11,837 research outputs found
The status of rotor noise technology: One man's opinion
The problem of establishing the state of the technology is approached by first identifying the various characteristics of rotor noise and then assessing the state of technology in understanding and predicting the most important of these rotor noise characteristics in a real-world environment
A method for determining the characteristic functions associated with the aeroelastic instabilities of helicopter rotors in forward flight
Computer program for determining characteristic functions of aeroelastic instabilities of helicopter rotor in forward fligh
Generation and measurement of nonstationary random processes technical note no. 3
Generation and measurement of nonstationary stochastic processes related to Monte Carlo studies with analog compute
Wind tunnel tests of a two bladed model rotor to evaluate the TAMI system in descending forward flight
A research investigation was conducted to assess the potential of the Tip Air Mass Injection system in reducing the noise output during blade vortex interaction in descending low speed flight. In general it was concluded that the noise output due to blade vortex interaction can be reduced by 4 to 6 db with an equivalent power expenditure of approximately 14 percent of installed power
Controlling the accuracy of the density matrix renormalization group method: The Dynamical Block State Selection approach
We have applied the momentum space version of the Density Matrix
Renormalization Group method (-DMRG) in quantum chemistry in order to study
the accuracy of the algorithm in the new context. We have shown numerically
that it is possible to determine the desired accuracy of the method in advance
of the calculations by dynamically controlling the truncation error and the
number of block states using a novel protocol which we dubbed Dynamical Block
State Selection (DBSS). The relationship between the real error and truncation
error has been studied as a function of the number of orbitals and the fraction
of filled orbitals. We have calculated the ground state of the molecules
CH, HO, and F as well as the first excited state of CH. Our
largest calculations were carried out with 57 orbitals, the largest number of
block states was 1500--2000, and the largest dimensions of the Hilbert space of
the superblock configuration was 800.000--1.200.000.Comment: 12 page
Comparative Morphology and Phylogenetic Relatedness Among Bobwhites in Southern U.S. and Mexico
We analyzed the morphology and phylogenetic relatedness of masked bobwhites (Colinus virginianus ridgwayi) and Texas bobwhites (C. v. texanus) to determine if the numerically stable Texas bobwhite might serve as a reasonable research and management model for the endangered masked bobwhite. We compared 26 external and 24 internal morphological features. Texas and masked bobwhites had similar body mass; however, masked bobwhites had smaller head and body dimensions and longer wing and thigh bones (P \u3c 0.01) than Texas bobwhites. Genomic DNA was extracted from heart or muscle tissue of captive masked bobwhites (n = 12) and from northern bobwhites obtained in Florida (n = 3), Tennessee (n = 5), Texas (n = 12), and Oklahoma (n = 3). Bobwhites from South Texas and masked bobwhites appear to form a relatively closely related assemblage, possibly representing a separate lineage from other bobwhite populations. Based on gross similarities between Texas and masked bobwhites in morphology and phylogenetic relatedness, as well as in habitat conditions on the semiarid rangelands they occupy, biological and management information from Texas bobwhites seems applicable to masked bobwhites
Electron Magnetic Resonance: The Modified Bloch Equation
We find a modified Bloch equation for the electronic magnetic moment when the
magnetic moment explicitly contains a diamagnetic contribution (a magnetic
field induced magnetic moment arising from the electronic orbital angular
momentum) in addition to the intrinsic magnetic moment of the electron. The
modified Bloch is coupled to equations of motion for the position and momentum
operators. In the presence of static and time varying magnetic field
components, the magnetic moment oscillates out of phase with the magnetic field
and power is absorbed by virtue of the magnetic field induced magnetic moment,
even in the absence of coupling to the environment. We explicitly work out the
spectrum and absorption for the case of a state electron
Evolution of the Density of States Gap in a Disordered Superconductor
It has only recently been possible to study the superconducting state in the
attractive Hubbard Hamiltonian via a direct observation of the formation of a
gap in the density of states N(w). Here we determine the effect of random
chemical potentials on N(w) and show that at weak coupling, disorder closes the
gap concurrently with the destruction of superconductivity. At larger, but
still intermediate coupling, a pseudo-gap in N(w) remains even well beyond the
point at which off-diagonal long range order vanishes. This change in the
elementary excitations of the insulating phase corresponds to a crossover
between Fermi- and Bose-Insulators. These calculations represent the first
computation of the density of states in a finite dimensional disordered fermion
model via the Quantum Monte Carlo and maximum entropy methods.Comment: 4 pages, 4 figure
Ising Expansion for the Hubbard Model
We develop series expansions for the ground state properties of the Hubbard
model, by introducing an Ising anisotropy into the Hamiltonian. For the
two-dimensional (2D) square lattice half-filled Hubbard model, the ground state
energy, local moment, sublattice magnetization, uniform magnetic susceptibility
and spin stiffness are calculated as a function of , where is the
Coulomb constant and is the hopping parameter. Magnetic susceptibility data
indicate a crossover around between spin density wave
antiferromagnetism and Heisenberg antiferromagnetism. Comparisons with Monte
Carlo simulations, RPA result and mean field solutions are also made.Comment: 22 pages, 6 Postscript figures, Revte
Pairing Correlations in the Two-Dimensional Hubbard Model
We present the results of a quantum Monte Carlo study of the extended and
the pairing correlation functions for the two-dimensional Hubbard
model, computed with the constrained-path method. For small lattice sizes and
weak interactions, we find that the pairing correlations are
stronger than the extended pairing correlations and are positive when the
pair separation exceeds several lattice constants. As the system size or the
interaction strength increases, the magnitude of the long-range part of both
correlation functions vanishes.Comment: 4 pages, RevTex, 4 figures included; submitted to Phys. Rev. Let
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