9,460 research outputs found
Anisotropic superconducting properties of aligned SmLaFeAsOF microcrystalline powder
The SmLaFeAsOF compound is a quasi-2D
layered superconductor with a superconducting transition temperature T = 52
K. Due to the Fe spin-orbital related anisotropic exchange coupling
(antiferromagnetic or ferromagnetic fluctuation), the tetragonal
microcrystalline powder can be aligned at room temperature using the
field-rotation method where the tetragonal -plane is parallel to the
aligned magnetic field B and -axis along the rotation axis.
Anisotropic superconducting properties with anisotropic diamagnetic ratio
2.4 + 0.6 was observed from low field susceptibility
(T) and magnetization M(B). The anisotropic low-field phase diagram
with the variation of lower critical field gives a zero-temperature penetration
depth (0) = 280 nm and (0) = 120 nm. The magnetic
fluctuation used for powder alignment at 300 K may be related with the pairing
mechanism of superconductivity at lower temperature.Comment: 4 pages, 6 figure
Excitonic effects in nonlinear optical responses: Exciton-state formalism and first-principles calculations
Nonlinear optical (NLO) responses have garnered tremendous interest for
decades due to their fundamental and technological interests. The theory and
calculations of NLO responses including electron-hole interactions, which is
especially crucial for reduced-dimensional materials, however, remain
underdeveloped. Here, we develop an ab initio approach to calculate
second-order nonlinear responses (such as second harmonic generation (SHG) and
shift current) with excitonic effects in an exciton-state basis, going beyond
the independent-particle approximation. We compute SHG in monolayer h-BN and
MoS2 employing exciton states from GW-Bethe-Salpeter equation (GW-BSE)
calculations and show both materials exhibit huge excitonic enhancement. The
physical origin of the enhancement is directly understood through the coupling
amplitudes among exciton states, assisted with diagrammatic representations.
Our method provides an accurate and ab initio description of second-order NLO
responses, capturing self-energy and electron-hole interaction effects.Comment: 14 pages, 3 figures; Minor revisio
Role of prostacyclin in pulmonary hypertension
Date of Acceptance: 11/12/2014 This is an open access article distributed under the terms of the Creative Commons Attribution license CC BY-4.0, which permits unrestricted use, distribution and reproduction in any medium, provided the original work is properly cited.Prostacyclin is a powerful cardioprotective hormone released by the endothelium of all blood vessels. Prostacyclin exists in equilibrium with other vasoactive hormones and a disturbance in the balance of these factors leads to cardiovascular disease including pulmonary arterial hypertension. Since it’s discovery in the 1980s concerted efforts have been made to make the best therapeutic utility of prostacyclin, particularly in the treatment of pulmonary arterial hypertension. This has centred on working out the detailed pharmacology of prostacyclin and then synthesising new molecules based on its structure that are more stable or more easily tolerated. In addition, newer molecules have been developed that are not analogues of prostacyclin but that target the receptors that prostacyclin activates. Prostacyclin and related drugs have without doubt revolutionised the treatment and management of pulmonary arterial hypertension but are seriously limited by side effects within the systemic circulation. With the dawn of nanomedicine and targeted drug or stem cell delivery systems it will, in the very near future, be possible to make new formulations of prostacyclin that can evade the systemic circulation allowing for safe delivery to the pulmonary vessels. In this way, the full therapeutic potential of prostacyclin can be realised opening the possibility that pulmonary arterial hypertension will become, if not curable, a chronic manageable disease that is no longer fatal. This review discusses these and other issues relating to prostacyclin and its use in pulmonary arterial hypertensionPeer reviewedFinal Published versio
On the Approximability and Hardness of the Minimum Connected Dominating Set with Routing Cost Constraint
In the problem of minimum connected dominating set with routing cost
constraint, we are given a graph , and the goal is to find the
smallest connected dominating set of such that, for any two
non-adjacent vertices and in , the number of internal nodes on the
shortest path between and in the subgraph of induced by is at most times that in . For general graphs, the only
known previous approximability result is an -approximation algorithm
() for by Ding et al. For any constant , we
give an -approximation
algorithm. When , we give an -approximation
algorithm. Finally, we prove that, when , unless , for any constant , the problem admits no
polynomial-time -approximation algorithm, improving
upon the bound by Du et al. (albeit under a stronger hardness
assumption)
Measurement of the c-axis optical reflectance of AFeAs (A=Ba, Sr) single crystals: Evidence of different mechanisms for the formation of two energy gaps
We present the c-axis optical reflectance measurement on single crystals of
BaFeAs and SrFeAs, the parent compounds of FeAs based
superconductors. Different from the ab-plane optical response where two
distinct energy gaps were observed in the SDW state, only the smaller energy
gap could be seen clearly for \textbf{E}c-axis. The very pronounced
energy gap structure seen at a higher energy scale for
\textbf{E}ab-plane is almost invisible. We propose a novel picture
for the band structure evolution across the SDW transition and suggest
different driving mechanisms for the formation of the two energy gaps.Comment: 4 page
Simple Front End Electronics for Multigap Resistive Plate Chambers
A simple circuit for the presentation of the signals from Multi-gap Resistive
Plate Chambers (MRPCs) to standard existing digitization electronics is
described. The circuit is based on "off-the-shelf" discrete components. An
optimization of the values of specific components is required to match the
aspects of the MRPCs for the given application. This simple circuit is an
attractive option for the initial signal processing for MRPC prototyping and
bench- or beam-testing efforts, as well as for final implementations of
small-area Time-of-Flight systems with existing data acquisition systems.Comment: submitted to Nucl. Inst. and Methods, Section
Symmetry Constraints and the Electronic Structures of a Quantum Dot with Thirteen Electrons
The symmetry constraints imposing on the quantum states of a dot with 13
electrons has been investigated. Based on this study, the favorable structures
(FSs) of each state has been identified. Numerical calculations have been
performed to inspect the role played by the FSs. It was found that, if a
first-state has a remarkably competitive FS, this FS would be pursued and the
state would be crystal-like and have a specific core-ring structure associated
with the FS. The magic numbers are found to be closely related to the FSs.Comment: 13 pages, 5 figure
Three dimensionality of band structure and a large residual quasiparticle population in BaKFeAs as revealed by the c-axis polarized optical measurement
We report on a c-axis polarized optical measurement on a
BaKFeAs single crystal. We find that the c-axis
optical response is significantly different from that of high-T cuprates.
The experiments reveal an anisotropic three-dimensional optical response with
the absence of the Josephson plasma edge in R() in the superconducting
state. Furthermore, different from the ab-plane optical response, a large
residual quasiparticle population down to was observed in
the c-axis polarized reflectance measurement. We elaborate that there exist
nodes for the superconducting gap in regions of the 3D Fermi surface that
contribute dominantly to the c-axis optical conductivity.Comment: 4 figure
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