Testing airplane fabrics

The following considerations determine the strength of airplane fabrics: 1. maximum air forces acting on the surfaces (including local stresses); 2. tensions produced in the fabrics, in the directions of both warp and filling; 3. factor of safety required. The question of the permissible depression of the fabric as affecting the aerodynamic requirements in regard to the maintenance of shape of the section, the tenacity and extensibility of the layer of dope, its strength and its permeability to water is almost as important

Collisionless microinstabilities in stellarators I - analytical theory of trapped-particle modes

This is the first of two papers about collisionless, electrostatic micro-instabilities in stellarators, with an emphasis on trapped-particle modes. It is found that, in so-called maximum-$J$ configurations, trapped-particle instabilities are absent in large regions of parameter space. Quasi-isodynamic stellarators have this property (approximately), and the theory predicts that trapped electrons are stabilizing to all eigenmodes with frequencies below the electron bounce frequency. The physical reason is that the bounce-averaged curvature is favorable for all orbits, and that trapped electrons precess in the direction opposite to that in which drift waves propagate, thus precluding wave-particle resonance. These considerations only depend on the electrostatic energy balance, and are independent of all geometric properties of the magnetic field other than the maximum-$J$ condition. However, if the aspect ratio is large and the instability phase velocity differs greatly from the electron and ion thermal speeds, it is possible to derive a variational form for the frequency showing that stability prevails in a yet larger part of parameter space than what follows from the energy argument. Collisionless trapped-electron modes should therefore be more stable in quasi-isodynamic stellarators than in tokamaks.Comment: 9 pages, 1 figur

La crítica del conocimiento a través del lenguaje en Nietzsche

Nietzsche's texts On Truth and Lies in a Nonmoral Sense and Description of Ancient Rhetoric belong to his period of intellectual production (between 1872 and 1875 as Lacoue-Labarthe has pointed out) in which he experimented in using elements of rhetorical analysis to explain the process of knowledge through language. On the one hand, rhetoric became a theoretical resource to analyze language, beginning from the activity of the body itself, that is, the activity of instincts. On the other hand, rhetoric facilitates the act of questioning of the statue of language that is presented as true, either in science or in philosophy, given that one considers language as originally tropic or figurative. The interest of studying the fragments and essays of this period lies in that the critics of the language of metaphysical thought that appear in Nietzsche's later works refer to his research of this period, even when he no longer uses the vocabulary of rhetoric.Los escritos de Nietzsche Sobre verdad y mentira en sentido extramoral y Descripción de la retórica antigua pertenecen a una época de su producción intelectual (entre 1872 y 1875 como ha señalado Lacoue-Labarthe) en la que ensaya tomar elementos de análisis de la retórica para explicar el proceso de conocimiento a partir del lenguaje. Por una parte, la retórica se convierte en un recurso teórico para analizar el lenguaje a partir de la actividad del propio cuerpo, esto es, la actividad de los instintos. Por otra, permite cuestionar el estatuto del lenguaje que se presenta como verdadero, ya sea el de la ciencia o el de la filosofía, dado que se considerará que el lenguaje es originariamente tropológico o figurativo. El interés del estudio de los fragmentos y ensayos de este período reside en que las críticas al lenguaje del pensamiento metafísico que aparecen en las obras posteriores de Nietzsche remiten a sus investigaciones de esta época, aun cuando ya no uti lice el vocabulario de la retóric

Collisionless microinstabilities in stellarators II - numerical simulations

Microinstabilities exhibit a rich variety of behavior in stellarators due to the many degrees of freedom in the magnetic geometry. It has recently been found that certain stellarators (quasi-isodynamic ones with maximum-$J$ geometry) are partly resilient to trapped-particle instabilities, because fast-bouncing particles tend to extract energy from these modes near marginal stability. In reality, stellarators are never perfectly quasi-isodynamic, and the question thus arises whether they still benefit from enhanced stability. Here the stability properties of Wendelstein 7-X and a more quasi-isodynamic configuration, QIPC, are investigated numerically and compared with the National Compact Stellarator Experiment (NCSX) and the DIII-D tokamak. In gyrokinetic simulations, performed with the gyrokinetic code GENE in the electrostatic and collisionless approximation, ion-temperature-gradient modes, trapped-electron modes and mixed-type instabilities are studied. Wendelstein 7-X and QIPC exhibit significantly reduced growth rates for all simulations that include kinetic electrons, and the latter are indeed found to be stabilizing in the energy budget. These results suggest that imperfectly optimized stellarators can retain most of the stabilizing properties predicted for perfect maximum-$J$ configurations.Comment: 15 pages, 40 figure

Neurophysiology

Contains reports on two research projects.Bell Telephone Laboratories Incorporate

An Integer Programming Approach to the Student-Project Allocation Problem with Preferences over Projects

The Student-Project Allocation problem with preferences over Projects (SPA-P) involves sets of students, projects and lecturers, where the students and lecturers each have preferences over the projects. In this context, we typically seek a stable matching of students to projects (and lecturers). However, these stable matchings can have different sizes, and the problem of finding a maximum stable matching (MAX-SPA-P) is NP-hard. There are two known approximation algorithms for MAX-SPA-P, with performance guarantees of 2 and 32 . In this paper, we describe an Integer Programming (IP) model to enable MAX-SPA-P to be solved optimally. Following this, we present results arising from an empirical analysis that investigates how the solution produced by the approximation algorithms compares to the optimal solution obtained from the IP model, with respect to the size of the stable matchings constructed, on instances that are both randomly-generated and derived from real datasets. Our main finding is that the 32 -approximation algorithm finds stable matchings that are very close to having maximum cardinality