2,642 research outputs found
Combustor concepts for aircraft gas turbine low-power emissions reduction
Several combustor concepts were designed and tested to demonstrate significant reductions in aircraft engine idle pollutant emissions. Each concept used a different approach for pollutant reductions: the hot wall combustor employs a thermal barrier coating and impingement cooled liners; the recuperative cooling combustor preheats the air before entering the combustion chamber; and the catalytic converter combustor is composed of a conventional primary zone followed by a catalytic bed for pollutant cleanup. The designs are discussed in detail and test results are presented for a range of aircraft engine idle conditions. The results indicate that ultralow levels of unburned hydrocarbons and carbon monoxide emissions can be achieved
A Bayesian Analogue of Gleason's Theorem
We introduce a novel notion of probability within quantum history theories
and give a Gleasonesque proof for these assignments. This involves introducing
a tentative novel axiom of probability. We also discuss how we are to interpret
these generalised probabilities as partially ordered notions of preference and
we introduce a tentative generalised notion of Shannon entropy. A Bayesian
approach to probability theory is adopted throughout, thus the axioms we use
will be minimal criteria of rationality rather than ad hoc mathematical axioms.Comment: 14 pages, v2: minor stylistic changes, v3: changes made in-line with
to-be-published versio
The auxiliary use of LANDSAT data in estimating crop acreages: Results of the 1975 Illinois crop-acreage experiment
The author has identified the following significant results. It was found that classifier performance was influenced by a number of temporal, methodological, and geographical factors. Best results were obtained when corn was tasselled and near the dough stage of development. Dates earlier or later in the growing season produced poor results. Atmospheric effects on results cannot be independently measured or completely separated from the effects due to the maturity stage of the crops. Poor classifier performance was observed in areas where considerable spectral confusion was present
Structural contributions to the pressure-tuned charge-density-wave to superconductor transition in ZrTe3: Raman scattering studies
Superconductivity evolves as functions of pressure or doping from
charge-ordered phases in a variety of strongly correlated systems, suggesting
that there may be universal characteristics associated with the competition
between superconductivity and charge order in these materials. We present an
inelastic light (Raman) scattering study of the structural changes that precede
the pressure-tuned charge-density-wave (CDW) to superconductor transition in
one such system, ZrTe3. In certain phonon bands, we observe dramatic linewidth
reductions that accompany CDW formation, indicating that these phonons couple
strongly to the electronic degrees of freedom associated with the CDW. The same
phonon bands, which represent internal vibrations of ZrTe3 prismatic chains,
are suppressed at pressures above ~10 kbar, indicating a loss of long-range
order within the chains, specifically amongst intrachain Zr-Te bonds. These
results suggest a distinct structural mechanism for the observed
pressure-induced suppression of CDW formation and provide insights into the
origin of pressure-induced superconductivity in ZrTe3.Comment: 6 pages, 5 figure
Assessing Depression-Related Mental Health Literacy among Young Adults
Background and Purpose: Young adults who are 18 to 25 years old have the highest prevalence of depression (10.9%). Depression is a risk factor for suicide. Mental health literacy (MHL) is a key component in assessing recognition and help-seeking for depression with suicidal ideation. This study investigated MHL as it relates to help-seeking for depression with suicidal ideation. Methods: A crosssectional survey design was used. Participants were young adults (n= 430, ages 18 to 24 years old) who lived, worked, and/or attended school in San Francisco, California. Reavley and colleagues’ MHL survey was modified and made available in English, Spanish, and Chinese. Results: Several background factors were positively, though weakly, correlated to MHL, based on the r coefficient. Significant factors were: being female [r=.12,
On Zurek's derivation of the Born rule
Recently, W. H. Zurek presented a novel derivation of the Born rule based on
a mechanism termed environment-assisted invariance, or "envariance" [W. H.
Zurek, Phys. Rev. Lett. 90(2), 120404 (2003)]. We review this approach and
identify fundamental assumptions that have implicitly entered into it,
emphasizing issues that any such derivation is likely to face.Comment: 8 pages; v2: minor clarifications added; v3: reference to Zurek's
quant-ph/0405161 added. To appear in Foundations of Physics (Cushing Volume
Integrable potentials on spaces with curvature from quantum groups
A family of classical integrable systems defined on a deformation of the
two-dimensional sphere, hyperbolic and (anti-)de Sitter spaces is constructed
through Hamiltonians defined on the non-standard quantum deformation of a sl(2)
Poisson coalgebra. All these spaces have a non-constant curvature that depends
on the deformation parameter z. As particular cases, the analogues of the
harmonic oscillator and Kepler--Coulomb potentials on such spaces are proposed.
Another deformed Hamiltonian is also shown to provide superintegrable systems
on the usual sphere, hyperbolic and (anti-)de Sitter spaces with a constant
curvature that exactly coincides with z. According to each specific space, the
resulting potential is interpreted as the superposition of a central harmonic
oscillator with either two more oscillators or centrifugal barriers. The
non-deformed limit z=0 of all these Hamiltonians can then be regarded as the
zero-curvature limit (contraction) which leads to the corresponding
(super)integrable systems on the flat Euclidean and Minkowskian spaces.Comment: 19 pages, 1 figure. Two references adde
Activation of brain regions vulnerable to Alzheimer\u27s disease: The effect of mild cognitive impairment
This study examined the functionality of the medial temporal lobe (MTL) and posterior cingulate (PC) in mild cognitive impairment amnestic type (MCI), a syndrome that puts patients at greater risk for developing Alzheimer disease (AD). Functional MRI (fMRI) was used to identify regions normally active during encoding of novel items and recognition of previously learned items in a reference group of 77 healthy young and middle-aged adults. The pattern of activation in this group guided further comparisons between 14 MCI subjects and 14 age-matched controls. The MCI patients exhibited less activity in the PC during recognition of previously learned items, and in the right hippocampus during encoding of novel items, despite comparable task performance to the controls. Reduced fMRI signal change in the MTL supports prior studies implicating the hippocampus for encoding new information. Reduced signal change in the PC converges with recent research on its role in recognition in normal adults as well as metabolic decline in people with genetic or cognitive risk for AD. Our results suggest that a change in function in the PC may account, in part, for memory recollection failure in AD. © 2005 Elsevier Inc. All rights reserved
Hormone effects on fMRI and cognitive measures of encoding: Importance of hormone preparation
We compared fMRI and cognitive data from nine hormone therapy (HT)-naive women with data from women exposed to either opposed conjugated equine estrogens (CEE) (n = 10) or opposed estradiol (n = 4). Exposure to either form of HT was associated with healthier fMRI response; however, CEE-exposed women exhibited poorer memory performance than either HT-naive or estradiol-exposed subjects. These preliminary findings emphasize the need to characterize differential neural effects of various HTs. ©2006AAN Enterprises, Inc
Unitarity as preservation of entropy and entanglement in quantum systems
The logical structure of Quantum Mechanics (QM) and its relation to other
fundamental principles of Nature has been for decades a subject of intensive
research. In particular, the question whether the dynamical axiom of QM can be
derived from other principles has been often considered. In this contribution,
we show that unitary evolutions arise as a consequences of demanding
preservation of entropy in the evolution of a single pure quantum system, and
preservation of entanglement in the evolution of composite quantum systems.Comment: To be submitted to the special issue of Foundations of Physics on the
occassion of the seventieth birthday of Emilio Santos. v2: 10 pages, no
figures, RevTeX4; Corrected and extended version, containing new results on
consequences of entanglement preservatio
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