Magnetotransport in Sr3PbO antiperovskite with three-dimensional massive Dirac electrons

Novel topological phenomena are anticipated for three-dimensional (3D) Dirac electrons. The magnetotransport properties of cubic ${\rm Sr_{3}PbO}$ antiperovskite, theoretically proposed to be a 3D massive Dirac electron system, are studied. The measurements of Shubnikov-de Haas oscillations and Hall resistivity indicate the presence of a low density ($\sim 1 \times 10^{18}$ ${\rm cm^{-3}}$) of holes with an extremely small cyclotron mass of 0.01-0.06$m_{e}$. The magnetoresistance $\Delta\rho_{xx}(B)$ is linear in magnetic field $B$ with the magnitude independent of temperature. These results are fully consistent with the presence of 3D massive Dirac electrons in ${\rm Sr_{3}PbO}$. The chemical flexibility of the antiperovskites and our findings in the family member, ${\rm Sr_{3}PbO}$, point to their potential as a model system in which to explore exotic topological phases

Model-independent test of gravity with a network of ground-based gravitational-wave detectors

The observation of gravitational waves with a global network of interferometric detectors such as advanced LIGO, advanced Virgo, and KAGRA will make it possible to probe into the nature of space-time structure. Besides Einstein's general theory of relativity, there are several theories of gravitation that passed experimental tests so far. The gravitational-wave observation provides a new experimental test of alternative theories of gravity because a gravitational wave may have at most six independent modes of polarization, of which properties and number of modes are dependent on theories of gravity. This paper proposes a method to reconstruct the independent modes of polarization in time-series data of an advanced detector network. Since the method does not rely on any specific model, it gives model-independent test of alternative theories of gravity

Preparaciones de base líquida vs. citología convencional: adecuación de las muestras y coincidencia de diagnóstico en lesiones orales

Objetivo: Comparar la efectividad de la muestra y la coincidencia de diagnostico entre preparaciones de base liquida y frotis convencionales en lesiones orales, y probar la viabilidad de la prueba inmuno-citoquimica en preparaciones de base liquida de lesiones de carcinoma oral. Material y Metodos: Se obtuvieron muestras de 44 pacientes. Primeramente se prepararon frotis convencionales, usando un dispositivo cytobrush. A continuacion se sumergio el cepillo que contenia el material residual en un liquido conservante. La muestra en el mismo fue procesada de acuerdo con las indicaciones del fabricante (AutoCyte, Inc. Elon College, North Carolina, USA). Se tineron preparaciones de ambas tecnicas de acuerdo con el metodo de Papanicolaou. Para la prueba inmuno-citoquimica se usaron conjuntamente AE1/AE3 (Dako, CA, USA) para las lesiones de carcinoma oral, de acuerdo con el metodo de la Estreptovidina-biotina-peroxidasa. Se uso la prueba exacta de Fisher; fijandose la probabilidad significativa en p . 0.05. Resultados: Ambas tecnicas coincidieron en el diagnostico citologico en todos los casos donde se uso una muestra adecuada; en 3 casos el frotis convencional mostro hipocelularidad y, por lo tanto, resulto inadecuado para el analisis. En el analisis de muestras, la citologia de base liquida mostro una mejora general estadisticamente significativa), de un 41% en espesura de frotis y de un 66% en la distribucion de celulas (p . 0.05), ademas de una reduccion en la superposicion de celulas y la presencia de sangre (p . 0.05). La morfologia celular se observó mejor en las preparaciones de base líquida. Las reacciones de la prueba inmuno-citoquímica fueron positivas en todos los casos de malignidad, siendo especialmente clara la observación de células inmuno-marcadas. Conclusión: Tanto las preparaciones de base líquida como los frotis convencionales son dignos de confianza desde el punto de vista del diagnóstico; el método de base líquida mostró una mejora general en la preservación de muestras, adecuación de ejemplares, observación de morfología celular y reproducibilidad.Objective: To compare specimen adequacy and diagnostic agreement between liquid-based preparations and conventional smears in oral lesions, and to test the viability of immunocytochemical assay in liquid-based preparations from oral carcinoma lesions. Material and Methods: Samples were collected from 44 patients. Conventional smears were prepared first, using a cytobrush device. Then the brush, containing the residual material, was immersed in a preservative fluid. The sample in the preservative fluid was processed according to the manufacturer directions (AutoCyte, Inc. Elon College, North Carolina, USA). Slides of both techniques were stained by Papanicolaou method. For immunocytochemical assay, a cytokeratin pool AE1/AE3 (Dako, CA, USA) was applied in liquid-based preparations from oral carcinoma lesions following the Streptavidin-biotinperoxidase method. Fisher's exact test was used; significance was set for p = 0.05. Results: Both techniques agreed on cytologic diagnosis in every case they yielded an adequate specimen; in 3 cases conventional smear resulted in hypocellularity and therefore inadequate for analysis. On specimen analysis, the liquid-based cytology demonstrated a statistically significant, 41% overall improvement in smear thickness and 66% in cell distribution (p = 0.05), and a reduction in cell overlapping and presence of blood (p = 0.05). The cell morphology was better visualized in the liquid-based preparations. The immunocytochemical assay reactions were positive in all malignant cases, the visualization of the immu-nostained cells being especially clear. Conclusion: Both, the liquid-based preparation and conventional smear, are diagnostically reliable; the liquid-based method showed an overall improvement on sample preservation, specimen adequacy, visualization of cell morphology and reproducibility

The hydration structure of Cu2+: More tetrahedral than octahedral?

A comprehensive multi-technique approach has been used to address the controversial question of the preferred geometric form of the Cu2+ aqua-ion hydration shell. A combination of H/D isotopic substitution neutron scattering and X-ray scattering has been used to refine atomistic models of 0.5 m and 2.0 m solutions of Cu(ClO4)2, that have also been constrained to simultaneously reproduce detailed local structure information about the cation environment obtained by X-ray Absorption spectroscopy. The adoption of the Empirical Potential Structure Refinement (EPSR) technique as a single unified analytical framework minimises the chances for biasing the result in favour of a specific pre-conceived outcome. The results are consistent with an average coordination for each Cu2+ ion of 4.5 ± 0.6 water molecules that matches the more recent picture of five-fold coordination in a 2.0 m solution, but interestingly this combined study highlights that the preferred local geometry of the ion sites is found to have a mixed character of tetrahedral, trigonal bipyramidal and octahedral components. A further point to note is that this new model adds support to a largely ignored result in the literature relating to the linear electric field effect induced g-shifts observed in the electron paramagnetic resonance spectra of glassy Cu2+ complexes (Peisach and Mims, Chem. Phys. Lett., 1976, 37, 307–310) that first highlighted the importance of tetrahedral distortions in the cation's hydration shell structure

Searches for gravitational waves associated with pulsar glitches using a coherent network algorithm

Pulsar glitches are a potential source of gravitational waves for current and future interferometric gravitational wave detectors. Some pulsar glitch events were observed by radio and X-ray telescopes during the fifth LIGO science run. It is expected that glitches from these same pulsars should also be seen in the future. We carried out Monte Carlo simulations to estimate the sensitivity of possible gravitational wave signals associated with a pulsar glitch using a coherent network analysis method. We show the detection efficiency and evaluate the reconstruction accuracy of gravitational waveforms using a matched filter analysis on the estimated gravitational waveforms from the coherent analysis algorithm.Comment: submitted to CQ

Inverse-perovskites A3BO (A = Sr, Ca, Eu/B = Pb, Sn) : a platform for control of Dirac and Weyl fermions

This work was partly supported by the Japan Society for the Promotion of Science (JSPS) KAKENHI (Grant Nos. 24224010, 15K13523, JP15H05852, JP15K21717, and 17H01140), EPSRC (Grant No. EP/P024564/1), and the Alexander von Humboldt FoundationBulk Dirac electron systems have attracted strong interest for their unique magnetoelectric properties as well as their close relation to topological (crystalline) insulators. Recently, the focus has been shifting toward the role of magnetism in stabilizing Weyl fermions as well as chiral surface states in such materials. While a number of nonmagnetic systems are well known, experimental realizations of magnetic analogs are a key focus of current studies. Here, we report on the physical properties of a large family of inverse perovskites A3BO (A = Sr, Ca, Eu/B = Pb, Sn) in which we are able to not only stabilize 3D Dirac electrons at the Fermi energy but also chemically control their properties. In particular, it is possible to introduce a controllable Dirac gap, change the Fermi velocity, tune the anisotropy of the Dirac dispersion, and—crucially—introduce complex magnetism into the system. This family of compounds therefore opens up unique possibilities for the chemical control and systematic investigation of the fascinating properties of such topological semimetals.Publisher PDFPeer reviewe

Extracting structural information of Au colloids at ultra-dilute concentrations: Identification of growth during nanoparticle immobilization

Sol-immobilization is increasingly used to achieve supported metal nanoparticles (NPs) with controllable size and shape; it affords a high degree of control of the metal particle size and yields a narrow particle size distribution. Using state-of-the-art beamlines, we demonstrate how X-ray absorption fine structure (XAFS) techniques are now able to provide accurate structural information on nano-sized colloidal Au solutions at mM concentrations. This study demonstrates: (i) the size of Au colloids can be accurately tuned by adjusting the temperature of reduction, (ii) Au concentration, from 50 mM to 1000 mM, has little influence on the average size of colloidal Au NPs in solution and (iii) the immobilization step is responsible for significant growth in Au particle size, which is further exacerbated at increased Au concentrations. The work presented demonstrates that an increased understanding of the primary steps in sol-immobilization allows improved optimization of materials for catalytic application