Electron Spin Dynamics in Impure Quantum Wells for Arbitrary Spin-Orbit Coupling

Strong interest has arisen recently on low-dimensional systems with strong spin-orbit interaction due to their peculiar properties of interest for some spintronic applications. Here, the time evolution of the electron spin polarization of a disordered two-dimensional electron gas is calculated exactly within the Boltzmann formalism for arbitrary couplings to a Rashba spin-orbit field. The classical Dyakonov-Perel mechanism of spin relaxation is shown to fail for sufficiently strong Rashba fields, in which case new regimes of spin decay are identified. These results suggest that spin manipulation can be greatly improved in strong spin-orbit interaction materials.Comment: 5 pages, 2 figures -revised versio

Polaronic and nonadiabatic phase diagram from anomalous isotope effects

Isotope effects (IEs) are powerful tool to probe directly the dependence of many physical properties on the lattice dynamics. In this paper we invenstigate the onset of anomalous IEs in the spinless Holstein model by employing the dynamical mean field theory. We show that the isotope coefficients of the electron effective mass and of the dressed phonon frequency are sizeable also far away from the strong coupling polaronic crossover and mark the importance of nonadiabatic lattice fluctuations in the weak to moderate coupling region. We characterize the polaronic regime by the appearence of huge IEs. We draw a nonadiabatic phase diagram in which we identify a novel crossover, not related to polaronic features, where the IEs attain their largest anomalies.Comment: 5 pages, 4 figure

Nonadiabatic Superconductivity and Vertex Corrections in Uncorrelated Systems

We investigate the issue of the nonadiabatic superconductivity in uncorrelated systems. A local approximation is employed coherently with the weak dependence on the involved momenta. Our results show that nonadiabatic vertex corrections are never negligible, but lead to a strong suppression of $T_c$ with respect to the conventional theory. This feature is understood in terms of the momentum-frequency dependence of the vertex function. In contrast to strongly correlated systems, where the small ${\bf q}$-selection probes the positive part of vertex function, vertex corrections in uncorrelated systems are essentially negative resulting in an effective reduction of the superconducting pairing. Our analysis shows that vertex corrections in nonadiabatic regime can be never disregarded independently of the degree of electronic correlation in the system.Comment: 4 pages, 3 eps fig

Nonadiabatic Pauli susceptibility in fullerene compounds

Pauli paramagnetic susceptibility $\chi$ is unaffected by the electron-phonon interaction in the Migdal-Eliashberg context. Fullerene compounds however do not fulfill the adiabatic assumption of Migdal's theorem and nonadiabatic effects are expected to be relevant in these materials. In this paper we investigate the Pauli spin susceptibility in nonadiabatic regime by following a conserving approach based on Ward's identity. We find that a sizable renormalization of $\chi$ due to electron-phonon coupling appears when nonadiabatic effects are taken into account. The intrinsic dependence of $\chi$ on the electron-phonon interaction gives rise to a finite and negative isotope effect which could be experimentally detected in fullerides. In addition, we find an enhancement of the spin susceptibility with temperature increasing, in agreement with the temperature dependence of $\chi$ observed in fullerene compounds. The role of electronic correlation is also discussed.Comment: Revtex, 10 pages, 8 figures include

Electron-phonon renormalization in small Fermi energy systems

The puzzling features of recent photoemission data in cuprates have been object of several analysis in order to identity the nature of the underlying electron-boson interaction. In this paper we point out that many basilar assumptions of the conventional analysis as expected to fail in small Fermi energy systems when, as the cuprates, the Fermi energy $E_{\rm F}$ is comparable with the boson energy scale. We discuss in details the novel features appearing in the self-energy of small Fermi energy systems and the possible implications on the ARPES data in cuprates.Comment: 4 pages, 5 eps figures include

Longitudinal and transversal piezoresistive response of granular metals

In this paper, we study the piezoresistive response and its anisotropy for a bond percolation model of granular metals. Both effective medium results and numerical Monte Carlo calculations of finite simple cubic networks show that the piezoresistive anisotropy is a strongly dependent function of bond probability p and of bond conductance distribution width \Delta g. We find that piezoresistive anisotropy is strongly suppressed as p is reduced and/or \Delta g is enhanced and that it vanishes at the percolation thresold p=p_c. We argue that a measurement of the piezoresistive anisotropy could be a sensitive tool to estimate critical metallic concentrations in real granular metals.Comment: 14 pages, 7 eps figure

The Longitudinal Interplay between Sleep, Anthropometric Indices, Eating Behaviors, and Nutritional Aspects: A Systematic Review and Meta-Analysis

Sleep is fundamental for adolescents’ healthy development but undergoes dramatic changes in quantity and quality due to the conflict between biological and social rhythms. Insufficient sleep has been associated with worse physical health status and irregular eating behaviors in adolescents. This review aims to systematically synthesize the longitudinal associations between adolescents’ sleep dimensions (i.e., duration, timing, quality, and insomnia symptoms) and physical health indicators (i.e., anthropometric indices, fat percentage, and risk of obesity), eating behaviors, and nutritional aspects (i.e., type of diet related to the intake of specific foods and nutrients, amount and timing of food consumption, energy expenditure). A total of 28 longitudinal studies were included. The meta-analytic results showed that longer sleep duration, better sleep quality, and lower insomnia symptoms were associated with lower BMI and fat percentage and that shorter sleep duration (<7 h) and lower sleep quality were associated with a higher risk of obesity. Conversely, anthropometric indices were not related to sleep over time. Limited literature examined the bidirectional association between adolescents’ sleep and their eating behaviors and nutritional aspects. Such knowledge sheds new light on the role of sleep for adolescents’ health, highlighting the need to examine further the interplay between these variables

Band-filling effects on electron-phonon properties of normal and superconducting state

We address the effect of band filling on the effective electron mass $m^*$ and the superconducting critical temperature $T_c$ in a electron-phonon system. We compare the vertex corrected theory with the non-crossing approximation of the Holstein model within a local approximation. We identify two regions of the electron density where $m^*$ and $T_c$ are enhanced or decreased by the inclusion of the vertex diagrams. We show that the crossover between the enhancement at low density and the decrease towards half filling is almost independent of the microscopic electron-phonon parameters. These different behaviors are explained in terms of the net sign of the vertex diagrams which is positive at low densities and negative close to half filling. Predictions of the present theory for doped MgB$_2$, which is argued to be in the low density regime, are discussed.Comment: 13 revtex pages, figures eps include

Características químicas de um gleissolo sob diferentes sistemas de uso, nas margens do rio Guamá, Belém, Pará.

Foram estudados os efeitos do uso do solo sobre a fertilidade, em Gleissolo sob três diferentes sistemas de manejo. As coletas foram feitas antes do período chuvoso nos seguintes sistemas de manejo: área cultivada com arroz (Oriza sativa L.) há aproximadamente 40 anos, com algumas interrupções ao longo deste período, com o cultivo algumas vezes mecanizado e uso de aração e gradagem; área sob pastagem de canarana erecta lisa (Echinochloa pyramidalis Hitch.), formada há cerca de 20 anos sem uso de adubações ou calagens; e área sob vegetação natural de floresta típica das áreas de várzea alta. As amostras de solo foram coletadas em dez pontos a partir de um transecto nas áreas, em quatro profundidades 0-10, 10-20, 20-30 e 30-40 cm. Os resultados demonstraram que o solo em condições naturais, de modo geral, apresentou atributos químicos que variaram de bons a muito bons, o que demonstra um grande potencial para o uso agrícola. O cultivo agrícola dos solos das várzeas do rio Guamá provocou uma redução da concentração de P e de K. O sistema de uso com pastagem apresentou maior sustentabilidade da fertilidade do que o sistema sob cultivo com arroz, visto que, além da melhoria das características químicas, a matéria orgânica elevou-se, também, em relação ao sistema natural

50 Hz Extremely Low Frequency Electromagnetic Fields Enhance Protein Carbonyl Groups Content in Cancer Cells: Effects on Proteasomal Systems

Electromagnetic fields are an assessed cause of prolonging free radicals lifespan. This study was carried out to investigate the influence of extremely low frequency electromagnetic fields on protein oxidation and on the 20S proteasome functionality, the complex responsible for the degradation of oxidized proteins. Caco 2 cells were exposed, for 24–72 hours, to 1 mT, 50 Hz electromagnetic fields. The treatment induced a time-dependent increase both in cell growth and in protein oxidation, more evident in the presence of TPA, while no changes in cell viability were detected. Exposing the cells to 50 Hz electromagnetic fields caused a global activation of the 20S proteasome catalytic components, particularly evident at 72 hours exposure and in the presence of TPA. The finding that EGCG, a natural antioxidant compound, counteracted the field-related pro-oxidant effects demonstrates that the increased proteasome activity was due to an enhancement in intracellular free radicals