8,670 research outputs found
Recent QCD Results from LEP-1 and LEP-2
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
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,
C/C, using either the multiplicity or
fragmentation functions of the jets. In addition, I discuss a recent
measurement of the rate of 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
Jet Structure Studies at LEP and HERA
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
Unbiased gluon jet multiplicity from ee three-jet events
The charged particle multiplicities of two- and three-jet events from the
reaction ee,\to ^0 \to hadrons^0r \equiv \ngluon/\nqr^{(1)} \equiv ({\mathrm{d}}\ngluon /{\mathrm{d}}y) /({\mathrm{d}}\nq
/ {\mathrm{d}}y)r^{(2)} \equiv ({\mathrm{d}}^2\ngluon
/{\mathrm{d}}y^2) /({\mathrm{d}}^2\nq / {\mathrm{d}}y^2)yr = 1.422\pm0.051r^{(1)} =
1.761\pm0.071r^{(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
Pilot-aided modulation for narrow-band satellite communications
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
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
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
Coronal heating by magnetohydrodynamic turbulence driven by reflected low-frequency waves
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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