894 research outputs found
Size of the Vela Pulsar's Emission Region at 18 cm Wavelength
We present measurements of the linear diameter of the emission region of the
Vela pulsar at observing wavelength lambda=18 cm. We infer the diameter as a
function of pulse phase from the distribution of visibility on the
Mopra-Tidbinbilla baseline. As we demonstrate, in the presence of strong
scintillation, finite size of the emission region produces a characteristic
W-shaped signature in the projection of the visibility distribution onto the
real axis. This modification involves heightened probability density near the
mean amplitude, decreased probability to either side, and a return to the
zero-size distribution beyond. We observe this signature with high statistical
significance, as compared with the best-fitting zero-size model, in many
regions of pulse phase. We find that the equivalent full width at half maximum
of the pulsar's emission region decreases from more than 400 km early in the
pulse to near zero at the peak of the pulse, and then increases again to
approximately 800 km near the trailing edge. We discuss possible systematic
effects, and compare our work with previous results
The Multi-Component Nature of the Vela Pulsar Nonthermal X-ray Spectrum
We report on our analysis of a 274 ks observation of the Vela pulsar with the
Rossi X-Ray Timing Explorer (RXTE). The double-peaked, pulsed emission at 2 -
30 keV, which we had previously detected during a 93 ks observation, is
confirmed with much improved statistics. There is now clear evidence, both in
the spectrum and the light curve, that the emission in the RXTE band is a blend
of two separate non-thermal components. The spectrum of the harder component
connects smoothly with the OSSE, COMPTEL and EGRET spectrum and the peaks in
the light curve are in phase coincidence with those of the high-energy light
curve. The spectrum of the softer component is consistent with an extrapolation
to the pulsed optical flux, and the second RXTE pulse is in phase coincidence
with the second optical peak. In addition, we see a peak in the 2-8 keV RXTE
pulse profile at the radio phase.Comment: 12 pages, 3 figures, accepted for publication in Astrophysical
Journa
Microstructure and kinematics of H2O masers in the massive star forming region IRAS 06061+2151
We have made multi-epoch VLBI observations of H2O maser emission in the
massive star forming region IRAS 06061+2151 with the Japanese VLBI network
(JVN) from 2005 May to 2007 October. The detected maser features are
distributed within an 1\arcsec1\arcsec (2000 au2000 au at the
source position) around the ultra-compact H {\small\bf II} region seen in radio
continuum emission. Their bipolar morphology and expanding motion traced
through their relative proper motions indicate that they are excited by an
energetic bipolar outflow. Our three-dimensional model fitting has shown that
the maser kinematical structure in IRAS 06061+2151 is able to be explained by a
biconical outflow with a large opening angle ( 50\degr). The position angle
of the flow major axis coincides very well with that of the large scale jet
seen in 2.1\:\mu\rmn{m} hydrogen emission. This maser geometry indicates the
existence of dual structures composed of a collimated jet and a less collimated
massive molecular flow. We have also detected a large velocity gradient in the
southern maser group. This can be explained by a very small (on a scale of
several tens of au) and clumpy (the density contrast by an order of magnitude
or more) structure of the parental cloud. Such a structure may be formed by
strong instability of shock front or splitting of high density core.Comment: 14 pages, 6 figures accepted for publication in MNRA
Noise in the Cross-Power Spectrum of the Vela Pulsar
We compare the noise in interferometric measurements of the Vela pulsar from
ground- and space-based antennas with theoretical predictions. The noise
depends on both the flux density and the interferometric phase of the source.
Because the Vela pulsar is bright and scintillating, these comparisons extend
into both the low and high signal-to-noise regimes. Furthermore, our diversity
of baselines explores the full range of variation in interferometric phase. We
find excellent agreement between theoretical expectations and our estimates of
noise among samples within the characteristic scintillation scales. Namely, the
noise is drawn from an elliptical Gaussian distribution in the complex plane,
centered on the signal. The major axis, aligned with the signal phase, varies
quadratically with the signal, while the minor axis, at quadrature, varies with
the same linear coefficients. For weak signal, the noise approaches a circular
Gaussian distribution. Both the variance and covariance of the noise are also
affected by artifacts of digitization and correlation. In particular, we show
that gating introduces correlations between nearby spectral channels
High-resolution absorption spectroscopy of the OH 2Pi 3/2 ground state line
The chemical composition of the interstellar medium is determined by gas
phase chemistry, assisted by grain surface reactions, and by shock chemistry.
The aim of this study is to measure the abundance of the hydroxyl radical (OH)
in diffuse spiral arm clouds as a contribution to our understanding of the
underlying network of chemical reactions. Owing to their high critical density,
the ground states of light hydrides provide a tool to directly estimate column
densities by means of absorption spectroscopy against bright background
sources. We observed onboard the SOFIA observatory the 2Pi3/2, J = 5/2 3/2 2.5
THz line of ground-state OH in the diffuse clouds of the Carina-Sagittarius
spiral arm. OH column densities in the spiral arm clouds along the sightlines
to W49N, W51 and G34.26+0.15 were found to be of the order of 10^14 cm^-2,
which corresponds to a fractional abundance of 10^-7 to 10^-8, which is
comparable to that of H_2O. The absorption spectra of both species have similar
velocity components, and the ratio of the derived H_2O to OH column densities
ranges from 0.3 to 1.0. In W49N we also detected the corresponding line of
^18OH
An integrative approach unveils FOSL1 as an oncogene vulnerability in KRAS-driven lung and pancreatic cancer
KRAS mutated tumours represent a large fraction of human cancers, but the vast majority remains refractory to current clinical therapies. Thus, a deeper understanding of the molecular mechanisms triggered by KRAS oncogene may yield alternative therapeutic strategies. Here we report the identification of a common transcriptional signature across mutant KRAS cancers of distinct tissue origin that includes the transcription factor FOSL1. High FOSL1 expression identifies mutant KRAS lung and pancreatic cancer patients with the worst survival outcome. Furthermore, FOSL1 genetic inhibition is detrimental to both KRAS-driven tumour types. Mechanistically, FOSL1 links the KRAS oncogene to components of the mitotic machinery, a pathway previously postulated to function orthogonally to oncogenic KRAS. FOSL1 targets include AURKA, whose inhibition impairs viability of mutant KRAS cells. Lastly, combination of AURKA and MEK inhibitors induces a deleterious effect on mutant KRAS cells. Our findings unveil KRAS downstream effectors that provide opportunities to treat KRAS-driven cancers
Sciadopitys verticillata Resin: Volatile Components and Impact on Plant Pathogenic and Foodborne Bacteria
Sciadopitys verticillata (Sv) produces a white, sticky, latex-like resin with antimicrobial properties. The aims of this research were to evaluate the effects of this resin (Sv resin) on bacterial populations and to determine the impact of its primary volatile components on bioactivity. The impact of sample treatment on chemical composition of Sv resin was analyzed using Fourier transform infrared spectroscopy (FTIR) coupled with principal component analysis. The presence and concentration of volatiles in lyophilized resin were determined using gas chromatography/mass spectrometry (GC/MS). Changes in bacterial population counts due to treatment with resin or its primary volatile components were monitored. Autoclaving of the samples did not affect the FTIR spectra of Sv resin; however, lyophilization altered spectra, mainly in the CH and C=O regions. Three primary bioactive compounds that constituted \u3e90% of volatiles (1R-α-pinene, tricyclene, and ÎČ-pinene) were identified in Sv resin. Autoclaved resin impacted bacterial growth. The resin was stimulatory for some plant and foodborne pathogens (Pseudomonas fluorescens, P. syringae, and Xanthomonas perforans) and antimicrobial for others (Escherichia coli, Bacillus cereus, Agrobacterium tumefaciens, and Erwinia amylovora). Treatment with either 1R-α-pinene or ÎČ-pinene reduced B. cereus population growth less than did autoclaved resin. The complex resin likely contains additional antimicrobial compounds that act synergistically to inhibit bacterial growth
Astrometric and Timing Effects of Gravitational Waves from Localized Sources
A consistent approach for an exhaustive solution of the problem of
propagation of light rays in the field of gravitational waves emitted by a
localized source of gravitational radiation is developed in the first
post-Minkowskian and quadrupole approximation of General Relativity. We
demonstrate that the equations of light propagation in the retarded
gravitational field of an arbitrary localized source emitting quadrupolar
gravitational waves can be integrated exactly. The influence of the
gravitational field on the light propagation is examined not only in the wave
zone but also in cases when light passes through the intermediate and near
zones of the source. Explicit analytic expressions for light deflection and
integrated time delay (Shapiro effect) are obtained accounting for all possible
retardation effects and arbitrary relative locations of the source of
gravitational waves, that of light rays, and the observer. It is shown that the
ADM and harmonic gauge conditions can both be satisfied simultaneously outside
the source of gravitational waves. Their use drastically simplifies the
integration of light propagation equations and those for the motion of light
source and observer in the field of the source of gravitational waves, leading
to the unique interpretation of observable effects. The two limiting cases of
small and large values of impact parameter are elaborated in more detail.
Explicit expressions for Shapiro effect and deflection angle are obtained in
terms of the transverse-traceless part of the space-space components of the
metric tensor. We also discuss the relevance of the developed formalism for
interpretation of radio interferometric and timing observations, as well as for
data processing algorithms for future gravitational wave detectors.Comment: 43 pages, 4 Postscript figures, uses revtex.sty, accepted to Phys.
Rev. D, minor corrections in formulae regarding algebraic sign
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