267 research outputs found
Experimental test of magnetic photons
A "magnetic" photon hypothesis associated with magnetic monopoles is tested
experimentally. These photons are predicted to easily penetrate metal.
Experimentally the optical transmittance T of a metal foil was less than 2 x
10^-17. The hypothesis is not supported since it predicts T = 2 x 10^-12
Studying nonlinear effects on the early stage of phase ordering using a decomposition method
Nonlinear effects on the early stage of phase ordering are studied using
Adomian's decomposition method for the Ginzburg-Landau equation for a
nonconserved order parameter. While the long-time regime and the linear
behavior at short times of the theory are well understood, the onset of
nonlinearities at short times and the breaking of the linear theory at
different length scales are less understood. In the Adomian's decomposition
method, the solution is systematically calculated in the form of a polynomial
expansion for the order parameter, with a time dependence given as a series
expansion. The method is very accurate for short times, which allows to
incorporate the short-time dynamics of the nonlinear terms in a analytical and
controllable way.Comment: 11 pages, 1 figure, to appear in Phys Lett
Charmonium - Pion Cross Section from QCD Sum Rules
The , and cross sections as a function of are evaluated in a QCD sum rule
calculation. We study the Borel sum rule for the four point function involving
pseudoscalar and vector meson currents, up to dimension four in the operator
product expansion. We find that our results are smaller than the cross sections obtained with models based on meson exchange,
but are close to those obtained with quark exchange models.Comment: revised version accepted for publication in Phys. Lett.
The vertex in a Sum Rule approach
The study of charmonium dissociation in heavy ion collisions is generally
performed in the framework of effective Lagrangians with meson exchange. Some
studies are also developed with the intention of calculate form factors and
coupling constants related with charmed and light mesons. These quantities are
important in the evaluation of charmonium cross sections. In this paper we
present a calculation of the vertex that is a possible interaction
vertex in some meson-exchange models spread in the literature. We used the
standard method of QCD Sum Rules in order to obtain the vertex form factor as a
function of the transferred momentum. Our results are compatible with the value
of this vertex form factor (at zero momentum transfer) obtained in the
vector-meson dominance model.Comment: Accepted for publication in Physics Letters
Diversity and patterns of marine nonânative species in the archipelagos of Macaronesia
Aims
The present study is the first attempt to grasp the scale and richness of marine biological invasions in Macaronesia. We pioneered a comprehensive non-native species (NNS), inventory in the region to determine their diversity patterns and native distribution origins. NNS were defined here as the result of both introductions and range expansions. We also used statistical modelling to examine relationships among NNS richness, anthropogenic activities, demographic and geographical variables across Macaronesia.
Location
Macaronesia.
Methods
A comprehensive literature search was conducted for marine NNS records in Macaronesia, registering the first record's location and year from 1884 to 2020. We used univariate and multivariate analyses to evaluate differences and similarities in community composition. By applying a Generalized Linear Model (GLM), we tested hypotheses regarding NNS richness as a function of anthropogenic activities, demographic and geographical variables.
Results
A total of 144 marine non-native species (NNS) were recorded for the whole of Macaronesia. The highest NNS richness was registered in the Canary Islands (76 NNS), followed by the Azores (66 NNS), Madeira (59 NNS) and finally Cabo Verde (18 NNS). Some differences amongst archipelagos were observed, such as the high number of non-native macroalgae in the Azores, fishes in the Canary Islands and tunicates in Cabo Verde. Overall, macroalgae, tunicates and bryozoans were the predominant taxonomic groups in the Macaronesian archipelagos. Madeira and Canary Islands were the archipelagos with more similarity in marine NNS, and Cabo Verde the most divergent. Finally, GLM suggested that non-native richness patterns across Macaronesia were dependent on the considered archipelago and strongly affected by (1) minimum distance to the mainland, (2) the total number of ports and marinas and (3) total marinas area (km2).
Conclusions
The model results and NNS listing in the present study will likely raise the awareness and response regarding marine NNS in the whole Macaronesia region, serving as a baseline for future research as well as implementing and enforcing regulations related to the introduction of marine NNS in oceanic islands
Applicability of perturbative QCD to decays
We develop perturbative QCD factorization theorem for the semileptonic heavy
baryon decay , whose form factors are
expressed as the convolutions of hard quark decay amplitudes with universal
and baryon wave functions. Large logarithmic
corrections are organized to all orders by the Sudakov resummation, which
renders perturbative expansions more reliable. It is observed that perturbative
QCD is applicable to decays for velocity transfer
greater than 1.2. Under requirement of heavy quark symmetry, we predict the
branching ratio , and determine
the and baryon wave functions.Comment: 12 pages in Latex file, 3 figures in postscript files, some results
are changed, but the conclusion is the sam
Hypotensive effect and endothelium-dependent vascular action of leaves of Alpinia purpurata (Vieill) K. Schum
The aims of this study were to evaluate the chemical profile, vascular reactivity, and acute hypotensive effect (AHE) of the ethanolic extract of leaves of Alpinia purpurata (Vieill) K. Schum (EEAP). Its chemical profile was evaluated using HPLC-UV, ICP-OES, and colorimetric quantification of total flavonoids and polyphenols. The vascular reactivity of the extract was determined using the mesenteric bed isolated from WKY. AHE dose-response curves were obtained for both EEAP and inorganic material isolated from AP (IAP) in WKY and SHR animals. Cytotoxic and mutagenic safety levels were determined by the micronucleus test. Rutin-like flavonoids were quantified in the EEAP (1.8 ± 0.03%), and the total flavonoid and polyphenol ratios were 4.1 ± 1.8% and 5.1 ± 0.3%, respectively. We observed that the vasodilation action of EEAP was partially mediated by nitric oxide (·NO). The IAP showed the presence of calcium (137.76 ± 4.08 Όg mg-1). The EEAP and IAP showed an AHE in WKY and SHR animals. EEAP did not have cytotoxic effects or cause chromosomic alterations. The AHE shown by EEAP could result from its endothelium-dependent vascular action. Rutin-like flavonoids, among other polyphenols, could contribute to these biological activities, and the calcium present in EEAP could act in a synergistic way
decays into and mesons
We consider the nonleptonic and semileptonic decays of -mesons into
and mesons. QCD sum rules are used to calculate the form
factors associated with these decays, and the correspondig decay rates. On the
basis of data on , which goes dominantly via the
transition , we conclude that there is space for a
sizeable light quark component on .Comment: 14 pages, RevTeX4 including 5 figures in ps file
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