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 $\mathbb R^{22}$.Comment: 9 page

Photometric Analysis of Recently Discovered Eclipsing Binary GSC 00008-00901

Photometric analysis of $BVR_C$ 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 lípidos 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 química 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) así 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