26,225 research outputs found
Numerical studies of collapsing interstellar clouds
Numerical simulation of the structure and evolution of interstellar clouds was initiated. Steps were taken toward an integrated treatment of the dynamical, thermal, and chemical processes entering model calculations. A detailed study was made of radiative transfer in molecular lines to allow model predictions to be tested against empirical data. The calculations have successfully reproduced and explained several observed cloud properties, including abundances of complex molecular species and the apparent depletion of CO in dense cores
Evaluation of wind tunnel performance testings of an advanced 45 deg swept 8-bladed propeller at Mach numbers from 0.45 to 0.85
The increased emphasis of fuel conservation in the world and the rapid increase in the cost of jet fuel has stimulated a series of studies of both conventional and unconventional propulsion systems for commercial aircraft. The results of these studies indicate that a fuel saving of 15 to 30 percent may be realized by the use of an advanced high-speed turboprop (Prop-Fan) compared to aircraft equipped with high bypass turbofan engines of equivalent technology. The Prop-Fan propulsion system is being investigated as part of the NASA Aircraft Energy Efficient Program. This effort includes the wind tunnel testing of a series of 8 and 10-blade Prop-Fan models incorporate swept blades. Test results indicate efficiency levels near the goal of 80 percent at Mach 0.8 cruise and an altitude of 10.67 km (35,000 ft). Each successive swept model has shown improved efficiency relative to the straight blade model. The fourth model, with 45 deg swept blades reported herein, shows a net efficiency of 78.2 at the design point with a power loading of 301 kW/sq meter and a tip speed of 243.8 m/sec (800 ft/sec.)
Risk of cancer following primary total hip replacement or primary resurfacing arthroplasty of the hip : A retrospective cohort study in Scotland
Acknowledgements: We are grateful to Lee Barnsdale, Doug Clark, and Richard Dobbie for advice and assistance with data preparation before analysis, and to the three anonymous referees for their helpful comments and suggestions.Peer reviewedPublisher PD
Hopf algebras and characters of classical groups
Schur functions provide an integral basis of the ring of symmetric functions.
It is shown that this ring has a natural Hopf algebra structure by identifying
the appropriate product, coproduct, unit, counit and antipode, and their
properties. Characters of covariant tensor irreducible representations of the
classical groups GL(n), O(n) and Sp(n) are then expressed in terms of Schur
functions, and the Hopf algebra is exploited in the determination of
group-subgroup branching rules and the decomposition of tensor products. The
analysis is carried out in terms of n-independent universal characters. The
corresponding rings, CharGL, CharO and CharSp, of universal characters each
have their own natural Hopf algebra structure. The appropriate product,
coproduct, unit, counit and antipode are identified in each case.Comment: 9 pages. Uses jpconf.cls and jpconf11.clo. Presented by RCK at
SSPCM'07, Myczkowce, Poland, Sept 200
Float-polishing process and analysis of float-polished quartz
A fluid-mechanical model is developed for the float-polishing process. In this model laminar flow between the sample and the lap results in pressure gradients at the grooves that support the sample on a fluid layer. The laminar fluid motion also produces supersmooth, damage-free surfaces. Quartz substrates for applications in high-stress environments were float polished, and their surfaces were analyzed by optical scatterometry, photoacoustic spectroscopy, and atomic force microscopy. The removal of 100 µm of material by a lapping-polishing process, with final float polishing, left low levels of subsurface damage, with a surface roughness of approximately 0.2-nm rms
Tunneling Via Individual Electronic States in Ferromagnetic Nanoparticles
We measure electron tunneling via discrete energy levels in ferromagnetic
cobalt particles less than 4 nm in diameter, using non-magnetic electrodes. Due
to magnetic anisotropy, the energy of each tunneling resonance shifts as an
applied magnetic field rotates the particle's magnetic moment. We see both
spin-increasing and decreasing tunneling transitions, but we do not observe the
spin degeneracy at small magnetic fields seen previously in non-magnetic
materials. The tunneling spectrum is denser than predicted for independent
electrons, possibly due to spin-wave excitations.Comment: 4 pages, 4 figures. Improved by comments from referees, to appear in
Phys. Rev. Let
Covariance, correlation and entanglement
Some new identities for quantum variance and covariance involving commutators
are presented, in which the density matrix and the operators are treated
symmetrically. A measure of entanglement is proposed for bipartite systems,
based on covariance. This works for two- and three-component systems but
produces ambiguities for multicomponent systems of composite dimension. Its
relationship to angular momentum dispersion for symmetric symmetric spin states
is described.Comment: 30 pages, Latex, to appear in J Phys
A Randomized, Controlled Trial of Meditation for Work Stress, Anxiety and Depressed Mood in Full-Time Workers
Objective. To assess the effect of meditation on work stress, anxiety and mood in full-time workers. Methods. 178 adult workers participated in an 8-week, 3-arm randomized controlled trial comparing a “mental silence” approach to meditation (n = 59) to a “relaxation” active control (n = 56) and a wait-list control (n = 63). Participants were assessed before and after using Psychological Strain Questionnaire (PSQ), a subscale of the larger Occupational Stress Inventory (OSI), the State component of the State/Trait Anxiety Inventory for Adults (STAI), and the depression-dejection (DD) subscale of the Profile of Mood States (POMS).
Results. There was a significant improvement for the meditation group compared to both the relaxation control and the wait-list groups the PSQ (P = .026), and DD (P = .019). Conclusions. Mental silence-orientated meditation, in this case Sahaja Yoga meditation, is a safe and effective strategy for dealing with work stress and depressive feelings. The findings suggest that “thought reduction” or “mental silence” may have specific effects relevant to work stress and hence occupational health
Gate-Voltage Studies of Discrete Electronic States in Al Nanoparticles
We have investigated the spectrum of discrete electronic states in single,
nm-scale Al particles incorporated into new tunneling transistors, complete
with a gate electrode. The addition of the gate has allowed (a) measurements of
the electronic spectra for different numbers of electrons in the same particle,
(b) greatly improved resolution and qualitatively new results for spectra
within superconducting particles, and (c) detailed studies of the gate-voltage
dependence of the resonance level widths, which have directly demonstrated the
effects of non-equilibrium excitations.Comment: 4 pages, 7 figure
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