36,641 research outputs found
Device and method for frictionally testing materials for ignitability
Test apparatus for determining ignition characteristics of various metal in oxidizer environments simulating operating conditions for materials is invented. The test apparatus has a chamber through which the oxidizing agent flows, and means for mounting a stationary test sample therein, a powered, rotating shaft in the chamber rigidly mounts a second test sample. The shaft is axially movable to bring the samples into frictional engagement and heated to the ignition point. Instrumentation connected to the apparatus provides for observation of temperatures, pressures, loads on and speeds of the rotating shaft, and torques whereby components of stressed oxygen systems can be selected which will avoid accidental fires under working conditions
Turbofan blade stresses induced by the flow distortion of a VTOL inlet at high angles of attack
A 51-cm-diameter turbofan with a tilt-nacelle VTOL inlet was tested in the Lewis Research Center's 9- by 15-Ft Low Speed Wind Tunnel at velocities up to 72 m/s and angles of attack up to 120 deg. Fan-blade vibratory stress levels were investigated over a full aircraft operating range. These stresses were due to inlet air flow distortion resulting from (1) internal flow separation in the inlet, and (2) ingestion of the exterior nacelle wake. Stress levels are presented, along with an estimated safe operating envelope, based on infinite blade fatigue life
VSTOL tilt nacelle aerodynamics and its relation to fan blade stresses
A scale model of a VSTOL tilt nacelle with a 0.508 m single stage fan was tested in a low speed wind tunnel to ascertain inlet aerodynamic and fan aeromechanical performance over the low speed flight envelope. Fan blade stress maxima occurred at discrete rotational speeds corresponding to integral engine order vibrations of the first flatwise bending mode. Increased fan blade stress levels coincided with internal boundary layer separation but became severe only when the separation location had progressed to the entry lip region of the inlet
Behavior of the Dripping Faucet over a Wide Range of the Flow Rate
The time interval of successive water-drips from a faucet was examined over a
wide range of the flow rate. The dripping interval alternately exhibits a
stable state and a chaotic state as the flow rate increases. In the stable
state, the volume of the drip is kept constant at fixed flow rates, and the
constant volume increases with the flow rate. In the chaotic state, in addition
to a mechanics that the drip is torn by its own weight, the vibration of the
drip on the faucet takes part in the strange behavior of the interval.Comment: 7 pages, 7 figures, to be published in J. Phys. Soc. Jpn vol
68-2(1999
Learning from MARQuIS: future direction of quality and safety in hospital care in the European Union.
This article summarises the significant lessons to be drawn from, and the policy implications of, the findings of the Methods of Assessing Response to Quality Improvement Strategies (MARQuIS) project--a part of the suite of research projects intended to support policy established by the European Commission through its Sixth Framework Programme. The article first reviews the findings of MARQuIS and their implications for healthcare providers (and particularly for hospitals), and then addresses the broader policy implications for member states of the European Union (EU) and for the commission itself. Against the background of the European Commission's Seventh Framework Programme, it then outlines a number of future areas for research to inform policy and practice in quality and safety in Europe. The article concludes that at this stage, a unique EU-wide quality improvement system for hospitals does not seem to be feasible or effective. Because of possible future community action in this field, attention should focus on the use of existing research on quality and safety strategies in healthcare, with the aim of combining soft measures to accelerate mutual learning. Concrete measures should be considered only in areas for which there is substantial evidence and effective implementation can be ensured
Near-infrared counterparts of three transient very faint neutron star X-ray binaries
We present near-infrared (NIR) imaging observations of three transient
neutron star X-ray binaries, SAX J1753.5-2349, SAX J1806.5-2215 and AX
J1754.2-2754. All three sources are members of the class of `very faint' X-ray
transients which exhibit X-ray luminosities erg s.
The nature of this class of sources is still poorly understood. We detect NIR
counterparts for all three systems and perform multi-band photometry for both
SAX J1753.5-2349 and SAX J1806.5-2215, including narrow-band Br
photometry for SAX J1806.5-2215. We find that SAX J1753.5-2349 is significantly
redder than the field population, indicating that there may be absorption
intrinsic to the system, or perhaps a jet is contributing to the infrared
emission. SAX J1806.5-2215 appears to exhibit absorption in Br,
providing evidence for hydrogen in the system. Our observations of AX
J1754.2--2754 represent the first detection of a NIR counterpart for this
system. We find that none of the measured magnitudes are consistent with the
expected quiescent magnitudes of these systems. Assuming that the infrared
radiation is dominated by either the disc or the companion star, the observed
magnitudes argue against an ultracompact nature for all three systems.Comment: 10 pages, 10 figures, accepted for publication in MNRA
Merged ionization/dissociation fronts in planetary nebulae
The hydrogen ionization and dissociation front around an ultraviolet
radiation source should merge when the ratio of ionizing photon flux to gas
density is sufficiently low and the spectrum is sufficiently hard. This regime
is particularly relevant to the molecular knots that are commonly found in
evolved planetary nebulae, such as the Helix Nebula, where traditional models
of photodissociation regions have proved unable to explain the high observed
luminosity in H_2 lines. In this paper we present results for the structure and
steady-state dynamics of such advection-dominated merged fronts, calculated
using the Cloudy plasma/molecular physics code. We find that the principal
destruction processes for H_2 are photoionization by extreme ultraviolet
radiation and charge exchange reactions with protons, both of which form H_2^+,
which rapidly combines with free electrons to undergo dissociative
recombination. Advection moves the dissociation front to lower column densities
than in the static case, which vastly increases the heating in the partially
molecular gas due to photoionization of He^0, H_2, and H^0. This causes a
significant fraction of the incident bolometric flux to be re-radiated as
thermally excited infrared H_2 lines, with the lower excitation pure rotational
lines arising in 1000 K gas and higher excitation H_2 lines arising in 2000 K
gas, as is required to explain the H_2 spectrum of the Helix cometary knots.Comment: 4 pages, accepted by ApJL, scheduled December 20 issu
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