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The transient observation-based particle (TOP) model and its potential application in radiation effects evaluation  [cached]
Benck Sylvie,Cyamukungu Mathias,Cabrera Juan,Mazzino Laura
Journal of Space Weather and Space Climate , 2013, DOI: 10.1051/swsc/2013024
Abstract: The evaluation of the radiation hazards on components used in space environment is based on the knowledge of the radiation level encountered on orbit. The models that are widely used to assess the near-Earth environment for a given mission are empirical trapped radiation models derived from a compilation of spacecraft measurements. However, these models are static and hence are not suited for describing the short timescale variations of geomagnetic conditions. The transient observation-based particle (TOP)-model tends to break with this classical approach by introducing dynamic features based on the observation and characterization of transient particle flux events in addition to classical mapping of steady-state flux levels. In order to get a preliminary version of an operational model (actually only available for electrons at low Earth orbit, LEO), (i) the steady-state flux level, (ii) the flux enhancements probability distribution functions, and (iii) the flux decay-time constants (at given energy and positions in space) were determined, and an original dynamic model skeleton with these input parameters has been developed. The methodology is fully described and first flux predictions from the model are presented. In order to evaluate the net effects of radiation on a component, it is important to have an efficient tool that calculates the transfer of the outer radiation environment through the spacecraft material, toward the location of the component under investigation. Using the TOP-model space radiation fluxes and the transmitted radiation environment characteristics derived through GEANT4 calculations, a case study for electron flux/dose variations in a small silicon volume is performed. Potential cases are assessed where the dynamic of the spacecraft radiation environment may have an impact on the observed radiation effects.
A Transient UWB Antenna Array Used with Complex Impedance Surfaces  [PDF]
A. Godard,L. Desrumaux,V. Bertrand,J. Andrieu,M. Lalande,B. Jecko,V. Couderc,M. Brishoual,R. Guillerey
International Journal of Antennas and Propagation , 2010, DOI: 10.1155/2010/243145
Abstract: The conception of a novel Ultra-Wideband (UWB) antenna array, designed especially for transient radar applications through the frequency band (300?MHz–3?GHz), is proposed in this paper. For these applications, the elementary antenna must be compact and nondispersive, and the array must be able to steer in two dimensions. The geometry of the elementary antenna and its radiation characteristics are presented. The array beam steering is analyzed and a technique making the increase of the transient front-to-back ratio possible is described. 1. Introduction In the recent years, investigations directed to the realization of Ultra-Wideband (UWB) systems that radiate transient waveforms and exhibit operating bandwidths of over one decade are made intensively in many countries. Such systems radiate impulses with rise times around 100?ps and duration of few nanoseconds. Such radiated waveforms make them interesting for many applications such as transient radar cross section (RCS) measurements [1] or UWB synthetic aperture radar (SAR) systems [2]. The main interest of such systems is that the radar resolution is proportional with the radiated bandwidth. Contrary to narrowband systems, a second advantage is the capacity of identifying stealth targets. This paper describes a novel antenna array appearing in the N generators/N antennas configuration, because it presents the advantage of increasing the radiation power on one hand and offering the agility to the array on the other hand. Moreover, this architecture permits a working continuity even if an elementary source is defective. With the frequency spectrum [300?MHz–3?GHz], this kind of system permits to detect hidden objects (wall, foliage, or ground penetration, etc.). A major difficulty of limiting the synchronization of the radiation source jitters yet exists. A solution which consists in using impulse optoelectronic devices permits to bypass this difficulty, with the generation of ultra short electrical waveforms with a small jitter (2?ps typically) [3]. Section 2 presents the elementary antenna and its radiation characteristics. Then, the array beam steering is analyzed in Section 3, and a technique involving a diminution of the back radiations and the amount of radiations in the transverse plane is presented in Section 4. Indeed, the increase of the transient front-to-back ratio is essential to limit fratricidal effects. 2. The Elementary Antenna The elementary antenna is inspired by a travelling wave antenna, the Valentine antenna [4], because it has good linearity properties. Moreover, the antenna
Gluon Radiation and Top Quark Physics  [PDF]
L. H. Orr,T. Stelzer,W. J. Stirling
Physics , 1996,
Abstract: Radiation of gluons gives rise to extra jets in top quark events that can lead to complications in event reconstruction and mass measurement. I review recent results for gluon radiation in top quark production and decay, and discuss their implications for top quark physics.
Gluon Radiation and Top Width Effects  [PDF]
L. H. Orr,Yu. L. Dokshitzer,V. A. Khoze,W. J. Stirling
Physics , 1993,
Abstract: The large width of the top quark influences the way gluons are radiated in top events, giving rise to interesting interference effects in top production and decay. We discuss top width effects in soft guon radiation in $\ee \to \tt$ at high energies and near $\tt$ threshold.
Radiation Pattern of Patch Antenna with Slits  [PDF]
V. Karthikeyan,V. J. Vijayalakshmi
Computer Science , 2014, DOI: 10.5121/ijit.2014.3101
Abstract: The Microstrip antenna has been commercially used in many applications, such as direct broadcast satellite service, mobile satellite communications, global positioning system, medical hyperthermia usage, etc. The patch antenna of the size reduction at a given operating frequency is obtained. Mobile personal communication systems and wireless computer networks are most commonly used nowadays and they are in need of antennas in different frequency bands. In regulate to without difficulty incorporate these antennas into individual systems, a micro strip scrap transmitter have been preferred and intended for a convinced divergence. There is also an analysis of radiation pattern, Gain of the antenna, Directivity of the antenna, Electric Far Field. The simulations results are obtained by using electromagnetic simulation software called feko software are presented and discussed
Gluon Radiation in Top Production and Decay  [PDF]
Cosmin Macesanu,Lynne H. Orr
Physics , 2000,
Abstract: We present the results of an exact calculation of gluon radiation in top production and decay at high energy electron-positron colliders. We include all spin correlations and interferences, the bottom quark mass, and finite top width effects in the matrix element calculation. We study properties of the radiated gluons and implications for top mass measurement.
On the Radiation Pattern of the L-Shaped Wire Antenna
Aurora Andújar;Jaume Anguera;Carles Puente;Antonio Pérez
PIER M , 2009, DOI: 10.2528/PIERM09012204
Abstract: An objective of the present study is to make a physical insight into the radiation properties of an L-shaped wire antenna. More specifically, the study is focused on the effects of the antenna geometry over the characteristic radiation pattern of an L-shaped wire antenna. Regarding the basic equations for the radiated field, three main regions according to the length-height ratio of an L-shaped wire antenna have been determined. The said regions depict the geometrical boundaries where the L-shaped wire antenna loses its characteristic monopoletype radiation pattern. In this sense and relating to the aspect ratio of the L-shaped antenna, the said radiation properties can be easily varied in order to achieve a half isotropic radiation pattern or even, a patch-type radiation pattern. Thus, the method described herein demonstrates that simple modifications applied to the geometry of a basic structure, allow obtaining radiation properties associated to more complex structures.
Human Body Impact on UWB Antenna Radiation
Alexander V. Vorobyov;Alexander Georgievic Yarovoy
PIER M , 2012, DOI: 10.2528/PIERM11112306
Abstract: We experimentally quantify the radiation of a small Ultra-Wideband (UWB) antenna placed on a human body. The measurements are performed for different antenna locations on the body, namely the head, torso and belt. First the antenna is measured in free space as reference, and then the influences of the body are investigated for different frequencies and antenna polarizations. We observe minimal signal blockage when the antenna is located on the head. It is around 5d B-10 dB loss for all polarizations. For the belt and torso, the blockage is 10 dB to 35 dB, for both polarizations.
Improved Radiation and Bandwidth of Triangular and Star Patch Antenna  [cached]
M. Ramkumar Prabhu,V. Reji,A. Sivabalan
Research Journal of Applied Sciences, Engineering and Technology , 2012,
Abstract: This study presents a hexagonal shape Defected Ground Structure (DGS) implemented on two element triangular patch microstrip antenna array. The radiation performance of the antenna is characterized by varying the geometry and dimension of the DGS and also by locating the DGS at specific position which were simulated. Simulation and measurement results have verified that the antenna with DGS had improved the antenna without DGS. Measurement results of the hexagonal DGS have axial ratio bandwidth enhancement of 10 MHz, return loss improvement of 35%, mutual coupling reduction of 3 dB and gain enhancement of 1 dB. A new wideband and small size star shaped patch antenna fed capacitively by a small diamond shape patch is proposed. To enhance the impedance bandwidth, posts are incorporated under the patch antenna. HFSS high frequency simulator is employed to analyze the proposed antenna and simulated results on the return loss, the E- and H-plane radiation patterns and Gain of the proposed antenna are presented at various frequencies. The antenna is able to achieve in the range of 4-8.8 GHz an impedance bandwidth of 81% for return loss of less than-10 dB.
Design of a Wide-Angle Biconical Antenna for Wideband Communications
Debalina Ghosh;Tapan Kumar Sarkar;Eric L. Mokole
PIER B , 2009, DOI: 10.2528/PIERB09061508
Abstract: The wide-angle bicone antenna terminated by a spherical cap is investigated. The antenna radiation patterns have been observed for various values of where represents the phase constant and represents the conical length. It is seen that for large values of the radiation pattern is limited within an angular sector bounded by the cones of the antenna. Next the antenna is optimized for ultra-wideband (UWB) operation through the use of loading techniques. The transient wideband radiated and received responses of the antenna have been observed and the relationship between the wave shapes of the transient field and the input pulse have been determined.
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