11,215 research outputs found
The Mass Function of Newly Formed Stars (Review)
The topic of the stellar "original mass function" has a nearly 50 year
history,dating to the publication in 1955 of Salpeter's seminal paper. In this
review I discuss the many more recent results that have emerged on the initial
mass function (IMF), as it is now called, from studies over the last decade of
resolved populations in star forming regions and young open clusters.Comment: 9 pages, 1 figure; to appear in "The Dense Instellar Medium in
Galaxies -- 4'th Cologne-Bonn-Zermatt-Symposium" editted by S. Pfalzner, C.
Kramer, C. Straubmeier and A. Heithausen, Springer-Verlag (2004
Cause and Effectors: whole genome comparisons reveal shared but rapidly evolving effector sets among host-specific plant-castrating fungi
International audienceWord Count: 240 16 17 Text Word Count: 6,466 1
Protolith age of Santa Maria Chico granulites dated on zircons from an associated amphibolite-facies granodiorite in southernmost Brazil
On the universal outcome of star-formation: Is there a link between stars and brown-dwarfs?
(abridged) The recent evidence obtained by Briceno et al. that star-formation
in Taurus-Auriga (TA) may be producing significantly fewer brown dwarfs (BDs)
per star than the ONC is investigated by setting up a realistic model stellar
plus BD population and explicitly taking into account a high binary proportion
and dynamical evolution in the TA groups and the ONC. The Briceno result is
reproduced almost exactly despite an identical IMF in both systems because many
BD-BD and star-BD binaries are disrupted in the ONC thus freeing BDs, while the
TA groups remain unevolved dynamically. However, the resulting populations do
not have the correct star-star, star-BD and expecially BD-BD binary properties,
even if a variable BD IMF is allowed for. The conclusion is therefore that BDs
need to be added as a separate population which has its own binary properties.
Such an extra population can have various origins which are briefly discussed
in this contribution but more fully in an associated paper.Comment: MNRAS, accepted, 23 pages, 14 figures, LaTeX, two references adde
Are There Age Spreads in Star Forming Regions?
A luminosity spread at a given effective temperature is ubiquitously seen in
the Hertzsprung-Russell (HR) diagrams of young star forming regions and often
interpreted in terms of a prolonged period (>=10 Myr) of star formation. I
review the evidence that the observed luminosity spreads are genuine and not
caused by astrophysical sources of scatter. I then address whether the
luminosity spreads necessarily imply large age spreads, by comparing HR diagram
ages with ages from independent clocks such as stellar rotation rate, the
presence of circumstellar material and lithium depletion. I argue that whilst
there probably is a true luminosity dispersion, there is little evidence to
support age spreads larger than a few Myr. This paradox could be resolved by
brief periods of rapid accretion during the class I pre main-sequence phase.Comment: To appear in the proceedings of JENAM10: Star Clusters in the Era of
Large Surveys, 8 page
Quantum-Well Infrared Photodetector (QWIP) Focal Plane Assembly
A paper describes the Thermal Infrared Sensor (TIRS), a QWIP-based instrument intended to supplement the Operational Land Imager (OLI) for the Landsat Data Continuity Mission (LDCM). The TIRS instrument is a far-infrared imager operating in the pushbroom mode with two IR channels: 10.8 and 12 microns. The focal plane will contain three 640x512 QWIP arrays mounted on a silicon substrate. The silicon substrate is a custom-fabricated carrier board with a single layer of aluminum interconnects. The general fabrication process starts with a 4-in. (approx.10-cm) diameter silicon wafer. The wafer is oxidized, a single substrate contact is etched, and aluminum is deposited, patterned, and alloyed. This technology development is aimed at incorporating three large-format infrared detecting arrays based on GaAs QWIP technology onto a common focal plane with precision alignment of all three arrays. This focal plane must survive the rigors of flight qualification and operate at a temperature of 43 K (-230 C) for five years while orbiting the Earth. The challenges presented include ensuring thermal compatibility among all the components, designing and building a compact, somewhat modular system and ensuring alignment to very tight levels. The multi-array focal plane integrated onto a single silicon substrate is a new application of both QWIP array development and silicon wafer scale integration. The Invar-based assembly has been tested to ensure thermal reliability
Swift/BAT detection of hard X-rays from Tycho's Supernova Remnant: Evidence for Titanium-44
We report Swift/BAT survey observations of the Tycho's supernova remnant,
performed over a period of 104 months since the mission's launch. The remnant
is detected with high significance (>10 sigma) below 50 keV. We detect
significant hard X-ray emission in the 60-85 keV band, above the continuum
level predicted by a simple synchrotron model. The location of the observed
excess is consistent with line emission from radioactive Titanium-44, so far
reported only for Type II supernova explosions. We discuss the implications of
these results in the context of the galactic supernova rate, and
nucleosynthesis in Type Ia supernova.Comment: 5 pages, 4 figures, accepted for publication in ApJ
Identification of chemokine receptors as potential modulators of endocrine resistance in oestrogen receptor–positive breast cancers
Introduction
Endocrine therapies target oestrogenic stimulation of breast cancer (BC) growth, but resistance remains problematic. Our aims in this study were (1) to identify genes most strongly associated with resistance to endocrine therapy by intersecting global gene transcription data from patients treated presurgically with the aromatase inhibitor anastrazole with those from MCF7 cells adapted to long-term oestrogen deprivation (LTED) (2) to assess the clinical value of selected genes in public clinical data sets and (3) to determine the impact of targeting these genes with novel agents.
Methods
Gene expression and Ki67 data were available from 69 postmenopausal women with oestrogen receptor–positive (ER+) early BC, at baseline and 2 weeks after anastrazole treatment, and from cell lines adapted to LTED. The functional consequences of target genes on proliferation, ER-mediated transcription and downstream cell signalling were assessed.
Results
By intersecting genes predictive of a poor change in Ki67 with those upregulated in LTED cells, we identified 32 genes strongly correlated with poor antiproliferative response that were associated with inflammation and/or immunity. In a panel of LTED cell lines, C-X-C chemokine receptor type 7 (CXCR7) and CXCR4 were upregulated compared to their wild types (wt), and CXCR7, but not CXCR4, was associated with reduced relapse-free survival in patients with ER+ BC. The CXCR4 small interfering RNA variant (siCXCR4) had no specific effect on the proliferation of wt-SUM44, wt-MCF7 and their LTED derivatives. In contrast, siCXCR7, as well as CCX733, a CXCR7 antagonist, specifically suppressed the proliferation of MCF7-LTED cells. siCXCR7 suppressed proteins associated with G1/S transition and inhibited ER transactivation in MCF7-LTED, but not wt-MCF7, by impeding association between ER and proline-, glutamic acid– and leucine-rich protein 1, an ER coactivator.
Conclusions
These data highlight CXCR7 as a potential therapeutic target warranting clinical investigation in endocrine-resistant BC
Effect of school based physical activity programme (KISS) on fitness and adiposity in primary schoolchildren: cluster randomised controlled trial
Objective To assess the effectiveness of a school based physical activity programme during one school year on physical and psychological health in young schoolchildren
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