The Effect of Strain on the Base Resistance and Transit Time of Ungraded and Compositional-Graded SiGe HBTs

NASA Technical Reports Server (NTRS)

Rosenfeld, D.; Alterovitz, S. A.

1994-01-01

A theoretical study of the effects of the strain on the base properties of ungraded and compositional-graded n-p-n SiGe Heterojunction Bipolar Transistors (HBT) is presented. The dependencies of the transverse hole mobility and longitudinal electron mobility upon strain, composition and doping, are formulated using published Monte-Carlo data and, consequently, the base resistance and transit time are modeled and calculated. The results are compared to results obtained using common formulas that ignore these dependencies. The differences between the two sets of results are shown. The paper's conclusion is that for the design, analysis and optimization of high frequency SiGe HBTs the strain effects on the base properties cannot be ignored.

Protocol dependence of mechanical properties in granular systems.

PubMed

Inagaki, S; Otsuki, M; Sasa, S

2011-11-01

We study the protocol dependence of the mechanical properties of granular media by means of computer simulations. We control a protocol of realizing disk packings in a systematic manner. In 2D, by keeping material properties of the constituents identical, we carry out compaction with various strain rates. The disk packings exhibit the strain rate dependence of the critical packing fraction above which the pressure becomes non-zero. The observed behavior contrasts with the well-studied jamming transitions for frictionless disk packings. We also observe that the elastic moduli of the disk packings depend on the strain rate logarithmically. Our results suggest that there exists a time-dependent state variable to describe macroscopic material properties of disk packings, which depend on its protocol.

Loading direction-dependent shear behavior at different temperatures of single-layer chiral graphene sheets

NASA Astrophysics Data System (ADS)

Zhao, Yang; Dong, Shuhong; Yu, Peishi; Zhao, Junhua

2018-06-01

The loading direction-dependent shear behavior of single-layer chiral graphene sheets at different temperatures is studied by molecular dynamics (MD) simulations. Our results show that the shear properties (such as shear stress-strain curves, buckling strains, and failure strains) of chiral graphene sheets strongly depend on the loading direction due to the structural asymmetry. The maximum values of both the critical buckling shear strain and the failure strain under positive shear deformation can be around 1.4 times higher than those under negative shear deformation. For a given chiral graphene sheet, both its failure strain and failure stress decrease with increasing temperature. In particular, the amplitude to wavelength ratio of wrinkles for different chiral graphene sheets under shear deformation using present MD simulations agrees well with that from the existing theory. These findings provide physical insights into the origins of the loading direction-dependent shear behavior of chiral graphene sheets and their potential applications in nanodevices.

Stress generation in a developmental context: the role of youth depressive symptoms, maternal depression, the parent-child relationship, and family stress.

PubMed

Chan, Priscilla T; Doan, Stacey N; Tompson, Martha C

2014-02-01

The present study examined stress generation in a developmental and family context among 171 mothers and their preadolescent children, ages 8-12 years, at baseline (Time 1) and 1-year follow-up (Time 2). In the current study, we examined the bidirectional relationship between children's depressive symptoms and dependent family stress. Results suggest that children's baseline level of depressive symptoms predicted the generation of dependent family stress 1 year later. However, baseline dependent family stress did not predict an increase in children's depressive symptoms 1 year later. In addition, we examined whether a larger context of both child chronic strain (indicated by academic, behavioral, and peer stress) and family factors, including socioeconomic status and parent-child relationship quality, would influence the stress generation process. Although both chronic strain and socioeconomic status were not associated with dependent family stress at Time 2, poorer parent-child relationship quality significantly predicted greater dependent family stress at Time 2. Child chronic strain, but neither socioeconomic status nor parent-child relationship quality, predicted children's depression symptoms at Time 2. Finally, gender, maternal depression history, and current maternal depressive symptoms did not moderate the relationship between level of dependent family stress and depressive symptoms. Overall, findings provide partial support for a developmental stress generation model operating in the preadolescent period.

Characterization of a Strain Rate Transient Along the San Andreas and San Jacinto Faults Following the October 1999 Hector Mine Earthquake.

NASA Astrophysics Data System (ADS)

Hernandez, D.; Holt, W. E.; Bennett, R. A.; Dimitrova, L.; Haines, A. J.

2006-12-01

We are continuing work on developing and refining a tool for recognizing strain rate transients as well as for quantifying the magnitude and style of their temporal and spatial variations. We determined time-averaged velocity values in 0.05 year epochs using time-varying velocity estimates for continuous GPS station data from the Southern California Integrated GPS Network (SCIGN) for the time period between October 1999 and February 2004 [Li et al., 2005]. A self-consistent model velocity gradient tensor field solution is determined for each epoch by fitting bi-cubic Bessel interpolation to the GPS velocity vectors and we determine model dilatation strain rates, shear strain rates, and the rotation rates. Departures of the time dependent model strain rate and velocity fields from a master solution, obtained from a time-averaged solution for the period 1999-2004, with imposed plate motion constraints and Quaternary fault data, are evaluated in order to best characterize the time dependent strain rate field. A particular problem in determining the transient strain rate fields is the level of smoothing or damping that is applied. Our current approach is to choose a damping that both maximizes the departure of the transient strain rate field from the long-term master solution and achieves a reduced chi-squared value between model and observed GPS velocities of around 1.0 for all time epochs. We observe several noteworthy time-dependent changes. First, in the Eastern California Shear Zone (ECSZ) region, immediately following the October 1999 Hector Mine earthquake, there occurs a significant spatial increase of relatively high shear strain rate, which encompasses a significant portion of the ECSZ. Second, also following the Hector Mine event, there is a strain rate corridor that extends through the Pinto Mt. fault connecting the ECSZ to the San Andreas fault segment in the Salton Trough region. As this signal slowly decays, shear strain rates on segments of the San Andreas fault, just east of Palm Springs, and the San Jacinto fault increase during 2001-2004. During this period shear strain rates increase by roughly 20 nanostrain per year on the San Andreas fault and 20-30 nanostrain per year on the San Jacinto fault (over a zone approximately 20 km wide). Lastly, a further investigation into this strain rate recovery reveals a power law flow mechanism during the first six months after the earthquake for the Anza segment, after which strain rates appear to reach a steady state for the remainder of the data. Moreover, seismicity rates increase along these segments following the period of shear strain rate increase. These results quantify the spatial coverage of the strain rate changes and provide some bounds on their magnitude and confidence, as well as constraints on the associated regional rheology and interseismic cycle strain rate pattern. The compiled epoch solution "movies" may be viewed at the additional resources site.

Tensile properties of latex paint films with TiO2 pigment

NASA Astrophysics Data System (ADS)

Hagan, Eric W. S.; Charalambides, Maria N.; Young, Christina T.; Learner, Thomas J. S.; Hackney, Stephen

2009-05-01

The tensile properties of latex paint films containing TiO2 pigment were studied with respect to temperature, strain-rate and moisture content. The purpose of performing these experiments was to assist museums in defining safe conditions for modern paintings held in collections. The glass transition temperature of latex paint binders is in close proximity to ambient temperature, resulting in high strain-rate dependence in typical exposure environments. Time dependence of modulus and failure strain is discussed in the context of time-temperature superposition, which was used to extend the experimental time scale. Nonlinear viscoelastic material models are also presented, which incorporate a Prony series with the Ogden or Neo-Hookean hyperelastic function for different TiO2 concentrations.

Computer program for predicting creep behavior of bodies of revolution

NASA Technical Reports Server (NTRS)

Adams, R.; Greenbaum, G.

1971-01-01

Computer program, CRAB, uses finite-element method to calculate creep behavior and predict steady-state stresses in an arbitrary body of revolution subjected to a time-dependent axisymmetric load. Creep strains follow a time hardening law and a Prandtl-Reuss stress-strain relationship.

Determination of forming limit diagrams of AA6013-T6 aluminum alloy sheet using a time and position dependent localized necking criterion

NASA Astrophysics Data System (ADS)

Dicecco, S.; Butcher, C.; Worswick, M.; Boettcher, E.; Chu, E.; Shi, C.

2016-11-01

The forming limit behaviour of AA6013-T6 aluminium alloy sheet was characterized under isothermal conditions at room temperature (RT) and 250°C using limiting dome height (LDH) tests. Full field strain measurements were acquired throughout testing using in situ stereoscopic digital image correlation (DIC) techniques. Limit strain data was generated from the resulting full field strain measurements using two localized necking criteria: ISO12004- 2:2008 and a time and position dependent criterion, termed the “Necking Zone” (NZ) approach in this paper, introduced by Martinez-Donaire et al. (2014). The limit strains resulting from the two localization detection schemes were compared. It was found that the ISO and NZ limit strains at RT are similar on the draw-side of the FLD, while the NZ approach yields a biaxial major limit strain 14.8% greater than the ISO generated major limit strain. At 250°C, the NZ generated major limit strains are 31-34% greater than the ISO generated major limit strains for near uniaxial, plane strain and biaxial loading conditions, respectively. The significant variance in limit strains between the two methodologies at 250°C highlights the need for a validation study regarding warm FLC determination.

Immunity against influenza A(H1N1) infections is determined by age at the time of initial strain circulation.

PubMed

Delabre, R M; Salez, N; Lapidus, N; Lemaitre, M; Leruez-Ville, M; de Lamballerie, X; Carrat, F

2017-01-01

We explored age-dependent patterns in haemagglutination inhibition (HI) titre to seasonal [1956 A(H1N1), 1977 A(H1N1), 2007 A(H1N1)] and pandemic [A(H1N1)pdm09] influenza strains using serological data collected from an adult French influenza cohort. Subjects were recruited by their general practitioners from 2008 to 2009 and followed until 2010. We explored age-related differences between strain-specific HI titres using 1053 serological samples collected over the study period from 398 unvaccinated subjects. HI titres against the tested seasonal and pandemic strains were determined using the HI technique. Geometric mean titres (GMTs) were estimated using regression models for interval-censored data. Generalized additive mixed models were fit to log-transformed HI estimates to study the relationship between HI titre and age (age at inclusion and/or age at initial strain circulation). GMT against one strain was consistently highest in the birth cohort exposed to that strain during childhood, with peak titres observed in subjects aged 7-8 years at the time of initial strain circulation. Our results complete previous findings on influenza A(H3N2) strains and identify a strain-dependent relationship between HI titre and age at initial strain circulation.

The development and validation of a numerical integration method for non-linear viscoelastic modeling

PubMed Central

Ramo, Nicole L.; Puttlitz, Christian M.

2018-01-01

Compelling evidence that many biological soft tissues display both strain- and time-dependent behavior has led to the development of fully non-linear viscoelastic modeling techniques to represent the tissue’s mechanical response under dynamic conditions. Since the current stress state of a viscoelastic material is dependent on all previous loading events, numerical analyses are complicated by the requirement of computing and storing the stress at each step throughout the load history. This requirement quickly becomes computationally expensive, and in some cases intractable, for finite element models. Therefore, we have developed a strain-dependent numerical integration approach for capturing non-linear viscoelasticity that enables calculation of the current stress from a strain-dependent history state variable stored from the preceding time step only, which improves both fitting efficiency and computational tractability. This methodology was validated based on its ability to recover non-linear viscoelastic coefficients from simulated stress-relaxation (six strain levels) and dynamic cyclic (three frequencies) experimental stress-strain data. The model successfully fit each data set with average errors in recovered coefficients of 0.3% for stress-relaxation fits and 0.1% for cyclic. The results support the use of the presented methodology to develop linear or non-linear viscoelastic models from stress-relaxation or cyclic experimental data of biological soft tissues. PMID:29293558

Time and dose-dependence evaluation of nitroheterocyclic drugs for improving efficacy following Trypanosoma cruzi infection: A pre-clinical study.

PubMed

Mazzeti, Ana Lia; Diniz, Lívia de F; Gonçalves, Karolina R; Nascimento, Alvaro F S; Spósito, Pollyanna A F; Mosqueira, Vanessa C F; Machado-Coelho, George L L; Ribeiro, Isabela; Bahia, Maria T

2018-02-01

Benznidazole and nifurtimox-treatments regimens currently used in human are supported by very limited experimental data. This study was designed to evaluate the time and dose dependence for efficacy of the most important nitroheterocyclic drugs in use for Chagas disease. In order to evaluate time dependence, Y strain-infected mice received benznidazole for a total of 1, 3, 7, 10, 20, and 40 days. Treatment courses of 3-10-day were effective in clearing parasitaemia and suppressing mortality, but parasitological cure was not achieved. Extending the treatments to 20 or 40 days clearly improved benznidazole efficacy. The 20-day treatment induced cure in 57.1% of Y strain infections (partially drug resistant) but failed to cure Colombian strain infections (full drug resistant), while the 40-day treatment resulted in cure of 100% of Y and 50% of Colombian strain infected mice. The increased cure rates in T. cruzi infected animals that received nifurtimox for 40 days confirm the relationship between the length of treatment and efficacy. An improvement in efficacy was observed with increasing benznidazole doses; cure was verified in 28.6% (75 mg/kg), 57.1% (100 mg/kg) and 80% (300 mg/kg). Overall, these nonclinical study data provide evidence that the efficacy of benznidazole is dose and time dependent. These findings may be relevant for optimizing treatment of human Chagas disease. Copyright © 2018 Elsevier Inc. All rights reserved.

The roles of time and displacement in velocity-dependent volumetric strain of fault zones

USGS Publications Warehouse

Beeler, N.M.; Tullis, T.E.

1997-01-01

The relationship between measured friction??A and volumetric strain during frictional sliding was determined using a rate and state variable dependent friction constitutive equation, a common work balance relating friction and volume change, and two types of experimental faults: initially bare surfaces of Westerly granite and rock surfaces separated by a 1 mm layer of < 90 ??m Westerly granite gouge. The constitutive equation is the sum of a constant term representing the nominal resistance to sliding and two smaller terms: a rate dependent term representing the shear viscosity of the fault surface (direct effect), and a term which represents variations in the area of contact (evolution effect). The work balance relationship requires that ??A differs from the frictional resistance that leads to shear heating by the derivative of fault normal displacement with respect shear displacement, d??n ld??s. An implication of this relationship is that the rate dependence of d??n ld??s contributes to the rate dependence of ??A. Experiments show changes in sliding velocity lead to changes in both fault strength and volume. Analysis of data with the rate and state equations combined with the work balance relationship preclude the conventional interpretation of the direct effect in the rate and state variable constitutive equations. Consideration of a model bare surface fault consisting of an undeformable indentor sliding on a deformable surface reveals a serious flaw in the work balance relationship if volume change is time-dependent. For the model, at zero slip rate indentation creep under the normal load leads to time-dependent strengthening of the fault surface but, according to the work balance relationship, no work is done because compaction or dilatancy can only be induced by shearing. Additional tests on initially bare surfaces and gouges show that fault normal strain in experiments is time-dependent, consistent with the model. This time-dependent fault normal strain, which is not accounted for in the work balance relationship, explains the inconsistency between the constitutive equations and the work balance. For initially bare surface faults, all rate dependence of volume change is due to time dependence. Similar results are found for gouge. We conclude that ??A reflects the frictional resistance that results in shear heating, and no correction needs to be made for the volume changes. The result that time-dependent volume changes do not contribute to ??A is a general result and extends beyond these experiments, the simple indentor model and particular constitutive equations used to illustrate the principle.

Comparative analysis of growth-phase-dependent gene expression in virulent and avirulent Streptococcus pneumoniae using a high-density DNA microarray.

PubMed

Ko, Kwan Soo; Park, Sulhee; Oh, Won Sup; Suh, Ji-Yoeun; Oh, Taejeong; Ahn, Sungwhan; Chun, Jongsik; Song, Jae-Hoon

2006-02-28

The global pattern of growth-dependent gene expres-sion in Streptococcus pneumoniae strains was evalu-ated using a high-density DNA microarray. Total RNAs obtained from an avirulent S. pneumoniae strain R6 and a virulent strain AMC96-6 were used to compare the expression patterns at seven time points (2.5, 3.5, 4.5, 5.5, 6.0, 6.5, and 8.0 h). The expression profile of strain R6 changed between log and station-ary growth (the Log-Stat switch). There were clear differences between the growth-dependent gene ex-pression profiles of the virulent and avirulent pneumo-coccal strains in 367 of 1,112 genes. Transcripts of genes associated with bacterial competence and capsular polysaccharide formation, as well as clpP and cbpA, were higher in the virulent strain. Our data suggest that late log or early stationary phase may be the most virulent phase of S. pneumoniae.

Experimental Characterization of Stress- and Strain-Dependent Stiffness in Grouted Rock Masses.

PubMed

Kim, Ji-Won; Chong, Song-Hun; Cho, Gye-Chun

2018-03-29

Grouting of fractured rock mass prior to excavation results in grout-filled discontinuities that govern the deformation characteristics of a site. The influence of joint characteristics on the properties of grouted rocks is important in assessing the effects of grouting on jointed rock mass. However, grouting remains a predominantly empirical practice and the effects of grouting on rock joint behavior and material properties have yet to be accurately assessed. Granular materials, including jointed rocks, typically display nonlinear strain-dependent responses that can be characterized by the shear modulus degradation curve. In this study, the effects of grouting on the strain-dependent shear stiffness of jointed rock mass were investigated at the small-strain (below 10 -5 ) and mid-strain (10 -5 to 10 -3 ) ranges using the quasi-static resonant column test and rock mass dynamic test devices. The effects of curing time, axial stress, initial joint roughness, and grouted joint thickness were examined. The results show that (1) grouting of rock joints leads to decreased stress sensitivity and increased small-strain shear stiffness for all tested samples; (2) the grouted rock samples display similar modulus degradation characteristics as the applied grout material; (3) the initial joint roughness determines the stress-dependent behaviors and general stiffness range of the jointed and grouted rocks, but the strain-dependent behaviors are dependent on the properties of the grout material; (4) increased grouted joint thickness results in larger contribution of the grout properties in the overall grouted rock mass.

Experimental Characterization of Stress- and Strain-Dependent Stiffness in Grouted Rock Masses

PubMed Central

Cho, Gye-Chun

2018-01-01

Grouting of fractured rock mass prior to excavation results in grout-filled discontinuities that govern the deformation characteristics of a site. The influence of joint characteristics on the properties of grouted rocks is important in assessing the effects of grouting on jointed rock mass. However, grouting remains a predominantly empirical practice and the effects of grouting on rock joint behavior and material properties have yet to be accurately assessed. Granular materials, including jointed rocks, typically display nonlinear strain-dependent responses that can be characterized by the shear modulus degradation curve. In this study, the effects of grouting on the strain-dependent shear stiffness of jointed rock mass were investigated at the small-strain (below 10−5) and mid-strain (10−5 to 10−3) ranges using the quasi-static resonant column test and rock mass dynamic test devices. The effects of curing time, axial stress, initial joint roughness, and grouted joint thickness were examined. The results show that (1) grouting of rock joints leads to decreased stress sensitivity and increased small-strain shear stiffness for all tested samples; (2) the grouted rock samples display similar modulus degradation characteristics as the applied grout material; (3) the initial joint roughness determines the stress-dependent behaviors and general stiffness range of the jointed and grouted rocks, but the strain-dependent behaviors are dependent on the properties of the grout material; (4) increased grouted joint thickness results in larger contribution of the grout properties in the overall grouted rock mass. PMID:29596371

Low-temperature creep of austenitic stainless steels

NASA Astrophysics Data System (ADS)

Reed, R. P.; Walsh, R. P.

2017-09-01

Plastic deformation under constant load (creep) in austenitic stainless steels has been measured at temperatures ranging from 4 K to room temperature. Low-temperature creep data taken from past and unreported austenitic stainless steel studies are analyzed and reviewed. Creep at cryogenic temperatures of common austenitic steels, such as AISI 304, 310 316, and nitrogen-strengthened steels, such as 304HN and 3116LN, are included. Analyses suggests that logarithmic creep (creep strain dependent on the log of test time) best describe austenitic stainless steel behavior in the secondary creep stage and that the slope of creep strain versus log time is dependent on the applied stress/yield strength ratio. The role of cold work, strain-induced martensitic transformations, and stacking fault energy on low-temperature creep behavior is discussed. The engineering significance of creep on cryogenic structures is discussed in terms of the total creep strain under constant load over their operational lifetime at allowable stress levels.

Time-dependent response of filamentary composite spherical pressure vessels

NASA Technical Reports Server (NTRS)

Dozier, J. D.

1983-01-01

A filamentary composite spherical pressure vessel is modeled as a pseudoisotropic (or transversely isotropic) composite shell, with the effects of the liner and fill tubes omitted. Equations of elasticity, macromechanical and micromechanical formulations, and laminate properties are derived for the application of an internally pressured spherical composite vessel. Viscoelastic properties for the composite matrix are used to characterize time-dependent behavior. Using the maximum strain theory of failure, burst pressure and critical strain equations are formulated, solved in the Laplace domain with an associated elastic solution, and inverted back into the time domain using the method of collocation. Viscoelastic properties of HBFR-55 resin are experimentally determined and a Kevlar/HBFR-55 system is evaluated with a FORTRAN program. The computed reduction in burst pressure with respect to time indicates that the analysis employed may be used to predict the time-dependent response of a filamentary composite spherical pressure vessel.

[Three-dimensional stress analysis of periodontal ligament of mandible incisors fixed bridge abutments under dynamic loads by finite element method].

PubMed

Ma, Da; Tang, Liang; Pan, Yan-Huan

2007-12-01

Three-dimensional finite method was used to analyze stress and strain distributions of periodontal ligament of abutments under dynamic loads. Finite element analysis was performed on the model under dynamic loads with vertical and oblique directions. The stress and strain distributions and stress-time curves were analyzed to study the biomechanical behavior of periodontal ligament of abutments. The stress and strain distributions of periodontal ligament under dynamic load were same with the static load. But the maximum stress and strain decreased apparently. The rate of change was between 60%-75%. The periodontal ligament had time-dependent mechanical behaviors. Some level of residual stress in periodontal ligament was left after one mastication period. The stress-free time under oblique load was shorter than that of vertical load. The maximum stress and strain decrease apparently under dynamic loads. The periodontal ligament has time-dependent mechanical behaviors during one mastication. There is some level of residual stress left after one mastication period. The level of residual stress is related to the magnitude and the direction of loads. The direction of applied loads is one important factor that affected the stress distribution and accumulation and release of abutment periodontal ligament.

Stress/strain changes and triggered seismicity at The Geysers, California

USGS Publications Warehouse

Gomberg, J.; Davis, S.

1996-01-01

The principal results of this study of remotely triggered seismicity in The Geysers geothermal field are the demonstration that triggering (initiation of earthquake failure) depends on a critical strain threshold and that the threshold level increases with decreasing frequency or equivalently, depends on strain rate. This threshold function derives from (1) analyses of dynamic strains associated with surface waves of the triggering earthquakes, (2) statistically measured aftershock zone dimensions, and (3) analytic functional representations of strains associated with power production and tides. The threshold is also consistent with triggering by static strain changes and implies that both static and dynamic strains may cause aftershocks. The observation that triggered seismicity probably occurs in addition to background activity also provides an important constraint on the triggering process. Assuming the physical processes underlying earthquake nucleation to be the same, Gomberg [this issue] discusses seismicity triggered by the MW 7.3 Landers earthquake, its constraints on the variability of triggering thresholds with site, and the implications of time delays between triggering and triggered earthquakes. Our results enable us to reject the hypothesis that dynamic strains simply nudge prestressed faults over a Coulomb failure threshold sooner than they would have otherwise. We interpret the rate-dependent triggering threshold as evidence of several competing processes with different time constants, the faster one(s) facilitating failure and the other(s) inhibiting it. Such competition is a common feature of theories of slip instability. All these results, not surprisingly, imply that to understand earthquake triggering one must consider not only simple failure criteria requiring exceedence of some constant threshold but also the requirements for generating instabilities.

Stress/strain changes and triggered seismicity at The Geysers, California

NASA Astrophysics Data System (ADS)

Gomberg, Joan; Davis, Scott

1996-01-01

The principal results of this study of remotely triggered seismicity in The Geysers geothermal field are the demonstration that triggering (initiation of earthquake failure) depends on a critical strain threshold and that the threshold level increases with decreasing frequency, or, equivalently, depends on strain rate. This threshold function derives from (1) analyses of dynamic strains associated with surface waves of the triggering earthquakes, (2) statistically measured aftershock zone dimensions, and (3) analytic functional representations of strains associated with power production and tides. The threshold is also consistent with triggering by static strain changes and implies that both static and dynamic strains may cause aftershocks. The observation that triggered seismicity probably occurs in addition to background activity also provides an important constraint on the triggering process. Assuming the physical processes underlying earthquake nucleation to be the same, Gomberg [this issue] discusses seismicity triggered by the MW 7.3 Landers earthquake, its constraints on the variability of triggering thresholds with site, and the implications of time delays between triggering and triggered earthquakes. Our results enable us to reject the hypothesis that dynamic strains simply nudge prestressed faults over a Coulomb failure threshold sooner than they would have otherwise. We interpret the rate-dependent triggering threshold as evidence of several competing processes with different time constants, the faster one(s) facilitating failure and the other(s) inhibiting it. Such competition is a common feature of theories of slip instability. All these results, not surprisingly, imply that to understand earthquake triggering one must consider not only simple failure criteria requiring exceedence of some constant threshold but also the requirements for generating instabilities.

Time dependent fracture and cohesive zones

NASA Technical Reports Server (NTRS)

Knauss, W. G.

1993-01-01

This presentation is concerned with the fracture response of materials which develop cohesive or bridging zones at crack tips. Of special interest are concerns regarding crack stability as a function of the law which governs the interrelation between the displacement(s) or strain across these zones and the corresponding holding tractions. It is found that for some materials unstable crack growth can occur, even before the crack tip has experienced a critical COD or strain across the crack, while for others a critical COD will guarantee the onset of fracture. Also shown are results for a rate dependent nonlinear material model for the region inside of a craze for exploring time dependent crack propagation of rate sensitive materials.

Strain partitioning in shales during elastic and creep deformation observed by synchrotron X-ray micro-tomography.

NASA Astrophysics Data System (ADS)

Sone, H.; Cheung, C.; Rivers, M. L.; Wang, Y.; Yu, T.

2016-12-01

Knowledge about the ductile time-dependent constitutive behavior of geological materials is essential when evaluating the long-term integrity of subsurface structures and predicting the long-term geomechanical response of the surrounding formations. To this end, it is not only important to measure the bulk time-dependent behavior but also essential to understand the microscale mechanism by which rocks exhibit time-dependence, because laboratory data needs to be extrapolated to time-scales much beyond laboratory experiments. We conducted long-term creep experiments using Green River shale samples and obtained synchrotron X-ray images during the tests in an attempt to capture the microscale strain-partitioning that occurs within the sample. Shale samples of few millimeter dimensions were stressed up to several tens of MPa by a spring-loaded device within an X-ray transparent load frame, and the load was held constant for up to several months to allow creep deformation. Tomographic images of about 5 micron resolution were reconstructed from images collected at different timings of the experiment, which allows us to investigate where and how much strain localized during elastic and creep deformation. Tracking the position of some outstanding features in the rock texture (e.g. pyrite grains, organic material patches) indicate that strain magnitudes expected from the sample elastic and relaxation modulus can be successfully recovered from the tomographic images. We also attempt to use digital volume correlation to track sub-voxel displacements and to characterize the spatial heterogeneity of the deformation.

Replacing Escherichia coli NAD-dependent glyceraldehyde 3-phosphate dehydrogenase (GAPDH) with a NADP-dependent enzyme from Clostridium acetobutylicum facilitates NADPH dependent pathways.

PubMed

Martínez, Irene; Zhu, Jiangfeng; Lin, Henry; Bennett, George N; San, Ka-Yiu

2008-11-01

Reactions requiring reducing equivalents, NAD(P)H, are of enormous importance for the synthesis of industrially valuable compounds such as carotenoids, polymers, antibiotics and chiral alcohols among others. The use of whole-cell biocatalysis can reduce process cost by acting as catalyst and cofactor regenerator at the same time; however, product yields might be limited by cofactor availability within the cell. Thus, our study focussed on the genetic manipulation of a whole-cell system by modifying metabolic pathways and enzymes to improve the overall production process. In the present work, we genetically engineered an Escherichia coli strain to increase NADPH availability to improve the productivity of products that require NADPH in its biosynthesis. The approach involved an alteration of the glycolysis step where glyceraldehyde-3-phosphate (GAP) is oxidized to 1,3 bisphophoglycerate (1,3-BPG). This reaction is catalyzed by NAD-dependent endogenous glyceraldehyde-3-phosphate dehydrogenase (GAPDH) encoded by the gapA gene. We constructed a recombinant E. coli strain by replacing the native NAD-dependent gapA gene with a NADP-dependent GAPDH from Clostridium acetobutylicum, encoded by the gene gapC. The beauty of this approach is that the recombinant E. coli strain produces 2 mol of NADPH, instead of NADH, per mole of glucose consumed. Metabolic flux analysis showed that the flux through the pentose phosphate (PP) pathway, one of the main pathways that produce NADPH, was reduced significantly in the recombinant strain when compared to that of the parent strain. The effectiveness of the NADPH enhancing system was tested using the production of lycopene and epsilon-caprolactone as model systems using two different background strains. The recombinant strains, with increased NADPH availability, consistently showed significant higher productivity than the parent strains.

Global Existence Results for Viscoplasticity at Finite Strain

NASA Astrophysics Data System (ADS)

Mielke, Alexander; Rossi, Riccarda; Savaré, Giuseppe

2018-01-01

We study a model for rate-dependent gradient plasticity at finite strain based on the multiplicative decomposition of the strain tensor, and investigate the existence of global-in-time solutions to the related PDE system. We reveal its underlying structure as a generalized gradient system, where the driving energy functional is highly nonconvex and features the geometric nonlinearities related to finite-strain elasticity as well as the multiplicative decomposition of finite-strain plasticity. Moreover, the dissipation potential depends on the left-invariant plastic rate, and thus depends on the plastic state variable. The existence theory is developed for a class of abstract, nonsmooth, and nonconvex gradient systems, for which we introduce suitable notions of solutions, namely energy-dissipation-balance and energy-dissipation-inequality solutions. Hence, we resort to the toolbox of the direct method of the calculus of variations to check that the specific energy and dissipation functionals for our viscoplastic models comply with the conditions of the general theory.

Effect of strain wave shape on low-cycle fatigue crack propagation of SUS 304 stainless steel at elevated temperatures

NASA Astrophysics Data System (ADS)

Okazaki, Masakazu; Hattori, Ichiro; Shiraiwa, Fujio; Koizumi, Takashi

1983-08-01

Effect of strain wave shape on strain-controlled low-cycle fatigue crack propagation of SUS 304 stainless steel was investigated at 600 and 700 °C. It was found that the rate of crack propagation in a cycle-dependent region was successfully correlated with the range of cyclic J-integral, Δ Jf, regardless of the strain wave shape, frequency, and test temperature. It was also shown that the rate of crack propagation gradually increased from cycle-dependent curve to time-dependent one with decreasing frequency and slow-fast strain wave shape, and that one of the factors governing the rate of crack propagation in such a region was the ratio of the range of creep J-integral to that of total J-integral, Δ J c/Δ JT. Based on the results thus obtained, an interaction damage rule proposed semi-empirically was interpreted, with regard to crack propagation. Furthermore, fatigue crack initiation mechanism in slow-fast strain wave shape was studied, and it was shown that grain boundary sliding took an important role in it.

A viscoelastic higher-order beam finite element

NASA Technical Reports Server (NTRS)

Johnson, Arthur R.; Tressler, Alexander

1996-01-01

A viscoelastic internal variable constitutive theory is applied to a higher-order elastic beam theory and finite element formulation. The behavior of the viscous material in the beam is approximately modeled as a Maxwell solid. The finite element formulation requires additional sets of nodal variables for each relaxation time constant needed by the Maxwell solid. Recent developments in modeling viscoelastic material behavior with strain variables that are conjugate to the elastic strain measures are combined with advances in modeling through-the-thickness stresses and strains in thick beams. The result is a viscous thick-beam finite element that possesses superior characteristics for transient analysis since its nodal viscous forces are not linearly dependent an the nodal velocities, which is the case when damping matrices are used. Instead, the nodal viscous forces are directly dependent on the material's relaxation spectrum and the history of the nodal variables through a differential form of the constitutive law for a Maxwell solid. The thick beam quasistatic analysis is explored herein as a first step towards developing more complex viscoelastic models for thick plates and shells, and for dynamic analyses. The internal variable constitutive theory is derived directly from the Boltzmann superposition theorem. The mechanical strains and the conjugate internal strains are shown to be related through a system of first-order, ordinary differential equations. The total time-dependent stress is the superposition of its elastic and viscous components. Equations of motion for the solid are derived from the virtual work principle using the total time-dependent stress. Numerical examples for the problems of relaxation, creep, and cyclic creep are carried out for a beam made from an orthotropic Maxwell solid.

A contribution to calculation of the mathematical pendulum

NASA Astrophysics Data System (ADS)

Anakhaev, K. N.

2014-11-01

In this work, as a continuation of rigorous solutions of the mathematical pendulum theory, calculated dependences were obtained in elementary functions (with construction of plots) for a complete description of the oscillatory motion of the pendulum with determination of its parameters, such as the oscillation period, deviation angles, time of motion, angular velocity and acceleration, and strains in the pendulum rod (maximum, minimum, zero, and gravitational). The results of calculations according to the proposed dependences closely (≪1%) coincide with the exact tabulated data for individual points. The conditions of ascending at which the angular velocity, angular acceleration, and strains in the pendulum rod reach their limiting values equal to and 5 m 1 g, respectively, are shown. It was revealed that the angular acceleration does not depend on the pendulum oscillation amplitude; the pendulum rod strain equal to the gravitation force of the pendulum R s = m 1 g at the time instant is also independent on the amplitude. The dependences presented in this work can also be invoked for describing oscillations of a physical pendulum, mass on a spring, electric circuit, etc.

Mechanical Properties of Polymers.

ERIC Educational Resources Information Center

Aklonis, J. J.

1981-01-01

Mechanical properties (stress-strain relationships) of polymers are reviewed, taking into account both time and temperature factors. Topics include modulus-temperature behavior of polymers, time dependence, time-temperature correspondence, and mechanical models. (JN)

Superinfection exclusion of the ruminant pathogen anaplasma marginale in the tick vector is dependent on time between exposures to the strains

USDA-ARS?s Scientific Manuscript database

The remarkable genetic diversity of vector-borne pathogens allows for the establishment of superinfection in the mammalian host. To have a long-term impact on population strain structure, the introduced strains must also be transmitted by a vector population that has been exposed to the existing pri...

The time-domain behavior of power-law noises. [of many geophysical phenomena

NASA Technical Reports Server (NTRS)

Agnew, Duncan C.

1992-01-01

The power spectra of many geophysical phenomena are well approximated by a power-law dependence on frequency or wavenumber. A simple expression for the root-mean-square variability of a process with such a spectrum over an interval of time or space is derived. The resulting expression yields the powerlaw time dependence characteristic of fractal processes, but can be generalized to give the temporal variability for more general spectral behaviors. The method is applied to spectra of crustal strain (to show what size of strain events can be detected over periods of months to seconds) and of sea level (to show the difficulty of extracting long-term rates from short records).

Days to Return to Participation After a Hamstrings Strain Among American Collegiate Soccer Players

PubMed Central

Cross, Kevin M.; Saliba, Susan A.; Conaway, Mark; Gurka, Kelly K.; Hertel, Jay

2015-01-01

Context Among US collegiate soccer players, the incidence rate and the event characteristics of hamstrings strains differ between sexes, but comparisons in the return-to-participation (RTP) time have not been reported. Objective To compare the RTP time between male and female collegiate soccer players and analyze the influence of event characteristics on the RTP time for each sex. Design Descriptive epidemiology study. Setting Data were collected from collegiate teams that voluntarily participated in the National Collegiate Athletic Association Injury Surveillance System. Patients or Other Participants Collegiate soccer athletes who sustained 507 hamstrings strains (306 men, 201 women) during the 2004 through 2009 fall seasons. Main Outcome Measure(s) Nonparametric statistics were used to evaluate RTP time differences between sexes and among categories of each event characteristic (ie, time of season, practice or competition, player position). Negative binomial regression was used to model the RTP time for each sex. All analyses were performed separately for first-time and recurrent strains. Results We found no differences in the RTP time between sexes for first-time (median: men = 7.0 days, women = 6.0 days; P = .07) or recurrent (median: men = 11 days, women = 5.5 days; P = .06) hamstrings strains. For male players with first-time strains, RTP time was increased when the strain occurred during competition or the in-season/postseason and varied depending on the division of play. Among female players with first-time strains, we found no differences in RTP time within characteristics. For male players with recurrent hamstrings strains, the RTP time was longer when the injury occurred during the in-season/postseason. Among female players with recurrent strains, RTP time was longer for forwards than for midfielders or defenders. Conclusions Although we found no differences in the RTP time after hamstrings strains in male and female collegiate soccer players, each sex had unique event characteristics that influenced RTP time. PMID:25978100

Damage Recovery in Carrara Marble

NASA Astrophysics Data System (ADS)

Meyer, G.; Brantut, N.; Mitchell, T. M.; Meredith, P. G.

2017-12-01

We investigate the effect of confining pressure on the recovery of elastic wave velocities following deformation episodes in Carrara Marble. Dry Carrara Marble cores were deformed in the ductile regime (Pc = 40 MPa) up to 3% axial strain. After deformation, samples were held at constant stress conditions for extended periods of time (5-8 days) whilst continuously recording volumetric strain and seismic wave velocities. The velocity data were used to invert for microcrack densities using an effective medium approach. Finally, thin sections were produced to characterise the microstructures after recovery. During deformation, elastic wave speeds decreased with increasing strain by more than 30% of the value for the intact rock due to the formation of distributed microcracks. Under constant hydrostatic pressure, wave speeds progressively recovered 12-90% of the initial drop, depending on the applied confining pressure. In contrast, the strain recovery (deformation towards the initial shape of the sample) during holding time is negligible (of the order of 10-4). Tests performed under nonhydrostatic (triaxial) stress conditions during recovery showed some time-dependent creep deformation together with very significant recovery of wave velocities. The recovery is interpreted as a progressive reduction in crack density within the sample. The process is highly dependent on confining pressure, which favours it. We propose that the driving process for wave speed recovery is the time-dependent increase of contact area between crack surfaces due to the formation and growth of asperity contacts. We develop a micromechanical model for crack closure driven by asperity creep, which shows a good fit to the experimental data. Most of the recovery is achieved in the initial few hours, implying it is the fastest recovery or healing process, and thus occurs prior to any chemical healing or mineral precipitation. Our data corroborate field observations of post-seismic fault behavior.

Time-dependent crashworthiness of polyurethane foam

NASA Astrophysics Data System (ADS)

Basit, Munshi Mahbubul; Cheon, Seong Sik

2018-05-01

Time-dependent stress-strain relationship as well as crashworthiness of polyurethane foam was investigated under constant impact energy with different velocities, considering inertia and strain-rate effects simultaneously during the impact testing. Even though the impact energies were same, the percentage in increase in densification strain due to higher impact velocities was found, which yielded the wider plateau region, i.e. growth in crashworthiness. This phenomenon is analyzed by the microstructure of polyurethane foam obtained from scanning electron microscopy. The equations, coupled with the Sherwood-Frost model and the impulse-momentum theory, were employed to build the constitutive equation of the polyurethane foam and calculate energy absorption capacity of the foam. The nominal stress-strain curves obtained from the constitutive equation were compared with results from impact tests and were found to be in good agreement. This study is dedicated to guiding designer use polyurethane foam in crashworthiness structures such as an automotive bumper system by providing crashworthiness data, determining the crush mode, and addressing a mathematical model of the crashworthiness.

Evidence for initiation of frictional partial slip as the mechanism behind nonlinear stress-strain hysteresis in rock fractures under seismic-frequency torsion

NASA Astrophysics Data System (ADS)

Saltiel, S.; Bonner, B. P.; Delbridge, B. G.; Ajo Franklin, J. B.

2016-12-01

We have adapted a low-frequency (0.1 - 64 Hz) torsional apparatus to explore the pure shear behavior of rock fractures under low normal stresses, simulating low effective stress environments - shallow depths and/or under high pore pressures. The instrument is unique in this ability to measure under very low confinement as well as to probe partial slip on the outside of asperities, before full slip nucleation occurs. Using a sinusoidal oscillation around this condition, we can probe the stress-strain constitutive relation at a range of strain amplitudes and the rate-dependence of the initiation of asperity slip. We find different, nonlinear, stress-strain constitutive relations for dolomite, rhyolite, and granite fractured samples, but all show softening at high strain amplitudes (above microstrain or micron-scale displacement). All measured samples exhibit qualitatively similar time-series hysteresis loops and frequency-dependence. The low frequency stress-strain loops stiffen at the high strain static end of the sinusoidal oscillation. This shape is determined by harmonic generation in the strain, while the stress signal has low power in harmonics, confirming that the driver and electronics are not the source of this nonlinearity. We also observe that this stiffening cusp does not occur as frequency increases above 8 Hz (opposite to normal dispersion seen at higher normal stresses). We monitor the fracture surface wear with repeated cycles to show the extent of slip on mapped asperities. These observations suggest that a rate dependent, healing, process causes the nonlinear responce of fracture faces under low normal stress to periodic shear. We propose that static friction at the low strain-rate part of the cycle, when given enough time at low oscillation frequencies, causes this stiffening cusp shape in the hysteretic stress-strain curve. An analytic model with idealized contact area is used to constrain the rate-state friction constitutive model parameters needed to provide this dynamic behavior.

Comparison of life history parameters of two Frankliniella occidentalis (Thysanoptera: Thripidae) strains in New Zealand.

PubMed

Nielsen, M-C; Teulon, D A J; Chapman, R B; Butler, R C; Drayton, G M; Philipsen, H

2010-04-01

Two strains of western flower thrips, Frankliniella occidentalis (Pergande), are reputedly found in New Zealand. One strain was recorded in 1934, and it is most common in flowers of Lupinus arboreus outdoors (lupin strain); the other strain was first recorded in New Zealand in 1992 and is found mostly indoors on greenhouse crops (greenhouse strain). Laboratory studies were conducted to compare the life history parameters of these two strains. Thrips from each strain were fed sucrose solution and capsicum or lupin pollen and reared at 25 degrees C, >60% RH, and 16 L:8 D photoperiod. Significant differences in life history parameters were found. Preoviposition time was significantly shorter, and oviposition rate and fecundity were markedly higher (four-fold) for the greenhouse than for the lupin strain. The lupin strain performed significantly better on the capsicum pollen, laying more than twice as many eggs than on the lupin pollen over a 14-d period. The greenhouse strain development time from larvae to adult was marginally faster (0.7-1.1 d less) than the lupin strain because of a shorter prepupal and a marginally shorter pupal development time. Females of the greenhouse strain lived on average 69% longer than females from the lupin strain. Large differences in the intrinsic growth rate (r(m)) were found, with r(m) being 1.4-1.8 times higher for the greenhouse strain than the lupin strain, depending on pollen source. The results are discussed in relation to different ecological requirements and pest status of the two strains.

Laser Induced Damage in Optical Materials: 1980.

DTIC Science & Technology

1981-10-01

is used to describe microplastic strain resulting from short duration loading, and the term microcreep refers to time dependent strains of small...effectively, and the maximum temperature rise will thus be at the Work supported by Naval Sea Systems Command, PflS-405, and Naval Weapons Center

Time-dependent combinatory effects of active mechanical loading and passive topographical cues on cell orientation.

PubMed

Wang, Qian; Huang, Hanyang; Wei, Kang; Zhao, Yi

2016-10-01

Mechanical stretching and topographical cues are both effective mechanical stimulations for regulating cell morphology, orientation, and behaviors. The competition of these two mechanical stimulations remains largely underexplored. Previous studies have suggested that a small cyclic mechanical strain is not able to reorient cells that have been pre-aligned by relatively large linear microstructures, but can reorient those pre-aligned by small linear micro/nanostructures if the characteristic dimension of these structures is below a certain threshold. Likewise, for micro/nanostructures with a given characteristic dimension, the strain must exceed a certain magnitude to overrule the topographic cues. There are however no in-depth investigations of such "thresholds" due to the lack of close examination of dynamic cell orientation during and shortly after the mechanical loading. In this study, the time-dependent combinatory effects of active and passive mechanical stimulations on cell orientation are investigated by developing a micromechanical stimulator. The results show that the cells pre-aligned by linear micro/nanostructures can be altered by cyclic in-plane strain, regardless of the structure size. During the loading, the micro/nanostructures can resist the reorientation effects by cyclic in-plane strain while the resistive capability (measured by the mean orientation angle change and the reorientation speed) increases with the increasing characteristic dimension. The micro/nanostructures also can recover the cell orientation after the cessation of cyclic in-plane strain, while the recovering capability increases with the characteristic dimension. The previously observed thresholds are largely dependent on the observation time points. In order to accurately evaluate the combinatory effects of the two mechanical stimulations, observations during the active loading with a short time interval or endpoint observations shortly after the loading are preferred. This study provides a microengineering solution to investigate the time-dependent combinatory effects of the active and passive mechanical stimulations and is expected to enhance our understanding of cell responses to complex mechanical environments. Biotechnol. Bioeng. 2016;113: 2191-2201. © 2016 Wiley Periodicals, Inc. © 2016 Wiley Periodicals, Inc.

Potential probiotic characteristics of Lactobacillus and Enterococcus strains isolated from traditional dadih fermented milk against pathogen intestinal colonization.

PubMed

Collado, M Carmen; Surono, Ingrid S; Meriluoto, Jussi; Salminen, Seppo

2007-03-01

Traditional fermented buffalo milk in Indonesia (dadih) has been believed to have a beneficial impact on human health, which could be related to the properties of the lactic acid bacteria (LAB) involved in its fermentation process. In previous studies, it was discovered that strains of dadih lactic isolates possessed some beneficial properties in vitro. In the present study, the adhesion capacity of specific LAB isolates from dadih to intestinal mucus was analyzed. Further, the ability to inhibit model human pathogens and displace them from mucus was assessed. The adhesion of tested LAB strains was strain-dependent and varied from 1.4 to 9.8%. The most adhesive Lactobacillus plantarum strain was IS-10506, with 9.8% adhesion. The competition assay between dadih LAB isolates and pathogens showed that a 2-h preincubation with L. plantarum at 37 degrees C significantly reduced pathogen adhesion to mucus. All tested LAB strains displaced and inhibited pathogen adhesion, but the results were strain-specific and dependent on time and pathogen strains. In general, L. plantarum IS-10506 showed the best ability against pathogen adhesion.

Experimental identification and mathematical modeling of viscoplastic material behavior

NASA Astrophysics Data System (ADS)

Haupt, P.; Lion, A.

1995-03-01

Uniaxial torsion and biaxial torsion-tension experiments on thin-walled tubes were carried out to investigate the viscoplastic behavior of stainless steel XCrNi18.9. A series of monotonic tests under strain and stress control shows nonlinear rate dependence and suggests the existence of equilibrium states, which are asymptotically approached during relaxation and creep processes. Strain controlled cyclic experiments display various hardening and softening phenomena that depend on strain amplitude and mean strain. All experiments indicate that the equilibrium states within the material depend on the history of the input process, whereas the history-dependence of the relaxation and creep behavior appears less significant. From the experiments the design of a constitutive model of viscoplasticity is motivated: The basic assumption is a decomposition of the total stress into an equilibrium stress and a non-equilibrium overstress: At constant strain, the overstress relaxes to zero, where the relaxation time depends on the overstress in order to account for the nonlinear rate-dependence. The equilibrium stress is assumed to be a rate independent functional of the total strain history. Classical plasticity is utilized with a kinematic hardening rule of the Armstrong-Frederick type. In order to incorporate the amplitude-dependent hardening and softening behavior, a generalized arc length representation is applied [14]. The introduction of an additional kinematic hardening variable facilitates consideration of additional hardening effects resulting from the non-radiality of the input process. Apart from the common yield and loading criterion of classical plasticity, the proposed constitutive model does not contain any further distinction of different cases. The experimental data are sufficient to identify the material parameters of the constitutive model. The results of the identification procedure demonstrate the ability of the model to represent the observed phenomena with satisfactory approximation.

Time-Dependent Behavior of Reinforced Polymer Concrete Columns under Eccentric Axial Loading

PubMed Central

Berardi, Valentino Paolo; Mancusi, Geminiano

2012-01-01

Polymer concretes (PCs) represent a promising alternative to traditional cementitious materials in the field of new construction. In fact, PCs exhibit high compressive strength and ultimate compressive strain values, as well as good chemical resistance. Within the context of these benefits, this paper presents a study on the time-dependent behavior of polymer concrete columns reinforced with different bar types using a mechanical model recently developed by the authors. Balanced internal reinforcements are considered (i.e., two bars at both the top and bottom of the cross-section). The investigation highlights relevant stress and strain variations over time and, consequently, the emergence of a significant decrease in concrete’s stiffness and strength over time. Therefore, the results indicate that deferred effects due to viscous flow may significantly affect the reliability of reinforced polymer concrete elements over time.

Postseismic viscoelastic deformation and stress. Part 2: Stress theory and computation; dependence of displacement, strain, and stress on fault parameters

NASA Technical Reports Server (NTRS)

Cohen, S. C.

1979-01-01

A viscoelastic model for deformation and stress associated with earthquakes is reported. The model consists of a rectangular dislocation (strike slip fault) in a viscoelastic layer (lithosphere) lying over a viscoelastic half space (asthenosphere). The time dependent surface stresses are analyzed. The model predicts that near the fault a significant fraction of the stress that was reduced during the earthquake is recovered by viscoelastic softening of the lithosphere. By contrast, the strain shows very little change near the fault. The model also predicts that the stress changes associated with asthenospheric flow extend over a broader region than those associated with lithospheric relaxation even though the peak value is less. The dependence of the displacements, stresses on fault parameters studied. Peak values of strain and stress drop increase with increasing fault height and decrease with fault depth. Under many circumstances postseismic strains and stresses show an increase with decreasing depth to the lithosphere-asthenosphere boundary. Values of the strain and stress at distant points from the fault increase with fault area but are relatively insensitive to fault depth.

Degradation pathway of 2-chloroethanol in Pseudomonas stutzeri strain JJ under denitrifying conditions.

PubMed

Dijk, John A; Gerritse, Jan; Schraa, Gosse; Stams, Alfons J M

2004-12-01

The pathway of 2-chloroethanol degradation in the denitrifying Pseudomonas stutzeri strain JJ was investigated. In cell-free extracts, activities of a phenazine methosulfate (PMS)-dependent chloroethanol dehydrogenase, an NAD-dependent chloroacetaldehyde dehydrogenase, and a chloroacetate dehalogenase were detected. This suggested that the 2-chloroethanol degradation pathway in this denitrifying strain is the same as found in aerobic bacteria that degrade chloroethanol. Activity towards primary alcohols, secondary alcohols, diols, and other chlorinated alcohols could be measured in cell-free extracts with chloroethanol dehydrogenase (CE-DH) activity. PMS and phenazine ethosulfate (PES) were used as primary electron acceptors, but not NAD, NADP or ferricyanide. Cells of strain JJ cultured in a continuous culture under nitrate limitation exhibited chloroethanol dehydrogenase activity that was a 12 times higher than in cells grown in batch culture. However, under chloroethanol-limiting conditions, CE-DH activity was in the same range as in batch culture. Cells grown on ethanol did not exhibit CE-DH activity. Instead, NAD-dependent ethanol dehydrogenase (E-DH) activity and PMS-dependent E-DH activity were detected.

Expression of GPD1 and SIP18 genes during rehydration in active dry industrial Saccharomyces cerevisiae cider-making yeast strains (ADY).

PubMed

Goncerzewicz, Anna; Kamińska-Wojteczek, Karolina; Młynarczyk, Izabella; Misiewicz, Anna

2017-01-01

In this study we determined the influence of different sugar concentration in media, time of rehydration and type of strain on relative expression level of GPD1 and SIP18 genes of active dry cider-making yeast strains, followed by the assessment of the impact of rehydration on the fermentation process. High expression of SIP18 at the beginning of rehydration was shown to be due to high transcription of the gene during the drying process. High sugar concentrations of media initiated transcription of the GPD1 gene and triggered the cellular glycerol biosynthesis pathway in examined strains. Rehydration time and type of strain showed to have no statistically significant impact on the course of the fermentation; RT qPCR results depended mainly on the time of rehydration and sugar concentration of the medium. This is the first attempt to confront rehydration time and molecular mechanisms acting upon rehydration with the course of the fermentation process.

A lengthy look at the daily grind: time series analysis of events, mood, stress, and satisfaction.

PubMed

Fuller, Julie A; Stanton, Jeffrey M; Fisher, Gwenith G; Spitzmuller, Christiane; Russell, Steven S; Smith, Patricia C

2003-12-01

The present study investigated processes by which job stress and satisfaction unfold over time by examining the relations between daily stressful events, mood, and these variables. Using a Web-based daily survey of stressor events, perceived strain, mood, and job satisfaction completed by 14 university workers, 1,060 occasions of data were collected. Transfer function analysis, a multivariate version of time series analysis, was used to examine the data for relationships among the measured variables after factoring out the contaminating influences of serial dependency. Results revealed a contrast effect in which a stressful event associated positively with higher strain on the same day and associated negatively with strain on the following day. Perceived strain increased over the course of a semester for a majority of participants, suggesting that effects of stress build over time. Finally, the data were consistent with the notion that job satisfaction is a distal outcome that is mediated by perceived strain. ((c) 2003 APA, all rights reserved)

A visco-hyperelastic-damage constitutive model for the analysis of the biomechanical response of the periodontal ligament.

PubMed

Natali, Arturo N; Carniel, Emanuele L; Pavan, Piero G; Sander, Franz G; Dorow, Christina; Geiger, Martin

2008-06-01

The periodontal ligament (PDL), as other soft biological tissues, shows a strongly non-linear and time-dependent mechanical response and can undergo large strains under physiological loads. Therefore, the characterization of the mechanical behavior of soft tissues entails the definition of constitutive models capable of accounting for geometric and material non-linearity. The microstructural arrangement determines specific anisotropic properties. A hyperelastic anisotropic formulation is adopted as the basis for the development of constitutive models for the PDL and properly arranged for investigating the viscous and damage phenomena as well to interpret significant aspects pertaining to ordinary and degenerative conditions. Visco-hyperelastic models are used to analyze the time-dependent mechanical response, while elasto-damage models account for the stiffness and strength decrease that can develop under significant loading or degenerative conditions. Experimental testing points out that damage response is affected by the strain rate associated with loading, showing a decrease in the damage limits as the strain rate increases. These phenomena can be investigated by means of a model capable of accounting for damage phenomena in relation to viscous effects. The visco-hyperelastic-damage model developed is defined on the basis of a Helmholtz free energy function depending on the strain-damage history. In particular, a specific damage criterion is formulated in order to evaluate the influence of the strain rate on damage. The model can be implemented in a general purpose finite element code. The accuracy of the formulation is evaluated by using results of experimental tests performed on animal model, accounting for different strain rates and for strain states capable of inducing damage phenomena. The comparison shows a good agreement between numerical results and experimental data.

Chimera states in multi-strain epidemic models with temporary immunity

NASA Astrophysics Data System (ADS)

Bauer, Larissa; Bassett, Jason; Hövel, Philipp; Kyrychko, Yuliya N.; Blyuss, Konstantin B.

2017-11-01

We investigate a time-delayed epidemic model for multi-strain diseases with temporary immunity. In the absence of cross-immunity between strains, dynamics of each individual strain exhibit emergence and annihilation of limit cycles due to a Hopf bifurcation of the endemic equilibrium, and a saddle-node bifurcation of limit cycles depending on the time delay associated with duration of temporary immunity. Effects of all-to-all and non-local coupling topologies are systematically investigated by means of numerical simulations, and they suggest that cross-immunity is able to induce a diverse range of complex dynamical behaviors and synchronization patterns, including discrete traveling waves, solitary states, and amplitude chimeras. Interestingly, chimera states are observed for narrower cross-immunity kernels, which can have profound implications for understanding the dynamics of multi-strain diseases.

Extension of Viscoplasticity Based on Overstress to Capture the Effects of Prior Aging on the Time Dependent Deformation Behavior of a High-Temperature Polymer: Experiments and Modeling

DTIC Science & Technology

2008-10-01

the standard model characterization procedure is based on creep and recovery tests, where loading and unloading occurs at a fast rate of 1.0 MPa/s...σ − g[ǫ] and on d̊g[ǫ] dǫ = E, where g̊ is defined as the equilibrium stress g[ ] for extremely fast loading. For this case, the stress-strain curves...Strain S tr es s Strain Rate Slow Strain Rate Medium Strain Rate Fast Plastic Flow Fully Established Figure 2.10: Stress Strain Curve Schematic

Time-dependent brittle deformation (creep) at Mt. Etna volcano

NASA Astrophysics Data System (ADS)

Heap, M. J.; Baud, P.; Meredith, P. G.; Vinciguerra, S.; Bell, A. F.; Main, I. G.

2009-04-01

Mt. Etna is the largest and most active volcano in Europe. Time-dependent weakening mechanisms, leading to slow fracturing, have been shown to act during pre-eruptive patterns of flank eruptions at Mt. Etna volcano. Due to the high permeability of its volcanic rocks, the volcanic edifice hosts one of the biggest hydrogeologic reservoirs of Sicily (Ogniben, 1966). The presence of a fluid phase in cracks within rock has been shown to dramatically affect both mechanical and chemical interactions. Chemically, it promotes time-dependent brittle deformation through such mechanisms as stress corrosion cracking that allows rocks to deform at stresses far below their short-term failure strength. Such crack growth is highly non-linear and accelerates towards dynamic failure over extended periods of time, even under constant applied stress; a phenomenon known as ‘brittle creep'. Here we report results from a study of time-dependent brittle creep in water-saturated samples of Etna basalt (EB) under triaxial stress conditions (confining pressure of 50 MPa and pore fluid pressure of 20 MPa). Samples of EB were loaded at a constant strain rate of 10-5 s-1 to a pre-determined percentage of the short-term strength and left to deform under constant stress until failure. Crack damage evolution was monitored throughout each experiment by measuring the independent damage proxies of axial strain, pore volume change and output of acoustic emission (AE) energy, during brittle creep of creep strain rates ranging over four orders of magnitude. Our data not only demonstrates that basalt creeps in the brittle regime but also that the applied differential stress exerts a crucial influence on both time-to-failure and creep strain rate in EB. Furthermore, stress corrosion is considered to be responsible for the acceleratory cracking and seismicity prior to volcanic eruptions and is invoked as an important mechanism in forecasting models. Stress-stepping creep experiments were then performed to allow the influence of the effective confining stress to be studied in detail. Experiments were performed under effective stress conditions of 10, 30 and 50 MPa (whilst maintaining a constant pore fluid pressure of 20 MPa). In addition to the purely mechanical influence of water, governed by the effective stress, which results in a shift of the creep strain rate curves to lower strain rates at higher effective stresses. Our results also demonstrate that the chemically-driven process of stress corrosion cracking appears to be inhibited at higher effective stress. This results in an increase in the gradient of the creep strain rate curves with increasing effective stress. We suggest that the most likely cause of this change is a decrease in water mobility due to a reduction in crack aperture and an increase in water viscosity at higher pressure. Finally, we show that a theoretical model based on mean-field damage mechanics creep laws is able to reproduce the experimental strain-time relations. Our results indicate that the local changes in the stress field and fluid circulation can have a profound impact in the time-to-failure properties of the basaltic volcanic pile.

Time-dependent brittle deformation at Mt. Etna volcano

NASA Astrophysics Data System (ADS)

Baud, Patrick; Heap, Michael; Meredith, Philip; Vinciguerra, Sergio; Bell, Andrew; Main, Ian

2010-05-01

Time-dependent weakening mechanisms, leading to slow fracturing, are likely to act during the build up to flank eruptions at Mt. Etna volcano and are potentially a primary control on pre-eruptive patterns of seismicity and deformation. Due to the high permeability of its volcanic rocks, the volcanic edifice hosts a large water reservoir (Ogniben, 1966). The presence of a fluid phase in cracks within rock has been shown to dramatically affect both mechanical and chemical interactions. Chemically, it promotes time-dependent brittle deformation through such mechanisms as stress corrosion cracking that allows rocks to deform at stresses far below their short-term failure strength. Such crack growth is highly non-linear and accelerates towards dynamic failure over extended periods of time, even under constant applied stress; a phenomenon known as ‘brittle creep'. Here we report results from a study of time-dependent brittle creep in water-saturated samples of Etna basalt (EB) under triaxial stress conditions (confining pressure of 50 MPa and pore fluid pressure of 20 MPa). Samples of EB were loaded at a constant strain rate of 10-5 s-1 to a pre-determined percentage of the short-term strength and left to deform under constant stress until failure. Crack damage evolution was monitored throughout each experiment by measuring the independent damage proxies of axial strain, pore volume change and output of acoustic emission (AE) energy, during brittle creep of creep strain rates ranging over four orders of magnitude. Our data not only demonstrates that basalt creeps in the brittle regime but also that the applied differential stress exerts a crucial influence on both time-to-failure and creep strain rate in EB. Furthermore, stress corrosion is considered to be responsible for the acceleratory cracking and seismicity prior to volcanic eruptions and is invoked as an important mechanism in forecasting models. Stress-stepping creep experiments were then performed to allow the influence of the effective confining stress to be studied in detail. Experiments were performed under effective stress conditions of 10, 30 and 50 MPa (whilst maintaining a constant pore fluid pressure of 20 MPa). In addition to the purely mechanical influence of water, governed by the effective stress, which results in a shift of the creep strain rate curves to lower strain rates at higher effective stresses. Our results also demonstrate that the chemically-driven process of stress corrosion cracking appears to be inhibited at higher effective stress. This results in an increase in the gradient of the creep strain rate curves with increasing effective stress. We suggest that the most likely cause of this change is a decrease in water mobility due to a reduction in crack aperture and an increase in water viscosity at higher pressure. Finally, we show that a theoretical model based on mean-field damage mechanics creep laws is able to reproduce the experimental strain-time relations and inverse seismicity plots using our experimental AE data. Our results indicate that the local changes in the stress field and fluid circulation can have a profound impact in the time-to-failure properties of the basaltic volcanic pile.

Determining a Prony Series for a Viscoelastic Material From Time Varying Strain Data

NASA Technical Reports Server (NTRS)

Tzikang, Chen

2000-01-01

In this study a method of determining the coefficients in a Prony series representation of a viscoelastic modulus from rate dependent data is presented. Load versus time test data for a sequence of different rate loading segments is least-squares fitted to a Prony series hereditary integral model of the material tested. A nonlinear least squares regression algorithm is employed. The measured data includes ramp loading, relaxation, and unloading stress-strain data. The resulting Prony series which captures strain rate loading and unloading effects, produces an excellent fit to the complex loading sequence.

The phosphotransferase system-dependent sucrose utilization regulon in enteropathogenic Escherichia coli strains is located in a variable chromosomal region containing iap sequences.

PubMed

Treviño-Quintanilla, Luis Gerardo; Escalante, Adelfo; Caro, Alma Delia; Martínez, Alfredo; González, Ricardo; Puente, José Luis; Bolívar, Francisco; Gosset, Guillermo

2007-01-01

The capacity to utilize sucrose as a carbon and energy source (Scr(+) phenotype) is a highly variable trait among Escherichia coli strains. In this study, seven enteropathogenic E. coli (EPEC) strains from different sources were studied for their capacity to grow using sucrose. Liquid media cultures showed that all analyzed strains have the Scr(+) phenotype and two distinct groups were defined: one of five and another of two strains displaying doubling times of 67 and 125 min, respectively. The genes conferring the Scr(+) phenotype in one of the fast-growing strains (T19) were cloned and sequenced. Comparative sequence analysis revealed that this strain possesses the scr regulon genes scrKYABR, encoding phosphoenolpyruvate:phosphotransferase system-dependent sucrose transport and utilization activities. Transcript level quantification revealed sucrose-dependent induction of scrK and scrR genes in fast-growing strains, whereas no transcripts were detected in slow-growing strains. Sequence comparison analysis revealed that the scr genes in strain T19 are almost identical to those present in the scr regulon of prototype EPEC E2348/69 and in both strains, the scr genes are inserted in the chromosomal intergenic region of hypothetical genes ygcE and ygcF. Comparison of the ygcE-ygcF intergenic region sequence of strains MG1655, enterohemorrhagic EDL933, uropathogenic ECFT073 and EPEC T19-E2348/69 revealed that the number of extragenic highly repeated iap sequences corresponded to nine, four, two and none, respectively. These results show that the iap sequence-containing chromosomal ygcE-ygcF intergenic region is highly variable in E. coli. Copyright (c) 2007 S. Karger AG, Basel.

Tetrahedron deformation and alignment of perceived vorticity and strain in a turbulent flow

NASA Astrophysics Data System (ADS)

Pumir, Alain; Bodenschatz, Eberhard; Xu, Haitao

2013-03-01

We describe the structure and dynamics of turbulence by the scale-dependent perceived velocity gradient tensor as supported by following four tracers, i.e., fluid particles, that initially form a regular tetrahedron. We report results from experiments in a von Kármán swirling water flow and from numerical simulations of the incompressible Navier-Stokes equation. We analyze the statistics and the dynamics of the perceived rate of strain tensor and vorticity for initially regular tetrahedron of size r0 from the dissipative to the integral scale. Just as for the true velocity gradient, at any instant, the perceived vorticity is also preferentially aligned with the intermediate eigenvector of the perceived rate of strain. However, in the perceived rate of strain eigenframe fixed at a given time t = 0, the perceived vorticity evolves in time such as to align with the strongest eigendirection at t = 0. This also applies to the true velocity gradient. The experimental data at the higher Reynolds number suggests the existence of a self-similar regime in the inertial range. In particular, the dynamics of alignment of the perceived vorticity and strain can be rescaled by t0, the turbulence time scale of the flow when the scale r0 is in the inertial range. For smaller Reynolds numbers we found the dynamics to be scale dependent.

Progress Report on Alloy 617 Time Dependent Allowables

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

Wright, Julie Knibloe

2015-06-01

Time dependent allowable stresses are required in the ASME Boiler and Pressure Vessel Code for design of components in the temperature range where time dependent deformation (i.e., creep) is expected to become significant. There are time dependent allowable stresses in Section IID of the Code for use in the non-nuclear construction codes, however, there are additional criteria that must be considered in developing time dependent allowables for nuclear components. These criteria are specified in Section III NH. St is defined as the lesser of three quantities: 100% of the average stress required to obtain a total (elastic, plastic, primary andmore » secondary creep) strain of 1%; 67% of the minimum stress to cause rupture; and 80% of the minimum stress to cause the initiation of tertiary creep. The values are reported for a range of temperatures and for time increments up to 100,000 hours. These values are determined from uniaxial creep tests, which involve the elevated temperature application of a constant load which is relatively small, resulting in deformation over a long time period prior to rupture. The stress which is the minimum resulting from these criteria is the time dependent allowable stress St. In this report data from a large number of creep and creep-rupture tests on Alloy 617 are analyzed using the ASME Section III NH criteria. Data which are used in the analysis are from the ongoing DOE sponsored high temperature materials program, form Korea Atomic Energy Institute through the Generation IV VHTR Materials Program and historical data from previous HTR research and vendor data generated in developing the alloy. It is found that the tertiary creep criterion determines St at highest temperatures, while the stress to cause 1% total strain controls at low temperatures. The ASME Section III Working Group on Allowable Stress Criteria has recommended that the uncertainties associated with determining the onset of tertiary creep and the lack of significant cavitation associated with early tertiary creep strain suggest that the tertiary creep criteria is not appropriate for this material. If the tertiary creep criterion is dropped from consideration, the stress to rupture criteria determines St at all but the lowest temperatures.« less

Constitutive relations describing creep deformation for multi-axial time-dependent stress states

NASA Astrophysics Data System (ADS)

McCartney, L. N.

1981-02-01

A THEORY of primary and secondary creep deformation in metals is presented, which is based upon the concept of tensor internal state variables and the principles of continuum mechanics and thermodynamics. The theory is able to account for both multi-axial and time-dependent stress and strain states. The wellknown concepts of elastic, anelastic and plastic strains follow naturally from the theory. Homogeneous stress states are considered in detail and a simplified theory is derived by linearizing with respect to the internal state variables. It is demonstrated that the model can be developed in such a way that multi-axial constant-stress creep data can be presented as a single relationship between an equivalent stress and an equivalent strain. It is shown how the theory may be used to describe the multi-axial deformation of metals which are subjected to constant stress states. The multi-axial strain response to a general cyclic stress state is calculated. For uni-axial stress states, square-wave loading and a thermal fatigue stress cycle are analysed.

1000 to 1200 K time-dependent compressive deformation of single-crystalline and polycrystalline B2 Ni-40Al

NASA Technical Reports Server (NTRS)

Whittenberger, J. D.; Noebe, R. D.; Kumar, K. S.; Mannan, S. K.; Cullers, C. L.

1991-01-01

The 1000-K and 1200-K time-dependent deformation of 100-line-oriented and non-100-line-oriented single crystals of Ni-40Al (made by a modified Bridgman technique) was examined over a large range of strain rates (from 0.1 to 10 to the -7th per sec). The results were compared with those for polycrystalline Ni-40Al made by hot pressing XD synthesized powder. The results from measurements of slow-plastic-strain-rate properties of the two materials show that single crystals offer no strength advantage over polycrystalline material. Both forms were found to deform via a dislocation climb mechanism.

New methodology for mechanical characterization of human superficial facial tissue anisotropic behaviour in vivo.

PubMed

Then, C; Stassen, B; Depta, K; Silber, G

2017-07-01

Mechanical characterization of human superficial facial tissue has important applications in biomedical science, computer assisted forensics, graphics, and consumer goods development. Specifically, the latter may include facial hair removal devices. Predictive accuracy of numerical models and their ability to elucidate biomechanically relevant questions depends on the acquisition of experimental data and mechanical tissue behavior representation. Anisotropic viscoelastic behavioral characterization of human facial tissue, deformed in vivo with finite strain, however, is sparse. Employing an experimental-numerical approach, a procedure is presented to evaluate multidirectional tensile properties of superficial tissue layers of the face in vivo. Specifically, in addition to stress relaxation, displacement-controlled multi-step ramp-and-hold protocols were performed to separate elastic from inelastic properties. For numerical representation, an anisotropic hyperelastic material model in conjunction with a time domain linear viscoelasticity formulation with Prony series was employed. Model parameters were inversely derived, employing finite element models, using multi-criteria optimization. The methodology provides insight into mechanical superficial facial tissue properties. Experimental data shows pronounced anisotropy, especially with large strain. The stress relaxation rate does not depend on the loading direction, but is strain-dependent. Preconditioning eliminates equilibrium hysteresis effects and leads to stress-strain repeatability. In the preconditioned state tissue stiffness and hysteresis insensitivity to strain rate in the applied range is evident. The employed material model fits the nonlinear anisotropic elastic results and the viscoelasticity model reasonably reproduces time-dependent results. Inversely deduced maximum anisotropic long-term shear modulus of linear elasticity is G ∞,max aniso =2.43kPa and instantaneous initial shear modulus at an applied rate of ramp loading is G 0,max aniso =15.38kPa. Derived mechanical model parameters constitute a basis for complex skin interaction simulation. Copyright © 2017. Published by Elsevier Ltd.

The impact of pneumolysin on the macrophage response to Streptococcus pneumoniae is strain-dependent.

PubMed

Harvey, Richard M; Hughes, Catherine E; Paton, Adrienne W; Trappetti, Claudia; Tweten, Rodney K; Paton, James C

2014-01-01

Streptococcus pneumoniae is the world's leading cause of pneumonia, bacteremia, meningitis and otitis media. A major pneumococcal virulence factor is the cholesterol-dependent cytolysin, which has the defining property of forming pores in cholesterol-containing membranes. In recent times a clinically significant and internationally successful serotype 1 ST306 clone has been found to express a non-cytolytic variant of Ply (Ply306). However, while the pneumococcus is a naturally transformable organism, strains of the ST306 clonal group have to date been virtually impossible to transform, severely restricting efforts to understand the role of non-cytolytic Ply in the success of this clone. In this study isogenic Ply mutants were constructed in the D39 background and for the first time in the ST306 background (A0229467) to enable direct comparisons between Ply variants for their impact on the immune response in a macrophage-like cell line. Strains that expressed cytolytic Ply were found to induce a significant increase in IL-1β release from macrophage-like cells compared to the non-cytolytic and Ply-deficient strains in a background-independent manner, confirming the requirement for pore formation in the Ply-dependent activation of the NLRP3 inflammasome. However, cytolytic activity in the D39 background was found to induce increased expression of the genes encoding GM-CSF (CSF2), p19 subunit of IL-23 (IL23A) and IFNβ (IFNB1) compared to non-cytolytic and Ply-deficient D39 mutants, but had no effect in the A0229467 background. The impact of Ply on the immune response to the pneumococcus is highly dependent on the strain background, thus emphasising the importance of the interaction between specific virulence factors and other components of the genetic background of this organism.

The Impact of Pneumolysin on the Macrophage Response to Streptococcus pneumoniae is Strain-Dependent

PubMed Central

Paton, Adrienne W.; Trappetti, Claudia; Tweten, Rodney K.; Paton, James C.

2014-01-01

Streptococcus pneumoniae is the world's leading cause of pneumonia, bacteremia, meningitis and otitis media. A major pneumococcal virulence factor is the cholesterol-dependent cytolysin, which has the defining property of forming pores in cholesterol-containing membranes. In recent times a clinically significant and internationally successful serotype 1 ST306 clone has been found to express a non-cytolytic variant of Ply (Ply306). However, while the pneumococcus is a naturally transformable organism, strains of the ST306 clonal group have to date been virtually impossible to transform, severely restricting efforts to understand the role of non-cytolytic Ply in the success of this clone. In this study isogenic Ply mutants were constructed in the D39 background and for the first time in the ST306 background (A0229467) to enable direct comparisons between Ply variants for their impact on the immune response in a macrophage-like cell line. Strains that expressed cytolytic Ply were found to induce a significant increase in IL-1β release from macrophage-like cells compared to the non-cytolytic and Ply-deficient strains in a background-independent manner, confirming the requirement for pore formation in the Ply-dependent activation of the NLRP3 inflammasome. However, cytolytic activity in the D39 background was found to induce increased expression of the genes encoding GM-CSF (CSF2), p19 subunit of IL-23 (IL23A) and IFNβ (IFNB1) compared to non-cytolytic and Ply-deficient D39 mutants, but had no effect in the A0229467 background. The impact of Ply on the immune response to the pneumococcus is highly dependent on the strain background, thus emphasising the importance of the interaction between specific virulence factors and other components of the genetic background of this organism. PMID:25105894

Electric field dynamics in nitride structures containing quaternary alloy (Al, In, Ga)N

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

Borysiuk, J., E-mail: jolanta.borysiuk@ifpan.edu.pl; Faculty of Physics, University of Warsaw, Pasteura 5, 02-093 Warsaw; Sakowski, K.

2016-07-07

Molecular beam epitaxy growth and basic physical properties of quaternary AlInGaN layers, sufficiently thick for construction of electron blocking layers (EBL), embedded in ternary InGaN layers are presented. Transmission electron microscopy (TEM) measurement revealed good crystallographic structure and compositional uniformity of the quaternary layers contained in other nitride layers, which are typical for construction of nitride based devices. The AlInGaN layer was epitaxially compatible to InGaN matrix, strained, and no strain related dislocation creation was observed. The strain penetrated for limited depth, below 3 nm, even for relatively high content of indium (7%). For lower indium content (0.6%), the strain wasmore » below the detection limit by TEM strain analysis. The structures containing quaternary AlInGaN layers were studied by time dependent photoluminescence (PL) at different temperatures and excitation powers. It was shown that PL spectra contain three peaks: high energy donor bound exciton peak from the bulk GaN (DX GaN) and the two peaks (A and B) from InGaN layers. No emission from quaternary AlInGaN layers was observed. An accumulation of electrons on the EBL interface in high-In sample and formation of 2D electron gas (2DEG) was detected. The dynamics of 2DEG was studied by time resolved luminescence revealing strong dependence of emission energy on the 2DEG concentration. Theoretical calculations as well as power-dependence and temperature-dependence analysis showed the importance of electric field inside the structure. At the interface, the field was screened by carriers and could be changed by illumination. From these measurements, the dynamics of electric field was described as the discharge of carriers accumulated on the EBL.« less

Dynamic shear rheology of colloidal suspensions of surface-modified silica nanoparticles in PEG

NASA Astrophysics Data System (ADS)

Swarna; Pattanayek, Sudip Kumar; Ghosh, Anup Kumar

2018-03-01

The present work illustrates the effect of surface modification of silica nanoparticles (500 nm) with 3-(glycidoxypropyl)trimethoxy silane which was carried out at different reaction times. The suspensions prepared from modified and unmodified silica nanoparticles were evaluated for their shear rate-dependent viscosity and strain-frequency-dependent modulus. The linear viscoelastic moduli, viz., storage modulus and loss modulus, were compared with those of nonlinear moduli. The shear-thickened suspensions displayed strain thinning at low-frequency smaller strains and a strong strain overshoot at higher strains, characteristics of a continuous shear thickening fluids. The shear-thinned suspension, conversely, exhibited a strong elastic dominance at smaller strains, but at higher strains, its strain softened observed in the steady shear viscosity plot indicating characteristics of yielding material. Considering higher order harmonic components, the decomposed elastic and viscous stress revealed a pronounced elastic response up to 10% strain and a high viscous damping at larger strains. The current work is one of a kind in demonstrating the effect of silica surface functionalization on the linear and nonlinear viscoelasticity of suspensions showing a unique rheological fingerprint. The suspensions can thus be predicted through rheological studies for their applicability in energy absorbing and damping materials with respect to their mechanical properties.

Ultrafast dynamic response of single-crystal β-HMX (octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine)

NASA Astrophysics Data System (ADS)

Zaug, Joseph M.; Austin, Ryan A.; Armstrong, Michael R.; Crowhurst, Jonathan C.; Goldman, Nir; Ferranti, Louis; Saw, Cheng K.; Swan, Raymond A.; Gross, Richard; Fried, Laurence E.

2018-05-01

We report experimental and computational studies of shock wave dynamics in single-crystal β-HMX on an ultrafast time scale. Here, a laser-based compression drive (˜1 ns in duration; stresses of up to ˜40 GPa) is used to propagate shock waves normal to the (110) and (010) lattice planes. Ultrafast time-domain interferometry measurements reveal distinct, time-dependent relationships between the shock wave velocity and particle velocity for each crystal orientation, which suggest evolving physical processes on a sub-nanosecond time scale. To help interpret the experimental data, elastic shock wave response was simulated using a finite-strain model of crystal thermoelasticity. At early propagation times (<500 ps), the model is in agreement with the data, which indicates that the mechanical response is dominated by thermoelastic deformation. The model agreement depends on the inclusion of nonlinear elastic effects in both the spherical and deviatoric stress-strain responses. This is achieved by employing an equation-of-state and a pressure-dependent stiffness tensor, which was computed via atomistic simulation. At later times (>500 ps), the crystal samples exhibit signatures of inelastic deformation, structural phase transformation, or chemical reaction, depending on the direction of wave propagation.

Matrix dominated stress/strain behavior in polymeric composites: Effects of hold time, nonlinearity and rate dependency

NASA Technical Reports Server (NTRS)

Gates, Thomas S.

1992-01-01

In order to understand matrix dominated behavior in laminated polymer matrix composites, an elastic/viscoplastic constitutive model was developed and used to predict stress strain behavior of off-axis and angle-ply symmetric laminates under in-plane, tensile axial loading. The model was validated for short duration tests at elevated temperatures. Short term stress relaxation and short term creep, strain rate sensitivity, and material nonlinearity were accounted for. The testing times were extended for longer durations, and periods of creep and stress relaxation were used to investigate the ability of the model to account for long term behavior. The model generally underestimated the total change in strain and stress for both long term creep and long term relaxation respectively.

Dependence of the Brillouin gain spectrum on linear strain distribution for optical time-domain reflectometer-type strain sensors

NASA Astrophysics Data System (ADS)

Naruse, Hiroshi; Tateda, Mitsuhiro; Ohno, Hiroshige; Shimada, Akiyoshi

2002-12-01

We theoretically derive the shape of the Brillouin gain spectrum, that is, the Brillouin backscattered-light power spectrum, produced in an optical fiber under conditions of a strain distribution that changes linearly with a constant slope. The modeled measurement system is an optical time-domain reflectometer-type strain sensor system. The linear strain distribution is one of the fundamental distributions and is produced in, for example, a beam to which a concentrated load is applied. By analyzing a function that expresses the shape of the derived Brillouin gain spectrum, we show that the strain calculated from the frequency at which the spectrum has a peak value coincides with that at the center of the effective pulsed light. In addition, the peak value and the full width at half-maximum of the Brillouin gain spectrum are both influenced by the strain difference between the two ends of the effective pulse. We investigate this influence in detail and obtain the relationship between strain difference and strain measurement error.

Survival of Salmonella enterica in poultry feed is strain dependent

PubMed Central

Andino, Ana; Pendleton, Sean; Zhang, Nan; Chen, Wei; Critzer, Faith; Hanning, Irene

2014-01-01

Feed components have low water activity, making bacterial survival difficult. The mechanisms of Salmonella survival in feed and subsequent colonization of poultry are unknown. The purpose of this research was to compare the ability of Salmonella serovars and strains to survive in broiler feed and to evaluate molecular mechanisms associated with survival and colonization by measuring the expression of genes associated with colonization (hilA, invA) and survival via fatty acid synthesis (cfa, fabA, fabB, fabD). Feed was inoculated with 1 of 15 strains of Salmonella enterica consisting of 11 serovars (Typhimurium, Enteriditis, Kentucky, Seftenburg, Heidelberg, Mbandanka, Newport, Bairely, Javiana, Montevideo, and Infantis). To inoculate feed, cultures were suspended in PBS and survival was evaluated by plating samples onto XLT4 agar plates at specific time points (0 h, 4 h, 8 h, 24 h, 4 d, and 7 d). To evaluate gene expression, RNA was extracted from the samples at the specific time points (0, 4, 8, and 24 h) and gene expression measured with real-time PCR. The largest reduction in Salmonella occurred at the first and third sampling time points (4 h and 4 d) with the average reductions being 1.9 and 1.6 log cfu per g, respectively. For the remaining time points (8 h, 24 h, and 7 d), the average reduction was less than 1 log cfu per g (0.6, 0.4, and 0.6, respectively). Most strains upregulated cfa (cyclopropane fatty acid synthesis) within 8 h, which would modify the fluidity of the cell wall to aid in survival. There was a weak negative correlation between survival and virulence gene expression indicating downregulation to focus energy on other gene expression efforts such as survival-related genes. These data indicate the ability of strains to survive over time in poultry feed was strain dependent and that upregulation of cyclopropane fatty acid synthesis and downregulation of virulence genes were associated with a response to desiccation stress. PMID:24570467

Survival of Salmonella enterica in poultry feed is strain dependent.

PubMed

Andino, Ana; Pendleton, Sean; Zhang, Nan; Chen, Wei; Critzer, Faith; Hanning, Irene

2014-02-01

Feed components have low water activity, making bacterial survival difficult. The mechanisms of Salmonella survival in feed and subsequent colonization of poultry are unknown. The purpose of this research was to compare the ability of Salmonella serovars and strains to survive in broiler feed and to evaluate molecular mechanisms associated with survival and colonization by measuring the expression of genes associated with colonization (hilA, invA) and survival via fatty acid synthesis (cfa, fabA, fabB, fabD). Feed was inoculated with 1 of 15 strains of Salmonella enterica consisting of 11 serovars (Typhimurium, Enteriditis, Kentucky, Seftenburg, Heidelberg, Mbandanka, Newport, Bairely, Javiana, Montevideo, and Infantis). To inoculate feed, cultures were suspended in PBS and survival was evaluated by plating samples onto XLT4 agar plates at specific time points (0 h, 4 h, 8 h, 24 h, 4 d, and 7 d). To evaluate gene expression, RNA was extracted from the samples at the specific time points (0, 4, 8, and 24 h) and gene expression measured with real-time PCR. The largest reduction in Salmonella occurred at the first and third sampling time points (4 h and 4 d) with the average reductions being 1.9 and 1.6 log cfu per g, respectively. For the remaining time points (8 h, 24 h, and 7 d), the average reduction was less than 1 log cfu per g (0.6, 0.4, and 0.6, respectively). Most strains upregulated cfa (cyclopropane fatty acid synthesis) within 8 h, which would modify the fluidity of the cell wall to aid in survival. There was a weak negative correlation between survival and virulence gene expression indicating downregulation to focus energy on other gene expression efforts such as survival-related genes. These data indicate the ability of strains to survive over time in poultry feed was strain dependent and that upregulation of cyclopropane fatty acid synthesis and downregulation of virulence genes were associated with a response to desiccation stress.

Experimental investigation of time dependent behavior of welded Topopah Spring Tuff

NASA Astrophysics Data System (ADS)

Ma, Lumin

Four types of laboratory tests have been performed. Specimens were attained from four lithophysal zones of the welded Topopah Spring Tuff unit at Yucca Mountain, Nevada: upper lithophysal, middle nonlithophysal, lower lithophysal and lower nonlithophysal zones. Two types of tests are conducted to study time-dependent behavior: constant strain rate and creep tests. Sixty-five specimens from the middle nonlithophysal zone were tested at six strain rates: 10-2, 10-4, 10-5, 10-6, 10-7, and 10-8 s-1. Test durations range from 2 seconds to 7 days. Fourteen specimens from middle nonlithophysal, lower lithophysal and lower nonlithophysal zones are creep tested by incremental stepwise loading. All the tests are conducted under uniaxial compression at room temperature and humidity. Specimens exhibit extremely brittle fracture and fail by axial splitting, and show very little dilatancy if any. It is assumed that microfracturing dominates the inelastic deformation and failure of the tuff. Nonlinear regression is applied to the results of the constant strain rate tests to estimate the relations between peak strength, peak axial strain, secant modulus and strain rate. All three these parameters decrease with a decrease of strain rate and follow power functions: sigmapeak = 271.37 3˙0.0212 0.0212, epsilonpeak = 0.006 3˙0.0083 , ES = 41985.4 3˙0.015 . Secant modulus is introduced mainly as a tool to analyze strain rate dependent axial strain. Two threshold stresses define creep behavior. Below about 50% of peak strength, a specimen does not creep. Above about 94% of peak strength, a specimen creeps at an accelerating rate. Between the two threshold stresses, a power law relates strain rate and stress. One hundred fifty-eight Brazilian (Indirect tensile splitting) tests have been performed at six different constant strain rates. Nineteen lithophysal specimens were tested in uniaxial compression to study their fracture pattern. These specimens have a far less brittle failure mode. They slowly crumble, collapse, and maintain considerable relative strength beyond the peak. Due to the presence of multiple relatively large lithophysal cavities, they are far weaker and softer than the nonlithophysal specimens.

Creep of Ni(3)Al in the temperature regime of anomalous flow behavior

NASA Astrophysics Data System (ADS)

Uchic, Michael David

Much attention has been paid to understanding the dynamics of dislocation motion and substructure formation in Ni3Al in the anomalous flow regime. However, most of the experimental work that has been performed in the lowest temperatures of the anomalous flow regime has been under constant-strain-rate conditions. An alternative and perhaps more fundamental way to probe the plastic behavior of materials is a monotonic creep test, in which the stress and temperature are held constant while the time-dependent strain is measured. The aim of this study is to use constant-stress experiments to further explore the plastic flow anomaly in L12 alloys at low temperatures. Tension creep experiments have been carried out on <123> oriented single crystals of Ni75Al24Ta1 at temperatures between 293 and 473 K. We have observed primary creep leading to exhaustion at all temperatures and stresses, with creep rates declining faster than predicted by the logarithmic creep law. The total strain and creep strain have an anomalous dependence on temperature, which is consistent with the flow stress anomaly. We have also observed other unusual behavior in our creep experiments; for example, the reinitiation of plastic flow at low temperatures after a modest increment in applied stress shows a sigmoidal response, i.e., there is a significant time delay before the plastic strain rate accelerates to a maximum value. We also examined the ability to reinitiate plastic flow in samples that have been crept to exhaustion by simply lowering the test temperature. In addition, we have also performed conventional constant-displacement-rate experiments in the same temperature range. From these experiments, we have discovered that unlike most metals, Ni3Al displays a negative dependence of the work hardening rate (WHR) with increasing strain rate. For tests at intermediate temperatures (373 and 423 K), the WHRs of crystals tested at moderately high strain rates (10-2 s-1) are half the WHRs of crystals tested at conventional strain rates (10 -5 s-1), and this anomalous dependence has also been shown to be reversible with changes in strain rate. The implications of all results are discussed in light of our efforts to model plastic deformation in these alloys.

Time-Temperature Dependent Response of Filament Wound Composites for Flywheel Rotors

NASA Technical Reports Server (NTRS)

Thesken, John C.; Bowman, Cheryl L.; Arnold, Steven M.; Thompson, Richard C.

2004-01-01

Flywheel energy storage offers an attractive alternative to battery systems used in space applications such as the International Space Station. Rotor designs capable of high specific energies benefit from the load carrying capacity of hoop wound carbon fibers but their long-term durability may be limited by time-temperature dependent radial deformations. This was investigated for the carbon/epoxy rotor material, IM7/8552. Coupon specimens were sectioned from filament wound panels. These were tested in compression and tension at room temperature (RT), 95 and 135 C for strain rates from 5x10(exp -6) per second to 5x10(exp -3) per second. Time, temperature and load sign dependent effects were significant transverse to the fiber. At -0.5 percent strain for 72 hr, compressive stresses relaxed 16.4 percent at 135 C and 13 percent at 95 C. Tensile stresses relaxed only 7 percent in 72 hr at 135 C for 0.5 percent strain. Using linear hereditary material response and Boltzmann s principle of superposition to describe this behavior is problematic if not intractable. Micromechanics analysis including the effects of processing residual stresses is needed to resolve the paradoxes. Uniaxial compressive stress relaxation data may be used to bound the loss of radial pre-load stresses in flywheel rotors.

Evaluation of Bacillus anthracis and Yersinia pestis sample collection from nonporous surfaces by quantitative real-time PCR.

PubMed

Hong-Geller, E; Valdez, Y E; Shou, Y; Yoshida, T M; Marrone, B L; Dunbar, J M

2010-04-01

We will validate sample collection methods for recovery of microbial evidence in the event of accidental or intentional release of biological agents into the environment. We evaluated the sample recovery efficiencies of two collection methods - swabs and wipes - for both nonvirulent and virulent strains of Bacillus anthracis and Yersinia pestis from four types of nonporous surfaces: two hydrophilic surfaces, stainless steel and glass, and two hydrophobic surfaces, vinyl and plastic. Sample recovery was quantified using real-time qPCR to assay for intact DNA signatures. We found no consistent difference in collection efficiency between swabs or wipes. Furthermore, collection efficiency was more surface-dependent for virulent strains than nonvirulent strains. For the two nonvirulent strains, collection efficiency was similar between all four surfaces, albeit B. anthracis Sterne exhibited higher levels of recovery compared to Y. pestis A1122. In contrast, recovery of B. anthracis Ames spores and Y. pestis CO92 from the hydrophilic glass or stainless steel surfaces was generally more efficient compared to collection from the hydrophobic vinyl and plastic surfaces. Our results suggest that surface hydrophobicity may play a role in the strength of pathogen adhesion. The surface-dependent collection efficiencies observed with the virulent strains may arise from strain-specific expression of capsular material or other cell surface receptors that alter cell adhesion to specific surfaces. These findings contribute to the validation of standard bioforensics procedures and emphasize the importance of specific strain and surface interactions in pathogen detection.

Impact of virus strain characteristics on early detection of highly pathogenic avian influenza infection in commercial table-egg layer flocks and implications for outbreak control.

PubMed

Weaver, J Todd; Malladi, Sasidhar; Goldsmith, Timothy J; Hueston, Will; Hennessey, Morgan; Lee, Brendan; Voss, Shauna; Funk, Janel; Der, Christina; Bjork, Kathe E; Clouse, Timothy L; Halvorson, David A

2012-12-01

Early detection of highly pathogenic avian influenza (HPAI) infection in commercial poultry flocks is a critical component of outbreak control. Reducing the time to detect HPAI infection can reduce the risk of disease transmission to other flocks. The timeliness of different types of detection triggers could be dependent on clinical signs that are first observed in a flock, signs that might vary due to HPAI virus strain characteristics. We developed a stochastic disease transmission model to evaluate how transmission characteristics of various HPAI strains might effect the relative importance of increased mortality, drop in egg production, or daily real-time reverse transcriptase (RRT)-PCR testing, toward detecting HPAI infection in a commercial table-egg layer flock. On average, daily RRT-PCR testing resulted in the shortest time to detection (from 3.5 to 6.1 days) depending on the HPAI virus strain and was less variable over a range of transmission parameters compared with other triggers evaluated. Our results indicate that a trigger to detect a drop in egg production would be useful for HPAI virus strains with long infectious periods (6-8 days) and including an egg-drop detection trigger in emergency response plans would lead to earlier and consistent reporting in some cases. We discuss implications for outbreak control and risk of HPAI spread attributed to different HPAI strain characteristics where an increase in mortality or a drop in egg production or both would be among the first clinical signs observed in an infected flock.

Development of steel foam processing methods and characterization of metal foam

NASA Astrophysics Data System (ADS)

Park, Chanman

2000-10-01

Steel foam was synthesized by a powder metallurgical route, resulting in densities less than half that of steel. Process parameters for foam synthesis were investigated, and two standard powder formulations were selected consisting of Fe-2.5% C and 0.2 wt% foaming agent (either MgCO3 or SrCO3). Compression tests were performed on annealed and pre-annealed foam samples of different density to determine mechanical response and energy absorption behavior. The stress-strain response was strongly affected by annealing, which reduced the carbon content and converted much of the pearlitic structure to ferrite. Different powder blending methods and melting times were employed and the effects on the geometric structure of steel foam were examined. Dispersion of the foaming agent affected the pore size distribution of the expanded foams. With increasing melt time, pores coalesced, leading to the eventual collapse of the foam. Inserting interlayer membranes in the powder compacts inhibited coalescence of pores and produced foams with more uniform cell size and distribution. The closed-cell foam samples exhibited anisotropy in compression, a phenomenon that was caused primarily by the ellipsoidal cell shapes within the foam. Yield strengths were 3x higher in the transverse direction than in the longitudinal direction. Yield strength also showed a power-law dependence on relative density (n ≅ 1.8). Compressive strain was highly localized and occurred in discrete bands that extended transverse to the loading direction. The yield strength of foam samples showed stronger strain rate dependence at higher strain rates. The increased strain rate dependence was attributed to microinertial hardening. Energy absorption was also observed to increase with strain rate. Measurements of cell wall curvature showed that an increased mean curvature correlated with a reduced yield strength, and foam strengths generally fell below predictions of Gibson-Ashby theory. Morphological defects reduced yield strength and altered the dependence on density. Microstructural analysis was performed on a porous Mg and AZ31 Mg alloy synthesized by the GASAR process. The pore distribution depended on the distance from the chill end of ingots. TEM observations revealed apparent gas tracks neat the pores and ternary intermetallic phases in the alloy.

Cysteine Inhibits Mercury Methylation by Geobacter sulfurreducens PCA Mutant Δ omcBESTZ

DOE PAGES

Lin, Hui; Lu, Xia; Liang, Liyuan; ...

2015-04-21

For cysteine enhances Hg uptake and methylation by Geobacter sulfurreducens PCA wild type (WT) strain in short-term assays. The prevalence of this enhancement in other strains remains poorly understood. We examined the influence of cysteine concentration on time-dependent Hg(II) reduction, sorption and methylation by PCA-WT and its c-type cytochrome-deficient mutant ( omcBESTZ) in phosphate buffered saline. Without cysteine, the mutant methylated twice as much Hg(II) as the PCA-WT, whereas addition of cysteine inhibited Hg methylation, regardless of the reaction time. PCA-WT, but, exhibited both time-dependent and cysteine concentration-dependent methylation. In 144 hour assay, nearly complete sorption of the Hg(II) bymore » PCA-WT occurred in the presence of 1 mM cysteine, resulting in our highest observed methylmercury production. Moreover, the chemical speciation modeling and experimental data suggest that uncharged Hg(II) species are more readily taken up, and that this uptake is kinetic limiting, thereby affecting Hg methylation by both mutant and WT.« less

Investigating the Strain, Temperature and Humidity Sensitivity of a Multimode Graded-Index Perfluorinated Polymer Optical Fiber with Bragg Grating

PubMed Central

Zheng, Yulong; Bremer, Kort

2018-01-01

In this work we investigate the strain, temperature and humidity sensitivity of a Fiber Bragg Grating (FBG) inscribed in a near infrared low-loss multimode perfluorinated polymer optical fiber based on cyclic transparent optical polymer (CYTOP). For this purpose, FBGs were inscribed into the multimode CYTOP fiber with a core diameter of 50 µm by using a krypton fluoride (KrF) excimer laser and the phase mask method. The evolution of the reflection spectrum of the FBG detected with a multimode interrogation technique revealed a single reflection peak with a full width at half maximum (FHWM) bandwidth of about 9 nm. Furthermore, the spectral envelope of the single FBG reflection peak can be optimized depending on the KrF excimer laser irradiation time. A linear shift of the Bragg wavelength due to applied strain, temperature and humidity was measured. Furthermore, depending on irradiation time of the KrF excimer laser, both the failure strain and strain sensitivity of the multimode fiber with FBG can be controlled. The inherent low light attenuation in the near infrared wavelength range (telecommunication window) of the multimode CYTOP fiber and the single FBG reflection peak when applying the multimode interrogation set-up will allow for new applications in the area of telecommunication and optical sensing. PMID:29734734

Investigating the Strain, Temperature and Humidity Sensitivity of a Multimode Graded-Index Perfluorinated Polymer Optical Fiber with Bragg Grating.

PubMed

Zheng, Yulong; Bremer, Kort; Roth, Bernhard

2018-05-05

In this work we investigate the strain, temperature and humidity sensitivity of a Fiber Bragg Grating (FBG) inscribed in a near infrared low-loss multimode perfluorinated polymer optical fiber based on cyclic transparent optical polymer (CYTOP). For this purpose, FBGs were inscribed into the multimode CYTOP fiber with a core diameter of 50 µm by using a krypton fluoride (KrF) excimer laser and the phase mask method. The evolution of the reflection spectrum of the FBG detected with a multimode interrogation technique revealed a single reflection peak with a full width at half maximum (FHWM) bandwidth of about 9 nm. Furthermore, the spectral envelope of the single FBG reflection peak can be optimized depending on the KrF excimer laser irradiation time. A linear shift of the Bragg wavelength due to applied strain, temperature and humidity was measured. Furthermore, depending on irradiation time of the KrF excimer laser, both the failure strain and strain sensitivity of the multimode fiber with FBG can be controlled. The inherent low light attenuation in the near infrared wavelength range (telecommunication window) of the multimode CYTOP fiber and the single FBG reflection peak when applying the multimode interrogation set-up will allow for new applications in the area of telecommunication and optical sensing.

Nonlinear effects on composite laminate thermal expansion

NASA Technical Reports Server (NTRS)

Hashin, Z.; Rosen, B. W.; Pipes, R. B.

1979-01-01

Analyses of Graphite/Polyimide laminates shown that the thermomechanical strains cannot be separated into mechanical strain and free thermal expansion strain. Elastic properties and thermal expansion coefficients of unidirectional Graphite/Polyimide specimens were measured as a function of temperature to provide inputs for the analysis. The + or - 45 degrees symmetric Graphite/Polyimide laminates were tested to obtain free thermal expansion coefficients and thermal expansion coefficients under various uniaxial loads. The experimental results demonstrated the effects predicted by the analysis, namely dependence of thermal expansion coefficients on load, and anisotropy of thermal expansion under load. The significance of time dependence on thermal expansion was demonstrated by comparison of measured laminate free expansion coefficients with and without 15 day delay at intermediate temperature.

Temperature-Dependent Expression of phzM and Its Regulatory Genes lasI and ptsP in Rhizosphere Isolate Pseudomonas sp. Strain M18▿

PubMed Central

Huang, Jiaofang; Xu, Yuquan; Zhang, Hongyan; Li, Yaqian; Huang, Xianqing; Ren, Bin; Zhang, Xuehong

2009-01-01

Pseudomonas sp. strain M18, an effective biological control agent isolated from the melon rhizosphere, has a genetic background similar to that of the opportunistic human pathogen Pseudomonas aeruginosa PAO1. However, the predominant phenazine produced by strain M18 is phenazine-1-carboxylic acid (PCA) rather than pyocyanin (PYO); the quantitative ratio of PCA to PYO is 105 to 1 at 28°C in strain M18, while the ratio is 1 to 2 at 37°C in strain PAO1. We first provided evidence that the differential production of the two phenazines in strains M18 and PAO1 is related to the temperature-dependent and strain-specific expression patterns of phzM, a gene involved in the conversion of PCA to PYO. Transcriptional levels of phzM were measured by quantitative real-time PCR, and the activities of both transcriptional and translational phzM′-′lacZ fusions were determined in strains M18 and PAO1, respectively. Using lasI::Gm and ptsP::Gm inactivation M18 mutants, we further show that expression of the phzM gene is positively regulated by the quorum-sensing protein LasI and negatively regulated by the phosphoenolpyruvate phosphotransferase protein PtsP. Surprisingly, the lasI and ptsP regulatory genes were also expressed in a temperature-dependent and strain-specific manner. The differential production of the phenazines PCA and PYO by strains M18 and PAO1 may be a consequence of selective pressure imposed on P. aeruginosa PAO1 and its relative M18 in the two different niches over a long evolutionary process. PMID:19717631

Development and application of a T7 RNA polymerase-dependent expression system for antibiotic production improvement in Streptomyces.

PubMed

Wei, Junhong; Tian, Jinjin; Pan, Guoqing; Xie, Jie; Bao, Jialing; Zhou, Zeyang

2017-06-01

To develop a reliable and easy to use expression system for antibiotic production improvement of Streptomyces. A two-compound T7 RNA polymerase-dependent gene expression system was developed to fulfill this demand. In this system, the T7 RNA polymerase coding sequence was optimized based on the codon usage of Streptomyces coelicolor. To evaluate the functionality of this system, we constructed an activator gene overexpression strain for enhancement of actinorhodin production. By overexpression of the positive regulator actII-ORF4 with this system, the maximum actinorhodin yield of engineered strain was 15-fold higher and the fermentation time was decreased by 48 h. The modified two-compound T7 expression system improves both antibiotic production and accelerates the fermentation process in Streptomyces. This provides a general and useful strategy for strain improvement of important antibiotic producing Streptomyces strains.

Biomechanics of fundamental frequency regulation: Constitutive modeling of the vocal fold lamina propria.

PubMed

Chan, Roger W; Siegmund, Thomas; Zhang, Kai

2009-12-01

Accurate characterization of biomechanical characteristics of the vocal fold is critical for understanding the regulation of vocal fundamental frequency (F(0)), which depends on the active control of the intrinsic laryngeal muscles as well as the passive biomechanical response of the vocal fold lamina propria. Specifically, the tissue stress-strain response and viscoelastic properties under cyclic tensile deformation are relevant, when the vocal folds are subjected to length and tension changes due to posturing. This paper describes a constitutive modeling approach quantifying the relationship between vocal fold stress and strain (or stretch), and establishes predictions of F(0) with the string model of phonation based on the constitutive parameters. Results indicated that transient and time-dependent changes in F(0), including global declinations in declarative sentences, as well as local F(0) overshoots and undershoots, can be partially attributed to the time-dependent viscoplastic response of the vocal fold cover.

Influences of misfit strains on liquid phase heteroepitaxial growth

NASA Astrophysics Data System (ADS)

Lu, Yanli; Peng, Yingying; Yu, Genggeng; Chen, Zheng

2017-10-01

Influences of misfit strains with different signs on liquid phase heteroepitaxial growth are studied by binary phase field crystal model. It is amazing to find that double islands are formed because of lateral and vertical separation. The morphological evolution of epitaxial layer depends on signs of misfit strains. The maximum atomic layer thickness of double islands under negative misfit strain is larger than that of under positive misfit strain at the same evolutional time, and size differences between light and dark islands is much smaller under negative misfit strain than that of under positive misfit strain. In addition, concentration field and density field approximately have similar variational law along x direction under the same misfit strain but show opposite variational trend under misfit strains with different signs. Generally, free energy of epitaxial growth systems keeps similar variational trend under misfit strains with different signs.

HIGH-RATE FORMABILITY OF HIGH-STRENGTH ALUMINUM ALLOYS: A STUDY ON OBJECTIVITY OF MEASURED STRAIN AND STRAIN RATE

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

Upadhyay, Piyush; Rohatgi, Aashish; Stephens, Elizabeth V.

2015-02-18

Al alloy AA7075 sheets were deformed at room temperature at strain-rates exceeding 1000 /s using the electrohydraulic forming (EHF) technique. A method that combines high speed imaging and digital image correlation technique, developed at Pacific Northwest National Laboratory, is used to investigate high strain rate deformation behavior of AA7075. For strain-rate sensitive materials, the ability to accurately model their high-rate deformation behavior is dependent upon the ability to accurately quantify the strain-rate that the material is subjected to. This work investigates the objectivity of software-calculated strain and strain rate by varying different parameters within commonly used commercially available digital imagemore » correlation software. Except for very close to the time of crack opening the calculated strain and strain rates are very consistent and independent of the adjustable parameters of the software.« less

Mitochondrial bioenergetics and drug-induced toxicity in a panel of mouse embryonic fibroblasts with mitochondrial DNA single nucleotide polymorphisms

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

Pereira, Claudia V.; Oliveira, Paulo J.; Will, Yvonne

2012-10-15

Mitochondrial DNA (mtDNA) variations including single nucleotide polymorphisms (SNPs) have been proposed to be involved in idiosyncratic drug reactions. However, current in vitro and in vivo models lack the genetic diversity seen in the human population. Our hypothesis is that different cell strains with distinct mtDNA SNPs may have different mitochondrial bioenergetic profiles and may therefore vary in their response to drug-induced toxicity. Therefore, we used an in vitro system composed of four strains of mouse embryonic fibroblasts (MEFs) with mtDNA polymorphisms. We sequenced mtDNA from embryonic fibroblasts isolated from four mouse strains, C57BL/6J, MOLF/EiJ, CZECHII/EiJ and PERA/EiJ, with themore » latter two being sequenced for the first time. The bioenergetic profile of the four strains of MEFs was investigated at both passages 3 and 10. Our results showed that there were clear differences among the four strains of MEFs at both passages, with CZECHII/EiJ having a lower mitochondrial robustness when compared to C57BL/6J, followed by MOLF/EiJ and PERA/EiJ. Seven drugs known to impair mitochondrial function were tested for their effect on the ATP content of the four strains of MEFs in both glucose- and galactose-containing media. Our results showed that there were strain-dependent differences in the response to some of the drugs. We propose that this model is a useful starting point to study compounds that may cause mitochondrial off-target toxicity in early stages of drug development, thus decreasing the number of experimental animals used. -- Highlights: ► mtDNA SNPs may be linked to individual predisposition to drug-induced toxicity. ► CZECHII/EiJ and PERA/EiJ mtDNA was sequenced for the first time in this study. ► Strain-dependent mitochondrial capacity differences were measured. ► Strain-dependent differences in response to mitochondrial toxicants were observed.« less

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

Treesearch

Scott E. Hamel; John C. Hermanson; Steven M. Cramer

2012-01-01

The thermoplastics within wood—plastic composites (WPCs) are known to experience significant time-dependent deformation or creep. In some formulations, creep deformation can be twice as much as the initial quasi-static strain in as little as 4 days. While extensive work has been done on the creep behavior of pure polymers, little information is available on the...

Heat strain in cold.

PubMed

Rintamäki, Hannu; Rissanen, Sirkka

2006-07-01

In spite of increased environmental cold stress, heat strain is possible also in a cold environment. The body heat balance depends on three factors: environmental thermal conditions, metabolic heat production and thermal insulation of clothing and other protective garments. As physical exercise may increase metabolic heat production from rest values by ten times or even more, the required thermal insulation of clothing may vary accordingly. However, in most outdoor work, and often in indoor cold work, too, the thermal insulation of clothing is impractical, difficult or impossible to adjust according to the changes in physical activity. This is especially true with whole body covering garments like chemical protective clothing. As a result of this imbalance, heat strain may develop. In cold all the signs of heat strain (core temperature above 38 degrees C, warm or hot thermal sensations, increased cutaneous circulation and sweating) may not be present at the same time. Heat strain in cold may be whole body heat strain or related only to torso or core temperature. Together with heat strain in torso or body core, there can be at the same time even cold strain in peripheral parts and/or superficial layers of the body. In cold environment both the preservation of insulation and facilitation of heat loss are important. Development of clothing design is still needed to allow easy adjustments of thermal insulation.

Mechanical Properties of EPON 826/DEA Epoxy

DTIC Science & Technology

2008-07-26

Eβ ( ε̇− ε̇pβ ) . (5b) Equations (2) and (5) are solved simultaneously as a system of time-dependant differential equations to determine the stress in...this implies that estimates of these underlying physical parameters are highly uncertain but also has a weak effect on the stress -strain relationships...20), 4923–4928 (1998) Chou, S.C., Robertson, K.D., et al.: The effect of strain rate and heat developed during deformation on the stress -strain curve

Reversible and Irreversible Time-Dependent Behavior of GRCop-84

NASA Technical Reports Server (NTRS)

Lerch, Bradley A.; Arnold, Steven M.; Ellis, David L.

2017-01-01

A series of mechanical tests were conducted on a high-conductivity copper alloy, GRCop-84, in order to understand the time dependent response of this material. Tensile, creep, and stress relaxation tests were performed over a wide range of temperatures, strain rates, and stress levels to excite various amounts of time-dependent behavior. At low applied stresses the deformation behavior was found to be fully reversible. Above a certain stress, termed the viscoelastic threshold, irreversible deformation was observed. At these higher stresses the deformation was observed to be viscoplastic. Both reversible and irreversible regions contained time dependent deformation. These experimental data are documented to enable characterization of constitutive models to aid in design of high temperature components.

Nonlinearity of bituminous mixtures

NASA Astrophysics Data System (ADS)

Mangiafico, S.; Babadopulos, L. F. A. L.; Sauzéat, C.; Di Benedetto, H.

2018-02-01

This paper presents an experimental characterization of the strain dependency of the complex modulus of bituminous mixtures for strain amplitude levels lower than about 110 μm/m. A series of strain amplitude sweep tests are performed at different temperatures (8, 10, 12 and 14°C) and frequencies (0.3, 1, 3 and 10 Hz), during which complex modulus is monitored. For each combination of temperature and frequency, four maximum strain amplitudes are targeted (50, 75, 100 and 110 μm/m). For each of them, two series of 50 loading cycles are applied, respectively at decreasing and increasing strain amplitudes. Before each decreasing strain sweep and after each increasing strain sweep, 5 cycles are performed at constant maximum targeted strain amplitude. Experimental results show that the behavior of the studied material is strain dependent. The norm of the complex modulus decreases and phase angle increases with strain amplitude. Results are presented in Black and Cole-Cole plots, where characteristic directions of nonlinearity can be identified. Both the effects of nonlinearity in terms of the complex modulus variation and of the direction of nonlinearity in Black space seem to validate the time-temperature superposition principle with the same shift factors as for linear viscoelasticity. The comparison between results obtained during increasing and decreasing strain sweeps suggests the existence of another phenomenon occurring during cyclic loading, which appears to systematically induce a decrease of the norm of the complex modulus and an increase of the phase angle, regardless of the type of the strain sweep (increasing or decreasing).

Strain-induced friction anisotropy between graphene and molecular liquids

NASA Astrophysics Data System (ADS)

Liao, Meng; To, Quy-Dong; Léonard, Céline; Monchiet, Vincent; Vo, Van-Hoang

2017-01-01

In this paper, we study the friction behavior of molecular liquids with anisotropically strained graphene. Due to the changes of lattice and the potential energy surface, the friction is orientation dependent and can be computed by tensorial Green-Kubo formula. Simple quantitative estimations are also proposed for the zero-time response and agree reasonably well with the molecular dynamics results. From simulations, we can obtain the information of structures, dynamics of the system, and study the influence of strain and molecular shapes on the anisotropy degree. It is found that unilateral strain can increase friction in all directions but the strain direction is privileged. Numerical evidences also show that nonspherical molecules are more sensitive to strain and give rise to more pronounced anisotropy effects.

Finite element simulation of location- and time-dependent mechanical behavior of chondrocytes in unconfined compression tests.

PubMed

Wu, J Z; Herzog, W

2000-03-01

Experimental evidence suggests that cells are extremely sensitive to their mechanical environment and react directly to mechanical stimuli. At present, it is technically difficult to measure fluid pressure, stress, and strain in cells, and to determine the time-dependent deformation of chondrocytes. For this reason, there are no data in the published literature that show the dynamic behavior of chondrocytes in articular cartilage. Similarly, the dynamic chondrocyte mechanics have not been calculated using theoretical models that account for the influence of cell volumetric fraction on cartilage mechanical properties. In the present investigation, the location- and time-dependent stress-strain state and fluid pressure distribution in chondrocytes in unconfined compression tests were simulated numerically using a finite element method. The technique involved two basic steps: first, cartilage was approximated as a macroscopically homogenized material and the mechanical behavior of cartilage was obtained using the homogenized model; second, the solution of the time-dependent displacements and fluid pressure fields of the homogenized model was used as the time-dependent boundary conditions for a microscopic submodel to obtain average location- and time-dependent mechanical behavior of cells. Cells and extracellular matrix were assumed to be biphasic materials composed of a fluid phase and a hyperelastic solid phase. The hydraulic permeability was assumed to be deformation dependent and the analysis was performed using a finite deformation approach. Numerical tests were made using configurations similar to those of experiments described in the literature. Our simulations show that the mechanical response of chondrocytes to cartilage loading depends on time, fluid boundary conditions, and the locations of the cells within the specimen. The present results are the first to suggest that chondrocyte deformation in a stress-relaxation type test may exceed the imposed system deformation by a factor of 3-4, that chondrocyte deformations are highly dynamic and do not reach a steady state within about 20 min of steady compression (in an unconfined test), and that cell deformations are very much location dependent.

Use of an otolith-deficient mutant in studies of fish behavior in microgravity

NASA Astrophysics Data System (ADS)

Ijiri, K.; Mizuno, R.; Eguchi, H.

2003-10-01

The mutant strain ( ha) of medaka ( Oryzias latipes) lack utricular otoliths as fry, and some never form otoliths for life. The cross (Fl generation) between the strain having good eyesight and another strain having ordinary eyesight augmented visual acuity of the Fl generation. Crossing the good eyesight strain and ha mutant produced fish having good eyesight and less sensitivity to gravity in the F2 population. Their tolerance to microgravity was tested by parabolic flight using an airplane. The fish exhibited less looping and no differences in degree of looping between light and dark conditions, suggesting that loss of eyesight (in darkness) is not a direct cause for looping behavior in microgravity. The ha embryos could not form utricular otoliths. They did form saccular otoliths, but with a delay. Fry of the mutant fish lacking the utricular otoliths are highly dependent on light upon hatching and exhibit a perfect dorsal-light response (DLR). As they grow, they eventually shift from being light-dependent to being gravity-dependent. Continuous treatment of the fry with altered light direction suppressed this shift to gravity dependence. Being less dependent on gravity, these fish can serve as models in studying the differences expected for the vestibular system of fish reared in microgravity. When these fish were exposed to microgravity (parabolic flights) of an airplane, they spent far less time looping than fish reared in an ordinary light regimen.

Measurement of Heavy Ion Irradiation Induced In-Plane Strain in Patterned Face-Centered-Cubic Metal Films: An in Situ Study

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

Yu, K. Y.; Chen, Y.; Li, J.

Nanocrystalline Ag, Cu, and Ni thin films and their coarse grained counterparts are patterned in this paper using focused ion beam and then irradiated by Kr ions within an electron microscope at room temperature. Irradiation induced in-plane strain of the films is measured by tracking the location of nanosized holes. The magnitude of the strain in all specimens is linearly dose-dependent and the strain rates of nanocrystalline metals are significantly greater as compared to that of the coarse grained metals. Finally, real-time microscopic observation suggests that substantial grain boundary migration and grain rotation are responsible for the significant in-plane strain.

Measurement of Heavy Ion Irradiation Induced In-Plane Strain in Patterned Face-Centered-Cubic Metal Films: An in Situ Study

DOE PAGES

Yu, K. Y.; Chen, Y.; Li, J.; ...

2016-11-28

Nanocrystalline Ag, Cu, and Ni thin films and their coarse grained counterparts are patterned in this paper using focused ion beam and then irradiated by Kr ions within an electron microscope at room temperature. Irradiation induced in-plane strain of the films is measured by tracking the location of nanosized holes. The magnitude of the strain in all specimens is linearly dose-dependent and the strain rates of nanocrystalline metals are significantly greater as compared to that of the coarse grained metals. Finally, real-time microscopic observation suggests that substantial grain boundary migration and grain rotation are responsible for the significant in-plane strain.

The Secret Life of Collagen: Temporal Changes in Nanoscale Fibrillar Pre-Strain and Molecular Organization during Physiological Loading of Cartilage.

PubMed

Inamdar, Sheetal R; Knight, David P; Terrill, Nicholas J; Karunaratne, Angelo; Cacho-Nerin, Fernando; Knight, Martin M; Gupta, Himadri S

2017-10-24

Articular cartilage is a natural biomaterial whose structure at the micro- and nanoscale is critical for healthy joint function and where degeneration is associated with widespread disorders such as osteoarthritis. At the nanoscale, cartilage mechanical functionality is dependent on the collagen fibrils and hydrated proteoglycans that form the extracellular matrix. The dynamic response of these ultrastructural building blocks at the nanoscale, however, remains unclear. Here we measure time-resolved changes in collagen fibril strain, using small-angle X-ray diffraction during compression of bovine and human cartilage explants. We demonstrate the existence of a collagen fibril tensile pre-strain, estimated from the D-period at approximately 1-2%, due to osmotic swelling pressure from the proteoglycan. We reveal a rapid reduction and recovery of this pre-strain which occurs during stress relaxation, approximately 60 s after the onset of peak load. Furthermore, we show that this reduction in pre-strain is linked to disordering in the intrafibrillar molecular packing, alongside changes in the axial overlapping of tropocollagen molecules within the fibril. Tissue degradation in the form of selective proteoglycan removal disrupts both the collagen fibril pre-strain and the transient response during stress relaxation. This study bridges a fundamental gap in the knowledge describing time-dependent changes in collagen pre-strain and molecular organization that occur during physiological loading of articular cartilage. The ultrastructural details of this transient response are likely to transform our understanding of the role of collagen fibril nanomechanics in the biomechanics of cartilage and other hydrated soft tissues.

Reversible strain effect on the magnetization of LaCoO3 films

NASA Astrophysics Data System (ADS)

Herklotz, A.; Rata, A. D.; Schultz, L.; Dörr, K.

2009-03-01

The magnetization (M) of a LaCoO3 film grown epitaxially on a piezoelectric substrate has been investigated in dependence on the biaxial in-plane strain. M decreases with the reversible release of tensile strain, with a maximum change of at least 6% per 0.1% of biaxial strain near the Curie temperature (TC) . The biaxial strain response of TC is estimated to be below 5 K/% in the tensile strain state. This is in agreement with results from statically strained films on various substrates. As possible origins of the strain-induced magnetization are considered (i) the strain-dependent Curie temperature, (ii) a strain-dependent magnetically inhomogeneous (phase-separated) state, and (iii) a strain-dependent magnetic moment (spin state) of Co ions. The TC shift is found insufficient to explain the measured strain-induced magnetization change but contributions from mechanism (ii) or (iii) must be involved.

Different patterns of extracellular proteolytic activity in W303a and BY4742 Saccharomyces cerevisiae strains.

PubMed

Seredyński, Rafał; Wolna, Dorota; Kędzior, Mateusz; Gutowicz, Jan

2017-01-01

Protease secretion in Saccharomyces cerevisiae cultures is a complex process, important for the application of this organism in the food industry and biotechnology. Previous studies provide rather quantitative data, yielding no information about the number of enzymes involved in proteolysis and their individual biochemical properties. Here we demonstrate that W303a and BY4742 S. cerevisiae strains reveal different patterns of spontaneous and gelatin-induced extracellular proteolytic activity. We applied the gelatin zymography assay to track changes of the proteolytic profile in time, finding the protease secretion dependent on the growth phase and the presence of the protein inducer. Detected enzymes were characterized regarding their substrate specificity, pH tolerance, and susceptibility to inhibitors. In case of the W303a strain, only one type of gelatin-degrading secretory protease (presumably metalloproteinase) was observed. However, the BY4742 strain secreted different proteases of the various catalytic types, depending on the substrate availability. Our study brings the evidence that S. cerevisiae strains secrete several kinds of proteases depending on the presence and type of the substrate. Protein induction may cause not only quantitative but also qualitative changes in the extracellular proteolytic patterns. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

History Dependence of the Microstructure on Time-Dependent Deformation During In-Situ Cooling of a Nickel-Based Single-Crystal Superalloy

NASA Astrophysics Data System (ADS)

Panwisawas, Chinnapat; D'Souza, Neil; Collins, David M.; Bhowmik, Ayan; Roebuck, Bryan

2018-05-01

Time-dependent plastic deformation through stress relaxation and creep deformation during in-situ cooling of the as-cast single-crystal superalloy CMSX-4® has been studied via neutron diffraction, transmission electron microscopy, electro-thermal miniature testing, and analytical modeling across two temperature regimes. Between 1000 °C and 900 °C, stress relaxation prevails and gives rise to softening as evidenced by a decreased dislocation density and the presence of long segment stacking faults in γ phase. Lattice strains decrease in both the γ matrix and γ' precipitate phases. A constitutive viscoplastic law derived from in-situ isothermal relaxation test under-estimates the equivalent plastic strain in the prediction of the stress and strain evolution during cooling in this case. It is thereby shown that the history dependence of the microstructure needs to be taken into account while deriving a constitutive law and which becomes even more relevant at high temperatures approaching the solvus. Higher temperature cooling experiments have also been carried out between 1300 °C and 1150 °C to measure the evolution of stress and plastic strain close to the γ' solvus temperature. In-situ cooling of samples using ETMT shows that creep dominates during high-temperature deformation between 1300 °C and 1220 °C, but below a threshold temperature, typically 1220 °C work hardening begins to prevail from increasing γ' fraction and resulting in a rapid increase in stress. The history dependence of prior accumulated deformation is also confirmed in the flow stress measurements using a single sample while cooling. The saturation stresses in the flow stress experiments show very good agreement with the stresses measured in the cooling experiments when viscoplastic deformation is dominant. This study demonstrates that experimentation during high-temperature deformation as well as the history dependence of the microstructure during cooling plays a key role in deriving an accurate viscoplastic constitutive law for the thermo-mechanical process during cooling from solidification.

Nonlinear primary resonance of micro/nano-beams made of nanoporous biomaterials incorporating nonlocality and strain gradient size dependency

NASA Astrophysics Data System (ADS)

Sahmani, S.; Aghdam, M. M.

2018-03-01

A wide range of biological applications such as drug delivery, biosensors and hemodialysis can be provided by nanoporous biomaterials due to their uniform pore size as well as considerable pore density. In the current study, the size dependency in the nonlinear primary resonance of micro/nano-beams made of nanoporous biomaterials is anticipated. To accomplish this end, a refined truncated cube is introduced to model the lattice structure of nanoporous biomaterial. Accordingly, analytical expressions for the mechanical properties of material are derived as functions of pore size. After that, based upon a nonlocal strain gradient beam model, the size-dependent nonlinear Duffing type equation of motion is constructed. The Galerkin technique together with the multiple time-scales method is employed to obtain the nonlocal strain gradient frequency-response and amplitude-response related to the nonlinear primary resonance of a micro/nano-beam made of the nanoporous biomaterial with different pore sizes. It is indicated that the nonlocality causes to decrease the response amplitudes associated with the both bifurcation points of the jump phenomenon, while the strain gradient size dependency causes to increase them. Also, it is found that increasing the pore size leads to enhance the nonlinearity, so the maximum deflection of response occurs at higher excitation frequency.

The influence of temperature on brittle creep in sandstones

NASA Astrophysics Data System (ADS)

Heap, M. J.; Baud, P.; Meredith, P. G.; Vinciguerra, S.

2009-04-01

The characterization of time-dependent brittle rock deformation is fundamental to understanding the long-term evolution and dynamics of the Earth's upper crust. The presence of water promotes time-dependent deformation through environment-dependent stress corrosion cracking that allows rocks to deform at stresses far below their short-term failure stress. Here we report results from an experimental study of the influence of an elevated temperature on time-dependent brittle creep in water-saturated samples of Darley Dale (initial porosity of 13%), Bentheim (23%) and Crab Orchard (4%) sandstones. We present results from both conventional creep experiments (or ‘static fatigue' tests) and stress-stepping creep experiments performed under 20°C and 75°C and an effective confining pressure of 30 MPa (50 MPa confining pressure and a 20 MPa pore fluid pressure). The evolution of crack damage was monitored throughout each experiment by measuring the three proxies for damage (1) axial strain (2) pore volume change and (3) the output of AE energy. Conventional creep experiments have demonstrated that, for any given applied differential stress, the time-to-failure is dramatically reduced and the creep strain rate is significantly increased by application of an elevated temperature. Stress-stepping creep experiments have allowed us to investigate the influence of temperature in detail. Results from these experiments show that the creep strain rate for Darley Dale and Bentheim sandstones increases by approximately 3 orders of magnitude, and for Crab Orchard sandstone increases by approximately 2 orders of magnitude, as temperature is increased from 20°C to 75°C at a fixed effective differential stress. We discuss these results in the context of the different mineralogical and microstructural properties of the three rock types and the micro-mechanical and chemical processes operating on them.

Extracellular signal-regulated kinases 1 and 2 activation in endothelial cells exposed to cyclic strain

NASA Technical Reports Server (NTRS)

Ikeda, M.; Takei, T.; Mills, I.; Kito, H.; Sumpio, B. E.

1999-01-01

The aim of this study was to determine whether extracellular signal-regulated kinases 1/2 (ERK1/ERK2) are activated and might play a role in enhanced proliferation and morphological change induced by strain. Bovine aortic endothelial cells (BAEC) were subjected to an average of 6 or 10% strain at a rate of 60 cycles/min for up to 4 h. Cyclic strain caused strain- and time-dependent phosphorylation and activation of ERK1/ERK2. Peak phosphorylation and activation of ERK1/ERK2 induced by 10% strain were at 10 min. A specific ERK1/ERK2 kinase inhibitor, PD-98059, inhibited phosphorylation and activation of ERK1/ERK2 but did not inhibit the increased cell proliferation and cell alignment induced by strain. Treatment of BAEC with 2,5-di-tert-butyl-1, 4-benzohydroquinone, to deplete inositol trisphosphate-sensitive calcium storage, and gadolinium chloride, a Ca2+ channel blocker, did not inhibit the activation of ERK1/ERK2. Strain-induced ERK1/ERK2 activation was partly inhibited by the protein kinase C inhibitor calphostin C and completely inhibited by the tyrosine kinase inhibitor genistein. These data suggest that 1) ERK1/ERK2 are not critically involved in the strain-induced cell proliferation and orientation, 2) strain-dependent activation of ERK1/ERK2 is independent of intracellular and extracellular calcium mobilization, and 3) protein kinase C activation and tyrosine kinase regulate strain-induced activation of ERK1/ERK2.

Viscoelasticity of human oral mucosa: implications for masticatory biomechanics.

PubMed

Sawada, A; Wakabayashi, N; Ona, M; Suzuki, T

2011-05-01

The dynamic behavior of oral soft tissues supporting removable prostheses is not well understood. We hypothesized that the stress and strain of the mucosa exhibited time-dependent behavior under masticatory loadings. Displacement of the mucosa on the maxillary residual ridge was measured in vivo by means of a magnetic actuator/sensor under vertical loading in partially edentulous individuals. Subject-specific finite element models of homogeneous bone and mucosa were constructed based on computed tomography images. A mean initial elastic modulus of 8.0 × 10(-5) GPa and relaxation time of 494 sec were obtained from the curve adaptation of the finite element output to the in vivo time-displacement relationship. Delayed increase of the maximum compressive strain on the surface of the mucosa was observed under sustained load, while the maximum strain inside the mucosa was relatively low and uninfluenced by the duration of the load. The compressive stress showed a slight decrease with sustained load, due to stress relaxation of the mucosa. On simulation of cyclic load, the increment of the maximum strain and the evidence of residual strain were revealed after each loading. The results support our hypothesis, and suggest that sustained and repetitive loads accumulate as surface strain on the mucosa.

Analysis of the efficiency of recombinant Escherichia coli strain cultivation in a gas-vortex bioreactor.

PubMed

Savelyeva, Anna V; Nemudraya, Anna A; Podgornyi, Vladimir F; Laburkina, Nadezhda V; Ramazanov, Yuriy A; Repkov, Andrey P; Kuligina, Elena V; Richter, Vladimir A

2017-09-01

The levels of aeration and mass transfer are critical parameters required for an efficient aerobic bioprocess, and directly depend on the design features of exploited bioreactors. A novel apparatus, using gas vortex for aeration and mass transfer processes, was constructed in the Center of Vortex Technologies (Novosibirsk, Russia). In this paper, we compared the efficiency of recombinant Escherichia coli strain cultivation using novel gas-vortex technology with conventional bioprocess technologies such as shake flasks and bioreactors with mechanical stirrers. We demonstrated that the system of aeration and agitation used in gas-vortex bioreactors provides 3.6 times higher volumetric oxygen transfer coefficient in comparison with mechanical bioreactor. The use of gas-vortex bioreactor for recombinant E. coli strain cultivation allows to increase the efficiency of target protein expression at 2.2 times for BL21(DE3)/pFK2 strain and at 3.5 times for auxotrophic C600/pRT strain (in comparison with stirred bioreactor). © 2016 International Union of Biochemistry and Molecular Biology, Inc.

Towards an acoustic model-based poroelastic imaging method: I. Theoretical foundation.

PubMed

Berry, Gearóid P; Bamber, Jeffrey C; Armstrong, Cecil G; Miller, Naomi R; Barbone, Paul E

2006-04-01

The ultrasonic measurement and imaging of tissue elasticity is currently under wide investigation and development as a clinical tool for the assessment of a broad range of diseases, but little account in this field has yet been taken of the fact that soft tissue is porous and contains mobile fluid. The ability to squeeze fluid out of tissue may have implications for conventional elasticity imaging, and may present opportunities for new investigative tools. When a homogeneous, isotropic, fluid-saturated poroelastic material with a linearly elastic solid phase and incompressible solid and fluid constituents is subjected to stress, the behaviour of the induced internal strain field is influenced by three material constants: the Young's modulus (E(s)) and Poisson's ratio (nu(s)) of the solid matrix and the permeability (k) of the solid matrix to the pore fluid. New analytical expressions were derived and used to model the time-dependent behaviour of the strain field inside simulated homogeneous cylindrical samples of such a poroelastic material undergoing sustained unconfined compression. A model-based reconstruction technique was developed to produce images of parameters related to the poroelastic material constants (E(s), nu(s), k) from a comparison of the measured and predicted time-dependent spatially varying radial strain. Tests of the method using simulated noisy strain data showed that it is capable of producing three unique parametric images: an image of the Poisson's ratio of the solid matrix, an image of the axial strain (which was not time-dependent subsequent to the application of the compression) and an image representing the product of the aggregate modulus E(s)(1-nu(s))/(1+nu(s))(1-2nu(s)) of the solid matrix and the permeability of the solid matrix to the pore fluid. The analytical expressions were further used to numerically validate a finite element model and to clarify previous work on poroelastography.

Origins of Negative Strain Rate Dependence of Stress Corrosion Cracking Initiation in Alloy 690, and Intergranular Crack Formation in Thermally Treated Alloy 690

NASA Astrophysics Data System (ADS)

Kim, Young Suk; Kim, Sung Soo

2016-09-01

We show that enhanced stress corrosion cracking (SCC) initiation in cold-rolled Alloy 690 with decreasing strain rate is related to the rate of short-range ordering (SRO) but not to the time-dependent corrosion process. Evidence for SRO is provided by aging tests on cold-rolled Alloy 690 at 623 K and 693 K (350 °C and 420 °C), respectively, which demonstrate its enhanced lattice contraction and hardness increase with aging temperature and time, respectively. Secondary intergranular cracks formed only in thermally treated and cold-rolled Alloy 690 during SCC tests, which are not SCC cracks, are caused by its lattice contraction by SRO before SCC tests but not by the orientation effect.

Comparison of two laryngeal tissue fiber constitutive models

NASA Astrophysics Data System (ADS)

Hunter, Eric J.; Palaparthi, Anil Kumar Reddy; Siegmund, Thomas; Chan, Roger W.

2014-02-01

Biological tissues are complex time-dependent materials, and the best choice of the appropriate time-dependent constitutive description is not evident. This report reviews two constitutive models (a modified Kelvin model and a two-network Ogden-Boyce model) in the characterization of the passive stress-strain properties of laryngeal tissue under tensile deformation. The two models are compared, as are the automated methods for parameterization of tissue stress-strain data (a brute force vs. a common optimization method). Sensitivity (error curves) of parameters from both models and the optimized parameter set are calculated and contrast by optimizing to the same tissue stress-strain data. Both models adequately characterized empirical stress-strain datasets and could be used to recreate a good likeness of the data. Nevertheless, parameters in both models were sensitive to measurement errors or uncertainties in stress-strain, which would greatly hinder the confidence in those parameters. The modified Kelvin model emerges as a potential better choice for phonation models which use a tissue model as one component, or for general comparisons of the mechanical properties of one type of tissue to another (e.g., axial stress nonlinearity). In contrast, the Ogden-Boyce model would be more appropriate to provide a basic understanding of the tissue's mechanical response with better insights into the tissue's physical characteristics in terms of standard engineering metrics such as shear modulus and viscosity.

Modeling the glass transition of amorphous networks for shape-memory behavior

NASA Astrophysics Data System (ADS)

Xiao, Rui; Choi, Jinwoo; Lakhera, Nishant; Yakacki, Christopher M.; Frick, Carl P.; Nguyen, Thao D.

2013-07-01

In this paper, a thermomechanical constitutive model was developed for the time-dependent behaviors of the glass transition of amorphous networks. The model used multiple discrete relaxation processes to describe the distribution of relaxation times for stress relaxation, structural relaxation, and stress-activated viscous flow. A non-equilibrium thermodynamic framework based on the fictive temperature was introduced to demonstrate the thermodynamic consistency of the constitutive theory. Experimental and theoretical methods were developed to determine the parameters describing the distribution of stress and structural relaxation times and the dependence of the relaxation times on temperature, structure, and driving stress. The model was applied to study the effects of deformation temperatures and physical aging on the shape-memory behavior of amorphous networks. The model was able to reproduce important features of the partially constrained recovery response observed in experiments. Specifically, the model demonstrated a strain-recovery overshoot for cases programmed below Tg and subjected to a constant mechanical load. This phenomenon was not observed for materials programmed above Tg. Physical aging, in which the material was annealed for an extended period of time below Tg, shifted the activation of strain recovery to higher temperatures and increased significantly the initial recovery rate. For fixed-strain recovery, the model showed a larger overshoot in the stress response for cases programmed below Tg, which was consistent with previous experimental observations. Altogether, this work demonstrates how an understanding of the time-dependent behaviors of the glass transition can be used to tailor the temperature and deformation history of the shape-memory programming process to achieve more complex shape recovery pathways, faster recovery responses, and larger activation stresses.

ADCC Develops Over Time during Persistent Infection with Live-Attenuated SIV and Is Associated with Complete Protection against SIVmac251 Challenge

PubMed Central

Alpert, Michael D.; Harvey, Jackson D.; Lauer, W. Anderson; Reeves, R. Keith; Piatak, Michael; Carville, Angela; Mansfield, Keith G.; Lifson, Jeffrey D.; Li, Wenjun; Desrosiers, Ronald C.; Johnson, R. Paul; Evans, David T.

2012-01-01

Live-attenuated strains of simian immunodeficiency virus (SIV) routinely confer apparent sterilizing immunity against pathogenic SIV challenge in rhesus macaques. Understanding the mechanisms of protection by live-attenuated SIV may provide important insights into the immune responses needed for protection against HIV-1. Here we investigated the development of antibodies that are functional against neutralization-resistant SIV challenge strains, and tested the hypothesis that these antibodies are associated with protection. In the absence of detectable neutralizing antibodies, Env-specific antibody-dependent cell-mediated cytotoxicity (ADCC) emerged by three weeks after inoculation with SIVΔnef, increased progressively over time, and was proportional to SIVΔnef replication. Persistent infection with SIVΔnef elicited significantly higher ADCC titers than immunization with a non-persistent SIV strain that is limited to a single cycle of infection. ADCC titers were higher against viruses matched to the vaccine strain in Env, but were measurable against viruses expressing heterologous Env proteins. In two separate experiments, which took advantage of either the strain-specificity or the time-dependent maturation of immunity to overcome complete protection against SIVmac251 challenge, measures of ADCC activity were higher among the SIVΔnef-inoculated macaques that remained uninfected than among those that became infected. These observations show that features of the antibody response elicited by SIVΔnef are consistent with hallmarks of protection by live-attenuated SIV, and reveal an association between Env-specific antibodies that direct ADCC and apparent sterilizing protection by SIVΔnef. PMID:22927823

Prediction of the Dynamic Yield Strength of Metals Using Two Structural-Temporal Parameters

NASA Astrophysics Data System (ADS)

Selyutina, N. S.; Petrov, Yu. V.

2018-02-01

The behavior of the yield strength of steel and a number of aluminum alloys is investigated in a wide range of strain rates, based on the incubation time criterion of yield and the empirical models of Johnson-Cook and Cowper-Symonds. In this paper, expressions for the parameters of the empirical models are derived through the characteristics of the incubation time criterion; a satisfactory agreement of these data and experimental results is obtained. The parameters of the empirical models can depend on some strain rate. The independence of the characteristics of the incubation time criterion of yield from the loading history and their connection with the structural and temporal features of the plastic deformation process give advantage of the approach based on the concept of incubation time with respect to empirical models and an effective and convenient equation for determining the yield strength in a wider range of strain rates.

Phenotypic Landscape of Saccharomyces cerevisiae during Wine Fermentation: Evidence for Origin-Dependent Metabolic Traits

PubMed Central

Camarasa, Carole; Sanchez, Isabelle; Brial, Pascale; Bigey, Frédéric; Dequin, Sylvie

2011-01-01

The species Saccharomyces cerevisiae includes natural strains, clinical isolates, and a large number of strains used in human activities. The aim of this work was to investigate how the adaptation to a broad range of ecological niches may have selectively shaped the yeast metabolic network to generate specific phenotypes. Using 72 S. cerevisiae strains collected from various sources, we provide, for the first time, a population-scale picture of the fermentative metabolic traits found in the S. cerevisiae species under wine making conditions. Considerable phenotypic variation was found suggesting that this yeast employs diverse metabolic strategies to face environmental constraints. Several groups of strains can be distinguished from the entire population on the basis of specific traits. Strains accustomed to growing in the presence of high sugar concentrations, such as wine yeasts and strains obtained from fruits, were able to achieve fermentation, whereas natural yeasts isolated from “poor-sugar” environments, such as oak trees or plants, were not. Commercial wine yeasts clearly appeared as a subset of vineyard isolates, and were mainly differentiated by their fermentative performances as well as their low acetate production. Overall, the emergence of the origin-dependent properties of the strains provides evidence for a phenotypic evolution driven by environmental constraints and/or human selection within S. cerevisiae. PMID:21949874

New Insights into Various Production Characteristics of Streptococcus thermophilus Strains

PubMed Central

Cui, Yanhua; Xu, Tingting; Qu, Xiaojun; Hu, Tong; Jiang, Xu; Zhao, Chunyu

2016-01-01

Streptococcus thermophilus is one of the most valuable homo-fermentative lactic acid bacteria, which, for a long time, has been widely used as a starter for the production of fermented dairy products. The key production characteristics of S. thermophilus, for example the production of extracellular polysaccharide, proteolytic enzymes and flavor substances as well as acidifying capacity etc., have an important effect on the quality of dairy products. The acidification capacity of the strains determines the manufacturing time and quality of dairy products. It depends on the sugar utilization ability of strains. The production of extracellular polysaccharide is beneficial for improving the texture of dairy products. Flavor substances increase the acceptability of dairy products. The proteolytic activity of the strain influences not only the absorption of the nitrogen source, but also the formation of flavor substances. Different strains have obvious differences in production characteristics via long-time evolution and adaptation to environment. Gaining new strains with novel and desirable characteristics is an important long-term goal for researchers and the fermenting industry. The understanding of the potential molecular mechanisms behind important characteristics of different strains will promote the screening and breeding of excellent strains. In this paper, key technological and functional properties of different S. thermophilus strains are discussed, including sugar metabolism, proteolytic system and amino acid metabolism, and polysaccharide and flavor substance biosynthesis. At the same time, diversity of genomes and plasmids of S. thermophilus are presented. Advances in research on key production characteristics and molecular levels of S. thermophilus will increase understanding of molecular mechanisms of different strains with different important characteristics, and improve the industrialization control level for fermented foods. PMID:27754312

Application of the time-temperature superposition principle to the mechanical characterization of elastomeric adhesives for crash simulation purposes

NASA Astrophysics Data System (ADS)

Rauh, A.; Hinterhölzl, R.; Drechsler, K.

2012-05-01

In the automotive industry, finite element simulation is widely used to ensure crashworthiness. Mechanical material data over wide strain rate and temperature ranges are required as a basis. This work proposes a method reducing the cost of mechanical material characterization by using the time-temperature superposition principle on elastomeric adhesives. The method is based on the time and temperature interdependence which is characteristic for mechanical properties of polymers. Based on the assumption that polymers behave similarly at high strain rates and at low temperatures, a temperature-dominated test program is suggested, which can be used to deduce strain rate dependent material behavior at different reference temperatures. The temperature shift factor is found by means of dynamic mechanical analysis according to the WLF-equation, named after Williams, Landel and Ferry. The principle is applied to the viscoelastic properties as well as to the failure properties of the polymer. The applicability is validated with high strain rate tests.

Strengthening of synthetic quartz-rich sediments during time-dependent compaction due to pressure solution-precipitation compaction creep

NASA Astrophysics Data System (ADS)

Noda, H.; Okazaki, K.; Katayama, I.

2013-12-01

During diagenesis, incohesive sediments are compacted and gain strength against shear deformation for a geologically long time scale. The evolution of shear strength as well as the change in the mechanical and hydraulic characteristics under shear deformation is of significant importance in considering deformation at shallow part of the subduction zones and in accretionary prisms. Sediments after induration due to time-dependent diagenesis process probably deform with increases in porosity and permeability much more significantly than normally compacted incohesive sediments. An active fault in a shallow incohesive medium may favor thermal pressurization of pore fluid when slid rapidly, while the lack of time-dependent healing effect may cause stable (e.g., rate-strengthening) frictional property there. On the other hand, indurated sediments may deform with significant post-failure weakening, and thus exhibit localization of deformation or unstable behavior. In order to investigate how the time-dependent compaction and induration affect the mechanical and hydraulic characteristics of sediments under deformation, we have conducted a series of compaction experiments under hydrothermal conditions (at temperatures from R.T. to 500 °C, 200 MPa confining pressure, 100 MPa pore water pressure, and for various time), and following triaxial deformation experiments for the compacted samples, with monitoring permeability and storage capacity with pore pressure oscillation method [Fischer and Paterson, 1992]. Previous work [e.g., Niemeijer et at., 2003] reported that under the adopted conditions, quartz aggregate deforms by pressure solution-precipitation creep. The initial synthetic sediments have been prepared by depositing commercially available crushed quartzite the grain size of which is about 6 μm on average. 4 cm long samples have been extracted from the middle of 10 cm long deposited columns. The experiments have been performed with a gas-medium apparatus in Hiroshima University. As the compaction time and temperature increases, compressional strain increases and the synthetic sediments gain shear strength, flow stress during triaxial deformation tests. An uncooked sample yielded immediately on application of differential stress, and showed strengthening during triaxial deformation test with σ1-σ3 about 150 MPa at 0.1 compressional strain. On the other hand, a sample compacted at 500 °C for 5 hours (about 0.1 of isotropic compressional strain) deformed mainly elastically up to about 100 MPa differential stress. At 0.02 compressional strain σ1-σ3 reached 200 MPa which is the experimental limitation due to compressional strength of porous alumina spacers. In the presentation, we will focus on the relation between mechanical behavior under shear and the compressional strain during preceding compaction experiments.

The Time-Dependency of Deformation in Porous Carbonate Rocks

NASA Astrophysics Data System (ADS)

Kibikas, W. M.; Lisabeth, H. P.; Zhu, W.

2016-12-01

Porous carbonate rocks are natural reservoirs for freshwater and hydrocarbons. More recently, due to their potential for geothermal energy generation as well as carbon sequestration, there are renewed interests in better understanding of the deformation behavior of carbonate rocks. We conducted a series of deformation experiments to investigate the effects of strain rate and pore fluid chemistry on rock strength and transport properties of porous limestones. Indiana limestone samples with initial porosity of 16% are deformed at 25 °C under effective pressures of 10, 30, and 50 MPa. Under nominally dry conditions, the limestone samples are deformed under 3 different strain rates, 1.5 x 10-4 s-1, 1.5 x 10-5 s-1 and 1.5 x 10-6 s-1 respectively. The experimental results indicate that the mechanical behavior is both rate- and pressure-dependent. At low confining pressures, post-yielding deformation changes from predominantly strain softening to strain hardening as strain rate decreases. At high confining pressures, while all samples exhibit shear-enhanced compaction, decreasing strain rate leads to an increase in compaction. Slower strain rates enhance compaction at all confining pressure conditions. The rate-dependence of deformation behaviors of porous carbonate rocks at dry conditions indicates there is a strong visco-elastic coupling for the degradation of elastic modulus with increasing plastic deformation. In fluid saturated samples, inelastic strain of limestone is partitioned among low temperature plasticity, cataclasis and solution transport. Comparison of inelastic behaviors of samples deformed with distilled water and CO2-saturated aqueous solution as pore fluids provide experimental constraints on the relative activities of the various mechanisms. Detailed microstructural analysis is conducted to take into account the links between stress, microstructure and the inelastic behavior and failure mechanisms.

Physical aging effects on the compressive linear viscoelastic creep of IM7/K3B composite

NASA Technical Reports Server (NTRS)

Veazie, David R.; Gates, Thomas S.

1995-01-01

An experimental study was undertaken to establish the viscoelastic behavior of 1M7/K3B composite in compression at elevated temperature. Creep compliance, strain recovery and the effects of physical aging on the time dependent response was measured for uniaxial loading at several isothermal conditions below the glass transition temperature (T(g)). The IM7/K3B composite is a graphite reinforced thermoplastic polyimide with a T(g) of approximately 240 C. In a composite, the two matrix dominated compliance terms associated with time dependent behavior occur in the transverse and shear directions. Linear viscoelasticity was used to characterize the creep/recovery behavior and superposition techniques were used to establish the physical aging related material constants. Creep strain was converted to compliance and measured as a function of test time and aging time. Results included creep compliance master curves, physical aging shift factors and shift rates. The description of the unique experimental techniques required for compressive testing is also given.

A small-scale turbulence model

NASA Technical Reports Server (NTRS)

Lundgren, T. S.

1992-01-01

A model for the small-scale structure of turbulence is reformulated in such a way that it may be conveniently computed. The model is an ensemble of randomly oriented structured two dimensional vortices stretched by an axially symmetric strain flow. The energy spectrum of the resulting flow may be expressed as a time integral involving only the enstrophy spectrum of the time evolving two-dimensional cross section flow, which may be obtained numerically. Examples are given in which a k(exp -5/3) spectrum is obtained by this method without using large wave number asymptotic analysis. The k(exp -5/3) inertial range spectrum is shown to be related to the existence of a self-similar enstrophy preserving range in the two-dimensional enstrophy spectrum. The results are insensitive to time dependence of the strain-rate, including even intermittent on-or-off strains.

Interaction of rate- and size-effect using a dislocation density based strain gradient viscoplasticity model

NASA Astrophysics Data System (ADS)

Nguyen, Trung N.; Siegmund, Thomas; Tomar, Vikas; Kruzic, Jamie J.

2017-12-01

Size effects occur in non-uniform plastically deformed metals confined in a volume on the scale of micrometer or sub-micrometer. Such problems have been well studied using strain gradient rate-independent plasticity theories. Yet, plasticity theories describing the time-dependent behavior of metals in the presence of size effects are presently limited, and there is no consensus about how the size effects vary with strain rates or whether there is an interaction between them. This paper introduces a constitutive model which enables the analysis of complex load scenarios, including loading rate sensitivity, creep, relaxation and interactions thereof under the consideration of plastic strain gradient effects. A strain gradient viscoplasticity constitutive model based on the Kocks-Mecking theory of dislocation evolution, namely the strain gradient Kocks-Mecking (SG-KM) model, is established and allows one to capture both rate and size effects, and their interaction. A formulation of the model in the finite element analysis framework is derived. Numerical examples are presented. In a special virtual creep test with the presence of plastic strain gradients, creep rates are found to diminish with the specimen size, and are also found to depend on the loading rate in an initial ramp loading step. Stress relaxation in a solid medium containing cylindrical microvoids is predicted to increase with decreasing void radius and strain rate in a prior ramp loading step.

Effects of polyaluminum chloride and lanthanum-modified bentonite on the growth rates of three Cylindrospermopsis raciborskii strains

PubMed Central

van Oosterhout, Frank; Becker, Vanessa; Attayde, José Luiz; Lürling, Miquel

2018-01-01

In tropical and subtropical lakes, eutrophication often leads to nuisance blooms of Cylindrospermopsis raciborskii. In laboratory experiments, we tested the combined effects of flocculant polyaluminum chloride (PAC) and lanthanum-modified bentonite (LMB) on the sinking and growth rates of three C. raciborskii strains. We tested the hypothesis that the combination of PAC and LMB would (1) effectively sink C. raciborskii in a test tube experiment and (2) impair C. raciborskii growth, irrespective of the biomass of the inoculum (bloom) and the strain in the growth experiment. We tested the recommended (LMB1) and a three-times higher dose of LMB (LMB3). The combined addition of PAC and LMB enhanced the sedimentation of all C. raciborskii strains. Moreover, both the PAC and LMB doses decreased the phosphate concentration. PAC and LMB1 decreased the growth rate of all strains, but the efficacy depended on the biomass and strain. The combined addition of PAC and LMB3 inhibited the growth of all strains independently of the biomass and strain. We conclude that a low dose of PAC in combination with the recommended dose of LMB decreases C. raciborskii blooms and that the efficiency of the technique depends on the biomass of the bloom. A higher dose of LMB is needed to obtain a more efficient control of C. raciborskii blooms. PMID:29614118

Effects of polyaluminum chloride and lanthanum-modified bentonite on the growth rates of three Cylindrospermopsis raciborskii strains.

PubMed

Araújo, Fabiana; van Oosterhout, Frank; Becker, Vanessa; Attayde, José Luiz; Lürling, Miquel

2018-01-01

In tropical and subtropical lakes, eutrophication often leads to nuisance blooms of Cylindrospermopsis raciborskii. In laboratory experiments, we tested the combined effects of flocculant polyaluminum chloride (PAC) and lanthanum-modified bentonite (LMB) on the sinking and growth rates of three C. raciborskii strains. We tested the hypothesis that the combination of PAC and LMB would (1) effectively sink C. raciborskii in a test tube experiment and (2) impair C. raciborskii growth, irrespective of the biomass of the inoculum (bloom) and the strain in the growth experiment. We tested the recommended (LMB1) and a three-times higher dose of LMB (LMB3). The combined addition of PAC and LMB enhanced the sedimentation of all C. raciborskii strains. Moreover, both the PAC and LMB doses decreased the phosphate concentration. PAC and LMB1 decreased the growth rate of all strains, but the efficacy depended on the biomass and strain. The combined addition of PAC and LMB3 inhibited the growth of all strains independently of the biomass and strain. We conclude that a low dose of PAC in combination with the recommended dose of LMB decreases C. raciborskii blooms and that the efficiency of the technique depends on the biomass of the bloom. A higher dose of LMB is needed to obtain a more efficient control of C. raciborskii blooms.

Infection dynamics of western equine encephalomyelitis virus (Togaviridae: Alphavirus) in four strains of Culex tarsalis (Diptera: Culicidae): an immunocytochemical study.

PubMed

Oviedo, Marco V Neira; Romoser, William S; James, Calvin Bl; Mahmood, Farida; Reisen, William K

2011-04-18

BACKGROUND: Vector competence describes the efficiency with which vector arthropods become infected with and transmit pathogens and depends on interactions between pathogen and arthropod genetics as well as environmental factors. For arbovirus transmission, the female mosquito ingests viremic blood, the virus infects and replicates in midgut cells, escapes from the midgut, and disseminates to other tissues, including the salivary glands. Virus-laden saliva is then injected into a new host. For transmission to occur, the virus must overcome several "barriers", including barriers to midgut infection and/or escape and salivary infection and/or escape. By examining the spatial/temporal infection dynamics of Culex tarsalis strains infected with western equine encephalomyelitis virus (WEEV), we identified tissue tropisms and potential tissue barriers, and evaluated the effects of viral dose and time postingestion. METHODS: Using immunostained paraffin sections, WEEV antigens were tracked in four Cx. tarsalis strains: two recently colonized California field strains - Coachella Valley, Riverside County (COAV) and Kern National Wildlife Refuge (KNWR); and two laboratory strains selected for WEEV susceptibility (high viremia producer, HVP), and WEEV resistance (WR). RESULTS AND CONCLUSIONS: Tissues susceptible to WEEV infection included midgut epithelium, neural ganglia, trachea, chorionated eggs, and salivary glands. Neuroendocrine cells in the retrocerebral complex were occasionally infected, indicating the potential for behavioral effects. The HVP and COAV strains vigorously supported viral growth, whereas the WR and KNWR strains were less competent. Consistent with earlier studies, WEEV resistance appeared to be related to a dose-dependent midgut infection barrier, and a midgut escape barrier. The midgut escape barrier was not dependent upon the ingested viral dose. Consistent with midgut infection modulation, disseminated infections were less common in the WR and KNWR strains than in the HVP and COAV strains. Once the virus disseminated from the midgut, all strains were able to develop salivary gland infections. The possible roles of observed pathology will be discussed in a subsequent paper.

Infection dynamics of western equine encephalomyelitis virus (Togaviridae: Alphavirus) in four strains of Culex tarsalis (Diptera: Culicidae): an immunocytochemical study

PubMed Central

Oviedo, Marco V Neira; Romoser, William S; James, Calvin BL; Mahmood, Farida; Reisen, William K

2012-01-01

Background Vector competence describes the efficiency with which vector arthropods become infected with and transmit pathogens and depends on interactions between pathogen and arthropod genetics as well as environmental factors. For arbovirus transmission, the female mosquito ingests viremic blood, the virus infects and replicates in midgut cells, escapes from the midgut, and disseminates to other tissues, including the salivary glands. Virus-laden saliva is then injected into a new host. For transmission to occur, the virus must overcome several “barriers”, including barriers to midgut infection and/or escape and salivary infection and/or escape. By examining the spatial/temporal infection dynamics of Culex tarsalis strains infected with western equine encephalomyelitis virus (WEEV), we identified tissue tropisms and potential tissue barriers, and evaluated the effects of viral dose and time postingestion. Methods Using immunostained paraffin sections, WEEV antigens were tracked in four Cx. tarsalis strains: two recently colonized California field strains – Coachella Valley, Riverside County (COAV) and Kern National Wildlife Refuge (KNWR); and two laboratory strains selected for WEEV susceptibility (high viremia producer, HVP), and WEEV resistance (WR). Results and conclusions Tissues susceptible to WEEV infection included midgut epithelium, neural ganglia, trachea, chorionated eggs, and salivary glands. Neuroendocrine cells in the retrocerebral complex were occasionally infected, indicating the potential for behavioral effects. The HVP and COAV strains vigorously supported viral growth, whereas the WR and KNWR strains were less competent. Consistent with earlier studies, WEEV resistance appeared to be related to a dose-dependent midgut infection barrier, and a midgut escape barrier. The midgut escape barrier was not dependent upon the ingested viral dose. Consistent with midgut infection modulation, disseminated infections were less common in the WR and KNWR strains than in the HVP and COAV strains. Once the virus disseminated from the midgut, all strains were able to develop salivary gland infections. The possible roles of observed pathology will be discussed in a subsequent paper. PMID:22629118

Peculiarities of dislocation motion in aluminum with allowance for the Peierls relief in the presence of ultrasound

NASA Astrophysics Data System (ADS)

Arakelyan, M. M.

2017-11-01

The effect of ultrasound on motion of the Frenkel-Kontorova dislocations in aluminum has been studied with inclusion of the Peierls relief. A dislocation moves at a variable rate when overcoming the Peierls barrier. The dislocation mean free path is changed under action of ultrasound at various frequencies comparable to the dislocation transition time to a neighboring valley. The stress-strain dependences have been obtained for high and low strain rates. In both the cases, a disordering takes place; however, the disordering rates and characters are different. At the resonance frequency, the strain resistance decreases, the hardening stage is shortened and the disordering stage is elongated. The dependence of the coefficient of hardening on coordinate has three segments different in characters. The coefficient of hardening decreases at the resonance frequency.

Effects of Recovery Behavior and Strain-Rate Dependence of Stress-Strain Curve on Prediction Accuracy of Thermal Stress Analysis During Casting

NASA Astrophysics Data System (ADS)

Motoyama, Yuichi; Shiga, Hidetoshi; Sato, Takeshi; Kambe, Hiroshi; Yoshida, Makoto

2017-06-01

Recovery behavior (recovery) and strain-rate dependence of the stress-strain curve (strain-rate dependence) are incorporated into constitutive equations of alloys to predict residual stress and thermal stress during casting. Nevertheless, few studies have systematically investigated the effects of these metallurgical phenomena on the prediction accuracy of thermal stress in a casting. This study compares the thermal stress analysis results with in situ thermal stress measurement results of an Al-Si-Cu specimen during casting. The results underscore the importance for the alloy constitutive equation of incorporating strain-rate dependence to predict thermal stress that develops at high temperatures where the alloy shows strong strain-rate dependence of the stress-strain curve. However, the prediction accuracy of the thermal stress developed at low temperatures did not improve by considering the strain-rate dependence. Incorporating recovery into the constitutive equation improved the accuracy of the simulated thermal stress at low temperatures. Results of comparison implied that the constitutive equation should include strain-rate dependence to simulate defects that develop from thermal stress at high temperatures, such as hot tearing and hot cracking. Recovery should be incorporated into the alloy constitutive equation to predict the casting residual stress and deformation caused by the thermal stress developed mainly in the low temperature range.

Time-dependent Brittle Deformation in Etna Basalt

NASA Astrophysics Data System (ADS)

Heap, M. J.; Baud, P.; Meredith, P. G.; Vinciguerra, S.; Bell, A. F.; Main, I. G.

2008-12-01

Mt Etna is the largest and most active volcano in Europe. Due to the high permeability of its volcanic rocks, the volcanic edifice hosts one of the biggest hydrogeologic reservoirs of Sicily (Ogniben, 1966). Pre-eruptive patterns of flank eruptions, closely monitored by means of ground deformation and seismicity, revealed the slow development of fracture systems at different altitudes, marked by repeated bursts of seismicity and accelerating/decelerating deformation patterns acting over the scale of months to days. The presence of a fluid phase in cracks within rock has been shown to dramatically affect both mechanical and chemical interactions. Chemically, it promotes time-dependent brittle deformation through such mechanisms as stress corrosion cracking that allows rocks to deform at stresses far below their short-term failure strength. Such crack growth is highly non-linear and accelerates towards dynamic failure over extended periods of time, even under constant applied stress; a phenomenon known as 'brittle creep'. Stress corrosion is considered to be responsible for the acceleratory cracking and seismicity prior to volcanic eruptions and is invoked as an important mechanism in forecasting models. Here we report results from a study of time-dependent brittle creep in water-saturated samples of Etna basalt (EB) under triaxial stress conditions (confining pressure of 50 MPa and pore fluid pressure of 20 MPa). Samples of EB were loaded at a constant strain rate of 10-5 s-1 to a pre-determined percentage of the short- term strength and left to deform under constant stress until failure. Crack damage evolution was monitored throughout each experiment by measuring the independent damage proxies of axial strain, pore volume change and output of acoustic emission (AE) energy, during brittle creep of creep strain rates ranging over four orders of magnitude. Our data demonstrate that the applied differential stress exerts a crucial influence on both time-to-failure and creep strain rate in EB. Stress-stepping creep experiments were then performed to allow the influence of the effective confining stress to be studied in detail. Experiments were performed under effective stress conditions of 10, 30 and 50 MPa (whilst maintaining a constant pore fluid pressure of 20 MPa). In addition to the purely mechanical influence of water, governed by the effective stress, which results in a shift of the creep strain rate curves to lower strain rates at higher effective stresses. Our results also demonstrate that the chemically-driven process of stress corrosion cracking appears to be inhibited at higher effective stress. This results in an increase in the gradient of the creep strain rate curves with increasing effective stress. We suggest that the most likely cause of this change is a decrease in water mobility due to a reduction in crack aperture and an increase in water viscosity at higher pressure. Finally, we show that a theoretical model based on mean-field damage mechanics creep laws is able to reproduce the experimental strain-time relations. Our results indicate that the local changes in the stress field and fluid circulation can have a profound impact in the time- to-failure properties of the basaltic volcanic pile.

Comparative Study of Mechanisms of Herpes Simplex Virus Inactivation by Sodium Lauryl Sulfate and n-Lauroylsarcosine

PubMed Central

Piret, Jocelyne; Roy, Sylvie; Gagnon, Mylène; Landry, Sébastien; Désormeaux, André; Omar, Rabeea F.; Bergeron, Michel G.

2002-01-01

The mechanisms of herpes simplex virus (HSV) inactivation by sodium lauryl sulfate (SLS) and n-lauroylsarcosine (LS), two anionic surfactants with protein denaturant potency, have been evaluated in cultured cells. Results showed that pretreatment of HSV type 1 (HSV-1) strain F and HSV-2 strain 333 with either surfactant inhibited, in a concentration- and time-dependent manner, their infectivities on Vero cells. SLS was a more potent inhibitor of HSV-2 strain 333 infectivity than LS with respect to the concentration (4.8-fold lower) and time (2.4-fold shorter) required to completely inactivate the virus. No inhibition of both herpesvirus strains infectivities was observed when Vero cells were pretreated with either surfactant. LS prevented the binding of HSV-2 strain 333 to cells without affecting the stable attachment and the rate of penetration into cells, whereas SLS exerted the opposite effect. Both SLS and LS inhibited, in a concentration-dependent manner, the HSV-2 strain 333-induced cytopathic effect, probably by affecting newly synthesized virions that come into contact with surfactant molecules present in culture medium. The pretreatment of HSV-2 strain 333 with specific combinations of SLS and LS concentrations inhibited the viral infectivity in a synergistic manner and resulted in only a small increase in their toxicities for exponentially growing Vero cells compared with that caused by each compound alone. Taken together, these results suggest that SLS and LS, alone or combined, could represent potent candidates as microbicides in topical vaginal formulations to prevent the transmission of herpes and possibly other pathogens that cause sexually transmitted diseases, including human immunodeficiency virus type 1. PMID:12183250

Associations of perceived work strain with nicotine dependence in a community sample.

PubMed

John, U; Riedel, J; Rumpf, H-J; Hapke, U; Meyer, C

2006-03-01

Little is known about work strain and smoking, and even less about work strain and nicotine dependence. To investigate the relations of perceived work strain with nicotine dependence among an adult general population sample. Cross sectional survey with a probability sample of residents of a northern German area with 4075 participants, aged 18-64 years (participation rate 70.2%). The current study is based on 2549 participants who were working 15 or more hours per week. Face to face at-home computer aided interviews (World Health Organization Composite International Diagnostic Interview) were carried out. Work strain, defined as high work demand and low work control, was assessed with a questionnaire. Nicotine dependence was diagnosed according to the Diagnostic and Statistical Manual (DSM-IV) of the American Psychiatric Association. In addition, the Fagerström Test for Nicotine Dependence (FTND) was used. Subjects with work strain had an odds ratio of 1.6 (95% CI 1.2 to 2.3) for nicotine dependence compared to those who had no work strain. In a general linear model, higher work strain was associated with a stronger relation between work demand and work control and the FTND. The findings were adjusted for alcohol use disorders, occupational status, age, and sex. Perceived work strain is related to nicotine dependence in this general adult population.

Strain in the Braincase and Its Sutures During Function

PubMed Central

Herring, Susan W.; Teng, Shengyi

2010-01-01

The skull is distinguished from other parts of the skeleton by its composite construction. The sutures between bony elements provide for interstitial growth of the cranium, but at the same time they alter the transmission of stress and strain through the skull. Strain gages were bonded to the frontal and parietal bones of miniature pigs and across the interfrontal, interparietal and coronal sutures. Strains were recorded 1) during natural mastication in conjunction with electromyographic activity from the jaw muscles and 2) during stimulation of various cranial muscles in anesthetized animals. Vault sutures exhibited vastly higher strains than did the adjoining bones. Further, bone strain primarily reflected torsion of the braincase set up by asymmetrical muscle contraction; the tensile axis alternated between +45° and −45° depending on which diagonal masseter/temporalis pair was most active. However, suture strains were not related to overall torsion but instead were responses to local muscle actions. Only the coronal suture showed significant strain (tension) during jaw opening; this was caused by the contraction of neck muscles. All sutures showed strain during jaw closing, but polarity depended on the pattern of muscle usage. For example, masseter contraction tensed the coronal suture and the anterior part of the interfrontal suture, whereas the temporalis caused compression in these locations. Peak tensile strains were larger than peak compressive strains. Histology suggested that the skull is bent at the sutures, with the ectocranial surface tensed and the endocranial surface predominantly compressed. Collectively, these results indicate that skulls with patent sutures should be analyzed as complexes of independent parts rather than solid structures. PMID:10918130

Creep-Fatigue Behavior of Alloy 617 at 850 and 950°C, Revision 2

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

Carroll, L.; Carroll, M.

Alloy 617 is the leading candidate material for an Intermediate Heat Exchanger (IHX) of the Very High Temperature Reactor (VHTR). To evaluate the behavior of this material in the expected service conditions, strain-controlled cyclic tests including hold times up to 9000 s at maximum tensile strain were conducted at 850 and 950 degrees C. At both temperatures, the fatigue resistance decreased when a hold time was added at peak tensile strain. The magnitude of this effect depended on the specific mechanisms and whether they resulted in a change in fracture mode from transgranular in pure fatigue to intergranular in creep-fatiguemore » for a particular temperature and strain range combination. Increases in the tensile hold duration beyond an initial value were not detrimental to the creep-fatigue resistance at 950 degrees C but did continue to degrade the lifetimes at 850 degrees C.« less

Experimental Study of Solder/Copper Interface Failure Under Varying Strain Rates

DTIC Science & Technology

2011-03-01

Factors Affecting Solder Joint Reliability Gu et al. [1] determined that during the life cycle of electronic assemblies, approximately 55 percent of...related to vibration and shock, with the remaining percentage associated with changes in 2 humidity. Research conducted by Ross et al. [2] adds...that creep strain is the most important time-dependent factor affecting the reliability of solder joints in electronic equipment. 2. Effects of

Viscoplastic Characterization of Ti-6-4: Experiments

NASA Technical Reports Server (NTRS)

Lerch, Bradley A.; Arnold, Steven M.

2016-01-01

As part of a continued effort to improve the understanding of material time-dependent response, a series of mechanical tests have been conducted on the titanium alloy, Ti-6Al-4V. Tensile, creep, and stress relaxation tests were performed over a wide range of temperatures and strain rates to engage various amounts of time-dependent behavior. Additional tests were conducted that involved loading steps, overloads, dwell periods, and block loading segments to characterize the interaction between plasticity and time-dependent behavior. These data will be used to characterize a recently developed, viscoelastoplastic constitutive model with a goal toward better estimates of aerospace component behavior, resulting in improved safety.

Time-dependence of the alpha to epsilon phase transformation in iron

DOE PAGES

Smith, R. F.; Eggert, J. H.; Swift, D. C.; ...

2013-12-11

Here, iron was ramp-compressed over timescales of 3 ≤ t(ns) ≤ 300 to study the time-dependence of the α→ε (bcc→hcp) phase transformation. Onset stresses (σ α→ε) for the transformation ~14.8-38.4 GPa were determined through laser and magnetic ramp-compression techniques where the transition strain-rate was varied between 10 6 ≤more » $$\\dot{μ}$$ α→ε(s ₋1) ≤ 5×10 8. We find σ α→ε= 10.8 + 0.55 ln($$\\dot{μ}$$ α→ε) for $$\\dot{μ}$$ α→ε < 10 6/s and σ α→ε= 1.15($$\\dot{μ}$$ α→ε) 0.18 for $$\\dot{μ}$$ α→ε > 10 6/s. This $$\\dot{μ}$$ response is quite similar to recent results on incipient plasticity in Fe suggesting that under high rate ramp compression the α→ε phase transition and plastic deformation occur through similar mechanisms, e.g., the rate limiting step for $$\\dot{μ}$$ > 10 6/s is due to phonon scattering from defects moving to relieve strain. We show that over-pressurization of equilibrium phase boundaries is a common feature exhibited under high strain-rate compression of many materials encompassing many orders of magnitude of strain-rate.« less

Finite-strain large-deflection elastic-viscoplastic finite-element transient response analysis of structures

NASA Technical Reports Server (NTRS)

Rodal, J. J. A.; Witmer, E. A.

1979-01-01

A method of analysis for thin structures that incorporates finite strain, elastic-plastic, strain hardening, time dependent material behavior implemented with respect to a fixed configuration and is consistently valid for finite strains and finite rotations is developed. The theory is formulated systematically in a body fixed system of convected coordinates with materially embedded vectors that deform in common with continuum. Tensors are considered as linear vector functions and use is made of the dyadic representation. The kinematics of a deformable continuum is treated in detail, carefully defining precisely all quantities necessary for the analysis. The finite strain theory developed gives much better predictions and agreement with experiment than does the traditional small strain theory, and at practically no additional cost. This represents a very significant advance in the capability for the reliable prediction of nonlinear transient structural responses, including the reliable prediction of strains large enough to produce ductile metal rupture.

The nonstationary strain filter in elastography: Part I. Frequency dependent attenuation.

PubMed

Varghese, T; Ophir, J

1997-01-01

The accuracy and precision of the strain estimates in elastography depend on a myriad number of factors. A clear understanding of the various factors (noise sources) that plague strain estimation is essential to obtain quality elastograms. The nonstationary variation in the performance of the strain filter due to frequency-dependent attenuation and lateral and elevational signal decorrelation are analyzed in this and the companion paper for the cross-correlation-based strain estimator. In this paper, we focus on the role of frequency-dependent attenuation in the performance of the strain estimator. The reduction in the signal-to-noise ratio (SNRs) in the RF signal, and the center frequency and bandwidth downshift with frequency-dependent attenuation are incorporated into the strain filter formulation. Both linear and nonlinear frequency dependence of attenuation are theoretically analyzed. Monte-Carlo simulations are used to corroborate the theoretically predicted results. Experimental results illustrate the deterioration in the precision of the strain estimates with depth in a uniformly elastic phantom. Theoretical, simulation and experimental results indicate the importance of high SNRs values in the RF signals, because the strain estimation sensitivity, elastographic SNRe and dynamic range deteriorate rapidly with a decrease in the SNRs. In addition, a shift in the strain filter toward higher strains is observed at large depths in tissue due to the center frequency downshift.

The genomic basis of circadian and circalunar timing adaptations in a midge.

PubMed

Kaiser, Tobias S; Poehn, Birgit; Szkiba, David; Preussner, Marco; Sedlazeck, Fritz J; Zrim, Alexander; Neumann, Tobias; Nguyen, Lam-Tung; Betancourt, Andrea J; Hummel, Thomas; Vogel, Heiko; Dorner, Silke; Heyd, Florian; von Haeseler, Arndt; Tessmar-Raible, Kristin

2016-12-01

Organisms use endogenous clocks to anticipate regular environmental cycles, such as days and tides. Natural variants resulting in differently timed behaviour or physiology, known as chronotypes in humans, have not been well characterized at the molecular level. We sequenced the genome of Clunio marinus, a marine midge whose reproduction is timed by circadian and circalunar clocks. Midges from different locations show strain-specific genetic timing adaptations. We examined genetic variation in five C. marinus strains from different locations and mapped quantitative trait loci for circalunar and circadian chronotypes. The region most strongly associated with circadian chronotypes generates strain-specific differences in the abundance of calcium/calmodulin-dependent kinase II.1 (CaMKII.1) splice variants. As equivalent variants were shown to alter CaMKII activity in Drosophila melanogaster, and C. marinus (Cma)-CaMKII.1 increases the transcriptional activity of the dimer of the circadian proteins Cma-CLOCK and Cma-CYCLE, we suggest that modulation of alternative splicing is a mechanism for natural adaptation in circadian timing.

Applications of NASTRAN to nuclear problems

NASA Technical Reports Server (NTRS)

Spreeuw, E.

1972-01-01

The extent to which suitable solutions may be obtained for one physics problem and two engineering type problems is traced. NASTRAN appears to be a practical tool to solve one-group steady-state neutron diffusion equations. Transient diffusion analysis may be performed after new levels that allow time-dependent temperature calculations are developed. NASTRAN piecewise linear anlaysis may be applied to solve those plasticity problems for which a smooth stress-strain curve can be used to describe the nonlinear material behavior. The accuracy decreases when sharp transitions in the stress-strain relations are involved. Improved NASTRAN usefulness will be obtained when nonlinear material capabilities are extended to axisymmetric elements and to include provisions for time-dependent material properties and creep analysis. Rigid formats 3 and 5 proved to be very convenient for the buckling and normal-mode analysis of a nuclear fuel element.

Dynamic Creep Buckling: Analysis of Shell Structures Subjected to Time-dependent Mechanical and Thermal Loading

NASA Technical Reports Server (NTRS)

Simitses, G. J.; Carlson, R. L.; Riff, R.

1985-01-01

The objective of the present research is to develop a general mathematical model and solution methodologies for analyzing the structural response of thin, metallic shell structures under large transient, cyclic, or static thermomechanical loads. Among the system responses associated with these loads and conditions are thermal buckling, creep buckling, and ratcheting. Thus geometric and material nonlinearities (of high order) can be anticipated and must be considered in developing the mathematical model. A complete, true ab-initio rate theory of kinematics and kinetics for continuum and curved thin structures, without any restriction on the magnitude of the strains or the deformations, was formulated. The time dependence and large strain behavior are incorporated through the introduction of the time rates of metric and curvature in two coordinate systems: fixed (spatial) and convected (material). The relations between the time derivative and the covariant derivative (gradient) were developed for curved space and motion, so the velocity components supply the connection between the equations of motion and the time rates of change of the metric and curvature tensors.

Thickness dependence of curvature, strain, and response time in ionic electroactive polymer actuators fabricated via layer-by-layer assembly

NASA Astrophysics Data System (ADS)

Montazami, Reza; Liu, Sheng; Liu, Yang; Wang, Dong; Zhang, Qiming; Heflin, James R.

2011-05-01

Ionic electroactive polymer (IEAP) actuators containing porous conductive network composites (CNCs) and ionic liquids can result in high strain and fast response times. Incorporation of spherical gold nanoparticles in the CNC enhances conductivity and porosity, while maintaining relatively small thickness. This leads to improved mechanical strain and bending curvature of the actuators. We have employed the layer-by-layer self-assembly technique to fabricate a CNC with enhanced curvature (0.43 mm-1) and large net intrinsic strain (6.1%). The results demonstrate that curvature and net strain of IEAP actuators due to motion of the anions increase linearly with the thickness of the CNC as a result of the increased volume in which the anions can be stored. In addition, after subtracting the curvature of a bare Nafion actuator without a CNC, it is found that the net intrinsic strain of the CNC layer is independent of thickness for the range of 20-80 nm, indicating that the entire CNC volume contributes equivalently to the actuator motion. Furthermore, the response time of the actuator due to anion motion is independent of CNC thickness, suggesting that traversal through the Nafion membrane is the limiting factor in the anion motion.

Nonlinear viscoelastic characterization of bovine trabecular bone.

PubMed

Manda, Krishnagoud; Wallace, Robert J; Xie, Shuqiao; Levrero-Florencio, Francesc; Pankaj, Pankaj

2017-02-01

The time-independent elastic properties of trabecular bone have been extensively investigated, and several stiffness-density relations have been proposed. Although it is recognized that trabecular bone exhibits time-dependent mechanical behaviour, a property of viscoelastic materials, the characterization of this behaviour has received limited attention. The objective of the present study was to investigate the time-dependent behaviour of bovine trabecular bone through a series of compressive creep-recovery experiments and to identify its nonlinear constitutive viscoelastic material parameters. Uniaxial compressive creep and recovery experiments at multiple loads were performed on cylindrical bovine trabecular bone samples ([Formula: see text]). Creep response was found to be significant and always comprised of recoverable and irrecoverable strains, even at low stress/strain levels. This response was also found to vary nonlinearly with applied stress. A systematic methodology was developed to separate recoverable (nonlinear viscoelastic) and irrecoverable (permanent) strains from the total experimental strain response. We found that Schapery's nonlinear viscoelastic constitutive model describes the viscoelastic response of the trabecular bone, and parameters associated with this model were estimated from the multiple load creep-recovery (MLCR) experiments. Nonlinear viscoelastic recovery compliance was found to have a decreasing and then increasing trend with increasing stress level, indicating possible stiffening and softening behaviour of trabecular bone due to creep. The obtained parameters from MLCR tests, expressed as second-order polynomial functions of stress, showed a similar trend for all the samples, and also demonstrate stiffening-softening behaviour with increasing stress.

Predicting grid-size-dependent fracture strains of DP980 with a microstructure-based post-necking model

DOE PAGES

Cheng, G.; Hu, X. H.; Choi, K. S.; ...

2017-07-08

Ductile fracture is a local phenomenon, and it is well established that fracture strain levels depend on both stress triaxiality and the resolution (grid size) of strain measurements. Two-dimensional plane strain post-necking models with different model sizes are used in this paper to predict the grid-size-dependent fracture strain of a commercial dual-phase steel, DP980. The models are generated from the actual microstructures, and the individual phase flow properties and literature-based individual phase damage parameters for the Johnson–Cook model are used for ferrite and martensite. A monotonic relationship is predicted: the smaller the model size, the higher the fracture strain. Thus,more » a general framework is developed to quantify the grid-size-dependent fracture strains for multiphase materials. In addition to the grid-size dependency, the influences of intrinsic microstructure features, i.e., the flow curve and fracture strains of the two constituent phases, on the predicted fracture strains also are examined. Finally, application of the derived fracture strain versus model size relationship is demonstrated with large clearance trimming simulations with different element sizes.« less

Predicting grid-size-dependent fracture strains of DP980 with a microstructure-based post-necking model

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

Cheng, G.; Hu, X. H.; Choi, K. S.

Ductile fracture is a local phenomenon, and it is well established that fracture strain levels depend on both stress triaxiality and the resolution (grid size) of strain measurements. Two-dimensional plane strain post-necking models with different model sizes are used in this paper to predict the grid-size-dependent fracture strain of a commercial dual-phase steel, DP980. The models are generated from the actual microstructures, and the individual phase flow properties and literature-based individual phase damage parameters for the Johnson–Cook model are used for ferrite and martensite. A monotonic relationship is predicted: the smaller the model size, the higher the fracture strain. Thus,more » a general framework is developed to quantify the grid-size-dependent fracture strains for multiphase materials. In addition to the grid-size dependency, the influences of intrinsic microstructure features, i.e., the flow curve and fracture strains of the two constituent phases, on the predicted fracture strains also are examined. Finally, application of the derived fracture strain versus model size relationship is demonstrated with large clearance trimming simulations with different element sizes.« less

Integrating genetic and toxicogenomic information for determining underlying susceptibility to developmental disorders.

PubMed

Robinson, Joshua F; Port, Jesse A; Yu, Xiaozhong; Faustman, Elaine M

2010-10-01

To understand the complex etiology of developmental disorders, an understanding of both genetic and environmental risk factors is needed. Human and rodent genetic studies have identified a multitude of gene candidates for specific developmental disorders such as neural tube defects (NTDs). With the emergence of toxicogenomic-based assessments, scientists now also have the ability to compare and understand the expression of thousands of genes simultaneously across strain, time, and exposure in developmental models. Using a systems-based approach in which we are able to evaluate information from various parts and levels of the developing organism, we propose a framework for integrating genetic information with toxicogenomic-based studies to better understand gene-environmental interactions critical for developmental disorders. This approach has allowed us to characterize candidate genes in the context of variables critical for determining susceptibility such as strain, time, and exposure. Using a combination of toxicogenomic studies and complementary bioinformatic tools, we characterize NTD candidate genes during normal development by function (gene ontology), linked phenotype (disease outcome), location, and expression (temporally and strain-dependent). In addition, we show how environmental exposures (cadmium, methylmercury) can influence expression of these genes in a strain-dependent manner. Using NTDs as an example of developmental disorder, we show how simple integration of genetic information from previous studies into the standard microarray design can enhance analysis of gene-environment interactions to better define environmental exposure-disease pathways in sensitive and resistant mouse strains. © Wiley-Liss, Inc.

Analysis of the Viscoelastic Properties of the Human Cornea Using Scheimpflug Imaging in Inflation Experiment of Eye Globes

PubMed Central

Lombardo, Giuseppe; Serrao, Sebastiano; Rosati, Marianna; Lombardo, Marco

2014-01-01

Purpose To demonstrate a Scheimpflug-based imaging procedure for investigating the depth- and time-dependent strain response of the human cornea to inflation testing of whole eye globes. Methods Six specimens, three of which with intact corneal epithelium, were mounted in a customized apparatus within a humidity and temperature-monitored wet chamber. Each specimen was subjected to two mechanical tests in order to measure corneal strain resulting from application of cyclic (cyclic regimen) and constant (creep regimen) stress by changing the intra-ocular pressure (IOP) within physiological ranges (18–42 mmHg). Corneal shape changes were analyzed as a function of IOP and both corneal stress-strain curves and creep curves were generated. Results The procedure was highly accurate and repeatable. Upon cyclic stress application, a biomechanical corneal elasticity gradient was found in the front-back direction. The average Young's modulus of the anterior cornea ranged between 2.28±0.87 MPa and 3.30±0.90 MPa in specimens with and without intact epithelium (P = 0.05) respectively. The Young's modulus of the posterior cornea was on average 0.21±0.09 MPa and 0.17±0.06 MPa (P>0.05) respectively. The time-dependent strain response of the cornea to creep testing was quantified by fitting data to a modified Zener model for extracting both the relaxation time and compliance function. Conclusion Cyclic and creep mechanical tests are valuable for investigating the strain response of the intact human cornea within physiological IOP ranges, providing meaningful results that can be translated to clinic. The presence of epithelium influences the results of anterior corneal shape changes when monitoring deformation via Scheimpflug imaging in inflation experiments of whole eye globes. PMID:25397674

Transient deformation from daily GPS displacement time series: postseismic deformation, ETS and evolving strain rates

NASA Astrophysics Data System (ADS)

Bock, Y.; Fang, P.; Moore, A. W.; Kedar, S.; Liu, Z.; Owen, S. E.; Glasscoe, M. T.

2016-12-01

Detection of time-dependent crustal deformation relies on the availability of accurate surface displacements, proper time series analysis to correct for secular motion, coseismic and non-tectonic instrument offsets, periodic signatures at different frequencies, and a realistic estimate of uncertainties for the parameters of interest. As part of the NASA Solid Earth Science ESDR System (SESES) project, daily displacement time series are estimated for about 2500 stations, focused on tectonic plate boundaries and having a global distribution for accessing the terrestrial reference frame. The "combined" time series are optimally estimated from independent JPL GIPSY and SIO GAMIT solutions, using a consistent set of input epoch-date coordinates and metadata. The longest time series began in 1992; more than 30% of the stations have experienced one or more of 35 major earthquakes with significant postseismic deformation. Here we present three examples of time-dependent deformation that have been detected in the SESES displacement time series. (1) Postseismic deformation is a fundamental time-dependent signal that indicates a viscoelastic response of the crust/mantle lithosphere, afterslip, or poroelastic effects at different spatial and temporal scales. It is critical to identify and estimate the extent of postseismic deformation in both space and time not only for insight into the crustal deformation and earthquake cycles and their underlying physical processes, but also to reveal other time-dependent signals. We report on our database of characterized postseismic motions using a principal component analysis to isolate different postseismic processes. (2) Starting with the SESES combined time series and applying a time-dependent Kalman filter, we examine episodic tremor and slow slip (ETS) in the Cascadia subduction zone. We report on subtle slip details, allowing investigation of the spatiotemporal relationship between slow slip transients and tremor and their underlying physical mechanisms. (3) We present evolving strain dilatation and shear rates based on the SESES velocities for regional subnetworks as a metric for assigning earthquake probabilities and detection of possible time-dependent deformation related to underlying physical processes.

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

NASA Astrophysics Data System (ADS)

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

2015-05-01

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

Intracellular activity of antibiotics in a model of human THP-1 macrophages infected by a Staphylococcus aureus small-colony variant strain isolated from a cystic fibrosis patient: pharmacodynamic evaluation and comparison with isogenic normal-phenotype and revertant strains.

PubMed

Nguyen, Hoang Anh; Denis, Olivier; Vergison, Anne; Theunis, Anne; Tulkens, Paul M; Struelens, Marc J; Van Bambeke, Françoise

2009-04-01

Small-colony variant (SCV) strains of Staphylococcus aureus show reduced antibiotic susceptibility and intracellular persistence, potentially explaining therapeutic failures. The activities of oxacillin, fusidic acid, clindamycin, gentamicin, rifampin, vancomycin, linezolid, quinupristin-dalfopristin, daptomycin, tigecycline, moxifloxacin, telavancin, and oritavancin have been examined in THP-1 macrophages infected by a stable thymidine-dependent SCV strain in comparison with normal-phenotype and revertant isogenic strains isolated from the same cystic fibrosis patient. The SCV strain grew slowly extracellularly and intracellularly (1- and 0.2-log CFU increase in 24 h, respectively). In confocal and electron microscopy, SCV and the normal-phenotype bacteria remain confined in acid vacuoles. All antibiotics tested, except tigecycline, caused a net reduction in bacterial counts that was both time and concentration dependent. At an extracellular concentration corresponding to the maximum concentration in human serum (total drug), oritavancin caused a 2-log CFU reduction at 24 h; rifampin, moxifloxacin, and quinupristin-dalfopristin caused a similar reduction at 72 h; and all other antibiotics had only a static effect at 24 h and a 1-log CFU reduction at 72 h. In concentration dependence experiments, response to oritavancin was bimodal (two successive plateaus of -0.4 and -3.1 log CFU); tigecycline, moxifloxacin, and rifampin showed maximal effects of -1.1 to -1.7 log CFU; and the other antibiotics produced results of -0.6 log CFU or less. Addition of thymidine restored intracellular growth of the SCV strain but did not modify the activity of antibiotics (except quinupristin-dalfopristin). All drugs (except tigecycline and oritavancin) showed higher intracellular activity against normal or revertant phenotypes than against SCV strains. The data may help rationalizing the design of further studies with intracellular SCV strains.

Comparative Analysis of the Relationship between Trichloroethylene Metabolism and Tissue-Specific Toxicity among Inbred Mouse Strains: Kidney Effects

PubMed Central

Yoo, Hong Sik; Bradford, Blair U.; Kosyk, Oksana; Uehara, Takeki; Shymonyak, Svitlana; Collins, Leonard B.; Bodnar, Wanda M.; Ball, Louise M.; Gold, Avram; Rusyn, Ivan

2014-01-01

Trichloroethylene (TCE) is a well-known environmental and occupational toxicant that is classified as carcinogenic to humans based on the epidemiological evidence of an association with higher risk of renal cell carcinoma. A number of scientific issues critical for assessing human health risks from TCE remain unresolved, such as the amount of kidney-toxic glutathione conjugation metabolites formed, inter-species and -individual differences, and the mode of action for kidney carcinogenicity. We hypothesized that TCE metabolite levels in the kidney are associated with kidney-specific toxicity. Oral dosing with TCE was conducted in sub-acute (600 mg/kg/d; 5 days; 7 inbred mouse strains) and sub-chronic (100 or 400 mg/kg/d; 1, 2, or 4 weeks; 2 inbred mouse strains) designs. We evaluated the quantitative relationship between strain-, dose-, and time-dependent formation of TCE metabolites from cytochrome P450-mediated oxidation [trichloroacetic acid (TCA), dichloroacetic acid (DCA), and trichloroethanol] and glutathione conjugation [S-(1,2-dichlorovinyl)-L-cysteine and S-(1,2-dichlorovinyl)glutathione], and various kidney toxicity phenotypes. In sub-acute study, we observed inter-strain differences in TCE metabolite levels in the kidney. In addition, we found that in several strains kidney-specific effects of TCE included induction of peroxisome proliferator-marker genes Cyp4a10 and Acox1, increased cell proliferation, and expression of KIM-1, a marker of tubular damage and regeneration. In sub-chronic study, peroxisome proliferator-marker gene induction and kidney toxicity diminished while cell proliferative response was elevated in a dose-dependent manner in NZW/LacJ, but not C57BL/6J mice. Overall, we show that TCE metabolite levels in the kidney are associated with kidney-specific toxicity and that these effects are strain-dependent. PMID:25424545

Effective Coping With Supervisor Conflict Depends on Control: Implications for Work Strains.

PubMed

Eatough, Erin M; Chang, Chu-Hsiang

2018-01-11

This study examined the interactive effects of interpersonal conflict at work, coping strategy, and perceived control specific to the conflict on employee work strain using multisource and time-lagged data across two samples. In Sample 1, multisource data was collected from 438 employees as well as data from participant-identified secondary sources (e.g., significant others, best friends). In Sample 2, time-lagged data from 100 full-time employees was collected in a constructive replication. Overall, findings suggested that the success of coping efforts as indicated by lower strains hinges on the combination of the severity of the stressor, perceived control over the stressor, and coping strategy used (problem-focused vs. emotion-focused coping). Results from the current study provide insights for why previous efforts to document the moderating effects of coping have been inconsistent, especially with regards to emotion-focused coping. (PsycINFO Database Record (c) 2018 APA, all rights reserved).

Influence of hyaluronic acid on bacterial and fungal species, including clinically relevant opportunistic pathogens.

PubMed

Ardizzoni, Andrea; Neglia, Rachele G; Baschieri, Maria C; Cermelli, Claudio; Caratozzolo, Manuela; Righi, Elena; Palmieri, Beniamino; Blasi, Elisabetta

2011-10-01

Hyaluronic acid (HA) has several clinical applications (aesthetic surgery, dermatology, orthopaedics and ophtalmology). Following recent evidence, suggesting antimicrobial and antiviral properties for HA, we investigated its effects on 15 ATCC strains, representative of clinically relevant bacterial and fungal species. The in vitro system employed allowed to assess optical density of broth cultures as a measure of microbial load in a time-dependent manner. The results showed that different microbial species and, sometimes, different strains belonging to the same species, are differently affected by HA. In particular, staphylococci, enterococci, Streptococcus mutans, two Escherichia coli strains, Pseudomonas aeruginosa, Candida glabrata and C. parapsilosis displayed a HA dose-dependent growth inhibition; no HA effects were detected in E. coli ATCC 13768 and C. albicans; S. sanguinis was favoured by the highest HA dose. Therefore, the influence of HA on bacteria and fungi warrants further studies aimed at better establishing its relevance in clinical applications.

Thermo-Mechanical Calculations of Hybrid Rotary Friction Welding at Equal Diameter Copper Bars and Effects of Essential Parameters on Dependent Special Variables

NASA Astrophysics Data System (ADS)

Parsa, M. H.; Davari, H.; Hadian, A. M.; Ahmadabadi, M. Nili

2007-05-01

Hybrid Rotary Friction Welding is a modified type of common rotary friction welding processes. In this welding method parameters such as pressure, angular velocity and time of welding control temperature, stress, strain and their variations. These dependent factors play an important rule in defining optimum process parameters combinations in order to improve the design and manufacturing of welding machines and quality of welded parts. Thermo-mechanical simulation of friction welding has been carried out and it has been shown that, simulation is an important tool for prediction of generated heat and strain at the weld interface and can be used for prediction of microstructure and evaluation of quality of welds. For simulation of Hybrid Rotary Friction Welding, a commercial finite element program has been used and the effects of pressure and rotary velocity of rotary part on temperature and strain variations have been investigated.

Thermal stresses in the laser disc from a tetragonal c-cut crystal

NASA Astrophysics Data System (ADS)

Yumashev, K. V.; Loiko, P. A.

2014-12-01

Analytical expressions for thermal stresses and strains, as well as displacements, are obtained for the laser disc from a tetragonal crystal cut along the [0 0 1] axis under plane stress approximation, for the first time, to our knowledge. This study illustrates that, in polar coordinates, the normal stresses, σr and σθ, are angular independent, while the shear one τrθ is zero. The thermal strains, εr and εθ, and displacements, u and υ, depend on both radial and tangential coordinates; this dependence has the shape of a four-leaf rose. For considered crystal cutting with isotropic in-plane thermal expansion, the displacements are not pure radial (υ≠0). The values of stresses, strains and displacements are calculated for the disc from a c-cut yttrium vanadate laser crystal, Nd:YVO4. The thermal fracture issues are analyzed for this crystal.

Shear banding leads to accelerated aging dynamics in a metallic glass

NASA Astrophysics Data System (ADS)

Küchemann, Stefan; Liu, Chaoyang; Dufresne, Eric M.; Shin, Jeremy; Maaß, Robert

2018-01-01

Traditionally, strain localization in metallic glasses is related to the thickness of the shear defect, which is confined to the nanometer scale. Using site-specific x-ray photon correlation spectroscopy, we reveal significantly accelerated relaxation dynamics around a shear band in a metallic glass at a length scale that is orders of magnitude larger than the defect itself. The relaxation time in the shear-band vicinity is up to ten times smaller compared to the as-cast matrix, and the relaxation dynamics occurs in a characteristic three-stage aging response that manifests itself in the temperature-dependent shape parameter known from classical stretched exponential relaxation dynamics of disordered materials. We demonstrate that the time-dependent correlation functions describing the aging at different temperatures can be captured and collapsed using simple scaling functions. These insights highlight how a ubiquitous nanoscale strain-localization mechanism in metallic glasses leads to a fundamental change of the relaxation dynamics at the mesoscale.

Shear banding leads to accelerated aging dynamics in a metallic glass

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

Küchemann, Stefan; Liu, Chaoyang; Dufresne, Eric M.

Traditionally, strain localization in metallic glasses is related to the thickness of the shear defect, which is confined to the nanometer scale. In this study, using site-specific x-ray photon correlation spectroscopy (XPCS), we reveal significantly accelerated relaxation dynamics around a shear band in a metallic glass at a length scale that is orders of magnitude larger than the defect itself. The relaxation time in the shear-band vicinity is up to ten-times smaller compared to the as-cast matrix, and the relaxation dynamics occurs in a characteristic three-stage aging response that manifests itself in the temperature-dependent shape parameter known from classical stretchedmore » exponential relaxation dynamics of disordered materials. We demonstrate that the time-dependent correlation functions describing the aging at different temperatures can be captured and collapsed using simple scaling functions. Finally, these insights highlight how an ubiquitous nano-scale strain-localization mechanism in metallic glasses leads to a fundamental change of the relaxation dynamics at the mesoscale.« less

Shear banding leads to accelerated aging dynamics in a metallic glass

DOE PAGES

Küchemann, Stefan; Liu, Chaoyang; Dufresne, Eric M.; ...

2018-01-11

Traditionally, strain localization in metallic glasses is related to the thickness of the shear defect, which is confined to the nanometer scale. In this study, using site-specific x-ray photon correlation spectroscopy (XPCS), we reveal significantly accelerated relaxation dynamics around a shear band in a metallic glass at a length scale that is orders of magnitude larger than the defect itself. The relaxation time in the shear-band vicinity is up to ten-times smaller compared to the as-cast matrix, and the relaxation dynamics occurs in a characteristic three-stage aging response that manifests itself in the temperature-dependent shape parameter known from classical stretchedmore » exponential relaxation dynamics of disordered materials. We demonstrate that the time-dependent correlation functions describing the aging at different temperatures can be captured and collapsed using simple scaling functions. Finally, these insights highlight how an ubiquitous nano-scale strain-localization mechanism in metallic glasses leads to a fundamental change of the relaxation dynamics at the mesoscale.« less

Colony Dimorphism in Bradyrhizobium Strains

PubMed Central

Sylvester-Bradley, Rosemary; Thornton, Philip; Jones, Peter

1988-01-01

Ten isolates of Bradyrhizobium spp. which form two colony types were studied; the isolates originated from a range of legume species. The two colony types differed in the amount of gum formed or size or both, depending on the strain. Whole 7-day-old colonies of each type were subcultured to determine the proportion of cells which had changed to the other type. An iterative computerized procedure was used to determine the rate of switching per generation between the two types and to predict proportions reached at equilibrium for each strain. The predicted proportions of the wetter (more gummy) or larger colony type at equilibrium differed significantly between strains, ranging from 0.9999 (strain CIAT 2383) to 0.0216 (strain CIAT 2469), because some strains switched faster from dry to wet (or small to large) and others switched faster from wet to dry (or large to small). Predicted equilibrium was reached after about 140 generations in strain USDA 76. In all but one strain (CIAT 3030) the growth rate of the wetter colony type was greater than or similar to that of the drier type. The mean difference in generation time between the two colony types was 0.37 h. Doubling times calculated for either colony type after 7 days of growth on the agar surface ranged from 6.0 to 7.3 h. The formation of two persistent colony types by one strain (clonal or colony dimorphism) may be a common phenomenon among Bradyrhizobium strains. Images PMID:16347599

Fabrication and material properties of fibrous PHBV scaffolds depending on the cross-ply angle for tissue engineering.

PubMed

Kim, Yang-Hee; Min, Young-Ki; Lee, Byong-Taek

2012-11-01

Fibrous PHBV cross-ply scaffolds were fabricated using the electrospinning technique. The electrospun fibers were arranged depending on angles of alignment, which were 180°, 90°, 60°, and 45°. The stress and strain values of the fibrous PHBV cross-ply scaffolds increased as the cross-ply angle increased. At 180°, the strength and strain values of the fibers depended on tensile loading directions. At an alignment of 90°, the PHBV scaffolds had a stress value of 3.5 MPa, which was more than two times higher than the random structure. The cell morphology and proliferation of L-929 cells was strongly dependant on the fiber alignment and the best results were observed when the angle alignment was high. The results of this study showed that the cross-ply structure of the PHBV scaffold affected not only the cell adhesion and spreading properties but also dictated the mechanical properties, which were dependent on the angles of alignment.

Xenorhabdus bovienii Strain Diversity Impacts Coevolution and Symbiotic Maintenance with Steinernema spp. Nematode Hosts

PubMed Central

Murfin, Kristen E.; Lee, Ming-Min; McDonald, Bradon R.; Larget, Bret; Forst, Steven; Stock, S. Patricia; Currie, Cameron R.

2015-01-01

ABSTRACT Microbial symbionts provide benefits that contribute to the ecology and fitness of host plants and animals. Therefore, the evolutionary success of plants and animals fundamentally depends on long-term maintenance of beneficial associations. Most work investigating coevolution and symbiotic maintenance has focused on species-level associations, and studies are lacking that assess the impact of bacterial strain diversity on symbiotic associations within a coevolutionary framework. Here, we demonstrate that fitness in mutualism varies depending on bacterial strain identity, and this is consistent with variation shaping phylogenetic patterns and maintenance through fitness benefits. Through genome sequencing of nine bacterial symbiont strains and cophylogenetic analysis, we demonstrate diversity among Xenorhabdus bovienii bacteria. Further, we identified cocladogenesis between Steinernema feltiae nematode hosts and their corresponding X. bovienii symbiont strains, indicating potential specificity within the association. To test the specificity, we performed laboratory crosses of nematode hosts with native and nonnative symbiont strains, which revealed that combinations with the native bacterial symbiont and closely related strains performed significantly better than those with more divergent symbionts. Through genomic analyses we also defined potential factors contributing to specificity between nematode hosts and bacterial symbionts. These results suggest that strain-level diversity (e.g., subspecies-level differences) in microbial symbionts can drive variation in the success of host-microbe associations, and this suggests that these differences in symbiotic success could contribute to maintenance of the symbiosis over an evolutionary time scale. PMID:26045536

Dynamic Brazilian Test of Rock Under Intermediate Strain Rate: Pendulum Hammer-Driven SHPB Test and Numerical Simulation

NASA Astrophysics Data System (ADS)

Zhu, W. C.; Niu, L. L.; Li, S. H.; Xu, Z. H.

2015-09-01

The tensile strength of rock subjected to dynamic loading constitutes many engineering applications such as rock drilling and blasting. The dynamic Brazilian test of rock specimens was conducted with the split Hopkinson pressure bar (SHPB) driven by pendulum hammer, in order to determine the indirect tensile strength of rock under an intermediate strain rate ranging from 5.2 to 12.9 s-1, which is achieved when the incident bar is impacted by pendulum hammer with different velocities. The incident wave excited by pendulum hammer is triangular in shape, featuring a long rising time, and it is considered to be helpful for achieving a constant strain rate in the rock specimen. The dynamic indirect tensile strength of rock increases with strain rate. Then, the numerical simulator RFPA-Dynamics, a well-recognized software for simulating the rock failure under dynamic loading, is validated by reproducing the Brazilian test of rock when the incident stress wave retrieved at the incident bar is input as the boundary condition, and then it is employed to study the Brazilian test of rock under the higher strain rate. Based on the numerical simulation, the strain-rate dependency of tensile strength and failure pattern of the Brazilian disc specimen under the intermediate strain rate are numerically simulated, and the associated failure mechanism is clarified. It is deemed that the material heterogeneity should be a reason for the strain-rate dependency of rock.

Atomistic Simulation of the Rate-Dependent Ductile-to-Brittle Failure Transition in Bicrystalline Metal Nanowires.

PubMed

Tao, Weiwei; Cao, Penghui; Park, Harold S

2018-02-14

The mechanical properties and plastic deformation mechanisms of metal nanowires have been studied intensely for many years. One of the important yet unresolved challenges in this field is to bridge the gap in properties and deformation mechanisms reported for slow strain rate experiments (∼10 -2 s -1 ), and high strain rate molecular dynamics (MD) simulations (∼10 8 s -1 ) such that a complete understanding of strain rate effects on mechanical deformation and plasticity can be obtained. In this work, we use long time scale atomistic modeling based on potential energy surface exploration to elucidate the atomistic mechanisms governing a strain-rate-dependent incipient plasticity and yielding transition for face centered cubic (FCC) copper and silver nanowires. The transition occurs for both metals with both pristine and rough surfaces for all computationally accessible diameters (<10 nm). We find that the yield transition is induced by a transition in the incipient plastic event from Shockley partials nucleated on primary slip systems at MD strain rates to the nucleation of planar defects on non-Schmid slip planes at experimental strain rates, where multiple twin boundaries and planar stacking faults appear in copper and silver, respectively. Finally, we demonstrate that, at experimental strain rates, a ductile-to-brittle transition in failure mode similar to previous experimental studies on bicrystalline silver nanowires is observed, which is driven by differences in dislocation activity and grain boundary mobility as compared to the high strain rate case.

Unraveling complex nonlinear elastic behaviors in rocks using dynamic acousto-elasticity

NASA Astrophysics Data System (ADS)

Riviere, J.; Guyer, R.; Renaud, G.; TenCate, J. A.; Johnson, P. A.

2012-12-01

In comparison with standard nonlinear ultrasonic methods like frequency mixing or resonance based measurements that allow one to extract average, bulk variations of modulus and attenuation versus strain level, dynamic acousto-elasticity (DAE) allows to obtain the elastic behavior over the entire dynamic cycle, detailing the full nonlinear behavior under tension and compression, including hysteresis and memory effects. This method consists of exciting a sample in Bulk-mode resonance at strains of 10-7 to 10-5 and simultaneously probing with a sequence of high frequency, low amplitude pulses. Time of flight and amplitudes of these pulses, respectively related to nonlinear elastic and dissipative parameters, can be plotted versus vibration strain level. Despite complex nonlinear signatures obtained for most rocks, it can be shown that for low strain amplitude (< 10-6), the nonlinear classical theory issued from a Taylor decomposition can explain the harmonic content. For higher strain, harmonic content becomes richer and the material exhibits more hysteretic behaviors, i.e. strain rate dependencies. Such observations have been made in the past (e.g., Pasqualini et al., JGR 2007), but not with the extreme detail of elasticity provided by DAE. Previous quasi-static measurements made in Berea sandstone (Claytor et al, GRL 2009), show that the hysteretic behavior disappears when the protocol is performed at a very low strain-rate (static limit). Therefore, future work will aim at linking quasi-static and dynamic observations, i.e. the frequency or strain-rate dependence, in order to understand underlying physical phenomena.

Biophysical Stimulation for Engineering Functional Skeletal Muscle.

PubMed

Somers, Sarah M; Spector, Alexander A; DiGirolamo, Douglas J; Grayson, Warren L

2017-08-01

Tissue engineering is a promising therapeutic strategy to regenerate skeletal muscle. However, ex vivo cultivation methods typically result in a low differentiation efficiency of stem cells as well as grafts that resemble the native tissues morphologically, but lack contractile function. The application of biomimetic tensile strain provides a potent stimulus for enhancing myogenic differentiation and engineering functional skeletal muscle grafts. We reviewed integrin-dependent mechanisms that potentially link mechanotransduction pathways to the upregulation of myogenic genes. Yet, gaps in our understanding make it challenging to use these pathways to theoretically determine optimal ex vivo strain regimens. A multitude of strain protocols have been applied to in vitro cultures for the cultivation of myogenic progenitors (adipose- and bone marrow-derived stem cells and satellite cells) and transformed murine myoblasts, C2C12s. Strain regimens are characterized by orientation, amplitude, and time-dependent factors (effective frequency, duration, and the rest period between successive strain cycles). Analysis of published data has identified possible minimum/maximum values for these parameters and suggests that uniaxial strains may be more potent than biaxial strains, possibly because they more closely mimic physiologic strain profiles. The application of these biophysical stimuli for engineering 3D skeletal muscle grafts is nontrivial and typically requires custom-designed bioreactors used in combination with biomaterial scaffolds. Consideration of the physical properties of these scaffolds is critical for effective transmission of the applied strains to encapsulated cells. Taken together, these studies demonstrate that biomimetic tensile strain generally results in improved myogenic outcomes in myogenic progenitors and differentiated myoblasts. However, for 3D systems, the optimization of the strain regimen may require the entire system including cells, biomaterials, and bioreactor, to be considered in tandem.

Strain dependence of perfluorinated polymer optical fiber Bragg grating measured at different wavelengths

NASA Astrophysics Data System (ADS)

Ishikawa, Ryo; Lee, Heeyoung; Lacraz, Amédée; Theodosiou, Antreas; Kalli, Kyriacos; Mizuno, Yosuke; Nakamura, Kentaro

2018-03-01

We measure the strain dependence of multiple Bragg wavelengths (corresponding to different diffraction orders) of a fiber Bragg grating (FBG) inscribed in a perfluorinated graded-index polymer optical fiber (PFGI-POF) in the wavelength range up to 1550 nm. On the basis of this result, we show that the fractional sensitivity, which has been conventionally used as a wavelength-independent index for fair comparison of the FBG performance measured at different wavelengths, is dependent on wavelength in this range. The reason for this behavior seems to originate from the non-negligible wavelength dependence of refractive index and its strain-dependence coefficient. Using the wavelength dependence of the refractive index already reported for bulk, we deduce the wavelength dependence of the strain coefficient of the refractive index. This information will be a useful archive in implementing PFGI-POF-based strain sensors based on not only FBGs but also Brillouin scattering in the future.

Tensile Lattice Strain Accelerates Oxygen Surface Exchange and Diffusion in La1–xSrxCoO3−δ Thin Films

PubMed Central

2013-01-01

The influence of lattice strain on the oxygen exchange kinetics and diffusion in oxides was investigated on (100) epitaxial La1–xSrxCoO3−δ (LSC) thin films grown by pulsed laser deposition. Planar tensile and compressively strained LSC films were obtained on single-crystalline SrTiO3 and LaAlO3. 18O isotope exchange depth profiling with ToF-SIMS was employed to simultaneously measure the tracer surface exchange coefficient k* and the tracer diffusion coefficient D* in the temperature range 280–475 °C. In accordance with recent theoretical findings, much faster surface exchange (∼4 times) and diffusion (∼10 times) were observed for the tensile strained films compared to the compressively strained films in the entire temperature range. The same strain effect—tensile strain leading to higher k* and D*—was found for different LSC compositions (x = 0.2 and x = 0.4) and for surface-etched films. The temperature dependence of k* and D* is discussed with respect to the contributions of strain states, formation enthalpy of oxygen vacancies, and vacancy mobility at different temperatures. Our findings point toward the control of oxygen surface exchange and diffusion kinetics by means of lattice strain in existing mixed conducting oxides for energy conversion applications. PMID:23527691

Development of constitutive models for cyclic plasticity and creep behavior of super alloys at high temperature

NASA Technical Reports Server (NTRS)

Haisler, W. E.

1983-01-01

An uncoupled constitutive model for predicting the transient response of thermal and rate dependent, inelastic material behavior was developed. The uncoupled model assumes that there is a temperature below which the total strain consists essentially of elastic and rate insensitive inelastic strains only. Above this temperature, the rate dependent inelastic strain (creep) dominates. The rate insensitive inelastic strain component is modelled in an incremental form with a yield function, blow rule and hardening law. Revisions to the hardening rule permit the model to predict temperature-dependent kinematic-isotropic hardening behavior, cyclic saturation, asymmetric stress-strain response upon stress reversal, and variable Bauschinger effect. The rate dependent inelastic strain component is modelled using a rate equation in terms of back stress, drag stress and exponent n as functions of temperature and strain. A sequence of hysteresis loops and relaxation tests are utilized to define the rate dependent inelastic strain rate. Evaluation of the model has been performed by comparison with experiments involving various thermal and mechanical load histories on 5086 aluminum alloy, 304 stainless steel and Hastelloy X.

Replication restart in UV-irradiated Escherichia coli involving pols II, III, V, PriA, RecA and RecFOR proteins.

PubMed

Rangarajan, Savithri; Woodgate, Roger; Goodman, Myron F

2002-02-01

In Escherichia coli, UV-irradiated cells resume DNA synthesis after a transient inhibition by a process called replication restart. To elucidate the role of several key proteins involved in this process, we have analysed the time dependence of replication restart in strains carrying a combination of mutations in lexA, recA, polB (pol II), umuDC (pol V), priA, dnaC, recF, recO or recR. We find that both pol II and the origin-independent primosome-assembling function of PriA are essential for the immediate recovery of DNA synthesis after UV irradiation. In their absence, translesion replication or 'replication readthrough' occurs approximately 50 min after UV and is pol V-dependent. In a wild-type, lexA+ background, mutations in recF, recO or recR block both pathways. Similar results were obtained with a lexA(Def) recF strain. However, lexA(Def) recO or lexA(Def) recR strains, although unable to facilitate PriA-pol II-dependent restart, were able to perform pol V-dependent readthrough. The defects in restart attributed to mutations in recF, recO or recR were suppressed in a recA730 lexA(Def) strain expressing constitutively activated RecA (RecA*). Our data suggest that in a wild-type background, RecF, O and R are important for the induction of the SOS response and the formation of RecA*-dependent recombination intermediates necessary for PriA/Pol II-dependent replication restart. In con-trast, only RecF is required for the activation of RecA that leads to the formation of pol V (UmuD'2C) and facilitates replication readthrough.

Implementation of Improved Transverse Shear Calculations and Higher Order Laminate Theory Into Strain Rate Dependent Analyses of Polymer Matrix Composites

NASA Technical Reports Server (NTRS)

Zhu, Lin-Fa; Kim, Soo; Chattopadhyay, Aditi; Goldberg, Robert K.

2004-01-01

A numerical procedure has been developed to investigate the nonlinear and strain rate dependent deformation response of polymer matrix composite laminated plates under high strain rate impact loadings. A recently developed strength of materials based micromechanics model, incorporating a set of nonlinear, strain rate dependent constitutive equations for the polymer matrix, is extended to account for the transverse shear effects during impact. Four different assumptions of transverse shear deformation are investigated in order to improve the developed strain rate dependent micromechanics model. The validities of these assumptions are investigated using numerical and theoretical approaches. A method to determine through the thickness strain and transverse Poisson's ratio of the composite is developed. The revised micromechanics model is then implemented into a higher order laminated plate theory which is modified to include the effects of inelastic strains. Parametric studies are conducted to investigate the mechanical response of composite plates under high strain rate loadings. Results show the transverse shear stresses cannot be neglected in the impact problem. A significant level of strain rate dependency and material nonlinearity is found in the deformation response of representative composite specimens.

Strain rate effects in stress corrosion cracking

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

Parkins, R.N.

Slow strain rate testing (SSRT) was initially developed as a rapid, ad hoc laboratory method for assessing the propensity for metals an environments to promote stress corrosion cracking. It is now clear, however, that there are good theoretical reasons why strain rate, as opposed to stress per se, will often be the controlling parameter in determining whether or not cracks are nucleated and, if so, are propagated. The synergistic effects of the time dependence of corrosion-related reactions and microplastic strain provide the basis for mechanistic understanding of stress corrosion cracking in high-pressure pipelines and other structures. However, while this maymore » be readily comprehended in the context of laboratory slow strain tests, its extension to service situations may be less apparent. Laboratory work involving realistic stressing conditions, including low-frequency cyclic loading, shows that strain or creep rates give good correlation with thresholds for cracking and with crack growth kinetics.« less

Nonlinear effects in thermal stress analysis of a solid propellant rocket motor

NASA Technical Reports Server (NTRS)

Francis, E. C.; Peeters, R. L.; Murch, S. A.

1976-01-01

Direct characterization procedures were used to determine the relaxation modulus as a function of time, temperature, and state of strain. Using the quasi-elastic method of linearviscoelasticity, these properties were employed in a finite element computer code to analyze a thick-walled, nonlinear viscoelastic cylinder in the state of plane strain bonded to a thin (but stiff) elastic casing and subjected to slow thermal cooling. The viscoelastic solution is then expressed as a sequence of elastic finite element solutions. The strain-dependent character of the relaxation modulus is included by replacing the single relaxation curve used in the linear viscoelastic theory by a family of relaxation functions obtained at various strain levels. These functions may be regarded as a collection of stress histories or responses to specific loads (in this case, step strains) with which the cooldown solution is made to agree by iterations on the modulus and strain level.

Study of the validity of a job-exposure matrix for the job strain model factors: an update and a study of changes over time.

PubMed

Niedhammer, Isabelle; Milner, Allison; LaMontagne, Anthony D; Chastang, Jean-François

2018-03-08

The objectives of the study were to construct a job-exposure matrix (JEM) for psychosocial work factors of the job strain model, to evaluate its validity, and to compare the results over time. The study was based on national representative data of the French working population with samples of 46,962 employees (2010 SUMER survey) and 24,486 employees (2003 SUMER survey). Psychosocial work factors included the job strain model factors (Job Content Questionnaire): psychological demands, decision latitude, social support, job strain and iso-strain. Job title was defined by three variables: occupation and economic activity coded using standard classifications, and company size. A JEM was constructed using a segmentation method (Classification and Regression Tree-CART) and cross-validation. The best quality JEM was found using occupation and company size for social support. For decision latitude and psychological demands, there was not much difference using occupation and company size with or without economic activity. The validity of the JEM estimates was higher for decision latitude, job strain and iso-strain, and lower for social support and psychological demands. Differential changes over time were observed for psychosocial work factors according to occupation, economic activity and company size. This study demonstrated that company size in addition to occupation may improve the validity of JEMs for psychosocial work factors. These matrices may be time-dependent and may need to be updated over time. More research is needed to assess the validity of JEMs given that these matrices may be able to provide exposure assessments to study a range of health outcomes.

Turbulent Plane Wakes Subjected to Successive Strains

NASA Technical Reports Server (NTRS)

Rogers, Michael M.

2003-01-01

Six direct numerical simulations of turbulent time-evolving strained plane wakes have been examined to investigate the response of a wake to successive irrotational plane strains of opposite sign. The orientation of the applied strain field has been selected so that the flow is the time-developing analogue of a spatially developing wake evolving in the presence of either a favourable or an adverse streamwise pressure gradient. The magnitude of the applied strain rate a is constant in time t until the total strain e(sup at) reaches about four. At this point, a new simulation is begun with the sign of the applied strain being reversed (the original simulation is continued as well). When the total strain is reduced back to its original value of one, yet another simulation is begun with the sign of the strain being reversed again back to its original sign. This process is done for both initially "favourable" and initially "adverse" strains, providing simulations for each of these strain types from three different initial conditions. The evolution of the wake mean velocity deficit and width is found to be very similar for all the adversely strained cases, with both measures rapidly achieving exponential growth at the rate associated with the cross-stream expansive strain e(sup at). In the "favourably" strained cases, the wake widths approach a constant and the velocity deficits ultimately decay rapidly as e(sup -2at). Although all three of these cases do exhibit the same asymptotic exponential behaviour, the time required to achieve this is longer for the cases that have been previously adversely strained (by at approx. equals 1). These simulations confirm the generality of the conclusions drawn in Rogers (2002) regarding the response of plane wakes to strain. The evolution of strained wakes is not consistent with the predictions of classical self-similar analysis; a more general equilibrium similarity solution is required to describe the results. At least for the cases considered here, the wake Reynolds number and the ratio of the turbulent kinetic energy to the square of the wake mean velocity deficit are determined nearly entirely by the total strain. For these measures the order in which the strains are applied does not matter and the changes brought about by the strain are nearly reversible. The wake mean velocity deficit and width, on the other hand, differ by about a factor of three when the total strain returns to one, depending on whether the wake was first "favourably" or "adversely" strained. The strain history is important for predicting the evolution of these quantities.

Predicting grid-size-dependent fracture strains of DP980 with a microstructure-based post-necking model

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

Cheng, G.; Hu, X. H.; Choi, K. S.

Ductile fracture is a local phenomenon, and it is well established that fracture strain levels depend on both stress triaxiality and the resolution (grid size) of strain measurements. Two-dimensional plane strain post-necking models with different representative volume element (RVE) sizes are used to predict the size-dependent fracture strain of a commercial dual-phase steel, DP980. The models are generated from the actual microstructures, and the individual phase flow properties and literature-based individual phase damage parameters for the Johnson-Cook model are used for ferrite and martensite. A monotonic relationship is predicted: the smaller the model size, the higher the fracture strain. Thus,more » a general framework is developed to quantify the size-dependent fracture strains for multiphase materials. In addition to the RVE sizes, the influences of intrinsic microstructure features, i.e., the flow curve and fracture strains of the two constituent phases, on the predicted fracture strains also are examined. Application of the derived fracture strain versus RVE size relationship is demonstrated with large clearance trimming simulations with different element sizes.« less

In-air and pressurized water reactor environment fatigue experiments of 316 stainless steel to study the effect of environment on cyclic hardening

NASA Astrophysics Data System (ADS)

Mohanty, Subhasish; Soppet, William K.; Majumdar, Saurindranath; Natesan, Krishnamurti

2016-05-01

Argonne National Laboratory (ANL), under the sponsorship of Department of Energy's Light Water Reactor Sustainability (LWRS) program, is trying to develop a mechanistic approach for more accurate life estimation of LWR components. In this context, ANL has conducted many fatigue experiments under different test and environment conditions on type 316 stainless steel (316 SS) material which is widely used in the US reactors. Contrary to the conventional S ∼ N curve based empirical fatigue life estimation approach, the aim of the present DOE sponsored work is to develop an understanding of the material ageing issues more mechanistically (e.g. time dependent hardening and softening) under different test and environmental conditions. Better mechanistic understanding will help develop computer-based advanced modeling tools to better extrapolate stress-strain evolution of reactor components under multi-axial stress states and hence help predict their fatigue life more accurately. Mechanics-based modeling of fatigue such as by using finite element (FE) tools requires the time/cycle dependent material hardening properties. Presently such time-dependent material hardening properties are hardly available in fatigue modeling literature even under in-air conditions. Getting those material properties under PWR environment, are even harder. Through this work we made preliminary attempt to generate time/cycle dependent stress-strain data both under in-air and PWR water conditions for further study such as for possible development of material models and constitutive relations for FE model implementation. Although, there are open-ended possibility to further improve the discussed test methods and related material estimation techniques we anticipate that the data presented in this paper will help the metal fatigue research community particularly, the researchers who are dealing with mechanistic modeling of metal fatigue such as using FE tools. In this paper the fatigue experiments under different test and environment conditions and related stress-strain results for 316 SS are discussed.

High temperature low cycle fatigue mechanisms for nickel base and a copper base alloy. M.S. Thesis Final Report

NASA Technical Reports Server (NTRS)

Shih, C. I.

1982-01-01

Damage mechanisms were studied in Rene' 95 and NARloy Z, using optical, scanning and transmission in microscopy. In necklace Rene' 95, crack initiation was mainly associated with cracking of surface MC carbides, except for hold time tests at higher strain ranges where initiation was associated more with a grain boundary mechanism. A mixed mode of propagation with a faceted fracture morphology was typical for all cycle characters. The dependence of life on maximum tensile stress can be demonstrated by the data falling onto three lines corresponding to the three tensile hold times, in the life against maximum tensile stress plot. In NARloy Z, crack initiation was always at the grain boundaries. The mode of crack propagation depended on the cycle character. The life decreased with decreasing strain rate and with tensile holds. In terms of damage mode, different life prediction laws may be applicable to different cycle characters.

Rheological observation of glassy dynamics of dilute polymer solutions near the coil-stretch transition in elongational flows.

PubMed

Sridhar, T; Nguyen, D A; Prabhakar, R; Prakash, J Ravi

2007-04-20

It has long been conjectured that the macroscopic dynamics of dilute polymer solutions may exhibit a glasslike slowdown caused by ergodicity breaking, in the vicinity of the coil-stretch transition in elongational flows. We report experimental observations using a filament stretching rheometer that confirm the existence of such glassy states. It is observed that different time-dependent elongational strain-rate profiles lead to a pronounced history dependence and aging effects within a narrow range of strain rates. The results have a direct bearing on the analysis and design of processes employing dilute polymer solutions, such as ink-jet printing, surface coating, and turbulent-drag reduction.

Monitoring of ultraviolet pulse rate dependent photomechanical actuation in carbon nanotubes using fiber Bragg gratings

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

Shivananju, B. N.; Suri, Ashish; Asokan, S.

2014-01-06

In this Letter, we present a non-contact method of controlling and monitoring photomechanical actuation in carbon nanotubes (CNT) by exposing it to ultra-violet radiation at different pulse rates (10 to 200 Hz). This is accomplished by imparting a reversible photo induced strain (5–330 με) on CNT coated fibre Bragg gratings; CNT undergoes an internal reversible structural change due to cyclic photon absorption that leads to the development of mechanical strain, which in turn allows reversible switching of the Bragg wavelength. The results also reveal an interesting pulse rate dependent rise and fall times of photomechanical actuation in CNT.

The Dependence of Portevin-Le Châtelier Effect on the γ' Precipitates in a Wrought Ni-Base Superalloy

NASA Astrophysics Data System (ADS)

Wang, Xinguang; Han, Guoming; Cui, Chuanyong; Guan, Shuai; Jin, Tao; Sun, Xiaofeng; Hu, Zhuangqi

2016-12-01

The dependence of Portevin-Le Châtelier (PLC) effect on the γ' precipitates of the Nimonic 263 alloy in different microstructural conditions has been studied by analyzing the parameters of the tensile curves and the deformation mechanisms. It is shown that the γ' precipitates with different sizes, edge-to-edge interprecipitate distance, and areal number density are obtained by altering the aging time. It is demonstrated that when the mean size of the γ' precipitates is less than 28 nm (aging less than 25 hours), the deformation mechanisms are dominated by APB-coupled a/2<101> dislocations shearing the small γ' precipitates and the slip bands continuously cutting the γ and γ' phases. When the γ' size is between 28 and 45 nm (aging time between 25 and 50 hours), the deformation mechanism is controlled by the APB-coupled a/2<101> dislocations shearing the small γ' precipitates, the a/6<112> Shockley partial dislocation continuously shearing the γ and γ' phases combined with matrix dislocations by-passing the γ' precipitates; If the γ' size over 45 nm (aging time more than 50 hours), Orowan by-passing becomes the main deformation mechanism. Moreover, with increasing the aging time, the critical plastic strain for the onset of the PLC effect increases and reaches a maximum after aging for 50 hours, and then gradually decreases. At last, the dependence of critical plastic strain on the deformation mechanisms is well explained by the elementary incremental strain (γ). The precipitation process of the γ' phase can directly influence the PLC effect by changing the interactions among solutes atoms, mobile dislocations, and forest dislocations.

Experimental studies of compaction and dilatancy during frictional sliding on faults containing gouge

USGS Publications Warehouse

Morrow, C.A.; Byerlee, J.D.

1989-01-01

Transient strength changes are observed in fault gouge materials when the velocity of shearing is varied. A transient stress peak is produced when the strain rate in the gouge is suddenly increased, whereas a transient stress drop results from a sudden change to a slower strain rate. We have studied the mechanism responsible for these observations by performing frictional sliding experiments on sawcut granite samples filled with a layer of several different fault gouge types. Changes in pore volume and strength were monitored as the sliding velocity alternated between fast and slow rates. Pore volume increased at the faster strain rate, indicating a dilation of the gouge layer, whereas volume decreased at the slower rate indicating compaction. These results verify that gouge dilation is a function of strain rate. Pore volume changed until an equilibrium void ratio of the granular material was reached for a particular rate of strain. Using arguments from soil mechanics, we find that the dense gouge was initially overconsolidated relative to the equilibrium level, whereas the loose gouge was initially underconsolidated relative to this level. Therefore, the transient stress behavior must be due to the overconsolidated state of the gouge at the new rate when the velocity is increased and to the underconsolidated state when the velocity is lowered. Time-dependent compaction was also shown to cause a transient stress response similar to the velocity-dependent behavior. This may be important in natural fault gouges as they become consolidated and stronger with time. In addition, the strain hardening of the gouge during shearing was found to be a function of velocity, rendering it difficult to quantify the change in equilibrium shear stress when velocity is varied under certain conditions. ?? 1989.

Experimental Techniques Verified for Determining Yield and Flow Surfaces

NASA Technical Reports Server (NTRS)

Lerch, Brad A.; Ellis, Rod; Lissenden, Cliff J.

1998-01-01

Structural components in aircraft engines are subjected to multiaxial loads when in service. For such components, life prediction methodologies are dependent on the accuracy of the constitutive models that determine the elastic and inelastic portions of a loading cycle. A threshold surface (such as a yield surface) is customarily used to differentiate between reversible and irreversible flow. For elastoplastic materials, a yield surface can be used to delimit the elastic region in a given stress space. The concept of a yield surface is central to the mathematical formulation of a classical plasticity theory, but at elevated temperatures, material response can be highly time dependent. Thus, viscoplastic theories have been developed to account for this time dependency. Since the key to many of these theories is experimental validation, the objective of this work (refs. 1 and 2) at the NASA Lewis Research Center was to verify that current laboratory techniques and equipment are sufficient to determine flow surfaces at elevated temperatures. By probing many times in the axial-torsional stress space, we could define the yield and flow surfaces. A small offset definition of yield (10 me) was used to delineate the boundary between reversible and irreversible behavior so that the material state remained essentially unchanged and multiple probes could be done on the same specimen. The strain was measured with an off-the-shelf multiaxial extensometer that could measure the axial and torsional strains over a wide range of temperatures. The accuracy and resolution of this extensometer was verified by comparing its data with strain gauge data at room temperature. The extensometer was found to have sufficient resolution for these experiments. In addition, the amount of crosstalk (i.e., the accumulation of apparent strain in one direction when strain in the other direction is applied) was found to be negligible. Tubular specimens were induction heated to determine the flow surfaces at elevated temperatures. The heating system induced a large amount of noise in the data. By reducing thermal fluctuations and using appropriate data averaging schemes, we could render the noise inconsequential. Thus, accurate and reproducible flow surfaces (see the figure) could be obtained.

Evaluation of Four Calcium Channel Blockers as Fluconazole Resistance Inhibitors in Candida glabrata.

PubMed

Alnajjar, Lina M; Bulatova, Nailya R; Darwish, Rula M

2018-04-14

In this study we aimed to evaluate the ability of four calcium channel blockers, verapamil, diltiazem, nicardipine and nifedipine to enhance sensitivity of Candida glabrata strains to fluconazole. The synergistic antifungal effect was examined by checkerboard method; fractional inhibitory concentration index (FIC) was determined. Time-kill curve method was used for the most promising combination to further evaluate the synergetic effects. nicardipine showed additive effect with fluconazole against fluconazole-resistant and fluconazole-susceptible-dose-dependent strains (DSY565 and CBS138) known to express efflux pumps but not against fluconazole-sensitive strains. Nifedipine exhibited additive effect with fluconazole in both checkerboard (0.5< FIC <1) and time-kill curve methods (<2 log10 colony-forming units (CFU)/ml decrease in viable count). Additionally, nifedipine had own antifungal effect consistently against most of the strains used in this study with minimum inhibitory concentration of 8μg/ml. nicardipine showed additive effect with fluconazole in fluconazole-resistant strains of Candida glabrata-most probably via efflux pump inhibition as demonstrated selectively in fluconazole-resistant strains with known efflux pumps. Nifedipine displayed promising antifungal effect alone and additive effects with fluconazole. Copyright © 2018. Published by Elsevier Ltd.

Dynamic strain-aging effect on fracture toughness of vessel steels

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

Kang, S.S.; Kim, I.S.

1992-03-01

In this paper the effect of dynamic strain aging (DSA) on fracture is investigated on the quenched and tempered specimens of American Society of Mechanical Engineers (ASME) standard SA508 class 3 nuclear pressure vessel steel. Serrated flow by DSA is observed between 180 and 340{degrees}C at a tensile strain rate of 2.08 {times} 10{sup {minus}4}/s and 1.25 {times} 10{sup {minus}3}/s. The DSA causes a sharp rise in the ultimate tensile strength and a marked decrease in ductility. The DSA range shifts to higher temperatures with increased strain rates. The temperature and strain rate dependence of the onset of serrations yieldsmore » an activation energy of 16.2 kcal/mol, which suggests that the process is controlled by interstitial diffusion of carbon and nitrogen in ferrite. The J{sub i} value obtained from the direct current potential drop (DCPD) method, for true crack initiation, is lowered by DSA. The drop in J{sub i} at elevated temperatures may be because of the interaction of the interstitial impurities with dislocations at the crack front.« less

Tensile Strength of Carbon Nanotubes Under Realistic Temperature and Strain Rate

NASA Technical Reports Server (NTRS)

Wei, Chen-Yu; Cho, Kyeong-Jae; Srivastava, Deepak; Biegel, Bryan (Technical Monitor)

2002-01-01

Strain rate and temperature dependence of the tensile strength of single-wall carbon nanotubes has been investigated with molecular dynamics simulations. The tensile failure or yield strain is found to be strongly dependent on the temperature and strain rate. A transition state theory based predictive model is developed for the tensile failure of nanotubes. Based on the parameters fitted from high-strain rate and temperature dependent molecular dynamics simulations, the model predicts that a defect free micrometer long single-wall nanotube at 300 K, stretched with a strain rate of 1%/hour, fails at about 9 plus or minus 1% tensile strain. This is in good agreement with recent experimental findings.

Hepatitis C Virus Strain-Dependent Usage of Apolipoprotein E Modulates Assembly Efficiency and Specific Infectivity of Secreted Virions.

PubMed

Weller, Romy; Hueging, Kathrin; Brown, Richard J P; Todt, Daniel; Joecks, Sebastian; Vondran, Florian W R; Pietschmann, Thomas

2017-09-15

Hepatitis C virus (HCV) is extraordinarily diverse and uses entry factors in a strain-specific manner. Virus particles associate with lipoproteins, and apolipoprotein E (ApoE) is critical for HCV assembly and infectivity. However, whether ApoE dependency is common to all HCV genotypes remains unknown. Therefore, we compared the roles of ApoE utilizing 10 virus strains from genotypes 1 through 7. ApoA and ApoC also support HCV assembly, so they may contribute to virus production in a strain-dependent fashion. Transcriptome sequencing (RNA-seq) revealed abundant coexpression of ApoE, ApoB, ApoA1, ApoA2, ApoC1, ApoC2, and ApoC3 in primary hepatocytes and in Huh-7.5 cells. Virus production was examined in Huh-7.5 cells with and without ApoE expression and in 293T cells where individual apolipoproteins (ApoE1, -E2, -E3, -A1, -A2, -C1, and -C3) were provided in trans All strains were strictly ApoE dependent. However, ApoE involvement in virus production was strain and cell type specific, because some HCV strains poorly produced infectious virus in ApoE-expressing 293T cells and because ApoE knockout differentially affected virus production of HCV strains in Huh-7.5 cells. ApoE allelic isoforms (ApoE2, -E3, and -E4) complemented virus production of HCV strains to comparable degrees. All tested strains assembled infectious progeny with ApoE in preference to other exchangeable apolipoproteins (ApoA1, -A2, -C1, and -C3). The specific infectivity of HCV particles was similar for 293T- and Huh-7.5-derived particles for most strains; however, it differed by more than 100-fold in some viruses. Collectively, this study reveals strain-dependent and host cell-dependent use of ApoE during HCV assembly. These differences relate to the efficacy of virus production and also to the properties of released virus particles and therefore govern viral fitness at the level of assembly and cell entry. IMPORTANCE Chronic HCV infections are a major cause of liver disease. HCV is highly variable, and strain-specific determinants modulate the response to antiviral therapy, the natural course of infection, and cell entry factor usage. Here we explored whether host factor dependency of HCV in particle assembly is modulated by strain-dependent viral properties. We showed that all examined HCV strains, which represent all seven known genotypes, rely on ApoE expression for assembly of infectious progeny. However, the degree of ApoE dependence is modulated in a strain-specific and cell type-dependent manner. This indicates that HCV strains differ in their assembly properties and host factor usage during assembly of infectious progeny. Importantly, these differences relate not only to the efficiency of virus production and release but also to the infectiousness of virus particles. Thus, strain-dependent features of HCV modulate ApoE usage, with implications for virus fitness at the level of assembly and cell entry. Copyright © 2017 Weller et al.

The mammary gland is a sensitive pubertal target in CD-1 and C57Bl/6 mice following perinatal perfluorooctanoic acid (PFOA) exposure.

PubMed

Tucker, Deirdre K; Macon, Madisa B; Strynar, Mark J; Dagnino, Sonia; Andersen, Erik; Fenton, Suzanne E

2015-07-01

Perfluorooctanoic acid (PFOA) is a developmental toxicant in mice, with varied strain outcomes depending on dose and period of exposure. The impact of PFOA on female mouse pubertal development at low doses (≤1mg/kg) has yet to be determined. Therefore, female offspring from CD-1 and C57Bl/6 dams exposed to PFOA, creating serum concentrations similar to humans, were examined for pubertal onset, including mammary gland development. Pups demonstrated a shorter PFOA elimination half-life than that reported for adult mice. Prenatal exposure to PFOA caused significant mammary developmental delays in female offspring in both strains. Delays started during puberty and persisted into young adulthood; severity was dose-dependent. Also an evaluation of female serum hormone levels and pubertal timing onset revealed no effects of PFOA compared to controls in either strain. These data suggest that the mammary gland is more sensitive to early low level PFOA exposures compared to other pubertal endpoints, regardless of strain. Published by Elsevier Inc.

The mammary gland is a sensitive pubertal target in CD-1 and C57Bl/6 mice following perinatal perfluorooctanoic acid (PFOA) exposure

PubMed Central

Tucker, Deirdre K.; Macon, Madisa B.; Strynar, Mark J.; Dagnino, Sonia; Andersen, Erik; Fenton, Suzanne E.

2015-01-01

Perfluorooctanoic acid (PFOA) is a known developmental toxicant in mice, with varied strain outcomes depending on dose and period of exposure. The impact of PFOA on female mouse pubertal development at low doses (≤1 mg/kg), however, has yet to be determined. Therefore, female offspring from CD-1 and C57Bl/6 dams exposed to PFOA, creating serum concentrations similar to humans, were examined for pubertal onset, including mammary gland development. Mouse pups demonstrated a shorter PFOA elimination half-life than that reported for adult mice. Prenatal exposure to PFOA caused significant mammary developmental delays in exposed female offspring in both strains. Delays started during puberty and persisted into young adulthood; severity was dose-dependent. In contrast, an evaluation of serum hormone levels and pubertal timing onset in the same offspring revealed no effects of PFOA compared to controls in either strain. Therefore, our data suggest that the mammary gland is more sensitive to the effects of early low level PFOA exposures compared to other pubertal endpoints, regardless of strain. PMID:25499722

Largely Tunable Band Structures of Few-Layer InSe by Uniaxial Strain.

PubMed

Song, Chaoyu; Fan, Fengren; Xuan, Ningning; Huang, Shenyang; Zhang, Guowei; Wang, Chong; Sun, Zhengzong; Wu, Hua; Yan, Hugen

2018-01-31

Because of the strong quantum confinement effect, few-layer γ-InSe exhibits a layer-dependent band gap, spanning the visible and near infrared regions, and thus recently has been drawing tremendous attention. As a two-dimensional material, the mechanical flexibility provides an additional tuning knob for the electronic structures. Here, for the first time, we engineer the band structures of few-layer and bulk-like InSe by uniaxial tensile strain and observe a salient shift of photoluminescence peaks. The shift rate of the optical gap is approximately 90-100 meV per 1% strain for four- to eight-layer samples, which is much larger than that for the widely studied MoS 2 monolayer. Density functional theory calculations well reproduce the observed layer-dependent band gaps and the strain effect and reveal that the shift rate decreases with the increasing layer number for few-layer InSe. Our study demonstrates that InSe is a very versatile two-dimensional electronic and optoelectronic material, which is suitable for tunable light emitters, photodetectors, and other optoelectronic devices.

Allele-dependent differences in quorum-sensing dynamics result in variant expression of virulence genes in Staphylococcus aureus.

PubMed

Geisinger, Edward; Chen, John; Novick, Richard P

2012-06-01

Agr is an autoinducing, quorum-sensing system that functions in many Gram-positive species and is best characterized in the pathogen Staphylococcus aureus, in which it is a global regulator of virulence gene expression. Allelic variations in the agr genes have resulted in the emergence of four quorum-sensing specificity groups in S. aureus, which correlate with different strain pathotypes. The basis for these predilections is unclear but is hypothesized to involve the phenomenon of quorum-sensing interference between strains of different agr groups, which may drive S. aureus strain isolation and divergence. Whether properties intrinsic to each agr allele directly influence virulence phenotypes within S. aureus is unknown. In this study, we examined group-specific differences in agr autoinduction and virulence gene regulation by utilizing congenic strains, each harboring a unique S. aureus agr allele, enabling a dissection of agr locus-dependent versus genotype-dependent effects on quorum-sensing dynamics and virulence factor production. Employing a reporter fusion to the principal agr promoter, P3, we observed allele-dependent differences in the timing and magnitude of agr activation. These differences were mediated by polymorphisms within the agrBDCA genes and translated to significant variations in the expression of a key transcriptional regulator, Rot, and of several important exoproteins and surface factors involved in pathogenesis. This work uncovers the contribution of divergent quorum-sensing alleles to variant expression of virulence determinants within a bacterial species.

Nonlinear viscoelastic response of highly filled elastomers under multiaxial finite deformation

NASA Technical Reports Server (NTRS)

Peng, Steven T. J.; Landel, Robert F.

1990-01-01

A biaxial tester was used to obtain precise biaxial stress responses of highly filled, high strain capability elastomers. Stress-relaxation experiments show that the time-dependent part of the relaxation response can be reasonably approximated by a function which is strain and biaxiality independent. Thus, isochronal data from the stress-relaxation curves can be used to determine the stored energy density function. The complex behavior of the elastomers under biaxial deformation may be caused by dewetting.

Creep Deformation of Allvac 718Plus

DOE PAGES

Hayes, Robert W.; Unocic, Raymond R.; Nasrollahzadeh, Maryam

2014-11-11

The creep deformation behavior of Allvac 718Plus was studied over the temperature range 650° to 732°C at initial applied stress levels ranging from 517 to 655 MPa. Over the entire experimental temperature stress regime this alloy exhibits Class M type creep behavior with all creep curves exhibiting a decelerating strain rate with strain or time throughout primary creep. However, unlike pure metals or simple solid solution alloys this gamma prime strengthened superalloy does not exhibit steady state creep. Rather, primary creep is instantly followed by a long duration of accelerating strain rate with strain or time. These creep characteristics aremore » common amongst the gamma prime strengthened superalloys. Allvac 718Plus also exhibits a very high temperature dependence of creep rate. Detailed TEM examination of the deformation structures of selected creep samples reveals dislocation mechanisms similar to those found in high volume fraction gamma prime strengthened superalloys. Strong evidence of microtwinning is found in several of the deformation structures. The presence of microtwinning may account for the strong temperature dependence of creep rate observed in this alloy. In addition, due to the presence of Nb and thus, grain boundary delta phase, matrix dislocation activity which is not present in non Nb bearing superalloys occurs in this alloy. The creep characteristics and dislocation mechanisms are presented and discussed in detail.« less

Pharmacokinetic-Pharmacodynamic Model To Evaluate Intramuscular Tetracycline Treatment Protocols To Prevent Antimicrobial Resistance in Pigs

PubMed Central

Ahmad, Amais; Græsbøll, Kaare; Christiansen, Lasse Engbo; Toft, Nils; Matthews, Louise

2014-01-01

High instances of antimicrobial resistance are linked to both routine and excessive antimicrobial use, but excessive or inappropriate use represents an unnecessary risk. The competitive growth advantages of resistant bacteria may be amplified by the strain dynamics; in particular, the extent to which resistant strains outcompete susceptible strains under antimicrobial pressure may depend not only on the antimicrobial treatment strategies but also on the epidemiological parameters, such as the composition of the bacterial strains in a pig. This study evaluated how variation in the dosing protocol for intramuscular administration of tetracycline and the composition of bacterial strains in a pig affect the level of resistance in the intestine of a pig. Predictions were generated by a mathematical model of competitive growth of Escherichia coli strains in pigs under specified plasma concentration profiles of tetracycline. All dosing regimens result in a clear growth advantage for resistant strains. Short treatment duration was found to be preferable, since it allowed less time for resistant strains to outcompete the susceptible ones. Dosing frequency appeared to be ineffective at reducing the resistance levels. The number of competing strains had no apparent effect on the resistance level during treatment, but possession of fewer strains reduced the time to reach equilibrium after the end of treatment. To sum up, epidemiological parameters may have more profound influence on growth dynamics than dosing regimens and should be considered when designing improved treatment protocols. PMID:25547361

A Dislocation Model of Seismic Wave Attenuation and Micro-creep in the Earth: Harold Jeffreys and the Rheology of the Solid Earth

NASA Astrophysics Data System (ADS)

Karato, S.

A microphysical model of seismic wave attenuation is developed to provide a physical basis to interpret temperature and frequency dependence of seismic wave attenuation. The model is based on the dynamics of dislocation motion in minerals with a high Peierls stress. It is proposed that most of seismic wave attenuation occurs through the migration of geometrical kinks (micro-glide) and/or nucleation/migration of an isolated pair of kinks (Bordoni peak), whereas the long-term plastic deformation involves the continuing nucleation and migration of kinks (macro-glide). Kink migration is much easier than kink nucleation, and this provides a natural explanation for the vast difference in dislocation mobility between seismic and geological time scales. The frequency and temperature dependences of attenuation depend on the geometry and dynamics of dislocation motion both of which affect the distribution of relaxation times. The distribution of relaxation times is largely controlled by the distribution in distance between pinning points of dislocations, L, and the observed frequency dependence of Q, Q, Q ωα is shown to require a distribution function of P(L) L-m with m=4-2α The activation energy of Q-1 in minerals with a high Peierls stress corresponds to that for kink nucleation and is similar to that of long-term creep. The observed large lateral variation in Q-1 strongly suggests that the Q-1 in the mantle is frequency dependent. Micro-deformation with high dislocation mobility will (temporarily) cease when all the geometrical kinks are exhausted. For a typical dislocation density of 108 m-2, transient creep with small viscosity related to seismic wave attenuation will persist up to the strain of 10-6, thus even a small strain ( 10-6-10-4) process such as post-glacial rebound is only marginally affected by this type of anelastic relaxation. At longer time scales continuing nucleation of kinks becomes important and enables indefinitely large strain, steady-state creep, causing viscous behavior.

Characterization of the species Malassezia pachydermatis and re-evaluation of its lipid dependence using a synthetic agar medium

PubMed Central

Puig, Laura; Castellá, Gemma

2017-01-01

The genus Malassezia includes lipophilic yeasts, which are part of the skin microbiota of various mammals and birds. Unlike the rest of Malassezia species, M. pachydermatis is described as non-lipid-dependent, as it is able to grow on Sabouraud glucose agar (SGA) without lipid supplementation. In this study we have examined the phenotypic variability within M. pachydermatis and confirmed its lipid-dependent nature using a synthetic agar medium. We used a selection of representative non-lipid-dependent strains from different animal species and three atypical lipid-dependent strains of this species, which were not able to grow after multiple passages on SGA. More than 400 lipid-dependent Malassezia isolates from animals were studied in order to detect the three lipid-dependent strains of M. pachydermatis. The identity of the atypical strains was confirmed by DNA sequencing. On the other hand, we have modified the Tween diffusion test, which is widely used in the characterization of these yeasts, by using a synthetic agar-based medium instead of SGA. This modification has proved to be useful for differentiation of M. pachydermatis strains, providing reproducible results and a straightforward interpretation. The finding of these peculiar lipid-dependent strains exemplifies the large variability within the species M. pachydermatis, which involves rare atypical strains with particular growth requirements. PMID:28586389

Characterization of the species Malassezia pachydermatis and re-evaluation of its lipid dependence using a synthetic agar medium.

PubMed

Puig, Laura; Bragulat, M Rosa; Castellá, Gemma; Cabañes, F Javier

2017-01-01

The genus Malassezia includes lipophilic yeasts, which are part of the skin microbiota of various mammals and birds. Unlike the rest of Malassezia species, M. pachydermatis is described as non-lipid-dependent, as it is able to grow on Sabouraud glucose agar (SGA) without lipid supplementation. In this study we have examined the phenotypic variability within M. pachydermatis and confirmed its lipid-dependent nature using a synthetic agar medium. We used a selection of representative non-lipid-dependent strains from different animal species and three atypical lipid-dependent strains of this species, which were not able to grow after multiple passages on SGA. More than 400 lipid-dependent Malassezia isolates from animals were studied in order to detect the three lipid-dependent strains of M. pachydermatis. The identity of the atypical strains was confirmed by DNA sequencing. On the other hand, we have modified the Tween diffusion test, which is widely used in the characterization of these yeasts, by using a synthetic agar-based medium instead of SGA. This modification has proved to be useful for differentiation of M. pachydermatis strains, providing reproducible results and a straightforward interpretation. The finding of these peculiar lipid-dependent strains exemplifies the large variability within the species M. pachydermatis, which involves rare atypical strains with particular growth requirements.

Two-year performance study of porous, thermoset, shape memory polyurethanes intended for vascular medical devices

NASA Astrophysics Data System (ADS)

Weems, Andrew C.; Boyle, Anthony J.; Maitland, Duncan J.

2017-03-01

The long-term shape-recovery behavior of shape memory polymers has often been shown to be dependent on the length of time the material has been stored in the secondary shape. Typically, recovery performance and shape fixity will decrease with increased time in the secondary shape. In medical materials, a shelf-life is crucial to establish as it sets the upper threshold for device performance in a clinical setting, and a reduction in shape recovery would limit the development of SMP medical devices. Here, we present a two-year study of strain recovery, strain fixity, and shape recovery kinetics for passively and actively actuated SMPs intended for vascular devices. While kinetic experiments using immersion DMA indicate slight material relaxation and a decrease in the time to recovery, these changes are not found for bulk recovery experiments. The results indicate that a two-year shelf-life for these SMPs is very reasonable, as there is no change in the recovery kinetics, strain recovery, or strain fixity associated with this aging time. Further, a thermal accelerated aging test is presented for more rapid testing of the shape memory behavior of these SMPs and is compared with the real time aging results, indicating that this test is a reasonable indicator of the two-year behavior.

In Vitro Pharmacodynamic Activities of ABT-492, a Novel Quinolone, Compared to Those of Levofloxacin against Streptococcus pneumoniae, Haemophilus influenzae, and Moraxella catarrhalis

PubMed Central

Gunderson, Shana M.; Hayes, Robert A.; Quinn, John P.; Danziger, Larry H.

2004-01-01

ABT-492 is a novel quinolone with potent activity against gram-positive, gram-negative, and atypical pathogens, making this compound an ideal candidate for the treatment of community-acquired pneumonia. We therefore compared the in vitro pharmacodynamic activity of ABT-492 to that of levofloxacin, an antibiotic commonly used for the treatment of pneumonia, through MIC determination and time-kill kinetic analysis. ABT-492 demonstrated potent activity against penicillin-sensitive, penicillin-resistant, and levofloxacin-resistant Streptococcus pneumoniae strains (MICs ranging from 0.0078 to 0.125 μg/ml); β-lactamase-positive and β-lactamase-negative Haemophilus influenzae strains (MICs ranging from 0.000313 to 0.00125 μg/ml); and β-lactamase-positive and β-lactamase-negative Moraxella catarrhalis strains (MICs ranging from 0.001 to 0.0025 μg/ml), with MICs being much lower than those of levofloxacin. Both ABT-492 and levofloxacin demonstrated concentration-dependent bactericidal activities in time-kill kinetics studies at four and eight times the MIC with 10 of 12 bacterial isolates exposed to ABT-492 and with 12 of 12 bacterial isolates exposed to levofloxacin. Sigmoidal maximal-effect models support concentration-dependent bactericidal activity. The model predicts that 50% of maximal activity can be achieved with concentrations ranging from one to two times the MIC for both ABT-492 and levofloxacin and that near-maximal activity (90% effective concentration) can be achieved at concentrations ranging from two to five times the MIC for ABT-492 and one to six times the MIC for levofloxacin. PMID:14693540

In vitro pharmacodynamic activities of ABT-492, a novel quinolone, compared to those of levofloxacin against Streptococcus pneumoniae, Haemophilus influenzae, and Moraxella catarrhalis.

PubMed

Gunderson, Shana M; Hayes, Robert A; Quinn, John P; Danziger, Larry H

2004-01-01

ABT-492 is a novel quinolone with potent activity against gram-positive, gram-negative, and atypical pathogens, making this compound an ideal candidate for the treatment of community-acquired pneumonia. We therefore compared the in vitro pharmacodynamic activity of ABT-492 to that of levofloxacin, an antibiotic commonly used for the treatment of pneumonia, through MIC determination and time-kill kinetic analysis. ABT-492 demonstrated potent activity against penicillin-sensitive, penicillin-resistant, and levofloxacin-resistant Streptococcus pneumoniae strains (MICs ranging from 0.0078 to 0.125 micro g/ml); beta-lactamase-positive and beta-lactamase-negative Haemophilus influenzae strains (MICs ranging from 0.000313 to 0.00125 micro g/ml); and beta-lactamase-positive and beta-lactamase-negative Moraxella catarrhalis strains (MICs ranging from 0.001 to 0.0025 micro g/ml), with MICs being much lower than those of levofloxacin. Both ABT-492 and levofloxacin demonstrated concentration-dependent bactericidal activities in time-kill kinetics studies at four and eight times the MIC with 10 of 12 bacterial isolates exposed to ABT-492 and with 12 of 12 bacterial isolates exposed to levofloxacin. Sigmoidal maximal-effect models support concentration-dependent bactericidal activity. The model predicts that 50% of maximal activity can be achieved with concentrations ranging from one to two times the MIC for both ABT-492 and levofloxacin and that near-maximal activity (90% effective concentration) can be achieved at concentrations ranging from two to five times the MIC for ABT-492 and one to six times the MIC for levofloxacin.

Stress-relaxation and fatigue behaviour of synthetic brow-suspension materials.

PubMed

Kwon, Kyung-Ah; Shipley, Rebecca J; Edirisinghe, Mohan; Rayment, Andrew W; Best, Serena M; Cameron, Ruth E; Salam, Tahrina; Rose, Geoffrey E; Ezra, Daniel G

2015-02-01

Ptosis describes a low position of the upper eyelid. When this condition is due to poor function of the levator palpebrae superioris muscle, responsible for raising the lid, "brow-suspension" ptosis correction is usually performed, which involves internally attaching the malpositioned eyelid to the forehead musculature using brow-suspension materials. In service, such materials are exposed to both rapid tensile loading and unloading sequences during blinking, and a more sustained tensile strain during extended periods of closure. In this study, various mechanical tests were conducted to characterise and compare some of commonly-used synthetic brow-suspension materials (Prolene(®), Supramid Extra(®) II, Silicone rods (Visitec(®) Seiff frontalis suspension set) and Mersilene(®) mesh) for their time-dependent response. At a given constant tensile strain or load, all of the brow-suspension materials exhibited stress-relaxation or creep, with Prolene(®) having a statistically different relaxation or creep ratio as compared with those of others. Uniaxial tensile cyclic tests through preconditioning and fatigue tests demonstrated drastically different time-dependent response amongst the various materials. Although the tests generated hysteresis force-strain loops for all materials, the mechanical properties such as the number of cycles required to reach the steady-state, the reduction in the peak force, and the cyclic energy dissipation varied considerably. To reach the steady-state, Prolene(®) and the silicone rod required the greatest and the least number of cycles, respectively. Furthermore, the fatigue tests at physiologically relevant conditions (15% strain controlled at 6.5 Hz) demonstrated that the reduction in the peak force during 100,000 cycles ranged from 15% to 58%, with Prolene(®) and the silicone rod exhibiting the greatest and the least value, respectively. Many factors need to be considered to select the most suitable brow-suspension material for ptosis correction. These novel data on the mechanical time-dependent performance could therefore help to guide clinicians in their decision-making process for optimal surgical outcome. Copyright © 2014 Elsevier Ltd. All rights reserved.

Rate laws for water-assisted compaction and stress-induced water-rock interaction in sandstones

NASA Astrophysics Data System (ADS)

Dewers, Thomas; Hajash, Andrew

1995-07-01

Mineral-water interactions under conditions of nonhydrostatic stress play a role in subjects as diverse as ductile creep in fault zones, phase relations in metamorphic rocks, mass redistribution and replacement reactions during diagenesis, and loss of porosity in deep sedimentary basins. As a step toward understanding the fundamental geochemical processes involved, using naturally rounded St. Peter sand, we have investigated the kinetics of pore volume loss and quartz-water reactions under nonhydrostatic, hydrothermal conditions in flow-through reactors. Rate laws for creep and mineral-water reaction are derived from the time rate of change of pore volume, sand-water dissolution kinetics, and (flow rate independent) steady state silica concentrations, and reveal functional dependencies of rates on grain size, volume strain, temperature, effective pressure (confining minus pore pressure), and specific surface areas. Together the mechanical and chemical rate laws form a self-consistent model for coupled deformation and water-rock interaction of porous sands under nonhydrostatic conditions. Microstructural evidence shows a progressive widening of nominally circular and nominally flat grain-grain contacts with increasing strain or, equivalently, porosity loss, and small quartz overgrowths occurring at grain contact peripheries. The mechanical and chemical data suggest that the dominant creep mechanism is due to removal of mass from grain contacts (termed pressure solution or solution transfer), with a lesser component of time-dependent crack growth and healing. The magnitude of a stress-dependent concentration increase is too large to be accounted for by elastic or dislocation strain energy-induced supersaturations, favoring instead the normal stress dependence of molar Gibbs free energy associated with grain-grain interfaces.

A constitutive material model for nonlinear finite element structural analysis using an iterative matrix approach

NASA Technical Reports Server (NTRS)

Koenig, Herbert A.; Chan, Kwai S.; Cassenti, Brice N.; Weber, Richard

1988-01-01

A unified numerical method for the integration of stiff time dependent constitutive equations is presented. The solution process is directly applied to a constitutive model proposed by Bodner. The theory confronts time dependent inelastic behavior coupled with both isotropic hardening and directional hardening behaviors. Predicted stress-strain responses from this model are compared to experimental data from cyclic tests on uniaxial specimens. An algorithm is developed for the efficient integration of the Bodner flow equation. A comparison is made with the Euler integration method. An analysis of computational time is presented for the three algorithms.

In Vitro Studies of Pharmacodynamic Properties of Vancomycin against Staphylococcus aureus and Staphylococcus epidermidis

PubMed Central

Löwdin, E.; Odenholt, I.; Cars, O.

1998-01-01

The bactericidal activities of vancomycin against two reference strains and two clinical isolates of Staphylococcus aureus and Staphylococcus epidermidis were studied with five different concentrations ranging from 2× to 64× the MIC. The decrease in the numbers of CFU at 24 h was at least 3 log10 CFU/ml for all strains. No concentration-dependent killing was observed. The postantibiotic effect (PAE) was determined by obtaining viable counts for two of the reference strains, and the viable counts varied markedly: 1.2 h for S. aureus and 6.0 h for S. epidermidis. The determinations of the PAE, the postantibiotic sub-MIC effect (PA SME), and the sub-MIC effect (SME) for all strains were done with BioScreen C, a computerized incubator for bacteria. The PA SMEs were longer than the SMEs for all strains tested. A newly developed in vitro kinetic model was used to expose the bacteria to continuously decreasing concentrations of vancomycin. A filter prevented the loss of bacteria during the experiments. One reference strain each of S. aureus and S. epidermidis and two clinical isolates of S. aureus were exposed to an initial concentration of 10× the MIC of vancomycin with two different half-lives (t1/2s): 1 or 5 h. The post-MIC effect (PME) was calculated as the difference in time for the bacteria to grow 1 log10 CFU/ml from the numbers of CFU obtained at the time when the MIC was reached and the corresponding time for an unexposed control culture. The difference in PME between the strains was not as pronounced as that for the PAE. Furthermore, the PME was shorter when a t1/2 of 5 h (approximate terminal t1/2 in humans) was used. The PMEs at t1/2s of 1 and 5 h were 6.5 and 3.6 h, respectively, for S. aureus. The corresponding figures for S. epidermidis were 10.3 and less than 6 h. The shorter PMEs achieved with a t1/2 of 5 h and the lack of concentration-dependent killing indicate that the time above the MIC is the parameter most important for the efficacy of vancomycin. PMID:9756787

The Pulse of the Crust: Slow fracture and rapid healing during the seismic cycle (Louis Néel Medal Lecture)

NASA Astrophysics Data System (ADS)

Meredith, Philip

2016-04-01

Earthquake ruptures and volcanic eruptions are the most dramatic manifestations of the dynamic failure of a critically stressed crust. However, these are actually very rare events in both space and time; and most of the crust spends most of its time in a highly stressed but subcritical state. Under upper crustal conditions most rocks accommodate applied stresses in a brittle manner through cracking, fracturing and faulting. Cracks can grow at all scales from the grain scale to the crustal scale, and under different stress regimes. Under tensile stresses, single, long cracks tend to grow at the expense of shorter ones; while under all-round compressive, multiple microcracks tend to coalesce to form macroscopic fractures or faults. Deformation in the crust also occurs over a wide range of strain rates, from the very slow rates associated with tectonic loading up to the very fast rates occurring during earthquake rupture. It is now well-established that reactions between chemically-active pore fluids and the rock matrix can lead to time-dependent, subcritical crack propagation and failure in rocks. In turn, this can allow them to deform and fail over extended periods of time at stresses well below their short-term strength, and even at constant stress; a process known as brittle creep. Such cracking at constant stress eventually leads to accelerated deformation and critical, dynamic failure. However, in the period between sequential dynamic failure events, fractures can become subject to chemically-enhanced time-dependent strength recovery processes such as healing or the growth of mineral veins. We show that such strengthening can be much faster than previously suggested and can occur over geologically very short time-spans. These observations of ultra-slow cracking and ultra-fast healing have profound implications for the evolution and dynamics of the Earth's crust. To obtain a complete understanding of crustal dynamics we require a detailed knowledge of all these time-dependent mechanisms. Such knowledge should be based on micromechanics, but also provide an adequate description at the macroscopic or crustal scale. One way of moving towards this is to establish a relationship between the internal, microstructural state of the rock and the macroscopically observable external quantities. Here, we present a number of examples of attempts to reconcile these ideas through external measurements of stress and strain evolution during deformation with simultaneous measurements of the evolution of key internal variables such as elastic wave speeds, acoustic emission output, porosity and permeability. Overall, the combined data are able to explain both the complexity of stress-strain relations during constant strain rate loading and the shape of creep curves during constant stress loading, thus providing a unifying framework to describe the time-dependent mechanical behaviour of crustal rocks.

The Evolution of the Seismic-Aseismic Transition During the Earthquake Cycle: Constraints from the Time-Dependent Depth Distribution of Aftershocks

NASA Astrophysics Data System (ADS)

Rolandone, F.; Bürgmann, R.; Nadeau, R.; Freed, A.

2003-12-01

We have demonstrated that in the aftermath of large earthquakes, the depth extent of aftershocks shows an immediate deepening from pre-earthquake levels, followed by a time-dependent postseismic shallowing. We use these seismic data to constrain the variation of the depth of the seismic-aseismic transition with time throughout the earthquake cycle. Most studies of the seismic-aseismic transition have focussed on the effect of temperature and/or lithology on the transition either from brittle faulting to viscous flow or from unstable to stable sliding. They have shown that the maximum depth of seismic activity is well correlated with the spatial variations of these two parameters. However, little has been done to examine how the maximum depth of seismogenic faulting varies locally, at the scale of a fault segment, during the course of the earthquake cycle. Geologic and laboratory observations indicate that the depth of the seismic-aseismic transition should vary with strain rate and thus change with time throughout the earthquake cycle. We quantify the time-dependent variations in the depth of seismicity on various strike-slip faults in California before and after large earthquakes. We specifically investigate (1) the deepening of the aftershocks relative to the background seismicity, (2) the time constant of the postseismic shallowing of the deepest earthquakes, and (3) the correlation of the time-dependent pattern with the coseismic slip distribution and the expected stress increase. Together with geodetic measurements, these seismological observations form the basis for developing more sophisticated models for the mechanical evolution of strike-slip shear zones during the earthquake cycle. We develop non-linear viscoelastic models, for which the brittle-ductile transition is not fixed, but varies with assumed temperature and calculated stress gradients. We use them to place constraints on strain rate at depth, on time-dependent rheology, and on the partitioning of deformation between brittle faulting and distributed viscous flow associated with the earthquake cycle.

Experimental evidence for dynamic friction on rock fractures from frequency-dependent nonlinear hysteresis and harmonic generation

NASA Astrophysics Data System (ADS)

Saltiel, Seth; Bonner, Brian P.; Mittal, Tushar; Delbridge, Brent; Ajo-Franklin, Jonathan B.

2017-07-01

Frictional properties affect the propagation of high-amplitude seismic waves across rock fractures and faults. Laboratory evidence suggests that these properties can be measured in active seismic surveys, potentially offering a route to characterizing friction in situ. We present experimental results from a subresonance torsional modulus and attenuation apparatus that utilizes micron-scale sinusoidal oscillations to probe the nonlinear stress-strain relation at a range of strain amplitudes and rates. Nonlinear effects are further quantified using harmonic distortion; however, time series data best illuminate underlying physical processes. The low-frequency stress-strain hysteretic loops show stiffening at the sinusoid's static ends, but stiffening is reduced above a threshold frequency. This shape is determined by harmonic generation in the strain; the stress signal has no harmonics, confirming that the fractured sample is the source of the nonlinearity. These qualitative observations suggest the presence of rate-dependent friction and are consistent between fractures in three different rock types. We propose that static friction at the low strain rate part of the cycle, when given sufficient "healing" time at low oscillation frequencies, causes this stiffening cusp shape in the hysteresis loop. While rate-and-state friction is commonly used to represent dynamic friction, it cannot capture static friction or negative slip velocities. So we implement another dynamic friction model, based on the work of Dahl, which describes this process and produces similar results. Since the two models have a similar form, parameterizations of field data could constraint fault model inputs, such as specific location velocity strengthening or weakening properties.

Molecular relationships between closely related strains and species of nematodes

NASA Technical Reports Server (NTRS)

Butler, M. H.; Wall, S. M.; Luehrsen, K. R.; Fox, G. E.; Hecht, R. M.

1981-01-01

Electrophoretic comparisons have been made for 24 enzymes in the Bergerac and Bristol strains of Caenorhabditis elegans and the related species, Caenorhabditis briggsae. No variation was detected between the two strains of C. elegans. In contrast, the two species, C. elegans and C. briggsae exhibited electrophoretic differences in 22 of 24 enzymes. A consensus 5S rRNA sequence was determined for C. elegans and found to be identical to that from C. briggsae. By analogy with other species with relatively well established fossil records it can be inferred that the time of divergence between the two nematode species is probably in the tens of millions of years. The limited anatomical evolution during a time period in which proteins undergo extensive changes supports the hypothesis that anatomical evolution is not dependent on overall protein changes.

Caregiver profiles in dementia related to quality of life, depression and perseverance time in the European Actifcare study: the importance of social health.

PubMed

Janssen, Eveline P C J; de Vugt, Marjolein; Köhler, Sebastian; Wolfs, Claire; Kerpershoek, Liselot; Handels, Ron L H; Orrell, Martin; Woods, Bob; Jelley, Hannah; Stephan, Astrid; Bieber, Anja; Meyer, Gabriele; Engedal, Knut; Selbaek, Geir; Wimo, Anders; Irving, Kate; Hopper, Louise; Gonçalves-Pereira, Manuel; Portolani, Elisa; Zanetti, Orazio; Verhey, Frans R

2017-01-01

To identify caregiver profiles of persons with mild to moderate dementia and to investigate differences between identified caregiver profiles, using baseline data of the international prospective cohort study Actifcare. A latent class analysis was used to discover different caregiver profiles based on disease related characteristics of 453 persons with dementia and their 453 informal caregivers. These profiles were compared with regard to quality of life (CarerQoL score), depressive symptoms (HADS-D score) and perseverance time. A 5-class model was identified, with the best Bayesian Information Criterion value, significant likelihood ratio test (p < 0.001), high entropy score (0.88) and substantive interpretability. The classes could be differentiated on two axes: (i) caregivers' age, relationship with persons with dementia, severity of dementia, and (ii) tendency towards stress and difficulty adapting to stress. Classes showed significant differences with all dependent variables, and were labelled 'older low strain', 'older intermediate strain', 'older high strain', 'younger low strain' and 'younger high strain'. Differences exist between types of caregivers that explain variability in quality of life, depressive symptoms and perseverance time. Our findings may give direction for tailored interventions for caregivers of persons with dementia, which may improve social health and reduce health care costs.

Sample collection of virulent and non-virulent B. anthracis and Y. pestis for bioforensics analysis

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

Hong-geller, Elizabeth; Valdez, Yolanda E; Shou, Yulin

2009-01-01

Validated sample collection methods are needed for recovery of microbial evidence in the event of accidental or intentional release of biological agents into the environment. To address this need, we evaluated the sample recovery efficiencies of two collection methods -- swabs and wipes -- for both non-virulent and virulent strains of B. anthracis and Y. pestis from four types of non-porous surfaces: two hydrophilic surfaces, stainless steel and glass, and two hydrophobic surfaces, vinyl and plastic. Sample recovery was quantified using Real-time qPCR to assay for intact DNA signatures. We found no consistent difference in collection efficiency between swabs ormore » wipes. Furthermore, collection efficiency was more surface-dependent for virulent strains than non-virulent strains. For the two non-virulent strains, B. anthracis Sterne and Y. pestis A1122, collection efficiency was approximately 100% and 1 %, respectively, from all four surfaces. In contrast, recovery of B. anthracis Ames spores and Y. pestis C092 from vinyl and plastic was generally lower compared to collection from glass or stainless steel, suggesting that surface hydrophobicity may playa role in the strength of pathogen adhesion. The surface-dependent collection efficiencies observed with the virulent strains may arise from strain-specific expression of capsular material or other cell surface receptors that alter cell adhesion to specific surfaces. These findings contribute to validation of standard bioforensics procedures and emphasize the importance of specific strain and surface interactions in pathogen detection.« less

3D inelastic analysis methods for hot section components

NASA Technical Reports Server (NTRS)

Dame, L. T.; Chen, P. C.; Hartle, M. S.; Huang, H. T.

1985-01-01

The objective is to develop analytical tools capable of economically evaluating the cyclic time dependent plasticity which occurs in hot section engine components in areas of strain concentration resulting from the combination of both mechanical and thermal stresses. Three models were developed. A simple model performs time dependent inelastic analysis using the power law creep equation. The second model is the classical model of Professors Walter Haisler and David Allen of Texas A and M University. The third model is the unified model of Bodner, Partom, et al. All models were customized for linear variation of loads and temperatures with all material properties and constitutive models being temperature dependent.

Scenarios for Russian Agricultural Development to 2021

DTIC Science & Technology

2011-12-01

dependence on government intervention in both good times and bad, and an unwieldy, inefficient bureaucracy strained to effectively carry out the myriad...information is estimated to average 1 hour per response, including the time for reviewing instruction, searching existing data sources, gathering and...issue analysis. Emerging issue analysis begins with the premise that problems develop gradually over time , and are often ignored until they reach

Rapid and accurate bacterial identification in probiotics and yoghurts by MALDI-TOF mass spectrometry.

PubMed

Angelakis, Emmanouil; Million, Matthieu; Henry, Mireille; Raoult, Didier

2011-10-01

Probiotic food is manufactured by adding probiotic strains simultaneously with starter cultures in fermentation tanks. Here, we investigate the accuracy and feasibility of matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry (MALDI-TOF MS) for bacterial identification at the species level in probiotic food and yoghurts. Probiotic food and yoghurts were cultured in Columbia and Lactobacillus specific agar and tested by quantitative real-time PCR (qPCR) for the detection and quantification of Lactobacillus sp. Bacterial identification was performed by MALDI-TOF analysis and by amplification and sequencing of tuf and 16S rDNA genes. We tested 13 probiotic food and yoghurts and we identified by qPCR that they presented 10(6) to 10(7) copies of Lactobacillus spp. DNA/g. All products contained very large numbers of living bacteria varying from 10(6) to 10(9) colony forming units/g. These bacteria were identified as Lactobacillus casei, Lactococcus lactis, Bifidobacterium animalis, Lactobacillus delbrueckii, and Streptococcus thermophilus. MALDI-TOF MS presented 92% specificity compared to the molecular assays. In one product we found L. lactis, instead of Bifidus spp. which was mentioned on the label and for another L. delbrueckii and S. thermophilus instead of Bifidus spp. MALDI-TOF MS allows a rapid and accurate bacterial identification at the species level in probiotic food and yoghurts. Although the safety and functionality of probiotics are species and strain dependent, we found a discrepancy between the bacterial strain announced on the label and the strain identified. Practical Application:  MALDI-TOF MS is rapid and specific for the identification of bacteria in probiotic food and yoghurts. Although the safety and functionality of probiotics are species and strain dependent, we found a discrepancy between the bacterial strain announced on the label and the strain identified. © 2011 Institute of Food Technologists®

Estimating Tunnel Strain in the Weak and Schistose Rock Mass Influenced by Stress Anisotropy: An Evaluation Based on Three Tunnel Cases from Nepal

NASA Astrophysics Data System (ADS)

Panthi, Krishna Kanta; Shrestha, Pawan Kumar

2018-06-01

Total plastic deformation in tunnels passing through weak and schistose rock mass consists of both time-independent and time-dependent deformations. The extent of this total deformation is heavily influenced by the rock mass deformability properties and in situ stress condition prevailing in the area. If in situ stress is not isotropic, the deformation magnitude is not only different along the longitudinal alignment but also along the periphery of the tunnel wall. This manuscript first evaluates the long-term plastic deformation records of three tunnel projects from the Nepal Himalaya and identifies interlink between the time-independent and time-dependent deformations using the convergence law proposed by Sulem et al. (Int J Rock Mech Min Sci Geomech 24(3):145-154, 1987a, Int J Rock Mech Min Sci Geomech 24(3):155-164, 1987b). Secondly, the manuscript attempts to establish a correlation between plastic deformations (tunnel strain) and rock mass deformable properties, support pressure and in situ stress conditions. Finally, patterns of time-independent and time-dependent plastic deformations are also evaluated and discussed. The long-term plastic deformation records of 24 tunnel sections representing four different rock types of three different headrace tunnel cases from Nepal Himalaya are extensively used in this endeavor. The authors believe that the proposed findings will be a step further in analysis of plastic deformations in tunnels passing through weak and schistose rock mass and along the anisotropic stress conditions.

Strain Recovery by TiNi Element Under Fast Heating

NASA Astrophysics Data System (ADS)

Volkov, Aleksandr E.; Miszuris, Wiktoria; Volkova, Natalia A.

2018-03-01

A theoretical and experimental study of strain recovery under fast heating of a shape memory alloy (SMA) rod preliminarily stretched in the martensitic state is carried out. Two theoretical models are considered: instantaneous heating and heating with temperature variation during a finite time. In the first case, it is supposed that the straight SMA rod experiences an instantaneous reverse martensitic transformation, and in the second the transformation is supposed to progress at a rate corresponding to the temperature rate. Analytical expression for the time dependence of the rod free-end displacement is obtained. In the experiment, a wire specimen made of titanium-nickel SMA was heated by a short impulse of electric current. The variation of the specimen length in time was registered. Thus, it has been shown that the minimum operation time of an SMA actuator (time needed for the strain recovery) can be reduced to 20 µs. Comparison of the theoretical results with the experimental ones leads to the conclusion that the displacement variation in time is controlled by the rate of heating and the inertia of the specimen. The incubation time of the martensitic transformation on the microscale apparently is estimated as less than 1 µs.

Strain Recovery by TiNi Element Under Fast Heating

NASA Astrophysics Data System (ADS)

Volkov, Aleksandr E.; Miszuris, Wiktoria; Volkova, Natalia A.

2018-01-01

A theoretical and experimental study of strain recovery under fast heating of a shape memory alloy (SMA) rod preliminarily stretched in the martensitic state is carried out. Two theoretical models are considered: instantaneous heating and heating with temperature variation during a finite time. In the first case, it is supposed that the straight SMA rod experiences an instantaneous reverse martensitic transformation, and in the second the transformation is supposed to progress at a rate corresponding to the temperature rate. Analytical expression for the time dependence of the rod free-end displacement is obtained. In the experiment, a wire specimen made of titanium-nickel SMA was heated by a short impulse of electric current. The variation of the specimen length in time was registered. Thus, it has been shown that the minimum operation time of an SMA actuator (time needed for the strain recovery) can be reduced to 20 µs. Comparison of the theoretical results with the experimental ones leads to the conclusion that the displacement variation in time is controlled by the rate of heating and the inertia of the specimen. The incubation time of the martensitic transformation on the microscale apparently is estimated as less than 1 µs.

Inpatient dependency in activities of daily living predicts informal caregiver strain: A cross-sectional study.

PubMed

Pérez Mármol, José Manuel; Flores Antigüedad, María Luz; Castro Sánchez, Adelaida María; Tapia Haro, Rosa María; García Ríos, María Del Carmen; Aguilar Ferrándiz, María Encarnación

2018-01-01

To investigate what factors influence caregiver strain in informal caregivers just before inpatients are discharged. Previous research has investigated the risk factors related to the burden on caregivers in different clinical contexts. However, the findings from studies analysing these factors just before inpatients are discharged are uncertain. A cross-sectional study design. The study involved 100 inpatients and 100 informal caregivers from seven different hospital units. Sociodemographic, clinical, functional and cognitive factors of inpatients-caregivers, and caregiver strains were recorded. Descriptive, bivariate correlation and multiple regression analyses were performed. Caregivers of inpatients at risk of ulcers had significantly higher scores of strain. Dependency in activities of daily living scores and cognitive status scores were statistically inversely proportional to caregiver strain. Almost 27% of total variance of caregiver strain was due to dependency in activities of daily living. Caregiver strain was mainly associated with those situations in which the hospitalised patients presented the risk of ulcers, dependency and cognitive disorders, with dependency in activities of daily living being the factor that most influenced informal caregiver strain. Dependency in activities of daily living, among other risk factors, should be evaluated at an early stage, monitored and controlled by hospital nursing staff. These strategies could protect and promote the well-being and quality of life of informal caregivers during patient hospitalisation and after discharge. © 2017 John Wiley & Sons Ltd.

Characterization of material parameters for high speed forming and cutting via experiment and inverse simulation

NASA Astrophysics Data System (ADS)

Scheffler, Christian; Psyk, Verena; Linnemann, Maik; Tulke, Marc; Brosius, Alexander; Landgrebe, Dirk

2018-05-01

High speed velocity effects in production technology provide a broad range of technological and economic advantages [1, 2]. However, exploiting them necessitates the knowledge of strain rate dependent material behavior in process modelling. In general, high speed material data characterization features several difficulties and requires sophisticated approaches in order to provide reliable material data. This paper proposes two innovative concepts with electromagnetic and pneumatic drive and an approach for material characterization in terms of strain rate dependent flow curves and parameters of failure or damage models. The test setups have been designed for investigations of strain rates up to 105 s-1. In principle, knowledge about the temporary courses and local distributions of stress and strain in the specimen is essential for identifying material characteristics, but short process times, fast changes of the measurement values, small specimen size and frequently limited accessibility of the specimen during the test hinder directly measuring these parameters at high-velocity testing. Therefore, auxiliary test parameters, which are easier to measure, are recorded and used as input data for an inverse numerical simulation that provides the desired material characteristics, e.g. the Johnson-Cook parameters, as a result. These parameters are a force equivalent strain signal on a measurement body and the displacement of the upper specimen edge.

Differential Requirements in Endocytic Trafficking for Penetration of Dengue Virus

PubMed Central

Acosta, Eliana G.; Castilla, Viviana; Damonte, Elsa B.

2012-01-01

The entry of DENV into the host cell appears to be a very complex process which has been started to be studied in detail. In this report, the route of functional intracellular trafficking after endocytic uptake of dengue virus serotype 1 (DENV-1) strain HW, DENV-2 strain NGC and DENV-2 strain 16681 into Vero cells was studied by using a susceptibility to ammonium chloride assay, dominant negative mutants of several members of the family of cellular Rab GTPases that participate in regulation of transport through endosome vesicles and immunofluorescence colocalization. Together, the results presented demonstrate that in spite of the different internalization route among viral serotypes in Vero cells and regardless of the viral strain, DENV particles are first transported to early endosomes in a Rab5-dependent manner. Then a Rab7-dependent pathway guides DENV-2 16681 to late endosomes, whereas a yet unknown sorting event controls the transport of DENV-2 NGC, and most probably DENV-1 HW, to the perinuclear recycling compartments where fusion membrane would take place releasing nucleocapsid into the cytoplasm. Besides the demonstration of a different intracellular trafficking for two DENV-2 strains that shared the initial clathrin-independent internalization route, these studies proved for the first time the involvement of the slow recycling pathway for DENV-2 productive infection. PMID:22970315

Strain and rate-dependent neuronal injury in a 3D in vitro compression model of traumatic brain injury

PubMed Central

Bar-Kochba, Eyal; Scimone, Mark T.; Estrada, Jonathan B.; Franck, Christian

2016-01-01

In the United States over 1.7 million cases of traumatic brain injury are reported yearly, but predictive correlation of cellular injury to impact tissue strain is still lacking, particularly for neuronal injury resulting from compression. Given the prevalence of compressive deformations in most blunt head trauma, this information is critically important for the development of future mitigation and diagnosis strategies. Using a 3D in vitro neuronal compression model, we investigated the role of impact strain and strain rate on neuronal lifetime, viability, and pathomorphology. We find that strain magnitude and rate have profound, yet distinctively different effects on the injury pathology. While strain magnitude affects the time of neuronal death, strain rate influences the pathomorphology and extent of population injury. Cellular injury is not initiated through localized deformation of the cytoskeleton but rather driven by excess strain on the entire cell. Furthermore we find that, mechanoporation, one of the key pathological trigger mechanisms in stretch and shear neuronal injuries, was not observed under compression. PMID:27480807

Minimum inhibitory (MIC) and minimum microbicidal concentration (MMC) of polihexanide and triclosan against antibiotic sensitive and resistant Staphylococcus aureus and Escherichia coli strains

PubMed Central

Assadian, Ojan; Wehse, Katrin; Hübner, Nils-Olaf; Koburger, Torsten; Bagel, Simone; Jethon, Frank; Kramer, Axel

2011-01-01

Background: An in-vitro study was conducted investigating the antimicrobial efficacy of polihexanide and triclosan against clinical isolates and reference laboratory strains of Staphylococcus aureus and Escherichia coli. Methods: The minimal inhibitory concentration (MIC) and the minimal microbicidal concentration (MMC) were determined following DIN 58940-81 using a micro-dilution assay and a quantitative suspension test following EN 1040. Polihexanide was tested in polyethylene glycol 4000, triclosan in aqueous solutions. Results: Against all tested strains the MIC of polihexanide ranged between 1–2 µg/mL. For triclosan the MICs varied depending on strains ranging between 0.5 µg/mL for the reference strains and 64 µg/mL for two clinical isolates. A logRF >5 without and logRF >3 with 0.2% albumin burden was achieved at 0.6 µg/mL triclosan. One exception was S. aureus strain H-5-24, where a triclosan concentration of 0.6 µg/mL required 1 minute without and 10 minutes with albumin burden to achieve the same logRFs. Polihexanide achieved a logRF >5 without and logRF >3 with albumin burden at a concentration of 0.6 µg/mL within 30 sec. The exception was the North-German epidemic MRSA strain, were an application time of 5 minutes was required. Conclusion: The clinical isolates of E. coli generally showed higher MICs against triclosan, both in the micro-dilution assay as well in the quantitative suspension test than comparable reference laboratory strains. For polihexanide and triclosan strain dependant susceptibility was shown. However, both antimicrobial compounds are effective when used in concentrations common in practice. PMID:22242087

Potential pitfalls of strain rate imaging: angle dependency

NASA Technical Reports Server (NTRS)

Castro, P. L.; Greenberg, N. L.; Drinko, J.; Garcia, M. J.; Thomas, J. D.

2000-01-01

Strain Rate Imaging (SRI) is a new echocardiographic technique that allows for the real-time determination of myocardial SR, which may be used for the early and accurate detection of coronary artery disease. We sought to study whether SR is affected by scan line alignment in a computer simulation and an in vivo experiment. Through the computer simulation and the in vivo experiment we generated and validated safe scanning sectors within the ultrasound scan sector and showed that while SRI will be an extremely valuable tool in detecting coronary artery disease there are potential pitfalls for the unwary clinician. Only after accounting for these affects due to angle dependency, can clinicians utilize SRI's potential as a valuable tool in detecting coronary artery disease.

Assertiveness of Lactobacillus sakei and Lactobacillus curvatus in a fermented sausage model.

PubMed

Janßen, Dorothee; Eisenbach, Lara; Ehrmann, Matthias A; Vogel, Rudi F

2018-04-20

Fresh meat harbors autochthonous microbiota with unknown risk potential, which is introduced in raw fermented sausages. Their growth can be limited by the use of safe, competitive starter strains. In the lack of time and cost-effective methods to track those starters at strain level, their assertiveness upon meat fermentation is widely unknown. Lactobacillus (L.) sakei and L. curvatus, which can be isolated from a variety of habitats, are frequently used as starter cultures. We monitored the assertiveness of 9 L. sakei and 9 L. curvatus strains in a model fermentation using MALDI-TOF-MS. An "in-house" MALDI-TOF-MS database with sub-proteome spectra of L. sakei and L. curvatus strains, as well as members of the autochthonous, spontaneously growing meat microbiota was established, validated and recognition rates were determined for each L. curvatus and L. sakei strain used. Competition studies were performed with standardized sausage batter, which was inoculated with a total of 10 6 cells of sets of 4-5 strains each of L. sakei and L. curvatus and 10 6 Staphylococcus carnosus ssp. carnosus cells. The pH and redox potential were monitored continuously. On days 0, 2 and 5 samples were taken to determine the CfU/g and a total of 96 isolates per sample were identified via MALDI-TOF-MS. MALDI-TOF-MS generally proved suitable for identification of isolates on strain level within the starter sets employed, but the recognition rate varied depending on the strain. Competition studies revealed dominance or co-dominance of strains within each set. However, their assertiveness significantly depended on the composition of the strain sets. Still, co-dominance or cooperation appeared effective to outgrow other members of the autochthonous meat microbiota, rather than dominance of single strains. For the latter, the ability to produce bacteriocins suggested itself for a crucial role in the assertiveness of starter strains. Copyright © 2018 Elsevier B.V. All rights reserved.

Strain-rate dependence of ramp-wave evolution and strength in tantalum

DOE PAGES

Lane, J. Matthew D.; Foiles, Stephen M.; Lim, Hojun; ...

2016-08-25

We have conducted molecular dynamics (MD) simulations of quasi-isentropic ramp-wave compression to very high pressures over a range of strain rates from 10 11 down to 10 8 1/s. Using scaling methods, we collapse wave profiles from various strain rates to a master profile curve, which shows deviations when material response is strain-rate dependent. Thus, we can show with precision where, and how, strain-rate dependence affects the ramp wave. We find that strain rate affects the stress-strain material response most dramatically at strains below 20%, and that above 30% strain the material response is largely independent of strain rate. Wemore » show good overall agreement with experimental stress-strain curves up to approximately 30% strain, above which simulated response is somewhat too stiff. We postulate that this could be due to our interatomic potential or to differences in grain structure and/or size between simulation and experiment. Strength is directly measured from per-atom stress tensor and shows significantly enhanced elastic response at the highest strain rates. As a result, this enhanced elastic response is less pronounced at higher pressures and at lower strain rates.« less

Screen-Printing Fabrication and Characterization of Stretchable Electronics

PubMed Central

Suikkola, Jari; Björninen, Toni; Mosallaei, Mahmoud; Kankkunen, Timo; Iso-Ketola, Pekka; Ukkonen, Leena; Vanhala, Jukka; Mäntysalo, Matti

2016-01-01

This article focuses on the fabrication and characterization of stretchable interconnects for wearable electronics applications. Interconnects were screen-printed with a stretchable silver-polymer composite ink on 50-μm thick thermoplastic polyurethane. The initial sheet resistances of the manufactured interconnects were an average of 36.2 mΩ/◽, and half the manufactured samples withstood single strains of up to 74%. The strain proportionality of resistance is discussed, and a regression model is introduced. Cycling strain increased resistance. However, the resistances here were almost fully reversible, and this recovery was time-dependent. Normalized resistances to 10%, 15%, and 20% cyclic strains stabilized at 1.3, 1.4, and 1.7. We also tested the validity of our model for radio-frequency applications through characterization of a stretchable radio-frequency identification tag. PMID:27173424

Association between specific plasmids and relapse in typhoid fever.

PubMed Central

Gotuzzo, E; Morris, J G; Benavente, L; Wood, P K; Levine, O; Black, R E; Levine, M M

1987-01-01

We studied isolates from 73 patients hospitalized with typhoid fever in Lima, Peru. Of these 73 patients, 11 (15%) suffered a clinical relapse, with fever and positive blood cultures, within 3 months of their original illness. Using plasmids as epidemiologic markers, we found that three patients who subsequently relapsed were initially infected with more than one strain of Salmonella typhi. There was a highly significant association between relapse and isolation of a strain containing either a 24- or a 38-kilobase plasmid at the time of the original infection; however, we were unable to show any evidence of homology between these two plasmids. Our data indicate that infection with multiple strains is not uncommon in this endemic area and suggest that relapse may be partly strain dependent. Images PMID:2821064

Modeling of Distributed Sensing of Elastic Waves by Fiber-Optic Interferometry

PubMed Central

Agbodjan Prince, Just; Kohl, Franz; Sauter, Thilo

2016-01-01

This paper deals with the transduction of strain accompanying elastic waves in solids by firmly attached optical fibers. Stretching sections of optical fibers changes the time required by guided light to pass such sections. Exploiting interferometric techniques, highly sensitive fiber-optic strain transducers are feasible based on this fiber-intrinsic effect. The impact on the actual strain conversion of the fiber segment’s shape and size, as well as its inclination to the elastic wavefront is studied. FEM analyses show that severe distortions of the interferometric response occur when the attached fiber length spans a noticeable fraction of the elastic wavelength. Analytical models of strain transduction are presented for typical transducer shapes. They are used to compute input-output relationships for the transduction of narrow-band strain pulses as a function of the mechanical wavelength. The described approach applies to many transducers depending on the distributed interaction with the investigated object. PMID:27608021

Static mechanical strain induces capillary endothelial cell cycle re-entry and sprouting.

PubMed

Zeiger, A S; Liu, F D; Durham, J T; Jagielska, A; Mahmoodian, R; Van Vliet, K J; Herman, I M

2016-08-16

Vascular endothelial cells are known to respond to a range of biochemical and time-varying mechanical cues that can promote blood vessel sprouting termed angiogenesis. It is less understood how these cells respond to sustained (i.e., static) mechanical cues such as the deformation generated by other contractile vascular cells, cues which can change with age and disease state. Here we demonstrate that static tensile strain of 10%, consistent with that exerted by contractile microvascular pericytes, can directly and rapidly induce cell cycle re-entry in growth-arrested microvascular endothelial cell monolayers. S-phase entry in response to this strain correlates with absence of nuclear p27, a cyclin-dependent kinase inhibitor. Furthermore, this modest strain promotes sprouting of endothelial cells, suggesting a novel mechanical 'angiogenic switch'. These findings suggest that static tensile strain can directly stimulate pathological angiogenesis, implying that pericyte absence or death is not necessarily required of endothelial cell re-activation.

Modeling of Distributed Sensing of Elastic Waves by Fiber-Optic Interferometry.

PubMed

Agbodjan Prince, Just; Kohl, Franz; Sauter, Thilo

2016-09-06

This paper deals with the transduction of strain accompanying elastic waves in solids by firmly attached optical fibers. Stretching sections of optical fibers changes the time required by guided light to pass such sections. Exploiting interferometric techniques, highly sensitive fiber-optic strain transducers are feasible based on this fiber-intrinsic effect. The impact on the actual strain conversion of the fiber segment's shape and size, as well as its inclination to the elastic wavefront is studied. FEM analyses show that severe distortions of the interferometric response occur when the attached fiber length spans a noticeable fraction of the elastic wavelength. Analytical models of strain transduction are presented for typical transducer shapes. They are used to compute input-output relationships for the transduction of narrow-band strain pulses as a function of the mechanical wavelength. The described approach applies to many transducers depending on the distributed interaction with the investigated object.

Ratcheting in a nonlinear viscoelastic adhesive

NASA Astrophysics Data System (ADS)

Lemme, David; Smith, Lloyd

2017-11-01

Uniaxial time-dependent creep and cycled stress behavior of a standard and toughened film adhesive were studied experimentally. Both adhesives exhibited progressive accumulation of strain from an applied cycled stress. Creep tests were fit to a viscoelastic power law model at three different applied stresses which showed nonlinear response in both adhesives. A third order nonlinear power law model with a permanent strain component was used to describe the creep behavior of both adhesives and to predict creep recovery and the accumulation of strain due to cycled stress. Permanent strain was observed at high stress but only up to 3% of the maximum strain. Creep recovery was under predicted by the nonlinear model, while cycled stress showed less than 3% difference for the first cycle but then over predicted the response above 1000 cycles by 4-14% at high stress. The results demonstrate the complex response observed with structural adhesives, and the need for further analytical advancements to describe their behavior.

Effects of anisotropy and irradiation on the deformation behavior of Zircaloy 2. Final report

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

Pelloux, R.M.; Ballinger, R.; Lucas, G.

1979-01-01

An experimental program investigated the effects of texture anisotropy and irradiation on the mechanical behavior of Zircaloy-2. Short time and time dependent mechanical behavior were considered. Irradiation effects were simulated through the use of 4.75 MeV protons. The temperature ranges investigated were 298/sup 0/K and 573 to 673/sup 0/K. Both cold worked-stress relieved and annealed material were used in this experimental program. Short time yield behavior of different crystallographic textures was determined by uniaxial and plane strain tests in the temperature range 298/sup 0/K and 573 to 673/sup 0/K. Monotonic flow loci were constructed for each texture. Yield behavior ismore » a strong function of the crystallographic texture number f at all temperatures investigated. The rotation of texture with increasing plastic strain was investigated as a function of initial texture at 298/sup 0/K and 623/sup 0/K. The rate of texture rotation df/epsilon/sub p/ was found to be a unique function of the initial texture for plastic strains less than 0.08. Time dependent mechanical behavior was investigated in the range 573 to 673/sup 0/K using constant load creep and stress relaxation tests. The tensile creep strength is proportional to the resolved fraction of basal poles in the test direction. In variable stress and temperature tests, the time-hardening rule was found to be inapplicable. The strain-hardening rule was applied with success to data obtained at temperatures less than or equal to 648/sup 0/K. Irradiation creep tests were conducted in vacuum at 598/sup 0/K and 102 to 241 MPa on 80..mu..m thick Zircaloy-2 foil specimens in both the recrystallized and cold worked-stress relieved condition. In the irradiation creep tests irradiation hardening and enhanced irradiation creep were observed. Radiation hardening effects were significant in annealed material but were attenuated in cold worked-stress relieved material.« less

Reduction of the Mg acceptor activation energy in GaN, AlN, Al0.83Ga0.17N and MgGa δ-doping (AlN)5/(GaN)1: the strain effect

NASA Astrophysics Data System (ADS)

Jiang, Xin-He; Shi, Jun-Jie; Zhang, Min; Zhong, Hong-Xia; Huang, Pu; Ding, Yi-Min; He, Ying-Ping; Cao, Xiong

2015-12-01

To resolve the p-type doping problem of Al-rich AlGaN alloys, we investigate the influence of biaxial and hydrostatic strains on the activation energy, formation energy and band gap of Mg-doped GaN, AlN, Al0.83Ga0.17N disorder alloy and (AlN)5/(GaN)1 superlattice based on first-principles calculations by combining the standard DFT and hybrid functional. We find that the Mg acceptor activation energy {{E}\\text{A}} , the formation energy {{E}\\text{f}} and the band gap {{E}\\text{g}} decrease with increasing the strain ɛ. The hydrostatic strain has a more remarkable impact on {{E}\\text{g}} and {{E}\\text{A}} than the biaxial strain. Both {{E}\\text{A}} and {{E}\\text{g}} have a linear dependence on the hydrostatic strain. For the biaxial strain, {{E}\\text{g}} shows a parabolic dependence on ɛ if \\varepsilon ≤slant 0 while it becomes linear if \\varepsilon ≥slant 0 . In GaN and (AlN)5/(GaN)1, {{E}\\text{A}} parabolically depends on the biaxial compressive strain and linearly depends on the biaxial tensible strain. However, the dependence is approximately linear over the whole biaxial strain range in AlN and Al0.83Ga0.17N. The Mg acceptor activation energy in (AlN)5/(GaN)1 can be reduced from 0.26 eV without strain to 0.16 (0.22) eV with the hydrostatic (biaxial) tensible strain 3%.

Nonlinearity in rock - Evidence from earth tides

NASA Technical Reports Server (NTRS)

Agnew, D. C.

1981-01-01

The earth is sinusoidally stressed by tidal forces; if the stress-strain relation for rock is nonlinear, energy should appear in an earth tide record at frequencies which are multiples of those of the larger tidal lines. An examination of the signals to be expected for different nonlinear deformation laws shows that for a nonlinear response without dissipation, the largest anomalous signal should occur at twice the forcing frequency, whereas for nonlinear laws involving dissipation (cusped hysteresis loops) the anomalous signal will be greatest at three times this frequency. The size of the signal in the dissipative case depends on the amount by which dissipation affects the particular response being measured. For measurements of strain tides this depends on whether dissipation is assumed to be present throughout the earth or localized around the point of measurement. An analysis of 5.7 years of strain tide records from Pinon Flat, California, shows a small signal at twice the frequency of the largest (M2) tide.

Stress-strain time-dependent behavior of A356.0 aluminum alloy subjected to cyclic thermal and mechanical loadings

NASA Astrophysics Data System (ADS)

Farrahi, G. H.; Ghodrati, M.; Azadi, M.; Rezvani Rad, M.

2014-08-01

This article presents the cyclic behavior of the A356.0 aluminum alloy under low-cycle fatigue (or isothermal) and thermo-mechanical fatigue loadings. Since the thermo-mechanical fatigue (TMF) test is time consuming and has high costs in comparison to low-cycle fatigue (LCF) tests, the purpose of this research is to use LCF test results to predict the TMF behavior of the material. A time-independent model, considering the combined nonlinear isotropic/kinematic hardening law, was used to predict the TMF behavior of the material. Material constants of this model were calibrated based on room-temperature and high-temperature low-cycle fatigue tests. The nonlinear isotropic/kinematic hardening law could accurately estimate the stress-strain hysteresis loop for the LCF condition; however, for the out-of-phase TMF, the condition could not predict properly the stress value due to the strain rate effect. Therefore, a two-layer visco-plastic model and also the Johnson-Cook law were applied to improve the estimation of the stress-strain hysteresis loop. Related finite element results based on the two-layer visco-plastic model demonstrated a good agreement with experimental TMF data of the A356.0 alloy.

Trypsin-dependent production of an antibacterial substance by a human Peptostreptococcus strain in gnotobiotic rats and in vitro.

PubMed

Ramare, F; Nicoli, J; Dabard, J; Corring, T; Ladire, M; Gueugneau, A M; Raibaud, P

1993-09-01

An antibacterial substance appeared within 1 day in feces of gnotobiotic rats harboring a human intestinal Peptostreptococcus strain. It disappeared when the rat bile-pancreatic duct was ligatured or when the rats ingested a trypsin inhibitor. Anaerobic cultures of the Peptostreptococcus strain in a medium supplemented with trypsin also exhibited an antibacterial activity, which was also inhibited by the trypsin inhibitor. In vitro the antibacterial substance from both feces and culture medium was active against several gram-positive bacteria, including other Peptostreptococcus spp., potentially pathogenic Clostridium spp. such as C. perfringens, C. difficile, C. butyricum, C. septicum, and C. sordellii, Eubacterium spp., Bifidobacterium spp., and Bacillus spp. Whatever the order of inoculation of the strains, a sensitive strain of C. perfringens was eliminated within 1 day from the intestine of rats monoassociated with the Peptostreptococcus strain. These findings demonstrate for the first time that very potent antibacterial substances can be produced through a mechanism involving intestinal bacteria and exocrine pancreatic secretions.

[Polygalacturonase activity of microscopic fungi of different trophic groups].

PubMed

Kurchenko, I N

2013-01-01

A comparative study of polygalacturonase activity of 85 saprophytic, plant pathogenic and endophytic strains of Fusarium poae, Alternaria alternata, Penicillium funiculosum and Mycelia sterilia was conducted. It was established that in general polygalacturonase activity of Mycelia sterilia and P. funiculosum strains was significantly higher than that of A. alternata and F. poae strains. The majority of the studied strains showed a middle level of polygalacturonase activity. High activity was characteristic of only endophytic F. poae, P. funiculosum and Mycelia sterilia strains. The dependence of polygalacturonase activity of the studied strains on their rate of linear growth, cultivation time, as well as species and organs of host plants, which they were isolated from, was not established. The polygalacturonase presence in the dominant and common species of endophytic fungi of the bog plants of Ukrainian Polesie suggests that endophytic microscopic fungi play an important role in the hydrolysis of pectic substances of plant tissues, as well as in migration of mineral elements in wetland ecosystems.

Variation of Shrinkage Strain within the Depth of Concrete Beams.

PubMed

Jeong, Jong-Hyun; Park, Yeong-Seong; Lee, Yong-Hak

2015-11-16

The variation of shrinkage strain within beam depth was examined through four series of time-dependent laboratory experiments on unreinforced concrete beam specimens. Two types of beam specimens, horizontally cast and vertically cast, were tested; shrinkage variation was observed in the horizontally cast specimens. This indicated that the shrinkage variation within the beam depth was due to water bleeding and tamping during the placement of the fresh concrete. Shrinkage strains were measured within the beam depth by two types of strain gages, surface-attached and embedded. The shrinkage strain distribution within the beam depth showed a consistent tendency for the two types of gages. The test beams were cut into four sections after completion of the test, and the cutting planes were divided into four equal sub-areas to measure the aggregate concentration for each sub-area of the cutting plane. The aggregate concentration increased towards the bottom of the beam. The shrinkage strain distribution was estimated by Hobbs' equation, which accounts for the change of aggregate volume concentration.

Variation of Shrinkage Strain within the Depth of Concrete Beams

PubMed Central

Jeong, Jong-Hyun; Park, Yeong-Seong; Lee, Yong-Hak

2015-01-01

The variation of shrinkage strain within beam depth was examined through four series of time-dependent laboratory experiments on unreinforced concrete beam specimens. Two types of beam specimens, horizontally cast and vertically cast, were tested; shrinkage variation was observed in the horizontally cast specimens. This indicated that the shrinkage variation within the beam depth was due to water bleeding and tamping during the placement of the fresh concrete. Shrinkage strains were measured within the beam depth by two types of strain gages, surface-attached and embedded. The shrinkage strain distribution within the beam depth showed a consistent tendency for the two types of gages. The test beams were cut into four sections after completion of the test, and the cutting planes were divided into four equal sub-areas to measure the aggregate concentration for each sub-area of the cutting plane. The aggregate concentration increased towards the bottom of the beam. The shrinkage strain distribution was estimated by Hobbs’ equation, which accounts for the change of aggregate volume concentration. PMID:28793677

Physical and thermal strain of firefighters according to the firefighting tactics used to suppress wildfires.

PubMed

Rodríguez-Marroyo, J A; Villa, J G; López-Satue, J; Pernía, R; Carballo, B; García-López, J; Foster, C

2011-11-01

The aim of this study was to analyse the physiological strain of firefighters, using heart rate (HR) and core temperature, during real wildfire suppression according to the type of attack performed (direct, indirect or mixed). Three intensity zones were established according to the HR corresponding to the ventilatory threshold (VT) and respiratory compensation threshold (RCT): zone 1, RCT. The exercise workload (training impulse (TRIMP)), the physiological strain index (PSI) and the cumulative heat strain index(CHSI) were calculated using the time spent in each zone, and the HR and core temperature, respectively. Significantly higher mean HR, time spent in Z2 and Z3 and TRIMP h(-1) were found in direct and mixed versus indirect attacks. The highest PSI and CHSI were observed in the direct attack. In conclusion, exercise strain and combined thermal strain, but not core temperature during wildfire suppression, are related to the type of attack performed. STATEMENT OF RELEVANCE: Our findings demonstrated that wildfire firefighting is associated with high physiological demands, which vary significantly depending on the tactics chosen for performing the task. These results should be kept in mind when planning programmes to improve wildland firefighters' physical fitness, which will allow improvement in their performance.

Strain distribution in the lumbar vertebrae under different loading configurations.

PubMed

Cristofolini, Luca; Brandolini, Nicola; Danesi, Valentina; Juszczyk, Mateusz M; Erani, Paolo; Viceconti, Marco

2013-10-01

The stress/strain distribution in the human vertebrae has seldom been measured, and only for a limited number of loading scenarios, at few locations on the bone surface. This in vitro study aimed at measuring how strain varies on the surface of the lumbar vertebral body and how such strain pattern depends on the loading conditions. Eight cadaveric specimens were instrumented with eight triaxial strain gauges each to measure the magnitude and direction of principal strains in the vertebral body. Each vertebra was tested in a three adjacent vertebrae segment fashion. The loading configurations included a compressive force aligned with the vertebral body but also tilted (15°) in each direction in the frontal and sagittal planes, a traction force, and torsion (both directions). Each loading configuration was tested six times on each specimen. The strain magnitude varied significantly between strain measurement locations. The strain distribution varied significantly when different loading conditions were applied (compression vs. torsion vs. traction). The strain distribution when the compressive force was tilted by 15° was also significantly different from the axial compression. Strains were minimal when the compressive force was applied coaxial with the vertebral body, compared with all other loading configurations. Also, strain was significantly more uniform for the axial compression, compared with all other loading configurations. Principal strains were aligned within 19° to the axis of the vertebral body for axial-compression and axial-traction. Conversely, when the applied force was tilted by 15°, the direction of principal strain varied by a much larger angle (15° to 28°). This is the first time, to our knowledge, that the strain distribution in the vertebral body is measured for such a variety of loading configurations and a large number of strain sensors. The present findings suggest that the structure of the vertebral body is optimized to sustain compressive forces, whereas even a small tilt angle makes the vertebral structure work under suboptimal conditions. Copyright © 2013 Elsevier Inc. All rights reserved.

Implementation of Fiber Substructuring Into Strain Rate Dependent Micromechanics Analysis of Polymer Matrix Composites

NASA Technical Reports Server (NTRS)

Goldberg, Robert K.

2001-01-01

A research program is in progress to develop strain rate dependent deformation and failure models for the analysis of polymer matrix composites subject to impact loads. Previously, strain rate dependent inelastic constitutive equations developed to model the polymer matrix were incorporated into a mechanics of materials based micromechanics method. In the current work, the micromechanics method is revised such that the composite unit cell is divided into a number of slices. Micromechanics equations are then developed for each slice, with laminate theory applied to determine the elastic properties, effective stresses and effective inelastic strains for the unit cell. Verification studies are conducted using two representative polymer matrix composites with a nonlinear, strain rate dependent deformation response. The computed results compare well to experimentally obtained values.

Creep and Stress-strain Behavior After Creep from Sic Fiber Reinforced, Melt-infiltrated Sic Matrix Composites

NASA Technical Reports Server (NTRS)

Morscher, Gregory N.; Pujar, Vijay

2004-01-01

Silicon carbide fiber (Hi-Nicalon Type S, Nippon Carbon) reinforced silicon carbide matrix composites containing melt-infiltrated Si were subjected to creep at 1315 C for a number of different stress conditions, This study is aimed at understanding the time-dependent creep behavior of CMCs for desired use-conditions, and also more importantly, how the stress-strain response changes as a result of the time-temperature-stress history of the crept material. For the specimens that did not rupture, fast fracture experiments were performed at 1315 C or at room temperature immediately following tensile creep. In many cases, the stress-strain response and the resulting matrix cracking stress of the composite change due to stress-redistribution between composite constituents during tensile creep. The paper will discuss these results and its implications on applications of these materials for turbine engine components.

Unified constitutive material models for nonlinear finite-element structural analysis. [gas turbine engine blades and vanes

NASA Technical Reports Server (NTRS)

Kaufman, A.; Laflen, J. H.; Lindholm, U. S.

1985-01-01

Unified constitutive material models were developed for structural analyses of aircraft gas turbine engine components with particular application to isotropic materials used for high-pressure stage turbine blades and vanes. Forms or combinations of models independently proposed by Bodner and Walker were considered. These theories combine time-dependent and time-independent aspects of inelasticity into a continuous spectrum of behavior. This is in sharp contrast to previous classical approaches that partition inelastic strain into uncoupled plastic and creep components. Predicted stress-strain responses from these models were evaluated against monotonic and cyclic test results for uniaxial specimens of two cast nickel-base alloys, B1900+Hf and Rene' 80. Previously obtained tension-torsion test results for Hastelloy X alloy were used to evaluate multiaxial stress-strain cycle predictions. The unified models, as well as appropriate algorithms for integrating the constitutive equations, were implemented in finite-element computer codes.

A Nonlinear Viscoelastic Model for Ceramics at High Temperatures

NASA Technical Reports Server (NTRS)

Powers, Lynn M.; Panoskaltsis, Vassilis P.; Gasparini, Dario A.; Choi, Sung R.

2002-01-01

High-temperature creep behavior of ceramics is characterized by nonlinear time-dependent responses, asymmetric behavior in tension and compression, and nucleation and coalescence of voids leading to creep rupture. Moreover, creep rupture experiments show considerable scatter or randomness in fatigue lives of nominally equal specimens. To capture the nonlinear, asymmetric time-dependent behavior, the standard linear viscoelastic solid model is modified. Nonlinearity and asymmetry are introduced in the volumetric components by using a nonlinear function similar to a hyperbolic sine function but modified to model asymmetry. The nonlinear viscoelastic model is implemented in an ABAQUS user material subroutine. To model the random formation and coalescence of voids, each element is assigned a failure strain sampled from a lognormal distribution. An element is deleted when its volumetric strain exceeds its failure strain. Element deletion has been implemented within ABAQUS. Temporal increases in strains produce a sequential loss of elements (a model for void nucleation and growth), which in turn leads to failure. Nonlinear viscoelastic model parameters are determined from uniaxial tensile and compressive creep experiments on silicon nitride. The model is then used to predict the deformation of four-point bending and ball-on-ring specimens. Simulation is used to predict statistical moments of creep rupture lives. Numerical simulation results compare well with results of experiments of four-point bending specimens. The analytical model is intended to be used to predict the creep rupture lives of ceramic parts in arbitrary stress conditions.

Reconstructing the calibrated strain signal in the Advanced LIGO detectors

NASA Astrophysics Data System (ADS)

Viets, A. D.; Wade, M.; Urban, A. L.; Kandhasamy, S.; Betzwieser, J.; Brown, Duncan A.; Burguet-Castell, J.; Cahillane, C.; Goetz, E.; Izumi, K.; Karki, S.; Kissel, J. S.; Mendell, G.; Savage, R. L.; Siemens, X.; Tuyenbayev, D.; Weinstein, A. J.

2018-05-01

Advanced LIGO’s raw detector output needs to be calibrated to compute dimensionless strain h(t) . Calibrated strain data is produced in the time domain using both a low-latency, online procedure and a high-latency, offline procedure. The low-latency h(t) data stream is produced in two stages, the first of which is performed on the same computers that operate the detector’s feedback control system. This stage, referred to as the front-end calibration, uses infinite impulse response (IIR) filtering and performs all operations at a 16 384 Hz digital sampling rate. Due to several limitations, this procedure currently introduces certain systematic errors in the calibrated strain data, motivating the second stage of the low-latency procedure, known as the low-latency gstlal calibration pipeline. The gstlal calibration pipeline uses finite impulse response (FIR) filtering to apply corrections to the output of the front-end calibration. It applies time-dependent correction factors to the sensing and actuation components of the calibrated strain to reduce systematic errors. The gstlal calibration pipeline is also used in high latency to recalibrate the data, which is necessary due mainly to online dropouts in the calibrated data and identified improvements to the calibration models or filters.

Psychosocial work conditions, unemployment, and leisure-time physical activity: a population-based study.

PubMed

Ali, Sadiq Mohammad; Lindström, Martin

2006-01-01

To investigate the association between psychosocial work conditions and unemployment, and low leisure-time physical activity. The 2000 public health survey in Scania is a cross-sectional postal questionnaire study with a 59% participation rate. A total of 5,180 persons aged 18-64 years who belonged to the workforce and the unemployed were included in this study. Logistic regression models were used to investigate the associations between psychosocial factors at work and unemployment, and low leisure-time physical activity. Psychosocial conditions at work were defined according to the Karasek-Theorell demand-control/decision latitudes into relaxed, active, passive, and job strain categories. The multivariate analyses included age, country of birth, education, economic stress, and social participation. In total, 16.1% of men and 14.8% of women had low leisure-time physical activity. The job strain (high demands/low control) and unemployed categories had significantly higher odds ratios of low leisure-time physical activity among both men and women compared with the relaxed (low demands/high control) reference category. However, the significant differences between the job strain, the unemployed, and the relaxed categories disappeared in the multivariate models. Respondents with job strain or unemployment have significantly higher odds ratios of low leisure-time physical activity than the relaxed category. However, after adjustments for education in particular the differences disappear. Nevertheless, the results suggest that the association between psychosocial work conditions, which are often dependent on education, and leisure-time physical activity may be interesting to study in more detail.

Characterization of specialized flocculent yeasts to improve sparkling wine fermentation.

PubMed

Tofalo, R; Perpetuini, G; Di Gianvito, P; Arfelli, G; Schirone, M; Corsetti, A; Suzzi, G

2016-06-01

Flocculent wine yeasts were characterized for the expression of FLO1, FLO5, FLO8, AMN1 and RGA1 genes, growth kinetics and physicochemical properties of the cell surface during a 6-month sparkling wine fermentation period. The expression of FLO1, FLO5, FLO8, AMN1 and RGA1 genes was determined by RT-qPCR. The physicochemical characterization of yeast surface properties was evaluated by the microbial adhesion to solvents method. FLO5 gene was the most expressed one and a linear correlation with the flocculent degree was found. Flocculent strains were more hydrophobic than the commercial wine strain EC1118. Gene expressions and the ability to face secondary wine fermentation conditions were strain dependent. The importance of FLO5 gene in developing the high flocculent characteristic of wine yeasts was highlighted. Cell surface properties depended on the time of fermentation. Better knowledge about the expression of some genes encoding the flocculent phenotype which could be useful to select suitable starter cultures to improve sparkling wine technology was achieved. A step forward in understanding the complexity and strain-specific nature of flocculation phenotype was done. © 2016 The Society for Applied Microbiology.

Echocardiographic assessment of right ventricle adaptation to endurance training in young rowers - speckle tracking echocardiography.

PubMed

Konopka, M; Krol, W; Burkhard-Jagodzinska, K; Jakubiak, A; Klusiewicz, A; Chwalbinska, J; Pokrywka, A; Sitkowski, D; Dluzniewski, M; Braksator, W

2016-12-01

The aim of this study was to determine the relationship between the degree of cardiorespiratory fitness and the function of the right ventricle (RV). 117 rowers, age 17.5±1.5 years. All subjects underwent cardiopulmonary exercise. Standard echocardiography and 2D speckle tracking echocardiography with evaluation of longitudinal strain in each segment of the RV (basal - RVLS-B; mid - RVLS-M, apical - RVLS-A) and global RV free-wall strain (RVLS-G) were performed. RVLS-B values were lower compared to the RVLS-M (-25.8±4.4 vs -29.3±3.5; p<0.001) and RVLS-A values (-25.8±4.4 vs -26.2±3.4; p=0.85). Correlations between VO 2 max and RVLS were observed in men: RVLS-G strain (r = 0.43; p <0.001); RVLS-B (r = 0.30; p = 0.02); RVLS-M (r = 0.38; p = 0.02). A similar relationship was not observed in the group of women. The strongest predictors corresponding to a change in global and basal strain were VO 2 max and training time: RVLS-G (VO 2 max: β = 0.18, p = 0.003; training time: β = -0.39; p = 0.02) and RVLS-B (VO 2 max: β = 0.23; p = 0.0001 training time: β = -1.16; p = 0.0001). The global and regional reduction of RV systolic function positively correlates with the level of fitness, and this relationship is observed already in young athletes. The character of the relationship between RV deformation parameters and the variables that determine the physical performance depend on gender. The dependencies apply to the proximal fragment of the RV inflow tract, which may be a response to the type of flow during exercise in endurance athletes.

Real-time noble gas release signaling rock deformation

NASA Astrophysics Data System (ADS)

Bauer, S. J.; Gardner, W. P.; Lee, H.

2016-12-01

We present empirical results/relationships of rock strain, microfracture density, acoustic emissions, and noble gas release from laboratory triaxial experiments for a granite and basalt. Noble gases are contained in most crustal rock at inter/intra granular sites, their release during natural and manmade stress and strain changes represents a signal of brittle/semi brittle deformation. The gas composition depends on lithology, geologic history and age, fluids present, and uranium, thorium and potassium-40 concentrations in the rocks that affect radiogenic noble gases (helium, argon) production. Noble gas emission and its relationship to crustal processes have been studied, including correlations to tectonic velocities and qualitative estimates of deep permeability from surface measurements, finger prints of nuclear weapon detonation, and as potential precursory signals to earthquakes attributed to gas release due to pre-seismic stress, dilatancy and/or rock fracturing. Helium emission has been shown as a precursor of volcanic activity. Real-time noble gas release is observed using an experimental system utilizing mass spectrometers to measure gases released during triaxial rock deformation. Noble gas release is shown to represent a sensitive precursor signal of rock deformation by relating real-time noble gas release to stress-strain state changes and acoustic emissions. We propose using noble gas release to also signal rock deformation in boreholes, mines and nuclear waste repositories. We postulate each rock exhibits a gas release signature which is microstructure, stress/strain state, and or permanent deformation dependent. Such relationships, when calibrated, may be used to sense rock deformation and then develop predictive models. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corp., for the US Dept. of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000. SAND2016-7468 A

Interferometric visualization and demodulation method for measuring quasi-static strain in fiber Bragg grating sensors by a simple rotating etalon filter

NASA Astrophysics Data System (ADS)

Rocco, Alessandra S.; Coppola, Giuseppe; Ferraro, Pietro; Foti, Giuseppe; Iodice, Mario

2004-09-01

Optical fiber sensors are the ideal system to monitor "smart structures" and on-site/real time stress measurements: they can be in fact easily embedded or attached to the structures under test and are not affected by electro- magnetic noise. In particular a signal from a Fiber Bragg grating sensor (FBG) may be processed such that its information remains immune to optical power fluctuations. Different interrogation methods can be used for reading out Bragg wavelength shifts. In this paper we propose a very simple interferometric method for interrogating FBG sensors, based on bi-polished silicon sample acting like an etalon tuneable filter (ETF). The Bragg wavelength shift can be evaluated by analyzing the spectral response of signal reflected by the FBG sensor and filtered by the ETF that is continuously and rapidly tuned. Tuning was obtained by rotating the ETF. Variation in the strain at the FBG causes a phase shift in the analyzed signal. The overall spectral signal, collected with time, consists in an interferometric figure which finesse and fringe contrast depending on the geometrical sizes and facets reflectivity of the silicon sample. The fringe pattern, expressed by the Airy's formula, depends on the wavelength l of the incident radiation and on the angle of incidence. The phase of fringe pattern can be retrieved by a standard FFT method giving quantitative measurements of the quasi-static strain variation sensed by the FBG. In this way, the method allows a valuable visualization of the time-evolution of the incremental strain applied to the FBG. Principle of functioning of this method is described and first results obtained employing such configuration, are reported.

Molecular analysis of an oyster-related norovirus outbreak.

PubMed

Nenonen, Nancy P; Hannoun, Charles; Olsson, Margareta B; Bergström, Tomas

2009-06-01

Contaminated raw oysters were implicated in a severe outbreak of norovirus (NoV) gastroenteritis affecting 30 restaurant guests. To define the outbreak source by using molecular methods to characterize NoV strains detected in patient and oyster samples. Molecular epidemiological studies based on nucleotide sequencing and phylogenetic analyses of patient and oyster NoV strains, and comparison to background dataset. NoV genotype (G) I.1 was detected in the one patient stool analyzed by in-house TaqMan real time RT-PCR and classical nested RT-PCR targeting NoV RNA-dependent polymerase (RdRp, 285 nt), and by nested RT-PCR targeting RdRp-capsid-poly(A)-3' (3085 nt). Patient strain showed >or=99% similarity (285 nt) with three NoV strains detected in two of five oysters examined by classical nested RT-PCR (RdRp). A third oyster tested positive for NoV GII.3. Phylogenetic analysis showed clustering of patient and oyster strains related to this outbreak with GI.1 strains from previous local outbreaks, and mussel studies. Sequence data revealed >or=99% similarity (285 nt) between NoV GI.1 strains detected in patient stool and suspect oysters, linking the contaminated oysters to the outbreak. Identification of human NoV GI and GII strains in oysters indicated contamination of human fecal origin, presumably from inappropriate storage in the harbor. Comparative long-fragment analysis of the patient strain revealed 99% similarity (3085 nt) with NoV GI.1 strains detected in previous outbreaks and environmental mussel studies from West Sweden, 87% with M87661 (Norwalk68) and 96% with L23828 (SRSV-KY-89/89/J). These results indicated considerable genomic stability of NoV GI.1 strains over time.

High Strain Rate and Shock-Induced Deformation in Metals

NASA Astrophysics Data System (ADS)

Ravelo, Ramon

2012-02-01

Large-scale non-equilibrium molecular Dynamics (MD) simulations are now commonly used to study material deformation at high strain rates (10^9-10^12 s-1). They can provide detailed information-- such as defect morphology, dislocation densities, and temperature and stress profiles, unavailable or hard to measure experimentally. Computational studies of shock-induced plasticity and melting in fcc and bcc single, mono-crystal metals, exhibit generic characteristics: high elastic limits, large directional anisotropies in the yield stress and pre-melting much below the equilibrium melt temperature for shock wave propagation along specific crystallographic directions. These generic features in the response of single crystals subjected to high strain rates of deformation can be explained from the changes in the energy landscape of the uniaxially compressed crystal lattice. For time scales relevant to dynamic shock loading, the directional-dependence of the yield strength in single crystals is shown to be due to the onset of instabilities in elastic-wave propagation velocities. The elastic-plastic transition threshold can accurately be predicted by a wave-propagation stability analysis. These strain-induced instabilities create incipient defect structures, which can be quite different from the ones, which characterize the long-time, asymptotic state of the compressed solid. With increase compression and strain rate, plastic deformation via extended defects gives way to amorphization associated with the loss in shear rigidity along specific deformation paths. The hot amorphous or (super-cooled liquid) metal re-crystallizes at rates, which depend on the temperature difference between the amorphous solid and the equilibrium melt line. This plastic-amorphous transition threshold can be computed from shear-waves stability analyses. Examples from selected fcc and bcc metals will be presented employing semi-empirical potentials of the embedded atom method (EAM) type as well as results from density functional theory calculations.

Exploration of mechanisms underlying the strain-rate-dependent mechanical property of single chondrocytes

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

Nguyen, Trung Dung; Gu, YuanTong, E-mail: yuantong.gu@qut.edu.au

2014-05-05

Based on the characterization by Atomic Force Microscopy, we report that the mechanical property of single chondrocytes has dependency on the strain-rates. By comparing the mechanical deformation responses and the Young's moduli of living and fixed chondrocytes at four different strain-rates, we explore the deformation mechanisms underlying this dependency property. We found that the strain-rate-dependent mechanical property of living cells is governed by both of the cellular cytoskeleton and the intracellular fluid when the fixed chondrocytes are mainly governed by their intracellular fluid, which is called the consolidation-dependent deformation behavior. Finally, we report that the porohyperelastic constitutive material model whichmore » can capture the consolidation-dependent behavior of both living and fixed chondrocytes is a potential candidature to study living cell biomechanics.« less

Dynamic response of polyurea subjected to nanosecond rise-time stress waves

NASA Astrophysics Data System (ADS)

Youssef, George; Gupta, Vijay

2012-08-01

Shaped charges and explosively formed projectiles used in modern warfare can attain speeds as high as 30,000 ft/s. Impacts from these threats are expected to load the armor materials in the 10 to 100 ns timeframe. During this time, the material strains are quite limited but the strain rates are extremely high. To develop armors against such threats it is imperative to understand the dynamic constitutive behavior of materials in the tens of nanoseconds timeframe. Material behavior in this parameter space cannot be obtained by even the most sophisticated plate-impact and split-Hopkinson bar setups that exist within the high energy materials field today. This paper introduces an apparatus and a test method that are based on laser-generated stress waves to obtain such material behaviors. Although applicable to any material system, the test procedures are demonstrated on polyurea which shows unusual dynamic properties. Thin polyurea layers were deformed using laser-generated stress waves with 1-2 ns rise times and 16 ns total duration. The total strain in the samples was less than 3%. Because of the transient nature of the stress wave, the strain rate varied throughout the deformation history of the sample. A peak value of 1.1×105 s-1 was calculated. It was found that the stress-strain characteristics, determined from experimentally recorded incident and transmitted wave profiles, matched satisfactorily with those computed from a 2D wave mechanics simulation in which the polyurea was modeled as a linearly viscoelastic solid with constants derived from the quasi-static experiments. Thus, the test data conformed to the Time-Temperature Superposition (TTS) principle even at extremely high strain rates of our test. This then extends the previous observations of Zhao et al. (Mech. Time-Depend. Mater. 11:289-308, 2007) who showed the applicability of the TTS principle for polyurea in the linearly viscoelastic regime up to peak strain rates of 1200 s-1.

Bactericidal activity and post-antibiotic effect of ozenoxacin against Propionibacterium acnes.

PubMed

Kanayama, Shoji; Okamoto, Kazuaki; Ikeda, Fumiaki; Ishii, Ritsuko; Matsumoto, Tatsumi; Hayashi, Naoki; Gotoh, Naomasa

2017-06-01

Ozenoxacin, a novel non-fluorinated topical quinolone, is used for the treatment of acne vulgaris in Japan. We investigated bactericidal activity and post-antibiotic effect (PAE) of ozenoxacin against Propionibacterium acnes, a major causative bacterium of acne vulgaris. The minimum inhibitory concentrations (MICs) of ozenoxacin against 3 levofloxacin-susceptible strains (MIC of levofloxacin; ≤4 μg/mL) and 3 levofloxacin-resistant strains (MIC of levofloxacin; ≥8 μg/mL) ranged from 0.03 to 0.06 μg/mL and from 0.25 to 0.5 μg/mL, respectively. These MICs of ozenoxacin were almost the same or lower than nadifloxacin and clindamycin. The minimum bactericidal concentrations (MBCs) of ozenoxacin against the levofloxacin-susceptible and -resistant strains were from 0.06 to 8 μg/mL and from 0.5 to 4 μg/mL, respectively. These MBCs were lower than those of nadifloxacin and clindamycin. In time-kill assay, ozenoxacin at 1/4, 1 and 4 times the respective MIC against both levofloxacin-susceptible and -resistant strains showed a concentration-dependent bactericidal activity. Ozenoxacin at 4 times the MICs against the levofloxacin-susceptible strains showed more potent and more rapid onset of bactericidal activity compared to nadifloxacin and clindamycin at 4 times the respective MICs. The PAEs of ozenoxacin at 4 times the MICs against the levofloxacin-susceptible strains were from 3.3 to 17.1 h, which were almost the same or longer than nadifloxacin and clindamycin. In contrast, the PAEs were hardly induced by any antimicrobial agents against the levofloxacin-resistant strains. The present findings suggest that ozenoxacin has a potent bactericidal activity against both levofloxacin-susceptible and -resistant P. acnes, and a long-lasting PAE against levofloxacin-susceptible P. acnes. Copyright © 2017 Japanese Society of Chemotherapy and The Japanese Association for Infectious Diseases. Published by Elsevier Ltd. All rights reserved.

Characterization of time-dependent changes in strength and stiffness of Florida base materials : final report, October 2008.

DOT National Transportation Integrated Search

2008-10-01

Resilient modulus and Youngs modulus are parameters increasingly used to fundamentally characterize the behavior : of pavement materials both in the laboratory and in the field. This study documents the small-strain Youngs modulus : and larger-...

A simplified method for prediction of long-term prestress loss in post-tensioned concrete bridges.

DOT National Transportation Integrated Search

2006-07-01

Creep and shrinkage of concrete and relaxation of prestressing steel cause time-dependent changes in : the stresses and strains of concrete structures. These changes result in continuous reduction in the : concrete compression stresses and in the ten...

An X-ray photoelectron spectroscopy study of the thermal nitridation of SiO2/Si

NASA Technical Reports Server (NTRS)

Vasquez, R. P.; Madhukar, A.; Grunthaner, F. J.; Naiman, M. L.

1986-01-01

The dependence of the nitrogen distribution in thermally nitrided SiO2 films on the nitridation time and temperature has been studied by means of X-ray photoelectron spectroscopy (XPS). The photoelectron peak intensities were measured by fitting Voigt profiles to the XPS spectra and were used to calculate the film composition as a function of film depth, applying an analytical method described in detail. The times of appearance of the maxima in interfacial nitrogen concentration are shown for 800, 1000, and 1150 C, and the data are related to a kinetic model of Vasquez and Madhukar (1985), which considers the effect of interfacial strain on the nitridation kinetics. In addition, the intensity of a fluorine marker (from the HF used in the etching step) was found to correlate with the nitrogen concentration. It is postulated that the F bonds preferentially to defects. This hypothesis and the measured F intensities are consistent with the proposed strain-dependent energy of defect formation.

Refined gradient theory of scale-dependent superthin rods

NASA Astrophysics Data System (ADS)

Lurie, S. A.; Kuznetsova, E. L.; Rabinskii, L. N.; Popova, E. I.

2015-03-01

A version of the refined nonclassical theory of thin beams whose thickness is comparable with the scale characteristic of the material structure is constructed on the basis of the gradient theory of elasticity which, in contrast to the classical theory, contains some additional physical characteristics depending on the structure scale parameters and is therefore most appropriate for modeling the strains of scale-dependent systems. The fundamental conditions for the well-posedness of the gradient theories are obtained for the first time, and it is shown that some of the known applied gradient theories do not generally satisfy the well-posedness criterion. A version of the well-posed gradient strain theory which satisfies the symmetry condition is proposed. The well-posed gradient theory is then used to implement the method of kinematic hypotheses for constructing a refined theory of scale-dependent beams. The equilibrium equations of the refined theory of scale-dependent Timoshenko and Bernoulli beams are obtained. It is shown that the scale effects are localized near the beam ends, and therefore, taking the scale effects into account does not give any correction to the bending rigidity of long beams as noted in the previously published papers dealing with the scale-dependent beams.

Time-dependent stress concentration and microcrack nucleation in TiAl

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

Yoo, M.H.

1995-07-01

Localized stress evolution associated with the interaction of slip or twinning with an interface is treated by means of a superposition of the {open_quotes}internal loading{close_quotes} of a crystalline subsystem by dynamic dislocation pile-up and the stress relaxation by climb of interfacial dislocations. The peak value of a stress concentration factor depends on both the angular function that includes the effect of mode mixity and the ratio of characteristic times for stress relaxation and internal loading. The available experimental data on orientation and strain-rate dependences of interfacial fracture mode in polysynthetically twinned TiAl crystals are discussed in view of the theoreticalmore » concepts presented in this paper.« less

Strain controlled ferromagnetic-ferrimagnetic transition and vacancy formation energy of defective graphene.

PubMed

Zhang, Yajun; Sahoo, Mpk; Wang, Jie

2016-09-23

Single vacancy (SV)-induced magnetism in graphene has attracted much attention motivated by its potential in achieving new functionalities. However, a much higher vacancy formation energy limits its direct application in electronic devices and the dependency of spin interaction on the strain is unclear. Here, through first-principles density-functional theory calculations, we investigate the possibility of strain engineering towards lowering vacancy formation energy and inducing new magnetic states in defective graphene. It is found that the SV-graphene undergoes a phase transition from an initial ferromagnetic state to a ferrimagnetic state under a biaxial tensile strain. At the same time, the biaxial tensile strain significantly lowers the vacancy formation energy. The charge density, density of states and band theory successfully identify the origin and underlying physics of the transition. The predicted magnetic phase transition is attributed to the strain driven spin flipping at the C-atoms nearest to the SV-site. The magnetic semiconducting graphene induced by defect and strain engineering suggests an effective way to modulate both spin and electronic degrees of freedom in future spintronic devices.

Effect of Creep and Oxidation on Reduced Creep-Fatigue life of Ni-based Alloy 617 at 850 C

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

Chen, Xiang; Yang, Zhiqing; Sokolov, Mikhail A

Low cycle fatigue (LCF) and creep fatigue testing of Ni-based alloy 617 was carried out at 850 C. Compared with its LCF life, the material s creep fatigue life decreases to different extents depending on test conditions. To elucidate the microstructure-fatigue property relationship for alloy 617 and the effect of creep and oxidation on its fatigue life, systematic microstructural investigations were carried out using scanning electron microscopy, energy-dispersive X-ray spectroscopy, and electron backscatter diffraction (EBSD). In LCF tests, as the total strain range increased, deformations concentrated near high angle grain boundaries (HAGBs). The strain hold period in the creep fatiguemore » tests introduced additional creep damage to the material, which revealed the detrimental effect of the strain hold time on the material fatigue life in two ways. First, the strain hold time enhanced the localized deformation near HAGBs, resulting in the promotion of intergranular cracking of alloy 617. Second, the strain hold time encouraged grain boundary sliding, which resulted in interior intergranular cracking of the material. Oxidation accelerated the initiation of intergranular cracking in alloy 617. In the crack propagation stage, if oxidation was promoted and the cyclic oxidation damage was greater than the fatigue damage, oxidation-assisted intergranular crack growth resulted in a significant reduction in the material s fatigue life.« less

Piezoelectric effect in non-uniform strained carbon nanotubes

NASA Astrophysics Data System (ADS)

Ilina, M. V.; Blinov, Yu F.; Ilin, O. I.; Rudyk, N. N.; Ageev, O. A.

2017-10-01

The piezoelectric effect in non-uniform strained carbon nanotubes (CNTs) has been studied. It is shown that the magnitude of strained CNTs surface potential depends on a strain value. It is established that the resistance of CNT also depends on the strain and internal electric field, which leads to the hysteresis in the current-voltage characteristics. Analysis of experimental studies of the non-uniform strained CNT with a diameter of 92 nm and a height of 2.1 μm allowed us to estimate the piezoelectric coefficient 0.107 ± 0.032 C/m2.

Strain-Tuning Atomic Substitution in Two-Dimensional Atomic Crystals.

PubMed

Li, Honglai; Liu, Hongjun; Zhou, Linwei; Wu, Xueping; Pan, Yuhao; Ji, Wei; Zheng, Biyuan; Zhang, Qinglin; Zhuang, Xiujuan; Zhu, Xiaoli; Wang, Xiao; Duan, Xiangfeng; Pan, Anlian

2018-05-22

Atomic substitution offers an important route to achieve compositionally engineered two-dimensional nanostructures and their heterostructures. Despite the recent research progress, the fundamental understanding of the reaction mechanism has still remained unclear. Here, we reveal the atomic substitution mechanism of two-dimensional atomic layered materials. We found that the atomic substitution process depends on the varying lattice constant (strain) in monolayer crystals, dominated by two strain-tuning (self-promoted and self-limited) mechanisms using density functional theory calculations. These mechanisms were experimentally confirmed by the controllable realization of a graded substitution ratio in the monolayers by controlling the substitution temperature and time and further theoretically verified by kinetic Monte Carlo simulations. The strain-tuning atomic substitution processes are of general importance to other two-dimensional layered materials, which offers an interesting route for tailoring electronic and optical properties of these materials.

Effect of route on inoculation on host resistance to Nocardia.

PubMed Central

Beaman, B L; Maslan, S; Scates, S; Rosen, J

1980-01-01

Virulent strains of Nocardia asteroides and Nocardia caviae were injected into mice by five different routes. When these organisms were grown to the same stage of growth in the same medium and otherwise prepared identically, it was found that they differed significantly in their ability to infect and kill the host, depending entirely upon the route of inoculation. Thus, N. caviae 112 was 30 times more virulent than N. asteroides GUH-2 when administered intranasally, whereas N. asteroides was at least 10 times more pathogenic than N. caviae when injected intravenously. They had similar degrees of virulence when given intraperitoneally. N. asteroides GUH-2 induced a more persistent and progressive infection than N. caviae 112 when injected into the footpads of mice; however, the latter strain was more lethal for the animals when given by this route. Different routes of infecting mice indicate a compartmentalization of the host response to different strains of nocardia. Therefore, the use of different strains of nocardia under carefully controlled and defined conditions should make it possible to dissect the nocardia-host interactions at the cellular levels. Images Fig. 1 PMID:6991437

Laboratory experiments from the toy store

NASA Technical Reports Server (NTRS)

Mcclelland, H. T.

1992-01-01

The following is a laboratory experiment designed to further understanding of materials science. This material could be taught to a typical student of materials science or manufacturing at the high school level or above. The objectives of this experiment are as follows: (1) to qualitatively demonstrate the concepts of elasticity, plasticity, and the strain rate and temperature dependence of the mechanical properties of engineering materials; (2) to qualitatively demonstrate the basics of extrusion including material flow, strain rate dependence of defects, lubrication effects, and the making of hollow shapes by extrusion (the two parts may be two separate experiments done at different times when the respective subjects are covered); and (3) to demonstrate the importance of qualitative observations and the amount of information which can be gathered without quantitative measurements.

A simplified orthotropic formulation of the viscoplasticity theory based on overstress

NASA Technical Reports Server (NTRS)

Sutcu, M.; Krempl, E.

1988-01-01

An orthotropic, small strain viscoplasticity theory based on overstress is presented. In each preferred direction the stress is composed of time (rate) independent (or plastic) and viscous (or rate dependent) contributions. Tension-compression asymmetry can depend on direction and is included in the model. Upon a proper choice of a material constant one preferred direction can exhibit linear elastic response while the other two deform in a viscoplastic manner.

Final Shape of Precision Molded Optics: Part 1 - Computational Approach, Material Definitions and the Effect of Lens Shape

DTIC Science & Technology

2012-05-15

subroutine by adding time-dependence to the thermal expansion coefficient. The user subroutine was written in Intel Visual Fortran that is compatible...temperature history dependent expansion and contraction, and the molds were modeled as elastic taking into account both mechanical and thermal strain. In...behavior was approximated by assuming the thermal coefficient of expansion to be a fourth order polynomial function of temperature. The authors

Fundamental experiments on hydride reorientation in zircaloy

NASA Astrophysics Data System (ADS)

Colas, Kimberly B.

In the current study, an in-situ X-ray diffraction technique using synchrotron radiation was used to follow directly the kinetics of hydride dissolution and precipitation during thermomechanical cycles. This technique was combined with conventional microscopy (optical, SEM and TEM) to gain an overall understanding of the process of hydride reorientation. Thus this part of the study emphasized the time-dependent nature of the process, studying large volume of hydrides in the material. In addition, a micro-diffraction technique was also used to study the spatial distribution of hydrides near stress concentrations. This part of the study emphasized the spatial variation of hydride characteristics such as strain and morphology. Hydrided samples in the shape of tensile dog-bones were used in the time-dependent part of the study. Compact tension specimens were used during the spatial dependence part of the study. The hydride elastic strains from peak shift and size and strain broadening were studied as a function of time for precipitating hydrides. The hydrides precipitate in a very compressed state of stress, as measured by the shift in lattice spacing. As precipitation proceeds the average shift decreases, indicating average stress is reduced, likely due to plastic deformation and morphology changes. When nucleation ends the hydrides follow the zirconium matrix thermal contraction. When stress is applied below the threshold stress for reorientation, hydrides first nucleate in a very compressed state similar to that of unstressed hydrides. After reducing the average strain similarly to unstressed hydrides, the average hydride strain reaches a constant value during cool-down to room temperature. This could be due to a greater ease of deforming the matrix due to the applied far-field strain which would compensate for the strains due to thermal contraction. Finally when hydrides reorient, the average hydride strains become tensile during the first precipitation regime and remain constant in the tensile direction during the second precipitation regime. This could be due to the fact that the face of reoriented hydride platelet is in compression once these platelets have grown to a sufficient size. The second goal of this study was to perform a spatially resolved study of the effect of a stress concentration such as a notch or a crack on hydride reorientation. Using SEM and image analysis, it was found that a sharp crack induces a different hydride microstructure than a blunt notch. In the case of sharp crack, hydrides are more localized and align more with the defect than for blunt notches. The hydride connectivity also increases close to a stress concentration which will assist in crack propagation during DHC. Using TEM, the microstructure of hydrides grown near crack tips were observed to be similar to that of circumferential hydrides grown in the bulk. The orientation relationship studied with SEM and micro-X-ray diffraction was found to be in most cases δ(111)// α(0002) for hydrides grown both near and far from stress concentrations. Using the same micro-X-ray diffraction technique local hydride and matrix elastic strains were measured and observed to vary significantly from grain to grain. It was however observed that hydrides grown close to the stress concentration are in tension in the face of the platelet, similar to reoriented hydrides, while those grown far from the stress concentration are in tension, similar to circumferential hydrides. The orders of magnitude of the measured strains in the hydrides and the zirconium matrix compared well to those predicted by finite element models. This study shows that it is possible to study hydride dissolution and precipitation in-situ using time-dependent techniques. It was found that the precipitation temperature is lowered by hydride reorientation. The evolution of hydride strains during precipitation was found to be different for unstressed, stressed and reoriented hydrides. The reoriented hydride fraction and connectivity increase with number of cycles which could lead to more dangerous microstructure for storage of spent fuel. Pre-existing cracks were also found to affect hydride connectivity and morphology which directly impacts DHC and fuel integrity. (Abstract shortened by UMI.).

Ochratoxin A production in relation to ecophysiological factors by Aspergillus section Nigri strains isolated from different substrates in Argentina.

PubMed

Astoreca, A; Magnoli, C; Barberis, C; Chiacchiera, S M; Combina, M; Dalcero, A

2007-12-15

Contamination of foodstuff with mycotoxins such as ochratoxins is a major matter of concern for human and animal health. In Aspergillus species, ochratoxin synthesis depends on several environmental factors. The aims of this work were to evaluate the effect of water activity (0.995-0.85), temperature (15, 25 and 30 degrees C), incubation time (7, 14 and 21 days) and their interactions on OTA production on peanut, maize kernels, dried grapes and coffee beans meal extract agar medium by eight strains of Aspergillus section Nigri isolated from human food in Argentina. The optimum temperature for OTA production was 25 or 30 degrees C depending on the strains assayed, in most cases the highest OTA levels were achieved after 7 days of incubation, whereas this situation occurred at 15 degrees C after 14 days of incubation for only one strain. The maximum OTA level was obtained at earlier growth states when incubation temperature increased. In general, OTA concentration increased as water activity (a(W)) increased with no significant production at 0.85-0.91 a(W) under all temperature levels tested. Production occurred over a range of temperatures (15-30 degrees C) with optimum production at 30 degrees C depending on a(W) assayed. The knowledge of Aspergillus section Nigri ecophysiology is critical in the development and prediction of the risk models of raw material and final product contamination by these species under fluctuating and interacting environmental parameters.

High-resolution spatiotemporal strain mapping reveals non-uniform deformation in micropatterned elastomers

NASA Astrophysics Data System (ADS)

Aksoy, B.; Rehman, A.; Bayraktar, H.; Alaca, B. E.

2017-04-01

Micropatterns are generated on a vast selection of polymeric substrates for various applications ranging from stretchable electronics to cellular mechanobiological systems. When these patterned substrates are exposed to external loading, strain field is primarily affected by the presence of microfabricated structures and similarly by fabrication-related defects. The capturing of such nonhomogeneous strain fields is of utmost importance in cases where study of the mechanical behavior with a high spatial resolution is necessary. Image-based non-contact strain measurement techniques are favorable and have recently been extended to scanning tunneling microscope and scanning electron microscope images for the characterization of mechanical properties of metallic materials, e.g. steel and aluminum, at the microscale. A similar real-time analysis of strain heterogeneity in elastomers is yet to be achieved during the entire loading sequence. The available measurement methods for polymeric materials mostly depend on cross-head displacement or precalibrated strain values. Thus, they suffer either from the lack of any real-time analysis, spatiotemporal distribution or high resolution in addition to a combination of these factors. In this work, these challenges are addressed by integrating a tensile stretcher with an inverted optical microscope and developing a subpixel particle tracking algorithm. As a proof of concept, the patterns with a critical dimension of 200 µm are generated on polydimethylsiloxane substrates and strain distribution in the vicinity of the patterns is captured with a high spatiotemporal resolution. In the field of strain measurement, there is always a tradeoff between minimum measurable strain value and spatial resolution. Current noncontact techniques on elastomers can deliver a strain resolution of 0.001% over a minimum length of 5 cm. More importantly, inhomogeneities within this quite large region cannot be captured. The proposed technique can overcome this challenge and provides a displacement measurement resolution of 116 nm and a strain resolution of 0.04% over a gage length of 300 µm. Similarly, the ability to capture inhomogeneities is demonstrated by mapping strain around a thru-hole. The robustness of the technique is also evaluated, where no appreciable change in strain measurement is observed despite the significant variations imposed on the measurement mesh. The proposed approach introduces critical improvements for the determination of displacement and strain gradients in elastomers regarding the real-time nature of strain mapping with a microscale spatial resolution.

Strain amplitude-dependent anelasticity in Cu-Ni solid solution due to thermally activated and athermal dislocation-point obstacle interactions

NASA Astrophysics Data System (ADS)

Kustov, S.; Gremaud, G.; Benoit, W.; Golyandin, S.; Sapozhnikov, K.; Nishino, Y.; Asano, S.

1999-02-01

Experimental investigations of the internal friction and the Young's modulus defect in single crystals of Cu-(1.3-7.6) at. % Ni have been performed for 7-300 K over a wide range of oscillatory strain amplitudes. Extensive data have been obtained at a frequency of vibrations around 100 kHz and compared with the results obtained for the same crystals at a frequency of ˜1 kHz. The strain amplitude dependence of the anelastic strain amplitude and the average friction stress acting on a dislocation due to solute atoms are also analyzed. Several stages in the strain amplitude dependence of the internal friction and the Young's modulus defect are revealed for all of the alloy compositions, at different temperatures and in different frequency ranges. For the 100 kHz frequency, low temperatures and low strain amplitudes (˜10-7-10-5), the amplitude-dependent internal friction and the Young's modulus defect are essentially temperature independent, and are ascribed to a purely hysteretic internal friction component. At higher strain amplitudes, a transition stage and a steep strain amplitude dependence of the internal friction and the Young's modulus defect are observed, followed by saturation at the highest strain amplitudes employed. These stages are temperature and frequency dependent and are assumed to be due to thermally activated motion of dislocations. We suggest that the observed regularities in the entire strain amplitude, temperature and frequency ranges correspond to a motion of dislocations in a two-component system of obstacles: weak but long-range ones, due to the elastic interaction of dislocations with solute atoms distributed in the bulk of the crystal; and strong short-range ones, due to the interaction of dislocations with solute atoms distributed close to dislocation glide planes. Based on these assumptions, a qualitative explanation is given for the variety of experimental observations.

Anticancer potential of pyrrole (1, 2, a) pyrazine 1, 4, dione, hexahydro 3-(2-methyl propyl) (PPDHMP) extracted from a new marine bacterium, Staphylococcus sp. strain MB30.

PubMed

Lalitha, P; Veena, V; Vidhyapriya, P; Lakshmi, Pragna; Krishna, R; Sakthivel, N

2016-05-01

Marine bacterium, strain MB30 isolated from the deep sea sediment of Bay of Bengal, India, exhibited antimicrobial activity against human pathogenic bacteria. Based on the 16S rRNA sequence homology and subsequent phylogenetic tree analysis, the strain MB30 was identified as Staphylococcus sp. The bioactive metabolite produced by the strain MB30 was purified through silica gel column chromatography and preparative HPLC. Purified metabolite was further characterized by FT-IR, LC-MS and NMR analyses. On the basis of spectroscopic data, the metabolite was identified as pyrrole (1, 2, a) pyrazine 1, 4, dione, hexahydro 3-(2-methyl propyl) (PPDHMP). The PPDHMP exhibited in vitro anticancer potential against lung (A549) and cervical (HeLa) cancer cells in a dose-dependent manner with the IC50 concentration of 19.94 ± 1.23 and 16.73 ± 1.78 μg ml(-1) respectively. The acridine orange (AO)/ethidium bromide (EB) and 4,6-diamidino-2-phenylindole dihydrochloride (DAPI) staining of the IC50 concentration of PPDHMP-treated cancer cells exhibited an array of morphological changes such as nuclear condensation, cell shrinkage and formation of apoptotic bodies. The PPDHMP-treated cancer cells induced the progressive accumulation of fragmented DNA in a time-dependent manner. Based on the flow cytometric analysis, it has become evident that the compound was also effective in arresting the cell cycle at G1 phase. Further, the Western blotting analysis confirmed the down-regulation of cyclin-D1, cyclin dependent kinase (CDK-2), anti-apoptotic Bcl-2 family proteins (Bcl-2 and Bcl-xL), activation of caspase-9 and 3 with the cleavage of PARP. The PPDHMP-treated cancer cells also showed the inhibition of migration and invasive capacity of cancer cells. In the present investigation, for the first time, we have reported the extraction, purification and characterization of an anticancer metabolite, PPDHMP from a new marine bacterium, Staphylococcus sp. strain MB30.

Strain Localization and Weakening Processes in Viscously Deforming Rocks: Numerical Modeling Based on Laboratory Torsion Experiments

NASA Astrophysics Data System (ADS)

Doehmann, M.; Brune, S.; Nardini, L.; Rybacki, E.; Dresen, G.

2017-12-01

Strain localization is an ubiquitous process in earth materials observed over a broad range of scales in space and time. Localized deformation and the formation of shear zones and faults typically involves material softening by various processes, like shear heating and grain size reduction. Numerical modeling enables us to study the complex physical and chemical weakening processes by separating the effect of individual parameters and boundary conditions. Using simple piece-wise linear functions for the parametrization of weakening processes allows studying a system at a chosen (lower) level of complexity (e.g. Cyprych et al., 2016). In this study, we utilize a finite element model to test two weakening laws that reduce the strength of the material depending on either the I) amount of accumulated strain or II) deformational work. Our 2D Cartesian models are benchmarked to single inclusion torsion experiments performed at elevated temperatures of 900 °C and pressures of up to 400 MPa (Rybacki et al., 2014). The experiments were performed on Carrara marble samples containing a weak Solnhofen limestone inclusion at a maximum strain rate of 2.0*10-4 s-1. Our models are designed to reproduce shear deformation of a hollow cylinder equivalent to the laboratory setup, such that material leaving one side of the model in shear direction enters again on the opposite side using periodic boundary conditions. Similar to the laboratory tests, we applied constant strain rate and constant stress boundary conditions.We use our model to investigate the time-dependent distribution of stress and strain and the effect of different parameters. For instance, inclusion rotation is shown to be strongly dependent on the viscosity ratio between matrix and inclusion and stronger ductile weakening increases the localization rate while decreasing shear zone width. The most suitable weakening law for representation of ductile rock is determined by combining the results of parameter tests with the comparison of our numerical models to the torsion experiments. In the future, this law will be applied first to investigate shear zone formation and then study localization in larger scale rift models.Cyprych, D. et al. (2016). Geochem Geophys, 17(9), 3608-3628. Rybacki, E. (2014). Tectonophysics, 634, 182-197.

Relationships of left ventricular strain and strain rate to wall stress and their afterload dependency.

PubMed

Murai, Daisuke; Yamada, Satoshi; Hayashi, Taichi; Okada, Kazunori; Nishino, Hisao; Nakabachi, Masahiro; Yokoyama, Shinobu; Abe, Ayumu; Ichikawa, Ayako; Ono, Kota; Kaga, Sanae; Iwano, Hiroyuki; Mikami, Taisei; Tsutsui, Hiroyuki

2017-05-01

Whether and how left ventricular (LV) strain and strain rate correlate with wall stress is not known. Furthermore, it is not determined whether strain or strain rate is less dependent on the afterload. In 41 healthy young adults, LV global peak strain and systolic peak strain rate in the longitudinal direction (LS and LSR, respectively) and circumferential direction (CS and CSR, respectively) were measured layer-specifically using speckle tracking echocardiography (STE) before and during a handgrip exercise. Among all the points before and during the exercise, all the STE parameters significantly correlated linearly with wall stress (LS: r = -0.53, p < 0.01, LSR: r = -0.28, p < 0.05, CS in the inner layer: r = -0.72, p < 0.01, CSR in the inner layer: r = -0.47, p < 0.01). Strain more strongly correlated with wall stress than strain rate (r = -0.53 for LS vs. r = -0.28 for LSR, p < 0.05; r = -0.72 for CS vs. r = -0.47 for CSR in the inner layer, p < 0.05), whereas the interobserver variability was similar between strain and strain rate (longitudinal 6.2 vs. 5.2 %, inner circumferential 4.8 vs. 4.7 %, mid-circumferential 7.9 vs. 6.9 %, outer circumferential 10.4 vs. 9.7 %), indicating that the differences in correlation coefficients reflect those in afterload dependency. It was thus concluded that LV strain and strain rate linearly and inversely correlated with wall stress in the longitudinal and circumferential directions, and strain more strongly depended on afterload than did strain rate. Myocardial shortening should be evaluated based on the relationships between these parameters and wall stress.

DaDyn-RS: a tool for the time-dependent simulation of damage, fluid pressure and long-term instability in alpine rock slopes

NASA Astrophysics Data System (ADS)

Riva, Federico; Agliardi, Federico; Amitrano, David; Crosta, Giovanni B.

2017-04-01

Large mountain slopes in alpine environments undergo a complex long-term evolution from glacial to postglacial environments, through a transient period of paraglacial readjustment. During and after this transition, the interplay among rock strength, topographic relief, and morpho-climatic drivers varying in space and time can lead to the development of different types of slope instability, from sudden catastrophic failures to large, slow, long-lasting yet potentially catastrophic rockslides. Understanding the long-term evolution of large rock slopes requires accounting for the time-dependence of deglaciation unloading, permeability and fluid pressure distribution, displacements and failure mechanisms. In turn, this is related to a convincing description of rock mass damage processes and to their transition from a sub-critical (progressive failure) to a critical (catastrophic failure) character. Although mechanisms of damage occurrence in rocks have been extensively studied in the laboratory, the description of time-dependent damage under gravitational load and variable external actions remains difficult. In this perspective, starting from a time-dependent model conceived for laboratory rock deformation, we developed Dadyn-RS, a tool to simulate the long-term evolution of real, large rock slopes. Dadyn-RS is a 2D, FEM model programmed in Matlab, which combines damage and time-to-failure laws to reproduce both diffused damage and strain localization meanwhile tracking long-term slope displacements from primary to tertiary creep stages. We implemented in the model the ability to account for rock mass heterogeneity and property upscaling, time-dependent deglaciation, as well as damage-dependent fluid pressure occurrence and stress corrosion. We first tested DaDyn-RS performance on synthetic case studies, to investigate the effect of the different model parameters on the mechanisms and timing of long-term slope behavior. The model reproduces complex interactions between topography, deglaciation rate, mechanical properties and fluid pressure occurrence, resulting in different kinematics, damage patterns and timing of slope instabilities. We assessed the role of groundwater on slope damage and deformation mechanisms by introducing time-dependent pressure cycling within simulations. Then, we applied DaDyn-RS to real slopes located in the Italian Central Alps, affected by an active rockslide and a Deep Seated Gravitational Slope Deformation, respectively. From Last Glacial Maximum to present conditions, our model allows reproducing in an explicitly time-dependent framework the progressive development of damage-induced permeability, strain localization and shear band differentiation at different times between the Lateglacial period and the Mid-Holocene climatic transition. Different mechanisms and timings characterize different styles of slope deformations, consistently with available dating constraints. DaDyn-RS is able to account for different long-term slope dynamics, from slow creep to the delayed transition to fast-moving rockslides.

Internal state variable plasticity-damage modeling of AISI 4140 steel including microstructure-property relations: temperature and strain rate effects

NASA Astrophysics Data System (ADS)

Nacif el Alaoui, Reda

Mechanical structure-property relations have been quantified for AISI 4140 steel. under different strain rates and temperatures. The structure-property relations were used. to calibrate a microstructure-based internal state variable plasticity-damage model for. monotonic tension, compression and torsion plasticity, as well as damage evolution. Strong stress state and temperature dependences were observed for the AISI 4140 steel. Tension tests on three different notched Bridgman specimens were undertaken to study. the damage-triaxiality dependence for model validation purposes. Fracture surface. analysis was performed using Scanning Electron Microscopy (SEM) to quantify the void. nucleation and void sizes in the different specimens. The stress-strain behavior exhibited. a fairly large applied stress state (tension, compression dependence, and torsion), a. moderate temperature dependence, and a relatively small strain rate dependence.

Lattice Rotation Patterns and Strain Gradient Effects in Face-Centered-Cubic Single Crystals Under Spherical Indentation

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

Gao, Y. F.; Larson, B. C.; Lee, J. H.

Strain gradient effects are commonly modeled as the origin of the size dependence of material strength, such as the dependence of indentation hardness on contact depth and spherical indenter radius. However, studies on the microstructural comparisons of experiments and theories are limited. First, we have extended a strain gradient Mises-plasticity model to its crystal plasticity version and implemented a finite element method to simulate the load-displacement response and the lattice rotation field of Cu single crystals under spherical indentation. The strain gradient simulations demonstrate that the forming of distinct sectors of positive and negative angles in the lattice rotation fieldmore » is governed primarily by the slip geometry and crystallographic orientations, depending only weakly on strain gradient effects, although hardness depends strongly on strain gradients. Second, the lattice rotation simulations are compared quantitatively with micron resolution, three-dimensional X-ray microscopy (3DXM) measurements of the lattice rotation fields under 100mN force, 100 mu m radius spherical indentations in < 111 >, < 110 >, and < 001 > oriented Cu single crystals. Third, noting the limitation of continuum strain gradient crystal plasticity models, two-dimensional discrete dislocation simulation results suggest that the hardness in the nanocontact regime is governed synergistically by a combination of strain gradients and source-limited plasticity. However, the lattice rotation field in the discrete dislocation simulations is found to be insensitive to these two factors but to depend critically on dislocation obstacle densities and strengths.« less

Biomechanical remodeling of obstructed guinea pig jejunum

PubMed Central

Zhao, Jingbo; Liao, Donghua; Yang, Jian; Gregersen, Hans

2010-01-01

Data on morphological and biomechanical remodeling are needed to understand the mechanisms behind intestinal obstruction. The effect of partial obstruction on mechanical properties with reference to the zero-stress state and on the histomorphological properties of the guinea pig small intestine was determined in this study. Partial obstruction and sham operation were surgically created in mid-jejunum of guinea pigs. The animals survived 2, 4, 7, and 14 days respectively. The age-matched guinea pigs that were not operated served as normal controls. The segment proximal to the obstruction site was used for histological analysis, no-load state and zero-stress state data, and distension test. The segment for distension was immersed in an organ bath and inflated to 10 cmH20. The outer diameter change during the inflation was monitored using a microscope with CCD camera. Circumferential stresses and strains were computed from the diameter, pressure and the zero-stress state data. The opening angle and absolute value of residual strain decreased (P<0.01 and P<0.001) whereas the wall thickness, wall cross-sectional area, and the wall stiffness increased after 7 days obstruction (P<0.05, P<0.01). Histologically, the muscle and submucosa layers, especially the circumferential muscle layer increased in thickness after obstruction. The opening angle and residual strain mainly depended on the thickness of the muscle layer whereas the wall stiffness mainly depended on the thickness of the submucosa layer. In conclusion, the histomorphological and biomechanical properties of small intestine (referenced for the first time to the zero-stress state) remodel proximal to the obstruction site in a time-dependent manner. PMID:20189575

Oscillatory shear response of moisture barrier coatings containing clay of different shape factor.

PubMed

Kugge, C; Vanderhoek, N; Bousfield, D W

2011-06-01

Oscillatory shear rheology of barrier coatings based on dispersed styrene-butadiene latex and clay of various shape factors or aspect ratio has been explored. Barrier performance of these coatings when applied to paperboard has been assessed in terms of water vapour transmission rates and the results related to shape factor, dewatering and critical strain. It has been shown that a system based on clay with high shape factor gives a lower critical strain, dewatering and water vapour transmission rate compared with clays of lower shape factor. The dissipated energy, as calculated from an amplitude sweep, indicated no attractive interaction between clay and latex implying a critical strain that appears to be solely dependent on the shape factor at a constant volume fraction. Particle size distribution was shown to have no effect on the critical strain while coatings of high elasticity exhibited high yield strains as expected. The loss modulus demonstrated strain hardening before the elastic to viscous transition. The loss modulus peak was identified by a maximum strain which was significantly lower for a coating based on clay with a high shape factor. The characteristic elastic time was found to vary between 0.6 and 1.3s. The zero shear viscosity of barrier dispersion coatings were estimated from the characteristic elastic time and the characteristic modulus to be of the order of 25-100 Pa s. Copyright © 2011 Elsevier Inc. All rights reserved.

A real-time heat strain risk classifier using heart rate and skin temperature.

PubMed

Buller, Mark J; Latzka, William A; Yokota, Miyo; Tharion, William J; Moran, Daniel S

2008-12-01

Heat injury is a real concern to workers engaged in physically demanding tasks in high heat strain environments. Several real-time physiological monitoring systems exist that can provide indices of heat strain, e.g. physiological strain index (PSI), and provide alerts to medical personnel. However, these systems depend on core temperature measurement using expensive, ingestible thermometer pills. Seeking a better solution, we suggest the use of a model which can identify the probability that individuals are 'at risk' from heat injury using non-invasive measures. The intent is for the system to identify individuals who need monitoring more closely or who should apply heat strain mitigation strategies. We generated a model that can identify 'at risk' (PSI 7.5) workers from measures of heart rate and chest skin temperature. The model was built using data from six previously published exercise studies in which some subjects wore chemical protective equipment. The model has an overall classification error rate of 10% with one false negative error (2.7%), and outperforms an earlier model and a least squares regression model with classification errors of 21% and 14%, respectively. Additionally, the model allows the classification criteria to be adjusted based on the task and acceptable level of risk. We conclude that the model could be a valuable part of a multi-faceted heat strain management system.

Characteristics of strain-sensitive photonic crystal cavities in a flexible substrate.

PubMed

No, You-Shin; Choi, Jae-Hyuck; Kim, Kyoung-Ho; Park, Hong-Gyu

2016-11-14

High-index semiconductor photonic crystal (PhC) cavities in a flexible substrate support strong and tunable optical resonances that can be used for highly sensitive and spatially localized detection of mechanical deformations in physical systems. Here, we report theoretical studies and fundamental understandings of resonant behavior of an optical mode excited in strain-sensitive rod-type PhC cavities consisting of high-index dielectric nanorods embedded in a low-index flexible polymer substrate. Using the three-dimensional finite-difference time-domain simulation method, we calculated two-dimensional transverse-electric-like photonic band diagrams and the three-dimensional dispersion surfaces near the first Γ-point band edge of unidirectionally strained PhCs. A broken rotational symmetry in the PhCs modifies the photonic band structures and results in the asymmetric distributions and different levels of changes in normalized frequencies near the first Γ-point band edge in the reciprocal space, which consequently reveals strain-dependent directional optical losses and selected emission patterns. The calculated electric fields, resonant wavelengths, and quality factors of the band-edge modes in the strained PhCs show an excellent agreement with the results of qualitative analysis of modified dispersion surfaces. Furthermore, polarization-resolved time-averaged Poynting vectors exhibit characteristic dipole-like emission patterns with preferentially selected linear polarizations, originating from the asymmetric band structures in the strained PhCs.

Longitudinal changes in MRI markers in a reversible unilateral ureteral obstruction mouse model: preliminary experience.

PubMed

Haque, Muhammad E; Franklin, Tammy; Bokhary, Ujala; Mathew, Liby; Hack, Bradley K; Chang, Anthony; Puri, Tipu S; Prasad, Pottumarthi V

2014-04-01

To evaluate longitudinal changes in renal oxygenation and diffusion measurements in a model of reversible unilateral ureteral obstruction (rUUO) which has been shown to induce chronic renal functional deficits in a strain dependent way. C57BL/6 mice show higher degree of functional deficit compared with BALB/c mice. Because hypoxia and development of fibrosis are associated with chronic kidney diseases and are responsible for progression, we hypothesized that MRI measurements would be able to monitor the longitudinal changes in this model and will show strain dependent differences in response. Here blood oxygenation level dependent (BOLD) and diffusion MRI measurements were performed at three time points over a 30 day period in mice with rUUO. The studies were performed on a 4.7T scanner with the mice anesthetized with isoflurane before UUO, 2 and 28 days postrelease of 6 days of obstruction. We found at the early time point (∼2 days after releasing the obstruction), the relative oxygenation in C57Bl/6 mice were lower compared with BALB/c. Diffusion measurements were lower at this time point and reached statistical significance in BALB/c These methods may prove valuable in better understanding the natural progression of kidney diseases and in evaluating novel interventions to limit progression. Copyright © 2013 Wiley Periodicals, Inc.

Use of the Microbial Growth Curve in Postantibiotic Effect Studies of Legionella pneumophila

PubMed Central

Smith, Raymond P.; Baltch, Aldona L.; Michelsen, Phyllis B.; Ritz, William J.; Alteri, Richard

2003-01-01

Using the standard Craig and Gudmundsson method (W. A. Craig and S. Gudmundsson, p. 296-329, in V. Lorian, ed., Antibiotics in Laboratory Medicine, 1996) as a guideline for determination of postantibiotic effects (PAE), we studied a large series of growth curves for two strains of Legionella pneumophila. We found that the intensity of the PAE was best determined by using a statistically fitted line over hours 3 to 9 following antibiotic removal. We further determined the PAE duration by using a series of observations of the assay interval from hours 3 to 24. We determined that inoculum reduction was not necessarily the only predictor of the PAE but that the PAE was subject to the type and dose of the drug used in the study. In addition, there was a variation between strains. Only levofloxacin at five and ten times the minimum inhibitory concentration (MIC) resulted in a PAE duration of 4 to 10 h for both strains of L. pneumophila tested. Ciprofloxacin at five and ten times the MIC and azithromycin at ten times the MIC caused a PAE for one strain only. No PAE could be demonstrated for either strain with erythromycin or doxycycline. Using the presently described method of measuring PAE for L. pneumophila, we were able to detect differences in PAE which were dependent upon the L. pneumophila strain, the antibiotic tested, and the antibiotic concentration. We suggest the use of mathematically fitted curves for comparison of bacterial growth in order to measure PAE for L. pneumophila. PMID:12604545

Dynamic strain aging and plastic instabilities

NASA Astrophysics Data System (ADS)

Mesarovic, Sinisa Dj.

1995-05-01

A constitutive model proposed by McCormick [(1988) Theory of flow localization due to dynamic strain ageing. Acta. Metall.36, 3061-3067] based on dislocation-solute interaction and describing dynamic strain aging behavior, is analyzed for the simple loading case of uniaxial tension. The model is rate dependent and includes a time-varying state variable, representing the local concentration of the impurity atoms at dislocations. Stability of the system and its post-instability behavior are considered. The methods used include analytical and numerical stability and bifurcation analysis with a numerical continuation technique. Yield point behavior and serrated yielding are found to result for well defined intervals of temperature and strain rate. Serrated yielding emerges as a branch of periodic solutions of the relaxation oscillation type, similar to frictional stick-slip. The distinction between the temporal and spatial (loss of homogeneity of strain) instability is emphasized. It is found that a critical machine stiffness exists above which a purely temporal instability cannot occur. The results are compared to the available experimental data.

Experiments and Model for Serration Statistics in Low-Entropy, Medium-Entropy, and High-Entropy Alloys

DOE PAGES

Carroll, Robert; Lee, Chi; Tsai, Che-Wei; ...

2015-11-23

In this study, high-entropy alloys (HEAs) are new alloys that contain five or more elements in roughly-equal proportion. We present new experiments and theory on the deformation behavior of HEAs under slow stretching (straining), and observe differences, compared to conventional alloys with fewer elements. For a specific range of temperatures and strain-rates, HEAs deform in a jerky way, with sudden slips that make it difficult to precisely control the deformation. An analytic model explains these slips as avalanches of slipping weak spots and predicts the observed slip statistics, stress-strain curves, and their dependence on temperature, strain-rate, and material composition. Themore » ratio of the weak spots’ healing rate to the strain-rate is the main tuning parameter, reminiscent of the Portevin- LeChatellier effect and time-temperature superposition in polymers. Our model predictions agree with the experimental results. The proposed widely-applicable deformation mechanism is useful for deformation control and alloy design.« less

Creep fatigue life prediction for engine hot section materials (isotropic)

NASA Technical Reports Server (NTRS)

Moreno, Vito; Nissley, David; Lin, Li-Sen Jim

1985-01-01

The first two years of a two-phase program aimed at improving the high temperature crack initiation life prediction technology for gas turbine hot section components are discussed. In Phase 1 (baseline) effort, low cycle fatigue (LCF) models, using a data base generated for a cast nickel base gas turbine hot section alloy (B1900+Hf), were evaluated for their ability to predict the crack initiation life for relevant creep-fatigue loading conditions and to define data required for determination of model constants. The variables included strain range and rate, mean strain, strain hold times and temperature. None of the models predicted all of the life trends within reasonable data requirements. A Cycle Damage Accumulation (CDA) was therefore developed which follows an exhaustion of material ductility approach. Material ductility is estimated based on observed similarities of deformation structure between fatigue, tensile and creep tests. The cycle damage function is based on total strain range, maximum stress and stress amplitude and includes both time independent and time dependent components. The CDA model accurately predicts all of the trends in creep-fatigue life with loading conditions. In addition, all of the CDA model constants are determinable from rapid cycle, fully reversed fatigue tests and monotonic tensile and/or creep data.

Work-family conflict and sleep disturbance: the Malaysian working women study.

PubMed

Aazami, Sanaz; Mozafari, Mosayeb; Shamsuddin, Khadijah; Akmal, Syaqirah

2016-01-01

This study aimed at assessing effect of the four dimensions of work-family conflicts (strain and time-based work interference into family and family interference into work) on sleep disturbance in Malaysian working women. This cross-sectional study was conducted among 325 Malaysian married working women. Multiple-stage simple random sampling method was used to recruit women from public service departments of Malaysia. Self-administrated questionnaires were used to measure the study variables and data were analyzed using SPSS version 21. We found that high level of the four dimensions of work-family conflicts significantly increase sleep disturbance. Our analyses also revealed an age-dependent effect of the work-family conflict on sleep disturbance. Women in their 20 to 30 yr old suffer from sleep disturbance due to high level of time-based and strain-based work-interference into family. However, the quality of sleep among women aged 30-39 were affected by strain-based family-interference into work. Finally, women older than 40 yr had significantly disturbed sleep due to strain-based work-interference into family as well as time-based family interference into work. Our findings showed that sleep quality of working women might be disturbed by experiencing high level of work-family conflict. However, the effects of inter-role conflicts on sleep varied among different age groups.

Creep and Rupture Strength of an Advanced CVD SiC Fiber

NASA Technical Reports Server (NTRS)

Goldsby, J. C.; Yun, H. M.; DiCarlo, J. A.

1997-01-01

In the as-produced condition the room temperature strength (approx. 6 GPa) of Textron Specialty Materials' 50 microns CVD SiC fiber represents the highest value thus far obtained for commercially produced polycrystalline SiC fibers. To understand whether this strength can be maintained after composite processing conditions, high temperature studies were performed on the effects of time, stress, and environment on 1400 deg. C tensile creep strain and stress rupture on as-produced, chemically vapor deposited SiC fibers. Creep strain results were consistent, allowing an evaluation of time and stress effects. Test environment had no influence on creep strain but I hour annealing at 1600 deg. C in argon gas significantly reduced the total creep strain and increased the stress dependence. This is attributed to changes in the free carbon morphology and its distribution within the CVD SiC fiber. For the as-produced and annealed fibers, strength at 1400 deg. C was found to decrease from a fast fracture value of 2 GPa to a 100-hr rupture strength value of 0. 8 GPa. In addition a loss of fast fracture strength from 6 GPa is attributed to thermally induced changes in the outer carbon coating and microstructure. Scatter in rupture times made a definitive analysis of environmental and annealing effects on creep strength difficult.

Verification of Experimental Techniques for Flow Surface Determination

NASA Technical Reports Server (NTRS)

Lissenden, Cliff J.; Lerch, Bradley A.; Ellis, John R.; Robinson, David N.

1996-01-01

The concept of a yield surface is central to the mathematical formulation of a classical plasticity theory. However, at elevated temperatures, material response can be highly time-dependent, which is beyond the realm of classical plasticity. Viscoplastic theories have been developed for just such conditions. In viscoplastic theories, the flow law is given in terms of inelastic strain rate rather than the inelastic strain increment used in time-independent plasticity. Thus, surfaces of constant inelastic strain rate or flow surfaces are to viscoplastic theories what yield surfaces are to classical plasticity. The purpose of the work reported herein was to validate experimental procedures for determining flow surfaces at elevated temperatures. Since experimental procedures for determining yield surfaces in axial/torsional stress space are well established, they were employed -- except inelastic strain rates were used rather than total inelastic strains. In yield-surface determinations, the use of small-offset definitions of yield minimizes the change of material state and allows multiple loadings to be applied to a single specimen. The key to the experiments reported here was precise, decoupled measurement of axial and torsional strain. With this requirement in mind, the performance of a high-temperature multi-axial extensometer was evaluated by comparing its results with strain gauge results at room temperature. Both the extensometer and strain gauges gave nearly identical yield surfaces (both initial and subsequent) for type 316 stainless steel (316 SS). The extensometer also successfully determined flow surfaces for 316 SS at 650 C. Furthermore, to judge the applicability of the technique for composite materials, yield surfaces were determined for unidirectional tungsten/Kanthal (Fe-Cr-Al).

Survival of genetically modified and self-cloned strains of commercial baker's yeast in simulated natural environments: environmental risk assessment.

PubMed

Ando, Akira; Suzuki, Chise; Shima, Jun

2005-11-01

Although genetic engineering techniques for baker's yeast might improve the yeast's fermentation characteristics, the lack of scientific data on the survival of such strains in natural environments as well as the effects on human health prevent their commercial use. Disruption of acid trehalase gene (ATH1) improves freeze tolerance, which is a crucial characteristic in frozen-dough baking. In this study, ATH1 disruptants constructed by genetic modification (GM) and self-cloning (SC) techniques were used as models to study such effects because these strains have higher freeze tolerance and are expected to be used commercially. Behavior of the strains in simulated natural environments, namely, in soil and water, was studied by measuring the change in the number of viable cells and in the concentration of DNA that contains ATH1 loci. Measurements were made using a real-time PCR method during 40 days of cultivation. Results showed that the number of viable cells of GM and SC strains decreased in a time-dependent manner and that the decrease rate was nearly equal to or higher than that for wild-type (WT) yeast. For all three strains (SC, GM, and WT) in the two simulated natural environments (water and soil), the DNA remained longer than did viable cells but the decrease patterns of either the DNA or the viable cells of SC and GM strains had tendencies similar to those of the WT strain. In conclusion, disruption of ATH1 by genetic engineering apparently does not promote the survival of viable cells and DNA in natural environments.

Development of a high-sensitivity strain measurement system based on a SH SAW sensor

NASA Astrophysics Data System (ADS)

Oh, Haekwan; Lee, Keekeun; Eun, Kyoungtae; Choa, Sung-Hoon; Yang, Sang Sik

2012-02-01

A strain measurement system based on a shear horizontal surface acoustic wave (SH SAW) was developed. The developed system is composed of a SAW microsensor, a printed circuit board (PCB), an adhesive and a strain gauge. When a compression force is applied to the PCB by the strain gauge, the PCB is bent so that external strain energy can be evenly delivered to the microsensor without any detachment of the sensor from the board. When a stretching force is applied to the PCB under the condition that one side of the PCB is fixed and the other side is modulated, the actual length of the SAW delay line between the two interdigital transducers (IDTs) is increased. The increase in the delay line length causes a change in the time for the propagating SAW to reach the output IDT. If strain energy is applied to the piezoelectric substrate, the substrate density is changed, which then changes the propagation velocity of the SAW. Coupling-of-modes modeling was conducted prior to fabrication to determine the optimal device parameters. Depending on the strain, the frequency difference was linearly modulated. The obtained sensitivity for stretching was 17.3 kHz/% for the SH wave mode and split electrode. And the obtained sensitivity for bending was 46.1 kHz/% for the SH wave mode and split electrode. The SH wave showed about 15% higher sensitivity than the Rayleigh wave, and the dog-bone PCB showed about 8% higher sensitivity than the rectangular PCB. The obtained sensitivity was about five times higher than that of existing SAW-based strain sensors.

Brittle Creep of Tournemire Shale: Orientation, Temperature and Pressure Dependences

NASA Astrophysics Data System (ADS)

Geng, Zhi; Bonnelye, Audrey; Dick, Pierre; David, Christian; Chen, Mian; Schubnel, Alexandre

2017-04-01

Time and temperature dependent rock deformation has both scientific and socio-economic implications for natural hazards, the oil and gas industry and nuclear waste disposal. During the past decades, most studies on brittle creep have focused on igneous rocks and porous sedimentary rocks. To our knowledge, only few studies have been carried out on the brittle creep behavior of shale. Here, we conducted a series of creep experiments on shale specimens coming from the French Institute for Nuclear Safety (IRSN) underground research laboratory located in Tournemire, France. Conventional tri-axial experiments were carried under two different temperatures (26˚ C, 75˚ C) and confining pressures (10 MPa, 80 MPa), for three orientations (σ1 along, perpendicular and 45˚ to bedding). Following the methodology developed by Heap et al. [2008], differential stress was first increased to ˜ 60% of the short term peak strength (10-7/s, Bonnelye et al. 2016), and then in steps of 5 to 10 MPa every 24 hours until brittle failure was achieved. In these long-term experiments (approximately 10 days), stress and strains were recorded continuously, while ultrasonic acoustic velocities were recorded every 1˜15 minutes, enabling us to monitor the evolution of elastic wave speed anisotropy. Temporal evolution of anisotropy was illustrated by inverting acoustic velocities to Thomsen parameters. Finally, samples were investigated post-mortem using scanning electron microscopy. Our results seem to contradict our traditional understanding of loading rate dependent brittle failure. Indeed, the brittle creep failure stress of our Tournemire shale samples was systematically observed ˜50% higher than its short-term peak strength, with larger final axial strain accumulated. At higher temperatures, the creep failure strength of our samples was slightly reduced and deformation was characterized with faster 'steady-state' creep axial strain rates at each steps, and larger final axial strain accumulated. At each creep step, ultrasonic wave velocities first decreased, and then increased gradually. The magnitude of elastic wave velocity variations showed an important orientation and temperature dependence. Velocities measured perpendicular to bedding showed increased variation, variation that was enhanced at higher temperature and higher pressure. The case of complete elastic anisotropy reversal was even observed for sample deformed perpendicular to bedding, with a reduction amount of axial strain needed to reach anisotropy reversal at higher temperature. Our data were indicative of competition between crack growth, sealing/healing, and possibly mineral rotation or anisotropic compaction during creep. SEM investigation confirmed evidence of time dependent pressure solution and crack sealing/healing. Our research not only has practical engineering consequence but, more importantly, can provide valuable insights into the underlying mechanisms of creep in complex media like shale. In particular, our study highlights that the short-term peak strength has little meaning in shale material, which can over-consolidate importantly by 'plastic' flow. In addition, we showed that elastic anisotropy can switch and even reverse over relatively short time periods (<10 days) and for relatively small amount of plastic deformation (<5%).

A small-scale turbulence model

NASA Technical Reports Server (NTRS)

Lundgren, T. S.

1993-01-01

A previously derived analytical model for the small-scale structure of turbulence is reformulated in such a way that the energy spectrum may be computed. The model is an ensemble of two-dimensional (2D) vortices with internal spiral structure, each stretched by an axially symmetric strain flow. Stretching and differential rotation produce an energy cascade to smaller scales in which the stretching represents the effect of instabilities and the spiral structure is the source of dissipation at the end of the cascade. The energy spectrum of the resulting flow may be expressed as a time integration involving only the enstrophy spectrum of the time evolving 2D cross section flow, which may be obtained numerically. Examples are given in which a k exp -5/3 spectrum is obtained by this method. The k exp -5/3 inertial range spectrum is shown to be related to the existence of a self-similar enstrophy preserving range in the 2D enstrophy spectrum. The results are found to be insensitive to time dependence of the strain rate, including even intermittent on-or-off strains.

A New Strain of Drosophila That Inhibits the Development of Symptoms in Imagoes Infected with Sigma Virus

PubMed Central

Herforth, R. S.

1978-01-01

A strain of Drosophila melanogaster bearing the mutant gene ebony has been found to slow the development of symptoms (carbon dioxide sensitivity) in adult flies inoculated with sigma virus, a member of the rhabdovirus group. This inhibition is made evident by comparing mean incubation times of the virus in ebony and wild-type (Oregon) flies. The increase in mean incubation time in ebony flies has ranged from about 3 to 8 days, depending on the virus strain, amount of virus injected, and the age of the flies at the time of inoculation. This delay in development of symptoms appears to be due to a dominant autosomal gene, although further work is needed to confirm this. When accumulation of infectious virus after inoculation is compared in ebony and Oregon flies, there seems to be no inhibition of multiplication in ebony at the level of the entire fly. The relationship of this work to current theories on the mechanism of symptom production by sigma virus is discussed. PMID:17248809

A seismological model for earthquakes induced by fluid extraction from a subsurface reservoir

NASA Astrophysics Data System (ADS)

Bourne, S. J.; Oates, S. J.; van Elk, J.; Doornhof, D.

2014-12-01

A seismological model is developed for earthquakes induced by subsurface reservoir volume changes. The approach is based on the work of Kostrov () and McGarr () linking total strain to the summed seismic moment in an earthquake catalog. We refer to the fraction of the total strain expressed as seismic moment as the strain partitioning function, α. A probability distribution for total seismic moment as a function of time is derived from an evolving earthquake catalog. The moment distribution is taken to be a Pareto Sum Distribution with confidence bounds estimated using approximations given by Zaliapin et al. (). In this way available seismic moment is expressed in terms of reservoir volume change and hence compaction in the case of a depleting reservoir. The Pareto Sum Distribution for moment and the Pareto Distribution underpinning the Gutenberg-Richter Law are sampled using Monte Carlo methods to simulate synthetic earthquake catalogs for subsequent estimation of seismic ground motion hazard. We demonstrate the method by applying it to the Groningen gas field. A compaction model for the field calibrated using various geodetic data allows reservoir strain due to gas extraction to be expressed as a function of both spatial position and time since the start of production. Fitting with a generalized logistic function gives an empirical expression for the dependence of α on reservoir compaction. Probability density maps for earthquake event locations can then be calculated from the compaction maps. Predicted seismic moment is shown to be strongly dependent on planned gas production.

Antagonistic effect of chosen lactic acid bacteria strains on Yersinia enterocolitica species in model set-ups, meat and fermented sausages.

PubMed

Gomółka-Pawlicka, M; Uradziński, J

2003-01-01

The present study was aimed at determining the influence of 15 strains of lactic acid bacteria on the growth of 8 Yersinia enterocolitica strains in model set-ups, and in meat and ageing fermented sausages. The investigations were performed within the framework of three alternate stages which differed in respect to the products studied, the number of Lactobacillus sp. strains and, partly, methodological approach. The ratio between lactic acid bacteria and Yersinia enterocolitica strains studied was, depending on the variant of experiment, 1:1, 1:2 and 2:1, respectively. The study also considered water activity (aw) and pH of the products investigated. The results suggest that all the lactic acid bacteria strains used within the framework of the model set-ups had antagonistic effect on all the Salmonella sp. strains. However, this ability was not observed with respect to of tested lactic acid bacteria strains in meat and fermented sausage. This ability was possessed by one of the strains investigated--Lactobacillus helveticus T 78. The temperature and time of the incubation of sausages, but not aw and pH, were found to have a distinct influence on the antagonistic interaction between the bacteria tested.

Carbon Nanofiber Cement Sensors to Detect Strain and Damage of Concrete Specimens Under Compression

PubMed Central

Baeza, F. Javier; Garcés, Pedro

2017-01-01

Cement composites with nano-additions have been vastly studied for their functional applications, such as strain and damage sensing. The capacity of a carbon nanofiber (CNF) cement paste has already been tested. However, this study is focused on the use of CNF cement composites as sensors in regular concrete samples. Different measuring techniques and humidity conditions of CNF samples were tested to optimize the strain and damage sensing of this material. In the strain sensing tests (for compressive stresses up to 10 MPa), the response depends on the maximum stress applied. The material was more sensitive at higher loads. Furthermore, the actual load time history did not influence the electrical response, and similar curves were obtained for different test configurations. On the other hand, damage sensing tests proved the capability of CNF cement composites to measure the strain level of concrete samples, even for loads close to the material’s strength. Some problems were detected in the strain transmission between sensor and concrete specimens, which will require specific calibration of each sensor one attached to the structure. PMID:29186797

Carbon Nanofiber Cement Sensors to Detect Strain and Damage of Concrete Specimens Under Compression.

PubMed

Galao, Oscar; Baeza, F Javier; Zornoza, Emilio; Garcés, Pedro

2017-11-24

Cement composites with nano-additions have been vastly studied for their functional applications, such as strain and damage sensing. The capacity of a carbon nanofiber (CNF) cement paste has already been tested. However, this study is focused on the use of CNF cement composites as sensors in regular concrete samples. Different measuring techniques and humidity conditions of CNF samples were tested to optimize the strain and damage sensing of this material. In the strain sensing tests (for compressive stresses up to 10 MPa), the response depends on the maximum stress applied. The material was more sensitive at higher loads. Furthermore, the actual load time history did not influence the electrical response, and similar curves were obtained for different test configurations. On the other hand, damage sensing tests proved the capability of CNF cement composites to measure the strain level of concrete samples, even for loads close to the material's strength. Some problems were detected in the strain transmission between sensor and concrete specimens, which will require specific calibration of each sensor one attached to the structure.

Knitted Strain Sensor Textiles of Highly Conductive All-Polymeric Fibers.

PubMed

Seyedin, Shayan; Razal, Joselito M; Innis, Peter C; Jeiranikhameneh, Ali; Beirne, Stephen; Wallace, Gordon G

2015-09-30

A scaled-up fiber wet-spinning production of electrically conductive and highly stretchable PU/PEDOT:PSS fibers is demonstrated for the first time. The PU/PEDOT:PSS fibers possess the mechanical properties appropriate for knitting various textile structures. The knitted textiles exhibit strain sensing properties that were dependent upon the number of PU/PEDOT:PSS fibers used in knitting. The knitted textiles show sensitivity (as measured by the gauge factor) that increases with the number of PU/PEDOT:PSS fibers deployed. A highly stable sensor response was observed when four PU/PEDOT:PSS fibers were co-knitted with a commercial Spandex yarn. The knitted textile sensor can distinguish different magnitudes of applied strain with cyclically repeatable sensor responses at applied strains of up to 160%. When used in conjunction with a commercial wireless transmitter, the knitted textile responded well to the magnitude of bending deformations, demonstrating potential for remote strain sensing applications. The feasibility of an all-polymeric knitted textile wearable strain sensor was demonstrated in a knee sleeve prototype with application in personal training and rehabilitation following injury.

THE FAILURE OF STRUCTURAL METALS SUBJECTED TO STRAIN-CYCLING CONDITIONS

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

Swindeman, R.W.; Douglas, D.A.

1958-11-01

Data showing the isothermal strain-cycling capacity of three metals, inconel, Hastelloy "B," and beryllium, are presented. It is noted that at frequencies of 0.5 cycles per minute the data satisfied am equation of the form N/ sup alpha / epsilon /sub p/ = K, where N is the number of cycles to failure, epsilon /sub p/ is the plastic strain per cycle, and alpha and K are constants whose values depend on the structure and test conditions. Data on Ihconel are given to establish the effect of grain size, specimen geometry, temperature, and frequency. It is found that at temperaturesmore » above 1300 F, grain sine amd frequency exert a pronounced effect on the rupture life. Fine-gralned metal survives more cycles before failure than coarsegrained material. Lomg time cycles shorten the number of cycles to failure when the strain per cycle is low. Thermal strain cycling dain for ihconel are compared to strain cycling data at the same mean temperature. Good correlation is found to exist between the two types of data. (auth)« less

Timing of mafic magmatism VS localization of the deformation: the Ivrea Zone (Italian Alps)

NASA Astrophysics Data System (ADS)

Bidault, M.; Geoffroy, L.; Arbaret, L.; Aubourg, C. T.

2017-12-01

Mafic magma emplacement is a common feature of continental extension systems, represented at initial stage by volcanic rifts and at more mature stage by volcanic passive margins. In those contexts, lithospheric extension is not isovolumic, magma being notably added to the crust while it is tectonically stretched and thinned. Crystal-scale power-law mechanisms responsible for the continuous flow of the lower crust during extension are composition- and temperature-dependent and additionally, very slow processes. However magma emplacement is a very rapid process. Its effect on the lower crust rheology is dual depending upon the time-scale of the processes: thermal weakening, when newly-formed hot intrusions emplace and heat their surrounding, and rheological chemical hardening when mafic intrusions are cold. Consequently, the localization and type of ductile deformation affecting the lower crust depend on the emplacement rate, volume and spatial organization of the mafic system. The Ivrea Zone is a well-known variscan continental crust section that underwent extension through first gravitational collapse in the Carboniferous and then lithospheric extension until the Permian. From the Late Carboniferous to the Permian, extension in the Ivrea Zone was associated with large volumes of magma intrusion within the lower crust. This volcanic rift stage predated the development of a non-volcanic passive margin during the Jurassic. The entire system was tilted 90° eastward during the Alpine orogeny but remained unaffected by significant metamorphism or pervasive strain. We combine new field observations, Anisotropy of Magnetic Susceptibility data and trace-element geochemistry to investigate the timing, tectonic-setting and consequences of magma emplacement in the in-extension Ivrea lower crust. We propose a new tectonic history, highlighting time-dependent strain transfer and localization in the lower crust, in connection with mafic magma intrusion.

Transcriptional profiling of the early stages of germination in Candida albicans by real-time RT-PCR.

PubMed

Toyoda, Mika; Cho, Tamaki; Kaminishi, Hidenori; Sudoh, Masayuki; Chibana, Hiroji

2004-12-01

By using real-time RT-PCR, we profiled the expression of CGR1, CaMSI3, EFG1, NRG1, and TUP1 in Candida albicans strains JCM9061 and CAI4 under several conditions, including induction of morphological transition, heat shock, and treatment with calcium inhibitors. Expression of CaMSI3 changed under these growth conditions except during heat shock. CGR1 expression increased during the early stages of hyphal growth in JCM9061, while expression was strain-dependent during heat shock. Both EFG1 and NRG1 were similarly expressed under hypha-inducing conditions and heat shock. Expression of TUP1 was slightly different from the expression of EFG1 or NRG1.

A noninterference blade vibration measurement system for gas turbine engines

NASA Astrophysics Data System (ADS)

Watkins, William B.; Chi, Ray M.

1987-06-01

A noninterfering blade vibration system has been demonstrated in tests of a gas turbine first stage fan. Conceptual design of the system, including its theory, design of case mounted probes, and data acquisition and signal processing hardware was done in a previous effort. The current effort involved instrumentation of an engine fan stage with strain gages; data acquisition using shaft-mounted reference and case-mounted optical probes; recording of data on a wideband tape recorder; and posttest processing using off-line analysis in a facility computer and a minicomputer-based readout system designed for near- real-time readout. Results are presented in terms of true blade vibration frequencies, time and frequency dependent vibration amplitudes and comparison of the optical noninterference results with strain gage readings.

Constitutive modeling for isotropic materials (HOST)

NASA Technical Reports Server (NTRS)

Lindholm, Ulric S.; Chan, Kwai S.; Bodner, S. R.; Weber, R. M.; Walker, K. P.; Cassenti, B. N.

1984-01-01

The results of the first year of work on a program to validate unified constitutive models for isotropic materials utilized in high temperature regions of gas turbine engines and to demonstrate their usefulness in computing stress-strain-time-temperature histories in complex three-dimensional structural components. The unified theories combine all inelastic strain-rate components in a single term avoiding, for example, treating plasticity and creep as separate response phenomena. An extensive review of existing unified theories is given and numerical methods for integrating these stiff time-temperature-dependent constitutive equations are discussed. Two particular models, those developed by Bodner and Partom and by Walker, were selected for more detailed development and evaluation against experimental tensile, creep and cyclic strain tests on specimens of a cast nickel base alloy, B19000+Hf. Initial results comparing computed and test results for tensile and cyclic straining for temperature from ambient to 982 C and strain rates from 10(exp-7) 10(exp-3) s(exp-1) are given. Some preliminary date correlations are presented also for highly non-proportional biaxial loading which demonstrate an increase in biaxial cyclic hardening rate over uniaxial or proportional loading conditions. Initial work has begun on the implementation of both constitutive models in the MARC finite element computer code.

Biaxial tensile strain tuned up-and-down behavior on lattice thermal conductivity in β-AsP monolayer

NASA Astrophysics Data System (ADS)

Guo, San-Dong; Dong, Jun

2018-07-01

Various two-dimensional (2D) materials with a graphene-like buckled structure have emerged, and the β-phase AsP monolayer has been recently proposed to be thermodynamically stable from first-principles calculations. The studies of thermal transport are very useful for these 2D materials-based nano-electronics devices. Motivated by this, a comparative study of strain-dependent phonon transport of AsP monolayers is performed by solving the linearized phonon Boltzmann equation within the single-mode relaxation time approximation (RTA). It is found that the lattice thermal conductivity () of the AsP monolayer is very close to the one of As monolayer with a similar buckled structure, which is due to neutralization between the reduction of phonon lifetimes and group velocity enhancement from As to AsP monolayer. The corresponding room-temperature sheet thermal conductance of AsP monolayer is 152.5 . It is noted that the increasing tensile strain can harden a long wavelength out-of-plane (ZA) acoustic mode, and soften the in-plane longitudinal acoustic (LA) and transversal acoustic (TA) modes. Calculated results show that of AsP monolayer presents a nonmonotonic up-and-down behavior with increased strain. The unusual strain dependence is due to the competition among the reduction of phonon group velocities, improved phonon lifetimes of ZA mode and nonmonotonic up-and-down phonon lifetimes of TA/LA mode. It is found that acoustic branches dominate the in the considered strain range, and the contribution from ZA branch increases with increased strain, while it is opposite for TA/LA branch. By analyzing cumulative with respect to phonon mean free path, tensile strain can modulate effectively the size effects on in the AsP monolayer. Our work enriches the studies of thermal transports of 2D materials with graphene-like buckled structures, and strengthens the idea to engineer thermal transport properties by simple mechanical strain, and stimulates further experimental works to synthesize AsP monolayers.

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.

Role of the epidermal growth factor receptor in signaling strain-dependent activation of the brain natriuretic peptide gene.

PubMed

Anderson, Hope D I; Wang, Feng; Gardner, David G

2004-03-05

The epidermal growth factor receptor (EGFR) and ectoshedding of heparin-binding epidermal growth factor (HBEGF), an EGFR ligand, have been linked to the development of cardiac myocyte hypertrophy. However, the precise role that the liganded EGFR plays in the transcriptional activation of the gene program that accompanies hypertrophy remains undefined. Utilizing the human (h) BNP gene as a model of hypertrophy-dependent gene activation, we show that activation of the EGFR plays an important role in mediating mechanical strain-dependent stimulation of the hBNP promoter. Strain promotes endothelin (ET) generation through NAD(P)H oxidase-dependent production of reactive oxygen species. ET in turn induces metalloproteinase-mediated cleavage of pro-HBEGF and ectoshedding of HBEGF, which activates the EGFR and stimulates hBNP promoter activity. HBEGF also stimulates other phenotypic markers of hypertrophy including protein synthesis and sarcomeric assembly. The antioxidant N-acetylcysteine or the NAD(P)H oxidase inhibitor, apocynin, inhibited strain-dependent activation of the ET-1 promoter, HBEGF shedding, and hBNP promoter activation. The metalloproteinase inhibitor, GM-6001, prevented the induction of HBEGF ectoshedding and the hBNP promoter response to strain, suggesting a critical role for the metalloproteinase-dependent cleavage event in signaling the strain response. These findings suggest that metalloproteinase activity as an essential step in this pathway may prove to be a relevant therapeutic target in the management of cardiac hypertrophy.

Breeding of a xylose-fermenting hybrid strain by mating genetically engineered haploid strains derived from industrial Saccharomyces cerevisiae.

PubMed

Inoue, Hiroyuki; Hashimoto, Seitaro; Matsushika, Akinori; Watanabe, Seiya; Sawayama, Shigeki

2014-12-01

The industrial Saccharomyces cerevisiae IR-2 is a promising host strain to genetically engineer xylose-utilizing yeasts for ethanol fermentation from lignocellulosic hydrolysates. Two IR-2-based haploid strains were selected based upon the rate of xylulose fermentation, and hybrids were obtained by mating recombinant haploid strains harboring heterogeneous xylose dehydrogenase (XDH) (wild-type NAD(+)-dependent XDH or engineered NADP(+)-dependent XDH, ARSdR), xylose reductase (XR) and xylulose kinase (XK) genes. ARSdR in the hybrids selected for growth rates on yeast extract-peptone-dextrose (YPD) agar and YP-xylose agar plates typically had a higher activity than NAD(+)-dependent XDH. Furthermore, the xylose-fermenting performance of the hybrid strain SE12 with the same level of heterogeneous XDH activity was similar to that of a recombinant strain of IR-2 harboring a single set of genes, XR/ARSdR/XK. These results suggest not only that the recombinant haploid strains retain the appropriate genetic background of IR-2 for ethanol production from xylose but also that ARSdR is preferable for xylose fermentation.

Dissolution and time-dependent compaction of albite sand: experiments at 100°C and 160°C in pH-buffered organic acids and distilled water

NASA Astrophysics Data System (ADS)

Hajash, Andrew; Carpenter, Thomas D.; Dewers, Thomas A.

1998-09-01

Aqueous fluids are important in the diagenesis and deformation of crustal rocks. Both chemical and physical interactions are involved and often they are strongly coupled. For example, pore waters not only dissolve, transport, and precipitate chemical species, but they also substantially affect the mechanical behavior of the rocks that contain them. Stresses magnified at grain contacts by differences in pore-fluid pressure ( Pp) and confining pressure ( Pc) can, in turn, influence the rate and extent of chemical exchange. To begin investigation of these coupled systems, compaction experiments were conducted using albite sand (250-500 μm) and distilled water (pH 5.8), 0.07 M acetate (pH 4.7), and 0.07 M acetate + 0.005 M citrate (pH 4.4) solutions in a hydrothermal flow-through system at conditions that simulate diagenesis. Pore-fluid chemistry and pore-volume loss were monitored to quantify the effects of organic acids on time-dependent compaction rates. The effects of stress and fluid chemistry on the dissolution kinetics were also examined. Albite dissolution rates, monitored by steady-state fluid chemistry, increased when an effective pressure ( Pe= Pc- Pp) was applied, probably due to increases in total surface area caused by grain breakage at contacts. These effects were transient in distilled water, however, Si and Al concentrations remained elevated in the acetate pore fluid. The average Si-based release rates indicate ≈35% increase in reactive surface area by application of Pe=34.5 MPa. At 100°C with Pe=34.5 MPa, steady-state Si concentrations were ≈2.3 times higher in 0.07 M acetate and 5.8 times higher in 0.07 M acetate + 0.005 M citrate than in distilled water. Al increased by even larger factors (3× in the acetate buffer and 10× in the citrate solution). These changes in fluid chemistry are attributed to both pH and ligand-enhanced reactions. Albite dissolution appears to be controlled by surface complexation reactions at Al sites. Rapid dissolution of albite in the organic acid solutions is probably due to the ability of organic acid ligands to selectively complex with aluminum. Time-dependent compaction was observed at 100 and 160°C with Pe=34.5 MPa. Strain rates increased with temperature from ≈10 -9 s -l at 100°C to ≈10 -8 s -l at 160°C and decreased with strain in all pore fluids, especially at 100°C. Compaction rates in distilled water and in the acetate solution had similar magnitudes and strain dependencies; however, small amounts of citrate species apparently enhance compaction compared to the other fluids at similar strains. Textural data indicate that time-dependent compaction of the albite sand occurred primarily by brittle mechanisms at these temperatures. However, the deformation is clearly thermally activated and may be chemically assisted by the aqueous pore fluid.

Strain dependency of the effects of nicotine and mecamylamine in a rat model of attention.

PubMed

Hahn, Britta; Riegger, Katelyn E; Elmer, Greg I

2016-04-01

Processes of attention have a heritable component, suggesting that genetic predispositions may predict variability in the response to attention-enhancing drugs. Among lead compounds with attention-enhancing properties are nicotinic acetylcholine receptor (nAChR) agonists. This study aims to test, by comparing three rat strains, whether genotype may influence the sensitivity to nicotine in the 5-choice serial reaction time task (5-CSRTT), a rodent model of attention. Strains tested were Long Evans (LE), Sprague Dawley (SD), and Wistar rats. The 5-CSRTT requires responses to light stimuli presented randomly in one of five locations. The effect of interest was an increased percentage of responses in the correct location (accuracy), the strongest indicator of improved attention. Nicotine (0.05-0.2 mg/kg s.c.) reduced omission errors and response latency and increased anticipatory responding in all strains. In contrast, nicotine dose-dependently increased accuracy in Wistar rats only. The nAChR antagonist mecamylamine (0.75-3 mg/kg s.c.) increased omissions, slowed responses, and reduced anticipatory responding in all strains. There were no effects on accuracy, which was surprising giving the clear improvement with nicotine in the Wistar group. The findings suggest strain differences in the attention-enhancing effects of nicotine, which would indicate that genetic predispositions predict variability in the efficacy of nAChR compounds for enhancing attention. The absence of effect of mecamylamine on response accuracy may suggest a contribution of nAChR desensitization to the attention-enhancing effects of nicotine.

Response of Leuconostoc strains against technological stress factors: Growth performance and volatile profiles.

PubMed

Cicotello, Joaquín; Wolf, Irma V; D'Angelo, Luisa; Guglielmotti, Daniela M; Quiberoni, Andrea; Suárez, Viviana B

2018-08-01

The ability of twelve strains belonging to three Leuconostoc species (Leuconostoc mesenteroides, Leuconostoc lactis and Leuconostoc pseudomesenteroides) to grow under diverse sub-lethal technological stress conditions (cold, acidic, alkaline and osmotic) was evaluated in MRS broth. Two strains, Leuconostoc lactis Ln N6 and Leuconostoc mesenteroides Ln MB7, were selected based on their growth under sub-lethal conditions, and volatile profiles in RSM (reconstituted skim milk) at optimal and under stress conditions were analyzed. Growth rates under sub-lethal conditions were strain- and not species-dependent. Volatilomes obtained from the two strains studied were rather diverse. Particularly, Ln N6 (Ln. lactis) produced more ethanol and acetic acid than Ln MB7 (Ln. mesenteroides) and higher amounts and diversity of the rest of volatile compounds as well, at all times of incubation. For the two strains studied, most of stress conditions applied diminished the amounts of ethanol and acetic acid produced and the diversity and levels of the rest of volatile compounds. These results were consequence of the different capacity of the strains to grow under each stress condition tested. Copyright © 2018 Elsevier Ltd. All rights reserved.

PhybalSIT — Fatigue Assessment and Life Time Calculation of the Ductile Cast Iron EN-GJS-600 at Ambient and Elevated Temperatures

NASA Astrophysics Data System (ADS)

Jost, Benjamin; Klein, Marcus; Eifler, Dietmar

This paper focuses on the ductile cast iron EN-GJS-600 which is often used for components of combustion engines. Under service conditions, those components are mechanically loaded at different temperatures. Therefore, this investigation targets at the fatigue behavior of EN-GJS-600 at ambient and elevated temperatures. Light and scanning electron microscopic investigations were done to characterize the sphericity of the graphite as well as the ferrite, pearlite and graphite fraction. At elevated temperatures, the consideration of dynamic strain ageing effects is of major importance. In total strain increase, temperature increase and constant total strain amplitude tests, the plastic strain amplitude, the stress amplitude, the change in temperature and the change in electrical resistance were measured. The measured values depend on plastic deformation processes in the bulk of the specimens and at the interfaces between matrix and graphite. The fatigue behavior of EN-GJS-600 is dominated by cyclic hardening processes. The physically based fatigue life calculation "PHYBALSIT" (SIT = strain increase test) was developed for total strain controlled fatigue tests. Only one temperature increase test is necessary to determine the temperature interval of pronounced dynamic strain ageing effects.

A model of partial differential equations for HIV propagation in lymph nodes

NASA Astrophysics Data System (ADS)

Marinho, E. B. S.; Bacelar, F. S.; Andrade, R. F. S.

2012-01-01

A system of partial differential equations is used to model the dissemination of the Human Immunodeficiency Virus (HIV) in CD4+T cells within lymph nodes. Besides diffusion terms, the model also includes a time-delay dependence to describe the time lag required by the immunologic system to provide defenses to new virus strains. The resulting dynamics strongly depends on the properties of the invariant sets of the model, consisting of three fixed points related to the time independent and spatial homogeneous tissue configurations in healthy and infected states. A region in the parameter space is considered, for which the time dependence of the space averaged model variables follows the clinical pattern reported for infected patients: a short scale primary infection, followed by a long latency period of almost complete recovery and third phase characterized by damped oscillations around a value with large HIV counting. Depending on the value of the diffusion coefficient, the latency time increases with respect to that one obtained for the space homogeneous version of the model. It is found that same initial conditions lead to quite different spatial patterns, which depend strongly on the latency interval.

Strain rate dependent activation of slip systems in calcite marbles from Syros (Cyclades, Greece)

NASA Astrophysics Data System (ADS)

Rogowitz, Anna; Grasemann, Bernhard; Morales, Luiz F. G.; Huet, Benjamin; White, Joseph C.

2017-04-01

The activation of certain slip systems in calcite has been experimentally proven to be highly temperature dependent, but also the strain rate plays an important role on the activation of the dominant slip system. In this study, observations from a flanking structure (i.e. shear zone) that developed under lower greenschist-facies conditions, in an almost pure calcite marble (Syros Island, Greece) are presented. The shear zone is characterized by a strain gradient from the slightly deformed tips (γ ˜ 50) to the highly strained centre (γ up to 1000) while the host rock is moderately deformed (γ ˜ 3). During the shear zone development, the strain gradient coincided with a strain rate gradient with strain rate varying from 10-13 to 10-9 s-1. The studied outcrop thus represents the final state of a natural experiment and gives us a great opportunity to get natural constraints on strain rate dependent mechanical behaviour in a calcite marble. Detailed microstructural analyses have been performed via optical microscopy, electron microscopy, electron backscatter diffraction mapping and transmission electron microscopy, on samples from the highly strained shear zone and the host rock. The analyses show that the calcite microfabric varies depending on position within the shear zone, indicating activation of different deformation, recrystallization mechanisms and slip systems at different strain rates. Up to strain rates of ˜10-10 s-1 the marble deformed exclusively within the dislocation creep field, showing a change in recrystallization mechanism and dominant active slip system. While the marble preferentially recrystallized by grain boundary migration at relatively low strain rates (˜10-13 s-1), subgrain rotation recrystallization seems to be the dominant mechanism at higher strain rates (˜10-12 to 10-10 s-1). At higher strain rates (˜10-9 s-1), the recrystallization mechanism is bulging, resulting in the development of an extremely fine grained ultramylonite (average grain size ˜3 μm) accompanied by a switch in deformation mechanism from dislocation creep to a combined deformation by grain boundary sliding and dislocation activity. Constraints on dominant active slip system depending on deformation strain rate have been made by a combination of misorientation analyses and viscoplastic self-consistent modelling.

A host-specific biological control of grape crown gall by Agrobacterium vitis strain F2/5: its regulation and population dynamics.

PubMed

Kaewnum, Supaporn; Zheng, Desen; Reid, Cheryl L; Johnson, Kameka L; Gee, Jodi C; Burr, Thomas J

2013-05-01

Nontumorigenic Agrobacterium vitis strain F2/5 is able to prevent crown gall caused by tumorigenic A. vitis on grape but not on other plant species such as tobacco. Mutations in a quorum-sensing transcription factor, aviR, and in caseinolytic protease (clp) component genes clpA and clpP1 resulted in reduced or loss of biological control. All mutants were complemented; however, restoration of biological control by complemented clpA and clpP1 mutants was dependent on the copy number of vector that was used as well as timing of application of the complemented mutants to grape wounds in relation to inoculation with pathogen. Mutations in other quorum-sensing and clp genes and in a gene associated with polyketide synthesis did not affect biological control. It was determined that, although F2/5 inhibits transformation by tumorigenic A. vitis strains on grape, it does not affect growth of the pathogen in wounded grape tissue over time.

Probabilistic seismic hazard in the San Francisco Bay area based on a simplified viscoelastic cycle model of fault interactions

USGS Publications Warehouse

Pollitz, F.F.; Schwartz, D.P.

2008-01-01

We construct a viscoelastic cycle model of plate boundary deformation that includes the effect of time-dependent interseismic strain accumulation, coseismic strain release, and viscoelastic relaxation of the substrate beneath the seismogenic crust. For a given fault system, time-averaged stress changes at any point (not on a fault) are constrained to zero; that is, kinematic consistency is enforced for the fault system. The dates of last rupture, mean recurrence times, and the slip distributions of the (assumed) repeating ruptures are key inputs into the viscoelastic cycle model. This simple formulation allows construction of stress evolution at all points in the plate boundary zone for purposes of probabilistic seismic hazard analysis (PSHA). Stress evolution is combined with a Coulomb failure stress threshold at representative points on the fault segments to estimate the times of their respective future ruptures. In our PSHA we consider uncertainties in a four-dimensional parameter space: the rupture peridocities, slip distributions, time of last earthquake (for prehistoric ruptures) and Coulomb failure stress thresholds. We apply this methodology to the San Francisco Bay region using a recently determined fault chronology of area faults. Assuming single-segment rupture scenarios, we find that fature rupture probabilities of area faults in the coming decades are the highest for the southern Hayward, Rodgers Creek, and northern Calaveras faults. This conclusion is qualitatively similar to that of Working Group on California Earthquake Probabilities, but the probabilities derived here are significantly higher. Given that fault rupture probabilities are highly model-dependent, no single model should be used to assess to time-dependent rupture probabilities. We suggest that several models, including the present one, be used in a comprehensive PSHA methodology, as was done by Working Group on California Earthquake Probabilities.

Pharmacodynamic Model To Describe the Concentration-Dependent Selection of Cefotaxime-Resistant Escherichia coli

PubMed Central

Olofsson, Sara K.; Geli, Patricia; Andersson, Dan I.; Cars, Otto

2005-01-01

Antibiotic dosing regimens may vary in their capacity to select mutants. Our hypothesis was that selection of a more resistant bacterial subpopulation would increase with the time within a selective window (SW), i.e., when drug concentrations fall between the MICs of two strains. An in vitro kinetic model was used to study the selection of two Escherichia coli strains with different susceptibilities to cefotaxime. The bacterial mixtures were exposed to cefotaxime for 24 h and SWs of 1, 2, 4, 8, and 12 h. A mathematical model was developed that described the selection of preexisting and newborn mutants and the post-MIC effect (PME) as functions of pharmacokinetic parameters. Our main conclusions were as follows: (i) the selection between preexisting mutants increased with the time within the SW; (ii) the emergence and selection of newborn mutants increased with the time within the SW (with a short time, only 4% of the preexisting mutants were replaced by newborn mutants, compared to the longest times, where 100% were replaced); and (iii) PME increased with the area under the concentration-time curve (AUC) and was slightly more pronounced with a long elimination half-life (T1/2) than with a short T1/2 situation, when AUC is fixed. We showed that, in a dynamic competition between strains with different levels of resistance, the appearance of newborn high-level resistant mutants from the parental strains and the PME can strongly affect the outcome of the selection and that pharmacodynamic models can be used to predict the outcome of resistance development. PMID:16304176

Rapid discrimination of strain-dependent fermentation characteristics among Lactobacillus strains by NMR-based metabolomics of fermented vegetable juice

PubMed Central

Nakamura, Toshihide; Sekiyama, Yasuyo; Kikuchi, Jun

2017-01-01

In this study, we investigated the applicability of NMR-based metabolomics to discriminate strain-dependent fermentation characteristics of lactic acid bacteria (LAB), which are important microorganisms for fermented food production. To evaluate the discrimination capability, six type strains of Lactobacillus species and six additional L. brevis strains were used focusing on i) the difference between homo- and hetero-lactic fermentative species and ii) strain-dependent characteristics within L. brevis. Based on the differences in the metabolite profiles of fermented vegetable juices, non-targeted principal component analysis (PCA) clearly separated the samples into those inoculated with homo- and hetero-lactic fermentative species. The separation was primarily explained by the different levels of dominant metabolites (lactic acid, acetic acid, ethanol, and mannitol). Orthogonal partial least squares discrimination analysis, based on a regions-of-interest (ROIs) approach, revealed the contribution of low-abundance metabolites: acetoin, phenyllactic acid, p-hydroxyphenyllactic acid, glycerophosphocholine, and succinic acid for homolactic fermentation; and ornithine, tyramine, and γ-aminobutyric acid (GABA) for heterolactic fermentation. Furthermore, ROIs-based PCA of seven L. brevis strains separated their strain-dependent fermentation characteristics primarily based on their ability to utilize sucrose and citric acid, and convert glutamic acid and tyrosine into GABA and tyramine, respectively. In conclusion, NMR metabolomics successfully discriminated the fermentation characteristics of the tested strains and provided further information on metabolites responsible for these characteristics, which may impact the taste, aroma, and functional properties of fermented foods. PMID:28759594

Strain Dependence of Photoluminescense of Individual Carbon Nanotubes

NASA Technical Reports Server (NTRS)

Nikolaev, Pavel N.; Leeuw, Tonya K.; Tsyboulski, Dmitri A.; Bachilo, Sergei M.; Weisman, Bruce; Arepalli, Sivaram

2007-01-01

We have investigated strain dependence of photoluminescense (PL) spectra of single wall carbon nanotubes (SWNT). Nanotubes were sparsely dispersed in a thin PMMA film applied to acrylic bar, and strained in both compression and extension by bending this bar in either direction in a homebuilt four-point bending rig. The average surface strain was measured with high accuracy by a resistive strain gage applied on top of the film. The near infrared imaging and spectroscopy were performed on the inverted microscope equipped with high numerical aperture reflective objective lens and InGaAs CCD cameras. PL was excited with a diode laser at either 658, 730 or 785 nm, linearly polarized in the direction of the strain. We were able to measure (n,m) types and orientation of individual nanotubes with respect to strain direction and strain dependence of their PL maxima. It was found that PL peak shifts with respect to the values measured in SDS micelles are a sum of three components. First, a small environmental shift due to difference in the dielectric constant of the surrounding media, that is constant and independent of the nanotube type. Second, shift due to isotropic compression of the film during drying. Third, shifts produced by the uniaxial loading of the film in the experiment. Second and third shifts follow expression based on the first-order expansion of the TB hamiltonian. Their magnitude is proportional to the nanotube chiral angle and strain, and direction is determined by the nanotube quantum number. PL strain dependence measured for a number of various nanotube types allows to estimate TB carbon-carbon transfer integral.

Temperature effect on the recovery process in stretched Bombyx mori silk fibers

NASA Astrophysics Data System (ADS)

Aksakal, Baki

2016-01-01

The recovery process in stretched Bombyx mori silk fibers at different strain levels from 3% to 17% was investigated at room conditions during long period of time from 5 min to 20 days and more. How the temperature affects the recovery process in the silk fibers stretched at room conditions was examined at temperatures from 25 to 125 °C. The results of the recovery process at 25 °C revealed that although the recovery process from strain values higher than 3% strain continued slowly which caused quite high remaining deformation, a complete recovery from 3% strain was observed after 3 days. However, better recovery process was observed with increasing temperature which led to lower remaining deformations. For instance, a complete recovery from 6% strain was observed after 144 h and 3 h for the recovery process at 100 °C and 125 °C, respectively which indicates an important result that the deformations induced by stretching the silk fibers up to 6% strain are reversible and increasing temperature affects the velocity of this process significantly. The recovery process expressed in the strain (ε) and logarithm time coordinates showed a linear dependence for which a linear equation was proposed. Thus, this linear equation enables to estimate the required time for a complete recovery from different strain levels and remaining deformation at any stage of the recovery at different temperatures. The ATR-FTIR spectra of the stretched silk fibers during the recovery process revealed some changes in the absorbance ratios and shifts in the positions of the bands assigned to Cα-C, N-H stretching vibrations, and the Amide III mode. It was suggested that new formation of the hydrogen bonds between polypeptide chains especially in amorphous regions and the changes in the intra-sheet hydrogen bonds in β-sheet crystalline regions greatly contribute to the recovery process.

Investigation into the Effects of Weapon Setback on Various Materials and Geometries.

DTIC Science & Technology

1978-07-01

taking the Laplace Transform of the dynamic equation, rearrangement and taking the inverse transform to find the time-dependent strain. The "dynamic...taking the inverse transform of the above equation: ■»-«fa-to*« 1 E’ ♦ ¥®*> B’ (s+-fj- )(S2+f )T If we neglect the residual strain on the system...partial fractions yields: *t) --f (fr JC-> K, K2 —L_ + + K3 »+-^ s+i(f) s-i(f) performing the inverse transform yields: 4©[K,^> ♦ K2

Mechanics of Carbon Nanotubes and their Polymer Composites

NASA Technical Reports Server (NTRS)

Wei, Chenyu; Cho, K. J.; Srivastava, Deepak; Tang, Harry (Technical Monitor)

2002-01-01

Contents include the folloving: carbon nanotube (CNT): structures, application of carbon nanotubes, simulation method, Elastic properties of carbon nanotubes, yield strain of CNT, yielding under tensile stress, yielding: strain-rate and temperature dependence, yield strain under tension, yielding at realistic conditions, nano fibers, polymer CNT composite, force field, density dependency on temperature, diffusion coefficients, young modulus, and conclusions.

Physically-based strength model of tantalum incorporating effects of temperature, strain rate and pressure

DOE PAGES

Lim, Hojun; Battaile, Corbett C.; Brown, Justin L.; ...

2016-06-14

In this work, we develop a tantalum strength model that incorporates e ects of temperature, strain rate and pressure. Dislocation kink-pair theory is used to incorporate temperature and strain rate e ects while the pressure dependent yield is obtained through the pressure dependent shear modulus. Material constants used in the model are parameterized from tantalum single crystal tests and polycrystalline ramp compression experiments. It is shown that the proposed strength model agrees well with the temperature and strain rate dependent yield obtained from polycrystalline tantalum experiments. Furthermore, the model accurately reproduces the pressure dependent yield stresses up to 250 GPa.more » The proposed strength model is then used to conduct simulations of a Taylor cylinder impact test and validated with experiments. This approach provides a physically-based multi-scale strength model that is able to predict the plastic deformation of polycrystalline tantalum through a wide range of temperature, strain and pressure regimes.« less

Molecular deformation and stress-strain behavior of poly(bisphenol-A-diphenyl sulfone)

NASA Technical Reports Server (NTRS)

Hong, S.-D.; Chung, S. Y.; Fedors, R. F.

1983-01-01

The strain-birefringence response of poly(bisphenol-A-diphenyl sulfone) is found to be independent of temperature at temperatures below -100 C; at higher temperatures, the response becomes slightly dependent on temperature, with lower birefringence seen at higher temperatures. The stress-strain behavior and the stress-birefringence response both depend on temperature over the entire testing temperature range (-179 C to 150 C) studied; this dependence, however, is not pronounced. The evidence is seen as suggesting that the polymer molecules respond to deformation by undergoing conformational rearrangements; the mode of the molecular deformation remains unchanged for temperatures of -100 C or lower. At higher temperatures, the average length of the chain segments involved in the rearrangement increases. The stress-strain response is attributed mainly to chain orientation. The entropic contribution deriving from chain orientation at temperatures below -100 C is still substantial. The modest temperature dependence of the stress-strain response suggests that the energy barriers for the chain segments involved in the rearrangement are relatively low.

Effects of physical exercise and social isolation on anxiety-related behaviors in two inbred rat strains.

PubMed

Mazur, F G; Oliveira, L F G; Cunha, M P; Rodrigues, A L S; Pértile, R A N; Vendruscolo, L F; Izídio, G S

2017-09-01

We investigated the effects of physical exercise (PE) on locomotor activity and anxiety-like behavior in Lewis (LEW) and Spontaneously Hypertensive Rats (SHR) male rats. Rats received either four weeks of forced training, 5days/week, on a treadmill (experiment 1) or were given 21days of free access to running wheels (experiment 2). We also tested the effects of social isolation (SI) (seven days of isolation - experiment 3) on behavior. In experiment 1, 20% of LEW rats and 63% of SHR rats completed the training protocol. PE significantly increased central and peripheral locomotion in the open field (OF) and entries into the open arms in the elevated plus-maze (EPM) in both strains. In experiment 2, the distance traveled by SHR rats on running wheels was significantly higher compared with LEW rats. PE on running wheels also increased the time spent in the center of the OF in SHR rats only. In experiment 3, SI decreased central and peripheral locomotion in the OF in both strains. In summary, forced PE on a treadmill reduced anxiety-like behavior and increased locomotion in male rats of both strains, whereas voluntary PE on running wheels decreased anxiety-like behavior in SHR rats only. SI decreased locomotion in both strains in the OF. This study suggests that spontaneous activity levels are genotype-dependent and the effects of PE depend on the type of exercise performed. Copyright © 2017 Elsevier B.V. All rights reserved.

Nanoscale diffractive probing of strain dynamics in ultrafast transmission electron microscopy

PubMed Central

Feist, Armin; Rubiano da Silva, Nara; Liang, Wenxi; Ropers, Claus; Schäfer, Sascha

2018-01-01

The control of optically driven high-frequency strain waves in nanostructured systems is an essential ingredient for the further development of nanophononics. However, broadly applicable experimental means to quantitatively map such structural distortion on their intrinsic ultrafast time and nanometer length scales are still lacking. Here, we introduce ultrafast convergent beam electron diffraction with a nanoscale probe beam for the quantitative retrieval of the time-dependent local deformation gradient tensor. We demonstrate its capabilities by investigating the ultrafast acoustic deformations close to the edge of a single-crystalline graphite membrane. Tracking the structural distortion with a 28-nm/700-fs spatio-temporal resolution, we observe an acoustic membrane breathing mode with spatially modulated amplitude, governed by the optical near field structure at the membrane edge. Furthermore, an in-plane polarized acoustic shock wave is launched at the membrane edge, which triggers secondary acoustic shear waves with a pronounced spatio-temporal dependency. The experimental findings are compared to numerical acoustic wave simulations in the continuous medium limit, highlighting the importance of microscopic dissipation mechanisms and ballistic transport channels. PMID:29464187

Nanoscale diffractive probing of strain dynamics in ultrafast transmission electron microscopy.

PubMed

Feist, Armin; Rubiano da Silva, Nara; Liang, Wenxi; Ropers, Claus; Schäfer, Sascha

2018-01-01

The control of optically driven high-frequency strain waves in nanostructured systems is an essential ingredient for the further development of nanophononics. However, broadly applicable experimental means to quantitatively map such structural distortion on their intrinsic ultrafast time and nanometer length scales are still lacking. Here, we introduce ultrafast convergent beam electron diffraction with a nanoscale probe beam for the quantitative retrieval of the time-dependent local deformation gradient tensor. We demonstrate its capabilities by investigating the ultrafast acoustic deformations close to the edge of a single-crystalline graphite membrane. Tracking the structural distortion with a 28-nm/700-fs spatio-temporal resolution, we observe an acoustic membrane breathing mode with spatially modulated amplitude, governed by the optical near field structure at the membrane edge. Furthermore, an in-plane polarized acoustic shock wave is launched at the membrane edge, which triggers secondary acoustic shear waves with a pronounced spatio-temporal dependency. The experimental findings are compared to numerical acoustic wave simulations in the continuous medium limit, highlighting the importance of microscopic dissipation mechanisms and ballistic transport channels.

Response of the mouse lung transcriptome to welding fume: effects of stainless and mild steel fumes on lung gene expression in A/J and C57BL/6J mice

PubMed Central

2010-01-01

Background Debate exists as to whether welding fume is carcinogenic, but epidemiological evidence suggests that welders are an at risk population for the development of lung cancer. Recently, we found that exposure to welding fume caused an acutely greater and prolonged lung inflammatory response in lung tumor susceptible A/J versus resistant C57BL/6J (B6) mice and a trend for increased tumor incidence after stainless steel (SS) fume exposure. Here, our objective was to examine potential strain-dependent differences in the regulation and resolution of the lung inflammatory response induced by carcinogenic (Cr and Ni abundant) or non-carcinogenic (iron abundant) metal-containing welding fumes at the transcriptome level. Methods Mice were exposed four times by pharyngeal aspiration to 5 mg/kg iron abundant gas metal arc-mild steel (GMA-MS), Cr and Ni abundant GMA-SS fume or vehicle and were euthanized 4 and 16 weeks after the last exposure. Whole lung microarray using Illumina Mouse Ref-8 expression beadchips was done. Results Overall, we found that tumor susceptibility was associated with a more marked transcriptional response to both GMA-MS and -SS welding fumes. Also, Ingenuity Pathway Analysis revealed that gene regulation and expression in the top molecular networks differed between the strains at both time points post-exposure. Interestingly, a common finding between the strains was that GMA-MS fume exposure altered behavioral gene networks. In contrast, GMA-SS fume exposure chronically upregulated chemotactic and immunomodulatory genes such as CCL3, CCL4, CXCL2, and MMP12 in the A/J strain. In the GMA-SS-exposed B6 mouse, genes that initially downregulated cellular movement, hematological system development/function and immune response were involved at both time points post-exposure. However, at 16 weeks, a transcriptional switch to an upregulation for neutrophil chemotactic genes was found and included genes such as S100A8, S100A9 and MMP9. Conclusions Collectively, our results demonstrate that lung tumor susceptibility may predispose the A/J strain to a prolonged dysregulation of immunomodulatory genes, thereby delaying the recovery from welding fume-induced lung inflammation. Additionally, our results provide unique insight into strain- and welding fume-dependent genetic factors involved in the lung response to welding fume. PMID:20525249

Response of the mouse lung transcriptome to welding fume: effects of stainless and mild steel fumes on lung gene expression in A/J and C57BL/6J mice.

PubMed

Zeidler-Erdely, Patti C; Kashon, Michael L; Li, Shengqiao; Antonini, James M

2010-06-03

Debate exists as to whether welding fume is carcinogenic, but epidemiological evidence suggests that welders are an at risk population for the development of lung cancer. Recently, we found that exposure to welding fume caused an acutely greater and prolonged lung inflammatory response in lung tumor susceptible A/J versus resistant C57BL/6J (B6) mice and a trend for increased tumor incidence after stainless steel (SS) fume exposure. Here, our objective was to examine potential strain-dependent differences in the regulation and resolution of the lung inflammatory response induced by carcinogenic (Cr and Ni abundant) or non-carcinogenic (iron abundant) metal-containing welding fumes at the transcriptome level. Mice were exposed four times by pharyngeal aspiration to 5 mg/kg iron abundant gas metal arc-mild steel (GMA-MS), Cr and Ni abundant GMA-SS fume or vehicle and were euthanized 4 and 16 weeks after the last exposure. Whole lung microarray using Illumina Mouse Ref-8 expression beadchips was done. Overall, we found that tumor susceptibility was associated with a more marked transcriptional response to both GMA-MS and -SS welding fumes. Also, Ingenuity Pathway Analysis revealed that gene regulation and expression in the top molecular networks differed between the strains at both time points post-exposure. Interestingly, a common finding between the strains was that GMA-MS fume exposure altered behavioral gene networks. In contrast, GMA-SS fume exposure chronically upregulated chemotactic and immunomodulatory genes such as CCL3, CCL4, CXCL2, and MMP12 in the A/J strain. In the GMA-SS-exposed B6 mouse, genes that initially downregulated cellular movement, hematological system development/function and immune response were involved at both time points post-exposure. However, at 16 weeks, a transcriptional switch to an upregulation for neutrophil chemotactic genes was found and included genes such as S100A8, S100A9 and MMP9. Collectively, our results demonstrate that lung tumor susceptibility may predispose the A/J strain to a prolonged dysregulation of immunomodulatory genes, thereby delaying the recovery from welding fume-induced lung inflammation. Additionally, our results provide unique insight into strain- and welding fume-dependent genetic factors involved in the lung response to welding fume.

Fluorescence XAS using Ge PAD: Application to High-Temperature Superconducting Thin Film Single Crystals

NASA Astrophysics Data System (ADS)

Oyanagi, H.; Tsukada, A.; Naito, M.; Saini, N. L.; Zhang, C.

2007-02-01

A Ge pixel array detector (PAD) with 100 segments was used in fluorescence x-ray absorption spectroscopy (XAS) study, probing local structure of high temperature superconducting thin film single crystals. Independent monitoring of individual pixel outputs allows real-time inspection of interference of substrates which has long been a major source of systematic error. By optimizing grazing-incidence angle and azimuthal orientation, smooth extended x-ray absorption fine structure (EXAFS) oscillations were obtained, demonstrating that strain effects can be studied using high-quality data for thin film single crystals grown by molecular beam epitaxy (MBE). The results of (La,Sr)2CuO4 thin film single crystals under strain are related to the strain dependence of the critical temperature of superconductivity.

Effect of loading rate on the monotonic tensile behavior of a continuous-fiber-reinforced glass-ceramic matrix composite

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

Soerensen, B.F.; Holmes, J.W.

The stress-strain behavior of a continuous-fiber-reinforced ceramic matrix composite has been measured over a wide range of loading rates (0.01 to 500 MPa/s). It was found that the loading rate has a strong effect on almost every feature of the stress-strain curve: the proportionality stress, the composite strength and failure strain increase with increasing loading rate. The microstructural damage varies also with the loading rate; with increasing loading rate, the average matrix crack spacing increases and the average fiber pullout length decreases. Using simple models, it is suggested that these phenomena are caused partly by time-dependent matrix cracking (due tomore » stress corrosion) and partly by an increasing interfacial shear stress with loading rate.« less

High temperature static strain gage development contract, tasks 1 and 2

NASA Technical Reports Server (NTRS)

Hulse, C. O.; Bailey, R. S.; Grant, H. P.; Przybyszewski, J. S.

1987-01-01

Results are presented for the first two tasks to develop resistive strain gage systems for use up to 1250 K on blades and vanes in gas turbine engines under tests. The objective of these two tasks was to further improve and evaluate two static strain gage alloys identified as candidates in a previous program. Improved compositions were not found for either alloy. Further efforts on the Fe-11.9Al-10.6Cr weigth percent alloy were discontinued because of time dependent drift problems at 1250 K in air. When produced as a 6.5 micrometer thick sputtered film, the Pd-13Cr weight percent alloys is not sufficiently stable for this use in air at 1250 K and a protective overcoat system will need to be developed.

Cyclic deformation and phase transformation of 6Mo superaustenitic stainless steel

NASA Astrophysics Data System (ADS)

Wang, Shing-Hoa; Wu, Chia-Chang; Chen, Chih-Yuan; Yang, Jer-Ren; Chiu, Po-Kay; Fang, Jason

2007-08-01

A fatigue behavior analysis was performed on superaustenitic stainless steel UNS S31254 (Avesta Sheffield 254 SMO), which contains about 6wt.% molybdenum, to examine the cyclic hardening/softening trend, hysteresis loops, the degree of hardening, and fatigue life during cyclic straining in the total strain amplitude range from 0.2 to 1.5%. Independent of strain rate, hardening occurs first, followed by softening. The degree of hardening is dependent on the magnitude of strain amplitude. The cyclic stress-strain curve shows material softening. The lower slope of the degree of hardening versus the strain amplitude curve at a high strain rate is attributed to the fast development of dislocation structures and quick saturation. The ɛ martensite formation, either in band or sheath form, depending on the strain rate, leads to secondary hardening at the high strain amplitude of 1.5%.

The Influence of Strain-Rate History and Temperature on the Shear Strength of Copper, Titanium and Mild Steel

DTIC Science & Technology

1976-03-01

Temperature dependence of flow stress of titanium, at (a) low and (b) high strain rates. 76 18 Strain dependence of apparent and intrinsic strain-rate...Cryostat in position surrounding specimen 98 B3 General view of low- temperature apparatus 98 CI Design of high - temperature titanium specimen and grip 99 C2... High - temperature titanium specimen and stainless- steel grips 100 C3 Transmission of torsional wave through mechanical connectors, at (a) 2000C (b

Studies of plant colonisation by closely related Bacillus amyloliquefaciens biocontrol agents using strain specific quantitative PCR assays.

PubMed

Johansson, Anna H; Bejai, Sarosh; Niazi, Adnan; Manzoor, Shahid; Bongcam-Rudloff, Erik; Meijer, Johan

2014-12-01

Certain strains of Bacillus amyloliquefaciens can colonize plants and improve growth and stress management. In order to study these effects, bacterial growth dynamics on plants and in the rhizosphere are of interest calling for specific analytical tools. For that purpose, quantitative real-time PCR (qPCR) assays were developed in order to differentiate among three closely related B. amyloliquefaciens subsp. plantarum strains (UCMB5033, UCMB5036, UCMB5113) and to determine their levels with high accuracy. Oligonucleotide primers were designed for strain unique gene sequences and used for SYBR green based qPCR analysis. Standard curves covered a wide linear range (10(6)) of DNA amounts with the lowest detection level at 50 fg. Post-reaction melting curve analysis showed only a single product. Accurate threshold cycles were obtained, even in the presence of high excess of related Bacillus strains and total bacterial DNA from soil. Analysis of Bacillus colonisation after seed treatment of two oilseed rape cultivars (Oase and Ritz) grown on agar support showed a time dependent effect but that the bacteria mostly were found on root tissues and little on green tissues. The colonisation on plants grown in soil varied among the Bacillus strains where Oase seemed to house more bacteria than Ritz. Applied as a mixture, all three Bacillus strains co-existed on the roots of plants grown in soil. The qPCR assay in combination with other techniques will be a powerful tool to study plant interactions of these B. amyloliquefaciens biocontrol agents to further understand the requirements for successful interactions and improvement of plant properties.

Strain localisation in the continental lithosphere, a scale-dependent process

NASA Astrophysics Data System (ADS)

Jolivet, Laurent; Burov, Evguenii

2013-04-01

Strain localisation in continents is a general question tackled by specialists of various disciplines in Earth Sciences. Field geologists working at regional scale are able to describe the succession of events leading to the formation of large strain zones that accommodate large displacement within plate boundaries. On the other end of the spectrum, laboratory experiments provide numbers that quantitatively describe the rheology of rock material at the scale of a few mm and at deformation rates up to 8-10 orders of magnitude faster than in nature. Extrapolating from the scale of the experiment to the scale of the continental lithosphere is a considerable leap across 8-10 orders of magnitude both in space and time. It is however quite obvious that different processes are at work for each scale considered. At the scale of a grain aggregate diffusion within individual grains, dislocation or grain boundary sliding, depending on temperature and fluid conditions, are of primary importance. But at the scale of a mountain belt, a major detachment or a strike-slip shear zone that have accommodated tens or hundreds of kilometres of relative displacement, other parameters will take over such as structural softening and the heterogeneity of the crust inherited from past tectonic events that have juxtaposed rock units of very different compositions and induced a strong orientation of rocks. Once the deformation is localised along major shear zones, grain size reduction, interaction between rocks and fluids and metamorphic reactions and other small-scale processes tend to further localise the strain. Because the crust is colder and more lithologically complex this heterogeneity is likely much more prominent in the crust than in the mantle and then the relative importance of "small-scale" and "large-scale" parameters will be very different in the crust and in the mantle. Thus, depending upon the relative thickness of the crust and mantle in the deforming lithosphere, the role of each mechanism will have more or less important consequences on strain localisation. This complexity sometimes leads to disregard of experimental parameters in large-scale thermo-mechanical models and to use instead ad hoc "large-scale" numbers that better fit the observed geological history. The goal of the ERC RHEOLITH project is to associate to each tectonic process the relevant rheological parameters depending upon the scale considered, in an attempt to elaborate a generalized "Preliminary Rheology Model Set for Lithosphere" (PReMSL), which will cover the entire time and spatial scale range of deformation.

Cavitation in Amorphous Solids

NASA Astrophysics Data System (ADS)

Guan, Pengfei; Lu, Shuo; Spector, Michael J. B.; Valavala, Pavan K.; Falk, Michael L.

2013-05-01

Molecular dynamics simulations of cavitation in a Zr50Cu50 metallic glass exhibit a waiting time dependent cavitation rate. On short time scales nucleation rates and critical cavity sizes are commensurate with a classical theory of nucleation that accounts for both the plastic dissipation during cavitation and the cavity size dependence of the surface energy. All but one parameter, the Tolman length, can be extracted directly from independent calculations or estimated from physical principles. On longer time scales strain aging in the form of shear relaxations results in a systematic decrease of cavitation rate. The high cavitation rates that arise due to the suppression of the surface energy in small cavities provide a possible explanation for the quasibrittle fracture observed in metallic glasses.

A physical model for strain accumulation in the San Francisco Bay Region

USGS Publications Warehouse

Pollitz, F.F.; Nyst, M.

2005-01-01

Strain accumulation in tectonically active regions is generally a superposition of the effects of background tectonic loading, steady-state dislocation processes, such as creep, and transient deformation. In the San Francisco Bay region (SFBR), the most uncertain of these processes is transient deformation, which arises primarily in association with large earthquakes. As such, it depends upon the history of faulting and the rheology of the crust and mantle, which together determine the pattern of longer term (decade-scale) post-seismic response to earthquakes. We utilize a set of 102 GPS velocity vectors in the SFBR in order to characterize the strain rate field and construct a physical model of its present deformation. We first perform an inversion for the continuous velocity gradient field from the discrete GPS velocity field, from which both tensor strain rate and rotation rate may be extracted. The present strain rate pattern is well described as a nearly uniform shear strain rate oriented approximately N34??W (140 nanostrain yr-1) plus a N56??E uniaxial compression rate averaging 20 nanostrain yr-1 across the shear zone. We fit the velocity and strain rate fields to a model of time-dependent deformation within a 135-kin-wide, arcuate shear zone bounded by strong Pacific Plate and Sierra Nevada block lithosphere to the SW and NE, respectively. Driving forces are purely lateral, consisting of shear zone deformation imposed by the relative motions between the thick Pacific Plate and Sierra Nevada block lithospheres. Assuming a depth-dependent viscoelastic structure within the shear zone, we account for the effects of steady creep on faults and viscoelastic relaxation following the 1906 San Francisco and 1989 Loma Prieta earthquakes, subject to constant velocity boundary conditions on the edges of the shear zone. Fault creep is realized by evaluating dislocations on the creeping portions of faults in the fluid limit of the viscoelastic model. A priori plate-boundary(PB)-parallel motion is set to 38 mm yr -1. A grid search based on fitting the observed strain rate pattern yields a mantle viscosity of 1.2 ?? 1019 Pa s and a PB-perpendicular convergence rate of ???3 mm yr-1. Most of this convergence appears to be uniformly distributed in the Pacific-Sierra Nevada plate boundary zone. ?? 2005 RAS.

Strength and Anisotropy in Tournemire Shale: Temperature, Pressure and Time Dependences

NASA Astrophysics Data System (ADS)

Bonnelye, A.; Schubnel, A.; Zhi, G.; David, C.; Dick, P.

2017-12-01

Time and temperature dependent rock deformation has both scientific and socio-economic implications for natural hazards, the oil and gas industry and nuclear waste disposal. During the past decades, most studies on brittle creep have focused on igneous rocks and porous sedimentary rocks. To our knowledge, only few studies have been carried out on the brittle creep behavior of shale. We conducted a series of creep experiments on shale specimens coming from the French Institute for Nuclear Safety (IRSN) underground research laboratory located in Tournemire, France, under two different temperatures (26°C, 75°C) and confining pressures (10 MPa, 80 MPa), for three orientations (σ1along, perpendicular and 45° to bedding). In these long-term experiments (approximately 10 days), stress and strains were recorded continuously, while ultrasonic acoustic velocities were recorded every 1 15 minutes. The brittle creep failure stress of our Tournemire shale samples was systematically observed 50% higher than its short-term peak strength, with larger final axial strain accumulated. During creep, ultrasonic wave velocities first decreased, and then increased gradually. The magnitude of elastic wave velocity variations showed an important orientation and temperature dependence: velocities measured perpendicular to bedding showed increased variation, variation that was enhanced at higher temperature and higher pressure. The case of complete elastic anisotropy reversal was observed for sample deformed perpendicular to bedding, with amount of axial strain needed to reach anisotropy reversal reduced at higher temperature. SEM observations highlight the competition between crack growth, sealing/healing, and possibly mineral rotation, pressure solution or anisotropic compaction during creep defromation. Our study highlights that the short-term peak strength has little meaning in shale material, which can over-consolidate importantly by `plastic' flow. In addition, we show that elastic anisotropy can switch and even reverse over relatively short time periods (<10 days) and for relatively small amount of plastic deformation (<5%).

Time-Dependent Reversible-Irreversible Deformation Threshold Determined Explicitly by Experimental Technique

NASA Technical Reports Server (NTRS)

Castelli, Michael G.; Arnold, Steven M.

2000-01-01

Structural materials for the design of advanced aeropropulsion components are usually subject to loading under elevated temperatures, where a material's viscosity (resistance to flow) is greatly reduced in comparison to its viscosity under low-temperature conditions. As a result, the propensity for the material to exhibit time-dependent deformation is significantly enhanced, even when loading is limited to a quasi-linear stress-strain regime as an effort to avoid permanent (irreversible) nonlinear deformation. An understanding and assessment of such time-dependent effects in the context of combined reversible and irreversible deformation is critical to the development of constitutive models that can accurately predict the general hereditary behavior of material deformation. To this end, researchers at the NASA Glenn Research Center at Lewis Field developed a unique experimental technique that identifies the existence of and explicitly determines a threshold stress k, below which the time-dependent material deformation is wholly reversible, and above which irreversible deformation is incurred. This technique is unique in the sense that it allows, for the first time, an objective, explicit, experimental measurement of k. The underlying concept for the experiment is based on the assumption that the material s time-dependent reversible response is invariable, even in the presence of irreversible deformation.

Conjugative Plasmid Transfer in Xylella fastidiosa Is Dependent on tra and trb Operon Functions

PubMed Central

Van Horn, Christopher R.

2017-01-01

ABSTRACT The insect-transmitted plant pathogen Xylella fastidiosa is capable of efficient horizontal gene transfer (HGT) and recombination. Natural transformation occurs at high rates in X. fastidiosa, but there also is evidence that certain strains of X. fastidiosa carry native plasmids equipped with transfer and mobilization genes, suggesting conjugation as an additional mechanism of HGT in some instances. Two operons, tra and trb, putatively encoding a conjugative type IV secretion system, are found in some but not all X. fastidiosa isolates, often on native plasmids. X. fastidiosa strains that carry the conjugative transfer genes can belong to different subspecies and frequently differ in host ranges. Using X. fastidiosa strain M23 (X. fastidiosa subsp. fastidiosa) or Dixon (X. fastidiosa subsp. multiplex) as the donor strain and Temecula (X. fastidiosa subsp. fastidiosa) as the recipient strain, plasmid transfer was characterized using the mobilizable broad-host-range vector pBBR5pemIK. Transfer of plasmid pBBR5pemIK was observed under in vitro conditions with both donor strains and was dependent on both tra and trb operon functions. A conjugative mechanism likely contributes to gene transfer between diverse strains of X. fastidiosa, possibly facilitating adaptation to new environments or different hosts. IMPORTANCE Xylella fastidiosa is an important plant pathogen worldwide, infecting a wide range of different plant species. The emergence of new diseases caused by X. fastidiosa, or host switching of existing strains, is thought to be primarily due to the high frequency of HGT and recombination in this pathogen. Transfer of plasmids by a conjugative mechanism enables movement of larger amounts of genetic material at one time, compared with other routes of gene transfer such as natural transformation. Establishing the prevalence and functionality of this mechanism in X. fastidiosa contributes to a better understanding of HGT, adaptation, and disease emergence in this diverse pathogen. PMID:28808128

Strain rate effect on fault slip and rupture evolution: Insight from meter-scale rock friction experiments

NASA Astrophysics Data System (ADS)

Xu, Shiqing; Fukuyama, Eiichi; Yamashita, Futoshi; Mizoguchi, Kazuo; Takizawa, Shigeru; Kawakata, Hironori

2018-05-01

We conduct meter-scale rock friction experiments to study strain rate effect on fault slip and rupture evolution. Two rock samples made of Indian metagabbro, with a nominal contact dimension of 1.5 m long and 0.1 m wide, are juxtaposed and loaded in a direct shear configuration to simulate the fault motion. A series of experimental tests, under constant loading rates ranging from 0.01 mm/s to 1 mm/s and under a fixed normal stress of 6.7 MPa, are performed to simulate conditions with changing strain rates. Load cells and displacement transducers are utilized to examine the macroscopic fault behavior, while high-density arrays of strain gauges close to the fault are used to investigate the local fault behavior. The observations show that the macroscopic peak strength, strength drop, and the rate of strength drop can increase with increasing loading rate. At the local scale, the observations reveal that slow loading rates favor generation of characteristic ruptures that always nucleate in the form of slow slip at about the same location. In contrast, fast loading rates can promote very abrupt rupture nucleation and along-strike scatter of hypocenter locations. At a given propagation distance, rupture speed tends to increase with increasing loading rate. We propose that a strain-rate-dependent fault fragmentation process can enhance the efficiency of fault healing during the stick period, which together with healing time controls the recovery of fault strength. In addition, a strain-rate-dependent weakening mechanism can be activated during the slip period, which together with strain energy selects the modes of fault slip and rupture propagation. The results help to understand the spectrum of fault slip and rock deformation modes in nature, and emphasize the role of heterogeneity in tuning fault behavior under different strain rates.

Conjugative Plasmid Transfer in Xylella fastidiosa Is Dependent on tra and trb Operon Functions.

PubMed

Burbank, Lindsey P; Van Horn, Christopher R

2017-11-01

The insect-transmitted plant pathogen Xylella fastidiosa is capable of efficient horizontal gene transfer (HGT) and recombination. Natural transformation occurs at high rates in X. fastidiosa , but there also is evidence that certain strains of X. fastidiosa carry native plasmids equipped with transfer and mobilization genes, suggesting conjugation as an additional mechanism of HGT in some instances. Two operons, tra and trb , putatively encoding a conjugative type IV secretion system, are found in some but not all X. fastidiosa isolates, often on native plasmids. X. fastidiosa strains that carry the conjugative transfer genes can belong to different subspecies and frequently differ in host ranges. Using X. fastidiosa strain M23 ( X. fastidiosa subsp. fastidiosa ) or Dixon ( X. fastidiosa subsp. multiplex ) as the donor strain and Temecula ( X. fastidiosa subsp. fastidiosa ) as the recipient strain, plasmid transfer was characterized using the mobilizable broad-host-range vector pBBR5pemIK. Transfer of plasmid pBBR5pemIK was observed under in vitro conditions with both donor strains and was dependent on both tra and trb operon functions. A conjugative mechanism likely contributes to gene transfer between diverse strains of X. fastidiosa , possibly facilitating adaptation to new environments or different hosts. IMPORTANCE Xylella fastidiosa is an important plant pathogen worldwide, infecting a wide range of different plant species. The emergence of new diseases caused by X. fastidiosa , or host switching of existing strains, is thought to be primarily due to the high frequency of HGT and recombination in this pathogen. Transfer of plasmids by a conjugative mechanism enables movement of larger amounts of genetic material at one time, compared with other routes of gene transfer such as natural transformation. Establishing the prevalence and functionality of this mechanism in X. fastidiosa contributes to a better understanding of HGT, adaptation, and disease emergence in this diverse pathogen.

Polymeric Materials Models in the Warrior Injury Assessment Manikin (WIAMan) Anthropomorphic Test Device (ATD) Tech Demonstrator

DTIC Science & Technology

2017-01-01

are the shear relaxation moduli and relaxation times , which make up the classical Prony series . A Prony- series expansion is a relaxation function...approximation for modeling time -dependent damping. The scalar parameters 1 and 2 control the nonlinearity of the Prony series . Under the...Velodyne that best fit the experimental stress-strain data. To do so, the Design Analysis Kit for Optimization and Terascale Applications (DAKOTA

Stress-sensitive tissue regeneration in viscoelastic biomaterials subjected to modulated tensile strain.

PubMed

Belfiore, Laurence A; Floren, Michael L; Paulino, Alexandre T; Belfiore, Carol J

2011-09-01

This research contribution addresses the mechanochemistry of intra-tissue mass transfer for nutrients, oxygen, growth factors, and other essential ingredients that anchorage-dependent cells require for successful proliferation on biocompatible surfaces. The unsteady state reaction-diffusion equation (i.e., modified diffusion equation) is solved according to the von Kármán-Pohlhausen integral method of boundary layer analysis when nutrient consumption and tissue regeneration are stimulated by harmonically imposed stress. The mass balance with diffusion and stress-sensitive kinetics represents a rare example where the Damköhler and Deborah numbers appear together in an effort to simulate the development of mass transfer boundary layers in porous viscoelastic biomaterials. The Boltzmann superposition integral is employed to calculate time-dependent strain in terms of the real and imaginary components of dynamic compliance for viscoelastic solids that transmit harmonic excitation to anchorage-dependent cells. Rates of nutrient consumption under stress-free conditions are described by third-order kinetics which include local mass densities of nutrients, oxygen, and attached cells that maintain dynamic equilibrium with active protein sites in the porous matrix. Thinner nutrient mass transfer boundary layers are stabilized at shorter dimensionless diffusion times when the stress-free intra-tissue Damköhler number increases above its initial-condition-sensitive critical value. The critical stress-sensitive intra-tissue Damköhler number, above which it is necessary to consider the effect of harmonic strain on nutrient consumption and tissue regeneration, is proportional to the Deborah number and corresponds to a larger fraction of the stress-free intra-tissue Damköhler number in rigid biomaterials. Copyright © 2011 Elsevier B.V. All rights reserved.

Production flush of Agaricus blazei on Brazilian casing layers

PubMed Central

Colauto, Nelson Barros; da Silveira, Adriano Reis; da Eira, Augusto Ferreira; Linde, Giani Andrea

2011-01-01

This study aimed to verify the biological efficiency and production flushes of Agaricus blazei strains on different casing layers during 90 cultivation days. Four casing layers were used: mixture of subsoil and charcoal (VCS), lime schist (LSC), São Paulo peat (SPP) and Santa Catarina peat (SCP); and two genetically distant A. blazei strains. The fungus was grown in composted substratum and, after total colonization, a pasteurized casing layer was added over the substratum, and fructification was induced. Mushrooms were picked up daily when the basidiocarp veil was stretched, but before the lamella were exposed. The biological efficiency (BE) was determined by the fresh basidiocarp mass divided by the substratum dry mass, expressed in percentage. The production flushes were also determined over time production. The BE and production flushes during 90 days were affected by the strains as well as by the casing layers. The ABL26 and LSC produced the best BE of 60.4%. Although VCS is the most used casing layer in Brazil, it is inferior to other casing layers, for all strains, throughout cultivation time. The strain, not the casing layer, is responsible for eventual variations of the average mushroom mass. In average, circa 50% of the mushroom production occurs around the first month, 30% in the second month, and 20% in third month. The casing layer water management depends on the casing layer type and the strain. Production flush responds better to water reposition, mainly with ABL26, and better porosity to LSC and SCP casing layers. PMID:24031673

Electromechanical properties of Na0.5Bi0.5TiO3-SrTiO3-PbTiO3 solid solutions

NASA Astrophysics Data System (ADS)

Svirskas, Šarūnas; Dunce, Marija; Birks, Eriks; Sternberg, Andris; Banys, Jūras

2018-03-01

Thorough studies of electric field-induced strain are presented in 0.4Na1/2Bi1/2TiO3-(0.6-x)SrTiO3-xPbTiO3 (NBT-ST-PT) ternary solid solutions. The increase of concentration of lead x induces crossover from relaxor to ferroelectric. Strain in a relaxor state can be described by electrostrictive behavior. The electrostrictive coefficients correspond to other well-known relaxor ferroelectrics. The concentration region with a stable ferroelectric phase revealed that the polarization dependence of strain does not exhibit nonlinearity, although they are inherent to the electric field dependence of strain. In this case, electric field dependence of strain is described in terms of the Rayleigh law and the role of domain wall contribution is extracted. Finally, the character of strain at the electric field-induced phase transition between the nonpolar and the ferroelectric states is studied. The data shows that in the vicinity of the electric field induced phase transition the strain vs. electric field displays electrostrictive character.

Grain Orientation Dependence of the Residual Lattice Strain in a Cold Rolled Interstitial-Free Steel

DOE PAGES

Xie, Qingge; Gorti, Sarma B.; Sidor, Jurij; ...

2018-01-10

The experimentally measured grain-orientation-dependent residual lattice strains, evolved in an interstitia-free steel after 70% cold rolling reduction, are studied by means of crystal elastic visco-plastic finite element simulations, which provides a very satisfactory prediction of deformation texture. The calculated residual lattice strain pole figure matches well with the experimentally measured counterpart within the highest density regions of major texture components observed. Both experimental evidence and results of modeling clearly indicate that the residual lattice strain is orientation dependent, based on comprehensive information on the evolution of residual lattice strain in various crystallographic orientations during plastic deformation. It appears that inmore » a cold rolled material, there is a general correlation between the stresses developed just prior to unloading and the residual lattice strains in particular directions. Here, it is also shown that the cumulative plastic shear does not reveal a clear correlation with the components of residual lattice strain while presented in the normal correlation plot, however, this relationship can be better understood by means of the orientation distribution function of residual lattice strain, which can be derived from the neutron or X-ray diffraction experiments.« less

Grain Orientation Dependence of the Residual Lattice Strain in a Cold Rolled Interstitial-Free Steel

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

Xie, Qingge; Gorti, Sarma B.; Sidor, Jurij

The experimentally measured grain-orientation-dependent residual lattice strains, evolved in an interstitia-free steel after 70% cold rolling reduction, are studied by means of crystal elastic visco-plastic finite element simulations, which provides a very satisfactory prediction of deformation texture. The calculated residual lattice strain pole figure matches well with the experimentally measured counterpart within the highest density regions of major texture components observed. Both experimental evidence and results of modeling clearly indicate that the residual lattice strain is orientation dependent, based on comprehensive information on the evolution of residual lattice strain in various crystallographic orientations during plastic deformation. It appears that inmore » a cold rolled material, there is a general correlation between the stresses developed just prior to unloading and the residual lattice strains in particular directions. Here, it is also shown that the cumulative plastic shear does not reveal a clear correlation with the components of residual lattice strain while presented in the normal correlation plot, however, this relationship can be better understood by means of the orientation distribution function of residual lattice strain, which can be derived from the neutron or X-ray diffraction experiments.« less

Evidence for history-dependence of influenza pandemic emergence

NASA Astrophysics Data System (ADS)

Hill, Edward M.; Tildesley, Michael J.; House, Thomas

2017-03-01

Influenza A viruses have caused a number of global pandemics, with considerable mortality in humans. Here, we analyse the time periods between influenza pandemics since 1700 under different assumptions to determine whether the emergence of new pandemic strains is a memoryless or history-dependent process. Bayesian model selection between exponential and gamma distributions for these time periods gives support to the hypothesis of history-dependence under eight out of nine sets of modelling assumptions. Using the fitted parameters to make predictions shows a high level of variability in the modelled number of pandemics from 2010-2110. The approach we take here relies on limited data, so is uncertain, but it provides cheap, safe and direct evidence relating to pandemic emergence, a field where indirect measurements are often made at great risk and cost.

Time dependence of composite shrinkage using halogen and LED light curing.

PubMed

Uhl, Alexander; Mills, Robin W; Rzanny, Angelika E; Jandt, Klaus D

2005-03-01

The polymerization shrinkage of light cured dental composites presents the major drawback for these aesthetically adaptable restorative materials. LED based light curing technology has recently become commercially available. Therefore, the aim of the present study was to investigate if there was a statistically significant difference in linear and volumetric composite shrinkage strain if a LED LCU is used for the light curing process rather than a conventional halogen LCU. The volumetric shrinkage strain was determined using the Archimedes buoyancy principle after 5, 10, 20, 40 s of light curing and after 120 s following the 40 s light curing time period. The linear shrinkage strain was determined with a dynamic mechanical analyzer for the composites Z100, Spectrum, Solitaire2 and Definite polymerized with the LCUs Trilight (halogen), Freelight I (LED) and LED63 (LED LCU prototype). The changes in irradiance and spectra of the LCUs were measured after 0, 312 and 360 min of duty time. In general there was no considerable difference in shrinkage of the composites Z100, Spectrum or Solitaire2 when the LED63 was used instead of the Trilight. There was, however, a statistically significant difference in shrinkage strain when the composite Definite was polymerized with the LED63 instead of the Trilight. The spectrum of the Trilight changed during the experiment considerably whereas the LED63 showed an almost constant light output. The Freelight I dropped considerably in irradiance and had to be withdrawn from the study because of technical problems. The composites containing only the photoinitiator camphorquinone showed similar shrinkage strain behaviour when a LED or halogen LCU is used for the polymerization. The irradiance of some LED LCUs can also decrease over time and should therefore be checked on a regular basis.

Numerical modelling of the evolution of conglomerate deformation up to high simple-shear strain

NASA Astrophysics Data System (ADS)

Ran, Hao; Bons, Paul D.; Wang, Genhou; Steinbach, Florian; Finch, Melanie; Ran, Shuming; Liang, Xiao; Zhou, Jie

2017-04-01

Deformed conglomerates have been widely used to investigate deformation history and structural analysis, using strain analyses techniques, such as the Rf-Φ and Fry methods on deformed pebbles. Although geologists have focused on the study of deformed conglomerates for several decades, some problems of the process and mechanism of deformation, such as the development of structures in pebbles and matrix, are still not understand well. Numerical modelling provides a method to investigate the process of deformation, as a function of different controlling parameters, up to high strains at conditions that cannot be achieved in the laboratory. We use the 2D numerical modelling platform Elle coupled to the full field crystal visco-plasticity code (VPFFT) to simulate the deformation of conglomerates under simple shear conditions, achieving high finite strains of ≥10. Probably for the first time, we included the effect of an anisotropy, i.e. mica-rich matrix. Our simulations show the deformation of pebbles not only depends on the viscosity contrast between pebbles and matrix but emphasises the importance of interaction between neighbouring pebbles. Under the same finite strain shearing the pebbles of conglomerates with high pebble densities show higher Rf and lower Φ than those of conglomerates with a low density pebbles. Strain localisation can be observed at both the margin of strong pebbles and in the bridging area between the pebbles. At low to medium finite strain, local areas show the opposite (antithetic) shear sense because of the different relative rotation and movement of pebbles or clusters of pebbles. Very hard pebbles retain their original shape and may rotate, depending on the anisotropy of the matrix. σ-clasts are formed by pebbles with moderate viscosity contrast between pebble and a softer matrix. By contrast, δ-clasts are not observed in our simulations with both isotropic and anisotropic matrices, which is consistent with their relative scarcity in natural mylonites. The formation of SC-fabrics is enhanced by anisotropy of the matrix, which facilitates strain partitioning in low-strain S-domains and high strain C-domains.

Influenza A Virus Infection Predisposes Hosts to Secondary Infection with Different Streptococcus pneumoniae Serotypes with Similar Outcome but Serotype-Specific Manifestation.

PubMed

Sharma-Chawla, Niharika; Sender, Vicky; Kershaw, Olivia; Gruber, Achim D; Volckmar, Julia; Henriques-Normark, Birgitta; Stegemann-Koniszewski, Sabine; Bruder, Dunja

2016-12-01

Influenza A virus (IAV) and Streptococcus pneumoniae are major causes of respiratory tract infections, particularly during coinfection. The synergism between these two pathogens is characterized by a complex network of dysregulated immune responses, some of which last until recovery following IAV infection. Despite the high serotype diversity of S. pneumoniae and the serotype replacement observed since the introduction of conjugate vaccines, little is known about pneumococcal strain dependency in the enhanced susceptibility to severe secondary S. pneumoniae infection following IAV infection. Thus, we studied how preinfection with IAV alters host susceptibility to different S. pneumoniae strains with various degrees of invasiveness using a highly invasive serotype 4 strain, an invasive serotype 7F strain, and a carrier serotype 19F strain. A murine model of pneumococcal coinfection during the acute phase of IAV infection showed a significantly increased degree of pneumonia and mortality for all tested pneumococcal strains at otherwise sublethal doses. The incidence and kinetics of systemic dissemination, however, remained bacterial strain dependent. Furthermore, we observed strain-specific alterations in the pulmonary levels of alveolar macrophages, neutrophils, and inflammatory mediators ultimately affecting immunopathology. During the recovery phase following IAV infection, bacterial growth in the lungs and systemic dissemination were enhanced in a strain-dependent manner. Altogether, this study shows that acute IAV infection predisposes the host to lethal S. pneumoniae infection irrespective of the pneumococcal serotype, while the long-lasting synergism between IAV and S. pneumoniae is bacterial strain dependent. These results hold implications for developing tailored therapeutic treatment regimens for dual infections during future IAV outbreaks. Copyright © 2016, American Society for Microbiology. All Rights Reserved.

AN ORGANOTYPIC UNIAXIAL STRAIN MODEL USING MICROFLUIDICS

PubMed Central

Dollé, Jean-Pierre; Morrison, Barclay; Schloss, Rene R.; Yarmush, Martin L.

2012-01-01

Traumatic brain injuries are the leading cause of disability each year in the US. The most common and devastating consequence is the stretching of axons caused by shear deformation that occurs during rotational acceleration of the brain during injury. The injury effects on axonal molecular and functional events are not fully characterized. We have developed a strain injury model that maintains the three dimensional cell architecture and neuronal networks found in vivo with the ability to visualize individual axons and their response to a mechanical injury. The advantage of this model is that it can apply uniaxial strains to axons that make functional connections between two organotypic slices and injury responses can be observed in real-time and over long term. This uniaxial strain model was designed to be capable of applying an array of mechanical strains at various rates of strain, thus replicating a range of modes of axonal injury. Long term culture, preservation of slice and cell orientation, and slice-slice connection on the device was demonstrated. The device has the ability to strain either individual axons or bundles of axons through the control of microchannel dimensions. The fidelity of the model was verified by observing characteristic responses to various strain injuries which included axonal beading, delayed elastic effects and breakdown in microtubules. Microtubule breakdown was shown to be dependent on the degree of the applied strain field, where maximal breakdown was observed at peak strain and minimal breakdown is observed at low strain. This strain injury model could be a powerful tool in assessing strain injury effects on functional axonal connections. PMID:23233120

Mouse genetic differences in voluntary wheel running, adult hippocampal neurogenesis and learning on the multi-strain-adapted plus water maze

PubMed Central

Merritt, Jennifer; Rhodes, Justin S.

2014-01-01

Moderate levels of aerobic exercise broadly enhance cognition throughout the lifespan. One hypothesized contributing mechanism is increased adult hippocampal neurogenesis. Recently, we measured the effects of voluntary wheel running on adult hippocampal neurogenesis in 12 different mouse strains, and found increased neurogenesis in all strains, ranging from 2 to 5 fold depending on the strain. The purpose of this study was to determine the extent to which increased neurogenesis from wheel running is associated with enhanced performance on the water maze for 5 of the 12 strains, chosen based on their levels of neurogenesis observed in the previous study (C57BL/6J, 129S1/SvImJ, B6129SF1/J, DBA/2J, and B6D2F1/J). Mice were housed with or without a running wheels for 30 days then tested for learning and memory on the plus water maze, adapted for multiple strains, and rotarod test of motor performance. The first 10 days, animals were injected with BrdU to label dividing cells. After behavioral testing animals were euthanized to measure adult hippocampal neurogenesis using standard methods. Levels of neurogenesis depended on strain but all mice had a similar increase in neurogenesis in response to exercise. All mice acquired the water maze but performance depended on strain. Exercise improved water maze performance in all strains to a similar degree. Rotarod performance depended on strain. Exercise improved rotarod performance only in DBA/2J and B6D2F1/J mice. Taken together, results demonstrate that despite different levels of neurogenesis, memory performance and motor coordination in these mouse strains, all strains have the capacity to increase neurogenesis and improve learning on the water maze through voluntary wheel running. PMID:25435316

High-cycle electromechanical aging of dielectric elastomer actuators with carbon-based electrodes

NASA Astrophysics Data System (ADS)

de Saint-Aubin, C. A.; Rosset, S.; Schlatter, S.; Shea, H.

2018-07-01

We present high-cycle aging tests of dielectric elastomer actuators (DEAs) based on silicone elastomers, reporting on the time-evolution of actuation strain and of electrode resistance over millions of cycles. We compare several types of carbon-based electrodes, and for the first time show how the choice of electrode has a dramatic influence on DEA aging. An expanding circle DEA configuration is used, consisting of a commercial silicone membrane with the following electrodes: commercial carbon grease applied manually, solvent-diluted carbon grease applied by stamping (pad printing), loose carbon black powder applied manually, carbon black powder suspension applied by inkjet-printing, and conductive silicone-carbon composite applied by stamping. The silicone-based DEAs with manually applied carbon grease electrodes show the shortest lifetime of less than 105 cycles at 5% strain, while the inkjet-printed carbon powder and the stamped silicone-carbon composite make for the most reliable devices, with lifetimes greater than 107 cycles at 5% strain. These results are valid for the specific dielectric and electrode configurations that were tested: using other dielectrics or electrode formulations would lead to different lifetimes and failure modes. We find that aging (as seen in the change in resistance and in actuation strain versus cycle number) is independent of the actuation frequency from 10 Hz to 200 Hz, and depends on the total accumulated time the DEA spends in an actuated state.

Work-family conflict and sleep disturbance: the Malaysian working women study

PubMed Central

AAZAMI, Sanaz; MOZAFARI, Mosayeb; SHAMSUDDIN, Khadijah; AKMAL, Syaqirah

2015-01-01

This study aimed at assessing effect of the four dimensions of work-family conflicts (strain and time-based work interference into family and family interference into work) on sleep disturbance in Malaysian working women. This cross-sectional study was conducted among 325 Malaysian married working women. Multiple-stage simple random sampling method was used to recruit women from public service departments of Malaysia. Self-administrated questionnaires were used to measure the study variables and data were analyzed using SPSS version 21. We found that high level of the four dimensions of work-family conflicts significantly increase sleep disturbance. Our analyses also revealed an age-dependent effect of the work-family conflict on sleep disturbance. Women in their 20 to 30 yr old suffer from sleep disturbance due to high level of time-based and strain-based work-interference into family. However, the quality of sleep among women aged 30–39 were affected by strain-based family-interference into work. Finally, women older than 40 yr had significantly disturbed sleep due to strain-based work-interference into family as well as time-based family interference into work. Our findings showed that sleep quality of working women might be disturbed by experiencing high level of work-family conflict. However, the effects of inter-role conflicts on sleep varied among different age groups. PMID:26423332

The dynamic compressive behavior and constitutive modeling of D1 railway wheel steel over a wide range of strain rates and temperatures

NASA Astrophysics Data System (ADS)

Jing, Lin; Su, Xingya; Zhao, Longmao

The dynamic compressive behavior of D1 railway wheel steel at high strain rates was investigated using a split Hopkinson pressure bar (SHPB) apparatus. Three types of specimens, which were derived from the different positions (i.e., the rim, web and hub) of a railway wheel, were tested over a wide range of strain rates from 10-3 s-1 to 2.4 × 103 s-1 and temperatures from 213 K to 973 K. Influences of the strain rate and temperature on flow stress were discussed, and rate- and temperature-dependent constitutive relationships were assessed by the Cowper-Symonds model, Johnson-Cook model and a physically-based model, respectively. The experimental results show that the compressive true stress versus true strain response of D1 wheel steel is strain rate-dependent, and the strain hardening rate during the plastic flow stage decreases with the elevation of strain rate. Besides, the D1 wheel steel displays obvious temperature-dependence, and the third-type strain aging (3rd SA) is occurred at the temperature region of 673-973 K at a strain rate of ∼1500 s-1. Comparisons of experimental results with theoretical predictions indicate that the physically-based model has a better prediction capability for the 3rd SA characteristic of the tested D1 wheel steel.

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.

Comparative proteomic profiles of Aspergillus fumigatus and Aspergillus lentulus strains by surface-enhanced laser desorption ionization time-of-flight mass spectrometry (SELDI-TOF-MS)

PubMed Central

2011-01-01

Background Surface-enhanced laser desorption ionization time-of-flight mass spectrometry (SELDI-TOF-MS) was applied to analyze the protein profiles in both somatic and metabolic extracts of Aspergillus species. The study was carried out on some Aspergillus species within the Fumigati section (Aspergillus fumigatus wild-types and natural abnormally pigmented mutants, and Aspergillus lentulus). The aim was to validate whether mass spectrometry protein profiles can be used as specific signatures to discriminate different Aspergillus species or even mutants within the same species. Results The growth conditions and the SELDI-TOF parameters were determined to generate characteristic protein profiles of somatic and metabolic extracts of Aspergillus fumigatus strains using five different ProteinChips®, eight growth conditions combining two temperatures, two media and two oxygenation conditions. Nine strains were investigated: three wild-types and four natural abnormally pigmented mutant strains of A. fumigatus and two strains of A. lentulus. A total of 242 fungal extracts were prepared. The spectra obtained are protein signatures linked to the physiological states of fungal strains depending on culture conditions. The best resolutions were obtained using the chromatographic surfaces CM10, NP20 and H50 with fractions of fungi grown on modified Sabouraud medium at 37°C in static condition. Under these conditions, the SELDI-TOF analysis allowed A. fumigatus and A. lentulus strains to be grouped into distinct clusters. Conclusions SELDI-TOF analysis distinguishes A. fumigatus from A. lentulus strains and moreover, permits separate clusters of natural abnormally pigmented A. fumigatus strains to be obtained. In addition, this methodology allowed us to point out fungal components specifically produced by a wild-type strain or natural mutants. It offers attractive potential for further studies of the Aspergillus biology or pathogenesis. PMID:21798007

Comparative proteomic profiles of Aspergillus fumigatus and Aspergillus lentulus strains by surface-enhanced laser desorption ionization time-of-flight mass spectrometry (SELDI-TOF-MS).

PubMed

Pinel, Claudine; Arlotto, Marie; Issartel, Jean-Paul; Berger, François; Pelloux, Hervé; Grillot, Renée; Symoens, Françoise

2011-07-28

Surface-enhanced laser desorption ionization time-of-flight mass spectrometry (SELDI-TOF-MS) was applied to analyze the protein profiles in both somatic and metabolic extracts of Aspergillus species. The study was carried out on some Aspergillus species within the Fumigati section (Aspergillus fumigatus wild-types and natural abnormally pigmented mutants, and Aspergillus lentulus). The aim was to validate whether mass spectrometry protein profiles can be used as specific signatures to discriminate different Aspergillus species or even mutants within the same species. The growth conditions and the SELDI-TOF parameters were determined to generate characteristic protein profiles of somatic and metabolic extracts of Aspergillus fumigatus strains using five different ProteinChips®, eight growth conditions combining two temperatures, two media and two oxygenation conditions. Nine strains were investigated: three wild-types and four natural abnormally pigmented mutant strains of A. fumigatus and two strains of A. lentulus. A total of 242 fungal extracts were prepared. The spectra obtained are protein signatures linked to the physiological states of fungal strains depending on culture conditions. The best resolutions were obtained using the chromatographic surfaces CM10, NP20 and H50 with fractions of fungi grown on modified Sabouraud medium at 37 °C in static condition. Under these conditions, the SELDI-TOF analysis allowed A. fumigatus and A. lentulus strains to be grouped into distinct clusters. SELDI-TOF analysis distinguishes A. fumigatus from A. lentulus strains and moreover, permits separate clusters of natural abnormally pigmented A. fumigatus strains to be obtained. In addition, this methodology allowed us to point out fungal components specifically produced by a wild-type strain or natural mutants. It offers attractive potential for further studies of the Aspergillus biology or pathogenesis. © 2011 Pinel et al; licensee BioMed Central Ltd.

Shear deformation-induced anisotropic thermal conductivity of graphene.

PubMed

Cui, Liu; Shi, Sanqiang; Wei, Gaosheng; Du, Xiaoze

2018-01-03

Graphene-based materials exhibit intriguing phononic and thermal properties. In this paper, we have investigated the heat conductance in graphene sheets under shear-strain-induced wrinkling deformation, using equilibrium molecular dynamics simulations. A significant orientation dependence of the thermal conductivity of graphene wrinkles (GWs) is observed. The directional dependence of the thermal conductivity of GWs stems from the anisotropy of phonon group velocities as revealed by the G-band broadening of the phonon density of states (DOS), the anisotropy of thermal resistance as evidenced by the G-band peak mismatch of the phonon DOS, and the anisotropy of phonon relaxation times as a direct result of the double-exponential-fitting of the heat current autocorrelation function. By analyzing the relative contributions of different lattice vibrations to the heat flux, we have shown that the contributions of different lattice vibrations to the heat flux of GWs are sensitive to the heat flux direction, which further indicates the orientation-dependent thermal conductivity of GWs. Moreover, we have found that, in the strain range of 0-0.1, the anisotropy ratio of GWs increases monotonously with increasing shear strain. This is induced by the change in the number of wrinkles, which is more influential in the direction perpendicular to the wrinkle texture. The findings elucidated here emphasize the utility of wrinkle engineering for manipulation of nanoscale heat transport, which offers opportunities for the development of thermal channeling devices.

A model for shrinkage strain in photo polymerization of dental composites.

PubMed

Petrovic, Ljubomir M; Atanackovic, Teodor M

2008-04-01

We formulate a new model for the shrinkage strain developed during photo polymerization in dental composites. The model is based on the diffusion type fractional order equation, since it has been proved that polymerization reaction is diffusion controlled (Atai M, Watts DC. A new kinetic model for the photo polymerization shrinkage-strain of dental composites and resin-monomers. Dent Mater 2006;22:785-91). Our model strongly confirms the observation by Atai and Watts (see reference details above) and their experimental results. The shrinkage strain is modeled by a nonlinear differential equation in (see reference details above) and that equation must be solved numerically. In our approach, we use the linear fractional order differential equation to describe the strain rate due to photo polymerization. This equation is solved exactly. As shrinkage is a consequence of the polymerization reaction and polymerization reaction is diffusion controlled, we postulate that shrinkage strain rate is described by a diffusion type equation. We find explicit form of solution to this equation and determine the strain in the resin monomers. Also by using equations of linear viscoelasticity, we determine stresses in the polymer due to the shrinkage. The time evolution of stresses implies that the maximal stresses are developed at the very beginning of the polymerization process. The stress in a dental composite that is light treated has the largest value short time after the treatment starts. The strain settles at the constant value in the time of about 100s (for the cases treated in Atai and Watts). From the model developed here, the shrinkage strain of dental composites and resin monomers is analytically determined. The maximal value of stresses is important, since this value must be smaller than the adhesive bond strength at cavo-restoration interface. The maximum stress determined here depends on the diffusivity coefficient. Since diffusivity coefficient increases as polymerization proceeds, it follows that the periods of light treatments should be shorter at the beginning of the treatment and longer at the end of the treatment, with dark interval between the initial low intensity and following high intensity curing. This is because at the end of polymerization the stress relaxation cannot take place.

Early zygote-specific nuclease in mitochondria of the true slime mold Physarum polycephalum.

PubMed

Moriyama, Yohsuke; Yamazaki, Tomokazu; Nomura, Hideo; Sasaki, Narie; Kawano, Shigeyuki

2005-11-01

The active, selective digestion of mtDNA from one parent is a possible molecular mechanism for the uniparental inheritance of mtDNA. In Physarum polycephalum, mtDNA is packed by DNA-binding protein Glom, which packs mtDNA into rod-shaped mt-nucleoids. After the mating, mtDNA from one parent is selectively digested, and the Glom began to disperse. Dispersed Glom was retained for at least 6 h after mtDNA digestion, but disappeared completely by about 12 h after mixing two strains. We identified two novel nucleases using DNA zymography with native-PAGE and SDS-PAGE. One is a Ca2+-dependent, high-molecular-weight nuclease complex (about 670 kDa), and the other is a Mn2+-dependent, high-molecular-weight nuclease complex (440-670 kDa); the activity of the latter was detected as a Mn2+-dependent, 13-kDa DNase band on SDS-PAGE. All mitochondria isolated from myxamoebae had mt-nucleoids, whereas half of the mitochondria isolated from the zygotes at 12 h after mixing had lost the mt-nucleoids. The activity of the Mn2+-dependent nuclease in the isolated mitochondria was detected at least 8 h after mixing of two strains. The timing and localization of the Mn2+-dependent DNase activity matched the selective digestion of mtDNA.

Virulence and competitive ability in genetically diverse malaria infections

PubMed Central

de Roode, Jacobus C.; Pansini, Riccardo; Cheesman, Sandra J.; Helinski, Michelle E. H.; Huijben, Silvie; Wargo, Andrew R.; Bell, Andrew S.; Chan, Brian H. K.; Walliker, David; Read, Andrew F.

2005-01-01

Explaining parasite virulence is a great challenge for evolutionary biology. Intuitively, parasites that depend on their hosts for their survival should be benign to their hosts, yet many parasites cause harm. One explanation for this is that within-host competition favors virulence, with more virulent strains having a competitive advantage in genetically diverse infections. This idea, which is well supported in theory, remains untested empirically. Here we provide evidence that within-host competition does indeed select for high parasite virulence. We examine the rodent malaria Plasmodium chabaudi in laboratory mice, a parasite–host system in which virulence can be easily monitored and competing strains quantified by using strain-specific real-time PCR. As predicted, we found a strong relationship between parasite virulence and competitive ability, so that more virulent strains have a competitive advantage in mixed-strain infections. In transmission experiments, we found that the strain composition of the parasite populations in mosquitoes was directly correlated with the composition of the blood-stage parasite population. Thus, the outcome of within-host competition determined relative transmission success. Our results imply that within-host competition is a major factor driving the evolution of virulence and can explain why many parasites harm their hosts. PMID:15894623

High-level penicillin resistance and penicillin-gentamicin synergy in Enterococcus faecium.

PubMed Central

Torres, C; Tenorio, C; Lantero, M; Gastañares, M J; Baquero, F

1993-01-01

Thirty-seven Enterococcus faecium strains with different levels of penicillin susceptibility were studied in time-kill experiments with a fixed concentration (5 micrograms/ml) of gentamicin combined with different penicillin concentrations (6 to 600 micrograms/ml). Synergy was defined as a relative decrease in counts of greater than 2 log10 CFU per milliliter after 24 h of incubation when the combination of the antibiotics was compared with its most active component alone. The minimal synergistic penicillin concentrations found were 6 micrograms/ml for 16 of 16 strains for which penicillin MICs were < or = 25 micrograms/ml, 20 to 100 micrograms/ml for 14 of 17 strains for which penicillin MICs were 50 to 200 micrograms/ml, and 200 to 500 micrograms/ml for 4 of 4 strains for which MICs penicillin were > 200 micrograms/ml. Penicillin-gentamicin synergy was observed even in high-level penicillin-resistant E. faecium strains at penicillin concentrations close to one-half the penicillin MIC. The possibility of treating infections caused by high-level penicillin-resistant E. faecium strains with penicillin-gentamicin combinations in particular cases may depend on the penicillin levels attainable in vivo. PMID:8285628

Isolation of hydrocarbon-degrading extremely halophilic archaea from an uncontaminated hypersaline pond (Camargue, France).

PubMed

Tapilatu, Yosmina H; Grossi, Vincent; Acquaviva, Monique; Militon, Cécile; Bertrand, Jean-Claude; Cuny, Philippe

2010-03-01

Little information exists about the ability of halophilic archaea present in hypersaline environments to degrade hydrocarbons. In order to identify the potential actors of hydrocarbon degradation in these environments, enrichment cultures were prepared using samples collected from a shallow crystallizer pond with no known contamination history in Camargue, France, with n-alkanes provided as source of carbon and energy. Five alkane-degrading halophilic archaeal strains were isolated: one (strain MSNC 2) was closely related to Haloarcula and three (strains MSNC 4, MSNC 14, and MSNC 16) to Haloferax. Biodegradation assays showed that depending on the strain, 32 to 95% (0.5 g/l) of heptadecane was degraded after 30 days of incubation at 40 degrees C in 225 g/l NaCl artificial medium. One of the strains (MSNC 14) was also able to degrade phenanthrene. This work clearly shows for the first time the potential role of halophilic archaea belonging to the genera Haloarcula and Haloferax in the degradation of hydrocarbons in both pristine and hydrocarbon-contaminated hypersaline environments.

Implementation of Laminate Theory Into Strain Rate Dependent Micromechanics Analysis of Polymer Matrix Composites

NASA Technical Reports Server (NTRS)

Goldberg, Robert K.

2000-01-01

A research program is in progress to develop strain rate dependent deformation and failure models for the analysis of polymer matrix composites subject to impact loads. Previously, strain rate dependent inelastic constitutive equations developed to model the polymer matrix were implemented into a mechanics of materials based micromechanics method. In the current work, the computation of the effective inelastic strain in the micromechanics model was modified to fully incorporate the Poisson effect. The micromechanics equations were also combined with classical laminate theory to enable the analysis of symmetric multilayered laminates subject to in-plane loading. A quasi-incremental trapezoidal integration method was implemented to integrate the constitutive equations within the laminate theory. Verification studies were conducted using an AS4/PEEK composite using a variety of laminate configurations and strain rates. The predicted results compared well with experimentally obtained values.

Modeling the Rate-Dependent Durability of Reduced-Ag SAC Interconnects for Area Array Packages Under Torsion Loads

NASA Astrophysics Data System (ADS)

Srinivas, Vikram; Menon, Sandeep; Osterman, Michael; Pecht, Michael G.

2013-08-01

Solder durability models frequently focus on the applied strain range; however, the rate of applied loading, or strain rate, is also important. In this study, an approach to incorporate strain rate dependency into durability estimation for solder interconnects is examined. Failure data were collected for SAC105 solder ball grid arrays assembled with SAC305 solder that were subjected to displacement-controlled torsion loads. Strain-rate-dependent (Johnson-Cook model) and strain-rate-independent elastic-plastic properties were used to model the solders in finite-element simulation. Test data were then used to extract damage model constants for the reduced-Ag SAC solder. A generalized Coffin-Manson damage model was used to estimate the durability. The mechanical fatigue durability curve for reduced-silver SAC solder was generated and compared with durability curves for SAC305 and Sn-Pb from the literature.

Dynamical heterogeneities and mechanical non-linearities: Modeling the onset of plasticity in polymer in the glass transition.

PubMed

Masurel, R J; Gelineau, P; Lequeux, F; Cantournet, S; Montes, H

2017-12-27

In this paper we focus on the role of dynamical heterogeneities on the non-linear response of polymers in the glass transition domain. We start from a simple coarse-grained model that assumes a random distribution of the initial local relaxation times and that quantitatively describes the linear viscoelasticity of a polymer in the glass transition regime. We extend this model to non-linear mechanics assuming a local Eyring stress dependence of the relaxation times. Implementing the model in a finite element mechanics code, we derive the mechanical properties and the local mechanical fields at the beginning of the non-linear regime. The model predicts a narrowing of distribution of relaxation times and the storage of a part of the mechanical energy --internal stress-- transferred to the material during stretching in this temperature range. We show that the stress field is not spatially correlated under and after loading and follows a Gaussian distribution. In addition the strain field exhibits shear bands, but the strain distribution is narrow. Hence, most of the mechanical quantities can be calculated analytically, in a very good approximation, with the simple assumption that the strain rate is constant.

NF-1 Dependent Gene Regulation in Drosophila Melanogaster

DTIC Science & Technology

2004-04-01

standard cornmeal medium at 25oC in a humidified incubator. Flies were collected and frozen in liquid nitrogen at the same time of day to minimize...melanogaster media, strains and heat-shock conditions Flies were raised at room temperature (22–248C) on standard cornmeal medium. The Nf1 mutants Nf1P1 and

Dependence of the optical conductivity on the uniaxial and biaxial strains in black phosphorene

NASA Astrophysics Data System (ADS)

Yang, C. H.; Zhang, J. Y.; Wang, G. X.; Zhang, C.

2018-06-01

By using the Kubo formula, the optical conductivity of strained black phosphorene was studied. The anisotropic band dispersion gives rise to an orientation dependent optical conductivity. The energy gap can be tuned by the uniaxial and biaxial strains which can be observed from the interband optical conductivity polarized along the armchair (x ) direction. The preferential conducting direction is along the x direction. The dependence of the intraband optical conductivity along the zigzag (y ) direction on the Fermi energy and strain exhibits increasing or decreasing monotonously. However, along the x direction this dependence is complicated which originates from the carriers' inverse-direction movements obtained by two types of the nearest phosphorus atom interactions. The modification of the biaxial strain on the energy structure and optical-absorption property is more effective. The imaginary part of the total optical conductivity (Im σ ) can be negative around the threshold of the interband optical transition by modifying the chemical potential. Away from this frequency region, Im σ exhibits positive value. It can be used in the application of the surface plasmon propagations in multilayer dielectric structures.

Influence of lactic acid and post-treatment recovery time on the heat resistance of Listeria monocytogenes.

PubMed

Omori, Yasuo; Miake, Kiyotaka; Nakamura, Hiromi; Kage-Nakadai, Eriko; Nishikawa, Yoshikazu

2017-09-18

The aim of this study was to evaluate the effect of lactic acid (LA) with and without organic material at various post-treatment recovery times on the heat resistance of Listeria monocytogenes (Lm). LA decreased Lm numbers; however, the effect was remarkably attenuated by the presence of organic matter. Five strains of Lm were treated with LA and the listericidal effects were compared. The effect of LA varied depending on the strain, with ≥3.0% (w/w) LA required to kill the Lm strains in a short time. The heat resistance of Lm treated with LA was examined with respect to the time interval between the acid treatment and the subsequent manufacturing step. The heat resistance of Lm was shown to significantly increase during the post-treatment period. Heat tolerance (D value) increased up to 3.4-fold compared with the non-treated control bacteria. RNA sequencing and RT-PCR analyses suggested that several stress chaperones, proteins controlled by RecA and associated with high-temperature survival, were involved in the mechanism of enhanced heat resistance. These results are applicable to manufacturers when LA and heat treatment methods are utilized for the effective control of Lm in foods. Copyright © 2017 The Authors. Published by Elsevier B.V. All rights reserved.

Multi-temporal InSAR analysis to reduce uncertainties and assess time-dependence of deformation in the northern Chilean forearc

NASA Astrophysics Data System (ADS)

Manjunath, D.; Gomez, F.; Loveless, J.

2005-12-01

Interferometric Synthetic Aperture Radar (InSAR) provides unprecedented spatial imaging of crustal deformation. However, for small deformations, such as those due to interseismic strain accumulation, potentially significant uncertainty may result from other sources of interferometric phase, such as atmospheric effects, errors in satellite baseline, and height errors in the reference digital elevation model (DEM). We aim to constrain spatial and temporal variations in crustal deformation of the northern Chilean forearc region of the Andean subduction zone (19° - 22°S) using multiple interferograms spanning 1995 - 2000. The study area includes the region of the 1995 Mw 8.1 Antofagasta earthquake and the region to the north. In contrast to previous InSAR-based studies of the Chilean forearc, we seek to distinguish interferometric phase contributions from linear and nonlinear deformation, height errors in the DEM, and atmospheric effects. Understanding these phase contributions reduces the uncertainties on the deformation rates and provides a view of the time-dependence of deformation. The inteferograms cover a 150 km-wide swath spanning two adjacent orbital tracks. Our study involves the analysis of more than 28 inteferograms along each track. Coherent interferograms in the hyper-arid Atacama Desert permit spatial phase unwrapping. Initial estimates of topographic phase were determined using 3'' DEM data from the SRTM mission. We perform a pixel-by-pixel analysis of the unwrapped phase to identify time- and baseline-dependent phase contributions, using the Gamma Remote Sensing radar software. Atmospheric phase, non-linear deformation, and phase noise were further distinguished using a combination of spatial and temporal filters. Non-linear deformation is evident for up to 2.5 years following the 1995 earthquake, followed by a return to time-linear, interseismic strain accumulation. The regional trend of linear deformation, characterized by coastal subsidence and relative uplift inland, is consistent with the displacement field expected for a locked subduction zone. Our improved determination of deformation rates is used to formulate a new elastic model of interseismic strain in the Chilean forearc.

Characterization of the time-dependent strain field at seismogenic depths using first-motion focal mechanisms: Observations of large-scale decadal variations in stress along the San Andrea fault system

USGS Publications Warehouse

Sipkin, S.A.; Silver, P.G.

2003-01-01

We present a method for summing moment tensors derived from first-motion focal mechanisms to study temporal dependence in features of the subsurface regional strain field. Time-dependent processes are inferred by comparing mechanisms summed over differing time periods. We apply this methodology to seismogenic zones in central and southern California using focal mechanisms produced by the Northern and Southern California Seismograph Networks for events during 1980-1999. We find a consistent pattern in both the style of deformation (strike-slip versus compressional) and seismicity rate across the entire region. If these temporal variations are causally related, it suggests a temporal change in the regional-scale stress field. One change consistent with the observations is a rotation in the regional maximum horizontal compressive stress direction, followed by a reversal to the original direction. Depending upon the dominant style of deformation locally, this change in orientation of the regional stress will tend to either enhance or hinder deformation. The mode of enhanced deformation can range from increased microseismicity and creep to major earthquakes. We hypothesize that these temporal changes in the regional stress field are the result of subtle changes in apparent relative plate motion between the Pacific and North American plates, perhaps due to long-range postseismic stress diffusion. Others have hypothesized that small changes in plate motion over thousands of years, and/or over decades, are responsible for changes in the style of deformation in southern California. We propose that such changes, over the course of just a few years, also affect the style of deformation.

Geodetic Strain Analysis Tool

NASA Technical Reports Server (NTRS)

Kedar, Sharon; Baxter, Sean C.; Parker, Jay W.; Webb, Frank H.; Owen, Susan E.; Sibthorpe, Anthony J.; Dong, Danan

2011-01-01

A geodetic software analysis tool enables the user to analyze 2D crustal strain from geodetic ground motion, and create models of crustal deformation using a graphical interface. Users can use any geodetic measurements of ground motion and derive the 2D crustal strain interactively. This software also provides a forward-modeling tool that calculates a geodetic velocity and strain field for a given fault model, and lets the user compare the modeled strain field with the strain field obtained from the user s data. Users may change parameters on-the-fly and obtain a real-time recalculation of the resulting strain field. Four data products are computed: maximum shear, dilatation, shear angle, and principal components. The current view and data dependencies are processed first. The remaining data products and views are then computed in a round-robin fashion to anticipate view changes. When an analysis or display parameter is changed, the affected data products and views are invalidated and progressively re-displayed as available. This software is designed to facilitate the derivation of the strain fields from the GPS and strain meter data that sample it to facilitate the understanding of the strengths and weaknesses of the strain field derivation from continuous GPS (CGPS) and other geodetic data from a variety of tectonic settings, to converge on the "best practices" strain derivation strategy for the Solid Earth Science ESDR System (SESES) project given the CGPS station distribution in the western U.S., and to provide SESES users with a scientific and educational tool to explore the strain field on their own with user-defined parameters.

Solitary waves in morphogenesis: Determination fronts as strain-cued strain transformations among automatous cells

NASA Astrophysics Data System (ADS)

Cox, Brian N.; Landis, Chad M.

2018-02-01

We present a simple theory of a strain pulse propagating as a solitary wave through a continuous two-dimensional population of cells. A critical strain is assumed to trigger a strain transformation, while, simultaneously, cells move as automata to tend to restore a preferred cell density. We consider systems in which the strain transformation is a shape change, a burst of proliferation, or the commencement of growth (which changes the shape of the population sheet), and demonstrate isomorphism among these cases. Numerical and analytical solutions describe a strain pulse whose height does not depend on how the strain disturbance was first launched, or the rate at which the strain transformation is achieved, or the rate constant in the rule for the restorative cell motion. The strain pulse is therefore very stable, surviving the imposition of strong perturbations: it would serve well as a timing signal in development. The automatous wave formulation is simple, with few model parameters. A strong case exists for the presence of a strain pulse during amelogenesis. Quantitative analysis reveals a simple relationship between the velocity of the leading edge of the pulse in amelogenesis and the known speed of migration of ameloblast cells. This result and energy arguments support the depiction of wave motion as an automatous cell response to strain, rather than as a response to an elastic energy gradient. The theory may also contribute to understanding the determination front in somitogenesis, moving fronts of convergent-extension transformation, and mitotic wavefronts in the syncytial drosophila embryo.

[Antigenic determination of human anti-rabies vaccine against viral street strains common in the wild animal population in Poland].

PubMed

Seroka, D

1994-01-01

The aim of the study was to compare the antigen properties of a vaccine strain with street strains isolated from various animal hosts throughout the country. Investigation was carried out using monoclonal antibodies against NC protein. Also, two tests were carried out: the modified NIH test for potency and the neutralization test using the sera of people vaccinated against rabies (PM vaccine strain). The investigated street strains were used in both tests as the challenge viruses. A suspension of these strains diluted five times made it possible to avoid extreme values of animal survival (0% or 100%) what, consequently, made calculation of the LD50 value easier. A different rabies virus serotype (EBLI virus) in the population of insectivore bats Eptesicus serotinus and antigen variants within the first serotype, having common epitopes with strains of the vaccine virus SAD B19 and the polar rabies virus, were found to be present throughout the country. The concentrated and purified vaccine containing the PM virus did not protect mice against infection with strains of viruses isolated from bats (protection index 10 and lower). For the remaining strains, depending on the animal source of their isolation, the protection index ranged from 10 to 1000 and higher. The properties neutralizing a dose of 5 i.u./ml of serum from the subject inoculated with the vaccine containing the PM strain were similar for all the investigated strains; 0,5 i.u./ml did not neutralize the strain isolated from a racoon dog.

Early Mitochondrial Adaptations in Skeletal Muscle to Diet-Induced Obesity Are Strain Dependent and Determine Oxidative Stress and Energy Expenditure But Not Insulin Sensitivity

PubMed Central

Sena, Sandra; Sloan, Crystal; Tebbi, Ali; Han, Yong Hwan; O'Neill, Brian T.; Cooksey, Robert C.; Jones, Deborah; Holland, William L.; McClain, Donald A.; Abel, E. Dale

2012-01-01

This study sought to elucidate the relationship between skeletal muscle mitochondrial dysfunction, oxidative stress, and insulin resistance in two mouse models with differential susceptibility to diet-induced obesity. We examined the time course of mitochondrial dysfunction and insulin resistance in obesity-prone C57B and obesity-resistant FVB mouse strains in response to high-fat feeding. After 5 wk, impaired insulin-mediated glucose uptake in skeletal muscle developed in both strains in the absence of any impairment in proximal insulin signaling. Impaired mitochondrial oxidative capacity preceded the development of insulin resistant glucose uptake in C57B mice in concert with increased oxidative stress in skeletal muscle. By contrast, mitochondrial uncoupling in FVB mice, which prevented oxidative stress and increased energy expenditure, did not prevent insulin resistant glucose uptake in skeletal muscle. Preventing oxidative stress in C57B mice treated systemically with an antioxidant normalized skeletal muscle mitochondrial function but failed to normalize glucose tolerance and insulin sensitivity. Furthermore, high fat-fed uncoupling protein 3 knockout mice developed increased oxidative stress that did not worsen glucose tolerance. In the evolution of diet-induced obesity and insulin resistance, initial but divergent strain-dependent mitochondrial adaptations modulate oxidative stress and energy expenditure without influencing the onset of impaired insulin-mediated glucose uptake. PMID:22510273

Biodegradation of malathion, α- and β-endosulfan by bacterial strains isolated from agricultural soil in Veracruz, Mexico.

PubMed

Jimenez-Torres, Catya; Ortiz, Irmene; San-Martin, Pablo; Hernandez-Herrera, R Idalia

2016-12-01

The objective of this study was to evaluate the capacity of two bacterial strains isolated, cultivated, and purified from agricultural soils of Veracruz, Mexico, for biodegradation and mineralisation of malathion (diethyl 2-(dimethoxyphosphorothioyl) succinate) and α- and β-endosulfan (6,7,8,9,10,10-hexachloro-1,5,5a,6,9,9a-hexahydro-6-9-methano-2,4,3-benzodioxathiepine-3-oxide). The isolated bacterial strains were identified using biochemical and morphological characterization and the analysis of their 16S rDNA gene, as Enterobacter cloacae strain PMM16 (E1) and E. amnigenus strain XGL214 (M1). The E1 strain was able to degrade endosulfan, whereas the M1 strain was capable of degrading both pesticides. The E1 strain degraded 71.32% of α-endosulfan and 100% of β-endosulfan within 24 days. The absence of metabolites, such as endosulfan sulfate, endosulfan lactone, or endosulfan diol, would suggest degradation of endosulfan isomers through non-oxidative pathways. Malathion was completely eliminated by the M1 strain. The major metabolite was butanedioic acid. There was a time-dependent increase in bacterial biomass, typical of bacterial growth, correlated with the decrease in pesticide concentration. The CO 2 production also increased significantly with the addition of pesticides to the bacterial growth media, demonstrating that, under aerobic conditions, the bacteria utilized endosulfan and malathion as a carbon source. Here, two bacterial strains are shown to metabolize two toxic pesticides into non-toxic intermediates.

Molecular and Serological Diversity of Neisseria meningitidis Carrier Strains Isolated from Italian Students Aged 14 to 22 Years

PubMed Central

Comanducci, Maurizio; Amicizia, Daniela; Ansaldi, Filippo; Canepa, Paola; Orsi, Andrea; Icardi, Giancarlo; Rizzitelli, Emanuela; De Angelis, Gabriella; Bambini, Stefania; Moschioni, Monica; Comandi, Sara; Simmini, Isabella; Boccadifuoco, Giueseppe; Brunelli, Brunella; Giuliani, Marzia Monica; Pizza, Mariagrazia

2014-01-01

Neisseria meningitidis is an obligate human commensal that commonly colonizes the oropharyngeal mucosa. Carriage is age dependent and very common in young adults. The relationships between carriage and invasive disease are not completely understood. In this work, we performed a longitudinal carrier study in adolescents and young adults (173 subjects). Overall, 32 subjects (18.5%) had results that were positive for meningococcal carriage in at least one visit (average monthly carriage rate, 12.1%). Only five subjects tested positive at all four visits. All meningococcal isolates were characterized by molecular and serological techniques. Multilocus sequence typing, PorA typing, and sequencing of the 4CMenB vaccine antigens were used to assess strain diversity. The majority of positive subjects were colonized by capsule null (34.4%) and capsular group B strains (28.1%), accounting for 23.5% and 29.4% of the total number of isolates, respectively. The fHbp and nhba genes were present in all isolates, while the nadA gene was present in 5% of the isolates. The genetic variability of the 4CMenB vaccine antigens in this collection was relatively high compared with that of other disease-causing strain panels. Indications about the persistence of the carriage state were limited to the time span of the study. All strains isolated from the same subject were identical or cumulated minor changes over time. The expression levels and antigenicities of the 4CMenB vaccine antigens in each strain were analyzed by the meningococcal antigen typing system (MATS), which revealed that expression can change over time in the same individual. Future analysis of antigen variability and expression in carrier strains after the introduction of the MenB vaccine will allow for a definition of its impact on nasopharyngeal/oropharyngeal carriage. PMID:24648565

Chronic Intermittent Ethanol Inhalation Increases Ethanol Self-administration in both C57BL/6J and DBA/2J Mice

PubMed Central

McCool, Brian A.; Chappell, Ann M.

2015-01-01

Inbred mouse strains provide significant opportunities to understand the genetic mechanisms controlling ethanol-directed behaviors and neurobiology. They have been specifically employed to understand cellular mechanisms contributing to ethanol consumption, acute intoxication, and sensitivities to chronic effects. However, limited ethanol consumption by some strains has restricted our understanding of clinically relevant endpoints such as dependence-related ethanol intake. Previous work with a novel tastant-substitution procedure using monosodium glutamate (MSG or umami flavor) has shown that the procedure greatly enhances ethanol consumption by mouse strains that express limited drinking phenotypes using other methods. In the current study, we employ this MSG-substitution procedure to examine how ethanol dependence, induced with passive vapor inhalation, modifies ethanol drinking in C57BL/6J and DBA/2J mice. These strains represent ‘high’ and ‘low’ drinking phenotypes, respectively. We found that the MSG substitution greatly facilitates ethanol drinking in both strains, and likewise, ethanol dependence increased ethanol consumption regardless of strain. However, DBA/2J mice exhibited greater sensitivity dependence-enhanced drinking, as represented by consumption behaviors directed at lower ethanol concentrations and relative to baseline intake levels. DBA/2J mice also exhibited significant withdrawal-associated anxiety-like behavior while C57BL/6J mice did not. These findings suggest that the MSG-substitution procedure can be employed to examine dependence-enhanced ethanol consumption across a range of drinking phenotypes, and that C57BL/6J and DBA/2J mice may represent unique neurobehavioral pathways for developing dependence-enhanced ethanol consumption. PMID:25659650

Quasi-static and ratcheting properties of trabecular bone under uniaxial and cyclic compression.

PubMed

Gao, Li-Lan; Wei, Chao-Lei; Zhang, Chun-Qiu; Gao, Hong; Yang, Nan; Dong, Li-Min

2017-08-01

The quasi-static and ratcheting properties of trabecular bone were investigated by experiments and theoretical predictions. The creep tests with different stress levels were completed and it is found that both the creep strain and creep compliance increase rapidly at first and then increase slowly as the creep time goes by. With increase of compressive stress the creep strain increases and the creep compliance decreases. The uniaxial compressive tests show that the applied stress rate makes remarkable influence on the compressive behaviors of trabecular bone. The Young's modulus of trabecular bone increases with increase of stress rate. The stress-strain hysteresis loops of trabecular bone under cyclic load change from sparse to dense with increase of number of cycles, which agrees with the change trend of ratcheting strain. The ratcheting strain rate rapidly decreases at first, and then exhibits a relatively stable and small value after 50cycles. Both the ratcheting strain and ratcheting strain rate increase with increase of stress amplitude or with decrease of stress rate. The creep model and the nonlinear viscoelastic constitutive model of trabecular bone were proposed and used to predict its creep property and rate-dependent compressive property. The results show that there are good agreements between the experimental data and predictions. Copyright © 2017 Elsevier B.V. All rights reserved.

Dependence of Strain Distribution on In Content in InGaN/GaN Quantum Wires and Spherical Quantum Dots

NASA Astrophysics Data System (ADS)

Sharma, Akant Sagar; Dhar, S.

2018-02-01

The distribution of strain, developed in zero-dimensional quantum spherical dots and one-dimensional cylindrical quantum wires of an InGaN/GaN system is calculated as functions of radius of the structure and indium mole fraction. The strain shows strong dependence on indium mole fraction at small distances from the center. The strain associated with both the structures is found to decrease exponentially with the increase in dot or cylinder radius and increases linearly with indium content.

An exponential scaling law for the strain dependence of the Nb3Sn critical current density

NASA Astrophysics Data System (ADS)

Bordini, B.; Alknes, P.; Bottura, L.; Rossi, L.; Valentinis, D.

2013-07-01

The critical current density of the Nb3Sn superconductor is strongly dependent on the strain applied to the material. In order to investigate this dependence, it is a common practice to measure the critical current of Nb3Sn strands for different values of applied axial strain. In the literature, several models have been proposed to describe these experimental data in the reversible strain region. All these models are capable of fitting the measurement results in the strain region where data are collected, but tend to predict unphysical trends outside the range of data, and especially for large strain values. In this paper we present a model of a new strain function, together with the results obtained by applying the new scaling law on relevant datasets. The data analyzed consisted of the critical current measurements at 4.2 K that were carried out under applied axial strain at Durham University and the University of Geneva on different strand types. With respect to the previous models proposed, the new scaling function does not present problems at large strain values, has a lower number of fitting parameters (only two instead of three or four), and is very stable, so that, starting from few experimental points, it can estimate quite accurately the strand behavior in a strain region where there are no data. A relationship is shown between the proposed strain function and the elastic strain energy, and an analogy is drawn with the exponential form of the McMillan equation for the critical temperature.

Time-dependent behavior of passive skeletal muscle

NASA Astrophysics Data System (ADS)

Ahamed, T.; Rubin, M. B.; Trimmer, B. A.; Dorfmann, L.

2016-03-01

An isotropic three-dimensional nonlinear viscoelastic model is developed to simulate the time-dependent behavior of passive skeletal muscle. The development of the model is stimulated by experimental data that characterize the response during simple uniaxial stress cyclic loading and unloading. Of particular interest is the rate-dependent response, the recovery of muscle properties from the preconditioned to the unconditioned state and stress relaxation at constant stretch during loading and unloading. The model considers the material to be a composite of a nonlinear hyperelastic component in parallel with a nonlinear dissipative component. The strain energy and the corresponding stress measures are separated additively into hyperelastic and dissipative parts. In contrast to standard nonlinear inelastic models, here the dissipative component is modeled using an evolution equation that combines rate-independent and rate-dependent responses smoothly with no finite elastic range. Large deformation evolution equations for the distortional deformations in the elastic and in the dissipative component are presented. A robust, strongly objective numerical integration algorithm is used to model rate-dependent and rate-independent inelastic responses. The constitutive formulation is specialized to simulate the experimental data. The nonlinear viscoelastic model accurately represents the time-dependent passive response of skeletal muscle.

Shoulder pain and time dependent structure in wheelchair propulsion variability

PubMed Central

Jayaraman, Chandrasekaran; Moon, Yaejin; Sosnoff, Jacob J.

2016-01-01

Manual wheelchair propulsion places considerable repetitive mechanical strain on the upper limbs leading to shoulder injury and pain. While recent research indicates that the amount of variability in wheelchair propulsion and shoulder pain may be related. There has been minimal inquiry into the fluctuation over time (i.e. time-dependent structure) in wheelchair propulsion variability. Consequently the purpose of this investigation was to examine if the time-dependent structure in the wheelchair propulsion parameters are related to shoulder pain. 27 experienced wheelchair users manually propelled their own wheelchair fitted with a SMARTWheel on a roller at 1.1 m/s for 3 minutes. Time-dependent structure of cycle-to-cycle fluctuations in contact angle and inter push time interval was quantified using sample entropy (SampEn) and compared between the groups with/without shoulder pain using non-parametric statistics. Overall findings were, (1) variability observed in contact angle fluctuations during manual wheelchair propulsion is structured (Z=3.15;p<0.05), (2) individuals with shoulder pain exhibited higher SampEn magnitude for contact angle during wheelchair propulsion than those without pain (χ2(1)=6.12;p<0.05); and (3) SampEn of contact angle correlated significantly with self-reported shoulder pain (rs (WUSPI) =0.41;rs (VAS)=0.56;p<0.05). It was concluded that the time-dependent structure in wheelchair propulsion may provide novel information for tracking and monitoring shoulder pain. PMID:27134151

Vestibular and Visual Contribution to Fish Behavior Under Microgravity

NASA Astrophysics Data System (ADS)

Ijiri, K.

Vestibular and visual information are two major factors fish use for controlling their posture under 1 G conditions. Parabolic flight experiments were carried out to observe the fish behavior under microgravity for several different strains of Medaka fish (Oryzias latipes). There existed a clear strain-difference in the behavioral response of the fish under microgravity: Some strains looped, while other strains did not loop at all. However, even the latter strains looped under microgravity conditions when kept in complete darkness, suggesting the contribution of visual information to the posture control under microgravity. In the laboratory, eyesight (visual acuity) was checked for each strain, using a rotating striped-drum apparatus. The results also showed a strain-difference, which gave a clue to the different degree of adaptability to microgravity among different strains. Beside loopings, some fish exhibited rolling movement around their body axis. Tracing each fish during and between parabolas, it was shown that to which side each fish rolls was determined specifically to each individual fish, and not to each strain. Thus, rolling direction is not genetically determined. This may support the otolith asymmetry hypothesis. Fish of a mutant strain (ha strain, having homozygous recessive of one gene ha) have some malfunction in otolith-vestibular system, and their behavior showed they are not dependent on gravity. Morphological abnormalities of their ear vesicles during the embryonic and baby stages were noted. Their eyesight and dorsal light responses were also studied. Progress in the project of establishing a new strain which has good eyesight and, at the same time, being deficient in otolith-vestibular system was reported. Crosses between the strain of good eyesight and ha strain were made, and to some extent, F2 fish have already shown such characteristics suited for living under microgravity conditions

Noble Gas Release Signal as a Precursor to Fracture

NASA Astrophysics Data System (ADS)

Bauer, S. J.; Lee, H.; Gardner, W. P.

2017-12-01

We present empirical results of rock strain, microfracturing, acoustic emissions, and noble gas release from laboratory triaxial experiments for a granite, basalt, shale and bedded rock salt. Noble gases are released and measured real-time during deformation using mass spectrometry. The gas release represents a precursive signal to macrofracture. Gas release is associated with increased acoustic emissions indicating that microfracturing is required to release gas and create pathways for the gas to be sensed. The gas released depends on initial gas content, pore structure and its evolution during deformation, the deformation amount, matrix permeability, deformation style and the stress/strain history. Gases are released from inter and intracrystalline sites; release rate increases as strain and microfracturing increases. The gas composition depends on lithology, geologic history and age, fluids present, and radioisotope concentrations that affect radiogenic noble gas isotope (e.g. 4He,40Ar) production. Noble gas emission and its relationship to crustal processes such as seismicity and volcanism, tectonic velocities, qualitative estimates of deep permeability, age dating of groundwater, and a signature of nuclear weapon detonation. Our result show that mechanical deformation of crustal materials is an important process controlling gas release from rocks and minerals, and should be considered in techniques which utilize gas release and/or accumulation. We propose using noble gas release to signal rock deformation in boreholes, mines and waste repositories. We postulate each rock exhibits a gas release signature which is microstructure, stress, strain, and/or permanent deformation dependent. Calibration of such relationships, for example relating gas release per rock unit volume to strain may be used to quantify rock deformation and develop predictive models.Sandia National Laboratories is a multimission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC., a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-NA0003525. SAND2017-7823A

Phylogenetic analysis of Columbid herpesvirus-1 in rock pigeons, birds of prey and non-raptorial birds in Poland

PubMed Central

2013-01-01

Background The identity of herpesviruses isolated in Europe from domestic pigeons (Columbid herpesvirus-1 - CoHV-1) as well as falcons and owls remains unknown. All these herpesviruses are antigenically and genetically related. The falcons and owls are thought to have become infected during the ingestion of pigeon meat thus suggesting the virus’s capacity to infect a wide range of hosts. The aim of the conducted study was to detect the occurrence of CoHV-1 and estimating the similarities and differences in the DNA-dependent DNA polymerase gene of herpesviruses isolated from domestic pigeons, birds of prey and non-raptorial free-ranging birds in Poland. Results The study has shown the presence of CoHV-1 in 20.4% (18/88) in the examined birds. In case of one CoHV-1, infected Peregrine Falcon (Falco peregrinus), neurological signs were observed. Nucleotide sequencing of the DNA-dependent DNA polymerase gene, showed a high similarity among Polish strains (100%), independently from the species of the affected birds. Only one compared CoHV-1 strain - KP 21/23 originating from Germany showed a slightly lower similarity at a level of 99.1%. Further analysis has shown the identity of DNA-dependent DNA polymerase of CoHV-1 strains and other herpesviruses present in poultry as well as other birds ranged from 35.4 to 44.9%. Interestingly CoHV-1 infection was also confirmed for the first time in four non-raptorial birds. Conclusions The current study has shown a high similarity of CoHV-1 strains and the possible transmission of herpesviruses between domestic rock pigeons and free-ranging birds including raptors and non-raptorial birds. Further studies focused on cloning and the analysis of the whole CoHV-1 genome which is needed to explain the role of the observed similarities and differences between field strains of columbid herpesviruses. PMID:23517888

Impact of crystalline defects and size on X-ray line broadening: A phenomenological approach for tetragonal SnO{sub 2} nanocrystals

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

Muhammed Shafi, P.; Chandra Bose, A., E-mail: acbose@nitt.edu

2015-05-15

Nanocrystalline tin oxide (SnO{sub 2}) powders with different grain size were prepared by chemical precipitation method. The reaction was carried out by varying the period of hydrolysis and the as-prepared samples were annealed at different temperatures. The samples were characterized using X-ray powder diffractometer and transmission electron microscopy. The microstrain and crystallite size were calculated for all the samples by using Williamson-Hall (W-H) models namely, isotropic strain model (ISM), anisotropic strain model (ASM) and uniform deformation energy density model (UDEDM). The morphology and particle size were determined using TEM micrographs. The directional dependant young’s modulus was modified as an equationmore » relating elastic compliances (s{sub ij}) and Miller indices of the lattice plane (hkl) for tetragonal crystal system and also the equation for elastic compliance in terms of stiffness constants was derived. The changes in crystallite size and microstrain due to lattice defects were observed while varying the hydrolysis time and the annealing temperature. The dependence of crystallite size on lattice strain was studied. The results were correlated with the available studies on electrical properties using impedance spectroscopy.« less

Assessment of the rhizosphere competency and pentachlorophenol-metabolizing activity of a pesticide-degrading strain of Trichoderma harzianum introduced into the root zone of corn seedlings.

PubMed

Rigot, Jerĵme; Matsumura, Fumio

2002-05-01

To develop a dependable approach to introduce laboratory selected, pesticide-degrading microorganisms into soil environments for the purpose of in situ bioremediation, we tested the possibility of utilizing plant rhizospheres as the vehicle. We first established the rhizosphere competency of a strain of the soil fungus Trichoderma harzianum, a biocontrol species well studied by plant pathologists to colonize plant rhizosphere in many parts of the world. The strain we chose, T.h.2023 is resistant to many fungicides, and it has been shown to metabolize several pesticides. Second, we found that it readily metabolized pentachlorophenol (PCP), which is quickly and stochiometrically converted to pentachloroanisole (PCA) in liquid culture. Taking advantage of this specific feature, we have developed a sensitive metabolic marker approach that allowed us to monitor for the continuous presence and activity of this fungal strain in the corn rhizosphere soil in situ over time.

Viscoelastic/damage modeling of filament-wound spherical pressure vessels

NASA Technical Reports Server (NTRS)

Hackett, Robert M.; Dozier, Jan D.

1987-01-01

A model of the viscoelastic/damage response of a filament-wound spherical vessel used for long-term pressure containment is developed. The matrix material of the composite system is assumed to be linearly viscoelastic. Internal accumulated damage based upon a quadratic relationship between transverse modulus and maximum circumferential strain is postulated. The resulting nonlinear problem is solved by an iterative routine. The elastic-viscoelastic correspondence is employed to produce, in the Laplace domain, the associated elastic solution for the maximum circumferential strain which is inverted by the method of collocation to yield the time-dependent solution. Results obtained with the model are compared to experimental observations.

Deformations and strains in adhesive joints by moire interferometry

NASA Technical Reports Server (NTRS)

Post, D.; Czarnek, R.; Wood, J.; John, D.; Lubowinski, S.

1984-01-01

Displacement fields in a thick adherend lap joint and a cracked lap shear specimen were measured by high sensitivity moire interferometry. Contour maps of in-plane U and V displacements were obtained across adhesive and adherent surfaces. Loading sequences ranged from modest loads to near-failure loads. Quantitative results are given for displacements and certain strains in the adhesive and along the adhesive/adherend boundary lines. The results show nonlinear displacements and strains as a function of loads or stresses and they show viscoelastic or time-dependent response. Moire interferometry is an excellent method for experimental studies of adhesive joint performance. Subwavelength displacement resolution of a few micro-inches, and spatial resolution corresponding to 1600 fringes/inch (64 fringes/mm), were obtained in these studies. The whole-field contour maps offer insights not available from local measurements made by high sensitivity gages.

The subcutaneous inoculation of pH 6 antigen mutants of Yersinia pestis does not affect virulence and immune response in mice.

PubMed

Anisimov, Andrey P; Bakhteeva, Irina V; Panfertsev, Evgeniy A; Svetoch, Tat'yana E; Kravchenko, Tat'yana B; Platonov, Mikhail E; Titareva, Galina M; Kombarova, Tat'yana I; Ivanov, Sergey A; Rakin, Alexander V; Amoako, Kingsley K; Dentovskaya, Svetlana V

2009-01-01

Two isogenic sets of Yersinia pestis strains were generated, composed of wild-type strains 231 and I-1996, their non-polar pH 6(-) mutants with deletions in the psaA gene that codes for its structural subunit or the whole operon, as well as strains with restored ability for temperature- and pH-dependent synthesis of adhesion pili or constitutive production of pH 6 antigen. The mutants were generated by site-directed mutagenesis of the psa operon and subsequent complementation in trans. It was shown that the loss of synthesis or constitutive production of pH 6 antigen did not influence Y. pestis virulence or the average survival time of subcutaneously inoculated BALB/c naïve mice or animals immunized with this antigen.

Effects of Adiabatic Heating on the High Strain Rate Deformation of Polymer Matrix Composites

NASA Technical Reports Server (NTRS)

Sorini, Chris; Chattopadhyay, Aditi; Goldberg, Robert K.

2017-01-01

Polymer matrix composites (PMCs) are increasingly being used in aerospace structures that are expected to experience complex dynamic loading conditions throughout their lifetime. As such, a detailed understanding of the high strain rate behavior of the constituents, particularly the strain rate, temperature, and pressure dependent polymer matrix, is paramount. In this paper, preliminary efforts in modeling experimentally observed temperature rises due to plastic deformation in PMCs subjected to dynamic loading are presented. To this end, an existing isothermal viscoplastic polymer constitutive formulation is extended to model adiabatic conditions by incorporating temperature dependent elastic properties and modifying the components of the inelastic strain rate tensor to explicitly depend on temperature. It is demonstrated that the modified polymer constitutive model is capable of capturing strain rate and temperature dependent yield as well as thermal softening associated with the conversion of plastic work to heat at high rates of strain. The modified constitutive model is then embedded within a strength of materials based micromechanics framework to investigate the manifestation of matrix thermal softening, due to the conversion of plastic work to heat, on the high strain rate response of a T700Epon 862 (T700E862) unidirectional composite. Adiabatic model predictions for high strain rate composite longitudinal tensile, transverse tensile, and in-plane shear loading are presented. Results show a substantial deviation from isothermal conditions; significant thermal softening is observed for matrix dominated deformation modes (transverse tension and in-plane shear), highlighting the importance of accounting for the conversion of plastic work to heat in the polymer matrix in the high strain rate analysis of PMC structures.

Thermal conductivity of graphene mediated by strain and size

DOE PAGES

Kuang, Youdi; Shi, Sanqiang; Wang, Xinjiang; ...

2016-06-09

Based on first-principles calculations and full iterative solution of the linearized Boltzmann–Peierls transport equation for phonons, we systematically investigate effects of strain, size and temperature on the thermal conductivity k of suspended graphene. The calculated size-dependent and temperature-dependent k for finite samples agree well with experimental data. The results show that, contrast to the convergent room-temperature k = 5450 W/m-K of unstrained graphene at a sample size ~8 cm, k of strained graphene diverges with increasing the sample size even at high temperature. Out-of-plane acoustic phonons are responsible for the significant size effect in unstrained and strained graphene due tomore » their ultralong mean free path and acoustic phonons with wavelength smaller than 10 nm contribute 80% to the intrinsic room temperature k of unstrained graphene. Tensile strain hardens the flexural modes and increases their lifetimes, causing interesting dependence of k on sample size and strain due to the competition between boundary scattering and intrinsic phonon–phonon scattering. k of graphene can be tuned within a large range by strain for the size larger than 500 μm. These findings shed light on the nature of thermal transport in two-dimensional materials and may guide predicting and engineering k of graphene by varying strain and size.« less

Strain Rate Effect on Tensile Flow Behavior and Anisotropy of a Medium-Manganese TRIP Steel

NASA Astrophysics Data System (ADS)

Alturk, Rakan; Hector, Louis G.; Matthew Enloe, C.; Abu-Farha, Fadi; Brown, Tyson W.

2018-06-01

The dependence of the plastic anisotropy on the nominal strain rate for a medium-manganese (10 wt.% Mn) transformation-induced plasticity (TRIP) steel with initial austenite volume fraction of 66% (balance ferrite) has been investigated. The material exhibited yield point elongation, propagative instabilities during hardening, and austenite transformation to α'-martensite either directly or through ɛ-martensite. Uniaxial strain rates within the range of 0.005-500 s-1 along the 0°, 45°, and 90° orientations were selected based upon their relevance to automotive applications. The plastic anisotropy ( r) and normal anisotropy ( r n) indices corresponding to each direction and strain rate were determined using strain fields obtained from stereo digital image correlation systems that enabled both quasistatic and dynamic measurements. The results provide evidence of significant, orientation-dependent strain rate effects on both the flow stress and the evolution of r and r n with strain. This has implications not only for material performance during forming but also for the development of future strain-rate-dependent anisotropic yield criteria. Since tensile data alone for the subject medium-manganese TRIP steel do not satisfactorily determine the microstructural mechanisms responsible for the macroscopic-scale behavior observed on tensile testing, additional tests that must supplement the mechanical test results presented herein are discussed.

Strain Rate Effect on Tensile Flow Behavior and Anisotropy of a Medium-Manganese TRIP Steel

NASA Astrophysics Data System (ADS)

Alturk, Rakan; Hector, Louis G.; Matthew Enloe, C.; Abu-Farha, Fadi; Brown, Tyson W.

2018-04-01

The dependence of the plastic anisotropy on the nominal strain rate for a medium-manganese (10 wt.% Mn) transformation-induced plasticity (TRIP) steel with initial austenite volume fraction of 66% (balance ferrite) has been investigated. The material exhibited yield point elongation, propagative instabilities during hardening, and austenite transformation to α'-martensite either directly or through ɛ-martensite. Uniaxial strain rates within the range of 0.005-500 s-1 along the 0°, 45°, and 90° orientations were selected based upon their relevance to automotive applications. The plastic anisotropy (r) and normal anisotropy (r n) indices corresponding to each direction and strain rate were determined using strain fields obtained from stereo digital image correlation systems that enabled both quasistatic and dynamic measurements. The results provide evidence of significant, orientation-dependent strain rate effects on both the flow stress and the evolution of r and r n with strain. This has implications not only for material performance during forming but also for the development of future strain-rate-dependent anisotropic yield criteria. Since tensile data alone for the subject medium-manganese TRIP steel do not satisfactorily determine the microstructural mechanisms responsible for the macroscopic-scale behavior observed on tensile testing, additional tests that must supplement the mechanical test results presented herein are discussed.

Implementation of an Associative Flow Rule Including Hydrostatic Stress Effects Into the High Strain Rate Deformation Analysis of Polymer Matrix Composites

NASA Technical Reports Server (NTRS)

Goldberg, Robert K.; Roberts, Gary D.; Gilat, Amos

2003-01-01

A previously developed analytical formulation has been modified in order to more accurately account for the effects of hydrostatic stresses on the nonlinear, strain rate dependent deformation of polymer matrix composites. State variable constitutive equations originally developed for metals have been modified in order to model the nonlinear, strain rate dependent deformation of polymeric materials. To account for the effects of hydrostatic stresses, which are significant in polymers, the classical J2 plasticity theory definitions of effective stress and effective inelastic strain, along with the equations used to compute the components of the inelastic strain rate tensor, are appropriately modified. To verify the revised formulation, the shear and tensile deformation of two representative polymers are computed across a wide range of strain rates. Results computed using the developed constitutive equations correlate well with experimental data. The polymer constitutive equations are implemented within a strength of materials based micromechanics method to predict the nonlinear, strain rate dependent deformation of polymer matrix composites. The composite mechanics are verified by analyzing the deformation of a representative polymer matrix composite for several fiber orientation angles across a variety of strain rates. The computed values compare well to experimentally obtained results.

Effects of cold-treatment and strain-rate on mechanical properties of NbTi/Cu superconducting composite wires.

PubMed

Guan, Mingzhi; Wang, Xingzhe; Zhou, Youhe

2015-01-01

During design and winding of superconducting magnets at room temperature, a pre-tension under different rate is always applied to improve the mechanical stability of the magnets. However, an inconsistency rises for superconductors usually being sensitive to strain and oversized pre-stress which results in degradation of the superconducting composites' critical performance at low temperature. The present study focused on the effects of the cold-treatment and strain-rate of tension deformation on mechanical properties of NbTi/Cu superconducting composite wires. The samples were immersed in a liquid nitrogen (LN2) cryostat for the adiabatic cold-treatment, respectively with 18-hour, 20-hour, 22-hour and 24-hour. A universal testing machine was utilized for tension tests of the NbTi/Cu superconducting composite wires at room temperature; a small-scale extensometer was used to measure strain of samples with variable strain-rate. The strength, elongation at fracture and yield strength of pre-cold-treatment NbTi/Cu composite wires were drawn. It was shown that, the mechanical properties of the superconducting wires are linearly dependent on the holding time of cold-treatment at lower tensile strain-rate, while they exhibit notable nonlinear features at higher strain-rate. The cold-treatment in advance and the strain-rate of pre-tension demonstrate remarkable influences on the mechanical property of the superconducting composite wires.

[Virus strain specific serum neutralizing antibodies in children and adolescents immunized with a Russian mumps vaccine].

PubMed

Otrashevskaia, E V; Krasil'nikov, I V; Ignat'ev, G M

2010-01-01

Postvaccination immunity was studied in the children and teenagers without a history of clinical mumps infection, who had been immunized with the Leningrad-3 mumps vaccine. The level of specific lgG in ELISA and that and spectrum of their neutralizing activity against a vaccine strain and three heterologous mumps virus (MV) strains (genotypes A, C, and H) were measured. The investigation included 151 sera from the vaccinees aged 3 to 17 years, possessing the detectable specific IgG titers in ELISA and the detectable neutralizing titers against the vaccine strain. 97.4% of the vaccinees had neutralizing activity against 1-3 heterologous MV strains. A preponderance of neutralizing titers against heterologous MV strains by 1-log2 in some sera (6.5-32.5 depending on age) was most likely to suggest that the vaccinees' had been in contact with these virus strains in the past. In our investigation, a combination of positive IgG titers and neutralizing titers against the vaccine strain 2-log2 or higher provided the protection of the vaccinated children and teenagers against the symptomatic infection. There was a pronounced buster effect of the second immunization and a drop in the neutralizing activity of the sera from the vaccinated children and adolescents over time after the first and second immunization.

Characterization of NADP-dependent 7 beta-hydroxysteroid dehydrogenases from Peptostreptococcus productus and Eubacterium aerofaciens.

PubMed Central

Hirano, S; Masuda, N

1982-01-01

Peptostreptococcus productus strain b-52 (a human fecal isolate) and Eubacterium aerofaciens ATCC 25986 were found to contain NADP-dependent 7 beta-hydroxysteriod dehydrogenase activity. The enzyme was synthesized constitutively by both organisms, and the enzyme yields were suppressed by the addition of 0.5 mM 7 beta-hydroxy bile acid to the growth medium. Purification of the enzyme by chromatography resulted in preparations with 3.5 (P. productus b-52, on Sephadex G-200) and 1.8 (E. aerofaciens, on Bio-Gel A-1.5 M) times the activity of the crude cell extracts. A pH optimum of 9.8 and a molecular weight of approximately 53,000 were shown for the enzyme of strain b-52, and an optimum pH at 10.5 and a molecular weight of 45,000 was shown for that from strain ATCC 25986. Kinetic studies revealed that both enzyme preparations oxidized the 7 beta-hydroxy group in unconjugated and conjugated bile acids, a lower Km value being demonstrated with free bile acid than with glycine and taurine conjugates. No measureable activity against 3 alpha-, 7 alpha-, or 12 alpha-hydroxy groups was detected in either enzyme preparation. When tested with strain ATCC 25986, little 7 beta-hydroxy-steroid dehydrogenase activity was detected in cells grown in the presence of glucose in excess. The enzyme from strain b-52 was found to be heat labile (90% inactivation at 50 degrees C for 3 min) and highly sensitive to sulfhydryl inhibitors. PMID:6954878

Fitness Impact of Obligate Intranuclear Bacterial Symbionts Depends on Host Growth Phase

PubMed Central

Bella, Chiara; Koehler, Lars; Grosser, Katrin; Berendonk, Thomas U.; Petroni, Giulio; Schrallhammer, Martina

2016-01-01

According to text book definition, parasites reduce the fitness of their hosts whereas mutualists provide benefits. But biotic and abiotic factors influence symbiotic interactions, thus under certain circumstances parasites can provide benefits and mutualists can harm their host. Here we addressed the question which intrinsic biotic factors shape a symbiosis and are crucial for the outcome of the interaction between the obligate intranuclear bacterium Holospora caryophila (Alphaproteobacteria; Rickettsiales) and its unicellular eukaryotic host Paramecium biaurelia (Alveolata; Ciliophora). The virulence of H. caryophila, i.e., the negative fitness effect on host division and cell number, was determined by growth assays of several P. biaurelia strains. The performances of genetically identical lines either infected with H. caryophila or symbiont-free were compared. Following factors were considered as potentially influencing the outcome of the interaction: (1) host strain, (2) parasite strain, and (3) growth phases of the host. All three factors revealed a strong effect on the symbiosis. In presence of H. caryophila, the Paramecium density in the stationary growth phase decreased. Conversely, a positive effect of the bacteria during the exponential phase was observed for several host × parasite combinations resulting in an increased growth rate of infected P. biaurelia. Furthermore, the fitness impact of the tested endosymbionts on different P. biaurelia lines was not only dependent on one of the two involved strains but distinct for the specific combination. Depending on the current host growth phase, the presence of H. caryophila can be harmful or advantageous for P. biaurelia. Thus, under the tested experimental conditions, the symbionts can switch from the provision of benefits to the exploitation of host resources within the same host population and a time-span of less than 6 days. PMID:28066397

Tensile strength and failure mechanisms of tantalum at extreme strain rates

NASA Astrophysics Data System (ADS)

Hahn, Eric; Fensin, Saryu; Germann, Timothy; Meyers, Marc

Non-equilibrium molecular dynamics simulations are used to probe the tensile response of monocrystalline, bicrystalline, and nanocrystalline tantalum over six orders of magnitude of strain rate. Our analysis of the strain rate dependence of strength is extended to over nine orders of magnitude by bridging the present simulations to recent laser-driven shock experiments. Tensile strength shows a power-law dependence with strain rate over this wide range, with different relationships depending on the initial microstructure and active deformation mechanism. At high strain rates, multiple spall events occur independently and continue to occur until communication occurs by means of relaxation waves. Temperature plays a significant role in the reduction of spall strength as the initial shock required to achieve such large strain rates also contributes to temperature rise, through pressure-volume work as well as visco-plastic heating, which leads to softening and sometimes melting upon release. At ultra-high strain rates, those approaching or exceeding the atomic vibrational frequency, spall strength saturates at the ultimate cohesive strength of the material. UC Research Laboratories Grant (09-LR-06-118456-MEYM); Department of Energy NNSA/SSAP (DE-NA0002080); DOE ASCR Exascale Co-design Center for Materials in Extreme Environments.

Mapping strain rate dependence of dislocation-defect interactions by atomistic simulations

PubMed Central

Fan, Yue; Osetskiy, Yuri N.; Yip, Sidney; Yildiz, Bilge

2013-01-01

Probing the mechanisms of defect–defect interactions at strain rates lower than 106 s−1 is an unresolved challenge to date to molecular dynamics (MD) techniques. Here we propose an original atomistic approach based on transition state theory and the concept of a strain-dependent effective activation barrier that is capable of simulating the kinetics of dislocation–defect interactions at virtually any strain rate, exemplified within 10−7 to 107 s−1. We apply this approach to the problem of an edge dislocation colliding with a cluster of self-interstitial atoms (SIAs) under shear deformation. Using an activation–relaxation algorithm [Kushima A, et al. (2009) J Chem Phys 130:224504], we uncover a unique strain-rate–dependent trigger mechanism that allows the SIA cluster to be absorbed during the process, leading to dislocation climb. Guided by this finding, we determine the activation barrier of the trigger mechanism as a function of shear strain, and use that in a coarse-graining rate equation formulation for constructing a mechanism map in the phase space of strain rate and temperature. Our predictions of a crossover from a defect recovery at the low strain-rate regime to defect absorption behavior in the high strain-rate regime are validated against our own independent, direct MD simulations at 105 to 107 s−1. Implications of the present approach for probing molecular-level mechanisms in strain-rate regimes previously considered inaccessible to atomistic simulations are discussed. PMID:24114271

Procedures for characterizing an alloy and predicting cyclic life with the total strain version of Strainrange Partitioning

NASA Technical Reports Server (NTRS)

Saltsman, James F.; Halford, Gary R.

1989-01-01

Procedures are presented for characterizing an alloy and predicting cyclic life for isothermal and thermomechanical fatigue conditions by using the total strain version of strainrange partitioning (TS-SRP). Numerical examples are given. Two independent alloy characteristics are deemed important: failure behavior, as reflected by the inelastic strainrange versus cyclic life relations; and flow behavior, as indicated by the cyclic stress-strain-time response (i.e., the constitutive behavior). Failure behavior is characterized by conducting creep-fatigue tests in the strain regime, wherein the testing times are reasonably short and the inelastic strains are large enough to be determined accurately. At large strainranges, stress-hold, strain-limited tests are preferred because a high rate of creep damage per cycle is inherent in this type of test. At small strainranges, strain-hold cycles are more appropriate. Flow behavior is characterized by conducting tests wherein the specimen is usually cycled far short of failure and the wave shape is appropriate for the duty cycle of interest. In characterizing an alloy pure fatigue, or PP, failure tests are conducted first. Then depending on the needs of the analyst a series of creep-fatigue tests are conducted. As many of the three generic SRP cycles are featured as are required to characterize the influence of creep on fatigue life (i.e., CP, PC, and CC cycles, respectively, for tensile creep only, compressive creep only, and both tensile and compressive creep). Any mean stress effects on life also must be determined and accounted for when determining the SRP inelastic strainrange versus life relations for cycles featuring creep. This is particularly true for small strainranges. The life relations thus are established for a theoretical zero mean stress condition.

Evaluating the coefficient of thermal expansion using time periods of minimal thermal gradient for a temperature driven structural health monitoring

NASA Astrophysics Data System (ADS)

Reilly, J.; Abdel-Jaber, H.; Yarnold, M.; Glisic, B.

2017-04-01

Structural Health Monitoring aims to characterize the performance of a structure from a combination of recorded sensor data and analytic techniques. Many methods are concerned with quantifying the elastic response of the structure, treating temperature changes as noise in the analysis. While these elastic profiles do demonstrate a portion of structural behavior, thermal loads on a structure can induce comparable strains to elastic loads. Understanding this relationship between the temperature of the structure and the resultant strain and displacement can provide in depth knowledge of the structural condition. A necessary parameter for this form of analysis is the Coefficient of Thermal Expansion (CTE). The CTE of a material relates the amount of expansion or contraction a material undergoes per degree change in temperature, and can be determined from temperature-strain relationship given that the thermal strain can be isolated. Many times with concrete, the actual amount of expansion with temperature in situ varies from the given values for the CTE due to thermally generated elastic strain, which complicates evaluation of the CTE. To accurately characterize the relationship between temperature and strain on a structure, the actual thermal behavior of the structure needs to be analyzed. This rate can vary for different parts of a structure, depending on boundary conditions. In a case of unrestrained structures, the strain in the structure should be linearly related to the temperature change. Thermal gradients in a structure can affect this relationship, as they induce curvature and deplanations in the cross section. This paper proposes a method that addresses these challenges in evaluating the CTE.

Carbohydrate catabolic flexibility in the mammalian intestinal commensal Lactobacillus ruminis revealed by fermentation studies aligned to genome annotations

PubMed Central

2011-01-01

Background Lactobacillus ruminis is a poorly characterized member of the Lactobacillus salivarius clade that is part of the intestinal microbiota of pigs, humans and other mammals. Its variable abundance in human and animals may be linked to historical changes over time and geographical differences in dietary intake of complex carbohydrates. Results In this study, we investigated the ability of nine L. ruminis strains of human and bovine origin to utilize fifty carbohydrates including simple sugars, oligosaccharides, and prebiotic polysaccharides. The growth patterns were compared with metabolic pathways predicted by annotation of a high quality draft genome sequence of ATCC 25644 (human isolate) and the complete genome of ATCC 27782 (bovine isolate). All of the strains tested utilized prebiotics including fructooligosaccharides (FOS), soybean-oligosaccharides (SOS) and 1,3:1,4-β-D-gluco-oligosaccharides to varying degrees. Six strains isolated from humans utilized FOS-enriched inulin, as well as FOS. In contrast, three strains isolated from cows grew poorly in FOS-supplemented medium. In general, carbohydrate utilisation patterns were strain-dependent and also varied depending on the degree of polymerisation or complexity of structure. Six putative operons were identified in the genome of the human isolate ATCC 25644 for the transport and utilisation of the prebiotics FOS, galacto-oligosaccharides (GOS), SOS, and 1,3:1,4-β-D-Gluco-oligosaccharides. One of these comprised a novel FOS utilisation operon with predicted capacity to degrade chicory-derived FOS. However, only three of these operons were identified in the ATCC 27782 genome that might account for the utilisation of only SOS and 1,3:1,4-β-D-Gluco-oligosaccharides. Conclusions This study has provided definitive genome-based evidence to support the fermentation patterns of nine strains of Lactobacillus ruminis, and has linked it to gene distribution patterns in strains from different sources. Furthermore, the study has identified prebiotic carbohydrates with the potential to promote L. ruminis growth in vivo. PMID:21995520

Penicillin resistance compromises Nod1-dependent proinflammatory activity and virulence fitness of neisseria meningitidis.

PubMed

Zarantonelli, Maria Leticia; Skoczynska, Anna; Antignac, Aude; El Ghachi, Meriem; Deghmane, Ala-Eddine; Szatanik, Marek; Mulet, Céline; Werts, Catherine; Peduto, Lucie; d'Andon, Martine Fanton; Thouron, Françoise; Nato, Faridabano; Lebourhis, Lionel; Philpott, Dana J; Girardin, Stephen E; Vives, Francina Langa; Sansonetti, Philippe; Eberl, Gérard; Pedron, Thierry; Taha, Muhamed-Kheir; Boneca, Ivo G

2013-06-12

Neisseria meningitidis is a life-threatening human bacterial pathogen responsible for pneumonia, sepsis, and meningitis. Meningococcal strains with reduced susceptibility to penicillin G (Pen(I)) carry a mutated penicillin-binding protein (PBP2) resulting in a modified peptidoglycan structure. Despite their antibiotic resistance, Pen(I) strains have failed to expand clonally. We analyzed the biological consequences of PBP2 alteration among clinical meningococcal strains and found that peptidoglycan modifications of the Pen(I) strain resulted in diminished in vitro Nod1-dependent proinflammatory activity. In an influenza virus-meningococcal sequential mouse model mimicking human disease, wild-type meningococci induced a Nod1-dependent inflammatory response, colonizing the lungs and surviving in the blood. In contrast, isogenic Pen(I) strains were attenuated for such response and were out-competed by meningococci sensitive to penicillin G. Our results suggest that antibiotic resistance imposes a cost to the success of the pathogen and may potentially explain the lack of clonal expansion of Pen(I) strains. Copyright © 2013 Elsevier Inc. All rights reserved.

ZIP2DL: An Elastic-Plastic, Large-Rotation Finite-Element Stress Analysis and Crack-Growth Simulation Program

NASA Technical Reports Server (NTRS)

Deng, Xiaomin; Newman, James C., Jr.

1997-01-01

ZIP2DL is a two-dimensional, elastic-plastic finte element program for stress analysis and crack growth simulations, developed for the NASA Langley Research Center. It has many of the salient features of the ZIP2D program. For example, ZIP2DL contains five material models (linearly elastic, elastic-perfectly plastic, power-law hardening, linear hardening, and multi-linear hardening models), and it can simulate mixed-mode crack growth for prescribed crack growth paths under plane stress, plane strain and mixed state of stress conditions. Further, as an extension of ZIP2D, it also includes a number of new capabilities. The large-deformation kinematics in ZIP2DL will allow it to handle elastic problems with large strains and large rotations, and elastic-plastic problems with small strains and large rotations. Loading conditions in terms of surface traction, concentrated load, and nodal displacement can be applied with a default linear time dependence or they can be programmed according to a user-defined time dependence through a user subroutine. The restart capability of ZIP2DL will make it possible to stop the execution of the program at any time, analyze the results and/or modify execution options and resume and continue the execution of the program. This report includes three sectons: a theoretical manual section, a user manual section, and an example manual secton. In the theoretical secton, the mathematics behind the various aspects of the program are concisely outlined. In the user manual section, a line-by-line explanation of the input data is given. In the example manual secton, three types of examples are presented to demonstrate the accuracy and illustrate the use of this program.

Postantibiotic effect of various antibiotics on Legionella pneumophila strains isolated from water systems.

PubMed

Birteksöz-Tan, Ayşe Seher; Zeybek, Zuhal

2012-11-01

The postantibiotic effects (PAE) of azithromycin, clarithromycin, ciprofloxacin, and levofloxacin were investigated against Legionella pneumophila (L. pneumophila) strains isolated from several hot water systems of different buildings in Istanbul. Each strain in logarithmic phase of growth was exposed to concentrations of antibiotics equal to minimum inhibitory concentration (MIC) and 4× MIC for 1 h. Recovery periods of test cultures were evaluated after centrifugation using the viable counting method. The mean values of PAEs for the strains of L. pneumophila, azithromycin at a concentration equal to and 4 times of MIC values were found 1.75 ± 0.28 h and 4.06 ± 0.44 h, for clarithromycin 2.98 ± 0.70 h and 4.18 ± 0.95 h, for ciprofloxacin 2.97 ± 0.63 h and 4.70 ± 0.63 h, for levofloxacin 2.05 ± 0.33 h and 3.78 ± 0.46 h, respectively. All of the antibiotics showed increased PAE values in a concentration-dependent manner. The findings of our study may play useful role in selecting the appropriate timing of doses during therapy with antimicrobials to treat patients infected with L. pneumophila.

Strain-enhanced stress relaxation impacts nonlinear elasticity in collagen gels

PubMed Central

Nam, Sungmin; Hu, Kenneth H.; Chaudhuri, Ovijit

2016-01-01

The extracellular matrix (ECM) is a complex assembly of structural proteins that provides physical support and biochemical signaling to cells in tissues. The mechanical properties of the ECM have been found to play a key role in regulating cell behaviors such as differentiation and malignancy. Gels formed from ECM protein biopolymers such as collagen or fibrin are commonly used for 3D cell culture models of tissue. One of the most striking features of these gels is that they exhibit nonlinear elasticity, undergoing strain stiffening. However, these gels are also viscoelastic and exhibit stress relaxation, with the resistance of the gel to a deformation relaxing over time. Recent studies have suggested that cells sense and respond to both nonlinear elasticity and viscoelasticity of ECM, yet little is known about the connection between nonlinear elasticity and viscoelasticity. Here, we report that, as strain is increased, not only do biopolymer gels stiffen but they also exhibit faster stress relaxation, reducing the timescale over which elastic energy is dissipated. This effect is not universal to all biological gels and is mediated through weak cross-links. Mechanistically, computational modeling and atomic force microscopy (AFM) indicate that strain-enhanced stress relaxation of collagen gels arises from force-dependent unbinding of weak bonds between collagen fibers. The broader effect of strain-enhanced stress relaxation is to rapidly diminish strain stiffening over time. These results reveal the interplay between nonlinear elasticity and viscoelasticity in collagen gels, and highlight the complexity of the ECM mechanics that are likely sensed through cellular mechanotransduction. PMID:27140623

Recent deformation rates on Venus

NASA Technical Reports Server (NTRS)

Grimm, Robert E.

1994-01-01

Constraints on the recent geological evolution of Venus may be provided by quantitative estimates of the rates of the principal resurfacing processes, volcanism and tectonism. This paper focuses on the latter, using impact craters as strain indicators. The total postimpact tectonic strain lies in the range 0.5-6.5%, which defines a recent mean strain rate of 10(exp -18)-10(exp -17)/s when divided by the mean surface age. Interpretation of the cratering record as one of pure production requires a decline in resurfacing rates at about 500 Ma (catastrophic resurfacing model). If distributed tectonic resurfacing contributed strongly before that time, as suggested by the widespread occurrence of tessera as inliers, the mean global strain rate must have been at least approximately 10(exp -15)/s, which is also typical of terrestrial active margins. Numerical calculations of the response of the lithosphere to inferred mantle convective forces were performed to test the hypothesis that a decrease in surface strain rate by at least two orders of magnitude could be caused by a steady decline in heat flow over the last billion years. Parameterized convection models predict that the mean global thermal gradient decreases by only about 5 K/km over this time; even with the exponential dependence of viscosity upon temperature, the surface strain rate drops by little more than one order of magnitude. Strongly unsteady cooling and very low thermal gradients today are necessary to satisfy the catastrophic model. An alternative, uniformitarian resurfacing hypothesis holds that Venus is resurfaced in quasi-random 'patches' several hundred kilometers in size that occur in response to changing mantle convection patterns.

Stress and strain relaxation in magnesium AZ31 rolled plate: In-situ neutron measurement and elastic viscoplastic polycrystal modeling

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

Wang, Huamiao; Clausen, Bjorn; Capolungo, Laurent

Continuous mechanical tests with strain holds (stress relaxation) and with stress holds (strain relaxation) are performed simultaneously with in-situ neutron measurements to analyze the mechanisms of stress and strain relaxation in Mg AZ31 rolled plate. A dislocation activity based constitutive model, accounting for internal stress statistical distributions, is proposed and implemented into an elastic viscoplastic self-consistent (EVPSC) framework to simultaneously describe both stress and strain relaxation. The model captures the experimental data in terms of macroscopic stress strain curves, evolution of stress and strain during holding, as well as evolution of the internal elastic strains. Model results indicate that themore » magnitude of the stress relaxed during strain holding is dependent on both, the magnitude of the flow stress and the spread of the resolved shear stress distribution. The magnitude of strain accumulated during stress holding is, on the other hand, dependent on the magnitude of the hardening rate and on the spread of the resolved shear stress distribution. Furthermore, the internal elastic strains are directly correlated with the stress state, and hence the stress relaxation during strain holds has a greater influence on the lattice strains than strain relaxation during stress holds.« less

Stress and strain relaxation in magnesium AZ31 rolled plate: In-situ neutron measurement and elastic viscoplastic polycrystal modeling

DOE PAGES

Wang, Huamiao; Clausen, Bjorn; Capolungo, Laurent; ...

2015-07-16

Continuous mechanical tests with strain holds (stress relaxation) and with stress holds (strain relaxation) are performed simultaneously with in-situ neutron measurements to analyze the mechanisms of stress and strain relaxation in Mg AZ31 rolled plate. A dislocation activity based constitutive model, accounting for internal stress statistical distributions, is proposed and implemented into an elastic viscoplastic self-consistent (EVPSC) framework to simultaneously describe both stress and strain relaxation. The model captures the experimental data in terms of macroscopic stress strain curves, evolution of stress and strain during holding, as well as evolution of the internal elastic strains. Model results indicate that themore » magnitude of the stress relaxed during strain holding is dependent on both, the magnitude of the flow stress and the spread of the resolved shear stress distribution. The magnitude of strain accumulated during stress holding is, on the other hand, dependent on the magnitude of the hardening rate and on the spread of the resolved shear stress distribution. Furthermore, the internal elastic strains are directly correlated with the stress state, and hence the stress relaxation during strain holds has a greater influence on the lattice strains than strain relaxation during stress holds.« less

Large strain dynamic compression for soft materials using a direct impact experiment

NASA Astrophysics Data System (ADS)

Meenken, T.; Hiermaier, S.

2006-08-01

Measurement of strain rate dependent material data of low density low strength materials like polymeric foams and rubbers still poses challenges of a different kind to the experimental set up. For instance, in conventional Split Hopkinson Pressure Bar tests the impedance mismatch between the bars and the specimen makes strain measurement almost impossible. Application of viscoelastic bars poses new problems with wave dispersion. Also, maximum achievable strains and strain rates depend directly on the bar lengths, resulting in large experimental set ups in order to measure relevant data for automobile crash applications. In this paper a modified SHPB will be presented for testing low impedance materials. High strains can be achieved with nearly constant strain rate. A thin film stress measurement has been applied to the specimen/bar interfaces to investigate the initial sample ring up process. The process of stress homogeneity within the sample was investigated on EPDM and PU rubber.

Interplay between strain, quantum confinement, and ferromagnetism in strained ferromagnetic semiconductor (In,Fe)As thin films

NASA Astrophysics Data System (ADS)

Sasaki, Daisuke; Anh, Le Duc; Nam Hai, Pham; Tanaka, Masaaki

2014-04-01

We systematically investigated the influence of strain on the electronic structure and ferromagnetism of (In,Fe)As thin films. It is found that while the shift of the critical point energies of compressive-strained (In,Fe)As layers grown on (In1-y,Gay)As (y = 0.05, 0.1) buffer layers can be explained by the hydrostatic deformation effect (HDE) alone, those of tensile-strained (In,Fe)As layers grown on (Ga1-z,Alz)Sb (z = 0, 0.5, 1) buffer layers can be explained by the combination of HDE and the quantum confinement effect (QCE). The Curie temperature TC of the (In,Fe)As layers strongly depends on the strain, and shows a maximum for the (In,Fe)As layer grown on a GaSb buffer layer. The strain dependence of TC can be explained by the s-d exchange mechanism taking into account HDE and QCE.

Time And Temperature Dependent Micromechanical Properties Of Solder Joints For 3D-Package Integration

NASA Astrophysics Data System (ADS)

Roellig, Mike; Meier, Karsten; Metasch, Rene

2010-11-01

The recent development of 3D-integrated electronic packages is characterized by the need to increase the diversity of functions and to miniaturize. Currently many 3D-integration concepts are being developed and all of them demand new materials, new designs and new processing technologies. The combination of simulation and experimental investigation becomes increasingly accepted since simulations help to shorten the R&D cycle time and reduce costs. Numerical calculations like the Finite-Element-Method are strong tools to calculate stress conditions in electronic packages resulting from thermal strains due to the manufacturing process and environmental loads. It is essential for the application of numerical calculations that the material data is accurate and describes sufficiently the physical behaviour. The developed machine allows the measurement of time and temperature dependent micromechanical properties of solder joints. Solder joints, which are used to mechanically and electrically connect different packages, are physically measured as they leave the process. This allows accounting for process influences, which may change material properties. Additionally, joint sizes and metallurgical interactions between solder and under bump metallization can be respected by this particular measurement. The measurement allows the determination of material properties within a temperature range of 20° C-200° C. Further, the time dependent creep deformation can be measured within a strain-rate range of 10-31/s-10-81/s. Solder alloys based on Sn-Ag/Sn-Ag-Cu with additionally impurities and joint sizes down to O/ 200 μm were investigated. To finish the material characterization process the material model coefficient were extracted by FEM-Simulation to increase the accuracy of data.

Chronic intermittent ethanol inhalation increases ethanol self-administration in both C57BL/6J and DBA/2J mice.

PubMed

McCool, Brian A; Chappell, Ann M

2015-03-01

Inbred mouse strains provide significant opportunities to understand the genetic mechanisms controlling ethanol-directed behaviors and neurobiology. They have been specifically employed to understand cellular mechanisms contributing to ethanol consumption, acute intoxication, and sensitivities to chronic effects. However, limited ethanol consumption by some strains has restricted our understanding of clinically relevant endpoints such as dependence-related ethanol intake. Previous work with a novel tastant-substitution procedure using monosodium glutamate (MSG or umami flavor) has shown that the procedure greatly enhances ethanol consumption by mouse strains that express limited drinking phenotypes using other methods. In the current study, we employ this MSG-substitution procedure to examine how ethanol dependence, induced with passive vapor inhalation, modifies ethanol drinking in C57BL/6J and DBA/2J mice. These strains represent 'high' and 'low' drinking phenotypes, respectively. We found that the MSG substitution greatly facilitates ethanol drinking in both strains, and likewise, ethanol dependence increased ethanol consumption regardless of strain. However, DBA/2J mice exhibited greater sensitivity dependence-enhanced drinking, as represented by consumption behaviors directed at lower ethanol concentrations and relative to baseline intake levels. DBA/2J mice also exhibited significant withdrawal-associated anxiety-like behavior while C57BL/6J mice did not. These findings suggest that the MSG-substitution procedure can be employed to examine dependence-enhanced ethanol consumption across a range of drinking phenotypes, and that C57BL/6J and DBA/2J mice may represent unique neurobehavioral pathways for developing dependence-enhanced ethanol consumption. Copyright © 2015 Elsevier Inc. All rights reserved.

The interpretation of crustal dynamics data in terms of plate motions and regional deformation near plate boundaries

NASA Technical Reports Server (NTRS)

Solomon, Sean C.

1987-01-01

The nature and dynamics of time-dependent deformation along major seismic zones including the influence of irregularities in fault geometry on the earthquake cycle, and the processes contributing to the state of stress and rates of strain in plate interior regions were studied. The principle findings of the research are discussed.

Growth of Matrix Cracks During Intermediate Temperature Stress Rupture of a SiC/SiC Composite in Air

NASA Technical Reports Server (NTRS)

Morscher, Gregory N.

2000-01-01

The crack density of woven Hi-Nicalon(sup TM) (Nippon Carbon, Japan) fiber, BN interphase, melt-infiltrated SiC matrix composites was determined for specimens subjected to tensile stress rupture at 815 C. A significant amount of matrix cracking occurs due to the growth of fiber-bridged microcracks even at stresses below the run-out condition. This increased cracking corresponded to time dependent strain accumulation and acoustic emission activity during the constant load test. However, the portion of the rupture specimens subjected to cooler temperatures (< 600 C than the hot section had significantly lower crack densities compared to the hotter regions. From the acoustic emission and time dependent strain data it can be inferred that most of the matrix crack growth occurred within the first few hours of the tensile rupture experiment. The crack growth was attributed to an interphase recession mechanism that is enhanced by the presence of a thin carbon layer between the fiber and the matrix as a result of the composite fabrication process. One important consequence of matrix crack growth at the lower stresses is poor retained strength at room temperature for specimens that did not fail.

Environmental degradation of 316 stainless steel in high temperature low cycle fatigue

NASA Technical Reports Server (NTRS)

Kalluri, Sreeramesh; Manson, S. Stanford; Halford, Gary R.

1987-01-01

Procedures based on modification of the conventional Strainrange Partitioning method are proposed to characterize the time-dependent degradation of engineering alloys in high-temperature, low-cycle fatigue. Creep-fatigue experiments were conducted in air using different waveforms of loading on 316 stainless steel at 816 C (1500 F) to determine the effect of exposure time on cyclic life. Reductions in the partitioned cyclic lives were observed with an increase in the time of exposure (or with the corresponding decrease in the steady-state creep rate) for all the waveforms involving creep strain. Excellent correlations of the experimental data were obtained by modifying the Conventional Strainrange Partitioning life relationships involving creep strain using a power-law term of either: (1) time of exposure, or (2) steady-state creep rate of the creep-fatigue test. Environmental degradation due to oxidation, material degradation due to the precipitation of carbides along the grain boundaries and detrimental deformation modes associated with the prolonged periods of creep were observed to be the main mechanisms responsible for life reductions at long exposure times.

High-temperature low-cycle-fatigue and crack-growth behaviors of three superalloys: HASTELLOY X, HAYNES 230, and HAYNES 188

NASA Astrophysics Data System (ADS)

Lu, Yulin

Low cycle fatigue (LCF) and fatigue crack growth (FCG) experiments on three superalloys HASTELLOY X, HAYNES 230, and HAYNES 188 have been conducted at temperatures from 649 to 982°C. Hold times were imposed at the maximum strain or load to investigate the hold-time effect. In general, the fatigue life decreased as the temperature or hold time increased. However, for the HAYNES 230 alloy at total strain ranges higher than 1.0% and without a hold time, the LCF life was longer at 927°C than at 816°C. This "abnormal" behavior was found to result from the smaller plastic strain amplitude at half-life at 927°C than that at 816°C. An increase in the temperature and/or the introduction of a hold time decreased the hardening rate and increased the softening rate for all the three alloys. The introduction of a hold time and/or the increase of the test temperature progressively changed the fracture mode from the transgranular to mixed trans/inter-granular, then to intergranular feature. Within the two phases of the fatigue process, crack initiation was more severely influenced by the change of the hold time and/or temperature. The FCG data of HASTELLOY X and HAYNES 230 alloys were analyzed with an emphasis on hold-time and temperature effects. The crack grew faster at a higher temperature and a longer hold time. Fracture-mechanics parameters, C*, Ct, and (Ct)avg, were applied to correlate the crack-growth rates. The fatigue-cracking path was mainly transgranular at 816 and 927°C. The cracking path became dominantly intergranular if the hold time increased to 2 min, indicating that the time-dependent damage mechanisms were in control. The Ct and (Ct)avg parameters were capable of consolidating time dependent crack growth rate from different temperatures and alloys. The tests were conducted in air. Therefore, the fracture surfaces were frequently covered with a dark layer of oxides, making fracture feature difficult to identify under scanning-electron-microscopy. To overcome this problem, an oxide-stripping technique has been developed. The sample is first boiled in a potassium permanganate solution for 1 h, and then electrolytically cleaned in an alkaline solution for 5 min.

Size-dependent axial instability of microtubules surrounded by cytoplasm of a living cell based on nonlocal strain gradient elasticity theory.

PubMed

Sahmani, S; Aghdam, M M

2017-06-07

Microtubules including tubulin heterodimers arranging in a parallel shape of cylindrical hollow plays an important role in the mechanical stiffness of a living cell. In the present study, the nonlocal strain gradient theory of elasticity including simultaneously the both nonlocality and strain gradient size dependency is put to use within the framework of a refined orthotropic shell theory with hyperbolic distribution of shear deformation to analyze the size-dependent buckling and postbuckling characteristics of microtubules embedded in cytoplasm under axial compressive load. The non-classical governing differential equations are deduced via boundary layer theory of shell buckling incorporating the nonlinear prebuckling deformation and microtubule-cytoplasm interaction in the living cell environment. Finally, with the aid of a two-stepped perturbation solution methodology, the explicit analytical expressions for nonlocal strain gradient stability paths of axially loaded microtubules are achieved. It is illustrated that by taking the nonlocal size effect into consideration, the critical buckling load of microtubule and its maximum deflection associated with the minimum postbuckling load decreases, while the strain gradient size dependency causes to increase them. Copyright © 2017 Elsevier Ltd. All rights reserved.

Strain-dependent characterization of electrode and polymer network of electrically activated polymer actuators

NASA Astrophysics Data System (ADS)

Töpper, Tino; Osmani, Bekim; Weiss, Florian M.; Winterhalter, Carla; Wohlfender, Fabian; Leung, Vanessa; Müller, Bert

2015-04-01

Fecal incontinence describes the involuntary loss of bowel content and affects about 45 % of retirement home residents and overall more than 12 % of the adult population. Artificial sphincter implants for treating incontinence are currently based on mechanical systems with failure rates resulting in revision after three to five years. To overcome this drawback, artificial muscle sphincters based on bio-mimetic electro-active polymer (EAP) actuators are under development. Such implants require polymer films that are nanometer-thin, allowing actuation below 24 V, and electrodes that are stretchable, remaining conductive at strains of about 10 %. Strain-dependent resistivity measurements reveal an enhanced conductivity of 10 nm compared to 30 nm sputtered Au on silicone for strains higher than 5 %. Thus, strain-dependent morphology characterization with optical microscopy and atomic force microscopy could demonstrate these phenomena. Cantilever bending measurements are utilized to determine elastic/viscoelastic properties of the EAP films as well as their long-term actuation behavior. Controlling these properties enables the adjustment of growth parameters of nanometer-thin EAP actuators.

Finite element analysis of residual stress field induced by laser shock peening

NASA Astrophysics Data System (ADS)

Nam, Taeksun

The finite element method is applied to analyze the laser shock peening process (LSP) for thick parts (considered as a semi-infinite half space) and thin parts (finite thickness domain). The technology of LSP is used to enhance mechanical properties such as fatigue life, fretting fatigue life, resistance to stress corrosion cracking and surface hardness. These enhanced material properties are directly related to the magnitude and distribution of the plastic strain and associated residual stresses due to shockwaves induced by LSP. To reduce the process development cost and time, the prediction of residual stress field is very useful to provide a base design guideline for selecting appropriate LSP conditions for evaluation. An axisymmetric Finite Element Analysis (FEA) code, named SHOCKWAVE, is developed in order to complement shortcomings of applying commercial FEA codes at extremely high strain rates (as high as 104 -106/sec). The rate dependent plasticity theory is applied along with the small strain assumption. The solution process consists of an explicit dynamic loading analysis for shock loading stage and a static unloading analysis (implicit) to determine the equilibrium state for the residual stress and plastic strain fields. Some of the highlights explored in this investigation entail: (i) overstress power law models for the rate dependence, (ii) various hardening models, (iii) a second-order accurate implicit algorithm for the plastic consistency condition, (iv) an adaptively expanding domain scheme to trace the stress-free boundary condition in a simple way, (v) a special uniform meshing scheme to avoid the usual assembly process and repeated calculations for the stiffness matrix, (vi) mesh sensitivity study, (vii) comparisons with measured data provided and supported by the LSP Technologies, Inc. The dynamic behavior of Ti-6Al-4V at high strain rates can be investigated by using the split torsional Hopkinson bar experiment and by a longitudinal shock loading simulation in uniaxial strain to obtain material parameters representing rate dependent plasticity. In case of the double-sided laser peening for a thin part, reversal in loading plays a significant role. The stress waves repeatedly recompose the pre-accumulated plastic strains because of the interaction of the primary and reflected stress waves. In an attempt to better represent the material behavior under repeated reversals and collapses in loading, a sequence of bend-reverse bend tests is performed to identify the material parameters of TI-6Al-4V needed for a nonlinear kinematic hardening model (Chaboche model). For a thick part (a semi-infinite domain), single shot as well as multiple shots (at the same location) cases are simulated and compared with measured data for two different loading magnitudes and three different hardening models. Some of the simulation results agree well with the measured data, depending on the choice of hardening model and the treatment of rate dependent material behavior at high strain rates. Only a single shot (on both sides) case is investigated for a thin part (a finite thickness domain) in terms of residual stress distribution. The disagreement between the computed results and the measured data is more pronounced in this case, needing further investigations on both sides of the fields.

Low cycle fatigue and creep fatigue interaction behavior of 9Cr-0.5Mo-1.8W-V-Nb heat-resistant steel at high temperature

NASA Astrophysics Data System (ADS)

Wang, Xiaowei; Zhang, Wei; Gong, Jianming; Wahab, Magd Abdel

2018-07-01

In this paper, Low Cycle Fatigue (LCF) and Creep-Fatigue Interaction (CFI) behavior of 9Cr-0.5Mo-1.8 W-V-Nb heat-resistant steel (ASME Grade P92 steel) at elevated temperature of 600 °C are investigated. Strain controlled LCF tests are conducted in fully reversed triangular waveform at different strain amplitudes ranging from 0.2% to 0.8%. CFI tests are conducted at 0.4% strain amplitude in trapezoid waveform with tensile hold time varying from 1 min to 60 min and compressive hold time varying from 1 min to 10 min. During LCF and CFI loadings, the evolution of cyclic stress, mean stress and stress relaxation behavior are investigated. It turns out that the softening behavior and lifetime degradation are dependent on strain amplitude, hold time and hold direction. In addition, the microstructure evolution and fracture behavior are characterized by optical, scanning and transmission electron microscope. The initial rapid softening behavior is attributed to the quick elimination of low angle boundaries, whereas no obvious microstructure alteration appears in the stable stage. Fracture behavior analysis reveals creep voids in long-term CFI tests facilitates the initiation and propagation of secondary cracks. The different responses of outer surface oxidation layer during cycling provides an explanation for severer damage of compressive hold and also accounts for the observed various fracture behavior of failed samples.

Power-law viscous materials for analogue experiments: New data on the rheology of highly-filled silicone polymers

NASA Astrophysics Data System (ADS)

Boutelier, D.; Schrank, C.; Cruden, A.

2008-03-01

The selection of appropriate analogue materials is a central consideration in the design of realistic physical models. We investigate the rheology of highly-filled silicone polymers in order to find materials with a power-law strain-rate softening rheology suitable for modelling rock deformation by dislocation creep and report the rheological properties of the materials as functions of the filler content. The mixtures exhibit strain-rate softening behaviour but with increasing amounts of filler become strain-dependent. For the strain-independent viscous materials, flow laws are presented while for strain-dependent materials the relative importance of strain and strain rate softening/hardening is reported. If the stress or strain rate is above a threshold value some highly-filled silicone polymers may be considered linear visco-elastic (strain independent) and power-law strain-rate softening. The power-law exponent can be raised from 1 to ˜3 by using mixtures of high-viscosity silicone and plasticine. However, the need for high shear strain rates to obtain the power-law rheology imposes some restrictions on the usage of such materials for geodynamic modelling. Two simple shear experiments are presented that use Newtonian and power-law strain-rate softening materials. The results demonstrate how materials with power-law rheology result in better strain localization in analogue experiments.

Capturing tensile size-dependency in polymer nanofiber elasticity.

PubMed

Yuan, Bo; Wang, Jun; Han, Ray P S

2015-02-01

As the name implies, tensile size-dependency refers to the size-dependent response under uniaxial tension. It defers markedly from bending size-dependency in terms of onset and magnitude of the size-dependent response; the former begins earlier but rises to a smaller value than the latter. Experimentally, tensile size-dependent behavior is much harder to capture than its bending counterpart. This is also true in the computational effort; bending size-dependency models are more prevalent and well-developed. Indeed, many have questioned the existence of tensile size-dependency. However, recent experiments seem to support the existence of this phenomenon. Current strain gradient elasticity theories can accurately predict bending size-dependency but are unable to track tensile size-dependency. To rectify this deficiency a higher-order strain gradient elasticity model is constructed by including the second gradient of the strain into the deformation energy. Tensile experiments involving 10 wt% polycaprolactone nanofibers are performed to calibrate and verify our model. The results reveal that for the selected nanofibers, their size-dependency begins when their diameters reduce to 600 nm and below. Further, their characteristic length-scale parameter is found to be 1095.8 nm. Copyright © 2014 Elsevier Ltd. All rights reserved.

Proof of concept: performance testing in models.

PubMed

Craig, W A

2004-04-01

Pharmacokinetic (PK) and pharmacodynamic (PD) principles that predict antimicrobial efficacy can be used to set targets for antimicrobial design and optimisation. Although current formulations of amoxicillin and amoxicillin/clavulanate have retained their efficacy against many, but not all, penicillin-nonsusceptible Streptococcus pneumoniae, additional coverage is required to address the growing problem of drug-resistant strains. Accordingly, two new oral formulations of amoxicillin/clavulanate, a paediatric formulation at 90/6.4 mg/kg/day and a pharmacokinetically enhanced formulation at 2000/125 mg twice daily for adults, were designed using PK/PD principles. These principles indicate that for amoxicillin and amoxicillin/clavulanate, a time above MIC of 35-40% of the dosing interval is predictive of high bacterial efficacy. In line with PK/PD predictions, simulation of human pharmacokinetics in in-vitro kinetic models and in a rat model of pneumonia, amoxicillin/clavulanate 2000/125 mg twice daily was highly effective against S. pneumoniae strains with amoxicillin MICs of 4 or 8 mg/L. Against strains with amoxicillin MICs of 4 mg/L, amoxicillin/clavulanate 2000/125 mg twice daily was significantly more effective than the conventional 875/125 mg twice daily formulation, azithromycin and levofloxacin, even though all levofloxacin MICs were < or = 1 mg/L. Following infection with S. pneumoniae strains with amoxicillin MICs of 8 mg/L, the amoxicillin/clavulanate 2000/125 mg twice daily formulation was more effective than the conventional amoxicillin/clavulanate formulations of 875/125 mg twice daily and three times daily and 1000/125 mg three times daily, and had similar or better efficacy than azithromycin and levofloxacin, depending on the strain. These data indicate the potential benefit of therapy with amoxicillin/clavulanate 2000/125 mg twice daily compared with conventional formulations and other marketed antimicrobials in the treatment of respiratory tract infection.

Finite element analysis of history-dependent damage in time-dependent fracture mechanics

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

Krishnaswamy, P.; Brust, F.W.; Ghadiali, N.D.

1993-11-01

The demands for structural systems to perform reliably under both severe and changing operating conditions continue to increase. Under these conditions time-dependent straining and history-dependent damage become extremely important. This work focuses on studying creep crack growth using finite element (FE) analysis. Two important issues, namely, (1) the use of history-dependent constitutive laws, and (2) the use of various fracture parameters in predicting creep crack growth, have both been addressed in this work. The constitutive model used here is the one developed by Murakami and Ohno and is based on the concept of a creep hardening surface. An implicit FEmore » algorithm for this model was first developed and verified for simple geometries and loading configurations. The numerical methodology developed here has been used to model stationary and growing cracks in CT specimens. Various fracture parameters such as the C[sub 1], C[sup *], T[sup *], J were used to compare the numerical predictions with experimental results available in the literature. A comparison of the values of these parameters as a function of time has been made for both stationary and growing cracks. The merit of using each of these parameters has also been discussed.« less

Systematic review of maritime field studies about stress and strain in seafaring.

PubMed

Oldenburg, M; Hogan, B; Jensen, H-J

2013-01-01

The aim of this study was to summarize and evaluate the current scientific literature on stress and strain on seafarers on board as defined by maritime field surveys. Using a systematic review, 109 studies on the stress and strain experienced by seafarers were identified for the period January 1990 to January 2012. Only 13 of the identified maritime studies were conducted as field studies, and in 10 of these studies, the focus was on the watch system and/or on fatigue. According to the study results, sleepiness tends to be stronger in the 2-watch system than in the 3-watch system (particularly between 4:00 and 6:00 a.m.). Occasional short sleep episodes appear to provide adequate recovery. Fatigue does not appear to depend on the seafarers' age and is often associated with poor sleep quality; noise and night shifts are also considered to contribute to fatigue. Stress among the seafarers was primarily recorded in sleep diaries (9 times) and with devices for measuring physical activity (4 times). As a rule, a questionnaire was used to assess the strain on the crew on board; 7 studies also additionally recorded biometrical parameters. Only in 6 cases were several groups with different ranks on board investigated. The conducted literature review makes it clear that most maritime field studies have focused on fatigue and watch systems in the shipping industry--in each case as univariate parameters. Thus, scientific field studies with comprehensive multivariate stress and strain analyses on board are required.

Structure, strain, and the ground state of the LaTiO3/LaAlO3 superlattice

NASA Astrophysics Data System (ADS)

Lee, Alex Taekyung; Han, Myung Joon

2014-03-01

The first-principles density functional theory calculations have been performed to understand LaTiO3/LaAlO3 superlattice. By taking into account of the structural distortions, U dependence, and the exchange correlation functional dependence, we show that the ferromagnetic spin and antiferro-orbital ordering is stabilized in the wide range of strains, which is notably different from the previous reports on the titanate systems. The ground-state spin and orbital configurations critically depend on the structural properties. Our results suggest a possible strain control of the magnetic property in transition-metal oxide heterostructures.

Light and phosphate competition between Cylindrospermopsis raciborskii and Microcystis aeruginosa is strain dependent.

PubMed

Marinho, Marcelo Manzi; Souza, Maria Betânia Gonçalves; Lürling, Miquel

2013-10-01

The hypothesis that outcomes of phosphorus and light competition between Cylindrospermopsis raciborskii and Microcystis aeruginosa are strain dependent was tested experimentally. Critical requirements of phosphorus (P*) and of light (I*) of two strains of each species were determined through monoculture experiments, which indicated a trade-off between species and also between Microcystis strains. Competition experiments between species were performed using the weakest predicted competitors (with the highest values of P* and of I*) and with the strongest predicted competitors (with the lowest values of P* and of I*). Under light limitation, competition between the weakest competitors led C. raciborskii to dominate. Between the strongest competitors, the opposite was observed, M. aeruginosa displaced C. raciborskii, but both strains co-existed in equilibrium. Under phosphate limitation, competition between the weakest competitors led C. raciborskii to exclude M. aeruginosa, and between the strongest competitors, the opposite was observed, M. aeruginosa displaced C. raciborskii, but the system did not reach an equilibrium and both strains were washed out. Hence, outcomes of the competition depended on the pair of competing strains and not only on species or on type of limitation. We concluded that existence of different trade-offs among strains and between species underlie our results showing that C. raciborskii can either dominate or be displaced by M. aeruginosa when exposed to different conditions of light or phosphate limitation.

Measurements of mechanical anisotropy in brain tissue and implications for transversely isotropic material models of white matter

PubMed Central

Feng, Yuan; Okamoto, Ruth J.; Namani, Ravi; Genin, Guy M.; Bayly, Philip V.

2013-01-01

White matter in the brain is structurally anisotropic, consisting largely of bundles of aligned, myelin-sheathed axonal fibers. White matter is believed to be mechanically anisotropic as well. Specifically, transverse isotropy is expected locally, with the plane of isotropy normal to the local mean fiber direction. Suitable material models involve strain energy density functions that depend on the I4 and I5 pseudo-invariants of the Cauchy–Green strain tensor to account for the effects of relatively stiff fibers. The pseudo-invariant I4 is the square of the stretch ratio in the fiber direction; I5 contains contributions of shear strain in planes parallel to the fiber axis. Most, if not all, published models of white matter depend on I4 but not on I5. Here, we explore the small strain limits of these models in the context of experimental measurements that probe these dependencies. Models in which strain energy depends on I4 but not I5 can capture differences in Young’s (tensile) moduli, but will not exhibit differences in shear moduli for loading parallel and normal to the mean direction of axons. We show experimentally, using a combination of shear and asymmetric indentation tests, that white matter does exhibit such differences in both tensile and shear moduli. Indentation tests were interpreted through inverse fitting of finite element models in the limit of small strains. Results highlight that: (1) hyperelastic models of transversely isotropic tissues such as white matter should include contributions of both the I4 and I5 strain pseudo-invariants; and (2) behavior in the small strain regime can usefully guide the choice and initial parameterization of more general material models of white matter. PMID:23680651

The anti-allergic effects of lactic acid bacteria are strain dependent and mediated by effects on both Th1/Th2 cytokine expression and balance.

PubMed

Fujiwara, Daisuke; Inoue, Sayo; Wakabayashi, Hideyuki; Fujii, Toshio

2004-11-01

There is growing interest in the immune-stimulating effect and in particular, the anti-allergic effect, of lactic acid bacteria (LAB). However, no comprehensive studies have been done that compare the immune-stimulating potential of LAB strains. The in vitro immune-stimulating effects on Th1/Th2 balance of more than 100 LAB strains were compared in splenocytes from ovalbumin-sensitized Th2-polarized mice. The in vivo anti-allergic ability of strain KW3110 was studied in the Th2-polarized model by detecting serum IgE concentration, Th1/Th2 cytokine secretion from splenocytes, and the expression of co-stimulatory molecules on macrophages. In vitro studies from Th2-polarized splenocytes, using IL-12 as a Th1 parameter and IL-4 secretion as a Th2 parameter revealed a wide variety of IL-12-inducing and IL-4-repressing activities, depending on the strain of LAB, not depending on the species. However, evaluation of individual strains in vivo revealed that after exposure to Lactobacillus paracasei KW3110 strain, the serum IgE elevation elicited by repeated OVA injection of mice was strongly inhibited. Cytokine secretion from splenocytes 20 weeks after KW3110 administration showed increased IL-12 and decreased IL-4 expression. Both CD40 and B7-1 expression on macrophages was upregulated by administration of KW3110. Improving the consequences of the Th1/Th2 imbalance by administration of LAB was dependent upon the LAB strain rather than the LAB species. Oral KW3110 administration in the mouse allergy model directed the Th1/Th2 balance toward Th1 through the maturation of APCs and inhibition of serum IgE elevation.

Unusual strain glassy phase in Fe doped Ni2Mn1.5In0.5

NASA Astrophysics Data System (ADS)

Nevgi, R.; Priolkar, K. R.

2018-01-01

Fe doped Ni2Mn1.5In0.5, particularly, Ni2Mn1.4Fe0.1In0.5, despite having an incommensurate, modulated 7M martensitic structure at room temperature exhibits frequency dependent behavior of storage modulus and loss which obeys the Vogel-Fulcher law as well as shows ergodicity breaking between zero field cooled and field cooled strain measurements just above the transition temperature. Both frequency dependence and ergodicity breaking are characteristics of a strain glassy phase and occur due to the presence of strain domains which are large enough to present signatures of long range martensitic order in diffraction but are non-interacting with other strain domains due to the presence of Fe impurities.

LS-DYNA Implementation of Polymer Matrix Composite Model Under High Strain Rate Impact

NASA Technical Reports Server (NTRS)

Zheng, Xia-Hua; Goldberg, Robert K.; Binienda, Wieslaw K.; Roberts, Gary D.

2003-01-01

A recently developed constitutive model is implemented into LS-DYNA as a user defined material model (UMAT) to characterize the nonlinear strain rate dependent behavior of polymers. By utilizing this model within a micromechanics technique based on a laminate analogy, an algorithm to analyze the strain rate dependent, nonlinear deformation of a fiber reinforced polymer matrix composite is then developed as a UMAT to simulate the response of these composites under high strain rate impact. The models are designed for shell elements in order to ensure computational efficiency. Experimental and numerical stress-strain curves are compared for two representative polymers and a representative polymer matrix composite, with the analytical model predicting the experimental response reasonably well.

Analytical Modeling of the High Strain Rate Deformation of Polymer Matrix Composites

NASA Technical Reports Server (NTRS)

Goldberg, Robert K.; Roberts, Gary D.; Gilat, Amos

2003-01-01

The results presented here are part of an ongoing research program to develop strain rate dependent deformation and failure models for the analysis of polymer matrix composites subject to high strain rate impact loads. State variable constitutive equations originally developed for metals have been modified in order to model the nonlinear, strain rate dependent deformation of polymeric matrix materials. To account for the effects of hydrostatic stresses, which are significant in polymers, the classical 5 plasticity theory definitions of effective stress and effective plastic strain are modified by applying variations of the Drucker-Prager yield criterion. To verify the revised formulation, the shear and tensile deformation of a representative toughened epoxy is analyzed across a wide range of strain rates (from quasi-static to high strain rates) and the results are compared to experimentally obtained values. For the analyzed polymers, both the tensile and shear stress-strain curves computed using the analytical model correlate well with values obtained through experimental tests. The polymer constitutive equations are implemented within a strength of materials based micromechanics method to predict the nonlinear, strain rate dependent deformation of polymer matrix composites. In the micromechanics, the unit cell is divided up into a number of independently analyzed slices, and laminate theory is then applied to obtain the effective deformation of the unit cell. The composite mechanics are verified by analyzing the deformation of a representative polymer matrix composite (composed using the representative polymer analyzed for the correlation of the polymer constitutive equations) for several fiber orientation angles across a variety of strain rates. The computed values compare favorably to experimentally obtained results.

Modified creep and shrinkage prediction model B3 for serviceability limit state analysis of composite slabs

NASA Astrophysics Data System (ADS)

Gholamhoseini, Alireza

2016-03-01

Relatively little research has been reported on the time-dependent in-service behavior of composite concrete slabs with profiled steel decking as permanent formwork and little guidance is available for calculating long-term deflections. The drying shrinkage profile through the thickness of a composite slab is greatly affected by the impermeable steel deck at the slab soffit, and this has only recently been quantified. This paper presents the results of long-term laboratory tests on composite slabs subjected to both drying shrinkage and sustained loads. Based on laboratory measurements, a design model for the shrinkage strain profile through the thickness of a slab is proposed. The design model is based on some modifications to an existing creep and shrinkage prediction model B3. In addition, an analytical model is developed to calculate the time-dependent deflection of composite slabs taking into account the time-dependent effects of creep and shrinkage. The calculated deflections are shown to be in good agreement with the experimental measurements.

Genetics of Amino Acid Taste and Appetite.

PubMed

Bachmanov, Alexander A; Bosak, Natalia P; Glendinning, John I; Inoue, Masashi; Li, Xia; Manita, Satoshi; McCaughey, Stuart A; Murata, Yuko; Reed, Danielle R; Tordoff, Michael G; Beauchamp, Gary K

2016-07-01

The consumption of amino acids by animals is controlled by both oral and postoral mechanisms. We used a genetic approach to investigate these mechanisms. Our studies have shown that inbred mouse strains differ in voluntary amino acid consumption, and these differences depend on sensory and nutritive properties of amino acids. Like humans, mice perceive some amino acids as having a sweet (sucrose-like) taste and others as having an umami (glutamate-like) taste. Mouse strain differences in the consumption of some sweet-tasting amino acids (d-phenylalanine, d-tryptophan, and l-proline) are associated with polymorphisms of a taste receptor, type 1, member 3 gene (Tas1r3), and involve differential peripheral taste responsiveness. Strain differences in the consumption of some other sweet-tasting amino acids (glycine, l-alanine, l-glutamine, and l-threonine) do not depend on Tas1r3 polymorphisms and so must be due to allelic variation in other, as yet unknown, genes involved in sweet taste. Strain differences in the consumption of l-glutamate may depend on postingestive rather than taste mechanisms. Thus, genes and physiologic mechanisms responsible for strain differences in the consumption of each amino acid depend on the nature of its taste and postingestive properties. Overall, mouse strain differences in amino acid taste and appetite have a complex genetic architecture. In addition to the Tas1r3 gene, these differences depend on other genes likely involved in determining the taste and postingestive effects of amino acids. The identification of these genes may lead to the discovery of novel mechanisms that regulate amino acid taste and appetite. © 2016 American Society for Nutrition.

Genetics of Amino Acid Taste and Appetite123

PubMed Central

Bosak, Natalia P; Glendinning, John I; Inoue, Masashi; Li, Xia; Manita, Satoshi; McCaughey, Stuart A; Murata, Yuko; Beauchamp, Gary K

2016-01-01

The consumption of amino acids by animals is controlled by both oral and postoral mechanisms. We used a genetic approach to investigate these mechanisms. Our studies have shown that inbred mouse strains differ in voluntary amino acid consumption, and these differences depend on sensory and nutritive properties of amino acids. Like humans, mice perceive some amino acids as having a sweet (sucrose-like) taste and others as having an umami (glutamate-like) taste. Mouse strain differences in the consumption of some sweet-tasting amino acids (d-phenylalanine, d-tryptophan, and l-proline) are associated with polymorphisms of a taste receptor, type 1, member 3 gene (Tas1r3), and involve differential peripheral taste responsiveness. Strain differences in the consumption of some other sweet-tasting amino acids (glycine, l-alanine, l-glutamine, and l-threonine) do not depend on Tas1r3 polymorphisms and so must be due to allelic variation in other, as yet unknown, genes involved in sweet taste. Strain differences in the consumption of l-glutamate may depend on postingestive rather than taste mechanisms. Thus, genes and physiologic mechanisms responsible for strain differences in the consumption of each amino acid depend on the nature of its taste and postingestive properties. Overall, mouse strain differences in amino acid taste and appetite have a complex genetic architecture. In addition to the Tas1r3 gene, these differences depend on other genes likely involved in determining the taste and postingestive effects of amino acids. The identification of these genes may lead to the discovery of novel mechanisms that regulate amino acid taste and appetite. PMID:27422518

Failure Mechanisms and Damage Model of Ductile Cast Iron Under Low-Cycle Fatigue Conditions

NASA Astrophysics Data System (ADS)

Wu, Xijia; Quan, Guangchun; MacNeil, Ryan; Zhang, Zhong; Sloss, Clayton

2014-10-01

Strain-controlled low-cycle fatigue (LCF) tests were conducted on ductile cast iron (DCI) at strain rates of 0.02, 0.002, and 0.0002/s in the temperature range from room temperature to 1073 K (800 °C). A constitutive-damage model was developed within the integrated creep-fatigue theory (ICFT) framework on the premise of strain decomposition into rate-independent plasticity and time-dependent creep. Four major damage mechanisms: (i) plasticity-induced fatigue, (ii) intergranular embrittlement (IE), (iii) creep, and (iv) oxidation were considered in a nonlinear creep-fatigue interaction model which represents the overall damage accumulation process consisting of oxidation-assisted fatigue crack nucleation and propagation in coalescence with internally distributed damage ( e.g., IE and creep), leading to final fracture. The model was found to agree with the experimental observations of the complex DCI-LCF phenomena, for which the linear damage summation rule would fail.

Autochthonous starter cultures and indigenous grape variety for regional wine production.

PubMed

Garofalo, C; El Khoury, M; Lucas, P; Bely, M; Russo, P; Spano, G; Capozzi, V

2015-06-01

To characterize Oenococcus oeni strains isolated from North-Apulian wines where malic acid degradation is usually achieved by spontaneous fermentations, and to determine the influence of bacterial inoculation time on the malolactic performances in 'Nero di Troia' wine using a complete autochthonous microbial regime. Oenococcus oeni strains from wines produced with the autochthonous (Apulia Region, southern Italy) grape variety 'Uva di Troia' were isolated, selected and characterized. Multilocus sequence typing and variable number tandem repeat analysis were used to investigate intraspecific diversity. Oenococcus oeni strains were tested in co-inoculation and in sequential inoculation, with two autochthonous yeast strains previously isolated from 'Nero di Troia' wine. After a preliminary screening using co-inoculation regime, the O. oeni strains were grouped in reason of the different behaviour in malic acid performances. Results suggested that the efficient degradation of malic acid in co-inoculation is a strain-dependent characteristic. Autochthonous yeast/bacterium combinations were identified as starter culture, and used in a co-inoculation approach, for vinification of regional wines. The 'microbial terroir' of typical fermented food and beverage production represents a dynamic sector of applied research in food microbiology. In this work, we propose the use of autochthonous bacteria and yeast for wine production from an indigenous grape variety. © 2015 The Society for Applied Microbiology.

Modelling deformation of partially melted rock using a poroviscoelastic rheology with dynamic power law viscosity

NASA Astrophysics Data System (ADS)

Simakin, A.; Ghassemi, A.

2005-03-01

A poroviscoelastic constitutive model is developed and used to study coupled rock deformation and fluid flow. The model allows the relaxation of both shear and symmetric components of the effective stress. Experimental results are usually interpreted in terms of the power law viscous material. However, in this work the effect of strain damage on viscosity is considered by treating the viscosity as a dynamic time-dependent parameter that varies proportionally to the second invariant of the strain rate. Healing is also taken into account so that the dynamic power law viscosity has a constant asymptotic at a given strain rate. The theoretical model is implemented in a finite element (FE) formulation that couples fluid flow and mechanical equilibrium equations. The FE method is applied to numerically study the triaxial compression of partially melted rocks at elevated PT conditions. It is found that the numerically calculated stress-strain curves demonstrate maxima similar to those observed in laboratory experiments. Also, the computed pattern of melt redistribution and strain localization at the contact between the rock sample and a stiff spacer is qualitatively similar to the experimental observations. The results also indicate that the matrix sensitivity to damage affects the scale of strain localization and melt redistribution.

Influence of quantum confinement and strain on orbital polarization of four-layer LaNiO 3 superlattices: A DFT+DMFT study

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

Park, Hyowon; Millis, Andrew J.; Marianetti, Chris A.

Atomically precise superlattices involving transition metal oxides provide a unique opportunity to engineer correlated electron physics using strain (modulated by choice of substate) and quantum confinement (controlled by layer thickness). We use the combination of density functional theory and dynamical mean field theory (DFT+DMFT) to study Ni E g d-orbital polarization in strained LaNiO 3/LaAlO 3 superlattices consisting of four layers of nominally metallic NiO 2 and four layers of insulating AlO 2 separated by LaO layers. The layer-resolved orbital polarization is calculated as a function of strain and analyzed in terms of structural, quantum confinement, and correlation effects. Wemore » determined that the effect of strain is from the dependence of the results on the Ni-O bondlength ratio and the octahedral rotation angles; quantum confinement is studied by comparison to bulk calculations with similar degrees of strain; correlation effects are inferred by varying interaction parameters within our DFT+DMFT calculations. The calculated dependence of orbital polarization on strain in superlattices is qualitatively consistent with recent X-ray absorption spectroscopy and resonant reflectometry data. But, interesting differences of detail are found between theory and experiment. Under tensile strain, the two inequivalent Ni ions display orbital polarization similar to that calculated for strained bulk LaNiO 3 and observed in experiment. Compressive strain produces a larger dependence of orbital polarization on Ni position and even the inner Ni layer exhibits orbital polarization different from that calculated for strained bulk LaNiO 3.« less

Influence of quantum confinement and strain on orbital polarization of four-layer LaNiO 3 superlattices: A DFT+DMFT study

DOE PAGES

Park, Hyowon; Millis, Andrew J.; Marianetti, Chris A.

2016-06-07

Atomically precise superlattices involving transition metal oxides provide a unique opportunity to engineer correlated electron physics using strain (modulated by choice of substate) and quantum confinement (controlled by layer thickness). We use the combination of density functional theory and dynamical mean field theory (DFT+DMFT) to study Ni E g d-orbital polarization in strained LaNiO 3/LaAlO 3 superlattices consisting of four layers of nominally metallic NiO 2 and four layers of insulating AlO 2 separated by LaO layers. The layer-resolved orbital polarization is calculated as a function of strain and analyzed in terms of structural, quantum confinement, and correlation effects. Wemore » determined that the effect of strain is from the dependence of the results on the Ni-O bondlength ratio and the octahedral rotation angles; quantum confinement is studied by comparison to bulk calculations with similar degrees of strain; correlation effects are inferred by varying interaction parameters within our DFT+DMFT calculations. The calculated dependence of orbital polarization on strain in superlattices is qualitatively consistent with recent X-ray absorption spectroscopy and resonant reflectometry data. But, interesting differences of detail are found between theory and experiment. Under tensile strain, the two inequivalent Ni ions display orbital polarization similar to that calculated for strained bulk LaNiO 3 and observed in experiment. Compressive strain produces a larger dependence of orbital polarization on Ni position and even the inner Ni layer exhibits orbital polarization different from that calculated for strained bulk LaNiO 3.« less

An individual-based model of rabbit viral haemorrhagic disease on European wild rabbits (Oryctolagus cuniculus)

USGS Publications Warehouse

Fa, John E.; Sharples, Colin M.; Bell, Diana J.; DeAngelis, Donald L.

2001-01-01

We developed an individual-based model of Rabbit Viral Hemorrhagic Disease (RVHD) for European wild rabbits (Oryctolagus cuniculus L.), representing up to 1000 rabbits in four hectares. Model output for productivity and recruitment matched published values. The disease was density-dependent and virulence affected outcome. Strains that caused death after several days produced greater overall mortality than strains in which rabbits either died or recovered very quickly. Disease effect also depended on time of year. We also elaborated a larger scale model representing 25 km2 and 100,000+ rabbits, split into a number of grid-squares. This was a more traditional model that did not represent individual rabbits, but employed a system of dynamic equations for each grid-square. Disease spread depended on probability of transmission between neighboring grid-squares. Potential recovery from a major population crash caused by the disease relied on disease virulence and frequency of recurrence. The model's dependence on probability of disease transmission between grid-squares suggests the way that the model represents the spatial distribution of the population affects simulation. Although data on RVHD in Europe are lacking, our models provide a basis for describing the disease in realistic detail and for assessing influence of various social and spatial factors on spread.

High Strain Rate Tensile Testing of Silver Nanowires: Rate-Dependent Brittle-to-Ductile Transition.

PubMed

Ramachandramoorthy, Rajaprakash; Gao, Wei; Bernal, Rodrigo; Espinosa, Horacio

2016-01-13

The characterization of nanomaterials under high strain rates is critical to understand their suitability for dynamic applications such as nanoresonators and nanoswitches. It is also of great theoretical importance to explore nanomechanics with dynamic and rate effects. Here, we report in situ scanning electron microscope (SEM) tensile testing of bicrystalline silver nanowires at strain rates up to 2/s, which is 2 orders of magnitude higher than previously reported in the literature. The experiments are enabled by a microelectromechanical system (MEMS) with fast response time. It was identified that the nanowire plastic deformation has a small activation volume (<10b(3)), suggesting dislocation nucleation as the rate controlling mechanism. Also, a remarkable brittle-to-ductile failure mode transition was observed at a threshold strain rate of 0.2/s. Transmission electron microscopy (TEM) revealed that along the nanowire, dislocation density and spatial distribution of plastic regions increase with increasing strain rate. Furthermore, molecular dynamic (MD) simulations show that deformation mechanisms such as grain boundary migration and dislocation interactions are responsible for such ductility. Finally, the MD and experimental results were interpreted using dislocation nucleation theory. The predicted yield stress values are in agreement with the experimental results for strain rates above 0.2/s when ductility is pronounced. At low strain rates, random imperfections on the nanowire surface trigger localized plasticity, leading to a brittle-like failure.

Spin-flip transitions in self-assembled quantum dots

NASA Astrophysics Data System (ADS)

Stavrou, V. N.

2017-12-01

Detailed realistic calculations of the spin-flip time (T 1) for an electron in a self-assembled quantum dot (SAQD) due to emission of an acoustic phonon, using only bulk properties with no fitting parameters, are presented. Ellipsoidal lens shaped Inx Ga1-x As quantum dots, with electronic states calculated using 8-band strain dependent {k \\cdot p} theory, are considered. The phonons are treated as bulk acoustic phonons coupled to the electron by both deformation potential and piezoelectric interactions. The dependence of T 1 on the geometry of SAQD, on the applied external magnetic field and on the lattice temperature is highlighted. The theoretical results are close to the experimental measurements on the spin-flip times for a single electron in QD.

Shoulder pain and time dependent structure in wheelchair propulsion variability.

PubMed

Jayaraman, Chandrasekaran; Moon, Yaejin; Sosnoff, Jacob J

2016-07-01

Manual wheelchair propulsion places considerable repetitive mechanical strain on the upper limbs leading to shoulder injury and pain. While recent research indicates that the amount of variability in wheelchair propulsion and shoulder pain may be related. There has been minimal inquiry into the fluctuation over time (i.e. time-dependent structure) in wheelchair propulsion variability. Consequently the purpose of this investigation was to examine if the time-dependent structure in the wheelchair propulsion parameters are related to shoulder pain. 27 experienced wheelchair users manually propelled their own wheelchair fitted with a SMARTWheel on a roller at 1.1m/s for 3min. Time-dependent structure of cycle-to-cycle fluctuations in contact angle and inter push time interval was quantified using sample entropy (SampEn) and compared between the groups with/without shoulder pain using non-parametric statistics. Overall findings were, (1) variability observed in contact angle fluctuations during manual wheelchair propulsion is structured (Z=3.15;p<0.05), (2) individuals with shoulder pain exhibited higher SampEn magnitude for contact angle during wheelchair propulsion than those without pain (χ(2)(1)=6.12;p<0.05); and (3) SampEn of contact angle correlated significantly with self-reported shoulder pain (rs (WUSPI) =0.41;rs (VAS)=0.56;p<0.05). It was concluded that the time-dependent structure in wheelchair propulsion may provide novel information for tracking and monitoring shoulder pain. Copyright © 2016 IPEM. Published by Elsevier Ltd. All rights reserved.

Strain-Rate Dependence of Deformation-Twinning in Tantalum

NASA Astrophysics Data System (ADS)

Abeywardhana, Jayalath; Germann, Tim; Ravelo, Ramon

2017-06-01

Large-Scale molecular dynamics (MD) simulations are used to model quasi-isentropic compression and expansion (QIC) in tantalum crystals varying the rate of deformation between the range 108 -1012s-1 and compressive pressures up to 100 GPa. The atomic interactions were modeled employing an embedded-atom method (EAM) potential of Ta. Isentropic expansion was done employing samples initially compressed to pressures of 60 and 100 GPa followed by uniaxial and quasi-isentropically expansion to zero pressure. The effect of initial dislocation density on twinning was also examined by varying the initial defect density of the Ta samples (1010 -1012cm-2). At these high-strain rates, a threshold in strain-rate on deformation twining is observed. Under expansion or compression, deformation twinning increases with strain rate for strain-rates >109s-1 . Below this value, small fraction of twins nucleates but anneal out with time. Samples with lower fraction of twins equilibrate to defect states containing higher screw dislocation densities from those with initially higher twinning fractions. This work was supported by the Department of Energy under contract DE-AC52-06NA25396 and by the Air Force Office of Scientific Research under AFOSR Award No. FA9550-12-1-0476.

Pseudomonas aeruginosa mutants resistant to urea inhibition of growth on acetanilide.

PubMed

Gregoriou, M; Brown, P R; Tata, R

1977-11-01

Pseudomonas aeruginosa AI 3 was able to grow in medium containing acetanilide (N-phenylacetamide) as a carbon source when NH4+ was the nitrogen source but not when urea was the nitrogen source. AIU mutants isolated from strain AI 3 grew on either medium. Urease levels in bacteria grown in the presence of urea were 10-fold lower when NH4+ or acetanilide was also in the medium, but there were no apparent differences in urease or its synthesis between strain AI 3 and mutant AIU 1N. The first metabolic step in the acetanilide utlization is catalyzed by an amidase. Amidases in several AIU strains showed altered physiochemical properties. Urea inhibited amidase in a time-dependent reaction, but the rates of the inhibitory reaction with amidases from the AIU mutants were slower than with AI 3 amidase. The purified amidase from AIU 1N showed a marked difference in its pH/activity profile from that obtained with purified AI 3 amidase. These observations indicate that the ability of strain AIU 1N and the other mutants to grow on acetanilide/urea medium is associated with a mutation in the amidase structural gene; this was confirmed for strain AIU 1N by transduction.

Constant strain rate and peri-implant bone modeling: an in vivo longitudinal micro-CT analysis.

PubMed

De Smet, Els; Jaecques, Siegfried V N; Wevers, Martine; Sloten, Jos Vander; Naert, Ignace E

2013-06-01

Strain, frequency, loading time, and strain rate, among others, determine mechanical parameters in osteogenic loading. We showed a significant osteogenic effect on bone mass (BM) by daily peri-implant loading at 1.600µε.s(-1) after 4 weeks. To study the peri-implant osteogenic effect of frequency and strain in the guinea pig tibia by in vivo longitudinal micro-computed tomography (CT) analysis. One week after implant installation in both hind limb tibiae, one implant was loaded daily for 10' during 4 weeks, while the other served as control. Frequencies (3, 10, and 30Hz) and strains varied alike in the three series to keep the strain rate constant at 1.600µε.s(-1) . In vivo micro-CT scans were taken of both tibiae: 1 week after implantation but before loading (v1) and after 2 (v2) and 4 weeks (v3) of loading as well as postmortem (pm). BM (BM (%) bone-occupied area fraction) was calculated as well as the difference between test and control sides (delta BM) RESULTS: All implants (n=78) were clinically stable at 4 weeks. Significant increase in BM was measured between v1 and v2 (p<.0001) and between v1 and v3 (p<.0001). A significant positive effect of loading on delta BM was observed in the distal peri-implant marrow 500 Region of Interest already 2 weeks after loading (p=.01) and was significantly larger (11%) in series 1 compared with series 2 (p=.006) and 3 (p=.016). Within the constraints of constant loading time and strain rate, the effect of early implant loading on the peri-implant bone is strongly dependent on strain and frequency. This cortical bone model has shown to be most sensitive for high force loading at low frequency. © 2011 Wiley Periodicals, Inc.

Mucor hiemalis mediated 14α-hydroxylation on steroids: in vivo and in vitro investigations of 14α-hydroxylase activity.

PubMed

Kolet, Swati P; Haldar, Saikat; Niloferjahan, Siddiqui; Thulasiram, Hirekodathakallu V

2014-07-01

Transformation of testosterone and progesterone into synthetically challenging 14α-hydroxy derivatives was achieved by using fungal strain Mucor hiemalis. Prolonged incubation led to the formation of corresponding 6β/7α,14α-dihydroxy metabolites. The position and stereochemistry of newly introduced hydroxyl group was determined by detailed spectroscopic analyses. The time course experiment indicated that fungal strain initiated transformation by hydroxylation at 14α-position followed by at 6β- or 7α-positions. Studies using cell-free extracts suggest that the 14α-hydroxylase activity is NADPH dependent and belongs to the cytochrome P450 family. Copyright © 2014 Elsevier Inc. All rights reserved.

The Influence of Temperature on Time-Dependent Deformation and Failure in Granite: A Mesoscale Modeling Approach

NASA Astrophysics Data System (ADS)

Xu, T.; Zhou, G. L.; Heap, Michael J.; Zhu, W. C.; Chen, C. F.; Baud, Patrick

2017-09-01

An understanding of the influence of temperature on brittle creep in granite is important for the management and optimization of granitic nuclear waste repositories and geothermal resources. We propose here a two-dimensional, thermo-mechanical numerical model that describes the time-dependent brittle deformation (brittle creep) of low-porosity granite under different constant temperatures and confining pressures. The mesoscale model accounts for material heterogeneity through a stochastic local failure stress field, and local material degradation using an exponential material softening law. Importantly, the model introduces the concept of a mesoscopic renormalization to capture the co-operative interaction between microcracks in the transition from distributed to localized damage. The mesoscale physico-mechanical parameters for the model were first determined using a trial-and-error method (until the modeled output accurately captured mechanical data from constant strain rate experiments on low-porosity granite at three different confining pressures). The thermo-physical parameters required for the model, such as specific heat capacity, coefficient of linear thermal expansion, and thermal conductivity, were then determined from brittle creep experiments performed on the same low-porosity granite at temperatures of 23, 50, and 90 °C. The good agreement between the modeled output and the experimental data, using a unique set of thermo-physico-mechanical parameters, lends confidence to our numerical approach. Using these parameters, we then explore the influence of temperature, differential stress, confining pressure, and sample homogeneity on brittle creep in low-porosity granite. Our simulations show that increases in temperature and differential stress increase the creep strain rate and therefore reduce time-to-failure, while increases in confining pressure and sample homogeneity decrease creep strain rate and increase time-to-failure. We anticipate that the modeling presented herein will assist in the management and optimization of geotechnical engineering projects within granite.

Granular materials flow like complex fluids

NASA Astrophysics Data System (ADS)

Kou, Binquan; Cao, Yixin; Li, Jindong; Xia, Chengjie; Li, Zhifeng; Dong, Haipeng; Zhang, Ang; Zhang, Jie; Kob, Walter; Wang, Yujie

2017-11-01

Granular materials such as sand, powders and foams are ubiquitous in daily life and in industrial and geotechnical applications. These disordered systems form stable structures when unperturbed, but in the presence of external influences such as tapping or shear they `relax', becoming fluid in nature. It is often assumed that the relaxation dynamics of granular systems is similar to that of thermal glass-forming systems. However, so far it has not been possible to determine experimentally the dynamic properties of three-dimensional granular systems at the particle level. This lack of experimental data, combined with the fact that the motion of granular particles involves friction (whereas the motion of particles in thermal glass-forming systems does not), means that an accurate description of the relaxation dynamics of granular materials is lacking. Here we use X-ray tomography to determine the microscale relaxation dynamics of hard granular ellipsoids subject to an oscillatory shear. We find that the distribution of the displacements of the ellipsoids is well described by a Gumbel law (which is similar to a Gaussian distribution for small displacements but has a heavier tail for larger displacements), with a shape parameter that is independent of the amplitude of the shear strain and of the time. Despite this universality, the mean squared displacement of an individual ellipsoid follows a power law as a function of time, with an exponent that does depend on the strain amplitude and time. We argue that these results are related to microscale relaxation mechanisms that involve friction and memory effects (whereby the motion of an ellipsoid at a given point in time depends on its previous motion). Our observations demonstrate that, at the particle level, the dynamic behaviour of granular systems is qualitatively different from that of thermal glass-forming systems, and is instead more similar to that of complex fluids. We conclude that granular materials can relax even when the driving strain is weak.

Comparison of Real-Time PCR and Conventional Biochemical Methods for Identification of Staphylococcus lugdunensis▿

PubMed Central

Pinsky, Benjamin A.; Samson, Divinia; Ghafghaichi, Laleh; Baron, Ellen J.; Banaei, Niaz

2009-01-01

Staphylococcus lugdunensis is an aggressive, virulent member of the coagulase-negative staphylococci (CoNS) that is responsible for severe, rapidly progressive skin and soft tissue infections and native valve endocarditis. To facilitate prompt identification and appropriate therapy, we describe here a rapid and robust multiplex real-time PCR assay that is able to definitively distinguish S. lugdunensis from other staphylococci. Using melting curve analysis, the assay also identifies Staphylococcus aureus and CoNS other than S. lugdunensis and determines MecA-dependent resistance to methicillin (meticillin). When applied to a panel of well-characterized staphylococcal reference strains, as well as 165 clinical isolates previously identified by conventional methods, the assay was both sensitive and specific for S. lugdunensis, correctly identifying the reference strain and all 47 S. lugdunensis isolates without inappropriate amplification of other staphylococci. Furthermore, rapid biochemical identification using the WEE-TAB system to detect ornithine decarboxylase activity was found to be unsuitable as an alternative to PCR identification, displaying just 31% sensitivity and 77% specificity when tested on a subset (90 isolates) of the clinical strains. We therefore propose that this simple, accurate PCR approach will allow for the routine and timely identification of S. lugdunensis in the clinical microbiology laboratory. PMID:19741081

Nisin depletes ATP and proton motive force in mycobacteria.

PubMed

Chung, H J; Montville, T J; Chikindas, M L

2000-12-01

This study examined the inhibitory effect of nisin and its mode of action against Mycobacterium smegmatis, a non-pathogenic species of mycobacteria, and M. bovis-Bacill Carmette Guerin (BCG), a vaccine strain of pathogenic M. bovis. In agar diffusion assays, 2.5 mg ml(-1) nisin was required to inhibit M. bovis-BCG. Nisin caused a slow, gradual, time- and concentration-dependent decrease in internal ATP levels in M. bovis-BCG, but no ATP efflux was detected. In mycobacteria, nisin decreased both components of proton motive force (membrane potential, Delta Psi and Delta pH) in a time- and concentration-dependent manner. However, mycobacteria maintained their intracellular ATP levels during the initial time period of Delta Psi and Delta pH dissipation. These data suggest that the mechanism of nisin in mycobacteria is similar to that in food-borne pathogens.

An autonomous dynamical system captures all LCSs in three-dimensional unsteady flows.

PubMed

Oettinger, David; Haller, George

2016-10-01

Lagrangian coherent structures (LCSs) are material surfaces that shape the finite-time tracer patterns in flows with arbitrary time dependence. Depending on their deformation properties, elliptic and hyperbolic LCSs have been identified from different variational principles, solving different equations. Here we observe that, in three dimensions, initial positions of all variational LCSs are invariant manifolds of the same autonomous dynamical system, generated by the intermediate eigenvector field, ξ 2 (x 0 ), of the Cauchy-Green strain tensor. This ξ 2 -system allows for the detection of LCSs in any unsteady flow by classical methods, such as Poincaré maps, developed for autonomous dynamical systems. As examples, we consider both steady and time-aperiodic flows, and use their dual ξ 2 -system to uncover both hyperbolic and elliptic LCSs from a single computation.

Control of Clostridium difficile Physiopathology in Response to Cysteine Availability

PubMed Central

Dubois, Thomas; Dancer-Thibonnier, Marie; Monot, Marc; Hamiot, Audrey; Bouillaut, Laurent; Soutourina, Olga; Martin-Verstraete, Isabelle

2016-01-01

The pathogenicity of Clostridium difficile is linked to its ability to produce two toxins: TcdA and TcdB. The level of toxin synthesis is influenced by environmental signals, such as phosphotransferase system (PTS) sugars, biotin, and amino acids, especially cysteine. To understand the molecular mechanisms of cysteine-dependent repression of toxin production, we reconstructed the sulfur metabolism pathways of C. difficile strain 630 in silico and validated some of them by testing C. difficile growth in the presence of various sulfur sources. High levels of sulfide and pyruvate were produced in the presence of 10 mM cysteine, indicating that cysteine is actively catabolized by cysteine desulfhydrases. Using a transcriptomic approach, we analyzed cysteine-dependent control of gene expression and showed that cysteine modulates the expression of genes involved in cysteine metabolism, amino acid biosynthesis, fermentation, energy metabolism, iron acquisition, and the stress response. Additionally, a sigma factor (SigL) and global regulators (CcpA, CodY, and Fur) were tested to elucidate their roles in the cysteine-dependent regulation of toxin production. Among these regulators, only sigL inactivation resulted in the derepression of toxin gene expression in the presence of cysteine. Interestingly, the sigL mutant produced less pyruvate and H2S than the wild-type strain. Unlike cysteine, the addition of 10 mM pyruvate to the medium for a short time during the growth of the wild-type and sigL mutant strains reduced expression of the toxin genes, indicating that cysteine-dependent repression of toxin production is mainly due to the accumulation of cysteine by-products during growth. Finally, we showed that the effect of pyruvate on toxin gene expression is mediated at least in part by the two-component system CD2602-CD2601. PMID:27297391

STRAIN-DEPENDENT SUSCEPTIBILITY TO TRANSPLACENTALLY-INDUCED MURINE LUNG TUMORS

EPA Science Inventory

STRAIN-DEPENDENT SUSCEPTIBILITY TO TRANSPLACENTALLY-INDUCED MURINE LUNG TUMORS
M S Miller, J E Moore, M Xu, G B Nelson, S T Dance, N D Kock, J A Ross Wake Forest University, Winston-Salem, NC and USEPA, Research Triangle Park, NC

Previously, our laboratory demonstrated...

Non-linear properties of metallic cellular materials with a negative Poisson's ratio

NASA Technical Reports Server (NTRS)

Choi, J. B.; Lakes, R. S.

1992-01-01

Negative Poisson's ratio copper foam was prepared and characterized experimentally. The transformation into re-entrant foam was accomplished by applying sequential permanent compressions above the yield point to achieve a triaxial compression. The Poisson's ratio of the re-entrant foam depended on strain and attained a relative minimum at strains near zero. Poisson's ratio as small as -0.8 was achieved. The strain dependence of properties occurred over a narrower range of strain than in the polymer foams studied earlier. Annealing of the foam resulted in a slightly greater magnitude of negative Poisson's ratio and greater toughness at the expense of a decrease in the Young's modulus.

Strain Dependent Electronic Structure and Band Offset Tuning at Heterointerfaces of ASnO3 (A=Ca, Sr, and Ba) and SrTiO3

PubMed Central

Baniecki, John D.; Yamazaki, Takashi; Ricinschi, Dan; Van Overmeere, Quentin; Aso, Hiroyuki; Miyata, Yusuke; Yamada, Hiroaki; Fujimura, Norifumi; Maran, Ronald; Anazawa, Toshihisa; Valanoor, Nagarajan; Imanaka, Yoshihiko

2017-01-01

The valence band (VB) electronic structure and VB alignments at heterointerfaces of strained epitaxial stannate ASnO3 (A=Ca, Sr, and Ba) thin films are characterized using in situ X-ray and ultraviolet photoelectron spectroscopies, with band gaps evaluated using spectroscopic ellipsometry. Scanning transmission electron microscopy with geometric phase analysis is used to resolve strain at atomic resolution. The VB electronic structure is strain state dependent in a manner that correlated with a directional change in Sn-O bond lengths with strain. However, VB offsets are found not to vary significantly with strain, which resulted in ascribing most of the difference in band alignment, due to a change in the band gaps with strain, to the conduction band edge. Our results reveal significant strain tuning of conduction band offsets using epitaxial buffer layers, with strain-induced offset differences as large as 0.6 eV possible for SrSnO3. Such large conduction band offset tunability through elastic strain control may provide a pathway to minimize the loss of charge confinement in 2-dimensional electron gases and enhance the performance of photoelectrochemical stannate-based devices. PMID:28195149

Controllable spin-charge transport in strained graphene nanoribbon devices

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

Diniz, Ginetom S., E-mail: ginetom@gmail.com; Guassi, Marcos R.; Qu, Fanyao

2014-09-21

We theoretically investigate the spin-charge transport in two-terminal device of graphene nanoribbons in the presence of a uniform uniaxial strain, spin-orbit coupling, exchange field, and smooth staggered potential. We show that the direction of applied strain can efficiently tune strain-strength induced oscillation of band-gap of armchair graphene nanoribbon (AGNR). It is also found that electronic conductance in both AGNR and zigzag graphene nanoribbon (ZGNR) oscillates with Rashba spin-orbit coupling akin to the Datta-Das field effect transistor. Two distinct strain response regimes of electronic conductance as function of spin-orbit couplings magnitude are found. In the regime of small strain, conductance ofmore » ZGNR presents stronger strain dependence along the longitudinal direction of strain. Whereas for high values of strain shows larger effect for the transversal direction. Furthermore, the local density of states shows that depending on the smoothness of the staggered potential, the edge states of AGNR can either emerge or be suppressed. These emerging states can be determined experimentally by either spatially scanning tunneling microscope or by scanning tunneling spectroscopy. Our findings open up new paradigms of manipulation and control of strained graphene based nanostructure for application on novel topological quantum devices.« less

Control of biaxial strain in single-layer molybdenite using local thermal expansion of the substrate

NASA Astrophysics Data System (ADS)

Plechinger, Gerd; Castellanos-Gomez, Andres; Buscema, Michele; van der Zant, Herre S. J.; Steele, Gary A.; Kuc, Agnieszka; Heine, Thomas; Schüller, Christian; Korn, Tobias

2015-03-01

Single-layer MoS2 is a direct-gap semiconductor whose electronic band structure strongly depends on the strain applied to its crystal lattice. While uniaxial strain can be easily applied in a controlled way, e.g., by bending of a flexible substrate with the atomically thin MoS2 layer on top, experimental realization of biaxial strain is more challenging. Here, we exploit the large mismatch between the thermal expansion coefficients of MoS2 and a silicone-based substrate to apply a controllable biaxial tensile strain by heating the substrate with a focused laser. The effect of this biaxial strain is directly observable in optical spectroscopy as a redshift of the MoS2 photoluminescence. We also demonstrate the potential of this method to engineer more complex strain patterns by employing highly absorptive features on the substrate to achieve non-uniform heat profiles. By comparison of the observed redshift to strain-dependent band structure calculations, we estimate the biaxial strain applied by the silicone-based substrate to be up to 0.2%, corresponding to a band gap modulation of 105 meV per percentage of biaxial tensile strain.

Dynamic Fumonisin B₂ Production by Aspergillus niger Intented Used in Food Industry in China.

PubMed

Han, Xiaomin; Jiang, Hongru; Xu, Jin; Zhang, Jing; Li, Fengqin

2017-07-09

There are a total of 30 strains including 27 strains of Aspergillus niger intended used in Chinese food industry, two strains used as control and one strain isolated from corn for fumonisin (FB) production on 3 media. It was found that FB₂ production by A. niger was function-dependent and highly related to culture media, as well as incubation time. All strains studied were unable to produce FB₁ and FB₃. Almost all strains were found to produce FB₂ on corn, rice and wheat bran. Based on their intended use in the food industry, the higher level of FB₂ producers were strains used for saccharifying enzyme ( n = 13) production, followed by organic acid ( n = 6), tannase ( n = 7) and β-galactosidase ( n = 1) production, with the FB₂ mean level of 3553-10,270 μg/kg, 1059-12,036 μg/kg, 3-7 μg/kg and 2-4 μg/kg on corn, 5455-9241 μg/kg, 559-2190 μg/kg, 4-9 μg/kg and 6-10 μg/kg on rice, 5959-7709 μg/kg, 9491-17,339 μg/kg, 8-14 μg/kg and 120-222 μg/kg on wheat bran, respectively. Comparatively, strains of Fusarium verticillioide were capable of producing fumonins simultaneously with broader spectrum including FB₁, FB₂ and FB₃, but at a much lower level. In conclusion, it is necessary to evaluate FB₂ production by A. niger before intended use in the food processing industry.

Viscous Creep in Dry Unconsolidated Gulf of Mexico Shale

NASA Astrophysics Data System (ADS)

Chang, C.; Zoback, M. D.

2002-12-01

We conducted laboratory experiments to investigate creep characteristics of dry unconsolidated shale recovered from the pathfinder well, Gulf of Mexico (GOM). We subjected jacketed cylindrical specimens (25.4 mm diameter) to hydrostatic pressure that increased from 10 to 50 MPa in steps of 5 MPa. We kept the pressure constant in each step for at least 6 hours and measured axial and lateral strains (provided by LVDTs) and ultrasonic velocities (provided by seismic-wave transducers). The dry shale exhibited pronounced creep strain at all pressure levels, indicating that the dry frame of the shale possesses an intrinsic viscous property. Interestingly, the creep behavior of the shale is different above and below 30 MPa confining pressure. Above 30 MPa, the amount of creep strain in 6 hours is nearly constant with equal pressurization steps, indicating a linear viscous rheology. Below 30 MPa, the amount of creep increases linearly as pressure is raised in constant incremental steps, suggesting that the creep deformation accelerates as pressure increases within this pressure range. Thus, the general creep behavior of the GOM shale is characterized by a bilinear dependence on pressure magnitude. This creep characteristic is quite different from that observed in unconsolidated reservoir sands (Hagin and Zoback, 2002), which exhibited nearly constant amount of creep regardless of the pressure magnitude for equal increasing steps of pressure. The shale exhibits a lack of creep (and nearly negligible strain recovery) when unloaded, suggesting that the creep strain is irrecoverable and can be considered viscoplastic deformation. SEM observations show that the major mechanism of compaction of the dry shale appears to be packing of clay and a progressive collapse of pore (void) spaces. Creep compaction is considerably more significant than compaction that occurs instantaneously, indicating that the process of shale compaction is largely time-dependent.

Epigenetics regulates transcription and pathogenesis in the parasite Trichomonas vaginalis.

PubMed

Pachano, Tomas; Nievas, Yesica R; Lizarraga, Ayelen; Johnson, Patricia J; Strobl-Mazzulla, Pablo H; de Miguel, Natalia

2017-06-01

Trichomonas vaginalis is a common sexually transmitted parasite that colonizes the human urogenital tract. Infections range from asymptomatic to highly inflammatory, depending on the host and the parasite strain. Different T. vaginalis strains vary greatly in their adherence and cytolytic capacities. These phenotypic differences might be attributed to differentially expressed genes as a consequence of extra-genetic variation, such as epigenetic modifications. In this study, we explored the role of histone acetylation in regulating gene transcription and pathogenesis in T. vaginalis. Here, we show that histone 3 lysine acetylation (H3KAc) is enriched in nucleosomes positioned around the transcription start site of active genes (BAP1 and BAP2) in a highly adherent parasite strain; compared with the low acetylation abundance in contrast to that observed in a less-adherent strain that expresses these genes at low levels. Additionally, exposition of less-adherent strain with a specific histone deacetylases inhibitor, trichostatin A, upregulated the transcription of BAP1 and BAP2 genes in concomitance with an increase in H3KAc abundance and chromatin accessibility around their transcription start sites. Moreover, we demonstrated that the binding of initiator binding protein, the transcription factor responsible for the initiation of transcription of ~75% of known T. vaginalis genes, depends on the histone acetylation state around the metazoan-like initiator to which initiator binding protein binds. Finally, we found that trichostatin A treatment increased parasite aggregation and adherence to host cells. Our data demonstrated for the first time that H3KAc is a permissive histone modification that functions to mediate both transcription and pathogenesis of the parasite T. vaginalis. © 2017 John Wiley & Sons Ltd.

Forming limit curves of DP600 determined in high-speed Nakajima tests and predicted by two different strain-rate-sensitive models

NASA Astrophysics Data System (ADS)

Weiß-Borkowski, Nathalie; Lian, Junhe; Camberg, Alan; Tröster, Thomas; Münstermann, Sebastian; Bleck, Wolfgang; Gese, Helmut; Richter, Helmut

2018-05-01

Determination of forming limit curves (FLC) to describe the multi-axial forming behaviour is possible via either experimental measurements or theoretical calculations. In case of theoretical determination, different models are available and some of them consider the influence of strain rate in the quasi-static and dynamic strain rate regime. Consideration of the strain rate effect is necessary as many material characteristics such as yield strength and failure strain are affected by loading speed. In addition, the start of instability and necking depends not only on the strain hardening coefficient but also on the strain rate sensitivity parameter. Therefore, the strain rate dependency of materials for both plasticity and the failure behaviour is taken into account in crash simulations for strain rates up to 1000 s-1 and FLC can be used for the description of the material's instability behaviour at multi-axial loading. In this context, due to the strain rate dependency of the material behaviour, an extrapolation of the quasi-static FLC to dynamic loading condition is not reliable. Therefore, experimental high-speed Nakajima tests or theoretical models shall be used to determine the FLC at high strain rates. In this study, two theoretical models for determination of FLC at high strain rates and results of experimental high-speed Nakajima tests for a DP600 are presented. One of the theoretical models is the numerical algorithm CRACH as part of the modular material and failure model MF GenYld+CrachFEM 4.2, which is based on an initial imperfection. Furthermore, the extended modified maximum force criterion considering the strain rate effect is also used to predict the FLC. These two models are calibrated by the quasi-static and dynamic uniaxial tensile tests and bulge tests. The predictions for the quasi-static and dynamic FLC by both models are presented and compared with the experimental results.

Dynamic characteristics of Non Newtonian fluid Squeeze film damper

NASA Astrophysics Data System (ADS)

Palaksha, C. P.; Shivaprakash, S.; Jagadish, H. P.

2016-09-01

The fluids which do not follow linear relationship between rate of strain and shear stress are termed as non-Newtonian fluid. The non-Newtonian fluids are usually categorized as those in which shear stress depends on the rates of shear only, fluids for which relation between shear stress and rate of shear depends on time and the visco inelastic fluids which possess both elastic and viscous properties. It is quite difficult to provide a single constitutive relation that can be used to define a non-Newtonian fluid due to a great diversity found in its physical structure. Non-Newtonian fluids can present a complex rheological behaviour involving shear-thinning, viscoelastic or thixotropic effects. The rheological characterization of complex fluids is an important issue in many areas. The paper analyses the damping and stiffness characteristics of non-Newtonian fluids (waxy crude oil) used in squeeze film dampers using the available literature for viscosity characterization. Damping and stiffness characteristic will be evaluated as a function of shear strain rate, temperature and percentage wax concentration etc.

Mathematics of Ventilator-induced Lung Injury.

PubMed

Rahaman, Ubaidur

2017-08-01

Ventilator-induced lung injury (VILI) results from mechanical disruption of blood-gas barrier and consequent edema and releases of inflammatory mediators. A transpulmonary pressure (P L ) of 17 cmH 2 O increases baby lung volume to its anatomical limit, predisposing to VILI. Viscoelastic property of lung makes pulmonary mechanics time dependent so that stress (P L ) increases with respiratory rate. Alveolar inhomogeneity in acute respiratory distress syndrome acts as a stress riser, multiplying global stress at regional level experienced by baby lung. Limitation of stress (P L ) rather than strain (tidal volume [V T ]) is the safe strategy of mechanical ventilation to prevent VILI. Driving pressure is the noninvasive surrogate of lung strain, but its relations to P L is dependent on the chest wall compliance. Determinants of lung stress (V T , driving pressure, positive end-expiratory pressure, and inspiratory flow) can be quantified in terms of mechanical power, and a safe threshold can be determined, which can be used in decision-making between safe mechanical ventilation and extracorporeal lung support.

A 1D thermomechanical network transition constitutive model coupled with multiple structural relaxation for shape memory polymers

NASA Astrophysics Data System (ADS)

Zeng, Hao; Xie, Zhimin; Gu, Jianping; Sun, Huiyu

2018-03-01

A new thermomechanical network transition constitutive model is proposed in the study to describe the viscoelastic behavior of shape memory polymers (SMPs). Based on the microstructure of semi-crystalline SMPs, a new simplified transformation equation is proposed to describe the transform of transient networks. And the generalized fractional Maxwell model is introduced in the paper to estimate the temperature-dependent storage modulus. In addition, a neo-KAHR theory with multiple discrete relaxation processes is put forward to study the structural relaxation of the nonlinear thermal strain in cooling/heating processes. The evolution equations of the time- and temperature-dependent stress and strain response are developed. In the model, the thermodynamical and mechanical characteristics of SMPs in the typical thermomechanical cycle are described clearly and the irreversible deformation is studied in detail. Finally, the typical thermomechanical cycles are simulated using the present constitutive model, and the simulation results agree well with the experimental results.

Acoustic-radiation stress in solids. I - Theory

NASA Technical Reports Server (NTRS)

Cantrell, J. H., Jr.

1984-01-01

The general case of acoustic-radiation stress associated with quasi-compressional and quasi-shear waves propagating in infinite and semiinfinite lossless solids of arbitrary crystalline symmetry is studied. The Boussinesq radiation stress is defined and found to depend directly on an acoustic nonlinearity parameter which characterizes the radiation-induced static strain, a stress-generalized nonlinearity parameter which characterizes the stress nonlinearity, and the energy density of the propagating wave. Application of the Boltzmann-Ehrenfest principle of adiabatic invariance to a self-constrained system described by the nonlinear equations of motion allows the acoustic-radiation-induced static strain to be identified with a self-constrained variation in the time-averaged product of the internal energy density and displacement gradient. The time-averaged product is scaled by the acoustic nonlinearity parameter and represents the first-order nonlinearity in the virial theorem. Finally, the relationship between the Boussinesq and the Cauchy radiation stress is obtained in a closed three-dimensional form.

Viscoelastic Response of the Titanium Alloy Ti-6-4: Experimental Identification of Time- and Rate-Dependent Reversible and Irreversible Deformation Regions

NASA Technical Reports Server (NTRS)

Lerch, Bradley A.; Arnold, Steven M.

2014-01-01

In support of an effort on damage prognosis, the viscoelastic behavior of Ti-6Al-4V (Ti-6-4) was investigated. This report documents the experimental characterization of this titanium alloy. Various uniaxial tests were conducted to low load levels over the temperature range of 20 to 538 C to define tensile, creep, and relaxation behavior. A range of strain rates (6x10(exp -7) to 0.001/s) were used to document rate effects. All tests were designed to include an unloading portion, followed by a hold time at temperature to allow recovery to occur either at zero stress or strain. The titanium alloy was found to exhibit viscoelastic behavior below the "yield" point and over the entire range of temperatures (although at lower temperatures the magnitude is extremely small). These experimental data will be used for future characterization of a viscoelastic model.

Spatial fluctuations in transient creep deformation

NASA Astrophysics Data System (ADS)

Laurson, Lasse; Rosti, Jari; Koivisto, Juha; Miksic, Amandine; Alava, Mikko J.

2011-07-01

We study the spatial fluctuations of transient creep deformation of materials as a function of time, both by digital image correlation (DIC) measurements of paper samples and by numerical simulations of a crystal plasticity or discrete dislocation dynamics model. This model has a jamming or yielding phase transition, around which power law or Andrade creep is found. During primary creep, the relative strength of the strain rate fluctuations increases with time in both cases—the spatially averaged creep rate obeys the Andrade law epsilont ~ t - 0.7, while the time dependence of the spatial fluctuations of the local creep rates is given by Δepsilont ~ t - 0.5. A similar scaling for the fluctuations is found in the logarithmic creep regime that is typically observed for lower applied stresses. We review briefly some classical theories of Andrade creep from the point of view of such spatial fluctuations. We consider these phenomenological, time-dependent creep laws in terms of a description based on a non-equilibrium phase transition separating evolving and frozen states of the system when the externally applied load is varied. Such an interpretation is discussed further by the data collapse of the local deformations in the spirit of absorbing state/depinning phase transitions, as well as deformation-deformation correlations and the width of the cumulative strain distributions. The results are also compared with the order parameter fluctuations observed close to the depinning transition of the 2d linear interface model or the quenched Edwards-Wilkinson equation.

Time dependent behavior of a graphite/thermoplastic composite and the effects of stress and physical aging

NASA Technical Reports Server (NTRS)

Gates, Thomas S.; Feldman, Mark

1993-01-01

Two complimentary studies were performed to determine the effects of stress and physical aging on the matrix dominated time dependent properties of IM7/8320 composite. The first of these studies, experimental in nature, used isothermal tensile creep/aging test techniques developed for polymers and adapted them for testing of the composite material. From these tests, the time dependent transverse (S22) and shear (S66) compliance's for an orthotropic plate were found from short term creep compliance measurements at constant, sub-T(sub g) temperatures. These compliance terms were shown to be affected by physical aging. Aging time shift factors and shift rates were found to be a function of temperature and applied stress. The second part of the study relied upon isothermal uniaxial tension tests of IM7/8320 to determine the effects of physical aging on the nonlinear material behavior at elevated temperature. An elastic/viscoplastic constitutive model was used to quantify the effects of aging on the rate-independent plastic and rate-dependent viscoplastic response. Sensitivity of the material constants required by the model to aging time were determined for aging times up to 65 hours. Verification of the analytical model indicated that the effects of prior aging on the nonlinear stress/strain/time data of matrix dominated laminates can be predicted.

Large Strain Behaviour of ZEK100 Magnesium Alloy at Various Strain Rates

NASA Astrophysics Data System (ADS)

Lévesque, Julie; Kurukuri, Srihari; Mishra, Raja; Worswick, Michael; Inal, Kaan

A constitutive framework based on a rate-dependent crystal plasticity theory is employed to simulate large strain deformation in hexagonal closed-packed metals that deform by slip and twinning. The model allows the twinned zones and the parent matrix to rotate independently. ZEK100 magnesium alloy sheets which significant texture weakening compared to AZ31 sheets are investigated using the model. There is considerable in-plane anisotropy and tension compression asymmetry in the flow behavior of ZEK100. Simulations of uniaxial tension in different directions at various strain rates and the accompanying texture evolution are performed and they are in very good agreement with experimental measurements. The effect of strain rate on the activation of the various slip systems and twinning show that differences in the strain rate dependence of yield stress and Rvalues in ZEK100 have their origin in the activation of different deformation mechanisms.

Dependence of Actuation Strain of Dielectric Elastomer on Equi-biaxial, Pure Shear and Uniaxial Modes of Pre-stretching

NASA Astrophysics Data System (ADS)

Kumar, Ajeet; Ahmad, Dilshad; Patra, Karali

2018-02-01

A dielectric elastomer is capable of large deformation under three basic modes of deformation: equi-biaxial, pure shear and uniaxial. Pre-stretching of dielectric elastomer improves the actuation strain appreciably. Experimental results shows that pre-stretching using equal biaxial mode can result to higher actuation strain compared to other two modes of stretching, i.e., uniaxial and pure shear. However, analysis of the experimental results shows that the actuation strain is independent of the modes of pre-stretching rather it is dependent upon the thickness stretch. For same thickness stretch at a particular voltage, the actuation strain is almost similar for all pre-stretching modes. Power trend lines are obtained to predict the actuation strain at any thickness stretch for a particular voltage. The present analysis opens the door to easily design the actuators, sensors and energy harvesting devices.

Computational Simulation of the High Strain Rate Tensile Response of Polymer Matrix Composites

NASA Technical Reports Server (NTRS)

Goldberg, Robert K.

2002-01-01

A research program is underway to develop strain rate dependent deformation and failure models for the analysis of polymer matrix composites subject to high strain rate impact loads. Under these types of loading conditions, the material response can be highly strain rate dependent and nonlinear. State variable constitutive equations based on a viscoplasticity approach have been developed to model the deformation of the polymer matrix. The constitutive equations are then combined with a mechanics of materials based micromechanics model which utilizes fiber substructuring to predict the effective mechanical and thermal response of the composite. To verify the analytical model, tensile stress-strain curves are predicted for a representative composite over strain rates ranging from around 1 x 10(exp -5)/sec to approximately 400/sec. The analytical predictions compare favorably to experimentally obtained values both qualitatively and quantitatively. Effective elastic and thermal constants are predicted for another composite, and compared to finite element results.

[History of development of the live poliomyelitis vaccine from Sabin attenuated strains in 1959 and idea of poliomyelitis eradication].

PubMed

Lashkevich, V A

2013-01-01

In 1958 Poliomyelitis Institute in Moscow and Institute of Experimental Medicine in St. Petersburg received from A. Sabin the attenuated strains of poliomyelitis virus. The characteristics of the strains were thoroughly studied by A. A. Smorodintsev and coworkers. They found that the virulence of the strains fluctuated slightly in 10 consecutive passages through the intestine of the non-immune children. A part of the Sabin material was used by A. A. Smorodintsev and M. P. Chumakov in the beginning of 1959 for immunizing approximately 40000 children in Estonia, Lithuania, and Latvia. Epidemic poliomyelitis rate in these republics decreased from approximately 1000 cases yearly before vaccination to less than 20 in the third quarter of 1959. This was a convincing proof of the efficacy and safety of the vaccine from the attenuated Sabin strains. In 1959, according to A. Sabin's recommendation, a technology of live vaccine production was developed at the Poliomyelitis Institute, and several experimental lots of vaccine were prepared. In the second part of 1959, 13.5 million children in USSR were immunized. The epidemic poliomyelitis rate decreased 3-5 times in different regions without paralytic cases, which could be attributed to the vaccination. These results were the final proof of high efficiency and safety of live poliomyelitis vaccine from the attenuated Sabin strains. Based on these results, A. Sabin and M. P. Chumakov suggested in 1960 the idea of poliomyelitis eradication using mass immunization of children with live vaccine. 72 million persons up to 20 years old were vaccinated in USSR in 1960 with a 5 times drop in the paralytic rate. 50-year-long use of live vaccine results in poliomyelitis eradication in almost all countries worldwide. More than 10 million children were rescued from the death and palsy. Poliomyelitis eradication in a few countries where it still exists depends not on medical services but is defined by the attitude of their leaders to fight against poliomyelitis. In some developing countries the vaccination data are falsified, thereby threatening the polio epidemics reappearance and the virus spreading to other countries. Methods must be developed for detection and dealing with extremely rare persistent virus carriers. Because of all these constraints the outcome of poliomyelitis eradication at present is uncertain and vaccination must be continued. The world has become poliovaccine dependent.

Growth-promoting effects of pepsin- and trypsin-treated caseinomacropeptide from bovine milk on probiotics.

PubMed

Robitaille, Gilles; Champagne, Claude P

2014-08-01

Probiotic Lactobacillus and Bifidobacterium species are generally fastidious bacteria and require rich media for propagation. In milk-based media, they grow poorly, and nitrogen supplementation is required to produce high bacterial biomass levels. It has been reported that caseinomacropeptide (CMP), a 7-kDa peptide released from κ-casein during renneting or gastric digestion, exhibits some growth-promoting activity for lactobacilli and bifidobacteria. During the digestive process, peptides derived from CMP are detected in the intestinal lumen The aim of this study was to evaluate the effects of peptic and tryptic digests of CMP on probiotic lactic acid bacteria growth in de Man, Rogosa and Sharpe broth (MRS) and in milk during fermentation at 37 °C under anaerobic conditions. The study showed that pepsin-treated CMP used as supplements at 0.5 g/l can promote the growth of probiotics even in peptone-rich environments such as MRS. The effect was strain-dependent and evident for the strains that grow poorly in MRS, with an improvement of >1.5 times (P<0.05) by addition of pepsin-treated CMP. Trypsin-treated CMP was much less efficient as growth promoter. Moreover, pepsin-treated CMP was effective in promoting the growth in milk of all probiotic lactic acid bacteria tested, with biomass levels being improved significantly, by 1.7 to 2.6 times (P<0.05), depending on the strain. Thus, supplementation of MRS and of milk with pepsin-treated CMP would be advantageous for the production of high biomass levels for Bifidobacteria and Lactobacilli.

FIBER BRAGG GRATING SENSORS FOR LOCALIZED STRAIN MEASUREMENTS AT LOW TEMPERATURE AND IN HIGH MAGNETIC FIELD

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

Ramalingam, Rajinikumar

2010-04-09

Study of magnetostrictive effects in the bulk superconductors is very essential and can give more knowledge about the effects like namely, flux pinning induced strain, pincushion distortions in the magnets and so on. Currently used electro mechanical sensors are magnetic field dependent and can only give the global stress/strain information but not the local stress/strains. But the information like radius position dependent strain and characterisation of shape distortion in non cylindrical magnets are interesting. Wavelength encoded multiplexed fiber Bragg Grating sensors inscribed in one fiber gives the possibility to measure magentostrictive effects spatially resolved in low temperature and high magneticmore » field. This paper specifies the design and technology requirements to adapt FBG sensors for such an application. Also reports the experiments demonstrate the properties of glass FBG at low temperature (4.2 K) and the results of strain measurement at 4.2 K/8 T. The sensor exhibits a linear wavelength change for the strain change.« less

Orientation dependence of phase diagrams and physical properties in epitaxial Ba0.6Sr0.4TiO3 films

NASA Astrophysics Data System (ADS)

Qiu, J. H.; Zhao, T. X.; Chen, Z. H.; Yuan, N. Y.; Ding, J. N.

2018-04-01

Orientation dependence of phase diagrams and physical properties of Ba0.6Sr0.4TiO3 films are investigated by using a phenomenological Landau-Devonshire theory. New ferroelectric phases, such as the tetragonal a1 phase and the orthorhombic a2 c phase in (110) oriented film and the monoclinic MA phase in (111) oriented film, appear in the "misfit strain-temperature" phase diagrams as compared with (001) oriented film. Moreover, the phase diagrams of (110) and (111) oriented films are more complex than that of (001) oriented film due to the nonlinear coupling terms appeared in the thermodynamic potential. The dielectric and piezoelectric properties largely depend on the misfit strain and orientation. (111) oriented film has the better piezoelectric property than (110) oriented film. Furthermore, the compressive misfit strain is prone to induce the larger piezoelectric property than tensile misfit strain.

Revisit to three-dimensional percolation theory: Accurate analysis for highly stretchable conductive composite materials

PubMed Central

Kim, Sangwoo; Choi, Seongdae; Oh, Eunho; Byun, Junghwan; Kim, Hyunjong; Lee, Byeongmoon; Lee, Seunghwan; Hong, Yongtaek

2016-01-01

A percolation theory based on variation of conductive filler fraction has been widely used to explain the behavior of conductive composite materials under both small and large deformation conditions. However, it typically fails in properly analyzing the materials under the large deformation since the assumption may not be valid in such a case. Therefore, we proposed a new three-dimensional percolation theory by considering three key factors: nonlinear elasticity, precisely measured strain-dependent Poisson’s ratio, and strain-dependent percolation threshold. Digital image correlation (DIC) method was used to determine actual Poisson’s ratios at various strain levels, which were used to accurately estimate variation of conductive filler volume fraction under deformation. We also adopted strain-dependent percolation threshold caused by the filler re-location with deformation. When three key factors were considered, electrical performance change was accurately analyzed for composite materials with both isotropic and anisotropic mechanical properties. PMID:27694856

Surface enhanced Raman scattering of monolayer MX2 with metallic nano particles

PubMed Central

Zhang, Duan; Wu, Ye-Cun; Yang, Mei; Liu, Xiao; Coileáin, Cormac Ó; Abid, Mourad; Abid, Mohamed; Wang, Jing-Jing; Shvets, Igor; Xu, Hongjun; Chun, Byong Sun; Liu, Huajun; Wu, Han-Chun

2016-01-01

Monolayer transition metal dichalcogenides MX2 (M = Mo, W; X = S) exhibit remarkable electronic and optical properties, making them candidates for application within flexible nano-optoelectronics. The ability to achieve a high optical signal, while quantitatively monitoring strain in real-time is the key requirement for applications in flexible sensing and photonics devices. Surface-enhanced Raman scattering (SERS) allows us to achieve both simultaneously. However, the SERS depends crucially on the size and shape of the metallic nanoparticles (NPs), which have a large impact on its detection sensitivity. Here, we investigated the SERS of monolayer MX2, with particular attention paid to the effect of the distribution of the metallic NPs. We show that the SERS depends crucially on the distribution of the metallic NPs and also the phonon mode of the MX2. Moreover, strong coupling between MX2 and metallic NPs, through surface plasmon excitation, results in splitting of the and modes and an additional peak becomes apparent. For a WS2-Ag system the intensity of the additional peak increases exponentially with local strain, which opens another interesting window to quantitatively measure the local strain using SERS. Our experimental study may be useful for the application of monolayer MX2 in flexible nano-optoelectronics. PMID:27457808

Anisotropic constitutive model for nickel base single crystal alloys: Development and finite element implementation

NASA Technical Reports Server (NTRS)

Dame, L. T.; Stouffer, D. C.

1986-01-01

A tool for the mechanical analysis of nickel base single crystal superalloys, specifically Rene N4, used in gas turbine engine components is developed. This is achieved by a rate dependent anisotropic constitutive model implemented in a nonlinear three dimensional finite element code. The constitutive model is developed from metallurigical concepts utilizing a crystallographic approach. A non Schmid's law formulation is used to model the tension/compression asymmetry and orientation dependence in octahedral slip. Schmid's law is a good approximation to the inelastic response of the material in cube slip. The constitutive equations model the tensile behavior, creep response, and strain rate sensitivity of these alloys. Methods for deriving the material constants from standard tests are presented. The finite element implementation utilizes an initial strain method and twenty noded isoparametric solid elements. The ability to model piecewise linear load histories is included in the finite element code. The constitutive equations are accurately and economically integrated using a second order Adams-Moulton predictor-corrector method with a dynamic time incrementing procedure. Computed results from the finite element code are compared with experimental data for tensile, creep and cyclic tests at 760 deg C. The strain rate sensitivity and stress relaxation capabilities of the model are evaluated.