We investigate the dynamics of the wave packet formed by two codirected strongly interacting waves propagating in a medium with cubic nonlinearity. We obtain a soliton solution of the nonlinear Schrödinger equation in the degenerate case where the wave packet is described by a single partial momentum. In the nondegenerate case, we use the variational method to find the equation for the pulse duration, which turns out to be analogous to the equation for the coordinate in the Kepler problem. Solving it, we find the dependences of the pulse duration on the propagation distance in the cases of finite and infinite propagation regimes. 相似文献
Most of the literature on coded excitation describes the signal-to-noise ratio gain of a coded waveform in terms of the time-bandwidth product. We have shown that in the context of ultrasound imaging, the expression for the SNR gain provided by matched filtering a coded waveform, can be reduced to the total number of chips in the transmit signal. Hence, the SNR gain is independent of both the bandwidth and the duration of a single-chip. This concept is described in detail, clarifying this seeming contradiction. The impact of bandwidth and pulse duration on the SNR, SNR gain and axial resolution is described. Bandwidth requirements and the impact of regulatory peak-power limitations are also addressed. 相似文献
This work seeks to determine how the mesostructure of seven types of cement composites containing alumina particles or not
controls their deviatoric strength, compaction law, and damage under high-pressure of confinement. First, the method of analysis
of quasi-oedometric compression tests is presented. Accuracy of the method for concrete is discussed by means of numerical
simulations. The confined compression tests performed show the effects of adding ceramic aggregates. Furthermore, an application
of post-mortem analysis by infiltration technique of each specimen is presented, revealing a highly micro-cracked pattern
depending of the mesostructure of these materials. From these observations, a discussion is presented on the influence that
the addition of ceramic aggregates exerts on the confined behaviour of these composites. The tests showed a highly beneficial
effect of the presence of particles, on both the deviatoric strength and the compaction law of the concretes considered. 相似文献
We report on ideas, problems and results, which occupied us during the past decade and which seem to extend the frontiers of information theory in several directions. The main contributions concern information transfer by channels. There are also new questions and some answers in new models of source coding. While many of our investigations are in an explorative state, there are also hard cores of mathematical theories. In particular we present a unified theory of information transfer, which naturally incorporates Shannon's theory of information transmission and the theory of identification in the presence of noise as extremal cases. It provides several novel coding theorems. On the source coding side we introduce data compression for identification. Finally we are led beyond information theory to new concepts of solutions for probabilistic algorithms.
The original paper [R. Ahlswede, General theory of information transfer, Preprint 97-118, SFB 343 Diskrete Strukturen in der Mathematik, Universität Bielefeld, 1997] gave to and received from the ZIF-project essential stimulations which resulted in contributions added as GTIT-Supplements “Search and channels with feedback” and “Noiseless coding for multiple purposes: a combinatorial model”.
Other contributions—also to areas initiated—are published in the recent book [R. Ahlswede et al. (Eds.), General Theory of Information Transfer and Combinatorics, Lecture Notes in Computer Science, vol. 4123, Springer, Berlin, 2006].
The readers are advised to study always the pioneering papers in a field—in this case the papers [R. Ahlswede, G. Dueck, Identification via channels, IEEE Trans. Inform. Theory 35 (1989) 15–29; R. Ahlswede, G. Dueck, Identification in the presence of feedback—a discovery of new capacity formulas, IEEE Trans. Inform. Theory 35 (1989) 30–39] on identification. It is not only the most rewarding way to come to new ideas, but it also helps to more quickly grasp the more advanced formalisms without going through too many technicalities. Perhaps also the recent Shannon Lecture [R. Ahlswede, Towards a General Theory of Information Transfer, Shannon Lecture at ISIT in Seattle 13th July 2006, IEEE Information Theory Society Newsletter, 2007], aiming at an even wider scope, gives further impetus. 相似文献
Wider dissemination of medical digital video libraries is affected by two correlated factors, resource effective content compression
that directly influences its diagnostic credibility. It has been proved that it is possible to meet these contradictory requirements
halfway for long-lasting and low motion surgery recordings at compression ratios close to 100 (bronchoscopic procedures were
a case study investigated). As the main supporting assumption, it has been accepted that the content can be compressed as
far as clinicians are not able to sense a loss of video diagnostic fidelity (a visually lossless compression).
Different market codecs were inspected by means of the combined subjective and objective tests toward their usability in medical
video libraries. Subjective tests involved a panel of clinicians who had to classify compressed bronchoscopic video content
according to its quality under the bubble sort algorithm. For objective tests, two metrics (hybrid vector measure and hosaka
Plots) were calculated frame by frame and averaged over a whole sequence. 相似文献