Signal detection for non-orthogonal space-time block coding over time-selective fading channels

In the case of non-quasi-static (i.e., time-selective fast fading) channels, which do exist in practice, the performance of the existing NO-STBC detectors can suffer from an irreducible error floor. To this end, this letter proposes a zero-forcing-based signal detector, which is not only computationally simple but also highly effective in mitigating the impact of channel variation on system performance.     

Effect of proactive inhibition upon the postdiscrimination generalization gradient.

Gave wavelength-discrimination or discrimination-reversal training to 8 groups of 12 naive domestic pigeons in an operant free-responding paradigm. 4 groups were trained, for 30 min. daily, to criterion. 2 of these groups learned the 2nd (reversal) task in a single continuous session (massed practice), while the 2 others continued with 30-min sessions (distributed practice). 4 control groups experienced only the 2nd discrimination, with either massed or distributed practice. All groups were then tested for generalization either immediately or 24 hr. after reaching criterion on the 2nd task. The reversal had no effect on immediate-test gradients. In the delayed test, however, the massed-practice reversal gradient was flatter and showed less area shift than the others, suggesting a proactive inhibition effect. (21 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of Pressing on Metal Powders

The effects of pressing in the fabrication of modern powder metallurgy parts is examined through literature of historical and practical significance. A theory of pressing and its effects, consistent with experimental results, is presented. A thorough list of references is included.     

Laser phase noise reduction for industrial interferometric applications

Laser ultrasound is a technique used for the ultrasonic inspection of composites during manufacturing of advanced jet fighters. With this technique laser interferometry is used to detect ultrasonic displacements generated by a laser. In theory, the signal-to-noise ratio is proportional to the square root of the collected detection light. In practice, laser phase noise limits the signal-to-noise ratio above a certain collected light level. Two techniques are presented to decrease effects due to laser noise. In one technique the dual-cavity Fabry-Perot currently used is replaced by an interferometer based on a photorefractive crystal. The other technique has a high-finesse Sagnac cavity that filters the phase noise from the detection laser. Experimental results demonstrate that these two techniques significantly reduce limitations due to laser noise.     

Signal detection for orthogonal space-time block coding over time-selective fading channels: The H/sub i/ systems

One major assumption in all orthogonal space-time block coding (O-STBC) schemes is that the channel remains static over the length of the code word. However, time-selective fading channels do exist, and in such case conventional O-STBC detectors can suffer from a large error floor in the high signal-to-noise ratio (SNR) cases. As a sequel to the authors' previous papers on this subject, this paper aims to eliminate the error floor of the H/sub i/-coded O-STBC system (i = 3 and 4) by employing the techniques of: 1) zero forcing (ZF) and 2) parallel interference cancellation (PIC). It is. shown that for an H/sub i/-coded system the PIC is a much better choice than the ZF in terms of both performance and computational complexity. Compared with the, conventional H/sub i/ detector, the PIC detector incurs a moderately higher computational complexity, but this can well be justified by the enormous improvement.     

Performance Evaluation of Interference Bound Backhaul Links in High Capacity Wireless Networks

An innovative architecture employing wireless backhaul in hierarchical wireless networks is considered in this paper to provide high throughput densities. Multi-beam antennas, combined with aggressive frequency reuse have recently been exploited to increase the throughput density in densely deployed wireless networks. However, large number of narrow beams cause not only co-channel interference but also inter-cell interference. To mitigate this problem, amplitude tapering in multi-beam antennas is investigated in this paper. Results show that tapered beams significantly improve the carrier to interference ratio from 5 to 8 dB and consequently achieve downlink throughput density over 0.65 Gbps/km $^2$ . An overall throughput density of 1.2 Gbps/km $^2$ is expected when taking both up- and downlinks into account.     

Fibre reinforcement of elastomers: nanocomposites based on sepiolite and poly(hydroxyethyl acrylate)

The reinforcement of poly(hydroxyethyl acrylate) provided by sepiolite particles has been analysed. Stress–strain measurements at equilibrium, as well as swelling experiments, were carried out on the unfilled and filled polymers. The state of dispersion of the filler was characterized by transmission electron microscopy. Moreover, an evaluation of chain orientation by infrared dichroism reveals a high orientation level in the filled system. The strong interaction between the two phases, combined with a good dispersion and a high shape factor of these clay particles, explain the improvement of the mechanical properties of the composites with respect to the pure polymer. Copyright © 2004 Society of Chemical Industry     

High temperature hydrogenolysis of bibenzyl

Bibenzyl was pyrolysed in the gas phase, in the presence of a large excess of hydrogen at 600–850 °C. Products formed were benzene, toluene, ethylbenzene and styrene; no stilbene or phenanthrene were formed. The yield of toluene decreased with increasing temperature, that of benzene increased, that of ethylbenzene dropped to zero and that of styrene slowly decreased. The decrease in toluene plus ethylbenzene yield was roughly equal to the increase in benzene yield. The apparent pseudo first order ‘activation energy’ for loss of bibenzyl under these conditions is 10.2 ± 0.8 kcal mol^?1. The nature of products formed, their variation with increasing temperature and the low activation energy can be interpreted in terms of a radical chain mechanism in which the chain carrier is the hydrogen atom.     

Seeing biological motion

One of the more stunning examples of the resourcefulness of human vision is the ability to see 'biological motion', which was first shown with an adaptation of earlier cinematic work: illumination of only the joints of a walking person is enough to convey a vivid, compelling impression of human animation, although the percept collapses to a jumble of meaningless lights when the walker stands still. The information is sufficient to discriminate the sex and other details of the walker, and can be interpreted by young infants. Here we measure the ability of the visual system to integrate this type of motion information over space and time, and compare this capacity with that for viewing simple translational motion. Sensitivity to biological motion increases rapidly with the number of illuminated joints, far more rapidly than for simple motion. Furthermore, this information is summed over extended temporal intervals of up to 3 seconds (eight times longer than for simple motion). The steepness of the summation curves indicates that the mechanisms that analyse biological motion do not integrate linearly over space and time with constant efficiency, as may occur for other forms of complex motion, but instead adapt to the nature of the stimulus.