2,227 research outputs found
Study of advanced fuel system concepts for commercial aircraft and engines
The impact on a commercial transport aircraft of using fuels which have relaxed property limits relative to current commercial jet fuel was assessed. The methodology of the study is outlined, fuel properties are discussed, and the effect of the relaxation of fuel properties analyzed. Advanced fuel system component designs that permit the satisfactory use of fuel with the candidate relaxed properties in the subject aircraft are described. The two fuel properties considered in detail are freezing point and thermal stability. Three candidate fuel system concepts were selected and evaluated in terms of performance, cost, weight, safety, and maintainability. A fuel system that incorporates insulation and electrical heating elements on fuel tank lower surfaces was found to be most cost effective for the long term
Fetal Environment and Schizophrenia
Schizophrenia and related disorders are adult-onset illnesses with no definitively established risk factors. Several studies report that exposures to infection and nutritional deprivation during early development may elevate the risk of later developing schizophrenia, specifically during the prenatal period. Preliminary evidence implicates lead exposure as well, suggesting that chemical exposures during early development may constitute a new class of risk factors for schizophrenia that has not been adequately investigated. Exposure to lead is given as an example of a chemical agent for which some effects have been described throughout the life course on both general neurodevelopmental outcomes and now on a specific psychiatric diagnosis. Findings from prospectively collected birth cohorts are offered as examples of both innovations in methodology and opportunities for future generations of investigators
The interplay between electron-electron interactions and impurities in one-dimensional rings
The persistent current and charge stiffness of a one-dimensional Luttinger
liquid on a ring threaded by a magnetic flux are calculated by Monte Carlo
simulation. By changing the random impurity potential strength and the
electron-electron interaction, we see a crossover behavior between weak and
strong impurity limits. For weak impurity potentials, interactions enhance
impurity effects, that is, interactions decrease the current and the stiffness.
On the other hand, interactions tend to screen impurities when the impurity
potential is strong. Temperature dependence of the persistent current and the
charge stiffness shows a peak at a characteristic temperature, consistent with
a recent single impurity study.Comment: 4 pages (ReVTeX3.0) + 3 figures (in uuencoded postscript format)
appended in the end of the fil
Local Electronic Structure of a Single Magnetic Impurity in a Superconductor
The electronic structure near a single classical magnetic impurity in a
superconductor is determined using a fully self-consistent Koster-Slater
algorithm. Localized excited states are found within the energy gap which are
half electron and half hole. Within a jellium model we find the new result that
the spatial structure of the positive-frequency (electron-like) spectral weight
(or local density of states), can differ strongly from that of the negative
frequency (hole-like) spectral weight. The effect of the impurity on the
continuum states above the energy gap is calculated with good spectral
resolution for the first time. This is also the first three-dimensional
self-consistent calculation for a strong magnetic impurity potential.Comment: 13 pages, RevTex, change in heuristic picture, no change in numerical
result
Quantum Transition between an Antiferromagnetic Mott Insulator and Superconductor in Two Dimensions
We consider a Hubbard model on a square lattice with an additional
interaction, , which depends upon the square of a near-neighbor hopping. At
half-filling and a constant value of the Hubbard repulsion, increasing the
strength of the interaction drives the system from an antiferromagnetic
Mott insulator to a superconductor. This conclusion is reached
on the basis of zero temperature quantum Monte Carlo simulations on lattice
sizes up to .Comment: 4 pages (latex) and 4 postscript figure
Permanent current from non-commutative spin algebra
We show that a spontaneous electric current is induced in a nano-scale
conducting ring just by putting three ferromagnets. The current is a direct
consequence of the non-commutativity of the spin algebra, and is proportional
to the non-coplanarity (chirality) of the magnetization vectors. The
spontaneous current gives a natural explanation to the chirality-driven
anomalous Hall effect.Comment: 7 pages, 4 figures on separate pag
Attachment, Social Support, and Perceived Mental Health of Adult Dog Walkers: What Does Age Have to Do With It?
In part of a larger pilot study of dog walking as a physical activity intervention we assessed levels of attachment, social supports, and perceived mental health of 75 dog owners, identified through a tertiary- care veterinary hospital. Owners completed the Medical Outcomes Study (MOS) Social Support Survey, mental health component of the Short-Form-12 (SF-12) Health Survey, and the Lexington Attachment to Pets Scale (LAPS). Of particular interest was that younger owners had stronger attachments to their dogs (r = -.488;p \u3c.001) and less social support (r = .269;p =.021). Our study suggests the importance of companion animals for social support, particularly for those without close friends/relatives. For younger owners, our study reveals vulnerabilities in support networks that may warrant referrals to human helping professionals. We suggest the use of Carstensen\u27s Socioemotional Selectivity Theory as an interpretive framework to underscore the importance of including companion animals as part of the human social convoy, especially in terms of providing affectionate and interactional social support
Persistent Currents in 1D Disordered Rings of Interacting Electrons
We calculate the persistent current of 1D rings of spinless fermions with
short-range interactions on a lattice with up to 20 sites, and in the presence
of disorder, for various band fillings. We find that {\it both} disorder and
interactions always decrease the persistent current by localizing the
electrons. Away from half-filling, the interaction has a much stronger
influence in the presence of disorder than in the pure case.Comment: Latex file, 11 pages, 5 figures available on request, Report
LPQTH-93/1
Reversing non-local transport through a superconductor by electromagnetic excitations
Superconductors connected to normal metallic electrodes at the nanoscale
provide a potential source of non-locally entangled electron pairs. Such states
would arise from Cooper pairs splitting into two electrons with opposite spins
tunnelling into different leads. In an actual system the detection of these
processes is hindered by the elastic transmission of individual electrons
between the leads, yielding an opposite contribution to the non-local
conductance. Here we show that electromagnetic excitations on the
superconductor can play an important role in altering the balance between these
two processes, leading to a dominance of one upon the other depending on the
spatial symmetry of these excitations. These findings allow to understand some
intriguing recent experimental results and open the possibility to control
non-local transport through a superconductor by an appropriate design of the
experimental geometry.Comment: 6 pages, 3 figure
Temperature Derivative of the Superfluid Density in the Attractive Hubbard model
Based on extensions of the grand-canonical Quantum Monte-Carlo algorithm to
incorporate magnetic fields, we provide numerical data confirming the existence
of a Kosterlitz-Thouless transition in the attractive Hubbard model. Here, we
calculate the temperature derivative of the superfluid density, to pin down the
transition. Away from half-band filling, the above quantity, shows a response
which increases with lattice size at the transition temperature. In contrast,
such a signal is not observed for the case of a half-band filling.Comment: Latex 8 pages, 3 figures (in postscript format) appendded at the end
of the fil
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