Berichtigung

Ohne ZusammenfassungFür die Mühe um die Klärung dieser Frage danken wir Hern Rost und Frl. Hinsch.     

Time-resolved X-Ray diffraction from coherent phonons during a laser-induced phase transition

Time-resolved x-ray diffraction with picosecond temporal resolution is used to observe scattering from impulsively generated coherent acoustic phonons in laser-excited InSb crystals. The observed frequencies and damping rates are in agreement with a model based on dynamical diffraction theory coupled to analytic solutions for the laser-induced strain profile. The results are consistent with a 12 ps thermal electron-acoustic phonon coupling time together with an instantaneous component from the deformation-potential interaction. Above a critical laser fluence, we show that the first step in the transition to a disordered state is the excitation of large amplitude, coherent atomic motion.     

The inclusion of fermions in dual N-point functions

Dual amplitudes of the five-point function for two fermions and three scalar bosons are constructed, and are used to obtain a consistent procedure for inclusing two fermions in the general N-point function.     

Polarized coincidence electroproduction scaling laws for the final state

We study the inclusive electroproduction of single hadrons off a polarized target. Bjorken scaling laws and the hadron azimuthal distribution are derived from the quark parton model.The polarization asymmetries scale when the target spin is along the direction of the virtual photon, and (apart from one significant exception) vanish for transverse spin. These results have a simple explanation; emphasis is given both to the general mathematical formalism and to intuitive physical reasoning.Through this framework we consider other cases: quarks with anomalous magnetic moment; renormalization group effects and asymptotic freedom; production of vector mesons (whose spin state is analysed by their decay); relation to large transverse momentum hadron production; and a covariant parton model calculation. We also look into spin-0 partons and Regge singularities.All of these cases (apart from the last two) modify the pattern of conclusions. Vector meson production shows polarization enhancements in the density matrix element ?₀₊; the renormalization group approach does not lead to any significant suppressions. They are also less severe in parton models for large p_T hadrons, and are not supported by the covariantly formulated calculation. The origins of these differences are isolated and used to exemplify the sensitivity that polarized hadron electroproduction has to delicate detail that is otherwise concealed.     

Computing risk profiles for composite low-probability high-consequence events

Low-probability high-consequence events play an important role is assessing the risk of catastrophic loss. Their risk profiles, however, can be difficult to obtain. This paper obtains the risk profiles of low-probability high-consequence events where the final consequence results from a number of intermediate events. Called composite events, these events occur, for example, in accidents releasing hazardous material. The structure of composite events is described and risk profile equations developed, both on a per-event and per-annum basis. The many extremely low valued terms, especially in the tail of the risk profile, make calculation nontrivial. Accordingly, algorithms are developed to compute these equations. In addition, formulae for means and variances are obtained, and an illustrative example is provided.     

Photodecomposition of iodopentanes in air: Product distributions from the self‐reactions of n‐pentyl peroxyl radicals

Product distributions from the 254‐nm photooxidation of the three iodopentane isomers were explored as a technique for studying the self‐reactions of individual pentyl peroxyl radicals (in air at ambient temperature and pressure). Pentanols and the associated carbonyl compounds (pentanal or pentanones) were major products as expected. Other major products resulted from the isomerization of pentan‐1‐oxyl and pentan‐2‐oxyl radicals, but their nature could not be identified. Minor products were alcohols and carbonyl compounds arising from the decomposition of pentoxyl radicals. Diols and mixed hydroxycarbonyl compounds from cross‐combination reactions were essentially absent, in contrast to expectation. The observed product distributions were evaluated to derive branching ratios for the radical‐preserving pathways of the self‐reactions, 0.42 ±0.17, 0.46 ± 0.10, 0.39 ± 0.08, for pentan‐1‐yl peroxyl, pentan‐2‐yl peroxyl, and pentan‐3‐yl peroxyl, respectively. Rate coefficients derived for the decomposition of the corresponding pentoxyl radicals, relative to their reaction with oxygen, are (5.1 ± 0.5) × 10¹⁸, (1.0 ± 0.2) × 10¹⁸, and (3.2 ± 0.3) × 10¹⁸ molecule cm^?3, respectively. Rate constants for the isomerization of pentan‐1‐oxyl and pentan‐2‐oxyl were estimated from the contributions of isomerization products to the total amounts of products as (4.0 ± 1.1) × 10⁵ s^?1 and (1.0 ± 2.0) × 10⁵ s^?1, respectively. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 34: 126–138, 2002     

Generation of femtosecond X-ray pulses via laser–electron beam interaction

The generation of femtosecond X-ray pulses will have important scientific applications by enabling the direct measurement of atomic motion and structural dynamics in condensed matter on the fundamental time scale of a vibrational period. Interaction of femtosecond laser pulses with relativistic electron beams is an effective approach to generating femtosecond pulses of X-rays. In this paper we present recent results from proof-of-principle experiments in which 300 fs pulses are generated from a synchrotron storage ring by using an ultrashort optical pulse to create femtosecond time structure on the stored electron bunch. A previously demonstrated approach for generating femtosecond X-rays via Thomson scattering between terawatt laser pulses and relativistic electrons is reviewed and compared with storage-ring based schemes.