7,980 research outputs found

    Recent QCD Results from LEP-1 and LEP-2

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    A summary is given of some recent QCD results from LEP. For LEP-2, the topics include event shape measurements, determinations of the strong coupling constant, and measurements of the charged particle multiplicity distribution at the recently completed run at 189 GeV. For LEP-1, the topics presented are a test of the flavor independence of the strong coupling constant and a study of gluon jets using a hemisphere definition to correspond to analytic calculations. For the combined LEP data samples, the topics include a test of power law corrections for hadronization effects and the running of the strong coupling strength.Comment: Contribution to the Proceedings, APS-Division of Particles and Fields Conference, DPF99, UCLA, Los Angeles, CA, Jan. 5-9, 199

    Tests of QCD using differences between gluon and quark jets

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    I present recent results from LEP which utilize differences between gluon and quark jets to make quantitative tests of QCD. The principal topic is a determination of the ratio of QCD color factors, CA_{\mathrm{A}}/CF_{\mathrm{F}}, using either the multiplicity or fragmentation functions of the jets. In addition, I discuss a recent measurement of the rate of η\eta mesons in gluon jets compared to quark jets.Comment: Talk given at the International Europhysics Conference, High Energy Physics 99, Tampere, Finland, 15-21 July 199

    Unbiased gluon jet multiplicity from e+^+e−^- three-jet events

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    The charged particle multiplicities of two- and three-jet events from the reaction e+^+e−^-,\to ZZ^0 \to hadronsaremeasuredforZ are measured for Z^0decaystolightquark(uds)flavors,usingthedatasampleoftheOPALCollaborationatLEP.Usingrecenttheoreticalexpressionstoaccountforbiasesfromeventselection,resultscorrespondingtounbiasedgluonjetsareextracted.Theunbiasedgluonjetdataarecomparedtocorrespondingresultsforquarkjets.Wedeterminetheratio decays to light quark (uds) flavors, using the data sample of the OPAL Collaboration at LEP. Using recent theoretical expressions to account for biases from event selection, results corresponding to unbiased gluon jets are extracted. The unbiased gluon jet data are compared to corresponding results for quark jets. We determine the ratio r \equiv \ngluon/\nqofmultiplicitiesbetweengluonandquarkjetsasafunctionofenergyscale.Wealsodeterminetheratioofslopes, of multiplicities between gluon and quark jets as a function of energy scale. We also determine the ratio of slopes, r^{(1)} \equiv ({\mathrm{d}}\ngluon /{\mathrm{d}}y) /({\mathrm{d}}\nq / {\mathrm{d}}y),andofcurvatures,, and of curvatures, r^{(2)} \equiv ({\mathrm{d}}^2\ngluon /{\mathrm{d}}y^2) /({\mathrm{d}}^2\nq / {\mathrm{d}}y^2),where, where yspecifiestheenergyscale.At30GeV,wefind specifies the energy scale. At 30 GeV, we find r = 1.422\pm0.051,, r^{(1)} = 1.761\pm0.071and and r^{(2)} = 1.98\pm0.13$, where the uncertainties are the statistical and systematic terms added in quadrature. These results are in general agreement with theoretical predictions.Comment: comments: 5 pages, 3 figures in eps, talk given at XXXI International Symposium on Multiparticle Dynamics, Sept 1-7, 2001, Datong China. URL http://ismd31.ccnu.edu.cn

    Jet Structure Studies at LEP and HERA

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    A summary of some recent studies in jet physics is given. Topics include leading particle production in light flavor events in e+e- annihilations, an analytical treatment of gluon and quark jets at the next-to-next-to-next-to-leading order (3NLO), and various studies performed at LEP and HERA involving separated gluon and quark jets.Comment: 7 pages including 8 figure

    Pilot-aided modulation for narrow-band satellite communications

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    This paper discusses a number of tone-aided modulation techniques which have been studied as part of the Mobile Satellite Experiment (MSAT-X) Program. In all instances tone(s) are inserted into data-free portions of the transmit spectrum and used by the receiver to sense the amplitude and frequency/phase distortions introduced by the channel. The receiver then uses this information in a feedforward manner to lessen the effect of the distortions on the data detection performance. Particular techniques discussed are the Tone Calibration Technique (TCT), the Dual Tone Calibrated Technique (DTCT), Transparent Tone-In-Band (TTIB), and Dual-Tone Single Sideband (DTSSB)

    Feedback control laws for highly maneuverable aircraft

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    The results of a study of the application of H infinity and mu synthesis techniques to the design of feedback control laws for the longitudinal dynamics of the High Angle of Attack Research Vehicle (HARV) are presented. The objective of this study is to develop methods for the design of feedback control laws which cause the closed loop longitudinal dynamics of the HARV to meet handling quality specifications over the entire flight envelope. Control law designs are based on models of the HARV linearized at various flight conditions. The control laws are evaluated by both linear and nonlinear simulations of typical maneuvers. The fixed gain control laws resulting from both the H infinity and mu synthesis techniques result in excellent performance even when the aircraft performs maneuvers in which the system states vary significantly from their equilibrium design values. Both the H infinity and mu synthesis control laws result in performance which compares favorably with an existing baseline longitudinal control law

    Free-piston Stirling engine conceptual design and technologies for space power, phase 1

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    As part of the SP-100 program, a phase 1 effort to design a free-piston Stirling engine (FPSE) for a space dynamic power conversion system was completed. SP-100 is a combined DOD/DOE/NASA program to develop nuclear power for space. This work was completed in the initial phases of the SP-100 program prior to the power conversion concept selection for the Ground Engineering System (GES). Stirling engine technology development as a growth option for SP-100 is continuing after this phase 1 effort. Following a review of various engine concepts, a single-cylinder engine with a linear alternator was selected for the remainder of the study. The relationships of specific mass and efficiency versus temperature ratio were determined for a power output of 25 kWe. This parametric study was done for a temperature ratio range of 1.5 to 2.0 and for hot-end temperatures of 875 K and 1075 K. A conceptual design of a 1080 K FPSE with a linear alternator producing 25 kWe output was completed. This was a single-cylinder engine designed for a 62,000 hour life and a temperature ratio of 2.0. The heat transport systems were pumped liquid-metal loops on both the hot and cold ends. These specifications were selected to match the SP-100 power system designs that were being evaluated at that time. The hot end of the engine used both refractory and superalloy materials; the hot-end pressure vessel featured an insulated design that allowed use of the superalloy material. The design was supported by the hardware demonstration of two of the component concepts - the hydrodynamic gas bearing for the displacer and the dynamic balance system. The hydrodynamic gas bearing was demonstrated on a test rig. The dynamic balance system was tested on the 1 kW RE-1000 engine at NASA Lewis

    America Can Win: The Case for Military Reform

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    Coronal heating by magnetohydrodynamic turbulence driven by reflected low-frequency waves

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    A candidate mechanism for the heating of the solar corona in open field line regions is described. The interaction of Alfvén waves, generated in the photosphere or chromosphere, with their reflections and the subsequent driving of quasi-two-dimensional MHD turbulence is considered. A nonlinear cascade drives fluctuations toward short wavelengths which are transverse to the mean field, thereby heating at rates insensitive to restrictive Alfvén timescales. A phenomenology is presented, providing estimates of achievable heating efficiency that are most favorable
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