Forward-angle incoherent photoproduction of pseudoscalar mesons off nuclei

The mechanism of forward angle incoherent photoproduction of pseudoscalar mesons off nuclei is revisited via the time-dependent multicollisional Monte Carlo (MCMC) intranuclear cascade model. Our results-combined with recent developments to address coherent photoproduction-reproduce with good accuracy recent JLab data of pi(0) photoproduction from carbon and lead at an average photon energy k similar to 5.2 GeV. For the case of. photoproduction, our results for k = 9 GeV suggest that future measurements to extract the eta ->gamma gamma decay width via the Primakoff method should be focused on light nuclei, where the disentanglement between the Coulomb and strong amplitudes is more easily achieved. The prospects to use heavy nuclei data to access the unknown eta N cross section in cold nuclear matter are also presented.Brazilian agency FAPES

Variação temporal da comunidade fitoplanctônica em curtos intervalos amostrais no reservatório de Mundaú, Nordeste brasileiro

The aim of this study was to determine how abiotic factors drive the phytoplankton community in a water supply reservoir within short sampling intervals. Samples were collected at the subsurface (0.1 m) and bottom of limnetic (8 m) and littoral (2 m) zones in both the dry and rainy seasons. The following abiotic variables were analyzed: water temperature, dissolved oxygen, electrical conductivity, total dissolved solids, turbidity, pH, total nitrogen, nitrite, nitrate, total phosphorus, total dissolved phosphorus and orthophosphate. Phytoplankton biomass was determined from biovolume values. The role abiotic variables play in the dynamics of phytoplankton species was determined by means of Canonical Correspondence Analysis. Algae biomass ranged from 1.17×10(4) to 9.21×10(4) µg.L-1; cyanobacteria had biomass values ranging from 1.07×10(4) to 8.21×10(4) µg.L-1. High availability of phosphorous, nitrogen limitation, alkaline pH and thermal stability all favored cyanobacteria blooms, particularly during the dry season. Temperature, pH, total phosphorous and turbidity were key factors in characterizing the phytoplankton community between sampling times and stations. Of the species studied, Cylindrospermopsis raciborskii populations were dominant in the phytoplankton in both the dry and rainy seasons. We conclude that the phytoplankton was strongly influenced by abiotic variables, particularly in relation to seasonal distribution patterns.O objetivo deste estudo foi detectar a influência dos fatores abióticos sobre a comunidade fitoplanctônica em um reservatório de abastecimento, em curtos intervalos amostrais. As amostras foram coletadas na subsuperfície (0,1 m) e fundo das regiões pelágica (8 m) e litorânea (2 m), durante dois períodos sazonais, estações seca e chuvosa. As variáveis abióticas analisadas foram: temperatura da água, oxigênio dissolvido, condutividade elétrica, sólidos totais dissolvidos, turbidez, pH, nitrogênio total, nitrito, nitrato, fósforo total, fósforo total dissolvido e ortofosfato. A biomassa fitoplanctônica foi determinada a partir de valores de biovolume. A influência das variáveis abióticas na dinâmica das espécies fitoplanctônicas foi determinada através da Análise de Correspondência Canônica. A biomassa algal variou de 1,17×10(4) a 9,21×10(4) µg.L-1, sendo que as cianobactérias apresentaram valores de biomassa entre 1,07×10(4) e 8,21×10(4) µg.L-1. A mais alta disponibilidade de fósforo, limitação de nitrogênio, pH alcalino e estabilidade térmica favoreceram florações de cianobactérias, especialmente durante o período seco. As diferenças entre os horários e as estações amostrais na distribuição da comunidade fitoplanctônica foram determinadas pelos valores de temperatura, pH, fósforo total e turbidez. As associações fitoplanctônicas que mais se destacaram foram do grupo funcional Sn, formado por Cylindrospermopsis raciborskii, que predominou no sistema em ambos períodos sazonais. Concluiu-se que o fitoplâncton apresentou uma forte influência das variáveis abióticas especialmente no estabelecimento de padrões sazonais de distribuição.Conselho Nacional de Desenvolvimento Científico (CNPq

Effects of light intensity and temperature on Cylindrospermopsis raciborskii (Cyanobacteria) with straight and coiled trichomes: growth rate and morphology

Cylindrospermopsis raciborskii (Woloszynska) Seenayya et Subba Raju (Ordem Nostocales) is one of the most troublesome bloom-forming species in Brazil. Understanding the population dynamics of the different morphotypes of C. raciborskii (straight and coiled) could assist in the prediction of favourable conditions for the proliferation of this potentially toxin-producing species. The aim of the present study was to assess the effects of two different light intensities and temperatures on the growth rate and morphology of the trichomes of the straight and coiled morphotypes. For such, two non-toxin producing strains of C. raciborskii were used - one with a coiled trichome (ITEP31) and another with a straight trichome (ITEP28). The strains were cultured in BG-11 medium in a climatic chamber under controlled conditions. Two light intensities (30 and 90 mu mol.m(-2).s(-1)) were combined at temperatures of 21 and 31 degrees C and the growth rate and morphological changes were analysed. The morphotypes responded differently to the different temperatures and light intensities. Both strains exhibited faster growth velocities when submitted to higher light intensity and temperature. The lower temperature and higher luminosity hampered the development of both strains. Variations in cellular morphology and an absence of akinetes in both strains were related to the lower temperature (21 C). The coiled morphotype demonstrated considerable phenotype plasticity, changing the morphology of trichome throughout its growth curve. Although molecular analysis does not sustain the separation of the morphotypes as distinct species, their different eco-physiological responses should be considered further knowledge of extreme importance for the population control of these potentially toxic organisms.CNPQ [Proc. 300794/2004-5, 500704/2004-0]FAPESP [Proc. 2004/00939-6, 2007/57509-1

Fragmentation of extracellular DNA by long-term exposure to radiation from uranium in aquatic environments

Persistent harmful scenarios associated with disposal of radioactive waste, high-background radiation areas and severe nuclear accidents are of great concern regarding consequences to both human health and the environment. Of particular concern is the extracellular DNA in aquatic environments contaminated by radiological substances. Strand breaks induced by radiation promote decrease in the transformation efficiency for extracellular DNA. The focus of this study is the quantification of DNA damage following long-term exposure (over one year) to low doses of natural uranium (an alpha particle emitter) to simulate natural conditions, since nothing is known about alpha radiation induced damage to extracellular DNA. A high-resolution Atomic Force Microscope was used to evaluate DNA fragments. Double-stranded plasmid pBS as a model for extracellular DNA was exposed to different amounts of natural uranium. It was demonstrated that low concentrations of U in water (50 to 150 ppm) produce appreciable numbers of double strand breaks, scaling with the square of the average doses. The importance of these findings for environment monitoring of radiological pollution is addressed.Brazilian agency FAPESPFAPESP Brazilian agencyCNPq Brazilian agencyBrazilian agency CNP

Giant Resonances Electric Quadrupole Photofission 236U 238U

Foram medidos os \"yields\" de eletrofissão do 236 ANTPOT u e 238 ANTPOT u na faixa de 5 a 30 MeV, bem como as distribuições angulares dos fragmentos de eletrofissão, utilizando o feixe de elétrons do Acelerador Linear do Instituto de Física da Universidade de São Paulo. É apresentado um formalismo para análise das distribuições angulares dos fragmentos de foto e eletrofissão, a partir do qual é estudada a competição entre os canais de quadrupolo na fotofissão do 238 ANTPOT u. Desenvolveu-se um novo método de análise para a obtenção de contribuições multipolares , diferentes de El, no processo da fotofissão, que permite obter o \"yield\" integrado dos multipolos adicionais a partir da análise simultânea da foto e eletrofissão, mais o formalismo dos fótons virtuais em DWBA. Através do \"unfolding\" das secções de choque dos multipolos adicionais foram obtidas ressonâncias gigantes de E2 para 236 ANTPOT u e 238 ANTPOT. U, com picos em (10,7 ± 0,2) MeV e (9,9 ± 0,2) MeV, e larguras de (7,8 ± 0,2) MeV e (8,7 ± 0,2) MeV, respectivamente . As posições das ressonâncias E2 estão em razoável acordo com as previsões de Bohr e Mottelson: Ep = 60. A POT -1/3 MeV. As larguras são compatíveis com um possível \"splitting\" triplo das ressonâncias. Foram mostradas evidências quanto a uma mistura de Ml na faixa 6-7 MeV.Measurements of electrofission yields of 236u and 238u were perfomed in the energy range of 5 to 30 MeV, as well as angular distribution of electrofission fragments using the electron beam of the Linear Accelerator of the Physics Institute of the University of São Paulo. A formalism for the analysis of angular distribution of photo and electrofission fragments is presented, from which a competition between the quadrupole channels in the photo fission of 238u is studied. A new method of analysis to obtain the multipole contribution, other than El, in the process of photofission was developed, which allows the obtainment of the integrated yield on the additional multipoles, from the simultaneous analysis of photo and electrofission using the formalism of virtual photons in OWBA. Through the unfolding of the additional multipoles cross sections the E2 giant resonances were obtained for the 236u and 238u, presenting peaks at (10.7 ± 0.2) MeV and (9.9 ± 0.2) MeV, and widths of (7.8 ± 0.2) MeV and (8.7±0.2) MeV, respectively. The positions of these E2 resonances are in reasonable agreement with the predictions of Bohr and Mottelson: Ep = 60 A -1/3 MeV. The width are compatible with a possible triple splitting of the resonances. Evidences of a Ml mixture were shown in the energy range of 6 to 7 MeV

Photo and electrofission of the 238 U\'\'

Foto e eletrofissão do 238 U\'\'Photo and electrofission of the 238 U\'\

Giant Resonances Electric Quadrupole Photofission 236U 238U

Foram medidos os \"yields\" de eletrofissão do 236 ANTPOT u e 238 ANTPOT u na faixa de 5 a 30 MeV, bem como as distribuições angulares dos fragmentos de eletrofissão, utilizando o feixe de elétrons do Acelerador Linear do Instituto de Física da Universidade de São Paulo. É apresentado um formalismo para análise das distribuições angulares dos fragmentos de foto e eletrofissão, a partir do qual é estudada a competição entre os canais de quadrupolo na fotofissão do 238 ANTPOT u. Desenvolveu-se um novo método de análise para a obtenção de contribuições multipolares , diferentes de El, no processo da fotofissão, que permite obter o \"yield\" integrado dos multipolos adicionais a partir da análise simultânea da foto e eletrofissão, mais o formalismo dos fótons virtuais em DWBA. Através do \"unfolding\" das secções de choque dos multipolos adicionais foram obtidas ressonâncias gigantes de E2 para 236 ANTPOT u e 238 ANTPOT. U, com picos em (10,7 ± 0,2) MeV e (9,9 ± 0,2) MeV, e larguras de (7,8 ± 0,2) MeV e (8,7 ± 0,2) MeV, respectivamente . As posições das ressonâncias E2 estão em razoável acordo com as previsões de Bohr e Mottelson: Ep = 60. A POT -1/3 MeV. As larguras são compatíveis com um possível \"splitting\" triplo das ressonâncias. Foram mostradas evidências quanto a uma mistura de Ml na faixa 6-7 MeV.Measurements of electrofission yields of 236u and 238u were perfomed in the energy range of 5 to 30 MeV, as well as angular distribution of electrofission fragments using the electron beam of the Linear Accelerator of the Physics Institute of the University of São Paulo. A formalism for the analysis of angular distribution of photo and electrofission fragments is presented, from which a competition between the quadrupole channels in the photo fission of 238u is studied. A new method of analysis to obtain the multipole contribution, other than El, in the process of photofission was developed, which allows the obtainment of the integrated yield on the additional multipoles, from the simultaneous analysis of photo and electrofission using the formalism of virtual photons in OWBA. Through the unfolding of the additional multipoles cross sections the E2 giant resonances were obtained for the 236u and 238u, presenting peaks at (10.7 ± 0.2) MeV and (9.9 ± 0.2) MeV, and widths of (7.8 ± 0.2) MeV and (8.7±0.2) MeV, respectively. The positions of these E2 resonances are in reasonable agreement with the predictions of Bohr and Mottelson: Ep = 60 A -1/3 MeV. The width are compatible with a possible triple splitting of the resonances. Evidences of a Ml mixture were shown in the energy range of 6 to 7 MeV

Nuclear incoherent photoproduction of pi(0) and eta from 4 to 12 GeV

The mechanism of incoherent pi(0) and eta photoproduction from complex nuclei is investigated from 4 to 12 GeV with an extended version of the multicollisional Monte Carlo (MCMC) intranuclear cascade model. The calculations take into account the elementary photoproduction amplitudes via a Regge model and the nuclear effects of photon shadowing, Pauli blocking, and meson-nucleus final-state interactions. The results for pi(0) photoproduction reproduced for the first time the magnitude and energy dependence of the measured rations sigma(gamma A)/sigma(gamma N) for several nuclei (Be, C, Al, Cu, Ag, and Pb) from a Cornell experiment. The results for eta photoproduction fitted the inelastic background in Cornell's yields remarkably well, which is clearly not isotropic as previously considered in Cornell's analysis. With this constraint for the background, the eta -> gamma gamma. decay width was extracted using the Primakoff method, combining Be and Cu data [Gamma(eta ->gamma gamma) = 0.476(62) keV] and using Be data only [Gamma(eta ->gamma gamma) = 0.512(90) keV]; where the errors are only statistical. These results are in sharp contrast (similar to 50-60%) with the value reported by the Cornell group [Gamma(eta ->gamma gamma). = 0.324(46) keV] and in line with the Particle Data Group average of 0.510(26) keV.Brazilian agency FAPES

eta ->gamma gamma decay width via the Primakoff cross section

Incoherent eta photoproduction in nuclei is evaluated at forward angles within 4 to 9 GeV using a multiple scattering Monte Carlo cascade calculation with full eta-nucleus final-state interactions. The Primakoff, nuclear coherent and nuclear incoherent components of the cross sections fit remarkably well previous measurements for Be and Cu from Cornell, suggesting a destructive interference between the Coulomb and nuclear coherent amplitudes for Cu. The inelastic background of the data is consistently attributed to the nuclear incoherent part, which is clearly not isotropic as previously considered in Cornell's analysis. The respective Primakoff cross sections from Be and Cu give Gamma(eta ->gamma gamma)=0.476(62) keV, where the quoted error is only statistical. This result is consistent with the Particle Data Group average of 0.510(26) keV and in sharp contrast (similar to 50%) with the value of 0.324(46) keV obtained at Cornell