45,672 research outputs found
Computing the Cramer-Rao bound of Markov random field parameters: Application to the Ising and the Potts models
No full textThis letter considers the problem of computing the Cramer–Rao bound for the parameters of a Markov random field. Computation of the exact bound is not feasible for most fields of interest because their likelihoods are intractable and have intractable derivatives. We show here how it is possible to formulate the computation of the bound as a statistical inference problem that can be solve approximately, but with arbitrarily high accuracy, by using a Monte Carlo method. The proposed methodology is successfully applied on the Ising and the Potts models
Measurement of the ratio of prompt χ c to J / ψ production in pp collisions at √s = 7 TeV
No full textThe prompt production of charmonium χ c and J / ψ states is studied in proton-proton collisions at a centre-of-mass energy of √s = 7 TeV at the Large Hadron Collider. The χ c and J / ψ mesons are identified through their decays χ c → J / ψ γ and J / ψ → μ + μ - using 36 pb - 1 of data collected by the LHCb detector in 2010. The ratio of the prompt production cross-sections for χ c and J / ψ, σ (χ c → J / ψ γ) / σ (J / ψ), is determined as a function of the J / ψ transverse momentum in the range 2 < p T J / ψ < 15 GeV / c. The results are in excellent agreement with next-to-leading order non-relativistic expectations and show a significant discrepancy compared with the colour singlet model prediction at leading order, especially in the low p T J / ψ region
Theoretical Models on the Cu2O2 Torture Track. Mechanistic Implications for Oxytyrosinase and Small-molecule Analogs
No full textAccurately describing the relative energetics of alternative bis(μ-oxo) and μ-η2:η2 peroxo isomers of Cu2O2 cores supported by 0, 2, 4, and 6 ammonia ligands is remarkably challenging for a wide variety of theoretical models, primarily owing to the difficulty of maintaining a balanced description of rapidly changing dynamical and nondynamical electron correlation effects and a varying degree of biradical character along the isomerization coordinate. The completely renormalized coupled-cluster level of theory including triple excitations and extremely efficient pure density functional levels of theory quantitatively agree with one another and also agree qualitatively with experimental results for Cu2O2 cores supported by analogous but larger ligands. Standard coupled-cluster methods, such as CCSD(T), are in most cases considerably less accurate and exhibit poor convergence in predicted relative energies. Hybrid density functionals significantly underestimate the stability of the bis(μ-oxo) form, with the magnitude of the error being directly proportional to the percentage Hartree−Fock exchange in the functional. Single-root CASPT2 multireference second-order perturbation theory, by contrast, significantly overestimates the stability of bis(μ-oxo) isomers. Implications of these results for modeling the mechanism of C−H bond activation by supported Cu2O2 cores, like that found in the active site of oxytyrosinase, are discussed
Letter from Carl T. Hayden to C. H. Gensler, Havasupai Reservation
No full textLetter from Carl T. Hayden to C. H. Gensler, Havasupai Indian Reservation, regarding Hualapai and Cataract Canyons geography
Título: Decisiones Rotae Bononiensis
No full textMarca tip. na portSign.: [], [astrisco], A-T, V, a-c, dAntepPort. a dúas tintasTexto a dúas co
DNA Charge Transfer in an External Field: An Atomistic Approach
No full textWe address the problem of charge transfer through DNA-gold junctions from a theoretical and numerical perspective. The geometry and the electronic structure of the DNA fragment is described on an atomistic level making use of an extended Su-Schrieffer-Heeger Hamiltonian. The emerging potential energy surfaces exhibit the characteristics of small polaron formation and can be analyzed to obtain the energy parameters relevant to Marcus' theory of charge transfer and the corresponding interbase hopping rates. At stationarity, the resulting master equations lead to a maximum current of 5 nA per A-DNA double strand upon the application of a potential of +/- 2 V, a value comparable to recent experimental findings. In addition, the overall shape of the I-V curves and their pronounced dependence upon the DNA sequence is reproduced
Iwr1 Directs RNA Polymerase II Nuclear Import
No full textRNA polymerase (Pol) II transcribes protein-coding genes in the nucleus of eukaryotic cells and consists of 12 polypeptide subunits. It is unknown how Pol II is imported into the nucleus. Here we show that Pol II nuclear import requires the protein Iwr1 and provide evidence for cyclic Iwr1 function. Iwr1 binds Pol II in the active center cleft between the two largest subunits, maybe facilitating or sensing complete Pol II assembly in the cytoplasm. Iwr1 then uses an N-terminal bipartite nuclear localization signal that is recognized by karyopherin a to direct Pol II nuclear import. In the nucleus, Iwr1 is displaced from Pol II by transcription initiation factors and nucleic acids, enabling its export and recycling. Iwr1 function is Pol II specific, transcription independent, and apparently conserved from yeast to human
A possible mechanism of superconductivity in high-T-c cuprates
No full textThis paper derives a generic T-c formula by using the long-range phase coherence condition in quantum phase fluctuation of the order parameter. Taking the two-local-spin-mediated interaction (TLSMI) proposed by Liu and Chen [Phys. Rev. B 58 (1998) 8812] as a Cooper pair potential, and the T-c formula, this paper explains five basic experimental facts in high-T-c cuprates. The aim of this paper is to show that TLSMI is a possible pairing mechanism of superconductivity in high-T-c cuprates. (C) 2000 Elsevier Science B.V. All rights reserved.Physics, AppliedSCI(E)EI0ARTICLE4276-28434
Memorandum from A. E. Demaray to E. C. Finney
No full textFour letters of correspondence about the purchase of Bright Angel Trail between A. E. Demaray, Acting Director of the Grand Canyon National Park; E. C. Finney, Department of the Interior First Assistant Secretary; Carl T. Hayden, Representative (AZ); and Stephen T. Mather, Director of the National Park Service
Organic field-effect transistor for label-free dopamine sensing
No full textWe describe a potentiometric sensor based on Electrolyte-Gated Organic Field-Effect Transistor (EGOFET) for "in vitro'' detection of dopamine. The sensing element of this device resides at the Au gate-aqueous solution interface by means of a self-assembled monolayer (SAM) composed by cysteamine and 4-formylphenyl boronic acid. The covalent and selective adsorption of dopamine induces a surface dipole potential which shifts the electrode work function and modulates the double layer capacitance. As a result, our device is capable to detect dopamine up to pico-molar concentration showing higher sensitivity with respect to other approaches. For this reason the interface engineering of our EGOFET gate is a promising route for diagnostic applications. (c) 2012 Elsevier B.V. All rights reserved
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