A non-trivial Fréchet quotient of the space of real analytic functions

We prove that the space of real analytic functions ${\cal A}(\Omega)$ on an arbitrary open set $\Omega \subseteq \mathbb{R}^d$ has a Fréchet infinite dimensional quotient space with a continuous norm. Received: 4 February 2002     

Heavy quark production in heavy ion colliders

We describe updated calculations of $Q\bar Q$ production in pp and π ^- p interactions. We compare these results to total cross section data and discuss how the baseline cross sections extrapolate to heavy ion collider energies. We touch upon the differences between leading and next-to-leading order heavy quark production. Finally, we discuss the implications of our calculations for quarkonium production. Our discussion here focuses on bottom quarks.     

Two-photon annihilation into baryon-antibaryon pairs

We study the handbag contribution to two-photon annihilation into baryon-antibaryon pairs at large energy and momentum transfer. We derive factorization of the process amplitude into a hard subprocess and form factors describing the soft transition, assuming that the process is dominated by configurations where the (anti)quark approximately carries the full momentum of the (anti)baryon. The form factors represent moments of time-like generalized parton distributions, so-called distribution amplitudes. A characteristic feature of the handbag mechanism is the absence of isospin-two components in the final state, which in combination with flavor symmetry provides relations among the form factors for the members of the lowest-lying baryon octet. Assuming dominance of the handbag contribution, we can describe current experimental data with form factors of plausible size, and predict the cross sections of presently unmeasured channels. Received: 3 July 2002 / Revised version: 7 October 2002 / Published online: 20 November 2002 RID="a" ID="a" e-mail: mdiehl@physik.rwth-aachen.de RID="b" ID="b" e-mail: kroll@physik.uni-wuppertal.de RID="c" ID="c" e-mail: cvogt@nordita.dk     

All-optical sampling with a monolithically integrated Mach-Zehnder interferometer gate

An all-optical sampler consisting of a polarization-independent monolithic Mach-Zehnder interferometer with integrated semiconductor optical amplifiers and a temporal resolution of 1 ps is presented. As an example, a simple 320-Gbit/s pattern has been successfully sampled, demonstrating the functionality of this scheme for high-bit-rate waveform characterizations in light-wave systems.     

On Quasi-Interpolation with Non-uniformly Distributed Centers on Domains and Manifolds

The paper studies quasi-interpolation by scaled shifts of a smooth and rapidly decaying function. The centers are images of a smooth mapping of the hZⁿ-lattice in R^s, sn, and the scaling parameters are proportional to h. We show that for a large class of generating functions the quasi-interpolants provide high order approximations up to some prescribed accuracy. Although in general the approximants do not converge as h tends to zero, the remaining saturation error is negligible in numerical computations if a scalar parameter is suitably chosen. The lack of convergence is compensated for by a greater flexibility in the choice of generating functions used in numerical methods for solving operator equations.     

Dynamics of individual atomic kinks during crystal dissolution

The dynamics of kink motion via atom removal/deposition as a fundamental step in dissolution/crystallization of solids have become directly accessible by a novel scanning tunneling microscopy technique. Results obtained for the electrochemical dissolution of Cu(100) in HCl solution show pronounced local dissolution/redeposition fluctuations at the individual kinks even at the onset of Cu dissolution with average kink propagation and reaction rates in the range 10(3) and 10(5) atoms s(-1), respectively. These experiments allow one to directly measure the central kinetic properties of this electrochemical reaction.     

Measurement of internuclear distances in solid-state NMR by a background-filtered REDOR experiment

A background-filtered version of the rotational-echo double resonance (REDOR) experiment is demonstrated. The experiment combines a traditional REDOR pulse sequence with a double-cross-polarization (DCP) sequence to select only those signals coming from spin pairs of interest. The relatively inefficient DCP sequence, which transfers polarization from (1)H to (15)N and subsequently to (13)C, is improved by the use of adiabatic passages through the (-1) sideband of the Hartmann-Hahn matching condition. The result is an efficient 2D-REDOR pulse sequence that does not require a reference experiment for removal of background signals. The data produced by the experiment are ideally suited to analysis by newly developed dipolar transform methods, such as the REDOR transform. The relevant features of the experiment are demonstrated on simple labeled amino acids. Relative efficiencies of several other potential filtering methods are also compared. Copyright 2000 Academic Press.     

Combinatorial synthesis and characterization of a ternary epitaxial film of Co and Mn doped Ge (0 0 1)

We report combinatorial molecular beam epitaxy synthesis and properties of a ternary epitaxial film of Co and Mn co-doped Ge grown on Ge (0 0 1) substrate. Structural effects were examined in situ by reflection high-energy electron diffraction and ex situ by microbeam X-ray diffraction techniques, and magnetic properties were probed by using magnetooptic Kerr effect. Ternary epitaxial phase diagrams have been studied for total doping concentrations up to 30 at.%, where regions of coherent epitaxy and rough disordered growth and those of near room temperature ferromagnetic ordering have been identified.     

Uncertainty evaluation of the spectral UV irradiance evaluated by using the UVSPEC radiative transfer model

The radiative transfer models allow calculating the spectral UV irradiance from some set of measured input quantities linked with the surface reflectivity, the solar zenith angle, the ozone column and the characteristics of clouds and aerosols. The spectral irradiance yielded by a model is influenced by errors in the measurement of the input quantities. In this paper, the influences of these errors are characterized and compared with other systematic effects through an uncertainty analysis. We evaluated the uncertainty of the spectral UV irradiance rendered by the UVSPEC model, under cloudless sky conditions. In order to express the uncertainty of the output quantities (the global, direct and diffuse irradiances) in terms of the standard uncertainties of the input quantities, we used a Monte Carlo-based uncertainty propagation technique. We found that the uncertainty of the irradiance in the UV-B part of the spectrum was strongly influenced by the uncertainty attributed to the ozone column datum. Moreover, the uncertainities associated with the aerosol parameters accounted for most of the UV-A global irradiance uncertainty; the latter increased from about 4% under low aerosol conditions, up to about 14% in case of polluted air. We conclude that the UV irradiance evaluation through radiative transfer models requires paying special attention to the assessment of the aerosols properties.     

Surface properties of plasma membrane vesicles isolated from melon (Cucumus melo L.) root cells differing in salinity tolerance

The hypotheses that genotypic differences in salinity tolerance may result from (i) differences in global surface charge density or (ii) from differences in global Ca²⁺ binding were tested. An attempt was made to correlate the differing salinity tolerance of four melon cultivars with surface properties of vesicles extracted from the plasma membrane (PM) of their root cells. Surface characterization involved measurements of electrophoretic mobility and sorption of ⁴⁵Ca²⁺ to the vesicles in the presence of varying concentrations of Ca²⁺, Na⁺ and Mg²⁺. Irrespective of salinity tolerance, vesicles from the four cultivars yielded similar ζ potentials under similar conditions, indicating similar global surface charge densities. Sorption studies with vesicles from two cultivars differing in salinity tolerance predicted independently this result of equal surface charge density. The estimated global binding affinities of Ca²⁺, Na⁺ and Mg²⁺ to the PM of both cultivars were the same with binding coefficients of 50, 0.8 and 9 M⁻¹, respectively. Consequently, the hypotheses enumerated above to interpret genotypic differences in salinity toxicity are rejected. However, vesicles from the salt-resistant strain sorbed 19% more Ca²⁺ per given amount of protein in the membrane, indicating the existence of a larger number of negatively charged surface sites per given amount of protein and a smaller amount of protein per given area of membrane. Genotypic differences in site-specific Ca²⁺-binding affinity (e.g. at ion channels) remain a viable hypothesis for genotypic differences in salinity tolerance.