4,847 research outputs found
The Network Design Problem with Relays
Cataloged from PDF version of article.The network design problem with relays (NDPR) is defined on an undirected graph G = (V,E,K), where V = {1,...,n} is
a vertex set, E = {(i,j):i,j 2 V,i < j} is an edge set. The set K = {(o(k),d(k))} is a set of communication pairs (or commodities):
o(k) 2 V and d(k) 2 V denote the origin and the destination of the kth commodity, respectively. With each edge (i,j)
are associated a cost cij and a length dij. With vertex i is associated a fixed cost fi of locating a relay at i. The NDPR consists
of selecting a subset E of edges of E and of locating relays at a subset V of vertices of V in such a way that: (1) the sum Q of
edge costs and relay costs is minimized; (2) there exists a path linking the origin and the destination of each commodity in
which the length between the origin and the first relay, the last relay and the destination, or any two consecutive relays does
not exceed a preset upper bound k. This article develops a lower bound procedure and four heuristics for the NPDR. These
are compared on several randomly generated instances with |V| 6 1002 and |E| 6 1930.
2006 Elsevier B.V. All rights reserved
The first Frontier Fields cluster: 4.5{\mu}m excess in a z~8 galaxy candidate in Abell 2744
We present in this letter the first analysis of a z~8 galaxy candidate found
in the Hubble and Spitzer imaging data of Abell 2744, as part of the Hubble
Frontier Fields legacy program. We applied the most commonly-used methods to
select exceptionally high-z galaxies by combining non-detection and
color-criteria using seven HST bands. We used GALFIT on IRAC images for fitting
and subtracting contamination of bright nearby sources. The physical properties
have been inferred from SED-fitting using templates with and without nebular
emission. This letter is focussed on the brightest candidate we found
(m=26.2) over the 4.9 arcmin field of view covered by the WFC3.
It shows a non-detection in the ACS bands and at 3.6{\mu}m whereas it is
clearly detected at 4.5{\mu}m with rather similar depths. This break in the
IRAC data could be explained by strong [OIII]+H{\beta} lines at z~8 which
contribute to the 4.5{\mu}m photometry. The best photo-z is found at
z~8.0, although solutions at low-redshift (z~1.9) cannot be
completely excluded, but they are strongly disfavoured by the SED-fitting work.
The amplification factor is relatively small at {\mu}=1.490.02. The Star
Formation Rate in this object is ranging from 8 to 60 Mo/yr, the stellar mass
is in the order of M=(2.5-10) x 10Mo and the size is
r~0.350.15 kpc. This object is one of the first z~8 LBG candidates showing
a clear break between 3.6{\mu}m and 4.5{\mu}m which is consistent with the IRAC
properties of the first spectroscopically confirmed galaxy at a similar
redshift. Due to its brightness, the redshift of this object could potentially
be confirmed by near infrared spectroscopy with current 8-10m telescopes. The
nature of this candidate will be revealed in the coming months with the arrival
of new ACS and Spitzer data, increasing the depth at optical and near-IR
wavelengths.Comment: 4 pages, 2 figures, Accepted for publication in Astronomy and
Astrophysics Letter
Resolving Ambiguities in the Inferred Star Formation Histories of Intense [O III] Emitters in the Reionisation Era
Early JWST spectroscopic campaigns have confirmed the presence of strong [O
III] line-emitting galaxies in the redshift interval . Although deduced
earlier from Spitzer photometry as indicative of young stellar populations,
some studies suggested the relevant photometric excesses attributed to [O III]
emission could, in part, be due to Balmer breaks arising from older stars. We
demonstrate that this is likely the case by exploiting medium-band
near-infrared JWST photometry in the Hubble Ultra Deep Field. We locate a
sample of 6 galaxies with redshifts 8.28.6 for which the relevant
medium-band filters enables us to separate the contributions of [O III]
emission and a Balmer break, thereby breaking earlier degeneracies of
interpretation. The technique is particularly valuable since it provides
photometric redshifts whose precision, , approaches
that of spectroscopic campaigns now underway with JWST. Although some sources
are young, a third of our sample have prominent Balmer breaks consistent with
stellar ages of 150 Myr. Our results indicate that even intense [O III]
emitters experienced episodes of earlier star formation to 10 and
beyond, as is now being independently deduced from direct detection of the
progenitors of similar systems.Comment: 8 pages, submitted to MNRA
The ALMA Frontier Fields Survey - IV. Lensing-corrected 1.1 mm number counts in Abell 2744, MACSJ0416.1-2403 and MACSJ1149.5+2223
[abridged] Characterizing the number counts of faint, dusty star-forming
galaxies is currently a challenge even for deep, high-resolution observations
in the FIR-to-mm regime. They are predicted to account for approximately half
of the total extragalactic background light at those wavelengths. Searching for
dusty star-forming galaxies behind massive galaxy clusters benefits from strong
lensing, enhancing their measured emission while increasing spatial resolution.
Derived number counts depend, however, on mass reconstruction models that
properly constrain these clusters. We estimate the 1.1 mm number counts along
the line of sight of three galaxy clusters, i.e. Abell 2744, MACSJ0416.1-2403
and MACSJ1149.5+2223, which are part of the ALMA Frontier Fields Survey. We
perform detailed simulations to correct these counts for lensing effects. We
use several publicly available lensing models for the galaxy clusters to derive
the intrinsic flux densities of our sources. We perform Monte Carlo simulations
of the number counts for a detailed treatment of the uncertainties in the
magnifications and adopted source redshifts. We find an overall agreement among
the number counts derived for the different lens models, despite their
systematic variations regarding source magnifications and effective areas. Our
number counts span ~2.5 dex in demagnified flux density, from several mJy down
to tens of uJy. Our number counts are consistent with recent estimates from
deep ALMA observations at a 3 level. Below 0.1 mJy, however,
our cumulative counts are lower by 1 dex, suggesting a flattening in
the number counts. In our deepest ALMA mosaic, we estimate number counts for
intrinsic flux densities 4 times fainter than the rms level. This
highlights the potential of probing the sub-10 uJy population in larger samples
of galaxy cluster fields with deeper ALMA observations.Comment: 19 pages, 14 figures, 3 tables. Accepted for publication in A&
Opening the doors of memory: Is declarative memory a natural kind?
Klein's target article argues that autonoetic consciousness is a necessary condition
for memory; this unusually narrow view of the scope of memory implies that only
episodic memory is, strictly speaking, memory. The narrow view is opposed to the
standard broad view, on which causal connection with past experience is sufficient
for memory; on the broad view, both declarative (i.e., episodic and semantic) and
procedural memory count as genuine forms of memory. Klein mounts a convincing
attack on the broad view, arguing that it opens the "doors of memory" too far, but this
commentary contends that the narrow view does not open them far enough. It may
be preferable to adopt an intermediate view of the scope of memory, on which
causal connection is sufficient for memory only when it involves encoding, storage,
and retrieval of content. More demanding than the simple causal condition but less
demanding than the autonoesis condition, the encoding-storage-retrieval condition
implies that both episodic and semantic memory count as genuine forms of memory
but that procedural memory does not
A zeta function approach to the relation between the numbers of symmetry planes and axes of a polytope
A derivation of the Ces\`aro-Fedorov relation from the Selberg trace formula
on an orbifolded 2-sphere is elaborated and extended to higher dimensions using
the known heat-kernel coefficients for manifolds with piecewise-linear
boundaries. Several results are obtained that relate the coefficients, ,
in the Shephard-Todd polynomial to the geometry of the fundamental domain. For
the 3-sphere we show that is given by the ratio of the volume of the
fundamental tetrahedron to its Schl\"afli reciprocal.Comment: Plain TeX, 26 pages (eqn. (86) corrected
Dynamic Collection Scheduling Using Remote Asset Monitoring: Case Study in the UK Charity Sector
Remote sensing technology is now coming onto the market in the waste collection sector. This technology allows waste and recycling receptacles to report their fill levels at regular intervals. This reporting enables collection schedules to be optimized dynamically to meet true servicing needs in a better way and so reduce transport costs and ensure that visits to clients are made in a timely fashion. This paper describes a real-life logistics problem faced by a leading UK charity that services its textile and book donation banks and its high street stores by using a common fleet of vehicles with various carrying capacities. Use of a common fleet gives rise to a vehicle routing problem in which visits to stores are on fixed days of the week with time window constraints and visits to banks (fitted with remote fill-monitoring technology) are made in a timely fashion so that the banks do not become full before collection. A tabu search algorithm was developed to provide vehicle routes for the next day of operation on the basis of the maximization of profit. A longer look-ahead period was not considered because donation rates to banks are highly variable. The algorithm included parameters that specified the minimum fill level (e.g., 50%) required to allow a visit to a bank and a penalty function used to encourage visits to banks that are becoming full. The results showed that the algorithm significantly reduced visits to banks and increased profit by up to 2.4%, with the best performance obtained when the donation rates were more variable
Young Galaxy Candidates in the Hubble Frontier Fields - III. MACSJ0717.5+3745
In this paper we present the results of our search for and study of galaxy candidates behind the third Frontier Fields (FF) cluster,
MACSJ0717.5+3745, and its parallel field, combining data from Hubble and
Spitzer. We select 39 candidates using the Lyman Break technique, for which the
clear non-detection in optical make the extreme mid- interlopers hypothesis
unlikely. We also take benefit from samples selected using
previous Frontier Fields datasets of Abell 2744 and MACS0416 to improve the
constraints on the properties of very high-redshift objects. We compute the
redshift and the physical properties, such emission lines properties, star
formation rate, reddening, and stellar mass for all Frontier Fields objects
from their spectral energy distribution using templates including nebular
emission lines. We study the relationship between several physical properties
and confirm the trend already observed in previous surveys for evolution of
star formation rate with galaxy mass, and between the size and the UV
luminosity of our candidates. The analysis of the evolution of the UV
Luminosity Function with redshift seems more compatible with an evolution of
density. Moreover, no robust 8.5 object is selected behind the cluster
field, and few 9 candidates have been selected in the two previous
datasets from this legacy survey, suggesting a strong evolution in the number
density of galaxies between 8 and 9. Thanks to the use of the lensing
cluster, we study the evolution of the star formation rate density produced by
galaxies with L0.03L, and confirm the strong decrease observed
between 8 and 9.Comment: 21 pages - Accepted for publication in ApJ - v2: small correction
The selective V1a receptor agonist FE 202158 does not cause von Willebrand factor release in sheep unlike arginine vasopressin
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