共查询到20条相似文献,搜索用时 0 毫秒
1.
Bastiaans MJ Alieva T 《Journal of the Optical Society of America. A, Optics, image science, and vision》2006,23(8):1875-1883
It is shown that a lossless first-order optical system whose real symplectic ray transformation matrix can be diagonalized and has only unimodular eigenvalues is similar to a separable fractional Fourier transformer in the sense that the ray transformation matrices of the unimodular system and the separable fractional Fourier transformer are related by means of a similarity transformation. Moreover, it is shown that the system that performs this similarity transformation is itself a lossless first-order optical system. Based on the fact that Hermite-Gauss functions are the eigenfunctions of a fractional Fourier transformer, the eigenfunctions of a unimodular first-order optical system can be formulated and belong to the recently introduced class of orthonormal Hermite-Gaussian-type modes. Two decompositions of a unimodular first-order optical system are considered, and one of them is used to derive an easy optical realization in more detail. 相似文献
2.
We present a synthesis algorithm to design an optical finite impulse response (FIR) filter for compensating a first-order polarization mode dispersion (PMD) by minimizing the differential group delay (DGD). The desired frequency response was approximated using two widely used methods in designing digital FIR filters: the Fourier series expansion method and the frequency sampling method. A numerical simulation was performed for an eighth-order filter to demonstrate the difference between the two methods. The simulation results produced a sharper cutoff for the Fourier series expansion and higher stopband attenuation for the frequency sampling method. The Fourier series method produced better results in reducing the DGD. 相似文献
3.
Lin PD Tsai CY 《Journal of the Optical Society of America. A, Optics, image science, and vision》2007,24(3):776-784
Current commercial software for analysis and design of optical systems use finite difference (FD) approximation methodology to estimate the gradient matrix of a ray with respect to system variables. However, FD estimates are intrinsically inaccurate, subject to gross error when the denominator is excessively small relative to the numerator. We avoid these problems and determine these gradients by the application of Snell's law. We give the background and basics for determining the first-order gradients of skew rays of optical systems, whereby the differential vector of any ray can be estimated by the product of the developed gradient matrix and differential changes of system variables. The most important application is for optical design by use of optimization methods where the merit function is defined as the spot size. FD used for such optimization is slow for large systems and subject to inaccuracy. The presented methodology is shown to be accurate and computationally faster than traditional FD. Two illustrative examples are provided to validate the proposed method. 相似文献
4.
5.
As a fundamental task in computer vision, optical flow estimation algorithms aim to establish dense pixel correspondences between image frames. This paper presents a novel optical flow estimation framework called GCPOF to handle large displacement and scale variations of scene objects, which appear frequently and pose great challenges in practice. Within the framework of GCPOF, large displacement and scale variations are captured by a new problem formulation leveraged by sparse ground control points. We present detailed theoretical derivation of the solution to the problem based on iterative reweighted least squares. Both qualitative and quantitative evaluations on synthetic and real images demonstrate that GCPOF is able to handle optical flow fields with large displacement and scale variations properly, and it runs significantly faster than relevant optical flow estimation methods. 相似文献
6.
7.
A simple, easy approach to the synthesis of nickel (Ni) doped zinc sulphide (ZnS) clusters is reported. The synthesis of Ni–ZnS clusters involved mixing and drying of zinc acetate, sodium sulphide and acrylic acid in appropriate ratio and adding Ni at proper conditions. These clusters were trapped in polyacrylic acid (PAA) to form a PAA capping to provide stability. The clusters were characterized using high resolution SEM for morphological investigation; XRD for its crystalline nature; photoluminescence (PL) for optical characterization and electrical conductivity measurement. Clusters of Ni–ZnS were formed of the size ~ 10 nm. 相似文献
8.
Summary A finite-difference solution of the transient natural convection flow of an incompressible viscous fluid past an impulsively started semi-infinite plate with uniform heat and mass flux is presented here, taking into account the homogeneous chemical reaction of first order. The velocity profiles are compared with the available theoretical solution and are found to be in good agreement. The steady-state velocity, temperature and concentration profiles are shown graphically. It is observed that due to the presence of first order chemical reaction the velocity decreases with increasing values of the chemical reaction parameter. The local as well as average skin-friction, Nusselt number and Sherwood number are shown graphically.List of symbols
C
concentration
-
C
species concentration in the fluid far away from the plate
-
C
w
species concentration near the plate
-
C
dimensionless concentration
-
D
mass diffusion coefficient
- Gc
mass Grashof number
- Gr
thermal Grashof number
-
g
acceleration due to gravity
-
j
mass flux per unit area at the plate
-
K
dimensionless chemical reaction parameter
-
K
l
chemical reaction parameter
-
k
thermal conductivity
- Nux
dimensionless local Nusselt number
-
dimensionless average Nusselt number
- Pr
Prandtl number
-
q
heat flux per unit area at the plate
- Sc
Schmidt number
- Shx
dimensionless local Sherwood number
-
dimensionless average Sherwood number
-
T
temperature
-
T
temperature of the fluid far away from the plate
-
T
w
temperature of the plate
-
T
dimensionless temperature
-
t
time
-
t
dimensionless time
-
u
0
velocity of the plate
-
U, V
dimensionless velocity components inX,Y-directions, respectively
-
u, v
velocity components inx, y-directions, respectively
-
X
dimensionless spatial coordinate along the plate
-
x
spatial coordinate along the plate
-
Y
dimensionless spatial coordinate normal to the plate
-
y
spatial coordinate normal to the plate
-
thermal diffusivity
-
volumetric coefficient of thermal expansion
- *
volumetric coefficient of expansion with concentration
-
coefficient of viscosity
-
kinematic viscosity
- x
dimensionless local skin-friction
-
dimensionless average skin-friction 相似文献
9.
《中国计量学院学报》2015,(3):341-346
随着数据量的不断增长,分布式搜索引擎的出现满足了大数据量的检索性能.现有的主从节点选举策略往往会导致主从节点分配不均而使得查询性能不均衡.现提出一种搜索引擎集群的主从节点选举策略,能保证正常情况下节点的分布均衡.当出现宕机时能重新切换主节点,保证检索功能有效;当宕机的服务器重新上线时,主从节点分布恢复正常,避免了负载不平衡的缺陷,达到合理利用每台服务器的性能并充分发挥集群的性能优势的目的. 相似文献
10.
Synthesis of thick optical thin-film filters with a layer-peeling inverse-scattering algorithm 总被引:1,自引:0,他引:1
We present an efficient and accurate method for synthesis of optical thin-film structures. The method is based on a differential inverse-scattering algorithm and considers therefore both phase and amplitude reflectance data. We apply the algorithm to the synthesis of filters with arbitrary index layers and two-material filters consisting of only high- and low-index layers. The layered structure is approximated by a stack of discrete reflectors with equal distance between all reflectors. This mirror stack is in turn determined from the desired, complex reflection spectrum by a layer-peeling inverse-scattering algorithm. The complexity of the design algorithm is approximately the same as that of the forward problem of computing the spectrum from a known structure. 相似文献
11.
A simple, easy approach to the synthesis of manganese Mn doped zinc sulphide (ZnS) clusters is reported. The synthesis of Mn–ZnS clusters involved mixing and drying of zinc acetate, sodium sulphide and acrylic acid in appropriate ratio and adding Mn at proper conditions. These clusters were trapped in polyacrylic acid (PAA) to form PAA capping to provide stability. The clusters were characterized using high resolution SEM for morphological investigation; XRD for its crystalline nature; photoluminescence (PL) for optical characterization and electrical conductivity measurement. Clusters of Mn–ZnS were formed of the size ~ 10 nm. 相似文献
12.
An improved stochastic separated flow (ISSF) model developed by the present authors is compared with two other widely used
trajectory models, the deterministic separated flow (DSF) model and the stochastic separated flow (SSF) model, in numerical
simulations of gas–particle flows behind a backward-facing step. The DSF and ISSF models are found to need only 250 computational
particles to obtain a statistically stationary solution of mean and fluctuating velocities of the particles, while the SSF
model requires as many as 10,000 computational particles. Apart from comparing the sensitivity of required computational particles
for different models, prediction capability of different models on mean velocities, fluctuating velocities and re-circulation
region are also compared in this paper. Predicted results of streamwise mean velocity of particle phase agree well with experimental
data for all the three models. For the mean fluctuating velocity of the particle phase, predictions using the ISSF model agree
well with experiment data, while the DSF and the SSF models have a significant difference. Only the SSF and the ISSF models
are capable of predicting re-circulation regions of the particle phase. As a comparison, the ISSF model has a distinct advantage
over the other two models both in terms of accuracy and efficiency.
Received 20 October 2001 / Accepted 5 February 2002 相似文献
13.
Zou W Rolland JP 《Journal of the Optical Society of America. A, Optics, image science, and vision》2005,22(5):938-951
An iterative zonal wave-front estimation algorithm for slope or gradient-type data in optical testing acquired with regular or irregular pupil shapes is presented. In the mathematical model proposed, the optical surface, or wave-front shape estimation, which may have any pupil shape or size, shares a predefined wave-front estimation matrix that we establish. Owing to the finite pupil of the instrument, the challenge of wave front shape estimation in optical testing lies in large part in how to properly handle boundary conditions. The solution we propose is an efficient iterative process based on Gerchberg-type iterations. The proposed method is validated with data collected from a 15 x 15-grid Shack-Hartmann sensor built at the Nanjing Astronomical Instruments Research Center in China. Results show that the rms deviation error of the estimated wave front from the original wave front is less than lambda/130-lambda/150 after approximately 12 iterations and less than lambda/100 (both for lambda = 632.8 nm) after as few as four iterations. Also, a theoretical analysis of algorithm complexity and error propagation is presented. 相似文献
14.
Fringe patterns with a multiplicative phase shift among them appear in experimental techniques as photoelasticity and RGB shadow moiré, among others. These patterns cannot be processed using standard phase-shifting demodulation techniques. In this work, we propose to use a multiframe regularized optical flow algorithm to obtain the interesting modulating phase. The proposed technique has been applied to simulated and experimental interferograms obtaining satisfactory results. 相似文献
15.
We have carried out 3-dimensional molecular dynamics simulations of a crystal growth technique known as laser heated pedestal growth. Previously, we simulated this technique in 2 dimensions and our current work is an attempt to extend those simulations to the more realistic 3D case. We demonstrate that such 3D simulations are feasible in a study of the influence of the growth speed and the influence of the laser heating on various aspects of the fiber growth. Although much more realistic than the 2D study, the moderate system sizes used in this study and other crude representations of the experimental process still prevent us from making quantitative comparisons with the latter. 相似文献
16.
《低温学》2017
There are several ways to organize the flow scheme of the helium liquefiers, such as arranging the expanders in parallel (reverse Brayton stage) or in series (modified Brayton stages). In this paper, the inlet mass flow and temperatures of expanders in Collins cycle are optimized using genetic algorithm (GA). Results show that maximum liquefaction rate can be obtained when the system is working at the optimal parameters. However, the reliability of the system is not well due to high wheel speed of the first turbine. Study shows that the scheme in which expanders are arranged in series with heat exchangers between them has higher operation reliability but lower plant efficiency when working at the same situation. Considering both liquefaction rate and system stability, another flow scheme is put forward hoping to solve the dilemma. The three configurations are compared from different aspects, they are respectively economic cost, heat exchanger size, system reliability and exergy efficiency. In addition, the effect of heat capacity ratio on heat transfer efficiency is discussed. A conclusion of choosing liquefier configuration is given in the end, which is meaningful for the optimal design of helium liquefier. 相似文献
17.
Mueller matrices provide a complete characterization of the optical polarization properties of biological tissue. A polarization-sensitive optical coherence tomography (OCT) system was built and used to investigate the optical polarization properties of biological tissues and other turbid media. The apparent degree of polarization (DOP) of the backscattered light was measured with both liquid and solid scattering samples. The DOP maintains the value of unity within the detectable depth for the solid sample, whereas the DOP decreases with the optical depth for the liquid sample. Two-dimensional depth-resolved images of both the Stokes vectors of the backscattered light and the full Mueller matrices of biological tissue were measured with this system. These polarization measurements revealed some tissue structures that are not perceptible with standard OCT. 相似文献
18.
19.
20.
Parallel detection algorithm for page-oriented optical memories 总被引:3,自引:0,他引:3
We present a parallel algorithm for the reliable detection of two-dimensional binary data in page-oriented memories. The development of the proposed pseudodecision-feedback equalization (PDFE) method is motivated by the classical decision-feedback equalization receiver. The technique takes advantage of the known or the estimated optical system characteristics to mitigate space-variant blur and additive thermal noise. We extend the method to correct for fixed-pattern errors including magnification, rotation, and transverse shift. Advantages of the PDFE algorithm include its parallel design, low computational complexity, and local connectivity. A system-capacity metric is used to compare the performance of the PDFE receiver with other conventional approaches, including the simple threshold, the 1:2 modulation code, and the Wiener filter. Results show the PDFE to outperform all the above techniques over a variety of channels for both incoherent and coherent systems. Implementation issues are discussed, and a MOSIS (Metal-Oxide Semiconductor Implementation Service) 2-mum design is presented. 相似文献