Computationally efficient thermal-mechanical modelling of selective laser melting

NASA Astrophysics Data System (ADS)

Yang, Yabin; Ayas, Can

2017-10-01

The Selective laser melting (SLM) is a powder based additive manufacturing (AM) method to produce high density metal parts with complex topology. However, part distortions and accompanying residual stresses deteriorates the mechanical reliability of SLM products. Modelling of the SLM process is anticipated to be instrumental for understanding and predicting the development of residual stress field during the build process. However, SLM process modelling requires determination of the heat transients within the part being built which is coupled to a mechanical boundary value problem to calculate displacement and residual stress fields. Thermal models associated with SLM are typically complex and computationally demanding. In this paper, we present a simple semi-analytical thermal-mechanical model, developed for SLM that represents the effect of laser scanning vectors with line heat sources. The temperature field within the part being build is attained by superposition of temperature field associated with line heat sources in a semi-infinite medium and a complimentary temperature field which accounts for the actual boundary conditions. An analytical solution of a line heat source in a semi-infinite medium is first described followed by the numerical procedure used for finding the complimentary temperature field. This analytical description of the line heat sources is able to capture the steep temperature gradients in the vicinity of the laser spot which is typically tens of micrometers. In turn, semi-analytical thermal model allows for having a relatively coarse discretisation of the complimentary temperature field. The temperature history determined is used to calculate the thermal strain induced on the SLM part. Finally, a mechanical model governed by elastic-plastic constitutive rule having isotropic hardening is used to predict the residual stresses.

On the plumbing system of volcanic complexes: field constraints from the Isle of Skye (UK) and FEM elasto-plastic modelling including gravity and tectonics.

NASA Astrophysics Data System (ADS)

Bistacchi, A.; Pisterna, R.; Romano, V.; Rust, D.; Tibaldi, A.

2009-04-01

The plumbing system that connects a sub-volcanic magma reservoir to the surface has been the object of field characterization and mechanical modelling efforts since the pioneering work by Anderson (1936), who produced a detailed account of the spectacular Cullin Cone-sheet Complex (Isle of Skye, UK) and a geometrical and mechanical model aimed at defining the depth to the magma chamber. Since this work, the definition of the stress state in the half space comprised between the magma reservoir and the surface (modelled either as a flat surface or a surface comprising a volcanic edifice) was considered the key point in reconstructing dike propagation paths from the magma chamber. In fact, this process is generally seen as the propagation in an elastic media of purely tensional joints (mode I or opening mode propagation), which follow trajectories perpendicular to the least compressive principal stress axis. Later works generally used different continuum mechanics methodologies (analytic, BEM, FEM) to solve the problem of a pressure source (the magma chamber, either a point source or a finite volume) in an elastic (in some cases heterogeneous) half space (bounded by a flat topography or topped by a "volcano"). All these models (with a few limited exceptions) disregard the effect of the regional stress field, which is caused by tectonic boundary forces and gravitational body load, and consider only the pressure source represented by the magma chamber (review in Gudmundsson, 2006). However, this is only a (sometimes subordinate) component of the total stress field. Grosfils (2007) first introduced the gravitational load (but not tectonic stresses) in an elastic model solved with FEM in a 2D axisymmetric half-space, showing that "failure to incorporate gravitational loading correctly" affect the calculated stress pattern and many of the predictions that can be drawn from the models. In this contribution we report on modelling results that include: 2D axisymmetric or true 3D geometry; gravitational body load; anisotropic tectonic stresses; different shapes and depths of the magma chamber; different overpressure levels in the magma chamber; different shapes of the topographic surface (e.g. flat, volcano, caldera); linear-elastic or elasto-plastic Drucker-Prager rheology. The latter point, which in our opinion constitutes a fundamental improvement in the model, has proven necessary because in a purely elastic model the stress state would rise at levels that cannot be sustained by geologic materials. Particularly around and above the magma chamber, yielding is expected, influencing the stress field in the remaining modelling domain. The non-linear problem has been solved with the commercial finite element package Comsol Multiphysics, using a parametric solver. At the same time, a field structural analysis of the classical Cuillin Cone-sheet Complex has been performed. This analysis has shown that four distinct families of cone sheets of different age do exist. Among these, the sheets with the higher dip angle range (80-65°) are confirmed as purely tensional joints, but those with a lower dip angle range (60-40°) are quite often (when suitable markers are available) associated with a measurable shear component. Combining these new field observations with mechanical modelling results, we propose a new interpretation for the Cuillin Cone Sheet Complex. The plumbing system was composed by both purely tensional joints and mesoscopic faults with a shear component, produced in response to the regional stress field perturbed by the magma chamber, and later passively re-used as magma emplacement conduits. Under this assumption, the observed geometry of the Cuillin Cone-sheet Complex is consistent with a relatively shallow magma chamber with a flattened laccolite shape. The shape of the palaeotopography, now completely eroded, has also been considered, but is more weakly constrained by modelling results. References: Anderson E.M., 1936. The dynamics of the formation of cone-sheets, ring-dykes and cauldron subsidences. Proc R Soc Edinburgh, 56, 128-157. Grosfils E.B., 2007. Magma reservoir failure on the terrestrial planets: Assessing the importance of gravitational loading in simple elastic models. Journal of Volcanology and Geothermal Research, 166 (2), 47-75. Gudmundsson A. , 2006. How local stresses control magma-chamber ruptures, dyke injections, and eruptions in composite volcanoes. Earth Science Reviews, 79 (1), 1-31.

Traction force and tension fluctuations in growing axons

NASA Astrophysics Data System (ADS)

Urbach, Jeffrey; Polackwich, Jamie; Koch, Daniel; McAllister, Ryan; Geller, Herbert

Actively generated mechanical forces play a central role in axon growth and guidance during nervous system development. We describe the dynamics of traction stresses from growth cones of actively advancing axons from postnatal rat DRG neurons. By tracking the movement of the growth cone and analyzing the traction stresses in a co-moving reference frame, we show that there is a clear and consistent average stress field underlying the complex spatial stresses present at any one time. The average stress field has strong maxima on the sides of the growth cone, directed inward toward the growth cone neck. This pattern represents a Contractile stress contained within the growth cone, and a net force that is balanced by the axon tension. In addition, using high time-resolution measurements, we show that the stress field is composed of fluctuating local stress peaks, with a population of peaks whose lifetime distribution follows an exponential decay, and a small number of very long-lived peaks. We also find that the tension appears to vary randomly over short time scales, roughly consistent with the lifetime of the stress peaks, suggesting that the tension fluctuations originate from stochastic adhesion dynamics.

Progress in turbulence modeling for complex flow fields including effects of compressibility

NASA Technical Reports Server (NTRS)

Wilcox, D. C.; Rubesin, M. W.

1980-01-01

Two second-order-closure turbulence models were devised that are suitable for predicting properties of complex turbulent flow fields in both incompressible and compressible fluids. One model is of the "two-equation" variety in which closure is accomplished by introducing an eddy viscosity which depends on both a turbulent mixing energy and a dissipation rate per unit energy, that is, a specific dissipation rate. The other model is a "Reynolds stress equation" (RSE) formulation in which all components of the Reynolds stress tensor and turbulent heat-flux vector are computed directly and are scaled by the specific dissipation rate. Computations based on these models are compared with measurements for the following flow fields: (a) low speed, high Reynolds number channel flows with plane strain or uniform shear; (b) equilibrium turbulent boundary layers with and without pressure gradients or effects of compressibility; and (c) flow over a convex surface with and without a pressure gradient.

Quantum field theory in spaces with closed time-like curves

NASA Astrophysics Data System (ADS)

Boulware, D. G.

Gott spacetime has closed timelike curves, but no locally anomalous stress-energy. A complete orthonormal set of eigenfunctions of the wave operator is found in the special case of a spacetime in which the total deficit angle is 27(pi). A scalar quantum field theory is constructed using these eigenfunctions. The resultant interacting quantum field theory is not unitary because the field operators can create real, on-shell, particles in the acausal region. These particles propagate for finite proper time accumulating an arbitrary phase before being annihilated at the same spacetime point as that at which they were created. As a result, the effective potential within the acausal region is complex, and probability is not conserved. The stress tensor of the scalar field is evaluated in the neighborhood of the Cauchy horizon; in the case of a sufficiently small Compton wavelength of the field, the stress tensor is regular and cannot prevent the formation of the Cauchy horizon.

Paleostress analysis of the upper-plate rocks of Anafi Island (Cyclades, Greece)

NASA Astrophysics Data System (ADS)

Soukis, Konstantinos; Lozios, Stylianos

2017-04-01

The Attic Cycladic complex (Aegean Sea, Greece) is an area where profound extension, as a result of the Hellenic trench retreat due to slab-rollback, has exhumed mid-crustal rocks to the surface. The remnants of the upper plate are observed in the form of clippen scattered throughout the complex, occupying a very small percentage of the area. Anafi Island, located at the southeastern rim of the Attic-Cycladic complex, represents one of the few areas where a significant part of the upper plate units can be observed and studied. The complex tectonostratigraphy of Anafi Island is characterized by inverted metamorphism and includes a series of medium to high-grade metamorphic rocks that are thrusted onto a non-metamorphosed Paleogene flysch. The uppermost amphibolitic-facies thrust sheets were intruded in the late Cretaceous by intermediate to felsic magmatic rocks. The nappe pile was later destroyed in the late Miocene - Pliocene through successive stages of normal faulting that included both low- and high-angle normal faults. During that stage, supra-detachment syn-extensional sedimentation has taken place thus giving the opportunity to put some age constraints on the fault activity. Paleostress analysis with the separation and stress inversion method TRM revealed two stress tensors that can explain the fault-slip data-set of Anafi Island related to NE-SW and N-S extension, respectively. The older NE-SW trend is related to the late Miocene stress field whereas the N-S is likely related to the present day stress field. These results show that there was a gradual rotation to the trend of least principal stress axis (σ3), that could be associated with regional events such as the escape of Anatolia towards the Aegean and fastest retreat of the Hellenic subduction zone.

Stress fields around two pores in an elastic body: exact quadrature domain solutions.

PubMed

Crowdy, Darren

2015-08-08

Analytical solutions are given for the stress fields, in both compression and far-field shear, in a two-dimensional elastic body containing two interacting non-circular pores. The two complex potentials governing the solutions are found by using a conformal mapping from a pre-image annulus with those potentials expressed in terms of the Schottky-Klein prime function for the annulus. Solutions for a three-parameter family of elastic bodies with two equal symmetric pores are presented and the compressibility of a special family of pore pairs is studied in detail. The methodology extends to two unequal pores. The importance for boundary value problems of plane elasticity of a special class of planar domains known as quadrature domains is also elucidated. This observation provides the route to generalization of the mathematical approach here to finding analytical solutions for the stress fields in bodies containing any finite number of pores.

Present-day stress field of Southeast Asia

NASA Astrophysics Data System (ADS)

Tingay, Mark; Morley, Chris; King, Rosalind; Hillis, Richard; Coblentz, David; Hall, Robert

2010-02-01

It is now well established that ridge push forces provide a major control on the plate-scale stress field in most of the Earth's tectonic plates. However, the Sunda plate that comprises much of Southeast Asia is one of only two plates not bounded by a major spreading centre and thus provides an opportunity to evaluate other forces that control the intraplate stress field. The Cenozoic tectonic evolution of the Sunda plate is usually considered to be controlled by escape tectonics associated with India-Eurasia collision. However, the Sunda plate is bounded by a poorly understood and complex range of convergent and strike-slip zones and little is known about the effect of these other plate boundaries on the intraplate stress field in the region. We compile the first extensive stress dataset for Southeast Asia, containing 275 A-D quality (177 A-C) horizontal stress orientations, consisting of 72 stress indicators from earthquakes (located mostly on the periphery of the plate), 202 stress indicators from breakouts and drilling-induced fractures and one hydraulic fracture test within 14 provinces in the plate interior. This data reveals that a variable stress pattern exists throughout Southeast Asia that is largely inconsistent with the Sunda plate's approximately ESE absolute motion direction. The present-day maximum horizontal stress in Thailand, Vietnam and the Malay Basin is predominately north-south, consistent with the radiating stress patterns arising from the eastern Himalayan syntaxis. However, the present-day maximum horizontal stress is primarily oriented NW-SE in Borneo, a direction that may reflect plate-boundary forces or topographic stresses exerted by the central Borneo highlands. Furthermore, the South and Central Sumatra Basins exhibit a NE-SW maximum horizontal stress direction that is perpendicular to the Indo-Australian subduction front. Hence, the plate-scale stress field in Southeast Asia appears to be controlled by a combination of Himalayan orogeny-related deformation, forces related to subduction (primarily trench suction and collision) and intraplate sources of stress such as topography and basin geometry.

Analysis of Stress-Responsive Gene Expression in Cultivated and Weedy Rice Differing in Cold Stress Tolerance

PubMed Central

Pereira, Andy; Tseng, Te-Ming; Zimmer, Paulo Dejalma; Burgos, Nilda Roma

2015-01-01

Rice (Oryza sativa L.) cultivars show impairment of growth in response to environmental stresses such as cold at the early seedling stage. Locally adapted weedy rice is able to survive under adverse environmental conditions, and can emerge in fields from greater soil depth. Cold-tolerant weedy rice can be a good genetic source for developing cold-tolerant, weed-competitive rice cultivars. An in-depth analysis is presented here of diverse indica and japonica rice genotypes, mostly weedy rice, for cold stress response to provide an understanding of different stress adaptive mechanisms towards improvement of the rice crop performance in the field. We have tested a collection of weedy rice genotypes to: 1) classify the subspecies (ssp.) grouping (japonica or indica) of 21 accessions; 2) evaluate their sensitivity to cold stress; and 3) analyze the expression of stress-responsive genes under cold stress and a combination of cold and depth stress. Seeds were germinated at 25°C at 1.5- and 10-cm sowing depth for 10d. Seedlings were then exposed to cold stress at 10°C for 6, 24 and 96h, and the expression of cold-, anoxia-, and submergence-inducible genes was analyzed. Control plants were seeded at 1.5cm depth and kept at 25°C. The analysis revealed that cold stress signaling in indica genotypes is more complex than that of japonica as it operates via both the CBF-dependent and CBF-independent pathways, implicated through induction of transcription factors including OsNAC2, OsMYB46 and OsF-BOX28. When plants were exposed to cold + sowing depth stress, a complex signaling network was induced that involved cross talk between stresses mediated by CBF-dependent and CBF-independent pathways to circumvent the detrimental effects of stresses. The experiments revealed the importance of the CBF regulon for tolerance to both stresses in japonica and indica ssp. The mechanisms for cold tolerance differed among weedy indica genotypes and also between weedy indica and cultivated japonica ssp. as indicated by the up/downregulation of various stress-responsive pathways identified from gene expression analysis. The cold-stress response is described in relation to the stress signaling pathways, showing complex adaptive mechanisms in different genotypes. PMID:26230579

Relaxor-ferroelectric crossover in (B i1 /2K1 /2)Ti O3 : Origin of the spontaneous phase transition and the effect of an applied external field

NASA Astrophysics Data System (ADS)

Hagiwara, Manabu; Ehara, Yoshitaka; Novak, Nikola; Khansur, Neamul H.; Ayrikyan, Azatuhi; Webber, Kyle G.; Fujihara, Shinobu

2017-07-01

The temperature evolution of polar order in an A -site complex perovskite (B i1 /2K1 /2)Ti O3 (BKT) has been investigated by measurements of dielectric permittivity, depolarization current, and stress-stain curves at elevated temperatures. Upon cooling from high temperatures, BKT first enters a relaxor state and then spontaneously transforms into a ferroelectric state. The analyses of temperature and frequency dependence of permittivity have revealed that polar nanoregions of the relaxor phase appear at temperatures higher than 560°C, and also that their freezing at 296°C triggers the spontaneous relaxor-ferroelectric transition. We discuss the key factors determining the development of long-range polar order in A -site complex perovskites through a comparison with the relaxor (B i1 /2N a1 /2)Ti O3 . We also show that application of biasing electric fields and compressive stresses to BKT favors its ferroelectric phase, resulting in a significant shift of the relaxor-ferroelectric transition temperature towards higher temperatures. Based on the obtained results, electric field-temperature and stress-temperature phase diagrams are firstly determined for BKT.

The interaction of two spheres in a simple-shear flow of complex fluids

NASA Astrophysics Data System (ADS)

Firouznia, Mohammadhossein; Metzger, Bloen; Ovarlez, Guillaume; Hormozi, Sarah

2017-11-01

We study the interaction of two small freely-moving spheres in a linear flow field of Newtonian, shear thinning and yield stress fluids. We perform a series of experiments over a range of shear rates as well as different shear histories using an original apparatus and with the aid of conventional rheometry, Particle Image Velocimetry and Particle Tracking Velocimetry. Showing that the non-Newtonian nature of the suspending fluid strongly affects the shape of particle trajectories and the irreversibility. An important point is that non-Newtonian effects can be varied and unusual. Depending on the shear rate, nonideal shear thinning and yield stress suspending fluids might show elasticity that needs to be taken into account. The flow field around one particle is studied in different fluids when subjected to shear. Then using these results to explain the two particle interactions in a simple-shear flow we show how particle-particle contact and non-Newtonian behaviors result in relative trajectories with fore-aft asymmetry. Well-resolved velocity and stress fields around the particles are presented here. Finally, we discuss how the relative particle trajectories may affect the microstructure of complex suspensions and consequently the bulk rheology. NSF (Grant No. CBET-1554044-CAREER).

The Somma Vesuvius stress field induced by regional tectonics: evidences from seismological and mesostructural data

NASA Astrophysics Data System (ADS)

Bianco, F.; Castellano, M.; Milano, G.; Ventura, G.; Vilardo, G.

1998-06-01

A detailed structural and geophysical study of the Somma-Vesuvius volcanic complex was carried out by integrating mesostructural measurements, focal mechanisms and shear-wave splitting analysis. Fault-slip and focal mechanism analysis indicate that the volcano is affected by NW-SE-, NE-SW-trending oblique-slip faults and by E-W-trending normal faults. Magma chamber(s) responsible for plinian/sub-plinian eruptions (i.e. A.D. 79 and 1631) formed inside the area bounded by E-W-trending normal faults. The post-1631 fissural eruptions (i.e. 1794 and 1861) occurred along the main oblique-slip fault segments. The movements of the Vesuvius faults are mainly related to the regional stress field. A local stress field superposed to the regional one is also present but evidences of magma or gravity induced stresses are lacking. The local stress field acts inside the caldera area being related to fault reactivation processes. The present-day Vesuvius seismic activity is due to both regional and local stress fields. Shear-wave splitting analysis reveals an anisotropic volume due to stress induced cracks NW-SE aligned by faulting processes. Since the depth extent of the anisotropic volume is at least 6 km b.s.l., we deduce the NW-SE-trending oblique-slip fault system represents the main discontinuity on which lies the volcano. This discontinuity is responsible for the morphological lowering of the edifice in its southwestern side.

On the mathematical modeling of the Reynolds stress's equations

NASA Technical Reports Server (NTRS)

Lin, Avi

1990-01-01

By considering the Reynolds stress equations as a possible descriptor of complex turbulent fields, pressure-velocity interaction and turbulence dissipation are studied as two of the main physical contributions to Reynolds stress balancing in turbulent flow fields. It is proven that the pressure interaction term contains turbulence generation elements. However, the usual 'return to isotropy' element appears more weakly than in the standard models. In addition, convection-like elements are discovered mathematically, but there is no mathematical evidence that the pressure fluctuations contribute to the turbulent transport mechanism. Calculations of some simple one-dimensional fields indicate that this extra convection, rather than the turbulent transport, is needed mathematically. Similarly, an expression for the turbulence dissipation is developed. The end result is a dynamic equation for the dissipation tensor which is based on the tensorial length scales.

The Stress-Strain State of Recent Structures in the Northeastern Sector of the Russian Arctic Region

NASA Astrophysics Data System (ADS)

Imaeva, L. P.; Imaev, V. S.; Mel'nikova, V. I.

2018-03-01

Complex research to determine the stress-strain state of the Earth's crust and the types of seismotectonic destruction for the northeastern sector of the Russian Arctic was conducted. The principles of regional ranking of neotectonic structures were developed according to the activity of geodynamic processes, and argumentation for their class differentiation is presented. The structural-tectonic position, the parameters of the deep structure, the system of active faults, and the tectonic stress fields, calculated on the basis of both tectonophysical analysis of discontinuous and folded late Cenozoic deformations and seismological data, were analyzed. This complex of investigations made it possible to determine the directions of the main axes of deformations of the stress-strain state of the Earth's crust and to reveal the regularity in the change of tectonic regimes.

Dynamics of Mount Somma-Vesuvius edifice: from stress field inversion to analogue and numerical modelling

NASA Astrophysics Data System (ADS)

De Matteo, Ada; Massa, Bruno; D'Auria, Luca; Castaldo, Raffaele

2017-04-01

Geological processes are generally very complex and too slow to be directly observed in their completeness; modelling procedures overcome this limit. The state of stress in the upper lithosphere is the main responsible for driving geodynamical processes; in order to retrieve the active stress field in a rock volume, stress inversion techniques can be applied on both seismological and structural datasets. This approach has been successfully applied to active tectonics as well as volcanic areas. In this context the best approach in managing heterogeneous datasets in volcanic environments consists in the analysis of spatial variations of the stress field by applying robust techniques of inversion. The study of volcanic seismicity is an efficient tool to retrieve spatial and temporal pattern of the pre-, syn- and inter-eruptive stress field: magma migration as well as dynamics of magma chamber and hydrothermal system are directly connected to the volcanic seismicity. Additionally, analysis of the temporal variations of stress field pattern in volcanoes could be a useful monitoring tool. Recently the stress field acting on several active volcanoes has been investigated by using stress inversion techniques on seismological datasets (Massa et al., 2016). The Bayesian Right Trihedra Method (BRTM; D'Auria and Massa, 2015) is able to successfully manage heterogeneous datasets allowing the identification of regional fields locally overcame by the stress field due to volcano specific dynamics. In particular, the analysis of seismicity and stress field inversion at the Somma-Vesuvius highlighted the presence of two superposed volumes characterized by different behaviour and stress field pattern: a top volume dominated by an extensional stress field, in accordance with a gravitational spreading-style of deformation, and a bottom volume related to a regional extensional stress field. In addition, in order to evaluate the dynamics of deformation, both analogue and numerical modelling are being performed. Scaled analogue models of the Somma-Vesuvius are being built accordingly with the actual geometrical asymmetry of the volcano, varying just few parameters connected to the uncertainty of the depth and thickness of a buried decoupling layer. Experiments are being monitored by an optical stereo image system, useful to build a 3D time-lapsed models used to retrieve the model deformations. Simultaneously, a time-dependent 3D Finite Element model is being carried out in a fluid-dynamic context by fixing the same parameters of the proposed analogue model. Finally, a comparative analysis is being made between the model deformations and the DInSAR measurements derived from satellite data in order to estimate the uncertain parameters (i.e., thickness and viscosity of ductile layer). Preliminary results of the analogue models fit with the hypothesis of a spreading deformation active at the Somma-Vesuvius.

Variations of stress fields in the Tunka Rift of the southwestern Baikal region

NASA Astrophysics Data System (ADS)

Lunina, O. V.; Gladkov, A. S.; Sherman, S. I.

2007-05-01

The stress fields in the Tunka Rift at the southwestern flank of the Baikal Rift Zone are reconstructed and analyzed on the basis of a detailed study of fracturing. The variation of these fields is of a systematic character and is caused by a complex morphological and fault-block structure of the studied territory. The rift was formed under conditions of oblique (relative to its axis) regional NW-SE extension against the background of three ancient tectonic boundaries (Sayan, Baikal, and Tuva-Mongolian) oriented in different directions. Such a geological history resulted in the development of several en echelon arranged local basins and interbasinal uplifted blocks, the strike-slip component of faulting, and the mosaic distribution of various stress fields with variable orientation of their principal vectors. The opening of basins was promoted by stress fields of a lower hierarchical rank with a near-meridional tension axis. The stress field in the western Tunka Rift near the Mondy and Turan basins is substantially complicated because the transform movements, which are responsible for the opening of the N-S-trending rift basins in Mongolia, become important as Lake Hövsgöl is approached. It is concluded that, for the most part, the Tunka Rift has not undergone multistage variation of its stress state since the Oligocene, the exception being a compression phase in the late Miocene and early Pliocene, which could be related to continental collision of the Eurasian and Indian plates. Later on, the Tunka Rift continued its tectonic evolution in the transtensional regime.

Long Term Analysis of Deformations in Salt Mines: Kłodawa Salt Mine Case Study, Central Poland

NASA Astrophysics Data System (ADS)

Cała, Marek; Tajduś, Antoni; Andrusikiewicz, Wacław; Kowalski, Michał; Kolano, Malwina; Stopkowicz, Agnieszka; Cyran, Katarzyna; Jakóbczyk, Joanna

2017-09-01

Located in central Poland, the Kłodawa salt dome is 26 km long and about 2 km wide. Exploitation of the dome started in 1956, currently rock salt extraction is carried out in 7 mining fields and the 12 mining levels at the depth from 322 to 625 meters below sea level (m.b.s.l.). It is planned to maintain the mining activity till 2052 and extend rock salt extraction to deeper levels. The dome is characterised by complex geological structure resulted from halokinetic and tectonic processes. Projection of the 3D numerical analysis took into account the following factors: mine working distribution within the Kłodawa mine (about 1000 rooms, 350 km of galleries), complex geological structure of the salt dome, complicated structure and geometry of mine workings and distinction in rocks mechanical properties e.g. rock salt and anhydrite. Analysis of past mine workings deformation and prediction of future rock mass behaviour was divided into four stages: building of the 3D model (state of mine workings in year 2014), model extension of the future mine workings planned for extraction in years 2015-2052, the 3D model calibration and stability analysis of all mine workings. The 3D numerical model of Kłodawa salt mine included extracted and planned mine workings in 7 mining fields and 14 mining levels (about 2000 mine workings). The dimensions of the model were 4200 m × 4700 m × 1200 m what was simulated by 33 million elements. The 3D model was calibrated on the grounds of convergence measurements and laboratory tests. Stability assessment of mine workings was based on analysis of the strength/stress ratio and vertical stress. The strength/stress ratio analysis enabled to indicate endangered area in mine workings and can be defined as the factor of safety. Mine workings in state close to collapse are indicated by the strength/stress ratio equals 1. Analysis of the vertical stress in mine workings produced the estimation of current state of stress in comparison to initial (pre-mining) conditions. The long-term deformation analysis of the Kłodawa salt mine for year 2014 revealed that stability conditions were fulfilled. Local disturbances indicated in the numerical analysis were connected with high chambers included in the mining field no 1 and complex geological structure in the vicinity of mine workings located in the mining fields no 2 and 3. Moreover, numerical simulations that projected the future extraction progress (till year 2052) showed positive performance. Local weakness zones in the mining field no 7 are associated with occurrence of carnallite layers and intensive mining which are planned in the mining field no 6 at the end of rock salt extraction.

Three-dimensional stress field around a membrane protein: atomistic and coarse-grained simulation analysis of gramicidin A.

PubMed

Yoo, Jejoong; Cui, Qiang

2013-01-08

Using both atomistic and coarse-grained (CG) models, we compute the three-dimensional stress field around a gramicidin A (gA) dimer in lipid bilayers that feature different degrees of negative hydrophobic mismatch. The general trends in the computed stress field are similar at the atomistic and CG levels, supporting the use of the CG model for analyzing the mechanical features of protein/lipid/water interfaces. The calculations reveal that the stress field near the protein-lipid interface exhibits a layered structure with both significant repulsive and attractive regions, with the magnitude of the stress reaching 1000 bar in certain regions. Analysis of density profiles and stress field distributions helps highlight the Trp residues at the protein/membrane/water interface as mechanical anchors, suggesting that similar analysis is useful for identifying tension sensors in other membrane proteins, especially membrane proteins involved in mechanosensation. This work fosters a connection between microscopic and continuum mechanics models for proteins in complex environments and makes it possible to test the validity of assumptions commonly made in continuum mechanics models for membrane mediated processes. For example, using the calculated stress field, we estimate the free energy of membrane deformation induced by the hydrophobic mismatch, and the results for regions beyond the annular lipids are in general consistent with relevant experimental data and previous theoretical estimates using elasticity theory. On the other hand, the assumptions of homogeneous material properties for the membrane and a bilayer thickness at the protein/lipid interface being independent of lipid type (e.g., tail length) appear to be oversimplified, highlighting the importance of annular lipids of membrane proteins. Finally, the stress field analysis makes it clear that the effect of even rather severe hydrophobic mismatch propagates to only about two to three lipid layers, thus putting a limit on the range of cooperativity between membrane proteins in crowded cellular membranes. Copyright © 2013 Biophysical Society. Published by Elsevier Inc. All rights reserved.

Understanding Water-Stress Responses in Soybean Using Hydroponics System—A Systems Biology Perspective

PubMed Central

Tripathi, Prateek; Rabara, Roel C.; Shulaev, Vladimir; Shen, Qingxi J.; Rushton, Paul J.

2015-01-01

The deleterious changes in environmental conditions such as water stress bring physiological and biochemical changes in plants, which results in crop loss. Thus, combating water stress is important for crop improvement to manage the needs of growing population. Utilization of hydroponics system in growing plants is questionable to some researchers, as it does not represent an actual field condition. However, trying to address a complex problem like water stress we have to utilize a simpler growing condition like the hydroponics system wherein every input given to the plants can be controlled. With the advent of high-throughput technologies, it is still challenging to address all levels of the genetic machinery whether a gene, protein, metabolite, and promoter. Thus, using a system of reduced complexity like hydroponics can certainly direct us toward the right candidates, if not completely help us to resolve the issue. PMID:26734044

Understanding Water-Stress Responses in Soybean Using Hydroponics System-A Systems Biology Perspective.

PubMed

Tripathi, Prateek; Rabara, Roel C; Shulaev, Vladimir; Shen, Qingxi J; Rushton, Paul J

2015-01-01

The deleterious changes in environmental conditions such as water stress bring physiological and biochemical changes in plants, which results in crop loss. Thus, combating water stress is important for crop improvement to manage the needs of growing population. Utilization of hydroponics system in growing plants is questionable to some researchers, as it does not represent an actual field condition. However, trying to address a complex problem like water stress we have to utilize a simpler growing condition like the hydroponics system wherein every input given to the plants can be controlled. With the advent of high-throughput technologies, it is still challenging to address all levels of the genetic machinery whether a gene, protein, metabolite, and promoter. Thus, using a system of reduced complexity like hydroponics can certainly direct us toward the right candidates, if not completely help us to resolve the issue.

New Madrid Seismotectonic Program. Final report

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

Buschbach, T.C.

1986-06-01

The New Madrid Seismotectonic Program was a large-scale multidisciplinary effort that was designed to define the structural setting and tectonic history of the New Madrid area in order to realistically evaluate earthquake risks in the siting of nuclear facilities. The tectonic model proposed to explain the New Madrid seismicity is the ''zone of weakness'' model, which suggests that an ancient rift complex formed a zone of weakness in the earth's crust along which regional stresses are relieved. The Reelfoot Rift portion of the proposed rift complex is currently seismically active, and it must be considered capable and likely to bemore » exposed to large-magnitude earthquakes in the future. Earthquakes that occur in the Wabash Valley area are less abundant and generally have deeper hypocenters than earthquakes in the New Madrid area. The area of the Southern Indiana Arm must be considered to have seismic risk, although a lesser extent than the Reelfoot Rift. The east-west trending Rough Creek Graben is practically aseismic, probably in large part due to its orientation in the current stress field. The northwest-trending St. Louis Arm of the proposed rift complex includes a pattern of seismicity that extends from southern Illinois along the Mississippi River. This arm must be considered to have seismic risk, but because of the lack of development of a graben associated with the arm and the orientation of the arm in the current stress field, the risk appears to be less than in the Reelfoot Rift portion of the rift complex.« less

Igneous sills record far-field and near-field stress interactions during volcano construction: Isle of Mull, Scotland

NASA Astrophysics Data System (ADS)

Stephens, T. L.; Walker, R. J.; Healy, D.; Bubeck, A.; England, R. W.; McCaffrey, K. J. W.

2017-11-01

Sill emplacement is typically associated with horizontally mechanically layered host rocks in a near-hydrostatic far-field stress state, where contrasting mechanical properties across the layers promote transitions from dykes, or inclined sheets, to sills. We used detailed field observations from the Loch Scridain Sill Complex (Isle of Mull, UK), and mechanical models to show that layering is not always the dominant control on sill emplacement. The studied sills have consistently shallow dips (1°-25°) and cut vertically bedded and foliated metamorphic basement rocks, and horizontally bedded cover sedimentary rocks and lavas. Horizontal and shallowly-dipping fractures in the host rock were intruded with vertical opening in all cases, whilst steeply-dipping discontinuities within the sequence (i.e. vertical fractures and foliation in the basement, and vertical polygonal joints in the lavas) were not intruded during sill emplacement. Mechanical models of slip tendency, dilation tendency, and fracture susceptibility for local and overall sill geometry data, support a radial horizontal compression during sill emplacement. Our models show that dykes and sills across Mull were emplaced during NW-SE horizontal shortening, related to a far-field tectonic stress state. The dykes generally accommodated phases of NE-SW horizontal tectonic extension, whereas the sills record the superposition of the far-field stress with a near-field stress state, imposed by emplacement of the Mull Central Volcano. We show that through detailed geometric characterisation coupled with mechanical modelling, sills may be used as an indication of fluctuations in the paleostress state.

SPAR reference manual. [for stress analysis

NASA Technical Reports Server (NTRS)

Whetstone, W. D.

1974-01-01

SPAR is a system of related programs which may be operated either in batch or demand (teletype) mode. Information exchange between programs is automatically accomplished through one or more direct access libraries, known collectively as the data complex. Card input is command-oriented, in free-field form. Capabilities available in the first production release of the system are fully documented, and include linear stress analysis, linear bifurcation buckling analysis, and linear vibrational analysis.

Multi-phase-field method for surface tension induced elasticity

NASA Astrophysics Data System (ADS)

Schiedung, Raphael; Steinbach, Ingo; Varnik, Fathollah

2018-01-01

A method, based on the multi-phase-field framework, is proposed that adequately accounts for the effects of a coupling between surface free energy and elastic deformation in solids. The method is validated via a number of analytically solvable problems. In addition to stress states at mechanical equilibrium in complex geometries, the underlying multi-phase-field framework naturally allows us to account for the influence of surface energy induced stresses on phase transformation kinetics. This issue, which is of fundamental importance on the nanoscale, is demonstrated in the limit of fast diffusion for a solid sphere, which melts due to the well-known Gibbs-Thompson effect. This melting process is slowed down when coupled to surface energy induced elastic deformation.

The neurobiology of social environmental risk for schizophrenia: an evolving research field.

PubMed

Akdeniz, Ceren; Tost, Heike; Meyer-Lindenberg, Andreas

2014-04-01

Schizophrenia is a severe and complex brain disorder that usually manifests in early adulthood and disturbs a wide range of human functions. More than 100 years after its initial description, the pathophysiology of the disorder is still incompletely understood. Many epidemiological studies strongly suggest a complex interaction between genetic and environmental risk factors for the development of the disorder. While there is considerable evidence for a social environmental component of this risk, the links between adverse social factors and altered brain function have just come into focus. In the present review, we first summarize epidemiological evidence for the significance of social environmental risk factors, outline the role of altered social stress processing in mental illness, and review the latest experimental evidence for the neural correlates of social environmental risk for schizophrenia. The studies we have discussed in this review provide a selection of the current work in the field. We suggest that many of the social environmental risk factors may impact on perceived social stress and engage neural circuits in the brain whose functional and structural architecture undergoes detrimental change in response to prolonged exposure. We conclude that multidisciplinary approaches involving various fields and thoroughly constructed longitudinal designs are necessary to capture complex structure of social environmental risks.

Compatible-strain mixed finite element methods for incompressible nonlinear elasticity

NASA Astrophysics Data System (ADS)

Faghih Shojaei, Mostafa; Yavari, Arash

2018-05-01

We introduce a new family of mixed finite elements for incompressible nonlinear elasticity - compatible-strain mixed finite element methods (CSFEMs). Based on a Hu-Washizu-type functional, we write a four-field mixed formulation with the displacement, the displacement gradient, the first Piola-Kirchhoff stress, and a pressure-like field as the four independent unknowns. Using the Hilbert complexes of nonlinear elasticity, which describe the kinematics and the kinetics of motion, we identify the solution spaces of the independent unknown fields. In particular, we define the displacement in H1, the displacement gradient in H (curl), the stress in H (div), and the pressure field in L2. The test spaces of the mixed formulations are chosen to be the same as the corresponding solution spaces. Next, in a conforming setting, we approximate the solution and the test spaces with some piecewise polynomial subspaces of them. Among these approximation spaces are the tensorial analogues of the Nédélec and Raviart-Thomas finite element spaces of vector fields. This approach results in compatible-strain mixed finite element methods that satisfy both the Hadamard compatibility condition and the continuity of traction at the discrete level independently of the refinement level of the mesh. By considering several numerical examples, we demonstrate that CSFEMs have a good performance for bending problems and for bodies with complex geometries. CSFEMs are capable of capturing very large strains and accurately approximating stress and pressure fields. Using CSFEMs, we do not observe any numerical artifacts, e.g., checkerboarding of pressure, hourglass instability, or locking in our numerical examples. Moreover, CSFEMs provide an efficient framework for modeling heterogeneous solids.

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

Bouchard, P.J.

A forthcoming revision to the R6 Leak-before-Break Assessment Procedure is briefly described. Practical application of the LbB concepts to safety-critical nuclear plant is illustrated by examples covering both low temperature and high temperature (>450{degrees}C) operating regimes. The examples highlight a number of issues which can make the development of a satisfactory LbB case problematic: for example, coping with highly loaded components, methodology assumptions and the definition of margins, the effect of crack closure owing to weld residual stresses, complex thermal stress fields or primary bending fields, the treatment of locally high stresses at crack intersections with free surfaces, the choicemore » of local limit load solution when predicting ligament breakthrough, and the scope of calculations required to support even a simplified LbB case for high temperature steam pipe-work systems.« less

Electrorheological suspensions of laponite in oil: rheometry studies.

PubMed

Parmar, K P S; Méheust, Y; Schjelderupsen, Børge; Fossum, J O

2008-03-04

We have studied the effect of an external direct current (DC) electric field ( approximately 1 kV/mm) on the rheological properties of colloidal suspensions consisting of aggregates of laponite particles in a silicone oil. Microscopy observations show that, under application of an electric field greater than a triggering electric field Ec approximately 0.6 kV/mm, laponite aggregates assemble into chain- and/or columnlike structures in the oil. Without an applied electric field, the steady-state shear behavior of such suspensions is Newtonian-like. Under application of an electric field larger than Ec, it changes dramatically as a result of the changes in the microstructure: a significant yield stress is measured, and under continuous shear the fluid is shear-thinning. The rheological properties, in particular the dynamic and static shear stress, were studied as a function of particle volume fraction for various strengths (including null) of the applied electric field. The flow curves at constant shear rate can be scaled with respect to both the particle fraction and electric field strength onto a master curve. This scaling is consistent with simple scaling arguments. The shape of the master curve accounts for the system's complexity; it approaches a standard power-law model at high Mason numbers. Both dynamic and static yield stresses are observed to depend on the particle fraction Phi and electric field E as PhibetaEalpha, with alpha approximately 1.85 and beta approximately 1 and 1.70 for the dynamic and static yield stresses, respectively. The yield stress was also determined as the critical stress at which there occurs a bifurcation in the rheological behavior of suspensions that are submitted to a constant shear stress; a scaling law with alpha approximately 1.84 and beta approximately 1.70 was obtained. The effectiveness of the latter technique confirms that such electrorheological (ER) fluids can be studied in the framework of thixotropic fluids. The method is very reproducible; we suggest that it could be used routinely for studying ER fluids. The measured overall yield stress behavior of the suspensions may be explained in terms of standard conduction models for electrorheological systems. Interesting prospects include using such systems for guided self-assembly of clay nanoparticles.

Damped regional-scale stress inversions: Methodology and examples for southern California and the Coalinga aftershock sequence

USGS Publications Warehouse

Hardebeck, J.L.; Michael, A.J.

2006-01-01

We present a new focal mechanism stress inversion technique to produce regional-scale models of stress orientation containing the minimum complexity necessary to fit the data. Current practice is to divide a region into small subareas and to independently fit a stress tensor to the focal mechanisms of each subarea. This procedure may lead to apparent spatial variability that is actually an artifact of overfitting noisy data or nonuniquely fitting data that does not completely constrain the stress tensor. To remove these artifacts while retaining any stress variations that are strongly required by the data, we devise a damped inversion method to simultaneously invert for stress in all subareas while minimizing the difference in stress between adjacent subareas. This method is conceptually similar to other geophysical inverse techniques that incorporate damping, such as seismic tomography. In checkerboard tests, the damped inversion removes the stress rotation artifacts exhibited by an undamped inversion, while resolving sharper true stress rotations than a simple smoothed model or a moving-window inversion. We show an example of a spatially damped stress field for southern California. The methodology can also be used to study temporal stress changes, and an example for the Coalinga, California, aftershock sequence is shown. We recommend use of the damped inversion technique for any study examining spatial or temporal variations in the stress field.

Magnetomechanical effect in silicon (Cz-Si) surface layers

NASA Astrophysics Data System (ADS)

Koplak, O. V.; Dmitriev, A. I.; Morgunov, R. B.

2012-07-01

The mechanical properties of near-surface layers of Czochralski-grown silicon crystals Cz- n-Si(111) have been found to undergo changes in response to an external constant magnetic field ( B ˜ 0.1 T). A magnetically induced variation in the microhardness, Young's modulus, and coefficient of plasticity of silicon crystals correlates with the change in the lattice parameter and internal stresses of the sample. The growth of an oxide film under exposure to a magnetic field plays the principal role in the magnetomechanical effect due to a decrease in the concentration of oxygen complexes in the near-surface layers of the sample. In microstructured silicon, where the surface is considerably more developed, the magnetic field induces more profound changes in the internal stresses as compared to single crystals.

Open-field temporal pattern of ambulation in Japanese quail genetically selected for contrasting adrenocortical responsiveness to brief manual restraint.

PubMed

Kembro, J M; Satterlee, D G; Schmidt, J B; Perillo, M A; Marin, R H

2008-11-01

Japanese quail selected for a low-stress (LS), rather than a high-stress (HS), plasma corticosterone response to brief restraint have been shown to possess lower fearfulness and a nonspecific reduction in stress responsiveness. Detrended fluctuation analysis provides information on the organization and complexity of temporal patterns of behavior. The present study evaluated the temporal pattern of ambulation of LS and HS quail in an open field that represented a novel environment. Time series of 4,200 data points were collected for each bird by registering the distance ambulated every 0.5 s during a 35-min test period. Consistent with their known reduced fearfulness, the LS quail initiated ambulation significantly sooner (P < 0.02) and tended to ambulate more (P < 0.09) than did their HS counterparts. Detrended fluctuation analyses showed a monofractal series (i.e., a series with similar complexity at different temporal scales) in 72% of the birds. These birds initiated their ambulatory activity in less than 600 s. Among these birds, a lower (P < 0.03) autosimilarity coefficient (alpha) was found in the LS quail than in their HS counterparts (alpha = 0.76 +/- 0.03 and 0.87 +/- 0.03, respectively), suggesting a more complex (less regular) ambulatory pattern in the LS quail. However, when the patterns of ambulation were reexamined by considering only the active period of the time series (i.e., after the birds had initiated their ambulatory activity), monofractal patterns were observed in 97% of the birds, and no differences were found between the lines. Collectively, the results suggest that during the active period of open-field testing, during which fear responses are likely less strong and other motivations are the driving forces of ambulation, the LS and HS lines have similar ambulatory organization.

Complex brittle deformation pattern along the Southern Patagonian Andes (Argentina)

NASA Astrophysics Data System (ADS)

Barberón, Vanesa; Sue, Christian; Ronda, Gonzalo; Ghiglione, Matías

2016-04-01

The Southern Patagonian Andes is located in the southern extreme of the Pacific subduction zone, where the Antartic oceanic plate sinks underneath South America. The history of the area begins with compression during Paleozoic, Jurassic extension associated to the rift and opening of the South Atlantic Ocean, then a sag stage in the Lower Cretaceous followed by a foreland phase as a result of plate tectonics (Ghiglione et al., 2016). The kinematic study is concentrated in the Argentinean foothills, between 46°40' and 48° SL. We measured around 800 fault planes and their striaes with the sense of movement in order to characterize the stress field. The software used to make the stress inversion were Tensor (Delvaux, 2011) and Multiple Inverse Method MIM (Yamaji et al., 2011). The stress field map was built with the results of the MIM. We present new data from 48 sites located in the northern sector of the Southern Patagonian Andes. The measurements were made in several rocks from Paleozoic to Lower Cretaceous, even though most were taken in pyroclastic jurassic rocks from El Quemado Complex. Paleostress tensors obtained are mostly strike-slip, although a 25% is normal and there are a few compresional. The pattern of faults found is complex. In some sites the tensor can be locally linked to satellite images and observations from the field or be related to a major thrust front. There is no clear correlation between the age and/or lithology with the tensor since the youngest rocks measured are Lower Cretaceous. Probably there are several generations of family faults connected to different and recent tectonic phases then the paleostress tensors might correspond to the latest tectonic events.

Full-Field Stress Determination Around Circular Discontinuity in a Tensile-Loaded Plate using x-displacements Only

NASA Astrophysics Data System (ADS)

Baek, Tae Hyun; Chung, Tae Jin; Panganiban, Henry

The significant effects of stress raisers demand well-defined evaluation techniques to accurately determine the stress along the geometric boundary. A simple and accurate method for the determination of stress concentration around circular geometric discontinuity in a tensile-loaded plate is illustrated. The method is based on the least-squares technique, mapping functions, and a complex power series representation (Laurent series) of the stress functions for the calculation of tangential stress around the hole. Traction-free conditions were satisfied at the geometric discontinuity using conformal mapping and analytic continuation. In this study, we use only a relatively small amount of x-component displacement data of points away from the discontinuity of concern with their respective coordinates. Having this information we can easily obtain full-field stresses at the edge of the geometric discontinuity. Excellent results were obtained when the number of terms of the power series expansions, m=1. The maximum stress concentration calculation results using the present method and FEM using ANSYS agree well by less than one per cent difference. Experimental advantage of the method underscores the use of relatively small amount of data which are conveniently determined being away from the edge. Moreover, the small amount of measured input data needed affords the approach suitable for applications such as the multi-parameter concept used to obtain stress intensity factors from measured data. The use of laser speckle interferometry and moiré interferometry are also potential future related fields since the optical system for one-directional measurement is much simple.

An electrochemical model for hot-salt stress-corrosion of titanium alloys

NASA Technical Reports Server (NTRS)

Garfinkle, M.

1972-01-01

An electrochemical model of hot-salt stress-corrosion cracking of titanium alloys is proposed based on an oxygen-concentration cell. Hydrogen embrittlement is proposed as the direct cause of cracking, the hydrogen being generated as the results of the hydrolysis of complex halides formed at the shielded anode of the electrochemical cell. The model found to be consistent with the diverse observations made both in this study and by many investigators in this field.

Calculation of Prestressed Pressure Vessel Taking into Account the Concrete Temperature Inhomogeneity

NASA Astrophysics Data System (ADS)

Andreev, Vladimir

2018-03-01

The paper deals with the problem of determining the stress state of the pressure vessel (PV) with considering the concrete temperature inhomogeneity. Such structures are widely used in heat power engineering, for example, in nuclear power engineering. The structures of such buildings are quite complex and a comprehensive analysis of the stress state in them can be carried out either by numerical or experimental methods. However, a number of fundamental questions can be solved on the basis of simplified models, in particular, studies of the effect on the stressed state of the inhomogeneity caused by the temperature field.

Stresses in Circular Plates with Rigid Elements

NASA Astrophysics Data System (ADS)

Velikanov, N. L.; Koryagin, S. I.; Sharkov, O. V.

2018-05-01

Calculations of residual stress fields are carried out by numerical and static methods, using the flat cross-section hypothesis. The failure of metal when exposed to residual stresses is, in most cases, brittle. The presence in the engineering structures of rigid elements often leads to the crack initiation and structure failure. This is due to the fact that rigid elements under the influence of external stresses are stress concentrators. In addition, if these elements are fixed by welding, the residual welding stresses can lead to an increase in stress concentration and, ultimately, to failure. The development of design schemes for such structures is a very urgent task for complex technical systems. To determine the stresses in a circular plate with a welded circular rigid insert under the influence of an external load, one can use the solution of the plane stress problem for annular plates in polar coordinates. The polar coordinates of the points are the polar radius and the polar angle, and the stress state is determined by normal radial stresses, tangential and shearing stresses. The use of the above mentioned design schemes, formulas, will allow more accurate determination of residual stresses in annular welded structures. This will help to establish the most likely directions of failure and take measures at the stages of designing, manufacturing and repairing engineering structures to prevent these failures. However, it must be taken into account that the external load, the presence of insulation can lead to a change in the residual stress field.

The effects of magnetic and mechanical microstructures on the twinning stress in Ni-Mn-Ga

NASA Astrophysics Data System (ADS)

Faran, Eilon; Benichou, Itamar; Givli, Sefi; Shilo, Doron

2015-12-01

The ferromagnetic 10M Ni-Mn-Ga alloy exhibits complex magnetic and mechanical microstructures, which are expected to form barriers for motion of macro twin boundaries. Here, the contributions of both microstructures to the magnitude of the twinning stress property are investigated experimentally. A series of uniaxial loading-unloading curves are taken under different orientation angles of a constant magnetic field. The different 180 ° magnetic domains microstructures that are formed across the twin boundary in each case are visualised using a magneto optical film. Analysis of the different loading curves and the corresponding magnetic microstructures show that the latter does not contribute to the barriers for twin boundary motion. In accordance, the internal resisting stress for twin boundary motion under any magnetic field can be taken as the twinning stress measured in the absence of an external field. In addition, a statistical analysis of the fine features in the loading profiles reveals that the barrier for twinning is associated with a μ m sized characteristic length scale. This length scale corresponds to the typical thickness of micro-twinning laminates that constitute a mechanical microstructure. These findings indicate that the magnitude of the twinning stress in 10M Ni-Mn-Ga is determined by the characteristic fine twinned mechanical microstructure of this alloy.

Thermal onset of cellular and endocrine stress responses correspond to ecological limits in brook trout, an iconic cold-water fish

USGS Publications Warehouse

Chadwick, Joseph G; Nislow, Kieth H; McCormick, Stephen

2015-01-01

Climate change is predicted to change the distribution and abundance of species, yet underlying physiological mechanisms are complex and methods for detecting populations at risk from rising temperature are poorly developed. There is increasing interest in using physiological mediators of the stress response as indicators of individual and population-level response to environmental stressors. Here, we use laboratory experiments to show that the temperature thresholds in brook trout (Salvelinus fontinalis) for increased gill heat shock protein-70 (20.7°C) and plasma glucose (21.2°C) are similar to their proposed thermal ecological limit of 21.0°C. Field assays demonstrated increased plasma glucose, cortisol and heat shock protein-70 concentrations at field sites where mean daily temperature exceeded 21.0°C. Furthermore, population densities of brook trout were lowest at field sites where temperatures were warm enough to induce a stress response, and a co-occurring species with a higher thermal tolerance showed no evidence of physiological stress at a warm site. The congruence of stress responses and proposed thermal limits supports the use of these thresholds in models of changes in trout distribution under climate change scenarios and suggests that the induction of the stress response by elevated temperature may play a key role in driving the distribution of species.

A Direct Approach to In-Plane Stress Separation using Photoelastic Ptychography

NASA Astrophysics Data System (ADS)

Anthony, Nicholas; Cadenazzi, Guido; Kirkwood, Henry; Huwald, Eric; Nugent, Keith; Abbey, Brian

2016-08-01

The elastic properties of materials, either under external load or in a relaxed state, influence their mechanical behaviour. Conventional optical approaches based on techniques such as photoelasticity or thermoelasticity can be used for full-field analysis of the stress distribution within a specimen. The circular polariscope in combination with holographic photoelasticity allows the sum and difference of principal stress components to be determined by exploiting the temporary birefringent properties of materials under load. Phase stepping and interferometric techniques have been proposed as a method for separating the in-plane stress components in two-dimensional photoelasticity experiments. In this paper we describe and demonstrate an alternative approach based on photoelastic ptychography which is able to obtain quantitative stress information from far fewer measurements than is required for interferometric based approaches. The complex light intensity equations based on Jones calculus for this setup are derived. We then apply this approach to the problem of a disc under diametrical compression. The experimental results are validated against the analytical solution derived by Hertz for the theoretical displacement fields for an elastic disc subject to point loading.

A Direct Approach to In-Plane Stress Separation using Photoelastic Ptychography

PubMed Central

Anthony, Nicholas; Cadenazzi, Guido; Kirkwood, Henry; Huwald, Eric; Nugent, Keith; Abbey, Brian

2016-01-01

The elastic properties of materials, either under external load or in a relaxed state, influence their mechanical behaviour. Conventional optical approaches based on techniques such as photoelasticity or thermoelasticity can be used for full-field analysis of the stress distribution within a specimen. The circular polariscope in combination with holographic photoelasticity allows the sum and difference of principal stress components to be determined by exploiting the temporary birefringent properties of materials under load. Phase stepping and interferometric techniques have been proposed as a method for separating the in-plane stress components in two-dimensional photoelasticity experiments. In this paper we describe and demonstrate an alternative approach based on photoelastic ptychography which is able to obtain quantitative stress information from far fewer measurements than is required for interferometric based approaches. The complex light intensity equations based on Jones calculus for this setup are derived. We then apply this approach to the problem of a disc under diametrical compression. The experimental results are validated against the analytical solution derived by Hertz for the theoretical displacement fields for an elastic disc subject to point loading. PMID:27488605

Design and manufacturing methods for the integral field unit of the nirspec instrument on JWST

NASA Astrophysics Data System (ADS)

Lobb, Dan; Robertson, David

2017-11-01

An integral field unit, to be used with the near-IR spectrometer instrument of the James Webb Space Telescope (JWST), is currently under development by SSTL and CfAI. Special problems in design and manufacture of the optical system are outlined, and manufacturing methods for critical optical elements are discussed. The optical system is complex, requiring a total of 95 mirrors to produce 30 output channels. Emphasis is placed on the advantages of free-form machining in aluminium. These include: resistance to launch stress, insensitivity to temperature variations from ambient to cryogenic, and the possibility of relatively complex mirror surface shapes.

Tracking Local Spatiotemporal Microfracturing Processes and Stress Field Evolution Before and After Laboratory Fault Slip

NASA Astrophysics Data System (ADS)

Kwiatek, G.; Orlecka-Sikora, B.; Goebel, T.; Martínez-Garzón, P.; Dresen, G.; Bohnhoff, M.

2017-12-01

In this study we investigate details of spatial and temporal evolution of the stress field and damage at a pre-existing fault plane in laboratory stick-slip friction experiments performed on Westerly Granite sample. Specimen of 10 cm height and 4 cm diameter was deformed at a constant strain rate of 3×10-6 s-1 and confining pressure of 150 MPa. Here we analyze a series of 6 macroscopic slip events occurring on a rough fault during the course of experiment. Each macroscopic slip was associated with an intense femtoseismic acoustic emission (AE) activity recorded using a 16-channel transient recording system. To monitor the the spatiotemporal damage evolution, and unravel the micromechanical processes governing nucleation and propagation of slip events, we analyzed AE source characteristics (magnitude, seismic moment tensors, focal mechanisms), as well as the statistical properties (b-, c-, d- value) of femtoseismicity. In addition, the calculated AE focal mechanisms were used to reveal the spatiotemporal evolution of local stress field orientations and stress shape ratio coefficients over the fault plane, as well as additional parameters quantifying proximity to failure of individual fault patches. The calculated characteristics are used to comprehensively describe the complexity of the spatial and temporal evolution of the stress over the fault plane, and properties of the corresponding seismicity before and after the macroscopic slips. The observed faulting processes and characteristics are discussed in the context of global strain and stress changes, fault maturation, and earthquake stress drop.

Estimation of Stresses in a Dry Sand Layer Tested on Shaking Table

NASA Astrophysics Data System (ADS)

Sawicki, Andrzej; Kulczykowski, Marek; Jankowski, Robert

2012-12-01

Theoretical analysis of shaking table experiments, simulating earthquake response of a dry sand layer, is presented. The aim of such experiments is to study seismic-induced compaction of soil and resulting settlements. In order to determine the soil compaction, the cyclic stresses and strains should be calculated first. These stresses are caused by the cyclic horizontal acceleration at the base of soil layer, so it is important to determine the stress field as function of the base acceleration. It is particularly important for a proper interpretation of shaking table tests, where the base acceleration is controlled but the stresses are hard to measure, and they can only be deduced. Preliminary experiments have shown that small accelerations do not lead to essential settlements, whilst large accelerations cause some phenomena typical for limit states, including a visible appearance of slip lines. All these problems should be well understood for rational planning of experiments. The analysis of these problems is presented in this paper. First, some heuristic considerations about the dynamics of experimental system are presented. Then, the analysis of boundary conditions, expressed as resultants of respective stresses is shown. A particular form of boundary conditions has been chosen, which satisfies the macroscopic boundary conditions and the equilibrium equations. Then, some considerations are presented in order to obtain statically admissible stress field, which does not exceed the Coulomb-Mohr yield conditions. Such an approach leads to determination of the limit base accelerations, which do not cause the plastic state in soil. It was shown that larger accelerations lead to increase of the lateral stresses, and the respective method, which may replace complex plasticity analyses, is proposed. It is shown that it is the lateral stress coefficient K0 that controls the statically admissible stress field during the shaking table experiments.

GIS-based Stress Field Modeling of the North Arm of Sulawesi (NAoS) and its application in mineral prospectivity assessment

NASA Astrophysics Data System (ADS)

Albert, Gáspár; Szentpéteri, Krisztián

2017-04-01

Remotely sensed and digital map data are useful sources for regional structural analysis, including stress calculations. If the type of a given fault is determined and is considered as Andersonian, and rather juvenile instead of a reactivated one, the tectonic stress can be calculated for each of the fault segments (Albert et al. 2016). The North Arm of Sulawesi, a west-east-trending land strip of the irregular shaped Sulawesi Island, is actively deforming and the upper plate tectonic setting is quite complex in this region since it is situated above a triple junction of the Eurasian, Pacific and Australian plates. The stress currently acting in this region not only creates neotectonics but triggers subduction-related volcanism shifting from west to east on the peninsula. The volcanic centers - adjacent to transfer faults and the colliding plates at depth - appear to be the most productive areas for epithermal-porphyry mineralization systems of economic potential (Szentpéteri et al. 2015). In this work we demonstrate how the derived stress field model helps to understand the location and clustering of various mineralization types in the NAoS. We examine if this method is applicable for mineral prospectively assessments. References Albert, G., Barancsuk, Á., and Szentpéteri, K., 2016, Stress field modelling from digital geological map data: Geophysical Research Abstracts, v. 18, EGU2016-14565. Szentpéteri, K., Albert, G., and Ungvári, Z., Plate tectonic - and stress field - modeling of the North Arm of Sulawesi, Indonesia, to better understand distribution of mineral deposits styles., in Proceedings SEG 2015 I World Class Ore Deposits: Discovery to Recovery, Wrest Point Convention Centre, Hobart, Australia, September 27 - 30. 2015.

Fatigue response of perforated titanium for application in laminar flow control

NASA Technical Reports Server (NTRS)

Johnson, W. Steven; Miller, Jennifer L.; Newman, Jr., James

1996-01-01

The room temperature tensile and fatigue response of non-perforated and perforated titanium for laminar flow control application was investigated both experimentally and analytically. Results showed that multiple perforations did not affect the tensile response, but did reduce the fatigue life. A two dimensional finite element stress analysis was used to determine that the stress fields from adjacent perforations did not influence one another. The stress fields around the holes did not overlap one another, allowing the materials to be modeled as a plate with a center hole. Fatigue life was predicted using an equivalent MW flow size approach to relate the experimental results to microstructural features of the titanium. Predictions using flaw sizes ranging from 1 to 15 microns correlated within a factor of 2 with the experimental results by using a flow stress of 260 MPa. By using two different flow stresses in the crack closure model and correcting for plasticity, the experimental results were bounded by the predictions for high applied stresses. Further analysis of the complex geometry of the perforations and the local material chemistry is needed to further understand the fatigue behavior of the perforated titanium.

Glacial isostatic stress shadowing by the Antarctic ice sheet

NASA Technical Reports Server (NTRS)

Ivins, E. R.; James, T. S.; Klemann, V.

2005-01-01

Numerous examples of fault slip that offset late Quaternary glacial deposits and bedrock polish support the idea that the glacial loading cycle causes earthquakes in the upper crust. A semianalytical scheme is presented for quantifying glacial and postglacial lithospheric fault reactivation using contemporary rock fracture prediction methods. It extends previous studies by considering differential Mogi-von Mises stresses, in addition to those resulting from a Coulomb analysis. The approach utilizes gravitational viscoelastodynamic theory and explores the relationships between ice mass history and regional seismicity and faulting in a segment of East Antarctica containing the great Antarctic Plate (Balleny Island) earthquake of 25 March 1998 (Mw 8.1). Predictions of the failure stress fields within the seismogenic crust are generated for differing assumptions about background stress orientation, mantle viscosity, lithospheric thickness, and possible late Holocene deglaciation for the D91 Antarctic ice sheet history. Similar stress fracture fields are predicted by Mogi-von Mises and Coulomb theory, thus validating previous rebound Coulomb analysis. A thick lithosphere, of the order of 150-240 km, augments stress shadowing by a late melting (middle-late Holocene) coastal East Antarctic ice complex and could cause present-day earthquakes many hundreds of kilometers seaward of the former Last Glacial Maximum grounding line.

Temporal Stress Changes Caused by Earthquakes: A Review

NASA Astrophysics Data System (ADS)

Hardebeck, Jeanne L.; Okada, Tomomi

2018-02-01

Earthquakes can change the stress field in the Earth's lithosphere as they relieve and redistribute stress. Earthquake-induced stress changes have been observed as temporal rotations of the principal stress axes following major earthquakes in a variety of tectonic settings. The stress changes due to the 2011 Mw9.0 Tohoku-Oki, Japan, earthquake were particularly well documented. Earthquake stress rotations can inform our understanding of earthquake physics, most notably addressing the long-standing problem of whether the Earth's crust at plate boundaries is "strong" or "weak." Many of the observed stress rotations, including that due to the Tohoku-Oki earthquake, indicate near-complete stress drop in the mainshock. This implies low background differential stress, on the order of earthquake stress drop, supporting the weak crust model. Earthquake stress rotations can also be used to address other important geophysical questions, such as the level of crustal stress heterogeneity and the mechanisms of postseismic stress reloading. The quantitative interpretation of stress rotations is evolving from those based on simple analytical methods to those based on more sophisticated numerical modeling that can capture the spatial-temporal complexity of the earthquake stress changes.

Characterising the Architecture of New Zealand's Geothermal Structural Fluid Flow Networks Using Borehole Images

NASA Astrophysics Data System (ADS)

McNamara, David; Milicich, Sarah; Massiot, Cécile

2017-04-01

Borehole imaging has been used worldwide since the 1950's to capture vital geological information on the lithology, structure, and stress conditions of the Earth's subsurface. In New Zealand both acoustic and resistivity based borehole image logs are utilised to explore the geological nature of the basement and volcanic rocks that contain the country's unique geothermal reservoirs. Borehole image logs in wells from three geothermal fields in the Taupo Volcanic Zone (TVZ) provide the first, direct, subsurface, structural orientation measurements in New Zealand geothermal reservoir lithologies. While showing an overall structural pattern aligned to the regional tectonic trend, heterogeneities are observed that provide insight into the complexity of the structurally controlled, geothermal, fluid flow pathways. Analysis of imaged stress induced features informs us that the stress field orientation in the TVZ is also not homogenous, but is variable at a local scale.

Temporal and spatial patterns in wind stress and wind stress curl over the central Southern California Bight

USGS Publications Warehouse

Noble, Marlene A.; Rosenberger, Kurt J.; Rosenfeld, Leslie K.; Robertson, George L.

2012-01-01

In 2001, the U.S. Geological Survey, together with several other federal and municipal agencies, began a series of field programs to determine along and cross-shelf transport patterns over the continental shelves in the central Southern California Bight. As a part of these programs, moorings that monitor winds were deployed off the Palos Verdes peninsula and within San Pedro Bay for six 3–4 month summer and winter periods between 2001 and 2008. In addition, nearly continuous records of winds for this 7-year period were obtained from a terrestrial site at the coast and from a basin site offshore of the long-term coastal site. The mean annual winds are downcoast at all sites. The alongshelf components of wind stress, which are the largest part of the low-frequency wind stress fields, are well correlated between basin, shelf and coastal sites. On average, the amplitude of alongshelf fluctuations in wind stress are 3–4 times larger over the offshore basin, compared to the coastal site, irrespective of whether the fluctuations represent the total, or just the correlated portion of the wind stress field. The curl in the large-scale wind stress tends to be positive, especially in the winter season when the mean wind stress is downcoast and larger at the offshore basin site than at the beach. However, since the fluctuation in wind stress amplitudes are usually larger than the mean, periods of weak negative curl do occur, especially in the summer season when the largest normalized differences in the amplitude of wind stress fluctuations are found in the nearshore region of the coastal ocean. Even though the low-frequency wind stress field is well-correlated over the continental shelf and offshore basins, out to distances of 35 km or more from the coast, winds even 10 km inshore of the beach do not represent the coastal wind field, at least in the summer months. The seasonal changes in the spatial structures in wind stress amplitudes suggest that an assessment of the amplitude of the responses of coastal ocean processes to wind forcing is complex and that the responses may have significant seasonal structures.

Hub Protein Controversy: Taking a Closer Look at Plant Stress Response Hubs

PubMed Central

Vandereyken, Katy; Van Leene, Jelle; De Coninck, Barbara; Cammue, Bruno P. A.

2018-01-01

Plant stress responses involve numerous changes at the molecular and cellular level and are regulated by highly complex signaling pathways. Studying protein-protein interactions (PPIs) and the resulting networks is therefore becoming increasingly important in understanding these responses. Crucial in PPI networks are the so-called hubs or hub proteins, commonly defined as the most highly connected central proteins in scale-free PPI networks. However, despite their importance, a growing amount of confusion and controversy seems to exist regarding hub protein identification, characterization and classification. In order to highlight these inconsistencies and stimulate further clarification, this review critically analyses the current knowledge on hub proteins in the plant interactome field. We focus on current hub protein definitions, including the properties generally seen as hub-defining, and the challenges and approaches associated with hub protein identification. Furthermore, we give an overview of the most important large-scale plant PPI studies of the last decade that identified hub proteins, pointing out the lack of overlap between different studies. As such, it appears that although major advances are being made in the plant interactome field, defining hub proteins is still heavily dependent on the quality, origin and interpretation of the acquired PPI data. Nevertheless, many hub proteins seem to have a reported role in the plant stress response, including transcription factors, protein kinases and phosphatases, ubiquitin proteasome system related proteins, (co-)chaperones and redox signaling proteins. A significant number of identified plant stress hubs are however still functionally uncharacterized, making them interesting targets for future research. This review clearly shows the ongoing improvements in the plant interactome field but also calls attention to the need for a more comprehensive and precise identification of hub proteins, allowing a more efficient systems biology driven unraveling of complex processes, including those involved in stress responses. PMID:29922309

Nonlinear Fluid Migration Patterns in Fractured Reservoirs due to Stress-Pressure Coupling induced Changes in Reservoir Permeabilities

NASA Astrophysics Data System (ADS)

Annewandter, R.; Geiger, S.; Main, I. G.

2011-12-01

Sustainable storage of carbon dioxide (CO2) requires a thorough understanding of injection induced pressure build-up and its effects on the storage formation's integrity, since it determines the cap rock's sealing properties as well as the total storable amount of carbon dioxide. Fractures are abundant in the subsurface and difficult to detect due to their subseismic characteristic. If present in the cap during injection, they can be primary pathways for CO2 leakage. The North Sea is considered as Europe's most important carbon dioxide storage area. However, almost all of the potential storage formations have been exposed to post-glacial lithospheric flexure, possibly causing the generation of new fracture networks in the overburden whilst rebounding. Drawing upon, fast carbon dioxide uprise can be facilitated due to opening of fractures caused by changes in the stress field over time. The overall effective permeability, and hence possible leakage rates, of a fractured storage formation is highly sensitive to the fracture aperture which itself depends on the far field and in situ stress field. For this reason, our in-house general purpose reservoir simulator Complex System Modeling Platform (CSMP++) has been expanded, which is particularly designed to simulate multiphase flow on fractured porous media. It combines finite element (FE) and finite volume (FV) methods on mixed-dimensional hybrid-element meshes. The unstructured FE-FV based scheme allows us to model complex geological structures, such as fractures, at great detail. The simulator uses a compositional model for NaCl-H2O-CO2-systems for compressible fluids for computing thermophysical properties as a function of formation pressure and temperature. A fixed stress-split sequential procedure is being used to calculate coupled fluid flow and geomechanics. Numerical proof of concept studies will be presented showing the impact of fracture opening and closure on fluid migration patterns due to coupled stress-pressure induced changes in effective permeabilities.

Quercitol and osmotic adaptation of field-grown Eucalyptus under seasonal drought stress.

PubMed

Arndt, Stefan K; Livesley, Stephen J; Merchant, Andrew; Bleby, Timothy M; Grierson, Pauline F

2008-07-01

This study investigated the role of quercitol in osmotic adjustment in field-grown Eucalyptus astringens Maiden subject to seasonal drought stress over the course of 1 year. The trees grew in a native woodland and a farm plantation in the semi-arid wheatbelt region of south Western Australia. Plantation trees allocated relatively more biomass to leaves than woodland trees, but they suffered greater drought stress over summer, as indicated by lower water potentials, CO(2)assimilation rates and stomatal conductances. In contrast, woodland trees had relatively fewer leaves and suffered less drought stress. Plantation trees under drought stress engaged in osmotic adjustment, but woodland trees did not. Quercitol made a significant contribution to osmotic adjustment in drought-stressed trees (25% of total solutes), and substantially more quercitol was measured in the leaves of plantation trees (5% dry matter) than in the leaves of woodland trees (2% dry matter). We found no evidence that quercitol was used as a carbon storage compound while starch reserves were depleted under drought stress. Differences in stomatal conductance, biomass allocation and quercitol production clearly indicate that E. astringens is both morphologically and physiologically 'plastic' in response to growth environment, and that osmotic adjustment is only one part of a complex strategy employed by this species to tolerate drought.

Stress and Thermal Analysis of the In-Vessel Resonant Magnetic Perturbation Coils on the J-TEXT Tokamak

NASA Astrophysics Data System (ADS)

Hao, Changduan; Zhang, Ming; Ding, Yonghua; Rao, Bo; Cen, Yishun; Zhuang, Ge

2012-01-01

A set of four in-vessel saddle coils was designed to generate a helical field on the J-TEXT tokamak to study the influences of the external perturbation field on plasma. The coils are fed with alternating current up to 10 kA at frequency up to 10 kHz. Due to the special structure, complex thermal environment and limited space in the vacuum chamber, it is very important to make sure that the coils will not be damaged when undergoing the huge electromagnetic forces in the strong toroidal field, and that their temperatures don't rise too much and destroy the insulation. A 3D finite element model is developed in this paper using the ANSYS code, stresses are analyzed to find the worst condition, and a mounting method is then established. The results of the stress and modal analyses show that the mounting method meets the strength requirements. Finally, a thermal analysis is performed to study the cooling process and the temperature distribution of the coils.

A Discrete Fracture Network Model with Stress-Driven Nucleation and Growth

NASA Astrophysics Data System (ADS)

Lavoine, E.; Darcel, C.; Munier, R.; Davy, P.

2017-12-01

The realism of Discrete Fracture Network (DFN) models, beyond the bulk statistical properties, relies on the spatial organization of fractures, which is not issued by purely stochastic DFN models. The realism can be improved by injecting prior information in DFN from a better knowledge of the geological fracturing processes. We first develop a model using simple kinematic rules for mimicking the growth of fractures from nucleation to arrest, in order to evaluate the consequences of the DFN structure on the network connectivity and flow properties. The model generates fracture networks with power-law scaling distributions and a percentage of T-intersections that are consistent with field observations. Nevertheless, a larger complexity relying on the spatial variability of natural fractures positions cannot be explained by the random nucleation process. We propose to introduce a stress-driven nucleation in the timewise process of this kinematic model to study the correlations between nucleation, growth and existing fracture patterns. The method uses the stress field generated by existing fractures and remote stress as an input for a Monte-Carlo sampling of nuclei centers at each time step. Networks so generated are found to have correlations over a large range of scales, with a correlation dimension that varies with time and with the function that relates the nucleation probability to stress. A sensibility analysis of input parameters has been performed in 3D to quantify the influence of fractures and remote stress field orientations.

Investigation of Rock Mass Stability Around the Tunnels in an Underground Mine in USA Using Three-Dimensional Numerical Modeling

NASA Astrophysics Data System (ADS)

Xing, Yan; Kulatilake, P. H. S. W.; Sandbak, L. A.

2018-02-01

The stability of the rock mass around the tunnels in an underground mine was investigated using the distinct element method. A three-dimensional model was developed based on the available geological, geotechnical, and mine construction information. It incorporates a complex lithological system, persistent and non-persistent faults, and a complex tunnel system including backfilled tunnels. The strain-softening constitutive model was applied for the rock masses. The rock mass properties were estimated using the Hoek-Brown equations based on the intact rock properties and the RMR values. The fault material behavior was modeled using the continuously yielding joint model. Sequential construction and rock supporting procedures were simulated based on the way they progressed in the mine. Stress analyses were performed to study the effect of the horizontal in situ stresses and the variability of rock mass properties on tunnel stability, and to evaluate the effectiveness of rock supports. The rock mass behavior was assessed using the stresses, failure zones, deformations around the tunnels, and the fault shear displacement vectors. The safety of rock supports was quantified using the bond shear and bolt tensile failures. Results show that the major fault and weak interlayer have distinct influences on the displacements and stresses around the tunnels. Comparison between the numerical modeling results and the field measurements indicated the cases with the average rock mass properties, and the K 0 values between 0.5 and 1.25 provide satisfactory agreement with the field measurements.

Characteristics of global strong earthquakes and their implications for the present-day stress pattern

NASA Astrophysics Data System (ADS)

Wei, Ju; Weifeng, Sun; Jinhui, Luo

2017-10-01

Earthquakes occurred on the surface of the Earth contain comprehensive and abundant geodynamic connotations, and can serve as important sources for describing the present-day stress field and regime. An important advantage of the earthquake focal mechanism solution is the ability to obtain the stress pattern information at depth in the lithosphere. During the past several decades, an increasing number of focal mechanisms were available for estimating the present-day stress field and regime. In the present study, altogether 553 focal mechanism data ranging from the year 1976 to 2017 with Mw ≥ 7.0 were compiled in the Global/Harvard centroid moment tensor (CMT) catalogue, the characteristics of global strong earthquakes and the present-day stress pattern were analyzed based on these data. The majority of global strong earthquakes are located around the plate boundaries, shallow-focus, and thrust faulting (TF) regime. We grouped 518 of them into 12 regions (Boxes) based on their geographical proximity and tectonic setting. For each box, the present-day stress field and regime were obtained by formal stress inversion. The results indicated that the maximum horizontal principal stress direction was ˜ N-S-trending in western North America continent and southwestern Indonesia, ˜ NNE-SSW-trending in western Middle America and central Asia, ˜ NE-SW in southeastern South America continent and northeastern Australia, ˜ NEE-SWW-trending in western South America continent and southeastern Asia, ˜ E-W-trending in southeastern Australia, and ˜ NW-SE-trending in eastern Asia. The results can provide additional constraints to the driving forces and geodynamic models, allowing them to explain the current plate interactions and crustal tectonic complexities better.

Surgeons' and surgical trainees' acute stress in real operations or simulation: A systematic review.

PubMed

Georgiou, Konstantinos; Larentzakis, Andreas; Papavassiliou, Athanasios G

2017-12-01

Acute stress in surgery is ubiquitous and has an immediate impact on surgical performance and patient safety. Surgeons react with several coping strategies; however, they recognise the necessity of formal stress management training. Thus, stress assessment is a direct need. Surgical simulation is a validated standardised training milieu designed to replicate real-life situations. It replicates stress, prevents biases, and provides objective metrics. The complexity of stress mechanisms makes stress measurement difficult to quantify and interpret. This systematic review aims to identify studies that have used acute stress estimation measurements in surgeons or surgical trainees during real operations or surgical simulation, and to collectively present the rationale of these tools, with special emphasis in salivary markers. A search strategy was implemented to retrieve relevant articles from MEDLINE and SCOPUS databases. The 738 articles retrieved were reviewed for further evaluation according to the predetermined inclusion/exclusion criteria. Thirty-three studies were included in this systematic review. The methods for acute stress assessment varied greatly among studies with the non-invasive techniques being the most commonly used. Subjective and objective tests for surgeons' acute stress assessment are being presented. There is a broad spectrum of acute mental stress assessment tools in the surgical field and simulation and salivary biomarkers have recently gained popularity. There is a need to maintain a consistent methodology in future research, towards a deeper understanding of acute stress in the surgical field. Copyright © 2017 Royal College of Surgeons of Edinburgh (Scottish charity number SC005317) and Royal College of Surgeons in Ireland. Published by Elsevier Ltd. All rights reserved.

Stress history and fracture pattern in fault-related folds based on limit analysis: application to the Sub-Andean thrust belt of Bolivia

NASA Astrophysics Data System (ADS)

Barbe, Charlotte; Leroy, Yves; Ben Miloud, Camille

2017-04-01

A methodology is proposed to construct the stress history of a complex fault-related fold in which the deformation mechanisms are essentially frictional. To illustrate the approach, fours steps of the deformation of an initially horizontally layered sand/silicone laboratory experiment (Driehaus et al., J. of Struc. Geol., 65, 2014) are analysed with the kinematic approach of limit analysis (LA). The stress, conjugate to the virtual velocity gradient in the sense of mechanicam power, is a proxy for the true statically admmissible stress field which prevailed over the structure. The material properties, friction angles and cohesion, including their time evolution are selected such that the deformation pattern predicted by the LA is consistent with the two main thrusting events, the first forward and the second backward once the layers have sufficiently rotated. The fractures associated to the stress field determined at each step are convected on today configuration to define the complete pattern which should be observed. The end results are presented along virtual vertical wells and could be used within the oil industry at an early phase of exploration to prepare drealing operations.

Edge delamination in angle-ply composite laminates, part 5

NASA Technical Reports Server (NTRS)

Wang, S. S.

1981-01-01

A theoretical method was developed for describing the edge delamination stress intensity characteristics in angle-ply composite laminates. The method is based on the theory of anisotropic elasticity. The edge delamination problem is formulated using Lekhnitskii's complex-variable stress potentials and an especially developed eigenfunction expansion method. The method predicts exact orders of the three-dimensional stress singularity in a delamination crack tip region. With the aid of boundary collocation, the method predicts the complete stress and displacement fields in a finite-dimensional, delaminated composite. Fracture mechanics parameters such as the mixed-mode stress intensity factors and associated energy release rates for edge delamination can be calculated explicity. Solutions are obtained for edge delaminated (theta/-theta theta/-theta) angle-ply composites under uniform axial extension. Effects of delamination lengths, fiber orientations, lamination and geometric variables are studied.

On the determination of stress fields and displacements in a thin elastoplastic plate containing elastic inclusion - a shim

NASA Astrophysics Data System (ADS)

Kovalev, A. V.; Rusina, E. Y.; Yakovlev, A. Y.

2018-03-01

The paper is devoted to the determination of the stress-strain state of a mechanical structure, which consists of a thin infinite elastoplastic plate with a hole and a continuous fine elastic inclusion. The complexity of this problem lies in the fact that the shape of the boundary between the elastic and plastic zones in the plate is not known in advance. The small parameter method is used as the solution method, while the small parameter characterizes the deviation of the shape of the contour from the circle and the perturbation of external static boundary conditions. As the zero solution, the axisymmetric elastoplastic state of the plate with inclusion is chosen. Two variants of inclusion fixation in a plate are considered: inclusion is enclosed with tension or soldered. As a result of solving the problem within the framework of ideal plasticity, the distribution of the stress and displacement fields and the shape of the elastoplastic boundary are obtained. To illustrate the case of a plane-stressed state, the results of a numerical experiment on the mathematical model obtained are presented.

Epilogue: meditations on psychosomatic medicine.

PubMed

Cobb, S

1975-01-01

Presented are some personal views on the state of psychosomatic medicine as a science. It is suggested that the field needs more precision in language including exorcism of value judgments from certain dimensions, less circularity in stress-strain reasoning, more complex hypotheses, more emphasis on social support as a central variable and more acceptance of divergent research styles.

Intergranular Strain Evolution During Biaxial Loading: A Multiscale FE-FFT Approach

NASA Astrophysics Data System (ADS)

Upadhyay, M. V.; Capek, J.; Van Petegem, S.; Lebensohn, R. A.; Van Swygenhoven, H.

2017-05-01

Predicting the macroscopic and microscopic mechanical response of metals and alloys subjected to complex loading conditions necessarily requires a synergistic combination of multiscale material models and characterization techniques. This article focuses on the use of a multiscale approach to study the difference between intergranular lattice strain evolution for various grain families measured during in situ neutron diffraction on dog bone and cruciform 316L samples. At the macroscale, finite element simulations capture the complex coupling between applied forces and gauge stresses in cruciform geometries. The predicted gauge stresses are used as macroscopic boundary conditions to drive a mesoscale full-field elasto-viscoplastic fast Fourier transform crystal plasticity model. The results highlight the role of grain neighborhood on the intergranular strain evolution under uniaxial and equibiaxial loading.

Temporal stress changes caused by earthquakes: A review

USGS Publications Warehouse

Hardebeck, Jeanne L.; Okada, Tomomi

2018-01-01

Earthquakes can change the stress field in the Earth’s lithosphere as they relieve and redistribute stress. Earthquake-induced stress changes have been observed as temporal rotations of the principal stress axes following major earthquakes in a variety of tectonic settings. The stress changes due to the 2011 Mw9.0 Tohoku-Oki, Japan, earthquake were particularly well documented. Earthquake stress rotations can inform our understanding of earthquake physics, most notably addressing the long-standing problem of whether the Earth’s crust at plate boundaries is “strong” or “weak.” Many of the observed stress rotations, including that due to the Tohoku-Oki earthquake, indicate near-complete stress drop in the mainshock. This implies low background differential stress, on the order of earthquake stress drop, supporting the weak crust model. Earthquake stress rotations can also be used to address other important geophysical questions, such as the level of crustal stress heterogeneity and the mechanisms of postseismic stress reloading. The quantitative interpretation of stress rotations is evolving from those based on simple analytical methods to those based on more sophisticated numerical modeling that can capture the spatial-temporal complexity of the earthquake stress changes.

Wall Shear Stress, Wall Pressure and Near Wall Velocity Field Relationships in a Whirling Annular Seal

NASA Technical Reports Server (NTRS)

Morrison, Gerald L.; Winslow, Robert B.; Thames, H. Davis, III

1996-01-01

The mean and phase averaged pressure and wall shear stress distributions were measured on the stator wall of a 50% eccentric annular seal which was whirling in a circular orbit at the same speed as the shaft rotation. The shear stresses were measured using flush mounted hot-film probes. Four different operating conditions were considered consisting of Reynolds numbers of 12,000 and 24,000 and Taylor numbers of 3,300 and 6,600. At each of the operating conditions the axial distribution (from Z/L = -0.2 to 1.2) of the mean pressure, shear stress magnitude, and shear stress direction on the stator wall were measured. Also measured were the phase averaged pressure and shear stress. These data were combined to calculate the force distributions along the seal length. Integration of the force distributions result in the net forces and moments generated by the pressure and shear stresses. The flow field inside the seal operating at a Reynolds number of 24,000 and a Taylor number of 6,600 has been measured using a 3-D laser Doppler anemometer system. Phase averaged wall pressure and wall shear stress are presented along with phase averaged mean velocity and turbulence kinetic energy distributions located 0.16c from the stator wall where c is the seal clearance. The relationships between the velocity, turbulence, wall pressure and wall shear stress are very complex and do not follow simple bulk flow predictions.

Streamwise Vorticity Generation in Laminar and Turbulent Jets

NASA Technical Reports Server (NTRS)

Demuren, Aodeji O.; Wilson, Robert V.

1999-01-01

Complex streamwise vorticity fields are observed in the evolution of non-circular jets. Generation mechanisms are investigated via Reynolds-averaged (RANS), large-eddy (LES) and direct numerical (DNS) simulations of laminar and turbulent rectangular jets. Complex vortex interactions are found in DNS of laminar jets, but axis-switching is observed only when a single instability mode is present in the incoming mixing layer. With several modes present, the structures are not coherent and no axis-switching occurs, RANS computations also produce no axis-switching. On the other hand, LES of high Reynolds number turbulent jets produce axis-switching even for cases with several instability modes in the mixing layer. Analysis of the source terms of the mean streamwise vorticity equation through post-processing of the instantaneous results shows that, complex interactions of gradients of the normal and shear Reynolds stresses are responsible for the generation of streamwise vorticity which leads to axis-switching. RANS computations confirm these results. k - epsilon turbulence model computations fail to reproduce the phenomenon, whereas algebraic Reynolds stress model (ASM) computations, in which the secondary normal and shear stresses are computed explicitly, succeeded in reproducing the phenomenon accurately.

Reversed-polarity regions

NASA Technical Reports Server (NTRS)

Tang, F.

1980-01-01

The 58 RPRS studied have a lifespan comparable to normal active regions and have no tendency to rotate toward a more normal alignment. They seem to have stable configurations with no apparent evidence suggesting stress due to their anomalous magnetic alignment. Magnetic complexity in RPRs is the key to flare productivity just as it is in normal regions - weak field RPRs produced no flares and regions with complex spots produced more flares than regions with noncomplex spots by a factor of 5. The RPRs however, differ from normal regions in the frequency of having complex spots, particularly the long lived complex spots, in them. Less than 17 percent of normal ARs have complex spots; less than 1.8 percent have long lived complex spots. In contrast, 41 percent of RPRs have complex spots and 24 percent have long lived complex spots.

Stress Study on Southern Segment of Longmenshan Fault Constrained by Focal Mechanism Data

NASA Astrophysics Data System (ADS)

Yang, Y.; Liang, C.; Su, J.; Zhou, L.

2016-12-01

The Longmenshan fault (LMSF) lies at the eastern margin of Tibetan plateau and constitutes the boundary of the active Bayankala block and rigid Sichuan basin. This fault was misinterpreted as an inactive fault before the great Wenchuan earthquake. Five years after the devastating event, the Lushan MS 7.0 stroke the southern segment of the LMSF but fractured in a very limited scale and formed a seismic gap between the two earthquakes. In this study, we determined focal mechanisms of earthquakes with magnitude M≥3 from Jan 2008 to July 2014 in the southern segment of LMSF, and then applied the damped linear inversion to derive the regional stress field based on the focal mechanisms. Focal mechanisms of 755 earthquakes in total were determined. We further used a damped linear inversion technique to produce a 2D stress map in upper crust in the study region. A dominant thrust regime is determined south of the seismic gap, with a horizontal maximum compression oriented in NWW-SEE. But in the area to the north of the seismic gap is characterized as a much more complex stress environment. To the west of the Dujiangyan city, there appear to be a seismic gap in the Pengguan complex. The maximum compressions show the anti-clockwise and clockwise patterns to the south and north of this small gap. Thus the small gap seems to be an asperity that causes the maximum compression to rotate around it. While combined the maximum compression pattern with the focal solutions of strong earthquakes (Mw≥5) in this region, two of those strong earthquakes located near the back-range-fault have strikes parallel to the Miyaluo fault. Considering a large amount of earthquakes in Lixian branch, the Miyaluo fault may be extended to LMSF following the great Wenchuan earthquake. Investigations on the stress field of different depths indicate complex spatial variations. The Pengguan complex is almost aseismic in shallow depth in its central part. In deeper depth, the maximum compressions show the NNW-SSE and NE-SW directions to the north and south of the seismic gap respectively, this are surprisingly different from that of the shallower depth. Thus the maximum compressions vary with depth may imply the movement in depth is decoupled from the movement in shallow depth. This work was partially supported by National Natural Science Foundation of China (41340009).

Untangling complex networks: risk minimization in financial markets through accessible spin glass ground states

PubMed Central

Lisewski, Andreas Martin; Lichtarge, Olivier

2010-01-01

Recurrent international financial crises inflict significant damage to societies and stress the need for mechanisms or strategies to control risk and tamper market uncertainties. Unfortunately, the complex network of market interactions often confounds rational approaches to optimize financial risks. Here we show that investors can overcome this complexity and globally minimize risk in portfolio models for any given expected return, provided the relative margin requirement remains below a critical, empirically measurable value. In practice, for markets with centrally regulated margin requirements, a rational stabilization strategy would be keeping margins small enough. This result follows from ground states of the random field spin glass Ising model that can be calculated exactly through convex optimization when relative spin coupling is limited by the norm of the network's Laplacian matrix. In that regime, this novel approach is robust to noise in empirical data and may be also broadly relevant to complex networks with frustrated interactions that are studied throughout scientific fields. PMID:20625477

Untangling complex networks: Risk minimization in financial markets through accessible spin glass ground states

NASA Astrophysics Data System (ADS)

Lisewski, Andreas Martin; Lichtarge, Olivier

2010-08-01

Recurrent international financial crises inflict significant damage to societies and stress the need for mechanisms or strategies to control risk and tamper market uncertainties. Unfortunately, the complex network of market interactions often confounds rational approaches to optimize financial risks. Here we show that investors can overcome this complexity and globally minimize risk in portfolio models for any given expected return, provided the margin requirement remains below a critical, empirically measurable value. In practice, for markets with centrally regulated margin requirements, a rational stabilization strategy would be keeping margins small enough. This result follows from ground states of the random field spin glass Ising model that can be calculated exactly through convex optimization when relative spin coupling is limited by the norm of the network’s Laplacian matrix. In that regime, this novel approach is robust to noise in empirical data and may be also broadly relevant to complex networks with frustrated interactions that are studied throughout scientific fields.

Untangling complex networks: risk minimization in financial markets through accessible spin glass ground states.

PubMed

Lisewski, Andreas Martin; Lichtarge, Olivier

2010-08-15

Recurrent international financial crises inflict significant damage to societies and stress the need for mechanisms or strategies to control risk and tamper market uncertainties. Unfortunately, the complex network of market interactions often confounds rational approaches to optimize financial risks. Here we show that investors can overcome this complexity and globally minimize risk in portfolio models for any given expected return, provided the relative margin requirement remains below a critical, empirically measurable value. In practice, for markets with centrally regulated margin requirements, a rational stabilization strategy would be keeping margins small enough. This result follows from ground states of the random field spin glass Ising model that can be calculated exactly through convex optimization when relative spin coupling is limited by the norm of the network's Laplacian matrix. In that regime, this novel approach is robust to noise in empirical data and may be also broadly relevant to complex networks with frustrated interactions that are studied throughout scientific fields.

Proteomic changes in rice leaves grown under open field high temperature stress conditions.

PubMed

Das, Smruti; Krishnan, P; Mishra, Vagish; Kumar, Ritesh; Ramakrishnan, B; Singh, N K

2015-11-01

The interactive effect of temperature with other climatic and soil factors has profound influences on the growth and development of rice. The responses of rice to high temperatures under field conditions are more important than those under the controlled conditions. To understand the genes associated with high temperature stress response in general and tolerance in particular, the expression of all those genes associated with adaptation and tolerance in rice requires proteomic analysis. High temperature stress-tolerant cv. N22 was subjected to 28/18 °C (control) and 42/32 °C (high temperature stress) at flowering stage. The plants were grown in the field under the free air temperature increment condition. The proteomic changes in rice leaves due to high temperature stress were discussed. The proteomes of leaves had about 3000 protein spots, reproducibly detected on 2-dimensional electrophoretic gels with 573 proteins differentially expressed between the control and the high temperature treatments. Putative physiological functions suggested five categories such as growth (15.4%), heat shock proteins (7.7%), regulatory proteins (26.9%), redox homeostasis proteins (11.5%) and energy and metabolism (38.5%) related proteins. The results of the present study suggest that cv. N22, an agronomically recognized temperature tolerant rice cultivar copes with high temperature stress in a complex manner. Several functional proteins play important roles in its responses. The predicted climate change events necessitate more studies using this cultivar under different simulated ecological conditions to identify proteomic changes and the associated genes to be used as biomarkers and to gain a better understanding on the biochemical pathways involved in tolerance.

Paternal stress prior to conception alters DNA methylation and behaviour of developing rat offspring.

PubMed

Mychasiuk, R; Harker, A; Ilnytskyy, S; Gibb, R

2013-06-25

Although there has been an abundance of research focused on offspring outcomes associated with maternal experiences, there has been limited examination of the relationship between paternal experiences and offspring brain development. As spermatogenesis is a continuous process, experiences that have the ability to alter epigenetic regulation in fathers may actually change developmental trajectories of offspring. The purpose of this study was to examine the effects of paternal stress prior to conception on behaviour and the epigenome of both male and female developing rat offspring. Male Long-Evans rats were stressed for 27 consecutive days and then mated with control female rats. Early behaviour was tested in offspring using the negative geotaxis task and the open field. At P21 offspring were sacrificed and global DNA methylation levels in the hippocampus and frontal cortex were analysed. Paternal stress prior to conception altered behaviour of all offspring on the negative geotaxis task, delaying acquisition of the task. In addition, male offspring demonstrated a reduction in stress reactivity in the open field paradigm spending more time than expected in the centre of the open field. Paternal stress also altered DNA methylation patterns in offspring at P21, global methylation was reduced in the frontal cortex of female offspring, but increased in the hippocampus of both male and female offspring. The results from this study clearly demonstrate that paternal stress during spermatogenesis can influence offspring behaviour and DNA methylation patterns, and these affects occur in a sex-dependent manner. Development takes place in the centre of a complex interaction between maternal, paternal, and environmental influences, which combine to produce the various phenotypes and individual differences that we perceive. Copyright © 2013 IBRO. Published by Elsevier Ltd. All rights reserved.

Toward a universal mass-momentum transfer relationship for predicting nutrient uptake and metabolite exchange in benthic reef communities

NASA Astrophysics Data System (ADS)

Falter, James L.; Lowe, Ryan J.; Zhang, Zhenlin

2016-09-01

Here we synthesize data from previous field and laboratory studies describing how rates of nutrient uptake and metabolite exchange (mass transfer) are related to form drag and bottom stresses (momentum transfer). Reanalysis of this data shows that rates of mass transfer are highly correlated (r2 ≥ 0.9) with the root of the bottom stress (τbot0.4) under both waves and currents and only slightly higher under waves (~10%). The amount of mass transfer that can occur per unit bottom stress (or form drag) is influenced by morphological features ranging anywhere from millimeters to meters in scale; however, surface-scale roughness (millimeters) appears to have little effect on actual nutrient uptake by living reef communities. Although field measurements of nutrient uptake by natural reef communities agree reasonably well with predictions based on existing mass-momentum transfer relationships, more work is needed to better constrain these relationships for more rugose and morphologically complex communities.

Static Stress Changes Inverted from Microseismicity in Eastern Aegean Sea

NASA Astrophysics Data System (ADS)

Leptokaropoulos, Konstantinos; Papadimitriou, Eleftheria; Orlecka-Sikora, Beata; Karakostas, Vassilios

2014-05-01

In this study we attempted to derive static stress field variations from the changes of earthquake production rates in Kusadasi bay and Samos island (eastern Aegean), by applying the Dieterich et al. (2000) Rate/State formulation. The calculation of stress changes from earthquake occurrence rates fluctuations should be obtained from catalogues which achieve adequate spatial and temporal resolution and well determined hypocenter coordinates. For this reason we took advantage of the data from a regional network operating since July of 2007, providing continuous monitoring of microseismicity, along with data available from seismological stations of the permanent Hellenic Unified Seismological Network (HUSN). The high accuracy and large sized regional catalogue is utilized for inverting seismicity rate changes into stress variation through a Rate/State dependent friction model. After explicitly determining the physical parameters incorporating in the modeling (reference seismicity rates, characteristic relaxation time, constitutive properties of fault zones) we investigated stress changes in both space and time regime and their possible connection with earthquake clustering and fault interactions. The main interest is focused on the June 2009 Samos Mw=5.1 event, which was followed by an intense seismic activity for several days. We attempt to reproduce and interpret stress changes both before and after the initiation of this seismic burst. The differences between the earthquake occurrence rates before and after the main shock are used as input data in a stress inversion algorithm based upon the Rate/State dependent friction concept in order to provide an estimation of stress changes. Diverse assumptions and combinations of the parameters values are tested for the model performance and sensitivity to be evaluated. The approach followed here could provide evidence of the robustness of the seismicity rate changes usage as a stress meter for both positive and negative stress steps in an actively tectonic region accommodating complex fault systems. Acknowledgements: Support from the bilateral agreement between Aristotle University of Thessaloniki and Institute of Geophysics of Polish Academy of Sciences during August 2013 and the research project titled as 'Seismotectonic properties of the eastern Aegean: Implications on the stress field evolution and seismic hazard assessment in a tectonically complex area', GSRT 10 T UR/1-3-9, Joint Research and Technology Programmes 2010-2011, financed by the Ministry of Education of Greece and the Scientific and Technological Research Council of Turkey (TUBITAK 109Y401) are acknowledged.

Does magmatism influence low-angle normal faulting?

USGS Publications Warehouse

Parsons, Thomas E.; Thompson, George A.

1993-01-01

Synextensional magmatism has long been recognized as a ubiquitous characteristic of highly extended terranes in the western Cordillera of the United States. Intrusive magmatism can have severe effects on the local stress field of the rocks intruded. Because a lower angle fault undergoes increased normal stress from the weight of the upper plate, it becomes more difficult for such a fault to slide. However, if the principal stress orientations are rotated away from vertical and horizontal, then a low-angle fault plane becomes more favored. We suggest that igneous midcrustal inflation occurring at rates faster than regional extension causes increased horizontal stresses in the crust that alter and rotate the principal stresses. Isostatic forces and continued magmatism can work together to create the antiformal or domed detachment surface commonly observed in the metamorphic core complexes of the western Cordillera. Thermal softening caused by magmatism may allow a more mobile mid-crustal isostatic response to normal faulting.

Model based estimation of sediment erosion in groyne fields along the River Elbe

NASA Astrophysics Data System (ADS)

Prohaska, Sandra; Jancke, Thomas; Westrich, Bernhard

2008-11-01

River water quality is still a vital environmental issue, even though ongoing emissions of contaminants are being reduced in several European rivers. The mobility of historically contaminated deposits is key issue in sediment management strategy and remediation planning. Resuspension of contaminated sediments impacts the water quality and thus, it is important for river engineering and ecological rehabilitation. The erodibility of the sediments and associated contaminants is difficult to predict due to complex time depended physical, chemical, and biological processes, as well as due to the lack of information. Therefore, in engineering practice the values for erosion parameters are usually assumed to be constant despite their high spatial and temporal variability, which leads to a large uncertainty of the erosion parameters. The goal of presented study is to compare the deterministic approach assuming constant critical erosion shear stress and an innovative approach which takes the critical erosion shear stress as a random variable. Furthermore, quantification of the effective value of the critical erosion shear stress, its applicability in numerical models, and erosion probability will be estimated. The results presented here are based on field measurements and numerical modelling of the River Elbe groyne fields.

The Defecation Index as a Measure of Emotionality: Questions Raised by HPA Axis and Prolactin Response to Stress in the Maudsley Model.

PubMed

Blizard, David A; Eldridge, J Charles; Jones, Byron C

2015-05-01

The Maudsley Reactive and Maudsley Non-Reactive strains have been selectively bred for differences in open-field defecation (OFD), a putative index of stress. We investigated whether variations in the hypothalamic-pituitary-adrenal (HPA) axis are correlated with strain differences in OFD in the Maudsley model. Exposure to the open-field test did not result in increases in ACTH in male rats of either strain and there were no strain differences in the large increases in ACTH and corticosteroid that occurred in response to intermittent footshock. Parallel studies of prolactin showed that Maudsley Reactive rats had greater response to the open-field and to footshock than Maudsley Non-Reactive rats. The lack of correlation between strain differences in OFD and reactivity of the HPA axis is consistent with the idea that HPA response to stress and OFD reflect the output of different neural systems and that individual differences in emotionality, as indexed by OFD do not influence other measures of stress-reactivity in a simple manner, if at all. The reactivity of the prolactin system to the open-field test and lack of response of ACTH to the same situation is consistent with the idea that the prolactin system is sensitive to lower levels of stress than the HPA axis, a finding at variance with the presumed extreme sensitivity of the latter system. Earlier comparisons of the HPA axis in these strains implicate local factors such as neuropeptide-Y peptide in the adrenal in attenuating the response of the adrenal cortex to ACTH and hints at the complexity of regulation of the HPA axis.

Chronic mild stress increases alcohol intake in mice with low dopamine D2 receptor levels.

PubMed

Delis, Foteini; Thanos, Panayotis K; Rombola, Christina; Rosko, Lauren; Grandy, David; Wang, Gene-Jack; Volkow, Nora D

2013-02-01

Alcohol use disorders emerge from a complex interaction between environmental and genetic factors. Stress and dopamine D2 receptor levels (DRD2) have been shown to play a central role in alcoholism. To better understand the interactions between DRD2 and stress in ethanol intake behavior, we subjected Drd2 wild-type (+/+), heterozygous (+/-), and knockout (-/-) mice to 4 weeks of chronic mild stress (CMS) and to an ethanol two-bottle choice during CMS weeks 2-4. Prior to and at the end of the experiment, the animals were tested in the forced swim and open field tests. We measured ethanol intake and preference, immobility in the force swim test, and activity in the open field. We show that under no CMS, Drd2+/- and Drd2-/- mice had lower ethanol intake and preference compared with Drd2+/+. Exposure to CMS decreased ethanol intake and preference in Drd2+/+ and increased them in Drd2+/- and Drd2-/- mice. At baseline, Drd2+/- and Drd2-/- mice had significantly lower activity in the open field than Drd2+/+, whereas no genotype differences were observed in the forced swim test. Exposure to CMS increased immobility during the forced swim test in Drd2+/- mice, but not in Drd2+/+ or Drd2-/- mice, and ethanol intake reversed this behavior. No changes were observed in open field test measures. These findings suggest that in the presence of a stressful environment, low DRD2 levels are associated with increased ethanol intake and preference and that under this condition, increased ethanol consumption could be used as a strategy to alleviate negative mood. (PsycINFO Database Record (c) 2013 APA, all rights reserved).

Speaking under pressure: low linguistic complexity is linked to high physiological and emotional stress reactivity.

PubMed

Saslow, Laura R; McCoy, Shannon; van der Löwe, Ilmo; Cosley, Brandon; Vartan, Arbi; Oveis, Christopher; Keltner, Dacher; Moskowitz, Judith T; Epel, Elissa S

2014-03-01

What can a speech reveal about someone's state? We tested the idea that greater stress reactivity would relate to lower linguistic cognitive complexity while speaking. In Study 1, we tested whether heart rate and emotional stress reactivity to a stressful discussion would relate to lower linguistic complexity. In Studies 2 and 3, we tested whether a greater cortisol response to a standardized stressful task including a speech (Trier Social Stress Test) would be linked to speaking with less linguistic complexity during the task. We found evidence that measures of stress responsivity (emotional and physiological) and chronic stress are tied to variability in the cognitive complexity of speech. Taken together, these results provide evidence that our individual experiences of stress or "stress signatures"-how our body and mind react to stress both in the moment and over the longer term-are linked to how complex our speech under stress. Copyright © 2013 Society for Psychophysiological Research.

Dynamic and magneto-optic properties of bent-core liquid crystals

NASA Astrophysics Data System (ADS)

Salili, Seyyed Muhammad

In this work, we describe dynamic behavior of free-standing bent-core liquid crystal filaments under dilative and axial compressive stresses in the B7 phase. We found that such filaments demonstrate very complex structures depending on the filament's temperature relative to the isotropic phase, initial filament thickness, and velocity at which the filament is pulled or compressed. We also present our experimental methods, results and analysis of the rupture and recoil properties of several bent-core liquid crystal filaments, anticipating that they may serve as a model system for complex biological fibers. After that, we systematically describe rheological measurements for dimeric liquid crystal compounds. We studied the shear-induced alignment properties, measured the viscoelastic properties as a function of temperature, shear rate, stress and frequency, and compared the results with the rheological properties of conventional chiral nematic and smectic phases. Then we present results of chiral nematic liquid crystals composed of flexible dimer molecules subject to large DC magnetic fields between 0 and 31T. We observe that these fields lead to selective reflection of light depending on temperature and magnetic field. The band of reflected wavelengths can be tuned from ultraviolet to beyond the IR-C band. A similar effect induced by electric fields has been presented previously, and was explained by a field-induced oblique-heliconical director deformation in accordance with early theoretical predictions. Finally, we report an unprecedented magnetic field-induced shifts of the isotropic-nematic phase transition temperature observed in liquid crystal dimers where two rigid linear mesogens are linked by flexible chains of either even- or odd-numbered hydrocarbon groups. This effect is explained in terms of quenching of the thermal fluctuations and decrease of the average bend angle of molecules in the odd-numbered dimers.

Combined structural analysis and dating of authigenic/synkinematic illite: A step towards unravelling brittle faulting processes in time and space

NASA Astrophysics Data System (ADS)

Viola, Giulio

2017-04-01

Faulting accommodates momentous deformation and its style reflects the complex interplay of often transient processes such as friction, fluid flow and rheological changes within generally dilatant systems. Brittle faults are thus unique archives of the stress state and the physical and chemical conditions at the time of both initial strain localization and subsequent slip(s) during structural reactivation. Opening those archives, however, may be challenging due to the commonly convoluted (if not even chaotic) nature of brittle fault architectures and fault rocks. This is because, once formed, faults are extremely sensitive to variations in stress field and environmental conditions and are prone to readily slip in a variety of conditions, also in regions affected by only weak, far-field stresses. The detailed, multi-scalar structural analysis of faults and of fault rocks has to be the starting point for any study aiming at reconstructing the complex framework of brittle deformation. However, considering that present-day exposures of faults only represent the end result of the faults' often protracted and heterogeneous histories, the obtained structural and mechanical results have to be integrated over the life span of the studied fault system. Dating of synkinematic illite/muscovite to constrain the time-integrated evolution of faults is therefore the natural addition to detailed structural studies. By means of selected examples it will be demonstrated how careful structural analysis integrated with illite characterization and K-Ar dating allows the high-resolution reconstruction of brittle deformation histories and, in turn, multiple constraints to be placed on strain localization, deformation mechanisms, fluid flow, mineral alteration and authigenesis within actively deforming brittle fault rocks. Complex and long brittle histories can thus be reconstructed and untangled in any tectonic setting.

In situ stress magnitude and rock strength in the Nankai accretionary complex: a novel approach using paired constraints from downhole data in two wells

NASA Astrophysics Data System (ADS)

Huffman, K. A.; Saffer, D. M.; Dugan, B.

2016-07-01

We present a method to simultaneously constrain both far-field horizontal stress magnitudes ( S hmin and S Hmax) and in situ rock unconfined compressive strength (UCS), using geophysical logging data from two boreholes located 70 m apart that access the uppermost accretionary prism of the Nankai subduction zone . The boreholes sample the same sediments and are affected by the same tectonic stress field, but were drilled with different annular pressures, thus providing a unique opportunity to refine estimates of both in situ stress magnitudes and rock strength. We develop a forward model to predict the angular width of compressional wellbore failures (borehole breakouts), and identify combinations of S Hmax and UCS that best match breakout widths observed in resistivity images from the two boreholes. The method requires knowledge of S hmin, which is defined by leak-off tests conducted during drilling. Our results define a normal to strike-slip stress regime from 900 to 1386 m below seafloor, consistent with observations from seismic and core data. Our analysis also suggests that in situ values of UCS are generally slightly lower that commonly assumed on the basis of published empirical relations between UCS and P-wave velocity.

Speaking under pressure: Low linguistic complexity is linked to high physiological and emotional stress reactivity

PubMed Central

Saslow, Laura R.; McCoy, Shannon; van der Löwe, Ilmo; Cosley, Brandon; Vartan, Arbi; Oveis, Christopher; Keltner, Dacher; Moskowitz, Judith T.; Epel, Elissa S.

2014-01-01

What can a speech reveal about someone's state? We tested the idea that greater stress reactivity would relate to lower linguistic cognitive complexity while speaking. In Study 1, we tested whether heart rate and emotional stress reactivity to a stressful discussion would relate to lower linguistic complexity. In Studies 2 and 3 we tested whether a greater cortisol response to a standardized stressful task including a speech (Trier Social Stress Test) would be linked to speaking with less linguistic complexity during the task. We found evidence that measures of stress responsivity (emotional and physiological) and chronic stress are tied to variability in the cognitive complexity of speech. Taken together, these results provide evidence that our individual experiences of stress or ‘stress signatures’—how our body and mind react to stress both in the moment and over the longer term—are linked to how complexly we speak under stress. PMID:24354732

Dynamic rupture modeling of the transition from thrust to strike-slip motion in the 2002 Denali fault earthquake, Alaska

USGS Publications Warehouse

Aagaard, Brad T.; Anderson, G.; Hudnut, K.W.

2004-01-01

We use three-dimensional dynamic (spontaneous) rupture models to investigate the nearly simultaneous ruptures of the Susitna Glacier thrust fault and the Denali strike-slip fault. With the 1957 Mw 8.3 Gobi-Altay, Mongolia, earthquake as the only other well-documented case of significant, nearly simultaneous rupture of both thrust and strike-slip faults, this feature of the 2002 Denali fault earthquake provides a unique opportunity to investigate the mechanisms responsible for development of these large, complex events. We find that the geometry of the faults and the orientation of the regional stress field caused slip on the Susitna Glacier fault to load the Denali fault. Several different stress orientations with oblique right-lateral motion on the Susitna Glacier fault replicate the triggering of rupture on the Denali fault about 10 sec after the rupture nucleates on the Susitna Glacier fault. However, generating slip directions compatible with measured surface offsets and kinematic source inversions requires perturbing the stress orientation from that determined with focal mechanisms of regional events. Adjusting the vertical component of the principal stress tensor for the regional stress field so that it is more consistent with a mixture of strike-slip and reverse faulting significantly improves the fit of the slip-rake angles to the data. Rotating the maximum horizontal compressive stress direction westward appears to improve the fit even further.

Not a load of rubbish: simulated field trials in large-scale containers.

PubMed

Hohmann, M; Stahl, A; Rudloff, J; Wittkop, B; Snowdon, R J

2016-09-01

Assessment of yield performance under fluctuating environmental conditions is a major aim of crop breeders. Unfortunately, results from controlled-environment evaluations of complex agronomic traits rarely translate to field performance. A major cause is that crops grown over their complete lifecycle in a greenhouse or growth chamber are generally constricted in their root growth, which influences their response to important abiotic constraints like water or nutrient availability. To overcome this poor transferability, we established a plant growth system comprising large refuse containers (120 L 'wheelie bins') that allow detailed phenotyping of small field-crop populations under semi-controlled growth conditions. Diverse winter oilseed rape cultivars were grown at field densities throughout the crop lifecycle, in different experiments over 2 years, to compare seed yields from individual containers to plot yields from multi-environment field trials. We found that we were able to predict yields in the field with high accuracy from container-grown plants. The container system proved suitable for detailed studies of stress response physiology and performance in pre-breeding populations. Investment in automated large-container systems may help breeders improve field transferability of greenhouse experiments, enabling screening of pre-breeding materials for abiotic stress response traits with a positive influence on yield. © 2016 John Wiley & Sons Ltd.

Have You Been to the Shore Before? A Marine Education Infusion Unit on Seashore and Aquarium Life. Revised Edition.

ERIC Educational Resources Information Center

Butzow, John W.; And Others

Classroom and field activities for fifth- through ninth-grade students comprise this teaching guide for the northern New England shore. Teacher background information contains an introduction to life at the shore and the animal classification of marine invertebrates. Activities stress two major concepts: (1) the diversity and complex interactions…

Qualification Strategies of Field Programmable Gate Arrays (FPGAs) for Space Application

NASA Technical Reports Server (NTRS)

Sheldon, Douglas; Schone, Harald

2005-01-01

This viewgraph document reviews the issue of using Field Programmable Gate Arrays (FPGAs) in Space Application, and the some of the strategies for qualifying the FPGA. Qualification and risk management of such complex systems requires new approaches. The paper presents a matrix approach to qualification has been presented that: - Complements historical specifications - Highlights the importance of device physics as a cornerstone to qualification. - Provides levels of risk management that expressly document trade offs. - Stresses the role of the FPGA vendor as team member in the development of modern spacecraft.

Finite Element Modeling of In-Situ Stresses near Salt Bodies

NASA Astrophysics Data System (ADS)

Sanz, P.; Gray, G.; Albertz, M.

2011-12-01

The in-situ stress field is modified around salt bodies because salt rock has no ability to sustain shear stresses. A reliable prediction of stresses near salt is important for planning safe and economic drilling programs. A better understanding of in-situ stresses before drilling can be achieved using finite element models that account for the creeping salt behavior and the elastoplastic response of the surrounding sediments. Two different geomechanical modeling techniques can be distinguished: "dynamic" modeling and "static" modeling. "Dynamic" models, also known as forward models, simulate the development of structural processes in geologic time. This technique provides the evolution of stresses and so it is used to simulate the initiation and development of structural features, such as, faults, folds, fractures, and salt diapers. The original or initial configuration and the unknown final configuration of forward models are usually significantly different therefore geometric non-linearities need to be considered. These models may be difficult to constrain when different tectonic, deposition, and erosion events, and the timing among them, needs to be accounted for. While dynamic models provide insight into the stress evolution, in many cases is very challenging, if not impossible, to forward model a configuration to its known present-day geometry; particularly in the case of salt layers that evolve into highly irregular and complex geometries. Alternatively, "static" models use the present-day geometry and present-day far-field stresses to estimate the present-day in-situ stress field inside a domain. In this case, it is appropriate to use a small deformation approach because initial and final configurations should be very similar, and more important, because the equilibrium of stresses should be stated in the present-day initial configuration. The initial stresses and the applied boundary conditions are constrained by the geologic setting and available data. This modeling technique does not predict the evolution of structural elements or stresses with time; therefore it does not provide any insight into the formation of fractures that were previously developed under a different stress condition or the development of overpressure generated by a high sedimentation rate. This work provides a validation for predicting in-situ stresses near salt using "static" models. We compare synthetic examples using both modeling techniques and show that stresses near salt predicted with "static" models are comparable to the ones generated by "dynamic" models.

Deformation driven by subduction and microplate collision: Geodynamics of Cook Inlet basin, Alaska

USGS Publications Warehouse

Bruhn, R.L.; Haeussler, Peter J.

2006-01-01

Late Neogene and younger deformation in Cook Inlet basin is caused by dextral transpression in the plate margin of south-central Alaska. Collision and subduction of the Yakutat microplate at the northeastern end of the Aleutian subduction zone is driving the accretionary complex of the Chugach and Kenai Mountains toward the Alaska Range on the opposite side of the basin. This deformation creates belts of fault-cored anticlines that are prolific traps of hydrocarbons and are also potential sources for damaging earthquakes. The faults dip steeply, extend into the Mesozoic basement beneath the Tertiary basin fill, and form conjugate flower structures at some localities. Comparing the geometry of the natural faults and folds with analog models created in a sandbox deformation apparatus suggests that some of the faults accommodate significant dextral as well as reverse-slip motion. We develop a tectonic model in which dextral shearing and horizontal shortening of the basin is driven by microplate collision with an additional component of thrust-type strain caused by plate subduction. This model predicts temporally fluctuating stress fields that are coupled to the recurrence intervals of large-magnitude subduction zone earthquakes. The maximum principal compressive stress is oriented east-southeast to east-northeast with nearly vertical least compressive stress when the basin's lithosphere is mostly decoupled from the underlying subduction megathrust. This stress tensor is compatible with principal stresses inferred from focal mechanisms of earthquakes that occur within the crust beneath Cook Inlet basin. Locking of the megathrust between great magnitude earthquakes may cause the maximum principal compressive stress to rotate toward the northwest. Moderate dipping faults that strike north to northeast may be optimally oriented for rupture in the ambient stress field, but steeply dipping faults within the cores of some anticlines are unfavorably oriented with respect to both modeled and observed stress fields, suggesting that elevated fluid pressure may be required to trigger fault rupture. ?? 2006 Geological Society of America.

Force and Stress along Simulated Dissociation Pathways of Cucurbituril-Guest Systems.

PubMed

Velez-Vega, Camilo; Gilson, Michael K

2012-03-13

The field of host-guest chemistry provides computationally tractable yet informative model systems for biomolecular recognition. We applied molecular dynamics simulations to study the forces and mechanical stresses associated with forced dissociation of aqueous cucurbituril-guest complexes with high binding affinities. First, the unbinding transitions were modeled with constant velocity pulling (steered dynamics) and a soft spring constant, to model atomic force microscopy (AFM) experiments. The computed length-force profiles yield rupture forces in good agreement with available measurements. We also used steered dynamics with high spring constants to generate paths characterized by a tight control over the specified pulling distance; these paths were then equilibrated via umbrella sampling simulations and used to compute time-averaged mechanical stresses along the dissociation pathways. The stress calculations proved to be informative regarding the key interactions determining the length-force profiles and rupture forces. In particular, the unbinding transition of one complex is found to be a stepwise process, which is initially dominated by electrostatic interactions between the guest's ammoniums and the host's carbonyl groups, and subsequently limited by the extraction of the guest's bulky bicyclooctane moiety; the latter step requires some bond stretching at the cucurbituril's extraction portal. Conversely, the dissociation of a second complex with a more slender guest is mainly driven by successive electrostatic interactions between the different guest's ammoniums and the host's carbonyl groups. The calculations also provide information on the origins of thermodynamic irreversibilities in these forced dissociation processes.

A comparison of long-term changes in seismicity at The Geysers, Salton Sea, and Coso geothermal fields

NASA Astrophysics Data System (ADS)

Trugman, Daniel T.; Shearer, Peter M.; Borsa, Adrian A.; Fialko, Yuri

2016-01-01

Geothermal energy is an important source of renewable energy, yet its production is known to induce seismicity. Here we analyze seismicity at the three largest geothermal fields in California: The Geysers, Salton Sea, and Coso. We focus on resolving the temporal evolution of seismicity rates, which provides important observational constraints on how geothermal fields respond to natural and anthropogenic loading. We develop an iterative, regularized inversion procedure to partition the observed seismicity rate into two components: (1) the interaction rate due to earthquake-earthquake triggering and (2) the smoothly varying background rate controlled by other time-dependent stresses, including anthropogenic forcing. We apply our methodology to compare long-term changes in seismicity to monthly records of fluid injection and withdrawal. At The Geysers, we find that the background seismicity rate is highly correlated with fluid injection, with the mean rate increasing by approximately 50% and exhibiting strong seasonal fluctuations following construction of the Santa Rosa pipeline in 2003. In contrast, at both Salton Sea and Coso, the background seismicity rate has remained relatively stable since 1990, though both experience short-term rate fluctuations that are not obviously modulated by geothermal plant operation. We also observe significant temporal variations in Gutenberg-Richter b value, earthquake magnitude distribution, and earthquake depth distribution, providing further evidence for the dynamic evolution of stresses within these fields. The differing field-wide responses to fluid injection and withdrawal may reflect differences in in situ reservoir conditions and local tectonics, suggesting that a complex interplay of natural and anthropogenic stressing controls seismicity within California's geothermal fields.

The Role of the Rock on Hydraulic Fracturing of Tight Shales

NASA Astrophysics Data System (ADS)

Suarez-Rivera, R.; Green, S.; Stanchits, S.; Yang, Y.

2011-12-01

Successful economic production of oil and gas from nano-darcy-range permeability, tight shale reservoirs, is achieved via massive hydraulic fracturing. This is so despite their limited hydrocarbon in place, on per unit rock volume basis. As a reference, consider a typical average porosity of 6% and an average hydrocarbon saturation of 50% to 75%. The importance of tight shales results from their large areal extent and vertical thickness. For example, the areal extent of the Anwar field in Saudi Arabia of 3230 square miles (and 300 ft thick), while the Marcellus shale alone is over 100,000 square miles (and 70 to 150 ft thick). The low permeability of the rock matrix, the predominantly mineralized rock fabric, and the high capillary forces to both brines and hydrocarbons, restrict the mobility of pore fluids in these reservoirs. Thus, one anticipates that fluids do not move very far within tight shales. Successful production, therefore results from maximizing the surface area of contact with the reservoir by massive hydraulic fracturing from horizontal bore holes. This was the conceptual breakthrough of the previous decade and the one that triggered the emergence of gas shales, and recently oily shales, as important economic sources of energy. It is now understood that the process can be made substantially more efficient, more sustainable, and more cost effective by understanding the rock. This will be the breakthrough of this decade. Microseismic monitoring, mass balance calculations, and laboratory experiments of hydraulic fracturing on tight shales indicate the development of fracture complexity and fracture propagation that can not be explained in detail in this layered heterogeneous media. It is now clear that in tight shales the large-scale formation fabric is responsible for fracture complexity. For example, the presence and pervasiveness of mineralized fractures, bed interfaces, lithologic contacts, and other types of discontinuities, and their orientation in relation to the in-situ stresses, have a dominant role in promoting fracture branching and abrupt changes in direction. In general, the problem can be conceptualized as a competition between the effect of stresses (traditional mechanics of homogeneous media) and the effect of rock fabric (the mechanics of heterogeneous media). When the stress difference is low and the rock fabric pronounced, the rock fabric defines the direction of propagation. When the stress difference is high and the fabric is weak, the stress contrast dominates the process. In real systems, both effects compete and result in the complexity that we infer from indirect observations. In this paper we discuss the role of rock fabric on fracture complexity during hydraulic fracture propagation. We show that understanding the far field stresses is not enough to understand fracture propagation and complexity. Understanding the rock-specifically the larger-scale textural features that define the reservoir fabric-is fundamental to understand fracture complexity and fracture containment. We use laboratory experiments with acoustic emission localization to monitor fracturing and making inferences about the large-scale rock behavior. We also show that the fracture geometry, even for the same connected surface area, has significant well production and reservoir recovery implications.

Evolution of the stress field in the southern Scotia Arc from the late Mesozoic to the present-day

NASA Astrophysics Data System (ADS)

Maestro, Adolfo; López-Martínez, Jerónimo; Galindo-Zaldívar, Jesús; Bohoyo, Fernando; Mink, Sandra

2014-12-01

The geological evolution of the Scotia Arc, which developed between Antarctica and South America, has facilitated the connection between the Pacific and Atlantic oceans and, has important global implications. To improve the knowledge of the late Mesozoic evolution of the southern Scotia Arc, over 6000 brittle mesostructures were measured over the last 20 years at different outcrops from the northern Antarctic Peninsula and the South Shetland Islands as well as the James Ross and South Orkney archipelagos. This dataset covers a length of more than 1000 km of the arc. Fault data were analysed using the Etchecopar, y-R, Right Dihedra, Stress Inversion and Search Grid Inversion Palaeostress Determination methods. A total of 275 stress tensors were obtained. The results showed that the maximum horizontal stress was in the ENE-WSW and the NW-SE orientations and that the horizontal extension tensors were oriented NE-SW and NW-SE. In addition, seismic activity and focal mechanism solutions were analysed using the Gephart method to establish the present-day stress field and characterise the active tectonics. The results obtained suggest that there is a regional NE-SW compression and a NW-SE extension regime at the present day. The Southern Scotia Arc has a complex geological history due to the different tectonic settings (transform, convergent and divergent) that have affected this sector during its geological evolution from the late Mesozoic until the present day. Six stress fields were obtained from the brittle mesostructure population analysis in the region. The NW-SE and N-S maximum horizontal stresses were related to a combination of Mesozoic oceanic subduction of the former Phoenix Plate under the Pacific margin of the Antarctic Plate, Mesozoic-Cenozoic subduction of the northern Weddell Sea and the Oligocene to the Middle Miocene dextral strike-slip movement between the Scotia and Antarctic plates along the South Scotia Ridge. The NE-SW compression was related to late Miocene to present-day sinistral transcurrent movement along the South Scotia Ridge. Finally, the NW-SE extensional stress field may be related to the development of the following back-arc basins: the Late Cretaceous-Eocene Larsen Basin, the Lower to Middle Miocene Jane Basin and the Pliocene to present-day Bransfield Basin. In addition, the NE-SW and the E-W tensional stress fields were related to the Oligocene opening of the Powell Basin.

A mechanical model for complex fault patterns induced by fluid overpressures due to dehydration reaction within evaporitic rocks

NASA Astrophysics Data System (ADS)

de Paola, N.; Collettini, C.; Trippetta, F.; Barchi, M. R.; Minelli, G.

2006-12-01

Complex fault patterns, i.e. faults which exhibit a diverse range of strikes, may develop under a weak/absent regional tectonic field (e.g. polygonal faults). We studied a complex synsedimentary fault pattern, geometrically similar to polygonal fault systems, developed during an early Jurassic faulting episode and exposed in the Umbria-Marche Apennines (Italy). Along the passive margin of the African plate, these faults disrupt the Early Jurassic platform overlying the Triassic Evaporites, and bound the subsiding basins where a pelagic succession was successively deposited. We digitised the fault pattern at the regional scale on the grounds of the available geological maps, characterising each fault in terms of attitude, length and throw (i.e. vertical displacement). Fault statistical analysis shows a largely scattered orientation, a high grade of fragmentation, an average length of about 10 km and a constant length/displacement ratio. The measured stratigraphic throw ranges from 300 m to 700 m leading to very low long-term fault slip rates (less than 0.1 mm/yr). We propose a mechanical model where Jurassic faulting has been strongly influenced by the onset of dehydration of the Triassic Evaporites, made of interbedded gypsum layers and dolostones. Dehydration, i.e. anhydritization of the gypsum rich layers, initiated during burial at 1000 m of depth. During initial phases of dehydration increasing fluid pressures trapped at the gypsum-dolostones interface, promote hydrofracturing and faulting within the dolostone layers and subsequent fluid release. Fluid expulsion produces volume contraction of the dehydrating rocks causing vertical thinning and horizontal isotropic extension. This state of non-plane strain is accommodated within the composite gypsum-dolostones sequence by a mix of ductile (flowage and boudinage) and brittle (hydrofracturing and faulting) deformation processes. The stress field caused by the former processes, consistent with an almost isotropic stress distribution within the horizontal plane, explains well the studied complex fault pattern and seems to be dominant over the far-field regional extensional tectonics.

Superradiant Instability and Backreaction of Massive Vector Fields around Kerr Black Holes.

PubMed

East, William E; Pretorius, Frans

2017-07-28

We study the growth and saturation of the superradiant instability of a complex, massive vector (Proca) field as it extracts energy and angular momentum from a spinning black hole, using numerical solutions of the full Einstein-Proca equations. We concentrate on a rapidly spinning black hole (a=0.99) and the dominant m=1 azimuthal mode of the Proca field, with real and imaginary components of the field chosen to yield an axisymmetric stress-energy tensor and, hence, spacetime. We find that in excess of 9% of the black hole's mass can be transferred into the field. In all cases studied, the superradiant instability smoothly saturates when the black hole's horizon frequency decreases to match the frequency of the Proca cloud that spontaneously forms around the black hole.

RNA-Seq Transcriptome Profiling of Upland Cotton (Gossypium hirsutum L.) Root Tissue under Water-Deficit Stress

PubMed Central

Bowman, Megan J.; Park, Wonkeun; Bauer, Philip J.; Udall, Joshua A.; Page, Justin T.; Raney, Joshua; Scheffler, Brian E.; Jones, Don. C.; Campbell, B. Todd

2013-01-01

An RNA-Seq experiment was performed using field grown well-watered and naturally rain fed cotton plants to identify differentially expressed transcripts under water-deficit stress. Our work constitutes the first application of the newly published diploid D5 Gossypium raimondii sequence in the study of tetraploid AD1 upland cotton RNA-seq transcriptome analysis. A total of 1,530 transcripts were differentially expressed between well-watered and water-deficit stressed root tissues, in patterns that confirm the accuracy of this technique for future studies in cotton genomics. Additionally, putative sequence based genome localization of differentially expressed transcripts detected A2 genome specific gene expression under water-deficit stress. These data will facilitate efforts to understand the complex responses governing transcriptomic regulatory mechanisms and to identify candidate genes that may benefit applied plant breeding programs. PMID:24324815

Loss of 'complexity' and aging. Potential applications of fractals and chaos theory to senescence

NASA Technical Reports Server (NTRS)

Lipsitz, L. A.; Goldberger, A. L.

1992-01-01

The concept of "complexity," derived from the field of nonlinear dynamics, can be adapted to measure the output of physiologic processes that generate highly variable fluctuations resembling "chaos." We review data suggesting that physiologic aging is associated with a generalized loss of such complexity in the dynamics of healthy organ system function and hypothesize that such loss of complexity leads to an impaired ability to adapt to physiologic stress. This hypothesis is supported by observations showing an age-related loss of complex variability in multiple physiologic processes including cardiovascular control, pulsatile hormone release, and electroencephalographic potentials. If further research supports this hypothesis, measures of complexity based on chaos theory and the related geometric concept of fractals may provide new ways to monitor senescence and test the efficacy of specific interventions to modify the age-related decline in adaptive capacity.

In situ rock strength and far field stress in the Nankai accretionary complex: Integration of downhole data from multiple wells

NASA Astrophysics Data System (ADS)

Huffman, K. A.; Saffer, D. M.

2014-12-01

Knowing the magnitude of tectonic stress and rock strength at seismically active margins is important towards understanding fault strength and failure mechanics, yet both are difficult to measure in situ. Recent work at subduction margins, including Integrated Ocean Drilling Program (IODP) Nankai Trough Subduction Zone Experiment (NanTroSEIZE) drillsites, uses the width of compressional wellbore breakouts (BO), which depends on far field stress conditions, rock strength, and borehole annular pressure (APRS), to estimate the magnitude of horizontal principal stresses (SHmax and Shmin); estimates are problematic due to uncertainty in rock strength (unconfined compressive strength/UCS- for which direct measurements are scarce) and rheology that govern stress distribution at the wellbore. We conduct a novel case study at IODP Site C0002, where a hole was drilled twice with different boundary conditions, providing an opportunity to define in situ stress and strength from field data. Site C0002 is the main deep riser borehole for NanTroSEIZE, located near the seaward edge of the Kumano Basin above the seismogenic plate boundary, ~30 km from the trench. Several boreholes were drilled at the site. During IODP Expedition 314 in 2007, Hole C0002A was drilled with a suite of logging while drilling (LWD) tools to 1401 mbsf in a riserless mode. Hole C0002F, ~70 m away, was drilled to 862 mbsf in riserless mode during Exp. 326 in 2010 and deepened to 2005 mbsf in a riser mode during Expedition 338 in 2012-2013. Increased APRS achieved by riser drilling stabilizes the borehole and suppresses BO, consistent with resistivity imaging data from Exp. 314 that document well-developed, continuous BO throughout the borehole, and data from Expedition 338 indicating few BO. We use a semi-Newtonian approach to solve for stress and UCS consistent with the observed BO width and measured APRS in the two holes over the interval from 862-2005 mbsf. Effective SHmax ranges from ~10-30 MPa and indicate a strike-slip or thrust regime. Our results indicate UCS is higher than predicted by empirical relations and a small suite of laboratory tests by as much as 20 MPa. This apparent discrepancy may indicate that the failure criterion, or assumed distribution of stresses around the wellbore in analyses of far field stress, may not be appropriate in this setting.

Stress Genes and Proteins in the Archaea

PubMed Central

Macario, Alberto J. L.; Lange, Marianne; Ahring, Birgitte K.; De Macario, Everly Conway

1999-01-01

The field covered in this review is new; the first sequence of a gene encoding the molecular chaperone Hsp70 and the first description of a chaperonin in the archaea were reported in 1991. These findings boosted research in other areas beyond the archaea that were directly relevant to bacteria and eukaryotes, for example, stress gene regulation, the structure-function relationship of the chaperonin complex, protein-based molecular phylogeny of organisms and eukaryotic-cell organelles, molecular biology and biochemistry of life in extreme environments, and stress tolerance at the cellular and molecular levels. In the last 8 years, archaeal stress genes and proteins belonging to the families Hsp70, Hsp60 (chaperonins), Hsp40(DnaJ), and small heat-shock proteins (sHsp) have been studied. The hsp70(dnaK), hsp40(dnaJ), and grpE genes (the chaperone machine) have been sequenced in seven, four, and two species, respectively, but their expression has been examined in detail only in the mesophilic methanogen Methanosarcina mazei S-6. The proteins possess markers typical of bacterial homologs but none of the signatures distinctive of eukaryotes. In contrast, gene expression and transcription initiation signals and factors are of the eucaryal type, which suggests a hybrid archaeal-bacterial complexion for the Hsp70 system. Another remarkable feature is that several archaeal species in different phylogenetic branches do not have the gene hsp70(dnaK), an evolutionary puzzle that raises the important question of what replaces the product of this gene, Hsp70(DnaK), in protein biogenesis and refolding and for stress resistance. Although archaea are prokaryotes like bacteria, their Hsp60 (chaperonin) family is of type (group) II, similar to that of the eukaryotic cytosol; however, unlike the latter, which has several different members, the archaeal chaperonin system usually includes only two (in some species one and in others possibly three) related subunits of ∼60 kDa. These form, in various combinations depending on the species, a large structure or chaperonin complex sometimes called the thermosome. This multimolecular assembly is similar to the bacterial chaperonin complex GroEL/S, but it is made of only the large, double-ring oligomers each with eight (or nine) subunits instead of seven as in the bacterial complex. Like Hsp70(DnaK), the archaeal chaperonin subunits are remarkable for their evolution, but for a different reason. Ubiquitous among archaea, the chaperonins show a pattern of recurrent gene duplication—hetero-oligomeric chaperonin complexes appear to have evolved several times independently. The stress response and stress tolerance in the archaea involve chaperones, chaperonins, other heat shock (stress) proteins including sHsp, thermoprotectants, the proteasome, as yet incompletely understood thermoresistant features of many molecules, and formation of multicellular structures. The latter structures include single- and mixed-species (bacterial-archaeal) types. Many questions remain unanswered, and the field offers extraordinary opportunities owing to the diversity, genetic makeup, and phylogenetic position of archaea and the variety of ecosystems they inhabit. Specific aspects that deserve investigation are elucidation of the mechanism of action of the chaperonin complex at different temperatures, identification of the partners and substitutes for the Hsp70 chaperone machine, analysis of protein folding and refolding in hyperthermophiles, and determination of the molecular mechanisms involved in stress gene regulation in archaeal species that thrive under widely different conditions (temperature, pH, osmolarity, and barometric pressure). These studies are now possible with uni- and multicellular archaeal models and are relevant to various areas of basic and applied research, including exploration and conquest of ecosystems inhospitable to humans and many mammals and plants. PMID:10585970

Effects of larvicidal and larval nutritional stresses on Anopheles gambiae development, survival and competence for Plasmodium falciparum.

PubMed

Vantaux, Amélie; Ouattarra, Issiaka; Lefèvre, Thierry; Dabiré, Kounbobr Roch

2016-04-23

Many studies have shown that the environment in which larvae develop can influence adult characteristics with consequences for the transmission of pathogens. We investigated how two environmental stresses (larviciding and nutritional stress) interact to affect Anopheles gambiae (previously An. gambiae S molecular form) life history traits and its susceptibility for field isolates of its natural malaria agent Plasmodium falciparum. Larvae were reared in the presence or not of a sub-lethal concentration of larvicide and under a high and low food regimen. Development time, individual size, adult survival and competence for P. falciparum were assessed. Individuals under low food regimen took more time to develop, had a lower development success and were smaller while there was no main effect of larvicide exposure on these traits. However, larvicide exposure impacted individual size in interaction with nutritional stress. Female survival was affected by the interaction between gametocytemia, parasite exposure and larval diet, as well as the interaction between gametocytemia, parasite exposure and larvicidal stress, and the interaction between gametocytemia, larvicidal exposure and larval diet. Among the 951 females dissected 7 days post-infection, 559 (58.78%) harboured parasites. Parasite prevalence was significantly affected by the interaction between larvicidal stress and larval diet. Indeed, females under low food regimen had a higher prevalence than females under high food regimen and this difference was greater under larvicidal stress. The two stresses did not impact parasite intensity. We found that larval nutritional and larvicidal stresses affect mosquito life history traits in complex ways, which could greatly affect P. falciparum transmission. Further studies combining field-based trials on larvicide use and mosquito experimental infections would give a more accurate understanding of the effects of this vector control tool on malaria transmission.

Repeated stressor exposure enhances contextual fear memory in a beta-adrenergic receptor-dependent process and increases impulsivity in a non-beta receptor-dependent fashion.

PubMed

Camp, Robert M; Johnson, John D

2015-10-15

Memory formation is promoted by stress via the release of norepinephrine and stimulation of beta-adrenergic receptors (β-ARs). Previous data demonstrate that repeated stressor exposure increases norepinephrine turnover and β-AR signaling within the amygdala, which led to the hypothesis that some stress-induced behavioral changes are likely due to facilitated associative learning. To test this, Fischer rats were exposed to chronic mild stress for four days. On day 5, subjects (including non-stressed controls) were injected with the beta-blocker propranolol or vehicle prior to conditioning in an operant box (animals receive two mild foot shocks) or passive avoidance apparatus (animals received a foot shock upon entry into the dark chamber). Twenty-four hours later, subjects were returned to the operant box for measurement of freezing or returned to the passive avoidance apparatus for measurement of latency to enter the dark chamber. Subjects were also tested in an open field to assess context-independent anxiety-like behavior. Animals exposed to chronic stress showed significantly more freezing behavior in the operant box than did controls, and this exaggerated freezing was blocked by propranolol during the conditioning trial. There was no effect of stress on behavior in the open field. Unexpectedly, retention latency was significantly reduced in subjects exposed to chronic stress. These results indicate that chronic exposure to stress results in complex behavioral changes. While repeated stress appears to enhance the formation of fearful memories, it also results in behavioral responses that resemble impulsive behaviors that result in poor decision-making. Copyright © 2015 Elsevier Inc. All rights reserved.

Dynamics and Instabilities of Acoustically Stressed Interfaces

NASA Astrophysics Data System (ADS)

Shi, William Tao

An intense sound field exerts acoustic radiation pressure on a transitional layer between two continuous fluid media, leading to the unconventional dynamical behavior of the interface in the presence of the sound field. An understanding of this behavior has applications in the study of drop dynamics and surface rheology. Acoustic fields have also been utilized in the generation of interfacial instability, which may further encourage the dispersion or coalescence of liquids. Therefore, the study of the dynamics of the acoustically stressed interfaces is essential to infer the mechanism of the various phenomena related to interfacial dynamics and to acquire the properties of liquid surfaces. This thesis studies the dynamics of acoustically stressed interfaces through a theoretical model of surface interactions on both closed and open interfaces. Accordingly, a boundary integral method is developed to simulate the motions of a stressed interface. The method has been employed to determine the deformation, oscillation and instability of acoustically levitated drops. The generalized computations are found to be in good agreement with available experimental results. The linearized theory is also derived to predict the instability threshold of the flat interface, and is then compared with experiments conducted to observe and measure the unstable motions of the horizontal interface. This thesis is devoted to describing and classifying the simplest mechanisms by which acoustic fields provide a surface interaction with a fluid. A physical picture of the competing processes introduced by the evolution of an interface in a sound field is presented. The development of an initial small perturbation into a sharp form is observed on either a drop surface or a horizontal interface, indicating a strong focusing of acoustic energy at certain spots of the interface. Emphasis is placed on understanding the basic coupling mechanisms, rather than on particular applications that may involve this coupling. The dynamical behavior of a stressed drop can be determined in terms of a given form of an incident sound field and three dimensionless quantities. Thus, the behavior of a complex dynamic system has been clarified, permitting the exploration and interpretation of the nature of liquid surface phenomena.

Insights on surface spalling of rock

NASA Astrophysics Data System (ADS)

Tarokh, Ali; Kao, Chu-Shu; Fakhimi, Ali; Labuz, Joseph F.

2016-07-01

Surface spalling is a complex failure phenomenon that features crack propagation and detachment of thin pieces of rock near free surfaces, particularly in brittle rock around underground excavations when large in situ stresses are involved. A surface instability apparatus was used to study failure of rock close to a free surface, and damage evolution was monitored by digital image correlation (DIC). Lateral displacement at the free face was used as the feedback signal to control the post-peak response of the specimen. DIC was implemented in order to obtain the incremental displacement fields during the spalling process. Displacement fields were computed in the early stage of loading as well as close to the peak stress. Fracture from the spalling phenomenon was revealed by incremental lateral displacement contours. The axial and lateral displacements suggested that the displacement gradient was uniform in both directions at early loading stages and as the load increased, the free-face effect started to influence the displacements, especially the lateral displacement field. A numerical approach, based on the discrete element method, was developed and validated from element testing. Damage evolution and localization observed in numerical simulations were similar to those observed in experiments. By performing simulations in two- and three-dimensions, it was revealed that the intermediate principal stress and platen-rock interfaces have important effects on simulation of surface spalling.

Psychological safety: The key to high performance in high stress, potentially traumatic environments

Treesearch

James Saveland

2011-01-01

Safety is typically talked about in a context of the absence of injury. The field of resilience engineering has been advocating that we think about safety differently, by taking a systems view and begin to see how people create safety in unsafe systems by managing risk. There is growing recognition that safety is an emergent behavior of our complex system of human...

Epitaxial growth of mosaic diamond: Mapping of stress and defects in crystal junction with a confocal Raman spectroscopy

NASA Astrophysics Data System (ADS)

Shu, Guoyang; Dai, Bing; Ralchenko, V. G.; Khomich, A. A.; Ashkinazi, E. E.; Bolshakov, A. P.; Bokova-Sirosh, S. N.; Liu, Kang; Zhao, Jiwen; Han, Jiecai; Zhu, Jiaqi

2017-04-01

We studied defects and stress distributions in mosaic epitaxial diamond film using a confocal Raman spectroscopy, with a special attention to the junction area between the crystals. The mosaics was grown by microwave plasma CVD on closely arranged (1 0 0)-oriented HPHT type Ib substrates. The width of stress affected and defect enriched region around the junction show a tendency of extending with the film thickness, from ≈40 μm on the film-substrate interface to ≈250 μm in the layer 500 μm above the substrate, as found from the mosaics analysis in cross-section. The stress field around the junction demonstrates a complex pattern, with mixed domains of tensile and compressive stress, with maximum value of σ ≈ 0.6 GPa. A similar non-uniform pattern was observed for defect distribution as well. No sign of amorphous sp2 carbon in the junction zone was revealed.

Fault geometries in basement-induced wrench faulting under different initial stress states

NASA Astrophysics Data System (ADS)

Naylor, M. A.; Mandl, G.; Supesteijn, C. H. K.

Scaled sandbox experiments were used to generate models for relative ages, dip, strike and three-dimensional shape of faults in basement-controlled wrench faulting. The basic fault sequence runs from early en échelon Riedel shears and splay faults through 'lower-angle' shears to P shears. The Riedel shears are concave upwards and define a tulip structure in cross-section. In three dimensions, each Riedel shear has a helicoidal form. The sequence of faults and three-dimensional geometry are rationalized in terms of the prevailing stress field and Coulomb-Mohr theory of shear failure. The stress state in the sedimentary overburden before wrenching begins has a substantial influence on the fault geometries and on the final complexity of the fault zone. With the maximum compressive stress (∂ 1) initially parallel to the basement fault (transtension), Riedel shears are only slightly en échelon, sub-parallel to the basement fault, steeply dipping with a reduced helicoidal aspect. Conversely, with ∂ 1 initially perpendicular to the basement fault (transpression), Riedel shears are strongly oblique to the basement fault strike, have lower dips and an exaggerated helicoidal form; the final fault zone is both wide and complex. We find good agreement between the models and both mechanical theory and natural examples of wrench faulting.

Equivalent circuit model of converse magnetoelectric effect for the tri-layer magnetoelectric laminates with thermal and stress loadings

NASA Astrophysics Data System (ADS)

Zhou, Hao-Miao; Li, Meng-Han; Liu, Hui; Cui, Xiao-Le

2015-12-01

For the converse magnetoelectric coupling effect of the piezoelectric/magnetostrictive/piezoelectric tri-layer symmetric magnetoelectric laminates, based on the nonlinear thermo-magneto-mechanical constitutive equations of the giant magnetostrictive materials and the thermo-electro-mechanical constitutive equations of the piezoelectric materials, according to Newton's second law and the magnetic circuit theorem, an equivalent circuit is established. Then an expression of the converse magnetoelectric coefficient describing nonlinear thermo-magneto-electro-mechanical coupling is established. The curve of the nonlinear converse magnetoelectric coefficient versus the bias magnetic field, is predicted effectively by the expression, and the predictions are in good agreement with the experimental result both qualitatively and quantitatively. Furthermore, the model can predict the complex influences of the bias magnetic field, the stress and the ambient temperature on the converse magnetoelectric coefficient. It can be found from these predictions that the converse magnetoelectric coefficient decreases with the increasing temperature and increases with the increasing tensile stress. Under the common effect of the ambient temperature and the stress, it is also found that the converse magnetoelectric coefficient changes sharply with the ambient temperature when the tensile stress is applied on the laminates, but it has a good stability of temperature when a large compressive stress is applied. Therefore, this work contributes to the researches on the giant converse magnetoelectric coefficient and the designs of magnetoelectric devices based on the converse magnetoelectric coupling.

Electrorheological fluid with an extraordinarily high yield stress

NASA Astrophysics Data System (ADS)

Zhang, Yuling; Lu, Kunquan; Rao, Guanghui; Tian, Yu; Zhang, Shaohua; Liang, Jingkui

2002-02-01

Surface modified complex strontium titanate microparticles are synthesized by means of a modified sol-gel technique. A suspension composed of these particles immersed in a silicone oil exhibits excellent electrorheological properties attractive to industry and technology applications: a yield stress as high as 27 kPa in an applied electric field of 3 kV/mm, a low leakage current, wide dynamic ranges in temperature and shear rate, and a long-term stability against sedimentation. In addition to the high dielectric constant of strontium titanate, surfactant and water-free character of the particles may be responsible for the dramatic improvement of the electrorheological properties of the suspension.

Thermomechanical and Environmental Durability of Environmental Barrier Coated Ceramic Matrix Composites Under Thermal Gradients

NASA Technical Reports Server (NTRS)

Zhu, Dongming; Bhatt, Ramakrishna T.; Harder, Bryan

2016-01-01

This paper presents the developments of thermo-mechanical testing approaches and durability performance of environmental barrier coatings (EBCs) and EBC coated SiCSiC ceramic matrix composites (CMCs). Critical testing aspects of the CMCs will be described, including state of the art instrumentations such as temperature, thermal gradient, and full field strain measurements; materials thermal conductivity evolutions and thermal stress resistance; NDE methods; thermo-mechanical stress and environment interactions associated damage accumulations. Examples are also given for testing ceramic matrix composite sub-elements and small airfoils to help better understand the critical and complex CMC and EBC properties in engine relevant testing environments.

Characterization of stress-induced suppression of long-term potentiation in the hippocampal CA1 field of freely moving rats.

PubMed

Hirata, Riki; Togashi, Hiroko; Matsumoto, Machiko; Yamaguchi, Taku; Izumi, Takeshi; Yoshioka, Mitsuhiro

2008-08-21

Several lines of evidence have shown that exposure to stress impairs long-term potentiation (LTP) in the CA1 field of the hippocampus, but the detailed mechanisms for this effect remain to be clarified. The present study elucidated the synaptic mechanism of stress-induced LTP suppression in conscious, freely moving rats using electrophysiological approaches. Open field stress (i.e., novel environment stress) and elevated platform stress (i.e., uncontrollable stress) were employed. Basal synaptic transmission was significantly reduced during exposure to elevated platform stress but not during exposure to open field stress. LTP induction was blocked by elevated platform stress but not influenced by open field stress. Significant increases in serum corticosterone levels were observed in the elevated platform stress group compared with the open field stress group. Furthermore, LTP suppression induced by elevated platform stress was prevented by pretreatment with an anxiolytic drug diazepam (1 mg/kg, i.p.). These results suggest that stress-induced LTP suppression depends on the relative intensity of the stressor. The inhibitory synaptic response induced by an intense psychological stress, such as elevated platform stress, may be attributable to LTP impairment in the CA1 field of the hippocampus.

Present-day stress field in subduction zones: Insights from 3D viscoelastic models and data

NASA Astrophysics Data System (ADS)

Petricca, Patrizio; Carminati, Eugenio

2016-01-01

3D viscoelastic FE models were performed to investigate the impact of geometry and kinematics on the lithospheric stress in convergent margins. Generic geometries were designed in order to resemble natural subduction. Our model predictions mirror the results of previous 2D models concerning the effects of lithosphere-mantle relative flow on stress regimes, and allow a better understanding of the lateral variability of the stress field. In particular, in both upper and lower plates, stress axes orientations depend on the adopted geometry and axes rotations occur following the trench shape. Generally stress axes are oriented perpendicular or parallel to the trench, with the exception of the slab lateral tips where rotations occur. Overall compression results in the upper plate when convergence rate is faster than mantle flow rate, suggesting a major role for convergence. In the slab, along-strike tension occurs at intermediate and deeper depths (> 100 km) in case of mantle flow sustaining the sinking lithosphere and slab convex geometry facing mantle flow or in case of opposing mantle flow and slab concave geometry facing mantle flow. Along-strike compression is predicted in case of sustaining mantle flow and concave slabs or in case of opposing mantle flow and convex slabs. The slab stress field is thus controlled by the direction of impact of mantle flow onto the slab and by slab longitudinal curvature. Slab pull produces not only tension in the bending region of subducted plate but also compression where upper and lower plates are coupled. A qualitative comparison between results and data in selected subductions indicates good match for South America, Mariana and Tonga-Kermadec subductions. Discrepancies, as for Sumatra-Java, emerge due to missing geometric (e.g., occurrence of fault systems and local changes in the orientation of plate boundaries) and rheological (e.g., plasticity associated with slab bending, anisotropy) complexities in the models.

Predicting Coral Recruitment in Palau’s Complex Reef Archipelago

PubMed Central

Golbuu, Yimnang; Wolanski, Eric; Idechong, Jacques Wasai; Victor, Steven; Isechal, Adelle Lukes; Oldiais, Noelle Wenty; Idip, David; Richmond, Robert H.; van Woesik, Robert

2012-01-01

Reproduction and recruitment are key processes that replenish marine populations. Here we use the Palau archipelago, in the western Pacific Ocean, as a case study to examine scales of connectivity and to determine whether an oceanographic model, incorporating the complex reef architecture, is a useful predictor of coral recruitment. We tested the hypothesis that the reefs with the highest retention also had the highest densities of juvenile coral density from 80 field sites. Field comparisons showed a significant correlation between the densities of juvenile Acropora colonies and total larval recruitment derived from the model (i.e., calculated as the sum of the densities of larvae that self-seeded and recruited from the other reefs in the archipelago). Long-distance larval imports may be too infrequent to sustain coral populations, but are critical for recovery in times of extreme local stress. PMID:23209842

Aquatic ecotoxicology: from the ecosystem to the cellular and molecular levels.

PubMed Central

Boudou, A; Ribeyre, F

1997-01-01

This review of aquatic ecotoxicology is presented in three parts. First, we discuss the fundamental concepts and stress the importance of its ecological basis and the complexity and diversity of the field of investigation, which result from actions and interactions between the physicochemical characteristics of the biotopes, the structural and functional properties of the living organisms, and the contamination modalities. Ecotoxicological mechanisms, regardless of the level of biological complexity, primarily depend on the bioavailability of the toxic products. Numerous processes control the chemical fate of contaminants in the water column and/or sediment compartments; accessibility to the biological barriers that separate the organisms from their surrounding medium depends directly on bioavailability. Second, we review the principal methodologies of the field, from in situ studies at the ecosystem/ecocomplex level to bioassays or single species tests. Third, we focus on mercury, selected as a reference contaminant, in order to illustrate the main ecotoxicological concepts, the complementarity between field and laboratory studies, and the indispensable multidisciplinarity of the approaches. PMID:9114275

Electrically induced microflows probed by fluorescence correlation spectroscopy.

PubMed

Ybert, C; Nadal, F; Salomé, R; Argoul, F; Bourdieu, L

2005-03-01

We report on the experimental characterisation of electrically induced flows at the micrometer scale through Fluorescence Correlation Spectroscopy (FCS) measurements. We stress the potential of FCS as a useful characterisation technique in microfluidics devices for transport properties cartography. The experimental results obtained in a model situation are in agreement with previous calculations (F. Nadal, F. Argoul, P. Kestener, B. Pouligny, C. Ybert, A. Ajdari, Eur. Phys. J. E 9, 387 (2002)) predicting the structure and electric-field dependency of the induced flow. Additionally, the present study evidences a complex behaviour of the probe nanobeads under electric field whose precise understanding might prove relevant for situations where nano-objects interact with an external electric field.

Acute stress influences the discrimination of complex scenes and complex faces in young healthy men.

PubMed

Paul, M; Lech, R K; Scheil, J; Dierolf, A M; Suchan, B; Wolf, O T

2016-04-01

The stress-induced release of glucocorticoids has been demonstrated to influence hippocampal functions via the modulation of specific receptors. At the behavioral level stress is known to influence hippocampus dependent long-term memory. In recent years, studies have consistently associated the hippocampus with the non-mnemonic perception of scenes, while adjacent regions in the medial temporal lobe were associated with the perception of objects, and faces. So far it is not known whether and how stress influences non-mnemonic perceptual processes. In a behavioral study, fifty male participants were subjected either to the stressful socially evaluated cold-pressor test or to a non-stressful control procedure, before they completed a visual discrimination task, comprising scenes and faces. The complexity of the face and scene stimuli was manipulated in easy and difficult conditions. A significant three way interaction between stress, stimulus type and complexity was found. Stressed participants tended to commit more errors in the complex scenes condition. For complex faces a descriptive tendency in the opposite direction (fewer errors under stress) was observed. As a result the difference between the number of errors for scenes and errors for faces was significantly larger in the stress group. These results indicate that, beyond the effects of stress on long-term memory, stress influences the discrimination of spatial information, especially when the perception is characterized by a high complexity. Copyright © 2016 Elsevier Ltd. All rights reserved.

Interface Propagation and Microstructure Evolution in Phase Field Models of Stress-Induced Martensitic Phase Transformations

DTIC Science & Technology

2010-01-01

ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi 3s1 ÿ s2 2b s x: ð8Þ Note that Eqs. (7) and (8) are nonlinear diffusion equations, and as such possess solitonic ...ðDGh ¼ 0Þ is approached, an Mÿ—Mþ interface splits into Mÿ—A and A—Mþ diffuse interfaces sepa- rated by a layer of A ( soliton splitting – Falk, 1983...in the bottom figure for g1, the dark blue field corresponds to g2 ¼ 1, i.e., with the variant M2. After passing through a complex microstructure

Successful new anti-sloughing drilling fluid application, Yanchang gas field, China

NASA Astrophysics Data System (ADS)

He, Peng; Liu, Hanmei; Du, Sen; He, Chenghai

2017-10-01

Borehole collapse had always been encountered when drilling the Shiqianfeng and Shihezi formations in Yan Chang gas field. By analyzing the reasons for the collapse can be obtained, "double layer of stone" brittle strong, pore development, water sensitivity and high mineral content filling skeleton particles, water lock effect and stress sensitivity is a potential factor in inducing strong wall collapse. According to the characteristics of the geological structure developed anti-sloughing drilling fluid system "double layer of stone," "complex fluid loss - dual inhibition - materialized block" multiple cooperative mechanism to achieve the purpose of anti-collapse.

Sensor for Boundary Shear Stress in Fluid Flow

NASA Technical Reports Server (NTRS)

Bao, Xiaoqi; Badescu, Mircea; Sherrit, Stewart; Bar-Cohen, Yoseph; Lih, Shyh-Shiuh; Chang, Zensheu; Trease, Brian P.; Kerenyi, Kornel; Widholm, Scott E.; Ostlund, Patrick N.

2012-01-01

The formation of scour patterns at bridge piers is driven by the forces at the boundary of the water flow. In most experimental scour studies, indirect processes have been applied to estimate the shear stress using measured velocity profiles. The estimations are based on theoretical models and associated assumptions. However, the turbulence flow fields and boundary layer in the pier-scour region are very complex and lead to low-fidelity results. In addition, available turbulence models cannot account accurately for the bed roughness effect. Direct measurement of the boundary shear stress, normal stress, and their fluctuations are attractive alternatives. However, most direct-measurement shear sensors are bulky in size or not compatible to fluid flow. A sensor has been developed that consists of a floating plate with folded beam support and an optical grid on the back, combined with a high-resolution optical position probe. The folded beam support makes the floating plate more flexible in the sensing direction within a small footprint, while maintaining high stiffness in the other directions. The floating plate converts the shear force to displacement, and the optical probe detects the plate s position with nanometer resolution by sensing the pattern of the diffraction field of the grid through a glass window. This configuration makes the sensor compatible with liquid flow applications.

Methodology and evaluation of intracranial pressure response in rats exposed to complex shock waves.

PubMed

Dal Cengio Leonardi, Alessandra; Keane, Nickolas J; Hay, Kathryn; Ryan, Anne G; Bir, Cynthia A; VandeVord, Pamela J

2013-12-01

Studies on blast neurotrauma have focused on investigating the effects of exposure to free-field blast representing the simplest form of blast threat scenario without considering any reflecting surfaces. However, in reality personnel are often located within enclosures or nearby reflecting walls causing a complex blast environment, that is, involving shock reflections and/or compound waves from different directions. The purpose of this study was to design a complex wave testing system and perform a preliminary investigation of the intracranial pressure (ICP) response of rats exposed to a complex blast wave environment (CBWE). The effects of head orientation in the same environment were also explored. Furthermore, since it is hypothesized that exposure to a CBWE would be more injurious as compared to a free-field blast wave environment (FFBWE), a histological comparison of hippocampal injury (cleaved caspase-3 and glial fibrillary acidic protein (GFAP)) was conducted in both environments. Results demonstrated that, regardless of orientation, peak ICP values were significantly elevated over the peak static air overpressure. Qualitative differences could be noticed compared to the ICP response in rats exposed to simulated FFBWE. In the CBWE scenario, after the initial loading the skull/brain system was not allowed to return to rest and was loaded again reaching high ICP values. Furthermore, results indicated consistent and distinct ICP-time profiles according to orientation, as well as distinctive values of impulse associated with each orientation. Histologically, cleaved caspase-3 positive cells were significantly increased in the CBWE as compared to the FFBWE. Overall, these findings suggest that the geometry of the skull and the way sutures are distributed in the rats are responsible for the difference in the stresses observed. Moreover, this increase stress contributes to correlation of increased injury in the CBWE.

Aspects of Complexity in Sleep Analysis

NASA Astrophysics Data System (ADS)

Leitão, José M. N.; Da Rosa, Agostinho C.

The paper presents a selection of sleep analysis problems where some aspects and concepts of complexity come about. Emphasis is given to the electroencephalogram (EEG) as the most important sleep related variable. The conception of the EEG as a message to be deciphered stresses the importance of the communication and information theories in this field. An optimal detector of K complexes and vertex sharp waves based on a stochastic model of sleep EEG is considered. Besides detecting, the algorithm is also able to follow the evolution of the basic ongoing activity. It is shown that both the ostructure and microstructure of sleep can be described in terms of symbols and interpreted as sentences of a language. Syntactic models and Markov chain representations play in this context an important role.

An in vitro experimental study of flow past aortic valve under varied pulsatile conditions

NASA Astrophysics Data System (ADS)

Zhang, Ruihang; Zhang, Yan

2017-11-01

Flow past aortic valve represents a complex fluid-structure interaction phenomenon that involves pulsatile, vortical, and turbulent conditions. The flow characteristics immediately downstream of the valve, such as the variation of pulsatile flow velocity, formation of vortices, distribution of shear stresses, are of particular interest to further elucidate the role of hemodynamics in various aortic diseases. However, the fluid dynamics of a realistic aortic valve is not fully understood. Particularly, it is unclear how the flow fields downstream of the aortic valve would change under varied pulsatile inlet boundary conditions. In this study, an in vitro experiment has been conducted to investigate the flow fields downstream of a silicone aortic valve model within a cardiovascular flow simulator. Phased-locked Particle Image Velocimetry measurements were performed to map the velocity fields and Reynolds normal and shear stresses at different phases in a cardiac cycle. Temporal variations of pressure across the valve model were measured using high frequency transducers. Results have been compared for different pulsatile inlet conditions, including varied frequencies (heart rates), magnitudes (stroke volumes), and cardiac contractile functions (shapes of waveforms).

Small strain multiphase-field model accounting for configurational forces and mechanical jump conditions

NASA Astrophysics Data System (ADS)

Schneider, Daniel; Schoof, Ephraim; Tschukin, Oleg; Reiter, Andreas; Herrmann, Christoph; Schwab, Felix; Selzer, Michael; Nestler, Britta

2018-03-01

Computational models based on the phase-field method have become an essential tool in material science and physics in order to investigate materials with complex microstructures. The models typically operate on a mesoscopic length scale resolving structural changes of the material and provide valuable information about the evolution of microstructures and mechanical property relations. For many interesting and important phenomena, such as martensitic phase transformation, mechanical driving forces play an important role in the evolution of microstructures. In order to investigate such physical processes, an accurate calculation of the stresses and the strain energy in the transition region is indispensable. We recall a multiphase-field elasticity model based on the force balance and the Hadamard jump condition at the interface. We show the quantitative characteristics of the model by comparing the stresses, strains and configurational forces with theoretical predictions in two-phase cases and with results from sharp interface calculations in a multiphase case. As an application, we choose the martensitic phase transformation process in multigrain systems and demonstrate the influence of the local homogenization scheme within the transition regions on the resulting microstructures.

Systematic identification of genes involved in metabolic acid stress resistance in yeast and their potential as cancer targets.

PubMed

Shin, John J; Aftab, Qurratulain; Austin, Pamela; McQueen, Jennifer A; Poon, Tak; Li, Shu Chen; Young, Barry P; Roskelley, Calvin D; Loewen, Christopher J R

2016-09-01

A hallmark of all primary and metastatic tumours is their high rate of glucose uptake and glycolysis. A consequence of the glycolytic phenotype is the accumulation of metabolic acid; hence, tumour cells experience considerable intracellular acid stress. To compensate, tumour cells upregulate acid pumps, which expel the metabolic acid into the surrounding tumour environment, resulting in alkalization of intracellular pH and acidification of the tumour microenvironment. Nevertheless, we have only a limited understanding of the consequences of altered intracellular pH on cell physiology, or of the genes and pathways that respond to metabolic acid stress. We have used yeast as a genetic model for metabolic acid stress with the rationale that the metabolic changes that occur in cancer that lead to intracellular acid stress are likely fundamental. Using a quantitative systems biology approach we identified 129 genes required for optimal growth under conditions of metabolic acid stress. We identified six highly conserved protein complexes with functions related to oxidative phosphorylation (mitochondrial respiratory chain complex III and IV), mitochondrial tRNA biosynthesis [glutamyl-tRNA(Gln) amidotransferase complex], histone methylation (Set1C-COMPASS), lysosome biogenesis (AP-3 adapter complex), and mRNA processing and P-body formation (PAN complex). We tested roles for two of these, AP-3 adapter complex and PAN deadenylase complex, in resistance to acid stress using a myeloid leukaemia-derived human cell line that we determined to be acid stress resistant. Loss of either complex inhibited growth of Hap1 cells at neutral pH and caused sensitivity to acid stress, indicating that AP-3 and PAN complexes are promising new targets in the treatment of cancer. Additionally, our data suggests that tumours may be genetically sensitized to acid stress and hence susceptible to acid stress-directed therapies, as many tumours accumulate mutations in mitochondrial respiratory chain complexes required for their proliferation. © 2016. Published by The Company of Biologists Ltd.

On factors controlling precursor slip fronts in the laboratory and their relation to slow slip events in nature

NASA Astrophysics Data System (ADS)

Selvadurai, Paul A.; Glaser, Steven D.; Parker, Jessica M.

2017-03-01

Spatial variations in frictional properties on natural faults are believed to be a factor influencing the presence of slow slip events (SSEs). This effect was tested on a laboratory frictional interface between two polymethyl methacrylate (PMMA) bodies. We studied the evolution of slip and slip rates that varied systematically based on the application of both high and low normal stress (σ0=0.8 or 0.4 MPa) and the far-field loading rate (VLP). A spontaneous, frictional rupture expanded from the central, weaker, and more compliant section of the fault that had fewer asperities. Slow rupture propagated at speeds Vslow˜0.8 to 26 mm s-1 with slip rates from 0.01 to 0.2 μm s-1, resulting in stress drops around 100 kPa. During certain nucleation sequences, the fault experienced a partial stress drop, referred to as precursor detachment fronts in tribology. Only at the higher level of normal stress did these fronts exist, and the slip and slip rates mimicked the moment and moment release rates during the 2013-2014 Boso SSE in Japan. The laboratory detachment fronts showed rupture propagation speeds Vslow/VR∈ (5 to 172) × 10-7 and stress drops ˜ 100 kPa, which both scaled to the aforementioned SSE. Distributions of asperities, measured using a pressure sensitive film, increased in complexity with additional normal stress—an increase in normal stress caused added complexity by increasing both the mean size and standard deviation of asperity distributions, and this appeared to control the presence of the detachment front.

Functional complexity and ecosystem stability: an experimental approach

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

Van Voris, P.; O'Neill, R.V.; Shugart, H.H.

1978-01-01

The complexity-stability hypothesis was experimentally tested using intact terrestrial microcosms. Functional complexity was defined as the number and significance of component interactions (i.e., population interactions, physical-chemical reactions, biological turnover rates) influenced by nonlinearities, feedbacks, and time delays. It was postulated that functional complexity could be nondestructively measured through analysis of a signal generated from the system. Power spectral analysis of hourly CO/sub 2/ efflux, from eleven old-field microcosms, was analyzed for the number of low frequency peaks and used to rank the functional complexity of each system. Ranking of ecosystem stability was based on the capacity of the system tomore » retain essential nutrients and was measured by net loss of Ca after the system was stressed. Rank correlation supported the hypothesis that increasing ecosystem functional complexity leads to increasing ecosystem stability. The results indicated that complex functional dynamics can serve to stabilize the system. The results also demonstrated that microcosms are useful tools for system-level investigations.« less

A simple method for determining stress intensity factors for a crack in bi-material interface

NASA Astrophysics Data System (ADS)

Morioka, Yuta

Because of violently oscillating nature of stress and displacement fields near the crack tip, it is difficult to obtain stress intensity factors for a crack between two dis-similar media. For a crack in a homogeneous medium, it is a common practice to find stress intensity factors through strain energy release rates. However, individual strain energy release rates do not exist for bi-material interface crack. Hence it is necessary to find alternative methods to evaluate stress intensity factors. Several methods have been proposed in the past. However they involve mathematical complexity and sometimes require additional finite element analysis. The purpose of this research is to develop a simple method to find stress intensity factors in bi-material interface cracks. A finite element based projection method is proposed in the research. It is shown that the projection method yields very accurate stress intensity factors for a crack in isotropic and anisotropic bi-material interfaces. The projection method is also compared to displacement ratio method and energy method proposed by other authors. Through comparison it is found that projection method is much simpler to apply with its accuracy comparable to that of displacement ratio method.

Assessing the relative importance of environmental effects, carry-over effects and species differences in thermal stress resistance: a comparison of Drosophilids across field and laboratory generations.

PubMed

Schiffer, Michele; Hangartner, Sandra; Hoffmann, Ary A

2013-10-15

There is increasing interest in comparing species of related organisms for their susceptibility to thermal extremes in order to evaluate potential vulnerability to climate change. Comparisons are typically undertaken on individuals collected from the field with or without a period of acclimation. However, this approach does not allow the potential contributions of environmental and carry-over effects across generations to be separated from inherent species differences in susceptibility. To assess the importance of these different sources of variation, we here considered heat and cold resistance in Drosophilid species from tropical and temperate sites in the field and across two laboratory generations. Resistance in field-collected individuals tended to be lower when compared with F1 and F2 laboratory generations, and species differences in field flies were only weakly correlated to differences established under controlled rearing conditions, unlike in F1-F2 comparisons. This reflected large environmental effects on resistance associated with different sites and conditions experienced within sites. For the 8 h cold recovery assay there was no strong evidence of carry-over effects, whereas for the heat knockdown and 2 h cold recovery assays there was some evidence for such effects. However, for heat these were species specific in direction. Variance components for inherent species differences were substantial for resistance to heat and 8 h cold stress, but small for 2 h cold stress, though this may be a reflection of the species being considered in the comparisons. These findings highlight that inherent differences among species are difficult to characterise accurately without controlling for environmental sources of variation and carry-over effects. Moreover, they also emphasise the complex nature of carry-over effects that vary depending on the nature of stress traits and the species being evaluated.

Monitoring of Freezing Dynamics in Trees: A Simple Phase Shift Causes Complexity1[OPEN

PubMed Central

Charra-Vaskou, Katline

2017-01-01

During winter, trees have to cope with harsh conditions, including extreme freeze-thaw stress. This study focused on ice nucleation and propagation, related water shifts and xylem cavitation, as well as cell damage and was based on in situ monitoring of xylem (thermocouples) and surface temperatures (infrared imaging), ultrasonic emissions, and dendrometer analysis. Field experiments during late winter on Picea abies growing at the alpine timberline revealed three distinct freezing patterns: (1) from the top of the tree toward the base, (2) from thin branches toward the main stem’s top and base, and (3) from the base toward the top. Infrared imaging showed freezing within branches from their base toward distal parts. Such complex freezing causes dynamic and heterogenous patterns in water potential and probably in cavitation. This study highlights the interaction between environmental conditions upon freezing and thawing and demonstrates the enormous complexity of freezing processes in trees. Diameter shrinkage, which indicated water fluxes within the stem, and acoustic emission analysis, which indicated cavitation events near the ice front upon freezing, were both related to minimum temperature and, upon thawing, related to vapor pressure deficit and soil temperature. These complex patterns, emphasizing the common mechanisms between frost and drought stress, shed new light on winter tree physiology. PMID:28242655

Recent Advances in Utilizing Transcription Factors to Improve Plant Abiotic Stress Tolerance by Transgenic Technology

PubMed Central

Wang, Hongyan; Wang, Honglei; Shao, Hongbo; Tang, Xiaoli

2016-01-01

Agricultural production and quality are adversely affected by various abiotic stresses worldwide and this will be exacerbated by the deterioration of global climate. To feed a growing world population, it is very urgent to breed stress-tolerant crops with higher yields and improved qualities against multiple environmental stresses. Since conventional breeding approaches had marginal success due to the complexity of stress tolerance traits, the transgenic approach is now being popularly used to breed stress-tolerant crops. So identifying and characterizing the critical genes involved in plant stress responses is an essential prerequisite for engineering stress-tolerant crops. Far beyond the manipulation of single functional gene, engineering certain regulatory genes has emerged as an effective strategy now for controlling the expression of many stress-responsive genes. Transcription factors (TFs) are good candidates for genetic engineering to breed stress-tolerant crop because of their role as master regulators of many stress-responsive genes. Many TFs belonging to families AP2/EREBP, MYB, WRKY, NAC, bZIP have been found to be involved in various abiotic stresses and some TF genes have also been engineered to improve stress tolerance in model and crop plants. In this review, we take five large families of TFs as examples and review the recent progress of TFs involved in plant abiotic stress responses and their potential utilization to improve multiple stress tolerance of crops in the field conditions. PMID:26904044

Interactome of Obesity: Obesidome : Genetic Obesity, Stress Induced Obesity, Pathogenic Obesity Interaction.

PubMed

Geronikolou, Styliani A; Pavlopoulou, Athanasia; Cokkinos, Dennis; Chrousos, George

2017-01-01

Obesity is a chronic disease of increasing prevalence reaching epidemic proportions. Genetic defects as well as epigenetic effects contribute to the obesity phenotype. Investigating gene (e.g. MC4R defects)-environment (behavior, infectious agents, stress) interactions is a relative new field of great research interest. In this study, we have made an effort to create an interactome (henceforth referred to as "obesidome"), where extrinsic stressors response, intrinsic predisposition, immunity response to inflammation and autonomous nervous system implications are integrated. These pathways are presented in one interactome network for the first time. In our study, obesity-related genes/gene products were found to form a complex interactions network.

Leaves of field-grown mastic trees suffer oxidative stress at the two extremes of their lifespan.

PubMed

Juvany, Marta; Müller, Maren; Munné-Bosch, Sergi

2012-08-01

Leaf senescence is a complex phenomenon occurring in all plant species, but it is still poorly understood in plants grown in Mediterranean field conditions and well-adapted to harsh climatic conditions. To better understand the physiological processes underlying leaf senescence in mastic trees (Pistacia lentiscus L.), we evaluated leaf growth, water and N content, photosystem II (PSII) photochemistry, lipid peroxidation and levels of photosynthetic pigments, antioxidants, abscisic acid, and salicylic acid and jasmonic acid during the complete leaf lifespan, from early expansion to late senescence in relation to natural climatic conditions in the field. While mature leaves suffered from water and N deficit during late spring and summer, both young (emerging) and old (senescing) leaves were most sensitive to photo-oxidative stress, as indicated by reductions in the F(v)/F(m) ratio and enhanced lipid peroxidation during late autumn and winter. Reductions in the F(v)/F(m) ratio were associated with low α-tocopherol (vitamin E) levels, while very old, senescing leaves additionally showed severe anthocyanin losses. We have concluded that both young (emerging) and old (senescing) leaves suffer oxidative stress in mastic trees, which may be linked in part to suboptimal temperatures during late autumn and winter as well as to low vitamin E levels. © 2012 Institute of Botany, Chinese Academy of Sciences.

Abiotic Stress Responses and Microbe-Mediated Mitigation in Plants: The Omics Strategies

PubMed Central

Meena, Kamlesh K.; Sorty, Ajay M.; Bitla, Utkarsh M.; Choudhary, Khushboo; Gupta, Priyanka; Pareek, Ashwani; Singh, Dhananjaya P.; Prabha, Ratna; Sahu, Pramod K.; Gupta, Vijai K.; Singh, Harikesh B.; Krishanani, Kishor K.; Minhas, Paramjit S.

2017-01-01

Abiotic stresses are the foremost limiting factors for agricultural productivity. Crop plants need to cope up adverse external pressure created by environmental and edaphic conditions with their intrinsic biological mechanisms, failing which their growth, development, and productivity suffer. Microorganisms, the most natural inhabitants of diverse environments exhibit enormous metabolic capabilities to mitigate abiotic stresses. Since microbial interactions with plants are an integral part of the living ecosystem, they are believed to be the natural partners that modulate local and systemic mechanisms in plants to offer defense under adverse external conditions. Plant-microbe interactions comprise complex mechanisms within the plant cellular system. Biochemical, molecular and physiological studies are paving the way in understanding the complex but integrated cellular processes. Under the continuous pressure of increasing climatic alterations, it now becomes more imperative to define and interpret plant-microbe relationships in terms of protection against abiotic stresses. At the same time, it also becomes essential to generate deeper insights into the stress-mitigating mechanisms in crop plants for their translation in higher productivity. Multi-omics approaches comprising genomics, transcriptomics, proteomics, metabolomics and phenomics integrate studies on the interaction of plants with microbes and their external environment and generate multi-layered information that can answer what is happening in real-time within the cells. Integration, analysis and decipherization of the big-data can lead to a massive outcome that has significant chance for implementation in the fields. This review summarizes abiotic stresses responses in plants in-terms of biochemical and molecular mechanisms followed by the microbe-mediated stress mitigation phenomenon. We describe the role of multi-omics approaches in generating multi-pronged information to provide a better understanding of plant–microbe interactions that modulate cellular mechanisms in plants under extreme external conditions and help to optimize abiotic stresses. Vigilant amalgamation of these high-throughput approaches supports a higher level of knowledge generation about root-level mechanisms involved in the alleviation of abiotic stresses in organisms. PMID:28232845

Abiotic Stress Responses and Microbe-Mediated Mitigation in Plants: The Omics Strategies.

PubMed

Meena, Kamlesh K; Sorty, Ajay M; Bitla, Utkarsh M; Choudhary, Khushboo; Gupta, Priyanka; Pareek, Ashwani; Singh, Dhananjaya P; Prabha, Ratna; Sahu, Pramod K; Gupta, Vijai K; Singh, Harikesh B; Krishanani, Kishor K; Minhas, Paramjit S

2017-01-01

Abiotic stresses are the foremost limiting factors for agricultural productivity. Crop plants need to cope up adverse external pressure created by environmental and edaphic conditions with their intrinsic biological mechanisms, failing which their growth, development, and productivity suffer. Microorganisms, the most natural inhabitants of diverse environments exhibit enormous metabolic capabilities to mitigate abiotic stresses. Since microbial interactions with plants are an integral part of the living ecosystem, they are believed to be the natural partners that modulate local and systemic mechanisms in plants to offer defense under adverse external conditions. Plant-microbe interactions comprise complex mechanisms within the plant cellular system. Biochemical, molecular and physiological studies are paving the way in understanding the complex but integrated cellular processes. Under the continuous pressure of increasing climatic alterations, it now becomes more imperative to define and interpret plant-microbe relationships in terms of protection against abiotic stresses. At the same time, it also becomes essential to generate deeper insights into the stress-mitigating mechanisms in crop plants for their translation in higher productivity. Multi-omics approaches comprising genomics, transcriptomics, proteomics, metabolomics and phenomics integrate studies on the interaction of plants with microbes and their external environment and generate multi-layered information that can answer what is happening in real-time within the cells. Integration, analysis and decipherization of the big-data can lead to a massive outcome that has significant chance for implementation in the fields. This review summarizes abiotic stresses responses in plants in-terms of biochemical and molecular mechanisms followed by the microbe-mediated stress mitigation phenomenon. We describe the role of multi-omics approaches in generating multi-pronged information to provide a better understanding of plant-microbe interactions that modulate cellular mechanisms in plants under extreme external conditions and help to optimize abiotic stresses. Vigilant amalgamation of these high-throughput approaches supports a higher level of knowledge generation about root-level mechanisms involved in the alleviation of abiotic stresses in organisms.

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

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

Joergensen, O.; Horsewell, A.

1997-08-01

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

Segmentation in cohesive systems constrained by elastic environments

NASA Astrophysics Data System (ADS)

Novak, I.; Truskinovsky, L.

2017-04-01

The complexity of fracture-induced segmentation in elastically constrained cohesive (fragile) systems originates from the presence of competing interactions. The role of discreteness in such phenomena is of interest in a variety of fields, from hierarchical self-assembly to developmental morphogenesis. In this paper, we study the analytically solvable example of segmentation in a breakable mass-spring chain elastically linked to a deformable lattice structure. We explicitly construct the complete set of local minima of the energy in this prototypical problem and identify among them the states corresponding to the global energy minima. We show that, even in the continuum limit, the dependence of the segmentation topology on the stretching/pre-stress parameter in this problem takes the form of a devil's type staircase. The peculiar nature of this staircase, characterized by locking in rational microstructures, is of particular importance for biological applications, where its structure may serve as an explanation of the robustness of stress-driven segmentation. This article is part of the themed issue 'Patterning through instabilities in complex media: theory and applications.'

Control superstructure of rigid polyelectrolytes in oppositely charged hydrogels via programmed internal stress

NASA Astrophysics Data System (ADS)

Takahashi, Riku; Wu, Zi Liang; Arifuzzaman, Md; Nonoyama, Takayuki; Nakajima, Tasuku; Kurokawa, Takayuki; Gong, Jian Ping

2014-08-01

Biomacromolecules usually form complex superstructures in natural biotissues, such as different alignments of collagen fibres in articular cartilages, for multifunctionalities. Inspired by nature, there are efforts towards developing multiscale ordered structures in hydrogels (recognized as one of the best candidates of soft biotissues). However, creating complex superstructures in gels are hardly realized because of the absence of effective approaches to control the localized molecular orientation. Here we introduce a method to create various superstructures of rigid polyanions in polycationic hydrogels. The control of localized orientation of rigid molecules, which are sensitive to the internal stress field of the gel, is achieved by tuning the swelling mismatch between masked and unmasked regions of the photolithographic patterned gel. Furthermore, we develop a double network structure to toughen the hydrogels with programmed superstructures, which deform reversibly under large strain. This work presents a promising pathway to develop superstructures in hydrogels and should shed light on designing biomimetic materials with intricate molecular alignments.

Dynamics of yield-stress droplets: Morphology of impact craters

NASA Astrophysics Data System (ADS)

Neufeld, Jerome; Sohr, David; Ferrari, Leo; Dalziel, Stuart

2017-11-01

Yield strength can play an important role for the dynamics of droplets impacting on surfaces, whether at the industrial or planetary scale, and can capture a zoo of impact crater morphologies, from simple parabolic craters, to more complex forms with forms with, for example, multiple rings, central peaks. Here we show that the morphology of planetary impact craters can be reproduced in the laboratory using carbopol, a transparent yield-stress fluid, as both impactor and bulk fluid. Using high-speed video photography, we characterise the universal, transient initial excavation stage of impact and show the dependence of the subsequent relaxation to final crater morphology on impactor size, impact speed and yield stress. To further interrogate our laboratory impacts, we dye our impactor to map its final distribution and use particle tracking to determine the flow fields during impact and the maximal extent of the yield surface. We characterise the flow-fields induced during impact, and the maximal extent of the yield surface, by tracking particles within the bulk fluid and map the distribution of impactor and bulk by tracing the final distribution of dyed impactor. The results of laboratory impact droplets are used to infer the properties of planetary impactors, and aid in inter.

To stress or not to stress: a question of models.

PubMed

Gray, J Megan; Chaouloff, Francis; Hill, Matthew N

2015-01-05

Stress research is a rapidly evolving field that encompasses numerous disciplines ranging from neuroscience to metabolism. With many new researchers migrating into the field, navigating the hows and whys of specific research questions can sometimes be enigmatic given the availability of so many models in the stress field. Additionally, as with every field, there are many seemingly minor experimental details that can have dramatic influences on data interpretation, although many of these are unknown to those not familiar with the field. The aim of this overview is to provide some suggestions and points to guide researchers moving into the stress field and highlight relevant methodological points that they should consider when choosing a model for stress and deciding how to structure a study. We briefly provide a primer on the basics of endpoint measurements in the stress field, factors to consider when choosing a model for acute stress, the difference between repeated and chronic stress, and importantly, influencing variables that modulate endpoints of analysis in stress work. Copyright © 2015 John Wiley & Sons, Inc.

Electric and Magnetic Interactions

NASA Astrophysics Data System (ADS)

Chabay, Ruth W.; Sherwood, Bruce A.

1994-08-01

The curriculum has been restructured so that students will have the necessary fundamental understanding of charges and fields before going on to more complex issues. Qualitative reasoning and quantitative analysis are discussed equally in order to provide a meaningful conceptual framework within which the quantitative work makes more sense. Atomic-level analysis is stressed and electrostatics and circuits are unified. Desktop experiments can be conducted at home or in the classroom and are tightly integrated with the theoretical treatment.

Micromechanics of composites with shape memory alloy fibers in uniform thermal fields

NASA Technical Reports Server (NTRS)

Birman, Victor; Saravanos, Dimitris A.; Hopkins, Dale A.

1995-01-01

Analytical procedures are developed for a composite system consisting of shape memory alloy fibers within an elastic matrix subject to uniform temperature fluctuations. Micromechanics for the calculation of the equivalent properties of the composite are presented by extending the multi-cell model to incorporate shape memory alloy fibers. A three phase concentric cylinder model is developed for the analysis of local stresses which includes the fiber, the matrix, and the surrounding homogenized composite. The solution addresses the complexities induced by the nonlinear dependence of the in-situ martensite fraction of the fibers to the local stresses and temperature, and the local stresses developed from interactions between the fibers and matrix during the martensitic and reverse phase transformations. Results are presented for a nitinol/epoxy composite. The applications illustrate the response of the composite in isothermal longitudinal loading and unloading, and in temperature induced actuation. The local stresses developed in the composite under various stages of the martensitic and reverse phase transformation are also shown.

Dynamics of vesicles in electric fields

NASA Astrophysics Data System (ADS)

Vlahovska, Petia; Gracia, Ruben

2007-11-01

Electromechanical forces are widely used for cell manipulation. Knowledge of the physical mechanisms underlying the interaction of cells and external fields is essential for practical applications. Vesicles are model cells made of a lipid bilayer membrane. They are examples of ``soft'' particles, i.e., their shape when subjected to flow or electric field is not given a priori but it is governed by the balance of membrane, fluid and electrical stresses. This generic ``softness'' gives rise to a very complex vesicle dynamics in external fields. In an AC electric field, as the frequency is increased, vesicles filled with a fluid less conducting than the surrounding fluid undergo shape transition from prolate to oblate ellipsoids. The opposite effect is observed with drops. We present an electro- hydrodynamic theory based on the leaky dielectric model that quantitatively describes experimental observations. We compare drops and vesicles, and show how their distinct behavior stems from different interfacial properties.

Reconstruction of the strain pattern in the Somma-Vesuvius area: field and remote sensing analyses

NASA Astrophysics Data System (ADS)

D'Assisi Tramparulo, Francesco; Bisson, Marina; Isaia, Roberto; Tadini, Alessandro; Vitale, Stefano

2016-04-01

Keywords: Somma-Vesuvio, structural analysis, volcano-tectonics. This study present a detailed structural analysis of the Somma-Vesuvio (SV) volcanic complex that couples field data about faults, fractures and dykes with the analysis of lineaments identified from high-resolution (1m) DTM deriving from LiDAR data. Field data were collected within the SV caldera,in some quarries along the volcano flanks, and in few outcrops along the carbonate reliefs bounding the southern sector of the Campania plain. A total of 8,500 orientation data have been analyzed through rose diagrams and inversion methods while a total of more than 4,000 lineaments were identified after the analyses of multiple hill shades obtained by applying different pseudo-illuminations (from NW, NE, SE and SW) and appropriate filters to the original DTM. Results indicate a complex interaction between volcanic (local) and tectonic (regional) stress fields. The preliminary analysis of lineaments indicate that most of them are radial with respect to the center of the caldera, however a "tectonic" component is present, mainly represented by the NNE-SSW, ENE-WSW and the well-known Apenninic (NW-SE) direction.

Emerging trends in the functional genomics of the abiotic stress response in crop plants.

PubMed

Vij, Shubha; Tyagi, Akhilesh K

2007-05-01

Plants are exposed to different abiotic stresses, such as water deficit, high temperature, salinity, cold, heavy metals and mechanical wounding, under field conditions. It is estimated that such stress conditions can potentially reduce the yield of crop plants by more than 50%. Investigations of the physiological, biochemical and molecular aspects of stress tolerance have been conducted to unravel the intrinsic mechanisms developed during evolution to mitigate against stress by plants. Before the advent of the genomics era, researchers primarily used a gene-by-gene approach to decipher the function of the genes involved in the abiotic stress response. However, abiotic stress tolerance is a complex trait and, although large numbers of genes have been identified to be involved in the abiotic stress response, there remain large gaps in our understanding of the trait. The availability of the genome sequences of certain important plant species has enabled the use of strategies, such as genome-wide expression profiling, to identify the genes associated with the stress response, followed by the verification of gene function by the analysis of mutants and transgenics. Certain components of both abscisic acid-dependent and -independent cascades involved in the stress response have already been identified. Information originating from the genome-wide analysis of abiotic stress tolerance will help to provide an insight into the stress-responsive network(s), and may allow the modification of this network to reduce the loss caused by stress and to increase agricultural productivity.

Correcting and coating thin walled X-ray Optics via a combination of controlled film deposition and magnetic smart materials

NASA Astrophysics Data System (ADS)

Ulmer, Melville

The project goal is to demonstrate that thin walled (<400 micron thick) X-ray optics can be controllably shaped to produce high quality (~1" or better) X-ray optics at an affordable price. Since the desired surface area for the next generation X-ray telescope is >10x that of Chandra, the >10x requirement is then for >200 m^2 of surface area with a surface finish of better than 0.5 nm. Therefore, replication of some sort is called for. Because no replication technology has been shown to achieve ≤1" angular resolution, post fabrication figure corrections are likely going to be necessary. Some have proposed to do this in orbit and others prelaunch including us. Our prelaunch approach is to apply in-plane stresses to the thin walled mirror shells via a magnetic field. The field will be held in by some magnetically hard material such as NiCo. By use of a so called magnetic smart material (MSM) such as Terfenol-D, we already shown that strong enough stresses can be generated. Preliminary work has also shown that the magnetic field can be held in well enough to apply the figure correcting stresses pre-launch. What we call "set-it and forget-it." However, what is unique about our approach is that at the cost of complexity and some areal coverage, our concept will also accommodate in-orbit adjustments. Furthermore, to the best of our knowledge ours is one of two known stress modification processes that are bi-axial. Our plan is first to validate set-it and forget-it first on cantilevers and then to expand this to working on 5 cm x 5 cm pieces. We will work both with NiCo and glass or Si coated with Terfenol-D. Except for the NiCo, substrates we will also coat the samples with NiCo in order to have a film that will hold in the magnetic field. As part of the coating process, we will control the stress of the film by varying the voltage bias while coating. The bias stress control can be used to apply films with minimal stress such as Terfenol-D and X-ray reflecting coatings such as Ir. Ir is a highly desirable coating for soft X-ray astronomy mirrors that can have significant built in stress unless some technique like our is used to apply the coating. An alternative use for the bias stress control coating process is to improve the initially fabricated mirror by applying spatially dependent stresses with a Cr film. We will also expand upon the work we have done that shows this method has promise to reduce the amount of corrections needed by the MSM plus the magnetic field process.

Heuristic modelling of laser written mid-infrared LiNbO₃ stressed-cladding waveguides.

PubMed

Nguyen, Huu-Dat; Ródenas, Airán; Vázquez de Aldana, Javier R; Martínez, Javier; Chen, Feng; Aguiló, Magdalena; Pujol, Maria Cinta; Díaz, Francesc

2016-04-04

Mid-infrared lithium niobate cladding waveguides have great potential in low-loss on-chip non-linear optical instruments such as mid-infrared spectrometers and frequency converters, but their three-dimensional femtosecond-laser fabrication is currently not well understood due to the complex interplay between achievable depressed index values and the stress-optic refractive index changes arising as a function of both laser fabrication parameters, and cladding arrangement. Moreover, both the stress-field anisotropy and the asymmetric shape of low-index tracks yield highly birefringent waveguides not useful for most applications where controlling and manipulating the polarization state of a light beam is crucial. To achieve true high performance devices a fundamental understanding on how these waveguides behave and how they can be ultimately optimized is required. In this work we employ a heuristic modelling approach based on the use of standard optical characterization data along with standard computational numerical methods to obtain a satisfactory approximate solution to the problem of designing realistic laser-written circuit building-blocks, such as straight waveguides, bends and evanescent splitters. We infer basic waveguide design parameters such as the complex index of refraction of laser-written tracks at 3.68 µm mid-infrared wavelengths, as well as the cross-sectional stress-optic index maps, obtaining an overall waveguide simulation that closely matches the measured mid-infrared waveguide properties in terms of anisotropy, mode field distributions and propagation losses. We then explore experimentally feasible waveguide designs in the search of a single-mode low-loss behaviour for both ordinary and extraordinary polarizations. We evaluate the overall losses of s-bend components unveiling the expected radiation bend losses of this type of waveguides, and finally showcase a prototype design of a low-loss evanescent splitter. Developing a realistic waveguide model with which robust waveguide designs can be developed will be key for exploiting the potential of the technology.

Deep-sequencing transcriptome analysis of field-grown Medicago sativa L. crown buds acclimated to freezing stress.

PubMed

Song, Lili; Jiang, Lin; Chen, Yue; Shu, Yongjun; Bai, Yan; Guo, Changhong

2016-09-01

Medicago sativa L. (alfalfa) 'Zhaodong' is an important forage legume that can safely survive in northern China where winter temperatures reach as low as -30 °C. Survival of alfalfa following freezing stress depends on the amount and revival ability of crown buds. In order to investigate the molecular mechanisms of frost tolerance in alfalfa, we used transcriptome sequencing technology and bioinformatics strategies to analyze crown buds of field-grown alfalfa during winter. We statistically identified a total of 5605 differentially expressed genes (DEGs) involved in freezing stress including 1900 upregulated and 3705 downregulated DEGs. We validated 36 candidate DEGs using qPCR to confirm the accuracy of the RNA-seq data. Unlike other recent studies, this study employed alfalfa plants grown in the natural environment. Our results indicate that not only the CBF orthologs but also membrane proteins, hormone signal transduction pathways, and ubiquitin-mediated proteolysis pathways indicate the presence of a special freezing adaptation mechanism in alfalfa. The antioxidant defense system may rapidly confer freezing tolerance to alfalfa. Importantly, biosynthesis of secondary metabolites and phenylalanine metabolism, which is of potential importance in coordinating freezing tolerance with growth and development, were downregulated in subzero temperatures. The adaptive mechanism for frost tolerance is a complex multigenic process that is not well understood. This systematic analysis provided an in-depth view of stress tolerance mechanisms in alfalfa.

Wedge disclination dipole in an embedded nanowire within the surface/interface elasticity

NASA Astrophysics Data System (ADS)

Shodja, Hossein M.; Rezazadeh-Kalehbasti, Shaghayegh; Gutkin, Mikhail Yu

2013-12-01

The elastic behavior of an arbitrary oriented wedge disclination dipole located inside a nanowire, which in turn is embedded in an infinite matrix, is studied within the surface/interface theory of elasticity. The corresponding boundary value problem is provided using complex potential functions. The potential functions are defined through modeling the wedge disclination in terms of an equivalent distribution of edge dislocations. The interface effects on the stress field and strain energy of the disclination dipole and image forces acting on it, the influence of relative shear moduli of the nanowire and the matrix, as well as the different characteristics of the interface are studied thoroughly. It is shown that the positive interface modulus leads to increased strain energy and extra repulsive forces on the disclination dipole. The noticeable effect of the negative interface modulus is the non-classical oscillations in the stress field of the disclination dipole and an extra attractive image force on it.

Work environment, job satisfaction, stress and burnout among haemodialysis nurses.

PubMed

Hayes, Bronwyn; Douglas, Clint; Bonner, Ann

2015-07-01

To examine the relationships among nurse and work characteristics, job satisfaction, stress, burnout and the work environment of haemodialysis nurses. Haemodialysis nursing is characterised by frequent and intense contact with patients in a complex and intense environment. A cross-sectional online survey of 417 haemodialysis nurses that included nurse and work characteristics, the Brisbane Practice Environment Measure, Index of Work Satisfaction, Nursing Stress Scale and the Maslach Burnout Inventory. Haemodialysis nurses reported an acceptable level of job satisfaction and perceived their work environment positively, although high levels of burnout were found. Nurses who were older and had worked in haemodialysis the longest had higher satisfaction levels, experienced less stress and lower levels of burnout than younger nurses. The in-centre type of haemodialysis unit had greater levels of stress and burnout than home training units. Greater satisfaction with the work environment was strongly correlated with job satisfaction, lower job stress and emotional exhaustion. Haemodialysis nurses experienced high levels of burnout even though their work environment was favourable and they had acceptable levels of job satisfaction. Targeted strategies are required to retain and avoid burnout in younger and less experienced nurses in this highly specialised field of nursing. © 2013 John Wiley & Sons Ltd.

Experimental study of vertical stress profiles of a confined granular bed under static and dynamic conditions.

PubMed

Mandato, S; Cuq, B; Ruiz, T

2012-07-01

In a wet agglomeration process inside a low shear mixer, the blade function is to induce i) homogenization of the liquid sprayed on the powder surface and ii) a stress field able to transfer the mechanical energy at the particle scale. In this work we study the mechanical state of a confined powder bed through the analysis of stress distributions (by force measurements) in a rectangular cell in two cases: for a classical model powder (i.e. glass beads) and a complex powder (i.e. wheat semolina). Two types of vertical stress profiles are obtained according to the type of measurements carried out in the powder bed, either locally (at different positions in the cell) or globally (at the entire base). The global vertical stress profile follows Janssen's model and the local vertical stress profile highlights a critical length, identified as the percolation threshold of the force network, and a shielding length near the bottom, which is similar to an influence length of the side walls. In the context of wet agglomeration, the results allow to consider the role of the characteristic lengths in the mixing bowl under vertical mechanical solicitation.

The effect of drought and heat stress on reproductive processes in cereals.

PubMed

Barnabás, Beáta; Jäger, Katalin; Fehér, Attila

2008-01-01

As the result of intensive research and breeding efforts over the last 20 years, the yield potential and yield quality of cereals have been greatly improved. Nowadays, yield safety has gained more importance because of the forecasted climatic changes. Drought and high temperature are especially considered as key stress factors with high potential impact on crop yield. Yield safety can only be improved if future breeding attempts will be based on the valuable new knowledge acquired on the processes determining plant development and its responses to stress. Plant stress responses are very complex. Interactions between plant structure, function and the environment need to be investigated at various phases of plant development at the organismal, cellular as well as molecular levels in order to obtain a full picture. The results achieved so far in this field indicate that various plant organs, in a definite hierarchy and in interaction with each other, are involved in determining crop yield under stress. Here we attempt to summarize the currently available information on cereal reproduction under drought and heat stress and to give an outlook towards potential strategies to improve yield safety in cereals.

Effect of Mechanical Heterogeneity on the Crack Driving Force of a Reactor Pressure Vessel Outlet Nozzle DMW Joint

NASA Astrophysics Data System (ADS)

Lingyan, Zhao; Yinghao, Cui; He, Xue

2017-12-01

The welding mechanical heterogeneity, load complexity, material and geometrical structure makes it very difficult to assess the structural integrity of dissimilar metal weld (DMW) joints. Based on a numerical simulated approach of the continuous change of material mechanical property in the buttering layer, a reactor pressure vessel (RPV) outlet nozzle DMW joint with service loads is studied, effect of mechanical heterogeneity on the stress-strain field and stress triaxiality at the semi-elliptical surface crack front are discussed. The analyses show that once the crack extends into the high hardness zone of Alloy 182 buttering, the strain decreases sharply, the strain gradient increases and the crack propagation slows down. The influence of strength mismatch on the stress triaxiality at the shallow crack front is greater than that at the deep crack front. The interaction between strength mismatch and crack depth directly affects the crack growth direction.

Irreducible Representations of Oscillatory and Swirling Flows in Active Soft Matter

NASA Astrophysics Data System (ADS)

Ghose, Somdeb; Adhikari, R.

2014-03-01

Recent experiments imaging fluid flow around swimming microorganisms have revealed complex time-dependent velocity fields that differ qualitatively from the stresslet flow commonly employed in theoretical descriptions of active matter. Here we obtain the most general flow around a finite sized active particle by expanding the surface stress in irreducible Cartesian tensors. This expansion, whose first term is the stresslet, must include, respectively, third-rank polar and axial tensors to minimally capture crucial features of the active oscillatory flow around translating Chlamydomonas and the active swirling flow around rotating Volvox. The representation provides explicit expressions for the irreducible symmetric, antisymmetric, and isotropic parts of the continuum active stress. Antisymmetric active stresses do not conserve orbital angular momentum and our work thus shows that spin angular momentum is necessary to restore angular momentum conservation in continuum hydrodynamic descriptions of active soft matter.

A coupled thermo-mechanical pseudo inverse approach for preform design in forging

NASA Astrophysics Data System (ADS)

Thomas, Anoop Ebey; Abbes, Boussad; Li, Yu Ming; Abbes, Fazilay; Guo, Ying-Qiao; Duval, Jean-Louis

2017-10-01

Hot forging is a process used to form difficult to form materials as well as to achieve complex geometries. This is possible due to the reduction of yield stress at high temperatures and a subsequent increase in formability. Numerical methods have been used to predict the material yield and the stress/strain states of the final product. Pseudo Inverse Approach (PIA) developed in the context of cold forming provides a quick estimate of the stress and strain fields in the final product for a given initial shape. In this paper, PIA is extended to include the thermal effects on the forging process. A Johnson-Cook thermo-viscoplastic material law is considered and a staggered scheme is employed for the coupling between the mechanical and thermal problems. The results are compared with available commercial codes to show the efficiency and the limitations of PIA.

Causal mechanisms of seismo-EM phenomena during the 1965-1967 Matsushiro earthquake swarm.

PubMed

Enomoto, Yuji; Yamabe, Tsuneaki; Okumura, Nobuo

2017-03-21

The 1965-1967 Matsushiro earthquake swarm in central Japan exhibited two unique characteristics. The first was a hydro-mechanical crust rupture resulting from degassing, volume expansion of CO 2 /water, and a crack opening within the critically stressed crust under a strike-slip stress. The other was, despite the lower total seismic energy, the occurrence of complexed seismo-electromagnetic (seismo-EM) phenomena of the geomagnetic intensity increase, unusual earthquake lights (EQLs) and atmospheric electric field (AEF) variations. Although the basic rupture process of this swarm of earthquakes is reasonably understood in terms of hydro-mechanical crust rupture, the associated seismo-EM processes remain largely unexplained. Here, we describe a series of seismo-EM mechanisms involved in the hydro-mechanical rupture process, as observed by coupling the electric interaction of rock rupture with CO 2 gas and the dielectric-barrier discharge of the modelled fields in laboratory experiments. We found that CO 2 gases passing through the newly created fracture surface of the rock were electrified to generate pressure-impressed current/electric dipoles, which could induce a magnetic field following Biot-Savart's law, decrease the atmospheric electric field and generate dielectric-barrier discharge lightning affected by the coupling effect between the seismic and meteorological activities.

Causal mechanisms of seismo-EM phenomena during the 1965–1967 Matsushiro earthquake swarm

PubMed Central

Enomoto, Yuji; Yamabe, Tsuneaki; Okumura, Nobuo

2017-01-01

The 1965–1967 Matsushiro earthquake swarm in central Japan exhibited two unique characteristics. The first was a hydro-mechanical crust rupture resulting from degassing, volume expansion of CO2/water, and a crack opening within the critically stressed crust under a strike-slip stress. The other was, despite the lower total seismic energy, the occurrence of complexed seismo-electromagnetic (seismo-EM) phenomena of the geomagnetic intensity increase, unusual earthquake lights (EQLs) and atmospheric electric field (AEF) variations. Although the basic rupture process of this swarm of earthquakes is reasonably understood in terms of hydro-mechanical crust rupture, the associated seismo-EM processes remain largely unexplained. Here, we describe a series of seismo-EM mechanisms involved in the hydro-mechanical rupture process, as observed by coupling the electric interaction of rock rupture with CO2 gas and the dielectric-barrier discharge of the modelled fields in laboratory experiments. We found that CO2 gases passing through the newly created fracture surface of the rock were electrified to generate pressure-impressed current/electric dipoles, which could induce a magnetic field following Biot-Savart’s law, decrease the atmospheric electric field and generate dielectric-barrier discharge lightning affected by the coupling effect between the seismic and meteorological activities. PMID:28322263

Causal mechanisms of seismo-EM phenomena during the 1965-1967 Matsushiro earthquake swarm

NASA Astrophysics Data System (ADS)

Enomoto, Yuji; Yamabe, Tsuneaki; Okumura, Nobuo

2017-03-01

The 1965-1967 Matsushiro earthquake swarm in central Japan exhibited two unique characteristics. The first was a hydro-mechanical crust rupture resulting from degassing, volume expansion of CO2/water, and a crack opening within the critically stressed crust under a strike-slip stress. The other was, despite the lower total seismic energy, the occurrence of complexed seismo-electromagnetic (seismo-EM) phenomena of the geomagnetic intensity increase, unusual earthquake lights (EQLs) and atmospheric electric field (AEF) variations. Although the basic rupture process of this swarm of earthquakes is reasonably understood in terms of hydro-mechanical crust rupture, the associated seismo-EM processes remain largely unexplained. Here, we describe a series of seismo-EM mechanisms involved in the hydro-mechanical rupture process, as observed by coupling the electric interaction of rock rupture with CO2 gas and the dielectric-barrier discharge of the modelled fields in laboratory experiments. We found that CO2 gases passing through the newly created fracture surface of the rock were electrified to generate pressure-impressed current/electric dipoles, which could induce a magnetic field following Biot-Savart’s law, decrease the atmospheric electric field and generate dielectric-barrier discharge lightning affected by the coupling effect between the seismic and meteorological activities.

Regulation of DNA conformations and dynamics in flows with hybrid field microfluidics.

PubMed

Ren, Fangfang; Zu, Yingbo; Kumar Rajagopalan, Kartik; Wang, Shengnian

2012-01-01

Visualizing single DNA dynamics in flow provides a wealth of physical insights in biophysics and complex flow study. However, large signal fluctuations, generated from diversified conformations, deformation history dependent dynamics and flow induced stochastic tumbling, often frustrate its wide adoption in single molecule and polymer flow study. We use a hybrid field microfluidic (HFM) approach, in which an electric field is imposed at desired locations and appropriate moments to balance the flow stress on charged molecules, to effectively regulate the initial conformations and the deformation dynamics of macromolecules in flow. With λ-DNA and a steady laminar shear flow as the model system, we herein studied the performance of HFM on regulating DNA trapping, relaxation, coil-stretch transition, and accumulation. DNA molecules were found to get captured in the focused planes when motions caused by flow, and the electric field were balanced. The trapped macromolecules relaxed in two different routes while eventually became more uniform in size and globule conformations. When removing the electric field, the sudden stretching dynamics of DNA molecules exhibited a more pronounced extension overshoot in their transient response under a true step function of flow stress while similar behaviors to what other pioneering work in steady shear flow. Such regulation strategies could be useful to control the conformations of other important macromolecules (e.g., proteins) and help better reveal their molecular dynamics.

Upper Ocean Momentum Response to Hurricane Forcing

NASA Astrophysics Data System (ADS)

Shay, L. K.; Jaimes de la Cruz, B.; Uhlhorn, E.

2016-02-01

The oceanic velocity response of the Loop Current (LC) and its complex warm and cold eddy field to hurricanes is critical to evaluate coupled operational forecast models. Direct velocity measurements of ocean current (including temperature and salinity) fields during hurricanes are needed to understand these complex interaction processes. As part of NOAA Intensity Forecasting Experiments, airborne expendable bathythermographs (AXBT), Conductivity-Temperature-Depth (AXCTD), and Current Profilers (AXCP) probes have been deployed in several major hurricanes from the NOAA research aircraft over the Gulf. Over the last decade, profilers were deployed in Isidore and Lili, Katrina and Rita, Gustav and Ike and Isaac-all of which interacted with the LC and warm eddy field. Central to these interactions under hurricane forcing is the level of sea surface cooling (typically about 1oC) induced by the wind-forced current response in the LC complex. Vertical current shear and instability (e.g., Richardson number) at the base of the oceanic mixed layer is often arrested by the strong upper ocean currents associated with the LC of 1 to 1.5 m s-1. By contrast, the SST cooling response often exceeds 3.5 to 4oC away from the LC complex in the Gulf Common Water. A second aspect of the interaction between the surface wind field and the LC is that the vorticity of the background flows (based on altimetry) enhances upwelling and downwelling processes by projecting onto the wind stress. This process modulates vertical mixing process at depth by keeping the Richardson numbers above criticality. Thus, the ocean cooling is less in the LC complex allowing for a higher and more sustained enthalpy flux as determined from global positioning system sondes deployed in these storms. This level of cooling (or lack thereof) in the LC complex significant impacts hurricane intensity that often reaches severe status which affects offshore structures and coastal communities at landfall in the northern Gulf of Mexico.

Modelling Fault Zone Evolution: Implications for fluid flow.

NASA Astrophysics Data System (ADS)

Moir, H.; Lunn, R. J.; Shipton, Z. K.

2009-04-01

Flow simulation models are of major interest to many industries including hydrocarbon, nuclear waste, sequestering of carbon dioxide and mining. One of the major uncertainties in these models is in predicting the permeability of faults, principally in the detailed structure of the fault zone. Studying the detailed structure of a fault zone is difficult because of the inaccessible nature of sub-surface faults and also because of their highly complex nature; fault zones show a high degree of spatial and temporal heterogeneity i.e. the properties of the fault change as you move along the fault, they also change with time. It is well understood that faults influence fluid flow characteristics. They may act as a conduit or a barrier or even as both by blocking flow across the fault while promoting flow along it. Controls on fault hydraulic properties include cementation, stress field orientation, fault zone components and fault zone geometry. Within brittle rocks, such as granite, fracture networks are limited but provide the dominant pathway for flow within this rock type. Research at the EU's Soultz-sous-Forệt Hot Dry Rock test site [Evans et al., 2005] showed that 95% of flow into the borehole was associated with a single fault zone at 3490m depth, and that 10 open fractures account for the majority of flow within the zone. These data underline the critical role of faults in deep flow systems and the importance of achieving a predictive understanding of fault hydraulic properties. To improve estimates of fault zone permeability, it is important to understand the underlying hydro-mechanical processes of fault zone formation. In this research, we explore the spatial and temporal evolution of fault zones in brittle rock through development and application of a 2D hydro-mechanical finite element model, MOPEDZ. The authors have previously presented numerical simulations of the development of fault linkage structures from two or three pre-existing joints, the results of which compare well to features observed in mapped exposures. For these simple simulations from a small number of pre-existing joints the fault zone evolves in a predictable way: fault linkage is governed by three key factors: Stress ratio of s1 (maximum compressive stress) to s3(minimum compressive stress), original geometry of the pre-existing structures (contractional vs. dilational geometries) and the orientation of the principle stress direction (σ1) to the pre-existing structures. In this paper we present numerical simulations of the temporal and spatial evolution of fault linkage structures from many pre-existing joints. The initial location, size and orientations of these joints are based on field observations of cooling joints in granite from the Sierra Nevada. We show that the constantly evolving geometry and local stress field perturbations contribute significantly to fault zone evolution. The location and orientations of linkage structures previously predicted by the simple simulations are consistent with the predicted geometries in the more complex fault zones, however, the exact location at which individual structures form is not easily predicted. Markedly different fault zone geometries are predicted when the pre-existing joints are rotated with respect to the maximum compressive stress. In particular, fault surfaces range from evolving smooth linear structures to producing complex ‘stepped' fault zone geometries. These geometries have a significant effect on simulations of along and across-fault flow.

Influence of fault geometry and tectonic driving stress orientation on the mechanics of multifault earthquakes

NASA Astrophysics Data System (ADS)

Madden, E. H.; Maerten, F.; Pollard, D. D.

2012-12-01

The M 7.3 28 June 1992 Landers, California earthquake was a well-documented event that highlighted the complex relationship between the earthquake and the multiple faults on which it occurred. Not only was fault slip data mapped in the field in detail, due to good exposure in the arid conditions of the Mojave Desert, but also it was one of the first earthquakes for which the surface displacement field was captured by satellite technology. In addition, precise aftershock relocations and fault plane solutions provide information about stress and fault behavior at depth. Study of fault interactions leading to the linkage of five right-lateral, strike-slip faults at Landers is aided by this abundance of available surface and subsurface data. While mapped near-field surface data often are restricted to the realm of the geologist, and subsurface data, such as aftershocks, often are restricted to the realm of the geophysicist, we find that integrating these data in mechanical forward models provides good constraint on the three-dimensional structures of the faults involved. Mechanical models also reveal that fault geometry and the orientation of the tectonic driving stress greatly influence whether or not slip is promoted across the extensional step between two of the faults along the southern-central rupture and elucidate the role of a crossing fault located within the step. Unfortunately, the orientation of the principal stresses are not well constrained near Landers or in many regions around the world. Previous determinations of the tectonic driving stress at Landers range from 7 degrees to 45 degrees, measured clockwise from North. We introduce a new stress inversion method that honors mechanical relationships among the remote stress state that is being inverted for, mainshock fault slip, the resulting total stress field following fault slip, and aftershocks. Use of the principal of superposition in this new algorithm obviates the need for the prohibitive computation times associated with running successive forward models. We apply the inverse method using aftershock, Interferometric Synthetic Aperture Radar (InSAR) and Global Positioning System (GPS) data associated with the Landers earthquake and address how fault geometry and aftershock size, timing, and focal mechanism quality influence inversion results. The advantages of this new method are that: (1) coseismic displacement data can be used, (2) the underlying model is better constrained to find a solution in the parameter space in the presence of fault slip perturbations, (3) absolute magnitudes can be recovered when using data with magnitude information such as GPS, InSAR and stress tensors inferred from aftershocks with known magnitudes. In addition, while one can choose to invert for an Andersonian fault regime, the method is not restricted to that particular case with one vertical principal stress.

Monitoring eruption activity using temporal stress changes at Mount Ontake volcano.

PubMed

Terakawa, Toshiko; Kato, Aitaro; Yamanaka, Yoshiko; Maeda, Yuta; Horikawa, Shinichiro; Matsuhiro, Kenjiro; Okuda, Takashi

2016-02-19

Volcanic activity is often accompanied by many small earthquakes. Earthquake focal mechanisms represent the fault orientation and slip direction, which are influenced by the stress field. Focal mechanisms of volcano-tectonic earthquakes provide information on the state of volcanoes via stresses. Here we demonstrate that quantitative evaluation of temporal stress changes beneath Mt. Ontake, Japan, using the misfit angles of focal mechanism solutions to the regional stress field, is effective for eruption monitoring. The moving average of misfit angles indicates that during the precursory period the local stress field beneath Mt. Ontake was deviated from the regional stress field, presumably by stress perturbations caused by the inflation of magmatic/hydrothermal fluids, which was removed immediately after the expulsion of volcanic ejecta. The deviation of the local stress field can be an indicator of increases in volcanic activity. The proposed method may contribute to the mitigation of volcanic hazards.

Monitoring eruption activity using temporal stress changes at Mount Ontake volcano

PubMed Central

Terakawa, Toshiko; Kato, Aitaro; Yamanaka, Yoshiko; Maeda, Yuta; Horikawa, Shinichiro; Matsuhiro, Kenjiro; Okuda, Takashi

2016-01-01

Volcanic activity is often accompanied by many small earthquakes. Earthquake focal mechanisms represent the fault orientation and slip direction, which are influenced by the stress field. Focal mechanisms of volcano-tectonic earthquakes provide information on the state of volcanoes via stresses. Here we demonstrate that quantitative evaluation of temporal stress changes beneath Mt. Ontake, Japan, using the misfit angles of focal mechanism solutions to the regional stress field, is effective for eruption monitoring. The moving average of misfit angles indicates that during the precursory period the local stress field beneath Mt. Ontake was deviated from the regional stress field, presumably by stress perturbations caused by the inflation of magmatic/hydrothermal fluids, which was removed immediately after the expulsion of volcanic ejecta. The deviation of the local stress field can be an indicator of increases in volcanic activity. The proposed method may contribute to the mitigation of volcanic hazards. PMID:26892716

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

Everett, J.R.; Russell, O.R.; Staskowski, R.J.

Analysis of 38 contiguous Landsat Multispectral Scanner scenes acquired over Myanmar (Burma) reveals numerous large-scale features associated with margins of the Burman plate, previously unidentified northeast-southwest-trending discontinuities, important extensions of previously mapped fault trends, and numerous structural features that appear favorable for petroleum exploration. A mosaic of these scenes at 1:1,000,000 scale shows a large number of tectonic elements and their spatial relationships. Within the area of investigation are portions of the Indian, Burman, Lhasa, and Shan-Thai plates, and perhaps other, smaller plates. The Himalayan front and Indo-Burman Ranges manifest effects of current and recently past plate movement. The complexitymore » of the kinematic history accounts for the diversity of structural features in the area. The last major event in this long and violent saga, which began in middle Miocene (approximately 11 Ma) time and continues to the present, is the recent change from a collisional to a right-lateral strike-slip transform margin between the Indian and Burman plates. The complexity of the structures visible is the product of multiple plate collisions, rotation of the Indian plate and parts of the Asian plate, and long-continued convergence that changed velocity and direction tbrough time. The most obvious evidence of this complexity, which is immediately apparent on geologic maps or the Landsat mosaic of the region, is the almost right-angle relationship of the folds of the Indo-Burman Ranges and the frontal thrusts and suture zones of the Himalaya. These two sets of compressive features imply maximum compressive stress axes that lie at right angles to each other. The implications are either that the orientation of the stress field changes rapidly over a short distance or that the stress field has changed through time. Both occurrences seem to be true.« less

Interior design for dentistry.

PubMed

Unthank, M; True, G

1999-11-01

In the increasingly complex, competitive and stressful field of dentistry, effectively designed dental offices can offer significant benefits. Esthetic, functional and life-cycle cost issues to be considered when developing your interior design scheme include color, finishes, lighting, furnishings, art and accessories. An appropriately designed dental office serves as a valuable marketing tool for your practice, as well as a safe and enjoyable work environment. Qualified interior design professionals can help you make design decisions that can yield optimum results within your budget.

Mechanical design of DNA nanostructures

NASA Astrophysics Data System (ADS)

Castro, Carlos E.; Su, Hai-Jun; Marras, Alexander E.; Zhou, Lifeng; Johnson, Joshua

2015-03-01

Structural DNA nanotechnology is a rapidly emerging field that has demonstrated great potential for applications such as single molecule sensing, drug delivery, and templating molecular components. As the applications of DNA nanotechnology expand, a consideration of their mechanical behavior is becoming essential to understand how these structures will respond to physical interactions. This review considers three major avenues of recent progress in this area: (1) measuring and designing mechanical properties of DNA nanostructures, (2) designing complex nanostructures based on imposed mechanical stresses, and (3) designing and controlling structurally dynamic nanostructures. This work has laid the foundation for mechanically active nanomachines that can generate, transmit, and respond to physical cues in molecular systems.Structural DNA nanotechnology is a rapidly emerging field that has demonstrated great potential for applications such as single molecule sensing, drug delivery, and templating molecular components. As the applications of DNA nanotechnology expand, a consideration of their mechanical behavior is becoming essential to understand how these structures will respond to physical interactions. This review considers three major avenues of recent progress in this area: (1) measuring and designing mechanical properties of DNA nanostructures, (2) designing complex nanostructures based on imposed mechanical stresses, and (3) designing and controlling structurally dynamic nanostructures. This work has laid the foundation for mechanically active nanomachines that can generate, transmit, and respond to physical cues in molecular systems. Electronic supplementary information (ESI) available. See DOI: 10.1039/c4nr07153k

The Role of Teacher Stress, Cognitive Complexity, and Career Maturity in Teacher Socialization.

ERIC Educational Resources Information Center

Franz, John B.; Dembo, Myron H.

A research study investigated the relationship of stress in teachers' work environment to teachers' level of cognitive complexity (level of thinking) and their career maturity, and the relationship of stress, cognitive complexity, and career maturity to teaching experience. Participants were teaching elementary school in an urban environment: 23…

Global Failure Modes in Composite Structures

NASA Technical Reports Server (NTRS)

Knauss, W. G.; Gonzalez, Luis

2001-01-01

Composite materials provide well-known advantages for space and aeronautical applications in terms of strength and rigidity to weight ratios and other mechanical properties. As a consequence, their use has experienced a constant increase in the past decades and it is anticipated that this trend will be maintained in the near future. At the same time, being these materials relatively new compared to metals, and having failure characteristics completely different from them, their damage growth and their failure mechanisms are not as well understood in a predictive sense. For example, while in metals fracture produces "clean" cracks with their well defined analytically stress fields at the crack tip, composite fracture is a more complex phenomenon. Instead of a crack, we confront a "damage zone" that may include fiber breakage, fiber microbuckling, fiber pullout, matrix cracking, delamination, debonding or any combination of all these different mechanisms. These phenomena are prevalent in any failure process through an aircraft structure, whether one addresses a global failure such as the ripping of a fuselage or wing section, or whether one is concerned with the failure initiation near a thickness change at stringers or other reinforcement. Thus the topic that has been under consideration has wide application in any real structure and is considered an essential contribution to the predictive failure analysis capability for aircraft containing composite components. The heterogeneity and the anisotropy of composites are not only advantageous but essential characteristics, yet these same features provide complex stress fields, especially in the presence of geometrical discontinuities such as notches, holes or cutouts or structural elements such as stiffeners, stringers, etc. To properly address the interaction between a damage/crack front and a hole with a stringer it is imperative that the stress and deformation fields of the former be (sufficiently well) characterized. The question of "scaling" is an essential concern in any structural materials investigation. For example, experiments in the past have shown that the "strength" of a composite depends on hole size. As a consequence the validity of traditional fracture mechanics concepts applied to composite materials failure must be questioned. The size of the fibers, the dimensions of the laminae, etc. together with the fact that, because of the layered anisotropy, the stress field is no longer two-dimensional, prevent the otherwise obviously confident use of "similarity concepts". Therefore, the question needs to be raised of whether in composites "size matters or not", i.e., whether the results obtained in a laboratory using small coupons are truly representative of the situation involving a full scale component.

Abiotic stress QTL in lettuce crop–wild hybrids: comparing greenhouse and field experiments

PubMed Central

Hartman, Yorike; Hooftman, Danny A P; Uwimana, Brigitte; Schranz, M Eric; van de Wiel, Clemens C M; Smulders, Marinus J M; Visser, Richard G F; Michelmore, Richard W; van Tienderen, Peter H

2014-01-01

The development of stress-tolerant crops is an increasingly important goal of current crop breeding. A higher abiotic stress tolerance could increase the probability of introgression of genes from crops to wild relatives. This is particularly relevant to the discussion on the risks of new GM crops that may be engineered to increase abiotic stress resistance. We investigated abiotic stress QTL in greenhouse and field experiments in which we subjected recombinant inbred lines from a cross between cultivated Lactuca sativa cv. Salinas and its wild relative L. serriola to drought, low nutrients, salt stress, and aboveground competition. Aboveground biomass at the end of the rosette stage was used as a proxy for the performance of plants under a particular stress. We detected a mosaic of abiotic stress QTL over the entire genome with little overlap between QTL from different stresses. The two QTL clusters that were identified reflected general growth rather than specific stress responses and colocated with clusters found in earlier studies for leaf shape and flowering time. Genetic correlations across treatments were often higher among different stress treatments within the same experiment (greenhouse or field), than among the same type of stress applied in different experiments. Moreover, the effects of the field stress treatments were more correlated with those of the greenhouse competition treatments than to those of the other greenhouse stress experiments, suggesting that competition rather than abiotic stress is a major factor in the field. In conclusion, the introgression risk of stress tolerance (trans-)genes under field conditions cannot easily be predicted based on genomic background selection patterns from controlled QTL experiments in greenhouses, especially field data will be needed to assess potential (negative) ecological effects of introgression of these transgenes into wild relatives. PMID:25360276

Analysis of stresses in finite anisotropic panels with centrally located cutouts

NASA Technical Reports Server (NTRS)

Britt, Vicki O.

1992-01-01

A method for analyzing biaxial- and shear-loaded anisotropic rectangular panels with centrally located circular and elliptical cutouts is presented in the present paper. The method is based on Lekhnitskii's complex variable equations of plane elastostatics combined with a boundary collocation method and a Laurent series approximation. Results are presented for anisotropic panels with elliptical cutouts and subjected to combined shear and compression loading. The effects on the stress field of panel aspect ratio, anisotropy, cutout size, and cutout orientation are addressed. Angle-ply laminates, unidirectional off-axis laminates, and ((+ or - 45/0/90)(sub 3))s, ((+ or - 45/0(sub 2))(sub 3))s, and ((+ or - 45/90(sub 2))(sub 3))s laminates are examined.

Exploratory behaviour in the open field test adapted for larval zebrafish: impact of environmental complexity.

PubMed

Ahmad, Farooq; Richardson, Michael K

2013-01-01

This study aimed to develop and characterize a novel (standard) open field test adapted for larval zebrafish. We also developed and characterized a variant of the same assay consisting of a colour-enriched open field; this was used to assess the impact of environmental complexity on patterns of exploratory behaviours as well to determine natural colour preference/avoidance. We report the following main findings: (1) zebrafish larvae display characteristic patterns of exploratory behaviours in the standard open field, such as thigmotaxis/centre avoidance; (2) environmental complexity (i.e. presence of colours) differentially affects patterns of exploratory behaviours and greatly attenuates natural zone preference; (3) larvae displayed the ability to discriminate colours. As reported previously in adult zebrafish, larvae showed avoidance towards blue and black; however, in contrast to the reported adult behaviour, larvae displayed avoidance towards red. Avoidance towards yellow and preference for green and orange are shown for the first time, (4) compared to standard open field tests, exposure to the colour-enriched open field resulted in an enhanced expression of anxiety-like behaviours. To conclude, we not only developed and adapted a traditional rodent behavioural assay that serves as a gold standard in preclinical drug screening, but we also provide a version of the same test that affords the possibility to investigate the impact of environmental stress on behaviour in larval zebrafish while representing the first test for assessment of natural colour preference/avoidance in larval zebrafish. In the future, these assays will improve preclinical drug screening methodologies towards the goal to uncover novel drugs. This article is part of a Special Issue entitled: insert SI title. Copyright © 2012 Elsevier B.V. All rights reserved.

Roles of URLs in Probing Controls on Induced Seismicity and Permeability Evolution

NASA Astrophysics Data System (ADS)

Elsworth, D.

2014-12-01

The generation and extension of new fractures and the development of controlled slip and opening are an implicit component in both forming and in enhancing flow pathways to unlock hydrocarbons and geothermal energy in otherwise very low permeability formations. The opposite is true for containment structures and caprocks. The complex stress state coupled with pre-existing fracture networks means that new flow pathways may develop in complex ways including varied modes of dilatation and slip, deformation that may be seismic or aseismic and permeability that may net increase of decrease. Where this deformation relies on either the reactivation, extension or development of fractures, this evolution is intrinsically scale dependent requiring that an improved understanding of this dynamic response must interrogate its evolution at representative scales - scales of decimeters to a few meters. We explore the controls on instability through frictional slip and instability including changes related to environmental conditions and physical properties. The former relate to changes in effective stress driven by fluid pressures, thermal and chemical stresses and the latter to changes in strength and stability conditioned on initial or evolving mineralogy. We identify important contemporary questions that are intrinsically scale dependent and may be effectively probed by field experimentation linking deformation and permeability.

Tectonic Uplift of the Danba Area in the Eastern Tibetan Plateau

NASA Astrophysics Data System (ADS)

Chang, C. P.; Ho, H. P.; Horng, C. S.; Hsu, Y. C.; Tan, X. B.

2017-12-01

The Danba anticline in the eastern Tibetan Plateau is located between the Longmenshan orogen to the east and the Xianshuihe sinistral fault zone to the west. This anticline has been recognized as an area with extreme exhumation by previous studies. The Tibetan plateau was built by the convergence between Indo-Australian plate and Eurasian plate since early Cenozoic. The eastward lower crustal flow under the plateau obstructed by the Yangtze craton soon after this convergence generated a very complex structural situation in the southeastern side of the Tibetan plateau. In this study, in order to understand the processes and mechanisms of the structural complexity of the Danba area, we apply two methods: stress analysis and magnetic measurement. By measuring the brittle deformation recorded in the strata, we carry out a series of stress analysis to demonstrate the stress field of this area. In addition, due to comprehend the magnetic characteristics of low-grade metamorphic rocks and volcanic rocks in this area, we process the rock magnetic measurement of hysteresis loop and X-ray diffraction analysis. The occurrence of pyrrhotite can be taken as an important isograd in low-grade metamorphic rocks, which is helpful for stratigraphic and structural studies. Based on our results, we try to explain the mechanism of this rapid uplift, which involves material, structural, and kinematic interaction.

The co-existence of depression, anxiety and post-traumatic stress symptoms in the perinatal period: A systematic review.

PubMed

Agius, Andee; Xuereb, Rita Borg; Carrick-Sen, Debbie; Sultana, Roberta; Rankin, Judith

2016-05-01

to identify and appraise the current international evidence regarding the presence and prevalence of the co-existence of depression, anxiety and post-traumatic stress symptoms in the antenatal and post partum period. using a list of keywords, Medline, CINHAL, Cochrane Library, EMBASE, PsychINFO, Web of Science and the Index of Theses and Conference Proceedings (Jan 1960 - Jan 2015) were systematically searched. Experts in the field were contacted to locate papers that were in progress or in press. Reference lists from relevant review articles were searched. Inclusion criteria included full papers published in English reporting concurrent depression, anxiety and post-traumatic stress symptoms in pregnant and post partum women. A validated data extraction review tool was used. 3424 citations were identified. Three studies met the full inclusion criteria. All reported findings in the postnatal period. No antenatal studies were identified. The prevalence of triple co-morbidity was relatively low ranging from 2% to 3%. triple co-morbidity does occur, although the prevalence appears to be low. Due to the presentation of complex symptoms, women with triple co-morbidity are likely to be difficult to identify, diagnose and treat. Clinical staff should be aware of the potential of complex symptomatology. Copyright © 2016 Elsevier Ltd. All rights reserved.

Triggers of the HSP70 stress response: environmental responses and laboratory manipulation in an Antarctic marine invertebrate (Nacella concinna)

PubMed Central

Peck, Lloyd S.

2009-01-01

The Antarctic limpet, Nacella concinna, exhibits the classical heat shock response, with up-regulation of duplicated forms of the inducible heat shock protein 70 (HSP70) gene in response to experimental manipulation of seawater temperatures. However, this response only occurs in the laboratory at temperatures well in excess of any experienced in the field. Subsequent environmental sampling of inter-tidal animals also showed up-regulation of these genes, but at temperature thresholds much lower than those required to elicit a response in the laboratory. It was hypothesised that this was a reflection of the complexity of the stresses encountered in the inter-tidal region. Here, we describe a further series of experiments comprising both laboratory manipulation and environmental sampling of N. concinna. We investigate the expression of HSP70 gene family members (HSP70A, HSP70B, GRP78 and HSC70) in response to a further suite of environmental stressors: seasonal and experimental cold, freshwater, desiccation, chronic heat and periodic emersion. Lowered temperatures (−1.9°C and −1.6°C), generally produced a down-regulation of all HSP70 family members, with some up-regulation of HSC70 when emerging from the winter period and increasing sea temperatures. There was no significant response to freshwater immersion. In response to acute and chronic heat treatments plus simulated tidal cycles, the data showed a clear pattern. HSP70A showed a strong but very short-term response to heat whilst the duplicated HSP70B also showed heat to be a trigger, but had a more sustained response to complex stresses. GRP78 expression indicates that it was acting as a generalised stress response under the experimental conditions described here. HSC70 was the major chaperone invoked in response to long-term stresses of varying types. These results provide intriguing clues not only to the complexity of HSP70 gene expression in response to environmental change but also insights into the stress response of a non-model species. PMID:19404777

Triggers of the HSP70 stress response: environmental responses and laboratory manipulation in an Antarctic marine invertebrate (Nacella concinna).

PubMed

Clark, Melody S; Peck, Lloyd S

2009-11-01

The Antarctic limpet, Nacella concinna, exhibits the classical heat shock response, with up-regulation of duplicated forms of the inducible heat shock protein 70 (HSP70) gene in response to experimental manipulation of seawater temperatures. However, this response only occurs in the laboratory at temperatures well in excess of any experienced in the field. Subsequent environmental sampling of inter-tidal animals also showed up-regulation of these genes, but at temperature thresholds much lower than those required to elicit a response in the laboratory. It was hypothesised that this was a reflection of the complexity of the stresses encountered in the inter-tidal region. Here, we describe a further series of experiments comprising both laboratory manipulation and environmental sampling of N. concinna. We investigate the expression of HSP70 gene family members (HSP70A, HSP70B, GRP78 and HSC70) in response to a further suite of environmental stressors: seasonal and experimental cold, freshwater, desiccation, chronic heat and periodic emersion. Lowered temperatures (-1.9 degrees C and -1.6 degrees C), generally produced a down-regulation of all HSP70 family members, with some up-regulation of HSC70 when emerging from the winter period and increasing sea temperatures. There was no significant response to freshwater immersion. In response to acute and chronic heat treatments plus simulated tidal cycles, the data showed a clear pattern. HSP70A showed a strong but very short-term response to heat whilst the duplicated HSP70B also showed heat to be a trigger, but had a more sustained response to complex stresses. GRP78 expression indicates that it was acting as a generalised stress response under the experimental conditions described here. HSC70 was the major chaperone invoked in response to long-term stresses of varying types. These results provide intriguing clues not only to the complexity of HSP70 gene expression in response to environmental change but also insights into the stress response of a non-model species.

Global warming and stress complexes in forests of western North America

Treesearch

Donald McKenzie; David L. Peterson; Jeremy J. Littell

2009-01-01

A warmer climate in western North America will likely affect forests directly through soil moisture stress and indirectly through increased extent and severity of disturbances. We propose that stress complexes, combinations of biotic and abiotic stresses, compromise the vigor and ultimate sustainability of forest ecosystems. Across...

A stress-free model for residual stress assessment using thermoelastic stress analysis

NASA Astrophysics Data System (ADS)

Howell, Geoffrey; Dulieu-Barton, Janice M.; Achintha, Mithila; Robinson, Andrew F.

2015-03-01

Thermoelastic Stress Analysis (TSA) has been proposed as a method of obtaining residual stresses. The results of a preliminary study demonstrated that when Al-2024 plate containing holes that were plastically deformed by cold expansion process to 2% and 4% strain the thermoelastic response in the material around the hole was different to that obtained from a plate that had not experienced any plastic cold expansion (i.e. a reference specimen). This observation provides an opportunity for obtaining residual stresses based on TSA data. In many applications a reference specimen (i.e. residual stress free specimen) may not be available for comparison, so a synthetic, digital bitmap has been proposed as an alternative. An elastic finite element model is created using commercially available software Abaqus/Standard and the resultant stress field is extracted. The simulated stress field from the model is mapped onto a grid that matches the TSA pixel data from a physical reference specimen. This stress field is then converted to a ΔT/T field that can be compared to the full-field TSA data. When the reference experimental data is subtracted from the, bitmap dataset the resultant ΔT/T field is approximately zero. Further work proposes replacing the experimental reference data with that from specimens that have undergone cold expansion with the aim of revealing the regions affected by residual stress through a departure from zero in the resultant stress field. The paper demonstrates the first steps necessary for deriving the residual stresses from a general specimen using TSA.

Stress Recovery and Error Estimation for 3-D Shell Structures

NASA Technical Reports Server (NTRS)

Riggs, H. R.

2000-01-01

The C1-continuous stress fields obtained from finite element analyses are in general lower- order accurate than are the corresponding displacement fields. Much effort has focussed on increasing their accuracy and/or their continuity, both for improved stress prediction and especially error estimation. A previous project developed a penalized, discrete least squares variational procedure that increases the accuracy and continuity of the stress field. The variational problem is solved by a post-processing, 'finite-element-type' analysis to recover a smooth, more accurate, C1-continuous stress field given the 'raw' finite element stresses. This analysis has been named the SEA/PDLS. The recovered stress field can be used in a posteriori error estimators, such as the Zienkiewicz-Zhu error estimator or equilibrium error estimators. The procedure was well-developed for the two-dimensional (plane) case involving low-order finite elements. It has been demonstrated that, if optimal finite element stresses are used for the post-processing, the recovered stress field is globally superconvergent. Extension of this work to three dimensional solids is straightforward. Attachment: Stress recovery and error estimation for shell structure (abstract only). A 4-node, shear-deformable flat shell element developed via explicit Kirchhoff constraints (abstract only). A novel four-node quadrilateral smoothing element for stress enhancement and error estimation (abstract only).

Recent tectonic stress field, active faults and geothermal fields (hot-water type) in China

NASA Astrophysics Data System (ADS)

Wan, Tianfeng

1984-10-01

It is quite probable that geothermal fields of the hot-water type in China do not develop in the absence of recently active faults. Such active faults are all controlled by tectonic stress fields. Using the data of earthquake fault-plane solutions, active faults, and surface thermal manifestations, a map showing the recent tectonic stress field, and the location of active faults and geothermal fields in China is presented. Data collected from 89 investigated prospects with geothermal manifestations indicate that the locations of geothermal fields are controlled by active faults and the recent tectonic stress field. About 68% of the prospects are controlled by tensional or tensional-shear faults. The angle between these faults and the direction of maximum compressive stress is less than 45°, and both tend to be parallel. About 15% of the prospects are controlled by conjugate faults. Another 14% are controlled by compressive-shear faults where the angle between these faults and the direction maximum compressive stress is greater than 45°.

Modeling the Collisional-Plastic Stress Transition for Bin Discharge of Granular Material

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

Pannala, Sreekanth; Daw, C Stuart; FINNEY, Charles E A

2009-01-01

We propose a heuristic model for the transition between collisional and frictional/plastic stresses in the flow of granular material. Our approach is based on a physically motivated, nonlinear blending function that produces a weighted average of the limiting stresses, depending on the local void fraction in the flow field. Previously published stress models are utilized to describe the behavior in the collisional (Lun et al., 1984) and quasi-static limits (Schaeffer, 1987 and Syamlal et al., 1993). Sigmoidal and hyperbolic tangent functions are used to mimic the observed smooth yet rapid transition between the collisional and plastic stress zones. We implementmore » our stress transition model in an opensource multiphase flow solver, MFIX (Multiphase Flow with Interphase eXchanges, www.mfix.org) and demonstrate its application to a standard bin discharge problem. The model s effectiveness is illustrated by comparing computational predictions to the experimentally derived Beverloo correlation. With the correct choice of function parameters, the model predicts bin discharge rates within the error margins of the Beverloo correlation and is more accurate than one of the alternative granular stress models proposed in the literature. Although a second granular stress model in the literature is also reasonably consistent with the Beverloo correlation, we propose that our alternative blending function is likely to be more adaptable to situations with more complex solids properties (e.g., sticky solids).« less

The significance of ACTH for the process of formation of complex heparin compounds in the blood during immobilization stress

NASA Technical Reports Server (NTRS)

Kudryashov, B. A.; Shapiro, F. B.; Lomovskaya, F. B.; Lyapina, L. A.

1979-01-01

Adrenocorticotropin (ACTH) was administered to rats at different times following adrenalectomy. Adrenocorticotropin caused a significant increase in the formation of heparin complexes even in the absence of stress factor. When ACTH secretion is blocked, immobilization stress is not accompanied by an increase in the process of complex formation. The effect of ACTH on the formation of heparin complexes was mediated through its stimulation of the adrenal cortex.

Fracture Mechanics of Thin, Cracked Plates Under Tension, Bending and Out-of-Plane Shear Loading

NASA Technical Reports Server (NTRS)

Zehnder, Alan T.; Hui, C. Y.; Potdar, Yogesh; Zucchini, Alberto

1999-01-01

Cracks in the skin of aircraft fuselages or other shell structures can be subjected to very complex stress states, resulting in mixed-mode fracture conditions. For example, a crack running along a stringer in a pressurized fuselage will be subject to the usual in-plane tension stresses (Mode-I) along with out-of-plane tearing stresses (Mode-III like). Crack growth and initiation in this case is correlated not only with the tensile or Mode-I stress intensity factor, K(sub I), but depends on a combination of parameters and on the history of crack growth. The stresses at the tip of a crack in a plate or shell are typically described in terms of either the small deflection Kirchhoff plate theory. However, real applications involve large deflections. We show, using the von-Karman theory, that the crack tip stress field derived on the basis of the small deflection theory is still valid for large deflections. We then give examples demonstrating the exact calculation of energy release rates and stress intensity factors for cracked plates loaded to large deflections. The crack tip fields calculated using the plate theories are an approximation to the actual three dimensional fields. Using three dimensional finite element analyses we have explored the relationship between the three dimensional elasticity theory and two dimensional plate theory results. The results show that for out-of-plane shear loading the three dimensional and Kirchhoff theory results coincide at distance greater than h/2 from the crack tip, where h/2 is the plate thickness. Inside this region, the distribution of stresses through the thickness can be very different from the plate theory predictions. We have also explored how the energy release rate varies as a function of crack length to plate thickness using the different theories. This is important in the implementation of fracture prediction methods using finite element analysis. Our experiments show that under certain conditions, during fatigue crack growth, the presence of out-of-plane shear loads induces a great deal of contact and friction on the crack surfaces, dramatically reducing crack growth rate. A series of experiments and a proposed computational approach for accounting for the friction is discussed.

Distributed Stress Sensing and Non-Destructive Tests Using Mechanoluminescence Materials

NASA Astrophysics Data System (ADS)

Rahimi, Mohammad Reza

Rapid aging of infrastructure systems is currently pervasive in the US and the anticipated cost until 2020 for rehabilitation of aging lifeline will reach 3.6 trillion US dollars (ASCE 2013). Reliable condition or serviceability assessment is critically important in decision-making for economic and timely maintenance of the infrastructure systems. Advanced sensors and nondestructive test (NDT) methods are the key technologies for structural health monitoring (SHM) applications that can provide information on the current state of structures. There are many traditional sensors and NDT methods, for examples, strain gauges, ultrasound, radiography and other X-ray, etc. to detect any defect on the infrastructure. Considering that civil infrastructure is typically large-scale and exhibits complex behavior, estimation of structural conditions by the local sensing and NDT methods is a challenging task. Non-contact and distributed (or full-field) sensing and NDT method are desirable that can provide rich information on the civil infrastructure's state. Materials with the ability of emitting light, especially in the visible range, are named as luminescent materials. Mechanoluminescence (ML) phenomenon is the light emission from luminescent materials as a response of an induced mechanical stress. ML materials offer new opportunities for SHM that can directly visualize the stress and crack distributions on the surface of structures through ML light emission. Although material research for ML phenomena have been made substantially, applications of the ML sensors to full-field stress and crack visualization are still at infant stage and have yet to be full-fledged. Moreover, practical applications of the ML sensors for SHM of civil infrastructure have difficulties since numerous challenging problems (e.g. environmental effect) arise in actual applications. In order to realize a practical SHM system employing ML sensors, more research needs to be conducted, for examples, fundamental understandings of physics of ML phenomenon, method for quantitative stress measurements, calibration method for ML sensors, improvement of sensitivity, optimal manufacturing and design of ML sensors, environmental effects of ML phenomenon (e.g. temperature), image processing and analysis, etc. In this research, fundamental ML phenomena of two most promising ML sensing materials were experimentally studied and a methodology for full-field quantitative strain measurements, for the first time, was proposed along with a standardized calibration method. Characteristics and behavior of ML composites and thin films coated on the structure have been studied under various material tests including compression, tension, pure shear, bending, etc. In addition, ML emission sensitivity to the manufacturing parameters and experimental conditions was addressed in order to find optimal design the ML sensor. A phenomenological stress-optics transduction model for predicting the ML light intensity from a thin-film ML coating sensor subjected to in-plane stresses was proposed. A new full-field quantitative strain measuring methodology by ML thin film sensor was developed, for the first time, in order to visualize and measure the strain field. The results from the ML sensor were compared and verified by finite element simulation results. For NDT applications of ML sensors, experimental tests were conducted to visualize the cracks on structural surfaces and detect damages on structural components. In summary, this research proposes and realizes a new distributed stress sensor and NDT method using ML sensing materials. The proposed method is experimentally validated to be effective for stress measurement and crack visualizations. Successful completion of this research provides a leap toward a commercial light intensity-based optic sensor to be used as a new full-field stress measurement technology and NDT method.

Battlefield ethics training: integrating ethical scenarios in high-intensity military field exercises.

PubMed

Thompson, Megan M; Jetly, Rakesh

2014-01-01

There is growing evidence that modern missions have added stresses and ethical complexities not seen in previous military operations and that there are links between battlefield stressors and ethical lapses. Military ethicists have concluded that the ethical challenges of modern missions are not well addressed by current military ethics educational programs. Integrating the extant research in the area, we propose that scenario-based operational ethics training in high-intensity military field training settings may be an important adjunct to traditional military ethics education and training. We make the case as to why this approach will enhance ethical operational preparation for soldiers, supporting their psychological well-being as well as mission effectiveness.

Battlefield ethics training: integrating ethical scenarios in high-intensity military field exercises

PubMed Central

Thompson, Megan M.; Jetly, Rakesh

2014-01-01

There is growing evidence that modern missions have added stresses and ethical complexities not seen in previous military operations and that there are links between battlefield stressors and ethical lapses. Military ethicists have concluded that the ethical challenges of modern missions are not well addressed by current military ethics educational programs. Integrating the extant research in the area, we propose that scenario-based operational ethics training in high-intensity military field training settings may be an important adjunct to traditional military ethics education and training. We make the case as to why this approach will enhance ethical operational preparation for soldiers, supporting their psychological well-being as well as mission effectiveness. PMID:25206947

A three-dimensional turbulent separated flow and related mesurements

NASA Technical Reports Server (NTRS)

Pierce, F. J.

1985-01-01

The applicability of and the limits on the applicability of 11 near wall similarity laws characterizing three-dimensional turbulent boundary layer flows were determined. A direct force sensing local wall shear stress meter was used in both pressure-driven and shear-driven three-dimensional turbulent boundary layers, together with extensive mean velocity field and wall pressure field data. This resulted in a relatively large number of graphical comparisons of the predictive ability of 10 of these 11 similarity models relative to measured data over a wide range of flow conditions. Documentation of a complex, separated three-dimensional turbulent flow as a standard test case for evaluating the predictive ability of numerical codes solving such flows is presented.

Theoretical Analysis of the Mechanism of Fracture Network Propagation with Stimulated Reservoir Volume (SRV) Fracturing in Tight Oil Reservoirs.

PubMed

Su, Yuliang; Ren, Long; Meng, Fankun; Xu, Chen; Wang, Wendong

2015-01-01

Stimulated reservoir volume (SRV) fracturing in tight oil reservoirs often induces complex fracture-network growth, which has a fundamentally different formation mechanism from traditional planar bi-winged fracturing. To reveal the mechanism of fracture network propagation, this paper employs a modified displacement discontinuity method (DDM), mechanical mechanism analysis and initiation and propagation criteria for the theoretical model of fracture network propagation and its derivation. A reasonable solution of the theoretical model for a tight oil reservoir is obtained and verified by a numerical discrete method. Through theoretical calculation and computer programming, the variation rules of formation stress fields, hydraulic fracture propagation patterns (FPP) and branch fracture propagation angles and pressures are analyzed. The results show that during the process of fracture propagation, the initial orientation of the principal stress deflects, and the stress fields at the fracture tips change dramatically in the region surrounding the fracture. Whether the ideal fracture network can be produced depends on the geological conditions and on the engineering treatments. This study has both theoretical significance and practical application value by contributing to a better understanding of fracture network propagation mechanisms in unconventional oil/gas reservoirs and to the improvement of the science and design efficiency of reservoir fracturing.

Theoretical Analysis of the Mechanism of Fracture Network Propagation with Stimulated Reservoir Volume (SRV) Fracturing in Tight Oil Reservoirs

PubMed Central

Su, Yuliang; Ren, Long; Meng, Fankun; Xu, Chen; Wang, Wendong

2015-01-01

Stimulated reservoir volume (SRV) fracturing in tight oil reservoirs often induces complex fracture-network growth, which has a fundamentally different formation mechanism from traditional planar bi-winged fracturing. To reveal the mechanism of fracture network propagation, this paper employs a modified displacement discontinuity method (DDM), mechanical mechanism analysis and initiation and propagation criteria for the theoretical model of fracture network propagation and its derivation. A reasonable solution of the theoretical model for a tight oil reservoir is obtained and verified by a numerical discrete method. Through theoretical calculation and computer programming, the variation rules of formation stress fields, hydraulic fracture propagation patterns (FPP) and branch fracture propagation angles and pressures are analyzed. The results show that during the process of fracture propagation, the initial orientation of the principal stress deflects, and the stress fields at the fracture tips change dramatically in the region surrounding the fracture. Whether the ideal fracture network can be produced depends on the geological conditions and on the engineering treatments. This study has both theoretical significance and practical application value by contributing to a better understanding of fracture network propagation mechanisms in unconventional oil/gas reservoirs and to the improvement of the science and design efficiency of reservoir fracturing. PMID:25966285

Incorporation of experimentally derived friction laws in numerical simulations of earthquake generated tsunamis

NASA Astrophysics Data System (ADS)

Murphy, Shane; Spagnuolo, Elena; Lorito, Stefano; Di Toro, Giulio; Scala, Antonio; Festa, Gaetano; Nielsen, Stefan; Piatanesi, Alessio; Romano, Fabrizio; Aretusini, Stefano

2016-04-01

Seismological, tsunami and geodetic observations have shown that subduction zones are complex systems where the properties of earthquake rupture vary with depth. For example nucleation and high frequency radiation generally occur at depth but low frequency radiation and large tsunami-genic slip appear to occur in the shallow crustal depth. Numerical simulations used to describe these features predominantly use standardised theoretical equations or experimental observations often assuming that their validity extends to all slip-rates, lithologies and tectonic environments. However recent rotary-shear experiments performed on a range of diverse materials and experimental conditions highlighted the large variability of the evolution of friction during slipping pointing to a more complex relationship between material type, slip rate and normal stress. Simulating dynamic rupture using a 2D spectral element methodology on a Tohoku like fault, we apply experimentally derived friction laws (i.e. thermal slip distance friction law, Di Toro et al. 2011) Choice of parameters for the friction law are based on expected material type (e.g. cohesive and non-cohesive clay rich material representative of an accretionary wedge), the normal stress which is controlled by the interaction between the regional stress field and the fault geometry. The shear stress distribution on the fault plane is fractal with the yield stress dependent on the static coefficient of friction and the normal stress, parameters that are dependent on the material type and geometry. We use metrics such as the slip distribution, ground motion and fracture energy to explore the effect of frictional behaviour, fault geometry and stress perturbations and its potential role in tsunami generation. Preliminary results will be presented. This research is funded by the European Union's Seventh Framework Programme (FP7/2007-2013) under grant agreement n° 603839 (Project ASTARTE - Assessment, Strategy and Risk Reduction for Tsunamis in Europe) and by the ERC CoG NOFEAR project 614705

A large-eddy simulation based power estimation capability for wind farms over complex terrain

NASA Astrophysics Data System (ADS)

Senocak, I.; Sandusky, M.; Deleon, R.

2017-12-01

There has been an increasing interest in predicting wind fields over complex terrain at the micro-scale for resource assessment, turbine siting, and power forecasting. These capabilities are made possible by advancements in computational speed from a new generation of computing hardware, numerical methods and physics modelling. The micro-scale wind prediction model presented in this work is based on the large-eddy simulation paradigm with surface-stress parameterization. The complex terrain is represented using an immersed-boundary method that takes into account the parameterization of the surface stresses. Governing equations of incompressible fluid flow are solved using a projection method with second-order accurate schemes in space and time. We use actuator disk models with rotation to simulate the influence of turbines on the wind field. Data regarding power production from individual turbines are mostly restricted because of proprietary nature of the wind energy business. Most studies report percentage drop of power relative to power from the first row. There have been different approaches to predict power production. Some studies simply report available wind power in the upstream, some studies estimate power production using power curves available from turbine manufacturers, and some studies estimate power as torque multiplied by rotational speed. In the present work, we propose a black-box approach that considers a control volume around a turbine and estimate the power extracted from the turbine based on the conservation of energy principle. We applied our wind power prediction capability to wind farms over flat terrain such as the wind farm over Mower County, Minnesota and the Horns Rev offshore wind farm in Denmark. The results from these simulations are in good agreement with published data. We also estimate power production from a hypothetical wind farm in complex terrain region and identify potential zones suitable for wind power production.

Simultaneous measurement of temperature, stress, and electric field in GaN HEMTs with micro-Raman spectroscopy.

PubMed

Bagnall, Kevin R; Moore, Elizabeth A; Badescu, Stefan C; Zhang, Lenan; Wang, Evelyn N

2017-11-01

As semiconductor devices based on silicon reach their intrinsic material limits, compound semiconductors, such as gallium nitride (GaN), are gaining increasing interest for high performance, solid-state transistor applications. Unfortunately, higher voltage, current, and/or power levels in GaN high electron mobility transistors (HEMTs) often result in elevated device temperatures, degraded performance, and shorter lifetimes. Although micro-Raman spectroscopy has become one of the most popular techniques for measuring localized temperature rise in GaN HEMTs for reliability assessment, decoupling the effects of temperature, mechanical stress, and electric field on the optical phonon frequencies measured by micro-Raman spectroscopy is challenging. In this work, we demonstrate the simultaneous measurement of temperature rise, inverse piezoelectric stress, thermoelastic stress, and vertical electric field via micro-Raman spectroscopy from the shifts of the E 2 (high), A 1 longitudinal optical (LO), and E 2 (low) optical phonon frequencies in wurtzite GaN. We also validate experimentally that the pinched OFF state as the unpowered reference accurately measures the temperature rise by removing the effect of the vertical electric field on the Raman spectrum and that the vertical electric field is approximately the same whether the channel is open or closed. Our experimental results are in good quantitative agreement with a 3D electro-thermo-mechanical model of the HEMT we tested and indicate that the GaN buffer acts as a semi-insulating, p-type material due to the presence of deep acceptors in the lower half of the bandgap. This implementation of micro-Raman spectroscopy offers an exciting opportunity to simultaneously probe thermal, mechanical, and electrical phenomena in semiconductor devices under bias, providing unique insight into the complex physics that describes device behavior and reliability. Although GaN HEMTs have been specifically used in this study to demonstrate its viability, this technique is applicable to any solid-state material with a suitable Raman response and will likely enable new measurement capabilities in a wide variety of scientific and engineering applications.

Simultaneous measurement of temperature, stress, and electric field in GaN HEMTs with micro-Raman spectroscopy

NASA Astrophysics Data System (ADS)

Bagnall, Kevin R.; Moore, Elizabeth A.; Badescu, Stefan C.; Zhang, Lenan; Wang, Evelyn N.

2017-11-01

As semiconductor devices based on silicon reach their intrinsic material limits, compound semiconductors, such as gallium nitride (GaN), are gaining increasing interest for high performance, solid-state transistor applications. Unfortunately, higher voltage, current, and/or power levels in GaN high electron mobility transistors (HEMTs) often result in elevated device temperatures, degraded performance, and shorter lifetimes. Although micro-Raman spectroscopy has become one of the most popular techniques for measuring localized temperature rise in GaN HEMTs for reliability assessment, decoupling the effects of temperature, mechanical stress, and electric field on the optical phonon frequencies measured by micro-Raman spectroscopy is challenging. In this work, we demonstrate the simultaneous measurement of temperature rise, inverse piezoelectric stress, thermoelastic stress, and vertical electric field via micro-Raman spectroscopy from the shifts of the E2 (high), A1 longitudinal optical (LO), and E2 (low) optical phonon frequencies in wurtzite GaN. We also validate experimentally that the pinched OFF state as the unpowered reference accurately measures the temperature rise by removing the effect of the vertical electric field on the Raman spectrum and that the vertical electric field is approximately the same whether the channel is open or closed. Our experimental results are in good quantitative agreement with a 3D electro-thermo-mechanical model of the HEMT we tested and indicate that the GaN buffer acts as a semi-insulating, p-type material due to the presence of deep acceptors in the lower half of the bandgap. This implementation of micro-Raman spectroscopy offers an exciting opportunity to simultaneously probe thermal, mechanical, and electrical phenomena in semiconductor devices under bias, providing unique insight into the complex physics that describes device behavior and reliability. Although GaN HEMTs have been specifically used in this study to demonstrate its viability, this technique is applicable to any solid-state material with a suitable Raman response and will likely enable new measurement capabilities in a wide variety of scientific and engineering applications.

Stress Physiology of Lactic Acid Bacteria

PubMed Central

Papadimitriou, Konstantinos; Alegría, Ángel; Bron, Peter A.; de Angelis, Maria; Gobbetti, Marco; Kleerebezem, Michiel; Lemos, José A.; Linares, Daniel M.; Ross, Paul; Stanton, Catherine; Turroni, Francesca; van Sinderen, Douwe; Varmanen, Pekka; Ventura, Marco; Zúñiga, Manuel; Tsakalidou, Effie

2016-01-01

SUMMARY Lactic acid bacteria (LAB) are important starter, commensal, or pathogenic microorganisms. The stress physiology of LAB has been studied in depth for over 2 decades, fueled mostly by the technological implications of LAB robustness in the food industry. Survival of probiotic LAB in the host and the potential relatedness of LAB virulence to their stress resilience have intensified interest in the field. Thus, a wealth of information concerning stress responses exists today for strains as diverse as starter (e.g., Lactococcus lactis), probiotic (e.g., several Lactobacillus spp.), and pathogenic (e.g., Enterococcus and Streptococcus spp.) LAB. Here we present the state of the art for LAB stress behavior. We describe the multitude of stresses that LAB are confronted with, and we present the experimental context used to study the stress responses of LAB, focusing on adaptation, habituation, and cross-protection as well as on self-induced multistress resistance in stationary phase, biofilms, and dormancy. We also consider stress responses at the population and single-cell levels. Subsequently, we concentrate on the stress defense mechanisms that have been reported to date, grouping them according to their direct participation in preserving cell energy, defending macromolecules, and protecting the cell envelope. Stress-induced responses of probiotic LAB and commensal/pathogenic LAB are highlighted separately due to the complexity of the peculiar multistress conditions to which these bacteria are subjected in their hosts. Induction of prophages under environmental stresses is then discussed. Finally, we present systems-based strategies to characterize the “stressome” of LAB and to engineer new food-related and probiotic LAB with improved stress tolerance. PMID:27466284

Project Final Report: Linking Plant Stress, Biogenic SOA, and CCN Production - A New Feedback in the Climate System?

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

VanReken, Timothy; Balasingam, Muhunthan

2017-05-01

This project worked toward understanding the role of variable biogenic emissions in the formation of secondary organic aerosol (SOA), and in turn the potential for this aerosol to affect cloud droplet formation. It was premised on the idea that a changing climate could impose biogenic and abiogenic stresses on plants that would affect the emissions of volatile organic compounds (VOCs). The transformation of these VOCs to SOA and cloud condensation nuclei (CCN) implied the possibility of a feedback mechanism within the biosphere/atmosphere/climate system. The project’s activities centered on laboratory experiments to study the effects of stresses on plants and plant-derivedmore » material under controlled conditions, observing both the VOC emissions and the aerosol that formed from the oxidation of those VOCs. The results highlighted the potentially important contributions of stress and decomposition mechanisms to biogenic SOA formation. Related field measurements elucidated the conditions when these factors could be important in the ambient environment. The project also revealed repeated the complexity of the stress/VOC emission relationship, and the difficulty in expressing these relationships in a comprehensive manner.« less

Seismic sensitivity of normal-mode coupling to Lorentz stresses in the Sun

NASA Astrophysics Data System (ADS)

Hanasoge, Shravan M.

2017-09-01

Understanding the governing mechanism of solar magnetism remains an outstanding challenge in astrophysics. Seismology is the most compelling technique to infer the internal properties of the Sun and stars. Waves in the Sun, nominally acoustic, are sensitive to the emergence and cyclical strengthening of magnetic field, evidenced by measured changes in resonant oscillation frequencies that are correlated with the solar cycle. The inference of internal Lorentz stresses from these measurements has the potential to significantly advance our appreciation of the dynamo. Indeed, seismological inverse theory for the Sun is well understood for perturbations in composition, thermal structure and flows but, is not fully developed for magnetism, owing to the complexity of the ideal magnetohydrodynamic (MHD) equation. Invoking first-Born perturbation theory to characterize departures from spherically symmetric hydrostatic models of the Sun and applying the notation of generalized spherical harmonics, we calculate sensitivity functions of seismic measurements to the general time-varying Lorentz stress tensor. We find that eigenstates of isotropic (I.e. acoustic only) background models are dominantly sensitive to isotropic deviations in the stress tensor and much more weakly than anisotropic stresses (and therefore challenging to infer). The apple cannot fall far from the tree.

Simulations of Turbulent Flow Over Complex Terrain Using an Immersed-Boundary Method

NASA Astrophysics Data System (ADS)

DeLeon, Rey; Sandusky, Micah; Senocak, Inanc

2018-02-01

We present an immersed-boundary method to simulate high-Reynolds-number turbulent flow over the complex terrain of Askervein and Bolund Hills under neutrally-stratified conditions. We reconstruct both the velocity and the eddy-viscosity fields in the terrain-normal direction to produce turbulent stresses as would be expected from the application of a surface-parametrization scheme based on Monin-Obukhov similarity theory. We find that it is essential to be consistent in the underlying assumptions for the velocity reconstruction and the eddy-viscosity relation to produce good results. To this end, we reconstruct the tangential component of the velocity field using a logarithmic velocity profile and adopt the mixing-length model in the near-surface turbulence model. We use a linear interpolation to reconstruct the normal component of the velocity to enforce the impermeability condition. Our approach works well for both the Askervein and Bolund Hills when the flow is attached to the surface, but shows slight disagreement in regions of flow recirculation, despite capturing the flow reversal.

Simulations of Turbulent Flow Over Complex Terrain Using an Immersed-Boundary Method

NASA Astrophysics Data System (ADS)

DeLeon, Rey; Sandusky, Micah; Senocak, Inanc

2018-06-01

We present an immersed-boundary method to simulate high-Reynolds-number turbulent flow over the complex terrain of Askervein and Bolund Hills under neutrally-stratified conditions. We reconstruct both the velocity and the eddy-viscosity fields in the terrain-normal direction to produce turbulent stresses as would be expected from the application of a surface-parametrization scheme based on Monin-Obukhov similarity theory. We find that it is essential to be consistent in the underlying assumptions for the velocity reconstruction and the eddy-viscosity relation to produce good results. To this end, we reconstruct the tangential component of the velocity field using a logarithmic velocity profile and adopt the mixing-length model in the near-surface turbulence model. We use a linear interpolation to reconstruct the normal component of the velocity to enforce the impermeability condition. Our approach works well for both the Askervein and Bolund Hills when the flow is attached to the surface, but shows slight disagreement in regions of flow recirculation, despite capturing the flow reversal.

Evaluation of the evolving stress field of the Yellowstone volcanic plateau, 1988 to 2010, from earthquake first-motion inversions

NASA Astrophysics Data System (ADS)

Russo, E.; Waite, G. P.; Tibaldi, A.

2017-03-01

Although the last rhyolite eruption occurred around 70 ka ago, the silicic Yellowstone volcanic field is still considered active due to high hydrothermal and seismic activity and possible recent magma intrusions. Geodetic measurements document complex deformation patterns in crustal strain and seismic activity likewise reveal spatial and temporal variations in the stress field. We use earthquake data recorded between 1988 and 2010 to investigate these variations and their possible causes in more detail. Earthquake relocations and a set of 369 well-constrained, double-couple, focal mechanism solutions were computed. Events were grouped according to location and time to investigate trends in faulting. The majority of the events have normal-faulting solutions, subordinate strike-slip kinematics, and very rarely, reverse motions. The dominant direction of extension throughout the 0.64 Ma Yellowstone caldera is nearly ENE, consistent with the perpendicular direction of alignments of volcanic vents within the caldera, but our study also reveals spatial and temporal variations. Stress-field solutions for different areas and time periods were calculated from earthquake focal mechanism inversion. A well-resolved rotation of σ3 was found, from NNE-SSW near the Hebgen Lake fault zone, to ENE-WSW near Norris Junction. In particular, the σ3 direction changed throughout the years around Norris Geyser Basin, from being ENE-WSW, as calculated in the study by Waite and Smith (2004), to NNE-SSW, while the other σ3 directions are mostly unchanged over time. The presence of ;chocolate tablet; structures, with two sets of nearly perpendicular normal faults, was identified in many stages of the deformation history both in the Norris Geyser Basin area and inside the caldera.

Nanoscale Probing of Thermal, Stress, and Optical Fields under Near-Field Laser Heating

PubMed Central

Tang, Xiaoduan; Xu, Shen; Wang, Xinwei

2013-01-01

Micro/nanoparticle induced near-field laser ultra-focusing and heating has been widely used in laser-assisted nanopatterning and nanolithography to pattern nanoscale features on a large-area substrate. Knowledge of the temperature and stress in the nanoscale near-field heating region is critical for process control and optimization. At present, probing of the nanoscale temperature, stress, and optical fields remains a great challenge since the heating area is very small (∼100 nm or less) and not immediately accessible for sensing. In this work, we report the first experimental study on nanoscale mapping of particle-induced thermal, stress, and optical fields by using a single laser for both near-field excitation and Raman probing. The mapping results based on Raman intensity variation, wavenumber shift, and linewidth broadening all give consistent conjugated thermal, stress, and near-field focusing effects at a 20 nm resolution (<λ/26, λ = 32 nm). Nanoscale mapping of near-field effects of particles from 1210 down to 160 nm demonstrates the strong capacity of such a technique. By developing a new strategy for physical analysis, we have de-conjugated the effects of temperature, stress, and near-field focusing from the Raman mapping. The temperature rise and stress in the nanoscale heating region is evaluated at different energy levels. High-fidelity electromagnetic and temperature field simulation is conducted to accurately interpret the experimental results. PMID:23555566

Tensorial analysis of Eshelby stresses in 3D supercooled liquids

NASA Astrophysics Data System (ADS)

Lemaître, Anaël

2015-10-01

It was recently proposed that the local rearrangements governing relaxation in supercooled liquids impress on the liquid medium long-ranged (Eshelby) stress fluctuations that accumulate over time. From this viewpoint, events must be characterized by elastic dipoles, which are second order tensors, and Eshelby fields are expected to show up in stress and stress increment correlations, which are fourth order tensor fields. We construct here an analytical framework that permits analyzing such tensorial correlations in isotropic media in view of accessing Eshelby fields. Two spherical bases are introduced, which correspond to Cartesian and spherical coordinates for tensors. We show how they can be used to decompose stress correlations and thus test such properties as isotropy and power-law scalings. Eshelby fields and the predicted stress correlations in an infinite medium are shown to belong to an algebra that can conveniently be described using the spherical tensor bases. Using this formalism, we demonstrate that the inherent stress field of 3D supercooled liquids is power law correlated and carries the signature of Eshelby fields, thus supporting the idea that relaxation events give rise to Eshelby stresses that accumulate over time.

Sleep Deprivation and Oxidative Stress in Animal Models: A Systematic Review

PubMed Central

Villafuerte, Gabriel; Miguel-Puga, Adán; Murillo Rodríguez, Eric; Machado, Sergio; Manjarrez, Elias; Arias-Carrión, Oscar

2015-01-01

Because the function and mechanisms of sleep are partially clear, here we applied a meta-analysis to address the issue whether sleep function includes antioxidative properties in mice and rats. Given the expansion of the knowledge in the sleep field, it is indeed ambitious to describe all mammals, or other animals, in which sleep shows an antioxidant function. However, in this paper we reviewed the current understanding from basic studies in two species to drive the hypothesis that sleep is a dynamic-resting state with antioxidative properties. We performed a systematic review of articles cited in Medline, Scopus, and Web of Science until March 2015 using the following search terms: Sleep or sleep deprivation and oxidative stress, lipid peroxidation, glutathione, nitric oxide, catalase or superoxide dismutase. We found a total of 266 studies. After inclusion and exclusion criteria, 44 articles were included, which are presented and discussed in this study. The complex relationship between sleep duration and oxidative stress is discussed. Further studies should consider molecular and genetic approaches to determine whether disrupted sleep promotes oxidative stress. PMID:25945148

Correlation of Electrical Resistance to CMC Stress-Strain and Fracture Behavior Under High Heat-Flux Thermal and Stress Gradients

NASA Technical Reports Server (NTRS)

Appleby, Matthew; Morscher, Gregory; Zhu, Dongming

2015-01-01

Because SiCSiC ceramic matrix composites (CMCs) are under consideration for use as turbine engine hot-section components in extreme environments, it becomes necessary to investigate their performance and damage morphologies under complex loading and environmental conditions. Monitoring of electrical resistance (ER) has been shown as an effective tool for detecting damage accumulation of woven melt-infiltrated SiCSiC CMCs. However, ER change under complicated thermo-mechanical loading is not well understood. In this study a systematic approach is taken to determine the capabilities of ER as a relevant non-destructive evaluation technique for high heat-flux testing, including thermal gradients and localized stress concentrations. Room temperature and high temperature, laser-based tensile tests were conducted in which stress-dependent damage locations were determined using modal acoustic emission (AE) monitoring and compared to full-field strain mapping using digital image correlation (DIC). This information is then compared with the results of in-situ ER monitoring, post-test ER inspection and fractography in order to correlate ER response to convoluted loading conditions and damage evolution.

Sensor for Direct Measurement of the Boundary Shear Stress in Fluid Flow

NASA Technical Reports Server (NTRS)

Bao, Xiaoqi; Badescu, Mircea; Bar-Cohen, Yoseph; Lih, Shyh-Shiuh; Sherrit, Stewart; Chang, Zensheu; Chen, Beck; Widholm, Scott; Ostlund, Patrick

2011-01-01

The formation of scour patterns at bridge piers is driven by the forces at the boundary of the water flow. In most experimental scour studies, indirect processes have been applied to estimate the shear and normal stress using measured velocity profiles. The estimations are based on theoretical models and associated assumptions. However, the turbulence flow fields and boundary layer in the pier-scour region are very complex. In addition, available turbulence models cannot account accurately for the bed roughness effect. Direct measurement of the boundary shear and normal stress and their fluctuations are attractive alternatives. However, this approach is a challenging one especially for high spatial resolution and high fidelity measurements. The authors designed and fabricated a prototype miniature shear stress sensor including an EDM machined floating plate and a high-resolution laser optical encoder. Tests were performed both in air as well as operation in water with controlled flow. The sensor sensitivity, stability and signal-to-noise level were measured and evaluated. The detailed test results and a discussion of future work will be presented in this paper.

Flow field and oscillatory shear stress in a tuning-fork-shaped model of the average human carotid bifurcation.

PubMed

Ding, Z; Wang, K; Li, J; Cong, X

2001-12-01

The oscillatory shear index (OSI) was developed based on the hypothesis that intimal hyperplasia was correlated with oscillatory shear stresses. However, the validity of the OSI was in question since the correlation between intimal thickness and the OSI at the side walls of the sinus in the Y-shaped model of the average human carotid bifurcation (Y-AHCB) was weak. The objectives of this paper are to examine whether the reason for the weak correlation lies in the deviation in geometry of Y-AHCB from real human carotid bifurcation, and whether this correlation is clearly improved in the tuning-fork-shaped model of the average human carotid bifurcation (TF-AHCB). The geometry of the TF-AHCB model was based on observation and statistical analysis of specimens from 74 cadavers. The flow fields in both models were studied and compared by using flow visualization methods under steady flow conditions and by using laser Doppler anemometer (LDA) under pulsatile flow conditions. The TF-shaped geometry leads to a more complex flow field than the Y-shaped geometry. This added complexity includes strengthened helical movements in the sinus, new flow separation zone, and directional changes in the secondary flow patterns. The results show that the OSI-values at the side walls of the sinus in the TF-shaped model were more than two times as large as those in the Y-shaped model. This study confirmed the stronger correlation between the OSI and intimal thickness in the tuning-fork geometry of human carotid bifurcation, and the TF-AHCB model is a significant improvement over the traditional Y-shaped model.

Segmentation in cohesive systems constrained by elastic environments

PubMed Central

Novak, I.

2017-01-01

The complexity of fracture-induced segmentation in elastically constrained cohesive (fragile) systems originates from the presence of competing interactions. The role of discreteness in such phenomena is of interest in a variety of fields, from hierarchical self-assembly to developmental morphogenesis. In this paper, we study the analytically solvable example of segmentation in a breakable mass–spring chain elastically linked to a deformable lattice structure. We explicitly construct the complete set of local minima of the energy in this prototypical problem and identify among them the states corresponding to the global energy minima. We show that, even in the continuum limit, the dependence of the segmentation topology on the stretching/pre-stress parameter in this problem takes the form of a devil's type staircase. The peculiar nature of this staircase, characterized by locking in rational microstructures, is of particular importance for biological applications, where its structure may serve as an explanation of the robustness of stress-driven segmentation. This article is part of the themed issue ‘Patterning through instabilities in complex media: theory and applications.’ PMID:28373383

Detecting drawdowns masked by environmental stresses with water-level models

USGS Publications Warehouse

Garcia, C.A.; Halford, K.J.; Fenelon, J.M.

2013-01-01

Detecting and quantifying small drawdown at observation wells distant from the pumping well greatly expands the characterized aquifer volume. However, this detection is often obscured by water level fluctuations such as barometric and tidal effects. A reliable analytical approach for distinguishing drawdown from nonpumping water-level fluctuations is presented and tested here. Drawdown is distinguished by analytically simulating all pumping and nonpumping water-level stresses simultaneously during the period of record. Pumping signals are generated with Theis models, where the pumping schedule is translated into water-level change with the Theis solution. This approach closely matched drawdowns simulated with a complex three-dimensional, hypothetical model and reasonably estimated drawdowns from an aquifer test conducted in a complex hydrogeologic system. Pumping-induced changes generated with a numerical model and analytical Theis model agreed (RMS as low as 0.007 m) in cases where pumping signals traveled more than 1 km across confining units and fault structures. Maximum drawdowns of about 0.05 m were analytically estimated from field investigations where environmental fluctuations approached 0.2 m during the analysis period.

Genome hypermethylation in Pinus silvestris of Chernobyl--a mechanism for radiation adaptation?

PubMed

Kovalchuk, Olga; Burke, Paula; Arkhipov, Andrey; Kuchma, Nikolaj; James, S Jill; Kovalchuk, Igor; Pogribny, Igor

2003-08-28

Adaptation is a complex process by which populations of organisms respond to long-term environmental stresses by permanent genetic change. Here we present data from the natural "open-field" radiation adaptation experiment after the Chernobyl accident and provide the first evidence of the involvement of epigenetic changes in adaptation of a eukaryote-Scots pine (Pinus silvestris), to chronic radiation exposure. We have evaluated global genome methylation of control and radiation-exposed pine trees using a method based on cleavage by a methylation-sensitive HpaII restriction endonuclease that leaves a 5' guanine overhang and subsequent single nucleotide extension with labeled [3H] dCTP. We have found that genomic DNA of exposed pine trees was considerably hypermethylated. Moreover, hypermethylation appeared to be dependent upon the radiation dose absorbed by the trees. Such hypermethylation may be viewed as a defense strategy of plants that prevents genome instability and reshuffling of the hereditary material, allowing survival in an extreme environment. Further studies are clearly needed to analyze in detail the involvement of DNA methylation and other epigenetic mechanisms in the complex process of radiation stress and adaptive response.

Fault interaction and stresses along broad oceanic transform zone: Tjörnes Fracture Zone, north Iceland

NASA Astrophysics Data System (ADS)

Homberg, C.; Bergerat, F.; Angelier, J.; Garcia, S.

2010-02-01

Transform motion along oceanic transforms generally occurs along narrow faults zones. Another class of oceanic transforms exists where the plate boundary is quite large (˜100 km) and includes several subparallel faults. Using a 2-D numerical modeling, we simulate the slip distribution and the crustal stress field geometry within such broad oceanic transforms (BOTs). We examine the possible configurations and evolution of such BOTs, where the plate boundary includes one, two, or three faults. Our experiments show that at any time during the development of the plate boundary, the plate motion is not distributed along each of the plate boundary faults but mainly occurs along a single master fault. The finite width of a BOT results from slip transfer through time with locking of early faults, not from a permanent distribution of deformation over a wide area. Because of fault interaction, the stress field geometry within the BOTs is more complex than that along classical oceanic transforms and includes stress deflections close to but also away from the major faults. Application of this modeling to the 100 km wide Tjörnes Fracture Zone (TFZ) in North Iceland, a major BOT of the Mid-Atlantic Ridge that includes three main faults, suggests that the Dalvik Fault and the Husavik-Flatey Fault developed first, the Grismsey Fault being the latest active structure. Since initiation of the TFZ, the Husavik-Flatey Fault accommodated most of the plate motion and probably persists until now as the main plate structure.

Social instability stress in adolescence increases anxiety and reduces social interactions in adulthood in male Long-Evans rats.

PubMed

Green, Matthew R; Barnes, Brittany; McCormick, Cheryl M

2013-12-01

We investigated the effects of social instability stress (daily 1-hr isolation, change of cage partner, postnatal day 30-45) in adolescence in male rats on open field exploration and social behavior in adulthood. Social stressed rats had longer latencies to enter the center of an open field and then took longer to approach an object placed in the center of the field. When another rat was placed in the open field, stressed rats spent less time in social interaction than control rats, particularly when paired with another stressed, rather than a control, rat. The groups did not differ in social approach tests (when a stimulus rat was separated by wire mesh) nor in novel object exploration (when controlling for open field anxiety). The results suggest social stress in adolescence increases open field anxiety while maintaining exploratory behavior, and alters social interactions in adulthood. © 2012 Wiley Periodicals, Inc.

PIV Measurement of Wall Shear Stress and Flow Structures within an Intracranial Aneurysm Model

NASA Astrophysics Data System (ADS)

Chow, Ricky; Sparrow, Eph; Campbell, Gary; Divani, Afshin; Sheng, Jian

2012-11-01

The formation and rupture of an intracranial aneurysm (IA) is a debilitating and often lethal event. Geometric features of the aneurysm bulb and upstream artery, such as bulb size, bulb shape, and curvature of the artery, are two groups of factors that define the flow and stresses within an IA. Abnormal flow stresses are related to rupture. This presentation discusses the development of a quasi-3D PIV technique and its application in various glass models at Re = 275 and 550 to experimentally assess at a preliminary level the impact of geometry and flow rate. Some conclusions are to be drawn linking geometry of the flow domain to rupture risk. The extracted results also serve as the baseline case and as a precursor to a companion presentation by the authors discussing the impact of flow diverters, a new class of medical devices. The PIV experiments were performed in a fully index-matched flow facility, allowing for unobstructed observations over complex geometry. A reconstruction and analysis method was devised to obtain 3D mean wall stress distributions and flow fields. The quasi 3D measurements were reconstructed from orthogonal planes encompassing the entire glass model, spaced 0.4mm apart. Wall shear stresses were evaluated from the near-wall flow viscous stresses.

Does Leisure Time as a Stress Coping Resource Increase Affective Complexity? Applying the Dynamic Model of Affect (DMA).

PubMed

Qian, Xinyi Lisa; Yarnal, Careen M; Almeida, David M

2013-01-01

Affective complexity, a manifestation of psychological well-being, refers to the relative independence between positive and negative affect (PA, NA). According to the Dynamic Model of Affect (DMA), stressful situations lead to highly inverse PA-NA relationship, reducing affective complexity. Meanwhile, positive events can sustain affective complexity by restoring PA-NA independence. Leisure, a type of positive events, has been identified as a coping resource. This study used the DMA to assess whether leisure time helps restore affective complexity on stressful days. We found that on days with more leisure time than usual, an individual experienced less negative PA-NA relationship after daily stressful events. The finding demonstrates the value of leisure time as a coping resource and the DMA's contribution to coping research.

Variability in the efficacy of psychopharmaceuticals: contributions from pharmacogenomics, ethnopsychopharmacology, and psychological and psychiatric anthropologies.

PubMed

Ninnemann, Kristi M

2012-03-01

Psychological and psychiatric anthropology have long questioned the universality of psychiatric diagnoses, bringing to light the fluidity of mental disorder, and recognizing that the experience and expression of psychopathology is influenced by complex and interacting genetic, environmental, and cultural factors. The majority of our discussions, however, have remained centered around the role of culture in shaping mental illness: drawing attention to subjective experiences of mental illness and culturally patterned modes of symptom presentation, and interrogating the cogency of universal diagnostic rubrics. Psychological and psychiatric anthropology have yet to robustly engage the broadly assumed universal validity of psychiatric medications and the ways in which they are prescribed and experienced. This article provides an introduction into the fields of pharmacogenomics and ethnopsychopharmacology, areas of inquiry seeking to understand the ways in which genetic variability occurring between, and within, large population groups influences individual ability to metabolize psychotropic medications. This piece further addresses the complex issue of psychopharmaceutical efficacy, stressing the ways in which, just as with psychopathology, medications and their outcomes are likewise influenced by the complex interactions of genes, environment, and culture. Lastly, ways in which anthropology can and should engage with the growing fields of pharmacogenomics and ethnopsychopharmacology are suggested.

Geometry of slab, intraslab stress field and its tectonic implication in the Nankai trough, Japan

NASA Astrophysics Data System (ADS)

Xu, J.; Kono, Y.

2002-07-01

The characteristics of geometry of slabs and the intraslab stress field in the Nankai subduction zone, Japan, were analyzed based on highly accurate hypocentral data and focal mechanism solutions. The results suggest that the shallow seismic zone of the Philippine Sea slab subducts with dip angels between 10 and 22 degrees beneath Shikoku and the Kii peninsula, and between 11 and 40 degrees beneath Kyushu. Two types of seismogenic stress field exist within the slab. The stress field of down-dip compression type can be seen in the slab beneath Shikoku and the Kii peninsula, where the horizontal component of regional compression stress is NNW. On the other hand the stress field of down-dip extension type within the slab is dominant in the region from western Shikoku to Kyushu, where the direction of horizontal compressive stress is near WWN. The existence of the two types of stress field is related to the differences of slab geometry and slab age of the subduciton zone. These properties imply that slab beneath Kyushu (40 Ma) probably is older than that beneath Shikoku and the Kii peninsula (11-20 Ma). The young slab of the oceanic Philippine Sea plate subducts with a shallow angle beneath the Eurasian plate in Shikoku and the Kii peninsula. The subduction has encountered strong resistance there, resulting in a down-dip compression stress field. The down-dip extension stress field may be related to the older slab of the Philippine Sea plate which subducts beneath Kyushu with a steeper dip angle.

A Comparison between Deep and Shallow Stress Fields in Korea Using Earthquake Focal Mechanism Inversions and Hydraulic Fracturing Stress Measurements

NASA Astrophysics Data System (ADS)

Lee, Rayeon; Chang, Chandong; Hong, Tae-kyung; Lee, Junhyung; Bae, Seong-Ho; Park, Eui-Seob; Park, Chan

2016-04-01

We are characterizing stress fields in Korea using two types of stress data: earthquake focal mechanism inversions (FMF) and hydraulic fracturing stress measurements (HF). The earthquake focal mechanism inversion data represent stress conditions at 2-20 km depths, whereas the hydraulic fracturing stress measurements, mostly conducted for geotechnical purposes, have been carried out at depths shallower than 1 km. We classified individual stress data based on the World Stress Map quality ranking scheme. A total of 20 FMF data were classified into A-B quality, possibly representing tectonic stress fields. A total of 83 HF data out of compiled 226 data were classified into B-C quality, which we use for shallow stress field characterization. The tectonic stress, revealed from the FMF data, is characterized by a remarkable consistency in its maximum stress (σ1) directions in and around Korea (N79±2° E), indicating a quite uniform deep stress field throughout. On the other hand, the shallow stress field, represented by HF data, exhibits local variations in σ1 directions, possibly due to effects of topography and geologic structures such as faults. Nonetheless, there is a general similarity in σ1 directions between deep and shallow stress fields. To investigate the shallow stress field statistically, we follow 'the mean orientation and wavelength analysis' suggested by Reiter et al. (2014). After the stress pattern analysis, the resulting stress points distribute sporadically over the country, not covering the entire region evenly. In the western part of Korea, the shallow σ1directions are generally uniform with their search radius reaching 100 km, where the average stress direction agrees well with those of the deep tectonic stress. We note two noticeable differences between shallow and deep stresses in the eastern part of Korea. First, the shallow σ1 orientations are markedly non-uniform in the southeastern part of Korea with their search radius less than 25 km. In this region, the average σ1orientation based on the entire B-C quality stress data is calculated to be 77±37° ; however, the average orientation is somewhat meaningless because of the high standard deviation. The southeastern part of Korea consists mainly of Cretaceous sedimentary basin, geologically younger than the rest of the country, where regional scale faults are intensely populated. The highly scattered stress directions in this region may represent the effect of the geologic structures on shallow stress field. Second, shallow σ1 directions in the northeastern part of Korea strike consistently to 135±12° , which is deviated by as much as 56° from the deep tectonic stress direction. This region is characterized by high altitude mountainous topography (an elevation of an order of 1 km) with its major ridge axis in the NW-SE direction. We interpret, as a rule of thumb, that the ridge-perpendicular shallow horizontal stress components may be weak, leading to the ridge-parallel components to be the maximum. Overall, there are similarity and also difference between shallow and deep stress fields. Thus, it will be necessary to differentiate the strategy to tackle the stress-related problems based on their natures.

"Complex" Posttraumatic Stress Disorder/Disorders of Extreme Stress (CP/DES) in Sexually Abused Children: An Exloratory Study.

ERIC Educational Resources Information Center

Hall, Darlene Kordich

1999-01-01

Compares three groups of young sexually abused children on seven "Complex" Posttraumatic Stress Disorder/Disorders of Extreme Stress (CP/DES) indices. As cumulative number of types of trauma increased, the number of CP/DES symptoms rose. Results suggest that CP/DES also characterizes sexually abused children, especially those who have…

Beyond allostatic load: rethinking the role of stress in regulating human development.

PubMed

Ellis, Bruce J; Del Giudice, Marco

2014-02-01

How do exposures to stress affect biobehavioral development and, through it, psychiatric and biomedical disorder? In the health sciences, the allostatic load model provides a widely accepted answer to this question: stress responses, while essential for survival, have negative long-term effects that promote illness. Thus, the benefits of mounting repeated biological responses to threat are traded off against costs to mental and physical health. The adaptive calibration model, an evolutionary-developmental theory of stress-health relations, extends this logic by conceptualizing these trade-offs as decision nodes in allocation of resources. Each decision node influences the next in a chain of resource allocations that become instantiated in the regulatory parameters of stress response systems. Over development, these parameters filter and embed information about key dimensions of environmental stress and support, mediating the organism's openness to environmental inputs, and function to regulate life history strategies to match those dimensions. Drawing on the adaptive calibration model, we propose that consideration of biological fitness trade-offs, as delineated by life history theory, is needed to more fully explain the complex relations between developmental exposures to stress, stress responsivity, behavioral strategies, and health. We conclude that the adaptive calibration model and allostatic load model are only partially complementary and, in some cases, support different approaches to intervention. In the long run, the field may be better served by a model informed by life history theory that addresses the adaptive role of stress response systems in regulating alternative developmental pathways.

The complexity of gene expression dynamics revealed by permutation entropy

PubMed Central

2010-01-01

Background High complexity is considered a hallmark of living systems. Here we investigate the complexity of temporal gene expression patterns using the concept of Permutation Entropy (PE) first introduced in dynamical systems theory. The analysis of gene expression data has so far focused primarily on the identification of differentially expressed genes, or on the elucidation of pathway and regulatory relationships. We aim to study gene expression time series data from the viewpoint of complexity. Results Applying the PE complexity metric to abiotic stress response time series data in Arabidopsis thaliana, genes involved in stress response and signaling were found to be associated with the highest complexity not only under stress, but surprisingly, also under reference, non-stress conditions. Genes with house-keeping functions exhibited lower PE complexity. Compared to reference conditions, the PE of temporal gene expression patterns generally increased upon stress exposure. High-complexity genes were found to have longer upstream intergenic regions and more cis-regulatory motifs in their promoter regions indicative of a more complex regulatory apparatus needed to orchestrate their expression, and to be associated with higher correlation network connectivity degree. Arabidopsis genes also present in other plant species were observed to exhibit decreased PE complexity compared to Arabidopsis specific genes. Conclusions We show that Permutation Entropy is a simple yet robust and powerful approach to identify temporal gene expression profiles of varying complexity that is equally applicable to other types of molecular profile data. PMID:21176199

Meta-Analysis of the Effect of Overexpression of Dehydration-Responsive Element Binding Family Genes on Temperature Stress Tolerance and Related Responses

PubMed Central

Dong, Chao; Ma, Yuanchun; Zheng, Dan; Wisniewski, Michael; Cheng, Zong-Ming

2018-01-01

Dehydration-responsive element binding proteins are transcription factors that play a critical role in plant response to temperature stress. Over-expression of DREB genes has been demonstrated to enhance temperature stress tolerance. A series of physiological and biochemical modifications occur in a complex and integrated way when plants respond to temperature stress, which makes it difficult to assess the mechanism underlying the DREB enhancement of stress tolerance. A meta-analysis was conducted of the effect of DREB overexpression on temperature stress tolerance and the various parameters modulated by overexpression that were statistically quantified in 75 published articles. The meta-analysis was conducted to identify the overall influence of DREB on stress-related parameters in transgenic plants, and to determine how different experimental variables affect the impact of DREB overexpression. Viewed across all the examined studies, 7 of the 8 measured plant parameters were significantly (p ≤ 0.05) modulated in DREB-transgenic plants when they were subjected to temperature stress, while 2 of the 8 parameters were significantly affected in non-stressed control plants. The measured parameters were modulated by 32% or more by various experimental variables. The modulating variables included, acclimated or non-acclimated, type of promoter, stress time and severity, source of the donor gene, and whether the donor and recipient were the same genus. These variables all had a significant effect on the observed impact of DREB overexpression. Further studies should be conducted under field conditions to better understand the role of DREB transcription factors in enhancing plant tolerance to temperature stress. PMID:29896212

Cellular IRES-mediated translation: the war of ITAFs in pathophysiological states.

PubMed

Komar, Anton A; Hatzoglou, Maria

2011-01-15

Translation of cellular mRNAs via initiation at Internal Ribosome Entry Sites (IRESs) has received increased attention during recent years due to its emerging significance for many physiological and pathological stress conditions in eukaryotic cells. Expression of genes bearing IRES elements in their mRNAs is controlled by multiple molecular mechanisms, with IRES-mediated translation favored under conditions when cap-dependent translation is compromised. In this review, we discuss recent advances in the field and future directions that may bring us closer to understanding the complex mechanisms that guide cellular IRES-mediated expression. We present examples in which the competitive action of IRES-transacting factors (ITAFs) plays a pivotal role in IRES-mediated translation and thereby controls cell-fate decisions leading to either pro-survival stress adaptation or cell death.

Present-day Horizontal Mobility in the Serbian Part of the Pannonian Basin; Inferences from the Geometric Analysis of Deformations

NASA Astrophysics Data System (ADS)

Sušić, Zoran; Toljić, Marinko; Bulatović, Vladimir; Ninkov, Toša; Stojadinović, Uroš

2016-10-01

In tectonically complex environments, such as the Pannonian Basin surrounded by the Alps-Dinarides and Carpathians orogens, monitoring of recent deformations represents very challenging matter. Efficient quantification of active continental deformations demands the use of a multidisciplinary approach, including neotectonic, seismotectonic and geodetic methods. The present-day tectonic mobility in the Pannonian Basin is predominantly controlled by the northward movement of the Adria micro-plate, which has produced compressional stresses that were party accommodated by the Alps-Dinarides thrust belt and partly transferred towards its hinterland. Influence of thus induced stresses on the recent strain field, deformations and tectonic mobility in the southern segment of the Pannonian Basin has been investigated using GPS measurements of the horizontal mobility in the Vojvodina area (northern Serbia).

Study on Finite Element Method of Stress Field in Aluminum Alloy High-Speed Milling Process

NASA Astrophysics Data System (ADS)

Zhang, Wei; Li, Shunming; Wu, Qijun; An, Zenghui

2017-11-01

Three-dimensional numerical simulation model has been built by means of Advantage FEM. Perform simulation the stress fields of 7050-T7451 aluminum alloy in high speed milling process at the speed range of 628 m/min∼5946 m/min. The dynamic change and speed’s influence of stress fields and residual stress in machined layer is systematically analyzed. Some conclusions were drawn. With the cutting process development, the stress field converts to the stress state that crushing stress occupies a leading position. The magnitudes of crushing stress in all directions reduce with milling processes as the effect of Thermal-Mechanical-Coupled weakens; With the cutting speed increasing the magnitudes of crushing stress in all directions fluctuate near -950Mpa first, and then increase at the speed of 3000m/min; The residual pulling stress beneath the surface 0.03mm has been found and the magnitude increases with the cutting speed. A good agreement was obtained between predictions and experiments.

Biothermomechanics of skin tissues

NASA Astrophysics Data System (ADS)

Xu, F.; Lu, T. J.; Seffen, K. A.

Biothermomechanics of skin is highly interdisciplinary involving bioheat transfer, burn damage, biomechanics and neurophysiology. During heating, thermally induced mechanical stress arises due to the thermal denaturation of collagen, resulting in macroscale shrinkage. Thus, the strain, stress, temperature and thermal pain/damage are highly correlated; in other words, the problem is fully coupled. The aim of this study is to develop a computational approach to examine the heat transfer process and the heat-induced mechanical response, so that the differences among the clinically applied heating modalities can be quantified. Exact solutions for temperature, thermal damage and thermal stress for a single-layer skin model were first derived for different boundary conditions. For multilayer models, numerical simulations using the finite difference method (FDM) and finite element method (FEM) were used to analyze the temperature, burn damage and thermal stress distributions in the skin tissue. The results showed that the thermomechanical behavior of skin tissue is very complex: blood perfusion has little effect on thermal damage but large influence on skin temperature distribution, which, in turn, influences significantly the resulting thermal stress field; the stratum corneum layer, although very thin, has a large effect on the thermomechanical behavior of skin, suggesting that it should be properly accounted for in the modeling of skin thermal stresses; the stress caused by non-uniform temperature distribution in the skin may also contribute to the thermal pain sensation.

Time-dependent rheological behavior of natural polysaccharide xanthan gum solutions in interrupted shear and step-incremental/reductional shear flow fields

NASA Astrophysics Data System (ADS)

Lee, Ji-Seok; Song, Ki-Won

2015-11-01

The objective of the present study is to systematically elucidate the time-dependent rheological behavior of concentrated xanthan gum systems in complicated step-shear flow fields. Using a strain-controlled rheometer (ARES), step-shear flow behaviors of a concentrated xanthan gum model solution have been experimentally investigated in interrupted shear flow fields with a various combination of different shear rates, shearing times and rest times, and step-incremental and step-reductional shear flow fields with various shearing times. The main findings obtained from this study are summarized as follows. (i) In interrupted shear flow fields, the shear stress is sharply increased until reaching the maximum stress at an initial stage of shearing times, and then a stress decay towards a steady state is observed as the shearing time is increased in both start-up shear flow fields. The shear stress is suddenly decreased immediately after the imposed shear rate is stopped, and then slowly decayed during the period of a rest time. (ii) As an increase in rest time, the difference in the maximum stress values between the two start-up shear flow fields is decreased whereas the shearing time exerts a slight influence on this behavior. (iii) In step-incremental shear flow fields, after passing through the maximum stress, structural destruction causes a stress decay behavior towards a steady state as an increase in shearing time in each step shear flow region. The time needed to reach the maximum stress value is shortened as an increase in step-increased shear rate. (iv) In step-reductional shear flow fields, after passing through the minimum stress, structural recovery induces a stress growth behavior towards an equilibrium state as an increase in shearing time in each step shear flow region. The time needed to reach the minimum stress value is lengthened as a decrease in step-decreased shear rate.

Rupture process of a multiple main shock sequence: analysis of teleseismic, local and field observations of the Tennant Creek, Australia, earthquakes of January 22, 1988

USGS Publications Warehouse

Choy, G.L.; Bowman, J.R.

1990-01-01

On January 22, 1988, three large intraplate earthquakes (with MS 6.3, 6.4 and 6.7) occurred within a 12-hour period near Tennant Creek, Australia. Broadband displacement and velocity records of body waves from teleseismically recorded data are analyzed to determine source mechanisms, depths, and complexity of rupture of each of the three main shocks. Hypocenters of an additional 150 foreshocks and aftershocks constrained by local arrival time data and field observations of surface rupture are used to complement the source characteristics of the main shocks. The interpretation of the combined data sets suggests that the overall rupture process involved unusually complicated stress release. Rupture characteristics suggest that substantial slow slip occurred on each of the three fault interfaces that was not accompanied by major energy release. Variation of focal depth and the strong increase of moment and radiated energy with each main shock imply that lateral variations of strength were more important than vertical gradients of shear stress in controlling the progression of rupture. -from Authors

Stress heterogeneity above and within a deep geothermal reservoir: From borehole observations to geomechanical modelling

NASA Astrophysics Data System (ADS)

Seithel, Robin; Peters, Max; Lesueur, Martin; Kohl, Thomas

2017-04-01

Overpressured reservoir conditions, local stress concentrations or a locally rotated stress field can initiate substantial problems during drilling or reservoir exploitation. Increasing geothermal utilization in the Molasse basin area in S-Germany is faced with such problems of deeply seated reservoir sections. In several wells, radial fluid flow systems are interpreted as highly porous layers. However, in nearby wells a combination of linear fluid flow, local stress heterogeneities and structural geology hint to a rather fault dominated reservoir (Seithel et al. 2015). Due to missing knowledge of the stress magnitude, stress orientation and their coupling to reservoir response, we will present a THMC model of critical formations and the geothermal reservoir targeting nearby faults. In an area south of Munich, where several geothermal wells are constructed, such wells are interpreted and integrated into a 30 x 30 km simulated model area. One of the main objectives here is to create a geomechanical reservoir model in a thermo-mechanical manner in order to understand the coupling between reservoir heterogeneities and stress distributions. To this end, stress analyses of wellbore data and laboratory tests will help to calibrate a reliable model. In order to implement the complex geological structure of the studied wedge-shaped foreland basin, an automatic export of lithology, fault and borehole data (e.g. from Petrel) into a FE mesh is used. We will present a reservoir-scale model that considers thermo-mechanic effects and analyze their influence on reservoir deformation, fluid flow and stress concentration. We use the currently developed finite element application REDBACK (https://github.com/pou036/redback), inside the MOOSE framework (Poulet et al. 2016). We show that mechanical heterogeneities nearby fault zones and their orientation within the stress field correlate to fracture pattern, interpreted stress heterogeneities or variegated flow systems within the reservoir. REFERENCES Poulet, T.; Paesold, M.; Veveakis, M. (2016), Multi-Physics Modelling of Fault Mechanics Using REDBACK. A Parallel Open-Source Simulator for Tightly Coupled Problems. Rock Mechanics and Rock Engineering. doi: 10.1007/s00603-016-0927-y. Seithel, R.; Steiner, U.; Müller, B.I.R.; Hecht, Ch.; Kohl, T. (2015), Local stress anomaly in the Bavarian Molasse Basin, Geothermal Energy 3(1), p.77. doi:10.1186/s40517-014-0023-z

New UK in-situ stress orientation for northern England and controls on borehole wall deformation identified using borehole imaging

NASA Astrophysics Data System (ADS)

Kingdon, Andrew; Fellgett, Mark W.; Waters, Colin N.

2016-04-01

The nascent development of a UK shale gas industry has highlighted the inadequacies of previous in-situ stress mapping which is fundamental to the efficacy and safety of potential fracturing operations. The limited number of stress inversions from earthquake focal plane mechanisms and overcoring measurements of in-situ stress in prospective areas increases the need for an up-to-date stress map. Borehole breakout results from 36 wells with newly interpreted borehole imaging data are presented. Across northern England these demonstrate a consistent maximum horizontal stress orientation (SHmax) orientation of 150.9° and circular standard deviation of 13.1°. These form a new and quality assured evidence base for both industry and its regulators. Widespread use of high-resolution borehole imaging tools has facilitated investigation of micro-scale relationships between stress and lithology, facilitating identification of breakouts as short as 25 cm. This is significantly shorter than those identified by older dual-caliper logging (typically 1-10+ m). Higher wall coverage (90%+ using the highest resolution tools) and decreasing pixel size (down to 4mm vertically by 2° of circumference) also facilitates identification of otherwise undetectable sub-centimetre width Drilling Induced Tensile Fractures (DIFs). Examination of borehole imaging from wells in North Yorkshire within the Carboniferous Pennine Coal Measures Group has showed that even though the stress field is uniform, complex micro-stress relationships exist. Different stress field indicators (SFI) are significantly affected by geology with differing failure responses from adjacent lithologies, highlighted by borehole imaging on sub-metre scales. Core-log-borehole imaging integration over intervals where both breakouts and DIFs have been identified allows accurate depth matching and thus allows a synthesis of failure for differing lithology and micro-structures under common in-situ conditions. Understanding these relationships requires detailed knowledge of the rock properties and how these affect deformation. Strength and brittleness of the facies are indicative of their likely failure-modes which are in turn controlled by their lithology, diagenesis and clay mineralisation, often highlighting dm-scale stress rotations around lithological boundaries. Breakouts are seen to concentrate within "seatearths" (palaeosol intervals directly under the coals), whereas intervals immediately above coals are marked disproportionately by DIFs. In-situ stress magnitude data information is not yet available for these wells, further work is required to quantify the geomechanical properties.

A Review of Tensors and Tensor Signal Processing

NASA Astrophysics Data System (ADS)

Cammoun, L.; Castaño-Moraga, C. A.; Muñoz-Moreno, E.; Sosa-Cabrera, D.; Acar, B.; Rodriguez-Florido, M. A.; Brun, A.; Knutsson, H.; Thiran, J. P.

Tensors have been broadly used in mathematics and physics, since they are a generalization of scalars or vectors and allow to represent more complex properties. In this chapter we present an overview of some tensor applications, especially those focused on the image processing field. From a mathematical point of view, a lot of work has been developed about tensor calculus, which obviously is more complex than scalar or vectorial calculus. Moreover, tensors can represent the metric of a vector space, which is very useful in the field of differential geometry. In physics, tensors have been used to describe several magnitudes, such as the strain or stress of materials. In solid mechanics, tensors are used to define the generalized Hooke’s law, where a fourth order tensor relates the strain and stress tensors. In fluid dynamics, the velocity gradient tensor provides information about the vorticity and the strain of the fluids. Also an electromagnetic tensor is defined, that simplifies the notation of the Maxwell equations. But tensors are not constrained to physics and mathematics. They have been used, for instance, in medical imaging, where we can highlight two applications: the diffusion tensor image, which represents how molecules diffuse inside the tissues and is broadly used for brain imaging; and the tensorial elastography, which computes the strain and vorticity tensor to analyze the tissues properties. Tensors have also been used in computer vision to provide information about the local structure or to define anisotropic image filters.

Nurse manager cognitive decision-making amidst stress and work complexity.

PubMed

Shirey, Maria R; Ebright, Patricia R; McDaniel, Anna M

2013-01-01

  The present study provides insight into nurse manager cognitive decision-making amidst stress and work complexity.   Little is known about nurse manager decision-making amidst stress and work complexity. Because nurse manager decisions have the potential to impact patient care quality and safety, understanding their decision-making processes is useful for designing supportive interventions.   This qualitative descriptive study interviewed 21 nurse managers from three hospitals to answer the research question: What decision-making processes do nurse managers utilize to address stressful situations in their nurse manager role? Face-to-face interviews incorporating components of the Critical Decision Method illuminated expert-novice practice differences. Content analysis identified one major theme and three sub-themes.   The present study produced a cognitive model that guides nurse manager decision-making related to stressful situations. Experience in the role, organizational context and situation factors influenced nurse manager cognitive decision-making processes.   Study findings suggest that chronic exposure to stress and work complexity negatively affects nurse manager health and their decision-making processes potentially threatening individual, patient and organizational outcomes.   Cognitive decision-making varies based on nurse manager experience and these differences have coaching and mentoring implications. This present study contributes a current understanding of nurse manager decision-making amidst stress and work complexity. © 2012 Blackwell Publishing Ltd.

Assembly of Slx4 signaling complexes behind DNA replication forks.

PubMed

Balint, Attila; Kim, TaeHyung; Gallo, David; Cussiol, Jose Renato; Bastos de Oliveira, Francisco M; Yimit, Askar; Ou, Jiongwen; Nakato, Ryuichiro; Gurevich, Alexey; Shirahige, Katsuhiko; Smolka, Marcus B; Zhang, Zhaolei; Brown, Grant W

2015-08-13

Obstructions to replication fork progression, referred to collectively as DNA replication stress, challenge genome stability. In Saccharomyces cerevisiae, cells lacking RTT107 or SLX4 show genome instability and sensitivity to DNA replication stress and are defective in the completion of DNA replication during recovery from replication stress. We demonstrate that Slx4 is recruited to chromatin behind stressed replication forks, in a region that is spatially distinct from that occupied by the replication machinery. Slx4 complex formation is nucleated by Mec1 phosphorylation of histone H2A, which is recognized by the constitutive Slx4 binding partner Rtt107. Slx4 is essential for recruiting the Mec1 activator Dpb11 behind stressed replication forks, and Slx4 complexes are important for full activity of Mec1. We propose that Slx4 complexes promote robust checkpoint signaling by Mec1 by stably recruiting Dpb11 within a discrete domain behind the replication fork, during DNA replication stress. © 2015 The Authors.

Does Leisure Time as a Stress Coping Resource Increase Affective Complexity? Applying the Dynamic Model of Affect (DMA)

PubMed Central

Qian, Xinyi (Lisa); Yarnal, Careen M.; Almeida, David M.

2013-01-01

Affective complexity, a manifestation of psychological well-being, refers to the relative independence between positive and negative affect (PA, NA). According to the Dynamic Model of Affect (DMA), stressful situations lead to highly inverse PA-NA relationship, reducing affective complexity. Meanwhile, positive events can sustain affective complexity by restoring PA-NA independence. Leisure, a type of positive events, has been identified as a coping resource. This study used the DMA to assess whether leisure time helps restore affective complexity on stressful days. We found that on days with more leisure time than usual, an individual experienced less negative PA-NA relationship after daily stressful events. The finding demonstrates the value of leisure time as a coping resource and the DMA’s contribution to coping research. PMID:24659826

Mechanical analysis of a heat-shock induced developmental defect

NASA Astrophysics Data System (ADS)

Crews, Sarah M.; McCleery, W. Tyler; Hutson, M. Shane

2014-03-01

Embryonic development in Drosophila is a complex process involving coordinated movements of mechanically interacting tissues. Perturbing this system with a transient heat shock can result in a number of developmental defects. In particular, a heat shock applied during the earliest morphogenetic movements of gastrulation can lead to apparent recovery, but then subsequent morphogenetic failure 5-6 hours later during germ band retraction. The process of germ band retraction requires an intact amnioserosa - a single layered extra-embryonic epithelial tissue - and heat shock at gastrulation can induce the later opening of holes in the amnioserosa. These holes are highly correlated with failures of germ band retraction. These holes could be caused by a combination of mechanical weakness in the amnioserosa or local increases in mechanical stress. Here, we assess the role of mechanical stress using confocal imaging to compare cell and tissue morphology in the amnioserosa of normal and heat-shocked embryos and laser hole drilling to map the stress field around the times and locations at which heat-shock induced holes open.

Transverse cracking and stiffness reduction in composite laminates

NASA Technical Reports Server (NTRS)

Yuan, F. G.; Selek, M. C.

1993-01-01

A study of transverse cracking mechanism in composite laminates is presented using a singular hybrid finite element model. The model provides the global structural response as well as the precise local crack-tip stress fields. An elasticity basis for the problem is established by employing Lekhnitskii's complex variable potentials and method of eigenfunction expansion. Stress singularities associated with the transverse crack are obtained by decomposing the deformation into the symmetric and antisymmetric modes and proper boundary conditions. A singular hybrid element is thereby formulated based on the variational principle of a modified hybrid functional to incorporate local crack singularities. Axial stiffness reduction due to transverse cracking is studied. The results are shown to be in very good agreement with the existing experimental data. Comparison with simple shear lag analysis is also given. The effects of stress intensity factors and strain energy density on the increase of crack density are analyzed. The results reveal that the parameters approach definite limits when crack densities are saturated, an evidence of the existence of characteristic damage state.

Genetic approaches for the study of PTSD: Advances and challenges

PubMed Central

Banerjee, Sunayana B.; Morrison, Filomene G.; Ressler, Kerry J.

2017-01-01

Post-traumatic stress disorder (PTSD) is a highly debilitating stress and anxiety-related disorder that occurs in response to specific trauma or abuse. Genetic risk factors may account for up to 30–40% of the heritability of PTSD. Understanding the gene pathways that are associated with PTSD, and how those genes interact with the fear and stress circuitry to mediate risk and resilience for PTSD will enable the development of targeted therapies to prevent the occurrence of or decrease the severity of this complex multi-gene disorder. This review will summarize recent research on genetic approaches to understanding PTSD risk and resilience in human populations, including candidate genes and their epigenetic modifications, genome-wide association studies and neural imaging genetics approaches. Despite challenges faced within this field of study such as inconsistent results and replications, genetic approaches still offer exciting opportunities for the identification and development of novel therapeutic targets and therapies in the future. PMID:28242325

Stress- and Structure-Induced Anisotropy in Southern California From Two Decades of Shear Wave Splitting Measurements

NASA Astrophysics Data System (ADS)

Li, Zefeng; Peng, Zhigang

2017-10-01

We measure shear wave splitting (SWS) parameters (i.e., fast direction and delay time) using 330,000 local earthquakes recorded by more than 400 stations of the Southern California Seismic Network (1995-2014). The resulting 232,000 SWS measurements (90,000 high-quality ones) provide a uniform and comprehensive database of local SWS measurements in Southern California. The fast directions at many stations are consistent with regional maximum compressional stress σHmax. However, several regions show clear deviations from the σHmax directions. These include linear sections along the San Andreas Fault and the Santa Ynez Fault, geological blocks NW to the Los Angeles Basin, regions around the San Jacinto Fault, the Peninsular Ranges near San Diego, and the Coso volcanic field. These complex patterns show that regional stresses and active faults cannot adequately explain the upper crustal anisotropy in Southern California. Other types of local structures, such as local rock types or tectonic features, also play significant roles.

Reynolds-Stress and Triple-Product Models Applied to a Flow with Rotation and Curvature

NASA Technical Reports Server (NTRS)

Olsen, Michael E.

2016-01-01

Turbulence models, with increasing complexity, up to triple product terms, are applied to the flow in a rotating pipe. The rotating pipe is a challenging case for turbulence models as it contains significant rotational and curvature effects. The flow field starts with the classic fully developed pipe flow, with a stationary pipe wall. This well defined condition is then subjected to a section of pipe with a rotating wall. The rotating wall introduces a second velocity scale, and creates Reynolds shear stresses in the radial-circumferential and circumferential-axial planes. Furthermore, the wall rotation introduces a flow stabilization, and actually reduces the turbulent kinetic energy as the flow moves along the rotating wall section. It is shown in the present work that the Reynolds stress models are capable of predicting significant reduction in the turbulent kinetic energy, but triple product improves the predictions of the centerline turbulent kinetic energy, which is governed by convection, dissipation and transport terms, as the production terms vanish on the pipe axis.

The stress intensity factor for the double cantilever beam

NASA Technical Reports Server (NTRS)

Fichter, W. B.

1983-01-01

Fourier transforms and the Wiener-Hopf technique are used in conjunction with plane elastostatics to examine the singular crack tip stress field in the double cantilever beam (DCB) specimen. In place of the Dirac delta function, a family of functions which duplicates the important features of the concentrated forces without introducing unmanageable mathematical complexities is used as a loading function. With terms of order h-squared/a-squared retained in the series expansion, the dimensionless stress intensity factor is found to be K (h to the 1/2)/P = 12 to the 1/2 (a/h + 0.6728 + 0.0377 h-squared/a-squared), in which P is the magnitude of the concentrated forces per unit thickness, a is the distance from the crack tip to the points of load application, and h is the height of each cantilever beam. The result is similar to that obtained by Gross and Srawley by fitting a line to discrete results from their boundary collocation analysis.

Nanoscale multiphase phase field approach for stress- and temperature-induced martensitic phase transformations with interfacial stresses at finite strains

NASA Astrophysics Data System (ADS)

Basak, Anup; Levitas, Valery I.

2018-04-01

A thermodynamically consistent, novel multiphase phase field approach for stress- and temperature-induced martensitic phase transformations at finite strains and with interfacial stresses has been developed. The model considers a single order parameter to describe the austenite↔martensitic transformations, and another N order parameters describing N variants and constrained to a plane in an N-dimensional order parameter space. In the free energy model coexistence of three or more phases at a single material point (multiphase junction), and deviation of each variant-variant transformation path from a straight line have been penalized. Some shortcomings of the existing models are resolved. Three different kinematic models (KMs) for the transformation deformation gradient tensors are assumed: (i) In KM-I the transformation deformation gradient tensor is a linear function of the Bain tensors for the variants. (ii) In KM-II the natural logarithms of the transformation deformation gradient is taken as a linear combination of the natural logarithm of the Bain tensors multiplied with the interpolation functions. (iii) In KM-III it is derived using the twinning equation from the crystallographic theory. The instability criteria for all the phase transformations have been derived for all the kinematic models, and their comparative study is presented. A large strain finite element procedure has been developed and used for studying the evolution of some complex microstructures in nanoscale samples under various loading conditions. Also, the stresses within variant-variant boundaries, the sample size effect, effect of penalizing the triple junctions, and twinned microstructures have been studied. The present approach can be extended for studying grain growth, solidifications, para↔ferro electric transformations, and diffusive phase transformations.

Quantifying the heterogeneity of the tectonic stress field using borehole data

USGS Publications Warehouse

Schoenball, Martin; Davatzes, Nicholas C.

2017-01-01

The heterogeneity of the tectonic stress field is a fundamental property which influences earthquake dynamics and subsurface engineering. Self-similar scaling of stress heterogeneities is frequently assumed to explain characteristics of earthquakes such as the magnitude-frequency relation. However, observational evidence for such scaling of the stress field heterogeneity is scarce.We analyze the local stress orientations using image logs of two closely spaced boreholes in the Coso Geothermal Field with sub-vertical and deviated trajectories, respectively, each spanning about 2 km in depth. Both the mean and the standard deviation of stress orientation indicators (borehole breakouts, drilling-induced fractures and petal-centerline fractures) determined from each borehole agree to the limit of the resolution of our method although measurements at specific depths may not. We find that the standard deviation in these boreholes strongly depends on the interval length analyzed, generally increasing up to a wellbore log length of about 600 m and constant for longer intervals. We find the same behavior in global data from the World Stress Map. This suggests that the standard deviation of stress indicators characterizes the heterogeneity of the tectonic stress field rather than the quality of the stress measurement. A large standard deviation of a stress measurement might be an expression of strong crustal heterogeneity rather than of an unreliable stress determination. Robust characterization of stress heterogeneity requires logs that sample stress indicators along a representative sample volume of at least 1 km.

Morphological and ecological determinants of body temperature of Geukensia demissa, the Atlantic ribbed mussel, and their effects on mussel mortality.

PubMed

Jost, Jennifer; Helmuth, Brian

2007-10-01

Measurements of body temperatures in the field have shown that spatial and temporal patterns are often far more complex than previously anticipated, particularly in intertidal regions, where temperatures are driven by both marine and terrestrial climates. We examined the effects of body size, body position within the sediment, and microhabitat (presence or absence of Spartina alterniflora) on the body temperature of the mussel Geukensia demissa. We then used these data to develop a laboratory study exposing mussels to an artificial "stressful" day, mimicking field conditions as closely as possible. Results suggested that G. demissa mortality increases greatly at average daily peak temperatures of 45 degrees C and higher. When these temperatures were compared to field data collected in South Carolina in the summer of 2004, our data indicated that mussels likely experienced mortality due to high-temperature stress at this site during this period. Our results also showed that body position in the mud is the most important environmental modifier of body temperature. This experiment suggested that the presence of marsh grass leads to increases in body temperature by reducing convection, overwhelming the effects of shading. These data add to a growing body of evidence showing that small-scale thermal variability can surpass large-scale gradients.

A cohesive-frictional force field (CFFF) for colloidal calcium-silicate-hydrates

NASA Astrophysics Data System (ADS)

Palkovic, Steven D.; Yip, Sidney; Büyüköztürk, Oral

2017-12-01

Calcium-silicate-hydrate (C-S-H) gel is a cohesive-frictional material that exhibits strength asymmetry in compression and tension and normal-stress dependency of the maximum shear strength. Experiments suggest the basic structural component of C-S-H is a colloidal particle with an internal layered structure. These colloids form heterogeneous assemblies with a complex pore network at the mesoscale. We propose a cohesive-frictional force field (CFFF) to describe the interactions in colloidal C-S-H materials that incorporates the strength anisotropy fundamental to the C-S-H molecular structure that has been omitted from recent mesoscale models. We parameterize the CFFF from reactive force field simulations of an internal interface that controls mechanical performance, describing the behavior of thousands of atoms through a single effective pair interaction. We apply the CFFF to study the mesoscale elastic and Mohr-Coulomb strength properties of C-S-H with varying polydispersity and packing density. Our results show that the consideration of cohesive-frictional interactions lead to an increase in stiffness, shear strength, and normal-stress dependency, while also changing the nature of local deformation processes. The CFFF and our coarse-graining approach provide an essential connection between nanoscale molecular interactions and macroscale continuum behavior for hydrated cementitious materials.

Wind speed and sediment transport recovery in the lee of a vegetated and denuded nebkha within a nebkha dune field

NASA Astrophysics Data System (ADS)

Gillies, John A.; Nield, Joanna M.; Nickling, William G.

2014-03-01

Field observations of scaled wind speed and sand transport recovery in the lee of a nebka within a field of nebkhas and then subsequently for the nebkha denuded of its vegetation cover were collected. The measurements of wind speed at 0.4 times the element height indicate that for both conditions wind speed recovery in the lee is exponential. The porous vegetation cover influences the rate of this recovery being more gradual for the vegetated form. The return to equilibrium wind speed occurs in both cases at approximately eight element heights. For either case the recovery of shear stress and the return to a constant value occurs much closer to the bluff body form than has been described for porous fences. The recovery of sand transport in the lee appears to be more rapid for the un-vegetated condition, which corresponds to the observed faster rate of wind speed increase. The observations did not show a continual increase in saltation flux with increasing downwind distance due to the increasing shear stress downwind and the increase that may be expected due to the fetch effect. The change in saltation flux with downwind distance was controlled by the sediment supply, which diminished with downwind distance. The interaction of a changing shear stress and the zone of influence created by the wind as it interacts with the roughness dimensions, along with the distribution of sediment available for transport bring increased complexity to modeling sand flux for this type of environment over different temporal scales.

Broad frequency band full field measurements for advanced applications: Point-wise comparisons between optical technologies

NASA Astrophysics Data System (ADS)

Zanarini, Alessandro

2018-01-01

The progress of optical systems gives nowadays at disposal on lightweight structures complex dynamic measurements and modal tests, each with its own advantages, drawbacks and preferred usage domains. It is thus more easy than before to obtain highly spatially defined vibration patterns for many applications in vibration engineering, testing and general product development. The potential of three completely different technologies is here benchmarked on a common test rig and advanced applications. SLDV, dynamic ESPI and hi-speed DIC are here first deployed in a complex and unique test on the estimation of FRFs with high spatial accuracy from a thin vibrating plate. The latter exhibits a broad band dynamics and high modal density in the common frequency domain where the techniques can find an operative intersection. A peculiar point-wise comparison is here addressed by means of discrete geometry transforms to put all the three technologies on trial at each physical point of the surface. Full field measurement technologies cannot estimate only displacement fields on a refined grid, but can exploit the spatial consistency of the results through neighbouring locations by means of numerical differentiation operators in the spatial domain to obtain rotational degrees of freedom and superficial dynamic strain distributions, with enhanced quality, compared to other technologies in literature. Approaching the task with the aid of superior quality receptance maps from the three different full field gears, this work calculates and compares rotational and dynamic strain FRFs. Dynamic stress FRFs can be modelled directly from the latter, by means of a constitutive model, avoiding the costly and time-consuming steps of building and tuning a numerical dynamic model of a flexible component or a structure in real life conditions. Once dynamic stress FRFs are obtained, spectral fatigue approaches can try to predict the life of a component in many excitation conditions. Different spectral shaping of the excitation can easily be used to enhance the comparison in the framework of any of the spectral approaches for fatigue life calculations, highlighting benefits and drawbacks of a direct experimental approach to failure and risk assessment in structural dynamics when dealing with complex patterns in real-life testing. Are optical measurements and spatially dense datasets really effective in advanced model updating of lightweight structures with complex structural dynamics? The noise shown in the raw signal of some experiments may pose issues in proficiently exploiting the added data in a fruitful model updating procedure. Model updating results are here compared between scanning and native full field technologies, with comments and details on the test rig, on the advantages and drawbacks of the approaches. The identification of EMA models highlights the increasing quality of shapes that can be obtained from native full field high resolution gears, against that (some time unexpectedly poor) of SLDV tested.

Biomechanical effects of two different collar implant structures on stress distribution under cantilever fixed partial dentures.

PubMed

Merıç, Gökçe; Erkmen, Erkan; Kurt, Ahmet; Eser, Atilim; özden, Ahmet Utku

2011-11-01

The purpose of the study was to compare the effects of two distinct collar geometries of implants on stress distribution in the bone around the implants supporting cantilever fixed partial dentures (CFPDs) as well as in the implant-abutment complex and superstructures. The three-dimensional finite element method was selected to evaluate the stress distribution. CFPDs which was supported by microthread collar structured (MCS) and non-microthread collar structured (NMCS) implants was modeled; 300 N vertical, 150 N oblique and 60 N horizontal forces were applied to the models separately. The stress values in the bone, implant-abutment complex and superstructures were calculated. In the MCS model, higher stresses were located in the cortical bone and implant-abutment complex in the case of vertical load while decreased stresses in cortical bone and implant-abutment complex were noted within horizontal and oblique loading. In the case of vertical load, decreased stresses have been noted in cancellous bone and framework. Upon horizontal and oblique loading, a MCS model had higher stress in cancellous bone and framework than the NMCS model. Higher von Mises stresses have been noted in veneering material for NMCS models. It has been concluded that stress distribution in implant-supported CFPDs correlated with the macro design of the implant collar and the direction of applied force.

A NEW LOOK AT THE EFFECTS OF ANXIETY AND STRESS ON THE PERFORMANCE OF COMPLEX INTELLECTUAL TASKS, STUDY II. SCHOOL ANXIETY AND COGNITIVE FUNCTIONING--EXPLORATORY STUDIES.

ERIC Educational Resources Information Center

DUNN, JAMES A.

THE EFFECTS OF TEST ANXIETY AND TEST STRESS ON THE PERFORMANCE OF TWO DIFFERENT INTELLECTUAL TASKS WERE STUDIED. IT WAS HYPOTHESIZED THAT THE DESCRIPTIVE EFFECTS OF ANXIETY WOULD BE GREATER FOR DIFFICULT BUT SIMPLE TASKS THAN FOR COMPLEX BUT EASY TASKS, AND THAT SITUATIONAL STRESS WOULD BE MORE DISRUPTIVE FOR COMPLEX TASKS THAN FOR SIMPLE TASKS. A…

[Role of psychosocial stress in complex diseases].

PubMed

Scantamburlo, G; Scheen, A J

2012-01-01

Complex diseases are chronic diseases where the interrelations between genetic predisposition and environmental factors play an essential role in the arisen and the maintenance of the pathology. Upon psychological stress, the hypothalamic-pituitary-adrenal axis and the sympathetic nervous system are activated resulting in release of glucocorticoids and catecholamines. Chronic stress may induce complex diseases where alterations of nervous, endocrine and immune systems are involved. Thus, chronic stress is more likely to induce a range of effects, depending on the capacity of the subject to cope with stress. CRH ("Corticotropin Releasing Hormone") is a key factor in the stress-immunity relationship. In this article, we propose an overview of the interrelations between central nervous, endocrine and immune systems and implications for health and diseases. The objective for the clinician is to propose therapeutic strategies targeting changes in human behaviour to cope with a potentially stressful environment.

Temporal and spatial stress-field reorientation in the footwall of two low-angle normal faults (lanf's): Implications for fault weakening and earthquake stress drops

NASA Astrophysics Data System (ADS)

Luther, A. L.; Axen, G. J.; Selverstone, J.

2011-12-01

Paleostress analyses from the footwall of the West Salton and Whipple detachment faults (WSD and WD, respectively), 2 lanfs, indicate both spatial and temporal stress field changes. Lanf's slip at a higher angle to S1 than predicted by Anderson. Hypotheses allowing slip on misoriented faults include a local stress field rotation in the fault zone, low friction materials, high pore-fluid pressure, and/or dynamic effects. The WSD, is part of the dextral-transtensional southern San Andreas fault system, slipped ~10 km from ~8 to 1 Ma, and the footwall exposures reflect only brittle deformation. The WD slipped at least ~40 km from ~25 to ~16 Ma, and has a mylonitic footwall overprinted by brittle deformation. Both lanf's were folded during extension. 80% of inversions that fit extension have a steeply-plunging S1, consistent with lanf slip at a high angle to S1. These require some weakening mechanism and the absence of known weak materials along these faults suggest pore-fluid pressure or dynamic effects are relevant. Most spatial S1 changes that occur are across minidetachments, which are faults sub-parallel to main faults that have similar damage zones that we interpret formed early in WD history, at the frictional-viscous transition [Selverstone et al. this session]. Their footwalls record a more moderately-plunging S1 than their hanging walls. Thus, we infer that older, deeper stress fields were rotated, consistent with a gradual rotation with depth. Alternating stress fields apparently affected many single outcrops and arise from mutually cross-cutting fracture sets that cannot be fit by a single stress field. In places where the alternation is between extensional and shortening fields, the shortening directions are subhorizontal, ~perpendicular to fold-axes and consistent with dextral-oblique slip in the case of the WSD. Commonly, S1 and S3 swap positions. In other places, two extensional stress fields differ, with S1 changing from a steep to a moderate angle to the lanf. We hypothesize that alternating stress fields result from earthquake stress drops large enough to allow at least 2 principal stresses to switch orientations. Either the differential stresses are small and similar to hypothesized stress drops or stress drops are larger than suggested by seismic data.

Stress, Anxiety, and Immunomodulation: A Pharmacological Analysis.

PubMed

Ray, A; Gulati, K; Rai, N

2017-01-01

Stress and stressful events are common occurrences in our daily lives and such aversive situations bring about complex changes in the biological system. Such stress responses influence the brain and behavior, neuroendocrine and immune systems, and these responses orchestrate to increase or decrease the ability of the organism to cope with such stressors. The brain via expression of complex behavioral paradigms controls peripheral responses to stress and a bidirectional link exists in the modulation of stress effects. Anxiety is a common neurobehavioral correlate of a variety of stressors, and both acute and chronic stress exposure could precipitate anxiety disorders. Psychoneuroimmunology involves interactions between the brain and the immune system, and it is now being increasingly recognized that the immune system could contribute to the neurobehavioral responses to stress. Studies have shown that the brain and its complex neurotransmitter networks could influence immune function, and there could be a possible link between anxiogenesis and immunomodulation during stress. Physiological and pharmacological data have highlighted this concept, and the present review gives an overview of the relationship between stress, anxiety, and immune responsiveness. © 2017 Elsevier Inc. All rights reserved.

Molecular and Epigenetic Mechanisms for the Complex Effects of Stress on Synaptic Physiology and Cognitive Functions

PubMed Central

Yuen, Eunice Y.; Wei, Jing

2017-01-01

Abstract Evidence over the past decades has found that stress, particularly through the corticosterone stress hormones, produces complex changes in glutamatergic signaling in prefrontal cortex, which leads to the alteration of cognitive processes medicated by this brain region. Interestingly, the effects of stress on glutamatergic transmission appear to be “U-shaped,” depending upon the duration and severity of the stressor. These biphasic effects of acute vs chronic stress represent the adaptive vs maladaptive responses to stressful stimuli. Animal studies suggest that the stress-induced modulation of excitatory synaptic transmission involves changes in presynaptic glutamate release, postsynaptic glutamate receptor membrane trafficking and degradation, spine structure and cytoskeleton network, and epigenetic control of gene expression. This review will discuss current findings on the key molecules involved in the stress-induced regulation of prefrontal cortex synaptic physiology and prefrontal cortex-mediated functions. Understanding the molecular and epigenetic mechanisms that underlie the complex effects of stress will help to develop novel strategies to cope with stress-related mental disorders. PMID:29016816

Molecular and Epigenetic Mechanisms for the Complex Effects of Stress on Synaptic Physiology and Cognitive Functions.

PubMed

Yuen, Eunice Y; Wei, Jing; Yan, Zhen

2017-11-01

Evidence over the past decades has found that stress, particularly through the corticosterone stress hormones, produces complex changes in glutamatergic signaling in prefrontal cortex, which leads to the alteration of cognitive processes medicated by this brain region. Interestingly, the effects of stress on glutamatergic transmission appear to be "U-shaped," depending upon the duration and severity of the stressor. These biphasic effects of acute vs chronic stress represent the adaptive vs maladaptive responses to stressful stimuli. Animal studies suggest that the stress-induced modulation of excitatory synaptic transmission involves changes in presynaptic glutamate release, postsynaptic glutamate receptor membrane trafficking and degradation, spine structure and cytoskeleton network, and epigenetic control of gene expression. This review will discuss current findings on the key molecules involved in the stress-induced regulation of prefrontal cortex synaptic physiology and prefrontal cortex-mediated functions. Understanding the molecular and epigenetic mechanisms that underlie the complex effects of stress will help to develop novel strategies to cope with stress-related mental disorders. © The Author 2017. Published by Oxford University Press on behalf of CINP.

Lysine acetyltransferase NuA4 and acetyl-CoA regulate glucose-deprived stress granule formation in Saccharomyces cerevisiae

PubMed Central

Huard, Sylvain; Morettin, Alan; Fullerton, Morgan D.; Côté, Jocelyn

2017-01-01

Eukaryotic cells form stress granules under a variety of stresses, however the signaling pathways regulating their formation remain largely unknown. We have determined that the Saccharomyces cerevisiae lysine acetyltransferase complex NuA4 is required for stress granule formation upon glucose deprivation but not heat stress. Further, the Tip60 complex, the human homolog of the NuA4 complex, is required for stress granule formation in cancer cell lines. Surprisingly, the impact of NuA4 on glucose-deprived stress granule formation is partially mediated through regulation of acetyl-CoA levels, which are elevated in NuA4 mutants. While elevated acetyl-CoA levels suppress the formation of glucose-deprived stress granules, decreased acetyl-CoA levels enhance stress granule formation upon glucose deprivation. Further our work suggests that NuA4 regulates acetyl-CoA levels through the Acetyl-CoA carboxylase Acc1. Altogether this work establishes both NuA4 and the metabolite acetyl-CoA as critical signaling pathways regulating the formation of glucose-deprived stress granules. PMID:28231279

3D Numerical Modeling of the Propagation of Hydraulic Fracture at Its Intersection with Natural (Pre-existing) Fracture

NASA Astrophysics Data System (ADS)

Dehghan, Ali Naghi; Goshtasbi, Kamran; Ahangari, Kaveh; Jin, Yan; Bahmani, Aram

2017-02-01

A variety of 3D numerical models were developed based on hydraulic fracture experiments to simulate the propagation of hydraulic fracture at its intersection with natural (pre-existing) fracture. Since the interaction between hydraulic and pre-existing fractures is a key condition that causes complex fracture patterns, the extended finite element method was employed in ABAQUS software to simulate the problem. The propagation of hydraulic fracture in a fractured medium was modeled in two horizontal differential stresses (Δ σ) of 5e6 and 10e6 Pa considering different strike and dip angles of pre-existing fracture. The rate of energy release was calculated in the directions of hydraulic and pre-existing fractures (G_{{frac}} /G_{{rock}}) at their intersection point to determine the fracture behavior. Opening and crossing were two dominant fracture behaviors during the hydraulic and pre-existing fracture interaction at low and high differential stress conditions, respectively. The results of numerical studies were compared with those of experimental models, showing a good agreement between the two to validate the accuracy of the models. Besides the horizontal differential stress, strike and dip angles of the natural (pre-existing) fracture, the key finding of this research was the significant effect of the energy release rate on the propagation behavior of the hydraulic fracture. This effect was more prominent under the influence of strike and dip angles, as well as differential stress. The obtained results can be used to predict and interpret the generation of complex hydraulic fracture patterns in field conditions.

Residual stress characterization of steel TIG welds by neutron diffraction and by residual magnetic stray field mappings

NASA Astrophysics Data System (ADS)

Stegemann, Robert; Cabeza, Sandra; Lyamkin, Viktor; Bruno, Giovanni; Pittner, Andreas; Wimpory, Robert; Boin, Mirko; Kreutzbruck, Marc

2017-03-01

The residual stress distribution of tungsten inert gas welded S235JRC+C plates was determined by means of neutron diffraction (ND). Large longitudinal residual stresses with maxima around 600 MPa were found. With these results as reference, the evaluation of residual stress with high spatial resolution GMR (giant magneto resistance) sensors was discussed. The experiments performed indicate a correlation between changes in residual stresses (ND) and the normal component of local residual magnetic stray fields (GMR). Spatial variations in the magnetic field strength perpendicular to the welds are in the order of the magnetic field of the earth.

Stress Physiology of Lactic Acid Bacteria.

PubMed

Papadimitriou, Konstantinos; Alegría, Ángel; Bron, Peter A; de Angelis, Maria; Gobbetti, Marco; Kleerebezem, Michiel; Lemos, José A; Linares, Daniel M; Ross, Paul; Stanton, Catherine; Turroni, Francesca; van Sinderen, Douwe; Varmanen, Pekka; Ventura, Marco; Zúñiga, Manuel; Tsakalidou, Effie; Kok, Jan

2016-09-01

Lactic acid bacteria (LAB) are important starter, commensal, or pathogenic microorganisms. The stress physiology of LAB has been studied in depth for over 2 decades, fueled mostly by the technological implications of LAB robustness in the food industry. Survival of probiotic LAB in the host and the potential relatedness of LAB virulence to their stress resilience have intensified interest in the field. Thus, a wealth of information concerning stress responses exists today for strains as diverse as starter (e.g., Lactococcus lactis), probiotic (e.g., several Lactobacillus spp.), and pathogenic (e.g., Enterococcus and Streptococcus spp.) LAB. Here we present the state of the art for LAB stress behavior. We describe the multitude of stresses that LAB are confronted with, and we present the experimental context used to study the stress responses of LAB, focusing on adaptation, habituation, and cross-protection as well as on self-induced multistress resistance in stationary phase, biofilms, and dormancy. We also consider stress responses at the population and single-cell levels. Subsequently, we concentrate on the stress defense mechanisms that have been reported to date, grouping them according to their direct participation in preserving cell energy, defending macromolecules, and protecting the cell envelope. Stress-induced responses of probiotic LAB and commensal/pathogenic LAB are highlighted separately due to the complexity of the peculiar multistress conditions to which these bacteria are subjected in their hosts. Induction of prophages under environmental stresses is then discussed. Finally, we present systems-based strategies to characterize the "stressome" of LAB and to engineer new food-related and probiotic LAB with improved stress tolerance. Copyright © 2016, American Society for Microbiology. All Rights Reserved.

Biogenesis of mitochondria in cauliflower (Brassica oleracea var. botrytis) curds subjected to temperature stress and recovery involves regulation of the complexome, respiratory chain activity, organellar translation and ultrastructure.

PubMed

Rurek, Michal; Woyda-Ploszczyca, Andrzej M; Jarmuszkiewicz, Wieslawa

2015-01-01

The biogenesis of the cauliflower curd mitochondrial proteome was investigated under cold, heat and the recovery. For the first time, two dimensional fluorescence difference gel electrophoresis was used to study the plant mitochondrial complexome in heat and heat recovery. Particularly, changes in the complex I and complex III subunits and import proteins, and the partial disintegration of matrix complexes were observed. The presence of unassembled subunits of ATP synthase was accompanied by impairment in mitochondrial translation of its subunit. In cold and heat, the transcription profiles of mitochondrial genes were uncorrelated. The in-gel activities of respiratory complexes were particularly affected after stress recovery. Despite a general stability of respiratory chain complexes in heat, functional studies showed that their activity and the ATP synthesis yield were affected. Contrary to cold stress, heat stress resulted in a reduced efficiency of oxidative phosphorylation likely due to changes in alternative oxidase (AOX) activity. Stress and stress recovery differently modulated the protein level and activity of AOX. Heat stress induced an increase in AOX activity and protein level, and AOX1a and AOX1d transcript level, while heat recovery reversed the AOX protein and activity changes. Conversely, cold stress led to a decrease in AOX activity (and protein level), which was reversed after cold recovery. Thus, cauliflower AOX is only induced by heat stress. In heat, contrary to the AOX activity, the activity of rotenone-insensitive internal NADH dehydrogenase was diminished. The relevance of various steps of plant mitochondrial biogenesis to temperature stress response and recovery is discussed. Copyright © 2015 Elsevier B.V. All rights reserved.

Modeling a distribution of point defects as misfitting inclusions in stressed solids

NASA Astrophysics Data System (ADS)

Cai, W.; Sills, R. B.; Barnett, D. M.; Nix, W. D.

2014-05-01

The chemical equilibrium distribution of point defects modeled as non-overlapping, spherical inclusions with purely positive dilatational eigenstrain in an isotropically elastic solid is derived. The compressive self-stress inside existing inclusions must be excluded from the stress dependence of the equilibrium concentration of the point defects, because it does no work when a new inclusion is introduced. On the other hand, a tensile image stress field must be included to satisfy the boundary conditions in a finite solid. Through the image stress, existing inclusions promote the introduction of additional inclusions. This is contrary to the prevailing approach in the literature in which the equilibrium point defect concentration depends on a homogenized stress field that includes the compressive self-stress. The shear stress field generated by the equilibrium distribution of such inclusions is proved to be proportional to the pre-existing stress field in the solid, provided that the magnitude of the latter is small, so that a solid containing an equilibrium concentration of point defects can be described by a set of effective elastic constants in the small-stress limit.

Thermoelastic stress in oceanic lithosphere due to hotspot reheating

NASA Technical Reports Server (NTRS)

Zhu, Anning; Wiens, Douglas A.

1991-01-01

The effect of hotspot reheating on the intraplate stress field is investigated by modeling the three-dimensional thermal stress field produced by nonuniform temperature changes in an elastic plate. Temperature perturbations are calculated assuming that the lithosphere is heated by a source in the lower part of the thermal lithosphere. A thermal stress model for the elastic lithosphere is calculated by superposing the stress fields resulting from temperature changes in small individual elements. The stress in an elastic plate resulting from a temperature change in each small element is expressed as an infinite series, wherein each term is a source or an image modified from a closed-from half-space solution. The thermal stress solution is applied to midplate swells in oceanic lithosphere with various thermal structures and plate velocities. The results predict a stress field with a maximum deviatoric stress on the order of 100 MPa covering a broad area around the hotspot plume. The predicted principal stress orientations show a complicated geographical pattern, with horizontal extension perpendicular to the hotspot track at shallow depths and compression along the track near the bottom of the elastic lithosphere.

Dynamics of skimming flow in the wake of a vegetation patch

NASA Astrophysics Data System (ADS)

Mayaud, Jerome R.; Wiggs, Giles F. S.; Bailey, Richard M.

2016-09-01

Dryland vegetation is often spatially patchy, and so affects wind flow in complex ways. Theoretical models and wind tunnel testing have shown that skimming flow develops above vegetation patches at high plant densities, resulting in little or no wind erosion in these zones. Understanding the dynamics of skimming flow is therefore important for predicting sediment transport and bedform development in dryland areas. However, no field-based data are available describing turbulent airflow dynamics in the wake of vegetation patches. In this study, turbulent wind flow was examined using high-frequency (10 Hz) sonic anemometry at four measurement heights (0.30 m, 0.55 m, 1.10 m and 1.65 m) along a transect in the lee of an extensive patch of shrubs (z = 1.10 m height) in Namibia. Spatial variations in mean wind velocity, horizontal Reynolds stresses and coherent turbulent structures were analysed. We found that wind velocity in the wake of the patch effectively recovered over ∼12 patch heights (h) downwind, which is 2-5 h longer than previously reported recovery lengths for individual vegetation elements and two-dimensional wind fences. This longer recovery can be attributed to a lack of flow moving around the obstacle in the patch case. The step-change in roughness between the patch canopy and the bare surface in its wake resulted in an initial peak in resultant horizontal shear stress (τr) followed by significant decrease downwind. In contrast to τr , horizontal normal Reynolds stress (u‧2 ‾) progressively increased along the patch wake. A separation of the upper shear layer at the leeside edge of the patch was observed, and a convergence of τr curves implies the formation of a constant stress layer by ∼20 h downwind. The use of τr at multiple heights is found to be a useful tool for identifying flow equilibration in complex aerodynamic regimes. Quadrant analysis revealed elevated frequencies of Q2 (ejection) and Q4 (sweep) events in the immediate lee of the patch, which contributed to the observed high levels of shear stress. The increasing downwind contribution of Q1 (outward interaction) events, which coincides with greater u‧2 ‾ and wind velocity, suggests that sediment transport potential increases with greater distance from the patch edge. Determining realistic, field-derived constraints on turbulent airflow dynamics in the wakes of vegetation patches is crucial for accurately parameterising sediment transport potential in larger-scale dryland landscape models. This will help to improve our understanding of how semi-vegetated desert surfaces might react to future environmental and anthropogenic stresses.

Modeling Coupled Processes for Multiphase Fluid Flow in Mechanically Deforming Faults

NASA Astrophysics Data System (ADS)

McKenna, S. A.; Pike, D. Q.

2011-12-01

Modeling of coupled hydrological-mechanical processes in fault zones is critical for understanding the long-term behavior of fluids within the shallow crust. Here we utilize a previously developed cellular-automata (CA) model to define the evolution of permeability within a 2-D fault zone under compressive stress. At each time step, the CA model calculates the increase in fluid pressure within the fault at every grid cell. Pressure surpassing a critical threshold (e.g., lithostatic stress) causes a rupture in that cell, and pressure is then redistributed across the neighboring cells. The rupture can cascade through the spatial domain and continue across multiple time steps. Stress continues to increase and the size and location of rupture events are recorded until a percolating backbone of ruptured cells exists across the fault. Previous applications of this model consider uncorrelated random fields for the compressibility of the fault material. The prior focus on uncorrelated property fields is consistent with development of a number of statistical physics models including percolation processes and fracture propagation. However, geologic materials typically express spatial correlation and this can have a significant impact on the results of the pressure and permeability distributions. We model correlation of the fault material compressibility as a multiGaussian random field with a correlation length defined as the full-width at half maximum (FWHM) of the kernel used to create the field. The FWHM is varied from < 0.001 to approximately 0.47 of the domain size. The addition of spatial correlation to the compressibility significantly alters the model results including: 1) Accumulation of larger amounts of strain prior to the first rupture event; 2) Initiation of the percolating backbone at lower amounts of cumulative strain; 3) Changes in the event size distribution to a combined power-law and exponential distribution with a smaller power; and 4) Evolution of the spatial-temporal distribution of rupture event locations from a purely Poisson process to a complex pattern of clustered events with periodic patterns indicative of emergent phenomena. Switching the stress field from compressive to quiescent, or extensional, during the CA simulation results in a fault zone with a complex permeability pattern and disconnected zones of over-pressured fluid that serves as the initial conditions for simulation of capillary invasion of a separate fluid phase. We use Modified Invasion Percolation to simulate the invasion of a less dense fluid into the fault zone. Results show that the variability in fluid displacement measures caused by the heterogeneous permeability field and initial pressure conditions are significant. This material is based upon work supported as part of the Center for Frontiers of Subsurface Energy Security, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Award Number DE-SC0001114. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000

Mechanic stress generated by a time-varying electromagnetic field on bone surface.

PubMed

Ye, Hui

2018-03-19

Bone cells sense mechanical load, which is essential for bone growth and remodeling. In a fracture, this mechanism is compromised. Electromagnetic stimulation has been widely used to assist in bone healing, but the underlying mechanisms are largely unknown. A recent hypothesis suggests that electromagnetic stimulation could influence tissue biomechanics; however, a detailed quantitative understanding of EM-induced biomechanical changes in the bone is unavailable. This paper used a muscle/bone model to study the biomechanics of the bone under EM exposure. Due to the dielectric properties of the muscle/bone interface, a time-varying magnetic field can generate both compressing and shear stresses on the bone surface, where many mechanical sensing cells are available for cellular mechanotransduction. I calculated these stresses and found that the shear stress is significantly greater than the compressing stress. Detailed parametric analysis suggests that both the compressing and shear stresses are dependent on the geometrical and electrical properties of the muscle and the bone. These stresses are also functions of the orientation of the coil and the frequency of the magnetic field. It is speculated that the EM field could apply biomechanical influence to fractured bone, through the fine-tuning of the controllable field parameters. Graphical abstract Mechanic stress on bone surface in a time-varying magnetic field.

Gravity-driven groundwater flow and slope failure potential: 1. Elastic effective-stress model

USGS Publications Warehouse

Iverson, Richard M.; Reid, Mark E.

1992-01-01

Hilly or mountainous topography influences gravity-driven groundwater flow and the consequent distribution of effective stress in shallow subsurface environments. Effective stress, in turn, influences the potential for slope failure. To evaluate these influences, we formulate a two-dimensional, steady state, poroelastic model. The governing equations incorporate groundwater effects as body forces, and they demonstrate that spatially uniform pore pressure changes do not influence effective stresses. We implement the model using two finite element codes. As an illustrative case, we calculate the groundwater flow field, total body force field, and effective stress field in a straight, homogeneous hillslope. The total body force and effective stress fields show that groundwater flow can influence shear stresses as well as effective normal stresses. In most parts of the hillslope, groundwater flow significantly increases the Coulomb failure potential Φ, which we define as the ratio of maximum shear stress to mean effective normal stress. Groundwater flow also shifts the locus of greatest failure potential toward the slope toe. However, the effects of groundwater flow on failure potential are less pronounced than might be anticipated on the basis of a simpler, one-dimensional, limit equilibrium analysis. This is a consequence of continuity, compatibility, and boundary constraints on the two-dimensional flow and stress fields, and it points to important differences between our elastic continuum model and limit equilibrium models commonly used to assess slope stability.

Hydrogen Assisted Cracking in Pearlitic Steel Rods: The Role of Residual Stresses Generated by Fatigue Precracking

PubMed Central

Toribio, Jesús; Aguado, Leticia; Lorenzo, Miguel; Kharin, Viktor

2017-01-01

Stress corrosion cracking (SCC) of metals is an issue of major concern in engineering since this phenomenon causes many catastrophic failures of structural components in aggressive environments. SCC is even more harmful under cathodic conditions promoting the phenomenon known as hydrogen assisted cracking (HAC), hydrogen assisted fracture (HAF) or hydrogen embrittlement (HE). A common way to assess the susceptibility of a given material to HAC, HAF or HE is to subject a cracked rod to a constant extension rate tension (CERT) test until it fractures in this harsh environment. This paper analyzes the influence of a residual stress field generated by fatigue precracking on the sample’s posterior susceptibility to HAC. To achieve this goal, numerical simulations were carried out of hydrogen diffusion assisted by the stress field. Firstly, a mechanical simulation of the fatigue precracking was developed for revealing the residual stress field after diverse cyclic loading scenarios and posterior stress field evolution during CERT loading. Afterwards, a simulation of hydrogen diffusion assisted by stress was carried out considering the residual stresses after fatigue and the superposed rising stresses caused by CERT loading. Results reveal the key role of the residual stress field after fatigue precracking in the HAC phenomena in cracked steel rods as well as the beneficial effect of compressive residual stress. PMID:28772845

A PERIPHERAL CHOLINERGIC PATHWAY MODULATES STRESS-INDUCED HYPERTHERMIA IN THE RAT EXPOSED TO AN OPEN FIELD.

EPA Science Inventory

Exposure to an open-field is psychologically stressful and leads to an elevation in core temperature (Tc). This increase in Tc associated with open-field is usually referred to as stress-induced hyperthermia (SIH) and can be blocked centrally with cyclooxygenase inhibitors suc...

Evolution of Deformation Studies on Active Hawaiian Volcanoes

USGS Publications Warehouse

Decker, Robert W.; Okamura, Arnold; Miklius, Asta; Poland, Michael

2008-01-01

Everything responds to pressure, even rocks. Deformation studies involve measuring and interpreting the changes in elevations and horizontal positions of the land surface or sea floor. These studies are variously referred to as geodetic changes or ground-surface deformations and are sometimes indexed under the general heading of geodesy. Deformation studies have been particularly useful on active volcanoes and in active tectonic areas. A great amount of time and energy has been spent on measuring geodetic changes on Kilauea and Mauna Loa Volcanoes in Hawai`i. These changes include the build-up of the surface by the piling up and ponding of lava flows, the changes in the surface caused by erosion, and the uplift, subsidence, and horizontal displacements of the surface caused by internal processes acting beneath the surface. It is these latter changes that are the principal concern of this review. A complete and objective review of deformation studies on active Hawaiian volcanoes would take many volumes. Instead, we attempt to follow the evolution of the most significant observations and interpretations in a roughly chronological way. It is correct to say that this is a subjective review. We have spent years measuring and recording deformation changes on these great volcanoes and more years trying to understand what makes these changes occur. We attempt to make this a balanced as well as a subjective review; the references are also selective rather than exhaustive. Geodetic changes caused by internal geologic processes vary in magnitude from the nearly infinitesimal - one micron or less, to the very large - hundreds of meters. Their apparent causes also are varied and include changes in material properties and composition, atmospheric pressure, tidal stress, thermal stress, subsurface-fluid pressure (including magma pressure, magma intrusion, or magma removal), gravity, and tectonic stress. Deformation is measured in units of strain or displacement. For example, tilt of the ground surface on the rim of Kilauea Caldera is measured in microradians, a strain unit that gives the change in angle from some reference. The direction in which the tilt is measured must be defined - north or south, or some direction normal to the maximum changes. For displacements related to surface faulting, the changes are normally given in linear measures of offset. Changes in the diameter of a caldera can be given in either displacements or strain units. In the later case, the displacement divided by the 'original' diameter gives the strain ratio. Strains are dimensionless numbers; displacements have the dimensions of length. Vectors commonly are used to show the direction and amount of displacements in plan view. Strain results from stress. It can be elastic strain, when the strain is linearly related to stress and is recoverable; it can be viscous strain, where the rate of strain is proportional to the stress and is not recoverable; or it can be plastic strain that is often some complex stress-strain relationship, for example, elastic up to some yield strength and viscous beyond. Volcanic rocks are brittle when cold and under near-surface pressures but plastic to viscous under higher temperature and pressure regimes. It is important in deformation studies to try to define the nature of the strain and the rheology of the rocks being deformed. A good text on rheology is 'The Structure and Rheology of Complex Fluids' by R.G. Larson, 1999. Under changing tensional or compressional stresses, tiny cracks in brittle rocks may open or close, causing a quasielastic strain response. If the stresses exceed the breaking strength of the rock, brittle failure occurs, and the stress-strain relationship breaks down. This is generally the situation with near-field deformation related to earthquakes. Stresses change in complex patterns in both the near- and far-fields of the fracture, and the near-fiel

Non-rocket Earth-Moon transport system

NASA Astrophysics Data System (ADS)

Bolonkin, Alexander

2003-06-01

This paper proposes a new transportation system for travel between Earth and Moon. This transportation system uses mechanical energy transfer and requires only minimal energy, using an engine located on Earth. A cable directly connects a pole of the Earth through a drive station to the lunar surface_ The equation for an optimal equal stress cable for complex gravitational field of Earth-Moon has been derived that allows significantly lower cable masses. The required strength could be provided by cables constructed of carbon nanotubes or carbon whiskers. Some of the constraints on such a system are discussed.

Audio-based, unsupervised machine learning reveals cyclic changes in earthquake mechanisms in the Geysers geothermal field, California

NASA Astrophysics Data System (ADS)

Holtzman, B. K.; Paté, A.; Paisley, J.; Waldhauser, F.; Repetto, D.; Boschi, L.

2017-12-01

The earthquake process reflects complex interactions of stress, fracture and frictional properties. New machine learning methods reveal patterns in time-dependent spectral properties of seismic signals and enable identification of changes in faulting processes. Our methods are based closely on those developed for music information retrieval and voice recognition, using the spectrogram instead of the waveform directly. Unsupervised learning involves identification of patterns based on differences among signals without any additional information provided to the algorithm. Clustering of 46,000 earthquakes of $0.3

Stage call: Cardiovascular reactivity to audition stress in musicians

PubMed Central

Chanwimalueang, Theerasak; Aufegger, Lisa; Adjei, Tricia; Wasley, David; Cruder, Cinzia; Mandic, Danilo P.

2017-01-01

Auditioning is at the very center of educational and professional life in music and is associated with significant psychophysical demands. Knowledge of how these demands affect cardiovascular responses to psychosocial pressure is essential for developing strategies to both manage stress and understand optimal performance states. To this end, we recorded the electrocardiograms (ECGs) of 16 musicians (11 violinists and 5 flutists) before and during performances in both low- and high-stress conditions: with no audience and in front of an audition panel, respectively. The analysis consisted of the detection of R-peaks in the ECGs to extract heart rate variability (HRV) from the notoriously noisy real-world ECGs. Our data analysis approach spanned both standard (temporal and spectral) and advanced (structural complexity) techniques. The complexity science approaches—namely, multiscale sample entropy and multiscale fuzzy entropy—indicated a statistically significant decrease in structural complexity in HRV from the low- to the high-stress condition and an increase in structural complexity from the pre-performance to performance period, thus confirming the complexity loss theory and a loss in degrees of freedom due to stress. Results from the spectral analyses also suggest that the stress responses in the female participants were more parasympathetically driven than those of the male participants. In conclusion, our findings suggest that interventions to manage stress are best targeted at the sensitive pre-performance period, before an audition begins. PMID:28437466

Near-field tsunami edge waves and complex earthquake rupture

USGS Publications Warehouse

Geist, Eric L.

2013-01-01

The effect of distributed coseismic slip on progressive, near-field edge waves is examined for continental shelf tsunamis. Detailed observations of edge waves are difficult to separate from the other tsunami phases that are observed on tide gauge records. In this study, analytic methods are used to compute tsunami edge waves distributed over a finite number of modes and for uniformly sloping bathymetry. Coseismic displacements from static elastic theory are introduced as initial conditions in calculating the evolution of progressive edge-waves. Both simple crack representations (constant stress drop) and stochastic slip models (heterogeneous stress drop) are tested on a fault with geometry similar to that of the M w = 8.8 2010 Chile earthquake. Crack-like ruptures that are beneath or that span the shoreline result in similar longshore patterns of maximum edge-wave amplitude. Ruptures located farther offshore result in reduced edge-wave excitation, consistent with previous studies. Introduction of stress-drop heterogeneity by way of stochastic slip models results in significantly more variability in longshore edge-wave patterns compared to crack-like ruptures for the same offshore source position. In some cases, regions of high slip that are spatially distinct will yield sub-events, in terms of tsunami generation. Constructive interference of both non-trapped and trapped waves can yield significantly larger tsunamis than those that produced by simple earthquake characterizations.

Drought stress and carbon uptake in an Amazon forest measured with spaceborne imaging spectroscopy

PubMed Central

Asner, Gregory P.; Nepstad, Daniel; Cardinot, Gina; Ray, David

2004-01-01

Amazônia contains vast stores of carbon in high-diversity ecosystems, yet this region undergoes major changes in precipitation affecting land use, carbon dynamics, and climate. The extent and structural complexity of Amazon forests impedes ground studies of ecosystem functions such as net primary production (NPP), water cycling, and carbon sequestration. Traditional modeling and remote-sensing approaches are not well suited to tropical forest studies, because (i) biophysical mechanisms determining drought effects on canopy water and carbon dynamics are poorly known, and (ii) remote-sensing metrics of canopy greenness may be insensitive to small changes in leaf area accompanying drought. New spaceborne imaging spectroscopy may detect drought stress in tropical forests, helping to monitor forest physiology and constrain carbon models. We combined a forest drought experiment in Amazônia with spaceborne imaging spectrometer measurements of this area. With field data on rainfall, soil water, and leaf and canopy responses, we tested whether spaceborne hyperspectral observations quantify differences in canopy water and NPP resulting from drought stress. We found that hyperspectral metrics of canopy water content and light-use efficiency are highly sensitive to drought. Using these observations, forest NPP was estimated with greater sensitivity to drought conditions than with traditional combinations of modeling, remote-sensing, and field measurements. Spaceborne imaging spectroscopy will increase the accuracy of ecological studies in humid tropical forests. PMID:15071182

Perspectives on the Etiology of Violence in Later Life.

PubMed

Mysyuk, Yuliya; Westendorp, Rudi G J; Lindenberg, Jolanda

2016-11-01

This article focuses on the development of a conceptual framework for explaining the etiology of violence in later life by various groups involved in the field of elder abuse. In this study, we explore this through eight focus groups with different professionals involved in the field of elder abuse and older persons themselves and in interviews with 35 experts in the field. Our findings show that dependency, vulnerability, power and control, social isolation, stress, and care burden play a central role in their explanations for the occurrence of violence in later life. The role of a history of violence in violence in later life is equivocal. The complexity and ambiguity of dependency and vulnerability, the notion of mutual dependency, and diverse attitudes and expectations toward them that arise with the aging process are distinct features of violence in later life that were found. © The Author(s) 2015.

Spatial variation of present-day stress field and tectonic regime in Tunisia and surroundings from formal inversion of focal mechanisms: Geodynamic implications for central Mediterranean

NASA Astrophysics Data System (ADS)

Soumaya, Abdelkader; Ben Ayed, Noureddine; Delvaux, Damien; Ghanmi, Mohamed

2015-06-01

We compiled 123 focal mechanisms from various sources for Tunisia and adjacent regions up to Sicily, to image the current stress field in the Maghrebides chain (from Tunisia to Sicily) and its foreland. Stress inversion of all the available data provides a first-order stress field with a N150°E horizontal compression (SHmax) and a transpressional tectonic regime, but the obtained stress tensor poorly fit to the data set. We separated them into regional subsets (boxes) in function of their geographical proximity, kinematic regime, homogeneity of kinematic orientations, and tectonic setting. Their respective inversion evidences second- and third-order spatial variations in tectonic regime and horizontal stress directions. The stress field gradually changes from compression in the Maghrebides thrust belt to transpression and strike slip in the Atlassic and Pelagian foreland, respectively, where preexisting NW-SE to E-W deep faults system are reactivated. This spatial variation of the sismotectonic stress field and tectonic regime is consistent with the neotectonic stress field determined by others from fault slip data. The major Slab Transfer Edge Propagator faults (i.e., North-South Axis-Hammamet relay and Malte Escarpment), which laterally delimit the subducting slabs, play an active role in second- and third-order lateral variations of the tectonic regime and stress field orientations over the Tunisian/Sicilian domain. The past and current tectonic deformations and kinematics of the central Mediterranean are subordinately guided by the plate convergence (i.e., Africa-Eurasia), controlled or influenced by lateral slab migration/segmentation and by deep dynamics such as lithosphere-mantle interaction.

Stress field rotation or block rotation: An example from the Lake Mead fault system

NASA Technical Reports Server (NTRS)

Ron, Hagai; Nur, Amos; Aydin, Atilla

1990-01-01

The Coulomb criterion, as applied by Anderson (1951), has been widely used as the basis for inferring paleostresses from in situ fault slip data, assuming that faults are optimally oriented relative to the tectonic stress direction. Consequently if stress direction is fixed during deformation so must be the faults. Freund (1974) has shown that faults, when arranged in sets, must generally rotate as they slip. Nur et al., (1986) showed how sufficiently large rotations require the development of new sets of faults which are more favorably oriented to the principal direction of stress. This leads to the appearance of multiple fault sets in which older faults are offset by younger ones, both having the same sense of slip. Consequently correct paleostress analysis must include the possible effect of fault and material rotation, in addition to stress field rotation. The combined effects of stress field rotation and material rotation were investigated in the Lake Meade Fault System (LMFS) especially in the Hoover Dam area. Fault inversion results imply an apparent 60 degrees clockwise (CW) rotation of the stress field since mid-Miocene time. In contrast structural data from the rest of the Great Basin suggest only a 30 degrees CW stress field rotation. By incorporating paleomagnetic and seismic evidence, the 30 degrees discrepancy can be neatly resolved. Based on paleomagnetic declination anomalies, it is inferred that slip on NW trending right lateral faults caused a local 30 degrees counter-clockwise (CCW) rotation of blocks and faults in the Lake Mead area. Consequently the inferred 60 degrees CW rotation of the stress field in the LMFS consists of an actual 30 degrees CW rotation of the stress field (as for the entire Great Basin) plus a local 30 degrees CCW material rotation of the LMFS fault blocks.

Stress field rotation or block rotation: An example from the Lake Mead fault system

NASA Astrophysics Data System (ADS)

Ron, Hagai; Nur, Amos; Aydin, Atilla

1990-02-01

The Coulomb criterion, as applied by Anderson (1951), has been widely used as the basis for inferring paleostresses from in situ fault slip data, assuming that faults are optimally oriented relative to the tectonic stress direction. Consequently if stress direction is fixed during deformation so must be the faults. Freund (1974) has shown that faults, when arranged in sets, must generally rotate as they slip. Nur et al., (1986) showed how sufficiently large rotations require the development of new sets of faults which are more favorably oriented to the principal direction of stress. This leads to the appearance of multiple fault sets in which older faults are offset by younger ones, both having the same sense of slip. Consequently correct paleostress analysis must include the possible effect of fault and material rotation, in addition to stress field rotation. The combined effects of stress field rotation and material rotation were investigated in the Lake Meade Fault System (LMFS) especially in the Hoover Dam area. Fault inversion results imply an apparent 60 degrees clockwise (CW) rotation of the stress field since mid-Miocene time. In contrast structural data from the rest of the Great Basin suggest only a 30 degrees CW stress field rotation. By incorporating paleomagnetic and seismic evidence, the 30 degrees discrepancy can be neatly resolved. Based on paleomagnetic declination anomalies, it is inferred that slip on NW trending right lateral faults caused a local 30 degrees counter-clockwise (CCW) rotation of blocks and faults in the Lake Mead area. Consequently the inferred 60 degrees CW rotation of the stress field in the LMFS consists of an actual 30 degrees CW rotation of the stress field (as for the entire Great Basin) plus a local 30 degrees CCW material rotation of the LMFS fault blocks.

Genome-wide expression profiling of maize in response to individual and combined water and nitrogen stresses

PubMed Central

2013-01-01

Background Water and nitrogen are two of the most critical inputs required to achieve the high yield potential of modern corn varieties. Under most agricultural settings however they are often scarce and costly. Fortunately, tremendous progress has been made in the past decades in terms of modeling to assist growers in the decision making process and many tools are now available to achieve more sustainable practices both environmentally and economically. Nevertheless large gaps remain between our empirical knowledge of the physiological changes observed in the field in response to nitrogen and water stresses, and our limited understanding of the molecular processes leading to those changes. Results This work examines in particular the impact of simultaneous stresses on the transcriptome. In a greenhouse setting, corn plants were grown under tightly controlled nitrogen and water conditions, allowing sampling of various tissues and stress combinations. A microarray profiling experiment was performed using this material and showed that the concomitant presence of nitrogen and water limitation affects gene expression to an extent much larger than anticipated. A clustering analysis also revealed how the interaction between the two stresses shapes the patterns of gene expression over various levels of water stresses and recovery. Conclusions Overall, this study suggests that the molecular signature of a specific combination of stresses on the transcriptome might be as unique as the impact of individual stresses, and hence underlines the difficulty to extrapolate conclusions obtained from the study of individual stress responses to more complex settings. PMID:23324127

A compressible Navier-Stokes solver with two-equation and Reynolds stress turbulence closure models

NASA Technical Reports Server (NTRS)

Morrison, Joseph H.

1992-01-01

This report outlines the development of a general purpose aerodynamic solver for compressible turbulent flows. Turbulent closure is achieved using either two equation or Reynolds stress transportation equations. The applicable equation set consists of Favre-averaged conservation equations for the mass, momentum and total energy, and transport equations for the turbulent stresses and turbulent dissipation rate. In order to develop a scheme with good shock capturing capabilities, good accuracy and general geometric capabilities, a multi-block cell centered finite volume approach is used. Viscous fluxes are discretized using a finite volume representation of a central difference operator and the source terms are treated as an integral over the control volume. The methodology is validated by testing the algorithm on both two and three dimensional flows. Both the two equation and Reynolds stress models are used on a two dimensional 10 degree compression ramp at Mach 3, and the two equation model is used on the three dimensional flow over a cone at angle of attack at Mach 3.5. With the development of this algorithm, it is now possible to compute complex, compressible high speed flow fields using both two equation and Reynolds stress turbulent closure models, with the capability of eventually evaluating their predictive performance.

Mechanical stress modified ferroelectric aging behavior

NASA Astrophysics Data System (ADS)

Xu, Tingting; Kan, Yi; Jin, Yaming; Sun, Hui; Du, Yingchao; Wu, Xiumei; Bo, Huifeng; Cai, Wei; Huang, Fengzhen; Lu, Xiaomei; Zhu, Jinsong

2013-05-01

Mechanical stress effect on aging behavior of Bi3.25La0.75Ti3O12 (BLT) and PbZr0.53Ti0.47O3 (PZT) films was investigated. It is found that the remnant polarization decreases with time while the coercive field increases in stress-free BLT films. For unconfined PZT films, both the remnant polarization and the coercive field decrease as time elapses. The applied tensile stress weakens the aging of remnant polarization of BLT films but strengthens the aging of coercive field, while the applied tensile stress possesses opposite effect. In contrary, the applied compressive stress simultaneously improves the aging behavior of both remnant polarization and coercive field of PZT films. Mechanical-stress-induced variation of domain wall mobility in different materials was suggested as the possible origin of these observations. This work indicates that the aging behavior modification using stress could be realized, and it is helpful for promoting the reliability of ferroelectric films for industrial applications.

Delamination Fracture in Graphite/Epoxy Materials.

DTIC Science & Technology

1986-06-01

stress fields for the two loading conditions. Figures 7-10 indicate the results of a finite element analysis % for the test coupons loaded in mode I and...results somewhat approximate, the difference in the shape of the Srespective stress fields and the different rates of decay of the _ stress fields...Shear deformation is dominant feature .: observed. 1000x (all). 7. ay stress contour plot of split laminate beam tested under . mode I conditions. 8

Measurement and prediction of propeller flow field on the PTA aircraft at speeds of up to Mach 0.85. [Propfan Test Assessment

NASA Technical Reports Server (NTRS)

Aljabri, Abdullah S.

1988-01-01

High speed subsonic transports powered by advanced propellers provide significant fuel savings compared to turbofan powered transports. Unfortunately, however, propfans must operate in aircraft-induced nonuniform flow fields which can lead to high blade cyclic stresses, vibration and noise. To optimize the design and installation of these advanced propellers, therefore, detailed knowledge of the complex flow field is required. As part of the NASA Propfan Test Assessment (PTA) program, a 1/9 scale semispan model of the Gulfstream II propfan test-bed aircraft was tested in the NASA-Lewis 8 x 6 supersonic wind tunnel to obtain propeller flow field data. Detailed radial and azimuthal surveys were made to obtain the total pressure in the flow and the three components of velocity. Data was acquired for Mach numbers ranging from 0.6 to 0.85. Analytical predictions were also made using a subsonic panel method, QUADPAN. Comparison of wind-tunnel measurements and analytical predictions show good agreement throughout the Mach range.

Resilience: the power within.

PubMed

Grafton, Eileen; Gillespie, Brigid; Henderson, Saras

2010-11-01

To advance understanding of resilience as an innate resource and its potential and relevance in the management of workplace stress for oncology nurses. Journal articles and research results, particularly seminal literature from a variety of Australian and international journals and published texts, including government and nursing organizations. Resilience is defined as an innate energy or motivating life force present to varying degrees in every individual, exemplified by the presence of particular traits or characteristics that, through application of dynamic processes, enable an individual to cope with, recover from, and grow as a result of stress or adversity. Literature from a wide variety of fields, including physics, medicine, theology, philosophy, psychology, and spirituality, was reviewed to build an overview of existing knowledge and evolving theories on the subject of resilience and further the understanding of resilience as an innate personal resource. Innate resilience can be developed or enhanced through cognitive transformational practices, education, and environmental support. Such processes may have use in ameliorating the effects of workplace stress. The complex nature of oncology and other specialty nursing roles creates a certain amount of inevitable stress that depletes the self and may lead to compassion fatigue and burnout. A greater understanding of resilience as an innate stress response resource highlights the need for processes that support resilience development and organizational and personal stress-management strategies for nurses to be part of mainstream nursing education.

Complex interplay between stress perturbations and viscoelastic relaxation in a two-asperity fault model

NASA Astrophysics Data System (ADS)

Lorenzano, Emanuele; Dragoni, Michele

2018-03-01

We consider a plane fault with two asperities embedded in a shear zone, subject to a uniform strain rate owing to tectonic loading. After an earthquake, the static stress field is relaxed by viscoelastic deformation in the asthenosphere. We treat the fault as a discrete dynamical system with 3 degrees of freedom: the slip deficits of the asperities and the variation of their difference due to viscoelastic deformation. The evolution of the fault is described in terms of inter-seismic intervals and slip episodes, which may involve the slip of a single asperity or both. We consider the effect of stress transfers connected to earthquakes produced by neighbouring faults. The perturbation alters the slip deficits of both asperities and the stress redistribution on the fault associated with viscoelastic relaxation. The interplay between the stress perturbation and the viscoelastic relaxation significantly complicates the evolution of the fault and its seismic activity. We show that the presence of viscoelastic relaxation prevents any simple correlation between the change of Coulomb stresses on the asperities and the anticipation or delay of their failures. As an application, we study the effects of the 1999 Hector Mine, California, earthquake on the post-seismic evolution of the fault that generated the 1992 Landers, California, earthquake, which we model as a two-mode event associated with the consecutive failure of two asperities.

Quantitative trait loci (QTLs) for water use and crop production traits co-locate with major QTL for tolerance to water deficit in a fine-mapping population of pearl millet (Pennisetum glaucum L. R.Br.).

PubMed

Tharanya, Murugesan; Kholova, Jana; Sivasakthi, Kaliamoorthy; Seghal, Deepmala; Hash, Charles Tom; Raj, Basker; Srivastava, Rakesh Kumar; Baddam, Rekha; Thirunalasundari, Thiyagarajan; Yadav, Rattan; Vadez, Vincent

2018-04-21

Four genetic regions associated with water use traits, measured at different levels of plant organization, and with agronomic traits were identified within a previously reported region for terminal water deficit adaptation on linkage group 2. Close linkages between these traits showed the value of phenotyping both for agronomic and secondary traits to better understand plant productive processes. Water saving traits are critical for water stress adaptation of pearl millet, whereas maximizing water use is key to the absence of stress. This research aimed at demonstrating the close relationship between traits measured at different levels of plant organization, some putatively involved in water stress adaptation, and those responsible for agronomic performance. A fine-mapping population of pearl millet, segregating for a previously identified quantitative trait locus (QTL) for adaptation to terminal drought stress on LG02, was phenotyped for traits at different levels of plant organization in different experimental environments (pot culture, high-throughput phenotyping platform, lysimeters, and field). The linkages among traits across the experimental systems were analysed using principal component analysis and QTL co-localization approach. Four regions within the LG02-QTL were found and revealed substantial co-mapping of water use and agronomic traits. These regions, identified across experimental systems, provided genetic evidence of the tight linkages between traits phenotyped at a lower level of plant organization and agronomic traits assessed in the field, therefore deepening our understanding of complex traits and then benefiting both geneticists and breeders. In short: (1) under no/mild stress conditions, increasing biomass and tiller production increased water use and eventually yield; (2) under severe stress conditions, water savings at vegetative stage, from lower plant vigour and fewer tillers in that population, led to more water available during grain filling, expression of stay-green phenotypes, and higher yield.

From erosion to earthquakes: A geomorphic model for intraplate seismicity in post-orogenic settings

NASA Astrophysics Data System (ADS)

Gallen, S. F.; Thigpen, J. R.

2017-12-01

Intraplate seismicity does not conform to plate tectonics theory and its driving mechanisms remain uncertain, yet it is recognized as a relevant seismic hazard to populated regions, such as eastern North America. A variety of models, mostly geodynamic or tectonic in origin, have been proposed to explain this enigma, but conclusive supporting evidence remains elusive. In order to identify high hazard areas and derive predictive models, it is imperative to identify the underlying processes responsible for intraplate seismicity. Here we conduct an interdisciplinary study of the Eastern Tennessee Seismic Zone (ETSZ), the second most seismically active region east of the Rocky Mountains in the North American continent, to clarify the potential mechanisms driving intraplate seismicity in post-orogenic and passive margin settings. Previous studies document that the Upper Tennessee drainage basin, which lies directly above the ETSZ, is in a transient state of adjustment to 150 m of base level fall that was provoked by river capture in the Late Miocene. Using quantitative geomorphology, we demonstrate that base level fall enhanced erosion rates in a 75 km wide 400 km long corridor of highly erodible rocks in the late Paleozoic (Alleghanian orogen) fold-thrust belt. The total volume of rock preferentially removed above the ETSZ since 9 Ma is 3,600 ± 150 km3. Stress modeling indicates spatially focused erosion has of reduced clamping stresses on ancient basement normal faults beneath the Appalachian fold-thrust belt on the order of 3.5 MPa, with a time-averaged unclamping rate of 0.4 Pa yr-1. Under the assumption that the crust is critically stressed, we argue that the preferential erosion of less competent rock units reduced clamping stresses on relict faults such to induce seismic activity in the ambient stress field. This model for surface process-induced intraplate seismicity is generally transferable to other continental settings where complex geology and landscape dynamics conspire to spatially focus erosion and perturb the stress field in the mid-to-upper crust.

Chronic stress may facilitate the recruitment of habit- and addiction-related neurocircuitries through neuronal restructuring of the striatum

PubMed Central

Taylor, S.B.; Anglin, J.M.; Paode, P.R.; Riggert, A.G.; Olive, M.F.; Conrad, C.D.

2014-01-01

Chronic stress is an established risk factor in the development of addiction. Addiction is characterized by a progressive transition from casual drug use to habitual and compulsive drug use. The ability of chronic stress to facilitate the transition to addiction may be mediated by increased engagement of the neurocircuitries underlying habitual behavior and addiction. In the present study, striatal morphology was evaluated after two weeks of chronic variable stress in male Sprague-Dawley rats. Dendritic complexity of medium spiny neurons was visualized and quantified with Golgi staining in the dorsolateral and dorsomedial striatum, as well as in the nucleus accumbens core and shell. In separate cohorts, the effects of chronic stress on habitual behavior and the acute locomotor response to methamphetamine were also assessed. Chronic stress resulted in increased dendritic complexity in the dorsolateral striatum and nucleus accumbens core, regions implicated in habitual behavior and addiction, while decreased complexity was found in the nucleus accumbens shell, a region critical for the initial rewarding effects of drugs of abuse. Chronic stress did not affect dendritic complexity in the dorsomedial striatum. A parallel shift toward habitual learning strategies following chronic stress was also identified. There was an initial reduction in acute locomotor response to methamphetamine, but no lasting effect as a result of chronic stress exposure. These findings suggest that chronic stress may facilitate the recruitment of habit- and addiction-related neurocircuitries through neuronal restructuring in the striatum. PMID:25242641

Stress-free microbes lack vitality.

PubMed

Hallsworth, John E

2018-06-01

Stress is an inextricable aspect of life, and stress biology has been a field of intensive study over the last 200-300 years. In human psychology, we consider a stress-free condition to be one of relaxation or happiness, yet with respect to microbial cells we do not have a concept that describes being non-stressed. Stresses within, and stress tolerance of, microbial systems lie at the crux of critical global challenges, such as optimising soil- and plant-health and crop yields; reducing food spoilage; bioremediation of polluted environments; effective biological control and biofuel production; gaining insight into aging processes in humans; and understanding astrobiology. There is no consensus on how to measure cellular stress, or even how we define it. 'Stress' implies that physical forces act on the microbial system in such a way that impairs its ability to function. Ironically, however, a cell that exhibits optimal growth also has reduced energy generation, is less resilient to change, and can have poor competitive ability. Furthermore, rapid growth is associated with a high level of oxidative damage and compromised vitality of the system. Stresses induced by temperature, pH, water activity, chaotropicity, reactive oxygen species, dehydration-rehydration cycles, ionizing radiation, and changes in turgor or other mechanical forces are well-known. Our knowledge of cellular stress responses, such as signal-transduction pathways, compatible-solute metabolism, protein-stabilization proteins, and plasma-membrane adaptations, is also considerable. However, we have limited understanding of the complex and dynamic stresses that typically occur in microbial habitats or industrial systems, and how these impact the biophysics, cellular biology and evolutionary trajectories of microbes. There is also a paucity of information on why the cellular system ultimately fails under extremes of stress, and it is even debatable whether any microbe can ever be completely stress-free. However, cells that exhibit optimal rates of biotic activity are likely to exhibit low ecological fitness compared with those that are moderately stressed; in other words, stress can enhance microbial vitality, vigour and resilience. 'Stress' is sometimes applied mistakenly to describe the effects of toxic substances that have target site-specific modes-of-action (e.g. antibiotics) rather than and do not inhibit the cell via any type of stress-mediated mechanism. Whereas terms such as 'rapid-growth stress', 'nutrient stress' and 'biotic stress' span a range of logical categories, their modes-of-action do usually involve a biophysical component. Stress can impact all levels of biology (from biomacromolecules to ecosystems), is a potent driver for evolutionary processes and - it could be argued - is an inherent property of life itself. The published articles that follow include a number of unprecedented findings and were compiled for this special issue Biology of Fungal Systems under Stress. Collectively, they are testament to the breadth and importance of the stress-biology field. Copyright © 2018. Published by Elsevier Ltd.

Dynamic rupture simulations of the 2016 Mw7.8 Kaikōura earthquake: a cascading multi-fault event

NASA Astrophysics Data System (ADS)

Ulrich, T.; Gabriel, A. A.; Ampuero, J. P.; Xu, W.; Feng, G.

2017-12-01

The Mw7.8 Kaikōura earthquake struck the Northern part of New Zealand's South Island roughly one year ago. It ruptured multiple segments of the contractional North Canterbury fault zone and of the Marlborough fault system. Field observations combined with satellite data suggest a rupture path involving partly unmapped faults separated by large stepover distances larger than 5 km, the maximum distance usually considered by the latest seismic hazard assessment methods. This might imply distant rupture transfer mechanisms generally not considered in seismic hazard assessment. We present high-resolution 3D dynamic rupture simulations of the Kaikōura earthquake under physically self-consistent initial stress and strength conditions. Our simulations are based on recent finite-fault slip inversions that constrain fault system geometry and final slip distribution from remote sensing, surface rupture and geodetic data (Xu et al., 2017). We assume a uniform background stress field, without lateral fault stress or strength heterogeneity. We use the open-source software SeisSol (www.seissol.org) which is based on an arbitrary high-order accurate DERivative Discontinuous Galerkin method (ADER-DG). Our method can account for complex fault geometries, high resolution topography and bathymetry, 3D subsurface structure, off-fault plasticity and modern friction laws. It enables the simulation of seismic wave propagation with high-order accuracy in space and time in complex media. We show that a cascading rupture driven by dynamic triggering can break all fault segments that were involved in this earthquake without mechanically requiring an underlying thrust fault. Our prefered fault geometry connects most fault segments: it does not features stepover larger than 2 km. The best scenario matches the main macroscopic characteristics of the earthquake, including its apparently slow rupture propagation caused by zigzag cascading, the moment magnitude and the overall inferred slip distribution. We observe a high sensitivity of cascading dynamics on fault-step over distance and off-fault energy dissipation.

Cardiac-Activity Measures for Assessing Airport Ramp-Tower Controller's Workload

NASA Technical Reports Server (NTRS)

Hayashi, Miwa; Dulchinos, Victoria

2016-01-01

Heart rate (HR) and heart rate variability (HRV) potentially offer objective, continuous, and non-intrusive measures of human-operators mental workload. Such measurement capability is attractive for workload assessment in complex laboratory simulations or safety-critical field testing. The present study compares mean HR and HRV data with self-reported subjective workload ratings collected during a high-fidelity human-in-the-loop simulation of airport ramp traffic control operations, which involve complex cognitive and coordination tasks. Mean HR was found to be weakly sensitive to the workload ratings, while HRV was not sensitive or even contradictory to the assumptions. Until more knowledge on stress response mechanisms of the autonomic nervous system is obtained, it is recommended that these cardiac-activity measures be used with other workload assessment tools, such as subjective measures.

Cardiac-Activity Measures for Assessing Airport Ramp-Tower Controller's Workload

NASA Technical Reports Server (NTRS)

Hayashi, Miwa; Dulchinos, Victoria L.

2016-01-01

Heart rate (HR) and heart rate variability (HRV) potentially offer objective, continuous, and non-intrusive measures of human-operator's mental workload. Such measurement capability is attractive for workload assessment in complex laboratory simulations or safety-critical field testing. The present study compares mean HR and HRV data with self-reported subjective workload ratings collected during a high-fidelity human-in-the-loop simulation of airport ramp traffic control operations, which involve complex cognitive and coordination tasks. Mean HR was found to be weakly sensitive to the workload ratings, while HRV was not sensitive or even contradictory to the assumptions. Until more knowledge on stress response mechanisms of the autonomic nervous system is obtained, it is recommended that these cardiac-activity measures be used with other workload assessment tools, such as subjective measures.

An investigation into psychological stress and its determinants in Xinjiang desert oil workers

PubMed Central

Ning, Li; Guan, Suzhen; Liu, Jiwen

2018-01-01

Abstract The present study aims to investigate psychological stress and its determinants in Xinjiang field oil workers. Specifically, we aim to elucidate the mechanisms underlying psychological stress by comprehensively and quantitatively evaluating the processes involved in psychological stress, the factors which influence it, and their relationship. The participants were 1200 field oil workers in Xinjiang who had been in service for at least 1 year. A structural equation model based on data from the symptom checklist, social support research scale, personality questionnaire, occupational burnout questionnaire, and occupational stress questionnaire was constructed to investigate the social (environmental) factors that influence physiological stress and the interplay among these factors. The positive incidence of psychological stress in the field oil workers in Xinjiang was 12.54%. The structural equation model indicated that the main factors that influenced psychological stress in these workers included social support (0.077), occupational role (0.165), personal strain response (0.139), personality (0.189), and occupational burnout (0.380). Among these factors, occupational role, personality, and occupational burnout had a relatively strong predictive power for psychological stress reactions. The cortisol level in workers with positive psychological stress was significantly higher than that in workers with negative psychological stress. Occupational stress, personality, and occupational burnout exert an impact on psychological stress in field oil workers. Therefore, interventions to address these factors should be taken to reduce the incidence of psychological stress. PMID:29642166

Long-term strength of metals in complex stress state (a survey)

NASA Astrophysics Data System (ADS)

Lokoshchenko, A. M.

2012-05-01

An analytic survey of experimental data and theoretical approaches characterizing the long-term strength of metals in complex stress state is given. In Sections 2 and 3, the results of plane stress tests (with opposite and equal signs of the nonzero principal stresses, respectively) are analyzed. In Section 4, the results of inhomogeneous stress tests (thick-walled tubes under the action of internal pressures and tensile forces) are considered. All known experimental data (35 test series) are analyzed by a criterion approach. An equivalent stress σ e is introduced as a characteristic of the stress state. Attention is mainly paid to the dependence of σ e on the principal stresses. Statistical methods are used to obtain an expression for σ e, which can be used to study various types of the complex stress state. It is shown that for the long-term strength criterion one can use the power or power-fractional dependence of the time to rupture on the equivalent stress. The methods proposed to describe the test results give a good correspondence between the experimental and theoretical values of the time to rupture. In Section 5, the possibilities of complicating the expressions for σ e by using additional material constants are considered.

Stress anisotropy and velocity anisotropy in low porosity shale

NASA Astrophysics Data System (ADS)

Kuila, U.; Dewhurst, D. N.; Siggins, A. F.; Raven, M. D.

2011-04-01

Shales are known for often marked intrinsic anisotropy of many of their properties, including strength, permeability and velocity for example. In addition, it is well known that anisotropic stress fields can also have a significant impact on anisotropy of velocity, even in an isotropic medium. This paper sets out to investigate the ultrasonic velocity response of well-characterised low porosity shales from the Officer Basin in Western Australia to both isotropic and anisotropic stress fields and to evaluate the velocity response to the changing stress field. During consolidated undrained multi-stage triaxial tests on core plugs cut normal to bedding, V pv increases monotonically with increasing effective stress and V s1 behaves similarly although with some scatter. V ph and V sh remain constant initially but then decrease within each stage of the multi-stage test, although velocity from stage to stage at any given differential stress increases. This has the impact of decreasing both P-wave (ɛ) and S-wave anisotropy (γ) through application of differential stress within each loading stage. However, increasing the magnitude of an isotropic stress field has little effect on the velocity anisotropies. The intrinsic anisotropy of the shale remains reasonably high at the highest confining pressures. The results indicate the magnitude and orientation of the stress anisotropy with respect to the shale microfabric has a significant impact on the velocity response to changing stress fields.

Explosion-induced stress changes estimated from vibrating-wire stressmeter measurements near the Mighty Epic event, Nevada Test Site

USGS Publications Warehouse

Ellis, William L.; Kibler, J.D.

1983-01-01

Explosion-induced compressive stress increases near an underground nuclear explosion are believed to contribute significantly to the containment of high-pressure gases within the explosion-produced cavity. These induced compressive stresses are predicted by computer calculations, but have never been adequately confirmed by field measurements, owing primarily to the unique difficulties of obtaining such field data. Vibrating-wire stressmeter measurements made near the Mighty Epic nuclear detonation, however, qualitatively indicate that within 150 meters of the working point, permanent compressive stress increases of several megapascals were present 15 weeks after the event. Additionally, stress-change magnitudes interpreted from the stressmeter data between the 75- and 260-meter range from the working point compare favorably with calculational predictions of the stress changes believed to be present shortly after detonation of the event. The measurements and calculations differ, however, with regard to the pattern of stress change radial and transverse to the explosion source. For the range of the field measurements from the working point, computer models predict the largest compressive-stress increase to be radial to the explosion source, while the field data indicate the transverse component of. stress change to be the most compressive. The significance of time-dependent modification of the initial explosion-induced stress distribution is, however, uncertain with regard to the comparison of the field measurements and theoretical predictions.

The Influence of Obliquity on Europan Cycloid Formation

NASA Technical Reports Server (NTRS)

Hurford, T. a.; Sarid, A. R.; Greenberg, R.; Bills, B. G.

2009-01-01

Tectonic patterns on Europa are influenced by tidal stress. An important well-organized component is associated with the orbital eccentricity, which produces a diurnally varying stress as Jupiter's apparent position in Europa's sky oscillates in longitude. Cycloidal lineaments seem to have formed as cracks propagated in this diurnally varying stress field. Maps of theoretical cycloid patterns capture many of the characteristics of the observed distribution on Europa. However, a few details of the observed cycloids distribution have not reproduced by previous models. Recently, it has been shown that Europa has a finite forced obliquity, so Jupiter's apparent positon in Europa's sky will also oscillate in latitude. We explore this new type of diurnal effect on cycloid formation. We find that stress from obliquity may be the key to explaining several characteristics of observed cycloids such as the shape of equator-crossing cycloids and the shift in the crack patterns in the Argadnel Regio region. All of those improvements of the fit between observaiton and theory seem to require Jupiter crossing Europa's equatorial plane 45 deg. to 180 deg after perijove passage. Suggestive of complex orbital dynamics that lock the direction of Europe's pericenter with the direction of the ascending node at the time these cracks were formed.

Post-traumatic stress disorder.

PubMed

Yehuda, Rachel; Hoge, Charles W; McFarlane, Alexander C; Vermetten, Eric; Lanius, Ruth A; Nievergelt, Caroline M; Hobfoll, Stevan E; Koenen, Karestan C; Neylan, Thomas C; Hyman, Steven E

2015-10-08

Post-traumatic stress disorder (PTSD) occurs in 5-10% of the population and is twice as common in women as in men. Although trauma exposure is the precipitating event for PTSD to develop, biological and psychosocial risk factors are increasingly viewed as predictors of symptom onset, severity and chronicity. PTSD affects multiple biological systems, such as brain circuitry and neurochemistry, and cellular, immune, endocrine and metabolic function. Treatment approaches involve a combination of medications and psychotherapy, with psychotherapy overall showing greatest efficacy. Studies of PTSD pathophysiology initially focused on the psychophysiology and neurobiology of stress responses, and the acquisition and the extinction of fear memories. However, increasing emphasis is being placed on identifying factors that explain individual differences in responses to trauma and promotion of resilience, such as genetic and social factors, brain developmental processes, cumulative biological and psychological effects of early childhood and other stressful lifetime events. The field of PTSD is currently challenged by fluctuations in diagnostic criteria, which have implications for epidemiological, biological, genetic and treatment studies. However, the advent of new biological methodologies offers the possibility of large-scale approaches to heterogeneous and genetically complex brain disorders, and provides optimism that individualized approaches to diagnosis and treatment will be discovered.

Acquisition and deconvolution of seismic signals by different methods to perform direct ground-force measurements

NASA Astrophysics Data System (ADS)

Poletto, Flavio; Schleifer, Andrea; Zgauc, Franco; Meneghini, Fabio; Petronio, Lorenzo

2016-12-01

We present the results of a novel borehole-seismic experiment in which we used different types of onshore-transient-impulsive and non-impulsive-surface sources together with direct ground-force recordings. The ground-force signals were obtained by baseplate load cells located beneath the sources, and by buried soil-stress sensors installed in the very shallow-subsurface together with accelerometers. The aim was to characterize the source's emission by its complex impedance, function of the near-field vibrations and soil stress components, and above all to obtain appropriate deconvolution operators to remove the signature of the sources in the far-field seismic signals. The data analysis shows the differences in the reference measurements utilized to deconvolve the source signature. As downgoing waves, we process the signals of vertical seismic profiles (VSP) recorded in the far-field approximation by an array of permanent geophones cemented at shallow-medium depth outside the casing of an instrumented well. We obtain a significant improvement in the waveform of the radiated seismic-vibrator signals deconvolved by ground force, similar to that of the seismograms generated by the impulsive sources, and demonstrates that the results obtained by different sources present low values in their repeatability norm. The comparison evidences the potentiality of the direct ground-force measurement approach to effectively remove the far-field source signature in VSP onshore data, and to increase the performance of permanent acquisition installations for time-lapse application purposes.

Active tectonics on Deception Island (West-Antarctica): A new approach by using the fractal anisotropy of lineaments, fault slip measurements and the caldera collapse shape

USGS Publications Warehouse

Pérez-López, R.; Giner-Robles, J.L.; Martínez-Díaz, J.J.; Rodríguez-Pascua, M.A.; Bejar, M.; Paredes, C.; González-Casado, J.M.

2007-01-01

The tectonic field on Deception Island (South Shetlands, West Antarctica) is determined from structural and fractal analyses. Three different analyses are applied to the study of the strain and stress fields in the area: (1) field measurements of faults (strain analysis), (2) fractal geometry of the spatial distribution of lineaments and (3) the caldera shape (stress analyses). In this work, the identified strain field is extensional with the maximum horizontal shortening trending NE-SW and NW-SE. The fractal technique applied to the spatial distribution of lineaments indicates a stress field with SHMAX oriented NE-SW. The elliptical caldera of Deception Island, determined from field mapping, satellite imagery, vents and fissure eruptions, has an elongate shape and a stress field with SHMAX trending NE-SW.

Estimation of left ventricular blood flow parameters: clinical application of patient-specific CFD simulations from 4D echocardiography

NASA Astrophysics Data System (ADS)

Larsson, David; Spühler, Jeannette H.; Günyeli, Elif; Weinkauf, Tino; Hoffman, Johan; Colarieti-Tosti, Massimiliano; Winter, Reidar; Larsson, Matilda

2017-03-01

Echocardiography is the most commonly used image modality in cardiology, assessing several aspects of cardiac viability. The importance of cardiac hemodynamics and 4D blood flow motion has recently been highlighted, however such assessment is still difficult using routine echo-imaging. Instead, combining imaging with computational fluid dynamics (CFD)-simulations has proven valuable, but only a few models have been applied clinically. In the following, patient-specific CFD-simulations from transthoracic dobutamin stress echocardiography have been used to analyze the left ventricular 4D blood flow in three subjects: two with normal and one with reduced left ventricular function. At each stress level, 4D-images were acquired using a GE Vivid E9 (4VD, 1.7MHz/3.3MHz) and velocity fields simulated using a presented pathway involving endocardial segmentation, valve position identification, and solution of the incompressible Navier-Stokes equation. Flow components defined as direct flow, delayed ejection flow, retained inflow, and residual volume were calculated by particle tracing using 4th-order Runge-Kutta integration. Additionally, systolic and diastolic average velocity fields were generated. Results indicated no major changes in average velocity fields for any of the subjects. For the two subjects with normal left ventricular function, increased direct flow, decreased delayed ejection flow, constant retained inflow, and a considerable drop in residual volume was seen at increasing stress. Contrary, for the subject with reduced left ventricular function, the delayed ejection flow increased whilst the retained inflow decreased at increasing stress levels. This feasibility study represents one of the first clinical applications of an echo-based patient-specific CFD-model at elevated stress levels, and highlights the potential of using echo-based models to capture highly transient flow events, as well as the ability of using simulation tools to study clinically complex phenomena. With larger patient studies planned for the future, and with the possibility of adding more anatomical features into the model framework, the current work demonstrates the potential of patient-specific CFD-models as a tool for quantifying 4D blood flow in the heart.

The generalized fracture criteria based on the multi-parameter representation of the crack tip stress field

NASA Astrophysics Data System (ADS)

Stepanova, L. V.

2017-12-01

The paper is devoted to the multi-parameter asymptotic description of the stress field near the crack tip of a finite crack in an infinite isotropic elastic plane medium subject to 1) tensile stress; 2) in-plane shear; 3) mixed mode loading for a wide range of mode-mixity situations (Mode I and Mode II). The multi-parameter series expansion of stress tensor components containing higher-order terms is obtained. All the coefficients of the multiparameter series expansion of the stress field are given. The main focus is on the discussion of the influence of considering the higher-order terms of the Williams expansion. The analysis of the higher-order terms in the stress field is performed. It is shown that the larger the distance from the crack tip, the more terms it is necessary to keep in the asymptotic series expansion. Therefore, it can be concluded that several more higher-order terms of the Williams expansion should be used for the stress field description when the distance from the crack tip is not small enough. The crack propagation direction angle is calculated. Two fracture criteria, the maximum tangential stress criterion and the strain energy density criterion, are used. The multi-parameter form of the two commonly used fracture criteria is introduced and tested. Thirty and more terms of the Williams series expansion for the near-crack-tip stress field enable the angle to be calculated more precisely.

Stabilizing Group Treatment for Complex Posttraumatic Stress Disorder Related to Childhood Abuse Based on Psycho-Education and Cognitive Behavioral Therapy: A Pilot Study

ERIC Educational Resources Information Center

Dorrepaal, Ethy; Thomaes, Kathleen; Smit, Johannes H.; van Balkom, Anton J. L. M.; van Dyck, Richard; Veltman, Dick J.; Draijer, Nel

2010-01-01

Objective: This study tests a Stabilizing Group Treatment protocol, designed for the management of the long-term sequelae of child abuse, that is, Complex Posttraumatic Stress Disorder (Complex PTSD). Evidence-based treatment for this subgroup of PTSD patients is largely lacking. This stabilizing treatment aims at improving Complex PTSD using…

Stress field models from Maxwell stress functions: southern California

NASA Astrophysics Data System (ADS)

Bird, Peter

2017-08-01

The lithospheric stress field is formally divided into three components: a standard pressure which is a function of elevation (only), a topographic stress anomaly (3-D tensor field) and a tectonic stress anomaly (3-D tensor field). The boundary between topographic and tectonic stress anomalies is somewhat arbitrary, and here is based on the modeling tools available. The topographic stress anomaly is computed by numerical convolution of density anomalies with three tensor Green's functions provided by Boussinesq, Cerruti and Mindlin. By assuming either a seismically estimated or isostatic Moho depth, and by using Poisson ratio of either 0.25 or 0.5, I obtain four alternative topographic stress models. The tectonic stress field, which satisfies the homogeneous quasi-static momentum equation, is obtained from particular second derivatives of Maxwell vector potential fields which are weighted sums of basis functions representing constant tectonic stress components, linearly varying tectonic stress components and tectonic stress components that vary harmonically in one, two and three dimensions. Boundary conditions include zero traction due to tectonic stress anomaly at sea level, and zero traction due to the total stress anomaly on model boundaries at depths within the asthenosphere. The total stress anomaly is fit by least squares to both World Stress Map data and to a previous faulted-lithosphere, realistic-rheology dynamic model of the region computed with finite-element program Shells. No conflict is seen between the two target data sets, and the best-fitting model (using an isostatic Moho and Poisson ratio 0.5) gives minimum directional misfits relative to both targets. Constraints of computer memory, execution time and ill-conditioning of the linear system (which requires damping) limit harmonically varying tectonic stress to no more than six cycles along each axis of the model. The primary limitation on close fitting is that the Shells model predicts very sharp shallow stress maxima and discontinuous horizontal compression at the Moho, which the new model can only approximate. The new model also lacks the spatial resolution to portray the localized stress states that may occur near the central surfaces of weak faults; instead, the model portrays the regional or background stress field which provides boundary conditions for weak faults. Peak shear stresses in one registered model and one alternate model are 120 and 150 MPa, respectively, while peak vertically integrated shear stresses are 2.9 × 1012 and 4.1 × 1012 N m-1. Channeling of deviatoric stress along the strong Great Valley and the western slope of the Peninsular Ranges is evident. In the neotectonics of southern California, it appears that deviatoric stress and long-term strain rate have a negative correlation, because regions of low heat flow are strong and act as stress guides, while undergoing very little internal deformation. In contrast, active faults lie preferentially in areas with higher heat flow, and their low strength keeps deviatoric stresses locally modest.

Analyzing a suitable elastic geomechanical model for Vaca Muerta Formation

NASA Astrophysics Data System (ADS)

Sosa Massaro, Agustin; Espinoza, D. Nicolas; Frydman, Marcelo; Barredo, Silvia; Cuervo, Sergio

2017-11-01

Accurate geomechanical evaluation of oil and gas reservoir rocks is important to provide design parameters for drilling, completion and predict production rates. In particular, shale reservoir rocks are geologically complex and heterogeneous. Wells need to be hydraulically fractured for stimulation and, in complex tectonic environments, it is to consider that rock fabric and in situ stress, strongly influence fracture propagation geometry. This article presents a combined wellbore-laboratory characterization of the geomechanical properties of a well in El Trapial/Curamched Field, over the Vaca Muerta Formation, located in the Neuquén Basin in Argentina. The study shows the results of triaxial tests with acoustic measurements in rock plugs from outcrops and field cores, and corresponding dynamic to static correlations considering various elastic models. The models, with increasing complexity, include the Isotropic Elastic Model (IEM), the Anisotropic Elastic Model (AEM) and the Detailed Anisotropic Elastic Model (DAEM). Each model shows advantages over the others. An IEM offers a quick overview, being easy to run without much detailed data for heterogeneous and anisotropic rocks. The DAEM requires significant amounts of data, time and a multidisciplinary team to arrive to a detailed model. Finally, an AEM suits well to an anisotropic and realistic rock without the need of massive amounts of data.

Network analyses based on comprehensive molecular interaction maps reveal robust control structures in yeast stress response pathways

PubMed Central

Kawakami, Eiryo; Singh, Vivek K; Matsubara, Kazuko; Ishii, Takashi; Matsuoka, Yukiko; Hase, Takeshi; Kulkarni, Priya; Siddiqui, Kenaz; Kodilkar, Janhavi; Danve, Nitisha; Subramanian, Indhupriya; Katoh, Manami; Shimizu-Yoshida, Yuki; Ghosh, Samik; Jere, Abhay; Kitano, Hiroaki

2016-01-01

Cellular stress responses require exquisite coordination between intracellular signaling molecules to integrate multiple stimuli and actuate specific cellular behaviors. Deciphering the web of complex interactions underlying stress responses is a key challenge in understanding robust biological systems and has the potential to lead to the discovery of targeted therapeutics for diseases triggered by dysregulation of stress response pathways. We constructed large-scale molecular interaction maps of six major stress response pathways in Saccharomyces cerevisiae (baker’s or budding yeast). Biological findings from over 900 publications were converted into standardized graphical formats and integrated into a common framework. The maps are posted at http://www.yeast-maps.org/yeast-stress-response/ for browse and curation by the research community. On the basis of these maps, we undertook systematic analyses to unravel the underlying architecture of the networks. A series of network analyses revealed that yeast stress response pathways are organized in bow–tie structures, which have been proposed as universal sub-systems for robust biological regulation. Furthermore, we demonstrated a potential role for complexes in stabilizing the conserved core molecules of bow–tie structures. Specifically, complex-mediated reversible reactions, identified by network motif analyses, appeared to have an important role in buffering the concentration and activity of these core molecules. We propose complex-mediated reactions as a key mechanism mediating robust regulation of the yeast stress response. Thus, our comprehensive molecular interaction maps provide not only an integrated knowledge base, but also a platform for systematic network analyses to elucidate the underlying architecture in complex biological systems. PMID:28725465

Fast Physically Accurate Rendering of Multimodal Signatures of Distributed Fracture in Heterogeneous Materials.

PubMed

Visell, Yon

2015-04-01

This paper proposes a fast, physically accurate method for synthesizing multimodal, acoustic and haptic, signatures of distributed fracture in quasi-brittle heterogeneous materials, such as wood, granular media, or other fiber composites. Fracture processes in these materials are challenging to simulate with existing methods, due to the prevalence of large numbers of disordered, quasi-random spatial degrees of freedom, representing the complex physical state of a sample over the geometric volume of interest. Here, I develop an algorithm for simulating such processes, building on a class of statistical lattice models of fracture that have been widely investigated in the physics literature. This algorithm is enabled through a recently published mathematical construction based on the inverse transform method of random number sampling. It yields a purely time domain stochastic jump process representing stress fluctuations in the medium. The latter can be readily extended by a mean field approximation that captures the averaged constitutive (stress-strain) behavior of the material. Numerical simulations and interactive examples demonstrate the ability of these algorithms to generate physically plausible acoustic and haptic signatures of fracture in complex, natural materials interactively at audio sampling rates.

Geologic setting of the proposed West Flank Forge Site, California: Suitability for EGS research and development

USGS Publications Warehouse

Sabin, Andrew; Blake, Kelly; Lazaro, Mike; Blankenship, Douglas; Kennedy, Mack; McCullough, Jess; DeOreo, S.B.; Hickman, Stephen H.; Glen, Jonathan; Kaven, Joern; Williams, Colin F.; Phelps, Geoffrey; Faulds, James E.; Hinz, Nicholas H.; Calvin, Wendy M.; Siler, Drew; Robertson-Tait, Ann

2017-01-01

The proposed West Flank FORGE site is within the China Lake Naval Air Weapons Station (NAWS), China Lake, CA. The West Flank is west of the Coso geothermal field, an area of China Lake NAWS dominated by the Quaternary Coso volcanic field largely comprised of rhyolite domes and their volcaniclastic and epiclastic horizons. The largest dome flow complex, Sugarloaf Mountain, marks the northwestern margin of the geothermal field. The West Flank is situated due west of Sugarloaf. The geologic setting of the West Flank was determined from one deep well (83-11) drilled as a potential production hole in 2009. The bottom-hole temperature (BHT) of well 83-11 approaches 600 oF (315˚C), but flow tests demonstrate very low, non-commercial permeabilities. With the exception of the upper 600 feet of volcaniclastic alluvium, well 83-11 is completed in granitic basement. The West Flank possesses the primary attributes of a FORGE site: non-commercial permeability (<10-16m2), a 175˚ to 225˚C temperature range in crystalline rocks, and a location outside an existing geothermal fieldThe Coso Mountains host the Coso volcanic field and are within a right-releasing stepover between the dextral Airport Lake (ALF) and Little Lake fault zones (LLFZ) and the Wild Horse Mesa and Owens Valley faults. Two distinct fault populations have been identified at Coso: WNW-trending and antithetical, NE-trending strike-slip faults and N- to NNE-trending normal faults. These faults are both high permeability drilling targets at depth within the main (productive) geothermal field and they locally segment the field into distinct hydrothermal regimes. The West Flank may be segmented from the rest of the field by one such northerly trending fault. The overall minimum principal stress orientation in the main geothermal field varies from 103˚ to 108˚; however, the minimum horizontal principal stress in 83-11 is rotated to 081˚.

Coupling Network Computing Applications in Air-cooled Turbine Blades Optimization

NASA Astrophysics Data System (ADS)

Shi, Liang; Yan, Peigang; Xie, Ming; Han, Wanjin

2018-05-01

Through establishing control parameters from blade outside to inside, the parametric design of air-cooled turbine blade based on airfoil has been implemented. On the basis of fast updating structure features and generating solid model, a complex cooling system has been created. Different flow units are modeled into a complex network topology with parallel and serial connection. Applying one-dimensional flow theory, programs have been composed to get pipeline network physical quantities along flow path, including flow rate, pressure, temperature and other parameters. These inner units parameters set as inner boundary conditions for external flow field calculation program HIT-3D by interpolation, thus to achieve full field thermal coupling simulation. Referring the studies in literatures to verify the effectiveness of pipeline network program and coupling algorithm. After that, on the basis of a modified design, and with the help of iSIGHT-FD, an optimization platform had been established. Through MIGA mechanism, the target of enhancing cooling efficiency has been reached, and the thermal stress has been effectively reduced. Research work in this paper has significance for rapid deploying the cooling structure design.

Field measurements of the linear and nonlinear shear moduli of cemented alluvium using dynamically loaded surface footings

NASA Astrophysics Data System (ADS)

Park, Kwangsoo

In this dissertation, a research effort aimed at development and implementation of a direct field test method to evaluate the linear and nonlinear shear modulus of soil is presented. The field method utilizes a surface footing that is dynamically loaded horizontally. The test procedure involves applying static and dynamic loads to the surface footing and measuring the soil response beneath the loaded area using embedded geophones. A wide range in dynamic loads under a constant static load permits measurements of linear and nonlinear shear wave propagation from which shear moduli and associated shearing strains are evaluated. Shear wave velocities in the linear and nonlinear strain ranges are calculated from time delays in waveforms monitored by geophone pairs. Shear moduli are then obtained using the shear wave velocities and the mass density of a soil. Shear strains are determined using particle displacements calculated from particle velocities measured at the geophones by assuming a linear variation between geophone pairs. The field test method was validated by conducting an initial field experiment at sandy site in Austin, Texas. Then, field experiments were performed on cemented alluvium, a complex, hard-to-sample material. Three separate locations at Yucca Mountain, Nevada were tested. The tests successfully measured: (1) the effect of confining pressure on shear and compression moduli in the linear strain range and (2) the effect of strain on shear moduli at various states of stress in the field. The field measurements were first compared with empirical relationships for uncemented gravel. This comparison showed that the alluvium was clearly cemented. The field measurements were then compared to other independent measurements including laboratory resonant column tests and field seismic tests using the spectral-analysis-of-surface-waves method. The results from the field tests were generally in good agreement with the other independent test results, indicating that the proposed method has the ability to directly evaluate complex material like cemented alluvium in the field.

Global Transcriptional Analysis Reveals the Complex Relationship between Tea Quality, Leaf Senescence and the Responses to Cold-Drought Combined Stress in Camellia sinensis

PubMed Central

Zheng, Chao; Wang, Yu; Ding, Zhaotang; Zhao, Lei

2016-01-01

In field conditions, especially in arid and semi-arid areas, tea plants are often simultaneously exposed to various abiotic stresses such as cold and drought, which have profound effects on leaf senescence process and tea quality. However, most studies of gene expression in stress responses focus on a single inciting agent, and the confounding effect of multiple stresses on crop quality and leaf senescence remain unearthed. Here, global transcriptome profiles of tea leaves under separately cold and drought stress were compared with their combination using RNA-Seq technology. This revealed that tea plants shared a large overlap in unigenes displayed “similar” (26%) expression pattern and avoid antagonistic responses (lowest level of “prioritized” mode: 0%) to exhibit very congruent responses to co-occurring cold and drought stress; 31.5% differential expressed genes and 38% of the transcriptome changes in response to combined stresses were unpredictable from cold or drought single-case studies. We also identified 319 candidate genes for enhancing plant resistance to combined stress. We then investigated the combined effect of cold and drought on tea quality and leaf senescence. Our results showed that drought-induced leaf senescence were severely delayed by (i) modulation of a number of senescence-associated genes and cold responsive genes, (ii) enhancement of antioxidant capacity, (iii) attenuation of lipid degradation, (iv) maintenance of cell wall and photosynthetic system, (v) alteration of senescence-induced sugar effect/sensitivity, as well as (vi) regulation of secondary metabolism pathways that significantly influence the quality of tea during combined stress. Therefore, care should be taken when utilizing a set of stresses to try and maximize leaf longevity and tea quality. PMID:28018394

Effects of berberine on a rat model of chronic stress and depression via gastrointestinal tract pathology and gastrointestinal flora profile assays.

PubMed

Zhu, Xiaohui; Sun, Yangdong; Zhang, Chenggang; Liu, Haifeng

2017-05-01

Chronic stress and depression are challenging conditions to treat, owing to their complexity and lack of clinically available and effective therapeutic agents. The aim of the present study was to investigate the mechanism by which berberine acts, by examining alterations to gastrointestinal tract histopathology and flora profile in a rat model, following the induction of stress. Research associating gastrointestinal flora and depression has increased, thus, the present study hypothesized that stress induces depression and changes in the gastrointestinal system. The chronic mild stress rat model was previously established based on a set of 10 chronic unpredictable stress methods. In the present study, the measurements of body weight, behavior, gastrointestinal tract histopathology and gastrointestinal flora profile were collected in order to elucidate understanding of chronic stress and depression in this region. In the present study, induced stress and the resulting depression was demonstrated to significantly decrease the body weight and sucrose preference of rats, as well as significantly increasing traverse time, vertical movement time, grooming time and motionless time in an open‑field test. Following modeling and subsequent treatment with low or high doses of berberine, the measurements were significantly different when compared with unstressed rats. Berberine appears to reverse the physical damage brought about by stress within the gastric mucosa and intestinal microvilli of the stomach, ileum, cecum and colon. Using enterobacterial repetitive intergenic consensus sequence‑based polymerase chain reaction analysis, several distinctive bands disappeared following modeling; however, novel distinctive bands appeared in response to the graded berberine treatment. In conclusion, the present study identified that high concentrations of berberine markedly protects rats from various symptoms of chronic stress and depression, with the potential of facilitating treatment within clinical practice.

Transcriptomic and metabolomic analysis of Yukon Thellungiella plants grown in cabinets and their natural habitat show phenotypic plasticity

PubMed Central

2012-01-01

Background Thellungiella salsuginea is an important model plant due to its natural tolerance to abiotic stresses including salt, cold, and water deficits. Microarray and metabolite profiling have shown that Thellungiella undergoes stress-responsive changes in transcript and organic solute abundance when grown under controlled environmental conditions. However, few reports assess the capacity of plants to display stress-responsive traits in natural habitats where concurrent stresses are the norm. Results To determine whether stress-responsive changes observed in cabinet-grown plants are recapitulated in the field, we analyzed leaf transcript and metabolic profiles of Thellungiella growing in its native Yukon habitat during two years of contrasting meteorological conditions. We found 673 genes showing differential expression between field and unstressed, chamber-grown plants. There were comparatively few overlaps between genes expressed under field and cabinet treatment-specific conditions. Only 20 of 99 drought-responsive genes were expressed both in the field during a year of low precipitation and in plants subjected to drought treatments in cabinets. There was also a general pattern of lower abundance among metabolites found in field plants relative to control or stress-treated plants in growth cabinets. Nutrient availability may explain some of the observed differences. For example, proline accumulated to high levels in cold and salt-stressed cabinet-grown plants but proline content was, by comparison, negligible in plants at a saline Yukon field site. We show that proline accumulated in a stress-responsive manner in Thellungiella plants salinized in growth cabinets and in salt-stressed seedlings when nitrogen was provided at 1.0 mM. In seedlings grown on 0.1 mM nitrogen medium, the proline content was low while carbohydrates increased. The relatively higher content of sugar-like compounds in field plants and seedlings on low nitrogen media suggests that Thellungiella shows metabolic plasticity in response to environmental stress and that resource availability can influence the expression of stress tolerance traits under field conditions. Conclusion Comparisons between Thellungiella plants responding to stress in cabinets and in their natural habitats showed differences but also overlap between transcript and metabolite profiles. The traits in common offer potential targets for improving crops that must respond appropriately to multiple, concurrent stresses. PMID:23025749

HIRA, a Conserved Histone Chaperone, Plays an Essential Role in Low-dose Stress Response via Transcriptional Stimulation in Fission Yeast*

PubMed Central

Chujo, Moeko; Tarumoto, Yusuke; Miyatake, Koichi; Nishida, Eisuke; Ishikawa, Fuyuki

2012-01-01

Cells that have been pre-exposed to mild stress (priming stress) acquire transient resistance to subsequent severe stress even under different combinations of stresses. This phenomenon is called cross-tolerance. Although it has been reported that cross-tolerance occurs in many organisms, the molecular basis is not clear yet. Here, we identified slm9+ as a responsible gene for the cross-tolerance in the fission yeast Schizosaccharomyces pombe. Slm9 is a homolog of mammalian HIRA histone chaperone. HIRA forms a conserved complex and gene disruption of other HIRA complex components, Hip1, Hip3, and Hip4, also yielded a cross-tolerance-defective phenotype, indicating that the fission yeast HIRA is involved in the cross-tolerance as a complex. We also revealed that Slm9 was recruited to the stress-responsive gene loci upon stress treatment in an Atf1-dependent manner. The expression of stress-responsive genes under stress conditions was compromised in HIRA disruptants. Consistent with this, Pol II recruitment and nucleosome eviction at these gene loci were impaired in slm9Δ cells. Furthermore, we found that the priming stress enhanced the expression of stress-responsive genes in wild-type cells that were exposed to the severe stress. These observations suggest that HIRA functions in stress response through transcriptional regulation. PMID:22589550

Dynamic equilibrium behaviour observed on two contrasting tidal flats from daily monitoring of bed-level changes

NASA Astrophysics Data System (ADS)

Hu, Zhan; van der Wal, Daphne; Cai, Huayang; van Belzen, Jim; Bouma, Tjeerd J.

2018-06-01

Dynamic equilibrium theory (DET) has been applied to tidal flats to systematically explain intertidal morphological responses to various distributions of bed shear stress (BSS). However, it is difficult to verify this theory with field observations because of the discrepancy between the idealized conceptions of theory and the complex reality of intertidal dynamics. The core relation between intertidal morphodynamics and BSS distribution can be easily masked by noise in complex datasets, leading to conclusions of insufficient field evidence to support DET. In the current study, hydrodynamic and morphodynamic data were monitored daily for one year on two tidal flats with contrasting wave exposures. BSS distribution was obtained by validated numerical models. Tidal flat dynamic equilibrium behaviour and BSS were linked via Empirical Orthogonal Function (EOF) analysis. We show that the principal morphodynamic modes corresponded well with the respective modes of BSS found at both sites. Tide-induced BSS was the dominant force at both sites, regardless of the level of wave exposure. The overall erosional and steepening trend found at the two flats can be attributed to the prevailing action of tidal forcing and reduced sediment supply. Hence, EOF analysis confirmed that tidal flat morphodynamics are consistent with DET, providing both field and model evidence to support this theory.

A Cartesian-based embedded geometry technique with adaptive high-order finite differences for compressible flow around complex geometries

NASA Astrophysics Data System (ADS)

Uddin, H.; Kramer, R. M. J.; Pantano, C.

2014-04-01

An immersed boundary methodology to solve the compressible Navier-Stokes equations around complex geometries in Cartesian fluid dynamics solvers is described. The objective of the new approach is to enable smooth reconstruction of pressure and viscous stresses around the embedded objects without spurious numerical artifacts. A standard level set represents the boundary of the object and defines a fictitious domain into which the flow fields are smoothly extended. Boundary conditions on the surface are enforced by an approach inspired by analytic continuation. Each fluid field is extended independently, constrained only by the boundary condition associated with that field. Unlike most existing methods, no jump conditions or explicit derivation of them from the boundary conditions are required in this approach. Numerical stiffness that arises when the fluid-solid interface is close to grid points of the mesh is addressed by preconditioning. In addition, the embedded geometry technique is coupled with a stable high-order adaptive discretization that is enabled around the object boundary to enhance resolution. The stencils used to transition the order of accuracy of the discretization are derived using the summation-by-parts technique that ensures stability. Applications to shock reflections, shock-ramp interactions, and supersonic and low-Mach number flows over two- and three-dimensional geometries are presented.

Response of Velocity Anisotropy of Shale Under Isotropic and Anisotropic Stress Fields

NASA Astrophysics Data System (ADS)

Li, Xiaying; Lei, Xinglin; Li, Qi

2018-03-01

We investigated the responses of P-wave velocity and associated anisotropy in terms of Thomsen's parameters to isotropic and anisotropic stress fields on Longmaxi shales cored along different directions. An array of piezoelectric ceramic transducers allows us to measure P-wave velocities along numerous different propagation directions. Anisotropic parameters, including the P-wave velocity α along a symmetry axis, Thomsen's parameters ɛ and δ, and the orientation of the symmetry axis, could then be extracted by fitting Thomsen's weak anisotropy model to the experimental data. The results indicate that Longmaxi shale displays weakly intrinsic velocity anisotropy with Thomsen's parameters ɛ and δ being approximately 0.05 and 0.15, respectively. The isotropic stress field has only a slight effect on velocity and associated anisotropy in terms of Thomsen's parameters. In contrast, both the magnitude and orientation of the anisotropic stress field with respect to the shale fabric are important in controlling the evolution of velocity and associated anisotropy in a changing stress field. For shale with bedding-parallel loading, velocity anisotropy is enhanced because velocities with smaller angles relative to the maximum stress increase significantly during the entire loading process, whereas those with larger angles increase slightly before the yield stress and afterwards decrease with the increasing differential stress. For shale with bedding-normal loading, anisotropy reversal is observed, and the anisotropy is progressively modified by the applied differential stress. Before reaching the yield stress, velocities with smaller angles relative to the maximum stress increase more significantly and even exceed the level of those with larger angles. After reaching the yield stress, velocities with larger angles decrease more significantly. Microstructural features such as the closure and generation of microcracks can explain the modification of the velocity anisotropy due to the applied stress anisotropy.

Machine learning reveals cyclic changes in seismic source spectra in Geysers geothermal field.

PubMed

Holtzman, Benjamin K; Paté, Arthur; Paisley, John; Waldhauser, Felix; Repetto, Douglas

2018-05-01

The earthquake rupture process comprises complex interactions of stress, fracture, and frictional properties. New machine learning methods demonstrate great potential to reveal patterns in time-dependent spectral properties of seismic signals and enable identification of changes in faulting processes. Clustering of 46,000 earthquakes of 0.3 < M L < 1.5 from the Geysers geothermal field (CA) yields groupings that have no reservoir-scale spatial patterns but clear temporal patterns. Events with similar spectral properties repeat on annual cycles within each cluster and track changes in the water injection rates into the Geysers reservoir, indicating that changes in acoustic properties and faulting processes accompany changes in thermomechanical state. The methods open new means to identify and characterize subtle changes in seismic source properties, with applications to tectonic and geothermal seismicity.

Electroporating Fields Target Oxidatively Damaged Areas in the Cell Membrane

PubMed Central

Vernier, P. Thomas; Levine, Zachary A.; Wu, Yu-Hsuan; Joubert, Vanessa; Ziegler, Matthew J.; Mir, Lluis M.; Tieleman, D. Peter

2009-01-01

Reversible electropermeabilization (electroporation) is widely used to facilitate the introduction of genetic material and pharmaceutical agents into living cells. Although considerable knowledge has been gained from the study of real and simulated model membranes in electric fields, efforts to optimize electroporation protocols are limited by a lack of detailed understanding of the molecular basis for the electropermeabilization of the complex biomolecular assembly that forms the plasma membrane. We show here, with results from both molecular dynamics simulations and experiments with living cells, that the oxidation of membrane components enhances the susceptibility of the membrane to electropermeabilization. Manipulation of the level of oxidative stress in cell suspensions and in tissues may lead to more efficient permeabilization procedures in the laboratory and in clinical applications such as electrochemotherapy and electrotransfection-mediated gene therapy. PMID:19956595

Mapping TES Temperature Sensitivity and Current Sensitivity as a Function of Temperature, Current, and Magnetic Field with IV Curve and Complex Admittance Measurements

NASA Astrophysics Data System (ADS)

Zhou, Y.; Ambarish, C. V.; Gruenke, R.; Jaeckel, F. T.; Kripps, K. L.; McCammon, D.; Morgan, K. M.; Wulf, D.; Zhang, S.; Adams, J. S.; Bandler, S. R.; Chervenak, J. A.; Datesman, A. M.; Eckart, M. E.; Ewin, A. J.; Finkbeiner, F. M.; Kelley, R. L.; Kilbourne, C. A.; Miniussi, A. R.; Porter, F. S.; Sadleir, J. E.; Sakai, K.; Smith, S. J.; Wakeham, N. A.; Wassell, E. J.; Yoon, W.

2018-05-01

We have specialized astronomical applications for X-ray microcalorimeters with superconducting transition edge sensors (TESs) that require exceptionally good TES performance, but which operate in the small-signal regime. We have therefore begun a program to carefully characterize the entire transition surface of TESs with and without the usual zebra stripes to see if there are reproducible local "sweet spots" where the performance is much better than average. These measurements require precise knowledge of the circuit parameters. Here, we show how the Shapiro effect can be used to precisely calibrate the value of the shunt resistor. We are also investigating the effects of stress and external magnetic fields to better understand reproducibility problems.

Hydraulic Fracture Extending into Network in Shale: Reviewing Influence Factors and Their Mechanism

PubMed Central

Ren, Lan; Zhao, Jinzhou; Hu, Yongquan

2014-01-01

Hydraulic fracture in shale reservoir presents complex network propagation, which has essential difference with traditional plane biwing fracture at forming mechanism. Based on the research results of experiments, field fracturing practice, theory analysis, and numerical simulation, the influence factors and their mechanism of hydraulic fracture extending into network in shale have been systematically analyzed and discussed. Research results show that the fracture propagation in shale reservoir is influenced by the geological and the engineering factors, which includes rock mineral composition, rock mechanical properties, horizontal stress field, natural fractures, treating net pressure, fracturing fluid viscosity, and fracturing scale. This study has important theoretical value and practical significance to understand fracture network propagation mechanism in shale reservoir and contributes to improving the science and efficiency of shale reservoir fracturing design. PMID:25032240

Endoplasmic reticulum stress-responsive transcription factor ATF6α directs recruitment of the Mediator of RNA polymerase II transcription and multiple histone acetyltransferase complexes.

PubMed

Sela, Dotan; Chen, Lu; Martin-Brown, Skylar; Washburn, Michael P; Florens, Laurence; Conaway, Joan Weliky; Conaway, Ronald C

2012-06-29

The basic leucine zipper transcription factor ATF6α functions as a master regulator of endoplasmic reticulum (ER) stress response genes. Previous studies have established that, in response to ER stress, ATF6α translocates to the nucleus and activates transcription of ER stress response genes upon binding sequence specifically to ER stress response enhancer elements in their promoters. In this study, we investigate the biochemical mechanism by which ATF6α activates transcription. By exploiting a combination of biochemical and multidimensional protein identification technology-based mass spectrometry approaches, we have obtained evidence that ATF6α functions at least in part by recruiting to the ER stress response enhancer elements of ER stress response genes a collection of RNA polymerase II coregulatory complexes, including the Mediator and multiple histone acetyltransferase complexes, among which are the Spt-Ada-Gcn5 acetyltransferase (SAGA) and Ada-Two-A-containing (ATAC) complexes. Our findings shed new light on the mechanism of action of ATF6α, and they outline a straightforward strategy for applying multidimensional protein identification technology mass spectrometry to determine which RNA polymerase II transcription factors and coregulators are recruited to promoters and other regulatory elements to control transcription.

A transitional volume beneath the Sannio-Irpinia border region (southern Apennines): Different tectonic styles at different depths

NASA Astrophysics Data System (ADS)

De Matteo, Ada; Massa, Bruno; Milano, Girolamo; D'Auria, Luca

2018-01-01

In this paper we investigate the border between the Sannio and Irpinia seismogenic regions, a sector of the southern Apennine chain considered among the most active seismic areas of the Italian peninsula, to shed further light on its complex seismotectonic setting. We integrated recent seismicity with literature data. A detailed analysis of the seismicity that occurred in the 2013-2016 time interval was performed. The events were relocated, after manual re-picking, using different approaches. To retrieve information about the stress field active in the area, inversion of Fault Plane Solutions was also carried out. Hypocentral distribution of the relocated events (ML ≤ 3.5), whose depth is included between 5 and 25 km with the deepest ones located in the NW sector of the study area, shows a different pattern between the northern sector and the southern one. The computed Fault Plane Solutions can be grouped in three depth ranges: < 12 km, dominated by normal dip-slip kinematics; 12-18 km, characterized by normal dip-slip and strike-slip kinematics; > 18 km, dominated by strike-slip kinematics. Stress field inversion across the whole area shows that we are dealing with an heterogeneous set of data, apparently governed by distinct stress fields. We built an upper crustal model profile through integration of geological data, well logs and seismic tomographic profiles. Our results suggest the co-existence of different tectonic styles at distinct crustal depths: the upper crust seems to be affected mostly by normal faulting, whereas strike-slip faulting prevails in the intermediate and lower crust. We infer about the existence of a transitional volume, located between 12 and 18 km depth, between the Sannio and Irpinia regions, acting as a vertical transfer zone.

Electrohydrodynamics of a viscous drop with inertia.

PubMed

Nganguia, H; Young, Y-N; Layton, A T; Lai, M-C; Hu, W-F

2016-05-01

Most of the existing numerical and theoretical investigations on the electrohydrodynamics of a viscous drop have focused on the creeping Stokes flow regime, where nonlinear inertia effects are neglected. In this work we study the inertia effects on the electrodeformation of a viscous drop under a DC electric field using a novel second-order immersed interface method. The inertia effects are quantified by the Ohnesorge number Oh, and the electric field is characterized by an electric capillary number Ca_{E}. Below the critical Ca_{E}, small to moderate electric field strength gives rise to steady equilibrium drop shapes. We found that, at a fixed Ca_{E}, inertia effects induce larger deformation for an oblate drop than a prolate drop, consistent with previous results in the literature. Moreover, our simulations results indicate that inertia effects on the equilibrium drop deformation are dictated by the direction of normal electric stress on the drop interface: Larger drop deformation is found when the normal electric stress points outward, and smaller drop deformation is found otherwise. To our knowledge, such inertia effects on the equilibrium drop deformation has not been reported in the literature. Above the critical Ca_{E}, no steady equilibrium drop deformation can be found, and often the drop breaks up into a number of daughter droplets. In particular, our Navier-Stokes simulations show that, for the parameters we use, (1) daughter droplets are larger in the presence of inertia, (2) the drop deformation evolves more rapidly compared to creeping flow, and (3) complex distribution of electric stresses for drops with inertia effects. Our results suggest that normal electric pressure may be a useful tool in predicting drop pinch-off in oblate deformations.

Analyses of Deformation and Stress of Oil-free Scroll Compressor Scroll

NASA Astrophysics Data System (ADS)

Peng, Bin; Li, Yaohong; Zhao, Shenxian

2017-12-01

The solid model of orbiting and fixed scroll is created by the Solidworks The deformation and stress of scrolls under gas force, temperature field, inertia force and the coupling field are analyzed using the Ansys software. The deformation for different thickness and height scroll tooth is investigated. The laws of deformation and stress for scrolls are gotten. The research results indicate that the stress and deformation of orbiting scroll are mainly affected by the temperature field. The maximum deformation occurs in the tooth head of scroll wrap because of the largest gas forces and the highest temperature in the tooth head of scroll wrap. The maximum stress is located in the end of the tooth, and the maximum stress of the coupling field is not the sum of loads. The scroll tooth is higher, and the deformation is bigger. The scroll tooth is thicker, and the deformation is smaller.

Chronic stress may facilitate the recruitment of habit- and addiction-related neurocircuitries through neuronal restructuring of the striatum.

PubMed

Taylor, S B; Anglin, J M; Paode, P R; Riggert, A G; Olive, M F; Conrad, C D

2014-11-07

Chronic stress is an established risk factor in the development of addiction. Addiction is characterized by a progressive transition from casual drug use to habitual and compulsive drug use. The ability of chronic stress to facilitate the transition to addiction may be mediated by increased engagement of the neurocircuitries underlying habitual behavior and addiction. In the present study, striatal morphology was evaluated after 2 weeks of chronic variable stress in male Sprague-Dawley rats. Dendritic complexity of medium spiny neurons was visualized and quantified with Golgi staining in the dorsolateral and dorsomedial striatum, as well as in the nucleus accumbens core and shell. In separate cohorts, the effects of chronic stress on habitual behavior and the acute locomotor response to methamphetamine were also assessed. Chronic stress resulted in increased dendritic complexity in the dorsolateral striatum and nucleus accumbens core, regions implicated in habitual behavior and addiction, while decreased complexity was found in the nucleus accumbens shell, a region critical for the initial rewarding effects of drugs of abuse. Chronic stress did not affect dendritic complexity in the dorsomedial striatum. A parallel shift toward habitual learning strategies following chronic stress was also identified. There was an initial reduction in acute locomotor response to methamphetamine, but no lasting effect as a result of chronic stress exposure. These findings suggest that chronic stress may facilitate the recruitment of habit- and addiction-related neurocircuitries through neuronal restructuring in the striatum. Copyright © 2014 IBRO. Published by Elsevier Ltd. All rights reserved.

The stress system generated by an electromagnetic field in a suspension of drops

NASA Technical Reports Server (NTRS)

Erdogan, M. E.

1982-01-01

The stress generated in a suspension of drops in the presence of a uniform electric field and a pure straining motion, taking into account that the magnetohydrodynamic effects are dominant was calculated. It was found that the stress generated in the suspension depended on the direction of the applied electric field, the dielectric constants, the vicosity coefficients, the conductivities, and the permeabilities of fluids inside and outside the drops. The expression of the particle stress shows that for fluids which are good conductors and poor dielectrics, especially for larger drops, magnetohydrodynamic effects end to reduce the dependence on the direction of the applied electric field.

Fingerprinting stress: stylolite and calcite twinning paleopiezometry reveal the complexity of stress distribution during the growth of the Monte Nero anticline (Apennines, Italy).

NASA Astrophysics Data System (ADS)

Beaudoin, Nicolas; Koehn, Daniel; Lacombe, Olivier; Lecouty, Alexandre; Billi, Andrea; Aharonov, Einat; Parlangeau, Camille

2016-04-01

This contribution presents for the first time how quantitative stress estimates can be derived by combining calcite twinning and stylolite roughness stress fingerprinting techniques in a structure part of a complex fold and thrust belts. We report a high-resolution deformation and stress history that was experienced by Meso-Cenozoic limestone strata in the overturned Monte Nero Anticline during its late Miocene-Pliocene growth in the Umbria-Marche Arcuate Ridge (northern Apennines, Italy). New methodological development enables an easier use for the inversion technique of sedimentary and tectonic stylolite roughness. A stylolite-fracture network developed during layer-parallel shortening (LPS), as well as syn- and post-folding. Stress fingerprinting shows how stress builds up in the sedimentary strata during LPS with variations of differential stress before folding around a value of 50 MPa. The stress regime oscillated between strike-slip and compressional during LPS and became transiently extensional in limbs of developing fold due to a coeval increase of vertical stress related to local burial and decrease of maximum horizontal stress related to hinge development, before ultimately becoming strike-slip again during late stage fold tightening. Our case study shows that stress fingerprinting is possible and that this novel method can be used to unravel complex temporal relationships that relate to local variations within evolving regional orogenic stresses. Beyond regional implication, this study validates our approach as a new exciting toolbox to high-resolution stress fingerprinting in basins and orogens.

Imaging the complexity of an active normal fault system: The 1997 Colfiorito (central Italy) case study

USGS Publications Warehouse

Chiaraluce, L.; Ellsworth, W.L.; Chiarabba, C.; Cocco, M.

2003-01-01

Six moderate magnitude earthquakes (5 < Mw < 6) ruptured normal fault segments of the southern sector of the North Apennine belt (central Italy) in the 1997 Colfiorito earthquake sequence. We study the progressive activation of adjacent and nearby parallel faults of this complex normal fault system using ???1650 earthquake locations obtained by applying a double-difference location method, using travel time picks and waveform cross-correlation measurements. The lateral extent of the fault segments range from 5 to 10 km and make up a broad, ???45 km long, NW trending fault system. The geometry of each segment is quite simple and consists of planar faults gently dipping toward SW with an average dip of 40??-45??. The fault planes are not listric but maintain a constant dip through the entire seismogenic volume, down to 8 km depth. We observe the activation of faults on the hanging wall and the absence of seismicity in the footwall of the structure. The observed fault segmentation appears to be due to the lateral heterogeneity of the upper crust: preexisting thrusts inherited from Neogene's compressional tectonic intersect the active normal faults and control their maximum length. The stress tensor obtained by inverting the six main shock focal mechanisms of the sequence is in agreement with the tectonic stress active in the inner chain of the Apennine, revealing a clear NE trending extension direction. Aftershock focal mechanisms show a consistent extensional kinematics, 70% of which are mechanically consistent with the main shock stress field.

Asymmetric three-dimensional topography over mantle plumes.

PubMed

Burov, Evgueni; Gerya, Taras

2014-09-04

The role of mantle-lithosphere interactions in shaping surface topography has long been debated. In general, it is supposed that mantle plumes and vertical mantle flows result in axisymmetric, long-wavelength topography, which strongly differs from the generally asymmetric short-wavelength topography created by intraplate tectonic forces. However, identification of mantle-induced topography is difficult, especially in the continents. It can be argued therefore that complex brittle-ductile rheology and stratification of the continental lithosphere result in short-wavelength modulation and localization of deformation induced by mantle flow. This deformation should also be affected by far-field stresses and, hence, interplay with the 'tectonic' topography (for example, in the 'active/passive' rifting scenario). Testing these ideas requires fully coupled three-dimensional numerical modelling of mantle-lithosphere interactions, which so far has not been possible owing to the conceptual and technical limitations of earlier approaches. Here we present new, ultra-high-resolution, three-dimensional numerical experiments on topography over mantle plumes, incorporating a weakly pre-stressed (ultra-slow spreading), rheologically realistic lithosphere. The results show complex surface evolution, which is very different from the smooth, radially symmetric patterns usually assumed as the canonical surface signature of mantle upwellings. In particular, the topography exhibits strongly asymmetric, small-scale, three-dimensional features, which include narrow and wide rifts, flexural flank uplifts and fault structures. This suggests a dominant role for continental rheological structure and intra-plate stresses in controlling dynamic topography, mantle-lithosphere interactions, and continental break-up processes above mantle plumes.

Telomeres and endocrine dysfunction of the adrenal and GH/IGF-1 axes.

PubMed

Aulinas, Anna; Ramírez, María José; Barahona, María José; Mato, Eugènia; Bell, Olga; Surrallés, Jordi; Webb, Susan M

2013-12-01

Telomeres, located at the end of linear chromosomes, are essential to maintain genomic stability. Telomere biology has recently emerged as an important player in the fields of ageing and disease. To maintain telomere length (TL) and reduce its degradation after mitosis, the telomerase enzyme complex is produced. Genetic, epigenetic, hormonal and environmental factors can regulate telomerase function. These include stress hormones such as cortisol and growth factors. The hypothalamic-pituitary-adrenal (HPA) axis has been evaluated in psychiatric diseases where hypercortisolism and oxidative stress are often present. Some researches have linked TL shortening to increases in stress-related cortisol, but others have not. The effects of cortisol on the telomere system are complex and may depend on the intensity and duration of exposure. On the other hand, low levels of IGF-1 are associated with inflammation and ageing-related diseases (ischaemic heart disease, congestive heart failure). Both IGF-1 and TL diminish with age and are positively and strongly correlated with each other. It is not clear whether this positive correlation reflects a single association or a cause-effect relationship. Further research will ideally investigate longitudinal changes in telomeres and both these hormonal axes. To our knowledge, TL dysfunction has not been described in either endogenous hypercortisolism (Cushing's syndrome) or acromegaly where excessive amounts of GH and consequently IGF-1 are produced. This review focuses on the possible relationships between telomere dysfunction and the hypothalamic-pituitary-adrenal (HPA) axis and GH-IGF-1 system. © 2013 John Wiley & Sons Ltd.

Dynamics of intrinsic axial flows in unsheared, uniform magnetic fields

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

Li, J. C.; Diamond, P. H.; Xu, X. Q.

2016-05-15

A simple model for the generation and amplification of intrinsic axial flow in a linear device, controlled shear decorrelation experiment, is proposed. This model proposes and builds upon a novel dynamical symmetry breaking mechanism, using a simple theory of drift wave turbulence in the presence of axial flow shear. This mechanism does not require complex magnetic field structure, such as shear, and thus is also applicable to intrinsic rotation generation in tokamaks at weak or zero magnetic shear, as well as to linear devices. This mechanism is essentially the self-amplification of the mean axial flow profile, i.e., a modulational instability.more » Hence, the flow development is a form of negative viscosity phenomenon. Unlike conventional mechanisms where the residual stress produces an intrinsic torque, in this dynamical symmetry breaking scheme, the residual stress induces a negative increment to the ambient turbulent viscosity. The axial flow shear is then amplified by this negative viscosity increment. The resulting mean axial flow profile is calculated and discussed by analogy with the problem of turbulent pipe flow. For tokamaks, the negative viscosity is not needed to generate intrinsic rotation. However, toroidal rotation profile gradient is enhanced by the negative increment in turbulent viscosity.« less

Implant-supported mandibular splinting affects temporomandibular joint biomechanics.

PubMed

Zaugg, Balthasar; Hämmerle, Christoph H F; Palla, Sandro; Gallo, Luigi M

2012-08-01

Mandibular functional movements lead to complex deformations of bony structures. The aim of this study was to test whether mandibular splinting influences condylar kinematics and temporomandibular joint (TMJ) loading patterns. Six subjects were analyzed by means of dynamic stereometry during jaw opening-closing with mandibles unconstrained as well as splinted transversally by a cast metal bar fixed bilaterally to two implant pairs in the (pre)molar region. Statistical analysis was performed by means of ANOVAs for repeated measurements (significance level α=0.05). Transversal splinting reduced mandibular deformation during jaw opening-closing as measured between two implants in the (pre)molar region on each side of the mandible significantly by 54%. Furthermore, splinting significantly reduced the distance between lateral condylar poles (average displacement vector magnitude of each pole: 0.84±0.36 mm; average mediolateral displacement component: 45±28% of the magnitude) and led to a medial displacement of their trajectories as well as a mediolateral displacement of stress-field paths. During jaw opening-closing, splinting of the mandible leads to a significant reduction of mandibular deformation and intercondylar distance and to altered stress-field paths, resulting in changed loading patterns of the TMJ structures. © 2011 John Wiley & Sons A/S.

Order parameter re-mapping algorithm for 3D phase field model of grain growth using FEM

DOE PAGES

Permann, Cody J.; Tonks, Michael R.; Fromm, Bradley; ...

2016-01-14

Phase field modeling (PFM) is a well-known technique for simulating microstructural evolution. To model grain growth using PFM, typically each grain is assigned a unique non-conserved order parameter and each order parameter field is evolved in time. Traditional approaches using a one-to-one mapping of grains to order parameters present a challenge when modeling large numbers of grains due to the computational expense of using many order parameters. This problem is exacerbated when using an implicit finite element method (FEM), as the global matrix size is proportional to the number of order parameters. While previous work has developed methods to reducemore » the number of required variables and thus computational complexity and run time, none of the existing approaches can be applied for an implicit FEM implementation of PFM. Here, we present a modular, dynamic, scalable reassignment algorithm suitable for use in such a system. Polycrystal modeling with grain growth and stress require careful tracking of each grain’s position and orientation which is lost when using a reduced order parameter set. In conclusion, the method presented in this paper maintains a unique ID for each grain even after reassignment, to allow the PFM to be tightly coupled to calculations of the stress throughout the polycrystal. Implementation details and comparative results of our approach are presented.« less

Deviant Earthquakes: Data-driven Constraints on the Variability in Earthquake Source Properties and Seismic Hazard

NASA Astrophysics Data System (ADS)

Trugman, Daniel Taylor

The complexity of the earthquake rupture process makes earthquakes inherently unpredictable. Seismic hazard forecasts often presume that the rate of earthquake occurrence can be adequately modeled as a space-time homogenenous or stationary Poisson process and that the relation between the dynamical source properties of small and large earthquakes obey self-similar scaling relations. While these simplified models provide useful approximations and encapsulate the first-order statistical features of the historical seismic record, they are inconsistent with the complexity underlying earthquake occurrence and can lead to misleading assessments of seismic hazard when applied in practice. The six principle chapters of this thesis explore the extent to which the behavior of real earthquakes deviates from these simplified models, and the implications that the observed deviations have for our understanding of earthquake rupture processes and seismic hazard. Chapter 1 provides a brief thematic overview and introduction to the scope of this thesis. Chapter 2 examines the complexity of the 2010 M7.2 El Mayor-Cucapah earthquake, focusing on the relation between its unexpected and unprecedented occurrence and anthropogenic stresses from the nearby Cerro Prieto Geothermal Field. Chapter 3 compares long-term changes in seismicity within California's three largest geothermal fields in an effort to characterize the relative influence of natural and anthropogenic stress transients on local seismic hazard. Chapter 4 describes a hybrid, hierarchical clustering algorithm that can be used to relocate earthquakes using waveform cross-correlation, and applies the new algorithm to study the spatiotemporal evolution of two recent seismic swarms in western Nevada. Chapter 5 describes a new spectral decomposition technique that can be used to analyze the dynamic source properties of large datasets of earthquakes, and applies this approach to revisit the question of self-similar scaling of southern California seismicity. Chapter 6 builds upon these results and applies the same spectral decomposition technique to examine the source properties of several thousand recent earthquakes in southern Kansas that are likely human-induced by massive oil and gas operations in the region. Chapter 7 studies the connection between source spectral properties and earthquake hazard, focusing on spatial variations in dynamic stress drop and its influence on ground motion amplitudes. Finally, Chapter 8 provides a summary of the key findings of and relations between these studies, and outlines potential avenues of future research.

The influence of topographic stresses on faulting, emphasizing the 2008 Wenchuan, China earthquake rupture

NASA Astrophysics Data System (ADS)

Styron, R. H.; Hetland, E. A.; Zhang, G.

2013-12-01

The weight of large mountains produces stresses in the crust that locally may be on the order of tectonic stresses (10-100 MPa). These stresses have a significant and spatially-variable deviatoric component that may be resolved as strong normal and shear stresses on range-bounding faults. In areas of high relief, the shear stress on faults can be comparable to inferred stress drops in earthquakes, and fault-normal stresses may be greater than 50 MPa, and thus may potentially influence fault rupture. Additionally, these stresses may be used to make inferences about the orientation and magnitude of tectonic stresses, for example by indicating a minimum stress needed to be overcome by tectonic stress. We are studying these effects in several tectonic environments, such as the Longmen Shan (China), the Denali fault (Alaska, USA) and the Wasatch Fault Zone (Utah, USA). We calculate the full topographic stress tensor field in the crust in a study region by convolution of topography with Green's functions approximating stresses from a point load on the surface of an elastic halfspace, using the solution proposed by Liu and Zoback [1992]. The Green's functions are constructed from Boussinesq's solutions for a vertical point load on an elastic halfspace, as well as Cerruti's solutions for a horizontal surface point load, accounting for irregular surface boundary and topographic spreading forces. The stress tensor field is then projected onto points embedded in the halfspace representing the faults, and the fault normal and shear stresses at each point are calculated. Our primary focus has been on the 2008 Wenchuan earthquake, as this event occurred at the base of one of Earth's highest and steepest topographic fronts and had a complex and well-studied coseismic slip distribution, making it an ideal case study to evaluate topographic influence on faulting. We calculate the topographic stresses on the Beichuan and Pengguan faults, and compare the results to the coseismic slip distribution, considering several published fault models. These models differ primarily in slip magnitude and planar vs. listric fault geometry at depth. Preliminary results indicate that topographic stresses are generally resistive to tectonic deformation, especially above ~10 km depth, where the faults are steep in all models. Down-dip topographic shear stresses on the fault are normal sense where the faults dip steeply, and reach 20 MPa on the fault beneath the Pengguan massif. Reverse-sense shear up to ~15 MPa is present on gently-dipping thrust flats at depth on listric fault models. Strike-slip shear stresses are sinistral on the steep, upper portions of faults but may be dextral on thrust flats. Topographic normal stress on the faults reaches ~80 MPa on thrust ramps and may be higher on flats. Coseismic slip magnitude is negatively correlated with topographic normal and down-dip shear stresses. The spatial patterns of topographic stresses and slip suggest that topographic stresses have significantly suppressed slip in certain areas: slip maxima occur in areas of locally lower topographic stresses, while areas of higher down-dip shear and normal stress show less slip than adjacent regions.

Effects of changing stress states on the development of caldera-bounding faults: Geological evidence from Kumano caldera, Japan

NASA Astrophysics Data System (ADS)

Miura, Daisuke

2005-06-01

Collapse of a large caldera can cause spatial and temporal perturbations of stress, and formation of "caldera faults." The stress variations influence the direction of slip vectors on the fault planes; hence, stress estimation is important for the study of caldera-forming processes. In our paleostress estimation, the stress variations in the collapse of the ca. 14 Ma Kumano caldera in Japan have been revealed. A stress inversion method based on the Wallace-Bott hypothesis was used to compute the orientation of the principal stress axes ( σ1≥ σ2≥ σ3) and the stress ratio ϕ=( σ2- σ3)/( σ1- σ3), where 0≤ ϕ≤1. The caldera faults formed simultaneously with the caldera-forming ash-flow tuff eruption. Therefore, paleostress solutions obtained from slip data measured on such faults show the spatial and temporal changes of the stress at the time of the caldera collapse. The computed stress ratio ϕ characterizes a pair of stress fields. In the early stage, the stress field with ϕ˜1.0 shows a semi-radial trajectory of stress σ2 and an eastern concentric trajectory of stress σ3. This stress regime, resulting from pre-collapse tumescence, counteracts the gravitational force and thus produces smaller net vertical stress. The regional tumescence above an inflated magma chamber is the most plausible source of the stress field, and it is consistent with the timing of the caldera formation. In the late stage, the stress field with ϕ˜0.5 shows the semi-radial trajectory of stress σ2 and the west-convex and concentric trajectory of stress σ3. Change of the stress ratio ϕ from 1.0 to 0.5 implies that increase in the relative magnitude of the stress σ1 caused the deeper subsidence of the caldera floor. Stress variations may be of significant value for reconstructing the structural history of the caldera.

Vulnerability of point-of-care test reagents and instruments to environmental stresses: implications for health professionals and developers.

PubMed

Louie, Richard F; Ferguson, William J; Curtis, Corbin M; Vy, John H; Kost, Gerald J

2014-03-01

Strategic integration of point-of-care (POC) diagnostic tools during crisis response can accelerate triage and improve management of victims. Timely differential diagnosis is essential wherever care is provided to rule out or rule in disease, expedite life-saving treatment, and improve utilization of limited resources. POC testing needs to be accurate in any environment in which it is used. Devices are exposed to potentially adverse storage and operating conditions, such as high/low temperature and humidity during emergencies and field rescues. Therefore, characterizing environmental conditions allows technology developers, operators, and responders to understand the broad operational requirements of test reagents, instruments, and equipment in order to improve the quality and delivery of care in complex emergencies, disasters, and austere environmental settings. This review aims to describe the effects of environmental stress on POC testing performance and its impact on decision-making, to describe how to study the effects, and to summarize ways to mitigate the effects of environmental stresses through good laboratory practice, development of robust reagents, and novel thermal packaging solutions.

Expression of Staphylococcal Enterotoxins under Stress Encountered during Food Production and Preservation.

PubMed

Schelin, Jenny; Susilo, Yusak Budi; Johler, Sophia

2017-12-15

Staphylococcal food poisoning (SFP) is the most prevalent cause of food-borne intoxications worldwide. Consumption of enterotoxins preformed in food causes violent vomiting and can be fatal in children and the elderly. While being repressed by competing bacteria in most matrices, Staphylococcus aureus benefits from crucial competitive advantages in foods with high osmolarity or low pH. During recent years, the long-standing belief in the feasibility of assessing SFP risk based on colony-forming units of S. aureus present in food products has been disproven. Instead, researchers and food business operators are acutely aware of the imminent threat arising from unforeseeable enterotoxin production under stress conditions. This paradigm shift led to a variety of new publications enabling an improved understanding of enterotoxin expression under stress conditions encountered in food. The wealth of data provided by these studies is extremely diverse, as it is based on different methodological approaches, staphylococcal strains, stressors, and enterotoxins. Therefore, in this review, we aggregated and critically evaluated the complex findings of these studies, to provide readers with a current overview of the state of research in the field.

DIRECT NUMERICAL SIMULATION OF TRANSITIONAL FLOW IN A STENOSED CAROTID BIFURCATION

PubMed Central

Lee, Seung E.; Lee, Sang-Wook; Fischer, Paul F.; Bassiouny, Hisham S.; Loth, Francis

2008-01-01

The blood flow dynamics of a stenosed, subject-specific, carotid bifurcation were numerically simulated using the spectral element method. Pulsatile inlet conditions were based on in vivo color Doppler ultrasound measurements of blood velocity. The results demonstrated the transitional or weakly turbulent state of the blood flow, which featured rapid velocity and pressure fluctuations in the post-stenotic region of the internal carotid artery during systole and laminar flow during diastole. High-frequency vortex shedding was greatest downstream of the stenosis during the deceleration phase of systole. Velocity fluctuations had a frequency within the audible range of 100–300 Hz. Instantaneous wall shear stress within the stenosis was relatively high during systole (~25-45 Pa) compared to that in a healthy carotid. In addition, high spatial gradients of wall shear stress were present due to flow separation on the inner wall. Oscillatory flow reversal and low pressure were observed distal to the stenosis in the internal carotid artery. This study predicts the complex flow field, the turbulence levels and the distribution of the biomechanical stresses present in vivo within a stenosed carotid artery. PMID:18656199

3D analysis of thermal and stress evolution during laser cladding of bioactive glass coatings.

PubMed

Krzyzanowski, Michal; Bajda, Szymon; Liu, Yijun; Triantaphyllou, Andrew; Mark Rainforth, W; Glendenning, Malcolm

2016-06-01

Thermal and strain-stress transient fields during laser cladding of bioactive glass coatings on the Ti6Al4V alloy basement were numerically calculated and analysed. Conditions leading to micro-cracking susceptibility of the coating have been investigated using the finite element based modelling supported by experimental results of microscopic investigation of the sample coatings. Consecutive temperature and stress peaks are developed within the cladded material as a result of the laser beam moving along the complex trajectory, which can lead to micro-cracking. The preheated to 500°C base plate allowed for decrease of the laser power and lowering of the cooling speed between the consecutive temperature peaks contributing in such way to achievement of lower cracking susceptibility. The cooling rate during cladding of the second and the third layer was lower than during cladding of the first one, in such way, contributing towards improvement of cracking resistance of the subsequent layers due to progressive accumulation of heat over the process. Copyright © 2016 Elsevier Ltd. All rights reserved.

Stress analysis in high-temperature superconductors under pulsed field magnetization

NASA Astrophysics Data System (ADS)

Wu, Haowei; Yong, Huadong; Zhou, Youhe

2018-04-01

Bulk high-temperature superconductors (HTSs) have a high critical current density and can trap a large magnetic field. When bulk superconductors are magnetized by the pulsed field magnetization (PFM) technique, they are also subjected to a large electromagnetic stress, and the resulting thermal stress may cause cracking of the superconductor due to the brittle nature of the sample. In this paper, based on the H-formulation and the law of heat transfer, we can obtain the distributions of electromagnetic field and temperature, which are in qualitative agreement with experiment. After that, based on the dynamic equilibrium equations, the mechanical response of the bulk superconductor is determined. During the PFM process, the change in temperature has a dramatic effect on the radial and hoop stresses, and the maximum radial and hoop stress are 24.2 {{MPa}} and 22.6 {{MPa}}, respectively. The mechanical responses of a superconductor for different cases are also studied, such as the peak value of the applied field and the size of bulk superconductors. Finally, the stresses are also presented for different magnetization methods.

Nursing staff stress from challenging behaviour of residents with dementia: a concept analysis.

PubMed

Hazelhof, T J G M; Schoonhoven, L; van Gaal, B G I; Koopmans, R T C M; Gerritsen, D L

2016-09-01

Provide insight into the concept of stress in the context of challenging behaviour of nursing home residents with dementia and its causes and consequences. Challenging behaviour is frequent in residents with dementia, but consequences for nursing staff are unclear. Challenging behaviour of residents can be enervating for nurses and may lead to stress. Although stress in general is associated with negative outcomes, an overview of stress in this context would be a welcome addition to the field. Concept analysis according to Walker and Avant. Identified antecedents of stress: physical and verbal aggression, conflicts, excessive demands and being unresponsive (residents), age, experience, tenure, nursing level and training (nursing staff). Defining attributes: disturbed homoeostasis and the personal appraisal of the situation. Identified consequences regard health, psychological aspects and behaviour. Intervening in the identified factors may contribute to prevention of stress in nursing staff. Given a lack of strong empirical studies, our analysis is not based on a high level of evidence and needs to be tested. Papers from before 1990 might have been missed. The concept analysis revealed that nursing staff stress in the context of challenging behaviour may result from resident and nursing staff factors. Besides health and psychological consequences, behavioural consequences can enormously impact the well-being of residents. Application in daily care to support teams in influencing resident and nursing staff factors could prevent stress, for instance using behavioural management training or recruiting higher educated nursing staff. Given the increasing complexity of care, creating specialized units with specifically trained staff for different groups of people with dementia may be desirable. © 2016 International Council of Nurses.

Numerical simulation on residual stress in Y-slit type cracking test of Q690E

NASA Astrophysics Data System (ADS)

Huang, Wenjian; Lin, Guozhen; Chen, Zhanglan; Chen, Wu

2018-03-01

Numerical simulation on residual stress in Y-slit type cracking test of Q690E is carried out by using ANSYS. First, the dynamic distribution of welding temperature field is calculated; second, the results of the temperature field are converted into corresponding stress by the method of indirect coupling. The testing results show that the longitudinal residual stress of the weld is greater than the transverse residual stress and the peak of transverse residual stress is on the weld groove.

Experimental dynamic metamorphism of mineral single crystals

USGS Publications Warehouse

Kirby, S.H.; Stern, L.A.

1993-01-01

This paper is a review of some of the rich and varied interactions between non-hydrostatic stress and phase transformations or mineral reactions, drawn mainly from results of experiments done on mineral single crystals in our laboratory or our co-authors. The state of stress and inelastic deformation can enter explicitly into the equilibrium phase relations and kinetics of mineral reactions. Alternatively, phase transformations can have prominent effects on theology and on the nature of inelastic deformation. Our examples represent five types of structural phase changes, each of which is distinguished by particular mechanical effects. In increasing structural complexity, these include: (1) displacive phase transformations involving no bond-breaking, which may produce anomalous brittle behavior. A primary example is the a-?? quartz transition which shows anomalously low fracture strength and tertiary creep behavior near the transition temperature; (2) martensitic-like transformations involving transformation strains dominated by shear deformation. Examples include the orthoenstatite ??? clinoenstatite and w u ??rtzite ??? sphalerite transformations; (3) coherent exsolution or precipitation of a mineral solute from a supersaturated solid-solution, with anisotropy of precipitation and creep rates produced under nonhydrostatic stress. Examples include exsolution of corundum from MgO ?? nAl2O3 spinels and Ca-clinopyroxene from orthopyroxene; (4) order-disorder transformations that are believed to cause anomalous plastic yield strengthening, such as MgO - nAl2O3 spinels; and (5) near-surface devolatilization of hydrous silicate single-crystals that produces a fundamental brittleness thought to be connected with dehydration at microcracks at temperatures well below nominal macroscopic dehydration temperatures. As none of these interactions between single-crystal phase transformations and non-hydrostatic stress is understood in detail, this paper serves as a challenge to field structural geologists to test whether interactions of these types occur in nature, and to theoreticians to reach a deeper understanding of the complex relations between phase transformations, the local state of stress and associated deformation and deformation rates. ?? 1993.

Increased oxidative stress in the mitochondria isolated from lymphocytes of bipolar disorder patients during depressive episodes.

PubMed

Valvassori, Samira S; Bavaresco, Daniela V; Feier, Gustavo; Cechinel-Recco, Kelen; Steckert, Amanda V; Varela, Roger B; Borges, Cenita; Carvalho-Silva, Milena; Gomes, Lara M; Streck, Emílio L; Quevedo, João

2018-06-01

The present study aims to investigate the oxidative stress parameters in isolated mitochondria, as well as looking at mitochondrial complex activity in patients with Bipolar Disorder (BD) during depressive or euthymic episodes. This study evaluated the levels of mitochondrial complex (I, II, II-III and IV) activity in lymphocytes from BD patients. We evaluated the following oxidative stress parameters: superoxide, thiobarbituric acid reactive species (TBARS) and carbonyl levels in submitochondrial particles of lymphocytes from bipolar patients. 51 bipolar patients were recruited into this study: 34 in the euthymic phase, and 17 in the depressive phase. Our results indicated that the depressive phase could increase the levels of mitochondrial superoxide, carbonyl and TBARS, and superoxide dismutase, and could decrease the levels of mitochondrial complex II activity in the lymphocytes of bipolar patients. It was also observed that there was a negative correlation between the Hamilton Depression Rating Scale (HDRS) and complex II activity in the lymphocytes of depressive bipolar patients. In addition, there was a positive correlation between HDRS and superoxide, superoxide dismutase, TBARS and carbonyl. Additionally, there was a negative correlation between complex II activity and oxidative stress parameters. In conclusion, our results suggest that mitochondrial oxidative stress and mitochondrial complex II dysfunction play important roles in the depressive phase of BD. Copyright © 2018. Published by Elsevier B.V.

Prediction of Composite Laminate Strength Properties Using a Refined Zigzag Plate Element

NASA Technical Reports Server (NTRS)

Barut, Atila; Madenci, Erdogan; Tessler, Alexander

2013-01-01

This study presents an approach that uses the refined zigzag element, RZE(exp2,2) in conjunction with progressive failure criteria to predict the ultimate strength of composite laminates based on only ply-level strength properties. The methodology involves four major steps: (1) Determination of accurate stress and strain fields under complex loading conditions using RZE(exp2,2)-based finite element analysis, (2) Determination of failure locations and failure modes using the commonly accepted Hashin's failure criteria, (3) Recursive degradation of the material stiffness, and (4) Non-linear incremental finite element analysis to obtain stress redistribution until global failure. The validity of this approach is established by considering the published test data and predictions for (1) strength of laminates under various off-axis loading, (2) strength of laminates with a hole under compression, and (3) strength of laminates with a hole under tension.

Wave propagation in viscoelastic horns using a fractional calculus rheology model

NASA Astrophysics Data System (ADS)

Margulies, Timothy

2003-10-01

The complex mechanical behavior of materials are characterized by fluid and solid models with fractional calculus differentials to relate stress and strain fields. Fractional derivatives have been shown to describe the viscoelastic stress from polymer chain theory for molecular solutions [Rouse and Sittel, J. Appl. Phys. 24, 690 (1953)]. Here the propagation of infinitesimal waves in one dimensional horns with a small cross-sectional area change along the longitudinal axis are examined. In particular, the linear, conical, exponential, and catenoidal shapes are studied. The wave amplitudes versus frequency are solved analytically and predicted with mathematical computation. Fractional rheology data from Bagley [J. Rheol. 27, 201 (1983); Bagley and Torvik, J. Rheol. 30, 133 (1986)] are incorporated in the simulations. Classical elastic and fluid ``Webster equations'' are recovered in the appropriate limits. Horns with real materials that employ fractional calculus representations can be modeled to examine design trade-offs for engineering or for scientific application.

Myxomatosis in the Mallee region of Victoria, Australia.

PubMed Central

Shepherd, R. C.; Edmonds, J. W.; Nolan, I. F.; Gocs, A.

1978-01-01

Sharp reductions in the wild rabbit (Oryctolagus cuniculus (L.)) population in the Mallee are associated with annual myxomatosis epizootics. The extent to which the population reductions are the direct result of the epizootics varies with time of epizootic occurrence. All grazing animals in the Mallee are under nutritional stress each summer and autumn. When the epizootic occurs during the early summer heavy losses occur in a previously healthy population. Similar losses which occur in the late summer and autumn are the result of a nutritional stress - epizootic complex. The end result in each case is a population reduction of about 80%. This reduction occurs in a population which is the most resistant to myxomatosis known in Victoria and in association with epizootics caused by field strains of myxoma virus of moderate virulence only. The earlier summer epizootics are of considerable economic importance because they sharply reduce the pressure on the limited food available for other grazing animals. PMID:701787

Myxomatosis in the Mallee region of Victoria, Australia.

PubMed

Shepherd, R C; Edmonds, J W; Nolan, I F; Gocs, A

1978-10-01

Sharp reductions in the wild rabbit (Oryctolagus cuniculus (L.)) population in the Mallee are associated with annual myxomatosis epizootics. The extent to which the population reductions are the direct result of the epizootics varies with time of epizootic occurrence. All grazing animals in the Mallee are under nutritional stress each summer and autumn. When the epizootic occurs during the early summer heavy losses occur in a previously healthy population. Similar losses which occur in the late summer and autumn are the result of a nutritional stress - epizootic complex. The end result in each case is a population reduction of about 80%. This reduction occurs in a population which is the most resistant to myxomatosis known in Victoria and in association with epizootics caused by field strains of myxoma virus of moderate virulence only. The earlier summer epizootics are of considerable economic importance because they sharply reduce the pressure on the limited food available for other grazing animals.

Childhood trauma and complex posttraumatic stress disorder symptoms in older adults: A study of direct effects and social-interpersonal factors as potential mediators.

PubMed

Krammer, Sandy; Kleim, Birgit; Simmen-Janevska, Keti; Maercker, Andreas

2016-01-01

Childhood traumatic events may lead to long-lasting psychological effects and contribute to the development of complex posttraumatic sequelae. These might be captured by the diagnostic concept of complex posttraumatic stress disorder (CPTSD) as an alternative to classic posttraumatic stress disorder (PTSD). CPTSD comprises a further set of symptoms in addition to those of PTSD, namely, changes in affect, self, and interpersonal relationships. Previous empirical research on CPTSD has focused on middle-aged adults but not on older adults. Moreover, predictor models of CPTSD are still rare. The current study investigated the association between traumatic events in childhood and complex posttraumatic stress symptoms in older adults. The mediation of this association by 2 social-interpersonal factors (social acknowledgment as a survivor and dysfunctional disclosure) was investigated. These 2 factors focus on the perception of acknowledgment by others and either the inability to disclose traumatic experiences or the ability to do so only with negative emotional reactions. A total of 116 older individuals (age range = 59-98 years) who had experienced childhood traumatic events completed standardized self-report questionnaires indexing childhood trauma, complex trauma sequelae, social acknowledgment, and dysfunctional disclosure of trauma. The results showed that traumatic events during childhood were associated with later posttraumatic stress symptoms but with classic rather than complex symptoms. Social acknowledgment and dysfunctional disclosure partially mediated this relationship. These findings suggest that childhood traumatic stress impacts individuals across the life span and may be associated with particular adverse psychopathological consequences.

Dyke-sill relationships in Karoo dolerites as indicators of propagation and emplacement processes of mafic magmas in the shallow crust

NASA Astrophysics Data System (ADS)

Coetzee, A.; Kisters, A. F. M.

2017-04-01

This paper describes the spatial and temporal relationships between Karoo-age (ca. 180 Ma) dolerite dykes and a regional-scale saucer-sill complex from the Secunda (coal mine) Complex in the northeastern parts of the Karoo Basin of South Africa. Unlike parallel dyke swarms of regional extensional settings, mafic dykes commonly show curved geometries and highly variable orientations, short strike extents and complex cross-cutting and intersecting relationships. Importantly, the dyke networks originate from the upper contacts of the first-order dolerite sill-saucer structure and are not the feeders of the saucer complex. Cross-cutting relationships indicate the largely contemporaneous formation of dykes and the inner sill and inclined sheets of the underlying saucer. Systematic dykes form a distinct boxwork-type pattern of two high-angle, interconnected dyke sets. The formation and orientation of this dyke set is interpreted to be related to the stretching of roof strata above elongated magma lobes that facilitated the propagation of the inner sill, similar to the "cracked lid" model described for large saucer complexes in Antarctica. Dyke patterns generally reflect the saucer emplacement process and the associated deformation of wall rocks rather than far-field regional stresses.

Anhedonia but not passive floating is an indicator of depressive-like behavior in two chronic stress paradigms.

PubMed

Stepanichev, Mikhail Yu; Tishkina, Anna O; Novikova, Margarita R; Levshina, Irina P; Freiman, Sofiya V; Onufriev, Mikhail V; Levchenko, Olga A; Lazareva, Natalia A; Gulyaeva, Natalia V

2016-01-01

Depression is the most common form of mental disability in the world. Depressive episodes may be precipitated by severe acute stressful events or by mild chronic stressors. Studies on the mechanisms of depression require both appropriate experimental models (most of them based on the exposure of animals to chronic stressors), and appropriate tests for assessment of depressive states. In this study male Wistar rats were exposed to two different chronic stress paradigms: an eight-week chronic unpredictable mild stress or a two-week combined chronic stress. The behavioral effects of stress were evaluated using sucrose preference, forced swim and open field tests. After the exposure to chronic unpredictable mild stress, anhedonia was developed, activity in the open field increased, while no changes in the duration of passive floating could be detected. After chronic combined stress, anhedonia was also evident, whereas behavior in the open field and forced swim test did not change. The levels of corticosterone in the blood and brain structures involved in stress-response did not differ from control in both experiments. The absence of significant changes in corticosterone levels and passive floating may be indicative of the adaptation of animals to chronic stress. Anhedonia appears to be a more sensitive indicator of depressive-like behavioral effects of chronic stress as compared to behavior in the forced swim or open field tests.

Determination of in situ state of stress at the Spent Fuel Test-Climax site, Climax Stock, Nevada Test Site

USGS Publications Warehouse

Ellis, W.L.; Magner, J.E.

1982-01-01

Determination of the in situ state of stress at the site of the Spent Fuel Test--Climax, using the U.S. Bureau of Mines overcore method, indicates principal stress magnitudes of 11.6 MPa, 7.1 MPa, and 2.8 MPa. The bearing and plunge of the maximum and minimum principal stress components are, respectively: N. 56? E., 29? NE; and N. 42? W., 14? NW. The vertical stress magnitude of 7.9 MPa calculated from the overcore data is significantly less than expected from overburden pressure, suggesting the stress field is influenced by local or areal geologic factors. Results from this investigation indicate (1) the stress state at the Spent Fuel Test--Climax site deviates significantly from a gravitational stress field, both in relative stress magnitudes and in orientation; (2) numerical modeling will not realistically simulate the near-field response of the Spent Fuel Test--Climax site if gravitational and (or) horizontal and vertical applied stress boundary conditions are assumed; and (3) substantial stress variations may occur spatially within the stock.

Estimation of in-situ Stress Magnitudes and Orientations in a Deep South African Gold Mine: Applications to Fault Mechanics and Mine Safety

NASA Astrophysics Data System (ADS)

Lucier, A. M.; Heesakkers, V.; Zoback, M. D.; Reches, Z.

2006-12-01

As part of the Natural Earthquake Laboratory in South African Mines (NELSAM) project, we are investigating the far-field in-situ stress state around the TauTona gold mine. The far-field stress state is used as a boundary condition to quantify the stresses within the active mining area, and to evaluate the potential for reactivation of existing faults (or creation of new faults) in the NELSAM study area. Our main goals are to gain insight into earthquake processes under induced faulting conditions and to guide mining practices in improving underground seismic safety. To characterize in-situ stresses, we use an integrated stress measurement strategy that incorporates rock properties with breakout and drilling-induced tensile fracture observations from camera log images of several boreholes in the NELSAM study area at a depth of 3.5 km below the ground surface. The quantification of the far-field in-situ stress state is based on breakouts observed in a sub-horizontal borehole that extends 418 m away from the mined region and intersects the Pretorius fault, the largest fault-zone in the mine. The location, width and orientation of these breakouts were interpreted along the length of the borehole. Breakouts occur along most of the length of the borehole, with widths ranging from 25-95 deg and orientations fluctuating up to 45 deg around the sidewalls of the borehole. The fluctuations in breakout orientations are presumably due to slip on fault segments, and modeling these fluctuations provides constraints on the far-field stress state. Rock properties (uniaxial compressive strength, Young's modulus and Poisson's ratio) from on-going laboratory experiments will further constrain the stress magnitudes. The results of the stress characterization in this long borehole have been compared with independent stress determinations made in several 10-40 m long boreholes within the mined region to ensure consistency between the modeled far-field stress magnitudes and the observed near-field stresses. Our preliminary results indicate a normal faulting to normal/strike-slip stress state. Once a final stress model has been obtained, we will use it to assess the potential for fault reactivation and to predict future stress changes associated with further mining operations. The study was supported by NSF Continental Dynamics grant 0409605.

Analysis and interpretation of stress indicators in deviated wells of the Coso Geothermal Field

USGS Publications Warehouse

Schoenball, Martin; Glen, Jonathan M. G.; Davatzes, Nicholas C.

2016-01-01

Characterizing the tectonic stress field is an integral part of the development of hydrothermal systems and especially for enhanced geothermal systems (EGS). With a well characterized stress field the propensity of fault slip on faults with known location and orientation can be identified. Faults that are critically oriented for faulting with respect to the stress field are known to provide natural fluid pathways. A high slip tendency makes a fault a likely candidate for reactivation during the creation of an EGS. Similarly, the stress state provides insight for the potential of larger, damaging earthquakes should extensive portions of well-oriented, larger faults be reactivated.The analysis of stress indicators such as drilling-induced fractures and borehole breakouts is the main tool to infer information on the stress state of a geothermal reservoir. The standard procedure is applicable to sub-vertical wellbore sections and highly deviated sections have to be discarded. However, in order to save costs and reduce the environmental impact most recent wells are directionally drilled with deviations that require appropriate consideration of the deviated trajectory. Here we present an analysis scheme applicable to arbitrary well trajectories or a combination of wells to infer the stress state. Through the sampling of the stress tensor along several directions additional information on the stress regime and even relative stress magnitudes can be obtained. We apply this method on image logs from the pair of wells 58-10 and 58A-10 that were drilled from the same well pad. Both wells have image logs of about 2km of their trajectories that are separated by less than 300m. For both wells we obtain a mean orientation of SHmax of N23° with large standard deviations of locations of stress indicators of 24° and 26°, respectively. While the local stress direction is highly variable along both wells with dominant wavelengths from around 50 to 500m, the mean directions are very consistent and also agree with previous stress estimates in the eastern part of the Coso Geothermal Field. In order to obtain a reliable estimation of the stress orientation in this setting, it is necessary to sample the stress field on an interval long to capture several of the dominant wavelengths.

The relation between intensity and complexity of coronary artery lesion and oxidative stress in patients with acute coronary syndrome.

PubMed

Turan, Turhan; Menteşe, Ümit; Ağaç, Mustafa Tarık; Akyüz, Ali Rıza; Kul, Selim; Aykan, Ahmet Çağrı; Bektaş, Hüseyin; Korkmaz, Levent; Öztaş Menteşe, Seda; Dursun, İhsan; Çelik, Şükrü

2015-10-01

Oxidative stress plays a major role in the development of atherosclerosis. However, the relationship between oxidative stress and complexity and intensity of coronary artery disease is less clear. The aim of this study is to assess the relationship between oxidative stress markers and the complexity and intensity of coronary artery disease in patients with acute coronary syndrome (ACS). Sixty-seven consecutive patients with an early phase of ACS (<3 h) were included in this single-centre, cross-sectional, prospective study. Syntax and Gensini scores were calculated based on angiographic findings. Patients were divided into two CAD complexity groups according to their Syntax scores: low SYNTAX score (<22) and moderate to high SYNTAX score (>=22). Likewise patients were divided into two CAD severity groups according to the median Gensini score of 64: less intensive CAD with Gensini score (<64) and intensive CAD with Gensini score >=64. Blood samples were taken in 1 hour within administration in order to measure total oxidative status (TOS) and total antioxidant capacity (TAC) levels determined by Erel method. Oxidative stress index (OSI) was calculated by TOS /TAC. There was no significant difference between the two SYNTAX groups for oxidative stress markers. Median TOS and OSI values were significantly high in the intensive CAD group (p=0.005, p=0.04, respectively). The Gensini score was positively correlated with TOS and OSI (p=0.003, p=0.02, respectively). Oxidative stress markers may be considered supportive laboratory parameters related to CAD intensity but not complexity in ACS patients.

Osmoregulation in Methanogens (and Other Interesting Organisms)

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

Roberts, Mary Fedarko

2014-12-03

Our research has been aimed at (i) identifying, (ii) determining mode of regulation, and (iii) understanding how different classes of compatible solutes (also termed osmolytes) affect macromolecular stability in response to osmotic and thermal stress. For solutes we have identified (e.g., di-inositol-1,1’-phosphate (DIP)), we used NMR to elucidate biosynthetic pathways and then cloned suspected enzymes in the pathway to explore how they are regulated. Compatible solutes are thought to protect proteins from thermal and osmotic stresses by being excluded from the surface, allowing critical water molecules to interact with the protein. This implies there are no specific binding interactions betweenmore » osmolytes and proteins. However, we and others have often observed very specific solute effects for proteins that suggest a more direct interaction between solute and protein is likely can occur. Measuring such a weak interaction is extremely difficult. We have developed a solution NMR method, high-resolution field cycling relaxometry, that can measure spin-lattice relaxation rates as a function of magnetic field from 11.7 (the field of a 500 MHz spectrometer) to 0.003 T. The methodology is ideal for nuclei in small molecules with moderately long relaxation times at high fields – phosphate groups (31P), enriched carbonyls (13C), or methyl groups (1H). The protein of interest is spin-labeled to introduce a large dipole on it that will dominate the relaxation of nuclei on any small molecules that bind transiently. The key is to measure relaxation below 1-2 T (and extract nuclei-spin label distances in the bound complex) where the small molecule relaxation will be dominated by dipolar mechanisms with a correlation time indicative of the large protein complex. Our explorations of an inositol monophosphatase (the last step in DIP generation) localized four discrete binding sides for the thermoprotectant α-glutamate. This is a novel approach, and while the work did not fully explain how this solute protected the IMPase from thermal denaturation, it did showcase a new and exciting method to monitor weak binding in biological systems.« less

Minimization principles for the coupled problem of Darcy-Biot-type fluid transport in porous media linked to phase field modeling of fracture

NASA Astrophysics Data System (ADS)

Miehe, Christian; Mauthe, Steffen; Teichtmeister, Stephan

2015-09-01

This work develops new minimization and saddle point principles for the coupled problem of Darcy-Biot-type fluid transport in porous media at fracture. It shows that the quasi-static problem of elastically deforming, fluid-saturated porous media is related to a minimization principle for the evolution problem. This two-field principle determines the rate of deformation and the fluid mass flux vector. It provides a canonically compact model structure, where the stress equilibrium and the inverse Darcy's law appear as the Euler equations of a variational statement. A Legendre transformation of the dissipation potential relates the minimization principle to a characteristic three field saddle point principle, whose Euler equations determine the evolutions of deformation and fluid content as well as Darcy's law. A further geometric assumption results in modified variational principles for a simplified theory, where the fluid content is linked to the volumetric deformation. The existence of these variational principles underlines inherent symmetries of Darcy-Biot theories of porous media. This can be exploited in the numerical implementation by the construction of time- and space-discrete variational principles, which fully determine the update problems of typical time stepping schemes. Here, the proposed minimization principle for the coupled problem is advantageous with regard to a new unconstrained stable finite element design, while space discretizations of the saddle point principles are constrained by the LBB condition. The variational principles developed provide the most fundamental approach to the discretization of nonlinear fluid-structure interactions, showing symmetric systems in algebraic update procedures. They also provide an excellent starting point for extensions towards more complex problems. This is demonstrated by developing a minimization principle for a phase field description of fracture in fluid-saturated porous media. It is designed for an incorporation of alternative crack driving forces, such as a convenient criterion in terms of the effective stress. The proposed setting provides a modeling framework for the analysis of complex problems such as hydraulic fracture. This is demonstrated by a spectrum of model simulations.

Tertiary and Quaternary tectonic faulting in southernmost Illinois

USGS Publications Warehouse

Nelson, W.J.; Denny, F.B.; Devera, J.A.; Follmer, L.R.; Masters, J.M.

1997-01-01

Tertiary and/or Quaternary tectonic faulting is documented in three areas of southernmost Illinois: the Fluorspar Area Fault Complex (FAFC) in Pope and Massac Counties, the Ste. Genevieve Fault Zone (SGFZ) in Alexander and Union Counties, and the Commerce Fault Zone (CFZ) in Alexander County. In the FAFC, faults that strike NE and NNE displace Mounds Gravel (late Miocene to early Pleistocene) and, locally, the Metropolis terrace gravel (Pleistocene; pre-Woodfordian). No Woodfordian or younger deposits are deformed. Faults typically outline narrow, linear grabens that formed under tension with a component of strike slip. North-south to NW-trending vertical faults near the southeast end of the SGFZ displace Eocene sediments. Again, faults outline narrow grabens and show indications of strike slip. Deformed Quaternary sediments have not been observed. The CFZ, which trends northeast, displaces Mounds Gravel in Illinois and units as young as Peoria Silt (Woodfordian) in Missouri. Quaternary movement has been interpreted as right-lateral strike-slip. The CFZ coincides with a subtle gravity and magnetic lineament and seems to reflect a major feature in the basement. Surface expression in Illinois is subtle, but mafic and ultramafic intrusions, hydrothermal alteration and small faults align with the Commerce geophysical lineament. Earthquake foci in Missouri and Illinois lie on or close to the CFZ; some focal mechanisms fit the fault trend. Among these structures, only the CFZ exhibits slip that conforms to the current stress field (principal compressive stress axis E-W to ENE-WSW). Possibly, the stress field changed during Neogene time. Alternatively, high fluid pressures or local stress concentrations may have induced slip on less favorably oriented fractures. Tighter constraints are needed on timing, magnitude, and direction of Neogene displacement. ?? 1997 Elsevier Science B.V.

Bentazon triggers the promotion of oxidative damage in the Portuguese ricefield cyanobacterium Anabaena cylindrica: response of the antioxidant system.

PubMed

Galhano, Victor; Peixoto, Francisco; Gomes-Laranjo, José

2010-10-01

Rice fields are frequently exposed to environmental contamination by herbicides and cyanobacteria, as primary producers of these aquatic ecosystems, are adversely affected. Anabaena cylindrica is a cyanobacterium with a significantly widespread occurrence in Portuguese rice fields. This strain was studied throughout 72 h in laboratory conditions for its stress responses to sublethal concentrations (0.75-2 mM) of bentazon, a selective postemergence herbicide recommended for integrated weed management in rice, with special reference to oxidative stress, role of proline and intracellular antioxidant enzymes in herbicide-induced free radicals detoxification. Activities of antioxidant enzymes such as superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), and glutathione S-transferase (GST) increased in a time- and herbicide dose-response manner and were higher than those in the control samples after 72 h. A time- and concentration-dependent increase of malondialdehyde (MDA) levels and the enhanced cell membrane leakage following bentazon exposure are indicative of lipid peroxidation, free radicals formation, and oxidative damage, while increased amounts of SOD, CAT, APX, GST, and proline indicated their involvement in free radical scavenging mechanisms. The appreciable decline in the reduced glutathione (GSH) pool after 72 h at higher bentazon concentrations could be explained by the reduction of the NADPH-dependent glutathione reductase (GR) activity. The obtained results suggested that the alterations of antioxidant systems in A. cylindrica might be useful biomarkers of bentazon exposure. As the toxic mechanism of bentazon is a complex phenomenon, this study also adds relevant findings to explain the oxidative stress pathways of bentazon promoting oxidative stress in cyanobacteria. © 2010 Wiley Periodicals, Inc. Environ Toxicol, 2010.

Nondestructive testing and characterization of residual stress field using an ultrasonic method

NASA Astrophysics Data System (ADS)

Song, Wentao; Xu, Chunguang; Pan, Qinxue; Song, Jianfeng

2016-03-01

To address the difficulty in testing and calibrating the stress gradient in the depth direction of mechanical components, a new technology of nondestructive testing and characterization of the residual stress gradient field by ultrasonic method is proposed based on acoustoelasticity theory. By carrying out theoretical analysis, the sensitivity coefficients of different types of ultrasonic are obtained by taking the low carbon steel(12%C) as a research object. By fixing the interval distance between sending and receiving transducers, the mathematical expressions of the change of stress and the variation of time are established. To design one sending-one receiving and oblique incidence ultrasonic detection probes, according to Snell law, the critically refracted longitudinal wave (LCR wave) is excited at a certain depth of the fixed distance of the tested components. Then, the relationship between the depth of LCR wave detection and the center frequency of the probe in Q235 steel is obtained through experimental study. To detect the stress gradient in the depth direction, a stress gradient LCR wave detection model is established, through which the stress gradient formula is derived by the relationship between center frequency and detecting depth. A C-shaped stress specimen of Q235 steel is designed to conduct stress loading tests, and the stress is measured with the five group probes at different center frequencies. The accuracy of ultrasonic testing is verified by X-ray stress analyzer. The stress value of each specific depth is calculated using the stress gradient formula. Accordingly, the ultrasonic characterization of residual stress field is realized. Characterization results show that the stress gradient distribution is consistent with the simulation in ANSYS. The new technology can be widely applied in the detection of the residual stress gradient field caused by mechanical processing, such as welding and shot peening.

A feasibility study of a hypersonic real-gas facility

NASA Technical Reports Server (NTRS)

Gully, J. H.; Driga, M. D.; Weldon, W. F.

1987-01-01

A four month feasibility study of a hypersonic real-gas free flight test facility for NASA Langley Research Center (LARC) was performed. The feasibility of using a high-energy electromagnetic launcher (EML) to accelerate complex models (lifting and nonlifting) in the hypersonic, real-gas facility was examined. Issues addressed include: design and performance of the accelerator; design and performance of the power supply; design and operation of the sabot and payload during acceleration and separation; effects of high current, magnetic fields, temperature, and stress on the sabot and payload; and survivability of payload instrumentation during acceleration, flight, and soft catch.

Precision injection molding of freeform optics

NASA Astrophysics Data System (ADS)

Fang, Fengzhou; Zhang, Nan; Zhang, Xiaodong

2016-08-01

Precision injection molding is the most efficient mass production technology for manufacturing plastic optics. Applications of plastic optics in field of imaging, illumination, and concentration demonstrate a variety of complex surface forms, developing from conventional plano and spherical surfaces to aspheric and freeform surfaces. It requires high optical quality with high form accuracy and lower residual stresses, which challenges both optical tool inserts machining and precision injection molding process. The present paper reviews recent progress in mold tool machining and precision injection molding, with more emphasis on precision injection molding. The challenges and future development trend are also discussed.

On the origin of diverse aftershock mechanisms following the 1989 Loma Prieta earthquake

USGS Publications Warehouse

Kilb, Debi; Ellis, M.; Gomberg, J.; Davis, S.

1997-01-01

We test the hypothesis that the origin of the diverse suite of aftershock mechanisms following the 1989 M 7.1 Loma Prieta, California, earthquake is related to the post-main-shock static stress field. We use a 3-D boundary-element algorithm to calculate static stresses, combined with a Coulomb failure criterion to calculate conjugate failure planes at aftershock locations. The post-main-shock static stress field is taken as the sum of a pre-existing stress field and changes in stress due to the heterogeneous slip across the Loma Prieta rupture plane. The background stress field is assumed to be either a simple shear parallel to the regional trend of the San Andreas fault or approximately fault-normal compression. A suite of synthetic aftershock mechanisms from the conjugate failure planes is generated and quantitatively compared (allowing for uncertainties in both mechanism parameters and earthquake locations) to well-constrained mechanisms reported in the US Geological Survey Northern California Seismic Network catalogue. We also compare calculated rakes with those observed by resolving the calculated stress tensor onto observed focal mechanism nodal planes, assuming either plane to be a likely rupture plane. Various permutations of the assumed background stress field, frictional coefficients of aftershock fault planes, methods of comparisons, etc. explain between 52 and 92 per cent of the aftershock mechanisms. We can explain a similar proportion of mechanisms however by comparing a randomly reordered catalogue with the various suites of synthetic aftershocks. The inability to duplicate aftershock mechanisms reliably on a one-to-one basis is probably a function of the combined uncertainties in models of main-shock slip distribution, the background stress field, and aftershock locations. In particular we show theoretically that any specific main-shock slip distribution and a reasonable background stress field are able to generate a highly variable suite of failure planes such that quite different aftershock mechanisms may be expected to occur within a kilometre or less of each other. This scale of variability is less than the probable location error of aftershock earthquakes in the Loma Prieta region. We successfully duplicate a measure of the variability in the mechanisms of the entire suite of aftershocks. If static stress changes are responsible for the generation of aftershock mechanisms, we are able to place quantitative constraints on the level of stress that must have existed in the upper crust prior to the Loma Prieta rupture. This stress level appears to be too low to generate the average slip across the main-shock rupture plane. Possible reasons for this result range from incorrect initial assumptions of homogeneity in the background stress field, friction and fault geometry to driving stresses that arise from deeper in the crust or upper mantle. Alternatively, aftershock focal mechanisms may be determined by processes other than, or in addition to, static stress changes, such as pore-pressure changes or dynamic stresses.

Modeling the Temperature Rise at the Tip of a Fast Crack

DTIC Science & Technology

1989-08-01

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

Effect of coarctation of the aorta and bicuspid aortic valve on flow dynamics and turbulence in the aorta using particle image velocimetry

NASA Astrophysics Data System (ADS)

Keshavarz-Motamed, Zahra; Garcia, Julio; Gaillard, Emmanuel; Maftoon, Nima; Di Labbio, Giuseppe; Cloutier, Guy; Kadem, Lyes

2014-03-01

Blood flow in the aorta has been of particular interest from both fluid dynamics and physiology perspectives. Coarctation of the aorta (COA) is a congenital heart disease corresponding to a severe narrowing in the aortic arch. Up to 85 % of patients with COA have a pathological aortic valve, leading to a narrowing at the valve level. The aim of the present work was to advance the state of understanding of flow through a COA to investigate how narrowing in the aorta (COA) affects the characteristics of the velocity field and, in particular, turbulence development. For this purpose, particle image velocimetry measurements were conducted at physiological flow and pressure conditions, with three different aorta configurations: (1) normal case: normal aorta + normal aortic valve; (2) isolated COA: COA (with 75 % reduction in aortic cross-sectional area) + normal aortic valve and (3) complex COA: COA (with 75 % reduction in aortic cross-sectional area) + pathological aortic valve. Viscous shear stress (VSS), representing the physical shear stress, Reynolds shear stress (RSS), representing the turbulent shear stress, and turbulent kinetic energy (TKE), representing the intensity of fluctuations in the fluid flow environment, were calculated for all cases. Results show that, compared with a healthy aorta, the instantaneous velocity streamlines and vortices were deeply changed in the presence of the COA. The normal aorta did not display any regions of elevated VSS, RSS and TKE at any moment of the cardiac cycle. The magnitudes of these parameters were elevated for both isolated COA and complex COA, with their maximum values mainly being located inside the eccentric jet downstream of the COA. However, the presence of a pathologic aortic valve, in complex COA, amplifies VSS (e.g., average absolute peak value in the entire aorta for a total flow of 5 L/min: complex COA: = 36 N/m2; isolated COA = 19 N/m2), RSS (e.g., average peak value in the entire aorta for a total flow of 5 L/min: complex COA: = 84.6 N/m2; isolated COA = 44 N/m2) and TKE (e.g., average peak value in the entire aorta for a total flow of 5 L/min: complex COA: = 215 N/m2; isolated COA = 100 N/m2). This demonstrates that the pathological aortic valve strongly interacts with the COA. Findings of this study indicate that the presence of both a COA and a pathological aortic valve significantly alters hemodynamics in the aorta and thus might contribute to the progression of the disease in this region. This study can partially explain the complications associated in patients with COA, in the presence of a pathological aortic valve and the consequent adverse outcome post-surgery.

Biomechanical comparison of two different collar structured implants supporting 3-unit fixed partial denture: a 3-D FEM study.

PubMed

Meriç, Gökçe; Erkmen, Erkan; Kurt, Ahmet; Eser, Atilim; Ozden, Ahmet Utku

2012-01-01

The purpose of the study was to compare the effects of two distinct collar geometries of implants on stress distribution in the bone as well as in the fixture-abutment complex, in the framework and in the veneering material of 3-unit fixed partial denture (FPD). The 3-dimensional finite element analysis method was selected to evaluate the stress distribution in the system composed of 3-unit FPD supported by two different dental implant systems with two distinct collar geometries; microthread collar structure (MCS) and non-microthread collar structure (NMCS). In separate load cases, 300 N vertical, 150 N oblique and 60 N horizontal, forces were utilized to simulate the multidirectional chewing forces. Tensile and compressive stress values in the cortical and cancellous bone and von Mises stresses in the fixture-abutment complex, in the framework and veneering material, were simulated as a body and investigated separately. In the cortical bone lower stress values were found in the MCS model, when compared with NMCS. In the cancellous bone, lower stress values were observed in the NMCS model when compared with MCS. In the implant-abutment complex, highest von Mises stress values were noted in the NMCS model; however, in the framework and veneering material, highest stress values were calculated in MCS model. MCS implants when compared with NMCS implants supporting 3-unit FPDs decrease the stress values in the cortical bone and implant-abutment complex. The results of the present study will be evaluated as a base for our ongoing FEA studies focused on stress distribution around the microthread and non-microthread collar geometries with various prosthesis design.

Mononuclear nonheme iron(III) complexes that show superoxide dismutase-like activity and antioxidant effects against menadione-mediated oxidative stress.

PubMed

Hitomi, Yutaka; Iwamoto, Yuji; Kashida, Akihiro; Kodera, Masahito

2015-05-21

This communication describes the superoxide dismutase (SOD)-like activity of mononuclear iron(III) complexes with pentadentate monocarboxylamido ligands. The SOD activity can be controlled by the electronic nature of the substituent group on the ligand. The nitro-substituted complex showed clear cytoprotective activity against menadione-mediated oxidative stress in cultured cells.

Estimating fluid-induced stress change from observed deformation

DOE PAGES

Vasco, D. W.; Harness, Paul; Pride, Steve; ...

2016-12-19

Observed deformation is sensitive to a changing stress field within the Earth. There are, however, several impediments to a direct inversion of geodetic measurements for changes in stress. Estimating six independent components of stress change from a smaller number of displacement or strain components is inherently non-unique. The reliance upon surface measurements leads to a loss of resolution, due to the attenuation of higher spatial frequencies in the displacement field with distance from a source. Here, we adopt a technique suited to the estimation of stress changes due to the injection and/or withdrawal of fluids at depth. In this approachmore » the surface displacement data provides an estimate of the volume change responsible for the deformation, rather than stress changes themselves. The inversion for volume change is constrained by the fluid fluxes into and out of the reservoir. The distribution of volume change is used to calculate the displacements in the region above the reservoir. Estimates of stress change follow from differentiating the displacement field in conjunction with a geomechanical model of the o verburden. We also apply the technique to Interferometric Synthetic Aperture Radar (InSAR) observations gathered over a petroleum reservoir in the San Joaquin Valley of California. An analysis of the InSAR range changes reveals that the stress field in the overburden varies rapidly both in space and in time. The inferred stress variations are found to be compatible with the documented failure of a well in the field.« less

Estimating fluid-induced stress change from observed deformation

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

Vasco, D. W.; Harness, Paul; Pride, Steve

Observed deformation is sensitive to a changing stress field within the Earth. There are, however, several impediments to a direct inversion of geodetic measurements for changes in stress. Estimating six independent components of stress change from a smaller number of displacement or strain components is inherently non-unique. The reliance upon surface measurements leads to a loss of resolution, due to the attenuation of higher spatial frequencies in the displacement field with distance from a source. Here, we adopt a technique suited to the estimation of stress changes due to the injection and/or withdrawal of fluids at depth. In this approachmore » the surface displacement data provides an estimate of the volume change responsible for the deformation, rather than stress changes themselves. The inversion for volume change is constrained by the fluid fluxes into and out of the reservoir. The distribution of volume change is used to calculate the displacements in the region above the reservoir. Estimates of stress change follow from differentiating the displacement field in conjunction with a geomechanical model of the o verburden. We also apply the technique to Interferometric Synthetic Aperture Radar (InSAR) observations gathered over a petroleum reservoir in the San Joaquin Valley of California. An analysis of the InSAR range changes reveals that the stress field in the overburden varies rapidly both in space and in time. The inferred stress variations are found to be compatible with the documented failure of a well in the field.« less

High-frequency spectral falloff of earthquakes, fractal dimension of complex rupture, b value, and the scaling of strength on faults

USGS Publications Warehouse

Frankel, A.

1991-01-01

The high-frequency falloff ??-y of earthquake displacement spectra and the b value of aftershock sequences are attributed to the character of spatially varying strength along fault zones. I assume that the high frequency energy of a main shock is produced by a self-similar distribution of subevents, where the number of subevents with radii greater than R is proportional to R-D, D being the fractal dimension. In the model, an earthquake is composed of a hierarchical set of smaller earthquakes. The static stress drop is parameterized to be proportional to R??, and strength is assumed to be proportional to static stress drop. I find that a distribution of subevents with D = 2 and stress drop independent of seismic moment (?? = 0) produces a main shock with an ??-2 falloff, if the subevent areas fill the rupture area of the main shock. By equating subevents to "islands' of high stress of a random, self-similar stress field on a fault, I relate D to the scaling of strength on a fault, such that D = 2 - ??. Thus D = 2 corresponds to constant stress drop scaling (?? = 0) and scale-invariant fault strength. A self-similar model of aftershock rupture zones on a fault is used to determine the relationship between the b value, the size distribution of aftershock rupture zones, and the scaling of strength on a fault. -from Author

Hybrid immersed interface-immersed boundary methods for AC dielectrophoresis

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

Hossan, Mohammad Robiul; Department of Engineering and Physics, University of Central Oklahoma, Edmond, OK 73034-5209; Dillon, Robert

2014-08-01

Dielectrophoresis, a nonlinear electrokinetic transport mechanism, has become popular in many engineering applications including manipulation, characterization and actuation of biomaterials, particles and biological cells. In this paper, we present a hybrid immersed interface–immersed boundary method to study AC dielectrophoresis where an algorithm is developed to solve the complex Poisson equation using a real variable formulation. An immersed interface method is employed to obtain the AC electric field in a fluid media with suspended particles and an immersed boundary method is used for the fluid equations and particle transport. The convergence of the proposed algorithm as well as validation of themore » hybrid scheme with experimental results is presented. In this paper, the Maxwell stress tensor is used to calculate the dielectrophoretic force acting on particles by considering the physical effect of particles in the computational domain. Thus, this study eliminates the approximations used in point dipole methods for calculating dielectrophoretic force. A comparative study between Maxwell stress tensor and point dipole methods for computing dielectrophoretic forces are presented. The hybrid method is used to investigate the physics of dielectrophoresis in microfluidic devices using an AC electric field. The numerical results show that with proper design and appropriate selection of applied potential and frequency, global electric field minima can be obtained to facilitate multiple particle trapping by exploiting the mechanism of negative dielectrophoresis. Our numerical results also show that electrically neutral particles form a chain parallel to the applied electric field irrespective of their initial orientation when an AC electric field is applied. This proposed hybrid numerical scheme will help to better understand dielectrophoresis and to design and optimize microfluidic devices.« less

New Computer Automated Holo-Photoelastic Method For Measuring Planar Principal Stress Magnitudes And Orientation

NASA Astrophysics Data System (ADS)

Brown, G. M.; Sullivan, J. L.

1987-09-01

A complete experimental determination of the stress and strain fields in an arbitrary deformed structure is generally unavailable. However, for two dimensional elasticity problems, such determinations are possible since in those cases one needs only to solve for three stresses (two normal and one shear). In fact, such determinations have been conducted quite often. By using isochromatic and isoclinic photoelastic data, the shear difference and numerical iteration techniques (1) and the least squares techniques (2) have been successfully used for complete stress field determinations of two dimensional elasticity problems. Though the shear difference technique can be particularly sensitive to cumulative errors resulting from numerical integration, the least squares technique is not affected by this and appears to yield better accuracy. The methods just cited use both experimental data and one or more mechanics conditions(e.g., the equations of equilibrium) to determine the stress field. However, the stress field can also be obtained from experimental data alone for planar elasticity problems, if there is enough of it to solve for the three stresses. For example, the Moire* technique or the combination of isochromatic, isoclinic, and isopachic data (for transparent models) can be used for such determinations. Further, with the marriage of advanced image processing equipment to computers, such analyses using this type of data can be conveniently conducted. It is even possible that such analyses could be more accurate than those using the combined experimental/numerical techniques cited above. The purposes of this report are two fold: i) to describe a single apparatus for obtaining isochromatic, isopachic, and isoclinic results for complete stress field determinations of two dimensional transparent models, and ii) to compare experimental and theoretical stress field values for an antisymmetrically loaded beam obtained using that apparatus.

Evidence for possible relation between local irregularities in the horizondal deformation field and microseismic activity of the Mygdonian basin(Northern Greece)

NASA Astrophysics Data System (ADS)

Contadakis, M. E.; Leventakis, G.-A. N.

1992-12-01

Geodetic methods have been proved very useful tools for the detection and monitoring of the earth crustal deformation. Using the repeated measurements in the decade 1979-1990 of the 16-point trigonometric network, located in the seismic active area of the lake Volvi in Northern Greece, a continuous strain field was determined for the area and for each epoch of the corresponding surveys. The dominant characteristic of the deformation field of the area relates, in a way, to the system of the surface faults, which appeared after the string earthquake of June 21, 1978. In addition, there is local as well as time variation of the strain field which is well correlated with the microseismic activity of the area. That is, although there is a general tendency of a N-S horizontal extension in accordance with the direction of the stress field of the area, regions of contraction appear in places where microseismic activity has taken place before the epochs of the respective survey. A few shocks in these region, for which reliable fault plane solutions could be defined by Scordilis on 1985,show focal mechanisms conformable to the geodetic results. Seismicity and fault plane solutions, based on a micro-earthquake study of the region during March and April of 1984 by Hatzfeld et al. with the help of a temporary network of 29 portable stations shows a rather complex pattern. The proposed model for the formation and the evolution of a complex graben system conform qualitatively to the geodetic results

Complex monitoring and alert network for electromagnetic, infrasound, acoustic seismotectonic phenomena

NASA Astrophysics Data System (ADS)

-Emilian Toader, Victorin; Moldovan, Iren-Adelina; Constantin, Ionescu

2014-05-01

The Romanian seismicity recorded in 2013 three important events: the largest seismic "silence", the shortest sequence of two earthquakes greater than 4.8R in less than 14 days after the "Romanian National Institute for Earth Physics" (NIEP) developed a digital network, and a very high crustal activity in Galati area. We analyze the variations of the telluric currents and local magnetic field, variations of the atmospheric electrostatic field, infrasound, temperature, humidity, wind speed and direction, atmospheric pressure, variations in the earth crust with inclinometers and animal behavior. The general effect is the first high seismic energy discontinuity that could be a precursor factor. Since 1977 Romania did not register any important earthquake that would generate a sense of fear among the population. In parallel with the seismic network NIEP developed a magneto-telluric, bioseismic, VLF and acoustic network. A large frequency spectrum is covered for mechanical vibration, magnetic and electric field with ground and air sensors. Special software was designed for acquisition, analysis and real time alert using internet direct connection, web page, email and SMS. Many examples show the sensitivity of telluric current, infrasound, acoustic records (from air-ground), and the effect of tectonic stress on the magnetic field or ground deformation. The next update of the multidisciplinary monitoring network will include measurement of ionization, radon emission, sky color, solar radiation and extension of infrasound and VL/LF equipment. NOAA Space Weather satellites transmit solar activity magnetic field data, X ray flux, electron, and proton flux information useful for complex analysis.

Measuring erosion rates of contaminated cohesive sediments using laboratory and in-situ devices in combination: experiences of investigations in River Elbe and Saale

NASA Astrophysics Data System (ADS)

Noack, Markus; Gerbersdorf, Sabine; Hillebrand, Gudrun; Kasimir, Petra; Wieprecht, Silke

2014-05-01

Deposition of contaminated sediments in areas of no or low flow velocity such as groyne fields or impounded river stretches represent a significant thread to water quality if long-deposited sediments are remobilized during flood and storm events. In contrast to non-cohesive sediments the dynamics of cohesive sediments is not fully understood mainly because of multiple physico-chemical factors and variable biological influence. Hence, site-specific investigations are required to develop water management strategies as well as modelling approaches to predict the dynamic behavior of cohesive material. The Institute for Modelling Hydraulic and Environmental Systems (IWS, University of Stuttgart) has a strong experience in developing measuring strategies and techniques to deal with the complex interactions between biological and sedimentary characteristics regarding erosion and remobilization of cohesive material. Specifically, the detection of critical shear stresses for incipient motion of cohesive particles has been realized for both one laboratory device (SETEG) and an in-situ device. For site-specific investigations ideally both methods should be combined. The first method (SETEG) includes the on-site extraction of sediment cores allowing for depth-dependent analysis under controlled laboratory conditions, while the second one measures the surface only but reduces possible artifacts due to sediment withdrawal and transport. Both methods were applied at groyne fields and deposition areas of the River Elbe and River Saale, which are both heavily affected by pollution of anthropogenic contaminants mainly originating from the release of chemical industry before 1990. Next to the detection of critical shear stresses and erosion rates, further sedimentary attributes are analyzed such as particle size distribution, water content and density as well as biological attributes such as TOC and microbial mass. The analyses of the sediment cores result in vertical profiles for all sedimentary and biological parameters giving highly complementary insights into the rather complex erosion and resuspension properties of cohesive fine sediments. Further, the detected critical shear stress between the in-situ and laboratory device are compared and especially in case of deviations the biological parameters can be highly beneficial to explain the measured critical shear stress and variances between in situ and laboratory devices. The investigations in both study sites have shown that the joint application of the measuring devices gives comprehensive information which is required to determine the risk of remobilization properly. Keywords: cohesive sediments, critical shear stress, contaminated sediments, incipient motion, biostabilization

Descriptions of crack growth behaviors in glass-ZrO2 bilayers under thermal residual stresses.

PubMed

Belli, Renan; Wendler, Michael; Zorzin, José I; Petschelt, Anselm; Tanaka, Carina B; Meira, Josete; Lohbauer, Ulrich

2016-09-01

This study was intended to separate residual stresses arising from the mismatch in coefficients of thermal expansion between glass and zirconia (ZrO2) from those stresses arising solely from the cooling process. Slow crack growth experimentes were undertaken to demonstrate how cracks grow in different residual stress fields. Aluminosilicate glass discs were sintered onto ZrO2 to form glass-ZrO2 bilayers. Glass discs were allowed to bond to the ZrO2 substrate during sintering or prevented from bonding by means of coating the ZrO2 with a thin boron nitrade coating. Residual stress gradients on "bonded" and "unbonded" bilayers were assessed using birefringence measurements. Unbonded glass discs were further tested under biaxial flexure in dynamic fatigue conditions in order to evaluate the effect of residual stress on the slow crack growth behavior. When fast-ccoling was induced, residual tensile stresses on the glass increased significantly on the side toward the ZrO2 substrate. By allowing the bond between glass and ZrO2, those tensile stresses observed in unbonded specimens are overwhelmed by the contraction mismatch stresses between the ZrO2 substrate and the glassy overlayer. Specimens containing residual tensile stresses on the bending surface showed a time-dependent strength increase in relation to stress-free annealed samples in the dynamic biaxial bending test, with this effect being dependent on the magnitude of the residual tensile stress. The phenomenon observed is explained here on the basis of the water toughening effect, in which water diffuses into the glass promoting local swelling. An additional residual tensile stress at the crack tip adds an applied-stress-independent (Kres) term to the total tip stress intensity factor (Ktip), increasing the stress-enhanced diffusion and the shielding of the crack tip through swelling of the crack faces. Residual stresses in the glass influence the crack growth behavior of veneered-ZrO2 bilayered dental prostheses. The role of water in crack growth might be of higher complexity when residual stresses are present in the glass layer. Copyright © 2016 The Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

Two phase modeling of the influence of plastic strain on the magnetic and magnetostrictive behaviors of ferromagnetic materials

NASA Astrophysics Data System (ADS)

Hubert, Olivier; Lazreg, Said

2017-02-01

A growing interest of automotive industry in the use of high performance steels is observed. These materials are obtained thanks to complex manufacturing processes whose parameters fluctuations lead to strong variations of microstructure and mechanical properties. The on-line magnetic non-destructive monitoring is a relevant response to this problem but it requires fast models sensitive to different parameters of the forming process. The plastic deformation is one of these important parameters. Indeed, ferromagnetic materials are known to be sensitive to stress application and especially to plastic strains. In this paper, a macroscopic approach using the kinematic hardening is proposed to model this behavior, considering a plastic strained material as a two phase system. Relationship between kinematic hardening and residual stress is defined in this framework. Since stress fields are multiaxial, an uniaxial equivalent stress is calculated and introduced inside the so-called magneto-mechanical multidomain modeling to represent the effect of plastic strain. The modeling approach is complemented by many experiments involving magnetic and magnetostrictive measurements. They are carried out with or without applied stress, using a dual-phase steel deformed at different levels. The main interest of this material is that the mechanically hard phase, soft phase and the kinematic hardening can be clearly identified thanks to simple experiments. It is shown how this model can be extended to single phase materials.

A numerical study of crack tip constraint in ductile single crystals

NASA Astrophysics Data System (ADS)

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

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

The structure of internal stresses in the uncompacted ice cover

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

Sukhorukov, K.K.

1995-12-31

Interactions between engineering structures and sea ice cover are associated with an inhomogeneous space/time field of internal stresses. Field measurements (e.g., Coon, 1989; Tucker, 1992) have revealed considerable local stresses depending on the regional stress field and ice structure. These stresses appear in different time and space scales and depend on rheologic properties of the ice. To estimate properly the stressed state a knowledge of a connection between internal stress components in various regions of the ice cover is necessary. To develop reliable algorithms for estimates of ice action on engineering structures new experimental data are required to take intomore » account both microscale (comparable with local ice inhomogeneities) and small-scale (kilometers) inhomogeneities of the ice cover. Studies of compacted ice (concentration N is nearly 1) are mostly important. This paper deals with the small-scale spatial distribution of internal stresses in the interaction zone between the ice covers of various concentrations and icebergs. The experimental conditions model a situation of the interaction between a wide structure and the ice cover. Field data on a drifting ice were collected during the Russian-US experiment in Antarctica WEDDELL-I in 1992.« less

[Effects of psychological stress on performances in open-field test of rats and tyrosine's modulation].

PubMed

Chen, Wei-Qiang; Cheng, Yi-Yong; Li, Shu-Tian; Hong, Yan; Wang, Dong-Lan; Hou, Yue

2009-02-01

To explore the effects of different doses of tyrosine modulation on behavioral performances in open field test of psychological stress rats. The animal model of psychological stress was developed by restraint stress for 21 days. Wistar rats were randomly assigned to five groups (n = 10) as follows: control group (CT), stress control group (SCT), low, medium and high-doses of tyrosine modulation stress groups (SLT, SMT and SIT). The changes of behavioral performances were examined by open-field test. Serum levels of cortisol, norepinephrine and dopamine were also detected. The levels of serum cortisol were all increased obviously in the four stress groups, and their bodyweight gainings were diminished. The behavioral performances of SCT rats in open-field test were changed significantly in contrast to that of CT rats. However, The behavioral performances of SMT and SHT rats were not different from that of CT rats. In addition, the serum levels of norepinephrine and dopamine were downregulated obviously in SCT and SLT groups, and no differences were observed in other groups. Psychological stress can impair body behavioral performances, and moderate tyrosine modulation may improve these abnormal changes. The related mechanisms may be involved with the changes of norepinephrine and dopamine.

The Cause of the Cauca, Colombia, Cluster of Intermediate-Depth Earthquakes From Earthquake Relocation and Focal Mechanisms

NASA Astrophysics Data System (ADS)

Warren, L. M.; Chang, Y.; Prieto, G. A.

2016-12-01

In subducting slabs, a high seismicity rate in a concentrated volume (an earthquake cluster) is often associated with geometric complexities such as slab detachment, tearing, or contortions. The intermediate-depth Cauca, Colombia, cluster (3.5°N-5.5°N), in contrast, appears to be located in a slab without such complexities. However, previous constraints on the slab geometry are based on global data. We use regional data to investigate the cause of the Cauca cluster by estimating its geometry from earthquake relocations and stress regime from focal mechanism calculations and stress inversions. The Cauca segment of the Nazca Plate is characterized by relatively sparse seismicity away from the cluster and a narrow volcanic arc. To the northeast of the Cauca cluster, six active volcanoes are concentrated within an 80-km along-trench distance and are isolated 180 km from the rest of the northern Andes volcanic arc. The Colombian National Seismic Network, from Jan 2010 to Mar 2014, reports 433 earthquakes in the cluster at depths of 50-200 km with local magnitudes ranging from 2.0-4.7. Earthquake relocations show a continuous 20-km-thick seismic zone dipping at 33°-43°, with the angle increasing to the south. In addition, earthquakes locate in two columns that extend normal to the slab and into the mantle wedge. The focal mechanisms show various types, including down-dip extension, strike slip, and trench-parallel compression, but are consistent with a predominantly down-dip extensional stress field. The maximum and intermediate stress axes are interchangeable because of their similar magnitudes. The down-dip extensional stress regime may expel dehydrated fluid from the slab into the mantle wedge. As the fluid moves through the mantle wedge, it may generate hydrofractures and the observed mantle-wedge earthquakes. The fluid in the mantle wedge may be transported along the trench, from the steeper southern section to the more shallowly-dipping northern section, and cause the volcanoes to the northeast of the Cauca cluster. The Cauca cluster, unlike most clusters, is not associated with a complex slab geometry. Instead, its high seismicity rate may result from a high dehydration rate in the slab and conditions that promote fluid migration into and earthquakes in the mantle wedge.

Swim stress, motion, and deformation of active matter: effect of an external field.

PubMed

Takatori, Sho C; Brady, John F

2014-12-21

We analyze the stress, dispersion, and average swimming speed of self-propelled particles subjected to an external field that affects their orientation and speed. The swimming trajectory is governed by a competition between the orienting influence (i.e., taxis) associated with the external (e.g., magnetic, gravitational, thermal, nutrient concentration) field versus the effects that randomize the particle orientations (e.g., rotary Brownian motion and/or an intrinsic tumbling mechanism like the flagella of bacteria). The swimmers' motion is characterized by a mean drift velocity and an effective translational diffusivity that becomes anisotropic in the presence of the orienting field. Since the diffusivity yields information about the micromechanical stress, the anisotropy generated by the external field creates a normal stress difference in the recently developed "swim stress" tensor [Takatori, Yan, and Brady, Phys. Rev. Lett., 2014]. This property can be exploited in the design of soft, compressible materials in which their size, shape, and motion can be manipulated and tuned by loading the material with active swimmers. Since the swimmers exert different normal stresses in different directions, the material can compress/expand, elongate, and translate depending on the external field strength. Such an active system can be used as nano/micromechanical devices and motors. Analytical solutions are corroborated by Brownian dynamics simulations.

Mechanisms mediating plant distributions across estuarine landscapes in a low-latitude tidal estuary.

PubMed

Guo, Hongyu; Pennings, Steven C

2012-01-01

Understanding of how plant communities are organized and will respond to global changes requires an understanding of how plant species respond to multiple environmental gradients. We examined the mechanisms mediating the distribution patterns of tidal marsh plants along an estuarine gradient in Georgia (USA) using a combination of field transplant experiments and monitoring. Our results could not be fully explained by the "competition-to-stress hypothesis" (the current paradigm explaining plant distributions across estuarine landscapes). This hypothesis states that the upstream limits of plant distributions are determined by competition, and the downstream limits by abiotic stress. We found that competition was generally strong in freshwater and brackish marshes, and that conditions in brackish and salt marshes were stressful to freshwater marsh plants, results consistent with the competition-to-stress hypothesis. Four other aspects of our results, however, were not explained by the competition-to-stress hypothesis. First, several halophytes found the freshwater habitat stressful and performed best (in the absence of competition) in brackish or salt marshes. Second, the upstream distribution of one species was determined by the combination of both abiotic and biotic (competition) factors. Third, marsh productivity (estimated by standing biomass) was a better predictor of relative biotic interaction intensity (RII) than was salinity or flooding, suggesting that productivity is a better indicator of plant stress than salinity or flooding gradients. Fourth, facilitation played a role in mediating the distribution patterns of some plants. Our results illustrate that even apparently simple abiotic gradients can encompass surprisingly complex processes mediating plant distributions.

A Infrared Absorption Study of Dopant-Hydrogen Complexes in Semiconductors

NASA Astrophysics Data System (ADS)

Kozuch, David Michael

1992-01-01

Hydrogen passivation of shallow electrical dopants in semiconductors has been investigated. In particular, the passivation of the shallow dopants tin, carbon, and silicon in gallium arsenide has been studied via Fourier transform infrared spectroscopy, thermal annealing, Hall effect, secondary ion mass spectroscopy, and uniaxial stress. The bond-stretching and bond-wagging vibrational modes of the rm Sn_{Ga} - H complex in GaAs have been identified at 1327.8 cm^{-1} and 967.7 cm ^{-1}, respectively. The presence of hydrogen in the defect pair is confirmed by the deuterium -shifted bond-stretching signal at 746.6 cm^ {-1}. Infrared and Hall data correlated the passivation of Sn_{rm Ga } donors with the formation of the rm Sn_{Ga} - H complexes. A series of isochronal anneals probed the thermal stability of the complex. Arguments supporting an antibonding configuration for the rm Sn_{Ga} - H complex are presented. Infrared measurements on highly carbon doped epi -layers reveal new absorption signals at 2643, 2651, and 2688 cm^{-1} in addition to the previously identified rm C_ {As} - H stretching vibration at 2636 cm^{-1}. These new signals are related to a family of carbon-hydrogen complexes: rm C_{x} - H. Deuterium -shifted counterparts for all these signals have been observed for the first time. Sources of hydrogen have been traced to the metalorganic precursors and carrier gas used during epi-layer growth. Hydrogen-containing annealing ambients were surprisingly effective for introducing hydrogen into the epi-layers. Several atomic arrangements for the new rm C_{x} - H complexes have been considered with the most likely candidate being a rm C_{As} - H complex perturbed by another C_{rm As} acceptor in a second nearest neighbor position. The first uniaxial stress measurements have been performed on the rm Si_{As} - H complex in GaAs. The stress-induced frequency shifts and the intensity ratios of the stress-split components of the 2094.45 cm^{-1} stretching frequency reveal that the complex has trigonal symmetry. Reorientation of the stress-aligned complexes occurred by thermally activated jumps of the hydrogen atom with an activation energy of E_{rm A} = 0.26 eV. The piezospectroscopic tensor of the rm Si_{As} - H complex has been determined. The similarities between the stress data for the rm Si_{As } - H complex and the well-studied B - H complex in silicon suggest a bond-centered configuration for the rm Si_{As} - H defect pair.

Copper-complexing ligands produced by an intact estuarine microbial community in response to copper stress.

NASA Astrophysics Data System (ADS)

Bingham, J.; Dryden, C.; Gordon, A.

2002-12-01

Copper is both an important nutrient and a pollutant in the marine environment. By studying the interactions between microorganisms and copper in the Elizabeth River (VA), home to a major Naval Base, we field tested the hypothesis that picoplankton and/or bacterioplankton produce strong, copper-complexing ligands in response to elevated copper concentrations. A simple light/ dark test was used to distinguish between heterotrophic and phototrophic ligand production. Samples were bottled and moored, submerged one meter, for a week. Direct counts using DAPI stain and epiflourescence were conducted to find concentrations of picoplankton and bacterioplankton. Using cathodic stripping voltammetry, we found the total copper concentrations, and then from a titration of the ligands by copper, the ligand concentrations and conditional stability constants were obtained. The Elizabeth River naturally had between 10-20 nM total dissolved copper concentrations. However when copper complexation was considered we found that the levels of bio-available Cu(II) ions were much lower. In fact in the natural samples the levels were not high enough to affect the relative reproductive rates of several microorganisms. Naturally there was a 50 nM "buffer zone" of ligand to total dissolved copper concentration. Furthermore, when stressed with excess copper, healthy picoplankton produced enough ligand to alleviate toxicity, and rebuild the buffer zone. However bacterioplankton only produced enough ligand so that they were no longer affected. Therefore, intact estuarine communities regulate copper bioavailability and toxicity with ligand production.

Exploring the role of flood transience in coarse bed load sediment transport

NASA Astrophysics Data System (ADS)

Phillips, C. B.; Singer, M. B.; Hill, K. M.; Paola, C.

2015-12-01

The rate of bed load transport under steady flow is known to vary both spatially and temporally due to various hydrologic and granular phenomena. Grain size distributions and riverbed properties (packing, imbrication, etc.) are known to affect flux for a particular value of applied flow stress, while hydrology is mainly assumed to control the magnitude of the applied bed stress above the threshold for bed material entrainment. The prediction of bed load sediment transport in field settings is further complicated by the inherent transience in flood hydrology, but little is known about how such flood transience influences bed load flux over a range of applied bed stress. Here we investigate the role of flood transience for gravel bed load transport through controlled laboratory experiments in a 28 m long 0.5 meter wide flume. We explore transient flow as the combination of unsteady and intermittent flow, where unsteady flow varies in magnitude over a given duration, and intermittent flow is characterized by turning the flow on and off. We systematically vary these details of flood hydrographs from one experiment to the next, and monitor the bed load as it varies with water discharge in real time by measuring sediment flux and tracking particles. We find that even with a narrow unimodal grain size distribution and constant sediment supply we observe hysteresis in bed load flux, different thresholds for entrainment and distrainment for the rising and falling limbs of a flood, and a threshold of entrainment that can vary one flood hydrograph to the next. Despite these complex phenomena we find that the total bed load transported for each flood plots along a linear trend with the integrated excess stress, consistent with prior field results. These results suggest that while the effects of transient flow and the shape of the hydrograph are measurable, they are second-order compared to the integrated excess stress.

Comparative Study of Earthquake Clustering in Relation to Hydraulic Activities at Geothermal Fields in California

NASA Astrophysics Data System (ADS)

Martínez-Garzón, P.; Zaliapin, I. V.; Ben-Zion, Y.; Kwiatek, G.; Bohnhoff, M.

2017-12-01

We investigate earthquake clustering properties from three geothermal reservoirs to clarify how earthquake patterns respond to hydraulic activities. We process ≈ 9 years from four datasets corresponding to the Geysers (both the entire field and a local subset), Coso and Salton Sea geothermal fields, California. For each, the completeness magnitude, b-value and fractal dimension are calculated and used to identify seismicity clusters using the nearest-neighbor approach of Zaliapin and Ben-Zion [2013a, 2013b]. Estimations of temporal evolution of different clustering properties in relation to hydraulic parameters point to different responses of earthquake dynamics to hydraulic operations in each case study. The clustering at the Geysers at local scale and Salton Sea are most and least affected by hydraulic activities, respectively. The response of the earthquake clustering from different datasets to the hydraulic activities may reflect the regional seismo-tectonic complexity as well as the dimension of the geothermal activities performed (e.g. number of active wells and superposition of injection + production activities).Two clustering properties significantly respond to hydraulic changes across all datasets: the background rates and the proportion of clusters consisting of a single event. Background rates are larger at the Geysers and Coso during high injection-production periods, while the opposite holds for the Salton Sea. This possibly reflects the different physical mechanisms controlling seismicity at each geothermal field. Additionally, a lower proportion of singles is found during time periods with higher injection-production rates. This may reflect decreasing effective stress in areas subjected to higher pore pressure and larger earthquake triggering by stress transfer.

Influence of the Roof Movement Control Method on the Stability of Remnant

NASA Astrophysics Data System (ADS)

Adach-Pawelus, Karolina

2017-12-01

In the underground mines, there are geological and mining situations that necessitate leaving behind remnants in the mining field. Remnants, in the form of small, irregular parcels, are usually separated in the case of: significant problems with maintaining roof stability, high rockburst hazard, the occurrence of complex geological conditions and for random reasons (ore remnants), as well as for economic reasons (undisturbed rock remnants). Remnants left in the mining field become sites of high stress values concentration and may affect the rock in their vicinity. The values of stress inside the remnant and its vicinity, as well as the stability of the remnant, largely depend on the roof movement control method used in the mining field. The article presents the results of the numerical analysis of the influence of roof movement control method on remnant stability and the geomechanical situation in the mining field. The numerical analysis was conducted for the geological and mining conditions characteristic of Polish underground copper mines owned by KGHM Polska Miedz S.A. Numerical simulations were performed in a plane strain state by means of Phase 2 v. 8.0 software, based on the finite element method. The behaviour of remnant and rock mass in its vicinity was simulated in the subsequent steps of the room and pillar mining system for three types of roof movement control method: roof deflection, dry backfill and hydraulic backfill. The parameters of the rock mass accepted for numerical modelling were calculated by means of RocLab software on the basis of the Hoek-Brown classification. The Mohr-Coulomb strength criterion was applied.

High-Precision Locations and the Stress Field from Instrumental Seismicity, Moment Tensors, and Short-Period Mechanisms through the Mina Deflection, Central Walker Lane

NASA Astrophysics Data System (ADS)

Ruhl, C. J.; Smith, K. D.

2012-12-01

The Mina Deflection (MD) region of the central Walker Lane of eastern California and western Nevada, is a complex zone of northeast-trending normal, and primarily left-lateral strike-slip to oblique-slip faulting that separates the Southern Walker Lane (SWL) from a series of east-tilted normal fault blocks in the Central Walker Lane (CWL) (Faulds and Henry, 2008; Surpless, 2008). The MD accommodates the transfer of right-lateral strike-slip motion from northwest-striking faults in the SWL to a series of left-stepping northwest-striking right-lateral strike-slip faults in the CWL, east of the Wassuk Range near Hawthorne, NV. The ~50 km wide ~80 km long right-step is a distinct transition in regional physiography that has been attributed to strain accommodation through pre-Cenozoic lithospheric structures. Several slip transfer mechanisms have been proposed within the MD, from clockwise rotation of high-angle fault blocks (Wesnousky, 2005), to low-angle displacement within the Silver Peak-Lone Mountain complex (Oldow et al., 2001), and curved fault arrays associated with localized basins and tectonic depressions (Ferranti et al., 2009). The region has been a regular source of M4+ events, the most recent being an extended sequence that included twenty-seven M 3.5+ earthquakes (largest event M 4.6) south of Hawthorne in 2011. These earthquakes (< 5 km depth) define shallow W-dipping (dip ~56°) and NW-dipping (dip ~70°) normal faulting constrained by moment tensor (MT) solutions and earthquake relocations. Temporary stations deployed in the source area provide good control. A distributed sequence in 2004, between Queen Valley and Mono Lake, primarily associated with the Huntoon Valley fault, included three M 5+ left-lateral strike-slip faulting events. A 1997 sequence in northern Fish Lake Valley (east of the White Mountains), with mainshock Mw 5.3 (Ichinose et al., 2003), also showed high-angle northeast-striking left-lateral strike-slip motion. Historical events include the 1934 M 6.5 Excelsior Mountains event south of Mina, NV, and the 1932 M 7.1 Cedar Mountains earthquake east of the Pilot Mountains. Another persistent feature in the seismicity is an ~40 km long arcuate distribution of activity extending from approximately Queen Valley, north of the White Mountains, to Mono Lake that appears to reflect a southwestern boundary to northeast-striking structures in the MD. Here we develop high-precision relocations of instrumental seismicity in the MD from 1984 through 2012, including relocations of the 2004 sequence, and account for the historical seismic record. MT solutions from published reports and computed from recent M 3.5+ earthquakes as well as available and developed short-period focal mechanisms are compiled to evaluate the stress field to assess mechanisms of slip accommodation. Based on the complex distribution of fault orientations, the stress field varies locally northward from the SWL throughout the MD; however, in many cases, fault plane alignments can be isolated from high-precision locations, providing better constraints on stress and slip orientations.

Full-field fabric stress mapping by micro Raman spectroscopy in a yarn push-out test.

PubMed

Lei, Z K; Qin, F Y; Fang, Q C; Bai, R X; Qiu, W; Chen, X

2018-02-01

The full-field stress distribution of a two-dimensional plain fabric was mapped using micro Raman spectroscopy (MRS) through a novel yarn push-out test, simulating a quasi-static projectile impact on the fabric. The stress-strain relationship for a single yarn was established using a digital image correlation method in a single-yarn tensile test. The relationship between Raman peak shift and aramid Kevlar 49 yarn stress was established using MRS in a single-yarn tensile test. An out-of-plane loading test was conducted on an aramid Kevlar 49 plain fabric, and the yarn stress was measured using MRS. From the full-field fabric stress distribution, it can be observed that there is a cross-shaped distribution of high yarn stress; this result would be helpful in further studies on load transfer on a fabric during a projectile impact.

Effects of stress on heart rate complexity--a comparison between short-term and chronic stress.

PubMed

Schubert, C; Lambertz, M; Nelesen, R A; Bardwell, W; Choi, J-B; Dimsdale, J E

2009-03-01

This study examined chronic and short-term stress effects on heart rate variability (HRV), comparing time, frequency and phase domain (complexity) measures in 50 healthy adults. The hassles frequency subscale of the combined hassles and uplifts scale (CHUS) was used to measure chronic stress. Short-term stressor reactivity was assessed with a speech task. HRV measures were determined via surface electrocardiogram (ECG). Because respiration rate decreased during the speech task (p<.001), this study assessed the influence of respiration rate changes on the effects of interest. A series of repeated-measures analyses of covariance (ANCOVA) with Bonferroni adjustment revealed that short-term stress decreased HR D2 (calculated via the pointwise correlation dimension PD2) (p<.001), but increased HR mean (p<.001), standard deviation of R-R (SDRR) intervals (p<.001), low (LF) (p<.001) and high frequency band power (HF) (p=.009). Respiratory sinus arrhythmia (RSA) and LF/HF ratio did not change under short-term stress. Partial correlation adjusting for respiration rate showed that HR D2 was associated with chronic stress (r=-.35, p=.019). Differential effects of chronic and short-term stress were observed on several HRV measures. HR D2 decreased under both stress conditions reflecting lowered functionality of the cardiac pacemaker. The results confirm the importance of complexity metrics in modern stress research on HRV.

Development of a numerical procedure for mixed mode K-solutions and fatigue crack growth in FCC single crystal superalloys

NASA Astrophysics Data System (ADS)

Ranjan, Srikant

2005-11-01

Fatigue-induced failures in aircraft gas turbine and rocket engine turbopump blades and vanes are a pervasive problem. Turbine blades and vanes represent perhaps the most demanding structural applications due to the combination of high operating temperature, corrosive environment, high monotonic and cyclic stresses, long expected component lifetimes and the enormous consequence of structural failure. Single crystal nickel-base superalloy turbine blades are being utilized in rocket engine turbopumps and jet engines because of their superior creep, stress rupture, melt resistance, and thermomechanical fatigue capabilities over polycrystalline alloys. These materials have orthotropic properties making the position of the crystal lattice relative to the part geometry a significant factor in the overall analysis. Computation of stress intensity factors (SIFs) and the ability to model fatigue crack growth rate at single crystal cracks subject to mixed-mode loading conditions are important parts of developing a mechanistically based life prediction for these complex alloys. A general numerical procedure has been developed to calculate SIFs for a crack in a general anisotropic linear elastic material subject to mixed-mode loading conditions, using three-dimensional finite element analysis (FEA). The procedure does not require an a priori assumption of plane stress or plane strain conditions. The SIFs KI, KII, and KIII are shown to be a complex function of the coupled 3D crack tip displacement field. A comprehensive study of variation of SIFs as a function of crystallographic orientation, crack length, and mode-mixity ratios is presented, based on the 3D elastic orthotropic finite element modeling of tensile and Brazilian Disc (BD) specimens in specific crystal orientations. Variation of SIF through the thickness of the specimens is also analyzed. The resolved shear stress intensity coefficient or effective SIF, Krss, can be computed as a function of crack tip SIFs and the resolved shear stress on primary slip planes. The maximum value of Krss and DeltaKrss was found to determine the crack growth direction and the fatigue crack growth rate respectively. The fatigue crack driving force parameter, DeltaK rss, forms an important multiaxial fatigue damage parameter that can be used to predict life in superalloy components.

Ultrasonic measurement of stress in 2219-T87 aluminum plate

NASA Technical Reports Server (NTRS)

Clotfelter, W. N.; Risch, E. R.

1976-01-01

The basic relationship of ultrasonic signal velocity to directional subsurface stress is reviewed. Inappropriateness of dependency on a single correlative value of constant for a three dimensional stress field in metallic materials is discussed. Implementation of conventional ultrasonic nondestructive testing capabilities integrated to provide a composite technique for the measurement of orthogonal stress components is described, and the procedures for performing the preparatory calibration and subsequent stress field measurements are presented. In conclusion, the prime effect of stress on ultrasonic signal velocity occurs only in the direction of material excitation or particle motion.

Profiled Roller Stress/Fatigue Life Analysis Methodology and Establishment of an Appropriate Stress/Life Exponent

NASA Technical Reports Server (NTRS)

1997-01-01

The objective of this work was to determine the three dimensional volumetric stress field, surface pressure distribution and actual contact area between a 0.50" square roller with different crown profiles and a flat raceway surface using Finite Element Analysis. The 3-dimensional stress field data was used in conjunction with several bearing fatigue life theories to extract appropriate values for stress-life exponents. Also, results of the FEA runs were used to evaluate the laminated roller model presently used for stress and life prediction.

True-triaxial experimental seismic velocities linked to an in situ 3D seismic velocity structure

NASA Astrophysics Data System (ADS)

Tibbo, M.; Young, R. P.

2017-12-01

Upscaling from laboratory seismic velocities to in situ field seismic velocities is a fundamental problem in rock physics. This study presents a unique situation where a 3D velocity structure of comparable frequency ranges is available both in situ and experimentally. The in situ data comes from the Underground Research Laboratory (URL) located in Manitoba, Canada. The velocity survey and oriented, cubic rock sample, are from the 420m level of the mine, where the geology is a homogeneous and isotropic granite. The triaxial in situ stress field at this level was determined and the Mine-by tunnel was excavated horizontally to maximize borehole break out. Ultrasonic velocity measurements for P-, S1-,and S2-waves were done in the tunnel sidewall, ceiling and far-field rock mass.The geophysical imaging cell (GIC) used in this study allows for true triaxial stress (σ1 > σ2 > σ3). Velocity surveys for P-, S1-, and S2-wave can be acquired along all three axes, and therefore the effects of σ1, σ2, σ3 on the velocity-stress relationship is obtained along all 3 axes. The cubic (80 mm) granite sample was prepared oriented to the in situ principle stress axis in the field. The stress path of the sample extraction from in situ stress was modeled in FLAC 3D (by Itasca inc ), and then reapplied in the GIC to obtain the laboratory velocities at in situ stress. Both laboratory and field velocities conclude the same maximum velocity axis, within error, to be along σ2 at 5880±60 m/s for P-wave. This deviation from the expected fast axis being σ1, is believed to be caused by an aligned microcrack fabric. The theory of acoustoelasticity, the dependence of acoustic wave velocity on stresses in the propagating isotropic medium, is applied to the borehole hoop and radial stresses produced by the Mine-by tunnel. The acoustoelastic effect involves determining the linear (second-order) and nonlinear (third-order) elastic constants, which are derived from the velocity-stress slopes obtained from both uniaxial and hydrostatic stress tests performed on the granite. The acoustoelastic model produces the in situ far field P-wave velocity, as well as similar near borehole field velocities. In summary, this study compares a 3D field and laboratory velocity structure, and shows the potential of the theory of acoustoelasticity for velocity-stress inversion.

Model-based image analysis of a tethered Brownian fibre for shear stress sensing

PubMed Central

2017-01-01

The measurement of fluid dynamic shear stress acting on a biologically relevant surface is a challenging problem, particularly in the complex environment of, for example, the vasculature. While an experimental method for the direct detection of wall shear stress via the imaging of a synthetic biology nanorod has recently been developed, the data interpretation so far has been limited to phenomenological random walk modelling, small-angle approximation, and image analysis techniques which do not take into account the production of an image from a three-dimensional subject. In this report, we develop a mathematical and statistical framework to estimate shear stress from rapid imaging sequences based firstly on stochastic modelling of the dynamics of a tethered Brownian fibre in shear flow, and secondly on a novel model-based image analysis, which reconstructs fibre positions by solving the inverse problem of image formation. This framework is tested on experimental data, providing the first mechanistically rational analysis of the novel assay. What follows further develops the established theory for an untethered particle in a semi-dilute suspension, which is of relevance to, for example, the study of Brownian nanowires without flow, and presents new ideas in the field of multi-disciplinary image analysis. PMID:29212755

Study on Calculation Model of Culvert Soil Pressure

NASA Astrophysics Data System (ADS)

Liu, Jing; Tian, Xiao-yan; Gao, Xiao-mei

2017-09-01

Culvert diseases are prevalent in highway engineering. There are many factors involved in the occurrence of the disease, and the problem is complex. However, the design cannot accurately determine the role of the soil pressure on the culvert is the main reason to the disease. Based on the theoretical analysis and field test, this paper studies the characteristics of the stress and deformation of the culvert-soil structure. According to the theory of soil mechanics, the calculation model of vertical soil pressure at the top of culvert is determined, and the formula of vertical soil pressure at the top of culvert is deduced. Through the field test of the vertical soil pressure at the top of culvert of several engineering examples, the calculation formula of this paper is verified, which can provide reference for future practical engineering.

Machine learning reveals cyclic changes in seismic source spectra in Geysers geothermal field

PubMed Central

Paisley, John

2018-01-01

The earthquake rupture process comprises complex interactions of stress, fracture, and frictional properties. New machine learning methods demonstrate great potential to reveal patterns in time-dependent spectral properties of seismic signals and enable identification of changes in faulting processes. Clustering of 46,000 earthquakes of 0.3 < ML < 1.5 from the Geysers geothermal field (CA) yields groupings that have no reservoir-scale spatial patterns but clear temporal patterns. Events with similar spectral properties repeat on annual cycles within each cluster and track changes in the water injection rates into the Geysers reservoir, indicating that changes in acoustic properties and faulting processes accompany changes in thermomechanical state. The methods open new means to identify and characterize subtle changes in seismic source properties, with applications to tectonic and geothermal seismicity. PMID:29806015

Geomechanical Engineering Concepts Applied to Deep Borehole Disposal Wells

NASA Astrophysics Data System (ADS)

Herrick, C. G.; Haimson, B. C.; Lee, M.

2015-12-01

Deep borehole disposal (DBD) of certain defense-generated radioactive waste forms is being considered by the US Department of Energy (DOE) as an alternative to mined repositories. The 17 inch diameter vertical boreholes are planned to be drilled in crystalline basement rock. As part of an initial field test program, the DOE will drill a demonstration borehole, to be used to test equipment for handling and emplacing prototype nonradioactive waste containers, and a second smaller diameter borehole, to be used for site characterization. Both boreholes will be drilled to a depth of 5 km. Construction of such boreholes is expected to be complex because of their overall length, large diameter, and anticipated downhole conditions of high temperatures, pore pressures, and stress regimes. It is believed that successful development of DBD boreholes can only be accomplished if geologic and tectonic conditions are characterized and drill activities are designed based on that understanding. Our study focuses primarily on using the in situ state of stress to mitigate borehole wall failure, whether tensile or compressive. The measured stresses, or their constrained estimates, will include pore pressure, the vertical stress, the horizontal stresses and orientations, and thermally induced stresses. Pore pressure will be measured directly or indirectly. Horizontal stresses will be estimated from hydraulic fracturing tests, leak off tests, and breakout characteristics. Understanding the site stress condition along with the rock's strength characteristics will aid in the optimization of mud weight and casing design required to control borehole wall failure and other drilling problems.Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000. SAND2015-6552A

Boundary element methods for the analysis of crack growth in the presence of residual stress fields

NASA Astrophysics Data System (ADS)

Leitao, V. M. A.; Aliabadi, M. H.; Rooke, D. P.; Cook, R.

1998-06-01

Two boundary element methods of simulating crack growth in the presence of residual stress fields are presented, and the results are compared to experimental measurements. The first method utilizes linear elastic fracture mechanics (LEFM) and superimposes the solutions due to the applied load and the residual stress field. In this method, the residual stress fields are obtained from an elastoplastic BEM analysis, and numerical weight functions are used to obtain the stress intensity factors due to the fatigue loading. The second method presented is an elastoplastic fracture mechanics (EPFM) approach for crack growth simulation. A nonlinear J-integral is used in the fatigue life calculations. The methods are shown to agree well with experimental measurements of crack growth in prestressed open hole specimens. Results are also presented for the case where the prestress is applied to specimens that have been precracked.

Actuated rheology of magnetic micro-swimmers suspensions: Emergence of motor and brake states

NASA Astrophysics Data System (ADS)

Vincenti, Benoit; Douarche, Carine; Clement, Eric

2018-03-01

We study the effect of magnetic field on the rheology of magnetic micro-swimmers suspensions. We use a model of a dilute suspension under simple shear and subjected to a constant magnetic field. Particle shear stress is obtained for both pusher and puller types of micro-swimmers. In the limit of low shear rate, the rheology exhibits a constant shear stress, called actuated stress, which only depends on the swimming activity of the particles. This stress is induced by the magnetic field and can be positive (brake state) or negative (motor state). In the limit of low magnetic fields, a scaling relation of the motor-brake effect is derived as a function of the dimensionless parameters of the model. In this case, the shear stress is an affine function of the shear rate. The possibilities offered by such an active system to control the rheological response of a fluid are finally discussed.

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

NASA Technical Reports Server (NTRS)

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

2003-01-01

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

Effects of upper mantle heterogeneities on the lithospheric stress field and dynamic topography

NASA Astrophysics Data System (ADS)

Osei Tutu, Anthony; Steinberger, Bernhard; Sobolev, Stephan V.; Rogozhina, Irina; Popov, Anton A.

2018-05-01

The orientation and tectonic regime of the observed crustal/lithospheric stress field contribute to our knowledge of different deformation processes occurring within the Earth's crust and lithosphere. In this study, we analyze the influence of the thermal and density structure of the upper mantle on the lithospheric stress field and topography. We use a 3-D lithosphere-asthenosphere numerical model with power-law rheology, coupled to a spectral mantle flow code at 300 km depth. Our results are validated against the World Stress Map 2016 (WSM2016) and the observation-based residual topography. We derive the upper mantle thermal structure from either a heat flow model combined with a seafloor age model (TM1) or a global S-wave velocity model (TM2). We show that lateral density heterogeneities in the upper 300 km have a limited influence on the modeled horizontal stress field as opposed to the resulting dynamic topography that appears more sensitive to such heterogeneities. The modeled stress field directions, using only the mantle heterogeneities below 300 km, are not perturbed much when the effects of lithosphere and crust above 300 km are added. In contrast, modeled stress magnitudes and dynamic topography are to a greater extent controlled by the upper mantle density structure. After correction for the chemical depletion of continents, the TM2 model leads to a much better fit with the observed residual topography giving a good correlation of 0.51 in continents, but this correction leads to no significant improvement of the fit between the WSM2016 and the resulting lithosphere stresses. In continental regions with abundant heat flow data, TM1 results in relatively small angular misfits. For example, in western Europe the misfit between the modeled and observation-based stress is 18.3°. Our findings emphasize that the relative contributions coming from shallow and deep mantle dynamic forces are quite different for the lithospheric stress field and dynamic topography.

Method for residual stress relief and retained austenite destabilization

DOEpatents

Ludtka, Gerard M.

2004-08-10

A method using of a magnetic field to affect residual stress relief or phase transformations in a metallic material is disclosed. In a first aspect of the method, residual stress relief of a material is achieved at ambient temperatures by placing the material in a magnetic field. In a second aspect of the method, retained austenite stabilization is reversed in a ferrous alloy by applying a magnetic field to the alloy at ambient temperatures.

New self-magnetically insulated connection of multilevel accelerators to a common load

DOE PAGES

VanDevender, J. Pace; Langston, William L.; Pasik, Michael F.; ...

2015-03-04

A new way to connect pulsed-power modules to a common load is presented. Unlike previous connectors, the clam shell magnetically insulated transmission line (CSMITL) has magnetic nulls only at large radius where the cathode electric field is kept below the threshold for emission, has only a simply connected magnetic topology to avoid plasma motion along magnetic field lines into highly stressed gaps, and has electron injectors that ensure efficient electron flow even in the limiting case of self-limited MITLs. Multilevel magnetically insulated transmission lines with a posthole convolute are the standard solution but associated losses limit the performance of state-of-the-artmore » accelerators. Mitigating these losses is critical for the next generation of pulsed-power accelerators. A CSMITL has been successfully implemented on the Saturn accelerator. A reference design for the Z accelerator is derived and presented. The design conservatively meets the design requirements and shows excellent transport efficiency in three simulations of increasing complexity: circuit simulations, electromagnetic fields only with Emphasis, fields plus electron and ion emission with Quicksilver.« less

Aerodynamic Flow Field Measurements for Automotive Systems

NASA Technical Reports Server (NTRS)

Hepner, Timothy E.

1999-01-01

The design of a modern automotive air handling system is a complex task. The system is required to bring the interior of the vehicle to a comfortable level in as short a time as possible. A goal of the automotive industry is to predict the interior climate of an automobile using advanced computational fluid dynamic (CFD) methods. The development of these advanced prediction tools will enable better selection of engine and accessory components. The goal of this investigation was to predict methods used by the automotive industry. To accomplish this task three separate experiments were performed. The first was a laboratory setup where laser velocimeter (LV) flow field measurements were made in the heating and air conditioning unit of a Ford Windstar. The second involved flow field measurements in the engine compartment of a Ford Explorer, with the engine running idle. The third mapped the flow field exiting the center dashboard panel vent inside the Explorer, while the circulating fan operated at 14 volts. All three experiments utilized full-coincidence three-component LV systems. This enabled the mean and fluctuating velocities to be measured along with the Reynolds stress terms.

Determining the Ocean's Role on the Variable Gravity Field and Earth Rotation

NASA Technical Reports Server (NTRS)

Ponte, Rui M.; Frey, H. (Technical Monitor)

2000-01-01

A number of ocean models of different complexity have been used to study changes in the oceanic angular momentum (OAM) and mass fields and their relation to the variable Earth rotation and gravity field. Time scales examined range from seasonal to a few days. Results point to the importance of oceanic signals in driving polar motion, in particular the Chandler and annual wobbles. Results also show that oceanic signals have a measurable impact on length-of-day variations. Various circulation features and associated mass signals, including the North Pacific subtropical gyre, the equatorial currents, and the Antarctic Circumpolar Current play a significant role in oceanic angular momentum variability. The impact on OAM values of an optimization procedure that uses available data to constrain ocean model results was also tested for the first time. The optimization procedure yielded substantial changes, in OAM, related to adjustments in both motion and mass fields,as well as in the wind stress torques acting on the ocean. Constrained OAM values were found to yield noticeable improvements in the agreement with the observed Earth rotation parameters, particularly at the seasonal timescale.

A spectral approach for discrete dislocation dynamics simulations of nanoindentation

NASA Astrophysics Data System (ADS)

Bertin, Nicolas; Glavas, Vedran; Datta, Dibakar; Cai, Wei

2018-07-01

We present a spectral approach to perform nanoindentation simulations using three-dimensional nodal discrete dislocation dynamics. The method relies on a two step approach. First, the contact problem between an indenter of arbitrary shape and an isotropic elastic half-space is solved using a spectral iterative algorithm, and the contact pressure is fully determined on the half-space surface. The contact pressure is then used as a boundary condition of the spectral solver to determine the resulting stress field produced in the simulation volume. In both stages, the mechanical fields are decomposed into Fourier modes and are efficiently computed using fast Fourier transforms. To further improve the computational efficiency, the method is coupled with a subcycling integrator and a special approach is devised to approximate the displacement field associated with surface steps. As a benchmark, the method is used to compute the response of an elastic half-space using different types of indenter. An example of a dislocation dynamics nanoindentation simulation with complex initial microstructure is presented.

Amphibolite boudins in marble on Naxos, Greece: 3D analysis of multiphase deformation on a retrograde P-T path

NASA Astrophysics Data System (ADS)

Virgo, Simon; von Hagke, Christoph; Urai, Janos L.

2017-04-01

Boudins are periodic structures that form by layer parallel extension in mechanically layered rocks. The characteristics of boudins such as orientation and geometry provide constraints on the paleo stress field as well as the rheology of the rocks during deformation. However, most characterizations of boudinage are based on 2D observations and do not consider the 3-dimensional complexity and potentially non-coaxial polyphase genesis of boudinage structures. In marble quarries in the high grade complex on Naxos, Greece, we studied spectacular outcrops of amphibolite and pegmatite boudins, in combination with serial slicing of quarried blocks to reconstruct the 3D boudin structures. We identified five boudin generations with two distinct generations of early, high grade pinch-and-swell followed by two generations of brittle shearband and torn boudins formed along the retrograde path under greenschist facies conditions. The five generations of boudinage indicate that E-W compression is the main mode of deformation in the marbles. The axis of extension changes from subvertical during pinch-and swell deformation to subhorizontal N-S extension at later stages of deformation. Later phases of boudinage are influenced by existing boudin geometries, producing complex structures in 3D. In 2D section the complexity is not directly apparent and reveals itself only after statistical analysis of long continuous sections. Apart from implications for the regional geology, our findings highlight the importance of 3D characterization of boudinage structures for boudin classification. The insights we gain from the analysis of multiphase boudinage structures on Naxos are the basis for quantitative boudin analysis to infer rheology, effective stress, vorticity and strain, and establish a boudin classification scheme with appeal to a complete mechanics.

High-precision relocation for aftershocks of the 2016 ML 5.8 Gyeongju earthquake in South Korea: Stress partitioning controlled by complex fault systems

NASA Astrophysics Data System (ADS)

Woo, J. U.; Rhie, J.; Kang, T. S.; Kim, S.; Chai, G.; Cho, E.

2017-12-01

Complex inherent fault system is one of key factors controlling the main shock occurrence and the pattern of aftershock sequence. Many field studies have shown that the fault systems in the Korean Peninsula are complex because they formed by various tectonic events since Proterozoic. Apart from that the mainshock is the largest one (ML 5.8) ever recorded in South Korea, the Gyeongju earthquake sequence shows particularly interesting features: ML 5.1 event preceded ML 5.8 event by 50 min and they are located closely to each other ( 1 km). In addition, ML 4.5 event occurred 2 3 km away from the two events after a week of the mainshock. Considering reported focal mechanisms and hypocenters of the three major events, it is unlikely that the earthquake sequence occurs on a single fault plane. To depict the detailed fault geometry associated with the sequence, we precisely determine the relative locations of 1,400 aftershocks recorded by 27 broadband stations, which started to be deployed less than one hour after the mainshock. Double difference algorithm is applied using relative travel time measurements by a waveform cross-correlation method. Relocated hypocenters show that a major fault striking NE-SW and some minor faults get involved in the sequence. In particular, aftershocks immediately following ML 4.5 event seem to occur on a fault striking NW-SE, which is orthogonal to the strike of a major fault. We expect that the Gyeongju earthquake sequence resulted from the stress transfer controlled by the complex inherent fault system in this region.

Relationship Between Far Field Stresses, Fluid Flow and High-Pressure Deserpentinization in Subducting Slabs: a Case Study From the Almirez Ultramafic Massif

NASA Astrophysics Data System (ADS)

Dilissen, Nicole; Hidas, Károly; Garrido, Carlos J.; López Sánchez-Vizcaíno, Vicente; Kahl, Wolf-Achim; Padrón-Navarta, José Alberto; Jesús Román-Alpiste, Manuel

2017-04-01

Serpentinite dehydration during prograde metamorphism plays a crucial role in subduction dynamics. Observations from exhumed paleo-subduction metamorphic terranes suggest that the discharge of deserpentinization fluids from the subducting slab takes place along different pathways and mechanisms [e.g. 1-3]. Analysis of intermediate-depth focal solutions in active subduction zones indicates that slabs are subjected to different principal stress fields characterized primarily by downdip compression and downdip tension [4]. Although it is well known that far field stresses play a crucial role on fluid flow channeling, their potential impact on the kinetics of serpentinite dehydration and subsequent fluid escape in subducting slabs is still poorly understood. Here, we present a detailed structural and microstructural study to investigate the relationships between far field stresses, fluid flow and high-pressure deserpentinization in the Almirez ultramafic massif (Betic Cordillera, SE Spain) [1, 2]. This massif preserves the high-pressure breakdown of antigorite (Atg-) serpentinite to prograde chlorite (Chl-) harzburgite, which are separated by a sharp isograd [2, 5]. The Chl-harzburgite reaction products show either a granofels or spinifex-like texture indicating crystallization under different overstepping of the Atg-out reaction. The two different textural types of Chl-harzburgite occur below the Atg-out isograd as alternating, meter-wide lenses with either a granofels or spinifex texture. From field measurements, we infer that during antigorite dehydration the minimum compressive stress was subnormal to the dehydration front and the paleo-slab surface. This stress field is consistent with subduction zones with slabs under downdip compression at intermediate depths [4]. The detailed microstructural study —combining µ-CT and EBSD-SEM [6]— of Chl-harzburgite across a c. 15 m wide lens reveals that the SPO and CPO of olivines with contrasting textures are strongly correlated with the inferred paleo-stress. The SPO of opaque phases and that of granofelsic olivine are aligned and have a single maximum in each sample. Across the studied lens these maxima are distributed along a plane that corresponds to the average orientation of Atg-serpentinite foliation in a nearby outcrop, and they show a strong maximum close to the intermediate compressive stress axis. Spinifex olivines form tablet-like crystals that are elongated parallel to [001]-axes in a plane perpendicular to their [100]-axes. These growth planes are oriented at high angle to the least compressional stress axis, and the olivine growth directions (i.e., [001]-axes) are dominantly oriented at the acute angle between the maximum and intermediate compressive stress axes. These results indicate that formation of spinifex crystals is preferred at enhanced reaction rates and it occurred along hydrofractures that opened as controlled by the stress field. Our data show that overpressured fluids escaped along the slab surface towards the maximum compression direction. We therefore propose that at periods of high fluid flux due to hydrofracturing in a dehydrating slab, the development of fluid network channels strongly depends on the principal stress field. REFERENCES 1. Padrón-Navarta, J.A., Tommasi, A., Garrido, C.J., López Sánchez-Vizcaíno, V., Gómez-Pugnaire, M.T., Jabaloy, A., Vauchez, A., 2010. Fluid transfer into the wedge controlled by high-pressure hydrofracturing in the cold top-slab mantle. Earth and Planetary Science Letters 297, 271-286. doi: 10.1016/j.epsl.2010.06.029. 2. Padrón-Navarta, J.A., López Sánchez-Vizcaíno, V., Garrido, C.J., Gómez-Pugnaire, M.T., 2011. Metamorphic Record of High-pressure Dehydration of Antigorite Serpentinite to Chlorite Harzburgite in a Subduction Setting (Cerro del Almirez, Nevado-Filábride Complex, Southern Spain). Journal of Petrology 52, 2047-2078. 3. Plümper, O., John, T., Podladchikov, Y.Y., Vrijmoed, J.C., Scambelluri, M., (in press). Fluid escape from subduction zones controlled by channel-forming reactive porosity. Nature Geoscience. 4. Chen, P.-F., Bina, C.R., Okal, E.A., 2004. A global survey of stress orientations in subducting slabs as revealed by intermediate-depth earthquakes. Geophysical Journal International 159, 721-733. 5. Padrón-Navarta, J.A., Tommasi, A., Garrido, C.J., López Sánchez-Vizcaíno, V., 2012. Plastic deformation and development of antigorite crystal preferred orientation in high-pressure serpentinites. Earth and Planetary Science Letters 349-350, 75-86. doi: 10.1016/j.epsl.2012.06.049 6. Kahl, W.-A., Hidas, K., Dilissen, N., Garrido, C.J., López-Sánchez Vizcaíno, V., Román-Alpiste, M.J. 2017. Reconstruction of the 3-D shape and crystal preferred orientation of olivine: a combined µ-CT and EBSD-SEM approach. Geophysical Research Abstracts 19, EGU2017-8061. Funding: Research leading to these results was funded by the EU-FP7 Marie Curie Initial Training Network ZIP - Zooming in between plates.

Recent state of stress change in the Walker Lane zone, western Basin and Range province, United States

NASA Astrophysics Data System (ADS)

Bellier, Olivier; Zoback, Mary Lou

1995-06-01

The NW to north-trending Walker Lane zone (WLZ) is located along the western boundary of the northern Basin and Range province with the Sierra Nevada. This zone is distinguished from the surrounding Basin and Range province on the basis of irregular topography and evidence for both normal and strike-slip Holocene faulting. Inversion of slip vectors from active faults, historic fault offsets, and earthquake focal mechanisms indicate two distinct Quaternary stress regimes within the WLZ, both of which are characterized by a consistent WNW σ3 axis; these are a normal faulting regime with a mean σ3 axis of N85°±9°W and a mean stress ratio (R value) (R=(σ2-σ1)/(σ3-σ1)) of 0.63-0.74 and a younger strike-slip faulting regime with a similar mean σ3 axis (N65° - 70°W) and R values ranging between ˜ 0.1 and 0.2. This younger regime is compatible with historic fault offsets and earthquake focal mechanisms. Both the extensional and strike-slip stress regimes reactivated inherited Mesozoic and Cenozoic structures and also produced new faults. The present-day strike-slip stress regime has produced strike-slip, normal oblique-slip, and normal dip-slip historic faulting. Previous workers have explained the complex interaction of active strike-slip, oblique, and normal faulting in the WLZ as a simple consequence of a single stress state with a consistent WNW σ3 axis and transitional between strike-slip and normal faulting (maximum horizontal stress approximately equal to vertical stress, or R ≈ 0 in both regimes) with minor local fluctuations. The slip data reported here support previous results from Owens Valley that suggest deformation within temporally distinct normal and strike-slip faulting stress regimes with a roughly constant WNW trending σ3 axis (Zoback, 1989). A recent change from a normal faulting to a strike-slip faulting stress regime is indicated by the crosscutting striae on faults in basalts <300,000 years old and is consistent with the dominantly strike-slip earthquake focal mechanisms and the youngest striae observed on faults in Plio-Quaternary deposits. Geologic control on the timing of the change is poor; it is impossible to determine if there has been a single recent absolute change or if there is, rather, an alternating or cyclical variation in stress magnitudes. Our slip data, in particular, the cross-cutting normal and strike-slip striae on the same fault plane, are inconsistent with postulated simple strain partitioning of deformation within a single regional stress field suggested for the WLZ by Wesnousky and Jones [1994]. The location of the WLZ between the deep-seated regional extension of the Basin and Range and the right-lateral strike-slip regional tectonics of the San Andreas fault zone is probably responsible for the complex interaction of tectonic regimes in this transition zone. In early to mid-Tertiary time the WLZ appears to have had a similarly complex deformational history, in this case as a back arc or intra-arc region, accommodating at least part of the right-lateral component of oblique convergence as well as a component of extension.

Ocean surface waves in Hurricane Ike (2008) and Superstorm Sandy (2012): Coupled model predictions and observations

NASA Astrophysics Data System (ADS)

Chen, Shuyi S.; Curcic, Milan

2016-07-01

Forecasting hurricane impacts of extreme winds and flooding requires accurate prediction of hurricane structure and storm-induced ocean surface waves days in advance. The waves are complex, especially near landfall when the hurricane winds and water depth varies significantly and the surface waves refract, shoal and dissipate. In this study, we examine the spatial structure, magnitude, and directional spectrum of hurricane-induced ocean waves using a high resolution, fully coupled atmosphere-wave-ocean model and observations. The coupled model predictions of ocean surface waves in Hurricane Ike (2008) over the Gulf of Mexico and Superstorm Sandy (2012) in the northeastern Atlantic and coastal region are evaluated with the NDBC buoy and satellite altimeter observations. Although there are characteristics that are general to ocean waves in both hurricanes as documented in previous studies, wave fields in Ike and Sandy possess unique properties due mostly to the distinct wind fields and coastal bathymetry in the two storms. Several processes are found to significantly modulate hurricane surface waves near landfall. First, the phase speed and group velocities decrease as the waves become shorter and steeper in shallow water, effectively increasing surface roughness and wind stress. Second, the bottom-induced refraction acts to turn the waves toward the coast, increasing the misalignment between the wind and waves. Third, as the hurricane translates over land, the left side of the storm center is characterized by offshore winds over very short fetch, which opposes incoming swell. Landfalling hurricanes produce broader wave spectra overall than that of the open ocean. The front-left quadrant is most complex, where the combination of windsea, swell propagating against the wind, increasing wind-wave stress, and interaction with the coastal topography requires a fully coupled model to meet these challenges in hurricane wave and surge prediction.

Response of Two Mytilids to a Heatwave: The Complex Interplay of Physiology, Behaviour and Ecological Interactions

PubMed Central

Gestoso, Ignacio; Lima, Fernando P.; Vázquez, Elsa; Comeau, Luc A.; Gomes, Filipa; Seabra, Rui

2016-01-01

Different combinations of behavioural and physiological responses may play a crucial role in the ecological success of species, notably in the context of biological invasions. The invasive mussel Xenostrobus securis has successfully colonised the inner part of the Galician Rias Baixas (NW Spain), where it co-occurs with the commercially-important mussel Mytilus galloprovincialis. This study investigated the effect of a heatwave on the physiological and behavioural responses in monospecific or mixed aggregations of these species. In a mesocosm experiment, mussels were exposed to simulated tidal cycles and similar temperature conditions to those experienced in the field during a heat-wave that occurred in the summer of 2013, when field robo-mussels registered temperatures up to 44.5°C at low tide. The overall responses to stress differed markedly between the two species. In monospecific aggregations M. galloprovincialis was more vulnerable than X. securis to heat exposure during emersion. However, in mixed aggregations, the presence of the invader was associated with lower mortality in M. galloprovincialis. The greater sensitivity of M. galloprovincialis to heat exposure was reflected in a higher mortality level, greater induction of Hsp70 protein and higher rates of respiration and gaping activity, which were accompanied by a lower heart rate (bradycardia). The findings show that the invader enhanced the physiological performance of M. galloprovincialis, highlighting the importance of species interactions in regulating responses to environmental stress. Understanding the complex interactions between ecological factors and physiological and behavioural responses of closely-related species is essential for predicting the impacts of invasions in the context of future climate change. PMID:27736896

Accounting for Genotype-by-Environment Interactions and Residual Genetic Variation in Genomic Selection for Water-Soluble Carbohydrate Concentration in Wheat.

PubMed

Ovenden, Ben; Milgate, Andrew; Wade, Len J; Rebetzke, Greg J; Holland, James B

2018-05-31

Abiotic stress tolerance traits are often complex and recalcitrant targets for conventional breeding improvement in many crop species. This study evaluated the potential of genomic selection to predict water-soluble carbohydrate concentration (WSCC), an important drought tolerance trait, in wheat under field conditions. A panel of 358 varieties and breeding lines constrained for maturity was evaluated under rainfed and irrigated treatments across two locations and two years. Whole-genome marker profiles and factor analytic mixed models were used to generate genomic estimated breeding values (GEBVs) for specific environments and environment groups. Additive genetic variance was smaller than residual genetic variance for WSCC, such that genotypic values were dominated by residual genetic effects rather than additive breeding values. As a result, GEBVs were not accurate predictors of genotypic values of the extant lines, but GEBVs should be reliable selection criteria to choose parents for intermating to produce new populations. The accuracy of GEBVs for untested lines was sufficient to increase predicted genetic gain from genomic selection per unit time compared to phenotypic selection if the breeding cycle is reduced by half by the use of GEBVs in off-season generations. Further, genomic prediction accuracy depended on having phenotypic data from environments with strong correlations with target production environments to build prediction models. By combining high-density marker genotypes, stress-managed field evaluations, and mixed models that model simultaneously covariances among genotypes and covariances of complex trait performance between pairs of environments, we were able to train models with good accuracy to facilitate genetic gain from genomic selection. Copyright © 2018 Ovenden et al.

Airborne Hyperspectral Imagery for the Detection of Agricultural Crop Stress

NASA Technical Reports Server (NTRS)

Cassady, Philip E.; Perry, Eileen M.; Gardner, Margaret E.; Roberts, Dar A.

2001-01-01

Multispectral digital imagery from aircraft or satellite is presently being used to derive basic assessments of crop health for growers and others involved in the agricultural industry. Research indicates that narrow band stress indices derived from hyperspectral imagery should have improved sensitivity to provide more specific information on the type and cause of crop stress, Under funding from the NASA Earth Observation Commercial Applications Program (EOCAP) we are identifying and evaluating scientific and commercial applications of hyperspectral imagery for the remote characterization of agricultural crop stress. During the summer of 1999 a field experiment was conducted with varying nitrogen treatments on a production corn-field in eastern Nebraska. The AVIRIS (Airborne Visible-Infrared Imaging Spectrometer) hyperspectral imager was flown at two critical dates during crop development, at two different altitudes, providing images with approximately 18m pixels and 3m pixels. Simultaneous supporting soil and crop characterization included spectral reflectance measurements above the canopy, biomass characterization, soil sampling, and aerial photography. In this paper we describe the experiment and results, and examine the following three issues relative to the utility of hyperspectral imagery for scientific study and commercial crop stress products: (1) Accuracy of reflectance derived stress indices relative to conventional measures of stress. We compare reflectance-derived indices (both field radiometer and AVIRIS) with applied nitrogen and with leaf level measurement of nitrogen availability and chlorophyll concentrations over the experimental plots (4 replications of 5 different nitrogen levels); (2) Ability of the hyperspectral sensors to detect sub-pixel areas under crop stress. We applied the stress indices to both the 3m and 18m AVIRIS imagery for the entire production corn field using several sub-pixel areas within the field to compare the relative sensitivity of each stress index; and (3) Comparative sensitivity of stress indices to realistic measurement uncertainties. We compare the stress indices calculated with several levels of spectral uncertainty (by shifting the wavelengths) and reflectance uncertainty (by systematically varying the reflectance retrieval code initialization).

Influence of natural fractures on hydraulic fracture propagation

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

Teufel, L.W.; Warpinski, N.R.

Hydraulic fracturing has become a valuable technique for the stimulation of oil, gas, and geothermal reservoirs in a variety of reservoir rocks. In many applications, only short fractures are needed for economic production. In low-permeability reservoirs, however, long penetrating fractures are generally needed, and in this case, natural fractures can be the cause of many adverse effects during a fracture treatment. Natural fractures can influence the overall geometry and effectiveness of the hydraulic fracture by: (1) arresting the vertical or lateral growth, (2) reducing total fracture length via fluid leakoff, (3) limiting proppant transport and placement, and (4) enhancing themore » creation of multiple or secondary fractures rather than a single planar hydraulic fracture. The result may range from negligible to catastrophic depending on the values of the ancillary treatment and reservoir parameters, such as the treating pressure, in-situ stresses, pore pressure, orientations of the natural fractures relative to principal in-situ stresses, spacing and distribution of the natural fractures, permeability, etc. Field observations from mineback experiments at DOE's Nevada Test Site and the multiwell experiment in Colorado, laboratory tests, and analyses of these data are integrated to describe the complex fracture behavior found and to provide guidelines for predicting when this complex fracturing will occur.« less

Influence of natural fractures on hydraulic fracture propagation

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

Teufel, L.W.; Warpinski, N.R.

Hydraulic fracturing has become a valuable technique for the stimulation of oil, gas, and geothermal reservoirs in a variety of reservoir rocks. In many applications, only short fractures are needed for economic production. In low-permeability reservoirs, however, long penetrating fractures are generally needed, and in this case, natural fractures can be the cause of many adverse effects during a fracture treatment. Natural fractures can influence the overall geometry and effectiveness of the hydraulic fracture by: (1) arresting the vertical or lateral growth, (2) reducing total fracture length via fluid leakoff, (3) limiting proppant transport and placement, and (4) enhancing themore » creation of multiple or secondary fractures rather than a single planar hydraulic fracture. The result may range from negligible to catastrophic depending on the values of the ancillary treatment and reservoir parameters, such as the treating pressure, in-situ stresses, pore pressure, orientations of the natural fractures relative to principle in-situ stresses, spacing and distribution of the natural fractures, permeability, etc. Field observations from mineback experiments at DOE's Nevada Test Site and the multiwell experiment in Colorado, laboratory tests, and analyses of these data are integrated to describe the complex fracture behavior found to an provide guidelines for predicting when this complex fracturing occurs.« less

Electric-field-induced structural changes in multilayer piezoelectric actuators during electrical and mechanical loading

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

Esteves, Giovanni; Fancher, Chris M.; Röhrig, Sören

The effects of electrical and mechanical loading on the behavior of domains and phases in Multilayer Piezoelectric Actuators (MAs) is studied using in situ high-energy X-ray diffraction (XRD) and macroscopic property measurements. Rietveld refinement is carried out on measured diffraction patterns using a two-phase tetragonal (P4mm) and rhombohedral (R3m) model. Applying an electric field promotes the rhombohedral phase, while increasing compressive uniaxial pre-stress prior to electric field application favors the tetragonal phase. The competition between electrical and mechanical energy leads to a maximal difference between electric-field-induced phase fractions at 70 MPa pre-stress. Additionally, the available volume fraction of non-180° domainmore » reorientation that can be accessed during electric field application increases with compressive pre-stress up to 70 MPa. The origin for enhanced strain and polarization with applied pre-stress is attributed to a combination of enhanced non-180° domain reorientation and electric-field-induced phase transitions. The suppression of both the electric-field-induced phase transitions and domain reorientation at high pre-stresses (>70 MPa) is attributed to a large mechanical energy barrier, and alludes to the competition of the electrical and mechanical energy within the MA during applied stimuli.« less

Electric-field-induced structural changes in multilayer piezoelectric actuators during electrical and mechanical loading

DOE PAGES

Esteves, Giovanni; Fancher, Chris M.; Röhrig, Sören; ...

2017-04-08

The effects of electrical and mechanical loading on the behavior of domains and phases in Multilayer Piezoelectric Actuators (MAs) is studied using in situ high-energy X-ray diffraction (XRD) and macroscopic property measurements. Rietveld refinement is carried out on measured diffraction patterns using a two-phase tetragonal (P4mm) and rhombohedral (R3m) model. Applying an electric field promotes the rhombohedral phase, while increasing compressive uniaxial pre-stress prior to electric field application favors the tetragonal phase. The competition between electrical and mechanical energy leads to a maximal difference between electric-field-induced phase fractions at 70 MPa pre-stress. Additionally, the available volume fraction of non-180° domainmore » reorientation that can be accessed during electric field application increases with compressive pre-stress up to 70 MPa. The origin for enhanced strain and polarization with applied pre-stress is attributed to a combination of enhanced non-180° domain reorientation and electric-field-induced phase transitions. The suppression of both the electric-field-induced phase transitions and domain reorientation at high pre-stresses (>70 MPa) is attributed to a large mechanical energy barrier, and alludes to the competition of the electrical and mechanical energy within the MA during applied stimuli.« less

The effect of stress and incentive magnetic field on the average volume of magnetic Barkhausen jump in iron

NASA Astrophysics Data System (ADS)

Shu, Di; Guo, Lei; Yin, Liang; Chen, Zhaoyang; Chen, Juan; Qi, Xin

2015-11-01

The average volume of magnetic Barkhausen jump (AVMBJ) v bar generated by magnetic domain wall irreversible displacement under the effect of the incentive magnetic field H for ferromagnetic materials and the relationship between irreversible magnetic susceptibility χirr and stress σ are adopted in this paper to study the theoretical relationship among AVMBJ v bar(magneto-elasticity noise) and the incentive magnetic field H. Then the numerical relationship among AVMBJ v bar, stress σ and the incentive magnetic field H is deduced. Utilizing this numerical relationship, the displacement process of magnetic domain wall for single crystal is analyzed and the effect of the incentive magnetic field H and the stress σ on the AVMBJ v bar (magneto-elasticity noise) is explained from experimental and theoretical perspectives. The saturation velocity of Barkhausen jump characteristic value curve is different when tensile or compressive stress is applied on ferromagnetic materials, because the resistance of magnetic domain wall displacement is different. The idea of critical magnetic field in the process of magnetic domain wall displacement is introduced in this paper, which solves the supersaturated calibration problem of AVMBJ - σ calibration curve.

Improved capacitive stress transducers for high-field superconducting magnets

NASA Astrophysics Data System (ADS)

Benson, Christopher Pete; Holik, Eddie Frank, III; Jaisle, Andrew; McInturff, A.; McIntyre, P.

2012-06-01

High-field (12-18 Tesla) superconducting magnets are required to enable an increase in the energy of future colliders. Such field strength requires the use of Nb3Sn superconductor, which has limited tolerance for compressive and shear strain. A strategy for stress management has been developed at Texas A&M University and is being implemented in TAMU3, a short-model 14 Tesla stress-managed Nb3Sn block dipole. The strategy includes the use of laminar capacitive stress transducers to monitor the stresses within the coil package. We have developed fabrication techniques and fixtures, which improve the reproducibility of the transducer response both at room temperature and during cryogenic operation. This is a report of the status of transducer development.

Thermal Stress FE Analysis of Large-scale Gas Holder Under Sunshine Temperature Field

NASA Astrophysics Data System (ADS)

Li, Jingyu; Yang, Ranxia; Wang, Hehui

2018-03-01

The temperature field and thermal stress of Man type gas holder is simulated by using the theory of sunshine temperature field based on ASHRAE clear-sky model and the finite element method. The distribution of surface temperature and thermal stress of gas holder under the given sunshine condition is obtained. The results show that the thermal stress caused by sunshine can be identified as one of the important factors for the failure of local cracked oil leakage which happens on the sunny side before on the shady side. Therefore, it is of great importance to consider the sunshine thermal load in the stress analysis, design and operation of large-scale steel structures such as the gas holder.

Yeh-Stratton Criterion for Stress Concentrations on Fiber-Reinforced Composite Materials

NASA Technical Reports Server (NTRS)

Yeh, Hsien-Yang; Richards, W. Lance

1996-01-01

This study investigated the Yeh-Stratton Failure Criterion with the stress concentrations on fiber-reinforced composites materials under tensile stresses. The Yeh-Stratton Failure Criterion was developed from the initial yielding of materials based on macromechanics. To investigate this criterion, the influence of the materials anisotropic properties and far field loading on the composite materials with central hole and normal crack were studied. Special emphasis was placed on defining the crack tip stress fields and their applications. The study of Yeh-Stratton criterion for damage zone stress fields on fiber-reinforced composites under tensile loading was compared with several fracture criteria; Tsai-Wu Theory, Hoffman Theory, Fischer Theory, and Cowin Theory. Theoretical predictions from these criteria are examined using experimental results.

Improved structural integrity through advances in reliable residual stress measurement: the impact of ENGIN-X

NASA Astrophysics Data System (ADS)

Edwards, L.; Santisteban, J. R.

The determination of accurate reliable residual stresses is critical to many fields of structural integrity. Neutron stress measurement is a non-destructive technique that uniquely provides insights into stress fields deep within engineering components and structures. As such, it has become an increasingly important tool within engineering, leading to improved manufacturing processes to reduce stress and distortion as well as to the definition of more precise lifing procedures. This paper describes the likely impact of the next generation of dedicated engineering stress diffractometers currently being constructed and the utility of the technique using examples of residual stresses both beneficial and detrimental to structural integrity.

Archaeal Genome Guardians Give Insights into Eukaryotic DNA Replication and Damage Response Proteins

PubMed Central

Shin, David S.; Pratt, Ashley J.; Tainer, John A.

2014-01-01

As the third domain of life, archaea, like the eukarya and bacteria, must have robust DNA replication and repair complexes to ensure genome fidelity. Archaea moreover display a breadth of unique habitats and characteristics, and structural biologists increasingly appreciate these features. As archaea include extremophiles that can withstand diverse environmental stresses, they provide fundamental systems for understanding enzymes and pathways critical to genome integrity and stress responses. Such archaeal extremophiles provide critical data on the periodic table for life as well as on the biochemical, geochemical, and physical limitations to adaptive strategies allowing organisms to thrive under environmental stress relevant to determining the boundaries for life as we know it. Specifically, archaeal enzyme structures have informed the architecture and mechanisms of key DNA repair proteins and complexes. With added abilities to temperature-trap flexible complexes and reveal core domains of transient and dynamic complexes, these structures provide insights into mechanisms of maintaining genome integrity despite extreme environmental stress. The DNA damage response protein structures noted in this review therefore inform the basis for genome integrity in the face of environmental stress, with implications for all domains of life as well as for biomanufacturing, astrobiology, and medicine. PMID:24701133

Correlation Between Fracture Network Properties and Stress Variability in Geological Media

NASA Astrophysics Data System (ADS)

Lei, Qinghua; Gao, Ke

2018-05-01

We quantitatively investigate the stress variability in fractured geological media under tectonic stresses. The fracture systems studied include synthetic fracture networks following power law length scaling and natural fracture patterns based on outcrop mapping. The stress field is derived from a finite-discrete element model, and its variability is analyzed using a set of mathematical formulations that honor the tensorial nature of stress data. We show that local stress perturbation, quantified by the Euclidean distance of a local stress tensor to the mean stress tensor, has a positive, linear correlation with local fracture intensity, defined as the total fracture length per unit area within a local sampling window. We also evaluate the stress dispersion of the entire stress field using the effective variance, that is, a scalar-valued measure of the overall stress variability. The results show that a well-connected fracture system under a critically stressed state exhibits strong local and global stress variabilities.

A pulsed magnetic stress applied to Drosophila melanogaster flies

NASA Astrophysics Data System (ADS)

Delle Side, D.; Bozzetti, M. P.; Friscini, A.; Giuffreda, E.; Nassisi, V.; Specchia, V.; Velardi, L.

2014-04-01

We report the development of a system to feed pulsed magnetic stress to biological samples. The device is based on a RLC circuit that transforms the energy stored in a high voltage capacitor into a magnetic field inside a coil. The field has been characterized and we found that charging the capacitor with 24 kV results in a peak field of 0.4 T. In order to test its effect, we applied such a stress to the Drosophila melanogaster model and we examined its bio-effects. We analysed, in the germ cells, the effects on the control of specific DNA repetitive sequences that are activated after different environmental stresses. The deregulation of these sequences causes genomic instability and chromosomes breaks leading to sterility. The magnetic field treatment did not produce effects on repetitive sequences in the germ cells of Drosophila. Hence, this field doesn't produce deleterious effects linked to repetitive sequences derepression.

Complex trauma and mental health in children and adolescents placed in foster care: findings from the National Child Traumatic Stress Network.

PubMed

Greeson, Johanna K P; Briggs, Ernestine C; Kisiel, Cassandra L; Layne, Christopher M; Ake, George S; Ko, Susan J; Gerrity, Ellen T; Steinberg, Alan M; Howard, Michael L; Pynoos, Robert S; Fairbank, John A

2011-01-01

Many children in the child welfare system (CWS) have histories of recurrent interpersonal trauma perpetrated by caregivers early in life often referred to as complex trauma. Children in the CWS also experience a diverse range of reactions across multiple areas of functioning that are associated with such exposure. Nevertheless, few CWSs routinely screen for trauma exposure and associated symptoms beyond an initial assessment of the precipitating event. This study examines trauma histories, including complex trauma exposure (physical abuse, sexual abuse, emotional abuse, neglect, domestic violence), posttraumatic stress, and behavioral and emotional problems of 2,251 youth (age 0 to 21; M = 9.5, SD = 4.3) in foster care who were referred to a National Child Traumatic Stress Network site for treatment. High prevalence rates of complex trauma exposure were observed: 70.4% of the sample reported at least two of the traumas that constitute complex trauma; 11.7% of the sample reported all 5 types. Compared to youth with other types of trauma, those with complex trauma histories had significantly higher rates of internalizing problems, posttraumatic stress, and clinical diagnoses, and differed on some demographic variables. Implications for child welfare practice and future research are discussed.

Selenium Supplementation Affects Physiological and Biochemical Processes to Improve Fodder Yield and Quality of Maize (Zea mays L.) under Water Deficit Conditions

PubMed Central

Nawaz, Fahim; Naeem, Muhammad; Ashraf, Muhammad Y.; Tahir, Muhammad N.; Zulfiqar, Bilal; Salahuddin, Muhammad; Shabbir, Rana N.; Aslam, Muhammad

2016-01-01

Climate change is one of the most complex challenges that pose serious threats to livelihoods of poor people who rely heavily on agriculture and livestock particularly in climate-sensitive developing countries of the world. The negative effects of water scarcity, due to climate change, are not limited to productivity food crops but have far-reaching consequences on livestock feed production systems. Selenium (Se) is considered essential for animal health and has also been reported to counteract various abiotic stresses in plants, however, understanding of Se regulated mechanisms for improving nutritional status of fodder crops remains elusive. We report the effects of exogenous selenium supply on physiological and biochemical processes that may influence green fodder yield and quality of maize (Zea mays L.) under drought stress conditions. The plants were grown in lysimeter tanks under natural conditions and were subjected to normal (100% field capacity) and water stress (60% field capacity) conditions. Foliar spray of Se was carried out before the start of tasseling stage (65 days after sowing) and was repeated after 1 week, whereas, water spray was used as a control. Drought stress markedly reduced the water status, pigments and green fodder yield and resulted in low forage quality in water stressed maize plants. Nevertheless, exogenous Se application at 40 mg L-1 resulted in less negative leaf water potential (41%) and enhanced relative water contents (30%), total chlorophyll (53%), carotenoid contents (60%), accumulation of total free amino acids (40%) and activities of superoxide dismutase (53%), catalase (30%), peroxidase (27%), and ascorbate peroxidase (27%) with respect to control under water deficit conditions. Consequently, Se regulated processes improved fodder yield (15%) and increased crude protein (47%), fiber (10%), nitrogen free extract (10%) and Se content (36%) but did not affect crude ash content in water stressed maize plants. We propose that Se foliar spray (40 mg L-1) is a handy, feasible and cost-effective approach to improve maize fodder yield and quality in arid and semi-arid regions of the world facing acute shortage of water. PMID:27729917

Residual stress measurement of PMMA by combining drilling-hole with digital speckle correlation method

NASA Astrophysics Data System (ADS)

Yao, X. F.; Xiong, T. C.; Xu, H. M.; Wan, J. P.; Long, G. R.

2008-11-01

The residual stresses of the PMMA (polymethyl methacrylate) specimens after being drilled, reamed and polished respectively are investigated using the digital speckle correlation experimental method,. According to the displacement fields around the correlated calculated region, the polynomial curve fitting method is used to obtain the continuous displacement fields, and the strain fields can be obtained from the derivative of the displacement fields. Considering the constitutive equation of the material, the expression of the residual stress can be presented. During the data processing, according to the fitting effect of the data, the calculation region of the correlated speckles and the degree of the polynomial fitting curve is decided. These results show that the maximum stress is at the hole-wall of the drilling hole specimen and with the increasing of the diameter of the drilled hole, the residual stress resulting from the hole drilling increases, whereas the process of reaming and polishing hole can reduce the residual stress. The relative large discrete degree of the residual stress is due to the chip removal ability of the drill bit, the cutting feed of the drill and other various reasons.

Children with medical complexity: a scoping review of interventions to support caregiver stress.

PubMed

Edelstein, H; Schippke, J; Sheffe, S; Kingsnorth, S

2017-05-01

Caring for children with chronic and complex medical needs places extraordinary stress on parents and other family members. A scoping review was undertaken to identify and describe the full range of current interventions for reducing caregiver stress. Applying a broad definition of caregiver stress, a systematic search of three scientific databases (CINAHL, Embase and Ovid Medline), a general internet search and hand searching of key peer-reviewed articles were conducted. Inclusion criteria were as follows: (i) published in English between 2004-2016; (ii) focused on familial caregivers, defined as parents, siblings or extended family; (iii) targeted children/youth with medical complexity between the ages of 1-24 years; and (iv) described an intervention and impact on caregiver stress. Data on type of intervention, study design and methods, measures and overall findings were extracted. Forty-nine studies were included from a list of 22 339 unique titles. Six domains of interventions were found: care coordination models (n = 23); respite care (n = 8); telemedicine (n = 5); peer and emotional support (n = 6); insurance and employment benefits (n = 4); and health and related supports (n = 3). Across studies, there was a wide variety of designs, outcomes and measures used. Positive findings of reductions in caregiver stress were noted within an emerging body of evidence on effective interventions for families of children with medical complexity. A commonality across domains was a significant focus on streamlining services and reducing the burden of care related to varied pressures experienced, including time, finances, care needs and service access, among others. There was non-conclusive evidence however around which of the six identified intervention domains or combination thereof are most effective for reducing stress. These promising findings demonstrate that stress reduction is possible with the right support and that multiple interventions may be effective in reducing burdens of care experienced by families of children with medical complexity. © 2016 John Wiley & Sons Ltd.

Experimental study of uniaxial stress effects on Coulomb-limited mobility in p-type metal-oxide-semiconductor field-effect transistors

NASA Astrophysics Data System (ADS)

Kobayashi, Shigeki; Saitoh, Masumi; Nakabayashi, Yukio; Uchida, Ken

2007-11-01

Uniaxial stress effects on Coulomb-limited mobility (μCoulomb) in Si metal-oxide-semiconductor field-effect transistors (MOSFETs) are investigated experimentally. By using the four-point bending method, uniaxial stress corresponding to 0.1% strain is applied to MOSFETs along the channel direction. It is found that μCoulomb in p-type MOSFETs is enhanced greatly by uniaxial stress; μCoulomb is as sensitive as phonon-limited mobility. The high sensitivity of μCoulomb in p-type MOSFETs to stress arises from the stress-induced change of hole effective mass.

Multi-scale analysis and characterization of the ITER pre-compression rings

NASA Astrophysics Data System (ADS)

Foussat, A.; Park, B.; Rajainmaki, H.

2014-01-01

The toroidal field (TF) system of ITER Tokamak composed of 18 "D" shaped Toroidal Field (TF) coils during an operating scenario experiences out-of-plane forces caused by the interaction between the 68kA operating TF current and the poloidal magnetic fields. In order to keep the induced static and cyclic stress range in the intercoil shear keys between coils cases within the ITER allowable limits [1], centripetal preload is introduced by means of S2 fiber-glass/epoxy composite pre-compression rings (PCRs). Those PCRs consist in two sets of three rings, each 5 m in diameter and 337 × 288 mm in cross-section, and are installed at the top and bottom regions to apply a total resultant preload of 70 MN per TF coil equivalent to about 400 MPa hoop stress. Recent developments of composites in the aerospace industry have accelerated the use of advanced composites as primary structural materials. The PCRs represent one of the most challenging composite applications of large dimensions and highly stressed structures operating at 4 K over a long term life. Efficient design of those pre-compression composite structures requires a detailed understanding of both the failure behavior of the structure and the fracture behavior of the material. Due to the inherent difficulties to carry out real scale testing campaign, there is a need to develop simulation tools to predict the multiple complex failure mechanisms in pre-compression rings. A framework contract was placed by ITER Organization with SENER Ingenieria y Sistemas SA to develop multi-scale models representative of the composite structure of the Pre-compression rings based on experimental material data. The predictive modeling based on ABAQUS FEM provides the opportunity both to understand better how PCR composites behave in operating conditions and to support the development of materials by the supplier with enhanced performance to withstand the machine design lifetime of 30,000 cycles. The multi-scale stress analysis has revealed a complete picture of the stress levels within the fiber and the matrix regarding the static and fatigue performance of the rings structure including the presence of a delamination defect of critical size. The analysis results of the composite material demonstrate that the rings performance objectives under all loading and strength conditions are met.

Analyse of socket-prosthesis-blunt complex for lower limb amputee using objective measure of patient's gait cycle.

PubMed

Rotariu, Mariana; Filep, R; Turnea, M; Ilea, M; Arotăriţei, D; Popescu, Marilena

2015-01-01

The prosthetic application is a highly complex process. Modeling and simulation of biomechanics processes in orthopedics is a certainly field of interest in current medical research. Optimization of socket in order to improve the quality of patient's life is a major objective in prosthetic rehabilitation. A variety of numerical methods for prosthetic application have been developed and studied. An objective method is proposed to evaluate the performance of a prosthetic patient according to surface pressure map over the residual limb. The friction coefficient due to various liners used in transtibial and transfemoral prosthesis is taken into account also. Creation of a bio-based modeling and mathematical simulation allows the design, construction and optimization of contact between the prosthesis cup and lack of functionality of the patient amputated considering the data collected and processed in real time and non-invasively. The von Mises stress distribution in muscle flap tissue at the bone ends shows a larger region subjected to elevated von Mises stresses in the muscle tissue underlying longer truncated bones. Finite element method was used to conduct a stress analysis and show the force distribution along the device. The results contribute to a better understanding the design of an optimized prosthesis that increase the patient's performance along with a god choice of liner, made by an appropriate material that fit better to a particular blunt. The study of prosthetic application is an exciting and important topic in research and will profit considerably from theoretical input. Interpret these results to be a permanent collaboration between math's and medical orthopedics.

Sensitivity analysis of the Aquacrop and SAFYE crop models for the assessment of water limited winter wheat yield in regional scale applications.

PubMed

Silvestro, Paolo Cosmo; Pignatti, Stefano; Yang, Hao; Yang, Guijun; Pascucci, Simone; Castaldi, Fabio; Casa, Raffaele

2017-01-01

Process-based models can be usefully employed for the assessment of field and regional-scale impact of drought on crop yields. However, in many instances, especially when they are used at the regional scale, it is necessary to identify the parameters and input variables that most influence the outputs and to assess how their influence varies when climatic and environmental conditions change. In this work, two different crop models, able to represent yield response to water, Aquacrop and SAFYE, were compared, with the aim to quantify their complexity and plasticity through Global Sensitivity Analysis (GSA), using Morris and EFAST (Extended Fourier Amplitude Sensitivity Test) techniques, for moderate to strong water limited climate scenarios. Although the rankings of the sensitivity indices was influenced by the scenarios used, the correlation among the rankings, higher for SAFYE than for Aquacrop, assessed by the top-down correlation coefficient (TDCC), revealed clear patterns. Parameters and input variables related to phenology and to water stress physiological processes were found to be the most influential for Aquacrop. For SAFYE, it was found that the water stress could be inferred indirectly from the processes regulating leaf growth, described in the original SAFY model. SAFYE has a lower complexity and plasticity than Aquacrop, making it more suitable to less data demanding regional scale applications, in case the only objective is the assessment of crop yield and no detailed information is sought on the mechanisms of the stress factors affecting its limitations.

Sensitivity analysis of the Aquacrop and SAFYE crop models for the assessment of water limited winter wheat yield in regional scale applications

PubMed Central

Pignatti, Stefano; Yang, Hao; Yang, Guijun; Pascucci, Simone; Castaldi, Fabio

2017-01-01

Process-based models can be usefully employed for the assessment of field and regional-scale impact of drought on crop yields. However, in many instances, especially when they are used at the regional scale, it is necessary to identify the parameters and input variables that most influence the outputs and to assess how their influence varies when climatic and environmental conditions change. In this work, two different crop models, able to represent yield response to water, Aquacrop and SAFYE, were compared, with the aim to quantify their complexity and plasticity through Global Sensitivity Analysis (GSA), using Morris and EFAST (Extended Fourier Amplitude Sensitivity Test) techniques, for moderate to strong water limited climate scenarios. Although the rankings of the sensitivity indices was influenced by the scenarios used, the correlation among the rankings, higher for SAFYE than for Aquacrop, assessed by the top-down correlation coefficient (TDCC), revealed clear patterns. Parameters and input variables related to phenology and to water stress physiological processes were found to be the most influential for Aquacrop. For SAFYE, it was found that the water stress could be inferred indirectly from the processes regulating leaf growth, described in the original SAFY model. SAFYE has a lower complexity and plasticity than Aquacrop, making it more suitable to less data demanding regional scale applications, in case the only objective is the assessment of crop yield and no detailed information is sought on the mechanisms of the stress factors affecting its limitations. PMID:29107963

Competitive ability, stress tolerance and plant interactions along stress gradients.

PubMed

Qi, Man; Sun, Tao; Xue, SuFeng; Yang, Wei; Shao, DongDong; Martínez-López, Javier

2018-04-01

Exceptions to the generality of the stress-gradient hypothesis (SGH) may be reconciled by considering species-specific traits and stress tolerance strategies. Studies have tested stress tolerance and competitive ability in mediating interaction outcomes, but few have incorporated this to predict how species interactions shift between competition and facilitation along stress gradients. We used field surveys, salt tolerance and competition experiments to develop a predictive model interspecific interaction shifts across salinity stress gradients. Field survey and greenhouse tolerance tests revealed tradeoffs between stress tolerance and competitive ability. Modeling showed that along salinity gradients, (1) plant interactions shifted from competition to facilitation at high salinities within the physiological limits of salt-intolerant plants, (2) facilitation collapsed when salinity stress exceeded the physiological tolerance of salt-intolerant plants, and (3) neighbor removal experiments overestimate interspecific facilitation by including intraspecific effects. A community-level field experiment, suggested that (1) species interactions are competitive in benign and, facilitative in harsh condition, but fuzzy under medium environmental stress due to niche differences of species and weak stress amelioration, and (2) the SGH works on strong but not weak stress gradients, so SGH confusion arises when it is applied across questionable stress gradients. Our study clarifies how species interactions vary along stress gradients. Moving forward, focusing on SGH applications rather than exceptions on weak or nonexistent gradients would be most productive. © 2018 by the Ecological Society of America.

Compressible Analysis of Bénard Convection of Magneto Rotatory Couple-Stress Fluid

NASA Astrophysics Data System (ADS)

Mehta, C. B.; Singh, M.

2018-02-01

Thermal Instability (Benard's Convection) in the presence of uniform rotation and uniform magnetic field (separately) is studied. Using the linearized stability theory and normal mode analyses the dispersion relation is obtained in each case. In the case of rotatory Benard's stationary convection compressibility and rotation postpone the onset of convection whereas the couple-stress have duel character onset of convection depending on rotation parameter. While in the absence of rotation couple-stress always postpones the onset of convection. On the other hand, magnetic field on thermal instability problem on couple-stress fluid for stationary convection couple-stress parameter and magnetic field postpones the onset of convection. The effect of compressibility also postpones the onset of convection in both cases as rotation and magnetic field. Graphs have been plotted by giving numerical values to the parameters to depict the stationary characteristics. Further, the magnetic field and rotation are found to introduce oscillatory modes which were non-existent in their absence and then the principle of exchange of stability is valid. The sufficient conditions for non-existence of overstability are also obtained.

Effects of external stress field on the charge stability of nitrogen vacancy centers in diamond

NASA Astrophysics Data System (ADS)

Yao, Miao-Miao; Zhu, Tian-Yuan; Shu, Da-Jun

2017-07-01

The interaction of the atom-like defects in semiconductors with external fields provides an avenue to quantum information processing and nanoscale sensors. Meanwhile, external fields may induce instability of the desired charge state of the defects. It is essential to understand how the charge state of a defect is affected by external fields that introduced in diverse applications. In this letter, we explore the stability of the negatively charged state (NV-) and the neutral state (NV0) of the nitrogen vacancy (NV) center in diamond under stress by first-principles calculations. We find that the relative stability of NV- to NV0 is always reduced by the stress if the NV center is free to relax its orientation. Once the NV center has formed and retains its orientation, however, the relative stability of NV- can be always enhanced by compressive stress along its trigonal symmetry axis. We believe that the results are not only significant for control of the charge stability of NV center but also enlightening for applications based on specific charge states of other kinds of defects in the stress field.

Analysis of the stress field and strain rate in Zagros-Makran transition zone

NASA Astrophysics Data System (ADS)

Ghorbani Rostam, Ghasem; Pakzad, Mehrdad; Mirzaei, Noorbakhsh; Sakhaei, Seyed Reza

2018-01-01

Transition boundary between Zagros continental collision and Makran oceanic-continental subduction can be specified by two wide limits: (a) Oman Line is the seismicity boundary with a sizeable reduction in seismicity rate from Zagros in the west to Makran in the east; and (b) the Zendan-Minab-Palami (ZMP) fault system is believed to be a prominent tectonic boundary. The purpose of this paper is to analyze the stress field in the Zagros-Makran transition zone by the iterative joint inversion method developed by Vavrycuk (Geophysical Journal International 199:69-77, 2014). The results suggest a rather uniform pattern of the stress field around these two boundaries. We compare the results with the strain rates obtained from the Global Positioning System (GPS) network stations. In most cases, the velocity vectors show a relatively good agreement with the stress field except for the Bandar Abbas (BABS) station which displays a relatively large deviation between the stress field and the strain vector. This deviation probably reflects a specific location of the BABS station being in the transition zone between Zagros continental collision and Makran subduction zones.

Crop improvement using life cycle datasets acquired under field conditions.

PubMed

Mochida, Keiichi; Saisho, Daisuke; Hirayama, Takashi

2015-01-01

Crops are exposed to various environmental stresses in the field throughout their life cycle. Modern plant science has provided remarkable insights into the molecular networks of plant stress responses in laboratory conditions, but the responses of different crops to environmental stresses in the field need to be elucidated. Recent advances in omics analytical techniques and information technology have enabled us to integrate data from a spectrum of physiological metrics of field crops. The interdisciplinary efforts of plant science and data science enable us to explore factors that affect crop productivity and identify stress tolerance-related genes and alleles. Here, we describe recent advances in technologies that are key components for data driven crop design, such as population genomics, chronological omics analyses, and computer-aided molecular network prediction. Integration of the outcomes from these technologies will accelerate our understanding of crop phenology under practical field situations and identify key characteristics to represent crop stress status. These elements would help us to genetically engineer "designed crops" to prevent yield shortfalls because of environmental fluctuations due to future climate change.

[OPEN FIELD BEHAVIOR AS A PREDICTIVE CRITERIA REFLECTING RATS CORTICOSTERONELEVEL BEFORE AND AFTER STRESS].

PubMed

Umriukhin, P E; Grigorchuk, O S

2015-12-01

In the presented study we investigated the possibility to use the open field behavior data for prediction of corticosterone level in rat blood plasma before and after stress. It is shown that the most reliable open field behavior parameters, reflecting high probability of significant upregulation of corticosterone after 3 hours of immobilization, are the short latency of first movement and low locomotor activity during the test. Rats with high corticosterone at normal non-stress conditions are characterized by low locomotor activity and on the contrary long latency period for the entrance of open field center.

Full-field stress determination in photoelasticity with phase shifting technique

NASA Astrophysics Data System (ADS)

Guo, Enhai; Liu, Yonggang; Han, Yongsheng; Arola, Dwayne; Zhang, Dongsheng

2018-04-01

Photoelasticity is an effective method for evaluating the stress and its spatial variations within a stressed body. In the present study, a method to determine the stress distribution by means of phase shifting and a modified shear-difference is proposed. First, the orientation of the first principal stress and the retardation between the principal stresses are determined in the full-field through phase shifting. Then, through bicubic interpolation and derivation of a modified shear-difference method, the internal stress is calculated from the point with a free boundary along its normal direction. A method to reduce integration error in the shear difference scheme is proposed and compared to the existing methods; the integration error is reduced when using theoretical photoelastic parameters to calculate the stress component with the same points. Results show that when the value of Δx/Δy approaches one, the error is minimum, and although the interpolation error is inevitable, it has limited influence on the accuracy of the result. Finally, examples are presented for determining the stresses in a circular plate and ring subjected to diametric loading. Results show that the proposed approach provides a complete solution for determining the full-field stresses in photoelastic models.

Effects of prenatal stress on vulnerability to stress in prepubertal and adult rats.

PubMed

Fride, E; Dan, Y; Feldon, J; Halevy, G; Weinstock, M

1986-01-01

This study investigated the hypotheses that unpredictable prenatal stress has effects on the offspring, similar to those induced by perinatal administration of glucocorticoids and increases the vulnerability to stressful situations at adulthood. Rats were exposed to random noise and light stress throughout pregnancy. Offspring were tested for the development of spontaneous alternation behavior (SA) and at adulthood, their response to novel or aversive situations, open field, extinction and punishment following acquisition of an appetitive response and two-way active avoidance, were assessed. In prenatally stressed rats, the development of SA was significantly delayed. On repeated exposure to an open field they were less active; control rats had elevated plasma corticosterone (CCS) on days 2 and 4 of open field exposure, while prenatally stressed rats had significantly raised plasma CCS after each exposure (days 1-8). Furthermore, punishment-induced suppression of an appetitive response was enhanced. Acquisition of active avoidance was faciliated in female but reduced in male prenatally stressed offspring. It is suggested that random prenatal noise and light stress may cause impairment of development of hippocampal function which lasts into adulthood. This impairment is manifested as an increase in vulnerability and a decrease in habituation to stressful stimuli.

A new procedure for investigating three-dimensional stress fields in a thin plate with a through-the-thickness crack

NASA Astrophysics Data System (ADS)

Yi, Dake; Wang, TzuChiang

2018-06-01

In the paper, a new procedure is proposed to investigate three-dimensional fracture problems of a thin elastic plate with a long through-the-thickness crack under remote uniform tensile loading. The new procedure includes a new analytical method and high accurate finite element simulations. In the part of theoretical analysis, three-dimensional Maxwell stress functions are employed in order to derive three-dimensional crack tip fields. Based on the theoretical analysis, an equation which can describe the relationship among the three-dimensional J-integral J( z), the stress intensity factor K( z) and the tri-axial stress constraint level T z ( z) is derived first. In the part of finite element simulations, a fine mesh including 153360 elements is constructed to compute the stress field near the crack front, J( z) and T z ( z). Numerical results show that in the plane very close to the free surface, the K field solution is still valid for in-plane stresses. Comparison with the numerical results shows that the analytical results are valid.

Recent Progress in Understanding the Shock Response of Ferroelectric Ceramics*

NASA Astrophysics Data System (ADS)

Setchell, Robert E.

2001-06-01

Ferroelectric ceramics exhibit a permanent remanent polarization, and the use of shock depoling of these materials to achieve pulsed sources of electrical power was proposed in the late 1950s. During the following twenty years, extensive studies were conducted to examine the shock response of ferroelectric ceramics primarily based on lead zirconate titanate (PZT). Under limited conditions, relatively simple analytical models were found to adequately describe the observed electrical behavior. In general, however, the studies indicated a complex behavior involving finite-rate depoling kinetics with stress and field dependencies. Dielectric relaxation and shock-induced conductivity were also suggested. Unfortunately, few experimental studies were undertaken over the next twenty years, and the development of more comprehensive models was inhibited. In recent years, a strong interest in advancing numerical simulation capabilities has motivated new experimental studies and corresponding model development. More than seventy gas gun experiments have examined several ferroelectric ceramics, with most experiments on lead zirconate titanate having a Zr:Ti ratio of 95:5 and modified with 2ferroelectric but is near an antiferroelectric phase boundary, and depoling results from a shock-driven phase transition. Experiments have examined unpoled, normally poled, and axially poled PZT 95/5 over broad ranges of shock pressure and peak electric field. The extensive base of new data provides quantitative insights into the stress and field dependencies of depoling kinetics and dielectric properties, and is being actively utilized to develop and refine material response models used in numerical simulations of pulsed power devices.

Study of wavefront error and polarization of a side mounted infrared window

NASA Astrophysics Data System (ADS)

Liu, Jiaguo; Li, Lin; Hu, Xinqi; Yu, Xin

2008-03-01

The wavefront error and polarization of a side mounted infrared window made of ZnS are studied. The Infrared windows suffer from temperature gradient and stress during their launch process. Generally, the gradient in temperature changes the refractive index of the material whereas stress produces deformation and birefringence. In this paper, a thermal finite element analysis (FEA) of an IR window is presented. For this purpose, we employed an FEA program Ansys to obtain the time-varying temperature field. The deformation and stress of the window are derived from a structural FEA with the aerodynamic force and the temperature field previously obtained as being the loads. The deformation, temperature field, stress field, ray tracing and Jones Calculus are used to calculate the wavefront error and the change of polarization state.

Calculation of open and closed system elastic coefficients for multicomponent solids

NASA Astrophysics Data System (ADS)

Mishin, Y.

2015-06-01

Thermodynamic equilibrium in multicomponent solids subject to mechanical stresses is a complex nonlinear problem whose exact solution requires extensive computations. A few decades ago, Larché and Cahn proposed a linearized solution of the mechanochemical equilibrium problem by introducing the concept of open system elastic coefficients [Acta Metall. 21, 1051 (1973), 10.1016/0001-6160(73)90021-7]. Using the Ni-Al solid solution as a model system, we demonstrate that open system elastic coefficients can be readily computed by semigrand canonical Monte Carlo simulations in conjunction with the shape fluctuation approach. Such coefficients can be derived from a single simulation run, together with other thermodynamic properties needed for prediction of compositional fields in solid solutions containing defects. The proposed calculation approach enables streamlined solutions of mechanochemical equilibrium problems in complex alloys. Second order corrections to the linear theory are extended to multicomponent systems.

Strategies to engineer tendon/ligament-to-bone interface: Biomaterials, cells and growth factors.

PubMed

Font Tellado, Sonia; Balmayor, Elizabeth R; Van Griensven, Martijn

2015-11-01

Integration between tendon/ligament and bone occurs through a specialized tissue interface called enthesis. The complex and heterogeneous structure of the enthesis is essential to ensure smooth mechanical stress transfer between bone and soft tissues. Following injury, the interface is not regenerated, resulting in high rupture recurrence rates. Tissue engineering is a promising strategy for the regeneration of a functional enthesis. However, the complex structural and cellular composition of the native interface makes enthesis tissue engineering particularly challenging. Thus, it is likely that a combination of biomaterials and cells stimulated with appropriate biochemical and mechanical cues will be needed. The objective of this review is to describe the current state-of-the-art, challenges and future directions in the field of enthesis tissue engineering focusing on four key parameters: (1) scaffold and biomaterials, (2) cells, (3) growth factors and (4) mechanical stimuli. Copyright © 2015 Elsevier B.V. All rights reserved.

Tool for simplifying the complex interactions within resilient communities

NASA Astrophysics Data System (ADS)

Stwertka, C.; Albert, M. R.; White, K. D.

2016-12-01

In recent decades, scientists have observed and documented impacts from climate change that will impact multiple sectors, will be impacted by decisions from multiple sectors, and will change over time. This complex human-engineered system has a large number of moving, interacting parts, which are interdependent and evolve over time towards their purpose. Many of the existing resilience frameworks and vulnerability frameworks focus on interactions between the domains, but do not include the structure of the interactions. We present an engineering systems approach to investigate the structural elements that influence a community's ability to be resilient. In this presentation we will present and analyze four common methods for building community resilience, utilizing our common framework. For several existing case studies we examine the stress points in the system and identify the impacts on the outcomes from the case studies. In ongoing research we will apply our system tool to a new case in the field.

Cracking mechanism of shale cracks during fracturing

NASA Astrophysics Data System (ADS)

Zhao, X. J.; Zhan, Q.; Fan, H.; Zhao, H. B.; An, F. J.

2018-06-01

In this paper, we set up a model for calculating the shale fracture pressure on the basis of Huang’s model by the theory of elastic-plastic mechanics, rock mechanics and the application of the maximum tensile stress criterion, which takes into account such factors as the crustal stress field, chemical field, temperature field, tectonic stress field, the porosity of shale and seepage of drilling fluid and so on. Combined with the experimental data of field fracturing and the experimental results of three axis compression of shale core with different water contents, the results show that the error between the present study and the measured value is 3.85%, so the present study can provide technical support for drilling engineering.

Basin scale permeability and thermal evolution of a magmatic hydrothermal system

NASA Astrophysics Data System (ADS)

Taron, J.; Hickman, S. H.; Ingebritsen, S.; Williams, C.

2013-12-01

Large-scale hydrothermal systems are potentially valuable energy resources and are of general scientific interest due to extreme conditions of stress, temperature, and reactive chemistry that can act to modify crustal rheology and composition. With many proposed sites for Enhanced Geothermal Systems (EGS) located on the margins of large-scale hydrothermal systems, understanding the temporal evolution of these systems contributes to site selection, characterization and design of EGS. This understanding is also needed to address the long-term sustainability of EGS once they are created. Many important insights into heat and mass transfer within natural hydrothermal systems can be obtained through hydrothermal modeling assuming that stress and permeability structure do not evolve over time. However, this is not fully representative of natural systems, where the effects of thermo-elastic stress changes, chemical fluid-rock interactions, and rock failure on fluid flow and thermal evolution can be significant. The quantitative importance of an evolving permeability field within the overall behavior of a large-scale hydrothermal system is somewhat untested, and providing such a parametric understanding is one of the goals of this study. We explore the thermal evolution of a sedimentary basin hydrothermal system following the emplacement of a magma body. The Salton Sea geothermal field and its associated magmatic system in southern California is utilized as a general backdrop to define the initial state. Working within the general framework of the open-source scientific computing initiative OpenGeoSys (www.opengeosys.org), we introduce full treatment of thermodynamic properties at the extreme conditions following magma emplacement. This treatment utilizes a combination of standard Galerkin and control-volume finite elements to balance fluid mass, mechanical deformation, and thermal energy with consideration of local thermal non-equilibrium (LTNE) between fluids and solids. Permeability is allowed to evolve under several constitutive models tailored to both porous media and fractures, considering the influence of both mechanical stress and diagenesis. In this first analysis, a relatively simple mechanical model is used; complexity will be added incrementally to represent specific characteristics of the Salton Sea hydrothermal field.

Electric foot shock stress adaptation: Does it exist or not?

PubMed

Bali, Anjana; Jaggi, Amteshwar Singh

2015-06-01

Stress adaptation is a protective phenomenon against repeated stress exposure and is characterized by a decreased responsiveness to a repeated stress stimulus. The adaptation is associated with a complex cascade of events, including the changes in behavior, neurotransmitter and gene expression levels. The non-adaptation or maladaptation to stress may underlie the affective disorders, such as anxiety, depression and post-traumatic stress disorder (PTSD). Electric foot shock is a complex stressor, which includes both physical and emotional components. Unlike immobilization, restraint and cold immersion stress, the phenomenon of stress adaptation is not very well defined in response to electric foot shock. A number of preclinical studies have reported the development of adaptation to electric foot shock stress. However, evidence also reveals the non-adaptive behavior in response to foot shocks. The distinct adaptive/non-adaptive responses may be possibly influenced by the type, intensity, and duration of the stress. The present review discusses the existence or non-existence of adaptation to electric foot shock stress along with possible mechanism. Copyright © 2015 Elsevier Inc. All rights reserved.

Prediction of Complex Aerodynamic Flows with Explicit Algebraic Stress Models

NASA Technical Reports Server (NTRS)

Abid, Ridha; Morrison, Joseph H.; Gatski, Thomas B.; Speziale, Charles G.

1996-01-01

An explicit algebraic stress equation, developed by Gatski and Speziale, is used in the framework of K-epsilon formulation to predict complex aerodynamic turbulent flows. The nonequilibrium effects are modeled through coefficients that depend nonlinearly on both rotational and irrotational strains. The proposed model was implemented in the ISAAC Navier-Stokes code. Comparisons with the experimental data are presented which clearly demonstrate that explicit algebraic stress models can predict the correct response to nonequilibrium flow.

Efficient modeling of photonic crystals with local Hermite polynomials

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

Boucher, C. R.; Li, Zehao; Albrecht, J. D.

2014-04-21

Developing compact algorithms for accurate electrodynamic calculations with minimal computational cost is an active area of research given the increasing complexity in the design of electromagnetic composite structures such as photonic crystals, metamaterials, optical interconnects, and on-chip routing. We show that electric and magnetic (EM) fields can be calculated using scalar Hermite interpolation polynomials as the numerical basis functions without having to invoke edge-based vector finite elements to suppress spurious solutions or to satisfy boundary conditions. This approach offers several fundamental advantages as evidenced through band structure solutions for periodic systems and through waveguide analysis. Compared with reciprocal space (planemore » wave expansion) methods for periodic systems, advantages are shown in computational costs, the ability to capture spatial complexity in the dielectric distributions, the demonstration of numerical convergence with scaling, and variational eigenfunctions free of numerical artifacts that arise from mixed-order real space basis sets or the inherent aberrations from transforming reciprocal space solutions of finite expansions. The photonic band structure of a simple crystal is used as a benchmark comparison and the ability to capture the effects of spatially complex dielectric distributions is treated using a complex pattern with highly irregular features that would stress spatial transform limits. This general method is applicable to a broad class of physical systems, e.g., to semiconducting lasers which require simultaneous modeling of transitions in quantum wells or dots together with EM cavity calculations, to modeling plasmonic structures in the presence of EM field emissions, and to on-chip propagation within monolithic integrated circuits.« less

Stress distribution calculations through a snow slab of varying elastic modulus; comparison with stability evaluation in the field

NASA Astrophysics Data System (ADS)

Swinkels, Laura; Borstad, Chris

2017-04-01

Field observations are the main tools for assessing the snow stability concerning dry snow slab avalanche release. Often, theoretical studies cannot directly be translated into useful information for avalanche recreationists and forecasters in the field, and vice versa; field observations are not always objective and quantifiable for theoretical studies. Moreover, numerical models often simplify the snowpack and generally use an isotropic single layer slab which is not representative of the real-life situation. The aim of this study is to investigate the stress distribution in a snowpack with an elastic modulus that continuously varies with depth. The focus lies on the difference between a slab with a gradient in hardness and a slab with isotropic hardness and the effect on the calculated maximum stress and the stability evaluation in the field. Approximately 20 different snow pits were evaluated in the mountains around Tromsø, Norway and Longyearbyen, Svalbard. In addition to the standard snowpack observations, the hardness was measured using a thin-blade gauge. Extended column tests were executed for stability evaluation. Measurements from the field were used as input for stress calculations for each snow pit using a line load solution for a sloping half space with a non-homogeneous elastic modulus. The hardness measurements were used to calculate the elastic modulus and a power law relation was fit through the modulus in the slab. The calculated shear stress was compared to the estimated stability and character of the specific snowpack The results show that the approach used for this study improves the calculation of stress at a given depth, although many assumptions and simplifications were still needed. Comparison with the snow profiles indicate that calculated stresses correlate well with the observed snowpack properties and stability. The calculated shear stresses can be introduced in the standard stability index and give a better indication for the snowpack stability. Further research is required to delimit the stresses needed for propagation of a weak layer fracture.

Shear flow of one-component polarizable fluid in a strong electric field

NASA Astrophysics Data System (ADS)

Sun, J. M.; Tao, R.

1996-04-01

A shear flow of one-component polarizable fluid in a strong electric field has a structural transition at a critical shear stress. When the shear stress is increased from zero up to the critical shear stress, the flow (in the x direction) has a flowing-chain (FC) structure, consisting of tilted or broken chains along the field (z direction). At the critical shear stress, the FC structure gives way to a flowing-hexagonal-layered (FHL) structure, consisting of several two-dimensional layers which are parallel to the x-z plane. Within one layer, particles form strings in the flow direction. Strings are constantly sliding over particles in strings right beneath. The effective viscosity drops dramatically at the structural change. As the shear stress reduces, the FHL structure persists even under a stress-free state if the thermal fluctuation is very weak. This structure change in the charging and discharging process produces a large hysteresis.

Correlation between the local stress and the grain misorientation in the polycrystalline Al2O3 measured by near-field luminescence spectroscopy

NASA Astrophysics Data System (ADS)

Tomimatsu, Toru; Takigawa, Ryo

2018-06-01

Owing to its high spatial resolution, near-field spectroscopy is a useful method for sensing the stress in a narrow region of submicron order. Here, on the basis of the highly resolved images obtained by near-field luminescence spectroscopy, we propose a statistical method of analyzing grain anisotropy-induced stress in polycrystalline Al2O3. We focus on two characteristics of a spectra: the intensity ratio and peak shift of luminescence of two lines (R1 and R2) from Al2O3 to discuss crystal orientation and stress, respectively. By incorporating the concept of the crystal misorientation parameter using intensity ratio, an apparent correlation between the magnitude of stress and the misorientation is found. This correlation analysis provides an important insight for the investigation of local thermal stress in Al2O3.

Dynamo magnetic-field generation in turbulent accretion disks

NASA Technical Reports Server (NTRS)

Stepinski, T. F.

1991-01-01

Magnetic fields can play important roles in the dynamics and evolution of accretion disks. The presence of strong differential rotation and vertical density gradients in turbulent disks allows the alpha-omega dynamo mechanism to offset the turbulent dissipation and maintain strong magnetic fields. It is found that MHD dynamo magnetic-field normal modes in an accretion disk are highly localized to restricted regions of a disk. Implications for the character of real, dynamically constrained magnetic fields in accretion disks are discussed. The magnetic stress due to the mean magnetic field is found to be of the order of a viscous stress. The dominant stress, however, is likely to come from small-scale fluctuating magnetic fields. These fields may also give rise to energetic flares above the disk surface, providing a possible explanation for the highly variable hard X-ray emission from objects like Cyg X-l.

Stress regimes in the northwest of Iran from stress inversion of earthquake focal mechanisms

NASA Astrophysics Data System (ADS)

Afra, Mahsa; Moradi, Ali; Pakzad, Mehrdad

2017-11-01

Northwestern Iran is one of the seismically active regions with a high seismic risk in the world. This area is a part of the complex tectonic system due to the interaction between Arabia, Anatolia and Eurasia. The purpose of this study is to deduce the stress regimes in the northwestern Iran and surrounding regions from stress inversion of earthquake focal mechanisms. We compile 92 focal mechanisms data from the Global CMT catalogue and other sources and also determine the focal mechanisms of 14 earthquakes applying the moment tensor inversion. We divide the studied region into 9 zones using similarity of the horizontal GPS velocities and existing focal mechanisms. We implement two stress inversion methods, Multiple Inverse Method and Iterative Joint Inversion Method, which provide comparable results in terms of orientations of maximum horizontal stress axes SHmax. The similar results of the two methods should make us more confident about the interpretations. We consider zones of exclusion surrounding all the earthquakes according to independent focal mechanisms hypothesis. The hypothesis says that the inversion should involve events that are far enough from each other in order that any previous event doesn't affect the stress field near the earthquake under consideration. Accordingly we deal with the matter by considering zones of exclusion around all the events. The result of exclusion is only significant for eastern Anatolia. The stress regime in this region changes from oblique to strike slip faulting because of the exclusion. In eastern Anatolia, the direction of maximum horizontal stress is nearly north-south. The direction alters to east-west in Talesh region. Errors of σ1 are lower in all zones comparing with errors of σ2 and σ3 and there is a trade-off between data resolution and covariance of the model. The results substantiate the strike-slip and thrust faulting stress regimes in the northwest of Iran.

Insights into the movements of landslides from combinations of field monitoring and novel direct shear testing

NASA Astrophysics Data System (ADS)

Petley, D. N.; Carey, J.; Massey, C. I.; Brain, M.

2015-12-01

The mechanisms of pre- and post-failure movement of translational landslides remain surprisingly poorly investigated. Previous approaches have focussed on field monitoring, for example through high resolution automated surveying and/or GPS measurements, or from modelling using dedicated codes. There has been some experimental work too, most notably using ring shear devices, although there are limitations as to the type of analyses that can be completed in these devices. In recent years the author has been involved in a series of studies that have sought to understand pre- and post-failure behaviour in translational landslides using both high precision monitoring and experimental investigation using novel apparatus. The latter approach has involved the use of the back pressured shear box, a direct shear machine that allows near-infinite variation of the normal and shear stress state, and measurement and control of the pore water pressure. More recently, a more advanced version of this machine has been developed that allows dynamic loading of both direct and normal shear stresses. This paper presents key lessons learnt about the behaviour of translational landslides from these approaches. The data highlight a number of key elements: The important differences in pre-failure behaviour for materials that show a brittle response compared with those that are ductile. In particular, some aspects of behaviour (e.g. the hyperbolic acceleration to failure) can only be replicated in materials that show brittle cracking processes; In the post-failure domain, all materials show a high level of sensitivity to small changes in pore water pressure when the Factor of Safety is close to unity; Rates of strain are not simply related to pore water pressure / stress state. In particular, some materials show a different deformation response during phases of increasing pore water pressure to that during periods of pore water pressure reduction. The reasons for this require further study; Dynamic behaviour is complex, with variations in behaviour between different materials types being greater than expected. These results show that the behaviour of materials in the post-failure domain is more complex than had been appreciated previously, suggesting that more work is needed to explain landslide behaviour in this regime.

Collaborative-Large scale Engineering Assessment Networks for Environmental Research: The Overview

NASA Astrophysics Data System (ADS)

Moo-Young, H.

2004-05-01

A networked infrastructure for engineering solutions and policy alternatives is necessary to assess, manage, and protect complex, anthropogenic ally stressed environmental resources effectively. Reductionist and discrete disciplinary methodologies are no longer adequate to evaluate and model complex environmental systems and anthropogenic stresses. While the reductonist approach provides important information regarding individual mechanisms, it cannot provide complete information about how multiple processes are related. Therefore, it is not possible to make accurate predictions about system responses to engineering interventions and the effectiveness of policy options. For example, experts cannot agree on best management strategies for contaminated sediments in riverine and estuarine systems. This is due, in part to the fact that existing models do not accurately capture integrated system dynamics. In addition, infrastructure is not available for investigators to exchange and archive data, to collaborate on new investigative methods, and to synthesize these results to develop engineering solutions and policy alternatives. Our vision for the future is to create a network comprising field facilities and a collaboration of engineers, scientists, policy makers, and community groups. This will allow integration across disciplines, across different temporal and spatial scales, surface and subsurface geographies, and air sheds and watersheds. Benefits include fast response to changes in system health, real-time decision making, and continuous data collection that can be used to anticipate future problems, and to develop sound engineering solutions and management decisions. CLEANER encompasses four general aspects: 1) A Network of environmental field facilities instrumented for the acquisition and analysis of environmental data; 2) A Virtual Repository of Data and information technology for engineering modeling, analysis and visualization of data, i.e. an environmental cyber-infrastructure; 3) A Mechanism for multidisciplinary research and education activities designed to exploit the output of the instrumented sites and networked information technology, to formulate engineering and policy options directed toward the protection, remediation, and restoration of stressed environments and sustainability of environmental resources; and 4) A Collaboration among engineers, natural and social scientists, educators, policy makers, industry, non-governmental organizations, the public, and other stakeholders.

Social defeat models in animal science: What we have learned from rodent models.

PubMed

Toyoda, Atsushi

2017-07-01

Studies on stress and its impacts on animals are very important in many fields of science, including animal science, because various stresses influence animal production and animal welfare. In particular, the social stresses within animal groups have profound impact on animals, with the potential to induce abnormal behaviors and health problems. In humans, social stress induces several health problems, including psychiatric disorders. In animal stress models, social defeat models are well characterized and used in various research fields, particularly in studies concerning mental disorders. Recently, we have focused on behavior, nutrition and metabolism in rodent models of social defeat to elucidate how social stresses affect animals. In this review, recent significant progress in studies related to animal social defeat models are described. In the field of animal science, these stress models may contribute to advances in the development of functional foods and in the management of animal welfare. © 2017 The Authors. Animal Science Journal published by John Wiley & Sons Australia, Ltd on behalf of Japanese Society of Animal Science.

Improved assumed-stress hybrid shell element with drilling degrees of freedom for linear stress, buckling, and free vibration analyses

NASA Technical Reports Server (NTRS)

Rengarajan, Govind; Aminpour, Mohammad A.; Knight, Norman F., Jr.

1992-01-01

An improved four-node quadrilateral assumed-stress hybrid shell element with drilling degrees of freedom is presented. The formulation is based on Hellinger-Reissner variational principle and the shape functions are formulated directly for the four-node element. The element has 12 membrane degrees of freedom and 12 bending degrees of freedom. It has nine independent stress parameters to describe the membrane stress resultant field and 13 independent stress parameters to describe the moment and transverse shear stress resultant field. The formulation encompasses linear stress, linear buckling, and linear free vibration problems. The element is validated with standard tests cases and is shown to be robust. Numerical results are presented for linear stress, buckling, and free vibration analyses.

Stress-tuned conductor-polymer composite for use in sensors

DOEpatents

Martin, James E; Read, Douglas H

2013-10-22

A method for making a composite polymeric material with electrical conductivity determined by stress-tuning of the conductor-polymer composite, and sensors made with the stress-tuned conductor-polymer composite made by this method. Stress tuning is achieved by mixing a miscible liquid into the polymer precursor solution or by absorbing into the precursor solution a soluble compound from vapor in contact with the polymer precursor solution. The conductor may or may not be ordered by application of a magnetic field. The composite is formed by polymerization with the stress-tuning agent in the polymer matrix. The stress-tuning agent is removed following polymerization to produce a conductor-polymer composite with a stress field that depends on the amount of stress-tuning agent employed.

Effects of stress on alcohol drinking: a review of animal studies

PubMed Central

Lopez, Marcelo F.; Doremus-Fitzwater, Tamara L.

2011-01-01

Rationale While stress is often proposed to play a significant role in influencing alcohol consumption, the relationship between stress and alcohol is complex and poorly understood. Over several decades, stress effects on alcohol drinking have been studied using a variety of animal models and experimental procedures, yet this large body of literature has generally produced equivocal results. Objectives This paper reviews results from animal studies in which alcohol consumption is evaluated under conditions of acute/sub-chronic stress exposure or models of chronic stress exposure. Evidence also is presented indicating that chronic intermittent alcohol exposure serves as a stressor that consequently influences drinking. Results The effects of various acute/sub-chronic stress procedures on alcohol consumption have generally been mixed, but most study outcomes suggest either no effect or decreased alcohol consumption. In contrast, most studies indicate that chronic stress, especially when administered early in development, results in elevated drinking later in adulthood. Chronic alcohol exposure constitutes a potent stressor itself, and models of chronic intermittent alcohol exposure reliably produce escalation of voluntary alcohol consumption. Conclusions A complex and dynamic interplay among a wide array of genetic, biological, and environmental factors govern stress responses, regulation of alcohol drinking, and the circumstances in which stress modulates alcohol consumption. Suggestions for future directions and new approaches are presented that may aid in developing more sensitive and valid animal models that not only better mimic the clinical situation, but also provide greater understanding of mechanisms that underlie the complexity of stress effects on alcohol drinking. PMID:21850445

Radiation Forces and Torques without Stress (Tensors)

ERIC Educational Resources Information Center

Bohren, Craig F.

2011-01-01

To understand radiation forces and torques or to calculate them does not require invoking photon or electromagnetic field momentum transfer or stress tensors. According to continuum electromagnetic theory, forces and torques exerted by radiation are a consequence of electric and magnetic fields acting on charges and currents that the fields induce…

Nonlocal elasticity tensors in dislocation and disclination cores

DOE PAGES

Taupin, V.; Gbemou, K.; Fressengeas, C.; ...

2017-01-07

We introduced nonlocal elastic constitutive laws for crystals containing defects such as dislocations and disclinations. Additionally, the pointwise elastic moduli tensors adequately reflect the elastic response of defect-free regions by relating stresses to strains and couple-stresses to curvatures, elastic cross-moduli tensors relating strains to couple-stresses and curvatures to stresses within convolution integrals are derived from a nonlocal analysis of strains and curvatures in the defects cores. Sufficient conditions are derived for positive-definiteness of the resulting free energy, and stability of elastic solutions is ensured. The elastic stress/couple stress fields associated with prescribed dislocation/disclination density distributions and solving the momentum andmore » moment of momentum balance equations in periodic media are determined by using a Fast Fourier Transform spectral method. Here, the convoluted cross-moduli bring the following results: (i) Nonlocal stresses and couple stresses oppose their local counterparts in the defects core regions, playing the role of restoring forces and possibly ensuring spatio-temporal stability of the simulated defects, (ii) The couple stress fields are strongly affected by nonlocality. Such effects favor the stability of the simulated grain boundaries and allow investigating their elastic interactions with extrinsic defects, (iii) Driving forces inducing grain growth or refinement derive from the self-stress and couple stress fields of grain boundaries in nanocrystalline configurations.« less

Stress measurements in Kuzbass mines using photoelastic sensors

NASA Astrophysics Data System (ADS)

Schastlivtsev, E.

1996-06-01

The basic amount of known measurements of stressed state in front of development workings' faces was carried out with the use of hydraulic sensors, which give an information about principal stresses without their separation. Besides, the availability of pipe-line and cumbersome equipment make more complicated and sometimes impossible the process of stresses' measurements during works in mining process. In our opinion, the borehole and photoelastic sensors at high degree satisfy with the conditions of stresses' measurements in front of mining workings' faces. The principal idea of the method is in the usage of proper face advancing aiming the estimation of the field stresses in its neighborhood. Borehole and photoelastic sensors, fixed in the advanced boreholes, drilled from the active face react to the field change of stresses or deformation caused by working face advancing. While obtaining this information we may judge about the distribution of additional stresses in rock of face's neighborhood and concentration of stresses in front of face. The usage of cavity (because of face advancing) in the quality of disturbing influence in combination with the properties of ring photoelastic sensor to given an information about magnitude and direction of secondary principle stresses, permits us to obtain rather a simple and not labor consuming method of investigation of field additional stresses in the working's face neighborhood.

Mapping residual stress fields from Vickers hardness indents using Raman microprobe spectroscopy

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

Sparks, R.G.; Enloe, W.S.; Paesler, M.A.

Micro-Raman spectroscopy is used to map the residual stress fields in the vicinity of Vickers hardness indents. Both 514.5 and 488.0 nm, light is used to excite the effect and the resulting shifted and broadened Raman peaks are analyzed using computer deconvolution. Half-wave plates are used to vary the orientation of the incident later light`s polarization state with respect to crystal orientation. The Raman scattered light is then analyzed for polarization dependences which are indicative of the various components of the Raman scattering tensor. Such studies can yield valuable information about the orientation of stress components in a well knownmore » stress field. The results can then be applied to the determination of stress components in machined semiconductor materials.« less

Fault reactivation and seismicity risk from CO2 sequestration in the Chinshui gas field, NW Taiwan

NASA Astrophysics Data System (ADS)

Sung, Chia-Yu; Hung, Jih-Hao

2015-04-01

The Chinshui gas field located in the fold-thrust belt of western Taiwan was a depleted reservoir. Recently, CO2 sequestration has been planned at shallower depths of this structure. CO2 injection into reservoir will generate high fluid pressure and trigger slip on reservoir-bounding faults. We present detailed in-situ stresses from deep wells in the Chinshui gas field and evaluated the risk of fault reactivation for underground CO2 injection. The magnitudes of vertical stress (Sv), formation pore pressure (Pf) and minimum horizontal stress (Shmin) were obtained from formation density logs, repeat formation tests, sonic logs, mud weight, and hydraulic fracturing including leak-off tests and hydraulic fracturing. The magnitude of maximum horizontal stress (SHmax) was constrained by frictional limit of critically stressed faults. Results show that vertical stress gradient is about 23.02 MPa/km (1.02 psi/ft), and minimum horizontal stress gradient is 18.05 MPa/km (0.80 psi/ft). Formation pore pressures were hydrostatic at depths 2 km, and increase with a gradient of 16.62 MPa/km (0.73 psi/ft). The ratio of fluid pressure and overburden pressure (λp) is 0.65. The upper bound of maximum horizontal stress constrained by strike-slip fault stress regime (SHmax>Sv>Shmin) and coefficient of friction (μ=0.6) is about 18.55 MPa/km (0.82 psi/ft). The orientation of maximum horizontal stresses was calculated from four-arm caliper tools through the methodology suggested by World Stress Map (WMS). The mean azimuth of preferred orientation of borehole breakouts are in ~65。N. Consequently, the maximum horizontal stress axis trends in 155。N and sub-parallel to the far-field plate-convergence direction. Geomechanical analyses of the reactivation of pre-existing faults was assessed using 3DStress and Traptester software. Under current in-situ stress, the middle block fault has higher slip tendency, but still less than frictional coefficient of 0.6 a common threshold value for motion on incohesive faults. The results also indicate that CO2 injection in the Chinshui gas field will not compromise the stability of faults.

Slope instability in complex 3D topography promoted by convergent 3D groundwater flow

NASA Astrophysics Data System (ADS)

Reid, M. E.; Brien, D. L.

2012-12-01

Slope instability in complex topography is generally controlled by the interaction between gravitationally induced stresses, 3D strengths, and 3D pore-fluid pressure fields produced by flowing groundwater. As an example of this complexity, coastal bluffs sculpted by landsliding commonly exhibit a progression of undulating headlands and re-entrants. In this landscape, stresses differ between headlands and re-entrants and 3D groundwater flow varies from vertical rainfall infiltration to lateral groundwater flow on lower permeability layers with subsequent discharge at the curved bluff faces. In plan view, groundwater flow converges in the re-entrant regions. To investigate relative slope instability induced by undulating topography, we couple the USGS 3D limit-equilibrium slope-stability model, SCOOPS, with the USGS 3D groundwater flow model, MODFLOW. By rapidly analyzing the stability of millions of potential failures, the SCOOPS model can determine relative slope stability throughout the 3D domain underlying a digital elevation model (DEM), and it can utilize both fully 3D distributions of pore-water pressure and material strength. The two models are linked by first computing a groundwater-flow field in MODFLOW, and then computing stability in SCOOPS using the pore-pressure field derived from groundwater flow. Using these two models, our analyses of 60m high coastal bluffs in Seattle, Washington showed augmented instability in topographic re-entrants given recharge from a rainy season. Here, increased recharge led to elevated perched water tables with enhanced effects in the re-entrants owing to convergence of groundwater flow. Stability in these areas was reduced about 80% compared to equivalent dry conditions. To further isolate these effects, we examined groundwater flow and stability in hypothetical landscapes composed of uniform and equally spaced, oscillating headlands and re-entrants with differing amplitudes. The landscapes had a constant slope for both headlands and re-entrants to minimize slope effects on stability. Despite these equal slopes, our analyses, given dry conditions, illustrated that the headlands can be 5-7% less stable than the re-entrants, owing to the geometry of the 3D failure mass with the lowest stability. We then simulated groundwater flow in these landscapes; flow was caused by recharge perching on a horizontal low permeability layer with discharge at the bluff faces. By systematically varying recharge, hydraulic conductivity of the material, and conductance at the bluffs, we created different 3D pore-pressure fields. Recharge rates and hydraulic conductivities controlled the height of the water table, whereas bluff conductance influenced the gradient of the water table near the bluff face. Given elevated water tables with steep gradients, bluffs in the re-entrants became unstable where flow converged. Thus, with progressively stronger effects from water flow, overall instability evolved from relatively unstable headlands to more uniform stability to relatively unstable re-entrants. Larger re-entrants led to more 3D flow convergence and greater localized instability. One- or two-dimensional models cannot fully characterize slope instability in complex topography.

Elevated lateral stress in unlithified sediment, Midcontinent, United States - geotechnical and geophysical indicators for a tectonic origin

USGS Publications Warehouse

Woolery, E.W.; Schaefer, J.A.; Wang, Z.

2003-01-01

Indirect and direct geotechnical measurements revealed the presence of high lateral earth pressure (Ko) in shallow, unlithified sediment at a site in the northernmost Mississippi embayment region of the central United States. Results from pile-load and pressuremeter tests showed maximum Ko values greater than 10; however, the complex geologic environment of the Midcontinent made defining an origin for the anomalous Ko based solely on these measurements equivocal. Although in situ sediment characteristics indicated that indirect tectonic or nontectonic geologic mechanisms that include transient overburden loads (e.g., fluvial deposition/erosion, glacial advance/retreat) and dynamic shear loads (e.g., earthquakes) were not the dominant cause, they were unable to provide indicators for a direct tectonic generation. Localized stresses induced anthropogenically by the geotechnical field tests were also considered, but ruled out as the primary origin. A high-resolution shear-wave (SH) reflection image of geologic structure in the immediate vicinity of the test site revealed compression-style neotectonism, and suggested that the elevated stress was a tectonic manifestation. Post-Paleozoic reflectors exhibit a Tertiary (?) structural inversion, as evidenced by post-Cretaceous fault displacement and pronounced positive folds in the hanging wall of the interpreted faults. The latest stratigraphic extent of the stress effects (i.e., all measurements were in the Late Cretaceous to Tertiary McNairy Formation), as well as the relationship of stress orientation with the orientation of local structure and regional stress, remain unknown. These are the subjects of ongoing studies. ?? 2003 Elsevier Science B.V. All rights reserved.

Stress fields in soft material induced by injection of highly-focused microjets

NASA Astrophysics Data System (ADS)

Miyazaki, Yuta; Endo, Nanami; Kawamoto, Sennosuke; Kiyama, Akihito; Tagawa, Yoshiyuki

2017-11-01

Needle-free drug injection systems using high-speed microjets are of great importance for medical innovations since they can solve problems of the conventional needle injection systems. However, the mechanical stress acting on the skin/muscle of patients during the penetration of liquid-drug microjets had not been clarified. In this study we investigate the stress caused by the penetration of microjets into soft materials, which is compared with the stress induced by the penetration of needles. In order to capture high-speed temporal evolution of the stress field inside the material, we utilized a high-speed polarized camera and gelatin that resembles human skin. Remarkably we find clear differences in the stress fields induced by microjets and needles. On one hand, high shear stress induced by the microjets is attenuated immediately after the injection, even though the liquid stays inside the soft material. On the other hand, high-shear stress induced by the needles stays and never decays unless the needles are entirely removed from the material. JSPS KAKENHI Grant Numbers 26709007 and 17H01246.

Fractured rock stress-permeability relationships from in situ data and effects of temperature and chemical-mechanical couplings

DOE PAGES

Rutqvist, J.

2014-09-19

The purpose of this paper is to (i) review field data on stress-induced permeability changes in fractured rock; (ii) describe estimation of fractured rock stress-permeability relationships through model calibration against such field data; and (iii) discuss observations of temperature and chemically mediated fracture closure and its effect on fractured rock permeability. The field data that are reviewed include in situ block experiments, excavation-induced changes in permeability around tunnels, borehole injection experiments, depth (and stress) dependent permeability, and permeability changes associated with a large-scale rock-mass heating experiment. Data show how the stress-permeability relationship of fractured rock very much depends on localmore » in situ conditions, such as fracture shear offset and fracture infilling by mineral precipitation. Field and laboratory experiments involving temperature have shown significant temperature-driven fracture closure even under constant stress. Such temperature-driven fracture closure has been described as thermal overclosure and relates to better fitting of opposing fracture surfaces at high temperatures, or is attributed to chemically mediated fracture closure related to pressure solution (and compaction) of stressed fracture surface asperities. Back-calculated stress-permeability relationships from field data may implicitly account for such effects, but the relative contribution of purely thermal-mechanical and chemically mediated changes is difficult to isolate. Therefore, it is concluded that further laboratory and in situ experiments are needed to increase the knowledge of the true mechanisms behind thermally driven fracture closure, and to further assess the importance of chemical-mechanical coupling for the long-term evolution of fractured rock permeability.« less

Fractured rock stress-permeability relationships from in situ data and effects of temperature and chemical-mechanical couplings

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

Rutqvist, J.

The purpose of this paper is to (i) review field data on stress-induced permeability changes in fractured rock; (ii) describe estimation of fractured rock stress-permeability relationships through model calibration against such field data; and (iii) discuss observations of temperature and chemically mediated fracture closure and its effect on fractured rock permeability. The field data that are reviewed include in situ block experiments, excavation-induced changes in permeability around tunnels, borehole injection experiments, depth (and stress) dependent permeability, and permeability changes associated with a large-scale rock-mass heating experiment. Data show how the stress-permeability relationship of fractured rock very much depends on localmore » in situ conditions, such as fracture shear offset and fracture infilling by mineral precipitation. Field and laboratory experiments involving temperature have shown significant temperature-driven fracture closure even under constant stress. Such temperature-driven fracture closure has been described as thermal overclosure and relates to better fitting of opposing fracture surfaces at high temperatures, or is attributed to chemically mediated fracture closure related to pressure solution (and compaction) of stressed fracture surface asperities. Back-calculated stress-permeability relationships from field data may implicitly account for such effects, but the relative contribution of purely thermal-mechanical and chemically mediated changes is difficult to isolate. Therefore, it is concluded that further laboratory and in situ experiments are needed to increase the knowledge of the true mechanisms behind thermally driven fracture closure, and to further assess the importance of chemical-mechanical coupling for the long-term evolution of fractured rock permeability.« less

Mechanical design of DNA nanostructures.

PubMed

Castro, Carlos E; Su, Hai-Jun; Marras, Alexander E; Zhou, Lifeng; Johnson, Joshua

2015-04-14

Structural DNA nanotechnology is a rapidly emerging field that has demonstrated great potential for applications such as single molecule sensing, drug delivery, and templating molecular components. As the applications of DNA nanotechnology expand, a consideration of their mechanical behavior is becoming essential to understand how these structures will respond to physical interactions. This review considers three major avenues of recent progress in this area: (1) measuring and designing mechanical properties of DNA nanostructures, (2) designing complex nanostructures based on imposed mechanical stresses, and (3) designing and controlling structurally dynamic nanostructures. This work has laid the foundation for mechanically active nanomachines that can generate, transmit, and respond to physical cues in molecular systems.

Finite element modeling as a tool for predicting the fracture behavior of robocast scaffolds.

PubMed

Miranda, Pedro; Pajares, Antonia; Guiberteau, Fernando

2008-11-01

The use of finite element modeling to calculate the stress fields in complex scaffold structures and thus predict their mechanical behavior during service (e.g., as load-bearing bone implants) is evaluated. The method is applied to identifying the fracture modes and estimating the strength of robocast hydroxyapatite and beta-tricalcium phosphate scaffolds, consisting of a three-dimensional lattice of interpenetrating rods. The calculations are performed for three testing configurations: compression, tension and shear. Different testing orientations relative to the calcium phosphate rods are considered for each configuration. The predictions for the compressive configurations are compared to experimental data from uniaxial compression tests.

Botanicals for age-related diseases: from field to practice1234

PubMed Central

Weaver, Connie M; Barnes, Stephen; Wyss, J Michael; Kim, Helen; Morré, Dorothy M; Morré, D James; Simon, James E; Lila, Mary Ann; Janle, Elsa M; Ferruzzi, Mario G

2009-01-01

The Purdue–University of Alabama Botanicals Research Center for Age Related Disease joins novel technologies to study the bioavailability of bioactive polyphenolic constituents and their relation to health. Many diseases that manifest with age relate to oxidative stress and tissue damage. Our goal is to follow the fate of bioactive constituents from a complex mixture to the organ affected by the disease and relate that to a protective mechanism. Equally important is to screen commercially available botanicals for their efficacy and safety. Botanicals and their relation to bone antiresorptive capacity, cognitive function, vascular effects, and cancer are principal themes in our center. PMID:18258645

Changes in paleostress and its magnitude related to seismic cycles in the Chelung-pu Fault, Taiwan

NASA Astrophysics Data System (ADS)

Hashimoto, Yoshitaka; Tobe, Kota; Yeh, En-Chao; Lin, Weiren; Song, Sheng-Rong

2015-12-01

Paleostress analysis was conducted through a multiple stress inversion method using slip data recoded for the core samples from the Taiwan Chelung-pu Fault Drilling Project (TCDP). Two stress fields were obtained; one of these had horizontally plunging σ1, and the other has horizontally plunging σ2 or σ3 in the compressional stress direction of the Chi-Chi earthquake. Stress magnitude for both the stress fields was constrained by stress polygons, which indicated larger SHmax for horizontally plunging σ1 than that in the case of horizontally plunging σ2 or σ3. These differences in stress orientations and stress magnitude suggest that the change in stress filed can be caused by stress drop and stress buildup associated with seismic cycles. The seismic cycles recoded in the core samples from TCDP could include many events at geological timescale and not only the 1999 Chi-Chi earthquake.

New seismogenic stress fields for southern Italy from a Bayesian approach

NASA Astrophysics Data System (ADS)

Totaro, Cristina; Orecchio, Barbara; Presti, Debora; Scolaro, Silvia; Neri, Giancarlo

2017-04-01

A new database of high-quality waveform inversion focal mechanism has been compiled for southern Italy by integrating the highest quality solutions, available from literature and catalogues, and 146 newly-computed ones. All the selected focal mechanisms are (i) coming from the Italian CMT, Regional CMT and TDMT catalogues (Pondrelli et al., PEPI 2006, PEPI 2011; http://www.ingv.it), or (ii) computed by using the Cut And Paste (CAP) method (Zhao & Helmberger, BSSA 1994; Zhu & Helmberger, BSSA 1996). Specific tests have been carried out in order to evaluate the robustness of the obtained solutions (e.g., by varying both seismic network configuration and Earth structure parameters) and to estimate uncertainties on the focal mechanism parameters. Only the resulting highest-quality solutions have been enclosed in the database, that has then been used for computation of posterior density distributions of stress tensor components by a Bayesian method (Arnold & Townend, GJI 2007). This algorithm furnishes the posterior density function of the principal components of stress tensor (maximum σ1, intermediate σ2, and minimum σ3 compressive stress, respectively) and the stress-magnitude ratio (R). Before stress computation, we applied the k-means clustering algorithm to subdivide the focal mechanism catalog on the basis of earthquake locations. This approach allows identifying the sectors to be investigated without any "a priori" constraint from faulting type distribution. The large amount of data and the application of the Bayesian algorithm allowed us to provide a more accurate local-to-regional scale stress distribution that has shed new light on the kinematics and dynamics of this very complex area, where lithospheric unit configuration and geodynamic engines are still strongly debated. The new high-quality information here furnished will then represent very useful tools and constraints for future geophysical analyses and geodynamic modeling.

Along fault friction and fluid pressure effects on the spatial distribution of fault-related fractures

NASA Astrophysics Data System (ADS)

Maerten, Laurent; Maerten, Frantz; Lejri, Mostfa

2018-03-01

Whatever the processes involved in the natural fracture development in the subsurface, fracture patterns are often affected by the local stress field during propagation. This homogeneous or heterogeneous local stress field can be of mechanical and/or tectonic origin. In this contribution, we focus on the fracture-pattern development where active faults perturb the stress field, and are affected by fluid pressure and sliding friction along the faults. We analyse and geomechanically model two fractured outcrops in UK (Nash Point) and in France (Les Matelles). We demonstrate that the observed local radial joint pattern is best explained by local fluid pressure along the faults and that observed fracture pattern can only be reproduced when fault friction is very low (μ < 0.2). Additionally, in the case of sub-vertical faults, we emphasize that the far field horizontal stress ratio does not affect stress trajectories, or fracture patterns, unless fault normal displacement (dilation or contraction) is relatively large.

Recent developments on polyphenol–protein interactions: effects on tea and coffee taste, antioxidant properties and the digestive system.

PubMed

Bandyopadhyay, Prasun; Ghosh, Amit K; Ghosh, Chandrasekhar

2012-06-01

Tea and coffee are widely consumed beverages across the world and they are rich sources of various polyphenols. Polyphenols are responsible for the bitterness and astringency of beverages and are also well known to impart antioxidant properties which is beneficial against several oxidative stress related diseases like cancer, cardiovascular diseases, and aging. On the other hand, proteins are also known to display many important roles in several physiological activities. Polyphenols can interact with proteins through hydrophobic or hydrophilic interactions, leading to the formation of soluble or insoluble complexes. According to recent studies, this complex formation can affect the bioavailability and beneficiary properties of both the individual components, in either way. For example, polyphenol-protein complex formation can reduce or enhance the antioxidant activity of polyphenols; similarly it can also affect the digestion ability of several digestive enzymes present in our body. Surprisingly, no review article has been published recently which has focused on the progress in this area, despite numerous articles having appeared in this field. This review summarizes the recent trends and patterns (2005 onwards) in polyphenol-protein interaction studies focusing on the characterization of the complex, the effect of this complex formation on tea and coffee taste, antioxidant properties and the digestive system.