3,027 research outputs found

    Neutron diffraction and Raman studies of the incorporation of sulfate in silicate glasses

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    The oxidation state, coordination and local environment of sulphur in alkali silicate (R2O-SiO2; R= Na, Li) and alkali-alkaline earth silicate (Na2O-MO-SiO2; M= Ca, Ba) glasses have been investigated using neutron diffraction and Raman spectroscopy. With analyses of both the individual total neutron correlation functions, and of suitable doped-undoped differences, the S-O bonds and (O-O)S correlations were clearly isolated from the other overlapping correlations due to Si-O and (O-O)Si distances in the SiO4 tetrahedra, and the modifier-oxygen (R-O and M-O) distances. Clear evidence was obtained that the sulphur is present as SO4 2- groups, confirmed by the observation in the Raman spectra of the symmetric S-O stretch mode of SO4 2- groups. The modifier-oxygen bond length distributions were deconvoluted from the neutron correlation functions by fitting. The Na-O and Li-O bond length distributions were clearly asymmetric, whereas no evidence was obtained for asymmetry of the Ca-O and Ba-O distributions. A consideration of the bonding shows that the oxygen atoms in the SO4 2- groups do not participate in the silicate network, and as such constitute a third type of oxygen, ‘non-network oxygen’, in addition to the bridging and non-bridging oxygens that are bonded to silicon atoms. Thus each individual sulphate group is surrounded by a shell of modifier, and is not connected directly to the silicate network. The addition of SO3 to the glass leads to a conversion of oxygen atoms within the silicate network from non-bridging to bridging, so that there is a repolymerisation of the silicate network. There is evidence that SO3 doping leads to changes in the form of the distribution of Na-O bond lengths, with a reduction in the fitted short bond coordination number, and an increase in the fitted long bond coordination number, and this is consistent with a repolymerisation of the silicate network. In contrast, there is no evidence that SO3 doping leads to a change in the distribution of Li-O bond lengths, with a total Li-O coordination number consistently in excess of four

    Matched Filtering of Numerical Relativity Templates of Spinning Binary Black Holes

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    Tremendous progress has been made towards the solution of the binary-black-hole problem in numerical relativity. The waveforms produced by numerical relativity will play a role in gravitational wave detection as either test-beds for analytic template banks or as template banks themselves. As the parameter space explored by numerical relativity expands, the importance of quantifying the effect that each parameter has on first the detection of gravitational waves and then the parameter estimation of their sources increases. In light of this, we present a study of equal-mass, spinning binary-black-hole evolutions through matched filtering techniques commonly used in data analysis. We study how the match between two numerical waveforms varies with numerical resolution, initial angular momentum of the black holes and the inclination angle between the source and the detector. This study is limited by the fact that the spinning black-hole-binaries are oriented axially and the waveforms only contain approximately two and a half orbits before merger. We find that for detection purposes, spinning black holes require the inclusion of the higher harmonics in addition to the dominant mode, a condition that becomes more important as the black-hole-spins increase. In addition, we conduct a preliminary investigation of how well a template of fixed spin and inclination angle can detect target templates of arbitrary spin and inclination for the axial case considered here

    Quid Pro Quo: Builders, Politicians, and Election Finance in India- Working Paper 276

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    In developing countries where elections are costly and accountability mechanisms weak, politicians often turn to illicit means of financing campaigns. This paper examines one such channel of illicit campaign finance: India’s real estate sector. Politicians and builders allegedly engage in a quid pro quo, whereby the former park their illicit assets with the latter, and the latter rely on the former for favorable dispensation. At election time, however, builders need to re-route funds to politicians as a form of indirect election finance. One observable implication is that the demand for cement, the indispensible raw material used in the sector, should contract during elections since builders need to inject funds into campaigns. Using a novel monthly-level data set, we demonstrate that cement consumption does exhibit a political business cycle consistent with our hypothesis. Additional tests provide confidence in the robustness and interpretation of our findings.elections, election finance, corruption, political economy, India

    Modi's Reform Agenda: Change You Can Believe In? Asia Policy Brief 2015/04, November 2015

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    Indian Prime Minister Narendra Modi entered office with a historic political mandate. For the first time in thirty years, a single party won a majority of seats in the lower house of Parliament (Lok Sabha). However, Modi faces skyhigh expectations to fulfill his campaign promises of getting India’s economy back on track. Eighteen months into his government’s term and in the wake of electoral defeats in the states of Delhi and Bihar, questions are being raised about its economic performance. While the Modi government has stabilized India’s macroeconomy and announced a series of incremental economic reforms, more sweeping changes have fallen victim to India’s nettlesome domestic politics, including roadblocks within the ruling alliance

    Intrinsic selection biases of ground-based gravitational wave searches for high-mass BH-BH mergers

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    The next generation of ground-based gravitational wave detectors may detect a few mergers of comparable-mass M\simeq 100-1000 Msun ("intermediate-mass'', or IMBH) spinning black holes. Black hole spin is known to have a significant impact on the orbit, merger signal, and post-merger ringdown of any binary with non-negligible spin. In particular, the detection volume for spinning binaries depends significantly on the component black hole spins. We provide a fit to the single-detector and isotropic-network detection volume versus (total) mass and arbitrary spin for equal-mass binaries. Our analysis assumes matched filtering to all significant available waveform power (up to l=6 available for fitting, but only l<= 4 significant) estimated by an array of 64 numerical simulations with component spins as large as S_{1,2}/M^2 <= 0.8. We provide a spin-dependent estimate of our uncertainty, up to S_{1,2}/M^2 <= 1. For the initial (advanced) LIGO detector, our fits are reliable for M[100,500]MM\in[100,500]M_\odot (M[100,1600]MM\in[100,1600]M_\odot). In the online version of this article, we also provide fits assuming incomplete information, such as the neglect of higher-order harmonics. We briefly discuss how a strong selection bias towards aligned spins influences the interpretation of future gravitational wave detections of IMBH-IMBH mergers.Comment: 18 pages, 15 figures, accepted by PRD. v2 is version accepted for publication, including minor changes in response to referee feedback and updated citation

    Topological Insulators and Metals in Atomic Optical Lattices

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    We propose the realization of topological quantum states with cold atoms trapped in an optical lattice. We discuss an experimental setup that generates a two-dimensional hexagonal lattice in the presence of a light-induced periodic vector potential, which represents a realization of the Haldane model with cold atoms. We determine theoretically the conditions necessary for observing the topological states and show that two of the key conditions are: 1) the realization of sharp boundaries and 2) the minimization of any smoothly varying component of the confining potential. We argue that, unlike their condensed matter counterparts, cold atom topological quantum states can be i) "seen", by mapping out the characteristic chiral edge states, and ii) controlled, by controlling the periodic vector potential and the properties of the confining potential.Comment: 4+ pages, 5 color figure

    Why do voters back corrupt and dishonest politicians? Interview with Milan Vaishnav

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    A candidate with criminal allegations hanging over them will repel voters – or will they? Not necessarily. In India, a third of the MPs elected in 2014 faced an ongoing criminal case. Milan Vaishnav, the author of a new book about the nexus of crime and democracy in India, talks to Ros Taylor about the appeal of a strongman who can ‘get things done’, even if it means breaking the law – and considers whether some US voters share the same instincts

    Image Compression & Transmission through Digital Communication System

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    Image Compression addresses the problem of reducing the amount of data required to represent the digital image. Compression is achieved by the removal of one or more of three basic data redundancies: (1) Coding redundancy, which is present when less than optimal (i.e. the smallest length) code words are used; (2) Interpixel redundancy, which results from correlations between the pixels of an image; &/or (3) psycho visual redundancy which is due to data that is ignored by the human visual system (i.e. visually nonessential information). Huffman codes contain the smallest possible number of code symbols (e.g., bits) per source symbol (e.g., grey level value) subject to the constraint that the source symbols are coded one at a time. So, Huffman coding & Shannon Coding , which remove coding redundancies , when combined with the technique of image compression using Discrete Cosine Transform (DCT) & Discrete Wavelet Transform (DWT) helps in compressing the image data to a very good extent. For the efficient transmission of an image across a channel, source coding in the form of image compression at the transmitter side & the image recovery at the receiver side are the integral process involved in any digital communication system. Other processes like channel encoding, signal modulation at the transmitter side & their corresponding inverse processes at the receiver side along with the channel equalization help greatly in minimizing the bit error rate due to the effect of noise & bandwidth limitations (or the channel capacity) of the channel
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