27,861 research outputs found
Study and Design of a Cesium Bombardment Ion Engine System
Cesium bombardment ion engine system design, modification, and testin
Optical enhancement of photomultiplier sensitivity
Transmission and reflection light losses are reduced by introducing light into end-window of device at an angle large enough to normal so total internal reflection occurs at both photocathode-vacuum and window-air interfaces
Optical enhancement of sensitivity in laser Doppler velocity systems
Utilization of optical enhancement techniques prevents loss of light by reflections at the photocathode of a photomultiplier and increases signal detection sensitivity
Laser velocimeter for simultaneous two-dimensional velocity measurements
Laser velocimeter provides simultaneous orthogonal measurements in manner which minimizes many problems attending prior systems, and allows spatial traversing of flowfield in order to obtain velocity profiles. Velocimeter permits rapid interrogation of unsteady flows where area of interest is of the order of one meter in extent and flow does not vary appreciably over time of about one second
Turbine Blade Temperature Measurements Using Thin Film Temperature Sensors
The development of thin film temperature sensors is discussed. The technology for sputtering 2 micron thin film platinum versus platinum 10 percent rhodium thermocouples on alumina forming coatings was improved and extended to applications on actual turbine blades. Good adherence was found to depend upon achieving a proper morphology of the alumina surface. Problems of adapting fabrication procedures to turbine blades were uncovered, and improvements were recommended. Testing at 1250 K at one atmosphere pressure was then extended to a higher Mach No. (0.5) in combustor flow for 60 hours and 71 thermal cycles. The mean time to failure was 47 hours accumulated during 1 hour exposures in the combustor. Calibration drift was about 0.1 percent per hour, attributable to oxidation of the rhodium in the thin films. An increase in film thickness and application of a protective overcoat are recommended to reduce drift in actual engine testing
Measuring unsteady pressure on rotating compressor blades
Miniature semiconductor strain gage pressure transducers mounted in several arrangements were studied. Both surface mountings and recessed flush mountings were tested. Test parameters included mounting arrangement, blade material, temperature, local strain in the acceleration normal to the transducer diaphragm, centripetal acceleration, and pressure. Test results show no failures of transducers or mountings and indicate an uncertainty of unsteady pressure measurement of approximately + or - 6 percent + 0.1 kPa for a typical application. Two configurations were used on a rotating fan flutter program. Examples of transducer data and correction factors are presented
Optimal eavesdropping on QKD without quantum memory
We consider the security of the BB84, six-state and SARG04 quantum key
distribution protocols when the eavesdropper doesn't have access to a quantum
memory. In this case, Eve's most general strategy is to measure her ancilla
with an appropriate POVM designed to take advantage of the post-measurement
information that will be released during the sifting phase of the protocol.
After an optimization on all the parameters accessible to Eve, our method
provides us with new bounds for the security of six-state and SARG04 against a
memoryless adversary. In particular, for the six-state protocol we show that
the maximum QBER for which a secure key can be extracted is increased from
12.6% (for collective attacks) to 20.4% with the memoryless assumption.Comment: 7 pages, 3 figures. Analysis of six-state and SARG04 QKD protocols
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Detection of x-rays from galaxy groups associated with the gravitationally lensed systems PG 1115+080 and B1422+231
Gravitational lenses that produce multiple images of background quasars can
be an invaluable cosmological tool. Deriving cosmological parameters, however,
requires modeling the potential of the lens itself. It has been estimated that
up to a quarter of lensing galaxies are associated with a group or cluster
which perturbs the gravitational potential. Detection of X-ray emission from
the group or cluster can be used to better model the lens. We report on the
first detection in X-rays of the group associated with the lensing system PG
1115+080 and the first X-ray image of the group associated with the system
B1422+231. We find a temperature and rest-frame luminosity of 0.8 +/- 0.1 keV
and 7 +/- 2 x 10^{42} ergs/s for PG 1115+080 and 1.0 +infty/-0.3 keV and 8 +/-
3 x 10^{42} ergs/s for B1422+231. We compare the spatial and spectral
characteristics of the X-ray emission to the properties of the group galaxies,
to lens models, and to the general properties of groups at lower redshift.Comment: Accepted for publication in ApJ. 17 pages, 5 figures. Minor changes
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