A theoretical study of the aerodynamic characteristics of lifting-body entry vehicles Summary report, Mar. 1965 - Mar. 1966

Aerodynamic characteristics of lifting-body entry vehicle

Phase-ordering of conserved vectorial systems with field-dependent mobility

The dynamics of phase-separation in conserved systems with an O(N) continuous symmetry is investigated in the presence of an order parameter dependent mobility M(\phi)=1-a \phi^2. The model is studied analytically in the framework of the large-N approximation and by numerical simulations of the N=2, N=3 and N=4 cases in d=2, for both critical and off-critical quenches. We show the existence of a new universality class for a=1 characterized by a growth law of the typical length L(t) ~ t^{1/z} with dynamical exponent z=6 as opposed to the usual value z=4 which is recovered for a<1.Comment: RevTeX, 8 pages, 13 figures, to be published in Phys. Rev.

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

Metastable helium molecules as tracers in superfluid liquid 4^{4}He

Metastable helium molecules generated in a discharge near a sharp tungsten tip operated in either pulsed mode or continuous field-emission mode in superfluid liquid $^{4}$He are imaged using a laser-induced-fluorescence technique. By pulsing the tip, a small cloud of He$_{2}^{*}$ molecules is produced. At 2.0 K, the molecules in the liquid follow the motion of the normal fluid. We can determine the normal-fluid velocity in a heat-induced counterflow by tracing the position of a single molecule cloud. As we run the tip in continuous field-emission mode, a normal-fluid jet from the tip is generated and molecules are entrained in the jet. A focused 910 nm pump laser pulse is used to drive a small group of molecules to the vibrational $a(1)$ state. Subsequent imaging of the tagged $a(1)$ molecules with an expanded 925 nm probe laser pulse allows us to measure the velocity of the normal fluid. The techniques we developed demonstrate for the first time the ability to trace the normal-fluid component in superfluid helium using angstrom-sized particles.Comment: 4 pages, 7 figures. Submitted to Phys. Rev. Let

Calibration of liquid argon and neon detectors with 83Krm^{83}Kr^m

We report results from tests of $^{83}$Kr$^{\mathrm{m}}$, as a calibration source in liquid argon and liquid neon. $^{83}$Kr$^{\mathrm{m}}$ atoms are produced in the decay of $^{83}$Rb, and a clear $^{83}$Kr$^{\mathrm{m}}$ scintillation peak at 41.5 keV appears in both liquids when filling our detector through a piece of zeolite coated with $^{83}$Rb. Based on this scintillation peak, we observe 6.0 photoelectrons/keV in liquid argon with a resolution of 6% ($\sigma$/E) and 3.0 photoelectrons/keV in liquid neon with a resolution of 19% ($\sigma$/E). The observed peak intensity subsequently decays with the $^{83}$Kr$^{\mathrm{m}}$ half-life after stopping the fill, and we find evidence that the spatial location of $^{83}$Kr$^{\mathrm{m}}$ atoms in the chamber can be resolved. $^{83}$Kr$^{\mathrm{m}}$ will be a useful calibration source for liquid argon and neon dark matter and solar neutrino detectors.Comment: 7 pages, 12 figure

Use of illicit substances and violent behaviour in psychotic disorders: two nationwide case-control studies and meta-analyses

Background. Substance use disorder explains much of the excess risk of violent behaviour in psychotic disorders. However, it is unclear to what extent the pharmacological properties and subthreshold use of illicit substances are associated with violence. Methods. Individuals with psychotic disorders were recruited for two nationwide projects: GROUP (N = 871) in the Netherlands and NEDEN (N = 921) in the United Kingdom. Substance use and violent behaviour were assessed with standardized instruments and multiple sources of information. First, we used logistic regression models to estimate the associations of daily and nondaily use with violence for cannabis, stimulants, depressants and hallucinogens in the GROUP and NEDEN samples separately. Adjustments were made for age, sex and educational level. We then combined the results in random-effects meta-analyses. Results. Daily use, compared with nondaily or no use, and nondaily use, compared with no use, increased the pooled odds of violence in people with psychotic disorders for all substance categories. The increases were significant for daily use of cannabis [pooled odds ratio (pOR) 1.6, 95% confidence interval (CI) 1.2–2.0), stimulants (pOR 2.8, 95% CI 1.7–4.5) and depressants (pOR 2.2, 95% CI 1.1–4.5), and nondaily use of stimulants (pOR 1.6, 95% CI 1.2–2.0) and hallucinogens (pOR 1.5, 95% CI 1.1–2.1). Daily use of hallucinogens, which could only be analysed in the NEDEN sample, significantly increased the risk of violence (adjusted odds ratio 3.3, 95% CI 1.2–9.3). Conclusions. Strategies to prevent violent behaviour in psychotic disorders should target any substance use