The effect of deuteration on organic magnetoresistance

NOTICE: this is the author’s version of a work that was accepted for publication in Synthetic Metals. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in SYNTHETIC METALS, 161, 7-8, (2011) DOI 10.1016/j.synthmet.2010.11.04

Light scattering from disordered overlayers of metallic nanoparticles

We develop a theory for light scattering from a disordered layer of metal nanoparticles resting on a sample. Averaging over different disorder realizations is done by a coherent potential approximation. The calculational scheme takes into account effects of retardation, multipole excitations, and interactions with the sample. We apply the theory to a system similar to the one studied experimentally by Stuart and Hall [Phys. Rev. Lett. {\bf 80}, 5663 (1998)] who used a layered Si/SiO$_2$/Si sample. The calculated results agree rather well with the experimental ones. In particular we find conspicuous maxima in the scattering intensity at long wavelengths (much longer than those corresponding to plasmon resonances in the particles). We show that these maxima have their origin in interference phenomena in the layered sample.Comment: 19 pages, 12 figure

Renal function is independently associated with circulating betatrophin

OBJECTIVE: Betatrophin has been identified as a marker linking liver with beta cell function and lipid metabolism in murine models. Until now, the regulation of circulating betatrophin in humans is not entirely clear. We here analyzed the relation of betatrophin levels to phenotypes of the metabolic syndrome and speculated that renal function might influence circulating betatrophin levels and explain age-dependent changes of betatrophin. SUBJECTS: We analyzed blood samples from 535 individuals participating in the Metabolic Syndrome Berlin Potsdam study. RESULTS: In a crude analysis we found a positive correlation between betatrophin levels and HbA1c (r = 0.24; p < 0.001), fasting glucose (r = 0.20; p < 0.001) and triglycerides (r = 0.12; p = 0.007). Furthermore betatrophin was positively correlated with age (r = 0.47; p <0.001), systolic blood pressure (r = 0.17; p < 0.001), intima media thickness (r = 0.26; p < 0.001) and negatively correlated with CKD-EPI eGFR (r = -0.33; p < 0.001) as an estimate of renal function. Notably, eGFR remained highly associated with betatrophin after adjustment for age, waist circumference, gender, HbA1c and lipid parameters in a multivariate linear regression model ({beta} = -0.197, p< 0.001). CONCLUSIONS: Our data suggest that circulating levels of betatrophin depend on age, gender, waist circumference, total/HDL cholesterol ratio and renal function. Especially the association to eGFR highlights the importance for future studies to address renal function as possible influence on betatrophin regulation and consider eGFR as potential confounder when analyzing the role of betatrophin in humans

Free fatty acids link metabolism and regulation of the insulin-sensitizing fibroblast growth factor-21

OBJECTIVE—Fibroblast growth factor (FGF)-21 improves insulin sensitivity and lipid metabolism in obese or diabetic animal models, while human studies revealed increased FGF-21 levels in obesity and type 2 diabetes. Given that FGF-21 has been suggested to be a peroxisome proliferator–activator receptor (PPAR) –dependent regulator of fasting metabolism, we hypothesized that free fatty acids (FFAs), natural agonists of PPAR, might modify FGF-21 levels. RESEARCH DESIGN AND METHODS—The effect of fatty acids on FGF-21 was investigated in vitro in HepG2 cells. Within a randomized controlled trial, the effects of elevated FFAs were studied in 21 healthy subjects (13 women and 8 men). Within a clinical trial including 17 individuals, the effect of insulin was analyzed using an hyperinsulinemic-euglycemic clamp and the effect of PPAR activation was studied subsequently in a rosiglitazone treatment trial over 8 weeks. RESULTS—Oleate and linoleate increased FGF-21 expression and secretion in a PPAR-dependent fashion, as demonstrated by small-interfering RNA–induced PPAR knockdown, while palmitate had no effect. In vivo, lipid infusion induced an increase of circulating FGF-21 in humans, and a strong correlation between the change in FGF-21 levels and the change in FFAs was observed. An artificial hyperinsulinemia, which was induced to delineate the potential interaction between elevated FFAs and hyperinsulinemia, revealed that hyperinsulinemia also increased FGF-21 levels in vivo, while rosiglitazone treatment had no effect. CONCLUSIONS—The results presented here offer a mechanism explaining the induction of the metabolic regulator FGF-21 in the fasting situation but also in type 2 diabetes and obesity

The effect of moderate alcohol consumption on adiponectin oligomers and muscle oxidative capacity: a human intervention study

Aims/hypothesis The aim of this study was to investigate whether moderate alcohol consumption increases plasma high molecular weight (HMW) adiponectin and/or muscle oxidative capacity. Materials and methods Eleven lean (BMI 18 - 25 kg/m(2)) and eight overweight ( BMI >= 27 kg/m(2)) men consumed 100 ml whisky (similar to 32 g alcohol) or water daily for 4 weeks in a randomised, controlled, crossover trial. After each treatment period, muscle biopsies and fasting blood samples were collected. Results Adiponectin concentrations increased ( p <0.001) by 12.5% after 4 weeks of moderate alcohol consumption. Moderate alcohol consumption tended to increase HMW adiponectin by 57% ( p= 0.07) and medium molecular weight adiponectin by 12.5% ( p= 0.07), but not low molecular weight (LMW) adiponectin. Skeletal muscle citrate synthase, cytochrome c oxidase and beta-3-hydroxyacyl coenzyme A dehydrogenase (beta-HAD) activity were not changed after moderate alcohol consumption, but an interaction between alcohol consumption and BMI was observed for cytochrome c oxidase ( p= 0.072) and citrate synthase ( p= 0.102) activity. Among lean men, moderate alcohol consumption tended to increase cytochrome c oxidase ( p= 0.08) and citrate synthase activity ( p= 0.12) by 23 and 26%, respectively, but not among overweight men. In particular, plasma HMW adiponectin correlated positively with activities of skeletal muscle citrate synthase ( r= 0.64, p= 0.009), cytochrome c oxidase ( p= 0.59, p= 0.009) and beta-HAD ( r= 0.46, p= 0.056), while such correlation was not present for LMW adiponectin. Whole-body insulin sensitivity and intramyocellular triacylglycerol content were not affected by moderate alcohol consumption. Conclusions/interpretation Moderate alcohol consumption increases adiponectin concentrations, and in particular HMW adiponectin. Concentrations of HMW adiponectin in particular were positively associated with skeletal muscle oxidative capacity

Coulomb-blockade transport in single-crystal organic thin-film transistors

Coulomb-blockade transport—whereby the Coulomb interaction between electrons can prohibit their transport around a circuit—occurs in systems in which both the tunnel resistance, RT, between neighbouring sites is large (»h/e2) and the charging energy, EC (EC = e2/2C, where C is the capacitance of the site), of an excess electron on a site is large compared to kT. (Here e is the charge of an electron, k is Boltzmann's constant, and h is Planck's constant.) The nature of the individual sites—metallic, superconducting, semiconducting or quantum dot—is to first order irrelevant for this phenomenon to be observed. Coulomb blockade has also been observed in two-dimensional arrays of normal-metal tunnel junctions, but the relatively large capacitances of these micrometre-sized metal islands results in a small charging energy, and so the effect can be seen only at extremely low temperatures. Here we demonstrate that organic thin-film transistors based on highly ordered molecular materials can, to first order, also be considered as an array of sites separated by tunnel resistances. And as a result of the sub-nanometre sizes of the sites (the individual molecules), and hence their small capacitances, the charging energy dominates at room temperature. Conductivity measurements as a function of both gate bias and temperature reveal the presence of thermally activated transport, consistent with the conventional model of Coulomb blockade.

Scaling Analysis of Magnetic Filed Tuned Phase Transitions in One-Dimensional Josephson Junction Arrays

We have studied experimentally the magnetic field-induced superconductor-insulator quantum phase transition in one-dimensional arrays of small Josephson junctions. The zero bias resistance was found to display a drastic change upon application of a small magnetic field; this result was analyzed in context of the superfluid-insulator transition in one dimension. A scaling analysis suggests a power law dependence of the correlation length instead of an exponential one. The dynamical exponents $z$ were determined to be close to 1, and the correlation length critical exponents were also found to be about 0.3 and 0.6 in the two groups of measured samples.Comment: 4 pages, 4 figure

Nonlinear Viscous Vortex Motion in Two-Dimensional Josephson-Junction Arrays

When a vortex in a two-dimensional Josephson junction array is driven by a constant external current it may move as a particle in a viscous medium. Here we study the nature of this viscous motion. We model the junctions in a square array as resistively and capacitively shunted Josephson junctions and carry out numerical calculations of the current-voltage characteristics. We find that the current-voltage characteristics in the damped regime are well described by a model with a {\bf nonlinear} viscous force of the form $F_D=\eta(\dot y)\dot y={{A}\over {1+B\dot y}}\dot y$, where $\dot y$ is the vortex velocity, $\eta(\dot y)$ is the velocity dependent viscosity and $A$ and $B$ are constants for a fixed value of the Stewart-McCumber parameter. This result is found to apply also for triangular lattices in the overdamped regime. Further qualitative understanding of the nature of the nonlinear friction on the vortex motion is obtained from a graphic analysis of the microscopic vortex dynamics in the array. The consequences of having this type of nonlinear friction law are discussed and compared to previous theoretical and experimental studies.Comment: 14 pages RevTex, 9 Postscript figure