Heterodyne temporal speckle-pattern interferometry

In temporal speckle-pattern interferometry deformation information is extracted by a Fourier transform technique from the speckle pattern that is recorded over a period of time as the object is deformed. A limitation of the experimental arrangements reported to date is that the direction of the deformation cannot be determined. We propose removing this limitation by using the heterodyne principle. Some experimental results that were obtained by use of a rotating half-wave-plate frequency shifter are presented.     

Compact optical temporal processors

Optical signal processing can be done with time-lens devices. A temporal processor based on chirp-z transformers is suggested. This configuration is more compact than a conventional 4-? temporal processor. On the basis of implementation aspects of such a temporal processor, we did a performance analysis. This analysis leads to the conclusion that an ultrafast optical temporal processor can be implemented.     

基于运动时空相关度的时域误码掩盖算法

针对视频通信中时域误码掩盖中运动矢量恢复存在偏差的问题,提出了一种依据相似三角形特点的运动矢量估算方法。同时,利用受损块与前续块、邻域块的运动的时空相关性,提出了一种基于运动时空相关度的时域掩盖算法:对于受损块,采用提出的相似三角形运动矢量估算法和拉格朗日插值法分别估算其运动时域相关和运动空域相关的运动矢量,然后评估受损块的运动时空相关度,据此对估算的运动时域和运动空域相关的运动矢量进行加权平均以得到最终掩盖的运动矢量,从而实现受损块的时域掩盖。仿真结果表明,对不同宏块丢失率或不同视频序列,该算法均可比传统算法恢复出更高质量的图像。     

Integrating cavities: temporal response

The temporal response of an integrating cavity is examined and compared with the results of a Monte Carlo analysis. An important parameter in the temporal response is the average distance d between successive reflections at the cavity wall; d was calculated for several specific cavity designs--spherical shell, cube, right circular cylinder, irregular tetrahedron, and prism; however, only the calculation for the spherical shell and the right circular cylinder will be presented. A completely general formulation of d for arbitrary cavity shapes is then derived, d =4V/S where V is the volume of the cavity, and S is the surface area of the cavity. Finally, we consider an arbitrary cavity shape for which each flat face is tangent to a single inscribed sphere of diameter D (a curved surface is considered to be an infinite number of flat surfaces). We will prove that for such a cavity d =2D/3, exactly the same as d for the inscribed sphere.     

Visual adjustments to temporal blur

After observers have adapted to an edge that is spatially blurred or sharpened, a focused edge appears too sharp or blurred, respectively. These adjustments to blur may play an important role in calibrating spatial sensitivity. We examined whether similar adjustments influence the perception of temporal edges, by measuring the appearance of a step change in the luminance of a uniform field after adapting to blurred or sharpened transitions. Stimuli were square-wave alternations (at 1 to 8 Hz) filtered by changing the slope of the amplitude spectrum. A two-alternative-forced-choice task was used to adjust the slope until it appeared as a step change, or until it matched the perceived transitions in a reference stimulus. Observers could accurately set the waveform to a square wave, but only at the slower alternation rates. However, these settings were strongly biased by prior adaptation to filtered stimuli, or when the stimuli were viewed within temporally filtered surrounds. Control experiments suggest that the latter induction effects result directly from the temporal blur and are not simply a consequence of brightness induction in the fields. These results suggest that adaptation and induction adjust visual coding so that images are focused not only in space but also in time.     

Processing of second-order motion stimuli in primate middle temporal area and medial superior temporal area

Two rhesus monkeys were subjects in a direction-discrimination task involving moving stimuli defined by either first- or second-order motion. Two different second-order motion stimuli were used: drift-balanced motion consisting of a rectangular field of stationary dots and theta motion consisting of the same rectangular field with dots moving in the direction opposite to that of the object. The two types of stimuli involved different segmentation cues between the moving object and the background: temporal structure of the luminance (flicker) in the case of drift-balanced motion and opposed motion in the case of the theta-motion stimulus. Our monkeys were able to correctly report the direction of each stimulus. Single-unit recordings from the middle temporal (MT) and medial superior temporal (MST) areas revealed that 16 out of 38 neurons (41%) from area MT and 34 out of 68 neurons (50%) from area MST responded in a directionally selective manner to the drift-balanced stimulus. The movement of an object defined by theta motion is not explicitly encoded in the neuronal activity in areas MT or MST. Our results do not support the hypothesis that the neuronal activity in these areas codes for the direction of stimulus movement independent of specific stimulus parameters. Furthermore, our results emphasize the relevance of different segmentation cues between figure and background. Therefore the notion that there are multiple sites responsible for the processing of second-order motion is strongly supported.     

A survey of temporal data mining

Data mining is concerned with analysing large volumes of (often unstructured) data to automatically discover interesting regularities or relationships which in turn lead to better understanding of the underlying processes. The field of temporal data mining is concerned with such analysis in the case of ordered data streams with temporal interdependencies. Over the last decade many interesting techniques of temporal data mining were proposed and shown to be useful in many applications. Since temporal data mining brings together techniques from different fields such as statistics, machine learning and databases, the literature is scattered among many different sources. In this article, we present an overview of techniques of temporal data mining. We mainly concentrate on algorithms for pattern discovery in sequential data streams. We also describe some recent results regarding statistical analysis of pattern discovery methods.     

Extended-range temporal electronic speckle pattern interferometry

In recent years the availability of high-speed digital video cameras has motivated the study of electronic speckle pattern interferometry (ESPI) in the time domain. To this end a properly sampled temporal sequence of N-fringe patterns is used to analyze the temporal experiment. Samples of temporal speckle images must fulfill the Nyquist criteria over the time axis. When the transient phenomena under study are too fast, the required sampling frequency over time may not be fulfilled. In that case one needs to extend the measuring range of the algorithm used to extract the modulating phase. We analyze how to use short laser pulses or short video acquisition times with fairly long temporal separation among them to estimate the modulating phase of a dynamic ESPI experiment. The only requirement is that the modulating phase being estimated be properly sampled in the spatial domain.     

Dynamic coding of temporal luminance variation

The range of variation in environmental stimuli is much larger than the visual system can represent. It is therefore sensible for the system to adjust its responses to the momentary input statistics of the environment, such as when our pupils contract to limit the light entering the eye. Previous evidence indicates that the visual system increasingly centers responses on the mean of the visual input and scales responses to its variation during adaptation. To what degree does adaptation to a stimulus varying in luminance over time result in such adjustment of responses? The first two experiments were designed to test whether sensitivity to changes in the amplitude and the mean of a 9.6° central patch varying sinusoidally in luminance at 0.6 Hz would increase or decrease with adaptation. This was also tested for a dynamic peripheral stimulus (random patches rotating on the screen) to test to what extent the effects uncovered in the first two experiments reflect retinotopic mechanisms. Sensitivity to changes in mean and amplitude of the temporal luminance variation increased sharply the longer the adaptation to the variation, both for the large patch and the peripheral patches. Adaptation to luminance variation leads to increased sensitivity to temporal luminance variation for both central and peripheral presentation, the latter result ruling retinotopic mechanisms out as sole explanations for the adaptation effects.     

Divergence temporal dynamics of a Q-switched laser

I address the influence of the direct coupling of the average lattice strains to the active ions on the pulse shape and the far-field beam spreading of a Q-switched laser. Calculations are made for the Cr(3+): sapphire system. The dynamic behavior of laser divergence as the pulse develops is studied without and with an internal aperture. The results can be used to search for similar effects in lasers involving other ions, such as Ti(3+) and Cr(4+).     

Spatial and temporal evolution of argon sparks

Optical emission spectroscopic studies of laser-created argon sparks are carried out. Pulses of 532 nm and 8 ns from a frequency-doubled Nd:YAG laser are used to create an argon spark at 1 atm. Gated photography of 2 ns is used to investigate spark evolution at early times. Electron temperature and density measurements are made from the spectral data. The Stark broadening of emission lines is used to determine the electron density, and the Boltzmann plot of the singly ionized argon-line intensities is exploited for determination of the electron temperature. The dependence on electron temperature and density on different experimental parameters, such as distance from the focal point, delay time after the initiation of the spark, and laser energy, are discussed.     

Adaptive phase-shifting algorithm for temporal phase evaluation

Most standard temporal-phase-shifting (TPS) algorithms evaluate the phase by computing a windowed Fourier transform (WFT) of the intensity signal at the carrier frequency of the system. However, displacement of the specimen during image acquisition may cause the peak of the transform to shift away from the carrier frequency, leading to phase errors and even unwrapping failure. We present a novel TPS method that searches for the peak of the WFT and evaluates the phase at that frequency instead of at the carrier frequency. The performance of this method is compared with that of standard algorithms by using numerical simulations. Experimental results from high-speed speckle interferometry studies of carbon fiber panels are also presented.     

Joint transform correlator for optical temporal signals

Correlation is considered to be a fundamental operation in the field of signal processing. The fact that this operation can be implemented optically in a relatively simple manner is an important advantage of utilizing optical systems for signal processing. The VanderLugt 4-f system and the joint transform correlator (JTC) are the two most popular configurations for performing a spatial correlation operation optically. So far the JTC architecture has been used for performing correlation between two images, which are illuminated by a quasi-monochromatic light source. We propose a generalization of the JTC that performs a correlation between two temporal optical signals.     

The resource renting problem subject to temporal constraints

We introduce a project scheduling problem subject to temporal constraints where the resource availability costs have to be minimized. As an extension of known project scheduling problems which consider only time-independent costs, this problem includes both time-independent procurement costs and time-dependent renting costs for the resources. Consequently, in addition to projects where all resources are bought, we can deal with projects where resources are rented. Based on the enumeration of a finite set of schedules which is proved to contain an optimal schedule, we develop a depth-first branch-and-bound procedure. Computational experience with a randomly generated test set containing 10800 problem instances is reported.

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Received: December 1, 1999 / Accepted: November 8, 2000     

Spatial and temporal visualisation techniques for crash analysis

Understanding the underlying structure of single vehicle crashes (SVCs) is essential for improving safety on the roads. Past research has found that SVCs tend to cluster both spatially and temporally. However, limited research has been conducted to investigate the interaction between the location of SVCs and the time they occur, especially at different levels of scales or spatial extents.This paper applied spatial, temporal and spatio-temporal techniques to investigate patterns of SVCs in Western Australia between 1999 and 2008, at different levels of scale. Spider graphs were adapted to identify temporal patterns of vehicle crashes at two different levels of scales: daily and weekly with respect to their causes. The spatial structures of vehicle crashes were analysed using Kernel Density Estimation analysis at three different scales: West Australia, Metropolitan area, and Perth Local Government Area (LGA). These are illustrated using spatial zooming theory. Comap was then used to demonstrate the spatio-temporal interaction effect on vehicle crashes. The results show significant differences in spatio-temporal patterns of SVCs for various crash causes. The techniques used here have the potential to help decision makers in developing effective road safety strategies.     

Spectral element methods for nonlinear temporal dynamical systems

The time spectral element (TSE) method is a high order accurate method for solving nonlinear and chaotic temporal dynamical systems. It's performance on the Hamiltonian Duffing equation and a bilinear oscillator is examined and compared with standard numerical schemes. These systems were chosen for analysis due to the availability of accurate solutions independent of spurious discretization effects. The implicit form of the TSE, is unconditionally stable in the linear case. For both systems p-convergence is exponential and the h-convergence rate of the end points is of order 2p2p+1, (where is the convergence rate and p the polynomial order).The explicit form of the TSE is conditionally stable for the linear system. The TSE method competes successfully with the other numerical schemes examined where high accuracy is desired and therefore proves an attractive numerical method for simulation of chaotic dynamical systems.     

Spatial and temporal visualisation techniques for crash analysis

Understanding the underlying structure of single vehicle crashes (SVCs) is essential for improving safety on the roads. Past research has found that SVCs tend to cluster both spatially and temporally. However, limited research has been conducted to investigate the interaction between the location of SVCs and the time they occur, especially at different levels of scales or spatial extents.This paper applied spatial, temporal and spatio-temporal techniques to investigate patterns of SVCs in Western Australia between 1999 and 2008, at different levels of scale. Spider graphs were adapted to identify temporal patterns of vehicle crashes at two different levels of scales: daily and weekly with respect to their causes. The spatial structures of vehicle crashes were analysed using Kernel Density Estimation analysis at three different scales: West Australia, Metropolitan area, and Perth Local Government Area (LGA). These are illustrated using spatial zooming theory. Comap was then used to demonstrate the spatio-temporal interaction effect on vehicle crashes. The results show significant differences in spatio-temporal patterns of SVCs for various crash causes. The techniques used here have the potential to help decision makers in developing effective road safety strategies.     

The temporal eigenvalues at a three-dimensional stagnation point

Summary We present an investigation into the temporal stability of the flow at a three-dimensional stagnation point. Both analytical and numerical methods are used in the treatment of the eigenvalue problem, and our work demonstrates that the flow at a two-dimensional stagnation point isless stable to a three-dimensional disturbance than to a two-dimensional one.With 3 Figures