829 research outputs found
Continued development of a detailed model of arc discharge dynamics
Using a previously developed set of codes (SEMC, CASCAD, ACORN), a parametric study was performed to quantify the parameters which describe the development of a single electron indicated avalanche into a negative tip streamer. The electron distribution function in Teflon is presented for values of the electric field in the range of four-hundred million volts/meter to four billon volts/meter. A formulation of the scattering parameters is developed which shows that the transport can be represented by three independent variables. The distribution of ionization sites is used to indicate an avalanche. The self consistent evolution of the avalanche is computed over the parameter range of scattering set
First principles numerical model of avalanche-induced arc discharges in electron-irradiated dielectrics
The model consists of four phases: single electron dynamics, single electron avalanche, negative streamer development, and tree formation. Numerical algorithms and computer code implementations are presented for the first three phases. An approach to developing a code description of fourth phase is discussed. Numerical results are presented for a crude material model of Teflon
Active-Coupling Mixing Times for a Stirred Binary Liquid
Mixing times measured for a stirred critical binary liquid mixture are seen to vary dramatically with Reynolds number, Prandtl number, and the initial value of the order parameter. These variations are far too large to be explained by passive-mixing calculations; they also differ in significant respects from the active-mixing predictions of Ruiz and Nelson
Mixed Weyl Symbol Calculus and Spectral Line Shape Theory
A new and computationally viable full quantum version of line shape theory is
obtained in terms of a mixed Weyl symbol calculus. The basic ingredient in the
collision--broadened line shape theory is the time dependent dipole
autocorrelation function of the radiator-perturber system. The observed
spectral intensity is the Fourier transform of this correlation function. A
modified form of the Wigner--Weyl isomorphism between quantum operators and
phase space functions (Weyl symbols) is introduced in order to describe the
quantum structure of this system. This modification uses a partial Wigner
transform in which the radiator-perturber relative motion degrees of freedom
are transformed into a phase space dependence, while operators associated with
the internal molecular degrees of freedom are kept in their original Hilbert
space form. The result of this partial Wigner transform is called a mixed Weyl
symbol. The star product, Moyal bracket and asymptotic expansions native to the
mixed Weyl symbol calculus are determined. The correlation function is
represented as the phase space integral of the product of two mixed symbols:
one corresponding to the initial configuration of the system, the other being
its time evolving dynamical value. There are, in this approach, two
semiclassical expansions -- one associated with the perturber scattering
process, the other with the mixed symbol star product. These approximations are
used in combination to obtain representations of the autocorrelation that are
sufficiently simple to allow numerical calculation. The leading O(\hbar^0)
approximation recovers the standard classical path approximation for line
shapes. The higher order O(\hbar^1) corrections arise from the noncommutative
nature of the star product.Comment: 26 pages, LaTeX 2.09, 1 eps figure, submitted to 'J. Phys. B.
Measurement of Forward Jets Produced in High-Transverse-Momentum Hadron-Proton Collisions
A measurement of charged-particle production is reported for the forward region in events triggered by high-transverse-momentum (p⊥) jets and single particles. The momentum distributions of forward-going particles are observed to scale in a simple p⊥-dependent longitudinal variable. Forward-going (beam) jets are observed to be tilted away from the original direction by an amount which agrees with muon-pair data when interpreted in a parton (quantum-chromodynamics) model
Jets Produced in π^-, π^+, and Proton Interactions at 200 GeV on Hydrogen and Aluminum Targets
This paper presents results from an experiment on the production of jets (groups of particles) with high p_⊥ produced in 200-GeV/c interactions. Results are presented on the comparison of jet cross sections on aluminum and hydrogen targets. The jet fragmentation distributions are also examined. Both the cross section and the jet structure are found to depend strongly on the beam and target types
Observation of the Production of Jets of Particles at High Transverse Momentum and Comparison with Inclusive Single-Particle Reactions
Data are presented on production by 200-GeV/c hadrons incident on beryllium of both single particles and jets (groups of particles) with high p_T (transverse momentum). The experiment was performed in a wide-aperture multiparticle spectrometer at Fermilab. The jet and single-particle cross sections have a similar shape from p_T=3 to 5 GeV/c but the jet cross section is over two orders of magnitude larger. The distributions of charged-particle momenta show striking similarities to those observed in lepton-induced processes
Experimental Tests of Quantum Chromodynamics in High-p_⊥ Jet Production in 200-GeV/c Hadron-Proton Collisions
Data on inclusive jet production in the transverse-momentum (p_⊥) range 0-8 GeV/c for 200-GeV/c p, π^-, π^+, K^-, K^+, and p incident on a hydrogen target are presented. The jet cross section is fully corrected for losses and biases, and compared with the predictions of a model based on quantum chromodynamics. Both the absolute cross section and the inclusive charged-particle distributions inside and outside the jet are in qualitative agreement with the model
Diffusing-wave spectroscopy of nonergodic media
We introduce an elegant method which allows the application of diffusing-wave
spectroscopy (DWS) to nonergodic, solid-like samples. The method is based on
the idea that light transmitted through a sandwich of two turbid cells can be
considered ergodic even though only the second cell is ergodic. If absorption
and/or leakage of light take place at the interface between the cells, we
establish a so-called "multiplication rule", which relates the intensity
autocorrelation function of light transmitted through the double-cell sandwich
to the autocorrelation functions of individual cells by a simple
multiplication. To test the proposed method, we perform a series of DWS
experiments using colloidal gels as model nonergodic media. Our experimental
data are consistent with the theoretical predictions, allowing quantitative
characterization of nonergodic media and demonstrating the validity of the
proposed technique.Comment: RevTeX, 12 pages, 6 figures. Accepted for publication in Phys. Rev.
Measurement of Antiproton-Proton Forward Charge-Exchange Scattering
There is a well-known forward peak in the np forward charge-exchange cross section, for momentum transfers |t|≲mπ2. We have performed an experiment to look for analogous behavior in the reaction p̅p→n̅n. The data cover the kinematical region 0≤|t|≤1.5mπ2 at an incident antiproton momentum of 1.80 GeV/c. A forward peak is observed, which is estimated (from results of other experiments) to be considerably smaller than that for np charge exchange. This result can be understood in terms of interference between one-pion exchange and exchange of a particle with even G parity
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