4,208 research outputs found
The Hot R Coronae Borealis Star DY Centauri is a Binary
The remarkable hot R Coronae Borealis (RCB) star DY Cen is revealed to be the first and only binary system to be found among the RCB stars and their likely relatives, including the extreme helium stars and the hydrogen-deficient carbon stars. Radial velocity determinations from 1982 to 2010 have shown that DY Cen is a single-lined spectroscopic binary in an eccentric orbit with a period of 39.67 days. It is also one of the hottest and most H-rich member of the class of RCB stars. The system may have evolved from a common envelope to its current form.Spanish Ministry of Economy and Competitiveness AYA-2011-27754McDonald Observator
Geometry Diagnostics of a Stellar Flare from Fluorescent X-rays
We present evidence of Fe fluorescent emission in the Chandra HETGS spectrum
of the single G-type giant HR 9024 during a large flare. In analogy to solar
X-ray observations, we interpret the observed Fe K line as being
produced by illumination of the photosphere by ionizing coronal X-rays, in
which case, for a given Fe photospheric abundance, its intensity depends on the
height of the X-ray source. The HETGS observations, together with 3D Monte
Carlo calculations to model the fluorescence emission, are used to obtain a
direct geometric constraint on the scale height of the flaring coronal plasma.
We compute the Fe fluorescent emission induced by the emission of a single
flaring coronal loop which well reproduces the observed X-ray temporal and
spectral properties according to a detailed hydrodynamic modeling. The
predicted Fe fluorescent emission is in good agreement with the observed value
within observational uncertainties, pointing to a scale height \rstar. Comparison of the HR 9024 flare with that recently observed on II
Peg by Swift indicates the latter is consistent with excitation by X-ray
photoionization.Comment: accepted for publication on the Astrophysical Journal Letter
Keyed User Datagram Protocol: Concepts and Operation of an Almost Reliable Connectionless Transport Protocol
Departing from the well-known problem of the excessive overhead and latency of connection
oriented protocols, this paper describes a new almost reliable connectionless protocol that uses user
datagram protocol (UDP) segment format and is UDP compatible. The problem is presented and described,
the motivation, the possible areas of interest and the concept and base operation modes for the protocol
named keyed UDP are presented (here called KUDP). Also, discussed are some of the possible manners in
which the KUDP can be used, addressing potential problems related with current networking technologies.
As UDP is a connectionless protocol, and KUDP allows for some degree of detection of loss and re-ordering
of segments received out-of-sequence, we also present a proposal for a stream reconstruction algorithm. This
paper ends by mentioning some of the research issues that still need to be addressed.info:eu-repo/semantics/publishedVersio
Methylation and protein expression of DNA repair genes: association with chemotherapy exposure and survival in sporadic ovarian and peritoneal carcinomas
<p>Abstract</p> <p>Background</p> <p>DNA repair genes critically regulate the cellular response to chemotherapy and epigenetic regulation of these genes may be influenced by chemotherapy exposure. Restoration of BRCA1 and BRCA2 mediates resistance to platinum chemotherapy in recurrent BRCA1 and BRCA2 mutated hereditary ovarian carcinomas. We evaluated BRCA1, BRCA2, and MLH1 protein expression in 115 sporadic primary ovarian carcinomas, of which 31 had paired recurrent neoplasms collected after chemotherapy. Additionally, we assessed whether promoter methylation of BRCA1, MLH1 or FANCF influenced response to chemotherapy or explained alterations in protein expression after chemotherapy exposure.</p> <p>Results</p> <p>Of 115 primary sporadic ovarian carcinomas, 39 (34%) had low BRCA1 protein and 49 (42%) had low BRCA2 expression. BRCA1 and BRCA2 protein expression were highly concordant (p < 0.0001). MLH1 protein loss occurred in 28/115 (24%) primary neoplasms. BRCA1 protein loss in primary neoplasms was associated with better survival (p = 0.02 Log Rank test) and remained significant after accounting for either stage or age in a multivariate model (p = 0.04, Cox proportional hazards). In paired specimens, BRCA1 protein expression increased in 13/21 (62%) and BRCA2 protein expression increased in 15/21 (71%) of recurrent carcinomas with low or intermediate protein in the paired primary. In contrast MLH1 expression was rarely decreased in recurrent carcinomas (1/33, 3%). Similar frequencies of MLH1, BRCA1, and FANCF promoter methylation occurred in primary carcinomas without previous chemotherapy, after neoadjuvant chemotherapy, or in recurrent neoplasms.</p> <p>Conclusion</p> <p>Low BRCA1 expression in primary sporadic ovarian carcinoma is associated with prolonged survival. Recurrent ovarian carcinomas commonly have increased BRCA1 and/or BRCA2 protein expression post chemotherapy exposure which could mediate resistance to platinum based therapies. However, alterations in expression of these proteins after chemotherapy are not commonly mediated by promoter methylation, and other regulatory mechanisms are likely to contribute to these alterations.</p
The Nearby Optical Galaxy Sample: The Local Galaxy Luminosity Function
In this paper we derive the galaxy luminosity function from the Nearby
Optical Galaxy (NOG) sample, which is a nearly complete, magnitude-limited
(B<14 mag), all-sky sample of nearby optical galaxies (~6400 galaxies with
cz<5500 km/s). For this local sample, we use galaxy distance estimates based on
different peculiar velocity models. Therefore, the derivation of the luminosity
function is carried out using the locations of field and grouped galaxies in
real distance space.
The local field galaxy luminosity function in the B system is well described
by a Schechter function. The exact values of the Schechter parameters slightly
depend on the adopted peculiar velocity field models.
The shape of the luminosity function of spiral galaxies does not differ
significantly from that of E-S0 galaxies. On the other hand, the late-type
spirals and irregulars have a very steeply rising luminosity function towards
the faint end, whereas the ellipticals appreciably decrease in number towards
low luminosities.
The presence of galaxy systems in the NOG sample does not affect
significantly the field galaxy luminosity function, since environmental effects
on the total luminosity function appear to be marginal.Comment: 35 pages including 7 figures and 4 tables. Accepted for publication
in Ap
Transgenic ZmMYB167 Miscanthus sinensis with increased lignin to boost bioenergy generation for the bioeconomy
Transgenic ZmMYB167 Miscanthus sinensis with increased lignin to boost bioenergy generation for the bioeconomy
DBS Under FCC and International Regulation
This Article examines the legal and technological development of DBS in both the domestic and international fora. Part II examines the development of DBS and information policy concerning DBS in the United States. The Article then in part III discusses the international positions of the developed nations, the developing countries, and the Soviet bloc on the DBS issues and reveals the results thus far in the policy debate among these nations and the United States. Part IV concludes the Article with a brief outline of the possibilities for international cooperation to solve the DBS controversy
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