Oscillatory passive active transition during the corrosion in nickel chromium layer systems

The electrochemical corrosion of the porous layer system nickel/chromium was investigated combining classical open circuit measurements, cyclic voltammetry, and zero-resistance Ammeter experiments. Under moderate conditions as there are low chloride concentration, pH 6, and high oxygen content the nickel layer acts as sacrificial anode, whereas at the chromium top layer oxygen reduction takes place. Under conditions of limited access of oxygen into pores potential oscillations occur which indicates a change of corrosion mechanism. Thereby the anode reaction changes between nickel and chromium dissolution. The respective cathode reaction is oxygen reduction or hydrogen evolution. The modeling of the potential oscillation reveals the character of the potential-dependent Flade potential as function of the proton concentration.     

Synthesis of pyran and pyranone natural products

An overview of the synthesis of the fungal metabolites (+)-dermolactone, (-)- semixanthomegnin, (+)- and (-)-mellein, (-)-ochratoxin alpha, (-)-(1R,3S)-thysanone, the enantiopure ventiloquinones L, E and G, and 8-desmethyleleutherin from a common chiral intermediate, is presented. Further methodology leading potentially toward extended quinones such as (3S,3'S)-xylindein is also outlined.     

Dynamical coupling between a Bose–Einstein condensate and a cavity optical lattice

A Bose–Einstein condensate is dispersively coupled to a single mode of an ultra-high finesse optical cavity. The system is governed by strong interactions between the atomic motion and the light field even at the level of single quanta. While coherently pumping the cavity mode the condensate is subject to the cavity optical lattice potential whose depth depends nonlinearly on the atomic density distribution. We observe optical bistability already below the single photon level and strong back-action dynamics which tunes the coupled system periodically out of resonance.     

Trends in hard X-ray fluorescence mapping: environmental applications in the age of fast detectors

Environmental samples are extremely diverse but share a tendency for heterogeneity and complexity. This heterogeneity poses methodological challenges when investigating biogeochemical processes. In recent years, the development of analytical tools capable of probing element distribution and speciation at the microscale have allowed this challenge to be addressed. Of these available tools, laterally resolved synchrotron techniques such as X-ray fluorescence mapping are key methods for the in situ investigation of micronutrients and inorganic contaminants in environmental samples. This article demonstrates how recent advances in X-ray fluorescence detector technology are bringing new possibilities to environmental research. Fast detectors are helping to circumvent major issues such as X-ray beam damage of hydrated samples, as dwell times during scanning are reduced. They are also helping to reduce temporal beamtime requirements, making particularly time-consuming techniques such as micro X-ray fluorescence (μXRF) tomography increasingly feasible. This article focuses on μXRF mapping of nutrients and metalloids in environmental samples, and suggests that the current divide between mapping and speciation techniques will be increasingly blurred by the development of combined approaches.     

Geometric and dynamic perspectives on phase-coherent and noncoherent chaos

Statistically distinguishing between phase-coherent and noncoherent chaotic dynamics from time series is a contemporary problem in nonlinear sciences. In this work, we propose different measures based on recurrence properties of recorded trajectories, which characterize the underlying systems from both geometric and dynamic viewpoints. The potentials of the individual measures for discriminating phase-coherent and noncoherent chaotic oscillations are discussed. A detailed numerical analysis is performed for the chaotic Ro?ssler system, which displays both types of chaos as one control parameter is varied, and the Mackey-Glass system as an example of a time-delay system with noncoherent chaos. Our results demonstrate that especially geometric measures from recurrence network analysis are well suited for tracing transitions between spiral- and screw-type chaos, a common route from phase-coherent to noncoherent chaos also found in other nonlinear oscillators. A detailed explanation of the observed behavior in terms of attractor geometry is given.     

Surface density oscillations in disordered binary alloys: X-ray reflectivity study of Cu3Au(001)

3 Au(001) surface using Synchrotron radiation and show that the intensity distribution along the specular rod exhibits the same features as in the case of liquid metals which has been discussed in recent literature. The results are discussed within the framework of the distorted wave Born approximation which allows a straightforward easy-to-apply scheme to analyze such reflectivity data in the entire -range including the total external reflection regime. The data analysis gives a direct evidence for an oscillating average density profile which is analoguous to the socalled surface layering at liquid surfaces. The experimental values for the thermal roughness indicate that surface roughness is suppressed in the ordered phase and allowed to softly grow with temperature above the bulk order-disorder phase transition. The presented experimental and theoretical study of X-ray reflectivity from binary alloys demonstrates the potential of this technique for the study of surface roughening, surface layering and surface segregation phenomena at solid and liquid surfaces. Received: 14 August 1996/Accepted: 7 October 1996     

Nanoporous metal organic framework materials for hydrogen storage

Hydrogen is expected to play an important role in future transportation as a promising alternative clean energy source to carbon-based fuels.One of the key challenges to commercialize hydrogen energy is to develop appropriate onboard hydrogen storage systems,capable of charging and discharging large quantities of hydrogen with fast enough kinetics to meet commercial requirements.Metal organic framework (MOF) is a new type of inorganic and organic hybrid nanoporous particulate materials.Its diverse networks can enhance hydrogen storage through tuning the structure and property of MOFs.The MOF materials so far developed adsorb hydrogen through weak disperston interactions,which allow significant quantity of hydrogen to be stored at cryogenic temperatures with fast kinetics.Novel MOFs are being developed to strengthen the interactions between hydrogen and MOFs in order to store hydrogen under ambient conditions.This review surveys the development of such candidate materials,their performance and future research needs.