40,083 research outputs found
Naming the newly found landforms on Venus
The mapping of Venus is unique in the history of cartigraphy; never has so much territory been discovered and mapped in so short a period of time. Therefore, in the interest of international scientific communication, there is a unique urgency to the development of a system of names for surface features on Venus. The process began with the naming of features seen on radar images taken from Earth and continued through mapping expeditions of the U.S. and U.S.S.R. However, the Magellan Mission resolves features twenty-five times smaller than those mapped previously, and its radar data will cover an area nearly equivalent to that of the continents and the sea-floors of the Earth combined. The International Astronomical Union (IAU) was charged with the formal endorsement of names of features on the planets. Proposed names are collected, approved, and applied through the IAU Working Group for Planetary System Nomenclature (WGPSN) and its task groups, prior to IAU approval by the IAU General Assembly. Names approved by the WGPSN and its task groups, prior to final approval may be used on published maps and articles, provided that their provisional nature is stipulated. The IAU has established themes for the names to be used on each of the planets; names of historical and mythological women are used on Venus. Names of political entities and those identified with active religions are not acceptable, and a person must have been deceased for three years or more to be considered. Any interested person may propose a name for consideration by the IAU
Double-discharge copper-vapor laser
Power supply for discharge pulses consists of two capacitors that are made to discharge synchronously with adjustable time intervals. First pulse is switched with hydrogen thyratron, and second by spark gap. Lasing action peaks for appropriate combination of these two parameters
Streakline flow visualization of discrete hole film cooling with holes inclined 30 deg to surface
Film injection from three rows of discrete holes angled 30 deg to the surface in line with mainstream flow and spaced 5 diameters apart in a staggered array was visualized by using helium bubbles as tracer particles. Both the main stream and the film injectant were ambient air. Detailed streaklines showing the turbulent motion of the film mixing with the main stream were obtained by photographing small, neutrally buoyant helium-filled soap bubbles which followed the flow field. The ratio of boundary layer thickness to hole diameter and the Reynolds number were typical of gas turbine film cooling applications. The results showed the behavior of the film and its interaction with the main stream for a range of blowing rates and two initial boundary layer thicknesses
Semi-Classical Description of Antiproton Capture on Atomic Helium
A semi-classical, many-body atomic model incorporating a momentum-dependent
Heisenberg core to stabilize atomic electrons is used to study antiproton
capture on Helium. Details of the antiproton collisions leading to eventual
capture are presented, including the energy and angular momentum states of
incident antiprotons which result in capture via single or double electron
ionization, i.e. into [He or He], and the
distribution of energy and angular momentum states following the Auger cascade.
These final states are discussed in light of recently reported, anomalously
long-lived antiproton states observed in liquid He.Comment: 15 pages, 9 figures may be obtained from authors, Revte
Influence of moving breathers on vacancies migration
A vacancy defect is described by a Frenkel--Kontorova model with a
discommensuration. This vacancy can migrate when interacts with a moving
breather. We establish that the width of the interaction potential must be
larger than a threshold value in order that the vacancy can move forward. This
value is related to the existence of a breather centred at the particles
adjacent to the vacancy.Comment: 11 pages, 10 figure
Mirror modes: Nonmaxwellian distributions
We perform direct analysis of mirror mode instabilities from the general
dielectric tensor for several model distributions, in the longwavelength limit.
The growth rate at the instability threshold depends on the derivative of the
distribution for zero parallel energy. The maximum growth rate is always and the instability is of nonresonant kind. The
instability growth rate and its dependence on the propagation angle depend on
the shape of the ion and electron distribution functions.Comment: 18 pages, 15 figures, revtex4, amsmath, amssymb,amsfonts,times,
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Transformation Optics with Photonic Band Gap Media
We introduce a class of optical media based on adiabatically modulated,
dielectric-only, and potentially extremely low-loss, photonic crystals. The
media we describe represent a generalization of the eikonal limit of
transformation optics (TO). The foundation of the concept is the possibility to
fit frequency isosurfaces in the k-space of photonic crystals with elliptic
surfaces, allowing them to mimic the dispersion relation of light in
anisotropic effective media. Photonic crystal cloaks and other TO devices
operating at visible wavelengths can be constructed from optically transparent
substances like glasses, whose attenuation coefficient can be as small as 10
dB/km, suggesting the TO design methodology can be applied to the development
of optical devices not limited by the losses inherent to metal-based, passive
metamaterials.Comment: 4 pages, 4 figure
The effects of solid rocket motor effluents on selected surfaces and solid particle size, distribution, and composition for simulated shuttle booster separation motors
A series of three tests was conducted using solid rocket propellants to determine the effects a solid rocket plume would have on thermal protective surfaces (TPS). The surfaces tested were those which are baselined for the shuttle vehicle. The propellants used were to simulate the separation solid rocket motors (SSRM) that separate the solid rocket boosters (SRB) from the shuttle launch vehicle. Data cover: (1) the optical effects of the plume environment on spacecraft related surfaces, and (2) the solid particle size, distribution, and composition at TPS sample locations
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