1,323 research outputs found
Dynamic characteristics of a space-station solar wing array
A solar-wing-array concept is described which meets space-station requirements for minimum fundamental frequency (0.4 Hz), component modularity, and growth potential. The basic wing-array design parameters are varied, and the resulting effects on the array vibration frequencies and mode shapes are assessed. The transient response of a free-free space station (incorporating a solar-wing-array point design) to a load applied at the space-station center is studied. The use of the transient response studies in identifying critically loaded structural members is briefly discussed. The final 150-kW space-station configuration has a fundamental elastic frequency of 0.403 Hz
Effect of wind turbine generator model and siting on wind power changes out of large WECS arrays
Methods of reducing the WECS generation change through selection of the wind turbine model for each site, selection of an appropriate siting configuration, and wind array controls are discussed. An analysis of wind generation change from an echelon and a farm for passage of a thunderstorm is presented. Reduction of the wind generation change over ten minutes is shown to reduce the increase in spinning reserve, unloadable generation and load following requirements on unit commitment when significant WECS generation is present and the farm penetration constraint is satisfied. Controls on the blade pitch angle of all wind turbines in an array or a battery control are shown to reduce both the wind generation change out of an array and the effective farm penetration in anticipation of a storm so that the farm penetration constraint may be satisfied
The Effect of Magnetization upon the Elasticity of Rods
In the Physical Review, Vol. II, No. 4 and Vol. III., No. 6, is described a series of important experiments which show the relation between temperature and elasticity in wire. In one of the papers the statement was made that the results seem to indicate that the magnetizing effect of the current through the wire increases the modulus of elasticity. The increase in temperature in the wire was produced by sending a current directly through it, and also by sending a current through the helix that surrounded it. The author stated that the magnetization produced by the first method had no appreciable effect on the result, and that if there is any difference in the effects produced upon the elasticity of a wire by magnetizing it, that difference is too small to be detected with any certainty by this experiment. This paper contains the results of some experiments whose object was to test the effect of magnetization upon the modulus of elasticity by the application of interference methods of measurement
Evolution of interfaces and expansion in width
Interfaces in a model with a single, real nonconserved order parameter and
purely dissipative evolution equation are considered. We show that a systematic
perturbative approach, called the expansion in width and developed for curved
domain walls, can be generalized to the interfaces. Procedure for calculating
curvature corrections is described. We also derive formulas for local velocity
and local surface tension of the interface. As an example, evolution of
spherical interfaces is discussed, including an estimate of critical size of
small droplets.Comment: Discussion of stability of the interface is added, and the numerical
estimates of width and velocity of the interface in the liquid crystal
example are corrected. 25 pages, Latex2
Dynamics of a Vortex in Two-Dimensional Superfluid He3-A: Force Caused by the l-Texture
Based on the Landau-Ginzburg Lagrangian, the dynamics of a vortex is studied
for superfluid He3-A characterized by the l-texture. The resultant equation of
motion for a vortex leads to the Magnus-type force caused by the l-texture. The
force is explicitly written in terms of the mapping degree from the
compactified 2-dimensional plane to the space of l-vector, which reflects the
quantitative differences of vortex configurations, especially the Mermin-Ho and
Anderson-Toulouse vortices. The formulation is applied to anisotropic
superconductors in which the Hall current is shown to incorporate changes
between vortex configurations.Comment: 4 pages, RevTex(twocolumn
Hall-Effect Sign Anomaly and Small-Polaronic Conduction in (La_{1-x}Gd_x)_{0.67}Ca_{0.33}MnO_3
The Hall coefficient of Gd-doped La_{2/3}Ca_{1/3}MnO_3 exhibits Arrhenius
behavior over a temperature range from 2T_c to 4T_c, with an activation energy
very close to 2/3 that of the electrical conductivity. Although both the doping
level and thermoelectric coefficient indicate hole-like conduction, the Hall
coefficient is electron-like. This unusual result provides strong evidence in
favor of small-polaronic conduction in the paramagnetic regime of the
manganites.Comment: 11 pages, 4 figures, uses revtex.st
Scaling Relations of Viscous Fingers in Anisotropic Hele-Shaw Cells
Viscous fingers in a channel with surface tension anisotropy are numerically
studied. Scaling relations between the tip velocity v, the tip radius and the
pressure gradient are investigated for two kinds of boundary conditions of
pressure, when v is sufficiently large. The power-law relations for the
anisotropic viscous fingers are compared with two-dimensional dendritic growth.
The exponents of the power-law relations are theoretically evaluated.Comment: 5 pages, 4 figure
Velocity Selection for Propagating Fronts in Superconductors
Using the time-dependent Ginzburg-Landau equations we study the propagation
of planar fronts in superconductors, which would appear after a quench to zero
applied magnetic field. Our numerical solutions show that the fronts propagate
at a unique speed which is controlled by the amount of magnetic flux trapped in
the front. For small flux the speed can be determined from the linear marginal
stability hypothesis, while for large flux the speed may be calculated using
matched asymptotic expansions. At a special point the order parameter and
vector potential are dual, leading to an exact solution which is used as the
starting point for a perturbative analysis.Comment: 4 pages, 2 figures; submitted to Phys. Rev. Letter
Nucleation and Growth of the Superconducting Phase in the Presence of a Current
We study the localized stationary solutions of the one-dimensional
time-dependent Ginzburg-Landau equations in the presence of a current. These
threshold perturbations separate undercritical perturbations which return to
the normal phase from overcritical perturbations which lead to the
superconducting phase. Careful numerical work in the small-current limit shows
that the amplitude of these solutions is exponentially small in the current; we
provide an approximate analysis which captures this behavior. As the current is
increased toward the stall current J*, the width of these solutions diverges
resulting in widely separated normal-superconducting interfaces. We map out
numerically the dependence of J* on u (a parameter characterizing the material)
and use asymptotic analysis to derive the behaviors for large u (J* ~ u^-1/4)
and small u (J -> J_c, the critical deparing current), which agree with the
numerical work in these regimes. For currents other than J* the interface
moves, and in this case we study the interface velocity as a function of u and
J. We find that the velocities are bounded both as J -> 0 and as J -> J_c,
contrary to previous claims.Comment: 13 pages, 10 figures, Revte
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