3,168 research outputs found
Chandra Observations of the X-Ray Jet of 3C273
We report results from Chandra observations of the X-ray jet of 3C~273 during
the calibration phase in 2000 January. The zeroeth-order images and spectra
from two 40-ks exposures with the HETG and LETG+ACIS-S show a complex X-ray
structure. The brightest optical knots are detected and resolved in the 0.2-8
keV energy band. The X-ray morphology tracks well the optical. However, while
the X-ray brightness decreases along the jet, the outer parts of the jet tend
to be increasingly bright with increasing wavelength. The spectral energy
distributions of four selected regions can best be explained by inverse Compton
scattering of (beamed) cosmic microwave background photons. The model
parameters are compatible with equipartition and a moderate Doppler factor,
which is consistent with the one-sidedness of the jet. Alternative models
either imply implausible physical conditions and energetics (the synchrotron
self-Compton model) or are sufficiently ad hoc to be unconstrained by the
present data (synchrotron radiation from a spatially or temporally distinct
particle population).Comment: 3 figures; Figure 1 in color. Accepted for publication by ApJ Letter
Electronic properties of Fabre charge-transfer salts under various temperature and pressure conditions
Using density functional theory, we determine parameters of tight-binding
Hamiltonians for a variety of Fabre charge transfer salts, focusing in
particular on the effects of temperature and pressure. Besides relying on
previously published crystal structures, we experimentally determine two new
sets of structures; (TMTTF)SbF at different temperatures and
(TMTTF)PF at various pressures. We find that a few trends in the
electronic behavior can be connected to the complex phase diagram shown by
these materials. Decreasing temperature and increasing pressure cause the
systems to become more two-dimensional. We analyze the importance of
correlations by considering an extended Hubbard model parameterized using
Wannier orbital overlaps and show that while charge order is strongly activated
by the inter-site Coulomb interaction, the magnetic order is only weakly
enhanced. Both orders are suppressed when the effective pressure is increased.Comment: 12 pages, 16 figure
Na2V3O7, a frustrated nanotubular system with spin-1/2 diamond rings
Following the recent discussion on the puzzling nature of the interactions in
the nanotubular system Na2V3O7, we present a detailed ab-initio microscopic
analysis of its electronic and magnetic properties. By means of a non-trivial
downfolding study we propose an effective model in terms of tubes of nine-site
rings with the geometry of a spin-diamond necklace with frustrated inter-ring
interactions. We show that this model provides a quantitative account of the
observed magnetic behavior.Comment: 5 pages, 5 figures. Phys. Rev. Lett. (in press
Large-Scale Regular Morphological Patterns in the Radio Jet of NGC 6251
We report on large-scale, regular morphological patterns found in the radio
jet of the nearby radio galaxy NGC 6251. Investigating morphological properties
of this radio jet from the nucleus to a radial distance of 300 arcsec
( 140 kpc) mapped at 1662 MHz and 4885 MHz by Perley, Bridle, &
Willis, we find three chains, each of which consists of five radio knots. We
also find that eight radio knots in the first two chains consist of three small
sub-knots (the triple-knotty substructures). We discuss the observational
properties of these regular morphological patterns.Comment: 8 figures, 15 pages, accepted for publication in A
Iceman Survived due to Cooling Device
Although mild hypothermia treatment is part of the standard postresuscitation care today, no standard method for treatment of accidental severe hypothermia has been yet established. Different strategies including invasive and noninvasive methods have been described in the literature. We present the case of a 75-year-old man with accidental severe hypothermia (23°C) and demonstrate that using a surface cooling device with automatic controlled temperature feedback mechanism (ArcticSun2000 Medivance, Louisville, Colorado, USA) is an effective and safe method for controlled rewarming in this life-threatening setting
Paroxysmal eyeâhead movements in Glut1 deficiency syndrome
Objective:To describe a characteristic paroxysmal eyeâhead movement disorder that occurs in infants with Glut1 deficiency syndrome (Glut1 DS).Methods:We retrospectively reviewed the medical charts of 101 patients with Glut1 DS to obtain clinical data about episodic abnormal eye movements and analyzed video recordings of 18 eye movement episodes from 10 patients.Results:A documented history of paroxysmal abnormal eye movements was found in 32/101 patients (32%), and a detailed description was available in 18 patients, presented here. Episodes started before age 6 months in 15/18 patients (83%), and preceded the onset of seizures in 10/16 patients (63%) who experienced both types of episodes. Eye movement episodes resolved, with or without treatment, by 6 years of age in 7/8 patients with documented long-term course. Episodes were brief (usually <5 minutes). Video analysis revealed that the eye movements were rapid, multidirectional, and often accompanied by a head movement in the same direction. Eye movements were separated by clear intervals of fixation, usually ranging from 200 to 800 ms. The movements were consistent with eyeâhead gaze saccades. These movements can be distinguished from opsoclonus by the presence of a clear intermovement fixation interval and the association of a same-direction head movement.Conclusions:Paroxysmal eyeâhead movements, for which we suggest the term aberrant gaze saccades, are an early symptom of Glut1 DS in infancy. Recognition of the episodes will facilitate prompt diagnosis of this treatable neurodevelopmental disorder.</jats:sec
The J_1-J_2 model revisited : Phenomenology of CuGeO_3
We present a mean field solution of the antiferromagnetic Heisenberg chain
with nearest (J_1) and next to nearest neighbor (J_2) interactions. This
solution provides a way to estimate the effects of frustration. We calculate
the temperature-dependent spin-wave velocity, v_s(T) and discuss the
possibility to determine the magnitude of frustration J_2/J_1 present in quasi
1D compounds from measurements of v_s(T). We compute the thermodynamic
susceptibility at finite temperatures and compare it with the observed
susceptibility of the spin-Peierls compound CuGeO_3. We also use the method to
study the two-magnon Raman continuum observed in CuGeO_3 above the spin-Peierls
transition.Comment: Phys. Rev.
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