University of Duisburg-Essen

About: University of Duisburg-Essen is a education organization based out in Essen, Nordrhein-Westfalen, Germany. It is known for research contribution in the topics: Population & Transplantation. The organization has 16072 authors who have published 39972 publications receiving 1109199 citations.

Electronic acceleration of atomic motions and disordering in bismuth

Abstract: The development of X-ray and electron diffraction methods with ultrahigh time resolution has made it possible to map directly, at the atomic level, structural changes in solids induced by laser excitation. This has resulted in unprecedented insights into the lattice dynamics of solids undergoing phase transitions. In aluminium, for example, femtosecond optical excitation hardly affects the potential energy surface of the lattice; instead, melting of the material is governed by the transfer of thermal energy between the excited electrons and the initially cold lattice. In semiconductors, in contrast, exciting approximately 10 per cent of the valence electrons results in non-thermal lattice collapse owing to the antibonding character of the conduction band. These different material responses raise the intriguing question of how Peierls-distorted systems such as bismuth will respond to strong excitations. The evolution of the atomic configuration of bismuth upon excitation of its A(1g) lattice mode, which involves damped oscillations of atoms along the direction of the Peierls distortion of the crystal, has been probed, but the actual melting of the material has not yet been investigated. Here we present a femtosecond electron diffraction study of the structural changes in crystalline bismuth as it undergoes laser-induced melting. We find that the dynamics of the phase transition depend strongly on the excitation intensity, with melting occurring within 190 fs (that is, within half a period of the unperturbed A(1g) lattice mode) at the highest excitation. We attribute the surprising speed of the melting process to laser-induced changes in the potential energy surface of the lattice, which result in strong acceleration of the atoms along the longitudinal direction of the lattice and efficient coupling of this motion to an unstable transverse vibrational mode. That is, the atomic motions in crystalline bismuth can be electronically accelerated so that the solid-to-liquid phase transition occurs on a sub-vibrational timescale.

Phosphatidylinositol 3-Kinase α–Selective Inhibition With Alpelisib (BYL719) in PIK3CA-Altered Solid Tumors: Results From the First-in-Human Study

Abstract: PurposeWe report the first-in-human phase Ia study to our knowledge (ClinicalTrialsgov identifier: NCT01219699) identifying the maximum tolerated dose and assessing safety and preliminary efficacy of single-agent alpelisib (BYL719), an oral phosphatidylinositol 3-kinase α (PI3Kα)–selective inhibitorPatients and MethodsIn the dose-escalation phase, patients with PIK3CA-altered advanced solid tumors received once-daily or twice-daily oral alpelisib on a continuous schedule In the dose-expansion phase, patients with PIK3CA-altered solid tumors and PIK3CA-wild-type, estrogen receptor–positive/human epidermal growth factor receptor 2–negative breast cancer received alpelisib 400 mg once dailyResultsOne hundred thirty-four patients received treatment Alpelisib maximum tolerated doses were established as 400 mg once daily and 150 mg twice daily Nine patients (132%) in the dose-escalation phase had dose-limiting toxicities of hyperglycemia (n = 6), nausea (n = 2), and both hyperglycemia and hypophosphatemi

Towards Reliable and Quantitative Surface-Enhanced Raman Scattering (SERS): From Key Parameters to Good Analytical Practice.

Abstract: Experimental results obtained in different laboratories world-wide by researchers using surface-enhanced Raman scattering (SERS) can differ significantly. We, an international team of scientists with long-standing expertise in SERS, address this issue from our perspective by presenting considerations on reliable and quantitative SERS. The central idea of this joint effort is to highlight key parameters and pitfalls that are often encountered in the literature. To that end, we provide here a series of recommendations on: a) the characterization of solid and colloidal SERS substrates by correlative electron and optical microscopy and spectroscopy, b) on the determination of the SERS enhancement factor (EF), including suitable Raman reporter/probe molecules, and finally on c) good analytical practice. We hope that both newcomers and specialists will benefit from these recommendations to increase the inter-laboratory comparability of experimental SERS results and further establish SERS as an analytical tool.

Semiclassical Foundation of Universality in Quantum Chaos

Abstract: Fully chaotic dynamics enjoy ergodicity and thus visit everywhere in the accessible space with uniform likeli- hood, over long periods of time. Even long periodic orbits bring about such uniform coverage. Moreover, classical ergodicity provides quantum chaos with universal char- acteristics. Given chaos, quantum energy levels are correlated within local few-level clusters but become statistically in- dependent as their distance grows much larger than the mean level spacing �. The decay of correlations on the scaleis empirically found system independent, within universality classes distinguished by presence or absence of time-reversal (T ) invariance (1, 2). The corresponding universal long-time characteristics act on the Heisenberg scale TH = 2π¯�, withPlanck's constant. Universal spectral fluctuations were conjectured as a manifestation of quantum chaos two decades ago (3). Now, the semiclassical core of a proof can be given. Based on Gutzwiller's periodic-orbit theory (4), our progress comes with two surprises: one lies in its simplicity, the other in the appearance of interesting mathematics (non- trivial properties of permutations). Moreover, the often disputed intimate relation between periodic orbits and quantum field theory is confirmed for good. We thus expect the underlying ideas to radiate beyond spectral fluctuations, like to transport and localization. Technically speaking, we want to show that each com- pletely hyberbolic classical dynamics has a quantum en- ergy spectrum with the same fluctuations as a random- matrix caricature HRMT of its Hamiltonian, even though that caricature has nothing in common with the Hamilto- nian but symmetry (absence or presence of T invariance). The theory of random matrices (RMT) (1, 2, 5), devel- oped by Wigner and Dyson to account for fluctuations in nuclear spectra yields analytic results for correlators of the level density ρ(E), by averaging over suitable ensem- bles of random matrices. Simplest is the two-point corre- lator ρ(E)ρ(E ' ) −ρ(E) ρ(E ' ), where the overlines denote ensemble average. Its Fourier transform with respect to the energy difference E − E ' , called spectral form factor K(τ), is predicted by RMT for systems without time re- versal invariance (unitary class) and with that symmetry (orthogonal class) as

Dynamically assisted Schwinger mechanism.

Abstract: We study electron-positron pair creation from the Dirac vacuum induced by a strong and slowly varying electric field (Schwinger effect) which is superimposed by a weak and rapidly changing electromagnetic field (dynamical pair creation). In the subcritical regime where both mechanisms separately are strongly suppressed, their combined impact yields a pair creation rate which is dramatically enhanced. Intuitively speaking, the strong electric field lowers the threshold for dynamical particle creation--or, alternatively, the fast electromagnetic field generates additional seeds for the Schwinger mechanism. These findings could be relevant for planned ultrahigh intensity lasers.