1,809 research outputs found
Coral diversity and the severity of disease outbreaks: a cross-regional comparison of Acropora White Syndrome in a species-rich region (American Samoa) with a species-poor region (Northwestern Hawaiian Islands)
The dynamics of the coral disease, Acropora white syndrome (AWS), was directly compared on reefs in the species-poor region of the Northwestern Hawaiian Islands (NWHI) and the species-rich region of American Samoa (AS) with results suggesting that biodiversity, which can affect the abundance of susceptible hosts, is important in influencing the impacts of coral disease outbreaks. The diversity-disease hypothesis predicts that decreased host species diversity should result in increased disease severity of specialist pathogens. We found that AWS was more prevalent and had a higher incidence within the NWHI as compared to AS. Individual Acropora colonies affected by AWS showed high mortality in both regions, but case fatality rate and disease severity was higher in the NWHI. The site within the NWHI had a monospecific stand of A. cytherea; a species that is highly susceptible to AWS. Once AWS entered the site, it spread easily amongst the abundant susceptible hosts. The site within AS contained numerous Acropora species, which differed in their apparent susceptibility to infection and disease severity, which in turn reduced disease spread. Manipulative studies showed AWS was transmissible through direct contact in three Acropora species. These results will help managers predict and respond to disease outbreaks
A new Euclidean tight 6-design
We give a new example of Euclidean tight 6-design in .Comment: 9 page
Photometric Analysis of Recently Discovered Eclipsing Binary GSC 00008-00901
Photometric analysis of light curves of newly discovered eclipsing
binary GSC 0008-00901 is presented. The orbital period is improved to
0.28948(11) days. Photometric parameters are determined, as well. The analysis
yielded to conclusion that system is an over-contact binary of W UMa type with
components not in thermal contact. The light curves from 2005 show the presence
of a spot on the surface of one of the components, while light curves from 2006
are not affected by maculation.Comment: Accepted for publication in Astrophysics & Space Scienc
El papel de los lÃpidos en el control del crecimiento microbiano
Many foods are, or contain, emulsions. Growth of microorganisms in emulsions may lend to spoilage by bacteria, yeasts, moulds or food-poisoning bacteria. In biphasic foods (e.g. oil-in-water or water-in-oil emulsions), food structure may influence both rate of growth and conditions under which growth is initiated. The site of occupancy of microorganisms is the aqueous phase. Therefore the chemical composition of this phase is what has a direct influence on the survival and growth of microorganisms. This paper describes the chemical effects of organic acids used as preservatives in oil-in-water (acetic and lactic acids) and water-in-oil (sorbic and benzoic acids) emulsions as well as the influence of their structures on the food stability.Numerosos alimentos son, o contienen, emulsiones. El crecimiento de bacterias en las emulsiones da lugar a alteraciones debido a bacterias, levaduras, mohos o bacterias que producen intoxicaciones alimentarias. En los alimentos constituidos por dos fases (por ejemplo emulsiones aceite-agua o agua-aceite) la estructura del alimento puede influir tanto en el ritmo de crecimiento como en las condiciones en las que se inicia el crecimiento. El lugar en el que se encuentran los microorganismos es la fase acuosa. Y, por tanto, es la composición quÃmica de esta la que influye directamente en la supervivencia y el crecimiento de los microorganismos. En esta contribución se describe el efecto de los ácidos orgánicos utilizados como conservantes en las emulsiones aceite-agua (ácidos acético y lácticos) y en las de agua-aceite (ácidos sórbico y benzoicos) asà como la influencia de sus estructuras en la estabilidad del alimento
Parity Invariance and Effective Light-Front Hamiltonians
In the light-front form of field theory, boost invariance is a manifest
symmetry. On the downside, parity and rotational invariance are not manifest,
leaving the possibility that approximations or incorrect renormalization might
lead to violations of these symmetries for physical observables. In this paper,
it is discussed how one can turn this deficiency into an advantage and utilize
parity violations (or the absence thereof) in practice for constraining
effective light-front Hamiltonians. More precisely, we will identify
observables that are both sensitive to parity violations and easily calculable
numerically in a non-perturbative framework and we will use these observables
to constrain the finite part of non-covariant counter-terms in effective
light-front Hamiltonians.Comment: REVTEX, 9 page
Renormalization of Hamiltonian Field Theory; a non-perturbative and non-unitarity approach
Renormalization of Hamiltonian field theory is usually a rather painful
algebraic or numerical exercise. By combining a method based on the coupled
cluster method, analysed in detail by Suzuki and Okamoto, with a Wilsonian
approach to renormalization, we show that a powerful and elegant method exist
to solve such problems. The method is in principle non-perturbative, and is not
necessarily unitary.Comment: 16 pages, version shortened and improved, references added. To appear
in JHE
Boost-Invariant Running Couplings in Effective Hamiltonians
We apply a boost-invariant similarity renormalization group procedure to a
light-front Hamiltonian of a scalar field phi of bare mass mu and interaction
term g phi^3 in 6 dimensions using 3rd order perturbative expansion in powers
of the coupling constant g. The initial Hamiltonian is regulated using momentum
dependent factors that approach 1 when a cutoff parameter Delta tends to
infinity. The similarity flow of corresponding effective Hamiltonians is
integrated analytically and two counterterms depending on Delta are obtained in
the initial Hamiltonian: a change in mu and a change of g. In addition, the
interaction vertex requires a Delta-independent counterterm that contains a
boost invariant function of momenta of particles participating in the
interaction. The resulting effective Hamiltonians contain a running coupling
constant that exhibits asymptotic freedom. The evolution of the coupling with
changing width of effective Hamiltonians agrees with results obtained using
Feynman diagrams and dimensional regularization when one identifies the
renormalization scale with the width. The effective light-front Schroedinger
equation is equally valid in a whole class of moving frames of reference
including the infinite momentum frame. Therefore, the calculation described
here provides an interesting pattern one can attempt to follow in the case of
Hamiltonians applicable in particle physics.Comment: 24 pages, LaTeX, included discussion of finite x-dependent
counterterm
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