A Vibratory Acoustic Gyroscope

No abstract availabl

Mechanization of and experience with a triplex fly-by-wire backup control system

A redundant three axis analog control system was designed and developed to back up a digital fly by wire control system for an F-8C airplane. The mechanization and operational experience with the backup control system, the problems involved in synchronizing it with the primary system, and the reliability of the system are discussed. The backup control system was dissimilar to the primary system, and it provided satisfactory handling through the flight envelope evaluated. Limited flight tests of a variety of control tasks showed that control was also satisfactory when the backup control system was controlled by a minimum displacement (force) side stick. The operational reliability of the F-8 digital fly by wire control system was satisfactory, with no unintentional downmodes to the backup control system in flight. The ground and flight reliability of the system's components is discussed

Mechanization of and experience with a triplex fly-by-wire backup control system

A redundant three-axis analog control system was designed and developed to back up a digital fly-by-wire control system for an F-8C airplane. Forty-two flights, involving 58 hours of flight time, were flown by six pilots. The mechanization and operational experience with the backup control system, the problems involved in synchronizing it with the primary system, and the reliability of the system are discussed. The backup control system was dissimilar to the primary system, and it provided satisfactory handling through the flight envelope evaluated. Limited flight tests of a variety of control tasks showed that control was also satisfactory when the backup control system was controlled by a minimum-displacement (force) side stick. The operational reliability of the F-8 digital fly-by-wire control system was satisfactory, with no unintentional downmodes to the backup control system in flight. The ground and flight reliability of the system's components is discussed

A Richness Study of 14 Distant X-ray Clusters From the 160 Square Degree Survey

We have measured the surface density of galaxies toward 14 X-ray-selected cluster candidates at redshifts greater than z=0.46, and we show that they are associated with rich galaxy concentrations. We find that the clusters range between Abell richness classes 0-2, and have a most probable richness class of one. We compare the richness distribution of our distant clusters to those for three samples of nearby clusters with similar X-ray luminosities. We find that the nearby and distant samples have similar richness distributions, which shows that clusters have apparently not evolved substantially in richness since redshift z =0.5. We compare the distribution of distant X-ray clusters in the L_x--richness plane to the distribution of optically-selected clusters from the Palomar Distant Cluster Survey. The optically-selected clusters appear overly rich for their X-ray luminosities when compared to X-ray-selected clusters. Apparently, X-ray and optical surveys do not necessarily sample identical mass concentrations at large redshifts. This may indicate the existence of a population of optically rich clusters with anomalously low X-ray emission. More likely, however, it reflects the tendency for optical surveys to select unvirialized mass concentrations, as might be expected when peering along large-scale filaments.Comment: The abstract has been abridged. Accepted for publication in the Astrophysical Journa

Mars and the early Sun

Global mean temperatures near 273 K on early Mars are difficult to explain in the context of standards solar evolution models. Even assuming maximum CO2 greenhouse warming, the required flux is approximately 15 percent too low. Here we consider two astrophysical models that could increase the flux by this amount. The first model is a nonstandard solar model in which the early Sun had a mass somewhat greater than today's mass (1.02-1.06 solar mass). The second model is based on a standard evolutionary solar model, but the ecliptic flux is increased due to focusing by an (expected) heavily spotted early Sun

Axisymmetric Stationary Solutions as Harmonic Maps

We present a method for generating exact solutions of Einstein equations in vacuum using harmonic maps, when the spacetime possesses two commutating Killing vectors. This method consists in writing the axisymmetric stationry Einstein equations in vacuum as a harmonic map which belongs to the group SL(2,R), and decomposing it in its harmonic "submaps". This method provides a natural classification of the solutions in classes (Weil's class, Lewis' class etc).Comment: 17 TeX pages, one table,( CINVESTAV- preprint 12/93

Improving the Information Security Model by using TFI

In the context of information systems and information technology, information security is a concept that is becoming widely used. The European Network of Excellence INTEROP classifies information security as a nonfunctional aspect of interoperability and as such it is an integral part of the design process for interoperable systems. In the last decade, academics and practitioners have shown their interest in information security, for example by developing security models for evaluating products and setting up security specifications in order to safeguard the confidentiality, integrity, availability and accountability of data. Earlier research has shown that measures to achieve information security in the administrative or organisational level are missing or inadequate. Therefore, there is a need to improve information security models by including vital elements of information security. In this paper, we introduce a holistic view of information security based on a Swedish model combined with a literature survey. Furthermore we suggest extending this model using concepts based on semiotic theory and adopting the view of an information system as constituted of the technical, formal and informal (TFI) parts. The aim is to increase the understanding of the information security domain in order to develop a well-founded theoretical framework, which can be used both in the analysis and the design phase of interoperable systems. Finally, we describe and apply the Information Security (InfoSec) model to the results of three different case studies in the healthcare domain. Limits of the model will be highlighted and an extension will be proposed.In the context of information systems and information technology, information security is a concept that is becoming widely used. The European Network of Excellence INTEROP classifies information security as a nonfunctional aspect of interoperability and as such it is an integral part of the design process for interoperable systems. In the last decade, academics and practitioners have shown their interest in information security, for example by developing security models for evaluating products and setting up security specifications in order to safeguard the confidentiality, integrity, availability and accountability of data. Earlier research has shown that measures to achieve information security in the administrative or organisational level are missing or inadequate. Therefore, there is a need to improve information security models by including vital elements of information security. In this paper, we introduce a holistic view of information security based on a Swedish model combined with a literature survey. Furthermore we suggest extending this model using concepts based on semiotic theory and adopting the view of an information system as constituted of the technical, formal and informal (TFI) parts. The aim is to increase the understanding of the information security domain in order to develop a well-founded theoretical framework, which can be used both in the analysis and the design phase of interoperable systems. Finally, we describe and apply the Information Security (InfoSec) model to the results of three different case studies in the healthcare domain. Limits of the model will be highlighted and an extension will be proposed.Monograph's chapter

Localized Excitons and Breaking of Chemical Bonds at III-V (110) Surfaces

Electron-hole excitations in the surface bands of GaAs(110) are analyzed using constrained density-functional theory calculations. The results show that Frenkel-type autolocalized excitons are formed. The excitons induce a local surface unrelaxation which results in a strong exciton-exciton attraction and makes complexes of two or three electron-hole pairs more favorable than separate excitons. In such microscopic exciton "droplets" the electron density is mainly concentrated in the dangling orbital of a surface Ga atom whereas the holes are distributed over the bonds of this atom to its As neighbors thus weakening the bonding to the substrate. This finding suggests the microscopic mechanism of a laser-induced emission of neutral Ga atoms from GaAs and GaP (110) surfaces.Comment: submitted to PRL, 10 pages, 4 figures available upon request from: [email protected]

Versatile single-molecule multi-color excitation and detection fluorescence setup for studying biomolecular dynamics

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/98644/1/RevSciInstrum_82_113702.pd

Asymptotic Structure of Symmetry Reduced General Relativity

Gravitational waves with a space-translation Killing field are considered. In this case, the 4-dimensional Einstein vacuum equations are equivalent to the 3-dimensional Einstein equations with certain matter sources. This interplay between 4- and 3- dimensional general relativity can be exploited effectively to analyze issues pertaining to 4 dimensions in terms of the 3-dimensional structures. An example is provided by the asymptotic structure at null infinity: While these space-times fail to be asymptotically flat in 4 dimensions, they can admit a regular completion at null infinity in 3 dimensions. This completion is used to analyze the asymptotic symmetries, introduce the analog of the 4-dimensional Bondi energy-momentum and write down a flux formula. The analysis is also of interest from a purely 3-dimensional perspective because it pertains to a diffeomorphism invariant 3-dimensional field theory with {\it local} degrees of freedom, i.e., to a midi-superspace. Furthermore, due to certain peculiarities of 3 dimensions, the description of null infinity does have a number of features that are quite surprising because they do not arise in the Bondi-Penrose description in 4 dimensions.Comment: 39 Pages, REVTEX, CGPG-96/5-