The s-d exchange model as the underlying mechanism of magnetoresistance in ZnO doped with alkali metals.

High field magnetoresistance has been studied in epitaxial n-type ZnO:Na and ZnO:Li thin films in a temperature range between 4 K and 150 K. The resulting negative magnetoresistance can be well fitted using a semiempirical model of Khosla and Fischer based on third order contributions to the s-d exchange Hamiltonian. The parameters obtained from this model were carefully analyzed. One of these parameters is related to a ratio between electron mobilities at zero field (a non-exchange scattering mobility [Formula: see text] and an exchange or spin dependent one [Formula: see text]). From Hall effect measurements [Formula: see text] was obtained, displaying a weak temperature dependence in accordance with highly n-doped ZnO while the extracted [Formula: see text] exhibits an anomalous T-dependence. On the other hand, our magnetoresistance data cannot be properly fitted using Kawabata's expression based on a weak-localization model.

Interpretation of experimental results on Kondo systems with crystal field.

We present a simple approach to calculate the thermodynamic properties of single Kondo impurities including orbital degeneracy and crystal field effects (CFE) by extending a previous proposal by Schotte and Schotte (1975 Phys. Lett. 55A 38). Comparison with exact solutions for the specific heat of a quartet ground state split into two doublets shows deviations below 10% in the absence of CFE and a quantitative agreement for moderate or large CFE. As an application, we fit the measured specific heat of the compounds CeCu2Ge2, CePd3Si0.3, CePdAl, CePt, Yb2Pd2Sn and YbCo2Zn20. The agreement between theory and experiment is very good or excellent depending on the compound, except at very low temperatures due to the presence of magnetic correlations (not accounted for in the model).

Association of neurexin 3 polymorphisms with smoking behavior.

The Neurexin 3 gene (NRXN3) has been associated with dependence on various addictive substances, as well as with the degree of smoking in schizophrenic patients and impulsivity among tobacco abusers. To further evaluate the role of NRXN3 in nicotine addiction, we analyzed single nucleotide polymorphisms (SNPs) and a copy number variant (CNV) within the NRXN3 genomic region. An initial study was carried out on 157 smokers and 595 controls, all of Spanish Caucasian origin. Nicotine dependence was assessed using the Fagerström index and the number of cigarettes smoked per day. The 45 NRXN3 SNPs genotyped included all the SNPs previously associated with disease, and a previously described deletion within NRXN3. This analysis was replicated in 276 additional independent smokers and 568 controls. Case-control association analyses were performed at the allele, genotype and haplotype levels. Allelic and genotypic association tests showed that three NRXN3 SNPs were associated with a lower risk of being a smoker. The haplotype analysis showed that one block of 16 Kb, consisting of two of the significant SNPs (rs221473 and rs221497), was also associated with lower risk of being a smoker in both the discovery and the replication cohorts, reaching a higher level of significance when the whole sample was considered [odds ratio = 0.57 (0.42-0.77), permuted P = 0.0075]. By contrast, the NRXN3 CNV was not associated with smoking behavior. Taken together, our results confirm a role for NRXN3 in susceptibility to smoking behavior, and strongly implicate this gene in genetic vulnerability to addictive behaviors.

Simultaneous versus delayed treatment of tobacco dependence in alcohol-dependent outpatients.

INTRODUCTION: There is a high prevalence of smoking among heavy drinkers, which is often forgotten even though it has important health consequences. AIM: To evaluate the effects that providing an intensive tobacco cessation treatment simultaneously with alcohol dependence treatment versus delayed treatment (first alcohol and 6 months later tobacco) has on alcohol and tobacco consumption. METHODS: Ninety-two alcohol-dependent smokers were randomized into either a simultaneous group, in which treatment was given concurrently for quitting both alcohol and tobacco, or a delayed group, in which help to quit smoking was given after 6 months. RESULTS: No differences were found in alcohol abstinence rates in time-to-first relapse or in cumulative abstinence at 6 months. Smoking cessation rates were low overall, but better at 3 months in the simultaneous group, although differences later disappeared. DISCUSSION: Participation in a smoking cessation program does not impair alcohol outcomes, at least during the first 6 months.

Phase-coherence effects in vortex transport entropy.

Nernst and electrical resistivity measurements in superconducting YBa2Cu3O7-delta and Bi2Sr2CaCu2O8+delta with and without columnar defects show a distinctive thermodynamics of the respective liquid vortex matter. At a field-dependent high temperature region in the H-T phase diagram, the Nernst signal is independent of structural defects in both materials. At lower temperatures, in YBa2Cu3O7-delta, defects contribute only to the vortex mobility, and the transport entropy is that of a system of vortex lines. The transition to lower temperatures in Bi2Sr2CaCu2O8+delta has a different origin; the maximum in the Nernst signal when decreasing temperature is not associated with transport properties but with the entropy behavior of pancake vortices in the presence of structural defects.

Vortex softening: origin of the second peak effect in Bi(2)Sr(2)CaCu(2)O(8+delta).

Magnetic hysteresis and transverse ac permeability measurements in Bi(2)Sr(2)CaCu(2)O(8+delta) allow a comparative analysis of the critical current with the elastic response of vortex structures, in equilibrium with their pinning potential, in the field and temperature region where the second peak is detected. This study provides strong evidence that the second peak has its origin in changes of the elastic equilibrium properties of the vortex structures.