Observation of correlations up to the micrometer scale in sliding charge-density waves

High-resolution coherent x-ray diffraction experiment has been performed on the charge density wave (CDW) system K$_{0.3}$MoO$_3$. The $2k_F$ satellite reflection associated with the CDW has been measured with respect to external dc currents. In the sliding regime, the $2k_F$ satellite reflection displays secondary satellites along the chain axis which corresponds to correlations up to the micrometer scale. This super long range order is 1500 times larger than the CDW period itself. This new type of electronic correlation seems inherent to the collective dynamics of electrons in charge density wave systems. Several scenarios are discussed.Comment: 4 pages, 3 figures Typos added, references remove

Le peuplement herpétologique d'un massif du Haut-Languedoc. 1 – Inventaire et répartition altitudinale des espèces

The amphibia and reptilia of a mountain range in Southern France (the north-eastern slope of "La Montagne Noire" in Languedoc) have been studied for three consecutive years. The community consists of seven amphibian species, six lizard species and nine snake species. The altitudinal distribution of each species is discussed particularly that of Coluber viridiflavus, Coronella girondica and Malpodon m. monspessulanus, whose altitudinal limits in the area studied differ from what is commonly observed elsewhere in Europe. Species richness is high for such a small study are a (ca 70 km2) ; however, it decreases as altitude increases. The Shannon Weaver index reaches its highest value at an altitude of 500 to 600 m. The occurence of melanism increases with altitud

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

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

Coherent X-ray Scattering from Manganite Charge and Orbital Domains

We report coherent x-ray scattering studies of charge and orbital domains in manganite systems. The experiments were carried out on LaMnO_3 and Pr_{0.6}Ca_{0.4}MnO_3, with the incident photon energy tuned near the Mn K edge. At room temperature, the orbital speckle pattern of LaMnO_3 was observed to be constant over a timescale of at least minutes, which is indicative of static orbital domains on this timescale. For Pr_{0.6}Ca_{0.4}MnO_3, both charge and orbital speckle patterns were observed. The observation of the latter rules out the presence of fast orbital fluctuations, while long time series data-- on the order of several minutes-- were suggestive of slow dynamic behavior. In contrast, the charge order speckle patterns were static.Comment: 6 pages, 4 figure

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

Developmental bias in cleavage-stage mouse blastomeres

BACKGROUND: The cleavage-stage mouse embryo is composed of superficially equivalent blastomeres that will generate both the embryonic inner cell mass (ICM) and the supportive trophectoderm (TE). However, it remains unsettled whether the contribution of each blastomere to these two lineages can be accounted for by chance. Addressing the question of blastomere cell fate may be of practical importance, because preimplantation genetic diagnosis requires removal of blastomeres from the early human embryo. To determine whether blastomere allocation to the two earliest lineages is random, we developed and utilized a recombination-mediated, noninvasive combinatorial fluorescent labeling method for embryonic lineage tracing. RESULTS: When we induced recombination at cleavage stages, we observed a statistically significant bias in the contribution of the resulting labeled clones to the trophectoderm or the inner cell mass in a subset of embryos. Surprisingly, we did not find a correlation between localization of clones in the embryonic and abembryonic hemispheres of the late blastocyst and their allocation to the TE and ICM, suggesting that TE-ICM bias arises separately from embryonic-abembryonic bias. Rainbow lineage tracing also allowed us to demonstrate that the bias observed in the blastocyst persists into postimplantation stages and therefore has relevance for subsequent development. CONCLUSIONS: The Rainbow transgenic mice that we describe here have allowed us to detect lineage-dependent bias in early development. They should also enable assessment of the developmental equivalence of mammalian progenitor cells in a variety of tissues

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

Multicolor Brainbow Imaging in Zebrafish

This protocol describes how to use the Brainbow strategy to label neurons in many different hues. The Brainbow system uses a random Cre/lox recombination to create varied combinations of red, blue, and green fluorescent proteins in each cell. The differences in color allow users to follow multiple cells, regardless of how closely they are positioned. This protocol describes how to use Brainbow imaging in zebrafish and provides examples of how to use color as a guide to trace axonal processes. We use the zebrafish trigeminal sensory ganglion as an example and discuss potential modifications for the general use of this technique.Molecular and Cellular Biolog