倾斜入射的波前编码系统的点扩散函数扩大效应分析

通过对坐标系统进行旋转,计算得到了三次型波前编码系统的倾斜入射的光瞳函数,并给出了近似表达式. 分析表明倾斜入射会产生三次相位扩大效应和离焦扩大效应,它们和入射角的正负无关,且随着入射角绝对值的增大而增大. 这表现在点扩散函数(point spread function, PSF)上会扩展PSF包络的两条直角边,表现在调制传递函数(modulation transfer function, MTF)上会降低MTF值. 子午面倾斜入射时,子午方向的三次相位扩大效应和离焦放大效应大于弧矢方向,从而导致子午方向 关键词： 倾斜入射 波前编码 三次相位扩大效应 离焦扩大效应     

倾斜入射的波前编码系统的点扩散函数扩大效应分析

通过对坐标系统进行旋转，计算得到了三次型波前编码系统的倾斜入射的光瞳函数，并给出了近似表达式. 分析表明倾斜入射会产生三次相位扩大效应和离焦扩大效应，它们和入射角的正负无关，且随着入射角绝对值的增大而增大. 这表现在点扩散函数(point spread function, PSF)上会扩展PSF包络的两条直角边，表现在调制传递函数(modulation transfer function, MTF)上会降低MTF值. 子午面倾斜入射时，子午方向的三次相位扩大效应和离焦放大效应大于弧矢方向，从而导致子午方向     

Behavior of the irreversibility line in the new superconductor La1.5+xBa1.5+x−yCayCu3Oz

The irreversibility properties of high-T_c superconductors are of major importance for technological applications. For example, a high irreversibility magnetic field is a more desirable quality for a superconductor [1]. The irreversibility line in the H–T plane is constituted by experimental points, which divides the irreversible and reversible behavior of the magnetization. The irreversibility lines for series of La_1.5+xBa_1.5+x−yCa_yCu₃O_z polycrystalline samples with different doping were investigated. The samples were synthesized using the usual solid estate reaction method. Rietveld-type refinement of x-ray diffraction patterns permitted to determine the crystallization of material in a tetragonal structure. Curves of magnetization ZFC–FC for the system La_1.5+xBa_1.5+x−yCa_yCu₃O_z, were measured in magnetic fields of the 10–20,000 Oe, and allowed to obtain the values for the irreversibility and critical temperatures. The data of irreversibility temperature allowed demarcating the irreversibility line, T_irr(H). Two main lines are used for the interpretation of the irreversibility line: one of those which suppose that the vortexes are activated thermally and the other proposes that associated to T_irr a phase transition occurs. The irreversibility line is described by a power law. The obtained results allow concluding that in the system La_1.5+xBa_1.5+x−yCa_yCu₃O_z a characteristic bend of the Almeida–Thouless (AT) tendency is dominant for low fields and a bend Gabay–Toulouse (GT) behavior for high magnetic fields. This feature of the irreversibility line has been reported as a characteristic of granular superconductors and it corroborates the topological effects of vortexes mentioned by several authors 1 and 2.     

Phase- and shape-controlled synthesis of cadmium hydroxyl chloride microstructures via an ammonia-assisted conversion of 1D CdQCl (Q=quinoline) complex microwires

In this paper we reported a NH₃·H₂O-assisted solvothermal route for successful synthesis of cadmium hydroxyl chlorides (Cd_x(OH)_yCl_z) microstructures with different phases and shapes, employing 1D CdQCl (Q=quinoline) complex microwires as the precursor. Experiments contained two processes: firstly, CdQCl complex microwires with 500–600 nm in diameter and several hundreds of micrometers in length were prepared by the complexation between CdCl₂·2.5H₂O and quinoline at room temperature; then, CdQCl microwires were solvothermally treated at 150 °C for 10 h in the presences of different amounts of NH₃·H₂O to produce Cd_x(OH)_yCl_z microstructures with various phases and shapes. The as-obtained precursor and Cd_x(OH)_yCl_z microstructures were characterized by scanning electron microscopy, transmission electron microscopy, Infrared spectrometry and X-ray powder diffraction. Experiments showed that hexagonal Cd(OH)Cl was obtained from water–methanol system, while rhombohedral Cd₄(OH)₅Cl₃ from methanol system. Also, it was found that the shapes of Cd_x(OH)_yCl_z could be tuned by the amounts of NH₃·H₂O. Furthermore, the UV diffuse reflection and photoluminescence spectra of the precursor and Cd_x(OH)_yCl_z were also investigated.     

Investigation of nonlinear optical parameters of zinc based amorphous chalcogenide films

Third order nonlinear optical properties of amorphous Zn_x–S_y–Se_100−x−y chalcogenide films have been investigated using single beam transmission z-scan technique at 1064 nm of Nd:YAG laser. Measurement of optical properties of amorphous Zn_x–S_y–Se_100−x−y chalcogenide films prepared by thermal evaporation technique has been made. X-ray diffraction patterns of chalcogenide films confirm the amorphous nature. Optical band gap (E_g) has been estimated using Tauc's plot method from transmission spectra that is found to decrease with increase in content due to valence band broadening and band tailing the system. Nonlinear refractive index (n₂), nonlinear absorption coefficient (β) and third order nonlinear susceptibility (χ³) of chalcogenide films have been estimated. Self-focusing effect has been observed in closed aperture and reverse saturable absorption in open aperture scheme. Limiting threshold and dynamic range have been calculated from optical limiting studies. The increase in nonlinearity with increase in Zn content has been observed that is understood to be due to decrease in band gap on Zn doping. High nonlinearity makes these films a potential candidate for waveguides, fibers and two photon absorption in optical limiters.     

相位板装配倾斜对波前编码系统点扩散函数的影响

分析了装配误差引起的相位板倾斜对波前编码系统的影响,通过坐标变换推导了相应条件下的广义光瞳函数。结果表明：倾斜因子对系统的相位板系数具有放大效果,其随倾斜角绝对值的增大而增大,而与倾斜角的正负无关。相位板倾斜会放大系统点扩散函数包络面的两条直角边,相应地降低其光学传递函数值。在子午倾斜的条件下,子午方向的相位板系数放大效果大于弧矢方向,从而导致点扩散函数包络面在子午方向的放大效果大于弧矢方向,子午方向光学传递函数值的降低效果大于弧矢方向。采用MATLAB以及商用光学软件进行仿真实验,验证了上述结论。     

Interaction of z component of magnetic field between two samples of GO material in the round rotational single sheet tester (RRSST)

The magnetic properties of two grain-oriented (GO) samples of the same grade were measured under alternating and rotational magnetic flux conditions. Two samples were measured separately and then together in different arrangement to each other. The interaction of magnetic field between two samples were measured by using a coil, which was placed in between. The results show that the _Hz$H_z$ component influence measured magnetic properties in the x–y plane.     

Transformation of phase to (x,y,z)-coordinates for the calibration of a fringe projection profilometer

In this work we present a phase to (x,y,z)-coordinates transformation method for the calibration of a fringe projection profilometer. Our technique is divided in two parts: (1) phase to z transformation (for axial calibration) based on the typical polynomial fitting which uses a flat plane placed at several z positions to measure the phase of the projected fringes. (2) Phase to x and y transformation (for transverse calibration) based on the use of a crossed gratings pattern and a Fourier phase measurement method to determine x and y coordinates at several z positions. As will be shown the use of the crossed gratings pattern and the Fourier phase measurement method for transverse calibration is advantageous in several aspects: an unique image can give us x and y information at once. It provides x and y coordinates at each pixel in the image avoiding the use of interpolation methods. We present some experimental results and explain the viability of the proposed technique.     

Structural phase transition and octahedral tilting in the calcium titanate perovskite CaTiO3

Crystal structure of the calcium titanate perovskite CaTiO₃ was refined by the Rietveld analysis of neutron diffraction data collected over the temperature range of 296 to 1720 K. The orthorhombic Pbnm-tetragonal I4/mcm phase transformation reversibly occurred at 1512 ± 13 K and the tetragonal I4/mcm-cubic Pm3?m transition was reversibly observed at 1635 ± 2 K. The structural phase transitions are characterized by the tilt of the TiO₆ octahedron. The tilt systems of the Pbnm, I4/mcm, and Pm3?m CaTiO₃ are ?_x^??_y^??_z⁺ (?_x^? = ?_y^?), ?_x⁰?_y⁰?_z^?, and ?_x⁰?_y⁰?_z⁰, respectively. Here the ?_x^?, ?_z⁺, and ?_x⁰ stand for the out-of-phase tilt angle of TiO₆ octahedron along x axis, the in-phase octahedral tilt angle along z axis, and no octahedral tilting along x axis, respectively. All the tilt angles, ?_x^?, ?_z⁺, and ?_z^? decreased with increasing temperature where the critical exponents were about 0.25. The ?_x^? and ?_y^? of the orthorhombic structure decreased discontinuously to ?_z^? of the tetragonal structure or 0° through the Pbnm-I4/mcm transition. The tilt angle, the unit-cell parameters and unit-cell volume discontinuously changed at the Pbnm-I4/mcm transition temperature, indicating the first-order nature. The increase of the cell volume in the Pbnm-I4/mcm transition was 0.088 vol.%. In contrast, the unit-cell volume continuously increased and the tilt angle ?_z^? continuously decreased with increasing temperature and became 0° at the I4/mcm-Pm3?m transition temperature, indicating a continuous nature of the transformation. The Pbnm-I4/mcm and I4/mcm-Pm3?m phase transitions are induced by the tilting of TiO₆ octahedra, indicating the displacive nature of the transitions. The larger thermal motion of O2 atom in I4/mcm CaTiO₃ indicates the larger positional disorder of O2 atom, which is consistent with the tilt system ?_x⁰?_y⁰?_z^?.     

Generalized beams in ABCDGH systems

For a generalized beam at the source plane passing through co-located aperture and a propagation path consisting of an off-axis x-y asymmetric ABCDGH system, the receiver plane irradiance expression is derived using the Collins integral. A collection of source beam profiles that are obtainable from the generalized beam formulation are illustrated. Plots are given for viewing the progress of selected generalized beam types along the propagation axis, containing a single thin lens, co-centric and misaligned in the x-direction. The received power falling onto a finite aperture surface is calculated for various misalignment situations.     

Exploration of layered-type pseudo four-component Li-Ni-Co-Ti oxides

A series of layered-type pseudo four-component Li-Ni-Co-Ti oxides were prepared to explore optimal cathode materials for a lithium-ion secondary battery. The new layered-type compounds were prepared using a combinatorial material-preparation system based on electrostatic spray deposition (the “M-ist Combi” system), and combinatorial powder X-ray diffraction. The composition region of the new compounds (Li_α(Ni_xCo_yTi_z)O₂ (α∼1, 0 ≤ x ≤ 1, 0 ≤ y ≤ 1, z∼0.2, x + y + z = 1.0)) was found to be wider than the composition region previously reported (LiNi_0.8−yCo_0.2Ti_yO₂ (0 ≤ y ≤ 0.1)).     

Causal particle detectors and topology

We investigate particle detector responses in some topologically non-trivial spacetimes. We extend a recently proposed regularization of the massless scalar field Wightman function in four-dimensional Minkowski space to arbitrary dimension, to the massive scalar field, to quotients of Minkowski space under discrete isometry groups and to the massless Dirac field. We investigate in detail the transition rate of inertial and uniformly accelerated detectors on the quotient spaces under groups generated by (t, x, y, z) ? (t, x, y, z + 2a), (t, x, y, z) ? (t, −x, y, z), (t, x, y, z) ? (t, −x, −y, z), (t, x, y, z) ? (t, −x, −y, z + a) and some higher dimensional generalizations. For motions in at constant y and z on the latter three spaces the response is time dependent. We also discuss the response of static detectors on the RP³ geon and inertial detectors on RP³ de Sitter space via their associated global embedding Minkowski spaces (GEMS). The response on RP³ de Sitter space, found both directly and in its GEMS, provides support for the validity of applying the GEMS procedure to detector responses and to quotient spaces such as RP³ de Sitter space and the RP³ geon where the embedding spaces are Minkowski spaces with suitable identifications.     

Effect of elevated concentrations of strontium and iron on the structural and dielectric characteristics of Ba(1−x−y)Sr(x)Ti Fe(y)O3 prepared through sol–gel technique

Nano-composite Ba_1−xSr_(x)TiO₃ (BST), where x=0.01–0.50 and doped with different concentrations of iron Ba_(1−x−y)Sr_(x)TiFe _(y)O₃ (BSTF), where x=0.01 and y=0.01–0.05 powders were prepared by sol–gel method.     

Optimized implementations of rational approximations for the Voigt and complex error function

Rational functions are frequently used as efficient yet accurate numerical approximations for real and complex valued functions. For the complex error function w(x+iy), whose real part is the Voigt function K(x,y), code optimizations of rational approximations are investigated. An assessment of requirements for atmospheric radiative transfer modeling indicates a y range over many orders of magnitude and accuracy better than 10⁻⁴. Following a brief survey of complex error function algorithms in general and rational function approximations in particular the problems associated with subdivisions of the x, y plane (i.e., conditional branches in the code) are discussed and practical aspects of Fortran and Python implementations are considered. Benchmark tests of a variety of algorithms demonstrate that programming language, compiler choice, and implementation details influence computational speed and there is no unique ranking of algorithms. A new implementation, based on subdivision of the upper half-plane in only two regions, combining Weideman's rational approximation for small |x|+y<15 and Humlicek's rational approximation otherwise is shown to be efficient and accurate for all x, y.     

Hydrothermal-induced oriented growth of Fe–Co alloy and Sm-substituted magnetite nanowire composites

Fe–Co alloy and Sm³⁺-substituted magnetite nanowire composites (Co_xFe_1−x/Co_yFe_1−ySm_zFe_2−zO₄) have been synthesized via a hydrothermal method without using surfactants or templates. The effects of substitution on structure and morphology were investigated by powder X-ray diffraction, X-ray photoelectron spectroscopy, Mössbauer spectroscopy, and transmission electron microscopy (TEM). The TEM image shows that the average diameter of the magnetite nanowires is about 40 nm and the length is several micrometers. The z=0.1 composite shows relatively high saturation magnetization (92.3 emu/g) detected by a vibrating sample magnetometer. The possible growth mechanism of the nanowires is discussed on the basis of the crystal structure of the materials. From the perspective of thermodynamics, we explain the postulated mechanism of the hydrothermal reaction.     

Comprehensive theory for reduction of products of spin operators

We present a comprehensive theory that reduces the total power of products of spin operators. This theory improves the previous one [P.J. Jensen, F. Aguilera-Granja, Phys. Lett. A 269 (2000) 158] in two aspects. One is that for the set of spin operators S⁺, S⁻, Sz, a new method is suggested where the expansion coefficients in the reduction formula can be solved from linear equations. This new method is of direct physical meaning and is easier to handle. The other is that we show a method to reduce the products of another set of spin operators Sx, Sy, Sz. For this set of operators, the use of permutation regulation of x→y, y→z and z→x can save much time in obtaining some reduction formula. The present comprehensive theory enables one to deal more easily with the decoupling problems in Green' function theory where the set of either S⁺, S⁻, Sz or Sx, Sy, Sz operators is used.     

A comparison of 2D and 3D PIV measurements in an oblique jet

A stereo PIV (SPIV) acquisition and analysis system was developed to measure three velocity components in planar flow fields. The analysis software is based on a third order mapping function method. The system was calibrated by imaging a square grid in three measurement planes with two Kodak Megaplus cameras oriented at 30 to the bisector between them. The camera images were dewarped into real coordinates by employing a set of transform matrices computed for each calibration plane. Bias and rms errors were determined by comparing displacements measured directly with displacements estimated from the dewarping and recombination algorithm. The bias errors in the directions parallel with the measurement plane were negligible while the bias in thez direction was about 0.6 pixel. The rms errors, 0.2–0.3 pixels, were largest in thez direction. These errors were thought to result from limitations in the calibration method. The SPIV system was tested in a two-dimensional oblique jet with Reynolds number of 1800. The three dimensional results were taken in a vertical (x, y) plane parallel with the jet span. The SPIV results were compared with LDV data and two-dimensional PIV data obtained in a vertical (y, z) plane of the same jet. The SPIV measurements yielded accurate values for the in-plane mean and rms velocity components. The measured out-of-plane mean component was underestimated due to the bias error mentioned above. The rms component was accurate in part of the field but overestimated in another part due to local variations in rms error. It is expected that in the future, the out-of-plane errors can be minimized by improving the calibration and transformation procedures.     

Effect of nitrogen content on the properties of CrNxOyCz coating prepared by DC reactive magnetron sputtering

The CrN_xO_yC_z coatings were deposited by planar DC reactive magnetron sputtering onto AZ31 Mg alloy and high speed tool steel (HSTS) substrates at a substrate temperature of 200 °C. The effect of N₂ content on composition and structure of the CrN_xO_yC_z coatings was investigated. The structure of the CrN_xO_yC_z coatings was analyzed by a glancing angle X-ray diffraction (GXRD). The cross-section morphology and thickness of the CrN_xO_yC_z coatings were checked by a field emission scanning electron microscope (FESEM), and the composition profile and chemical state were carried out by an X-ray photoelectron spectroscopy (XPS). The experimental results showed that the structure and phase composition of the CrN_xO_yC_z coatings depended on N₂ content. The evolution of the structure of CrN_xO_yC_z coatings was consistent with CrN_x-based coatings, and the CrN_xO_yC_z coatings contained Cr₂O₃, CrO₂, CrO, Cr₃C₂, CrN_x (Cr, CrN, Cr₂N), as well as different chromium oxynitride. However, the carbide and oxynitride were oxidized after annealing.     

波前编码系统景深延拓性能研究

波前编码景深延拓技术是在非相干光学系统的出瞳处加入三次位相板,对成像进行解码处理而获得清晰图像以扩大光学系统景深的技术.文章通过深入研究波前编码光学成像系统的调制传递函数(MTF),分析离焦量和位相板的调制系数对MTF的影响,并通过数值计算和曲线拟合得到位相板调制系数、系统带宽、景深延拓性能之间的关系.该研究成果为位相板的调制系数的选择和景深延拓光学系统的设计提供依据. 关键词： 波前编码 景深延拓 调制传递函数 三次位相板     

Rapid surface roughness measurements of silicone thin films with different thicknesses

A rapid optical measurement system for rapid surface roughness measurement of polycrystalline silicon (poly-Si) thin films was developed in this study. Two kinds of thickness of poly-Si thin films were used to study rapid surface roughness measurements. Six different incident angles were employed for measuring the surface roughness of poly-Si thin films. The results reveal that the incident angle of 20° was found to be a good candidate for measuring the surface roughness of poly-Si thin films. Surface roughness (y) of poly-Si thin films can be determined rapidly from the average value of reflected peak power density (x) measured by the optical system developed using the trend equation of y = ?0.1876x + 1.4067. The maximum measurement error rate of the optical measurement system developed was less than 8.61%. The savings in measurement time of the surface roughness of poly-Si thin films was up to 83%.