2,070 research outputs found
Subgrade geology beneath railways in Manchester
It is not sufficient to identify fine-grained soils, only, as locations for potential subgrade problems as could be done using a traditional 2D geological map. More information is required about the geological structure, lithological variability, mineralogy, moisture content and geotechnical properties of the soil, much of which can be supplied by modern 3D geospatial databases. These databases can be interrogated at key depths to show the wide variability of geological materials and conditions beneath the ground surface. Geological outcrop and thickness of bedrock an superficial deposits (soils), plus the permeability and water table level are predicted from the Manchester geospatial model that is based on 6500 borehole records. Geological sections along railway routes are modelled and the locations of problem soils such as alluvium, till and glaciolacustrine deposits at outcrop and shallow subcrop are identified. Spatial attribution of geotechnical data and simple methods to recast sections in engineering geological terms are demonstrated
An Estimation of the Gamma-Ray Burst Afterglow Apparent Optical Brightness Distribution Function
By using recent publicly available observational data obtained in conjunction
with the NASA Swift gamma-ray burst mission and a novel data analysis
technique, we have been able to make some rough estimates of the GRB afterglow
apparent optical brightness distribution function. The results suggest that 71%
of all burst afterglows have optical magnitudes with mR < 22.1 at 1000 seconds
after the burst onset, the dimmest detected object in the data sample. There is
a strong indication that the apparent optical magnitude distribution function
peaks at mR ~ 19.5. Such estimates may prove useful in guiding future plans to
improve GRB counterpart observation programs. The employed numerical techniques
might find application in a variety of other data analysis problems in which
the intrinsic distributions must be inferred from a heterogeneous sample.Comment: 15 pages including 2 tables and 7 figures, accepted for publication
in Ap
TDIR: Time-Delay Interferometric Ranging for Space-Borne Gravitational-Wave Detectors
Space-borne interferometric gravitational-wave detectors, sensitive in the
low-frequency (mHz) band, will fly in the next decade. In these detectors, the
spacecraft-to-spacecraft light-travel times will necessarily be unequal and
time-varying, and (because of aberration) will have different values on up- and
down-links. In such unequal-armlength interferometers, laser phase noise will
be canceled by taking linear combinations of the laser-phase observables
measured between pairs of spacecraft, appropriately time-shifted by the light
propagation times along the corresponding arms. This procedure, known as
time-delay interferometry (TDI), requires an accurate knowledge of the
light-time delays as functions of time. Here we propose a high-accuracy
technique to estimate these time delays and study its use in the context of the
Laser Interferometer Space Antenna (LISA) mission. We refer to this ranging
technique, which relies on the TDI combinations themselves, as Time-Delay
Interferometric Ranging (TDIR). For every TDI combination, we show that, by
minimizing the rms power in that combination (averaged over integration times
s) with respect to the time-delay parameters, we obtain estimates
of the time delays accurate enough to cancel laser noise to a level well below
the secondary noises. Thus TDIR allows the implementation of TDI without the
use of dedicated inter-spacecraft ranging systems, with a potential
simplification of the LISA design. In this paper we define the TDIR procedure
formally, and we characterize its expected performance via simulations with the
\textit{Synthetic LISA} software package.Comment: 5 pages, 2 figure
Topology and shape optimization of induced-charge electro-osmotic micropumps
For a dielectric solid surrounded by an electrolyte and positioned inside an
externally biased parallel-plate capacitor, we study numerically how the
resulting induced-charge electro-osmotic (ICEO) flow depends on the topology
and shape of the dielectric solid. In particular, we extend existing
conventional electrokinetic models with an artificial design field to describe
the transition from the liquid electrolyte to the solid dielectric. Using this
design field, we have succeeded in applying the method of topology optimization
to find system geometries with non-trivial topologies that maximize the net
induced electro-osmotic flow rate through the electrolytic capacitor in the
direction parallel to the capacitor plates. Once found, the performance of the
topology optimized geometries has been validated by transferring them to
conventional electrokinetic models not relying on the artificial design field.
Our results show the importance of the topology and shape of the dielectric
solid in ICEO systems and point to new designs of ICEO micropumps with
significantly improved performance.Comment: 18 pages, latex IOP-style, 7 eps figure
Point Source Extraction with MOPEX
MOPEX (MOsaicking and Point source EXtraction) is a package developed at the
Spitzer Science Center for astronomical image processing. We report on the
point source extraction capabilities of MOPEX. Point source extraction is
implemented as a two step process: point source detection and profile fitting.
Non-linear matched filtering of input images can be performed optionally to
increase the signal-to-noise ratio and improve detection of faint point
sources. Point Response Function (PRF) fitting of point sources produces the
final point source list which includes the fluxes and improved positions of the
point sources, along with other parameters characterizing the fit. Passive and
active deblending allows for successful fitting of confused point sources.
Aperture photometry can also be computed for every extracted point source for
an unlimited number of aperture sizes. PRF is estimated directly from the input
images. Implementation of efficient methods of background and noise estimation,
and modified Simplex algorithm contribute to the computational efficiency of
MOPEX. The package is implemented as a loosely connected set of perl scripts,
where each script runs a number of modules written in C/C++. Input parameter
setting is done through namelists, ASCII configuration files. We present
applications of point source extraction to the mosaic images taken at 24 and 70
micron with the Multiband Imaging Photometer (MIPS) as part of the Spitzer
extragalactic First Look Survey and to a Digital Sky Survey image. Completeness
and reliability of point source extraction is computed using simulated data.Comment: 20 pages, 13 Postscript figures, accepted for publication in PAS
Phase-resolved far-ultraviolet HST spectroscopy of the peculiar magnetic white dwarf RE J0317-853
We present phase resolved FUV HST FOS spectra of the rapidly rotating, highly
magnetic white dwarf RE J0317-853. Using these data, we construct a new model
for the magnetic field morphology across the stellar surface. From an expansion
into spherical harmonics, we find the range of magnetic field strengths present
is 180-800MG. For the first time we could identify an absorption feature
present at certain phases at 1160A as a ``forbidden'' 1s_0 -> 2s_0 component,
due to the combined presence of an electric and magnetic field.Comment: 15 pages including 4 figures. Accepted for publication in ApJ Letter
Molecular Line Profile Fitting with Analytic Radiative Transfer Models
We present a study of analytic models of starless cores whose line profiles
have ``infall asymmetry,'' or blue-skewed shapes indicative of contracting
motions. We compare the ability of two types of analytical radiative transfer
models to reproduce the line profiles and infall speeds of centrally condensed
starless cores whose infall speeds are spatially constant and range between 0
and 0.2 km s-1. The model line profiles of HCO+ (J=1-0) and HCO+ (J=3-2) are
produced by a self-consistent Monte Carlo radiative transfer code. The analytic
models assume that the excitation temperature in the front of the cloud is
either constant (``two-layer'' model) or increases inward as a linear function
of optical depth (``hill'' model). Each analytic model is matched to the line
profile by rapid least-squares fitting.
The blue-asymmetric line profiles with two peaks, or with a blue shifted peak
and a red shifted shoulder, can be well fit by the ``HILL5'' model (a five
parameter version of the hill model), with an RMS error of 0.02 km s-1. A peak
signal to noise ratio of at least 30 in the molecular line observations is
required for performing these analytic radiative transfer fits to the line
profiles.Comment: 48 pages, 20 figures, accepted for publication in Ap
Nuclear energy density optimization: Large deformations
A new Skyrme-like energy density suitable for studies of strongly elongated
nuclei has been determined in the framework of the Hartree-Fock-Bogoliubov
theory using the recently developed model-based, derivative-free optimization
algorithm POUNDerS. A sensitivity analysis at the optimal solution has revealed
the importance of states at large deformations in driving the parameterization
of the functional. The good agreement with experimental data on masses and
separation energies, achieved with the previous parameterization UNEDF0, is
largely preserved. In addition, the new energy density UNEDF1 gives a much
improved description of the fission barriers in 240Pu and neighboring nuclei.Comment: 16 pages, 11 figures, accepted for publication in Phys. Rev.
Data analysis of gravitational-wave signals from spinning neutron stars. V. A narrow-band all-sky search
We present theory and algorithms to perform an all-sky coherent search for
periodic signals of gravitational waves in narrow-band data of a detector. Our
search is based on a statistic, commonly called the -statistic,
derived from the maximum-likelihood principle in Paper I of this series. We
briefly review the response of a ground-based detector to the
gravitational-wave signal from a rotating neuron star and the derivation of the
-statistic. We present several algorithms to calculate efficiently
this statistic. In particular our algorithms are such that one can take
advantage of the speed of fast Fourier transform (FFT) in calculation of the
-statistic. We construct a grid in the parameter space such that
the nodes of the grid coincide with the Fourier frequencies. We present
interpolation methods that approximately convert the two integrals in the
-statistic into Fourier transforms so that the FFT algorithm can
be applied in their evaluation. We have implemented our methods and algorithms
into computer codes and we present results of the Monte Carlo simulations
performed to test these codes.Comment: REVTeX, 20 pages, 8 figure
Efficient statistical inference for stochastic reaction processes
We address the problem of estimating unknown model parameters and state
variables in stochastic reaction processes when only sparse and noisy
measurements are available. Using an asymptotic system size expansion for the
backward equation we derive an efficient approximation for this problem. We
demonstrate the validity of our approach on model systems and generalize our
method to the case when some state variables are not observed.Comment: 4 pages, 2 figures, 2 tables; typos corrected, remark about Kalman
smoother adde
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