261 research outputs found
EUVE J0425.6-5714: A Newly Discovered AM Herculis Star
We detected a new AM Her star serendipitously in a 25 day observation with
the EUVE satellite. A coherent period of 85.82 min is present in the EUVE Deep
Survey imager light curve of this source. A spectroscopic identification is
made with a 19th magnitude blue star that has H and He emission lines, and
broad cyclotron humps typical of a magnetic cataclysmic variable. A lower limit
to the polar magnetic field of 46 MG is estimated from the spacing of the
cyclotron harmonics. EUVE J0425.6-5714 is also detected in archival ROSAT HRI
observations spanning two months, and its stable and highly structured light
curve permits us to fit a coherent ephemeris linking the ROSAT and EUVE data
over a 1.3 yr gap. The derived period is 85.82107 +/- 0.00020 min, and the
ephemeris should be accurate to 0.1 cycles until the year 2005. A narrow but
partial X-ray eclipse suggests that this object belongs to the group of Am Her
stars whose viewing geometry is such that the accretion stream periodically
occults the soft X-ray emitting accretion spot on the surface of the white
dwarf. A non-detection of hard X-rays from ASCA observations that are
contemporaneous with the ROSAT HRI shows that the soft X-rays must dominate by
at least an order of magnitude, which is consistent with a known trend among AM
Her stars with large magnetic field. This object should not be confused with
the Seyfert galaxy 1H 0419-577 (= LB 1727), another X-ray/EUV source which lies
only 4' away, and was the principal target of these monitoring observations.Comment: 13 pages, 5 figures, to appear in PASP, Dec. 1998 issu
New Low Accretion-Rate Magnetic Binary Systems and their Significance for the Evolution of Cataclysmic Variables
Discoveries of two new white dwarf plus M star binaries with striking optical
cyclotron emission features from the Sloan Digital Sky Survey (SDSS) brings to
six the total number of X-ray faint, magnetic accretion binaries that accrete
at rates < 10^{-13} Msun/yr, or <1% of the values normally encountered in
cataclysmic variables. This fact, coupled with donor stars that underfill their
Roche lobes and very cool white dwarfs, brand the binaries as post
common-envelope systems whose orbits have not yet decayed to the point of
Roche-lobe contact. They are pre-magnetic CVs, or pre-Polars. The systems
exhibit spin/orbit synchronism and apparently accrete by efficient capture of
the stellar wind from the secondary star, a process that has been dubbed a
``magnetic siphon''. Because of this, period evolution of the binaries will
occur solely by gravitational radiation, which is very slow for periods >3 hr.
Optical surveys for the cyclotron harmonics appear to be the only means of
discovery, so the space density of pre-Polars could rival that of Polars, and
the binaries provide an important channel of progenitors (in addition to the
asynchronous Intermediate Polars). Both physical and SDSS observational
selection effects are identified that may help to explain the clumping of all
six systems in a narrow range of magnetic field strength around 60 MG.Comment: 25 pages, 13 figures, Accepted to Ap
Upregulated Glucose Metabolism Correlates Inversely with CD8(+) T-cell Infiltration and Survival in Squamous Cell Carcinoma
Antibodies that block T-cell–regulatory checkpoints have recently emerged as a transformative approach to cancer treatment. However, the clinical efficacy of checkpoint blockade depends upon inherent tumor immunogenicity, with variation in infiltrating T cells contributing to differences in objective response rates. Here, we sought to understand the molecular correlates of tumor-infiltrating T lymphocytes (TIL) in squamous cell carcinoma (SCC), using a systems biologic approach to integrate publicly available omics datasets with histopathologic features. We provide evidence that links TIL abundance and therapeutic outcome to the regulation of tumor glycolysis by EGFR and HIF, both of which are attractive molecular targets for use in combination with immunotherapeutics
The Three Dimensional Structure of EUV Accretion Regions in AM Herculis Stars: Modeling of EUV Photometric and Spectroscopic Observations
We have developed a model of the high-energy accretion region for magnetic
cataclysmic variables and applied it to {\it Extreme Ultraviolet Explorer}
observations of 10 AM Herculis type systems. The major features of the EUV
light curves are well described by the model. The light curves exhibit a large
variety of features such as eclipses of the accretion region by the secondary
star and the accretion stream, and dips caused by material very close to the
accretion region. While all the observed features of the light curves are
highly dependent on viewing geometry, none of the light curves are consistent
with a flat, circular accretion spot whose lightcurve would vary solely from
projection effects. The accretion region immediately above the WD surface is a
source of EUV radiation caused by either a vertical extent to the accretion
spot, or Compton scattering off electrons in the accretion column, or, very
likely, both. Our model yields spot sizes averaging 0.06 R, or the WD surface area, and average spot heights of 0.023
R. Spectra extracted during broad dip phases are softer than spectra
during the out-of-dip phases. This spectral ratio measurement leads to the
conclusion that Compton scattering, some absorption by a warm absorber,
geometric effects, an asymmetric temperature structure in the accretion region
and an asymmetric density structure of the accretion columnare all important
components needed to fully explain the data. Spectra extracted at phases where
the accretion spot is hidden behind the limb of the WD, but with the accretion
column immediately above the spot still visible, show no evidence of emission
features characteristic of a hot plasma.Comment: 30 Pages, 11 Figure
Superhumps in Cataclysmic Binaries. XXIII. V442 Ophiuchi and RX J1643.7+3402
We report the results of long observing campaigns on two novalike variables:
V442 Ophiuchi and RX J1643.7+3402. These stars have high-excitation spectra,
complex line profiles signifying mass loss at particular orbital phases, and
similar orbital periods (respectively 0.12433 and 0.12056 d). They are
well-credentialed members of the SW Sex class of cataclysmic variables. Their
light curves are also quite complex. V442 Oph shows periodic signals with
periods of 0.12090(8) and 4.37(15) days, and RX J1643.7+3402 shows similar
signals at 0.11696(8) d and 4.05(12) d. We interpret these short and long
periods respectively as a "negative superhump" and the wobble period of the
accretion disk. The superhump could then possibly arise from the heating of the
secondary (and structures fixed in the orbital frame) by inner-disk radiation,
which reaches the secondary relatively unimpeded since the disk is not
coplanar.
At higher frequencies, both stars show another type of variability:
quasi-periodic oscillations (QPOs) with a period near 1000 seconds. Underlying
these strong signals of low stability may be weak signals of higher stability.
Similar QPOs, and negative superhumps, are quite common features in SW Sex
stars. Both can in principle be explained by ascribing strong magnetism to the
white dwarf member of the binary; and we suggest that SW Sex stars are
borderline AM Herculis binaries, usually drowned by a high accretion rate. This
would provide an ancestor channel for AM Hers, whose origin is still
mysterious.Comment: PDF, 41 pages, 4 tables, 16 figures; accepted, in press, to appear
December 2002, PASP; more info at http://cba.phys.columbia.edu
HPV, tumour metabolism and novel target identification in head and neck squamous cell carcinoma
Background Metabolic changes in tumour cells are used in clinical imaging and may provide potential therapeutic targets. Human papillomavirus (HPV) status is important in classifying head and neck cancers (HNSCC), identifying a distinct clinical phenotype; metabolic differences between these HNSCC subtypes remain poorly understood. Methods We used RNA sequencing to classify the metabolic expression profiles of HPV+ve and HPV−ve HNSCC, performed a meta-analysis on FDG-PET imaging characteristics and correlated results with in vitro extracellular flux analysis of HPV−ve and HPV+ve HNSCC cell lines. The monocarboxylic acid transporter-1 (MCT1) was identified as a potential metabolic target and tested in functional assays. Results Specific metabolic profiles were associated with HPV status, not limited to carbohydrate metabolism. There was dominance of all energy pathways in HPV-negative disease, with elevated expression of genes associated with glycolysis and oxidative phosphorylation. In vitro analysis confirmed comparative increased rates of oxidative phosphorylation and glycolysis in HPV-negative cell lines. PET SUV(max) scores however were unable to reliably differentiate between HPV-positive and HPV-negative tumours. MCT1 expression was significantly increased in HPV-negative tumours, and inhibition suppressed tumour cell invasion, colony formation and promoted radiosensitivity. Conclusion HPV-positive and negative HNSCC have different metabolic profiles which may have potential therapeutic applications
Irregular Mass Transfer in the Polars VV Puppis and V393 Pavonis during the Low State
The polars VV Pup and V393 Pav were observed with XMM-Newton during states of
low accretion rate with peak X-ray luminosities of ~1 x 10^30 and ~1 x 10^31
erg/s, respectively. In both polars, accretion onto the white dwarf was
extremely irregular, and the accretion rate varied by more than 1 order of
magnitude on timescales of ~1 hr. Our observations suggest that this type of
irregular accretion is a common phenomenon in polars during the low state. The
likely cause of the accretion rate fluctuations are coronal mass ejections or
solar flares on the companion star that intermittently increase the mass
transfer into the accretion stream. Our findings demonstrate that the companion
stars in cataclysmic variables possess highly active atmospheres.Comment: Accepted for publication in ApJ, 16 pages, 3 figure
The new cataclysmic variable RX J1554.2+2721 in the period gap
We report on the results of a spectroscopic and photometric study of a new
cataclysmic variable, identified as optical counterpart of the X-ray source RX
J1554.2+2721 detected by ROSAT. The spectroscopic observations of the
relatively bright (~16.5mag) object show systematic radial velocity variations
with a semi-amplitude of ~140 km/sec. Besides the clear presence of distinct
low and high states there are periodic photometric light variations with an
amplitude of about 0.15 magnitude in the R band. The orbital period is 2.753h
thus being within the period gap, at its upper border. The flux distribution in
the spectrum of the object shows a substantial contribution of a M4V secondary,
and also bears clear signs of cyclotron emission. Thus, we classify the
discovered object as a new member of the AM Her class of magnetic cataclysmic
variables. This classification is further supported by the soft X-ray spectrum,
the characteristic profiles of the emission lines, the tomography map and the
shape of the orbital light curve. A simple fitting of the spectrum in the low
and high states suggests a reduced mass transfer rate in RX J1554.2+2721,
compared to similar objects outside the period gap.Comment: 11 pages, 11 figures, accepted in A&
Gender-dependent differences in plasma matrix metalloproteinase-8 elevated in pulmonary tuberculosis.
Tuberculosis (TB) remains a global health pandemic and greater understanding of underlying pathogenesis is required to develop novel therapeutic and diagnostic approaches. Matrix metalloproteinases (MMPs) are emerging as key effectors of tissue destruction in TB but have not been comprehensively studied in plasma, nor have gender differences been investigated. We measured the plasma concentrations of MMPs in a carefully characterised, prospectively recruited clinical cohort of 380 individuals. The collagenases, MMP-1 and MMP-8, were elevated in plasma of patients with pulmonary TB relative to healthy controls, and MMP-7 (matrilysin) and MMP-9 (gelatinase B) were also increased. MMP-8 was TB-specific (p<0.001), not being elevated in symptomatic controls (symptoms suspicious of TB but active disease excluded). Plasma MMP-8 concentrations inversely correlated with body mass index. Plasma MMP-8 concentration was 1.51-fold higher in males than females with TB (p<0.05) and this difference was not due to greater disease severity in men. Gender-specific analysis of MMPs demonstrated consistent increase in MMP-1 and -8 in TB, but MMP-8 was a better discriminator for TB in men. Plasma collagenases are elevated in pulmonary TB and differ between men and women. Gender must be considered in investigation of TB immunopathology and development of novel diagnostic markers
Spitzer IRS Spectroscopy of Intermediate Polars: Constraints on Mid-Infrared Cyclotron Emission
We present Spitzer Infrared Spectrograph (IRS) observations of eleven
intermediate polars (IPs). Spectra covering the wavelength range from 5.2 to 14
m are presented for all eleven objects, and longer wavelength spectra are
presented for three objects (AE Aqr, EX Hya, and V1223 Sgr). We also present
new, moderate resolution (R 2000) near-infrared spectra for five of the
program objects. We find that, in general, the mid-infrared spectra are
consistent with simple power laws that extend from the optical into the
mid-infrared. There is no evidence for discrete cyclotron emission features in
the near- or mid-infrared spectra for any of the IPs investigated. If cyclotron
emission is occurring in the 5.2 to 14.0 m bandpass it constitutes less
than 1% of the bolometric luminosity of any of the IPs. We discuss our results
in the context of the standard model for IPs.Comment: 43 pages, including 17 figures, accepted by the Astrophysical Journa
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