48,982 research outputs found
Town centre improvements through sustainable procurement
The project is investigating the potential to reduce town centre business costs and negative environmental impacts through the use of innovations in procurement and freight transport. These innovations include collaborative procurement, Business Improvement Districts, and Delivery and Servicing Plans. These approaches were being trialled and evaluated in three British towns: Cambridge, Lowestoft and Norwich. 17 companies were developing and applying a Delivery and Servicing Plan. Transport reduction effects were achieved
An Optimal Control Theory for the Traveling Salesman Problem and Its Variants
We show that the traveling salesman problem (TSP) and its many variants may
be modeled as functional optimization problems over a graph. In this
formulation, all vertices and arcs of the graph are functionals; i.e., a
mapping from a space of measurable functions to the field of real numbers. Many
variants of the TSP, such as those with neighborhoods, with forbidden
neighborhoods, with time-windows and with profits, can all be framed under this
construct. In sharp contrast to their discrete-optimization counterparts, the
modeling constructs presented in this paper represent a fundamentally new
domain of analysis and computation for TSPs and their variants. Beyond its
apparent mathematical unification of a class of problems in graph theory, the
main advantage of the new approach is that it facilitates the modeling of
certain application-specific problems in their home space of measurable
functions. Consequently, certain elements of economic system theory such as
dynamical models and continuous-time cost/profit functionals can be directly
incorporated in the new optimization problem formulation. Furthermore, subtour
elimination constraints, prevalent in discrete optimization formulations, are
naturally enforced through continuity requirements. The price for the new
modeling framework is nonsmooth functionals. Although a number of theoretical
issues remain open in the proposed mathematical framework, we demonstrate the
computational viability of the new modeling constructs over a sample set of
problems to illustrate the rapid production of end-to-end TSP solutions to
extensively-constrained practical problems.Comment: 24 pages, 8 figure
HST STIS Ultraviolet Spectral Evidence of Outflow in Extreme Narrow-line Seyfert 1 Galaxies: II. Modeling and Interpretation
We present modeling to explore the conditions of the broad-line emitting gas
in two extreme Narrow-line Seyfert 1 galaxies, using the observational results
described in the first paper of this series. Photoionization modeling using
Cloudy was conducted for the broad, blueshifted wind lines and the narrow,
symmetric, rest-wavelength-centered disk lines separately. A broad range of
physical conditions were explored for the wind component, and a figure of merit
was used to quantitatively evaluate the simulation results. Of the three minima
in the figure-of-merit parameter space, we favor the solution characterized by
an X-ray weak continuum, elevated abundances, a small column density
(log(N_H)\approx 21.4), relatively high ionization parameter (log(U)\approx
-1.2 - -0.2), a wide range of densities (log(n)\approx 7 - 11), and a covering
fraction of ~0.15. The presence of low-ionization emission lines implies the
disk component is optically thick to the continuum, and the SiIII]/CIII] ratio
implies a density of 10^10 - 10^10.25 cm^-3. A low ionization parameter
(log(U)=-3) is inferred for the intermediate-ionization lines, unless the
continuum is ``filtered'' through the wind before illuminating the
intermediate-line emitting gas, in which case log(U)=-2.1. The location of the
emission regions was inferred from the photoionization modeling and a simple
``toy'' dynamical model. A large black hole mass (1.3 x 10^8 M_\odot) radiating
at 11% of the Eddington luminosity is consistent with the kinematics of both
the disk and wind lines, and an emission radius of ~10^4 R_S is inferred for
both. We compare these results with previous work and discuss implications.Comment: 45 pages, 15 figures (4 color), accepted for publication in ApJ,
abstract shortene
Fast Mesh Refinement in Pseudospectral Optimal Control
Mesh refinement in pseudospectral (PS) optimal control is embarrassingly easy
--- simply increase the order of the Lagrange interpolating polynomial and
the mathematics of convergence automates the distribution of the grid points.
Unfortunately, as increases, the condition number of the resulting linear
algebra increases as ; hence, spectral efficiency and accuracy are lost in
practice. In this paper, we advance Birkhoff interpolation concepts over an
arbitrary grid to generate well-conditioned PS optimal control discretizations.
We show that the condition number increases only as in general, but
is independent of for the special case of one of the boundary points being
fixed. Hence, spectral accuracy and efficiency are maintained as increases.
The effectiveness of the resulting fast mesh refinement strategy is
demonstrated by using \underline{polynomials of over a thousandth order} to
solve a low-thrust, long-duration orbit transfer problem.Comment: 27 pages, 12 figures, JGCD April 201
Beef Cattle Instance Segmentation Using Fully Convolutional Neural Network
In this paper we present a novel instance segmentation algorithm that extends a fully convolutional network to learn to label objects separately without prediction of regions of interest. We trained the new algorithm on a challenging CCTV recording of beef cattle, as well as benchmark MS COCO and Pascal VOC datasets. Extensive experimentation showed that our approach outperforms the state-of-the-art solutions by up to 8% on our data
Simple algorithm for the correction of MRI image artefacts due to random phase fluctuations
Grant support: This work was supported by EPSRC [grant numbers EP/E036775/1, EP/K020293/1] and received funding from the European Union's Horizon 2020 research and innovation programme [grant agreement No 668119, project âIDentIFYâ]Peer reviewedPublisher PD
UV Imaging Polarimetry of the Seyfert 2 Galaxy Mrk 3
We present UV imaging polarimetry data of the Seyfert 2 galaxy Mrk 3 taken by
the Hubble Space Telescope. The polarized flux is found to be extended to ~1
kpc from the nucleus, and the position angles of polarization are
centrosymmetric, confirming that the polarization is caused by scattering. We
determine the location of the hidden nucleus as the center of this
centrosymmetric pattern. From the polarization images taken in two broad bands,
we have obtained the color distribution of the polarized flux. Some regions
have blue polarized flux, consistent with optically-thin dust scattering, but
some bright knots have a color similar to that of Seyfert 1 nucleus. Also, the
recent Chandra X-ray observation suggests that the ratio of scattered UV flux
to scattered X-ray flux is rather similar to the intrinsic UV/X-ray ratio in a
Seyfert 1 nucleus, if the observed extended X-ray continuum is scattered light.
While the scattered X-ray would be essentially from electron scattering, the UV
slope and UV/X-ray ratio both being similar to Seyfert 1's would lead to two
possibilities as to the nature of the UV scatterers. One is that the UV may
also be scattered by electrons, in which case the scattering gas is somehow
dust-free. The other is that the UV is scattered by dust grains, but the
wavelength-independent UV scattering with low efficiency indicated by the UV
slope and UV/X-ray ratio would suggest that the grains reside in UV-opaque
clouds, or the dust might be mainly composed of large grains and lacks
small-grain population.Comment: 15 pages, 8 figures (plus 2 color versions of grayscale figures), To
appear in ApJ; minor corrections for the proofs of the manuscrip
Ultraluminous X-ray Sources Powered by Radiatively Efficient Two-Phased Super-Eddington Accretion onto Stellar Mass Black holes
The radiation spectra of many of the brightest ultraluminous X-ray sources
(ULXs) are dominated by a hard power law component, likely powered by a hot,
optically thin corona that Comptonizes soft seed photons emitted from a cool,
optically thick black hole accretion disk. Before its dissipation and
subsequent conversion into coronal photon power, the randomized gravitational
binding energy responsible for powering ULX phenomena must separate from the
mass of its origin by a means other than, and quicker than, electron
scattering-mediated radiative diffusion. Therefore, the release of accretion
power in ULXs is not necessarily subject to Eddington-limited photon trapping,
as long as it occurs in a corona. Motivated by these basic considerations, we
present a model of ULXs powered by geometrically thin accretion onto stellar
mass black holes. We argue that the radiative efficiency of the flow remains
high if the corona is magnetized or optically thin and the majority of the
accretion power escapes in the form of radiation rather than an outflow. Within
the context of the current black hole X-ray binary paradigm, our ULX model may
be viewed as an extension of the very high state observed in Galactic sources.
(abridged)Comment: 11 page
Multi-Temperature Blackbody Spectra of Thin Accretion Disks With and Without a Zero-Torque Inner Boundary Condition
The standard spectral model for analyzing the soft component of thermal
emission from a thin accretion disk around a black hole is the
multi-temperature blackbody (MTB) model. The widely used implementation of this
model, which is known as ``diskbb,'' assumes nonzero torque at the inner edge
of the accretion disk. This assumption is contrary to the classic and current
literature on thin-disk accretion, which advocates the use of a zero-torque
boundary condition. Consequently, we have written code for a zero-torque model,
``ezdiskbb,'' which we compare to the nonzero-torque model diskbb by fitting
RXTE spectra of three well-known black hole binaries: 4U 1543-47, XTE
J1550-564, and GRO J1655-40. The chief difference we find is that the
zero-torque model gives a value for the inner disk radius that is about 2.2
times smaller than the value given by diskbb. This result has important
implications, especially for the determination of black-hole angular momentum
and mass accretion rate.Comment: 27 pages, 9 figures, submitted to Ap
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