4,393 research outputs found

    Charm, Beauty and Top at HERA

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    Results on open charm and beauty production and on the search for top production in high-energy electron-proton collisions at HERA are reviewed. This includes a discussion of relevant theoretical aspects, a summary of the available measurements and measurement techniques, and their impact on improved understanding of QCD and its parameters, such as parton density functions and charm- and beauty-quark masses. The impact of these results on measurements at the LHC and elsewhere is also addressed.Comment: 103 pages, 60 figures, to be published in Prog. Part. Nucl. Phy

    Coupling of THz radiation with intervalence band transitions in microcavities

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    The strong coupling of THz radiation and material excitations can improve the quantum efficiency of THz emitters. In this paper, we investigate THz polaritons and antipolaritons based on valence band transitions, which allow TE coupling in a simple configuration. The approach can improve the quantum efficiency of THz based devices based on TE mode in the strong coupling regime of THz radiations and intervalence bands transitions in a GaAs/AlGaAs quantum wells. A Nonequilibrium Many Body Approach for the optical response beyond the Hartree-Fock approximation is used as input to the effective dielectric function formalism for the polariton/antipolariton problem. The energy dispersion relations in the THz range are obtained by adjusting the full numerical solutions to simple analytical expressions, which can be used for non specialists in a wide number of new structures and material systems. The combination of manybody and nonparabolicity at high densities leads to dramatic changes in the polariton spectra in a nonequilibrium configuration, which is only possible for intervalence band transitions

    Structural Equation Modeling of Multiple-Indicator Multimethod-Multioccasion Data: A Primer

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    We provide a tutorial on how to analyze multiple-indicator multi-method (MM) longitudinal (multi-occasion, MO) data. Multiple-indicator MM-MO data presents specific challenges due to (1) different types of method effects, (2) longitudinal and cross-method measurement equivalence (ME) testing, (3) the question as to which process characterizes the longitudinal course of the construct under study, and (4) the issue of convergent validity versus method-specificity of different methods such as multiple informants. We present different models for multiple-indicator MM-MO data and discuss a modeling strategy that begins with basic single-method longitudinal confirmatory factor models and ends with more sophisticated MM-MO models. Our proposed strategy allows researchers to identify a well-fitting and possibly parsimonious model through a series of model comparisons. We illustrate our proposed MM-MO modeling strategy based on mother and father reports of inattention in a sample of N = 805 Spanish children

    The role of auditory cortices in the retrieval of single-trial auditory-visual object memories.

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    Single-trial encounters with multisensory stimuli affect both memory performance and early-latency brain responses to visual stimuli. Whether and how auditory cortices support memory processes based on single-trial multisensory learning is unknown and may differ qualitatively and quantitatively from comparable processes within visual cortices due to purported differences in memory capacities across the senses. We recorded event-related potentials (ERPs) as healthy adults (n = 18) performed a continuous recognition task in the auditory modality, discriminating initial (new) from repeated (old) sounds of environmental objects. Initial presentations were either unisensory or multisensory; the latter entailed synchronous presentation of a semantically congruent or a meaningless image. Repeated presentations were exclusively auditory, thus differing only according to the context in which the sound was initially encountered. Discrimination abilities (indexed by d') were increased for repeated sounds that were initially encountered with a semantically congruent image versus sounds initially encountered with either a meaningless or no image. Analyses of ERPs within an electrical neuroimaging framework revealed that early stages of auditory processing of repeated sounds were affected by prior single-trial multisensory contexts. These effects followed from significantly reduced activity within a distributed network, including the right superior temporal cortex, suggesting an inverse relationship between brain activity and behavioural outcome on this task. The present findings demonstrate how auditory cortices contribute to long-term effects of multisensory experiences on auditory object discrimination. We propose a new framework for the efficacy of multisensory processes to impact both current multisensory stimulus processing and unisensory discrimination abilities later in time