1,116 research outputs found
Integrated electrical and mechanical modelling of integrated-full-electric-propulsion systems
Integrated Full Electric Propulsion (IFEP) systems are the subject of much interest at present. Current research is focused on analysing and improving aspects of subsystem and system performance. However, there is a great need to look more widely at the `multi-physics' problem of characterising the dynamic interactions between the electrical and mechanical systems. This paper will discuss the changing nature of modelling and simulation to aid research into IFEP systems, outlining the alternative angle taken by the Advanced Marine Electrical Propulsion Systems (AMEPS) project to characterise and investigate electrical-mechanical system interactions. The paper will describe this approach and highlight the unique challenges associated with the problem, discussing the suitable methods that will be adopted to address these challenges. Finally, an overview of the present and future research opportunities facilitated via the AMEPS project will be presented
Tunneling spectra of submicron BiSrCaCuO intrinsic Josephson junctions: evolution from superconducting gap to pseudogap
Tunneling spectra of near optimally doped, submicron
BiSrCaCuO intrinsic Josephson junctions are presented,
and examined in the region where the superconducting gap evolves into
pseudogap. The spectra are analyzed using a self-energy model, proposed by
Norman {\it et al.}, in which both quasiparticle scattering rate and
pair decay rate are considered. The density of states derived
from the model has the familiar Dynes' form with a simple replacement of
by = ( + )/2. The
parameter obtained from fitting the experimental spectra shows a roughly linear
temperature dependence, which puts a strong constraint on the relation between
and . We discuss and compare the Fermi arc behavior
in the pseudogap phase from the tunneling and angle-resolved photoemission
spectroscopy experiments. Our results indicate an excellent agreement between
the two experiments, which is in favor of the precursor pairing view of the
pseudogap.Comment: 7 pages, 6 figure
Highlighting when animals expend excessive energy for travel using dynamic body acceleration
Travel represents a major cost for many animals so there should be selection pressure for it to be efficient – at minimum cost. However, animals sometimes exceed minimum travel costs for reasons that must be correspondingly important. We use Dynamic Body Acceleration (DBA), an acceleration-based metric, as a proxy for movement-based power, in tandem with vertical velocity (rate of change in depth) in a shark (Rhincodon typus) to derive the minimum estimated power required to swim at defined vertical velocities. We show how subtraction of measured DBA from the estimated minimum power for any given vertical velocity provides a “proxy for power above minimum” metric (PPAmin), highlighting when these animals travel above minimum power. We suggest that the adoption of this metric across species has value in identifying where and when animals are subject to compelling conditions that lead them to deviate from ostensibly judicious energy expenditure
Mixed-State Quasiparticle Spectrum for d-wave Superconductors
Controversy concerning the pairing symmetry of high- materials has
motivated an interest in those measurable properties of superconductors for
which qualitative differences exist between the s-wave and d-wave cases. We
report on a comparison between the microscopic electronic properties of d-wave
and s-wave superconductors in the mixed state. Our study is based on
self-consistent numerical solutions of the mean-field Bogoliubov-de Gennes
equations for phenomenological BCS models which have s-wave and d-wave
condensates in the absence of a magnetic field. We discuss differences between
the s-wave and the d-wave local density-of-states, both near and away from
vortex cores. Experimental implications for both scanning-tunneling-microscopy
measurements and specific heat measurements are discussed.Comment: 10 pages, REVTEX3.0, 3 figures available upon reques
Application of density functional theory in the synthesis of electroactive polymers
A wide range of conjugated organic compounds undergo anodic electropolymerisation to produce polymers of high conductivity. However, electrooxidation does not always result in the formation of electroactive materials, since some reactions produce insulating films or soluble oligomers. Density functional theory (DFT) has been used to predict the outcome of electropolymerisation reactions by calculating the unpaired electron π-spin density distribution of monomeric radical cations, in order to determine coupling positions in the resultant polymers. π-Spin densities calculated for pyrrole, thiophene and (E)-stilbene are found to be in good agreement with experimental values. DFT has been used to investigate the low conductivity and redox inactivity of poly[(E)-3-styrylthiophenes] and poly[(E)-2-styrylheterocycles]. High positive spin densities at the alkene spacer linkage in the corresponding monomeric radical cations were found, suggesting crosslinking of the polymers via the double bond. In contrast, electroactive polymers of improved conductivity are formed from the electropolymerisation of some (Z)-2-α,β-diarylacrylonitriles. For these monomers, DFT calculations show the positions of highest spin density to be located at the α-positions of the heterocyclic rings, suggesting the presence of α,α′-linked monomeric couplings necessary for electroactivity
Epidemiological Features of the Selenium Status in Cattle of Northern California
Selenium (Se) is an essential mineral for animal
health. Deficiencies result in white muscle
disease (WMD), retained placenta, and ill thrift in
cattle. These health problems are known to occur
in some northern California herds. This survey was
initiated to provide knowledge on the epidemiological
features of Se deficiency in cattle in this region.
Blood samples were drawn from 10 cows on each
of 10 ranches in each of the northern 22 counties.
Whole blood Se and glutathione peroxidase (GSH-Px)
activities were determined, and these values were
statistically compared with each other and with data
obtained by questionnaire. The latter included
information on animal diseases, soils, forages, and
general ranch descriptors like elevation and rainfall.
The GSH-Px spot test produced either a positive
(+), negative (-) or intermediate (+/-) enzyme
activity classification for each cow. Herd
classification was identified as + or - if > 70%
cow-values fell in that class, otherwise it was identified
as +/-.
The overall geometric mean blood-Se value was
47.6 ng/ml. Regressions of individual and herd
GSH-Px-class against blood-Se values produced
r = .75 and r = .82, respectively. Significantly
low blood-Se levels were recorded in herds with:
1) negative GSH-Px values, 2) past histories of WMD
and ill thrift, 3) predominantly hay diet, 4) pregnant
and early lactating cows, and 5) pure bred
cows. The Se status of herds using Se-salt blocks
was not different from non-supplemented herds. Descriptive
ranch variables did not reliably assess
the Se status of herds in this study
Epidemiological features of the selenium status in cattle of northern California
Selenium (Se) is an essential mineral for animal
health. Deficiencies result in white muscle
disease (40), retained placenta, and ill thrift in
cattle. These health problems are known to occur
in some northern California herds. This survey was
initiated to provide knowledge on the epidemiological
features of Se deficiency in cattle in this region.
Blood samples were drawn from 10 cows on each
of 10 ranches in each of the northern 22 counties.
Whole blood Se and glutathione peroxidase (GBH-Px)
activities were determined, and these values were
statistically compared with each other and with data
obtained by questionnaire. The latter included
information on animal diseases, soils, forages, and
general ranch descriptors like elevation and rainfall.
The GSH-Px spot test produced either a positive
(+), negative (-) or intermediate (+/-) enzyme
activity classification for each cow. Herd
classification was identified as + or - if >70%
cow-values fell in that class, otherwise it was identified
as +/-.
The overall geometric mean blood-Se value was
47.6 ng/ml. Regressions of individual and herd
GSH-Px-class against blood-Se values produced
r = .75 and r = .82, respectively. Significantly
low blood-Se levels were recorded in herds with:
1) negative GSH-Px values, 2) past histories of WMD
and ill thrift, 3) predominantly hay diet, 4) pregnant
and early lactating cows, and 5) pure bred
cows. The Se status of herds using Se-salt blocks
was not different from non- supplemented herds. Descriptive
ranch variables did not reliably assess
the Se status of herds in this study
Direct observation of particle-hole mixing in the superconducting state by angle-resolved photoemission
Particle-hole (p-h) mixing is a fundamental consequence of the existence of a
pair condensate. We present direct experimental evidence for p-h mixing in the
angle-resolved photoemission (ARPES) spectra in the superconducting state of
Bi_2Sr_2CaCu_2O_{8+\delta}. In addition to its pedagogical importance, this
establishes unambiguously that the gap observed in ARPES is associated with
superconductivity.Comment: 3 pages, revtex, 4 postscript figure
Low energy collective modes, Ginzburg-Landau theory, and pseudogap behavior in superconductors with long-range pairing interactions
We study the superconducting instability in systems with long but finite
ranged, attractive, pairing interactions. We show that such long-ranged
superconductors exhibit a new class of fluctuations in which the internal
structure of the Cooper pair wave function is soft, and thus lead to
"pseudogap" behavior in which the actual transition temperature is greatly
depressed from its mean field value. These fluctuations are {\it not} phase
fluctuations of the standard superconducting order parameter, and lead to a
highly unusual Ginzburg-Landau description. We suggest that the crossover
between the BCS limit of a short-ranged attraction and our problem is of
interest in the context of superconductivity in the underdoped cuprates.Comment: 20 pages with one embedded ps figure. Minor revisions to the text and
references. Final version to appear in PRB on Nov. 1st, 200
Ginzburg-Landau-Gor'kov Theory of Magnetic oscillations in a type-II 2-dimensional Superconductor
We investigate de Haas-van Alphen (dHvA) oscillations in the mixed state of a
type-II two-dimensional superconductor within a self-consistent Gor'kov
perturbation scheme. Assuming that the order parameter forms a vortex lattice
we can calculate the expansion coefficients exactly to any order. We have
tested the results of the perturbation theory to fourth and eight order against
an exact numerical solution of the corresponding Bogoliubov-de Gennes
equations. The perturbation theory is found to describe the onset of
superconductivity well close to the transition point . Contrary to
earlier calculations by other authors we do not find that the perturbative
scheme predicts any maximum of the dHvA-oscillations below . Instead we
obtain a substantial damping of the magnetic oscillations in the mixed state as
compared to the normal state. We have examined the effect of an oscillatory
chemical potential due to particle conservation and the effect of a finite
Zeeman splitting. Furthermore we have investigated the recently debated issue
of a possibility of a sign change of the fundamental harmonic of the magnetic
oscillations. Our theory is compared with experiment and we have found good
agreement.Comment: 39 pages, 8 figures. This is a replacement of supr-con/9608004.
Several sections changed or added, including a section on the effect of spin
and the effect of a conserved number of particles. To be published in Phys.
Rev.
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