11,900 research outputs found
An asymmetrical synchrotron model for knots in the 3C 273 jet
To interpret the emission of knots in the 3C 273 jet from radio to X-rays, we
propose a synchrotron model in which, owing to the shock compression effect,
the injection spectra from a shock into the upstream and downstream emission
regions are asymmetric. Our model could well explain the spectral energy
distributions of knots in the 3C 273 jet, and predictions regarding the knots
spectra could be tested by future observations.Comment: 9 pages, 1 figure, 1 table, new version accepted for publication in
Ap
Intrinsic Josephson junctions in the iron-based multi-band superconductor (V2Sr4O6)Fe2As2
In layered superconductors, Josephson junctions may be formed within the unit
cell due to sufficiently low interlayer coupling. These intrinsic Josephson
junction (iJJ) systems have attracted considerable interest for their
application potential in quantum computing as well as efficient sources of THz
radiation, closing the famous "THz gap". So far, iJJ have been demonstrated in
single-band, copper-based high-Tc superconductors, mainly in Ba-Sr-Ca-Cu-O.
Here we report clear experimental evidence for iJJ behavior in the iron-based
superconductor (V2Sr4O6)Fe2As2. The intrinsic junctions are identified by
periodic oscillations of the flux flow voltage upon increasing a well aligned
in-plane magnetic field. The periodicity is well explained by commensurability
effects between the Josephson vortex lattice and the crystal structure, which
is a hallmark signature of Josephson vortices confined into iJJ stacks. This
finding adds (V2Sr4O6)Fe2As2 as the first iron-based, multi-band superconductor
to the copper-based iJJ materials of interest for Josephson junction
applications, and in particular novel devices based on multi-band Josephson
coupling may be realized.Comment: Accepted in Nature Physic
Optical Excitation of a Nanoparticle Cu/p-NiO Photocathode Improves Reaction Selectivity for COâ‚‚ Reduction in Aqueous Electrolytes
We report the light-induced modification of catalytic selectivity for photoelectrochemical COâ‚‚ reduction in aqueous media using copper (Cu) nanoparticles dispersed onto p-type nickel oxide (p-NiO) photocathodes. Optical excitation of Cu nanoparticles generates hot electrons available for driving COâ‚‚ reduction on the Cu surface, while charge separation is accomplished by hot-hole injection from the Cu nanoparticles into the underlying p-NiO support. Photoelectrochemical studies demonstrate that optical excitation of plasmonic Cu/p-NiO photocathodes imparts increased selectivity for COâ‚‚ reduction over hydrogen evolution in aqueous electrolytes. Specifically, we observed that plasmon-driven COâ‚‚ reduction increased the production of carbon monoxide and formate, while simultaneously reducing the evolution of hydrogen. Our results demonstrate an optical route toward steering the selectivity of artificial photosynthetic systems with plasmon-driven photocathodes for photoelectrochemical COâ‚‚ reduction in aqueous media
Collective Excitations, Nambu-Goldstone Modes and Instability of Inhomogeneous Polariton Condensates
We study non-equilibrium microcavity-polariton condensates (MPCs) in a
harmonic potential trap theoretically. We calculate and analyze the steady
state, collective-excitation modes and instability of MPCs. Within excitation
modes, there exist Nambu-Goldstone modes that can reveal the pattern of the
spontaneous symmetry breaking of MPCs. Bifurcation of the stable and unstable
modes is identified in terms of the pumping power and spot size. The unstable
mechanism associated with the inward supercurrent flow is characterized by the
existence of a supersonic region within the condensate.Comment: 16 pages, 3 figure
The Nullity of Bicyclic Signed Graphs
Let \Gamma be a signed graph and let A(\Gamma) be the adjacency matrix of
\Gamma. The nullity of \Gamma is the multiplicity of eigenvalue zero in the
spectrum of A(\Gamma). In this paper we characterize the signed graphs of order
n with nullity n-2 or n-3, and introduce a graph transformation which preserves
the nullity. As an application we determine the unbalanced bicyclic signed
graphs of order n with nullity n-3 or n-4, and signed bicyclic signed graphs
(including simple bicyclic graphs) of order n with nullity n-5
(Sr_3Sc_2O_5)Fe_2As_2 as a possible parent compound for FeAs-based superconductors
A new compound with the FeAs-layers, namely (Sr_3Sc_2O_5)Fe_2As_2
(abbreviated as FeAs-32522), was successfully fabricated. It has a layered
structure with the space group of I4/mmm, and with the lattice constants a =
4.069 and c = 26.876 . The in-plane Fe ions construct a square
lattice which is close to that of other FeAs-based superconductors, such as
REFeAsO (RE = rare earth elements) and (Ba,Sr)Fe_2As_2. However the inter
FeAs-layer spacing in the new compound is greatly enlarged. The temperature
dependence of resistivity exhibits a weak upturn in the low temperature region,
but a metallic behavior was observed above about 60 K. The magnetic
susceptibility shows also a non-monotonic behavior. Interestingly, the
well-known resistivity anomaly which was discovered in all other parent
compounds, such as REFeAsO, (Ba,Sr)Fe_2As_2 and (Sr,Ca,Eu)FeAsF and associated
with the Spin-Density-Wave (SDW)/structural transition has not been found in
the new system either on the resistivity data or the magnetization data. This
could be induced by the large spacing distance between the FeAs-planes,
therefore the antiferromagnetic correlation between the moments of Fe ions in
neighboring FeAs-layers cannot be established. Alternatively it can also be
attributed to the self-doping effect between Fe and Sc ions. The Hall
coefficient R_H is negative but strongly temperature dependent in wide
temperature region, which indicates the dominance of electrical conduction by
electron-like charge carriers and probably a multi-band effect or a spin
related scattering effect. It is found that the magnetoresistance cannot be
described by the Kohler's rule, which gives further support to above arguments.Comment: 5 pages, 5 figures, some contents added, and one figure adde
The Differential Role of Human Cationic Trypsinogen (PRSS1) p.R122H Mutation in Hereditary and Nonhereditary Chronic Pancreatitis: A Systematic Review and Meta-Analysis.
Background:Environmental factors and genetic mutations have been increasingly recognized as risk factors for chronic pancreatitis (CP). The PRSS1 p.R122H mutation was the first discovered to affect hereditary CP, with 80% penetrance. We performed here a systematic review and meta-analysis to evaluate the associations of PRSS1 p.R122H mutation with CP of diverse etiology. Methods:The PubMed, EMBASE, and MEDLINE database were reviewed. The pooled odds ratio (OR) with 95% confidence intervals was used to evaluate the association of p.R122H mutation with CP. Initial analysis was conducted with all etiologies of CP, followed by a subgroup analysis for hereditary and nonhereditary CP, including alcoholic or idiopathic CP. Results:A total of eight case-control studies (1733 cases and 2415 controls) were identified and included. Overall, PRSS1 p.R122H mutation was significantly associated with an increased risk of CP (OR = 4.78[1.13-20.20]). Further analysis showed p.R122H mutation strongly associated with the increased risk of hereditary CP (OR = 65.52[9.09-472.48]) but not with nonhereditary CP, both alcoholic and idiopathic CP. Conclusions:Our study showing the differential role of p.R122H mutation in various etiologies of CP indicates that this complex disorder is likely influenced by multiple genetic factors as well as environmental factors
Hall effect and magnetoresistance in single crystals of NdFeAsOF
Hall effect and magnetoresistance have been measured on single crystals of
with x = 0 ( = 0 K) and x = 0.18 ( = 50 K). For the undoped samples, strong Hall effect and magnetoresistance with
strong temperature dependence were found below about 150 K. The
magnetoresistance was found to be as large as 30% at 15 K at a magnetic field
of 9 T. From the transport data we found that the transition near 155 K was
accomplished in two steps: first one occurs at 155 K which may be associated
with the structural transition, the second one takes place at about 140 K which
may correspond to the spin-density wave like transition. In the superconducting
sample with = 50 K, it is found that the Hall coefficient also reveals
a strong temperature dependence with a negative sign. But the magnetoresistance
becomes very weak and does not satisfy the Kohler's scaling law. These
dilemmatic results (strong Hall effect and very weak magnetoresistance) prevent
to understand the normal state electric conduction by a simple multi-band model
by taking account the electron and hole pockets. Detailed analysis further
indicates that the strong temperature dependence of cannot be easily
understood with the simple multi-band model either. A picture concerning a
suppression to the density of states at the Fermi energy in lowering
temperature is more reasonable. A comparison between the Hall coefficient of
the undoped sample and the superconducting sample suggests that the doping may
remove the nesting condition for the formation of the SDW order, since both
samples have very similar temperature dependence above 175 K.Comment: 8 pages, 9 figure
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