Extremely low frequency based communication link

The paper discusses the literature review and the possibility of using the ground itself as transmission medium for various users’ transceivers and an administrator transceiver using Multi-Carrier-Direct Sequence-Code Division Multiple Access (MC-DS-CDMA), Orthogonal Frequency Division Multiplexing (OFDM),16-Quadrature Amplitude Modulation (16-QAM), Frequency Division Duplex (FDD) and Extremely Low Frequency (ELF) band for the applications of Oil Well Telemetry, remote control of power substations or any system that its responding time is not critical

Microscopic origin of universality in Casimir forces

The microscopic mechanisms for universality of Casimir forces between macroscopic conductors are displayed in a model of classical charged fluids. The model consists of two slabs in empty space at distance $d$ containing classical charged particles in thermal equilibrium (plasma, electrolyte). A direct computation of the average force per unit surface yields, at large distance, the usual form of the Casimir force in the classical limit (up to a factor 2 due to the fact that the model does not incorporate the magnetic part of the force). Universality originates from perfect screening sum rules obeyed by the microscopic charge correlations in conductors. If one of the slabs is replaced by a macroscopic dielectric medium, the result of Lifshitz theory for the force is retrieved. The techniques used are Mayer expansions and integral equations for charged fluids.Comment: 31 pages, 0 figures, submitted to Journal of Statistical Physic

Studies of the shellside performance of shell-and-tube heat exchangers

Accurate prediction of shellside pressure drop in a baffled shell-and-tube heat exchanger is very difficult because of the complicated shellside geometry. Ideally, all the shellside fluid should be alternately deflected across the tube bundle as it traverses from inlet to outlet. In practice, up to 60% of the shellside fluid may bypass the tube bundle or leak through the baffles. This short-circuiting of the main flow reduces the efficiency of the exchanger. Of the various shellside methods, it is shown that only the multi-stream methods, which attempt to obtain the shellside flow distribution, predict the pressure drop with any degree of accuracy, the various predictions ranging from -30% to +70%, generally overpredicting. It is shown that the inaccuracies are mainly due to the manner in which baffle leakage is modelled. The present multi-stream methods do not allow for interactions of the various flowstreams, and yet it is shown that three main effects are identified, a) there is a strong interaction between the main cross flow and the baffle leakage streams, enhancing the crossflow pressure drop, b) there is a further short-circuit not considered previously i.e. leakage in the window, and c) the crossflow does not penetrate as far, on average, as previously supposed. Models are developed for each of these three effects, along with a new windowflow pressure drop model, and it is shown that the effect of baffle leakage in the window is the most significant. These models developed to allow for various interactions, lead to an improved multi-stream method, named the "STREAM-INTERACTION" method. The overall method is shown to be consistently more accurate than previous methods, with virtually all the available shellside data being predicted to within ±30% and over 60% being within ±20%. The method is, thus, strongly recommended for use as a design method

Neutrino fluxes from CNO cycle in the Sun in the non stationary case with mixing

The computational analyses is presented of the non stationary case with mixing of the solar model when the neutrino flux $F_{13}$ from the decay of $^{13}N$ is higher than a standard solar model predictsComment: 6 pages, 3figure

Optical fibre digital pulse-position-modulation assuming a Gaussian received pulse shape

The abundance in bandwidth available in the best monomode fibres may be exchanged for improved receiver sensitivity by employing digital PPM. The paper presents a performance and optimisation analysis for a digital PPM coding scheme operating over a fibre channel employing a PIN-BJT receiver and assuming a Gaussian received pulse shape. The authors present original results for a 50 Mbit/s, 1.3 μm wavelength digital PPM system and conclude that, provided the fibre bandwidth is several times that of the data rate, digital PPM can outperform commercially available PIN-BJT binary PCM system

Performance of Di-code Pulse Position Modulation Technique in Diffuse Indoor Wireless Optical Communication Systems

The bandwidth of the indoor optical wireless Pulse Position Modulation (PPM) system can be exploited to improve the receiver sensitivity by using Di-code Pulse Position Modulation (Di-PPM) technique. This paper analysis the receiver sensitivity of indoor optical wireless Di-PPM systems, over a slightly dispersive channel, uses a bandwidth-limited PIN-bipolar (PINBJT) optical receiver, zero guard interval and pre-detection filter based on a simple third-order Butterworth filter, that authorizes the receiver to operate over channels with bandwidth as low as 1.2 times the bit rate. The received pulse shape is a convolution between the impulse response of a diffuse optical wireless link in a ceiling bounce model and rectangular waveform, the operating bit-rate chosen is 100Mbit/s. In this paper the performance analysis is extended in order to include the effects of intersymbol interference (ISI) on error probability and some important errors: wrong slot, erasure and false alarm. A mathematical model is then presented showing how the transfer function of the indoor optical wireless Di-PPM receiver can be calculated. Results are obtained and the pulse shape at input of receiver decision device is illustrated by using MathCAD software

Utilisation des méthodes d'extractions chimiques sélectives pour la prospection géochimique en milieu latéritique

L'étude par extractions chimiques sélectives d'échantillons latéritiques (Musongati, Burundi) permet de montrer l'association de différents éléments en traces avec certaines phases porteuses préférentielles. Elle met également en correspondance l'évolution de la cristallinité de la goethite avec le contenu en traces métalliques de ce minéral. Le respect de conditions cinétiques bien précises affine l'interprétation de données de prospection géochimique grâce à la prise en compte du type d'altération ayant affecté les horizons échantillonné

WLAN 802.11e evaluation performance using OPNET

The low cost and easy deployment of Wireless LAN 802.11 standard means it becomes more and more popular, but it has a vital drawback with regard to Quality of Service (QoS). QoS defines the ability of network to introduce consistent services for data transmission, and is evaluated in terms of specific parameters such as jitter, delay, and packet loss. These parameters describe data traffic quality over a network. Service differentiation should be offered to let higher priority multimedia traffic to get a preferred treatment. This deficiency of Wireless LAN 802.11 MAC mechanisms in offering QoS support is a major obstacle in the adaptation of modern multimedia applications in Wireless LAN 802.11 networks. This paper aims to build different scenarios to evaluate QoS characteristics and to examine the effect of enhancement on the QoS. The evaluation, implemented using the OPNET simulator, will contain the different parameters of Wireless LAN 802.11e to see how this enhancement in distributed channel access increases the performance over the Wireless LAN 802.11 standard. The results give a clear picture that the enhanced standard offers a very effective service mechanism to provide QoS support

Climate change and cattle farming

Issues raised by cattle farming in relation to climate change extend beyond discussion of greenhouse gas emissions and global warming. There are profound consequences for water availability, soil degradation, biodiversity and local ecology, as well as in terms of conflict for energy supplies. Although climate change impacts on cattle farming (through effects on water availability, heat stress and flooding, for example), this article focuses on how cattle farming impacts on climate change. It explores the issues in terms of the impact of cattle farming on the environment, and how to measure and reduce climate change impacts at farm level. Managing the complex and conflicting balance of factors required for sustainable food production offers an important role for the veterinary surgeon