600 research outputs found
On the use of new methods and multimedia
In the STEPS project the working group WG2 studied “New teaching and learning methods” and “The use of new multimedia”. Both were surveyed in Bachelor and Master studies of all STEPS members An inventory among universities
and alumni on tools, software, programming languages and the importance of transferable skills was made. A list of categorized methods, tools and transferable skills resulted. The WG2 evaluated MultiMedia (MM) with the MPTL group. In 2009 the project STEPS TWO started. The WG2 focuses on project-based and student centred learning, also trying out some best practice materials with students and
teachers. We address some problems found in categorizing and evaluating methods and materials We describe some didactical aspects and conditions for an effective
integration of MM
Spin-wave softening and Hund's coupling in ferromagnetic manganites
Using one-orbital model of hole-doped manganites, we show with the help of
Holstein-Primakov transformation that finite Hund's coupling is responsible for
the spin-wave softening in the ferromagnetic -phase manganites. We obtain an
analytical result for the spin-wave spectrum for \JH\gg t. In the limit of
infinte Hund's coupling, the spectrum is the conventional nearest-neighbor
Heisenberg ferromagnetic spin-wave. The o(t/\JH)-order correction is negative
and thus accounts for the softening near the zone boundary.Comment: 5 pages, 3 figure
Single-electron tunneling in InP nanowires
We report on the fabrication and electrical characterization of field-effect
devices based on wire-shaped InP crystals grown from Au catalyst particles by a
vapor-liquid-solid process. Our InP wires are n-type doped with diameters in
the 40-55 nm range and lengths of several microns. After being deposited on an
oxidized Si substrate, wires are contacted individually via e-beam fabricated
Ti/Al electrodes. We obtain contact resistances as low as ~10 kOhm, with minor
temperature dependence. The distance between the electrodes varies between 0.2
and 2 micron. The electron density in the wires is changed with a back gate.
Low-temperature transport measurements show Coulomb-blockade behavior with
single-electron charging energies of ~1 meV. We also demonstrate energy
quantization resulting from the confinement in the wire.Comment: 4 pages, 3 figure
Orbital liquid in ferromagnetic manganites: The orbital Hubbard model for electrons
We have analyzed the symmetry properties and the ground state of an orbital
Hubbard model with two orbital flavors, describing a partly filled
spin-polarized band on a cubic lattice, as in ferromagnetic manganites.
We demonstrate that the off-diagonal hopping responsible for transitions
between and orbitals, and the absence of SU(2) invariance
in orbital space, have important implications. One finds that superexchange
contributes in all orbital ordered states, the Nagaoka theorem does not apply,
and the kinetic energy is much enhanced as compared with the spin case.
Therefore, orbital ordered states are harder to stabilize in the Hartree-Fock
approximation (HFA), and the onset of a uniform ferro-orbital polarization and
antiferro-orbital instability are similar to each other, unlike in spin case.
Next we formulate a cubic (gauge) invariant slave boson approach using the
orbitals with complex coefficients. In the mean-field approximation it leads to
the renormalization of the kinetic energy, and provides a reliable estimate for
the ground state energy of the disordered state. Using this approach one finds
that the HFA fails qualitatively in the regime of large Coulomb repulsion
-- the orbital order is unstable, and instead a strongly
correlated orbital liquid with disordered orbitals is realized at any electron
filling.Comment: 25 pages, 9 figure
Evaluation of all-electric secondary power for transport aircraft
This report covers a study by Douglas Aircraft Company (DAC) of electrical power systems for advanced transport aircraft based upon an all-electric design concept. The concept would eliminate distributed hydraulic and pneumatic secondary power systems, and feature an expanded secondary electrical power system redesigned to supply power to the loads customarily supplied by hydraulic or pneumatic power. The initial study was based on an advanced 20-kHz electrical power transmission and distribution system, using a system architecture supplied by NASA-Lewis Research Center for twin-engine aircraft with many advanced power conversion concepts. NASA-LeRC later requested DAC to refocus the study on 400-Hz secondary power distribution. Subsequent work was based on a three-engine MD-11 aircraft, selected by DAC as a baseline system design that would provide data for the comparative cost/benefit analysis. The study concluded that the 20-kHz concept produced many expected benefits, and that the all-electric trijet weight savings on hardware redesign would be 2,304 pounds plus a 2.1-percent fuel reduction and resized for a total weight reduction of 11,000 pounds. Cost reductions for a fleet of 800 aircraft in a 15-year production program were estimated at 76.71 million for RDT&E; 2.74 million per aircrat for production; 120,000 per aircraft for product support; and 1.914 billion saved or a future value of $10.496 billion saved
Influences of multilocus heterozygosity on size during early life
Genetic diversity has been hypothesized to promote fitness of individuals and populations, but few studies have examined how genetic diversity varies with ontogeny. We examined patterns in population and individual genetic diversity and the effect of genetic diversity on individual fitness among life stages (adults and juveniles) and populations of captive yellow perch (Perca flavescens) stocked into two ponds and allowed to spawn naturally. Significant genetic structure developed between adults and offspring in a single generation, even as heterozygosity and allelic richness remained relatively constant. Heterozygosity had no effect on adult growth or survival, but was significantly and consistently positively related to offspring length throughout the first year of life in one pond but not the other. The largest individuals in the pond exhibiting this positive relationship were more outbred than averaged size individuals and also more closely related to one another than they were to average‐sized individuals, suggesting potential heritability of body size or spawn timing effects. These results indicate that the influence of heterozygosity may be mediated through an interaction, likely viability selection, between ontogeny and environment that is most important during early life. In addition, populations may experience significant genetic change within a single generation in captive environments, even when allowed to reproduce naturally. Accounting for the dynamic influences of genetic diversity on early life fitness could lead to improved understanding of recruitment and population dynamics in both wild and captive populations.Heterozygosity is assumed to increase the fitness of individuals throughout life, but ontogenetic variance in heterozygosity–fitness correlations (HFCs) is poorly understood. We observed significant differences in HFCs between yellow perch populations and among life stages, suggesting the influence of heterozygosity may be mediated through an interaction, likely viability selection, between ontogeny and environment that is most important during early life. Accounting for the dynamic influences of genetic diversity on early life fitness could lead to improved understanding of recruitment and population dynamics in both wild and captive populations.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/136477/1/ece32781.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/136477/2/ece32781_am.pd
Mivacurium Sensitivity at the Adductor Pollicis and Hand Grip Muscles: Differences Between Males and Females
Background: Males lose more handgrip strength (HGS) than females when adductor pollicis (AP) TOF ratio decreases. The reason is unclear.
Objectives: The primary aim of this study was to explore gender-related differences in neuromuscular sensitivity to mivacurium. As a secondary aim, clearance of mivacurium was determined.
Methods: In 10 healthy males and 10 healthy females, constant-rate infusions of mivacurium were administered to obtain three different levels of stable neuromuscular block (normalized acceleromyography AP TOF ratio 80, 60, and 40%) in each study subject. Arterial blood samples were collected to determine mivacurium plasma concentrations. The HGS was measured every five minutes. A Hill equation was fitted to data on mivacurium concentration versus normalized AP TOF ratio and HGS to determine drug concentrations associated with 50% maximum effect (C50 AP TOF ratio and C50 HGS). Differences within and between genders were tested with the parametric t-test. Clearance of mivacurium was calculated at each block level as the ratio between drug infusion rate and concentration. Gender-related differences in relationships between AP TOF ratio and HGS, mivacurium infusion rates, and mivacurium plasma concentrations were determined with linear mixed-models.
Results: The C50 AP TOF ratio was significantly greater than C50HGSin males, yet not in females. Mivacurium infusion rates, needed to maintain stable neuromuscular blocks, were significantly greater in males, while clearance was similar between genders. Males lost significantly more HGS with decreasing AP TOF ratio than females, both in absolute (kg) and relative (percentage of baseline) terms.
Conclusions: In males, yet not in females, the AP was significantly less sensitive to the effect of mivacurium than the muscles involved in the handgrip function. Thisfindingexplainswhyhandgripstrength decreasesmorein males than females with decreasing AP TOF ratio during the mivacurium block
Pairing Correlations in a Generalized Hubbard Model for the Cuprates
Using numerical diagonalization of a 4x4 cluster, we calculate on-site s,
extended s and d pairing correlation functions (PCF) in an effective
generalized Hubbard model for the cuprates, with nearest-neighbor correlated
hopping and next nearest-neighbor hopping t'. The vertex contributions (VC) to
the PCF are significantly enhanced, relative to the t-t'-U model. The behavior
of the PCF and their VC, and signatures of anomalous flux quantization,
indicate superconductivity in the d-wave channel for moderate doping and in the
s-wave channel for high doping and small U.Comment: 5 pages, 5 figure
Damped orbital excitations in the titanates
A possible mechanism for the removal of the orbital degeneracy in RTiO3
(where R=La, Y, ...) is considered. The calculation is based on the
Kugel-Khomskii Hamiltonian for electrons residing in the t2g orbitals of the Ti
ions, and uses a self-consistent pe rturbation expansion in the interaction
between the orbital and the spin degrees of freedom. The latter are assumed to
be ordered in a Neel state, brought about by delicate interactions that are not
included in the Kugel-Khomskii Hamiltonian. Within our model calculations, each
of the t2g bands is found to acquire a finite, temperature-dependent
dispersion, that lifts the orbital degeneracy. The orbital excitations are
found to be heavily damped over a rather wide band. Consequently, they do not
participate as a separate branch of excitations in the low-temperature
thermodynamics.eComment: 6 pages, 3 figure
Microscopic modelling of doped manganites
Colossal magneto-resistance manganites are characterised by a complex
interplay of charge, spin, orbital and lattice degrees of freedom. Formulating
microscopic models for these compounds aims at meeting to conflicting
objectives: sufficient simplification without excessive restrictions on the
phase space. We give a detailed introduction to the electronic structure of
manganites and derive a microscopic model for their low energy physics.
Focussing on short range electron-lattice and spin-orbital correlations we
supplement the modelling with numerical simulations.Comment: 20 pages, 10 figs, accepted for publ. in New J. Phys., Focus issue on
Orbital Physic
- …