586 research outputs found
Repeated X-ray Flaring Activity in Sagittarius A*
Investigating the spectral and temporal characteristics of the X-rays coming
from Sagittarius A* (Sgr A*) is essential to our development of a more complete
understanding of the emission mechanisms in this supermassive black hole
located at the center of our Galaxy. Several X-ray flares with varying
durations and spectral features have already been observed from this object.
Here we present the results of two long XMM-Newton observations of the Galactic
nucleus carried out in 2004, for a total exposure time of nearly 500 ks. During
these observations we detected two flares from Sgr A* with peak 2-10 keV
luminosities about 40 times (L ~ 9x10^34 erg s−1) above the quiescent
luminosity: one on 2004 March 31 and another on 2004 August 31. The first flare
lasted about 2.5 ks and the second about 5 ks. The combined fit on the Epic
spectra yield photon indeces of about 1.5 and 1.9 for the first and second
flare respectively. This hard photon index strongly suggests the presence of an
important population of non-thermal electrons during the event and supports the
view that the majority of flaring events tend to be hard and not very luminous.Comment: 8 pages, 7 figures, Accepted for publication in the Astrophysical
Journa
Comparison of splice sites in mammals and chicken.
We have carried out an initial analysis of the dynamics of the recent evolution of the splice-sites sequences on a large collection of human, rodent (mouse and rat), and chicken introns. Our results indicate that the sequences of splice sites are largely homogeneous within tetrapoda. We have also found that orthologous splice signals between human and rodents and within rodents are more conserved than unrelated splice sites, but the additional conservation can be explained mostly by background intron conservation. In contrast, additional conservation over background is detectable in orthologous mammalian and chicken splice sites. Our results also indicate that the U2 and U12 intron classes seem to have evolved independently since the split of mammals and birds; we have not been able to find a convincing case of interconversion between these two classes in our collections of orthologous introns. Similarly, we have not found a single case of switching between AT-AC and GT-AG subtypes within U12 introns, suggesting that this event has been a rare occurrence in recent evolutionary times. Switching between GT-AG and the noncanonical GC-AG U2 subtypes, on the contrary, does not appear to be unusual; in particular, T to C mutations appear to be relatively well tolerated in GT-AG introns with very strong donor sites
Increased net muscle protein balance in response to simultaneous and separate ingestion of carbohydrate and essential amino acids following resistance exercise
Relative to essential amino acids (EAAs), carbohydrate (CHO) ingestion stimulates a delayed response of net muscle protein balance (NBAL). We investigated if staggered ingestion of CHO and EAA would superimpose the response of NBAL following resistance exercise, thus resulting in maximal anabolic stimulation. Eight recreationally trained subjects completed 2 trials: combined (COMB - drink 1, CHO+EAA; drink 2, placebo) and separated (SEP - drink 1, CHO; drink 2, EAA) post-exercise ingestion of CHO and EAA. Drink 1 was administered 1 h following an acute exercise bout and was followed 1 h later by drink 2. A primed, continuous infusion of l-[ring-13C6]-phenylalanine was combined with femoral arteriovenous sampling and muscle biopsies for the determination of muscle protein kinetics. Arterial amino acid concentrations increased following ingestion of EAA in both conditions. No difference between conditions was observed for phenylalanine delivery to the leg (COMB: 167 ± 23 μmol·min-1·(100 mL leg vol)-1 × 6 h; SEP: 167 ± 21 μmol·min-1·(100 mL leg vol)-1 × 6 h, P > 0.05). In the first hour following ingestion of the drink containing EAA, phenylalanine uptake was 50% greater for the SEP trial than the COMB trial. However, phenylalanine uptake was similar for COMB (110 ± 19 mg) and SEP (117 ± 24 mg) over the 6 h period. These data suggest that whereas separation of CHO and EAA ingestion following exercise may have a transient physiological impact on NBAL, this response is not reflected over a longer period. Thus, separation of CHO and EAA ingestion is unnecessary to optimize post-exercise muscle protein metabolism
Differentiable Simulator For Dynamic & Stochastic Optimal Gas & Power Flows
In many power systems, particularly those isolated from larger
intercontinental grids, operational dependence on natural gas becomes pivotal,
especially during fluctuations or unavailability of renewables coupled with
uncertain consumption patterns. Efficient orchestration and inventive
strategies are imperative for the smooth functioning of these standalone
gas-grid systems. This paper delves into the challenge of synchronized dynamic
and stochastic optimization for independent transmission-level gas-grid
systems. Our approach's novelty lies in amalgamating the staggered-grid method
for the direct assimilation of gas-flow PDEs with an automated sensitivity
analysis facilitated by SciML/Julia, further enhanced by an intuitive linkage
between gas and power grids via nodal flows. We initiate with a single pipe to
establish a versatile and expandable methodology, later showcasing its
effectiveness with increasingly intricate examples.Comment: 7 pages, 7 figures, submitted to PSCC 202
System-Wide Emergency Policy for Transitioning from Main to Secondary Fuel
Inspired by the challenges of running the Israel's power system -- with its
increasing integration of renewables, significant load uncertainty, and primary
reliance on natural gas -- we investigate an emergency scenario where there's a
need to transition temporarily to a pricier secondary fuel until the emergency
resolves. Our objective is to devise tools that can assist power system
operators in making decisions during such critical periods. We frame this
challenge as a Markov Decision Process (MDP) optimization, considering
uncertainties like potential failures of dual-fuel generators during the
transition, operator attentiveness under stress, available but finite amount of
primary fuel (linepack available in the natural gas part of the system), power
forecast (net demand after renewable production), and the cost implications of
unavoidable load shedding. By solving the MDP in a simplified context, we
identify viable policies through simulations of multiple parametrized Markov
Processes (MPs). We verify our methodology using a realistic open-source model
replicating Israel's power-gas infrastructure and outline next steps for
refining and adapting this approach.Comment: 7 pages, 6 figure
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Managing Persistent Hypoxemia: what is new?
Mechanical ventilation is the standard life-support technique for patients with severe acute respiratory failure. However, some patients develop persistent and refractory hypoxemia because their lungs are so severely damaged that they are unable to respond to the application of high inspired oxygen concentration and high levels of positive end-expiratory pressure. In this article, we review current knowledge on managing persistent hypoxemia in patients with injured lungs
The PDF4LHC report on PDFs and LHC data: Results from Run I and preparation for Run II
The accurate determination of the Parton Distribution Functions (PDFs) of the
proton is an essential ingredient of the Large Hadron Collider (LHC) program.
PDF uncertainties impact a wide range of processes, from Higgs boson
characterisation and precision Standard Model measurements to New Physics
searches. A major recent development in modern PDF analyses has been to exploit
the wealth of new information contained in precision measurements from the LHC
Run I, as well as progress in tools and methods to include these data in PDF
fits. In this report we summarise the information that PDF-sensitive
measurements at the LHC have provided so far, and review the prospects for
further constraining PDFs with data from the recently started Run II. This
document aims to provide useful input to the LHC collaborations to prioritise
their PDF-sensitive measurements at Run II, as well as a comprehensive
reference for the PDF-fitting collaborations.Comment: 55 pages, 13 figure
Comparison of mouse and human genomes followed by experimental verification yields an estimated 1,019 additional genes.
A primary motivation for sequencing the mouse genome was to accelerate the discovery of mammalian genes by using sequence conservation between mouse and human to identify coding exons. Achieving this goal proved challenging because of the large proportion of the mouse and human genomes that is apparently conserved but apparently does not code for protein. We developed a two-stage procedure that exploits the mouse and human genome sequences to produce a set of genes with a much higher rate of experimental verification than previously reported prediction methods. RT-PCR amplification and direct sequencing applied to an initial sample of mouse predictions that do not overlap previously known genes verified the regions flanking one intron in 139 predictions, with verification rates reaching 76%. On average, the confirmed predictions show more restricted expression patterns than the mouse orthologs of known human genes, and two-thirds lack homologs in fish genomes, demonstrating the sensitivity of this dual-genome approach to hard-to-find genes. We verified 112 previously unknown homologs of known proteins, including two homeobox proteins relevant to developmental biology, an aquaporin, and a homolog of dystrophin. We estimate that transcription and splicing can be verified for >1,000 gene predictions identified by this method that do not overlap known genes. This is likely to constitute a significant fraction of the previously unknown, multiexon mammalian genes
The COSPIX mission: focusing on the energetic and obscured Universe
Tracing the formation and evolution of all supermassive black holes,
including the obscured ones, understanding how black holes influence their
surroundings and how matter behaves under extreme conditions, are recognized as
key science objectives to be addressed by the next generation of instruments.
These are the main goals of the COSPIX proposal, made to ESA in December 2010
in the context of its call for selection of the M3 mission. In addition,
COSPIX, will also provide key measurements on the non thermal Universe,
particularly in relation to the question of the acceleration of particles, as
well as on many other fundamental questions as for example the energetic
particle content of clusters of galaxies. COSPIX is proposed as an observatory
operating from 0.3 to more than 100 keV. The payload features a single long
focal length focusing telescope offering an effective area close to ten times
larger than any scheduled focusing mission at 30 keV, an angular resolution
better than 20 arcseconds in hard X-rays, and polarimetric capabilities within
the same focal plane instrumentation. In this paper, we describe the science
objectives of the mission, its baseline design, and its performances, as
proposed to ESA.Comment: 7 pages, accepted for publication in Proceedings of Science, for the
25th Texas Symposium on Relativistic Astrophysics (eds. F. Rieger & C.
van Eldik), PoS(Texas 2010)25
EGASP: the human ENCODE Genome Annotation Assessment Project
Background: Non-long terminal repeat (non-LTR) retrotransposons have contributed to shaping the structure and function of genomes. In silico and experimental approaches have been used to identify the non-LTR elements of the urochordate Ciona intestinalis. Knowledge of the types and abundance of non-LTR elements in urochordates is a key step in understanding their contribution to the structure and function of vertebrate genomes. Results: Consensus elements phylogenetically related to the I, LINE1, LINE2, LOA and R2 elements of the 14 eukaryotic non-LTR clades are described from C. intestinalis. The ascidian elements showed conservation of both the reverse transcriptase coding sequence and the overall structural organization seen in each clade. The apurinic/apyrimidinic endonuclease and nucleic-acid-binding domains encoded upstream of the reverse transcriptase, and the RNase H and the restriction enzyme-like endonuclease motifs encoded downstream of the reverse transcriptase were identified in the corresponding Ciona families. Conclusions: The genome of C. intestinalis harbors representatives of at least five clades of non-LTR retrotransposons. The copy number per haploid genome of each element is low, less than 100, far below the values reported for vertebrate counterparts but within the range for protostomes. Genomic and sequence analysis shows that the ascidian non-LTR elements are unmethylated and flanked by genomic segments with a gene density lower than average for the genome. The analysis provides valuable data for understanding the evolution of early chordate genomes and enlarges the view on the distribution of the non-LTR retrotransposons in eukaryotes
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