1,112 research outputs found
F-8C digital CCV flight control laws
A set of digital flight control laws were designed for the NASA F-8C digital fly-by-wire aircraft. The control laws emphasize Control Configured Vehicle (CCV) benefits. Specific pitch axis objectives were improved handling qualities, angle-of-attack limiting, gust alleviation, drag reduction in steady and maneuvering flight, and a capability to fly with reduced static stability. The lateral-directional design objectives were improved Dutch roll damping and turn coordination over a wide range in angle-of-attack. An overall program objective was to explore the use of modern control design methodilogy to achieve these specific CCV benefits. Tests for verifying system integrity, an experimental design for handling qualities evaluation, and recommended flight test investigations were specified
Control networks for the Galilean satellites, November 1979
Pictures of the four Galilean satellites taken as the two Voyager spacecraft approached Jupiter during March and July 1979 are presented. Control nets of the Galilean satellites, computed photogrammetrically, and measurements of the mean radii are presented. The pictures in the control nets are identified, the coordinates of the control points are given, and identifications of some of the control points are shown on figures. The use of star field pictures to compute the focal lengths of the camera is discussed and the geometric relationship between the narrow and wide and angle cameras is reported. A description of the coordinate systems of the Galilean satellites is presented and the status of the control net computations is reported
Number-of-Particle Fluctuations and Stability of Bose-Condensed Systems
In this paper we show that a normal total number-of-particle fluctuation can
be obtained consistently from the static thermodynamic relation and dynamic
compressibility sum rule. In models using the broken U(1) gauge symmetry, in
order to keep the consistency between statics and dynamics, it is important to
identify the equilibrium state of the system with which the density response
function is calculated, so that the condensate particle number , the
number of thermal depletion particles , and the number of
non-condensate particles can be unambiguously defined. We also show
that the chemical potential determined from the Hugenholtz-Pines theorem should
be consistent with that determined from the equilibrium equation of state. The
anomalous fluctuation of the number of non-condensate particles is an
intrinsic feature of the broken U(1) gauge symmetry. However, this anomalous
fluctuation does not imply the instability of the system. Using the random
phase approximation, which preserves the U(1) gauge symmetry, such an anomalous
fluctuation of the number of non-condensate particles is completely absentComment: 9 pages, submitted to PR
Collective Antenna Effects in the Terahertz and Infrared Response of Highly Aligned Carbon Nanotube Arrays
We study macroscopically-aligned single-wall carbon nanotube arrays with
uniform lengths via polarization-dependent terahertz and infrared transmission
spectroscopy. Polarization anisotropy is extreme at frequencies less than
3 THz with no sign of attenuation when the polarization is perpendicular
to the alignment direction. The attenuation for both parallel and perpendicular
polarizations increases with increasing frequency, exhibiting a pronounced and
broad peak around 10 THz in the parallel case. We model the electromagnetic
response of the sample by taking into account both radiative scattering and
absorption losses. We show that our sample acts as an effective antenna due to
the high degree of alignment, exhibiting much larger radiative scattering than
absorption in the mid/far-infrared range. Our calculated attenuation spectrum
clearly shows a non-Drude peak at 10 THz in agreement with the
experiment.Comment: 5 pages, 5 figure
A new model for simulating colloidal dynamics
We present a new hybrid lattice-Boltzmann and Langevin molecular dynamics
scheme for simulating the dynamics of suspensions of spherical colloidal
particles. The solvent is modeled on the level of the lattice-Boltzmann method
while the molecular dynamics is done for the solute. The coupling between the
two is implemented through a frictional force acting both on the solvent and on
the solute, which depends on the relative velocity. A spherical colloidal
particle is represented by interaction sites at its surface. We demonstrate
that this scheme quantitatively reproduces the translational and rotational
diffusion of a neutral spherical particle in a liquid and show preliminary
results for a charged spherical particle. We argue that this method is
especially advantageous in the case of charged colloids.Comment: For a movie click on the link below Fig
Surface correlations for two-dimensional Coulomb fluids in a disc
After a brief review of previous work, two exactly solvable two-dimensional
models of a finite Coulomb fluid in a disc are studied. The charge correlation
function near the boundary circle is computed. When the disc radius is large
compared to the bulk correlation length, a correlation function of the surface
charge density can be defined. It is checked, on the solvable models, that this
correlation function does have the generic long-range behaviour, decaying as
the inverse square distance, predicted by macroscopic electrostatics. In the
case of a two-component plasma (Coulomb fluid made of two species of particles
of opposite charges), the density correlation function on the boundary circle
itself is conjectured to have a temperature-independent behaviour, decaying as
the -4 power of the distance.Comment: 15 pages, Latex, submitted to J.Phys.:Condens.Matte
Thermodynamic formalism for the Lorentz gas with open boundaries in dimensions
A Lorentz gas may be defined as a system of fixed dispersing scatterers, with
a single light particle moving among these and making specular collisions on
encounters with the scatterers. For a dilute Lorentz gas with open boundaries
in dimensions we relate the thermodynamic formalism to a random flight
problem. Using this representation we analytically calculate the central
quantity within this formalism, the topological pressure, as a function of
system size and a temperature-like parameter \ba. The topological pressure is
given as the sum of the topological pressure for the closed system and a
diffusion term with a \ba-dependent diffusion coefficient. From the
topological pressure we obtain the Kolmogorov-Sinai entropy on the repeller,
the topological entropy, and the partial information dimension.Comment: 7 pages, 5 figure
The Faraday Quantum Clock and Non-local Photon Pair Correlations
We study the use of the Faraday effect as a quantum clock for measuring
traversal times of evanescent photons through magneto-refractive structures.
The Faraday effect acts both as a phase-shifter and as a filter for circular
polarizations. Only measurements based on the Faraday phase-shift properties
are relevant to the traversal time measurements. The Faraday polarization
filtering may cause the loss of non-local (Einstein-Podolsky-Rosen) two-photon
correlations, but this loss can be avoided without sacrificing the clock
accuracy. We show that a mechanism of destructive interference between
consecutive paths is responsible for superluminal traversal times measured by
the clock.Comment: 6 figure
Plasma Analogy and Non-Abelian Statistics for Ising-type Quantum Hall States
We study the non-Abelian statistics of quasiparticles in the Ising-type
quantum Hall states which are likely candidates to explain the observed Hall
conductivity plateaus in the second Landau level, most notably the one at
filling fraction nu=5/2. We complete the program started in Nucl. Phys. B 506,
685 (1997) and show that the degenerate four-quasihole and six-quasihole
wavefunctions of the Moore-Read Pfaffian state are orthogonal with equal
constant norms in the basis given by conformal blocks in a c=1+1/2 conformal
field theory. As a consequence, this proves that the non-Abelian statistics of
the excitations in this state are given by the explicit analytic continuation
of these wavefunctions. Our proof is based on a plasma analogy derived from the
Coulomb gas construction of Ising model correlation functions involving both
order and (at most two) disorder operators. We show how this computation also
determines the non-Abelian statistics of collections of more than six
quasiholes and give an explicit expression for the corresponding conformal
block-derived wavefunctions for an arbitrary number of quasiholes. Our method
also applies to the anti-Pfaffian wavefunction and to Bonderson-Slingerland
hierarchy states constructed over the Moore-Read and anti-Pfaffian states.Comment: 68 pages, 3 figures; v2: substantial revisions and additions for
clarity, minor correction
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