Ballistic phonon emission from electron-hole droplets: Application to the nuclear recoil problem

The production of phonons after photoexcitation of Si is greatly influenced by electron-hole droplets. At moderate excitation densities droplets are formed and the process of quasidiffusion is bypassed by emission of ballistic phonons from droplets. We review these ideas and discuss the possibility of droplet formation in the course of plasma cooling which follows the ionization process of a nuclear recoil.     

Development and testing of a prototype of low-power water–ammonia absorption equipment for solar energy applications

This article outlines the development and testing of a prototype of a water–ammonia absorption system designed for solar-powered refrigeration in small rural operations. The objective is to design a 2 kW refrigeration equipment for isolated areas with a high level of solar radiation to meet refrigeration requirements. The equipment has been designed to operate with a concentrating solar power system to obtain the required temperatures. The heat exchangers, which act as condensers, as well as the absorber and evaporator, are all made of galvanized steel piping having fins. The design uses natural convection; the generator and energy-saving heat exchanger have a multi-tubular arrangement and a transfer tank is used in place of a pump for displacing the ammonia solution. All of the operations are manually controlled. Overall, the test results showed unsatisfactory operation of the equipment having low efficiency. Nevertheless, the proposed objectives have been met and it is evident that with several important modifications the equipment will operate satisfactorily. In conclusion, based on the development phase, it is apparent that future prototypes must be more compact and more efficient.     

HVOF-Deposited WCCoCr as Replacement for Hard Cr in Landing Gear Actuators

WCCoCr coatings deposited by HVOF can replace hard Cr on landing gear components. Powders with two different WC particle sizes (micro and nano-) and geometries have been employed to study the effects on the coating’s properties. Moreover, coatings produced employing two sets of parameters resulting in high and low flame temperatures have been evaluated. Minor differences in microstructure and morphology were observed for the two powders employing the same spraying parameters, but the nano-sized powder exhibited a higher spraying efficiency. However, more significant microstructural changes result when the low- and high-energy spray parameters are used. Moreover, results of various tests which include adhesion, wear, salt fog corrosion resistance, liquid immersion, and axial fatigue strength, indicate that the coatings produced with high-energy flame are similar in behavior. On the other hand, the nanostructured low-energy flame coating exhibited a significantly lower salt fog corrosion resistance.     

A phenomenological spice model for magneto‐impedance sensors

In this paper a lumped circuit model of magneto‐impedance (MI) sensors that can be easily implemented in Spice‐like simulators is proposed. The model is based on the equivalent circuit of a Padé's approximation derived from the impedance relied on Bessel functions. Thus, the model can simulate the transient and frequency responses from DC to several megahertz for a fix external magnetic field. Besides, the model can predict the impedance changes of the sensors as a nonlinear function of an external magnetic field via behavioral sources. This allows simulating MI sensors using magnetic feedback for controlling their response to improve linearity and dynamic range. The model has been verified using Spice simulations together with measurement results from a discrete prototype for generating the pulse voltage source, a simple modulation‐type configuration, and a feedback structure. Copyright © 2010 John Wiley & Sons, Ltd.     

Multiple operating points in a square‐root domain first‐order filter

In this paper novel corrective circuits to avoid multiple operating points in a square‐root domain first‐order filter are proposed. By employing a DC test it is demonstrated that the filter possesses three operating points (two stable and one unstable) and the corrective circuits enforce the proper operating mode. The corrective circuits and filter are able to operate with very low supply voltages (as low as V_GS+2V_DSsat). Moreover, a detailed analysis concerning the impact that produces the corrective circuits on the filter performance is discussed. Both measurement and simulation results are provided to validate the circuits and analysis employed. Copyright © 2006 John Wiley & Sons, Ltd.     

Optimization of constrained multiple-objective reliability problems using evolutionary algorithms

This paper illustrates the use of multi-objective optimization to solve three types of reliability optimization problems: to find the optimal number of redundant components, find the reliability of components, and determine both their redundancy and reliability. In general, these problems have been formulated as single objective mixed-integer non-linear programming problems with one or several constraints and solved by using mathematical programming techniques or special heuristics. In this work, these problems are reformulated as multiple-objective problems (MOP) and then solved by using a second-generation Multiple-Objective Evolutionary Algorithm (MOEA) that allows handling constraints. The MOEA used in this paper (NSGA-II) demonstrates the ability to identify a set of optimal solutions (Pareto front), which provides the Decision Maker with a complete picture of the optimal solution space. Finally, the advantages of both MOP and MOEA approaches are illustrated by solving four redundancy problems taken from the literature.     

Wideband modelling of cascaded H-plane waveguide junctions using the generalised impedance matrix representation

A strong interest in H-plane waveguide components composed of a large number of cascaded planar junctions is recently renewed. Therefore, the more efficient development of full-wave analysis tools of such devices is again receiving consideration, specially for its potential use within modern design tools. A novel technique for providing the wideband generalised impedance matrix representation of the inductive devices in the form of pole expansions, thus extracting the most expensive computations from the frequency loop is proposed. For such purpose, the whole device is first decomposed into simpler building blocks, i.e. planar junctions and uniform waveguides, which are modelled in terms of the proposed wideband matrices. Then, a novel iterative algorithm for the efficient combination of such matrices is followed. The complete technique has been successfully applied to the full-wave analysis of several inductive waveguide filters of great practical interest.     

Airport electric vehicle powered by fuel cell

Nowadays, new technologies and breakthroughs in the field of energy efficiency, alternative fuels and added-value electronics are leading to bigger, more sustainable and green thinking applications. Within the Automotive Industry, there is a clear declaration of commitment with the environment and natural resources. The presence of passenger vehicles of hybrid architecture, public transport powered by cleaner fuels, non-aggressive utility vehicles and an encouraging social awareness, are bringing to light a new scenario where conventional and advanced solutions will be in force.     

Robust Indoor Positioning Provided by Real-Time RSSI Values in Unmodified WLAN Networks

The positioning methods based on received signal strength (RSS) measurements, link the RSS values to the position of the mobile station(MS) to be located. Their accuracy depends on the suitability of the propagation models used for the actual propagation conditions. In indoor wireless networks, these propagation conditions are very difficult to predict due to the unwieldy and dynamic nature of the RSS. In this paper, we present a novel method which dynamically estimates the propagation models that best fit the propagation environments, by using only RSS measurements obtained in real time. This method is based on maximizing compatibility of the MS to access points (AP) distance estimates. Once the propagation models are estimated in real time, it is possible to accurately determine the distance between the MS and each AP. By means of these distance estimates, the location of the MS can be obtained by trilateration. The method proposed coupled with simulations and measurements in a real indoor environment, demonstrates its feasibility and suitability, since it outperforms conventional RSS-based indoor location methods without using any radio map information nor a calibration stage.