Optical Dipole Trapping beyond Rotating Wave Approximation: The case of Large Detuning

We show that the inclusion of counter-rotating terms, usually dropped in evaluations of interaction of an electric dipole of a two level atom with the electromagnetic field, leads to significant modifications of trapping potential in the case of large detuning. The results are shown to be in excellent numerical agreement with recent experimental findings, for the case of modes of Laguerre-Gauss spatial profile.Comment: 13 pages, 2 figure

Different Melting Behavior in Pentane and Heptane Monolayers on Graphite; Molecular Dynamics Simulations

Molecular dynamics simulations are utilized to study the melting transition in pentane (C5H12) and heptane (C7H16), physisorbed onto the basal plane of graphite at near-monolayer coverages. Through use of the newest, optimized version of the anisotropic united-atom model (AUA4) to simulate both systems at two separate coverages, this study provides evidence that the melting transition for pentane and heptane monolayers are significantly different. Specifically, this study proposes a very rapid transition from the solid crystalline rectangular-centered (RC) phase to a fluid phase in pentane monolayers, whereas heptane monolayers exhibit a slower transition that involves a more gradual loss of RC order in the solid-fluid phase transition. Through a study of the melting behavior, encompassing variations where the formation of gauche defects in the alkyl chains are eliminated, this study proposes that this gradual melting behavior for heptane monolayers is a result of less orientational mobility of the heptane molecules in the solid RC phase, as compared to the pentane molecules. This idea is supported through a study of a nonane monolayer, which gives the gradual melting signature that heptane monolayers also seem to indicate. The results of this work are compared to previous experiment over pentane and heptane monolayers, and are found to be in good agreement

Face-seal lubrication. 2: Theory of response to angular misalignement

A theoretical analysis was made of a hypothetical seal operating mode. The hypothetical seal model provides for three degrees of primary ring motion and includes the force and moments induced by primary ring response to seat angular misalignment. This ring response causes a relative angular misalignment between the faces of the primary seal. Hydrodynamic pressure generation is produced by this misalignment. The analysis is based on the Reynolds equation in short bearing form and on a balance of forces and moments that arise from hydrodynamic and secondary seal friction effects. A closed form solution was obtained that can be solved for film thickness and relative angular misalignment

Spiral-grooved shaft seals substantially reduce leakage and wear

Rotating shaft seals used in space power systems have spiral grooves in one or both of the opposing seal faces. These grooves induce a pumping action which displaces the intervening fluid radially inward toward the shaft and counters the centrifugal forces which tend to displace the fluid outward

Simplifying the construction of domain-specific automatic programming systems: The NASA automated software development workstation project

An overview is presented of the Automated Software Development Workstation Project, an effort to explore knowledge-based approaches to increasing software productivity. The project focuses on applying the concept of domain specific automatic programming systems (D-SAPSs) to application domains at NASA's Johnson Space Center. A version of a D-SAPS developed in Phase 1 of the project for the domain of space station momentum management is described. How problems encountered during its implementation led researchers to concentrate on simplifying the process of building and extending such systems is discussed. Researchers propose to do this by attacking three observed bottlenecks in the D-SAPS development process through the increased automation of the acquisition of programming knowledge and the use of an object oriented development methodology at all stages of the program design. How these ideas are being implemented in the Bauhaus, a prototype workstation for D-SAPS development is discussed

PUBLIC LAND POLICY AND THE VALUE OF GRAZING PERMITS

This article provides an empirical test of the traditional theory of permit value and investigates the impact of recent changes in public land policies on the value of grazing permits. Results suggest that the cost advantage for grazing on public lands has been capitalized into substantial permit values, but other economic and hedonic factors influencing land prices also have contributed to the value of grazing permits. Public land grazing permits have fallen in value relative to deeded land as grazing fees have increased and as assurance has waned that public land policies will continue to be favorable to ranchers.Land Economics/Use,

Elementary Excitations of a Bose-Einstein Condensate in an Effective Magnetic Field

We calculate the low energy elementary excitations of a Bose-Einstein Condensate in an effective magnetic field. The field is created by the interplay between light beams carrying orbital angular momentum and the trapped atoms. We examine the role of the homogeneous magnetic field, familiar from studies of rotating condensates, and also investigate spectra for vector potentials with a more general radial dependence. We discuss the instabilities which arise and how these may be manifested.Comment: 8 pages, 4 figure

A learning apprentice for software parts composition

An overview of the knowledge acquisition component of the Bauhaus, a prototype computer aided software engineering (CASE) workstation for the development of domain-specific automatic programming systems (D-SAPS) is given. D-SAPS use domain knowledge in the refinement of a description of an application program into a compilable implementation. The approach to the construction of D-SAPS was to automate the process of refining a description of a program, expressed in an object-oriented domain language, into a configuration of software parts that implement the behavior of the domain objects

Effect of phonon-phonon interactions on localization

We study the heat current J in a classical one-dimensional disordered chain with on-site pinning and with ends connected to stochastic thermal reservoirs at different temperatures. In the absence of anharmonicity all modes are localized and there is a gap in the spectrum. Consequently J decays exponentially with system size N. Using simulations we find that even a small amount of anharmonicity leads to a J~1/N dependence, implying diffusive transport of energy.Comment: 4 pages, 2 figures, Published versio