Synthesis and characterization of tungsten disulphide films grown by pulsed-laser deposition

The synthesis and characterization of tungsten disulphide (WS₂) films grown on 440C stainless steel substrates using the 248 nm line from a KrF excimer laser are reported. Film properties could be adjusted by controlling substrate temperature and by laser or thermal anneals. X-ray photoelectron spectroscopy, glancing angle XRD, Raman spectroscopy and high-resolution scanning electron microscopy were used to evaluate film chemistry, crystallinity and morphology. Films grown at room temperature were amorphous, near stoichiometric, and had a multiplicity of chemical states. Local order and bonding were improved most dramatically through post-deposition laser anneals. Crystallite size could be increased by raising the substrate temperature during deposition and, to a lesser degree, by post-deposition thermal anneals. Local disorder was observed within the larger crystallites compared to those that were laser annealed. Crystallinity was induced in amorphous films by mechanical rubbing at room temperature under conditions where frictional heating was negligible. The degree of control over film properties provided by PLD demonstrates its value for growing/designing tribological coatings.     

Instability due to Viscosity Stratification Downstream of a Centerline Injector

A common injector geometry upstream of a static mixer is the centerline injector. A flow instability can arise due to viscosity differences between the injected core‐flow and the outer co‐flow. This instability can adversely affect the effectiveness of the mixing operation. An experimental investigation of miscible viscosity‐stratified flow in a circular geometry was performed using Laser Induced Fluorescence (LIF) and Particle Image Velocimetry (PIV). The experimental results for the stable region agree with the analytical results. The unstable region exhibits different modes depending on the viscosity ratio, volume flux ratio, and Reynolds number. The modes include wavy core‐flow with fissures and wavy core‐flow with core breakup. The time‐averaged experiment velocity profiles for the unstable core indicate a broadening of the jet at the centerline, which is consistent with the LIF visualization.     

Spectrum efficiency analysis for microcellular mobile radio systems

Spectrum efficiency is analysed in a microcellular mobile radio environment considering an appropriate model for UHF ground-wave path loss. The influence of cluster size and reuse distance on the spectrum efficiency is investigated by obtaining the probability of cochannel interference for uncorrelated Rayleigh fading interferers and Rician fading desired signal. The effect of traffic intensity is also considered in evaluating the spectrum efficiency.<>     

Scanned electron beam irradiation of Ti Schottky contacts to n-GaAs

Ti Schottky contacts were formed on n-GaAs surfaces and irradiated using a low energy scanned electron beam at various fluence levels from 10¹⁵ to 10¹⁸ cm^–2. For fluence levels up to 10¹⁷ cm^–2, the Schottky contacts were found to exhibit a reduction in their leakage currents and increased barrier voltages. For fluence levels in excess of 10¹⁷ cm^–2, the Schottky diodes were found to exhibit significantly increased leakage currents and barrier voltages. The changes in leakage currents were consistent with the changes in their respective interface state density (D _it) values. However, the electron beam irradiation had little or no effect on the diode ideality factorn.     

Function dependent fully testable programmable logic array

Two techniques for designing function-dependent easily testable programmable logic arrays are presented. The techniques can detect all the multiple stuck-at, crosspoint and bridging faults, as compared with most of the existing techniques where some of the faults, especially bridging faults, remain undetected.<>     

One-, two-, and three-photon pumped lasing in a novel liquid dye salt system

We report the observation of one-, two-, and three-photon pumped lasing in the same medium, a novel liquid dye salt system when excited by pulsed 0.532-, 1.06-, and /spl sim/1.49-/spl mu/m coherent radiation pulses, respectively. Since the gain medium is a liquid and not a solution, it contains a significantly higher effective dye concentration and, therefore, is highly suitable for multiphoton pumped lasing and optical power limiting applications. The lasing spectra, temporal waveforms, near- and far-field intensity distributions, and output/input efficiency were measured under the conditions of one-, two-, and three-photon pump configurations.     

Outage Theorems for MIMO Block-Fading Channels

The connection between the average codeword or frame error probability (FEP) of space-time codes and the outage probability over general block-fading multiple-input multiple-output (MIMO) channels is established. Three archetypal problems are considered under general fading distributions in a single framework wherein the receiver has channel state information whereas the transmitter knows a) the fading distribution but not the channel realization b) the channel realization but must follow a short term (per codeword) average power constraint, and c) the channel realization but is constrained only by a long-term average power constraint. Three telescoping sets of space-time codes are defined for a given rate and it is shown that average FEPs arbitrarily close to the respective outage probabilities for each of the three cases a)-c) can be achieved by codes in each set for sufficiently large frame lengths. For the smallest set among the three which contains codes with a spectral norm constraint that is stricter than the average or maximum energy constraints commonly assumed, firm sphere-packing lower bounds on the FEP are obtained, and, consequently, strong converse theorems are proved which assert that the respective outage probabilities also represent the best achievable FEP in the large frame-length limit. Moreover, the set of spectral norm constrained codes are also shown to be large enough to contain universal codes that can communicate reliably over any channel realization for which the mutual information exceeds the information rate of the code     

A Class of Algorithms for Collision Resolution with Multiplicity Estimation

The wireless connectivity in pervasive computing has ephemeral character and can be used for creating ad hoc networks, sensor networks, connection with RFID (Radio Frequency Identification) tags etc. The communication tasks in such wireless networks often involve an inquiry over a shared channel, which can be invoked for: discovery of neighboring devices in ad hoc networks, counting the number of RFID tags that have a certain property, estimating the mean value contained in a group of sensors etc. Such an inquiry solicits replies from possibly large number of terminals n. This necessitates the usage of algorithms for resolving batch collisions (conflicts) with unknown conflict multiplicity n. In this paper we present a novel approach to the problem of collision resolution for batch conflicts. We show how the conventional tree algorithms for collision resolution can be used to obtain progressively accurate estimation of the multiplicity. We use the estimation to propose a more efficient binary tree algorithm, termed Estimating Binary Tree (EBT) algorithm. The EBT algorithm is suited for implementation when the conflicting nodes are passive, such as e.g. RFID tags. We extend the approach to design the Interval Estimation Conflict Resolution (IECR) algorithm. For n→∞ we prove that the efficiency achieved by IECR for batch arrivals is identical with the efficiency that Gallager’s FCFS algorithm achieves for Poisson packet arrivals. For finite n, the simulation results show that IECR is, to the best of our knowledge, the most efficient batch resolution algorithm reported to date.     

Modelling and experimental investigation of devolatilizing wood in a fluidized bed combustor

A two-dimensional model is developed for the determination of devolatilization time and char yield of cylindrical wood particles in a bubbling fluidized bed combustor. By using the concept of shape factor, the model is extended to particles of cuboid shape. The model prediction of the devolatilization time agrees with the measured data (present and those reported in the literature) for cylindrical and cuboidal shaped particles within ±20% while the char yield is predicted within ±17%. Influence of some important parameters namely, thermal diffusivity, external heat transfer coefficient and shrinkage, on the devolatilization time and char yield are studied. Thermal diffusivity shows noticeable influence on devolatilization time. The external heat transfer coefficient shows little influence beyond a value of 300 W/(m² K). However particle shrinkage shows negligible effect on the devolatilization time but has a significant influence on the char yield.