108,071 research outputs found
Preliminary investigation of labyrinth packing pressure drops at onset of swirl-induced rotor instability
Backward and forward subsynchronous instability was observed in a flexible model test rotor under the influence of swirl flow in a straight-through labyrinth packing. The packing pressure drop at the onset of instability was then measured for a range of operating speeds, clearances and inlet swirl conditions. The trend in these measurements for forward swirl and forward instability is generally consistent with the short packing rotor force formulations of Benchert and Wachter. Diverging clearances were also destabilizing and had a forward orbit with forward swirl and a backward orbit with reverse swirl. A larger, stiff rotor model system is now being assembled which will permit testing steam turbine-type straight-through and hi-lo labyrinth packings. With calibrated and adjustable bearings in this new apparatus, direct measure of the net destabilizing force generated by the packings can be made
Increasing EHR Use for Quality Improvement in Community Health Centers: The Role of Networks
Describes how five community health center networks helped implement electronic health records to improve chronic and preventive care, as well as the obstacles they faced, including limited software capabilities, funding, and ability to share resources
Glueball enhancement by color de-confinement
High energy heavy ion collisions lead to the formation of a strong coupling
de-confined phase in which the lightest glueballs are numerous and stable. We
analyze how their properties manifest themselves in experimental spectra and
show that they provide a good signature for color de-confinement.Comment: 9 pages, 4 figure
Models of q-algebra representations: Tensor products of special unitary and oscillator algebras
This paper begins a study of one- and two-variable function space models of irreducible representations of q analogs of Lie enveloping algebras, motivated by recurrence relations satisfied by q-hypergeometric functions. The algebras considered are the quantum algebra Uq(su2) and a q analog of the oscillator algebra (not a quantum algebra). In each case a simple one-variable model of the positive discrete series of finite- and infinite-dimensional irreducible representations is used to compute the Clebsch–Gordan coefficients. It is shown that various q analogs of the exponential function can be used to mimic the exponential mapping from a Lie algebra to its Lie group and the corresponding matrix elements of the ``group operators'' on these representation spaces are computed. It is shown that the matrix elements are polynomials satisfying orthogonality relations analogous to those holding for true irreducible group representations. It is also demonstrated that general q-hypergeometric functions can occur as basis functions in two-variable models, in contrast with the very restricted parameter values for the q-hypergeometric functions arising as matrix elements in the theory of quantum groups
STS-1 mission contamination evaluation approach
The space transportation system 1 mission will be the first opportunity to assess the induced environment of the orbiter payload bay region. Two tools were developed to aid in this assessment. The shuttle payload contamination evaluation computer program was developed to provide an analytical tool for prediction of the induced molecular contamination environment of the space shuttle orbiter during its onorbit operations. An induced environment contamination monitor was constructed and tested to measure the space shuttle orbiter contamination environment inside the payload bay during ascent and descent and inside and outside the payload bay during the onorbit phase. Measurements are to be performed during the four orbital flight test series. Measurements planned for the first flight are described and predicted environmental data are discussed. The results indicate that the expected data are within the measurement range of the induced environment contamination monitor instruments evaluated, and therefore it is expected that useful contamination environmental data will be available after the first flight
Design considerations and test facilities for accelerated radiation effects testing
Test design parameters for accelerated dose rate radiation effects tests for spacecraft parts and subsystems used in long term mission (years) are detailed. A facility for use in long term accelerated and unaccelerated testing is described
Relativistic simulations of the phase-transition-induced collapse of neutron stars
An increase in the central density of a neutron star may trigger a phase
transition from hadronic matter to deconfined quark matter in the core, causing
it to collapse to a more compact hybrid-star configuration. We present a study
of this, building on previous work by Lin et al. (2006). We follow them in
considering a supersonic phase transition and using a simplified equation of
state, but our calculations are general relativistic (using 2D simulations in
the conformally flat approximation) as compared with their 3D Newtonian
treatment. We also improved the treatment of the initial phase transformation,
avoiding the introduction of artificial convection. As before, we find that the
emitted gravitational-wave spectrum is dominated by the fundamental
quasi-radial and quadrupolar pulsation modes but the strain amplitudes are much
smaller than suggested previously, which is disappointing for the detection
prospects. However, we see significantly smaller damping and observe a
nonlinear mode resonance which substantially enhances the emission in some
cases. We explain the damping mechanisms operating, giving a different view
from the previous work. Finally, we discuss the detectability of the
gravitational waves, showing that the signal-to-noise ratio for current or
second generation interferometers could be high enough to detect such events in
our Galaxy, although third generation detectors would be needed to observe them
out to the Virgo cluster, which would be necessary for having a reasonable
event rate.Comment: 28 pages, 27 figures. Minor changes to be consistent with published
versio
Helix Formation and Folding in an Artificial Peptide
We study the relation between -helix formation and folding for a
simple artificial peptide, Ala-Gly-Ala. Our data rely on
multicanonical Monte Carlo simulations where the interactions among all atoms
are taken into account. The free-energy landscape of the peptide is evaluated
for various temperatures. Our data indicate that folding of this peptide is a
two-step process: in a first step two -helices are formed which
afterwards re-arrange themselves into a U-like structure.Comment: 15 pages, with 9 eps figure
Shuttle on-orbit contamination and environmental effects
Ensuring the compatibility of the space shuttle system with payloads and payload measurements is discussed. An extensive set of quantitative requirements and goals was developed and implemented by the space shuttle program management. The performance of the Shuttle system as measured by these requirements and goals was assessed partly through the use of the induced environment contamination monitor on Shuttle flights 2, 3, and 4. Contamination levels are low and generally within the requirements and goals established. Additional data from near-term payloads and already planned contamination measurements will complete the environment definition and allow for the development of contamination avoidance procedures as necessary for any payload
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