Casimir torque between corrugated metallic plates

We consider two parallel corrugated plates and show that a Casimir torque arises when the corrugation directions are not aligned. We follow the scattering approach and calculate the Casimir energy up to second order in the corrugation amplitudes, taking into account nonspecular reflections, polarization mixing and the finite conductivity of the metals. We compare our results with the proximity force approximation, which overestimates the torque by a factor 2 when taking the conditions that optimize the effect. We argue that the Casimir torque could be measured for separation distances as large as 1 $\mu{\rm m}.$Comment: 7 pages, 3 figures, contribution to QFEXT07 proceeding

Dielectric properties measurements of brown and white adipose tissue in rats from 0.5 to 10 GHz

Brown adipose tissue (BAT) plays an important role in whole body metabolism and with appropriate stimulus could potentially mediate weight gain and insulin sensitivity. Although imaging techniques are available to detect subsurface BAT, there are currently no viable methods for continuous acquisition of BAT energy expenditure. Microwave (MW) radiometry is an emerging technology that allows the quantification of tissue temperature variations at depths of several centimeters. Such temperature differentials may be correlated with variations in metabolic rate, thus providing a quantitative approach to monitor BAT metabolism. In order to optimize MW radiometry, numerical and experimental phantoms with accurate dielectric properties are required to develop and calibrate radiometric sensors. Thus, we present for the first time, the characterization of relative permittivity and electrical conductivity of brown (BAT) and white (WAT) adipose tissues in rats across the MW range 0.5-10GHz. Measurements were carried out in situ and post mortem in six female rats of approximately 200g. A Cole-Cole model was used to fit the experimental data into a parametric model that describes the variation of dielectric properties as a function of frequency. Measurements confirm that the dielectric properties of BAT (εr = 14.0-19.4, σ = 0.3-3.3S/m) are significantly higher than those of WAT (εr = 9.1-11.9, σ = 0.1-1.9S/m), in accordance with the higher water content of BAT

Urban Cholera transmission hotspots and their implications for Reactive Vaccination: evidence from Bissau city, Guinea Bissau

Use of cholera vaccines in response to epidemics (reactive vaccination) may provide an effective supplement to traditional control measures. In Haiti, reactive vaccination was considered but, until recently, rejected in part due to limited global supply of vaccine. Using Bissau City, Guinea-Bissau as a case study, we explore neighborhood-level transmission dynamics to understand if, with limited vaccine and likely delays, reactive vaccination can significantly change the course of a cholera epidemic

Radar Studies of Height-Dependent Equatorial F Region Vertical and Zonal Plasma Drifts

We present the results of an analysis of long-term measurements of ionospheric F region E × B plasma drifts in the American/Peruvian sector. The analysis used observations made between 1986 and 2017 by the incoherent scatter radar of the Jicamarca Radio Observatory. Unlike previous studies, we analyzed both vertical and zonal components of the plasma drifts to derive the geomagnetically quiet time climatological variation of the drifts as a function of height and local time. We determine the average behavior of the height profiles of the drifts for different seasons and distinct solar flux conditions. Our results show good agreement with previous height-averaged climatological results of vertical and zonal plasma drifts, despite that they are obtained from different sets of measurements. More importantly, our results quantify average height variations in the drifts. The results show, for example, the solar flux control over the height variation of the vertical drifts. The results also show the weak dependence of the daytime zonal drift profiles on solar and seasonal variations. We quantify the effects of seasonal and solar flux variations on the morphology of the vertical shear in the zonal plasma drifts associated with the evening plasma vortex. Assuming interchangeability between local time and longitude, we tested the curl-free condition for the F region electric fields with very good results for all seasons and solar flux conditions. We envision the use of our results to aid numerical modeling of ionospheric electrodynamics and structuring and to assist with the interpretation of satellite observations of low-latitude plasma drifts

A Kolmogorov-Zakharov Spectrum in AdSAdS Gravitational Collapse

We study black hole formation during the gravitational collapse of a massless scalar field in asymptotically $AdS_D$ spacetimes for $D=4,5$. We conclude that spherically symmetric gravitational collapse in asymptotically $AdS$ spaces is turbulent and characterized by a Kolmogorov-Zakharov spectrum. Namely, we find that after an initial period of weakly nonlinear evolution, there is a regime where the power spectrum of the Ricci scalar evolves as $\omega^{-s}$ with the frequency, $\omega$, and $s\approx 1.7\pm 0.1$.Comment: 5 pages, 4 figures. v2: Typos, other initial profile considered for universality, error analysis, close to PRL versio

The lateral Casimir force beyond the proximity force approximation: a nontrivial interplay between geometry and quantum vacuum

The lateral Casimir force between two corrugated metallic plates makes possible a study of the nontrivial interplay of geometry and Casimir effect appearing beyond the regime of validity of the Proximity Force Approximation (PFA). Quantitative evaluations can be obtained by using scattering theory in a perturbative expansion valid when the corrugation amplitudes are smaller than the three other length scales: the mean separation distance $L$ of the plates, the corrugation period \lambda_\C and the plasma wavelength $\lambda_\P$. Within this perturbative expansion, evaluations are obtained for arbitrary relative values of $L$, \lambda_\C and $\lambda_\P$ while limiting cases, some of them already known, are recovered when these values obey some specific orderings. The consequence of these results for comparison with existing experiments is discussed in the end of the paper

Time Dependent Current Oscillations Through a Quantum Dot

Time dependent phenomena associated to charge transport along a quantum dot in the charge quantization regime is studied. Superimposed to the Coulomb blockade behaviour the current has novel non-linear properties. Together with static multistabilities in the negative resistance region of the I-V characteristic curve, strong correlations at the dot give rise to self-sustained current and charge oscillations. Their properties depend upon the parameters of the quantum dot and the external applied voltages.Comment: 4 pages, 3 figures; to appear in PR