Evaluation of Dynamic Channel and Power Assignment for Cognitive Networks

In this paper, we develop a unifying optimization formulation to describe the Dynamic Channel and Power Assignment (DCPA) problem and an evaluation method for comparing DCPA algorithms. DCPA refers to the allocation of transmit power and frequency channels to links in a cognitive network so as to maximize the total number of feasible links while minimizing the aggregate transmit power. We apply our evaluation method to five representative DPCA algorithms proposed in the literature. This comparison illustrates the tradeoffs between control modes (centralized versus distributed) and channel/power assignment techniques. We estimate the complexity of each algorithm. Through simulations, we evaluate the effectiveness of the algorithms in achieving feasible link allocations in the network, and their power efficiency. Our results indicate that, when few channels are available, the effectiveness of all algorithms is comparable and thus the one with smallest complexity should be selected. The Least Interfering Channel and Iterative Power Assignment algorithm does not require cross-link gain information, has the overall lowest run time, and achieves the highest feasibility ratio of all the distributed algorithms; however, this comes at a cost of higher average power per link.     

Adaptive Power Control Scheme for Mobile Wireless Sensor Networks

Wireless Personal Communications - One of the major factors that affects the performance of wireless sensor networks (WSN) is its limited battery capacity. Mobile wireless sensor networks (MWSN)...     

Effect of Au additions on the structure and properties of (Fe0.5Co0.5)71Nb4Si5B20 bulk metallic glass

The effect of addition of gold (Au) on the structure and mechanical properties of (Fe_0.5Co_0.5)₇₁Nb₄Si₅B₂₀ BMG alloy was studied. Addition of Au formed crystals in the BMG alloy. Gradual increase in the amount of Au added to the BMG alloy resulted in an increase in the amount of crystallinity and hardness of the alloy. Hardness values in excess of 1100 H_V were found in all the alloys with a maximum value of 1245 H_V. The thermal transition temperatures were also found to increase with an increasing amount of Au. Corner cracks were produced in the alloy with 1.5?at.-% Au content showing a low indentation fracture toughness value of 2.98?MPa-m^0.5.     

Thermodynamic and heat-hydrogen transfer analyses of novel multistage hydrogen-alloy sorption heat pump

The requirement of simultaneous heating and cooling effects at different zones of a building demands for the development of an energy-efficient air-conditioning system for heating and cooling outputs. In order to fulfil this requirement, a novel multistage hydrogen-alloy–based sorption heat pump (H-A SHP) for space air-conditioning is proposed in the present work. The proposed system produces multiple cooling and heating outputs at 20°C and 45°C, respectively, with single heat input at 160°C. A set of MmNi₅, La_0.8Ce_0.2Ni₅, MmNi_4.4Al_0.6, and LaNi_4.6Al_0.4 metal hydrides (MHs) is chosen to operate at the above-mentioned temperature range with hydrogen as working fluid. The proposed system can completely eliminate the requirement of conventional compressor because it operates using waste heat, and useful outputs (cooling-heating) result from reaction enthalpies (MH + H₂ interaction). The thermodynamic and heat-hydrogen transfer analyses of H-A SHP are carried out through finite volume approach, in which heat and mass transfer equations are solved to foresee the variations in MH bed temperature, hydrogen concentration, and heat interactions during cycle operation as well as the amount of cooling and heating outputs delivered to the air-conditioning space. The numerical code is validated with experimental pressure-concentration isotherms (PCIs) measured through Sievert's apparatus. The maximum heat exchange during the cooling and heating processes, at a particular instant of time, is observed as 257.5 and 286.1 W with cooling temperature of 10°C and heating temperature of 53°C, respectively. The thermodynamic performance is estimated as 178.5 kJ of cooling effect, 265.5 kJ of upgraded heat with overall coefficient of performance (COP) of 6.8, and overall specific alloy output of 396.5 W/0.34 kg of alloy.     

Retention in unseren Flüssen

Whenever there is flooding, the retention of floodwater in different river reaches is always at the heart of public discussions. The following article describes the retention processes and provides answers to common questions on topics such as the effects of river flow regulation, of decentralized measures, and of river restorations. The article goes on to describe the characteristics of optimal retention. In many cases the effects of decreased retention space or those of retention-improving measures are overestimated, as retention is a non-linear process and often produces the best results in connection with flow rates below those of a flood. Accordingly a differentiated, river- and event-specific approach is called for.     

Synthesis and characterization of uniform fine particles of copper oxalate

Copper oxalate particles were synthesized in various shapes and sizes by mixing appropriate volumes of known concentration of oxalic acid and copper nitrate at 25 and 85 °C. Temperature and reactants concentration had significant effect on the morphology of the precipitated particles and therefore extensive optimizations of the experimental parameters were carried out in order to obtain maximum uniformity in particles' morphological features. Selected batch of the copper oxalate particles was characterized by various physical methods.     

Cytotoxicity of Metal Ions Released from Nitinol Alloys on Endothelial Cells

Most implantable medical devices are expected to function in the body over an extended period of time. Therefore, immersion tests under simulated conditions can be useful for assessing the amount of metal ions released in situ. In this investigation, dissolved ions from as-received binary and ternary Nitinol alloys in cell culture media were periodically measured under static and dynamic conditions. Endothelial cells were grown in aliquots of culture media obtained and the effect of dissolved ions on cell proliferation and viability of endothelial cells (HUVEC) was studied by cytotoxicity assays. The concentration of metal ions in the media was measured by inductively coupled plasma mass spectrometry.     

Assessment of Corrosion Resistance and Metal Ion Leaching of Nitinol Alloys

Nitinol usage for biomedical implant devices has received significant attention due to its high corrosion resistance and biocompatibility. However, surface treatments are known to affect surface charge, surface chemistry, morphology, wettability, and corrosion resistance. In this investigation, the corrosion resistance of a binary and various ternary Nitinol alloys was determined after being subjected to electropolishing, magnetoelectropolishing, and water boiling and passivation. Cyclic polarization in vitro corrosion tests were conducted in Phosphate Buffer Saline (PBS) in compliance with ASTM F 2129-08 before and after surface treatments. The concentrations of dissolved metal ions in the electrolyte were also determined by ICPMS.