El pasto marino de Perezoso en el Parque Nacional Cahuita, costa Caribe de Costa Rica, se está monitoreando con el protocolo de CARICOMP. La productividad (2.7±1.15 g/m²/d, n=74) resultó intermedia, comparada con otros sitios del Caribe. La biomasa total resultó de intermedia a alta (750-1 500 g/m²) en la mayoría de los sitios CARICOMP (Colombia, Cuba, Mexico, Puerto Rico y Venezuela) incluyendo Costa Rica (822.8±391.84 g/m², n=32). Las tasas de recambio son altas (5.5±1.36%, n=74) comparadas con lo que se encontró en marzo y agosto en otros sitios. La densidad promedio es de 725 plántulas/m², en la región Caribe, mientras que en Costa Rica resultó mayor (1 184±335.5 plántulas/m²). El largo y ancho de hoja promedio en toda la región es de 14.4 cm y 10.6 mm, respectivamente, similar a lo que se encontró en este estudio, pero el índice de área foliar promedio es de 3.4 m²m-2, mayor a lo que se encontró en Costa Rica (0.92 m²m-2). En Cahuita la productividad del pasto es significativamente menor comparado con los seis años previos, y la biomasa disminuyó en el tiempo. La productividad y biomasa de los pastos se está viendo afectada por las temperaturas máximas que aumentaron casi 10 °C de 1999 a 2005, y muestran una alta correlación negativa. La tasa de recambio y la temperatura no mostraron correlación. La actividad por botes, nadadores y la alta carga de nutrientes proveniente de la contaminación local por aguas negras, la deforestación y las actividades agrícolas en tierras costeras y rivereñas son fuentes potenciales de impacto en los pastos marinos de Cahuita.

Seagrass monitoring at Perezoso, Cahuita, Costa Rica (CARICOMP site). The seagrass of Perezoso (Cahuita National Park, Caribbean coast of Costa Rica) was monitored using the CARICOMP protocol. Productivity (2.7±1.15 g/m²/d; n=74) was intermediate, compared to other Caribbean sites. Total biomass was intermediate to high (750-1500 g/m²) at most CARICOMP sites (Colombia, Cuba, Mexico, Puerto Rico and Venezuela) including Costa Rica (822.8±391.84 g/m²; n=32). Turnover rates were high (5.5±1.36 %; n=74) compared to what was found in March and August at other sites. Shoot densities average 725 shoots/m², in the Caribbean region, while in Costa Rica the value was higher (1184±335.5 shoots/m²). Average leaf length and width in the entire region were 14.4 cm and 10.6 mm, respectively, similar to what we found, but leaf area index average 3.4 m²m-2, higher than what was found in Costa Rica (0.92 m²m-2). At Cahuita, seagrass productivity was significantly lower in March 2005 compared with the previous six years, and biomass has decreased with time. Seagrass productivity and biomass are being affected by the maximum temperatures, which increased by almost 10 °C from 1999 to 2005, and show a high negative correlation. Turnover rate and temperature were not correlated. Recreational boating, swimming and nutrient loading from deforested lands in the coast, the upstream rivers and local pollution are potential sources of impact to the seagrass beds at Cahuita. Rev. Biol. Trop. 55 (1): 55-66. Epub 2007 March. 31.

We calculate the coupling constants of D*Ds K and Ds*DK vertices using the QCD sum rules technique. We compare our results with results obtained in the limit of SU(4) symmetry and we found that the symmetry is broken at the order of 40%.

In this work, we evaluate the D+sJ(2317), D(0)0(2308), D(0)0(2407) and D+0(2403) masses. These are scalar mesons recently discovered in the BABAR, BELLE and FOCUS Collaborations. The nature of these particles is intensely discussed nowadays. We treat them as a diquark-antidiquark configuration and treat the problem using the QCD sum rules (QCDSR) approach.

Using the QCD sum rule approach we investigate the vertex associated with the decay D0(0+)-> D+pi-, where the scalar meson D0(0+) is considered as a four-quark state $(cd)(\bar{u}\bar{d})$. Although our results for the mass and partial decay width are smaller than the mass and the total decay width of the broad scalar meson D0*0(2308) reported by BELLE Collaboration, we can not discard the possibility that the BELLE's resonance can be interpreted as the four-quark state studied here.

We review the existing mass and decay width determinations of pentaquarks with QCD Sum Rules (QCDSR). We give special attention to the intermediate assumptions and choices which we are obliged to do in this approach. As an example, we present the full calculation of the pentaquark mass with Borel sum rules and also with Finite Energy Sum Rules (FESR). We also work out the calculation of the theta decay width. We take the opportunity to comment our publications on this subject and include new and unpublished material.

The D*Dpi form factor is evaluated at low and moderate Q² in a hadronic loop model, for off-shell D mesons. The results contain arbitrary constants, which are fixed so as to match a previous QCD sum rule calculation valid at higher Q². The form factor obtained in this way is used to extract the coupling constant, which is in very good agreement with the experimental value.

We calculate the J/psiD*D* form factor and coupling constant from QCD Sum Rules in the cases where J/psi and D* mesons are off-shell. The results show that this method is consistent and allows to extract the same coupling constant for the vertex.

In this work we calculate the meson cloud effects on the pion electromagnetic form factor and perform a comparison with experimental data. We show that, even though the cloud is not the only non-perturbative process to be considered, its contribution is significant. We also study the influence of the cutoff choices on the results.

We update the calculation of c - <img id="_x0000_i1026" src="../../img/revistas/bjp/v34n1a/a19img02.gif" align=absbottom>production in the initial stage of nucleus - nucleus collisions and within quark gluon plasma, using the most recent and most accepted values for the ingredients, such as nuclear parton distributions, quark masses, couplings and fireball parameters. We find a large discrepancy in the charm yields, depending on the input choices. A global analysis of all the different cases suggests that the “in-plasma” production is a significant fraction of the total yield.

We employ QCD sum rules to calculate the J/psiDD* form factors and coupling constant by studying the threepoint J/psiD*D correlation function. We find that the momentum dependence of the form factor depends on the off-shell meson. We get a value for the coupling which is in agreement with estimates based on constituent quark model.

We calculate the cross section for the dissociation of J/psi by kaons within the framework of a meson exchange model. We find that, depending on the values of the coupling constants used, the cross section can vary from 5 mb to 30 mb at <img id="_x0000_i1026" src="../../img/revistas/bjp/v34n1a/a11img03.gif" align=absbottom>~ 5 GeV.

We study the Borel sum rule for the tensor amplitude of the processes J/<FONT FACE=Symbol>y p ®</FONT> <IMG SRC="/img/revistas/bjp/v33n2/a30img01.gif" >D*,<IMG SRC="/img/revistas/bjp/v33n2/a30img01.gif"> D, <IMG SRC="/img/revistas/bjp/v33n2/a30img01.gif" >*D* and <IMG SRC="/img/revistas/bjp/v33n2/a30img01.gif" >D*. We also evaluate the cross sections as a function of <IMG SRC="/img/revistas/bjp/v33n2/a30img02.gif" >. We find that our results are smaller than the J/<FONT FACE=Symbol>y p ®</FONT> charmed mesons cross sections obtained with models based on meson exchange, but are close to those obtained with quark exchange models.

The <FONT FACE="Symbol">d</font>-expansion is a nonperturbative approach for field theoretic models wich combines the techniques of perturbation theory and the variational principle. Different ways of implemeting the principle of minimal sensitivity to the <FONT FACE="Symbol">d</font>-expansion produce in general different results for observables. For illustration we use the Nambu- Jona-Lasinio model for chiral symmetry restoration at finite density and compare results with those obtained with the Hartree-Fock approximation.

In this work we extend previous kaon loop calculations, including the vector K* meson and estimate the strangeness radius of the nucleon and its strange magnetic moment. We find out that, in contrast to naive expectations, this contribution is very important and gives large values for both the radius and the magnetic moment