17,923 research outputs found
Investigation of abort procedures for space shuttle-type vehicles
An investigation has been made of abort procedures for space shuttle-type vehicles using a point mass trajectory optimization program known as POST. This study determined the minimum time gap between immediate and once-around safe return to the launch site from a baseline due-East launch trajectory for an alternate space shuttle concept which experiences an instantaneous loss of 25 percent of the total main engine thrust
Exact Integration of the High Energy Scale in Doped Mott Insulators
We expand on our earlier work (cond-mat/0612130, Phys. Rev. Lett. {\bf 99},
46404 (2007)) in which we constructed the exact low-energy theory of a doped
Mott insulator by explicitly integrating (rather than projecting) out the
degrees of freedom far away from the chemical potential. The exact low-energy
theory contains degrees of freedom that cannot be obtained from projective
schemes. In particular a new charge bosonic field emerges at low
energies that is not made out of elemental excitations. Such a field accounts
for dynamical spectral weight transfer across the Mott gap. At half-filling, we
show that two such excitations emerge which play a crucial role in preserving
the Luttinger surface along which the single-particle Green function vanishes.
In addition, the interactions with the bosonic fields defeat the artificial
local SU(2) symmetry that is present in the Heisenberg model. We also apply
this method to the Anderson-U impurity and show that in addition to the Kondo
interaction, bosonic degrees of freedom appear as well. Finally, we show that
as a result of the bosonic degree of freedom, the electron at low energies is
in a linear superposition of two excitations--one arising from the standard
projection into the low-energy sector and the other from the binding of a hole
and the boson.Comment: Published veriso
A phenomenological model of the superconducting state of the Bechgaard salts
We present a group theoretical analysis of the superconducting state of the
Bechgaard salts, e.g., (TMTSF)_2PF_6 or (TMTSF)_2ClO_6. We show that there are
eight symmetry distinct superconducting states. Of these only the (fully
gapped, even frequency, p-wave, triplet) 'polar state' is consistent with the
full range of the experiments on the Bechgaard salts. The gap of the polar
state is d(k) (psi_uk,0,0), where psi_uk may be any odd parity function that is
translationally invariant.Comment: 4 pages, no figure
Similarity models for viscous vortex cores
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/76178/1/AIAA-1990-592-491.pd
Assessing movements of three buoy line types using DSTmilli Loggers: Implications for entanglements of bottlenose dolphins in the crab pot fishery
A study was conducted in October 2006 in the Charleston, South Carolina area to test the movements of three different buoy line types to determine which produced a preferred profile that could reduce the risk of dolphin entanglement. Tests on diamond-braided nylon commonly used in the crab pot fishery were compared with stiffened line of Esterpro and calf types in both shallow and deep water environments using DSTmilli data loggers. Loggers were placed at intervals along the lines to record depth, and thus movements, over a 24 hour period. Three observers viewed video animations and charts created for each of the six trial days from the collected logger data and provided their opinions on the most desirable line type that fit set criteria. A quantitative analysis (ANCOVA) of the data was conducted taking into consideration daily tidal fluctuations and logger movements. Loggers tracking the tides had an r2 value approaching 1.00 and produced little movement other than with the tides. Conversely, r2 values approaching 0.00 were less affected by tidal movement and influenced by currents that cause more erratic movement. Results from this study showed that stiffened line, in particular the medium lay Esterpro type, produced the more desirable profiles that could reduce risk of dolphin entanglement. Combining the observer’s results with the ANCOVA results, Esterpro was chosen nearly 60% of the time as opposed to the nylon line which was only chosen 10% of the time. ANCOVA results showed that the stiffened lines performed better in both the shallow and deep water environments, while the nylon line only performed better during one trial in a deep water set, most probably due to the increased current velocities experienced that day. (58pp.)(PDF contains 68 pages
Study of several factors affecting crew escape trajectories from the Space Shuttle Orbiter at low-subsonic speeds
Factors affecting the bailout characteristics from the space shuttle orbiter at low-subsonic speeds were investigated. In the 12-foot low-speed tunnel and the 4 by 7-meter tunnel with 0.03-scale models. The effect of crew-model exit velocity, body position, and body weight were studied with egress from the main side hatch with the orbiter upright and from the upper cabin hatch with the orbiter inverted. Crew model drag and flow field measurements around the orbiter were estimated. The high-angle-of-attack trim characteristics of the orbiter was determined by force tests in an attempt to improve bailout conditions. A computer simulation was made to evaluate the maneuver necessary to attain the high-angle-of-attack trim
Supersonic performance, stability and control characteristics of a 0.01875 scale model Rockwell International 089B-139B orbiter configuration (LA8C)
An investigation was made in the Langley Unitary Plan Wind Tunnel at Mach numbers of 1.9 and 2.86 to study the supersonic aerodynamic characteristics of a Rockwell International shuttle orbiter configuration. Tests were made at a Reynolds number of 1.5 million per foot with an angle-of-attack range of minus 4 to 28 deg and sideslip variations of minus 6 to 8 deg. The effects of elevon and aileron deflections were investigated
Relation between the eigenfrequencies of Bogoliubov excitations of Bose-Einstein condensates and the eigenvalues of the Jacobian in a time-dependent variational approach
We study the relation between the eigenfrequencies of the Bogoliubov
excitations of Bose-Einstein condensates, and the eigenvalues of the Jacobian
stability matrix in a variational approach which maps the Gross-Pitaevskii
equation to a system of equations of motion for the variational parameters. We
do this for Bose-Einstein condensates with attractive contact interaction in an
external trap, and for a simple model of a self-trapped Bose-Einstein
condensate with attractive 1/r interaction. The stationary solutions of the
Gross-Pitaevskii equation and Bogoliubov excitations are calculated using a
finite-difference scheme. The Bogoliubov spectra of the ground and excited
state of the self-trapped monopolar condensate exhibits a Rydberg-like
structure, which can be explained by means of a quantum defect theory. On the
variational side, we treat the problem using an ansatz of time-dependent
coupled Gaussians combined with spherical harmonics. We first apply this ansatz
to a condensate in an external trap without long-range interaction, and
calculate the excitation spectrum with the help of the time-dependent
variational principle. Comparing with the full-numerical results, we find a
good agreement for the eigenfrequencies of the lowest excitation modes with
arbitrary angular momenta. The variational method is then applied to calculate
the excitations of the self-trapped monopolar condensates, and the
eigenfrequencies of the excitation modes are compared.Comment: 15 pages, 12 figure
An adaptive embedded mesh procedure for leading-edge vortex flows
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/76634/1/AIAA-1989-80-667.pd
The role of the electromagnetic field in the formation of domains in the process of symmetry breaking phase transitions
In the framework of quantum field theory we discuss the emergence of a phase
locking among the electromagnetic modes and the matter components on an
extended space-time region. We discuss the formation of extended domains
exhibiting in their fundamental states non-vanishing order parameters, whose
existence is not included in the Lagrangian. Our discussion is motivated by the
interest in the study of the general problem of the stability of mesoscopic and
macroscopic complex systems arising from fluctuating quantum components in
connection with the problem of defect formation during the process of
non-equilibrium symmetry breaking phase transitions characterized by an order
parameter.Comment: Physical Review A, in the pres
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