First Stages of Internal Oxidation in Ag-0.29 and 2.89 at. % Mg Single-Crystal Alloys

Internal oxidation of Ag-0.29 and 2.89 at.% Mg alloys was studied by in-situ X-ray measurements at 300°C. The kinetics and lattice-parameter changes as a function of time are discussed in terms of the formation of elementary MgO* species and non-stoichiometric clusters, during the first stages of oxidation. Studies were made using synchrotron radiation on single-crystal samples. The distorted zone, formed near the surface, was detected by measuring the position and the intensity of the (022) silver peak in the solid-solution alloy. From the diffraction-peak changes, information is deduced on the growth kinetics of the expanded layer. Oxygen diffusivity in silver, C ₀ D ₀, is calculated on the basis of Wagner’s law. At an early stage, the oxygen diffusivity is slightly lower than the theoretical value. During a second stage, accelerated kinetics give a very high C ₀ D ₀ value. We determined the O/Mg ratios at different stages during oxidation.     

In-situ study of stress evolution during solid state reaction of Pd with Si(001) using synchrotron radiation

Using X-ray diffraction experiments and curvature measurements, in-situ real-time measurements of stress are performed during solid state reaction of a palladium thin film with Si(001). From X-ray diffraction measurements and using the sin²ψ method, we found out that the stress in the metal and in the silicide is compressive. This stress decreases all along the solid-state reaction for the silicide. We then compared our results with the qualitative model proposed by Zhang and d’Heurle. This model suggests the development of a high compressive stress (−2.4 GPa) in the silicide.     

E-field assessment errors associated with RF dosemeters for different angles of arrival

In this paper, an analysis of the surface electric field on a human body based on finite-difference time-domain simulations is presented. A statistical analysis of the dosemeter interaction with the human body has been made by means of the variations of the relative orientation of the human body from the RF source. Variations of the RF source frequency have also been made, by comparing three different services FM, GSM-900 and DCS-1800. Three different scenarios have been simulated where the angle of arrival of the main RF contribution impinges on the human body with a certain probability. Despite the differences between the scenarios, the variations in the electric field strength at each frequency are negligible where the dosemeter would be located.     

Strain and temperature distribution in broad-area high-power laser diodes under operation determined by high resolution X-ray diffraction and topography

Broad-area lasers were investigated by high resolution X-ray diffraction (HRXRD) and topography, before and during laser operation. Rocking curves were taken at different positions of the 150 μm wide and 2 mm long laser stripe, using high-precision motorized slits with a spatial resolution of 40×40 μm². From the series of rocking curves recorded at different lateral positions and driving currents, the curvature and temperature profiles along the stripe could be estimated for different driving currents. X-ray topographs revealed regions with higher strain compared to the surrounding area. At lateral positions within the stripe, where the highest temperature was determined by HRXRD, regions of dark contrasts, indicating defects, were detected by cathodoluminescence. Transmission electron microscopy revealed that the highly strained regions act as sinks for point defects, since no dislocations or dislocation loops were detected. Thus, a clear correlation between temperature rise, high local strain and defect formation was found.     

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.     

Ranking of TOA Measurements Based on the Estimate of the NLOS Propagation Contribution in a Wireless Location System

The presence of non-line-of-sight (NLOS) propagation is a key issue that limits the accuracy of wireless location systems. The lack of direct sight causes the measurements obtained by location systems to be so unpredictable that they can produce high inaccuracies in the estimation of the mobile station location. In this paper we propose a novel technique to improve location reliability and accuracy in cases where NLOS propagation is present. For that, in registers of time of arrival (TOA) measurements taken from each base station (BS) in view, we detect the presence of NLOS propagation and estimate the ratio of the measurements coming from NLOS propagation. With this estimate we can assess how much is NLOS propagation affecting the measurements taken from each BS and then we can identify the best measurements and BSs to achieve the highest accuracies in location.