11,202 research outputs found
GEOS I tracking station positions on the SAO standard earth /C-5/
GEOS 1 tracking station positions on SAO standard earth C-5 mode
Variability Flagging in the Wide-field Infrared Survey Explorer Preliminary Data Release
The Wide-field Infrared Survey Explorer Preliminary Data Release Source Catalog contains over 257 million objects. We describe the method used to flag variable source candidates in the Catalog. Using a method based on the chi-square of single-exposure flux measurements, we generated a variability flag for each object, and have identified almost 460,000 candidate sources that exhibit significant flux variability with greater than ~7Ï confidence. We discuss the flagging method in detail and describe its benefits and limitations. We also present results from the flagging method, including example light curves of several types of variable sources including Algol-type eclipsing binaries, RR Lyr, W UMa, and a blazar candidate
Effect of acylation on the interaction of the N-Terminal segment of pulmonary surfactant protein SP-C with phospholipid membranes.
AbstractSP-C, the smallest pulmonary surfactant protein, is required for the formation and stability of surface-active films at the airâliquid interface in the lung. The protein consists of a hydrophobic transmembrane α-helix and a cationic N-terminal segment containing palmitoylated cysteines. Recent evidence suggests that the N-terminal segment is of critical importance for SP-C function. In the present work, the role of palmitoylation in modulating the lipidâprotein interactions of the N-terminal segment of SP-C has been studied by analyzing the effect of palmitoylated and non-palmitoylated synthetic peptides designed to mimic the N-terminal segment on the dynamic properties of phospholipid bilayers, recorded by spin-label electron spin resonance (ESR) spectroscopy. Both palmitoylated and non-palmitoylated peptides decrease the mobility of phosphatidylcholine (5-PCSL) and phosphatidylglycerol (5-PGSL) spin probes in dipalmitoylphosphatidylcholine (DPPC) or dipalmitoylphosphatidylglycerol (DPPG) bilayers. In zwitterionic DPPC membranes, both peptides have a greater effect at temperatures below than above the main gel-to-liquid-crystalline phase transition, the palmitoylated peptide inducing greater immobilisation of the lipid than does the non-palmitoylated form. In anionic DPPG membranes, both palmitoylated and non-palmitoylated peptides have similar immobilizing effects, probably dominated by electrostatic interactions. Both palmitoylated and non-palmitoylated peptides have effects comparable to whole native SP-C, as regards improving the gel phase solubility of phospholipid spin probes and increasing the polarity of the bilayer surface monitored by pK shifts of fatty acid spin probes. This indicates that a significant part of the perturbing properties of SP-C in phospholipid bilayers is mediated by interactions of the N-terminal segment. The effect of SP-C N-terminal peptides on the chain flexibility gradient of DPPC and DPPG bilayers is consistent with the existence of a peptide-promoted interdigitated phase at temperatures below the main gel-to-liquid-crystalline phase transition. The palmitoylated peptide, but not the non-palmitoylated version, is able to stably segregate interdigitated and non-interdigitated populations of phospholipids in DPPC bilayers. This feature suggests that the palmitoylated N-terminal segment stabilizes ordered domains such as those containing interdigitated lipids. We propose that palmitoylation may be important to promote and facilitate association of SP-C and SP-C-containing membranes with ordered lipid structures such as those potentially existing in highly compressed states of the interfacial surfactant film
Plasma deposition of constrained layer damping coatings
Plasma techniques are used to generate constrained layer damping (CLD) coatings on metallic substrates. The process involves the deposition of relatively thick, hard ceramic layers on to soft polymeric damping materials while maintaining the integrity of both layers. Reactive plasma sputter-deposition from an aluminium alloy target is used to deposit alumina layers, with Young's modulus in the range 77-220GPa and thickness up to 335 Ό, on top of a silicone film. This methodology is also used to deposit a 40 Ό alumina layer on a conventional viscoelastic damping film to produce an integral damping coating. Plasma CLD systems are shown to give at least 50 per cent more damping than equivalent metal-foil-based treatments. Numerical methods for rapid prediction of the performance of such coatings are discussed and validated by comparison with experimental results
Stability and Evolution of Supernova Fallback Disks
We show that thin accretion disks made of Carbon or Oxygen are subject to the
same thermal ionization instability as Hydrogen and Helium disks. We argue that
the instability applies to disks of any metal content. The relevance of the
instability to supernova fallback disks probably means that their power-law
evolution breaks down when they first become neutral. We construct simple
analytical models for the viscous evolution of fallback disks to show that it
is possible for these disks to become neutral when they are still young (ages
of a few 10^3 to 10^4 years), compact in size (a few 10^9 cm to 10^11 cm) and
generally accreting at sub-Eddington rates (Mdot ~ a few 10^14 - 10^18 g/s).
Based on recent results on the nature of viscosity in the disks of close
binaries, we argue that this time may also correspond to the end of the disk
activity period. Indeed, in the absence of a significant source of viscosity in
the neutral phase, the entire disk will likely turn to dust and become passive.
We discuss various applications of the evolutionary model, including anomalous
X-ray pulsars and young radio pulsars. Our analysis indicates that metal-rich
fallback disks around newly-born neutron stars and black holes become neutral
generally inside the tidal truncation radius (Roche limit) for planets, at
\~10^11 cm. Consequently, the efficiency of the planetary formation process in
this context will mostly depend on the ability of the resulting disk of rocks
to spread via collisions beyond the Roche limit. It appears easier for the
merger product of a doubly degenerate binary, whether it is a massive white
dwarf or a neutron star, to harbor planets because it can spread beyond the
Roche limit before becoming neutral.[Abridged]Comment: 34 pages, 2 figures, accepted for publication in Ap
Academic self-concept, gender and single-sex schooling
This paper assesses gender differences in academic self-concept for a cohort of children born in 1958 (the National Child Development Study). We address the question of whether attending single-sex or co-educational schools affected studentsâ perceptions of their own academic abilities (academic self-concept). Academic selfconcept was found to be highly gendered, even controlling for prior test scores. Boys had higher self-concepts in maths and science, and girls in English. Single-sex schooling reduced the gender gap in self-concept, while selective schooling was linked to lower academic self-concept overall
Gravitational Helioseismology?
The magnitudes of the external gravitational perturbations associated with
the normal modes of the Sun are evaluated to determine whether these solar
oscillations could be observed with the proposed Laser Interferometer Space
Antenna (LISA), a network of satellites designed to detect gravitational
radiation. The modes of relevance to LISA---the , low-order , and
-modes---have not been conclusively observed to date. We find that the
energy in these modes must be greater than about in order
to be observable above the LISA detector noise. These mode energies are larger
than generally expected, but are much smaller than the current observational
upper limits. LISA may be confusion-limited at the relevant frequencies due to
the galactic background from short-period white dwarf binaries. Present
estimates of the number of these binaries would require the solar modes to have
energies above about to be observable by LISA.Comment: 8 pages; prepared with REVTEX 3.0 LaTeX macro
The Distance of the Gamma-ray Binary 1FGL J1018.6-5856
The recently discovered gamma-ray binary 1FGL J1018.6-5856 has a proposed
optical/near-infrared (OIR) counterpart 2MASS 10185560-5856459. We present
Stromgren photometry of this star to investigate its photometric variability
and measure the reddening and distance to the system. We find that the
gamma-ray binary has E(B-V) = 1.34 +/- 0.04 and d = 5.4^+4.6_-2.1 kpc. While
E(B-V) is consistent with X-ray observations of the neutral hydrogen column
density, the distance is somewhat closer than some previous authors have
suggested.Comment: Accepted to PAS
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