5,347 research outputs found
Testing of a spacecraft model in a combined environment simulator
A scale model of a satellite was tested in a large vacuum facility under electron bombardment and vacuum ultraviolet radiation to investigate the charging of dielectric materials on curved surfaces. The model was tested both stationary and rotating relative to the electron sources as well as grounded through one megohm and floating relative to the chamber. Surface potential measurements are presented and compared with the predictions of computer modelling of the stationary tests. Discharge activity observed during the stationary tests is discussed and signals from sensing devices located inside and outside of the model are presented
Quantum Dynamical coBoundary Equation for finite dimensional simple Lie algebras
For a finite dimensional simple Lie algebra g, the standard universal
solution R(x) in of the Quantum Dynamical Yang--Baxter
Equation can be built from the standard R--matrix and from the solution F(x) in
of the Quantum Dynamical coCycle Equation as
It has been conjectured that, in the case
where g=sl(n+1) n greater than 1 only, there could exist an element M(x) in
such that in which is
the universal cocycle associated to the Cremmer--Gervais's solution. The aim of
this article is to prove this conjecture and to study the properties of the
solutions of the Quantum Dynamical coBoundary Equation. In particular, by
introducing new basic algebraic objects which are the building blocks of the
Gauss decomposition of M(x), we construct M(x) in as an explicit
infinite product which converges in every finite dimensional representation. We
emphasize the relations between these basic objects and some Non Standard Loop
algebras and exhibit relations with the dynamical quantum Weyl group.Comment: 46 page
Inelastic Quantum Transport and Peierls-like Mechanism in Carbon Nanotubes
We report on a theoretical study of inelastic quantum transport in
carbon nanotubes. By using a many-body description of the electron-phonon
interaction in Fock space, a novel mechanism involving optical phonon emission
(absorption) is shown to induce an unprecedented energy gap opening at half the
phonon energy, , above (below) the charge neutrality point.
This mechanism, which is prevented by Pauli blocking at low bias voltages, is
activated at bias voltages in the order of .Comment: 4 pages, 4 figure
On Automorphisms and Universal R-Matrices at Roots of Unity
Invertible universal R-matrices of quantum Lie algebras do not exist at roots
of unity. There exist however quotients for which intertwiners of tensor
products of representations always exist, i.e. R-matrices exist in the
representations. One of these quotients, which is finite dimensional, has a
universal R-matrix. In this paper, we answer the following question: on which
condition are the different quotients of U_q(sl(2)) (Hopf)-equivalent? In the
case when they are equivalent, the universal R-matrix of one can be transformed
into a universal R-matrix of the other. We prove that this happens only when
q^4=1, and we explicitly give the expressions for the automorphisms and for the
transformed universal R-matrices in this case.Comment: 11 pages, minor TeXnical revision to allow automatic TeXin
Fingerprints of Inelastic Transport at the Surface of the Topological Insulator Bi2Se3: Role of Electron-Phonon Coupling
We report on electric-field and temperature dependent transport measurements
in exfoliated thin crystals of BiSe topological insulator. At low
temperatures ( K) and when the chemical potential lies inside the bulk
gap, the crystal resistivity is strongly temperature dependent, reflecting
inelastic scattering due to the thermal activation of optical phonons. A linear
increase of the current with voltage is obtained up to a threshold value at
which current saturation takes place. We show that the activated behavior, the
voltage threshold and the saturation current can all be quantitatively
explained by considering a single optical phonon mode with energy meV. This phonon mode strongly interacts with the surface states of
the material and represents the dominant source of scattering at the surface at
high electric fields.Comment: Supplementary Material at:
http://journals.aps.org/prl/supplemental/10.1103/PhysRevLett.112.086601/TIPhonon_SM.pd
A note on the generalised Lie algebra sl(2)q
In a recent paper, V. Dobrev and A. Sudbery classified the highest-weight and
lowest-weight finite dimensional irreducible representations of the quantum Lie
algebra sl(2)_q introduced by V. Lyubashenko and A. Sudbery. The aim of this
note is to add to this classification all the finite dimensional irreducible
representations which have no highest weight and/or no lowest weight, in the
case when q is a root of unity. For this purpose, we give a description of the
enlarged centre.Comment: Latex2e, 7 page
6J Symbols Duality Relations
It is known that the Fourier transformation of the square of (6j) symbols has
a simple expression in the case of su(2) and U_q(su(2)) when q is a root of
unit. The aim of the present work is to unravel the algebraic structure behind
these identities. We show that the double crossproduct construction H_1\bowtie
H_2 of two Hopf algebras and the bicrossproduct construction H_2^{*}\lrbicross
H_1 are the Hopf algebras structures behind these identities by analysing
different examples. We study the case where D= H_1\bowtie H_2 is equal to the
group algebra of ISU(2), SL(2,C) and where D is a quantum double of a finite
group, of SU(2) and of U_q(su(2)) when q is real.Comment: 28 pages, 2 figure
Medicine without borders: a literature review of short-term international medical missions
AbstractBackgroundEach year, medical providers and trainees travel to low-income and middle-income countries to deliver direct medical care via short-term medical missions (STMMs) lasting between 1 day and 2 years. In spite of the high prevalence of STMMs, little aggregate information exists about where STMMs go, the services they deliver, and their relationship to the recipient country's health-care system. Our objective was to review the literature on STMMs to better understand their characteristics and identify how they link to the in-country health system.MethodsWe searched MEDLINE-indexed articles on STMMs published between January, 2010, and August, 2014. Exclusion criteria included publications with exclusive focus on medical school curricula, commentaries, and publications on military or disaster medicine. Of 1538 identified articles, 152 met our criteria. Data extracted from the full text of the eligible articles included article type, subject, and STMM details such as location and duration.FindingsNearly half of all articles (72 [47%]) described one or more specific STMMs without any evaluation of the STMM's work; 48 (32%) broadly discussed the concept of STMMs (eg, ethics, best practices); and 32 (21%) evaluated some aspect of an STMM, such as cost-effectiveness or post-operative complication rates. Most articles focused on the implementation of STMMs (66 [43%]), personal experiences of STMMs (36 [24%]), or ethical issues (23 [15%]). Data from 102 articles that detailed an STMM reveal that most medical teams came from the USA, and most STMMs went to Latin America (42 [42%]) or sub-Saharan Africa (34 [34%]). About 40% of articles (41) explicitly state that students were involved in the STMM. About a third (36 [35%]) of these articles did not specify how long the STMM lasted, and approximately half (53[52%]) did not specify how many people were involved in the STMM. Most publications also lacked essential details about STMMs' link to the destination countries' existing health systems. There was little description of the local health needs or how the STMM would affect local health-care delivery, either favourably or unfavourably.InterpretationPublished articles suggest that the prevalence of international STMMs is on the rise. However, very few publications include rigorous evaluation of the services rendered or describe how STMMs link to the recipient country's health-care system.FundingNone
Orbital, precessional and flaring variability of Cygnus X-1
We present the results of a 2.5-year multiwavelength monitoring programme of
Cygnus X-1, making use of hard and soft X-ray data, optical spectroscopy,
UBVJHK photometry and radio data. In particular we confirm that the 5.6-day
orbital period is apparent in all wavebands and note the existence of a
wavelength-dependence to the modulation, in the sense that higher energies
reach minimum first. We also find a strong modulation at a period of 142 +/- 7
days, which we suggest is due to precession and/or radiative warping of the
accretion disc. Strong modulation of the hard and soft X-ray flux at this long
period may not be compatible with simple models of an optically thin accretion
flow and corona in the low state. We present the basic components required for
more detailed future modelling of the system - including a partially optically
thick jet, quasi-continuous in the low state, the base of which acts as the
Comptonising corona. In addition, we find that there are a number of flares
which appear to be correlated in at least two wavebands and generally in more.
We choose two of these flares to study in further detail and find that the hard
and soft X-rays are well-correlated in the first and that the soft X-rays and
radio are correlated in the second. In general, the optical and infrared show
similar behaviour to each other but are not correlated with the X-rays or
radio.Comment: Accepted for publication in MNRAS, 2 figures in colou
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