Mass and spin co-evolution during the alignment of a black hole in a warped accretion disc

In this paper, we explore the gravitomagnetic interaction of a black hole (BH) with a misaligned accretion disc to study BH spin precession and alignment jointly with BH mass M BH and spin parameter a evolution, under the assumption that the disc is continually fed, in its outer region, by matter with angular momentum fixed on a given direction . We develop an iterative scheme based on the adiabatic approximation to study the BH–disc co-evolution: in this approach, the accretion disc transits through a sequence of quasi-steady warped states (Bardeen–Petterson effect) and interacts with the BH until the spin J BH aligns with . For a BH aligning with a corotating disc, the fractional increase in mass is typically less than a few per cent, while the spin modulus can increase up to a few tens of per cent. The alignment time-scale is of ∼10 5 –10 6 yr for a maximally rotating BH accreting at the Eddington rate. BH–disc alignment from an initially counter-rotating disc tends to be more efficient compared to the specular corotating case due to the asymmetry seeded in the Kerr metric: counter-rotating matter carries a larger and opposite angular momentum when crossing the innermost stable orbit, so that the spin modulus decreases faster and so the relative inclination angle.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/74763/1/j.1365-2966.2009.15427.x.pd

Transcriptomic and Epigenetic Regulation of Disuse Atrophy and the Return to Activity in Skeletal Muscle

Physical inactivity and disuse are major contributors to age-related muscle loss. Denervation of skeletal muscle has been previously used as a model with which to investigate muscle atrophy following disuse. Although gene regulatory networks that control skeletal muscle atrophy after denervation have been established, the transcriptome in response to the recovery of muscle after disuse and the associated epigenetic mechanisms that may function to modulate gene expression during skeletal muscle atrophy or recovery have yet to be investigated. We report that silencing the tibialis anterior muscle in rats with tetrodotoxin (TTX)—administered to the common peroneal nerve—resulted in reductions in muscle mass of 7, 29, and 51% with corresponding reductions in muscle fiber cross-sectional area of 18, 42, and 69% after 3, 7, and 14 d of TTX, respectively. Of importance, 7 d of recovery, during which rodents resumed habitual physical activity, restored muscle mass from a reduction of 51% after 14 d TTX to a reduction of only 24% compared with sham control. Returning muscle mass to levels observed at 7 d TTX administration (29% reduction). Transcriptome-wide analysis demonstrated that 3714 genes were differentially expressed across all conditions at a significance of P ≤ 0.001 after disuse-induced atrophy. Of interest, after 7 d of recovery, the expression of genes that were most changed during TTX had returned to that of the sham control. The 20 most differentially expressed genes after microarray analysis were identified across all conditions and were cross-referenced with the most frequently occurring differentially expressed genes between conditions. This gene subset included myogenin (MyoG), Hdac4, Ampd3, Trim63 (MuRF1), and acetylcholine receptor subunit α1 (Chrna1). Transcript expression of these genes and Fboxo32 (MAFbx), because of its previously identified role in disuse atrophy together with Trim63 (MuRF1), were confirmed by real-time quantitative RT-PCR, and DNA methylation of their promoter regions was analyzed by PCR and pyrosequencing. MyoG, Trim63 (MuRF1), Fbxo32 (MAFbx), and Chrna1 demonstrated significantly decreased DNA methylation at key time points after disuse-induced atrophy that corresponded with significantly increased gene expression. Of importance, after TTX cessation and 7 d of recovery, there was a marked increase in the DNA methylation profiles of Trim63 (MuRF1) and Chrna1 back to control levels. This also corresponded with the return of gene expression in the recovery group back to baseline expression observed in sham-operated controls. To our knowledge, this is the first study to demonstrate that skeletal muscle atrophy in response to disuse is accompanied by dynamic epigenetic modifications that are associated with alterations in gene expression, and that these epigenetic modifications and gene expression profiles are reversible after skeletal muscle returns to normal activity

The chlL ( frxC ) gene: Phylogenetic distribution in vascular plants and DNA sequence from Polystichum acrostichoides ( Pteridophyta ) and Synechococcus sp. 7002 ( Cyanobacteria )

We examined chlL ( frxC ) gene evolution using several approaches. Sequences from the chloroplast genome of the fern Polystichum acrostichoides and from the cyanobacterium Synechococcus sp. 7002 were determined and found to be highly conserved. A complete physical map of the fern chloroplast genome and partial maps of other vascular plant taxa show that chlL is located primarily in the small single copy region as in Marchantia polymorpha. A survey of a wide variety of non-angiospermous vascular plant DNAs shows that chlL is widely distributed but has been lost in the pteridophyte Psilotum and (presumably independently) within the Gnetalean gymnosperms.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/41636/1/606_2004_Article_BF00994092.pd

Study of the high pressure effect on nanoparticles GdVO4: Eu3+optical properties

This study considers the effects of hydrostatic pressure on the line position and fluorescence lifetime \u3c4 for 5D0 \u2192 7F2 transitions in GdVO4: Eu3+ nanocrystals. The results indicate that the pressure induced the red shift toward longer wavelengths for all the considered lines with different rate. The fluorescence lifetime \u3c4 nonlinearly decreases with pressure in the considered pressure range. High pressure induced the fluorescence lifetime \u3c4 that can be explained with a simple theoretical model. The measured line position and \u3c4 are in a satisfactory agreement with the theoretical calculations

Calculations of free energy barriers for local mechanisms of hydrogen diffusion in alanates

Brute force histogram calculation and a recently developed method to efficiently reconstruct the free energy profile of complex systems ( the single-sweep method) are combined with ab initio molecular dynamics to study possible local mechanisms for the diffusion of hydrogen in sodium alanates. These compounds may help to understand key properties of solid state hydrogen storage materials. In this work, the identity of a mobile species observed in experiments characterizing the first dissociation reaction of sodium alanates is investigated. The activation barrier of two suggested processes for hydrogen diffusion in Na(3)AlH(6) is evaluated and, by comparing our results with available experimental information, we are able to discriminate among them and to show that one is compatible with the observed signal while the other is not

Calculations of free energy barriers for local mechanisms of hydrogen diffusion in alanates

Brute force histogram calculation and a recently developed method to efficiently reconstruct the free energy profile of complex systems (the single-sweep method) are combined with ab initio molecular dynamics to study possible local mechanisms for the diffusion of hydrogen in sodium alanates. These compounds may help to understand key properties of solid state hydrogen storage materials. In this work, the identity of a mobile species observed in experiments characterizing the first dissociation reaction of sodium alanates is investigated. The activation barrier of two suggested processes for hydrogen diffusion in Na3AlH6 is evaluated and, by comparing our results with available experimental information, we are able to discriminate among them and to show that one is compatible with the observed signal while the other is not