927 research outputs found
An evolved disk surrounding the massive main sequence star MWC 297?
We present the results of the interferometric observations of the
circumstellar disk surrounding MWC 297 in the continuum at 230 GHz (1.3 mm) and
in the (J=2-1) rotational transitions of CO,CO and CO
using the Submillimeter Array. At a distance of 250 pc, MWC 297 is one of the
closest, young massive stars (M 10 M) to us. Compact
continuum emission is detected towards MWC 297 from which we estimate a disk
mass (gas+dust) of 0.07 M and a disk radius of 80 AU. Our
result demonstrates that circumstellar disks can survive around massive stars
well into their main sequence phase even after they have become optically
visible. Complementing our observations with the data compiled from the
literature, we find the submm dust opacity index to be between 0.1 and
0.3. If the emission is optically thin, the low value of indicates the
presence of relatively large grains in the disk, possibly because of grain
growth. We do not detect any CO emission associated with the continuum source.
We argue that the CO emission from the disk is likely optically thin, in
which case, we derive an upper limit to the gas mass which implies significant
depletion of molecular gas in the disk. The mass of this disk and the
evolutionary trends observed are similar to those found for intermediate mass
Herbig Ae stars and low mass T Tauri stars.Comment: 4 pages, 3 Figures, accepted for publication in ApJ
Phase Transition between the Cholesteric and Twist Grain Boundary C Phases
The upper critical temperature Tc2 for the phase transition between the
Cholesteric phase (N*) and the Twist Grain Boundary C phase with the layer
inclination tilted to the pitch axis (TGBct) in thermotropic liquid crystals is
determined by the mean field Chen-Lubensky approach. We show that the N*-TGBct
phase transition is split in two with the appearance of either the TGBA or the
TGB2q phase in a narrow temperature interval below Tc2. The latter phase is
novel in being superposed from two degenerate
TGBct phases with different (left and right) layers inclinations to the pitch
axis.Comment: Phys. Rev. E, to be publ; 24 pages, RevTeX + 3 ps figure
Cosmic strings, loops, and linear growth of matter perturbations
We describe the detailed study and results of high-resolution numerical
simulations of string-induced structure formation in open universes and those
with a non-zero cosmological constant. The effect from small loops generated
from the string network has also been investigated. We provide a
semi-analytical model which can reproduce these simulation results. A detailed
study of cosmic string network properties regarding structure formation is also
given, including the correlation time, the topological analysis of the source
spectrum, the correlation between long strings and loops, and the evolution of
long-string and loop energy densities. For models with 8 h^{-1}\sigma_8$, and an overall shape which are consistent within
uncertainties with those currently inferred from galaxy surveys. The cosmic
string scenario with hot dark matter requires a strongly scale-dependent bias
in order to agree with observations.Comment: 60 pages, 24 figure
DNA Methylation Maintains Allele-specific KIR Gene Expression in Human Natural Killer Cells
Killer immunoglobulin-like receptors (KIR) bind self–major histocompatibility complex class I molecules, allowing natural killer (NK) cells to recognize aberrant cells that have down-regulated class I. NK cells express variable numbers and combinations of highly homologous clonally restricted KIR genes, but uniformly express KIR2DL4. We show that NK clones express both 2DL4 alleles and either one or both alleles of the clonally restricted KIR 3DL1 and 3DL2 genes. Despite allele-independent expression, 3DL1 alleles differed in the core promoter by only one or two nucleotides. Allele-specific 3DL1 gene expression correlated with promoter and 5′ gene DNA hypomethylation in NK cells in vitro and in vivo. The DNA methylase inhibitor, 5-aza-2′-deoxycytidine, induced KIR DNA hypomethylation and heterogeneous expression of multiple KIR genes. Thus, NK cells use DNA methylation to maintain clonally restricted expression of highly homologous KIR genes and alleles
Restriction landmark genomic scanning (RLGS) spot identification by second generation virtual RLGS in multiple genomes with multiple enzyme combinations.
BackgroundRestriction landmark genomic scanning (RLGS) is one of the most successfully applied methods for the identification of aberrant CpG island hypermethylation in cancer, as well as the identification of tissue specific methylation of CpG islands. However, a limitation to the utility of this method has been the ability to assign specific genomic sequences to RLGS spots, a process commonly referred to as "RLGS spot cloning."ResultsWe report the development of a virtual RLGS method (vRLGS) that allows for RLGS spot identification in any sequenced genome and with any enzyme combination. We report significant improvements in predicting DNA fragment migration patterns by incorporating sequence information into the migration models, and demonstrate a median Euclidian distance between actual and predicted spot migration of 0.18 centimeters for the most complex human RLGS pattern. We report the confirmed identification of 795 human and 530 mouse RLGS spots for the most commonly used enzyme combinations. We also developed a method to filter the virtual spots to reduce the number of extra spots seen on a virtual profile for both the mouse and human genomes. We demonstrate use of this filter to simplify spot cloning and to assist in the identification of spots exhibiting tissue-specific methylation.ConclusionThe new vRLGS system reported here is highly robust for the identification of novel RLGS spots. The migration models developed are not specific to the genome being studied or the enzyme combination being used, making this tool broadly applicable. The identification of hundreds of mouse and human RLGS spot loci confirms the strong bias of RLGS studies to focus on CpG islands and provides a valuable resource to rapidly study their methylation
Generalized Painleve-Gullstrand descriptions of Kerr-Newman black holes
Generalized Painleve-Gullstrand metrics are explicitly constructed for the
Kerr-Newman family of charged rotating black holes. These descriptions are free
of all coordinate singularities; moreover, unlike the Doran and other proposed
metrics, an extra tunable function is introduced to ensure all variables in the
metrics remain real for all values of the mass M, charge Q, angular momentum
aM, and cosmological constant \Lambda > - 3/(a^2). To describe fermions in
Kerr-Newman spacetimes, the stronger requirement of non-singular vierbein
one-forms at the horizon(s) is imposed and coordinate singularities are
eliminated by local Lorentz boosts. Other known vierbein fields of Kerr-Newman
black holes are analysed and discussed; and it is revealed that some of these
descriptions are actually not related by physical Lorentz transformations to
the original Kerr-Newman expression in Boyer-Lindquist coordinates - which is
the reason complex components appear (for certain ranges of the radial
coordinate) in these metrics. As an application of our constructions the
correct effective Hawking temperature for Kerr black holes is derived with the
method of Parikh and Wilczek.Comment: 5 pages; extended to include application to derivation of Hawking
radiation for Kerr black holes with Parikh-Wilczek metho
Making Maps Of The Cosmic Microwave Background: The MAXIMA Example
This work describes Cosmic Microwave Background (CMB) data analysis
algorithms and their implementations, developed to produce a pixelized map of
the sky and a corresponding pixel-pixel noise correlation matrix from time
ordered data for a CMB mapping experiment. We discuss in turn algorithms for
estimating noise properties from the time ordered data, techniques for
manipulating the time ordered data, and a number of variants of the maximum
likelihood map-making procedure. We pay particular attention to issues
pertinent to real CMB data, and present ways of incorporating them within the
framework of maximum likelihood map-making. Making a map of the sky is shown to
be not only an intermediate step rendering an image of the sky, but also an
important diagnostic stage, when tests for and/or removal of systematic effects
can efficiently be performed. The case under study is the MAXIMA data set.
However, the methods discussed are expected to be applicable to the analysis of
other current and forthcoming CMB experiments.Comment: Replaced to match the published version, only minor change
Temporal RNA Integrity Analysis of Archived Spaceflight Biological Samples from ALSDA from 1991 to 2016
The purpose of this study is to assess the quality of spaceflight tissues stored in Ames Life Science Data Archive (ALSDA) freezers. Garnering information for downstream functional analysis such as generation of omics datasets from tissues is, in part, dependent on the state of sample preservation. To assess the viability of a select group of tissues, RNA integrity number (RIN) values were calculated for RNA extracted from rodent livers. Rat livers from Spacelab Life Sciences 1 (SLS-1) and mouse livers from Commercial Biomedical Test Module 3 (CBTM-3), Rodent Research 1 (RR1), and Rodent Research 3 (RR3) were tested. It was found that mean RIN values from CBTM3, RR1, and RR3 were suitable for downstream functional analysis (RIN greater than 5) while the mean RIN value for SLS-1 was not (RIN equal to 2.5 plus or minus 0.1). Information from this study could lay the foundation for future efforts in determining the types of assays that are most appropriate for different tissues in ALSDA freezers, which would maximize the scientific return on rare spaceflight samples
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