98,031 research outputs found
A Navier-Stokes Solution of Hull-Ring Wing-Thruster Interaction
Navier-Stokes simulations of high Reynolds number flow around an axisymmetric body supported in a water tunnel were made. The numerical method is based on a finite-differencing high resolution second-order accurate implicit upwind scheme. Four different configurations were investigated, these are: (1) barebody; (2) body with an operating propeller; (3) body with a ring wing; and (4) body with a ring wing and an operating propeller. Pressure and velocity components near the stern region were obtained computationally and are shown to compare favorably with the experimental data. The method correctly predicts the existence and extent of stern flow separation for the barebody and the absence of flow separation for the three other configurations with ring wing and/or propeller
WHO BENEFITS FROM FUNDS OF HEDGE FUNDS? A CRITIQUE OF ALTERNATIVE ORGANIZATIONAL STRUCTURES IN THE HEDGE FUND INDUSTRY (I)
This paper provides a critique of alternative organizational structures in the hedge fund industry. Our critique is facilitated by several stylized models describing alternative industry structures. The models include: (1) An insideonly hedge fund model; (2) A straddling hedge fund model; (3) A straddling “feeder” fund of funds (FOF) hedge fund model; (4) A stand-alone outside hedge fund; and (5) An outside “feeder” FOF hedge fund model. Our discussion of these models, which centers on benefits vs. fundamental problems related to illiquidity, information asymmetry, and conflicts of interest, leads to several hypotheses about the differential characteristics and return performance of both individual hedge funds and FOFs.Hedge funds, Funds of funds, Illiquidity, Information asymmetry, Conflicts of interest, Adjacency risk, Contagion, Return performance
Logarithmic corrections to finite size spectrum of SU(N) symmetric quantum chains
We consider SU(N) symmetric one dimensional quantum chains at finite
temperature. For such systems the correlation lengths, ground state energy, and
excited state energies are investigated in the framework of conformal field
theory. The possibility of different types of excited states are discussed.
Logarithmic corrections to the ground state energy and different types of
excited states in the presence of a marginal opeartor, are calculated. Known
results for SU(2) and SU(4) symmetric systems follow from our general formula.Comment: 5 pages, 1 figure; Typos corrected and minor changes made for clarit
Modifying the photodetachment near a metal surface by a weak electric field
We show the photodetachment cross sections of H near a metal surface can be
modified using a weak static electric field. The modification is possible
because the oscillatory part of the cross section near a metal surface is
directly connected with the transit-time and the action of the
detached-electron closed-orbit which can be changed systematically by varying
the static electric field strength. Photodetachment cross sections for various
photon energies and electric field values are calculated and displayed.Comment: 16 pages, 7 figure
A two-dimensional numerical study of the flow inside the combustion chambers of a motored rotary engine
A numerical study was performed to investigate the unsteady, multidimensional flow inside the combustion chambers of an idealized, two-dimensional, rotary engine under motored conditions. The numerical study was based on the time-dependent, two-dimensional, density-weighted, ensemble-averaged conservation equations of mass, species, momentum, and total energy valid for two-component ideal gas mixtures. The ensemble-averaged conservation equations were closed by a K-epsilon model of turbulence. This K-epsilon model of turbulence was modified to account for some of the effects of compressibility, streamline curvature, low-Reynolds number, and preferential stress dissipation. Numerical solutions to the conservation equations were obtained by the highly efficient implicit-factored method of Beam and Warming. The grid system needed to obtain solutions were generated by an algebraic grid generation technique based on transfinite interpolation. Results of the numerical study are presented in graphical form illustrating the flow patterns during intake, compression, gaseous fuel injection, expansion, and exhaust
Decoherence of coupled electron spins via nuclear spin dynamics in quantum dots
In double quantum dots, the exchange interaction between two electron spins
renormalizes the excitation energy of pair-flips in the nuclear spin bath,
which in turn modifies the non-Markovian bath dynamics. As the energy
renormalization varies with the Overhauser field mismatch between the quantum
dots, the electron singlet-triplet decoherence resulting from the bath dynamics
depends on sampling of nuclear spin states from an ensemble, leading to the
transition from exponential decoherence in single-sample dynamics to power-law
decay under ensemble averaging. In contrast, the decoherence of a single
electron spin in one dot is essentially the same for different choices of the
nuclear spin configuration.Comment: 4 pages 3 figure
Description of spin transport and precession in spin-orbit coupling systems and a general equation of continuity
By generalizing the usual current density to a matrix with respect to spin
variables, a general equation of continuity satisfied by the density matrix and
current density matrix has been derived. This equation holds in arbitrary
spin-orbit coupling systems as long as its Hamiltonian can be expressed in
terms of a power series in momentum. Thereby, the expressions of the current
density matrix and a torque density matrix are obtained. The current density
matrix completely describes both the usual current and spin current as well;
while the torque density matrix describes the spin precession caused by a total
effective magnetic field, which may include a realistic and an effective one
due to the spin-orbit coupling. In contrast to the conventional definition of
spin current, this expression contains an additional term if the Hamiltonian
includes nonlinear spin-orbit couplings. Moreover, if the degree of the full
Hamiltonian , then the particle current must also be modified in order
to satisfy the local conservation law of number.Comment: 9 page
Higher-order vortex solitons, multipoles, and supervortices on a square optical lattice
We predict new generic types of vorticity-carrying soliton complexes in a
class of physical systems including an attractive Bose-Einstein condensate in a
square optical lattice (OL) and photonic lattices in photorefractive media. The
patterns include ring-shaped higher-order vortex solitons and supervortices.
Stability diagrams for these patterns, based on direct simulations, are
presented. The vortex ring solitons are stable if the phase difference \Delta
\phi between adjacent solitons in the ring is larger than \pi/2, while the
supervortices are stable in the opposite case, \Delta \phi <\pi /2. A
qualitative explanation to the stability is given.Comment: 9 pages, 4 figure
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