132,943 research outputs found
Local atomic arrangement and martensitic transformation in NiMnIn: An EXAFS Study
Heusler alloys that undergo martensitic transformation in ferromagnetic state
are of increasing scientific and technological interest. These alloys show
large magnetic field induced strains upon martensitic phase change thus making
it a potential candidate for magneto-mechanical actuation. The crystal
structure of martensite is an important factor that affects both the magnetic
anisotropy and mechanical properties of such materials. Moreover, the local
chemical arrangement of constituent atoms is vital in determining the overall
physical properties. NiMnIn is one such ferromagnetic
shape memory alloy that displays exotic properties like large magnetoresistance
at moderate field values. In this work, we present the extended x-ray
absorption fine-structure measurements (EXAFS) on the bulk
NiMnIn which reveal the local structural change that
occurs upon phase transformation. The change in the bond lengths between
different atomic species helps in understanding the type of hybridization which
is an important factor in driving such Ni-Mn based systems towards martensitic
transformation
Higher Descent Data as a Homotopy Limit
We define the 2-groupoid of descent data assigned to a cosimplicial
2-groupoid and present it as the homotopy limit of the cosimplicial space
gotten after applying the 2-nerve in each cosimplicial degree. This can be
applied also to the case of -groupoids thus providing an analogous
presentation of "descent data" in higher dimensions.Comment: Appeared in JHR
Dipole and Quadrupole electroexcitations of the isovector T=1 particle-hole states in C-12
Electroexcitations of the dominantly T=1 particle-hole states of C-12 are
studied in the framework of the harmonic oscillator shell model. All possible
T=1 single-particle-hole states of all allowed angular momenta are considered
in a basis including single-particle states up to the 1f-2p shell. The
Hamiltonian is diagnoalized in this space in the presence of the modified
surface delta interaction. Correlation in the ground state wave functions by
mixing more than one configuration is considered and shows a major contribution
that leads to enhance the calculations of the form factors. A comparison with
the experiment shows that this model is able to fit the location of states and
a simple scaling of the results give a good fit to the experimental form
factors.Comment: 5 pages, 4 figures, 5 tables, Late
Metabolism impacts upon Candida immunogenicity and pathogenicity at multiple levels
Copyright © 2014 The Authors. Published by Elsevier Ltd.. All rights reserved. Open Access funded by Wellcome TrustNon peer reviewedPublisher PD
Solar Flare X-ray Source Motion as a Response to Electron Spectral Hardening
Context: Solar flare hard X-rays (HXRs) are thought to be produced by
nonthermal coronal electrons stopping in the chromosphere, or remaining trapped
in the corona. The collisional thick target model (CTTM) predicts that sources
produced by harder power-law injection spectra should appear further down the
legs or footpoints of a flare loop. Therefore, hardening of the injected
power-law electron spectrum during flare onset should be concurrent with a
descending hard X-ray source.
Aims: To test this implication of the CTTM by comparing its predicted HXR
source locations with those derived from observations of a solar flare which
exhibits a nonthermally-dominated spectrum before the peak in HXRs, known as an
early impulsive event.
Methods: HXR images and spectra of an early impulsive C-class flare were
obtained using the Ramaty High-Energy Solar Spectroscopic Imager (RHESSI).
Images were reconstructed to produce HXR source height evolutions for three
energy bands. Spatially-integrated spectral analysis was performed to isolate
nonthermal emission, and to determine the power-law index of the electron
injection spectrum. The observed height-time evolutions were then fit with
CTTM-based simulated heights for each energy.
Results: A good match between model and observed source heights was reached,
requiring a density model that agreed well with previous studies of flare loop
densities.
Conclusions: The CTTM has been used to produce a descent of model HXR source
heights that compares well with observations of this event. Based on this
interpretation, downward motion of nonthermal sources should indeed occur in
any flare where there is spectral hardening in the electron distribution during
a flare. However, this would often be masked by thermal emission associated
with flare plasma pre-heating.Comment: 8 pages, 5 figure
Smart Materials as Intelligent Insulation
In order to provide a robust infrastructure for the transmission and distribution of electrical power, understanding and monitoring equipment ageing and failure is of paramount importance. Commonly, failure is associated with degradation of the dielectric material; therefore the introduction of a smart moiety into the material is a potentially attractive means of continual condition monitoring. It is important that any introduction of smart groups into the dielectric does not have any detrimental effect on the desirable electrical and mechanical properties of the bulk material. Initial work focussed on the introduction of fluorophores into a model dielectric system. Fluorescence is known to be a visible effect even at very low concentrations of active fluorophores and therefore was thought well suited to such an application. It was necessary both to optimise the active fluorophore itself and to determine the most appropriate manner in which to introduce the fluorophores into the insulating system. This presentation will describe the effect of introducing fluorophores into polymeric systems on the dielectric properties of the material and the findings thus far [1]. Alternative smart material systems will also be discussed along with the benefits and limitations of smart materials as electric field sensors
Characterization of a spheromak plasma gun: The effect of refractory electrode coatings
In order to investigate the proposition that high-Z impurities are responsible for the anomalously short lifetime of the Caltech spheromak, the center electrode of the spheromak plasma gun has been coated with a variety of metals (bare steel, copper, nickel, chromium, rhodium, and tungsten). Visible light (230–890 nm) emitted directly from the plasma in the gun breech was monitored for each of the coated electrodes. Plasma density and temperature and spheromak lifetime were compared for each electrode. Results indicate little difference in gun performance or macroscopic plasma parameters. The chromium and tungsten electrodes performed marginally better in that a previously reported helicity injection effect [Phys. Rev. Lett. 64, 2144 (1990)] is only observed in discharges using these electrode coatings. There are subtle differences in the detailed line emission spectra from the different electrodes, but the spectra are remarkably similar. The fact that (1) contrary to expectations, attempts to reduce high-Z impurities had only marginal effect on the spheromak lifetime coupled with (2) an estimate of Zeff<2 based on a 0-D model suggests that it is not impurities but some other mechanism that limits the lifetime of small, cold spheromaks. We will discuss the general characteristics of the spheromak gun as well as effects due to the coatings
Cold atom realizations of Brownian motors
Brownian motors are devices which "rectify" Brownian motion, i.e. they can
generate a current of particles out of unbiased fluctuations. Brownian motors
are important for the understanding of molecular motors, and are also promising
for the realization of new nanolelectronic devices. Among the different systems
that can be used to study Brownian motors, cold atoms in optical lattices are
quite an unusual one: there is no thermal bath and both the potential and the
fluctuations are determined by laser fields. In this article recent
experimental implementations of Brownian motors using cold atoms in optical
lattices are reviewed
Simultaneous interplanetary scintillation and Heliospheric Imager observations of a coronal mass ejection
We describe simultaneous Interplanetary Scintillation (IPS) and STEREO Heliospheric Imager (HI) observations of a coronal mass ejection (CME) on 16 May 2007. Strong CME signatures were present throughout the IPS observation. The IPS raypath lay within the field-of-view of HI-1 on STEREO-A and comparison of the observations shows that the IPS measurements came from a region within a faint CME front observed by HI-1A. This front may represent the merging of two converging CMEs. Plane-of-sky velocity estimates based on time-height plots of the two converging CME structures were 325 kms?1 and 550 kms?1 for the leading and trailing fronts respectively. The plane-of-sky velocities determined from IPS ranged from 420 ± 10 kms?1 to 520 ± 20 kms?1. IPS results reveal the presence of micro-structure within the CME front which may represent interaction between the two separate CME events. This is the first time that it has been possible to interpret IPS observations of small-scale structure within an interplanetary CME in terms of the global structure of the event
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