5,122 research outputs found
100 years of deep-sea tubeworms in the collections of the Natural History Museum, London
Despite having being discovered relatively recently, the Siboglinidae family of poly- chaetes have a controversial taxonomic history. They are predominantly deep sea tube- dwelling worms, often referred to simply as âtubewormsâ that include the magnificent me- tre-long Riftia pachyptila from hydrothermal vents, the recently discovered âbone-eatingâ Osedax and a diverse range of other thin, tube-dwelling species. For a long time they were considered to be in a completely separate Phylum, the Pogonophora, but with the discovery of a segmented posterior and then conclusive DNA evidence, they were re- stored to the Phylum Annelida. In this project curation and research teams have com- bined to enhance the Museumâs collection. This has been facilitated through targeted donation requests, comprehensive digitisation, a location move to the rightful taxonomic place and teaming up with global database initiatives to promote the collection.NatSCA supports open access publication as part of its mission is to promote and support natural science collections. NatSCA uses the Creative Commons Attribution License (CCAL)
http://creativecommons.org/licenses/by/2.5/Â Â for all works we publish. Under CCAL authors retain ownership of the copyright for their article, but authors allow anyone to download, reuse, reprint, modify, distribute, and/or copy articles in NatSCA publications, so long as the original authors and source are cited. The attached file is the published version of the article
Contribution of Scalar Loops to the Three-Photon Decay of the Z
I corrected 3 mistakes from the first version: that were an omitted Feynman
integration in the function f^3_{ij}, a factor of 2 in front of log f^3_{ij} in
eq.2 and an overall factor of 2 in Fig.1 c). The final result is changed
drastically. Doing an expansion in the Higgs mass I show that the matrix
element is identically 0 in the order (MZ/MH)^2, which is due to gauge
invariance. Left with an amplitude of the order (MZ/MH)^4 the final result is
that the scalar contribution to this decay rate is several orders of magnitude
smaller than those of the W boson and fermions.Comment: 6 pages, plain Tex, 1 figure available under request via fax or mail,
OCIP/C-93-5, UQAM-PHE-93/0
A length scale for the superconducting Nernst signal above T in NbSi
We present a study of the Nernst effect in amorphous superconducting thin
films of NbSi. The field dependence of the Nernst coefficient
above T displays two distinct regimes separated by a field scale set by
the Ginzburg-Landau correlation length. A single function , with the
correlation length as its unique argument set either by the zero-field
correlation length (in the low magnetic field limit) or by the magnetic length
(in the opposite limit), describes the Nernst coefficient. We conclude that the
Nernst signal observed on a wide temperature () and field () range is exclusively generated by short-lived Cooper pairs.Comment: 4 pages, 4 figure
Enhancing Parallel Cooperative Trajectory Based Metaheuristics with Path Relinking
This paper proposes a novel algorithm combining path relinking with a set of cooperating trajectory based parallel algorithms to yield a new metaheuristic of enhanced search features. Algorithms based on the exploration of the neighborhood of a single solution, like simulated annealing (SA), have offered accurate results for a large number of real-world problems in the past. Because of their trajectory based nature, some advanced models such as the cooperative one are competitive in academic problems, but still show many limitations in addressing large scale instances. In addition, the field of parallel models for trajectory methods has not deeply been studied yet (at least in comparison with parallel population based models). In this work, we propose a new hybrid algorithm which improves cooperative single solution techniques by using path relinking, allowing both to reduce the global execution time and to improve the efficacy of the method. We test here this new model using a large benchmark of instances of two well-known NP-hard problems: MAXSAT and QAP, with competitive results.Universidad de MĂĄlaga. Campus de Excelencia Internacional AndalucĂa Tech
Isolated Prompt Photon Production in Hadronic Final States of Annihilation
We provide complete analytic expressions for the isolated prompt photon
production cross section in annihilation reactions through one-loop
order in quantum chromodynamics (QCD) perturbation theory. Functional
dependences on the isolation cone size and isolation energy parameter
are derived. The energy dependence as well as the full angular
dependence of the cross section on are displayed, where
specifies the direction of the photon with respect to the
collision axis. We point out that conventional perturbative QCD
factorization breaks down for isolated photon production in
annihilation reactions in a specific region of phase space. We discuss the
implications of this breakdown for the extraction of fragmentation functions
from annihilation data and for computations of prompt photon
production in hadron-hadron reactions.Comment: 54 pages RevTeX plus 19 postscript figures submitted together in one
compressed fil
Inclusive Prompt Photon Production in Hadronic Final States of Annihilation
We provide complete analytic expressions for the inclusive prompt photon
production cross section in hadronic final states of annihilation
reactions through one-loop order in quantum chromodynamics perturbation theory.
Computed explicitly are direct photon production through first order in the
electromagnetic strength and the quark-to-photon and
gluon-to-photon fragmentation contributions through first order in the strong
coupling . The full angular dependence of the cross sections is
displayed, separated into transverse and
longitudinal components, where
specifies the direction of the photon with respect to the collision
axis. We discuss extraction of fragmentation functions from data.Comment: 40 pages, RevTex, 30 figures in postscript available in a separate
fil
The singular behavior of massive QCD amplitudes
We discuss the structure of infrared singularities in on-shell QCD amplitudes
with massive partons and present a general factorization formula in the limit
of small parton masses. The factorization formula gives rise to an all-order
exponentiation of both, the soft poles in dimensional regularization and the
large collinear logarithms of the parton masses. Moreover, it provides a
universal relation between any on-shell amplitude with massive external partons
and its corresponding massless amplitude. For the form factor of a heavy quark
we present explicit results including the fixed-order expansion up to three
loops in the small mass limit. For general scattering processes we show how our
constructive method applies to the computation of all singularities as well as
the constant (mass-independent) terms of a generic massive n-parton QCD
amplitude up to the next-to-next-to-leading order corrections.Comment: version to appear in JHEP (sec. 3 with expanded discussion and
appendix with added results
Factorization and soft-gluon divergences in isolated-photon cross sections
We study the production of isolated photons in annihilation and give
the proof of the all-order factorization of the collinear singularities. These
singularities are absorbed in the standard fragmentation functions of partons
into a photon, while the effects of the isolation are consistently included in
the short-distance cross section. We compute this cross section at order \as
and show that it contains large double logarithms of the isolation parameters.
We explain the physical origin of these logarithms and discuss the possibility
to resum them to all orders in \as.Comment: 18 pages, LaTex, 2 eps figures, few modifications in the text,
results unchange
Energy Siting in Utah: A Programming Model
Using a conceptual model of a multiple-product firm, the necessary conditions for an optimal input and output allocation were determined for a region constrained by resource availabilities and/or policy constraints. A linear programming model was developed to deteremine the optimal allocation of water between agricultural and coal-fired electrical generating entities as well as the trade offs which could occur if electrical generation were increased. Other areas of potential trade offs such as coal source restrictions and air quality regualtions were also examined. Coal mining and transportation costs were included as were SO2, Nox, and particulate emission rates on a coal and plant basis. Few trade offs between electrical power generation and irrigated agriculture were noted. However, substantial changes within the energy sector were discovered as coal capacities and air quality energy sector were discovered as coal capacities and air quality standards were changed. Net revenues declined sharply as air costs after and/or pollution and coal capacity restrictions were imposed and/or increased. It was determined that substantial changes in regional economic activity occurred as a result of these restrictions on development
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