Dual band fss with fractal elements

Experimental and computed results of a frequency selective surface (FSS) based on a certain type of fractal element are presented. The fractal element is a two iteration Sierpinski gasket dipole. Owing to the dual band behaviour of the two iteration Sierpinski gasket dipole, two stopbands are exhibited within the operating frequency band. This behaviour is obtained by arraying one simple element in a single layer frequency selective surface (FSS)Peer ReviewedPostprint (published version

The phyogenetic principles of mma: A hypothetical biostratigraphic model

Two erectoid hominids from Sarstedt prompted a detailed examination of the course of the impressions of the Arteria meningea media and their characteristics within the line of hominidae

Cluster-Robust Variance Estimation for Dyadic Data

Dyadic data are common in the social sciences, although inference for such settings involves accounting for a complex clustering structure. Many analyses in the social sciences fail to account for the fact that multiple dyads share a member, and that errors are thus likely correlated across these dyads. We propose a nonparametric sandwich-type robust variance estimator for linear regression to account for such clustering in dyadic data. We enumerate conditions for estimator consistency. We also extend our results to repeated and weighted observations, including directed dyads and longitudinal data, and provide an implementation for generalized linear models such as logistic regression. We examine empirical performance with simulations and applications to international relations and speed dating

Resampling adaptive cloth simulations onto fixed-topology meshes

We describe a method for converting an adaptively remeshed simulation of cloth into an animated mesh with fixed topology. The topology of the mesh may be specified by the user or computed automatically. In the latter case, we present a method for computing the optimal output mesh, that is, a mesh with spatially varying resolution which is fine enough to resolve all the detail present in the animation. This technique allows adaptive simulations to be easily used in applications that expect fixed-topology animated meshes

Spacecraft Antennas

Some of the various categories of issues that must be considered in the selection and design of spacecraft antennas for a Personal Access Satellite System (PASS) are addressed, and parametric studies for some of the antenna concepts to help the system designer in making the most appropriate antenna choice with regards to weight, size, and complexity, etc. are provided. The question of appropriate polarization for the spacecraft as well as for the User Terminal Antenna required particular attention and was studied in some depth. Circular polarization seems to be the favored outcome of this study. Another problem that has generally been a complicating factor in designing the multiple beam reflector antennas, is the type of feeds (single vs. multiple element and overlapping vs. non-overlapping clusters) needed for generating the beams. This choice is dependent on certain system design factors, such as the required frequency reuse, acceptable interbeam isolation, antenna efficiency, number of beams scanned, and beam-forming network (BFN) complexity. This issue is partially addressed, but is not completely resolved. Indications are that it may be possible to use relatively simple non-overlapping clusters of only a few elements, unless a large frequency reuse and very stringent isolation levels are required

Des tentatives de dépasser les relations de pouvoir. Chercheurs et travailleurs sociaux : même combat ?

À partir d’une expérience concrète de recherche, l’article aborde les ambiguïtés de la position du chercheur en sciences sociales qui tente de modifier sa relation aux enquêtés pour la rendre plus égalitaire. Il explore les rapports de force et l’utilitarisme opposant chercheur et enquêté, tente d’en cerner les racines à travers l’exemple de la sociologie et son histoire. Enfin, il propose trois pistes pour répondre à ces ambiguïtés : la clarification des motivations du chercheur, la redéfinition de l’égalité et le travail de reconnaissance pour démocratiser la relation dissymétrique. Les questions abordées sont mises en parallèle avec la relation intervenant-usager en travail social.This article takes roots in a ground experience of research to focus on the ambiguity of the scientist’s position when it comes to modify the relationship to the investigated person, trying to reach some kind of equity. It explores how the researcher and the investigated person make use of each other as well as the history of this relationship through the exemple of sociology. Three possible answers will be proposed to remediate these ambiguities : a clarification of the researcher’s motivations, a redefinition of equality, and a work of recognition in order to democratize this asymetrical relation. A parallel will be drawn between this topics and the links which bind social workers and users

Trajectory computation during a maneuver: Thrust estimation with the Goddard Trajectory Determination System (GTDS)

Existing thrust modeling capabilities of the Goddard Trajectory Determination System (GTDS) have been enhanced to allow calibration of the onboard propulsion system. These enhancements provide one or more thrust scale factors, based on estimation using the batch least-squares technique, for the case of along-track thrust and the case of attitude-dependent thrust. The enhancements are evaluated using simulated tracking measurements for a test spacecraft and using actual tracking measurements for the Earth Radiation Budget Satellite (ERBS). The effects of tracking measurement noise and distribution on the accuracy of the estimation are investigated and found to be significant. Results and conclusions of the analysis are presented