Accommodating degradation results within a qualification procedure

A qualification procedure may comprise different tests which may either be successful or a failure. However, there are cases of degradation which should be taken into account. The reliability of a consecutive k-out-of-n:G set of tests is evaluated, along with the possibility of degradation. The problem is formulated as a difference equation that is transformed into a digital filter equation. Numerical results indicate improved chances of success for a set of tests that take into account the case of degradation.     

An upper bound solution for closed die sinter forging of hexagonal shapes

The paper reports on an investigation into the various aspects of closed die cold forging of hexagonal powder preforms, which have been compacted and sintered from atomized powder. It is found that for certain dimensional ratios of the preform, the die pressure is minimum. An attempt has been made determine the die pressures developed during the closed die forging of the hexagonal powder preform by using an upper bound approach. The results so obtained are discussed critically to illustrate the interaction of various process parameters involved and are presented graphically     

Six-fold hexagonal symmetric nanostructures with various periodic shapes on GaAs substrates for efficient antireflection and hydrophobic properties

We fabricated various periodic nanostructures with a six-fold hexagonal symmetry on gallium arsenide (GaAs) substrates using simple process steps, together with a theoretical analysis of their antireflective properties. Elliptical photoresist (PR) nanopillars, which are inevitably generated by the asymmetric intensity distribution of the laser interference, were converted to rounded lens-like patterns by a thermal reflow process without any additional complex optic systems, thus leading to an exact six-fold hexagonal symmetry. Various shaped periodic nanostructures including nanorods, cones, truncated cones, and even parabolic patterns were obtained under different etching conditions using the rounded lens-like PR patterns formed by the reflow process. For the parabolic structure, the calculated lowest average reflectance of ～ 2.3% was obtained. To achieve better antireflection characteristics, an aluminum-doped zinc oxide (AZO) film was deposited on the GaAs parabolas, which forms an AZO/GaAs parabolic nanostructure. The structure exhibited a low average reflectance of ～ 1.2% over a wide wavelength region of 350-1800?nm and a hydrophobic surface with a water contact angle of θ(c) ～ 115°. The calculated reflectances were reasonably consistent with the measured results.     

Spatially resolved determination of atomic particle densities and line shapes within an arc plasma by tomographic resonance interferometry

The particle density of ground-state chromium atoms within one cross section of an arc plasma was measured spatially resolved, and the spatial distribution of the line shape of the chromium resonance line at 427.48 nm was partly determined. The measurements were performed with a newly developed setup that combines the methods of resonance interferometry and refractive tomography. The wavelength of a dye laser was scanned over the investigated transition, and the refractive index was measured spatially and spectrally resolved by use of tomography. For each spatial point the particle density and the local line shape were calculated from the measured spectral refractivity distribution by the method of resonance interferometry. We describe the physical principles, the optical arrangement, and the numerical apparatus, and we discuss the results and further possibilities.     

单片与双片式可调节人工晶体屈光调节力研究

给出了一种双片式可调节人工晶体模型,并通过符合实际人眼情况的模拟方法,即人工晶体在眼内移动后,在接近相同人眼成像质量条件下,比较了正透镜-正透镜、负透镜-正透镜、正透镜-负透镜三种不同组合形式的双片式可调节人工晶体和单片式可调节人工晶体对人眼屈光调节力影响,结果表明:当正透镜-负透镜组合的双片式可调节人工晶体的正透镜在相对负透镜移动的距离与单片式可调节人工晶体在眼内移动距离相等时,该型双片式可调节人工晶体使人眼获得的屈光调节力明显较高,且屈光调节力的大小随正透镜和负透镜屈光度的增大而增大,正透镜-正透镜-负透镜-正透镜型人工晶体屈光调节力低于单片式人工晶体,对人眼成像质量影响较大的球差Z40项从0.096到0.263变化,人眼屈光调节力仅改变0.03D,以上所得结论为设计新一代的双片式可调节人工晶体提供了一定的理论基础.     

Indentation on two-dimensional hexagonal quasicrystals

This paper is concerned with contact problem for a half-space of two-dimensional hexagonal quasi-crystal punched by three common indenters (cylindrical flat-ended, conical and spherical punches). Based on the Green’s functions for the half-space subjected to an external phonon source exerted on the surface, the superposition principle is applied to constructing the boundary integral equation. Relations between the indentation force and the penetration depth, and the indentation stiffness constants are explicitly obtained for these three indenters. Complete and exact fields in the half-space are given in terms of elementary functions. The present theoretical solutions can not only serve as benchmark for computational contact mechanics, but also apply to guiding future indentation experiments.     

Laminar flow inside hexagonal ducts

Analytical solutions are obtained for fully developed laminar flow inside hexagonal ducts and, as a special case, rhombic ducts, through application of the recently advanced generalized integral transform technique for the solution of diffusion-type problems within irregular domains. First, the formal complete solution of the original problem is obtained, in terms of a denumerable system of coupled ordinary differential equations. Then, an explicit and quite straightforward lowest order solution results from the appropriate simplification of the coupled system. Quantities of particular interest in the field of heat exchanger thermohydraulics are then systematically presented, and utilized to establish the accuracy and suggest application ranges for the approximate solution.Communicated by S. N. Atluri, May 11, 1989     

Mirrors with regular hexagonal segments

The point-spread function and emissivity are calculated for a mirror made from regular hexagonal segments of just a few different sizes. A mirror of this type has many similar segments, which is an advantage for manufacturing, and for an approximately f/1 mirror with > or = 1000 segments and > or = 4 sizes of regular hexagons the increase in intersegment gap area is negligible. This result raises the possibility of making a mirror from very large numbers of identical small segments that are warped to the required figure.     

Anisotropic elasticity in hexagonal crystals

The general expressions for the compliance s_ijkl^′, Young's modulus E(hkl) and Poisson's ratio υ(hkl) are given for an arbitrary plane (hkl) of hexagonal crystal. The calculations have also been made for 12 hexagonal metals Be, Cd, Co, Hf, Mg, Re, Ru, Sc, Ti, Y, Zr and Zn, and the representation surfaces, for which the radius vector deviated an angle ψ from the crystallographic Z-axis is proportional to or υ(hkl) are constructed. For convenient applications, the expressions of Young's modulus E(hkl) and Poisson's ratio υ(hkl) are also given in terms of the Miller indices of the lattice plane (hkl). With these expressions, the X-ray elastic constants (REC) can be obtained readily for a particular plane (hkl) chosen for measurement.     

Graphene-like bilayer hexagonal silicon polymorph

We present molecular dynamics simulation evidence for a freezing transition from liquid silicon to quasi-two-dimensional (quasi-2D) bilayer silicon in a slit nanopore. This new quasi-2D polymorph of silicon exhibits a bilayer hexagonal structure in which the covalent coordination number of every silicon atom is four. Quantum molecular dynamics simulations show that the stand-alone bilayer silicon (without the confinement) is still stable at 400 K. Electronic band-structure calculations suggest that the bilayer hexagonal silicon is a quasi-2D semimetal, similar to a graphene monolayer, but with an indirect zero band gap.      

Hydrothermal controllable synthesis to convert ZnO hexagonal nanotubes to hexagonal nanorods and their photocatalytic application

Zinc oxide (ZnO) thick films were analyzed by high-resolution X-ray diffraction (HR-XRD), field emission scanning electron microscopy, and photoluminescence (PL) spectroscopy at room temperature. The films were grown on glass substrates using different molar concentrations of aqueous solution (0.02, 0.04, and 0.06 M) via a simple hydrothermal method. This method uses glass bottles with rubber caps as reactor vessels (100 mL) and, thus, is classified as a green chemistry technique. Hexahedral zinc nitrate (Zn (NO₃)₂·6H₂O), hexamethylenetetramine (C₆H₁₂N₄), and deionized water were used as starting materials and were reacted in the presence of heat. HR-XRD measurements confirmed that the diffraction peaks of the polycrystalline structure films can be assigned to the hexagonal-shaped wurtzite ZnO. In addition, the PL spectra show that the integrated intensity decreases with the increase in ZnO content. The SEM images also revealed the existence of hexagonal ZnO nanotubes in the 0.02 M sample, and these nanotubes are gradually converted into hexagonal nanorods with the increase in ZnO content. Moreover, the photocatalytic activity of both nanostructures was measured based on the degradation of methyl blue (MB) by using ultraviolet light (λ = 366 nm). Results showed that the ZnO nanotubes degraded MB more effectively than the nanorods.     

数字放映机3D功能设置方法与技巧

本文对数字电影放映机在实现3D放映时的基本原理和一些重要参数进行了解释,并详细介绍了数字放映机3D功能的设置方法和经验技巧,为目前和今后的数字3D放映设备安装提供了指南.     

一种应对窄带主动噪声控制中频率不匹配的方法

窄带前馈主动噪声控制系统中,参考信号通常通过非声学传感器获取。由于传感器老化磨损等原因,所测同步频率与目标噪声真实频率间将存在误差,即产生频率不匹配(FM)。结合AR模型,提出一种改进的FM补偿方法,加入一个延迟模块和一个相应的幅值相位调节器,本质上是通过延迟和叠加构造出隐含真实频率的信号,同时提高相位匹配速度和精度。仿真结果与分析表明,设计的FM补偿方法能有效应对15%以上的频率不匹配量,且系统收敛速度更快。     

Dynamic crushing strength of hexagonal honeycombs

Based on the repeatable collapsing mechanism of cells’ structure under dynamic crushing, an analytical formula of the dynamic crushing strength of regular hexagonal honeycombs is derived in terms of impact velocity and cell walls’ thickness ratio. It is consistent with the equation obtained from the shock wave theory that regards cellular material as continuum, in which the key parameter is approximately measured from the “stress–strain” curve of the cellular material. The effect of unequal thickness of cell walls on the honeycomb's dynamic crushing strength is discussed, and the result shows that the dynamic crushing strength of the hexagonal honeycomb with some double-thickness walls is about 1.3 times of that of the hexagonal honeycomb without double-thickness wall. All of the analytical predictions are compared with the numerical simulation results, showing good agreements.     

Radiant heating of simple shapes

Steady and unsteady radiant heating of a plate and a cylinder are analyzed, and a first-approximation solution is obtained by a method of averaging correction functions.     

Formation of cadmium-containing W-type hexagonal ferrite

The main steps of the phase formation processes which take place in samples of W-type hexaferrites containing cadmium, prepared by chemical coprecipitation, have been analysed. The processes were followed by Mössbauer spectroscopy, powder X-ray diffraction, thermomagnetic analysis and magnetic measurements. For samples heated in the temperature range 1000–1100°C, the phase formation processes are the same as those verified for the other zinc, nickel, cobalt W-type compounds: forT _h=1000°C the only phases present are SrFe₁₂O₁₉ (M-type ferrite) and CdFe₂O₄ (spinel ferrite); in contrast, forT _h>1100°C, the solid state reaction between the M-type and the spinel phases does not take place and the spinel phase decomposes, leading to the formation of -Fe₂O₃.