908 research outputs found
Phase-field crystal study of grain-boundary premelting
We study the phenomenon of grain-boundary premelting for temperatures below
the melting point in the phase-field crystal model of a pure material with
hexagonal ordering in two dimensions. We investigate the structures of
symmetric tilt boundaries as a function of misorientation for two different
inclinations and compute in the grand canonical ensemble the disjoining
potential V(w) that governs the fundamental interaction between crystal-melt
interfaces as a function of the premelted layer width w. The results reveal
qualitatively different behaviors for high-angle grain boundaries that are
uniformly wetted, with w diverging logarithmically as the melting point is
approached from below, and low-angle boundaries that are punctuated by liquid
pools surrounding dislocations, separated by solid bridges. This qualitative
difference between high and low angle boundaries is reflected in the
w-dependence of the disjoining potential that is purely repulsive (V'(w)<0 for
all w) above a critical misorientation, but switches from repulsive at small w
to attractive at large w for low angles. In the latter case, V(w) has a minimum
that corresponds to a premelted boundary of finite width at the melting point.
Furthermore, we find that the standard wetting condition (the grain boundary
energy is equal to twice the solid-liquid free energy) gives a much too low
estimate of the critical misorientation when a low-temperature value of the
grain boundary energy is used. In contrast, a reasonable estimate is obtained
if the grain boundary energy is extrapolated to the melting point, taking into
account both the elastic softening of the material at high temperature and
local melting around dislocations.Comment: 24 pages, 13 figures, some figure files with reduced resolution
because of submission size limitations. In the 2nd version, some parts (and
figures) have been modified, especially in Sec. V (discussion
Effects of reaction control system jet simulation on the stability and control characteristics of a 0.015-scale space shuttle orbiter model in the Ames Research Center 3.5-foot hypersonic wind tunnel
An experimental investigation was performed in the Ames Research Center 3.5-Foot Hypersonic Wind Tunnel to obtain detailed effects which interactions between the RCS jet flow field and the local orbiter flow field have on orbiter hypersonic stability and control characteristics. Six-component force data were obtained through an angle-of-attack range of 15 to 35 deg with 0 deg angle of sideslip. The test was conducted with yaw, pitch and roll jet simulation at a free-stream Mach number of 10.3. These data simulate two SSV reentry flight conditions at Mach numbers of 28.3 and 10.3. Fuselage base pressures and pressures on the nonmetric RCS pods were obtained in addition to the basic force measurements. Model 42-0 was used for these tests
Results of tests of a 0.010- and 0.015-scale models of space shuttle orbiter configurations 3 and 3A in the Ames Research Center 3.5 foot hypersonic wind tunnel (OA23)
Longitudinal and lateral-directional stability and control characteristics were evaluated at Mach numbers of 5.3, 7.3 and 10.3 at angles of attack up to 50 degrees with Beta = 0 degrees and, for a few cases, Beta = 5 degrees. Component force data, fuselage base pressures and shadowgraph patterns were recorded
Wind-tunnel Tests of a 0.16-scale Model of the X-3 Airplane at High Subsonic Speeds : Wing and Fuselage Pressure Distribution
Wind-tunnel Tests of a 0.16-scale Model of the X-3 Airplane at High Subsonic Speeds : Additional Stability and Control Characteristics and the Aerodynamic Effects of External Stores and Ram Jets
Investigation at Mach Numbers of 0.20 to 3.50 of a Blended Diamond Wing and Body Combination of Sonic Design but with Low Wave-Drag Increase with Increasing Mach Number
A diamond wing and body combination was designed to have an area distribution which would result in near optimum zero-lift wave-drag coefficients at a Mach number of 1.00, and decreasing wave-drag coefficient with increasing Mach number up to near sonic leading-edge conditions for the wing. The airfoil section were computed by varying their shape along with the body radii (blending process) to match the selected area distribution and the given plan form. The exposed wing section had an average maximum thickness of about 3 percent of the local chords, and the maximum thickness of the center-line chord was 5.49 percent. The wing had an aspect ratio of 2 and a leading-edge sweep of 45 deg. Test data were obtained throughout the Mach number range from 0.20 to 3.50 at Reynolds numbers based on the mean aerodynamic chord of roughly 6,000,000 to 9,000,000. The zero-lift wave-drag coefficients of the diamond model satisfied the design objectives and were equal to the low values for the Mach number 1.00 equivalent body up to the limit of the transonic tests. From the peak drag coefficient near M = 1.00 there was a gradual decrease in wave-drag coefficient up to M = 1.20. Above sonic leading-edge conditions of the wing there was a rise in the wave-drag coefficient which was attributed in part to the body contouring as well as to the wing geometry. The diamond model had good lift characteristics, in spite of the prediction from low-aspect-ratio theory that the rear half of the diamond wing would carry little lift. The experimental lift-curve slope obtained at supersonic speeds were equal to or greater than the values predicted by linear theory. Similarly the other basic aerodynamic parameters, aerodynamic center position, and maximum lift-drag ratios were satisfactorily predicted at supersonic speeds
Wind-Tunnel Tests of a 0.16-Scale Model of the Douglas MX-656 Airplane at High Subsonic Speeds. II - Wing and Fuselage Pressure Distribution
Measurements of wing and fuselage pressure distributions were made at low and high subsonic Much numbers on a 0.16-scale model of the projected MX-656 research airplane. The MX-656 is a supersonic design utilizing a low-aspect-ratio wing and tail. Pressure-distribution measurements indicated that, although the critical Mach number of the wing was approximately 0.81 at 0 degree angle of attack, compressibility effects were of little significance below a Mach number of at least 0.90. The principal effect of compressibility was an increase in the pressure gradient over the after 30 percent of the wing chord, causing a tendency for the flow to separate. At 0.40 Mach number, the wing stalled abruptly at approximately 12 deg, angle of attack. The wing-pressure distribution showed this stall was a result of complete separation of the flow from the upper surface of the wing, Deflecting the leading-edge flaps delayed the stall to a higher angle of attack with some increase in the maximum section normal force
Wind tunnel test of the 0.010-scale space shuttle integrated vehicle in the NASA-Ames 3.5 foot hypersonic wind tunnel (IA10)
Experimental aerodynamic investigations were conducted in the NASA Ames Research Center 3.5-Foot Hypersonic Wind Tunnel on a 0.010-scale model of the space shuttle vehicle orbiter and external tank (model no. 32 0T). The purpose of the test was to evaluate the basic hypersonic stability characteristics of the external tank and orbiter and to define orbiter plume effects on aero characteristics using solid plumes. The test was conducted at angles of attack from minus 10 deg to 30 deg and angles of sideslip of minus 10 deg thru 10 deg. Six component force data and static base pressures were recorded during the test
Investigations to the space shuttle orbiter 2A configuration 0.015-scale model in the NASA Ames Research Center 3.5-foot hypersonic wind tunnel at Mach numbers 5, 7 and 10 (OA11B)
The results of a wind tunnel test to determine the force, moment, and hinge-moment characteristics of the Configuration 2A Space Shuttle Vehicle Orbiter at Mach numbers 5, 7 and 10 are presented. The model was an 0.015-scale representation of the Orbiter Configuration 2A used in test 0A11A and later tests. Six-component aerodynamic force and moment data were recorded from a 1.50-inch internal strain-gage balance, and base pressures were taken for axial and drag force corrections. Hinge-moment data were obtained for the rudder and the inboard and outboard elevon panels of the starboard wing
Measurement of the cross-section and charge asymmetry of bosons produced in proton-proton collisions at TeV with the ATLAS detector
This paper presents measurements of the and cross-sections and the associated charge asymmetry as a
function of the absolute pseudorapidity of the decay muon. The data were
collected in proton--proton collisions at a centre-of-mass energy of 8 TeV with
the ATLAS experiment at the LHC and correspond to a total integrated luminosity
of 20.2~\mbox{fb^{-1}}. The precision of the cross-section measurements
varies between 0.8% to 1.5% as a function of the pseudorapidity, excluding the
1.9% uncertainty on the integrated luminosity. The charge asymmetry is measured
with an uncertainty between 0.002 and 0.003. The results are compared with
predictions based on next-to-next-to-leading-order calculations with various
parton distribution functions and have the sensitivity to discriminate between
them.Comment: 38 pages in total, author list starting page 22, 5 figures, 4 tables,
submitted to EPJC. All figures including auxiliary figures are available at
https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/STDM-2017-13
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