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

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

Considerações sobre índices de produtividade da pecuária de corte em Mato Grosso do Sul.

A pecuária de corte, apesar de ser um dos segmentos mais importantes da economia do Estado de Mato Grosso do Sul, desde o inicio da década de 90 vem apresentando queda na produtividade geral. Isso esta ocorrendo como conseqüência da redução da produtividade das pastagens, que por sua vez, e resultado de uma serie de fatores que vão desde a escolha da espécie forrageira e o manejo de formação ate a escolha do animal a ser utilizado. Pode-se ressaltar, no entanto, que uma das principais causas e o manejo inadequado das pastagens, em especial, no que diz respeito a pratica generalizada do excesso de lotação. O reflexo primário de tal pratica faz-se sentir na degradação das pastagens com serias conseqüências ambientais, em especial em solos mas arenosos. Do ponto de vista econômico, este cenário resulta em diminuição da rentabilidade do sistema de produção. Em ultima instancia, o que se verifica e sua inviabilidade do sistema de produção. Em ultima instancia, o que se verifica e sua inviabilidade bioeconômica. Apesar de a capacidade de suporte media das pastagens, no Estado, ser de 0,9 cabeça/hectare, ela apresenta variações acentuadas em função das condições de solo, clima e sistema de produção. Todavia, e possível, utilizando-se de tecnologias já disponíveis, reduzir tais variáveis e/ou implementar alternativas que possibilitem, em algumas regiões, a sua melhoria. Para isso, fazem-se necessárias, na maioria dos casos, a recuperação e a manutenção das pastagens. Torna-se, portanto, indispensável o uso de fertilizantes, o que por sua vez, em muitas situações, e impraticável, quer seja pela inviabilidade econômica, quer seja pela baixa disponibilidade de adubos. Assim, para se aumentar a produtividade da pecuária de corte em MS, e imprescindível que diferentes setores se unam para viabilizar a geração, a transferência e a validação de tecnologias. Aliado a isso e importante criar condições para que os sistemas tenham gerenciamento mais eficientes, e para que os créditos sejam mais compatíveis com a atividade.bitstream/item/135978/1/DOC-70.pd

Universal Parametric Correlations of Eigenvalues of Random Matrix Ensemble

Eigenvalue correlations of random matrix ensembles as a function of an external perturbation are investigated vis the Dyson Brownian Motion Model in the situation where the level density has a hard edge singularity. By solving a linearized hydrodynamical equation, a universal dependence of the density-density correlator on the external field is found. As an application we obtain a formula for the variance of linear statistics with the parametric dependence exhibited as a Laplace transform.Comment: 23 pages, late