1,532 research outputs found
A Survey of Local Group Galaxies Currently Forming Stars: III. A Search for Luminous Blue Variables and Other H-alpha Emission-Lined Stars
We describe a search for H-alpha emission-lined stars in M31, M33, and seven
dwarfs in or near the Local Group (IC 10, NGC 6822, WLM, Sextans B, Sextans A,
Pegasus and the Phoenix dwarf) using interference filter imaging with the KPNO
and CTIO 4-m telescope and Mosaic cameras. The survey is aimed primarily at
identifying new Luminous Blue Variables (LBVs) from their spectroscopic
similarity to known LBVs, avoiding the bias towards photometric variability,
which may require centuries to manifest itself if LBVs go through long
quiescent periods. Followup spectroscopy with WIYN confirms that our survey
detected a wealth of stars whose spectra are similar to the known LBVs. We
"classify" the spectra of known LBVs, and compare these to the spectra of the
new LBV candidates. We demonstrate spectacular spectral variability for several
of the new LBV candidates, such as AM2, previously classified as a Wolf-Rayet
star, which now shows FeI, FeII and Balmer emission lines but neither the NIII
4634,42 nor HeII 4686 emission that it did in 1982. Profound spectral changes
are also noted for other suspected and known LBVs. Several of the LBV
candidates also show >0.5 mag changes in V over the past 10-20 years. The
number of known or suspected LBVs is now 24 in M31, 37 in M33, 1 in NGC 6822,
and 3 in IC 10. We estimate that the total number of LBVs in M31 and M33 may be
several hundred, in contrast to the 8 known historically through large-scale
photometric variability. This has significant implications for the time scale
of the LBV phase. We also identify a few new WRs and peculiar emission-lined
objects.Comment: Accepted by the Astronomical Journal. Version with higher quality
figures may be downloaded from http://www.lowell.edu/users/massey/has.pdf.g
A multi-wavelength survey of AGN in the XMM-LSS field: I. Quasar selection via the KX technique
AIMS: We present a sample of candidate quasars selected using the
KX-technique. The data cover 0.68 deg^2 of the X-ray Multi-Mirror (XMM)
Large-Scale Structure (LSS) survey area where overlapping multi-wavelength
imaging data permits an investigation of the physical nature of selected
sources. METHODS: The KX method identifies quasars on the basis of their
optical (R and z') to near-infrared (Ks) photometry and point-like morphology.
We combine these data with optical (u*,g'r',i',z') and mid-infrared (3.6-24
micron) wavebands to reconstruct the spectral energy distributions (SEDs) of
candidate quasars. RESULTS: Of 93 sources selected as candidate quasars by the
KX method, 25 are classified as quasars by the subsequent SED analysis.
Spectroscopic observations are available for 12/25 of these sources and confirm
the quasar hypothesis in each case. Even more, 90% of the SED-classified
quasars show X-ray emission, a property not shared by any of the false
candidates in the KX-selected sample. Applying a photometric redshift analysis
to the sources without spectroscopy indicates that the 25 sources classified as
quasars occupy the interval 0.7 < z < 2.5. The remaining 68/93 sources are
classified as stars and unresolved galaxies.Comment: 13 pages, 9 figures, A&A 494, p. 579-589. Replaced with published
version. Fig. 9 in first astro-ph submission has been update
Overexpression of Mcl-1 exacerbates lymphocyte accumulation and autoimmune kidney disease in lpr mice
Cell death by apoptosis has a critical role during embryonic development and in maintaining tissue homeostasis. In mammals,
there are two converging apoptosis pathways: the ‘extrinsic’ pathway, which is triggered by engagement of cell surface ‘death
receptors’ such as Fas/APO-1; and the ‘intrinsic’ pathway, which is triggered by diverse cellular stresses, and is regulated by prosurvival
and pro-apoptotic members of the Bcl-2 family of proteins. Pro-survival Mcl-1, which can block activation of the proapoptotic
proteins, Bax and Bak, appears critical for the survival and maintenance of multiple haemopoietic cell types. To
investigate the impact on haemopoiesis of simultaneously inhibiting both apoptosis pathways, we introduced the vavP-Mcl-1
transgene, which causes overexpression of Mcl-1 protein in all haemopoietic lineages, into Faslpr/lpr mice, which lack functional
Fas and are prone to autoimmunity. The combined mutations had a modest impact on myelopoiesis, primarily an increase in the
macrophage/monocyte population in Mcl-1tg/lpr mice compared with lpr or Mcl-1tg mice. The impact on lymphopoiesis was
striking, with a marked elevation in all major lymphoid subsets, including the non-conventional double-negative (DN) T cells
(TCRβ+
CD4–
CD8–
B220+
) characteristic of Faslpr/lpr mice. Of note, the onset of autoimmunity was markedly accelerated in Mcl-1tg/lpr
mice compared with lpr mice, and this was preceded by an increase in immunoglobulin (Ig)-producing cells and circulating
autoantibodies. This degree of impact was surprising, given the relatively mild phenotype conferred by the vavP-Mcl-1 transgene
by itself: a two- to threefold elevation of peripheral B and T cells, no significant increase in the non-conventional DN T-cell
population and no autoimmune disease. Comparison of the phenotype with that of other susceptible mice suggests that the
development of autoimmune disease in Mcl-1tg/lpr mice may be influenced not only by Ig-producing cells but also other
haemopoietic cell types
Cold Dust in Three Massive Evolved Stars in the LMC
Massive evolved stars can produce large amounts of dust, and far-infrared
(IR) data are essential for determining the contribution of cold dust to the
total dust mass. Using Herschel, we search for cold dust in three very dusty
massive evolved stars in the Large Magellanic Cloud: R71 is a Luminous Blue
Variable, HD36402 is a Wolf-Rayet triple system, and IRAS05280-6910 is a red
supergiant. We model the spectral energy distributions using radiative transfer
codes and find that these three stars have mass-loss rates up to 10^-3 solar
masses/year, suggesting that high-mass stars are important contributors to the
life-cycle of dust. We found far-IR excesses in two objects, but these excesses
appear to be associated with ISM and star-forming regions. Cold dust (T < 100
K) may thus not be an important contributor to the dust masses of evolved
stars.Comment: accepted to A&A as part of the Herschel first results special issu
Experimental and numerical analysis of initial plasticity in P91 steel small punch creep samples
To date, the complex behaviour of small punch creep test (SPCT) specimens has not been completely understood, making the test hard to numerically model and the data difficult to interpret. This paper presents a novel numerical model able to generate results that match the experimental findings. For the first time, pre-strained uniaxial creep test data of a P91 steel at 600 °C have been implemented in a conveniently modified Liu and Murakami creep damage model in order to simulate the effects of the initial localised plasticity on the subsequent creep response of a small punch creep test specimen. Finite element (FE) results, in terms of creep displacement rate and time to failure, obtained by the modified Liu and Murakami model are in good agreement with experimental small punch creep test data. The rupture times obtained by the FE calculations which make use of the non-modified creep damage model are one order of magnitude shorter than those obtained by using the modified constitutive model. Although further investigation is needed, this novel approach has confirmed that the effects of initial localised plasticity, taking place in the early stages of small punch creep test, cannot be neglected. The new results, obtained by using the modified constitutive model, show a significant improvement with respect to those obtained by a state of the art creep damage constitutive model (the Liu and Murakami constitutive model) both in terms of minimum load-line displacement rate and time to rupture. The new modelling method will potentially lead to improved capability for SPCT data interpretatio
Quantitative analysis of WC stars: Constraints on neon abundances from ISO/SWS spectroscopy
Neon abundances are derived in four Galactic WC stars -- gamma Vel (WR11,
WC8+O7.5III), HD156385 (WR90, WC7), HD192103 (WR135, WC8), and WR146 (WC5+O8) -
using mid-infrared fine structure lines obtained with ISO/SWS. Stellar
parameters for each star are derived using a non-LTE model atmospheric code
(Hillier & Miller 1998) together with ultraviolet (IUE), optical (INT, AAT) and
infrared (UKIRT, ISO) spectroscopy. In the case of gamma Vel, we adopt results
from De Marco et al. (2000), who followed an identical approach.
ISO/SWS datasets reveal the [NeIII] 15.5um line in each of our targets, while
[NeII] 12.8um, [SIV] 10.5um and [SIII] 18.7um are observed solely in gamma Vel.
Using a method updated from Barlow et al. (1988) to account for clumped winds,
we derive Ne/He=3-4x10^-3 by number, plus S/He=6x10^-5 for gamma Vel. Neon is
highly enriched, such that Ne/S in gamma Vel is eight times higher than cosmic
values. However, observed Ne/He ratios are a factor of two times lower than
predictions of current evolutionary models of massive stars. An imprecise
mass-loss and distance were responsible for the much greater discrepancy in
neon content identified by Barlow et al.
Our sample of WC5--8 stars span a narrow range in T* (=55--71kK), with no
trend towards higher temperature at earlier spectral type, supporting earlier
results for a larger sample by Koesterke & Hamann (1995). Stellar luminosities
range from 100,000 to 500,000 Lo, while 10^-5.1 < Mdot/(Mo/yr) < 10^-4.5,
adopting clumped winds, in which volume filling factors are 10%. In all cases,
wind performance numbers are less than 10, significantly lower than recent
estimates. Carbon abundances span 0.08 < C/He < 0.25 by number, while oxygen
abundances remain poorly constrained.Comment: 16 pages,7 figures accepted for MNRA
Laparoscopic resection of a lymphangiomatous cyst of the colon: a case report
<p>Abstract</p> <p>Introduction</p> <p>Lymphangiomatous cysts are submucosal masses that are rarely found in the gastrointestinal tract and more often in the neck, oral cavity, and skin. These cysts are benign tumors and mostly clinically silent. Symptoms include abdominal pain, diarrhea, and rectal bleeding. Their pathogenesis remains unclear.</p> <p>Case presentation</p> <p>During a routine ultrasound examination of a Caucasian 25-year-old woman, a structure that raised our suspicions of an ovarian cyst was found. MRI showed a 4.5 cm cystic lesion in the cecal region. Laparoscopic exploration revealed unexpected contact with the ascending colon. The cyst, including its base and of portion of the colon, was resected laparoscopically. The histological examination revealed cystic lymphangioma.</p> <p>Conclusion</p> <p>Lymphangiomatous cysts of the colon are very rare lesions. Although their pathology is benign, the recommended treatment is resection, which can be performed with minimal invasiveness.</p
Attainment rate as a surrogate indicator of the intervertebral neutral zone length in lateral bending: An in vitro proof of concept study
Background
Lumbar segmental instability is often considered to be a cause of chronic low back pain. However, defining its measurement has been largely limited to laboratory studies. These have characterised segmental stability as the intrinsic resistance of spine specimens to initial bending moments by quantifying the dynamic neutral zone. However these measurements have been impossible to obtain in vivo without invasive procedures, preventing the assessment of intervertebral stability in patients. Quantitative fluoroscopy (QF), measures the initial velocity of the attainment of intervertebral rotational motion in patients, which may to some extent be representative of the dynamic neutral zone. This study sought to explore the possible relationship between the dynamic neutral zone and intervertebral rotational attainment rate as measured with (QF) in an in vitro preparation. The purpose was to find out if further work into this concept is worth pursuing.
Method
This study used passive recumbent QF in a multi-segmental porcine model. This assessed the intrinsic intervertebral responses to a minimal coronal plane bending moment as measured with a digital force guage. Bending moments about each intervertebral joint were calculated and correlated with the rate at which global motion was attained at each intervertebral segment in the first 10° of global motion where the intervertebral joint was rotating.
Results
Unlike previous studies of single segment specimens, a neutral zone was found to exist during lateral bending. The initial attainment rates for left and right lateral flexion were comparable to previously published in vivo values for healthy controls. Substantial and highly significant levels of correlation between initial attainment rate and neutral zone were found for left (Rho = 0.75, P = 0.0002) and combined left-right bending (Rho = 0.72, P = 0.0001) and moderate ones for right alone (Rho = 0.55, P = 0.0012).
Conclusions
This study found good correlation between the initial intervertebral attainment rate and the dynamic neutral zone, thereby opening the possibility to detect segmental instability from clinical studies. However the results must be treated with caution. Further studies with multiple specimens and adding sagittal plane motion are warranted
Communally breeding bats use physiological and behavioural adjustments to optimise daily energy expenditure
Small endotherms must change roosting and thermoregulatory behaviour in response to changes in ambient conditions if they are to achieve positive energy balance. In social species, for example many bats, energy expenditure is influenced by environmental conditions, such as ambient temperature, and also by social thermoregulation. Direct measurements of daily fluctuations in metabolic rates in response to ambient and behavioural variables in the field have not been technologically feasible until recently. During different reproductive periods, we investigated the relationships between ambient temperature, group size and energy expenditure in wild maternity colonies of Bechstein’s bats (Myotis bechsteinii). Bats used behavioural and physiological adjustments to regulate energy expenditure. Whether bats maintained normothermia or used torpor, the number of bats in the roosts as well changed with reproductive status and ambient temperature. During pregnancy and lactation, bats remained mostly normothermic and daily group sizes were relatively large, presumably to participate in the energetic benefits of social thermoregulation. In contrast, smaller groups were formed on days when bats used torpor, which occurred mostly during the post-lactation period. Thus, we were able to demonstrate on wild animals under natural conditions the significance of behavioural and physiological flexibility for optimal thermoregulatory behaviour in small endotherms
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