7,860 research outputs found
Agricultural aviation research
A compilation of papers, comments, and results is provided during a workshop session. The purpose of the workshop was to review and evaluate the current state of the art of agricultural aviation, to identify and rank potentially productive short and long range research and development areas, and to strengthen communications between research scientists and engineers involved in agricultural research. Approximately 71 individuals actively engaged in agricultural aviation research were invited to participate in the workshop. These were persons familiar with problems related to agricultural aviation and processing expertise which are of value for identifying and proposing beneficial research
Diffusive foam wetting process in microgravity
We report the experimental study of aqueous foam wetting in microgravity. The
liquid fraction along the bubble edges is measured and is found to be a
relevant dynamical parameter during the capillary process. The penetration of
the liquid in the foam, the foam inflation, and the rigidity loss are shown all
to obey strict diffusion processes.Comment: 4 pages, 6 figures, submitted to Phys. Rev. Let
Summary of theoretical considerations and wind tunnel tests of an aerodynamic spoiler for stall proofing a general aviation airplane
An airplane stall proofing system utilizing a spoiler was investigated for application on a low wing airplane representative of typical general aviation aircraft. Tests of the full scale airplane were conducted in the NASA Langley 30 x 60 foot full scale wind tunnel. The test velocity was 86 feet per second, corresponding to a Reynolds number of 2.20 million. The stall proofing capability of the spoiler is shown and a theoretical approach to the design of the spoiler and analysis of the spoiler's contribution to the airplane's trim and longitudinal stability is verified. Controlled spoiler deployment in a narrow angle of attack range, 4 degrees, immediately preceding the stall angle will stall proof the airplane. The results also show some of the limitations of flight tests to determine spoiler deployment rate for good handling qualities
X-ray Spectroscopy of Candidate Ultracompact X-ray Binaries
We present high-resolution spectroscopy of the neutron star/low-mass X-ray
binaries (LMXBs) 4U 1850-087 and 4U 0513-40 as part of our continuing study of
known and candidate ultracompact binaries. The LMXB 4U 1850-087 is one of four
systems in which we had previously inferred an unusual Ne/O ratio in the
absorption along the line of sight, most likely from material local to the
binaries. However, our recent Chandra X-ray Observatory LETGS spectrum of 4U
1850-087 finds a Ne/O ratio by number of 0.22+/-0.05, smaller than previously
measured and consistent with the expected interstellar value. We propose that
variations in the Ne/O ratio due to source variability, as previously observed
in these sources, can explain the difference between the low- and
high-resolution spectral results for 4U 1850-087. Our XMM-Newton RGS
observation of 4U 0513-40 also shows no unusual abundance ratios in the
absorption along the line of sight. We also present spectral results from a
third candidate ultracompact binary, 4U 1822-000, whose spectrum is well fit by
an absorbed power-law + blackbody model with absorption consistent with the
expected interstellar value. Finally, we present the non-detection of a fourth
candidate ultracompact binary, 4U 1905+000, with an upper limit on the source
luminosity of < 1 x 10^{32} erg s^{-1}. Using archival data, we show that the
source has entered an extended quiescent state.Comment: 8 pages, 3 figures, accepted for publication to the Astrophysical
Journa
Influence of the r-mode instability on hypercritically accreting neutron stars
We have investigated an influence of the r-mode instability on
hypercritically accreting () neutron stars in
close binary systems during their common envelope phases based on the scenario
proposed by Bethe et al. \shortcite{bethe-brown-lee}. On the one hand neutron
stars are heated by the accreted matter at the stellar surface, but on the
other hand they are also cooled down by the neutrino radiation. At the same
time, the accreted matter transports its angular momentum and mass to the star.
We have studied the evolution of the stellar mass, temperature and rotational
frequency.
The gravitational-wave-driven instability of the r-mode oscillation strongly
suppresses spinning-up of the star, whose final rotational frequency is well
below the mass-shedding limit, typically as small as 10% of that of the
mass-shedding state. On a very short time scale the rotational frequency tends
to approach a certain constant value and saturates there as far as the amount
of the accreted mass does not exceed a certain limit to collapse to a black
hole. This implies that the similar mechanism of gravitational radiation as the
so-called Wagoner star may work in this process. The star is spun up by
accretion until the angular momentum loss by gravitational radiation balances
the accretion torque. The time-integrated dimensionless strain of the radiated
gravitational wave may be large enough to be detectable by the gravitational
wave detectors such as LIGO II.Comment: 6 pages, 3 figure
An adjustable law of motion for relativistic spherical shells
A classical and a relativistic law of motion for an advancing shell are
deduced applying the thin layer approximation. A new parameter connected with
the quantity of absorbed matter in the expansion is introduced; this allows of
matching theory and observation.Comment: 15 pages, 10 figures and article in press; Central European Journal
of Physics 201
Low frequency radio and X-ray properties of core-collapse supernovae
Radio and X-ray studies of young supernovae probe the interaction between the
supernova shock waves and the surrounding medium and give clues to the nature
and past of the progenitor star. Here we discuss the early emission from type
Ic SN 2002ap and argue that repeated Compton boosting of optical photons by hot
electrons presents the most natural explanation of the prompt X-ray emission.
We describe the radio spectrum of another type Ic SN 2003dh (GRB030329)
obtained with combined GMRT and VLA data. We report on the low frequency radio
monitoring of SN 1995N and our objectives of distinguishing between competing
models of X-ray emission from this SN and the nature of its progenitor by X-ray
spectroscopy. Radio studies on SN 2001gd, SN 2001ig and SN 2002hh are
mentioned.Comment: 5 pages, 4 figures. Uses svmult.cls. To appear in proceedings of IAU
Colloquium 192 "Supernovae (10 years of SN 1993J)", April 2003, Valencia,
Spain, eds. J. M. Marcaide and K. W. Weile
Remote optical addressing of single nano-objects
We present a scheme for remotely addressing single nano-objects by means of
near-field optical microscopy that makes only use of one of the most
fundamental properties of electromagnetic radiation: its polarization. A medium
containing optically active nano-objects is covered with a thin metallic film
presenting sub-wavelength holes. When the optical tip is positioned some
distance away from a hole, surface plasmons in the metal coating are generated
which, by turning the polarization plane of the excitation light, transfer the
excitation towards a chosen hole and induce emission from the underlying
nano-objects. The method, easily applicable to other systems, is demonstrated
for single quantum dots (QDs) at low temperature. It may become a valuable tool
for future optical applications in the nanoworld
The high energy gamma-ray emission expected from Tycho's supernova remnant
A nonlinear kinetic model of cosmic ray (CR) acceleration in supernova
remnants (SNRs) is used to describe the properties of Tycho's SNR. Observations
of the expansion characteristics and of the nonthermal radio and X-ray emission
spectra, assumed to be of synchrotron origin, are used to constrain the overall
dynamical evolution and the particle acceleration parameters of the system, in
addition to what is known from independent estimates of the distance and
thermal X-ray observations. It is shown that a very efficient production of
nuclear cosmic rays, leading to strong shock modification, and a large
downstream magnetic field strength B_d approx 240muG are required to reproduce
the observed synchrotron emission from radio to X-ray frequencies. This field
strength is still well within the upper bound for the effective magnetic field,
consistent with the acceleration process. The pi^0-decay gamma-ray flux turns
out to be somewhat greater than the inverse Compton (IC) flux off the Cosmic
Microwave Background at energies below 1 TeV, dominating it strongly at 10 TeV.
The predicted TeV gamma-ray flux is consistent with but close to the very low
upper limit recently obtained by HEGRA. A future detection at E_gamma ~ 10 TeV
would clearly indicate hadronic emission.Comment: 8 pages, 6 figures. Accepted in Astronomy and Astrophyic
Expected gamma-ray emission of supernova remnant SN 1987A
A nonlinear kinetic theory of cosmic ray (CR) acceleration in supernova
remnants is employed to re-examine the nonthermal properties of the remnant of
SN 1987A for an extended evolutionary period of 5--100 yr. It is shown that an
efficient production of nuclear CRs leads to a strong modification of the outer
supernova remnant shock and to a large downstream magnetic field
mG. The shock modification and the strong field are
required to yield the steep radio emission spectrum observed, as well as to
considerable synchrotron cooling of high energy electrons which diminishes
their X-ray synchrotron flux. These features are also consistent with the
existing X-ray observations. The expected \gr energy flux at TeV-energies at
the current epoch is nearly erg cms under reasonable assumptions about the overall
magnetic field topology and the turbulent perturbations of this field. The
general nonthermal strength of the source is expected to increase roughly by a
factor of two over the next 15 to 20 yrs; thereafter it should decrease with
time in a secular form.Comment: 7 pages, 5 figures, accepted for publication in ApJ, a number of
changes have been made, even though these are not changing the main results
of the pape
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