A. C. A. Dos Santos

Temporal variations in phytoplankton primary production in a tropical reservoir (Barra Bonita, SP - Brazil)

Temporal variations of phytoplankton primary production in Barra Bonita Reservoir (22° 29′ 5 S, 48° 34′ W, São Paulo State, Brazil) were evaluated by monthly in situ observations in the period July 1993 to June 1994 and by frequent (every 2 days for 4 weeks) sampling during the dry and colder (July) and wet and warmer (January/February) periods. Highest primary production was observed in April (654 mgC m−2 h−1), which also coincided with the period of longest theoretical water retention time. In July, the primary production was the lowest (20 mgC m−2 h−1). Nanoplankton production was the highest in October (192 mgC m−2 h−1) corresponding to 81% of the total. June represented the period with the lowest share of nanoplankton production (17%, 9 mgC m−2 h−1). Nanoplankton was predominant during 8 of the 12 months of observation, representing an average of 41% of the total community primary production. During January/February, most organisms were smaller than 20 μm. Microphytoplankton production was higher in the colder and dryer period. The production values found during the periods of intensive measurements were higher in the wet January/February period, with the average value of 135 mgC m−2 h−1, while the lowest production values were found in the dry winter (July) when they represented 90 mgC m−2 h−1. The cause of the high January values was partially bigger loads of nutrients from the watershed during the high flow, but probably also faster nutrient regeneration at higher temperatures. Barra Bonita primary production is currently three times higher than that observed 15 years ago.

Short-term changes in the Barra Bonita reservoir (São Paulo, Brazil): emphasis on the phytoplankton communities

We investigated the biomass, primary productivity, species diversity and their controlling factors in the deeper region of the Barra Bonita reservoir (22°29′S and 48°34′W) in the State of São Paulo, Brazil. To accomplish this, short term changes (days and month) were measured during two periods of the year, winter 1993 and summer 1994. The response of the phytoplankton communities to the variability of the system, taking into account the Intermediate Disturbance Hypothesis (IDH), indicated that the frequency and intensity of the disturbances have a critical influence on the establishment of the communities. In Barra Bonita Reservoir the conditions for mixing in the winter were probably important for maintaining high diversity. On the other hand, in summer, the concentrations of suspended material, the high temperatures, and the greater stability of the water column, were probably responsible for permitting the establishment of Microcystis aeruginosa.

Survival strategies of some species of the phytoplankton community in the Barra Bonita Reservoir (São Paulo, Brazil)

The dynamics of the phytoplankton community in the Barra Bonita Reservoir (São Paulo, Brazil) were studied through daily sampling in the field (integrated samples from the euphotic zone) and microcosm experiments, for two short periods: the winter of 1993 (June 30 to July 10) and the summer of 1994 (January 24 to February 2). The goal of the study was to evaluate and compare the variations in the composition of isolated phytoplankton community which occur over short periods of time. Three series were separated into Erlenmeyer flasks for each study period, with samples from the euphotic zone divided into three portions: total, smaller than 64 µm, and smaller than 20 µm. All of the Erlenmeyer flasks were inclubated in situ at the sampling station. The maximum period of incubation was 10 d. Variations of the community in the euphotic zone were characterised by high diversity and a community in a state of non-equilibrium in winter, without the predominance of any species. In the summer, the community presented a low diversity and a state of equilibrium, with the predominance of Microcystis aeruginosa. The microcosm experiments showed that the confinement of the community in the Erlenmeyer flasks, and therefore in isolation from the physical variability of the ecosystem, especially in relation to the mixing patterns, stimulated the return of the community to the initial phases of succession with the predominance of small species and those which grow rapidly (r-selective or C-strategist).

Nutrient addition experiments in Lago Jacaretinga, Central Amazon, Brazil: 2. The effect of humic and fulvic acids

Enrichment experiments consisting of additions of nutrients (nitrogen and phosphorus) and humic and fulvic acids were carried out using natural phytoplankton assemblages from Lago Jacaretinga, Central Amazon, Brazil. The addition of nutrients resulted in greatly stimulated primary production whereas addition of humic and fulvic acids had no effect. When both nutrients and humic and fulvic acids were added in combination, algal community response was identical to treatments in which only nutrients had been added. The result contrasts with previous phytoplankton culture studies in which the addition of humic material to the culture media increased production. Comparison of absorbance spectra indicated a severe reduction in the quantity and quality of light in Amazonian ‘black waters’ relative to that in ‘white waters’.

The utilization of crisp code in hybrid reactor studies

One of the main applications of the Hybrid Reactors (ADS - Accelerator Driven System) is the incineration of transuranics (TRU) by fast neutrons that emerge from a spallation source in a sub critical reactor waste burner [1, 2]. For this application, an accurate description and prediction of spallation reaction is necessary, including all the characteristics concerning spatial and energetic angular distributions, spallation products and neutron multiplicity. To describe the nuclear reactions at intermediate and high energies, Monte Carlo calculations have been used. The CRISP package considers the intranuclear cascade (INC) that occurs during the spallation process in a realistic time-sequence approach in which all particles inside the nucleus can participate in the cascade and the nuclear density fluctuations are naturally taken into account during the process. The occupation number of each single particle level is considered as a function of time and a more realistic Pauli blocking mechanism can be performed. None of the existing models have effectively used all those features. The evaporation of protons and alpha particles are taken into account making possible the correct prediction of fissilities of actinides and pre-actinides [3]. Another implementation is the NN single-pion production reaction. This reaction is especially relevant if one is interested in neutron or proton multiplicities, since the creation/emission of pions is directly related with the excitation energy of the residual nucleus. We will present some results obtained with the CRISP package for proton-nucleus reaction at intermediate and high energies. This package was obtained by the coupling of the MCMC [4] and MCEF [5] codes, with the introduction of some improvements, such as better Pauli blocking mechanism, which constrains the residual nucleus energetic evolution to the Pauli Principle from the ground-state to the final compound-nucleus formed at the end of the intranuclear cascade process, and introduction of the most relevant resonant excitation and the NN single pion production channel. The results of interest for ADS development are consistent with the experimental data at different proton energies. More detailed calculations are being performed for studying other features of proton-nucleus reactions and with different targets.

Developement of crisp package for spallation reaction studies and its utilization in ADS (Accelerator Driven System)

The progress of nuclear physics had allowed a better understanding of nuclear structure and reaction mechanisms, but also enables important applications of nuclear energy in our modern way of life. We can point out those ones related to power generation from nuclear reactors, providing an almost inexhaustive power source due to the huge quantities of nuclear fuel existent in our planet, which guaranties its utilization for thousands of years. The main interest is the so-called Hybrid Reactors (ADS - Accelerator Driven System), in which the reactor has a sub critical core and the chain reaction is sustained by an external source that comes from spallation reactions induced by high energy protons (about 1 GeV) from an accelerator, producing a large number of secondary particles (mainly neutrons). For those applications, precise knowledge about nuclear structure and nuclear reaction characteristics is needed.

Synthetic Organotellurium Compounds Sensitize Drug-Resistant Candida albicans Clinical Isolates to Fluconazole

ABSTRACT Invasive Candida albicans infections are a serious health threat for immunocompromised individuals. Fluconazole is most commonly used to treat these infections, but resistance due to the overexpression of multidrug efflux pumps is of grave concern. This study evaluated the ability of five synthetic organotellurium compounds to reverse the fluconazole resistance of C. albicans clinical isolates. Compounds 1 to 4, at <10 μg/ml, ameliorated the fluconazole resistance of Saccharomyces cerevisiae strains overexpressing the major C. albicans multidrug efflux pumps Cdr1p and Mdr1p, whereas compound 5 only sensitized Mdr1p-overexpressing strains to fluconazole. Compounds 1 to 4 also inhibited efflux of the fluorescent substrate rhodamine 6G and the ATPase activity of Cdr1p, whereas all five of compounds 1 to 5 inhibited Nile red efflux by Mdr1p. Interestingly, all five compounds demonstrated synergy with fluconazole against efflux pump-overexpressing fluconazole-resistant C. albicans clinical isolates, isolate 95-142 overexpressing CDR1 and CDR2, isolate 96-25 overexpressing MDR1 and ERG11, and isolate 12-99 overexpressing CDR1, CDR2, MDR1, and ERG11. Overall, organotellurium compounds 1 and 2 were the most promising fluconazole chemosensitizers of fluconazole-resistant C. albicans isolates. Our data suggest that these novel organotellurium compounds inhibit pump efflux by two very important and distinct families of fungal multidrug efflux pumps: the ATP-binding cassette transporter Cdr1p and the major facilitator superfamily transporter Mdr1p.

Study of Humification Dynamics of Organic Residues on Vermicomposting Process

This work aims the study of humification of three organic residues (cattle manure, orange pomace, and filter cake) submitted to vermicomposting during 6 months. Some parameters were studied such as pH, temperature, total carbon, total nitrogen, and C/N ratio. The data showed typical behavior of the composting process including mesophilic, thermophilic, cooling and maturation phases and the important preliminary results on the dynamics of the process of vermicomposting.

2-Cyclo-hexyl-4-methyl-tetra-hydro-pyran-4-ol.

In the title compound, C12H22O2, the 4-methyltetrahydropyran-4-ol ring adopts a conformation close to that of a chair and with the two O atoms syn; the cyclohexyl group occupies an equatorial position and adopts a chair conformation. In the crystal packing, supramolecular chains along the b axis are sustained by O—H⋯O hydrogen bonds. These are connected into undulating layers in the ab plane by C—H⋯O interactions.