Annihilation of single-species charged particles based on Dyson gas dynamics.

We analyze the annihilation of equally charged particles based on the Brownian motion model built by Dyson for N particles with charge q interacting via the log-Coulomb potential on the unitary circle at a reduced inverse temperature ß, defined as ß=q^{2}/(k_{B}T). We derive an analytical approach to describe the large-t asymptotic behavior for the number density decay, which can be described as a power law, n∼t^{-ν}. For a sufficiently large ß, the power-law exponent ν behaves as (ß+1)^{-1}, which was corroborated through several computational simulations. For small ß, in the diffusive regime, we recover the exponent of 1/2 as predicted by single-species uncharged annihilation.

Plasmonic directional couplers using channel waveguides in random arrays of metal nanoparticles.

Plasmonic directional couplers based on channel waveguides embedded in random arrays of metal nanoparticles (NPs) operating in near-infrared are fabricated using electron-beam lithography and investigated experimentally characterizing their performance with leakage-radiation microscopy. The power exchange between coupled waveguides, its spatial period and efficiency, along with the overall power transmission, are determined in the wavelength range from 700 to 800 nm. We introduce a simple coupled-mode approach based on three coupled waveguides. The composite system considers a waveguide consisting of NP-filled stripe with characteristics distinctly different from those of the channel waveguides. Using this model, we describe the performance of investigated composite plasmonic configurations and obtain good qualitative agreement with experimental observations.

Siparuna guianensis Aublet (negramina): uma revisão / Siparuna guianensis Aublet (negramina): a review

As pesquisas realizadas a partir de recursos genéticos de espécies medicinais nativas somente serão aplicadas se o material genético estiver seguro quanto à sobrevivência e disponibilidade. O objetivo deste artigo foi realizar uma revisão bibliográfica adotando como critério a escolha de artigos publicados em conceituadas revistas nacionais e internacionais, que permitissem melhor entendimento dos aspectos etnobotânicos, ecológicos e químicos de importante planta medicinal e aromática: Siparuna guianensis Aublet. Como tem sido apontada como uma das espécies prioritárias de conservação para a região do cerrado brasileiro, os estudos da propagação devem ser incentivados para que este recurso genético esteja disponível às gerações futuras.

Studies with genetic resources of native medicinal species will only be applied if their genetic material is safe regarding survival and availability. The aim of this study was to do a literature review adopting as criterion the choice of papers published in renowned national and international journals to allow better understanding on ethnobotanical, ecological and chemical aspects of an important medicinal and aromatic plant, Siparuna guianensis Aublet. Since the latter has been considered one of the major species for the conservation of Brazilian cerrado, studies on its propagation should be encouraged in order to make this genetic resource available to future generations.

Shape of the 8B alpha and neutrino spectra.

The beta-delayed alpha spectrum from the decay of 8B has been measured with a setup that minimized systematic uncertainties that affected previous measurements. Consequently the deduced neutrino spectrum presents much smaller uncertainties than the previous recommendation [J. N. Bahcall et al., Phys. Rev. C 54, 411 (1996)]. The 8B nu spectrum is found to be harder than previously recommended with about (10-20)% more neutrinos at energies between 12-14 MeV. The integrated cross sections of the 37Cl, 71Ga, 40Ar, and Super-Kamiokande detectors are, respectively, 3.6%, 1.4%, 5.7%, and 2.1% larger than previously thought.

Metabolic control of the K+ channel of human red cells.

The effects of cAMP, ATP and GTP on the Ca2(+)-dependent K+ channel of fresh (1-2 days) or cold-stored (28-36 days) human red cells were studied using atomic absorption flame photometry of Ca2(+)-EGTA loaded ghosts which had been resealed to monovalent cations in dextran solution. When high-K+ ghosts were incubated in an isotonic Na+ medium, the rate constant of Ca2(+)-dependent K+ efflux was reduced by a half on increasing the theophylline concentration to 40 mM. This effect was observed in ghosts from both fresh and stored cells, but only if they were previously loaded with ATP. The inhibition was more marked when Mg2+ was added together with ATP, and it was abolished by raising free Ca2+ to the micromolar level. Like theophylline, isobutyl methylxanthine (10 mM) also affected K+ efflux. cAMP (0.2-0.5 mM), added both internally and externally (as free salt, dibutyryl or bromide derivatives), had no significant effect on K+ loss when the ghost free-Ca2+ level was below 1 microM, but it was slightly inhibitory at higher concentrations. The combined presence of cAMP (0.2 mM) plus either theophylline (10 mM), or isobutyl methylxanthine (0.5 mM), was more effective than cAMP alone. This inhibition showed a strict requirement for ATP plus Mg2+ and it was not overcome by raising internal Ca2+. Ghosts from stored cells seemed more sensitive than those from fresh cells, to the combined action of cAMP and methylxanthines. Loading ATP into ghosts from fresh or stored cells markedly decreased K+ loss. Although this effect was observed in the absence of added Mg2+ (0.5 mM EDTA present), it was potentiated upon adding 2 mM Mg2+. The K+ efflux from ATP-loaded ghosts was not altered by dithio-bis-nitrobenzoic acid (10 mM) or acridine orange (100 microM), while it was increased two- to fourfold by incubating with MgF2 (10 mM), or MgF2 (10 mM) + theophylline (40 mM), respectively. By contrast, a marked efflux reduction was obtained by incorporating 0.5 mM GTP into ATP-containing ghosts. The degree of phosphorylation obtained by incubating membranes with (gamma-32P)ATP under various conditions affecting K+ channel activity, was in direct correspondence to their effect on K+ efflux. The results suggest that the K+ channel of red cells is under complex metabolic control, via cAMP-mediated and nonmediated mechanisms, some which require ATP and presumably, involve phosphorylation of the channel proteins.

Electrogenic behavior of the human red cell Ca2+ pump revealed by disulfonic stilbenes.

A systematic study was made of the action of 4-acet-amido-4'-isothiocyanostilbene-2,2'-disulfonic acid (SITS) and 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS) on active Ca2+ transport of human erythrocytes. Pumping activity was estimated in inside-out vesicles (IOV's) by means of Ca2+-selective electrodes or use of tracer 45Ca2+. The stilbenes exhibited an approximately equal inhibitory potency and their action could be overcome by carbonyl cyanide p-trifluoromethoxyphenylhydrazone (FCCP) at low but not at high stilbene concentrations. In the absence of DIDS, Ca2+ transport was not affected upon addition of valinomycin, but it was appreciably reduced when vesicles were preincubated with low DIDS concentrations. Such an effect was strictly dependent on the external K+ concentration and it was abolished when valinomycin was added together with FCCP. Similar results were obtained using IOV's prepared from intact cells which had been previously exposed to the stilbene. The findings clearly demonstrate the presence in human red cells of a partially electrogenic Ca2+ pump, exchanging one Ca2+ ion for one proton.