Ferromagnetism in magnetically doped III-V semiconductors

The origin of ferromagnetism in semimagnetic III-V materials is discussed. The indirect exchange interaction caused by virtual electron excitations from magnetic impurity level in the bandgap to the valence band can explain ferromagnetism in GaAs(Mn) no matter samples are degenerated or not. Formation of ferromagnetic clusters and percolation picture of phase transition describes well all available experimental data and allows to predict the Mn-composition dependence of transition temperature in wurtzite (Ga,In,Al)N epitaxial layers.Comment: 4 pages with 3 figure

Fundamental Curie temperature limit in ferromagnetic GaMnAs

We provide experimental evidence that the upper limit of ~110 K commonly observed for the Curie temperature T_C of Ga(1-x)Mn(x)As is caused by the Fermi-level-induced hole saturation. Ion channeling, electrical and magnetization measurements on a series of Ga(1-x-y)Mn(x)Be(y)As layers show a dramatic increase of the concentration of Mn interstitials accompanied by a reduction of T_C with increasing Be concentration, while the free hole concentration remains relatively constant at ~5x10^20 cm^-3. These results indicate that the concentrations of free holes and ferromagnetically active Mn spins are governed by the position of the Fermi level, which controls the formation energy of compensating interstitial Mn donors.Comment: 14 pages, 3 figure

No Effect of One-Year Treatment with Indomethacin on Alzheimer's Disease Progression: A Randomized Controlled Trial

Contains fulltext : 71117.pdf (publisher's version ) (Open Access)BACKGROUND: The objective of this study was to determine whether treatment with the nonselective nonsteroidal anti-inflammatory drug (NSAID) indomethacin slows cognitive decline in patients with Alzheimer's disease (AD). METHODOLOGY/PRINCIPAL FINDINGS: This double-blind, randomized, placebo-controlled trial was conducted between May 2000 and September 2005 in two hospitals in the Netherlands. 51 patients with mild to moderate AD were enrolled into the study. Patients received 100 mg indomethacin or placebo daily for 12 months. Additionally, all patients received omeprazole. The primary outcome measure was the change from baseline after one year of treatment on the cognitive subscale of the AD Assessment Scale (ADAS-cog). Secondary outcome measures included the Mini-Mental State Examination, the Clinician's Interview Based Impression of Change with caregiver input, the noncognitive subscale of the ADAS, the Neuropsychiatric Inventory, and the Interview for Deterioration in Daily life in Dementia. Considerable recruitment problems of participants were encountered, leading to an underpowered study. In the placebo group, 19 out of 25 patients completed the study, and 19 out of 26 patients in the indomethacin group. The deterioration on the ADAS-cog was less in the indomethacin group (7.8+/-7.6), than in the placebo group (9.3+/-10.0). This difference (1.5 points; CI -4.5-7.5) was not statistically significant, and neither were any of the secondary outcome measures. CONCLUSIONS/SIGNIFICANCE: The results of this study are inconclusive with respect to the hypothesis that indomethacin slows the progression of AD

Carrier-induced breakdown of ferromagnetism

Magnetization, susceptibility and specific-heat data for PbSn(Mn)Te and Sn(Mn)Te will be reported for various carrier concentrations. For the first time a carrier-concentration–induced breakdown of a ferromagnetic state has been observed. Based on a simple geometrical argument, a phase diagram for this new transition in RKKY-driven systems will be derived and will be compared with the ferromagnetic–to–spin-glass transition predicted by the well-known Sherrington-Kirkpatrick model.</p

Chlorine and bromine isotope evolution within a fully developed Upper Permian natural salt sequence

The behaviour of chlorine and bromine isotopes in evaporite deposits differs significantly. We studied the isotope variations of both elements in a fully developed natural salt sequence from Zechstein evaporite deposits (Wuchiapingian, Upper Permian) in the Northern Netherlands. We observed that the Cl isotope variations follow previously predicted characteristics, showing slightly positive δ37Cl (relative to seawater) in halite (NaCl) dominated layers (up to +0.05‰), decreasing to moderately negative values in carnallite (KMgCl3·6H2O) and bischofite (MgCl2·6H2O) dominated layers (down to −0.55‰). Bromine isotope variations, the first ever measured in marine evaporite samples, show a different characteristic. δ81Br values decrease quickly in layers dominated by halite (from +0.2 to −0.5‰) and increase again in layers dominated by carnallite and bischofite (up to −0.1 ± 0.2‰). These observations suggest that the Br isotope fractionation (103lnα) during precipitation of halite can be as high as +1.3, 3.8 times as large as Cl isotope fractionation. The increasing δ81Br values during precipitation of magnesium salts may suggest a negative fractionation (103lnα) of −0.9, meaning that the Br isotope ratio in the precipitated salt is lower than in the brine. We suggest that the difference in behaviour between Cl and Br can be explained by the fact that Br, as a minor component in the brine, has to compete with Cl to fit into the crystal lattice of Cl salts, where it does not fit perfectly due to its slightly larger ionic radius than Cl, resulting in relatively large isotope fractionation. Further research is however needed to confirm or reject this suggestion

Occurrence of Vibrio parahaemolyticus in Dutch mussels.

A study was carried out on the occurrence of Vibrio parahaemolyticus in Dutch mussels originating from the East Schelde Estuary. In a totol of 79 10-g tissue samples, 3 (3.8%) were found to contain V. parahaemolyticus. In a second survey, 6 out of 23 bags of mussels (26%) contained one or more strains of V. parahaemolyticus in 5-g tissue samples. The many limitations of current methodology used in such surveys are stressed. Positive samples can be missed because viable cells may die during refrigerated transport. Surviving cells also may not be detected because they have been sublethally stressed. In addition, the unreliability of the identification criterion of no growth in 10% NaCl was demonstrated