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.

The innate immune repertoire in Cnidaria - ancestral complexity and stochastic gene loss

PubMed Central

Miller, David J; Hemmrich, Georg; Ball, Eldon E; Hayward, David C; Khalturin, Konstantin; Funayama, Noriko; Agata, Kiyokazu; Bosch, Thomas CG

2007-01-01

Background Characterization of the innate immune repertoire of extant cnidarians is of both fundamental and applied interest - it not only provides insights into the basic immunological 'tool kit' of the common ancestor of all animals, but is also likely to be important in understanding the global decline of coral reefs that is presently occurring. Recently, whole genome sequences became available for two cnidarians, Hydra magnipapillata and Nematostella vectensis, and large expressed sequence tag (EST) datasets are available for these and for the coral Acropora millepora. Results To better understand the basis of innate immunity in cnidarians, we scanned the available EST and genomic resources for some of the key components of the vertebrate innate immune repertoire, focusing on the Toll/Toll-like receptor (TLR) and complement pathways. A canonical Toll/TLR pathway is present in representatives of the basal cnidarian class Anthozoa, but neither a classic Toll/TLR receptor nor a conventional nuclear factor (NF)-κB could be identified in the anthozoan Hydra. Moreover, the detection of complement C3 and several membrane attack complex/perforin domain (MAC/PF) proteins suggests that a prototypic complement effector pathway may exist in anthozoans, but not in hydrozoans. Together with data for several other gene families, this implies that Hydra may have undergone substantial secondary gene loss during evolution. Such losses are not confined to Hydra, however, and at least one MAC/PF gene appears to have been lost from Nematostella. Conclusion Consideration of these patterns of gene distribution underscores the likely significance of gene loss during animal evolution whilst indicating ancient origins for many components of the vertebrate innate immune system. PMID:17437634

A numerical investigation of grain shape and crystallographic texture effects on the plastic strain localization in friction stir weld zones

NASA Astrophysics Data System (ADS)

Romanova, V.; Balokhonov, R.; Batukhtina, E.; Shakhidjanov, V.

2015-10-01

Crystal plasticity approaches were adopted to build models accounting for the microstructure and texture observed in different friction stir weld zones. To this end, a numerical investigation of crystallographic texture and grain shape effects on the plastic strain localization in a friction stir weld of an aluminum-base alloy was performed. The presence of texture was found to give rise to pronounced mesoscale plastic strain localization.

Flaw characterization through nonlinear ultrasonics and wavelet cross-correlation algorithms

NASA Astrophysics Data System (ADS)

Bunget, Gheorghe; Yee, Andrew; Stewart, Dylan; Rogers, James; Henley, Stanley; Bugg, Chris; Cline, John; Webster, Matthew; Farinholt, Kevin; Friedersdorf, Fritz

2018-04-01

Ultrasonic measurements have become increasingly important non-destructive techniques to characterize flaws found within various in-service industrial components. The prediction of remaining useful life based on fracture analysis depends on the accurate estimation of flaw size and orientation. However, amplitude-based ultrasonic measurements are not able to estimate the plastic zones that exist ahead of crack tips. Estimating the size of the plastic zone is an advantage since some flaws may propagate faster than others. This paper presents a wavelet cross-correlation (WCC) algorithm that was applied to nonlinear analysis of ultrasonically guided waves (GW). By using this algorithm, harmonics present in the waveforms were extracted and nonlinearity parameters were used to indicate both the tip of the cracks and size of the plastic zone. B-scans performed with the quadratic nonlinearities were sensitive to micro-damage specific to plastic zones.

Assessment of Cracks in Stress Concentration Regions with Localized Plastic Zones

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

Friedman, E.

1998-11-25

Marty brittle fracture evaluation procedures include plasticity corrections to elastically computed stress intensity factors. These corrections, which are based on the existence of a plastic zone in the vicinity of the crack tip, can overestimate the plasticity effect for a crack embedded in a stress concentration region in which the elastically computed stress exceeds the yield strength of the material in a localized zone. The interactions between the crack, which acts to relieve the high stresses driving the crack, plasticity effects in the stress concentration region, and the nature and source of the loading are examined by formulating explicit flawmore » finite element models for a crack emanating from the root of a notch located in a panel subject to an applied tensile stress. The results of these calculations provide conditions under which a crack-tip plasticity correction based on the Irwin plastic zone size overestimates the plasticity effect. A failure assessment diagram (FAD) curve is used to characterize the effect of plasticity on the crack driving force and to define a less restrictive plasticity correction for cracks at notch roots when load-controlled boundary conditions are imposed. The explicit flaw finite element results also demonstrate that stress intensity factors associated with load-controlled boundary conditions, such as those inherent in the ASME Boiler and Pressure Vessel Code as well as in most handbooks of stress intensity factors, can be much higher than those associated with displacement-controlled conditions, such as those that produce residual or thermal stresses. Under certain conditions, the inclusion of plasticity effects for cracks loaded by displacement-controlled boundary conditions reduces the crack driving force thus justifying the elimination of a plasticity correction for such loadings. The results of this study form the basis for removing unnecessary conservatism from flaw evaluation procedures that utilize plasticity corrections.« less

Deformation fields near a steady fatigue crack with anisotropic plasticity

DOE PAGES

Gao, Yanfei

2015-11-30

In this work, from finite element simulations based on an irreversible, hysteretic cohesive interface model, a steady fatigue crack can be realized if the crack extension exceeds about twice the plastic zone size, and both the crack increment per loading cycle and the crack bridging zone size are smaller than the plastic zone size. The corresponding deformation fields develop a plastic wake behind the crack tip and a compressive residual stress field ahead of the crack tip. In addition, the Hill’s plasticity model is used to study the role of plastic anisotropy on the retardation of fatigue crack growth andmore » the elastic strain fields. It is found that for Mode-I cyclic loading, an enhanced yield stress in directions that are inclined from the crack plane will lead to slower crack growth rate, but this retardation is insignificant for typical degrees of plastic anisotropy. Furthermore, these results provide key inputs for future comparisons to neutron and synchrotron diffraction measurements that provide full-field lattice strain mapping near fracture and fatigue crack tips, especially in textured materials such as wrought or rolled Mg alloys.« less

Deformation fields near a steady fatigue crack with anisotropic plasticity

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

Gao, Yanfei

In this work, from finite element simulations based on an irreversible, hysteretic cohesive interface model, a steady fatigue crack can be realized if the crack extension exceeds about twice the plastic zone size, and both the crack increment per loading cycle and the crack bridging zone size are smaller than the plastic zone size. The corresponding deformation fields develop a plastic wake behind the crack tip and a compressive residual stress field ahead of the crack tip. In addition, the Hill’s plasticity model is used to study the role of plastic anisotropy on the retardation of fatigue crack growth andmore » the elastic strain fields. It is found that for Mode-I cyclic loading, an enhanced yield stress in directions that are inclined from the crack plane will lead to slower crack growth rate, but this retardation is insignificant for typical degrees of plastic anisotropy. Furthermore, these results provide key inputs for future comparisons to neutron and synchrotron diffraction measurements that provide full-field lattice strain mapping near fracture and fatigue crack tips, especially in textured materials such as wrought or rolled Mg alloys.« less

Impacts of macro - and microplastic on macrozoobenthos abundance in intertidal zone

NASA Astrophysics Data System (ADS)

Bangun, A. P.; Wahyuningsih, H.; Muhtadi, A.

2018-02-01

Plastics pollution in coastal areas is one of the topics that have received more attention over the past few years. The intertidal zone is a waters area that is directly affected by contamination of plastic waste from land and sea. The purpose of this study was to analyze the types and abundance of plastic waste in the intertidal zone and its impact on macrozoobenthos abundance. This research was conducted at Pesisir Desa Jaring Halus in February-April 2017. Macrozoobenthos and macro - micro plastic were collected by using quadratic transect. Sediments were collected with a core, to a depth of 30 cm. Microplastic and macroplastic abundances were analyzed using separation of sediment density and hand sorting. The dominant micro plastic types were film (52.30%), fiber (24.88%), fragments (22.74%), followed by pellets (0.1%). The total number of microplastics were 326,33 items and macro plastic were 308 items. Macroplastic abundance is positively correlated with microplastic (0.765). The abundance of macrozoobenthos is negatively correlated with microplastic abundance (-0.368) and with macro plastic abundance (-0.633). The management strategies were suggested clean up marine debris, decrease plastic using and built up the station of debris processing.

Phase-field modelling of ductile fracture: a variational gradient-extended plasticity-damage theory and its micromorphic regularization

PubMed Central

Teichtmeister, S.; Aldakheel, F.

2016-01-01

This work outlines a novel variational-based theory for the phase-field modelling of ductile fracture in elastic–plastic solids undergoing large strains. The phase-field approach regularizes sharp crack surfaces within a pure continuum setting by a specific gradient damage modelling. It is linked to a formulation of gradient plasticity at finite strains. The framework includes two independent length scales which regularize both the plastic response as well as the crack discontinuities. This ensures that the damage zones of ductile fracture are inside of plastic zones, and guarantees on the computational side a mesh objectivity in post-critical ranges. PMID:27002069

Plastic zone size and crack tip opening displacement of a Dugdale crack interacting with a coated circular inclusion

NASA Astrophysics Data System (ADS)

Hoh, H. J.; Xiao, Z. M.; Luo, J.

2010-09-01

An analytical investigation on the plastic zone size of a crack near a coated circular inclusion under three different loading conditions of uniaxial tension, uniform tension and pure shear was carried out. Both the crack and coated circular inclusion are embedded in an infinite matrix, with the crack oriented along the radial direction of the inclusion. In the solution procedure, the crack is simulated as a continuous distribution of edge dislocations. With the Dugdale model of small-scale yielding [J. Mech. Phys. Solids 8 (1960) p. 100], two thin strips of yielded plastic zones are introduced at both crack tips. Using the solution for a coated circular inclusion interacting with a single dislocation as the Green's function, the physical problem is formulated into a set of singular integral equations. Using the method of Erdogan and Gupta [Q. J. Appl. Math. 29 (1972) p. 525] and iterative numerical procedures, the singular integral equations are solved numerically for the plastic zone sizes and crack tip opening displacement.

Modeling the Temperature Rise at the Tip of a Fast Crack

DTIC Science & Technology

1989-08-01

plastic deformation in the plastic zone, the strain rate and the temperature dependence of the flow stress have been incorporated in the determination ...of dislocation generation in the plastic zone. The stress field 1 associated with a moving elastic crack tip is used to determine the increment of...yield stress and the crack tip stress field for a given mode of the applied stress. The fracture toughness of several materials, determined

Phase-field modelling of ductile fracture: a variational gradient-extended plasticity-damage theory and its micromorphic regularization.

PubMed

Miehe, C; Teichtmeister, S; Aldakheel, F

2016-04-28

This work outlines a novel variational-based theory for the phase-field modelling of ductile fracture in elastic-plastic solids undergoing large strains. The phase-field approach regularizes sharp crack surfaces within a pure continuum setting by a specific gradient damage modelling. It is linked to a formulation of gradient plasticity at finite strains. The framework includes two independent length scales which regularize both the plastic response as well as the crack discontinuities. This ensures that the damage zones of ductile fracture are inside of plastic zones, and guarantees on the computational side a mesh objectivity in post-critical ranges. © 2016 The Author(s).

Determination of post-shakedown quantities of a pipe bend via the simplified theory of plastic zones compared with load history dependent incremental analysis

NASA Astrophysics Data System (ADS)

Vollrath, Bastian; Hübel, Hartwig

2018-01-01

The Simplified Theory of Plastic Zones (STPZ) may be used to determine post-shakedown quantities such as strain ranges and accumulated strains at plastic or elastic shakedown. The principles of the method are summarized. Its practical applicability is shown by the example of a pipe bend subjected to constant internal pressure along with cyclic in-plane bending or/and cyclic radial temperature gradient. The results are compared with incremental analyses performed step-by-step throughout the entire load history until the state of plastic shakedown is achieved.

Heterogeneous material distribution, an important reason for generation of strain-localized mylonite and frictional slip zones in the Hidaka metamorphic belt, Hokkaido, Japan

NASA Astrophysics Data System (ADS)

Tanaka, Hidemi; Shimada, Koji; Toyoshima, Tsuyoshi; Obara, Tomohiro; Niizato, Tadafumi

2004-12-01

Lithological heterogeneity of low P/T metamorphic rocks in southern area of Hidaka metamorphic belt (HMB) was formed through historical development of HMB while these rocks had been laid in ductile lower crust. Many strain-localized mylonite zones (<100 m in thickness) are preferentially developed within S-type tonalite and pelitic gneiss, which are characterized by a large modal amount of phyllosilicates (biotite+muscovite+chlorite) and quartz, compared to other lithofacies in HMB. Mylonitic foliations are more conspicuous with close to the center of the shear zone associated with increase in amounts of phyllosilicate minerals, indicating fluidenhanced weakening mechanisms were operated in plastic shear zones. Pseudotachylyte veins are observed exclusively in these mylonite zones, which were generated during exhumation stage of HMB. We conclude the seismic slip zones in southern HMB had been initiated in the ductile lower crust by concentration of localized plastic shear zones within the phyllosilicate- and quartz-rich lithofacies, which were heterogeneously formed by old metamorphic and magmatic events. Then these zones were further weakened by fluid-enhanced plastic deformation, and finally seismic slips occurred at the bottom of seismogenic upper crust, during exhumation of HMB.

76 FR 4283 - Foreign-Trade Zone 153-San Diego, CA; Application for Manufacturing Authority; Abbott...

Federal Register 2010, 2011, 2012, 2013, 2014

2011-01-25

..., Murrieta. The facilities are used for the production of cardiovascular devices including stents, catheters... finished product) include: resins, plastic tubing, stent components, plastic packaging, plastic clips...

Inclined indentation of smooth wedge in rock mass

NASA Astrophysics Data System (ADS)

Chanyshev, AI; Podyminogin, GM; Lukyashko, OA

2018-03-01

The article focuses on the inclined rigid wedge indentation into a rigid-plastic half-plane of rocks with the Mohr–Coulomb-Mohr plasticity. The limiting loads on different sides of the wedge are determined versus the internal friction angle, cohesion and wedge angle. It is shown that when the force is applied along the symmetry axis of the wedge, the zone of plasticity is formed only on one wedge side. In order to form the plasticity zone on both sides of the wedge, it is necessary to apply the force asymmetrically relative to the wedge symmetry axis. An engineering solution for the asymmetrical case implementation is suggested.

Protected areas in the Atlantic facing the hazards of micro-plastic pollution: first diagnosis of three islands in the Canary Current.

PubMed

Baztan, Juan; Carrasco, Ana; Chouinard, Omer; Cleaud, Muriel; Gabaldon, Jesús E; Huck, Thierry; Jaffrès, Lionel; Jorgensen, Bethany; Miguelez, Aquilino; Paillard, Christine; Vanderlinden, Jean-Paul

2014-03-15

Coastal zones and the biosphere as a whole show signs of cumulative degradation due to the use and disposal of plastics. To better understand the manifestation of plastic pollution in the Atlantic Ocean, we partnered with local communities to determine the concentrations of micro-plastics in 125 beaches on three islands in the Canary Current: Lanzarote, La Graciosa, and Fuerteventura. We found that, in spite of being located in highly-protected natural areas, all beaches in our study area are exceedingly vulnerable to micro-plastic pollution, with pollution levels reaching concentrations greater than 100 g of plastic in 1l of sediment. This paper contributes to ongoing efforts to develop solutions to plastic pollution by addressing the questions: (i) Where does this pollution come from?; (ii) How much plastic pollution is in the world's oceans and coastal zones?; (iii) What are the consequences for the biosphere?; and (iv) What are possible solutions? Copyright © 2014 Elsevier Ltd. All rights reserved.

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.

Microplastic-associated bacterial assemblages in the intertidal zone of the Yangtze Estuary.

PubMed

Jiang, Peilin; Zhao, Shiye; Zhu, Lixin; Li, Daoji

2018-05-15

Plastic trash is common in oceans. Terrestrial and marine ecosystem interactions occur in the intertidal zone where accumulation of plastic frequently occurs. However, knowledge of the plastic-associated microbial community (the plastisphere) in the intertidal zone is scanty. We used high-throughput sequencing to profile the bacterial communities attached to microplastic samples from intertidal locations around the Yangtze estuary in China. The structure and composition of plastisphere communities varied significantly among the locations. We found the taxonomic composition on microplastic samples was related to their sedimentary and aquatic origins. Correlation network analysis was used to identify keystone bacterial genera (e.g. Rhodobacterales, Sphingomonadales and Rhizobiales), which represented important microbial associations within the plastisphere community. Other species (i.e. potential pathogens) were considered as hitchhikers in the plastic attached microbial communities. Metabolic pathway analysis suggested adaptations of these bacterial assemblages to the plastic surface-colonization lifestyle. These adaptations included reduced "cell motility" and greater "xenobiotics biodegradation and metabolism." The findings illustrate the diverse microbial assemblages that occur on microplastic and increase our understanding of plastisphere ecology. Copyright © 2017 Elsevier B.V. All rights reserved.

Hybrid friction stir welding for dissimilar materials through electro-plastic effect

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

Liu, Xun; Lan, Shuhuai; Ni, Jun

A hybrid Friction Stir Welding approach and device for dissimilar materials joining employing Electro-Plastic Effect. The approach and device include an introduction of high density, short period current pulses into traditional friction stir welding process, which therefore can generate a localized softened zone in the workpiece during plastic stirring without significant additional temperature increase. This material softened zone is created by high density current pulses based on Electro-Plastic Effect and will move along with the friction stir welding tool. Smaller downward force, larger processing window and better joint quality for dissimilar materials are expected to be achieved through this hybridmore » welding technique.« less

Incidence of plastic debris in Sooty Tern nests: A preliminary study on Trindade Island, a remote area of Brazil.

PubMed

de Souza Petersen, Elisa; Krüger, Lucas; Dezevieski, Alexandre; Petry, MariaVirginia; Montone, Rosalinda Carmela

2016-04-15

Plastic is abundant in the oceans, reaching pelagic zones away from continents. Here we present the first recordings of plastic used as nest material in Sooty Tern nests, on a remote oceanic island. We describe our findings in terms of quantity, size and color of plastic debris. A total of 78 plastics were noted in 54 nests. Four color categories were found: Blue, White, Green and Red. Blue fragments were the most frequent color, present three times as much as white debris. This pattern was present despite blue fragments being smaller and lighter. The plastic debris of lowest frequency were the larger and heavier pieces (red). To our knowledge this is the first record of plastic in Sooty Tern nests. Trindade Island is on an oceanic zone expected to accumulate garbage due to the dynamic ocean currents. Such findings call for a closer inspection of pollution in the Atlantic Ocean. Copyright © 2016 Elsevier Ltd. All rights reserved.

Biofilm and Diatom Succession on Polyethylene (PE) and Biodegradable Plastic Bags in Two Marine Habitats: Early Signs of Degradation in the Pelagic and Benthic Zone?

PubMed Central

Laforsch, Christian; Weber, Miriam

2015-01-01

The production of biodegradable plastic is increasing. Given the augmented littering of these products an increasing input into the sea is expected. Previous laboratory experiments have shown that degradation of plastic starts within days to weeks. Little is known about the early composition and activity of biofilms found on biodegradable and conventional plastic debris and its correlation to degradation in the marine environment. In this study we investigated the early formation of biofilms on plastic shopper bags and its consequences for the degradation of plastic. Samples of polyethylene and biodegradable plastic were tested in the Mediterranean Sea for 15 and 33 days. The samples were distributed equally to a shallow benthic (sedimentary seafloor at 6 m water depth) and a pelagic habitat (3 m water depth) to compare the impact of these different environments on fouling and degradation. The amount of biofilm increased on both plastic types and in both habitats. The diatom abundance and diversity differed significantly between the habitats and the plastic types. Diatoms were more abundant on samples from the pelagic zone. We anticipate that specific surface properties of the polymer types induced different biofilm communities on both plastic types. Additionally, different environmental conditions between the benthic and pelagic experimental site such as light intensity and shear forces may have influenced unequal colonisation between these habitats. The oxygen production rate was negative for all samples, indicating that the initial biofilm on marine plastic litter consumes oxygen, regardless of the plastic type or if exposed in the pelagic or the benthic zone. Mechanical tests did not reveal degradation within one month of exposure. However, scanning electron microscopy (SEM) analysis displayed potential signs of degradation on the plastic surface, which differed between both plastic types. This study indicates that the early biofilm formation and composition are affected by the plastic type and habitat. Further, it reveals that already within two weeks biodegradable plastic shows signs of degradation in the benthic and pelagic habitat. PMID:26394047

Biofilm and Diatom Succession on Polyethylene (PE) and Biodegradable Plastic Bags in Two Marine Habitats: Early Signs of Degradation in the Pelagic and Benthic Zone?

PubMed

Eich, Andreas; Mildenberger, Tobias; Laforsch, Christian; Weber, Miriam

2015-01-01

The production of biodegradable plastic is increasing. Given the augmented littering of these products an increasing input into the sea is expected. Previous laboratory experiments have shown that degradation of plastic starts within days to weeks. Little is known about the early composition and activity of biofilms found on biodegradable and conventional plastic debris and its correlation to degradation in the marine environment. In this study we investigated the early formation of biofilms on plastic shopper bags and its consequences for the degradation of plastic. Samples of polyethylene and biodegradable plastic were tested in the Mediterranean Sea for 15 and 33 days. The samples were distributed equally to a shallow benthic (sedimentary seafloor at 6 m water depth) and a pelagic habitat (3 m water depth) to compare the impact of these different environments on fouling and degradation. The amount of biofilm increased on both plastic types and in both habitats. The diatom abundance and diversity differed significantly between the habitats and the plastic types. Diatoms were more abundant on samples from the pelagic zone. We anticipate that specific surface properties of the polymer types induced different biofilm communities on both plastic types. Additionally, different environmental conditions between the benthic and pelagic experimental site such as light intensity and shear forces may have influenced unequal colonisation between these habitats. The oxygen production rate was negative for all samples, indicating that the initial biofilm on marine plastic litter consumes oxygen, regardless of the plastic type or if exposed in the pelagic or the benthic zone. Mechanical tests did not reveal degradation within one month of exposure. However, scanning electron microscopy (SEM) analysis displayed potential signs of degradation on the plastic surface, which differed between both plastic types. This study indicates that the early biofilm formation and composition are affected by the plastic type and habitat. Further, it reveals that already within two weeks biodegradable plastic shows signs of degradation in the benthic and pelagic habitat.

Evolution of plastic deformation and its effect on mechanical properties of laser additive repaired Ti64ELI titanium alloy

NASA Astrophysics Data System (ADS)

Zhao, Zhuang; Chen, Jing; Tan, Hua; Lin, Xin; Huang, Weidong

2017-07-01

In this paper, laser additive manufacturing (LAM) technology with powder feeding has been employed to fabricate 50%LAMed specimens (i.e. the volume fraction of the laser deposited zone was set to 50%). With aid of the 3D-DIC technique, the tensile deformation behavior of 50%LAMed Ti64ELI titanium alloy was investigated. The 50%LAMed specimen exhibits a significant characteristic of strength mismatch due to the heterogeneous microstructure. The tensile fracture of 50%LAMed specimen occurs in WSZ (wrought substrate zone), but the tensile strength is slightly higher and the plastic elongation is significantly lower than that of the wrought specimen. The 3D-DIC results shows that the 50%LAMed specimen exhibits a characteristic of dramatic plastic strain heterogeneity and the maximal strain is invariably concentrated in WSZ. The ABAQUS simulation indicates that, the LDZ (laser deposited zone) can constrain the plastic deformation of the WSZ and biaxial stresses develop at the interface after yielding.

Mapping and analysis of microplasticity in tensile-deformed double-notched silicon crystals by computer-aided X-ray rocking curve analyzer

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

Liu, H.Y.; Mayo, W.E.; Weissmann, S.

A computer-aided X-ray rocking curve analyzer (CARCA) was developed to map and analyze rapidly the distribution of plastic and elastic strains in deformed single crystals. Double-notched silicon crystal, tensile deformed at 800 C, was selected as a model material. For small stresses the interaction effects of the strained plastic zones were negligible. With increased deformation interaction of microplasticity caused modifications of the characteristics of the plastic zones at the notch tips. The microplastic trajectory of the internotch zone outlined the future fracture path at an early stage of deformation. The observed decrease of micrplasticity with depth from the surface ismore » explained both from the micro and macromechanics viewpoint.« less

The relation of sediment texture to macro- and microplastic abundance in intertidal zone

NASA Astrophysics Data System (ADS)

Wahyuningsih, H.; Bangun, A. P.; Muhtadi, A.

2018-02-01

The intertidal zone is a waters area directly affected by the contamination of plastic debris from land and sea. The aim of this research were to analyze the relation of sediment texture to macro- and micro plastic abundance and also to determine appropriate management strategy. This research was conducted in intertidal zone Jaring Halus Village Langkat Regency North Sumatera Province on February-April 2017. Plastic debris was collected using quadrat transect. Sediment was collected with correct, up to a depth of least 30 cm. Abundance of micro plastic in Station 1 were positively tolerated with clay (0.509), and silt (0.787) and negatively correlations with sand (0.709) Station 2 were positively correlations with sand (0.645) and negatively correlations with clay (0.575), and silt (0.626) Station 3 were positively correlations with clay (0.435), and silt (0.466) and negatively correlations with sand (0.599). The abundance of microplastic was positively correlations with the abundance of microplastic (0.765). Microplastic density is directly proportional to the content of clay and dust. The higher the clay and dust content the higher the micro plastic density.

Elementary model of severe plastic deformation by KoBo process

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

Gusak, A.; Storozhuk, N.; Danielewski, M., E-mail: daniel@agh.edu.pl

2014-01-21

Self-consistent model of generation, interaction, and annihilation of point defects in the gradient of oscillating stresses is presented. This model describes the recently suggested method of severe plastic deformation by combination of pressure and oscillating rotations of the die along the billet axis (KoBo process). Model provides the existence of distinct zone of reduced viscosity with sharply increased concentration of point defects. This zone provides the high extrusion velocity. Presented model confirms that the Severe Plastic Deformation (SPD) in KoBo may be treated as non-equilibrium phase transition of abrupt drop of viscosity in rather well defined spatial zone. In thismore » very zone, an intensive lateral rotational movement proceeds together with generation of point defects which in self-organized manner make rotation possible by the decrease of viscosity. The special properties of material under KoBo version of SPD can be described without using the concepts of nonequilibrium grain boundaries, ballistic jumps and amorphization. The model can be extended to include different SPD processes.« less

Microplastic-associated Bacterial Assemblages in the Intertidal Zone

NASA Astrophysics Data System (ADS)

Jiang, P.; Zhao, S.; Zhu, L.; Li, D.

2017-12-01

Plastic debris is posing a planetary-scale threat. As a zone where terrestrial and marine ecosystems interactions occur, the accumulation of plastic marine debris (PMD) in intertidal environments has been well documented. But the information of plastic-associated microbial community (the "Plastisphere") in the intertidal zone is scanty. Utilizing the high-throughput sequencing, we profiled the bacterial communities attached to microplastic samples from the intertidal locations around Yangtze estuary. The structure and composition of Plastisphere communities in current study varied significantly with geographical stations. The taxonomic composition on microplastic samples implied their sedimental and aquatic origins. Some members of hydrocarbon degrading microorganisms and potential pathogens were detected on microplastic. Overall, our findings fuel the evidence for the occurrence of diverse microbial assemblages on PMD and improving our understanding of Plastisphere ecology, which could support the management action and policy change related to PMD.

Viscoelasticity and plasticity mechanisms of human dentin

NASA Astrophysics Data System (ADS)

Borodin, E. N.; Seyedkavoosi, S.; Zaitsev, D.; Drach, B.; Mikaelyan, K. N.; Panfilov, P. E.; Gutkin, M. Yu.; Sevostianov, I.

2018-01-01

Theoretical models of viscoelastic behavior and plastic deformation mechanisms of human dentin are considered. Using the linear viscoelasticity theory in which creep and relaxation kernels have the form of fraction-exponential functions, numerical values of instantaneous and long-time Young's moduli and other characteristics of dentin viscoelasticity under uniaxial compression are found. As dentin plastic deformation mechanisms, mutual collagen fiber sliding in the region of contact of their side surfaces, separation of these fibers from each other, and irreversible tension of some collagen fibers, are proposed. It is shown that the second mechanism activation requires a smaller stress than that for activating others. The models of plastic zones at the mode I crack tip, which correspond to these mechanisms, are studied. It is shown that the plastic zone size can increase from a few hundreds of nanometers to hundreds of micrometers with increasing applied stress.

Rapid Grain Size Reduction in the Upper Mantle at a Plate Boundary

NASA Astrophysics Data System (ADS)

Kidder, S. B.; Scott, J.; Prior, D. J.; Lubicich, E. J.

2017-12-01

A few spinel peridotite xenoliths found near the Alpine Fault, New Zealand, exhibit a mylonitic texture and, locally, an extremely fine 30 micron grain size. The harzburgite xenoliths were emplaced in a 200 km-long elongate dike zone interpreted as a gigantic tension fracture or Reidel shear associated with Alpine Fault initiation 25 Ma. The presence of thin ( 1 mm) ultramylonite zones with px-ol phase mixing and fine grain sizes, minimal crustal-scale strain associated with the dike swarm, and the absence of mylonites at four of the five xenolith localities associated with the dike swarm indicate that upper mantle deformation was highly localized. Strings of small, recrystallized grains (planes in 3D) are found in the interiors of olivine porphyroclasts. In some cases, bands 1-2 grains thick are traced from the edges of olivine grains and terminate in their interiors. Thicker zones of recrystallized grains are also observed crossing olivine porphyroclasts without apparent offset of the unrecrystallized remnants of the porphyroclasts. We suggest a brittle-plastic origin for these features since the traditional recrystallization mechanisms associated with dislocation creep require much more strain than occurred within these porphyroclasts. Analogous microstructures in quartz and feldspar in mid-crust deformation zones are attributed to brittle-plastic processes. We hypothesize that such fine-grained zones were the precursors of the observed, higher-strain ultramylonite zones. Given the size of the new grains preserved in the porphyroclasts ( 100 micron) and a moho temperature > 650°C, grain growth calculations indicate that the observed brittle-plastic deformation occurred <10,000 yrs. prior to eruption. It is likely then that either brittle-plastic deformation was coeval with the ductile shearing occurring in the ultramylonite bands, or possibly, if deformation can be separated into brittle-plastic (early) and ductile (later) phases, that the entire localization process was very rapid (<10,000 yrs). In either case we interpret that semi-brittle deformation was a key process responsible for rapid localization in this initiating plate-scale mantle shear zone.

Fabric transition with dislocation creep of a carbonate fault zone in the brittle regime

NASA Astrophysics Data System (ADS)

Kim, Sungshil; Ree, Jin-Han; Han, Raehee; Kim, Nahyeon; Jung, Haemyeong

2018-01-01

Fabric transition by a switch in the dominant slip system of minerals in the plastic regime can be induced by changes in temperature, strain rate, or water content. We propose here this fabric transition by frictional heating in seismogenic fault zones in the brittle regime. The Garam Thrust in the Taebaeksan Basin of South Korea has a hanging wall of Cambrian dolostone juxtaposed against a footwall of Ordovician limestone and records a minimum displacement of 120 m. In a 10 cm thick plastically deformed layer adjacent to the principal slip layer of the fault zone, the lattice preferred orientation of calcite grains suggests that the dominant slip system changes, approaching the principal slip layer, from r 〈02-21〉 and e-twinning, through r 〈02-21〉 and basal 〈a〉, to basal 〈a〉. This fabric transition requires a high temperature-gradient of 40 °C/cm, which we infer to result from frictional heating of the seismic fault zone. We suggest that fabric transition within a thin plastically deformed layer adjacent to the principal slip layer of a fault zone indicates an unusually steep temperature gradient and provides strong evidence of seismic slip.

Pore-forming toxins in Cnidaria.

PubMed

Podobnik, Marjetka; Anderluh, Gregor

2017-12-01

The ancient phylum of Cnidaria contains many aquatic species with peculiar lifestyle. In order to survive, these organisms have evolved attack and defense mechanisms that are enabled by specialized cells and highly developed venoms. Pore-forming toxins are an important part of their venomous arsenal. Along some other types, the most representative are examples of four protein families that are commonly found in other kingdoms of life: actinoporins, Cry-like proteins, aerolysin-like toxins and MACPF/CDC toxins. Some of the homologues of pore-forming toxins may serve other functions, such as in food digestion, development and response against pathogenic organisms. Due to their interesting physico-chemical properties, the cnidarian pore-forming toxins may also serve as tools in medical research and nanobiotechnological applications. Copyright © 2017 Elsevier Ltd. All rights reserved.

Elastic-plastic deformation of a metal-matrix composite coupon with a center slot

NASA Technical Reports Server (NTRS)

Post, D.; Czarnek, R.; Joh, D.; Jo, J.; Guo, Y.

1985-01-01

A comprehensive experimental analysis of deformations of the surface of a metal-matrix specimen is reported. The specimen is a 6-ply 0 + or - 45 sub s boron-aluminum tensile coupon with a central slot. Moire interferometry is used for high-sensitivity whole-field measurements of in-plane displacements. Normal and shear strains are calculated from displacement gradients. Displacement fields are analyzed at various load levels from 15% to 95% of the failure load. Deformations of the boron fibers could be distinguished from those of the matrix. Highly localized plastic slip zones occur tangent to the ends of the slot. Shear strains and concurrent transverse compressive strains in the slip zones reach approximately 10% and 1%, respectively. Upon unloading, elastic recovery in surrounding regions causes a reverse plastic shear strain in the slip zone of about 4%. Longitudinal normal strains on the unslotted ligament peak at the slot boundary at about 1% strain. The strain concentration factor at the end of the slot decreases with load level and the advance of plasticity.

Dynamic rupture simulations on complex fault zone structures with off-fault plasticity using the ADER-DG method

NASA Astrophysics Data System (ADS)

Wollherr, Stephanie; Gabriel, Alice-Agnes; Igel, Heiner

2015-04-01

In dynamic rupture models, high stress concentrations at rupture fronts have to to be accommodated by off-fault inelastic processes such as plastic deformation. As presented in (Roten et al., 2014), incorporating plastic yielding can significantly reduce earlier predictions of ground motions in the Los Angeles Basin. Further, an inelastic response of materials surrounding a fault potentially has a strong impact on surface displacement and is therefore a key aspect in understanding the triggering of tsunamis through floor uplifting. We present an implementation of off-fault-plasticity and its verification for the software package SeisSol, an arbitrary high-order derivative discontinuous Galerkin (ADER-DG) method. The software recently reached multi-petaflop/s performance on some of the largest supercomputers worldwide and was a Gordon Bell prize finalist application in 2014 (Heinecke et al., 2014). For the nonelastic calculations we impose a Drucker-Prager yield criterion in shear stress with a viscous regularization following (Andrews, 2005). It permits the smooth relaxation of high stress concentrations induced in the dynamic rupture process. We verify the implementation by comparison to the SCEC/USGS Spontaneous Rupture Code Verification Benchmarks. The results of test problem TPV13 with a 60-degree dipping normal fault show that SeisSol is in good accordance with other codes. Additionally we aim to explore the numerical characteristics of the off-fault plasticity implementation by performing convergence tests for the 2D code. The ADER-DG method is especially suited for complex geometries by using unstructured tetrahedral meshes. Local adaptation of the mesh resolution enables a fine sampling of the cohesive zone on the fault while simultaneously satisfying the dispersion requirements of wave propagation away from the fault. In this context we will investigate the influence of off-fault-plasticity on geometrically complex fault zone structures like subduction zones or branched faults. Studying the interplay of stress conditions and angle dependence of neighbouring branches including inelastic material behaviour and its effects on rupture jumps and seismic activation helps to advance our understanding of earthquake source processes. An application is the simulation of a real large-scale subduction zone scenario including plasticity to validate the coupling of our dynamic rupture calculations to a tsunami model in the framework of the ASCETE project (http://www.ascete.de/). Andrews, D. J. (2005): Rupture dynamics with energy loss outside the slip zone, J. Geophys. Res., 110, B01307. Heinecke, A. (2014), A. Breuer, S. Rettenberger, M. Bader, A.-A. Gabriel, C. Pelties, A. Bode, W. Barth, K. Vaidyanathan, M. Smelyanskiy and P. Dubey: Petascale High Order Dynamic Rupture Earthquake Simulations on Heterogeneous Supercomputers. In Supercomputing 2014, The International Conference for High Performance Computing, Networking, Storage and Analysis. IEEE, New Orleans, LA, USA, November 2014. Roten, D. (2014), K. B. Olsen, S.M. Day, Y. Cui, and D. Fäh: Expected seismic shaking in Los Angeles reduced by San Andreas fault zone plasticity, Geophys. Res. Lett., 41, 2769-2777.

Methods for minimizing plastic flow of oil shale during in situ retorting

DOEpatents

Lewis, Arthur E.; Mallon, Richard G.

1978-01-01

In an in situ oil shale retorting process, plastic flow of hot rubblized oil shale is minimized by injecting carbon dioxide and water into spent shale above the retorting zone. These gases react chemically with the mineral constituents of the spent shale to form a cement-like material which binds the individual shale particles together and bonds the consolidated mass to the wall of the retort. This relieves the weight burden borne by the hot shale below the retorting zone and thereby minimizes plastic flow in the hot shale. At least a portion of the required carbon dioxide and water can be supplied by recycled product gases.

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.

Multi `omics reveals role of phenotypic plasticity in governing biogeochemical hotspots within the groundwater-surface water (hyporheic) mixing zone

NASA Astrophysics Data System (ADS)

Graham, E.; Tfaily, M. M.; Crump, A.; Arntzen, E.; Romero, E. B.; Goldman, A. E.; Resch, T.; Kennedy, D.; Nelson, W. C.; Stegen, J.

2017-12-01

Subsurface groundwater-surface water mixing zones (hyporheic zones) contain spatially heterogeneous hotspots of enhanced biogeochemical activity that contribute disproportionately to river corridor function. We have a poor understanding of the processes governing hotspots, but recent advances have enabled greater mechanistic understanding. We employ a suite of ultra-high resolution measurements to investigate the mechanisms underlying biogeochemical cycles in hyporheic zone hotspots. We use Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS), metagenomic shotgun sequencing, and mass spectrometry of metaproteomes to characterize metabolite structure and metabolic transformations, microbiome structure and functional potential, and expressed microbiome functions in hyporheic sediments from the Columbia River in central Washington State. Surprisingly, microbiome structure and function in biogeochemical hotspots were indistinguishable from low-activity sediments. Metabolites were uncorrelated to protein expression but strongly related to aerobic respiration. Hotspot metabolites were distinguished by high molecular weight compounds and protein-, lignin-, and lipid-like molecules. Although the most common metabolic transformations were similar between hotspots and low-activity samples, hotspots contained a greater proportion of rare pathways, which in turn were correlated to metabolism. Our results contradicted our expectations that hotspots would be characterized by a unique microbiome with distinct physiology. Instead, our results indicate that microbial phenotypic plasticity underlies elevated hyporheic zone function, whereby the activity of rare pathways is stimulated by substrate availability. We therefore hypothesize that microbiome plasticity couples meso- (e.g., local root distribution) and macro-scale (e.g., landscape vegetation) resource heterogeneity to ecosystem-scale function. This indicates a need to mechanistically understand and represent microbiome physiological plasticity in predictive hydrobiogeochemical models that include the hyporheic zone.

Polybrominated diphenyl ethers (PBDEs) in fish tissue may be an indicator of plastic contamination in marine habitats.

PubMed

Rochman, Chelsea M; Lewison, Rebecca L; Eriksen, Marcus; Allen, Harry; Cook, Anna-Marie; Teh, Swee J

2014-04-01

The accumulation of plastic debris in pelagic habitats of the subtropical gyres is a global phenomenon of growing concern, particularly with regard to wildlife. When animals ingest plastic debris that is associated with chemical contaminants, they are at risk of bioaccumulating hazardous pollutants. We examined the relationship between the bioaccumulation of hazardous chemicals in myctophid fish associated with plastic debris and plastic contamination in remote and previously unmonitored pelagic habitats in the South Atlantic Ocean. Using a published model, we defined three sampling zones where accumulated densities of plastic debris were predicted to differ. Contrary to model predictions, we found variable levels of plastic debris density across all stations within the sampling zones. Mesopelagic lanternfishes, sampled from each station and analyzed for bisphenol A (BPA), alkylphenols, alkylphenol ethoxylates, polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs), exhibited variability in contaminant levels, but this variability was not related to plastic debris density for most of the targeted compounds with the exception of PBDEs. We found that myctophid sampled at stations with greater plastic densities did have significantly larger concentrations of BDE#s 183 -209 in their tissues suggesting that higher brominated congeners of PBDEs, added to plastics as flame-retardants, are indicative of plastic contamination in the marine environment. Our results provide data on a previously unsampled pelagic gyre and highlight the challenges associated with characterizing plastic debris accumulation and associated risks to wildlife. Copyright © 2014 Elsevier B.V. All rights reserved.

Materiel Testing in the Tropics (6th Ed)

DTIC Science & Technology

1979-04-01

ceramics Test methodology Panama Canal Zone Textiles Plastics Tropic Test Center Protective coatings Tropical animals 20. (cont) of Materiel Testing in...Canal Zone . .. 1-3 D Materiel Testing in the Panama Canal Zone . . . . . . . ... . 1-5 E Canal Zone Environment--Brief Overview .. .. .... ...... 1-6...trapped there, and by the heavy biomass of the canopy itself. E. CANAL ZONE ENVIRONMENT--BRIEF OVERVIEW The Canal Zone (see frontispiece) bisects the

Laboratory Test Methods to Determine the Degradation of Plastics in Marine Environmental Conditions

PubMed Central

Tosin, Maurizio; Weber, Miriam; Siotto, Michela; Lott, Christian; Degli Innocenti, Francesco

2012-01-01

In this technology report, three test methods were developed to characterize the degradation of plastic in marine environment. The aim was to outline a test methodology to measure the physical and biological degradation in different habitats where plastic waste can deposit when littered in the sea. Previously, research has focused mainly on the conditions encountered by plastic items when floating in the sea water (pelagic domain). However, this is just one of the possible habitats that plastic waste can be exposed to. Waves and tides tend to wash up plastic waste on the shoreline, which is also a relevant habitat to be studied. Therefore, the degradation of plastic items buried under sand kept wet with sea water has been followed by verifying the disintegration (visual disappearing) as a simulation of the tidal zone. Most biodegradable plastics have higher densities than water and also as a consequence of fouling, they tend to sink and lay on the sea floor. Therefore, the fate of plastic items lying on the sediment has been followed by monitoring the oxygen consumption (biodegradation). Also the effect of a prolonged exposure to the sea water, to simulate the pelagic domain, has been tested by measuring the decay of mechanical properties. The test material (Mater-Bi) was shown to degrade (total disintegration achieved in less than 9 months) when buried in wet sand (simulation test of the tidal zone), to lose mechanical properties but still maintain integrity (tensile strength at break = −66% in 2 years) when exposed to sea water in an aquarium (simulation of pelagic domain), and substantially biodegrade (69% in 236 days; biodegradation relative to paper: 88%) when located at the sediment/sea water interface (simulation of benthic domain). This study is not conclusive as the methodological approach must be completed by also determining degradation occurring in the supralittoral zone, on the deep sea floor, and in the anoxic sediment. PMID:22737147

Laboratory test methods to determine the degradation of plastics in marine environmental conditions.

PubMed

Tosin, Maurizio; Weber, Miriam; Siotto, Michela; Lott, Christian; Degli Innocenti, Francesco

2012-01-01

In this technology report, three test methods were developed to characterize the degradation of plastic in marine environment. The aim was to outline a test methodology to measure the physical and biological degradation in different habitats where plastic waste can deposit when littered in the sea. Previously, research has focused mainly on the conditions encountered by plastic items when floating in the sea water (pelagic domain). However, this is just one of the possible habitats that plastic waste can be exposed to. Waves and tides tend to wash up plastic waste on the shoreline, which is also a relevant habitat to be studied. Therefore, the degradation of plastic items buried under sand kept wet with sea water has been followed by verifying the disintegration (visual disappearing) as a simulation of the tidal zone. Most biodegradable plastics have higher densities than water and also as a consequence of fouling, they tend to sink and lay on the sea floor. Therefore, the fate of plastic items lying on the sediment has been followed by monitoring the oxygen consumption (biodegradation). Also the effect of a prolonged exposure to the sea water, to simulate the pelagic domain, has been tested by measuring the decay of mechanical properties. The test material (Mater-Bi) was shown to degrade (total disintegration achieved in less than 9 months) when buried in wet sand (simulation test of the tidal zone), to lose mechanical properties but still maintain integrity (tensile strength at break = -66% in 2 years) when exposed to sea water in an aquarium (simulation of pelagic domain), and substantially biodegrade (69% in 236 days; biodegradation relative to paper: 88%) when located at the sediment/sea water interface (simulation of benthic domain). This study is not conclusive as the methodological approach must be completed by also determining degradation occurring in the supralittoral zone, on the deep sea floor, and in the anoxic sediment.

Local microstructure evolution at shear bands in metallic glasses with nanoscale phase separation

PubMed Central

He, Jie; Kaban, Ivan; Mattern, Norbert; Song, Kaikai; Sun, Baoan; Zhao, Jiuzhou; Kim, Do Hyang; Eckert, Jürgen; Greer, A. Lindsay

2016-01-01

At room temperature, plastic flow of metallic glasses (MGs) is sharply localized in shear bands, which are a key feature of the plastic deformation in MGs. Despite their clear importance and decades of study, the conditions for formation of shear bands, their structural evolution and multiplication mechanism are still under debate. In this work, we investigate the local conditions at shear bands in new phase-separated bulk MGs containing glassy nanospheres and exhibiting exceptional plasticity under compression. It is found that the glassy nanospheres within the shear band dissolve through mechanical mixing driven by the sharp strain localization there, while those nearby in the matrix coarsen by Ostwald ripening due to the increased atomic mobility. The experimental evidence demonstrates that there exists an affected zone around the shear band. This zone may arise from low-strain plastic deformation in the matrix between the bands. These results suggest that measured property changes originate not only from the shear bands themselves, but also from the affected zones in the adjacent matrix. This work sheds light on direct visualization of deformation-related effects, in particular increased atomic mobility, in the region around shear bands. PMID:27181922

Elastic-Plastic Fracture Mechanics Analysis of Small Cracks

DTIC Science & Technology

1982-09-01

by the plastic zone size (Eq. (6)), LEM and the elastic-plastic fracture mechanics ( EPFM ) results in Figure 4 can be displayed as in Figure 5. The...8d). Figure 8a shows the growth of a crack for LEFM conditions while Figures 8b, c, and d include EPFM considerations as illustrated in Figure 7. The

Emergent Spatial Patterns of Excitatory and Inhibitory Synaptic Strengths Drive Somatotopic Representational Discontinuities and their Plasticity in a Computational Model of Primary Sensory Cortical Area 3b

PubMed Central

Grajski, Kamil A.

2016-01-01

Mechanisms underlying the emergence and plasticity of representational discontinuities in the mammalian primary somatosensory cortical representation of the hand are investigated in a computational model. The model consists of an input lattice organized as a three-digit hand forward-connected to a lattice of cortical columns each of which contains a paired excitatory and inhibitory cell. Excitatory and inhibitory synaptic plasticity of feedforward and lateral connection weights is implemented as a simple covariance rule and competitive normalization. Receptive field properties are computed independently for excitatory and inhibitory cells and compared within and across columns. Within digit representational zones intracolumnar excitatory and inhibitory receptive field extents are concentric, single-digit, small, and unimodal. Exclusively in representational boundary-adjacent zones, intracolumnar excitatory and inhibitory receptive field properties diverge: excitatory cell receptive fields are single-digit, small, and unimodal; and the paired inhibitory cell receptive fields are bimodal, double-digit, and large. In simulated syndactyly (webbed fingers), boundary-adjacent intracolumnar receptive field properties reorganize to within-representation type; divergent properties are reacquired following syndactyly release. This study generates testable hypotheses for assessment of cortical laminar-dependent receptive field properties and plasticity within and between cortical representational zones. For computational studies, present results suggest that concurrent excitatory and inhibitory plasticity may underlie novel emergent properties. PMID:27504086

Kinetics of Accumulation of Damage in Surface Layers of Lithium-Containing Aluminum Alloys in Fatigue Tests with Rigid Loading Cycle and Corrosive Effect of Environment

NASA Astrophysics Data System (ADS)

Morozova, L. V.; Zhegina, I. P.; Grigorenko, V. B.; Fomina, M. A.

2017-07-01

High-resolution methods of metal physics research including electron, laser and optical microscopy are used to study the kinetics of the accumulation of slip lines and bands and the corrosion damage in the plastic zone of specimens of aluminum-lithium alloys 1441 and B-1469 in rigid-cycle fatigue tests under the joint action of applied stresses and corrosive environment. The strain parameters (the density of slip bands, the sizes of plastic zones near fracture, the surface roughness in singled-out zones) and the damage parameters (the sizes of pits and the pitting area) are evaluated.

Two Back Stress Hardening Models in Rate Independent Rigid Plastic Deformation

NASA Astrophysics Data System (ADS)

Yun, Su-Jin

In the present work, the constitutive relations based on the combination of two back stresses are developed using the Armstrong-Frederick, Phillips and Ziegler’s type hardening rules. Various evolutions of the kinematic hardening parameter can be obtained by means of a simple combination of back stress rate using the rule of mixtures. Thus, a wide range of plastic deformation behavior can be depicted depending on the dominant back stress evolution. The ultimate back stress is also determined for the present combined kinematic hardening models. Since a kinematic hardening rule is assumed in the finite deformation regime, the stress rate is co-rotated with respect to the spin of substructure obtained by incorporating the plastic spin concept. A comparison of the various co-rotational rates is also included. Assuming rigid plasticity, the continuum body consists of the elastic deformation zone and the plastic deformation zone to form a hybrid finite element formulation. Then, the plastic deformation behavior is investigated under various loading conditions with an assumption of the J2 deformation theory. The plastic deformation localization turns out to be strongly dependent on the description of back stress evolution and its associated hardening parameters. The analysis for the shear deformation with fixed boundaries is carried out to examine the deformation localization behavior and the evolution of state variables.

Simulating spontaneous aseismic and seismic slip events on evolving faults

NASA Astrophysics Data System (ADS)

Herrendörfer, Robert; van Dinther, Ylona; Pranger, Casper; Gerya, Taras

2017-04-01

Plate motion along tectonic boundaries is accommodated by different slip modes: steady creep, seismic slip and slow slip transients. Due to mainly indirect observations and difficulties to scale results from laboratory experiments to nature, it remains enigmatic which fault conditions favour certain slip modes. Therefore, we are developing a numerical modelling approach that is capable of simulating different slip modes together with the long-term fault evolution in a large-scale tectonic setting. We extend the 2D, continuum mechanics-based, visco-elasto-plastic thermo-mechanical model that was designed to simulate slip transients in large-scale geodynamic simulations (van Dinther et al., JGR, 2013). We improve the numerical approach to accurately treat the non-linear problem of plasticity (see also EGU 2017 abstract by Pranger et al.). To resolve a wide slip rate spectrum on evolving faults, we develop an invariant reformulation of the conventional rate-and-state dependent friction (RSF) and adapt the time step (Lapusta et al., JGR, 2000). A crucial part of this development is a conceptual ductile fault zone model that relates slip rates along discrete planes to the effective macroscopic plastic strain rates in the continuum. We test our implementation first in a simple 2D setup with a single fault zone that has a predefined initial thickness. Results show that deformation localizes in case of steady creep and for very slow slip transients to a bell-shaped strain rate profile across the fault zone, which suggests that a length scale across the fault zone may exist. This continuum length scale would overcome the common mesh-dependency in plasticity simulations and question the conventional treatment of aseismic slip on infinitely thin fault zones. We test the introduction of a diffusion term (similar to the damage description in Lyakhovsky et al., JMPS, 2011) into the state evolution equation and its effect on (de-)localization during faster slip events. We compare the slip spectrum in our simulations to conventional RSF simulations (Liu and Rice, JGR, 2007). We further demonstrate the capability of simulating the evolution of a fault zone and simultaneous occurrence of slip transients. From small random initial distributions of the state variable in an otherwise homogeneous medium, deformation localizes and forms curved zones of reduced states. These spontaneously formed fault zones host slip transients, which in turn contribute to the growth of the fault zone.

Paper microzone plates.

PubMed

Carrilho, Emanuel; Phillips, Scott T; Vella, Sarah J; Martinez, Andres W; Whitesides, George M

2009-08-01

This paper describes 96- and 384-microzone plates fabricated in paper as alternatives to conventional multiwell plates fabricated in molded polymers. Paper-based plates are functionally related to plastic well plates, but they offer new capabilities. For example, paper-microzone plates are thin (approximately 180 microm), require small volumes of sample (5 microL per zone), and can be manufactured from inexpensive materials ($0.05 per plate). The paper-based plates are fabricated by patterning sheets of paper, using photolithography, into hydrophilic zones surrounded by hydrophobic polymeric barriers. This photolithography used an inexpensive formulation photoresist that allows rapid (approximately 15 min) prototyping of paper-based plates. These plates are compatible with conventional microplate readers for quantitative absorbance and fluorescence measurements. The limit of detection per zone loaded for fluorescence was 125 fmol for fluorescein isothiocyanate-labeled bovine serum albumin, and this level corresponds to 0.02 the quantity of analyte per well used to achieve comparable signal-to-noise in a 96-well plastic plate (using a solution of 25 nM labeled protein). The limits of detection for absorbance on paper was approximately 50 pmol per zone for both Coomassie Brilliant Blue and Amaranth dyes; these values were 0.4 that required for the plastic plate. Demonstration of quantitative colorimetric correlations using a scanner or camera to image the zones and to measure the intensity of color, makes it possible to conduct assays without a microplate reader.

The Dugdale model for the compact specimen

NASA Technical Reports Server (NTRS)

Mall, S.; Newman, J. C., Jr.

1983-01-01

Plastic zone size and crack tip opening displacement (CTOD) equations were developed. Boundary collocation analyses were used to analyze the compact specimen subjected to various loading conditions (pin loads, concentrated forces, and uniform pressure acting on the crack surface). Stress intensity factor and crack surface displacement equations for some of these loadings were developed and used to obtain the Dugdale model. The results from the equations for plastic zone size and CTOD agreed well with numerical values calculated by Terada for crack length to width ratios greater than 0.4.

Local zone-wise elastic-plastic constitutive parameters of Laser-welded aluminium alloy 6061 using digital image correlation

NASA Astrophysics Data System (ADS)

Bai, Ruixiang; Wei, Yuepeng; Lei, Zhenkun; Jiang, Hao; Tao, Wang; Yan, Cheng; Li, Xiaolei

2018-02-01

The mechanical properties of aluminium alloys can be affected by the local high temperature in laser welding. In this paper, an inversion identification method of local zone-wise elastic-plastic constitutive parameters for laser welding of aluminium alloy 6061 was proposed based on full-field optical measurement data using digital image correlation (DIC). Three regions, i.e., the fusion zone, heat-affected zone, and base zone, of the laser-welded joint were distinguished by means of microstructure optical observation and micrometer hardness measurement. The stress data were obtained using a laser-welded specimen via a uniaxial tensile test. Meanwhile, the local strain data of the laser-welded specimen were obtained by the DIC technique. Thus, the stress-strain relationship for different local regions was established. Finally, the constitutive parameters of the Ramberg-Osgood model were identified by least-square fitting to the experimental stress-strain data. Experimental results revealed that the mechanical properties of the local zones of the welded joints clearly weakened, and these results are consistent with the results of the hardness measurement.

A New Paradigm For Modeling Fault Zone Inelasticity: A Multiscale Continuum Framework Incorporating Spontaneous Localization and Grain Fragmentation.

NASA Astrophysics Data System (ADS)

Elbanna, A. E.

2015-12-01

The brittle portion of the crust contains structural features such as faults, jogs, joints, bends and cataclastic zones that span a wide range of length scales. These features may have a profound effect on earthquake nucleation, propagation and arrest. Incorporating these existing features in modeling and the ability to spontaneously generate new one in response to earthquake loading is crucial for predicting seismicity patterns, distribution of aftershocks and nucleation sites, earthquakes arrest mechanisms, and topological changes in the seismogenic zone structure. Here, we report on our efforts in modeling two important mechanisms contributing to the evolution of fault zone topology: (1) Grain comminution at the submeter scale, and (2) Secondary faulting/plasticity at the scale of few to hundreds of meters. We use the finite element software Abaqus to model the dynamic rupture. The constitutive response of the fault zone is modeled using the Shear Transformation Zone theory, a non-equilibrium statistical thermodynamic framework for modeling plastic deformation and localization in amorphous materials such as fault gouge. The gouge layer is modeled as 2D plane strain region with a finite thickness and heterogeenous distribution of porosity. By coupling the amorphous gouge with the surrounding elastic bulk, the model introduces a set of novel features that go beyond the state of the art. These include: (1) self-consistent rate dependent plasticity with a physically-motivated set of internal variables, (2) non-locality that alleviates mesh dependence of shear band formation, (3) spontaneous evolution of fault roughness and its strike which affects ground motion generation and the local stress fields, and (4) spontaneous evolution of grain size and fault zone fabric.

Microstructural record of pressure solution and crystal plastic deformation in carbonate fault rocks from a shallow crustal strike-slip fault, Northern Calcareous Alps (Austria)

NASA Astrophysics Data System (ADS)

Bauer, Helene; Rogowitz, Anna; Grasemann, Benhard; Decker, Kurt

2017-04-01

This study presents microstructural investigations of natural carbonate fault rocks that formed by a suite of different deformation processes, involving hydro-fracturing, dissolution-precipitation creep and cataclasis. Some fault rocks show also clear indications of crystal plastic deformation, which is quite unexpected, as the fault rocks were formed in an upper crustal setting, raising the question of possible strongly localised, low temperature ductile deformation in carbonate rocks. The investigated carbonate fault rocks are from an exhumed, sinistral strike-slip fault at the eastern segment of the Salzachtal-Ennstal-Mariazell-Puchberg (SEMP) fault system in the Northern Calcareous Alps (Austria). The SEMP fault system formed during eastward lateral extrusion of the Eastern Alps in the Oligocene to Lower Miocene. Based on vitrinite reflectance data form intramontane Teritary basins within the Northern Calcareous Alps, a maximum burial depth of 4 km for the investigated fault segment is estimated. The investigated fault accommodated sinistral slip of several hundreds of meters. Microstructural analysis of fault rocks includes scanning electron microscopy, optical microscopy and electron backscattered diffraction mapping. The data show that fault rocks underwent various stages of evolution including early intense veining (hydro-fracturing) and stylolite formation reworked by localised shear zones. Cross cutting relationship reveals that veins never cross cut clay seams accumulated along stylolites. We conclude that pressure solution processes occured after hydro-fracturing. Clay enriched zones localized further deformation, producing a network of small-scale clay-rich shear zones of up to 1 mm thickness anastomosing around carbonate microlithons, varying from several mm down to some µm in size. Clay seams consist of kaolinit, chlorite and illite matrix and form (sub) parallel zones in which calcite was dissolved. Beside pressure solution, calcite microlithons show also ductile deformation microstructures, including deformation twinning, undulose extinction, subgrain rotation recrystallization and even grain boundary migration. Especially coarse grained calcites from veins localized ductile deformation and record dislocation glide. The investigated fault rocks are excellent examples of frictional, pressure solution and crystal plastic deformation processes. We speculated that crystal plastic deformation typical for higher metamorphic shear zones in marbles, can be either produced under much lower temperature conditions or the temperature necessary for crystal plastic deformation was generated by frictional slip or strain heating within the fault zone.

Environmental fatigue of an Al-Li-Cu alloy. Part 2: Microscopic hydrogen cracking processes

NASA Technical Reports Server (NTRS)

Piascik, Robert S.; Gangloff, Richard P.

1992-01-01

Based on a fractographic analysis of fatigue crack propagation (FCP) in Al-Li-Cu alloy 2090 stressed in a variety of inert and embrittling environments, microscopic crack paths are identified and correlated with intrinsic da/dN-delta K kinetics. FCP rates in 2090 are accelerated by hydrogen producing environments (pure water vapor, moist air, and aqueous NaCl), as defined in Part 1. For these cases, subgrain boundary fatigue cracking (SGC) dominates for delta K values where the crack tip process zone, a significant fraction of the cyclic plastic zone, is sufficiently large to envelop 5 micron subgrains in the unrecrystallized microstructure. SGC may be due to strong hydrogen trapping at T1 precipitates concentrated at sub-boundaries. At low delta K, the plastic zone diameter is smaller than the subgrain size and FCP progresses along (100) planes due to either local lattice decohesion or aluminum-lithium hydride cracking. For inert environments (vacuum, helium, and oxygen), or at high delta K where the hydrogen effect on da/dN is small, FCP is along (111) slip planes; this mode does not transition with increasing delta K and plastic zone size. The SGC and (100) crystallographic cracking modes, and the governing influence of the crack tip process zone volume (delta K), support hydrogen embrittlement rather than a surface film rupture and anodic dissolution mechanism for environmental FCP. Multi-sloped log da/dN-log delta K behavior is produced by changes in process zone hydrogen-microstructure interactions, and not by purely micromechanical-microstructure interactions, in contradiction to microstructural distance-based fatigue models.

Plastic pollution in the South Pacific subtropical gyre.

PubMed

Eriksen, Marcus; Maximenko, Nikolai; Thiel, Martin; Cummins, Anna; Lattin, Gwen; Wilson, Stiv; Hafner, Jan; Zellers, Ann; Rifman, Samuel

2013-03-15

Plastic marine pollution in the open ocean of the southern hemisphere is largely undocumented. Here, we report the result of a (4489 km) 2424 nautical mile transect through the South Pacific subtropical gyre, carried out in March-April 2011. Neuston samples were collected at 48 sites, averaging 50 nautical miles apart, using a manta trawl lined with a 333 μm mesh. The transect bisected a predicted accumulation zone associated with the convergence of surface currents, driven by local winds. The results show an increase in surface abundance of plastic pollution as we neared the center and decrease as we moved away, verifying the presence of a garbage patch. The average abundance and mass was 26,898 particles km(-2) and 70.96 g km(-2), respectively. 88.8% of the plastic pollution was found in the middle third of the samples with the highest value of 396,342 particles km(-2) occurring near the center of the predicted accumulation zone. Copyright © 2013 Elsevier Ltd. All rights reserved.

Effect of Severe Plastic Deformation on Structure and Properties of Al-Sc-Ta and Al-Sc-Ti Alloys

NASA Astrophysics Data System (ADS)

Berezina, Alla; Monastyrska, Tetiana; Davydenko, Olexandr; Molebny, Oleh; Polishchuk, Sergey

2017-03-01

The comparative analysis of the effect of monotonous and non-monotonous severe plastic deformations (SPD) on the structure and properties of aluminum alloys has been carried out. Conventional hydrostatic extrusion (HE) with a constant deformation direction and equal-channel angular hydroextrusion (ECAH) with an abrupt change in the deformation direction were chosen for the cases of monotonous and non-monotonous SPD, respectively. Model cast hypoeutectic Al-0.3%Sc alloys and hypereutectic Al-0.6%Sc alloys with Ta and Ti additives were chosen for studying. It was demonstrated that SPD of the alloys resulted in the segregation of the material into active and inactive zones which formed a banded structure. The active zones were shown to be bands of localized plastic deformation. The distance between zones was found to be independent of the accumulated strain degree and was in the range of 0.6-1 μm. Dynamic recrystallization in the active zones was observed using TEM. The dynamic recrystallization was accompanied by the formation of disclinations, deformation bands, low-angle, and high-angle boundaries, i.e., rotational deformation modes developed. The dynamic recrystallization was more intense during the non-monotonous deformation as compared with the monotonous one, which was confirmed by the reduction of texture degree in the materials after ECAH.

Microplastics in sea coastal zone: Lessons learned from the Baltic amber.

PubMed

Chubarenko, Irina; Stepanova, Natalia

2017-05-01

Baltic amber, adored for its beauty already in Homer's Odyssey (ca. 800 B.C.E), has its material density close to that of wide-spread plastics like polyamide, polystyrene, or acrylic. Migrations of amber stones in the sea and their massive washing ashore have been monitored by Baltic citizens for ages. Based on the collected information, we present the hypothesis on the behaviour of microplastic particles in sea coastal zone. Fresh-to-strong winds generate surface waves, currents and roll-structures, whose joint effect washes ashore from the underwater slope both amber stones and plastics - and carries them back to the sea in a few days. Analysis of underlying hydrophysical processes suggests that sea coastal zone under stormy winds plays a role of a mill for plastics, and negatively buoyant pieces seem to repeatedly migrate between beaches and underwater slopes until they are broken into small enough fragments that can be transported by currents to deeper areas and deposited out of reach of stormy waves. Direct observations on microplastics migrations are urged to prove the hypothesis. Copyright © 2017 Elsevier Ltd. All rights reserved.

Microstructural examination of

NASA Astrophysics Data System (ADS)

Fukuoka, C.; Yoshizawa, H.; Nakagawa, Y. G.; Lapides, M. E.

1993-10-01

Fatigue tests were performed to examine how microstructural conditioning influences crack initiation and propagation in SA508 class 3 low-carbon steel. A 3-mm-long crack was introduced in compact tension (CT) fatigue test specimens under four different loads in order to obtain crack tip plastic zones at different stress intensity factor ranges, ΔK = 18, 36, 54, and 72 MPa√m. The microstructure of the plastic zones around the crack tip were examined by trans- mission electron microscopy (TEM) and selected area electron diffraction (SAD). Micro- orientation of the dislocation cells in the plastic zones of all of the CT samples increased to 4 deg from the level of an as-received sample. Four-point bending fatigue tests were performed for plate shape samples with a large cyclic strain range. The SAD value of the bending samples was also 4 deg in the damaged area where cracks already initiated at an early stage of the fatigue process. These test results indicate that the microstructural conditioning is a prerequisite for the fatigue crack initiation and propagation in SA508. These observations may lead to better under- standing of how fatigue initiation processes transit to cracks.

Features of plastic strain localization at the yield plateau in Hadfield steel single crystals

NASA Astrophysics Data System (ADS)

Barannikova, S. A.; Zuev, L. B.

2008-07-01

Spatiotemporal distributions of local components of the plastic distortion tensor in Hadfield steel single crystals oriented for single twinning have been studied under active tensile straining conditions using the double-exposure speckle photography technique. Features of the macroscopically inhomogeneous strain localization at the yield plateau are considered. Relations between local components of the plastic distortion tensor in the zone of strain localization are analyzed.

Mapping the cyclic plastic zone to elucidate the mechanisms of crack tip deformation in bulk metallic glasses

NASA Astrophysics Data System (ADS)

Scudino, S.; Shahid, R. N.; Escher, B.; Stoica, M.; Li, B. S.; Kruzic, J. J.

2017-02-01

Developing damage-tolerant bulk metallic glasses (BMGs) requires knowledge of the physical mechanisms governing crack propagation. While fractography suggests that fatigue crack propagation occurs in an incremental manner, conclusive evidence of alternating crack tip blunting and resharpening is lacking. By mapping the strain fields in both the monotonic and cyclic plastic zones, it is shown that the characteristic compressive stresses required to resharpen the crack tip are developed in a BMG upon unloading. This result confirms the mechanism of fatigue crack propagation in BMGs. Broader implications of these findings are that the effect of shear banding is rather diffuse and plastic deformation ahead of a stress concentration, such as a crack tip, appears to extend well beyond the extent of visible shear bands on the sample surface.

Visualization and Quantitative Analysis of Crack-Tip Plastic Zone in Pure Nickel

NASA Astrophysics Data System (ADS)

Kelton, Randall; Sola, Jalal Fathi; Meletis, Efstathios I.; Huang, Haiying

2018-05-01

Changes in surface morphology have long been thought to be associated with crack propagation in metallic materials. We have studied areal surface texture changes around crack tips in an attempt to understand the correlations between surface texture changes and crack growth behavior. Detailed profiling of the fatigue sample surface was carried out at short fatigue intervals. An image processing algorithm was developed to calculate the surface texture changes. Quantitative analysis of the crack-tip plastic zone, crack-arrested sites near triple points, and large surface texture changes associated with crack release from arrested locations was carried out. The results indicate that surface texture imaging enables visualization of the development of plastic deformation around a crack tip. Quantitative analysis of the surface texture changes reveals the effects of local microstructures on the crack growth behavior.

78 FR 34335 - Foreign-Trade Zone (FTZ) 141-Monroe County, New York; Notification of Proposed Production...

Federal Register 2010, 2011, 2012, 2013, 2014

2013-06-07

... steel, fire and water resistant storage chests, gun safes, security safes, portable security safes, cash..., touchpads, plastic gun racks, keypad assemblies, panel lock assemblies, door backs, plastic trays, drawers..., wood gun shelf racks, cable assemblies, communication cables, gasket kits, door springs, metal handles...

Factors affecting tumor ablation during high intensity focused ultrasound treatment.

PubMed

Hassanuddin, Aizan; Choi, Jun-Ho; Seo, Dong-Wan; Ryu, Choong Heon; Kim, Su-Hui; Park, Do Hyun; Lee, Sang Soo; Lee, Sung Koo; Kim, Myung-Hwan

2014-07-01

High intensity focused ultrasound (HIFU) utilizes a targeted extracorporeal focused ultrasound beam to ablate neoplastic pancreatic tissue. We used an in vitro model to examine the effects of bone, metallic stents, plastic stents, metal plates, and cyst-like lesions on HIFU treatment. HIFU was delivered to the phantom models implanted with foreign bodies, and the location, shape, and size of the ablated zones were evaluated. Bone and metallic plates reflected the ultrasound beam, shifting the ablation zone from the focal zone to the prefocal area. In the phantoms containing metal stent, plastic stent, and cyst, most of the ablative energy was reflected to the prefocal area by the surface, with the remainder penetrating through the phantom. The area of the ablated margins was significantly larger in size and volume than the intended focal ablation zone. During HIFU therapy, artificial or anatomical barriers could affect the direction of the ultrasound beams, shifting the ablation zone from the focal area to a prefocal site with a larger than expected ablation zone. These factors should be considered prior to HIFU treatment for pancreatic tumors because they could limit ablation success, in addition to causing complications.

Fatigue crack layer propagation in silicon-iron

NASA Technical Reports Server (NTRS)

Birol, Y.; Welsch, G.; Chudnovsky, A.

1986-01-01

Fatigue crack propagation in metal is almost always accompanied by plastic deformation unless conditions strongly favor brittle fracture. The analysis of the plastic zone is crucial to the understanding of crack propagation behavior as it governs the crack growth kinetics. This research was undertaken to study the fatigue crack propagation in a silicon iron alloy. Kinetic and plasticity aspects of fatigue crack propagation in the alloy were obtained, including the characterization of damage evolution.

Determining Crack Tip Field Parameters for Elastic-Plastic Materials via an Estimation Scheme

DTIC Science & Technology

1981-07-01

of the Materials Laboratory was the Project Monitor for this study of the application of the Nonlinear Fracture Mechanics (NLFM) parameters to the...fracture mechanics (LEFM) is applicable . If the plastic zone size is large, compared to the case of small scale yielding, LEFM is not applicable . The...above HRR field equations are applicable only for the case of stationary cracks. 2.2 PARAMETER DETERMINATION For elastic-plastic materials, the

Global Crustal Dynamics of Magnetars in Relation to Their Bright X-Ray Outbursts

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

Thompson, Christopher; Yang, Huan; Ortiz, Néstor

2017-05-20

This paper considers the yielding response of a neutron star crust to smooth, unbalanced Maxwell stresses imposed at the core–crust boundary, and the coupling of the dynamic crust to the external magnetic field. Stress buildup and yielding in a magnetar crust are global phenomena: an elastic distortion radiating from one plastically deforming zone is shown to dramatically increase the creep rate in distant zones. Runaway creep to dynamical rates is shown to be possible, being enhanced by in situ heating and suppressed by thermal conduction and shearing of an embedded magnetic field. A global and time-dependent model of elastic, plastic,more » magnetic, and thermal evolution is developed. Fault-like structures develop naturally, and a range of outburst timescales is observed. Transient events with time profiles similar to giant magnetar flares (millisecond rise, ∼0.1 s duration, and decaying power-law tails) result from runaway creep that starts in localized sub-kilometer-sized patches and spreads across the crust. A one-dimensional model of stress relaxation in the vertically stratified crust shows that a modest increase in applied stress allows embedded magnetic shear to escape the star over ∼3–10 ms, dissipating greater energy if the exterior field is already sheared. Several such zones coupled to each other naturally yield a burst of duration ∼0.1 s, as is observed over a wide range of burst energies. The collective interaction of many plastic zones forces an overstability of global elastic modes of the crust, consistent with quasi-periodic oscillation (QPO) activity extending over ∼100 s. Giant flares probably involve sudden meltdown in localized zones, with high-frequency (≫100 Hz) QPOs corresponding to standing Alfvén waves within these zones.« less

The expression of Helicobacter pylori tfs plasticity zone cluster is regulated by pH and adherence, and its composition is associated with differential gastric IL-8 secretion.

PubMed

Silva, Bruno; Nunes, Alexandra; Vale, Filipa F; Rocha, Raquel; Gomes, João Paulo; Dias, Ricardo; Oleastro, Mónica

2017-08-01

Helicobacter pylori virulence is associated with different clinical outcomes. The existence of an intact dupA gene from tfs4b cluster has been suggested as a predictor for duodenal ulcer development. However, the role of tfs plasticity zone clusters in the development of ulcers remains unclear. We studied several H. pylori strains to characterize the gene arrangement of tfs3 and tfs4 clusters and their impact in the inflammatory response by infected gastric cells. The genome of 14 H. pylori strains isolated from Western patients, pediatric (n=10) and adult (n=4), was fully sequenced using the Illumina platform MiSeq, in addition to eight pediatric strains previously sequenced. These strains were used to infect human gastric cells, and the secreted interleukin-8 (IL-8) was quantified by ELISA. The expression of virB2, dupA, virB8, virB10, and virB6 was assessed by quantitative PCR in adherent and nonadherent fractions of H. pylori during in vitro co-infection, at different pH values. We have found that cagA-positive H. pylori strains harboring a complete tfs plasticity zone cluster significantly induce increased production of IL-8 from gastric cells. We have also found that the region spanning from virB2 to virB10 genes constitutes an operon, whose expression is increased in the adherent fraction of bacteria during infection, as well as in both adherent and nonadherent fractions at acidic conditions. A complete tfs plasticity zone cluster is a virulence factor that may be important for the colonization of H. pylori and to the development of severe outcomes of the infection with cagA-positive strains. © 2017 John Wiley & Sons Ltd.

Presynaptic Active Zone Density during Development and Synaptic Plasticity.

PubMed

Clarke, Gwenaëlle L; Chen, Jie; Nishimune, Hiroshi

2012-01-01

Neural circuits transmit information through synapses, and the efficiency of synaptic transmission is closely related to the density of presynaptic active zones, where synaptic vesicles are released. The goal of this review is to highlight recent insights into the molecular mechanisms that control the number of active zones per presynaptic terminal (active zone density) during developmental and stimulus-dependent changes in synaptic efficacy. At the neuromuscular junctions (NMJs), the active zone density is preserved across species, remains constant during development, and is the same between synapses with different activities. However, the NMJ active zones are not always stable, as exemplified by the change in active zone density during acute experimental manipulation or as a result of aging. Therefore, a mechanism must exist to maintain its density. In the central nervous system (CNS), active zones have restricted maximal size, exist in multiple numbers in larger presynaptic terminals, and maintain a constant density during development. These findings suggest that active zone density in the CNS is also controlled. However, in contrast to the NMJ, active zone density in the CNS can also be increased, as observed in hippocampal synapses in response to synaptic plasticity. Although the numbers of known active zone proteins and protein interactions have increased, less is known about the mechanism that controls the number or spacing of active zones. The following molecules are known to control active zone density and will be discussed herein: extracellular matrix laminins and voltage-dependent calcium channels, amyloid precursor proteins, the small GTPase Rab3, an endocytosis mechanism including synaptojanin, cytoskeleton protein spectrins and β-adducin, and a presynaptic web including spectrins. The molecular mechanisms that organize the active zone density are just beginning to be elucidated.

Presynaptic Active Zone Density during Development and Synaptic Plasticity

PubMed Central

Clarke, Gwenaëlle L.; Chen, Jie; Nishimune, Hiroshi

2012-01-01

Neural circuits transmit information through synapses, and the efficiency of synaptic transmission is closely related to the density of presynaptic active zones, where synaptic vesicles are released. The goal of this review is to highlight recent insights into the molecular mechanisms that control the number of active zones per presynaptic terminal (active zone density) during developmental and stimulus-dependent changes in synaptic efficacy. At the neuromuscular junctions (NMJs), the active zone density is preserved across species, remains constant during development, and is the same between synapses with different activities. However, the NMJ active zones are not always stable, as exemplified by the change in active zone density during acute experimental manipulation or as a result of aging. Therefore, a mechanism must exist to maintain its density. In the central nervous system (CNS), active zones have restricted maximal size, exist in multiple numbers in larger presynaptic terminals, and maintain a constant density during development. These findings suggest that active zone density in the CNS is also controlled. However, in contrast to the NMJ, active zone density in the CNS can also be increased, as observed in hippocampal synapses in response to synaptic plasticity. Although the numbers of known active zone proteins and protein interactions have increased, less is known about the mechanism that controls the number or spacing of active zones. The following molecules are known to control active zone density and will be discussed herein: extracellular matrix laminins and voltage-dependent calcium channels, amyloid precursor proteins, the small GTPase Rab3, an endocytosis mechanism including synaptojanin, cytoskeleton protein spectrins and β-adducin, and a presynaptic web including spectrins. The molecular mechanisms that organize the active zone density are just beginning to be elucidated. PMID:22438837

Effect of Severe Plastic Deformation on Structure and Properties of Al-Sc-Ta and Al-Sc-Ti Alloys.

PubMed

Berezina, Alla; Monastyrska, Tetiana; Davydenko, Olexandr; Molebny, Oleh; Polishchuk, Sergey

2017-12-01

The comparative analysis of the effect of monotonous and non-monotonous severe plastic deformations (SPD) on the structure and properties of aluminum alloys has been carried out. Conventional hydrostatic extrusion (HE) with a constant deformation direction and equal-channel angular hydroextrusion (ECAH) with an abrupt change in the deformation direction were chosen for the cases of monotonous and non-monotonous SPD, respectively. Model cast hypoeutectic Al-0.3%Sc alloys and hypereutectic Al-0.6%Sc alloys with Ta and Ti additives were chosen for studying. It was demonstrated that SPD of the alloys resulted in the segregation of the material into active and inactive zones which formed a banded structure. The active zones were shown to be bands of localized plastic deformation. The distance between zones was found to be independent of the accumulated strain degree and was in the range of 0.6-1 μm. Dynamic recrystallization in the active zones was observed using TEM. The dynamic recrystallization was accompanied by the formation of disclinations, deformation bands, low-angle, and high-angle boundaries, i.e., rotational deformation modes developed. The dynamic recrystallization was more intense during the non-monotonous deformation as compared with the monotonous one, which was confirmed by the reduction of texture degree in the materials after ECAH.

Patterns of residual stresses due to welding

NASA Technical Reports Server (NTRS)

Botros, B. M.

1983-01-01

Residual stresses caused by welding result from the nonuniform rate of cooling and the restrained thermal contraction or non-uniform plastic deformation. From the zone of extremely high temperature at the weld, heat flows into both the adjoining cool body and the surrounding atmosphere. The weld metal solidifies under very rapid cooling. The plasticity of the hot metal allows adjustment initially, but as the structure cools the rigidity of the surrounding cold metal inhibits further contraction. The zone is compressed and the weld is put under tensile stresses of high magnitude. The danger of cracking in these structural elements is great. Change in specific volume is caused by the change in temperature.

Microstructural examination of fatigue crack tip in high strength steel

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

Fukuoka, C.; Yoshizawa, H.; Nakagawa, Y.G.

1993-10-01

Fatigue tests were performed to examine how microstructural conditioning influences crack initiation and propagation in SA508 class 3 low-carbon steel. A 3-mm-long crack was introduced in compact tension (CT) fatigue test specimens under four different loads in order to obtain crack tip plastic zones at different stress intensity factor ranges, [Delta]K = 18, 36, 54, and 72 MPa[radical]m. The microstructure of the plastic zones around the crack tip were examined by transmission electron microscopy (TEM) and selected area electron diffraction (SAD). Micro-orientation of the dislocation cells in the plastic zones of all of the CT samples increased to 4 degmore » from the level of an as-received sample. Four-point bending fatigue tests were performed for plate shape samples with a large cyclic strain range. The SAD value of the bending samples was also 4 deg in the damaged area where cracks already initiated at an early stage of the fatigue process. These test results indicate that the microstructural conditioning is a prerequisite for the fatigue crack initiation and propagation in SA508. These observations may lead to better understanding of how fatigue initiation processes transit to cracks.« less

Dynamic rupture models of subduction zone earthquakes with off-fault plasticity

NASA Astrophysics Data System (ADS)

Wollherr, S.; van Zelst, I.; Gabriel, A. A.; van Dinther, Y.; Madden, E. H.; Ulrich, T.

2017-12-01

Modeling tsunami-genesis based on purely elastic seafloor displacement typically underpredicts tsunami sizes. Dynamic rupture simulations allow to analyse whether plastic energy dissipation is a missing rheological component by capturing the complex interplay of the rupture front, emitted seismic waves and the free surface in the accretionary prism. Strike-slip models with off-fault plasticity suggest decreasing rupture speed and extensive plastic yielding mainly at shallow depths. For simplified subduction geometries inelastic deformation on the verge of Coulomb failure may enhance vertical displacement, which in turn favors the generation of large tsunamis (Ma, 2012). However, constraining appropriate initial conditions in terms of fault geometry, initial fault stress and strength remains challenging. Here, we present dynamic rupture models of subduction zones constrained by long-term seismo-thermo-mechanical modeling (STM) without any a priori assumption of regions of failure. The STM model provides self-consistent slab geometries, as well as stress and strength initial conditions which evolve in response to tectonic stresses, temperature, gravity, plasticity and pressure (van Dinther et al. 2013). Coseismic slip and coupled seismic wave propagation is modelled using the software package SeisSol (www.seissol.org), suited for complex fault zone structures and topography/bathymetry. SeisSol allows for local time-stepping, which drastically reduces the time-to-solution (Uphoff et al., 2017). This is particularly important in large-scale scenarios resolving small-scale features, such as the shallow angle between the megathrust fault and the free surface. Our dynamic rupture model uses a Drucker-Prager plastic yield criterion and accounts for thermal pressurization around the fault mimicking the effect of pore pressure changes due to frictional heating. We first analyze the influence of this rheology on rupture dynamics and tsunamigenic properties, i.e. seafloor displacement, in 2D. Finally, we use the same rheology in a large-scale 3D scenario of the 2004 Sumatra earthquake to shed light to the source process that caused the subsequent devastating tsunami.

Finite Element Analysis of Plastic Deformation During Impression Creep

NASA Astrophysics Data System (ADS)

Naveena; Ganesh Kumar, J.; Mathew, M. D.

2015-04-01

Finite element (FE) analysis of plastic deformation associated with impression creep deformation of 316LN stainless steel was carried out. An axisymmetric FE model of 10 × 10 × 10 mm specimen with 1-mm-diameter rigid cylindrical flat punch was developed. FE simulation of impression creep deformation was performed by assuming elastic-plastic-power-law creep deformation behavior. Evolution of the stress with time under the punch during elastic, plastic, and creep processes was analyzed. The onset of plastic deformation was found to occur at a nominal stress about 1.12 times the yield stress of the material. The size of the developed plastic zone was predicted to be about three times the radius of the punch. The material flow behavior and the pile-up on specimen surface have been modeled.

Full-Field Strain Measurement On Titanium Welds And Local Elasto-Plastic Identification With The Virtual Fields Method

NASA Astrophysics Data System (ADS)

Tattoli, F.; Pierron, F.; Rotinat, R.; Casavola, C.; Pappalettere, C.

2011-01-01

One of the main problems in welding is the microstructural transformation within the area affected by the thermal history. The resulting heterogeneous microstructure within the weld nugget and the heat affected zones is often associated with changes in local material properties. The present work deals with the identification of material parameters governing the elasto—plastic behaviour of the fused and heat affected zones as well as the base material for titanium hybrid welded joints (Ti6Al4V alloy). The material parameters are identified from heterogeneous strain fields with the Virtual Fields Method. This method is based on a relevant use of the principle of virtual work and it has been shown to be useful and much less time consuming than classical finite element model updating approaches applied to similar problems. The paper will present results and discuss the problem of selection of the weld zones for the identification.

Spatial and temporal variation of macro-, meso- and microplastic abundance on a remote coral island of the Maldives, Indian Ocean.

PubMed

Imhof, Hannes K; Sigl, Robert; Brauer, Emilia; Feyl, Sabine; Giesemann, Philipp; Klink, Saskia; Leupolz, Kathrin; Löder, Martin G J; Löschel, Lena A; Missun, Jan; Muszynski, Sarah; Ramsperger, Anja F R M; Schrank, Isabella; Speck, Susan; Steibl, Sebastian; Trotter, Benjamin; Winter, Isabel; Laforsch, Christian

2017-03-15

Plastic debris is ubiquitous in the marine environment and the world's shores represent a major sink. However, knowledge about plastic abundance in remote areas is scarce. Therefore, plastic abundance was investigated on a small island of the Maldives. Plastic debris (>1mm) was sampled once in natural long-term accumulation zones at the north shore and at the high tide drift line of the south shore on seven consecutive days to quantify daily plastic accumulation. Reliable identification of plastic debris was ensured by FTIR spectroscopy. Despite the remoteness of the island a considerable amount of plastic debris was present. At both sites a high variability in plastic abundance on a spatial and temporal scale was observed, which may be best explained by environmental factors. In addition, our results show that snapshot sampling may deliver biased results and indicate that future monitoring programs should consider spatial and temporal variation of plastic deposition. Copyright © 2017 Elsevier Ltd. All rights reserved.

Plastic accumulation in the Mediterranean sea.

PubMed

Cózar, Andrés; Sanz-Martín, Marina; Martí, Elisa; González-Gordillo, J Ignacio; Ubeda, Bárbara; Gálvez, José Á; Irigoien, Xabier; Duarte, Carlos M

2015-01-01

Concentrations of floating plastic were measured throughout the Mediterranean Sea to assess whether this basin can be regarded as a great accumulation region of plastic debris. We found that the average density of plastic (1 item per 4 m2), as well as its frequency of occurrence (100% of the sites sampled), are comparable to the accumulation zones described for the five subtropical ocean gyres. Plastic debris in the Mediterranean surface waters was dominated by millimeter-sized fragments, but showed a higher proportion of large plastic objects than that present in oceanic gyres, reflecting the closer connection with pollution sources. The accumulation of floating plastic in the Mediterranean Sea (between 1,000 and 3,000 tons) is likely related to the high human pressure together with the hydrodynamics of this semi-enclosed basin, with outflow mainly occurring through a deep water layer. Given the biological richness and concentration of economic activities in the Mediterranean Sea, the affects of plastic pollution on marine and human life are expected to be particularly frequent in this plastic accumulation region.

Can plastic mulching replace irrigation in dryland agriculture?

NASA Astrophysics Data System (ADS)

Wang, L.; Daryanto, S.; Jacinthe, P. A.

2017-12-01

Increasing water use efficiency (WUE) is a key strategy to maintaining crops yield without over-exploiting the scarce water resource. Plastic mulching technology for wheat and maize has been commonly used in China, but their effect on yield, soil moisture, evapotranspiration (ET), and WUE has not been compared with traditional irrigation method. Using a meta-analysis approach, we quantitatively examined the efficacy of plastic mulching in comparison with traditional irrigation in dryland agriculture. Our results showed that plastic mulching technique resulted in yield increase comparable to irrigated crops but used 24% less water. By covering the ridges with plastic and channeling rainwater into a very narrow planting zone (furrow), plastic mulching increased WUE and available soil moisture. Higher WUE in plastic-mulched croplands was likely a result of greater proportion of available water being used for transpiration than evaporation. If problems related to production costs and residual plastic pollution could be managed, plastic mulching technology would become a promising strategy for dryland farming in other regions.

Coseismic microstructures of experimental fault zones in Carrara marble

NASA Astrophysics Data System (ADS)

Ree, Jin-Han; Ando, Jun-ichi; Han, Raehee; Shimamoto, Toshihiko

2014-09-01

Experimental fault zones developed in Carrara marble that were deformed at seismic slip rates (1.18-1.30 m s-1) using a high-velocity-rotary-shear apparatus exhibit very low friction (friction coefficient as low as 0.06) at steady state due to nanoparticle lubrication of the decomposition product (lime). The fault zones show a layered structure; a central slip-localization layer (5-60 μm thick) of lime nanograins mantled by gouge layers (5-150 μm thick) and a plastically deformed layer (45-500 μm thick) between the wall rock and gouge layer in the marginal portion of cylindrical specimens. Calcite grains of the wall rock adjacent to the slip zone deform by dislocation glide when subjected to frictional heating and a lower strain rate than that of the principal slip zone. The very fine (2-5 μm) calcite grains in the gouge layer show a foam structure with relatively straight grain boundaries and 120° triple junctions. This foam structure is presumed to develop by welding at high temperature and low strain once slip is localized along the central layer. We suggest that a seismic event can be inferred from deformed marbles, given: (i) the presence of welded gouge with foam structure in a fault zone where wall rocks show no evidence of thermal metamorphism and (ii) a thin plastically deformed layer immediately adjacent to the principal slip zone of a cataclastic fault zone.

Pollutants in Plastics within the North Pacific Subtropical Gyre.

PubMed

Chen, Qiqing; Reisser, Julia; Cunsolo, Serena; Kwadijk, Christiaan; Kotterman, Michiel; Proietti, Maira; Slat, Boyan; Ferrari, Francesco F; Schwarz, Anna; Levivier, Aurore; Yin, Daqiang; Hollert, Henner; Koelmans, Albert A

2018-01-16

Here we report concentrations of pollutants in floating plastics from the North Pacific accumulation zone (NPAC). We compared chemical concentrations in plastics of different types and sizes, assessed ocean plastic potential risks using sediment quality criteria, and discussed the implications of our findings for bioaccumulation. Our results suggest that at least a fraction of the NPAC plastics is not in equilibrium with the surrounding seawater. For instance, "hard plastic" samples had significantly higher PBDE concentrations than "nets and ropes" samples, and 29% of them had PBDE composition similar to a widely used flame-retardant mixture. Our findings indicate that NPAC plastics may pose a chemical risk to organisms as 84% of the samples had at least one chemical exceeding sediment threshold effect levels. Furthermore, our surface trawls collected more plastic than biomass (180 times on average), indicating that some NPAC organisms feeding upon floating particles may have plastic as a major component of their diets. If gradients for pollutant transfer from NPAC plastic to predators exist (as indicated by our fugacity ratio calculations), plastics may play a role in transferring chemicals to certain marine organisms.

The impact law of confining pressure and plastic parameter on Dilatancy of rock

NASA Astrophysics Data System (ADS)

Wang, Bin; Zhang, Zhenjie; Zhu, Jiebing

2017-08-01

Based on cyclic loading-unloading triaxle test of marble, the double parameter dilation angle model is established considering confining pressure effect and plastic parameter. Research shows that not only the strength but also the militancy behavior is highly depended on its confining pressure and plastic parameter during process of failure. Dilation angle evolution law shows obvious nonlinear characteristic almost with a rapid increase to the peak and then decrease gradually with plastic increasing, and the peak dilation angle value is inversely proportional with confining pressure. The proposed double parameter nonlinear dilation angle model can be used to well describe the Dilatancy of rock, which helps to understand the failure mechanism of surrounding rock mass and predict the range of plastic zone.

New approach to the boundary-parallel plastic / viscous diapiric flow patterns in the curvilinear boundary zones: an implication for structural geology studies

NASA Astrophysics Data System (ADS)

Sarkarinejad, Khalil

2010-05-01

New approach to the boundary-parallel plastic / viscous diapiric flow patterns in the curvilinear boundary zones: an implication for structural geology studies Khalil Sarkarinejad and Abdolreza Partabian Department of Earth Sciences, College of Sciences, Shiraz University, Shiraz, Iran (Sarkarinejad@geology.susc.ac.ir). In the oceanic diverging away plates, the asthenospheric flow at solidus high-temperature conditions typically produces mineral foliations and lineations in peridotites. Foliation and lineation of mantle are defined by preferred flattening and alignment of olivine, pyroxene and spinel. In the areas with steep foliations trajectories which are associated with the steeply plunging stretching lineation trajectories, reflecting localized vertical flow and has been related to mantle diapir. The mantle flow patterns are well documented through detail structural mapping of the Neyriz ophiolite along the Zagros inclined dextral transpression and Oman ophiolite. Such models of the diverging asthenaspheric mantle flow and formation of mantle diapir are rarely discussed and paid any attention in the mathematical models of transpressional deformation in converging continental crusts. Systematic measurements of the mineral preferred orientations and construction of the foliation and lineation trajectories of the Zagros high-strain zone reveal two diapers with the shape of the inclined NW-SE boundary-parallel semi-ellipses shape and one rotated asymmetric diapir. These diapers made of quartzo-feldspathic gneiss and garnet amphibolite core with phyllite, phyllonite, muscovite schist and deformed conglomerate as a cover sequences. These boundary-parallel and rotated diapirs are formed by the interaction of Afro-Arabian lower to middle continental detachment and hot subdacting Tethyan oceanic crust, due to increasing effective pressure and temperature. The plastic/viscous gneissic diapers were squeezed between in Zagros transpression curvilinear boundary zones in an angle alpha=25°. Constructed finite strain ellipsoid based on the X-axes of the elliptical shaped deformed markers of the diapir cover sequences show trend X-axis of the strain ellipsoid making an angle phai=2° with the boundary zones. The steep plunging stretching lineation primarily controlled by the plastic/viscous flow. This also show that during inclined upwelling boundary-parallel diapers, X-, Y-axes of the strain ellipsoid rotated clockwise and Z-axis experienced counter clockwise rotation with triclinic symmetries relative to the Zagros curvilinear transpression boundary zones with an orientation of N42°plus/minus 24°W.

Assessment of mild steel damage characteristics by physical methods

NASA Astrophysics Data System (ADS)

Botvina, L. R.; Soldatenkov, A. P.; Levin, V. P.; Tyutin, M. R.; Demina, Yu. A.; Petersen, T. B.; Dubov, A. A.; Semashko, N. A.

2016-01-01

The deformation and fracture localization characteristics are estimated by the methods of replicas, acoustic emission, metal magnetic memory, ultrasonic attenuation, microhardness, and electrical resistance. The relation between the estimated physical parameters on the one hand and the plastic zone size and the microcrack concentration in this zone, on the other, is considered.

Quantitative Analysis of Microstructural Constituents in Welded Transformation-Induced-Plasticity Steels

NASA Astrophysics Data System (ADS)

Amirthalingam, M.; Hermans, M. J. M.; Zhao, L.; Richardson, I. M.

2010-02-01

A quantitative analysis of retained austenite and nonmetallic inclusions in gas tungsten arc (GTA)-welded aluminum-containing transformation-induced-plasticity (TRIP) steels is presented. The amount of retained austenite in the heat-affected and fusion zones of welded aluminum-containing TRIP steel with different base metal austenite fractions has been measured by magnetic saturation measurements, to study the effect of weld thermal cycles on the stabilization of austenite. It is found that for base metals containing 3 to 14 pct of austenite, 4 to 13 pct of austenite is found in the heat-affected zones and 6 to 10 pct in the fusion zones. The decomposition kinetics of retained austenite in the base metal and welded samples was also studied by thermomagnetic measurements. The decomposition kinetics of the austenite in the fusion zone is found to be slower compared to that in the base metal. Thermomagnetic measurements indicated the formation of ferromagnetic ɛ carbides above 290 °C and paramagnetic η( ɛ') transient iron carbides at approximately 400 °C due to the decomposition of austenite during heating.

Stepwise visualization of membrane pore formation by suilysin, a bacterial cholesterol-dependent cytolysin.

PubMed

Leung, Carl; Dudkina, Natalya V; Lukoyanova, Natalya; Hodel, Adrian W; Farabella, Irene; Pandurangan, Arun P; Jahan, Nasrin; Pires Damaso, Mafalda; Osmanović, Dino; Reboul, Cyril F; Dunstone, Michelle A; Andrew, Peter W; Lonnen, Rana; Topf, Maya; Saibil, Helen R; Hoogenboom, Bart W

2014-12-02

Membrane attack complex/perforin/cholesterol-dependent cytolysin (MACPF/CDC) proteins constitute a major superfamily of pore-forming proteins that act as bacterial virulence factors and effectors in immune defence. Upon binding to the membrane, they convert from the soluble monomeric form to oligomeric, membrane-inserted pores. Using real-time atomic force microscopy (AFM), electron microscopy (EM), and atomic structure fitting, we have mapped the structure and assembly pathways of a bacterial CDC in unprecedented detail and accuracy, focussing on suilysin from Streptococcus suis. We show that suilysin assembly is a noncooperative process that is terminated before the protein inserts into the membrane. The resulting ring-shaped pores and kinetically trapped arc-shaped assemblies are all seen to perforate the membrane, as also visible by the ejection of its lipids. Membrane insertion requires a concerted conformational change of the monomeric subunits, with a marked expansion in pore diameter due to large changes in subunit structure and packing.

Stepwise visualization of membrane pore formation by suilysin, a bacterial cholesterol-dependent cytolysin

PubMed Central

Lukoyanova, Natalya; Hodel, Adrian W; Farabella, Irene; Pandurangan, Arun P; Jahan, Nasrin; Pires Damaso, Mafalda; Osmanović, Dino; Reboul, Cyril F; Dunstone, Michelle A; Andrew, Peter W; Lonnen, Rana; Topf, Maya

2014-01-01

Membrane attack complex/perforin/cholesterol-dependent cytolysin (MACPF/CDC) proteins constitute a major superfamily of pore-forming proteins that act as bacterial virulence factors and effectors in immune defence. Upon binding to the membrane, they convert from the soluble monomeric form to oligomeric, membrane-inserted pores. Using real-time atomic force microscopy (AFM), electron microscopy (EM), and atomic structure fitting, we have mapped the structure and assembly pathways of a bacterial CDC in unprecedented detail and accuracy, focussing on suilysin from Streptococcus suis. We show that suilysin assembly is a noncooperative process that is terminated before the protein inserts into the membrane. The resulting ring-shaped pores and kinetically trapped arc-shaped assemblies are all seen to perforate the membrane, as also visible by the ejection of its lipids. Membrane insertion requires a concerted conformational change of the monomeric subunits, with a marked expansion in pore diameter due to large changes in subunit structure and packing. DOI: http://dx.doi.org/10.7554/eLife.04247.001 PMID:25457051

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.

Discrete shear-transformation-zone plasticity modeling of notched bars

NASA Astrophysics Data System (ADS)

Kondori, Babak; Amine Benzerga, A.; Needleman, Alan

2018-02-01

Plane strain tension analyses of un-notched and notched bars are carried out using discrete shear transformation zone plasticity. In this framework, the carriers of plastic deformation are shear transformation zones (STZs) which are modeled as Eshelby inclusions. Superposition is used to represent a boundary value problem solution in terms of discretely modeled Eshelby inclusions, given analytically for an infinite elastic medium, and an image solution that enforces the prescribed boundary conditions. The image problem is a standard linear elastic boundary value problem that is solved by the finite element method. Potential STZ activation sites are randomly distributed in the bars and constitutive relations are specified for their evolution. Results are presented for un-notched bars, for bars with blunt notches and for bars with sharp notches. The computed stress-strain curves are serrated with the magnitude of the associated stress-drops depending on bar size, notch acuity and STZ evolution. Cooperative deformation bands (shear bands) emerge upon straining and, in some cases, high stress levels occur within the bands. Effects of specimen geometry and size on the stress-strain curves are explored. Depending on STZ kinetics, notch strengthening, notch insensitivity or notch weakening are obtained. The analyses provide a rationale for some conflicting findings regarding notch effects on the mechanical response of metallic glasses.

Variations of a global constraint factor in cracked bodies under tension and bending loads

NASA Technical Reports Server (NTRS)

Newman, J. C., Jr.; Crews, J. H., Jr.; Bigelow, C. A.; Dawicke, D. S.

1994-01-01

Elastic-plastic finite-element analyses were used to calculate stresses and displacements around a crack in finite-thickness plates for an elastic-perfectly plastic material. Middle- and edge-crack specimens were analyzed under tension and bending loads. Specimens were 1.25 to 20 mm thick with various widths and crack lengths. A global constraint factor alpha(sub g), an averaged normal-stress to flow-stress ratio over the plastic region, was defined to simulate three-dimensional (3D) effects in two-dimensional (2D) models. For crack lengths and uncracked ligament lengths greater than four times the thickness, the global constraint factor was found to be nearly a unique function of a normalized stress-intensity factor (related to plastic-zone size to thickness ratio) from small- to large-scale yielding conditions for various specimen types and thickness. For crack length-to-thickness ratios less than four, the global constraint factor was specimen type, crack length and thickness dependent. Using a 2D strip-yield model and the global constraint factors, plastic-zone sizes and crack-tip displacements agreed reasonably well with the 3D analyses. For a thin sheet aluminum alloy, the critical crack-tip-opening angle during stable tearing was found to be independent of specimen type and crack length for crack length-to-thickness ratios greater than 4.

Thermomechanical coupling and dynamic strain ageing in ductile fracture

NASA Astrophysics Data System (ADS)

Delafosse, David

1995-01-01

This work is concerned with plastic deformation at the tip of a ductile tearing crack during propagation. Two kinds of effects are investigated: the thermomechanical coupling at the tip of a mobile ductile crack, and the influence of Dynamic Strain Aging (DSA) on ductile fracture. Three alloys are studied: a nickel based superalloy (N18), a soft carbon steel, and an Al-Li light alloy (2091). The experimental study of the thermo mechanical coupling effects by means of infrared thermography stresses the importance of plastic dissipation in the energy balance of ductile fracture. Numerical simulations involving plastic deformation as the only dissipation mechanism account for the main part of the measured heating. The effects of DSA on ductile tearing are investigated in the 2091 Al-Li alloy. Based on the strain rate/temperature dependence predicted by the standard model of DSA, an experimental procedure is set up for this purpose. Three main effects are evidenced. A maximum in tearing resistance is shown to be associated with the minimum of strain rate sensitivity. Through a simple model, this peak in tearing resistance is attributed to an increase in plastic dissipation as the strain rate sensitivity is decreased. Heterogenous plastic deformation is observed in the crack tip plastic zone. Comparison with uniaxial testing allows us to identify the observed strain heterogeneities as Portevin-Le Chatelier instabilities in the crack tip plastic zone. We perform a simplified numerical analysis of the effect of strain localization on crack tip screening. Finally, small crack propagation instabilities appear at temperatures slightly above that of the tearing resistance peak. These are interpreted as resulting from a positive feed-back between the local heating at the tip of a moving crack and the decrease in tearing resistance with increasing temperature.

Environmental fatigue of an Al-Li-Cu alloy. Part 3: Modeling of crack tip hydrogen damage

NASA Technical Reports Server (NTRS)

Piascik, Robert S.; Gangloff, Richard P.

1992-01-01

Environmental fatigue crack propagation rates and microscopic damage modes in Al-Li-Cu alloy 2090 (Parts 1 and 2) are described by a crack tip process zone model based on hydrogen embrittlement. Da/dN sub ENV equates to discontinuous crack advance over a distance, delta a, determined by dislocation transport of dissolved hydrogen at plastic strains above a critical value; and to the number of load cycles, delta N, required to hydrogenate process zone trap sites that fracture according to a local hydrogen concentration-tensile stress criterion. Transgranular (100) cracking occurs for process zones smaller than the subgrain size, and due to lattice decohesion or hydride formation. Intersubgranular cracking dominates when the process zone encompasses one or more subgrains so that dislocation transport provides hydrogen to strong boundary trapping sites. Multi-sloped log da/dN-log delta K behavior is produced by process zone plastic strain-hydrogen-microstructure interactions, and is determined by the DK dependent rates and proportions of each parallel cracking mode. Absolute values of the exponents and the preexponential coefficients are not predictable; however, fractographic measurements theta sub i coupled with fatigue crack propagation data for alloy 2090 established that the process zone model correctly describes fatigue crack propagation kinetics. Crack surface films hinder hydrogen uptake and reduce da/dN and alter the proportions of each fatigue crack propagation mode.

Finite element solutions for crack-tip behavior in small-scale yielding

NASA Technical Reports Server (NTRS)

Tracey, D. M.

1976-01-01

The subject considered is the stress and deformation fields in a cracked elastic-plastic power law hardening material under plane strain tensile loading. An incremental plasticity finite element formulation is developed for accurate analysis of the complete field problem including the extensively deformed near tip region, the elastic-plastic region, and the remote elastic region. The formulation has general applicability and was used to solve the small scale yielding problem for a set of material hardening exponents. Distributions of stress, strain, and crack opening displacement at the crack tip and through the elastic-plastic zone are presented as a function of the elastic stress intensity factor and material properties.

Plastic Accumulation in the Mediterranean Sea

PubMed Central

Cózar, Andrés; Sanz-Martín, Marina; Martí, Elisa; González-Gordillo, J. Ignacio; Ubeda, Bárbara; Gálvez, José Á.; Irigoien, Xabier; Duarte, Carlos M.

2015-01-01

Concentrations of floating plastic were measured throughout the Mediterranean Sea to assess whether this basin can be regarded as a great accumulation region of plastic debris. We found that the average density of plastic (1 item per 4 m2), as well as its frequency of occurrence (100% of the sites sampled), are comparable to the accumulation zones described for the five subtropical ocean gyres. Plastic debris in the Mediterranean surface waters was dominated by millimeter-sized fragments, but showed a higher proportion of large plastic objects than that present in oceanic gyres, reflecting the closer connection with pollution sources. The accumulation of floating plastic in the Mediterranean Sea (between 1,000 and 3,000 tons) is likely related to the high human pressure together with the hydrodynamics of this semi-enclosed basin, with outflow mainly occurring through a deep water layer. Given the biological richness and concentration of economic activities in the Mediterranean Sea, the affects of plastic pollution on marine and human life are expected to be particularly frequent in this plastic accumulation region. PMID:25831129

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

Plastic pollution in the Labrador Sea: An assessment using the seabird northern fulmar Fulmarus glacialis as a biological monitoring species.

PubMed

Avery-Gomm, Stephanie; Provencher, Jennifer F; Liboiron, Max; Poon, Florence E; Smith, Paul A

2018-02-01

Plastic is now one among one of the most pervasive pollutants on the planet, and ocean circulation models predict that the Arctic will become another accumulation zone. As solutions to address marine plastic emerge, is essential that baselines are available to monitor progress towards targets. The northern fulmar (Fulmarus glacialis), a widely-distributed seabird species, has been used as a biological monitor for plastic pollution in the North Sea, and could be a useful monitoring species elsewhere. We quantified plastic ingested by northern fulmars from the southeastern Canadian waters of the Labrador Sea with the objective of establishing a standardized baseline for future comparisons. Over two years we sampled 70 fulmars and found that 79% had ingested plastic, with an average of 11.6 pieces or 0.151g per bird. Overall, 34% of all fulmars exceeded the Ecological Quality Objective for marine litter, having ingested >0.1g of plastic. Copyright © 2017 Elsevier Ltd. All rights reserved.

Modelling global distribution, risk and mitigation strategies of floating plastic pollution

NASA Astrophysics Data System (ADS)

van Sebille, Erik; Wilcox, Chris; Sherman, Peter; Hardesty, Britta Denise; Lavender Law, Kara

2016-04-01

Microplastic debris floating at the ocean surface can harm marine life. Understanding the severity of this harm requires knowledge of plastic abundance and distributions. Dozens of expeditions measuring microplastics have been carried out since the 1970s, but they have primarily focused on the North Pacific and North Atlantic accumulation zones, with much sparser coverage elsewhere. Here, we use the largest dataset of microplastic measurements assembled to date to assess the confidence we can have in global estimates of microplastic abundance and mass. We use a rigorous statistical framework to standardise a global dataset of plastic marine debris measured using surface-trawling plankton nets and couple this with three different ocean circulation models to spatially interpolate the observations. Our estimates show that the accumulated number of microplastic particles in 2014 ranges from 15 to 51 trillion particles, weighing between 93 and 236 thousand metric tons. A large fraction of the uncertainty in these estimates comes from sparse sampling in coastal and Southern Hemisphere regions. We then use this global distribution of small floating plastic debris to map out where in the ocean the risk to marine life (in particular seabirds and plankton growth) is greatest, using a quantitative risk framework. We show that the largest risk occurs not necessarily in regions of high plastic concentration, but rather in regions of extensive foraging with medium-high plastic concentrations such as coastal upwelling regions and the Southern Ocean. Finally, we use the estimates of distribution to investigate where in the ocean plastic can most optimally be removed, assuming hypothetical clean-up booms following the ideas from The Ocean Cleanup project. We show that mitigation of the plastic problem can most aptly be done near coastlines, particularly in Asia, rather than in the centres of the gyres. Based on these results, we propose more focus on the coastal zones when considering future efforts in sampling, risk management and mitigation.

Plastic debris in the open ocean

PubMed Central

Cózar, Andrés; Echevarría, Fidel; González-Gordillo, J. Ignacio; Irigoien, Xabier; Úbeda, Bárbara; Hernández-León, Santiago; Palma, Álvaro T.; Navarro, Sandra; García-de-Lomas, Juan; Ruiz, Andrea; Fernández-de-Puelles, María L.; Duarte, Carlos M.

2014-01-01

There is a rising concern regarding the accumulation of floating plastic debris in the open ocean. However, the magnitude and the fate of this pollution are still open questions. Using data from the Malaspina 2010 circumnavigation, regional surveys, and previously published reports, we show a worldwide distribution of plastic on the surface of the open ocean, mostly accumulating in the convergence zones of each of the five subtropical gyres with comparable density. However, the global load of plastic on the open ocean surface was estimated to be on the order of tens of thousands of tons, far less than expected. Our observations of the size distribution of floating plastic debris point at important size-selective sinks removing millimeter-sized fragments of floating plastic on a large scale. This sink may involve a combination of fast nano-fragmentation of the microplastic into particles of microns or smaller, their transference to the ocean interior by food webs and ballasting processes, and processes yet to be discovered. Resolving the fate of the missing plastic debris is of fundamental importance to determine the nature and significance of the impacts of plastic pollution in the ocean. PMID:24982135

Plastic debris in the open ocean.

PubMed

Cózar, Andrés; Echevarría, Fidel; González-Gordillo, J Ignacio; Irigoien, Xabier; Ubeda, Bárbara; Hernández-León, Santiago; Palma, Alvaro T; Navarro, Sandra; García-de-Lomas, Juan; Ruiz, Andrea; Fernández-de-Puelles, María L; Duarte, Carlos M

2014-07-15

There is a rising concern regarding the accumulation of floating plastic debris in the open ocean. However, the magnitude and the fate of this pollution are still open questions. Using data from the Malaspina 2010 circumnavigation, regional surveys, and previously published reports, we show a worldwide distribution of plastic on the surface of the open ocean, mostly accumulating in the convergence zones of each of the five subtropical gyres with comparable density. However, the global load of plastic on the open ocean surface was estimated to be on the order of tens of thousands of tons, far less than expected. Our observations of the size distribution of floating plastic debris point at important size-selective sinks removing millimeter-sized fragments of floating plastic on a large scale. This sink may involve a combination of fast nano-fragmentation of the microplastic into particles of microns or smaller, their transference to the ocean interior by food webs and ballasting processes, and processes yet to be discovered. Resolving the fate of the missing plastic debris is of fundamental importance to determine the nature and significance of the impacts of plastic pollution in the ocean.

Density variations of plastic carriers in metallic glasses during aging

NASA Astrophysics Data System (ADS)

Fan, Yue; Iwashita, Takuya; Egami, Takeshi

Thermally induced deformation in metallic glasses was investigated by sampling the potential energy landscape (PEL) and probing the changes in the atomic properties (e.g. energy, displacement, stress). We demonstrate that there exists a universal plastic carrier in amorphous materials, which corresponds to the hopping between local minima on PEL. However very interestingly, the density of plastic carrier is largely affected by the aging history of the glasses. The higher fictive temperature (i . e . fast cooling rate), the larger density of plastic carrier is contained in the system. In particular, we observe a scaling of ρ~exp(- α/Tfic) , which is consistent with the prediction of shear transformation zone theory. The work is supported by U.S. Department of Energy.

Character of High Temperature Mylonitic Shear Zones Associated with Oceanic Detachment Faults at the Ultra-Slow Mid-Cayman Rise

NASA Astrophysics Data System (ADS)

Marr, C.; John, B. E.; Cheadle, M. J.; German, C. R.

2014-12-01

Two well-preserved core complexes at the Mid-Cayman Rise (MCR), Mt Dent and Mt Hudson, provide an opportunity to examine the deformation history and rheology of detachment faults at an ultra-slow spreading ridge. Samples from the CAYTROUGH (1976-77) project and the Nautilus NA034 cruise (2013) were selected for detailed petrographic and microstructural study. Surface samples from Mt. Dent (near the center of the MCR) provide insight into lateral variation in footwall rock type and deformation history across a core complex in both the across and down dip directions. In contrast, sampling of Mt. Hudson (SE corner of the MCR) focuses on a high-angle, crosscutting normal fault scarp, which provides a cross section of the detachment fault system. Sampling across Mt Dent reveals that the footwall is composed of heterogeneously-distributed gabbro (47%) and peridotite (20%) with basaltic cover (33%) dominating the top of the core complex. Sampling of Mt Hudson is restricted to the normal fault scarp cutting the core complex and suggests the interior is dominated by gabbro (85% gabbro, 11% peridotite, 4% basalt). At Mt. Dent, peridotite is exposed within ~4km of the breakaway indicating that the Mt. Dent detachment does not cut Penrose-style oceanic crust. The sample set provides evidence of a full down-temperature sequence of detachment related-fault rocks, from possible granulite and clear amphibolite mylonitizatization to prehnite-pumpellyite brittle deformation. Both detachments show low-temperature brittle deformation overprinting higher temperature plastic fabrics. Fe-Ti oxide gabbro mylonites dominate the sample set, and plastic deformation of plagioclase is recorded in samples collected as near as ~4km from the inferred breakaway along the southern flank of Mt. Dent, suggesting the brittle-plastic transition was initially at ~3km depth. Recovered samples suggest strain associated with both detachment systems is localized into discrete mylonitic shear zones (~1-10cm thick), implying that the plastic portion of the fault consists of a broad zone of thin, anastomosing shear zones. Concentrations of Ti-rich magmatic hornblende and interstitial Fe-Ti oxides in the high strain horizons are consistent with the lowermost part of the fault(s) localizing in the margins of the mush zone of a shallow magma chamber.

Strain localisation in mechanically layered rocks beneath detachment zones: insights from numerical modelling

NASA Astrophysics Data System (ADS)

Le Pourhiet, L.; Huet, B.; Labrousse, L.; Yao, K.; Agard, P.; Jolivet, L.

2013-04-01

We have designed a series of fully dynamic numerical simulations aimed at assessing how the orientation of mechanical layering in rocks controls the orientation of shear bands and the depth of penetration of strain in the footwall of detachment zones. Two parametric studies are presented. In the first one, the influence of stratification orientation on the occurrence and mode of strain localisation is tested by varying initial dip of inherited layering in the footwall with regard to the orientation of simple shear applied at the rigid boundary simulating a rigid hanging wall, all scaling and rheological parameter kept constant. It appears that when Mohr-Coulomb plasticity is being used, shear bands are found to localise only when the layering is being stretched. This corresponds to early deformational stages for inital layering dipping in the same direction as the shear is applied, and to later stages for intial layering dipping towards the opposite direction of shear. In all the cases, localisation of the strain after only γ=1 requires plastic yielding to be activated in the strong layer. The second parametric study shows that results are length-scale independent and that orientation of shear bands is not sensitive to the viscosity contrast or the strain rate. However, decreasing or increasing strain rate is shown to reduce the capacity of the shear zone to localise strain. In the later case, the strain pattern resembles a mylonitic band but the rheology is shown to be effectively linear. Based on the results, a conceptual model for strain localisation under detachment faults is presented. In the early stages, strain localisation occurs at slow rates by viscous shear instabilities but as the layered media is exhumed, the temperature drops and the strong layers start yielding plastically, forming shear bands and localising strain at the top of the shear zone. Once strain localisation has occured, the deformation in the shear band becomes extremely penetrative but the strength cannot drop since the shear zone has a finite thickness.

Co- and post-seismic shallow fault physics from near-field geodesy, seismic tomography, and mechanical modeling

NASA Astrophysics Data System (ADS)

Nevitt, J.; Brooks, B. A.; Catchings, R.; Goldman, M.; Criley, C.; Chan, J. H.; Glennie, C. L.; Ericksen, T. L.; Madugo, C. M.

2017-12-01

The physics governing near-surface fault slip and deformation are largely unknown, introducing significant uncertainty into seismic hazard models. Here we combine near-field measurements of surface deformation from the 2014 M6.0 South Napa earthquake with high-resolution seismic imaging and finite element models to investigate the effects of rupture speed, elastic heterogeneities, and plasticity on shallow faulting. We focus on two sites that experienced either predominantly co-seismic or post-seismic slip. We measured surface deformation with mobile laser scanning of deformed vine rows within 300 m of the fault at 1 week and 1 month after the event. Shear strain profiles for the co- and post-seismic sites are similar, with maxima of 0.012 and 0.013 and values exceeding 0.002 occurring within 26 m- and 18 m-wide zones, respectively. That the rupture remained buried at the two sites and produced similar deformation fields suggests that permanent deformation due to dynamic stresses did not differ significantly from the quasi-static case, which might be expected if the rupture decelerated as it approached the surface. Active-source seismic surveys, 120 m in length with 1 m geophone/shot spacing, reveal shallow compliant zones of reduced shear modulus. For the co- and post-seismic sites, the tomographic anomaly (Vp/Vs > 5) at 20 m depth has a width of 80 m and 50 m, respectively, much wider than the observed surface displacement fields. We investigate this discrepancy with a suite of finite element models in which a planar fault is buried 5 m below the surface. The model continuum is defined by either homogeneous or heterogeneous elastic properties, with or without Drucker-Prager plastic yielding, with properties derived from lab testing of similar near-surface materials. We find that plastic yielding can greatly narrow the surface displacement zone, but that the width of this zone is largely insensitive to changes in the elastic structure (i.e., the presence of a compliant zone).

Municipal solid waste characterization and quantification as a measure towards effective waste management in Ghana.

PubMed

Miezah, Kodwo; Obiri-Danso, Kwasi; Kádár, Zsófia; Fei-Baffoe, Bernard; Mensah, Moses Y

2015-12-01

Reliable national data on waste generation and composition that will inform effective planning on waste management in Ghana is absent. To help obtain this data on a regional basis, selected households in each region were recruited to obtain data on rate of waste generation, physical composition of waste, sorting and separation efficiency and per capita of waste. Results show that rate of waste generation in Ghana was 0.47 kg/person/day, which translates into about 12,710 tons of waste per day per the current population of 27,043,093. Nationally, biodegradable waste (organics and papers) was 0.318 kg/person/day and non-biodegradable or recyclables (metals, glass, textiles, leather and rubbers) was 0.096 kg/person/day. Inert and miscellaneous waste was 0.055 kg/person/day. The average household waste generation rate among the metropolitan cities, except Tamale, was high, 0.72 kg/person/day. Metropolises generated higher waste (average 0.63 kg/person/day) than the municipalities (0.40 kg/person/day) and the least in the districts (0.28 kg/person/day) which are less developed. The waste generation rate also varied across geographical locations, the coastal and forest zones generated higher waste than the northern savanna zone. Waste composition was 61% organics, 14% plastics, 6% inert, 5% miscellaneous, 5% paper, 3% metals, 3% glass, 1% leather and rubber, and 1% textiles. However, organics and plastics, the two major fractions of the household waste varied considerably across the geographical areas. In the coastal zone, the organic waste fraction was highest but decreased through the forest zone towards the northern savanna. However, through the same zones towards the north, plastic waste rather increased in percentage fraction. Households did separate their waste effectively averaging 80%. However, in terms of separating into the bin marked biodegradables, 84% effectiveness was obtained whiles 76% effectiveness for sorting into the bin labeled other waste was achieved. Copyright © 2015 The Authors. Published by Elsevier Ltd.. All rights reserved.

A hidden variable in shear transformation zone volume versus Poisson's ratio relation in metallic glasses

NASA Astrophysics Data System (ADS)

Kim, S. Y.; Oh, H. S.; Park, E. S.

2017-10-01

Herein, we elucidate a hidden variable in a shear transformation zone (STZ) volume (Ω) versus Poisson's ratio (ν) relation and clarify the correlation between STZ characteristics and the plasticity of metallic glasses (MGs). On the basis of cooperative shear model and atomic stress theories, we carefully formulate Ω as a function of molar volume (Vm) and ν. The twofold trend in Ω and ν is attributed to a relatively large variation of Vm as compared to that of ν as well as an inverse relation between Vm and ν. Indeed, the derived equation reveals that the number of atoms in an STZ instead of Ω is a microstructural characteristic which has a close relationship with plasticity since it reflects the preference of atomistic behaviors between cooperative shearing and the generation of volume strain fluctuation under stress. The results would deepen our understanding of the correlation between microscopic behaviors (STZ activation) and macroscopic properties (plasticity) in MGs and enable a quantitative approach in associating various STZ-related macroscopic behaviors with intrinsic properties of MGs.

Macroscopic Source Properties from Dynamic Rupture Styles in Plastic Media

NASA Astrophysics Data System (ADS)

Gabriel, A.; Ampuero, J. P.; Dalguer, L. A.; Mai, P. M.

2011-12-01

High stress concentrations at earthquake rupture fronts may generate an inelastic off-fault response at the rupture tip, leading to increased energy absorption in the damage zone. Furthermore, the induced asymmetric plastic strain field in in-plane rupture modes may produce bimaterial interfaces that can increase radiation efficiency and reduce frictional dissipation. Off-fault inelasticity thus plays an important role for realistic predictions of near-fault ground motion. Guided by our previous studies in the 2D elastic case, we perform rupture dynamics simulations including rate-and-state friction and off-fault plasticity to investigate the effects on the rupture properties. We quantitatively analyze macroscopic source properties for different rupture styles, ranging from cracks to pulses and subshear to supershear ruptures, and their transitional mechanisms. The energy dissipation due to off-fault inelasticity modifies the conditions to obtain each rupture style and alters macroscopic source properties. We examine apparent fracture energy, rupture and healing front speed, peak slip and peak slip velocity, dynamic stress drop and size of the process and plastic zones, slip and plastic seismic moment, and their connection to ground motion. This presentation focuses on the effects of rupture style and off-fault plasticity on the resulting ground motion patterns, especially on characteristic slip velocity function signatures and resulting seismic moments. We aim at developing scaling rules for equivalent elastic models, as function of background stress and frictional parameters, that may lead to improved "pseudo-dynamic" source parameterizations for ground-motion calculation. Moreover, our simulations provide quantitative relations between off-fault energy dissipation and macroscopic source properties. These relations might provide a self-consistent theoretical framework for the study of the earthquake energy balance based on observable earthquake source parameters.

Development of a Fatigue Crack Growth Coupon for Highly Plastic Stress Conditions

NASA Technical Reports Server (NTRS)

Allen, Phillip A.; Aggarwal, Pravin K.; Swanson, Gregory R.

2003-01-01

The analytical approach used to develop a novel fatigue crack growth coupon for highly plastic stress field condition is presented in this paper. The flight hardware investigated is a large separation bolt that has a deep notch, which produces a large plastic zone at the notch root when highly loaded. Four test specimen configurations are analyzed in an attempt to match the elastic-plastic stress field and crack constraint conditions present in the separation bolt. Elastic-plastic finite element analysis is used to compare the stress fields and critical fracture parameters. Of the four test specimens analyzed, the modified double-edge notch tension - 3 (MDENT-3) most closely approximates the stress field, J values, and crack constraint conditions found in the flight hardware. The MDENT-3 is also most insensitive to load misalignment and/or load redistribution during crack growth.

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.

Nano-deformation behavior of silicon (100) film studied by depth sensing indentation and nanoscratch technique

NASA Astrophysics Data System (ADS)

Geetha, D.; Pratyank, R.; Kiran, P.

2018-04-01

Silicon being the most important material applied in microelectronic and photovoltaic technology, repeated investigation of the mechanical properties becomes essential. The nanoscale elastic-plastic deformation characteristics of Si (100) film were analyzed using nanoindentation and nanoscratch techniques. The hardness and elastic modulus values of the film obtained from nanoindentation tests were found to be consistent with the reported values. The load-displacement curves showed discontinuities and kinks which confirms the plastic behaviour of Si. The indentation induced plastic deformations were the consequences of the phase transformations. The critical shear stress, tensile strength and plastic zone size, of the Si film when subjected to nanoindentation were determined. The nanoscratch tests were performed to understand the tribological properties of the film. The SPM images of both the nanoindentation and nanoscratch profiles were useful in revealing the plastic character in terms of the piling up of matter in the vicinity of the dents. Conclusions were drawn in quantifying the plastic deformations and phase transformations.

The Arctic Ocean as a dead end for floating plastics in the North Atlantic branch of the Thermohaline Circulation

PubMed Central

Cózar, Andrés; Martí, Elisa; Duarte, Carlos M.; García-de-Lomas, Juan; van Sebille, Erik; Ballatore, Thomas J.; Eguíluz, Victor M.; González-Gordillo, J. Ignacio; Pedrotti, Maria L.; Echevarría, Fidel; Troublè, Romain; Irigoien, Xabier

2017-01-01

The subtropical ocean gyres are recognized as great marine accummulation zones of floating plastic debris; however, the possibility of plastic accumulation at polar latitudes has been overlooked because of the lack of nearby pollution sources. In the present study, the Arctic Ocean was extensively sampled for floating plastic debris from the Tara Oceans circumpolar expedition. Although plastic debris was scarce or absent in most of the Arctic waters, it reached high concentrations (hundreds of thousands of pieces per square kilometer) in the northernmost and easternmost areas of the Greenland and Barents seas. The fragmentation and typology of the plastic suggested an abundant presence of aged debris that originated from distant sources. This hypothesis was corroborated by the relatively high ratios of marine surface plastic to local pollution sources. Surface circulation models and field data showed that the poleward branch of the Thermohaline Circulation transfers floating debris from the North Atlantic to the Greenland and Barents seas, which would be a dead end for this plastic conveyor belt. Given the limited surface transport of the plastic that accumulated here and the mechanisms acting for the downward transport, the seafloor beneath this Arctic sector is hypothesized as an important sink of plastic debris. PMID:28439534

The Arctic Ocean as a dead end for floating plastics in the North Atlantic branch of the Thermohaline Circulation.

PubMed

Cózar, Andrés; Martí, Elisa; Duarte, Carlos M; García-de-Lomas, Juan; van Sebille, Erik; Ballatore, Thomas J; Eguíluz, Victor M; González-Gordillo, J Ignacio; Pedrotti, Maria L; Echevarría, Fidel; Troublè, Romain; Irigoien, Xabier

2017-04-01

The subtropical ocean gyres are recognized as great marine accummulation zones of floating plastic debris; however, the possibility of plastic accumulation at polar latitudes has been overlooked because of the lack of nearby pollution sources. In the present study, the Arctic Ocean was extensively sampled for floating plastic debris from the Tara Oceans circumpolar expedition. Although plastic debris was scarce or absent in most of the Arctic waters, it reached high concentrations (hundreds of thousands of pieces per square kilometer) in the northernmost and easternmost areas of the Greenland and Barents seas. The fragmentation and typology of the plastic suggested an abundant presence of aged debris that originated from distant sources. This hypothesis was corroborated by the relatively high ratios of marine surface plastic to local pollution sources. Surface circulation models and field data showed that the poleward branch of the Thermohaline Circulation transfers floating debris from the North Atlantic to the Greenland and Barents seas, which would be a dead end for this plastic conveyor belt. Given the limited surface transport of the plastic that accumulated here and the mechanisms acting for the downward transport, the seafloor beneath this Arctic sector is hypothesized as an important sink of plastic debris.

Non-linear programming in shakedown analysis with plasticity and friction

NASA Astrophysics Data System (ADS)

Spagnoli, A.; Terzano, M.; Barber, J. R.; Klarbring, A.

2017-07-01

Complete frictional contacts, when subjected to cyclic loading, may sometimes develop a favourable situation where slip ceases after a few cycles, an occurrence commonly known as frictional shakedown. Its resemblance to shakedown in plasticity has prompted scholars to apply direct methods, derived from the classical theorems of limit analysis, in order to assess a safe limit to the external loads applied on the system. In circumstances where zones of plastic deformation develop in the material (e.g., because of the large stress concentrations near the sharp edges of a complete contact), it is reasonable to expect an effect of mutual interaction of frictional slip and plastic strains on the load limit below which the global behaviour is non dissipative, i.e., both slip and plastic strains go to zero after some dissipative load cycles. In this paper, shakedown of general two-dimensional discrete systems, involving both friction and plasticity, is discussed and the shakedown limit load is calculated using a non-linear programming algorithm based on the static theorem of limit analysis. An illustrative example related to an elastic-plastic solid containing a frictional crack is provided.

Numerical analysis of the effect of surface roughness on mechanical fields in polycrystalline aggregates

NASA Astrophysics Data System (ADS)

Guilhem, Yoann; Basseville, Stéphanie; Curtit, François; Stéphan, Jean-Michel; Cailletaud, Georges

2018-06-01

This paper is dedicated to the study of the influence of surface roughness on local stress and strain fields in polycrystalline aggregates. Finite element computations are performed with a crystal plasticity model on a 316L stainless steel polycrystalline material element with different roughness states on its free surface. The subsequent analysis of the plastic strain localization patterns shows that surface roughness strongly affects the plastic strain localization induced by crystallography. Nevertheless, this effect mainly takes place at the surface and vanishes under the first layer of grains, which implies the existence of a critical perturbed depth. A statistical analysis based on the plastic strain distribution obtained for different roughness levels provides a simple rule to define the size of the affected zone depending on the rough surface parameters.

Modelling highly deformable metal extrusion using SPH

NASA Astrophysics Data System (ADS)

Prakash, Mahesh; Cleary, Paul W.

2015-05-01

Computational modelling is often used to reduce trial extrusions through accurate defect prediction. Traditionally, metal extrusion is modelled using mesh based finite element methods. However, large plastic deformations can lead to heavy re-meshing and numerical diffusion. Here we use the mesh-less smoothed particle hydrodynamics method since it allows simulation of large deformations without re-meshing and the tracking of history dependent properties such as plastic strain making it suitable for defect prediction. The variation in plastic strain and deformation for aluminium alloy in a cylindrical 3D geometry with extrusion ratio and die angle is evaluated. The extrusion process is found to have three distinct phases consisting of an initial sharp rise in extrusion force, a steady phase requiring constant force and terminating in a sharp decline in force as metal is completely extruded. Deformation and plastic strain increased significantly with extrusion ratio but only moderately with die angle. Extrusion force increased by 150 % as the extrusion ratio increased from 2:1 to 4:1 but had only a marginal change with die angle. A low strain zone in the centre of the extruded product was found to be a function of extrusion ratio but was persistent and did not vary with die angle. Simulation of a complex 3D building industry component showed large variations in plastic strain along the length of the product at two scales. These were due to change in metal behaviour as extrusion progressed from phase 1 to phase 2. A stagnation zone at the back of the die was predicted that could lead to the "funnel" or "pipe" defect.

Enduring critical period plasticity visualized by transcranial flavoprotein imaging in mouse primary visual cortex.

PubMed

Tohmi, Manavu; Kitaura, Hiroki; Komagata, Seiji; Kudoh, Masaharu; Shibuki, Katsuei

2006-11-08

Experience-dependent plasticity in the visual cortex was investigated using transcranial flavoprotein fluorescence imaging in mice anesthetized with urethane. On- and off-responses in the primary visual cortex were elicited by visual stimuli. Fluorescence responses and field potentials elicited by grating patterns decreased similarly as contrasts of visual stimuli were reduced. Fluorescence responses also decreased as spatial frequency of grating stimuli increased. Compared with intrinsic signal imaging in the same mice, fluorescence imaging showed faster responses with approximately 10 times larger signal changes. Retinotopic maps in the primary visual cortex and area LM were constructed using fluorescence imaging. After monocular deprivation (MD) of 4 d starting from postnatal day 28 (P28), deprived eye responses were suppressed compared with nondeprived eye responses in the binocular zone but not in the monocular zone. Imaging faithfully recapitulated a critical period for plasticity with maximal effects of MD observed around P28 and not in adulthood even under urethane anesthesia. Visual responses were compared before and after MD in the same mice, in which the skull was covered with clear acrylic dental resin. Deprived eye responses decreased after MD, whereas nondeprived eye responses increased. Effects of MD during a critical period were tested 2 weeks after reopening of the deprived eye. Significant ocular dominance plasticity was observed in responses elicited by moving grating patterns, but no long-lasting effect was found in visual responses elicited by light-emitting diode light stimuli. The present results indicate that transcranial flavoprotein fluorescence imaging is a powerful tool for investigating experience-dependent plasticity in the mouse visual cortex.

Study on Crystallographic Orientation Effect on Surface Generation of Aluminum in Nano-cutting

NASA Astrophysics Data System (ADS)

Xu, Feifei; Fang, Fengzhou; Zhu, Yuanqing; Zhang, Xiaodong

2017-04-01

The material characteristics such as size effect are one of the most important factors that could not be neglected in cutting the material at nanoscale. The effects of anisotropic nature of single crystal materials in nano-cutting are investigated employing the molecular dynamics simulation. Results show that the size effect of the plastic deformation is based on different plastic carriers, such as the twin, stacking faults, and dislocations. The minimum uncut chip thickness is dependent on cutting direction, where even a negative value is obtained when the cutting direction is {110}<001>. It also determines the material deformation and removal mechanism (e.g., shearing, extruding, and rubbing mechanism) with a decrease in uncut chip thickness. When material is deformed by shearing, the primary shearing zone expands from the stagnation point or the tip of stagnation zone. When a material is deformed by extruding and rubbing, the primary deformation zone almost parallels to the cutting direction and expands from the bottom of the cutting edge merging with the tertiary deformation zone. The generated surface quality relates to the crystallographic orientation and the minimum uncut chip thickness. The cutting directions of {110}<001>, {110}<1-10>, and {111}<1-10>, whose minimum uncut chip thickness is relatively small, have better surface qualities compared to the other cutting direction.

Study on Crystallographic Orientation Effect on Surface Generation of Aluminum in Nano-cutting.

PubMed

Xu, Feifei; Fang, Fengzhou; Zhu, Yuanqing; Zhang, Xiaodong

2017-12-01

The material characteristics such as size effect are one of the most important factors that could not be neglected in cutting the material at nanoscale. The effects of anisotropic nature of single crystal materials in nano-cutting are investigated employing the molecular dynamics simulation. Results show that the size effect of the plastic deformation is based on different plastic carriers, such as the twin, stacking faults, and dislocations. The minimum uncut chip thickness is dependent on cutting direction, where even a negative value is obtained when the cutting direction is {110}<001>. It also determines the material deformation and removal mechanism (e.g., shearing, extruding, and rubbing mechanism) with a decrease in uncut chip thickness. When material is deformed by shearing, the primary shearing zone expands from the stagnation point or the tip of stagnation zone. When a material is deformed by extruding and rubbing, the primary deformation zone almost parallels to the cutting direction and expands from the bottom of the cutting edge merging with the tertiary deformation zone. The generated surface quality relates to the crystallographic orientation and the minimum uncut chip thickness. The cutting directions of {110}<001>, {110}<1-10>, and {111}<1-10>, whose minimum uncut chip thickness is relatively small, have better surface qualities compared to the other cutting direction.

Shear Strains, Strain Rates and Temperature Changes in Adiabatic Shear Bands

DTIC Science & Technology

1980-05-01

X14A. It has been found that when bainitic and martensitic steels are sheared adiabatically, a layer of material within ths shear zone is altezed and...Sooiety for Metals, Metals Park, Ohio, 1978, pp. 148-0. 21 TABLE II SOLID-STATE TRANSFORMATIONS IN BAINITIC STEEL TRANSFORMATION TRANSFORMATION...shear, thermoplastic, plasticity, plastic deformation, armor, steel IL AnSRACT ( -=nba asoa.tm a naeoesM iN faity by bleak n bet/2972 Experiments

Fatigue crack closure behavior at high stress ratios

NASA Technical Reports Server (NTRS)

Turner, C. Christopher; Carman, C. Davis; Hillberry, Ben M.

1988-01-01

Fatigue crack delay behavior at high stress ratio caused by single peak overloads was investigated in two thicknesses of 7475-T731 aluminum alloy. Closure measurements indicated no closure occurred before or throughout the overload plastic zones following the overload. This was further substantiated by comparing the specimen compliance following the overload with the compliance of a low R ratio test when the crack was fully open. Scanning electron microscope studies revealed that crack tunneling and possibly reinitiation of the crack occurred, most likely a result of crack-tip blunting. The number of delay cycles was greater for the thinner mixed mode stress state specimen than for the thicker plane strain stress state specimen, which is similar to low R ratio test results and may be due to a larger plastic zone for the mixed mode cased.

On the temperature independence of statistical model parameters for cleavage fracture in ferritic steels

NASA Astrophysics Data System (ADS)

Qian, Guian; Lei, Wei-Sheng; Niffenegger, M.; González-Albuixech, V. F.

2018-04-01

The work relates to the effect of temperature on the model parameters in local approaches (LAs) to cleavage fracture. According to a recently developed LA model, the physical consensus of plastic deformation being a prerequisite to cleavage fracture enforces any LA model of cleavage fracture to observe initial yielding of a volume element as its threshold stress state to incur cleavage fracture in addition to the conventional practice of confining the fracture process zone within the plastic deformation zone. The physical consistency of the new LA model to the basic LA methodology and the differences between the new LA model and other existing models are interpreted. Then this new LA model is adopted to investigate the temperature dependence of LA model parameters using circumferentially notched round tensile specimens. With the published strength data as input, finite element (FE) calculation is conducted for elastic-perfectly plastic deformation and the realistic elastic-plastic hardening, respectively, to provide stress distributions for model calibration. The calibration results in temperature independent model parameters. This leads to the establishment of a 'master curve' characteristic to synchronise the correlation between the nominal strength and the corresponding cleavage fracture probability at different temperatures. This 'master curve' behaviour is verified by strength data from three different steels, providing a new path to calculate cleavage fracture probability with significantly reduced FE efforts.

Switching deformation mode and mechanisms during subduction of continental crust: a case study from Alpine Corsica

NASA Astrophysics Data System (ADS)

Molli, Giancarlo; Menegon, Luca; Malasoma, Alessandro

2017-04-01

The switching in deformation mode (from distributed to localized) and mechanism (viscous versus frictional) represent a relevant issue in the frame of processes of crustal deformation in turn connected with the concept of the brittle-"ductile" transition and seismogenesis. On the other hand the role of brittle precursors in nucleating crystal-plastic shear zones has received more and more consideration being now recognized as having a fundamental role in the localization of deformation and shear zone development, thus representing a case in which switching deformation mode and mechanisms interact and relate to each other. This contribution analyses an example of a crystal plastic shear zone localized by brittle precursor formed within a host granitic-mylonite during deformation in subduction-related environment. The studied sample come from the external Corsican continental crust units involved in alpine age subduction and characterized by a low grade blueschist facies peak assemblages. The blueschist facies host rock is cut by a thin (< 1 cm thick) brittle-viscous shear zone that preserves domains with a cataclastic microstructure overprinted by mylonitic deformation. Blue amphibole is stable in the shear zone foliation, which therefore formed under HP/LT metamorphic conditions in a subduction environment. Quartz microstructure in the damage zone flanking the brittle-viscous shear zone shows evidence of both microcracking and dislocation glide, with limited recrystallization localized in intracrystalline bands. In the mylonite portion of the shear zone, quartz forms polycrystalline ribbons of dynamically recrystallized grains with a crossed-girdle c-axis CPO. Extrapolation of laboratory-derived flow laws indicates strain rate of ca. 3.5 * 10-12 s-1 during viscous flow in the shear zone. The studied structures, possibly formed by transient instability related to episodic stress/strain rate variations, may be considered as a small scale example of fault behaviour associated with a cycle of interseismic creep with coseismic rupture and then a fossil example of stick-slip strain accommodation in subduction environment of continental crust.

Molecular-dynamics Simulation-based Cohesive Zone Representation of Intergranular Fracture Processes in Aluminum

NASA Technical Reports Server (NTRS)

Yamakov, Vesselin I.; Saether, Erik; Phillips, Dawn R.; Glaessgen, Edward H.

2006-01-01

A traction-displacement relationship that may be embedded into a cohesive zone model for microscale problems of intergranular fracture is extracted from atomistic molecular-dynamics simulations. A molecular-dynamics model for crack propagation under steady-state conditions is developed to analyze intergranular fracture along a flat 99 [1 1 0] symmetric tilt grain boundary in aluminum. Under hydrostatic tensile load, the simulation reveals asymmetric crack propagation in the two opposite directions along the grain boundary. In one direction, the crack propagates in a brittle manner by cleavage with very little or no dislocation emission, and in the other direction, the propagation is ductile through the mechanism of deformation twinning. This behavior is consistent with the Rice criterion for cleavage vs. dislocation blunting transition at the crack tip. The preference for twinning to dislocation slip is in agreement with the predictions of the Tadmor and Hai criterion. A comparison with finite element calculations shows that while the stress field around the brittle crack tip follows the expected elastic solution for the given boundary conditions of the model, the stress field around the twinning crack tip has a strong plastic contribution. Through the definition of a Cohesive-Zone-Volume-Element an atomistic analog to a continuum cohesive zone model element - the results from the molecular-dynamics simulation are recast to obtain an average continuum traction-displacement relationship to represent cohesive zone interaction along a characteristic length of the grain boundary interface for the cases of ductile and brittle decohesion. Keywords: Crack-tip plasticity; Cohesive zone model; Grain boundary decohesion; Intergranular fracture; Molecular-dynamics simulation

A brief history of plastic surgery in Iran.

PubMed

Kalantar-Hormozi, Abdoljalil

2013-03-01

 Although the exact time of performing plastic surgery is not addressed in the medical and historical literature, it can be supposed that these surgical procedures have a long and fascinating history.  Recent excavations provided many documents regarding the application of medical instruments, surgical and even reconstructive procedures during the pre-historic and ancient periods. Actually, there is no historical definite time-zone separating general and cosmetic operations in the pre-modern time; however, historically there have been many surgeons who tried to perform reconstructive procedures during their usual medical practice. This article presents a brief look at the history of plastic surgery form the ancient to the contemporary era, with a special focus on Iran.

Plastic deformation and failure mechanisms in nano-scale notched metallic glass specimens under tensile loading

NASA Astrophysics Data System (ADS)

Dutta, Tanmay; Chauniyal, Ashish; Singh, I.; Narasimhan, R.; Thamburaja, P.; Ramamurty, U.

2018-02-01

In this work, numerical simulations using molecular dynamics and non-local plasticity based finite element analysis are carried out on tensile loading of nano-scale double edge notched metallic glass specimens. The effect of acuteness of notches as well as the metallic glass chemical composition or internal material length scale on the plastic deformation response of the specimens are studied. Both MD and FE simulations, in spite of the fundamental differences in their nature, indicate near-identical deformation features. Results show two distinct transitions in the notch tip deformation behavior as the acuity is increased, first from single shear band dominant plastic flow localization to ligament necking, and then to double shear banding in notches that are very sharp. Specimens with moderately blunt notches and composition showing wider shear bands or higher material length scale characterizing the interaction stress associated with flow defects display profuse plastic deformation and failure by ligament necking. These results are rationalized from the role of the interaction stress and development of the notch root plastic zones.

Mechanisms of strain accommodation in plastically-deformed zircon under simple shear deformation conditions during amphibolite-facies metamorphism

NASA Astrophysics Data System (ADS)

Kovaleva, Elizaveta; Klötzli, Urs; Wheeler, John; Habler, Gerlinde

2018-02-01

This study documents the strain accommodation mechanisms in zircon under amphibolite-facies metamorphic conditions in simple shear. Microstructural data from undeformed, fractured and crystal-plastically deformed zircon crystals are described in the context of the host shear zone, and evaluated in the light of zircon elastic anisotropy. Our work challenges the existing model of zircon evolution and shows previously undescribed rheological characteristics for this important accessory mineral. Crystal-plastically deformed zircon grains have axis oriented parallel to the foliation plane, with the majority of deformed grains having axis parallel to the lineation. Zircon accommodates strain by a network of stepped low-angle boundaries, formed by switching between tilt dislocations with the slip systems <100>{010} and < 1 bar 10>{110} and rotation axis [001], twist dislocations with the rotation axis [001], and tilt dislocations with the slip system <100>{001} and rotation axis [010]. The slip system < 1 bar 10>{110} is newly described for zircon. Most misorientation axes in plastically-deformed zircon grains are parallel to the XY plane of the sample and have [001] crystallographic direction. Such behaviour of strained zircon lattice is caused by elastic anisotropy that has a direct geometric control on the rheology, deformation mechanisms and dominant slip systems in zircon. Young's modulus and P wave velocity have highest values parallel to zircon [001] axis, indicating that zircon is elastically strong along this direction. Poisson ratio and Shear modulus demonstrate that zircon is also most resistant to shearing along [001]. Thus, [001] axis is the most common rotation axis in zircon. The described zircon behaviour is important to take into account during structural and geochronological investigations of (poly)metamorphic terrains. Geometry of dislocations in zircon may help reconstructing the geometry of the host shear zone(s), large-scale stresses in the crust, and, possibly, the timing of deformation, if the isotopic systems of deformed zircon were reset.

Self-disinfecting plastics for intravenous catheters and prosthetic inserts.

PubMed Central

Kingston, D.; Seal, D. V.; Hill, I. D.

1986-01-01

A disinfectant (2,4,4'-trichloro-2'-hydroxydiphenyl ether: Irgasan, Ciba-Geigy) was incorporated into plastic washers fabricated from ethylvinyl acetate (EVA), polyethylene, polypropylene or TPX. Plastics containing 0.2 and 2% Irgasan gave zones of inhibition on nutrient and blood agar plates seeded with micro-organisms (Staphylococcus aureus, Staph. epidermidis, Escherichia coli, Proteus mirabilis or Candida albicans) even after thorough washing. Exceptionally, C. albicans was inhibited only by 2% Irgasan, and EVA gave good inhibition only against the staphylococci. Similar washers of each plastic were implanted subcutaneously into the flanks of rabbits; before insertion each was washed, had thread woven into it and was surrounded by a plasma clot containing 2 X 10(8) Staph. aureus. All the plastics without Irgasan gave rise to abscesses, none of the plastics impregnated with 2% Irgasan did, though from 2 out of 12 sites small numbers of Staph. aureus were isolated at post mortem. Using either clinical or bacteriological criteria, the results were highly significant (P less than 0.00001 and P less than 0.001 respectively), demonstrating the effectiveness of this technique in preventing plastic-associated infection. Images Fig. 2 Fig. 2(Contd.) PMID:3517154

L-form plastics in the treatment of post-burn trophic ulcers and cicatrices of the foot calcaneal area.

PubMed

Shakirov, Babur M; Tagaev, Komil R; Tursunov, Bachron S; Achtamov, Dgamshed A

2009-03-01

The burn trauma of the posterior surface of calcaneus region and ankle joint followed by cicatrix formation in the Achilles tendon zone is often complicated by unhealing trophic ulcers. Eleven patients (seven men and four women, aged 9-54 years) have been operated on under our observation for prolonged unhealing ulcers and cicatrices located in the Achilles tendon zone. After cicatrices dissection, L-form plastic surgery was performed. The postoperative period was smooth; a skin graft was appropriately fixed to the proper tissues and the wound margins. Good results were achieved in 10 cases, and no complications were noted. However, in only one patient a marginal necrosis of the external talus part adjoining the ulcer due to tissue changes has been noted, but that had no influence on the good results of the operation.

Coupled THM processes in EDZ of crystalline rocks using an elasto-plastic cellular automaton

NASA Astrophysics Data System (ADS)

Pan, Peng-Zhi; Feng, Xia-Ting; Huang, Xiao-Hua; Cui, Qiang; Zhou, Hui

2009-05-01

This paper aims at a numerical study of coupled thermal, hydrological and mechanical processes in the excavation disturbed zones (EDZ) around nuclear waste emplacement drifts in fractured crystalline rocks. The study was conducted for two model domains close to an emplacement tunnel; (1) a near-field domain and (2) a smaller wall-block domain. Goodman element and weak element were used to represent the fractures in the rock mass and the rock matrix was represented as elasto-visco-plastic material. Mohr-Coulomb criterion and a non-associated plastic flow rule were adopted to consider the viscoplastic deformation in the EDZ. A relation between volumetric strain and permeability was established. Using a self-developed EPCA2D code, the elastic, elasto-plastic and creep analyses to study the evolution of stress and deformations, as well as failure and permeability evolution in the EDZ were conducted. Results indicate a strong impact of fractures, plastic deformation and time effects on the behavior of EDZ especially the evolution of permeability around the drift.

Microstructure and Mechanical Characterization of Friction-Stir-Welded Dual-Phase Brass

NASA Astrophysics Data System (ADS)

Ramesh, R.; Dinaharan, I.; Akinlabi, E. T.; Murugan, N.

2018-03-01

Friction stir welding (FSW) is an ideal process to join brass to avoid the evaporation of zinc. In the present investigation, 6-mm-thick dual-phase brass plates were joined efficiently using FSW at various tool rotational speeds. The microstructures were studied using optical microscopy, electron backscattered diffraction and transmission electron microscopy. The optical micrographs revealed the evolution of various zones across the joint line. The microstructure of the heat-affected zone was similar to that of base metal. The weld zone exhibited finer grains due to dynamic recrystallization. The recrystallization was inhomogeneous and the inhomogeneity reduced with increased tool rotational speed. The dual phase was preserved in the weld zone due to the retention of zinc. The severe plastic deformation created a lot of dislocations in the weld zone. The weld zone was strengthened after welding. The role of tool rotational speed on the joint strength is further reported.

Thermal Recovery of Plastic Deformation in Dissimilar Metal Weld

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

Qiao, Dongxiao; Yu, Xinghua; Zhang, Wei

Stainless steel has been widely used in challenging environments typical to nuclear power plant structures, due its excellent corrosion resistance. Nickel filler metals containing high chromium concentration, including Alloy 82/182, are used for joining stainless steel to carbon steel components to achieve similar high resistance to stress corrosion cracking. However, the joint usually experience weld metal stress corrosion cracking (SCC), which affects the safety and structural integrity of light water nuclear reactor systems. A primary driving force for SCC is the high tensile residual stress in these welds. Due to large dimension of pressure vessel and limitations in the field,more » non-destructive residual stress measurement is difficult. As a result, finite element modeling has been the de facto method to evaluate the weld residual stresses. Recent studies on this subject from researchers worldwide report different residual stress value in the weldments [5]. The discrepancy is due to the fact that most of investigations ignore or underestimate the thermal recovery in the heat-affect zone or reheated region in the weld. In this paper, the effect of heat treatment on thermal recovery and microhardness is investigated for materials used in dissimilar metal joint. It is found that high equivalent plastic strains are predominately accumulated in the buttering layer, the root pass, and the heat affected zone, which experience multiple welding thermal cycles. The final cap passes, experiencing only one or two welding thermal cycles, exhibit less plastic strain accumulation. Moreover, the experimental residual plastic strains are compared with those predicted using an existing weld thermo-mechanical model with two different strain hardening rules. The importance of considering the dynamic strain hardening recovery due to high temperature exposure in welding is discussed for the accurate simulation of weld residual stresses and plastic strains. In conclsuion, the experimental result reveals that the typical post-buttering heat treatment for residual stress relief may not be adequate to completely eliminate the residual plastic strains in the buttering layer.« less

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.

The Glenn A. Fry Award Lecture 2012: Plasticity of the visual system following central vision loss.

PubMed

Chung, Susana T L

2013-06-01

Following the onset of central vision loss, most patients develop an eccentric retinal location outside the affected macular region, the preferred retinal locus (PRL), as their new reference for visual tasks. The first goal of this article is to present behavioral evidence showing the presence of experience-dependent plasticity in people with central vision loss. The evidence includes the presence of oculomotor re-referencing of fixational saccades to the PRL; the characteristics of the shape of the crowding zone (spatial region within which the presence of other objects affects the recognition of a target) at the PRL are more "foveal-like" instead of resembling those of the normal periphery; and the change in the shape of the crowding zone at a para-PRL location that includes a component referenced to the PRL. These findings suggest that there is a shift in the referencing locus of the oculomotor and the sensory visual system from the fovea to the PRL for people with central vision loss, implying that the visual system for these individuals is still plastic and can be modified through experiences. The second goal of the article is to demonstrate the feasibility of applying perceptual learning, which capitalizes on the presence of plasticity, as a tool to improve functional vision for people with central vision loss. Our finding that visual function could improve with perceptual learning presents an exciting possibility for the development of an alternative rehabilitative strategy for people with central vision loss.

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.

77 FR 20356 - Foreign-Trade Zone 277-Western Maricopa County, AZ; Application for Manufacturing Authority...

Federal Register 2010, 2011, 2012, 2013, 2014

2012-04-04

... facility is used for the manufacture of 275 and 290 watt solar panels for industrial use. Components and... boxes, silicone sealant, putty/caulking compounds, plastic sheets, glass, tin-coated copper strips...

75 FR 15679 - Foreign-Trade Zone 272-Lehigh Valley, Pennsylvania Application for Subzone Grundfos Pumps...

Federal Register 2010, 2011, 2012, 2013, 2014

2010-03-30

... from abroad (representing 65% of the value of the finished pumps) include: Pump parts, electric motors, plastic closures and o- rings, rubber o-rings and gaskets, labels, pipe fittings, fasteners, motor...

78 FR 45911 - Foreign-Trade Zone (FTZ) 38-Spartanburg County, South Carolina, Notification of Proposed...

Federal Register 2010, 2011, 2012, 2013, 2014

2013-07-30

... chargers; magnets; magnetic chucks; lead-acid, power pack, NiMH and lithium ion batteries; SA battery packs...-bags; battery caps; blister packs; shrink-heat tubing; plastic handles and knobs; O- rings; seals...

Odours from marine plastic debris induce food search behaviours in a forage fish.

PubMed

Savoca, Matthew S; Tyson, Chris W; McGill, Michael; Slager, Christina J

2017-08-16

Plastic pollution is an anthropogenic stressor in marine ecosystems globally. Many species of marine fish (more than 50) ingest plastic debris. Ingested plastic has a variety of lethal and sublethal impacts and can be a route for bioaccumulation of toxic compounds throughout the food web. Despite its pervasiveness and severity, our mechanistic understanding of this maladaptive foraging behaviour is incomplete. Recent evidence suggests that the chemical signature of plastic debris may explain why certain species are predisposed to mistaking plastic for food. Anchovy ( Engraulis sp.) are abundant forage fish in coastal upwelling systems and a critical prey resource for top predators. Anchovy ingest plastic in natural conditions, though the mechanism they use to misidentify plastic as prey is unknown. Here, we presented wild-caught schools of northern anchovy ( Engraulis mordax ) with odour solutions made of plastic debris and clean plastic to compare school-wide aggregation and rheotactic responses relative to food and food odour presentations. Anchovy schools responded to plastic debris odour with increased aggregation and reduced rheotaxis. These results were similar to the effects food and food odour presentations had on schools. Conversely, these behavioural responses were absent in clean plastic and control treatments. To our knowledge, this is the first experimental evidence that adult anchovy use odours to forage. We conclude that the chemical signature plastic debris acquires in the photic zone can induce foraging behaviours in anchovy schools. These findings provide further support for a chemosensory mechanism underlying plastic consumption by marine wildlife. Given the trophic position of forage fish, these findings have considerable implications for aquatic food webs and possibly human health. © 2017 The Author(s).

Fatigue pre-cracking and fracture toughness in polycrystalline tungsten and molybdenum

NASA Astrophysics Data System (ADS)

Taguchi, Katsuya; Nakadate, Kazuhito; Matsuo, Satoru; Tokunaga, Kazutoshi; Kurishita, Hiroaki

2018-01-01

Fatigue pre-cracking performance and fracture toughness in polycrystalline tungsten (W) and molybdenum (Mo) have been investigated in relation to grain boundary (GB) configuration with respect to the crack advance direction. Sub-sized, single edge notched bend (SENB) specimens with three different orientations, R-L (ASTM notation) for a forged Mo rod and L-S and T-S for a rolled W plate, were pre-cracked in two steps: fully uniaxial compression fatigue loading to provoke crack initiation and its stable growth from the notch root, and subsequent 3-point bend (3PB) fatigue loading to extend the crack. The latter step intends to minimize the influence of the residual tensile stresses generated during compression fatigue by moving the crack tip away from the plastic zone. It is shown that fatigue pre-cracking performance, especially pre-crack extension behavior, is significantly affected by the specimen orientation. The R-L orientation, giving the easiest cracking path, permitted crack extension completely beyond the plastic zone, while the L-S and T-S orientations with the thickness cracking direction of the rolled plate sustained the crack lengths around or possibly within the plastic zone size due to difficulty in crack advance through an aligned grain structure. Room temperature fracture toughness tests revealed that the 3PB fatigued specimens exhibited appreciably higher fracture toughness by about 30% for R-L, 40% for L-S and 60% for T-S than the specimens of each orientation pre-cracked by compression fatigue only. This indicates that 3PB fatigue provides the crack tip front out of the residual tensile stress zone by crack extension or leads to reduction in the residual stresses at the crack tip front. Strong dependence of fracture toughness on GB configuration was evident. The obtained fracture toughness values are compared with those in the literature and its strong GB configuration dependence is discussed in connection with the appearance of pop-in.

Investigation on Characteristic Variation of the FBG Spectrum with Crack Propagation in Aluminum Plate Structures

PubMed Central

Jin, Bo; Zhang, Weifang; Zhang, Meng; Ren, Feifei; Dai, Wei; Wang, Yanrong

2017-01-01

In order to monitor the crack tip propagation of aluminum alloy, this study investigates the variation of the spectrum characteristics of a fiber Bragg grating (FBG), combined with an analysis of the spectrum simulation. The results identify the location of the subordinate peak as significantly associated with the strain distribution along the grating, corresponding to the different plastic zones ahead of the crack tip with various crack lengths. FBG sensors could observe monotonic and cyclic plastic zones ahead of the crack tip, with the quadratic strain distribution along the grating at the crack tip-FBG distance of 1.2 and 0.7 mm, respectively. FBG sensors could examine the process zones ahead of the crack tip with the cubic strain distribution along the grating at the crack tip-FBG distance of 0.5 mm. The spectrum oscillation occurs as the crack approaches the FBG where the highly heterogeneous strain is distributed. Another idea is to use a finite element method (FEM), together with a T-matrix method, to analyze the reflection intensity spectra of FBG sensors for various crack sizes. The described crack propagation detection system may apply in structural health monitoring. PMID:28772949

Investigation on Characteristic Variation of the FBG Spectrum with Crack Propagation in Aluminum Plate Structures.

PubMed

Jin, Bo; Zhang, Weifang; Zhang, Meng; Ren, Feifei; Dai, Wei; Wang, Yanrong

2017-05-27

In order to monitor the crack tip propagation of aluminum alloy, this study investigates the variation of the spectrum characteristics of a fiber Bragg grating (FBG), combined with an analysis of the spectrum simulation. The results identify the location of the subordinate peak as significantly associated with the strain distribution along the grating, corresponding to the different plastic zones ahead of the crack tip with various crack lengths. FBG sensors could observe monotonic and cyclic plastic zones ahead of the crack tip, with the quadratic strain distribution along the grating at the crack tip-FBG distance of 1.2 and 0.7 mm, respectively. FBG sensors could examine the process zones ahead of the crack tip with the cubic strain distribution along the grating at the crack tip-FBG distance of 0.5 mm. The spectrum oscillation occurs as the crack approaches the FBG where the highly heterogeneous strain is distributed. Another idea is to use a finite element method (FEM), together with a T -matrix method, to analyze the reflection intensity spectra of FBG sensors for various crack sizes. The described crack propagation detection system may apply in structural health monitoring.

Three-dimensional frictional plastic strain partitioning during oblique rifting

NASA Astrophysics Data System (ADS)

Duclaux, Guillaume; Huismans, Ritske S.; May, Dave

2017-04-01

Throughout the Wilson cycle the obliquity between lithospheric plate motion direction and nascent or existing plate boundaries prompts the development of intricate three-dimensional tectonic systems. Where oblique divergence dominates, as in the vast majority of continental rift and incipient oceanic domains, deformation is typically transtensional and large stretching in the brittle upper crust is primarily achieved by the accumulation of displacement on fault networks of various complexity. In continental rift depressions such faults are initially distributed over tens to hundreds of kilometer-wide regions, which can ultimately stretch and evolve into passive margins. Here, we use high-resolution 3D thermo-mechanical finite element models to investigate the relative timing and distribution of localised frictional plastic deformation in the upper crust during oblique rift development in a simplified layered lithosphere. We vary the orientation of a wide oblique heterogeneous weak zone (representing a pre-existing geologic feature like a past orogenic domain), and test the sensitivity of the shear zones orientation to a range of noise distribution. These models allow us to assess the importance of material heterogeneities for controlling the spatio-temporal shear zones distribution in the upper crust during oblique rifting, and to discuss the underlying controls governing oblique continental breakup.

Petrologic and chemical changes in ductile shear zones as a function of depth in the continental crust

NASA Astrophysics Data System (ADS)

Yang, Xin-Yue

Petrologic and geochemical changes in ductile shear zones are important for understanding deformational and geochemical processes of the continental crust. This study examines three shear zones that formed under conditions varying from lower greenschist facies to upper amphibolite facies in order to document the petrologic and geochemical changes of deformed rocks at various metamorphic grades. The studied shear zones include two greenschist facies shear zones in the southern Appalachians and an upper amphibolite facies shear zone in southern Ontario. The mylonitic gneisses and mylonites in the Roses Mill shear zone of central Virginia are derived from a ferrodiorite protolith and characterized by a lower greenschist facies mineral assemblage. Both pressure solution and recrystallization were operative deformation mechanisms during mylonitization in this shear zone. Strain-driven dissolution and solution transfer played an important role in the mobilization of felsic components (Si, Al, K, Na, and Ca). During mylonitization, 17% to 32% bulk rock volume losses of mylonites are mainly attributed to removal of these mobile felsic components by a fluid phase. Mafic components (Fe, Mg, Ti, Mn and P) and trace elements, REE, Y, V and Sc, were immobile. At Rosman, North Carolina, the Brevard shear zone (BSZ) shows a deformational transition from the coarse-grained Henderson augen gneiss (HAG) to proto-mylonite, mylonite and ultra-mylonite. The mylonites contain a retrograde mineral assemblage as a product of fluid-assisted chemical breakdown of K-feldspar and biotite at higher greenschist facies conditions. Recrystallization and intra-crystalline plastic deformation are major deformation mechanisms in the BSZ. Fluid-assisted mylonitization in the BSZ led to 6% to 23% bulk volume losses in mylonites. During mylonitization, both major felsic and mafic elements and trace elements, Rb, Sr, Zr, V, Sc, and LREE were mobile; however, the HREEs were likely immobile. A shear zone in the Parry Sound domain, Ontario, formed at upper amphibolite facies conditions. The deformation process of the shear zone involves fully plastic deformation and high-temperature dynamic recrystallization and annealing recovery of both quartz and plagioclase. Geochemical evidence indicates that the chemical changes in the deformed rocks resulted from mixing of mafic and felsic layers together with fluid-assisted mass transfer within the shear zone. A geochemical model that incorporates closed-system two-component mixing with open-system mass transfer can well explain the observed major and trace element data.

The noncontinuum crack tip deformation behavior of surface microcracks

NASA Astrophysics Data System (ADS)

Morris, W. L.

1980-07-01

The crack tip opening displacement (CTOD) of small surface fatigue cracks (lengths of the grain size) in Al 2219-T851 depends upon the location of a crack relative to the grain boundaries. Both CTOD and crack tip closure stress are greatest when the crack tip is a large distance from the next grain boundary in the direction of crack propagation. Contrary to behavioral trends predicted by continuum fracture mechanics, crack length has no detectable effect on the contribution of plastic deformation to CTOD. It is apparent from these observations that the region of significant plastic deformation is confined by the grain boundaries, resulting in a plastic zone size that is insensitive to crack length and to external load.

76 FR 66685 - Foreign-Trade Zone 37-Orange County, NY, Application for Subzone, ITT Water Technology, Inc...

Federal Register 2010, 2011, 2012, 2013, 2014

2011-10-27

... (representing 39% of the value of the finished pumps) include: electric motors, pump parts, mechanical seals, plastic o-rings, rubber o-rings, shafts, flanges, motor and shaft couplings, and fasteners (duty rates...

Cave Buttes Dam Foundation Report. Gila River Basin: Phoenix, Arizona and Vicinity (Including New River).

DTIC Science & Technology

1983-08-01

bedrock. Reservoir deposits are rich in silt and clay as shown by the plastic nature of material behind Cave Creek Dam. Recent alluvium is directly...formation and the zone I, impervious material. Then rolling with the rubber tired equipment would fill voids and small cracks with the clayey, plastic ...Assoclates US " 2 t 64urvey air J.1y 1969. ___OSOWRS g.Aorizatnfa( conirol ji 45 on G1A - EEA fSI Alaon~ral ieodtc Survey Dafum. Yerftci 4 1 -5 AtE

Indentation studies on Y[sub 2]O[sub 3]-stabilized ZrO[sub 2]; 1: Development of indentation-induced cracks

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

Kaliszewski, M.S.; Behrens, G.; Heuer, A.H.

1994-05-01

The development of Vickers indent-induced cracks with increasing indent load has been studied in two Y[sub 2]O[sub 3]-stabilized ZrO[sub 2] ceramics. Such cracks form as radial or Palmqvist cracks at low loads, assume kidney'' shapes at intermediate loads, and finally form median (half-penny) cracks at high loads. The plastic zone directly beneath the indent is uncracked; a significant portion of the plasticity induced by indentation occurs by martensitic transformation.

Marine Plastic Pollution in Waters around Australia: Characteristics, Concentrations, and Pathways

PubMed Central

Reisser, Julia; Shaw, Jeremy; Wilcox, Chris; Hardesty, Britta Denise; Proietti, Maira; Thums, Michele; Pattiaratchi, Charitha

2013-01-01

Plastics represent the vast majority of human-made debris present in the oceans. However, their characteristics, accumulation zones, and transport pathways remain poorly assessed. We characterised and estimated the concentration of marine plastics in waters around Australia using surface net tows, and inferred their potential pathways using particle-tracking models and real drifter trajectories. The 839 marine plastics recorded were predominantly small fragments (“microplastics”, median length = 2.8 mm, mean length = 4.9 mm) resulting from the breakdown of larger objects made of polyethylene and polypropylene (e.g. packaging and fishing items). Mean sea surface plastic concentration was 4256.4 pieces km−2, and after incorporating the effect of vertical wind mixing, this value increased to 8966.3 pieces km−2. These plastics appear to be associated with a wide range of ocean currents that connect the sampled sites to their international and domestic sources, including populated areas of Australia's east coast. This study shows that plastic contamination levels in surface waters of Australia are similar to those in the Caribbean Sea and Gulf of Maine, but considerably lower than those found in the subtropical gyres and Mediterranean Sea. Microplastics such as the ones described here have the potential to affect organisms ranging from megafauna to small fish and zooplankton. PMID:24312224

Marine plastic pollution in waters around Australia: characteristics, concentrations, and pathways.

PubMed

Reisser, Julia; Shaw, Jeremy; Wilcox, Chris; Hardesty, Britta Denise; Proietti, Maira; Thums, Michele; Pattiaratchi, Charitha

2013-01-01

Plastics represent the vast majority of human-made debris present in the oceans. However, their characteristics, accumulation zones, and transport pathways remain poorly assessed. We characterised and estimated the concentration of marine plastics in waters around Australia using surface net tows, and inferred their potential pathways using particle-tracking models and real drifter trajectories. The 839 marine plastics recorded were predominantly small fragments ("microplastics", median length = 2.8 mm, mean length = 4.9 mm) resulting from the breakdown of larger objects made of polyethylene and polypropylene (e.g. packaging and fishing items). Mean sea surface plastic concentration was 4256.4 pieces km(-2), and after incorporating the effect of vertical wind mixing, this value increased to 8966.3 pieces km(-2). These plastics appear to be associated with a wide range of ocean currents that connect the sampled sites to their international and domestic sources, including populated areas of Australia's east coast. This study shows that plastic contamination levels in surface waters of Australia are similar to those in the Caribbean Sea and Gulf of Maine, but considerably lower than those found in the subtropical gyres and Mediterranean Sea. Microplastics such as the ones described here have the potential to affect organisms ranging from megafauna to small fish and zooplankton.

Mechanisms of fatigue crack retardation following single tensile overloads in powder metallurgy aluminum alloys

NASA Technical Reports Server (NTRS)

Bray, G. H.; Reynolds, A. P.; Starke, E. A., Jr.

1992-01-01

In ingot metallurgy (IM) alloys, the number of delay cycles following a single tensile overload typically increases from a minimum at an intermediate baseline stress intensity range, Delta-K(B), with decreasing Delta-K(B) approaching threshold and increasing Delta-K(B) approaching unstable fracture to produce a characteristic 'U' shaped curve. Two models have been proposed to explain this behavior. One model is based on the interaction between roughness and plasticity-induced closure, while the other model only utilizes plasticity-induced closure. This article examines these models, using experimental results from constant amplitude and single overload fatigue tests performed on two powder metallurgy (PM) aluminum alloys, AL-905XL and AA 8009. The results indicate that the 'U'-shaped curve is primarily due to plasticity-induced closure, and that the plasticity-induced retardation effect is through-thickness in nature, occurring in both the surface and interior regions. However, the retardation effect is greater at the surface, because the increase in plastic strain at the crack tip and overload plastic zone size are larger in the plane-stress surface regions than in the plane-strain interior regions. These results are not entirely consistent with either of the proposed models.

Development of a Fatigue Crack Growth Coupon for Highly Plastic Stress Conditions

NASA Technical Reports Server (NTRS)

Allen, Phillip A.; Aggarwal, Pravin K.; Swanson, Gregory R.

2003-01-01

This paper presents an analytical approach used to develop a novel fatigue crack growth coupon for a highly plastic 3-D stress field condition. The flight hardware investigated in this paper is a large separation bolt that fractures using pyrotechnics at the appointed time during the flight sequence. The separation bolt has a deep notch that produces a severe stress concentration and a large plastic zone when highly loaded. For this geometry, linear-elastic fracture mechanics (LEFM) techniques are not valid due to the large nonlinear stress field. Unfortunately, industry codes that are generally available for fracture mechanics analysis and fatigue crack growth (e.g. NASGRO (11) are limited to LEFM and are available for only a limited number of geometries. The results of LEFM based codes are questionable when used on geometries with significant plasticity. Therefore elastic-plastic fracture mechanics (EPFM) techniques using the finite element method (FEM) were used to analyze the bolt and test coupons. scale flight hardware is very costly in t e r n of assets, laboratory resources, and schedule. Therefore to alleviate some of these problems, a series of novel test coupons were developed to simulate the elastic-plastic stress field present in the bolt.

49 CFR 173.4 - Small quantities for highway and rail.

Code of Federal Regulations, 2014 CFR

2014-10-01

... Division 6.1, Packing Group I, Hazard Zone A or B material; and (iv) [Reserved] (v) Thirty (30) mL water... of plastic having a minimum thickness of no less than 0.2 mm (0.008 inch), or earthenware, glass, or...

The distribution of microplastics in soil aggregate fractions in southwestern China.

PubMed

Zhang, G S; Liu, Y F

2018-06-09

Plastic particle accumulation in arable soils is a growing contaminant of concern with unknown consequences for soil productivity and quality. This study aimed to investigate abundance and distribution of plastic particles among soil aggregate fractions in four cropped areas and an established riparian forest buffer zone at Dian Lake, southwestern China. Plastic particles (10-0.05 mm) from fifty soil samples were extracted and then sorted by size, counted, and categorized. Plastic particles were found in all soil samples. The concentration of plastic particles ranges from 7100 to 42,960 particles kg -1 (mean 18,760 particles kg -1 ). 95% of the sampled plastic particles are in the microplastic size (1-0.05 mm) range. The predominant form is plastic fibers, making up on average 92% of each sample followed by fragments and films that contributed with to 8%. Results of this study also show that 72% of plastic particles are associated with soil aggregates, and 28% of plastic particles are dispersed. The abundance of aggregate-associated plastic fibers is significantly greater in the micro-aggregate than that in the macro-aggregate, whereas the less concentrations of plastic films and fragments are found in the micro-aggregate. Compared to the adjacent vegetable soil, the less concentration of plastic particles in the buffer soil implicates that application of soil amendments and irrigation with wastewater must be controlled to reduce accumulation of microplastics in agricultural soils. While the implications of microplastic on ecological and human health are poorly understood, the staggering number of microplastic in agricultural soils should be continually concerned in the future. Copyright © 2018 Elsevier B.V. All rights reserved.

Plastics and microplastics in the oceans: From emerging pollutants to emerged threat.

PubMed

Avio, Carlo Giacomo; Gorbi, Stefania; Regoli, Francesco

2017-07-01

Plastic production has increased dramatically worldwide over the last 60 years and it is nowadays recognized as a serious threat to the marine environment. Plastic pollution is ubiquitous, but quantitative estimates on the global abundance and weight of floating plastics are still limited, particularly for the Southern Hemisphere and the more remote regions. Some large-scale convergence zones of plastic debris have been identified, but there is the urgency to standardize common methodologies to measure and quantify plastics in seawater and sediments. Investigations on temporal trends, geographical distribution and global cycle of plastics have management implications when defining the origin, possible drifting tracks and ecological consequences of such pollution. An elevated number of marine species is known to be affected by plastic contamination, and a more integrated ecological risk assessment of these materials has become a research priority. Beside entanglement and ingestion of macro debris by large vertebrates, microplastics are accumulated by planktonic and invertebrate organisms, being transferred along food chains. Negative consequences include loss of nutritional value of diet, physical damages, exposure to pathogens and transport of alien species. In addition, plastics contain chemical additives and efficiently adsorb several environmental contaminants, thus representing a potential source of exposure to such compounds after ingestion. Complex ecotoxicological effects are increasingly reported, but the fate and impact of microplastics in the marine environment are still far to be fully clarified. Copyright © 2016 Elsevier Ltd. All rights reserved.

Elastic-plastic models for multi-site damage

NASA Technical Reports Server (NTRS)

Actis, Ricardo L.; Szabo, Barna A.

1994-01-01

This paper presents recent developments in advanced analysis methods for the computation of stress site damage. The method of solution is based on the p-version of the finite element method. Its implementation was designed to permit extraction of linear stress intensity factors using a superconvergent extraction method (known as the contour integral method) and evaluation of the J-integral following an elastic-plastic analysis. Coarse meshes are adequate for obtaining accurate results supported by p-convergence data. The elastic-plastic analysis is based on the deformation theory of plasticity and the von Mises yield criterion. The model problem consists of an aluminum plate with six equally spaced holes and a crack emanating from each hole. The cracks are of different sizes. The panel is subjected to a remote tensile load. Experimental results are available for the panel. The plasticity analysis provided the same limit load as the experimentally determined load. The results of elastic-plastic analysis were compared with the results of linear elastic analysis in an effort to evaluate how plastic zone sizes influence the crack growth rates. The onset of net-section yielding was determined also. The results show that crack growth rate is accelerated by the presence of adjacent damage, and the critical crack size is shorter when the effects of plasticity are taken into consideration. This work also addresses the effects of alternative stress-strain laws: The elastic-ideally-plastic material model is compared against the Ramberg-Osgood model.

Transmission, Development, and Plasticity of Synapses

PubMed Central

Harris, Kathryn P.

2015-01-01

Chemical synapses are sites of contact and information transfer between a neuron and its partner cell. Each synapse is a specialized junction, where the presynaptic cell assembles machinery for the release of neurotransmitter, and the postsynaptic cell assembles components to receive and integrate this signal. Synapses also exhibit plasticity, during which synaptic function and/or structure are modified in response to activity. With a robust panel of genetic, imaging, and electrophysiology approaches, and strong evolutionary conservation of molecular components, Drosophila has emerged as an essential model system for investigating the mechanisms underlying synaptic assembly, function, and plasticity. We will discuss techniques for studying synapses in Drosophila, with a focus on the larval neuromuscular junction (NMJ), a well-established model glutamatergic synapse. Vesicle fusion, which underlies synaptic release of neurotransmitters, has been well characterized at this synapse. In addition, studies of synaptic assembly and organization of active zones and postsynaptic densities have revealed pathways that coordinate those events across the synaptic cleft. We will also review modes of synaptic growth and plasticity at the fly NMJ, and discuss how pre- and postsynaptic cells communicate to regulate plasticity in response to activity. PMID:26447126

Marine debris ingestion by Magellanic penguins, Spheniscus magellanicus (Aves: Sphenisciformes), from the Brazilian coastal zone.

PubMed

Brandão, Martha L; Braga, Karina M; Luque, José L

2011-10-01

Magellanic penguins (Spheniscus magellanicus) are non-breeding winter visitors to the Brazilian coast. In 2008 and 2010, plastic items and other marine debris were found in the stomachs and intestines of 15% of 175 dead penguins collected in the Lagos Region of the state of Rio de Janeiro. One bird had its stomach perforated by a plastic straw, which may have caused its death. There are few records of penguins ingesting plastic litter, but previous studies have found similar levels of debris ingestion among Magellanic penguins stranded on the Brazilian coast (35.8% of 397 birds). The high incidence of marine debris in this species in Brazil may result at least in part from the predominance of juveniles reaching these waters, as juvenile penguins may have a broader diet than adults. It is unclear to what extent plastic ingestion affects the mortality rate in this species and whether the incidence in stranded birds reflects that in the entire population. The present study addresses the increasing impact of plastic debris on marine life. Copyright © 2011 Elsevier Ltd. All rights reserved.

Creep deformation at crack tips in elastic-viscoplastic solids

NASA Astrophysics Data System (ADS)

Riedel, H.

1981-02-01

THE EVALUATION of crack growth tests under creep conditions must be based on the stress analysis of a cracked body taking into account elastic, plastic and creep deformation. In addition to the well-known analysis of a cracked body creeping in secondary (steady-state) creep, the stress field at the tip of a stationary crack is calculated for primary (strain-hardening) or tertiary (strain-softening) creep of the whole specimen. For the special hardening creep-law considered, a path-independent integral C∗h, can be defined which correlates the near-tip field to the applied load. It is also shown how, after sudden load application, creep strains develop in the initially elastic or, for a higher load level, plastic body. Characteristic times are derived to distinguish between short times when the creep-zones, in which creep strains are concentrated, are still small, and long times when the whole specimen creeps extensively in primary and finally in secondary and tertiary creep. Comparing the creep-zone sizes with the specimen dimensions or comparing the characteristic times with the test duration, one can decide which deformation mechanism prevails in the bulk of the specimen and which load parameter enters into the near-tip stress field and determines crack growth behavior. The governing load parameter is the stress intensity factor K 1 if the bulk of the specimen is predominantly elastic and it is the J-integral in a fully-plastic situation when large creep strains are still confined to a small zone. The C∗h-integral applies if the bulk of the specimen deforms in primary or tertiary creep, and C∗ is the relevant load parameter for predominantly secondary creep of the whole specimen.

A Unified Constitutive Model for Subglacial Till, Part I: The Disturbed State Concept

NASA Astrophysics Data System (ADS)

Jenson, J. W.; Desai, C. S.; Clark, P. U.; Contractor, D. N.; Sane, S. M.; Carlson, A. E.

2006-12-01

Classical plasticity models such as Mohr-Coulomb may not adequately represent the full range of possible motion and failure in tills underlying ice sheets. Such models assume that deformations are initially elastic, and that when a peak or failure stress level is reached the system experiences sudden failure, after which the stress remains constant and the deformations can tend to infinite magnitudes. However, theory suggests that the actual behavior of deforming materials, including granular materials such as glacial till, can involve plastic or irreversible strains almost from the beginning, in which localized zones of microcracking and "failure" can be distributed over the material element. As the loading increases, and with associated plastic and creep deformations, the distributed failure zones coalesce. When the extent of such coalesced zones reaches critical values of stresses and strains, the critical condition (failure) can occur in the till, which would cause associated movements of the ice sheet. Failure or collapse then may occur at much larger strain levels. Classical models (e.g., Mohr-Coulomb) may therefore not be able to fully and realistically characterize deformation behavior and the gradual developments of localized failures tending to the global failure and movements. We present and propose the application of the Disturbed State Concept (DSC), a unified model that incorporates the actual pre- and post-failure behavior, for characterizing the behavior of subglacial tills. In this presentation (Part I), we describe the DSC and propose its application to subglacial till. Part II (Desai et al.) describes our application of the DSC with laboratory testing, model calibration, and validations to evaluate the mechanical properties of two regionally significant Pleistocene tills.

The Glenn A. Fry Award Lecture 2012: Plasticity of the Visual System Following Central Vision Loss

PubMed Central

Chung, Susana T. L.

2013-01-01

Following the onset of central vision loss, most patients develop an eccentric retinal location outside the affected macular region, the preferred retinal locus (PRL), as their new reference for visual tasks. The first goal of this paper is to present behavioral evidence showing the presence of experience-dependent plasticity in people with central vision loss. The evidence includes (1) the presence of oculomotor re-referencing of fixational saccades to the PRL; (2) the characteristics of the shape of the crowding zone (spatial region within which the presence of other objects affects the recognition of a target) at the PRL are more “foveal-like” instead of resembling those of the normal periphery; and (3) the change in the shape of the crowding zone at a para-PRL location that includes a component referenced to the PRL. These findings suggest that there is a shift in the referencing locus of the oculomotor and the sensory visual system from the fovea to the PRL for people with central vision loss, implying that the visual system for these individuals is still plastic and can be modified through experiences. The second goal of the paper is to demonstrate the feasibility of applying perceptual learning, which capitalizes on the presence of plasticity, as a tool to improve functional vision for people with central vision loss. Our finding that visual function could improve with perceptual learning presents an exciting possibility for the development of an alternative rehabilitative strategy for people with central vision loss. PMID:23670125

Surface topography and roughness of high-speed milled AlMn1Cu

NASA Astrophysics Data System (ADS)

Wang, Zhenhua; Yuan, Juntang; Yin, Zengbin; Hu, Xiaoqiu

2016-10-01

The aluminum alloy AlMn1Cu has been broadly applied for functional parts production because of its good properties. But few researches about the machining mechanism and the surface roughness were reported. The high-speed milling experiments are carried out in order to improve the machining quality and reveal the machining mechanism. The typical topography features of machined surface are observed by scan electron microscope(SEM). The results show that the milled surface topography is mainly characterized by the plastic shearing deformation surface and material piling zone. The material flows plastically along the end cutting edge of the flat-end milling tool and meanwhile is extruded by the end cutting edge, resulting in that materials partly adhere to the machined surface and form the material piling zone. As the depth of cut and the feed per tooth increase, the plastic flow of materials is strengthened and the machined surface becomes rougher. However, as the cutting speed increases, the plastic flow of materials is weakened and the milled surface becomes smoother. The cutting parameters (e.g. cutting speed, feed per tooth and depth of cut) influencing the surface roughness are analyzed. It can be concluded that the roughness of the machined surface formed by the end cutting edge is less than that by the cylindrical cutting edge when a cylindrical flat-end mill tool is used for milling. The proposed research provides the typical topography features of machined surface of the anti-rust aluminum alloy AlMn1Cu in high speed milling.

The interaction of fatigue cracks with a residual stress field using thermoelastic stress analysis and synchrotron X-ray diffraction experiments

PubMed Central

Amjad, Khurram; Asquith, David; Sebastian, Christopher M.; Wang, Wei-Chung

2017-01-01

This article presents an experimental study on the fatigue behaviour of cracks emanating from cold-expanded holes utilizing thermoelastic stress analysis (TSA) and synchrotron X-ray diffraction (SXRD) techniques with the aim of resolving the long-standing ambiguity in the literature regarding potential relaxation, or modification, of beneficial compressive residual stresses as a result of fatigue crack propagation. The crack growth rates are found to be substantially lower as the crack tip moved through the residual stress zone induced by cold expansion. The TSA results demonstrated that the crack tip plastic zones were reduced in size by the presence of the residual compressive stresses induced by cold expansion. The crack tip plastic zones were found to be insignificant in size in comparison to the residual stress zone resulting from cold expansion, which implied that they were unlikely to have had a notable impact on the surrounding residual stresses induced by cold expansion. The residual stress distributions measured along the direction of crack growth, using SXRD, showed no signs of any significant stress relaxation or redistribution, which validates the conclusions drawn from the TSA data. Fractographic analysis qualitatively confirmed the influence on crack initiation of the residual stresses induced by the cold expansion. It was found that the application of single compressive overload caused a relaxation, or reduction in the residual stresses, which has wider implications for improving the fatigue life. PMID:29291095

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.

The evolution of rifting process in the tectonic history of the Earth

NASA Technical Reports Server (NTRS)

Milanovsky, E. E.; Nikishin, A. M.

1985-01-01

The continental rifting is the response of the lithosphere to the oriented tension. The distribution of viscosity in the lithosphere plays an essential role during all stages of the rifting. The viscosity is a function of the temperature, the lithostatic pressure, the rock composition, the deformation rate and other factors. The temperature is the most important factor. The vertical section of continental lithosphere of the rift zone may be divided into the following layers: the upper crust, in which brittle deformation prevails; the medialcrust, in which the role of plastic deformation increases; the lower crust, in which plastic deformation prevails; and the uppermost plastic part of the mantle overlapping asthenosphere. The depth of the boundaries in the crust layers are mainly controlled by the temperature.

Fourwing saltbush (Atriplex canescens) seed transfer zones

Treesearch

Stewart C. Sanderson; Durant E. McArthur

2004-01-01

Atriplex canescens (Pursh.) Nutt. is the most widespread species of perennial Atriplex in North America. Throughout its distributional range, A. canescens shows considerable between-population variation. Some of this variation may be due to phenotypic plasticity but most of it appears to be genetic. Mutations,...

Evaluation of warning lights on maintenance of traffic devices and development of possible alternatives : [summary].

DOT National Transportation Integrated Search

2013-01-01

Orange plastic drums are common on Florida roadways, warning motorists and guiding them safely through work zones. The orange color is mandated by the Manual on Uniform Traffic Control Devices, which also requires that drums bear retroreflective whit...

Deformation Microstructures Near Vickers Indentations in SNO2/SI Coated Systems

NASA Astrophysics Data System (ADS)

Daria, G.; Evghenii, H.; Olga, S.; Zinaida, D.; Iana, M.; Victor, Z.

The micromechanical properties (hardness and brittleness) of the hard-on-hard SnO2 / Si-coated system (CS) and their modification depending the on load value has been studied. A nonmonotonic changing of microhardness with load growth was detected. The brittle/plastic behavior of the rigid/hard-on-hard SnO2 / Si CS and its response to concentrated load action explains it.A specific evolution of the indentation-deformed zone vs. load value attributed to the change in the internal stress redistribution between film and substrate was detected. It results in a brittleness indentation size effect (BISE) of the SnO2 / Si CS revealed in this experiment.It was shown that the greater portion of internal stresses under indentation is concentrated in the coating layer at small loads. This fact causes a strong elastic-plastic relaxation in the film and its delamination from substrate. The increase of brittle failure in the indentation-deformed zone with a decrease of indentation load was revealed.

Indentation size effects in single crystal copper as revealed by synchrotron x-ray microdiffraction

NASA Astrophysics Data System (ADS)

Feng, G.; Budiman, A. S.; Nix, W. D.; Tamura, N.; Patel, J. R.

2008-08-01

For a Cu single crystal, we find that indentation hardness increases with decreasing indentation depth, a phenomenon widely observed before and called the indentation size effect (ISE). To understand the underlying mechanism, we measure the lattice rotations in indentations of different sizes using white beam x-ray microdiffraction (μXRD); the indentation-induced lattice rotations are directly measured by the streaking of x-ray Laue spots associated with the indentations. The magnitude of the lattice rotations is found to be independent of indentation size, which is consistent with the basic tenets of the ISE model. Using the μXRD data together with an ISE model, we can estimate the effective radius of the indentation plastic zone, and the estimate is consistent with the value predicted by a finite element analysis. Using these results, an estimate of the average dislocation densities within the plastic zones has been made; the findings are consistent with the ISE arising from a dependence of the dislocation density on the depth of indentation.

Lateral Variations of Interplate Coupling along the Mexican Subduction Interface: Relationships with Long-Term Morphology and Fault Zone Mechanical Properties

NASA Astrophysics Data System (ADS)

Rousset, Baptiste; Lasserre, Cécile; Cubas, Nadaya; Graham, Shannon; Radiguet, Mathilde; DeMets, Charles; Socquet, Anne; Campillo, Michel; Kostoglodov, Vladimir; Cabral-Cano, Enrique; Cotte, Nathalie; Walpersdorf, Andrea

2016-10-01

Although patterns of interseismic strain accumulation above subduction zones are now routinely characterised using geodetic measurements, their physical origin, persistency through time, and relationships to seismic hazard and long-term deformation are still debated. Here, we use GPS and morphological observations from southern Mexico to explore potential mechanical links between variations in inter-SSE (in between slow slip events) coupling along the Mexico subduction zone and the long-term topography of the coastal regions from Guerrero to Oaxaca. Inter-SSE coupling solutions for two different geometries of the subduction interface are derived from an inversion of continuous GPS time series corrected from slow slip events. They reveal strong along-strike variations in the shallow coupling (i.e. at depths down to 25 km), with high-coupling zones (coupling >0.7) alternating with low-coupling zones (coupling <0.3). Coupling below the continent is typically strong (>0.7) and transitions to uncoupled, steady slip at a relatively uniform ˜ 175-km inland from the trench. Along-strike variations in the coast-to-trench distances are strongly correlated with the GPS-derived forearc coupling variations. To explore a mechanical explanation for this correlation, we apply Coulomb wedge theory, constrained by local topographic, bathymetric, and subducting-slab slopes. Critical state areas, i.e. areas where the inner subduction wedge deforms, are spatially correlated with transitions at shallow depth between uncoupled and coupled areas of the subduction interface. Two end-member models are considered to explain the correlation between coast-to-trench distances and along-strike variations in the inter-SSE coupling. The first postulates that the inter-SSE elastic strain is partitioned between slip along the subduction interface and homogeneous plastic permanent deformation of the upper plate. In the second, permanent plastic deformation is postulated to depend on frictional transitions along the subduction plate interface. Based on the location and friction values of the critical state areas identified by our Coulomb wedge analysis, we parameterise frictional transitions in plastic-static models of deformation over several seismic cycles. This predicts strong shear dissipation above frictional transitions on the subduction interface. The comparison of modelled surface displacements over a critical zone at a frictional transition and over a stable area with no internal wedge deformation shows differences of long-term uplift consistent with the observed along-strike variations in the coast-to-trench distances. Our work favours a model in which frictional asperities partly control short-term inter-SSE coupling as measured by geodesy and in which those asperities persist through time.

Modeling of coulpled deformation and permeability evolution during fault reactivation induced by deep underground injection of CO2

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

Cappa, F.; Rutqvist, J.

2010-06-01

The interaction between mechanical deformation and fluid flow in fault zones gives rise to a host of coupled hydromechanical processes fundamental to fault instability, induced seismicity, and associated fluid migration. In this paper, we discuss these coupled processes in general and describe three modeling approaches that have been considered to analyze fluid flow and stress coupling in fault-instability processes. First, fault hydromechanical models were tested to investigate fault behavior using different mechanical modeling approaches, including slip interface and finite-thickness elements with isotropic or anisotropic elasto-plastic constitutive models. The results of this investigation showed that fault hydromechanical behavior can be appropriatelymore » represented with the least complex alternative, using a finite-thickness element and isotropic plasticity. We utilized this pragmatic approach coupled with a strain-permeability model to study hydromechanical effects on fault instability during deep underground injection of CO{sub 2}. We demonstrated how such a modeling approach can be applied to determine the likelihood of fault reactivation and to estimate the associated loss of CO{sub 2} from the injection zone. It is shown that shear-enhanced permeability initiated where the fault intersects the injection zone plays an important role in propagating fault instability and permeability enhancement through the overlying caprock.« less

Numerical simulations of microcrack-related damage and ignition behavior of mild-impacted polymer bonded explosives.

PubMed

Yang, Kun; Wu, Yanqing; Huang, Fenglei

2018-08-15

A physical model is developed to describe the viscoelastic-plastic deformation, cracking damage, and ignition behavior of polymer-bonded explosives (PBXs) under mild impact. This model improves on the viscoelastic-statistical crack mechanical model (Visco-SCRAM) in several respects. (i) The proposed model introduces rate-dependent plasticity into the framework which is more suitable for explosives with relatively high binder content. (ii) Damage evolution is calculated by the generalized Griffith instability criterion with the dominant (most unstable) crack size rather than the averaged crack size over all crack orientations. (iii) The fast burning of cracks following ignition and the effects of gaseous products on crack opening are considered. The predicted uniaxial and triaxial stress-strain responses of PBX9501 sample under dynamic compression loading are presented to illustrate the main features of the materials. For an uncovered cylindrical PBX charge impacted by a flat-nosed rod, the simulated results show that a triangular-shaped dead zone is formed beneath the front of the rod. The cracks in the dead zone are stable due to friction-locked stress state, whereas the cracks near the front edges of dead zone become unstable and turn into hotspots due to high-shear effects. Copyright © 2018 Elsevier B.V. All rights reserved.

Did the Basement-Involved Main Caucasus Thrust Form during the Cenozoic Arabia-Eurasia Collision?

NASA Astrophysics Data System (ADS)

Vasey, D. A.; Cowgill, E.; Niemi, N. A.; Godoladze, T.; Javakhishvili, Z.; Skhirtladze, I.; Boichenko, G.

2017-12-01

The Greater Caucasus Mountains lie between the Black and Caspian Seas at the northern margin of the active Arabia-Eurasia collision zone. The north-dipping Main Caucasus Thrust (MCT) is commonly assumed to be a first-order structure within the range that places Paleozoic crystalline basement to the north over metasedimentary cover of inferred Mesozoic age to the south. Although most workers assume this juxtaposition occurred during Cenozoic growth of the range, the timing of ductile (quartz-plastic) shearing along the MCT remains to be established. Here, we present data to discriminate between two competing models of quartz-plastic deformation along the proposed MCT location at the basement-cover contact. In the first model, quartz-plastic deformation occurred during the Cenozoic Arabia-Eurasia collision, whereas in the second, this deformation took place during an older orogenic event, such as the Paleozoic Variscan orogeny. To test these models, we are combining field observations, microstructural investigations, and thermochronologic analyses on two 10 km-long traverses in the Republic of Georgia, separated by 200 km along strike, across the MCT. Our fieldwork and microstructural analyses along the basement-cover contact document north-dipping zones of high strain that are 100 m thick and show quartz-plastic deformation, top-to-the-south shear sense, and greenschist-facies metamorphism. Zircon (U-Th)/He (ZHe) analyses along the eastern traverse near Stepantsminda yielded latest Miocene ( 7-8 Ma) ages in both the MCT shear zone and 150 m structurally above the MCT. In contrast, along the western traverse near Nakra, a sample 300 m structurally below the MCT yielded an early Oligocene ( 31 Ma) ZHe age. These data require Cenozoic exhumation from temperatures >180° and are compatible with recent ductile shear along the MCT. However, results from biotite and muscovite 40Ar/39Ar analyses in progress are needed to confirm this hypothesis. The MCT appears to have exhumed rocks from crustal depths of at least 6 km since the Oligocene and may be a key first-order structure in the Arabia-Eurasia collision.

Numerical Simulation of Pipeline Deformation Caused by Rockfall Impact

PubMed Central

Liang, Zheng; Han, Chuanjun

2014-01-01

Rockfall impact is one of the fatal hazards in pipeline transportation of oil and gas. The deformation of oil and gas pipeline caused by rockfall impact was investigated using the finite element method in this paper. Pipeline deformations under radial impact, longitudinal inclined impact, transverse inclined impact, and lateral eccentric impact of spherical and cube rockfalls were discussed, respectively. The effects of impact angle and eccentricity on the plastic strain of pipeline were analyzed. The results show that the crater depth on pipeline caused by spherical rockfall impact is deeper than by cube rockfall impact with the same volume. In the inclined impact condition, the maximum plastic strain of crater caused by spherical rockfall impact appears when incidence angle α is 45°. The pipeline is prone to rupture under the cube rockfall impact when α is small. The plastic strain distribution of impact crater is more uneven with the increasing of impact angle. In the eccentric impact condition, plastic strain zone of pipeline decreases with the increasing of eccentricity k. PMID:24959599

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

40 CFR 147.305 - Requirements for all wells.

Code of Federal Regulations, 2013 CFR

2013-07-01

... Section 147.305 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY (CONTINUED) WATER PROGRAMS... (2) A Caliper log. (b) The owner or operator of a new injection well cased with plastic (PVC, ABS... injection zone; and (3) Use cement: (i) Of sufficient quantity and quality to withstand the maximum...

40 CFR 147.305 - Requirements for all wells.

Code of Federal Regulations, 2012 CFR

2012-07-01

... Section 147.305 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY (CONTINUED) WATER PROGRAMS... (2) A Caliper log. (b) The owner or operator of a new injection well cased with plastic (PVC, ABS... injection zone; and (3) Use cement: (i) Of sufficient quantity and quality to withstand the maximum...

40 CFR 147.305 - Requirements for all wells.

Code of Federal Regulations, 2014 CFR

2014-07-01

... Section 147.305 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY (CONTINUED) WATER PROGRAMS... (2) A Caliper log. (b) The owner or operator of a new injection well cased with plastic (PVC, ABS... injection zone; and (3) Use cement: (i) Of sufficient quantity and quality to withstand the maximum...

Plastification of polymers in twin-screw-extruders: New visualization technic using high-speed imaging

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

Knieper, A., E-mail: Alexander.Knieper@lbf.fraunhofer.de, E-mail: Christian.Beinert@lbf.fraunhofer.de; Beinert, C., E-mail: Alexander.Knieper@lbf.fraunhofer.de, E-mail: Christian.Beinert@lbf.fraunhofer.de

The initial melting of the first granules through plastic energy dissipation (PED) at the beginning of the melting zone, in the co-rotating twin-screw extruder is visualized in this work. The visualization was created through the use of a high speed camera in the cross section of the melting zone. The parameters screw speed, granule-temperature, temperature-profile, type of polymer and back pressure were examined. It was shown that the screw speed and the temperature-profile have significant influence on the rate of initial melting.

Transform push, oblique subduction resistance, and intraplate stress of the Juan de Fuca plate

USGS Publications Warehouse

Wang, K.; He, J.; Davis, E.E.

1997-01-01

The Juan de Fuca plate is a small oceanic plate between the Pacific and North America plates. In the southernmost region, referred to as the Gorda deformation zone, the maximum compressive stress a, constrained by earthquake focal mechanisms is N-S. Off Oregon, and possibly off Washington, NW trending left-lateral faults cutting the Juan de Fuca plate indicate a a, in a NE-SW to E-W direction. The magnitude of differential stress increases from north to south; this is inferred from the plastic yielding and distribution of earthquakes throughout the Gorda deformation zone. To understand how tectonic forces determine the stress field of the Juan de Fuca plate, we have modeled the intraplate stress using both elastic and elastic-perfectly plastic plane-stress finite element models. We conclude that the right-lateral shear motion of the Pacific and North America plates is primarily responsible for the stress pattern of the Juan de Fuca plate. The most important roles are played by a compressional force normal to the Mendocino transform fault, a result of the northward push by the Pacific plate and a horizontal resistance operating against the northward, or margin-parallel, component of oblique subduction. Margin-parallel subduction resistance results in large N-S compression in the Gorda deformation zone because the force is integrated over the full length of the Cascadia subduction zone. The Mendocino transform fault serves as a strong buttress that is very weak in shear but capable of transmitting large strike-normal compressive stresses. Internal failure of the Gorda deformation zone potentially places limits on the magnitude of the fault-normal stresses being transmitted and correspondingly on the magnitude of strike-parallel subduction resistance. Transform faults and oblique subduction zones in other parts of the world can be expected to transmit and create stresses in the same manner. Copyright 1997 by the American Geophysical Union.

Plastic deformation behaviors of Ni- and Zr-based bulk metallic glasses subjected to nanoindentation

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

Weizhong, Liang, E-mail: wzliang1966@126.com; Zhiliang, Ning; Zhenqian, Dang

2013-12-15

Plastic deformation behaviors of Ni{sub 42}Ti{sub 20}Zr{sub 21.5}Al{sub 8}Cu{sub 5}Si{sub 3.5} and Zr{sub 51}Ti{sub 5}Ni{sub 10}Cu{sub 25}Al{sub 9} bulk metallic glasses at room temperature were studied by nanoindentation testing and atomic force microscopy under equivalent indentation experimental conditions. The different chemical composition of these two bulk metallic glasses produced variant tendencies for displacement serrated flow to occur during the loading process. The nanoindentation strain rate was calculated as a function of indentation displacement in order to verify the occurrence of displacement serrated flow at different loading rates. Atomic force microscopy revealed decreasing numbers of discrete shear bands around the indentationmore » sites as loading rates increased from 0.025 to 2.5 mNs{sup −1}. Variations in plastic deformation behaviors between Ni and Zr-based glasses materials can be explained by the different metastable microstructures and thermal stabilities of the two materials. The mechanism governing plastic deformation of these metallic glasses was analyzed in terms of an established model of the shear transformation zone. - Highlights: • Plastic deformation of Ni- and Zr-based BMG is studied under identical conditions • Zr-based BMG undergoes a greater extent of plastic deformation than Ni-based BMG • Nanoindentation strain rate is studied to clarify variation in plastic deformation • Metastable microstructure, thermal stability affect BMG plastic deformation.« less

Evidence that the Great Pacific Garbage Patch is rapidly accumulating plastic.

PubMed

Lebreton, L; Slat, B; Ferrari, F; Sainte-Rose, B; Aitken, J; Marthouse, R; Hajbane, S; Cunsolo, S; Schwarz, A; Levivier, A; Noble, K; Debeljak, P; Maral, H; Schoeneich-Argent, R; Brambini, R; Reisser, J

2018-03-22

Ocean plastic can persist in sea surface waters, eventually accumulating in remote areas of the world's oceans. Here we characterise and quantify a major ocean plastic accumulation zone formed in subtropical waters between California and Hawaii: The Great Pacific Garbage Patch (GPGP). Our model, calibrated with data from multi-vessel and aircraft surveys, predicted at least 79 (45-129) thousand tonnes of ocean plastic are floating inside an area of 1.6 million km 2 ; a figure four to sixteen times higher than previously reported. We explain this difference through the use of more robust methods to quantify larger debris. Over three-quarters of the GPGP mass was carried by debris larger than 5 cm and at least 46% was comprised of fishing nets. Microplastics accounted for 8% of the total mass but 94% of the estimated 1.8 (1.1-3.6) trillion pieces floating in the area. Plastic collected during our study has specific characteristics such as small surface-to-volume ratio, indicating that only certain types of debris have the capacity to persist and accumulate at the surface of the GPGP. Finally, our results suggest that ocean plastic pollution within the GPGP is increasing exponentially and at a faster rate than in surrounding waters.

Generation of sonic power during welding

NASA Technical Reports Server (NTRS)

Mc Campbell, W. M.

1969-01-01

Generation of intense sonic and ultrasonic power in the weld zone, close to the puddle, reduces the porosity and refinement of the grain. The ac induction brazing power supply is modified with long cables for deliberate addition of resistance to that circuit. The concept is extensible to the molding of metals and plastics.

78 FR 23220 - Foreign-Trade Zone (FTZ) 230-Piedmont Triad Area, North Carolina; Notification of Proposed...

Federal Register 2010, 2011, 2012, 2013, 2014

2013-04-18

...-backed paperboard and to laminate plastic film (the laminating activity is not ``production'' activity...--Piedmont Triad Area, North Carolina; Notification of Proposed Production Activity; Oracle Flexible..., grantee of FTZ 230, submitted a notification of proposed production activity on behalf of Oracle Flexible...

40 CFR 147.2104 - Requirements for all wells.

Code of Federal Regulations, 2012 CFR

2012-07-01

... Section 147.2104 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY (CONTINUED) WATER PROGRAMS... analysis log; or (2) A caliper log. (b) The owner or operator of a new injection well cased with plastic... injection zone; and (3) Use cement: (i) Of sufficient quantity and quality to withstand the maximum...

40 CFR 147.2104 - Requirements for all wells.

Code of Federal Regulations, 2013 CFR

2013-07-01

... Section 147.2104 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY (CONTINUED) WATER PROGRAMS... analysis log; or (2) A caliper log. (b) The owner or operator of a new injection well cased with plastic... injection zone; and (3) Use cement: (i) Of sufficient quantity and quality to withstand the maximum...

40 CFR 147.2104 - Requirements for all wells.

Code of Federal Regulations, 2014 CFR

2014-07-01

... Section 147.2104 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY (CONTINUED) WATER PROGRAMS... analysis log; or (2) A caliper log. (b) The owner or operator of a new injection well cased with plastic... injection zone; and (3) Use cement: (i) Of sufficient quantity and quality to withstand the maximum...

Evidence for Seismic and Aseismic Slip along a Foreland Thrust Fault, Southern Appalachians

NASA Astrophysics Data System (ADS)

Newman, J.; Wells, R. K.; Holyoke, C. W.; Wojtal, S. F.

2013-12-01

Studies of deformation along ancient thrust faults form the basis for much of our fundamental understanding of fault and shear zone processes. These classic studies interpreted meso- and microstructures as formed during aseismic creep. Recent experimental studies, and studies of naturally deformed rocks in seismically active regions, reveal similar microstructures to those observed locally in a carbonate foreland thrust from the southern Appalachians, suggesting that this thrust fault preserves evidence of both seismic and aseismic deformation. The Copper Creek thrust, TN, accommodated 15-20 km displacement, at depths of 4-6 km, as estimated from balanced cross-sections. At the Diggs Gap exposure of the Copper Creek thrust, an approximately 2 cm thick, vein-like shear zone separates shale layers in the hanging wall and footwall. The shear zone is composed of anastomosing layers of ultrafine-grained calcite and/or shale as well as aggregate clasts of ultrafine-grained calcite or shale. The boundary between the shear zone and the hanging wall is sharp, with slickensides along the boundary, parallel to the shear zone movement direction. A 350 μm-thick layer of ultrafine-grained calcite separates the shear zone and the footwall. Fault parallel and perpendicular calcite veins are common in the footwall and increase in density towards the shear zone. Microstructures within the vein-like shear zone that are similar to those observed in experimental studies of unstable slip include: ultrafine-grained calcite (~0.34 μm), nano-aggregate clasts (100-300 nm), injection structures, and vein-wrapped and matrix-wrapped clasts. Not all structures within the shear zone and ultrafine-grained calcite layer suggest seismic slip. Within the footwall veins and calcite aggregate clasts within the shear zone, pores at twin-twin intersections suggest plasticity-induced fracturing as the main mechanism for grain size reduction. Interpenetrating grain boundaries in ultrafine-grained calcite and a lack of a lattice preferred orientation suggest ultrafine-grained calcite deformed by diffusion creep accommodated grain boundary sliding. These structures suggest a strain-rate between 10-15 - 10-11 s-1, using calcite flow laws at temperatures 150-250 °C. Microstructures suggest both seismic and aseismic slip along this ancient fault zone. During periods of aseismic slip, deformation is accommodated by plasticity-induced fracturing and diffusion creep. Calcite veins suggest an increase in pore-fluid pressure, contributing to fluidized and unstable flow, but also providing the calcite that deformed by diffusion creep during aseismic creep.

Variation in life-history traits and their plasticities to elevational transplantation among seed families suggests potential for adaptative evolution of 15 tropical plant species to climate change.

PubMed

Ensslin, Andreas; Fischer, Markus

2015-08-01

• Because not all plant species will be able to move in response to global warming, adaptive evolution matters largely for plant persistence. As prerequisites for adaptive evolution, genetic variation in and selection on phenotypic traits are needed, but these aspects have not been studied in tropical species. We studied how plants respond to transplantation to different elevations on Mt. Kilimanjaro, Tanzania, and whether there is quantitative genetic (among-seed family) variation in and selection on life-history traits and their phenotypic plasticity to the different environments.• We reciprocally transplanted seed families of 15 common tropical, herbaceous species of the montane and savanna vegetation zone at Mt. Kilimanjaro to a watered experimental garden in the montane (1450 m) and in the savanna (880 m) zone at the mountain's slope and measured performance, reproductive, and phenological traits.• Plants generally performed worse in the savanna garden, indicating that the savanna climate was more stressful and thus that plants may suffer from future climate warming. We found significant quantitative genetic variation in all measured performance and reproductive traits in both gardens and for several measures of phenotypic plasticity in response to elevational transplantation. Moreover, we found positive selection on traits at low and intermediate trait values levelling to neutral or negative selection at high values.• We conclude that common plants at Mt. Kilimanjaro express quantitative genetic variation in fitness-relevant traits and in their plasticities, suggesting potential to adapt evolutionarily to future climate warming and increased temperature variability. © 2015 Botanical Society of America, Inc.

Thermography detection on the fatigue damage

NASA Astrophysics Data System (ADS)

Yang, Bing

It has always been a great temptation in finding new methods to in-situ "watch" the material fatigue-damage processes so that in-time reparations will be possible, and failures or losses can be minimized to the maximum extent. Realizing that temperature patterns may serve as fingerprints for stress-strain behaviors of materials, a state-of-art infrared (IR) thermography camera has been used to "watch" the temperature evolutions of both crystalline and amorphous materials "cycle by cycle" during fatigue experiments in the current research. The two-dimensional (2D) thermography technique records the surface-temperature evolutions of materials. Since all plastic deformations are related to heat dissipations, thermography provides an innovative method to in-situ monitor the heat-evolution processes, including plastic-deformation, mechanical-damage, and phase-transformation characteristics. With the understanding of the temperature evolutions during fatigue, thermography could provide the direct information and evidence of the stress-strain distribution, crack initiation and propagation, shear-band growth, and plastic-zone evolution, which will open up wide applications in studying the structural integrity of engineering components in service. In the current research, theoretical models combining thermodynamics and heat-conduction theory have been developed. Key issues in fatigue, such as in-situ stress-strain states, cyclic softening and hardening observations, and fatigue-life predictions, have been resolved by simply monitoring the specimen-temperature variation during fatigue. Furthermore, in-situ visulizations as well as qualitative and quantitative analyses of fatigue-damage processes, such as Luders-band evolutions, crack propagation, plastic zones, and final fracture, have been performed by thermography. As a method requiring no special sample preparation or surface contact by sensors, thermography provides an innovative and convenient method to in-situ monitor and analyze the mechanical-damage processes of materials and components.

Neural Stem Cells: Implications for the Conventional Radiotherapy of Central Nervous System Malignancies

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

Barani, Igor J.; Benedict, Stanley H.; Lin, Peck-Sun

Advances in basic neuroscience related to neural stem cells and their malignant counterparts are challenging traditional models of central nervous system tumorigenesis and intrinsic brain repair. Neurogenesis persists into adulthood predominantly in two neurogenic centers: subventricular zone and subgranular zone. Subventricular zone is situated adjacent to lateral ventricles and subgranular zone is confined to the dentate gyrus of the hippocampus. Neural stem cells not only self-renew and differentiate along multiple lineages in these regions, but also contribute to intrinsic brain plasticity and repair. Ionizing radiation can depopulate these exquisitely sensitive regions directly or impair in situ neurogenesis by indirect, dose-dependentmore » and inflammation-mediated mechanisms, even at doses <2 Gy. This review discusses the fundamental neural stem cell concepts within the framework of cumulative clinical experience with the treatment of central nervous system malignancies using conventional radiotherapy.« less

Modeling aluminum-lithium alloy welding characteristics

NASA Technical Reports Server (NTRS)

Bernstein, Edward L.

1996-01-01

The purpose of this project was to develop a finite element model of the heat-affected zone in the vicinity of a weld line on a plate in order to determine an accurate plastic strain history. The resulting plastic strain increments calculated by the finite element program were then to be used to calculate the measure of damage D. It was hoped to determine the effects of varying welding parameters, such as beam power, efficiency, and weld speed, and the effect of different material properties on the occurrence of microfissuring. The results were to be compared first to the previous analysis of Inconel 718, and then extended to aluminum 2195.

Failure Mechanisms of Thermomechanically Loaded SnAgCu/Plastic Core Solder Ball Composite Joints in Low-Temperature Co-Fired Ceramic/Printed Wiring Board Assemblies

NASA Astrophysics Data System (ADS)

Nousiainen, O.; Putaala, J.; Kangasvieri, T.; Rautioaho, R.; Vähäkangas, J.

2007-03-01

The thermal fatigue endurance of completely lead-free 95.5Sn4Ag0.7Cu/plastic core solder ball (PCSB) composite joint structures in low-temperature Co-fired ceramic/printed wiring board (LTCC/PWB) assemblies was investigated using thermal cycling tests over the temperature ranges of -40°C 125°C and 0°C 100°C. Two separate creep/fatigue failures initiated and propagated in the joints during the tests: (1) a crack along the intermetallic compound (IMC)/solder interface on the LTCC side of the joint, which formed at the high-temperature extremes; and (2) a crack in the solder near the LTCC solder land, which formed at the low-temperature extremes. Moreover, localized recrystallization was detected at the outer edge of the joints that were tested in the harsh (-40°C 125°C) test conditions. The failure mechanism was creep/fatigue-induced mixed intergranular and transgranular cracking in the recrystallized zone, but it was dominated by transgranular thermal fatigue failure beyond the recrystallized zone. The change in the failure mechanism increased the rate of crack growth. When the lower temperature extreme was raised from -40°C to 0°C, no recrystallized zone was detected and the failure was due to intergranular cracks.

Detailed physico-chemical characterization of microplastics from North Atlantic Gyre

NASA Astrophysics Data System (ADS)

ter Halle, A.; Ladirat, L.; Gendre, X.; Goudouneche, D.; Pusineri, C.; Routaboul, C.; Tenailleau, C.; Duployer, B.; Perez, E.

2016-02-01

More than 260 million tonnes of plastic are used each year. Based on population density and economic status of costal countries the mass of land based plastic waste entering the ocean was recently estimated between 4.8 to 12.7 million metric tons per year1. Most striking is the estimation for 2025 that this amount will increase by an order of magnitude if waste management infrastructures are not improved. Plastic debris is abundant and widespread in the marine habitat. Marine plastic pollution has been recently recognized as a global environmental threat2. There is still a need for detailed research in terms of estimating the global scale of plastic inputs, their fate in the environment as well as the biological responses to plastic exposure in a variety of marine organisms. In this context, the present study aimed at giving a detailed physico-chemical characterization of the microplastics collected at the surface of the North Atlantic accumulation zone. A detailed description of the plastics is given in terms of size, width, density and weight together with a microscopic and infrared spectroscopy characterization. In this study, also we introduce a new fragmentation mechanism of the microplastics based on the physico-chemical data collected. This approach will be helpful for oceanographic modelling. The results will be also very useful to better understand the biological response to the plastic in terms of transfer of chemical in case of ingestion or to better understand the formation and development of the plastisphere. 1 Jambeck, J. R.; Geyer, R.; Wilcox, C.; Siegler, T. R.; Perryman, M.; Andrady, A.; Narayan, R.; Lavender Law, K., Plastic waste inputs from land into the ocean 2 Moore, C. J., Synthetic polymers in the marine environment: A rapidly increasing, long-term threat. Environmental Research 2008, 108, (2), 131-139.

77 FR 39209 - Foreign-Trade Zone 74-Baltimore, MD, Notification of Proposed Production Activity, J.D. Neuhaus...

Federal Register 2010, 2011, 2012, 2013, 2014

2012-07-02

... from abroad include: air and hydraulic powered hoist and trolley subassemblies and parts, cranes/ winches and related parts, hoist chain, lubricating oils, plastic air hoses, rubber gaskets and o-rings, fasteners, springs, air filters, air pressure regulators, valves and related parts, and bearings and bearing...

77 FR 11401 - Marine Sanitation Devices (MSDs): No Discharge Zone (NDZ) for California State Marine Waters

Federal Register 2010, 2011, 2012, 2013, 2014

2012-02-27

... Plastic Pollution Research and Control Act of 1987, and the Ocean Dumping Act, address pollution within... related legislation in 2003-2005 to limit pollution from large passenger and large oceangoing vessels. In...; (3) to further regulate landside sources of pollution; (4) to improve inspection and testing...

Characterization of Plastic flow and Resulting Micro-Textures in a Friction Stir Weld

NASA Technical Reports Server (NTRS)

Schneider, J. A.; Nunes, A. C., Jr.

2003-01-01

The mechanically affected zone of a friction stir weld (FSW) cross section exhibits two distinct microstructural regions, possibly the residues of two distinct currents of metal in the FSW flow process. In this study the respective textures of these microstructural regions are investigated using orientation image mapping (OIM).

Special Features of Strain Localization and Nanodipoles of Partial Disclinations in the Region of Elastic Distortions

NASA Astrophysics Data System (ADS)

Tyumentsev, A. N.; Ditenberg, I. A.; Sukhanov, I. I.

2018-02-01

In the zones of strain localization in the region of elastic distortions and nanodipoles of partial disclinations representing the defects of elastically deformed medium, a theoretical analysis of the elastically stressed state and the energy of these defects, including the cases of their transformation into more complex ensembles of interrelated disclinations, is performed. Using the analytical results, the mechanisms of strain localization are discussed in the stages of nucleation and propagation of the bands of elastic and plastic strain localization formed in these zones (including the cases of nanocrystalline structure formation).

Ecological plasticity of Trichoderma fungi in leached chernozem

NASA Astrophysics Data System (ADS)

Svistova, I. D.; Senchakova, T. Yu.

2010-03-01

The autecological properties of Trichoderma fungi ecotypes isolated from the leached chernozem of the forest-steppe zone of the European part of Russia have been studied. We were the first who carried out the complex study of the synecological relations of micromycetes of such kinds in a system including the soil, microbial community, and plants, i.e., their relations with soil saprotrophic fungi, bacteria, actinomycetes, plants, and pathogenic fungi. It was shown that the ecological plasticity of the Trichoderma genus in the soil of this zone is determined by its growth rate, the optimum pH and temperature, the biosynthesis of extracellular hydrolytic enzymes, the biological action of mycotoxins, and the ability for parasitism. The efficiency of the introduction of Trichoderma species typical and atypical for the leached chernozem into this soil and their influence on the structure of the microbial community were evaluated. The T. pseudokoningii ecotype, which produces cellulolytic enzymes, is very promising for industrial biotechnology, and the T. harzianum ecotype can be used in soil biotechnology for the biocontrol of chernozem. The addition of a commercial trichodermin preparation into the chernozem damages the structure of its microbial community.

Modeling of plasticity and fracture of metals at shock loading

NASA Astrophysics Data System (ADS)

Mayer, A. E.; Khishchenko, K. V.; Levashov, P. R.; Mayer, P. N.

2013-05-01

In this paper, we present a model of dislocation plasticity and fracture of metals, which in combination with the wide-range equation of state and the continuum mechanics equations is a necessary component for simulation of the shock-wave loading. We take into account immobilization of dislocations and nucleation of micro-voids in weakened zones of substance; this is distinguished feature of the present version of the model. Accounting of the dislocations immobilization provides a better description of the unloading wave structure, while the detailed consideration of processes in the weakened zones expands the domain of applicability of fracture model to higher strain rates. We compare our results with the experimental data for the shock loading of aluminum, copper, and nickel samples; the comparison indicates satisfactory description of the elastic precursor, unloading wave, and spall pulse. Using the model, we investigate intently the early stage of the shock formation in solids; it is found out that the elastic precursor is formed even for a strong shock wave, and initially the precursor has very large amplitude and propagation velocity.

Equilibrium stability of a cylindrical body subject to the internal structure of the material and inelastic behaviour of the completely compressed matrix

NASA Astrophysics Data System (ADS)

Gotsev, D. V.; Perunov, N. S.; Sviridova, E. N.

2018-03-01

The mathematical model describing the stress-strain state of a cylindrical body under the uniform radial compression effect is constructed. The model of the material is the porous medium model. The compressed skeleton of the porous medium possesses hardening elastic-plastic properties. Deforming of the porous medium under the specified compressive loads is divided into two stages: elastic deforming of the porous medium and further elastic-plastic deforming of the material with completely compressed matrix. The analytical relations that define the fields of stress and displacement at each stage of the deforming are obtained. The influence of the porosity and other physical, mechanical and geometric parameters of the construction on the size of the plastic zone is evaluated. The question of the ground state equilibrium instability is investigated within the framework of the three-dimensional linearized relationships of the stability theory of deformed bodies.

Modeling marine surface microplastic transport to assess optimal removal locations

NASA Astrophysics Data System (ADS)

Sherman, Peter; van Sebille, Erik

2016-01-01

Marine plastic pollution is an ever-increasing problem that demands immediate mitigation and reduction plans. Here, a model based on satellite-tracked buoy observations and scaled to a large data set of observations on microplastic from surface trawls was used to simulate the transport of plastics floating on the ocean surface from 2015 to 2025, with the goal to assess the optimal marine microplastic removal locations for two scenarios: removing the most surface microplastic and reducing the impact on ecosystems, using plankton growth as a proxy. The simulations show that the optimal removal locations are primarily located off the coast of China and in the Indonesian Archipelago for both scenarios. Our estimates show that 31% of the modeled microplastic mass can be removed by 2025 using 29 plastic collectors operating at a 45% capture efficiency from these locations, compared to only 17% when the 29 plastic collectors are moored in the North Pacific garbage patch, between Hawaii and California. The overlap of ocean surface microplastics and phytoplankton growth can be reduced by 46% at our proposed locations, while sinks in the North Pacific can only reduce the overlap by 14%. These results are an indication that oceanic plastic removal might be more effective in removing a greater microplastic mass and in reducing potential harm to marine life when closer to shore than inside the plastic accumulation zones in the centers of the gyres.

Sinuous Flow in Cutting of Metals

NASA Astrophysics Data System (ADS)

Yeung, Ho; Viswanathan, Koushik; Udupa, Anirudh; Mahato, Anirban; Chandrasekar, Srinivasan

2017-11-01

Using in situ high-speed imaging, we unveil details of a highly unsteady plastic flow mode in the cutting of annealed and highly strain-hardening metals. This mesoscopic flow mode, termed sinuous flow, is characterized by repeated material folding, large rotation, and energy dissipation. Sinuous flow effects a very large shape transformation, with local strains of ten or more, and results in a characteristic mushroomlike surface morphology that is quite distinct from the well-known morphologies of metal-cutting chips. Importantly, the attributes of this unsteady flow are also fundamentally different from other well-established unsteady plastic flows in large-strain deformation, like adiabatic shear bands. The nucleation and development of sinuous flow, its dependence on material properties, and its manifestation across material systems are demonstrated. Plastic buckling and grain-scale heterogeneity are found to play key roles in triggering this flow at surfaces. Implications for modeling and understanding flow stability in large-strain plastic deformation, surface quality, and preparation of near-strain-free surfaces by cutting are discussed. The results point to the inadequacy of the widely used shear-zone models, even for ductile metals.

Multiple deformation mechanisms operating at seismogenic depths: Tectonic pseudotachylyte and associated deformation from the central Sierra Nevada, California

NASA Astrophysics Data System (ADS)

Prante, M. R.; Evans, J. P.

2012-12-01

Description and identification of fault-related deformation products that are diagnostic of seismic slip have implications for the energy budget of earthquakes, fault strength, and fault-rock assemblages. We describe tectonic pseduotachylyte, cataclastic rocks, crystal-plastic deformation, and hydrothermal alteration form faults exhumed from seismogenic depths in the Volcanic Lakes area, in northern Sequoia and Kings Canyon National Park, CA, USA. Fault rock protoliths include Mesozoic granite and granodiorite plutonic and limited metasedimentary and metavolcanic rocks. These plutonic and metamorphic rocks are cross-cut by the E-W striking, steeply dipping, left-lateral strike-slip Granite Pass (GPF) and Glacier Lakes faults (GLF). Cross-cutting relationships and microstructural data suggest that the GPF is the oldest fault in the area and preserves evidence for coeval brittle and plastic crystal deformation, and hydrothermal fluid-flow. Tectonic pseudotachylyte from the area has been dated using the 40Ar/39Ar method at 76.6 ± 0.3 Ma; when placed into a thermochronologic framework for the plutonic host rock it can be inferred that the pseudotachylyte formed at depths between 2.4-6.0 km with ambient temperatures between 110-160°C. Exceptionally well preserved tectonic pseudotachylyte from the GLF and GPF contain evidence for a frictional melt origin including: 1) plagioclase spherulites and microlites, 2) injection vein morphology, 3) amygdules, 4) viscous flow banding and folds, and 5) embayed and corroded clasts. Pseudotachylyte from the GPF and GLF is associated with brittle and plastic deformation in the damage zone of the faults. Evidence for plastic deformation includes undulose extinction, deformation lamellae, subgrain development, and grain boundary bulging in quartz; and limited undulose extinction in feldspar. Additionally, abundant hydrothermal alteration and mineralization has been documented in the GPF and GLF fault zones, including, chlorite pseudomorphs after biotite and alteration of mafic phases to epidote, sericite and calcite alteration of albite, and calcite and chlorite filled veins. Cross-cutting calcite veins contain fine-grained calcite with abundant twins up to 20 μm-thick. Multiple pseudotachylyte injection veins and reworked pseudotachylyte in cataclastic rock suggest multiple earthquakes along the GPF and GLF at depths favorable to pseudotachylyte formation. Abundant hydrothermal alteration and cross-cutting calcite veins with thick (> 1 μm) twins is consistent with ambient temperatures between 170 and 200°C. These temperatures are generally consistent with the reported ambient temperature conditions during pseudotachylyte formation. Crystal-plastic deformation of quartz and feldspar in the GPF and GLF zones is consistent with deformation at temperatures between 200-400°C. Frictional melt and associated brittle and plastic deformation, and fluid alteration are presumed to have occurred at similar temperature conditions and may be coeval. These results have important implication for understanding energy sinks associated with seismic slip and the conditions of tectonic pseudotachylyte formation.

Strain softening along the MCT zone from the Sikkim Himalaya: Relative roles of Quartz and Micas

NASA Astrophysics Data System (ADS)

Bhattacharyya, Kathakali; Mitra, Gautam

2011-06-01

In the Darjeeling - Sikkim Himalaya, two distinct faults form the Main Central thrust (MCT), the structurally higher MCT1 and the lower MCT2; each has accommodated translation greater than 100 km. The lower MCT2 places Greater Himalayan amphibolite grade Paro-Lingtse gneiss over Lesser Himalayan greenschist grade Daling metapelites. The MCT2 is folded by the underlying Lesser Himalayan duplex and is exposed at different structural positions of the fold. At Pelling, the MCT2 zone is exposed as a ˜373 m thick NW dipping fault zone that exposes ˜19 m of hanging wall mylonitized Lingtse gneiss. The Lingtse protolith shows evidence of amphibolite grade plastic deformation features in quartz and feldspar. Within the hanging wall mylonite zone (HWMZ), quartz and feldspar have undergone grain-size reduction by different deformation mechanisms and feldspars are sericitized suggesting the presence of fluids during deformation. We estimate a temperature of ˜300 °C within the fault zone during fluid-assisted retrogression and deformation. Reaction softening of feldspars produced a large proportion of intrinsically weak matrix. This, in combination with development of a strong foliation defined by parallel mica grains, resulted in strain softening along the MCT2 zone, and concentrated the deformation along a thin zone or zones.

A comprehensive analysis of Helicobacter pylori plasticity zones reveals that they are integrating conjugative elements with intermediate integration specificity.

PubMed

Fischer, Wolfgang; Breithaupt, Ute; Kern, Beate; Smith, Stella I; Spicher, Carolin; Haas, Rainer

2014-04-27

The human gastric pathogen Helicobacter pylori is a paradigm for chronic bacterial infections. Its persistence in the stomach mucosa is facilitated by several mechanisms of immune evasion and immune modulation, but also by an unusual genetic variability which might account for the capability to adapt to changing environmental conditions during long-term colonization. This variability is reflected by the fact that almost each infected individual is colonized by a genetically unique strain. Strain-specific genes are dispersed throughout the genome, but clusters of genes organized as genomic islands may also collectively be present or absent. We have comparatively analysed such clusters, which are commonly termed plasticity zones, in a high number of H. pylori strains of varying geographical origin. We show that these regions contain fixed gene sets, rather than being true regions of genome plasticity, but two different types and several subtypes with partly diverging gene content can be distinguished. Their genetic diversity is incongruent with variations in the rest of the genome, suggesting that they are subject to horizontal gene transfer within H. pylori populations. We identified 40 distinct integration sites in 45 genome sequences, with a conserved heptanucleotide motif that seems to be the minimal requirement for integration. The significant number of possible integration sites, together with the requirement for a short conserved integration motif and the high level of gene conservation, indicates that these elements are best described as integrating conjugative elements (ICEs) with an intermediate integration site specificity.

Cyclic Stable-Unstable Slip Preserved along an Appalachian Fault

NASA Astrophysics Data System (ADS)

Wells, R. K.; Newman, J.; Holyoke, C. W., III; Wojtal, S. F.

2017-12-01

The inactive Copper Creek thrust, southern Appalachians, TN, preserves evidence suggesting cyclic aseismic and unstable slip. The Copper Creek thrust is a low-temperature (4-6 km burial depth) foreland thrust with an estimated net slip of 15-20 km. Immediately below the 2 cm thick calcite-shale fault zone, the footwall is composed of shale with cross-cutting calcite veins and is separated from the fault zone by a 300 µm thick layered calcite vein. Optical and electron microscopy indicates that this complex vein layer experienced grain size reduction by plasticity-induced fracturing followed by aseismic diffusion creep. The fault zone calcite exhibits interpenetrating grain boundaries and four-grain junctions suggesting diffusion creep, but also contains nanoscale grains (7 nm), vesicular calcite, and partially-coated clasts indicating unstable, possibly seismic, slip. Well-preserved clasts of deformed calcite vein layer material within the fault zone indicate repeated cycle(s) of aseismic diffusion creep. In addition, nanoscale calcite grains, 30 nm, with straight grain boundaries that form triple junctions, may represent earlier nanoscale grains formed during unstable slip that have experienced grain growth during periods of aseismic creep. Based on the spatial and temporal relations of these preserved microstructures, we propose a sequence of deformation processes consistent with cyclic episodes of unstable slip separated by intervals of aseismic creep. Formation of calcite-filled veins is followed by grain size reduction in vein calcite by plasticity-induced fracturing and aseismic grain-size sensitive diffusion creep deformation in fine-grained calcite. During aseismic creep, the combination of grain growth, resulting in fault strengthening, and an increase in pore fluid pressure, reducing the effective fault strength, leads to new fractures and/or an unstable slip event. During unstable slip, nanograins and vesicular calcite form as a result of thermal decomposition and coated clasts form as a result of fluidization of the fault zone, and are then incorporated within ductilely deforming calcite during a new interval of aseismic creep.

Distribution of surface plastic debris in the eastern Pacific Ocean from an 11-year data set.

PubMed

Law, Kara Lavender; Morét-Ferguson, Skye E; Goodwin, Deborah S; Zettler, Erik R; Deforce, Emelia; Kukulka, Tobias; Proskurowski, Giora

2014-05-06

We present an extensive survey of floating plastic debris in the eastern North and South Pacific Oceans from more than 2500 plankton net tows conducted between 2001 and 2012. From these data we defined an accumulation zone (25 to 41 °N, 130 to 180 °W) in the North Pacific subtropical gyre that closely corresponds to centers of accumulation resulting from the convergence of ocean surface currents predicted by several oceanographic numerical models. Maximum plastic concentrations from individual surface net tows exceeded 10(6) pieces km(-2), with concentrations decreasing with increasing distance from the predicted center of accumulation. Outside the North Pacific subtropical gyre the median plastic concentration was 0 pieces km(-2). We were unable to detect a robust temporal trend in the data set, perhaps because of confounded spatial and temporal variability. Large spatiotemporal variability in plastic concentration causes order of magnitude differences in summary statistics calculated over short time periods or in limited geographic areas. Utilizing all available plankton net data collected in the eastern Pacific Ocean (17.4 °S to 61.0 °N; 85.0 to 180.0 °W) since 1999, we estimated a minimum of 21,290 t of floating microplastic.

Finite element simulation of the T-shaped ECAP processing of round samples

NASA Astrophysics Data System (ADS)

Shaban Ghazani, Mehdi; Fardi-Ilkhchy, Ali; Binesh, Behzad

2018-05-01

Grain refinement is the only mechanism that increases the yield strength and toughness of the materials simultaneously. Severe plastic deformation is one of the promising methods to refine the microstructure of materials. Among different severe plastic deformation processes, the T-shaped equal channel angular pressing (T-ECAP) is a relatively new technique. In the present study, finite element analysis was conducted to evaluate the deformation behavior of metals during T-ECAP process. The study was focused mainly on flow characteristics, plastic strain distribution and its homogeneity, damage development, and pressing force which are among the most important factors governing the sound and successful processing of nanostructured materials by severe plastic deformation techniques. The results showed that plastic strain is localized in the bottom side of sample and uniform deformation cannot be possible using T-ECAP processing. Friction coefficient between sample and die channel wall has a little effect on strain distributions in mirror plane and transverse plane of deformed sample. Also, damage analysis showed that superficial cracks may be initiated from bottom side of sample and their propagation will be limited due to the compressive state of stress. It was demonstrated that the V shaped deformation zone are existed in T-ECAP process and the pressing load needed for execution of deformation process is increased with friction.

The Role of Adult-Born Neurons in the Constantly Changing Olfactory Bulb Network

PubMed Central

Malvaut, Sarah; Saghatelyan, Armen

2016-01-01

The adult mammalian brain is remarkably plastic and constantly undergoes structurofunctional modifications in response to environmental stimuli. In many regions plasticity is manifested by modifications in the efficacy of existing synaptic connections or synapse formation and elimination. In a few regions, however, plasticity is brought by the addition of new neurons that integrate into established neuronal networks. This type of neuronal plasticity is particularly prominent in the olfactory bulb (OB) where thousands of neuronal progenitors are produced on a daily basis in the subventricular zone (SVZ) and migrate along the rostral migratory stream (RMS) towards the OB. In the OB, these neuronal precursors differentiate into local interneurons, mature, and functionally integrate into the bulbar network by establishing output synapses with principal neurons. Despite continuous progress, it is still not well understood how normal functioning of the OB is preserved in the constantly remodelling bulbar network and what role adult-born neurons play in odor behaviour. In this review we will discuss different levels of morphofunctional plasticity effected by adult-born neurons and their functional role in the adult OB and also highlight the possibility that different subpopulations of adult-born cells may fulfill distinct functions in the OB neuronal network and odor behaviour. PMID:26839709

High Power Picosecond Laser Surface Micro-texturing of H13 Tool Steel and Pattern Replication onto ABS Plastics via Injection Moulding

NASA Astrophysics Data System (ADS)

Otanocha, Omonigho B.; Li, Lin; Zhong, Shan; Liu, Zhu

2016-03-01

H13 tool steels are often used as dies and moulds for injection moulding of plastic components. Certain injection moulded components require micro-patterns on their surfaces in order to modify the physical properties of the components or for better mould release to reduce mould contamination. With these applications it is necessary to study micro-patterning to moulds and to ensure effective pattern transfer and replication onto the plastic component during moulding. In this paper, we report an investigation into high average powered (100 W) picosecond laser interactions with H13 tool steel during surface micro-patterning (texturing) and the subsequent pattern replication on ABS plastic material through injection moulding. Design of experiments and statistical modelling were used to understand the influences of laser pulse repetition rate, laser fluence, scanning velocity, and number of scans on the depth of cut, kerf width and heat affected zones (HAZ) size. The characteristics of the surface patterns are analysed. The process parameter interactions and significance of process parameters on the processing quality and efficiency are characterised. An optimum operating window is recommended. The transferred geometry is compared with the patterns generated on the dies. A discussion is made to explain the characteristics of laser texturing and pattern replication on plastics.

Localization of ductile deformation in lithosphere and rocks: the role of grain boundary sliding

NASA Astrophysics Data System (ADS)

Dimanov, Alexandre; Rahanel, Jean; Bornert, Michel; Bourcier, Mathieu; Gaye, Ag; Heripre, Eva; Ludwig, Wolfgang

2017-04-01

Ductile strain of the lithosphere localizes in multi-scale shear zones, ranging from km to mm scales. The resulting mylonites/ultramylonites present microstructural signatures of several concomitant deformation mechanisms. Besides cataclastic features, crystal plasticity dominates in volume, but grain boundary sliding and diffusive/solution mass transport act along interfaces. Considering solely the inherited natural microstructures does not make clear the chronology of appearance and the interactions between these mechanisms. Therefore, inference of the overall mylonitic rheology seems illusory. We have therefore realized over the last decade a systematic rheological characterization of the high temperature flow of various synthetic anorthite - diopside mixtures. The data clearly suggest Newtonian type of rheology as best adapted to the materials representative of the lower crust mylonites. However, the post mortem microstructures undoubtedly evidenced the coexistence of both crystal plasticity and grain boundary sliding processes. Yet, the specific roles of each mechanism in the localization process remained unclear. In order to clarify these aspects we realized a multi-scale micromechanical in situ investigation of the ductile deformation of synthetic rock-salt. The mechanical tests were combined with in-situ optical microscopy, scanning electron microscopy and X-ray tomography (MCT). Digital image correlation (DIC) techniques allowed for measurements and characterization of the multi-scale organization of 2D and 3D full strain fields. Macroscopic and mesoscopic shear bands appear at the sample and microstructure scales, respectively. DIC evidenced the development of discrete slip bands within individual grains, and hence of dominant crystal plasticity. Combination of DIC and EBSD allowed for identification of active slip systems. Conversely, DIC allowed for the identification and the precise quantification of minor activity (< 5% contribution) of grain boundary sliding (GBS). Most importantly, GBS is continuously operating along with crystal slip plasticity, which indicates that in spite of being a secondary mechanism it is a necessary one. GBS seems to accommodate very efficiently for plastic strain incompatibilities between neighboring grains. Our finding is strengthened by finite element (FE) modeling of the viscoplastic behavior of rock-salt, which appears inadequate in detail if solely based on crystal plasticity. Moreover, the local GBS appears to i) trigger the formation of localized shear bands at the microstructure scale, and ii) allow for homogenization of ductile strain throughout the whole specimen. Our major conclusions are that crystal plasticity and GBS are not really dissociable. They are co-operative mechanisms that accommodate each other depending on microstructure and loading conditions. Minor GBS is always necessary in order to accommodate for the pronounced plastic anisotropy of minerals. Conversely, localized minor crystal plasticity is necessary to accommodate dominant GBS. Finally, GBS is directly involved in the initial development of localized ductile strain at the aggregate scale. But, GBS might take over as the dominant mechanism within fine grained mylonites and contribute to the large scale shear zone localization.

Microplastic distribution in global marine surface waters: results of an extensive citizen science study

NASA Astrophysics Data System (ADS)

Barrows, A.; Petersen, C.

2017-12-01

Plastic is a major pollutant throughout the world. The majority of the 322 million tons produced annually is used for single-use packaging. What makes plastic an attractive packaging material: cheap, light-weight and durable are also the features that help make it a common and persistent pollutant. There is a growing body of research on microplastic, particles less than 5 mm in size. Microfibers are the most common microplastic in the marine environment. Global estimates of marine microplastic surface concentrations are based on relatively small sample sizes when compared to the vast geographic scale of the ocean. Microplastic residence time and movement along the coast and sea surface outside of the gyres is still not well researched. This five-year project utilized global citizen scientists to collect 1,628 1-liter surface grab samples in every major ocean. The Artic and Southern oceans contained highest average of particles per liter of surface water. Open ocean samples (further than 12 nm from land, n = 686) contained a higher particle average (17 pieces L-1) than coastal samples (n = 723) 6 pieces L-1. Particles were predominantly 100 µm- 1.5 mm in length (77%), smaller than what has been captured in the majority of surface studies. Utilization of citizen scientists to collect data both in fairly accessible regions of the world as well as from areas hard to reach and therefore under sampled, provides us with a wider perspective of global microplastics occurrence. Our findings confirm global microplastic accumulation zone model predictions. The open ocean and poles have sequestered and trapped plastic for over half a century, and show that not only plastics, but anthropogenic fibers are polluting the environment. Continuing to fill knowledge gaps on microplastic shape, size and color in remote ocean areas will drive more accurate oceanographic models of plastic accumulation zones. Incorporation of smaller-sized particles in these models, which has previously been lacking, will help to better understand potential fate and transformation microplastic and anthropogenic particles in the marine environment.

Elucidating the atomistic mechanisms underpinning plasticity in Li-Si nanostructures

NASA Astrophysics Data System (ADS)

Yan, Xin; Gouissem, Afif; Guduru, Pradeep R.; Sharma, Pradeep

2017-10-01

Amorphous lithium-silicon (a-Li-Si), especially in nanostructure form, is an attractive high-capacity anode material for next-generation Li-ion batteries. During cycles of charging and discharging, a-Li-Si undergoes substantive inelastic deformation and exhibits microcracking. The mechanical response to repeated lithiation-delithiation eventually results in the loss of electrical contact and consequent decrease of capacity, thus underscoring the importance of studying the plasticity of a-Li-Si nanostructures. In recent years, a variety of phenomenological continuum theories have been introduced that purport to model plasticity and the electro-chemo-mechanical behavior of a-Li-Si. Unfortunately, the micromechanisms and atomistic considerations underlying plasticity in Li-Si material are not yet fully understood and this impedes the development of physics-based constitutive models. Conventional molecular dynamics, although extensively used to study this material, is grossly inadequate to resolve this matter. As is well known, conventional molecular dynamics simulations can only address phenomena with characteristic time scales of (at most) a microsecond. Accordingly, in such simulations, the mechanical behavior is deduced under conditions of very high strain rates (usually, 108s-1 or even higher). This limitation severely impacts a realistic assessment of rate-dependent effects. In this work, we attempt to circumvent the time-scale bottleneck of conventional molecular dynamics and provide novel insights into the mechanisms underpinning plastic deformation of Li-Si nanostructures. We utilize an approach that allows imposition of slow strain rates and involves the employment of a new and recently developed potential energy surface sampling method—the so-called autonomous basin climbing—to identify the local minima in the potential energy surface. Combined with other techniques, such as nudged elastic band, kinetic Monte Carlo and transition state theory, we assess the behavior of a-Li-Si nanostructures under tensile strain rates ranging from 103 to 108s-1 . We find significant differences in the deformation behavior across the strain rates and discover that the well-known shear transformation zones (widely discussed in the context of amorphous materials) are formed by a "diffusionlike" process. We identify the rotation of the shear transformation zone as a key dissipation mechanism.

77 FR 69789 - Foreign-Trade Zone 171-Liberty County, TX; Application for Reorganization/Expansion Under...

Federal Register 2010, 2011, 2012, 2013, 2014

2012-11-21

..., Cleveland; Site 2 (45 acres)-- Port of Liberty County Industrial Park located on Trinity River, Liberty; Site 3 (27 acres)--Port of Liberty County Industrial Park located on the Trinity River some 2 miles..., Highway FM 787, Liberty; Site 5 (583.081 acres)--Sjolander Plastics Storage Railyard facility, adjacent to...

Heat transfer in composite materials disintegrating under high-rate one-sided heating

NASA Astrophysics Data System (ADS)

Isaev, K. B.

1993-12-01

A mathematical model of heat transfer in heat-protective materials is suggested with the proviso of a squarelaw temperature depence of the material density in the zone of thermal destruction of its binder. The influence of certain factors on the experimental temperature field and thermal conductivity of a glass-reinforced epoxy plastic material is shown.

Isolation of native soil microorganisms with potential for breaking down biodegradable plastic mulch films used in agriculture.

PubMed

Bailes, Graham; Lind, Margaret; Ely, Andrew; Powell, Marianne; Moore-Kucera, Jennifer; Miles, Carol; Inglis, Debra; Brodhagen, Marion

2013-05-10

Fungi native to agricultural soils that colonized commercially available biodegradable mulch (BDM) films were isolated and assessed for potential to degrade plastics. Typically, when formulations of plastics are known and a source of the feedstock is available, powdered plastic can be suspended in agar-based media and degradation determined by visualization of clearing zones. However, this approach poorly mimics in situ degradation of BDMs. First, BDMs are not dispersed as small particles throughout the soil matrix. Secondly, BDMs are not sold commercially as pure polymers, but rather as films containing additives (e.g. fillers, plasticizers and dyes) that may affect microbial growth. The procedures described herein were used for isolates acquired from soil-buried mulch films. Fungal isolates acquired from excavated BDMs were tested individually for growth on pieces of new, disinfested BDMs laid atop defined medium containing no carbon source except agar. Isolates that grew on BDMs were further tested in liquid medium where BDMs were the sole added carbon source. After approximately ten weeks, fungal colonization and BDM degradation were assessed by scanning electron microscopy. Isolates were identified via analysis of ribosomal RNA gene sequences. This report describes methods for fungal isolation, but bacteria also were isolated using these methods by substituting media appropriate for bacteria. Our methodology should prove useful for studies investigating breakdown of intact plastic films or products for which plastic feedstocks are either unknown or not available. However our approach does not provide a quantitative method for comparing rates of BDM degradation.

Isolation of Native Soil Microorganisms with Potential for Breaking Down Biodegradable Plastic Mulch Films Used in Agriculture

PubMed Central

Bailes, Graham; Lind, Margaret; Ely, Andrew; Powell, Marianne; Moore-Kucera, Jennifer; Miles, Carol; Inglis, Debra; Brodhagen, Marion

2013-01-01

Fungi native to agricultural soils that colonized commercially available biodegradable mulch (BDM) films were isolated and assessed for potential to degrade plastics. Typically, when formulations of plastics are known and a source of the feedstock is available, powdered plastic can be suspended in agar-based media and degradation determined by visualization of clearing zones. However, this approach poorly mimics in situ degradation of BDMs. First, BDMs are not dispersed as small particles throughout the soil matrix. Secondly, BDMs are not sold commercially as pure polymers, but rather as films containing additives (e.g. fillers, plasticizers and dyes) that may affect microbial growth. The procedures described herein were used for isolates acquired from soil-buried mulch films. Fungal isolates acquired from excavated BDMs were tested individually for growth on pieces of new, disinfested BDMs laid atop defined medium containing no carbon source except agar. Isolates that grew on BDMs were further tested in liquid medium where BDMs were the sole added carbon source. After approximately ten weeks, fungal colonization and BDM degradation were assessed by scanning electron microscopy. Isolates were identified via analysis of ribosomal RNA gene sequences. This report describes methods for fungal isolation, but bacteria also were isolated using these methods by substituting media appropriate for bacteria. Our methodology should prove useful for studies investigating breakdown of intact plastic films or products for which plastic feedstocks are either unknown or not available. However our approach does not provide a quantitative method for comparing rates of BDM degradation. PMID:23712218

Structural and Lithologic Characterization of the SAFOD Pilot Hole and Phase One Main Hole

NASA Astrophysics Data System (ADS)

Barton, D. C.; Bradbury, K.; Solum, J. G.; Evans, J. P.

2005-12-01

Petrological and microstructural analyses of drill cuttings were conducted for the San Andreas Fault Observatory at Depth (SAFOD) Pilot Hole and Main Hole projects. Grain mounts were produced at ~30 m (100 ft) intervals from drill cuttings collected from the Pilot Hole to a depth of 2164 m (7100 ft) and from Phase 1 of the SAFOD main hole to a depth of 3067 m (10062 ft). . Thin-section grain mount analysis included identification of mineral composition, alteration, and deformation within individual grains, measured at .5 mm increments on an equally spaced, 300 point grid pattern. Lithologic features in the Quaternary/Tertiary deposits from 30 - 640 m (100-2100 ft) in the Pilot Hole, and 670 - 792 m (2200 - 2600 ft) in the Phase 1 main hole, include fine-grained, thinly bedded sediments with clasts of fine-grained volcanic groundmass. Preliminary grain mount analysis from 1920 - 3067 m (6300 - 10062) in the Phase 1 main hole, indicates a sedimentary sequence consisting of fine-grained lithic fragments of very fine-grained shale. Deformation mechanisms observed within the cuttings of granitic rocks from 914 - 1860 m (3000 - 6100 ft.) include intracrystalline plasticity and cataclasis. Intracrystalline plastic deformation within quartz and feldspar grains is indicated by undulatory extinction, ribbon grains, chessboard patterns, and deformation twins and lamellae. Cataclastic deformation is characterized by intra- and intergranular microfractures, angular grains, gouge zones, iron-oxide banding, and comminution. Mineral and cataclasite abundances were plotted as a function of weight percent vs. depth. Plots of quartz and feldspar abundances are also correlated with XRD weight percent data from 1160 - 1890 m (3800 - 6200 ft.) in the granitic and granodioritic sequences of the Phase 1 main hole. Regions of the both of the drill holes with cataclasite abundances ranging from 20 - 30 wt% are interpreted as shear zones. Shear zones identified in this study from 1150 - 1420 m (3773 - 4659 ft.) in the Pilot Hole occur in the same location as shear zones recognized by Boness and Zoback (2004) using borehole geophysical data. These shear zones may possibly be correlated to shear zones identified in the Phase I main hole from 1615 - 2012 m (5300 - 6600 ft). If this is the case, it can be explained by steeply dipping subsidiary fault zones, likely associated with the San Andreas Fault system.

Calibrated heat flow model for the determination of different heat-affected zones in single-pass laser-cut CFRP using a cw CO2 laser

NASA Astrophysics Data System (ADS)

Mucha, P.; Berger, P.; Weber, R.; Speker, N.; Sommer, B.; Graf, T.

2015-03-01

Laser machining has great potential for automated manufacturing of parts made of carbon-fiber-reinforced plastic (CFRP) due to the nearly force and tool-wear free processing. The high vaporization temperatures and the large heat conductivity of the carbon fibers, however, lead to unintentional heat conduction into the material causing damage in zones close to the process. In this paper, the matrix damage zone (MDZ) is subdivided into a matrix sublimation zone (MSZ) where the matrix material was sublimated and a zone where the temperature temporarily exceeded a value causing structural damage in the matrix. In order to investigate the extent of these zones, a one-dimensional heat flow model was applied, which was calibrated by cutting experiments using temperature sensors embedded in the CFRP samples. The investigations showed that the extents of the MSZ and MDZ are dominated by a total interaction time, which includes the passage of the laser beam and the continued interaction of the cloud of hot ablation products with the carbon fibers at the kerf wall and that from a practical point of view, the experimentally determined effective heat conductivity is suitable for simple estimations of the heat-affected zones in CFRP.

Imaging the deep structures of the convergent plates along the Ecuadorian subduction zone through receiver function analysis

NASA Astrophysics Data System (ADS)

Galve, A.; Charvis, P.; Regnier, M. M.; Font, Y.; Nocquet, J. M.; Segovia, M.

2017-12-01

The Ecuadorian subduction zone was affected by several large M>7.5 earthquakes. While we have low resolution on the 1942, 1958 earthquakes rupture zones extension, the 2016 Pedernales earthquake, that occurs at the same location than the 1942 earthquake, give strong constraints on the deep limit of the seismogenic zone. This downdip limit is caused by the onset of plasticity at a critical temperature (> 350-450 °C for crustal materials, or serpentinized mantle wedge, and eventually > 700 °C for dry mantle). However we still don't know exactly where is the upper plate Moho and therefore what controls the downdip limit of Ecuadorian large earthquakes seismogenic zone. For several years Géoazur and IG-EPN have maintained permanent and temporary networks (ADN and JUAN projects) along the margin to register the subduction zone seismological activity. Although Ecuador is not a good place to perform receiver function due to its position with respect to the worldwide teleseismic sources, the very long time deployment compensate this issue. We performed a frequency dependent receiver function analysis to derive (1) the thickness of the downgoing plate, (2) the interplate depth and (3) the upper plate Moho. These constraints give the frame to interpretation on the seismogenic zone of the 2016 Pedernales earthquake.

Investigation of Three-Dimensional Stress Fields and Slip Systems for FCC Single Crystal Superalloy Notched Specimens

NASA Technical Reports Server (NTRS)

Arakere, Nagaraj K.; Magnan, Shannon; Ebrahimi, Fereshteh; Ferroro, Luis

2004-01-01

Metals and their alloys, except for a few intermetallics, are inherently ductile, i.e. plastic deformation precedes fracture in these materials. Therefore, resistance to fracture is directly related to the development of the plastic zone at the crack tip. Recent studies indicate that the fracture toughness of single crystals depends on the crystallographic orientation of the notch as well as the loading direction. In general, the dependence of crack propagation resistance on crystallographic orientation arises from the anisotropy of (i) elastic constants, (ii) plastic deformation (or slip), and (iii) the weakest fracture planes (e.g. cleavage planes). Because of the triaxial stress state at the notch tips, many slip systems that otherwise would not be activated during uniaxial testing, become operational. The plastic zone formation in single crystals has been tackled theoretically by Rice and his co-workers and only limited experimental work has been conducted in this area. The study of the stresses and strains in the vicinity of a FCC single crystal notch tip is of relatively recent origin. We present experimental and numerical investigation of 3D stress fields and evolution of slip sector boundaries near notches in FCC single crystal tension test specimens, and demonstrate that a 3D linear elastic finite element model that includes the effect of material anisotropy is shown to predict active slip planes and sectors accurately. The slip sector boundaries are shown to have complex curved shapes with several slip systems active simultaneously near the notch. Results are presented for surface and mid-plane of the specimens. The results demonstrate that accounting for 3D elastic anisotropy is very important for accurate prediction of slip activation near FCC single crystal notches loaded in tension. Results from the study will help establish guidelines for fatigue damage near single crystal notches.

Improvements to the single screw extruder

NASA Technical Reports Server (NTRS)

Hiemenz, C.; Ziegmann, G.; Franzkoch, B.; Hoffmanns, W.; Michaeli, W.

1977-01-01

The extrusion on a single screw extruder is examined. The process is divided into several steps: the dosage of the materials to be conveyed; the modification of the shape of the feeding opening which influences the feeding process and consequently the throughput of the extruder; optimizing the shape of the feeding zone to meet the specific material requirements; and plasticizing and homogenizing.

Microstructure and mesh sensitivities of mesoscale surrogate driving force measures for transgranular fatigue cracks in polycrystals

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

Castelluccio, Gustavo M.; McDowell, David L.

The number of cycles required to form and grow microstructurally small fatigue cracks in metals exhibits substantial variability, particularly for low applied strain amplitudes. This variability is commonly attributed to the heterogeneity of cyclic plastic deformation within the microstructure, and presents a challenge to minimum life design of fatigue resistant components. Our paper analyzes sources of variability that contribute to the driving force of transgranular fatigue cracks within nucleant grains. We also employ crystal plasticity finite element simulations that explicitly render the polycrystalline microstructure and Fatigue Indicator Parameters (FIPs) averaged over different volume sizes and shapes relative to the anticipatedmore » fatigue damage process zone. Volume averaging is necessary to both achieve description of a finite fatigue damage process zone and to regularize mesh dependence in simulations. Furthermore, results from constant amplitude remote applied straining are characterized in terms of the extreme value distributions of volume averaged FIPs. Grain averaged FIP values effectively mitigate mesh sensitivity, but they smear out variability within grains. Furthermore, volume averaging over bands that encompass critical transgranular slip planes appear to present the most attractive approach to mitigate mesh sensitivity while preserving variability within grains.« less

Microstructure and mesh sensitivities of mesoscale surrogate driving force measures for transgranular fatigue cracks in polycrystals

DOE PAGES

Castelluccio, Gustavo M.; McDowell, David L.

2015-05-22

The number of cycles required to form and grow microstructurally small fatigue cracks in metals exhibits substantial variability, particularly for low applied strain amplitudes. This variability is commonly attributed to the heterogeneity of cyclic plastic deformation within the microstructure, and presents a challenge to minimum life design of fatigue resistant components. Our paper analyzes sources of variability that contribute to the driving force of transgranular fatigue cracks within nucleant grains. We also employ crystal plasticity finite element simulations that explicitly render the polycrystalline microstructure and Fatigue Indicator Parameters (FIPs) averaged over different volume sizes and shapes relative to the anticipatedmore » fatigue damage process zone. Volume averaging is necessary to both achieve description of a finite fatigue damage process zone and to regularize mesh dependence in simulations. Furthermore, results from constant amplitude remote applied straining are characterized in terms of the extreme value distributions of volume averaged FIPs. Grain averaged FIP values effectively mitigate mesh sensitivity, but they smear out variability within grains. Furthermore, volume averaging over bands that encompass critical transgranular slip planes appear to present the most attractive approach to mitigate mesh sensitivity while preserving variability within grains.« less

Deformation field heterogeneity in punch indentation

PubMed Central

Murthy, Tejas G.; Saldana, Christopher; Hudspeth, Matthew; M'Saoubi, Rachid

2014-01-01

Plastic heterogeneity in indentation is fundamental for understanding mechanics of hardness testing and impression-based deformation processing methods. The heterogeneous deformation underlying plane-strain indentation was investigated in plastic loading of copper by a flat punch. Deformation parameters were measured, in situ, by tracking the motion of asperities in high-speed optical imaging. These measurements were coupled with multi-scale analyses of strength, microstructure and crystallographic texture in the vicinity of the indentation. Self-consistency is demonstrated in description of the deformation field using the in situ mechanics-based measurements and post-mortem materials characterization. Salient features of the punch indentation process elucidated include, among others, the presence of a dead-metal zone underneath the indenter, regions of intense strain rate (e.g. slip lines) and extent of the plastic flow field. Perhaps more intriguing are the transitions between shear-type and compression-type deformation modes over the indentation region that were quantified by the high-resolution crystallographic texture measurements. The evolution of the field concomitant to the progress of indentation is discussed and primary differences between the mechanics of indentation for a rigid perfectly plastic material and a strain-hardening material are described. PMID:24910521

A global inventory of small floating plastic debris

NASA Astrophysics Data System (ADS)

van Sebille, Erik; Wilcox, Chris; Lebreton, Laurent; Maximenko, Nikolai; Hardesty, Britta Denise; van Franeker, Jan A.; Eriksen, Marcus; Siegel, David; Galgani, Francois; Lavender Law, Kara

2015-12-01

Microplastic debris floating at the ocean surface can harm marine life. Understanding the severity of this harm requires knowledge of plastic abundance and distributions. Dozens of expeditions measuring microplastics have been carried out since the 1970s, but they have primarily focused on the North Atlantic and North Pacific accumulation zones, with much sparser coverage elsewhere. Here, we use the largest dataset of microplastic measurements assembled to date to assess the confidence we can have in global estimates of microplastic abundance and mass. We use a rigorous statistical framework to standardize a global dataset of plastic marine debris measured using surface-trawling plankton nets and coupled this with three different ocean circulation models to spatially interpolate the observations. Our estimates show that the accumulated number of microplastic particles in 2014 ranges from 15 to 51 trillion particles, weighing between 93 and 236 thousand metric tons, which is only approximately 1% of global plastic waste estimated to enter the ocean in the year 2010. These estimates are larger than previous global estimates, but vary widely because the scarcity of data in most of the world ocean, differences in model formulations, and fundamental knowledge gaps in the sources, transformations and fates of microplastics in the ocean.

Plastic strain arrangement in copper single crystals in sliding

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

Chumaevskii, Andrey V., E-mail: tch7av@gmail.com; Lychagin, Dmitry V., E-mail: dvl-tomsk@mail.ru; Tarasov, Sergei Yu., E-mail: tsy@ispms.tsc.ru

2014-11-14

Deformation of tribologically loaded contact zone is one of the wear mechanisms in spite of the fact that no mass loss may occur during this process. Generation of optimal crystallographic orientations of the grains in a polycrystalline materials (texturing) may cause hardening and reducing the deformation wear. To reveal the orientation dependence of an individual gain and simplify the task we use copper single crystals with the orientations of the compression axis along [111] and [110]. The plastic deformation was investigated by means of optical, scanning electron microscopy and EBSD techniques. It was established that at least four different zonesmore » were generated in the course of sliding test, such as non-deformed base metal, plastic deformation layer sliding, crystalline lattice reorientation layer and subsurface grain structure layer. The maximum plastic strain penetration depth was observed on [110]-single crystals. The minimum stability of [111]-crystals with respect to rotation deformation mode as well as activation of shear in the sliding contact plane provide for rotation deformation localization below the worn surface. The high-rate accumulation of misorientations and less strain penetration depth was observed on [111]-crystals as compared to those of [110]-oriented ones.« less

Selection and screening of microbial consortia for efficient and ecofriendly degradation of plastic garbage collected from urban and rural areas of Bangalore, India.

PubMed

Skariyachan, Sinosh; Megha, M; Kini, Meghna Niranjan; Mukund, Kamath Manali; Rizvi, Alya; Vasist, Kiran

2015-01-01

Industrialization and urbanization have led to massive accumulation of plastic garbage all over India. The persistence of plastic in soil and aquatic environment has become ecological threat to the metropolitan city such as Bangalore, India. Present study investigates an ecofriendly, efficient and cost-effective approach for plastic waste management by the screening of novel microbial consortia which are capable of degrading plastic polymers. Plastic-contaminated soil and water samples were collected from six hot spots of urban and rural areas of Bangalore. The plastic-degrading bacteria were enriched, and degradation ability was determined by zone of clearance method. The percentage of polymer degradation was initially monitored by weight loss method, and the main isolates were characterized by standard microbiology protocols. These isolates were used to form microbial consortia, and the degradation efficiency of the consortia was compared with individual isolate and known strains obtained from the Microbial Type Culture Collection (MTCC) and Gene Bank, India. One of the main enzymes responsible for polymer degradation was identified, and the biodegradation mechanism was hypothesized by bioinformatics studies. From this study, it is evident that the bacteria utilized the plastic polymer as a sole source of carbon and showed 20-50% weight reduction over a period of 120 days. The two main bacteria responsible for the degradation were microbiologically characterized to be Pseudomonas spp. These bacteria could grow optimally at 37 °C in pH 9.0 and showed 35-40% of plastic weight reduction over 120 days. These isolates were showed better degradation ability than known strains from MTCC. The current study further revealed that the microbial consortia formulated by combining Psuedomonas spp. showed 40 plastic weight reduction over a period of 90 days. Further, extracellular lipase, one of the main enzymes responsible for polymer degradation, was identified. The computational docking studies suggested that polyethylene glycol and polystyrene present in the plastics might have good interaction towards the microbial lipase with stable binding and interacting forces which probably could be one of the reasons for the degradative mechanisms.

Laser cutting: influence on morphological and physicochemical properties of polyhydroxybutyrate.

PubMed

Lootz, D; Behrend, D; Kramer, S; Freier, T; Haubold, A; Benkiesser, G; Schmitz, K P; Becher, B

2001-09-01

Polyhydroxybutyrate (PHB) is a biocompatible and resorbable implant material. For these reasons, it has been used for the fabrication of temporary stents, bone plates, nails and screws (Peng et al. Biomaterials 1996;17:685). In some cases, the brittle mechanical properties of PHB homopolymer limit its application. A typical plasticizer, triethylcitrate (TEC), was used to overcome such limitations by making the material more pliable. In the past few years, CO2-laser cutting of PHB was used in the manufacturing of small medical devices such as stents. Embrittlement of plasticized PHB tubes has been observed, after laser machining. Consequently, the physicochemical and morphological properties of laser-processed surfaces and cut edges of plasticized polymer samples were examined to determine the extent of changes in polymer properties as a result of laser machining. These studies included determination of the depth of the laser-induced heat affected zone by polariscopy of thin polymer sections. Molecular weight changes and changes in the TEC content as a function of distance from the laser-cut edge were determined. In a preliminary test, the cellular response to the processed material was investigated by cell culture study of L929 mouse fibroblasts on laser-machined surfaces. The heat-affected zone was readily classified into four different regions with a total depth of about 60 to 100 microm (Klamp, Master Thesis, University of Rostock, 1998). These results correspond well with the chemical analysis and molecular weight measurements. Furthermore, it was found that cells grew preferentially on the laser-machined area. These findings have significant implications for the manufacture of medical implants from PHB by laser machining.

Analysis of the waste selective collection at drop-off systems: Case study including the income level and the seasonal variation.

PubMed

Gallardo, A; Carlos, M; Colomer, F J; Edo-Alcón, N

2018-01-01

There are several factors which have an influence in the selective collection of the municipal waste. To define a selective collection system, the waste generation pattern should be firstly determined and these factors should be analyzed in depth. This paper tries to analyze the economic income level and the seasonal variation on the collection and the purity of light-packaging waste to determine actions to improve the waste management plan of a town. In the first stage of the work, waste samples of the light-packaging containers were collected in two zones of the town with different economic characteristics in different seasons during one year. In the second stage, the samples were characterized to analyze the composition and purity of the waste. They were firstly separated into four fractions: metals; plastic; beverage cartons; and misplaced materials. The misplaced fraction was in its turn separated into cardboard, rubber and leather, inert waste, organic matter, paper, hazardous waste, clothes and shoes, glass and others. The plastic fraction was separated into five types of plastics and the metal fraction into three. In the third stage, the data have been analyzed and conclusions have been extracted. The main result is that the quality of the light-packaging fraction collected in these zones during both seasons were similar. This methodology can be extrapolated to towns with similar characteristics. It will be useful when implementing a system to collect the waste selectively and to develop actions to achieve a good participation in the selective collection of the waste.

Composition, spatial distribution and sources of macro-marine litter on the Gulf of Alicante seafloor (Spanish Mediterranean).

PubMed

García-Rivera, Santiago; Lizaso, Jose Luis Sánchez; Millán, Jose María Bellido

2017-08-15

The composition, spatial distribution and source of marine litter in the Spanish Southeast Mediterranean were assessed. The data proceed from a marine litter retention programme implemented by commercial trawlers and were analysed by GIS. By weight, 75.9% was plastic, metal and glass. Glass and plastics were mainly found close to the coast. A high concentration of metal was observed in some isolated zones of both open and coastal waters. Fishing activity was the source of 29.16% of the macro-marine litter, almost 68.1% of the plastics, and 25.1% of the metal. The source of the other 60.84% could not be directly identified, revealing the high degree of uncertainty regarding its specific origin. Indirectly however, a qualitative analysis of marine traffic shows that the likely sources were merchant ships mainly in open waters and recreational and fishing vessels in coastal waters. Copyright © 2017 Elsevier Ltd. All rights reserved.

Ductile Crack Initiation Criterion with Mismatched Weld Joints Under Dynamic Loading Conditions.

PubMed

An, Gyubaek; Jeong, Se-Min; Park, Jeongung

2018-03-01

Brittle failure of high toughness steel structures tends to occur after ductile crack initiation/propagation. Damages to steel structures were reported in the Hanshin Great Earthquake. Several brittle failures were observed in beam-to-column connection zones with geometrical discontinuity. It is widely known that triaxial stresses accelerate the ductile fracture of steels. The study examined the effects of geometrical heterogeneity and strength mismatches (both of which elevate plastic constraints due to heterogeneous plastic straining) and loading rate on critical conditions initiating ductile fracture. This involved applying the two-parameter criterion (involving equivalent plastic strain and stress triaxiality) to estimate ductile cracking for strength mismatched specimens under static and dynamic tensile loading conditions. Ductile crack initiation testing was conducted under static and dynamic loading conditions using circumferentially notched specimens (Charpy type) with/without strength mismatches. The results indicated that the condition for ductile crack initiation using the two parameter criterion was a transferable criterion to evaluate ductile crack initiation independent of the existence of strength mismatches and loading rates.

[The detector, the command neuron and plastic convergence].

PubMed

Sokolov, E N

1977-01-01

The paper deals with the structure of detectors, the function of commanding neurones and the problem of relationship between detectors and commanding neurons. An example of hierarchial organization of detectors is provided by the colour analyser in which a layer of receptors, a layer of opponent neurones and a layer of colour-selective detectors are singled out. The colour detector is selectively sensitive to a certain combination of excitations at the input. If the detector is selectively activated by a certain combination of excitations at the input, the selective activation of the commanding neurone through a pool of motoneurones brings about a reaction at the output, specific in its organization. The reflexogenic zone of the reaction is determined by the detectors which converge on the commanding neurone controlling the given reaction. The plasticity of the reaction results from a plastic convergence of the detectors on the commanding neurone which controls the reaction. This comprises selective switching off the detectors from the commanding neurone (habituation) and connecting the detectors to the commanding neurone (facilitation).

Molecular Mechanism of Active Zone Organization at Vertebrate Neuromuscular Junctions

PubMed Central

Nishimune, Hiroshi

2013-01-01

Organization of presynaptic active zones is essential for development, plasticity, and pathology of the nervous system. Recent studies indicate a trans-synaptic molecular mechanism that organizes the active zones by connecting the pre- and the postsynaptic specialization. The presynaptic component of this trans-synaptic mechanism is comprised of cytosolic active zone proteins bound to the cytosolic domains of voltage-dependent calcium channels (P/Q-, N-, and L-type) on the presynaptic membrane. The postsynaptic component of this mechanism is the synapse organizer (laminin β2) that is expressed by the postsynaptic cell and accumulates specifically on top of the postsynaptic specialization. The pre- and the postsynaptic components interact directly between the extracellular domains of calcium channels and laminin β2 to anchor the presynaptic protein complex in front of the postsynaptic specialization. Hence, the presynaptic calcium channel functions as a scaffolding protein for active zone organization and as an ion-conducting channel for synaptic transmission. In contrast to the requirement of calcium influx for synaptic transmission, the formation of the active zone does not require the calcium influx through the calcium channels. Importantly, the active zones of adult synapses are not stable structures and require maintenance for their integrity. Furthermore, aging or diseases of the central and peripheral nervous system impair the active zones. This review will focus on the molecular mechanisms that organize the presynaptic active zones and summarize recent findings at the neuromuscular junctions and other synapses. PMID:22135013

Strain localization and elastic-plastic coupling during deformation of porous sandstone

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

Dewers, Thomas A.; Issen, Kathleen A.; Holcomb, David J.

Results of axisymmetric compression tests on weak, porous Castlegate Sandstone (Cretaceous, Utah, USA), covering a range of dilational and compactional behaviors, are examined for localization behavior. Assuming isotropy, bulk and shear moduli evolve as increasing functions of mean stress and Mises equivalent shear stress respectively, and as decreasing functions of work-conjugate plastic strains. Acoustic emissions events located during testing show onset of localization and permit calculation of observed shear and low-angle compaction localization zones, or bands, as localization commences. Total strain measured experimentally partitions into: A) elastic strain with constant moduli, B) elastic strain due to stress dependence of moduli,more » C) elastic strain due to moduli degradation with increasing plastic strain, and D) plastic strain. The third term is the elastic-plastic coupling strain, and though often ignored, contributes significantly to pre-failure total strain for brittle and transitional tests. Constitutive parameters and localization predictions derived from experiments are compared to theoretical predictions. In the brittle regime, predictions of band angles (angle between band normal and maximum compression) demonstrate good agreement with observed shear band angles. Compaction localization was observed in the transitional regime in between shear localization and spatially pervasive compaction, over a small range of mean stresses. In contrast with predictions however, detailed acoustic emissions analyses in this regime show low angle, compaction-dominated but shear-enhanced, localization.« less

Fractography of a bis-GMA resin.

PubMed

Davis, D M; Waters, N E

1989-07-01

The fracture behavior of a bis-GMA resin was studied by means of the double-torsion test. The fracture parameter measured was the stress-intensity factor. Fracture occurred in either a stick-slip (unstable) or continuous (stable) manner, depending upon the test conditions. When stick-slip propagation occurred, the fracture surfaces showed characteristic crack-arrest lines. The fracture surfaces were examined by use of a reflected-light optical microscope. The stress-intensity factor for crack initiation was found to be related to the size of the crack-arrest line which, in turn, could be related to the Dugdale model for plastic zone size. The evidence supported the concept that the behavior of the crack during propagation was controlled by the amount of plastic deformation occurring at the crack tip.

Impact deformation behavior of duplex and superaustenitic stainless steels welds by split Hopkinson pressure bar

NASA Astrophysics Data System (ADS)

Wang, Shing-Hoa; Huang, Chih-Sheng; Lee, Woei-Shyan; Chen, Tao-Hsing; Wu, Chia-Chang; Lien, Charles; Tsai, Hung-Yin

2009-12-01

A considerable volume of γ phase increases in the fusion zone (weld metal) for two duplex stainless steels after a high-strain-rate impact. The strain-induced γ phase formation in the fusion zone results in local hardness variation depending on the strain rate. The α phase content in the fusion zone decreases as the impact strain rate increases for SAF 2205 DSS and SAF 2507 DSS. The results of the two-phase content measured by Ferritoscope correspond to that assessed by image analyses. In contrast, superaustenite stainless steel is unaffected by such an impact owing to its fully stable austenization. Impacted welds at a high strain rate of 5 × 103 s-1 reveal feather-like surface creases along the solidified curved columnar grain boundaries. The apparent surface creases are formed due to the presence of diffuse Lüders bands, which are caused by heavy plastic deformation in coarse-grain materials.

Computational Modeling of Interfacial Behaviors in Nanocomposite Materials

PubMed Central

Lin, Liqiang; Wang, Xiaodu; Zeng, Xiaowei

2017-01-01

Towards understanding the bulk material response in nanocomposites, an interfacial zone model was proposed to define a variety of material interface behaviors (e.g. brittle, ductile, rubber-like, elastic-perfectly plastic behavior etc.). It also has the capability to predict bulk material response though independently control of the interface properties (e.g. stiffness, strength, toughness). The mechanical response of granular nanocomposite (i.e. nacre) was investigated through modeling the “relatively soft” organic interface as an interfacial zone among “hard” mineral tablets and simulation results were compared with experimental measurements of stress-strain curves in tension and compression tests. Through modeling varies material interfaces, we found out that the bulk material response of granular nanocomposite was regulated by the interfacial behaviors. This interfacial zone model provides a possible numerical tool for qualitatively understanding of structure-property relationships through material interface design. PMID:28983123

Permafrost and Subsurface Ice in the Solar System

NASA Technical Reports Server (NTRS)

Anderson, D. M.

1985-01-01

The properties and behavior of planetary permafrost are discussed with reference to the ability of such surfaces to sustain loads characteristics of spacecraft landing and planetary bases. In most occurrences, water ice is in close proximity to, or in contact with, finely divided silicate mineral matter. When ice contacts silicate mineral surfaces, a liquid-like, transition zone is created. Its thickness ranges from several hundred Angstron units at temperatures near 0 degrees C to about three Angstrom units at -150 degrees C. When soluble substances are present, the resulting brine enlarges the interfacial zone. When clays are involved, although the interfacial zone may be small, its extent is large. The unfrozen, interfacial water may amount to 100% or more weight at a temperature of -5 degrees C. The presence of this interfacial unfrozen water acts to confer plasticity to permafrost, enabling it to exhibit creep at all imposed levels of stress. Nucleation processes and load-bearing capacity are examined.

Measurement of Persistent Organic Pollutants (POPs) in plastic resin pellets from remote islands : Toward establishment of baseline level for International Pellet Watch

NASA Astrophysics Data System (ADS)

Takada, H.; Heskett, M.; Yamashita, R.; Yuyama, M.; Itoh, M.; Geok, Y. B.; Ogata, Y.

2011-12-01

Plastic resin pellets collected from remote islands in open oceans (Canary, St. Helena, Cocos, Hawaii, Maui Islands and Barbados) were sorted and yellowing polyethylene (PE) pellets were measured for polychlorinated biphenyls (PCBs), dichlorodiphenyltrichloroethane and the degradation products (DDTs), and hexachlorocyclohexanes (HCHs) by gas chromatograph equipped with mass spectrometer (GC-MS) and with electron capture detector (GC-ECD). PCBs were detected from all the pellet samples, confirming the global dispersion of PCBs. Median concentrations of PCBs (sum of 13 congeners : CB-66, CB-101, CB-110, CB-118, CB-105, CB-149, CB-153, CB-138, CB-128, CB-187, CB-180, CB-170, CB-206) in the remote island pellets ranged from 0.1 to 10 ng/g-pellet. These were one to three orders of magnitude lower than those observed for pellets from industrialized coastal zones (hundreds ng/g in Los Angeles, Boston, Tokyo; Ogata et al., 2009). Because these remote islands are far (>100 km) from industrialized zones, these concentrations (i.e., 0.1 to 10 ng/g-pellet) can be regarded as global "baseline" level of PCB pollution. Concentrations of DDTs in the remote island pellets ranged from 0.2 to 5.5 ng/g-pellet. At some locations, DDT was dominant over the degradation products (DDE and DDD), suggesting current usage of the pesticides in the islands. HCHs concentrations were 0.4 - 1.8 ng/g-pellet and lower than PCBs and DDTs, except for St. Helena Island at 18.8 ng/g-pellet where the current usage of the pesticides are of concern. The analyses of pellets from the remote islands provided "baseline" level of POPs (PCBs < 10 ng/g-pellet, DDTs < 6 ng/g-pellet, HCHs < 2 ng/g-pellet). However, the present samples were from tropical and subtropical areas. To establish global baseline, especially to understand the effects of global distillation, pellet samples from remote islands in higher latitude regions are necessary. From the eco-toxicological point of view, the fact that sporadic high concentrations of POPs were detected in some pellet samples from the remote islands is underscored. Some plastic debris which were contaminated in industrialized coastal zones may have rapidly transported to the remote islands before they would reach equilibrium (i.e., desorption completed). Because POPs concentrations in the other media are at trace levels in these remote environments, the sporadic high concentrations of POPs in the plastic debris may pose threat to the ecosystem in the remote islands.

Nonequilibrium thermodynamics of the shear-transformation-zone model

NASA Astrophysics Data System (ADS)

Luo, Alan M.; Ã-ttinger, Hans Christian

2014-02-01

The shear-transformation-zone (STZ) model has been applied numerous times to describe the plastic deformation of different types of amorphous systems. We formulate this model within the general equation for nonequilibrium reversible-irreversible coupling (GENERIC) framework, thereby clarifying the thermodynamic structure of the constitutive equations and guaranteeing thermodynamic consistency. We propose natural, physically motivated forms for the building blocks of the GENERIC, which combine to produce a closed set of time evolution equations for the state variables, valid for any choice of free energy. We demonstrate an application of the new GENERIC-based model by choosing a simple form of the free energy. In addition, we present some numerical results and contrast those with the original STZ equations.

Using the neutral zone to obtain maxillomandibular relationship records for complete denture patients.

PubMed

Alfano, S G; Leupold, R J

2001-06-01

A technique for obtaining maxillomandibular registration for complete denture patients is presented. The maxillary rim is formed with the use of conventional techniques. The mandibular rim is made from modeling plastic impression compound on a record base formed by the patient into the neutral zone. The mandibular rim then is reheated, and the patient determines the occlusal vertical dimension by swallowing. An imprint of the maxillary rim is made on the mandibular rim at the occlusal vertical dimension. The posterior extent of the mandibular rim is relieved 1 mm. Orientation notches are placed in both rims, and centric relation is recorded with a fast-setting vinyl polysiloxane material.

Mechanics of Thin Films

DTIC Science & Technology

1992-02-06

dependence of the dimensions H, D of the results of Lau et al. [14] in which the angular the plastic zone on the hardening exponent n for variation of the...01 0. 03 04MMS 10I Trh~knea (m) l| Thcrm (a-) FIG. 8. Variation of k., and t/kf, vst for EBE TiO1/AO at5- and 10-g films deposited on silicon [Table

Establishment of a Cutting Fluid Control System (Phase 1)

DTIC Science & Technology

1981-01-01

that prevent or reduce welding of contacting areas and minimize both material transfer and generation of metallic debris within the contact zone...not on ceramic abrasives. Welding between ceramics and workpiece materials is, however, less of a problem than metal-metal contact phenomena in...fluid film (hatched area) - no wear and low friction. Mating surfaces contacting at asperities with local plastic deformation and welding - wear with

Design and fabrication of the progressive addition lenses

NASA Astrophysics Data System (ADS)

Qin, Linling; Qian, Lin; Yu, Jingchi

2011-11-01

The use of progressive addition lenses (PALs) for the correction of presbyopia has increased dramatically in recent years. These lenses are now being used as the preferred alternative to bifocal and trifocal lenses in many parts of the world. Progressive addition lenses are a kind of opthalmic lenses with freeform surface. The surface curvature of the Progressive addition lenses varies gradually from a minimum value in the upper area, to a maximum value in the lower area. Thus a PAL has a surface with three zones which have very small astigmatism: far-view zone, near-view zone, and intermediate zone. The far view zone and near view zone have relatively constant powers and connected by the intermediate zone with power varies progressively. The design and fabrication technologies of progressive addition lenses have fast progresses because of the massive development of the optical simulation software, multi-axis ultraprecision machining technologies and CNC machining technologies. The design principles of progressive addition lenses are discussed in a historic review. Several kinds of design methods are illustrated, and their advantages and disadvantages are also represented. In the current study, it is shown that the optical characteristics of the different progressive addition lenses designs are significantly different from one another. The different fabrication technologies of Progressive addition lenses are also discussed in the paper. Plastic injection molding and precision-machine turning are the common fabrication technologies for exterior PALs and Interior PALs respectively.

Twin-spot laser welding of advanced high-strength multiphase microstructure steel

NASA Astrophysics Data System (ADS)

Grajcar, Adam; Morawiec, Mateusz; Różański, Maciej; Stano, Sebastian

2017-07-01

The study addresses the results concerning the laser welding of TRIP (TRansformation Induced Plasticity) steel using a beam focused at two spots (also referred to as twin-spot laser welding). The analysis involved the effect of variable welding thermal cycles on the properties and microstructure of welded joints. The tests were performed using a linear energy of 0.048 and 0.060 kJ/mm and the laser beam power distribution of 50%:50%, 60%:40% and 70%:30%. The tests also involved welding performed using a linear energy of 0.150 kJ/mm and the laser beam power distribution of 70%:30%. In addition, the research included observations of the microstructure of the fusion zone, heat affected zone and the transition zone using light microscopy and scanning electron microscopy. The fusion zone was composed of blocky-lath martensite whereas the HAZ (heat-affected zone) was characterised by the lath microstructure containing martensite, bainite and retained austenite. The distribution of twin-spot laser beam power significantly affected the microstructure and hardness profiles of welded joints. The highest hardness (480-505 HV), regardless of welding variants used, was observed in the HAZ.

Characterization of Multilayered Multipass Friction Stir Weld on ASTM A572 G50 Steel

DOE PAGES

Lim, Yong Chae; Sanderson, Samuel; Mahoney, Murray; ...

2014-01-01

A multilayered multipass friction stir weld (MM-FSW) on ASTM A572 Grade 50 steel was characterized to understand its potential application for thick-section structures. The 15-mm-thick section was fabricated by stacking up three steel plates and then friction stir welding the plates together in a total of 5 passes. The unique butt/lap joint configuration encountered in the multilayer weld was examined to understand the effect of tool rotation direction on the joint quality especially the formation of hooking defect. Charpy V-notch impact toughness tests showed generally higher impact toughness energy for the stir zone than the base metal with a ductilemore » fracture mode. The microhardness value was measured from 195 to 220 HV in the stir zone, while the base metal showed an average value of 170 HV. The microstructure in the stir zone and the adjacent heat affected zone was quantified using Optical and Scanning Electron Microscopy (SEM) including Electron Backscatter Diffraction (EBSD). The increased toughness and hardness were correlated with the refined microstructure in stir zone, resulting from severe plastic deformation and subsequent dynamic recrystallization during friction stir welding.« less

Geochemical and microstructural evidence for interseismic changes in fault zone permeability and strength, Alpine Fault, New Zealand

NASA Astrophysics Data System (ADS)

Boulton, Carolyn; Menzies, Catriona D.; Toy, Virginia G.; Townend, John; Sutherland, Rupert

2017-01-01

Oblique dextral motion on the central Alpine Fault in the last circa 5 Ma has exhumed garnet-oligoclase facies mylonitic fault rocks from ˜35 km depth. During exhumation, deformation, accompanied by fluid infiltration, has generated complex lithological variations in fault-related rocks retrieved during Deep Fault Drilling Project (DFDP-1) drilling at Gaunt Creek, South Island, New Zealand. Lithological, geochemical, and mineralogical results reveal that the fault comprises a core of highly comminuted cataclasites and fault gouges bounded by a damage zone containing cataclasites, protocataclasites, and fractured mylonites. The fault core-alteration zone extends ˜20-30 m from the principal slip zone (PSZ) and is characterized by alteration of primary phases to phyllosilicate minerals. Alteration associated with distinct mineral phases occurred proximal the brittle-to-plastic transition (T ≤ 300-400°C, 6-10 km depth) and at shallow depths (T = 20-150°C, 0-3 km depth). Within the fault core-alteration zone, fractures have been sealed by precipitation of calcite and phyllosilicates. This sealing has decreased fault normal permeability and increased rock mass competency, potentially promoting interseismic strain buildup.

Phenotypic plasticity in blood–oxygen transport in highland and lowland deer mice

PubMed Central

Tufts, Danielle M.; Revsbech, Inge G.; Cheviron, Zachary A.; Weber, Roy E.; Fago, Angela; Storz, Jay F.

2013-01-01

SUMMARY In vertebrates living at high altitude, arterial hypoxemia may be ameliorated by reversible changes in the oxygen-carrying capacity of the blood (regulated by erythropoiesis) and/or changes in blood–oxygen affinity (regulated by allosteric effectors of hemoglobin function). These hematological traits often differ between taxa that are native to different elevational zones, but it is often unknown whether the observed physiological differences reflect fixed, genetically based differences or environmentally induced acclimatization responses (phenotypic plasticity). Here, we report measurements of hematological traits related to blood–O2 transport in populations of deer mice (Peromyscus maniculatus) that are native to high- and low-altitude environments. We conducted a common-garden breeding experiment to assess whether altitude-related physiological differences were attributable to developmental plasticity and/or physiological plasticity during adulthood. Under conditions prevailing in their native habitats, high-altitude deer mice from the Rocky Mountains exhibited a number of pronounced hematological differences relative to low-altitude conspecifics from the Great Plains: higher hemoglobin concentrations, higher hematocrits, higher erythrocytic concentrations of 2,3-diphosphoglycerate (an allosteric regulator of hemoglobin–oxygen affinity), lower mean corpuscular hemoglobin concentrations and smaller red blood cells. However, these differences disappeared after 6 weeks of acclimation to normoxia at low altitude. The measured traits were also indistinguishable between the F1 progeny of highland and lowland mice, indicating that there were no persistent differences in phenotype that could be attributed to developmental plasticity. These results indicate that the naturally occurring hematological differences between highland and lowland mice are environmentally induced and are largely attributable to physiological plasticity during adulthood. PMID:23239893

Modelling the global distribution and risk of small floating plastic debris

NASA Astrophysics Data System (ADS)

van Sebille, E.; Wilcox, C.; Lebreton, L.; Maximenko, N. A.; Sherman, P.; Hardesty, B. D.; van Franeker, J. A.; Eriksen, M.; Siegel, D.; Galgani, F.; Lavender Law, K. L.

2016-02-01

Microplastic debris floating at the ocean surface can harm marine life. Understanding the severity of this harm requires knowledge of plastic abundance and distributions. Dozens of expeditions measuring microplastics have been carried out since the 1970s, but they have primarily focused on the North Pacific and North Atlantic accumulation zones, with much sparser coverage elsewhere. Here, we use the largest dataset of microplastic measurements collated to date to assess the confidence we can have in global estimates of microplastic abundance and mass. We use a rigorous statistical framework to standardize a global dataset of plastic marine debris measured using surface-trawling plankton nets and coupled this with three different ocean circulation models to spatially interpolate the observations. Our estimates show that the accumulated number of microplastic particles in 2014 ranges from 15 to 51 trillion particles, weighing between 93 and 236 thousand metric tons, which is only approximately 1% of global plastic waste available to enter the ocean in the year 2010. These estimates are larger than previous global estimates, but vary widely because the scarcity of data in most of the world ocean, differences in model formulations, and fundamental knowledge gaps in the sources, transformations and fates of microplastics in the ocean. We then use this global distribution of small floating plastic debris to (i) map out where in the ocean the risk to marine life (seabirds, plankton growth) is greatest and to (ii) show that mitigation of the plastic problem can most aptly be done near coastlines, particularly in Asia, rather than in the centres of the gyres.

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.

Revealing accumulation zones of plastic pellets in sandy beaches.

PubMed

Moreira, Fabiana T; Balthazar-Silva, Danilo; Barbosa, Lucas; Turra, Alexander

2016-11-01

Microplastics such as pellets are reported worldwide on sandy beaches, and have possible direct and indirect impacts on the biota and physical characteristics of the habitats where they accumulate. Evaluations of their standing stock at different spatial scales generate data on levels of contamination. This information is needed to identify accumulation zones and the specific beach habitats and communities that are likely to be most affected. Standing stocks of plastic pellets were evaluated in 13 sandy beaches in São Paulo state, Brazil. The sampling strategy incorporated across-shore transects from coastal dunes and backshores, and vertical profiles of the accumulated pellets down to 1 m depth below the sediment surface. Accumulation zones were identified at regional (among beaches) and local (between compartments) scales. At the regional scale pellet density tended to increase at beaches on the central and southwestern coast, near ports and factories that produce and transport the largest amounts of pellets in the country. At the local scale coastal dunes showed larger accumulations of pellets than backshores. For both compartments pellets tended to occur deeper in areas where standing stocks were larger. Most of the pellets were concentrated from the surface down to 0.4 m depth, suggesting that organisms inhabiting this part of the sediment column are more exposed to the risks associated with the presence of pellets. Our findings shed light on the local and regional scales of spatial variability of microplastics and their consequences for assessment and monitoring schemes in coastal compartments. Copyright © 2016. Published by Elsevier Ltd.

Initiation of a Low-Angle Normal Fault Active Across the Upper Brittle-Plastic Transition, Chemehuevi Mountains, CA

NASA Astrophysics Data System (ADS)

LaForge, J.; John, B. E.; Grimes, C. B.; Stunitz, H.; Heilbronner, R.

2016-12-01

The Chemehuevi detachment fault system, part of the regionally developed Colorado River extensional corridor, hosts exceptional exposures of a denuded fault system related to Miocene extension. Here, we characterize the early history of extension associated with a small slip (1-2 km) low-angle normal fault, the Mohave Wash fault (MWF), initially active across the brittle-plastic transition. Strain localized in three principal ways across the 23-km down-dip exposure (T <150° to >400°C): a brittle fault zone, localized, disseminated quartz mylonites, and syntectonic dikes hosting mylonitic fabrics. Brittle deformation in these crystalline rocks was concentrated into a 10-62-m thick brittle fault zone hosting localized, unmineralized to chlorite-epidote-quartz mineralized zones of cataclasite series fault rocks ≤3 m thick and rare pseudotachylite. Mylonitic deformation played an increased role in deformation down dip (NE), with mylonites increasing in quantity and average thickness. At shallow structural levels, footwall mylonites are absent; at 9-18 km down dip, cm-scale quartz mylonites are common; ≥18 km down dip, meter-scale syntectonic intermediate-felsic dikes are mylonitic, are attenuated into parallelism with the MWF, and host well-developed L-S fabric; 23 km down dip, the footwall hosts meter-thick zones of disseminated mylonitic quartz of varying intensities. These mylonites host microstructures that record progressively higher deformation temperature down dip, with dislocation-creep in quartz indicative of T of 280-400°C to ≥500°C, and diffusion creep with grain boundary sliding in dikes suggestive of even higher T deformation. Dike emplacement in the system is syntectonic with MWF slip; mafic-intermediate composition dikes intruded damage zone fractures and cataclasites, and were in turn fractured; Pb/U zircon ages of intermediate-felsic dikes range from ca. 1.5 ± 1 Ma to 3.8 ± 1 Ma after the onset of regional extension, but predate rapid slip. Cross cutting relations and absolute dating suggest the early history of the MWF evolved in two distinct phases: 1) seismogenic rupture with contemporaneous localized footwall mylonitization, followed by 2) additional cataclasis, episodic localized and magmatism, mylonitization and fluid-flow.

Double-Sided Single-Pass Submerged Arc Welding for 2205 Duplex Stainless Steel

NASA Astrophysics Data System (ADS)

Luo, Jian; Yuan, Yi; Wang, Xiaoming; Yao, Zongxiang

2013-09-01

The duplex stainless steel (DSS), which combines the characteristics of ferritic steel and austenitic steel, is used widely. The submerged arc welding (SAW) method is usually applied to join thick plates of DSS. However, an effective welding procedure is needed in order to obtain ideal DSS welds with an appropriate proportion of ferrite (δ) and austenite (γ) in the weld zone, particularly in the melted zone and heat-affected zone. This study evaluated the effectiveness of a high efficiency double-sided single-pass (DSSP) SAW joining method for thick DSS plates. The effectiveness of the converse welding procedure, characterizations of weld zone, and mechanical properties of welded joint are analyzed. The results show an increasing appearance and continuous distribution feature of the σ phase in the fusion zone of the leading welded seam. The converse welding procedure promotes the σ phase to precipitate in the fusion zone of leading welded side. The microhardness appears to significantly increase in the center of leading welded side. Ductile fracture mode is observed in the weld zone. A mixture fracture feature appears with a shear lip and tears in the fusion zone near the fusion line. The ductility, plasticity, and microhardness of the joints have a significant relationship with σ phase and heat treatment effect influenced by the converse welding step. An available heat input controlling technology of the DSSP formation method is discussed for SAW of thick DSS plates.

Fe-Ti-oxide textures and microstructures in shear zones from oceanic gabbros at Atlantis Bank, Southwest Indian Ridge

NASA Astrophysics Data System (ADS)

Till, Jessica; Morales, Luiz F. G.; Rybacki, Erik

2016-04-01

Ocean drilling expeditions at several oceanic core complexes formed at slow- and ultra-slow-spreading ridges have recovered cores containing numerous zones of oxide-rich gabbros containing ilmenite and magnetite. In these cores, high modal concentrations of Fe-Ti-oxides are systematically associated with high-temperature plastic deformation features in silicates. We present observations of Fe-Ti-oxide mineral structures and textural characteristics from a series of oxide-rich shear zones from Atlantis Bank (ODP Site 735B) on the Southwest Indian Ridge aimed at determining how oxide mineral abundances relate to strain localization. Fe-Ti-oxide minerals in undeformed oxide gabbros and in highly deformed samples from natural shear zones generally have morphologies characteristic of crystallized melt, including highly cuspate grains and low dihedral angles. Anisotropy of magnetic susceptibility in oxide-rich shear zones is very strong, with fabrics mainly characterized by strong magnetic foliations parallel to the macroscopic foliation. Crystallographic preferred orientations (CPO) in magnetite are generally weak, with occasionally well-defined textures. Ilmenite typically displays well-developed CPOs, however, the melt-like ilmenite grain shapes indicate that at least part of the crystallographic texture results from oriented ilmenite growth during post-deformation crystallization. The oxides are hypothesized to have initially been present as isolated pockets of trapped melt (intercumulus liquid) in a load-bearing silicate framework. Progressive plastic deformation of silicate phases at high-temperature mainly produced two features: (i) elongated melt pockets, which crystallized to form strings of opaque minerals and (ii), interconnected networks of melt regions. The latter lead to intense strain localization of the rock, which appears as oxide-rich mylonites in the samples. In some samples, abundant low-angle grain boundaries in both magnetite and ilmenite suggest that deformation may have continued after crystallization of the late melt, imposing a weak strain on the oxides. Recent experimental deformation results indicate that magnetite and ilmenite should be weaker than most mafic silicates under anhydrous conditions. However, melt-like oxide morphologies observed in Atlantis Bank shear zones indicate that the redistribution of Fe-Ti-oxide melts may have more influence on the strength and strain localization behavior of oceanic gabbros than their solid-state rheology.

Brittle to ductile transition in a model of sheared granular materials

NASA Astrophysics Data System (ADS)

Ma, X.; Elbanna, A. E.

2016-12-01

Understanding the fundamental mechanisms of deformation and failure in sheared fault gouge is critical for the development of physics-based earthquake rupture simulations that are becoming an essential ingredient in next generation hazard and risk models. To that end, we use the shear transformation zone (STZ) theory, a non-equilibrium statistical thermodynamics framework to describe viscoplastic deformation and localization in gouge materials as a first step towards developing multiscale models for earthquake source processes that are informed by high-resolution fault zone physics. The primary ingredient of the STZ theory is that inelastic deformation occurs at rare and local non-interacting soft zones known as the shear transformation zones. The larger the number of these STZs the more disordered (the more loose) the layer is. We will describe an implementation of this theory in a 2D/3D finite element framework, accounting for finite deformation, under both axial and shear loading and for dry and saturated conditions. We examine conditions under which a localized shear band may form and show that the initial value of disorder (or the initial porosity) plays an important role. In particular, our simulations suggest that if the material is more compact initially, the behavior is more brittle and the plastic deformation localizes with generating large strength drop. On the other hand, an initially loose material will show a more ductile response and the plastic deformations will be distributed more broadly. We will further show that incorporation of pore fluids alters the localization pattern and changes the stress slip response due to coupling between gouge volume changes (compaction and dilation) and pore pressure build up. We validate the model predictions by comparing them to available experimental observations on strain localization and fault gouge strength evolution. Finally, we discuss the implications of our model for gouge friction and dynamic weakening.

Evaluation of a local exhaust system used in the manufacture of small parts made of reinforced plastic.

PubMed

Lazure, L P

2000-09-01

Fiber-reinforced plastics are used to manufacture a large variety of products, particularly for the transportation sector. Hand lay-up molding and projection molding are the main methods of manufacture. The users of these processes are exposed to appreciable emissions of styrene; in Quebec, more than 3000 workers work in this industry. A statistical analysis of styrene concentrations measured over a five-year period by the Institut de recherche en santé et en sécurité du travail (IRSST, Occupational Health and Safety Research Institute) reveals that for all of the main manufacturing sectors involved, between 40 percent and 78 percent of the results exceed the exposure standard of 50 ppm. This study evaluated the effectiveness of a ventilated table in controlling worker exposure to styrene and acetone in a shop that manufactures fiber-reinforced plastics parts. The evaluated local extraction system consists of a ventilated table with a surface area of 1.2 m x 1.2 m. During molding, the styrene emissions are exhausted through the ventilated table as well as through the slots in a lateral hood. Replacement air, introduced vertically through a supply air shower located above the worker, limits the diffusion of contaminants toward the worker's breathing zone. The reduction in worker exposure to styrene and acetone during hand lay-up molding was measured in the breathing zone for two sizes of molds. The results show that exhaust ventilation reduced the styrene concentrations by 91 percent and that the introduction of replacement air increased the efficiency of the ventilated table to 96 percent. The evaluation performed indicates that the ventilated table adequately controls worker exposure to styrene and acetone during the molding of small components.

Mantle exhumation at magma-poor rifted margin: a competition between frictional shear zones and thermally weakened necking domains. Consequences on time of breakup at Galicia/Newfoundland margins.

NASA Astrophysics Data System (ADS)

Theunissen, T.; Huismans, R. S.

2017-12-01

Here we present a new analysis and interpretation of basement topography of the transitional domain from continental to oceanic crust along the conjugate margin sections SCREETCH-1 (Newfoundland) and WE-1/ISE-1 (Galicia Bank). The absence of significant syn-rift magmatism in this area allows using 2-D thermo-mechanical modelling to understand the formation of the distal margin and exhumed mantle. We show that plastic strain weakening of the exhumed mantle is required to explain observations on basement morphology, and detachment faulting. Our models predict that the evolution of detachment faulting within the transitional domain depends on the degree of frictional-plastic strain-weakening and varies from a single unique steady state asymmetric low angle detachment fault for large degree of strain weakening to multiple out-of-sequence forming detachments with or without dip reversal for lower amounts of strain-weakening. The model behaviour is a consequence of the competition between weak frictional-plastic shear zones and the thermally weakened necking domain in the footwall. The forward models reproduce elevations, wavelength of exhumed mantle ridges for a narrow range of rift velocitiesbetween 10 and 15 mm/yr and considering the increasing thermal conductivity of peridotites at shallow depth. This causes an efficient cooling of the footwall that has then enough strength to support high topography. The forward models also predict that the peridotite ridge is the breakaway of a second detachment fault that dates the crustal breakup and that rocks on top of the peridotite ridge have experimented a fast cooling (< 2 Ma). We use predictions from these forward models to discuss time of breakup and the position of the first steady state oceanic ridge at Galicia/Newfounlandconjugate margins.

Changed Synaptic Plasticity in Neural Circuits of Depressive-Like and Escitalopram-Treated Rats

PubMed Central

Li, Xiao-Li; Yuan, Yong-Gui; Xu, Hua; Wu, Di; Gong, Wei-Gang; Geng, Lei-Yu; Wu, Fang-Fang; Tang, Hao; Xu, Lin

2015-01-01

Background: Although progress has been made in the detection and characterization of neural plasticity in depression, it has not been fully understood in individual synaptic changes in the neural circuits under chronic stress and antidepressant treatment. Methods: Using electron microscopy and Western-blot analyses, the present study quantitatively examined the changes in the Gray’s Type I synaptic ultrastructures and the expression of synapse-associated proteins in the key brain regions of rats’ depressive-related neural circuit after chronic unpredicted mild stress and/or escitalopram administration. Meanwhile, their depressive behaviors were also determined by several tests. Results: The Type I synapses underwent considerable remodeling after chronic unpredicted mild stress, which resulted in the changed width of the synaptic cleft, length of the active zone, postsynaptic density thickness, and/or synaptic curvature in the subregions of medial prefrontal cortex and hippocampus, as well as the basolateral amygdaloid nucleus of the amygdala, accompanied by changed expression of several synapse-associated proteins. Chronic escitalopram administration significantly changed the above alternations in the chronic unpredicted mild stress rats but had little effect on normal controls. Also, there was a positive correlation between the locomotor activity and the maximal synaptic postsynaptic density thickness in the stratum radiatum of the Cornu Ammonis 1 region and a negative correlation between the sucrose preference and the length of the active zone in the basolateral amygdaloid nucleus region in chronic unpredicted mild stress rats. Conclusion: These findings strongly indicate that chronic stress and escitalopram can alter synaptic plasticity in the neural circuits, and the remodeled synaptic ultrastructure was correlated with the rats’ depressive behaviors, suggesting a therapeutic target for further exploration. PMID:25899067

Effect of Pre-strain and High Stresses on the Bainitic Transformation of Manganese-boron Steel 22MnB5

NASA Astrophysics Data System (ADS)

Said Schicchi, Diego; Hunkel, Martin

2018-03-01

During the last decade, the use of press-hardened components in the automotive industry has grown considerably. The so-called tailored tempering, also known as partial press hardening, employs locally heated tools seeking to obtain bainitic transformations. This leads to (seamless) zones within the formed parts with higher ductility. Due to the intrinsic nature of this process, phase transformations happen under the influence of high loads and in pre-deformed austenite. The austenite pre-strain state and applied stresses affect the kinetics of the bainitic transformation. Moreover, stresses have an additional relevant effect in this process, the so-called transformation plasticity. Linear transformation plasticity models have been successfully used to predict the behavior in the presence of low stresses. Nonetheless, because of the process's severe conditions, these tend to fail. A strong nonlinearity of the transformation plasticity strain is observed for applied stresses above the austenite yield strength. Using thermomechanical tests on sheet specimens of a manganese-boron steel (22MnB5), widely utilized in the industry, the effect on the bainitic transformation of various degrees of deformation in the range of 0 to 18 pct, applied stresses in the range of 0 to 250 MPa and the transformation plasticity effect are investigated in this work.

High-Strain-Rate Material Behavior and Adiabatic Material Instability in Impact of Micron-Scale Al-6061 Particles

NASA Astrophysics Data System (ADS)

Chen, Qiyong; Alizadeh, Arash; Xie, Wanting; Wang, Xuemei; Champagne, Victor; Gouldstone, Andrew; Lee, Jae-Hwang; Müftü, Sinan

2018-04-01

Impact of spherical particles onto a flat sapphire surface was investigated in 50-950 m/s impact speed range experimentally and theoretically. Material parameters of the bilinear Johnson-Cook model were determined based on comparison of deformed particle shapes from experiment and simulation. Effects of high-strain-rate plastic flow, heat generation due to plasticity, material damage, interfacial friction and heat transfer were modeled. Four distinct regions were identified inside the particle by analyzing temporal variation of material flow. A relatively small volume of material near the impact zone becomes unstable due to plasticity-induced heating, accompanied by severe drop in the flow stress for impact velocity that exceeds 500 m/s. Outside of this region, flow stress is reduced due to temperature effects without the instability. Load carrying capacity of the material degrades and the material expands horizontally leading to jetting. The increase in overall plastic and frictional dissipation with impact velocity was found to be inherently lower than the increase in the kinetic energy at high speeds, leading to the instability. This work introduces a novel method to characterize HSR (109 s-1) material properties and also explains coupling between HSR material behavior and mechanics that lead to extreme deformation.

Socioeconomic and Ecological Factors Influencing Aedes aegypti Prevalence, Abundance, and Distribution in Dhaka, Bangladesh

PubMed Central

Dhar-Chowdhury, Parnali; Haque, C. Emdad; Lindsay, Robbin; Hossain, Shakhawat

2016-01-01

This study examined household risk factors and prevalence, abundance, and distribution of immature Aedes aegypti and Aedes albopictus, and their association with socioeconomic and ecological factors at urban zonal and household levels in the city of Dhaka, Bangladesh. During the 2011 monsoon, 826 households in 12 randomly selected administrative wards were surveyed for vector mosquitoes. Results revealed that the abundance and distribution of immature Ae. aegypti and Ae. albopictus, and pupae-per-person indices did not vary significantly among the zones with varied socioeconomic status. Of 35 different types of identified wet containers, 30 were infested, and among the 23 pupae-positive container types, nine were defined as the “most productive” for pupae including: disposable plastic containers (12.2% of 550), sealable plastic barrels (12.0%), tires (10.4%), abandoned plastic buckets (9.6%), flower tub and trays (8.5%), refrigerator trays (6.5%), plastic bottles (6.4%), clay pots (4.9%), and water tanks (1.6%). When the function of the containers was assessed, ornamental, discarded, and household repairing and reconstruction-related container categories were found significantly associated with the number of pupae in the households. The purpose of storing water and income variables were significant predictors of possession of containers that were infested by vector mosquitoes. PMID:27022149

Effect of Pre-strain and High Stresses on the Bainitic Transformation of Manganese-boron Steel 22MnB5

NASA Astrophysics Data System (ADS)

Said Schicchi, Diego; Hunkel, Martin

2018-06-01

During the last decade, the use of press-hardened components in the automotive industry has grown considerably. The so-called tailored tempering, also known as partial press hardening, employs locally heated tools seeking to obtain bainitic transformations. This leads to (seamless) zones within the formed parts with higher ductility. Due to the intrinsic nature of this process, phase transformations happen under the influence of high loads and in pre-deformed austenite. The austenite pre-strain state and applied stresses affect the kinetics of the bainitic transformation. Moreover, stresses have an additional relevant effect in this process, the so-called transformation plasticity. Linear transformation plasticity models have been successfully used to predict the behavior in the presence of low stresses. Nonetheless, because of the process's severe conditions, these tend to fail. A strong nonlinearity of the transformation plasticity strain is observed for applied stresses above the austenite yield strength. Using thermomechanical tests on sheet specimens of a manganese-boron steel (22MnB5), widely utilized in the industry, the effect on the bainitic transformation of various degrees of deformation in the range of 0 to 18 pct, applied stresses in the range of 0 to 250 MPa and the transformation plasticity effect are investigated in this work.

Socioeconomic and Ecological Factors Influencing Aedes aegypti Prevalence, Abundance, and Distribution in Dhaka, Bangladesh.

PubMed

Dhar-Chowdhury, Parnali; Haque, C Emdad; Lindsay, Robbin; Hossain, Shakhawat

2016-06-01

This study examined household risk factors and prevalence, abundance, and distribution of immature Aedes aegypti and Aedes albopictus, and their association with socioeconomic and ecological factors at urban zonal and household levels in the city of Dhaka, Bangladesh. During the 2011 monsoon, 826 households in 12 randomly selected administrative wards were surveyed for vector mosquitoes. Results revealed that the abundance and distribution of immature Ae. aegypti and Ae. albopictus, and pupae-per-person indices did not vary significantly among the zones with varied socioeconomic status. Of 35 different types of identified wet containers, 30 were infested, and among the 23 pupae-positive container types, nine were defined as the "most productive" for pupae including: disposable plastic containers (12.2% of 550), sealable plastic barrels (12.0%), tires (10.4%), abandoned plastic buckets (9.6%), flower tub and trays (8.5%), refrigerator trays (6.5%), plastic bottles (6.4%), clay pots (4.9%), and water tanks (1.6%). When the function of the containers was assessed, ornamental, discarded, and household repairing and reconstruction-related container categories were found significantly associated with the number of pupae in the households. The purpose of storing water and income variables were significant predictors of possession of containers that were infested by vector mosquitoes. © The American Society of Tropical Medicine and Hygiene.

Investigation of Carbon Fiber Reinforced Plastics Machining Using 355 nm Picosecond Pulsed Laser

NASA Astrophysics Data System (ADS)

Hu, Jun; Zhu, Dezhi

2018-06-01

Carbon fiber reinforced plastics (CFRP) has been widely used in the aircraft industry and automobile industry owing to its superior properties. In this paper, a Nd:YVO4 picosecond pulsed system emitting at 355 nm has been used for CFRP machining experiments to determine optimum milling conditions. Milling parameters including laser power, milling speed and hatch distance were optimized by using box-behnken design of response surface methodology (RSM). Material removal rate was influenced by laser beam overlap ratio which affects mechanical denudation. The results in heat affected zones (HAZ) and milling quality were discussed through the machined surface observed with scanning electron microscope. A re-focusing technique based on the experiment with different focal planes was proposed and milling mechanism was also analyzed in details.

Continuous coal processing method

NASA Technical Reports Server (NTRS)

Ryason, P. R. (Inventor)

1980-01-01

A coal pump is provided in which solid coal is heated in the barrel of an extruder under pressure to a temperature at which the coal assumes plastic properties. The coal is continuously extruded, without static zones, using, for example, screw extrusion preferably without venting through a reduced diameter die to form a dispersed spray. As a result, the dispersed coal may be continuously injected into vessels or combustors at any pressure up to the maximum pressure developed in the extrusion device. The coal may be premixed with other materials such as desulfurization aids or reducible metal ores so that reactions occur, during or after conversion to its plastic state. Alternatively, the coal may be processed and caused to react after extrusion, through the die, with, for example, liquid oxidizers, whereby a coal reactor is provided.

Soil quality as a factor of the distribution of damages at the meizoseismal area of the Kozani-Grevena 1995 earthquake, in Greece ( Ms = 6.6)

NASA Astrophysics Data System (ADS)

Christaras, B.; Dimitriou, An; Lemoni, Hel

The physical and mechanical properties of the soil formations were related to the damages observed in Kozani and Grevena area, in Northern Greece, after the earth-quake of 13th May 1995 ( Ms = 6.6). Properties such as grain size distribution, plasticity, shear strength, compression index, permeability and ultrasonic velocity were measured in order to classify the suitability of the soil formations, for urban planning, and correlate their mechanical behaviour with the damages observed in the construction. According to our observations, a great number of recent buildings were damaged also in areas far away from the seismotectonic zones, where silty and clayey soils dominate, presenting very low permeability, low ultrasonic velocity together with high plasticity and compressibility.

Early Alcohol Exposure Disrupts Visual Cortex Plasticity in Mice

PubMed Central

Lantz, Crystal L.; Wang, Weili; Medina, Alexandre E.

2012-01-01

There is growing evidence that deficits in neuronal plasticity underlie the cognitive problems seen in fetal alcohol spectrum disorders (FASD). However, the mechanisms behind these deficits are not clear. Here we test the effects of early alcohol exposure on ocular dominance plasticity (ODP) in mice and the reversibility of these effects by phosphodiesterase (PDE) inhibitors. Mouse pups were exposed to 5 g/kg of 25% ethanol i.p. on postnatal days (P) 5, 7 and 9. This type of alcohol exposure mimics binge drinking during the third trimester equivalent of human gestation. To assess ocular dominance plasticity animals were monocularly deprived at P21 for 10 days, and tested using optical imaging of intrinsic signals. During the period of monocular deprivation animals were treated with vinpocetine (20mg/kg; PDE1 inhibitor), rolipram (1.25 mg/Kg; PDE4 inhibitor), vardenafil (3 mg/Kg; PDE5 inhibitor) or vehicle solution. Monocular deprivation resulted in the expected shift in ocular dominance of the binocular zone in saline controls but not in the ethanol group. While vinpocetine successfully restored ODP in the ethanol group, rolipram and vardenafil did not. However, when rolipram and vardenafil were given simultaneously ODP was restored. PDE4 and PDE5 are specific to cAMP and cGMP respectively, while PDE1 acts on both of these nucleotides. Our findings suggest that the combined activation of the cAMP and cGMP cascades may be a good approach to improve neuronal plasticity in FASD models. PMID:22617459

Plasticity of orientation preference maps in the visual cortex of adult cats.

PubMed

Godde, Ben; Leonhardt, Ralph; Cords, Sven M; Dinse, Hubert R

2002-04-30

In contrast to the high degree of experience-dependent plasticity usually exhibited by cortical representational maps, a number of experiments performed in visual cortex suggest that the basic layout of orientation preference maps is only barely susceptible to activity-dependent modifications. In fact, most of what we know about activity-dependent plasticity in adults comes from experiments in somatosensory, auditory, or motor cortex. Applying a stimulation protocol that has been proven highly effective in other cortical areas, we demonstrate here that enforced synchronous cortical activity induces major changes of orientation preference maps (OPMs) in adult cats. Combining optical imaging of intrinsic signals and electrophysiological single-cell recordings, we show that a few hours of intracortical microstimulation (ICMS) lead to an enlargement of the cortical representational zone at the ICMS site and an extensive restructuring of the entire OPM layout up to several millimeters away, paralleled by dramatic changes of pinwheel numbers and locations. At the single-cell level, we found that the preferred orientation was shifted toward the orientation of the ICMS site over a region of up to 4 mm. Our results show that manipulating the synchronicity of cortical activity locally without invoking training, attention, or reinforcement, OPMs undergo large-scale reorganization reminiscent of plastic changes observed for nonvisual cortical maps. However, changes were much more widespread and enduring. Such large-scale restructuring of the visual cortical networks indicates a substantial capability for activity-dependent plasticity of adult visual cortex and may provide the basis for cognitive learning processes.

Computer Software Management and Information Center

NASA Technical Reports Server (NTRS)

1983-01-01

Computer programs for passive anti-roll tank, earth resources laboratory applications, the NIMBUS-7 coastal zone color scanner derived products, transportable applications executive, plastic and failure analysis of composites, velocity gradient method for calculating velocities in an axisymmetric annular duct, an integrated procurement management system, data I/O PRON for the Motorola exorcisor, aerodynamic shock-layer shape, kinematic modeling, hardware library for a graphics computer, and a file archival system are documented.

Investigation of Interface Bonding Mechanism of an Explosively Welded Tri-Metal Titanium/Aluminum/Magnesium Plate by Nanoindentation

NASA Astrophysics Data System (ADS)

Zhang, T. T.; Wang, W. X.; Zhou, J.; Cao, X. Q.; Yan, Z. F.; Wei, Y.; Zhang, W.

2018-04-01

A tri-metal titanium/aluminum/magnesium (Ti/Al/Mg) cladding plate, with an aluminum alloy interlayer plate, was fabricated for the first time by explosive welding. Nanoindentation tests and associated microstructure analysis were conducted to investigate the interface bonding mechanisms of the Ti/Al/Mg cladding plate. A periodic wavy bonding interface (with an amplitude of approximately 30 μm and a wavelength of approximately 160 μm) without a molten zone was formed between the Ti and Al plates. The bonding interface between the Al and the Mg demonstrated a similar wavy shape, but the wave at this location was much larger with an amplitude of approximately 390 μm and a wavelength of approximately 1580 μm, and some localized melted zones also existed at this location. The formation of the wavy interface was found to result from a severe deformation at the interface, which was caused by the strong impact or collision. The nanoindentation tests showed that the material hardness decreased with increasing distance from the bonding interface. Material hardness at a location was found to be correlated with the degree of plastic deformation at that site. A larger plastic deformation was correlated with an increase in hardness.

Patterns of brittle deformation under extension on Venus

NASA Technical Reports Server (NTRS)

Neumann, G. A.; Zuber, M. T.

1994-01-01

The development of fractures at regular length scales is a widespread feature of Venusian tectonics. Models of lithospheric deformation under extension based on non-Newtonian viscous flow and brittle-plastic flow develop localized failure at preferred wavelengths that depend on lithospheric thickness and stratification. The characteristic wavelengths seen in rift zones and tessera can therefore provide constraints on crustal and thermal structure. Analytic solutions were obtained for growth rates in infinitesimal perturbations imposed on a one-dimensional, layered rheology. Brittle layers were approximated by perfectly-plastic, uniform strength, overlying ductile layers exhibiting thermally-activated power-law creep. This study investigates the formation of faults under finite amounts of extension, employing a finite-element approach. Our model incorporates non-linear viscous rheology and a Coulomb failure envelope. An initial perturbation in crustal thickness gives rise to necking instabilities. A small amount of velocity weakening serves to localize deformation into planar regions of high strain rate. Such planes are analogous to normal faults seen in terrestrial rift zones. These 'faults' evolve to low angle under finite extension. Fault spacing, orientation and location, and the depth to the brittle-ductile transition, depend in a complex way on lateral variations in crustal thickness. In general, we find that multiple wavelengths of deformation can arise from the interaction of crustal and mantle lithosphere.

Effect of Different Mulches under Rainfall Concentration System on Corn Production in the Semi-arid Areas of the Loess Plateau

NASA Astrophysics Data System (ADS)

Ren, Xiaolong; Zhang, Peng; Chen, Xiaoli; Guo, Jingjing; Jia, Zhikuan

2016-01-01

The ridge and furrow farming system for rainfall concentration (RC) has gradually been popularized to improve the water availability for crops and to increase the water use efficiency (WUE), thereby stabilizing high yields. In the RC system, plastic-covered ridges are rainfall harvesting zones and furrows are planting zones. In this study, we optimized the mulching patterns for RC planting to mitigate the risks of drought during crop production in semi-arid agricultural areas. We conducted a four-year field study to determine the effects on corn production of mulching with 0.08-mm plastic film, maize straw, 8% biodegradable film, liquid film, bare furrow, and conventional flat (CF) farming. We found that RC significantly increased (P > 0.05) the soil moisture storage in the top 0-100 cm layer and the topsoil temperature (0-10 cm) during the corn-growing season. Combining RC with mulching further improved the rain-harvesting, moisture-retaining, and yield-increasing effects in furrows. Compared with CF, the four-year average yield increased by 1497.1 kg ha-1 to 2937.3 kg ha-1 using RC with mulch treatments and the WUE increased by 2.3 kg ha-1 mm-1 to 5.1 kg ha-1 mm-1.

Effect of Different Mulches under Rainfall Concentration System on Corn Production in the Semi-arid Areas of the Loess Plateau.

PubMed

Ren, Xiaolong; Zhang, Peng; Chen, Xiaoli; Guo, Jingjing; Jia, Zhikuan

2016-01-11

The ridge and furrow farming system for rainfall concentration (RC) has gradually been popularized to improve the water availability for crops and to increase the water use efficiency (WUE), thereby stabilizing high yields. In the RC system, plastic-covered ridges are rainfall harvesting zones and furrows are planting zones. In this study, we optimized the mulching patterns for RC planting to mitigate the risks of drought during crop production in semi-arid agricultural areas. We conducted a four-year field study to determine the effects on corn production of mulching with 0.08-mm plastic film, maize straw, 8% biodegradable film, liquid film, bare furrow, and conventional flat (CF) farming. We found that RC significantly increased (P > 0.05) the soil moisture storage in the top 0-100 cm layer and the topsoil temperature (0-10 cm) during the corn-growing season. Combining RC with mulching further improved the rain-harvesting, moisture-retaining, and yield-increasing effects in furrows. Compared with CF, the four-year average yield increased by 1497.1 kg ha(-1) to 2937.3 kg ha(-1) using RC with mulch treatments and the WUE increased by 2.3 kg ha(-1) mm(-1) to 5.1 kg ha(-1) mm(-1).

Evaluation of the energy transfer in the char zone during ablation. Part 2: In-depth response of ablative composites, volume 1. Ph.D. Thesis, 1975. Final Report

NASA Technical Reports Server (NTRS)

Pike, R. W.; Delvalle, E. G.

1974-01-01

The decomposition of ablative composites is described along with the transport phenomena of pyrolysis gases which result from the decomposition of these plastics as they flow through the porous char of char-forming ablators. The pyrolysis products are those formed by the thermal degradation of nylon-phenolic resin and silicone elastomer composites. Emphasis is placed on the nature and extent of chemical reactions of the pyrolysis products and the char, along with the energy absorbed by the combined pyrolysis and char zone. Chemical reactions with thermodynamically consistent kinetic data are determined in order to develop a realistic analysis for predicting the thermal performance of ablative heat shields.

A silent slip event on the deeper Cascadia subduction interface.

PubMed

Dragert, G; Wang, K; James, T S

2001-05-25

Continuous Global Positioning System sites in southwestern British Columbia, Canada, and northwestern Washington state, USA, have been moving landward as a result of the locked state of the Cascadia subduction fault offshore. In the summer of 1999, a cluster of seven sites briefly reversed their direction of motion. No seismicity was associated with this event. The sudden displacements are best explained by approximately 2 centimeters of aseismic slip over a 50-kilometer-by-300-kilometer area on the subduction interface downdip from the seismogenic zone, a rupture equivalent to an earthquake of moment magnitude 6.7. This provides evidence that slip of the hotter, plastic part of the subduction interface, and hence stress loading of the megathrust earthquake zone, can occur in discrete pulses.

Mechanistic Study of Delamination Fracture in Al-Li Alloy C458 (2099)

NASA Technical Reports Server (NTRS)

Tayon, W. A.; Crooks, R. E.; Domack, M. S.; Wagner, J. A.; Beaudoin, A. J.; McDonald, R. J.

2009-01-01

Delamination fracture has limited the use of lightweight Al-Li alloys. In the present study, electron backscattered diffraction (EBSD) methods were used to characterize crack paths in Al-Li alloy C458 (2099). Secondary delamination cracks in fracture toughness samples showed a pronounced tendency for fracture between grain variants of the same deformation texture component. These results were analyzed by EBSD mapping methods and simulated with finite element analyses. Simulation procedures include a description of material anisotropy, local grain orientations, and fracture utilizing crystal plasticity and cohesive zone elements. Taylor factors computed for each grain orientation subjected to normal and shear stresses indicated that grain pairs with the largest Taylor factor differences were adjacent to boundaries that failed by delamination. Examination of matching delamination fracture surface pairs revealed pronounced slip bands in only one of the grains bordering the delamination. These results, along with EBSD studies, plasticity simulations, and Auger electron spectroscopy observations support a hypothesis that delamination fracture occurs due to poor slip accommodation along boundaries between grains with greatly differing plastic response.

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.

A numerical study of crack tip constraint in ductile single crystals

NASA Astrophysics Data System (ADS)

Patil, Swapnil D.; Narasimhan, R.; Mishra, R. K.

In this work, the effect of crack tip constraint on near-tip stress and deformation fields in a ductile FCC single crystal is studied under mode I, plane strain conditions. To this end, modified boundary layer simulations within crystal plasticity framework are performed, neglecting elastic anisotropy. The first and second terms of the isotropic elastic crack tip field, which are governed by the stress intensity factor K and T-stress, are prescribed as remote boundary conditions and solutions pertaining to different levels of T-stress are generated. It is found that the near-tip deformation field, especially, the development of kink or slip shear bands, is sensitive to the constraint level. The stress distribution and the size and shape of the plastic zone near the crack tip are also strongly influenced by the level of T-stress, with progressive loss of crack tip constraint occurring as T-stress becomes more negative. A family of near-tip fields is obtained which are characterized by two terms (such as K and T or J and a constraint parameter Q) as in isotropic plastic solids.

Effect of glycerol and zinc oxide addition on antibacterial activity of biodegradable bioplastics from chitosan-kepok banana peel starch

NASA Astrophysics Data System (ADS)

Agustin, Y. E.; Padmawijaya, K. S.

2017-07-01

Bioplastic is a biopolymer plastic that can be degraded easily by microorganisms so it can be used as alternative replaced commercial plastic. This research aims to study the effects of additive (glycerol and zinc oxide) addition in the characteristic of antimicrobial activity and biodegradability bioplastic from chitosan and Kepok banana peel starch. In this research, bioplastics were synthesized by chitosan as the backbone and antimicrobial, Kepok banana peel starch as filler, glycerol as plasticizer, also ZnO as an amplifier. Bioplastics were characterized their antimicrobial activity using agar diffusion method (zone inhibition assay) and biodegradability test using microbe (EM4). The result showed the optimum composition of bioplastic is kitosan 4 - 30% starch - 5 mL glycerol - 5% ZnO gives the good antimicrobial activity towards gram positive and gram negative bacteria, and this bioplastic will be degraded within an hour and 12 min. Thus, this bioplastics may have potential to be use for food packaging by having biodegradable properties and also inhibit bacterial growth.

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.

Effective temperature dynamics of shear bands in metallic glasses

NASA Astrophysics Data System (ADS)

Daub, Eric G.; Klaumünzer, David; Löffler, Jörg F.

2014-12-01

We study the plastic deformation of bulk metallic glasses with shear transformation zone (STZ) theory, a physical model for plasticity in amorphous systems, and compare it with experimental data. In STZ theory, plastic deformation occurs when localized regions rearrange due to applied stress and the density of these regions is determined by a dynamically evolving effective disorder temperature. We compare the predictions of STZ theory to experiments that explore the low-temperature deformation of Zr-based bulk metallic glasses via shear bands at various thermal temperatures and strain rates. By following the evolution of effective temperature with time, strain rate, and temperature through a series of approximate and numerical solutions to the STZ equations, we successfully model a suite of experimentally observed phenomena, including shear-band aging as apparent from slide-hold-slide tests, a temperature-dependent steady-state flow stress, and a strain-rate- and temperature-dependent transition from stick-slip (serrated flow) to steady-sliding (nonserrated flow). We find that STZ theory quantitatively matches the observed experimental data and provides a framework for relating the experimentally measured energy scales to different types of atomic rearrangements.

North America-Pacific plate boundary, an elastic-plastic megashear - Evidence from very long baseline interferometry

NASA Technical Reports Server (NTRS)

Ward, Steven N.

1988-01-01

Data obtained by Mark III VLBI measurements of radio signals from permanent and mobile VLBI sites for 5.5 years of observations, starting in October 1982, were used to derive a picture of the earth crust deformation near the North America-Pacific plate boundary. The data, which included the vector positions of the VLBI sites and their rate of change, were used for comparison with a number of lithospheric deformation models based upon the concept that the motions of points near the North America-Pacific plate boundary are a linear combination of North America and Pacific velocities. The best of these models were found to fit 95 percent of the variance in 139 VLBI length and transverse velocity observations. Instantaneous shear deformation associated with plate tectonics is apparently developing in a zone 450 km wide paralleling the San Andreas Fault; some of this deformation will be recovered through elastic rebound, while the rest will be permanently set through plastic processes. Because the VLBI data have not been collected for a significant fraction of the earthquake cycle, they cannot discriminate between elastic and plastic behaviors.

Bassoon-disruption slows vesicle replenishment and induces homeostatic plasticity at a CNS synapse

PubMed Central

Mendoza Schulz, Alejandro; Jing, Zhizi; María Sánchez Caro, Juan; Wetzel, Friederike; Dresbach, Thomas; Strenzke, Nicola; Wichmann, Carolin; Moser, Tobias

2014-01-01

Endbulb of Held terminals of auditory nerve fibers (ANF) transmit auditory information at hundreds per second to bushy cells (BCs) in the anteroventral cochlear nucleus (AVCN). Here, we studied the structure and function of endbulb synapses in mice that lack the presynaptic scaffold bassoon and exhibit reduced ANF input into the AVCN. Endbulb terminals and active zones were normal in number and vesicle complement. Postsynaptic densities, quantal size and vesicular release probability were increased while vesicle replenishment and the standing pool of readily releasable vesicles were reduced. These opposing effects canceled each other out for the first evoked EPSC, which showed unaltered amplitude. We propose that ANF activity deprivation drives homeostatic plasticity in the AVCN involving synaptic upscaling and increased intrinsic BC excitability. In vivo recordings from individual mutant BCs demonstrated a slightly improved response at sound onset compared to ANF, likely reflecting the combined effects of ANF convergence and homeostatic plasticity. Further, we conclude that bassoon promotes vesicular replenishment and, consequently, a large standing pool of readily releasable synaptic vesicles at the endbulb synapse. PMID:24442636

Investigating Some Technical Issues on Cohesive Zone Modeling of Fracture

NASA Technical Reports Server (NTRS)

Wang, John T.

2011-01-01

This study investigates some technical issues related to the use of cohesive zone models (CZMs) in modeling fracture processes. These issues include: why cohesive laws of different shapes can produce similar fracture predictions; under what conditions CZM predictions have a high degree of agreement with linear elastic fracture mechanics (LEFM) analysis results; when the shape of cohesive laws becomes important in the fracture predictions; and why the opening profile along the cohesive zone length needs to be accurately predicted. Two cohesive models were used in this study to address these technical issues. They are the linear softening cohesive model and the Dugdale perfectly plastic cohesive model. Each cohesive model constitutes five cohesive laws of different maximum tractions. All cohesive laws have the same cohesive work rate (CWR) which is defined by the area under the traction-separation curve. The effects of the maximum traction on the cohesive zone length and the critical remote applied stress are investigated for both models. For a CZM to predict a fracture load similar to that obtained by an LEFM analysis, the cohesive zone length needs to be much smaller than the crack length, which reflects the small scale yielding condition requirement for LEFM analysis to be valid. For large-scale cohesive zone cases, the predicted critical remote applied stresses depend on the shape of cohesive models used and can significantly deviate from LEFM results. Furthermore, this study also reveals the importance of accurately predicting the cohesive zone profile in determining the critical remote applied load.

Evolution of a calcite marble shear zone complex on Thassos Island, Greece: microstructural and textural fabrics and their kinematic significance

NASA Astrophysics Data System (ADS)

Bestmann, Michel; Kunze, Karsten; Matthews, Alan

2000-11-01

The deformation history of a monophase calcite marble shear zone complex on Thassos Island, Northern Greece, is reconstructed by detailed geometric studies of the textural and microstructural patterns relative to a fixed reference system (shear zone boundary, SZB). Strain localization within the massive marble complex is linked to decreasing P- T conditions during the exhumation process of the metamorphic core complex. Solvus thermometry indicates that temperatures of 300-350°C prevailed during part of the shear zone deformation history. The coarse-grained marble protolith outside the shear zone is characterized by symmetrically oriented twin sets due to early coaxial deformation. A component of heterogeneous non-coaxial deformation is first recorded within the adjacent protomylonite. Enhanced strain weakening by dynamic recrystallization promoted strong localization of plastic deformation in the ultramylonite of the calcite shear zone, where high strain was accommodated by non-coaxial flow. This study demonstrates that both a pure shear and a simple shear strain path can result in similar crystallographic preferred orientations (single c-axis maximum perpendicular to the SZB) by different dominant deformation mechanisms. Separated a-axis pole figures (+ a- and - a-axis) show different density distributions with orthorhombic texture symmetry in the protolith marble and monoclinic symmetry in the ultramylonite marble consistently with the observed grain fabric symmetry.

Modelling Earthquakes Using a Poro-Elastic Two-Phase Flow Formulation

NASA Astrophysics Data System (ADS)

Petrini, C.; Gerya, T.; van Dinther, Y.; Connolly, J. A.; Madonna, C.

2017-12-01

Seismicity along subduction zones ranges from large devastating megathrust earthquakes to aseismic slow slip events. These different slip phenomena are widely believed to be influenced by fluids and interactions of fluids with the host rock. To understand the slip or strain mode along the megathrust interface, it is thus crucial to understand the role of fluids. Considering the spatiotemporal limitations of observations, a promising approach is to develop a numerical model that couples the deformation of both fluids and solids in a single framework. The objective of this study is the development of such a seismo-hydro-mechanical approach and the subsequent identification of parameters that control the mode of slip. We present a newly developed finite difference visco-elasto-plastic numerical code with marker-in-cell technique, which fully couples inertial mechanical deformation and fluid flow. It allows for the accurate treatment of localised brittle/plastic deformation through global iterations. To accurately simulate both long- and short-term deformation an adaptive time step is introduced. This makes it possible to resolve seismic event with time steps on the order of milliseconds. We use this new tool to investigate how the presence of fluids in the pore space of an visco-elasto-brittle/plastic (de)compacting rock matrix affects elastic stress accumulation and release along a fluid-bearing subduction interface. The model is able to simulate spontaneous quasi-periodic seismic events, nucleating near the brittle-ductile transition zone, along self-consistently forming highly localized ruptures, which accommodate shear displacement between two plates. The generated elastic rebound events show slip velocities on the order of m/s. The governing gradual strength decrease along the propagating fracture is related to a drop in total pressure due to shear localization in combination with an increase in fluid pressure due to elastic compaction of the pore space in a rock with low permeability (6e-19 m2). Reduction of the differential pressure decreases brittle/plastic strength of fluid-bearing rocks along the rupture, thus providing a dynamic feedback mechanism for the accumulated elastic stress release at the subduction interface.

Deformation processes and weakening mechanisms within the frictional viscous transition zone of major crustal-scale faults: insights from the Great Glen Fault Zone, Scotland

NASA Astrophysics Data System (ADS)

Stewart, M.; Holdsworth, R. E.; Strachan, R. A.

2000-05-01

The Great Glen Fault Zone (GGFZ), Scotland, is a typical example of a crustal-scale, reactivated strike-slip fault within the continental crust. Analysis of intensely strained fault rocks from the core of the GGFZ near Fort William provides a unique insight into the nature of deformation associated with the main phase of (sinistral) movements along the fault zone. In this region, an exhumed sequence of complex mid-crustal deformation textures that developed in the region of the frictional-viscous transition (ca. 8-15 km depth) is preserved. Fault rock fabrics vary from mylonitic in quartzites to cataclastic in micaceous shear zones and feldspathic psammites. Protolith mineralogy exerted a strong control on the initial textural development and distribution of the fault rocks. At lower strains, crystal-plastic deformation occurred in quartz-dominated lithologies to produce mylonites simultaneously with widespread fracturing and cataclasis in feldspar- and mica-dominated rocks. At higher strains, shearing appears to increasingly localise into interconnected networks of cataclastic shear zones, many of which are strongly foliated. Textures indicative of fluid-assisted diffusive mass transfer mechanisms are widespread in such regions and suggest that a hydrous fluid-assisted, grainsize-controlled switch in deformation behaviour followed the brittle comminution of grains. The fault zone textural evolution implies that a strain-induced, fluid-assisted shallowing and narrowing of the frictional-viscous transition occurred with increasing strain. It is proposed that this led to an overall weakening of the fault zone and that equivalent processes may occur along many other long-lived, crustal-scale dislocations.

Integrated petrographic - rock mechanic borecore study from the metamorphic basement of the Pannonian Basin, Hungary

NASA Astrophysics Data System (ADS)

Molnár, László; Vásárhelyi, Balázs; Tóth, Tivadar M.; Schubert, Félix

2015-01-01

The integrated evaluation of borecores from the Mezősas-Furta fractured metamorphic hydrocarbon reservoir suggests significantly distinct microstructural and rock mechanical features within the analysed fault rock samples. The statistical evaluation of the clast geometries revealed the dominantly cataclastic nature of the samples. Damage zone of the fault can be characterised by an extremely brittle nature and low uniaxial compressive strength, coupled with a predominately coarse fault breccia composition. In contrast, the microstructural manner of the increasing deformation coupled with higher uniaxial compressive strength, strain-hardening nature and low brittleness indicate a transitional interval between the weakly fragmented damage zone and strongly grinded fault core. Moreover, these attributes suggest this unit is mechanically the strongest part of the fault zone. Gougerich cataclasites mark the core zone of the fault, with their widespread plastic nature and locally pseudo-ductile microstructure. Strain localization tends to be strongly linked with the existence of fault gouge ribbons. The fault zone with ˜15 m total thickness can be defined as a significant migration pathway inside the fractured crystalline reservoir. Moreover, as a consequence of the distributed nature of the fault core, it may possibly have a key role in compartmentalisation of the local hydraulic system.

Strain rate dependent calcite microfabric evolution - An experiment carried out by nature

NASA Astrophysics Data System (ADS)

Rogowitz, Anna; Grasemann, Bernhard; Huet, Benjamin; Habler, Gerlinde

2014-12-01

A flanking structure developed along a secondary shear zone in calcite marbles, on Syros (Cyclades, Greece), provides a natural laboratory for directly studying the effects of strain rate variations on calcite deformation at identical pressure and temperature conditions. The presence and rotation of a fracture during progressive deformation caused extreme variations in finite strain and strain rate, forming a localized ductile shear zone that shows different microstructures and textures. Textures and the degree of intracrystalline deformation were measured by electron backscattered diffraction. Marbles from the host rocks and the shear zone, which deformed at various strain rates, display crystal-preferred orientation, suggesting that the calcite preferentially deformed by intracrystalline-plastic deformation. Increasing strain rate results in a switch from subgrain rotation to bulging recrystallization in the dislocation-creep regime. With increasing strain rate, we observe in fine-grained (3 μm) ultramylonitic zones a change in deformation regime from grain-size insensitive to grain-size sensitive. Paleowattmeter and the paleopiezometer suggest strain rates for the localized shear zone around 10-10 s-1 and for the marble host rock around 10-12 s-1. We conclude that varying natural strain rates can have a first-order effect on the microstructures and textures that developed under the same metamorphic conditions.

3D Dynamic Rupture Simulations along Dipping Faults, with a focus on the Wasatch Fault Zone, Utah

NASA Astrophysics Data System (ADS)

Withers, K.; Moschetti, M. P.

2017-12-01

We study dynamic rupture and ground motion from dip-slip faults in regions that have high-seismic hazard, such as the Wasatch fault zone, Utah. Previous numerical simulations have modeled deterministic ground motion along segments of this fault in the heavily populated regions near Salt Lake City but were restricted to low frequencies ( 1 Hz). We seek to better understand the rupture process and assess broadband ground motions and variability from the Wasatch Fault Zone by extending deterministic ground motion prediction to higher frequencies (up to 5 Hz). We perform simulations along a dipping normal fault (40 x 20 km along strike and width, respectively) with characteristics derived from geologic observations to generate a suite of ruptures > Mw 6.5. This approach utilizes dynamic simulations (fully physics-based models, where the initial stress drop and friction law are imposed) using a summation by parts (SBP) method. The simulations include rough-fault topography following a self-similar fractal distribution (over length scales from 100 m to the size of the fault) in addition to off-fault plasticity. Energy losses from heat and other mechanisms, modeled as anelastic attenuation, are also included, as well as free-surface topography, which can significantly affect ground motion patterns. We compare the effect of material structure and both rate and state and slip-weakening friction laws have on rupture propagation. The simulations show reduced slip and moment release in the near surface with the inclusion of plasticity, better agreeing with observations of shallow slip deficit. Long-wavelength fault geometry imparts a non-uniform stress distribution along both dip and strike, influencing the preferred rupture direction and hypocenter location, potentially important for seismic hazard estimation.

Enhancing workability in sheet production of high silicon content electrical steel through large shear deformation

DOE PAGES

Kustas, Andrew B.; Johnson, David R.; Trumble, Kevin P.; ...

2018-07-01

Enhanced workability, as characterized by the magnitude and heterogeneity of accommodated plastic strains during sheet processing, is demonstrated in high Si content Fe-Si alloys containing 4 and 6.5 wt% Si using two single-step, simple-shear deformation techniques – peeling and large strain extrusion machining (LSEM). The model Fe-Si material system was selected for its intrinsically poor material workability, and well-known applications potential in next-generation electric machines. In a comparative study of the deformation characteristics of the shear processes with conventional rolling, two distinct manifestations of workability are observed. For rolling, the relatively diffuse and unconfined deformation zone geometry leads to crackingmore » at low strains, with sheet structures characterized by extensive deformation twinning and banding. Workpiece pre-heating is required to improve the workability in rolling. In contrast, peeling and LSEM produce continuous sheet at large plastic strains without cracking, the result of more confined deformation geometries that enhances the workability. Peeling, however, results in heterogeneous, shear-banded microstructures, pointing to a second type of workability issue – flow localization – that limits sheet processing. This shear banding is to a large extent facilitated by unrestricted flow at the sheet surface, unavoidable in peeling. With additional confinement of this free surface deformation and appropriately designed deformation zone geometry, LSEM is shown to suppress shear banding, resulting in continuous sheet with homogeneous microstructure. Thus LSEM is shown to produce the greatest enhancement in process workability for producing sheet. In conclusion, these workability findings are explained and discussed based on differences in process mechanics and deformation zone geometry.« less

Enhancing workability in sheet production of high silicon content electrical steel through large shear deformation

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

Kustas, Andrew B.; Johnson, David R.; Trumble, Kevin P.

Enhanced workability, as characterized by the magnitude and heterogeneity of accommodated plastic strains during sheet processing, is demonstrated in high Si content Fe-Si alloys containing 4 and 6.5 wt% Si using two single-step, simple-shear deformation techniques – peeling and large strain extrusion machining (LSEM). The model Fe-Si material system was selected for its intrinsically poor material workability, and well-known applications potential in next-generation electric machines. In a comparative study of the deformation characteristics of the shear processes with conventional rolling, two distinct manifestations of workability are observed. For rolling, the relatively diffuse and unconfined deformation zone geometry leads to crackingmore » at low strains, with sheet structures characterized by extensive deformation twinning and banding. Workpiece pre-heating is required to improve the workability in rolling. In contrast, peeling and LSEM produce continuous sheet at large plastic strains without cracking, the result of more confined deformation geometries that enhances the workability. Peeling, however, results in heterogeneous, shear-banded microstructures, pointing to a second type of workability issue – flow localization – that limits sheet processing. This shear banding is to a large extent facilitated by unrestricted flow at the sheet surface, unavoidable in peeling. With additional confinement of this free surface deformation and appropriately designed deformation zone geometry, LSEM is shown to suppress shear banding, resulting in continuous sheet with homogeneous microstructure. Thus LSEM is shown to produce the greatest enhancement in process workability for producing sheet. In conclusion, these workability findings are explained and discussed based on differences in process mechanics and deformation zone geometry.« less

Dysregulated post-synaptic density and endocytic zone in the amygdala of human heroin and cocaine abusers

PubMed Central

Ökvist, Anna; Fagergren, Pernilla; Whittard, John; Garcia-Osta, Ana; Drakenberg, Katarina; Horvath, Monika Cs.; Schmidt, Carl J.; Keller, Eva; Bannon, Michael J.; Hurd, Yasmin L.

2010-01-01

Background Glutamatergic transmission in the amygdala is hypothesized as an important mediator of stimulus-reward associations contributing to drug-seeking behavior and relapse. Insight is, however, lacking regarding the amygdala glutamatergic system in human drug abusers. Methods We examined glutamate receptors and scaffolding proteins associated with the post-synaptic density (PSD) of excitatory synapses in the human post-mortem amygdala. mRNA or protein levels were studied in a multi-drug (7 heroin, 8 cocaine, 7 heroin/cocaine and 7 control) or predominant heroin (29 heroin and 15 control) population of subjects. Results The amygdala of drug abusers was characterized by a striking positive correlation (r > 0.8) between AMPA GluA1 and post-synaptic protein-95 (PSD-95) mRNA levels, which was not evident in controls. Structural equation multi-group analysis of protein correlations also identified the relationship between GluA1 and PSD-95 protein levels as the distinguishing feature of abusers. In line with the GluA1—PSD-95 implications of enhanced synaptic plasticity, Homer 1b/c protein expression was significantly increased in both heroin and cocaine users as was its binding partner dynamin-3, localized to the endocytic zone. Furthermore, there was a positive relationship between Homer 1b/c and dynamin-3 in drug abusers that reflected an increase in the direct physical coupling between the proteins. A noted age-related decline of Homer 1b/c—dynamin-3 interactions, as well as GluA1 levels, was blunted in abusers. Conclusions Impairment of key components of the amygdala PSD and coupling to the endocytic zone, critical for the regulation of glutamate receptor cycling, may underlie heightened synaptic plasticity in human drug abusers. PMID:21126734

On the feedback between forearc morphotectonics and megathrust earthquakes in subduction zones

NASA Astrophysics Data System (ADS)

Rosenau, M.; Oncken, O.

2008-12-01

An increasing number of observations suggest an intrinsic relationship between short- and long-term deformation processes in subduction zones. These include the global correlation between megathrust earthquake slip patterns with morphotectonic forearc features, the historical predominance of giant earthquakes (M > 9) along accretionary margins and the occurrence of (slow and shallow) tsunami earthquakes along erosive margins. To gain insight into the interplay between seismogenesis and tectonics in subduction settings we have developed a new modeling technique which joins analog and elastic dislocation approaches. Using elastoplastic wedges overlying a rate- and state-dependent interface, we demonstrate how analog earthquakes drive permanent wedge deformation consistent with the dynamic Coulomb wedge theory and how wedge deformation in turn controls basal "seismicity". During an experimental run, elastoplastic wedges evolve from those comparable to accretionary margins, characterized by plastic wedge shortening, to those mimicking erosive margins, characterized by minor plastic deformation. Permanent shortening localizes at the periphery of the "seismogenic" zone leading to a "morphotectonic" segmentation of the upper plate. Along with the evolving segmentation of the wedge, the magnitude- frequency relationship and recurrence distribution of analog earthquakes develop towards more periodic events of similar size (i.e. characteristic earthquakes). From the experiments we infer a positive feedback between short- and long-term deformation processes which tends to stabilize the spatiotemporal patterns of elastoplastic deformation in subduction settings. We suggest (1) that forearc anatomy reflects the distribution of seismic and aseismic slip at depth, (2) that morphotectonic segmentation assists the occurrence of more characteristic earthquakes, (3) that postseismic near-trench shortening relaxes coseismic compression by megathrust earthquakes and thus reduces tsunami earthquake risk in accretionary settings and (4) that permanent coastal shortening allows adjacent segments to fail more synchronized thus triggering much greater earthquakes in accretionary settings.

Plasticity of the dense hydrous magnesium silicate phase A at subduction zones conditions

DOE PAGES

Gouriet, K.; Hilairet, N.; Amiguet, E.; ...

2015-09-12

The plasticity of the dense hydrous magnesium silicate (DHMS) phase A, a key hydrous mineral within cold subduction zones, was investigated by two complementary approaches: high-pressure deformation experiments and computational methods. The deformation experiments were carried out at 11 GPa, 400 and 580 °C, with in situ measurements of stress, strain and lattice preferred orientations (LPO). Based on viscoplastic self-consistent modeling (VPSC) of the observed LPO, the deformation mechanisms at 580 °C are consistent with glide on the (0 0 0 1) basal and prismatic planes. At 400 °C the deformation mechanisms involve glide on prismatic, (0 0 0 1)more » basal and pyramidal planes. Both give flow stresses of 2.5–3 GPa at strain rates of 2–4 × 10-5 s-1. We use the Peierls–Nabarro–Galerkin (PNG) approach, relying on first-principles calculations of generalized stacking fault (γ-surface), and model the core structure of potential dislocations in basal and prismatic planes. The computations show multiple dissociations of the and dislocations (⟨a⟩ and ⟨b⟩ dislocations) in the basal plane, which is compatible with the ubiquity of basal slip in the experiments. The γ-surface calculations also suggest and dislocations (⟨a+c⟩ or ⟨c-b⟩ directions) in prismatic and pyramidal planes, which is also consistent with the experimental data. Phase A has a higher flow strength than olivine. When forming at depths from the dehydration of weak and highly anisotropic hydrated ultramafic rocks, phase A may not maintain the mechanical softening antigorite can provide. The seismic properties calculated for moderately deformed aggregates suggest that S-wave seismic anisotropy of phase A-bearing rocks is lower than hydrous subduction zone lithologies such as serpentinites and blueschists.« less

Resource Partitioning in Food, Space and Time between Arctic Charr (Salvelinus alpinus), Brown Trout (Salmo trutta) and European Whitefish (Coregonus lavaretus) at the Southern Edge of Their Continuous Coexistence.

PubMed

Jensen, Hallvard; Kiljunen, Mikko; Knudsen, Rune; Amundsen, Per-Arne

2017-01-01

Arctic charr and European whitefish are considered to be strong competitors in lakes, with the latter usually being the superior species. However, high niche plasticity and lake morphometry may suggestively facilitate resource partitioning and coexistence between charr and whitefish. Here, we explore the trophic niche utilization (diet and habitat use) of charr and whitefish co-occurring with brown trout in the deep and oligotrophic Lake Fyresvatnet, southern Norway (59°05'N, 8°10'E). Using CPUE, stomach contents and stable isotope analyses, a distinct resource partitioning was revealed between brown trout and the other two species. Brown trout typically occupied the littoral zone, feeding on benthic invertebrates, surface insects and small-sized whitefish. In contrast, charr and whitefish were predominantly zooplanktivorous, but diverged somewhat in habitat utilization as charr shifted seasonally between the profundal and the littoral zone, whereas whitefish were found in the upper water layers (littoral and pelagic habitats). Accordingly, the stable isotope values of carbon (δ13C) reflected a pelagic orientated prey resource use for both charr and whitefish, whereas brown trout had elevated carbon and nitrogen (δ15N) signatures that reflected their benthivore and piscivore diet, respectively. The findings suggest that charr may not rely upon the profundal zone as a feeding habitat but as a refuge area, and may coexist with whitefish if a third competitive and predatory species like brown trout co-occur in the lake. The study indicates that a general high habitat plasticity of Arctic charr may be essential in the presently observed coexistence with a competitively superior fish species like whitefish, and that a third fish species like brown trout may facilitate this particular fish community structure.

Modeling of sheet metal fracture via cohesive zone model and application to spot welds

NASA Astrophysics Data System (ADS)

Wu, Joseph Z.

Even though the cohesive zone model (CZM) has been widely used to analyze ductile fracture, it is not yet clearly understood how to calibrate the cohesive parameters including the specific work of separation (the work of separation per unit crack area) and the peak stress. A systematic approach is presented to first determine the cohesive values for sheet metal and then apply the calibrated model to various structure problems including the failure of spot welds. Al5754-0 was chosen for this study since it is not sensitive to heat treatment so the effect of heat-affected-zone (HAZ) can be ignored. The CZM has been applied to successfully model both mode-I and mode-III fracture for various geometries including Kahn specimens, single-notch specimens, and deep double-notch specimens for mode-I and trouser specimens for mode-III. The mode-I fracture of coach-peel spot-weld nugget and the mixed-mode fracture of nugget pull-out have also been well simulated by the CZM. Using the mode-I average specific work of separation of 13 kJ/m2 identified in a previous work and the mode-III specific work of separation of 38 kJ/m 2 found in this thesis, the cohesive peak stress has been determined to range from 285 MPa to 600 MPa for mode-I and from 165 MPa to 280 MPa for mode-III, depending on the degree of plastic deformation. The uncertainty of these cohesive values has also been examined. It is concluded that, if the specific work of separation is a material constant, the peak stress changes with the degree of plastic deformation and is therefore geometry-dependent.

Numerical modeling of seismic anomalies at impact craters on a laboratory scale

NASA Astrophysics Data System (ADS)

Wuennemann, K.; Grosse, C. U.; Hiermaier, S.; Gueldemeister, N.; Moser, D.; Durr, N.

2011-12-01

Almost all terrestrial impact craters exhibit a typical geophysical signature. The usually observed circular negative gravity anomaly and reduced seismic velocities in the vicinity of crater structures are presumably related to an approximately hemispherical zone underneath craters where rocks have experienced intense brittle plastic deformation and fracturing during formation (see Fig.1). In the framework of the "MEMIN" (multidisciplinary experimental and modeling impact crater research network) project we carried out hypervelocity cratering experiments at the Fraunhofer Institute for High-Speed Dynamics on a decimeter scale to study the spatiotemporal evolution of the damage zone using ultrasound, acoustic emission techniques, and numerical modeling of crater formation. 2.5-10 mm iron projectiles were shot at 2-5.5 km/s on dry and water-saturated sandstone targets. The target material was characterized before, during and after the impact with high spatial resolution acoustic techniques to detect the extent of the damage zone, the state of rocks therein and to record the growth of cracks. The ultrasound measurements are applied analog to seismic surveys at natural craters but used on a different - i.e. much smaller - scale. We compare the measured data with dynamic models of crater formation, shock, plastic and elastic wave propagation, and tensile/shear failure of rocks in the impacted sandstone blocks. The presence of porosity and pore water significantly affects the propagation of waves. In particular the crushing of pores due to shock compression has to be taken into account. We present preliminary results showing good agreement between experiments and numerical model. In a next step we plan to use the numerical models to upscale the results from laboratory dimensions to the scale of natural impact craters.

A Hydrous Seismogenic Fault Rock Indicating A Coupled Lubrication Mechanism

NASA Astrophysics Data System (ADS)

Okamoto, S.; Kimura, G.; Takizawa, S.; Yamaguchi, H.

2005-12-01

In the seismogenic subduction zone, the predominant mechanisms have been considered to be fluid induced weakening mechanisms without frictional melting because the subduction zone is fundamentally quite hydrous under low temperature conditions. However, recently geological evidence of frictional melting has been increasingly reported from several ancient accretionary prisms uplifted from seismogenic depths of subduction zones (Ikesawa et al., 2003; Austrheim and Andersen, 2004; Rowe et al., 2004; Kitamura et al., 2005) but relationship between conflicting mechanisms; e.g. thermal pressurization of fluid and frictional melting is still unclear. We found a new exposure of pseudotachylyte from a fossilized out-of-sequence thrust (OOST) , Nobeoka thrust in the accretionary complex, Kyushu, southwest Japan. Hanging-wall and foot-wall are experienced heating up to maximum temperature of about 320/deg and about 250/deg, respectively. Hanging-wall rocks of the thrust are composed of shales and sandstones deformed plastically. Foot-wall rocks are composed of shale matrix melange with sandstone and basaltic blocks deformed in a brittle fashion (Kondo et al, 2005). The psudotachylyte was found from one of the subsidiary faults in the hanging wall at about 10 m above the fault core of the Nobeoka thrust. The fault is about 1mm in width, and planer rupture surface. The fault maintains only one-time slip event because several slip surfaces and overlapped slip textures are not identified. The fault shows three deformation stages: The first is plastic deformation of phyllitic host rocks; the second is asymmetric cracking formed especially in the foot-wall of the fault. The cracks are filled by implosion breccia hosted by fine carbonate minerals; the third is frictional melting producing pseudotachylyte. Implosion breccia with cracking suggests that thermal pressurization of fluid and hydro-fracturing proceeded frictional melting.

Single-Molecule Discrimination within Dendritic Spines of Discrete Perisynaptic Sites of Actin Filament Assembly Driving Postsynaptic Reorganization

NASA Astrophysics Data System (ADS)

Blanpied, Thomas A.

2013-03-01

In the brain, the strength of synaptic transmission between neurons is principally set by the organization of proteins within the receptive, postsynaptic cell. Synaptic strength at an individual site of contact can remain remarkably stable for months or years. However, it also can undergo diverse forms of plasticity which change the strength at that contact independent of changes to neighboring synapses. Such activity-triggered neural plasticity underlies memory storage and cognitive development, and is disrupted in pathological physiology such as addiction and schizophrenia. Much of the short-term regulation of synaptic plasticity occurs within the postsynaptic cell, in small subcompartments surrounding the synaptic contact. Biochemical subcompartmentalization necessary for synapse-specific plasticity is achieved in part by segregation of synapses to micron-sized protrusions from the cell called dendritic spines. Dendritic spines are heavily enriched in the actin cytoskeleton, and regulation of actin polymerization within dendritic spines controls both basal synaptic strength and many forms of synaptic plasticity. However, understanding the mechanism of this control has been difficult because the submicron dimensions of spines limit examination of actin dynamics in the spine interior by conventional confocal microscopy. To overcome this, we developed single-molecule tracking photoactivated localization microscopy (smtPALM) to measure the movement of individual actin molecules within living spines. This revealed inward actin flow from broad areas of the spine plasma membrane, as well as a dense central core of heterogeneous filament orientation. The velocity of single actin molecules along filaments was elevated in discrete regions within the spine, notably near the postsynaptic density but surprisingly not at the endocytic zone which is involved in some forms of plasticity. We conclude that actin polymerization is initiated at many well-separated foci within spines, an organization that may be necessary for the finely tuned adjustment of synaptic molecular content that underlies functional plasticity. Indeed, further single-molecule mapping studies confirm that actin polymerization drives reorganization of molecular organization at the synapse itself.

Off-fault plasticity in three-dimensional dynamic rupture simulations using a modal Discontinuous Galerkin method on unstructured meshes: Implementation, verification, and application

NASA Astrophysics Data System (ADS)

Wollherr, Stephanie; Gabriel, Alice-Agnes; Uphoff, Carsten

2018-05-01

The dynamics and potential size of earthquakes depend crucially on rupture transfers between adjacent fault segments. To accurately describe earthquake source dynamics, numerical models can account for realistic fault geometries and rheologies such as nonlinear inelastic processes off the slip interface. We present implementation, verification, and application of off-fault Drucker-Prager plasticity in the open source software SeisSol (www.seissol.org). SeisSol is based on an arbitrary high-order derivative modal Discontinuous Galerkin (ADER-DG) method using unstructured, tetrahedral meshes specifically suited for complex geometries. Two implementation approaches are detailed, modelling plastic failure either employing sub-elemental quadrature points or switching to nodal basis coefficients. At fine fault discretizations the nodal basis approach is up to 6 times more efficient in terms of computational costs while yielding comparable accuracy. Both methods are verified in community benchmark problems and by three dimensional numerical h- and p-refinement studies with heterogeneous initial stresses. We observe no spectral convergence for on-fault quantities with respect to a given reference solution, but rather discuss a limitation to low-order convergence for heterogeneous 3D dynamic rupture problems. For simulations including plasticity, a high fault resolution may be less crucial than commonly assumed, due to the regularization of peak slip rate and an increase of the minimum cohesive zone width. In large-scale dynamic rupture simulations based on the 1992 Landers earthquake, we observe high rupture complexity including reverse slip, direct branching, and dynamic triggering. The spatio-temporal distribution of rupture transfers are altered distinctively by plastic energy absorption, correlated with locations of geometrical fault complexity. Computational cost increases by 7% when accounting for off-fault plasticity in the demonstrating application. Our results imply that the combination of fully 3D dynamic modelling, complex fault geometries, and off-fault plastic yielding is important to realistically capture dynamic rupture transfers in natural fault systems.

Micromechanisms of Crack Growth in Ceramics and Glasses in Corrosive Environments.

DTIC Science & Technology

1980-05-01

Resistance Mecanique du Verre et les Moyens de l’Amelioree, Union Scientifique Continentale du Verre , Charleroix, Belgium, (1962). 8. B. A. Proctor, I...exhibit similar types of delayed failure curves. Failure occurs most rapidly at high loads. Below a critical value of the load known as the stress...fracture for the three types of materials differ greatly. Polymers and metals have plastic zones at their crack tips, so that stress corrosion

Causes and Prevention of Structural Materials Failures in Naval Environments.

DTIC Science & Technology

1984-01-01

atomic hydrogen as the first step; (iii) creation of elastic-plastic zones near the crack tip region due to movement of dislocations under applied...sodium tellurate is added to the charging solution. There is a dramatic drop in hydrogen permeation current due to the reduction of the tellurate ...effect of tellurium which has been deposited. Thus it has been shown that the tellurate ion, an electron acceptor, can delay the production of hydrogen

Fife organizes synaptic vesicles and calcium channels for high-probability neurotransmitter release

PubMed Central

Rao, Monica; Ukken, Fiona

2017-01-01

The strength of synaptic connections varies significantly and is a key determinant of communication within neural circuits. Mechanistic insight into presynaptic factors that establish and modulate neurotransmitter release properties is crucial to understanding synapse strength, circuit function, and neural plasticity. We previously identified Drosophila Piccolo-RIM-related Fife, which regulates neurotransmission and motor behavior through an unknown mechanism. Here, we demonstrate that Fife localizes and interacts with RIM at the active zone cytomatrix to promote neurotransmitter release. Loss of Fife results in the severe disruption of active zone cytomatrix architecture and molecular organization. Through electron tomographic and electrophysiological studies, we find a decrease in the accumulation of release-ready synaptic vesicles and their release probability caused by impaired coupling to Ca2+ channels. Finally, we find that Fife is essential for the homeostatic modulation of neurotransmission. We propose that Fife organizes active zones to create synaptic vesicle release sites within nanometer distance of Ca2+ channel clusters for reliable and modifiable neurotransmitter release. PMID:27998991

Modeling of AA5083 Material-Microstructure Evolution During Butt Friction-Stir Welding

NASA Astrophysics Data System (ADS)

Grujicic, M.; Arakere, G.; Yalavarthy, H. V.; He, T.; Yen, C.-F.; Cheeseman, B. A.

2010-07-01

A concise yet a fairly comprehensive overview of the friction stir welding (FSW) process is provided. This is followed by a computational investigation in which FSW behavior of a prototypical solution-strengthened and strain-hardened aluminum alloy, AA5083-H131, is modeled using a fully coupled thermo-mechanical finite-element procedure developed in our prior study. Particular attention is given to proper modeling of the welding work-piece material behavior during the FSW process. Specifically, competition and interactions between plastic-deformation and dynamic-recrystallization processes are considered to properly account for the material-microstructure evolution in the weld nugget zone. The results showed that with proper modeling of the material behavior under high-temperature/severe-plastic-deformation conditions, significantly improved agreement can be attained between the computed and measured post-FSW residual-stress and material-strength distribution results.

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

Godby, M.; Ugolini, C.; Lyman, M.

In response to a request from the Allied Industrial Workers Union, an investigation was begun into possible hazardous working conditions at Bryan Custom Plastics (SIC-3089), Bryan, Ohio. The company manufactured plastic television cabinets and interior automotive door panels by an extrusion molding process. Full shift, personal breathing zone and area sampling revealed no excess levels of exposure to total paint mist, toluene, xylene, ethyl-benzene, methyl-methacrylate, methyl-ethyl-ketone, methyl-isobutyl-ketone, or n-butanol. Carbon-monoxide concentrations ranged up to 34 and 90 parts per million in the spray finishing areas and quality control areas, respectively. The author concludes that health hazards from exposure to airbornemore » particulates and organic solvents were not found at the time of the survey. There was a potential for overexposures to carbon-monoxide. The author recommends that carbon-monoxide levels be reduced, and work practices improved.« less

X-ray fractography on fatigue fractured surface of austenitic stainless steel

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

Yajima, Zenjiro; Tokuyama, Hideki; Kibayashi, Yasuo

1995-12-31

X-ray diffraction observation of the material internal structure beneath fracture surfaces provide fracture analysis with useful information to investigate the conditions and mechanisms of fracture. X-ray fractography is a generic name given to this technique. In the present study, X-ray fractography was applied to fatigue fracture surfaces of austenitic stainless steel (AISI 304) which consisted of solution treatment. The fatigue tests were carried out on compact tension (CT) specimens. The plastic strain on the fracture surface was estimated from measuring the line broadening of X-ray diffraction profiles. The line broadening of X-ray diffraction profiles was measured on and beneath fatiguemore » fracture surfaces. The depth of the plastic zone left on fracture surfaces was evaluated from the line broadening. The results are discussed on the basis of fracture mechanics.« less

Modelling accumulation of marine plastics in the coastal zone; what are the dominant physical processes?

NASA Astrophysics Data System (ADS)

Critchell, Kay; Lambrechts, Jonathan

2016-03-01

Anthropogenic marine debris, mainly of plastic origin, is accumulating in estuarine and coastal environments around the world causing damage to fauna, flora and habitats. Plastics also have the potential to accumulate in the food web, as well as causing economic losses to tourism and sea-going industries. If we are to manage this increasing threat, we must first understand where debris is accumulating and why these locations are different to others that do not accumulate large amounts of marine debris. This paper demonstrates an advection-diffusion model that includes beaching, settling, resuspension/re-floating, degradation and topographic effects on the wind in nearshore waters to quantify the relative importance of these physical processes governing plastic debris accumulation. The aim of this paper is to prioritise research that will improve modelling outputs in the future. We have found that the physical characteristic of the source location has by far the largest effect on the fate of the debris. The diffusivity, used to parameterise the sub-grid scale movements, and the relationship between debris resuspension/re-floating from beaches and the wind shadow created by high islands also has a dramatic impact on the modelling results. The rate of degradation of macroplastics into microplastics also have a large influence in the result of the modelling. The other processes presented (settling, wind drift velocity) also help determine the fate of debris, but to a lesser degree. These findings may help prioritise research on physical processes that affect plastic accumulation, leading to more accurate modelling, and subsequently management in the future.

Atomic-level deformation of CuxZr100-x metallic glasses under shock loading

NASA Astrophysics Data System (ADS)

Demaske, Brian J.; Wen, Peng; Phillpot, Simon R.; Spearot, Douglas E.

2018-06-01

Plastic deformation mechanisms in CuxZr100-x bulk metallic glasses (MGs) subjected to shock are investigated using molecular dynamics simulations. MGs with Cu compositions between 30 and 70 at. % subjected to shock waves generated via piston velocities that range from 0.125 to 2.0 km/s are considered. In agreement with prior studies, plastic deformation is initiated via formation of localized regions of high von Mises shear strain, known as shear transformation zones (STZs). At low impact velocities, but above the Hugoniot elastic limit, STZ nucleation is dispersed behind the shock front. As impact velocity is increased, STZ nucleation becomes more homogeneous, eventually leading to shock-induced melting, which is identified in this work via high atomic diffusivity. The shear stress necessary to initiate plastic deformation within the shock front is independent of composition at shock intensities near the elastic limit but increases with increasing Cu content at high shock intensities. By contrast, both the flow stress in the plastically deformed MG and the critical shock pressure associated with melting behind the shock front are found to increase with increasing Cu content over the entire range of impact velocities. The evolution of the short-range order in the MG samples during shock wave propagation is analyzed using a polydisperse Voronoi tessellation method. Cu-centered polyhedra with full icosahedral symmetry are found to be most resistant to change under shock loading independent of the MG composition. A saturation is observed in the involvement of select Cu-centered polyhedra in the plastic deformation processes at a piston velocity around 0.75 km/s.

Analysis of stress-strain state of support ring of vertical steel tank RVS-20000

NASA Astrophysics Data System (ADS)

Chepur, P. V.; Tarasenko, A. A.; Gruchenkova, A. A.

2018-05-01

The refined finite element model of the joint of a fixed roof with a support ring for a large-size vertical steel tank RVS-20000 is executed. It considers the real geometry of metal shell plates - in accordance with the TP-704-1-60 design, geometric and physical nonlinearity, and features of the non-axisymmetric design loading scheme of the structure. Dependences of the SSS parameters of the support joint design on the size of the subsidence zone of the outer contour of the RVS-20000 bottom are obtained. It is established that at the value of subsidence zone coefficient n ≤ 1, a region of critical values occurs, exceeding which leads to the appearance of unacceptable plastic deformations of metal structures. The authors performed interpretation of the postprocessing of the finite element analysis, as a result of which the dependences of the parameters of the stress-strain state on the value of the zone of warping were obtained. The graphs of the dependence of the values of strains and stresses of the metal structure of the support ring on the size of the subsidence zone along the arc of the outer contour of the bottom are presented.

In-depth quantitative analysis of the microstructures produced by Surface Mechanical Attrition Treatment (SMAT)

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

Samih, Y., E-mail: youssef.samih@univ-lorraine.fr; Université de Lorraine, Laboratory of Excellence on Design of Alloy Metals for low-mAss Structures; Beausir, B.

2013-09-15

Electron BackScattered Diffraction (EBSD) maps are used to characterize quantitatively the graded microstructure formed by Surface Mechanical Attrition Treatment (SMAT) and applied here to the 316L stainless steel. In particular, the analysis of GNDs – coupled with relevant and reliable criteria – was used to depict the thickness of each zone identified in the SMAT-affected layers: (i) the “ultrafine grain” (UFG) zone present at the extreme top surface, (ii), the “transition zone” where grains were fragmented under the heavy plastic deformation and, finally, (iii) the “deformed zone” where initial grains are simply deformed. The interest of this procedure is illustratedmore » through the comparative analysis of the effect of some SMAT processing parameters (amplitude of vibration and treatment duration). The UFG and transition zones are more significantly modified than the overall affected thickness under our tested conditions. - Highlights: • EBSD maps are used to characterize quantitatively the microstructure of SMAT treated samples. • Calculation of the GND density to quantify strain gradients • A new method to depict the different zone thicknesses in the SMAT affected layer • Effects of SMAT processing parameters on the surface microstructure evolution.« less

Deformation of compound shells under action of internal shock wave loading

NASA Astrophysics Data System (ADS)

Chernobryvko, Marina; Kruszka, Leopold; Avramov, Konstantin

2015-09-01

The compound shells under the action of internal shock wave loading are considered. The compound shell consists of a thin cylindrical shell and two thin parabolic shells at the edges. The boundary conditions in the shells joints satisfy the equality of displacements. The internal shock wave loading is modelled as the surplus pressure surface. This pressure is a function of the shell coordinates and time. The strain rate deformation of compound shell takes place in both the elastic and in plastic stages. In the elastic stage the equations of the structure motions are obtained by the assumed-modes method, which uses the kinetic and potential energies of the cylindrical and two parabolic shells. The dynamic behaviour of compound shells is treated. In local plastic zones the 3-D thermo-elastic-plastic model is used. The deformations are described by nonlinear model. The stress tensor elements are determined using dynamic deformation theory. The deformation properties of materials are influenced by the strain rate behaviour, the influence of temperature parameters, and the elastic-plastic properties of materials. The dynamic yield point of materials and Pisarenko-Lebedev's criterion of destruction are used. The modified adaptive finite differences method of numerical analysis is suggested for those simulations. The accuracy of the numerical simulation is verified on each temporal step of calculation and in the case of large deformation gradients.

The Silurian Hoedongri Formation in the Taebaeksan Basin of Korea Revisited: its Significance in the Tectonic Reconstruction of East Asia

NASA Astrophysics Data System (ADS)

Chae, S.; Hong, J.; Jung, S.; Ree, J.

2011-12-01

The Silurian Hoedongri Formation of the Taebaeksan Basin of South Korea has been used as a key unit to the correlation of tectonic provinces of East Asia since the South China craton (or Yangtz block) contains Silurian-Devonian sequences as well as Cambrian-Ordovician ones in the Paleozoic basins while the North China craton (or Sino-Korea block) is devoid of Silurian-Devonian sequences. In the Biryongdong area near the type locality of the Hoedongri Formation, it has been reported that the gray limestone of the Hoedongri Formation unconformably overlies brownish gray limestone of the Ordovician Haengmae Formation. However, our detailed examination on the Biryongdong section reveals that both of the brownish gray and gray limestones are mylonitic marbles with the boundary between the two units being a healed fault breccia zone (~ 12 m thick). The main difference of the two units is that repeated cycles of plastic deformation and fracturing occurred in the underlying brownish gray marble ('Haengmae') while the gray marble ('Hoedongri') deformed mainly by intracrystalline plasticity. The mylonitic foliation strikes NW with a low to moderate dip angle (20-60°) to NE. The ridge-in-groove type lineation on foliation surface trends NNW. The shape-preferred foliation of elongated calcite grains are oblique to the mylonitic foliation defined by layers with a grain-size variation, indicating a top-to-the-SSE shear sense. The mylonitic marble consists of elongated remnant grains (80-120 μm) with deformation twins and dynamically recrystallized matrix grains (10-40 μm). Grain boundaries and twin boundaries are lobate or wavy, indicating dynamic boundary migration. Some layers of the gray mylonitic marble are composed entirely of larger (80-120 μm) elongated calcite grains. In the brownish gray mylonitic marble unit, layers of brittle fracturing overprinting mylonitic foliation occur. In some of these layers, fragments (several cm - tens of cm) of the mylonitic marble are angular to subangular with coarse calcite fillings between the fragments. In other layers, mylonitic marble fragments are elongated with matrix foliation wrapping around them. These features suggest repeated cycles of plastic deformation and fracturing. Tectonic significance of this shear zone (at least 90 m thick) is not clear at present, and the regional extent and absolute age constraint of the shear zone should be clarified.

The Impact of Fe-Ti Oxide Concentration on the Structural Rigidity of the Lower Oceanic Crust, Atlantis Bank, Southwest Indian Ridge

NASA Astrophysics Data System (ADS)

Deans, J. R.; Winkler, D. A.

2017-12-01

Fe-Ti oxides are important components of oceanic core complexes (OCC) formed at slow-spreading ridges, since Fe-Ti oxide phases form throughout the crustal column and are weaker than silicate phases. This study investigated the predicted relationship between the presence and concentration of Fe-Ti oxides and the presence/intensity of crystal-plastic deformation in samples from Atlantis Bank, Southwest Indian Ridge (SWIR). Atlantis Bank is an OCC that formed through the exhumation of lower oceanic crust along a detachment shear zone/fault. OCCs form along slow-spreading ridges and are characterized by the complex interactions between magmatism and crustal extension, thus, making them more susceptible to crystal-plastic deformation at higher temperatures and for weaker phases like Fe-Ti oxides to preferentially partition strain. Atlantis Bank has been the focus of many scientific expeditions to various sites including; Ocean Drilling Program (ODP) Holes 735B and 1105A, and the International Oceanic Discovery Program (IODP) Hole U1473A. A total of 589 thin sections from all three holes were analyzed using the software package Fiji to calculate the Fe-Ti oxide concentration within the thin sections. The Fe-Ti oxide percentage was correlated with the crystal-plastic fabric (CPF) intensity, from 0-5 (no foliation - ultramylonite), for each thin section using the statistical software R. All three holes show a positive correlation between the abundance of Fe-Ti oxides and the CPF intensity. Specifically, 76.3% of samples with a concentration of 5% or more Fe-Ti oxides have a corresponding CPF intensity value of 2 or more (porphyroclastic foliation - ultramylonitic). The positive correlation may be explained by the Fe-Ti oxides preferentially partitioning strain, especially at temperatures below where dry plagioclase can recrystallize. This allows for a mechanism of continued slip along the shear zone or form new shear zones at amphibolite grade conditions while the lower crust is being exhumed. Additionally, IODP U1473A and ODP 1105A had similar correlation values of 0.11 (on a scale of -1 to 1), whereas ODP Hole 735B had double the correlation value of 0.24. Since ODP Hole 735B has older rocks than the other two holes, it may have recorded more deformation comparatively speaking.

Microstructural study of the Mertz shear zone, East Antarctica. Implications for deformation processes and seismic anisotropy.

NASA Astrophysics Data System (ADS)

Lamarque, Gaëlle; Bascou, Jérôme; Maurice, Claire; Cottin, Jean-Yves; Ménot, René-Pierre

2015-04-01

The Mertz Shear Zone (MSZ; 146°E 67°S; East Antarctica) is one major lithospheric-scale structure which outcrops on the eastern edge of the Terre Adélie Craton (Ménot et al., 2007) and that could connected with shear zones of South Australia (e.g., Kalinjala or Coorong shear zone (Kleinschmidt and Talarico, 2000; Gibson et al., 2013)) before the Cretaceous opening of the Southern Ocean. Geochronological and metamorphic studies indicated an MSZ activity at 1.7 and 1.5 Ga respectively in amphibolite and greenschists facies conditions. The deformation affects both the intermediate and lower crust levels, without associated voluminous magma injection. Granulite crop out in the area of the MSZ. They were dated at 2.4 Ga (Ménot et al., 2005) and could represent some preserved Neoarchean tectonites. These rocks show various degrees of deformation including penetrative structures that may display comparable features with that observed in amphibolite and greenschists facies rocks, i.e. NS-striking and steeply dipping foliation with weekly plunging lineation. In the field, cinematic indicators for the MSZ argue for a dominant dextral shear sense. We proceed to optical analysis and crystallographic preferred orientation (CPO) measurements using EBSD technique in order to better constrain the deformation processes. Our results highlight (1) a microstructural gradient from highly deformed rocks (mylonites), forming plurimetric large shear bands and showing evidences of plastic deformation, to slightly deformed rocks in preserved cores with no evidences of plastic deformation or with a clear strong static recrystallization; (2) CPO of minerals related with variations on deformation conditions. Feldspar and quartz CPO argue for plastic deformation at high temperature in the most deformed domains and for the absence of deformation or an important stage of static recrystallization in preserved cores; (3) uncommon CPO in orthopyroxene which are characterized by [010]-axes perpendicular to the foliation and [001]-axes parallel to the lineation. These CPO seem to be related to static recrystallization processes. Seismic properties of amphibolite and granulite rocks from the MSZ were calculated in order to evaluate the impact of deformation observed in amphibolite and granulite tectonites to seismic anisotropy. Computations were performed from measured CPO, single crystal elastic stiffness matrix, modal composition and density of characteristic samples. P- and S-waves anisotropies of the cratonic crust affected by the MSZ are small and even tend to be isotropic in the case of S-waves propagating vertically in the crust. These results permit us to better discuss seismic studies and in particular SKS analysis which were recently carried out in this area (Lamarque et al., 2015).

Preliminary observations of Labrador Sea marginal ice zone rheology using C-band SAR

NASA Technical Reports Server (NTRS)

Drinkwater, Mark R.; Squire, Vernon A.

1989-01-01

SAR imagery collected in the Labrador Sea during Limex '87 are used to interpret modes of sea-ice deformation. The ice canopy exhibited two distinct rheologies separated by a clear line of shear; a quasi-brittle inner regime and a nonlinear viscous outer regime. A single constitutive relation capable of modeling both is unlikely within a plastic rate-independent formulation. Rate dependent effects are discussed as an explanation for brittle fracture in ductile materials.

Investigation of the ElectroPuls E3000 Test Machine for Fatigue Testing of Structural Materials

DTIC Science & Technology

2016-12-01

sharpening of the crack tip and deformation of a portion of the newly formed surface (the surface created during loading portion of the cycle) during...cracking process is that the size of the final plastic zone formed by pre-cracking can affect the crack growth rate in subsequent testing. To...similar. In other structural materials, such as aluminium , striations are often well-defined. Typically, fatigue striations on an aluminium fracture

Three-dimensional numerical simulations of crustal-scale wrenching using a non-linear failure criterion

NASA Astrophysics Data System (ADS)

Braun, Jean

1994-08-01

We have developed a three-dimensional finite element model to study wrench deformation of the crust regarded as an elasto-plastic material obeying Murrell's extension of Griffith's failure criterion. Numerical experiments using this model predict that the imposed basal wrenching is accommodated by an array of oblique Riedel-like shears and Y-shears (parallel to the direction of wrenching). The partitioning of deformation between the two types of structure depends on the width of the zone of imposed basal wrenching and the existence of a component of deformation in the x-direction (normal to the direction of wrenching). The Riedel shears are arranged in spiral-like structures that root into the basal wrench zone. In cross-section, the Riedel shears resemble wedge-shaped flower structures similar to those often observed in seismic cross-sections. The 'polarity' of the flower structures is positive (or palm-tree-like) in transpression experiments and negative (or tulip-like) in transtension experiments. The orientation of the Riedel shears throughout the crust obeys Mohr's hypothesis for incipient faulting combined with Murrell's failure criterion. The model also predicts plastic dilatancy inversely proportional to the square root of the confining pressure; this result agrees qualitatively with field observations and the results of sand-box experiments and quantitatively with direct measurement of dilatancy during high-pressure rock-deformation experiments.

Extensive tissue-specific transcriptomic plasticity in maize primary roots upon water deficit.

PubMed

Opitz, Nina; Marcon, Caroline; Paschold, Anja; Malik, Waqas Ahmed; Lithio, Andrew; Brandt, Ronny; Piepho, Hans-Peter; Nettleton, Dan; Hochholdinger, Frank

2016-02-01

Water deficit is the most important environmental constraint severely limiting global crop growth and productivity. This study investigated early transcriptome changes in maize (Zea mays L.) primary root tissues in response to moderate water deficit conditions by RNA-Sequencing. Differential gene expression analyses revealed a high degree of plasticity of the water deficit response. The activity status of genes (active/inactive) was determined by a Bayesian hierarchical model. In total, 70% of expressed genes were constitutively active in all tissues. In contrast, <3% (50 genes) of water deficit-responsive genes (1915) were consistently regulated in all tissues, while >75% (1501 genes) were specifically regulated in a single root tissue. Water deficit-responsive genes were most numerous in the cortex of the mature root zone and in the elongation zone. The most prominent functional categories among differentially expressed genes in all tissues were 'transcriptional regulation' and 'hormone metabolism', indicating global reprogramming of cellular metabolism as an adaptation to water deficit. Additionally, the most significant transcriptomic changes in the root tip were associated with cell wall reorganization, leading to continued root growth despite water deficit conditions. This study provides insight into tissue-specific water deficit responses and will be a resource for future genetic analyses and breeding strategies to develop more drought-tolerant maize cultivars. © The Author 2015. Published by Oxford University Press on behalf of the Society for Experimental Biology.

Numerical Simulation of Hysteretic Live Load Effect in a Soil-Steel Bridge

NASA Astrophysics Data System (ADS)

Sobótka, Maciej

2014-03-01

The paper presents numerical simulation of hysteretic live load effect in a soil-steel bridge. The effect was originally identified experimentally by Machelski [1], [2]. The truck was crossing the bridge one way and the other in the full-scale test performed. At the same time, displacements and stress in the shell were measured. The major conclusion from the research was that the measured quantities formed hysteretic loops. A numerical simulation of that effect is addressed in the present work. The analysis was performed using Flac finite difference code. The methodology of solving the mechanical problems implemented in Flac enables us to solve the problem concerning a sequence of load and non-linear mechanical behaviour of the structure. The numerical model incorporates linear elastic constitutive relations for the soil backfill, for the steel shell and the sheet piles, being a flexible substructure for the shell. Contact zone between the shell and the soil backfill is assumed to reflect elastic-plastic constitutive model. Maximum shear stress in contact zone is limited by the Coulomb condition. The plastic flow rule is described by dilation angle ψ = 0. The obtained results of numerical analysis are in fair agreement with the experimental evidence. The primary finding from the performed simulation is that the slip in the interface can be considered an explanation of the hysteresis occurrence in the charts of displacement and stress in the shell.

Effect of Different Mulches under Rainfall Concentration System on Corn Production in the Semi-arid Areas of the Loess Plateau

PubMed Central

Ren, Xiaolong; Zhang, Peng; Chen, Xiaoli; Guo, Jingjing; Jia, Zhikuan

2016-01-01

The ridge and furrow farming system for rainfall concentration (RC) has gradually been popularized to improve the water availability for crops and to increase the water use efficiency (WUE), thereby stabilizing high yields. In the RC system, plastic-covered ridges are rainfall harvesting zones and furrows are planting zones. In this study, we optimized the mulching patterns for RC planting to mitigate the risks of drought during crop production in semi-arid agricultural areas. We conducted a four-year field study to determine the effects on corn production of mulching with 0.08-mm plastic film, maize straw, 8% biodegradable film, liquid film, bare furrow, and conventional flat (CF) farming. We found that RC significantly increased (P > 0.05) the soil moisture storage in the top 0–100 cm layer and the topsoil temperature (0–10 cm) during the corn-growing season. Combining RC with mulching further improved the rain-harvesting, moisture-retaining, and yield-increasing effects in furrows. Compared with CF, the four-year average yield increased by 1497.1 kg ha–1 to 2937.3 kg ha–1 using RC with mulch treatments and the WUE increased by 2.3 kg ha–1 mm–1 to 5.1 kg ha–1 mm–1. PMID:26751619

Success of free flap anastomoses performed within the zone of trauma in acute lower limb reconstruction.

PubMed

Bendon, Charlotte L; Giele, Henk P

2016-07-01

Traditionally, in free flap cover of lower limb injuries, every attempt is made to perform anastomoses proximal to the zone of injury. We report on the success of anastomoses within the zone of trauma, at the level of the fracture, avoiding further dissection and exposure. The records of free flap reconstructions for fractures of the lower extremity at a tertiary trauma centre between 2004 and 2010 were retrospectively reviewed. A total of 48 lower limb fractures required free flap reconstruction, performed at 28 days post injury (0-275 days). Anastomoses were proximal (21), distal (5) or within the zone of trauma (22). There was no significant difference (p > 0.05) in return to theatre, revision of anastomosis or flap survival between groups. Of the 22 performed within the zone of injury, five returned to theatre but only two for revision of anastomosis and 20 (91%) of these flaps survived. Of the 48 free flaps, arterial anastomoses were end to end in 34 (71%) and end to side in 14 (30%). There was no significant difference (p > 0.05) in return to theatre, revision of anastomosis or flap survival between the end-to-end and end-to-side groups. There was a tendency for arterial anastomoses to be performed end to end outside the zone of trauma (23/26) compared to within the zone of trauma (11/22). Our data suggest that free flap anastomoses can be performed safely in the zone of trauma in lower limb injuries. Copyright © 2016 British Association of Plastic, Reconstructive and Aesthetic Surgeons. Published by Elsevier Ltd. All rights reserved.

SMAS Fusion Zones Determine the Subfascial and Subcutaneous Anatomy of the Human Face: Fascial Spaces, Fat Compartments, and Models of Facial Aging.

PubMed

Pessa, Joel E

2016-05-01

Fusion zones between superficial fascia and deep fascia have been recognized by surgical anatomists since 1938. Anatomical dissection performed by the author suggested that additional superficial fascia fusion zones exist. A study was performed to evaluate and define fusion zones between the superficial and the deep fascia. Dissection of fresh and minimally preserved cadavers was performed using the accepted technique for defining anatomic spaces: dye injection combined with cross-sectional anatomical dissection. This study identified bilaminar membranes traveling from deep to superficial fascia at consistent locations in all specimens. These membranes exist as fusion zones between superficial and deep fascia, and are referred to as SMAS fusion zones. Nerves, blood vessels and lymphatics transition between the deep and superficial fascia of the face by traveling along and within these membranes, a construct that provides stability and minimizes shear. Bilaminar subfascial membranes continue into the subcutaneous tissues as unilaminar septa on their way to skin. This three-dimensional lattice of interlocking horizontal, vertical, and oblique membranes defines the anatomic boundaries of the fascial spaces as well as the deep and superficial fat compartments of the face. This information facilitates accurate volume augmentation; helps to avoid facial nerve injury; and provides the conceptual basis for understanding jowls as a manifestation of enlargement of the buccal space that occurs with age. © 2016 The American Society for Aesthetic Plastic Surgery, Inc. Reprints and permission: journals.permissions@oup.com.

Plastic pollution on the Baltic beaches of Kaliningrad region, Russia.

PubMed

Esiukova, Elena

2017-01-30

Contamination of sandy beaches of the Baltic Sea in Kaliningrad region is evaluated on the base of surveys carried out from June 2015 to January 2016. Quantity of macro/meso/microplastic objects in the upper 2cm of the sandy sediments of the wrack zone at 13 sampling sites all along the Russian coast is reported. Occurrence of paraffin and amber pieces at the same sites is pointed out. Special attention is paid to microplastics (range 0.5-5mm): its content ranges between 1.3 and 36.3 items per kg dry sediment. The prevailing found type is foamed plastic. No sound differences in contamination are discovered between beaches with high and low anthropogenic load. Mean level of contamination is of the same order of magnitude as has been reported by other authors for the Baltic Sea beaches. Copyright © 2016 Elsevier Ltd. All rights reserved.

Effects of microplastics on sessile invertebrates in the eastern coast of Thailand: An approach to coastal zone conservation.

PubMed

Thushari, Gajahin Gamage Nadeeka; Senevirathna, Jayan Duminda Mahesh; Yakupitiyage, Amararatne; Chavanich, Suchana

2017-11-15

This study assessed the microplastic contamination of 3 most abundant sessile and intertidal invertebrates (Rock Oyster: Saccostrea forskalii, Striped Barnacle: Balanus amphitrite, Periwinkle: Littoraria sp.) in 3 beaches of the eastern coasts of Thailand. The results showed a significant accumulation of microplastics in the invertebrates at rates of 0.2-0.6 counts/g indicating higher pollution levels along the coastline. Filter feeding organisms showed comparatively higher accumulation rates of microplastics. Thus, contaminated bivalves pose potential health risks for seafood consumers. The plastic pollutant prevalence in sessile and intertidal communities was corresponded with pollution characteristics of contaminated beach habitats where they live. Thus, bivalves, gastropods and barnacles can be used as indicators for contamination of microplastics in the areas. This study also demonstrated the need for controlling plastic pollution in Thai coastal areas. Copyright © 2017 The Authors. Published by Elsevier Ltd.. All rights reserved.

A new insight into ductile fracture of ultrafine-grained Al-Mg alloys.

PubMed

Yu, Hailiang; Tieu, A Kiet; Lu, Cheng; Liu, Xiong; Liu, Mao; Godbole, Ajit; Kong, Charlie; Qin, Qinghua

2015-04-08

It is well known that when coarse-grained metals undergo severe plastic deformation to be transformed into nano-grained metals, their ductility is reduced. However, there are no ductile fracture criteria developed based on grain refinement. In this paper, we propose a new relationship between ductile fracture and grain refinement during deformation, considering factors besides void nucleation and growth. Ultrafine-grained Al-Mg alloy sheets were fabricated using different rolling techniques at room and cryogenic temperatures. It is proposed for the first time that features of the microstructure near the fracture surface can be used to explain the ductile fracture post necking directly. We found that as grains are refined to a nano size which approaches the theoretical minimum achievable value, the material becomes brittle at the shear band zone. This may explain the tendency for ductile fracture in metals under plastic deformation.

A new insight into ductile fracture of ultrafine-grained Al-Mg alloys

PubMed Central

Yu, Hailiang; Tieu, A. Kiet; Lu, Cheng; Liu, Xiong; Liu, Mao; Godbole, Ajit; Kong, Charlie; Qin, Qinghua

2015-01-01

It is well known that when coarse-grained metals undergo severe plastic deformation to be transformed into nano-grained metals, their ductility is reduced. However, there are no ductile fracture criteria developed based on grain refinement. In this paper, we propose a new relationship between ductile fracture and grain refinement during deformation, considering factors besides void nucleation and growth. Ultrafine-grained Al-Mg alloy sheets were fabricated using different rolling techniques at room and cryogenic temperatures. It is proposed for the first time that features of the microstructure near the fracture surface can be used to explain the ductile fracture post necking directly. We found that as grains are refined to a nano size which approaches the theoretical minimum achievable value, the material becomes brittle at the shear band zone. This may explain the tendency for ductile fracture in metals under plastic deformation. PMID:25851228

Molecular dynamics study of strengthening mechanism of nanolaminated graphene/Cu composites under compression.

PubMed

Weng, Shayuan; Ning, Huiming; Fu, Tao; Hu, Ning; Zhao, Yinbo; Huang, Cheng; Peng, Xianghe

2018-02-15

Molecular dynamics simulations of nanolaminated graphene/Cu (NGCu) and pure Cu under compression are conducted to investigate the underlying strengthening mechanism of graphene and the effect of lamella thickness. It is found that the stress-strain curves of NGCu undergo 3 regimes i.e. the elastic regime I, plastic strengthening regime II and plastic flow regime III. Incorporating graphene monolayer is proved to simultaneously contribute to the strength and ductility of the composites and the lamella thickness has a great effect on the mechanical properties of NGCu composites. Different strengthening mechanisms play main role in different regimes, the transition of mechanisms is found to be related to the deformation behavior. Graphene affected zone is developed and integrated with rule of mixtures and confined layer slip model to describe the elastic properties of NGCu and the strengthening effect of the incorporated graphene.

Specific mineral associations of hydrothermal shale (South Kamchatka)

NASA Astrophysics Data System (ADS)

Rychagov, S. N.; Sergeeva, A. V.; Chernov, M. S.

2017-11-01

The sequence of hydrothermal shale from the East Pauzhet thermal field within the Pauzhet hydrothermal system (South Kamchatka) was studied in detail. It was established that the formation of shale resulted from argillization of an andesitic lava flow under the influence of an acidic sulfate vapor condensate. The horizons with radically different compositions and physical properties compared to those of the overlying homogeneous plastic shale were distinguished at the base of the sequence. These horizons are characterized by high (up to two orders of magnitude in comparison with average values in hydrothermal shale) concentrations of F, P, Na, Mg, K, Ca, Sc, Ti, V, Cr, Cu, and Zn. We suggested a geological-geochemical model, according to which a deep metal-bearing chloride-hydrocarbonate solution infiltrated into the permeable zone formed at the root of the andesitic lava flow beneath plastic shale at a certain stage of evolution of the hydrothermal system.

Stenotrophomonas sp. RZS 7, a novel PHB degrader isolated from plastic contaminated soil in Shahada, Maharashtra, Western India.

PubMed

Wani, S J; Shaikh, S S; Tabassum, B; Thakur, R; Gulati, A; Sayyed, R Z

2016-12-01

This paper reports an isolation and identification of novel poly-β-hydroxybutyrate (PHB) degrading bacterium Stenotrophomonas sp. RZS 7 and studies on its extracellular PHB degrading depolymerase enzyme. The bacterium isolated from soil samples of plastic contaminated sites of municipal area in Shahada, Maharashtra, Western India. It was identified as Stenotrophomonas sp. RZS 7 based on polyphasic approach. The bacterium grew well in minimal salt medium (MSM) and produced a zone (4.2 mm) of PHB hydrolysis on MSM containing PHB as the only source of nutrient. An optimum yield of enzyme was obtained on the fifth day of incubation at 37 °C and at pH 6.0. Further increase in enzyme production was recorded with Ca 2+ ions, while other metal ions like Fe 2+ (1 mM) and chemical viz. mercaptoethanol severally affected the production of enzyme.

Oxygen-assisted multipass cutting of carbon fiber reinforced plastics with ultra-short laser pulses

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

Kononenko, T. V.; Komlenok, M. S.; Konov, V. I.

Deep multipass cutting of bidirectional and unidirectional carbon fiber reinforced plastics (CFRP) with picosecond laser pulses was investigated in different static atmospheres as well as with the assistance of an oxygen or nitrogen gas flow. The ablation rate was determined as a function of the kerf depth and the resulting heat affected zone was measured. An assisting oxygen gas flow is found to significantly increase the cutting productivity, but only in deep kerfs where the diminished evaporative ablation due to the reduced laser fluence reaching the bottom of the kerf does not dominate the contribution of reactive etching anymore. Oxygen-supportedmore » cutting was shown to also solve the problem that occurs when cutting the CFRP parallel to the fiber orientation where a strong deformation and widening of the kerf, which temporarily slows down the process speed, is revealed to be typical for processing in standard air atmospheres.« less

[POSSIBILITIES OF VACUUM THERAPY APPLICATION IN DISORDERS OF VENOUS OUTFLOW IN ISLET GRAFTS].

PubMed

Badyul, P O; Samoylenko, G E; Nor, N M; Slesarenko, K S

2015-07-01

The experience of "distressed" (problematic) flaps application in 33 patients with soft tissue defects over 2010-2014 years were analysed. It was proposed to use the local negative pressure for the prevention and treatment of complications associated with venous insufficiency or trombosis in using of plastics with vascularised complexes of tissues. Vacuum-therapy was conducted with the help of negative pressure apparatus "AGATE-Dnepr" (Ukraine) by attaching silver-containing polyurethane sponge on the operating zone, covering the flap with the surrounding skin netting band "Grassolind". The recommended standard of negative pressure of 75-125 mm Hg, both in impulse and in continuous mode was used. The high efficiency of vacuum-therapy for survival of grafts has been demonstrated. Thus, it might be considered as an effective element of prevention and treatment of complications associated with venous insufficiency or trombosis using of vascularised tissue complex plastics of defects.

Esthetics in periodontics and implantology.

PubMed

Zucchelli, Giovanni; Sharma, Praveen; Mounssif, Ilham

2018-06-01

Periodontal plastic surgery comprises an increasing part of clinical periodontology. Clinical trials have traditionally used professionals to judge esthetic outcome, and few studies have addressed patient needs and requests (true end points). Development of universally accepted and validated methods for professional esthetic assessment, together with standardized questionnaires for patient-perceived outcome, may help to provide better insights into the true needs and benefits of periodontal and implant-associated plastic surgery. In this volume of Periodontology 2000, experienced researchers and clinicians from different subdisciplines of periodontology evaluate: treatment of gingival recession with or without papilla elevation; clinical crown lengthening in the natural dentition and in prosthodontic preparative treatment; periodontal regeneration around natural teeth; and soft-tissue augmentation in edentulous areas. Similarly, experts in different areas of implant science address esthetic outcomes with single and multiple implant rehabilitation, alveolar ridge preservation, implant positioning and immediate implant placement in the esthetic zone. © 2018 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.

A new insight into ductile fracture of ultrafine-grained Al-Mg alloys

NASA Astrophysics Data System (ADS)

Yu, Hailiang; Tieu, A. Kiet; Lu, Cheng; Liu, Xiong; Liu, Mao; Godbole, Ajit; Kong, Charlie; Qin, Qinghua

2015-04-01

It is well known that when coarse-grained metals undergo severe plastic deformation to be transformed into nano-grained metals, their ductility is reduced. However, there are no ductile fracture criteria developed based on grain refinement. In this paper, we propose a new relationship between ductile fracture and grain refinement during deformation, considering factors besides void nucleation and growth. Ultrafine-grained Al-Mg alloy sheets were fabricated using different rolling techniques at room and cryogenic temperatures. It is proposed for the first time that features of the microstructure near the fracture surface can be used to explain the ductile fracture post necking directly. We found that as grains are refined to a nano size which approaches the theoretical minimum achievable value, the material becomes brittle at the shear band zone. This may explain the tendency for ductile fracture in metals under plastic deformation.

Vertical forearc tectonic displacements offer insights into underlying interplate thrust zone processes: 104-105 yr uplift/subsidence cycles in Southwest Pacific arcs may represent recoverable plastic deformation that is often falsely attributed to other causes

NASA Astrophysics Data System (ADS)

Taylor, F. W.; Lavier, L. L.; Frohlich, C.; Thirumalai, K.; Papabatu, A. K.

2015-12-01

In the forearcs of subduction zones, the characteristics of both short-term (temporary earthquake cycle) and longer-term permanent vertical deformation offer insights into processes by which plates subduct. But permanent vertical deformation may be a product of several simultaneous processes, including tectonic erosion/underplating, changing dip of the slab, upward displacement due to buoyancy or bathymetric features, and plastic shortening/extension of the forearc wedge. Here we note the rarely recognized, but possibly common, phenomenon of intermediate time scale transient vertical movements (TVM's). Both the central New Hebrides and Western Solomon forearcs have uplifted ≥500 m over time scales of 105 yr. Uplift started abruptly (over ≤10 ky) and proceeded at localized rates up to 7-8 mm/yr. Both initial uplifts terminated preceding rapid subsidence of similar dimensions and rates that, in turn, had followed yet older uplift. However, these uplifts and subsidences are superimposed on a yet longer-term trend of uplift on time scales >105 yr. The most recent uplifts extended 100-200 km along-arc and 60-90 km cross-arc while plate convergence was <10 km. These 105 yr vertical oscillations are most likely due to plastic shortening/extension driven by strong horizontal forces related to rugged seafloor bathymetry impinging on the outer forearc. Subsidence follows uplift when horizontal force abates temporarily and uplift is no longer supported by enhanced interplate coupling. Over the 105 yr time frame when interplate slip is <10 km, it is difficult to account for the timing, geography, and amounts of up and down motion by processes such as buoyancy or volumetric displacement of downgoing bathymetric features or by tectonic underplating/erosion. Instead, ~1% of shortening within the upper plate is sufficient to account for up to several hundred m of uplift across a large area of the forearc.

Phenomena after meteoroid penetration of a bumper plate

NASA Technical Reports Server (NTRS)

Todd, F. C.

1971-01-01

The analysis of hypervelocity impact of particles on a detector in space, with flow and shock penetration through fluid, plastic, and elastic zones was studied. The original paper and computer program on this topic is presented. Improvements in the program for the study of the formation of a cone of debris are discussed. The truncated apex of the cone is at the hole formed by the penetration of an initially spherical rock through a thin plate. A solution for the penetration of the thin plate was sought.

Park River, Local Protection Auxiliary Conduit Tunnel As-Built Foundation Report, Hartford, Connecticut. Volume II. Appendices.

DTIC Science & Technology

1982-12-01

AUXILIARY TUNNEL AS-BUILT FOUNDATION REPORT It. KEY WORDS (Cenlasa on icteic. &#it* it necessary ad Identifpy block o"Whow) Strain Gages Settlement PeB...anomalously high bedding angles, severe brecciation and fracturing and an approximately 65-ft- wide zone of a plastic mixture of sand, silt and clay with some...wetted and partially filled with a mortar cement mix with Sika #2 added as a hardening agent. The mount assembly was then inserted into the holes so

On the indentation failure of carbon-epoxy cross-ply laminates, and its suppression by elasto-plastic interleaves

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

Joergensen, O.; Horsewell, A.

1997-08-01

Elastic and elasto-plastic modelling of indentation in CFRP cross-ply laminates has been performed. Detailed knowledge of the field solutions in the volume below the indentor forms the basis for the reported micromechanical interpretation of the observed damage in test specimens. The analysis shows that matrix cracks originate at sites of maximum tensile stress perpendicular to fibers. The predicted stress fields due to indentation show that stress concentrations occur in the interface between alternating plies. It is found that microcracking in this zone is a precursor to the observed failure. This analysis is supported by in-situ scanning electron microscopy during loadingmore » by a cylindrical indentor onto the laminate supported on a rigid substrate. The microscopy reveals microdamage in the region of interfacial tensile stress concentrations. The onset of indentation failure in these layered composites suggests that plastic interleaves would delay failure. It is shown numerically that plastic deformation of the interleaves redistributes stresses and thereby weakens the tensile stress concentrations which arise during indentation. Experimentally it is shown that aluminium interleaves affect the formation of indentation failure. In a cross-ply laminate, where alternating ply groups are separated by aluminium sheets, matrix cracking and delamination failures are suppressed by the occurrence of plastic deformation. Since the aluminium is likely to be weakly bonded to the plies, it is seen that weak interlaminar fracture toughness does not necessarily cause delaminations, nor lead to a lower indentation strength. High indentation strength and delamination resistance are complex qualities which, among others, seem to be achieved in laminate geometries which have a minimum of stress concentration at interfaces between ply groups of different orientation.« less

Subcritical crack propagation due to chemical rock weakening: macroscale chemo-plasticity and chemo-elasticity modeling

NASA Astrophysics Data System (ADS)

Hueckel, T.; Hu, M.

2015-12-01

Crack propagation in a subcritically stressed rock subject to chemically aggressive environment is analyzed and numerically simulated. Chemically induced weakening is often encountered in hydraulic fracturing of low-permeability oil/gas reservoirs and heat reservoirs, during storage of CO2 and nuclear waste corroding canisters, and other circumstances when rock matrix acidizing is involved. Upon acidizing, mineral mass dissolution is substantially enhanced weakening the rock and causing crack propagation and eventually permeability changes in the medium. The crack process zone is modeled mathematically via a chemo-plastic coupling and chemo-elastic coupling model. In plasticity a two-way coupling is postulated between mineral dissolution and a yield limit of rock matrix. The rate of dissolution is described by a rate law, but the mineral mass removal per unit volume is also a function of a variable internal specific surface area, which is in turn affected by the micro-cracking (treated as a plastic strain). The behavior of the rock matrix is modeled as rigid-plastic adding a chemical softening capacity to Cam-Clay model. Adopting the Extended Johnson's approximation of processes around the crack tip, the evolution of the stress field and deformation as a function of the chemically enhanced rock damage is modeled in a simplified way. In addition, chemical reactive transport is made dependent on plastic strain representing micro-cracking. Depending on mechanical and chemical boundary conditions, the area of enhanced chemical softening is near or somewhat away from the crack tip.In elasticity, chemo-mechanical effect is postulated via a chemical volumetric shrinkage strain proportional to mass removal variable, conceived analogously to thermal expansion. Two versions are considered: of constant coefficient of shrinkage and a variable one, coupled to deviatoric strain. Airy Potential approach used for linear elasticity is extended considering an extra term, which is uncoupled or coupled to strain. The later case requires iterations with solution of reactive transport equation. A decrease of stress intensity factor with time of reaction is well reproduced.

Partial cordierite breakdown during post-seismic recovery: the significance of plastic deformation for cation diffusion and metamorphic equilibrium

NASA Astrophysics Data System (ADS)

Büttner, Steffen; Costin, Gelu

2010-05-01

Brittle intra-crystal fracturing occurred during a microseismic event in migmatites of the Ordovician Sierras Pampeanas (NW Argentina), forming micro-shear zones and brittle fragments in cordierite. The seismic event occurred at amphibolite facies P-T conditions under high strain rates (≥ 10-7 s-1). During post-seismic recovery and coarsening of crystal fragments, primary cordierite (XMg=0.65) underwent partial breakdown along the deformation zone, forming a secondary mineral assemblage in an alteration zone along grain boundaries of coarsened crystal fragments. The secondary assemblage is restricted to the recovery zone. The breakdown of primary cordierite (CrdP) is accompanied by the formation of secondary sillimanite, magnetite, staurolite (XMg=0.24, ~0.5 wt% ZnO), quartz, and secondary cordierite (CrdS; XMg=0.70-0.80). CrdS, volumetrically the most important secondary phase, forms by diffusion of Mg and Fe, altering CrdP by Fe loss and uptake of Mg. All other secondary phases form by nucleation. Two simultaneous cordierite breakdown reactions have been balanced using CSpace 1.01: 100 CrdP (XMg 0.65) = 21.8 Sil +12.8 Mag + 33.5 Qtz + 5.6 H2O + 89.1 CrdS (XMg 0.75) 100 CrdP (XMg0.65) = 8.1 Mag + 53.6 Qtz + 4.5 H2O + 8.1 St (XMg0.24) + 83.3 CrdS (XMg 0.75) The bulk chemical major element composition of the alteration zone is nearly identical to the composition of primary cordierite, suggesting that elemental exchange between the alteration zone and the cordierite matrix is limited. However, minor fluid influx, supplying Zn, K, Si, and O is indicated by the composition of staurolite, minor formation of biotite and quartz, and by the oxidation of Fe2+ within the alteration zone. The modal composition of the alteration zone has been determined by point counting, which yields similar results like CSpace results (converted into vol%), and MODAN calculations, which calculates modes based on the average alteration zone composition, and the compositions of secondary phases. The average modal composition of the alteration zone is: 2.3 Sil + 2.0 Mag + 4.3 Qtz + 3.9 St+ 87.5 CrdS (vol%) Thermodynamic modelling of primary cordierite breakdown using Theriak Domino shows that the observed breakdown is possible only in a small P -T window around P =450 MPa and T =555 ° C, which is in good agreement with the retrograde P - T path of the Sierra de Quilmes migmatites. Modes calculated using Theriak Domino are similar to results using descriptive methods (point counting), or methods based on chemistry and petrography (MODAN, CSpace). Since modes predicted on the assumption of petrological equilibrium are close to the observed modes, the breakdown reaction seen in the alteration zone most likely represents conditions of, or close to, thermodynamic equilibrium. The formation of the secondary mineral assemblage in the alteration zone depends upon the efficient supply of cations, essentially Si, Al, Fe and Mg. The bulk composition of new secondary minerals (Qtz, St, Mag, Sil) is enriched in Fe compared to CrdP, whereas CrdS is Fe depleted. The provision of Si and Al required for Sil, Qtz, and St can be assigned to partial cordierite breakdown. The excess Fe needed for Mag and St, and the removal of surplus Mg from CrdP breakdown, depends on Fe-Mg diffusion within CrdS. Since CrdS forms exclusively in the post-seismic recovery zone, we interpret dislocation creep, and hence cation diffusion related to plastic deformation, as the key process for the formation of reaction products reflecting thermodynamic equilibrium.

Neurogenesis in the aging brain.

PubMed

Apple, Deana M; Solano-Fonseca, Rene; Kokovay, Erzsebet

2017-10-01

Adult neurogenesis is the process of producing new neurons from neural stem cells (NSCs) for integration into the brain circuitry. Neurogenesis occurs throughout life in the ventricular-subventricular zone (V-SVZ) of the lateral ventricle and the subgranular zone (SGZ) of the hippocampal dentate gyrus. However, during aging, NSCs and their progenitors exhibit reduced proliferation and neuron production, which is thought to contribute to age-related cognitive impairment and reduced plasticity that is necessary for some types of brain repair. In this review, we describe NSCs and their niches during tissue homeostasis and how they undergo age-associated remodeling and dysfunction. We also discuss some of the functional ramifications in the brain from NSC aging. Finally, we discuss some recent insights from interventions in NSC aging that could eventually translate into therapies for healthy brain aging. Copyright © 2017 Elsevier Inc. All rights reserved.

Fracture mechanics in fiber reinforced composite materials, taking as examples B/A1 and CRFP

NASA Technical Reports Server (NTRS)

Peters, P. W. M.

1982-01-01

The validity of linear elastic fracture mechanics and other fracture criteria was investigated with laminates of boron fiber reinforced aluminum (R/A1) and of carbon fiber reinforced epoxide (CFRP). Cracks are assessed by fracture strength Kc or Kmax (critical or maximum value of the stress intensity factor). The Whitney and Nuismer point stress criterion and average stress criterion often show that Kmax of fiber composite materials increases with increasing crack length; however, for R/A1 and CFRP the curve showing fracture strength as a function of crack length is only applicable in a small domain. For R/A1, the reason is clearly the extension of the plastic zone (or the damage zone n the case of CFRP) which cannot be described with a stress intensity factor.

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

Influence of the lithosphere-asthenosphere boundary on the stress field northwest of the Alps

NASA Astrophysics Data System (ADS)

Maury, J.; Cornet, F. H.; Cara, M.

2014-11-01

In 1356, a magnitude 6-7 earthquake occurred near Basel, in Switzerland. But recent compilations of GPS measurements reveal that measured horizontal deformation rates in northwestern continental Europe are smaller than error bars on the measurements, proving present tectonic activity, if any, is very small in this area. We propose to reconcile these apparently antinomic observations with a mechanical model of the lithosphere that takes into account the geometry of the lithosphere-asthenosphere boundary, assuming that the only loading mechanism is gravity. The lithosphere is considered to be an elastoplastic material satisfying a Von Mises plasticity criterion. The model, which is 400 km long, 360 km wide and 230 km thick, is centred near Belfort in eastern France, with its width oriented parallel to the N145°E direction. It also takes into account the real topography of both the ground surface and that of the Moho discontinuity. Not only does the model reproduce observed principal stress directions orientations, it also identifies a plastic zone that fits roughly the most seismically active domain of the region. Interestingly, a somewhat similar stress map may be produced by considering an elastic lithosphere and an ad-hoc horizontal `tectonic' stress field. However, for the latter model, examination of the plasticity criterion suggests that plastic deformation should have taken place. It is concluded that the present-day stress field in this region is likely controlled by gravity and rheology, rather than by active Alpine tectonics.

CX3CR1 Deficiency Alters Hippocampal-Dependent Plasticity Phenomena Blunting the Effects of Enriched Environment

PubMed Central

Maggi, Laura; Scianni, Maria; Branchi, Igor; D’Andrea, Ivana; Lauro, Clotilde; Limatola, Cristina

2011-01-01

In recent years several evidence demonstrated that some features of hippocampal biology, like neurogenesis, synaptic transmission, learning, and memory performances are deeply modulated by social, motor, and sensorial experiences. Fractalkine/CX3CL1 is a transmembrane chemokine abundantly expressed in the brain by neurons, where it modulates glutamatergic transmission and long-term plasticity processes regulating the intercellular communication between glia and neurons, being its specific receptor CX3CR1 expressed by microglia. In this paper we investigated the role of CX3CL1/CX3CR1 signaling on experience-dependent hippocampal plasticity processes. At this aim wt and CX3CR1GFP/GFP mice were exposed to long-lasting-enriched environment (EE) and the effects on hippocampal functions were studied by electrophysiological recordings of long-term potentiation of synaptic activity, behavioral tests of learning and memory in the Morris water maze paradigm and analysis of neurogenesis in the subgranular zone of the dentate gyrus (DG). We found that CX3CR1 deficiency increases hippocampal plasticity and spatial memory, blunting the potentiating effects of EE. In contrast, exposure to EE increased the number and migration of neural progenitors in the DG of both wt and CX3CR1GFP/GFP mice. These data indicate that CX3CL1/CX3CR1-mediated signaling is crucial for a normal experience-dependent modulation of hippocampal functions. PMID:22025910

Degradation and depolymerization of plastic waste by local bacterial isolates and bubble column reactor

NASA Astrophysics Data System (ADS)

Hussein, Amal A.; Alzuhairi, Mohammed; Aljanabi, Noor H.

2018-05-01

Accumulation of plastics, especially Polyethylene terephthalate (PET), is an ever increasing ecological threat due to its excessive usage in everyday human life. Nowadays, there are many methods to get rid of plastic wastes including burning, recycling and burying. However, these methods are not very active since their long period, anaerobic conditions that increase the rate of toxic materials released into the environment. This work aims to study the biological degradation of PET microorganism isolated from soil sample. Thirty eight (38) bacterial isolates were isolated from ten soil and plastic waste sample collected from four different waste disposal sites in Baghdad city during different periods between December 2016 and March 2017. Isolation was performed using enrichment culture method (flasks method) by culturing the soil samples in flasks with MSM medium where there is no carbon source only PET. Results showed that Al-Za'farania sample gave a higher number of isolates (13 isolates), while other samples gave less number of isolates. Screening was performed depending on their ability to grow in liquid MSM which contains PET powder and pieces and change the color of the PET-emulsified liquid medium as well as their ability to form the clear zone on PET-MSM agar. The results showed that NH-D-1 isolate has the higher ability to degrade DPET and PET pieces. According to morphological, biochemical characterization and Vitek-2 technique, the most active isolate was identified as Acinetobacter baumannii.

A Review of Natural Joint Systems and Numerical Investigation of Bio-Inspired GFRP-to-Steel Joints

PubMed Central

Avgoulas, Evangelos I.; Sutcliffe, Michael P. F.

2016-01-01

There are a great variety of joint types used in nature which can inspire engineering joints. In order to design such biomimetic joints, it is at first important to understand how biological joints work. A comprehensive literature review, considering natural joints from a mechanical point of view, was undertaken. This was used to develop a taxonomy based on the different methods/functions that nature successfully uses to attach dissimilar tissues. One of the key methods that nature uses to join dissimilar materials is a transitional zone of stiffness at the insertion site. This method was used to propose bio-inspired solutions with a transitional zone of stiffness at the joint site for several glass fibre reinforced plastic (GFRP) to steel adhesively bonded joint configurations. The transition zone was used to reduce the material stiffness mismatch of the joint parts. A numerical finite element model was used to identify the optimum variation in material stiffness that minimises potential failure of the joint. The best bio-inspired joints showed a 118% increase of joint strength compared to the standard joints. PMID:28773688

Anomalous shear band characteristics and extra-deep shock-affected zone in Zr-based bulk metallic glass treated with nanosecond laser peening.

PubMed

Wei, Yanpeng; Xu, Guangyue; Zhang, Kun; Yang, Zhe; Guo, Yacong; Huang, Chenguang; Wei, Bingchen

2017-03-07

The effects of nanosecond laser peening on Zr 41 Ti 14 Cu 12.5 Ni 10 Be 22.5 metallic glass were investigated in this study. The peening treatment produced an extra-deep shock-affected zone compared to crystal metal. As opposed to the conventional shear bands, numerous arc shear bands appeared and aggregated in the vertical direction of the laser beam, forming basic units for accommodating plastic deformation. The arc shear bands exhibited short and discrete features near the surface of the material, then grew longer and fewer at deeper peened layer depths, which was closely related to the laser shock wave attenuation. An energy dissipation model was established based on Hugoniot Elastic Limit and shear band characteristics to represent the formation of an extra-deep shock-affected zone. The results presented here suggest that the bulk modification of metallic glass with a considerable affected depth is feasible. Further, they reveal that nanosecond laser peening is promising as an effective approach to tuning shear bands for improved MGs ductility.

Prediction of the Grain-Microstructure Evolution Within a Friction Stir Welding (FSW) Joint via the Use of the Monte Carlo Simulation Method

NASA Astrophysics Data System (ADS)

Grujicic, M.; Ramaswami, S.; Snipes, J. S.; Avuthu, V.; Galgalikar, R.; Zhang, Z.

2015-09-01

A thermo-mechanical finite element analysis of the friction stir welding (FSW) process is carried out and the evolution of the material state (e.g., temperature, the extent of plastic deformation, etc.) monitored. Subsequently, the finite-element results are used as input to a Monte-Carlo simulation algorithm in order to predict the evolution of the grain microstructure within different weld zones, during the FSW process and the subsequent cooling of the material within the weld to room temperature. To help delineate different weld zones, (a) temperature and deformation fields during the welding process, and during the subsequent cooling, are monitored; and (b) competition between the grain growth (driven by the reduction in the total grain-boundary surface area) and dynamic-recrystallization grain refinement (driven by the replacement of highly deformed material with an effectively "dislocation-free" material) is simulated. The results obtained clearly revealed that different weld zones form as a result of different outcomes of the competition between the grain growth and grain refinement processes.

Theoretical Model of the Effect of Crack Tip Blunting on the Ultimate Tensile Strength of Welds in 2219-T87 Aluminum

NASA Technical Reports Server (NTRS)

Beil, R. J.

1982-01-01

A theoretical model representing blunting of a crack tip radius through diffusion of vacancies is presented. The model serves as the basis for a computer program which calculates changes, due to successive weld heat passes, in the ultimate tensile strength of 2219-T81 aluminum. In order for the model to yield changes of the same order in the ultimate tensile strength as that observed experimentally, a crack tip radius of the order of .001 microns is required. Such sharp cracks could arise in the fusion zone of a weld from shrinkage cavities or decohered phase boundaries between dendrites and the eutectic phase, or, possibly, from plastic deformation due to thermal stresses encountered during the welding process. Microstructural observations up to X2000 (resolution of about .1 micron) did not, in the fusion zone, show structural details which changed significantly under the influence of a heat pass, with the exception of possible small changes in the configuration of the interdendritic eutectic and in porosity build-up in the remelt zone.

A Review of Natural Joint Systems and Numerical Investigation of Bio-Inspired GFRP-to-Steel Joints.

PubMed

Avgoulas, Evangelos I; Sutcliffe, Michael P F

2016-07-12

There are a great variety of joint types used in nature which can inspire engineering joints. In order to design such biomimetic joints, it is at first important to understand how biological joints work. A comprehensive literature review, considering natural joints from a mechanical point of view, was undertaken. This was used to develop a taxonomy based on the different methods/functions that nature successfully uses to attach dissimilar tissues. One of the key methods that nature uses to join dissimilar materials is a transitional zone of stiffness at the insertion site. This method was used to propose bio-inspired solutions with a transitional zone of stiffness at the joint site for several glass fibre reinforced plastic (GFRP) to steel adhesively bonded joint configurations. The transition zone was used to reduce the material stiffness mismatch of the joint parts. A numerical finite element model was used to identify the optimum variation in material stiffness that minimises potential failure of the joint. The best bio-inspired joints showed a 118% increase of joint strength compared to the standard joints.

Brain plasticity and rehabilitation in stroke patients.

PubMed

Hara, Yukihiro

2015-01-01

In recent years, our understanding of motor learning, neuroplasticity and functional recovery after the occurrence of brain lesion has grown significantly. Novel findings in basic neuroscience have provided an impetus for research in motor rehabilitation. The brain reveals a spectrum of intrinsic capacities to react as a highly dynamic system which can change the properties of its neural circuits. This brain plasticity can lead to an extreme degree of spontaneous recovery and rehabilitative training may modify and boost the neuronal plasticity processes. Animal studies have extended these findings, providing insight into a broad range of underlying molecular and physiological events. Neuroimaging studies in human patients have provided observations at the systems level that often parallel findings in animals. In general, the best recoveries are associated with the greatest return toward the normal state of brain functional organization. Reorganization of surviving central nervous system elements supports behavioral recovery, for example, through changes in interhemispheric lateralization, activity of association cortices linked to injured zones, and organization of cortical representational maps. Evidence from animal models suggests that both motor learning and cortical stimulation alter intracortical inhibitory circuits and can facilitate long-term potentiation and cortical remodeling. Current researches on the physiology and use of cortical stimulation animal models and in humans with stroke related hemiplegia are reviewed in this article. In particular, electromyography (EMG) -controlled electrical muscle stimulation improves the motor function of the hemiparetic arm and hand. A multi-channel near-infrared spectroscopy (NIRS) studies in which the hemoglobin levels in the brain were non-invasively and dynamically measured during functional activity found that the cerebral blood flow in the injured sensory-motor cortex area is greatest during an EMG-controlled FES session. Only a few idea is, however, known for the optimal timing of the different processes and therapeutic interventions and for their interactions in detail. Finding optimal rehabilitation paradigms requires an optimal organization of the internal processes of neural plasticity and the therapeutic interventions in accordance with defined plastic time windows. In this review the mechanisms of spontaneous plasticity after stroke and experimental interventions to enhance plasticity are summarized, with an emphasis on functional electrical stimulation therapy.

Deriving strain from crystallographic preferred orientation for a ductile shear zone in north western Turkey.

NASA Astrophysics Data System (ADS)

Farrell, K.; Lloyd, G. E. E.; Wallis, D.; Phillips, R. J.

2015-12-01

Understanding the behaviour of active continental-scale fault zones at depth, and in particular how displacements observed at the Earth's surface are accommodated through the crust, is crucial to improving understanding of the earthquake cycle. This behaviour can be inferred by study of exhumed portions of ductile shear zones using methods such as recording strain profile(s) across the fault zone. However, due to the nature of mid-crustal rocks, strain markers tend to be rare and/or discontinuously distributed. The intensity (I) of crystallographic preferred orientation (CPO) of deformed minerals provides a proxy for strain that is continuous across fault zones. CPO are collected via electron back scattered diffraction in the scanning electron microscope. The strength of the CPO can be quantified using eigenvalue-based intensity parameters. Calibration of intensity with strain is achieved via comparison with visco-plastic self-consistency models of CPO evolution, although the temperature-dependent critical resolved shear stresses of potential crystal slip systems must be known. As an example, we consider the dextral strike-slip Eskişehir shear zone, NW Turkey, which was active during the Oligocene and accommodated ~100km of displacement, including a component of late oblique-normal slip. An exhumed mid-crustal section of this fault zone is exposed in the Uludağ Massif, comprising of high-grade metamorphic rocks of the Uludağ Group, intruded by the Central and South Uludağ granites. Sample transects focussed on the pure calcic marbles that dominate the stratigraphy. Fortunately, the availability of experimental data for calcite crystal slip behaviour at different temperatures makes the application of the CPO intensity strain proxy method relatively straightforward. The Uludağ Massif and Eskişehir shear zone provide a field based analogue for the ductile shear zone beneath the currently active North Anatolian Fault. The results of our CPO intensity-based strain profiles allow us to speculate on the current behaviour of the North Anatolian Fault, a major seismogenic feature, at depth.

An investigation into the mechanism for enhanced mechanical properties in friction stir welded AA2024-T3 joints coated with cold spraying

NASA Astrophysics Data System (ADS)

Li, N.; Li, W. Y.; Yang, X. W.; Feng, Y.; Vairis, A.

2018-05-01

Using cold spraying (CS), a surface layer with a modified microstructure and enhanced mechanical properties was formed on a 3.2 mm thick friction stir welded (FSWed) AA2024-T3 joint. The combined effect of "shot peening effect (SPE)" and "heat flow effect (HFE)" during CS were used to enhance joint mechanical properties. The microstructure evolution of the FSWed AA2024-T3 joints in the surface layer following CS coatings and their effect on mechanical properties were systematically characterized with electron back-scattered diffraction, transmission electron microscopy, differential scanning calorimetry and mechanical tests. Based on these experiments, a grain refinement, finer and more S phases, and improved amount of Guinier-Preston-Bagaryatsky (GPB) zones produced by CS treatments are proposed. The deposition of aluminum coating on the joint, lead to hardness recovery in the stir zone and the development of two low hardness zones as the density of GPB increased. The tensile properties of FSWed AA2024-T3 joints improved with the application of the aluminum coatings. Experiments and analysis of the enhanced mechanical properties mechanism indicate that SPE with a high plastic deformation and HFE with an intensive heat flow are necessary for the production of refined grains and increased numbers of GPB zones.

Material Interactions in a Novel Pinless Tool Approach to Friction Stir Spot Welding Thin Aluminum Sheet

NASA Astrophysics Data System (ADS)

Bakavos, Dimitrios; Chen, Yingchun; Babout, Laurent; Prangnell, Phil

2011-05-01

The requirement for a probe, or pin, in friction stir spot welding (FSSW) leads to an undesirable keyhole and "hooking," which can influence the fracture path and weld strength. Furthermore, the full weld cycle for FSSW is typically longer than ideal for the automotive industry, being 2 to 5 seconds. Here, it is shown that using a novel pinless tool design it is possible to achieve high lap shear strength (~3.4 kN) in thin aluminum sheet (~1 mm thick), with short weld cycle times (<1 second). Several techniques have been exploited to study the material flow and mechanisms of weld formation in pinless FSSW, including high-resolution X-ray tomography, to understand the role of the tool design and weld parameters. Despite the "simple" nature of a pinless tool, material flow in the weld zone was found to be surprisingly complex and strongly influenced by surface features on the tool, which greatly increased the penetration of the plastic zone into the bottom sheet. Because of the rapid thermal cycle and high level of grain refinement, the weld zone was found to develop a higher strength than the parent material with little evidence of a heat affected zone (HAZ) after postweld natural aging.

A viscoplastic shear-zone model for episodic slow slip events in oceanic subduction zones

NASA Astrophysics Data System (ADS)

Yin, A.; Meng, L.

2016-12-01

Episodic slow slip events occur widely along oceanic subduction zones at the brittle-ductile transition depths ( 20-50 km). Although efforts have been devoted to unravel their mechanical origins, it remains unclear about the physical controls on the wide range of their recurrence intervals and slip durations. In this study we present a simple mechanical model that attempts to account for the observed temporal evolution of slow slip events. In our model we assume that slow slip events occur in a viscoplastic shear zone (i.e., Bingham material), which has an upper static and a lower dynamic plastic yield strength. We further assume that the hanging wall deformation is approximated as an elastic spring. We envision the shear zone to be initially locked during forward/landward motion but is subsequently unlocked when the elastic and gravity-induced stress exceeds the static yield strength of the shear zone. This leads to backward/trenchward motion damped by viscous shear-zone deformation. As the elastic spring progressively loosens, the hanging wall velocity evolves with time and the viscous shear stress eventually reaches the dynamic yield strength. This is followed by the termination of the trenchward motion when the elastic stress is balanced by the dynamic yield strength of the shear zone and the gravity. In order to account for the zig-saw slip-history pattern of typical repeated slow slip events, we assume that the shear zone progressively strengthens after each slow slip cycle, possibly caused by dilatancy as commonly assumed or by progressive fault healing through solution-transport mechanisms. We quantify our conceptual model by obtaining simple analytical solutions. Our model results suggest that the duration of the landward motion increases with the down-dip length and the static yield strength of the shear zone, but decreases with the ambient loading velocity and the elastic modulus of the hanging wall. The duration of the backward/trenchward motion depends on the thickness, viscosity, and dynamic yield strength of the shear zone. Our model predicts a linear increase in slip with time during the landward motion and an exponential decrease in slip magnitude during the trenchward motion.

Subduction zone decoupling/retreat modeling explains south Tibet (Xigaze) and other supra-subduction zone ophiolites and their UHP mineral phases

NASA Astrophysics Data System (ADS)

Butler, Jared P.; Beaumont, Christopher

2017-04-01

The plate tectonic setting in which proto-ophiolite 'oceanic' lithosphere is created remains controversial with a number of environments suggested. Recent opinions tend to coalesce around supra-subduction zone (SSZ) forearc extension, with a popular conceptual model in which the proto-ophiolite forms during foundering of oceanic lithosphere at the time of spontaneous or induced onset of subduction. This mechanism is favored in intra-oceanic settings where the subducting lithosphere is old and the upper plate is young and thin. We investigate an alternative mechanism; namely, decoupling of the subducting oceanic lithosphere in the forearc of an active continental margin, followed by subduction zone (trench) retreat and creation of a forearc oceanic rift basin, containing proto-ophiolite lithosphere, between the continental margin and the retreating subduction zone. A template of 2D numerical model experiments examines the trade-off between strength of viscous coupling in the lithospheric subduction channel and net slab pull of the subducting lithosphere. Three tectonic styles are observed: 1) C, continuous subduction without forearc decoupling; 2) R, forearc decoupling followed by rapid subduction zone retreat; 3) B, breakoff of subducting lithosphere followed by re-initiation of subduction and in some cases, forearc decoupling (B-R). In one case (BA-B-R; where BA denotes backarc) subduction zone retreat follows backarc rifting. Subduction zone decoupling is analyzed using frictional-plastic yield theory and the Stefan solution for the separation of plates containing a viscous fluid. The numerical model results are used to explain the formation of Xigaze group ophiolites, southern Tibet, which formed in the Lhasa terrane forearc, likely following earlier subduction and not necessarily during subduction initiation. Either there was normal coupled subduction before subduction zone decoupling, or precursor slab breakoff, subduction re-initiation and then decoupling. Rapid deep upper-mantle circulation in the models during subduction zone retreat can exhume and emplace material in the forearc proto-ophiolite from as deep as the mantle transition zone, thereby explaining diamonds and other 10-15 GPa UHP phases in Tibetan ophiolites.

Brittle to ductile transition in a model of sheared granular materials

NASA Astrophysics Data System (ADS)

Elbanna, Ahmed; Ma, Xiao

Understanding the fundamental mechanisms of deformation and failure in sheared fault gouge is critical for the development of physics-based earthquake rupture simulations that are becoming an essential ingredient in next generation hazard and risk models. To that end, we use the shear transformation zone (STZ) theory, a non-equilibrium statistical thermodynamics framework to describe viscoplastic deformation and localization in gouge materials as a first step towards developing multiscale models for earthquake source processes that are informed by high-resolution fault zone physics. We will describe an implementation of this theory in a 2D/3D finite element framework, accounting for finite deformation, under both axial and shear loading and for dry and saturated conditions. We examine conditions under which a localized shear band may form and show that the initial value of disorder plays an important role. In particular, our simulations suggest that if the material is more compact initially, the behavior is more brittle and the plastic deformation localizes with large strength drop. On the other hand, an initially loose material will show a more ductile response and the plastic deformations will be distributed more broadly. We will further show that incorporation of pore fluids alters the localization pattern and changes the stress slip response due to coupling between gouge volume changes (compaction and dilation) and pore pressure build up. Finally, we discuss the implications of our model for gouge friction and dynamic weakening.

Importance of numerical analyses for determining support systems in tunneling: A comparative study from the trabzon-gumushane tunnel, Turkey

NASA Astrophysics Data System (ADS)

Kanik, Mustafa; Gurocak, Zulfu

2018-07-01

In this study, we determined the consistency of support elements from empirical rock mass classification systems, to obtain optimum support elements via comparative numerical analyses. For this purpose, the Macka tunnel, on the Trabzon-Gumushane highway and still under construction, was selected as the study area. Along the tunnel route, Late Cretaceous-aged Catak, Macka and Esiroglu Formations crop out. All the formations are cut by a Late Cretaceous Kackar Rhyodacite. Laboratory and field studies were done to determine the properties of the rock material and discontinuities. The results were used to define rock mass properties. Preliminary support systems were defined by using Rock Mass Rating (RMR), Rock Mass Quality (Q) and Rock Mass Index (RMi) systems, respectively. The suggested support elements of all classification systems were in turn evaluated using the Finite Elements Method (FEM), allowing the thickness of the plastic zone and total displacement values to be determined. Results of the analyses showed that it is possible to remove the instabilities around the tunnel section by applying lower numbers of support elements. When using the support systems from the numerical analyses it was found that the optimum support systems were compatible with the support systems suggested by the RMi system. Besides, when the shotcrete strength was increased to 40 MPa, the displacements and thickness of the plastic zone around the tunnel could be reduced to minimal values.

Hydrogen-assisted stable crack growth in iron-3 wt% silicon steel

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

Marrow, T.J.; Prangnell, P.; Aindow, M.

1996-08-01

Observations of internal hydrogen cleavage in Fe-3Si are reported. Hydrogen-assisted stable crack growth (H-SCG) is associated with cleavage striations of a 300 nm spacing, observed using scanning electron microscopy (SEM) and atomic force microscopy (AFM). High resolution SEM revealed finer striations, previously undetected, with a spacing of approximately 30 nm. These were parallel to the coarser striations. Scanning tunneling microscopy (STM) also showed the fine striation spacing, and gave a striation height of approximately 15 nm. The crack front was not parallel to the striations. Transmission electron microscopy (TEM) of crack tip plastic zones showed {l_brace}112{r_brace} and {l_brace}110{r_brace} slip, withmore » a high dislocation density (around 10{sup 14}m{sup {minus}2}). The slip plane spacing was approximately 15--30 nm. Parallel arrays of high dislocation density were observed in the wake of the hydrogen cleavage crack. It is concluded that H-ScG in Fe-3Si occurs by periodic brittle cleavage on the {l_brace}001{r_brace} planes. This is preceded by dislocation emission. The coarse striations are produced by crack tip blunting and the fine striations by dislocations attracted by image forces to the fracture surface after cleavage. The effects of temperature, pressure and yield strength on the kinetics of H-SCG can be predicted using a model for diffusion of hydrogen through the plastic zone.« less

Seismo-thermo-mechanical modeling of mature and immature transform faults

NASA Astrophysics Data System (ADS)

Preuss, Simon; Gerya, Taras; van Dinther, Ylona

2016-04-01

Transform faults (TF) are subdivided into continental and oceanic ones due to their markedly different tectonic position, structure, surface expression, dynamics and seismicity. Both continental and oceanic TFs are zones of rheological weakness, which is a pre-requisite for their existence and long-term stability. Compared to subduction zones, TFs are typically characterized by smaller earthquake magnitudes as both their potential seismogenic width and length are reduced. However, a few very large magnitude (Mw>8) strike-slip events were documented, which are presumably related to the generation of new transform boundaries and/or sudden reactivation of pre-existing fossil structures. In particular, the 11 April 2012 Sumatra Mw 8.6 earthquake is challenging the general concept that such high magnitude events only occur at megathrusts. Hence, the processes of TF nucleation, propagation and their direct relation to the seismic cycle and long-term deformation at both oceanic and continental transforms needs to be investigated jointly to overcome the restricted direct observations in time and space. To gain fundamental understanding of involved physical processes the numerical seismo-thermo-mechanical (STM) modeling approach, validated in a subduction zone setting (Van Dinther et al. 2013), will be adapted for TFs. A simple 2D plane view model geometry using visco-elasto-plastic material behavior will be adopted. We will study and compare seismicity patterns and evolution in two end member TF setups, each with strain-dependent and rate-dependent brittle-plastic weakening processes: (1) A single weak and mature transform fault separating two strong plates (e.g., in between oceanic ridges) and (2) A nucleating or evolving (continental) TF system with disconnected predefined faults within a plate subjected to simple shear deformation (e.g., San Andreas Fault system). The modeling of TFs provides a first tool to establish the STM model approach for transform faults in a more general case.

Resource Partitioning in Food, Space and Time between Arctic Charr (Salvelinus alpinus), Brown Trout (Salmo trutta) and European Whitefish (Coregonus lavaretus) at the Southern Edge of Their Continuous Coexistence

PubMed Central

Kiljunen, Mikko; Knudsen, Rune; Amundsen, Per-Arne

2017-01-01

Arctic charr and European whitefish are considered to be strong competitors in lakes, with the latter usually being the superior species. However, high niche plasticity and lake morphometry may suggestively facilitate resource partitioning and coexistence between charr and whitefish. Here, we explore the trophic niche utilization (diet and habitat use) of charr and whitefish co-occurring with brown trout in the deep and oligotrophic Lake Fyresvatnet, southern Norway (59°05’N, 8°10’E). Using CPUE, stomach contents and stable isotope analyses, a distinct resource partitioning was revealed between brown trout and the other two species. Brown trout typically occupied the littoral zone, feeding on benthic invertebrates, surface insects and small-sized whitefish. In contrast, charr and whitefish were predominantly zooplanktivorous, but diverged somewhat in habitat utilization as charr shifted seasonally between the profundal and the littoral zone, whereas whitefish were found in the upper water layers (littoral and pelagic habitats). Accordingly, the stable isotope values of carbon (δ13C) reflected a pelagic orientated prey resource use for both charr and whitefish, whereas brown trout had elevated carbon and nitrogen (δ15N) signatures that reflected their benthivore and piscivore diet, respectively. The findings suggest that charr may not rely upon the profundal zone as a feeding habitat but as a refuge area, and may coexist with whitefish if a third competitive and predatory species like brown trout co-occur in the lake. The study indicates that a general high habitat plasticity of Arctic charr may be essential in the presently observed coexistence with a competitively superior fish species like whitefish, and that a third fish species like brown trout may facilitate this particular fish community structure. PMID:28122061

Snap, Crackle, Pop: Dilational fault breccias record seismic slip below the brittle-plastic transition

NASA Astrophysics Data System (ADS)

Melosh, Ben L.; Rowe, Christie D.; Smit, Louis; Groenewald, Conrad; Lambert, Christopher W.; Macey, Paul

2014-10-01

Off-fault dynamic tensile cracks form behind an earthquake rupture front with distinct orientation and spacing. These cracks explode the wall rock and create breccias, which we hypothesize will preserve a unique fingerprint of dynamic rupture. Identification of these characteristic breccias may enable a new tool for identifying paleoseismic slip surfaces in the rock record. Using previous experimental and theoretical predictions, we develop a field-based model of dynamic dilational breccia formation. Experimental studies find that secondary tensile fracture networks comprise closely spaced fractures at angles of 70-90° from a slip surface, as well as fractures that branch at angles of ∼ 30 ° from a primary mode I fracture. The Pofadder Shear Zone, in Namibia and South Africa, preserves breccias formed in the brittle-ductile transition zone displaying fracture patterns consistent with those described above. Fracture spacing is approximately two orders of magnitude less than predicted by quasi-static models. Breccias are clast-supported, monomict and can display an abrupt transition from fracture network crackle breccia to mosaic breccia textures. Brecciation occurs by the intersection of off-fault dynamic fractures and wall rock fabric; this is in contrast to previous models of fluid pressure gradient-driven failure ;implosion breccias;. This mechanism tends to form many similar sized clasts with particle size distributions that may not display self-similarity; where self-similarity is observed the distributions have relatively low D-values of 1.47 ± 0.37, similar to other studies of dynamic processes. We measure slip distances at dilational breccia stepovers, estimating earthquake magnitudes between Mw 2.8-5.8 and associated rupture lengths of 0.023-3.3 km. The small calculated rupture dimensions, in combination with our geologic observations, suggest that some earthquakes nucleated within the quartz-plastic transitional zone and potentially record deep seismic slip.

Research on the use of particles coming from almond husk as fillers for vinyl plastisols to manufacture hollow pieces with similar surface finishing than wood by using a rotational moulding process

NASA Astrophysics Data System (ADS)

Crespo Amoros, Jose Enrique

PVC pastes or plasticized PVC offer great possibilities in the industrial field in which this research work has been developed since they show great relevance in plastic processing. On one hand, it is important to study these materials from different points of view: quality improvement, wide range of performance, high versatility, low costs,.... On the other hand, most of the industrial fields that usually employ these polymeric materials are characterized by developing products on which aesthetic considerations and surface finishing acquire special relevance. These industrial fields include all those on which new designs require complex shapes and new and novelty surface finishing such as interior design (furniture, wood products,...) toys industry, houseware, shoe industry,.... The main aim of this work is to improve the use of PVC plastisols in these industrial fields by optimizing formulations with new additives (low toxicity plasticizers) and fillers (lignocellulosic wastes) to obtain new materials that minimize damages to environment. In this work, we have developed new plastisol formulations based on the use of low toxicity plasticizers to obtain more ecological plastisols. We have used a biodegradable plasticizer DINCH which is a derivative of a dicarboxilate as substitute of traditional plasticizers based on phthalates. As we are working with relatively new plasticizers (specially at industrial level) we have performed a whole study of its properties by using different experimental analysis techniques such as differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), dynamical-mechanical analysis (DMA) and espectrofotometric techniques (visible and infrared). Furthermore a complete mechanical characterization has been carried out to analyze the most important parameters that influence on materials properties such as processing parameters (temperature and time) and plastisol formulations (mainly plasticizer content). We have also performed a comparative study regarding the results obtained with the most used plasticizer at industrial level, di-octyl phthalate (DOP). After this characterization, a study on the addition of cellulosic fillers was carried out to obtain materials with similar surface finishing than wood products. We used three different lignocellulosic fillers coming from wastes: almond husk residues since these wastes are quite abundant in our influence zone, rice husk and sawdust residues since they are produced everywhere in high amounts. It was studied the influence of the morphology and particle size on the final properties of the prepared mixtures to optimize formulations. These new plastisol formulations allow obtaining new materials in a wide range of mechanical properties, easy processing, interesting surface finishing and partially biodegradable, more careful with environment.

Bioinspired toughening mechanism: lesson from dentin.

PubMed

An, Bingbing; Zhang, Dongsheng

2015-07-09

Inspired by the unique microstructure of dentin, in which the hard peritubular dentin surrounding the dentin tubules is embedded in the soft intertubular dentin, we explore the crack propagation in the bioinspired materials with fracture process zone possessing a dentin-like microstructure, i.e. the composite structure consisting of a soft matrix and hard reinforcements with cylindrical voids. A micromechanical model under small-scale yielding conditions is developed, and numerical simulations are performed, showing that the rising resistant curve (R-curve) is observed for crack propagation caused by the plastic collapse of the intervoid ligaments in the fracture process zone. The dentin-like microstructure in the fracture process zone exhibits enhanced fracture toughness, compared with the case of voids embedded in the homogeneous soft matrix. Further computational simulations show that the dentin-like microstructure can retard void growth, thereby promoting fracture toughness. The typical fracture mechanism of the bioinspired materials with fracture process zone possessing the dentin-like structure is void by void growth, while it is the multiple void interaction in the case of voids in the homogeneous matrix. Based on the results, we propose a bioinspired material design principle, which is that the combination of a hard inner material encompassing voids and a soft outer material in the fracture process zone can give rise to exceptional fracture toughness, achieving damage tolerance. It is expected that the proposed design principle could shed new light on the development of novel man-made engineering materials.

Grapevine Plasticity in Response to an Altered Microclimate: Sauvignon Blanc Modulates Specific Metabolites in Response to Increased Berry Exposure

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

Young, Philip R.; Eyeghe-Bickong, Hans A.; du Plessis, Kari

In this paper, the metabolic and physiological impacts of an altered microclimate on quality-associated primary and secondary metabolites in grape (Vitis vinifera) ‘Sauvignon Blanc’ berries was determined in a high-altitude vineyard. The leaf and lateral shoot removal in the bunch zones altered the microclimate by increasing the exposure of the berries. The physical parameters (berry diameter and weight), primary metabolites (sugars and organic acids), as well as bunch temperature and leaf water potential were predominantly not affected by the treatment. The increased exposure led to higher levels of specific carotenoids and volatile terpenoids in the exposed berries, with earlier berrymore » stages reacting distinctly from the later developmental stages. Plastic/nonplastic metabolite responses could be further classified to identify metabolites that were developmentally controlled and/or responded to the treatment in a predictable fashion (assessed over two consecutive vintages). The study demonstrates that grapevine berries exhibit a degree of plasticity within their secondary metabolites and respond physiologically to the increased exposure by increasing metabolites with potential antioxidant activity. Finally, taken together, the data provide evidence that the underlying physiological responses relate to the maintenance of stress pathways by modulating antioxidant molecules in the berries.« less

Grapevine Plasticity in Response to an Altered Microclimate: Sauvignon Blanc Modulates Specific Metabolites in Response to Increased Berry Exposure

DOE PAGES

Young, Philip R.; Eyeghe-Bickong, Hans A.; du Plessis, Kari; ...

2015-12-01

In this paper, the metabolic and physiological impacts of an altered microclimate on quality-associated primary and secondary metabolites in grape (Vitis vinifera) ‘Sauvignon Blanc’ berries was determined in a high-altitude vineyard. The leaf and lateral shoot removal in the bunch zones altered the microclimate by increasing the exposure of the berries. The physical parameters (berry diameter and weight), primary metabolites (sugars and organic acids), as well as bunch temperature and leaf water potential were predominantly not affected by the treatment. The increased exposure led to higher levels of specific carotenoids and volatile terpenoids in the exposed berries, with earlier berrymore » stages reacting distinctly from the later developmental stages. Plastic/nonplastic metabolite responses could be further classified to identify metabolites that were developmentally controlled and/or responded to the treatment in a predictable fashion (assessed over two consecutive vintages). The study demonstrates that grapevine berries exhibit a degree of plasticity within their secondary metabolites and respond physiologically to the increased exposure by increasing metabolites with potential antioxidant activity. Finally, taken together, the data provide evidence that the underlying physiological responses relate to the maintenance of stress pathways by modulating antioxidant molecules in the berries.« less

Antimicrobial, Rheological, and Thermal Properties of Plasticized Polylactide Films Incorporated with Essential Oils to Inhibit Staphylococcus aureus and Campylobacter jejuni.

PubMed

Ahmed, Jasim; Hiremath, Nikhil; Jacob, Harsha

2016-02-01

Polylactide (PLA) is the most mature biobased and biodegradable polymer. Due to its inherent brittleness, the polymer cannot be used as a packaging material without plasticizer. An attempt was made to develop antimicrobial plasticized PLA film by incorporating polyethylene glycol (PEG) and 3 essential oils (EO), namely cinnamon, garlic, and clove by solvent casting method. Physical, thermal, and rheological properties of those films were evaluated for practical applications whereas the antimicrobial properties were tested against Staphylococcus aureus and Campylobacter jejuni-pathogens related to poultry industry. Both PEG and EOs led to the formation of flexible PLA/PEG/EO films with significant drop in the glass transition temperature (Tg ), and mechanical property. Time-temperature superposition (TTS) principle was employed to melt rheology of EO-based films at selected temperature, and rheological moduli superimposed well in an extended frequency range. Among EOs, cinnamon and clove oil-based films (PLA/PEG/CIN and PLA/PEG/CLO) exhibited a complete zone of inhibition against C. jejuni at the maximum concentration (1.6 mL per 2 g PLA/PEG blend) whereas the garlic oil-based film (PLA/PEG/GAR) had the lowest activity. © 2016 Institute of Food Technologists®

Effects of foreign object damage from small hard particles on the high-cycle fatigue life of titanium-(6)aluminum-(4)vanadium

NASA Astrophysics Data System (ADS)

Hamrick, Joseph L., II

Thin rectangular samples of Ti-6Al-4V were damaged by four methods to represent foreign object damage found in turbine engine blades: (1) impact with 2 mm. and 5 mm diameter glass spheres at 305 m/s, (2) impact with 2 mm and 4 mm diameter steel spheres at 305 m/s, (3) quasi-static displacement controlled indentation using steel chisels with 1 mm, 2 nun and 5 mm diameter tips and (4) shearing notches with a 2 mm. diameter chisel point under a quasi-static loading condition. Finite element analysis was used to study the relationship between the stress state created by the plastic damage and the fatigue strength. A new method of quantifying the amount of plastic damage from multiple methods was developed. The fatigue strength required for crack initiation at 10E7 cycles was found to be a function of the total depth from the edge of the undeformed specimen up to the end of the plastically deformed zone. For damage depths less than 1750 mum, the reduction in fatigue strength is proportional to the depth of total damage. For depths > 1750 mum, there appears to be a threshold value of fatigue strength.

Characterization of crack-tip microstructures via synchrotron fractography in Mo and Mo-Nb alloy crystals

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

Hmelo, A.B.

1987-01-01

The nature of the plastic relaxation associated with the semi-brittle cleavage fracture of a series of pre-cracked molybdenum-niobium alloy single crystals was investigated as a function of composition and temperature from 77/sup 0/ to 298/sup 0/K. Conventional optical microscopy and white-beam Synchrotron X-Ray Fractography (SXRF) were used to examined the structure of a thin layer a few microns thick at the remnant of the precursor crack plastic zone. The plastic work of fracture was evaluated by measuring the lattice curvature associated with networks of dislocations beneath the cleavage surface. Using SXRF, lattice curvature is detected as asterism on photographic plates,more » and is associated with an excess density of edge dislocations of one sign. The results are in qualitative agreement with a previous determination of the fracture toughness of these specimens. Excess edge-dislocation density of one sign has been shown to vary as a function of temperature and composition, in a way consistent with previous studies of total dislocation content in these materials. Unlike the etch-pit analysis that can reveal the total dislocation content only, the tensor bases analysis described here allows the activity on individual slip systems to be distinguished.« less

Grapevine Plasticity in Response to an Altered Microclimate: Sauvignon Blanc Modulates Specific Metabolites in Response to Increased Berry Exposure.

PubMed

Young, Philip R; Eyeghe-Bickong, Hans A; du Plessis, Kari; Alexandersson, Erik; Jacobson, Dan A; Coetzee, Zelmari; Deloire, Alain; Vivier, Melané A

2016-03-01

In this study, the metabolic and physiological impacts of an altered microclimate on quality-associated primary and secondary metabolites in grape (Vitis vinifera) 'Sauvignon Blanc' berries was determined in a high-altitude vineyard. The leaf and lateral shoot removal in the bunch zones altered the microclimate by increasing the exposure of the berries. The physical parameters (berry diameter and weight), primary metabolites (sugars and organic acids), as well as bunch temperature and leaf water potential were predominantly not affected by the treatment. The increased exposure led to higher levels of specific carotenoids and volatile terpenoids in the exposed berries, with earlier berry stages reacting distinctly from the later developmental stages. Plastic/nonplastic metabolite responses could be further classified to identify metabolites that were developmentally controlled and/or responded to the treatment in a predictable fashion (assessed over two consecutive vintages). The study demonstrates that grapevine berries exhibit a degree of plasticity within their secondary metabolites and respond physiologically to the increased exposure by increasing metabolites with potential antioxidant activity. Taken together, the data provide evidence that the underlying physiological responses relate to the maintenance of stress pathways by modulating antioxidant molecules in the berries. © 2016 American Society of Plant Biologists. All Rights Reserved.

Grapevine Plasticity in Response to an Altered Microclimate: Sauvignon Blanc Modulates Specific Metabolites in Response to Increased Berry Exposure1

PubMed Central

du Plessis, Kari; Jacobson, Dan A.

2016-01-01

In this study, the metabolic and physiological impacts of an altered microclimate on quality-associated primary and secondary metabolites in grape (Vitis vinifera) ‘Sauvignon Blanc’ berries was determined in a high-altitude vineyard. The leaf and lateral shoot removal in the bunch zones altered the microclimate by increasing the exposure of the berries. The physical parameters (berry diameter and weight), primary metabolites (sugars and organic acids), as well as bunch temperature and leaf water potential were predominantly not affected by the treatment. The increased exposure led to higher levels of specific carotenoids and volatile terpenoids in the exposed berries, with earlier berry stages reacting distinctly from the later developmental stages. Plastic/nonplastic metabolite responses could be further classified to identify metabolites that were developmentally controlled and/or responded to the treatment in a predictable fashion (assessed over two consecutive vintages). The study demonstrates that grapevine berries exhibit a degree of plasticity within their secondary metabolites and respond physiologically to the increased exposure by increasing metabolites with potential antioxidant activity. Taken together, the data provide evidence that the underlying physiological responses relate to the maintenance of stress pathways by modulating antioxidant molecules in the berries. PMID:26628747

What is CAR doing in the middle of the adult neurogenic road?

PubMed Central

Junyent, Felix; Coré, Nathalie; Cremer, Harold

2017-01-01

ABSTRACT The molecular and cellular basis of adult neurogenesis has attracted considerable attention for fundamental and clinical applications because neural stem cells and newborn neurons may, one day, be harnessed to replace neurons and allow cognitive improvement in the diseased brain. In rodents, neural progenitors are located in the dentate gyrus and the sub/periventricular zone. In the dentate gyrus the generation of newborn neurons is associated with plasticity, including regulation of memory. The role of subventricular zone neural precursors that migrate to the olfactory bulb is less characterized. Identifying factors that impact neural stem cell proliferation, migration and differentiation is therefore sine qua non before we can harness their potential. Here, we expand upon our recent results showing that CAR, the coxsackievirus and adenovirus receptor, is among the developing list of key players when it comes to the complex process of integrating newborn neurons into existing circuits in the mature brain. PMID:28516108

Littoral foraging by red phalaropes during spring in the northern Bering Sea

USGS Publications Warehouse

Haney, J. Christopher; Stone, Amy E.

1988-01-01

Phalaropes demonstrate considerable plasticity in their choice of foraging habitats. The Red Phalarope (Phalaropus fulicaria) alternates use of pelagic environments in winter and migration (Taning 1933, Stanford 1953, Briggs et al 1984) with wet tundra habitats during the breeding season (Kistchinski 1975, Mayfield 1979, Ridley 1980). Foods available and taken in littoral zones of the Arctic Ocean in fall have been identified (Conners and Risebrough 1978, Johnson and Richardson 1980), but otherwise little attention has been devoted to the transition between the marine and terrestrial periods of the Red Phalarope’s life history. We report phalarope use of littoral areas during spring in the northern Bering Sea and Kongkok Bay, St. Lawrence Island, Alaska. In addition, we describe phalarope foraging tactics and foods available in the sur zone, emphasizing this form of littoral foraging as an opportunistic and facultative feeding strategy.

Control technology for fiber reinforced plastics industry at AMF Hatteras Yachts, New Bern Division, New Bern, North Carolina

NASA Astrophysics Data System (ADS)

Todd, W. F.

1984-05-01

Area and breathing zone samples were analyzed for styrene (100425) at AMF Hatteras Yachts (SIC-3079), New Bern, North Carolina, in September, 1983. Control technology at the facility was inspected. Breathing zone styrene concentrations were 8 to 74 parts per million (ppm), the highest concentrations occurring in the lamination and gel coating departments. Area samples ranged from 1 to 20ppm. The OSHA standard is 100ppm. The hull lamination and assembly areas were ventilated by air make up units and exhaust blowers. Air exhausted through the lamination booths in the small parts work area was considerably less than the supply air from the make up units. The air flow in two of the three lamination booths was considered inadequate. Respirators were available if needed. Industrial hygiene sampling at the facility was supervised by the industrial hygienist.

Modelling of deformation around magmatic intrusions with application to gold-related structures in the Yilgarn Craton, Western Australia

NASA Astrophysics Data System (ADS)

Zhang, Y.; Karrech, A.; Schaubs, P. M.; Regenauer-Lieb, K.; Poulet, T.; Cleverley, J. S.

2012-03-01

This study simulates rock deformation around high temperature granite intrusions and explores how gold bearing shear zones near intrusions were developed in the Yilgarn, using a new continuum damage mechanics algorithm that considers the temperature and time dependent elastic-visco-plastic constitutive behaviour of crustal materials. The results demonstrate that strain rates have the most significant effects on structural patterns for both extensional and compressional cases. Smaller strain rates promote the formation of narrow high-strain shear zones and strong strain localisation along the flank or shoulder areas of the intrusion and cold granite dome. Wider diffuse shear zones are developed under higher strain rates due to strain hardening. The cooling of the intrusion to background temperatures occurred over a much shorter time interval when compared to the duration of deformation and shear zones development. Strong strain localisation near the intrusion and shear zone development in the crust occurred under both extensional and compressional conditions. There is always clear strain localisation around the shoulders of the intrusion and the flanks of the "cold" granitic dome in early deformation stages. In the models containing a pre-existing fault, strain localisation near the intrusion became asymmetric with much stronger localisation and the development of a damage zone at the shoulder adjacent to the reactivated fault. At higher deformation stages, the models produced a range of structural patterns including graben and half graben basin (extension), "pop-up" wedge structures (compression), tilted fault blocks and switch of shear movement from reverse to normal on shear zones. The model explains in part why a number of gold deposits (e.g. Wallaby and Paddington deposits) in the Yilgarn were formed near the flank of granite-cored domes and deep "tapping" faults, and shows that the new modelling approach is capable of realistically simulating high strain localisation and shear zone development.

Structural Inelasticity (28th), A Finite Element ’Vectorization’ Method for the Solution of Crack Growth Problems in Two or Three Dimensions.

DTIC Science & Technology

1986-02-01

analitic and numerical paws which have aieared In the literature. A more detail accbunt is contained In the review article by Rice [91. The...where Y is the initial yield stress. Based on the stress change A011O) we predict thA the element o for which...solution predicts an applied load of 0.93, which is 7% greater than the measured value. The plastic zones at different leves of lied load are shown

Elastoplastic State of an Elliptical Cylindrical Shell with a Circular Hole

NASA Astrophysics Data System (ADS)

Storozhuk, E. A.; Chernyshenko, I. S.; Pigol', O. V.

2017-11-01

Static problems for an elastoplastic elliptical cylindrical shell with a circular hole are formulated and a numerical method for solving it is developed. The basic equations are derived using the Kirchhoff-Love theory of deep shells and the theory of small elastoplastic strains. The method employs the method of additional stresses and the finite-element method. The influence of plastic strains and geometrical parameters of the shell subject to internal pressure on the distributions of stresses, strains, and displacements in the zone of their concentration is studied.

A Combined Experimental and Analytical Modeling Approach to Understanding Friction Stir Welding

NASA Technical Reports Server (NTRS)

Nunes, Arthur C., Jr.; Stewart, Michael B.; Adams, Glynn P.; Romine, Peter

1998-01-01

In the Friction Stir Welding (FSW) process a rotating pin tool joins the sides of a seam by stirring them together. This solid state welding process avoids problems with melting and hot-shortness presented by some difficult-to weld high-performance light alloys. The details of the plastic flow during the process are not well understood and are currently a subject of research. Two candidate models of the FSW process, the Mixed Zone (MZ) and the Single Slip Surface (S3) model are presented and their predictions compared to experimental data.

C-band SAR observations of marginal ice zone rheology in the Labrador Sea

NASA Technical Reports Server (NTRS)

Drinkwater, Mark R.; Squire, Vernon A.

1989-01-01

Synthetic-aperture radar (SAR) imagery collected during the LIMEX'87 field program in the Labrador Sea is used to qualitatively interpret the deformational modes in play throughout the experiment. The ice cover exhibited two distinct rheologies separated by a clear line of shear: a nonlinear viscous outer regime, and a quasi-brittle inner regime. A single constitutive relation capable of effectively modeling both is unlikely within a plastic rate-independent formulation. Rate-dependent effects are discussed in relation to favoring brittle fraction in an otherwise ductile material.

Shock response of nanoporous Cu--A molecular dynamics simulation

NASA Astrophysics Data System (ADS)

Zhao, Fengpeng

2015-06-01

Shock response of porous materials can be of crucial significance for shock physics and bears many practical applications in materials synthesis and engineering. Molecular dynamics simulations are carried out to investigate shock response of nanoporous metal materials, including elastic-plastic deformation, Hugoniot states, shock-induced melting, partial or complete void collapse, hotspot formation, nanojetting, and vaporization. A model nanoporous Cu with cylindrical voids and a high porosity under shocking is established to investigate such physical properties as velocity, temperature, density, stress and von Mises stress at different stages of compression and release. The elastic-plastic and overtaking shocks are observed at different shock strengths. A modified power-law P- α model is proposed to describe the Hugoniot states. The Grüneisen equation of state is validated. Shock-induced melting shows no clear signs of bulk premelting or superheating. Void collapse via plastic flow nucleated from voids, and the exact processes are shock strength dependent. With increasing shock strengths, void collapse transits from the ``geometrical'' mode (collapse of a void is dominated by crystallography and void geometry and can be different from that of one another) to ``hydrodynamic'' mode (collapse of a void is similar to one another). The collapse may be achieved predominantly by plastic flows along the {111} slip planes, by way of alternating compression and tension zones, by means of transverse flows, via forward and transverse flows, or through forward nano-jetting. The internal jetting induces pronounced shock front roughening, leading to internal hotspot formation and sizable high speed jets on atomically flat free surfaces. P. O. Box 919-401, Mianyang, 621900, Sichuan, PRC.

When three traits make a line: evolution of phenotypic plasticity and genetic assimilation through linear reaction norms in stochastic environments.

PubMed

Ergon, T; Ergon, R

2017-03-01

Genetic assimilation emerges from selection on phenotypic plasticity. Yet, commonly used quantitative genetics models of linear reaction norms considering intercept and slope as traits do not mimic the full process of genetic assimilation. We argue that intercept-slope reaction norm models are insufficient representations of genetic effects on linear reaction norms and that considering reaction norm intercept as a trait is unfortunate because the definition of this trait relates to a specific environmental value (zero) and confounds genetic effects on reaction norm elevation with genetic effects on environmental perception. Instead, we suggest a model with three traits representing genetic effects that, respectively, (i) are independent of the environment, (ii) alter the sensitivity of the phenotype to the environment and (iii) determine how the organism perceives the environment. The model predicts that, given sufficient additive genetic variation in environmental perception, the environmental value at which reaction norms tend to cross will respond rapidly to selection after an abrupt environmental change, and eventually becomes equal to the new mean environment. This readjustment of the zone of canalization becomes completed without changes in genetic correlations, genetic drift or imposing any fitness costs of maintaining plasticity. The asymptotic evolutionary outcome of this three-trait linear reaction norm generally entails a lower degree of phenotypic plasticity than the two-trait model, and maximum expected fitness does not occur at the mean trait values in the population. © 2016 The Authors. Journal of Evolutionary Biology published by John Wiley & Sons Ltd on behalf of European Society for Evolutionary Biology.

Granular flows in constrained geometries

NASA Astrophysics Data System (ADS)

Murthy, Tejas; Viswanathan, Koushik

Confined geometries are widespread in granular processing applications. The deformation and flow fields in such a geometry, with non-trivial boundary conditions, determine the resultant mechanical properties of the material (local porosity, density, residual stresses etc.). We present experimental studies of deformation and plastic flow of a prototypical granular medium in different nontrivial geometries- flat-punch compression, Couette-shear flow and a rigid body sliding past a granular half-space. These geometries represent simplified scaled-down versions of common industrial configurations such as compaction and dredging. The corresponding granular flows show a rich variety of flow features, representing the entire gamut of material types, from elastic solids (beam buckling) to fluids (vortex-formation, boundary layers) and even plastically deforming metals (dead material zone, pile-up). The effect of changing particle-level properties (e.g., shape, size, density) on the observed flows is also explicitly demonstrated. Non-smooth contact dynamics particle simulations are shown to reproduce some of the observed flow features quantitatively. These results showcase some central challenges facing continuum-scale constitutive theories for dynamic granular flows.

Effect of irradiation-induced plastic flow localization on ductile crack resistance behavior of a 9%Cr tempered martensitic steel

NASA Astrophysics Data System (ADS)

Chaouadi, R.

2008-01-01

This paper examines the effect of irradiation-induced plastic flow localization on the crack resistance behavior. Tensile and crack resistance measurements were performed on Eurofer-97 that was irradiated at 300 °C to neutron doses ranging between 0.3 and 2.1 dpa. A severe degradation of crack resistance behavior is experimentally established at quasi-static loading, in contradiction with the Charpy impact data and the dynamic crack resistance measurements. This degradation is attributed to the dislocation channel deformation phenomenon. At quasi-static loading rate, scanning electron microscopy observations of the fracture surfaces revealed a significant change of fracture topography, mainly from equiaxed dimples (mode I) to shear dimples (mode I + II). With increasing loading rate, the high peak stresses that develop inside the process zone activate much more dislocation sources resulting in a higher density of cross cutting dislocation channels and therefore an almost unaffected crack resistance. These explanations provide a rational to all experimental observations.

Thermal effect of laser ablation on the surface of carbon fiber reinforced plastic during laser processing

NASA Astrophysics Data System (ADS)

Ohkubo, Tomomasa; Sato, Yuji; Matsunaga, Ei-ichi; Tsukamoto, Masahiro

2018-02-01

Although laser processing is widely used for many applications, the cutting quality of carbon fiber reinforced plastic (CFRP) decreases around the heat-affected zone (HAZ) during laser processing. Carbon fibers are exposed around the HAZ, and tensile strength decreases with increasing length of the HAZ. Some theoretical studies of thermal conductions that do not consider fluid dynamics have been performed; however, theoretical considerations that include the dynamics of laser ablation are scarce. Using removed mass and depth observed from experiments, the dynamics of laser ablation of CFRP with high-temperature and high-pressure of compressive gas is simulated herein. In this calculation, the mushroom-like shape of laser ablation is qualitatively simulated compared with experiments using a high-speed camera. Considering the removal temperature of the resin and the temperature distribution at each point on the surface, the simulation results suggest that a wide area of the resin is removed when the processing depth is shallow, and a rounded kerf is generated as the processing depth increases.

Low-cost ultra-thin broadband terahertz beam-splitter.

PubMed

Ung, Benjamin S-Y; Fumeaux, Christophe; Lin, Hungyen; Fischer, Bernd M; Ng, Brian W-H; Abbott, Derek

2012-02-27

A low-cost terahertz beam-splitter is fabricated using ultra-thin LDPE plastic sheeting coated with a conducting silver layer. The beam splitting ratio is determined as a function of the thickness of the silver layer--thus any required splitting ratio can be printed on demand with a suitable rapid prototyping technology. The low-cost aspect is a consequence of the fact that ultra-thin LDPE sheeting is readily obtainable, known more commonly as domestic plastic wrap or cling wrap. The proposed beam-splitter has numerous advantages over float zone silicon wafers commonly used within the terahertz frequency range. These advantages include low-cost, ease of handling, ultra-thin thickness, and any required beam splitting ratio can be readily fabricated. Furthermore, as the beam-splitter is ultra-thin, it presents low loss and does not suffer from Fabry-Pérot effects. Measurements performed on manufactured prototypes with different splitting ratios demonstrate a good agreement with our theoretical model in both P and S polarizations, exhibiting nearly frequency-independent splitting ratios in the terahertz frequency range.

Effect of high-temperature water and hydrogen on the fracture behavior of a low-alloy reactor pressure vessel steel

NASA Astrophysics Data System (ADS)

Roychowdhury, S.; Seifert, H.-P.; Spätig, P.; Que, Z.

2016-09-01

Structural integrity of reactor pressure vessels (RPV) is critical for safety and lifetime. Possible degradation of fracture resistance of RPV steel due to exposure to coolant and hydrogen is a concern. In this study tensile and elastic-plastic fracture mechanics (EPFM) tests in air (hydrogen pre-charged) and EFPM tests in hydrogenated/oxygenated high-temperature water (HTW) was done, using a low-alloy RPV steel. 2-5 wppm hydrogen caused embrittlement in air tensile tests at room temperature (25 °C) and at 288 °C, effects being more significant at 25 °C and in simulated weld coarse grain heat affected zone material. Embrittlement at 288 °C is strain rate dependent and is due to localized plastic deformation. Hydrogen pre-charging/HTW exposure did not deteriorate the fracture resistance at 288 °C in base metal, for investigated loading rate range. Clear change in fracture morphology and deformation structures was observed, similar to that after air tests with hydrogen.

Microplastic fibers in the intertidal ecosystem surrounding Halifax Harbor, Nova Scotia.

PubMed

Mathalon, Alysse; Hill, Paul

2014-04-15

Humans continue to increase the use and disposal of plastics by producing over 240 million tonnes per year, polluting the oceans with persistent waste. The majority of plastic in the oceans are microplastics (<5 mm). In this study, the contamination of microplastic fibers was quantified in sediments from the intertidal zones of one exposed beach and two protected beaches along Nova Scotia's Eastern Shore. From the two protected beaches, polychaete worm fecal casts and live blue mussels (Mytilus edulis) were analyzed for microplastic content. Store-bought mussels from an aquaculture site were also analyzed. The average microplastic abundance observed from 10 g sediment subsamples was between 20 and 80 fibers, with higher concentrations at the high tide line from the exposed beach and at the low tide line from the protected beaches. Microplastic concentrations from polychaete fecal casts resembled concentrations quantified from low tide sediments. In two separate mussel analyses, significantly more microplastics were enumerated in farmed mussels compared to wild ones. Copyright © 2014 Elsevier Ltd. All rights reserved.

Biases and best approaches for assessing debris ingestion in sea turtles, with a case study in the Mediterranean.

PubMed

Casale, Paolo; Freggi, Daniela; Paduano, Valentina; Oliverio, Marco

2016-09-15

In a sample of 567 loggerhead turtles (Caretta caretta) from the central Mediterranean, debris occurrence varied according to methods and turtle source, and was up to 80% in pelagic turtles. Frequencies of plastic types, size and color are also reported. These results and a critical review of 49 studies worldwide indicate that: (i) the detected occurrence of plastic (% turtles) is affected by several factors (e.g., necropsy/feces, ecological zone, type and date of finding, captivity period for feces collection), (ii) mixed dataset and opportunistic approaches provide results which are biased , not comparable, and ultimately of questionable value, (iii) only turtles assumed to have had a normal feeding behaviour at the time of capture or death should be considered, (iv) turtle foraging ecology and possible selectivity may undermine the use of turtles as indicator species for monitoring marine litter, as recently proposed for the Mediterranean. Copyright © 2016 Elsevier Ltd. All rights reserved.

Marine debris ingestion by coastal dolphins: what drives differences between sympatric species?

PubMed

Di Beneditto, Ana Paula Madeira; Ramos, Renata Maria Arruda

2014-06-15

This study compared marine debris ingestion of the coastal dolphins Pontoporia blainvillei and Sotalia guianensis in a sympatric area in Atlantic Ocean. Among the 89 stomach contents samples of P. blainvillei, 14 (15.7%) contained marine debris. For S. guianensis, 77 stomach contents samples were analyzed and only one of which (1.30%) contained marine debris. The debris recovered was plastic material: nylon yarns and flexible plastics. Differences in feeding habits between the coastal dolphins were found to drive their differences regarding marine debris ingestion. The feeding activity of P. blainvillei is mainly near the sea bottom, which increases its chances of ingesting debris deposited on the seabed. In contrast, S. guianensis has a near-surface feeding habit. In the study area, the seabed is the main zone of accumulation of debris, and species with some degree of association with the sea bottom may be local bioindicators of marine debris pollution. Copyright © 2014 Elsevier Ltd. All rights reserved.

The neuroscience of observing consciousness & mirror neurons in therapeutic hypnosis.

PubMed

Rossi, Ernest L; Rossi, Kathryn L

2006-04-01

Neuroscience documents the activity of "mirror neurons" in the human brain as a mechanism whereby we experience empathy and recognize the intentions of others by observing their behavior and automatically matching their brain activity. This neural basis of empathy finds support in research on dysfunctions in the mirror systems of humans with autism and fMRI research on normal subjects designed to assess intentionality, emotions, and complex cognition. Such empathy research now appears to be consistent with the historical and research literature on hypnotic induction, rapport, and many of the classical phenomena of suggestion. A preliminary outline of how mirror neurons may function as a rapport zone mediating between observing consciousness, the gene expression/protein synthesis cycle, and brain plasticity in therapeutic hypnosis and psychosomatic medicine is proposed. Brain plasticity is generalized in the theory, research, and practice of utilizing mirror neurons as an explanatory framework in developing and training new skill sets for facilitating an activity-dependent approach to creative problem solving, mind-body healing, and rehabilitation with therapeutic hypnosis.

Size effects resolve discrepancies in 40 years of work on low-temperature plasticity in olivine

PubMed Central

Kumamoto, Kathryn M.; Thom, Christopher A.; Wallis, David; Hansen, Lars N.; Armstrong, David E. J.; Warren, Jessica M.; Goldsby, David L.; Wilkinson, Angus J.

2017-01-01

The strength of olivine at low temperatures and high stresses in Earth’s lithospheric mantle exerts a critical control on many geodynamic processes, including lithospheric flexure and the formation of plate boundaries. Unfortunately, laboratory-derived values of the strength of olivine at lithospheric conditions are highly variable and significantly disagree with those inferred from geophysical observations. We demonstrate via nanoindentation that the strength of olivine depends on the length scale of deformation, with experiments on smaller volumes of material exhibiting larger yield stresses. This “size effect” resolves discrepancies among previous measurements of olivine strength using other techniques. It also corroborates the most recent flow law for olivine, which proposes a much weaker lithospheric mantle than previously estimated, thus bringing experimental measurements into closer alignment with geophysical constraints. Further implications include an increased difficulty of activating plasticity in cold, fine-grained shear zones and an impact on the evolution of fault surface roughness due to the size-dependent deformation of nanometer- to micrometer-sized asperities. PMID:28924611

Plane stress problems using hysteretic rigid body spring network models

NASA Astrophysics Data System (ADS)

Christos, Sofianos D.; Vlasis, Koumousis K.

2017-10-01

In this work, a discrete numerical scheme is presented capable of modeling the hysteretic behavior of 2D structures. Rigid Body Spring Network (RBSN) models that were first proposed by Kawai (Nucl Eng Des 48(1):29-207, 1978) are extended to account for hysteretic elastoplastic behavior. Discretization is based on Voronoi tessellation, as proposed specifically for RBSN models to ensure uniformity. As a result, the structure is discretized into convex polygons that form the discrete rigid bodies of the model. These are connected with three zero length, i.e., single-node springs in the middle of their common facets. The springs follow the smooth hysteretic Bouc-Wen model which efficiently incorporates classical plasticity with no direct reference to a yield surface. Numerical results for both static and dynamic loadings are presented, which validate the proposed simplified spring-mass formulation. In addition, they verify the model's applicability on determining primarily the displacement field and plastic zones compared to the standard elastoplastic finite element method.

Seaweeds and plastic debris can influence the survival of faecal indicator organisms in beach environments.

PubMed

Quilliam, Richard S; Jamieson, Julie; Oliver, David M

2014-07-15

The revised Bathing Water Directive (rBWD) introduces more stringent standards for microbial water quality and promotes more pro-active management of the beach environment through the production of a bathing water profile (BWP). The aim of this study was to determine whether living seaweeds in the littoral zone are colonised by faecal indicator organisms (FIOs), and to quantify the survival dynamics of waterborne Escherichia coli in microcosms containing senescing seaweeds. Living seaweed (Fucus spiralis) was not associated with FIO colonisation, although could be providing a protected environment in the underlying sand. Senescing seaweeds enhanced waterborne E. coli survival compared to plastic debris, with the brown seaweed Laminaria saccharina facilitating greater E. coli persistence than either Chondrus crispus or Ulva lactuca. This has important implications for FIO survival on bathing beaches as the majority of beach-cast biomass is composed of brown seaweeds, which could support significant levels of FIOs. Copyright © 2014 Elsevier Ltd. All rights reserved.

Shape optimization of shear fracture specimen considering plastic anisotropy

NASA Astrophysics Data System (ADS)

Zhang, S.; Yoon, J. W.; Lee, S.; Lou, Y.

2017-10-01

It is important to fabricate fracture specimens with minimum variation of triaxiality in order to characterize the failure behaviors experimentally. Fracture in ductile materials is usually calibrated by uniaxial tensile, shear and plane strain tests. However, it is often observed that triaxiality for shear specimen changes severely during shear fracture test. The nonlinearity of triaxiality is most critical for shear test. In this study, a simple in-plane shear specimen is optimized by minimizing the variation of stress triaxiality in the shear zone. In the optimization, the Hill48 and Yld2000-2d criteria are employed to model the anisotropic plastic deformation of an aluminum alloy of 6k21. The evolution of the stress triaxiality of the optimized shear specimen is compared with that of the initial design of the shear specimen. The comparison reveals that the stress triaxiality changes much less for the optimized shear specimen than the evolution of the stress triaxiality with the original design of the shear specimen.

Modeling Mantle Shear Zones, Melt Focusing and Stagnation - Are Non Volcanic Margins Really Magma Poor?

NASA Astrophysics Data System (ADS)

Lavier, L. L.; Muntener, O.

2011-12-01

Mantle peridotites from ocean-continent transition zones (OCT's) and ultraslow spreading ridges question the commonly held assumption of a simple link between mantle melting and MORB. 'Ancient' and partly refertilized mantle in rifts and ridges illustrates the distribution of the scale of upper mantle heterogeneity even on a local scale. Upwelling of partial melts that enter the conductive lithospheric mantle inevitably leads to freezing of the melt and metasomatized lithosphere. Field data and petrology demonstrates that ancient, thermally undisturbed, pyroxenite-veined subcontinental mantle blobs formed parts of the ocean floor next to thinned continental crust. Similar heterogeneity might be created in the oceanic lithosphere where the thermal boundary layer (TBM) is thick and veined with metasomatic assemblages. This cold, ancient, 'subcontinental domain' is separated by ductile shear zones (or some other form of permeability barriers) from an infiltrated ('hot') domain dominated by refertilized spinel and/or plagioclase peridotite. The footwall of these mantle shear zones display complex refertilization processes and high-temperature deformation. We present numerical models that illustrate the complex interplay of km-scale refertilization with active deformation and melt focusing on top of the mantle. Melt lubricated shear zones focus melt flow in shear fractures (melt bands) occurring along grain boundaries. Continuous uplift and cooling leads to crystallization, and crystal plastic deformation prevails in the subsolidus state. Below 800oC if water is present deformation by shearing of phyllosilicates may become prevalent. We develop physical boundary conditions for which stagnant melt beneath a permeability barrier remains trapped rather than being extracted to the surface via melt-filled fractures. We explore the parameter space for fracturing and drainage and development of anastomozing impermeable shear zones. Our models might be useful to constrain the conditions and enigmatic development of magma-poor and magma rich margins.

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.

Hollow Cylinder Tests on Boom Clay: Modelling of Strain Localization in the Anisotropic Excavation Damaged Zone

NASA Astrophysics Data System (ADS)

François, Bertrand; Labiouse, Vincent; Dizier, Arnaud; Marinelli, Ferdinando; Charlier, Robert; Collin, Frédéric

2014-01-01

Boom Clay is extensively studied as a potential candidate to host underground nuclear waste disposal in Belgium. To guarantee the safety of such a disposal, the mechanical behaviour of the clay during gallery excavation must be properly predicted. In that purpose, a hollow cylinder experiment on Boom Clay has been designed to reproduce, in a small-scale test, the Excavation Damaged Zone (EDZ) as experienced during the excavation of a disposal gallery in the underground. In this article, the focus is made on the hydro-mechanical constitutive interpretation of the displacement (experimentally obtained by medium resolution X-ray tomography scanning). The coupled hydro-mechanical response of Boom Clay in this experiment is addressed through finite element computations with a constitutive model including strain hardening/softening, elastic and plastic cross-anisotropy and a regularization method for the modelling of strain localization processes. The obtained results evidence the directional dependency of the mechanical response of the clay. The softening behaviour induces transient strain localization processes, addressed through a hydro-mechanical second grade model. The shape of the obtained damaged zone is clearly affected by the anisotropy of the materials, evidencing an eye-shaped EDZ. The modelling results agree with experiments not only qualitatively (in terms of the shape of the induced damaged zone), but also quantitatively (for the obtained displacement in three particular radial directions).

Detonation wave profiles measured in plastic bonded explosives using 1550 nm photon doppler velocimetry (PDV)

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

Gustavsen, Richard L; Bartram, Brian D; Sanchez, Nathaniel

2009-01-01

We present detonation wave profiles measured in two TATB based explosives and two HMX based explosives. Profiles were measured at the interface of the explosive and a Lithium-Fluoride (LiF) window using 1550 nm Photon Doppler Velocimetry (PDV). Planar detonations were produced by impacting the explosive with a projectile launched in a gas-gun. The impact state was varied to produce varied distance to detonation, and therefore varied support of the Taylor wave following the Chapman-Jouget (CJ) or sonic state. Profiles from experiments with different support should be the same between the Von-Neumann (VN) spike and CJ state and different thereafter. Comparisonmore » of profiles with differing support, therefore, allows us to estimate reaction zone lengths. For the TATB based explosive, a reaction zone length of {approx} 3.9 mm, 500 ns was measured in EDC-35, and a reaction zone length of {approx} 6.3 mm, 800 ns was measured in PBX 9502 pre-cooled to -55 C. The respective VN spike state was 2.25 {+-} 0.05 km/s in EDC-35 and 2.4 {+-} 0.1 km/s in the cooled PBX 9502. We do not believe we have resolved either the VN spike state (> 2.6 km/s) nor the reaction zone length (<< 50 ns) in the HMX based explosives.« less

Presynaptic PICK1 facilitates trafficking of AMPA-receptors between active zone and synaptic vesicle pool.

PubMed

Haglerød, C; Hussain, S; Nakamura, Y; Xia, J; Haug, F-M S; Ottersen, O P; Henley, J M; Davanger, S

2017-03-06

Previous studies have indicated that presynaptic α-amino-3-hydroxy-5-methyl-4-isoxazole propionate receptors (AMPARs) contribute to the regulation of neurotransmitter release. In hippocampal synapses, the presynaptic surface expression of several AMPAR subunits, including GluA2, is regulated in a ligand-dependent manner. However, the molecular mechanisms underlying the presynaptic trafficking of AMPARs are still unknown. Here, using bright-field immunocytochemistry, western blots, and quantitative immunogold electron microscopy of the hippocampal CA1 area from intact adult rat brain, we demonstrate the association of AMPA receptors with the presynaptic active zone and with small presynaptic vesicles, in Schaffer collateral synapses in CA1 of the hippocampus. Furthermore, we show that GluA2 and protein interacting with C kinase 1 (PICK1) are colocalized at presynaptic vesicles. Similar to postsynaptic mechanisms, overexpression of either PICK1 or pep2m, which inhibit the N-ethylmaleimide sensitive fusion protein (NSF)-GluA2 interaction, decreases the concentration of GluA2 in the presynaptic active zone membrane. These data suggest that the interacting proteins PICK1 and NSF act as regulators of presynaptic GluA2-containing AMPAR trafficking between the active zone and a vesicle pool that may provide the basis of presynaptic components of synaptic plasticity. Copyright © 2017 IBRO. All rights reserved.

Ignition and growth modeling of detonation reaction zone experiments on single crystals of PETN and HMX

NASA Astrophysics Data System (ADS)

White, Bradley W.; Tarver, Craig M.

2017-01-01

It has long been known that detonating single crystals of solid explosives have much larger failure diameters than those of heterogeneous charges of the same explosive pressed or cast to 98 - 99% theoretical maximum density (TMD). In 1957, Holland et al. demonstrated that PETN single crystals have failure diameters of about 8 mm, whereas heterogeneous PETN charges have failure diameters of less than 0.5 mm. Recently, Fedorov et al. quantitatively determined nanosecond time resolved detonation reaction zone profiles of single crystals of PETN and HMX by measuring the interface particle velocity histories of the detonating crystals and LiF windows using a PDV system. The measured reaction zone time durations for PETN and HMX single crystal detonations were approximately 100 and 260 nanoseconds, respectively. These experiments provided the necessary data to develop Ignition and Growth (I&G) reactive flow model parameters for the single crystal detonation reaction zones. Using these parameters, the calculated unconfined failure diameter of a PETN single crystal was 7.5 +/- 0.5 mm, close to the 8 mm experimental value. The calculated failure diameter of an unconfined HMX single crystal was 15 +/- 1 mm. The unconfined failure diameter of an HMX single crystal has not yet been determined precisely, but Fedorov et al. detonated 14 mm diameter crystals confined by detonating a HMX-based plastic bonded explosive (PBX) without initially overdriving the HMX crystals.

Rupture dynamics with energy loss outside the slip zone

USGS Publications Warehouse

Andrews, D.J.

2005-01-01

Energy loss in a fault damage zone, outside the slip zone, contributes to the fracture energy that determines rupture velocity of an earthquake. A nonelastic two-dimensional dynamic calculation is done in which the slip zone is modeled as a fault plane and material off the fault is subject to a Coulomb yield condition. In a mode 2 crack-like solution in which an abrupt uniform drop of shear traction on the fault spreads from a point, Coulomb yielding occurs on the extensional side of the fault. Plastic strain is distributed with uniform magnitude along the fault, and it has a thickness normal to the fault proportional to propagation distance. Energy loss off the fault is also proportional to propagation distance, and it can become much larger than energy loss on the fault specified by the fault constitutive relation. The slip velocity function could be produced in an equivalent elastic problem by a slip-weakening friction law with breakdown slip Dc increasing with distance. Fracture energy G and equivalent Dc will be different in ruptures with different initiation points and stress drops, so they are not constitutive properties; they are determined by the dynamic solution that arrives at a particular point. Peak slip velocity is, however, a property of a fault location. Nonelastic response can be mimicked by imposing a limit on slip velocity on a fault in an elastic medium.

Ductile shear zone rheology: the viewpoint of experimentally crept lower crustal rocks and analogues

NASA Astrophysics Data System (ADS)

Dimanov, Alexandre; Raphanel, Jean; Bornert, Michel; Bourcier, Mathieu; Gaye, Ababacar; Ludwig, Wolfgang

2015-04-01

With respect to lithosphere rheology, we are especially interested in the mechanical behavior and evolution of ductile shear zones at depth, which present polyphase and heterogeneous character and multi-scale strain localization patterns. According to structural geology, most strain concentrates in ultramylonitic layers, which exhibit along with metamorphism overprinted or concomitant microstructural signatures from several deformation mechanisms. The latter are either active in volume (crystal slip plasticity and dislocation recovery processes), or in the vicinity and along interfaces (grain sliding, phase transformations and solution mass transfer). Because all of these contribute to the drastic evolution of microstructures with respect to the wall rock and the protomylonite, and because the chronology of their activation and their interactions are unclear, inference of the overall rheology from these microstructural records seems illusory. Therefore, since more than a decade we investigate experimentally and numerically the rheology of synthetic rocks representative of lower crustal mineralogy (namely plagioclases and clinopyroxenes). Samples are elaborated with different microstructures and with variable phases, fluid and melt contents for the purpose of being representative of diverse geodynamical contexts. Experiments were performed either at constant stress or strain rate, in co-axial compression or in torsion. For macroscopic non-Newtonian flow we clearly identified dislocation glide and creep mechanisms. That is to say that power law rheology relates to dominant crystal slip plasticity accommodated by recovery processes, including dislocation climb and pile-up, sub-grain rotation and marginal recrystallization. We further refer to this regime as RCSP (recovery crystal slip plasticity). Conversely, Newtonian (linear viscous) behavior mostly involves grain boundary sliding (GBS) accommodated by diffusional mass transfer and grain boundary dislocation mechanisms, but local RCSP can still be active as well. We realized finite element (FE) modelling of a representative elementary volume (REV) constituted of volumetrically dominant fine-grained matrix and strong inclusions subjected to simple shear. The results confirmed that the microstructural heterogeneity and the contrasting rheology of the constituent phases induce very strong local stress and strain partitioning. On the one hand, GBS mechanisms dominate the overall response, which indicates Newtonian rheology as most appropriate for modelling the steady state mechanical behavior of deep crustal shear zones. On the other hand, the local stress heterogeneities trigger combined RCSP and GBS, which intimate interactions remain unclear. To clarify the respective roles of CSP and GBS we realized a multi-scale full field measurement investigation during deformation of rock analog synthetic halite. Uniaxial compression tests were performed in-situ a scanning electron microscope (SEM) and under X-ray contrast tomography (MCT). Full in-plane and volume strain fields were computed thanks to Digital Image Correlation (DIC) analysis performed at consecutive loading steps. Cooperative CSP and GBS were identified within early localized shear bands. When CSP dominates, GBS contributes as an accommodation mechanism for the local incompatibilities of plastic strain across some grain boundaries. Conversely, when GBS is pronounced strongly localized CSP allows for sliding accommodation at triple junctions. In opposition to the common assumption, our results indicate that GBS and CSP cannot be really dissociated as competing and independent strain mechanisms. They both and cooperatively ensure macroscopically homogeneous flow.

Tensile Property of ANSI 304 Stainless Steel Weldments Subjected to Cavitation Erosion Based on Treatment of Laser Shock Processing.

PubMed

Zhang, Lei; Liu, Yue-Hua; Luo, Kai-Yu; Zhang, Yong-Kang; Zhao, Yong; Huang, Jian-Yun; Wu, Xu-Dong; Zhou, Chuang

2018-05-16

Tensile property was one important index of mechanical properties of ANSI 304 stainless steel laser weldments subjected to cavitation erosion (CE). Laser shock processing (LSP) was utilized to strengthen the CE resistance, and the tensile property and fracture morphology were analyzed through three replicated experiment times. Results showed tensile process of treated weldments was composed of elastic deformation, plastic deformation, and fracture. The elastic limit, elastic modulus, elongation, area reduction, and ultimate tensile strength of tensile sample after CE were higher in view of LSP. In the fracture surface, the fiber zone, radiation zone and shear lip zone were generated, and those were more obvious through LSP. The number and size of pores in the fracture surface were smaller, and the fracture surface was smoother and more uniform. The dimples were elongated along the unified direction due to effects of LSP, and the elongated direction was in agreement with the crack propagation direction. Their distribution and shape were uniform with deeper depth. It could be reflected that the tensile property was improved by LSP and the CE resistance was also enhanced.

Tensile Property of ANSI 304 Stainless Steel Weldments Subjected to Cavitation Erosion Based on Treatment of Laser Shock Processing

PubMed Central

Zhang, Lei; Liu, Yue-Hua; Luo, Kai-Yu; Zhang, Yong-Kang; Zhao, Yong; Huang, Jian-Yun; Wu, Xu-Dong; Zhou, Chuang

2018-01-01

Tensile property was one important index of mechanical properties of ANSI 304 stainless steel laser weldments subjected to cavitation erosion (CE). Laser shock processing (LSP) was utilized to strengthen the CE resistance, and the tensile property and fracture morphology were analyzed through three replicated experiment times. Results showed tensile process of treated weldments was composed of elastic deformation, plastic deformation, and fracture. The elastic limit, elastic modulus, elongation, area reduction, and ultimate tensile strength of tensile sample after CE were higher in view of LSP. In the fracture surface, the fiber zone, radiation zone and shear lip zone were generated, and those were more obvious through LSP. The number and size of pores in the fracture surface were smaller, and the fracture surface was smoother and more uniform. The dimples were elongated along the unified direction due to effects of LSP, and the elongated direction was in agreement with the crack propagation direction. Their distribution and shape were uniform with deeper depth. It could be reflected that the tensile property was improved by LSP and the CE resistance was also enhanced. PMID:29772661

A calorimetric study of precipitation in aluminum alloy 2219

NASA Astrophysics Data System (ADS)

Papazian, John M.

1981-02-01

Precipitate microstructures in aluminum alloy 2219 were characterized using transmission electron microscopy (TEM) and differential scanning calorimetry (DSC). The DSC signatures of individual precipitate phases were established by comparing the DSC and TEM results from samples that had been aged such that only one precipitate phase was present. These signatures were then used to analyze the commercial tempers. It was found that DSC could readily distinguish between the T3, T4, T6, T8 and O tempers but could not distinguish amongst T81, T851 and T87. Small amounts of plastic deformation between solution treatment and aging had a significant effect on the thermograms. Aging experiments at 130 and 190 °C showed that the aging sequence and DSC response of this alloy were similar to those of pure Al-Cu when the increased copper content is taken into account. Further aging experiments at temperatures between room temperature and 130 °C showed pronounced changes of the GP zone dissolution peak as a function of aging conditions. These changes were found to be related to the effect of GP zone size on the metastable phase boundary and on the GP zone dissolution kinetics.

The importance of Thermo-Hydro-Mechanical couplings and microstructure to strain localization in 3D continua with application to seismic faults. Part I: Theory and linear stability analysis

NASA Astrophysics Data System (ADS)

Rattez, Hadrien; Stefanou, Ioannis; Sulem, Jean

2018-06-01

A Thermo-Hydro-Mechanical (THM) model for Cosserat continua is developed to explore the influence of frictional heating and thermal pore fluid pressurization on the strain localization phenomenon. A general framework is presented to conduct a bifurcation analysis for elasto-plastic Cosserat continua with THM couplings and predict the onset of instability. The presence of internal lengths in Cosserat continua enables to estimate the thickness of the localization zone. This is done by performing a linear stability analysis of the system and looking for the selected wavelength corresponding to the instability mode with fastest finite growth coefficient. These concepts are applied to the study of fault zones under fast shearing. For doing so, we consider a model of a sheared saturated infinite granular layer. The influence of THM couplings on the bifurcation state and the shear band width is investigated. Taking representative parameters for a centroidal fault gouge, the evolution of the thickness of the localized zone under continuous shear is studied. Furthermore, the effect of grain crushing inside the shear band is explored by varying the internal length of the constitutive law.

Numerical simulation on zonal disintegration in deep surrounding rock mass.

PubMed

Chen, Xuguang; Wang, Yuan; Mei, Yu; Zhang, Xin

2014-01-01

Zonal disintegration have been discovered in many underground tunnels with the increasing of embedded depth. The formation mechanism of such phenomenon is difficult to explain under the framework of traditional rock mechanics, and the fractured shape and forming conditions are unclear. The numerical simulation was carried out to research the generating condition and forming process of zonal disintegration. Via comparing the results with the geomechanical model test, the zonal disintegration phenomenon was confirmed and its mechanism is revealed. It is found to be the result of circular fracture which develops within surrounding rock mass under the high geostress. The fractured shape of zonal disintegration was determined, and the radii of the fractured zones were found to fulfill the relationship of geometric progression. The numerical results were in accordance with the model test findings. The mechanism of the zonal disintegration was revealed by theoretical analysis based on fracture mechanics. The fractured zones are reportedly circular and concentric to the cavern. Each fracture zone ruptured at the elastic-plastic boundary of the surrounding rocks and then coalesced into the circular form. The geometric progression ratio was found to be related to the mechanical parameters and the ground stress of the surrounding rocks.

Numerical Simulation on Zonal Disintegration in Deep Surrounding Rock Mass

PubMed Central

Chen, Xuguang; Wang, Yuan; Mei, Yu; Zhang, Xin

2014-01-01

Zonal disintegration have been discovered in many underground tunnels with the increasing of embedded depth. The formation mechanism of such phenomenon is difficult to explain under the framework of traditional rock mechanics, and the fractured shape and forming conditions are unclear. The numerical simulation was carried out to research the generating condition and forming process of zonal disintegration. Via comparing the results with the geomechanical model test, the zonal disintegration phenomenon was confirmed and its mechanism is revealed. It is found to be the result of circular fracture which develops within surrounding rock mass under the high geostress. The fractured shape of zonal disintegration was determined, and the radii of the fractured zones were found to fulfill the relationship of geometric progression. The numerical results were in accordance with the model test findings. The mechanism of the zonal disintegration was revealed by theoretical analysis based on fracture mechanics. The fractured zones are reportedly circular and concentric to the cavern. Each fracture zone ruptured at the elastic-plastic boundary of the surrounding rocks and then coalesced into the circular form. The geometric progression ratio was found to be related to the mechanical parameters and the ground stress of the surrounding rocks. PMID:24592166

Caffeine Modulates Vesicle Release and Recovery at Cerebellar Parallel Fibre Terminals, Independently of Calcium and Cyclic AMP Signalling

PubMed Central

Dobson, Katharine L.; Jackson, Claire; Balakrishnan, Saju; Bellamy, Tomas C.

2015-01-01

Background Cerebellar parallel fibres release glutamate at both the synaptic active zone and at extrasynaptic sites—a process known as ectopic release. These sites exhibit different short-term and long-term plasticity, the basis of which is incompletely understood but depends on the efficiency of vesicle release and recycling. To investigate whether release of calcium from internal stores contributes to these differences in plasticity, we tested the effects of the ryanodine receptor agonist caffeine on both synaptic and ectopic transmission. Methods Whole cell patch clamp recordings from Purkinje neurons and Bergmann glia were carried out in transverse cerebellar slices from juvenile (P16-20) Wistar rats. Key Results Caffeine caused complex changes in transmission at both synaptic and ectopic sites. The amplitude of postsynaptic currents in Purkinje neurons and extrasynaptic currents in Bergmann glia were increased 2-fold and 4-fold respectively, but paired pulse ratio was substantially reduced, reversing the short-term facilitation observed under control conditions. Caffeine treatment also caused synaptic sites to depress during 1 Hz stimulation, consistent with inhibition of the usual mechanisms for replenishing vesicles at the active zone. Unexpectedly, pharmacological intervention at known targets for caffeine—intracellular calcium release, and cAMP signalling—had no impact on these effects. Conclusions We conclude that caffeine increases release probability and inhibits vesicle recovery at parallel fibre synapses, independently of known pharmacological targets. This complex effect would lead to potentiation of transmission at fibres firing at low frequencies, but depression of transmission at high frequency connections. PMID:25933382

Overexpression of synapsin Ia in the rat calyx of Held accelerates short-term plasticity and decreases synaptic vesicle volume and active zone area

PubMed Central

Vasileva, Mariya; Renden, Robert; Horstmann, Heinz; Gitler, Daniel; Kuner, Thomas

2013-01-01

Synapsins are synaptic vesicle (SV) proteins organizing a component of the reserve pool of vesicles at most central nervous system synapses. Alternative splicing of the three mammalian genes results in multiple isoforms that may differentially contribute to the organization and maintenance of the SV pools. To address this, we first characterized the expression pattern of synapsin isoforms in the rat calyx of Held. At postnatal day 16, synapsins Ia, Ib, IIb and IIIa were present, while IIa—known to sustain repetitive transmission in glutamatergic terminals—was not detectable. To test if the synapsin I isoforms could mediate IIa-like effect, and if this depends on the presence of the E-domain, we overexpressed either synapsin Ia or synapsin Ib in the rat calyx of Held via recombinant adeno-associated virus-mediated gene transfer. Although the size and overall structure of the perturbed calyces remained unchanged, short-term depression and recovery from depression were accelerated upon overexpression of synapsin I isoforms. Using electron microscopic three-dimensional reconstructions we found a redistribution of SV clusters proximal to the active zones (AZ) alongside with a decrease of both AZ area and SV volume. The number of SVs at individual AZs was strongly reduced. Hence, our data indicate that the amount of synapsin Ia expressed in the calyx regulates the rate and extent of short-term synaptic plasticity by affecting vesicle recruitment to the AZ. Finally, our study reveals a novel contribution of synapsin Ia to define the surface area of AZs. PMID:24391547

Effect of Critical Displacement Parameter on Slip Regime at Subduction Fault

NASA Astrophysics Data System (ADS)

Muldashev, Iskander; Sobolev, Stephan

2016-04-01

It is widely accepted that for the simple fault models value of critical displacement parameter (Dc) in Ruina-Dietrich's rate-and-state friction law is responsible for the transition from stick-slip regime at low Dc to non-seismic creep regime at large Dc. However, neither the value of "transition" Dc parameter nor the character of the transition is known for the realistic subduction zone setting. Here we investigate effect of Dc on regime of slip at subduction faults for two setups, generic model similar to simple shear elastic slider under quasistatic loading and full subduction model with appropriate geometry, stress and temperature distribution similar to the setting at the site of the Great Chile Earthquake of 1960. In our modeling we use finite element numerical technique that employs non-linear elasto-visco-plastic rheology in the entire model domain with rate-and-state plasticity within the fault zone. The model generates spontaneous earthquake sequence. Adaptive time-step integration procedure varies time step from 40 seconds at instability (earthquake), and gradually increases it to 5 years during postseismic relaxation. The technique allows observing the effect of Dc on period, magnitude of earthquakes through the cycles. We demonstrate that our modeling results for the generic model are consistent with the previous theoretical and numeric modeling results. For the full subduction model we obtain transition from non-seismic creep to stick-slip regime at Dc about 20 cm. We will demonstrate and discuss the features of the transition regimes in both generic and realistic subduction models.

Viscous shear heating instabilities in a 1-D viscoelastic shear zone

NASA Astrophysics Data System (ADS)

Homburg, J. M.; Coon, E. T.; Spiegelman, M.; Kelemen, P. B.; Hirth, G.

2010-12-01

Viscous shear instabilities may provide a possible mechanism for some intermediate depth earthquakes where high confining pressure makes it difficult to achieve frictional failure. While many studies have explored the feedback between temperature-dependent strain rate and strain-rate dependent shear heating (e.g. Braeck and Podladchikov, 2007), most have used thermal anomalies to initiate a shear instability or have imposed a low viscosity region in their model domain (John et al., 2009). By contrast, Kelemen and Hirth (2007) relied on an initial grain size contrast between a predetermined fine-grained shear zone and coarse grained host rock to initiate an instability. This choice is supported by observations of numerous fine grained ductile shear zones in shallow mantle massifs as well as the possibility that annealed fine grained fault gouge, formed at oceanic transforms, subduction related thrusts and ‘outer rise’ faults, could be carried below the brittle/ductile transition by subduction. Improving upon the work of Kelemen and Hirth (2007), we have developed a 1-D numerical model that describes the behavior of a Maxwell viscoelastic body with the rheology of dry olivine being driven at a constant velocity at its boundary. We include diffusion and dislocation creep, dislocation accommodated grain boundary sliding, and low-temperature plasticity (Peierls mechanism). Initial results suggest that including low-temperature plasticity inhibits the ability of the system to undergo an instability, similar to the results of Kameyama et al. (1999). This is due to increased deformation in the background allowing more shear heating to take place, and thus softening the system prior to reaching the peak stress. However if the applied strain rate is high enough (e.g. greater than 0.5 x 10-11 s-1 for a domain size of 2 km, an 8 m wide shear zone, a background grain size of 1 mm, a shear zone grain size of 150 μm, and an initial temperature of 650°C) dramatic instabilities can occur. The instability is enhanced by the development of a self-localizing thermal perturbation in the fine grained zone that is narrower than the original width of the fine-grained zone. To examine the effect of melting, we include a parameterization of partially molten rock viscosity as a function of temperature assuming a simple relationship between melt fraction and temperature. At T > ~1400°C, all other deformation mechanisms are deactivated but shear heating continues, allowing for continued temperature evolution. In addition a strain rate cap proportional to the shear wave velocity in olivine has been imposed, reflecting the maximum rate that changes in stress can be communicated through the system. While Kelemen and Hirth (2007) allowed for grain size evolution, this has not yet been implemented in our model. Adding grain size evolution as an additional strain softening mechanism would probably allow instabilities to develop at more geologically reasonable applied strain rates. In addition to discussing the stability of the olivine only system, we will explore grain size evolution during system evolution and evaluate the consequences that the grain size evolution and lithology have on the stability of the system.

Pseudotachylytes of the Deep Crust: Examples from a Granulite-Facies Shear Zone

NASA Astrophysics Data System (ADS)

Orlandini, O.; Mahan, K. H.; Regan, S.; Williams, M. L.; Leite, A.

2013-12-01

The Athabasca Granulite Terrane is an exhumed section of deep continental crust exposed in the western Canadian shield. The terrane hosts the 1.88 Ga Cora Lake shear zone, a 3-5 km wide sinistral and extensional oblique-slip system that was active at high-pressure granulite-grade conditions ( ~1.0 GPa, >800°C to ~0.8 GPa and 700 °C). Pseudotachylyte, a glassy vein-filling substance that results from frictional melting during seismic slip, is common in ultramylonitic strands of the shear zone, where veins run for tens of meters subparallel to foliation. Some but not all PST veins have been overprinted with the Cora Lake shear zone foliation, and undeformed PST locally bears microlitic garnet. The frictional melts that quench into PST may reach >1400 °C, but are extremely localized and cool to country rock temperatures within minutes, resulting in glass and/or microlitic mineral growths. The melt itself is thought by many to be in disequilibrium with the host rock due to its rapid nature, but during cooling equilibrium is probably reached at small scales. This allows for microprobe analysis of adjacent microlites for thermobarometric calculations. Preliminary results from undeformed (e.g., youngest of multiple generations) PST suggest that quenching occurred in upper amphibolite facies ambient conditions and is compatible with later stages of Cora Lake shear zone activity. Host-rock mylonites contain abundant garnet and pyroxene sigma clasts indicating sinistral shear, and where PST-bearing slip surfaces are found at low angles to the foliation, they display sinistral offset. The host rock contains abundant macroscopic and microscopic sinistral shear fracture systems (e.g., Riedel [R], Y, and P displacement surfaces) within the immediate proximity of PST veins, indicating a complex interplay of brittle and ductile behavior that is interpreted to be genetically related to the formation of the PST. The shear fracture systems are characterized by sharply bounded surfaces or zones populated by equant 1-15 μm grains, including orthopyroxene. These grains show no evidence of fracturing under backscatter-electron images and preserve cohesion with all surrounding grains, suggesting crystal-plastic behavior. There is evidence for multiple generations of subparallel shear fracture sets, as R shears of an earlier fracture set are cut by Y shears of a later set. The PST generation veins are overprinted in much the same way, and are consistently found in an orientation that suggests they nucleated on Y shear surfaces. Given that available data on the Cora Lake PST indicates formation under conditions where crystal-plastic deformation typically dominates, the downward propagation of faults from the traditional seismogenic zone seems the most reasonable model for emplacement. The propagation of fault slips to depths of 30-50 km has been actively observed for several Mw >7.5 strike-slip and thrust earthquakes, but the deformation mechanisms and specific conditions that allow PST formation at such depths is not well understood. The almost exclusive contemporaneous localization of brittle PST systems into highly ductile ultramylonites suggests an interesting paradox of rheological response to constant regional strain fields .

Earthquake rupture at focal depth, part II: mechanics of the 2004 M2.2 earthquake along the Pretorius Fault, TauTona Mine, South Africa

USGS Publications Warehouse

Heesakkers, V.; Murphy, S.; Lockner, D.A.; Reches, Z.

2011-01-01

We analyze here the rupture mechanics of the 2004, M2.2 earthquake based on our observations and measurements at focal depth (Part I). This event ruptured the Archean Pretorius fault that has been inactive for at least 2 Ga, and was reactivated due to mining operations down to a depth of 3.6 km depth. Thus, it was expected that the Pretorius fault zone will fail similarly to an intact rock body independently of its ancient healed structure. Our analysis reveals a few puzzling features of the M2.2 rupture-zone: (1) the earthquake ruptured four, non-parallel, cataclasite bearing segments of the ancient Pretorius fault-zone; (2) slip occurred almost exclusively along the cataclasite-host rock contacts of the slipping segments; (3) the local in-situ stress field is not favorable to slip along any of these four segments; and (4) the Archean cataclasite is pervasively sintered and cemented to become brittle and strong. To resolve these observations, we conducted rock mechanics experiments on the fault-rocks and host-rocks and found a strong mechanical contrast between the quartzitic cataclasite zones, with elastic-brittle rheology, and the host quartzites, with damage, elastic–plastic rheology. The finite-element modeling of a heterogeneous fault-zone with the measured mechanical contrast indicates that the slip is likely to reactivate the ancient cataclasite-bearing segments, as observed, due to the strong mechanical contrast between the cataclasite and the host quartzitic rock.

Langerhans cell sarcoma following marginal zone lymphoma: expanding the knowledge on mature B cell plasticity.

PubMed

Ambrosio, Maria Raffaella; De Falco, Giulia; Rocca, Bruno Jim; Barone, Aurora; Amato, Teresa; Bellan, Cristiana; Lazzi, Stefano; Leoncini, Lorenzo

2015-10-01

The concept of unidirectional differentiation of the haematopoietic stem cell has been challenged after recent findings that human B cell progenitors and even mature B cells can be reprogrammed into histiocytic/dendritic cells by altering expression of lineage-associated transcription factors. The conversion of mature B cell lymphomas to Langerhans cell neoplasms is not well documented. Three previous reports have described clonally related follicular lymphoma and Langerhans cell tumours, whereas no case has been published of clonally related marginal zone lymphoma and Langerhans cell sarcoma. We describe the case of a 77-year-old patient who developed a Langerhans cell sarcoma and 6 years later a nodal marginal zone lymphoma. Mutation status examination showed 100 % gene identity to the germline sequence, suggesting direct trans-differentiation or dedifferentiation of the nodal marginal zone lymphoma to the Langerhans cell sarcoma rather than a common progenitor. We found inactivation of paired box 5 (PAX-5) in the lymphoma cells by methylation, along with duplication of part of the long arm of chromosomes 16 and 17 in the sarcoma cells. The absence of PAX-5 could have triggered B cells to differentiate into macrophages and dendritic cells. On the other hand, chromosomal imbalances might have activated genes involved in myeloid lineage maturation, transcription activation and oncogenesis. We hypothesize that this occurred because of previous therapies for nodal marginal zone lymphoma. Better understanding of this phenomenon may help in unravelling the molecular interplay between transcription factors during haematopoietic lineage commitment and may expand the spectrum of clonally related mature B cell neoplasms and Langerhans cell tumours.

Numerical modelling of collapsing volcanic edifices

NASA Astrophysics Data System (ADS)

Costa, Ana; Marques, Fernando; Kaus, Boris

2017-04-01

The flanks of Oceanic Volcanic Edifice's (OVEs) can occasionally become unstable. If that occurs, they can deform in two different modes: either slowly along localization failure zones (slumps) or catastrophically as debris avalanches. Yet the physics of this process is incompletely understood, and the role of factors such as the OVE's strength (viscosity, cohesion, friction angle), dimensions, geometry, and existence of weak layers remain to be addressed. Here we perform numerical simulations to study the interplay between viscous and plastic deformation on the gravitational collapse of an OVE (diffuse deformation vs. localization of failure along discrete structures). We focus on the contribution of the edifice's strength parameters for the mode of deformation, as well as on the type of basement. Tests were performed for a large OVE (7.5 km high, 200 km long) and either purely viscous (overall volcano edifice viscosities between 1019-1023 Pa.s), or viscoplastic rheology (within a range of cohesion and friction angle values). Results show that (a) for a strong basement (no slip basal boundary condition), the deformation pattern suggests wide/diffuse "listric" deformation within the volcanic edifice, without the development of discrete plastic failure zones; (b) for a weak basement (free slip basal boundary condition), rapid collapse of the edifice through the propagation of plastic failure structures within the edifice occurs. Tests for a smaller OVE (4.5 km by 30 km) show that failure localization along large-scale listric structures occurs more readily for different combinations of cohesion and friction angles. In these tests, high cohesion values combined with small friction angles lead to focusing of deformation along a narrower band. Tests with a weak layer underlying part of the volcanic edifice base show deformation focused along discrete structures mainly dipping towards the distal sector of the volcano. These tests for a small OVE constitute a promising basis for the study of a currently active slump in the SE flank of Pico Island (Azores, Portugal). We will also address the effect of lithospheric flexure, and discuss initial 3D modelling results.

Evolution of crustal stress, pressure and temperature around shear zones during orogenic wedge formation: a 2D thermo-mechanical numerical study

NASA Astrophysics Data System (ADS)

Markus Schmalholz, Stefan; Jaquet, Yoann

2016-04-01

We study the formation of an orogenic wedge during lithospheric shortening with 2D numerical simulations. We consider a viscoelastoplastic rheology, thermo-mechanical coupling by shear heating and temperature-dependent viscosities, gravity and erosion. In the initial model configuration there is either a lateral temperature variation at the model base or a lateral variation in crustal thickness to generate slight stress variations during lithospheric shortening. These stress variations can trigger the formation of shear zones which are caused by thermal softening associated with shear heating. We do not apply any kind of strain softening, such as reduction of friction angle with progressive plastic strain. The first major shear zone that appears during shortening crosscuts the entire crust and initiates the asymmetric subduction/underthrusting of mainly the mechanically strong lower crust. After some deformation, the first shear zone in the upper crust is abandoned, the deformation propagates towards the foreland and a new shear zone forms only in the upper crust. The shear zone propagation occurs several times where new shear zones form in the upper crust and the mechanically strong top of the lower crust acts as detachment horizon. We calculate the magnitudes of the maximal and minimal principal stresses and of the mean stress (or dynamic pressure), and we record also the temperature for several marker points in the upper and lower crust. We analyse the evolution of stresses and temperature with burial depth and time. Deviatoric stresses (half the differential stress) in the upper crust are up to 200 MPa and associated shear heating in shear zones ranges between 40 - 80 °C. Lower crustal rocks remain either at the base of the orogenic wedge at depths of around 50 km or are subducted to depths of up to 120 km, depending on their position when the first shear zone formed. Largest deviatotric stresses in the strong part of the lower crust are about 1000 MPa and maximal shear heating in shear zones is approximately 200 °C. Marker points can migrate through the main shear zone in the lower crust which remains active throughout lithospheric shortening. Some pressure-temperature paths show an anti-clockwise evolution. The impact of various model parameters on the results is discussed as well as applications of the results to geological data.

The mechanism of earthquake

NASA Astrophysics Data System (ADS)

Lu, Kunquan; Cao, Zexian; Hou, Meiying; Jiang, Zehui; Shen, Rong; Wang, Qiang; Sun, Gang; Liu, Jixing

2018-03-01

The physical mechanism of earthquake remains a challenging issue to be clarified. Seismologists used to attribute shallow earthquake to the elastic rebound of crustal rocks. The seismic energy calculated following the elastic rebound theory and with the data of experimental results upon rocks, however, shows a large discrepancy with measurement — a fact that has been dubbed as “the heat flow paradox”. For the intermediate-focus and deep-focus earthquakes, both occurring in the region of the mantle, there is not reasonable explanation either. This paper will discuss the physical mechanism of earthquake from a new perspective, starting from the fact that both the crust and the mantle are discrete collective system of matters with slow dynamics, as well as from the basic principles of physics, especially some new concepts of condensed matter physics emerged in the recent years. (1) Stress distribution in earth’s crust: Without taking the tectonic force into account, according to the rheological principle of “everything flows”, the normal stress and transverse stress must be balanced due to the effect of gravitational pressure over a long period of time, thus no differential stress in the original crustal rocks is to be expected. The tectonic force is successively transferred and accumulated via stick-slip motions of rock blocks to squeeze the fault gouge and then exerted upon other rock blocks. The superposition of such additional lateral tectonic force and the original stress gives rise to the real-time stress in crustal rocks. The mechanical characteristics of fault gouge are different from rocks as it consists of granular matters. The elastic moduli of the fault gouges are much less than those of rocks, and they become larger with increasing pressure. This peculiarity of the fault gouge leads to a tectonic force increasing with depth in a nonlinear fashion. The distribution and variation of the tectonic stress in the crust are specified. (2) The strength of crust rocks: The gravitational pressure can initiate the elasticity-plasticity transition in crust rocks. By calculating the depth dependence of elasticity-plasticity transition and according to the actual situation analysis, the behaviors of crust rocks can be categorized in three typical zones: elastic, partially plastic and fully plastic. As the proportion of plastic portion reaches about 10% in the partially plastic zone, plastic interconnection may occur and the variation of shear strength in rocks is mainly characterized by plastic behavior. The equivalent coefficient of friction for the plastic slip is smaller by an order of magnitude, or even less than that for brittle fracture, thus the shear strength of rocks by plastic sliding is much less than that by brittle breaking. Moreover, with increasing depth a number of other factors can further reduce the shear yield strength of rocks. On the other hand, since earthquake is a large-scale damage, the rock breaking must occur along the weakest path. Therefore, the actual fracture strength of rocks in a shallow earthquake is assuredly lower than the average shear strength of rocks as generally observed. The typical distributions of the average strength and actual fracture strength in crustal rocks varying with depth are schematically illustrated. (3) The conditions for earthquake occurrence and mechanisms of earthquake: An earthquake will lead to volume expansion, and volume expansion must break through the obstacle. The condition for an earthquake to occur is as follows: the tectonic force exceeds the sum of the fracture strength of rock, the friction force of fault boundary and the resistance from obstacles. Therefore, the shallow earthquake is characterized by plastic sliding of rocks that break through the obstacles. Accordingly, four possible patterns for shallow earthquakes are put forward. Deep-focus earthquakes are believed to result from a wide-range rock flow that breaks the jam. Both shallow earthquakes and deep-focus earthquakes are the energy release caused by the slip or flow of rocks following a jamming-unjamming transition. (4) The energetics and impending precursors of earthquake: The energy of earthquake is the kinetic energy released from the jamming-unjamming transition. Calculation shows that the kinetic energy of seismic rock sliding is comparable with the total work demanded for rocks’ shear failure and overcoming of frictional resistance. There will be no heat flow paradox. Meanwhile, some valuable seismic precursors are likely to be identified by observing the accumulation of additional tectonic forces, local geological changes, as well as the effect of rock state changes, etc.

Experimental evidence for intraplate deformation controlled by netlike plastic-flow in central-eastern Asia

NASA Astrophysics Data System (ADS)

Wang, Sheng-zu; Li, Jian-guo; Zhou, Yong-sheng

2007-12-01

The experimental results of brittle/ductile two-layer analogue models verify that intraplate tectonic deformation in central-eastern Asia is controlled mainly by the netlike plastic-flow (NPF) occurring in the lower lithosphere, including the lower crust and lithospheric mantle. The ductile lower layer in the model, corresponding to the lower lithosphere in the natural prototype, is made of a mixture of gum rosin and turpentine oil and the brittle upper one, to the upper crust, is formed by the consolidation of talc-powder slurry. The NPF hypothesis for continental dynamics can be regarded as a combination and development of two kinds of seemingly mutually exclusive ones, which are based on the theories of slip-line field and viscous (plastic) flow, respectively. In contrast to "homogeneous" viscous (plastic) flow considered usually in fluid mechanics and rheology, NPF is a viscous (plastic) flow accompanied with shear strain localization, forming plastic-flow network in the flow field. Plastic-flow network, being composed of two families of plastic-flow belts intersecting each other with their initial conjugate angles (i.e. the included angles facing the compression direction) equal to 90°, is similar to but different from the traditional slip-line network, which is assumed as a critical state of yield in elastoplastic medium. The experiments show that there are several NPF-controlled tectonic network systems to be developed in the models and two of them correspond to those in central-eastern Asia, which have the Himalayan and Taiwan arcs as their driving boundaries, respectively. The existence of "stable blocks" in the ductile lower layer has promoted some types of tectonic deformation, including the formation of large-scale compressional basins, corresponding to the Tarim, Ordos, Sichuan basins, etc., the development of compression-shear tectonic zones between some of these basins, corresponding to those shown by the Tianshan and Altay mountain ranges, and the uplift of some areas of the "plateau", corresponding to a contribution to the formation of the Qinghai-Tibet plateau. The distributions of maximum compressive stress directions and strains in the ductile lower layer estimated using the "conjugate-angle-bisector" and "conjugate-angle-increment" methods, respectively, are coincident in general tendency and framework with those in the prototype for the major part of the central-eastern Asian continent. It is also inferred that the westward influence of the horizontal compression component of the Pacific plate has reached North China by means of the interaction between adjacent plastic-flow networks although the tectonic network resulting directly from this horizontal compression has not spread westward beyond the Japan Sea.

Slip events propagating along a ductile mid-crustal strike-slip shear zone (Malpica-Lamego line, Variscan Orogen, NW Iberia)

NASA Astrophysics Data System (ADS)

Llana-Fúnez, Sergio; de Paola, Nicola; Pozzi, Giacomo; Lopez-Sanchez, Marco Antonio

2017-04-01

The current level of erosion in NW Iberian peninsula exposes Variscan mid-crustal depths, where widespread deformation during orogenesis produced dominantly ductile structures. It constitutes an adequate window for the observation of structures close to the brittle-plastic transition in the continental crust. The shear zone object of this work is the Malpica-Lamego line (MLL), a major Variscan structure formed in the late stages of the Variscan collision. The MLL is a mostly strike-slip major structure that offsets laterally by several kilometres the assembly of allochthonous complexes, that contain a sub-horizontal suture zone, which are the remnants of the plate duplication during the Variscan convergence. The shear zone is exposed along the northern coast of Galicia (NW Spain). It is characterized by phyllonites and quartz-mylonites in a zone which is tens of meters in thickness. Within the phyllonites, a few seams of cataclastic rocks have been found in bands along the main fabric. Their cohesive character, the parallelism between the different bands, the fact that host rocks maintain mineral assemblage and that no cross-cutting relations in the field were identified, are considered indicative of these brittle structures forming coetaneously with the ductile shearing producing the phyllonites. Samples from the phyllonites, also from quartz-mylonites, were prepared and powdered to characterize friction properties in a rotary shear apparatus at high, seismic velocities (m/s). Preliminary experiments run at room temperature and effective normal stresses between 10 to 25 MPa, show that friction coefficients µ are relatively high and a limited drop in friction coefficient occurs after 10-20 cm of slip, with µ decreasing from 0.7 to 0.5. Fracturing seems coetaneous with dominant ductile shearing within the shear zone, however, given the frictional properties of the phyllonites, it is unlikely that brittle deformation nucleates within these fault rocks. Instead, it seems that faulting originated in other sectors of the fault zone, and then propagated through the studied section.

Can grain size sensitive flow lubricate faults during the initial stages of earthquake propagation?

NASA Astrophysics Data System (ADS)

De Paola, Nicola; Holdsworth, Robert E.; Viti, Cecilia; Collettini, Cristiano; Bullock, Rachael

2015-12-01

Recent friction experiments carried out under upper crustal P-T conditions have shown that microstructures typical of high temperature creep develop in the slip zone of experimental faults. These mechanisms are more commonly thought to control aseismic viscous flow and shear zone strength in the lower crust/upper mantle. In this study, displacement-controlled experiments have been performed on carbonate gouges at seismic slip rates (1 m s-1), to investigate whether they may also control the frictional strength of seismic faults at the higher strain rates attained in the brittle crust. At relatively low displacements (<1 cm) and temperatures (≤100 °C), brittle fracturing and cataclasis produce shear localisation and grain size reduction in a thin slip zone (150 μm). With increasing displacement (up to 15 cm) and temperatures (T up to 600 °C), due to frictional heating, intracrystalline plasticity mechanisms start to accommodate intragranular strain in the slip zone, and play a key role in producing nanoscale subgrains (≤100 nm). With further displacement and temperature rise, the onset of weakening coincides with the formation in the slip zone of equiaxial, nanograin aggregates exhibiting polygonal grain boundaries, no shape or crystal preferred orientation and low dislocation densities, possibly due to high temperature (>900 °C) grain boundary sliding (GBS) deformation mechanisms. The observed micro-textures are strikingly similar to those predicted by theoretical studies, and those observed during experiments on metals and fine-grained carbonates, where superplastic behaviour has been inferred. To a first approximation, the measured drop in strength is in agreement with our flow stress calculations, suggesting that strain could be accommodated more efficiently by these mechanisms within the weaker bulk slip zone, rather than by frictional sliding along the main slip surfaces in the slip zone. Frictionally induced, grainsize-sensitive GBS deformation mechanisms can thus account for the self-lubrication and dynamic weakening of carbonate faults during earthquake propagation in nature.

Modeling the Collisional-Plastic Stress Transition for Bin Discharge of Granular Material

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

Pannala, Sreekanth; Daw, C Stuart; FINNEY, Charles E A

2009-01-01

We propose a heuristic model for the transition between collisional and frictional/plastic stresses in the flow of granular material. Our approach is based on a physically motivated, nonlinear blending function that produces a weighted average of the limiting stresses, depending on the local void fraction in the flow field. Previously published stress models are utilized to describe the behavior in the collisional (Lun et al., 1984) and quasi-static limits (Schaeffer, 1987 and Syamlal et al., 1993). Sigmoidal and hyperbolic tangent functions are used to mimic the observed smooth yet rapid transition between the collisional and plastic stress zones. We implementmore » our stress transition model in an opensource multiphase flow solver, MFIX (Multiphase Flow with Interphase eXchanges, www.mfix.org) and demonstrate its application to a standard bin discharge problem. The model s effectiveness is illustrated by comparing computational predictions to the experimentally derived Beverloo correlation. With the correct choice of function parameters, the model predicts bin discharge rates within the error margins of the Beverloo correlation and is more accurate than one of the alternative granular stress models proposed in the literature. Although a second granular stress model in the literature is also reasonably consistent with the Beverloo correlation, we propose that our alternative blending function is likely to be more adaptable to situations with more complex solids properties (e.g., sticky solids).« less

Surgery without papilla incision: tunneling flap procedures in plastic periodontal and implant surgery.

PubMed

Zuhr, Otto; Rebele, Stephan F; Cheung, Stefani L; Hürzeler, Markus B

2018-06-01

Diverse clinical advancements, together with some relevant technical innovations, have led to an increase in popularity of tunneling flap procedures in plastic periodontal and implant surgery in the recent past. This trend is further promoted by the fact that these techniques have lately been introduced to a considerably expanded range of indications. While originally described for the treatment of gingival recession-type defects, tunneling flap procedures may now be applied successfully in a variety of clinical situations in which augmentation of the soft tissues is indicated in the esthetic zone. Potential clinical scenarios include surgical thickening of thin buccal gingiva or peri-implant mucosa, alveolar ridge/socket preservation and implant second-stage surgery, as well as soft-tissue ridge augmentation or pontic site development. In this way, tunneling flap procedures developed from a technique, originally merely intended for surgical root coverage, into a capacious surgical conception in plastic periodontal and implant surgery. The purpose of this article is to provide a comprehensive overview on tunneling flap procedures, to introduce the successive development of the approach along with underlying ideas on surgical wound healing and to present contemporary clinical scenarios in step-by-step photograph-illustrated sequences, which aim to provide clinicians with guidance to help them integrate tunneling flap procedures into their daily clinical routine. © 2018 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.

Fructose consumption reduces hippocampal synaptic plasticity underlying cognitive performance

PubMed Central

Cisternas, Pedro; Salazar, Paulina; Serrano, Felipe G.; Montecinos-Oliva, Carla; Arredondo, Sebastián B.; Varela-Nallar, Lorena; Barja, Salesa; Vio, Carlos P.; Gomez-Pinilla, Fernando; Inestrosa, Nibaldo C.

2017-01-01

Metabolic syndrome (MetS) is a global epidemic, which involves a spectrum of metabolic disorders comprising diabetes and obesity. The impact of MetS on the brain is becoming to be a concern, however, the poor understanding of mechanisms involved has limited the development of therapeutic strategies. We induced a MetS-like condition by exposing mice to fructose feeding for 7 weeks. There was a dramatic deterioration in the capacity of the hippocampus to sustain synaptic plasticity in the forms of long-term potentiation (LTP) and long-term depression (LTD). Mice exposed to fructose showed a reduction in the number of contact zones and the size of postsynaptic densities (PSDs) in the hippocampus, as well as a decrease in hippocampal neurogenesis. There was an increase in lipid peroxidation likely associated with a deficiency in plasma membrane excitability. Consistent with an overall hippocampal dysfunction, there was a subsequent decrease in hippocampal dependent learning and memory performance, i.e., spatial learning and episodic memory. Most of the pathological sequel of MetS in the brain was reversed three month after discontinue fructose feeding. These results are novel to show that MetS triggers a cascade of molecular events, which disrupt hippocampal functional plasticity, and specific aspects of learning and memory function. The overall information raises concerns about the risk imposed by excessive fructose consumption on the pathology of neurological disorders. PMID:26300486

[Effects of different patterns surface mulching on soil properties and fruit trees growth and yield in an apple orchard].

PubMed

Zhang, Yi; Xie, Yong-Sheng; Hao, Ming-De; She, Xiao-Yan

2010-02-01

Taking a nine-year-old Fuji apple orchard in Loess Plateau as test object, this paper studied the effects of different patterns surface mulching (clean tillage, grass cover, plastic film mulch, straw mulch, and gravel mulch) on the soil properties and fruit trees growth and yield in this orchard. Grass cover induced the lowest differentiation of soil moisture profile, while gravel mulch induced the highest one. In treatment gravel mulch, the soil moisture content in apple trees root zone was the highest, which meant that there was more water available to apple trees. Surface mulching had significant effects on soil temperature, and generally resulted in a decrease in the maximum soil temperature. The exception was treatment plastic film mulch, in which, the soil temperature in summer exceeded the maximum allowable temperature for continuous root growth and physiological function. With the exception of treatment plastic film mulch, surface mulching increased the soil CO2 flux, which was the highest in treatment grass cover. Surface mulching also affected the proportion of various branch types and fruit yield. The proportion of medium-sized branches and fruit yield were the highest in treatment gravel mulch, while the fruit yield was the lowest in treatment grass cover. Factor analysis indicated that among the test surface mulching patterns, gravel mulch was most suitable for the apple orchards in gully region of Loess Plateau.

Knockdown of FoxP2 alters spine density in Area X of the zebra finch.

PubMed

Schulz, S B; Haesler, S; Scharff, C; Rochefort, C

2010-10-01

Mutations in the gene encoding the transcription factor FoxP2 impair human speech and language. We have previously shown that deficits in vocal learning occur in zebra finches after reduction of FoxP2 in Area X, a striatal nucleus involved in song acquisition. We recently showed that FoxP2 is expressed in newly generated spiny neurons (SN) in adult Area X as well as in the ventricular zone (VZ) from which the SN originates. Moreover, their recruitment to Area X increases transiently during the song learning phase. The present report therefore investigated whether FoxP2 is involved in the structural plasticity of Area X. We assessed the proliferation, differentiation and morphology of SN after lentivirally mediated knockdown of FoxP2 in Area X or in the VZ during the song learning phase. Proliferation rate was not significantly affected by knockdown of FoxP2 in the VZ. In addition, FoxP2 reduction both in the VZ and in Area X did not affect the number of new neurons in Area X. However, at the fine-structural level, SN in Area X bore fewer spines after FoxP2 knockdown. This effect was even more pronounced when neurons received the knockdown before differentiation, i.e. as neuroblasts in the VZ. These results suggest that FoxP2 might directly or indirectly regulate spine dynamics in Area X and thereby influence song plasticity. Together, these data present the first evidence for a role of FoxP2 in the structural plasticity of dendritic spines and complement the emerging evidence of physiological synaptic plasticity in FoxP2 mouse models. Genes, Brain and Behavior © 2010 Blackwell Publishing Ltd and International Behavioural and Neural Genetics Society. No claim to original US government works.

“Oriental anthropometry” in plastic surgery

PubMed Central

Senna-Fernandes, Vasco

2008-01-01

Background: According to Chinese medicine, the acupuncture-points' (acupoints) locations are proportionally and symmetrically distributed in well-defined compartment zones on the human body surface Oriental Anthropometry” (OA). Acupoints, if considered as aesthetic-loci, might be useful as reference guides in plastic surgery (PS). Aim: This study aimed to use aesthetic-loci as anatomical reference in surgical marking of Aesthetic Plastic Surgery. Method: This was an observational study based on aesthetic surgeries performed in private clinic. This study was based on 106 cases, comprising of 102 women and 4 men, with ages varying from 07 to 73 years, and with heights of between 1.34 m and 1.80 m. Patients were submitted to aesthetic surgical planning by relating aesthetic-loci to conventional surgical marking, including breast surgeries, abdominoplasty, rhytidoplasty, blepharoplasty, and hair implant. The aesthetic-surgical-outcome (ASO) of the patients was assessed by a team of plastic surgeons (who were not involved in the surgical procedures) over a follow-up period of one year by using a numeric-rating-scale in percentage (%) terms. A four-point-verbal-rating-scale was used to record the patients' opinion of therapeutic-satisfaction (TS). Results: ASO was 75.3 ± 9.4% and TS indicated that most patients (58.5%) obtained “good” results. Of the remainder, 38.7% found the results “excellent”, and 2.8% found them “fair”. Discussion and Conclusion: The data suggested that the use of aesthetic-loci may be a useful tool for PS as an anatomical reference for surgical marking. However, further investigation is required to assess the efficacy of the OA by providing the patients more reliable balance and harmony in facial and body contours surgeries. PMID:19753249

Patterns and perspectives in applied fracture mechanics

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

Merkle, J.G.

1994-12-31

This lecture begins with a overview of applied fracture mechanics pertinent to safety of pressure vessels. It then progresses to a chronological panorama of experimental and analytical results. To be useful and dependable in safety analysis of real structures, new analysis developments must be physically realistic, which means that they must accurately describe physical cause and effect. Consequently, before mathematical modeling can begin, cause and effect must be established from experimental data. This can be difficult and time consuming, but worth the effort. Accordingly, the theme of this paper is that the search for patterns is constant and vital. Thismore » theme is illustrated by the development of small, single-specimen, fracture toughness testing techniques. It is also illustrated by the development, based on two different published large-strain, elastic-plastic, three-dimensional finite-element analyses, of a hypothesis concerning three-dimensional loss of constraint. When a generalization of Irwin`s thickness-normalized plastic-zone parameter, reaches a value close to 2{pi}, the through-thickness contraction strain at the apex of the near-tip logarithmic-spiral slip-line region becomes the dominant negative strain accommodating crack opening. Because slip lines passing from the midplane to the stress-free side surfaces do not have to curve, once these slip lines are established, stresses near the crack tip are only elevated by strain hardening and constraint becomes significantly relaxed. This hypothesis, based on published three-dimensional elastic-plastic analyses, provides a potentially valuable means for gaining additional insight into constraint effects on fracture toughness by considering the roles played by the plastic strains as well as the stresses that develop near a crack tip.« less

Distribution of Asellus aquaticus and microinvertebrates in a non-chlorinated drinking water supply system--effects of pipe material and sedimentation.

PubMed

Christensen, Sarah C B; Nissen, Erling; Arvin, Erik; Albrechtsen, Hans-Jørgen

2011-05-01

Danish drinking water supplies based on ground water without chlorination were investigated for the presence of the water louse, Asellus aquaticus, microinvertebrates (<2 mm) and annelida. In total, 52 water samples were collected from fire hydrants at 31 locations, and two elevated tanks (6000 and 36,000 m(3)) as well as one clean water tank at a waterworks (700 m(3)) were inspected. Several types of invertebrates from the phyla: arthropoda, annelida (worms), plathyhelminthes (flatworms) and mollusca (snails) were found. Invertebrates were found at 94% of the sampling sites in the piped system with A. aquaticus present at 55% of the sampling sites. Populations of A. aquaticus were present in the two investigated elevated tanks but not in the clean water tank at a waterworks. Both adult and juvenile A. aquaticus (length of 2-10 mm) were found in tanks as well as in pipes. A. aquaticus was found only in samples collected from two of seven investigated distribution zones (zone 1 and 2), each supplied directly by one of the two investigated elevated tanks containing A. aquaticus. Microinvertebrates were distributed throughout all zones. The distribution pattern of A. aquaticus had not changed considerably over 20 years when compared to data from samples collected in 1988-89. Centrifugal pumps have separated the distribution zones during the whole period and may have functioned as physical barriers in the distribution systems, preventing large invertebrates such as A. aquaticus to pass alive. Another factor characterising zone 1 and 2 was the presence of cast iron pipes. The frequency of A. aquaticus was significantly higher in cast iron pipes than in plastic pipes. A. aquaticus caught from plastic pipes were mainly single living specimens or dead specimens, which may have been transported passively trough by the water flow, while cast iron pipes provided an environment suitable for relatively large populations of A. aquaticus. Sediment volume for each sample was measured and our study described for the first time a clear connection between sediment volume and living A. aquaticus since living A. aquaticus were nearly only found in samples with sediment contents higher than 100 ml/m(3) sample. Presence of A. aquaticus was not correlated to turbidity of the water. Measurements by ATP, heterotrophic plate counting and Colilert(®) showed that the microbial quality of the water was high at all locations with or without animals. Four other large Danish drinking water supplies were additionally sampled (nine pipe samples and one elevated tank), and invertebrates were found in all systems, three of four containing A. aquaticus, indicating a nationwide occurrence. Copyright © 2011 Elsevier Ltd. All rights reserved.

Algae Bioreactor Using Submerged Enclosures with Semi-Permeable Membranes

NASA Technical Reports Server (NTRS)

Flynn, Michael T (Inventor); Baertsch, Robert (Inventor); Trent, Jonathan D (Inventor); Liggett, Travis A (Inventor); Gormly, Sherwin J (Inventor); Delzeit, Lance D (Inventor); Buckwalter, Patrick W (Inventor); Embaye, Tsegereda N (Inventor)

2013-01-01

Methods for producing hydrocarbons, including oil, by processing algae and/or other micro-organisms in an aquatic environment. Flexible bags (e.g., plastic) with CO.sub.2/O.sub.2 exchange membranes, suspended at a controllable depth in a first liquid (e.g., seawater), receive a second liquid (e.g., liquid effluent from a "dead zone") containing seeds for algae growth. The algae are cultivated and harvested in the bags, after most of the second liquid is removed by forward osmosis through liquid exchange membranes. The algae are removed and processed, and the bags are cleaned and reused.

Anaesthesia in a disaster zone: a report on the experience of an Australian medical team in Banda Aceh following the 'Boxing Day Tsunami'.

PubMed

Paix, B R; Capps, R; Neumeister, G; Semple, T

2005-10-01

We report on the experience of a 23-member Australian medical team in Banda Aceh, Indonesia, following the 2004 Boxing Day tsunami. Arriving 13 days after the tsunami that devastated the city, killed 100,000 of its inhabitants and injured thousands more, we carried out 130 surgical procedures in austere conditions over a 12-day period. Most surgery was peripheral, principally for plastic surgical or orthopaedic procedures to lower limb injuries. Intravenous ketamine anaesthesia was the technique of choice, with good surgical conditions and few significant side-effects.

Overload effect and fatigue crack propagation in amorphous metallic alloys

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

Chaki, T.K.; Li, J.C.M.

1984-07-01

Fatigue crack propagation in amorphous metals has an overload effect which usually increases with the number of overload cycles. The variation of overload effect with delta K is explained by the size of the plastic zone which depends on delta K. A comparison of the spacing between striations and da/dN shows that the crack jumps a step about every hundred cycles. The featureless region is probably due to shear fracture along a shear band during overload. Both crack tip blunting and branching occur during the application of overload. Work hardening is not a necessary factor for the overloading effect.

Dynamic triggering

USGS Publications Warehouse

Hill, David P.; Prejean, Stephanie; Schubert, Gerald

2015-01-01

Dynamic stresses propagating as seismic waves from large earthquakes trigger a spectrum of responses at global distances. In addition to locally triggered earthquakes in a variety of tectonic environments, dynamic stresses trigger tectonic (nonvolcanic) tremor in the brittle–plastic transition zone along major plate-boundary faults, activity changes in hydrothermal and volcanic systems, and, in hydrologic domains, changes in spring discharge, water well levels, soil liquefaction, and the eruption of mud volcanoes. Surface waves with periods of 15–200 s are the most effective triggering agents; body-wave trigger is less frequent. Triggering dynamic stresses can be < 1 kPa.

In situ observation of the water-sediment interface in combined sewers, using endoscopy.

PubMed

Oms, C; Gromaire, M C; Chebbo, G

2003-01-01

A new method for water-sediment interface observation has been designed. This system is based on a small diameter endoscope protected by a graduated plastic tube. It makes it possible to visualise in a non-destructive manner the sediments and the water-sediment interface. The endoscope was used to investigate Le Marais catchment (Paris): an immobile organic layer was observed at the water-sediment interface. This layer appears in pools of gross bed sediment, at the upstream of collectors, in zones where velocity is slow and where bed shear stress is less than 0.03 N/m2.

Morphological plasticity of the depth generalist coral, Montastraea cavernosa, on mesophotic reefs in Bermuda.

PubMed

Goodbody-Gringley, Gretchen; Waletich, Justin

2018-04-02

Scleractinian corals have global ecological, structural, social, and economic importance that is disproportionately large relative to their areal extent. These reef building corals form the architectural framework for shallow water tropical reef systems, supporting the most productive and biologically diverse marine ecosystems on Earth (Veron, 1995). Reef-building scleractinian species are dependent on photosynthetic products supplied by symbiotic zooxanthellae of the genus Symbiodinium, restricting their distribution to the photic zone (Stambler, 2011). This article is protected by copyright. All rights reserved. This article is protected by copyright. All rights reserved.

Everyman's prostate phantom: kiwi-fruit substitute for human prostates at magnetic resonance imaging, diffusion-weighted imaging and magnetic resonance spectroscopy.

PubMed

Mueller-Lisse, Ullrich G; Murer, Sophie; Mueller-Lisse, Ulrike L; Kuhn, Marissa; Scheidler, Juergen; Scherr, Michael

2017-08-01

To apply an easy-to-assemble phantom substitute for human prostates in T2-weighted magnetic resonance imaging (T2WI), diffusion-weighted imaging (DWI) and 3D magnetic resonance spectroscopy (MRS). Kiwi fruit were fixed with gel hot and cold compress packs on two plastic nursery pots, separated by a plastic plate, and submerged in tap water inside a 1-L open-spout plastic watering can for T2WI (TR/TE 7500/101 ms), DWI (5500/61 ms, ADC b50-800 s/mm 2 map) and MRS (940/145 ms) at 3.0 T, with phased array surface coils. One green kiwi fruit was additionally examined with an endorectal coil. Retrospective comparison with benign peripheral zone (PZ) and transitional zone (TZ) of prostate (n = 5), Gleason 6-7a prostate cancer (n = 8) and Gleason 7b-9 prostate cancer (n = 7) validated the phantom. Mean contrast between central placenta (CP) and outer pericarp (OP, 0.346-0.349) or peripheral placenta (PP, 0.364-0.393) of kiwi fruit was similar to Gleason 7b-9 prostate cancer and PZ (0.308) in T2WI. ADC values of OP and PP (1.27 ± 0.07-1.37 ± 0.08 mm 2 /s × 10 -3 ) resembled PZ and TZ (1.39 ± 0.17-1.60 ± 0.24 mm 2 /s × 10 -3 ), while CP (0.91 ± 0.14-0.99 ± 0.10 mm 2 /s × 10 -3 ) resembled Gleason 7b-9 prostate cancer (1.00 ± 0.25 mm 2 /s × 10 -3 ). MR spectra showed peaks of citrate and myo-inositol in kiwi fruit, and citrate and "choline+creatine" in prostates. The phantom worked with an endorectal coil, too. The kiwi fruit phantom reproducibly showed zones similar to PZ, TZ and cancer in human prostates in T2WI and DWI and two metabolite peaks in MRS and appears suitable to compare different MR protocols, coil systems and scanners. • Kiwi fruit appear suitable as phantoms for human prostate in MR examinations. • Kiwi fruit show zonal anatomy like human prostates in T2-weighted MRI and DWI. • MR spectroscopy reliably shows peaks in kiwi fruit (citrate/inositol) and human prostates (citrate/choline+creatine). • The kiwi fruit phantom works both with and without an endorectal coil. • EU regulation No. 543/2011 specifies physical and biochemical properties of kiwi fruit.

The use of a polymer inclusion membrane in a paper-based sensor for the selective determination of Cu(II).

PubMed

Jayawardane, B Manori; Coo, Lilibeth dlC; Cattrall, Robert W; Kolev, Spas D

2013-11-25

A disposable paper-based sensor (PBS) is described for the determination of Cu(II) in natural and waste waters at approximately 2 cents per measurement. The device makes use of a polymer inclusion membrane (PIM) to provide the selectivity for Cu(II). The PIM consists of 40 wt% di(2-ethlyhexyl) phosphoric acid (D2EHPA) as the carrier, 10 wt% dioctyl phthalate (DOP) as a plasticizer, 49.5 wt% poly(vinyl chloride) (PVC) as the base polymer and 0.5 wt% (mm(-1)) 1-(2'-pyridylazo)-2-naphthol (PAN) as the colourimetric reagent. High selectivity under mildly acidic conditions (HCl, pH 2.0) is achieved for Cu(II) in the presence of frequently encountered metal ions in natural and waste waters such as Fe(III), Al(III), Zn(II), Cd(II), Pb(II), Ca(II), Mg(II), and Ni(II). The laminated PBS consists of a PIM sensing disc (2mm in diameter) attached to the centre of a circular hydrophilic zone (7 mm in diameter) pretreated with 0.01 M HCl. This hydrophilic zone separates the sample port (a circular hole in the plastic cover) from the PIM sensing disc. After introducing 19.2 μL of a sample/standard solution to the sample port, Cu(II) diffuses across the hydrophilic zone and is extracted into the PIM disc as the Cu(II)-D2EHPA complex which subsequently reacts with PAN to produce the red-purple coloured Cu(II)-PAN complex. The colour intensity of the PIM disc is measured 15 min after sample/standard introduction by scanning using a flatbed scanner. Under optimal conditions the device is characterized by a limit of detection (LOD) and limit of quantitation (LOQ) of 0.06 and 0.21 mg L(-1) Cu(II), respectively, with two linear ranges together covering the Cu(II) concentration range from 0.1 to 30.0 mg L(-1). The PBS was successfully applied to the determination of Cu(II) in hot tap water and mine tailings water. Copyright © 2013 Elsevier B.V. All rights reserved.

The effect of hydrogen on the deformation behavior of a single crystal nickel-base superalloy

NASA Technical Reports Server (NTRS)

Walston, W. S.; Thompson, A. W.; Bernstein, I. M.

1989-01-01

The effect of hydrogen on the tensile deformation behavior of PWA 1480 is presented. Tensile tests were interrupted at different plastic strain levels to observe the development of the dislocation structure. Transmission electron microscopy (TEM) foils were cut perpendicular to the tensile axis to allow the deformation of both phases to be simultaneously observed as well as parallel to zone axes (III) to show the superdislocations on their slip planes. Similar to other nickel-base superalloys, hydrogen was detrimental to the room temperature tensile properties of PWA 1480. There was little effect on strength, however the material was severely embrittled. Even without hydrogen, the elongation-to-failure was only approximately 3 percent. The tensile fracture surface was made up primarily of ductile voids with regions of cleavage fracture. These cleavage facets are the eutectic (gamma') in the microstructure. It was shown by quantitative fractography that hydrogen embrittles the eutectic (gamma') and causes the crack path to seek out and fracture through the eutectic (gamma'). There was two to three times the amount of cleavage on the fracture surface of the hydrogen-charged samples than on the surface of the uncharged samples. The effect of hydrogen can also be seen in the dislocation structure. There is a marked tendency for dislocation trapping in the gamma matrix with and without hydrogen at all plastic strain levels. Without hydrogen there is a high dislocation density in the gamma matrix leading to strain exhaustion in this region and failure through the matrix. The dislocation structure at failure with hydrogen is slightly different. The TEM foils cut parallel to zone axes (III) showed dislocations wrapping around gamma precipitates. Zone axes (001) foils show that there is a lower dislocation density in the gamma matrix which can be linked to the effects of hydrogen on the fracture behavior. The primary activity in the gamma precipitates is in the form of superlattice intrinsic stacking faults (SISFs). These faults have also been reported in other ordered alloys and superalloys.

Experimental Evaluation of Beam to Diamond Box Column Connection with Through Plate in Moment Frames

NASA Astrophysics Data System (ADS)

Keshavarzi, Farhad; Mirghaderi, Rasoul; Torabian, Shahabeddin; Imanpour, Ali

2008-07-01

Moment resisting frames with built up section have very enhanced features due to high bending stiffness and strength characteristics in two principal axes and access to column faces for beam to column easy connections. But due to proper transfer of beam stresses to column faces there were always some specific controvertibly issues that how to make the load transfer through and in plane manner in order to mobilize the forces in column faces. Using diamond column instead of box column provide possibility to mobilize the load transfer mechanism in column faces. This section as a column has considerable benefit such as high plastic to elastic section modulus ratio which is an effective factor for force controlled components. Typical connection has no chance to be applied with diamond column. This paper elucidates the seismic behavior of through-plates moment connections to diamond box columns for use in steel moment resisting frames. This connection has a lot of economical benefits such as no need to horizontal continuity plates and satisfying the weak beam—strong column criteria in the connection region. They might serve as panel zone plates as well. According to high shear demand in panel zone of beam to column joint one should use the doublers plates in order to decrease the shear strength demand in this sensitive part of structure but these plates have no possibility to mobilize the load transfer mechanism in column web and transfer them to column flanges. In this type of connection, column faces have effective role in order to decrease the demands on through plate and they are impressive factors for improving the performance of the connection. Experimental analysis was conducted to elucidate the seismic behavior of this connection. The results of Experimental analysis established the effectiveness of the through plate in mitigating local stress concentrations and forming the plastic hinge zone in the beam away from the beam to column interface. The moment-rotation graphs form sub-assemblage show a desirable seismic performance of this connection

Microstructure and Mechanical Properties of Laser Welded Joints of DZ125L and IN718 Nickel Base Superalloys

NASA Astrophysics Data System (ADS)

Liang, Taosha; Wang, Lei; Liu, Yang; Song, Xiu

2018-05-01

The microstructure and mechanical properties of the laser welded joint of DZ125L and IN718 nickel base superalloys were investigated. The results show that the fusion zone (FZ) mainly consists of fine dendrite structure with fine γ', Laves phases and MC carbides inhomogeneously distributed. The high welding temperature induces the partial dissolution of γ' in the heat-affected zone (HAZ) of DZ125L and liquation of grain boundaries in both of the HAZs. After post-weld heat treatment (PWHT), fine γ″ and γ' phases precipitate in the FZ, IN718 HAZ and IN718 base metal (BM), and fine γ' precipitate in the γ channel of the HAZ and BM of DZ125L. With tensile testing, the joints after PWHT show higher strengths than that of the weaker DZ125L alloy. Plastic deformation mainly concentrates in the weaker DZ125L and the joint finally fails in the DZ125L BM.

Test results from a comparative evaluation of a condensation nuclei fire detector

NASA Technical Reports Server (NTRS)

Bricker, R. W.

1985-01-01

The fire/smoke alarm response of a condensation nuclei fire detector (CNFD) was compared with photoelectric and ionization detectors. Tests were conducted in a former control room 8.5 m by 8.9 with a 2.7 m ceiling. The room had air supplied from above the ceiling and under the floor with return air exiting from ceiling grills. The environment was varied from 278 to 305 K and relative humidities from 8 to 65%. Four detection zones were located in the room. Each zone contained a sampling head for the CNDF, a photodetector, and an ionization detector so that each detector system had four opportunities to alarm during tests. The particle level in the test room was also monitored during tests with a condensation nuclei particle counter. The CNFD responded to 90% of exposures to smoldering plastic and 84% of exposures to visible fire. The photoelectric response was 43 and 12.5% respectively for the same conditions. The ionization response was 9 and 48 respectively.

Spatio-temporal variation of anthropogenic marine debris on Chilean beaches.

PubMed

Hidalgo-Ruz, Valeria; Honorato-Zimmer, Daniela; Gatta-Rosemary, Magdalena; Nuñez, Paloma; Hinojosa, Iván A; Thiel, Martin

2018-01-01

We examined the hypothesis that in an emerging economy such as Chile the abundances of Anthropogenic Marine Debris (AMD) on beaches are increasing over time. The citizen science program Científicos de la Basura ("Litter Scientists") conducted three national surveys (2008, 2012 and 2016) to determine AMD composition, abundance, spatial patterns and temporal trends. AMD was found on all beaches along the entire Chilean coast. Highest percentages of AMD in all surveys were plastics and cigarette butts, which can be attributed to local sources (i.e. beach users). The Antofagasta region in northern Chile had the highest abundance of AMD compared with all other zones. Higher abundances of AMD were found at the upper stations from almost all zones. No significant tendency of increasing or decreasing AMD densities was observed during the 8years covered by our study, which suggests that economic development alone cannot explain temporal trends in AMD densities. Copyright © 2017 Elsevier Ltd. All rights reserved.

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

Lieou, Charles Ka Cheong; Daub, Eric G.; Ecke, Robert E.

Rock materials often display long-time relaxation, commonly termed aging or “slow dynamics”, after the cessation of acoustic perturbations. In this paper, we focus on unconsolidated rock materials and propose to explain such nonlinear relaxation through the Shear-Transformation-Zone (STZ) theory of granular media, adapted for small stresses and strains. The theory attributes the observed relaxation to the slow, irreversible change of positions of constituent grains, and posits that the aging process can be described in three stages: fast recovery before some characteristic time associated with the subset of local plastic events or grain rearrangements with a short time scale, log-linear recoverymore » of the elastic modulus at intermediate times, and gradual turnover to equilibrium steady-state behavior at long times. Here we demonstrate good agreement with experiments on aging in granular materials such as simulated fault gouge after an external disturbance. These results may provide insights into observed modulus recovery after strong shaking in the near surface region of earthquake zones.« less

Photoacoustic microscopic imaging of surface and subsurface damages in CFRP

NASA Astrophysics Data System (ADS)

Nakahata, Kazuyuki; Ogi, Keiji; Namita, Takeshi; Ohira, Katsumi; Maruyama, Masayuki; Shiina, Tsuyoshi

2018-04-01

Photoacoustic imaging comprises an optical excitation within a target zone and the detection of the ultrasonic wave so created. A pulsed laser illuminates the target zone, and this illumination causes rapid thermoelastic expansion that generates a broadband high-frequency ultrasonic wave (photoacoustic wave, PA). In this paper, we report proof-of-concept experiments for nondestructive testing of laminar materials using a PA microscope. A specimen containing carbon-fiber-reinforced plastic (CFRP) was used in this experiment and involved an artificial delamination. A 532-nm-wavelength laser irradiates the top surface of the specimen, and the resulting ultrasonic waves are received by a point-focusing immersion transducer on the same side. Our system estimated the depth and dimension of the subsurface delamination accurately. By coating a light-absorbing material on the surface, the amplitude of the PA wave increased. This finding shows that the signal-noise (S/N) ratio of the scattered wave from delaminations can be improved with the surface coatings.

Slow dynamics and strength recovery in unconsolidated granular earth materials: a mechanistic theory

DOE PAGES

Lieou, Charles Ka Cheong; Daub, Eric G.; Ecke, Robert E.; ...

2017-09-08

Rock materials often display long-time relaxation, commonly termed aging or “slow dynamics”, after the cessation of acoustic perturbations. In this paper, we focus on unconsolidated rock materials and propose to explain such nonlinear relaxation through the Shear-Transformation-Zone (STZ) theory of granular media, adapted for small stresses and strains. The theory attributes the observed relaxation to the slow, irreversible change of positions of constituent grains, and posits that the aging process can be described in three stages: fast recovery before some characteristic time associated with the subset of local plastic events or grain rearrangements with a short time scale, log-linear recoverymore » of the elastic modulus at intermediate times, and gradual turnover to equilibrium steady-state behavior at long times. Here we demonstrate good agreement with experiments on aging in granular materials such as simulated fault gouge after an external disturbance. These results may provide insights into observed modulus recovery after strong shaking in the near surface region of earthquake zones.« less

The Effect of Ionic Correlations on Radiative Properties in the Solar Interior and Terrestrial Experiments

NASA Astrophysics Data System (ADS)

Krief, Menahem; Kurzweil, Yair; Feigel, Alexander; Gazit, Doron

2018-04-01

With the aim of solving the decade-old problem of solar opacity, we report substantial photoabsorption uncertainty due to the effect of ion–ion correlations. By performing detailed opacity calculations of the solar mixture, we find that taking into account the ionic structure changes the Rosseland opacity near the convection zone by ∼10%. We also report a ∼15% difference in the Rosseland opacity for iron, which was recently measured at the Sandia Z facility, where the temperature reached that prevailing in the convection zone boundary while the density was 2.5 times lower. Finally, we propose a method to measure opacities at solar temperatures and densities that have never been reached in the past via laboratory radiation flow experiments, by using plastic foams doped with permilles of dominant photon absorbers in the Sun. The method is advantageous for an experimental study of solar opacities that may lead to a resolution of the solar abundance problem.

Slow Dynamics and Strength Recovery in Unconsolidated Granular Earth Materials: A Mechanistic Theory

NASA Astrophysics Data System (ADS)

Lieou, Charles K. C.; Daub, Eric G.; Ecke, Robert E.; Johnson, Paul A.

2017-10-01

Rock materials often display long-time relaxation, commonly termed aging or "slow dynamics," after the cessation of acoustic perturbations. In this paper, we focus on unconsolidated rock materials and propose to explain such nonlinear relaxation through the shear-transformation-zone theory of granular media, adapted for small stresses and strains. The theory attributes the observed relaxation to the slow, irreversible change of positions of constituent grains and posits that the aging process can be described in three stages: fast recovery before some characteristic time associated with the subset of local plastic events or grain rearrangements with a short time scale, log linear recovery of the elastic modulus at intermediate times, and gradual turnover to equilibrium steady state behavior at long times. We demonstrate good agreement with experiments on aging in granular materials such as simulated fault gouge after an external disturbance. These results may provide insights into observed modulus recovery after strong shaking in the near surface region of earthquake zones.

Properties of the dead zone due to the gas cushion effect in PBX 9502

NASA Astrophysics Data System (ADS)

Anderson, William

2017-06-01

The gas cushion effect is a well-known phenomenon in which gas trapped between an impactor and an explosive precompresses and deadens a layer of the explosive. We have conducted a series of impact experiments, with and without a trapped gas layer, on the plastic bonded explosive PBX 9502 (95% TATB and 5% Kel-F 800). In each experiment, a 100-oriented LiF window was glued, with an intervening Al foil (a reflector for VISAR), to the surface of a thin (2.5-3.3 mm) PBX 9502 sample and the opposite surface impacted by an impactor at a velocity sufficient to produce an overdriven detonation. VISAR was used to observe arrival of the resulting shock wave and reverberations between the LiF window and the impactor. In three experiments, a gap of 25-38 mm, filled with He gas at a pressure of 0.79 bar, existed between the impactor and the sample at the beginning of the experiment. In these three experiments, a low-amplitude wave reflected from the interface between the reacted explosive and the dead zone was observed to precede the reflection from the impactor. We have used the observed wave amplitudes and arrival times to quantify the properties of the dead zone and, by comparison to existing EOS data for reacted and unreacted PBX 9502, estimate the extent of reaction in the dead zone. This work was supported by the US Department of Energy under contract DE-AC52-06NA25396.

[Classification of Priority Area for Soil Environmental Protection Around Water Sources: Method Proposed and Case Demonstration].

PubMed

Li, Lei; Wang, Tie-yu; Wang, Xiaojun; Xiao, Rong-bo; Li, Qi-feng; Peng, Chi; Han, Cun-liang

2016-04-15

Based on comprehensive consideration of soil environmental quality, pollution status of river, environmental vulnerability and the stress of pollution sources, a technical method was established for classification of priority area of soil environmental protection around the river-style water sources. Shunde channel as an important drinking water sources of Foshan City, Guangdong province, was studied as a case, of which the classification evaluation system was set up. In detail, several evaluation factors were selected according to the local conditions of nature, society and economy, including the pollution degree of heavy metals in soil and sediment, soil characteristics, groundwater sensitivity, vegetation coverage, the type and location of pollution sources. Data information was mainly obtained by means of field survey, sampling analysis, and remote sensing interpretation. Afterwards, Analytical Hierarchy Process (AHP) was adopted to decide the weight of each factor. The basic spatial data layers were set up respectively and overlaid based on the weighted summation assessment model in Geographical Information System (GIS), resulting in a classification map of soil environmental protection level in priority area of Shunde channel. Accordingly, the area was classified to three levels named as polluted zone, risky zone and safe zone, which respectively accounted for 6.37%, 60.90% and 32.73% of the whole study area. Polluted zone and risky zone were mainly distributed in Lecong, Longjiang and Leliu towns, with pollutants mainly resulted from the long-term development of aquaculture and the industries containing furniture, plastic constructional materials and textile and clothing. In accordance with the main pollution sources of soil, targeted and differentiated strategies were put forward. The newly established evaluation method could be referenced for the protection and sustainable utilization of soil environment around the water sources.

An Evaluation of Global and Local Tensile Properties of Friction-Stir Welded DP980 Dual-Phase Steel Joints Using a Digital Image Correlation Method

PubMed Central

Lee, Hyoungwook; Kim, Cheolhee; Song, Jung Han

2015-01-01

The effect of the microstructure heterogeneity on the tensile plastic deformation characteristic of friction-stir-welded (FSW) dual-phase (DP) steel was investigated for the potential applications on the lightweight design of vehicles. Friction-stir-welded specimens with a butt joint configuration were prepared, and quasi-static tensile tests were conducted, to evaluate the tensile properties of DP980 dual-phase steels. The friction-stir welding led to the formation of martensite and a significant hardness rise in the stir zone (SZ), but the presence of a soft zone in the heat-affected zone (HAZ) was caused by tempering of the pre-existing martensite. Owing to the appearance of severe soft zone, DP980 FSW joint showed almost 93% joint efficiency with the view-point of ultimate tensile strength and relatively low ductility than the base metal (BM). The local tensile deformation characteristic of the FSW joints was also examined using the digital image correlation (DIC) methodology by mapping the global and local strain distribution, and was subsequently analyzed by mechanics calculation. It is found that the tensile deformation of the FSW joints is highly heterogeneous, leading to a significant decrease in global ductility. The HAZ of the joints is the weakest region where the strain localizes early, and this localization extends until fracture with a strain near 30%, while the strain in the SZ and BM is only 1% and 4%, respectively. Local constitutive properties in different heterogeneous regions through the friction-stir-welded joint was also briefly evaluated by assuming iso-stress conditions. The local stress-strain curves of individual weld zones provide a clear indication of the heterogeneity of the local mechanical properties. PMID:28793720

Microstructure Characterization of Fiber Laser Welds of S690QL High-Strength Steels

NASA Astrophysics Data System (ADS)

Li, Baoming; Xu, Peiquan; Lu, Fenggui; Gong, Hongying; Cui, Haichao; Liu, Chuangen

2018-02-01

The use of fiber laser welding to join S690QL steels has attracted interest in the field of construction and assembly. Herein, 13-mm-thick S690QL welded joints were obtained without filler materials using the fiber laser. The as-welded microstructures and the impact energies of the joints were characterized and measured using electron microscopy in conjunction with high-resolution transmission electron images, X-ray diffraction, and impact tests. The results indicated that a single-sided welding technique could be used to join S690QL steels up to a thickness of 12 mm (fail to fuse the joint in the root) when the laser power is equal to 12 kW (scan speed 1 m/min). Double-side welding technique allows better weld penetration and better control of heat distribution. Observation of the samples showed that the fusion zone exhibited bainitic and martensitic microstructures with increased amounts of martensites (Ms) compared with the base materials. Also, the grains in the fusion zone increased in coarseness as the heat input was increased. The fusion zone exhibited increased hardness (397 HV0.2) while exhibiting a simultaneous decrease in the impact toughness. The maximum impact energy value of 26 J was obtained from the single-side-welded sample, which is greater than those obtained from the double-side-welded samples (maximum of 18 J). Many more dislocations and plastic deformations were found in the fusion zone than the heat-affected zone in the joint, which hardened the joints and lowered the impact toughness. The microstructures characterized by FTEM-energy-dispersive X-ray spectrometer also exhibited laths of M, as well as stacking faults and dislocations featuring high-density, interfacial structure ledges that occur between the high-angle grain boundaries and the M and bainite.

An Evaluation of Global and Local Tensile Properties of Friction-Stir Welded DP980 Dual-Phase Steel Joints Using a Digital Image Correlation Method.

PubMed

Lee, Hyoungwook; Kim, Cheolhee; Song, Jung Han

2015-12-04

The effect of the microstructure heterogeneity on the tensile plastic deformation characteristic of friction-stir-welded (FSW) dual-phase (DP) steel was investigated for the potential applications on the lightweight design of vehicles. Friction-stir-welded specimens with a butt joint configuration were prepared, and quasi-static tensile tests were conducted, to evaluate the tensile properties of DP980 dual-phase steels. The friction-stir welding led to the formation of martensite and a significant hardness rise in the stir zone (SZ), but the presence of a soft zone in the heat-affected zone (HAZ) was caused by tempering of the pre-existing martensite. Owing to the appearance of severe soft zone, DP980 FSW joint showed almost 93% joint efficiency with the view-point of ultimate tensile strength and relatively low ductility than the base metal (BM). The local tensile deformation characteristic of the FSW joints was also examined using the digital image correlation (DIC) methodology by mapping the global and local strain distribution, and was subsequently analyzed by mechanics calculation. It is found that the tensile deformation of the FSW joints is highly heterogeneous, leading to a significant decrease in global ductility. The HAZ of the joints is the weakest region where the strain localizes early, and this localization extends until fracture with a strain near 30%, while the strain in the SZ and BM is only 1% and 4%, respectively. Local constitutive properties in different heterogeneous regions through the friction-stir-welded joint was also briefly evaluated by assuming iso-stress conditions. The local stress-strain curves of individual weld zones provide a clear indication of the heterogeneity of the local mechanical properties.

Anomalous Seismic Radiation in the Shallow Subduction Zone Explained by Extensive Poroplastic Deformation in the Overriding Wedge

NASA Astrophysics Data System (ADS)

Hirakawa, E. T.; Ma, S.

2012-12-01

The deficiency of high-frequency seismic radiation from shallow subduction zone earthquakes was first recognized in tsunami earthquakes (Kanamori, 1972), which produce larger tsunamis than expected from short-period (20 s) surface wave excitation. Shallow subduction zone earthquakes were also observed to have unusually low energy-to-moment ratios compared to regular subduction zone earthquakes (e.g., Newman and Okal, 1998; Venkataraman and Kanamori, 2004; Lay et al., 2012). What causes this anomalous radiation and how it relates to large tsunami generation has remained unclear. Here we show that these anomalous observations can be due to extensive poroplastic deformation in the overriding wedge, which provides a unifying interpretation. Ma (2012) showed that the pore pressure increase in the wedge due to up-dip rupture propagation significantly weakens the wedge, leading to widespread Coulomb failure in the wedge. Widespread failure gives rise to slow rupture velocity and large seafloor uplift (landward from the trench) in the case of a shallow fault dip. Here we extend this work and demonstrate that the large seafloor uplift due to the poroplastic deformation significantly dilates the fault behind the rupture front, which reduces the normal stress on the fault and increases the stress drop, slip, and rupture duration. The spectral amplitudes of the moment-rate time function is significantly less at high frequencies than those from elastic simulations. Large tsunami generation and deficiency of high-frequency radiation are thus two consistent manifestations of the same mechanism (poroplastic deformation). Although extensive poroplastic deformation in the wedge represents a significant portion of total seismic moment release, the plastic deformation is shown to act as a large energy sink, leaving less energy to be radiated and leading to low energy-to-moment ratios as observed for shallow subduction zone earthquakes.

Resistance spot welding of ultra-fine grained steel sheets produced by constrained groove pressing: Optimization and characterization

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

Khodabakhshi, F.; Kazeminezhad, M., E-mail: mkazemi@sharif.edu; Kokabi, A.H.

2012-07-15

Constrained groove pressing as a severe plastic deformation method is utilized to produce ultra-fine grained low carbon steel sheets. The ultra-fine grained sheets are joined via resistance spot welding process and the characteristics of spot welds are investigated. Resistance spot welding process is optimized for welding of the sheets with different severe deformations and their results are compared with those of as-received samples. The effects of failure mode and expulsion on the performance of ultra-fine grained sheet spot welds have been investigated in the present paper and the welding current and time of resistance spot welding process according to thesemore » subjects are optimized. Failure mode and failure load obtained in tensile-shear test, microhardness, X-ray diffraction, transmission electron microscope and scanning electron microscope images have been used to describe the performance of spot welds. The region between interfacial to pullout mode transition and expulsion limit is defined as the optimum welding condition. The results show that optimum welding parameters (welding current and welding time) for ultra-fine grained sheets are shifted to lower values with respect to those for as-received specimens. In ultra-fine grained sheets, one new region is formed named recrystallized zone in addition to fusion zone, heat affected zone and base metal. It is shown that microstructures of different zones in ultra-fine grained sheets are finer than those of as-received sheets. - Highlights: Black-Right-Pointing-Pointer Resistance spot welding process is optimized for joining of UFG steel sheets. Black-Right-Pointing-Pointer Optimum welding current and time are decreased with increasing the CGP pass number. Black-Right-Pointing-Pointer Microhardness at BM, HAZ, FZ and recrystallized zone is enhanced due to CGP.« less

Probing the transition between seismically coupled and decoupled segments along an ancient subduction interface

NASA Astrophysics Data System (ADS)

Angiboust, Samuel; Kirsch, Josephine; Oncken, Onno; Glodny, Johannes; Monié, Patrick; Rybacki, Erik

2015-06-01

The transition zone at the downdip end of seismic coupling along subduction interfaces is often the site of megathrust earthquake nucleation and concentrated postseismic afterslip, as well as the focus site of episodic tremor and slip features. Exhumed remnants of the former Alpine subduction zone found in the Swiss Alps allow analyzing fluid and deformation processes near the transition zone region (30-40 km paleodepth). The Dent Blanche Thrust (DBT) is a lower blueschist-facies shear zone interpreted as a fossilized subduction interface where granitic mylonites overlie a metamorphosed accretionary wedge. We report field observations from the DBT region where multiple, several tens of meters thick foliated cataclastic networks are interlayered within the basal DBT mylonites. Petrological results and microstructural observations indicate that the various cataclasis events took place at near-peak metamorphic conditions (400-500°C, 1.1-1.3 GPa) during subduction of the Tethyan seafloor in Eocene times (42-48 Ma). Some of these networks exhibit mutual crosscutting relationships between mylonites, foliated cataclasites, and vein systems indicating mutual overprinting between brittle deformation and ductile creep. Whole-rock chemical compositions, in situ 40Ar-39Ar age data of recrystallized phengite, and Sr isotopic signatures reveal that DBT rocks also underwent multiple hydrofracturing and metasomatic events via the infiltration of fluids mainly derived from the oceanic metasediments underneath the DBT. From the rock fabrics, we infer strain rate fluctuations of several orders of magnitude beyond subduction strain rates (˜10-12 s-1) accompanied by fluctuation of supralithostatic and quasi-lithostatic fluid pressures (1 ≥ λ > 0.95). DBT brittle-plastic deformation switches highlight the diversity of deformation processes and fluid-rock interactions in the transition zone region of the subduction interface.

A viscoplastic shear-zone model for deep (15-50 km) slow-slip events at plate convergent margins

NASA Astrophysics Data System (ADS)

Yin, An; Xie, Zhoumin; Meng, Lingsen

2018-06-01

A key issue in understanding the physics of deep (15-50 km) slow-slip events (D-SSE) at plate convergent margins is how their initially unstable motion becomes stabilized. Here we address this issue by quantifying a rate-strengthening mechanism using a viscoplastic shear-zone model inspired by recent advances in field observations and laboratory experiments. The well-established segmentation of slip modes in the downdip direction of a subduction shear zone allows discretization of an interseismic forearc system into the (1) frontal segment bounded by an interseismically locked megathrust, (2) middle segment bounded by episodically locked and unlocked viscoplastic shear zone, and (3) interior segment that slips freely. The three segments are assumed to be linked laterally by two springs that tighten with time, and the increasing elastic stress due to spring tightening eventually leads to plastic failure and initial viscous shear. This simplification leads to seven key model parameters that dictate a wide range of mechanical behaviors of an idealized convergent margin. Specifically, the viscoplastic rheology requires the initially unstable sliding to be terminated nearly instantaneously at a characteristic velocity, which is followed by stable sliding (i.e., slow-slip). The characteristic velocity, which is on the order of <10-7 m/s for the convergent margins examined in this study, depends on the (1) effective coefficient of friction, (2) thickness, (3) depth, and (4) viscosity of the viscoplastic shear zone. As viscosity decreases exponentially with temperature, our model predicts faster slow-slip rates, shorter slow-slip durations, more frequent slow-slip occurrences, and larger slow-slip magnitudes at warmer convergent margins.

Lithospheric rheological heterogeneity across an intraplate rift basin (Linfen Basin, North China) constrained from magnetotelluric data: Implications for seismicity and rift evolution

NASA Astrophysics Data System (ADS)

Yin, Yaotian; Jin, Sheng; Wei, Wenbo; Ye, Gaofeng; Jing, Jian'en; Zhang, Letian; Dong, Hao; Xie, Chengliang; Liang, Hongda

2017-10-01

We take the Linfen Basin, which is the most active segment of the Cenozoic intraplate Shanxi Rift, as an example, showing how to use magnetotelluric data to constrain lithospheric rheological heterogeneities of intraplate tectonic zones. Electrical resistivity models, combined with previous rheological numerical simulation, show a good correlation between resistivity and rheological strength, indicating the mechanisms of enhanced conductivity could also be reasons of reduced viscosity. The crust beneath the Linfen Basin shows overall stratified features in both electrical resistivity and rheology. The uppermost crustal conductive layer is dominated by friction sliding-type brittle fracturing. The high-resistivity mid-crust is inferred to be high-viscosity metamorphic basement being intersected by deep fault. The plastic lower crust show significantly high-conductivity feature. Seismicity appears to be controlled by crustal rheological heterogeneity. Micro-earthquakes mainly distribute at the brittle-ductile transition zones as indicated by high- to low-resistivity interfaces or the high pore pressure fault zones while the epicenters of two giant destructive historical earthquakes occur within the high-resistivity and therefore high-strength blocks near the inferred rheological interfaces. The lithosphere-scale lateral rheological heterogeneity along the profile can also be illustrated. The crust and upper mantle beneath the Ordos Block, Lüliang Mountains and Taihang Mountains are of high rheological strength as indicated by large-scale high-resistivity zones while a significant high-conductivity, lithosphere-scale weak zone exists beneath the eastern margin of the Linfen Basin. According to previous geodynamic modeling works, we suggest that this kind of lateral rheological heterogeneity may play an essential role for providing driving force for the formation and evolution of the Shanxi Rift, regional lithospheric deformation and earthquake activities under the far-field effects of the India-Eurasian Collision.

Antibacterial hydroxypropyl methyl cellulose edible films containing nanoemulsions of Thymus daenensis essential oil for food packaging.

PubMed

Moghimi, Roya; Aliahmadi, Atousa; Rafati, Hasan

2017-11-01

Edible films containing essential oils (EO) as natural antibacterial agents are promising systems for food preservation. In this work, nanoemulsions of Thymus daenensis EO (wild; F1 and cultivated; F2) were loaded in hydroxyl propyl methyl cellulose (HPMC) films and the effect of different parameters (polymer, plasticizer, and EO concentration) on the film properties were analyzed and optimized. Prepared HPMC films were characterized in terms of EO loading, morphology, mechanical properties, and the antibacterial activity. The results of SEM showed uniform incorporation of nanoemulsions into the edible film. Investigation of the mechanical properties of two edible films revealed a plasticizing effect of T. daenensis EO on the films. Also, edible films had noticeable antimicrobial activity against selected microorganisms, i.e. 47.0±2.5mm and 22.6±0.5mm zone of inhibition against S. aureus for films containing F1 and F2, respectively. Incorporation of nanoemulsions into the HPMC films can be used for active food preservation. Copyright © 2017 Elsevier Ltd. All rights reserved.

Parametric analysis of plastic strain and force distribution in single pass metal spinning

NASA Astrophysics Data System (ADS)

Choudhary, Shashank; Tejesh, Chiruvolu Mohan; Regalla, Srinivasa Prakash; Suresh, Kurra

2013-12-01

Metal spinning also known as spin forming is one of the sheet metal working processes by which an axis-symmetric part can be formed from a flat sheet metal blank. Parts are produced by pressing a blunt edged tool or roller on to the blank which in turn is mounted on a rotating mandrel. This paper discusses about the setting up a 3-D finite element simulation of single pass metal spinning in LS-Dyna. Four parameters were considered namely blank thickness, roller nose radius, feed ratio and mandrel speed and the variation in forces and plastic strain were analysed using the full-factorial design of experiments (DOE) method of simulation experiments. For some of these DOE runs, physical experiments on extra deep drawing (EDD) sheet metal were carried out using En31 tool on a lathe machine. Simulation results are able to predict the zone of unsafe thinning in the sheet and high forming forces that are hint to the necessity for less-expensive and semi-automated machine tools to help the household and small scale spinning workers widely prevalent in India.

Perinatal exposure to a noncoplanar polychlorinated biphenyl alters tonotopy, receptive fields, and plasticity in rat primary auditory cortex

PubMed Central

Kenet, T.; Froemke, R. C.; Schreiner, C. E.; Pessah, I. N.; Merzenich, M. M.

2007-01-01

Noncoplanar polychlorinated biphenyls (PCBs) are widely dispersed in human environment and tissues. Here, an exemplar noncoplanar PCB was fed to rat dams during gestation and throughout three subsequent nursing weeks. Although the hearing sensitivity and brainstem auditory responses of pups were normal, exposure resulted in the abnormal development of the primary auditory cortex (A1). A1 was irregularly shaped and marked by internal nonresponsive zones, its topographic organization was grossly abnormal or reversed in about half of the exposed pups, the balance of neuronal inhibition to excitation for A1 neurons was disturbed, and the critical period plasticity that underlies normal postnatal auditory system development was significantly altered. These findings demonstrate that developmental exposure to this class of environmental contaminant alters cortical development. It is proposed that exposure to noncoplanar PCBs may contribute to common developmental disorders, especially in populations with heritable imbalances in neurotransmitter systems that regulate the ratio of inhibition and excitation in the brain. We conclude that the health implications associated with exposure to noncoplanar PCBs in human populations merit a more careful examination. PMID:17460041

Shock temperature dependent rate law for plastic bonded explosives

NASA Astrophysics Data System (ADS)

Aslam, Tariq D.

2018-04-01

A reactive flow model for the tri-amino-tri-nitro-benzene (TATB) based plastic bonded explosive PBX 9502 (95% TATB, 5% polymeric binder Kel-F 800) is presented. This newly devised model is based primarily on the shock temperature of the material, along with local pressure, and accurately models a broader range of detonation and initiation scenarios. Specifically, sensitivity changes to the initial explosive temperature are accounted for naturally and with a single set of parameters. The equation of state forms for the reactants and products, as well as the thermodynamic closure of pressure and temperature equilibration, are carried over from the Wescott-Stewart-Davis (WSD) model [Wescott et al., J. Appl. Phys. 98, 053514 (2005) and "Modeling detonation diffraction and dead zones in PBX-9502," in Proceedings of the Thirteenth International Detonation Symposium (2006)]. This newly devised model, with Arrhenius state dependence on the shock temperature, based on the WSD equation of states, is denoted by AWSD. Modifying an existing implementation of the WSD model to the AWSD model in a hydrocode is a rather straightforward procedure.

Marine Litter Distribution and Density in European Seas, from the Shelves to Deep Basins

PubMed Central

Pham, Christopher K.; Ramirez-Llodra, Eva; Alt, Claudia H. S.; Amaro, Teresa; Bergmann, Melanie; Canals, Miquel; Company, Joan B.; Davies, Jaime; Duineveld, Gerard; Galgani, François; Howell, Kerry L.; Huvenne, Veerle A. I.; Isidro, Eduardo; Jones, Daniel O. B.; Lastras, Galderic; Morato, Telmo; Gomes-Pereira, José Nuno; Purser, Autun; Stewart, Heather; Tojeira, Inês; Tubau, Xavier; Van Rooij, David; Tyler, Paul A.

2014-01-01

Anthropogenic litter is present in all marine habitats, from beaches to the most remote points in the oceans. On the seafloor, marine litter, particularly plastic, can accumulate in high densities with deleterious consequences for its inhabitants. Yet, because of the high cost involved with sampling the seafloor, no large-scale assessment of distribution patterns was available to date. Here, we present data on litter distribution and density collected during 588 video and trawl surveys across 32 sites in European waters. We found litter to be present in the deepest areas and at locations as remote from land as the Charlie-Gibbs Fracture Zone across the Mid-Atlantic Ridge. The highest litter density occurs in submarine canyons, whilst the lowest density can be found on continental shelves and on ocean ridges. Plastic was the most prevalent litter item found on the seafloor. Litter from fishing activities (derelict fishing lines and nets) was particularly common on seamounts, banks, mounds and ocean ridges. Our results highlight the extent of the problem and the need for action to prevent increasing accumulation of litter in marine environments. PMID:24788771

X-ray topographic fractography of single crystals of molybdenum and niobium

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

Hmelo, A.B.

1982-12-01

The semi-brittle (001) cleavage fracture at 77/sup 0/K of Mo and outgassed Nb single crystals was related to their fracture toughness. Berg-Barrett x-ray reflection topography and White Beam Synchrotron Fractography were used. Calibrated electropolishing in layers followed by Synchrotron Fractography revealed that under the conditions which existed at the tip of the running crack, Mo underwent general yielding which resulted in a plastically curved lattice. This result correlates with the substantial fracture toughness for Mo measured previously. On the other hand, double (112) slip was observed for Nb. The plastic zone associated with the crack-tip is shown to have amore » structure typicla of shock-loaded materials, consisting of arrays of screw dislocations, micro- and macrotwins. This result correlates with the low fracture toughness of Nb at 77/sup 0/K. It is proposed that these extremes in cleavage behavior for Mo vs Nb can be rationalized in terms of the capacity of a bcc structure to undergo a slip to twinning transition at high strain rates. 32 figures, 5 tables.« less

Pseudomonas aeruginosa biofilm formation and UV/irradiation exposure change surface and chemical structures of Pre-Production Resin Pellets

NASA Astrophysics Data System (ADS)

Stam, C. N.; Neal, A.; Park, S.; Mielke, R.; Tsapin, A. I.; Bhartia, R.; Salas, E.; Hug, W.; Behar, A. E.; Nadeau, J. L.

2011-12-01

Microbial interactions with synthetic polymers in open ocean is poorly understood. Plastics are a major and persistent contaminant of ocean waters. Many of these plastics are contaminated with toxic and synthetic chemicals that persist in the environment with minimal degradation. The purpose of this study is to look at the effects that microbial biofilm communities have on both surface and chemical structures of pre-production resin pellets (PRPs). Pseudomonas aeruignosa was grown with PRPs under multiple growth and nutrient conditions. These conditions were combined with varying lengths of UV exposures common to ocean environments. Material degradation of the PRPs and the changing surface and chemical structures of these synthetic polymers was evaluated using a combination of Fourier transform infrared spectroscopy, environmental scanning electron microscopy, scanning transmission electron microscopy, X-ray microtomography, and ArcGIS mapping. This study correlates with previous studies conducted on environmental PRP's , collected on the 2009 Project Kaisei expedition in the Subtropical Convergence Zone of the North Pacific Gyre. Further studies are needed to develop a full understanding of degradation rates of synthetic polymers in oceanic environments.

On the determination of stress fields and displacements in a thin elastoplastic plate containing elastic inclusion - a shim

NASA Astrophysics Data System (ADS)

Kovalev, A. V.; Rusina, E. Y.; Yakovlev, A. Y.

2018-03-01

The paper is devoted to the determination of the stress-strain state of a mechanical structure, which consists of a thin infinite elastoplastic plate with a hole and a continuous fine elastic inclusion. The complexity of this problem lies in the fact that the shape of the boundary between the elastic and plastic zones in the plate is not known in advance. The small parameter method is used as the solution method, while the small parameter characterizes the deviation of the shape of the contour from the circle and the perturbation of external static boundary conditions. As the zero solution, the axisymmetric elastoplastic state of the plate with inclusion is chosen. Two variants of inclusion fixation in a plate are considered: inclusion is enclosed with tension or soldered. As a result of solving the problem within the framework of ideal plasticity, the distribution of the stress and displacement fields and the shape of the elastoplastic boundary are obtained. To illustrate the case of a plane-stressed state, the results of a numerical experiment on the mathematical model obtained are presented.

Effect of the Microstructure on the Fracture Mode of Short-Fiber Reinforced Plastic Composites

NASA Astrophysics Data System (ADS)

Nishikawa, Masaaki; Okabe, Tomonaga; Takeda, Nobuo

A numerical simulation was presented to discuss the microscopic damage and its influence on the strength and energy-absorbing capability of short-fiber reinforced plastic composites. The dominant damage includes matrix crack and/or interfacial debonding, when the fibers are shorter than the critical length for fiber breakage. The simulation addressed the matrix crack with a continuum damage mechanics (CDM) model and the interfacial debonding with an embedded process zone (EPZ) model. Fictitious free-edge effects on the fracture modes were successfully eliminated with the periodic-cell simulation. The advantage of our simulation was pointed out by demonstrating that the simulation with edge effects significantly overestimates the dissipative energy of the composites. We then investigated the effect of the material microstructure on the fracture modes in the composites. The simulated results clarified that the inter-fiber distance affects the breaking strain of the composites and the fiber-orientation angle affects the position of the damage initiation. These factors influence the strength and energy-absorbing capability of short fiber-reinforced composites.

Texture and elastic anisotropy of a mylonitic anorthosite from the Morin Shear Zone (Quebec, Canada)

NASA Astrophysics Data System (ADS)

Gómez Barreiro, Juan; Wenk, Hans-Rudolf; Vogel, Sven

2015-02-01

A sample of anorthosite from the granulite facies Morin Shear Zone (Quebec, Canada) was investigated for crystal preferred orientation and elastic anisotropy. Time-of-flight neutron diffraction data obtained with the HIPPO diffractometer at LANSCE were analyzed with the Rietveld method to obtain orientation distribution functions of the principal phases (plagioclase, clinopyroxene and orthopyroxene). Texture and microstructures are compatible with the plastic deformation of the aggregate under high-T conditions. All mineral phases depict a significant preferred orientation that could be related to the general top-to-the north shearing history of the Morin Shear Zone. Texture patterns suggest that (010)[001] in plagioclase and (110)[001] in clinopyroxene are likely dominant slip systems. Using preferred orientation data P- and S-waves velocities and elastic anisotropy were calculated and compared with previous studies to explore elastic properties of rocks with different pyroxene-plagioclase mixtures. P-wave velocity, S-wave splitting and anisotropy increase with clinopyroxene content. Seismic anisotropy is linked to the texture symmetry which can lead to large deviations between actual anisotropy and that measured along Cartesian XYZ sample directions (lineation/foliation reference frame). This is significant for the prediction and interpretation of seismic data, particularly for monoclinic or triclinic texture symmetries.

An improved measurement of Vickers indentation behaviour through enhanced instrumentation

NASA Astrophysics Data System (ADS)

Faisal, N. H.; Reuben, R. L.; Ahmed, R.

2011-01-01

This work presents an enhanced instrumented Vickers indentation technique capable of recording force, displacement and acoustic emission (AE) during loading condition. Four materials were chosen for examination; copper, aluminium, steel and as-sprayed HVOF WC-12%Co coating. Results indicate that force-displacement (P-h) profiles are essentially bilinear with two characteristic slopes separated by a distinct displacement arrest for all loads above 98 N. The P-h curve indicates three distinct loading stages (I, II and III) and the stage III mechanical energy increases with loads. About 66% of the hardened steel indentations but only about 18% of the as-sprayed HVOF WC-12%Co coating indentations exhibited an AE record that could be separated into three distinct zones (A, B and C). Where zoning was possible the AE corresponding to a zone correlated well with the AE associated with a loading stage. It is concluded that plastic deformation in soft metals produced little AE, whereas brittle fracture in hardened steel and as-sprayed HVOF WC-12%Co coating produced significant AE. AE may or may not be focused onto particular stages of the indentation and a full measure of crack prevalence would require fractal dimension analysis, which is time consuming, offering a motivation for AE-based indentation testing.

Implementation of Smoothed Particle Hydrodynamics for Detonation of Explosive with Application to Rock Fragmentation

NASA Astrophysics Data System (ADS)

Pramanik, R.; Deb, D.

2015-07-01

The paper presents a methodology in the SPH framework to analyze physical phenomena those occur in detonation process of an explosive. It mainly investigates the dynamic failure mechanism in surrounding brittle rock media under blast-induced stress wave and expansion of high pressure product gases. A program burn model is implemented along with JWL equation of state to simulate the reaction zone in between unreacted explosive and product gas. Numerical examples of detonation of one- and two-dimensional explosive slab have been carried out to investigate the effect of reaction zone in detonation process and outward dispersion of gaseous product. The results are compared with those obtained from existing solutions. A procedure is also developed in SPH framework to apply continuity conditions between gas and rock interface boundaries. The modified Grady-Kipp damage model for the onset of tensile yielding and Drucker-Prager model for shear failure are implemented for elasto-plastic analysis of rock medium. The results show that high compressive stress causes high crack density in the vicinity of blast hole. The major principal stress (tensile) is responsible for forming radial cracks from the blast hole. Spalling zones are also developed due to stress waves reflected from the free surfaces.

Effects of application methods of metam sodium and plastic covers on horizontal and vertical distributions of methyl isothiocyanate in bedded field plots.

PubMed

Ou, Li-Tse; Thomas, John E; Allen, L Hartwell; Vu, Joseph C; Dickson, Donald W

2006-08-01

This study was conducted to examine the effects of three application methods of metam sodium (broadcast, single irrigation drip tape delivery, and double irrigation drip tape delivery) and two plastic covers (polyethylene film and virtually impermeable film) on volatilization and on horizontal and vertical distributions of the biologically active product of metam sodium, methyl isothiocyanate (MITC), in field plots in a Florida sandy soil. Volatilization of MITC from field beds lasted for about 20 hours after completion of metam sodium application regardless of application methods. Virtually impermeable film (VIF) was a better barrier to reduce volatilization loss than polyethylene film (PE). Since water was not applied during broadcast application, MITC was mainly retained in the shallow soil layer (0- to 20-cm depth) and downward movement of MITC was limited to about 30 cm. Large values of standard deviation indicated that initial spatial distribution of MITC in the root zone (10- and 20-cm depths) of the two broadcast applied beds covered with PE or VIF was variable. Twice more water was delivered through the single drip tape than through individual tapes of double drip tape treatments during drip application of metam sodium. More water from the single drip tape likely facilitated downward movement of MITC to at least 60-cm depth, but MITC did not penetrate to this depth in the double drip tape beds. On the other hand, horizontal distribution of MITC in the root zone (10- and 20-cm depths) in the double drip tape beds was more uniform than in the single drip tape beds. More MITC was retained in the subsurface of the VIF-covered beds regardless of application methods than in the PE-covered beds.

Retinal lesions induce fast intrinsic cortical plasticity in adult mouse visual system.

PubMed

Smolders, Katrien; Vreysen, Samme; Laramée, Marie-Eve; Cuyvers, Annemie; Hu, Tjing-Tjing; Van Brussel, Leen; Eysel, Ulf T; Nys, Julie; Arckens, Lutgarde

2016-09-01

Neuronal activity plays an important role in the development and structural-functional maintenance of the brain as well as in its life-long plastic response to changes in sensory stimulation. We characterized the impact of unilateral 15° laser lesions in the temporal lower visual field of the retina, on visually driven neuronal activity in the afferent visual pathway of adult mice using in situ hybridization for the activity reporter gene zif268. In the first days post-lesion, we detected a discrete zone of reduced zif268 expression in the contralateral hemisphere, spanning the border between the monocular segment of the primary visual cortex (V1) with extrastriate visual area V2M. We could not detect a clear lesion projection zone (LPZ) in areas lateral to V1 whereas medial to V2M, agranular and granular retrosplenial cortex showed decreased zif268 levels over their full extent. All affected areas displayed a return to normal zif268 levels, and this was faster in higher order visual areas than in V1. The lesion did, however, induce a permanent LPZ in the retinorecipient layers of the superior colliculus. We identified a retinotopy-based intrinsic capacity of adult mouse visual cortex to recover from restricted vision loss, with recovery speed reflecting the areal cortical magnification factor. Our observations predict incomplete visual field representations for areas lateral to V1 vs. lack of retinotopic organization for areas medial to V2M. The validation of this mouse model paves the way for future interrogations of cortical region- and cell-type-specific contributions to functional recovery, up to microcircuit level. © 2015 Federation of European Neuroscience Societies and John Wiley & Sons Ltd.

Forming Ganymede's grooves at smaller strain: Toward a self-consistent local and global strain history for Ganymede

NASA Astrophysics Data System (ADS)

Bland, Michael T.; McKinnon, William B.

2015-01-01

The ubiquity of tectonic features formed in extension, and the apparent absence of ones formed in contraction, has led to the hypothesis that Ganymede has undergone global expansion in its past. Determining the magnitude of such expansion is challenging however, and extrapolation of locally or regionally inferred strains to global scales often results in strain estimates that exceed those based on global constraints. Here we use numerical simulations of groove terrain formation to develop a strain history for Ganymede that is generally consistent at local, regional, and global scales. These simulations reproduce groove-like amplitudes, wavelengths, and average slopes at modest regional extensions (10-15%). The modest strains are more consistent with global constraints on Ganymede's expansion. Yet locally, we also find that surface strains can be much larger (30-60%) in the same simulations, consistent with observations of highly-extended impact craters. Thus our simulations satisfy both the smallest-scale and largest-scale inferences of strain on Ganymede. The growth rate of the topography is consistent with (or exceeds) predictions of analytical models, and results from the use of a non-associated plastic rheology that naturally permits localization of brittle failure (plastic strain) into linear fault-like shear zones. These fault-like zones are organized into periodically-spaced graben-like structures with stepped, steeply-dipping faults. As in previous work, groove amplitudes and wavelengths depend on both the imposed heat flux and surface temperature, but because our brittle strength increases with depth, we find (for the parameters explored) that the growth rate of topography is initially faster for lower heat flows. We observe a transition to narrow rifting for higher heat flows and larger strains, which is a potential pathway for breakaway margin or band formation.

Forming Ganymede’s grooves at smaller strain: Toward a self-consistent local and global strain history for Ganymede

USGS Publications Warehouse

Bland, Michael T.; McKinnon, W. B.

2015-01-01

The ubiquity of tectonic features formed in extension, and the apparent absence of ones formed in contraction, has led to the hypothesis that Ganymede has undergone global expansion in its past. Determining the magnitude of such expansion is challenging however, and extrapolation of locally or regionally inferred strains to global scales often results in strain estimates that exceed those based on global constraints. Here we use numerical simulations of groove terrain formation to develop a strain history for Ganymede that is generally consistent at local, regional, and global scales. These simulations reproduce groove-like amplitudes, wavelengths, and average slopes at modest regional extensions (10–15%). The modest strains are more consistent with global constraints on Ganymede’s expansion. Yet locally, we also find that surface strains can be much larger (30–60%) in the same simulations, consistent with observations of highly-extended impact craters. Thus our simulations satisfy both the smallest-scale and largest-scale inferences of strain on Ganymede. The growth rate of the topography is consistent with (or exceeds) predictions of analytical models, and results from the use of a non-associated plastic rheology that naturally permits localization of brittle failure (plastic strain) into linear fault-like shear zones. These fault-like zones are organized into periodically-spaced graben-like structures with stepped, steeply-dipping faults. As in previous work, groove amplitudes and wavelengths depend on both the imposed heat flux and surface temperature, but because our brittle strength increases with depth, we find (for the parameters explored) that the growth rate of topography is initially faster for lower heat flows. We observe a transition to narrow rifting for higher heat flows and larger strains, which is a potential pathway for breakaway margin or band formation.

Rheological behavior of the crust and mantle in subduction zones in the time-scale range from earthquake (minute) to mln years inferred from thermomechanical model and geodetic observations

NASA Astrophysics Data System (ADS)

Sobolev, Stephan; Muldashev, Iskander

2016-04-01

The key achievement of the geodynamic modelling community greatly contributed by the work of Evgenii Burov and his students is application of "realistic" mineral-physics based non-linear rheological models to simulate deformation processes in crust and mantle. Subduction being a type example of such process is an essentially multi-scale phenomenon with the time-scales spanning from geological to earthquake scale with the seismic cycle in-between. In this study we test the possibility to simulate the entire subduction process from rupture (1 min) to geological time (Mln yr) with the single cross-scale thermomechanical model that employs elasticity, mineral-physics constrained non-linear transient viscous rheology and rate-and-state friction plasticity. First we generate a thermo-mechanical model of subduction zone at geological time-scale including a narrow subduction channel with "wet-quartz" visco-elasto-plastic rheology and low static friction. We next introduce in the same model classic rate-and state friction law in subduction channel, leading to stick-slip instability. This model generates spontaneous earthquake sequence. In order to follow in details deformation process during the entire seismic cycle and multiple seismic cycles we use adaptive time-step algorithm changing step from 40 sec during the earthquake to minute-5 year during postseismic and interseismic processes. We observe many interesting deformation patterns and demonstrate that contrary to the conventional ideas, this model predicts that postseismic deformation is controlled by visco-elastic relaxation in the mantle wedge already since hour to day after the great (M>9) earthquakes. We demonstrate that our results are consistent with the postseismic surface displacement after the Great Tohoku Earthquake for the day-to-4year time range.

The brittle-viscous-plastic evolution of shear bands in the South Armorican Shear Zone

NASA Astrophysics Data System (ADS)

Bukovská, Zita; Jeřábek, Petr; Morales, Luiz F. G.; Lexa, Ondrej; Milke, Ralf

2014-05-01

Shear bands are microscale shear zones that obliquely crosscut an existing anisotropy such as a foliation. The resulting S-C fabrics are characterized by angles lower than 45° and the C plane parallel to shear zone boundaries. The S-C fabrics typically occur in granitoids deformed at greenschist facies conditions in the vicinity of major shear zones. Despite their long recognition, mechanical reasons for localization of deformation into shear bands and their evolution is still poorly understood. In this work we focus on microscale characterization of the shear bands in the South Armorican Shear Zone, where the S-C fabrics were first recognized by Berthé et al. (1979). The initiation of shear bands in the right-lateral South Armorican Shear Zone is associated with the occurrence of microcracks crosscutting the recrystallized quartz aggregates that define the S fabric. In more advanced stages of shear band evolution, newly formed dominant K-feldspar, together with plagioclase, muscovite and chlorite occur in the microcracks, and the shear bands start to widen. K-feldspar replaces quartz by progressively bulging into the grain boundaries of recrystallized quartz grains, leading to disintegration of quartz aggregates and formation of fine-grained multiphase matrix mixture. The late stages of shear band development are marked by interconnection of fine-grained white mica into a band that crosscuts the original shear band matrix. In its extremity, the shear band widening may lead to the formation of ultramylonites. With the increasing proportion of shear band matrix from ~1% to ~12%, the angular relationship between S and C fabrics increases from ~30° to ~40°. The matrix phases within shear bands show differences in chemical composition related to distinct evolutionary stages of shear band formation. The chemical evolution is well documented in K-feldspar, where the albite component is highest in porphyroclasts within S fabric, lower in the newly formed grains within microcracks and nearly absent in matrix grains in the well developed C bands. The chemical variation between primary and secondary new-formed micas was clearly identified by the Mg-Ti-Na content. The microstructural analysis documents a progressive decrease in quartz grain size and increasing interconnectivity of K-feldspar and white mica towards more mature shear bands. The contact-frequency analysis demonstrates that the phase distribution in shear bands tends to evolve from quartz aggregate distribution via randomization to K-feldspar aggregate distribution. The boundary preferred orientation is absent in quartz-quartz contacts either inside of outside the C bands, while it changes from random to parallel to the C band for the K-feldspar and and K-feldspar-quartz boundaries. The lack of crystallographic preferred orientation of the individual phases in the mixed matrix of the C planes suggests a dominant diffusion-assisted grain boundary sliding deformation mechanism. In the later stages of shear band development, the deformation is accommodated by crystal plasticity of white mica in micaceous bands. The crystallographic and microstructural data thus indicate two important switches in deformation mechanisms, from (i) brittle to Newtonian viscous behavior in the initial stages of shear band evolution and from (ii) Newtonian viscous to power law in the later evolutionary stages. The evolution of shear bands in the South Armorican Shear Zone thus document the interplay between deformation mechanisms and chemical reactions in deformed granitoids.

Electron Backscatter Diffraction (EBSD) Analysis and U-Pb Geochronology of the Oldest Lunar Zircon: Constraining Early Lunar Differentiation and Dating Impact-Related Deformation

NASA Technical Reports Server (NTRS)

Timms, Nick; Nemchin, Alexander; Grange, Marion; Reddy, Steve; Pidgeon, Bob; Geisler, Thorsten; Meyer, Chuck

2009-01-01

The evolution of the early moon was dominated by two processes (i) crystallization of the Lunar Magma Ocean (LMO) and differentiation of potassium-rare earth element-phosphorous-rich residual magma reservoir referred to as KREEP, and (ii) an intense meteorite bombardment referred to as lunar cataclysm . The exact timing of these processes is disputed, and resolution relies on collection and interpretation of precise age data. This study examines the microstructure and geochronology of zircon from lunar impact breccias collected during the Apollo 17 mission. A large zircon clast within lunar breccia 72215,195 shows sector zoning in optical microscopy, cathodoluminescence (CL) imaging and Raman mapping, and indicates that it was a relict fragment of a much larger magmatic grain. Sensitive high resolution ion microprobe (SHRIMP) U-Pb analysis of the zircon shows that U and Th concentration correlate with sector zoning, with darkest CL domains corresponding with high-U and Th (approx.150 and approx.100 ppm respectively), and the brightest-CL sectors containing approx.30-50 ppm U and approx.10-20 ppm Th. This indicates that variations in optical CL and Raman properties correspond to differential accumulation of alpha-radiation damage in each sector. Electron backscatter diffraction (EBSD) mapping shows that the quality of electron backscatter patterns (band contrast) varies with sector zoning, with the poorest quality patterns obtained from high-U and Th, dark-CL zones. EBSD mapping also reveals a deformation microstructure that is cryptic in optical, CL and Raman imaging. Two orthogonal sets of straight discrete and gradational low-angle boundaries accommodate approx.12 misorientation across the grain. The deformation bands are parallel to the crystallographic {a}-planes of the zircon, have misorientation axes parallel to the c-axis, and are geometrically consistent with formation by dislocation creep associated with <100>{010} slip. The deformation bands are unlike curved morphology of crystal-plastic microstructures in tectonically deformed terrestrial zircon, and geometrically similar to dislocation microstructures reported in experimentally shocked zircon. We interpret these crystal-plastic deformation microstructures to have resulted from a significant impact, either directly from impact shock, or during ductile flow directly following the impact. The deformation bands appear to continue undeflected through the non-indexed, radiation-damaged areas of the grain, which suggests that the orientation variation predates any significant mechanical weakening from radiation damage in the grain, and therefore occurred early in its history.

Frictional behavior of carbonate-rich sediments in subduction zones

NASA Astrophysics Data System (ADS)

Rabinowitz, H. S.; Savage, H. M.; Carpenter, B. M.; Collettini, C.

2016-12-01

Deformation in rocks and sediments is controlled by multiple mechanisms, each governed by its own pressure- (P), temperature- (T), and slip velocity- (v) dependent kinetics. Frictional behavior depends on which of these mechanisms are dominant, and, thus, varies with P, T, and v. Carbonates are a useful material with which to interrogate the PTv controls on friction due to the fact that a wide range of mechanisms can be easily accessed in the lab at geologically relevant conditions. In addition, carbonate-rich layers make up a significant component of subducting sediments around the world and may impact the frictional behavior of shallow subduction zones. In order to investigate the effect of carbonate subduction and the evolution of friction at subduction zone conditions, we conducted deformation experiments on input sediments for two subduction zones, the Hikurangi trench, New Zealand (ODP Site 1124) and the Peru trench (DSDP Site 321), which have carbonate/clay contents of 40/60 wt% and 80/20 wt%, respectively. Samples were saturated with distilled water mixed with 35g/l sea salt and deformed at room temperature. Experiments were conducted at σeff = 1-100 MPa and T = 20-100 °C with sliding velocities of 1-300 μm/s and hold times of 1-1000 s. We test the changes in velocity dependence and healing over these PT conditions to elucidate the frictional behavior of carbonates in subduction zone settings. The mechanical results are complemented by microstructural analysis. In lower stress experiments, there is no obvious shear localization; however, by 25 MPa, pervasive boundary-parallel shears become dominant, particularly in the Peru samples. Optical observations of these shear zones under cross-polarized light show evidence of plastic deformation (CPO development) while SEM-EDS observations indicate phase segregation in the boundary shears. Degree of microstructural localization appears to correspond with the trends observed in velocity-dependence. Our preliminary results indicate that carbonate/clay compositions could have a significant impact on the frictional behavior of subducting sediments.

Modelling of the Vajont rockslide displacements by delayed plasticity of interacting sliding blocks

NASA Astrophysics Data System (ADS)

Castellanza, riccardo; Hedge, Amarnath; Crosta, Giovanni; di Prisco, Claudio; Frigerio, Gabriele

2015-04-01

In order to model complex sliding masses subject to continuous slow movements related to water table fluctuations it is convenient to: i) model the time-dependent mechanical behaviour of the materials by means of a viscous-plastic constitutive law; ii) assume the water table fluctuation as the main input to induce displacement acceleration; iii) consider, the 3D constrains by maintaining a level of simplicity such to allow the implementation into EWS (Early Warning System) for risk management. In this work a 1D pseudo-dynamic visco-plastic model (Secondi et al. 2011), based on Perzyna's delayed plasticity theory is applied. The sliding mass is considered as a rigid block subject to its self weight, inertial forces and seepage forces varying with time. All non-linearities are lumped in a thin layer positioned between the rigid block and the stable bedrock. The mechanical response of this interface is assumed to be visco-plastic. The viscous nucleus is assumed to be of the exponential type, so that irreversible strains develop for both positive and negative values of the yield function; the sliding mass is discretized in blocks to cope with complex rockslide geometries; the friction angle is assumed to reduce with strain rate assuming a sort of strain - rate law (Dietrich-Ruina law). To validate the improvements introduced in this paper the simulation of the displacements of the Vajont rockslide from 1960 to the failure, occurred on October the 9th 1963, is perfomed. It will be shown that, in its modified version, the model satisfactorily fits the Vajont pre-collapse displacements triggered by the fluctuation of the Vajont lake level and the associated groundwater level. The model is able to follow the critical acceleration of the motion with a minimal change in friction properties.The discretization in interacting sliding blocks confirms its suitability to model the complex 3D rockslide behaviour. We are currently implementing a multi-block model capable to include the mutual influence of multiple blocks, characterized by different geometry and groundwater levels, shear zone properties and type of interconnection. Secondi M., Crosta G., Di Prisco C., Frigerio G., Frattini P., Agliardi F. (2011) "Landslide motion forecasting by a dynamic visco-plastic model", Proc. The Second World Landslide Forum, L09 - Advances in slope modelling, Rome, 3-9 October 2011, paper WLF2-2011-0571

Application of FE software Elmer to the modeling of crustal-scale processes

NASA Astrophysics Data System (ADS)

Maierová, Petra; Guy, Alexandra; Lexa, Ondrej; Cadek, Ondrej

2010-05-01

We extended Elmer (the open source finite element software for multiphysical problems, http://www.csc.fi/english/pages/elmer) by user-written procedures for the two-dimensional modeling of crustal-scale processes. The standard version of Elmer is an appropriate tool for modeling of thermomechanical convection with non-linear viscous rheology. In geophysics, it might be suitable for some type of mantle convection modeling. Unlike the mantle, the crust is very heterogeneous. It consists of materials with distinct rheological properties that are subject to highly varied conditions: low pressure and temperature near the surface of the Earth and relatively high pressure and temperature at a depth of several tens of kilometers. Moreover, the deformation in the upper crust is mostly brittle and the strain is concentrated into narrow shear zones and thrusts. In order to simulate the brittle behavior of the crust, we implemented pressure-dependent visco-plastic rheology. The material heterogeneity and chemical convection is implemented in terms of active markers. Another special feature of the crust, the moving free surface, is already included in Elmer by means of a moving computational grid. Erosion can easily be added in this scheme. We tested the properties of our formulation of plastic flow on several numerical experiments simulating the deformation of material under compressional and extensional stresses. In the first step, we examined angles of shear zones that form in a plastically deforming material for different material parameters and grid resolutions. A more complex setting of "sandbox-type" experiments containing heterogeneous material, strain-softening and boundary friction was considered as a next testing case. To illustrate the abilities of the extended Elmer software in crustal deformation studies, we present two models of geological processes: diapirism of the lower crust and a channel flow forced by indentation. Both these processes are assumed to take place during the late stage of the Variscan orogeny in the area of the Bohemian Massif and they are well documented in the geological record. Extensive geological data are thus available and they can be compared with the results of our numerical simulations. Firstly, we model the indentation of a stiff block into a thick and hot crustal root and the consequent flow of the orogenic crust. For the development of the flow, the free surface deformation and erosion are essential. The importance of plastic deformation varies with the thermal structure of the domain. Secondly, we show an influence of thermal, density and viscosity structure of the crust on the time evolution and the final geometry of diapirs. The importance of the strain-rate dependence of viscosity, which is neglected in some numerical models, is discussed.

Characterization and antimicrobial activity of sweetpotato starch-based edible film containing origanum (Thymus capitatus) oil.

PubMed

Ehivet, Fabienne E; Min, Byungjin; Park, Mi-Kyung; Oh, Jun-Hyun

2011-01-01

The objectives of this research were to characterize the mechanical and barrier properties of sweetpotato starch (SPS)-based film (SPSF) and to investigate the antimicrobial activity of SPSF containing origanum oil (OG) against foodborne pathogenic bacteria. The SPSF was fabricated with the SPS extracted from commercial sweetpotato roots. Tensile strength (TS), percent elongation at break (E), and water vapor permeability (WVP) were determined to characterize the SPSF fabricated with selected SPS concentrations, plasticizers, and the concentrations of plasticizers. The agar diffusion assay was used to determine the antimicrobial activity of SPSF containing selective concentrations of OG against Salmonella Enteritidis, Escherichia coli O157:H7, and Listeria monocytogenes. The SPSF fabricated with 2.5% SPS exhibited the greatest TS (4.58 MPa). The TS, E, and WVP of SPSF plasticized with 40% sorbitol exhibited 7.96 MPa, 77.92%, 0.212 ng m/m(2) S Pa, respectively. Therefore, the SPSF fabricated with 2.5% SPS and 40% sorbitol was determined as the optimum film. The antimicrobial activity of the SPSF containing OG increased as the concentration of OG increased. And the SPSF containing OG exhibited greater inhibitory effects against the gram-negative bacteria such as S. Enteritidis and E. coli O157:H7 than the gram-positive L. monocytogenes. The greatest antimicrobial activity was observed against S. Enteritidis when the SPSF containing 2% OG was applied, and the maximum square of zone width was 18.43 mm(2).

Quality of Tourist Beaches in Huatulco, SW of Mexico: Multiproxy Studies

NASA Astrophysics Data System (ADS)

Retama, I.; Jonathan, M. P.; Rodriguez-Espinosa, P. F.

2014-12-01

40 beach water and sediment samples were collected from the inter-tidal zones of tourist beaches of Huatulco in the State of Oaxaca, South Western part of Mexico. The samples were collected in an aim to know the concentration pattern of metals (Cu, Cd, Cr, Ni, Pb, Zn, Co, Mn, Fe, As, Hg) in sediments and microplastics. Physico-chemical parameters like temperature, pH, dissolved oxygen, conductivity and total dissolved solids, salinity and redox potential. Collection of samples was done during the peak season in April 2013. Our results from water samples indicate that the physico-chemical conditions of the beach water have been altered due to human activities in large numbers. The bioavailable metal concentrations indicate that enrichment of Pb, Cd, Cr and As and it is also supported by the higher values observed from the calculation of enrichment factor and geoaccumulation index. The higher values in the sediments is either due to natural sources like chemical weathering of rocks and external sources, which points to high tourism, agricultural activities in the region. Identification of micro-plastics was done through SEM photographs, indicating the type of plastic wastes deposited into the beach regions which can indicate the density, durability and the persistence level in the sediments. Eventhough the enrichment of metals and modification of beach water quality is observed, care need to be taken to avoid further damage to the coastal ecosystem. Keywords: Tourism, Beach sediments, Beach water, Micro plastics, Trace metals, Contamination indices, Huatulco, Mexico.