282 research outputs found
Spectroscopic Signatures of the Tidal Disruption of Stars by Massive Black Holes
During the tidal disruption of a star by a massive black hole (BH) of mass
MBH <~ 10^7 Msun, stellar debris falls back to the BH at a rate well above the
Eddington rate. A fraction of this gas is subsequently blown away from the BH,
producing an optically bright flare of radiation. We predict the spectra and
spectral evolution of tidal disruption events, focusing on the photoionized gas
outside this outflow's photosphere. The spectrum will show absorption lines
that are strongly blueshifted relative to the host galaxy, very broad
(0.01-0.1c), and strongest at UV wavelengths (e.g., C IV, Ly alpha, O VI),
lasting ~ 1 month for a 10^6 Msun BH. Meanwhile, supernovae in galactic nuclei
are a significant source of confusion in optical surveys for tidal disruption
events: we estimate that nuclear Type Ia supernovae are two orders of magnitude
more common than tidal disruption events at z ~ 0.1 for ground-based surveys.
Nuclear Type II supernovae occur at a comparable rate but can be excluded by
pre-selecting red galaxies. Supernova contamination can be reduced to a
manageable level using high-resolution follow-up imaging with adaptive optics
or the Hubble Space Telescope. Our predictions should help optical transient
surveys capitalize on their potential for discovering tidal disruption events.Comment: 14 pages, 5 figures; accepted for publication in MNRAS; some added
discussion in Section
A stochastic movement simulator improves estimates of landscape connectivity
Acknowledgments This publication issued from the project TenLamas funded by the French MinistĂšre de l'Energie, de l'Ecologie, du DĂ©veloppement Durable et de la Mer through the EU FP6 BiodivERsA Eranet; by the Agence Nationale de la Recherche (ANR) through the open call INDHET and 6th extinction MOBIGEN to V. M. Stevens, M. Baguette, and A. Coulon, and young researcher GEMS (ANR-13-JSV7-0010-01) to V. M. Stevens and M. Baguette; and by a VLIR-VLADOC scholarship awarded to J. Aben. L. Lens, J. Aben, D. Strubbe, and E. Matthysen are grateful to the Research Foundation Flanders (FWO) for financial support of fieldwork and genetic analysis (grant G.0308.13). V. M. Stevens and M. Baguette are members of the âLaboratoire d'Excellenceâ (LABEX) entitled TULIP (ANR-10-LABX-41). J. M. J. Travis and S. C. F. Palmer also acknowledge the support of NERC. A. Coulon and J. Aben contributed equally to the work.Peer reviewedPublisher PD
Overfeeding, Autonomic Regulation and Metabolic Consequences
The autonomic nervous system plays an important role in the regulation of body processes in health and disease. Overfeeding and obesity (a disproportional increase of the fat mass of the body) are often accompanied by alterations in both sympathetic and parasympathetic autonomic functions. The overfeeding-induced changes in autonomic outflow occur with typical symptoms such as adiposity and hyperinsulinemia. There might be a causal relationship between autonomic disturbances and the consequences of overfeeding and obesity. Therefore studies were designed to investigate autonomic functioning in experimentally and genetically hyperphagic rats. Special emphasis was given to the processes that are involved in the regulation of peripheral energy substrate homeostasis. The data revealed that overfeeding is accompanied by increased parasympathetic outflow. Typical indices of vagal activity (such as the cephalic insulin release during food ingestion) were increased in all our rat models for hyperphagia. Overfeeding was also accompanied by increased sympathetic tone, reflected by enhanced baseline plasma norepinephrine (NE) levels in both VMH-lesioned animals and rats rendered obese by hyperalimentation. Plasma levels of NE during exercise were, however, reduced in these two groups of animals. This diminished increase in the exercise-induced NE outflow could be normalized by prior food deprivation. It was concluded from these experiments that overfeeding is associated with increased parasympathetic and sympathetic tone. In models for hyperphagia that display a continuously elevated nutrient intake such as the VMH-lesioned and the overfed rat, this increased sympathetic tone was accompanied by a diminished NE response to exercise. This attenuated outflow of NE was directly related to the size of the fat reserves, indicating that the feedback mechanism from the periphery to the central nervous system is altered in the overfed state.
Inverse Layer Dependence of Friction on Chemically Doped MoS_{2}
We present the results of atomic-force-microscopy-based friction measurements
on Re-doped molybdenum disulfide (MoS2). In stark contrast to the seemingly
universal observation of decreasing friction with increasing number of layers
on two-dimensional (2D) materials, friction on Re-doped MoS2 exhibits an
anomalous, i.e. inverse dependency on the number of layers. Raman spectroscopy
measurements revealed signatures of Re intercalation, leading to a decoupling
between neighboring MoS2 layers and enhanced electron-phonon interactions, thus
resulting in increasing friction with increasing number of layers: a new
paradigm in the mechanics of 2D materials.Comment: 15 pages incl. Supplemental Material, 5 figure
Barred Galaxies at z > 0.7: NICMOS HDFN Observations
Previous optical studies found an unexpected deficit of bars at z > 0.7. To
investigate the effects of bandshifting, we have studied the fraction of barred
spirals in the NICMOS Deep Field North. At z > 0.7 we find at least four barred
spirals, doubling the number previously detected. The number of barred galaxies
is small because these (and previous) data lack adequate spatial resolution. A
typical 5 kpc bar at z > 0.7 is only marginally detectable for WFPC2 at
0.8microns; the NICMOS data have even lower resolution and can only find the
largest bars. The average size of the four bars seen at z > 0.7 is 12 kpc. The
fraction of such large bars (4/95) is higher than that seen in nearby spirals
(1/44); all known selection effects suggest that the observed fraction is a
lower limit. However, important caveats such as small numbers and difficulties
in defining comparable samples at high and low redshifts should be noted. We
conclude that there is no significant evidence for a decrease in the fraction
of barred spirals beyond z ~ 0.7.Comment: Accepted for publication in ApJ Letters, 4 pages in emulate-apj
style, includes 3 figure
Galanin in the PVN increases nutrient intake and changes peripheral honnone levels in the rat
Abstract In self-selection feeding paradigms, rats display differential patterns of nutrient (protein, carbohydrate or fat) intake. Factors known to influence this selection include brain peptides as well as circadian parameters. In this series of experiments we investigated the role of PVN galanin in nutrient intake during the early and late dark periods in the rat. Rats were allowed to select between three isocaloric diets enriched in protein, carbohydrate or fat. Following a 2-week adaptation period, the animals' 24-h intake was monitored for 4 weeks. Galanin was injected into the PVN and food intake was measured 1, 2 and 24 h post-injection. Galanin significantly increased the 1 h total food intake but it failed to increase the intake of any particular nutrient. Galanin had no effect 2 or 24 h post-injection. Analysis of the data grouped by preference based on the rats 24 h baseline selection patterns over the 4-week period revealed that galanin seem to increase the preferred nutrient. That is, galanin preferentially increased the intake of the carbohydrate-or fatrich diet in animals with high (over 40% of the total food intake) 24-h baselines in this particular nutrient. Finally, analysis of the plasma hormone levels after paraventricular galanin administration revealed a significant increase in noradrenaline levels, a small reduction in plasma insulin with no effects on adrenaline, glucose or corticosterone. The data revealed that galanin in the PVN influences both food intake and metabolic functioning. PVN galanin significantly increases sympathetic outflow and seems to stimulate the intake of the individual rat's preferred macronutrient
- âŠ