Selective receiver switching scheme for space time block coding with full code rate and non-orthogonal design

It is desirable to construct a transmission matrix with full code rate as well as full transmit diversity in the design of space time block coding (STBC). For an arbitrary complex constellation, only full rate and full diversity signal matrix with size 2 by 2 is possible, said as Alamouti Code. For a real signal matrix with a size above 8 by 8, it is also impossible to acquire full code rate and full transmit diversity simultaneously. An efficient selective receiver switching scheme is proposed for STBC with the full code rate and non-orthogonal design. In the proposed scheme with the aid of beamforming, the authors divide the received signals into two groups according to the encoded matrix. By this way, the authors can eliminate the interference from the neighbouring signals almost by half. The simulation results with the example of matrix demonstrate that the proposed scheme can provide the improved performance and more under imperfect channel estimation.     

Assembly code generation from a feature-based geometric model

Design and implementation of a system for assembly code generation (from a feature-based geometric model) is discussed. Assembly code is further used in design for assembly evaluation procedures for produce assembly analysis. Assembly features are classified into three groups: geometric assembly features, non-geometric assembly features and operational assembly features. The first two groups of features have existed in computer-aided design databases, while the last one has existed in an assembly sequence. Algorithms for identifying the first two groups of features are presented. A tree processor to convert assembly features into assembly code is also developed. Finally, examples are presented.     

Prediction of freezing and thawing times for foods of two-dimensional irregular shape by using a semi-analytical geometric factor

Semi-analytical solutions for conduction and convection heat transfer problems with phase change were used to derive formulae for a geometric factor that describes the effect of product shape on freezing and thawing times for two-dimensional irregular products. These formulae depend only on the Biot number and three geometric parameters: the characteristic dimension, the volume and the surface area of the product. The accuracy of these formulae is demonstrated by comparisons with numerically calculated data and experimental freezing and thawing data for irregular objects. The new formulae out-perform all geometric factors previously proposed.     

State space approach to two-dimensional generalized thermo-viscoelasticity with two relaxation times

The model of the two-dimensional equations of generalized thermo-viscoelasticity with two relaxation times is established. The state space formulation for two-dimensional problems is introduced. Laplace and Fourier integral transforms are used. The resulting formulation is applied to a problem of a thick plate subject to heating on parts of the upper and lower surfaces of the plate that varies exponentially with time. The Fourier transforms are inverted analytically. A numerical method is employed for the inversion of the Laplace transforms. Numerical results are given and illustrated graphically for the problem considered. Comparisons are made with the results predicted by the coupled theory.     

Topology optimization with geometric uncertainties by perturbation techniques

The aim of this paper was to present a topology optimization methodology for obtaining robust designs insensitive to small uncertainties in the geometry. The variations are modeled using a stochastic field. The model can represent spatially varying geometry imperfections in devices produced by etching techniques. Because of under‐etching or over‐etching parts of the structure may become thinner or thicker than a reference design supplied to the manufacturer. The uncertainties are assumed to be small and their influence on the system response is evaluated using perturbation techniques. Under the above assumptions, the proposed algorithm provides a computationally cheap alternative to previously introduced stochastic optimization methods based on Monte Carlo sampling. The method is demonstrated on the design of a minimum compliance cantilever beam and a compliant mechanism. Copyright © 2012 John Wiley & Sons, Ltd.     

Love waves on a half-space with a gradient piezoelectric layer by the geometric integration method

The propagation of Love waves on an elastic homogeneous half-space with a piezoelectric gradient covering layer is studied by the geometric integration method in this article. First, the state transfer equation of a Love wave is derived from the governing equations and constitutive relations. Then, the transfer matrix of the state vector is obtained by solving the state transfer equation of a Love wave and then the stiffness matrix is obtained. By combining transfer matrices and the stiffness matrices of the gradient covering layer and the homogeneous half-space, the total surface stiffness matrix of a Love wave is obtained. Lastly, the application of the electrically open circuit and short circuit conditions and mechanically traction-free conditions gives the frequency dispersive relation of a Love wave. For the gradient covering layer, the material constants at the bottom of the covering layer may be greater or smaller than that at the top of the covering layer. The two situations and three kinds of gradient profiles for each of these two situations are investigated. The numerical results show that the Love wave speed is sensitive to not only the material constants at the bottom and the top of the covering layer, but also the gradient profiles of the covering layer.     

Optical encryption system with a binary key code

A double-random-phase optical encryption system that uses a binary key code is proposed. The key code is generated as a binary computer-generated hologram. The binary key code can be displayed on a binary spatial light modulator (SLM) such as a ferroelectric liquid-crystal display. The use of a binary SLM enables us to renew the key at high speed. A joint transform correlator based on a photorefractive crystal in the Fourier domain is used to perform shift-invariant encryption and decryption. Computer simulations of the effects of using a binary encoded key code instead of a complex amplitude key code are shown. Preliminary optical experimental results are presented to demonstrate the effectiveness of the proposed system.     

用光纤进行树脂基复合材料的成型过程监测

研究了用光纤对碳纤维环氧树脂复合材料成型监测的方法和系统。通过测量复合材料成型过程中树脂折射率的变化来反映树脂的粘度变化和固化过程。     

Radiant heat transfer of a nongray gas with gray surfaces

In practical calculations of radiant heat transfer the chamber volume is regarded as a single zone with a uniform effective temperature. The walls are gray. Exact and approximate methods of calculation for such a model are given.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 18, No. 1, pp. 5–11, January, 1970.     

Parallel image restoration with a two-dimensional likelihood-based algorithm

We describe a pixelwise parallel algorithm for the restoration of images that have been corrupted by a low-pass optical channel and additive noise. This new algorithm is based on an iterative soft-decision method of error correction (i.e., turbo decoding) and offers performance on binary-valued imagery that is comparable to the Viterbi algorithm. We quantify the restoration performance of this new algorithm on random binary imagery for which it is superior to both the Wiener filter and the projection onto convex sets algorithms over a wide range of channels. For typical optical channels, the new algorithm is within 0.5 dB of the two-dimensional Viterbi restoration method [J. Opt. Soc. Am. A 17, 265 (2000)]. We also demonstrate the extension of our new algorithm to correlated and gray-scale images using vector quantization to mitigate the associated complexity burden. A highly parallel focal-plane implementation is also discussed, and a design study is presented to quantify the capabilities of such a VLSI hardware solution. We find that video-rate restoration on 252 x 252 pixel images is possible using current technology.     

Transmission of radiation by a medium in two-dimensional problems

General formulas for the transmission characteristics of a medium for the simplest two-dimensional systems with an exponential law of absorption are given. These characteristics are the coefficients of irradiation, the coefficients of spatial distribution of the incident flux, and the coefficient of utilization of a point source. The emission characteristic of real surfaces is expressed by a cosine power series.     

The use of profile reduction algorithms with a frontal code

We study profile reduction algorithms when used to order the elements for the frontal solution of a system of linear equations with a symmetric sparsity pattern. We consider two distinct procedures for producing an efficient element ordering; one based on assembling the pattern of the finite-element matrix, reordering the variables and using the new variable order to resequence the elements, and the other based on generating adjacency lists for the elements themselves and reordering the elements directly. We compare the results of using several variants of these algorithms in conjunction with the Harwell frontal code, MA32, on the CRAY-2 for a range of practical problems. We find that, given suitable enhancements, both approaches are practical and neither is consistently superior to the other.     

Design optimization of a two-dimensional hydrofoil by applying a genetic algorithm

In an effort to optimize river-flow training structures, a study is undertaken to explore the utility of genetic algorithms. The study includes the development of a numerical procedure for optimization of a two-dimensional hydrofoil; the optimization of shape is performed using a genetic algorithm. A formula utilizing two Bezier splines for the construction of the foil shape is introduced. The search for the optimal shape is translated to one of determining the coordinates of the vertex points of the two Bezier splines which control the upper and lower surfaces of the foil. A genetic algorithm is employed as an optimization tool. The methodology developed is applied to the determination of hydrofoil shapes under three different objective functions. The shapes produced by the genetic algorithm all yield good performance with high lift and low drag, which are the desirable characteristics for river-flow training structures.     

Characteristics of a dye laser amplifier transversely pumped by copper vapor lasers with a two-dimensional calculation model

A two-dimensional rate equation model, taking into consideration the transverse absorption loss of pump laser power, is proposed to evaluate the characteristics of a dye laser amplifier with a large input laser beam diameter pumped by high average power copper vapor lasers. The calculations are in good agreement with the measurements taken with a Rhodamine 6G dye, and the model can be used for evaluation of the dye concentration at any wavelength.     

Electroporation of mammalian cells in a microfluidic channel with geometric variation

Electroporation has been widely used to load impermeant exogenous molecules into cells. Rapid electrical lysis based on electroporation has also been applied to analyze intracellular materials at single-cell level. There has been increasing demand to implement electroporation in a microfluidic format as a basic tool for applications ranging from screening of drugs and genes to studies of intracellular dynamics. In this report, we have developed a simple technique to electroporate mammalian cells with high throughput on a microfluidic platform. In our design, electroporation only happened in a defined section of a microfluidic channel due to the local field amplification by geometric variation. The time of exposure of the cells to this high field was determined by the velocity of the cells and the length of the section. The change in the cell morphology during electroporation was observed in real time. We determined that electroporation of Chinese hamster ovary cells occurred when the local field strength was increased to approximately 400 V/cm. The internalization of membrane-impermeant molecules (SYTOX green) with cell viability preserved was also carried out to demonstrate transient electropermeabilization. The influence of the operational parameters of the device on cell viability was determined. A large percentage of cells remained viable after electroporation when the parameters were tuned. We also studied rapid cell lysis when the field intensity was in the range of 600-1200 V/cm. The rupture of cell membrane happened within 30 ms when the field strength was 1200 V/cm. Given the simplicity, high throughput, and high compatibility with other devices, this microfluidic electroporation technique may increase the application of microfluidic systems in screening of drugs and biomolecules and chemical cytometry.     

Recovering physical fields with a two-dimensional fiber-optics measurement grid

A tomographic fiber-optics grid can be used to record two-dimensional field patterns. The structure of the grid is described, and a processing algorithm has been tested, which reduces the number of fiber lines required by a factor of 4. An experimental model has been tested successfully in the recovery of the two-dimensional transverse vibration pattern at the surface of a ship's fuel tank. Translated from Izmeritel'naya Tekhnika, No. 3, pp. 24–30, March, 1999.     

Generation of reconfigurable interconnections with a two-dimensional acousto-optic deflector

We detail the technical considerations for producing reconfigurable spot patterns with an integrated two-dimensional acousto-optic deflector. Practical limitations concerning the generation of high-density interconnect arrays are described. Experimental results for 13 × 13, 21 × 21, and 50 × 50 spot arrays are presented.     

CNTs/ UHMWPE composites with a two-dimensional conductive network

A low percolation threshold can be achieved for the conductive polymer composites(CPC) materials having a segregated structure in which the conductive particles like carbon black (CB), carbon nanotubes (CNTs), etc. are only located on the interface of the polymer matrix particles instead of being randomly distributed in the whole system. Multiwalled carbon nanotubes (MWNTs) were experienced alcohol-assisted dispersion under ultrasonication and intense mechanical mixing, and only located on the interfaces of the ultrahigh molecular weight polyethylene (UHMWPE) matrix particles to form a segregated structure. The morphological observation and the critical exponent t value obtained from the classical threshold mechanism indicate that the MWNTs/UHMWPE composites form a 2-dimension conductive network, which leads to a very low percolation of 0.072vol%.     

A lens acoustic microscope with a two-dimensional ultrasound array

A lens acoustic microscope is proposed in which a two-dimensional high-frequency ultrasound array is used instead of a single converter. In this microscope, electronic scanning of the region of naturally occurring focus of the acoustic lens can be performed and the focus can be held electronically at different distances, including inside solid objects. It was demonstrated that the multielement microscope has potentially higher performance compared with a single-element scanning microscope and is not inferior in resolution power.     

Imaging characteristics of a wavefront coding system with off-axis aberrations

Imaging characteristics are analyzed for a wavefront coding system suffering from off-axis aberrations such as primary astigmatism and primary coma. Some analytical expressions for the optical transfer function are obtained by using the stationary-phase method. These expressions give the relationship between the optical transfer function and the off-axis aberrations. Some cases are computed and illustrated graphically. It is shown that the wavefront coding system has a high tolerance to primary astigmatism and a low sensitivity to primary coma.