1,846 research outputs found
Capture numbers and islands size distributions in models of submonolayer surface growth
The capture numbers entering the rate equations (RE) for submonolayer film
growth are determined from extensive kinetic Monte Carlo (KMC) simulations for
simple representative growth models yielding point, compact, and fractal island
morphologies. The full dependence of the capture numbers on island size, and on
both the coverage and the D/F ratio between the adatom diffusion coefficient D
and deposition rate F is determined. Based on this information, the RE are
solved to give the RE island size distribution (RE-ISD). The RE-ISDs are shown
to agree well with the corresponding KMC-ISDs for all island morphologies. For
compact morphologies, however, this agreement is only present for coverages
smaller than about 5% due to a significantly increased coalescence rate
compared to fractal morphologies. As found earlier, the scaled KMC-ISDs as a
function of scaled island size approach, for fixed coverage, a limiting curve
for D/F going to infinity. Our findings provide evidence that the limiting
curve is independent of the coverage for point islands, while the results for
compact and fractal island morphologies indicate a dependence on the coverage.Comment: 13 pages, 12 figure
SUSY-QCD corrections in the squark-gluino sector
A status report is given of the calculations of next-to-leading-order ()
supersymmetric QCD corrections to the production of squarks and gluinos in
collisions. The implementation of these SUSY-QCD corrections
leads to more stable theoretical predictions and to a substantial increase of
the production cross-sections. In addition we give a discussion of the use of
the scheme for renormalizing the coupling constants in the QCD
sector of () supersymmetric theories.Comment: 6 two-column pages, tar'ed gzip'ed uuencoded files, LaTeX, 7
Encapsulated Postscript figures, uses epsfig and espcrc2. To appear in the
proceedings of the 1996 Zeuthen Workshop on Elementary Particle Theory: "QCD
and QED in Higher Orders", J.Bl\"umlein, F.Jegerlehner, and T.Riemann eds.
Complete postscript file available at
http://rulgm4.LeidenUniv.nl/preprints.htm
Azimuthal correlation between the and planes in the semileptonic rest frame decay of a polarized top quark: An effect
The azimuthal correlation between the planes formed by the vectors
and in the
semileptonic rest frame decay of a polarized top quark belongs to a class of polarization observables involving the
top quark which vanish at the Born term level in the standard model. We
determine the next--to--leading order QCD corrections to the afore-mentioned
azimuthal correlation and compare the result to the corresponding contribution
of a non--standard--model right--chiral quark current.Comment: latex, 12 pages with 2 figures in the text, typos removed,comment and
references added, replaced with published versio
Search for New Physics in the Semileptonic D_{l4} Decays, D->K \pi l \nu
New physics effects through the direct CP violation and the decay rate change
are investigated in the semileptonic decays, , by including a scalar-exchange interaction with a complex coupling. In
the decay process, we included various excited states as intermediate states
decaying to the final hadrons, , and found that among the intermediate
states only the lowest state () is dominant and the other higher excited
states are negligible, contrary to the decays. We also obtained
constraints on the new complex coupling within the multi-Higgs doublet model
and the scalar leptoquark models.Comment: LaTeX, 16 pages, including 3 figure
Helicity Analysis of Semileptonic Hyperon Decays Including Lepton Mass Effects
Using the helicity method we derive complete formulas for the joint angular
decay distributions occurring in semileptonic hyperon decays including lepton
mass and polarization effects. Compared to the traditional covariant
calculation the helicity method allows one to organize the calculation of the
angular decay distributions in a very compact and efficient way. In the
helicity method the angular analysis is of cascade type, i.e. each decay in the
decay chain is analyzed in the respective rest system of that particle. Such an
approach is ideally suited as input for a Monte Carlo event generation program.
As a specific example we take the decay () followed by the nonleptonic decay for which we show a few examples of decay distributions which are
generated from a Monte Carlo program based on the formulas presented in this
paper. All the results of this paper are also applicable to the semileptonic
and nonleptonic decays of ground state charm and bottom baryons, and to the
decays of the top quark.Comment: Published version. 40 pages, 11 figures included in the text. Typos
corrected, comments added, references added and update
Engineering Quantum States, Nonlinear Measurements, and Anomalous Diffusion by Imaging
We show that well-separated quantum superposition states, measurements of
strongly nonlinear observables, and quantum dynamics driven by anomalous
diffusion can all be achieved for single atoms or molecules by imaging
spontaneous photons that they emit via resonance florescence. To generate
anomalous diffusion we introduce continuous measurements driven by L\'evy
processes, and prove a number of results regarding their properties. In
particular we present strong evidence that the only stable L\'evy density that
can realize a strictly continuous measurement is the Gaussian.Comment: revtex4-1, 17 pages, 7 eps figure
Aperture synthesis imaging of the circumstellar dust disk around DO Tauri
We have detected the T~Tauri star, DO Tauri, in a 0.6''-resolution VLA map of 43.3 GHz (\lambda = 7 mm) continuum emission. The 43 GHz flux density lies on the same power-law slope defined by 89 to 232 GHz measurements, F_\nu \propto \nu^{\alpha} with index \alpha = 2.39\pm0.23, confirming that the 43.3 GHz emission is thermal radiation from circumstellar dust. Upper limits to the flux densities at 8.4 and 22.5 GHz constrain the contribution of free-free emission from a compact ionized wind to less than 49\%. The dust emissivity index, \beta, is 0.39\pm0.23, if the emission is optically thin. Fitting a model of a thin circumstellar disk to the observed spectral energy distribution gives \beta = 0.6\pm0.3, consistent with the power-law derivation. Both values are substantially lower than is generally accepted for the interstellar medium, suggesting grain growth. Given the youth of DO Tau and the early evolutionary state of its circumstellar disk, this result implies that mm-size grains have already formed by the early T-Tauri phase
SU(3)_flavor analysis of two-body weak decays of charmed baryons
We study two-body weak decays of charmed baryons \Lambda_c and \Xi_c into an
octet or decuplet baryon and a pseudoscalar meson employing the SU(3) flavor
symmetry. Using certain measured Cabibbo-favored modes, we fix the reduced
amplitudes and predict the branching ratios of various decays of charmed
baryons in the Cabibbo-enhanced, -suppressed and -doubly suppressed modes.Comment: 25 pages, No figure, Phys. Rev. D (to appear
Order and nFl Behavior in UCu4Pd
We have studied the role of disorder in the non-Fermi liquid system UCu4Pd
using annealing as a control parameter. Measurement of the lattice parameter
indicates that this procedure increases the crystallographic order by
rearranging the Pd atoms from the 16e to the 4c sites. We find that the low
temperature properties depend strongly on annealing. Whereas the non-Fermi
liquid behavior in the specific heat can be observed over a larger temperature
range after annealing, the clear non-Fermi liquid behavior of the resistivity
of the unannealed sample below 10 K disappears. We come to the conclusion that
this argues against the Kondo disorder model as an explanation for the
non-Fermi liquid properties of both as-prepared and annealed UCu4Pd
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