A generalized finite-difference time-domain quantum method for the N-body interacting Hamiltonian

The Quantum Finite-Difference Time-Domain (FDTD-Q) method is a numerical method for solving the time evolution of the Schrödinger equation. It can be applied to systems of interacting particles, allowing for realistic simulations of quantum mechanics of various experimental systems. One of the drawbacks of the method is that divergences in the numerical evolution occur rather easily in the presence of interactions, which necessitates a large number of evolution steps or imaginary time evolution. We present a generalized (GFDTD-Q) method for solving the time-dependent Schrödinger equation including interactions between the particles. The new scheme provides a more relaxed condition for stability when the finite difference approximations for spatial derivatives are employed, as compared with the original FDTD-Q scheme. We demonstrate our scheme by simulating the time evolution of a two-particle interaction Hamiltonian. Our results show that the generalized method allows for stable time evolutions, in contrast to the original FDTD-Q scheme which produces a divergent solution.     

Orientation dependence of fracture toughness measured by indentation methods and its relation to surface energy in single crystal silicon

Fracture toughness of silicon crystals has been investigated using indentation methods, and their surface energies have been calculated by molecular dynamics (MD). In order to determine the most preferential fracture plane at room temperature among the crystallographic planes containing the 〈001〉, 〈110〉 and 〈111〉 directions, a conical indenter was forced into (001), (110) and (111) silicon wafers at room temperature. Dominant {110}, {111} and {110} cracks were introduced from the indents on (001), (011) and (111) wafers, respectively. Fracture occurs most easily along {110}, {111} and {110} planes among the crystallographic planes containing the 〈001〉, 〈011〉 and 〈111〉 directions, respectively. A series of surface energies of those planes were calculated by MD to confirm the orientation dependence of fracture toughness. The surface energy of the {110} plane is the minimum of 1.50 Jm⁻² among planes containing the 〈001〉 and 〈111〉 directions, respectively, and that of the {111} plane is the minimum of 1.19 Jm⁻² among the planes containing the 〈011〉 direction. Fracture toughness of those planes was also derived from the calculated surface energies. It was shown that the K _IC value of the {110} crack plane was the minimum among those for the planes containing the 〈001〉 and 〈111〉 directions, respectively, and that K _IC value of the {111} crack plane was the minimum among those for the planes containing the 〈011〉 direction. These results are in good agreement with that obtained conical indentation.     

Comparisons of computed mobile phone induced SAR in the SAM phantom to that in anatomically correct models of the human head

The specific absorption rates (SAR) determined computationally in the specific anthropomorphic mannequin (SAM) and anatomically correct models of the human head when exposed to a mobile phone model are compared as part of a study organized by IEEE Standards Coordinating Committee 34, Sub-Committee 2, and Working Group 2, and carried out by an international task force comprising 14 government, academic, and industrial research institutions. The detailed study protocol defined the computational head and mobile phone models. The participants used different finite-difference time-domain software and independently positioned the mobile phone and head models in accordance with the protocol. The results show that when the pinna SAR is calculated separately from the head SAR, SAM produced a higher SAR in the head than the anatomically correct head models. Also the larger (adult) head produced a statistically significant higher peak SAR for both the 1- and 10-g averages than did the smaller (child) head for all conditions of frequency and position.     

Cavity and crater depth in hypervelocity impact

We discuss the depth of cavities and craters caused by hypervelocity impacts as a function of impact parameters such as impact velocity, projectile and target densities, and projectile diameter, in two extreme cases: the penetration of intact projectiles at low impact pressure and the hemispherical excavation at very high impact pressure. The relations between the depth and the impact parameters are obtained. Then, previous experimental results are compiled; crater depth normalized by projectile diameter and the ratio of projectile and target densities is plotted for glass, plastic, and metal projectiles and metal, rock, ice, foam, sheet-stack, and aerogel targets. The trends of the data are consistent with the relations in the extreme cases.     

Shaped silicon-crystal wafers obtained by plastic deformation and their application to silicon-crystal lenses.

Plastic deformation is an unlikely process by which to mould pristine silicon wafers into three-dimensional shapes owing to the inevitable detrimental impact that the resulting mechanically induced defects would have on their electrical properties. However, if one were to find a way of doing so without substantial degradation of these properties, a range of new applications might be opened up. Here we report on the successful plastic deformation of silicon crystal wafers for the preparation of wafers with various shapes. A silicon wafer was set between dies and pressed at high temperatures. One application of shaped wafers is as well-shaped concave silicon crystal lenses or mirrors. The lattice plane of such a crystal lens has a curvature exactly along the surface. A concave spheroidal X-ray lens, in the form of two-dimensional Johann and Johansson's monochromators, is proposed for an X-ray optical component system. We propose and demonstrate a new solar cell system with the concave silicon crystal mirror used as both a solar cell and a focused mirror. This system can make use of the reflected photons from solar cells.     

LaBGeO5 single crystals in glass and second-harmonic generation

Flower-shaped crystals with diameters of 100–200 μm consisting of LaBGeO₅ (LBGO) single crystals similar to petals were observed in the interior of transparent LBGO surface-crystallized glasses. Each flower-shaped crystal was radially grown from the surface of the included bubbles. A more intense second-harmonic generation was observed from the LBGO crystallized glasses with the flower-shaped LBGO single crystals compared to the samples without such crystals based on the Maker fringe technique and second-harmonic (SH) generation microscopy. The SH intensity for the flower-shaped LBGO single crystals monotonically decreased with increasing temperature up to 350 °C, less than the Curie temperature reported so far (530 °C). It is considered that the internal compressive stress induced by the difference in the thermal expansion between the LBGO single crystal and the corresponding glass affect the ferroelectric property of the flower-shaped LBGO single crystals in glass.     

螺杆压缩机性能模拟的误差分析及稳定性判据

在螺杆压缩机作动室的压力脉动模拟分析中,针对采用的数值计算方法———Rouge＿Kutta法可能由于计算舍入误差累积而造成计算发散,提出导入Simpson误差评价公式,建立了评价作动室排气过程中的计算误差的数学模型.同时针对排气行程中,由于作动室压力和排气室压力非常接近,造成计算误差增大的倾向,通过数学推证,得到对处于排气行程的作动室的压力脉动进行数值计算的稳定性判据,对模拟计算结果的收敛性提供保障.     

Czochralski growth of Yb doped oxyapatite for high power laser application

Ca₈(La,Yb)₂(PO₄)₆O₂ (Yb:CLPA) single crystals with the apatite-type structure could be grown from the melt using the Czochralski method. Grown crystal was 18 mm in diameter and 110 mm in length. It is transparent with slightly blue color. Neither visible inclusion nor crack was observed. Thermal conductivity of Yb:CLPA was calculated from the values of thermal diffusivity, heat capacity measurement and density. Luminescent characterization was carried out from the results of emission, absorption and Raman spectrum.     

Nonmagnetic indenter-type high-pressure cell for magnetic measurements

An indenter-type high-pressure cell has been developed for electric and magnetic measurements in low-temperature and high-magnetic-field environments. The maximum pressure achieved at low temperatures is more than 4.5 GPa, which is higher than that of a conventional piston-cylinder cell. The typical sample space at maximum pressure is 1.6 mm in diameter and approximately 0.7 mm in depth, and magnetic measurements such as ac-susceptibility and nuclear magnetic resonance can be performed using a miniature coil. All the components of the indenter cell are made of nonmagnetic materials that have enough thermal conductivity for low-temperature experiments using a 3He/4He dilution refrigerator. Another indenter-type cell designed for a commercial superconducting quantum interference device magnetometer is also reported.