5,007 research outputs found

    Treatment for Landfill Leachate via Physicochemical Approaches: An Overview

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    Leachate waste consists of various mixtures of organic, inorganic, and heavy metal contaminants, which are responsible for groundwater and surface water contamination. Landfills apply physical, chemical, and biological processes for the treatment of leachate. Most studies on leachate treatment by coagulation and flocculation are based on the selection and performance of natural based biopolymers in comparison with various inorganic metal salts and grafted polymers used for the removal of contaminants. In addition, adsorption processes utilizing non-conventional activated carbons as absorbents are the current emerging focus of the researchers in leachate treatment. These adsorbents are low-in-cost, efficient, and renewable compared to conventional adsorbents. The present paper aimed to evaluate and review the technology utilising various greener approaches in coagulation, flocculation, and adsorption as the physicochemical approaches to leachate treatment. The challenges and future work regarding the development of these green products in the commercial markets were comprehensively evaluated. This work is licensed under a Creative Commons Attribution 4.0 International License

    Localized Excitons and Breaking of Chemical Bonds at III-V (110) Surfaces

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    Electron-hole excitations in the surface bands of GaAs(110) are analyzed using constrained density-functional theory calculations. The results show that Frenkel-type autolocalized excitons are formed. The excitons induce a local surface unrelaxation which results in a strong exciton-exciton attraction and makes complexes of two or three electron-hole pairs more favorable than separate excitons. In such microscopic exciton "droplets" the electron density is mainly concentrated in the dangling orbital of a surface Ga atom whereas the holes are distributed over the bonds of this atom to its As neighbors thus weakening the bonding to the substrate. This finding suggests the microscopic mechanism of a laser-induced emission of neutral Ga atoms from GaAs and GaP (110) surfaces.Comment: submitted to PRL, 10 pages, 4 figures available upon request from: [email protected]

    Spreading Width for Decay out of a Superdeformed Band

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    The attenuation factor F responsible for the decay out of a superdeformed (SD) band is calculated with the help of a statistical model. This factor is given by 1/F = (1 + Gamma(down) / Gamma(S)). Here, Gamma(S) is the width for the collective E2 transition within the superdeformed band, and Gamma(down) is the spreading width which describes the mixing between a state in the SD band and the normally deformed (ND) states of equal spin. The attenuation factor F is independent of the statistical E1 decay widths Gamma(N) of the ND states provided that the Gamma(N) are much larger than both Gamma(down) and Gamma(S). This condition is generically met. Previously measured values of F are used to determine Gamma(down).Comment: Submitted to Physical Review Letter

    A New Parameterization for the Lagrangian Density of Relativistic Mean Field Theory

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    A new parameterization for an effective non-linear Lagrangian density of relativistic mean field (RMF) theory is proposed, which is able to provide an excellent description not only for the properties of stable nuclei but also for those far from the valley of beta-stability. In addition recently measured superdeformed mimima in the Hg-region are reproduced with high accuracy.Comment: 8 pages, Latex, 1 ps figur

    The morphogenetic role of midline mesendoderm and ectoderm in the development of the forebrain and the midbrain of the mouse embryo

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    The anterior midline tissue (AML) of the late gastrula mouse embryo comprises the axial mesendoderm and the ventral neuroectoderm of the prospective forebrain, midbrain and rostral hindbrain. In this study, we have investigated the morphogenetic role of defined segments of the AML by testing their inductive and patterning activity and by assessing the impact of their ablation on the patterning of the neural tube at the early-somite-stage. Both rostral and caudal segments of the AML were found to induce neural gene activity in the host tissue; however, the de novo gene activity did not show any regional characteristic that might be correlated with the segmental origin of the AML. Removal of the rostral AML that contains the prechordal plate resulted in a truncation of the head accompanied by the loss of several forebrain markers. However, the remaining tissues reconstituted Gsc and Shh activity and expressed the ventral forebrain marker Nkx2.1. Furthermore, analysis of Gsc-deficient embryos reveals that the morphogenetic function of the rostral AML requires Gsc activity. Removal of the caudal AML led to a complete loss of midline molecular markers anterior to the 4th somite. In addition, Nkx2.1 expression was not detected in the ventral neural tube. The maintenance and function of the rostral AML therefore require inductive signals emanating from the caudal AML. Our results point to a role for AML in the refinement of the anteroposterior patterning and morphogenesis of the brain

    Spectroscopy of 194^{194}Po

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    Prompt, in-beam γ\gamma rays following the reaction 170^{170}Yb + 142 MeV 28^{28}Si were measured at the ATLAS facility using 10 Compton-suppressed Ge detectors and the Fragment Mass Analyzer. Transitions in 194^{194}Po were identified and placed using γ\gamma-ray singles and coincidence data gated on the mass of the evaporation residues. A level spectrum up to J\approx10\hbar was established. The structure of 194^{194}Po is more collective than that observed in the heavier polonium isotopes and indicates that the structure has started to evolve towards the more collective nature expected for deformed nuclei.Comment: 8 pages, revtex 3.0, 4 figs. available upon reques
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