14,196 research outputs found
Modelling the multi-wavelength emissions from PSR B1259-63/LS 2883: the effects of the stellar disc on shock radiations
PSR B1259-63/LS 2883 is an elliptical pulsar/Be star binary and emits
broadband emissions from radio to TeV -rays. The massive star possesses
an equatorial disc, which is inclined with the orbital plane of the pulsar. The
non-thermal emission from the system is believed to be produced by the pulsar
wind shock and the double-peak profiles in the X-ray and TeV -ray light
curves are related to the phases of the pulsar passing through the disc region
of the star. In this paper, we investigate the interactions between the pulsar
wind and stellar outflows, especially with the presence of the disc, and
present a multi-wavelength modelling of the emission from this system. We show
that the double-peak profiles of X-ray and TeV -ray light curves are
caused by the enhancements of the magnetic field and the soft photons at the
shock during the disc passages. As the pulsar is passing through the equatorial
disc, the additional pressure of the disc pushes the shock surface closer to
the pulsar, which causes the enhancement of magnetic field in the shock, and
thus increases the synchrotron luminosity. The TeV -rays due to the
inverse-Compton (IC) scattering of shocked electrons with seed photons from the
star is expected to peak around periastron which is inconsistent with
observations. However, the shock heating of the stellar disc could provide
additional seed photons for IC scattering during the disc passages, and thus
produces the double-peak profiles as observed in the TeV -ray light
curve. Our model can possibly be examined and applied to other similar
gamma-ray binaries, such as PSR J2032+4127/MT91 213, HESS J0632+057, and LS
I+61303.Comment: 14 pages, 6 figure
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GPER-induced signaling is essential for the survival of breast cancer stem cells.
G protein-coupled estrogen receptor-1 (GPER), a member of the G protein-coupled receptor (GPCR) superfamily, mediates estrogen-induced proliferation of normal and malignant breast epithelial cells. However, its role in breast cancer stem cells (BCSCs) remains unclear. Here we showed greater expression of GPER in BCSCs than non-BCSCs of three patient-derived xenografts of ER- /PR+ breast cancers. GPER silencing reduced stemness features of BCSCs as reflected by reduced mammosphere forming capacity in vitro, and tumor growth in vivo with decreased BCSC populations. Comparative phosphoproteomics revealed greater GPER-mediated PKA/BAD signaling in BCSCs. Activation of GPER by its ligands, including tamoxifen (TMX), induced phosphorylation of PKA and BAD-Ser118 to sustain BCSC characteristics. Transfection with a dominant-negative mutant BAD (Ser118Ala) led to reduced cell survival. Taken together, GPER and its downstream signaling play a key role in maintaining the stemness of BCSCs, suggesting that GPER is a potential therapeutic target for eradicating BCSCs
Fermions in gravity and gauge backgrounds on a brane world
We solve the fermionic zero modes in gravity and gauge backgrounds on a brane
involving a warped geometry, and study the localization of spin 1/2 fermionic
field on the brane world. The result is that there exist massless spin 1/2
fermions which can be localized on the bulk with the exponentially decreasing
warp factor if including U(1) gauge background. Two special cases of gauge
backgrounds on the extra dimensional manifold are discussed.Comment: 11 pages, no figures, final versio
Information Flow in Interaction Networks
Interaction networks, consisting of agents linked by their interactions, are
ubiquitous across many disciplines of modern science. Many methods of analysis
of interaction networks have been proposed, mainly concentrating on node degree
distribution or aiming to discover clusters of agents that are very strongly
connected between themselves. These methods are principally based on
graph-theory or machine learning.
We present a mathematically simple formalism for modelling context-specific
information propagation in interaction networks based on random walks. The
context is provided by selection of sources and destinations of information and
by use of potential functions that direct the flow towards the destinations. We
also use the concept of dissipation to model the aging of information as it
diffuses from its source.
Using examples from yeast protein-protein interaction networks and some of
the histone acetyltransferases involved in control of transcription, we
demonstrate the utility of the concepts and the mathematical constructs
introduced in this paper.Comment: 30 pages, 5 figures. This paper was published in 2007 in Journal of
Computational Biology. The version posted here does not include post
peer-review change
RAId_DbS: Peptide Identification using Database Searches with Realistic Statistics
<p>Abstract</p> <p>Background</p> <p>The key to mass-spectrometry-based proteomics is peptide identification. A major challenge in peptide identification is to obtain realistic <it>E</it>-values when assigning statistical significance to candidate peptides.</p> <p>Results</p> <p>Using a simple scoring scheme, we propose a database search method with theoretically characterized statistics. Taking into account possible skewness in the random variable distribution and the effect of finite sampling, we provide a theoretical derivation for the tail of the score distribution. For every experimental spectrum examined, we collect the scores of peptides in the database, and find good agreement between the collected score statistics and our theoretical distribution. Using Student's <it>t</it>-tests, we quantify the degree of agreement between the theoretical distribution and the score statistics collected. The T-tests may be used to measure the reliability of reported statistics. When combined with reported <it>P</it>-value for a peptide hit using a score distribution model, this new measure prevents exaggerated statistics. Another feature of RAId_DbS is its capability of detecting multiple co-eluted peptides. The peptide identification performance and statistical accuracy of RAId_DbS are assessed and compared with several other search tools. The executables and data related to RAId_DbS are freely available upon request.</p
RAId_DbS: mass-spectrometry based peptide identification web server with knowledge integration
<p>Abstract</p> <p>Background</p> <p>Existing scientific literature is a rich source of biological information such as disease markers. Integration of this information with data analysis may help researchers to identify possible controversies and to form useful hypotheses for further validations. In the context of proteomics studies, individualized proteomics era may be approached through consideration of amino acid substitutions/modifications as well as information from disease studies. Integration of such information with peptide searches facilitates speedy, dynamic information retrieval that may significantly benefit clinical laboratory studies.</p> <p>Description</p> <p>We have integrated from various sources annotated single amino acid polymorphisms, post-translational modifications, and their documented disease associations (if they exist) into one enhanced database per organism. We have also augmented our peptide identification software RAId_DbS to take into account this information while analyzing a tandem mass spectrum. In principle, one may choose to respect or ignore the <it>correlation </it>of amino acid polymorphisms/modifications within each protein. The former leads to targeted searches and avoids scoring of unnecessary polymorphism/modification combinations; the latter explores possible polymorphisms in a controlled fashion. To facilitate new discoveries, RAId_DbS also allows users to conduct searches permitting <it>novel </it>polymorphisms as well as to search a knowledge database created by the users.</p> <p>Conclusion</p> <p>We have finished constructing enhanced databases for 17 organisms. The web link to RAId_DbS and the enhanced databases is <url>http://www.ncbi.nlm.nih.gov/CBBResearch/qmbp/RAId_DbS/index.html</url>. The relevant databases and binaries of RAId_DbS for Linux, Windows, and Mac OS X are available for download from the same web page.</p
McVA: A Multi-comparison Visual Analysis System for Maximum Residue Limit Standard in Food Safety
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