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991.
Probability theory is applied to the analysis of fMRI data. The posterior distribution of the parameters is shown to incorporate all the information available from the data, the hypotheses, and the prior information. Under appropriate simplifying conditions, the theory reduces to the standard statistical test, including the general linear model. The theory is particularly suited to handle the spatial variations in the noise present in fMRI, allowing the comparison of activated voxels that have different, and unknown, noise. The theory also explicitly includes prior information, which is shown to be critical in the attainment of reliable activation maps. 相似文献
992.
993.
994.
Qiang Wu Kon Max Wong 《Signal Processing, IEEE Transactions on》1994,42(9):2331-2343
A new approach is proposed for the consistent estimation of the directions of arrival (DOA) of signals in an unknown spatially-correlated noise environment. The signal and noise model used is based on the assumption that the data are received by two arrays well separated so that their noise outputs are uncorrelated. The generalized correlation decomposition of the cross-correlation matrix between the two arrays is then introduced. Of particular interest is the canonical correlation decomposition. The analysis of the generalized correlation leads to various interesting geometric and asymptotic properties of the eigenspace structure. Two algorithms, UN-MUSIC and UN-CLE, are developed to estimate the DOA of signals in unknown spatially correlated noise based on the utilization of these properties. Computer simulations show that these methods are superior in performance compared to conventional methods. Furthermore, it is demonstrated that the new methods are equally effective even when only one sensor array is employed 相似文献
995.
Taylor C.T. Notcutt M. Eng Kiong Wong Mann A.G. Blair D.G. 《IEEE transactions on instrumentation and measurement》1997,46(2):183-185
We present measurements of the frequency-temperature dependence of an all-sapphire Fabry-Perot optical cavity to be used as an optical frequency reference. Measurements were made by tracking the frequency of the cavity relative to a second high-stability cryogenic sapphire-spaced cavity-a technique with impressive resolution for measurements of the coefficient of thermal expansion (CTE). Measurements presented here cover the temperature range of 11 K to 26 K. We find that the CTE of the all-sapphire cavity for these temperatures is given by αcavity=(7.7±0.9)×10$ -13 T/sup (3.23±0.05/) 相似文献
996.
TiB_2基烧结材料再度受到材料研究者的关注,是因为它有一系列优异性能,并将成为新一代的陶瓷和硬质合金。本文报导了近几年国外对TiB_2基烧结材料研究现状和进展。 相似文献
997.
Studies were conducted at Radford Army Ammunition Plant (RAAP) to compare selected wastewater treatment methods, to define the treatment parameters and to prepare the design criteria for facilities to treat wastewater containing dissolved nitroguanidine (NGu), nitroglycerin (NG) and other nitrate esters and colloidal nitrocellulose (NC).The design criteria for two pretreatment facilities were prepared based on the results of the pilot plant evaluation and transmitted to the Army Corps of Engineers who constructed the facilities at RAAP. 相似文献
998.
Wilson Wai-Shing Wong Kaan Erkorkmaz 《The International Journal of Advanced Manufacturing Technology》2010,50(1-4):275-288
This paper presents a genetic algorithm (GA) for identifying virtual models of machine tool drives with minimal intervention to the production machine. The proposed solution builds on the “rapid identification” concept reported earlier in literature, in which a short series of motion data is captured from the Computer Numerical Control (CNC) and used for closed-loop transfer function identification subject to stability constraints. Compared to the Lagrange multipliers solution that was used in the original implementation of rapid identification, the proposed GA is both significantly faster and better suited for industrial use. The novel contributions in the paper include the reduction of the search space from eight unknown variables down to three, which also enables stability constraints to be incorporated in a natural manner, and the re-formulation of the objective function, which streamlines the convergence of the GA by two to three orders of magnitude. Following initial verification in simulations, the GA has been used to identify the closed-loop dynamics of a stand-alone ball screw drive and the x- and y-axes of a five-axis machining center. In experimental results, it is shown that drive models constructed using the GA can be successfully used to predict the tracking and contouring errors for different part programs in a virtual process planning environment. 相似文献
999.
Interferometry proves to be an efficient way to measure thin lubricant film thickness. However, there are very few reports
on the film thickness measurement of conformal lubricated contacts using optical interferometry due to experimental difficulties.
In this article, a custom-built test apparatus is introduced, in which a lubricated conformal contact is made between a stationary
fixed-incline slider and a moving transparent disc. With a flexible holder, the slider can be positioned in such a way that
a specified inclination with respect to the flat disc plane can be obtained. When the disc rotates and the slider is loaded
against it, lubricating films are generated. The minimum film thickness h
m at the exit can be determined by interference intensity changes. Measurement error correction in the film thickness was discussed.
Case experiments were carried out using the new test apparatus. The credibility of the measurement system is validated by
good correlation between the experiments and the theoretical results. The applicability is demonstrated by the film thickness
measurement under different inclinations, loads, velocities, lubricants and slider materials. Amongst those case experiments,
it is highlighted that the influences of solid/liquid interface properties on the lubrication behaviours can be clearly identified
in terms of film thickness. 相似文献
1000.
We investigate the feasibility of switching return-to-zero signals with 3-ps pulsewidth by byte-level parametric wavelength exchange (PWE) numerically and experimentally. Square-wave modulated pumps are used in PWE for pump gating. Simultaneous bit swapping for two signals at the same time slot is achieved. Error-free operation is achieved for both signal channels with ap3.5-dB power penalty at 10-9 bit-error rate. 相似文献