Dielectric properties of Li2O-3B2O3 glasses

The frequency and temperature dependence of the dielectric constant and the electrical conductivity of the transparent glasses in the composition Li2O-3B2O3 (LBO) were investigated in the 100 Hz- 10 MHz frequency range. The dielectric constant and the loss in the low frequency regime were electrode material dependent. Dielectric and electrical relaxations were respectively analyzed using the Cole-Cole and electric modulus formalisms. The dielectric relaxation mechanism was discussed in the framework of electrode and charge carrier (hopping of the ions) related polarization using generalized Cole-Cole expression. The frequency dependent electrical conductivity was rationalized using Jonscher's power law. The activation energy associated with the dc conductivity was 0.80 \pm 0.02 eV, which was ascribed to the motion of Li+ ions in the glass matrix. The activation energy associated with dielectric relaxation was almost equal to that of the dc conductivity, indicating that the same species took part in both the processes. Temperature dependent behavior of the frequency exponent (n) suggested that the correlated barrier hopping model was the most apposite to rationalize the electrical transport phenomenon in Li2O-3B2O3 glasses. These glasses on heating at 933 K/10h resulted in the known non-linear optical phase LiB3O5.Comment: 32 pages, 13 figure

Charge and momentum transfer in supercooled melts: Why should their relaxation times differ?

The steady state values of the viscosity and the intrinsic ionic-conductivity of quenched melts are computed, in terms of independently measurable quantities. The frequency dependence of the ac dielectric response is estimated. The discrepancy between the corresponding characteristic relaxation times is only apparent; it does not imply distinct mechanisms, but stems from the intrinsic barrier distribution for $\alpha$-relaxation in supercooled fluids and glasses. This type of intrinsic ``decoupling'' is argued not to exceed four orders in magnitude, for known glassformers. We explain the origin of the discrepancy between the stretching exponent $\beta$, as extracted from $\epsilon(\omega)$ and the dielectric modulus data. The actual width of the barrier distribution always grows with lowering the temperature. The contrary is an artifact of the large contribution of the dc-conductivity component to the modulus data. The methodology allows one to single out other contributions to the conductivity, as in ``superionic'' liquids or when charge carriers are delocalized, implying that in those systems, charge transfer does not require structural reconfiguration.Comment: submitted to J Chem Phy

Evidence of secondary relaxations in the dielectric spectra of ionic liquids

We investigated the dynamics of a series of room temperature ionic liquids based on the same 1-butyl-3-methyl imidazolium cation and different anions by means of broadband dielectric spectroscopy covering 15 decades in frequency (10^(-6)-10^9 Hz), and in the temperature range from 400 K down to 35 K. An ionic conductivity is observed above the glass transition temperature T_{g} with a relaxation in the electric modulus representation. Below T_{g}, two relaxation processes appear, with the same features as the secondary relaxations typically observed in molecular glasses. The activation energy of the secondary processes and their dependence on the anion are different. The slower process shows the characteristics of an intrinsic Johari-Goldstein relaxation, in particular an activation energy E_{beta}=24k_{B}T_{g} is found, as observed in molecular glasses.Comment: Major revision, submitted to Phys. Rev. Let

Animal Production from Tropical Pastures Renovated by Subsoiling and Fertilization in the Cerrados of Brazil

A grazing trial was conducted, to study the effects of fertilization on the maintenance of the productivity of four tropical grasses. The paddocks were subsoiled, and dived into halves: one (LF1) received 400 kg/ha of a fertilizer formula 0-20-20.and the other (LF2) 800 kg/ha of the same fertilizers, in January 1995. Annually, 50 kg/ha of N was applied. The productivity on LF2 pastures was greater than that on FL1 pastures, averaging 520 and 410 kg of liveweight gain/ha/year. A double strategy should be followed to sustain animal production in the savanna: maintain soil P over a critical value of 3.0 mg P(Mehlich-1)/dm3, and annual N application

Evaluation of \u3ci\u3eBrachiaria brizantha\u3c/i\u3e Ecotypes under Grazing in Small Plots

An intense search for new cultivars amongst recently collected and introduced ecotypes from Africa is in effect since 1988, at the National Beef Cattle Research Center, of the Brazilian Agricultural Research Corporation (Embrapa Beef Cattle). After agronomic evaluations of a large collection, 21 ecotypes were pre-selected for multilocational trials and from these, eight were elected for evaluation under grazing. The objective of this trial was thus to evaluate the persistence and carrying capacity of these eight new Brachiaria brizantha ecotypes after two years of grazing. The experimental design was a randomized complete block with nine treatments and two replicates. The experimental area was divided into 18 paddocks of 1000 m2. They were grazed according to a deferred flexible system. After two years, it was possible to select four ecotypes, which were indicated for animal performance trials aiming at releasing at least one of them as a new cultivar in 2002

Kinetic description of particle interaction with a gravitational wave

The interaction of charged particles, moving in a uniform magnetic field, with a plane-polarized gravitational wave is considered using the Fokker-Planck- Kolmogorov (FPK) approach. By using a stochasticity criterion, we determine the exact locations in phase space, where resonance overlapping occurs. We investigate the diffusion of orbits around each primary resonance of order (m) by deriving general analytical expressions for an effective diffusion coeficient. A solution to the corresponding diffusion equation (Fokker-Planck equation) for the static case is found. Numerical integration of the full equations of motion and subsequent calculation of the diffusion coefficient verifies the analytical results.Comment: LaTeX file, 15 page

Stable spontaneously-scalarized black holes in generalized scalar-tensor theories

It has been shown that the synergy of a scalar field coupling with both the Ricci scalar and the Gauss-Bonnet invariant significantly affects the properties of scalarized black holes and neutron stars, including their domain of existence and the amount of scalar hair they carry. Here we study the radial stability of scalarized black-hole solutions. We demonstrate that they are stable against radial perturbations for Ricci couplings consistent with both a late-time cosmological attractor and the evasion of binary pulsar constraints. In addition, we investigate the effect of the Ricci coupling on the hyperbolicity of the equation governing linear, radial perturbations and show that it significantly reduces the region over which hyperbolicity is lost.Comment: 11 pages, 8 figure

Animal Performance and Productivity of New Ecotypes of Brachiaria Brizantha in Brazil

Brazil has the competitive advantage of a very dynamic and cost effective animal production system on pastures over other countries. The pursuit for more productive forages that will result in higher quality beef at a lower cost is then justified. Brachiaria is the most important forage genus utilised in Brazil, thus an intense search for new cultivars amongst collected and introduced ecotypes from Africa is underway. Following agronomic evaluation of this material in plots, 8 pre-selected Brachiaria ecotypes were tested under intermittent grazing in paddocks (Euclides et al., 2001). Continuing on the process of cultivar development, two out of the eight, selected for superior agronomic characteristics were compared to the standard cultivar Marandu, under grazing and the results are presented in this paper