787 research outputs found
Swift Observations of the Be/X-ray Transient System 1A 1118-615
We report results of Swift observations for the high mass Be/X-ray binary
system 1A 1118-615, during an outburst stage in January, 2009 and at a flaring
stage in March, 2009. Using the epoch-folding method, we successfully detected
a pulsed period of 407.69(2) sec in the outburst of January and of 407.26(1)
sec after the flare detection in March. We find that the spectral detection for
the source during outburst can be described by a blackbody model with a high
temperature (kT ~ 1-3 keV) and a small radius (R ~ 1 km), indicating that the
emission results from the polar cap of the neutron star. On the other hand, the
spectra obtained after the outburst can further be described by adding an
additional component with a lower temperature (kT ~ 0.1-0.2 keV) and a larger
emission radius (R ~ 10-500 km), which indicates the emission from around the
inner region of an accretion disk. We find that the thermal emission from the
hot spot of the accreting neutron star dominates the radiation in outburst; the
existence of both this X-ray contribution and the additional soft component
suggest that the polar cap and the accretion disk emission might co-exist after
the outburst. Because the two-blackbody signature at the flaring stage is a
unique feature of 1A 1118-615, our spectral results may provide a new insight
to interpret the X-ray emission for the accreting neutron star. The time
separation between the three main outbursts of this system is ~17 years and it
might be related to the orbital period. We derive and discuss the associated
physical properties by assuming the elongated orbit for this specific Be/X-ray
transient.Comment: 9 pages, 3 figures and 4 tables; accepted by MNRA
Could there be light at the end of the tunnel? Mesocaval shunting for refractory esophageal varices in patients with contraindications to transjugular intrahepatic portosystemic shunt.
Cirrhotic patients with recurrent variceal bleeds who have failed prior medical and endoscopic therapies and are not transjugular intrahepatic portosystemic shunt candidates face a grim prognosis with limited options. We propose that mesocaval shunting be offered to this group of patients as it has the potential to decrease portal pressures and thus decrease the risk of recurrent variceal bleeding. Mesocaval shunts are stent grafts placed by interventional radiologists between the mesenteric system, most often the superior mesenteric vein, and the inferior vena cava. This allows flow to bypass the congested hepatic system, reducing portal pressures. This technique avoids the general anesthesia and morbidity associated with surgical shunt placement and has been successful in several case reports. In this paper we review the technique, candidate selection, potential pitfalls and benefits of mesocaval shunt placement
High Resolution X-Ray Imaging of the Center of IC342
We presented the result of a high resolution (FWHM~0.5'') 12 ks Chandra HRC-I
observation of the starburst galaxy IC342 taken on 2 April 2006. We identified
23 X-ray sources within the central 30' x 30' region of IC342. Our HRC-I
observation resolved the historical Ultraluminous X-ray sources (ULX), X3, near
the nucleus into 2 sources, namely C12 and C13, for the first time. The
brighter source C12, with L(0.08-10keV)=(6.66\pm0.45)\times10^{38}ergs^-1, was
spatially extended (~82 pc x 127 pc). From the astrometric registration of the
X-ray image, C12 was at R.A.=03h:46m:48.43s, decl.=+68d05m47.45s, and was
closer to the nucleus than C13. Thus we concluded that source was not an ULX
and must instead be associated with the nucleus. The fainter source C13, with
L(0.08-10keV)=(5.1\pm1.4) x 10^{37}ergs^-1 was consistent with a point source
and located $6.51'' at P.A. 240 degree of C12.
We also analyzed astrometrically corrected optical Hubble Space Telescope and
radio Very Large Array images, a comparison with the X-ray image showed
similarities in their morphologies. Regions of star formation within the
central region of IC342 were clearly visible in HST H alpha image and this was
the region where 3 optical star clusters and correspondingly our detected X-ray
source C12 were observed. We found that a predicted X-ray emission from
starburst was very close to the observed X-ray luminosity of C12, suggesting
that nuclear X-ray emission in IC342 was dominated by starburst. Furthermore,
we discussed the possibility of AGN in the nucleus of IC342. Although our data
was not enough to give a firm existence of an AGN, it could not be discarded.Comment: 29 page, 8 figures, accepted by Ap
Long-term X-ray Variability Study of IC342 from XMM-Newton Observations
We presented the results of an analysis of four XMM-Newton observations of
the starburst galaxy IC342 taken over a four-year span from 2001 to 2005, with
an emphasis on investigating the long-term flux and spectral variability of the
X-ray point sources. We detected a total of 61 X-ray sources within 35'
30' of the galaxy down to a luminosity of (1-2)1037 erg s-1
depending on the local background. We found that 39 of the 61 detected sources
showed long-term variability, in which 26 of them were classified as X-ray
transients. We also found 19 sources exhibiting variations in hardness ratios
or undergoing spectral transitions among observations, and were identified as
spectral variables. In particular, 8 of the identified X-ray transients showed
spectral variability in addition to flux variability. The diverse patterns of
variability observed is indicative of a population of X-ray binaries. We used
X-ray colors, flux and spectral variability, and in some cases the optical or
radio counterparts to classify the detected X-ray sources into several stellar
populations. We identified a total of 11 foreground stars, 1 supersoft sources
(SSS), 3 quasisoft sources (QSS), and 2 supernova remnants (SNR). The
identified SSS/QSS are located near or on the spiral arms, associate with young
stellar populations; the 2 SNR are very close to the starburst nucleus where
current star formation activities are dominated. We also discovered a spectral
change in the nuclear source of IC342 for the first time by a series of X-ray
spectrum analysis.Comment: 45 pages, 6 figures accepted by Ap
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Medieval menarche: changes in pubertal timing in the aftermath of the Black Death
OBJECTIVES: Bioarchaeological evidence suggests stature increased in males but decreased in females after the Black Death (1348-1350 CE). Because tradeoffs between growth and reproduction can result in earlier ages at menarche and lower limb length, we assess menarcheal age between 1120 and 1540 CE to better understand the health of medieval adolescent females before and after the plague.
MATERIALS AND METHODS: Our sample comprises 74 adolescent females from St Mary Spital, London (1120-1540 CE) within the age range during which menarche occurs (10-25 years). They were assessed as being pre- or post-menarcheal and divided into three groups: Early Pre-Black Death (n=13), Late Pre-Black Death (n=38), and Post-Black Death (n=23). Changes in the ages of pre- and post-menarcheal females were assessed using Mann-Whitney tests.
RESULTS: The average age of post-menarcheal females increased from the Early- to Late Pre-Black Death periods and declined after the Black Death.
CONCLUSIONS: Short stature can reflect unfavorable growth environments, while younger menarcheal age indicates improved living conditions. The paradoxical pattern of female, but not male, stature reduction after the Black Death might reflect the association of early menarche with lower limb length and signal that adolescent females experienced improved health conditions after the epidemic. Our focus on pre- and post-menarche within a limited age span provides a novel approach for inferring average ages of menarche over time. Pathways to skeletal development and reproductive investment are part of an integrated system, providing a bridge between life history research in bioarchaeology and human biology
Spintronics: Fundamentals and applications
Spintronics, or spin electronics, involves the study of active control and
manipulation of spin degrees of freedom in solid-state systems. This article
reviews the current status of this subject, including both recent advances and
well-established results. The primary focus is on the basic physical principles
underlying the generation of carrier spin polarization, spin dynamics, and
spin-polarized transport in semiconductors and metals. Spin transport differs
from charge transport in that spin is a nonconserved quantity in solids due to
spin-orbit and hyperfine coupling. The authors discuss in detail spin
decoherence mechanisms in metals and semiconductors. Various theories of spin
injection and spin-polarized transport are applied to hybrid structures
relevant to spin-based devices and fundamental studies of materials properties.
Experimental work is reviewed with the emphasis on projected applications, in
which external electric and magnetic fields and illumination by light will be
used to control spin and charge dynamics to create new functionalities not
feasible or ineffective with conventional electronics.Comment: invited review, 36 figures, 900+ references; minor stylistic changes
from the published versio
A Study of Time-Dependent CP-Violating Asymmetries and Flavor Oscillations in Neutral B Decays at the Upsilon(4S)
We present a measurement of time-dependent CP-violating asymmetries in
neutral B meson decays collected with the BABAR detector at the PEP-II
asymmetric-energy B Factory at the Stanford Linear Accelerator Center. The data
sample consists of 29.7 recorded at the
resonance and 3.9 off-resonance. One of the neutral B mesons,
which are produced in pairs at the , is fully reconstructed in
the CP decay modes , , , () and , or in flavor-eigenstate
modes involving and (). The flavor of the other neutral B meson is tagged at the time of
its decay, mainly with the charge of identified leptons and kaons. The proper
time elapsed between the decays is determined by measuring the distance between
the decay vertices. A maximum-likelihood fit to this flavor eigenstate sample
finds . The value of the asymmetry amplitude is determined from
a simultaneous maximum-likelihood fit to the time-difference distribution of
the flavor-eigenstate sample and about 642 tagged decays in the
CP-eigenstate modes. We find , demonstrating that CP violation exists in the neutral B meson
system. (abridged)Comment: 58 pages, 35 figures, submitted to Physical Review
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