1,088 research outputs found
Improved Skin Friction Interferometer
An improved system for measuring aerodynamic skin friction which uses a dual-laser-beam oil-film interferometer was developed. Improvements in the optical hardware provided equal signal characteristics for each beam and reduced the cost and complexity of the system by replacing polarization rotation by a mirrored prism for separation of the two signals. An automated, objective, data-reduction procedure was implemented to eliminate tedious manual manipulation of the interferometry data records. The present system was intended for use in two-dimensional, incompressible flows over a smooth, level surface without pressure gradient, but the improvements discussed are not limited to this application
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Assessment of the roles of the Advanced Neutron Source Operators
The Advanced Neutron Source (ANS) is unique in the extent to which human factors engineering (HFE) principles are being applied at the conceptual design stage. initial HFE accomplishments include the development of an ANS HFE program plan, operating philosophy, and functional analysis. In FY 1994, HFE activities focused on the role of the ANS control room reactor operator (RO). An operator-centered control room model was used in conjunction with information gathered from existing ANS system design descriptions and other literature to define a list of RO responsibilities. From this list, a survey instrument was developed and administered to ANS design engineers, operations management personnel at Oak Ridge National Laboratory`s High Flux Isotope Reactor (HFIR), and HFIR ROs to detail the nature of the RO position. Initial results indicated that the RO will function as a high-level system supervisor with considerable monitoring, verification, and communication responsibilities. The relatively high level of control automation has resulted in a reshaping of the RO`s traditional safety and investment protection roles
Operator Role Definition: An Initial Step in the Human Factors Engineering Design of the Advanced Neutron Source (ANS)
The Advanced Neutron Source (ANS) is a new basic and applied research facility sponsored by the U.S. Department of Energy that is proposed for construction. It will provide neutron beams for measurements and experiments in the fields of materials science and engineering, biology, chemistry, materials analysis, and nuclear science. The facility will provide a useful neutron beam flux that is at least five times more than is available at the world`s best existing facilities. It will also provide world-class facilities for isotopes production, materials irradiation testing, materials analysis, and the production of positrons. ANS will be unique in the United States in the extent to which human factors engineering (HFE) principles will be included in its design and construction. Initial HFE accomplishments include the development of a functional analysis, an operating philosophy, and a program plan. In fiscal year 1994, HFE activities are focusing on the role of the ANS control room reactor operator (RO). An operator-centered control room model was used in conjunction with information gathered from existing ANS system design descriptions and other literature to define RO responsibilities. From this list, a survey instrument was developed and administered to ANS design engineers, operations management personnel at Oak Ridge National Laboratory`s High Flux Isotope Reactor (HFIR), and HFIR ROs to detail the nature of the RO position. Initial results indicated that the RO should function as a high-level system supervisor with considerable monitoring, verification, and communication responsibilities. The relatively high level of control automation has resulted in a reshaping of the RO`s traditional safety and investment protection roles
Gravitational Radiation from Nonaxisymmetric Instability in a Rotating Star
We present the first calculations of the gravitational radiation produced by
nonaxisymmetric dynamical instability in a rapidly rotating compact star. The
star deforms into a bar shape, shedding of its mass and
of its angular momentum. The gravitational radiation is calculated in the
quadrupole approximation. For a mass M and radius km, the gravitational waves have frequency kHz and amplitude
at the distance of the Virgo Cluster. They carry off
energy and radiate angular momentum .Comment: 16 pages, LaTeX with REVTEX macros, reprints available - send mailing
address to [email protected]. Published: PRL 72, 1314 (1994
Gravitational Radiation from Rotational Instabilities in Compact Stellar Cores with Stiff Equations of State
We carry out 3-D numerical simulations of the dynamical instability in
rapidly rotating stars initially modeled as polytropes with n = 1.5, 1.0, and
0.5. The calculations are done with a SPH code using Newtonian gravity, and the
gravitational radiation is calculated in the quadrupole limit. All models
develop the global m=2 bar mode, with mass and angular momentum being shed from
the ends of the bar in two trailing spiral arms. The models then undergo
successive episodes of core recontraction and spiral arm ejection, with the
number of these episodes increasing as n decreases: this results in
longer-lived gravitational wave signals for stiffer models. This instability
may operate in a stellar core that has expended its nuclear fuel and is
prevented from further collapse due to centrifugal forces. The actual values of
the gravitational radiation amplitudes and frequencies depend sensitively on
the radius of the star R_{eq} at which the instability develops.Comment: 39 pages, uses Latex 2.09. To be published in the Dec. 15, 1996 issue
of Physical Review D. 21 figures (bitmapped). Originals available in
compressed Postscript format at ftp://zonker.drexel.edu/papers/bars
Anoxic contractile failure in rat heart myocytes is caused by failure of intracellular calcium release due to alteration of the action potential.
Hyperphosphorylation of the cardiac ryanodine receptor at serine 2808 is not involved in cardiac dysfunction after myocardial infarction.
RATIONALE: Abnormal behavior of the cardiac ryanodine receptor (RyR2) has been linked to cardiac arrhythmias and heart failure (HF) after myocardial infarction (MI). It has been proposed that protein kinase A (PKA) hyperphosphorylation of the RyR2 at a single residue, Ser-2808, is a critical mediator of RyR dysfunction, depressed cardiac performance, and HF after MI.
OBJECTIVE: We used a mouse model (RyRS2808A) in which PKA hyperphosphorylation of the RyR2 at Ser-2808 is prevented to determine whether loss of PKA phosphorylation at this site averts post MI cardiac pump dysfunction.
METHODS AND RESULTS: MI was induced in wild-type (WT) and S2808A mice. Myocyte and cardiac function were compared in WT and S2808A animals before and after MI. The effects of the PKA activator Isoproterenol (Iso) on L-type Ca(2+) current (I(CaL)), contractions, and [Ca(2+)](I) transients were also measured. Both WT and S2808A mice had depressed pump function after MI, and there were no differences between groups. MI size was also identical in both groups. L type Ca(2+) current, contractions, Ca(2+) transients, and SR Ca(2+) load were also not significantly different in WT versus S2808A myocytes either before or after MI. Iso effects on Ca(2+) current, contraction, Ca(2+) transients, and SR Ca(2+) load were identical in WT and S2808A myocytes before and after MI at both low and high concentrations.
CONCLUSIONS: These results strongly support the idea that PKA phosphorylation of RyR-S2808 is irrelevant to the development of cardiac dysfunction after MI, at least in the mice used in this study
Stability and collapse of rapidly rotating, supramassive neutron stars: 3D simulations in general relativity
We perform 3D numerical simulations in full general relativity to study the
stability of rapidly rotating, supramassive neutron stars at the mass-shedding
limit to dynamical collapse. We adopt an adiabatic equation of state with
and focus on uniformly rotating stars. We find that the onset of
dynamical instability along mass-shedding sequences nearly coincides with the
onset of secular instability. Unstable stars collapse to rotating black holes
within about one rotation period. We also study the collapse of stable stars
which have been destabilized by pressure depletion (e.g. via a phase
transition) or mass accretion. In no case do we find evidence for the formation
of massive disks or any ejecta around the newly formed Kerr black holes, even
though the progenitors are rapidly rotating.Comment: 16 pages, to appear in Phys. Rev.
Di-μ-methacrylato-κ4 O:O′-bisÂ[aquaÂbis(1,10-phenanthroline-κ2 N,N′)copper(II)] dinitrate dihydrate
The title complex, [Cu2(C4H5O2)2(C12H8N2)2(H2O)2](NO3)2·2H2O, contains a dimeric [Cu2(C4H5O2)2(C12H8N2)2(H2O)2]2+ dication with two five-coordinated CuII ions linked by two methacrylate ions in a syn–syn bridging arrangement. The dication possesses pseudo-twofold rotational symmetry. The pentaÂcoordination of each CuII ion has a distorted square-pyramidal geometry, with two N donors from a phenanthroline ligand and two carboxylÂate O atoms occupying basal sites and the apical position being occupied by a water molÂecule. In the crystal packing, molÂecules are linked to form a three-dimensional framework by O—H⋯O and C—H⋯O hydrogen bonds and π–π interÂactions [centroid–centroid distances of 3.6039 (15), 3.5301 (15), 3.6015 (15), 3.6496 (15) and 3.6858 (15) Å]
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