Spin density wave dislocation in chromium probed by coherent x-ray diffraction

We report on the study of a magnetic dislocation in pure chromium. Coherent x-ray diffraction profiles obtained on the incommensurate Spin Density Wave (SDW) reflection are consistent with the presence of a dislocation of the magnetic order, embedded at a few micrometers from the surface of the sample. Beyond the specific case of magnetic dislocations in chromium, this work may open up a new method for the study of magnetic defects embedded in the bulk.Comment: 8 pages, 7 figure

Critical temperature of a fully anisotropic three-dimensional Ising model

The critical temperature of a three-dimensional Ising model on a simple cubic lattice with different coupling strengths along all three spatial directions is calculated via the transfer matrix method and a finite size scaling for L x L oo clusters (L=2 and 3). The results obtained are compared with available calculations. An exact analytical solution is found for the 2 x 2 oo Ising chain with fully anisotropic interactions (arbitrary J_x, J_y and J_z).Comment: 17 pages in tex using preprint.sty for IOP journals, no figure

Repair of a Reinforced Earth Wall

The facing of a Reinforced Earth retaining wall, built at an altitude of 1200 m, was damaged during the winter 1981. The repair was achieved quickly and under traffic. The instrumentation carried out on the repairs and the tests run on the backfill material have revealed the action of the frost and its increase in the fortuitous presence of water

Combined coherent x-ray micro-diffraction and local mechanical loading on copper nanocrystals

Coherent x-ray micro-diffraction and local mechanical loading can be combined to investigate the mechanical deformation in crystalline nanostructures. Here we present measurements of plastic deformation in a copper crystal of sub-micron size obtained by loading the sample with an Atomic Force Microscopy tip. The appearance of sharp features in the diffraction pattern, while conserving its global shape, is attributed to crystal defects induced by the tip

Effect of Aloe Vera wastes on physico-chemical properties and microbiological activity in soils

The aim of the present study was to explore the potential for using aloe vera wastes as amendment for soil to improve its fertility. Soil was exposed to four concentrations of aloin (rich in HAP) for 0, 7, 14 and 28 days. Physico-chemical parameters were analyzed: soil Ph, organic matter (OM), nitrogen, phosphorus, and cation exchange capacity (CEC). The activity of seven enzymes implicated in the C, N and S cycles were measured. Microbial Biomass was determined by the method of substrate induced respiration. BiologEcoplates (Biolog Inc., Hayward, CA) were used to estimate soil microbial functional diversity. Our findings suggested a decrease on phosphorus and nitrogen content and an increase on CEC after aloin addition. Also, a decrease on microbial biomass and enzymes activities was observed, except for FDA. Ecoplates results demonstrate a decrease on microbial activities depending on the incubation time. Moreover, our results indicated that bacterial communities of the tested soils have more affinity to consume substrates as Amino acids and polymers. Our results should be carefully considered in view of the agriculture waists reuse for a sustainable agricultur

Adult neural stem cells and multiciliated ependymal cells share a common lineage regulated by the Geminin family members

Adult neural stem cells and multiciliated ependymalcells are glial cells essential for neurological func-tions. Together, they make up the adult neurogenicniche. Using both high-throughput clonal analysisand single-cell resolution of progenitor division pat-terns and fate, we show that these two componentsof the neurogenic niche are lineally related: adult neu-ral stem cells are sister cells to ependymal cells,whereas most ependymal cells arise from the termi-nal symmetric divisions of the lineage. Unexpectedly,we found that the antagonist regulators of DNA repli-cation, GemC1 and Geminin, can tune the proportionof neural stem cells and ependymal cells. Our find-ings reveal the controlled dynamic of the neurogenicniche ontogeny and identify the Geminin familymembers as key regulators of the initial pool of adultneural stem cells

A genetically encoded reporter of synaptic activity in vivo

To image synaptic activity within neural circuits, we tethered the genetically encoded calcium indicator (GECI) GCaMP2 to synaptic vesicles by fusion to synaptophysin. The resulting reporter, SyGCaMP2, detected the electrical activity of neurons with two advantages over existing cytoplasmic GECIs: it identified the locations of synapses and had a linear response over a wider range of spike frequencies. Simulations and experimental measurements indicated that linearity arises because SyGCaMP2 samples the brief calcium transient passing through the presynaptic compartment close to voltage-sensitive calcium channels rather than changes in bulk calcium concentration. In vivo imaging in zebrafish demonstrated that SyGCaMP2 can assess electrical activity in conventional synapses of spiking neurons in the optic tectum and graded voltage signals transmitted by ribbon synapses of retinal bipolar cells. Localizing a GECI to synaptic terminals provides a strategy for monitoring activity across large groups of neurons at the level of individual synapses

Ising Universality in Three Dimensions: A Monte Carlo Study

We investigate three Ising models on the simple cubic lattice by means of Monte Carlo methods and finite-size scaling. These models are the spin-1/2 Ising model with nearest-neighbor interactions, a spin-1/2 model with nearest-neighbor and third-neighbor interactions, and a spin-1 model with nearest-neighbor interactions. The results are in accurate agreement with the hypothesis of universality. Analysis of the finite-size scaling behavior reveals corrections beyond those caused by the leading irrelevant scaling field. We find that the correction-to-scaling amplitudes are strongly dependent on the introduction of further-neighbor interactions or a third spin state. In a spin-1 Ising model, these corrections appear to be very small. This is very helpful for the determination of the universal constants of the Ising model. The renormalization exponents of the Ising model are determined as y_t = 1.587 (2), y_h = 2.4815 (15) and y_i = -0.82 (6). The universal ratio Q = ^2/ is equal to 0.6233 (4) for periodic systems with cubic symmetry. The critical point of the nearest-neighbor spin-1/2 model is K_c=0.2216546 (10).Comment: 25 pages, uuencoded compressed PostScript file (to appear in Journal of Physics A