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

Inclusive Semileptonic Decays in QCD Including Lepton Mass Effects

Starting from an Operator Product Expansion in the Heavy Quark Effective Theory up to order 1/m_b^2 we calculate the inclusive semileptonic decays of unpolarized bottom hadrons including lepton mass effects. We calculate the differential decay spectra d\Gamma/(dE_\tau ), and the total decay rate for B meson decays to final states containing a \tau lepton.Comment: 16 pages + 4 figs. appended in uuencoded form, LaTeX, MZ-TH/93-3

Island size distributions in submonolayer growth: successful prediction by mean field theory with coverage dependent capture numbers

We show that mean-field rate equations for submonolayer growth can successfully predict island size distributions in the pre-coalescence regime if the full dependence of capture numbers on both the island size and the coverage is taken into account. This is demonstrated by extensive Kinetic Monte Carlo simulations for a growth kinetics with hit and stick aggregation. A detailed analysis of the capture numbers reveals a nonlinear dependence on the island size for small islands. This nonlinearity turns out to be crucial for the successful prediction of the island size distribution and renders an analytical treatment based on a continuum limit of the mean-field rate equations difficult.Comment: 4 pages, 4 figue

Analyticity, crossing and the absorptive parts of the one-loop contributions to the quark-quark-gluon gauge boson four-point function

Starting from the known one-loop result for the $e^{+}e^{-}$-annihilation process $e^{+}e^{-}\stackrel{\gamma,Z} {\longrightarrow} q\bar{q}g$ with massless quarks we employ analyticity and crossing to determine the absorptive parts of the corresponding one-loop contributions in Deep Inelastic Scattering (DIS) and in the Drell-Yan process (DY). Whereas the ${\cal O}(\alpha_s^2)$ absorptive parts generate a non-measurable phase factor in the $e^{+}e^{-}$-annihilation channel one obtains measurable phase effects from the one-loop contributions in the deep inelastic and in the Drell-Yan case. We compare our results with the results of previous calculations where the absorptive parts in DIS and in the DY process were calculated directly in the respective channels. We also present some new results on the dispersive and absorptive contributions of the triangle anomaly graph to the DIS process.Comment: 23 pages, 5 figures, typos corrected. Version to appear in Phys. Rev.

Effects of QCD Resummation on Distributions of Leptons from the Decay of Electroweak Vector Bosons

We study the distributions of leptons from the decay of electroweak vector bosons produced in hadron collisions. The effects of the initial state multiple soft-gluon emission, using the Collins--Soper resummation formalism, are included. The resummed results are compared with the next-to-leading-order results for the distributions of the transverse momentum, rapidity asymmetry, and azimuthal angle of the decay leptons.Comment: 12 pages, 3 figures uuencoded, LaTeX, uses epsf.tex for figures. (Was replaced on 5/2/95 because of mailer problems.

Two-body Cabibbo-suppressed Decays of Charmed Baryons into Vector Mesons and into Photons

The heavy quark effective theory and the factorization approximation are used to treat the Cabibbo-suppressed decays of charmed baryons to vector mesons, $\Lambda_C\rightarrow p{\rho^0}, p\omega$, $\Xi_C^{+,0}\rightarrow\Sigma^{+,0}\phi, \Sigma^{+,0}{\rho^0}, \Sigma^{+,0}\omega$ and $\Xi_C^{0}\rightarrow\Lambda\phi, \Lambda\rho, \Lambda\omega$. The input from two recent experimental results on $\Lambda_C$ decays allows the estimation of the branching ratios for these modes, which turn out to be between $10^{-4}$ and $10^{-3}$. The long distance contribution of these transitions via vector meson dominance to the radiative weak processes $\Lambda_C\rightarrow p\gamma$, $\Xi_C\rightarrow\Sigma\gamma$ and $\Xi_C^0\rightarrow\Lambda\gamma$ leads to quite small branching ratios, $10^{-6}-10^{-9}$; the larger value holds if a sum rule between the coupling constants of the vector mesons is broken.Comment: 11 pages, latex, no figure

Analysis of Two-Body Decays of Charmed Baryons Using the Quark-Diagram Scheme

We give a general formulation of the quark-diagram scheme for the nonleptonic weak decays of baryons. We apply it to all the decays of the antitriplet and sextet charmed baryons and express their decay amplitudes in terms of the quark-diagram amplitudes. We have also given parametrizations for the effects of final-state interactions. For SU(3) violation effects, we only parametrize those in the horizontal $W$-loop quark diagrams whose contributions are solely due to SU(3)-violation effects. In the absence of all these effects, there are many relations among various decay modes. Some of the relations are valid even in the presence of final-state interactions when each decay amplitude in the relation contains only a single phase shift. All these relations provide useful frameworks to compare with future experiments and to find out the effects of final-state interactions and SU(3) symmetry violations.Comment: 28 pages, 20 Tables in landscape form, 4 figures. Main changes are: (i) some errors in the Tables and in the relations between the quark-diagram amplitudes of this paper and those of Ref.[10] are corrected, (ii) improvements are made in the presentation so that comparisons with previous works and what have been done to include SU(3) breaking and final-state interactions are more clearly stated; to appear in the Physical Review

Quark and Pole Models of Nonleptonic Decays of Charmed Baryons

Quark and pole models of nonleptonic decays of charmed baryons are analysed from the point of view of their symmetry properties. The symmetry structure of the parity conserving amplitudes that corresponds to the contribution of the ground-state intermediate baryons is shown to differ from the one hitherto employed in the symmetry approach. It is pointed out that the "subtraction" of sea quark effects in hyperon decays leads to an estimate of $W$-exchange contributions in charmed baryon decays that is significantly smaller than naively expected on the basis of $SU(4)$. An $SU(2)_{W}$ constraint questioning the reliability of the factorization technique is exhibited. Finally, a successful fit to the available data is presented.Comment: 25 pages, LATEX, 1643/PH IFJ Krako

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

Observation and Numerical Simulation of Melt Pool Dynamic and Beam Powder Interaction During Selective Electron Beam Melting

Selective electron beam melting (SEBM) is an additive manufacturing method used to produce complex parts in a layer-by-layer process utilizing Ti6Al4V powder. To improve the very good properties of built parts even more and to use the full capacity of the process, the fundamental understanding of the beam powder interaction is of essential relevance. Numerical simulations and observation with a high speed camera of powder melting show the strong melt pool dynamic and its lateral extent clearly. Furthermore, the immediate effect of beam parameters, e.g. beam current and velocity, on the melting behavior of the powder can be resolved in time steps of a few milliseconds.Mechanical Engineerin