23,172 research outputs found

    THE INVESTMENT PROJECT PIPELINE COST ESCALATION, LEAD-TIME, SUCCESS, FAILURE AND SPEED1

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    As they involve expectations about the future and long lead times for planning and construction, the evolution of investment projects is usually complex and volatile. This paper analyses an important aspect of this volatility by studying the nature of the investment process, from the initial bright idea to the final construction and operational phase of a project. We refer to this process as the “project pipeline”. Using a rich source of information on recent Australian resource development projects, an index-number approach is employed to measure the escalation of costs of projects in the pipeline and the time spent there (the lead time). The determinants of the probability of ultimate success of projects is analysed with a binary choice model. Finally, a Markov chain approach is used to model the transitions of projects from one stage in the pipeline to the next, and to examine the implications of regulatory reform that has the effect of speeding up the flow of projects.

    Mixed QCD and Weak Corrections to ttˉt\bar{t} Production by Quark-Antiquark Annihilation

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    We report on our computation of the mixed QCD and weak corrections to qqˉttˉq {\bar q} \to t\bar{t} including t,tˉt, \bar t spin effects, in particular on single top spin asymmetries.Comment: Talk given at "International Conference on QCD and Hadronic Physics", Beijing, China, 16-20 Jun 200

    Spin properties of top quark pairs produced at hadron colliders

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    We discuss the spin properties of top quark pairs produced at hadron colliders at next-to-leading order in the coupling constant alpha_s of the strong interaction. Specifically we present, for some decay channels, results for differential angular distributions that are sensitive to t tbar spin correlations.Comment: Invited talk given by A. Brandenburg at the Cracow epiphany conference on heavy flavours, 3 - 6 January 2003, Cracow, Polan

    Investigation of Top quark spin correlations at hadron collider

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    We report on our results about hadronic ttˉt\bar t production at NLO QCD including t,tˉt, \bar t spin effects, especially on ttˉt\bar t spin correlations.Comment: talk given at the 32nd International Conference on High Energy Physics (ICHEP'04), Beijing, China, 16-22 Aug. 200

    Unusual persistence of superconductivity against high magnetic fields in the strongly-correlated iron-chalcogenide film FeTe:Ox_{x}

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    We report an unusual persistence of superconductivity against high magnetic fields in the iron chalcogenide film FeTe:Ox_{x} below ~ 2.5 K. Instead of saturating like a mean-field behavior with a single order parameter, the measured low-temperature upper critical field increases progressively, suggesting a large supply of superconducting states accessible via magnetic field or low-energy thermal fluctuations. We demonstrate that superconducting states of finite momenta can be realized within the conventional theory, despite its questionable applicability. Our findings reveal a fundamental characteristic of superconductivity and electronic structure in the strongly-correlated iron-based superconductors.Comment: 10 pages, 3 figure

    Epitaxial Thin Films of the Giant-Dielectric-Constant Material CaCu_3Ti_4O_{12} Grown by Pulsed-laser Deposition

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    Pulsed-laser deposition has been used to grow epitaxial thin films of the giant-dielectric-constant material CaCu_3Ti_4O_{12} on LaAlO_3 and SrTiO_3 substrates with or without various conducting buffer layers. The latter include YBa_2Cu_3O_7, La_{1.85}Sr_{0.15}CuO_{4+\delta} and LaNiO_3. Above 100K - 150K the thin films have a temperature independent dielectric constant as do single crystals. The value of the dielectric constant is of the order of 1500 over a wide temperature region, potentially making it a good candidate for many applications. The frequency dependence of its dielectric properties below 100K - 150K indicates an activated relaxation process.Comment: 11 pages, 4 figure

    Top quark spin correlations at hadron colliders: Predictions at next-to-leading order QCD

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    The collider experiments at the Tevatron and the LHC will allow for detailed investigations of the properties of the top quark. This requires precise predictions of the hadronic production of ttˉt\bar t pairs and of their subsequent decays. In this Letter we present for the reactions ppˉ,ppttˉ+X+Xp {\bar p}, p p \to t{\bar t} + X \to \ell^+\ell'^-X the first calculation of the dilepton angular distribution at next-to-leading order (NLO) in the QCD coupling, keeping the full dependence on the spins of the intermediate ttˉt\bar{t} state. The angular distribution reflects the degree of correlation of the tt and tˉ\bar t spins which we determine for different choices of tt and tˉ\bar t spin bases. In the case of the Tevatron, the QCD corrections are sizeable, and the distribution is quite sensitive to the parton content of the proton.Comment: 9 pages, 2 figure

    Top Quark Pair Production and Decay including Spin Effects at Hadron Colliders: Predictions at NLO QCD

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    Top quark-antiquark (ttˉt\bar t) pairs will be produced copiously at the Tevatron collider and in huge numbers at the LHC. This will make possible detailed investigations of the properties and interactions of this quark flavor. The analysis and interpretation of future data requires precise predictions of the hadronic production of ttˉt\bar t pairs and of their subsequent decays. In this talk the reactions ppˉ,ppttˉ+Xl+l+Xp {\bar p}, p p \to t{\bar t} + X \to l^+ l'^- + X are considered and results are presented of our calculation of the dilepton angular distribution at next-to-leading order QCD, keeping the full dependence on the spins of the intermediate ttˉt\bar{t} state. The angular distribution is determined for different choices of reference axes that can be identified with the tt and tˉ\bar t spin axes. While the QCD corrections to the leading-order distribution turn out to be small in the case of the LHC, we find them to be sizeable in the case of the Tevatron and find, moreover, the angular distribution to be sensitive to the parton content of the proton.Comment: Talk given at 3rd Circum-Pan-Pacific Symposium on "High Energy Spin Physics", Beijing, China, 8-13, 200

    Birth/birth-death processes and their computable transition probabilities with biological applications

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    Birth-death processes track the size of a univariate population, but many biological systems involve interaction between populations, necessitating models for two or more populations simultaneously. A lack of efficient methods for evaluating finite-time transition probabilities of bivariate processes, however, has restricted statistical inference in these models. Researchers rely on computationally expensive methods such as matrix exponentiation or Monte Carlo approximation, restricting likelihood-based inference to small systems, or indirect methods such as approximate Bayesian computation. In this paper, we introduce the birth(death)/birth-death process, a tractable bivariate extension of the birth-death process. We develop an efficient and robust algorithm to calculate the transition probabilities of birth(death)/birth-death processes using a continued fraction representation of their Laplace transforms. Next, we identify several exemplary models arising in molecular epidemiology, macro-parasite evolution, and infectious disease modeling that fall within this class, and demonstrate advantages of our proposed method over existing approaches to inference in these models. Notably, the ubiquitous stochastic susceptible-infectious-removed (SIR) model falls within this class, and we emphasize that computable transition probabilities newly enable direct inference of parameters in the SIR model. We also propose a very fast method for approximating the transition probabilities under the SIR model via a novel branching process simplification, and compare it to the continued fraction representation method with application to the 17th century plague in Eyam. Although the two methods produce similar maximum a posteriori estimates, the branching process approximation fails to capture the correlation structure in the joint posterior distribution
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