Torsional suspension system for testing space structures

A low frequency torsional suspension system for testing a space structure uses a plurality of suspension stations attached to the space structure along the length thereof in order to suspend the space structure from an overhead support. Each suspension station includes a disk pivotally mounted to the overhead support, and two cables which have upper ends connected to the disk and lower ends connected to the space structure. The two cables define a parallelogram with the center of gravity of the space structure being vertically beneath the pivot axis of the disk. The vertical distance between the points of attachment of the cables to the disk and the pivot axis of the disk is adjusted to lower the frequency of the suspension system to a level which does not interfere with frequency levels of the space structure, thereby enabling accurate measurement

Factors Associated to Purchase of Quality-Labelled Beef

The aim of the present study is to identify the factors associated to purchase of quality-labelled beef. For this purpose a total of 364 surveys were carried out on buyers of beef in three Spanish cities. The sample was divided into three groups of buyers according to the beef purchasing habits with a quality label. A logistic regression analysis was used to estimate the differences between groups. The results show the importance of the production region as a quality aspect. Income level, association of quality-labelled beef with “guarantee and tradition” aspects, purchasing frequency, place of purchase, production systems and lifestyles are all variables that enabled us to establish differences between groups.beef quality, quality label, consumer perception, Demand and Price Analysis,

Muchas emergencias y aún más llamadas

Optimizar la distribuci´on y el despacho de los recursos es un tema prioritario en la atenci´on a emergencias, por lo que identificar las posibles llamadas que provienen de un mismo evento resulta determinante para su correcta atenci´on. Se analizar´a el problema tomando en cuenta las caracter´ısticas de una llamada de emergencia y los datos disponibles a partir de los cuales se pueden relacionar distintos reportes y, mediante un modelo de regresi´on log´ıstica, se encontrar´an criterios ´optimos para relacionar dos reportes

Suspension systems for ground testing large space structures

A research program is documented for the development of improved suspension techniques for ground vibration testing of large, flexible space structures. The suspension system must support the weight of the structure and simultaneously allow simulation of the unconstrained rigid-body movement as in the space environment. Exploratory analytical and experimental studies were conducted for suspension systems designed to provide minimum vertical, horizontal, and rotational degrees of freedom. The effects of active feedback control added to the passive system were also investigated. An experimental suspension apparatus was designed, fabricated, and tested. This test apparatus included a zero spring rate mechanism (ZSRM) designed to support a range of weights from 50 to 300 lbs and provide vertical suspension mode frequencies less than 0.1 Hz. The lateral suspension consisted of a pendulum suspended from a moving cart (linear bearing) which served to increase the effective length of the pendulum. The torsion suspension concept involved dual pendulum cables attached from above to a pivoting support (bicycle wheel). A simple test structure having variable weight and stiffness characteristics was used to simulate the vibration characteristics of a large space structure. The suspension hardware for the individual degrees of freedom was analyzed and tested separately and then combined to achieve a 3 degree of freedom suspension system. Results from the exploratory studies should provide useful guidelines for the development of future suspension systems for ground vibration testing of large space structures

Analysis of the Risley prism duction procedure for sources of error

Analysis of the Risley prism duction procedure for sources of erro

Cálculo del ranking acumulado para la encuesta de expectativas de inflación y tasa de cambio nominal, a través de una prueba no paramétrica

En este documento se presenta una metodología para el cálculo del Ranking acumulado de las entidades financieras que participan en la encuesta mensual de expectativas de inflación y tasa de cambio nominal (TRM), realizada por el Banco de la República. La metodología se basa en la prueba estadística no paramétrica propuesta por Jonckheere (1954), que consiste en un sistema de hipótesis de igualdad de distribuciones de probabilidad acumulada con alternativa de ordenamiento estricto para k muestras (k = 2). La metodología busca determinar el orden óptimo con el cual se rechaza la hipótesis nula, esto último se hace por medio de permutaciones. Ésta metodología es implementada en el programa R.Encuesta de expectativas económicas, Prueba de hipótesis no paramétrica, Prueba de Jonckheere. Classification JEL:C12, C14, D00, D21.

An Analytical Treatment of Aircraft Propeller Precession Instability

An analytical investigation is made of a precession-type instability which can occur in a flexibly supported aircraft-engine-propeller combination. By means of an idealized mathematical model which is comprised of a rigid power-plant system flexibly mounted in pitch and yaw to a fixed backup structure, the conditions required for neutral stability are determined. The paper also examines the sensitivity of the stability boundaries to changes in such parameters as stiffness, damping, and asymmetries in the engine mount, propeller speed, airspeed, Mach number, propeller thrust, and location of pitch and yaw axes. Stability is found to depend strongly on the damping and stiffness in the system. With the use of nondimensional charts, theoretical stability boundaries are compared with experimental results obtained in wind-tunnel tests of an aeroelastic airplane model. In general, the theoretical results, which do not account for wing response, show the same trends as observed experimentally; however, for a given set of conditions calculated airspeeds for neutral stability are consistently lower than the measured values. Evidently, this result is due to the fact that wing response tends to add damping to the system