An apparent statistical relationship between polar heat budget and zonal circulation

Apparent statistical correlation between Arctic heat budget and zonal circulatio

Temperature dependent anisotropy of the penetration depth and coherence length in MgB$_2

We report measurements of the temperature dependent anisotropies ($\gamma_\lambda$ and $\gamma_\xi$) of both the London penetration depth $\lambda$ and the upper critical field of MgB$_2$. Data for $\gamma_\lambda=\lambda_c/\lambda_a$ was obtained from measurements of $\lambda_{a}$ and $\lambda_c$ on a single crystal sample using a tunnel diode oscillator technique. $\gamma_\xi=H_{c2}^{\parallel c}/H_{c2}^{\bot c}$ was deduced from field dependent specific heat measurements on the same sample. $\gamma_\lambda$ and $\gamma_\xi$ have opposite temperature dependencies, but close to $T_c$ tend to a common value ($\gamma_\lambda\simeq \gamma_\xi=1.75\pm0.05$). These results are in good agreement with theories accounting for the two gap nature of MgB$_2$Comment: 4 pages with figures (New version

The spectral content of SDO/AIA 1600 and 1700 \AA\ filters from flare and plage observations

The strong enhancement of the ultraviolet emission during solar flares is usually taken as an indication of plasma heating in the lower solar atmosphere caused by the deposition of the energy released during these events. Images taken with broadband ultraviolet filters by the {\em Transition Region and Coronal Explorer} (TRACE) and {\em Atmospheric Imaging Assembly} (AIA 1600 and 1700~\AA) have revealed the morphology and evolution of flare ribbons in great detail. However, the spectral content of these images is still largely unknown. Without the knowledge of the spectral contribution to these UV filters, the use of these rich imaging datasets is severely limited. Aiming to solve this issue, we estimate the spectral contributions of the AIA UV flare and plage images using high-resolution spectra in the range 1300 to 1900~\AA\ from the Skylab NRL SO82B spectrograph. We find that the flare excess emission in AIA 1600~\AA\ is { dominated by} the \ion{C}{4} 1550~\AA\ doublet (26\%), \ion{Si}{1} continua (20\%), with smaller contributions from many other chromospheric lines such as \ion{C}{1} 1561 and 1656~\AA\ multiplets, \ion{He}{2} 1640~\AA, \ion{Si}{2} 1526 and 1533~\AA. For the AIA 1700~\AA\ band, \ion{C}{1} 1656~\AA\ multiplet is the main contributor (38\%), followed by \ion{He}{2} 1640 (17\%), and accompanied by a multitude of other, { weaker} chromospheric lines, with minimal contribution from the continuum. Our results can be generalized to state that the AIA UV flare excess emission is of chromospheric origin, while plage emission is dominated by photospheric continuum emission in both channels.Comment: Accepted for publication in ApJ Skylab NRL SO82B data used in this work available at http://dx.doi.org/10.5525/gla.researchdata.68

RC J1148+0455 identification: gravitational lens or group of galaxies ?

The structure of the radio source RC B1146+052 of the ``Cold'' catalogue is investigated by data of the MIT-GB-VLA survey at 4850 MHz. This source belongs to the steep spectrum radio sources subsample of the RC catalogue. Its spectral index is $\alpha$ = -1.04. The optical image of this source obtained with 6m telescope is analysed. The radio source center is situated in a group of 8 galaxies of about 24$^m$ in the R-filter. The possible explanations of the complex structure of radio components are considered.Comment: 6 pages, 5 figures, uses psfig.sty. This was the poster as presented on Gamow Memorial Internat. Conference GMIC'99 "Early Universe: Cosmological Problems and Instrumental Technologies" in St.Petersburg, 23-27 Aug., 1999. Submitted to Proceedings to be published in A&A Transaction

Relations between concurrent hard X-ray sources in solar flares

Context: Solar flares release a large fraction of their energy into non-thermal electrons, but it is not clear where and how. Bremsstrahlung X-rays are observed from the corona and chromosphere. Aims: We aim to characterize the acceleration process by the coronal source and its leakage toward the footpoints in the chromosphere. The relations between the sources reflect the geometry and constrict the configuration of the flare. Methods: We studied solar flares of GOES class larger than M1 with three or more hard X-ray sources observed simultaneously in the course of the flare. The events were observed with the X-ray satellite RHESSI from February 2002 until July 2005. We used imaging spectroscopy methods to determine the spectral evolution of each source in each event. The images of all of the five events show two sources visible only at high energies (footpoints) and one source only visible at low energies (coronal or looptop source, in two cases situated over the limb). Results: We find soft-hard-soft behavior in both, coronal source and footpoints. The coronal source is nearly always softer than the footpoints. The footpoint spectra differ significantly only in one event out of five. Conclusions: The observations are consistent with acceleration in the coronal source and an intricate connection between the corona and chromosphere.Comment: accepted for publication in A&A, 11 pages, 9 figure

Detection of brain functional-connectivity difference in post-stroke patients using group-level covariance modeling

Functional brain connectivity, as revealed through distant correlations in the signals measured by functional Magnetic Resonance Imaging (fMRI), is a promising source of biomarkers of brain pathologies. However, establishing and using diagnostic markers requires probabilistic inter-subject comparisons. Principled comparison of functional-connectivity structures is still a challenging issue. We give a new matrix-variate probabilistic model suitable for inter-subject comparison of functional connectivity matrices on the manifold of Symmetric Positive Definite (SPD) matrices. We show that this model leads to a new algorithm for principled comparison of connectivity coefficients between pairs of regions. We apply this model to comparing separately post-stroke patients to a group of healthy controls. We find neurologically-relevant connection differences and show that our model is more sensitive that the standard procedure. To the best of our knowledge, these results are the first report of functional connectivity differences between a single-patient and a group and thus establish an important step toward using functional connectivity as a diagnostic tool

Detection of 3-Minute Oscillations in Full-Disk Lyα\alpha Emission During A Solar Flare

In this Letter we report the detection of chromospheric 3-minute oscillations in disk-integrated EUV irradiance observations during a solar flare. A wavelet analysis of detrended Lyman-alpha (from GOES/EUVS) and Lyman continuum (from SDO/EVE) emission from the 2011 February 15 X-class flare (SOL2011-02-15T01:56) revealed a $\sim$3-minute period present during the flare's main phase. The formation temperature of this emission locates this radiation to the flare's chromospheric footpoints, and similar behaviour is found in the SDO/AIA 1600\AA\ and 1700\AA\ channels, which are dominated by chromospheric continuum. The implication is that the chromosphere responds dynamically at its acoustic cutoff frequency to an impulsive injection of energy. Since the 3-minute period was not found at hard X-ray energies (50-100 keV) in RHESSI data we can state that this 3-minute oscillation does not depend on the rate of energization of non-thermal electrons. However, a second period of 120 s found in both hard X-ray and chromospheric emission is consistent with episodic electron energization on 2-minute timescales. Our finding on the 3-minute oscillation suggests that chromospheric mechanical energy should be included in the flare energy budget, and the fluctuations in the Lyman-alpha line may influence the composition and dynamics of planetary atmospheres during periods of high activity.Comment: 6 pages, 5 figures. Accepted for publication in Astrophysics Journal Letter

Observations of the post shock break-out emission of SN 2011dh with XMM-Newton

After the occurrence of the type cIIb SN 2011dh in the nearby spiral galaxy M 51 numerous observations were performed with different telescopes in various bands ranging from radio to gamma-rays. We analysed the XMM-Newton and Swift observations taken 3 to 30 days after the SN explosion to study the X-ray spectrum of SN 2011dh. We extracted spectra from the XMM-Newton observations, which took place ~7 and 11 days after the SN. In addition, we created integrated Swift/XRT spectra of 3 to 10 days and 11 to 30 days. The spectra are well fitted with a power-law spectrum absorbed with Galactic foreground absorption. In addition, we find a harder spectral component in the first XMM-Newton spectrum taken at t ~ 7 d. This component is also detected in the first Swift spectrum of t = 3 - 10 d. While the persistent power-law component can be explained as inverse Compton emission from radio synchrotron emitting electrons, the harder component is most likely bremsstrahlung emission from the shocked stellar wind. Therefore, the harder X-ray emission that fades away after t ~ 10 d can be interpreted as emission from the shocked circumstellar wind of SN 2011dh.Comment: Accepted for publication as a Research Note in Astronomy and Astrophysic

The spectral evolution of impulsive solar X-ray flares

The time evolution of the spectral index and the non-thermal flux in 24 impulsive solar hard X-ray flares of GOES class M was studied in RHESSI observations. The high spectral resolution allows for a clean separation of thermal and non-thermal components in the 10-30 keV range, where most of the non-thermal photons are emitted. Spectral index and flux can thus be determined with much better accuracy than before. The spectral soft-hard-soft behavior in rise-peak-decay phases is discovered not only in the general flare development, but even more pronounced in subpeaks. An empirically found power-law dependence between the spectral index and the normalization of the non-thermal flux holds during the rise and decay phases of the emission peaks. It is still present in the combined set of all flares. We find an asymmetry in this dependence between rise and decay phases of the non-thermal emission. There is no delay between flux peak and spectral index minimum. The soft-hard-soft behavior appears to be an intrinsic signature of the elementary electron acceleration process.Comment: 10 pages, 7 figures. Accepted for publication by A&

Cellular IP₆ Levels Limit HIV Production while Viruses that Cannot Efficiently Package IP₆ Are Attenuated for Infection and Replication

Summary: HIV-1 hijacks host proteins to promote infection. Here we show that HIV is also dependent upon the host metabolite inositol hexakisphosphate (IP6) for viral production and primary cell replication. HIV-1 recruits IP6 into virions using two lysine rings in its immature hexamers. Mutation of either ring inhibits IP6 packaging and reduces viral production. Loss of IP6 also results in virions with highly unstable capsids, leading to a profound loss of reverse transcription and cell infection. Replacement of one ring with a hydrophobic isoleucine core restores viral production, but IP6 incorporation and infection remain impaired, consistent with an independent role for IP6 in stable capsid assembly. Genetic knockout of biosynthetic kinases IPMK and IPPK reveals that cellular IP6 availability limits the production of diverse lentiviruses, but in the absence of IP6, HIV-1 packages IP5 without loss of infectivity. Together, these data suggest that IP6 is a critical cofactor for HIV-1 replication