Effect Of External Stress Research Articles

Brood chamber isolation during salinity stress in two estuarine mollusk species: from a protective nursery to a dangerous prison

Faced with environmental stress, the females of many marine invertebrate species can isolate their brood chambers from the external environment for prolonged periods. Although brood chambers have therefore typically been assumed to protect the brooded embryos, the effects of continued isolation on conditions within brood chambers have not been examined. In the present research, we investigated the effects of external stress on conditions in the brood chambers for 2 sympatric species, the gastropod Crepipatella dilatata and the bivalve Ostrea chilensis. Both species incubate their embryos in the pallial cavity for at least 4 wk before the young emerge as larvae (oyster) or juveniles (gastropod). Brooding and non-brooding females were stimulated to isolate the pallial cavity from the external environment by exposing them to water of reduced salinity (<22 to 24 psu). We then recorded subsequent changes in salinity, dissolved oxygen, pH, and ammonium ion concentration within the pallial fluid. Although salinity within the pallial cavity remained high for both species, oxygen availability for brooding females of C. dilatata and O. chilensis dropped to hypoxic levels (<1.5 mg O2 l -1 ) within 12 h and 20 min, respectively. In addition, pH of the intrapal- lial fluid dropped substantially with prolonged maternal isolation, suggesting a possible impact on shell formation for brooded veligers. Indeed, in the case of C. dilatata, the pH of pallial fluid initially fell to 6.4, but then tended to become more basic after 6 h of maternal isolation, a possible conse- quence of shell dissolution. On the other hand, ammonium ion concentration increased progressively with prolonged maternal isolation. Our data show that, whereas initially the isolation mechanism protected incubated embryos from exposure to low salinity stress, continued isolation from the exterior transformed the brood cavity from a protective environment to an oppressive one, i.e. from a protective nursery to more of a prison.

The Pursuit of Hysteresis in Polycrystalline Ferromagnetic Materials Under Stress

External stresses alter the magnetic properties of ferromagnetic materials such as iron and steel, a fact that has been the basis of substantial study in nondestructive testing. Existing theories and models have so far not proven reliable or accurate enough to develop a practical means of using the developed theory relating stress and magnetization to measure biaxial strains without prior knowledge of the strain or magnetic history of the sample. A deterministic model of ferromagnetic hysteresis and the effects of external stresses in materials such as iron and steel is introduced by this study. Changes in hysteresis loops due to stress are explained via changes in the magnetocrystalline anisotropy at the crystal-unit level, and are extended to the macroscopic effects that are seen in experiments. An original equation is presented which accurately describes experimentally acquired major hysteresis loops and directly relates two parameters to the two perpendicular principal strain axes thereby providing a technique able to determine the absolute stress/strain experienced by the sample. This model will potentially enable quantitative, nondestructive stress measuring devices to be developed.

523 原子炉用黒鉛材料の大気中酸化に及ぼす外部応力の影響と酸化された黒鉛の機械的性質(環境対応型材料の特性・評価)

523 原子炉用黒鉛材料の大気中酸化に及ぼす外部応力の影響と酸化された黒鉛の機械的性質(環境対応型材料の特性・評価)

Dislocation dynamics simulation on stability of high dense dislocation structure interacting with coarsening defects

This paper examined the stability of high-dense dislocation substructures (HDDSs) associated with martensite laths in High Cr steels supposed to be used for FBR, based on a series of dislocation dynamics (DD) simulations. The DD simulations considered interactions of dislocations with impurity atoms and precipitates which substantially stabilize the structure. For simulating the dissociation processes, a point defect model is developed and implemented into a discrete DD code. Wall structure composed of high dense dislocations with and without small precipitates were artificially constructed in a simulation cell, and the stability/instability conditions of the walls were systematically investigated in the light of experimentally observed coarsening behavior of the precipitates, i.e., stress dependency of the coarsening rate and the effect of external stress. The effect of stress-dependent coarsening of the precipitates together with application of external stress on the subsequent behavior of initially stabilized dislocation structures was examined.

Coupling effects of chemical stresses and external mechanical stresses on diffusion

Interaction between diffusion and stress fields has been investigated extensively in the past. However, most of the previous investigations were focused on the effect of chemical stress on diffusion due to the unbalanced mass transport. In this work, the coupling effects of external mechanical stress and chemical stress on diffusion are studied. A self-consistent diffusion equation including the chemical stress and external mechanical stress gradient is developed under the framework of the thermodynamic theory and Fick's law. For a thin plate subjected to unidirectional tensile stress fields, the external stress coupled diffusion equation is solved numerically with the help of the finite difference method for one-side and both-side charging processes. Results show that, for such two types of charging processes, the external stress gradient will accelerate the diffusion process and thus increase the value of concentration while reducing the magnitude of chemical stress when the direction of diffusion is identical to that of the stress gradient . In contrast, when the direction of diffusion is opposite to that of the stress gradient , the external stress gradient will obstruct the process of solute penetration by decreasing the value of concentration and increasing the magnitude of chemical stress. For both-side charging process, compared with that without the coupling effect of external stress, an asymmetric distribution of concentration is produced due to the asymmetric mechanical stress field feedback to diffusion.

Stress and its related effects on the fatigue behavior of Bi 3.25La 0.75Ti 3O 12 thin films

The effects of external stress cooperated with temperature, measuring frequency and measuring electric field on the fatigue properties of Bi 3.25La 0.75Ti 3O 12 thin films are investigated. The fatigue properties can be improved by the external stress (both tensile and compressive). The larger the stress is, the more obvious the improvement is. Meanwhile, the stress-induced improvement is more distinct in the films annealed at a higher temperature. In addition, when measured at a higher frequency or at a larger electric field, the films show better fatigue properties, and the improvement caused by stress is more evident. The experimental results can be explained well by the mechanism in which the charged defects pin the domain walls during electric cycling.

Effect of external stress on the thermal melting of DNA

We discuss the effects of external stress on the thermal denaturation of homogeneous DNA. Pulling double-stranded DNA at each end exerts a profound effect on the thermal denaturation, or melting, of a long segment of this molecule. We discuss the effects on this transition of a stretching force applied to opposite ends of the DNA, including full consideration of the consequences of excluded volume, the analysis of which is greatly simplified in this case. We find that in three dimensions the heat capacity acquires a logarithmic dependence on reduced temperature.

Large Optical Transitions in Rewritable Digital Versatile Discs: An Interlayer Atomic Zipper in a SbTe Alloy

ABSTRACTChalcogenides, in particular germanium-antimony-tellurium (GeSbTe) and antimony-rich tellurium (R-SbTe) based alloys, are the most technologically significant alloys currently being applied to recordable optical storage as typified by rewritable digital versatile discs (DVD-RW), DVD random access memory, (DVD-RAM). The same alloys are also being applied to nonvolatile random access memory electrical memory in the form of phase change random access memory (PCRAM). In 2004, the phase transition mechanism of GeSbTe was first revealed, demonstrating that the amorphous state is not a random configurational network but is locally well-ordered with the crystalline to amorphous switching process being based upon Ge atoms moving between octahedral and tetrahedral symmetry positions. The kinetic barrier between these two states gives rise to the non-volatile nature of GeSbTe as a storage medium. In contrast, no theoretical analysis has been proposed for SbTe alloys because a Ge-free system. In this paper, the Sb2Te structure has been investigated using the local density approximation (LDA) using a plane-wave basis and compared with experimental results. The effect of external stress on the structure was also investigated. It was found that Sb2Te undergoes two phase-transitions at around 18 GPa (compressive) and −3 GPa (tensile). In the case of negative stress, the c-axis was found to expanded more than the other axes, giving rise a large refractive index change. We report on coherent (uniaxial) melting induced by the breaking a sigma bond between Sb2Te3 and Sb superlattices. We believe this to be the origin of the phase transition that induces a large change in physical properties.

Formation of shear bands and strain-induced martensite during plastic deformation of metastable austenitic stainless steels

Formation of shear bands and strain-induced ε- and α′-martensite phases during tensile deformation of austenitic stainless steels was studied. Stacking fault energies (SFE) of the studied steels were measured by X-ray diffraction. Effects of external stress and SFE on the width of the stacking faults were analysed. An excellent correlation between the calculations and actual microstructures examined by scanning electron microscopy was found. Effect of overlapping of stacking faults on the fault width was discussed. Based on the discussions and experimental results, compositional, temperature and strain rate dependencies of the strain-induced α′-martensite transformation are believed to be governed mainly by the variation in the SFE.

Effects of external stress on defect complexes in semiconductors

Crystal field gradients that exist at lattice sites in solids depend on the symmetry of chargedistribution around atomic sites. The charge symmetry could be broken either by thepresence of impurity complexes in the host matrix or by external stress on the samples,which leads to an observable magnitude of electric field gradients (EFGs). The perturbedγ–γ angular correlation (PAC) method is employed here to investigate the effect of uniaxial stress on111Cd sites in crystalline doped semiconductors.

Micromagnetic Simulation of Size Effects on the Properties of Ferromagnetic Materials

Micromagnetic simulation was carried out to investigate the behavior of ferromagnetic materials at a very small length scale, at which the materials usually exhibit different properties compared with those of the corresponding bulk materials. By solving the time and spatial dependent Landau-Lifshitz-Gilbert (LLG) equation in reciprocal space using fast Fourier transformation (FFT) technique, the equilibrium magnetization state was, thus, achieved. The hysteresis loops were also simulated, from which the relation of coercivity and characteristic length was established. Besides, the effect of external stress on coercivity was also taken into consideration. The results showed that at such length scales the external stress strongly affected the magnetic behavior of ferromagnetic materials.

Atomistic modeling of an Fe system with a small concentration of C

An Fe–C potential based on the Embedded Atom Method has been derived, adjusted on ab initio data. This potential is dedicated to the study of ferritic FeC solid solutions for low carbon concentrations. This potential has been validated by checking its behaviour in the simulation of C diffusion in α-Fe and by determining the interaction of C atoms with a screw dislocation. The evolution of the matrix lattice parameter versus C content, related to the tetragonal lattice structure has also been evaluated as well as external stress effects on the diffusion energy barrier. The theoretical results are in good agreement with the experimental data available.

THE INFLUENCE OF STRESS ON THE SPONTANEOUS POLARIZATION IN 2-d Bi4Ti3O12 FILMS

ABSTRACT The influence of stress on the spontaneous polarization in two-dimensional Bi4Ti3O12 (BiT) films is investigated by modified Landau—Devonshire thermodynamic theory. Three orientation cases of BiT unit, nine ferroelectric phases are discussed under the mechanism of strain-polarization coupling. Results show that the effect of stress on out-of-plane spontaneous polarization for all cases is small and can not clarify the origin of the effect of external stress on the net-switched charge in Nd- and La-doped Bi4Ti3O12 films. So there is a need to consider stress-induced reorientation of domains.

Recrystallization-induced plasticity

Using the dilatometric method, it has been found that during heating of the hardened Fe-3% Si alloy under loading, the deformation starts at a considerably lower temperature than regular creep takes place. The temperature of the start of the deformation is determined by the temperature of the start of recrystallization. The deformation induced by recrystallization increases exponentially with increasing load and temperature. An assumption has been made that the increased plasticity upon recrystallization appears as a result of lifting of spatial degeneracy under the effect of external stresses, appearing a preferred direction, and the oriented motion of defects along this preferred direction during recrystallization. Structural superplasticity can be considered as a result of dynamical recrystallization.

Effect of external stress on phase diagrams and dielectric properties of epitaxial ferroelectric thin films grown on orthorhombic substrates

A Landau-Ginsburg-Devonshire(LD)-type thermodynamic theory was used to describe the effect of external stress on phase diagrams and dielectric properties of epitaxial ferroelectric thin films grown on orthorhombic substrates which induce nonequally biaxial misfit strains in the films plane. The “misfit strain-external stress” and “external stress-temperature” phase diagrams were constructed for single-domain BaTiO 3(BT) and PbTiO 3(PT) thin films. It is shown that the external stress may lead to the rotation of the spontaneous polarization and a gradual change of its magnitude, which may result in phase transition. Nonequally biaxial misfit strains dependence of the stability of polarization states may be governed by external stress. At room temperature, stress-induced ferroelectric/paraelectric phase transition which occurs in film on cubic substrate does not take place in the ferroelectric thin film grown on orthorhombic substrate. It is also shown that the nonequally misfit strains in the film plane may lead to the appearance of new phases which do not form in films grown on cubic substrates under external stress. The dependence of the dielectric response on the external stress is also studied. It is shown that the dielectric constants of single-domain PT and BT films are very sensitive to the external stress under the given anisotropic misfit strains-temperature conditions. It presents theoretical evidence that the external stress and anisotropic misfit strains can be employed for improving the thin films physical properties.

Liquid Ga Penetration along Al Grain Boundaries: Effect of External Stress and Ga Undercooling

The effects of compressive stress and undercooling of Ga to liquid gallium penetration along grain boundaries (GBs) of aluminum were investigated. It was shown that the penetration rate does not change with the temperature if gallium is in liquid state. The effect of compressive stress applied to Al samples was demonstrated. The time to wetting of all aluminum GBs increased several orders of magnitude if the compressive stress was between 0.1 and 6 MPa. It was proved that solid-liquid transformation does not take place during penetration process.

Surprising shrinkage of expanding gels under an external load

Hydrogels are fascinating and useful in that they can show large volume changes in response to various stimuli, such as temperature or chemical environment. Here we report the peculiar observation that chemically crosslinked hydrogels that normally expand owing to a change in electrolyte pH can be made to shrink in certain circumstances. Specifically, these hydrogels contract when tested at a constant compressive force and subjected to a pH change that causes expansion in the absence of the applied load. When tested under tension, the gels always expand. Although the effects of external stress on the swelling of gels is known, the concomitant change in gel mechanical properties during pH switching was found to be a more dominant effect in our studies. However, existing mechanical models used to predict dimensional changes in actuator materials could not explain both the tensile and compression results. In addition, we show that the friction between metal plates of the apparatus and the gel is a key factor in explaining the contractile actuation under compressive loads. The observations reported in this paper are important for the successful design and use of hydrogel actuators in devices such as valves for microfluidics.

Dys‐regulation of clusterin in human hepatoma is not associated with tumorigenesis but is secondary to cell response to external tresses

It becomes feasible to perform genome-wide differential gene or protein expression in the post genome era. However, little has been addressed on the effects of external stresses and microenvironment alterations on the outcomes of gene and protein expression. To identify downregulated genes during hepatoma development, we combined the cDNA representational difference analysis (RDA) and reverse Northern blot analysis identifying eight genes. Of interest, the expression of the clusterin gene was either down or upregulated in 8 and 7 out of the 20 hepatoma tissues, respectively. Further analysis revealed that its expression was independent of patients' age, gender, causes of liver disease, tumor size, tumor histological stage, or clinical outcome, but was strongly associated with the methods of hepatectomy procedures. In vitro studies disclosed that the clusterin mRNA was increased twofold in early exponential phase of cell proliferation followed by downregulation in the subsequent quiescence phase, whereas it was rapidly increased up to twelvefold upon UV-induced apoptosis. These results suggest that dys-regulation of the clusterin gene in human hepatoma was most likely due to cellular responses to external stresses especially during the procedures for sample collection rather than any correlation to hepatoma development or progression. Our findings that external stresses or microenvironmental changes could greatly affect gene or protein expression offer a general caution to all the studies conducted via genomic and proteomic approaches.

Hygrothermal aging behaviour of VARTMed three-dimensional braided carbon-epoxy composites under external stresses

The hygrothermal aging of three-dimensional braided carbon fibre-epoxy resin composites prepared by vacuum assisted resin transfer moulding (VARTM) was investigated. Emphasis was given to the effect of external stresses, both tensile and compressive modes at stress levels of 10 and 20% ultimate tensile strength (UTS). Unstressed, tensile-stressed and compressive-stressed specimens were immersed in distilled water at 37 °C. Specimens were characterized by examining weight changes and evaluating variations of flexural and shear properties due to moisture ingress. It was concluded that the application of external stresses did not change the mechanism of moisture sorption. However, external stresses exerted apparent effects on moisture uptake, equilibrium moisture content and mechanical degradation. Moisture sorption was promoted and resisted, respectively under the actions of tensile and compressive stresses. The degree of mechanical deterioration of the composites depended on the level of moisture content. A mechanism which attributed the external stresses effects to changes of matrix strain, propagation of matrix cracks, and moisture transport at interfaces was proposed. Moreover, a comparison between the 3D and unidirectional composites was made to assess the influence of fibre structure.

Effect of external stress on discontinuous precipitation on {100} planes in Cu–5.7 wt% Ag single crystals

The application of external stress during ageing induces the oriented formation of disc-shaped aggregates consisting of rod-shaped Ag precipitates and a Cu matrix on {100} planes in single crystals of a Cu–5.7 wt% Ag alloy. Tensile stress along the [001] axis induces preferential formation of the aggregates perpendicular to the [001] axis and compressive stress induces the same parallel to the stress axis. The stress-orienting effect is determined during the initial stage of precipitation, when the formation of the aggregates starts on dislocations. The experimental result can be understood if the misfit strain of the aggregates in a direction perpendicular to the disc plane is larger than that in the parallel direction. This idea is supported by length-change measurements during ageing.