7,574 research outputs found
Two-Gaussian excitations model for the glass transition
We develop a modified "two-state" model with Gaussian widths for the site
energies of both ground and excited states, consistent with expectations for a
disordered system. The thermodynamic properties of the system are analyzed in
configuration space and found to bridge the gap between simple two state models
("logarithmic" model in configuration space) and the random energy model
("Gaussian" model in configuration space). The Kauzmann singularity given by
the random energy model remains for very fragile liquids but is suppressed or
eliminated for stronger liquids. The sharp form of constant volume heat
capacity found by recent simulations for binary mixed Lennard Jones and soft
sphere systems is reproduced by the model, as is the excess entropy and heat
capacity of a variety of laboratory systems, strong and fragile. The ideal
glass in all cases has a narrow Gaussian, almost invariant among molecular and
atomic glassformers, while the excited state Gaussian depends on the system and
its width plays a role in the thermodynamic fragility. The model predicts the
existence of first-order phase transition for fragile liquids.Comment: 12 pages, 12 figure
The ALMA Early Science View of FUor/EXor objects. IV. Misaligned Outflows in the Complex Star-forming Environment of V1647 Ori and McNeil's Nebula
We present Atacama Large Millimeter/sub-millimeter Array (ALMA) observations
of the star-forming environment surrounding V1647 Ori, an outbursting FUor/EXor
pre-MS star. Dust continuum and the (J = 2 - 1) CO, CO, CO
molecular emission lines were observed to characterize the V1647 Ori
circumstellar disc and any large scale molecular features present. We detect
continuum emission from the circumstellar disc and determine a radius r = 40
au, inclination i = 17 and total disc mass of
M of ~0.1 M. We do not identify any disc structures
associated with nearby companions, massive planets or fragmentation. The
molecular cloud environment surrounding V1647 Ori is both structured and
complex. We confirm the presence of an excavated cavity north of V1647 Ori and
have identified dense material at the base of the optical reflection nebula
(McNeil's Nebula) that is actively shaping its surrounding environment. Two
distinct outflows have been detected with dynamical ages of ~11,700 and 17,200
years. These outflows are misaligned suggesting disc precession over ~5500
years as a result of anisotropic accretion events is responsible. The
collimated outflows exhibit velocities of ~2 km s, similar in velocity
to that of other FUor objects presented in this series but significantly slower
than previous observations and model predictions. The V1647 Ori system is
seemingly connected by an "arm" of material to a large unresolved structure
located ~20 to the west. The complex environment surrounding V1647 Ori
suggests it is in the early stages of star formation which may relate to its
classification as both an FUor and EXor type object.Comment: 18 pages, 14 figures, 4 tables; accepted for publication in MNRA
The impact of a large object with Jupiter in July 2009
On 2009 July 19, we observed a single, large impact on Jupiter at a
planetocentric latitude of 55^{\circ}S. This and the Shoemaker-Levy 9 (SL9)
impacts on Jupiter in 1994 are the only planetary-scale impacts ever observed.
The 2009 impact had an entry trajectory opposite and with a lower incidence
angle than that of SL9. Comparison of the initial aerosol cloud debris
properties, spanning 4,800 km east-west and 2,500 km north-south, with those
produced by the SL9 fragments, and dynamical calculations of pre-impact orbit,
indicate that the impactor was most probably an icy body with a size of 0.5-1
km. The collision rate of events of this magnitude may be five to ten times
more frequent than previously thought. The search for unpredicted impacts, such
as the current one, could be best performed in 890-nm and K (2.03-2.36 {\mu}m)
filters in strong gaseous absorption, where the high-altitude aerosols are more
reflective than Jupiter's primary cloud.Comment: 15 pages, 5 figure
The ALMA Early Science View of FUor/EXor Objects - V. Continuum Disc Masses and Sizes
Low-mass stars build a significant fraction of their total mass during short outbursts of enhanced accretion known as FUor and EXor outbursts. FUor objects are characterized by a sudden brightening of ∼5 mag at visible wavelengths within 1 yr and remain bright for decades. EXor objects have lower amplitude outbursts on shorter time-scales. Here we discuss a 1.3 mm Atacama Large Millimeter/submillimeter Array (ALMA) mini-survey of eight outbursting sources (three FUors, four EXors, and the borderline object V1647 Ori) in the Orion Molecular Cloud. While previous papers in this series discuss the remarkable molecular outflows observed in the three FUor objects and V1647 Ori, here we focus on the continuum data and the differences and similarities between the FUor and EXor populations. We find that FUor discs are significantly more massive (∼80–600 MJup) than the EXor objects (∼0.5–40 MJup). We also report that the EXor sources lack the prominent outflows seen in the FUor population. Even though our sample is small, the large differences in disc masses and outflow activity suggest that the two types of objects represent different evolutionary stages. The FUor sources seem to be rather compact (Rc \u3c 20–40 au) and to have a smaller characteristic radius for a given disc mass when compared to T Tauri stars. V1118 Ori, the only known close binary system in our sample, is shown to host a disc around each one of the stellar components. The disc around HBC 494 is asymmetric, hinting at a structure in the outer disc or the presence of a second disc
Emitted Power Of Jupiter Based On Cassini CIRS And VIMS Observations
The emitted power of Jupiter and its meridional distribution are determined from observations by the Composite Infrared Spectrometer (CIRS) and Visual and Infrared Spectrometer (VIMS) onboard Cassini during its flyby en route to Saturn in late 2000 and early 2001. Jupiter's global- average emitted power and effective temperature are measured to be 14.10+/-0.03 W/sq m and 125.57+/-0.07 K, respectively. On a global scale, Jupiter's 5-micron thermal emission contributes approx. 0.7+/-0.1 % to the total emitted power at the global scale, but it can reach approx. 1.9+/-0.6% at 15degN. The meridional distribution of emitted power shows a significant asymmetry between the two hemispheres with the emitted power in the northern hemisphere 3.0+/-0.3% larger than that in the southern hemisphere. Such an asymmetry shown in the Cassini epoch (2000-01) is not present during the Voyager epoch (1979). In addition, the global-average emitted power increased approx. 3.8+/-1.0% between the two epochs. The temporal variation of Jupiter's total emitted power is mainly due to the warming of atmospheric layers around the pressure level of 200 mbar. The temporal variation of emitted power was also discovered on Saturn (Li et al., 2010). Therefore, we suggest that the varying emitted power is a common phenomenon on the giant planets
Molecular adaptations of the blood–brain barrier promote stress resilience vs. depression
Preclinical and clinical studies suggest that inflammation and
vascular dysfunction contribute to the pathogenesis of major
depressive disorder (MDD). Chronic social stress alters blood–brain
barrier (BBB) integrity through loss of tight junction protein
claudin-5 (cldn5) in male mice, promoting passage of circulating
proinflammatory cytokines and depression-like behaviors. This effect is prominent within the nucleus accumbens, a brain region
associated with mood regulation; however, the mechanisms involved are unclear. Moreover, compensatory responses leading
to proper behavioral strategies and active resilience are unknown.
Here we identify active molecular changes within the BBB associated with stress resilience that might serve a protective role for
the neurovasculature. We also confirm the relevance of such
changes to human depression and antidepressant treatment. We
show that permissive epigenetic regulation of cldn5 expression
and low endothelium expression of repressive cldn5-related transcription factor foxo1 are associated with stress resilience. Regionand endothelial cell-specific whole transcriptomic analyses revealed
molecular signatures associated with stress vulnerability vs. resilience. We identified proinflammatory TNFα/NFκB signaling and
hdac1 as mediators of stress susceptibility. Pharmacological inhibition of stress-induced increase in hdac1 activity rescued cldn5 expression in the NAc and promoted resilience. Importantly, we
confirmed changes in HDAC1 expression in the NAc of depressed
patients without antidepressant treatment in line with CLDN5 loss.
Conversely, many of these deleterious CLDN5-related molecular
changes were reduced in postmortem NAc from antidepressanttreated subjects. These findings reinforce the importance of considering stress-induced neurovascular pathology in depression
and provide therapeutic targets to treat this mood disorder
and promote resilience
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