005-08-16

A sacrificial plastic mold having an electroplatable backing is provided. One embodiment consists of the infusion of a softened or molten thermoplastic through a porous metal substrate (sheet, screen, mesh or foam) and into the features of a micro-scale molding tool contacting the porous metal substrate. Upon demolding, the porous metal substrate will be embedded within the thermoplastic and will project a plastic structure with features determined by the mold tool. This plastic structure, in turn, provides a sacrificial plastic mold mechanically bonded to the porous metal substrate which provides a conducting support suitable for electroplating either contiguous or non-contiguous metal replicates. After electroplating and lapping, the sacrificial plastic can be dissolved to leave the desired metal structure bonded to the porous metal substrate. Optionally, the electroplated structures may be debonded from the porous substrate by selective dissolution of the porous substrate or a coating thereon.

Wastewater treatment with submerged fixed bed biofilm reactor systems--design rules, operating experiences and ongoing developments.

PubMed

Schlegel, S; Koeser, H

2007-01-01

Wastewater treatment systems using bio-films that grow attached to a support media are an alternative to the widely used suspended growth activated sludge process. Different fixed growth biofilm reactors are commercially used for the treatment of municipal as well as industrial wastewater. In this paper a fairly new fixed growth biofilm system, the submerged fixed bed biofilm reactor (SFBBR), is discussed. SFBBRs are based on aerated submerged fixed open structured plastic media for the support of the biofilm. They are generally operated without sludge recirculation in order to avoid clogging of the support media and problems with the control of the biofilm. Reactor and process design considerations for these reactors are reviewed. Measures to ensure the development and maintenance of an active biofilm are examined. SFBBRs have been applied successfully to small wastewater treatment plants where complete nitrification but no high degree of denitrification is necessary. For the pre-treatment of industrial wastewater the use of SFBBRs is advantageous, especially in cases of wastewater with high organic loading or high content of compounds with low biodegradability. Performance data from exemplary commercial plants are given. Ongoing research and development efforts aim at achieving a high simultaneous total nitrogen (TN) removal of aerated SFBBRs and at improving the efficiency of TN removal in anoxic SFBBRs.

Evaluation of engineering plastic for rollover protective structure (ROPS) mounting.

PubMed

Comer, R S; Ayers, P D; Liu, J

2007-04-01

Agriculture has one of the highest fatality rates of any industry in America. Tractor rollovers are a significant contributor to the high death rate. Rollover protective structures (ROPS) have helped lower these high fatality rates on full-size tractors. However, a large number of older tractors still do not use ROPS due to the difficulty of designing and creating a mounting structure. To help reduce this difficulty, engineering plastics were evaluated for use in a ROPS mounting structure on older tractors. The use of engineering plastics around axle housings could provide a uniform mounting configuration as well as lower costs for aftermarket ROPS. Various plastics were examined through shear testing, scale model testing, and compressive strength testing. Once a material was chosen based upon strength and cost, full-scale testing of the plastic's strength on axle housings was conducted. Finally, a mounting structure was tested in static ROPS tests, and field upset tests were performed in accordance with SAE Standard J2194. Initial tests revealed that the ROPS mounting structure and axle housing combination had higher torsional strength with less twisting than the axle housing alone. An engineering plastic ROPS mounting structure was easily successful in withstanding the forces applied during the static longitudinal and lateral ROPS tests. Field upset testing revealed that the mounting structure could withstand the impact loads seen during actual upsets without a failure. During both static testing and field upset testing, no permanent twisting of the mounting structure was found. Engineering plastic could therefore be a viable option for a universal ROPS mounting structure for older tractors.

Time Within:. the Perceptual Rivalry Switch as a Neural Clock

NASA Astrophysics Data System (ADS)

Pettigrew, John D.; Tilden, Jan D.

2005-10-01

Attention is drawn to weaknesses in the case for an external, physical basis for time's perceptual phenomena, raising the possibility of a Darwinian evolutionary explanation for the apparent flow, structure and arrow of time. We develop the hypothesis that, of all arrows of time identified by physicists and philosophers, the most fundamental is the psychological arrow. Based on findings of an on-going program of empirical research, we suggest a neural basis for time phenomena in the rhythmicity and plasticity of one of the brainstem dopaminergic nuclei, the venetral tegmental area (VTA). We examine links between neural time-keeping and perceptual rivalry and discuss evidence that rivalry is mediated by the VTA which functions as an ultradian oscillator. Further research is suggested, which could challenge or support the hypothesis of the VTA as an important neural time-keeper and the subjective basis of the asymmetric phenomena of time.

AUDITORY ASSOCIATIVE MEMORY AND REPRESENTATIONAL PLASTICITY IN THE PRIMARY AUDITORY CORTEX

PubMed Central

Weinberger, Norman M.

2009-01-01

Historically, the primary auditory cortex has been largely ignored as a substrate of auditory memory, perhaps because studies of associative learning could not reveal the plasticity of receptive fields (RFs). The use of a unified experimental design, in which RFs are obtained before and after standard training (e.g., classical and instrumental conditioning) revealed associative representational plasticity, characterized by facilitation of responses to tonal conditioned stimuli (CSs) at the expense of other frequencies, producing CS-specific tuning shifts. Associative representational plasticity (ARP) possesses the major attributes of associative memory: it is highly specific, discriminative, rapidly acquired, consolidates over hours and days and can be retained indefinitely. The nucleus basalis cholinergic system is sufficient both for the induction of ARP and for the induction of specific auditory memory, including control of the amount of remembered acoustic details. Extant controversies regarding the form, function and neural substrates of ARP appear largely to reflect different assumptions, which are explicitly discussed. The view that the forms of plasticity are task-dependent is supported by ongoing studies in which auditory learning involves CS-specific decreases in threshold or bandwidth without affecting frequency tuning. Future research needs to focus on the factors that determine ARP and their functions in hearing and in auditory memory. PMID:17344002

A computer program for cyclic plasticity and structural fatigue analysis

NASA Technical Reports Server (NTRS)

Kalev, I.

1980-01-01

A computerized tool for the analysis of time independent cyclic plasticity structural response, life to crack initiation prediction, and crack growth rate prediction for metallic materials is described. Three analytical items are combined: the finite element method with its associated numerical techniques for idealization of the structural component, cyclic plasticity models for idealization of the material behavior, and damage accumulation criteria for the fatigue failure.

Plasticity in the Human Visual Cortex: An Ophthalmology-Based Perspective

PubMed Central

Rosa, Andreia Martins; Silva, Maria Fátima; Murta, Joaquim

2013-01-01

Neuroplasticity refers to the ability of the brain to reorganize the function and structure of its connections in response to changes in the environment. Adult human visual cortex shows several manifestations of plasticity, such as perceptual learning and adaptation, working under the top-down influence of attention. Plasticity results from the interplay of several mechanisms, including the GABAergic system, epigenetic factors, mitochondrial activity, and structural remodeling of synaptic connectivity. There is also a downside of plasticity, that is, maladaptive plasticity, in which there are behavioral losses resulting from plasticity changes in the human brain. Understanding plasticity mechanisms could have major implications in the diagnosis and treatment of ocular diseases, such as retinal disorders, cataract and refractive surgery, amblyopia, and in the evaluation of surgical materials and techniques. Furthermore, eliciting plasticity could open new perspectives in the development of strategies that trigger plasticity for better medical and surgical outcomes. PMID:24205505

Using Biophysical Models to Understand the Effect of tDCS on Neurorehabilitation: Searching for Optimal Covariates to Enhance Poststroke Recovery

PubMed Central

Malerba, Paola; Straudi, Sofia; Fregni, Felipe; Bazhenov, Maxim; Basaglia, Nino

2017-01-01

Stroke is a leading cause of worldwide disability, and up to 75% of survivors suffer from some degree of arm paresis. Recently, rehabilitation of stroke patients has focused on recovering motor skills by taking advantage of use-dependent neuroplasticity, where high-repetition of goal-oriented movement is at times combined with non-invasive brain stimulation, such as transcranial direct current stimulation (tDCS). Merging the two approaches is thought to provide outlasting clinical gains, by enhancing synaptic plasticity and motor relearning in the motor cortex primary area. However, this general approach has shown mixed results across the stroke population. In particular, stroke location has been found to correlate with the likelihood of success, which suggests that different patients might require different protocols. Understanding how motor rehabilitation and stimulation interact with ongoing neural dynamics is crucial to optimize rehabilitation strategies, but it requires theoretical and computational models to consider the multiple levels at which this complex phenomenon operate. In this work, we argue that biophysical models of cortical dynamics are uniquely suited to address this problem. Specifically, biophysical models can predict treatment efficacy by introducing explicit variables and dynamics for damaged connections, changes in neural excitability, neurotransmitters, neuromodulators, plasticity mechanisms, and repetitive movement, which together can represent brain state, effect of incoming stimulus, and movement-induced activity. In this work, we hypothesize that effects of tDCS depend on ongoing neural activity and that tDCS effects on plasticity may be also related to enhancing inhibitory processes. We propose a model design for each step of this complex system, and highlight strengths and limitations of the different modeling choices within our approach. Our theoretical framework proposes a change in paradigm, where biophysical models can contribute to the future design of novel protocols, in which combined tDCS and motor rehabilitation strategies are tailored to the ongoing dynamics that they interact with, by considering the known biophysical factors recruited by such protocols and their interaction. PMID:28280482

75 FR 7931 - Airworthiness Directives; Airbus Model A380-841, -842, and -861 Airplanes

Federal Register 2010, 2011, 2012, 2013, 2014

2010-02-23

... addition, delamination has been observed within the monolithic Carbon Fibre Reinforced Plastic (CFRP... observed within the monolithic Carbon Fibre Reinforced Plastic (CFRP) structure around the pivot support... monolithic Carbon Fibre Reinforced Plastic (CFRP) structure around the pivot support-ring. This condition, if...

An elastic-plastic contact model for line contact structures

NASA Astrophysics Data System (ADS)

Zhu, Haibin; Zhao, Yingtao; He, Zhifeng; Zhang, Ruinan; Ma, Shaopeng

2018-06-01

Although numerical simulation tools are now very powerful, the development of analytical models is very important for the prediction of the mechanical behaviour of line contact structures for deeply understanding contact problems and engineering applications. For the line contact structures widely used in the engineering field, few analytical models are available for predicting the mechanical behaviour when the structures deform plastically, as the classic Hertz's theory would be invalid. Thus, the present study proposed an elastic-plastic model for line contact structures based on the understanding of the yield mechanism. A mathematical expression describing the global relationship between load history and contact width evolution of line contact structures was obtained. The proposed model was verified through an actual line contact test and a corresponding numerical simulation. The results confirmed that this model can be used to accurately predict the elastic-plastic mechanical behaviour of a line contact structure.

Solar photovoltaic reflective trough collection structure

DOEpatents

Anderson, Benjamin J.; Sweatt, William C.; Okandan, Murat; Nielson, Gregory N.

2015-11-19

A photovoltaic (PV) solar concentration structure having at least two troughs encapsulated in a rectangular parallelepiped optical plastic structure, with the troughs filled with an optical plastic material, the troughs each having a reflective internal surface and approximately parabolic geometry, and the troughs each including photovoltaic cells situated so that light impinging on the optical plastic material will be concentrated onto the photovoltaic cells. Multiple structures can be connected to provide a solar photovoltaic collection system that provides portable, efficient, low-cost electrical power.

Self-Organization of Microcircuits in Networks of Spiking Neurons with Plastic Synapses.

PubMed

Ocker, Gabriel Koch; Litwin-Kumar, Ashok; Doiron, Brent

2015-08-01

The synaptic connectivity of cortical networks features an overrepresentation of certain wiring motifs compared to simple random-network models. This structure is shaped, in part, by synaptic plasticity that promotes or suppresses connections between neurons depending on their joint spiking activity. Frequently, theoretical studies focus on how feedforward inputs drive plasticity to create this network structure. We study the complementary scenario of self-organized structure in a recurrent network, with spike timing-dependent plasticity driven by spontaneous dynamics. We develop a self-consistent theory for the evolution of network structure by combining fast spiking covariance with a slow evolution of synaptic weights. Through a finite-size expansion of network dynamics we obtain a low-dimensional set of nonlinear differential equations for the evolution of two-synapse connectivity motifs. With this theory in hand, we explore how the form of the plasticity rule drives the evolution of microcircuits in cortical networks. When potentiation and depression are in approximate balance, synaptic dynamics depend on weighted divergent, convergent, and chain motifs. For additive, Hebbian STDP these motif interactions create instabilities in synaptic dynamics that either promote or suppress the initial network structure. Our work provides a consistent theoretical framework for studying how spiking activity in recurrent networks interacts with synaptic plasticity to determine network structure.

Self-Organization of Microcircuits in Networks of Spiking Neurons with Plastic Synapses

PubMed Central

Ocker, Gabriel Koch; Litwin-Kumar, Ashok; Doiron, Brent

2015-01-01

The synaptic connectivity of cortical networks features an overrepresentation of certain wiring motifs compared to simple random-network models. This structure is shaped, in part, by synaptic plasticity that promotes or suppresses connections between neurons depending on their joint spiking activity. Frequently, theoretical studies focus on how feedforward inputs drive plasticity to create this network structure. We study the complementary scenario of self-organized structure in a recurrent network, with spike timing-dependent plasticity driven by spontaneous dynamics. We develop a self-consistent theory for the evolution of network structure by combining fast spiking covariance with a slow evolution of synaptic weights. Through a finite-size expansion of network dynamics we obtain a low-dimensional set of nonlinear differential equations for the evolution of two-synapse connectivity motifs. With this theory in hand, we explore how the form of the plasticity rule drives the evolution of microcircuits in cortical networks. When potentiation and depression are in approximate balance, synaptic dynamics depend on weighted divergent, convergent, and chain motifs. For additive, Hebbian STDP these motif interactions create instabilities in synaptic dynamics that either promote or suppress the initial network structure. Our work provides a consistent theoretical framework for studying how spiking activity in recurrent networks interacts with synaptic plasticity to determine network structure. PMID:26291697

Social media use and impact on plastic surgery practice.

PubMed

Vardanian, Andrew J; Kusnezov, Nicholas; Im, Daniel D; Lee, James C; Jarrahy, Reza

2013-05-01

Social media platforms have revolutionized the way human beings communicate, yet there is little evidence describing how the plastic surgery community has adopted social media. In this article, the authors evaluate current trends in social media use by practicing plastic surgeons. An anonymous survey on the use of social media was distributed to members of the American Society of Plastic Surgeons. Prevalent patterns of social media implementation were elucidated. One-half of respondents were regular social media users. Reasons for using social media included the beliefs that incorporation of social media into medical practice is inevitable (56.7 percent), that they are an effective marketing tool (52.1 percent), and that they provide a forum for patient education (49 percent). Surgeons with a primarily aesthetic surgery practice were more likely to use social media. Most respondents (64.6 percent) stated that social media had no effect on their practice, whereas 33.8 percent reported a positive impact and 1.5 percent reported a negative impact. This study depicts current patterns of social media use by plastic surgeons, including motivations driving its implementation and impressions on its impact. Many feel that social media are an effective marketing tool that generates increased exposure and referrals. A small number of surgeons have experienced negative repercussions from social media involvement. Our study reveals the presence of a void. There is a definite interest among those surveyed in developing best practice standards and oversight to ensure ethical use of social media platforms throughout the plastic surgery community. Continuing discussion regarding these matters should be ongoing as our experience with social media in plastic surgery evolves.

Medical aspects of pediatric rehabilitation after moderate to severe traumatic brain injury.

PubMed

Cantore, Lisa; Norwood, Kenneth; Patrick, Peter

2012-01-01

Recovery from severe traumatic brain injury (TBI) is prolonged, complicated and challenging. Medical rehabilitation is the bridge from acute medical care and stabilization to community reintegration. The process of caring for the recovering brain introduces unknown challenges of neural plasticity with demands to restore and to also move the child and family back to the developmental trajectory they once knew. While the ongoing focus is to maintain and advance medical stability, co- morbid conditions are addressed, and a plan for ongoing health is established. While no one manuscript can cover all of the medical aspects, this article will present in a "systems review" manner the most challenging and demanding medical conditions that children may confront following severe brain injury.

Structural and Functional Plasticity in the Maternal Brain Circuitry

ERIC Educational Resources Information Center

Pereira, Mariana

2016-01-01

Parenting recruits a distributed network of brain structures (and neuromodulators) that coordinates caregiving responses attuned to the young's affect, needs, and developmental stage. Many of these structures and connections undergo significant structural and functional plasticity, mediated by the interplay between maternal hormones and social…

An experiment on the use of disposable plastics as a reinforcement in concrete beams

NASA Technical Reports Server (NTRS)

Chowdhury, Mostafiz R.

1992-01-01

Illustrated here is the concept of reinforced concrete structures by the use of computer simulation and an inexpensive hands-on design experiment. The students in our construction management program use disposable plastic as a reinforcement to demonstrate their understanding of reinforced concrete and prestressed concrete beams. The plastics used for such an experiment vary from plastic bottles to steel reinforced auto tires. This experiment will show the extent to which plastic reinforcement increases the strength of a concrete beam. The procedure of using such throw-away plastics in an experiment to explain the interaction between the reinforcement material and concrete, and a comparison of the test results for using different types of waste plastics are discussed. A computer analysis to simulate the structural response is used to compare the test results and to understand the analytical background of reinforced concrete design. This interaction of using computers to analyze structures and to relate the output results with real experimentation is found to be a very useful method for teaching a math-based analytical subject to our non-engineering students.

Invasive Cortical Stimulation to Promote Recovery of Function After Stroke

PubMed Central

Plow, Ela B.; Carey, James R.; Nudo, Randolph J.; Pascual-Leone, Alvaro

2011-01-01

Background and Purpose Residual motor deficits frequently linger after stroke. Search for newer effective strategies to promote functional recovery is ongoing. Brain stimulation, as a means of directing adaptive plasticity, is appealing. Animal studies and Phase I and II trials in humans have indicated safety, feasibility, and efficacy of combining rehabilitation and concurrent invasive cortical stimulation. However, a recent Phase III trial showed no advantage of the combination. We critically review results of various trials and discuss the factors that contributed to the distinctive result. Summary of Review Regarding cortical stimulation, it is important to determine the (1) location of peri-infarct representations by integrating multiple neuroanatomical and physiological techniques; (2) role of other mechanisms of stroke recovery; (3) viability of peri-infarct tissue and descending pathways; (4) lesion geometry to ensure no alteration/displacement of current density; and (5) applicability of lessons generated from noninvasive brain stimulation studies in humans. In terms of combining stimulation with rehabilitation, we should understand (1) the principle of homeostatic plasticity; (2) the effect of ongoing cortical activity and phases of learning; and (3) that subject-specific intervention may be necessary. Conclusions Future cortical stimulation trials should consider the factors that may have contributed to the peculiar results of the Phase III trial and address those in future study designs. PMID:19359643

Adaptation to a latitudinal thermal gradient within a widespread copepod species: the contributions of genetic divergence and phenotypic plasticity

PubMed Central

2017-01-01

Understanding how populations adapt to heterogeneous thermal regimes is essential for comprehending how latitudinal gradients in species diversification are formed, and how taxa will respond to ongoing climate change. Adaptation can occur by innate genetic factors, by phenotypic plasticity, or by a combination of both mechanisms. Yet, the relative contribution of such mechanisms to large-scale latitudinal gradients of thermal tolerance across conspecific populations remains unclear. We examine thermal performance in 11 populations of the intertidal copepod Tigriopus californicus, ranging from Baja California Sur (Mexico) to British Columbia (Canada). Common garden experiments show that survivorship to acute heat-stress differs between populations (by up to 3.8°C in LD50 values), reflecting a strong genetic thermal adaptation. Using a split-brood experiment with two rearing temperatures, we also show that developmental phenotypic plasticity is beneficial to thermal tolerance (by up to 1.3°C), and that this effect differs across populations. Although genetic divergence in heat tolerance strongly correlates with latitude and temperature, differences in the plastic response do not. In the context of climate warming, our results confirm the general prediction that low-latitude populations are most susceptible to local extinction because genetic adaptation has placed physiological limits closer to current environmental maxima, but our results also contradict the prediction that phenotypic plasticity is constrained at lower latitudes. PMID:28446698

Analysis of reverse martensitic transformation of prehardened 16XCH steel

NASA Astrophysics Data System (ADS)

Muravyev, Vasily; Frolov, Alexey; Lonchakov, Sergey; Bakhmatov, Pavel

2015-10-01

In the paper the structural evolution of previously tempered 16XCH steel is investigated. The influence of temperature and time conditions of heating on temperature of austenization is revealed and the influence of structural changes on steel properties is defined. The analysis of the obtained results showed an increase of plasticity at the initial stage of reverse martensitic transformation and an increase of plasticity at increased durability. It is experimentally found that reverse transformation of packet and lath martensite into the initial phase (holding for a fraction of a second, temperature 400-450°C) leads to a sharp, more than 2-fold, reduction of strength and increase of plasticity. The effect of increased plasticity under reverse martensitic transformation conditions is observed. The structure of packet and lath martensite is more fine-grained in comparison with initial quenching; the durability and plasticity are much higher. Despite the derived results, the revealed effects of increased plasticity and strength require further exploration to increase the reliability of constructions made of low-alloyed steels.

High-Aspect-Ratio Ridge Structures Induced by Plastic Deformation as a Novel Microfabrication Technique.

PubMed

Takei, Atsushi; Jin, Lihua; Fujita, Hiroyuki; Takei, A; Fujita, H; Jin, Lihua

2016-09-14

Wrinkles on thin film/elastomer bilayer systems provide functional surfaces. The aspect ratio of these wrinkles is critical to their functionality. Much effort has been dedicated to creating high-aspect-ratio structures on the surface of bilayer systems. A highly prestretched elastomer attached to a thin film has recently been shown to form a high-aspect-ratio structure, called a ridge structure, due to a large strain induced in the elastomer. However, the prestretch requirements of the elastomer during thin film attachment are not compatible with conventional thin film deposition methods, such as spin coating, dip coating, and chemical vapor deposition (CVD). Thus, the fabrication method is complex, and ridge structure formation is limited to planar surfaces. This paper presents a new and simple method for constructing ridge structures on a nonplanar surface using a plastic thin film/elastomer bilayer system. A plastic thin film is attached to a stress-free elastomer, and the resulting bilayer system is highly stretched one- or two-dimensionally. Upon the release of the stretch load, the deformation of the elastomer is reversible, while the plastically deformed thin film stays elongated. The combination of the length mismatch and the large strain induced in the elastomer generates ridge structures. The morphology of the plastic thin film/elastomer bilayer system is experimentally studied by varying the physical parameters, and the functionality and the applicability to a nonplanar surface are demonstrated. Finally, we simulate the effect of plasticity on morphology. This study presents a new technique for generating microscale high-aspect-ratio structures and its potential for functional surfaces.

Dense-body aggregates as plastic structures supporting tension in smooth muscle cells.

PubMed

Zhang, Jie; Herrera, Ana M; Paré, Peter D; Seow, Chun Y

2010-11-01

The wall of hollow organs of vertebrates is a unique structure able to generate active tension and maintain a nearly constant passive stiffness over a large volume range. These properties are predominantly attributable to the smooth muscle cells that line the organ wall. Although smooth muscle is known to possess plasticity (i.e., the ability to adapt to large changes in cell length through structural remodeling of contractile apparatus and cytoskeleton), the detailed structural basis for the plasticity is largely unknown. Dense bodies, one of the most prominent structures in smooth muscle cells, have been regarded as the anchoring sites for actin filaments, similar to the Z-disks in striated muscle. Here, we show that the dense bodies and intermediate filaments formed cable-like structures inside airway smooth muscle cells and were able to adjust the cable length according to cell length and tension. Stretching the muscle cell bundle in the relaxed state caused the cables to straighten, indicating that these intracellular structures were connected to the extracellular matrix and could support passive tension. These plastic structures may be responsible for the ability of smooth muscle to maintain a nearly constant tensile stiffness over a large length range. The finding suggests that the structural plasticity of hollow organs may originate from the dense-body cables within the smooth muscle cells.

Principles of auditory processing differ between sensory and premotor structures of the songbird forebrain

PubMed Central

Vicario, David S.

2017-01-01

Sensory and motor brain structures work in collaboration during perception. To evaluate their respective contributions, the present study recorded neural responses to auditory stimulation at multiple sites simultaneously in both the higher-order auditory area NCM and the premotor area HVC of the songbird brain in awake zebra finches (Taeniopygia guttata). Bird’s own song (BOS) and various conspecific songs (CON) were presented in both blocked and shuffled sequences. Neural responses showed plasticity in the form of stimulus-specific adaptation, with markedly different dynamics between the two structures. In NCM, the response decrease with repetition of each stimulus was gradual and long-lasting and did not differ between the stimuli or the stimulus presentation sequences. In contrast, HVC responses to CON stimuli decreased much more rapidly in the blocked than in the shuffled sequence. Furthermore, this decrease was more transient in HVC than in NCM, as shown by differential dynamics in the shuffled sequence. Responses to BOS in HVC decreased more gradually than to CON stimuli. The quality of neural representations, computed as the mutual information between stimuli and neural activity, was higher in NCM than in HVC. Conversely, internal functional correlations, estimated as the coherence between recording sites, were greater in HVC than in NCM. The cross-coherence between the two structures was weak and limited to low frequencies. These findings suggest that auditory communication signals are processed according to very different but complementary principles in NCM and HVC, a contrast that may inform study of the auditory and motor pathways for human speech processing. NEW & NOTEWORTHY Neural responses to auditory stimulation in sensory area NCM and premotor area HVC of the songbird forebrain show plasticity in the form of stimulus-specific adaptation with markedly different dynamics. These two structures also differ in stimulus representations and internal functional correlations. Accordingly, NCM seems to process the individually specific complex vocalizations of others based on prior familiarity, while HVC responses appear to be modulated by transitions and/or timing in the ongoing sequence of sounds. PMID:28031398

Determination of the structural changes by Raman and {sup 13}C CP/MAS NMR spectroscopy on native corn starch with plasticizers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cozar, O.; Filip, C.; Tripon, C.

The plasticizing - antiplasticizing effect of water and glycerol contents on native corn starch samples is investigated by FT-Raman and {sup 13}C CP/MAS NMR spectroscopy. The presence of both amorphous and crystalline structural phases was evidenced in pure native corn starch and also in the samples containing plasticizers. Among the crystalline starch structures, the A- and V- types were suggested by CP/MAS NMR spectra.

The effects of musical training on structural brain development: a longitudinal study.

PubMed

Hyde, Krista L; Lerch, Jason; Norton, Andrea; Forgeard, Marie; Winner, Ellen; Evans, Alan C; Schlaug, Gottfried

2009-07-01

Long-term instrumental music training is an intense, multisensory and motor experience that offers an ideal opportunity to study structural brain plasticity in the developing brain in correlation with behavioral changes induced by training. Here, for the first time, we demonstrate structural brain changes after only 15 months of musical training in early childhood, which were correlated with improvements in musically relevant motor and auditory skills. These findings shed light on brain plasticity, and suggest that structural brain differences in adult experts (whether musicians or experts in other areas) are likely due to training-induced brain plasticity.

Detection of structural changes and mechanical properties of light alloys after severe plastic deformation

NASA Astrophysics Data System (ADS)

Krasnoveikin, V. A.; Kozulin, A. A.; Skripnyak, V. A.

2017-11-01

Severe plastic deformation by equal channel angular pressing has been performed to produce light aluminum and magnesium alloy billets with ultrafine-grained structure. The physical and mechanical properties of the processed alloys are examined by studying their microstructure, measuring microhardness, yield strength, and uniaxial tensile strength. A nondestructive testing technique using three-dimensional X-ray tomography is proposed for detecting internal structural defects and monitoring damage formation in the structure of alloys subjected to severe plastic deformation. The investigation results prove the efficiency of the chosen method and selected mode of producing ultrafine-grained light alloys.

Analysis of fluid-structure interaction in a frame pipe undergoing plastic deformations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Khamlichi, A.; Jezequel, L.; Jacques, Y.

1995-11-01

Water hammer pressure waves of sufficiently large magnitude can cause plastic flexural deformations in a frame pipe. In this study, the authors propose a modelization of this problem based on plane wave approximation for the fluid equations and approximation of the structure motion by a single-degree-of-freedom elastic-plastic oscillator. Direct analytical integration of elastic-plastic equations through pipe sections, then over the pipe length is performed in order to identify the oscillator parameters. Comparison of the global load-displacement relationship obtained with the finite element solution was considered and has shown good agreement. Fluid-structure coupling is achieved by assuming elbows to act likemore » plane monopole sources, where localized jumps of fluid velocity occur and where net pressure forces are exerted on the structure. The authors have applied this method to analyze the fluid-structure interaction in this range of deformations. Energy exchange between the fluid and the structure and energy dissipation are quantified.« less

Beneficial effects of benzodiazepine diazepam on chronic stress-induced impairment of hippocampal structural plasticity and depression-like behavior in mice.

PubMed

Zhao, Yunan; Wang, Zhongli; Dai, Jianguo; Chen, Lin; Huang, Yufang; Zhan, Zhen

2012-03-17

Whether benzodiazepines (BZDs) have beneficial effects on the progress of chronic stress-induced impairment of hippocampal structural plasticity and major depression is uncertain. The present study designed four preclinical experiments to determine the effects of BZDs using chronic unpredictable stress model. In Experiment 1, several time course studies on behavior and hippocampus response to stress were conducted using the forced swim and tail suspension tests (FST and TST) as well as hippocampal structural plasticity markers. Chronic stress induced depression-like behavior in the FST and TST as well as decreased hippocampal structural plasticity that returned to normal within 3 wk. In Experiment 2, mice received p.o. administration of three diazepam dosages prior to each variate stress session for 4 wk. This treatment significantly antagonized the elevation of stress-induced corticosterone levels. Only low- (0.5mg/kg) and medium-dose (1mg/kg) diazepam blocked the detrimental effects of chronic stress. In Experiment 3, after 7 wk of stress sessions, daily p.o. diazepam administration during 1 wk recovery phase dose-dependently accelerated the recovery of stressed mice. In Experiment 4, 1 wk diazepam administration to control mice enhanced significantly hippocampal structural plasticity and induced an antidepressant-like behavioral effect, whereas 4 wk diazepam administration produced opposite effects. Hence, diazepam can slow the progress of chronic stress-induced detrimental consequences by normalizing glucocorticoid hormones. Considering the adverse effect of long-term diazepam administration on hippocampal plasticity, the preventive effects of diazepam may depend on the proper dose. Short-term diazepam treatment enhances hippocampal structural plasticity and is beneficial to recovery following chronic stress. Copyright © 2011 Elsevier B.V. All rights reserved.

Nogo-A regulates spatial learning as well as memory formation and modulates structural plasticity in the adult mouse hippocampus.

PubMed

Zagrebelsky, Marta; Lonnemann, Niklas; Fricke, Steffen; Kellner, Yves; Preuß, Eike; Michaelsen-Preusse, Kristin; Korte, Martin

2017-02-01

Behavioral learning has been shown to involve changes in the function and structure of synaptic connections of the central nervous system (CNS). On the other hand, the neuronal circuitry in the mature brain is characterized by a high degree of stability possibly providing a correlate for long-term storage of information. This observation indicates the requirement for a set of molecules inhibiting plasticity and promoting stability thereby providing temporal and spatial specificity to plastic processes. Indeed, signaling of Nogo-A via its receptors has been shown to play a crucial role in restricting activity-dependent functional and structural plasticity in the adult CNS. However, whether Nogo-A controls learning and memory formation and what are the cellular and molecular mechanisms underlying this function is still unclear. Here we show that Nogo-A signaling controls spatial learning and reference memory formation upon training in the Morris water maze and negatively modulates structural changes at spines in the mouse hippocampus. Learning processes and the correlated structural plasticity have been shown to involve changes in excitatory as well as in inhibitory neuronal connections. We show here that Nogo-A is highly expressed not only in excitatory, but also in inhibitory, Parvalbumin positive neurons in the adult hippocampus. By this means our current and previous data indicate that Nogo-A loss-of-function positively influences spatial learning by priming the neuronal structure to a higher plasticity level. Taken together our results link the role of Nogo-A in negatively regulating plastic processes to a physiological function in controlling learning and memory processes in the mature hippocampus and open the interesting possibility that it might mainly act by controlling the function of the hippocampal inhibitory circuitry. Copyright © 2016 Elsevier Inc. All rights reserved.

51F activities

NASA Image and Video Library

2009-06-25

51F-12-034 (29 July-6 Aug 1985) --- A ball of liquid floats aboard Challenger as one of the Spacelab 2 crewmembers continues the ongoing fascination of liquids in weightlessness. Coffe, grape juice, orange juice, strawberry punch and various other beverages have been formed into globules, usually by the means of plastic straws, on a number of previous Shuttle missions as well as earlier NASA spacecraft. A second crewmember photographed this closeup with a 35 mm camera.

Studies on the effect of storage time and plasticizers on the structural variations in thermoplastic starch.

PubMed

Schmitt, H; Guidez, A; Prashantha, K; Soulestin, J; Lacrampe, M F; Krawczak, P

2015-01-22

Starch was combined with plasticizers such as glycerol, sorbitol, glycerol/sorbitol and urea/ethanolamine blends by means of high shear extrusion process to prepare thermoplastic starch (TPS). Effect of storage time and plasticizers on the structural stability of melt processed TPS was investigated. Morphological observation, X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy reveal that melt extrusion process is efficient in transforming granular starch into a plasticized starch for all plasticizer compositions. XRD analysis highlights major changes in the microstructure of plasticized starch, and dependence of crystalline type and degree of crystallinity mainly on the plasticizer composition and storage time. Dynamical mechanical analysis (DMA) yields a decrease of the peak intensity of loss factor with aging time. The effect of ageing on tensile strength also appears to be highly dependent on the plasticizer composition. Thus, through different plasticizer combinations and ageing, starch-based materials with significant differences in tensile properties can be obtained, which may be tuned to meet the requirements of a wide range of applications. Copyright © 2014 Elsevier Ltd. All rights reserved.

Plasticity mechanism for copper extrusion in through-silicon vias for three-dimensional interconnects

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jiang, Tengfei; Spinella, Laura; Im, Jay

2013-11-18

In this paper, we demonstrated the plasticity mechanism for copper (Cu) extrusion in through-silicon via structures under thermal cycling. The local plasticity was directly observed by synchrotron x-ray micro-diffraction near the top of the via with the amount increasing with the peak temperature. The Cu extrusion was confirmed by Atomic Force Microscopy (AFM) measurements and found to be consistent with the observed Cu plasticity behavior. A simple analytical model elucidated the role of plasticity during thermal cycling, and finite element analyses were carried out to confirm the plasticity mechanism as well as the effect of the via/Si interface. The modelmore » predictions were able to account for the via extrusions observed in two types of experiments, with one representing a nearly free sliding interface and the other a strongly bonded interface. Interestingly, the AFM extrusion profiles seemed to contour with the local grain structures near the top of the via, suggesting that the grain structure not only affects the yield strength of the Cu and thus its plasticity but could also be important in controlling the pop-up behavior and the statistics for a large ensemble of vias.« less

The negotiated equilibrium model of spinal cord function.

PubMed

Wolpaw, Jonathan R

2018-04-16

The belief that the spinal cord is hardwired is no longer tenable. Like the rest of the CNS, the spinal cord changes during growth and aging, when new motor behaviours are acquired, and in response to trauma and disease. This paper describes a new model of spinal cord function that reconciles its recently appreciated plasticity with its long recognized reliability as the final common pathway for behaviour. According to this model, the substrate of each motor behaviour comprises brain and spinal plasticity: the plasticity in the brain induces and maintains the plasticity in the spinal cord. Each time a behaviour occurs, the spinal cord provides the brain with performance information that guides changes in the substrate of the behaviour. All the behaviours in the repertoire undergo this process concurrently; each repeatedly induces plasticity to preserve its key features despite the plasticity induced by other behaviours. The aggregate process is a negotiation among the behaviours: they negotiate the properties of the spinal neurons and synapses that they all use. The ongoing negotiation maintains the spinal cord in an equilibrium - a negotiated equilibrium - that serves all the behaviours. This new model of spinal cord function is supported by laboratory and clinical data, makes predictions borne out by experiment, and underlies a new approach to restoring function to people with neuromuscular disorders. Further studies are needed to test its generality, to determine whether it may apply to other CNS areas such as the cerebral cortex, and to develop its therapeutic implications. This article is protected by copyright. All rights reserved. This article is protected by copyright. All rights reserved.

INTERACTIONS BETWEEN PLASTIC DEBRIS, PERSISTENT ORGANIC POLLUTANTS AND MICROORGANISMS IN OCEAN SURFACE WATERS

EPA Science Inventory

The chemical structure of plastics greatly differs from natural marine particulate matter and therefore plastics likely are creating new and unique niches for microorganisms in the ocean. It is hypothesized that the microbes found on plastic particles will be taxonomically ...

Emergent spatial synaptic structure from diffusive plasticity.

PubMed

Sweeney, Yann; Clopath, Claudia

2017-04-01

Some neurotransmitters can diffuse freely across cell membranes, influencing neighbouring neurons regardless of their synaptic coupling. This provides a means of neural communication, alternative to synaptic transmission, which can influence the way in which neural networks process information. Here, we ask whether diffusive neurotransmission can also influence the structure of synaptic connectivity in a network undergoing plasticity. We propose a form of Hebbian synaptic plasticity which is mediated by a diffusive neurotransmitter. Whenever a synapse is modified at an individual neuron through our proposed mechanism, similar but smaller modifications occur in synapses connecting to neighbouring neurons. The effects of this diffusive plasticity are explored in networks of rate-based neurons. This leads to the emergence of spatial structure in the synaptic connectivity of the network. We show that this spatial structure can coexist with other forms of structure in the synaptic connectivity, such as with groups of strongly interconnected neurons that form in response to correlated external drive. Finally, we explore diffusive plasticity in a simple feedforward network model of receptive field development. We show that, as widely observed across sensory cortex, the preferred stimulus identity of neurons in our network become spatially correlated due to diffusion. Our proposed mechanism of diffusive plasticity provides an efficient mechanism for generating these spatial correlations in stimulus preference which can flexibly interact with other forms of synaptic organisation. © 2016 Federation of European Neuroscience Societies and John Wiley & Sons Ltd.

Effects of plasticization and shear stress on phase structure development and properties of soy protein blends.

PubMed

Chen, Feng; Zhang, Jinwen

2010-11-01

In this study, soy protein concentrate (SPC) was used as a plastic component to blend with poly(butylene adipate-co-terephthalate) (PBAT). Effects of SPC plasticization and blend composition on its deformation during mixing were studied in detail. Influence of using water as the major plasticizer and glycerol as the co-plasticizer on the deformation of the SPC phase during mixing was explored. The effect of shear stress, as affected by SPC loading level, on the phase structure of SPC in the blends was also investigated. Quantitative analysis of the aspect ratio of SPC particles was conducted by using ImageJ software, and an empirical model predicting the formation of percolated structure was applied. The experimental results and the model prediction showed a fairly good agreement. The experimental results and statistic analysis suggest that both SPC loading level and its water content prior to compounding had significant influences on development of the SPC phase structure and were correlated in determining the morphological structures of the resulting blends. Consequently, physical and mechanical properties of the blends greatly depended on the phase morphology and PBAT/SPC ratio of the blends.

Cajal and the Conceptual Weakness of Neural Sciences

PubMed Central

Delgado-García, José M.

2015-01-01

The experimental and conceptual contributions of Santiago Ramón y Cajal remain almost as fresh and valuable as when his original proposals were published more than a century ago—a rare example, contrasting with other related sciences. His basic concepts on the neuron as the main building block of the central nervous system, the dynamic polarization principle as a way to understand how neurons deal with ongoing active processes, and brain local structural arrangements as a result of the functional specialization of selected neural circuits are concepts still surviving in present research papers dealing with brain function during the performance of cognitive and/or behavioral activities. What is more, the central dogma of the Neuroscience of today, i.e., brain plasticity as the morpho-functional substrate of memory and learning processes, was already proposed and documented with notable insights by Ramón y Cajal. From this background, I will try to discuss in this chapter which new functional and structural concepts have been introduced in contemporary Neuroscience and how we will be able to construct a set of basic principles underlying brain functions for the twenty-first century. PMID:26483644

Neuroanatomical prerequisites for language functions in the maturing brain.

PubMed

Brauer, Jens; Anwander, Alfred; Friederici, Angela D

2011-02-01

The 2 major language-relevant cortical regions in the human brain, Broca's area and Wernicke's area, are connected via the fibers of the arcuate fasciculus/superior longitudinal fasciculus (AF/SLF). Here, we compared this pathway in adults and children and its relation to language processing during development. Comparison of fiber properties demonstrated lower anisotropy in children's AF/SLF, arguing for an immature status of this particular pathway with conceivably a lower degree of myelination. Combined diffusion tensor imaging (DTI) data and functional magnetic resonance imaging (fMRI) data indicated that in adults the termination of the AF/SLF fiber projection is compatible with functional activation in Broca's area, that is pars opercularis. In children, activation in Broca's area extended from the pars opercularis into the pars triangularis revealing an alternative connection to the temporal lobe (Wernicke's area) via the ventrally projecting extreme capsule fiber system. fMRI and DTI data converge to indicate that adults make use of a more confined language network than children based on ongoing maturation of the structural network. Our data suggest relations between language development and brain maturation and, moreover, indicate the brain's plasticity to adjust its function to available structural prerequisites.

Application of an Elastic-Plastic Methodology to Structural Integrity Evaluation,

DTIC Science & Technology

The elastic plastic fracture mechanics ( EPFM ) technology has advanced to the point where it can be used to make a realistic assessment of the...concepts of EPFM into a structural stability evaluation. The structure is modeled as a cracked test specimen either in series or parallel with a spring

Bacterial Contamination on Household Toys and Association with Water, Sanitation and Hygiene Conditions in Honduras

PubMed Central

Stauber, Christine E.; Walters, Adam; de Aceituno, Anna M. Fabiszewski; Sobsey, Mark D.

2013-01-01

There is growing evidence that household water treatment interventions improve microbiological water quality and reduce diarrheal disease risk. Few studies have examined, however, the impact of water treatment interventions on household-level hygiene and sanitation. This study examined the association of four water and sanitation conditions (access to latrines, improved sanitation, improved water and the plastic biosand filter) on the levels of total coliforms and E. coli on existing and introduced toys during an on-going randomized controlled trial of the plastic biosand filter (plastic BSF). The following conditions were associated with decreased bacterial contamination on children’s toys: access to a latrine, access to improved sanitation and access to the plastic BSF. Overall, compared to existing toys, introduced toys had significantly lower levels of both E. coli and total coliforms. Results suggest that levels of fecal indicator bacteria contamination on children’s toys may be associated with access to improved water and sanitation conditions in the home. In addition, the fecal indicator bacteria levels on toys probably vary with duration in the household. Additional information on how these toys become contaminated is needed to determine the usefulness of toys as indicators or sentinels of water, sanitation and hygiene conditions, behaviors and risks. PMID:23598302

Bacterial contamination on household toys and association with water, sanitation and hygiene conditions in Honduras.

PubMed

Stauber, Christine E; Walters, Adam; Fabiszewski de Aceituno, Anna M; Sobsey, Mark D

2013-04-18

There is growing evidence that household water treatment interventions improve microbiological water quality and reduce diarrheal disease risk. Few studies have examined, however, the impact of water treatment interventions on household-level hygiene and sanitation. This study examined the association of four water and sanitation conditions (access to latrines, improved sanitation, improved water and the plastic biosand filter) on the levels of total coliforms and E. coli on existing and introduced toys during an on-going randomized controlled trial of the plastic biosand filter (plastic BSF). The following conditions were associated with decreased bacterial contamination on children's toys: access to a latrine, access to improved sanitation and access to the plastic BSF. Overall, compared to existing toys, introduced toys had significantly lower levels of both E. coli and total coliforms. Results suggest that levels of fecal indicator bacteria contamination on children's toys may be associated with access to improved water and sanitation conditions in the home. In addition, the fecal indicator bacteria levels on toys probably vary with duration in the household. Additional information on how these toys become contaminated is needed to determine the usefulness of toys as indicators or sentinels of water, sanitation and hygiene conditions, behaviors and risks.

PLANS: A finite element program for nonlinear analysis of structures. Volume 1: Theoretical manual

NASA Technical Reports Server (NTRS)

Pifko, A.; Levine, H. S.; Armen, H., Jr.

1975-01-01

The PLANS system is described which is a finite element program for nonlinear analysis. The system represents a collection of special purpose computer programs each associated with a distinct physical problem class. Modules of PLANS specifically referenced and described in detail include: (1) REVBY, for the plastic analysis of bodies of revolution; (2) OUT-OF-PLANE, for the plastic analysis of 3-D built-up structures where membrane effects are predominant; (3) BEND, for the plastic analysis of built-up structures where bending and membrane effects are significant; (4) HEX, for the 3-D elastic-plastic analysis of general solids; and (5) OUT-OF-PLANE-MG, for material and geometrically nonlinear analysis of built-up structures. The SATELLITE program for data debugging and plotting of input geometries is also described. The theoretical foundations upon which the analysis is based are presented. Discussed are the form of the governing equations, the methods of solution, plasticity theories available, a general system description and flow of the programs, and the elements available for use.

Synaptic Effects of Electric Fields

NASA Astrophysics Data System (ADS)

Rahman, Asif

Learning and sensory processing in the brain relies on the effective transmission of information across synapses. The strength and efficacy of synaptic transmission is modifiable through training and can be modulated with noninvasive electrical brain stimulation. Transcranial electrical stimulation (TES), specifically, induces weak intensity and spatially diffuse electric fields in the brain. Despite being weak, electric fields modulate spiking probability and the efficacy of synaptic transmission. These effects critically depend on the direction of the electric field relative to the orientation of the neuron and on the level of endogenous synaptic activity. TES has been used to modulate a wide range of neuropsychiatric indications, for various rehabilitation applications, and cognitive performance in diverse tasks. How can a weak and diffuse electric field, which simultaneously polarizes neurons across the brain, have precise changes in brain function? Designing therapies to maximize desired outcomes and minimize undesired effects presents a challenging problem. A series of experiments and computational models are used to define the anatomical and functional factors leading to specificity of TES. Anatomical specificity derives from guiding current to targeted brain structures and taking advantage of the direction-sensitivity of neurons with respect to the electric field. Functional specificity originates from preferential modulation of neuronal networks that are already active. Diffuse electric fields may recruit connected brain networks involved in a training task and promote plasticity along active synaptic pathways. In vitro, electric fields boost endogenous synaptic plasticity and raise the ceiling for synaptic learning with repeated stimulation sessions. Synapses undergoing strong plasticity are preferentially modulated over weak synapses. Therefore, active circuits that are involved in a task could be more susceptible to stimulation than inactive circuits. Moreover, stimulation polarity has asymmetric effects on synaptic strength making it easier to enhance ongoing plasticity. These results suggest that the susceptibility of brain networks to an electric field depends on the state of synaptic activity. Combining a training task, which activates specific circuits, with TES may lead to functionally-specific effects. Given the simplicity of TES and the complexity of brain function, understanding the mechanisms leading to specificity is fundamental to the rational advancement of TES.

Fragile X Mental Retardation Protein and Dendritic Local Translation of the Alpha Subunit of the Calcium/Calmodulin-Dependent Kinase II Messenger RNA Are Required for the Structural Plasticity Underlying Olfactory Learning.

PubMed

Daroles, Laura; Gribaudo, Simona; Doulazmi, Mohamed; Scotto-Lomassese, Sophie; Dubacq, Caroline; Mandairon, Nathalie; Greer, Charles August; Didier, Anne; Trembleau, Alain; Caillé, Isabelle

2016-07-15

In the adult brain, structural plasticity allowing gain or loss of synapses remodels circuits to support learning. In fragile X syndrome, the absence of fragile X mental retardation protein (FMRP) leads to defects in plasticity and learning deficits. FMRP is a master regulator of local translation but its implication in learning-induced structural plasticity is unknown. Using an olfactory learning task requiring adult-born olfactory bulb neurons and cell-specific ablation of FMRP, we investigated whether learning shapes adult-born neuron morphology during their synaptic integration and its dependence on FMRP. We used alpha subunit of the calcium/calmodulin-dependent kinase II (αCaMKII) mutant mice with altered dendritic localization of αCaMKII messenger RNA, as well as a reporter of αCaMKII local translation to investigate the role of this FMRP messenger RNA target in learning-dependent structural plasticity. Learning induces profound changes in dendritic architecture and spine morphology of adult-born neurons that are prevented by ablation of FMRP in adult-born neurons and rescued by an metabotropic glutamate receptor 5 antagonist. Moreover, dendritically translated αCaMKII is necessary for learning and associated structural modifications and learning triggers an FMRP-dependent increase of αCaMKII dendritic translation in adult-born neurons. Our results strongly suggest that FMRP mediates structural plasticity of olfactory bulb adult-born neurons to support olfactory learning through αCaMKII local translation. This reveals a new role for FMRP-regulated dendritic local translation in learning-induced structural plasticity. This might be of clinical relevance for the understanding of critical periods disruption in autism spectrum disorder patients, among which fragile X syndrome is the primary monogenic cause. Copyright © 2016 Society of Biological Psychiatry. Published by Elsevier Inc. All rights reserved.

Evidence for structural plasticity in humans: comment on Thomas and Baker (2012).

PubMed

Erickson, Kirk I

2013-06-01

Thomas and Baker (2012) have provided a balanced and critical review of the scientific evidence claiming that training interventions have the capacity to alter the structural morphology of the brain. Here I provide some additional considerations when reading and interpreting both the review and the original empirical articles. Research proposing to examine the capacity for structural brain plasticity needs to contemplate methodological issues and factors that could moderate or mask potentially interesting effects. Overall, although this area of research is in need of circumspection, it also could have transformative implications if structural brain plasticity in humans is possible. Copyright © 2012 Elsevier Inc. All rights reserved.

Role of endoscopic retrograde cholangiopancreatography in the management of benign biliary strictures: What’s new?

PubMed Central

Ferreira, Rosa; Loureiro, Rui; Nunes, Nuno; Santos, António Alberto; Maio, Rui; Cravo, Marília; Duarte, Maria Antónia

2016-01-01

Benign biliary strictures comprise a heterogeneous group of diseases. The most common strictures amenable to endoscopic treatment are post-cholecystectomy, post-liver transplantation, related to primary sclerosing cholangitis and to chronic pancreatitis. Endoscopic treatment of benign biliary strictures is widely used as first line therapy, since it is effective, safe, noninvasive and repeatable. Endoscopic techniques currently used are dilation, multiple plastic stents insertion and fully covered self-expandable metal stents. The main indication for dilation alone is primary sclerosing cholangitis related strictures. In the vast majority of the remaining cases, temporary placement of multiple plastic stents with/without dilation is considered the treatment of choice. Although this approach is effective, it requires multiple endoscopic sessions due to the short duration of stent patency. Fully covered self-expandable metal stents appear as a good alternative to plastic stents, since they have an increased radial diameter, longer stent patency, easier insertion technique and similar efficacy. Recent advances in endoscopic technique and various devices have allowed successful treatment in most cases. The development of novel endoscopic techniques and devices is still ongoing. PMID:26962404

Assessing Microplastic Loads in the Mississippi River and Its Major Tributaries

NASA Astrophysics Data System (ADS)

Hasenmueller, E. A.; Martin, K. M.; Conkle, J. L.; White, J. R.

2017-12-01

Plastic debris is ubiquitous in marine environments and can cause significant harm to aquatic life when organisms become entangled in the plastic or mistake it for food. Macroplastic debris (plastic >5 mm in diameter) has received significant attention from the public, government agencies, and the scientific community. However, the majority of plastics in aquatic environments are microplastics (plastic <5 mm in diameter), emerging contaminants that, due to their small size, were understudied until the last decade. Estimates of plastic debris in the world's ocean vary widely from 244,000 tonnes floating at the water's surface to 4.8-12.7 million tonnes loaded from terrestrial sources annually. Many of these terrestrial inputs of plastic debris to the ocean have not yet been systematically quantified. The Mississippi River is likely one of the largest sources of marine plastic debris, not only to the Gulf of Mexico, but also the global ocean. Therefore, this research, funded by the National Oceanic and Atmospheric Administration (NOAA) Marine Debris Program, has quantified and characterized microplastics (i.e., size, shape, and resin type) at the surface and at depth along the mainstem of the Mississippi River, including near major cities such as St. Louis and New Orleans, as well as in some of the Mississippi River's major tributaries (i.e., the Missouri River, Ohio River, and Illinois River). Sampling is ongoing, but our datasets will allow us to characterize: 1) total microplastic concentrations and loads, 2) spatial and temporal trends in microplastic abundances, and 3) land-use effects on microplastic levels across the Mississippi River watershed. Our data will also provide estimates of the total discharge of microplastics from the Mississippi River to the Gulf of Mexico. These efforts will provide a baseline for future research relating to the fate and effects of microplastics in aquatic environments and can guide federal and local policy makers in creating and assessing mitigation strategies to improve water quality.

Flaw-induced plastic-flow dynamics in bulk metallic glasses under tension

PubMed Central

Chen, S. H.; Yue, T. M.; Tsui, C. P.; Chan, K. C.

2016-01-01

Inheriting amorphous atomic structures without crystalline lattices, bulk metallic glasses (BMGs) are known to have superior mechanical properties, such as high strength approaching the ideal value, but are susceptible to catastrophic failures. Understanding the plastic-flow dynamics of BMGs is important for achieving stable plastic flow in order to avoid catastrophic failures, especially under tension, where almost all BMGs demonstrate limited plastic flow with catastrophic failure. Previous findings have shown that the plastic flow of BMGs displays critical dynamics under compression tests, however, the plastic-flow dynamics under tension are still unknown. Here we report that power-law critical dynamics can also be achieved in the plastic flow of tensile BMGs by introducing flaws. Differing from the plastic flow under compression, the flaw-induced plastic flow under tension shows an upward trend in the amplitudes of the load drops with time, resulting in a stable plastic-flow stage with a power-law distribution of the load drop. We found that the flaw-induced plastic flow resulted from the stress gradients around the notch roots, and the stable plastic-flow stage increased with the increase of the stress concentration factor ahead of the notch root. The findings are potentially useful for predicting and avoiding the catastrophic failures in tensile BMGs by tailoring the complex stress fields in practical structural-applications. PMID:27779221

Shrink-induced superhydrophobic and antibacterial surfaces in consumer plastics.

PubMed

Freschauf, Lauren R; McLane, Jolie; Sharma, Himanshu; Khine, Michelle

2012-01-01

Structurally modified superhydrophobic surfaces have become particularly desirable as stable antibacterial surfaces. Because their self-cleaning and water resistant properties prohibit bacteria growth, structurally modified superhydrophobic surfaces obviate bacterial resistance common with chemical agents, and therefore a robust and stable means to prevent bacteria growth is possible. In this study, we present a rapid fabrication method for creating such superhydrophobic surfaces in consumer hard plastic materials with resulting antibacterial effects. To replace complex fabrication materials and techniques, the initial mold is made with commodity shrink-wrap film and is compatible with large plastic roll-to-roll manufacturing and scale-up techniques. This method involves a purely structural modification free of chemical additives leading to its inherent consistency over time and successive recasting from the same molds. Finally, antibacterial properties are demonstrated in polystyrene (PS), polycarbonate (PC), and polyethylene (PE) by demonstrating the prevention of gram-negative Escherichia coli (E. coli) bacteria growth on our structured plastic surfaces.

Defective cerebellar control of cortical plasticity in writer’s cramp

PubMed Central

Hubsch, Cecile; Roze, Emmanuel; Popa, Traian; Russo, Margherita; Balachandran, Ammu; Pradeep, Salini; Mueller, Florian; Brochard, Vanessa; Quartarone, Angelo; Degos, Bertrand; Vidailhet, Marie; Kishore, Asha

2013-01-01

A large body of evidence points to a role of basal ganglia dysfunction in the pathophysiology of dystonia, but recent studies indicate that cerebellar dysfunction may also be involved. The cerebellum influences sensorimotor adaptation by modulating sensorimotor plasticity of the primary motor cortex. Motor cortex sensorimotor plasticity is maladaptive in patients with writer’s cramp. Here we examined whether putative cerebellar dysfunction in dystonia is linked to these patients’ maladaptive plasticity. To that end we compared the performances of patients and healthy control subjects in a reaching task involving a visuomotor conflict generated by imposing a random deviation (−40° to 40°) on the direction of movement of the mouse/cursor. Such a task is known to involve the cerebellum. We also compared, between patients and healthy control subjects, how the cerebellum modulates the extent and duration of an ongoing sensorimotor plasticity in the motor cortex. The cerebellar cortex was excited or inhibited by means of repeated transcranial magnetic stimulation before artificial sensorimotor plasticity was induced in the motor cortex by paired associative stimulation. Patients with writer’s cramp were slower than the healthy control subjects to reach the target and, after having repeatedly adapted their trajectories to the deviations, they were less efficient than the healthy control subjects to perform reaching movement without imposed deviation. It was interpreted as impaired washing-out abilities. In healthy subjects, cerebellar cortex excitation prevented the paired associative stimulation to induce a sensorimotor plasticity in the primary motor cortex, whereas cerebellar cortex inhibition led the paired associative stimulation to be more efficient in inducing the plasticity. In patients with writer’s cramp, cerebellar cortex excitation and inhibition were both ineffective in modulating sensorimotor plasticity. In patients with writer’s cramp, but not in healthy subjects, behavioural parameters reflecting their capacity for adapting to the rotation and for washing-out of an earlier adaptation predicted the efficacy of inhibitory cerebellar conditioning to influence sensorimotor plasticity: the better the online adaptation, the smaller the influence of cerebellar inhibitory stimulation on motor cortex plasticity. Altered cerebellar encoding of incoming afferent volleys may result in decoupling the motor component from the afferent information flow, and also in maladjusted sensorimotor calibration. The loss of cerebellar control over sensorimotor plasticity might also lead to building up an incorrect motor program to specific adaptation tasks such as writing. PMID:23801734

Plastic-aluminum composites in transportation infrastructure.

DOT National Transportation Integrated Search

2017-03-01

This report presents an initial investigation of the mechanics of I-beams developed with plastic-aluminum composite technology. Plastic-aluminum composites in structural beam/frame/truss elements are a relatively new concept that has seen little, if ...

Study on Collision of Ship Side Structure by Simplified Plastic Analysis Method

NASA Astrophysics Data System (ADS)

Sun, C. J.; Zhou, J. H.; Wu, W.

2017-10-01

During its lifetime, a ship may encounter collision or grounding and sustain permanent damage after these types of accidents. Crashworthiness has been based on two kinds of main methods: simplified plastic analysis and numerical simulation. A simplified plastic analysis method is presented in this paper. Numerical methods using the non-linear finite-element software LS-DYNA are conducted to validate the method. The results show that, as for the accuracy of calculation results, the simplified plasticity analysis are in good agreement with the finite element simulation, which reveals that the simplified plasticity analysis method can quickly and accurately estimate the crashworthiness of the side structure during the collision process and can be used as a reliable risk assessment method.

Dynamic Re-wiring of Neural Circuits in the Motor Cortex in Mouse Models of Parkinson's Disease

PubMed Central

Lalchandani, Rupa R.; Cui, Yuting; Shu, Yu; Xu, Tonghui; Ding, Jun B.

2015-01-01

SUMMARY Dynamic adaptations in synaptic plasticity are critical for learning new motor skills and maintaining memory throughout life, which rapidly decline with Parkinson's disease (PD). Plasticity in the motor cortex is important for acquisition and maintenance of novel motor skills, but how the loss of dopamine in PD leads to disrupted structural and functional plasticity in the motor cortex is not well understood. Here, we utilized mouse models of PD and 2-photon imaging to show that dopamine depletion resulted in structural changes in the motor cortex. We further discovered that dopamine D1 and D2 receptor signaling were linked to selectively and distinctly regulating these aberrant changes in structural and functional plasticity. Our findings suggest that both D1 and D2 receptor signaling regulate motor cortex plasticity, and loss of dopamine results in atypical synaptic adaptations that may contribute to the impairment of motor performance and motor memory observed in PD. PMID:26237365

The role of sleep in regulating structural plasticity and synaptic strength: Implications for memory and cognitive function.

PubMed

Raven, Frank; Van der Zee, Eddy A; Meerlo, Peter; Havekes, Robbert

2018-06-01

Dendritic spines are the major sites of synaptic transmission in the central nervous system. Alterations in the strength of synaptic connections directly affect the neuronal communication, which is crucial for brain function as well as the processing and storage of information. Sleep and sleep loss bidirectionally alter structural plasticity, by affecting spine numbers and morphology, which ultimately can affect the functional output of the brain in terms of alertness, cognition, and mood. Experimental data from studies in rodents suggest that sleep deprivation may impact structural plasticity in different ways. One of the current views, referred to as the synaptic homeostasis hypothesis, suggests that wake promotes synaptic potentiation whereas sleep facilitates synaptic downscaling. On the other hand, several studies have now shown that sleep deprivation can reduce spine density and attenuate synaptic efficacy in the hippocampus. These data are the basis for the view that sleep promotes hippocampal structural plasticity critical for memory formation. Altogether, the impact of sleep and sleep loss may vary between regions of the brain. A better understanding of the role that sleep plays in regulating structural plasticity may ultimately lead to novel therapeutic approaches for brain disorders that are accompanied by sleep disturbances and sleep loss. Copyright © 2017 Elsevier Ltd. All rights reserved.

DYCAST: A finite element program for the crash analysis of structures

NASA Technical Reports Server (NTRS)

Pifko, A. B.; Winter, R.; Ogilvie, P.

1987-01-01

DYCAST is a nonlinear structural dynamic finite element computer code developed for crash simulation. The element library contains stringers, beams, membrane skin triangles, plate bending triangles and spring elements. Changing stiffnesses in the structure are accounted for by plasticity and very large deflections. Material nonlinearities are accommodated by one of three options: elastic-perfectly plastic, elastic-linear hardening plastic, or elastic-nonlinear hardening plastic of the Ramberg-Osgood type. Geometric nonlinearities are handled in an updated Lagrangian formulation by reforming the structure into its deformed shape after small time increments while accumulating deformations, strains, and forces. The nonlinearities due to combined loadings are maintained, and stiffness variation due to structural failures are computed. Numerical time integrators available are fixed-step central difference, modified Adams, Newmark-beta, and Wilson-theta. The last three have a variable time step capability, which is controlled internally by a solution convergence error measure. Other features include: multiple time-load history tables to subject the structure to time dependent loading; gravity loading; initial pitch, roll, yaw, and translation of the structural model with respect to the global system; a bandwidth optimizer as a pre-processor; and deformed plots and graphics as post-processors.

Metabolic and reproductive plasticity of core and marginal populations of the eurythermic saline water bug Sigara selecta (Hemiptera: Corixidae) in a climate change context.

PubMed

Carbonell, J A; Bilton, D T; Calosi, P; Millán, A; Stewart, A; Velasco, J

2017-04-01

Ongoing climate change is driving dramatic range shifts in diverse taxa worldwide, and species responses to global change are likely to be determined largely by population responses at geographical range margins. Here we investigate the metabolic and reproductive plasticity in response to water temperature and salinity variation of two populations of the eurythermic saline water bug Sigara selecta: one population located close to the northern edge of its distribution, in a relatively cold, thermally stable region (SE England - 'marginal'), and one close to the range centre, in a warmer and more thermally variable Mediterranean climate (SE Spain - 'core'). We compared metabolic and oviposition rates and egg size, following exposure to one of four different combinations of temperature (15 and 25°C) and salinity (10 and 35gL -1 ). Oviposition rate was significantly higher in the marginal population, although eggs laid were smaller overall. No significant differences in oxygen consumption rates were found between core and marginal populations, although the marginal population showed higher levels of plasticity in both metabolic and reproductive traits. Our results suggest that population-specific responses to environmental change are complex and may be mediated by differences in phenotypic plasticity. In S. selecta, the higher plasticity of the marginal population may facilitate both its persistence in current habitats and northward expansion with future climatic warming. The less plastic core population may be able to buffer current environmental variability with minor changes in metabolism and fecundity, but could be prone to extinction if temperature and salinity changes exceed physiological tolerance limits in the future. Copyright © 2016 Elsevier Ltd. All rights reserved.

Plasticity-mediated collapse and recrystallization in hollow copper nanowires: a molecular dynamics simulation.

PubMed

Dutta, Amlan; Raychaudhuri, Arup Kumar; Saha-Dasgupta, Tanusri

2016-01-01

We study the thermal stability of hollow copper nanowires using molecular dynamics simulation. We find that the plasticity-mediated structural evolution leads to transformation of the initial hollow structure to a solid wire. The process involves three distinct stages, namely, collapse, recrystallization and slow recovery. We calculate the time scales associated with different stages of the evolution process. Our findings suggest a plasticity-mediated mechanism of collapse and recrystallization. This contradicts the prevailing notion of diffusion driven transport of vacancies from the interior to outer surface being responsible for collapse, which would involve much longer time scales as compared to the plasticity-based mechanism.

Simultaneous increase in the strength, plasticity, and corrosion resistance of an ultrafine-grained Ti-4Al-2V pseudo-alpha-titanium alloy

NASA Astrophysics Data System (ADS)

Chuvil'deev, V. N.; Kopylov, V. I.; Nokhrin, A. V.; Bakhmet'ev, A. M.; Sandler, N. G.; Kozlova, N. A.; Tryaev, P. V.; Tabachkova, N. Yu.; Mikhailov, A. S.; Ershova, A. V.; Gryaznov, M. Yu.; Chegurov, M. K.; Sysoev, A. N.; Smirnova, E. S.

2017-05-01

The influence of severe plastic deformation on the structural-phase state of grain boundaries in a Ti-4Al-2V (commercial PT3V grade) pseudo-alpha-titanium alloy has been studied. It is established that increase in the strength, plasticity, and corrosion resistance of this alloy is related to the formation of an ultrafine- grained structure. In particular, it is shown that an increase in the resistance to hot-salt intergranular corrosion is due to diffusion-controlled redistribution of aluminum and vanadium atoms at the grain boundaries of titanium formed during thermal severe plastic deformation.

The influences of soil and nearby structures on dispersion characteristics of wave propagating along buried plastic pipes

NASA Astrophysics Data System (ADS)

Liu, Shuyong; Jiang, J.; Parr, Nicola

2016-09-01

Water loss in distribution systems is a global problem for the water industry and governments. According to the international water supply association (IWSA), as a result of leaks from distribution pipes, 20% to 30% of water is lost while in transit from treatment plants to consumers. Although governments have tried to push the water industry to reduce the water leaks, a lot of experts have pointed out that a wide use of plastic pipes instead of metal pipes in recent years has caused difficulties in the detection of leaks using current acoustic technology. Leaks from plastic pipes are much quieter than traditional metal pipes and comparing to metal pipes the plastic pipes have very different coupling characteristics with soil, water and surrounding structures, such as other pipes, road surface and building foundations. The dispersion characteristics of wave propagating along buried plastic pipes are investigated in this paper using finite element and boundary element based models. Both empty and water- filled pipes were considered. Influences from nearby pipes and building foundations were carefully studied. The results showed that soil condition and nearby structures have significant influences on the dispersion characteristics of wave propagating along buried plastic pipes.

Effect of the conditions of prepreg preparation on the strength of structural plastics

NASA Astrophysics Data System (ADS)

Zaborskaya, L. V.; Yurkevich, O. R.

1995-05-01

A study is made of the effect of the temperature and duration of heat treatment of polymer composite prepregs on their strength. It is established that heat treatment under conditions ensuring close to maximal adhesive interaction between the components of the prepreg and subsequent shaping makes it possible to more than double the strength of the plastic (Table 1), A new approach is proposed to optimizing the conditions of formation of structural plastics.

Elasto-limited plastic analysis of structures for probabilistic conditions

NASA Astrophysics Data System (ADS)

Movahedi Rad, M.

2018-06-01

With applying plastic analysis and design methods, significant saving in material can be obtained. However, as a result of this benefit excessive plastic deformations and large residual displacements might develop, which in turn might lead to unserviceability and collapse of the structure. In this study, for deterministic problem the residual deformation of structures is limited by considering a constraint on the complementary strain energy of the residual forces. For probabilistic problem the constraint for the complementary strain energy of the residual forces is given randomly and critical stresses updated during the iteration. Limit curves are presented for the plastic limit load factors. The results show that these constraints have significant effects on the load factors. The formulations of the deterministic and probabilistic problems lead to mathematical programming which are solved by the use of nonlinear algorithm.

TEM-nanoindentation studies of semiconducting structures.

PubMed

Le Bourhis, E; Patriarche, G

2007-01-01

This paper reviews the application of nanoindentation coupled with transmission electron microscopy (TEM) to investigations of the plastic behaviour of semiconducting structures and its implication for device design. Instrumented nanoindentation has been developed to extract the mechanical behaviour of small volumes scaled to those encountered in semiconductor heterostructures. We illustrate that TEM is a powerful complementary tool for the study of local plasticity induced by nanoindentation. TEM-nanoindentation allows for detailed understanding of the plastic deformation in semiconducting structures and opens practical routes for improvement of devices. Performances of heterostructures are deteriously affected by dislocations that relax the lattice mismatched layers. Different ways to obtain compliant substructures are being developed in order to concentrate the plastic relaxation underneath the heterostructure. Such approaches allow for mechanical design of micro- and opto-electronic devices to be considered throughout the fabrication process.

Influence of Severe Plastic Deformation on the Structure and Properties of Al-Li-Cu-Mg-Zr-Sc-Zn Alloy

NASA Astrophysics Data System (ADS)

Kaigorodova, L. I.; Rasposienko, D. Yu.; Pushin, V. G.; Pilyugin, V. P.; Smirnov, S. V.

2018-02-01

The structural and phase transformations in the Al-Li-Cu-Mg-Zr-Sc-Zn alloy have been studied by the electron microscopy after the aging for the maximum strength and in the nanostructured state after severe plastic deformation by high-pressure torsion. It has been shown that severe plastic deformation leads to the formation of a nanostructured state in the alloy, the nature of which is determined by the magnitude of deformation and the degree of completeness of the dynamic recrystallization. It has been established that deformation also causes a change in the phase composition of the alloy. The influence of the structural components of the severely deformed alloy on the level of mechanical properties, such as the hardness, plasticity, elastic modulus, and stiffness has been discussed.

[Independence in Plastic Surgery - Benefit or Barrier? Analysis of the Publication Performance in Academic Plastic Surgery Depending on Varying Organisational Structures].

PubMed

Schubert, C D; Leitsch, S; Haertnagl, F; Haas, E M; Giunta, R E

2015-08-01

Despite its recognition as an independent specialty, at German university hospitals the field of plastic surgery is still underrepresented in terms of independent departments with a dedicated research focus. The aim of this study was to analyse the publication performance within the German academic plastic surgery environment and to compare independent departments and dependent, subordinate organisational structures regarding their publication performance. Organisational structures and number of attending doctors in German university hospitals were examined via a website analysis. A pubmed analysis was applied to assess the publication performance (number of publications, cumulative impact factor, impact factor/publication, number of publications/MD, number of publications/unit) between 2009 and 2013. In a journal analysis the distribution of the cumulative impact factor and number of publications in different journals as well as the development of the impact factor in the top journals were analysed. Out of all 35 university hospitals there exist 12 independent departments for plastic surgery and 8 subordinate organisational structures. In 15 university hospitals there were no designated plastic surgery units. The number of attending doctors differed considerably between independent departments (3.6 attending doctors/unit) and subordinate organisational structures (1.1 attending doctors/unit). The majority of publications (89.0%) and of the cumulative impact factor (91.2%) as well as most of the publications/MD (54 publications/year) and publications/unit (61 publications/year) were created within the independent departments. Only in departments top publications with an impact factor > 5 were published. In general a negative trend regarding the number of publications (- 13.4%) and cumulative impact factor (- 28.9%) was observed. 58.4% of all publications were distributed over the top 10 journals. Within the latter the majority of articles were published in English journals (60% of publications, 79.9% of the cumulative impact factor). The average impact factor of the top 10 journals increased by 13.5% from 2009 to 2013. In contrast to subordinate and dependent organisational structures, independent departments of plastic surgery are the key performers within German academic plastic surgery which, however, suffers from a general declining publication performance. Hence, the type of organisational structure has a crucial influence on the research performance. © Georg Thieme Verlag KG Stuttgart · New York.

Improved tank car design development : ongoing studies on sandwich structures

DOT National Transportation Integrated Search

2009-03-02

The Government and industry have a common interest in : improving the safety performance of railroad tank cars carrying : hazardous materials. Research is ongoing to develop strategies : to maintain the structural integrity of railroad tank cars carr...

Three-dimensional elastic-plastic finite-element analysis of fatigue crack propagation

NASA Technical Reports Server (NTRS)

Goglia, G. L.; Chermahini, R. G.

1985-01-01

Fatigue cracks are a major problem in designing structures subjected to cyclic loading. Cracks frequently occur in structures such as aircraft and spacecraft. The inspection intervals of many aircraft structures are based on crack-propagation lives. Therefore, improved prediction of propagation lives under flight-load conditions (variable-amplitude loading) are needed to provide more realistic design criteria for these structures. The main thrust was to develop a three-dimensional, nonlinear, elastic-plastic, finite element program capable of extending a crack and changing boundary conditions for the model under consideration. The finite-element model is composed of 8-noded (linear-strain) isoparametric elements. In the analysis, the material is assumed to be elastic-perfectly plastic. The cycle stress-strain curve for the material is shown Zienkiewicz's initial-stress method, von Mises's yield criterion, and Drucker's normality condition under small-strain assumptions are used to account for plasticity. The three-dimensional analysis is capable of extending the crack and changing boundary conditions under cyclic loading.

Shrink-Induced Superhydrophobic and Antibacterial Surfaces in Consumer Plastics

PubMed Central

Freschauf, Lauren R.; McLane, Jolie; Sharma, Himanshu; Khine, Michelle

2012-01-01

Structurally modified superhydrophobic surfaces have become particularly desirable as stable antibacterial surfaces. Because their self-cleaning and water resistant properties prohibit bacteria growth, structurally modified superhydrophobic surfaces obviate bacterial resistance common with chemical agents, and therefore a robust and stable means to prevent bacteria growth is possible. In this study, we present a rapid fabrication method for creating such superhydrophobic surfaces in consumer hard plastic materials with resulting antibacterial effects. To replace complex fabrication materials and techniques, the initial mold is made with commodity shrink-wrap film and is compatible with large plastic roll-to-roll manufacturing and scale-up techniques. This method involves a purely structural modification free of chemical additives leading to its inherent consistency over time and successive recasting from the same molds. Finally, antibacterial properties are demonstrated in polystyrene (PS), polycarbonate (PC), and polyethylene (PE) by demonstrating the prevention of gram-negative Escherichia coli (E. coli) bacteria growth on our structured plastic surfaces. PMID:22916100

Constitutive modeling and structural analysis considering simultaneous phase transformation and plastic yield in shape memory alloys

NASA Astrophysics Data System (ADS)

Hartl, D. J.; Lagoudas, D. C.

2009-10-01

The new developments summarized in this work represent both theoretical and experimental investigations of the effects of plastic strain generation in shape memory alloys (SMAs). Based on the results of SMA experimental characterization described in the literature and additional testing described in this work, a new 3D constitutive model is proposed. This phenomenological model captures both the conventional shape memory effects of pseudoelasticity and thermal strain recovery, and additionally considers the initiation and evolution of plastic strains. The model is numerically implemented in a finite element framework using a return mapping algorithm to solve the constitutive equations at each material point. This combination of theory and implementation is unique in its ability to capture the simultaneous evolution of recoverable transformation strains and irrecoverable plastic strains. The consideration of isotropic and kinematic plastic hardening allows the derivation of a theoretical framework capturing the interactions between irrecoverable plastic strain and recoverable strain due to martensitic transformation. Further, the numerical integration of the constitutive equations is formulated such that objectivity is maintained for SMA structures undergoing moderate strains and large displacements. The implemented model has been used to perform 3D analysis of SMA structural components under uniaxial and bending loads, including a case of local buckling behavior. Experimentally validated results considering simultaneous transformation and plasticity in a bending member are provided, illustrating the predictive accuracy of the model and its implementation.

Memory Maintenance in Synapses with Calcium-Based Plasticity in the Presence of Background Activity

PubMed Central

Higgins, David; Graupner, Michael; Brunel, Nicolas

2014-01-01

Most models of learning and memory assume that memories are maintained in neuronal circuits by persistent synaptic modifications induced by specific patterns of pre- and postsynaptic activity. For this scenario to be viable, synaptic modifications must survive the ubiquitous ongoing activity present in neural circuits in vivo. In this paper, we investigate the time scales of memory maintenance in a calcium-based synaptic plasticity model that has been shown recently to be able to fit different experimental data-sets from hippocampal and neocortical preparations. We find that in the presence of background activity on the order of 1 Hz parameters that fit pyramidal layer 5 neocortical data lead to a very fast decay of synaptic efficacy, with time scales of minutes. We then identify two ways in which this memory time scale can be extended: (i) the extracellular calcium concentration in the experiments used to fit the model are larger than estimated concentrations in vivo. Lowering extracellular calcium concentration to in vivo levels leads to an increase in memory time scales of several orders of magnitude; (ii) adding a bistability mechanism so that each synapse has two stable states at sufficiently low background activity leads to a further boost in memory time scale, since memory decay is no longer described by an exponential decay from an initial state, but by an escape from a potential well. We argue that both features are expected to be present in synapses in vivo. These results are obtained first in a single synapse connecting two independent Poisson neurons, and then in simulations of a large network of excitatory and inhibitory integrate-and-fire neurons. Our results emphasise the need for studying plasticity at physiological extracellular calcium concentration, and highlight the role of synaptic bi- or multistability in the stability of learned synaptic structures. PMID:25275319

A Spiking Working Memory Model Based on Hebbian Short-Term Potentiation.

PubMed

Fiebig, Florian; Lansner, Anders

2017-01-04

A dominant theory of working memory (WM), referred to as the persistent activity hypothesis, holds that recurrently connected neural networks, presumably located in the prefrontal cortex, encode and maintain WM memory items through sustained elevated activity. Reexamination of experimental data has shown that prefrontal cortex activity in single units during delay periods is much more variable than predicted by such a theory and associated computational models. Alternative models of WM maintenance based on synaptic plasticity, such as short-term nonassociative (non-Hebbian) synaptic facilitation, have been suggested but cannot account for encoding of novel associations. Here we test the hypothesis that a recently identified fast-expressing form of Hebbian synaptic plasticity (associative short-term potentiation) is a possible mechanism for WM encoding and maintenance. Our simulations using a spiking neural network model of cortex reproduce a range of cognitive memory effects in the classical multi-item WM task of encoding and immediate free recall of word lists. Memory reactivation in the model occurs in discrete oscillatory bursts rather than as sustained activity. We relate dynamic network activity as well as key synaptic characteristics to electrophysiological measurements. Our findings support the hypothesis that fast Hebbian short-term potentiation is a key WM mechanism. Working memory (WM) is a key component of cognition. Hypotheses about the neural mechanism behind WM are currently under revision. Reflecting recent findings of fast Hebbian synaptic plasticity in cortex, we test whether a cortical spiking neural network model with such a mechanism can learn a multi-item WM task (word list learning). We show that our model can reproduce human cognitive phenomena and achieve comparable memory performance in both free and cued recall while being simultaneously compatible with experimental data on structure, connectivity, and neurophysiology of the underlying cortical tissue. These findings are directly relevant to the ongoing paradigm shift in the WM field. Copyright © 2017 Fiebig and Lansner.

A Spiking Working Memory Model Based on Hebbian Short-Term Potentiation

PubMed Central

Fiebig, Florian

2017-01-01

A dominant theory of working memory (WM), referred to as the persistent activity hypothesis, holds that recurrently connected neural networks, presumably located in the prefrontal cortex, encode and maintain WM memory items through sustained elevated activity. Reexamination of experimental data has shown that prefrontal cortex activity in single units during delay periods is much more variable than predicted by such a theory and associated computational models. Alternative models of WM maintenance based on synaptic plasticity, such as short-term nonassociative (non-Hebbian) synaptic facilitation, have been suggested but cannot account for encoding of novel associations. Here we test the hypothesis that a recently identified fast-expressing form of Hebbian synaptic plasticity (associative short-term potentiation) is a possible mechanism for WM encoding and maintenance. Our simulations using a spiking neural network model of cortex reproduce a range of cognitive memory effects in the classical multi-item WM task of encoding and immediate free recall of word lists. Memory reactivation in the model occurs in discrete oscillatory bursts rather than as sustained activity. We relate dynamic network activity as well as key synaptic characteristics to electrophysiological measurements. Our findings support the hypothesis that fast Hebbian short-term potentiation is a key WM mechanism. SIGNIFICANCE STATEMENT Working memory (WM) is a key component of cognition. Hypotheses about the neural mechanism behind WM are currently under revision. Reflecting recent findings of fast Hebbian synaptic plasticity in cortex, we test whether a cortical spiking neural network model with such a mechanism can learn a multi-item WM task (word list learning). We show that our model can reproduce human cognitive phenomena and achieve comparable memory performance in both free and cued recall while being simultaneously compatible with experimental data on structure, connectivity, and neurophysiology of the underlying cortical tissue. These findings are directly relevant to the ongoing paradigm shift in the WM field. PMID:28053032

Filament Winding of a Ship Hull. A Study of the Design of a 30 Ft. Filament Wound Model of a 150 Ft. GRP (Glass Reinforced Plastic) Ship.

DTIC Science & Technology

1983-10-01

by block number) Naval Ship Structures; Composites . Glass Reinforced Plastics, Filament Winding, Minesweepers. 20. ABSTRACT (Continue on reverse side...associated with this method of manufacturing a ship hull out of Glass Reinforced Plastic (GRP). Winding machine and man- drel concepts were reviewed... machine and mandrel concepts were reviewed, as well as the structural requirements and possible materials. A design of a 1/5th scale (30 ft) model

The role of cyclic plastic zone size on fatigue crack growth behavior in high strength steels

NASA Astrophysics Data System (ADS)

Korda, Akhmad A.; Miyashita, Y.; Mutoh, Y.

2015-09-01

The role of cyclic plastic zone in front of the crack tip was studied in high strength steels. Estimated plastic zone size would be compared with actual observation. Strain controlled fatigue tests of the steels were carried out to obtain cyclic stress-strain curves for plastic zone estimation. Observations of plastic zone were carried out using in situ SEM fatigue crack growth tests under a constant-ΔK. Hard microstructures in structural steels showed to inhibit the extent of plastic deformation around the crack tip. The rate of crack growth can be correlated with the size of plastic zone. The smaller the plastic zone size, the slower the fatigue crack growth.

Small Schools, Real Gains.

ERIC Educational Resources Information Center

Wasley, Patricia A.; Lear, Richard J.

2001-01-01

Small school size (fewer than 400 students) makes possible success-enhancing structures and practices: strong, ongoing student/adult and home/school relationships; flat organizational structure; concentration on a few goals; ongoing, site-specific professional development; a respectful culture; and community engagement. Implementation barriers are…

Marine litter plastics and microplastics and their toxic chemicals components: the need for urgent preventive measures.

PubMed

Gallo, Frederic; Fossi, Cristina; Weber, Roland; Santillo, David; Sousa, Joao; Ingram, Imogen; Nadal, Angel; Romano, Dolores

2018-01-01

Persistent plastics, with an estimated lifetime for degradation of hundreds of years in marine conditions, can break up into micro- and nanoplastics over shorter timescales, thus facilitating their uptake by marine biota throughout the food chain. These polymers may contain chemical additives and contaminants, including some known endocrine disruptors that may be harmful at extremely low concentrations for marine biota, thus posing potential risks to marine ecosystems, biodiversity and food availability. Although there is still need to carry out focused scientific research to fill the knowledge gaps about the impacts of plastic litter in the marine environment (Wagner et al. in Environ Sci Eur 26:9, 2014), the food chain and human health, existing scientific evidence and concerns are already sufficient to support actions by the scientific, industry, policy and civil society communities to curb the ongoing flow of plastics and the toxic chemicals they contain into the marine environment. Without immediate strong preventive measures, the environmental impacts and the economic costs are set only to become worse, even in the short term. Continued increases in plastic production and consumption, combined with wasteful uses, inefficient waste collection infrastructures and insufficient waste management facilities, especially in developing countries, mean that even achieving already established objectives for reductions in marine litter remains a huge challenge, and one unlikely to be met without a fundamental rethink of the ways in which we consume plastics. This document was prepared by a working group of Regional Centres of the Stockholm and Basel Conventions and related colleagues intended to be a background document for discussion in the 2017 Conference of the Parties (COP) of the Basel Convention on hazardous wastes and the Stockholm Convention on persistent organic pollutants (POPs). The COP finally approved that the issue of plastic waste could be dealt by its Regional Centres and consistently report their activities on the matter to next COP's meetings.

Process combinations for the manufacturing of metal-plastic hybrid parts

NASA Astrophysics Data System (ADS)

Drossel, W.-G.; Lies, C.; Albert, A.; Haase, R.; Müller, R.; Scholz, P.

2016-03-01

The usage of innovative lightweight materials and processing technologies gains importance in manifold industrial scopes. Especially for moving parts and mobility products the weight is decisively. The aerospace and automotive industries use light and high-strength materials to reduce weight and energy consumption and thereby improve the performance of their products. Composites with reinforced plastics are of particular importance. They offer a low density in combination with high specific stiffness and strength. A pure material substitution through reinforced plastics is still not economical. The approach of using hybrid metal-plastic structures with the principle of “using the right material at the right place” is a promising solution for the economical realization of lightweight structures with a high achievement potential. The article shows four innovative manufacturing possibilities for the realization of metal-plastic-hybrid parts.

Self-actuating and self-diagnosing plastically deforming piezo-composite flapping wing MAV

NASA Astrophysics Data System (ADS)

Harish, Ajay B.; Harursampath, Dineshkumar; Mahapatra, D. Roy

2011-04-01

In this work, we propose a constitutive model to describe the behavior of Piezoelectric Fiber Reinforced Composite (PFRC) material consisting of elasto-plastic matrix reinforced by strong elastic piezoelectric fibers. Computational efficiency is achieved using analytical solutions for elastic stifness matrix derived from Variational Asymptotic Methods (VAM). This is extended to provide Structural Health Monitoring (SHM) based on plasticity induced degradation of flapping frequency of PFRC. Overall this work provides an effective mathematical tool that can be used for structural self-health monitoring of plasticity induced flapping degradation of PFRC flapping wing MAVs. The developed tool can be re-calibrated to also provide SHM for other forms of failures like fatigue, matrix cracking etc.

Plasticity-mediated collapse and recrystallization in hollow copper nanowires: a molecular dynamics simulation

PubMed Central

Raychaudhuri, Arup Kumar; Saha-Dasgupta, Tanusri

2016-01-01

Summary We study the thermal stability of hollow copper nanowires using molecular dynamics simulation. We find that the plasticity-mediated structural evolution leads to transformation of the initial hollow structure to a solid wire. The process involves three distinct stages, namely, collapse, recrystallization and slow recovery. We calculate the time scales associated with different stages of the evolution process. Our findings suggest a plasticity-mediated mechanism of collapse and recrystallization. This contradicts the prevailing notion of diffusion driven transport of vacancies from the interior to outer surface being responsible for collapse, which would involve much longer time scales as compared to the plasticity-based mechanism. PMID:26977380

Multiscale Modeling of Structurally-Graded Materials Using Discrete Dislocation Plasticity Models and Continuum Crystal Plasticity Models

NASA Technical Reports Server (NTRS)

Saether, Erik; Hochhalter, Jacob D.; Glaessgen, Edward H.

2012-01-01

A multiscale modeling methodology that combines the predictive capability of discrete dislocation plasticity and the computational efficiency of continuum crystal plasticity is developed. Single crystal configurations of different grain sizes modeled with periodic boundary conditions are analyzed using discrete dislocation plasticity (DD) to obtain grain size-dependent stress-strain predictions. These relationships are mapped into crystal plasticity parameters to develop a multiscale DD/CP model for continuum level simulations. A polycrystal model of a structurally-graded microstructure is developed, analyzed and used as a benchmark for comparison between the multiscale DD/CP model and the DD predictions. The multiscale DD/CP model follows the DD predictions closely up to an initial peak stress and then follows a strain hardening path that is parallel but somewhat offset from the DD predictions. The difference is believed to be from a combination of the strain rate in the DD simulation and the inability of the DD/CP model to represent non-monotonic material response.

Non-Destructive Quantification of Plastic Deformation in Steel: Employing X-Ray Diffraction Peak Broadening Analysis

DTIC Science & Technology

2013-09-01

pattern of an alloy, such as steel , reveals, among other properties (ex., phase composition, crystal structure), information about the strain state...This, together with elastic strain / residual stress analysis, would enable better evaluation of the current state of health of steel structures and...plastic strain in a component/structure may better evaluate the current state of health of steel structures and components as they near predetermined

Deformation mechanisms to ameliorate the mechanical properties of novel TRIP/TWIP Co-Cr-Mo-(Cu) ultrafine eutectic alloys

PubMed Central

Kim, J. T.; Hong, S. H.; Park, H. J.; Kim, Y. S.; Suh, J. Y.; Lee, J. K.; Park, J. M.; Maity, T.; Eckert, J.; Kim, K. B.

2017-01-01

In the present study, the microstructural evolution and the modulation of the mechanical properties have been investigated for a Co-Cr-Mo (CCM) ternary eutectic alloy by addition of a small amount of copper (0.5 and 1 at.%). The microstructural observations reveal a distinct dissimilarity in the eutectic structure such as a broken lamellar structure and a well-aligned lamellar structure and an increasing volume fraction of Co lamellae as increasing amount of copper addition. This microstructural evolution leads to improved plasticity from 1% to 10% without the typical tradeoff between the overall strength and compressive plasticity. Moreover, investigation of the fractured samples indicates that the CCMCu alloy exhibits higher plastic deformability and combinatorial mechanisms for improved plastic behavior. The improved plasticity of CCMCu alloys originates from several deformation mechanisms; i) slip, ii) deformation twinning, iii) strain-induced transformation and iv) shear banding. These results reveal that the mechanical properties of eutectic alloys in the Co-Cr-Mo system can be ameliorated by micro-alloying such as Cu addition. PMID:28067248

Rheological and structural characterisation of film-forming solutions and biodegradable edible film made from kefiran as affected by various plasticizer types.

PubMed

Ghasemlou, Mehran; Khodaiyan, Faramarz; Oromiehie, Abdulrasoul

2011-11-01

The rheological properties of kefiran film-forming solutions, as well as the structural characterisation of the resulting films, were investigated as a function of various plasticizer types. The behaviours of the storage (G') and loss (G″) moduli as a function of frequency were typical of gel-like material, with the G' higher than the G″. Kefiran-based films, which may find application as edible films, were prepared by a casting and solvent-evaporation method. Possible interaction between the adjacent chains in the kefiran polymer and various plasticizers was proven by Fourier-transform infrared spectroscopy (FT-IR). The crystallinity of plasticized kefiran film was also analysed using X-ray diffraction (XRD); this revealed an amorphous-crystalline structure. These results were explained by the film's microstructure, which was analysed by atomic force microscopy (AFM) and scanning electron microscopy (SEM). The present study has helped determine possible interactions of kefiran, plasticizer and water molecules in determining film properties. Copyright © 2011 Elsevier B.V. All rights reserved.

Description of plastic deformation of structural materials in triaxial loading

NASA Astrophysics Data System (ADS)

Lagzdins, A.; Zilaucs, A.

2008-03-01

A model of nonassociated plasticity is put forward for initially isotropic materials deforming with residual changes in volume under the action of triaxial normal stresses. The model is based on novel plastic loading and plastic potential functions, which define closed, convex, every where smooth surfaces in the 6D space of symmetric second-rank stress tensors. By way of example, the plastic deformation of a cylindrical concrete specimen wrapped with a CFRP tape and loaded in axial compression is described.

Mirror trends of plasticity and stability indicators in primate prefrontal cortex.

PubMed

García-Cabezas, Miguel Á; Joyce, Mary Kate P; John, Yohan J; Zikopoulos, Basilis; Barbas, Helen

2017-10-01

Research on plasticity markers in the cerebral cortex has largely focused on their timing of expression and role in shaping circuits during critical and normal periods. By contrast, little attention has been focused on the spatial dimension of plasticity-stability across cortical areas. The rationale for this analysis is based on the systematic variation in cortical structure that parallels functional specialization and raises the possibility of varying levels of plasticity. Here, we investigated in adult rhesus monkeys the expression of markers related to synaptic plasticity or stability in prefrontal limbic and eulaminate areas that vary in laminar structure. Our findings revealed that limbic areas are impoverished in three markers of stability: intracortical myelin, the lectin Wisteria floribunda agglutinin, which labels perineuronal nets, and parvalbumin, which is expressed in a class of strong inhibitory neurons. By contrast, prefrontal limbic areas were enriched in the enzyme calcium/calmodulin-dependent protein kinase II (CaMKII), known to enhance plasticity. Eulaminate areas have more elaborate laminar architecture than limbic areas and showed the opposite trend: they were enriched in markers of stability and had lower expression of the plasticity-related marker CaMKII. The expression of glial fibrillary acidic protein (GFAP), a marker of activated astrocytes, was also higher in limbic areas, suggesting that cellular stress correlates with the rate of circuit reshaping. Elevated markers of plasticity may endow limbic areas with flexibility necessary for learning and memory within an affective context, but may also render them vulnerable to abnormal structural changes, as seen in neurologic and psychiatric diseases. © 2017 Federation of European Neuroscience Societies and John Wiley & Sons Ltd.

A Lesson Plan to Develop Structured Discussion of the Benefits and Disadvantages of Selected Plastics Using the Product-Testing Method

ERIC Educational Resources Information Center

Burmeister, Mareike; Eilks, Ingo

2014-01-01

People use many different products made from plastics every day. But conventional plastics such as polyvinyl chloride (PVC) do not always have a good reputation in society at large. Bioplastics such as thermoplastic starch (TPS) promise to be better alternatives but are they really better than conventional plastics? This article presents a new…

Neuropsychology of aging, past, present and future: Contributions of Morris Moscovitch.

PubMed

Reuter-Lorenz, Patricia A; Cooke, Katherine A

2016-09-01

In this review we provide a broad overview of major trends in the cognitive neuroscience of aging and illustrate their roots in the pioneering ideas and discoveries of Morris Moscovitch and his close collaborators, especially Gordon Winocur. These trends include an on-going focus on the specific and dissociable contributions of medial temporal and frontal lobe processes to cognitive aging, especially in the memory domain, the role of individual variability stemming from different patterns of underlying neural decline, the possibility of compensatory neural and cognitive influences that alter the expression of neurobiological aging, and the investigation of lifestyle and psychosocial factors that affect plasticity and may contribute to the rate and level of neurocognitive decline. These prescient ideas, evident in the early work of Moscovitch and Winocur, continue to drive on-going research efforts in the cognitive neuroscience of aging. Copyright © 2016 Elsevier Ltd. All rights reserved.

Network, cellular, and molecular mechanisms underlying long-term memory formation.

PubMed

Carasatorre, Mariana; Ramírez-Amaya, Víctor

2013-01-01

The neural network stores information through activity-dependent synaptic plasticity that occurs in populations of neurons. Persistent forms of synaptic plasticity may account for long-term memory storage, and the most salient forms are the changes in the structure of synapses. The theory proposes that encoding should use a sparse code and evidence suggests that this can be achieved through offline reactivation or by sparse initial recruitment of the network units. This idea implies that in some cases the neurons that underwent structural synaptic plasticity might be a subpopulation of those originally recruited; However, it is not yet clear whether all the neurons recruited during acquisition are the ones that underwent persistent forms of synaptic plasticity and responsible for memory retrieval. To determine which neural units underlie long-term memory storage, we need to characterize which are the persistent forms of synaptic plasticity occurring in these neural ensembles and the best hints so far are the molecular signals underlying structural modifications of the synapses. Structural synaptic plasticity can be achieved by the activity of various signal transduction pathways, including the NMDA-CaMKII and ACh-MAPK. These pathways converge with the Rho family of GTPases and the consequent ERK 1/2 activation, which regulates multiple cellular functions such as protein translation, protein trafficking, and gene transcription. The most detailed explanation may come from models that allow us to determine the contribution of each piece of this fascinating puzzle that is the neuron and the neural network.

Plastic covering on airfoil structure provides smooth uninterrupted surface

NASA Technical Reports Server (NTRS)

Kinzler, J. A.; Fehrenkamp, L. G.; Heffernam, J. T.; Lee, W. S.

1975-01-01

Primed surface is covered with adhesive. Sheet of plastic film is stretched over adhesive and mechanical holder is used to apply tension to ends of sheet to make it conform to surface of airfoil. After adhesive cures, plastic can be trimmed with sharp cutting tool.

Biodegradability of plastics.

PubMed

Tokiwa, Yutaka; Calabia, Buenaventurada P; Ugwu, Charles U; Aiba, Seiichi

2009-08-26

Plastic is a broad name given to different polymers with high molecular weight, which can be degraded by various processes. However, considering their abundance in the environment and their specificity in attacking plastics, biodegradation of plastics by microorganisms and enzymes seems to be the most effective process. When plastics are used as substrates for microorganisms, evaluation of their biodegradability should not only be based on their chemical structure, but also on their physical properties (melting point, glass transition temperature, crystallinity, storage modulus etc.). In this review, microbial and enzymatic biodegradation of plastics and some factors that affect their biodegradability are discussed.

Biodegradability of Plastics

PubMed Central

Tokiwa, Yutaka; Calabia, Buenaventurada P.; Ugwu, Charles U.; Aiba, Seiichi

2009-01-01

Plastic is a broad name given to different polymers with high molecular weight, which can be degraded by various processes. However, considering their abundance in the environment and their specificity in attacking plastics, biodegradation of plastics by microorganisms and enzymes seems to be the most effective process. When plastics are used as substrates for microorganisms, evaluation of their biodegradability should not only be based on their chemical structure, but also on their physical properties (melting point, glass transition temperature, crystallinity, storage modulus etc.). In this review, microbial and enzymatic biodegradation of plastics and some factors that affect their biodegradability are discussed. PMID:19865515

Structural plasticity of 4-α-helical bundles exemplified by the puzzle-like molecular assembly of the Rop protein

PubMed Central

Amprazi, Maria; Kotsifaki, Dina; Providaki, Mary; Kapetaniou, Evangelia G.; Fellas, Georgios; Kyriazidis, Ioannis; Pérez, Javier; Kokkinidis, Michael

2014-01-01

The dimeric Repressor of Primer (Rop) protein, a widely used model system for the study of coiled-coil 4-α-helical bundles, is characterized by a remarkable structural plasticity. Loop region mutations lead to a wide range of topologies, folding states, and altered physicochemical properties. A protein-folding study of Rop and several loop variants has identified specific residues and sequences that are linked to the observed structural plasticity. Apart from the native state, native-like and molten-globule states have been identified; these states are sensitive to reducing agents due to the formation of nonnative disulfide bridges. Pro residues in the loop are critical for the establishment of new topologies and molten globule states; their effects, however, can be in part compensated by Gly residues. The extreme plasticity in the assembly of 4-α-helical bundles reflects the capacity of the Rop sequence to combine a specific set of hydrophobic residues into strikingly different hydrophobic cores. These cores include highly hydrated ones that are consistent with the formation of interchain, nonnative disulfide bridges and the establishment of molten globules. Potential applications of this structural plasticity are among others in the engineering of bio-inspired materials. PMID:25024213

Postsynaptic density 95 (PSD-95) serine 561 phosphorylation regulates a conformational switch and bidirectional dendritic spine structural plasticity.

PubMed

Wu, Qian; Sun, Miao; Bernard, Laura P; Zhang, Huaye

2017-09-29

Postsynaptic density 95 (PSD-95) is a major synaptic scaffolding protein that plays a key role in bidirectional synaptic plasticity, which is a process important for learning and memory. It is known that PSD-95 shows increased dynamics upon induction of plasticity. However, the underlying structural and functional changes in PSD-95 that mediate its role in plasticity remain unclear. Here we show that phosphorylation of PSD-95 at Ser-561 in its guanylate kinase (GK) domain, which is mediated by the partitioning-defective 1 (Par1) kinases, regulates a conformational switch and is important for bidirectional plasticity. Using a fluorescence resonance energy transfer (FRET) biosensor, we show that a phosphomimetic mutation of Ser-561 promotes an intramolecular interaction between GK and the nearby Src homology 3 (SH3) domain, leading to a closed conformation, whereas a non-phosphorylatable S561A mutation or inhibition of Par1 kinase activity decreases SH3-GK interaction, causing PSD-95 to adopt an open conformation. In addition, S561A mutation facilitates the interaction between PSD-95 and its binding partners. Fluorescence recovery after photobleaching imaging reveals that the S561A mutant shows increased stability, whereas the phosphomimetic S561D mutation increases PSD-95 dynamics at the synapse. Moreover, molecular replacement of endogenous PSD-95 with the S561A mutant blocks dendritic spine structural plasticity during chemical long-term potentiation and long-term depression. Endogenous Ser-561 phosphorylation is induced by synaptic NMDA receptor activation, and the SH3-GK domains exhibit a Ser-561 phosphorylation-dependent switch to a closed conformation during synaptic plasticity. Our results provide novel mechanistic insight into the regulation of PSD-95 in dendritic spine structural plasticity through phosphorylation-mediated regulation of protein dynamics and conformation. © 2017 by The American Society for Biochemistry and Molecular Biology, Inc.

Crystal plasticity in Cu damascene interconnect lines undergoing electromigration as revealed by synchrotron x-ray microdiffraction

NASA Astrophysics Data System (ADS)

Budiman, A. S.; Nix, W. D.; Tamura, N.; Valek, B. C.; Gadre, K.; Maiz, J.; Spolenak, R.; Patel, J. R.

2006-06-01

Plastic deformation was observed in damascene Cu interconnect test structures during an in situ electromigration experiment and before the onset of visible microstructural damage (voiding, hillock formation). We show here, using a synchrotron technique of white beam x-ray microdiffraction, that the extent of this electromigration-induced plasticity is dependent on the linewidth. In wide lines, plastic deformation manifests itself as grain bending and the formation of subgrain structures, while only grain rotation is observed in the narrower lines. The deformation geometry leads us to conclude that dislocations introduced by plastic flow lie predominantly in the direction of electron flow and may provide additional easy paths for the transport of point defects. Since these findings occur long before any observable voids or hillocks are formed, they may have direct bearing on the final failure stages of electromigration.

Dislocation dynamics simulations of plasticity at small scales

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhou, Caizhi

2010-01-01

As metallic structures and devices are being created on a dimension comparable to the length scales of the underlying dislocation microstructures, the mechanical properties of them change drastically. Since such small structures are increasingly common in modern technologies, there is an emergent need to understand the critical roles of elasticity, plasticity, and fracture in small structures. Dislocation dynamics (DD) simulations, in which the dislocations are the simulated entities, offer a way to extend length scales beyond those of atomistic simulations and the results from DD simulations can be directly compared with the micromechanical tests. The primary objective of this researchmore » is to use 3-D DD simulations to study the plastic deformation of nano- and micro-scale materials and understand the correlation between dislocation motion, interactions and the mechanical response. Specifically, to identify what critical events (i.e., dislocation multiplication, cross-slip, storage, nucleation, junction and dipole formation, pinning etc.) determine the deformation response and how these change from bulk behavior as the system decreases in size and correlate and improve our current knowledge of bulk plasticity with the knowledge gained from the direct observations of small-scale plasticity. Our simulation results on single crystal micropillars and polycrystalline thin films can march the experiment results well and capture the essential features in small-scale plasticity. Furthermore, several simple and accurate models have been developed following our simulation results and can reasonably predict the plastic behavior of small scale materials.« less

Research on Submarine Pipeline Steel with High Performance

NASA Astrophysics Data System (ADS)

Ren, Yi; Liu, Wenyue; Zhang, Shuai; Wang, Shuang; Gao, Hong

Submarine pipeline steel has largely uniform elongation, low yield ratio and good balance between high strength and high plasticity because of the microstructure with dual phase. In this work, the microstructure and properties of the submarine pipeline steel are studied. The results show that the matrix structure is consisted of ferrite, bainite and martensite -austenite islands. The structure has a tight relationship with the thermal-mechanical controlled process. Fine dual phase shows good plasticity and low yield ratio, which can support the good balance between high strength and high plasticity.

Intravital imaging of dendritic spine plasticity

PubMed Central

Sau Wan Lai, Cora

2014-01-01

Abstract Dendritic spines are the postsynaptic part of most excitatory synapses in the mammalian brain. Recent works have suggested that the structural and functional plasticity of dendritic spines have been associated with information coding and memories. Advances in imaging and labeling techniques enable the study of dendritic spine dynamics in vivo. This perspective focuses on intravital imaging studies of dendritic spine plasticity in the neocortex. I will introduce imaging tools for studying spine dynamics and will further review current findings on spine structure and function under various physiological and pathological conditions. PMID:28243511

Oxidative Modulation of Voltage-Gated Potassium Channels

PubMed Central

Sahoo, Nirakar; Hoshi, Toshinori

2014-01-01

Abstract Significance: Voltage-gated K+ channels are a large family of K+-selective ion channel protein complexes that open on membrane depolarization. These K+ channels are expressed in diverse tissues and their function is vital for numerous physiological processes, in particular of neurons and muscle cells. Potentially reversible oxidative regulation of voltage-gated K+ channels by reactive species such as reactive oxygen species (ROS) represents a contributing mechanism of normal cellular plasticity and may play important roles in diverse pathologies including neurodegenerative diseases. Recent Advances: Studies using various protocols of oxidative modification, site-directed mutagenesis, and structural and kinetic modeling provide a broader phenomenology and emerging mechanistic insights. Critical Issues: Physicochemical mechanisms of the functional consequences of oxidative modifications of voltage-gated K+ channels are only beginning to be revealed. In vivo documentation of oxidative modifications of specific amino-acid residues of various voltage-gated K+ channel proteins, including the target specificity issue, is largely absent. Future Directions: High-resolution chemical and proteomic analysis of ion channel proteins with respect to oxidative modification combined with ongoing studies on channel structure and function will provide a better understanding of how the function of voltage-gated K+ channels is tuned by ROS and the corresponding reducing enzymes to meet cellular needs. Antioxid. Redox Signal. 21, 933–952. PMID:24040918

Texture and structure contribution to low-temperature plasticity enhancement of Mg-Al-Zn-Mn Alloy MA2-1hp after ECAP and annealing

NASA Astrophysics Data System (ADS)

Serebryany, V. N.; D'yakonov, G. S.; Kopylov, V. I.; Salishchev, G. A.; Dobatkin, S. V.

2013-05-01

Equal channel angular pressing (ECAP) in magnesium alloys due to severe plastic shear deformations provides both grain refinement and the slope of the initial basal texture at 40°-50° to the pressing direction. These changes in microstructure and texture contribute to the improvement of low-temperature plasticity of the alloys. Quantitative texture X-ray diffraction analysis and diffraction of backscattered electrons are used to study the main textural and structural factors responsible for enhanced low-temperature plasticity based on the example of magnesium alloy MA2-1hp of the Mg-Al-Zn-Mn system. The possible mechanisms of deformation that lead to this positive effect are discussed.

Visual Cortex Plasticity: A Complex Interplay of Genetic and Environmental Influences

PubMed Central

Maya-Vetencourt, José Fernando; Origlia, Nicola

2012-01-01

The central nervous system architecture is highly dynamic and continuously modified by sensory experience through processes of neuronal plasticity. Plasticity is achieved by a complex interplay of environmental influences and physiological mechanisms that ultimately activate intracellular signal transduction pathways regulating gene expression. In addition to the remarkable variety of transcription factors and their combinatorial interaction at specific gene promoters, epigenetic mechanisms that regulate transcription have emerged as conserved processes by which the nervous system accomplishes the induction of plasticity. Experience-dependent changes of DNA methylation patterns and histone posttranslational modifications are, in fact, recruited as targets of plasticity-associated signal transduction mechanisms. Here, we shall concentrate on structural and functional consequences of early sensory deprivation in the visual system and discuss how intracellular signal transduction pathways associated with experience regulate changes of chromatin structure and gene expression patterns that underlie these plastic phenomena. Recent experimental evidence for mechanisms of cross-modal plasticity following congenital or acquired sensory deprivation both in human and animal models will be considered as well. We shall also review different experimental strategies that can be used to achieve the recovery of sensory functions after long-term deprivation in humans. PMID:22852098

Hippocampal Structural Plasticity Accompanies the Resulting Contextual Fear Memory Following Stress and Fear Conditioning

ERIC Educational Resources Information Center

Giachero, Marcelo; Calfa, Gaston D.; Molina, Victor A.

2013-01-01

The present research investigated the resulting contextual fear memory and structural plasticity changes in the dorsal hippocampus (DH) following stress and fear conditioning. This combination enhanced fear retention and increased the number of total and mature dendritic spines in DH. Intra-basolateral amygdala (BLA) infusion of midazolam prior to…

A unified approach to the analysis and design of elasto-plastic structures with mechanical contact

NASA Technical Reports Server (NTRS)

Bendsoe, Martin P.; Olhoff, Niels; Taylor, John E.

1990-01-01

With structural design in mind, a new unified variational model has been developed which represents the mechanics of deformation elasto-plasticity with unilateral contact conditions. For a design problem formulated as maximization of the load carrying capacity of a structure under certain constraints, the unified model allows for a simultaneous analysis and design synthesis for a whole range of mechanical behavior.

Task Analysis - Aircraft Structural Maintenance AFSC 458X2

DTIC Science & Technology

1989-08-01

GAGES OR METERS 13 10 23 SELECT WEIGHT MEASURING SCALES 15 6 21 RECALL TYPES, PROPERTIES, AND CHARACTERISTICS 8 11 19 OF PLASTICS SELECT COMMON...SURFACES (K0494) 121 00480 SHOT PEEN METAL SURFACES (K0498) 123 00490 BALANCE AIRCRAFT CONTROL SURFACES 125 00500 CLEAN PLASTICS (0275) 127 00510...STORE TRANSPARENT PLASTICS IN PROPER ENVIRONMENT (J0299) 128 00520 POLISH OUT SURFACE SCRATCHES 129 00530 CUT PLASTICS 131 00540 RESEARCH AIRCRAFT

24 CFR 35.1220 - Ongoing lead-based paint maintenance activities.

Code of Federal Regulations, 2014 CFR

2014-04-01

... 24 Housing and Urban Development 1 2014-04-01 2014-04-01 false Ongoing lead-based paint..., Department of Housing and Urban Development LEAD-BASED PAINT POISONING PREVENTION IN CERTAIN RESIDENTIAL STRUCTURES Tenant-Based Rental Assistance § 35.1220 Ongoing lead-based paint maintenance activities...

24 CFR 35.1220 - Ongoing lead-based paint maintenance activities.

Code of Federal Regulations, 2012 CFR

2012-04-01

... 24 Housing and Urban Development 1 2012-04-01 2012-04-01 false Ongoing lead-based paint..., Department of Housing and Urban Development LEAD-BASED PAINT POISONING PREVENTION IN CERTAIN RESIDENTIAL STRUCTURES Tenant-Based Rental Assistance § 35.1220 Ongoing lead-based paint maintenance activities...

24 CFR 35.1220 - Ongoing lead-based paint maintenance activities.

Code of Federal Regulations, 2011 CFR

2011-04-01

... 24 Housing and Urban Development 1 2011-04-01 2011-04-01 false Ongoing lead-based paint..., Department of Housing and Urban Development LEAD-BASED PAINT POISONING PREVENTION IN CERTAIN RESIDENTIAL STRUCTURES Tenant-Based Rental Assistance § 35.1220 Ongoing lead-based paint maintenance activities...

24 CFR 35.1220 - Ongoing lead-based paint maintenance activities.

Code of Federal Regulations, 2013 CFR

2013-04-01

... 24 Housing and Urban Development 1 2013-04-01 2013-04-01 false Ongoing lead-based paint..., Department of Housing and Urban Development LEAD-BASED PAINT POISONING PREVENTION IN CERTAIN RESIDENTIAL STRUCTURES Tenant-Based Rental Assistance § 35.1220 Ongoing lead-based paint maintenance activities...

24 CFR 35.1220 - Ongoing lead-based paint maintenance activities.

Code of Federal Regulations, 2010 CFR

2010-04-01

... 24 Housing and Urban Development 1 2010-04-01 2010-04-01 false Ongoing lead-based paint..., Department of Housing and Urban Development LEAD-BASED PAINT POISONING PREVENTION IN CERTAIN RESIDENTIAL STRUCTURES Tenant-Based Rental Assistance § 35.1220 Ongoing lead-based paint maintenance activities...

An Auxetic structure configured as oesophageal stent with potential to be used for palliative treatment of oesophageal cancer; development and in vitro mechanical analysis.

PubMed

Ali, Murtaza N; Rehman, Ihtesham Ur

2011-11-01

Oesophageal cancer is the ninth leading cause of malignant cancer death and its prognosis remains poor. Dysphagia which is an inability to swallow is a presenting symptom of oesophageal cancer and is indicative of incurability. The goal of this study was to design and manufacture an Auxetic structure film and to configure this film as an Auxetic stent for the palliative treatment of oesophageal cancer, and for the prevention of dysphagia. Polypropylene was used as a material for its flexibility and non-toxicity. The Auxetic (rotating-square geometry) structure was made by laser cutting the polypropylene film. This flat structure was welded together to form a tubular form (stent), by an adjustable temperature control soldering iron station: following this, an annealing process was also carried out to ease any material stresses. Poisson's ratio was estimated and elastic and plastic deformation of the Auxetic structure was evaluated. The elastic and plastic deformation behaviours of the Auxetic polypropylene film were evaluated by applying repetitive uniaxial tensile loads. Observation of the structure showed that it was initially elastically deformed, thereafter plastic deformation occurred. This research discusses a novel way of fabricating an Auxetic structure (rotating-squares connected together through hinges) on Polypropylene films, by estimating the Poisson's ratio and evaluating the plastic deformation relevant to the expansion behaviour of an Auxetic stent within the oesophageal lumen.

Facile characterization of polymer fractions from waste electrical and electronic equipment (WEEE) for mechanical recycling.

PubMed

Taurino, Rosa; Pozzi, Paolo; Zanasi, Tania

2010-12-01

In view of the environmental problem involved in the management of WEEE, and then in the recycling of post-consumer plastic of WEEE there is a pressing need for rapid measurement technologies for simple identification of the various commercial plastic materials and of the several contaminants, to improve the recycling of such wastes. This research is focused on the characterization and recycling of two types of plastics, namely plastic from personal computer (grey plastic) and plastic from television (black plastic). Various analytical techniques were used to monitor the compositions of WEEE. Initially, the chemical structure of each plastic material was identified by Fourier transform infrared (FTIR) spectroscopy and differential scanning calorimetry (DSC). Polymeric contaminants of these plastics, in particular brominated flame retardants (BFRs) were detected in grey plastics only using different techniques. These techniques are useful for a rapid, correct and economics identification of a large volumes of WEEE plastics. Copyright © 2010 Elsevier Ltd. All rights reserved.

Are the Most Plastic Species the Most Abundant Ones? An Assessment Using a Fish Assemblage

PubMed Central

Vidal, Nicolás; Zaldúa, Natalia; D'Anatro, Alejandro; Naya, Daniel E.

2014-01-01

Few studies have evaluated phenotypic plasticity at the community level, considering, for example, plastic responses in an entire species assemblage. In addition, none of these studies have addressed the relationship between phenotypic plasticity and community structure. Within this context, here we assessed the magnitude of seasonal changes in digestive traits (seasonal flexibility), and of changes during short-term fasting (flexibility during fasting), occurring in an entire fish assemblage, comprising ten species, four trophic levels, and a 37-fold range in body mass. In addition, we analyzed the relationship between estimates of digestive flexibility and three basic assemblage structure attributes, i.e., species trophic position, body size, and relative abundance. We found that: (1) Seasonal digestive flexibility was not related with species trophic position or with body size; (2) Digestive flexibility during fasting tended to be inversely correlated with body size, as expected from scaling relationships; (3) Digestive flexibility, both seasonal and during fasting, was positively correlated with species relative abundance. In conclusion, the present study identified two trends in digestive flexibility in relation to assemblage structure, which represents an encouraging departure point in the search of general patterns in phenotypic plasticity at the local community scale. PMID:24651865

The influence of James and Darwin on Cajal and his research into the neuron theory and evolution of the nervous system.

PubMed

Ferreira, Francisco R M; Nogueira, Maria I; Defelipe, Javier

2014-01-01

In this article we discuss the influence of William James and Charles Darwin on the thoughts of Santiago Ramón y Cajal concerning the structure, plasticity, and evolution of the nervous system at the cellular level. Here we develop Cajal's notion that neuronal theory is a necessary condition to explain the plasticity of neural connections. Although the roots of the term "plasticity" in reference to neuroscience are not completely clear, Cajal was an important figure in the propagation and popularization of its use. It is true that he carried out a large number of studies throughout his career in favor of the neuronal theory, but perhaps one of the most interesting aspects of his studies was his innovative capacity to interpret structure as being the result of evolutionary mechanisms, i.e., natural selection. This capacity would ultimately lead Cajal to the conclusion that, in relation to the histology of the nervous system, such selection occurs in the establishment of connections between cells. The present article is divided into five sections: (1) Learning and general notions of organic plasticity in the 19th century; (2) The idea of "mental" plasticity proposed by James; (3) Neuronal theory and "structural" plasticity: general considerations; (4) Evolutionary factors of the nervous system in Cajal's work; and (5) Final considerations.

The Effect of Different Shape and Perforated rHDPE in Concrete Structures on Flexural Strength

NASA Astrophysics Data System (ADS)

Yuhazri, MY; Hafiz, KM; Myia, YZA; Jia, CP; Sihombing, H.; Sapuan, SM; Badarulzaman, NA

2017-10-01

This research was carried out to develop a reinforcing structure from recycled HDPE plastic lubricant containers to be embedded in concrete structure. Different forms and shapes of recycled HDPE plastic are designed as reinforcement incorporate with cement. In this study, the reinforcing structure was prepared by washing, cutting, dimensioning and joining of the waste HDPE containers (direct technique without treatment on plastic surface). Then, the rHDPE reinforced concrete was produced by casting based on standard of procedure in civil engineering technique. Eight different shapes of rHDPE in concrete structure were used to determine the concrete’s ability in terms of flexural strength. Embedded round shape in solid and perforated of rHDPE in concrete system drastically improved flexural strength at 17.78 % and 13.79 %. The result would seem that the concrete with reinforcing rHDPE structure exhibits a more gradual or flexible properties than concrete beams without reinforcement that has the properties of fragile.

Transition of temporal scaling behavior in percolation assisted shear-branching structure during plastic deformation

DOE PAGES

Ren, Jingli; Chen, Cun; Wang, Gang; ...

2017-03-22

This study explores the temporal scaling behavior induced shear-branching structure in response to variant temperatures and strain rates during plastic deformation of Zr-based bulk metallic glass (BMG). The data analysis based on the compression tests suggests that there are two states of shear-branching structures: the fractal structure with a long-range order at an intermediate temperature of 223 K and a larger strain rate of 2.5 × 10 –2 s –1; the disordered structure dominated at other temperature and strain rate. It can be deduced from the percolation theory that the compressive ductility, ec, can reach the maximum value at themore » intermediate temperature. Furthermore, a dynamical model involving temperature is given for depicting the shear-sliding process, reflecting the plastic deformation has fractal structure at the temperature of 223 K and strain rate of 2.5 × 10 –2 s –1.« less

Learning to learn – intrinsic plasticity as a metaplasticity mechanism for memory formation

PubMed Central

Sehgal, Megha; Song, Chenghui; Ehlers, Vanessa L.; Moyer, James R.

2013-01-01

“Use it or lose it” is a popular adage often associated with use-dependent enhancement of cognitive abilities. Much research has focused on understanding exactly how the brain changes as a function of experience. Such experience-dependent plasticity involves both structural and functional alterations that contribute to adaptive behaviors, such as learning and memory, as well as maladaptive behaviors, including anxiety disorders, phobias, and posttraumatic stress disorder. With the advancing age of our population, understanding how use-dependent plasticity changes across the lifespan may also help to promote healthy brain aging. A common misconception is that such experience-dependent plasticity (e.g., associative learning) is synonymous with synaptic plasticity. Other forms of plasticity also play a critical role in shaping adaptive changes within the nervous system, including intrinsic plasticity – a change in the intrinsic excitability of a neuron. Intrinsic plasticity can result from a change in the number, distribution or activity of various ion channels located throughout the neuron. Here, we review evidence that intrinsic plasticity is an important and evolutionarily conserved neural correlate of learning. Intrinsic plasticity acts as a metaplasticity mechanism by lowering the threshold for synaptic changes. Thus, learning-related intrinsic changes can facilitate future synaptic plasticity and learning. Such intrinsic changes can impact the allocation of a memory trace within a brain structure, and when compromised, can contribute to cognitive decline during the aging process. This unique role of intrinsic excitability can provide insight into how memories are formed and, more interestingly, how neurons that participate in a memory trace are selected. Most importantly, modulation of intrinsic excitability can allow for regulation of learning ability – this can prevent or provide treatment for cognitive decline not only in patients with clinical disorders but also in the aging population. PMID:23871744

Allotropic forms of carbon in the Invar Fe-Ni-C alloy before and after plastic deformation by upsetting

NASA Astrophysics Data System (ADS)

Nadutov, V. M.; Vashchuk, D. L.; Karbivskii, V. L.; Volosevich, P. Yu.; Davydenko, O. A.

2018-04-01

The effect of cold plastic deformation by upsetting (e = 1.13) on structure and hybridised bonds of carbon in the fcc Invar Fe-30.9%Ni-1.23% C alloy was studied by means of X-ray phase analysis and X-ray photoelectron spectroscopy. Carbon precipitates along grain boundaries and inside of grains in the alloy after annealing and plastic deformation were revealed. The presence of mainly sp2- and sp3-hybridised C-C bonds attributing to graphite and amorphous carbon as well as the carbon bonds with impurity atoms and metallic Fe and Ni atoms in austenitic phase were revealed in the annealed and deformed alloy. It was shown for the first time that plastic deformation of the alloy results in partial destruction of the graphite crystal structure, increasing the relative part of amorphous carbon, and redistribution of carbon between structural elements as well as in a solid solution of austenitic phase.

Molecular simulation and mathematical modelling of glass transition temperature depression induced by CO2 plasticization in Polysulfone membranes

NASA Astrophysics Data System (ADS)

Lock, S. S. M.; Lau, K. K.; Lock Sow Mei, Irene; Shariff, A. M.; Yeong, Y. F.; Bustam, A. M.

2017-08-01

A sequence of molecular modelling procedure has been proposed to simulate experimentally validated membrane structure characterizing the effect of CO2 plasticization, whereby it can be subsequently employed to elucidate the depression in glass transition temperature (Tg ). Based on the above motivation, unswollen and swollen Polysulfone membrane structures with different CO2 loadings have been constructed, whereby the accuracy has been validated through good compliance with experimentally measured physical properties. It is found that the presence of CO2 constitutes to enhancement in polymeric chain relaxation, which consequently promotes the enlargement of molecular spacing and causes dilation in the membrane matrix. A series of glass transition temperature treatment has been conducted on the verified molecular structure to elucidate the effect of CO2 loadings to the depression in Tg induced by plasticization. Subsequently, a modified Michealis-Menten (M-M) function has been implemented to quantify the effect of CO2 loading attributed to plasticization towards Tg .

Molecular Mechanisms at the Basis of Plasticity in the Developing Visual Cortex: Epigenetic Processes and Gene Programs

PubMed Central

Maya-Vetencourt, José Fernando; Pizzorusso, Tommaso

2013-01-01

Neuronal circuitries in the mammalian visual system change as a function of experience. Sensory experience modifies neuronal networks connectivity via the activation of different physiological processes such as excitatory/inhibitory synaptic transmission, neurotrophins, and signaling of extracellular matrix molecules. Long-lasting phenomena of plasticity occur when intracellular signal transduction pathways promote epigenetic alterations of chromatin structure that regulate the induction of transcription factors that in turn drive the expression of downstream targets, the products of which then work via the activation of structural and functional mechanisms that modify synaptic connectivity. Here, we review recent findings in the field of visual cortical plasticity while focusing on how physiological mechanisms associated with experience promote structural changes that determine functional modifications of neural circuitries in V1. We revise the role of microRNAs as molecular transducers of environmental stimuli and the role of immediate early genes that control gene expression programs underlying plasticity in the developing visual cortex. PMID:25157210

24 CFR 35.935 - Ongoing lead-based paint maintenance activities.

Code of Federal Regulations, 2011 CFR

2011-04-01

..., Department of Housing and Urban Development LEAD-BASED PAINT POISONING PREVENTION IN CERTAIN RESIDENTIAL STRUCTURES Rehabilitation § 35.935 Ongoing lead-based paint maintenance activities. In the case of a rental... 24 Housing and Urban Development 1 2011-04-01 2011-04-01 false Ongoing lead-based paint...

24 CFR 35.935 - Ongoing lead-based paint maintenance activities.

Code of Federal Regulations, 2012 CFR

2012-04-01

..., Department of Housing and Urban Development LEAD-BASED PAINT POISONING PREVENTION IN CERTAIN RESIDENTIAL STRUCTURES Rehabilitation § 35.935 Ongoing lead-based paint maintenance activities. In the case of a rental... 24 Housing and Urban Development 1 2012-04-01 2012-04-01 false Ongoing lead-based paint...

24 CFR 35.935 - Ongoing lead-based paint maintenance activities.

Code of Federal Regulations, 2014 CFR

2014-04-01

..., Department of Housing and Urban Development LEAD-BASED PAINT POISONING PREVENTION IN CERTAIN RESIDENTIAL STRUCTURES Rehabilitation § 35.935 Ongoing lead-based paint maintenance activities. In the case of a rental... 24 Housing and Urban Development 1 2014-04-01 2014-04-01 false Ongoing lead-based paint...

24 CFR 35.935 - Ongoing lead-based paint maintenance activities.

Code of Federal Regulations, 2010 CFR

2010-04-01

..., Department of Housing and Urban Development LEAD-BASED PAINT POISONING PREVENTION IN CERTAIN RESIDENTIAL STRUCTURES Rehabilitation § 35.935 Ongoing lead-based paint maintenance activities. In the case of a rental... 24 Housing and Urban Development 1 2010-04-01 2010-04-01 false Ongoing lead-based paint...

24 CFR 35.935 - Ongoing lead-based paint maintenance activities.

Code of Federal Regulations, 2013 CFR

2013-04-01

..., Department of Housing and Urban Development LEAD-BASED PAINT POISONING PREVENTION IN CERTAIN RESIDENTIAL STRUCTURES Rehabilitation § 35.935 Ongoing lead-based paint maintenance activities. In the case of a rental... 24 Housing and Urban Development 1 2013-04-01 2013-04-01 false Ongoing lead-based paint...

24 CFR 35.825 - Ongoing lead-based paint maintenance and reevaluation.

Code of Federal Regulations, 2013 CFR

2013-04-01

... 24 Housing and Urban Development 1 2013-04-01 2013-04-01 false Ongoing lead-based paint..., Department of Housing and Urban Development LEAD-BASED PAINT POISONING PREVENTION IN CERTAIN RESIDENTIAL STRUCTURES HUD-Owned and Mortgagee-in-Possession Multifamily Property § 35.825 Ongoing lead-based paint...

24 CFR 35.825 - Ongoing lead-based paint maintenance and reevaluation.

Code of Federal Regulations, 2012 CFR

2012-04-01

... 24 Housing and Urban Development 1 2012-04-01 2012-04-01 false Ongoing lead-based paint..., Department of Housing and Urban Development LEAD-BASED PAINT POISONING PREVENTION IN CERTAIN RESIDENTIAL STRUCTURES HUD-Owned and Mortgagee-in-Possession Multifamily Property § 35.825 Ongoing lead-based paint...

24 CFR 35.825 - Ongoing lead-based paint maintenance and reevaluation.

Code of Federal Regulations, 2014 CFR

2014-04-01

... 24 Housing and Urban Development 1 2014-04-01 2014-04-01 false Ongoing lead-based paint..., Department of Housing and Urban Development LEAD-BASED PAINT POISONING PREVENTION IN CERTAIN RESIDENTIAL STRUCTURES HUD-Owned and Mortgagee-in-Possession Multifamily Property § 35.825 Ongoing lead-based paint...

24 CFR 35.825 - Ongoing lead-based paint maintenance and reevaluation.

Code of Federal Regulations, 2011 CFR

2011-04-01

... 24 Housing and Urban Development 1 2011-04-01 2011-04-01 false Ongoing lead-based paint..., Department of Housing and Urban Development LEAD-BASED PAINT POISONING PREVENTION IN CERTAIN RESIDENTIAL STRUCTURES HUD-Owned and Mortgagee-in-Possession Multifamily Property § 35.825 Ongoing lead-based paint...

24 CFR 35.825 - Ongoing lead-based paint maintenance and reevaluation.

Code of Federal Regulations, 2010 CFR

2010-04-01

... 24 Housing and Urban Development 1 2010-04-01 2010-04-01 false Ongoing lead-based paint..., Department of Housing and Urban Development LEAD-BASED PAINT POISONING PREVENTION IN CERTAIN RESIDENTIAL STRUCTURES HUD-Owned and Mortgagee-in-Possession Multifamily Property § 35.825 Ongoing lead-based paint...

Demonstrating the Effects of Processing on the Structure and Physical Properties of Plastic Using Disposable PETE Cups

ERIC Educational Resources Information Center

Erk, Kendra A.; Rhein, Morgan; Krafcik, Matthew J.; Ydstie, Sophie

2015-01-01

An educational activity is described in which the structure and physical properties of disposable plastic cups were directly related to the method of processing. The mechanical properties of specimens cut from the walls of poly(ethylene terephthalate) (PETE) cups, oriented parallel and perpendicular to the thermoforming direction, were measured in…

Anisotropy of machine building materials

NASA Technical Reports Server (NTRS)

Ashkenazi, Y. K.

1981-01-01

The results of experimental studies of the anisotropy of elastic and strength characteristics of various structural materials, including pressure worked metals and alloys, laminated fiberglass plastics, and laminated wood plastics, are correlated and classified. Strength criteria under simple and complex stresses are considered as applied to anisotropic materials. Practical application to determining the strength of machine parts and structural materials is discussed.

Learning to Perceive Structure from Motion and Neural Plasticity in Patients with Alzheimer's Disease

ERIC Educational Resources Information Center

Kim, Nam-Gyoon; Park, Jong-Hee

2010-01-01

Recent research has demonstrated that Alzheimer's disease (AD) affects the visual sensory pathways, producing a variety of visual deficits, including the capacity to perceive structure-from-motion (SFM). Because the sensory areas of the adult brain are known to retain a large degree of plasticity, the present study was conducted to explore whether…

Two distinct β-sheet structures in Italian-mutant amyloid-beta fibrils: a potential link to different clinical phenotypes.

PubMed

Hubin, Ellen; Deroo, Stéphanie; Schierle, Gabriele Kaminksi; Kaminski, Clemens; Serpell, Louise; Subramaniam, Vinod; van Nuland, Nico; Broersen, Kerensa; Raussens, Vincent; Sarroukh, Rabia

2015-12-01

Most Alzheimer's disease (AD) cases are late-onset and characterized by the aggregation and deposition of the amyloid-beta (Aβ) peptide in extracellular plaques in the brain. However, a few rare and hereditary Aβ mutations, such as the Italian Glu22-to-Lys (E22K) mutation, guarantee the development of early-onset familial AD. This type of AD is associated with a younger age at disease onset, increased β-amyloid accumulation, and Aβ deposition in cerebral blood vessel walls, giving rise to cerebral amyloid angiopathy (CAA). It remains largely unknown how the Italian mutation results in the clinical phenotype that is characteristic of CAA. We therefore investigated how this single point mutation may affect the aggregation of Aβ1-42 in vitro and structurally characterized the resulting fibrils using a biophysical approach. This paper reports that wild-type and Italian-mutant Aβ both form fibrils characterized by the cross-β architecture, but with distinct β-sheet organizations, resulting in differences in thioflavin T fluorescence and solvent accessibility. E22K Aβ1-42 oligomers and fibrils both display an antiparallel β-sheet structure, in comparison with the parallel β-sheet structure of wild-type fibrils, characteristic of most amyloid fibrils described in the literature. Moreover, we demonstrate structural plasticity for Italian-mutant Aβ fibrils in a pH-dependent manner, in terms of their underlying β-sheet arrangement. These findings are of interest in the ongoing debate that (1) antiparallel β-sheet structure might represent a signature for toxicity, which could explain the higher toxicity reported for the Italian mutant, and that (2) fibril polymorphism might underlie differences in disease pathology and clinical manifestation.

Formation of the structure and properties of an Mg-Al-Zn-Mn alloy during plastic deformation by rolling

NASA Astrophysics Data System (ADS)

Bozhko, S. A.; Betsofen, S. Ya.; Kolobov, Yu. R.; Vershinina, T. N.

2015-03-01

The laws of formation of an ultrafine structure in an Mg-Al-Zn-Mn alloy (MA5 alloy) under severe plastic deformation have been studied during lengthwise section rolling at a strain e = 1.59. The deformation behavior and the physical factors of anisotropy of yield strength during compression tests in various directions with respect to axis of rolling are analyzed. The role of crystallographic texture and twinning processes in the generation of strength processes and the development of plastic deformation of the alloy is analyzed.

Light-induced plasticity in leaf hydraulics, venation, anatomy, and gas exchange in ecologically diverse Hawaiian lobeliads.

PubMed

Scoffoni, Christine; Kunkle, Justin; Pasquet-Kok, Jessica; Vuong, Christine; Patel, Amish J; Montgomery, Rebecca A; Givnish, Thomas J; Sack, Lawren

2015-07-01

Leaf hydraulic conductance (Kleaf ) quantifies the capacity of a leaf to transport liquid water and is a major constraint on light-saturated stomatal conductance (gs ) and photosynthetic rate (Amax ). Few studies have tested the plasticity of Kleaf and anatomy across growth light environments. These provided conflicting results. The Hawaiian lobeliads are an excellent system to examine plasticity, given the striking diversity in the light regimes they occupy, and their correspondingly wide range of Amax , allowing maximal carbon gain for success in given environments. We measured Kleaf , Amax , gs and leaf anatomical and structural traits, focusing on six species of lobeliads grown in a common garden under two irradiances (300/800 μmol photons m(-2)  s(-1) ). We tested hypotheses for light-induced plasticity in each trait based on expectations from optimality. Kleaf , Amax , and gs differed strongly among species. Sun/shade plasticity was observed in Kleaf , Amax, and numerous traits relating to lamina and xylem anatomy, venation, and composition, but gs was not plastic with growth irradiance. Species native to higher irradiance showed greater hydraulic plasticity. Our results demonstrate that a wide set of leaf hydraulic, stomatal, photosynthetic, anatomical, and structural traits tend to shift together during plasticity and adaptation to diverse light regimes, optimizing performance from low to high irradiance. © 2015 The Authors New Phytologist © 2015 New Phytologist Trust.

Investigation of Expedient Ground Surfacing with a Glass Fiber-Resin Mixture by a Spray-Deposition Technique,

DTIC Science & Technology

PAVEMENTS, *REINFORCED PLASTICS), LANDING FIELDS, SPRAYS, GLASS TEXTILES, LAMINATED PLASTICS, TEST METHODS, FOUNDATIONS(STRUCTURES), SANDWICH CONSTRUCTION, SOILS, FEASIBILITY STUDIES, LOAD DISTRIBUTION

Searching for Factors Underlying Cerebral Plasticity in the Normal and Injured Brain

ERIC Educational Resources Information Center

Kolb, Bryan; Muhammad, Arif; Gibb, Robbin

2011-01-01

Brain plasticity refers to the capacity of the nervous system to change its structure and ultimately its function over a lifetime. There have been major advances in our understanding of the principles of brain plasticity and behavior in laboratory animals and humans. Over the past decade there have been advances in the application of these…

Whereas Short-Term Facilitation Is Presynaptic, Intermediate-Term Facilitation Involves Both Presynaptic and Postsynaptic Protein Kinases and Protein Synthesis

ERIC Educational Resources Information Center

Jin, Iksung; Kandel, Eric R.; Hawkins, Robert D.

2011-01-01

Whereas short-term plasticity involves covalent modifications that are generally restricted to either presynaptic or postsynaptic structures, long-term plasticity involves the growth of new synapses, which by its nature involves both pre- and postsynaptic alterations. In addition, an intermediate-term stage of plasticity has been identified that…

Plasticity and stability of visual field maps in adult primary visual cortex

PubMed Central

Wandell, Brian A.; Smirnakis, Stelios M.

2010-01-01

Preface It is important to understand the balance between cortical plasticity and stability in various systems and spatial scales in the adult brain. We review measurements of adult plasticity in primary visual cortex (V1), a structure that has a key role in distributing visual information. There are claims of plasticity at multiple spatial scales in adult V1, but many inconsistencies in the data raise questions about the extent and nature of such plasticity. Understanding is further limited by a lack of quantitative models to guide the interpretation of the data. These problems limit efforts to translate research findings about adult cortical plasticity into significant clinical, educational and policy applications. PMID:19904279

Studying plastic shear localization in aluminum alloys under dynamic loading

NASA Astrophysics Data System (ADS)

Bilalov, D. A.; Sokovikov, M. A.; Chudinov, V. V.; Oborin, V. A.; Bayandin, Yu. V.; Terekhina, A. I.; Naimark, O. B.

2016-12-01

An experimental and theoretical study of plastic shear localization mechanisms observed under dynamic deformation using the shear-compression scheme on a Hopkinson-Kolsky bar has been carried out using specimens of AMg6 alloy. The mechanisms of plastic shear instability are associated with collective effects in the microshear ensemble in spatially localized areas. The lateral surface of the specimens was photographed in the real-time mode using a CEDIP Silver 450M high-speed infrared camera. The temperature distribution obtained at different times allowed us to trace the evolution of the localization of the plastic strain. Based on the equations that describe the effect of nonequilibrium transitions on the mechanisms of structural relaxation and plastic flow, numerical simulation of plastic shear localization has been performed. A numerical experiment relevant to the specimen-loading scheme was carried out using a system of constitutive equations that reflect the part of the structural relaxation mechanisms caused by the collective behavior of microshears with the autowave modes of the evolution of the localized plastic flow. Upon completion of the experiment, the specimens were subjected to microstructure analysis using a New View-5010 optical microscope-interferometer. After the dynamic deformation, the constancy of the Hurst exponent, which reflects the relationship between the behavior of defects and roughness induced by the defects on the surfaces of the specimens is observed in a wider range of spatial scales. These investigations revealed the distinctive features in the localization of the deformation followed by destruction to the script of the adiabatic shear. These features may be caused by the collective multiscale behavior of defects, which leads to a sharp decrease in the stress-relaxation time and, consequently, a localized plastic flow and generation of fracture nuclei in the form of adiabatic shear. Infrared scanning of the localization zone of the plastic strain in situ and the subsequent study of the defect structure corroborated the hypothesis about the decisive role of non-equilibrium transitions in defect ensembles during the evolution of a localized plastic flow.

Matrix metalloproteinase-9 involvement in the structural plasticity of dendritic spines

PubMed Central

Stawarski, Michal; Stefaniuk, Marzena; Wlodarczyk, Jakub

2014-01-01

Dendritic spines are the locus for excitatory synaptic transmission in the brain and thus play a major role in neuronal plasticity. The ability to alter synaptic connections includes volumetric changes in dendritic spines that are driven by scaffolds created by the extracellular matrix (ECM). Here, we review the effects of the proteolytic activity of ECM proteases in physiological and pathological structural plasticity. We use matrix metalloproteinase-9 (MMP-9) as an example of an ECM modifier that has recently emerged as a key molecule in regulating the morphology and dysmorphology of dendritic spines that underlie synaptic plasticity and neurological disorders, respectively. We summarize the influence of MMP-9 on the dynamic remodeling of the ECM via the cleavage of extracellular substrates. We discuss its role in the formation, modification, and maintenance of dendritic spines in learning and memory. Finally, we review research that implicates MMP-9 in aberrant synaptic plasticity and spine dysmorphology in neurological disorders, with a focus on morphological abnormalities of dendritic protrusions that are associated with epilepsy. PMID:25071472

Deformation bands, the LEDS theory, and their importance in texture development: Part II. Theoretical conclusions

NASA Astrophysics Data System (ADS)

Kuhlmann-Wilsdorf, D.

1999-09-01

The facts regarding “regular” deformation bands (DBs) outlined in Part I of this series of articles are related to the low-energy dislocation structure (LEDS) theory of dislocation-based plasticity. They prompt an expansion of the theory by including the stresses due to strain gradients on account of changing selections of slip systems to the previously known dislocation driving forces. This last and until now neglected driving force is much smaller than the components considered hitherto, principally due to the applied stress and to mutual stress-screening among neighbor dislocations. As a result, it permits a near-proof of the LEDS hypothesis, to wit that among all structures which, in principle, are accessible to the dislocations, that one is realized which has the lowest free energy. Specifically, the temperature rises that would result from annihilating the largest DBs amount to only several millidegrees Centigrade, meaning that they, and by implication the entire dislocation structures, are close to thermodynamical equilibrium. This is in stark contrast to the assumption of the presently widespread self-organizing dislocation structures (SODS) modeling that plastic deformation occurs far from equilibrium and is subject to Prigogine’s thermodynamics of energy-flow-through systems. It also holds out promise for future rapid advances in the construction of constitutive equations, since the LEDS hypothesis is the principal basis of the LEDS theory of plastic deformation and follows directly from the second law of thermodynamics in conjunction with Newton’s third law. By contrast, all other known models of metal plasticity are in conflict with the LEDS hypothesis. In regard to texture modeling, the present analysis shows that Taylor’s criterion of minimum plastic work is incorrect and should be replaced by the criterion of minimum free energy in the stressed state. Last, the LEDS hypothesis is but a special case of the more general low-energy structure (LES) hypothesis, applying to plastic deformation independent of the deformation mechanism. It is thus seen that plastic deformation is one of nature’s means to generate order, as a byproduct of the entropy generation when mechanical work is largely converted into heat.

Homeostatic structural plasticity can account for topology changes following deafferentation and focal stroke.

PubMed

Butz, Markus; Steenbuck, Ines D; van Ooyen, Arjen

2014-01-01

After brain lesions caused by tumors or stroke, or after lasting loss of input (deafferentation), inter- and intra-regional brain networks respond with complex changes in topology. Not only areas directly affected by the lesion but also regions remote from the lesion may alter their connectivity-a phenomenon known as diaschisis. Changes in network topology after brain lesions can lead to cognitive decline and increasing functional disability. However, the principles governing changes in network topology are poorly understood. Here, we investigated whether homeostatic structural plasticity can account for changes in network topology after deafferentation and brain lesions. Homeostatic structural plasticity postulates that neurons aim to maintain a desired level of electrical activity by deleting synapses when neuronal activity is too high and by providing new synaptic contacts when activity is too low. Using our Model of Structural Plasticity, we explored how local changes in connectivity induced by a focal loss of input affected global network topology. In accordance with experimental and clinical data, we found that after partial deafferentation, the network as a whole became more random, although it maintained its small-world topology, while deafferentated neurons increased their betweenness centrality as they rewired and returned to the homeostatic range of activity. Furthermore, deafferentated neurons increased their global but decreased their local efficiency and got longer tailed degree distributions, indicating the emergence of hub neurons. Together, our results suggest that homeostatic structural plasticity may be an important driving force for lesion-induced network reorganization and that the increase in betweenness centrality of deafferentated areas may hold as a biomarker for brain repair.

Significance of Objective Structured Clinical Examinations to Plastic Surgery Residency Training.

PubMed

Simmons, Brian J; Zoghbi, Yasmina; Askari, Morad; Birnbach, David J; Shekhter, Ilya; Thaller, Seth R

2017-09-01

Objective structured clinical examinations (OSCEs) have proven to be a powerful tool. They possess more than a 30-year track record in assessing the competency of medical students, residents, and fellows. Objective structured clinical examinations have been used successfully in a variety of medical specialties, including surgery. They have recently found their way into the subspecialty of plastic surgery. This article uses a systematic review of the available literature on OSCEs and their recent use in plastic surgery. It incorporates survey results assessing program directors' views on the use of OSCEs. Approximately 40% of programs surveyed use OSCEs to assess the Accreditation Council for Graduate Medical Education core competencies. We found that 40% use OSCEs to evaluate specific plastic surgery milestones. Objective structured clinical examinations are usually performed annually. They cost anywhere between $100 and more than $1000 per resident. Four milestones giving residents the most difficulties on OSCEs were congenital anomalies, noncancer breast surgery, breast reconstruction, and practice-based learning and improvement. It was determined that challenges with milestones were due to lack of adequate general knowledge and surgical ward patient care, as well as deficits in professionalism and system-based problems. Programs were able to remediate weakness found by OSCEs using a variety of methods. Objective structured clinical examinations offer a unique tool to objectively assess the proficiency of residents in key areas of the Accreditation Council for Graduate Medical Education core competencies. In addition, they can be used to assess the specific milestones that plastic surgery residents must meet. This allows programs to identify and improve identified areas of weakness.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hopmann, Ch.; Weber, M.; Schöngart, M.

Micro structured optical plastics components are intensively used i. e. in consumer electronics, for optical sensors in metrology, innovative LED-lighting or laser technology. Injection moulding has proven to be successful for the large-scale production of those parts. However, the production of those parts still causes difficulties due to challenges in the moulding and demoulding of plastics parts created with laser structured mould inserts. A complete moulding of the structures often leads to increased demoulding forces, which then cause a breaking of the structures and a clogging of the mould. An innovative approach is to combine PVD-coated (physical vapour deposition), lasermore » structured inserts and a variothermal moulding process to create functional mic8iüro structures in a one-step process. Therefore, a PVD-coating is applied after the laser structuring process in order to improve the wear resistance and the anti-adhesive properties against the plastics melt. In a series of moulding trials with polycarbonate (PC) and polymethylmethacrylate (PMMA) using different coated moulds, the mould temperature during injection was varied in the range of the glass transition and the melt temperature of the polymers. Subsequently, the surface topography of the moulded parts is evaluated by digital 3D laser-scanning microscopy. The influence of the moulding parameters and the coating of the mould insert on the moulding accuracy and the demoulding behaviour are being analysed. It is shown that micro structures created by ultra-short pulse laser ablation can be successfully replicated in a variothermal moulding process. Due to the mould coating, significant improvements could be achieved in producing micro structured optical plastics components.« less

Crash simulation of hybrid structures considering the stress and strain rate dependent material behavior of thermoplastic materials

NASA Astrophysics Data System (ADS)

Hopmann, Ch.; Schöngart, M.; Weber, M.; Klein, J.

2015-05-01

Thermoplastic materials are more and more used as a light weight replacement for metal, especially in the automotive industry. Since these materials do not provide the mechanical properties, which are required to manufacture supporting elements like an auto body or a cross bearer, plastics are combined with metals in so called hybrid structures. Normally, the plastics components are joined to the metal structures using different technologies like welding or screwing. Very often, the hybrid structures are made of flat metal parts, which are stiffened by a reinforcement structure made of thermoplastic materials. The loads on these structures are very often impulsive, for example in the crash situation of an automobile. Due to the large stiffness variation of metal and thermoplastic materials, complex states of stress and very high local strain rates occur in the contact zone under impact conditions. Since the mechanical behavior of thermoplastic materials is highly dependent on these types of load, the crash failure of metal plastic hybrid parts is very complex. The problem is that the normally used strain rate dependent elastic/plastic material models are not capable to simulate the mechanical behavior of thermoplastic materials depended on the state of stress. As part of a research project, a method to simulate the mechanical behavior of hybrid structures under impact conditions is developed at the IKV. For this purpose, a specimen for the measurement of mechanical properties dependet on the state of stress and a method for the strain rate depended characterization of thermoplastic materials were developed. In the second step impact testing is performed. A hybrid structure made from a metal sheet and a reinforcement structure of a Polybutylenterephthalat Polycarbonate blend is tested under impact conditions. The measured stress and strain rate depended material data are used to simulate the mechanical behavior of the hybrid structure under highly dynamic load with impact velocities up to 5 m/s. The mechanical behavior of the plastics structure is simulated using a quadratic yield surface, which takes the state of stress and the strain rate into account. The FE model is made from mid surface elements to reduce the computing time.

Injection moulding of optical functional micro structures using laser structured, PVD-coated mould inserts

NASA Astrophysics Data System (ADS)

Hopmann, Ch.; Weber, M.; Schöngart, M.; Schäfer, C.; Bobzin, K.; Bagcivan, N.; Brögelmann, T.; Theiß, S.; Münstermann, T.; Steger, M.

2015-05-01

Micro structured optical plastics components are intensively used i. e. in consumer electronics, for optical sensors in metrology, innovative LED-lighting or laser technology. Injection moulding has proven to be successful for the large-scale production of those parts. However, the production of those parts still causes difficulties due to challenges in the moulding and demoulding of plastics parts created with laser structured mould inserts. A complete moulding of the structures often leads to increased demoulding forces, which then cause a breaking of the structures and a clogging of the mould. An innovative approach is to combine PVD-coated (physical vapour deposition), laser structured inserts and a variothermal moulding process to create functional mic8iüro structures in a one-step process. Therefore, a PVD-coating is applied after the laser structuring process in order to improve the wear resistance and the anti-adhesive properties against the plastics melt. In a series of moulding trials with polycarbonate (PC) and polymethylmethacrylate (PMMA) using different coated moulds, the mould temperature during injection was varied in the range of the glass transition and the melt temperature of the polymers. Subsequently, the surface topography of the moulded parts is evaluated by digital 3D laser-scanning microscopy. The influence of the moulding parameters and the coating of the mould insert on the moulding accuracy and the demoulding behaviour are being analysed. It is shown that micro structures created by ultra-short pulse laser ablation can be successfully replicated in a variothermal moulding process. Due to the mould coating, significant improvements could be achieved in producing micro structured optical plastics components.

[Structural plasticity associated with drugs addiction].

PubMed

Zhu, Jie; Cao, Guo-fen; Dang, Yong-hui; Chen, Teng

2011-12-01

An essential feature of drug addiction is that an individual continues to use drug despite the threat of severely adverse physical or psychosocial consequences. Persistent changes in behavior and psychological function that occur as a function of drugs of abuse are thought to be due to the reorganization of synaptic connections (structural plasticity) in relevant brain circuits (especially the brains reward circuits). In this paper we summarized evidence that, indeed, exposure to amphetamine, cocaine, nicotine or morphine produced persistent changes in the structure of dendrites and dendritic spines on cells in relevant brain regions. We also approached the potential molecular mechanisms of these changes. It is suggested that structural plasticity associated with exposure to drugs of abuse reflects a reorganization of patterns of synaptic connectivity in these neural systems, a reorganization that alters their operation, thus contributing to some of the persistent sequela associated with drug use-including addiction.

Plastic material investment in load-bearing silk attachments in spiders.

PubMed

Wolff, Jonas O; Jones, Braxton; Herberstein, Marie E

2018-05-17

The nature and size of attachments is a fundamental element of animal constructions. Presumably, these adhesive structures are plastically deployed to balance material investment and attachment strength. Here we studied plasticity in dragline anchorages of the golden orb web spider, Nephila plumipes. Specifically, we predict that spiders adjust the size and structure of dragline anchorages with load, i.e. spider mass. Mass was manipulated by attaching lead pieces to the spider's abdomen resulting in a 50 percent increase in mass. Loaded spiders spun larger but structurally similar thread anchorages than unloaded spiders. Thus, the spinning program that determines the overall anchor structure is highly stereotypic, and flexibility is introduced through varying the anchor size by increasing material investment. Our study showcases substrate attachments as suitable models to investigate the interplay between innate and changeable elements in the economy of building behaviours. Copyright © 2018 Elsevier GmbH. All rights reserved.

Plasticization effect of triacetin on structure and properties of starch ester film.

PubMed

Zhu, Jie; Li, Xiaoxi; Huang, Chen; Chen, Ling; Li, Lin

2013-05-15

The aim of this work was to evaluate the plasticizing effect of triacetin on the structure and properties of starch ester film and further establish the structure-property relationships. The presence of triacetin resulted in multiple structure changes of the film. The mobility of macromolecular chain was increased to form scattered crystallite during the film formation process. The amorphous region was enlarged to contain more triacetin squeezed from crystalline region. The plasticization of triacetin and restriction of crystallite oppositely influenced the mobility of macromolecular chains in different regions. The thermal stability of triacetin changed along with its fluctuant interaction with macromolecules. Comparatively, the enhanced ether bond and the restriction from crystalline regions on the mobility of the amorphous chain consequently improved the thermal stability of the film matrix. The interaction between triacetin and starch ester was essential to film forming but unexpectedly lowered the triacetin stability. Copyright © 2013 Elsevier Ltd. All rights reserved.

PLANS; a finite element program for nonlinear analysis of structures. Volume 2: User's manual

NASA Technical Reports Server (NTRS)

Pifko, A.; Armen, H., Jr.; Levy, A.; Levine, H.

1977-01-01

The PLANS system, rather than being one comprehensive computer program, is a collection of finite element programs used for the nonlinear analysis of structures. This collection of programs evolved and is based on the organizational philosophy in which classes of analyses are treated individually based on the physical problem class to be analyzed. Each of the independent finite element computer programs of PLANS, with an associated element library, can be individually loaded and used to solve the problem class of interest. A number of programs have been developed for material nonlinear behavior alone and for combined geometric and material nonlinear behavior. The usage, capabilities, and element libraries of the current programs include: (1) plastic analysis of built-up structures where bending and membrane effects are significant, (2) three dimensional elastic-plastic analysis, (3) plastic analysis of bodies of revolution, and (4) material and geometric nonlinear analysis of built-up structures.

Learning Discloses Abnormal Structural and Functional Plasticity at Hippocampal Synapses in the APP23 Mouse Model of Alzheimer's Disease

ERIC Educational Resources Information Center

Middei, Silvia; Roberto, Anna; Berretta, Nicola; Panico, Maria Beatrice; Lista, Simone; Bernardi, Giorgio; Mercuri, Nicola B.; Ammassari-Teule, Martine; Nistico, Robert

2010-01-01

B6-Tg/Thy1APP23Sdz (APP23) mutant mice exhibit neurohistological hallmarks of Alzheimer's disease but show intact basal hippocampal neurotransmission and synaptic plasticity. Here, we examine whether spatial learning differently modifies the structural and electrophysiological properties of hippocampal synapses in APP23 and wild-type mice. While…

Evaluation of three types of structured floating plastic media in moving bed biofilters for total ammonia nitrogen removal in a low salinity hatchery recirculating aquaculture system

USDA-ARS?s Scientific Manuscript database

Three different commercially available structural plastic media were evaluated in triplicate in moving bed toriod filters under low salinity (11-12 ppt) warm water culture conditions and two different feed loading rates. The culture system consisted of nine separate modules that include a double dra...

Big Atoms for Small Children: Building Atomic Models from Common Materials to Better Visualize and Conceptualize Atomic Structure

ERIC Educational Resources Information Center

Cipolla, Laura; Ferrari, Lia A.

2016-01-01

A hands-on approach to introduce the chemical elements and the atomic structure to elementary/middle school students is described. The proposed classroom activity presents Bohr models of atoms using common and inexpensive materials, such as nested plastic balls, colored modeling clay, and small-sized pasta (or small plastic beads).

Plasticity in single neuron and circuit computations

NASA Astrophysics Data System (ADS)

Destexhe, Alain; Marder, Eve

2004-10-01

Plasticity in neural circuits can result from alterations in synaptic strength or connectivity, as well as from changes in the excitability of the neurons themselves. To better understand the role of plasticity in the brain, we need to establish how brain circuits work and the kinds of computations that different circuit structures achieve. By linking theoretical and experimental studies, we are beginning to reveal the consequences of plasticity mechanisms for network dynamics, in both simple invertebrate circuits and the complex circuits of mammalian cerebral cortex.

Assessment of Mechanical Performance of Bone Architecture Using Rapid Prototyping Models

NASA Astrophysics Data System (ADS)

Saparin, Peter; Woesz, Alexander; Thomsen, Jasper S.; Fratzl, Peter

2008-06-01

The aim of this on-going research project is to assess the influence of bone microarchitecture on the mechanical performance of trabecular bone. A testing chain consist-ing of three steps was established: 1) micro computed tomography (μCT) imaging of human trabecular bone; 2) building of models of the bone from a light-sensitive polymer using Rapid Prototyping (RP); 3) mechanical testing of the models in a material testing machine. A direct resampling procedure was developed to convert μCT data into the format of the RP machine. Standardized parameters for production and testing of the plastic models were established by use of regular cellular structures. Next, normal, osteoporotic, and extreme osteoporotic vertebral trabecular bone architectures were re-produced by RP and compression tested. We found that normal architecture of vertebral trabecular bone exhibit behaviour characteristic of a cellular structure. In normal bone the fracture occurs at much higher strain values that in osteoporotic bone. After the fracture a normal trabecular architecture is able to carry much higher loads than an osteoporotic architecture. However, no statistically significant differences were found in maximal stress during uniaxial compression of the central part of normal, osteoporotic, and extreme osteoporotic vertebral trabecular bone. This supports the hypothesis that osteoporotic trabecular bone can compensate for a loss of trabeculae by thickening the remaining trabeculae in the loading direction (compensatory hypertrophy). The developed approach could be used for mechanical evaluation of structural data acquired non-invasively and assessment of changes in performance of bone architecture.

Academic Status of Plastic Surgery in the United States and the Relevance of Independence.

PubMed

Liu, P; Singh, M; Eriksson, E

2016-04-01

The basic administrative structures at most academic institutions were implemented more than 50 years ago and have remained largely unchanged. Since the surgical specialties were in nascent stages during that time, they were clubbed together within the department of surgery. There has been extensive growth in the breadth and depth of plastic surgery over the past few decades and current administrative structures might not truly reflect the current standing of plastic surgery. The goal of this article was to review the academic status of Plastic Surgery in the United States and assess the relevance of independence from the department of surgery. A national survey of 94 hospitals with plastic surgery residency training programs in the United States was conducted to investigate the academic status of plastic surgery. 25 out of those 94 programs had department status with their respective hospitals while another 9 programs were actively planning on transitioning to department status. Out of the 25 plastic surgery hospital departments, 17 programs were also University departments. The number of plastic surgery departments has more than doubled over the past 10 years and continues to rise as more plastic surgery divisions seek department status. There are multiple advantages to seeking department status such as financial and administrative autonomy, ability to participate in medical school curricula, easier access to interdepartmental institutes and faculties, parity with other specialties, and increased control of resident education. There has been concerted advocacy for separating from surgery departments and seeking independent departmental status for plastic surgery. However, the transition from a division to department is a slow and demanding process and requires a well-planned strategy. © Georg Thieme Verlag KG Stuttgart · New York.

‘White revolution’ to ‘white pollution’—agricultural plastic film mulch in China

NASA Astrophysics Data System (ADS)

Liu, E. K.; He, W. Q.; Yan, C. R.

2014-09-01

Plastic film mulching has played an important role in Chinese agriculture due to its soil warming and moisture conservation effects. With the help of plastic film mulch technology, grain and cash crop yields have increased by 20-35% and 20-60%, respectively. The area of plastic film coverage in China reached approximately 20 million hectares, and the amount of plastic film used reached 1.25 million tons in 2011. While producing huge benefits, plastic film mulch technology has also brought on a series of pollution hazards. Large amounts of residual plastic film have detrimental effects on soil structure, water and nutrient transport and crop growth, thereby disrupting the agricultural environment and reducing crop production. To control pollution, the Chinese government urgently needs to elevate plastic film standards. Meanwhile, research and development of biodegradable mulch film and multi-functional mulch recovery machinery will help promote effective control and management of residual mulch pollution.

Evading the strength–ductility trade-off dilemma in steel through gradient hierarchical nanotwins

PubMed Central

Wei, Yujie; Li, Yongqiang; Zhu, Lianchun; Liu, Yao; Lei, Xianqi; Wang, Gang; Wu, Yanxin; Mi, Zhenli; Liu, Jiabin; Wang, Hongtao; Gao, Huajian

2014-01-01

The strength–ductility trade-off has been a long-standing dilemma in materials science. This has limited the potential of many structural materials, steels in particular. Here we report a way of enhancing the strength of twinning-induced plasticity steel at no ductility trade-off. After applying torsion to cylindrical twinning-induced plasticity steel samples to generate a gradient nanotwinned structure along the radial direction, we find that the yielding strength of the material can be doubled at no reduction in ductility. It is shown that this evasion of strength–ductility trade-off is due to the formation of a gradient hierarchical nanotwinned structure during pre-torsion and subsequent tensile deformation. A series of finite element simulations based on crystal plasticity are performed to understand why the gradient twin structure can cause strengthening and ductility retention, and how sequential torsion and tension lead to the observed hierarchical nanotwinned structure through activation of different twinning systems. PMID:24686581

Active listening: task-dependent plasticity of spectrotemporal receptive fields in primary auditory cortex.

PubMed

Fritz, Jonathan; Elhilali, Mounya; Shamma, Shihab

2005-08-01

Listening is an active process in which attentive focus on salient acoustic features in auditory tasks can influence receptive field properties of cortical neurons. Recent studies showing rapid task-related changes in neuronal spectrotemporal receptive fields (STRFs) in primary auditory cortex of the behaving ferret are reviewed in the context of current research on cortical plasticity. Ferrets were trained on spectral tasks, including tone detection and two-tone discrimination, and on temporal tasks, including gap detection and click-rate discrimination. STRF changes could be measured on-line during task performance and occurred within minutes of task onset. During spectral tasks, there were specific spectral changes (enhanced response to tonal target frequency in tone detection and discrimination, suppressed response to tonal reference frequency in tone discrimination). However, only in the temporal tasks, the STRF was changed along the temporal dimension by sharpening temporal dynamics. In ferrets trained on multiple tasks, distinctive and task-specific STRF changes could be observed in the same cortical neurons in successive behavioral sessions. These results suggest that rapid task-related plasticity is an ongoing process that occurs at a network and single unit level as the animal switches between different tasks and dynamically adapts cortical STRFs in response to changing acoustic demands.

Simulations of surface stress effects in nanoscale single crystals

NASA Astrophysics Data System (ADS)

Zadin, V.; Veske, M.; Vigonski, S.; Jansson, V.; Muszinsky, J.; Parviainen, S.; Aabloo, A.; Djurabekova, F.

2018-04-01

Onset of vacuum arcing near a metal surface is often associated with nanoscale asperities, which may dynamically appear due to different processes ongoing in the surface and subsurface layers in the presence of high electric fields. Thermally activated processes, as well as plastic deformation caused by tensile stress due to an applied electric field, are usually not accessible by atomistic simulations because of the long time needed for these processes to occur. On the other hand, finite element methods, able to describe the process of plastic deformations in materials at realistic stresses, do not include surface properties. The latter are particularly important for the problems where the surface plays crucial role in the studied process, as for instance, in the case of plastic deformations at a nanovoid. In the current study by means of molecular dynamics (MD) and finite element simulations we analyse the stress distribution in single crystal copper containing a nanovoid buried deep under the surface. We have developed a methodology to incorporate the surface effects into the solid mechanics framework by utilizing elastic properties of crystals, pre-calculated using MD simulations. The method leads to computationally efficient stress calculations and can be easily implemented in commercially available finite element software, making it an attractive analysis tool.

Computational modeling of neural plasticity for self-organization of neural networks.

PubMed

Chrol-Cannon, Joseph; Jin, Yaochu

2014-11-01

Self-organization in biological nervous systems during the lifetime is known to largely occur through a process of plasticity that is dependent upon the spike-timing activity in connected neurons. In the field of computational neuroscience, much effort has been dedicated to building up computational models of neural plasticity to replicate experimental data. Most recently, increasing attention has been paid to understanding the role of neural plasticity in functional and structural neural self-organization, as well as its influence on the learning performance of neural networks for accomplishing machine learning tasks such as classification and regression. Although many ideas and hypothesis have been suggested, the relationship between the structure, dynamics and learning performance of neural networks remains elusive. The purpose of this article is to review the most important computational models for neural plasticity and discuss various ideas about neural plasticity's role. Finally, we suggest a few promising research directions, in particular those along the line that combines findings in computational neuroscience and systems biology, and their synergetic roles in understanding learning, memory and cognition, thereby bridging the gap between computational neuroscience, systems biology and computational intelligence. Copyright © 2014 Elsevier Ireland Ltd. All rights reserved.

Semantic modeling of the structural and process entities during plastic deformation of crystals and rocks

NASA Astrophysics Data System (ADS)

Babaie, Hassan; Davarpanah, Armita

2016-04-01

We are semantically modeling the structural and dynamic process components of the plastic deformation of minerals and rocks in the Plastic Deformation Ontology (PDO). Applying the Ontology of Physics in Biology, the PDO classifies the spatial entities that participate in the diverse processes of plastic deformation into the Physical_Plastic_Deformation_Entity and Nonphysical_Plastic_Deformation_Entity classes. The Material_Physical_Plastic_Deformation_Entity class includes things such as microstructures, lattice defects, atoms, liquid, and grain boundaries, and the Immaterial_Physical_Plastic_Deformation_Entity class includes vacancies in crystals and voids along mineral grain boundaries. The objects under the many subclasses of these classes (e.g., crystal, lattice defect, layering) have spatial parts that are related to each other through taxonomic (e.g., Line_Defect isA Lattice_Defect), structural (mereological, e.g., Twin_Plane partOf Twin), spatial-topological (e.g., Vacancy adjacentTo Atom, Fluid locatedAlong Grain_Boundary), and domain specific (e.g., displaces, Fluid crystallizes Dissolved_Ion, Void existsAlong Grain_Boundary) relationships. The dynamic aspect of the plastic deformation is modeled under the dynamical Process_Entity class that subsumes classes such as Recrystallization and Pressure_Solution that define the flow of energy amongst the physical entities. The values of the dynamical state properties of the physical entities (e.g., Chemical_Potential, Temperature, Particle_Velocity) change while they take part in the deformational processes such as Diffusion and Dislocation_Glide. The process entities have temporal parts (phases) that are related to each other through temporal relations such as precedes, isSubprocessOf, and overlaps. The properties of the physical entities, defined under the Physical_Property class, change as they participate in the plastic deformational processes. The properties are categorized into dynamical, constitutive, spatial, temporal, statistical, and thermodynamical. The dynamical properties, categorized under the Dynamical_Rate_Property and Dynamical_State_Property classes, subsume different classes of properties (e.g., Fluid_Flow_Rate, Temperature, Chemical_Potential, Displacement, Electrical_Charge) based on the physical domain (e.g., fluid, heat, chemical, solid, electrical). The properties are related to the objects under the Physical_Entity class through diverse object type (e.g., physicalPropertyOf) and data type (e.g., Fluid_Pressure unit 'MPa') properties. The changes of the dynamical properties of the physical entities, described by the empirical laws (equations) modeled by experimental structural geologists, are modeled through the Physical_Property_Dependency class that subsumes the more specialized constitutive, kinetic, and thermodynamic expressions of the relationships among the dynamic properties. Annotation based on the PDO will make it possible to integrate and reuse experimental plastic deformation data, knowledge, and simulation models, and conduct semantic-based search of the source data originating from different rock testing laboratories.

Evidence-Based Medicine: Reduction Mammaplasty.

PubMed

Greco, Richard; Noone, Barrett

2017-01-01

After reading this article, the participant should be able to: 1. Understand the multiple reduction mammaplasty techniques available for patients and describe the advantages and disadvantages associated with each. 2. Describe the indications for the treatment of macromastia in patients younger than 18 years. 3. Identify the preoperative indications for breast imaging before surgery. 4. Describe the benefits of breast infiltration with local anesthesia with epinephrine before surgery. 5. Understand the use of deep venous thrombosis prophylaxis in breast reduction surgery. 6. Describe when the use of drains is indicated after breast reduction surgery. The goal of this Continuing Medical Education module is to summarize key evidence-based data available to plastic surgeons to improve their care of patients with breast hypertrophy. The authors' goal is to present the current controversies regarding their treatment and provide a discussion of the various options in their care. The article was prepared to accompany practice-based assessment with ongoing surgical education for the Maintenance of Certification Program of the American Board of Plastic Surgery.

Clinical application of adipose stem cells in plastic surgery.

PubMed

Kim, Yong-Jin; Jeong, Jae-Ho

2014-04-01

Adipose stem cells (ASCs) are a type of adult stem cells that share common characteristics with typical mesenchymal stem cells. In the last decade, ASCs have been shown to be a useful cell resource for tissue regeneration. The major role of regenerative medicine in this century is based on cell therapy in which ASCs hold a key position. Active research on this new type of adult stem cell has been ongoing and these cells now have several clinical applications, including fat grafting, overcoming wound healing difficulties, recovery from local tissue ischemia, and scar remodeling. The application of cultured cells will increase the efficiency of cell therapy. However, the use of cultured stem cells is strictly controlled by government regulation to ensure patient safety. Government regulation is a factor that can limit more versatile clinical application of ASCs. In this review, current clinical applications of ASCs in plastic surgery are introduced. Future stem cell applications in clinical field including culturing and banking of ASCs are also discussed in this review.

Study of properties of the plastic scintillator EJ-260 under irradiation with 150 MeV protons and 1.2MeV gamma-rays

NASA Astrophysics Data System (ADS)

Dormenev, V.; Brinkmann, K.-T.; Korjik, M.; Novotny, R. W.

2017-11-01

One of the most critical aspects for the application of a scintillation material in high energy physics is the degradation of properties of the material in an environment of highly ionizing particles in particular due to hadrons. There are presently several detector concepts in consideration being based on organic scintillator material for fast timing of charged particles or sampling calorimeters. We have tested different samples of the organic plastic scintillator EJ-260 produced by the company Eljen Technology (Sweetwater, TX, USA). The ongoing activity has characterized the relevant parameters such as light output, kinetics and temperature dependence. The study has focused on the change of performance after irradiation with 150 MeV protons up to an integral fluence of 5·1013 protons/cm2 as well as with a strong 60Co γ-source accumulating an integral dose of 100 Gy. The paper will report on the obtained results.

Plastic waste associated with disease on coral reefs.

PubMed

Lamb, Joleah B; Willis, Bette L; Fiorenza, Evan A; Couch, Courtney S; Howard, Robert; Rader, Douglas N; True, James D; Kelly, Lisa A; Ahmad, Awaludinnoer; Jompa, Jamaluddin; Harvell, C Drew

2018-01-26

Plastic waste can promote microbial colonization by pathogens implicated in outbreaks of disease in the ocean. We assessed the influence of plastic waste on disease risk in 124,000 reef-building corals from 159 reefs in the Asia-Pacific region. The likelihood of disease increases from 4% to 89% when corals are in contact with plastic. Structurally complex corals are eight times more likely to be affected by plastic, suggesting that microhabitats for reef-associated organisms and valuable fisheries will be disproportionately affected. Plastic levels on coral reefs correspond to estimates of terrestrial mismanaged plastic waste entering the ocean. We estimate that 11.1 billion plastic items are entangled on coral reefs across the Asia-Pacific and project this number to increase 40% by 2025. Plastic waste management is critical for reducing diseases that threaten ecosystem health and human livelihoods. Copyright © 2018, The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works.

[The behavior of fiber-reinforced plastics during laser cutting].

PubMed

Emmrich, M; Levsen, K; Trasser, F J

1992-06-01

The pattern of the organic emissions, which are produced by processing of fibre reinforced plastics (epoxy resins reinforced by aramid and glass fibres and phenol resins reinforced by aramid fibre) with laser beam was studied and the concentrations of the main components determined. Despite the application of plastic materials with different chemical structures, the observed patterns are very similar. Mainly aromatic hydrocarbons are emitted, especially benzene and toluene, as well as some heteroatom-containing aromatic hydrocarbons (e.g. phenol). By use of oxygen as process gas the emissions during cutting of glass fibre reinforced plastics can be reduced, while they will be constantly high with aramid fibre reinforced plastics.

Thermal degradation and plasticizing mechanism of poly(vinyl chloride) plasticized with a novel cardanol derived plasticizer

NASA Astrophysics Data System (ADS)

Chen, J.; Nie, X. A.; Jiang, J. C.; Zhou, Y. H.

2018-01-01

A natural plasticizer cardanol derivatives glycidyl ether (CGE) was synthesized and employed as a plasticizer for the poly(vinyl chloride). The effect of CGE on thermal degradation of PVC films and its plasticizing mechanism were firstly reported. The molecular structure of CGE was characterized with Fourier transform infrared spectroscopy (FTIR). Thermal properties, degradation properties and compatibility of the PVC films were investigated by Differential scanning calorimeter analysis (DSC), Thermogravimetric analysis (TGA) and FTIR, respectively. Compared with the commercial plasticizers dioctylphthalate (DOP), CGE can endow PVC film with a decrease of 4.31 °C in glass transition temperature (Tg), an increase of 24.01 °C and 25.53 °C in 10% weight loss (T 10) and 50% weight loss (T 50) respectively, and a higher activetion energy of thermal degradation (Ea ).

Physics in Plastics Technology.

ERIC Educational Resources Information Center

Thomas, Ken

1980-01-01

Discusses the increasing role of the physicist in plastics technology. Relationships of molecular structure to material behavior, design which is related to the material, and the practical problems of fabricating a material into an article are included. (HM)

[Osseontegration of trial implants of carbon fiber reinforced plastics].

PubMed

Schreiner, U; Schwarz, M; Scheller, G; Schroeder-Boersch, H; Jani, L

2000-01-01

To what extent are carbon fibre-reinforced plastics (CFRP) suitable as an osseous integration surface for implants? CFRP test implants having a plexus-structured, rhombus-structured, and plexus-structured, hydroxyapatite surface were implanted in the femura of mini-plgs. Exposure time lasted 12 weeks. The implants were subjected to a macroradiological, a histological-histomorphometrical, and a fluorescence-microscopical evaluation. One half of the uncoated, plexus-structured implants were not osteointegrated, the other half displayed an osteointegration rate of 11.8% in the spongy area and 29.8% in the cortex layer. The HA-coated test implants showed an osteointegration of 29.5% in the spongiosa and 56.8% in the cortex layer. The rhombus-structured test implants had an osteointegration of 29.2% (spongiosa) and 46.2% (cortex layer). Compared to the osteointegration of metallic, especially titanium surfaces the CFRP surfaces tested by us fared worse, especially the uncoated, plexus-structured surfaces. For this reason we view very critically the use of carbon-fibre reinforced plastics together with the surfaces tested by us as osteointegrating surfaces.

Numerical and Experimental Studies on Impact Loaded Concrete Structures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Saarenheimo, Arja; Hakola, Ilkka; Karna, Tuomo

2006-07-01

An experimental set-up has been constructed for medium scale impact tests. The main objective of this effort is to provide data for the calibration and verification of numerical models of a loading scenario where an aircraft impacts against a nuclear power plant. One goal is to develop and take in use numerical methods for predicting response of reinforced concrete structures to impacts of deformable projectiles that may contain combustible liquid ('fuel'). Loading, structural behaviour, like collapsing mechanism and the damage grade, will be predicted by simple analytical methods and using non-linear FE-method. In the so-called Riera method the behavior ofmore » the missile material is assumed to be rigid plastic or rigid visco-plastic. Using elastic plastic and elastic visco-plastic material models calculations are carried out by ABAQUS/Explicit finite element code, assuming axisymmetric deformation mode for the missile. With both methods, typically, the impact force time history, the velocity of the missile rear end and the missile shortening during the impact were recorded for comparisons. (authors)« less

Prospects of pyrolysis oil from plastic waste as fuel for diesel engines: A review

NASA Astrophysics Data System (ADS)

Mangesh, V. L.; Padmanabhan, S.; Ganesan, S.; PrabhudevRahul, D.; Reddy, T. Dinesh Kumar

2017-05-01

The purpose ofthis study is to review the existing literature about chemical recycling of plastic waste and its potential as fuel for diesel engines. This is a review covering on the field of converting waste plastics into liquid hydrocarbon fuels for diesel engines. Disposal and recycling of waste plastics have become an incremental problem and environmental threat with increasing demand for plastics. One of the effective measures is by converting waste plastic into combustible hydrocarbon liquid as an alternative fuel for running diesel engines. Continued research efforts have been taken by researchers to convert waste plastic in to combustible pyrolysis oil as alternate fuel for diesel engines. An existing literature focuses on the study of chemical structure of the waste plastic pyrolysis compared with diesel oil. Converting waste plastics into fuel oil by different catalysts in catalytic pyrolysis process also reviewed in this paper. The methodology with subsequent hydro treating and hydrocracking of waste plastic pyrolysis oil can reduce unsaturated hydrocarbon bonds which would improve the combustion performance in diesel engines as an alternate fuel.

Network evolution induced by asynchronous stimuli through spike-timing-dependent plasticity.

PubMed

Yuan, Wu-Jie; Zhou, Jian-Fang; Zhou, Changsong

2013-01-01

In sensory neural system, external asynchronous stimuli play an important role in perceptual learning, associative memory and map development. However, the organization of structure and dynamics of neural networks induced by external asynchronous stimuli are not well understood. Spike-timing-dependent plasticity (STDP) is a typical synaptic plasticity that has been extensively found in the sensory systems and that has received much theoretical attention. This synaptic plasticity is highly sensitive to correlations between pre- and postsynaptic firings. Thus, STDP is expected to play an important role in response to external asynchronous stimuli, which can induce segregative pre- and postsynaptic firings. In this paper, we study the impact of external asynchronous stimuli on the organization of structure and dynamics of neural networks through STDP. We construct a two-dimensional spatial neural network model with local connectivity and sparseness, and use external currents to stimulate alternately on different spatial layers. The adopted external currents imposed alternately on spatial layers can be here regarded as external asynchronous stimuli. Through extensive numerical simulations, we focus on the effects of stimulus number and inter-stimulus timing on synaptic connecting weights and the property of propagation dynamics in the resulting network structure. Interestingly, the resulting feedforward structure induced by stimulus-dependent asynchronous firings and its propagation dynamics reflect both the underlying property of STDP. The results imply a possible important role of STDP in generating feedforward structure and collective propagation activity required for experience-dependent map plasticity in developing in vivo sensory pathways and cortices. The relevance of the results to cue-triggered recall of learned temporal sequences, an important cognitive function, is briefly discussed as well. Furthermore, this finding suggests a potential application for examining STDP by measuring neural population activity in a cultured neural network.

PLAN2D - A PROGRAM FOR ELASTO-PLASTIC ANALYSIS OF PLANAR FRAMES

NASA Technical Reports Server (NTRS)

Lawrence, C.

1994-01-01

PLAN2D is a FORTRAN computer program for the plastic analysis of planar rigid frame structures. Given a structure and loading pattern as input, PLAN2D calculates the ultimate load that the structure can sustain before collapse. Element moments and plastic hinge rotations are calculated for the ultimate load. The location of hinges required for a collapse mechanism to form are also determined. The program proceeds in an iterative series of linear elastic analyses. After each iteration the resulting elastic moments in each member are compared to the reserve plastic moment capacity of that member. The member or members that have moments closest to their reserve capacity will determine the minimum load factor and the site where the next hinge is to be inserted. Next, hinges are inserted and the structural stiffness matrix is reformulated. This cycle is repeated until the structure becomes unstable. At this point the ultimate collapse load is calculated by accumulating the minimum load factor from each previous iteration and multiplying them by the original input loads. PLAN2D is based on the program STAN, originally written by Dr. E.L. Wilson at U.C. Berkeley. PLAN2D has several limitations: 1) Although PLAN2D will detect unloading of hinges it does not contain the capability to remove hinges; 2) PLAN2D does not allow the user to input different positive and negative moment capacities and 3) PLAN2D does not consider the interaction between axial and plastic moment capacity. Axial yielding and buckling is ignored as is the reduction in moment capacity due to axial load. PLAN2D is written in FORTRAN and is machine independent. It has been tested on an IBM PC and a DEC MicroVAX. The program was developed in 1988.

The Dependence of Strength in Plastics upon Polymer Chain Length and Chain Orientation: An Experiment Emphasizing the Statistical Handling and Evaluation of Data.

ERIC Educational Resources Information Center

Spencer, R. Donald

1984-01-01

Describes an experiment (using plastic bags) designed to give students practical understanding on using statistics to evaluate data and how statistical treatment of experimental results can enhance their value in solving scientific problems. Students also gain insight into the orientation and structure of polymers by examining the plastic bags.…

Workflow for Integrating Mesoscale Heterogeneities in Materials Structure with Process Simulation of Titanium Alloys (Postprint)

DTIC Science & Technology

2014-10-01

offer a practical solution to calculating the grain -scale hetero- geneity present in the deformation field. Consequently, crystal plasticity models...process/performance simulation codes (e.g., crystal plasticity finite element method). 15. SUBJECT TERMS ICME; microstructure informatics; higher...iii) protocols for direct and efficient linking of materials models/databases into process/performance simulation codes (e.g., crystal plasticity

Bacterial Community Profiling of Plastic Litter in the Belgian Part of the North Sea.

PubMed

De Tender, Caroline A; Devriese, Lisa I; Haegeman, Annelies; Maes, Sara; Ruttink, Tom; Dawyndt, Peter

2015-08-18

Bacterial colonization of marine plastic litter (MPL) is known for over four decades. Still, only a few studies on the plastic colonization process and its influencing factors are reported. In this study, seafloor MPL was sampled at different locations across the Belgian part of the North Sea to study bacterial community structure using 16S metabarcoding. These marine plastic bacterial communities were compared with those of sediment and seawater, and resin pellets sampled on the beach, to investigate the origin and uniqueness of plastic bacterial communities. Plastics display great variation of bacterial community composition, while each showed significant differences from those of sediment and seawater, indicating that plastics represent a distinct environmental niche. Various environmental factors correlate with the diversity of MPL bacterial composition across plastics. In addition, intrinsic plastic-related factors such as pigment content may contribute to the differences in bacterial colonization. Furthermore, the differential abundance of known primary and secondary colonizers across the various plastics may indicate different stages of bacterial colonization, and may confound comparisons of free-floating plastics. Our studies provide insights in the factors that shape plastic bacterial colonization and shed light on the possible role of plastic as transport vehicle for bacteria through the aquatic environment.

Porous media heat transfer for injection molding

DOEpatents

Beer, Neil Reginald

2016-05-31

The cooling of injection molded plastic is targeted. Coolant flows into a porous medium disposed within an injection molding component via a porous medium inlet. The porous medium is thermally coupled to a mold cavity configured to receive injected liquid plastic. The porous medium beneficially allows for an increased rate of heat transfer from the injected liquid plastic to the coolant and provides additional structural support over a hollow cooling well. When the temperature of the injected liquid plastic falls below a solidifying temperature threshold, the molded component is ejected and collected.

Structural Transformations in Metallic Materials During Plastic Deformation

NASA Astrophysics Data System (ADS)

Zasimchuk, E.; Turchak, T.; Baskova, A.; Chausov, N.; Hutsaylyuk, V.

2017-03-01

In this paper, the structure formation during the plastic deformation of polycrystalline nickel and aluminum based alloy 2024-T3 is investigated. The possibility of the relaxation and synergetic structure formation is examined. It is shown the deformation softening to be due to the crystallization of the amorphous structure of hydrodynamics flow channels (synergetic structure) HC as micrograins and their subsequent growth. The possible mechanism of micrograins' growth is proposed. The deformation processes change the phase composition of the multiphase alloy 2024-T3. It is shown by the quantitative analysis of the structures which were deformed in different regimes of the alloy samples. A method for increasing of the fatigue life through a dynamic pre-deformation is suggested.

Beach macro-litter monitoring and floating microplastic in a coastal area of Indonesia.

PubMed

Syakti, Agung Dhamar; Bouhroum, Rafika; Hidayati, Nuning Vita; Koenawan, Chandra Joei; Boulkamh, Abdelaziz; Sulistyo, Isdy; Lebarillier, Stephanie; Akhlus, Syafsir; Doumenq, Pierre; Wong-Wah-Chung, Pascal

2017-09-15

Qualitative analysis of the structures of the polymers composing floating plastic debris was performed using attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR), and the aging of the debris was assessed by measuring carbonyl group formation on the particle surfaces. Plastic material made up >75% of the 2313 items collected during a three-year survey. The size, shape and color of the microplastic were correlated with the polymer structure. The most abundant plastic materials were polypropylene (68%) and low-density polyethylene (11%), and the predominant colors of the plastics were white, blue and green. Cilacap Bay, Indonesia, was contaminated with microplastic at a concentration of 2.5mg·m 3 . The carbonyl index demonstrated that most of the floating microplastic was only slightly degraded. This study highlights the need to raise environmental awareness through citizen science education and adopting good environmental practices. Copyright © 2017 Elsevier Ltd. All rights reserved.

Self-organization in Balanced State Networks by STDP and Homeostatic Plasticity

PubMed Central

Effenberger, Felix; Jost, Jürgen; Levina, Anna

2015-01-01

Structural inhomogeneities in synaptic efficacies have a strong impact on population response dynamics of cortical networks and are believed to play an important role in their functioning. However, little is known about how such inhomogeneities could evolve by means of synaptic plasticity. Here we present an adaptive model of a balanced neuronal network that combines two different types of plasticity, STDP and synaptic scaling. The plasticity rules yield both long-tailed distributions of synaptic weights and firing rates. Simultaneously, a highly connected subnetwork of driver neurons with strong synapses emerges. Coincident spiking activity of several driver cells can evoke population bursts and driver cells have similar dynamical properties as leader neurons found experimentally. Our model allows us to observe the delicate interplay between structural and dynamical properties of the emergent inhomogeneities. It is simple, robust to parameter changes and able to explain a multitude of different experimental findings in one basic network. PMID:26335425

Emergence of small-world structure in networks of spiking neurons through STDP plasticity.

PubMed

Basalyga, Gleb; Gleiser, Pablo M; Wennekers, Thomas

2011-01-01

In this work, we use a complex network approach to investigate how a neural network structure changes under synaptic plasticity. In particular, we consider a network of conductance-based, single-compartment integrate-and-fire excitatory and inhibitory neurons. Initially the neurons are connected randomly with uniformly distributed synaptic weights. The weights of excitatory connections can be strengthened or weakened during spiking activity by the mechanism known as spike-timing-dependent plasticity (STDP). We extract a binary directed connection matrix by thresholding the weights of the excitatory connections at every simulation step and calculate its major topological characteristics such as the network clustering coefficient, characteristic path length and small-world index. We numerically demonstrate that, under certain conditions, a nontrivial small-world structure can emerge from a random initial network subject to STDP learning.

Limitations of a morphological criterion of adaptive inference in the fossil record.

PubMed

Ravosa, Matthew J; Menegaz, Rachel A; Scott, Jeremiah E; Daegling, David J; McAbee, Kevin R

2016-11-01

Experimental analyses directly inform how an anatomical feature or complex functions during an organism's lifetime, which serves to increase the efficacy of comparative studies of living and fossil taxa. In the mammalian skull, food material properties and feeding behaviour have a pronounced influence on the development of the masticatory apparatus. Diet-related variation in loading magnitude and frequency induce a cascade of changes at the gross, tissue, cellular, protein and genetic levels, with such modelling and remodelling maintaining the integrity of oral structures vis-à-vis routine masticatory stresses. Ongoing integrative research using rabbit and rat models of long-term masticatory plasticity offers unique insight into the limitations of functional interpretations of fossilised remains. Given the general restriction of the palaeontological record to bony elements, we argue that failure to account for the disparity in the hierarchical network of responses of hard versus soft tissues may overestimate the magnitude of the adaptive divergence that is inferred from phenotypic differences. Second, we note that the developmental onset and duration of a loading stimulus associated with a given feeding behaviour can impart large effects on patterns of intraspecific variation that can mirror differences observed among taxa. Indeed, plasticity data are relevant to understanding evolutionary transformations because rabbits raised on different diets exhibit levels of morphological disparity comparable to those found between closely related primate species that vary in diet. Lastly, pronounced variation in joint form, and even joint function, can also characterise adult conspecifics that differ solely in age. In sum, our analyses emphasise the importance of a multi-site and hierarchical approach to understanding determinants of morphological variation, one which incorporates critical data on performance. © 2015 Cambridge Philosophical Society.

The evolution of γ-Mg17Al12 intermetallic compound during accumulative back extrusion and subsequent ageing treatment

NASA Astrophysics Data System (ADS)

Maghsoudi, M. H.; Zarei-Hanzaki, A.; Abedi, H. R.; Shamsolhodaei, A.

2015-11-01

Accumulative back extrusion (ABE) processing, as a novel severe plastic deformation (SPD) method, has been recently justified to be capable of modifying the microstructural characteristics of alloys. In line to its ongoing researches, the present work has been planned to study the evolution of γ-Mg17Al12 intermetallic phase during ABE and subsequent ageing treatment in a high Al-bearing Mg-Al-Zn alloy. The behaviour of γ intermetallic has been systematically examined as following points of view: (i) strain-temperature-dependent morphology changes, (ii) strain-induced dissolution, and (iii) re-ageing behaviour as a function of time and temperature. Aiming to analyse the morphology of eutectic γ compound with respect to the strain and temperature, 2D projections of effective diameter, shape factor and globularity have been made in strain/temperature graphs. The processing conditions (strain and temperature) corresponding to the desired and undesired morphologies are introduced and microstructurally explained through underlying plasticity mechanisms, i.e., 'necking-thinning-particle separation' and 'brittle fragmentation.' The former mechanism is suggested to be in relation with partial strain-induced dissolution of eutectic γ phase, leading to generation of a supersaturated solid solution. This has resulted to the observation of 'off-stoichiometry' phenomena in Mg17Al12 phase and has been justified through dislocation-assisted deformation mechanism at elevated temperature. Surprisingly, a unique re-ageing behaviour has been found for the obtained solid solutions, where a modified kinetics and morphology of γ phase precipitation were characterized. The altered precipitation behaviour is attributed to the specific defect structure achieved by SPD acting as fast diffusion channel for Al solutes.

Low vulnerability explosives (LOVEX) for mass-use warheads

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pruneda, C.; Jessop, E.; McGuire, R.

1990-03-13

There is an ongoing effort at Lawrence Livermore National Laboratory to develop explosives with a significantly lower vulnerability to battlefield environments (bullets, fragments, sympathetic detonation) than current explosives (TNT and Comp B) without sacrificing performance or increasing costs. The approach taken is to develop a composite explosive which is comprised of inexpensive fillers such as RDX, NaNO{sub 3}, Al and a low modulus binder system. The binder system uses nitroglycerin/triacetin as an energetic plasticizer. This paper discusses the experimental results to date in vulnerability, performance and processing. 7 refs., 8 figs., 6 tabs.

Correlating Fluorescence and High-Resolution Scanning Electron Microscopy (HRSEM) for the study of GABAA receptor clustering induced by inhibitory synaptic plasticity.

PubMed

Orlando, Marta; Ravasenga, Tiziana; Petrini, Enrica Maria; Falqui, Andrea; Marotta, Roberto; Barberis, Andrea

2017-10-23

Both excitatory and inhibitory synaptic contacts display activity dependent dynamic changes in their efficacy that are globally termed synaptic plasticity. Although the molecular mechanisms underlying glutamatergic synaptic plasticity have been extensively investigated and described, those responsible for inhibitory synaptic plasticity are only beginning to be unveiled. In this framework, the ultrastructural changes of the inhibitory synapses during plasticity have been poorly investigated. Here we combined confocal fluorescence microscopy (CFM) with high resolution scanning electron microscopy (HRSEM) to characterize the fine structural rearrangements of post-synaptic GABA A Receptors (GABA A Rs) at the nanometric scale during the induction of inhibitory long-term potentiation (iLTP). Additional electron tomography (ET) experiments on immunolabelled hippocampal neurons allowed the visualization of synaptic contacts and confirmed the reorganization of post-synaptic GABA A R clusters in response to chemical iLTP inducing protocol. Altogether, these approaches revealed that, following the induction of inhibitory synaptic potentiation, GABA A R clusters increase in size and number at the post-synaptic membrane with no other major structural changes of the pre- and post-synaptic elements.

[Adherence to the Ongoing Education Program for family doctors in a southeastern Brazilian state].

PubMed

d'Ávila, Luciana Souza; Assis, Lucília Nunes de; Melo, Marilene Barros de; Brant, Luiz Carlos

2014-02-01

Ongoing Health Education is a strategy for transformation of health practices, though the adherence of professionals is one of the challenges facing its implementation. Thus, the objective of this study was to investigate the factors associated with adherence of family doctors to the Ongoing Education Program in a southeastern Brazilian state from the perception of supervisors. It is a cross-sectional and quantitative study with the use of online questionnaires. Data were analyzed using the chi-square test with ongoing correction to determine the association between structure, topics, activities and difficulties of the supervisors working in Ongoing Health Education, difficulties of the physicians in Primary Health Care (PHC) and poor and good adherence to the program. Excellent medical participation was statistically related to the adequacy of physical space (p = 0.001), a multidisciplinary approach (p = 0.035) and epidemiological aspects (p = 0.043). Low adherence was associated with the inadequacy of the physical structure, difficulty understanding the methodology, less time in a supervisory position, multiple workdays, among others. A good adherence to Ongoing Health Education is a possibility for collective reconstruction of the everyday work of physicians in Primary Health Care.

Mechanical and time-dependent behavior of wood-plastic composites subjected to bending

Treesearch

S. E. Hamel; John Hermanson; S. M. Cramer

2015-01-01

The most popular use of wood–plastic composite (WPC) members in the United States has been as outdoor decking material in residential construction. If the use of these products expands into more structural applications, such as beams and joists, it is imperative that the material’s mechanical behavior be understood. Since most of the potential structural uses of this...

[Survey of plasticizers in polyvinyl chloride toys].

PubMed

Abe, Yutaka; Yamaguchi, Miku; Mutsuga, Motoh; Hirahara, Yoshichika; Kawamura, Yoko

2012-01-01

Plasticizers in 101 samples of polyvinyl chloride (PVC) toys on the Japanese market were surveyed. No phthalates were detected in designated toys, though bis(2-ethylhexyl)phthalate, diisononyl phthalate, diisobutyl phthalate, dibutyl phthalate, diisodecyl phthalate and benzyl butyl phthalate were detected in more than half of other toys. 2,2,4-Tributyl-1,3-pentanediol diisobutylate, o-acetyl tributyl citrate, adipates and diacetyl lauroyl glycerol, which are alternative plasticizers to phthalates, were detected. The results of structural analysis confirmed the presence of di(2-ethylhexyl)terephthalate, tributyl citrate, diisononyl 1,2-cyclohexanedicarboxylate and neopentyl glycol esters; these have not previonsly been reported in Japan. There appears to be a shift in plasticizers used for designated toys from phthalates to new plasticizers, and the number of different plasticizers is increasing.

Filopodia: A Rapid Structural Plasticity Substrate for Fast Learning

PubMed Central

Ozcan, Ahmet S.

2017-01-01

Formation of new synapses between neurons is an essential mechanism for learning and encoding memories. The vast majority of excitatory synapses occur on dendritic spines, therefore, the growth dynamics of spines is strongly related to the plasticity timescales. Especially in the early stages of the developing brain, there is an abundant number of long, thin and motile protrusions (i.e., filopodia), which develop in timescales of seconds and minutes. Because of their unique morphology and motility, it has been suggested that filopodia can have a dual role in both spinogenesis and environmental sampling of potential axonal partners. I propose that filopodia can lower the threshold and reduce the time to form new dendritic spines and synapses, providing a substrate for fast learning. Based on this proposition, the functional role of filopodia during brain development is discussed in relation to learning and memory. Specifically, it is hypothesized that the postnatal brain starts with a single-stage memory system with filopodia playing a significant role in rapid structural plasticity along with the stability provided by the mushroom-shaped spines. Following the maturation of the hippocampus, this highly-plastic unitary system transitions to a two-stage memory system, which consists of a plastic temporary store and a long-term stable store. In alignment with these architectural changes, it is posited that after brain maturation, filopodia-based structural plasticity will be preserved in specific areas, which are involved in fast learning (e.g., hippocampus in relation to episodic memory). These propositions aim to introduce a unifying framework for a diversity of phenomena in the brain such as synaptogenesis, pruning and memory consolidation. PMID:28676753

The expression of plasticity-related genes in an acute model of stress is modulated by chronic desipramine in a time-dependent manner within medial prefrontal cortex.

PubMed

Nava, Nicoletta; Treccani, Giulia; Müller, Heidi Kaastrup; Popoli, Maurizio; Wegener, Gregers; Elfving, Betina

2017-01-01

It is well established that stress plays a major role in the pathogenesis of neuropsychiatric diseases. Stress-induced alteration of synaptic plasticity has been hypothesized to underlie the morphological changes observed by neuroimaging in psychiatric patients in key regions such as hippocampus and prefrontal cortex (PFC). We have recently shown that a single acute stress exposure produces significant short-term alterations of structural plasticity within medial PFC. These alterations were partially prevented by previous treatment with chronic desipramine (DMI). In the present study we evaluated the effects of acute Foot-shock (FS)-stress and pre-treatment with the traditional antidepressant DMI on the gene expression of key regulators of synaptic plasticity and structure. Expression of Homer, Shank, Spinophilin, Densin-180, and the small RhoGTPase related gene Rac1 and downstream target genes, Limk1, Cofilin1 and Rock1 were investigated 1 day (1d), 7 d and 14d after FS-stress exposure. We found that DMI specifically increases the short-term expression of Spinophilin, as well as Homer and Shank family genes, and that both acute stress and DMI exert significant long-term effects on mRNA levels of genes involved in spine plasticity. These findings support the knowledge that acute FS stress and antidepressant treatment induce both rapid and sustained time-dependent alterations in structural components of synaptic plasticity in rodent medial PFC. Copyright © 2016 Elsevier B.V. and ECNP. All rights reserved.

Morphological alterations in the hippocampus of the Ts65Dn mouse model for Down Syndrome correlate with structural plasticity markers.

PubMed

Villarroya, Olga; Ballestín, Raúl; López-Hidalgo, Rosa; Mulet, Maria; Blasco-Ibáñez, José Miguel; Crespo, Carlos; Nacher, Juan; Gilabert-Juan, Javier; Varea, Emilio

2018-01-01

Down syndrome (DS) is the most common chromosomal aneuploidy. Although trisomy on chromosome 21 can display variable phenotypes, there is a common feature among all DS individuals: the presence of intellectual disability. This condition is partially attributed to abnormalities found in the hippocampus of individuals with DS and in the murine model for DS, Ts65Dn. To check if all hippocampal areas were equally affected in 4-5 month adult Ts65Dn mice, we analysed the morphology of dentate gyrus granule cells and cornu ammonis pyramidal neurons using Sholl method on Golgi-Cox impregnated neurons. Structural plasticity has been analysed using immunohistochemistry for plasticity molecules followed by densitometric analysis (Brain Derived Neurotrophic Factor (BDNF), Polysialylated form of the Neural Cell Adhesion Molecule (PSA-NCAM) and the Growth Associated Protein 43 (GAP43)). We observed an impairment in the dendritic arborisation of granule cells, but not in the pyramidal neurons in the Ts65Dn mice. When we analysed the expression of molecules related to structural plasticity in trisomic mouse hippocampus, we observed a reduction in the expression of BDNF and PSA-NCAM, and an increment in the expression of GAP43. These alterations were restricted to the regions related to dentate granule cells suggesting an interrelation. Therefore the impairment in dendritic arborisation and molecular plasticity is not a general feature of all Down syndrome principal neurons. Pharmacological manipulations of the levels of plasticity molecules could provide a way to restore granule cell morphology and function.

Plasticity - Theory and finite element applications.

NASA Technical Reports Server (NTRS)

Armen, H., Jr.; Levine, H. S.

1972-01-01

A unified presentation is given of the development and distinctions associated with various incremental solution procedures used to solve the equations governing the nonlinear behavior of structures, and this is discussed within the framework of the finite-element method. Although the primary emphasis here is on material nonlinearities, consideration is also given to geometric nonlinearities acting separately or in combination with nonlinear material behavior. The methods discussed here are applicable to a broad spectrum of structures, ranging from simple beams to general three-dimensional bodies. The finite-element analysis methods for material nonlinearity are general in the sense that any of the available plasticity theories can be incorporated to treat strain hardening or ideally plastic behavior.

Analysis of Transformation Plasticity in Steel Using a Finite Element Method Coupled with a Phase Field Model

PubMed Central

Cho, Yi-Gil; Kim, Jin-You; Cho, Hoon-Hwe; Cha, Pil-Ryung; Suh, Dong-Woo; Lee, Jae Kon; Han, Heung Nam

2012-01-01

An implicit finite element model was developed to analyze the deformation behavior of low carbon steel during phase transformation. The finite element model was coupled hierarchically with a phase field model that could simulate the kinetics and micro-structural evolution during the austenite-to-ferrite transformation of low carbon steel. Thermo-elastic-plastic constitutive equations for each phase were adopted to confirm the transformation plasticity due to the weaker phase yielding that was proposed by Greenwood and Johnson. From the simulations under various possible plastic properties of each phase, a more quantitative understanding of the origin of transformation plasticity was attempted by a comparison with the experimental observation. PMID:22558295

Embrittlement and Flow Localization in Reactor Structural Materials

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xianglin Wu; Xiao Pan; James Stubbins

2006-10-06

Many reactor components and structural members are made from metal alloys due, in large part, to their strength and ability to resist brittle fracture by plastic deformation. However, brittle fracture can occur when structural material cannot undergo extensive, or even limited, plastic deformation due to irradiation exposure. Certain irradiation conditions lead to the development of a damage microstructure where plastic flow is limited to very small volumes or regions of material, as opposed to the general plastic flow in unexposed materials. This process is referred to as flow localization or plastic instability. The true stress at the onset of neckingmore » is a constant regardless of the irradiation level. It is called 'critical stress' and this critical stress has strong temperature dependence. Interrupted tensile testes of 316L SS have been performed to investigate the microstructure evolution and competing mechanism between mechanic twinning and planar slip which are believed to be the controlling mechanism for flow localization. Deformation twinning is the major contribution of strain hardening and good ductility for low temperatures, and the activation of twinning system is determined by the critical twinning stress. Phases transform and texture analyses are also discussed in this study. Finite element analysis is carried out to complement the microstructural analysis and for the prediction of materaials performance with and without stress concentration and irradiation.« less

Expansive Cements

DTIC Science & Technology

1970-10-01

plastic or semi- plastic concrete and place no stress on the restraint provided. If, on the other hand, the ettringite continues to form rapidly for too...yield, I and wp.ter-cement ratio. Such a change in cement content may cause a greater change in expansion caracteristics than the change in...the tendency toward plastic shrinkage is increased. During the w’nter znths most structural concrete installations hare had adequate heating and no

Mutational robustness accelerates the origin of novel RNA phenotypes through phenotypic plasticity.

PubMed

Wagner, Andreas

2014-02-18

Novel phenotypes can originate either through mutations in existing genotypes or through phenotypic plasticity, the ability of one genotype to form multiple phenotypes. From molecules to organisms, plasticity is a ubiquitous feature of life, and a potential source of exaptations, adaptive traits that originated for nonadaptive reasons. Another ubiquitous feature is robustness to mutations, although it is unknown whether such robustness helps or hinders the origin of new phenotypes through plasticity. RNA is ideal to address this question, because it shows extensive plasticity in its secondary structure phenotypes, a consequence of their continual folding and unfolding, and these phenotypes have important biological functions. Moreover, RNA is to some extent robust to mutations. This robustness structures RNA genotype space into myriad connected networks of genotypes with the same phenotype, and it influences the dynamics of evolving populations on a genotype network. In this study I show that both effects help accelerate the exploration of novel phenotypes through plasticity. My observations are based on many RNA molecules sampled at random from RNA sequence space, and on 30 biological RNA molecules. They are thus not only a generic feature of RNA sequence space but are relevant for the molecular evolution of biological RNA. Copyright © 2014 Biophysical Society. Published by Elsevier Inc. All rights reserved.

Development of non-water soluble, ductile mung bean starch based edible film with oxygen barrier and heat sealability.

PubMed

Rompothi, Onjira; Pradipasena, Pasawadee; Tananuwong, Kanitha; Somwangthanaroj, Anongnat; Janjarasskul, Theeranun

2017-02-10

This research determined the effects of starch concentration (3.5-5.0%w/w), and plasticizer [glycerol (0-30%w/w) or sorbitol (0-60%w/w)] on properties of mung bean starch (MBS) films. The result showed that increasing plasticizer concentration tended to decrease tensile strength (TS), elastic modulus (EM) and oxygen permeability (OP); but increase elongation (%E), solubility, water vapor permeability (WVP) and seal strength. The extent of those changes also depended on starch concentration. Glycerol provided better plasticizer efficiency than sorbitol. A bimodal melting endotherm of retrograded structure was evident in non-plasticized film. However, only a low temperature endotherm was observed in polyol-plasticized films, indicating a plasticizer-induced structural modification. The developed ductile MBS films, (TS of 7.14±0.95 to 46.30±3.09MPa, %E of 2.46±0.21 to 56.95±4.34% and EM of 16.29±3.40 to 1428.45±148.72MPa) with an OP of 0.2397±0.0365 to 1.1520±0.1782 ccmm/m 2 daykPa and seal strength up to 422.36±7.93N/m, demonstrated in this study indicate the potential for food packaging applications. Copyright © 2016 Elsevier Ltd. All rights reserved.

Spatial and seasonal variation in diversity and structure of microbial biofilms on marine plastics in Northern European waters.

PubMed

Oberbeckmann, Sonja; Loeder, Martin G J; Gerdts, Gunnar; Osborn, A Mark

2014-11-01

Plastic pollution is now recognised as a major threat to marine environments and marine biota. Recent research highlights that diverse microbial species are found to colonise plastic surfaces (the plastisphere) within marine waters. Here, we investigate how the structure and diversity of marine plastisphere microbial community vary with respect to season, location and plastic substrate type. We performed a 6-week exposure experiment with polyethylene terephthalate (PET) bottles in the North Sea (UK) as well as sea surface sampling of plastic polymers in Northern European waters. Scanning electron microscopy revealed diverse plastisphere communities comprising prokaryotic and eukaryotic microorganisms. Denaturing gradient gel electrophoresis (DGGE) and sequencing analysis revealed that plastisphere microbial communities on PET fragments varied both with season and location and comprised of bacteria belonging to Bacteroidetes, Proteobacteria, Cyanobacteria and members of the eukaryotes Bacillariophyceae and Phaeophyceae. Polymers sampled from the sea surface mainly comprised polyethylene, polystyrene and polypropylene particles. Variation within plastisphere communities on different polymer types was observed, but communities were primarily dominated by Cyanobacteria. This research reveals that the composition of plastisphere microbial communities in marine waters varies with season, geographical location and plastic substrate type. © 2014 Federation of European Microbiological Societies. Published by John Wiley & Sons Ltd. All rights reserved.

Psychedelics Promote Structural and Functional Neural Plasticity.

PubMed

Ly, Calvin; Greb, Alexandra C; Cameron, Lindsay P; Wong, Jonathan M; Barragan, Eden V; Wilson, Paige C; Burbach, Kyle F; Soltanzadeh Zarandi, Sina; Sood, Alexander; Paddy, Michael R; Duim, Whitney C; Dennis, Megan Y; McAllister, A Kimberley; Ori-McKenney, Kassandra M; Gray, John A; Olson, David E

2018-06-12

Atrophy of neurons in the prefrontal cortex (PFC) plays a key role in the pathophysiology of depression and related disorders. The ability to promote both structural and functional plasticity in the PFC has been hypothesized to underlie the fast-acting antidepressant properties of the dissociative anesthetic ketamine. Here, we report that, like ketamine, serotonergic psychedelics are capable of robustly increasing neuritogenesis and/or spinogenesis both in vitro and in vivo. These changes in neuronal structure are accompanied by increased synapse number and function, as measured by fluorescence microscopy and electrophysiology. The structural changes induced by psychedelics appear to result from stimulation of the TrkB, mTOR, and 5-HT2A signaling pathways and could possibly explain the clinical effectiveness of these compounds. Our results underscore the therapeutic potential of psychedelics and, importantly, identify several lead scaffolds for medicinal chemistry efforts focused on developing plasticity-promoting compounds as safe, effective, and fast-acting treatments for depression and related disorders. Copyright © 2018 The Author(s). Published by Elsevier Inc. All rights reserved.

Stochastic metallic-glass cellular structures exhibiting benchmark strength.

PubMed

Demetriou, Marios D; Veazey, Chris; Harmon, John S; Schramm, Joseph P; Johnson, William L

2008-10-03

By identifying the key characteristic "structural scales" that dictate the resistance of a porous metallic glass against buckling and fracture, stochastic highly porous metallic-glass structures are designed capable of yielding plastically and inheriting the high plastic yield strength of the amorphous metal. The strengths attainable by the present foams appear to equal or exceed those by highly engineered metal foams such as Ti-6Al-4V or ferrous-metal foams at comparable levels of porosity, placing the present metallic-glass foams among the strongest foams known to date.

Probing elastically or plastically induced structural heterogeneities in bulk metallic glasses by nanoindentation pop-in tests

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Tingkun; Gao, Yanfei; Bei, Hongbin

Shear banding dynamics in bulk metallic glasses (BMGs) is manifested by the spatiotemporal evolution of strain fields which in turn depend on structural heterogeneities. The spacing of these heterogeneities, as a characteristic length scale, was determined from the analysis of nanoindentation pop-in tests using a stochastic model. Furthermore, the pre-stress by elastic bending and residual stress by plastic bending of BMG plates were found to dramatically decrease such spacings, thus increasing heterogeneity density and mechanically rejuvenating the glass structure.

Probing elastically or plastically induced structural heterogeneities in bulk metallic glasses by nanoindentation pop-in tests

DOE PAGES

Liu, Tingkun; Gao, Yanfei; Bei, Hongbin

2017-07-21

Shear banding dynamics in bulk metallic glasses (BMGs) is manifested by the spatiotemporal evolution of strain fields which in turn depend on structural heterogeneities. The spacing of these heterogeneities, as a characteristic length scale, was determined from the analysis of nanoindentation pop-in tests using a stochastic model. Furthermore, the pre-stress by elastic bending and residual stress by plastic bending of BMG plates were found to dramatically decrease such spacings, thus increasing heterogeneity density and mechanically rejuvenating the glass structure.

Structural defects in natural plastically deformed diamonds: Evidence from EPR spectroscopy

NASA Astrophysics Data System (ADS)

Mineeva, R. M.; Titkov, S. V.; Speransky, A. V.

2009-06-01

Structural defects formed as a result of plastic deformation in natural diamond crystals have been studied by EPR spectroscopy. The spectra of brown, pink-brown, black-brown, pink-purple, and gray plastically deformed diamonds of type Ia from deposits in Yakutia and the Urals were recorded. The results of EPR spectroscopy allowed us to identify various deformation centers in the structure of natural diamonds and to show that nitrogen centers were transformed under epigenetic mechanical loading. Abundant A centers, consisting of two isomorphic nitrogen atoms located in neighboring structural sites, were destroyed as a result of this process to form a series of N1, N4, W7, M2, and M3 nitrogen centers. Such centers are characterized by an anisotropic spatial distribution and a positive charge, related to the mechanism of their formation. In addition, N2 centers (probably, deformation-produced dislocations decorated by nitrogen) were formed in all plastically deformed diamonds and W10 and W35 centers (the models have not been finally ascertained) were formed in some of them. It has been established that diamonds with various types of deformation-induced color contain characteristic associations of these deformation centers. The diversity of associations of deformation centers indicates appreciable variations in conditions of disintegration of deep-seated rocks, transfer of diamonds to the Earth’s surface, and formation of kimberlitic deposits. Depending on the conditions of mechanical loading, the diamond crystals were plastically deformed by either dislocation gliding or mechanical twinning. Characteristic features of plastic deformation by dislocation gliding are the substantial prevalence of the N2 centers over other deformation centers and the occurrence of the high-spin W10 and W35 centers. The attributes of less frequent plastic deformation by mechanical twinning are unusual localization of the M2 centers and, in some cases, the N1 centers in microtwinned lamellae. Numerous data on models of deformation centers in natural diamonds, including the M2 and M3 centers, which were observed in the studied collection for the first time, are discussed.

Structural Components of Synaptic Plasticity and Memory Consolidation

PubMed Central

Bailey, Craig H.; Kandel, Eric R.; Harris, Kristen M.

2015-01-01

Consolidation of implicit memory in the invertebrate Aplysia and explicit memory in the mammalian hippocampus are associated with remodeling and growth of preexisting synapses and the formation of new synapses. Here, we compare and contrast structural components of the synaptic plasticity that underlies these two distinct forms of memory. In both cases, the structural changes involve time-dependent processes. Thus, some modifications are transient and may contribute to early formative stages of long-term memory, whereas others are more stable, longer lasting, and likely to confer persistence to memory storage. In addition, we explore the possibility that trans-synaptic signaling mechanisms governing de novo synapse formation during development can be reused in the adult for the purposes of structural synaptic plasticity and memory storage. Finally, we discuss how these mechanisms set in motion structural rearrangements that prepare a synapse to strengthen the same memory and, perhaps, to allow it to take part in other memories as a basis for understanding how their anatomical representation results in the enhanced expression and storage of memories in the brain. PMID:26134321

Plastics as structural materials for aircraft

NASA Technical Reports Server (NTRS)

Kline, G M

1937-01-01

The purpose here is to consider the mechanical characteristics of reinforced phenol-formaldehyde resin as related to its use as structural material for aircraft. Data and graphs that have appeared in the literature are reproduced to illustrate the comparative behavior of plastics and materials commonly used in aircraft construction. Materials are characterized as to density, static strength, modulus of elasticity, resistance to long-time loading, strength under repeated impact, energy absorption, corrosion resistance, and ease of fabrication.

Evolution of microstructure and mechanical properties of steel in the course of pressing-drawing

NASA Astrophysics Data System (ADS)

Lezhnev, S. N.; Volokitina, I. E.; Volokitin, A. V.

2017-11-01

The combined continuous pressing-drawing process is proposed after a comprehensive analysis of available plastic structure-forming techniques taking into account the promising trends in their development. This combination of severe plastic deformation in equal-channel step die and drawing allows one to obtain a wire of desired size and shape in the cross section with an ultrafine-grained structure after a few deformation cycles. It also enables initial workpieces of any length to be processed and, therefore, allows one to obtain finished products up to several tens of meters in length. The aim of this study is to investigate the effect of new combined pressing-drawing technique of plastic deformation on the structure and mechanical properties of the steel. These studies have shown that the proposed deformation technique has a significant advantage of the techniques currently used to manufacture a steel wire.

Energy Dissipation in Earthquake Soil Structure Interaction: The September 3rd, 2016 M5.8 Pawnee Oklahoma Earthquake

NASA Astrophysics Data System (ADS)

Yang, H.; Sinha, S. K.; Feng, Y.; Jeremic, B.

2016-12-01

The M5.8 earthquake occurred in Pawnee, Oklahoma on September 3rd 2016 is the strongest seismic event recorded in Oklahoma. Soil structure interaction (SSI) played an important role in this tragic event. As a major aspect of SSI analysis, the propagation and dissipation of seismic energy will be studied in depth, with particular focus on the ground motion recorded in this earthquake. Seismic energy propagates from seismic source to the SSI system and is dissipated within and around the SSI system. Energy dissipation with the SSI system is related to inelastic behavior of soil, rock, contact zone (foundation-soil/rock), structural components and energy dissipators. Accurate evaluation of seismic energy can be used to optimize SSI system for safety and economy. The SSI system can be designed so that majority of seismic energy is dissipated within soil and soil-foundation contact zone, away from the structure.Accurate and theoretically sound modeling of propagation and dissipation is essential to use of seismic energy for design and assessment. The rate of plastic work is defined as the product of stress and the rate of plastic strain. On the other hand, plastic dissipation is defined as a form of heat transfer. The difference between these two quantities, which has been neglected in many studies, is a plastic part of the free energy. By considering energy storage and dissipation at both micro (particle) scale and macro (continuum) scale, it can be shown that the plastic free energy is an intrinsic attribute at the continuum scale due to particle rearrangement. Proper application of thermodynamics to finite element simulations, plastic dissipation can be correctly modeled. Examples will be used to illustrate above point on both constitutive, single element and SSI model scales. In addition, propagation of seismic energy, its dissipation (timing and location) will be used to illustrate use in design and assessment.

REVERSING CYCLIC ELASTO-PLASTIC DEMANDS ON STRUCTURES DURING STRONG MOTION EARTHQUAKE EXCITATION.

USGS Publications Warehouse

Perez, V.; Brady, A.G.; Safak, E.

1986-01-01

Using the horizontal components from El Centro 1940, Taft 1952, and 4 accelerograms from the San Fernando earthquake of 2/9/71, the time history of the elasto-plastic displacement response was calculated for oscillators having periods within the range of 1 to 6 s and ductility factors within the range of 3 to 6. The Nth largest peak of the elasto-plastic response (N equals 2,4,8,16), when expressed as a percentage of maximum response (that is, N equals 1), is fairly independent of period within our period range. When considering only plastic peaks occurring, sometimes in a one-directional group of peaks, in the reverse direction from the preceding plastic peak, the amplitude of the Nth reversing plastic peak is similar to the Nth elastic peak, regardless of the ductility factor.

Composite Materials and Sandwich Structures - A Primer

DTIC Science & Technology

2010-05-01

cooling through a temperature range characteristic of the plastic. In the softened stage the plastic can be formed in a desired shape by molding or...which components are placed in a mold , and the composite is built up and worked by hand. Hybrid- A composite laminate comprised of laminae of two or...ply orientation is symmetrical about the laminate mid- plane. Thermoplastic - A plastic that can be repeatedly softened by heating, and hardened by

Localized coating removal using plastic media blasting

NASA Technical Reports Server (NTRS)

Novak, Howard L.; Wyckoff, Michael G.; Zook, Lee M.

1988-01-01

Steps taken to qualify the use of plastic media blasting for safely and effectively removing paint and other coatings from solid rocket booster aluminum structures are described. As a result of the effort, an improvement was made in the design of surface finishing equipment for processing flight hardware, in addition to a potentially patentable idea on improved plastic media composition. The general arrangement of the blast equipment and the nozzle configuration are presented.

Extracellular matrix control of dendritic spine and synapse structure and plasticity in adulthood

PubMed Central

Levy, Aaron D.; Omar, Mitchell H.; Koleske, Anthony J.

2014-01-01

Dendritic spines are the receptive contacts at most excitatory synapses in the central nervous system. Spines are dynamic in the developing brain, changing shape as they mature as well as appearing and disappearing as they make and break connections. Spines become much more stable in adulthood, and spine structure must be actively maintained to support established circuit function. At the same time, adult spines must retain some plasticity so their structure can be modified by activity and experience. As such, the regulation of spine stability and remodeling in the adult animal is critical for normal function, and disruption of these processes is associated with a variety of late onset diseases including schizophrenia and Alzheimer’s disease. The extracellular matrix (ECM), composed of a meshwork of proteins and proteoglycans, is a critical regulator of spine and synapse stability and plasticity. While the role of ECM receptors in spine regulation has been extensively studied, considerably less research has focused directly on the role of specific ECM ligands. Here, we review the evidence for a role of several brain ECM ligands and remodeling proteases in the regulation of dendritic spine and synapse formation, plasticity, and stability in adults. PMID:25368556

The Extracellular Environment of the CNS: Influence on Plasticity, Sprouting, and Axonal Regeneration after Spinal Cord Injury

PubMed Central

Forbes, Lindsey H.

2018-01-01

The extracellular environment of the central nervous system (CNS) becomes highly structured and organized as the nervous system matures. The extracellular space of the CNS along with its subdomains plays a crucial role in the function and stability of the CNS. In this review, we have focused on two components of the neuronal extracellular environment, which are important in regulating CNS plasticity including the extracellular matrix (ECM) and myelin. The ECM consists of chondroitin sulfate proteoglycans (CSPGs) and tenascins, which are organized into unique structures called perineuronal nets (PNNs). PNNs associate with the neuronal cell body and proximal dendrites of predominantly parvalbumin-positive interneurons, forming a robust lattice-like structure. These developmentally regulated structures are maintained in the adult CNS and enhance synaptic stability. After injury, however, CSPGs and tenascins contribute to the structure of the inhibitory glial scar, which actively prevents axonal regeneration. Myelin sheaths and mature adult oligodendrocytes, despite their important role in signal conduction in mature CNS axons, contribute to the inhibitory environment existing after injury. As such, unlike the peripheral nervous system, the CNS is unable to revert to a “developmental state” to aid neuronal repair. Modulation of these external factors, however, has been shown to promote growth, regeneration, and functional plasticity after injury. This review will highlight some of the factors that contribute to or prevent plasticity, sprouting, and axonal regeneration after spinal cord injury. PMID:29849554

Dynamic strength properties of the surface of an ultra-fine-grained aluminum alloy under conditions of high-speed erosion

NASA Astrophysics Data System (ADS)

Kazarinov, N. A.; Evstifeev, A. D.; Petrov, Yu. V.; Lashkov, V. A.

2016-05-01

The influence of severe plastic deformation on the material surface is investigated under highspeed erosion conditions. The AD1 aluminum alloy was tested with the structure changed by severe plastic torsional deformation.

Plastic masters-rigid templates for soft lithography.

PubMed

Desai, Salil P; Freeman, Dennis M; Voldman, Joel

2009-06-07

We demonstrate a simple process for the fabrication of rigid plastic master molds for soft lithography directly from (poly)dimethysiloxane devices. Plastics masters (PMs) provide a cost-effective alternative to silicon-based masters and can be easily replicated without the need for cleanroom facilities. We have successfully demonstrated the use of plastics micromolding to generate both single and dual-layer plastic structures, and have characterized the fidelity of the molding process. Using the PM fabrication technique, world-to-chip connections can be integrated directly into the master enabling devices with robust, well-aligned fluidic ports directly after molding. PMs provide an easy technique for the fabrication of microfluidic devices and a simple route for the scaling-up of fabrication of robust masters for soft lithography.

Evaluation of biodegradable plastics for rubber seedling applications

NASA Astrophysics Data System (ADS)

Mansor, Mohd Khairulniza; Dayang Habibah A. I., H.; Kamal, Mazlina Mustafa

2015-08-01

The main negative consequence of conventional plastics in agriculture is related to handling the wastes plasticand the associated environmental impact. Hence, a study of different types of potentially biodegradable plastics used for nursery applications have been evaluated on its mechanical,water absorption propertiesand Fourier transform infra-red (FTIR) spectroscopy. Supplied samples from different companies were designated as SF, CF and CO. Most of the polybags exhibited mechanical properties quite similar to the conventional plastics (polybag LDPE). CO polybag which is based on PVA however had extensively higher tensile strength and water absorption properties. FTIR study revealed a characteristics absorbance of conventional plastic, SF, CF and CO biodegradable polybag are associated with polyethylene, poly(butylene adipate-co-terephthalate) (PBAT), polyethylene and polyvinyl alcohol (PVA) structures respectively.

Indestructible plastic: the neuroscience of the new aging brain.

PubMed

Holman, Constance; de Villers-Sidani, Etienne

2014-01-01

In recent years, research on experience-dependent plasticity has provided valuable insight on adaptation to environmental input across the lifespan, and advances in understanding the minute cellular changes underlying the brain's capacity for self-reorganization have opened exciting new possibilities for treating illness and injury. Ongoing work in this line of inquiry has also come to deeply influence another field: cognitive neuroscience of the normal aging. This complex process, once considered inevitable or beyond the reach of treatment, has been transformed into an arena of intense investigation and strategic intervention. However, important questions remain about this characterization of the aging brain, and the assumptions it makes about the social, cultural, and biological space occupied by cognition in the older individual and body. The following paper will provide a critical examination of the move from basic experiments on the neurophysiology of experience-dependent plasticity to the growing market for (and public conception of) cognitive aging as a medicalized space for intervention by neuroscience-backed technologies. Entangled with changing concepts of normality, pathology, and self-preservation, we will argue that this new understanding, led by personalized cognitive training strategies, is approaching a point where interdisciplinary research is crucial to provide a holistic and nuanced understanding of the aging process. This new outlook will allow us to move forward in a space where our knowledge, like our new conception of the brain, is never static.

Cholinergic Plasticity of Oscillating Neuronal Assemblies in Mouse Hippocampal Slices

PubMed Central

Zylla, Maura M.; Zhang, Xiaomin; Reichinnek, Susanne; Draguhn, Andreas; Both, Martin

2013-01-01

The mammalian hippocampus expresses several types of network oscillations which entrain neurons into transiently stable assemblies. These groups of co-active neurons are believed to support the formation, consolidation and recall of context-dependent memories. Formation of new assemblies occurs during theta- and gamma-oscillations under conditions of high cholinergic activity. Memory consolidation is linked to sharp wave-ripple oscillations (SPW-R) during decreased cholinergic tone. We hypothesized that increased cholinergic tone supports plastic changes of assemblies while low cholinergic tone favors their stability. Coherent spatiotemporal network patterns were measured during SPW-R activity in mouse hippocampal slices. We compared neuronal activity within the oscillating assemblies before and after a transient phase of carbachol-induced gamma oscillations. Single units maintained their coupling to SPW-R throughout the experiment and could be re-identified after the transient phase of gamma oscillations. However, the frequency of SPW-R-related unit firing was enhanced after muscarinic stimulation. At the network level, these changes resulted in altered patterns of extracellularly recorded SPW-R waveforms. In contrast, recording of ongoing SPW-R activity without intermittent cholinergic stimulation revealed remarkably stable repetitive activation of assemblies. These results show that activation of cholinergic receptors induces plasticity at the level of oscillating hippocampal assemblies, in line with the different role of gamma- and SPW-R network activity for memory formation and –consolidation, respectively. PMID:24260462

Indestructible plastic: the neuroscience of the new aging brain

PubMed Central

Holman, Constance; de Villers-Sidani, Etienne

2014-01-01

In recent years, research on experience-dependent plasticity has provided valuable insight on adaptation to environmental input across the lifespan, and advances in understanding the minute cellular changes underlying the brain’s capacity for self-reorganization have opened exciting new possibilities for treating illness and injury. Ongoing work in this line of inquiry has also come to deeply influence another field: cognitive neuroscience of the normal aging. This complex process, once considered inevitable or beyond the reach of treatment, has been transformed into an arena of intense investigation and strategic intervention. However, important questions remain about this characterization of the aging brain, and the assumptions it makes about the social, cultural, and biological space occupied by cognition in the older individual and body. The following paper will provide a critical examination of the move from basic experiments on the neurophysiology of experience-dependent plasticity to the growing market for (and public conception of) cognitive aging as a medicalized space for intervention by neuroscience-backed technologies. Entangled with changing concepts of normality, pathology, and self-preservation, we will argue that this new understanding, led by personalized cognitive training strategies, is approaching a point where interdisciplinary research is crucial to provide a holistic and nuanced understanding of the aging process. This new outlook will allow us to move forward in a space where our knowledge, like our new conception of the brain, is never static. PMID:24782746

Plastic brain mechanisms for attaining auditory temporal order judgment proficiency.

PubMed

Bernasconi, Fosco; Grivel, Jeremy; Murray, Micah M; Spierer, Lucas

2010-04-15

Accurate perception of the order of occurrence of sensory information is critical for the building up of coherent representations of the external world from ongoing flows of sensory inputs. While some psychophysical evidence reports that performance on temporal perception can improve, the underlying neural mechanisms remain unresolved. Using electrical neuroimaging analyses of auditory evoked potentials (AEPs), we identified the brain dynamics and mechanism supporting improvements in auditory temporal order judgment (TOJ) during the course of the first vs. latter half of the experiment. Training-induced changes in brain activity were first evident 43-76 ms post stimulus onset and followed from topographic, rather than pure strength, AEP modulations. Improvements in auditory TOJ accuracy thus followed from changes in the configuration of the underlying brain networks during the initial stages of sensory processing. Source estimations revealed an increase in the lateralization of initially bilateral posterior sylvian region (PSR) responses at the beginning of the experiment to left-hemisphere dominance at its end. Further supporting the critical role of left and right PSR in auditory TOJ proficiency, as the experiment progressed, responses in the left and right PSR went from being correlated to un-correlated. These collective findings provide insights on the neurophysiologic mechanism and plasticity of temporal processing of sounds and are consistent with models based on spike timing dependent plasticity. Copyright 2010 Elsevier Inc. All rights reserved.

Local selection modifies phenotypic divergence among Rana temporaria populations in the presence of gene flow.

PubMed

Richter-Boix, Alex; Teplitsky, Céline; Rogell, Björn; Laurila, Anssi

2010-02-01

In ectotherms, variation in life history traits among populations is common and suggests local adaptation. However, geographic variation itself is not a proof for local adaptation, as genetic drift and gene flow may also shape patterns of quantitative variation. We studied local and regional variation in means and phenotypic plasticity of larval life history traits in the common frog Rana temporaria using six populations from central Sweden, breeding in either open-canopy or partially closed-canopy ponds. To separate local adaptation from genetic drift, we compared differentiation in quantitative genetic traits (Q(ST)) obtained from a common garden experiment with differentiation in presumably neutral microsatellite markers (F(ST)). We found that R. temporaria populations differ in means and plasticities of life history traits in different temperatures at local, and in F(ST) at regional scale. Comparisons of differentiation in quantitative traits and in molecular markers suggested that natural selection was responsible for the divergence in growth and development rates as well as in temperature-induced plasticity, indicating local adaptation. However, at low temperature, the role of genetic drift could not be separated from selection. Phenotypes were correlated with forest canopy closure, but not with geographical or genetic distance. These results indicate that local adaptation can evolve in the presence of ongoing gene flow among the populations, and that natural selection is strong in this system.

Adaptation and acclimatization to ocean acidification in marine ectotherms: an in situ transplant experiment with polychaetes at a shallow CO2 vent system

PubMed Central

Calosi, Piero; Rastrick, Samuel P. S.; Lombardi, Chiara; de Guzman, Heidi J.; Davidson, Laura; Jahnke, Marlene; Giangrande, Adriana; Hardege, Jörg D.; Schulze, Anja; Spicer, John I.; Gambi, Maria-Cristina

2013-01-01

Metabolic rate determines the physiological and life-history performances of ectotherms. Thus, the extent to which such rates are sensitive and plastic to environmental perturbation is central to an organism's ability to function in a changing environment. Little is known of long-term metabolic plasticity and potential for metabolic adaptation in marine ectotherms exposed to elevated pCO2. Consequently, we carried out a series of in situ transplant experiments using a number of tolerant and sensitive polychaete species living around a natural CO2 vent system. Here, we show that a marine metazoan (i.e. Platynereis dumerilii) was able to adapt to chronic and elevated levels of pCO2. The vent population of P. dumerilii was physiologically and genetically different from nearby populations that experience low pCO2, as well as smaller in body size. By contrast, different populations of Amphiglena mediterranea showed marked physiological plasticity indicating that adaptation or acclimatization are both viable strategies for the successful colonization of elevated pCO2 environments. In addition, sensitive species showed either a reduced or increased metabolism when exposed acutely to elevated pCO2. Our findings may help explain, from a metabolic perspective, the occurrence of past mass extinction, as well as shed light on alternative pathways of resilience in species facing ongoing ocean acidification. PMID:23980245

Adaptation and acclimatization to ocean acidification in marine ectotherms: an in situ transplant experiment with polychaetes at a shallow CO2 vent system.

PubMed

Calosi, Piero; Rastrick, Samuel P S; Lombardi, Chiara; de Guzman, Heidi J; Davidson, Laura; Jahnke, Marlene; Giangrande, Adriana; Hardege, Jörg D; Schulze, Anja; Spicer, John I; Gambi, Maria-Cristina

2013-01-01

Metabolic rate determines the physiological and life-history performances of ectotherms. Thus, the extent to which such rates are sensitive and plastic to environmental perturbation is central to an organism's ability to function in a changing environment. Little is known of long-term metabolic plasticity and potential for metabolic adaptation in marine ectotherms exposed to elevated pCO2. Consequently, we carried out a series of in situ transplant experiments using a number of tolerant and sensitive polychaete species living around a natural CO2 vent system. Here, we show that a marine metazoan (i.e. Platynereis dumerilii) was able to adapt to chronic and elevated levels of pCO2. The vent population of P. dumerilii was physiologically and genetically different from nearby populations that experience low pCO2, as well as smaller in body size. By contrast, different populations of Amphiglena mediterranea showed marked physiological plasticity indicating that adaptation or acclimatization are both viable strategies for the successful colonization of elevated pCO2 environments. In addition, sensitive species showed either a reduced or increased metabolism when exposed acutely to elevated pCO2. Our findings may help explain, from a metabolic perspective, the occurrence of past mass extinction, as well as shed light on alternative pathways of resilience in species facing ongoing ocean acidification.

Use-Dependent Dendritic Regrowth Is Limited after Unilateral Controlled Cortical Impact to the Forelimb Sensorimotor Cortex

PubMed Central

Jones, Theresa A.; Liput, Daniel J.; Maresh, Erin L.; Donlan, Nicole; Parikh, Toral J.; Marlowe, Dana

2012-01-01

Abstract Compensatory neural plasticity occurs in both hemispheres following unilateral cortical damage incurred by seizures, stroke, and focal lesions. Plasticity is thought to play a role in recovery of function, and is important for the utility of rehabilitation strategies. Such effects have not been well described in models of traumatic brain injury (TBI). We examined changes in immunoreactivity for neural structural and plasticity-relevant proteins in the area surrounding a controlled cortical impact (CCI) to the forelimb sensorimotor cortex (FL-SMC), and in the contralateral homotopic cortex over time (3–28 days). CCI resulted in considerable motor deficits in the forelimb contralateral to injury, and increased reliance on the ipsilateral forelimb. The density of dendritic processes, visualized with immunostaining for microtubule-associated protein-2 (MAP-2), were bilaterally decreased at all time points. Synaptophysin (SYN) immunoreactivity increased transiently in the injured hemisphere, but this reflected an atypical labeling pattern, and it was unchanged in the contralateral hemisphere compared to uninjured controls. The lack of compensatory neuronal structural plasticity in the contralateral homotopic cortex, despite behavioral asymmetries, is in contrast to previous findings in stroke models. In the cortex surrounding the injury (but not the contralateral cortex), decreases in dendrites were accompanied by neurodegeneration, as indicated by Fluoro-Jade B (FJB) staining, and increased expression of the growth-inhibitory protein Nogo-A. These studies indicate that, following unilateral CCI, the cortex undergoes neuronal structural degradation in both hemispheres out to 28 days post-injury, which may be indicative of compromised compensatory plasticity. This is likely to be an important consideration in designing therapeutic strategies aimed at enhancing plasticity following TBI. PMID:22352953

Use-dependent dendritic regrowth is limited after unilateral controlled cortical impact to the forelimb sensorimotor cortex.

PubMed

Jones, Theresa A; Liput, Daniel J; Maresh, Erin L; Donlan, Nicole; Parikh, Toral J; Marlowe, Dana; Kozlowski, Dorothy A

2012-05-01

Compensatory neural plasticity occurs in both hemispheres following unilateral cortical damage incurred by seizures, stroke, and focal lesions. Plasticity is thought to play a role in recovery of function, and is important for the utility of rehabilitation strategies. Such effects have not been well described in models of traumatic brain injury (TBI). We examined changes in immunoreactivity for neural structural and plasticity-relevant proteins in the area surrounding a controlled cortical impact (CCI) to the forelimb sensorimotor cortex (FL-SMC), and in the contralateral homotopic cortex over time (3-28 days). CCI resulted in considerable motor deficits in the forelimb contralateral to injury, and increased reliance on the ipsilateral forelimb. The density of dendritic processes, visualized with immunostaining for microtubule-associated protein-2 (MAP-2), were bilaterally decreased at all time points. Synaptophysin (SYN) immunoreactivity increased transiently in the injured hemisphere, but this reflected an atypical labeling pattern, and it was unchanged in the contralateral hemisphere compared to uninjured controls. The lack of compensatory neuronal structural plasticity in the contralateral homotopic cortex, despite behavioral asymmetries, is in contrast to previous findings in stroke models. In the cortex surrounding the injury (but not the contralateral cortex), decreases in dendrites were accompanied by neurodegeneration, as indicated by Fluoro-Jade B (FJB) staining, and increased expression of the growth-inhibitory protein Nogo-A. These studies indicate that, following unilateral CCI, the cortex undergoes neuronal structural degradation in both hemispheres out to 28 days post-injury, which may be indicative of compromised compensatory plasticity. This is likely to be an important consideration in designing therapeutic strategies aimed at enhancing plasticity following TBI.

Local yield stress statistics in model amorphous solids

NASA Astrophysics Data System (ADS)

Barbot, Armand; Lerbinger, Matthias; Hernandez-Garcia, Anier; García-García, Reinaldo; Falk, Michael L.; Vandembroucq, Damien; Patinet, Sylvain

2018-03-01

We develop and extend a method presented by Patinet, Vandembroucq, and Falk [Phys. Rev. Lett. 117, 045501 (2016), 10.1103/PhysRevLett.117.045501] to compute the local yield stresses at the atomic scale in model two-dimensional Lennard-Jones glasses produced via differing quench protocols. This technique allows us to sample the plastic rearrangements in a nonperturbative manner for different loading directions on a well-controlled length scale. Plastic activity upon shearing correlates strongly with the locations of low yield stresses in the quenched states. This correlation is higher in more structurally relaxed systems. The distribution of local yield stresses is also shown to strongly depend on the quench protocol: the more relaxed the glass, the higher the local plastic thresholds. Analysis of the magnitude of local plastic relaxations reveals that stress drops follow exponential distributions, justifying the hypothesis of an average characteristic amplitude often conjectured in mesoscopic or continuum models. The amplitude of the local plastic rearrangements increases on average with the yield stress, regardless of the system preparation. The local yield stress varies with the shear orientation tested and strongly correlates with the plastic rearrangement locations when the system is sheared correspondingly. It is thus argued that plastic rearrangements are the consequence of shear transformation zones encoded in the glass structure that possess weak slip planes along different orientations. Finally, we justify the length scale employed in this work and extract the yield threshold statistics as a function of the size of the probing zones. This method makes it possible to derive physically grounded models of plasticity for amorphous materials by directly revealing the relevant details of the shear transformation zones that mediate this process.

Influence of deformation on structural-phase state of weld material in St3 steel

NASA Astrophysics Data System (ADS)

Smirnov, Alexander; Kozlov, Eduard; Ababkov, Nicolay; Popova, Natalya; Nikonenko, Elena; Ozhiganov, Yevgeniy; Zboykova, Nadezhda; Koneva, Nina

2016-01-01

The structural-phase condition of the weld material subjected to the plastic deformation was investigated using the translucent diffraction electron microscopy method. The investigations were carried out near the joint of the weld and the base metal. The seam was done by the method of manual arc welding without artificial defects. The St3 steel was taken as the welded material. Influence of the plastic deformation on morphology, phase composition, defect structure and its parameters of weld metal was revealed. All investigations were done at the distance of 0.5 mm from the joint of the weld and the base metal at the deformation degrees from 0 to 5% and after destruction of a sample. It was established that deformation of the sample did not lead to qualitative changes in the structure (the structure is still presented by ferrite-pearlite mixture) but changed the quantitative parameters of the structure, namely, with the increase of plastic deformation a part of the pearlite component becomes more and more imperfect. In the beginning it turns into the destroyed pearlite then into ferrite, the volume fraction of pearlite is decreased. The polarization of dislocation structure takes place but it doesn't lead to the internal stresses that can destroy the sample.

[Establishment and Evaluation of a Microsurgery Course for Medical Students].

PubMed

Beier, J P; Horch, R E; Boos, A M; Taeger, C D; Breuer, G; Arkudas, A

2015-12-01

Very few microsurgical courses have been offered for medical students in Germany to date. To raise early interest in this technique, which is essential for plastic and reconstructive surgery, and to guide eligible medical students to choose plastic surgery as their specialist field, the Department of Plastic and Hand Surgery, supported by the Faculty of Medicine of the Friedrich-Alexander-University of Erlangen-Nuremberg, implemented a microsurgical course for students in 2011. This study describes the implementation of that course and evaluates its impact on the subsequent choice of the participants' specialist fields. Since the summer of 2011, the microsurgery course for medical students has taken place regularly 3 times per term. It is free of charge for participants and is guided by senior physicians of the Department of Plastic and Hand Surgery together with student tutors from the Faculty of Medicine. The arterial end-to-end anastomosis in the fresh chicken leg is used as a training model. Based on a questionnaire survey the participants were evaluated and statistically analysed regarding their course satisfaction, self-assessment of their own eligibility before and after the course, the anticipated future choice of their medical specialist field and how their choice was influenced by this course. After the successful implementation of the microsurgical course in 2011, a significant number of students were interested in microsurgery. According to the questionnaire, the level of enthusiasm was high among all participants. The self-assessment of microsurgical skills improved significantly after the course compared with the pre-course assessment. In 82% of the participants, the course had a strong positive influence on the future choice of their specialist field. The regular implementation of a microsurgical course for students in the form described here is practicable and possible without undue personnel and cost of materials. The ongoing interest among students in such an offer is enormous and the satisfaction of the participants is very high. This might be a way to recruit future plastic surgeons by raising early enthusiasm for microsurgery. These future plastic surgeons, in turn, would be given the chance to experience a very fascinating aspect of plastic surgery, which might help them to decide on their specialisation within that field at a later point in their career. © Georg Thieme Verlag KG Stuttgart · New York.

Synaptic Plasticity and Learning Behaviors Mimicked in Single Inorganic Synapses of Pt/HfOx/ZnOx/TiN Memristive System

NASA Astrophysics Data System (ADS)

Wang, Lai-Guo; Zhang, Wei; Chen, Yan; Cao, Yan-Qiang; Li, Ai-Dong; Wu, Di

2017-01-01

In this work, a kind of new memristor with the simple structure of Pt/HfOx/ZnOx/TiN was fabricated completely via combination of thermal-atomic layer deposition (TALD) and plasma-enhanced ALD (PEALD). The synaptic plasticity and learning behaviors of Pt/HfOx/ZnOx/TiN memristive system have been investigated deeply. Multilevel resistance states are obtained by varying the programming voltage amplitudes during the pulse cycling. The device conductance can be continuously increased or decreased from cycle to cycle with better endurance characteristics up to about 3 × 103 cycles. Several essential synaptic functions are simultaneously achieved in such a single double-layer of HfOx/ZnOx device, including nonlinear transmission properties, such as long-term plasticity (LTP), short-term plasticity (STP), and spike-timing-dependent plasticity. The transformation from STP to LTP induced by repetitive pulse stimulation is confirmed in Pt/HfOx/ZnOx/TiN memristive device. Above all, simple structure of Pt/HfOx/ZnOx/TiN by ALD technique is a kind of promising memristor device for applications in artificial neural network.

Detection of plasticity mechanisms in an energetic molecular crystal through shock-like 3D unidirectional compressions: A Molecular Dynamics study

NASA Astrophysics Data System (ADS)

Lafourcade, Paul; Denoual, Christophe; Maillet, Jean-Bernard

2017-06-01

TATB crystal structure consists in graphitic-like sheets arranged in the a-b plane where a, b and c define the edge vectors of the unit cell. This type of stacking provides the TATB monocrystal very anisotropic physical, chemical and mechanical properties. In order to explore which mechanisms are involved in TATB plasticity, we use a Molecular Dynamics code in which the overall deformation is prescribed as a function of time, for any deformation path. Furthermore, a computation of the Green-Lagrange strain tensor is proposed, which helps reveal various defects and plasticity mechanisms. Through prescribed large strain of shock-like deformations, a three-dimensional characterization of TATB monocrystal yield stress has been obtained, confirming the very anisotropic behavior of this energetic material. Various plasticity mechanisms are triggered during these simulations, including counter intuitive defects onset such as gliding along transveral planes containing perfect dislocations and twinning. Gliding in the a-b plane occurs systematically and does not lead to significant plastic behavior, in accordance with a previous study on dislocation core structures for this plane, based on a coupling between the Peierls-Nabarro-Galerkin method and Molecular Dynamics simulations.

Creep prediction of a layered fiberglass plastic

NASA Astrophysics Data System (ADS)

Aniskevich, K.; Korsgaard, J.; Mālmeisters, A.; Jansons, J.

1998-05-01

The results of short-term creep tests of a layered glass fiber/polyester resin plastic in tension at angles of 90, 70, and 45° to the direction of the principal fiber orientation are presented. The applicability of the principle of time-temperature analogy for the prediction of long-term creep of the composite and its structural components is revealed. The possibility of evaluating the viscoelastic properties of the composite from the properties of structural components is shown.

Structural and mechanical modifications induced on Zr-based bulk metallic glass by laser shock peening

NASA Astrophysics Data System (ADS)

Zhu, Yunhu; Fu, Jie; Zheng, Chao; Ji, Zhong

2016-12-01

In this study, surface modification of a Zr41.2Ti13.8Cu12.5Ni10Be22.5 (vit1) bulk metallic glass (BMG) has been studied in an effort to improve the mechanical properties by laser shock peening (LSP) treatment. The phase structure, mechanical properties, and microstructural evolution of the as-cast and LSP treated specimens were systematically investigated. It was found that the vit1 BMG still consisted of fully amorphous structure after LSP treatment. Measurements of the heat relaxation indicate that a large amount of free volume is introduced into vit1 BMG during LSP process. LSP treatment causes a decrease of hardness attributable to generation of free volume. The plastic deformation ability of vit1 BMG was investigated under three-point bending conditions. The results demonstrate that the plastic strain of LSP treated specimen is 1.83 times as large as that of the as-cast specimen. The effect of LSP technology on the hardness and plastic deformation ability of vit1 BMG is discussed on the basis of free volume theory. The high dense shear bands on the side surface, the increase of striations and critical shear displacement on the tensile fracture region, and more uniform dimples structure on the compressive fracture region also demonstrate that the plasticity of vit1 BMG can be enhanced by LSP.

SKILLED BIMANUAL TRAINING DRIVES MOTOR CORTEX PLASTICITY IN CHILDREN WITH UNILATERAL CEREBRAL PALSY

PubMed Central

Friel, Kathleen M.; Kuo, Hsing-Ching; Fuller, Jason; Ferre, Claudio L.; Brandão, Marina; Carmel, Jason B.; Bleyenheuft, Yannick; Gowatsky, Jaimie L.; Stanford, Arielle D.; Rowny, Stefan B.; Luber, Bruce; Bassi, Bruce; Murphy, David LK; Lisanby, Sarah H.; Gordon, Andrew M.

2015-01-01

Background Intensive bimanual therapy can improve hand function in children with unilateral spastic cerebral palsy (USCP). We compared the effects of structured bimanual skill training vs. unstructured bimanual practice on motor outcomes and motor map plasticity in children with USCP. Objective We hypothesized that structured skill training would produce greater motor map plasticity than unstructured practice. Methods Twenty children with USCP (average age 9,5; 12 males) received therapy in a day-camp-setting, 6 h/day, 5 days/week, for 3 weeks. In structured skill training (n=10), children performed progressively more difficult movements and practiced functional goals. In unstructured practice (n=10), children engaged in bimanual activities but did not practice skillful movements or functional goals. We used the Assisting Hand Assessment (AHA), Jebsen-Taylor test of Hand Function (JTTHF) and Canadian Occupational Performance Measure (COPM) to measure hand function. We used single-pulse transcranial magnetic stimulation (TMS) to map the representation of first dorsal interosseous (FDI) and flexor carpi radialis (FCR) muscles bilaterally. Results Both groups showed significant improvements in bimanual hand use (AHA; p<0.05) and hand dexterity (JTTHF; p<0.001). However, only the structured skill group showed increases in the size of the affected hand motor map and amplitudes of motor evoked potentials (p<0.01). Most children who showed the most functional improvements (COPM) had the largest changes in map size. Conclusions These findings uncover a dichotomy of plasticity: the unstructured practice group improved hand function but did not show changes in motor maps. Skill training is important for driving motor cortex plasticity in children with USCP. PMID:26867559

Visual system plasticity in mammals: the story of monocular enucleation-induced vision loss

PubMed Central

Nys, Julie; Scheyltjens, Isabelle; Arckens, Lutgarde

2015-01-01

The groundbreaking work of Hubel and Wiesel in the 1960’s on ocular dominance plasticity instigated many studies of the visual system of mammals, enriching our understanding of how the development of its structure and function depends on high quality visual input through both eyes. These studies have mainly employed lid suturing, dark rearing and eye patching applied to different species to reduce or impair visual input, and have created extensive knowledge on binocular vision. However, not all aspects and types of plasticity in the visual cortex have been covered in full detail. In that regard, a more drastic deprivation method like enucleation, leading to complete vision loss appears useful as it has more widespread effects on the afferent visual pathway and even on non-visual brain regions. One-eyed vision due to monocular enucleation (ME) profoundly affects the contralateral retinorecipient subcortical and cortical structures thereby creating a powerful means to investigate cortical plasticity phenomena in which binocular competition has no vote.In this review, we will present current knowledge about the specific application of ME as an experimental tool to study visual and cross-modal brain plasticity and compare early postnatal stages up into adulthood. The structural and physiological consequences of this type of extensive sensory loss as documented and studied in several animal species and human patients will be discussed. We will summarize how ME studies have been instrumental to our current understanding of the differentiation of sensory systems and how the structure and function of cortical circuits in mammals are shaped in response to such an extensive alteration in experience. In conclusion, we will highlight future perspectives and the clinical relevance of adding ME to the list of more longstanding deprivation models in visual system research. PMID:25972788

46 CFR 160.035-1 - Applicable specifications.

Code of Federal Regulations, 2010 CFR

2010-10-01

... Laminates, Fibrous Glass Reinforced, Marine Structural. MIL-P-19644—Plastic Foam, Molded Polystyrene..., Polyester, Low Pressure Laminating, Fire Retardant. MIL-P-21929—Plastic Material, Cellular Polyurethane, Rigid, Foam-In-Place, Low Density. (3) Federal specifications: TT-P-59—Paint, Ready-Mixed, International...

46 CFR 160.035-1 - Applicable specifications.

Code of Federal Regulations, 2011 CFR

2011-10-01

... Laminates, Fibrous Glass Reinforced, Marine Structural. MIL-P-19644—Plastic Foam, Molded Polystyrene..., Polyester, Low Pressure Laminating, Fire Retardant. MIL-P-21929—Plastic Material, Cellular Polyurethane, Rigid, Foam-In-Place, Low Density. (3) Federal specifications: TT-P-59—Paint, Ready-Mixed, International...

Colour stability of aesthetic brackets: ceramic and plastic.

PubMed

Filho, Hibernon Lopes; Maia, Lúcio Henrique; Araújo, Marcus V; Eliast, Carlos Nelson; Ruellas, Antônio Carlos O

2013-05-01

The colour stability of aesthetic brackets may differ according to their composition, morphology and surface property, which may consequently influence their aesthetic performance. To assess the colour stability of aesthetic brackets (ceramic and plastic) after simulating aging and staining. Twelve commercially manufactured ceramic brackets and four different plastic brackets were assessed. To determine possible colour change (change of E*(ab)) and the value of the NBS (National Bureau of Standards) unit system, spectrophotometric colour measurements for CIE L*, a* and b* were taken before and after the brackets were aged and stained. Statistical analysis was undertaken using a one-way ANOVA analysis of variance and a Tukey multiple comparison test (alpha = 0.05). The colour change between the various (ceramic and plastic) materials was not significant (p > 0.05), but still varied significantly (p < 0.001) between the brackets of the same composition or crystalline structure and among commercial brands. Colour stability cannot be confirmed simply by knowing the type of material and crystalline composition or structure.

Numerical modeling of the effect of heat and mass transfer in porous low-temperature heat insulation in composite material structures on the magnitude of stresses which develop

NASA Astrophysics Data System (ADS)

Kuznetsov, G. V.; Rudzinskaya, N. V.

1997-05-01

The stressed state of multilayer low-temperature heat insulation for a cryogenic fuel tank is considered. Account is taken of heat and mass transfer in foam plastic (the main heat insulation material) occurring at cryogenic temperatures. A method is developed for solving a set of differential equations and boundary conditions. Numerical studies of the main features of these processes are performed. It is established that below 200 K the stresses which arise in foam plastic markedly exceed the ultimate strength for this material. Stresses develop as a result of both a reduction in temperature and a drop in pressure in the foam plastic pores connected with material cooling. On the basis of the results obtained it is established that the combination of thermophysical processes which occur in foam plastic during cooling to cryogenic temperatures leads to changes in the stress-strained state of structure, which should be considered in planning aerospace technology.

Respiratory Muscle Plasticity

PubMed Central

Gransee, Heather M.; Mantilla, Carlos B.; Sieck, Gary C.

2014-01-01

Muscle plasticity is defined as the ability of a given muscle to alter its structural and functional properties in accordance with the environmental conditions imposed on it. As such, respiratory muscle is in a constant state of remodeling, and the basis of muscle’s plasticity is its ability to change protein expression and resultant protein balance in response to varying environmental conditions. Here, we will describe the changes of respiratory muscle imposed by extrinsic changes in mechanical load, activity, and innervation. Although there is a large body of literature on the structural and functional plasticity of respiratory muscles, we are only beginning to understand the molecular-scale protein changes that contribute to protein balance. We will give an overview of key mechanisms regulating protein synthesis and protein degradation, as well as the complex interactions between them. We suggest future application of a systems biology approach that would develop a mathematical model of protein balance and greatly improve treatments in a variety of clinical settings related to maintaining both muscle mass and optimal contractile function of respiratory muscles. PMID:23798306

Ultrasound Velocity Measurements in High-Chromium Steel Under Plastic Deformation

NASA Astrophysics Data System (ADS)

Lunev, Aleksey; Bochkareva, Anna; Barannikova, Svetlana; Zuev, Lev

2016-04-01

In the present study, the variation of the propagation velocity of ultrasound in the plastic deformation of corrosion-resistant high-chromium steel 40X13 with ferrite-carbide (delivery status), martensitic (quenched) and sorbitol (after high-temperature tempering) structures have beem studied/ It is found that each state shows its view of the loading curve. In the delivery state diagram loading is substantially parabolic throughout, while in the martensitic state contains only linear strain hardening step and in the sorbitol state the plastic flow curve is three-step. The velocity of ultrasonic surface waves (Rayleigh waves) was measured simultaneously with the registration of the loading curve in the investigated steel in tension. It is shown that the dependence of the velocity of ultrasound in active loading is determined by the law of plastic flow, that is, the staging of the corresponding diagram of loading. Structural state of the investigated steel is not only changing the type of the deformation curve under uniaxial tension, but also changes the nature of ultrasound speed of deformation.

Structuring policy problems for plastics, the environment and human health: reflections from the UK

PubMed Central

Shaxson, Louise

2009-01-01

How can we strengthen the science–policy interface for plastics, the environment and human health? In a complex policy area with multiple stakeholders, it is important to clarify the nature of the particular plastics-related issue before trying to understand how to reconcile the supply and demand for evidence in policy. This article proposes a simple problem typology to assess the fundamental characteristics of a policy issue and thus identify appropriate processes for science–policy interactions. This is illustrated with two case studies from one UK Government Department, showing how policy and science meet over the environmental problems of plastics waste in the marine environment and on land. A problem-structuring methodology helps us understand why some policy issues can be addressed through relatively linear flows of science from experts to policymakers but why others demand a more reflexive approach to brokering the knowledge between science and policy. Suggestions are given at the end of the article for practical actions that can be taken on both sides. PMID:19528061

Structuring policy problems for plastics, the environment and human health: reflections from the UK.

PubMed

Shaxson, Louise

2009-07-27

How can we strengthen the science-policy interface for plastics, the environment and human health? In a complex policy area with multiple stakeholders, it is important to clarify the nature of the particular plastics-related issue before trying to understand how to reconcile the supply and demand for evidence in policy. This article proposes a simple problem typology to assess the fundamental characteristics of a policy issue and thus identify appropriate processes for science-policy interactions. This is illustrated with two case studies from one UK Government Department, showing how policy and science meet over the environmental problems of plastics waste in the marine environment and on land. A problem-structuring methodology helps us understand why some policy issues can be addressed through relatively linear flows of science from experts to policymakers but why others demand a more reflexive approach to brokering the knowledge between science and policy. Suggestions are given at the end of the article for practical actions that can be taken on both sides.

The mechanical properties of as-grown noncubic organic molecular crystals assessed by nanoindentation

DOE PAGES

Taw, Matthew R.; Yeager, John D.; Hooks, Daniel E.; ...

2017-06-19

Organic molecular crystals are often noncubic and contain significant steric hindrance within their structure to resist dislocation motion. Plastic deformation in these systems can be imparted during processing (tableting and comminution of powders), and the defect density impacts subsequent properties and performance. This paper measured the elastic and plastic properties of representative monoclinic, orthorhombic, and triclinic molecular crystalline structures using nanoindentation of as-grown sub-mm single crystals. The variation in modulus due to in-plane rotational orientation, relative to a Berkovich tip, was approximately equal to the variation of a given crystal at a fixed orientation. The onset of plasticity occurs consistentlymore » at shear stresses between 1 and 5% of the elastic modulus in all three crystal systems, and the hardness to modulus ratio suggests conventional Berkovich tips do not generate fully self-similar plastic zones in these materials. Finally, this provides guidance for mechanical models of tableting, machining, and property assessment of molecular crystals.« less

Macroscopic tensile plasticity by scalarizating stress distribution in bulk metallic glass

PubMed Central

Gao, Meng; Dong, Jie; Huan, Yong; Wang, Yong Tian; Wang, Wei-Hua

2016-01-01

The macroscopic tensile plasticity of bulk metallic glasses (BMGs) is highly desirable for various engineering applications. However, upon yielding, plastic deformation of BMGs is highly localized into narrow shear bands and then leads to the “work softening” behaviors and subsequently catastrophic fracture, which is the major obstacle for their structural applications. Here we report that macroscopic tensile plasticity in BMG can be obtained by designing surface pore distribution using laser surface texturing. The surface pore array by design creates a complex stress field compared to the uniaxial tensile stress field of conventional glassy specimens, and the stress field scalarization induces the unusual tensile plasticity. By systematically analyzing fracture behaviors and finite element simulation, we show that the stress field scalarization can resist the main shear band propagation and promote the formation of larger plastic zones near the pores, which undertake the homogeneous tensile plasticity. These results might give enlightenment for understanding the deformation mechanism and for further improvement of the mechanical performance of metallic glasses. PMID:26902264

Light reintroduction after dark exposure reactivates plasticity in adults via perisynaptic activation of MMP-9

PubMed Central

2017-01-01

The sensitivity of ocular dominance to regulation by monocular deprivation is the canonical model of plasticity confined to a critical period. However, we have previously shown that visual deprivation through dark exposure (DE) reactivates critical period plasticity in adults. Previous work assumed that the elimination of visual input was sufficient to enhance plasticity in the adult mouse visual cortex. In contrast, here we show that light reintroduction (LRx) after DE is responsible for the reactivation of plasticity. LRx triggers degradation of the ECM, which is blocked by pharmacological inhibition or genetic ablation of matrix metalloproteinase-9 (MMP-9). LRx induces an increase in MMP-9 activity that is perisynaptic and enriched at thalamo-cortical synapses. The reactivation of plasticity by LRx is absent in Mmp9−/− mice, and is rescued by hyaluronidase, an enzyme that degrades core ECM components. Thus, the LRx-induced increase in MMP-9 removes constraints on structural and functional plasticity in the mature cortex. PMID:28875930

Brain plasticity and motor practice in cognitive aging.

PubMed

Cai, Liuyang; Chan, John S Y; Yan, Jin H; Peng, Kaiping

2014-01-01

For more than two decades, there have been extensive studies of experience-based neural plasticity exploring effective applications of brain plasticity for cognitive and motor development. Research suggests that human brains continuously undergo structural reorganization and functional changes in response to stimulations or training. From a developmental point of view, the assumption of lifespan brain plasticity has been extended to older adults in terms of the benefits of cognitive training and physical therapy. To summarize recent developments, first, we introduce the concept of neural plasticity from a developmental perspective. Secondly, we note that motor learning often refers to deliberate practice and the resulting performance enhancement and adaptability. We discuss the close interplay between neural plasticity, motor learning and cognitive aging. Thirdly, we review research on motor skill acquisition in older adults with, and without, impairments relative to aging-related cognitive decline. Finally, to enhance future research and application, we highlight the implications of neural plasticity in skills learning and cognitive rehabilitation for the aging population.

Role of the visual experience-dependent nascent proteome in neuronal plasticity

PubMed Central

Liu, Han-Hsuan; McClatchy, Daniel B; Schiapparelli, Lucio; Shen, Wanhua; Yates, John R

2018-01-01

Experience-dependent synaptic plasticity refines brain circuits during development. To identify novel protein synthesis-dependent mechanisms contributing to experience-dependent plasticity, we conducted a quantitative proteomic screen of the nascent proteome in response to visual experience in Xenopus optic tectum using bio-orthogonal metabolic labeling (BONCAT). We identified 83 differentially synthesized candidate plasticity proteins (CPPs). The CPPs form strongly interconnected networks and are annotated to a variety of biological functions, including RNA splicing, protein translation, and chromatin remodeling. Functional analysis of select CPPs revealed the requirement for eukaryotic initiation factor three subunit A (eIF3A), fused in sarcoma (FUS), and ribosomal protein s17 (RPS17) in experience-dependent structural plasticity in tectal neurons and behavioral plasticity in tadpoles. These results demonstrate that the nascent proteome is dynamic in response to visual experience and that de novo synthesis of machinery that regulates RNA splicing and protein translation is required for experience-dependent plasticity. PMID:29412139

FTIR spectroscopy supported by statistical techniques for the structural characterization of plastic debris in the marine environment: Application to monitoring studies.

PubMed

Mecozzi, Mauro; Pietroletti, Marco; Monakhova, Yulia B

2016-05-15

We inserted 190 FTIR spectra of plastic samples in a digital database and submitted it to Independent Component Analysis (ICA) to extract the "pure" plastic polymers present. These identified plastics were polypropylene (PP), high density polyethylene (HDPE), low density polyethylene (LDPE), high density polyethylene terephthalate (HDPET), low density polyethylene terephthalate (LDPET), polystyrene (PS), Nylon (NL), polyethylene oxide (OPE), and Teflon (TEF) and they were used to establish the similarity with unknown plastics using the correlation coefficient (r), and the crosscorrelation function (CC). For samples with r<0.8 we determined the Mahalanobis Distance (MD) as additional tool of identification. For instance, for the four plastic fragments found in the Carretta carretta, one plastic sample was assigned to OPE due to its r=0.87; for all the other three plastic samples, due to the r values ranging between 0.83 and0.70, the support of MD suggested LDPET and OPE as co-polymer constituents. Copyright © 2016 Elsevier Ltd. All rights reserved.

Social networks uncovered: 10 tips every plastic surgeon should know.

PubMed

Dauwe, Phillip; Heller, Justin B; Unger, Jacob G; Graham, Darrell; Rohrich, Rod J

2012-11-01

Understanding online social networks is of critical importance to the plastic surgeon. With knowledge, it becomes apparent that the numerous networks available are similar in their structure, usage, and function. The key is communication between Internet media such that one maximizes exposure to patients. This article focuses on 2 social networking platforms that we feel provide the most utility to plastic surgeons. Ten tips are provided for incorporation of Facebook and Twitter into your practice.

The effects of perturbations on the strain distribution in numerical simulations - elasto-viscoplastic modeling of boudinage as a case study

NASA Astrophysics Data System (ADS)

Peters, Max; Karrech, Ali; Poulet, Thomas; Herwegh, Marco; Regenauer-Lieb, Klaus

2014-05-01

During necking of a mechanically stiffer layer embedded in a weaker matrix, relatively large amounts of strain localize in small areas. As this deformation style appears under distinct geological conditions, necking phenomena, e.g. boudinaged veins, are associated with a variety of deformation modes. So far, there exists rather limited knowledge about the origin of instabilities and their role as precursory structures, i.e. strong localization of elastic energy affecting further plastic deformation (e.g. Regenauer-Lieb & Yuen, 1998; 2004; Karrech et al., 2011a). We applied the finite element solver ABAQUS in order to investigate the 2-D strain distribution in layers including different mechanical material properties during plane strain co-axial deformation. First, linear perturbation analyses were performed in order to evaluate the imperfection sensitivity in the elastic and viscous regimes. We perform a classical modal analysis to determine the natural mode shapes and frequencies of our geological structure during arbitrary vibrations. This analysis aims at detecting the eigenmodes of the geological structure, which are sinusoidal vibrations with geometry specific natural modal shapes and frequencies. The eigenvalues represent the nodal points where the onset of (visco)-elasto-plastic localization can initiate in the structure (Rice, 1977). The eigenmodes, eigenvalues and eigenvectors are highly sensitive to the layer-box' aspect ratio and differences in Young's moduli, or effective viscosity, respectively. Boundary effect-free strain propagation occurs for layer-box aspect ratios smaller than 1:10. Second, these preloading structures were used as seeds for imperfections in elasto-viscoplastic numerical modeling of continuous necking of a coarse-grained mineral layer embedded in a finer-grained matrix (pinch-and-swell type of boudinage), following the thermo-mechanical coupling of grain size evolutions by Herwegh et al. (in press). The evolution of symmetric necks seems to coincide with the transition from dislocation to diffusion creep dominated viscous flow with dramatic grain size reduction and grain growth from swell to neck, respectively, at relatively high extensional strains. Strain propagates from initial stress concentrations in the layer (necks) at an angle of 45° into the matrix, in form of conjugate shear band sets. Preliminary results show that pre-calculated eigenmodes (and corresponding imperfection sizes) amplify these concentrations and lead to a significant reduction of computational time for individual simulations. Moreover, the strain imperfections seeded around the pre-calculated distribution severely change the geometry of necking structures and amount of accommodated plastic strain. We reveal that elastic stress concentrations control localized visco-plastic deformation, which is expressed in the plastic strain energy increase in necking structures. These findings underline the importance of the transient (elasticity and strain hardening) deformation regimes as triggers for plastic deformation and the need for thermodynamics-based (total) energy considerations. REFERENCES Herwegh, M., Poulet, T., Karrech, A. and Regenauer-Lieb, K. (in press). From transient to steady state deformation and grain size: A thermodynamic approach using elasto-visco-plastic numerical modeling. Journal of Geophysical Research. Karrech, A., Regenauer-Lieb, K. and Poulet, T. (2011a). A Damaged visco-plasticity model for pressure and temperature sensitive geomaterials. Journal of Engineering Science 49. Regenauer-Lieb, K., Yuen, D., 1998: Rapid conversion of elastic energy into plastic shear heating during incipient necking of the lithosphere. Geophysical Research Letters, 25. Regenauer-Lieb, K., Yuen, D., 2004. Positive feedback of interacting ductile faults from coupling of equation of state, rheology and thermal-mechanics. Physics of the Earth and Planetary Interiors, 142. Rice, J. R. (1977). The localization of plastic deformation. Theoretical and Applied Mechanics. W. T. Koiter. Amsterdam, North-Holland: 207-220.

Cortical oscillatory activity and the induction of plasticity in the human motor cortex.

PubMed

McAllister, Suzanne M; Rothwell, John C; Ridding, Michael C

2011-05-01

Repetitive transcranial magnetic stimulation paradigms such as continuous theta burst stimulation (cTBS) induce long-term potentiation- and long-term depression-like plasticity in the human motor cortex. However, responses to cTBS are highly variable and may depend on the activity of the cortex at the time of stimulation. We investigated whether power in different electroencephalogram (EEG) frequency bands predicted the response to subsequent cTBS, and conversely whether cTBS had after-effects on the EEG. cTBS may utilize similar mechanisms of plasticity to motor learning; thus, we conducted a parallel set of experiments to test whether ongoing electroencephalography could predict performance of a visuomotor training task, and whether training itself had effects on the EEG. Motor evoked potentials (MEPs) provided an index of cortical excitability pre- and post-intervention. The EEG was recorded over the motor cortex pre- and post-intervention, and power spectra were computed. cTBS reduced MEP amplitudes; however, baseline power in the delta, theta, alpha or beta frequencies did not predict responses to cTBS or learning of the visuomotor training task. cTBS had no effect on delta, theta, alpha or beta power. In contrast, there was an increase in alpha power following visuomotor training that was positively correlated with changes in MEP amplitude post-training. The results suggest that the EEG is not a useful state-marker for predicting responses to plasticity-inducing paradigms. The correlation between alpha power and changes in corticospinal excitability following visuomotor training requires further investigation, but may be related to disengagement of the somatosensory system important for motor memory consolidation. © 2011 The Authors. European Journal of Neuroscience © 2011 Federation of European Neuroscience Societies and Blackwell Publishing Ltd.

Quantitative estimation of film forming polymer-plasticizer interactions by the Lorentz-Lorenz Law.

PubMed

Dredán, J; Zelkó, R; Dávid, A Z; Antal, I

2006-03-09

Molar refraction as well as refractive index has many uses. Beyond confirming the identity and purity of a compound, determination of molecular structure and molecular weight, molar refraction is also used in other estimation schemes, such as in critical properties, surface tension, solubility parameter, molecular polarizability, dipole moment, etc. In the present study molar refraction values of polymer dispersions were determined for the quantitative estimation of film forming polymer-plasticizer interactions. Information can be obtained concerning the extent of interaction between the polymer and the plasticizer from the calculation of molar refraction values of film forming polymer dispersions containing plasticizer.

Optical sensors based on plastic fibers.

PubMed

Bilro, Lúcia; Alberto, Nélia; Pinto, João L; Nogueira, Rogério

2012-01-01

The recent advances of polymer technology allowed the introduction of plastic optical fiber in sensor design. The advantages of optical metrology with plastic optical fiber have attracted the attention of the scientific community, as they allow the development of low-cost or cost competitive systems compared with conventional technologies. In this paper, the current state of the art of plastic optical fiber technology will be reviewed, namely its main characteristics and sensing advantages. Several measurement techniques will be described, with a strong focus on interrogation approaches based on intensity variation in transmission and reflection. The potential applications involving structural health monitoring, medicine, environment and the biological and chemical area are also presented.

24 CFR 3280.608 - Hangers and supports.

Code of Federal Regulations, 2010 CFR

2010-04-01

... Hangers and supports. (a) Strains and stresses. Piping in a plumbing system shall be installed without undue strains and stresses, and provision shall be made for expansion, contraction, and structural..., plastic drainage piping shall be supported at intervals not to exceed 4 feet and plastic water piping...

24 CFR 3280.608 - Hangers and supports.

Code of Federal Regulations, 2011 CFR

2011-04-01

... Hangers and supports. (a) Strains and stresses. Piping in a plumbing system shall be installed without undue strains and stresses, and provision shall be made for expansion, contraction, and structural..., plastic drainage piping shall be supported at intervals not to exceed 4 feet and plastic water piping...

Human Maternal Brain Plasticity: Adaptation to Parenting

ERIC Educational Resources Information Center

Kim, Pilyoung

2016-01-01

New mothers undergo dynamic neural changes that support positive adaptation to parenting and the development of mother-infant relationships. In this article, I review important psychological adaptations that mothers experience during pregnancy and the early postpartum period. I then review evidence of structural and functional plasticity in human…

Probabilistic analysis of structures involving random stress-strain behavior

NASA Technical Reports Server (NTRS)

Millwater, H. R.; Thacker, B. H.; Harren, S. V.

1991-01-01

The present methodology for analysis of structures with random stress strain behavior characterizes the uniaxial stress-strain curve in terms of (1) elastic modulus, (2) engineering stress at initial yield, (3) initial plastic-hardening slope, (4) engineering stress at point of ultimate load, and (5) engineering strain at point of ultimate load. The methodology is incorporated into the Numerical Evaluation of Stochastic Structures Under Stress code for probabilistic structural analysis. The illustrative problem of a thick cylinder under internal pressure, where both the internal pressure and the stress-strain curve are random, is addressed by means of the code. The response value is the cumulative distribution function of the equivalent plastic strain at the inner radius.

Rab3-GAP controls the progression of synaptic homeostasis at a late stage of vesicle release.

PubMed

Müller, Martin; Pym, Edward C G; Tong, Amy; Davis, Graeme W

2011-02-24

Homeostatic signaling systems stabilize neural function through the modulation of neurotransmitter receptor abundance, ion channel density, and presynaptic neurotransmitter release. Molecular mechanisms that drive these changes are being unveiled. In theory, molecular mechanisms may also exist to oppose the induction or expression of homeostatic plasticity, but these mechanisms have yet to be explored. In an ongoing electrophysiology-based genetic screen, we have tested 162 new mutations for genes involved in homeostatic signaling at the Drosophila NMJ. This screen identified a mutation in the rab3-GAP gene. We show that Rab3-GAP is necessary for the induction and expression of synaptic homeostasis. We then provide evidence that Rab3-GAP relieves an opposing influence on homeostasis that is catalyzed by Rab3 and which is independent of any change in NMJ anatomy. These data define roles for Rab3-GAP and Rab3 in synaptic homeostasis and uncover a mechanism, acting at a late stage of vesicle release, that opposes the progression of homeostatic plasticity. Copyright © 2011 Elsevier Inc. All rights reserved.

Applications of Acupuncture Therapy in Modulating Plasticity of Central Nervous System.

PubMed

Xiao, Ling-Yong; Wang, Xue-Rui; Yang, Ye; Yang, Jing-Wen; Cao, Yan; Ma, Si-Ming; Li, Tian-Ran; Liu, Cun-Zhi

2017-11-07

Acupuncture is widely applied for treatment of various neurological disorders. This manuscript will review the preclinical evidence of acupuncture in mediating neural plasticity, the mechanisms involved. We searched acupuncture, plasticity, and other potential related words at the following sites: PubMed, EMBASE, Cochrane Library, Chinese National Knowledge Infrastructure (CNKI), and VIP information data base. The following keywords were used: acupuncture, electroacupuncture, plasticity, neural plasticity, neuroplasticity, neurogenesis, neuroblast, stem cell, progenitor cell, BrdU, synapse, synapse structure, synaptogenesis, axon, axon regeneration, synaptic plasticity, LTP, LTD, neurotrophin, neurotrophic factor, BDNF, GDNF, VEGF, bFGF, EGF, NT-3, NT-4, NT-5, p75NTR, neurotransmitter, acetylcholine, norepinephrine, noradrenaline, dopamine, monamine. We assessed the effects of acupuncture on plasticity under pathological conditions in this review. Relevant references were reviewed and presented to reflect the effects of acupuncture on neural plasticity. The acquired literatures mainly focused on neurogenesis, alterations of synapses, neurotrophins (NTs), and neurotranimitters. Acupuncture methods mentioned in this article include manual acupuncture and electroacupuncture. The cumulative evidences demonstrated that acupuncture could induce neural plasticity in rodents exposed to cerebral ischemia. Neural plasticity mediated by acupuncture in other neural disorders, such as Alzheimer's disease, Parkinson's disease, and depression, were also investigated and there is evidence of positive role of acupuncture induced plasticity in these disorders as well. Mediation of neural plasticity by acupuncture is likely associated with its modulation on NTs and neurotransmitters. The exact mechanisms underlying acupuncture's effects on neural plasticity remain to be elucidated. Neural plasticity may be the potential bridge between acupuncture and the treatment of various neurological diseases. © 2017 International Neuromodulation Society.

Reduced ultraviolet light transmission increases insecticide longevity in protected culture raspberry production.

PubMed

Leach, Heather; Wise, John C; Isaacs, Rufus

2017-12-01

High tunnels are large protective structures used for season extension of many crops, including raspberries. These structures are often covered in plastic films to reduce and diffuse ultraviolet light transmission for pest and disease control, but this may also affect the photodegradation and efficacy of pesticides applied under these tunnels. We compared the residue levels of ten insecticides under three tunnel plastics with varying levels of UV transmission and open field conditions. Raspberry plants placed in research-scale tunnels were treated with insecticides and residues on fruit and foliage were monitored for one or two weeks in early 2015 and early and late 2016. Plastics that reduce UV transmission resulted in 50% greater residues of some insecticides compared to transparent plastics, and 60% compared to uncovered tunnels. This increased persistence of residues was evident within 1 day and remained consistently higher for up to 14 days. This pattern was demonstrated for multiple insecticides, including bifenthrin, esfenvalerate, imidacloprid, thiamethoxam, and spinosad. In contrast, the insecticide malathion degraded rapidly regardless of the plastic treatment, indicating less sensitivity to photodegradation. Bioassays using insecticide-treated leaves that were under UV-blocking plastic revealed higher mortality of the invasive fruit pest, Drosophila suzukii, compared to leaves that were uncovered. This indicates that the activity of pesticides under high tunnels covered in UV-reducing plastics may be prolonged, allowing for fewer insecticide applications and longer intervals between sprays. This information can be used to help optimize pest control in protected culture berry production. Copyright © 2017 Elsevier Ltd. All rights reserved.

Comparison of Plastic Surgery Residency Training in United States and China.

PubMed

Zheng, Jianmin; Zhang, Boheng; Yin, Yiqing; Fang, Taolin; Wei, Ning; Lineaweaver, William C; Zhang, Feng

2015-12-01

Residency training is internationally recognized as the only way for the physicians to be qualified to practice independently. China has instituted a new residency training program for the specialty of plastic surgery. Meanwhile, plastic surgery residency training programs in the United States are presently in a transition because of restricted work hours. The purpose of this study is to compare the current characteristics of plastic surgery residency training in 2 countries. Flow path, structure, curriculum, operative experience, research, and evaluation of training in 2 countries were measured. The number of required cases was compared quantitatively whereas other aspects were compared qualitatively. Plastic surgery residency training programs in 2 countries differ regarding specific characteristics. Requirements to become a plastic surgery resident in the United States are more rigorous. Ownership structure of the regulatory agency for residency training in 2 countries is diverse. Training duration in the United States is more flexible. Clinical and research training is more practical and the method of evaluation of residency training is more reasonable in the United States. The job opportunities after residency differ substantially between 2 countries. Not every resident has a chance to be an independent surgeon and would require much more training time in China than it does in the United States. Plastic surgery residency training programs in the United States and China have their unique characteristics. The training programs in the United States are more standardized. Both the United States and China may complement each other to create training programs that will ultimately provide high-quality care for all people.

Deformation Behavior and Structure of i-Al-Cu-Fe Quasicrystalline Alloy in Vicinity of Nanoindenter Indentation

NASA Astrophysics Data System (ADS)

Shalaeva, E. V.; Selyanin, I. O.; Smirnova, E. O.; Smirnov, S. V.; Novachek, D. D.

2018-02-01

The nanoindentation tests have been carried out for the quasicrystalline polygrain Al62.4Cu25.3Fe12.3 alloy with the icosahedral structure i; the load P-displacement h diagrams have been used to estimate the contributions of plastic deformation (monotonic and intermittent), and the structures of the transverse microscopic sections have been studied in the vicinity of indentations by electron microscopy. It is shown that several systems of deformation bands are formed in the elasto-plastic zone in the vicinity of the indentations along the close-packed planes of the i lattice with the five-fold and two-fold symmetry axes; the bands often begin from cracks and manifest the signs of the dislocation structure. The traces of the phase transformation with the formation of the β-phase areas are observed only in a thin layer under an indenter. The effects of intermittent deformation are up to 50% of the total inelastic deformation and are related to the plastic behavior of the quasicrystal-activation and passage of deformation bands and also the formation of undersurface micro- and nanosized cracks.

New Trends on Green Buildings: Investigation of the Feasibility of Using Plastic Members in RC Buildings with SWs

NASA Astrophysics Data System (ADS)

Arslan, M. H.; Arslan, H. D.

2017-08-01

Shear walled (SW) reinforced concrete (RC) buildings are considered to be a type of high seismic safety building. Although this structural system has an important seismic advantage, it also has some disadvantages, especially in acoustic and thermal comfort. In this study, experimental studies have been conducted on RC members produced with plastic material having circular sections to determine structural performance. RC members have been produced with and without 6 cm diameter balls to analyze the structural behaviour under loading and to investigate the thermal performance and sound absorption behaviour of the members. In the study, structural parameters have been determined for RC members such as slabs and SWs produced with and without balls to discover the feasibility of the research and discuss the findings comparatively. The results obtained from the experimental studies show that PB used in RC with suitable positions do not significantly decrease strength but improve the thermal and acoustic features. It has been also seen that using plastic balls reduce the total concrete materials.

A Constitutive Model for Strain-Controlled Strength Degradation of Rockmasses (SDR)

NASA Astrophysics Data System (ADS)

Kalos, A.; Kavvadas, M.

2017-11-01

The paper describes a continuum, rate-independent, incremental plasticity constitutive model applicable in weak rocks and heavily fractured rockmasses, where mechanical behaviour is controlled by rockmass strength rather than structural features (discontinuities). The model describes rockmass structure by a generalised Hoek-Brown Structure Envelope (SE) in the stress space. Stress paths inside the SE are nonlinear and irreversible to better simulate behaviour at strains up to peak strength and under stress reversals. Stress paths on the SE have user-controlled volume dilatancy (gradually reducing to zero at large shear strains) and can model post-peak strain softening of brittle rockmasses via a structure degradation (damage) mechanism triggered by accumulated plastic shear strains. As the SE may strain harden with plastic strains, ductile behaviour can also be modelled. The model was implemented in the Finite Element Code Simulia ABAQUS and was applied in plane strain (2D) excavation of a cylindrical cavity (tunnel) to predict convergence-confinement curves. It is shown that small-strain nonlinearity, variable volume dilatancy and post-peak hardening/softening strongly affect the predicted curves, resulting in corresponding differences of lining pressures in real tunnel excavations.

Crystal structures reveal metal-binding plasticity at the metallo-β-lactamase active site of PqqB from Pseudomonas putida

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tu, Xiongying; Latham, John A.; Klema, Valerie J.

PqqB is an enzyme involved in the biosynthesis of pyrroloquinoline quinone and a distal member of the metallo-β-lactamase (MBL) superfamily. PqqB lacks two residues in the conserved signature motif HxHxDH that makes up the key metal-chelating elements that can bind up to two metal ions at the active site of MBLs and other members of its superfamily. Here, we report crystal structures of PqqB bound to Mn2+, Mg2+, Cu2+, and Zn2+. These structures demonstrate that PqqB can still bind metal ions at the canonical MBL active site. The fact that PqqB can adapt its side chains to chelate a widemore » spectrum of metal ions with different coordination features on a uniform main chain scaffold demonstrates its metal-binding plasticity. This plasticity may provide insights into the structural basis of promiscuous activities found in ensembles of metal complexes within this superfamily. Furthermore, PqqB belongs to a small subclass of MBLs that contain an additional CxCxxC motif that binds a structural Zn2+. Our data support a key role for this motif in dimerization.« less

Two-zone elastic-plastic single shock waves in solids.

PubMed

Zhakhovsky, Vasily V; Budzevich, Mikalai M; Inogamov, Nail A; Oleynik, Ivan I; White, Carter T

2011-09-23

By decoupling time and length scales in moving window molecular dynamics shock-wave simulations, a new regime of shock-wave propagation is uncovered characterized by a two-zone elastic-plastic shock-wave structure consisting of a leading elastic front followed by a plastic front, both moving with the same average speed and having a fixed net thickness that can extend to microns. The material in the elastic zone is in a metastable state that supports a pressure that can substantially exceed the critical pressure characteristic of the onset of the well-known split-elastic-plastic, two-wave propagation. The two-zone elastic-plastic wave is a general phenomenon observed in simulations of a broad class of crystalline materials and is within the reach of current experimental techniques.

Activity-dependent plasticity in spinal cord injury

PubMed Central

Lynskey, James V.; Belanger, Adam; Jung, Ranu

2008-01-01

The adult mammalian central nervous system (CNS) is capable of considerable plasticity, both in health and disease. After spinal neurotrauma, the degrees and extent of neuroplasticity and recovery depend on multiple factors, including the level and extent of injury, postinjury medical and surgical care, and rehabilitative interventions. Rehabilitation strategies focus less on repairing lost connections and more on influencing CNS plasticity for regaining function. Current evidence indicates that strategies for rehabilitation, including passive exercise, active exercise with some voluntary control, and use of neuroprostheses, can enhance sensorimotor recovery after spinal cord injury (SCI) by promoting adaptive structural and functional plasticity while mitigating maladaptive changes at multiple levels of the neuraxis. In this review, we will discuss CNS plasticity that occurs both spontaneously after SCI and in response to rehabilitative therapies. PMID:18566941

Effect of ageing time on mechanical properties of plasticized poly(hydroxybutyrate) (PHB)

NASA Astrophysics Data System (ADS)

Farris, Giuseppe; Cinelli, Patrizia; Anguillesi, Irene; Salvadori, Sara; Coltelli, Maria-Beatrice; Lazzeri, Andrea

2014-05-01

Polyhydroxybutyrate (PHB) based materials were prepared by melt extrusion by using different plasticizers, such as poly(ethylene glycol)s (PEG)s having different molecular weight (400, 1500 and 4000). The plasticizers content was varied in the range 10-20% by weight versus the PHB polymeric matrix. The variation of tensile properties of the different samples was monitored as a function of time of ageing to study the stability of the material. The elastic modulus and tensile strength increased as a function of time, whereas the strain at break decreased. The experimental results were explained by considering both the demixing of the plasticizers and the occurring of secondary crystallization. Moreover the variation in mechanical properties was correlated to the structure and concentration of the different plasticizers employed.

Flexible crossbar-structured resistive memory arrays on plastic substrates via inorganic-based laser lift-off.

PubMed

Kim, Seungjun; Son, Jung Hwan; Lee, Seung Hyun; You, Byoung Kuk; Park, Kwi-Il; Lee, Hwan Keon; Byun, Myunghwan; Lee, Keon Jae

2014-11-26

Crossbar-structured memory comprising 32 × 32 arrays with one selector-one resistor (1S-1R) components are initially fabricated on a rigid substrate. They are transferred without mechanical damage via an inorganic-based laser lift-off (ILLO) process as a result of laser-material interaction. Addressing tests of the transferred memory arrays are successfully performed to verify mitigation of cross-talk on a plastic substrate. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Application of a substructuring technique to the problem of crack extension and closure

NASA Technical Reports Server (NTRS)

Armen, H., Jr.

1974-01-01

A substructuring technique, originally developed for the efficient reanalysis of structures, is incorporated into the methodology associated with the plastic analysis of structures. An existing finite-element computer program that accounts for elastic-plastic material behavior under cyclic loading was modified to account for changing kinematic constraint conditions - crack growth and intermittent contact of crack surfaces in two dimensional regions. Application of the analysis is presented for a problem of a centercrack panel to demonstrate the efficiency and accuracy of the technique.

Effect of small perturbations on the evolution of polycrystalline structure during plastic deformation

NASA Astrophysics Data System (ADS)

Korznikova, E. A.; Baimova, Yu. A.; Kistanov, A. A.; Dmitriev, S. V.; Korznikov, A. V.

2014-09-01

The method of molecular dynamics has been used to study the influence of initial perturbations on the evolution of grain boundaries during the shear plastic deformation of a two-dimensional polycrystalline material with nanoscale grains. It has been shown that short-term thermalization-induced small perturbations result in noticeable differences in grain boundaries configurations at the deformation of 0.05 and the polycrystal completely loses its initial grain boundary structure at the deformation of 0.4.

Molecular Mechanisms of Neuroplasticity: An Expanding Universe.

PubMed

Gulyaeva, N V

2017-03-01

Biochemical processes in synapses and other neuronal compartments underlie neuroplasticity (functional and structural alterations in the brain enabling adaptation to the environment, learning, memory, as well as rehabilitation after brain injury). This basic molecular level of brain plasticity covers numerous specific proteins (enzymes, receptors, structural proteins, etc.) participating in many coordinated and interacting signal and metabolic processes, their modulation forming a molecular basis for brain plasticity. The articles in this issue are focused on different "hot points" in the research area of biochemical mechanisms supporting neuroplasticity.

Attenuation of stress waves in single and multi-layered structures. [mitigation of elastic and plastic stress waves during spacecraft landing

NASA Technical Reports Server (NTRS)

Yang, J. C. S.; Tsui, C. Y.

1972-01-01

Analytical and experimental studies were made of the attenuation of the stress waves during passage through single and multilayer structures. The investigation included studies on elastic and plastic stress wave propagation in the composites and those on shock mitigating material characteristics such as dynamic stress-strain relations and energy absorbing properties. The results of the studies are applied to methods for reducing the stresses imposed on a spacecraft during planetary or ocean landings.

Solution NMR characterization of chemokine CXCL8/IL-8 monomer and dimer binding to glycosaminoglycans: structural plasticity mediates differential binding interactions

PubMed Central

Joseph, Prem Raj B.; Mosier, Philip D.; Desai, Umesh R.; Rajarathnam, Krishna

2015-01-01

Chemokine CXCL8/interleukin-8 (IL-8) plays a crucial role in directing neutrophils and oligodendrocytes to combat infection/injury and tumour cells in metastasis development. CXCL8 exists as monomers and dimers and interaction of both forms with glycosaminoglycans (GAGs) mediate these diverse cellular processes. However, very little is known regarding the structural basis underlying CXCL8–GAG interactions. There are conflicting reports on the affinities, geometry and whether the monomer or dimer is the high-affinity GAG ligand. To resolve these issues, we characterized the binding of a series of heparin-derived oligosaccharides [heparin disaccharide (dp2), heparin tetrasaccharide (dp4), heparin octasaccharide (dp8) and heparin 14-mer (dp14)] to the wild-type (WT) dimer and a designed monomer using solution NMR spectroscopy. The pattern and extent of binding-induced chemical shift perturbation (CSP) varied between dimer and monomer and between longer and shorter oligosaccharides. NMR-based structural models show that different interaction modes coexist and that the nature of interactions varied between monomer and dimer and oligosaccharide length. MD simulations indicate that the binding interface is structurally plastic and provided residue-specific details of the dynamic nature of the binding interface. Binding studies carried out under conditions at which WT CXCL8 exists as monomers and dimers provide unambiguous evidence that the dimer is the high-affinity GAG ligand. Together, our data indicate that a set of core residues function as the major recognition/binding site, a set of peripheral residues define the various binding geometries and that the structural plasticity of the binding interface allows multiplicity of binding interactions. We conclude that structural plasticity most probably regulates in vivo CXCL8 monomer/dimer–GAG interactions and function. PMID:26371375

Effects of crack tip plastic zone on corrosion fatigue cracking of alloy 690(TT) in pressurized water reactor environments

NASA Astrophysics Data System (ADS)

Xiao, J.; Qiu, S. Y.; Chen, Y.; Fu, Z. H.; Lin, Z. X.; Xu, Q.

2015-01-01

Alloy 690(TT) is widely used for steam generator tubes in pressurized water reactor (PWR), where it is susceptible to corrosion fatigue. In this study, the corrosion fatigue behavior of Alloy 690(TT) in simulated PWR environments was investigated. The microstructure of the plastic zone near the crack tip was investigated and labyrinth structures were observed. The relationship between the crack tip plastic zone and fatigue crack growth rates and the environment factor Fen was illuminated.

Early musical training is linked to gray matter structure in the ventral premotor cortex and auditory-motor rhythm synchronization performance.

PubMed

Bailey, Jennifer Anne; Zatorre, Robert J; Penhune, Virginia B

2014-04-01

Evidence in animals and humans indicates that there are sensitive periods during development, times when experience or stimulation has a greater influence on behavior and brain structure. Sensitive periods are the result of an interaction between maturational processes and experience-dependent plasticity mechanisms. Previous work from our laboratory has shown that adult musicians who begin training before the age of 7 show enhancements in behavior and white matter structure compared with those who begin later. Plastic changes in white matter and gray matter are hypothesized to co-occur; therefore, the current study investigated possible differences in gray matter structure between early-trained (ET; <7) and late-trained (LT; >7) musicians, matched for years of experience. Gray matter structure was assessed using voxel-wise analysis techniques (optimized voxel-based morphometry, traditional voxel-based morphometry, and deformation-based morphometry) and surface-based measures (cortical thickness, surface area and mean curvature). Deformation-based morphometry analyses identified group differences between ET and LT musicians in right ventral premotor cortex (vPMC), which correlated with performance on an auditory motor synchronization task and with age of onset of musical training. In addition, cortical surface area in vPMC was greater for ET musicians. These results are consistent with evidence that premotor cortex shows greatest maturational change between the ages of 6-9 years and that this region is important for integrating auditory and motor information. We propose that the auditory and motor interactions required by musical practice drive plasticity in vPMC and that this plasticity is greatest when maturation is near its peak.

New experimental platform to study high density laser-compressed matter

DOE PAGES

Doppner, T.; LePape, S.; Ma, T.; ...

2014-09-26

We have developed a new experimental platform at the Linac Coherent Light Source (LCLS) which combines simultaneous angularly and spectrally resolved x-ray scatteringmeasurements. This technique offers a new insights on the structural and thermodynamic properties of warm dense matter. The < 50 fs temporal duration of the x-ray pulse provides near instantaneous snapshots of the dynamics of the compression. We present a proof of principle experiment for this platform to characterize a shock-compressed plastic foil. We observe the disappearance of the plastic semi-crystal structure and the formation of a compressed liquid ion-ion correlation peak. As a result, the plasma parametersmore » of shock-compressed plastic can be measured as well, but requires an averaging over a few tens of shots.« less

Elastic, plastic, fracture analysis of masonry arches: A multi-span bridge case study

NASA Astrophysics Data System (ADS)

Lacidogna, Giuseppe; Accornero, Federico

2018-01-01

In this work a comparison is presented between elastic, plastic, and fracture analysis of the monumental arch bridge of Porta Napoli, Taranto (Italy). By means of a FEM model and applying the Mery's Method, the behavior of the curved structure under service loads is verified, while considering the Safe Theorem approach byHeyman, the ultimate carrying capacity of the structure is investigated. Moreover, by using Fracture Mechanics concepts, the damage process which takes place when the conditions assessed through linear elastic analysis are no longer valid, and before the set-in of the conditions established by means of the plastic limit analysis, is numerically analyzed. The study of these transitions returns an accurate and effective whole service life assessment of the Porta Napoli masonry arch bridge.

[Application of biodegradable plastic film to reduce plastic film residual pollution in Chinese agriculture].

PubMed

Yan, Changrong; He, Wenqing; Xue, Yinghao; Liu, Enke; Liu, Qin

2016-06-25

Plastic film has become an important agriculture production material in recent years. Over the past three decades, the amount and application area of plastic film have increased steadily, and in 2014, which are 1.4 million tons and more than 180 million hm² respectively. It plays a key role for ensuring the supply of agricultural goods in China. Meanwhile, plastic film residual pollution becomes more and more serious, and in some regions, the amount of plastic film residues has reached over 250 kg/hm². In part of the Northwest region, soil structure of farmland has been destroyed by plastic film residues and then crop growth and farming operations were suppressed. It is recognized as a good choice to replace plastic film with biodegradable plastic film, an effective measure to solve the plastic film residue pollution. Now, it is in a critical stage of study and assessment of biodegradable plastic film in China and fortunately some biodegradable plastic films show effects in the production of potatoes, peanuts and tobacco. Overall, a series of challenges has still been faced by the biodegradable plastic film, mainly including improving the quality of biodegradable plastic products, such as tensile strength, flexibility, improving the controllability of rupture and degradation, enhancing the ability of increasing soil temperature and preserving soil moisture, and to satisfy the demand of crops production with mulching. In addition, it is essential to reduce the cost of the biodegradable film and promote the application of biodegradable film on large-scale. With the development of biodegradable plastic technology and agricultural production environment, the application of the biodegradable film will have a good future.

Bi-Metallic Composite Structures With Designed Internal Residual Stress Field

NASA Technical Reports Server (NTRS)

Brice, Craig A.

2014-01-01

Shape memory alloys (SMA) have a unique ability to recover small amounts of plastic strain through a temperature induced phase change. For these materials, mechanical displacement can be accomplished by heating the structure to induce a phase change, through which some of the plastic strain previously introduced to the structure can be reversed. This paper introduces a concept whereby an SMA phase is incorporated into a conventional alloy matrix in a co-continuous reticulated arrangement forming a bi-metallic composite structure. Through memory activation of the mechanically constrained SMA phase, a controlled residual stress field is developed in the interior of the structure. The presented experimental data show that the memory activation of the SMA composite component significantly changes the residual stress distribution in the overall structure. Designing the structural arrangement of the two phases to produce a controlled residual stress field could be used to create structures that have much improved durability and damage tolerance properties.

Characterizing wood-plastic composites via data-driven methodologies

Treesearch

John G. Michopoulos; John C. Hermanson; Robert Badaliance

2007-01-01

The recent increase of wood-plastic composite materials in various application areas has underlined the need for an efficient and robust methodology to characterize their nonlinear anisotropic constitutive behavior. In addition, the multiplicity of various loading conditions in structures utilizing these materials further increases the need for a characterization...

Synthesis and application of a natural plasticizer based on cardanol for poly(vinyl chloride)

USDA-ARS?s Scientific Manuscript database

A natural plasticizer with multifunctional groups, similar in structure to phthalates, cardanol derivatives glycidyl ether (CGE) was synthesized from cardanol by a two-step modification process and characterized by FT-IR, 1-HNMR, and 13-CNMR. The resulting product was incorporated to PVC (CGE/PVC), ...

Microstructure and Plastic Deformation of the As-Welded Invar Fusion Zones

NASA Astrophysics Data System (ADS)

Yao, D. J.; Zhou, D. R.; Xu, P. Q.; Lu, F. G.

2017-05-01

The as-welded Invar fusion zones were fabricated between cemented carbides and carbon steel using a Fe-Ni Invar interlayer and laser welding method. Three regions in the as-welded Invar fusion zones were defined to compare microstructures, and these were characterized and confirmed by scanning electron microscopy and X-ray diffractometry. The structure and plastic deformation mechanism for initial Invar Fe-Ni alloys and the as-welded Invar fusion zones are discussed. (1) After undergoing high-temperature thermal cycles, the microstructure of the as-welded Invar fusion zones contains γ-(Fe, Ni) solid solution (nickel dissolving in γ-Fe) with a face-centered cubic (fcc) crystal structure and mixed carbides (eutectic colonies, mixed carbides between two adjacent grains). The mixed carbides exhibited larger, coarser eutectic microstructures with a decrease in welding speed and an increase in heat input. (2) The structure of the initial Invar and the as-welded Invar is face-centered cubic γ-(Fe, Ni). (3) The as-welded Invar has a larger plastic deformation than initial Invar with an increase in local strain field and dislocation density. Slip deformation is propagated along the (111) plane. This finding helps us to understand microstructure and the formation of dislocation and plastic deformation when the Invar Fe-Ni alloy undergoes a high-temperature process.

Bidirectional synaptic structural plasticity after chronic cocaine administration occurs through Rap1 small GTPase signaling

PubMed Central

Cahill, Michael E.; Bagot, Rosemary C.; Gancarz, Amy M.; Walker, Deena M.; Sun, HaoSheng; Wang, Zi-Jun; Heller, Elizabeth A.; Feng, Jian; Kennedy, Pamela J.; Koo, Ja Wook; Cates, Hannah M.; Neve, Rachael L.; Shen, Li; Dietz, David M.

2016-01-01

Summary Dendritic spines are the sites of most excitatory synapses in the CNS, and opposing alterations in the synaptic structure of medium spiny neurons (MSNs) of the nucleus accumbens, a primary brain reward region, are seen at early vs. late time points after cocaine administration. Here we investigate the time-dependent molecular and biochemical processes that regulate this bidirectional synaptic structural plasticity of NAc MSNs and associated changes in cocaine reward in response to chronic cocaine exposure. Our findings reveal key roles for the bidirectional synaptic expression of the Rap1b small GTPase and an associated local-synaptic protein translation network in this process. The transcriptional mechanisms and pathway-specific inputs to NAc that regulate Rap1b expression are also characterized. Collectively, these findings provide a precise mechanism by which nuclear to synaptic interactions induce “metaplasticity” in NAc MSNs, and we reveal the specific effects of this plasticity on reward behavior in a brain circuit-specific manner. PMID:26844834

Multiple solvent crystal structures of ribonuclease A: An assessment of the method

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dechene, Michelle; Wink, Glenna; Smith, Mychal

2010-11-12

The multiple solvent crystal structures (MSCS) method uses organic solvents to map the surfaces of proteins. It identifies binding sites and allows for a more thorough examination of protein plasticity and hydration than could be achieved by a single structure. The crystal structures of bovine pancreatic ribonuclease A (RNAse A) soaked in the following organic solvents are presented: 50% dioxane, 50% dimethylformamide, 70% dimethylsulfoxide, 70% 1,6-hexanediol, 70% isopropanol, 50% R,S,R-bisfuran alcohol, 70% t-butanol, 50% trifluoroethanol, or 1.0M trimethylamine-N-oxide. This set of structures is compared with four sets of crystal structures of RNAse A from the protein data bank (PDB) andmore » with the solution NMR structure to assess the validity of previously untested assumptions associated with MSCS analysis. Plasticity from MSCS is the same as from PDB structures obtained in the same crystal form and deviates only at crystal contacts when compared to structures from a diverse set of crystal environments. Furthermore, there is a good correlation between plasticity as observed by MSCS and the dynamic regions seen by NMR. Conserved water binding sites are identified by MSCS to be those that are conserved in the sets of structures taken from the PDB. Comparison of the MSCS structures with inhibitor-bound crystal structures of RNAse A reveals that the organic solvent molecules identify key interactions made by inhibitor molecules, highlighting ligand binding hot-spots in the active site. The present work firmly establishes the relevance of information obtained by MSCS.« less

Inelastic behavior of structural components

NASA Technical Reports Server (NTRS)

Hussain, N.; Khozeimeh, K.; Toridis, T. G.

1980-01-01

A more accurate procedure was developed for the determination of the inelastic behavior of structural components. The actual stress-strain curve for the mathematical of the structure was utilized to generate the force-deformation relationships for the structural elements, rather than using simplified models such as elastic-plastic, bilinear and trilinear approximations. relationships were generated for beam elements with various types of cross sections. In the generational of these curves, stress or load reversals, kinematic hardening and hysteretic behavior were taken into account. Intersections between loading and unloading branches were determined through an iterative process. Using the inelastic properties obtained, the plastic static response of some simple structural systems composed of beam elements was computed. Results were compared with known solutions, indicating a considerable improvement over response predictions obtained by means of simplified approximations used in previous investigations.

Refractive index sensor based on plastic optical fiber with tapered structure.

PubMed

De-Jun, Feng; Guan-Xiu, Liu; Xi-Lu, Liu; Ming-Shun, Jiang; Qing-Mei, Sui

2014-04-01

This work reports a refractive index sensor made of plastic optical fiber (POF) with tapered structure. Transmission loss is measured when the external environment's refractive index changes from 1.33 to 1.41. Three wavelengths (532, 633, and 780 nm) are used to evaluate the sensitivity of the sensor, and results indicate that 633 nm is the best sensing wavelength due to the increased levels of sensitivity achieved at this wavelength. A biconical sensing structure is designed to enhance the sensitivity of the sensor. A sensitivity of 950 μW/RIU at 633 nm is obtained for a biconical sensing structure when launched power is 1 mW. Due to its sensitivity to the refractive index and simple construction, POF with tapered structure has potential applications in the biosensing field.

The continuing conundrum of the LEA proteins.

PubMed

Tunnacliffe, Alan; Wise, Michael J

2007-10-01

Research into late embryogenesis abundant (LEA) proteins has been ongoing for more than 20 years but, although there is a strong association of LEA proteins with abiotic stress tolerance particularly dehydration and cold stress, for most of that time, their function has been entirely obscure. After their initial discovery in plant seeds, three major groups (numbered 1, 2 and 3) of LEA proteins have been described in a range of different plants and plant tissues. Homologues of groups 1 and 3 proteins have also been found in bacteria and in certain invertebrates. In this review, we present some new data, survey the biochemistry, biophysics and bioinformatics of the LEA proteins and highlight several possible functions. These include roles as antioxidants and as membrane and protein stabilisers during water stress, either by direct interaction or by acting as molecular shields. Along with other hydrophilic proteins and compatible solutes, LEA proteins might also serve as "space fillers" to prevent cellular collapse at low water activities. This multifunctional capacity of the LEA proteins is probably attributable in part to their structural plasticity, as they are largely lacking in secondary structure in the fully hydrated state, but can become more folded during water stress and/or through association with membrane surfaces. The challenge now facing researchers investigating these enigmatic proteins is to make sense of the various in vitro defined functions in the living cell: Are the LEA proteins truly multi-talented, or are they still just misunderstood?

Evaluation of Inelastic Constitutive Models for Nonlinear Structural Analysis

NASA Technical Reports Server (NTRS)

Kaufman, A.

1983-01-01

The influence of inelastic material models on computed stress-strain states, and therefore predicted lives, was studied for thermomechanically loaded structures. Nonlinear structural analyses were performed on a fatigue specimen which was subjected to thermal cycling in fluidized beds and on a mechanically load cycled benchmark notch specimen. Four incremental plasticity creep models (isotropic, kinematic, combined isotropic-kinematic, combined plus transient creep) were exercised. Of the plasticity models, kinematic hardening gave results most consistent with experimental observations. Life predictions using the computed strain histories at the critical location with a Strainrange Partitioning approach considerably overpredicted the crack initiation life of the thermal fatigue specimen.

Assessment of compressive failure process of cortical bone materials using damage-based model.

PubMed

Ng, Theng Pin; R Koloor, S S; Djuansjah, J R P; Abdul Kadir, M R

2017-02-01

The main failure factors of cortical bone are aging or osteoporosis, accident and high energy trauma or physiological activities. However, the mechanism of damage evolution coupled with yield criterion is considered as one of the unclear subjects in failure analysis of cortical bone materials. Therefore, this study attempts to assess the structural response and progressive failure process of cortical bone using a brittle damaged plasticity model. For this reason, several compressive tests are performed on cortical bone specimens made of bovine femur, in order to obtain the structural response and mechanical properties of the material. Complementary finite element (FE) model of the sample and test is prepared to simulate the elastic-to-damage behavior of the cortical bone using the brittle damaged plasticity model. The FE model is validated in a comparative method using the predicted and measured structural response as load-compressive displacement through simulation and experiment. FE results indicated that the compressive damage initiated and propagated at central region where maximum equivalent plastic strain is computed, which coincided with the degradation of structural compressive stiffness followed by a vast amount of strain energy dissipation. The parameter of compressive damage rate, which is a function dependent on damage parameter and the plastic strain is examined for different rates. Results show that considering a similar rate to the initial slope of the damage parameter in the experiment would give a better sense for prediction of compressive failure. Copyright © 2016 Elsevier Ltd. All rights reserved.

Neuronal plasticity and seasonal reproduction in sheep

PubMed Central

Lehman, Michael N.; Ladha, Zamin; Coolen, Lique M.; Hileman, Stanley M.; Connors, John M.; Goodman, Robert L.

2010-01-01

Seasonal reproduction represents a naturally occurring example of functional plasticity in the adult brain since it reflects changes in neuroendocrine pathways controlling GnRH secretion and, in particular, the responsiveness of GnRH neurons to estradiol negative feedback. Structural plasticity within this neural circuitry may, in part, be responsible for seasonal switches in the negative feedback control of GnRH secretion that underlies annual reproductive transitions. In this paper, we review evidence for structural changes in the circuitry responsible for seasonal inhibition of GnRH secretion in sheep. These include changes in synaptic inputs onto GnRH neurons, as well as onto dopamine neurons in the A15 cell group, a nucleus that play a key role in estradiol negative feedback. We also present preliminary data suggesting a role for neurotrophins and neurotrophin receptors as an early mechanistic step in the plasticity that accompanies seasonal reproductive transitions in the sheep. Finally, we review recent evidence suggesting that kisspeptin cells of the arcuate nucleus constitute a critical intermediary in the control of seasonal reproduction. While a majority of the data for a role of neuronal plasticity in seasonal reproduction has come from the sheep model, the players and principles are likely to have relevance for reproduction in a wide variety of vertebrates, including humans, and in both health and disease. PMID:21143669

Attractor Structures of Signaling Networks: Consequences of Different Conformational Barcode Dynamics and Their Relations to Network-Based Drug Design.

PubMed

Szalay, Kristóf Z; Nussinov, Ruth; Csermely, Peter

2014-06-01

Conformational barcodes tag functional sites of proteins and are decoded by interacting molecules transmitting the incoming signal. Conformational barcodes are modified by all co-occurring allosteric events induced by post-translational modifications, pathogen, drug binding, etc. We argue that fuzziness (plasticity) of conformational barcodes may be increased by disordered protein structures, by integrative plasticity of multi-phosphorylation events, by increased intracellular water content (decreased molecular crowding) and by increased action of molecular chaperones. This leads to increased plasticity of signaling and cellular networks. Increased plasticity is both substantiated by and inducing an increased noise level. Using the versatile network dynamics tool, Turbine (www.turbine.linkgroup.hu), here we show that the 10 % noise level expected in cellular systems shifts a cancer-related signaling network of human cells from its proliferative attractors to its largest, apoptotic attractor representing their health-preserving response in the carcinogen containing and tumor suppressor deficient environment modeled in our study. Thus, fuzzy conformational barcodes may not only make the cellular system more plastic, and therefore more adaptable, but may also stabilize the complex system allowing better access to its largest attractor. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Regulation of cellular plasticity and resilience by mood stabilizers: the role of AMPA receptor trafficking

PubMed Central

Du, Jing; Quiroz, Jorge A.; Gray, Neil A.; Szabo, Steve T.; Zarate Jr, Carlos A.; Manji, Husseini K.

2004-01-01

There is increasing evidence from a variety of sources that severe mood disorders are associated with regional reductions in brain volume, as well as reductions in the number, size, and density of glia and neurons in discrete brain areas. Although the precise pathophysiology underlying these morphometric changes remains to be fully elucidated, the data suggest that severe mood disorders are associated with impairments of structural plasticity and cellular resilience. In this context, it is noteworthy that a growing body of data suggests that the glutamaiergic system (which is known to play a major role in neuronal plasticity and cellular resilience) may be involved in the pathophysiology and treatment of mood disorders. Glutamate α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) GluR1 receptor trafficking plays a critical role in regulating various forms of neural plasticity. It is thus noteworthy that recent studies have shown that structurally dissimilar mood stabilizers lithium and valproate regulate GluR1 receptor subunit trafficking and localization at synapses. These studies suggest that regulation of glutamatergically mediated synaptic plasticity may play a role in the treatment of mood disorders, and raises the possibility that agents more directly affecting synaptic GluR1 represent novel therapies for these devastating illnesses. PMID:22034247

Low-frequency transcranial magnetic stimulation is beneficial for enhancing synaptic plasticity in the aging brain.

PubMed

Zhang, Zhan-Chi; Luan, Feng; Xie, Chun-Yan; Geng, Dan-Dan; Wang, Yan-Yong; Ma, Jun

2015-06-01

In the aging brain, cognitive function gradually declines and causes a progressive reduction in the structural and functional plasticity of the hippocampus. Transcranial magnetic stimulation is an emerging and novel neurological and psychiatric tool used to investigate the neurobiology of cognitive function. Recent studies have demonstrated that low-frequency transcranial magnetic stimulation (≤1 Hz) ameliorates synaptic plasticity and spatial cognitive deficits in learning-impaired mice. However, the mechanisms by which this treatment improves these deficits during normal aging are still unknown. Therefore, the current study investigated the effects of transcranial magnetic stimulation on the brain-derived neurotrophic factor signal pathway, synaptic protein markers, and spatial memory behavior in the hippocampus of normal aged mice. The study also investigated the downstream regulator, Fyn kinase, and the downstream effectors, synaptophysin and growth-associated protein 43 (both synaptic markers), to determine the possible mechanisms by which transcranial magnetic stimulation regulates cognitive capacity. Transcranial magnetic stimulation with low intensity (110% average resting motor threshold intensity, 1 Hz) increased mRNA and protein levels of brain-derived neurotrophic factor, tropomyosin receptor kinase B, and Fyn in the hippocampus of aged mice. The treatment also upregulated the mRNA and protein expression of synaptophysin and growth-associated protein 43 in the hippocampus of these mice. In conclusion, brain-derived neurotrophic factor signaling may play an important role in sustaining and regulating structural synaptic plasticity induced by transcranial magnetic stimulation in the hippocampus of aging mice, and Fyn may be critical during this regulation. These responses may change the structural plasticity of the aging hippocampus, thereby improving cognitive function.

Sustainable and Selective Separation of PVC and ABS from a WEEE Plastic Mixture Using Microwave and/or Mild-Heat Treatment with Froth Flotation.

PubMed

Thanh Truc, Nguyen Thi; Lee, Byeong-Kyu

2016-10-04

This study reports simple, selective, and sustainable separation of chlorinated plastic (polyvinyl chloride, PVC) and acrylonitrile butadiene styrene (ABS) containing brominated flame retardants (BFRs) from mixed waste electrical and electronic equipment (WEEE) plastics using microwave and/or mild-heat treatment. Microwave treatment after plastic coating with powdered activated carbon (PAC) selectively increased the hydrophilicity of the PVC surface, which facilitated PVC separation (100% recovery and purity) from the WEEE plastic mixture under the optimum flotation conditions. A further mild-heat treatment for 100 s facilitated selective separation with the highest recovery and purity (100%) of PAC-coated ABS containing BFRs from the remaining plastic mixture due to selective formation of a twisted structure with a lower density than water and the untreated ABS. Mild-heat treatment only of PAC-coated WEEE plastic mixture resulted in successful recovery of (100%) the ABS and PVC. However, the recovered PVC had slightly reduced purity (96.8%) as compared to that obtained using the combined heat and microwave treatments. The combination of both treatments with flotation facilitated selective and sustainable separation of PVC and ABS from WEEE plastics to improve their recycling quality.

A neuromorphic implementation of multiple spike-timing synaptic plasticity rules for large-scale neural networks

PubMed Central

Wang, Runchun M.; Hamilton, Tara J.; Tapson, Jonathan C.; van Schaik, André

2015-01-01

We present a neuromorphic implementation of multiple synaptic plasticity learning rules, which include both Spike Timing Dependent Plasticity (STDP) and Spike Timing Dependent Delay Plasticity (STDDP). We present a fully digital implementation as well as a mixed-signal implementation, both of which use a novel dynamic-assignment time-multiplexing approach and support up to 226 (64M) synaptic plasticity elements. Rather than implementing dedicated synapses for particular types of synaptic plasticity, we implemented a more generic synaptic plasticity adaptor array that is separate from the neurons in the neural network. Each adaptor performs synaptic plasticity according to the arrival times of the pre- and post-synaptic spikes assigned to it, and sends out a weighted or delayed pre-synaptic spike to the post-synaptic neuron in the neural network. This strategy provides great flexibility for building complex large-scale neural networks, as a neural network can be configured for multiple synaptic plasticity rules without changing its structure. We validate the proposed neuromorphic implementations with measurement results and illustrate that the circuits are capable of performing both STDP and STDDP. We argue that it is practical to scale the work presented here up to 236 (64G) synaptic adaptors on a current high-end FPGA platform. PMID:26041985

Durability Characteristics Analysis of Plastic Worm Wheel with Glass Fiber Reinforced Polyamide.

PubMed

Kim, Gun-Hee; Lee, Jeong-Won; Seo, Tae-Il

2013-05-10

Plastic worm wheel is widely used in the vehicle manufacturing field because it is favorable for weight lightening, vibration and noise reduction, as well as corrosion resistance. However, it is very difficult for general plastics to secure the mechanical properties that are required for vehicle gears. If the plastic resin is reinforced by glass fiber in the fabrication process of plastic worm wheel, it is possible to achieve the mechanical properties of metallic material levels. In this study, the mechanical characteristic analysis of the glass-reinforced plastic worm wheel, according to the contents of glass fiber, is performed by analytic and experimental methods. In the case of the glass fiber-reinforced resin, the orientation and contents of glass fibers can influence the mechanical properties. For the characteristic prediction of plastic worm wheel, computer-aided engineering (CAE) analysis processes such as structural and injection molding analysis were executed with the polyamide resin reinforcement glass fiber (25 wt %, 50 wt %). The injection mold for fabricating the prototype plastic worm wheel was designed and made to reflect the CAE analysis results. Finally, the durability of prototype plastic worm wheel fabricated by the injection molding process was evaluated by the experimental method and the characteristics according to the glass fiber contents.

Durability Characteristics Analysis of Plastic Worm Wheel with Glass Fiber Reinforced Polyamide

PubMed Central

Kim, Gun-Hee; Lee, Jeong-Won; Seo, Tae-Il

2013-01-01

Plastic worm wheel is widely used in the vehicle manufacturing field because it is favorable for weight lightening, vibration and noise reduction, as well as corrosion resistance. However, it is very difficult for general plastics to secure the mechanical properties that are required for vehicle gears. If the plastic resin is reinforced by glass fiber in the fabrication process of plastic worm wheel, it is possible to achieve the mechanical properties of metallic material levels. In this study, the mechanical characteristic analysis of the glass-reinforced plastic worm wheel, according to the contents of glass fiber, is performed by analytic and experimental methods. In the case of the glass fiber-reinforced resin, the orientation and contents of glass fibers can influence the mechanical properties. For the characteristic prediction of plastic worm wheel, computer-aided engineering (CAE) analysis processes such as structural and injection molding analysis were executed with the polyamide resin reinforcement glass fiber (25 wt %, 50 wt %). The injection mold for fabricating the prototype plastic worm wheel was designed and made to reflect the CAE analysis results. Finally, the durability of prototype plastic worm wheel fabricated by the injection molding process was evaluated by the experimental method and the characteristics according to the glass fiber contents. PMID:28809248

Different universality classes at the yielding transition of amorphous systems

NASA Astrophysics Data System (ADS)

Jagla, E. A.

2017-08-01

We study the yielding transition of a two-dimensional amorphous system under shear by using a mesoscopic elasto-plastic model. The model combines a full (tensorial) description of the elastic interactions in the system and the possibility of structural reaccommodations that are responsible for the plastic behavior. The possible structural reaccommodations are encoded in the form of a "plastic disorder" potential, which is chosen independently at each position of the sample to account for local heterogeneities. We observe that the stress must exceed a critical value σc in order for the system to yield. In addition, when the system yields a flow curve (relating stress σ and strain rate γ ˙) of the form γ ˙˜(σ-σc) β is obtained. Remarkably, we observe the value of β to depend on some details of the plastic disorder potential. For smooth potentials a value of β ≃2.0 is obtained, whereas for potentials obtained as a concatenation of smooth pieces a value β ≃1.5 is observed in the simulations. This indicates a dependence of critical behavior on details of the plastic behavior. In addition, by integrating out nonessential, harmonic degrees of freedom, we derive a simplified scalar version of the model that represents a collection of interacting Prandtl-Tomlinson particles. A mean-field treatment of this interaction reproduces the difference of β exponents for the two classes of plastic disorder potentials and provides values of β that compare favorably with those found in the full simulations.

Optical Sensors Based on Plastic Fibers

PubMed Central

Bilro, Lúcia; Alberto, Nélia; Pinto, João L.; Nogueira, Rogério

2012-01-01

The recent advances of polymer technology allowed the introduction of plastic optical fiber in sensor design. The advantages of optical metrology with plastic optical fiber have attracted the attention of the scientific community, as they allow the development of low-cost or cost competitive systems compared with conventional technologies. In this paper, the current state of the art of plastic optical fiber technology will be reviewed, namely its main characteristics and sensing advantages. Several measurement techniques will be described, with a strong focus on interrogation approaches based on intensity variation in transmission and reflection. The potential applications involving structural health monitoring, medicine, environment and the biological and chemical area are also presented. PMID:23112707

The Thermal and Microstructural Effect of Plasticizing HMX-Nitrocellulose Composites

DOE PAGES

Yeager, John David; Watkins, Erik Benjamin; Duque, Amanda Lynn; ...

2017-03-15

Thermal ignition via self-heating (cook-off) of cyclotetramethylene-tetranitramine (HMX)-containing plastic-bonded explosives (PBXs) is driven by the β → δ phase transition in the HMX, which is affected if not dominated by microstructure. Here, we studied the HMX-binder interface and phase transition for several variations of PBX 9404 (HMX with plasticized nitrocellulose [NC] binder). Neutron reflectometry was used to examine the interface under several conditions—pristine, after aging, and after thermal treatment. The initial interfacial structure depended on the plasticizer, but the interface homogenized over time. Thermal and optical analyses showed that all formulated materials had higher transition temperatures than neat HMX. Thismore » effect increased with NC content.« less

Raman and AFM study of gamma irradiated plastic bottle sheets

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ali, Yasir; Kumar, Vijay; Dhaliwal, A. S.

2013-02-05

In this investigation, the effects of gamma irradiation on the structural properties of plastic bottle sheet are studied. The Plastic sheets were exposed with 1.25MeV {sup 60}Co gamma rays source at various dose levels within the range from 0-670 kGy. The induced modifications were followed by micro-Raman and atomic force microscopy (AFM). The Raman spectrum shows the decrease in Raman intensity and formation of unsaturated bonds with an increase in the gamma dose. AFM image displays rough surface morphology after irradiation. The detailed Raman analysis of plastic bottle sheets is presented here, and the results are correlated with the AFMmore » observations.« less

The Thermal and Microstructural Effect of Plasticizing HMX-Nitrocellulose Composites

NASA Astrophysics Data System (ADS)

Yeager, John D.; Watkins, Erik B.; Higginbotham Duque, Amanda L.; Majewski, Jaroslaw

2018-01-01

Thermal ignition via self-heating (cook-off) of cyclotetramethylene-tetranitramine (HMX)-containing plastic-bonded explosives (PBXs) is driven by the β → δ phase transition in the HMX, which is affected if not dominated by microstructure. Here, the HMX-binder interface and phase transition were studied for several variations of PBX 9404 (HMX with plasticized nitrocellulose [NC] binder). Neutron reflectometry was used to examine the interface under several conditions-pristine, after aging, and after thermal treatment. The initial interfacial structure depended on the plasticizer, but the interface homogenized over time. Thermal and optical analyses showed that all formulated materials had higher transition temperatures than neat HMX. This effect increased with NC content.

Impact resistance of fiber composites

NASA Technical Reports Server (NTRS)

Chamis, C. C.; Sinclair, J. H.

1982-01-01

Stress-strain curves are obtained for a variety of glass fiber and carbon fiber reinforced plastics in dynamic tension, over the stress-strain range of 0.00087-2070/sec. The test method is of the one-bar block-to-bar type, using a rotating disk or a pendulum as the loading apparatus and yielding accurate stress-strain curves up to the breaking strain. In the case of glass fiber reinforced plastic, the tensile strength, strain to peak impact stress, total strain and total absorbed energy all increase significantly as the strain rate increases. By contrast, carbon fiber reinforced plastics show lower rates of increase with strain rate. It is recommended that hybrid composites incorporating the high strength and rigidity of carbon fiber reinforced plastic with the high impact absorption of glass fiber reinforced plastics be developed for use in structures subjected to impact loading.

Numerical Study of the Plasticity-Induced Stabilization Effect on Martensitic Transformations in Shape Memory Alloys

NASA Astrophysics Data System (ADS)

Junker, Philipp; Hempel, Philipp

2017-12-01

It is well known that plastic deformations in shape memory alloys stabilize the martensitic phase. Furthermore, the knowledge concerning the plastic state is crucial for a reliable sustainability analysis of construction parts. Numerical simulations serve as a tool for the realistic investigation of the complex interactions between phase transformations and plastic deformations. To account also for irreversible deformations, we expand an energy-based material model by including a non-linear isotropic hardening plasticity model. An implementation of this material model into commercial finite element programs, e.g., Abaqus, offers the opportunity to analyze entire structural components at low costs and fast computation times. Along with the theoretical derivation and expansion of the model, several simulation results for various boundary value problems are presented and interpreted for improved construction designing.

Removal of brominated flame retardant from electrical and electronic waste plastic by solvothermal technique.

PubMed

Zhang, Cong-Cong; Zhang, Fu-Shen

2012-06-30

Brominated flame retardants (BFRs) in electrical and electronic (E&E) waste plastic are toxic, bioaccumulative and recalcitrant. In the present study, tetrabromobisphenol A (TBBPA) contained in this type of plastic was tentatively subjected to solvothermal treatment so as to obtain bromine-free plastic. Methanol, ethanol and isopropanol were examined as solvents for solvothermal treatment and it was found that methanol was the optimal solvent for TBBPA removal. The optimum temperature, time and liquid to solid ratio for solvothermal treatment to remove TBBPA were 90°C, 2h and 15:1, respectively. After the treatment with various alcohol solvents, it was found that TBBPA was finally transferred into the solvents and bromine in the extract was debrominated catalyzed by metallic copper. Bisphenol A and cuprous bromide were the main products after debromination. The morphology and FTIR properties of the plastic were generally unchanged after the solvothermal treatment indicating that the structure of the plastic maintained after the process. This work provides a clean and applicable process for BFRs-containing plastic disposal. Copyright © 2012 Elsevier B.V. All rights reserved.

The Ethics of Sharing Plastic Surgery Videos on Social Media: Systematic Literature Review, Ethical Analysis, and Proposed Guidelines.

PubMed

Dorfman, Robert G; Vaca, Elbert E; Fine, Neil A; Schierle, Clark F

2017-10-01

Recent videos shared by plastic surgeons on social media applications such as Snapchat, Instagram, and YouTube, among others, have blurred the line between entertainment and patient care. This has left many in the plastic surgery community calling for the development of more structured oversight and guidance regarding video sharing on social media. To date, no official guidelines exist for plastic surgeons to follow. Little is known about the ethical implications of social media use by plastic surgeons, especially with regard to video sharing. A systematic review of the literature on social media use in plastic surgery was performed on October 31, 2016, with an emphasis on ethics and professionalism. An ethical analysis was conducted using the four principles of medical ethics. The initial search yielded 87 articles. Thirty-four articles were included for analyses that were found to be relevant to the use of social media in plastic surgery. No peer-reviewed articles were found that mentioned Snapchat or addressed the ethical implications of sharing live videos of plastic surgery on social media. Using the four principles of medical ethics, it was determined that significant ethical concerns exist with broadcasting these videos. This analysis fills an important gap in the plastic surgery literature by addressing the ethical issues concerning live surgery broadcasts on social media. Plastic surgeons may use the guidelines proposed here to avoid potential pitfalls.

RELATIONSHIP BETWEEN STRUCTURAL AND STRENGTH CHARACTERISTICS OF FIBER-GLASS LAMINATES,

DTIC Science & Technology

REINFORCED PLASTICS, STRUCTURAL PROPERTIES, LAMINATES, EPOXY RESINS, GLASS TEXTILES, LOADS(FORCES), TENSILE PROPERTIES, COMPRESSIVE PROPERTIES, LIFE EXPECTANCY(SERVICE LIFE), USSR, MECHANICAL PROPERTIES.

Solution structure of the isolated Pelle death domain.

PubMed

Moncrieffe, Martin C; Stott, Katherine M; Gay, Nicholas J

2005-07-18

The interaction between the death domains (DDs) of Tube and the protein kinase Pelle is an important component of the Toll pathway. Published crystallographic data suggests that the Pelle-Tube DD interface is plastic and implies that in addition to the two predominant Pelle-Tube interfaces, a third interaction is possible. We present the NMR solution structure of the isolated death domain of Pelle and a study of the interaction between the DDs of Pelle and Tube. Our data suggests the solution structure of the isolated Pelle DD is similar to that of Pelle DD in complex with Tube. Additionally, they suggest that the plasticity observed in the crystal structure may not be relevant in the functioning death domain complex.

Lynx1 Limits Dendritic Spine Turnover in the Adult Visual Cortex

PubMed Central

Sajo, Mari

2016-01-01

Dendritic spine turnover becomes limited in the adult cerebral cortex. Identification of specific aspects of spine dynamics that can be unmasked in adulthood and its regulatory molecular mechanisms could provide novel therapeutic targets for inducing plasticity at both the functional and structural levels for robust recovery from brain disorders and injuries in adults. Lynx1, an endogenous inhibitor of nicotinic acetylcholine receptors, was previously shown to increase its expression in adulthood and thus to limit functional ocular dominance plasticity in adult primary visual cortex (V1). However, the role of this “brake” on spine dynamics is not known. We examined the contribution of Lynx1 on dendritic spine turnover before and after monocular deprivation (MD) in adult V1 with chronic in vivo imaging using two-photon microscopy and determined the spine turnover rate of apical dendrites of layer 5 (L5) and L2/3 pyramidal neurons in adult V1 of Lynx1 knock-out (KO) mice. We found that the deletion of Lynx1 doubled the baseline spine turnover rate, suggesting that the spine dynamics in the adult cortex is actively limited by the presence of Lynx1. After MD, adult Lynx1-KO mice selectively exhibit higher rate of spine loss with no difference in gain rate in L5 neurons compared with control wild-type counterparts, revealing a key signature of spine dynamics associated with robust functional plasticity in adult V1. Overall, Lynx1 could be a promising therapeutic target to induce not only functional, but also structural plasticity at the level of spine dynamics in the adult brain. SIGNIFICANCE STATEMENT Dendritic spine turnover becomes limited in the adult cortex. In mouse visual cortex, a premier model of experience-dependent plasticity, we found that the deletion of Lynx1, a nicotinic “brake” for functional plasticity, doubled the baseline spine turnover in adulthood, suggesting that the spine dynamics in the adult cortex is actively limited by Lynx1. After visual deprivation, spine loss, but not gain rate, remains higher in adult Lynx1 knock-out mice than in control wild-type mice, revealing a key signature of spine dynamics associated with robust functional plasticity. Lynx1 would be a promising target to induce not only functional, but also structural plasticity at the level of spine dynamics in adulthood. PMID:27605620

Tension and Compression Creep Apparatus for wood-Plastic Composites

Treesearch

Scott E. Hamel; John C. Hermanson; Steven M. Cramer

2011-01-01

Design of structural members made of wood-plastic composites (WPC) is not possible without accurate test data for tension and compression. The viscoelastic behavior of these materials means that these data are required for both the quasi-static stress-strain response, and the long-term creep response. Their relative incompressibility causes inherent difficulties in...

Thermal behavior of epoxidized cardanol diethyl phosphate as novel renewable plasticizer for poly(vinyl chloride)

USDA-ARS?s Scientific Manuscript database

A novel plasticizer, epoxidized cardanol diethyl phosphate (ECEP), based on cardanol was synthesized. Chemical structure of ECEP was characterized by fourier transform infrared (FTIR), 1H-nuclear magnetic resonance(1H NMR) and 13C-nuclear magnetic resonance(13C NMR) spectroscopy. Effects of ECEP sub...

State-of-the-Art Review on Composite Material Fatigue/Damage Tolerance.

DTIC Science & Technology

1985-12-01

Automobile Structures," Plastic Rubber Material Application, Vol. 3, No. 2, May 1978. 148. Nguyen, D.T., Arora, J.S., and Belegundu, A.D., "Design...Vanthier, D., " Kunststoff -Verstaerkung MIT Kevlar 49," [Reinforcing Plastics With "Kevlar" 49], Plastverarbeiter, Vol. 31, No. 9, September 1980. 232

Norepinephrine Triggers Metaplasticity of LTP by Increasing Translation of Specific mRNAs

ERIC Educational Resources Information Center

Maity, Sabyasachi; Rah, Sean; Sonenberg, Nahum; Gkogkas, Christos G.; Nguyen, Peter V.

2015-01-01

Norepinephrine (NE) is a key modulator of synaptic plasticity in the hippocampus, a brain structure crucially involved in memory formation. NE boosts synaptic plasticity mostly through initiation of signaling cascades downstream from beta (ß)-adrenergic receptors (ß-ARs). Previous studies demonstrated that a ß-adrenergic receptor agonist,…

Proceedings of USAF Structural Integrity Program (ASIP, ENSIP) conference Held in Sacramento, California on 2-4 December 1986

DTIC Science & Technology

1986-12-01

Reliability Studies ............................................................ 295 NDI for Corrosion .................................................... (Not...available at time of printing) Plastic Bead Blast Materials Characterization Study ................................................ 313 In-Service... Studies Ward Rummel, Martin-Marietta Aerospace AGENDA (Continued) 2. NOI for Corrosion Jeff Rowe, Lockheed-Georgia 3. Plastic Bead Blast Materials R. D

Translational control of auditory imprinting and structural plasticity by eIF2α.

PubMed

Batista, Gervasio; Johnson, Jennifer Leigh; Dominguez, Elena; Costa-Mattioli, Mauro; Pena, Jose L

2016-12-23

The formation of imprinted memories during a critical period is crucial for vital behaviors, including filial attachment. Yet, little is known about the underlying molecular mechanisms. Using a combination of behavior, pharmacology, in vivo surface sensing of translation (SUnSET) and DiOlistic labeling we found that, translational control by the eukaryotic translation initiation factor 2 alpha (eIF2α) bidirectionally regulates auditory but not visual imprinting and related changes in structural plasticity in chickens. Increasing phosphorylation of eIF2α (p-eIF2α) reduces translation rates and spine plasticity, and selectively impairs auditory imprinting. By contrast, inhibition of an eIF2α kinase or blocking the translational program controlled by p-eIF2α enhances auditory imprinting. Importantly, these manipulations are able to reopen the critical period. Thus, we have identified a translational control mechanism that selectively underlies auditory imprinting. Restoring translational control of eIF2α holds the promise to rejuvenate adult brain plasticity and restore learning and memory in a variety of cognitive disorders.

Palmitoylation of LIM Kinase-1 ensures spine-specific actin polymerization and morphological plasticity

PubMed Central

George, Joju; Soares, Cary; Montersino, Audrey; Beique, Jean-Claude; Thomas, Gareth M

2015-01-01

Precise regulation of the dendritic spine actin cytoskeleton is critical for neurodevelopment and neuronal plasticity, but how neurons spatially control actin dynamics is not well defined. Here, we identify direct palmitoylation of the actin regulator LIM kinase-1 (LIMK1) as a novel mechanism to control spine-specific actin dynamics. A conserved palmitoyl-motif is necessary and sufficient to target LIMK1 to spines and to anchor LIMK1 in spines. ShRNA knockdown/rescue experiments reveal that LIMK1 palmitoylation is essential for normal spine actin polymerization, for spine-specific structural plasticity and for long-term spine stability. Palmitoylation is critical for LIMK1 function because this modification not only controls LIMK1 targeting, but is also essential for LIMK1 activation by its membrane-localized upstream activator PAK. These novel roles for palmitoylation in the spatial control of actin dynamics and kinase signaling provide new insights into structural plasticity mechanisms and strengthen links between dendritic spine impairments and neuropathological conditions. DOI: http://dx.doi.org/10.7554/eLife.06327.001 PMID:25884247

Plastically bendable crystals of probenecid and its cocrystal with 4,4‧-Bipyridine

NASA Astrophysics Data System (ADS)

Nath, Naba K.; Hazarika, Mousumi; Gupta, Poonam; Ray, Nisha R.; Paul, Amit K.; Nauha, Elisa

2018-05-01

Recent findings of plastically bendable molecular crystals led to the realization that design based strategies are required for these materials to be useful in real life application. We have coincidentally discovered plastically bendable crystals of a drug molecule probenecid. Based on the structural features of its crystals at room temperature, we hypothesized that introduction of a molecular spacer between two hydrogen bonded molecules of probenecid, by replacing the carboxylic acid homodimer with similar dimeric hydrogen bonding synthon, would not disturb the layered molecular packing of probenecid. As a consequence, the new multi-component crystal would retain flexibility similar to the original probenecid crystals. Herein we have attempted to prove this hypothesis and we were successful in the case of probenecid: 4,4‧-bipyridine cocrystal. As designed, in the crystal structure 4,4‧-bypyridine molecule acted as spacer and connected two probenecid molecules resulting in the retention of the slip planes which are necessary for a molecular crystal to be plastically bendable. DFT computational calculations were carried out to account for the hydrogen bonding synthons between probenecid and the coformers under study.

Low-grade inflammation disrupts structural plasticity in the human brain.

PubMed

Szabó, C; Kelemen, O; Kéri, S

2014-09-05

Increased low-grade inflammation is thought to be associated with several neuropsychiatric disorders characterized by decreased neuronal plasticity. The purpose of the present study was to investigate the relationship between structural changes in the human brain during cognitive training and the intensity of low-grade peripheral inflammation in healthy individuals (n=56). A two-month training (30 min/day) with a platformer video game resulted in a significantly increased volume of the right hippocampal formation. The number of stressful life events experienced during the past year was associated with less pronounced enlargement of the hippocampus. However, the main predictor of hippocampal volume expansion was the relative peripheral expression of Nuclear Factor-κB (NF-κB), a transcription factor playing a central role in the effect of pro-inflammatory cytokines. Interleukin-6 (IL-6) and C-reactive protein levels were not related to hippocampal plasticity when NF-κB was taken into consideration. These results suggest that more intensive peripheral inflammation is associated with weaker neuronal plasticity during cognitive training. Copyright © 2014 IBRO. Published by Elsevier Ltd. All rights reserved.

Microbial colonization and degradation of polyethylene and biodegradable plastic bags in temperate fine-grained organic-rich marine sediments.

PubMed

Nauendorf, Alice; Krause, Stefan; Bigalke, Nikolaus K; Gorb, Elena V; Gorb, Stanislav N; Haeckel, Matthias; Wahl, Martin; Treude, Tina

2016-02-15

To date, the longevity of plastic litter at the sea floor is poorly constrained. The present study compares colonization and biodegradation of plastic bags by aerobic and anaerobic benthic microbes in temperate fine-grained organic-rich marine sediments. Samples of polyethylene and biodegradable plastic carrier bags were incubated in natural oxic and anoxic sediments from Eckernförde Bay (Western Baltic Sea) for 98 days. Analyses included (1) microbial colonization rates on the bags, (2) examination of the surface structure, wettability, and chemistry, and (3) mass loss of the samples during incubation. On average, biodegradable plastic bags were colonized five times higher by aerobic and eight times higher by anaerobic microbes than polyethylene bags. Both types of bags showed no sign of biodegradation during this study. Therefore, marine sediment in temperate coastal zones may represent a long-term sink for plastic litter and also supposedly compostable material. Copyright © 2016 Elsevier Ltd. All rights reserved.

Critical neural networks with short- and long-term plasticity.

PubMed

Michiels van Kessenich, L; Luković, M; de Arcangelis, L; Herrmann, H J

2018-03-01

In recent years self organized critical neuronal models have provided insights regarding the origin of the experimentally observed avalanching behavior of neuronal systems. It has been shown that dynamical synapses, as a form of short-term plasticity, can cause critical neuronal dynamics. Whereas long-term plasticity, such as Hebbian or activity dependent plasticity, have a crucial role in shaping the network structure and endowing neural systems with learning abilities. In this work we provide a model which combines both plasticity mechanisms, acting on two different time scales. The measured avalanche statistics are compatible with experimental results for both the avalanche size and duration distribution with biologically observed percentages of inhibitory neurons. The time series of neuronal activity exhibits temporal bursts leading to 1/f decay in the power spectrum. The presence of long-term plasticity gives the system the ability to learn binary rules such as xor, providing the foundation of future research on more complicated tasks such as pattern recognition.

Critical neural networks with short- and long-term plasticity

NASA Astrophysics Data System (ADS)

Michiels van Kessenich, L.; Luković, M.; de Arcangelis, L.; Herrmann, H. J.

2018-03-01

In recent years self organized critical neuronal models have provided insights regarding the origin of the experimentally observed avalanching behavior of neuronal systems. It has been shown that dynamical synapses, as a form of short-term plasticity, can cause critical neuronal dynamics. Whereas long-term plasticity, such as Hebbian or activity dependent plasticity, have a crucial role in shaping the network structure and endowing neural systems with learning abilities. In this work we provide a model which combines both plasticity mechanisms, acting on two different time scales. The measured avalanche statistics are compatible with experimental results for both the avalanche size and duration distribution with biologically observed percentages of inhibitory neurons. The time series of neuronal activity exhibits temporal bursts leading to 1 /f decay in the power spectrum. The presence of long-term plasticity gives the system the ability to learn binary rules such as xor, providing the foundation of future research on more complicated tasks such as pattern recognition.

Study of the Micro-Nonuniformity of the Plastic Deformation of Steel

NASA Technical Reports Server (NTRS)

Chechulin, B. B.

1957-01-01

The plastic flow during deformation of real polycrystalline metals has specific characteristics which distinguish the plastic deformation of metals from the deformation of ordinary isotropic bodies. One of these characteristics is the marked micro-nonuniformity of the plastic deformation of metals. P.O. Pashkov demonstrated the presence of a considerable micro-nonuniformity of the plastic deformation of coarse-grained steel wit medium or low carbon content. Analogous results in the case of tension of coarse-grained aluminum were obtained by W. Boas, who paid particular attention to the role of the grain boundaries in plastic flow. The nonuniformit of the plastic deformation in microvolumes was also recorded by T.N. Gudkova and others, on the alloy KhN80T. N.F. Lashko pointed out the nonuniformity of the plastic deformation for a series of pure polycrystalline metals and one-phase alloys. In his later reports, P.O. Pashkov arrives at he conclusion that the nonuniformity of the distribution of the deformation along the individual grains has a significant effect on the strength and plastic characteristics of polycrystalline metals in the process of plastic flow. However, until now there has not existed any systematic investigation of the general rules of the microscopic nonuniformit of plastic deformation even though the real polycrystalline metals are extremely simple with regard to structure. In the present report, an attempt is made to study the micrononuniformity of the flow of polycrystalline metals by the method of statistical analysis of the variation of the frequency diagrams of the nonuniformity of the grains in the process of plastic deformation.

Internal state variable plasticity-damage modeling of AISI 4140 steel including microstructure-property relations: temperature and strain rate effects

NASA Astrophysics Data System (ADS)

Nacif el Alaoui, Reda

Mechanical structure-property relations have been quantified for AISI 4140 steel. under different strain rates and temperatures. The structure-property relations were used. to calibrate a microstructure-based internal state variable plasticity-damage model for. monotonic tension, compression and torsion plasticity, as well as damage evolution. Strong stress state and temperature dependences were observed for the AISI 4140 steel. Tension tests on three different notched Bridgman specimens were undertaken to study. the damage-triaxiality dependence for model validation purposes. Fracture surface. analysis was performed using Scanning Electron Microscopy (SEM) to quantify the void. nucleation and void sizes in the different specimens. The stress-strain behavior exhibited. a fairly large applied stress state (tension, compression dependence, and torsion), a. moderate temperature dependence, and a relatively small strain rate dependence.

Finite element analysis of large transient elastic-plastic deformations of simple structures, with application to the engine rotor fragment containment/deflection problem

NASA Technical Reports Server (NTRS)

Wu, R. W.; Witmer, E. A.

1972-01-01

Assumed-displacement versions of the finite-element method are developed to predict large-deformation elastic-plastic transient deformations of structures. Both the conventional and a new improved finite-element variational formulation are derived. These formulations are then developed in detail for straight-beam and curved-beam elements undergoing (1) Bernoulli-Euler-Kirchhoff or (2) Timoshenko deformation behavior, in one plane. For each of these categories, several types of assumed-displacement finite elements are developed, and transient response predictions are compared with available exact solutions for small-deflection, linear-elastic transient responses. The present finite-element predictions for large-deflection elastic-plastic transient responses are evaluated via several beam and ring examples for which experimental measurements of transient strains and large transient deformations and independent finite-difference predictions are available.

24 CFR 35.1355 - Ongoing lead-based paint maintenance and reevaluation activities.

Code of Federal Regulations, 2012 CFR

2012-04-01

... Secretary, Department of Housing and Urban Development LEAD-BASED PAINT POISONING PREVENTION IN CERTAIN RESIDENTIAL STRUCTURES Methods and Standards for Lead-Paint Hazard Evaluation and Hazard Reduction Activities... 24 Housing and Urban Development 1 2012-04-01 2012-04-01 false Ongoing lead-based paint...

24 CFR 35.1355 - Ongoing lead-based paint maintenance and reevaluation activities.

Code of Federal Regulations, 2013 CFR

2013-04-01

... Secretary, Department of Housing and Urban Development LEAD-BASED PAINT POISONING PREVENTION IN CERTAIN RESIDENTIAL STRUCTURES Methods and Standards for Lead-Paint Hazard Evaluation and Hazard Reduction Activities... 24 Housing and Urban Development 1 2013-04-01 2013-04-01 false Ongoing lead-based paint...

24 CFR 35.1355 - Ongoing lead-based paint maintenance and reevaluation activities.

Code of Federal Regulations, 2011 CFR

2011-04-01

... Secretary, Department of Housing and Urban Development LEAD-BASED PAINT POISONING PREVENTION IN CERTAIN RESIDENTIAL STRUCTURES Methods and Standards for Lead-Paint Hazard Evaluation and Hazard Reduction Activities... 24 Housing and Urban Development 1 2011-04-01 2011-04-01 false Ongoing lead-based paint...

24 CFR 35.1355 - Ongoing lead-based paint maintenance and reevaluation activities.

Code of Federal Regulations, 2014 CFR

2014-04-01

... Secretary, Department of Housing and Urban Development LEAD-BASED PAINT POISONING PREVENTION IN CERTAIN RESIDENTIAL STRUCTURES Methods and Standards for Lead-Paint Hazard Evaluation and Hazard Reduction Activities... 24 Housing and Urban Development 1 2014-04-01 2014-04-01 false Ongoing lead-based paint...

Climate change and evolution: disentangling environmental and genetic responses.

PubMed

Gienapp, P; Teplitsky, C; Alho, J S; Mills, J A; Merilä, J

2008-01-01

Rapid climate change is likely to impose strong selection pressures on traits important for fitness, and therefore, microevolution in response to climate-mediated selection is potentially an important mechanism mitigating negative consequences of climate change. We reviewed the empirical evidence for recent microevolutionary responses to climate change in longitudinal studies emphasizing the following three perspectives emerging from the published data. First, although signatures of climate change are clearly visible in many ecological processes, similar examples of microevolutionary responses in literature are in fact very rare. Second, the quality of evidence for microevolutionary responses to climate change is far from satisfactory as the documented responses are often - if not typically - based on nongenetic data. We reinforce the view that it is as important to make the distinction between genetic (evolutionary) and phenotypic (includes a nongenetic, plastic component) responses clear, as it is to understand the relative roles of plasticity and genetics in adaptation to climate change. Third, in order to illustrate the difficulties and their potential ubiquity in detection of microevolution in response to natural selection, we reviewed the quantitative genetic studies on microevolutionary responses to natural selection in the context of long-term studies of vertebrates. The available evidence points to the overall conclusion that many responses perceived as adaptations to changing environmental conditions could be environmentally induced plastic responses rather than microevolutionary adaptations. Hence, clear-cut evidence indicating a significant role for evolutionary adaptation to ongoing climate warming is conspicuously scarce.

Effects of water stress on irradiance acclimation of leaf traits in almond trees.

PubMed

Egea, Gregorio; González-Real, María M; Baille, Alain; Nortes, Pedro A; Conesa, María R; Ruiz-Salleres, Isabel

2012-04-01

Photosynthetic acclimation to highly variable local irradiance within the tree crown plays a primary role in determining tree carbon uptake. This study explores the plasticity of leaf structural and physiological traits in response to the interactive effects of ontogeny, water stress and irradiance in adult almond trees that have been subjected to three water regimes (full irrigation, deficit irrigation and rain-fed) for a 3-year period (2006-08) in a semiarid climate. Leaf structural (dry mass per unit area, N and chlorophyll content) and photosynthetic (maximum net CO(2) assimilation, A(max), maximum stomatal conductance, g(s,max), and mesophyll conductance, g(m)) traits and stem-to-leaf hydraulic conductance (K(s-l)) were determined throughout the 2008 growing season in leaves of outer south-facing (S-leaves) and inner northwest-facing (NW-leaves) shoots. Leaf plasticity was quantified by means of an exposure adjustment coefficient (ε=1-X(NW)/X(S)) for each trait (X) of S- and NW-leaves. Photosynthetic traits and K(s-l) exhibited higher irradiance-elicited plasticity (higher ε) than structural traits in all treatments, with the highest and lowest plasticity being observed in the fully irrigated and rain-fed trees, respectively. Our results suggest that water stress modulates the irradiance-elicited plasticity of almond leaves through changes in crown architecture. Such changes lead to a more even distribution of within-crown irradiance, and hence of the photosynthetic capacity, as water stress intensifies. Ontogeny drove seasonal changes only in the ε of area- and mass-based N content and mass-based chlorophyll content, while no leaf age-dependent effect was observed on ε as regards the physiological traits. Our results also indicate that the irradiance-elicited plasticity of A(max) is mainly driven by changes in leaf dry mass per unit area, in g(m) and, most likely, in the partitioning of the leaf N content.

Neuronal plasticity and neurotrophic factors in drug responses

PubMed Central

Castrén, Eero; Antila, Hanna

2017-01-01

Neurotrophic factors, particularly brain-derived neurotrophic factor (BDNF) and other members of the neurotrophin family, are central mediators of the activity-dependent plasticity through which environmental experiences, such as sensory information are translated into the structure and function of neuronal networks. Synthesis, release and action of BDNF is regulated by neuronal activity and BDNF in turn leads to trophic effects such as formation, stabilization and potentiation of synapses through its high-affinity TrkB receptors. Several clinically available drugs directly activate neurotrophins and neuronal plasticity. In particular, antidepressant drugs rapidly activate TrkB signaling and gradually increase BDNF expression, and the behavioral effects of antidepressants are mediated by and dependent on BDNF signaling through TrkB at least in rodents. These findings indicate that antidepressants, widely used drugs, effectively act as TrkB activators. They further imply that neuronal plasticity is a central mechanism in the action of antidepressant drugs. Indeed, it was recently discovered that antidepressants reactivate a state of plasticity in the adult cerebral cortex that closely resembles the enhanced plasticity normally observed during postnatal critical periods. This state of induced plasticity, known as iPlasticity, allows environmental stimuli to beneficially reorganize networks abnormally wired during early life. iPlasticity has been observed in cortical as well as subcortical networks and is induced by several pharmacological and non-pharmacological treatments. iPlasticity is a new pharmacological principle where drug treatment and rehabilitation cooperate: the drug acts permissively to enhance plasticity and rehabilitation provides activity to guide the appropriate wiring of the plastic network. Optimization of iPlastic drug treatment with novel means of rehabilitation may help improve the efficacy of available drug treatments and expand the use of currently existing drugs into new indications. PMID:28397840

Characterization via atomic force microscopy of discrete plasticity in collagen fibrils from mechanically overloaded tendons: Nano-scale structural changes mimic rope failure.

PubMed

Baldwin, Samuel J; Kreplak, Laurent; Lee, J Michael

2016-07-01

Tendons exposed to tensile overload show a structural alteration at the fibril scale termed discrete plasticity. Serial kinks appear along individual collagen fibrils that are susceptible to enzymatic digestion and are thermally unstable. Using atomic force microscopy we mapped the topography and mechanical properties in dehydrated and hydrated states of 25 control fibrils and 25 fibrils displaying periodic kinks, extracted from overloaded bovine tail tendons. Using the measured modulus of the hydrated fibrils as a probe of molecular density, we observed a non-linear negative correlation between molecular density and kink density of individual fibrils. This is accompanied by an increase in water uptake with kink density and a doubling of the coefficient of variation of the modulus between kinked, and control fibrils. The mechanical property maps of kinked collagen fibrils show radial heterogeneity that can be modeled as a high-density core surrounded by a low-density shell. The core of the fibril contains the kink structures characteristic of discrete plasticity; separated by inter-kink regions, which often retain the D-banding structure. We propose that the shell and kink structures mimic characteristic damage motifs observed in laid rope strands. Copyright © 2016 Elsevier Ltd. All rights reserved.

Evaluating predisposition and training in shaping the musician's brain: the need for a developmental perspective.

PubMed

Zuk, Jennifer; Gaab, Nadine

2018-05-24

The study of music training as a model for structural plasticity has evolved significantly over the past 15 years. Neuroimaging studies have identified characteristic structural brain alterations in musicians compared to nonmusicians in school-age children and adults, using primarily cross-sectional designs. Despite this emerging evidence and advances in pediatric neuroimaging techniques, hardly any studies have examined brain development in early childhood (before age 8) in association with musical training, and longitudinal studies starting in infancy or preschool are particularly scarce. Consequently, it remains unclear whether the characteristic "musician brain" is solely the result of musical training, or whether certain predispositions may have an impact on its development. Moving toward a developmental perspective, the present review considers various factors that may contribute to early brain structure prior to the onset of formal musical training. This review introduces a model for potential neurobiological pathways leading to the characteristic "musician brain," which involves a developmental interaction between predisposition and its temporal dynamics, environmental experience, and training-induced plasticity. This perspective illuminates the importance of studying the brain structure associated with musical training through a developmental lens, and the need for longitudinal studies in early childhood to advance our understanding of music training-induced structural plasticity. © 2018 New York Academy of Sciences.

On the Structure of Some Pentaerythritol-Related Molecular Crystals with Pseudotetrahedral Molecular Structure. Ordered Structure of 2,2-Bis(bromomethyl)-1,3-propanediol and Orientationally Disordered Structure of 2-Chloromethyl-2-methyl-1,3-dichloropropane; 35Cl NQR

NASA Astrophysics Data System (ADS)

Dou, Shi-qi; Fuess, Hartmut; Strauß, Roman; Weiss, Alarich

1996-06-01

C(CH2Cl)3(CH3), melting point Tm = 291.3 K, shows in the DTA/DSC experiment a phase tran-sition from an orientationally disordered plastic phase I into an ordered phase II at TI ⃗ II = 235.9 K. From 77 K up to TII ⃗ I the 35Cl NQR spectrum is a triplet with (ν in MHz, T=77 K) ν1 = 34.213, ν2 = 34.183, ν3 = 33.786. The 35Cl NQR fade-out temperature Tf = 247 K coincides with TII ⃗ I found from the DSC experiment. The plastic phase of 2-chloromethyl-2-methyl-l,3-propanediol is cubic bcc, Im3m, Z = 2 and the lattice constant increases linearly 755 pm at 235 K to 768 pm at 283 K. In the heating cycle we found (ΔH in kJ/mol): ΔHII ⃗ I = 12.0, ΔSm/R = 1.0. The compound belongs to the group of plastic molecules formed by ellipsoid like distorted tetrahedra and is derived by substitution from methane. The crystal structure of 2,2-bis(bromomethyl)-1,3-propanediol was determined. DTA-DSC show that an orientationally disordered plastic phase does not exist. At room temperature C(CH2Br)2(CH2OH)2 crystallizes monoclinic, space group Cc, Z = 4, a = 628.2 pm, 6 = 2015.5 pm, c = 659.6 pm, β = 94.27°. The molecules interact by intermolecular hydrogen bonds between the OH-groups and by van der Waals forces Br…Br.

The use of standardized patients in the plastic surgery residency curriculum: teaching core competencies with objective structured clinical examinations.

PubMed

Davis, Drew; Lee, Gordon

2011-07-01

As of 2006, the Accreditation Council for Graduate Medical Education had defined six "core competencies" of residency education: interpersonal communication skills, medical knowledge, patient care, professionalism, practice-based learning and improvement, and systems-based practice. Objective structured clinical examinations using standardized patients are becoming effective educational tools, and the authors developed a novel use of the examinations in plastic surgery residency education that assesses all six competencies. Six plastic surgery residents, two each from postgraduate years 4, 5, and 6, participated in the plastic surgery-specific objective structured clinical examination that focused on melanoma. The examination included a 30-minute videotaped encounter with a standardized patient actor and a postencounter written exercise. The residents were scored on their performance in all six core competencies by the standardized patients and faculty experts on a three-point scale (1 = novice, 2 = moderately skilled, and 3 = proficient). Resident performance was averaged for each postgraduate year, stratified according to core competency, and scored from a total of 100 percent. Residents overall scored well in interpersonal communications skills (84 percent), patient care (83 percent), professionalism (86 percent), and practice-based learning (84 percent). Scores in medical knowledge showed a positive correlation with level of training (86 percent). All residents scored comparatively lower in systems-based practice (65 percent). The residents reported unanimously that the objective structured clinical examination was realistic and educational. The objective structured clinical examination provided comprehensive and meaningful feedback and identified areas of strengths and weakness for the residents and for the teaching program. The examination is an effective assessment tool for the core competencies and a valuable adjunct to residency training.

Structural studies with the use of XRD and Mössbauer spectroscopy of new high Manganese steels

NASA Astrophysics Data System (ADS)

Jablonska, Magdalena Barbara

2014-04-01

New high-strength austenitic and austenitic-ferritic manganese steels represent a significant potential in applications for structural components in the automotive and railway industry due to the excellent combination of high mechanical properties and good plasticity. They belong to the group of steels called AHSS (Advanced High Strength Steels) and UHSS (Ultra High Strength Steels). Application of this combination of properties allows a reduction in the weight of vehicles by the use of reduced cross-section components, and thus to reduce fuel consumption. The development and implementation of industrial production of such interesting and promising steel and its use as construction material requires an improvement of their casting properties and susceptibility to deformation in plastic working conditions. In this work, XRD, Transmission Mössbauer Spectroscopy and Conversion Electron Mössbauer Spectroscopy were employed in a study of the new high-manganese steels with a austenite and austenite-ferrite structure. The influence of the plastic deformation parameters on the changes in the structure, distribution of ferrite and disclosure of the presence of carbides was determined. The analysis of phase transformations in various times using CEMS method made possible to reveal their fine details.

Repeated Structural Imaging Reveals Nonlinear Progression of Experience-Dependent Volume Changes in Human Motor Cortex.

PubMed

Wenger, Elisabeth; Kühn, Simone; Verrel, Julius; Mårtensson, Johan; Bodammer, Nils Christian; Lindenberger, Ulman; Lövdén, Martin

2017-05-01

Evidence for experience-dependent structural brain change in adult humans is accumulating. However, its time course is not well understood, as intervention studies typically consist of only 2 imaging sessions (before vs. after training). We acquired up to 18 structural magnetic resonance images over a 7-week period while 15 right-handed participants practiced left-hand writing and drawing. After 4 weeks, we observed increases in gray matter of both left and right primary motor cortices relative to a control group; 3 weeks later, these differences were no longer reliable. Time-series analyses revealed that gray matter in the primary motor cortices expanded during the first 4 weeks and then partially renormalized, in particular in the right hemisphere, despite continued practice and increasing task proficiency. Similar patterns of expansion followed by partial renormalization are also found in synaptogenesis, cortical map plasticity, and maturation, and may qualify as a general principle of structural plasticity. Research on human brain plasticity needs to encompass more than 2 measurement occasions to capture expansion and potential renormalization processes over time. © The Author 2016. Published by Oxford University Press. All rights reserved. For Permissions, please e-mail: journals.permissions@oup.com.

Finite element analysis of the biaxial cyclic tensile loading of the elastoplastic plate with the central hole: asymptotic regimes

NASA Astrophysics Data System (ADS)

Turkova, Vera; Stepanova, Larisa

2018-03-01

For elastistoplastic structure elements under cyclic loading three types of asymptotic behavior are well known: shakedown, cyclic plasticity or ratcheting. In structure elements operating in real conditions ratcheting must always be excluded since it caused the incremental fracture of structure by means of the accumulation of plastic strains. In the present study results of finite-element (FEM) calculations of the asymptotical behavior of an elastoplastic plate with the central circular and elliptic holes under the biaxial cyclic loading for three different materials are presented. Incremental cyclic loading of the sample with stress concentrator (the central hole) is performed in the multifunctional finite-element package SIMULIA Abaqus. The ranges of loads found for shakedown, cyclic plasticity and ratcheting are presented. The results obtained are generalized and analyzed. Convenient normalization is suggested. The chosen normalization allows us to present all computed results, corresponding to separate materials, within one common curve with minimum scattering of the points. Convenience of the generalized diagram consists in a possibility to find an asymptotical behavior of an inelastic structure for materials for which computer calculations were not made.

Drawing dependent structures, mechanical properties and cyclization behaviors of polyacrylonitrile and polyacrylonitrile/carbon nanotube composite fibers prepared by plasticized spinning.

PubMed

Li, Xiang; Qin, Aiwen; Zhao, Xinzhen; Liu, Dapeng; Wang, Haiye; He, Chunju

2015-09-14

Drawing to change the structural properties and cyclization behaviors of the polyacrylonitrile (PAN) chains in crystalline and amorphous regions is carried out on PAN and PAN/carbon nanotube (CNT) composite fibers. Various characterization methods including Fourier transform infrared spectroscopy, differential scanning calorimetry, X-ray diffraction and thermal gravimetric analysis are used to monitor the structural evolution and cyclization behaviors of the fibers. With an increase of the draw ratio during the plasticized spinning process, the structural parameters of the fibers, i.e. crystallinity and planar zigzag conformation, are decreased at first, and then increased, which are associated with the heat exchange rate and the oriented-crystallization rate. A possible mechanism for plasticized spinning is proposed to explain the changing trends of crystallinity and planar zigzag conformation. PAN and PAN/CNT fibers exhibit various cyclization behaviors induced by drawing, e.g., the initiation temperature for the cyclization (Ti) of PAN fibers is increased with increasing draw ratio, while Ti of PAN/CNT fibers is decreased. Drawing also facilitates cyclization and lowers the percentage of β-amino nitrile for PAN/CNT fibers during the stabilization.

Structural disorder in plant proteins: where plasticity meets sessility.

PubMed

Covarrubias, Alejandra A; Cuevas-Velazquez, Cesar L; Romero-Pérez, Paulette S; Rendón-Luna, David F; Chater, Caspar C C

2017-09-01

Plants are sessile organisms. This intriguing nature provokes the question of how they survive despite the continual perturbations caused by their constantly changing environment. The large amount of knowledge accumulated to date demonstrates the fascinating dynamic and plastic mechanisms, which underpin the diverse strategies selected in plants in response to the fluctuating environment. This phenotypic plasticity requires an efficient integration of external cues to their growth and developmental programs that can only be achieved through the dynamic and interactive coordination of various signaling networks. Given the versatility of intrinsic structural disorder within proteins, this feature appears as one of the leading characters of such complex functional circuits, critical for plant adaptation and survival in their wild habitats. In this review, we present information of those intrinsically disordered proteins (IDPs) from plants for which their high level of predicted structural disorder has been correlated with a particular function, or where there is experimental evidence linking this structural feature with its protein function. Using examples of plant IDPs involved in the control of cell cycle, metabolism, hormonal signaling and regulation of gene expression, development and responses to stress, we demonstrate the critical importance of IDPs throughout the life of the plant.

Correlative STED and Atomic Force Microscopy on Live Astrocytes Reveals Plasticity of Cytoskeletal Structure and Membrane Physical Properties during Polarized Migration

PubMed Central

Curry, Nathan; Ghézali, Grégory; Kaminski Schierle, Gabriele S.; Rouach, Nathalie; Kaminski, Clemens F.

2017-01-01

The plasticity of the cytoskeleton architecture and membrane properties is important for the establishment of cell polarity, adhesion and migration. Here, we present a method which combines stimulated emission depletion (STED) super-resolution imaging and atomic force microscopy (AFM) to correlate cytoskeletal structural information with membrane physical properties in live astrocytes. Using STED compatible dyes for live cell imaging of the cytoskeleton, and simultaneously mapping the cell surface topology with AFM, we obtain unprecedented detail of highly organized networks of actin and microtubules in astrocytes. Combining mechanical data from AFM with optical imaging of actin and tubulin further reveals links between cytoskeleton organization and membrane properties. Using this methodology we illustrate that scratch-induced migration induces cytoskeleton remodeling. The latter is caused by a polarization of actin and microtubule elements within astroglial cell processes, which correlates strongly with changes in cell stiffness. The method opens new avenues for the dynamic probing of the membrane structural and functional plasticity of living brain cells. It is a powerful tool for providing new insights into mechanisms of cell structural remodeling during physiological or pathological processes, such as brain development or tumorigenesis. PMID:28469559

Optimal Shakedown of the Thin-Wall Metal Structures Under Strength and Stiffness Constraints

NASA Astrophysics Data System (ADS)

Alawdin, Piotr; Liepa, Liudas

2017-06-01

Classical optimization problems of metal structures confined mainly with 1st class cross-sections. But in practice it is common to use the cross-sections of higher classes. In this paper, a new mathematical model for described shakedown optimization problem for metal structures, which elements are designed from 1st to 4th class cross-sections, under variable quasi-static loads is presented. The features of limited plastic redistribution of forces in the structure with thin-walled elements there are taken into account. Authors assume the elastic-plastic flexural buckling in one plane without lateral torsional buckling behavior of members. Design formulae for Methods 1 and 2 for members are analyzed. Structures stiffness constrains are also incorporated in order to satisfy the limit serviceability state requirements. With the help of mathematical programming theory and extreme principles the structure optimization algorithm is developed and justified with the numerical experiment for the metal plane frames.

Spike Train Auto-Structure Impacts Post-Synaptic Firing and Timing-Based Plasticity

PubMed Central

Scheller, Bertram; Castellano, Marta; Vicente, Raul; Pipa, Gordon

2011-01-01

Cortical neurons are typically driven by several thousand synapses. The precise spatiotemporal pattern formed by these inputs can modulate the response of a post-synaptic cell. In this work, we explore how the temporal structure of pre-synaptic inhibitory and excitatory inputs impact the post-synaptic firing of a conductance-based integrate and fire neuron. Both the excitatory and inhibitory input was modeled by renewal gamma processes with varying shape factors for modeling regular and temporally random Poisson activity. We demonstrate that the temporal structure of mutually independent inputs affects the post-synaptic firing, while the strength of the effect depends on the firing rates of both the excitatory and inhibitory inputs. In a second step, we explore the effect of temporal structure of mutually independent inputs on a simple version of Hebbian learning, i.e., hard bound spike-timing-dependent plasticity. We explore both the equilibrium weight distribution and the speed of the transient weight dynamics for different mutually independent gamma processes. We find that both the equilibrium distribution of the synaptic weights and the speed of synaptic changes are modulated by the temporal structure of the input. Finally, we highlight that the sensitivity of both the post-synaptic firing as well as the spike-timing-dependent plasticity on the auto-structure of the input of a neuron could be used to modulate the learning rate of synaptic modification. PMID:22203800

Removing brakes on adult brain plasticity: from molecular to behavioral interventions

PubMed Central

Bavelier, D.; Levi, D.M.; Li, R.W.; Dan, Y.; Hensch, T.K.

2010-01-01

Adult brain plasticity, although possible, remains more restricted in scope than during development. Here, we address conditions under which circuit rewiring may be facilitated in the mature brain. At a cellular and molecular level, adult plasticity is actively limited. Some of these “brakes” are structural, such as peri-neuronal nets or myelin, which inhibit neurite outgrowth. Others are functional, acting directly upon excitatory-inhibitory balance within local circuits. Plasticity in adulthood can be induced either by lifting these brakes through invasive interventions or by exploiting endogenous permissive factors, such as neuromodulators. Using the amblyopic visual system as a model, we discuss genetic, pharmacological, and environmental removal of brakes to enable recovery of vision in adult rodents. Although these mechanisms remain largely uncharted in the human, we consider how they may provide a biological foundation for the remarkable increase in plasticity after action video game play by amblyopic subjects. PMID:21068299

Loss of Cdc42 leads to defects in synaptic plasticity and remote memory recall.

PubMed

Kim, Il Hwan; Wang, Hong; Soderling, Scott H; Yasuda, Ryohei

2014-07-08

Cdc42 is a signaling protein important for reorganization of actin cytoskeleton and morphogenesis of cells. However, the functional role of Cdc42 in synaptic plasticity and in behaviors such as learning and memory are not well understood. Here we report that postnatal forebrain deletion of Cdc42 leads to deficits in synaptic plasticity and in remote memory recall using conditional knockout of Cdc42. We found that deletion of Cdc42 impaired LTP in the Schaffer collateral synapses and postsynaptic structural plasticity of dendritic spines in CA1 pyramidal neurons in the hippocampus. Additionally, loss of Cdc42 did not affect memory acquisition, but instead significantly impaired remote memory recall. Together these results indicate that the postnatal functions of Cdc42 may be crucial for the synaptic plasticity in hippocampal neurons, which contribute to the capacity for remote memory recall.

Structure and properties of polymeric composite materials during 1501 days outer space exposure at Salyut-7 orbital station

NASA Technical Reports Server (NTRS)

Startsev, Oleg V.; Nikishin, Eugene F.

1995-01-01

Specimens of polymeric composite materials for aviation and space applications such as glass fiber reinforced plastics (GFRP), carbon fiber reinforced plastics (CFRP), organic fiber reinforced plastics (OFRP), and hybrid plastics (HP) based on epoxy compounds were exposed to the space environment on the surface of Salyut-7 orbital station. The space exposure lasted 1501 days as a maximum. The data relating to the change in mechanical properties, mass losses, glass transition temperature, linear thermal expansion coefficient, and microstructure after various periods of exposure are given. It has been found that the change in properties is caused by the processes of binder postcuring and microerosion of the exposed surface of plastics. The phenomenon of strengthening of the surface layer of hybrid composites, due to which the nature of destruction changes at bending loads, has been revealed.

Development of Methods of Characterizing Coal in Its Plastic State

NASA Technical Reports Server (NTRS)

Lloyd, W. G.

1978-01-01

Coal in its plastic state (typically 400-460 C) was examined by the isothermal Gieseler plastometry of seven selected coals of widely varying plastic properties. Kinetic models were proposed for the isothermal plastometric curves. Plastic behavior was compared with a variety of laboratory analyses and characterizations of these coals, including classical coal analysis; mineral analysis; microstructural analysis (extractable fractions, surface area measurement, and petrographic analysis); and thermal analysis (thermogravimetric analysis, thermomechanical analysis, and differential scanning calorimetry). The phenomenon of a sharp, large, poorly reproducible exotherm in the differential scanning calorimetric analysis of coking coals was examined. Several coal extrudates show mineral distribution, organic maceral composition and overall calorific value to be little affected by 800 F extrusion. Volatile matter and plastic properties are moderately reduced, and the network structure (as gauged by extractables) appears to be slightly degraded in the extrusion process.

Neuronal plasticity and antidepressant actions

PubMed Central

Castrén, Eero; Hen, René

2013-01-01

Antidepressant treatments enhance plasticity and increase neurogenesis in the adult brain, but it has been unclear how these effects influence mood. We propose that like environmental enrichment and exercise, antidepressant treatments enhance adaptability by increasing structural variability within the nervous system at many levels, from proliferating precursors to immature synaptic contacts. Conversely, sensory deprivation and chronic stress reduce this structural variability. Activity-dependent competition within the mood-related circuits, guided by rehabilitation, then selects for the survival and stabilization of those structures that best represent the internal or external milieu. Increased variability together with competition-mediated selection facilitates normal function, such as pattern separation within the dentate gyrus and other mood-related circuits, thereby enhancing adaptability towards novel experiences. PMID:23380665

Organization and dynamics of the actin cytoskeleton during dendritic spine morphological remodeling.

PubMed

Chazeau, Anaël; Giannone, Grégory

2016-08-01

In the central nervous system, most excitatory post-synapses are small subcellular structures called dendritic spines. Their structure and morphological remodeling are tightly coupled to changes in synaptic transmission. The F-actin cytoskeleton is the main driving force of dendritic spine remodeling and sustains synaptic plasticity. It is therefore essential to understand how changes in synaptic transmission can regulate the organization and dynamics of actin binding proteins (ABPs). In this review, we will provide a detailed description of the organization and dynamics of F-actin and ABPs in dendritic spines and will discuss the current models explaining how the actin cytoskeleton sustains both structural and functional synaptic plasticity.

Computer program: Jet 3 to calculate the large elastic plastic dynamically induced deformations of free and restrained, partial and/or complete structural rings

NASA Technical Reports Server (NTRS)

Wu, R. W.; Witmer, E. A.

1972-01-01

A user-oriented FORTRAN 4 computer program, called JET 3, is presented. The JET 3 program, which employs the spatial finite-element and timewise finite-difference method, can be used to predict the large two-dimensional elastic-plastic transient Kirchhoff-type deformations of a complete or partial structural ring, with various support conditions and restraints, subjected to a variety of initial velocity distributions and externally-applied transient forcing functions. The geometric shapes of the structural ring can be circular or arbitrarily curved and with variable thickness. Strain-hardening and strain-rate effects of the material are taken into account.

Remodeling Functional Connectivity in Multiple Sclerosis: A Challenging Therapeutic Approach.

PubMed

Stampanoni Bassi, Mario; Gilio, Luana; Buttari, Fabio; Maffei, Pierpaolo; Marfia, Girolama A; Restivo, Domenico A; Centonze, Diego; Iezzi, Ennio

2017-01-01

Neurons in the central nervous system are organized in functional units interconnected to form complex networks. Acute and chronic brain damage disrupts brain connectivity producing neurological signs and/or symptoms. In several neurological diseases, particularly in Multiple Sclerosis (MS), structural imaging studies cannot always demonstrate a clear association between lesion site and clinical disability, originating the "clinico-radiological paradox." The discrepancy between structural damage and disability can be explained by a complex network perspective. Both brain networks architecture and synaptic plasticity may play important roles in modulating brain networks efficiency after brain damage. In particular, long-term potentiation (LTP) may occur in surviving neurons to compensate network disconnection. In MS, inflammatory cytokines dramatically interfere with synaptic transmission and plasticity. Importantly, in addition to acute and chronic structural damage, inflammation could contribute to reduce brain networks efficiency in MS leading to worse clinical recovery after a relapse and worse disease progression. These evidence suggest that removing inflammation should represent the main therapeutic target in MS; moreover, as synaptic plasticity is particularly altered by inflammation, specific strategies aimed at promoting LTP mechanisms could be effective for enhancing clinical recovery. Modulation of plasticity with different non-invasive brain stimulation (NIBS) techniques has been used to promote recovery of MS symptoms. Better knowledge of features inducing brain disconnection in MS is crucial to design specific strategies to promote recovery and use NIBS with an increasingly tailored approach.

[The recent news in endoscopic surgery: a review of the literature and meta-analysis].

PubMed

Klimenko, K É

2012-01-01

During a few recent years, endonasal surgery has become the principal tool for the operative treatment of many pathologies affecting the base of the skull. The present work was designed to estimate the possibilities of using endoscopic endonasal surgery to treat sinus and skull base lesions and illustrate the recent progress in the development of endoscopic equipment and instrumentation. The meta-analysis of the results of on-going research on the application of the endonasal endoscopic technology is described with the special emphasis on the plastic treatment of liquor fistulas, removal of juvenile nasopharyngeal angiofibromas, treatment of pathological changes in the clivial region and odontoid cervicomedullary junction.

Bartsocas-Papas Syndrome: A Case Report and Review of the Literature.

PubMed

Erturan, Gurhan; Holton, James; Wall, Steven; Giele, Henk

2016-04-01

Bartsocas-Papas syndrome (BPS) is an autosomal recessively inherited form of the popliteal pterygium syndrome characterized by severe growth retardation, midface hypoplasia, popliteal pterygia, and syndactyly. Almost all affected babies die in utero or infancy. We report the difficulties of reconstruction and ongoing plastic surgical management in an 8-year-old child with BPS. With increasingly sophisticated resuscitation and supportive techniques, it is possible that more patients with BPS will survive beyond the neonatal period. This raises new challenges with reconstruction highlighted by this case with a difficult balance between trying to overcome some of the profound effects of the syndrome versus diminishing quality of life for the child by repeated and often unsuccessful surgical procedures.

Group psychotherapy and neuro-plasticity: an attachment theory perspective.

PubMed

Flores, Philip J

2010-10-01

This article selectively highlights relevant areas of neuroscience research which have direct application for attachment theory and group psychotherapy. Emerging evidence from the neurosciences is revealing that the developing brain of the infant, sculpted by the earliest attachment relationships, continues to be malleable in adulthood and can be profoundly influenced by ongoing relationships throughout one's lifespan. Advances in the neurosciences are also supporting the idea that strong attachment bonds and external interpersonal interactions that arise within the context of these attachments are registered as a person's neurophysiology and neurobiology. Attachment theory in particular provides a common language and conceptual framework from which the contributions from the neurosciences can be made applicable to group psychotherapy.

Method for formation of thin film transistors on plastic substrates

DOEpatents

Carey, Paul G.; Smith, Patrick M.; Sigmon, Thomas W.; Aceves, Randy C.

1998-10-06

A process for formation of thin film transistors (TFTs) on plastic substrates replaces standard thin film transistor fabrication techniques, and uses sufficiently lower processing temperatures so that inexpensive plastic substrates may be used in place of standard glass, quartz, and silicon wafer-based substrates. The process relies on techniques for depositing semiconductors, dielectrics, and metals at low temperatures; crystallizing and doping semiconductor layers in the TFT with a pulsed energy source; and creating top-gate self-aligned as well as back-gate TFT structures. The process enables the fabrication of amorphous and polycrystalline channel silicon TFTs at temperatures sufficiently low to prevent damage to plastic substrates. The process has use in large area low cost electronics, such as flat panel displays and portable electronics.

On a phase field approach for martensitic transformations in a crystal plastic material at a loaded surface

NASA Astrophysics Data System (ADS)

Schmitt, Regina; Kuhn, Charlotte; Müller, Ralf

2017-07-01

A continuum phase field model for martensitic transformations is introduced, including crystal plasticity with different slip systems for the different phases. In a 2D setting, the transformation-induced eigenstrain is taken into account for two martensitic orientation variants. With aid of the model, the phase transition and its dependence on the volume change, crystal plastic material behavior, and the inheritance of plastic deformations from austenite to martensite are studied in detail. The numerical setup is motivated by the process of cryogenic turning. The resulting microstructure qualitatively coincides with an experimentally obtained martensite structure. For the numerical calculations, finite elements together with global and local implicit time integration scheme are employed.

Characterization of plasticized PEO-PAM blend polymer electrolyte system

NASA Astrophysics Data System (ADS)

Dave, Gargi; Kanchan, Dinesh

2017-05-01

Present study reports characterization studies of NaCF3SO3 based PEO-PAM Blend Polymer Electrolyte (BPE) system with varying amount of EC+PC as plasticizer prepared by solution cast technique. Structural analysis and surface topography have been performed using FTIR and SEM studies. To understand, thermal properties, DSC studies have been undertaken in the present paper

Synthesis and application of a novel environmental C26 diglycidyl ester plasticizer based on castor oil for poly(vinyl chloride)

USDA-ARS?s Scientific Manuscript database

In this work, for the first time, a castor oil derived diglycidyl ester plasticizer (C26-DGE) was prepared and incorporated into poly(vinyl chloride) (PVC). The chemical structure of the product was characterized by Fourier transform infrared spectroscopy (FT-IR), proton nuclear magnetic resonance (...

Age-Related Cognitive Impairments in Mice with a Conditional Ablation of the Neural Cell Adhesion Molecule

ERIC Educational Resources Information Center

Bisaz, Reto; Boadas-Vaello, Pere; Genoux, David; Sandi, Carmen

2013-01-01

Most of the mechanisms involved in neural plasticity support cognition, and aging has a considerable effect on some of these processes. The neural cell adhesion molecule (NCAM) of the immunoglobulin superfamily plays a pivotal role in structural and functional plasticity and is required to modulate cognitive and emotional behaviors. However,…

A Constitutive Relationship between Crack Propagation and Specific Damping Capacity in Steel

DTIC Science & Technology

1990-10-01

diagnostic tool for detecting crack growth in structures. The model must be simple to act as a tool, but it must be comprehensive to provide accuracy...strain for static fracture u ECritical strain above which plastic strain occursP EAverage value of the cyclic plastic-strain rangeP E t ln(Ao/AI), true

A Novel Probabilistic Multi-Scale Modeling and Sensing Framework for Fatigue Life Prediction of Aerospace Structures and Materials: DCT Project

DTIC Science & Technology

2012-08-25

Accel- erated Crystal Plasticity FEM Simulations (submitted). 5. M. Anahid, M. Samal and S. Ghosh, Dwell fatigue crack nucleation model based on using...4] M. Anahid, M. K. Samal , and S. Ghosh. Dwell fatigue crack nucleation model based on crystal plasticity finite element simulations of

Long-Term Exercise Is Needed to Enhance Synaptic Plasticity in the Hippocampus

ERIC Educational Resources Information Center

Patten, Anna R.; Sickmann, Helle; Hryciw, Brett N.; Kucharsky, Tessa; Parton, Roberta; Kernick, Aimee; Christie, Brian R.

2013-01-01

Exercise can have many benefits for the body, but it also benefits the brain by increasing neurogenesis, synaptic plasticity, and performance on learning and memory tasks. The period of exercise needed to realize the structural and functional benefits for the brain have not been well delineated, and previous studies have used periods of exercise…

Structural synaptic plasticity in the hippocampus induced by spatial experience and its implications in information processing.

PubMed

Carasatorre, M; Ramírez-Amaya, V; Díaz Cintra, S

2016-10-01

Long-lasting memory formation requires that groups of neurons processing new information develop the ability to reproduce the patterns of neural activity acquired by experience. Changes in synaptic efficiency let neurons organise to form ensembles that repeat certain activity patterns again and again. Among other changes in synaptic plasticity, structural modifications tend to be long-lasting which suggests that they underlie long-term memory. There is a large body of evidence supporting that experience promotes changes in the synaptic structure, particularly in the hippocampus. Structural changes to the hippocampus may be functionally implicated in stabilising acquired memories and encoding new information. Copyright © 2012 Sociedad Española de Neurología. Publicado por Elsevier España, S.L.U. All rights reserved.

Functional recovery of the dentate gyrus after a focal lesion is accompanied by structural reorganization in the adult rat.

PubMed

Zepeda, Angélica; Aguilar-Arredondo, Andrea; Michel, Gabriela; Ramos-Languren, Laura Elisa; Escobar, Martha L; Arias, Clorinda

2013-03-01

The adult brain is highly plastic and tends to undergo substantial reorganization after injury to compensate for the lesion effects. It has been shown that such reorganization mainly relies on anatomical and biochemical modifications of the remaining cells which give rise to a network rewiring without reinstating the original morphology of the damaged region. However, few studies have analyzed the neurorepair potential of a neurogenic structure. Thus, the aim of this work was to analyze if the DG could restore its original morphology after a lesion and to establish if the structural reorganization is accompanied by behavioral and electrophysiological recovery. Using a subepileptogenic injection of kainic acid (KA), we induced a focal lesion in the DG and assessed in time (1) the loss and recovery of dependent and non dependent DG cognitive functions, (2) the anatomical reorganization of the DG using a stereological probe and immunohistochemical markers for different neuronal maturation stages and, (3) synaptic plasticity as assessed through the induction of in vivo long-term potentiation (LTP) in the mossy fiber pathway (CA3-DG). Our results show that a DG focal lesion with KA leads to a well delimited region of neuronal loss, disorganization of the structure, the loss of associated mnemonic functions and the impairment to elicit LTP. However, behavioral and synaptic plasticity expression occurs in a time dependent fashion and occurs along the morphological restoration of the DG. These results provide novel information on neural plasticity events associated to functional reorganization after damage.

High within-canopy variation in isoprene emission potentials in temperate trees: Implications for predicting canopy-scale isoprene fluxes

NASA Astrophysics Data System (ADS)

Niinemets, ÜLo; Copolovici, Lucian; Hüve, Katja

2010-12-01

Isoprene emission potential (ES) varies in tree canopies, and such variations have potentially major implications for predicting canopy level emissions. So far, quantitative relationships of ES with irradiance are missing, and interspecific variation in ES plasticity and potential effects on canopy level emissions have not been characterized. ES, foliage structural, chemical, and photosynthetic characteristics were studied relative to integrated within-canopy daily quantum flux density (Qint) in temperate deciduous tree species Quercus robur, Populus tremula, Salix alba, and Salix caprea, and canopy isoprene emissions were calculated considering observed variation in ES and under different simplifying assumptions. Strong positive curvilinear relationships between nitrogen and dry mass per unit area, photosynthetic potentials and ES per area with Qint were observed. Structural, chemical, and photosynthetic traits varied 1.5-fold to 4-fold and ES per area 3-fold to 27-fold within the canopy. ES variation reflected accumulation of mesophyll cell layers and greater emission capacity of average cells. Species with largest structural and photosynthetic plasticity had greatest plasticity in ES. Relative to the simulation considering within-canopy variation in ES, the bias from assuming a constant ES varied between -8% and +68%, and it scaled positively with ES plasticity. The bias of big-leaf simulations varied between -22% and -35%, and it scaled negatively with ES plasticity. A generalized canopy response function of ES developed for all species resulted in the lowest bias between -11% and 6% and can be recommended for practical applications. The results highlight huge within-canopy and interspecific variation in ES and demonstrate that ignoring these variations strongly biases canopy emission predictions.

Investigations of plastic composite materials for highway safety structures

DOT National Transportation Integrated Search

1998-08-01

This report presents a basic overview and assessment of different concepts and technologies of using polymer composites in structures generally used for highway safety. The structural systems included a highway barrier guardrail with its posts and bl...

Biodegradability of degradable plastic waste.

PubMed

Agamuthu, P; Faizura, Putri Nadzrul

2005-04-01

Plastic waste constitutes the third largest waste volume in Malaysian municipal solid waste (MSW), next to putrescible waste and paper. The plastic component in MSW from Kuala Lumpur averages 24% (by weight), whereas the national mean is about 15%. The 144 waste dumps in the country receive about 95% of the MSW, including plastic waste. The useful life of the landfills is fast diminishing as the plastic waste stays un-degraded for more than 50 years. In this study the compostability of polyethylene and pro-oxidant additive-based environmentally degradable plastics (EDP) was investigated. Linear low-density polyethylene (LLDPE) samples exposed hydrolytically or oxidatively at 60 degrees C showed that the abiotic degradation path was oxidative rather than hydrolytic. There was a weight loss of 8% and the plastic has been oxidized as shown by the additional carbonyl group exhibited in the Fourier transform infra red (FTIR) Spectrum. Oxidation rate seemed to be influenced by the amount of pro-oxidant additive, the chemical structure and morphology of the plastic samples, and the surface area. Composting studies during a 45-day experiment showed that the percentage elongation (reduction) was 20% for McD samples [high-density polyethylene, (HDPE) with 3% additive] and LL samples (LLDPE with 7% additive) and 18% reduction for totally degradable plastic (TDP) samples (HDPE with 3% additive). Lastly, microbial experiments using Pseudomonas aeroginosa on carbon-free media with degradable plastic samples as the sole carbon source, showed confirmatory results. A positive bacterial growth and a weight loss of 2.2% for degraded polyethylene samples were evident to show that the degradable plastic is biodegradable.

Plastic Surgery Training Worldwide: Part 1. The United States and Europe

PubMed Central

Kamali, Parisa; van Paridon, Maaike W.; Ibrahim, Ahmed M. S.; Paul, Marek A.; Winters, Henri A.; Martinot-Duquennoy, Veronique; Noah, Ernst Magnus; Pallua, Norbert

2016-01-01

Background: Major differences exist in residency training, and the structure and quality of residency programs differ between different countries and teaching centers. It is of vital importance that a better understanding of the similarities and differences in plastic surgery training be ascertained as a means of initiating constructive discussion and commentary among training programs worldwide. In this study, the authors provide an overview of plastic surgery training in the United States and Europe. Methods: A survey was sent to select surgeons in 10 European countries that were deemed to be regular contributors to the plastic surgery literature. The questions focused on pathway to plastic surgery residency, length of training, required pretraining experience, training scheme, research opportunities, and examinations during and after plastic surgery residency. Results: Plastic surgery residency training programs in the United States differ from the various (selected) countries in Europe and are described in detail. Conclusions: Plastic surgery education is vastly different between the United States and Europe, and even within Europe, training programs remain heterogeneous. Standardization of curricula across the different countries would improve the interaction of different centers and facilitate the exchange of vital information for quality control and future improvements. The unique characteristics of the various training programs potentially provide a basis from which to learn and to gain from one another. PMID:27257571

Comparing the strength of behavioural plasticity and consistency across situations: animal personalities in the hermit crab Pagurus bernhardus.

PubMed

Briffa, Mark; Rundle, Simon D; Fryer, Adam

2008-06-07

Many phenotypic traits show plasticity but behaviour is often considered the 'most plastic' aspect of phenotype as it is likely to show the quickest response to temporal changes in conditions or 'situation'. However, it has also been noted that constraints on sensory acuity, cognitive structure and physiological capacities place limits on behavioural plasticity. Such limits to plasticity may generate consistent differences in behaviour between individuals from the same population. It has recently been suggested that these consistent differences in individual behaviour may be adaptive and the term 'animal personalities' has been used to describe them. In many cases, however, a degree of both behavioural plasticity and relative consistency is probable. To understand the possible functions of animal personalities, it is necessary to determine the relative strength of each tendency and this may be achieved by comparison of statistical effect sizes for tests of difference and concordance. Here, we describe a new statistical framework for making such comparisons and investigate cross-situational plasticity and consistency in the duration of startle responses in the European hermit crab Pagurus bernhardus, in the field and the laboratory. The effect sizes of tests for behavioural consistency were greater than for tests of behavioural plasticity, indicating for the first time the presence of animal personalities in a crustacean model.

Formation and remodeling of the brain extracellular matrix in neural plasticity: Roles of chondroitin sulfate and hyaluronan.

PubMed

Miyata, Shinji; Kitagawa, Hiroshi

2017-10-01

The extracellular matrix (ECM) of the brain is rich in glycosaminoglycans such as chondroitin sulfate (CS) and hyaluronan. These glycosaminoglycans are organized into either diffuse or condensed ECM. Diffuse ECM is distributed throughout the brain and fills perisynaptic spaces, whereas condensed ECM selectively surrounds parvalbumin-expressing inhibitory neurons (PV cells) in mesh-like structures called perineuronal nets (PNNs). The brain ECM acts as a non-specific physical barrier that modulates neural plasticity and axon regeneration. Here, we review recent progress in understanding of the molecular basis of organization and remodeling of the brain ECM, and the involvement of several types of experience-dependent neural plasticity, with a particular focus on the mechanism that regulates PV cell function through specific interactions between CS chains and their binding partners. We also discuss how the barrier function of the brain ECM restricts dendritic spine dynamics and limits axon regeneration after injury. The brain ECM not only forms physical barriers that modulate neural plasticity and axon regeneration, but also forms molecular brakes that actively controls maturation of PV cells and synapse plasticity in which sulfation patterns of CS chains play a key role. Structural remodeling of the brain ECM modulates neural function during development and pathogenesis. Genetic or enzymatic manipulation of the brain ECM may restore neural plasticity and enhance recovery from nerve injury. This article is part of a Special Issue entitled Neuro-glycoscience, edited by Kenji Kadomatsu and Hiroshi Kitagawa. Copyright © 2017 Elsevier B.V. All rights reserved.

Cortico-fugal output from visual cortex promotes plasticity of innate motor behaviour.

PubMed

Liu, Bao-Hua; Huberman, Andrew D; Scanziani, Massimo

2016-10-20

The mammalian visual cortex massively innervates the brainstem, a phylogenetically older structure, via cortico-fugal axonal projections. Many cortico-fugal projections target brainstem nuclei that mediate innate motor behaviours, but the function of these projections remains poorly understood. A prime example of such behaviours is the optokinetic reflex (OKR), an innate eye movement mediated by the brainstem accessory optic system, that stabilizes images on the retina as the animal moves through the environment and is thus crucial for vision. The OKR is plastic, allowing the amplitude of this reflex to be adaptively adjusted relative to other oculomotor reflexes and thereby ensuring image stability throughout life. Although the plasticity of the OKR is thought to involve subcortical structures such as the cerebellum and vestibular nuclei, cortical lesions have suggested that the visual cortex might also be involved. Here we show that projections from the mouse visual cortex to the accessory optic system promote the adaptive plasticity of the OKR. OKR potentiation, a compensatory plastic increase in the amplitude of the OKR in response to vestibular impairment, is diminished by silencing visual cortex. Furthermore, targeted ablation of a sparse population of cortico-fugal neurons that specifically project to the accessory optic system severely impairs OKR potentiation. Finally, OKR potentiation results from an enhanced drive exerted by the visual cortex onto the accessory optic system. Thus, cortico-fugal projections to the brainstem enable the visual cortex, an area that has been principally studied for its sensory processing function, to plastically adapt the execution of innate motor behaviours.

A feasibility study for using ABS plastic and a low-cost 3D printer for patient-specific brachytherapy mould design.

PubMed

Harris, Benjamin D; Nilsson, Sanna; Poole, Christopher M

2015-09-01

This feasibility study aims to determine if a low-cost 3D printer (BitsFromBytes 3D Touch) with ABS plastic can print custom mould structures and catheter channels defined in a brachytherapy treatment planning system (Nucletron Oncentra) for patient-specific treatment. Printer accuracy was evaluated through physical measurement, and print quality was investigated by adjusting print parameters (print speed, layer thickness, percentage infill). Catheter positioning and reproducibility were measured over repeated insertions. ABS plastic water equivalency was investigated by comparing Ir-192 HDR source dose distributions, measured with radiochromic film, in ABS plastic and in water. Structures and catheter channels were printed accurately to within 0.5 mm laterally and 1 mm in the vertical print direction. Adjusting print parameters could reduce print time, albeit with reduced print quality. 3.5 mm channel diameters allowed for easy catheter insertion. Catheter positioning was reproducible to within 0.5 mm but, because of catheter flex within the channel, was on average 1 mm offset from defined TPS positions. This offset could be accounted for by repeating the treatment planning CT scan with the printed mould positioned on the patient. Dose attenuation in ABS plastic and in water was equivalent to within the measurement limitations. While clinical uses for this particular low-cost printer and ABS plastic are limited by print size restrictions and non-certification for biocompatibility, it has been demonstrated that a low-cost 3D printer set-up can accurately create custom moulds and catheter channels potentially acceptable for clinical use.

mTORC1 controls long-term memory retrieval.

PubMed

Pereyra, Magdalena; Katche, Cynthia; de Landeta, Ana Belén; Medina, Jorge H

2018-06-08

Understanding how stored information emerges is a main question in the neurobiology of memory that is now increasingly gaining attention. However, molecular events underlying this memory stage, including involvement of protein synthesis, are not well defined. Mammalian target of rapamycin complex 1 (mTORC1), a central regulator of protein synthesis, has been implicated in synaptic plasticity and is required for memory formation. Using inhibitory avoidance (IA), we evaluated the role of mTORC1 in memory retrieval. Infusion of a selective mTORC1 inhibitor, rapamycin, into the dorsal hippocampus 15 or 40 min but not 3 h before testing at 24 h reversibly disrupted memory expression even in animals that had already expressed IA memory. Emetine, a general protein synthesis inhibitor, provoked a similar impairment. mTORC1 inhibition did not interfere with short-term memory retrieval. When infused before test at 7 or 14 but not at 28 days after training, rapamycin impaired memory expression. mTORC1 blockade in retrosplenial cortex, another structure required for IA memory, also impaired memory retention. In addition, pretest intrahippocampal rapamycin infusion impaired object location memory retrieval. Our results support the idea that ongoing protein synthesis mediated by activation of mTORC1 pathway is necessary for long but not for short term memory.

Another stage of development: Biological degeneracy and the study of bodily ageing.

PubMed

Mason, Paul H; Maleszka, Ryszard; Dominguez D, Juan F

2017-04-01

Ageing is a poorly understood process of human development mired by a scientific approach that struggles to piece together distributed variable factors involved in ongoing transformations of living systems. Reconfiguring existing research paradigms, we review the concept of 'degeneracy', which has divergent popular and technical definitions. The technical meaning of degeneracy refers to the structural diversity underlying functional plasticity. Degeneracy is a distributed system property that can be observed within individual brains or across different brains. For example, dementias with similar behavioural anomalies can result from a diverse range of cellular "faults", which is an example of degeneracy because the symptoms are similar in spite of different underlying mechanisms. Degeneracy is a valuable epistemological tool that can transformatively enhance scientific models of bodily ageing. We propose that movement science is one of the first areas that can productively integrate degeneracy into models of bodily ageing. We also propose model organisms such as eusocial honey bees in which degeneracy can be studied at the molecular and cellular level. Developing a vocabulary for thinking about how distributed variable factors are interlinked is important if we are to understand bodily ageing not as a single entity, but as the heterogeneous construction of changing biological, social, and environmental processes. Copyright © 2016 Elsevier Ireland Ltd. All rights reserved.

Microbes on a Bottle: Substrate, Season and Geography Influence Community Composition of Microbes Colonizing Marine Plastic Debris.

PubMed

Oberbeckmann, Sonja; Osborn, A Mark; Duhaime, Melissa B

2016-01-01

Plastic debris pervades in our oceans and freshwater systems and the potential ecosystem-level impacts of this anthropogenic litter require urgent evaluation. Microbes readily colonize aquatic plastic debris and members of these biofilm communities are speculated to include pathogenic, toxic, invasive or plastic degrading-species. The influence of plastic-colonizing microorganisms on the fate of plastic debris is largely unknown, as is the role of plastic in selecting for unique microbial communities. This work aimed to characterize microbial biofilm communities colonizing single-use poly(ethylene terephthalate) (PET) drinking bottles, determine their plastic-specificity in contrast with seawater and glass-colonizing communities, and identify seasonal and geographical influences on the communities. A substrate recruitment experiment was established in which PET bottles were deployed for 5-6 weeks at three stations in the North Sea in three different seasons. The structure and composition of the PET-colonizing bacterial/archaeal and eukaryotic communities varied with season and station. Abundant PET-colonizing taxa belonged to the phylum Bacteroidetes (e.g. Flavobacteriaceae, Cryomorphaceae, Saprospiraceae-all known to degrade complex carbon substrates) and diatoms (e.g. Coscinodiscophytina, Bacillariophytina). The PET-colonizing microbial communities differed significantly from free-living communities, but from particle-associated (>3 μm) communities or those inhabiting glass substrates. These data suggest that microbial community assembly on plastics is driven by conventional marine biofilm processes, with the plastic surface serving as raft for attachment, rather than selecting for recruitment of plastic-specific microbial colonizers. A small proportion of taxa, notably, members of the Cryomorphaceae and Alcanivoraceae, were significantly discriminant of PET but not glass surfaces, conjuring the possibility that these groups may directly interact with the PET substrate. Future research is required to investigate microscale functional interactions at the plastic surface.

Microbes on a Bottle: Substrate, Season and Geography Influence Community Composition of Microbes Colonizing Marine Plastic Debris

PubMed Central

Osborn, A. Mark

2016-01-01

Plastic debris pervades in our oceans and freshwater systems and the potential ecosystem-level impacts of this anthropogenic litter require urgent evaluation. Microbes readily colonize aquatic plastic debris and members of these biofilm communities are speculated to include pathogenic, toxic, invasive or plastic degrading-species. The influence of plastic-colonizing microorganisms on the fate of plastic debris is largely unknown, as is the role of plastic in selecting for unique microbial communities. This work aimed to characterize microbial biofilm communities colonizing single-use poly(ethylene terephthalate) (PET) drinking bottles, determine their plastic-specificity in contrast with seawater and glass-colonizing communities, and identify seasonal and geographical influences on the communities. A substrate recruitment experiment was established in which PET bottles were deployed for 5–6 weeks at three stations in the North Sea in three different seasons. The structure and composition of the PET-colonizing bacterial/archaeal and eukaryotic communities varied with season and station. Abundant PET-colonizing taxa belonged to the phylum Bacteroidetes (e.g. Flavobacteriaceae, Cryomorphaceae, Saprospiraceae—all known to degrade complex carbon substrates) and diatoms (e.g. Coscinodiscophytina, Bacillariophytina). The PET-colonizing microbial communities differed significantly from free-living communities, but from particle-associated (>3 μm) communities or those inhabiting glass substrates. These data suggest that microbial community assembly on plastics is driven by conventional marine biofilm processes, with the plastic surface serving as raft for attachment, rather than selecting for recruitment of plastic-specific microbial colonizers. A small proportion of taxa, notably, members of the Cryomorphaceae and Alcanivoraceae, were significantly discriminant of PET but not glass surfaces, conjuring the possibility that these groups may directly interact with the PET substrate. Future research is required to investigate microscale functional interactions at the plastic surface. PMID:27487037

The influence of James and Darwin on Cajal and his research into the neuron theory and evolution of the nervous system

PubMed Central

Ferreira, Francisco R. M.; Nogueira, Maria I.; DeFelipe, Javier

2014-01-01

In this article we discuss the influence of William James and Charles Darwin on the thoughts of Santiago Ramón y Cajal concerning the structure, plasticity, and evolution of the nervous system at the cellular level. Here we develop Cajal’s notion that neuronal theory is a necessary condition to explain the plasticity of neural connections. Although the roots of the term “plasticity” in reference to neuroscience are not completely clear, Cajal was an important figure in the propagation and popularization of its use. It is true that he carried out a large number of studies throughout his career in favor of the neuronal theory, but perhaps one of the most interesting aspects of his studies was his innovative capacity to interpret structure as being the result of evolutionary mechanisms, i.e., natural selection. This capacity would ultimately lead Cajal to the conclusion that, in relation to the histology of the nervous system, such selection occurs in the establishment of connections between cells. The present article is divided into five sections: (1) Learning and general notions of organic plasticity in the 19th century; (2) The idea of “mental” plasticity proposed by James; (3) Neuronal theory and “structural” plasticity: general considerations; (4) Evolutionary factors of the nervous system in Cajal’s work; and (5) Final considerations. PMID:24523676

Allocation, morphology, physiology, architecture: the multiple facets of plant above- and below-ground responses to resource stress.

PubMed

Freschet, Grégoire T; Violle, Cyrille; Bourget, Malo Y; Scherer-Lorenzen, Michael; Fort, Florian

2018-06-01

Plants respond to resource stress by changing multiple aspects of their biomass allocation, morphology, physiology and architecture. To date, we lack an integrated view of the relative importance of these plastic responses in alleviating resource stress and of the consistency/variability of these responses among species. We subjected nine species (legumes, forbs and graminoids) to nitrogen and/or light shortages and measured 11 above-ground and below-ground trait adjustments critical in the alleviation of these stresses (plus several underlying traits). Nine traits out of 11 showed adjustments that improved plants' potential capacity to acquire the limiting resource at a given time. Above ground, aspects of plasticity in allocation, morphology, physiology and architecture all appeared important in improving light capture, whereas below ground, plasticity in allocation and physiology were most critical to improving nitrogen acquisition. Six traits out of 11 showed substantial heterogeneity in species plasticity, with little structuration of these differences within trait covariation syndromes. Such comprehensive assessment of the complex nature of phenotypic responses of plants to multiple stress factors, and the comparison of plant responses across multiple species, makes a clear case for the high (but largely overlooked) diversity of potential plastic responses of plants, and for the need to explore the potential rules structuring them. © 2018 The Authors. New Phytologist © 2018 New Phytologist Trust.

Conformational Plasticity of the Influenza A M2 Transmembrane Helix in Lipid Bilayers Under Varying pH, Drug Binding and Membrane Thickness

PubMed Central

Hu, Fanghao; Luo, Wenbin; Cady, Sarah D.; Hong, Mei

2010-01-01

Membrane proteins change their conformations to respond to environmental cues, thus conformational plasticity is important for function. The influenza A M2 protein forms an acid-activated proton channel important for the virus lifecycle. Here we have used solid-state NMR spectroscopy to examine the conformational plasticity of membrane-bound transmembrane domain of M2 (M2TM). 13C and 15N chemical shifts indicate coupled conformational changes of several pore-facing residues due to changes in bilayer thickness, drug binding and pH. The structural changes are attributed to the formation of a well-defined helical kink at G34 in the drug-bound state and in thick lipid bilayers, non-ideal backbone conformation of the secondary-gate residue V27 in the presence of drug, and non-ideal conformation of the proton-sensing residue H37 at high pH. The chemical shifts constrained the (ϕ, ψ) torsion angles for three basis states, the equilibrium among which explains the multiple resonances per site in the NMR spectra under different combinations of bilayer thickness, drug binding and pH conditions. Thus, conformational plasticity is important for the proton conduction and inhibition of M2TM. The study illustrates the utility of NMR chemical shifts for probing the structural plasticity and folding of membrane proteins. PMID:20883664

Reprint of: Effects of cold deformation, electron irradiation and extrusion on deuterium desorption behavior in Zr-1%Nb alloy

NASA Astrophysics Data System (ADS)

Morozov, O.; Mats, O.; Mats, V.; Zhurba, V.; Khaimovich, P.

2018-01-01

The present article introduces the data of analysis of ranges of ion-implanted deuterium desorption from Zr-1% Nb alloy. The samples studied underwent plastic deformation, low temperature extrusion and electron irradiation. Plastic rolling of the samples at temperature ∼300 K resulted in plastic deformation with the degree of ε = 3.9 and the formation of nanostructural state with the average grain size of d = 61 nm. The high degree of defectiveness is shown in thermodesorption spectrum as an additional area of the deuterium desorption in the temperature ranges 650-850 K. The further processing of the sample (that had undergone plastic deformation by plastic rolling) with electron irradiation resulted in the reduction of the average grain size (58 nm) and an increase in borders concentration. As a result the amount of deuterium desorpted increased in the temperature ranges 650-900 K. In case of Zr-1% Nb samples deformed by extrusion the extension of desorption area is observed towards the temperature reduction down to 420 K. The formation of the phase state of deuterium solid solution in zirconium was not observed. The structural state behavior is a control factor in the process of deuterium thermodesorption spectrum structure formation with a fixed implanted deuterium dose (hydrogen diagnostics). It appears as additional temperature ranges of deuterium desorption depending on the type, character and defect content.

Elastic precursor wave decay in shock-compressed aluminum over a wide range of temperature

NASA Astrophysics Data System (ADS)

Austin, Ryan A.

2018-01-01

The effect of temperature on the dynamic flow behavior of aluminum is considered in the context of precursor wave decay measurements and simulations. In this regard, a dislocation-based model of high-rate metal plasticity is brought into agreement with previous measurements of evolving wave profiles at 300 to 933 K, wherein the amplification of the precursor structure with temperature arises naturally from the dislocation mechanics treatment. The model suggests that the kinetics of inelastic flow and stress relaxation are governed primarily by phonon scattering and radiative damping (sound wave emission from dislocation cores), both of which intensify with temperature. The manifestation of these drag effects is linked to low dislocation density ahead of the precursor wave and the high mobility of dislocations in the face-centered cubic lattice. Simulations performed using other typical models of shock wave plasticity do not reproduce the observed temperature-dependence of elastic/plastic wave structure.

Atomistic basis for the plastic yield criterion of metallic glass.

PubMed

Schuh, Christopher A; Lund, Alan C

2003-07-01

Because of their disordered atomic structure, amorphous metals (termed metallic glasses) have fundamentally different deformation mechanisms compared with polycrystalline metals. These different mechanisms give metallic glasses high strength, but the extent to which they affect other macroscopic deformation properties is uncertain. For example, the nature of the plastic-yield criterion is a point of contention, with some studies reporting yield behaviour roughly in line with that of polycrystalline metals, and others indicating strong fundamental differences. In particular, it is unclear whether pressure- or normal stress-dependence needs to be included in the plastic-yield criterion of metallic glasses, and how such a dependence could arise from their disordered structure. In this work we provide an atomic-level explanation for pressure-dependent yield in amorphous metals, based on an elementary unit of deformation. This simple model compares favourably with new atomistic simulations of metallic glasses, as well as existing experimental data.

Spatial Organization Plasticity as an Adaptive Driver of Surface Microbial Communities

PubMed Central

Bridier, Arnaud; Piard, Jean-Christophe; Pandin, Caroline; Labarthe, Simon; Dubois-Brissonnet, Florence; Briandet, Romain

2017-01-01

Biofilms are dynamic habitats which constantly evolve in response to environmental fluctuations and thereby constitute remarkable survival strategies for microorganisms. The modulation of biofilm functional properties is largely governed by the active remodeling of their three-dimensional structure and involves an arsenal of microbial self-produced components and interconnected mechanisms. The production of matrix components, the spatial reorganization of ecological interactions, the generation of physiological heterogeneity, the regulation of motility, the production of actives enzymes are for instance some of the processes enabling such spatial organization plasticity. In this contribution, we discussed the foundations of architectural plasticity as an adaptive driver of biofilms through the review of the different microbial strategies involved. Moreover, the possibility to harness such characteristics to sculpt biofilm structure as an attractive approach to control their functional properties, whether beneficial or deleterious, is also discussed. PMID:28775718

A simplified method for elastic-plastic-creep structural analysis

NASA Technical Reports Server (NTRS)

Kaufman, A.

1984-01-01

A simplified inelastic analysis computer program (ANSYPM) was developed for predicting the stress-strain history at the critical location of a thermomechanically cycled structure from an elastic solution. The program uses an iterative and incremental procedure to estimate the plastic strains from the material stress-strain properties and a plasticity hardening model. Creep effects are calculated on the basis of stress relaxation at constant strain, creep at constant stress or a combination of stress relaxation and creep accumulation. The simplified method was exercised on a number of problems involving uniaxial and multiaxial loading, isothermal and nonisothermal conditions, dwell times at various points in the cycles, different materials and kinematic hardening. Good agreement was found between these analytical results and nonlinear finite element solutions for these problems. The simplified analysis program used less than 1 percent of the CPU time required for a nonlinear finite element analysis.

A simplified method for elastic-plastic-creep structural analysis

NASA Technical Reports Server (NTRS)

Kaufman, A.

1985-01-01

A simplified inelastic analysis computer program (ANSYPM) was developed for predicting the stress-strain history at the critical location of a thermomechanically cycled structure from an elastic solution. The program uses an iterative and incremental procedure to estimate the plastic strains from the material stress-strain properties and a plasticity hardening model. Creep effects are calculated on the basis of stress relaxation at constant strain, creep at constant stress or a combination of stress relaxation and creep accumulation. The simplified method was exercised on a number of problems involving uniaxial and multiaxial loading, isothermal and nonisothermal conditions, dwell times at various points in the cycles, different materials and kinematic hardening. Good agreement was found between these analytical results and nonlinear finite element solutions for these problems. The simplified analysis program used less than 1 percent of the CPU time required for a nonlinear finite element analysis.

Observed Personality in Childhood: Psychometric and Behavioral Genetic Evidence of Two Broad Personality Factors

PubMed Central

Wang, Zhe; Chen, Nan; Petrill, Stephen A.; Deater-Deckard, Kirby

2014-01-01

We examined broad dimensions of children’s personalities (total n = 1056; age = 3.5 to 12 years) based on observers’ perceptions following a few hours of structured interaction. Siblings’ behaviors during a two-hour cognitive assessment in the home were rated separately by two different observers. Exploratory and confirmatory factor analyses clearly revealed a two-factor solution in three different samples. There was correspondence between parent-rated temperament and the observer-rated factors. Cross-sectional analyses indicated lower Plasticity among older children and higher Stability among older children. Sex differences were negligible. Plasticity and Stability were correlated in the .2 to .3 range. Most of the sibling similarity in the Plasticity was due to additive genetic influences, whereas most sibling similarity in Stability was attributable to shared environmental influences. The findings implicate a biometric factor structure to childhood personality that fits well with emerging bio-social theories of personality development. PMID:24932065

Conformational plasticity of the Ebola virus matrix protein.

PubMed

Radzimanowski, Jens; Effantin, Gregory; Weissenhorn, Winfried

2014-11-01

Filoviruses are the causative agents of a severe and often fatal hemorrhagic fever with repeated outbreaks in Africa. They are negative sense single stranded enveloped viruses that can cross species barriers from its natural host bats to primates including humans. The small size of the genome poses limits to viral adaption, which may be partially overcome by conformational plasticity. Here we review the different conformational states of the Ebola virus (EBOV) matrix protein VP40 that range from monomers, to dimers, hexamers, and RNA-bound octamers. This conformational plasticity that is required for the viral life cycle poses a unique opportunity for development of VP40 specific drugs. Furthermore, we compare the structure to homologous matrix protein structures from Paramyxoviruses and Bornaviruses and we predict that they do not only share the fold but also the conformational flexibility of EBOV VP40. © 2014 The Protein Society.

Structure and mechanical properties of aging Al-Li-Cu-Zr-Sc-Ag alloy after severe plastic deformation by high-pressure torsion

NASA Astrophysics Data System (ADS)

Kaigorodova, L. I.; Rasposienko, D. Yu.; Pushin, V. G.; Pilyugin, V. P.; Smirnov, S. V.

2015-04-01

The structural and phase transformations have been studied in aging commercial aluminum-lithium alloy Al-1.2 Li-3.2 Cu-0.09 Zr-0.11 Sc-0.4 Ag-0.3 Mg in the as-delivered state and after severe plastic deformation by torsion for 1, 5 and 10 revolutions under a high pressure of 4 GPa. Deformation-induced nanofragmentation and dynamic recrystallization have been found to occur in the alloy. The degree of recrystallization increases with deformation. Nanofragmentation and recrystallization processes are accompanied by the deformation-induced decomposition of solid solution and changes in both the nucleation mechanism of precipitation and the phase composition of the alloy. The influence of a nanostructured nanophase state of the alloy on its mechanical properties (microhardness, plasticity, elastic modulus, and stiffness) is discussed.

Advantages and disadvantages of pinless external fixation.

PubMed

Thomas, S R; Giele, H; Simpson, A H

2000-12-01

The AO pinless external fixator (PEF) uses trocar tipped clamps to grip the outer tibial cortex rather than pins to transfix it. Its main advantage is to avoid further contamination of the medullary canal in open tibial fractures where a nail may subsequently be used. We tested the anatomical safety of this device and its effect on plastic surgical procedures compared with a standard unilateral external fixator (UEF).The PEF and UEF were placed on two amputated limbs which were then dissected. Structures at risk were traced on ten cadaver limbs. We found that important anatomical structures were endangered by the PEF and that safe zones could not always be defined. The UEF avoided these structures. Plastic surgical approaches were made more difficult by the PEF which imposed limitations on local flap design and endangered the arterial perforators which supply them. We conclude that safety is compromised by the PEF because margins for error are small. It poses additional problems in soft tissue reconstruction and highlights the need for co-operation between plastic surgical and orthopaedic teams in choice of fixation device.

Intramolecular structural model for photoinduced plasticity in chalcogenide glasses

NASA Astrophysics Data System (ADS)

Yannopoulos, S. N.

2003-08-01

Selected spectral features of Raman spectra of glassy As2S3 subjected to elongation stress and sub-band-gap light illumination are analyzed and compared with polarization-dependent information obtained from the bulk glass at room temperature and near the glass transition temperature. The data are suggestive of specific structural changes which involve the transformation of atomic arrangements from realgarlike As4S4 molecules, originally present in virgin (untreated) fibers, into planar orpimentlike clusters. Implications of these atomic rearrangements to the incipient photoinduced fluidity—the onset of plastic deformation—in As2S3 glass are discussed. Kinetics of photoinduced plastic changes is compared to that of Raman spectra changes, revealing a qualitative similar behavior. An approximate estimation of the relative contribution of intermolecular rearrangements and the intramolecular structural mechanism proposed in this paper has revealed that the latter is responsible for almost 30% of the photoinduced elongation of the fiber’s length at room temperature. The proposed mechanism can as well serve as rationale for understanding the photoinduced volume expansion observed in chalcogenide glasses.

Intrinsic Bauschinger effect and recoverable plasticity in pentatwinned silver nanowires tested in tension.

PubMed

Bernal, Rodrigo A; Aghaei, Amin; Lee, Sangjun; Ryu, Seunghwa; Sohn, Kwonnam; Huang, Jiaxing; Cai, Wei; Espinosa, Horacio

2015-01-14

Silver nanowires are promising components of flexible electronics such as interconnects and touch displays. Despite the expected cyclic loading in these applications, characterization of the cyclic mechanical behavior of chemically synthesized high-quality nanowires has not been reported. Here, we combine in situ TEM tensile tests and atomistic simulations to characterize the cyclic stress-strain behavior and plasticity mechanisms of pentatwinned silver nanowires with diameters thinner than 120 nm. The experimental measurements were enabled by a novel system allowing displacement-controlled tensile testing of nanowires, which also affords higher resolution for capturing stress-strain curves. We observe the Bauschinger effect, that is, asymmetric plastic flow, and partial recovery of the plastic deformation upon unloading. TEM observations and atomistic simulations reveal that these processes occur due to the pentatwinned structure and emerge from reversible dislocation activity. While the incipient plastic mechanism through the nucleation of stacking fault decahedrons (SFDs) is fully reversible, plasticity becomes only partially reversible as intersecting SFDs lead to dislocation reactions and entanglements. The observed plastic recovery is expected to have implications to the fatigue life and the application of silver nanowires to flexible electronics.

The Contingency of Cocaine Administration Accounts for Structural and Functional Medial Prefrontal Deficits and Increased Adrenocortical Activation

PubMed Central

Anderson, Rachel M.; Cosme, Caitlin V.; Glanz, Ryan M.; Miller, Mary C.; Romig-Martin, Sara A.; LaLumiere, Ryan T.

2015-01-01

The prelimbic region (PL) of the medial prefrontal cortex (mPFC) is implicated in the relapse of drug-seeking behavior. Optimal mPFC functioning relies on synaptic connections involving dendritic spines in pyramidal neurons, whereas prefrontal dysfunction resulting from elevated glucocorticoids, stress, aging, and mental illness are each linked to decreased apical dendritic branching and spine density in pyramidal neurons in these cortical fields. The fact that cocaine use induces activation of the stress-responsive hypothalamo-pituitary-adrenal axis raises the possibility that cocaine-related impairments in mPFC functioning may be manifested by similar changes in neuronal architecture in mPFC. Nevertheless, previous studies have generally identified increases, rather than decreases, in structural plasticity in mPFC after cocaine self-administration. Here, we use 3D imaging and analysis of dendritic spine morphometry to show that chronic cocaine self-administration leads to mild decreases of apical dendritic branching, prominent dendritic spine attrition in PL pyramidal neurons, and working memory deficits. Importantly, these impairments were largely accounted for in groups of rats that self-administered cocaine compared with yoked-cocaine- and saline-matched counterparts. Follow-up experiments failed to demonstrate any effects of either experimenter-administered cocaine or food self-administration on structural alterations in PL neurons. Finally, we verified that the cocaine self-administration group was distinguished by more protracted increases in adrenocortical activity compared with yoked-cocaine- and saline-matched controls. These studies suggest a mechanism whereby increased adrenocortical activity resulting from chronic cocaine self-administration may contribute to regressive prefrontal structural and functional plasticity. SIGNIFICANCE STATEMENT Stress, aging, and mental illness are each linked to decreased prefrontal plasticity. Here, we show that chronic cocaine self-administration in rats leads to decrements in medial prefrontal structural and functional plasticity. Notably, these impairments were largely accounted for in rats that self-administered cocaine compared with yoked counterparts. Moreover, we verified previous reports showing that adrenocortical output is augmented by cocaine administration and is more protracted in rats that were permitted to receive the drug contingently instead of passively. These studies suggest that increased adrenocortical activity resulting from cocaine self-administration may contribute to regressive prefrontal structural and functional plasticity. PMID:26311772

Slip Zone versus Damage Zone Micromechanics, Arima-Takasuki Tectonic Line, Japan

NASA Astrophysics Data System (ADS)

White, J. C.; Lin, A.

2017-12-01

The Arima-Takasuki Tectonic Line (ATTL) of southern Honshu, Japan is defined by historically active faults and multiple splays producing M7 earthquakes. The damage zone of the ATTL comprises a broad zone of crushed, comminuted and pulverized granite/rhyolite1,2containing cm-scale slip zones and highly comminuted injection veins. In this presentation, prior work on the ATTL fault rocks is extending to include microstructural characterization by transmission electron microscopy (TEM) from recent trenching of the primary slip zone, as well as secondary slip zones. This is necessary to adequately characterize the extremely fine-grained material (typically less than 1mm) in both damage and core zones. Damage zone material exhibits generally random textures3 whereas slip zones are macroscopically foliated, and compositionally layered, notwithstanding a fairly homogeneous protolith. The latter reflects fluid-rock interaction during both coseismic and interseismic periods. The slip zones are microstructurally heterogeneous at all scales, comprising not only cataclasites and phyllosilicate (clay)-rich gouge zones, but Fe/Mn pellets or clasts that are contained within gouge. These structures appear to have rolled and would suggest rapid recrystallization and/or growth. A central question related to earthquake recurrence along existing faults is the nature of the gouge. In both near-surface exposures and ongoing drilling at depth, "plastic" or "viscous" gouge zones comprise ultra-fine-grained clay-siliciclastic particles that would not necessarily respond in a simple frictional manner. Depending on whether the plastic nature of these slip zones develops during or after slip, subsequent focusing of slip within them could be complicated. 1 Mitchell, T.A., Ben-Zion, Y., Shimamoto, T., 2011. Ear. Planet. Sci. Lett. 308, 284-297. 2 Lin, A., Yamashita, K, Tanaka, M. J., 2013. Struc. Geol. 48, 3-13. 3 White, J.C., Lin, A. 2016. Proc. AGU Fall Mtg., T42-02 San Francisco.

Age-related changes in the plasticity and toughness of human cortical bone at multiple length-scales

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zimmermann, Elizabeth A.; Schaible, Eric; Bale, Hrishikesh

2011-08-10

The structure of human cortical bone evolves over multiple length-scales from its basic constituents of collagen and hydroxyapatite at the nanoscale to osteonal structures at nearmillimeter dimensions, which all provide the basis for its mechanical properties. To resist fracture, bone’s toughness is derived intrinsically through plasticity (e.g., fibrillar sliding) at structural-scales typically below a micron and extrinsically (i.e., during crack growth) through mechanisms (e.g., crack deflection/bridging) generated at larger structural-scales. Biological factors such as aging lead to a markedly increased fracture risk, which is often associated with an age-related loss in bone mass (bone quantity). However, we find that age-relatedmore » structural changes can significantly degrade the fracture resistance (bone quality) over multiple lengthscales. Using in situ small-/wide-angle x-ray scattering/diffraction to characterize sub-micron structural changes and synchrotron x-ray computed tomography and in situ fracture-toughness measurements in the scanning electron microscope to characterize effects at micron-scales, we show how these age-related structural changes at differing size-scales degrade both the intrinsic and extrinsic toughness of bone. Specifically, we attribute the loss in toughness to increased non-enzymatic collagen cross-linking which suppresses plasticity at nanoscale dimensions and to an increased osteonal density which limits the potency of crack-bridging mechanisms at micron-scales. The link between these processes is that the increased stiffness of the cross-linked collagen requires energy to be absorbed by “plastic” deformation at higher structural levels, which occurs by the process of microcracking.« less

The limits of modifying migration speed to adjust to climate change

NASA Astrophysics Data System (ADS)

Schmaljohann, Heiko; Both, Christiaan

2017-08-01

Predicting the range of variation over which organisms can adjust to environmental change is a major challenge in ecology. This is exemplified in migratory birds which experience changes in different habitats throughout the annual cycle. Earlier studies showed European population trends declining strongest in migrant species with least adjustment in spring arrival time. Thus, the increasing mismatches with other trophic levels in seasonal breeding areas probably contribute to their large-scale decline. Here we quantify the potential range of adjusting spring arrival dates through modifying migration speeds by reviewing 49 tracking studies. Among-individual variation in migration speed was mainly determined by the relatively short stop-over duration. Assuming this population response reflects individual phenotypic plasticity, we calculated the potential for phenotypic plasticity to speed-up migration by reducing stop-over duration. Even a 50% reduction would lead to a mere two-day advance in arrival, considering adjustments on the final 2,000 km of the spring journey. Hence, in contrast to previous studies, flexibility in the major determinant of migration duration seems insufficient to adjust to ongoing climate change, and is unlikely to explain some of the observed arrival advancements in long-distance migrants.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ren, Jingli; Chen, Cun; Wang, Gang

This study explores the temporal scaling behavior induced shear-branching structure in response to variant temperatures and strain rates during plastic deformation of Zr-based bulk metallic glass (BMG). The data analysis based on the compression tests suggests that there are two states of shear-branching structures: the fractal structure with a long-range order at an intermediate temperature of 223 K and a larger strain rate of 2.5 × 10 –2 s –1; the disordered structure dominated at other temperature and strain rate. It can be deduced from the percolation theory that the compressive ductility, ec, can reach the maximum value at themore » intermediate temperature. Furthermore, a dynamical model involving temperature is given for depicting the shear-sliding process, reflecting the plastic deformation has fractal structure at the temperature of 223 K and strain rate of 2.5 × 10 –2 s –1.« less

SSME structural computer program development. Volume 2: BOPACE users manual

NASA Technical Reports Server (NTRS)

Vos, R. G.

1973-01-01

A computer program for use with a thermal-elastic-plastic-creep structural analyzer is presented. The following functions of the computer program are discussed: (1) analysis of very high temperature and large plastic-creep effects, (2) treatment of cyclic thermal and mechanical loads, (3) development of constitutive theory which closely follows actual behavior under variable temperature conditions, (4) stable numerical solution approach which avoids cumulative errors, and (5) capability of handling up to 1000 degrees of freedom. The computer program is written in FORTRAN IV and has been run on the IBM 360 and UNIVAC 1108 computer systems.

Algorithms for elasto-plastic-creep postbuckling

NASA Technical Reports Server (NTRS)

Padovan, J.; Tovichakchaikul, S.

1984-01-01

This paper considers the development of an improved constrained time stepping scheme which can efficiently and stably handle the pre-post-buckling behavior of general structure subject to high temperature environments. Due to the generality of the scheme, the combined influence of elastic-plastic behavior can be handled in addition to time dependent creep effects. This includes structural problems exhibiting indefinite tangent properties. To illustrate the capability of the procedure, several benchmark problems employing finite element analyses are presented. These demonstrate the numerical efficiency and stability of the scheme. Additionally, the potential influence of complex creep histories on the buckling characteristics is considered.

Analytical, Numerical and Experimental Examination of Reinforced Composites Beams Covered with Carbon Fiber Reinforced Plastic

NASA Astrophysics Data System (ADS)

Kasimzade, A. A.; Tuhta, S.

2012-03-01

In the article, analytical, numerical (Finite Element Method) and experimental investigation results of beam that was strengthened with fiber reinforced plastic-FRP composite has been given as comparative, the effect of FRP wrapping number to the maximum load and moment capacity has been evaluated depending on this results. Carbon FRP qualitative dependences have been occurred between wrapping number and beam load and moment capacity for repair-strengthen the reinforced concrete beams with carbon fiber. Shown possibilities of application traditional known analysis programs, for the analysis of Carbon Fiber Reinforced Plastic (CFRP) strengthened structures.

Heuristic rule for binary superlattice coassembly: mixed plastic mesophases of hard polyhedral nanoparticles.

PubMed

Khadilkar, Mihir R; Escobedo, Fernando A

2014-10-17

Sought-after ordered structures of mixtures of hard anisotropic nanoparticles can often be thermodynamically unfavorable due to the components' geometric incompatibility to densely pack into regular lattices. A simple compatibilization rule is identified wherein the particle sizes are chosen such that the order-disorder transition pressures of the pure components match (and the entropies of the ordered phases are similar). Using this rule with representative polyhedra from the truncated-cube family that form pure-component plastic crystals, Monte Carlo simulations show the formation of plastic-solid solutions for all compositions and for a wide range of volume fractions.

Quantitative measurement of adhesion of ink on plastic films with a Nano Indenter and a Scanning Probe Microscope

NASA Astrophysics Data System (ADS)

Shen, Weidian

2005-03-01

Plastic film packaging is widely used these days, especially in the convenience food industry due to its flexibility, boilability, and microwavability. Almost every package is printed with ink. The adhesion of ink on plastic films merits increasing attention to ensure quality packaging. However, inks and plastic films are polymeric materials with complicated molecular structures. The thickness of the jelly-like ink is only 500nm or less, and the thickness of the soft and flexible film is no more than 50μm, which make the quantitative measurement of their adhesion very challenging. Up to now, no scientific quantitative measurement method for the adhesion of ink on plastic films has been documented. We have tried a technique, in which a Nano-Indenter and a Scanning Probe Microscope were used to evaluate the adhesion strength of ink deposited on plastic films, quantitatively, as well as examine the configurations of adhesion failure. It was helpful in better understanding the adhesion mechanism, thus giving direction as to how to improve the adhesion.

Long-Term Plasticity of Neurotransmitter Release: Emerging Mechanisms and Contributions to Brain Function and Disease.

PubMed

Monday, Hannah R; Younts, Thomas J; Castillo, Pablo E

2018-04-25

Long-lasting changes of brain function in response to experience rely on diverse forms of activity-dependent synaptic plasticity. Chief among them are long-term potentiation and long-term depression of neurotransmitter release, which are widely expressed by excitatory and inhibitory synapses throughout the central nervous system and can dynamically regulate information flow in neural circuits. This review article explores recent advances in presynaptic long-term plasticity mechanisms and contributions to circuit function. Growing evidence indicates that presynaptic plasticity may involve structural changes, presynaptic protein synthesis, and transsynaptic signaling. Presynaptic long-term plasticity can alter the short-term dynamics of neurotransmitter release, thereby contributing to circuit computations such as novelty detection, modifications of the excitatory/inhibitory balance, and sensory adaptation. In addition, presynaptic long-term plasticity underlies forms of learning and its dysregulation participates in several neuropsychiatric conditions, including schizophrenia, autism, intellectual disabilities, neurodegenerative diseases, and drug abuse. Expected final online publication date for the Annual Review of Neuroscience Volume 41 is July 8, 2018. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Translational control of auditory imprinting and structural plasticity by eIF2α

PubMed Central

Batista, Gervasio; Johnson, Jennifer Leigh; Dominguez, Elena; Costa-Mattioli, Mauro; Pena, Jose L

2016-01-01

The formation of imprinted memories during a critical period is crucial for vital behaviors, including filial attachment. Yet, little is known about the underlying molecular mechanisms. Using a combination of behavior, pharmacology, in vivo surface sensing of translation (SUnSET) and DiOlistic labeling we found that, translational control by the eukaryotic translation initiation factor 2 alpha (eIF2α) bidirectionally regulates auditory but not visual imprinting and related changes in structural plasticity in chickens. Increasing phosphorylation of eIF2α (p-eIF2α) reduces translation rates and spine plasticity, and selectively impairs auditory imprinting. By contrast, inhibition of an eIF2α kinase or blocking the translational program controlled by p-eIF2α enhances auditory imprinting. Importantly, these manipulations are able to reopen the critical period. Thus, we have identified a translational control mechanism that selectively underlies auditory imprinting. Restoring translational control of eIF2α holds the promise to rejuvenate adult brain plasticity and restore learning and memory in a variety of cognitive disorders. DOI: http://dx.doi.org/10.7554/eLife.17197.001 PMID:28009255

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bishop, Joseph E.; Emery, John M.; Battaile, Corbett C.

Two fundamental approximations in macroscale solid-mechanics modeling are (1) the assumption of scale separation in homogenization theory and (2) the use of a macroscopic plasticity material model that represents, in a mean sense, the multitude of inelastic processes occurring at the microscale. With the goal of quantifying the errors induced by these approximations on engineering quantities of interest, we perform a set of direct numerical simulations (DNS) in which polycrystalline microstructures are embedded throughout a macroscale structure. The largest simulations model over 50,000 grains. The microstructure is idealized using a randomly close-packed Voronoi tessellation in which each polyhedral Voronoi cellmore » represents a grain. An face centered cubic crystal-plasticity model is used to model the mechanical response of each grain. The overall grain structure is equiaxed, and each grain is randomly oriented with no overall texture. The detailed results from the DNS simulations are compared to results obtained from conventional macroscale simulations that use homogeneous isotropic plasticity models. The macroscale plasticity models are calibrated using a representative volume element of the idealized microstructure. Furthermore, we envision that DNS modeling will be used to gain new insights into the mechanics of material deformation and failure.« less

Developmental metaplasticity in neural circuit codes of firing and structure.

PubMed

Baram, Yoram

2017-01-01

Firing-rate dynamics have been hypothesized to mediate inter-neural information transfer in the brain. While the Hebbian paradigm, relating learning and memory to firing activity, has put synaptic efficacy variation at the center of cortical plasticity, we suggest that the external expression of plasticity by changes in the firing-rate dynamics represents a more general notion of plasticity. Hypothesizing that time constants of plasticity and firing dynamics increase with age, and employing the filtering property of the neuron, we obtain the elementary code of global attractors associated with the firing-rate dynamics in each developmental stage. We define a neural circuit connectivity code as an indivisible set of circuit structures generated by membrane and synapse activation and silencing. Synchronous firing patterns under parameter uniformity, and asynchronous circuit firing are shown to be driven, respectively, by membrane and synapse silencing and reactivation, and maintained by the neuronal filtering property. Analytic, graphical and simulation representation of the discrete iteration maps and of the global attractor codes of neural firing rate are found to be consistent with previous empirical neurobiological findings, which have lacked, however, a specific correspondence between firing modes, time constants, circuit connectivity and cortical developmental stages. Copyright © 2016 Elsevier Ltd. All rights reserved.

New mesoscopic constitutive model for deformation of pearlitic steels up to moderate strains

NASA Astrophysics Data System (ADS)

Alkorta, J.; Martínez-Esnaola, J. M.; de Jaeger, P.; Gil Sevillano, J.

2017-07-01

A new constitutive model for deformation of pearlitic steels has been developed that describes the mechanical behaviour and microstructural evolution of lamellar multi-colony pearlite. The model, a two-phase continuum model, considers the plastic anisotropy of ferrite derived from its lamellar structure but ignores any anisotropy associated with cementite and does not consider the crystal structure of either constituent. The resulting plastic constitutive equation takes into account a dependence on both the pearlitic spacing (arising from the confined slip of dislocations in the lamellae) and on strengthening from the evolving intra-lamellar dislocation density. A Kocks-Mecking strain hardening/recovery model is used for the lamellar ferrite, whereas perfect-plastic behaviour is assumed for cementite. The model naturally captures the microstructural evolution and the internal micro-stresses developed due to the different mechanical behaviour of both phases. The model is also able to describe the lamellar evolution (orientation and interlamellar spacing) with good accuracy. The role of plastic anisotropy in the ferritic phase has also been studied, and the results show that anisotropy has an important impact on both microstructural evolution and strengthening of heavily drawn wires.

Soft storey effects on plastic hinge propagation of moment resisting reinforced concrete building subjected to Ranau earthquake

NASA Astrophysics Data System (ADS)

Tan, Chee Ghuan; Chia, Wei Ting; Majid, Taksiah A.; Nazri, Fadzli Mohamed; Adiyanto, Mohd Irwan

2017-10-01

On 5th June 2015, a moderate earthquake with Mw 5.9 hit Ranau, resulted in damages of the existing non-seismically designed buildings, such that 61 buildings, including mosques, schools, hospitals and Ranau police headquarters were suffered from different level structural damages. Soft storey irregularity is one of the main reasons of the building damage. This study is to investigate the soft-story effect on the propagation path of plastic hinges RC building under seismic excitation. The plastic hinges formation and seismic performance of five moment resisting RC frames with different infill configurations are studied. The seismic performance of building is evaluated by Incremental Dynamic Analysis (IDA). Open ground soft storey structure shows the lowest seismic resistance, collapses at 0.55g pga. The maximum interstorey drift ratio (IDRmax) in soft storey buildings ranging from 0.53% to 2.96% which are far greater than bare frame ranging from 0.095% to 0.69%. The presence of infill walls creates stiffer upper stories causing moments concentrate at the soft storey, resulting the path of plastic hinge propagation is dominant at the soft storey columns. Hence, the buildings with soft storey are very susceptible under earthquake load.

Types and Origins of Debris Found on Maui Shorelines: Implications for Mitigation Policies and Strategies

NASA Astrophysics Data System (ADS)

Blickley, L.; Currie, J. J.; Kaufman, G. D.

2016-02-01

Marine debris is an identified concern for coastal areas and is known to accumulate in large quantities in the North Pacific Ocean. The proximity of the Main Hawaiian Islands to these "garbage patches" represents an ongoing concern with little understanding of debris origins or efficacy of current mitigation policies. Debris accumulation surveys were conducted monthly between October 2013 and August 2014 and daily during January 2015 at 3 beaches on Maui's coastline. Debris accumulation rates, loads, and sources varied between sites and were influenced by both environmental and anthropogenic factors. Debris accumulation was strongly influenced by the temporal scale of sampling, with daily surveys showing a significant increase in accumulation rate. Plastics were the most common debris item at each site ranging from local, land-based debris including cigarette butts, straws, and food wrappers, to foreign, ocean-based debris such as oyster spacer tubes and hagfish traps. The results of this study indicate that the passage of a tobacco free beaches bill on Maui has not significantly reduced the amount of tobacco related debris. Alternatively, a ban on plastic grocery bags has eliminated this type of debris from Maui's shorelines, with no bags found at any of the sampling sites. The wide spread origins of collected debris further suggests that mitigation strategies to reduce debris will need to take place across hundreds of local municipalities. The efficacy of marine debris policies furthermore depends on enforcement and implementation strategy, as current results suggest policy enforcement at the producer level affords more effective results than that at the consumer level. Local debris mitigation actions have nevertheless been shown to affect debris loads, and municipalities are therefore encouraged to adopt a holistic combination of policy, community-based debris removal programs, increased public awareness, and ongoing monitoring to address marine debris.

Plastic and evolutionary responses to heat stress in a temperate dung fly: negative correlation between basal and induced heat tolerance?

PubMed

Esperk, T; Kjaersgaard, A; Walters, R J; Berger, D; Blanckenhorn, W U

2016-05-01

Extreme weather events such as heat waves are becoming more frequent and intense. Populations can cope with elevated heat stress by evolving higher basal heat tolerance (evolutionary response) and/or stronger induced heat tolerance (plastic response). However, there is ongoing debate about whether basal and induced heat tolerance are negatively correlated and whether adaptive potential in heat tolerance is sufficient under ongoing climate warming. To evaluate the evolutionary potential of basal and induced heat tolerance, we performed experimental evolution on a temperate source population of the dung fly Sepsis punctum. Offspring of flies adapted to three thermal selection regimes (Hot, Cold and Reference) were subjected to acute heat stress after having been exposed to either a hot-acclimation or non-acclimation pretreatment. As different traits may respond differently to temperature stress, several physiological and life history traits were assessed. Condition dependence of the response was evaluated by exposing juveniles to different levels of developmental (food restriction/rearing density) stress. Heat knockdown times were highest, whereas acclimation effects were lowest in the Hot selection regime, indicating a negative association between basal and induced heat tolerance. However, survival, adult longevity, fecundity and fertility did not show such a pattern. Acclimation had positive effects in heat-shocked flies, but in the absence of heat stress hot-acclimated flies had reduced life spans relative to non-acclimated ones, thereby revealing a potential cost of acclimation. Moreover, body size positively affected heat tolerance and unstressed individuals were less prone to heat stress than stressed flies, offering support for energetic costs associated with heat tolerance. Overall, our results indicate that heat tolerance of temperate insects can evolve under rising temperatures, but this response could be limited by a negative relationship between basal and induced thermotolerance, and may involve some but not other fitness-related traits. © 2016 European Society For Evolutionary Biology. Journal of Evolutionary Biology © 2016 European Society For Evolutionary Biology.

Dynamic elastic-plastic response of a 2-DOF mass-spring system.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Corona, Edmundo

The objective of the work presented here arose from abnormal, drop scenarios and specifically the question of how the accelerations and accumulation of plastic strains of internal components could be a ected by the material properties of the external structure. In some scenarios, the impact loads can induce cyclic motion of the internal components. Therefore, a second objective was to explore di erences that could be expected when simulations are conducted using isotropic hardening vs. kinematic hardening plasticity models. The simplest model that can be used to investigate the objectives above is a two-degree-offreedom mass/spring model where the springs exhibitmore » elastic-plastic behavior. The purpose of this memo is to develop such model and present a few results that address the objectives.« less

Method for formation of thin film transistors on plastic substrates

DOEpatents

Carey, P.G.; Smith, P.M.; Sigmon, T.W.; Aceves, R.C.

1998-10-06

A process for formation of thin film transistors (TFTs) on plastic substrates replaces standard thin film transistor fabrication techniques, and uses sufficiently lower processing temperatures so that inexpensive plastic substrates may be used in place of standard glass, quartz, and silicon wafer-based substrates. The process relies on techniques for depositing semiconductors, dielectrics, and metals at low temperatures; crystallizing and doping semiconductor layers in the TFT with a pulsed energy source; and creating top-gate self-aligned as well as back-gate TFT structures. The process enables the fabrication of amorphous and polycrystalline channel silicon TFTs at temperatures sufficiently low to prevent damage to plastic substrates. The process has use in large area low cost electronics, such as flat panel displays and portable electronics. 5 figs.

Sensitivity analysis of limit state functions for probability-based plastic design

NASA Technical Reports Server (NTRS)

Frangopol, D. M.

1984-01-01

The evaluation of the total probability of a plastic collapse failure P sub f for a highly redundant structure of random interdependent plastic moments acted on by random interdepedent loads is a difficult and computationally very costly process. The evaluation of reasonable bounds to this probability requires the use of second moment algebra which involves man statistical parameters. A computer program which selects the best strategy for minimizing the interval between upper and lower bounds of P sub f is now in its final stage of development. The relative importance of various uncertainties involved in the computational process on the resulting bounds of P sub f, sensitivity is analyzed. Response sensitivities for both mode and system reliability of an ideal plastic portal frame are shown.

Modulation of hippocampal neural plasticity by glucose-related signaling.

PubMed

Mainardi, Marco; Fusco, Salvatore; Grassi, Claudio

2015-01-01

Hormones and peptides involved in glucose homeostasis are emerging as important modulators of neural plasticity. In this regard, increasing evidence shows that molecules such as insulin, insulin-like growth factor-I, glucagon-like peptide-1, and ghrelin impact on the function of the hippocampus, which is a key area for learning and memory. Indeed, all these factors affect fundamental hippocampal properties including synaptic plasticity (i.e., synapse potentiation and depression), structural plasticity (i.e., dynamics of dendritic spines), and adult neurogenesis, thus leading to modifications in cognitive performance. Here, we review the main mechanisms underlying the effects of glucose metabolism on hippocampal physiology. In particular, we discuss the role of these signals in the modulation of cognitive functions and their potential implications in dysmetabolism-related cognitive decline.

Gradient Plasticity Model and its Implementation into MARMOT

DOE Office of Scientific and Technical Information (OSTI.GOV)

Barker, Erin I.; Li, Dongsheng; Zbib, Hussein M.

2013-08-01

The influence of strain gradient on deformation behavior of nuclear structural materials, such as boby centered cubic (bcc) iron alloys has been investigated. We have developed and implemented a dislocation based strain gradient crystal plasticity material model. A mesoscale crystal plasticity model for inelastic deformation of metallic material, bcc steel, has been developed and implemented numerically. Continuum Dislocation Dynamics (CDD) with a novel constitutive law based on dislocation density evolution mechanisms was developed to investigate the deformation behaviors of single crystals, as well as polycrystalline materials by coupling CDD and crystal plasticity (CP). The dislocation density evolution law in thismore » model is mechanism-based, with parameters measured from experiments or simulated with lower-length scale models, not an empirical law with parameters back-fitted from the flow curves.« less

Rapid induction bonding of composites, plastics, and metals

NASA Technical Reports Server (NTRS)

Buckley, John D.; Fox, Robert L.

1991-01-01

The Toroid Bonding Gun is and induction heating device. It is a self contained, portable, low powered induction welding system developed for bonding or joining plastic, ceramic, or metallic parts. Structures can be bonded in a factory or in a the field. This type of equipment allows for applying heat directly to the bond lines and/or to the adhesives without heating the entire structure, supports, and fixtures of a bonding assembly. The induction heating gun originally developed for use in the fabrication of space Gangs of bonders are now used to rapidly join composite sheet and structural components. Other NASA-developed applications of this bonding technique include the joining of thermoplastic composites, thermosetting composites, metals, and combinations of these materials.

Root plasticity buffers competition among plants: theory meets experimental data.

PubMed

Schiffers, Katja; Tielbörger, Katja; Tietjen, Britta; Jeltsch, Florian

2011-03-01

Morphological plasticity is a striking characteristic of plants in natural communities. In the context of foraging behavior particularly, root plasticity has been documented for numerous species. Root plasticity is known to mitigate competitive interactions by reducing the overlap of the individuals' rhizospheres. But despite its obvious effect on resource acquisition, plasticity has been generally neglected in previous empirical and theoretical studies estimating interaction intensity among plants. In this study, we developed a semi-mechanistic model that addresses this shortcoming by introducing the idea of compensatory growth into the classical-zone-of influence (ZOI) and field-of-neighborhood (FON) approaches. The model parameters describing the belowground plastic sphere of influence (PSI) were parameterized using data from an accompanying field experiment. Measurements of the uptake of a stable nutrient analogue at distinct distances to the neighboring plants showed that the study species responded plastically to belowground competition by avoiding overlap of individuals' rhizospheres. An unexpected finding was that the sphere of influence of the study species Bromus hordeaceus could be best described by a unimodal function of distance to the plant's center and not with a continuously decreasing function as commonly assumed. We employed the parameterized model to investigate the interplay between plasticity and two other important factors determining the intensity of competitive interactions: overall plant density and the distribution of individuals in space. The simulation results confirm that the reduction of competition intensity due to morphological plasticity strongly depends on the spatial structure of the competitive environment. We advocate the use of semi-mechanistic simulations that explicitly consider morphological plasticity to improve our mechanistic understanding of plant interactions.

Analytical Finite Element Simulation Model for Structural Crashworthiness Prediction

DOT National Transportation Integrated Search

1974-02-01

The analytical development and appropriate derivations are presented for a simulation model of vehicle crashworthiness prediction. Incremental equations governing the nonlinear elasto-plastic dynamic response of three-dimensional frame structures are...

Structure formation control of foam concrete

NASA Astrophysics Data System (ADS)

Steshenko, Aleksei; Kudyakov, Aleksander; Konusheva, Viktoriya; Syrkin, Oleg

2017-01-01

The process of predetermined foam concrete structure formation is considered to be a crucial issue from the point of process control and it is currently understudied thus defining the need for additional research. One of the effective ways of structure formation control in naturally hardening foam concrete is reinforcement with dispersed fibers or introduction of plasticizers. The paper aims at studying the patterns of influence of microreinforcing and plasticizing additives on the structure and performance properties of foam concrete. Preparation of foam concrete mix has been conducted using one-step technology. The structure of modified foam concrete has been studied by means of electron microscopy. The cellular structure of foam concrete samples with the additives is homogeneous; the pores are uniformly distributed over the total volume. It has been revealed that introduction of the Neolas 5.2 plasticizer and microreinforcing fibers in the foam concrete mixture in the amount of 0.4 - 0.1 % by weight of cement leads to reduction of the average pore diameter in the range of 45.3 to 30.2 microns and the standard deviation of the pore average diameter from 23.6 to 9.2 in comparison with the sample without additive. Introduction of modifying additives has stimulated formation of a large number of closed pores. Thus porosity of conditionally closed pores has increased from 16.06 % to 34.48 %, which has lead to increase of frost resistance brand of foam concrete from F15 to F50 and to reduction of its water absorption by weight by 20 %.

The Effect of Spaceflight on the Ultrastructure of the Cerebellum

NASA Technical Reports Server (NTRS)

Holstein, Gay R.; Martinelli, Giorgio P.

2003-01-01

In weightlessness, astronauts and cosmonauts may experience postural illusions as well as motion sickness symptoms known as the space adaptation syndrome. Upon return to Earth, they have irregularities in posture and balance. The adaptation to microgravity and subsequent re-adaptation to Earth occurs over several days. At the cellular level, a process called neuronal plasticity may mediate this adaptation. The term plasticity refers to the flexibility and modifiability in the architecture and functions of the nervous system. In fact, plastic changes are thought to underlie not just behavioral adaptation, but also the more generalized phenomena of learning and memory. The goal of this experiment was to identify some of the structural alterations that occur in the rat brain during the sensory and motor adaptation to microgravity. One brain region where plasticity has been studied extensively is the cerebellar cortex-a structure thought to be critical for motor control, coordination, the timing of movements, and, most relevant to the present experiment, motor learning. Also, there are direct as well as indirect connections between projections from the gravity-sensing otolith organs and several subregions of the cerebellum. We tested the hypothesis that alterations in the ultrastructural (the structure within the cell) architecture of rat cerebellar cortex occur during the early period of adaptation to microgravity, as the cerebellum adapts to the absence of the usual gravitational inputs. The results show ultrastructural evidence for neuronal plasticity in the central nervous system of adult rats after 24 hours of spaceflight. Qualitative studies conducted on tissue from the cerebellar cortex (specifically, the nodulus of the cerebellum) indicate that ultrastructural signs of plasticity are present in the cerebellar zones that receive input from the gravity-sensing organs in the inner ear (the otoliths). These changes are not observed in this region in cagematched ground control animals. The specific changes include the formation of lamellar bodies, profoundly enlarged Purkinje cell mitochondria, the presence of inter-neuronal cellular protrusions in the molecular layer, and signs of degeneration in the distal dendrites of the Purkinje cells. Since these morphologic signs are not apparent in the control animals, they are not likely to be due to caging or tissue processing effects. The particular nature of the structural alterations in the nodulus, most notably the formation of lamellar bodies and the presence of degeneration, further suggests that excitotoxicity (damaging overstimulation of neurons) may play a role in the short-term neural response to spaceflight. These findings suggest a structural basis for the neuronal and synaptic plasticity accompanying the central nervous system response to altered gravity and help identify the cellular bases underlying the vestibular abnormalities experienced by astronauts during periods of adaptation and re-adaptation to different gravitational forces. Also, since the short- and long-term changes in neural structure occurring during such periods of adaptation resemble the neuronal alterations that occur in some neurologic disorders such as stroke, these findings may offer guidance in the development of strategies for rehabilitation and treatment of such disorders.

Soft sediment deformation structures in the Maastrichtian Ajali Formation Western Flank of Anambra Basin, Southern Nigeria

NASA Astrophysics Data System (ADS)

Olabode, Solomon Ojo

2014-01-01

Soft sediment deformation structures were recognized in the Maastrichtian shallow marine wave to tide influenced regressive sediments of Ajali Formation in the western flank of Anambra basin, southern Nigerian. The soft sediment deformation structures were in association with cross bedded sands, clay and silt and show different morphological types. Two main types recognised are plastic deformations represented by different types of recumbent folds and injection structure represented by clastic dykes. Other structures in association with the plastic deformation structures include distorted convolute lamination, subsidence lobes, pillars, cusps and sand balls. These structures are interpreted to have been formed by liquefaction and fluidization mechanisms. The driving forces inferred include gravitational instabilities and hydraulic processes. Facies analysis, detailed morphologic study of the soft sediment deformation structures and previous tectonic history of the basin indicate that the main trigger agent for deformation is earthquake shock. The soft sediment deformation structures recognised in the western part of Anambra basin provide a continuous record of the tectonic processes that acted on the regressive Ajali Formation during the Maastrichtian.

SU-E-T-486: In Vivo Skin Dosimetry Using the Exradin W1 Plastic Scintillation Detector for Passively Scattered Proton Beam Therapy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Alsanea, F; Kudchadker, R; Usama, M

Purpose: To evaluate the accuracy and usefulness of plastic scintillation detectors used for skin dosimetry of patients undergoing passive scatter proton therapy. Methods: Following an IRB approved protocol, six patients undergoing passively scattered proton beam therapy for prostate cancer were selected for in vivo skin dosimetry using the Exradin W1 plastic scintillator. The detector was calibrated on a Cobalt-60 unit, and phantom measurements in the proton beam with the W1 and a calibrated parallel plate ion chamber were used to account for the under-response due to high LET at energies used for treatment. Measurements made in a heated water tankmore » were used to account for temperature dependence. For in vivo measurements, the W1 is fixed to the patient’s skin with medical tape in the center of each of two laterally opposed treatment fields. Measurements will be performed once per week for each patient for the duration of treatment, for a total of thirty six measurements. The measured dose will be compared to the expected dose, extracted from the Eclipse treatment planning system. The average difference over all measurements and per-patient will be computed, as well as standard deviations. Results: The calibrated detector exhibited a 7% under-response in 225 and 250 MeV beams, and a 4% under-response when used at 37 °C (relative to the response at the calibration temperature of 20 °C). Patient measurements are ongoing. Conclusion: The Exradin W1 plastic scintillator detector is a strong candidate for in vivo skin dosimetry in passively scattered proton beams as PSDs are water equivalent and very small (2mm in diameter), permitting accurate measurements that do not perturb the delivered dose. This project was supported in part by award number CA182450 from the National Cancer Institute.« less

Knowledge, attitude, and practices on usage, disposal, and effect of plastic bags on sheep and goats.

PubMed

Otsyina, H R; Nguhiu-Mwangi, J; Mogoa, E G M; Mbuthia, P G; Ogara, W O

2018-06-01

The objective of this study was to evaluate knowledge, attitudes, and practices of people in the Nairobi and Kajiado Counties, Kenya, on the usage, disposal, and effect of plastic waste on sheep and goats (shoats). A semi-structured questionnaire was used to collect data from 384 respondents in four communities in the two counties. Most of the people irrespective of their age, occupation, and educational status used plastic bags of some type on a daily basis. A high proportion of the respondents (37.0%, 142) used plastic bags because of the low cost. Approximately, 79.1% (304) disposed used plastic bags in open dumps. A total of 147 (38.3%) households kept shoats. Out of these, 38.1% (56) purchased feed and also allowed their animals to roam. Most of them (45.3%, 174) thought that lack of feed for the animals was the main reason why shoats roam and scavenge at refuse dump sites and road sides. A large proportion of the respondents (44.5%, 143) mentioned death of animals as the ultimate consequence of ingestion of waste plastic bags. Though, the respondents were aware that indiscriminate disposal of used plastic bags could result in death of the animals from which they derive their livelihoods, they nevertheless continued with the practice. There is a need for a paradigm shift in the way and manner plastic bags are used and disposed.

Plasticity in variation of xylem and phloem cell characteristics of Norway spruce under different local conditions

PubMed Central

Gričar, Jožica; Prislan, Peter; de Luis, Martin; Gryc, Vladimír; Hacurová, Jana; Vavrčík, Hanuš; Čufar, Katarina

2015-01-01

There is limited information on intra-annual plasticity of secondary tissues of tree species growing under different environmental conditions. To increase the knowledge about the plasticity of secondary growth, which allows trees to adapt to specific local climatic regimes, we examined climate–radial growth relationships of Norway spruce [Picea abies (L.) H. Karst.] from three contrasting locations in the temperate climatic zone by analyzing tree-ring widths for the period 1932–2010, and cell characteristics in xylem and phloem increments formed in the years 2009–2011. Variation in the structure of xylem and phloem increments clearly shows that plasticity in seasonal dynamics of cambial cell production and cell differentiation exists on xylem and phloem sides. Anatomical characteristics of xylem and phloem cells are predominantly site-specific characteristics, because they varied among sites but were fairly uniform among years in trees from the same site. Xylem and phloem tissues formed in the first part of the growing season seemed to be more stable in structure, indicating their priority over latewood and late phloem for tree performance. Long-term climate and radial growth analyses revealed that growth was in general less dependent on precipitation than on temperature; however, growth sensitivity to local conditions differed among the sites. Only partial dependence of radial growth of spruce on climatic factors on the selected sites confirms its strategy to adapt the structure of wood and phloem increments to function optimally in local conditions. PMID:26442044

Brain-derived neurotrophic factor/neurotrophin 3 regulate axon initial segment location and affect neuronal excitability in cultured hippocampal neurons.

PubMed

Guo, Yu; Su, Zi-Jun; Chen, Yi-Kun; Chai, Zhen

2017-07-01

Plasticity of the axon initial segment (AIS) has aroused great interest in recent years because it regulates action potential initiation and neuronal excitability. AIS plasticity manifests as modulation of ion channels or variation in AIS structure. However, the mechanisms underlying structural plasticity of the AIS are not well understood. Here, we combined immunofluorescence, patch-clamp recordings, and pharmacological methods in cultured hippocampal neurons to investigate the factors participating in AIS structural plasticity during development. With lowered neuronal density, the distance between the AIS and the soma increased, while neuronal excitability decreased, as shown by the increased action potential threshold and current threshold for firing an action potential. This variation in the location of the AIS was associated with cellular secretory substances, including brain-derived neurotrophic factor (BDNF) and neurotrophin 3 (NT3). Indeed, blocking BDNF and NT3 with TrkB-Fc eliminated the effect of conditioned medium collected from high-density cultures on AIS relocation. Elevating the extracellular concentration of BDNF or NT3 promoted movement of the AIS proximally to the soma and increased neuronal excitability. Furthermore, knockdown of neurotrophin receptors TrkB and TrkC caused distal movement of the AIS. Our results demonstrate that BDNF and NT3 regulate AIS location and neuronal excitability. These regulatory functions of neurotrophic factors provide insight into the molecular mechanisms underlying AIS biology. © 2017 International Society for Neurochemistry.

Local elasticity map and plasticity in a model Lennard-Jones glass.

PubMed

Tsamados, Michel; Tanguy, Anne; Goldenberg, Chay; Barrat, Jean-Louis

2009-08-01

In this work we calculate the local elastic moduli in a weakly polydispersed two-dimensional Lennard-Jones glass undergoing a quasistatic shear deformation at zero temperature. The numerical method uses coarse-grained microscopic expressions for the strain, displacement, and stress fields. This method allows us to calculate the local elasticity tensor and to quantify the deviation from linear elasticity (local Hooke's law) at different coarse-graining scales. From the results a clear picture emerges of an amorphous material with strongly spatially heterogeneous elastic moduli that simultaneously satisfies Hooke's law at scales larger than a characteristic length scale of the order of five interatomic distances. At this scale, the glass appears as a composite material composed of a rigid scaffolding and of soft zones. Only recently calculated in nonhomogeneous materials, the local elastic structure plays a crucial role in the elastoplastic response of the amorphous material. For a small macroscopic shear strain, the structures associated with the nonaffine displacement field appear directly related to the spatial structure of the elastic moduli. Moreover, for a larger macroscopic shear strain we show that zones of low shear modulus concentrate most of the strain in the form of plastic rearrangements. The spatiotemporal evolution of this local elasticity map and its connection with long term dynamical heterogeneity as well as with the plasticity in the material is quantified. The possibility to use this local parameter as a predictor of subsequent local plastic activity is also discussed.

Structural plasticity: how intermetallics deform themselves in response to chemical pressure, and the complex structures that result.

PubMed

Berns, Veronica M; Fredrickson, Daniel C

2014-10-06

Interfaces between periodic domains play a crucial role in the properties of metallic materials, as is vividly illustrated by the way in which the familiar malleability of many metals arises from the formation and migration of dislocations. In complex intermetallics, such interfaces can occur as an integral part of the ground-state crystal structure, rather than as defects, resulting in such marvels as the NaCd2 structure (whose giant cubic unit cell contains more than 1000 atoms). However, the sources of the periodic interfaces in intermetallics remain mysterious, unlike the dislocations in simple metals, which can be associated with the exertion of physical stresses. In this Article, we propose and explore the concept of structural plasticity, the hypothesis that interfaces in complex intermetallic structures similarly result from stresses, but ones that are inherent in a defect-free parent structure, rather than being externally applied. Using DFT-chemical pressure analysis, we show how the complex structures of Ca2Ag7 (Yb2Ag7 type), Ca14Cd51 (Gd14Ag51 type), and the 1/1 Tsai-type quasicrystal approximant CaCd6 (YCd6 type) can all be traced to large negative pressures around the Ca atoms of a common progenitor structure, the CaCu5 type with its simple hexagonal 6-atom unit cell. Two structural paths are found by which the compounds provide relief to the Ca atoms' negative pressures: a Ca-rich pathway, where lower coordination numbers are achieved through defects eliminating transition metal (TM) atoms from the structure; and a TM-rich path, along which the addition of spacer Cd atoms provides the Ca coordination environments greater independence from each other as they contract. The common origins of these structures in the presence of stresses within a single parent structure highlights the diverse paths by which intermetallics can cope with competing interactions, and the role that structural plasticity may play in navigating this diversity.

Cortico-fugal output from visual cortex promotes plasticity of innate motor behaviour

PubMed Central

Liu, Bao-hua; Huberman, Andrew D.; Scanziani, Massimo

2017-01-01

The mammalian visual cortex massively innervates the brainstem, a phylogenetically older structure, via cortico-fugal axonal projections1. Many cortico-fugal projections target brainstem nuclei that mediate innate motor behaviours, but the function of these projections remains poorly understood1–4. A prime example of such behaviours is the optokinetic reflex (OKR), an innate eye movement mediated by the brainstem accessory optic system3,5,6, that stabilizes images on the retina as the animal moves through the environment and is thus crucial for vision5. The OKR is plastic, allowing the amplitude of this reflex to be adaptively adjusted relative to other oculomotor reflexes and thereby ensuring image stability throughout life7–11. Although the plasticity of the OKR is thought to involve subcortical structures such as the cerebellum and vestibular nuclei10–13, cortical lesions have suggested that the visual cortex might also be involved9,14,15. Here we show that projections from the mouse visual cortex to the accessory optic system promote the adaptive plasticity of the OKR. OKR potentiation, a compensatory plastic increase in the amplitude of the OKR in response to vestibular impairment11,16–18, is diminished by silencing visual cortex. Furthermore, targeted ablation of a sparse population of cortico-fugal neurons that specifically project to the accessory optic system severely impairs OKR potentiation. Finally, OKR potentiation results from an enhanced drive exerted by the visual cortex onto the accessory optic system. Thus, cortico-fugal projections to the brainstem enable the visual cortex, an area that has been principally studied for its sensory processing function19, to plastically adapt the execution of innate motor behaviours. PMID:27732573

High Resilience of Seed Dispersal Webs Highlighted by the Experimental Removal of the Dominant Disperser.

PubMed

Timóteo, Sérgio; Ramos, Jaime Albino; Vaughan, Ian Phillip; Memmott, Jane

2016-04-04

The pressing need to conserve and restore habitats in the face of ongoing species loss [1, 2] requires a better understanding of what happens to communities when species are lost or reinstated [3, 4]. Theoretical models show that communities are relatively insensitive to species loss [5, 6]; however, they disagree with field manipulations showing a cascade of extinctions [7, 8] and have seldom been tested under field conditions (e.g., [9]). We experimentally removed the most abundant seed-dispersing ant species from seed dispersal networks in a Mediterranean landscape, replicating the experiment in three types of habitat, and then compared these communities to un-manipulated control communities. Removal did not result in large-scale changes in network structure. It revealed extensive structural plasticity of the remaining community, which rearranged itself through rewiring, while maintaining its functionality. The remaining ant species widened their diet breadth in a way that maintained seed dispersal, despite the identity of many interactions changing. The species interaction strength decreased; thus, the importance of each ant species for seed dispersal became more homogeneous, thereby reducing the dependence of seed species on one dominant ant species. Compared to the experimental results, a simulation model that included rewiring considerably overestimated the effect of species loss on network robustness. If community-level species loss models are to be of practical use in ecology or conservation, they need to include behavioral and population responses, and they need to be routinely tested under field conditions; doing this would be to the advantage of both empiricists and theoreticians. Copyright © 2016 Elsevier Ltd. All rights reserved.

Changes in the Hippocampal Proteome Associated with Spatial Memory Impairment after Exposure to Low (20 cGy) Doses of 1 GeV/n 56Fe Radiation.

PubMed

Britten, Richard A; Jewell, Jessica S; Davis, Leslie K; Miller, Vania D; Hadley, Melissa M; Semmes, O John; Lonart, György; Dutta, Sucharita M

2017-03-01

Exposure to low (∼20 cGy) doses of high-energy charged (HZE) particles, such as 1 GeV/n 56 Fe, results in impaired hippocampal-dependent learning and memory (e.g., novel object recognition and spatial memory) in rodents. While these findings raise the possibility that astronauts on deep-space missions may develop cognitive deficits, not all rats develop HZE-induced cognitive impairments, even after exposure to high (200 cGy) HZE doses. The reasons for this differential sensitivity in some animals that develop HZE-induced cognitive failure remain speculative. We employed a robust quantitative mass spectrometry-based workflow, which links early-stage discovery to next-stage quantitative verification, to identify differentially active proteins/pathways in rats that developed spatial memory impairment at three months after exposure to 20 cGy of 1 GeV/n 56 Fe (20/impaired), and in those rats that managed to maintain normal cognitive performance (20/functional). Quantitative data were obtained on 665-828 hippocampal proteins in the various cohorts of rats studied, of which 580 were expressed in all groups. A total of 107 proteins were upregulated in the irradiated rats irrespective of their spatial memory performance status, which included proteins involved in oxidative damage response, calcium transport and signaling. Thirty percent (37/107) of these "radiation biomarkers" formed a functional interactome of the proteasome and the COP9 signalosome. These data suggest that there is persistent oxidative stress, ongoing autophagy and altered synaptic plasticity in the irradiated hippocampus, irrespective of the spatial memory performance status, suggesting that the ultimate phenotype may be determined by how well the hippocampal neurons compensate to the ongoing oxidative stress and associated side effects. There were 67 proteins with expression that correlated with impaired spatial memory performance. Several of the "impaired biomarkers" have been implicated in poor spatial memory performance, neurodegeneration, neuronal loss or neuronal susceptibility to apoptosis, or neuronal synaptic or structural plasticity. Therefore, in addition to the baseline oxidative stress and altered adenosine metabolism observed in all irradiated rats, the 20/impaired rats expressed proteins that led to poor spatial memory performance, enhanced neuronal loss and apoptosis, changes in synaptic plasticity and dendritic remodeling. A total of 46 proteins, which were differentially upregulated in the sham-irradiated and 20/functional rat cohorts, can thus be considered as markers of good spatial memory, while another 95 proteins are associated with the maintenance of good spatial memory in the 20/functional rats. The loss or downregulation of these "good spatial memory" proteins would most likely exacerbate the situation in the 20/impaired rats, having a major impact on their neurocognitive status, given that many of those proteins play an important role in neuronal homeostasis and function. Our large-scale comprehensive proteomic analysis has provided some insight into the processes that are altered after exposure, and the collective data suggests that there are multiple problems with the functionality of the neurons and astrocytes in the irradiated hippocampi, which appear to be further exacerbated in the rats that have impaired spatial memory performance or partially compensated for in the rats with good spatial memory.

Epigenomics in marine fishes.

PubMed

Metzger, David C H; Schulte, Patricia M

2016-12-01

Epigenetic mechanisms are an underappreciated and often ignored component of an organism's response to environmental change and may underlie many types of phenotypic plasticity. Recent technological advances in methods for detecting epigenetic marks at a whole-genome scale have launched new opportunities for studying epigenomics in ecologically relevant non-model systems. The study of ecological epigenomics holds great promise to better understand the linkages between genotype, phenotype, and the environment and to explore mechanisms of phenotypic plasticity. The many attributes of marine fish species, including their high diversity, variable life histories, high fecundity, impressive plasticity, and economic value provide unique opportunities for studying epigenetic mechanisms in an environmental context. To provide a primer on epigenomic research for fish biologists, we start by describing fundamental aspects of epigenetics, focusing on the most widely studied and most well understood of the epigenetic marks: DNA methylation. We then describe the techniques that have been used to investigate DNA methylation in marine fishes to date and highlight some new techniques that hold great promise for future studies. Epigenomic research in marine fishes is in its early stages, so we first briefly discuss what has been learned about the establishment, maintenance, and function of DNA methylation in fishes from studies in zebrafish and then summarize the studies demonstrating the pervasive effects of the environment on the epigenomes of marine fishes. We conclude by highlighting the potential for ongoing research on the epigenomics of marine fishes to reveal critical aspects of the interaction between organisms and their environments. Copyright © 2016 Elsevier B.V. All rights reserved.

The AMPA receptor potentiator Org 26576 modulates stress-induced transcription of BDNF isoforms in rat hippocampus.

PubMed

Fumagalli, Fabio; Calabrese, Francesca; Luoni, Alessia; Shahid, Mohammed; Racagni, Giorgio; Riva, Marco A

2012-02-01

Brain derived neurotrophic factor (BDNF) is a key mediator of brain plasticity. The modulation of its expression and function is important for cognition and represents a key strategy to enhance neuronal resilience. Within this context, there exists a close interaction between glutamatergic neurotransmission and BDNF activity towards regulating cellular homeostasis and plasticity. The aim of the current study was to investigate the ability of the AMPA receptor potentiator Org 26576 to modulate BDNF expression in selected brain regions under basal conditions or in response to an acute swim stress. Rats subjected to a single intraperitoneal injection with Org 26576 (10mg/kg) or saline were exposed to a swim stress session (5 min) and sacrificed 15 min after the end of stress. Real-time PCR assay was used to determine changes in BDNF transcription in different brain regions. Total BDNF mRNA levels were significantly increased in the hippocampus of animals exposed to the combination of Org 26576 and stress whereas, in prefrontal and frontal cortices, BDNF mRNA levels were modulated by the acute stress, independently from drug treatment. The analysis of BDNF transcripts in the hippocampus revealed a major contribution of exons I and IV. Our results suggest that AMPA receptor potentiation by Org 26576 exerts a positive modulatory influence on BDNF expression during ongoing neuronal activity. Given that these mechanisms are critical for neuronal plasticity, we hypothesized that such changes may facilitate learning/coping mechanisms associated with a mild stressful experience. Copyright © 2011 Elsevier Ltd. All rights reserved.

Homeostatic Scaling of Excitability in Recurrent Neural Networks

PubMed Central

Remme, Michiel W. H.; Wadman, Wytse J.

2012-01-01

Neurons adjust their intrinsic excitability when experiencing a persistent change in synaptic drive. This process can prevent neural activity from moving into either a quiescent state or a saturated state in the face of ongoing plasticity, and is thought to promote stability of the network in which neurons reside. However, most neurons are embedded in recurrent networks, which require a delicate balance between excitation and inhibition to maintain network stability. This balance could be disrupted when neurons independently adjust their intrinsic excitability. Here, we study the functioning of activity-dependent homeostatic scaling of intrinsic excitability (HSE) in a recurrent neural network. Using both simulations of a recurrent network consisting of excitatory and inhibitory neurons that implement HSE, and a mean-field description of adapting excitatory and inhibitory populations, we show that the stability of such adapting networks critically depends on the relationship between the adaptation time scales of both neuron populations. In a stable adapting network, HSE can keep all neurons functioning within their dynamic range, while the network is undergoing several (patho)physiologically relevant types of plasticity, such as persistent changes in external drive, changes in connection strengths, or the loss of inhibitory cells from the network. However, HSE cannot prevent the unstable network dynamics that result when, due to such plasticity, recurrent excitation in the network becomes too strong compared to feedback inhibition. This suggests that keeping a neural network in a stable and functional state requires the coordination of distinct homeostatic mechanisms that operate not only by adjusting neural excitability, but also by controlling network connectivity. PMID:22570604

Sensory trait variation in an echolocating bat suggests roles for both selection and plasticity

PubMed Central

2014-01-01

Background Across heterogeneous environments selection and gene flow interact to influence the rate and extent of adaptive trait evolution. This complex relationship is further influenced by the rarely considered role of phenotypic plasticity in the evolution of adaptive population variation. Plasticity can be adaptive if it promotes colonization and survival in novel environments and in doing so may increase the potential for future population differentiation via selection. Gene flow between selectively divergent environments may favour the evolution of phenotypic plasticity or conversely, plasticity itself may promote gene flow, leading to a pattern of trait differentiation in the presence of gene flow. Variation in sensory traits is particularly informative in testing the role of environment in trait and population differentiation. Here we test the hypothesis of ‘adaptive differentiation with minimal gene flow’ in resting echolocation frequencies (RF) of Cape horseshoe bats (Rhinolophus capensis) across a gradient of increasingly cluttered habitats. Results Our analysis reveals a geographically structured pattern of increasing RF from open to highly cluttered habitats in R. capensis; however genetic drift appears to be a minor player in the processes influencing this pattern. Although Bayesian analysis of population structure uncovered a number of spatially defined mitochondrial groups and coalescent methods revealed regional-scale gene flow, phylogenetic analysis of mitochondrial sequences did not correlate with RF differentiation. Instead, habitat discontinuities between biomes, and not genetic and geographic distances, best explained echolocation variation in this species. We argue that both selection for increased detection distance in relatively less cluttered habitats and adaptive phenotypic plasticity may have influenced the evolution of matched echolocation frequencies and habitats across different populations. Conclusions Our study reveals significant sensory trait differentiation in the presence of historical gene flow and suggests roles for both selection and plasticity in the evolution of echolocation variation in R. capensis. These results highlight the importance of population level analyses to i) illuminate the subtle interplay between selection, plasticity and gene flow in the evolution of adaptive traits and ii) demonstrate that evolutionary processes may act simultaneously and that their relative influence may vary across different environments. PMID:24674227

Sensory trait variation in an echolocating bat suggests roles for both selection and plasticity.

PubMed

Odendaal, Lizelle J; Jacobs, David S; Bishop, Jacqueline M

2014-03-27

Across heterogeneous environments selection and gene flow interact to influence the rate and extent of adaptive trait evolution. This complex relationship is further influenced by the rarely considered role of phenotypic plasticity in the evolution of adaptive population variation. Plasticity can be adaptive if it promotes colonization and survival in novel environments and in doing so may increase the potential for future population differentiation via selection. Gene flow between selectively divergent environments may favour the evolution of phenotypic plasticity or conversely, plasticity itself may promote gene flow, leading to a pattern of trait differentiation in the presence of gene flow. Variation in sensory traits is particularly informative in testing the role of environment in trait and population differentiation. Here we test the hypothesis of 'adaptive differentiation with minimal gene flow' in resting echolocation frequencies (RF) of Cape horseshoe bats (Rhinolophus capensis) across a gradient of increasingly cluttered habitats. Our analysis reveals a geographically structured pattern of increasing RF from open to highly cluttered habitats in R. capensis; however genetic drift appears to be a minor player in the processes influencing this pattern. Although Bayesian analysis of population structure uncovered a number of spatially defined mitochondrial groups and coalescent methods revealed regional-scale gene flow, phylogenetic analysis of mitochondrial sequences did not correlate with RF differentiation. Instead, habitat discontinuities between biomes, and not genetic and geographic distances, best explained echolocation variation in this species. We argue that both selection for increased detection distance in relatively less cluttered habitats and adaptive phenotypic plasticity may have influenced the evolution of matched echolocation frequencies and habitats across different populations. Our study reveals significant sensory trait differentiation in the presence of historical gene flow and suggests roles for both selection and plasticity in the evolution of echolocation variation in R. capensis. These results highlight the importance of population level analyses to i) illuminate the subtle interplay between selection, plasticity and gene flow in the evolution of adaptive traits and ii) demonstrate that evolutionary processes may act simultaneously and that their relative influence may vary across different environments.