229 research outputs found
ALMA and VLA Observations of EX Lupi in its Quiescent State
Extreme outbursts in young stars may be a common stage of pre-main-sequence
stellar evolution. These outbursts, caused by enhanced accretion and
accompanied by increased luminosity, can also strongly impact the evolution of
the circumstellar environment. We present ALMA and VLA observations of EX Lupi,
a prototypical outburst system, at 100 GHz, 45 GHz, and 15 GHz. We use these
data, along with archival ALMA 232 GHz data, to fit radiative transfer models
to EX Lupi's circumstellar disk in its quiescent state following the extreme
outburst in 2008. The best fit models show a compact disk with a characteristic
dust radius of 45 au and a total mass of 0.01 M. Our modeling
suggests grain growth to sizes of at least 3 mm in the disk, possibly spurred
by the recent outburst, and an ice line that has migrated inward to
au post-outburst. At 15 GHz, we detected significant emission over the expected
thermal disk emission which we attribute primarily to stellar (gyro)synchrotron
and free-free disk emission. Altogether, these results highlight what may be a
common impact of outbursts on the circumstellar dust.Comment: Accepted to ApJ, 15 pages, 8 figure
MRI-driven Accretion on to Magnetized stars: Global 3D MHD Simulations of Magnetospheric and Boundary Layer Regimes
We discuss results of global 3D MHD simulations of accretion on to a rotating
magnetized star with a tilted dipole magnetic field, where the accretion is
driven by the magneto-rotational instability (MRI). The simulations show that
MRI-driven turbulence develops in the disc, and angular momentum is transported
outwards due primarily to the magnetic stress. The turbulent flow is strongly
inhomogeneous and the densest matter is in azimuthally-stretched turbulent
cells. We investigate two regimes of accretion: a magnetospheric regime and a
boundary layer (BL) regime. In the magnetospheric regime, the accretion disc is
truncated by the star's magnetic field within a few stellar radii from the
star, and matter flows to the star in funnel streams. The funnel streams
flowing towards the south and north magnetic poles but are not equal due to the
inhomogeneity of the flow. In the BL regime, matter accretes to the surface of
the star through the boundary layer. The magnetic field in the inner disc is
strongly amplified by the shear of the accretion flow, and the matter and
magnetic stresses become comparable. Accreting matter forms a belt-shaped
region on the surface of the star. The belt has inhomogeneous density
distribution which varies in time due to variable accretion rate. Results of
simulations can be applied to classical T Tauri stars, accreting brown dwarfs,
millisecond pulsars, dwarf novae cataclysmic variables, and other stars with
magnetospheres smaller than several stellar radii.Comment: 15 pages, 13 figures, accepted by MNRA
A live cell assay of GPCR coupling allows identification of optogenetic tools for controlling Go and Gi signaling
Interplay between n-3 and n-6 long-chain polyunsaturated fatty acids and the endocannabinoid system in brain protection and repair.
The brain is enriched in arachidonic acid (ARA) and docosahexaenoic acid (DHA), long-chain polyunsaturated fatty acids (LCPUFA) of the n-6 and n-3 series, respectively. Both are essential for optimal brain development and function. Dietary enrichment with DHA and other long-chain n-3 PUFA, such as eicosapentaenoic acid (EPA) have shown beneficial effects on learning and memory, neuroinflammatory processes and synaptic plasticity and neurogenesis. ARA, DHA and EPA are precursors to a diverse repertoire of bioactive lipid mediators, including endocannabinoids. The endocannabinoid system comprises cannabinoid receptors, their endogenous ligands, the endocannabinoids, and their biosynthetic and degradation enzymes. Anandamide (AEA) and 2-archidonoylglycerol (2-AG) are the most widely studied endocannabinoids, and are both derived from phospholipid-bound ARA. The endocannabinoid system also has well established roles in neuroinflammation, synaptic plasticity and neurogenesis, suggesting an overlap in the neuroprotective effects observed with these different classes of lipids. Indeed, growing evidence suggests a complex interplay between n-3 and n-6 LCPUFA and the endocannabinoid system. For example, long-term DHA and EPA supplementation reduces AEA and 2-AG levels, with reciprocal increases in levels of the analogous endocannabinoid-like DHA and EPA-derived molecules. This review summarises current evidence of this interplay and discusses the therapeutic potential for brain protection and repair
Postnatal Development of Numbers and Mean Sizes of Pancreatic Islets and Beta-Cells in Healthy Mice and GIPRdn Transgenic Diabetic Mice
The aim of this study was to examine postnatal islet and beta-cell expansion in healthy female control mice and its disturbances in diabetic GIPRdn transgenic mice, which exhibit an early reduction of beta-cell mass. Pancreata of female control and GIPRdn transgenic mice, aged 10, 45, 90 and 180 days were examined, using state-of-the-art quantitative-stereological methods. Total islet and beta-cell volumes, as well as their absolute numbers increased significantly until 90 days in control mice, and remained stable thereafter. The mean islet volumes of controls also increased slightly but significantly between 10 and 45 days of age, and then remained stable until 180 days. The total volume of isolated beta-cells, an indicator of islet neogenesis, and the number of proliferating (BrdU-positive) islet cells were highest in 10-day-old controls and declined significantly between 10 and 45 days. In GIPRdn transgenic mice, the numbers of islets and beta-cells were significantly reduced from 10 days of age onwards vs. controls, and no postnatal expansion of total islet and beta-cell volumes occurred due to a reduction in islet neogenesis whereas early islet-cell proliferation and apoptosis were unchanged as compared to control mice. Insulin secretion in response to pharmacological doses of GIP was preserved in GIPRdn transgenic mice, and serum insulin to pancreatic insulin content in response to GLP-1 and arginine was significantly higher in GIPRdn transgenic mice vs. controls. We could show that the increase in islet number is mainly responsible for expansion of islet and beta-cell mass in healthy control mice. GIPRdn transgenic mice show a disturbed expansion of the endocrine pancreas, due to perturbed islet neogenesis
Cotranslational protein assembly imposes evolutionary constraints on homomeric proteins
Cotranslational protein folding can facilitate rapid formation of functional structures. However, it might also cause premature assembly of protein complexes, if two interacting nascent chains are in close proximity. By analyzing known protein structures, we show that homomeric protein contacts are enriched towards the C-termini of polypeptide chains across diverse proteomes. We hypothesize that this is the result of evolutionary constraints for folding to occur prior to assembly. Using high-throughput imaging of protein homomers in vivo in E. coli and engineered protein constructs with N- and C-terminal oligomerization domains, we show that, indeed, proteins with C-terminal homomeric interface residues consistently assemble more efficiently than those with N-terminal interface residues. Using in vivo, in vitro and in silico experiments, we identify features that govern successful assembly of homomers, which have implications for protein design and expression optimization
Development and organization of polarity-specific segregation of primary vestibular afferent fibers in mice
A striking feature of vestibular hair cells is the polarized arrangement of their stereocilia as the basis for their directional sensitivity. In mammals, each of the vestibular end organs is characterized by a distinct distribution of these polarized cells. We utilized the technique of post-fixation transganglionic neuronal tracing with fluorescent lipid soluble dyes in embryonic and postnatal mice to investigate whether these polarity characteristics correlate with the pattern of connections between the endorgans and their central targets; the vestibular nuclei and cerebellum. We found that the cerebellar and brainstem projections develop independently from each other and have a non-overlapping distribution of neurons and afferents from E11.5 on. In addition, we show that the vestibular fibers projecting to the cerebellum originate preferentially from the lateral half of the utricular macula and the medial half of the saccular macula. In contrast, the brainstem vestibular afferents originate primarily from the medial half of the utricular macula and the lateral half of the saccular macula. This indicates that the line of hair cell polarity reversal within the striola region segregates almost mutually exclusive central projections. A possible interpretation of this feature is that this macular organization provides an inhibitory side-loop through the cerebellum to produce synergistic tuning effects in the vestibular nuclei. The canal cristae project to the brainstem vestibular nuclei and cerebellum, but the projection to the vestibulocerebellum originates preferentially from the superior half of each of the cristae. The reason for this pattern is not clear, but it may compensate for unequal activation of crista hair cells or may be an evolutionary atavism reflecting a different polarity organization in ancestral vertebrate ears
Theoretical Estimation of Vibrational Frequencies Involving Transition Metal Compounds
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