291,722 research outputs found

    Particle-laden weakly swirling free jets: Measurements and predictions

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    A theoretical and experimental investigation of particle-laden, weakly swirling, turbulent free jets was conducted. Glass particles, having a Sauter mean diameter of 39 microns with a standard deviation of 15 microns, were used. A single loading ratio of 0.2 was used in the experiments. Measurements are reported for three swirl numbers, ranging from 0.0 to 0.3. The measurements included mean and fluctuating velocities of both phases, and particle mass flux distributions. Measurements were compared with predictions from three types of multiphase flow analysis: locally homogeneous flow (LHF); deterministic separated flow (DSF); and stochastic separated flow (SSF). For the particle-laden jets, the LHF and DSF models did not provide very satisfactory predictions. The LHF model generally overestimated the rate of decay of particle mean axial and angular velocities with streamwise distance, due to the neglect of particle inertia. The LHF model predictions of particle mass flux also showed poor agreement with measurements due to the assumption of no-slip between phases. The DSF model also performed quite poorly for predictions of particle mass flux, because turbulent dispersion of the particles was neglected. The SSF model, which accounts for both particle inertia and turbulent dispersion of the particles, yielded reasonably good predictions throughout the flow field for the particle-laden jets

    How is Fear Constructed? A Narrative Approach to Social Dread in Literature

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    Fear-inducing narratives can be divided into two subtypes of horror and dread. While horror stories concentrate on a concrete visible object such as a monster, in dread narratives the object of fear is abstract or absent altogether. Pure forms of either are rare and most narratives mix both types, usually with dominant in one or the other. An interesting subtype of dread narratives is the narrative of social dread, where the fear is social in nature. One of the few narratologists to study construction of fear in arts, Yvonne Leffler suggests a variety of narrative techniques often used in horror fiction. Adjusting Leffler’s list of techniques for tales of dread instead of horror helps analysing the nature and amount of dread present in a range of different narratives from light reading and literary fiction to non-fiction. A narrative approach helps to reveal how non-fiction texts use similar techniques, and sometimes more extensively than fictional texts. Lionel Shriver’s We Need to Talk About Kevin (2003) is an excellent example of social dread in fiction, where societal failures are a big part of the fears induced, and the questions raised in the narrative are denied definite answers. Kanae Minato’s Confessions (2008) is closer to a thriller, because despite raising issues of societal failure, the work gives conclusive answers to all of the questions raised during the narrative. Although Haruki Murakami’s Underground (1997–98) is a nonfiction compiled from interviews of terror attack survivors, it nevertheless has the hallmarks of a social dread narrative, such as question-answer structure and abstractness of the source of fear. More importantly, Murakami’s work alternates between identifying and anticipatory readings, gives no definitive answers to the questions it poses, and the fear it conveys is social in nature

    Investigation of exit-velocity stratification effects on jets in a crossflow (STRJET)

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    Program determines flow field about jets with velocity stratification exhausting into crossflow. Jets with three different types of exit-velocity stratification have been considered: (a) jets with relatively high-velocity core, (b) jets with relatively low-velocity core, and (c) jets originating from vaned nozzle

    Comparison of the Geometrical Characters Inside Quark- and Gluon-jet Produced by Different Flavor Quarks

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    The characters of the angular distributions of quark jets and gluon jets with different flavors are carefully studied after introducing the cone angle of jets. The quark jets and gluon jets are identified from the 3-jet events which are produced by Monte Carlo simulation Jetset7.4 in e+e- collisions at s\sqrt s=91.2GeV. It turns out that the ranges of angular distributions of gluon jets are obviously wider than that of quark jets at the same energies. The average cone angles of gluon jets are much larger than that of quark jets. As the multiplicity or the transverse momentum increases, the cone-angle distribution without momentum weight of both the quark jet and gluon jet all increases, i.e the positive linear correlation are present, but the cone-angle distribution with momentum weight decreases at first, then increases when n > 4 or p_t > 2 GeV. The characters of cone angular distributions of gluon jets produced by quarks with different flavors are the same, while there are obvious differences for that of the quark jets with different flavors.Comment: 13 pages, 6 figures, to be published on the International Journal of Modern Physics

    A Chandra Survey of Quasar Jets: First Results

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    We present results from Chandra X-ray imaging and spectroscopy of a flux-limited sample of flat spectrum radio-emitting quasars with jet-like extended structure. Twelve of twenty quasar jets are detected in 5 ks ACIS-S exposures. The quasars without X-ray jets are not significantly different from those in the sample with detected jets except that the extended radio emission is generally fainter. New radio maps are combined with the X-ray images in order to elucidate the relation between radio and X-ray emission in spatially resolved structures. We find a variety of morphologies, including long straight jets and bends up to 90 degrees. All X-ray jets are one-sided although the radio images used for source selection often show lobes opposite the X-ray jets. The FR II X-ray jets can all be interpreted as inverse Compton scattering of cosmic microwave background photons by electrons in large-scale relativistic jets although deeper observations are required to test this interpretation in detail. Applying this interpretation to the jets as a population, we find that the jets would be aligned to within 30 degrees of the line of sight generally, assuming that the bulk Lorentz factor of the jets is 10.Comment: 25 pages with 5 pages of color figures; accepted for publication in the Astrophysical Journal Supplements; higher resolution jpeg images are available at http://space.mit.edu/home/jonathan/jets

    N-Jettiness: An Inclusive Event Shape to Veto Jets

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    Jet vetoes are essential in many Higgs and new-physics analyses at the LHC and Tevatron. The signals are typically characterized by a specific number of hard jets, leptons, or photons, while the backgrounds often have additional jets. In such cases vetoing undesired additional jets is an effective way to discriminate signals and background. Given an inclusive event sample with N or more jets, the veto to have only N energetic jets defines an "exclusive" N-jet cross section. This strongly restricts the phase space of the underlying inclusive N-jet cross section and causes large double logarithms in perturbation theory that must be summed to obtain theory predictions. Jet vetoes are typically implemented using jet algorithms. This yields complicated phase-space restrictions and one often relies on parton-shower Monte Carlos, which are limited to leading-logarithmic accuracy. We introduce a global event shape "N-jettiness", tau_N, which is defined for events with N signal jets and vanishes in the limit of exactly N infinitely narrow jets. Requiring tau_N << 1 constrains radiation between the N signal jets and vetoes additional undesired jets. This provides an inclusive method to veto jets and to define an exclusive N-jet cross section that can be well-controlled theoretically. N-jettiness yields a factorization formula with inclusive jet and beam functions.Comment: 4 pages, 1 figure, v2: typos corrected, journal versio

    The Ratio of W + N jets To Z/gamma + N jets As a Precision Test of the Standard Model

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    We suggest replacing measurements of the individual cross-sections for the production of W + N jets and Z/gamma + N jets in searches for new high-energy phenomena at hadron colliders by the precision measurement of the ratios (W+0 jet)/(Z+0 jet), (W+1 jet)/(Z+1 jet), (W+2 jets)/(Z+2 jets),... (W+N jets)/(Z+N jets), with N as large as 6 (the number of jets in ttbarH). These ratios can also be formed for the case where one or more of the jets is tagged as a b or c quark. Existing measurements of the individual cross sections for Wenu + N jets at the Tevatron have systematic uncertainties that grow rapidly with N, being dominated by uncertainties in the identification of jets and the jet energy scale. These systematics, and also those associated with the luminosity, parton distribution functions (PDF's), detector acceptance and efficiencies, and systematics of jet finding and b-tagging, are expected to substantially cancel in calculating the ratio of W to Z production in each N-jet channel, allowing a greater sensitivity to new contributions in these channels in Run II at the Tevatron and at the LHC.Comment: 10 pages, 8 figures, added reference
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