Quantum-to-classical transition in cavity quantum electrodynamics

The quantum properties of electromagnetic, mechanical or other harmonic oscillators can be revealed by investigating their strong coherent coupling to a single quantum two level system in an approach known as cavity quantum electrodynamics (QED). At temperatures much lower than the characteristic energy level spacing the observation of vacuum Rabi oscillations or mode splittings with one or a few quanta asserts the quantum nature of the oscillator. Here, we study how the classical response of a cavity QED system emerges from the quantum one when its thermal occupation-or effective temperature-is raised gradually over 5 orders of magnitude. In this way we explore in detail the continuous quantum-to-classical crossover and demonstrate how to extract effective cavity field temperatures from both spectroscopic and time-resolved vacuum Rabi measurements.     

A measurement of the lifetimes of Ξ0 and Λ hyperons

The mean lifetimes of the Λ and Ξ⁰ hyperons have been measured in a short neutral beam at the CERN Proton Synchrotron. Λ and Ξ⁰ decays have been identified by measuring their decay products in a magnetic spectrometer and in a lead glass hodoscope. The experimental results, based on 53 000 Λ decays and 6300 Ξ⁰ decays are

From the result for τ_Ξ⁰ together with existing data on τ_Ξ^? we obtain a violation of the $\text{ΔI =}\text{1}\text{2}$ rule in non-leptonic Ξ decays.     

Micro-mechanical studies on the effect of various stress-states on ductile damage and failure

The paper deals with the effect of different stress states on damage and failure behavior of ductile materials. To be able to model these effects a continuum damage model has been proposed taking into account the dependence of the stress intensity, the stress triaxiality and the Lode parameter on the constitutive equations. The model is based on the introduction of damaged and fictitious undamaged configurations. Only experiments are not adequate enough to determine all constitutive parameters. Therefore, additional three-dimensional micro-mechanical simulations of representative volume elements have been performed to get more insight in the complex damage mechanisms. These simulations cover a wide range of different void sizes, void shapes and void distributions. After all, the results from the micro-mechanical simulations are used to propose the damage equations and to identify corresponding parameters. (© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Lensless diffractive imaging using tabletop coherent high-harmonic soft-X-ray beams

We present the first experimental demonstration of lensless diffractive imaging using coherent soft x rays generated by a tabletop soft-x-ray source. A 29 nm high harmonic beam illuminates an object, and the subsequent diffraction is collected on an x-ray CCD camera. High dynamic range diffraction patterns are obtained by taking multiple exposures while blocking small-angle diffraction using beam blocks of varying size. These patterns reconstruct to images with 214 nm resolution. This work demonstrates a practical tabletop lensless microscope that promises to find applications in materials science, nanoscience, and biology.     

Tin-rich Phases RE2Au3Sn6 with RE = La,Ce, Pr,Nd, Sm – Synthesis,Structure, Magnetic Properties,and 119Sn Mössbauer Spectra

The stannides RE₂Au₃Sn₆ (RE = La, Ce, Pr, Nd, Sm) were synthesized from the elements by arc-melting. Small single crystals were grown by annealing samples in sealed tantalum tubes in an induction furnace with a special annealing sequence. The polycrystalline phases were characterized through their X-ray powder diffraction pattern. The structures of Ce₂Au₃Sn₆, Pr₂Au₃Sn₆, and Nd₂Au₃Sn₆ were refined from single-crystal X-ray diffractometer data. The RE₂Au₃Sn₆ stannides crystallize with the orthorhombic La₂Zn₃Ge₆ type, space group Cmcm. The basic structural building units are Au1@Sn₄ tetrahedra and Au2@Sn₅ square pyramids. These units are condensed to layers and the structure can be described by a simple stacking of tetrahedral and pyramidal layers with the rare earth cations in between. Temperature dependent susceptibility studies indicate that all rare earth atoms are in the trivalent oxidation state, as their effective magnetic moments match the expected values of the free RE³⁺ ions. Pr₂Au₃Sn₆ and Nd₂Au₃Sn₆ exhibit antiferromagnetic ordering at T_N = 6.3(1) and 6.7(1) K. Investigations of the electrical resistivity of La₂Au₃Sn₆ and Ce₂Au₃Sn₆ confirmed that these compounds are metallic, for La₂Au₃Sn₆ a lower resistivity was observed, in line with the absence of screening unpaired electrons. ¹¹⁹Sn Mössbauer spectra for La₂Au₃Sn₆, Ce₂Au₃Sn₆, Pr₂Au₃Sn₆ and Nd₂Au₃Sn₆ show a complex superposition of three sub-spectra which can be differentiated through their distinctly different quadrupole splitting parameters. The isomer shifts (1.87 to 2.22 mm · s^–1) indicate significant s electron density at the tin nuclei.     

Evidence for Electron Transfer between Graphene and Non-Covalently Bound π-Systems

Hybridizing graphene and molecules possess a high potential for developing materials for new applications. However, new methods to characterize such hybrids must be developed. Herein, the wet-chemical non-covalent functionalization of graphene with cationic π-systems is presented and the interaction between graphene and the molecules is characterized in detail. A series of tricationic benzimidazolium salts with various steric demand and counterions was synthesized, characterized and used for the fabrication of graphene hybrids. Subsequently, the doping effects were studied. The molecules are adsorbed onto graphene and studied by Raman spectroscopy, XPS as well as ToF-SIMS. The charged π-systems show a p-doping effect on the underlying graphene. Consequently, the tricationic molecules are reduced through a partial electron transfer process from graphene, a process which is accompanied by the loss of counterions. DFT calculations support this hypothesis and the strong p-doping could be confirmed in fabricated monolayer graphene/hybrid FET devices. The results are the basis to develop sensor applications, which are based on analyte/molecule interactions and effects on doping.     

Tutte's 5-flow conjecture for graphs of nonorientable genus 5

We develop four constructions for nowhere-zero 5-flows of 3-regular graphs that satisfy special structural conditions. Using these constructions we show a minimal counter-example to Tutte's 5-Flow Conjecture is of order ≥44 and therefore every bridgeless graph of nonorientable genus ≤5 has a nowhere-zero 5-flow. One of the structural properties is formulated in terms of the structure of the multigraph G(F) obtained from a given 3-regular graph G by contracting the cycles of a 2-factor F in G. © 1996 John Wiley & Sons, Inc.     

The catalysis of the stereospecific butadiene polymerization by Allyl Nickel and Allyl Lanthanide complexes — A mechanistic comparison

A short overview on the general mechanistic principles of the allyl metal complex catalyzed stereo-specific butadiene polymerization is given. The present state of knowledge on the mechanism of stereoregulation and in the understanding of the catalytic structure reactivity relationships is discussed comparatively for allyl nickel and allyl lanthanide catalysts.