Symbol rate and modulation level-controlled adaptivemodulation/TDMA/TDD system for high-bit-rate wireless data transmission

This paper proposes a time-division multiple-access/time-division duplex (TDMA/TDD)-based symbol rate and modulation level-controlled adaptive modulation system for high-bit-rate data transmission. The proposed system controls both the symbol rate and modulation level for the next transmission time slot according to the estimated carrier power to noise spectral density ratio (C/N₀) and delay spread for the time slot to achieve higher bit rate and higher transmission quality as well as higher delay-spread immunity. It is demonstrated by computer simulation and laboratory experiments that the proposed system can achieve a higher average bit rate with higher transmission quality in comparison with the fixed-rate quaternary phase-shift keying (QPSK) system and modulation level-controlled adaptive modulation system in both flat Rayleigh and frequency-selective fading environments. The simulated and experimental results also show that the proposed adaptive modulation techniques can be applied to 1-2-Mb/s indoor and outdoor microcellular systems with its delay spread of up to 250 ns and its terminal mobility of up to pedestrian speed without employing any special antifrequency-selective fading techniques, such as the adaptive equalizer and space diversity     

Photoluminescence of cadmium telluride recrystallized by nanosecond pulsed laser irradiation

The influence of nanosecond pulsed laser irradiation on the morphology and low-temperature photoluminescence of n-type CdTe at energy densities sufficient to melt the material (0.2–0.5 J/cm²) is investigated. After recrystallization the material has an “orange-peel” appearance. The low-temperature photoluminescence spectrum corresponds to low-grade single-crystalline p-type CdTe containing a large number of dislocations and clusters of point defects. The laser treatment has a long-range effect, significantly altering the impurity-defect system in a way characteristic of n→p conductivity conversion at distances greater than 50 μm from the site where laser radiation is absorbed. Fiz. Tekh. Poluprovodn. 32, 32–35 (January 1998)     

On finite-dimensional approximation of solutions of ill-posed problems

We show that the modified method for finite-dimensional approximation of solutions of Fredholm integral equations of the first kind presented in this paper is more economical than traditional methods for finite-dimensional approximation. Institute of Mathematies, Ukrainian Academy of Science, Kiev. Translated from Ukrainskii Matematicheskii Zhurnal, Vol. 49, No. 2, pp. 289–295, February, 1997.     

Vector algorithm for Reed-Muller expansions

A novel vector algorithm for Reed-Muller (RM) expansions is proposed which can save as many as a factor of 2^n-1 memory elements compared with previous matrix algorithms     

The effect of multiple time scales and subexponentiality in MPEGvideo streams on queueing behavior

Guided by the empirical observation that real-time MPEG video streams exhibit both multiple time scale and subexponential characteristics, we construct a video model that captures both of these characteristics and is amenable to queueing analysis. We investigate two fundamental approaches for extracting the model parameters: using sample path and second-order statistics-based methods. The model exhibits the following two canonical queueing behaviors. When strict stability conditions are satisfied, i.e., the conditional mean of each scene is smaller than the capacity of the server, precise modeling of the interscene dynamics (long-term dependency) is not essential for the accurate prediction of small to moderately large queue sizes. In this case, the queue length distribution is determined using quasistationary (perturbation theory) analysis. When weak stability conditions are satisfied, i.e., the conditional mean of at least one scene type is greater than the capacity of the server, the dominant effect for building a large queue size is the subexponential (long-tailed) scene length distribution. In this case, precise modeling of intrascene statistics is of secondary importance for predicting the large queueing behavior. A fluid model, whose arrival process is obtained from the video data by replacing scene statistics with their means, is shown to asymptotically converge to the exact queue distribution. Using the transition scenario of moving from one stability region to the other by a change in the value of the server capacity, we synthesize recent queueing theoretic advances and ad hoc results in video modeling, and unify a broad range of seemingly contradictory experimental observations found in the literature. As a word of caution for the widespread usage of second-order statistics modeling methods, we construct two processes with the same second-order statistics that produce distinctly different queueing behaviors     

Toughening of epoxies via craze-like damage

The fracture behavior of a core-shell rubber (CSR) modified epoxy is investigated using both fracture mechanics and microscopy tools. The CSR-modified epoxy is found to be toughened via numerous line-array cavitations of the CSR particles, followed by plastic flow of the epoxy matrix. The toughening effect via the above craze-like damage process is found to be as effective as that of the well-known widespread rubber cavitation/matrix shear yielding mechanisms. The conditions for triggering the craze-like damage appear to be both stress state and rubber concentration dependent. The type of rubber tougheners utilized also plays a critical role in triggering this rather unusual craze-like damage in epoxy systems. © 1993 John Wiley & Sons, Inc.     

Superconductivity and magnetism in niobium doped YBa2Cu3O7 Related high Tc ceramics

Magnetic characterization has been performed on the members of the cuprateniobate RBa₂Cu₂NbO₈ (R = Pr, Nd, and La) series and R_1.5Ce_0.5Sr₂Cu₂NbO₁₀ (R = Pr, Eu, Nd, and Sm) series. The PrBCNO samples show a signature in the magnetization of a magnetic ordering at 12K. The PrCSCNO sample is nonsuperconducting and shows two distinct orderings at 17K and 53K. No such magnetic phase transition is observed down to 2K in the Nd and La based RBCNO materials or the Nd, Sm, and Eu based RCSCNO materials. Measurements of the lower critical field curve, dc irreversibility line, and critical curent densities are reported for each of the superconducting NdCSCNO, SmCSCNO, and EuCSCNO compounds.     

Effect of annealing in an atomic-hydrogen atmosphere on the properties of amorphous hydrated silicon films and the parameters of p-i-n structures based on them

The decrease in the density of dangling silicon-silicon bonds in a-Si:H films as a result of annealing in an atomic-hydrogen atmosphere is determined by their density in the initial (nonannealed) film. The change in the total hydrogen density in a-Si:H films, annealed in an atomic-hydrogen atmosphere, is determined by the type of silicon-hydrogen bonds and the impurity content: The hydrogen content can decrease to 1 at. % in the presence of monohydride bonds (2020 cm⁻¹) and no change is observed in the hydrogen content in the presence of oxygen (≲0.1 at. %). A decrease in the defect density as a result of annealing in an atomic-hydrogen atmosphere is observed for all films. The Staebler-Wronski effect — AM-1 irradiation for 10 h — is observed for all films irrespective of the total hydrogen density, the type of silicon-hydrogen bonds, and the presence of oxygen. Fiz. Tekh. Poluprovodn. 32, 620–626 (May 1998)     

Evaluation of Qbd for electrons tunneling fromthe Si/SiO2 interface compared to electron tunneling from thepoly-Si/SiO2 interface

Electrical time-to-breakdown (TTB) measurements have shown the charge to breakdown Q_bd of gate oxide capacitors fabricated on n-type well (n-well) substrates always to be higher than that of capacitors on p-type well (p-well) substrates on the same wafer when both are biased into accumulation under normal test conditions. Here the authors correlate the higher n-well Q_bd to smooth capacitor oxide/substrate interfaces and minimized grain boundary cusps at the poly-Si gate/oxide interfaces, confirming that Fowler-Nordheim tunneling is the dominant current conduction mechanisms through the oxide. They correlate higher Q_bd to higher barrier height for a given substrate type and observe that the slope of the barrier height versus temperature plot is lower for both p-well and n-well cases with electrons tunneling from the silicon substrate. This is attributed to surface roughness at the poly-Si gate/SiO₂ interface. A poly-Si gate deposition and annealing process with clean, smooth oxide/substrate interfaces will improve the p-well breakdown characteristics and allow higher Q_bd to be achieved