Modelling mechanical percolation in graphene-reinforced elastomer nanocomposites

Graphene is considered an ideal filler for the production of multifunctional nanocomposites; as a result, considerable efforts have been focused on the evaluation and modeling of its reinforcement characteristics. In this work, we modelled successfully the mechanical percolation phenomenon, observed on a thermoplastic elastomer (TPE) reinforced by graphene nanoplatelets (GNPs), by designing a new set of equations for filler contents below and above the percolation threshold volume fraction (Vp). The proposed micromechanical model is based on a combination of the well-established shear-lag theory and the rule-of-mixtures and was introduced to analyse the different stages and mechanisms of mechanical reinforcement. It was found that when the GNPs content is below Vp, reinforcement originates from the inherent ability of individual GNPs flakes to transfer stress efficiently. Furthermore, at higher filler contents and above Vp, the nanocomposite materials displayed accelerated stiffening due to the reduction of the distance between adjacent flakes. The model derived herein, was consistent with the experimental data and the reasons why the superlative properties of graphene cannot be fully utilized in this type of composites, were discussed in depth.Comment: 29 pages, 12 figure

Long range magnetic ordering in Na2_2IrO3_3

We report a combined experimental and theoretical investigation of the magnetic structure of the honeycomb lattice magnet Na$_2$IrO$_3$, a strong candidate for a realization of a gapless spin-liquid. Using resonant x-ray magnetic scattering at the Ir L$_3$-edge, we find 3D long range antiferromagnetic order below T$_N$=13.3 K. From the azimuthal dependence of the magnetic Bragg peak, the ordered moment is determined to be predominantly along the {\it a}-axis. Combining the experimental data with first principles calculations, we propose that the most likely spin structure is a novel "zig-zag" structure

Direct amplification of nodD from community DNA reveals the genetic diversity of Rhizobium leguminosarum in soil

Sequences of nodD, a gene found only in rhizobia, were amplified from total community DNA isolated from a pasture soil. The polymerase chain reaction (PCR) primers used, Y5 and Y6, match nodD from Rhizobium leguminosarum biovar trifolii, R. leguminosarum biovar viciae and Sinorhizobium meliloti. The PCR product was cloned and yielded 68 clones that were identified by restriction pattern as derived from biovar trifolii [11 restriction fragment length polymorphism (RFLP) types] and 15 clones identified as viciae (seven RFLP types). These identifications were confirmed by sequencing. There were no clones related to S. meliloti nodD. For comparison, 122 strains were isolated from nodules of white clover (Trifolium repens) growing at the field site, and 134 from nodules on trap plants of T. repens inoculated with the soil. The nodule isolates were of four nodD RFLP types, with 77% being of a single type. All four of these patterns were also found among the clones from soil DNA, and the same type was the most abundant, although it made up only 34% of the trifolii-like clones. We conclude that clover selects specific genotypes from the available soil population, and that R. leguminosarum biovar trifolii was approximately five times more abundant than biovar viciae in this pasture soil, whereas S. meliloti was rare

Crystallization of hepatocyte nuclear factor 4α (HNF4α) in complex with the HNF1α promoter element

Sample preparation, characterization, crystallization and preliminary X-ray analysis are reported for the HNF4α–DNA binary complex

Multiwavelength Observations of Small-Scale Reconnection Events triggered by Magnetic Flux Emergence in the Solar Atmosphere

The interaction between emerging magnetic flux and the pre-existing ambient field has become a "hot" topic for both numerical simulations and high-resolution observations of the solar atmosphere. The appearance of brightenings and surges during episodes of flux emergence is believed to be a signature of magnetic reconnection processes. We present an analysis of a small-scale flux emergence event in NOAA 10971, observed simultaneously with the Swedish 1-m Solar Telescope on La Palma and the \emph{Hinode} satellite during a joint campaign in September 2007. Extremely high-resolution G-band, H$\alpha$, and \ion{Ca}{2} H filtergrams, \ion{Fe}{1} and \ion{Na}{1} magnetograms, EUV raster scans, and X-ray images show that the emerging region was associated with chromospheric, transition region and coronal brightenings, as well as with chromospheric surges. We suggest that these features were caused by magnetic reconnection at low altitude in the atmosphere. To support this idea, we perform potential and linear force-free field extrapolations using the FROMAGE service. The extrapolations show that the emergence site is cospatial with a 3D null point, from which a spine originates. This magnetic configuration and the overall orientation of the field lines above the emerging flux region are compatible with the structures observed in the different atmospheric layers, and remain stable against variations of the force-free field parameter. Our analysis supports the predictions of recent 3D numerical simulations that energetic phenomena may result from the interaction between emerging flux and the pre-existing chromospheric and coronal field.Comment: In press for Ap

The incidence and risk factors for new onset atrial fibrillation in the PROSPER study

Aims Atrial fibrillation/flutter (AF) is the most common arrhythmia in older people. It associates with reduced exercise capacity, increased risk of stroke, and mortality. We aimed to determine retrospectively whether pravastatin reduces the incidence of AF and whether any electrocardiographic measures or clinical conditions might be risk factors for its development. Methods and results The PROspective Study of Pravastatin in the Elderly at Risk (PROSPER) was a randomized, double-blind controlled trial that recruited 5804 individuals aged 70-82 years with a history of, or risk factors for, vascular disease. A total of 2891 were allocated to pravastatin and 2913 to placebo; mean follow-up was 3.2 years. Electrocardiograms (ECGs), which were recorded at baseline, annually thereafter, and at run-out, were processed by computer and reviewed manually. In all, 264 of 2912 (9.1%) of the placebo group and 283 of 2888 (9.8%) of the pravastatin-treated group developed AF [hazard ratio 1.08 (0.92,1.28), P = 0.35)]. Multivariate analysis showed that PR and QTc intervals, age, left ventricular hypertrophy, and ST-T abnormalities were related to development of AF after adjustment for many variables including alcohol consumption, which itself was univariately predictive of developing AF. Previous myocardial infarction on the ECG was not a risk factor. A history of vascular disease was strongly linked with developing AF but not diabetes and hypertension. Conclusion Pravastatin does not reduce the incidence of AF in older people at risk of vascular disease, at least in the short-medium term. Risk factors for AF include older age, prolongation of PR or QTc intervals, left ventricular hypertrophy, and ST-T abnormalities on the EC