33,649 research outputs found
Flight investigation of insect contamination and its alleviation
An investigation of leading edge contamination by insects was conducted with a JetStar airplane instrumented to detect transition on the outboard leading edge flap and equipped with a system to spray the leading edge in flight. The results of airline type flights with the JetStar indicated that insects can contaminate the leading edge during takeoff and climbout. The results also showed that the insects collected on the leading edges at 180 knots did not erode at cruise conditions for a laminar flow control airplane and caused premature transition of the laminar boundary layer. None of the superslick and hydrophobic surfaces tested showed any significant advantages in alleviating the insect contamination problem. While there may be other solutions to the insect contamination problem, the results of these tests with a spray system showed that a continouous water spray while encountering the insects is effective in preventing insect contamination of the leading edges
Critical behavior of the three-dimensional bond-diluted Ising spin glass: Finite-size scaling functions and Universality
We study the three-dimensional (3D) bond-diluted Edwards-Anderson (EA) model
with binary interactions at a bond occupation of 45% by Monte Carlo (MC)
simulations. Using an efficient cluster MC algorithm we are able to determine
the universal finite-size scaling (FSS) functions and the critical exponents
with high statistical accuracy. We observe small corrections to scaling for the
measured observables. The critical quantities and the FSS functions indicate
clearly that the bond-diluted model for dilutions above the critical dilution
p*, at which a spin glass (SG) phase appears, lies in the same universality
class as the 3D undiluted EA model with binary interactions. A comparison with
the FSS functions of the 3D site-diluted EA model with Gaussian interactions at
a site occupation of 62.5% gives very strong evidence for the universality of
the SG transition in the 3D EA model.Comment: Revised version. 10 pages, 9 figures, 2 table
Overconstrained dynamics in galaxy redshift surveys
The least-action principle (LAP) method is used on four galaxy redshift
surveys to measure the density parameter Omega_m and the matter and
galaxy-galaxy power spectra. The datasets are PSCz, ORS, Mark III and SFI. The
LAP method is applied on the surveys simultaneously, resulting in an
overconstrained dynamical system that describes the cosmic overdensities and
velocity flows. The system is solved by relaxing the constraint that each
survey imposes upon the cosmic fields. A least-squares optimization of the
errors that arise in the process yields the cosmic fields and the value of
Omega_m that is the best fit to the ensemble of datasets. The analysis has been
carried out with a high-resolution Gaussian smoothing of 500 km/s and over a
spherical selected volume of radius 9,000 km/s. We have assigned a weight to
each survey, depending on their density of sampling, and this parameter
determines their relative influence in limiting the domain of the overall
solution. The influence of each survey on the final value of Omega_m, the
cosmographical features of the cosmic fields and the power spectra largely
depends on the distribution function of the errors in the relaxation of the
constraints. We find that PSCz and Mark III are closer to the final solution
than ORS and SFI. The likelihood analysis yields Omega_m= 0.37\pm 0.01 to
1sigma level. PSCz and SFI are the closest to this value, whereas ORS and Mark
III predict a somewhat lower Omega_m. The model of bias employed is a
scale-dependent one, and we retain up to 42 bias coefficients b_{rl} in the
spherical harmonics formalism. The predicted power spectra are estimated in the
range of wavenumbers 0.02-0.49h Mpc^{-1}, and we compare these results with
measurements recently reported in the literature.Comment: 10 pages, no figure
Percolation Analysis of a Wiener Reconstruction of the IRAS 1.2 Jy Redshift Catalog
We present percolation analyses of Wiener Reconstructions of the IRAS 1.2 Jy
Redshift Survey. There are ten reconstructions of galaxy density fields in real
space spanning the range to , where
, is the present dimensionless density and
is the bias factor. Our method uses the growth of the largest cluster
statistic to characterize the topology of a density field, where Gaussian
randomized versions of the reconstructions are used as standards for analysis.
For the reconstruction volume of radius, Mpc,
percolation analysis reveals a slight `meatball' topology for the real space,
galaxy distribution of the IRAS survey.
cosmology-galaxies:clustering-methods:numericalComment: Revised version accepted for publication in The Astrophysical
Journal, January 10, 1997 issue, Vol.47
Exact renormalization of the random transverse-field Ising spin chain in the strongly ordered and strongly disordered Griffiths phases
The real-space renormalization group (RG) treatment of random
transverse-field Ising spin chains by Fisher ({\it Phys. Rev. B{\bf 51}, 6411
(1995)}) has been extended into the strongly ordered and strongly disordered
Griffiths phases and asymptotically exact results are obtained. In the
non-critical region the asymmetry of the renormalization of the couplings and
the transverse fields is related to a non-linear quantum control parameter,
, which is a natural measure of the distance from the quantum critical
point. , which is found to stay invariant along the RG trajectories and
has been expressed by the initial disorder distributions, stands in the
singularity exponents of different physical quantities (magnetization,
susceptibility, specific heat, etc), which are exactly calculated. In this way
we have observed a weak-universality scenario: the Griffiths-McCoy
singularities does not depend on the form of the disorder, provided the
non-linear quantum control parameter has the same value. The exact scaling
function of the magnetization with a small applied magnetic field is calculated
and the critical point magnetization singularity is determined in a simple,
direct way.Comment: 11 page
Maximum-Likelihood Comparisons of Tully-Fisher and Redshift Data: Constraints on Omega and Biasing
We compare Tully-Fisher (TF) data for 838 galaxies within cz=3000 km/sec from
the Mark III catalog to the peculiar velocity and density fields predicted from
the 1.2 Jy IRAS redshift survey. Our goal is to test the relation between the
galaxy density and velocity fields predicted by gravitational instability
theory and linear biasing, and thereby to estimate where is the linear bias parameter for IRAS galaxies.
Adopting the IRAS velocity and density fields as a prior model, we maximize the
likelihood of the raw TF observables, taking into account the full range of
selection effects and properly treating triple-valued zones in the
redshift-distance relation. Extensive tests with realistic simulated galaxy
catalogs demonstrate that the method produces unbiased estimates of
and its error. When we apply the method to the real data, we model the presence
of a small but significant velocity quadrupole residual (~3.3% of Hubble flow),
which we argue is due to density fluctuations incompletely sampled by IRAS. The
method then yields a maximum likelihood estimate
(1-sigma error). We discuss the constraints on and biasing that follow
if we assume a COBE-normalized CDM power spectrum. Our model also yields the
1-D noise noise in the velocity field, including IRAS prediction errors, which
we find to be be 125 +/- 20 km/sec.Comment: 53 pages, 20 encapsulated figures, two tables. Submitted to the
Astrophysical Journal. Also available at http://astro.stanford.edu/jeff
Quantum critical phenomena of long-range interacting bosons in a time-dependent random potential
We study the superfluid-insulator transition of a particle-hole symmetric
system of long-range interacting bosons in a time-dependent random potential in
two dimensions, using the momentum-shell renormalization-group method. We find
a new stable fixed point with non-zero values of the parameters representing
the short- and long-range interactions and disorder when the interaction is
asymptotically logarithmic. This is contrasted to the non-random case with a
logarithmic interaction, where the transition is argued to be first-order, and
to the Coulomb interaction case, where either a first-order transition or
an XY-like transition is possible depending on the parameters. We propose that
our model may be relevant in studying the vortex liquid-vortex glass transition
of interacting vortex lines in point-disordered type-II superconductors.Comment: 10 pages, 3 figure
Vectorial Loading of Processive Motor Proteins: Implementing a Landscape Picture
Individual processive molecular motors, of which conventional kinesin is the
most studied quantitatively, move along polar molecular tracks and, by exerting
a force on a tether, drag cellular cargoes, {\em in
vivo}, or spherical beads, {\em in vitro}, taking up to hundreds of
nanometer-scale steps. From observations of velocities and the dispersion of
displacements with time, under measured forces and controlled fuel supply
(typically ATP), one may hope to obtain insight into the molecular motions
undergone in the individual steps. In the simplest situation, the load force
may be regarded as a scalar resisting force, , acting
parallel to the track: however, experiments, originally by Gittes {\em et al.}
(1996), have imposed perpendicular (or vertical) loads, , while more
recently Block and coworkers (2002, 2003) and Carter and Cross (2005) have
studied {\em assisting} (or reverse) loads, , and also sideways (or
transverse) loads
Radial Redshift Space Distortions
The radial component of the peculiar velocities of galaxies cause
displacements in their positions in redshift space. We study the effect of the
peculiar velocities on the linear redshift space two point correlation
function. Our analysis takes into account the radial nature of the redshift
space distortions and it highlights the limitations of the plane parallel
approximation. We consider the problem of determining the value of \beta and
the real space two point correlation function from the linear redshift space
two point correlation function. The inversion method proposed here takes into
account the radial nature of the redshift space distortions and can be applied
to magnitude limited redshift surveys that have only partial sky coverage.Comment: 26 pages including 11 figures, to appear in Ap
IRAS versus POTENT Density Fields on Large Scales: Biasing and Omega
The galaxy density field as extracted from the IRAS 1.2 Jy redshift survey is
compared to the mass density field as reconstructed by the POTENT method from
the Mark III catalog of peculiar velocities. The reconstruction is done with
Gaussian smoothing of radius 12 h^{-1}Mpc, and the comparison is carried out
within volumes of effective radii 31-46 h^{-1}Mpc, containing approximately
10-26 independent samples. Random and systematic errors are estimated from
multiple realizations of mock catalogs drawn from a simulation that mimics the
observed density field in the local universe. The relationship between the two
density fields is found to be consistent with gravitational instability theory
in the mildly nonlinear regime and a linear biasing relation between galaxies
and mass. We measure beta = Omega^{0.6}/b_I = 0.89 \pm 0.12 within a volume of
effective radius 40 h^{-1}Mpc, where b_I is the IRAS galaxy biasing parameter
at 12 h^{-1}Mpc. This result is only weakly dependent on the comparison volume,
suggesting that cosmic scatter is no greater than \pm 0.1. These data are thus
consistent with Omega=1 and b_I\approx 1. If b_I>0.75, as theoretical models of
biasing indicate, then Omega>0.33 at 95% confidence. A comparison with other
estimates of beta suggests scale-dependence in the biasing relation for IRAS
galaxies.Comment: 35 pages including 10 figures, AAS Latex, Submitted to The
Astrophysical Journa
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