Improving the quality of shortwave broadcast reception indoors byusing an anti-fading probe antenna

When shortwave (SW) broadcasts are received on self-contained receivers indoors, there generally is a reduction in signal strength and an increase in the speed and depth of fading in comparison with reception in open spaces outdoors. Even when the received signal level is adequate, the quality of reception indoors is degraded. This comes about because the fields indoors are a superposition of components of radiated signal from the distant transmitter plus other components representing energy reradiated or scattered by nearby conductors such as house wiring or plumbing. Since many of the near-field components originate very close to the receiver, it is possible to reduce their effect by deriving the receiver input from two or more probes-i.e., pickup devices specially designed to respond to fields in their immediate vicinity without disturbing those fields. To achieve the desired probe action, advantage can be taken of the high input impedance of portable, battery-powered receivers designed for use with small telescoping whip antennas. Spacing of multiple probes in the order of a few tens of centimeters suffices to give an output significantly smoother and of higher quality than that obtainable with the receiver's whip antenna by itself. The high signal levels of many SW broadcasts make it practical to use small, inefficient antennas. This article describes an Anti-Fading Probe Antenna (APA), which produces a worthwhile improvement in reception quality indoors. It is simple to build, requires no adjustment, and may even improve received signal quality in some outdoor situations     

Column selection and method development for the separation of nucleoside phosphotriester diastereoisomers, new potential anti-viral drugs. Application to cellular extract analysis

Analytical HPLC methods using derivatized cellulose and amylose chiral stationary phases used in normal and reversed-phase modes were developed for the diastereoisomeric separation of mononucleotide prodrugs (pronucleotides) of 3'-azido-2',3'-dideoxythymidine (AZT). The resolutions were performed with two silica-based celluloses using normal and reversed-phase methodologies: Tris-3,5-dimethylphenylcarbamate (Chiralcel OD-H and Chiracel OD-RH) and Tris-methylbenzoate (Chiralcel OJ and OJ-R). Two amyloses phases, Tris-3,5-dimethylphenylcarbamate (Chiralpak AD) and Tris-(S)-1-phenylethylcarbamate (Chiralpak AS), were used in normal-phase mode. Additionally, we developed separation using two stationary phases with immobilized cyclodextrins in reversed-phase and polar-organic modes. The mobile phase and the chiral stationary phase were varied to achieve the best resolution. Different types and concentration of aliphatic alcohols, acetonitrile or water in the mobile phase were also tested for the different separation modes. An optimal baseline separation (Rs > 1.5) was readily obtained with all silica-based celluloses and amyloses using a normal-phase methodology. The different columns gave complementary results in term of resolution. Limits of detection and quantification were 0.12-0.20 and 0.40-0.67 microm, respectively. This analytical method was applied in a preliminary study for the pronucleotide 2 quantification in cellular extract.     

ULF/ELF electromagnetic fields produced in a conducting medium of infinite extent by a linear current source of finite length

A linear current source of finite length embedded in a conducting medium of infinite extent is considered. Assuming a sea-water medium, the components of the electric and magnetic fields are numerically evaluated for two frequencies in the ULF/ELF range (frequencies less than 3 kHz). Comparison is made between the electric field vectors produced at the two different frequencies, and curves are plotted for one of the frequencies showing the variation with distance of the amplitudes of the electric and magnetic field components. A parametric approach is outlined that generalizes the field data presented in the figures and which enables the data to be extended to conducting media other than sea water and to other frequencies in the ULF/ELF range. Some practical applications of the data are discussed.     

A comparison framework for breathing motion estimation methods from 4-D imaging

Motion estimation is an important issue in radiation therapy of moving organs. In particular, motion estimates from 4-D imaging can be used to compute the distribution of an absorbed dose during the therapeutic irradiation. We propose a strategy and criteria incorporating spatiotemporal information to evaluate the accuracy of model-based methods capturing breathing motion from 4-D CT images. This evaluation relies on the identification and tracking of landmarks on the 4-D CT images by medical experts. Three different experts selected more than 500 landmarks within 4-D CT images of lungs for three patients. Landmark tracking was performed at four instants of the expiration phase. Two metrics are proposed to evaluate the tracking performance of motion-estimation models. The first metric cumulates over the four instants the errors on landmark location. The second metric integrates the error over a time interval according to an a priori breathing model for the landmark spatiotemporal trajectory. This latter metric better takes into account the dynamics of the motion. A second aim of this paper is to estimate the impact of considering several phases of the respiratory cycle as compared to using only the extreme phases (end-inspiration and end-expiration). The accuracy of three motion estimation models (two image registration-based methods and a biomechanical method) is compared through the proposed metrics and statistical tools. This paper points out the interest of taking into account more frames for reliably tracking the respiratory motion.     

Analysis and optimization of lateral thin-film Silicon-on-insulator (SOI) MOSFET transistors

This paper is focused on the analysis and optimization of power N-type LDMOS (LDNMOS) transistors (V_BR > 120 V) with the purpose of being integrated in a new generation of Smart-Power technology based upon a 0.18 μm SOI-CMOS technology. The influence of some important design parameters such as the shallow trench isolation (STI) length (L_STI), the N-well doping profile and the relative position of the N-well mask to the STI block are analyzed in terms of voltage capability (V_BR), specific on-state resistance (R_on-sp) and electrical safe-operating area (SOA) by means of Technology Computer-Aided Design (TCAD) numerical simulations. The evolution of the measured and simulated V_BR as a function of the substrate (handle wafer) voltage (HWV) gives good physical insight of the optimal LDNMOS drift region design configuration. LDNMOS transistors with STI lengths partially covering the drift region length leads to better combined action of R_on-sp/V_BR trade-off and electrical SOA results.     

Simulation du drapé des tissus par maillages adaptatifsAdaptive meshing for cloth draping

Numerical simulation methods regarding fabric and cloth draping are generally based on mechanical models. These models are usually applied to uniform grids representing the true geometry of the fabric. Fabrics being a very flexible material, wrinkles appear on its surface when submitted to free or constrained motion. The main problem of the simulation is to represent realistically cloth surface motion. This is strongly dependent on the surface discretization. We present a new cloth animation scheme based on adaptive surface discretization. It can be seen as a multi-grid method which allows us to obtain realistic simulations. We propose also a new mechanical model well suited to our adaptive meshing strategy. A numerical example is given to show the efficiency of the method. To cite this article: J. Villard et al., C. R. Acad. Sci. Paris, Ser. I 335 (2002) 561–566.     

Polarization analysis of the light emitted by an optically pumped3He gas

Optical measurements of the nuclear polarizationM of an optically pumped pure³He gas have been performed. They consist in monitoring the circular polarization of various helium lines emitted by the discharge. We have demonstrated the possibility to use the orange line (587.5 nm) to measureM and we have calibrated this technique over the pressure range 0.4–6.5 Torr. The circular polarization of the light has been analyzed using a new device which includes a static polarimeter and photodiodes as light sensors. The intensity of the discharge was modulated and the detection was made at the frequency of modulation.Laboratoire associé au Centre National de la Recherche Scientifique et a l'Université P. M. Curie     

Achievement of homogeneous AuSn solder by pulsed laser-assisted deposition

The deposition of AuSn solder at the eutectic composition (80 wt.% Au, 20 wt.% Sn) on a wetted, chemically inert metallic barrier has been studied in relation to its use in optoelectronic packaging. The bonding structure, consisting of a W barrier, the top part of which is doped with Ni (or Ti) to provide wetting by molten AuSn, and the homogeneous 80–20 AuSn solder several micrometers thick, has been grown by the Pulsed Laser-assisted Deposition (PLD) technique on 2″ silicon wafers. The composition of the AuSn layer was controlled within better than 1 wt.% as probed by EDX across the wafer diameter. The molten solder exhibited good wetting properties on the W modified layer and the whole structure was found to be chemically stable against thermal cycling at 320°C for over 3 min. The use of molten AuSn targets makes the PLD technique a most competitive one for the achievement of high quality and reliable AuSn solder.