Efficient dynamic focus control for three-dimensional imaging using two-dimensional arrays

An efficient dynamic focus control scheme for a delay-and-sum-based beamformer is proposed. The scheme simplifies dynamic focus control by exploiting the range-dependent characteristics of the focusing delay. Specifically, the overall delay is divided into a range-independent steering term and a range-dependent focusing term. Because the focusing term is inversely proportional to range, approximation can be made to simplify dynamic focus control significantly at the price of minimal degradation in focusing quality at shallow depths. In addition, the aperture growth controlled by a constant f//sub number/ can also be utilized to devise a nonuniform quantization scheme for the focusing delay values. Efficacy of the proposed scheme is demonstrated using simulated beam plots of a fully sampled, two-dimensional array. Design procedures are also described in detail. One design example shows that, with the proposed dynamic focus control scheme, a 4096-element array only requires 227 independent controllers for the range-dependent focusing term. Moreover, only 28 non-uniform quantization levels are required to achieve the same focusing quality as that of a conventional scheme with 784 uniform quantization levels. The beam plots of a fully sampled array show that sidelobes are slightly increased below the -30 dB level for imaging depths less than 3 cm. At greater depths, there is no observable degradation.     

An adaptive scheme for compressed video steganography using temporal and spatial features of the video signal

Steganography is the art and science of data hiding. This article proposes an adaptive steganographic algorithm that embeds secret data in a compressed video stream using temporal and spatial features of the video signal and human visual system characteristics. Qualified‐DCT coefficients of I‐VOP and motion vectors of P‐VOP and B‐VOP are used for spatial and temporal features of the video, respectively. Embedded‐data are extracted without using the original video and there is no need for full decompression. Experimental results demonstrate that the proposed algorithm has high imperceptibility and capacity. Furthermore, the bit rate remains approximately constant. © 2009 Wiley Periodicals, Inc. Int J Imaging Syst Technol, 19, 306–315, 2009     

Efficient multi-user detection scheme for overloaded group-orthogonal MC-CDMA systems

An efficient multi-user detection scheme for overloaded MC-CDMA systems is presented. The proposed detection scheme for overloaded systems achieves the optimal performance for constant-modulus modulation schemes, for example MPSK, and provides near-optimal performance for non-constant-modulus modulation, for example M-QAM. Moreover, it has overall lower complexity than the other optimal detection algorithms, especially suitable for group-orthogonal MC-CDMA systems, where group-based technique keeps multi-user receiver size relatively small.     

SiC颗粒增强铝基复合材料的纯铜中间层液相扩散焊

采用Cu箔中间层在Ar气氛保护、550℃条件下过渡液相扩散焊(TLP)焊接SiC颗粒(SiCp)增强Al基复合材料SiCp/ZL101和SiCp/Al(SiCp10vol％),对母材与焊接接头的微观组织、剪切强度、焊接接头剪切断面与断裂路径等进行分析.结果表明:在铸Al(ZL101)与纯Al(Al)基体中,分别通过共晶...     

Design of exponential control charts using a sequential sampling scheme

Control charts for monitoring the time between events can be applied in various areas. In this study, we focus on the exponential control chart and consider the phase II problem (when process parameters are known) as well as the phase I problem (when process parameters are unknown). An exponential chart designed with the conventional approach has the disadvantage that the Average Run Length (ARL) value may increase when the process deviates from the nominal state. An ARL-unbiased design approach is therefore proposed for both phase II and phase I exponential charts. A sequential sampling scheme is adopted for the phase I exponential chart. The proposed ARL-unbiased design approach has several advantages over the conventional one, as it provides a self-starting feature and can significantly improve the ARL performance. Specific guidelines are suggested regarding the time to stop updating the estimates of parameters and control limits based on the actual false alarm rate. The phase I exponential chart can be calibrated to a constant in-control ARL value for each successive event accumulated to date. Simulated and real data examples are given to demonstrate the use and efficiency of the proposed design approach.     

Adaptive PID control scheme for full car suspension control

The objective of this paper is to design an adaptive proportional, integral, and derivative (APID) control strategy for a full car active suspension system. A nonlinear full car model is used to capture all the dynamics of a real vehicle suspension system. A vehicle’s stability and ride comfort is affected by road disturbances and can be improved by using an APID-based active suspension system. This paper presents performance assessment of the vehicle suspension system in terms of displacement and acceleration of seat, heave, pitch, and roll. The update parameters of APID are tuned online using the gradient descent method. The convergence of the proposed technique is guaranteed in the closed-loop control system. Simulation results show that the APID control scheme improves the convergence speed and robustness of the APID control strategy significantly for an active suspension system.     

CONDIF: A modified central-difference scheme for convective flows

For most practical purposes, the central-difference scheme (CDS) would be ideal only if it were unconditionally stable. It is a simple and second-order scheme which is easy to implement. It does not introduce any second-order ‘diffusion’ like truncation error. However, for grid Peclet numbers larger than 2, the CDS leads to over- and under-shoots and is unstable. This paper presents a method, called CONDIF, which eliminates this undesirable feature of the CDS. It modifies the CDS by introducing a controlled amount of numerical diffusion based on the local gradients. The numerical diffusion can be adjusted to be negligibly low for most problems. CONDIF has been used to solve a number of test problems which have been widely used for comparative study of numerical schemes in the published literature. For all these problems the CONDIF results are significantly more accurate than those obtained from the hybrid scheme when the Peclet number is very high (→∞) and the flow is at large angles (→45 degrees) to the grid. In general the computational effort for CONDIF is comparable (within 20 per cent) to that for the hybrid scheme. However, in one instance the rate of convergence was found to be significantly slower.     

Fair power control for wireless ad hoc networks using game theory with pricing scheme

Resource allocation in wireless ad hoc networks is usually modelled in a non-cooperative game theoretic framework with the objective of maximising individual utility. However, the selfishness of autonomous users under such framework may lead to throughput unfairness which only benefits certain users. To alleviate this unfairness problem, the authors propose a payment-based power control scheme using game theory where each user announces a set of price coefficients that reflects different compensations paid by other users for the interference they produce. Users who generate higher interference are required to pay more by transmitting at a lower power to give other users a fairer chance of sharing the throughput.Without any incentive to play fairly, users could misbehave by broadcasting high price coefficients to force other users to transmit at a lower power. The authors treat this problem casting it into a price game which resembles a Prisoner's Dilemma game. Users who play this game iteratively will behave cooperatively and broadcast the price coefficients truthfully. Together with analytical proof, the proposed approach is shown to converge to Nash equilibrium where at this point it is able to provide a fairer throughput share among users at the expense of a slight loss in total throughput.     

Nanometer-level path-length control scheme for nulling interferometry

A method of stabilizing a dual-output rotational shearing inteferometer to the nanometer-level accuracy required for deep starlight nulling in planet searches is presented. In this approach one of the nulling beam combiner s two balanced outputs is used to control the other through a combination of external and internal path-length offsets. The path-length offsets sum to zero for the nulling output and to lambda/4 for the control, or the quadrature, output. In the quadrature output a 1-nm path-length error corresponds to a 1% output-power variation, thus allowing subnanometer control.     

A novel multimodal medical image fusion using sparse representation and modified spatial frequency

Fusion of multimodal imaging data supports medical experts with ample information for better disease diagnosis and further clinical investigations. Recently, sparse representation (SR)‐based fusion algorithms has been gaining importance for their high performance. Building a compact, discriminative dictionary with reduced computational effort is a major challenge to these algorithms. Addressing this key issue, we propose an adaptive dictionary learning approach for fusion of multimodal medical images. The proposed approach consists of three steps. First, zero informative patches of source images are discarded by variance computation. Second, the structural information of remaining image patches is evaluated using modified spatial frequency (MSF). Finally, a selection rule is employed to separate the useful informative patches of source images for dictionary learning. At the fusion step, batch‐OMP algorithm is utilized to estimate the sparse coefficients. A novel fusion rule which measures the activity level in both spatial domain and transform domain is adopted to reconstruct the fused image with the sparse vectors and trained dictionary. Experimental results of various medical image pairs and clinical data sets reveal that the proposed fusion algorithm gives better visual quality and competes with existing methodologies both visually and quantitatively.     

Investigation and characterization of a control scheme for multivariate quality control

A new scheme for multivariate statistical quality control is investigated and characterized. The control scheme consists of three steps and it will identify any out-of-control samples, select the subset of variables that are out of control, and diagnose the out-of-control variables. A new control variable selection algorithm, the backward selection algorithm, and a new control variable diagnosis method, the hyperplane methods, are proposed. It is shown by simulation that the control scheme is useful in cases where the process variables are correlated and where they are uncorrelated.     

An efficient access control scheme for files protection

Abstract

A dynamic access control mechanism suitable for hardware implementation is proposed. Each file is safeguarded by q lock values, where q is number of the possible access classes. The access right of a user to some file can be revealed very efficiently. In addition, dynamic operations such as changing a privilege value, insertion or deletion of a user, and insertion or deletion of a file can be done easily. Compared to Wu and Hwangs’ and Chang's methods, the computation of lock values is simple and the verification of an access request is quite efficient. The storage required is proportional to m?n which is less than that of the above‐mentioned methods, where m is the number of users and n is the number of files.     

Microstructural based models for bcc and fcc metals with temperature and strain rate dependency

Microstructural physical based constitutive models are developed in this work in order to characterize the deformation behavior of body centered cubic (bcc) and face centered cubic (fcc) metals under different strain rates and temperatures. The concept of thermal activation energy as well as the dislocations interaction mechanisms is used in the derivation procedure taking into consideration the effect of the mobile dislocation density evolution on the flow stress of the deformed material. The derivation of the Zerilli–Armstrong (Z–A) physical based model for both (bcc) and (fcc) metals is investigated and a number of modifications are incorporated such as the evolution of mobile dislocation density. The authors conclude that in spite of the physical basis used in the derivation of the Z–A model, its parameters can not be interpreted physically since the approximation ln(1 + x) ≈ x is used in the final step of the derivation. This expansion, however, is valid only for values x ≪ 1.0 which is not the case at high strain rates and temperatures. New bcc and fcc relations for the flow stress are therefore suggested and derived using the exact results of the expansion of ln(1 + x). Several experimental data obtained by different authors for tantalum (Ta), niobium (Nb), molybdenum, (Mo), vanadium (V) (bcc metals) and Oxygen Free High Conductivity (OFHC) Copper (Cu) (an fcc metal) are used in evaluating the proposed models. A good agreement between the experimental results and the proposed models are obtained. Moreover, the predicted results show that the assumption of ignoring the generation of dislocation density during the plastic deformation is not appropriate particularly in the case of high strain rates and temperatures. This causes the values of the thermal stresses to be overestimated. Numerical identification for the physical quantities used in the definition of the model parameters is also presented.     

Efficient sampling for spatial uncertainty quantification in multibody system dynamics applications

We present two methods for efficiently sampling the response (trajectory space) of multibody systems operating under spatial uncertainty, when the latter is assumed to be representable with Gaussian processes. In this case, the dynamics (time evolution) of the multibody systems depends on spatially indexed uncertain parameters that span infinite‐dimensional spaces. This places a heavy computational burden on existing methodologies, an issue addressed herein with two new conditional sampling approaches. When a single instance of the uncertainty is needed in the entire domain, we use a fast Fourier transform technique. When the initial conditions are fixed and the path distribution of the dynamical system is relatively narrow, we use an incremental sampling approach that is fast and has a small memory footprint. Both methods produce the same distributions as the widely used Cholesky‐based approaches. We illustrate this convergence at a smaller computational effort and memory cost for a simple non‐linear vehicle model. Copyright © 2009 John Wiley & Sons, Ltd.     

Optimal placement of piezoelectric actuators on plate structures for active vibration control via modified control matrix and singular value decomposition approach using modified heuristic genetic algorithm

The present work deals with the optimal placement of piezoelectric actuators on a thin plate using modified control matrix and singular value decomposition (MCSVD) approach. The MCSVD is considered as the fitness function and optimal positions of the actuators are obtained by maximizing it with MHGA (modified heuristic genetic algorithm). Vibration suppression has been studied for simply supported plate with piezoelectric patches in optimal positions to suppress first specified modes using LQR (linear quadratic regulator) controller. It is observed that the positions of patches obtained with this approach give greater vibration suppression, reduced computational requirements, and provide global optimum solution only.     

Two-dimensional encoding scheme for digital spatial domainmultiplexed large-scale optical fiber sensor arrays

This paper studies a novel two-dimensional (2-D) encoding scheme to increase the multiplexing capacity of the newly developed digital spatial domain multiplexing technique used for integration of large-scale interferometric fiber-sensor arrays. The feasibility of the scheme is assessed via computer simulation and a preliminary experiment which involved strain measurement at multipositions on a cantilever beam     

Precise trajectory tracking of a piezoactuator-driven stage using an adaptive backstepping control scheme

In this paper, an adaptive backstepping control scheme is proposed for precise trajectory tracking of a piezoactuator-driven stage. Differential equations consisting of dynamics of a linear motion system and a hysteresis function are investigated first for describing the dynamics of motion of the piezoactuator-driven stage with hysteresis behavior. Then, to identify the uncertain parameters designed in the differential equations, the Powell method of a numerical optimization technique is used. From the differential equations identified, an equivalent state-space model is developed, then a linear state-space model through a state transformation is established. In the linear state-space model, the hysteresis function is approximated by the first three terms of a Taylor series expansion. Based on the linear state-space model, we developed an adaptive backstepping control for the trajectory tracking. By using the proposed control approach to trajectory tracking of the piezoactuator-driven stage, improvements in the tracking performance, steady-state error, and robustness to disturbance can be obtained. To validate the proposed control scheme, a computer-controlled, single-axis piezoactuator-driven stage with a laser displacement interferometer was set up. Experimental results illustrate the feasibility of the proposed control for practical applications in trajectory tracking.     

A two-phase computational scheme for solving bang-bang control problems

This paper focuses on numerical methods for solving time-optimal control problems using discrete-valued controls. A numerical Two-Phase Scheme, which combines admissible optimal control problem formulation with enhanced branch-and-bound algorithms, is introduced to efficiently solve bang-bang control problems in the field of engineering. In Phase I, the discrete restrictions are relaxed, and the resulting continuous problem is solved by an existing optimal control solver. The information on switching times obtained in Phase I is then used in Phase II wherein the discrete-valued control problem is solved using the proposed algorithm. Two numerical examples, including a third-order system and the F-8 fighter aircraft control problem, are presented to demonstrate the use of this proposed scheme. Comparing to STC and CPET methods proposed in the literature, the proposed scheme provides a novel method to find a different switching structure with a better minimum time for the F-8 fighter jet control problem.     

A modified cutting-plane time integration scheme with adaptive substepping for elasto-viscoplastic models

Integration of stress-strain-time relationship is a key issue for the application of elasto-viscoplastic models to engineering practice. This article presents a novel adaptive substepping cutting-plane time integration scheme for elasto-viscoplastic models keeping the advantage of original cutting-plane (OCP) with only the first derivatives of loading surface required. The deficiency of OCP time integration algorithm is first discussed taking a simple overstress theory based elasto-viscoplastic modified Cam-Clay model (EVP-MCC) as example. To overcome this, a new algorithm is developed with three features: (1) an evolution function for the hardening variable of dynamic loading surface is innovatively deduced for the Taylor series approximation, (2) the elastic predictor is modified to account for the initial viscoplastic strain rate with more accuracy, and (3) a new adaptive substepping technique for restricting simultaneously both strain and time incremental sizes based on the overstress distance is proposed. For easy understanding, the proposed algorithm is first presented for one-dimensional condition, and then extended to three-dimensional condition. The new integrated EVP-MCC model using the proposed algorithm is examined by simulating laboratory tests at both levels of integration point and finite element with a good performance in terms of accuracy and convergence.     

Efficient bit‐plane coding scheme for fine granular scalable video coding

In this paper, we propose a new efficient bit‐plane coding method for fine granular scalable (FGS) video coding. The general structure of the proposed bit‐plane coding method is based on the traditional bit‐plane coding scheme in MPEG‐4 FGS. However, to enhance coding efficiency of bit‐plane encoding, we apply an efficient probability estimation scheme through employing the binary arithmetic coding. For probability estimation, various context models are designed to take advantage of the characteristics of each bit‐plane as well as the correlations of symbols among different bit‐planes. Experimental results show that the proposed FGS coding scheme provides better coding performance, compared to the well‐known FGS coding schemes in MPEG‐4 FGS and JSVM. © 2007 Wiley Periodicals, Inc. Int J Imaging Syst Technol, 16, 113–120, 2006.