Friedmann-Robertson-Walker metric in curvature coordinates and its applications

For the first time, we express the general Friedmann-Robertson-Walker (FRW) metric (k = +1, 0,?1) into explicit “Schwarzschild” or “Curvature” form, which is important from the viewpoint of cosmology. With this form of the FRW metric, we reconsider the old problem of embedding a Schwarzschild mass (SM) in a pre-existing FRW background from the viewpoints of both (1) the enigmatic McVittie metric, obtained in 1933 and (2) the Einstein-Straus approach (1945) of scooping out a spherical cavity in the same background. Since the exterior of the SM is, by definition, described in the Schwarzschild coordinates, for a definitive study of the Einstein-Straus approach we employ this form of the FRW metric. We find that a necessary condition for a SM to participate in the cosmic expansion is that the background fluid is dust.     

State-dependent routing on symmetric loss networks with trunkreservations. I

The aggregated-least-busy-alternative (ALBA), a distributed, state-dependent, dynamic routing strategy for circuit-switched loss networks is discussed. The networks considered are symmetric and fully connected. The offered calls form Poisson streams, and routes have at most two links. In ALBA(K), the states of each link are lumped into K (K⩾2) aggregates, and the route of each call is determined by local information on the aggregate states of the links of the alternate routes at the time of the call's arrival. The last aggregate is always the set of states reserved for direct traffic. A fixed-point model for ALBA(K) for general K is presented. The particular case of ALBA in which there is no aggregation is least busy alternative (LBA); ALBA(2) represents the other extreme of aggregation. Simulation and analytic results for LBA are compared. An asymptotic scaling based on the fixed-point models is also discussed. It is shown that there is a dichotomy in network behavior: if the offered traffic is below a threshold, then the network loss probability decreases exponentially with increasing network size, and above the threshold, performance is poor     

Effective bandwidth of general Markovian traffic sources andadmission control of high speed networks

A prime instrument for controlling congestion in a high-speed network is admission control, which limits calls and guarantees a grade of service determined by delay and loss probability in the multiplexer. It is shown that for general Markovian traffic sources it is possible to assign a notional effective bandwidth to each source that is an explicitly identified, simply computed quantity with provably correct properties in the natural asymptotic regime of small loss probabilities. It is the maximal real eigenvalue of a matrix that is directly obtained from the source characteristics and the admission criterion, and for several sources it is simply additive. Both fluid and point process models are considered. Numerical results show that the acceptance set for heterogeneous classes of sources is closely approximated and conservatively bounded by the set obtained from the effective bandwidth approximation. The bandwidth-reducing properties of the leaky bucket regulator are exhibited numerically     

Modeling subjectively perceived annoyance of H.264/AVC video as a function of perceived artifact strength

This paper is concerned with the subjective perception of video coding artifacts in H.264/AVC encoded and decoded video. Our objective is to model the perceived annoyance of such low bit rate video sequences as a function of perceived artifact strength. We introduce a new method for determining this function and apply it to the data from two psychophysical experiments. Both experiments produced numerical judgments of the subjectively perceived annoyance of artifact combinations and the perceived strength of the respective coding artifacts. Our method produces a discrete multi-dimensional representation of the relationships in the data from which the function relating annoyance to artifact strength is derived. The method is applied to the data of the first experiment and the resulting function is shown to describe the data from the second experiment as well.     

Reduced-rank multistage receivers for DS-CDMA in frequency-selective fading channels

Multistage (MS) implementation of the minimum mean-square error (MMSE), minimum output energy (MOE), best linear unbiased estimation (BLUE), and maximum-likelihood (ML) filter banks (FBs) is developed based on the concept of the MS Wiener filtering (MSWF) introduced by Goldstein et al. These FBs are shown to share a common MS structure for interference suppression, modulo a distinctive scaling matrix at each filter's output. Based on this finding, a framework is proposed for joint channel estimation and multiuser detection (MUD) in frequency-selective fading channels. Adaptive reduced-rank equal gain combining (EGC) schemes for this family of FBs (MMSE, MOE, BLUE, and ML) are proposed for noncoherent blind MUD of direct-sequence code-division multiple-access systems, and contrasted with the maximal ratio combining counterparts that are also formed with the proposed common structure under the assumption of known channel-state information. The bit-error rate, steady-state output signal-to-interference plus noise ratio (SINR), and convergence of the output SINRs are investigated via computer simulation. Simulation results indicate that the output SINRs attain full-rank performance with much lower rank for a highly loaded system, and that the adaptive reduced-rank EGC BLUE/ML FBs outperform the EGC MMSE/MOE FBs, due to the unbiased nature of the implicit BLUE channel estimators employed in the EGC BLUE/ML schemes.     

Gesture Recognition: A Survey

Gesture recognition pertains to recognizing meaningful expressions of motion by a human, involving the hands, arms, face, head, and/or body. It is of utmost importance in designing an intelligent and efficient human-computer interface. The applications of gesture recognition are manifold, ranging from sign language through medical rehabilitation to virtual reality. In this paper, we provide a survey on gesture recognition with particular emphasis on hand gestures and facial expressions. Applications involving hidden Markov models, particle filtering and condensation, finite-state machines, optical flow, skin color, and connectionist models are discussed in detail. Existing challenges and future research possibilities are also highlighted     

MOVPE growth of HgCdTe for high performance 3–5 µm photodiodes operating at 100–180K

New results are reported on the growth of high performance medium wavelength infrared (3–5 μm) (MWIR) HgCdTe photodiodes in the three-layer P-n-N configuration. The detector structures were grown in situ by metalorganic vapor phase epitaxy (MOVPE) on (211)B oriented CdZnTe substrates. The mobilities of the single n-type layers with x-values of ∼0.30 are in the range of (3–4.5)×10⁴ cm²/V-s at 80K. The lifetimes on unpassivated films range from 1–5 and 4–10 μs at 80 and 180K, respectively, which are within a factor of two or less of the lifetimes calculated for Auger-1 and radiative recombination. The P-n-N films were processed into variable-area backside-illuminated diagnostic arrays and tested for quantum efficiency, spectral response, R_DA, I–V curves and 1/f noise in the 120–180K range. The internal one-dimensional quantum efficiencies are in the range of 85–100%. The optical collection lengths are typically ∼25 μm. I–V curves showed that diffusion current is the dominant junction current mechanism for temperatures ≥100K. R₀A values are at the one-dimensional limit for n-side diffusion currents over the 100–180K range. 1/f noise was measured to be very low at 120K and is the same as that measured in similarly processed arrays from recent LPE grown P-on-N heterojunctions. The results demonstrate that MOVPE growth can be used for large area, high performance MWIR HgCdTe detector arrays operating in the 120–180K temperature range.     

Characterization of CdS Nanowires Self-Assembled in a Nanoporous Alumina Template

CdS nanowires were self-assembled in a thin film (～200 nm) anodic aluminum oxide template on an indium tin oxide-coated glass substrate via dc electrodeposition. Raman spectral studies were done to probe the vibrational properties of scattering CdS phonons. Strong 1 longitudinal optical (LO), 2 LO, and 3 LO peaks were observed at 302 cm^?1, 603 cm^?1, and 906 cm^?1 having an energy separation of 37 meV, which is in accordance with the CdS bulk values. The photoluminescence spectra showed improved intensity of emission on annealing of the CdS nanowires. Field-emission scanning microscopy confirms the growth of nanowires of diameters ranging from 10 nm to 25 nm for these templates. These diameters agreed with those extracted from the luminescence emission energies.     

Quantized UWB Transmitted Reference Systems

Digital implementation of ultra-wideband receivers requires analog-to-digital conversion (ADC) at an extremely high speed, thereby limiting the available bit resolution. Herein, the effect of low bit resolution quantization on the performance of UWB transmitted reference receivers is investigated. It is verified that the gain of the automatic-gain-control (AGC) has a significant effect on the achievable performance. Because of the considerable performance loss of conventional transmitted reference receivers in the presence of a low resolution ADC a new family of receiver structures optimized and tailored to quantized observations is presented. In particular, the generalized- likelihood ratio test (GLRT) based on the quantized samples is derived and shown to provide modest performance gains relative to the infinite resolution GLRT rule employed on the quantized received signal suggesting that conventional receiver structures can also be employed in the presence of a low resolution ADC. Results reveal that four bits of resolution in combination with an optimal choice for the AGC gain are sufficient to closely approach the performance of an infinite resolution receiver.