534 research outputs found
Structure of Titan â s induced magnetosphere under varying background magnetic fi eld conditions: Survey of Cassini magnetometer data from fl ybys TA â T85
Cassini magnetic field observations between 2004 and 2012 suggest the ambient field conditions near Titanâs orbit to differ significantly from the frequently applied pre-Cassini picture (background magnetic field homogeneous and perpendicular to Titanâs orbital plane, stationary upstream conditions). In this study, we analyze the impact of these varying background field conditions on the structure of Titanâs induced magnetosphere by conducting a systematic survey of Cassini magnetic field observations in the interaction region during flybys TAâT85 (July 2004âJuly 2012). We introduce a set of criteria that allow to identify deviations in the structure of Titanâs induced magnetosphereâas seen by the Cassini magnetometer (MAG)âfrom the picture of steady-state field line draping. These disruptions are classified as âweakâ, âmoderateâ, or âstrongâ. After applying this classification scheme to all available Titan encounters, we survey the data for a possible correlation between the disruptions of the draping pattern and the ambient magnetospheric field conditions, as characterized by Simon et al. [2010a]. Our major findings are: (1) When Cassini is embedded in the northern or southern lobe of Saturnâs magnetodisk within a ` 3 h interval around closest approach, Titanâs induced magnetosphere shows little or no deviations at all from the steady-state draping picture. (2) Even when Titan is embedded in perturbed current sheet fields during an encounter, the notion of draping the average background field around the moonâs ionosphere is still applicable to explain MAG observations from numerous Titan flybys. (3) Only when Titan is exposed to intense north- south oscillations of Saturnâs current sheet at the time of an encounter, the signatures of the moonâs induced magnetosphere may be completely obscured by the ambient field perturbations. (4) So far, T70 is the only flyby that fully meets the idealized pre-Cassini picture of the Titan interaction (steady background field perpendicular to Titanâs orbital plane, steady upstream flow, unperturbed induced magnetosphere).Fil: Simon, Sven. University of Cologne. Institute of Geophysics and Meteorology; AlemaniaFil: van Treeck, Shari C.. University of Cologne. Institute of Geophysics and Meteorology; AlemaniaFil: Wennmacher, Alexandre. University of Cologne. Institute of Geophysics and Meteorology; AlemaniaFil: Saur, Joachim. University of Cologne. Institute of Geophysics and Meteorology; AlemaniaFil: Neubauer, Fritz M.. University of Cologne. Institute of Geophysics and Meteorology; AlemaniaFil: Bertucci, Cesar. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Oficina de CoordinaciĂłn Administrativa Ciudad Universitaria. Instituto de AstronomĂa y FĂsica del Espacio(i); ArgentinaFil: Dougherty, Michele K.. Imperial College Of Science And Technology. Space and Atmospheric Physics Group; Reino Unid
ROSAT X-ray sources in the field of the LMC I.Total LMC gas from the background AGN spectral fits
We analyzed a sample of 26 background X-ray sources in a ~60 square degree
field of the Large Magellanic Cloud observed with the ROSAT PSPC. The sample
has been selected from previously classified and optically identified X-ray
sources. In addition pointlike and spectrally hard sources with at least 100 to
200 observed counts have been used for the analysis. We performed X-ray
spectral fitting and derived total hydrogen absorbing column densities due to
LMC gas in the range 10^20 - 2. 10^21 cm^-2. We compared these columns with the
HI columns derived from a 21-cm Parkes survey of the LMC. For 7 optically
identified sources we find, within the uncertainties derived from the X-ray
spectral fit, agreement for both columns. For further 19 sources we constrain
the LMC columns from the X-ray spectral fit assuming that the powerlaw photon
index is that of AGN type spectra. We derive for 20 sources gas columns which
are within the uncertainties in agreement with the HI columns. We derive for
two background sources (RX J0536.9-6913 and RX J0547.0-7040) hydrogen absorbing
column densities due to LMC gas, which are in excess to the HI columns. These
sources - located in regions of large (~3. 10^21 cm^-2) LMC HI column densities
- could be seen through additional gas which may be warm and diffuse, cold or
molecular. For 10 sources we derive upper limits for the gas columns additional
to HI and constrain the molecular mass fraction to <(30-140)%.Comment: Accepted by A&
Interleukin-7 deficiency in rheumatoid arthritis: consequences for therapy-induced lymphopenia
We previously demonstrated prolonged, profound CD4+ T-lymphopenia in rheumatoid arthritis (RA) patients following lymphocyte-depleting therapy. Poor reconstitution could result either from reduced de novo T-cell production through the thymus or from poor peripheral expansion of residual T-cells. Interleukin-7 (IL-7) is known to stimulate the thymus to produce new T-cells and to allow circulating mature T-cells to expand, thereby playing a critical role in T-cell homeostasis. In the present study we demonstrated reduced levels of circulating IL-7 in a cross-section of RA patients. IL-7 production by bone marrow stromal cell cultures was also compromised in RA. To investigate whether such an IL-7 deficiency could account for the prolonged lymphopenia observed in RA following therapeutic lymphodepletion, we compared RA patients and patients with solid cancers treated with high-dose chemotherapy and autologous progenitor cell rescue. Chemotherapy rendered all patients similarly lymphopenic, but this was sustained in RA patients at 12 months, as compared with the reconstitution that occurred in cancer patients by 3â4 months. Both cohorts produced naĂŻve T-cells containing T-cell receptor excision circles. The main distinguishing feature between the groups was a failure to expand peripheral T-cells in RA, particularly memory cells during the first 3 months after treatment. Most importantly, there was no increase in serum IL-7 levels in RA, as compared with a fourfold rise in non-RA control individuals at the time of lymphopenia. Our data therefore suggest that RA patients are relatively IL-7 deficient and that this deficiency is likely to be an important contributing factor to poor early T-cell reconstitution in RA following therapeutic lymphodepletion. Furthermore, in RA patients with stable, well controlled disease, IL-7 levels were positively correlated with the T-cell receptor excision circle content of CD4+ T-cells, demonstrating a direct effect of IL-7 on thymic activity in this cohort
Timeâdependent global MHD simulations of Cassini T32 flyby: From magnetosphere to magnetosheath
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95383/1/jgra19655.pd
The Sunyaev-Zel'dovich effect in WMAP data
Using WMAP 5 year data, we look for the average Sunyaev-Zel'dovich effect
(SZE) signal from clusters of galaxies by stacking the regions around hundreds
of known X-ray clusters. We detect the average SZE at a very high significance
level. The average cluster signal is spatially resolved in the W band. This
mean signal is compared with the expected signal from the same clusters
calculated on the basis of archival ROSAT data. From the comparison we conclude
that the observed SZE seems to be less than the expected signal derived from
X-ray measurements when a standard beta-model is assumed for the gas
distribution. This conclusion is model dependent. Our predictions depend mostly
on the assumptions made about the core radius of clusters and the slope of the
gas density profile. Models with steeper profiles are able to simultaneously
fit both X-ray and WMAP data better than a beta-model. However, the agreement
is not perfect and we find that it is still difficult to make the X-ray and SZE
results agree. A model assuming point source contamination in SZE clusters
renders a better fit to the one-dimensional SZE profiles thus suggesting that
contamination from point sources could be contributing to a diminution of the
SZE signal. Selecting a model that better fits both X-ray and WMAP data away
from the very central region, we estimate the level of contamination and find
that on average, the point source contamination is on the level of 16 mJy (at
41 GHz), 26 mJy (at 61 GHz) and 18 mJy (at 94 GHz). These estimated fluxes are
marginally consistent with the estimated contamination derived from radio and
infrared surveys thus suggesting that the combination of a steeper gas profile
and the contribution from point sources allows us to consistently explain the
X-ray emission and SZE in galaxy clusters as measured by ROSAT and WMAP.Comment: 17 pages and 17 figures. Submited to MNRA
Triticum durum metallothionein: isolation of the gene and structural characterization of the protein using solution scattering and molecular modeling
A novel gene sequence, with two exons and one intron, encoding a metallothionein (MT) has been identified in durum wheat Triticum durum cv. Balcali85 genomic DNA. Multiple alignment analyses on the cDNA and the translated protein sequences showed that T. durum MT (dMT) can be classified as a type 1 MT. dMT has three Cys-X-Cys motifs in each of the N- and C-terminal domains and a 42-residue-long hinge region devoid of cysteines. dMT was overexpressed in Escherichia coli as a fusion protein (GSTdMT), and bacteria expressing the fusion protein showed increased tolerance to cadmium in the growth medium compared with controls. Purified GSTdMT was characterized by SDS- and native-PAGE, size exclusion chromatography, and matrix-assisted laser desorption ionization time-of-flight mass spectrometry. It was shown that the recombinant protein binds 4 ± 1 mol of cadmium/mol of protein and has a high tendency to form stable oligomeric structures. The structure of GSTdMT and dMT was investigated by synchrotron x-ray solution scattering and computational methods. X-ray scattering measurements indicated a strong tendency for GSTdMT to form dimers and trimers in solution and yielded structural models that were compatible with a stable dimeric form in which dMT had an extended conformation. Results of homology modeling and ab initio solution scattering approaches produced an elongated dMT structure with a long central hinge region. The predicted model and those obtained from x-ray scattering are in agreement and suggest that dMT may be involved in functions other than metal detoxification
Discovery of X-rays from Venus with Chandra
On January 10 and 13, 2001, Venus was observed for the first time with an
X-ray astronomy satellite. The observation, performed with the ACIS-I and
LETG/ACIS-S instruments on Chandra, yielded data of high spatial, spectral, and
temporal resolution. Venus is clearly detected as a half-lit crescent, with
considerable brightening on the sunward limb. The morphology agrees well with
that expected from fluorescent scattering of solar X-rays in the planetary
atmosphere. The radiation is observed at discrete energies, mainly at the
O-K_alpha energy of 0.53 keV. Fluorescent radiation is also detected from
C-K_alpha at 0.28 keV and, marginally, from N-K_alpha at 0.40 keV. An
additional emission line is indicated at 0.29 keV, which might be the signature
of the C 1s --> pi* transition in CO_2 and CO. Evidence for temporal
variability of the X-ray flux was found at the 2.6 sigma level, with
fluctuations by factors of a few times indicated on time scales of minutes. All
these findings are fully consistent with fluorescent scattering of solar
X-rays. No other source of X-ray emission was detected, in particular none from
charge exchange interactions between highly charged heavy solar wind ions and
atmospheric neutrals, the dominant process for the X-ray emission of comets.
This is in agreement with the sensitivity of the observation.Comment: 12 pages, 9 figure
AMPK activation protects against diet induced obesity through Ucp1-independent thermogenesis in subcutaneous white adipose tissue
Obesity results from a chronic imbalance between energy intake and energy output but remains difficult to prevent or treat in humans. Adenosine monophosphate (AMP)-activated protein kinase (AMPK) is an important regulator of energy homeostasis1,2,3 and is a molecular target of drugs used for the treatment of metabolic diseases, including obesity4,5. Here we show that mice expressing a gain-of-function AMPK mutant6 display a change in morphology of subcutaneous white adipocytes that is reminiscent of browning. However, despite a dramatic increase in mitochondrial content, Ucp1 expression is undetectable in these adipocytes. In response to a high-fat diet (HFD), expression of skeletal muscleâassociated genes is induced in subcutaneous white adipocytes from the gain-of-function AMPK mutant mice. Chronic genetic AMPK activation results in protection against diet-induced obesity due to an increase in whole-body energy expenditure, most probably because of a substantial increase in the oxygen consumption rate of white adipose tissue. These results suggest that AMPK activation enriches, or leads to the emergence of, a population of subcutaneous white adipocytes that produce heat via Ucp1-independent uncoupling of adenosine triphosphate (ATP) production on a HFD. Our findings indicate that AMPK activation specifically in adipose tissue may have therapeutic potential for the treatment of obesity
Visual adaptation alters the apparent speed of real-world actions
The apparent physical speed of an object in the field of view remains constant despite variations in retinal velocity due to viewing conditions (velocity constancy). For example, people and cars appear to move across the field of view at the same objective speed regardless of distance. In this study a series of experiments investigated the visual processes underpinning judgements of objective speed using an adaptation paradigm and video recordings of natural human locomotion. Viewing a video played in slow-motion for 30seconds caused participants to perceive subsequently viewed clips played at standard speed as too fast, so playback had to be slowed down in order for it to appear natural; conversely after viewing fast-forward videos for 30seconds, playback had to be speeded up in order to appear natural. The perceived speed of locomotion shifted towards the speed depicted in the adapting video (âre-normalisationâ). Results were qualitatively different from those obtained in previously reported studies of retinal velocity adaptation. Adapting videos that were scrambled to remove recognizable human figures or coherent motion caused significant, though smaller shifts in apparent locomotion speed, indicating that both low-level and high-level visual properties of the adapting stimulus contributed to the changes in apparent speed
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