5,192 research outputs found
Microwave Remote Sensing of Ocean Surface Wind Speed and Rain Rates over Tropical Storms
The value of using narrowly spaced frequencies within a microwave band to measure wind speeds and rain rates over tropical storms with radiometers is reviewed. The technique focuses on results obtained in the overflights of Hurricane Allen during 5 and 8 of August, 1980
Propfan Test Assessment (PTA): Flight test report
The Propfan Test Assessment (PTA) aircraft was flown to obtain glade stress and noise data for a 2.74m (9 ft.) diameter single rotation propfan. Tests were performed at Mach numbers to 0.85 and altitudes to 12,192m (40,000 ft.). The propfan was well-behaved structurally over the entire flight envelope, demonstrating that the blade design technology was completely adequate. Noise data were characterized by strong signals at blade passage frequency and up to 10 harmonics. Cabin noise was not so high as to preclude attainment of comfortable levels with suitable wall treatment. Community noise was not excessive
The Impact on Space Radiation Requirements and Effects on ASIMS
The evolution of highly miniaturized electronic and mechanical systems will be accompanied by new problems and issues regarding the radiation response of these systems in the space environment. In this paper we discuss some of the more prominent radiation problems brought about by miniaturization. For example, autonomous micro-spacecraft will require large amounts of high density memory, most likely in the form of stacked, multichip modules of DRAM's, that must tolerate the radiation environment. However, advanced DRAM's (16 to 256 Mbit) are quite susceptible to radiation, particularly single event effects, and even exhibit new radiation phenomena that were not a problem for older, less dense memory chips. Another important trend in micro-spacecraft electronics is toward the use of low-voltage microelectronic systems that consume less power. However, the reduction in operating voltage also caries with it an increased susceptibility to radiation. In the case of application specific integrated microcircuits (ASIM's), advanced devices of this type, such as high density field programmable gate arrays (FPGA's) exhibit new single event effects (SEE), such as single particle reprogramming of anti-fuse links. New advanced bipolar circuits have been shown recently to degrade more rapidly in the low dose rate space environment than in the typical laboratory total dose radiation test used to qualify such devices. Thus total dose testing of these parts is no longer an appropriately conservative measure to be used for hardness assurance. We also note that the functionality of micromechanical Si-based devices may be altered due to the radiation-induced deposition of charge in the oxide passivation layers
Systematic derivation of a rotationally covariant extension of the 2-dimensional Newell-Whitehead-Segel equation
An extension of the Newell-Whitehead-Segel amplitude equation covariant under
abritrary rotations is derived systematically by the renormalization group
method.Comment: 8 pages, to appear in Phys. Rev. Letters, March 18, 199
On the Properties of Plastic Ablators in Laser-Driven Material Dynamics Experiments
Radiation hydrodynamics simulations were used to study the effect of plastic
ablators in laser-driven shock experiments. The sensitivity to composition and
equation of state was found to be 5-10% in ablation pressure. As was found for
metals, a laser pulse of constant irradiance gave a pressure history which
decreased by several percent per nanosecond. The pressure history could be made
more constant by adjusting the irradiance history. The impedance mismatch with
the sample gave an increase o(100%) in the pressure transmitted into the
sample, for a reduction of several tens of percent in the duration of the peak
load applied to the sample, and structured the release history by adding a
release step to a pressure close to the ablation pressure. Algebraic relations
were found between the laser pulse duration, the ablator thickness, and the
duration of the peak pressure applied to the sample, involving quantities
calculated from the equations of state of the ablator and sample using shock
dynamics.Comment: Typos fixe
Large-scale physical modelling of soil-filled masonry arch bridges
The presence of soil backfill has been shown to have a significant influence on the load-carrying capacity of masonry
arch bridges, with the soil fill providing a number of important functions, including inter alia, the distribution of
surface loads and passive resistance to arch deformation during loading. Large-scale physical modelling allows highquality
data to be collected under controlled conditions, while enabling essential aspects of the interaction between
the soil fill, the masonry arch and the abutments to be observed. This paper considers the design and construction of
a unique test facility that allows large-scale soil-filled masonry arch structures to be studied under both quasi-static
and cycling loading regimes. The key challenges that were needed to be overcome to develop this facility are
presented and discussed
Influence of railway loading on the performance of soil-filled masonry arch bridges
Masonry arch bridges are found in large numbers on the rail networks of Europe and other parts of the world. However, the mode of response of masonry arch structures subjected to railway loading is little understood. To address this, an experimental study involving large-scale physical models of backfilled masonry arch bridges subjected to railway loading conditions has recently been conducted. This has explored the influence of the rail track bed system on bridge behaviour and on load carrying capacity. Tests indicate that the track bed system fundamentally alters the mode of response of the bridge system, and significantly increases load carrying capacity. Using the same test facility, load tests have also been used to explore and characterise the behaviour and performance of damaged arch bridges, with the test results obtained suggesting that although there is likely to be a reduction in overall capacity, even a significantly damaged arch bridge can still perform adequately under loading. This has important implications for bridge owners and assessment engineers.
Keywords: masonry arch bridges, physical modelling, cyclic loading, rail track system, backfill
Mass-radius relationships for exoplanets
For planets other than Earth, interpretation of the composition and structure
depends largely on comparing the mass and radius with the composition expected
given their distance from the parent star. The composition implies a
mass-radius relation which relies heavily on equations of state calculated from
electronic structure theory and measured experimentally on Earth. We lay out a
method for deriving and testing equations of state, and deduce mass-radius and
mass-pressure relations for key materials whose equation of state is reasonably
well established, and for differentiated Fe/rock. We find that variations in
the equation of state, such as may arise when extrapolating from low pressure
data, can have significant effects on predicted mass- radius relations, and on
planetary pressure profiles. The relations are compared with the observed
masses and radii of planets and exoplanets. Kepler-10b is apparently 'Earth-
like,' likely with a proportionately larger core than Earth's, nominally 2/3 of
the mass of the planet. CoRoT-7b is consistent with a rocky mantle over an
Fe-based core which is likely to be proportionately smaller than Earth's. GJ
1214b lies between the mass-radius curves for H2O and CH4, suggesting an 'icy'
composition with a relatively large core or a relatively large proportion of
H2O. CoRoT-2b is less dense than the hydrogen relation, which could be
explained by an anomalously high degree of heating or by higher than assumed
atmospheric opacity. HAT-P-2b is slightly denser than the mass-radius relation
for hydrogen, suggesting the presence of a significant amount of matter of
higher atomic number. CoRoT-3b lies close to the hydrogen relation. The
pressure at the center of Kepler-10b is 1.5+1.2-1.0 TPa. The central pressure
in CoRoT-7b is probably close to 0.8TPa, though may be up to 2TPa.Comment: Added more recent exoplanets. Tidied text and references. Added extra
"rock" compositions. Responded to referee comment
A Pre-Protostellar Core in L1551
Large field surveys of NH3, C2S, 13CO and C18O in the L1551 dark cloud have
revealed a prolate, pre-protostellar molecular core (L1551-MC) in a relatively
quiescent region to the northwest of the well-known IRS 5 source. The kinetic
temperature is measured to be 9K, the total mass is ~2Msun, and the average
particle density is 10^4-10^5 cm^(-3). L1551-MC is 2.25' x 1.11' in projection
oriented at a position angle of 133deg. The turbulent motions are on the order
of the sound speed in the medium and contain 4% of the gravitational energy,
E_{grav}, of the core. The angular momentum vector is projected along the major
axis of L1551-MC corresponding to a rotational energy of 2.5E-3(sin
i)^(-2)|E_{grav}|. The thermal energy constitutes about a third of |E_{grav}|
and the virial mass is approximately equal to the total mass. L1551-MC is
gravitationally bound and in the absence of strong, ~160 microgauss, magnetic
fields will likely contract on a ~0.3 Myr time scale. The line profiles of many
molecular species suggest that the cold quiescent interior is surrounded by a
dynamic, perhaps infalling envelope which is embedded within the ambient
molecular gas of L1551.Comment: 27 pages, 7 figures, ApJ accepte
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