11,574 research outputs found
Decoupling control technology for medium STOL transports
The advanced control technology is considered that is necessary to cope with the medium STOL transport landing problem and, in particular, the necessity to decouple with active control techniques. It is shown that the need to decouple is independent of the powered lift concept but that the provisioning for decoupling is most greatly dependent on the preassumed piloting technique. The implications of decoupling and active control techniques with respect to pilot technique options, handling quality criteria, flight control mechanization, and the use of piloted simulation as a design tool, are also discussed
Experimental Demonstration of Focal Plane Array Beamforming in a Prototype Radiotelescope
Focal plane arrays are being developed to provide dishes with a wide field of view for both the next generation of radiotelescopes and to retrofit existing large radiotelescopes. We describe a prototype radiotelescope, comprising a two dish interferometer with real-time digital beamformer that was built to study focal plane array systems. Two beamformer weightings were applied to the system: A normalized conjugate match and the maximum sensitivity (G/T). Both incorporate the uncorrelated noise from the receiver chains and the latter includes correlated noise from spillover and coupling in the array. A black box approach is taken where the assembled system is considered and the only accessible data is that typically available from an operational radiotelescope. This approach is particularly suitable for complex active antennas where there is insufficient knowledge of the system for beamformer weights to be set a priori. It also allows adaptation to changes such as electronic gain drift, partial failures and alterations in the environment
Long-Lived Superheavy Particles in Dynamical Supersymmetry-Breaking Models in Supergravity
Superheavy particles of masses with lifetimes
are very interesting, since their decays may
account for the ultra-high energy (UHE) cosmic rays discovered beyond the
Greisen-Zatsepin-Kuzmin cut-off energy . We show
that the presence of such long-lived superheavy particles is a generic
prediction of QCD-like SU(N_c) gauge theories with N_f flavors of quarks and
antiquarks and the large number of colors N_c. We construct explicit models
based on supersymmetric SU(N_c) gauge theories and show that if the dynamical
scale and N_c = 6-10 the lightest
composite baryons have the desired masses and lifetimes to explain the UHE
cosmic rays. Interesting is that in these models the gaugino condensation
necessarily occurs and hence these models may play a role of so-called hidden
sector for supersymmetry breaking in supergravity.Comment: 13 pages, Late
Bounds on long-lived charged massive particles from Big Bang nucleosynthesis
The Big Bang nucleosynthesis (BBN) in the presence of charged massive
particles (CHAMPs) is studied in detail. All currently known effects due to the
existence of bound states between CHAMPs and nuclei, including possible
late-time destruction of Li6 and Li7 are included. The study sets conservative
bounds on CHAMP abundances in the decay time range 3x10^2 sec - 10^12 sec. It
is stressed that the production of Li6 at early times T ~ 10keV is
overestimated by a factor ~ 10 when the approximation of the Saha equation for
the He4 bound state fraction is utilised. To obtain conservative limits on the
abundance of CHAMPs, a Monte-Carlo analysis with ~ 3x10^6 independent BBN runs,
varying reaction rates of nineteen different reactions, is performed (see
attached erratum, however). The analysis yields the surprising result that
except for small areas in the particle parameter space conservative constraints
on the abundance of decaying charged particles are currently very close to
those of neutral particles. It is shown that, in case a number of heretofore
unconsidered reactions may be determined reliably in future, it is conceivable
that the limit on CHAMPs in the early Universe could be tightened by orders of
magnitude. An ERRATUM gives limits on primordial CHAMP densities when the by
Ref. Kamimura et al. recently more accurately determined CHAMP reaction rates
are employed.Comment: includes Erratum showing most up to date limits after determination
of the most important reaction rate
Segregation of an intruder in a heated granular dense gas
A recent segregation criterion [V. Garz\'o, Phys. Rev. E \textbf{78},
020301(R) (2008)] based on the thermal diffusion factor of an
intruder in a heated granular gas described by the inelastic Enskog equation is
revisited. The sign of provides a criterion for the transition
between the Brazil-nut effect (BNE) and the reverse Brazil-nut effect (RBNE).
The present theory incorporates two extra ingredients not accounted for by the
previous theoretical attempt. First, the theory is based upon the second Sonine
approximation to the transport coefficients of the mass flux of intruder.
Second, the dependence of the temperature ratio (intruder temperature over that
of the host granular gas) on the solid volume fraction is taken into account in
the first and second Sonine approximations. In order to check the accuracy of
the Sonine approximation considered, the Enskog equation is also numerically
solved by means of the direct simulation Monte Carlo (DSMC) method to get the
kinetic diffusion coefficient . The comparison between theory and
simulation shows that the second Sonine approximation to yields an
improvement over the first Sonine approximation when the intruder is lighter
than the gas particles in the range of large inelasticity. With respect to the
form of the phase diagrams for the BNE/RBNE transition, the kinetic theory
results for the factor indicate that while the form of these diagrams
depends sensitively on the order of the Sonine approximation considered when
gravity is absent, no significant differences between both Sonine solutions
appear in the opposite limit (gravity dominates the thermal gradient). In the
former case (no gravity), the first Sonine approximation overestimates both the
RBNE region and the influence of dissipation on thermal diffusion segregation.Comment: 9 figures; to be published in Phys. Rev.
Mixing by polymers: experimental test of decay regime of mixing
By using high molecular weight fluorescent passive tracers with different
diffusion coefficients and by changing the fluid velocity we study dependence
of a characteristic mixing length on the Peclet number, , which controls
the mixing efficiency. The mixing length is found to be related to by a
power law, , and increases faster than
expected for an unbounded chaotic flow. Role of the boundaries in the mixing
length abnormal growth is clarified. The experimental findings are in a good
quantitative agreement with the recent theoretical predictions.Comment: 4 pages,5 figures. accepted for publication in PR
Prediction of strong shock structure using the bimodal distribution function
A modified Mott-Smith method for predicting the one-dimensional shock wave
solution at very high Mach numbers is constructed by developing a system of
fluid dynamic equations. The predicted shock solutions in a gas of Maxwell
molecules, a hard sphere gas and in argon using the newly proposed formalism
are compared with the experimental data, direct-simulation Monte Carlo (DSMC)
solution and other solutions computed from some existing theories for Mach
numbers M<50. In the limit of an infinitely large Mach number, the predicted
shock profiles are also compared with the DSMC solution. The density,
temperature and heat flux profiles calculated at different Mach numbers have
been shown to have good agreement with the experimental and DSMC solutionsComment: 22 pages, 9 figures, Accepted for publication in Physical Review
Improving support for older people looking after someone with advanced cancer
This briefing paper is about the findings and
recommendations from a research project
conducted at the University of Nottingham,
with funding awarded by Macmillan Cancer
Support. The project was set up to study the
experiences and main support needs of
older carers* looking after someone with
advanced cancer and to facilitate the active
involvement of carers in the research
proces
Resonant conversions of extremely high energy neutrinos in dark matter halos
We study the effect of adiabatically resonant conversion in galactic halos of
neutrinos at the highest energies ( - eV), when the
source is in the center of a galaxy. Using the standard neutrino
properties and the standard cosmological scenario for the hot dark part of
matter, we find that interesting conversions may take place just for neutrino
parameters relevant to the solar and atmospheric neutrino problem. The effect
is due to the large enhancement in the density in galactic halos and to
the form of the effective matter potential both below and above the pole of the
resonance.Comment: 8 pages, revtex, some comments and references added, to appear in
Phys. Rev.
Suzaku Observations of Four Heavily Absorbed HMXBs
We report on Suzaku observations of four unidentified sources from the
INTEGRAL and Swift BAT Galactic plane surveys. All the sources have a large
neutral hydrogen column density and are likely members of an emerging class of
heavily absorbed high mass X-ray binary (HMXB) first identified in INTEGRAL
observations. Two of the sources in our sample are approximately constant flux
sources, one source shows periodic variation and one source exhibited a short,
bright X-ray outburst. The periodicity is transient, suggesting it is produced
by a neutron star in an elliptical orbit around a stellar wind source. We
analyze the flaring source in several segments to look for spectral variation
and discuss the implications of the findings for the nature of the source. We
conclude that all four sources in our sample can be identified with the
emerging class of highly absorbed HMXBs, that one is a newly identified
transient X-ray pulsar and that at least one is a newly identified supergiant
fast X-ray transient (SFXT).Comment: 22 pages, 5 figures, submitted to Ap
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