12,073 research outputs found
Heat-Kernel Calculation of Quark Determinant and Computer Algebra
In this paper there we describe the calculational background of deriving a
strong meson Lagrangian from the Nambu--Jona-Lasinio quark model using the
computer algebra systems FORM and REDUCE in recursive algorithms, based on the
heat-kernel method for the calculation of the quark determinant.Comment: LATEX, 11 p., DESY 92-15
Relativistic effects in the production of pseudoscalar and vector doubly heavy mesons from e^+e^- annihilation
On the basis of the perturbative QCD and the relativistic quark model we
investigate the relativistic and bound state effects in the production
processes of a pair of -wave doubly heavy mesons with opposite charge
conjugation consisting of and quarks. All possible relativistic
corrections in the production amplitude including the terms connected with the
transformation law of the bound state wave function to the reference frame of
the moving pseudoscalar and vector mesons are taken
into account. We obtain a growth of the cross section for the reaction
due to considered effects by a factor
in the range of the center-of-mass energy GeV.Comment: 18 pages, 4 figure
Relativistic description of the charmonium mass spectrum
The charmonium mass spectrum is considered in the framework of the
constituent quark model with the relativistic treatment of the c quark. The
obtained masses are in good agreement with the existing experimental data
including the mass of eta_c(2S).Comment: 5 page
Streamer branching rationalized by conformal mapping techniques
Spontaneous branching of discharge channels is frequently observed, but not
well understood. We recently proposed a new branching mechanism based on
simulations of a simple continuous discharge model in high fields. We here
present analytical results for such streamers in the Lozansky-Firsov limit
where they can be modelled as moving equipotential ionization fronts. This
model can be analyzed by conformal mapping techniques which allow the reduction
of the dynamical problem to finite sets of nonlinear ordinary differential
equations. The solutions illustrate that branching is generic for the intricate
head dynamics of streamers in the Lozansky-Firsov-limit.Comment: 4 pages, 2 figure
Segment Motion in the Reptation Model of Polymer Dynamics. II. Simulations
We present simulation data for the motion of a polymer chain through a
regular lattice of impenetrable obstacles (Evans-Edwards model). Chain lengths
range from N=20 to N=640, and time up to Monte Carlo steps. For we for the central segment find clear -behavior as an
intermediate asymptote. The also expected -range is not yet developed.
For the end segment also the -behavior is not reached. All these data
compare well to our recent analytical evaluation of the reptation model, which
shows that for shorter times (t \alt 10^{4}) the discreteness of the
elementary motion cannot be neglected, whereas for longer times and short
chains (N \alt 100) tube renewal plays an essential role also for the central
segment. Due to the very broad crossover behavior both the diffusion
coefficient and the reptation time within the range of our simulation do not
reach the asymptotic power laws predicted by reptation theory. We present
results for the center-of-mass motion, showing the expected intermediate
-behavior, but again only for very long chains. In addition we show
results for the motion of the central segment relative to the center of mass,
where in some intermediate range we see the expected increase of the effective
power beyond the -law, before saturation sets in. Analysis and
simulations agree on defining a new set of criteria as characteristic for
reptation of finite chains.Comment: 19 pages in latex plus 13 ps figures, submitted to J. Stat. Phys. on
September 18, 199
Segment Motion in the Reptation Model of Polymer Dynamics. I. Analytical Investigation
We analyze the motion of individual beads of a polymer chain using a discrete
version of De Gennes' reptation model that describes the motion of a polymer
through an ordered lattice of obstacles. The motion within the tube can be
evaluated rigorously, tube renewal is taken into account in an approximation
motivated by random walk theory. We find microstructure effects to be present
for remarkably large times and long chains, affecting essentially all present
day computer experiments. The various asymptotic power laws, commonly
considered as typical for reptation, hold only for extremely long chains.
Furthermore, for an arbitrary segment even in a very long chain, we find a rich
variety of fairly broad crossovers, which for practicably accessible chain
lengths overlap and smear out the asymptotic power laws. Our analysis suggests
observables specifically adapted to distinguish reptation from motions
dominated by disorder of the environment.Comment: 38 pages in latex plus 8 ps figures, submitted to J. Stat. Phys. on
September 18, 1997, please note part II on cond-mat/971006
Inequality and Envy
Using a simple axiomatic structure we characterise two classes ofinequality indices - absolute and relative - that take into account "envy"in the income distribution. The concept of envy incorporated hereconcerns the distance of each person's income from his or herimmediately richer neighbour. This is shown to be similar to justiceconcepts based on income relativities.Inequality, envy, transfer principle.
Complaints and Inequality
Temkin (1986,1993) sets out a philosophical basis for the analysis of income inequality that provides an important alternative to the mainstream welfarist approach. We show that the Temkin principles can be characterised by a parsimonious axiomatic structure and we use this structure to derive a new class of inequality indices and an inequality ordering. This class of indices has a family relationship to well-known measures of inequality, deprivation and poverty. The ordering is shown to have properties analogous to second-order dominance results.Inquality, complaints, transfer principle.
Spontaneous Branching of Anode-Directed Streamers between Planar Electrodes
Non-ionized media subject to strong fields can become locally ionized by
penetration of finger-shaped streamers. We study negative streamers between
planar electrodes in a simple deterministic continuum approximation. We observe
that for sufficiently large fields, the streamer tip can split. This happens
close to Firsov's limit of `ideal conductivity'. Qualitatively the tip
splitting is due to a Laplacian instability quite like in viscous fingering.
For future quantitative analytical progress, our stability analysis of planar
fronts identifies the screening length as a regularization mechanism.Comment: 4 pages, 6 figures, submitted to PRL on Nov. 16, 2001, revised
version of March 10, 200
- …