Sunrise and sunset effects as observed on microwave propagation over a line-of-sight path

Microwave signal propagation provides an effective measure of studying the variable nature of the atmosphere. Sunrise and sunset periods are characterized by the dissolution and formation of nighttime temperature inversions. Signal amplitude recordings at 6.7 GHz over DumDum-Andul line-of-sight (LOS) communication link during post-sunrise period are characterized by the appearance of an enhancement in signal strength (as high as 20 dB). The sunset effect or the evening transition is observed as an enhancement in signal amplitude of about 10- 12 dB over the link. The signal characteristics observed during transition periods over the 6.7 GHz DumDum-Andul link are studied herein.     

Two-dimensional time-dependent simulation of contaminant transport from a landfill

A numerical model to simulate solute transport in flowing groundwater is developed using finite-difference solutions to the groundwater flow equation and the solute transport equation.The use of the model is illustrated by its application to a problem of groundwater contamination in a waste-disposal area in Miami, Florida. The model integrates the effects of several factors that controlled changes in iron concentrations, and successfully reproduced the record of contamination observed during a one-year period.The model was found to be insensitive to chemical parameters, but sensitive to an aquifer dispersion coefficient and the groundwater flow velocity. This implies that there can be sites where the chemical attenuation can be approximated without a significant impact on results.     

A double parasitic loop counterpoise antenna and its application to aircraft navigation systems

The radiation properties of a double parasitic loop counterpoise antenna capable of bringing out superior performance from the existing VHF omnirange (VOR) systems are discussed. It is shown that such an antenna when suitably designed will reduce considerably the siting errors inherent in the existing VOR systems.     

Magneto-elastic stresses of an infinite anisotropic medium with cylindrical hole

The paper is concerned with the derivation of a two dimensional theory of magneto-elasticity of anisotropic solids with cylindrical hole. The theory has been developed in complex variable formalism and illustrated by considering a particular type of magnetic field.Lastly, the authors are grateful to the Referee for his useful suggestions for the improvement of the paper.     

Interactions of 10.6 GeV/nucleon gold nuclei in nuclear emulsion

Stacks of nuclear emulsion were exposed at the Brookhaven AGS to a 10.6 GeV/n beam of gold nuclei in the BNL 868 experiment. A preliminary analysis of the main features of the interactions of these nuclei is reported here and compared with those observed previously at lower energies,E<1 GeV/n. The multiplicity and pseudo-rapidity distributions of the singly charged particles emitted both in central and in minimum bias samples of interactions have been analyzed in order to look for any non random effects indicative of the nuclear state during the interactions. The fragmentation characteristics of the gold projectiles appear to be different at 10.6 GeV/n from those at ≦1 GeV/n incident energy. Fission of the gold projectiles, which was relatively frequent at low energy, is almost entirely suppressed. Some of alpha particles from the projectile are emitted with very large transverse momenta. In gold-emulsion interactions the residual target nuclei are significantly smaller than in oxygen and sulfur interactions in emulsion.

     

Preconfiguring IP-over-Optical Networks to Handle Router Failures and Unpredictable Traffic

We consider the realization of traffic-oblivious routing in IP-over-optical networks where routers are interconnected over a switched optical backbone. The traffic-oblivious routing we consider is a scheme where incoming traffic is first distributed in a preset manner to a set of intermediate nodes. The traffic is then routed from the intermediate nodes to the final destination. This splitting of the routing into two phases simplifies network configuration significantly. In implementing this scheme, the first and second phase paths are realized at the optical layer with router packet grooming at a single intermediate node only. Given this unreliability of routers, we consider how two-phase routing in IP-over-optical networks can be made resilient against router node failures. We propose two different schemes for provisioning the optical layer to handle router node failures-one that is failure node independent and static, and the other that is failure node dependent and dynamic We develop linear programming formulations for both schemes and a fast combinatorial algorithm for the second scheme so as to maximize network throughput. In each case, we determine (i) the optimal distribution of traffic to various intermediate routers for both normal (no-failure) and failure conditions, and (ii) provisioning of optical layer circuits to provide the needed inter-router links. We evaluate the performance of the two router failure protection schemes and compare it with that of unprotected routing     

Medium Access Control Protocol Design for Vehicle–Vehicle Safety Messages

We propose a medium access control protocol design for a vehicle to send safety messages to other vehicles. We develop a Quality-of-Service (QoS) model for safety messages that are consistent with the active vehicle safety systems literature. Each message has a range and useful lifetime. The QoS target has each message received with high probability within its specified lifetime by each vehicle within its specified range. The protocol design is based on rapidly rebroadcasting each message multiple times within its lifetime in combination with the 802.11 Distributed Coordination Function. This makes the design compatible with emerging standards for Dedicated Short-Range Communication. Six different design variations are proposed. We derive equations and develop a simulation tool to assess the performance of the designs. Using these, we identify the best and most easily implemented designs. Design performance depends on the number of rebroadcasts, power, modulation, coding, and vehicular traffic volumes. We show that under certain assumptions on the loss probability tolerated by safety applications, the design is able to transport safety messages in vehicular ad hoc networks     

Time-Space Harmonic Polynomials for Continuous-Time Processes and an Extension

A time-space harmonic polynomial for a stochastic process M=(M _t) is a polynomial P in two variables such that P(t, M _t) is a martingale. In this paper, we investigate conditions for the existence of such polynomials of each degree in the second, space, argument. We also describe various properties a sequence of time-space harmonic polynomials may possess and the interaction of these properties with distributional properties of the underlying process. Thus, continuous-time conterparts to the results of Goswami and Sengupta,⁽²⁾ where the analoguous problem in discrete time was considered, are derived. A few additional properties are also considered. The resulting properties of the process include independent increments, stationary independent increments and semi-stability. Finally, a generalization to a measure proposed by Hochberg⁽³⁾ on path space is obtained.     

Effect of a buffer layer, composition and annealing on the performance of a bulk heterojunction polythiophene/fullerene composite photovoltaic device

Post-annealing of P3HT/C₆₀-based plastic solar cells, composite ratio and, incorporation of a buffer layers at the ITO–polymer/fullerene composite interface and the polymer/fullerene composite–Al interface have shown significant improvement in the performance of the photovoltaic device, both in terms of open-circuit voltage and short-circuit current. The annealing temperature, time duration and P3HT/C₆₀ composite ratios have been optimized for the best performance of typical ITO/PEDOT:PSS/P3HT:C₆₀/LiF/Al solar cell. The C₆₀ content is very crucial because it improves the photocurrent in the beginning but after a certain value it leads to decrease in absorption, thereby decreasing the photocurrent.