7,381 research outputs found
Sonic boom effect on fish: Observations
Motion pictures of fish in a small tank at the time a bullet traveling 1200 m/sec passes a few centimeters above indicate that fish sense the passage of the shock wave but suffer no ill effects. The pressure rise at the bow shock wave was 0.26 atm or 275 times that associated with a strong sonic boom, for example, from the proposed supersonic transport
Giotto Extended Mission (GEM)
The primary objectives of the Giotto Extended Mission (GEM), are to determine the composition and physical state of the Grigg Skjellerup Comet's nucleus; to determine the processes that govern the composition and distribution of neutral and ionized species in the cometary atmosphere. Giotto consists of a single European Space Agency (ESA) spacecraft that was launched in 1985 from Center Spatial Guyanis in French Guiana on an Ariane launch vehicle. After a successful launch into geostationary orbit and a heliocentric transfer trajectory, the spacecraft successfully encountered Halley's Comet in 1986. One month after encountering Halley's Comet, Mar. 1986, the spacecraft was placed in hibernation in a heliocentric orbit slightly less than 1 AU. Between Feb. and Jul. 1990 the spacecraft was successfully reactivated, checked out, and placed on a trajectory course to intercept comet Grigg Skjellerup. The spacecraft has been in hibernation since Jul. 1990. Information is presented in tabular form in the following areas: coverage goals, Deep Space Network Support, frequency assignments, telemetry, command, and tracking support responsibility
Free flight determination of boundary layer transition on small scale cones in the presence of surface ablation
To assess the possibility of achieving extensive laminar flow on conical vehicles during hyperbolic entry, the Ames Research Center has had an ongoing program to study boundary-layer transition on ablating cones. Boundary layer transition results are presented from ballistic range experiments with models that ablated at dimensionless mass transfer rates comparable to those expected for full scale flight at speeds up to 17 km/sec. It was found possible to measure the surface recession and hence more accurately identify regions of laminar, transitional, and turbulent flow along generators of the recovered cones. Some preliminary results using this technique are presented
Nuclear quantum effects in water exchange around lithium and fluoride ions
We employ classical and ring polymer molecular dynamics simulations to study
the effect of nuclear quantum fluctuations on the structure and the water
exchange dynamics of aqueous solutions of lithium and fluoride ions. While we
obtain reasonably good agreement with experimental data for solutions of
lithium by augmenting the Coulombic interactions between the ion and the water
molecules with a standard Lennard-Jones ion-oxygen potential, the same is not
true for solutions of fluoride, for which we find that a potential with a
softer repulsive wall gives much better agreement. A small degree of
destabilization of the first hydration shell is found in quantum simulations of
both ions when compared with classical simulations, with the shell becoming
less sharply defined and the mean residence time of the water molecules in the
shell decreasing. In line with these modest differences, we find that the
mechanisms of the exchange processes are unaffected by quantization, so a
classical description of these reactions gives qualitatively correct and
quantitatively reasonable results. We also find that the quantum effects in
solutions of lithium are larger than in solutions of fluoride. This is partly
due to the stronger interaction of lithium with water molecules, partly due to
the lighter mass of lithium, and partly due to competing quantum effects in the
hydration of fluoride, which are absent in the hydration of lithium.Comment: 12 pages, 8 figure
Chucalissa and Moundville: A Comparison
This paper compares the site of Chucalissa to the site of Moundville using various qualitative and quantitative criteria
Mean-Field Theory of Water-Water Correlations in Electrolyte Solutions
Long-range ion induced water-water correlations were recently observed in
femtosecond elastic second harmonic scattering experiments of electrolyte
solutions. To further the qualitative understanding of these correlations, we
derive an analytical expression that quantifies ion induced dipole-dipole
correlations in a non-interacting gas of dipoles. This model is a logical
extension of Debye-H\"uckel theory that can be used to qualitatively understand
how the combined electric field of the ions induces correlations in the
orientational distributions of the water molecules in an aqueous solution. The
model agrees with results from molecular dynamics simulations and provides an
important starting point for further theoretical work
X-ray reverberation around accreting black holes
Luminous accreting stellar mass and supermassive black holes produce
power-law continuum X-ray emission from a compact central corona. Reverberation
time lags occur due to light travel time-delays between changes in the direct
coronal emission and corresponding variations in its reflection from the
accretion flow. Reverberation is detectable using light curves made in
different X-ray energy bands, since the direct and reflected components have
different spectral shapes. Larger, lower frequency, lags are also seen and are
identified with propagation of fluctuations through the accretion flow and
associated corona. We review the evidence for X-ray reverberation in active
galactic nuclei and black hole X-ray binaries, showing how it can be best
measured and how it may be modelled. The timescales and energy-dependence of
the high frequency reverberation lags show that much of the signal is
originating from very close to the black hole in some objects, within a few
gravitational radii of the event horizon. We consider how these signals can be
studied in the future to carry out X-ray reverberation mapping of the regions
closest to black holes.Comment: 72 pages, 32 figures. Accepted for publication in The Astronomy and
Astrophysics Review. Corrected for mostly minor typos, but in particular
errors are corrected in the denominators of the covariance and rms spectrum
error equations (Eqn. 14 and 15
Discovery of high-frequency iron K lags in Ark 564 and Mrk 335
We use archival XMM-Newton observations of Ark 564 and Mrk 335 to calculate
the frequency dependent time-lags for these two well-studied sources. We
discover high-frequency Fe K lags in both sources, indicating that the red wing
of the line precedes the rest frame energy by roughly 100 s and 150 s for Ark
564 and Mrk 335, respectively. Including these two new sources, Fe K
reverberation lags have been observed in seven Seyfert galaxies. We examine the
low-frequency lag-energy spectrum, which is smooth, and shows no feature of
reverberation, as would be expected if the low-frequency lags were produced by
distant reflection off circumnuclear material. The clear differences in the low
and high frequency lag-energy spectra indicate that the lags are produced by
two distinct physical processes. Finally, we find that the amplitude of the Fe
K lag scales with black hole mass for these seven sources, consistent with a
relativistic reflection model where the lag is the light travel delay
associated with reflection of continuum photons off the inner disc.Comment: 10 pages, 12 figures, accepted for publication in MNRA
Management of the Rice Tungro Virus Vector \u3ci\u3eNephotettix virescens\u3c/i\u3e (Homoptera: Cicadellidae) with Controlled-Release Formulations of Carbofuran
Field trials were conducted in lowland flooded rice in the Philippines to evaluate a number of carbofuran controlled-release formulations in comparison with commercial formulations. The test formulations were based on a biodegradable matrix of pine kraft lignin and were used as granules of different sizes and also in the form of small strips. The release rates were assessed under field conditions by bioassaying rice plants in the field, using adult rice green leafhopper, Nephotettix virescens Distant. The lignin formulations with a high level of active ingredient (15–45% by weight) gave as good or better control than the commercial 3% granules in tests based on three application techniques: broadcast into the floodwater, soil incorporation, and root zone injection. The improvements in control levels of green leafhoppers were most marked with soil incorporation and root zone application. The best lignin-based formulation reduced levels of tungro virus infection from 23% for a conventional flowable carbofuran formulation to 1.0% at an application rate of 0.5 kg (AI)/ha. At the same rate, the grain yield was increased from 3.56 t/ha to 5.5 t/ha, using the controlled-released formulation
The Closest Look at 1H0707-495: X-ray Reverberation Lags with 1.3 Ms of Data
Reverberation lags in AGN were first discovered in the NLS1 galaxy,
1H0707-495. We present a follow-up analysis using 1.3 Ms of data, which allows
for the closest ever look at the reverberation signature of this remarkable
source. We confirm previous findings of a hard lag of ~100 seconds at
frequencies v ~ [0.5 - 4] e-4 Hz, and a soft lag of ~30 seconds at higher
frequencies, v ~ [0.6 - 3] e-3 Hz. These two frequency domains clearly show
different energy dependences in their lag spectra. We also find evidence for a
signature from the broad Fe K line in the high frequency lag spectrum. We use
Monte Carlo simulations to show how the lag and coherence measurements respond
to the addition of Poisson noise and to dilution by other components. With our
better understanding of these effects on the lag, we show that the lag-energy
spectra can be modelled with a scenario in which low frequency hard lags are
produced by a compact corona responding to accretion rate fluctuations
propagating through an optically thick accretion disc, and the high frequency
soft lags are produced by short light-travel delay associated with reflection
of coronal power-law photons off the disc.Comment: 11 pages, 10 figures. Accepted for publication in MNRA
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