Competing tunneling trajectories in a 2D potential with variable topology as a model for quantum bifurcations

We present a path - integral approach to treat a 2D model of a quantum bifurcation. The model potential has two equivalent minima separated by one or two saddle points, depending on the value of a continuous parameter. Tunneling is therefore realized either along one trajectory or along two equivalent paths. Zero point fluctuations smear out the sharp transition between these two regimes and lead to a certain crossover behavior. When the two saddle points are inequivalent one can also have a first order transition related to the fact that one of the two trajectories becomes unstable. We illustrate these results by numerical investigations. Even though a specific model is investigated here, the approach is quite general and has potential applicability for various systems in physics and chemistry exhibiting multi-stability and tunneling phenomena.Comment: 11 pages, 8 eps figures, Revtex-

Specific heat of quasi-2D antiferromagnetic Heisenberg models with varying inter-planar couplings

We have used the stochastic series expansion (SSE) quantum Monte Carlo (QMC) method to study the three-dimensional (3D) antiferromagnetic Heisenberg model on cubic lattices with in-plane coupling J and varying inter-plane coupling J_perp < J. The specific heat curves exhibit a 3D ordering peak as well as a broad maximum arising from short-range 2D order. For J_perp << J, there is a clear separation of the two peaks. In the simulations, the contributions to the total specific heat from the ordering across and within the layers can be separated, and this enables us to study in detail the 3D peak around T_c (which otherwise typically is dominated by statistical noise). We find that the peak height decreases with decreasing J_perp, becoming nearly linear below J_perp = 0.2J. The relevance of these results to the lack of observed specific heat anomaly at the ordering transition of some quasi-2D antiferromagnets is discussed.Comment: 7 pages, 8 figure

Short report: Severe Plasmodium falciparum malaria in Cameroon: associated with the glutathione S-transferase M1 null genotype.

Contains fulltext : 49315.pdf (publisher's version ) (Open Access)Glutathione S-transferases (GST) are a family of enzymes involved in phase-II detoxification of endogenous and xenobiotic compounds. Polymorphisms in GST genes have been associated with susceptibility to different diseases. In this study we determined the frequencies of polymorphisms in GSTM1, GSTT1, and GSTP1 in DNA of 138 children from Cameroon, presenting with uncomplicated malaria (N = 19), malaria with minor complications (N = 81), or severe malaria (N = 38). Analyses of GSTM1 and GSTT1 were performed using PCR-multiplex procedure, while GSTP1 was done by PCR-RFLP. Subjects presenting with malaria with complications were found more often of the GSTM1-null genotype (58-64%) as compared with those with uncomplicated malaria (32%), a difference that was statistically significant. We conclude that the GSTM1-null genotype is associated with malaria with complications

Association of insulin resistance with hyperglycemia in streptozotocin-diabetic pigs - Effects of metformin at isoenergetic feeding in a type 2-like diabetic pig model

Insulin-mediated glucose metabolism was investigated in streptozotocin (STZ)¿treated diabetic pigs to explore if the STZ-diabetic pig can be a suitable model for insulin-resistant, type 2 diabetes mellitus. Pigs (40 kg) were meal-fed with a low-fat (5%) diet. Hyperinsulinemic (1, 2, and 8 mU kg¿1 min¿1) clamps and/or 6,6-2H-glucose infusion studies were performed in 36 pigs. Diabetic (slow, 30-minute infusion of 130 mg STZ/kg) vs normal pigs were nonketotic, showed fasting hyperglycemia (21.7 ± 1.1 vs 5.3 ± 0.2 mmol/L), comparable plasma insulin (9 ± 7 vs 5 ± 1 mU/L), and elevated triglyceride concentrations (1.0 ± 0.3 vs 0.2 ± 0.1 mmol/L). After a standard meal, plasma triglycerides, cholesterol, and nonesterified fatty acid concentrations were significantly higher in diabetic vs normal pigs (1.2 ± 0.3 vs 0.3 ± 0.1, 2.3 ± 0.2 vs 1.7 ± 0.1, and 1.5 ± 0.5 vs 0.2 ± 0.1 mmol/L, respectively, P <.05). Fasting whole-body glucose uptake, hepatic glucose production, and urinary glucose excretion were increased (P <.01) in diabetic vs normal pigs (9.1 ± 0.6 vs 4.8 ± 0.4, 11.4 ± 0.6 vs 4.8 ± 0.4, and 2.3 ± 0.2 vs 0.0 ± 0.0 mg kg¿1 min¿1). During hyperinsulinemic euglycemia (6 mmol/L), whole-body glucose uptake was severely reduced (P <.01) and hepatic glucose production was moderately increased (P <.05) in diabetic vs normal pigs (6.7 ± 1.3 vs 21.1 ± 2.2 and 1.7 ± 0.5 vs 0.8 ± 0.3 mg kg¿1 min¿1) despite plasma insulin concentrations of 45 ± 5 vs 24 ± 5 mU/L, respectively. Metformin vs placebo treatment of diabetic pigs (twice 1.5 g/d) for 2 weeks during isoenergetic feeding (1045 kJ/kg body weight0.75) resulted in a reduction in both fasting and postprandial hyperglycemia (14.7 ± 1.5 vs 19.4 ± 0.6 and 24.9 ± 2.2 vs 35.5 ± 4.9 mmol/L), a reduction in daily urinary glucose excretion (250 vs 350 g/kg food), and an increase in insulin-stimulated glucose disposal (9.4 ± 2.2 vs 5.8 ± 1.7 mg kg¿1 min¿1; P <.05), respectively. In conclusion, a slow infusion of STZ (130 mg/kg) in pigs on a low-fat diet induces the characteristic metabolic abnormalities of type 2 diabetes mellitus and its sensitivity to oral metformin therapy. It is therefore a suitable humanoid animal model for studying different aspects of metabolic changes in type 2 diabetes mellitus. Insulin resistance in STZ-diabetic pigs is most likely secondary to hyperglycemia and/or hyperlipidemia and therefore of metabolic origin

Humoral protection against mosquito bite-transmitted Plasmodium falciparum infection in humanized mice

Contains fulltext : 189906.pdf (publisher's version ) (Open Access

Common genotypic polymorphisms in glutathione S-transferases in mild and severe falciparum malaria in Tanzanian children.

Malaria infection induces oxidative stress in the host cells. Antioxidant enzymes such as glutathione S-transferases (GSTs) are responsible for fighting reactive oxygen species and reduction of oxidative stress. Common GST polymorphisms have been associated with susceptibility to different diseases whose pathologies involve oxidative stress. In this study, we tested the hypothesis that GST polymorphisms that lead to reduced or lack of enzyme activity are associated with severe Plasmodium falciparum malarial anemia. We studied the genotypic distribution of GSTM1, GSTT1, and GSTP1 polymorphisms between mild malaria (N = 107) and severe malarial anemia (N = 50) in Tanzanian children. We did not find a significant relationship with the GSTT1 polymorphism. GSTM1-null was higher in the severe malaria anemia group but the difference was not significant (P = 0.08). However, a significant association of GSTP1 I105V genotype with severe malarial anemia was discovered (26.0% against 10.3% mild malaria, P = 0.004). We concluded that GSTP1 and possibly GSTM1 may protect against severe falciparum malaria in children

alpha-Thalassaemia trait is associated with Antibody prevalence against Malaria Antigens AMA-1 and MSP-1

A longitudinal study was conducted in a low endemic area in northern Tanzania to examine the influence of the alpha-thalassaemia trait on malaria incidence and antibody responses to malaria apical membrane antigen-1 (AMA-1) and merozoite surface protein1-19 (MSP-119). Out of 394 children genotyped for alpha-thalassaemia trait, 4.1% (16 of 394) and 30.7% (121 of 394) were homozygous and heterozygous, respectively. During the 1 year follow-up, four incidents of malaria cases were detected without an evident association with alpha-thalassaemia. Being heterozygous or homozygous for alpha-thalassaemia was associated with an increased prevalence of antibodies to AMA-1 [odds ratio (OR): 1.83, 95% confidence interval (CI): 1.07-3.12, p = 0.027] and MSP-1 (OR: 2.04, 95% CI: 1.16-3.60, p = 0.013) after adjustment for age and reported bednet use. The observed association between alpha-thalassaemia and malaria antibody responses may reflect longer-term differences in antigen exposure or differences in antibody acquisition upon exposure in this low endemic setting

A Potent Anti-Malarial Human Monoclonal Antibody Targets Circumsporozoite Protein Minor Repeats and Neutralizes Sporozoites in the Liver

Contains fulltext : 226211.pdf (Publisher’s version ) (Closed access