Analysis of dynamic stall using unsteady boundary-layer theory

The unsteady turbulent boundary layer and potential flow about a pitching airfoil are analyzed using numerical methods to determine the effect of pitch rate on the delay in forward movement of the rear flow reversal point. An explicit finite difference scheme is used to integrate the unsteady boundary layer equations, which are coupled at each instant of time to a fully unsteady and nonlinear potential flow analysis. A substantial delay in forward movement of the reversal point is demonstrated with increasing pitch rate, and it is shown that the delay results partly from the alleviation of the gradients in the potential flow, and partly from the effects of unsteadiness in the boundary layer itself. The predicted delay in flow-reversal onset, and its variation with pitch rate, are shown to be in reasonable agreement with experimental data relating to the delay in dynamic stall. From the comparisons it can be concluded (a) that the effects of time-dependence are sufficient to explain the failure of the boundary layer to separate during the dynamic overshoot, and (b) that there may be some link between forward movement of the reversal point and dynamic stall

A statistical model for the intrinsically broad superconducting to normal transition in quasi-two-dimensional crystalline organic metals

Although quasi-two-dimensional organic superconductors such as $\kappa$-(BEDT-TTF)$_2$Cu(NCS)$_2$ seem to be very clean systems, with apparent quasiparticle mean-free paths of several thousand \AA, the superconducting transition is intrinsically broad (e.g $\sim 1$ K wide for $T_c \approx 10$ K). We propose that this is due to the extreme anisotropy of these materials, which greatly exacerbates the statistical effects of spatial variations in the potential experienced by the quasiparticles. Using a statistical model, we are able to account for the experimental observations. A parameter $\bar{x}$, which characterises the spatial potential variations, may be derived from Shubnikov-de Haas oscillation experiments. Using this value, we are able to predict a transition width which is in good agreement with that observed in MHz penetration-depth measurements on the same sample.Comment: 8 pages, 2 figures, submitted to J. Phys. Condens. Matte

Electromagnetic field angular momentum in condensed matter systems

Various electromagnetic systems can carry an angular momentum in their {\bf E} and {\bf B} fields. The electromagnetic field angular momentum (EMAM) of these systems can combine with the spin angular momentum to give composite fermions or composite bosons. In this paper we examine the possiblity that an EMAM could provide an explanation of the fractional quantum Hall effect (FQHE) which is complimentary to the Chern-Simons explanation. We also examine a toy model of a non-BCS superconductor (e.g. high $T_c$ superconductors) in terms of an EMAM. The models presented give a common, simple picture of these two systems in terms of an EMAM. The presence of an EMAM in these systems might be tested through the observation of the decay modes of a charged, spin zero unstable particle inside one of these systems.Comment: 17 pages, no figures, to be published in Phys. Rev.

Quantum Oscillations in the Underdoped Cuprate YBa2Cu4O8

We report the observation of quantum oscillations in the underdoped cuprate superconductor YBa2Cu4O8 using a tunnel-diode oscillator technique in pulsed magnetic fields up to 85T. There is a clear signal, periodic in inverse field, with frequency 660+/-15T and possible evidence for the presence of two components of slightly different frequency. The quasiparticle mass is m*=3.0+/-0.3m_e. In conjunction with the results of Doiron-Leyraud et al. for YBa2Cu3O6.5, the present measurements suggest that Fermi surface pockets are a general feature of underdoped copper oxide planes and provide information about the doping dependence of the Fermi surface.Comment: Contains revisions addressing referees' comments including a different Fig 1b. 4 pages, 4 figure

Weak anisotropy of the superconducting upper critical field in Fe1.11Te0.6Se0.4 single crystals

We have determined the resistive upper critical field Hc2 for single crystals of the superconductor Fe1.11Te0.6Se0.4 using pulsed magnetic fields of up to 60T. A rather high zero-temperature upper critical field of mu0Hc2(0) approx 47T is obtained, in spite of the relatively low superconducting transition temperature (Tc approx 14K). Moreover, Hc2 follows an unusual temperature dependence, becoming almost independent of the magnetic field orientation as the temperature T=0. We suggest that the isotropic superconductivity in Fe1.11Te0.6Se0.4 is a consequence of its three-dimensional Fermi-surface topology. An analogous result was obtained for (Ba,K)Fe2As2, indicating that all layered iron-based superconductors exhibit generic behavior that is significantly different from that of the high-Tc cuprates.Comment: 4 pages, 4 figures, submit to PR

Risky Substance Use Behaviors Among Adults Residing in Non-Metropolitan and Metropolitan Counties in the United States, 2017-2018

Overview of Key Findings Tobacco Use. Non-metropolitan adults had significantly higher prevalence rates of past year tobacco use (34.7% vs. 27.9%), daily cigarette use in the past 30 days (16.5% vs. 10.3%), and smoking at least 1 pack of cigarettes per day in the past 30 days (46.9% vs. 39.1%) than metropolitan adults. Alcohol Use. Non-metropolitan adults had a lower prevalence rate of past year alcohol use (64.0% vs. 71.0%), past 30-day alcohol use (48.7% vs. 56.6%), and past 30-day binge drinking (24.5% vs. 26.7%) than metropolitan adults. Illicit Drug Use. Overall illicit drug use was significantly less prevalent among non-metropolitan than metropolitan adults, both in the past year (16.0% vs. 20.1%) and the past 30 days (9.7% and 12.1%). The past year prevalence of use or misuse of several drugs was lower among non-metropolitan than metropolitan adults, including marijuana (12.4% vs. 16.3%), cocaine (1.6% vs. 2.4%), tranquilizers (1.8% vs. 2.3%), hallucinogens (1.2% vs. 2.1%), stimulants (1.4% vs. 2.1%), and inhalants (0.3% vs. 0.6%). A notable exception was past year methamphetamine use, which was significantly more prevalent among non-metropolitan than metropolitan adults (1.0% vs. 0.7%)

Cyclotron resonance of the quasi-two-dimensional electron gas at Hg1-xCdxTe grain boundaries

The magnetotransmission of a p-type Hg0.766Cd0.234Te bicrystal containing a single grain boundary with an inversion layer has been investigated in the submillimetre wavelength range. For the first time the cyclotron resonance lines belonging to the various electric subbands of a quasi-two-dimensional carrier system at a grain boundary could be detected. The measured cyclotron masses and the subband densities determined from Shubnikov-de Haas experiments are compared with theoretical predictions and it is found that the data can be explained very well within the framework of a triangular well approximation model which allows for non-parabolic effects

Risky Substance Use Behaviors Among Adolescents Residing in Non-Metropolitan and Metropolitan Counties in the United States, 2017-2018

Overview of Key Findings Tobacco Use. The prevalence of any past year tobacco use was significantly higher among non-metropolitan than metropolitan adolescents (13.9% vs. 8.3%). Daily cigarette use in the past 30 days was more than 3 times more prevalent among non-metropolitan than metropolitan adolescents (1.0% vs. 0.3%) and the difference was also statistically significant. Alcohol Use. Alcohol was the most commonly used substance among both non-metropolitan and metropolitan adolescents, although the differences in prevalence rates for past year and past 30-day alcohol use were not statistically significant. In the past year, 21.8% of non-metropolitan and 21.7% of metropolitan adolescents drank alcohol. In the past 30 days, 9.3% of non-metropolitan adolescents and 9.6% of metropolitan adolescents drank alcohol, and more than half of each group reported binge drinking. Illicit Drug Use. Prevalence rates for most illicit drugs were similar among non-metropolitan and metropolitan adolescents, with two exceptions. The prevalence of past year methamphetamine use was significantly higher among non-metropolitan than metropolitan adolescents (0.3% vs 0.2%), and the prevalence of past 30-day hallucinogen use was significantly lower among non-metropolitan than metropolitan adolescents (0.2% vs. 0.6%)

The magnetoresistance and Hall effect in CeFeAsO: a high magnetic field study

The longitudinal electrical resistivity and the transverse Hall resistivity of CeFeAsO are simultaneously measured up to a magnetic field of 45T using the facilities of pulsed magnetic field at Los Alamos. Distinct behaviour is observed in both the magnetoresistance Rxx({\mu}0H) and the Hall resistance Rxy({\mu}0H) while crossing the structural phase transition at Ts \approx 150K. At temperatures above Ts, little magnetoresistance is observed and the Hall resistivity follows linear field dependence. Upon cooling down the system below Ts, large magnetoresistance develops and the Hall resistivity deviates from the linear field dependence. Furthermore, we found that the transition at Ts is extremely robust against the external magnetic field. We argue that the magnetic state in CeFeAsO is unlikely a conventional type of spin-density-wave (SDW).Comment: 4 pages, 3 figures SCES2010, To appear in J. Phys.: Conf. Ser. for SCES201