207 research outputs found
Nonthermal Emission from a Supernova Remnant in a Molecular Cloud
In evolved supernova remnants (SNRs) interacting with molecular clouds, such
as IC 443, W44, and 3C391, a highly inhomogeneous structure consisting of a
forward shock of moderate Mach number, a cooling layer, a dense radiative shell
and an interior region filled with hot tenuous plasma is expected. We present a
kinetic model of nonthermal electron injection, acceleration and propagation in
that environment and find that these SNRs are efficient electron accelerators
and sources of hard X- and gamma-ray emission. The energy spectrum of the
nonthermal electrons is shaped by the joint action of first and second order
Fermi acceleration in a turbulent plasma with substantial Coulomb losses.
Bremsstrahlung, synchrotron, and inverse Compton radiation of the nonthermal
electrons produce multiwavelength photon spectra in quantitative agreement with
the radio and the hard emission observed by ASCA and EGRET from IC 443. We
distinguish interclump shock wave emission from molecular clump shock wave
emission accounting for a complex structure of molecular cloud. Spatially
resolved X- and gamma- ray spectra from the supernova remnants IC 443, W44, and
3C391 as might be observed with BeppoSAX, Chandra XRO, XMM, INTEGRAL and GLAST
would distinguish the contribution of the energetic lepton component to the
gamma-rays observed by EGRET.Comment: 14 pages, 4 figure, Astrophysical Journal, v.538, 2000 (in press
Theory of vortex excitation imaging via an NMR relaxation measurement
The temperature dependence of the site-dependent nuclear spin relaxation time
T_1 around vortices is studied in s-wave and d-wave superconductors.Reflecting
low energy electronic excitations associated with the vortex core, temperature
dependences deviate from those of the zero-field case, and T_1 becomes faster
with approaching the vortex core. In the core region, T_1^{-1} has a new peak
below T_c. The NMR study by the resonance field dependence may be a new method
to prove the spatial resolved vortex core structure in various superconductors.Comment: 5 pages, 3 figure
Site-selective nuclear magnetic relaxation time in a superconducting vortex state
The temperature and field dependences of the site-selective nuclear spin
relaxation time T_1 around vortices are studied comparatively both for s-wave
and d-wave superconductors, based on the microscopic Bogoliubov-de Gennes
theory. Reflecting low energy electronic excitations associated with the vortex
core, the site selective temperature dependences deviate from those of the
zero-field case, and T_1 becomes faster with approaching the vortex core. In
the core region, T_1^{-1} has a new peak below the superconducting transition
temperature T_c. The field dependence of the overall T_1(T) behaviors for
s-wave and d-wave superconductors is investigated and analyzed in terms of the
local density of states. The NMR study by the resonance field dependence may be
a new method to probe the spatial resolved vortex core structure in various
conventional and unconventional superconductors.Comment: 14Pages, 26 figures, revte
A magnetization and B NMR study of MgAlB superconductors
We demonstrate for the first time the magnetic field distribution of the pure
vortex state in lightly doped MgAlB () powder
samples, by using B NMR in magnetic fields of 23.5 and 47 kOe. The
magnetic field distribution at T=5 K is Al-doping dependent, revealing a
considerable decrease of anisotropy in respect to pure MgB. This result
correlates nicely with magnetization measurements and is consistent with
-band hole driven superconductivity for MgB
Heliospheric Response to Different Possible Interstellar Environments
At present, the heliosphere is embedded in a warm, low-density interstellar cloud that belongs to a cloud system flowing through the local standard of rest with a velocity near ~18 km s-1. The velocity structure of the nearest interstellar material (ISM), combined with theoretical models of the local interstellar cloud (LIC), suggest that the Sun passes through cloudlets on timescales of â€103-104 yr, so the heliosphere has been, and will be, exposed to different interstellar environments over time. By means of a multifluid model that treats plasma and neutral hydrogen self-consistently, the interaction of the solar wind with a variety of partially ionized ISM is investigated, with the focus on low-density cloudlets such as are currently near the Sun. Under the assumption that the basic solar wind parameters remain/were as they are today, a range of ISM parameters (from cold neutral to hot ionized, with various densities and velocities) is considered. In response to different interstellar boundary conditions, the heliospheric size and structure change, as does the abundance of interstellar and secondary neutrals in the inner heliosphere, and the cosmic-ray level in the vicinity of Earth. Some empirical relations between interstellar parameters and heliospheric boundary locations, as well as neutral densities, are extracted from the models
B NMR study of pure and lightly carbon doped MgB superconductors
We report a B NMR line shape and spin-lattice relaxation rate
() study of pure and lightly carbon doped MgBC for
, 0.02, and 0.04, in the vortex state and in magnetic field of 23.5 kOe.
We show that while pure MgB exhibits the magnetic field distribution from
superposition of the normal and the Abrikosov state, slight replacement of
boron with carbon unveils the magnetic field distribution of the pure Abrikosov
state. This indicates a considerable increase of with carbon doping
with respect to pure MgB. The spin-lattice relaxation rate
demonstrates clearly the presence of a coherence peak right below in pure
MgB, followed by a typical BCS decrease on cooling. However, at
temperatures lower than K strong deviation from the BCS behavior is
observed, probably from residual contribution of the vortex dynamics. In the
carbon doped systems both the coherence peak and the BCS temperature dependence
of weaken, an effect attributed to the gradual shrinking of the
hole cylinders of the Fermi surface with electron doping.Comment: 8 pages, 6 figures, submitted to Phys. Rev.
Self-Reported Time in Bed and Sleep Quality in Association with Internalizing and Externalizing Symptoms in School-Age Youth
This study investigated the relationship between self-reported time in bed and sleep quality in association with self-reported internalizing and externalizing symptoms in a sample of 285 elementary school students (52% female) recruited from a rural Midwestern elementary school. Path models were used to estimate proposed associations, controlling for grade level and gender. Curvilinear associations were found between time in bed and anxiety, depressive symptoms, and irritability. Marginal curvilinear trends were found between time in bed and emotion dysregulation, reactive aggression, and proactive aggression. Sleep quality was negatively associated with anxiety, depressive symptoms, irritability, reactive aggression, and delinquency engagement. Gender and grade differences were found across models. Findings suggest that examining self-reported time in bed (both linear and quadratic) and sleep quality is important for understanding internalizing and externalizing symptoms associated with sleep in school-age youth. Incorporating self-reported sleep assessments into clinical practice and school-based evaluations may have implications for a childâs adjustment
Can the Future Influence the Present?
One widely accepted model of classical electrodynamics assumes that a moving charged particle produces both retarded and advanced fields. This formulation first appeared at least 75 years ago. It was popularized in the 1940\u27s by work of Wheeler and Feynman. But the most fundamental question associated with the model has remained unanswered: When (if ever) does the two-body problem have a unique solution? The present paper gives an answer in one special case. Imagine two identical charged particles alone in the universe moving symmetrically along the x axis. One is at x(t) and the other is at âx(t). Their motion is then governed by a system of functional differential equations involving both retarded and advanced arguments. This system together with the Newtonian initial data x(0)=x0\u3e0 and xâČ(0)=0 has a unique solution for all time provided x0 is sufficiently large. Perhaps the existence and uniqueness proof given for this special case will pave the way for more general results on this curious two-body problem
Expression of the Na(+)/l(- )symporter (NIS) is markedly decreased or absent in gastric cancer and intestinal metaplastic mucosa of Barrett esophagus
BACKGROUND: The sodium/iodide symporter (NIS) is a plasma membrane glycoprotein that mediates iodide (I(-)) transport in the thyroid, lactating breast, salivary glands, and stomach. Whereas NIS expression and regulation have been extensively investigated in healthy and neoplastic thyroid and breast tissues, little is known about NIS expression and function along the healthy and diseased gastrointestinal tract. METHODS: Thus, we investigated NIS expression by immunohistochemical analysis in 155 gastrointestinal tissue samples and by immunoblot analysis in 17 gastric tumors from 83 patients. RESULTS: Regarding the healthy Gl tract, we observed NIS expression exclusively in the basolateral region of the gastric mucin-producing epithelial cells. In gastritis, positive NIS staining was observed in these cells both in the presence and absence of Helicobacter pylori. Significantly, NIS expression was absent in gastric cancer, independently of its histological type. Only focal faint NIS expression was detected in the direct vicinity of gastric tumors, i.e., in the histologically intact mucosa, the expression becoming gradually stronger and linear farther away from the tumor. Barrett mucosa with junctional and fundic-type columnar metaplasia displayed positive NIS staining, whereas Barrett mucosa with intestinal metaplasia was negative. NIS staining was also absent in intestinalized gastric polyps. CONCLUSION: That NIS expression is markedly decreased or absent in case of intestinalization or malignant transformation of the gastric mucosa suggests that NIS may prove to be a significant tumor marker in the diagnosis and prognosis of gastric malignancies and also precancerous lesions such as Barrett mucosa, thus extending the medical significance of NIS beyond thyroid disease
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