Sintering study of injection molded W-8%Ni-2%Cu compacts from mixed powders by thermoanalytical techniques

Heavy alloy parts from W-8%Ni-2%Cu powder mix were fabricated by MIM using a feedstock with 50 vol.% binder. The binder was removed by solvent de-binding followed by thermal de-binding. Sintering of the heavy alloy brown parts was investigated by employing various thermoanalytical techniques such as DIL, TGA and DTA up to 1460 °C. During sintering, the evolved gases were analyzed in a mass spectrometer which was coupled to the dilatometer. Thermal analysis helps to understand the sintering process regarding phase transformation, melting of alloy matrix and chemical reactions. From these thermoanalytical measurements, a kinetic analysis was made. High sintered density (> 99%) and fine-grained homogeneous microstructures were achieved by rate controlled sintering as confirmed by metallographic analysis.     

Effectiveness of nocturnal ventilative passive cooling strategy in the maritime desert climate of the Arabian Gulf region

This paper presents results of the first set of experiments carried out to investigate the potential of nocturnal ventilative cooling techniques in detached residential buildings in the Arabian Gulf region. This experiment is part of a wider research programme in the field of passive solar cooling strategies at the King Faisal University, sponsored by the “Joint United States-Saudi Arabian Program for Cooperation in the field of Solar Energy” (SOLERAS). The experiments were structured to identify the comfort enhancement potential of direct and induced nocturnal convective cooling techniques through the use of controlled ventilation during predetermined periods of favourable ambient conditions. Horizontally placed, vertically hung openings were designed in accordance with the results of the analysis of weather data and located in the North and South walls of the optimum orientation of the full-scale prototype test house. Conventional concrete block, load bearing construction with external insulation and heavy internal thermal mass were used. Fanger Predicted Mean Vote, as a function of dry bulb temperature, wet bulb temperature air velocity, and mean radiant temperature, were calculated and recorded continuously every 3 min of the duration of the experiment. These values have been averaged to evaluate hourly comfort conditions in various zones of the test house. These were compared with the ambient weather conditions during the period of the experiment to evaluate the potential of this passive cooling technique in conserving a very substantial part of the energy wasted in mechanical cooling.     

Multi-objective optimization of oblique turning operations using finite element model and genetic algorithm

Multi-objective optimization of oblique turning operations while machining AISI H13 tool steel has been carried out using developed finite element (FE) model and multi-objective genetic algorithm (MOGA-II). The turning operation is optimized in terms of cutting force and temperature with constraints on required material removal rate and cutting power. The developed FE model is capable to simulate cutting forces, temperature and stress distributions, and chip morphology. The tool is modeled as a rigid body, whereas the workpiece is considered as elastic–thermoplastic with strain rate sensitivity and thermal softening effect. The effects of cutting speed, feed rate, rake angle, and inclination angle are modeled and compared with experimental findings. FE model is run with different parameters with central composite design used to develop a response surface model (RSM). The developed RSM is used as a solver for the MOGA-II. The optimal processing parameters are validated using FE model and experiments.     

Evaluation of a TEST-yolk sperm capacitation system for use in bovine in vitro fertilization.

Bovine sperm acquire the ability to penetrate zona-free hamster oocytes (capacitation) after incubation in TEST-yolk buffer. Our objective was to determine whether such sperm could penetrate zona-intact bovine oocytes in vitro. Bovine cumulus enclosed oocytes from 2- to 5-mm follicles were incubated in maturation medium for 24 h at 37 degrees C. Ejaculated bovine semen was diluted 1: 10 in TEST-yolk buffer, cooled to 4 degrees C, and stored for 8 h to induce capacitation. Sperm were then washed thrice in pH 7.6, .15 M NaCl containing .1% bovine serum albumin V (37 degrees C) and diluted to 2 x 10(6) sperm/ml in fertilization medium. Droplets of fertilization medium containing capacitated sperm, killed sperm, or no sperm were made under paraffin oil. Oocytes (matured 24 h) were added and cocultured with sperm for 8 h and then transferred to fresh fertilization medium for 40 h. After 24 h, 53% of the oocytes had matured (metaphase II). The fertilization rate of the metaphase II oocytes (203) with TEST-yolk capacitated sperm was 87%, whereas the parthenogenetic controls were 2 and 0%, respectively. Therefore, TEST-yolk buffer can be used to capacitate bull sperm for in vitro fertilization.     

A Multiagent Based Scheme for Unlicensed Spectrum Access in CR Networks

In recent wireless network domains static spectrum access is a major concern. Generally, this access leads to spectrum scarcity problem by creating empty holes or white spaces. However, the scarcity is temporary and can be alleviated if spectrum access is performed dynamically and efficiently. One important step towards dynamic spectrum access is the development of cognitive radio (CR) technology, which senses nearby spectrum portions (or bands) and tries to use them either opportunistically or by negotiating with the neighboring users. Nonetheless, dynamic spectrum access raises several challenges which need to be addressed in detail. These challenges include efficient allocation of spectrum for users in order to maximize spectrum utilization and to avoid user level conflicts both under licensed and unlicensed bands. In this paper, considering the relative rarity of solutions for unlicensed spectrum access and their inadequacy, we propose a scheme, where the CR devices (equipped with agents) interact with their neighbors to form several coalitions over the unlicensed bands. These types of coalitions can provide a less-conflicted access as the agents mutually agree for spectrum sharing and they allow other CR users to enter in their vicinity of acquired spectrum via bilateral message exchanges. Further, we present continuous time Markov chains to model the spectrum access process in continuous time and derive important performance metric as the blocking probability for without and with queuing systems. Amongst others, the important comparisons we made between analytical and simulation results in terms of blocking probability verify that our proposed model is correct. In essence, our proposed solution aims to increase dynamic spectrum usage by enabling cooperation between the users.     

A prospective, controlled study of Helicobacter pylori seroprevalence in coronary artery disease

OBJECTIVE: Recent studies have suggested that chronic infections may be a risk factor for coronary artery disease. The aim of this study was to determine whether Helicobacter pylori (H. pylori) infection was an independent risk factor for coronary artery disease. METHODS: A total of 179 patients undergoing coronary angiography for suspected coronary artery disease were prospectively studied. Angiograms were read by experienced invasive cardiologists blinded to the results of H. pylori serology, which was determined by a validated multiwell ELISA assay. RESULTS: A total of 121 patients (68%) had evidence of coronary artery disease, whereas 58 patients (32%) had normal coronary angiograms. Of the 121 patients with coronary artery disease, 29 had single vessel disease, 39 had double vessel disease, and 53 had triple vessel disease, respectively. There was no significant difference in seroprevalence of H. pylori infection in patients with and without coronary artery disease (p = 0.63). The odds ratio (after adjustment for other known risk factors) for coronary artery disease in H. pylori-infected subjects was 0.45 (95% CI = 0.15, 1.37; p = 0.107). In patients with coronary artery disease, H. pylori infection did not increase the likelihood of severe disease (odds ratio for triple vessel disease = 0.53; 95% CI 0.18, 1.60; p = 0.201). CONCLUSION: H. pylori infection rates are similar in patients with normal and abnormal coronary arteries, and infection with H. pylori is not an independent risk factor for coronary artery disease. In patients who have coronary artery disease, H. pylori infection is not a risk factor for more severe disease. These data argue against a causal role for H. pylori in the pathogenesis of coronary artery disease.     

Simulations Based Design for a Large Displacement Electrostatically Actuated Microrelay

An electrostatically actuated microrelay with large displacement, small actuation voltage and limited plate surface dimensions is designed to meet stringent telecommunication switching requirements. Fabrication feasibility and performance characteristics of the device are evaluated using a commercial CAD for MEMS tool. Simulation results of the device performance including pull-in voltages for different suspension stiffness variations, natural frequencies, stresses and restoring forces are presented.     

Capacity Consideration in Reliability Analysis of Communication Systems

This paper presents a simple method for deriving a symbolic reliability expression of some practical systems such as a communication system having fixed channel capacities of its links, a power distribution system having limited power ratings of its power lines, a transport system which might not allow traffic more than a particular value, or a chemical system in which oil or gas flow through pipes is permissible only up to some safe limits. A system is good if and only if it is possible to transmit successfully the required capacity from source node to the sink node. This paper defines a group as a set of branches such that success of these branches ensures system success, as defined above. All such groups are obtained from a knowledge of the minimal paths of the system graph. The method is computerized and implemented on DEC-20 computer. Two examples are considered and their solutions presented to illustrate the technique.