1,472 research outputs found
VASCOMP 2. The V/STOL aircraft sizing and performance computer program. Volume 6: User's manual, revision 3
This report describes the use of the V/STOL Aircraft Sizing and Performance Computer Program (VASCOMP II). The program is useful in performing aircraft parametric studies in a quick and cost efficient manner. Problem formulation and data development were performed by the Boeing Vertol Company and reflects the present preliminary design technology. The computer program, written in FORTRAN IV, has a broad range of input parameters, to enable investigation of a wide variety of aircraft. User oriented features of the program include minimized input requirements, diagnostic capabilities, and various options for program flexibility
Signature of Schwinger's pair creation rate via radiation generated in graphene by strong electric current
Electron - hole pairs are copuously created by an applied electric field near
the Dirac point in graphene or similar 2D electronic systems. It was shown
recently that for sufficiently large electric fields and ballistic times the
I-V characteristics become strongly nonlinear due to Schwinger's pair creation.
Since there is no energy gap the radiation from the pairs' annihilation is
enhanced. The spectrum of radiation is calculated. The angular and polarization
dependence of the emitted photons with respect to the graphene sheet is quite
distinctive. For very large currents the recombination rate becomes so large
that it leads to the second Ohmic regime due to radiation friction.Comment: 9 pages, 7 figure
V/STOL tilt rotor aircraft study mathematical model for a real time simulation of a tilt rotor aircraft (Boeing Vertol Model 222), volume 8
A mathematical model for a real time simulation of a tilt rotor aircraft was developed. The mathematical model is used for evaluating aircraft performance and handling qualities. The model is based on an eleven degree of freedom total force representation. The rotor is treated as a point source of forces and moments with appropriate response time lags and actuator dynamics. The aerodynamics of the wing, tail, rotors, landing gear, and fuselage are included
Interplay of Anisotropy and Disorder in the Doping-Dependent Melting and Glass Transitions of Vortices in BiSrCaCuO
We study the oxygen doping dependence of the equilibrium first-order melting
and second-order glass transitions of vortices in
BiSrCaCuO. Doping affects both anisotropy and
disorder. Anisotropy scaling is shown to collapse the melting lines only where
thermal fluctuations are dominant. Yet, in the region where disorder breaks
that scaling, the glass lines are still collapsed. A quantitative fit to
melting and replica symmetry breaking lines of a 2D Ginzburg-Landau model
further reveals that disorder amplitude weakens with doping, but to a lesser
degree than thermal fluctuations, enhancing the relative role of disorder.Comment: 4 pages, 4 figure
Electrical conductivity beyond linear response in layered superconductors under magnetic field
The time-dependent Ginzburg-Landau approach is used to investigate nonlinear
response of a strongly type-II superconductor. The dissipation takes a form of
the flux flow which is quantitatively studied beyond linear response. Thermal
fluctuations, represented by the Langevin white noise, are assumed to be strong
enough to melt the Abrikosov vortex lattice created by the magnetic field into
a moving vortex liquid and marginalize the effects of the vortex pinning by
inhomogeneities. The layered structure of the superconductor is accounted for
by means of the Lawrence-Doniach model. The nonlinear interaction term in
dynamics is treated within Gaussian approximation and we go beyond the often
used lowest Landau level approximation to treat arbitrary magnetic fields. The
I-V curve is calculated for arbitrary temperature and the results are compared
to experimental data on high- superconductor
YBaCuO.Comment: 8 pages, 3 figure
Nature of 45 degree vortex lattice reorientation in tetragonal superconductors
The transformation of the vortex lattice in a tetragonal superconductor which
consists of its 45 degree reorientation relative to the crystal axes is studied
using the nonlocal London model. It is shown that the reorientation occurs as
two successive second order (continuous) phase transitions. The transition
magnetic fields are calculated for a range of parameters relevant for
borocarbide superconductors in which the reorientation has been observed
Field cooling memory effect in Bi2212 and Bi2223 single crystals
A memory effect in the Josephson vortex system created by magnetic field in
the highly anisotropic superconductors Bi2212 and Bi2223 is demonstrated using
microwave power absorption. This surprising effect appears despite a very low
viscosity of Josephson vortices compared to Abrikosov vortices. The
superconductor is field cooled in DC magnetic field H_{m} oriented parallel to
the CuO planes through the critical temperature T_{c} down to 4K, with
subsequent reduction of the field to zero and again above H_{m}. Large
microwave power absorption signal is observed at a magnetic field just above
the cooling field clearly indicating a memory effect. The dependence of the
signal on deviation of magnetic field from H_{m} is the same for a wide range
of H_{m} from 0.15T to 1.7T
Precision calculation of magnetization and specific heat of vortex liquids and solids in type II superconductors
A new systematic calculation of magnetization and specific heat contributions
of vortex liquids and solids (not very close to the melting line) is presented.
We develop an optimized perturbation theory for the Ginzburg - Landau
description of thermal fluctuations effects in the vortex liquids. The
expansion is convergent in contrast to the conventional high temperature
expansion which is asymptotic. In the solid phase we calculate first two orders
which are already quite accurate. The results are in good agreement with
existing Monte Carlo simulations and experiments. Limitations of various
nonperturbative and phenomenological approaches are noted. In particular we
show that there is no exact intersection point of the magnetization curves both
in 2D and 3D.Comment: 4 pages, 3 figure
Equation of state for the 2+1 dimensional Gross-Neveu model at order 1/N
We calculate the equation of state of the Gross-Neveu model in 2+1 dimensions
at order 1/N, where N is the number of fermion species. We make use of a
general formula valid for four-fermion theories, previously applied to the
model in 1+1 dimensions. We consider both the discrete and continuous symmetry
versions of the model. We show that the pion-like excitations give the dominant
contribution at low temperatures. The range of validity for such pion dominance
is analyzed. The complete analysis from low to high temperatures also shows
that in the critical region the role of composite states is relevant, even for
quite large N, and that the free-component behaviour at high T starts at about
twice the mean field critical temperature.Comment: 19 pages, RevTeX, 10 figures.p
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