Papers by Keyword: Hydrostatic Pressure

Abstract: Taking into account the effective mass approximation and the two-band model, we have studied the combined effects of hydrostatic pressure and temperature on the unbound excitonic properties of a cylinder-shaped quantum dot. The two finite confinement potentials along the radial direction and one finite confinement potential along the axial direction have been considered. We have calculated the electronic energy with and without light hole effect as a function of the core radius, hydrostatic pressure and temperature. The numerical results show that the effect of the confinement potential is dominant over the effect of the hydrostatic pressure and the temperature. Also, the light hole effect on the electronic properties has a significant influence mainly under the external perturbation

Abstract: Within the effective mass approximation and the infinite confinement potential, this work focused on studying the electronic properties of spherical quantum dot (SQD) nanostructure through the finite difference method. The effects of shallow donor impurity position, temperature (T), and hydrostatic pressure (P) on the binding energy, the electron spatial extension <r_e> and the average electron-impurity distance <r_D-e> in a SQD have been evaluated. Our findings show that the binding energy increases as a function of hydrostatic pressure and decreases with the temperature effect. However, the binding energy presents very clear maximum around the spherical nanostructure center depending on the impurity position. For higher SQD, the impact of externals perturbations (P and T) on the electron spatial extension are more significant. The distance <r_e> decreases with the augmentation of hydrostatic pressure when the impurity is near the center, which is conversely when the impurity is near the edge. In addition, applying the hydrostatic pressure and temperature leads to decreasing and increasing the average distance <r_D-e>, respectively.

Abstract: The study looks at features the formation of the structure of the surface layer of pure-iron after hardening treatment with surface plastic deformation (SPD) by a multiradius roller (MP-roller). Earlier authors with the help of the method of finite-element modelling (FEM) of the MP-roller SPD process proved the possibility of creating high hydrostatic pressure in the deformation center of the part being processed. The methods of optical (OM) and atomic-force microscopy (AFM) and X-ray structural analysis have determined that the MR-roller SPD results in the formation of an intensively deformed surface layer of the component with characteristic ferrite grains, stretched in the direction of the current of the metal and an average size of 20-30 μm. Analysis of the results of the X-ray structural analysis showed that the processing of the SPD by the MP-roller results in a significant increase in the microdistortion of the crystal lattice, which is characteristic of the nanodimensional structure. The data obtained are well consistent with the results of the finite element modelling previously obtained.

Abstract: The influence of hydrostatic pressure on the binding energy of hydrogenic impurity state in a wurtzite Al_yGa_1-yN/Al_xGa_1-xN parabolic quantum well and GaN/Al_xGa_1-xN square quantum well are studied using the variational method. The ground-state binding energies are presented as the functions of hydrostatic pressure, well width, composition and impurity center position. The anisotropic properties of the parameters in the system, and the changes (dependence) of electron effective mass, the dielectric constant, band gap with pressure and coordinate are considered in the numerical calculations. The results show that the hydrostatic pressure has obvious influence on the binding energy. The binding energy increase slowly with increasing the hydrostatic pressure p and the composition x, while the binding energy decrease significantly with increasing the well width and the position of impurity center. It is seen that the changing trends of the binding energy as a function of well width, pressure and the composition in the Al_yGa_1-yN/Al_xGa_1-xN parabolic quantum well are basically the same with that in the GaN/Al_xGa_1-xN square quantum well, but the changing trends of the binding energy as a function of impurity center position in the Al_yGa_1-yN/Al_xGa_1-xN parabolic quantum well are significantly greater than that in the GaN/Al_xGa_1-xN square quantum well.

Abstract: The Cd₃As₂+MnAs composite with 20 mole % of MnAs has been studied complexly in a wide ranges of temperatures, pressures and magnetic fields. Negative magnetic resistance has been found in the sample. This anomalous behavior is considered as a result of changes in tunneling processes due to reduce of distance between magnetic moment of ferromagnetic and structural transitions caused by pressure.

Abstract: The influence of hydrostatic pressure on the polaron energy level in wurtzite GaN/Al_xGa_1-xN quantum well is studied by a Lee-Low-Pines variational method, and the numerical results of the ground state energy, transition energy and contributions of different phonons to polaron energy (polaron effects) are given as functions of pressure p and composition x. The results show that the ground state energy and transition energy in the wurtzite GaN/Al_xGa_1-xN quantum well decrease with the increase of the hydrostatic pressure p, and increase with the increase of the composition x. The contributions of different phonons to polaron energy with pressure p and composition x are obviously different. With the increase of hydrostatic pressure, the contribution of half-space phonon, confined phonon and the total contribution of phonons of all branches increases obviously, while the contribution of interface phonon slowly increases. During the increase of the composition, the contribution of interface phonon decreases and the contribution of half-space phonon increases slowly, while the contribution of confined phonon and the total contribution of phonons increases significantly. In general, the electron-optical phonon interaction play an important role in electronic states of GaN/Al_xGa_1-xN quantum wells and can not be neglected.

Abstract: Reducing automobile weight has been necessarily accelerated to save energy and improve drivability. Accordingly, use of high strength steel and hollow sections help in weight reduction. In this study, the effect of trapped oil has been investigated to improve the metal flow in upsetting of a hollow workpiece using no mandrel. It was found that the ideal deformation without friction between the dies and the workpiece was nearly achieved when a low and thick ring with trapped oil was upset. The inner diameter of the oil-filled ring was expanded more than that of the benchmark ring. The effect of the expansion of the ring and the reduction of the friction proved helpful in trial forming of a gear preform.

Abstract: The paper presents the findings of the research into neoprene-like soft foamed materials during compression in water. The specific features of the internal structure of such materials lead to complex deformations. This is related to the specific features of the internal structure of materials that contain a large amount of inert air. The paper also presents the findings of structural studies which explained the relationship between the elastic properties of materials and the strength of polymer bonds forming internal air cavities. When foamed the polymer sections are destroyed under compression, it results in the loss of enclosed volume of air voids. This changes the total volume and thickness of the material, which defines some physical and thermal properties of products made of such material. Hydrostatic pressure environments have their own specific features. Rheological properties of soft polymers in a hydrostatic pressure environment give rise to a composite effect of compression deformation. The study of recent developments in the research into polymer deformations in a hydrostatic pressure environment shows that it is difficult to record the stages of reversible and nonreversible compression deformation in near-real experimental simulation of diving operations. The paper presents the developments and findings of experimental design studies for a product (wetsuit) made of foamed materials that were conducted in a hydrostatic pressure environment in an enclosed volume using special Drucktank equipment by the Marine Engineering Department of the University of Rostock

Abstract: Chemical composition Pb_0.97La_0.02(Zr_0.75Sn_0.136Ti_0.114)O₃ (PLZST) ceramic was fabricated by conventional solid-state reaction of oxide method. The composition is close to the AFE/FE phase boundary of PLZST ceramic phase diagram. The dependence of remanent polarization of Pb (Zr,Sn,Ti)O₃ ceramic poled under different electric fields on hydrostatic pressure was investigated with special hydrostatic pressure equipment. The results show that PLZST ceramic poled at different DC electric field is metastable state ferroelectric phase. The remanent polarization decreases sharply and is depolarization completely when hydrostatic pressure increases to a bound.

Abstract: This study aims to develop a cutting method, which enables to generate a localized hydrostatic pressure field in the vicinity of cutting zone in order to improve the machined surface integrity without causing unnecessary plastic deformation. In the previous work, a molecular dynamics simulation was performed using a newly developed cutting tool equipped with a planer jig with a rectangular hole for the cutting chip elimination, and it was confirmed that the developed cutting tool has advantages in giving a relatively high-hydrostatic stress field in the vicinity of the cutting zone and in suppressing the burr formation. In this report, further molecular dynamics simulation was performed in order to clarify the influence of jig shape on the cutting phenomena and machined surface integrity. As a result, it is found that a cutting tool of which front and side except for the rectangular hole are covered by the planer jig is the most advantageous for supplying high hydrostatic pressure and suppressing burr formation.