5,562 research outputs found
A possible route to spontaneous reduction of the heat conductivity by a temperature gradient driven instability in electron-ion plasmas
We have shown that there exists low-frequency growing modes driven by a
global temperature gradient in electron and ion plasmas, by linear perturbation
analysis within the frame work of plasma Kinetic theory. The driving force of
the instability is the local deviation of the distribution function from the
Maxwell-Boltzmann due to global temperature gradient. Application to the
intracluster medium shows that scattering of the particles due to waves excited
by the instability is possible to reduce mean free paths of electron and ion
down to five to seven order of magnitude than the mean free paths due to
Coulomb collisions. This may provide a hint to explain why hot and cool gas can
co-exist in the intracluster medium in spite of the very short evaporation time
scale due to thermal conduction if the conductivity is the classical Spitzer
value. Our results suggest that the realization of the global thermal
equilibrium is postponed by the local instability which is induced for quicker
realization of local thermal equilibrium state in plasmas. The instability
provides a new possibility to create and grow cosmic magnetic fields without
any seed magnetic field.Comment: Accepted for publication in ApJ: 16 pages, 1figur
Anisotropic magnetic fluctuations in the ferromagnetic superconductor UCoGe studied by angle-resolved ^{59}Co NMR
We have carried out direction-dependent ^{59}Co NMR experiments on a single
crystal sample of the ferromagnetic superconductor UCoGe in order to study the
magnetic properties in the normal state. The Knight shift and nuclear
spin-lattice relaxation rate measurements provide microscopic evidence that
both static and dynamic susceptibilities are ferromagnetic with strong Ising
anisotropy. We discuss that superconductivity induced by these magnetic
fluctuations prefers spin-triplet pairing state.Comment: 4 pages, 4 figure
Can One Distinguish Tau Neutrinos from Antineutrinos in Neutral-Current Pion Production Processes?
A potential way to distinguish tau-neutrinos from antineutrinos, below the
tau-production threshold, but above the pion production one, is presented. It
is based on the different behavior of the neutral current pion production off
the nucleon, depending on whether it is induced by neutrinos or antineutrinos.
This procedure for distinguishing tau-neutrinos from antineutrinos neither
relies on any nuclear model, nor it is affected by any nuclear effect
(distortion of the outgoing nucleon waves, etc...). We show that
neutrino-antineutrino asymmetries occur both in the totally integrated cross
sections and in the pion azimuthal differential distributions. To define the
asymmetries for the latter distributions we just rely on Lorentz-invariance.
All these asymmetries are independent of the lepton family and can be
experimentally measured by using electron or muon neutrinos, due to the lepton
family universality of the neutral current neutrino interaction. Nevertheless
and to estimate their size, we have also used the chiral model of
hep-ph/0701149 at intermediate energies. Results are really significant since
the differences between neutrino and antineutrino induced reactions are always
large in all physical channels.Comment: Revised version. 8 pages, 3 figures. The abstract has been changed
and discussion extende
The semantic effects of verb raising and its consequences in second language grammars
This article considers whether highly proficient second language speakers of English can distinguish meaning contrasts associated with constructions where there is a raising be, and constructions where there is a non-raising thematic verb, as illustrated in the difference between (1a) and (1b): 1a. Kim is reading a novel (`event-in-progress/existential ? interpretation
A massive star origin for an unusual helium-rich supernova in an elliptical galaxy
The unusual helium-rich (type Ib) supernova SN 2005E is distinguished from
any supernova hitherto observed by its faint and rapidly fading light curve,
prominent calcium lines in late-phase spectra and lack of any mark of recent
star formation near the supernova location. These properties are claimed to be
explained by a helium detonation in a thin surface layer of an accreting white
dwarf (Perets et al. 2010). Here we report on observations of SN 2005cz
appeared in an elliptical galaxy, whose observed properties resemble those of
SN 2005E in that it is helium-rich and unusually faint, fades rapidly, shows
much weaker oxygen emission lines than those of calcium in the well-evolved
spectrum. We argue that these properties are best explained by a core-collapse
supernova at the low-mass end () of the range of massive stars
that explode (Smartt 2009). Such a low mass progenitor had lost its
hydrogen-rich envelope through binary interaction, having very thin oxygen-rich
and silicon-rich layers above the collapsing core, thus ejecting a very small
amount of radioactive Ni and oxygen. Although the host galaxy NGC 4589
is an elliptical, some studies have revealed evidence of recent star-formation
activity (Zhang et al. 2008), consistent with the core-collapse scenario.Comment: Accepted by Nature (24 March 2010), 32 pages including Supplementary
Informatio
Origin of the tetragonal-to-orthorhombic (nematic) phase transition in FeSe: a combined thermodynamic and NMR study
The nature of the tetragonal-to-orthorhombic structural transition at
K in single crystalline FeSe is studied using shear-modulus,
heat-capacity, magnetization and NMR measurements. The transition is shown to
be accompanied by a large shear-modulus softening, which is practically
identical to that of underdoped Ba(Fe,Co)As, suggesting very similar
strength of the electron-lattice coupling. On the other hand, a
spin-fluctuation contribution to the spin-lattice relaxation rate is only
observed below . This indicates that the structural, or "nematic", phase
transition in FeSe is not driven by magnetic fluctuations
Manifestations of fine features of the density of states in the transport properties of KOs2O6
We performed high-pressure transport measurements on high-quality single
crystals of KOs2O6, a beta-pyrochlore superconductor. While the resistivity at
high temperatures might approach saturation, there is no sign of saturation at
low temperatures, down to the superconducting phase. The anomalous resistivity
is accompanied by a nonmetallic behavior in the thermoelectric power (TEP) up
to temperatures of at least 700 K, which also exhibits a broad hump with a
maximum at 60 K. The pressure influences mostly the low-energy electronic
excitations. A simple band model based on enhanced density of states in a
narrow window around the Fermi energy (EF) explains the main features of this
unconventional behavior in the transport coefficients and its evolution under
pressure
Superconductivity induced by longitudinal ferromagnetic fluctuations in UCoGe
From detailed angle-resolved NMR and Meissner measurements on a ferromagnetic
(FM) superconductor UCoGe (T_Curie ~ 2.5 K and T_SC ~ 0.6 K), we show that
superconductivity in UCoGe is tightly coupled with longitudinal FM spin
fluctuations along the c axis. We found that magnetic fields along the c axis
(H || c) strongly suppress the FM fluctuations and that the superconductivity
is observed in the limited magnetic field region where the longitudinal FM spin
fluctuations are active. These results combined with model calculations
strongly suggest that the longitudinal FM spin fluctuations tuned by H || c
induce the unique spin-triplet superconductivity in UCoGe. This is the first
clear example that FM fluctuations are intimately related with
superconductivity.Comment: 4 pages, 5 figures, to appear in PR
Evolution of Multiphase Hot Interstellar Medium in Elliptical Galaxies
We present the results of a variety of simulations concerning the evolution
of multiphase (inhomogeneous) hot interstellar medium (ISM) in elliptical
galaxies. We assume the gases ejected from stars do not mix globally with the
circumferential gas. The ejected gas components evolve separately according to
their birth time, position, and origin. We consider cases where supernova
remnants (SNRs) mix with local ISM. The components with high metal abundance
and/or high density cool and drop out of the hot ISM gas faster than the other
components because of their high metal abundance and/or density. This makes the
average metal abundance of the hot ISM low. Furthermore, since the metal
abundance of mass-loss gas decreases with radius, gas inflow from outer region
makes the average metal abundance of the hot ISM smaller than that of mass-loss
gas in the inner region. As gas ejection rate of stellar system decreases, mass
fraction of mass-loss gas ejected at outer region increases in a galaxy. If the
mixing of SNRs is ineffective, our model predicts that observed [Si/Fe] and
[Mg/Fe] should decrease towards the galactic center because of strong iron
emission by SNRs. In the outer region, where the cooling of time of the ISM is
long, the selective cooling is ineffective and most of gas components remain
hot. Thus, the metal abundance of the ISM in this region directly reflects that
of the gas ejected from stars. Our model shows that supernovae are not
effective heating sources in the inner region of elliptical galaxies, because
most of the energy released by them radiates. Therefore, cooling flow is
established even if the supernova rate is high. Mixing of SNRs with ambient ISM
makes the energy transfer between supernova explosion and ambient ISM more
effective.Comment: 21 pages (AASTeX), 14 figures, accepted for publication in The
Astrophysical Journa
Far-infrared all sky diffuse mapping with AKARI
We discuss the capability of AKARI in recovering diffuse far-infrared
emission, and examine the achieved reliability. Critical issues in making
images of diffuse emission are the transient response and long-term stability
of the far-infrared detectors. Quantitative evaluation of these characteristics
are the key to achieving sensitivity comparable to or better than that for
point sources (< 20 -- 95 MJy sr-1). We describe current activity and progress
toward the production of high quality images of the diffuse far-infrared
emission using the AKARI all-sky survey data.Comment: 4 pages, 8 figures, to appear in the Proceedings of the Conference
"AKARI, a light to illuminate the misty Universe", Fukutake Hall, The
University of Tokyo, Japan, 16-19 February 200
- …