1,798 research outputs found
SGR 1806-20 Is a Set of Independent Relaxation Systems
The Soft Gamma Repeater 1806-20 produced patterns of bursts during its 1983
outburst that indicate multiple independent energy accumulation sites, each
driven by a continuous power source, with sudden, incomplete releases of the
accumulated energy. The strengths of the power sources and their durations of
activity vary over several orders of magnitude.Comment: Accepted ApJLett, 15 pages, 3 figure
Effect of surface roughness on friction behaviour of steel under boundary lubrication
The friction behaviour of grinded and polished surfaces was evaluated by using a reciprocal sliding tester under lubrication with PAO, PAO + ZnDTP and PAO + ZnDTP + MoDTC. Friction coefficients on the smooth surfaces showed higher values compared to those on the rough surfaces. For lubrication incorporating PAO and PAO + ZnDTP + MoDTC, friction coefficients on both the smoothest and the roughest surfaces decreased with sliding time. On the other hand, friction coefficients between these extremes decreased with sliding time. In this paper, the effects of surface roughness on friction behaviour are discussed
The âmaternal effectâ on epilepsy risk: Analysis of familial epilepsies and reassessment of prior evidence
Objective: Previous studies have observed that epilepsy risk is higher among offspring of affected women thanoffspring of affected men. We tested whether this âmaternal effectâ was present in familial epilepsies, which areenriched for genetic factors that contribute to epilepsy risk.Methods: We assessed evidence of a maternal effect in a cohort of families containing â„3 persons with epilepsyusing three methods: (1) âdownward-lookingâ analysis, comparing the rate of epilepsy in offspring of affectedwomen versus men; (2) âupward-lookingâ analysis, comparing the rate of the epilepsy among mothers versusfathers of affected individuals; (3) lineage analysis, comparing the the proportion of affected individuals withfamily history of epilepsy on the maternal versus paternal side.Results: Downward-looking analysis revealed no difference in epilepsy rates among offspring of affectedmothers versus fathers (prevalence ratio 1.0, 95% CI 0.8, 1.2). Upward-looking analysis revealed more affectedmothers than affected fathers; this effect was similar for affected and unaffected sibships (odds ratio 0.8, 95%CI 0.5, 1.2) and was explained by a combination of differential fertility and participation rates. Lineage analysisrevealed no significant difference in the likelihood of maternal versus paternal family history of epilepsy.Interpretation: We found no evidence of a maternal effect on epilepsy risk in this familial epilepsy cohort.Confounding sex imbalances can create the appearance of a maternal effect in upward-looking analyses andmay have impacted prior studies. We discuss possible explanations for the lack of evidence, in familialepilepsies, of the maternal effect observed in population-based studie
X-ray Line Emission from the Hot Stellar Wind of theta 1 Ori C
We present a first emission line analysis of a high resolution X-ray spectrum
of the stellar wind of theta 1 Ori C obtained with the High Energy Transmission
grating Spectrometer onboard the Chandra X-ray Observatory. The spectra are
resolved into a large number of emission lines from H- and He-like O, Ne, Mg,
Si, S, Ar and Fe ions. The He-like Fe XXV and Li-like Fe XXIV appear quite
strong indicating very hot emitting regions. From H/He flux ratios, as well as
from Fe He/Li emission measure ratios we deduce temperatures ranging from 0.5
to 6.1 x 10^7 K. The He-triplets are very sensitive to density as well. At
these temperatures the relative strengths of the intercombination and forbidden
lines indicate electron densities well above 10^12 cm^-3. The lines appear
significantly broadened from which we deduce a mean velocity of 770 km/s with a
spread between 400 and 2000 km/s. Along with results of the deduced emission
measure we conclude that the X-ray emission could originate in dense and hot
regions with a characteristic size of less then 4 x 10^10 cm.Comment: 4 pages, 3 figure
A Radio Polarimetric Study of the Galactic Center Threads
Multi-frequency, polarimetric VLA observations of the non-thermal filaments
(NTF's), G0.08+0.15, and G359.96+0.09, also known as the Northern and Southern
Threads are presented at 20, 6, 3.6 and 2 cm, with high enough spatial
resolution to be resolved for the first time at 6 and 3.6 cm. The 20 cm image
reveals a wealth of new detail in the radio sources lying within the inner 60
pc of the Galaxy. The Southern Thread has a prominent split along its length,
similar to splitting at the ends of previously studied NTF's. With resolutions
as fine as 2'', the 3.6 and 6 cm images reveal a high degree of continuity and
little substructure internal to the filament. The spectral index of the
Northern Thread has been determined over a broad range of frequencies. Its flux
density falls with frequency, alpha=-0.5 between 90 and 6 cm, and becomes much
steeper (alpha=-2.0) between 6 and 2 cm. The spectral index does not vary
significantly along the length of the Northern Thread, which implies either
that the diffusion timescale for the emitting electrons is less than their
synchrotron lifetime, or that the emitting electrons are reaccelerated
continuously at multiple positions along the filament. Because of the lack of
spectral index variation, we have not located the source of relativistic
electrons. Polarization observations at 6 and 3.6 cm confirm the non-thermal
nature of the emission from the Northern Thread. The fractional polarization in
the Northern Thread reaches 70% in some regions, although the polarized
emission is patchy. Large rotation measures (RM > 2000 rad/m2) have been
observed with irregular variations across the filament.The intrinsic magnetic
field in the Northern Thread is predominantly aligned along its long axis.Comment: 19 pages, incl. 24 figs; to appear in the Astrophysical Journa
First Detection of HCO+ Emission at High Redshift
We report the detection of HCO+(1-0) emission towards the Cloverleaf quasar
(z=2.56) through observations with the Very Large Array. This is the first
detection of ionized molecular gas emission at high redshift (z>2). HCO+
emission is a star formation indicator similar to HCN, tracing dense molecular
hydrogen gas (n(H_2) ~= 10^5 cm^{-3}) within star-forming molecular clouds. We
derive a lensing-corrected HCO+ line luminosity of L'(HCO+) = 3.5 x 10^9 K km/s
pc^2. Combining our new results with CO and HCN measurements from the
literature, we find a HCO+/CO luminosity ratio of 0.08 and a HCO+/HCN
luminosity ratio of 0.8. These ratios fall within the scatter of the same
relationships found for low-z star-forming galaxies. However, a HCO+/HCN
luminosity ratio close to unity would not be expected for the Cloverleaf if the
recently suggested relation between this ratio and the far-infrared luminosity
were to hold. We conclude that a ratio between HCO+ and HCN luminosity close to
1 is likely due to the fact that the emission from both lines is optically
thick and thermalized and emerges from dense regions of similar volumes. The
CO, HCN and HCO+ luminosities suggest that the Cloverleaf is a composite
AGN--starburst system, in agreement with the previous finding that about 20% of
the total infrared luminosity in this system results from dust heated by star
formation rather than heating by the AGN. We conclude that HCO+ is potentially
a good tracer for dense molecular gas at high redshift.Comment: 5 pages, 3 figures, ApJL, in press (accepted May 17, 2006
Nonlinear Integral Equations for Thermodynamics of the U_{q}(\hat{sl(r+1)}) Perk-Schultz Model
We propose a system of nonlinear integral equations (NLIE) which describes
the thermodynamics of the U_{q}(\hat{sl(r+1)}) Perk-Schultz model. These NLIE
correspond to a trigonometric analogue of our previous result
(cond-mat/0212280), and contain only r unknown functions. In particular, they
reduce to Takahashi's NLIE for the XXZ spin chain (cond-mat/0010486) if r=1. We
also calculate the high temperature expansion of the free energy. In particular
for r=1 case, we have succeeded to derive the coefficients of order
O((\frac{J}{T})^{99}).Comment: 19 pages, 4 figures, only the Mathematica file for the high
temperature expansion is replaced, to appear in J.Phys.Soc.Jpn.Vol.74 No.3
(2005
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