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ABSTRACTThe microstructure, martensitic transformation (MT) and shape memory effect (SME) of the dual-phase Ni58Mn25Ga17−xGdx(x = 0, 0.1, 0.2, 0.5, 1) alloys have been investigated. The results show that the refined the grain size and adjust the distribution of γ phase by added rare earth Gd in the Ni58Mn25Ga17−xGdxalloys. With increasing Gd content, the MT temperatures of Ni58Mn25Ga17−xGdxalloys first gradually decrease and then increase with the increasing content of Gd, reaching their minimum values when the content of Gd is 0.5 at.-%. In addition, the Ni58Mn25Ga16.9Gd0.1has a SME of 5.1% owing to the favourable γ phase distribution, which is mainly attributable to the γ phase grain refined and weaken resistance of reverse MT.

The microstructure, martensitic transformation (MT) and shape memory effect (SME) of the dual-phase Ni58Mn25Ga17-xGdx(x?=?0, 0.1, 0.2, 0.5, 1) alloys have been investigated. The results show that the refined the grain size and adjust the distribution of ? phase by added rare earth Gd in the Ni58Mn25Ga17-xGdxalloys. With increasing Gd content, the MT temperatures of Ni58Mn25Ga17-xGdxalloys first gradually decrease and then increase with the increasing content of Gd, reaching their minimum values when the content of Gd is 0.5?at.-%. In addition, the Ni58Mn25Ga16.9Gd0.1has a SME of 5.1% owing to the favourable ? phase distribution, which is mainly attributable to the ? phase grain refined and weaken resistance of reverse MT.

AbstractThe effect of Cuxsubstituted for Gaxon the thermodynamic characteristic, evolution of phases and fracture behavior in Ni50Mn30Ga20 − xCuxalloys have been investigated. The results show that the martensitic transformation, reverse transformation temperatures and average interface temperature of Ni50Mn30Ga20 − xCuxsample increase remarkably with increased content of Cu. The hysteresis temperature of the austenite to martensite transition firstly showed a steep rising trend, then almost reduced to a lower rate with the increased content of Cu up to 4 at.% (the maximum level of copper addition studied). The (202) diffraction peak position was observed to shifted towards high angles, when the Cu content was lower than 1 at.%. Further, the, M202diffraction peak was found to split into two diffraction peaks when the Cu content was more than 1 at.%. In addition, the compressive strength and fracture strain of alloys is clearly enhanced with increased content of Cu. Furthermore, the fracture type of Ni50Mn30Ga20 − xCuxalloys was found to changes from intergranular fracture for the Ni–Mn–Ga alloys, to transgranular cleavage fracture with increase in Cu content.

The present paper deals with the thermal- and stress-induced martensitic transformations, effects of bias magnetic field and external compressive stress on transformation- and magnetic-field-induced strain in Ni-Mn-Ga alloys. The effect of the external magnetic field and compressive stress on the reorientation of martensitic variants is discussed. It is found that the stress-induced spear-like martensitic crystal forms at the beginning of loading at the temperature a little higher than Ms. The interfaces between the parent phase and the stress-induced martensite migrate reversibly under the increasing/decreasing stress, showing the characteristics of thermoelastic martensitic transformation. When the Ni52Mn24Ga24single crystal is cooled down to 200K, an intermartensitie transformation occurs, however there is no appearance of this case for the powder sample of the same alloy with average particle size ofabout 50 μm. About 1.8% magnetic-field-induced strain is obtained in the [100] direction of Ni2MnGa singte crystal when a 1.5T pulse magnetic field is applied at the Mstemperature.

The internal friction behaviors of B2 FeAl alloys were examined to understand the correlation between the ordering and the movement of the atomic defects. A new internal friction peak was found at around 540 °C and 570 °C in the oil-quenched Fe57Al43 and Fe47Al53 alloys, respectively, while in the furnace-cooled specimens, the peak disappeared. The peak has the typical phase transition characters, and it is suggested that the peak probably originates from the elevation of the degree of order, which is caused by the jump of antisite atoms to their own sublattice sites by means of the nearest neighboring vacancies. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Internal friction behaviors of B2 Fe–Al alloys were examined to understand the correlation between the anelasticity and thermal vacancies. Three internal friction peaks were found in the rapidly cooled specimens at around 210 °C (P1), 410 °C (P2) and 520 °C (P3), respectively, while in the slowly cooled specimens, the P1 peak was significantly decreased and the P2 peak was decomposed into two peaks (P2L and P2H). All the internal friction peaks showed relaxational nature and they shifted toward high temperature with increasing frequency. It is suggested that the P1 peak originates from the reorientation of the divacancies composed of Fe vacancies and the nearest-neighboring Al vacancies, the P2L peak from the dissociation and diffusion of the interstitial carbon atoms from the carbon-vacancy complexes and the P2H peak from the reorientation of the triple defects. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

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In complex forging processes, it is essential to find the optimal deformation path and the optimal preform shape that will lead to the desired final shape and service properties. A sensitivity analysis and optimization for preform billet shape in thermo-mechanical coupled simulation is developed in this work. Non-linear sensitivity analysis of temperatures, flow-stresses, strains and strain-rates are presented with respect to design variables. Both analytical and finite-difference gradients are employed to validate the effectiveness of sensitivity analysis developed in this work. Numerous iterations of coupled thermo-mechanical analysis are performed to determine an optimum preform shape based on a given criterion of minimizing the objective function on effective strain variance within the final forging. The design constraints are imposed on die underfill, material scrap, folding defects and temperatures. In addition, a method for material data processing is given in order to determine the flow stress and its derivatives. The shape optimization scheme is demonstrated with the preform designs of an axisymmetric disk and a plane strain problem. Copyright © 1999 John Wiley & Sons, Ltd.

To understand the role of the insulin receptor pathway in beta-cell function, we have generated stable beta-cells (betaIRS1-A) that overexpress by 2-fold the insulin receptor substrate-1 (IRS-1) and compared them to vector-expressing controls. IRS-1 overexpression dramatically increased basal cytosolic Ca2+ levels from 81 to 278 nM, but it did not affect Ca2+ response to glucose. Overexpression of the insulin receptor also caused an increase in cytosolic Ca2+. Increased cytosolic Ca2+ was due to inhibition of Ca2+ uptake by the endoplasmic reticulum, because endoplasmic reticulum Ca2+ uptake and content were reduced in betaIRS1-A cells. Fractional insulin secretion was significantly increased 2-fold, and there was a decrease in betaIRS1-A insulin content and insulin biosynthesis. Steady-state insulin mRNA levels and glucose-stimulated ATP were unchanged. High IRS-1 levels also reduced beta-cell proliferation. These data demonstrate a direct link between the insulin receptor signaling pathway and the Ca2+-dependent pathways regulating insulin secretion of beta-cells. We postulate that during regulated insulin secretion, released insulin binds the beta-cell insulin receptor and activates IRS-1, thus further increasing cytosolic Ca2+ by reducing Ca2+ uptake. We suggest the existence of a novel pathway of autocrine regulation of intracellular Ca2+ homeostasis and insulin secretion in the beta-cell of the endocrine pancreas.

In this paper, we present certain sufficient conditions for (feedback) stabilizability of controlled stochastic systems. Theoretical results are illustrated by three examples applied to electrically suspended gyros.

This paper deals with non-linear stochastic systems with state-dependent noise. Based on the solution of the stochastic algebraic Riccati equation, sufficient conditions are derived which assure the existence of state feedback control laws such that the closed-loop system is locally and globally stable in probability.

Oxytocin (OT) produced a dose-dependent increase in somatostatin, glucagon and insulin release by isolated mouse islets. A small effect on somatostatin release was observed with 0.1 nM-OT, but 1-10 nM-OT was required to affect A- and B- cells significantly. The effects of OT on somatostatin and glucagon release were similar in the presence of 3 mM- and 10 mM-glucose. No change in insulin release was produced by OT in 3 mM-glucose, but a stimulation was still observed in the presence of a maximally effective concentration of glucose (30 mM). The increase in insulin release produced by OT (in 15 mM-glucose) was accompanied by small accelerations of 86Rb and 45Ca efflux from islet cells. Omission of extracellular Ca2+ accentuated the effect of OT on 86Rb efflux, attenuated that on 45Ca efflux, and abolished that on release. OT never inhibited 86Rb efflux. It did not affect the resting potential of B-cells, but slightly increased the Ca2(+)-dependent electrical activity induced by 15 mM-glucose. OT did not affect cyclic AMP levels, but increased inositol phosphate levels in islet cells. It is suggested that the amplification of glucose-induced insulin release that OT produces is due to a stimulation of phosphoinositide metabolism, and presumably an activation of protein kinase C, rather than to a change in cyclic AMP levels or a direct action on the membrane potential. Since OT is present in the pancreas, it is possible that it exerts a neuropeptidergic control of the islet function.

The amyloid precursor protein (APP) can be cleaved by a beta-secretase to generate a beta-amyloid peptide, which has been implicated in the pathogenesis of Alzheimer's disease. However, APP can also be cleaved by an alpha-secretase to form a non-amyloidogenic secreted form of APP (APP-S). APP-S secretion can be physiologically regulated. This study examined the glutamatergic regulation of APP in the human neuronal Ntera 2 (NT2N) cell line. Metabotropic glutamate receptor subtypes 1alpha/beta and 5alpha were identified in the NT2N neurons by reverse transcription-polymerase chain reaction. Stimulation of these phosphatidylinositol-linked receptors with glutamate or specific receptor agonists resulted in a dose- and time-dependent increase in the secretion of the amyloid precursor protein (APP-S), measured by the immunoprecipitation of APP-S from the medium of [35S]methionine-labeled NT2N neurons. The glutamate-induced APP-S secretion was maximal at 30 min and at a concentration of 1 mM glutamate. Glutamate-induced APP-S secretion required activation of phospholipase C, which resulted in inositol 1, 4,5-trisphosphate production, as shown by the rapid glutamate-induced accumulation of inositol 1,4,5-trisphosphate. Glutamate also caused an increase in intracellular Ca2+. The protein kinase C activator phorbol 12-myristate 13-acetate, a phorbol ester, as well as 1-oleoyl-2-acetoyl-3-glycerol, a cell-permeable diacylglycerol analog, also stimulated APP-S secretion. These findings suggest that APP-S secretion from NT2N neurons can be regulated by the activation of phosphatidylinositol-linked metabotropic glutamate receptor signaling pathway.

The singular eigenstate with respect to the stress and electric displacement at the vertex of a V-notch in a piezoelectric plate is investigated. The displacement and electric potential near the vertex of a V-notch are expressed as series asymptotic expansions, and their typical terms are substituted into the governing equations to establish the singularity eigenequations, from which the singularity orders and angular eigenfunctions can be yielded by the interpolating matrix method. The coupling effect of elastic and electric singularities can be found by distinguishing the singularity orders from their angular eigenfunctions. There are most four singularity orders for the V-notch in a piezoelectric Reissner plate, which is one more than the one in a homogeneous plate. Two orders are corresponding to the singularity of bending moment and electric displacement in the thickness direction, and another two orders are with respect to the singularity of shear force and electric displacement in the mid-plane. The free and electrically opened, and clamped and electrically closed boundary conditions are respectively introduced to investigate the influence of boundary conditions on the singularity. It is found that the singularity orders with respect to bending moment and electric displacement in the thickness direction change with boundary conditions, while the singularity orders with respect to shear force and electric displacement in the mid-plane are identical under these two kinds of boundary conditions.