Selective Spin-State Switch and Metal-Insulator Transition in \boldmath GdBaCo2O5.5\rm GdBaCo_2O_{5.5}

Ultra-high resolution synchrotron diffraction data for $\rm GdBaCo_2O_{5.5}$ throw new light on the metal-insulator transition of Co$^{3+}$ Ba-cobaltites. An anomalous expansion of CoO$_6$ octahedra is observed at the phase transition on heating, while CoO$_5$ pyramids show the normal shrinking at the closing of the gap. The insulator-to-metal transition is attributed to a sudden excitation of some electrons in the octahedra ($t_{2g}^6$ state) into the Co $e_g$ band (final $t_{2g}^4e_g^2$ state). The $t_{2g}^5e_g^1$ state in the pyramids does not change and the structural study also rules out a $d_{3x^2-r^2}/d_{3y^2-r^2}$ orbital ordering at $T_{MI}$.Comment: Phys. Rev. B (to appear

Overview of optical remote sensing of marine oil spills and hydrocarbon seepage

The remote detection and quantification of oil spills and hydrocarbon seepage represent a key research direction in marine environment monitoring and resource management. Passive optical remote sensing using sunlight has been used for several decades, and significant progress has been made in recent years. It exhibits the following characteristics.(1)The optical detection and classification of oil spills and hydrocarbon seepage are based on their different optical properties from oil-free water. These properties include oil slicks of different thicknesses, oil-water mixture(i.e., oil emulsion of different concentrations), thick floating oil, and thin oil slicks, and hydrocarbon gas from seabed hydrocarbon seepage. (2) These different oil and hydrocarbon forms undergo different optical processes when interacting with light because they can reflect, absorb, and scatter the incident light, resulting in different levels of optical contrast from surrounding oil-free water and thus providing a theoretical basis for their detection, classification, and quantification through optical remote sensing. (3) The Fresnel reflection of different surfaces, such as oil-free water or oiled surfaces with different refractive indexes and roughness, helps detection but presents challenges on classification and quantification. This paper provides a brief review of the characteristics of marine oil spills and hydrocarbon seepage in their various forms, and discusses the advantages and challenges in their optical detection and quantification. Many space borne and airborne multi/hyper-spectral or multi-angle optical sensors, such as MODIS, MERIS, AVIRIS, MISR, Hyperion, and Landsat, have been used to detect, quantify, and map oil spills or natural seepage, as shown in the most recent oil spill disasters and natural seepage estimates in the Gulf of Mexico. In these applications, lab-based experimental results provide optical models and key parameters to improve the quantification of surface oil from remote sensing images. Environmental conditions, such as sea state and solar/viewing geometry from a real spill case, can be dramatically different from those in the lab experiments. Thus, applying lab-based results to aquatic environments becomes technically challenging. Significant process has been made in understanding the oil-water spatial and spectral contrasts of these different oil forms under different environmental conditions. However, some key issues still need to be investigated further. These issues include sensor capability (i.e., spectral, spatial, and radiometric resolutions), relationship between spectral/spatial oil-water contrast and oil type and thickness, and optical models for improved detection and quantification at various scales. The fundamental difficulty in determining oil thickness or volume in the field needs to be overcome to refine lab-based models and validate remote sensing estimates. Nevertheless, optical remote sensing is expected to make continuous progress to eventually overcome these challenges and thereby play an increasingly important role in assessing marine oil spills and hydrocarbon seepage

Long-range angular correlations on the near and away side in p-Pb collisions at root S-NN=5.02 TeV

Angular correlations between charged trigger and associated particles are measured by the ALICE detector in p-Pb collisions at a nucleon-nucleon centre-of-mass energy of 5.02 TeV for transverse momentum ranges within 0.5 < P-T,P-assoc < P-T,P-trig < 4 GeV/c. The correlations are measured over two units of pseudorapidity and full azimuthal angle in different intervals of event multiplicity, and expressed as associated yield per trigger particle. Two long-range ridge-like structures, one on the near side and one on the away side, are observed when the per-trigger yield obtained in low-multiplicity events is subtracted from the one in high-multiplicity events. The excess on the near-side is qualitatively similar to that recently reported by the CMS Collaboration, while the excess on the away-side is reported for the first time. The two-ridge structure projected onto azimuthal angle is quantified with the second and third Fourier coefficients as well as by near-side and away-side yields and widths. The yields on the near side and on the away side are equal within the uncertainties for all studied event multiplicity and p(T) bins, and the widths show no significant evolution with event multiplicity or p(T). These findings suggest that the near-side ridge is accompanied by an essentially identical away-side ridge. (c) 2013 CERN. Published by Elsevier B.V. All rights reserved

Production of charged pions, kaons and protons at large transverse momenta in pp and Pb–Pb collisions at s

Transverse momentum spectra of pi(+/-), K-+/- and p((p) over bar) up to p(T) = 20 GeV/c at mid-rapidity in pp, peripheral (60-80%) and central (0-5%) Pb-Pb collisions at v root s(NN) = 2.76 TeV have been measured using the ALICE detector at the Large Hadron Collider. The proton-to-pion and the kaon-to-pionratios both show a distinct peak at p(T) approximate to 3 GeV/c in central Pb-Pb collisions. Below the peak, p(T) 10 GeV/c particle ratios in pp and Pb-Pb collisions are in agreement and the nuclear modification factors for pi(+/-), K-+/- and p((p) over bar) indicate that, within the systematic and statistical uncertainties, the suppression is the same. This suggests that the chemical composition of leading particles from jets in the medium is similar to that of vacuum jets

Production of charged pions, kaons and protons at large transverse momenta in pp and Pb–Pb collisions at sNN=2.76\sqrt{s_{NN}}=2.76 TeV

Transverse momentum spectra of pi(+/-), K-+/- and p((p) over bar) up to p(T) = 20 GeV/c at mid-rapidity in pp, peripheral (60-80%) and central (0-5%) Pb-Pb collisions at v root s(NN) = 2.76 TeV have been measured using the ALICE detector at the Large Hadron Collider. The proton-to-pion and the kaon-to-pionratios both show a distinct peak at p(T) approximate to 3 GeV/c in central Pb-Pb collisions. Below the peak, p(T) 10 GeV/c particle ratios in pp and Pb-Pb collisions are in agreement and the nuclear modification factors for pi(+/-), K-+/- and p((p) over bar) indicate that, within the systematic and statistical uncertainties, the suppression is the same. This suggests that the chemical composition of leading particles from jets in the medium is similar to that of vacuum jets

Production of charged pions, kaons and protons at large transverse momenta in pp and Pb–Pb collisions at sNN=2.76\sqrt{s_{NN}}=2.76 TeV

Transverse momentum spectra of pi(+/-), K-+/- and p((p) over bar) up to p(T) = 20 GeV/c at mid-rapidity in pp, peripheral (60-80%) and central (0-5%) Pb-Pb collisions at v root s(NN) = 2.76 TeV have been measured using the ALICE detector at the Large Hadron Collider. The proton-to-pion and the kaon-to-pionratios both show a distinct peak at p(T) approximate to 3 GeV/c in central Pb-Pb collisions. Below the peak, p(T) 10 GeV/c particle ratios in pp and Pb-Pb collisions are in agreement and the nuclear modification factors for pi(+/-), K-+/- and p((p) over bar) indicate that, within the systematic and statistical uncertainties, the suppression is the same. This suggests that the chemical composition of leading particles from jets in the medium is similar to that of vacuum jets