Numerical prediction of sound generated from flows with a low Mach number

Numerical computations of sound generated from flows with a low Mach number are presented based on Lighthill’s acoustic analogy with an assumption that sound does not alter the flow field from which it is generated. The source fluctuations of the flow field are computed by a large-eddy simulation (LES) with Dynamic Smagorinsky Model (DSM) and they are fed to the following acoustical computation as input data. An explicit/implicit finite element method with second order accuracy both in time and space is used for flow field discretization. The method is applied to the prediction of sound in three different classes of problems: far-field sound generated from flow around a bluff body, sound resulting from blade-stator interaction of turbomachinery and sound due to a turbulent boundary layer on an aerofoil. The computed frequency spectra of the sound show a fairly good agreement with the measured spectra for all the cases.     

自组织InAs/GaAs量子点的表面氮化研究

用低温光荧光(PL)和透射电子显微镜(TEM)研究了表面氮化自组织InAs/GaAs量子点的光学性能和微观结构。结果表明氮化后形成薄层的InAsN薄膜作为应变缓和层覆盖在量子点的表面,使得随着氮化时间的增加,InAs量子点的位错密度提高、尺寸变大、纵横比提高、发光波长变长、强度变低。     

The optical alignment system of the ZEUS microvertex detector

The laser alignment system of the ZEUS microvertex detector is described. The detector was installed in 2001 as part of an upgrade programme in preparation for the second phase of electron–proton physics at the HERA collider. The alignment system monitors the position of the vertex detector support structure with respect to the central tracking detector using semi-transparent amorphous-silicon sensors and diode lasers. The system is fully integrated into the general environmental monitoring of the ZEUS detector and data has been collected over a period of 5 years. The primary aim of defining periods of stability for track-based alignment has been achieved and the system is able to measure movements of the support structure to a precision around .     

Bond-order potential for transition metal carbide cluster for the growth simulation of a single-walled carbon nanotube

A classical many-body potential for transition metal carbide cluster is developed in the form of the bond-order type potential function. The parameter sets between carbon atoms and several transition metal atoms (Fe, Co and Ni) are constructed by fitting binding energies from Density Functional Theory (DFT) calculations. Using the potential function, clustering process of carbon atoms to a small metal cluster is studied by classical molecular dynamics (MD) simulation. The number of hexagonal rings in the Co cluster increases about twice as fast as in the Fe cluster. This implies that the graphitic lattice interacts more strongly with Co atoms than with Fe atoms. A Co cluster has a crystal structure where metal atoms are regularly allocated and embedded in the hexagonal carbon network in the simulation. In contrast, carbon atoms cover the entire surface in case of the Fe cluster. Additionally, the potential energy surface that a carbon atom feels from a 2D closed-packed facet is examined using a hypothetical FCC(1 1 1) facet of several transition metals. The potential energy minima are distributed on the hexagonal network showing the 2D closed-packed facet can be a template where a graphene is formed.     

Possible 3He Boltzmann Gas Formed on Three-Dimensional Nanopores Preplated with 4He

We have measured the heat capacity of ³He adsorbed on three-dimensionally connected nanopores, 2.7 nm in diameter, preplated with about 1.3 atomic layers of ⁴He. At low coverages of ³He, the ³He heat capacity is roughly constant at the measured temperatures between 0.1 and 1 K. Its molar heat capacity is on the order of the gas constant R, between 1.1R and 1.8R. This suggests a Boltzmann gas state of the adsorbed ³He. At high coverages, the heat capacity is likely approaching linear in T at low temperatures, which suggests a degenerate state at further lower temperatures.     

Urban growth and change analysis using remote sensing and spatial metrics from 1975 to 2003 for Hanoi,Vietnam

Since the beginning of the ‘Doi Moi’ policy in 1986, Hanoi has witnessed significant changes in its urban areas. Landsat and Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) scenes were used to identify built-up areas in Hanoi, and spatial metrics were used to characterize urban change patterns from 1975 to 2003. Firstly, a spatial metric called the ‘percentage of like adjacency’ was used to discern urban growth patterns, which were classified into three sub-patterns: expansion growth, infill growth and outlying growth. Secondly, the driving force underlying the urbanization of the city for the 1975–1984, 1984–1992, 1992–2001, 2001–2003 periods was investigated using a spatial metric analysis programme (FRAGSTATS). The expansion of urban areas along major transportation routes in the latter 1980s was identified as the main form of urbanization in Hanoi. This paper shows the potential application of spatial metrics as secondary sources of information for supporting remotely sensed data and their use to characterize urban growth patterns.     

Depth from Refraction Using a Transparent Medium with Unknown Pose and Refractive Index

In this paper, we introduce a novel method for depth acquisition based on refraction of light. A scene is captured directly by a camera and by placing a transparent medium between the scene and the camera. A depth map of the scene is then recovered from the displacements of scene points in the images. Unlike other existing depth from refraction methods, our method does not require prior knowledge of the pose and refractive index of the transparent medium, but instead can recover them directly from the input images. By analyzing the displacements of corresponding scene points in the images, we derive closed form solutions for recovering the pose of the transparent medium and develop an iterative method for estimating the refractive index of the medium. Experimental results on both synthetic and real-world data are presented, which demonstrate the effectiveness of the proposed method.     

Capillary rise properties of porous mullite ceramics prepared by an extrusion method with various diameters of fiber pore formers

Porous mullite ceramics with unidirectionally oriented pores were prepared by an extrusion method using rayon fibers as the pore formers. Rayon fibers of 8.1, 9.6, 16.8, and 37.6 μm in diameter were used as the pore formers and were kneaded with alumina powder, kaolin clay, China earthen clay, and water to form pastes. These pastes were extruded into cylindrical tubes, dried, and fired at 1500 °C for 4 h. The apparent porosities ranged from 45.7 to 48.2 %. The pore size distributions showed a sharp peak at 9.4, 10.0, 15.6, and 30 μm with increasing fiber diameters. The height of the capillary rise was 1780, 1670, 1320, and 950 mm with increasing fiber diameter. The maximum capillary rise is much higher than previously reported. The contact angle and effective pore radius that determine the capillary rise ability were calculated by fitting the capillary rise curves using the Fries and Dreyer’s equation.     

Preparation of helical carbon and graphite films using morphology-retaining carbonization

Helical carbon and graphite films were prepared from iodine-doped helical polyacetylene (H-PA) film using currently developing morphology-retaining carbonization. It was found from scanning electron microscopy (SEM) observations that the hierarchical helical morphology of the H-PA film remains unchanged even after the carbonization at 800 °C. Besides, the weight loss of the film due to the carbonization was very small, which was only a few percent to the weight of the film before doping. Furthermore, the graphite film prepared by the subsequent heating at 2600 °C still retained the same morphology as those in the original H-PA film and in the helical carbon film prepared at 800 °C. X-ray diffraction (XRD) and Raman scattering measurements were then pursued. The results showed that graphitic crystallization proceeds in the carbon film through the heat treatment at 2600 °C. Transmission electron microscopy (TEM) image of a single helical graphitic fibril was also observed by ultrasonicating the graphite film in ethanol. Carbonization of the H-PA films by way of iodine doping was found to afford helical carbon and graphite films, where spiral morphologies and even helical fibril structures were completely preserved.     

Super‐reflective color LCD with PDLC technology

Abstract— A novel reflective color LCD without polarizers has been developed using a PDLC film and a retro‐reflector. Bright color images including moving images are achievable with ambient light. This novel LCD will enable the new application area of electronic paper.