Velocities of Venus clouds derived from VIRTIS observations

Retrograde superrotation is a well known feature of the atmosphere of Venus, with Venus’ cloud tops rotating in only 4.4 days, much faster than the 243-day rotation period of the solid globe. A good characterization of the circulation of the venusian atmosphere is essential in order to understand the mechanisms controlling superrota- tion. VIRTIS, onboard ESA’s Venus Express, is one of the most flexible instruments for such a characterization. The VIRTIS-M imaging spectrometer, operating in the range 0.25 to 5 micrometers, has acquired images of Venus’ clouds from the cloud tops, in visible wavelengths, to the lower cloud layer, close to 40 km, at infrared wavelengths. We present velocity determinations from automated cloud tracking in the night side at 1.74, 2.3 and 5 micrometers, from high to mid latitudes in the south- ern hemisphere. The method is based on a digital correlator which compares two or more consecutive images and identifies patterns by maximizing correlations between image blocks (Luz, Berry and Roos-Serote, 2008, New Ast. 13, 224). Notable features are the variability of the winds and the detection of a clear transition region between 75S and 80S. The meridional component is suggestive of a polar Hadley cell. Wave motions are detected at the transition latitudes with wavenumbers 3 and 8 for the zonal and meridional components. We estimate the contribution from the subsolar to antisolar-point wind component to be higher than 10 m/s

Three-dimensional modeling of lightning-induced electromagnetic pulses on Venus, Jupiter and Saturn

While lightning activity in Venus is still controversial, its existence in Jupiter and Saturn was first detected by the Voyager missions and later on confirmed by Cassini and New Horizons optical recordings in the case of Jupiter, and recently by Cassini on Saturn in 2009. Based on a recently developed 3D model we investigate the influence of lightning-emitted electromagnetic pulses (EMP) on the upper atmosphere of Venus, Saturn and Jupiter. We explore how different lightning properties such as total energy released and orientation (vertical, horizontal, oblique) can produce mesospheric transient optical emissions of different shapes, sizes and intensities. Moreover, we show that the relatively strong background magnetic field of Saturn can enhance the lightning-induced quasi-electrostatic and inductive electric field components above 1000 km of altitude producing stronger transient optical emissions that could be detected from orbital probes

South polar dynamics of the Venusian atmosphere from VIRTIS/Venus Express mapping in the thermal range

We report on measurements of Venus cloud velocities from VIRTIS/Venus Express observations of the south polar region of Venus. Cloud tracking has been performed using a method of automated digital correlation. Tracking has been performed on pairs of monochromatic VIRTIS images selected mainly in the 5 μm window, but also at 1.74, 2.3, 3.93 micrometers. Wind measurements from vector retrievals based on automated feature tracking show high variability, indicating the presence of important transient motions. The time-averaged zonal winds indicate different day and night side regimes. On the day side both the zonal wind component (u) and the meridional one (v) are approximately uniform between 84S and 76S, with u ∼ −40 m/s and v ∼ −10 m/s. On the night side the zonal wind decreases poleward, from a maximum at 76S. The meridional wind is smaller than on the day side and appears to change sign from poleward to equatorward at 76S. The cold collar boundary appears to be a transition region not only for the temperature, but for the winds as well. In this region wave motions are also apparent, with amplitudes on the order of 40 m/s for u′ and 10 m/s for v′

Winds and cloud morphology in the southern polar region of Venus

Spinning on average 60 times faster than the surface, the atmosphere of Venus is superrotational, a state in which the averaged angular momentum is much greater than that corresponding to co-rotation with the solid globe. The rapid mean flow, which is main- tained by momentum transports in the deep atmo- sphere, presents a puzzle to the atmospheric and plan- etary sciences[1]. After previous missions revealed a bright polar feature at the north pole[9, 10], the Venus Express spacecraft discovered a fast-rotating counter- part at the southern polar region[6], which has been identified as a vortex[2]. The southern polar vortex can be observed at 5.0 μm as a bright, highly vari- able structure which is ∼ 15 K warmer than the sur- rounding air[6]. Although the Venus superrotation has been measured by tracking cloud features at UV and infrared wavelengths[7, 4, 8, 5], the winds in the po- lar region remain poorly constrained. Characterizing the zonal and meridional circulation in this region, as well as their variability, is crucial for understanding the mechanisms that maintain superrotation. In partic- ular, mean zonal winds are necessary to understand the nature of the polar vortex, how it is connected with the general circulation of the atmosphere, and to diagnose momentum transports. Winds at 45 and 65 km can be detected from cloud motion monitoring by the VIRTIS-M subsection on- board the Venus Express (VEX) spacecraft. Our ob- jective is to provide direct wind measurements at cloud tops and in the lower cloud level, in order to help in- terpret the VEX observations concerning the meso- spheric wind regime and temperature fields. In par- ticular, we present direct measurements of the zonal and meridional winds at both altitudes. For this work we selected nadir-pointing, high- spatial resolution VIRTIS data cubes obtained from apocenter in order to minimize the geometric distortion of the polar region. On average these contain lat- itudes extending from the pole to 70S. Since the VIR- TIS field of view is rectangular, lower latitudes are also present but cannot be observed over full latitude circles. Cloud tracking has been performed using the method of digital correlation described in a previous article[3]. VEX orbits were selected so as to have in each one at least one pair of images suitable for track- ing, i.e., with a considerable spatial overlap. Tracking has been performed on pairs of monochromatic im- ages at wavelengths of 1.74 μm, 2.3 μm, 3.93 μm and 5 μm. In the data cubes obtained with longer integration times (3s) the long-wavelength range of the spectrum, above 4.3 μm, is saturated. In those cases we se- lected the 3.93 μm radiance map instead of the one at 5 μm. The monochromatic radiance maps are first ex- tracted from data cubes that have undergone the stan- dard VIRTIS calibration procedures. The maps are then projected onto a polar stereographic grid and the wind retrieval procedure is applied. A total of 20 lat- itude bins, separated by 1 degree were used. For the analysis of transient motions the spatial averaging was done in 72 longitude bins at 5 degree intervals. In order to evaluate the variability over the time scale of one orbit, we have computed the orbital aver- ages, i.e., averages of all measurements coming from one given orbit. These orbital averages are only ap- proximations to temporal averages, since they do not cover one full rotation. The differences between same- orbit averages are apparent in both day and night side averages. Some notable features indicating different day and night side regimes are also apparent in the or- bit averages, and the boundary of the cold collar ap- pears to be a transition latitude. Moreover, the vari- ability that can be observed from orbit to orbit and be- tween series of observations from the same orbit indi- cates that departures from this mean flow are large and a persistent feature of the global circulation

The decay of unstable k-strings in SU(N) gauge theories at zero and finite temperature

Sources in higher representations of SU(N) gauge theory at T=0 couple with apparently stable strings with tensions depending on the specific representation rather than on its N-ality. Similarly at the deconfining temperature these sources carry their own representation-dependent critical exponents. It is pointed out that in some instances one can evaluate exactly these exponents by fully exploiting the correspondence between the 2+1 dimensional critical gauge theory and the 2d conformal field theory in the same universality class. The emerging functional form of the Polyakov-line correlators suggests a similar form for Wilson loops in higher representations which helps in understanding the behaviour of unstable strings at T=0. A generalised Wilson loop in which along part of its trajectory a source is converted in a gauge invariant way into higher representations with same N-ality could be used as a tool to estimate the decay scale of the unstable strings.Comment: 18 pages, 4 figures v2: typos correcte

D-Brane Interactions in a Gravitational Shock Wave Background

We study D-branes in the background of a gravitational shock wave. We consider the case of parallel D-branes located on opposite sides with respect to the shock wave. Their interaction is studied by evaluating the cylinder diagram using the boundary states technique. Boundary states are defined at each D-brane and their scalar product is evaluated after propagation through the shock wave. Taking the limit where the gravitational shock wave vanishes we show that the amplitude evaluated is consistent with the flat space-time result.Comment: To be published in Modern Physics Letters A, revised version with references added, 12 page

Impact of IFN lambda 3/4 single nucleotide polymorphisms on the cytomegalovirus reactivation in autologous stem cell transplant patients

Cytomegalovirus (CMV) infection represents one of the main cause mortality after Stem Cell Transplantation. Recently, a protective effect of the T allele of rs12979860 IL28B Single Nucleotide Polymorphisms (SNPs) against CMV infection in the allogenic stem cell transplantation was suggested. We investigate whether the rs12979860 IL28B SNP and the relative rs368234815 (IFNλ4) genotype may affect the incidence of active CMV infection in Autologous stem cell transplantation (Auto-SCT) setting. The study included 99 patients who underwent to Auto-SCT. IL28 and IFNΔ4 SNPs were correlated with CMV reactivation along with other clinical and treatment parameters. CMV reactivation by CMV DNAemia was evaluated once a week until day 100 from Auto-SCT. CMV reactivation was documented in 50% (TT-ΔG/ΔG), 35% (CC-TT/TT) and 29.2% (CT-TT/ΔG) of the patients respectively. No differences in CMV copies number were recorded at reactivation between different IL28/IFNλ4 genotypes. The analysis of patients older than 60 years showed a significantly higher incidence of active CMV infection in the TT-ΔG/ΔG (83%) population with respect to CC-TT/TT (21%) and CT-TT/ΔG (40%) patients. Our data suggest a negative role of TT-ΔG/ΔG genotype in the CMV reactivation in Auto-SCT. The exposure to rituximab and the pre-infusion presence of anti CMV IgG also significantly influenced CMV reactivation

PG 1613+426: a new sdB pulsator

We report the detection of short period oscillations in the hot subdwarf B (sdB) star PG 1613+426 from time-series photometry carried out with the 91-cm Cassegrain telescope of the Catania Astrophysical Observatory. This star, which is brighter than the average of the presently known sdB pulsators, with B = 14.14 mag, has $T_{\rm eff}=34 400 {\rm K}$ and $\log g = 5.97$, its position is near the hot end of the sdB instability strip, and it is a pulsator with a well observed peak in the power spectrum at $144.18\pm 0.06 \rm s$. This star seems to be well suited for high precision measurements, which could detect a possible multi-mode pulsation behaviourComment: 3 pages, 4 figures. to appear on A&

Distribution of Relaxation Times Based on Lasso Regression: A Tool for High-Resolution Analysis of IMPS Data in Photoelectrochemical Systems

Intensity-modulated photocurrent spectroscopy (IMPS) has been largely employed in semiconductor characterization for solar energy conversion devices to probe the operando behavior with widely available facilities. However, the implementation of IMPS data analysis to complex structures, whether based on the physical rate constant model (RCM) or the assumption-free distribution of relaxation times (DRT), is generally limited to a semi-quantitative description of the charge carrier kinetics of the system. In this study, a new algorithm for the analysis of IMPS data is developed, providing unprecedented time resolution to the investigation of μs to s charge carrier dynamics in semiconductor-based systems used in photoelectrochemistry and photovoltaics. The algorithm, based on the previously developed DRT analysis, is herein modified with a Lasso regression method and available to the reader free of charge. A validation of this new algorithm is performed on a α-Fe2O3 photoanode for photoelectrochemical water splitting, identified as a standard platform in the field, highlighting multiple potential-dependent charge transfer paths, otherwise hidden in the conventional IMPS data analysis