24,107 research outputs found
Uprated OMS Engine Status-Sea Level Testing Results
The current Space Shuttle Orbital Maneuvering Engine (OME) is pressure fed, utilizing storable propellants. Performance uprating of this engine, through the use of a gas generator driven turbopump to increase operating pressure, is being pursued by the NASA Johnson Space Center (JSC). Component level design, fabrication, and test activities for this engine system have been on-going since 1984. More recently, a complete engine designated the Integrated Component Test Bed (ICTB), was tested at sea level conditions by Aerojet. A description of the test hardware and results of the sea level test program are presented. These results, which include the test condition operating envelope and projected performance at altitude conditions, confirm the capability of the selected Uprated OME (UOME) configuration to meet or exceed performance and operational requirements. Engine flexibility, demonstrated through testing at two different operational mixture ratios, along with a summary of projected Space Shuttle performance enhancements using the UOME, are discussed. Planned future activities, including ICTB tests at simulated altitude conditions, and recommendations for further engine development, are also discussed
Forced convection and flow boiling with and without enhancement devices for top-side-heated horizontal channels
The effect of enhancement devices on flow boiling heat transfer in coolant channels, which are heated either from the top side or uniformly was studied. Studies are completed of the variations in the local (axial and circumferential) and mean heat transfer coefficients in horizontal, top-heated coolant channels with smooth walls and internal heat transfer enhancement devices. The working fluid is freon-11. The objectives are to: (1) examine the variations in both the mean and local (axial and circumferential) heat transfer coefficients for a circular coolant channel with either smooth walls or with both a twisted tape and spiral finned walls; (2) examine the effect of channel diameter (and the length-to-diameter aspect ratio) variations for the smooth wall channel; and (3) develop and improved data reduction analysis. The case of the top-heated, horizontal flow channel with smooth wall (1.37 cm inside diameter, and 122 cm heated length) was completed. The data were reduced using a preliminary analysis based on the heated hydraulic diameter. Preliminary examination of the local heat transfer coefficient variations indicated that there are significant axial and circumferential variations. However, it appears that the circumferential variation is more significant than the axial ones. In some cases, the circumferential variations were as much as a factor of ten. The axial variations rarely exceeded a factor of three
NUMBER AND TYPE OF OPERATING CYCLES FOR THE FFTF
The choice of materials and other vessel design decisions necessary to provide the desired life expectancy for the FTR vessel are partially dependent upon estimates of the number and type of reactor shutdowns and startups which may be anticipated. Current estimates of these so-called "cycles" are given, including scram frequency, experimental outage frequency, standard shutdowns and startups, and rapid controlled shutdowns. Also discussed are abnormal heatup or cooldown, and tentative goals for temperature controls. MTR, ETR, and typical PRTR operating histories are tabulated
Flow boiling with enhancement devices for cold plate coolant channel design
The effects of enhancement devices on flow boiling heat transfer in circular coolant channels, which are heated over a fraction of their perimeters, are studied. The variations were examined in both the mean and local (axial, and circumferential) heat transfer coefficients for a circular coolant channel with either smooth walls or with both a twisted tape and spiral finned walls. Improvements were initiated in the present data reduction analysis. These efforts should lead to the development of heat transfer correlations which include effects of single side heat flux and enhancement device configuration. It is hoped that a stage will be set for the study of heat transfer and pressure drop in single sided heated systems under zero gravity conditions
Quantum-secured imaging
We have built an imaging system that uses a photon's position or
time-of-flight information to image an object, while using the photon's
polarization for security. This ability allows us to obtain an image which is
secure against an attack in which the object being imaged intercepts and
resends the imaging photons with modified information. Popularly known as
"jamming," this type of attack is commonly directed at active imaging systems
such as radar. In order to jam our imaging system, the object must disturb the
delicate quantum state of the imaging photons, thus introducing statistical
errors that reveal its activity.Comment: 10 pages (double spaced), 5 figure
Scanning Tunneling Spectroscopic Studies of the Effects of Dielectrics and Metallic Substrates on the Local Electronic Characteristics of Graphene
Atomically resolved imaging and spectroscopic characteristics of
graphene grown by chemical vapor deposition (CVD) on copper
foils are investigated and compared with those of mechanical
exfoliated graphene on SiO_2. For exfoliated graphene, the local
spectral deviations from ideal behavior may be attributed to strain
induced by the SiO_2 substrate. For CVD grown graphene, the
lattice structure appears strongly distorted by the underlying
copper, with regions in direct contact with copper showing nearly
square lattices whereas suspended regions from thermal relaxation
exhibiting nearly honeycomb or hexagonal lattice structures. The
electronic density of states (DOS) correlates closely with the
atomic arrangements of carbon, showing excess zero-bias
tunneling conductance and nearly energy-independent DOS for
strongly distorted graphene, in contrast to the linearly dispersive
DOS for suspended graphene. These results suggest that graphene
can interact strongly with both metallic and dielectric materials in
close proximity, leading to non-negligible modifications to the
electronic properties
Phase Variation in the Pulse Profile of SMC X-1
We present the results of timing and spectral analysis of X-ray high state
observations of the high-mass X-ray pulsar SMC X-1 with Chandra, XMM-Newton,
and ROSAT, taken between 1991 and 2001. The source has L_X ~ 3-5 x 10^38
ergs/s, and the spectra can be modeled as a power law plus blackbody with kT_BB
\~ 0.18 keV and reprocessed emission radius R_BB ~ 2 x 10^8 cm, assuming a
distance of 60 kpc to the source. Energy-resolved pulse profiles show several
distinct forms, more than half of which include a second pulse in the soft
profile, previously documented only in hard energies. We also detect
significant variation in the phase shift between hard and soft pulses, as has
recently been reported in Her X-1. We suggest an explanation for the observed
characteristics of the soft pulses in terms of precession of the accretion
disk.Comment: 4 pages, 4 figures, accepted for publication in ApJL; v2 minor
corrections, as will appear in ApJ
Analytical model of brittle destruction based on hypothesis of scale similarity
The size distribution of dust particles in nuclear fusion devices is close to
the power function. A function of this kind can be the result of brittle
destruction. From the similarity assumption it follows that the size
distribution obeys the power law with the exponent between -4 and -1. The model
of destruction has much in common with the fractal theory. The power exponent
can be expressed in terms of the fractal dimension. Reasonable assumptions on
the shape of fragments concretize the power exponent, and vice versa possible
destruction laws can be inferred on the basis of measured size distributions.Comment: 10 pages, 3 figure
Perspectives de carrières professionnelles
Cet article traite de l'éducation, de l'emploi et de l'utilisation de certains professionnels en contexte nord-américain.This paper is concerned with the education, employment and utilization of selected professionals in Canada. Comparisons are also made with other studies on both sides of the North Atlantic.During the rapid expansion of higher education in the 1950s and 1960s (par-ticularly in engineering and science), research focussed on total enrollment, occupa-tional choice and the supply of manpower to various occupations. Much less attention was paid to the content and structure of university-level courses. And there was little worry about placement and utilization. But now the question "Are too many people being educated for the wrong kind of jobs?" is increasingly heard. Research carried out by the authors indicates that education, employment and utilization should always be examined as a triad, not in isolation for each other.The career patterns of engineering and science graduates showed definite similarities, but notable differences also occurred, e.g. relatively more engineers moved eventually into managerial positions while many science graduates preferred university teaching posts. Recent trends - including cutbacks in university enrollments and faculty positions, rising unemployment rates for both engineers and scientists, job-bumping, and underemployment - indicate problems in the pursuit of high-level careers and that the rise in educational levels are not being matched by a corresponding increase in skill requirements.The data gathered on utilization show further that degree requirements tend to be unrealistically high. Also, the more specialized professionals are highly vulnerable if recession comes. But better curriculum designs can improve the processes of job-getting and job-holding. Coping with the rise in underemployment and unemployment of highly trained professionals in the future will require specific measures, including better manpower forecasts, a more rigorous but diversified educational stream, and a greater measure of informed choice about careers
New Constraints on Dispersive Form Factor Parameterizations from the Timelike Region
We generalize a recent model-independent form factor parameterization derived
from rigorous dispersion relations to include constraints from data in the
timelike region. These constraints dictate the convergence properties of the
parameterization and appear as sum rules on the parameters. We further develop
a new parameterization that takes into account finiteness and asymptotic
conditions on the form factor, and use it to fit to the elastic \pi
electromagnetic form factor. We find that the existing world sample of timelike
data gives only loose bounds on the form factor in the spacelike region, but
explain how the acquisition of additional timelike data or fits to other form
factors are expected to give much better results. The same parameterization is
seen to fit spacelike data extremely well.Comment: 24 pages, latex (revtex), 3 eps figure
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