Application of AA-PSP to hypersonic flows: the double ramp model

Anodized Aluminium Pressure Sensitive Paint (AA-PSP) is known for its rapid response characteristics, making it a highly desirable technique when studying high-speed phenomenon on a global scale. The current study examines the efficacy of the AA-PSP technique, which is prepared with a more practical approach than that reported in literature, in analysing the flow characteristics of a double ramp model placed in hypersonic flow of M = 5. Three different flow angles of 0°, −2°, and −4° are studied. Two-dimensional colour schlieren visualisation, using a colour wheel, is employed alongside high sensitivity Kulite pressure tap data to corroborate the AA-PSP findings. The AA-PSP results show good correlation between the qualitative schlieren and ±8.9% discrepency with the quantitative pressure tap data. The more practical AA-PSP preparation proposed in the current study, which uses aluminium alloy 6-series rather than pure aluminium, is proved to have the response time and the accuracy to be applied to unsteady high-speed flows

A Spectroscopic Survey of a Sample of Active M Dwarfs

A moderate resolution spectroscopic survey of Fleming's sample of 54 X-ray selected M dwarfs with photometric distances less than 25 pc is presented. Radial and rotation velocities have been measured by fits to the H-alpha profiles. Radial velocities have been measured by cross correlation. Artificial broadening of an observed spectrum has produced a relationship between H-alpha FWHM and rotation speed, which we use to infer rotation speeds for the entire sample by measurement of the H-alpha emission line. We find 3 ultra-fast rotators (UFRs, vsini > 100km/s), and 8 stars with 30 < vsini < 100 km/s. The UFRs have variable emission. Cross-correlation velocities measured for ultra-fast rotators (UFRs) are shown to depend on rotation speed and the filtering used. The radial velocity dispersion of the sample is 17 km/s. A new double emission line spectroscopic binary with a period of 3.55 days has been discovered, and another known one is in the sample. Three other objects are suspected spectroscopic binaries, and at least six are visual doubles. The only star in the sample observed to have significant lithium is a known TW Hya Association member, TWA 8A. These results show that there are a number of young (< 10^8 yr) and very young (< 10^7 yr) low mass stars in the immediate solar neighbourhood. The H-alpha activity strength does not depend on rotation speed. Our fast rotators are less luminous than similarly fast rotators in the Pleiades. They are either younger than the Pleiades, or gained angular momentum in a different way.Comment: 38 pages incl. 14 figures and 4 tables, plus 12 pages of table for electronic journal only; LaTeX, aastex.cls. Accepted 07/18/02 for publication in The Astronomical Journa

Investigation of the double ramp in hypersonic flow using luminescent measurement systems

Compression ramp flows in supersonic and hypersonic environments present unique flow patterns for shock wave-boundary layer interaction studies. They also represent the generic geometry of two-dimensional inlets and deflected control surfaces for re-entry vehicles. Therefore, a detailed knowledge of the flow behaviour created by such geometries is critical for optimum design. The flow is made more complicated due to the presence of separation regions and streamwise Görtler vortices. The objective of the current research is to study the behaviour and characteristics of the flow over the double ramp model placed in hypersonic flow at freestream Mach number of 5. Three different incidence angles of 0°, −2°, and −4° are studied using colour Schlieren and luminescent paints consisting of anodized aluminium pressure-sensitive paint (AA-PSP) and the temperature-sensitive paint (TSP) technique. The colour Schlieren provides description of the external flow while the global surface pressure and temperature distribution is obtained through the AA-PSP and TSP methods. The TSP technique also proves that it is very effective in identifying the location and properties of the Görtler vortices; revealing the effect of incidence on the magnitude and pattern of Görtler vortices formed

Evidence for Surface Andreev Bound states in Cuprate Superconductors from Penetration Depth Measurements

Tunneling and theoretical studies have suggested that Andreev bound states form at certain surfaces of unconventional superconductors. Through studies of the temperature and field dependence of the in-plane magnetic penetration depth lambda_ab at low temperature, we have found strong evidence for the presence of these states in clean single crystal YBCO and BSCCO. Crystals cut to expose a [110] interface show a strong upturn in lambda_ab at around 7K, when the field is oriented so that the supercurrents flow around this surface. In YBCO this upturn is completely suppressed by a field of ~0.1 T.Comment: 4 pages 2 column revtex + 4 postscript figures. Submitted to PR

Conservatism in Laboratory Microsocieties: Unpredictable Payoffs Accentuate Group-Specific Traditions

Theoretical work predicts that individuals should strategically increase their reliance on social learning when individual learning would be costly or risky, or when the payoffs for individually-learned behaviors are uncertain. Using a method known to elicit cumulative cultural evolution in the laboratory, we investigated the degree of within-group similarity, and between-group variation, in design choices made by participants under conditions of varying uncertainty about the likely effectiveness of those designs. Participants were required to build a tower from spaghetti and modeling clay, their goal being to build the tower as high as possible. In one condition, towers were measured immediately on completion, and therefore participants were able to judge the success of their design during building. In the other condition, participants’ towers were measured five minutes after completion, following a deliberate attempt to test the tower’s stability, making it harder for participants to judge whether an innovative solution was liable to result in a good score on the final measurement. Cultural peculiarity (i.e. the extent to which a design could be identified as belonging to a particular chain) was stronger in the delayed measure condition, indicating that participants were placing greater reliance on social learning. Furthermore in this condition there was only very weak evidence of successive improvement in performance over learner generations, whereas in the immediate measure condition there was a clear effect of steadily increasing scores on the goal measurement. Increasing the risk associated with learning for oneself may favor the development of arbitrary traditions

Campbell Penetration Depth of a Superconductor in the Critical State

The magnetic penetration depth $\lambda(T,H,j)$ was measured in the presence of a slowly relaxing supercurrent, $j$. In single crystal $\mathrm{Bi_2Sr_2CaCu_2O_8}$ below approximately 25 K, $\lambda(T,H,j)$ is strongly hysteretic. We propose that the irreversibility arises from a shift of the vortex position within its pinning well as $j$ changes. The Campbell length depends upon the ratio $j/j_{c}$ where $j_{c}$ is the critical current defined through the Labusch parameter. Similar effects were observed in other cuprates and in an organic superconductor