Si-induced superconductivity and structural transformations in DyRh4B4

DyRh4B4 has been known to crystallize in the primitive tetragonal (pt)-structure and to exhibit a ferromagnetic transition at 12 K, the highest magnetic transition temperature in the entire series of the RRh4B4 materials [1]. We show here that our silicon-added samples of the nominal composition DyRh4B4Si0.2 exhibit superconductivity below Tc ~ 4.5 K and an antiferromagnetic transition below TN ~ 2.7 K. The 12 K transition observed in the pt-DyRh4B4 is completely suppressed. Our annealed samples mainly consist of domains of the chemical composition DyRh3.9B4.2Si0.08. These domains contain two crystallographic phases belonging to the body-centred tetragonal (bct)-structure and the orthorhombic (o)-structure. We have reasons to suggest that superconductivity and antiferromagnetic ordering arise from bct- DyRh4B4 phase and, therefore, coexist below TN ~ 2.7 K.Comment: 11 pages, 6 figures, Accepted for publication in Journal of Alloys and Compound

Friedmann limits of rotating hypersurface-homogeneous dust models

The existence of Friedmann limits is systematically investigated for all the hypersurface-homogeneous rotating dust models, presented in previous papers by this author. Limiting transitions that involve a change of the Bianchi type are included. Except for stationary models that obviously do not allow it, the Friedmann limit expected for a given Bianchi type exists in all cases. Each of the 3 Friedmann models has parents in the rotating class; the k = +1 model has just one parent class, the other two each have several parent classes. The type IX class is the one investigated in 1951 by Goedel. For each model, the consecutive limits of zero rotation, zero tilt, zero shear and spatial isotropy are explicitly calculated.Comment: 39 pages, LaTeX, 1 postscript figure. Subjects: General relativity, exact solutions, cosmolog

Noncanonical, Dopamine-Dependent Long-Term Potentiation at Hippocampal Output Synapses in a Rodent Model of First-Episode Psychosis

Cognitive deficits and positive symptoms in schizophrenia have both been linked to hippocampal dysfunction. Recently, subregion-specific aberrant and maladaptive hippocampal synaptic plasticity has been suggested as one of the mechanistic underpinnings. The subiculum is the final output hub of the hippocampus and orchestrates hippocampal information transfer to other brain regions. While most CA1 pyramidal neurons show regular-spiking behavior, subicular output neurons comprise bursting and regular-firing pyramidal cells. These two cell types target different brain regions and express unique forms of synaptic plasticity. Here, we used a single systemic application of the noncompetitive glutamatergic N-methyl-D-aspartate receptor (NMDAR) antagonist MK-801 to model first-episode psychosis in rats and studied long-term potentiation (LTP) in subicular regular-firing cells in acute hippocampal slices. Previously, we have reported a facilitation of a presynaptic, late-onset LTP in subicular bursting pyramidal cells after systemic NMDAR antagonism. Here, we show that single systemic NMDAR antagonist application also facilitates the induction of a noncanonical, but postsynaptic NMDAR-independent LTP in ventral subicular but not in CA1 regular-firing pyramidal cells. This form of LTP was dependent on D1/D5 dopamine receptor activation. Activation of D1/D5 dopamine receptors by a specific agonist mimicked and occluded LTP induced by electrical high-frequency stimulation (HFS). Furthermore, our results indicate that this form of LTP relies on postsynaptic Ca2+ signaling and requires the activation of protein kinase A. Considering the pivotal role of the subiculum as information gatekeeper between the hippocampus and other brain regions, this aberrant LTP in ventral subicular regular-firing neurons is expected to interfere with physiological hippocampal output processing and might thereby contribute to hippocampal dysfunction in psychotic events

Magnetic anomalies in single crystalline ErPd2Si2

Considering certain interesting features in the previously reported 166Er Moessbauer effect and neutron diffraction data on the polycrystalline form of ErPd2Si2 crystallizing in ThCr2Si2-type tetragonal structure, we have carried out magnetic measurements (1.8 to 300 K) on the single crystalline form of this compound. We observe significant anisotropy in the absolute values of magnetization (indicating that the easy axis is c-axis) as well as in the features due to magnetic ordering in the plot of magnetic susceptibility (chi) versus temperature (T) at low temperatures. The chi(T) data reveal that there is a pseudo-low dimensional magnetic order setting in at 4.8 K, with a three-dimensional antiferromagnetic ordering setting in at a lower temperature (3.8 K). A new finding in the chi(T) data is that, for H//, but not for H//, there is a broad shoulder in the range 8-20 K, indicative of the existence of magnetic correlations above 5 K as well, which could be related to the previously reported slow-relaxation-dominated Moessbauer spectra. Interestingly, the temperature coefficient of electrical resistivity is found to be isotropic; no feature due to magnetic ordering could be detected in the electrical resistivity data at low temperatures, which is attributed to magnetic Brillioun-zone boundary gap effects. The results reveal complex nature of the magnetism of this compound

An Overview of the Rotational Behavior of Metal--Poor Stars

The present paper describes the behavior of the rotational velocity in metal--poor stars ([Fe/H]<-0.5 dex) in different evolutionary stages, based on Vsini values from the literature. Our sample is comprised of stars in the field and some Galactic globular clusters, including stars on the main sequence, the red giant branch (RGB), and the horizontal branch (HB). The metal--poor stars are, mainly, slow rotators, and their Vsini distribution along the HR diagram is quite homogeneous. Nevertheless, a few moderate to high values of Vsini are found in stars located on the main sequence and on the HB. We show that the overall distribution of Vsini values is basically independent of metallicity for the stars in our sample. In particular, the fast-rotating main sequence stars in our sample present similar rotation rates as their metal-rich counterparts, suggesting that some of them may actually be fairly young, in spite of their low metallicity, or else that at least some of them would be better classified as blue straggler stars. We do not find significant evidence of evolution in Vsini values as a function of position on the RGB; in particular, we do not confirm previous suggestions that stars close to the RGB tip rotate faster than their less evolved counterparts. While the presence of fast rotators among moderately cool blue HB stars has been suggested to be due to angular momentum transport from a stellar core that has retained significant angular momentum during its prior evolution, we find that any such transport mechanisms must likely operate very fast as the star arrives on the zero-age HB (ZAHB), since we do not find a link between evolution off the ZAHB and Vsini values. We present an extensive tabulation of all quantities discussed in this paper, including rotation velocities, temperatures, gravitieComment: 22 pages, 10 figure

Effect of Time-of-Flight and Regularized Reconstructions on Quantitative Measurements and Qualitative Assessments in Newly Diagnosed Prostate Cancer With 18F-Fluorocholine Dual Time Point PET/MRI.

Recent technical advances in positron emission tomography/magnetic resonance imaging (PET/MRI) technology allow much improved time-of-flight (TOF) and regularized iterative PET reconstruction regularized iterative reconstruction (RIR) algorithms. We evaluated the effect of TOF and RIR on standardized uptake values (maximum and peak SUV [SUVmax and SUVpeak]) and their metabolic tumor volume dependencies and visual image quality for 18F-fluorocholine PET/MRI in patients with newly diagnosed prostate cancer. Fourteen patients were administered with 3 MBq/kg of 18F-fluorocholine and scanned dynamically for 30 minutes. Positron emission tomography images were divided to early and late time points (1-6 minutes summed and 7-30 minutes summed). The values of the different SUVs were documented for dominant PET-avid lesions, and metabolic tumor volume was estimated using a 50% isocontour and SUV threshold of 2.5. Image quality was assessed via visual acuity scoring (VAS). We found that incorporation of TOF or RIR increased lesion SUVs. The lesion to background ratio was not improved by TOF reconstruction, while RIR improved the lesion to background ratio significantly ( P &lt; .05). The values of the different VAS were all significantly higher ( P &lt; .05) for RIR images over TOF, RIR over non-TOF, and TOF over non-TOF. In conclusion, our data indicate that TOF or RIR should be incorporated into current protocols when available

Multiscale blind source separation.

We provide a new methodology for statistical recovery of single linear mixtures of piecewise constant signals (sources) with unknown mixing weights and change points in a multiscale fashion. We show exact recovery within an epsilon-neighborhood of the mixture when the sources take only values in a known finite alphabet. Based on this we provide the SLAM (Separates Linear Alphabet Mixtures) estimators for the mixing weights and sources. For Gaussian error, we obtain uniform confidence sets and optimal rates (up to log-factors) for all quantities. SLAM is efficiently computed as a nonconvex optimization problem by a dynamic program tailored to the finite alphabet assumption. Its performance is investigated in a simulation study. Finally, it is applied to assign copy-number aberrations from genetic sequencing data to different clones and to estimate their proportions

Electron-Phonon Coupling Origin of the resistivity in YNi_{2}B_{2}C Single Crystals

Resistivity measurements from 4.2 K up to 300 K were made on YNi_{2}B_{2}C single crystals with Tc=15.5 K. The resulting rho(T) curve shows a perfect Bloch-Grueneisen (BG) behavior, with a very small residual resistivity which indicates the low impurity content and the high cristallographic quality of the samples. The value lambda_{tr}=0.53 for the transport electron-phonon coupling constant was obtained by using the high-temperature constant value of d(rho)/dT and the plasma frequency reported in literature. The BG expression for the phononic part of the resistivity rho_{ph}(T) was then used to fit the data in the whole temperature range, by approximating alpha^{2}_{tr}F(Omega) with the experimental phonon spectral density G(Omega) multiplied by a two-step weighting function to be determined by the fit. The resulting fitting curve perfectly agrees with the experimental points. We also solved the real-axis Eliashberg equations in both s- and d-wave symmetries under the approximation alpha^{2}F(Omega)= alpha^{2}_{tr}F(Omega). We found that the value of lambda_{tr} here determined in single-band approximation is quite compatible with Tc and the gap Delta experimentally observed. Finally, we calculated the normalized tunneling conductance, whose comparison with break-junction tunnel data gives indication of the possible s-wave symmetry for the order parameter in YNi_{2}B_{2}C.Comment: 6 pages, 5 figures. Proceedings of SATT10 Conference, to be published in Int. J. Mod. Phys.

Ballistic heat transport of quantum spin excitations as seen in SrCuO2

Fundamental conservation laws predict ballistic, i.e., dissipationless transport behaviour in one-dimensional quantum magnets. Experimental evidence, however, for such anomalous transport has been lacking ever since. Here we provide experimental evidence for ballistic heat transport in a S=1/2 Heisenberg chain. In particular, we investigate high purity samples of the chain cuprate SrCuO2 and observe a huge magnetic heat conductivity $\kappa_{mag}$. An extremely large spinon mean free path of more than a micrometer demonstrates that $\kappa_{mag}$ is only limited by extrinsic scattering processes which is a clear signature of ballistic transport in the underlying spin model

Automated hippocampal segmentation in patients with epilepsy: Available free online

Hippocampal sclerosis, a common cause of refractory focal epilepsy, requires hippocampal volumetry for accurate diagnosis and surgical planning. Manual segmentation is time-consuming and subject to interrater/intrarater variability. Automated algorithms perform poorly in patients with temporal lobe epilepsy. We validate and make freely available online a novel automated method