Multiquantum vibrational excitation of NO scattered from Au(111): quantitative comparison of benchmark data to ab initio theories of nonadiabatic molecule-surface interactions

Surface phenomena: measurements of absolute probabilities are reported for the vibrational excitation of NO(v=0→1,2) molecules scattered from a Au(111) surface. These measurements were quantitatively compared to calculations based on ab?initio theoretical approaches to electronically nonadiabatic molecule-surface interactions. Good agreement was found between theory and experiment (see picture; T(s) =surface temperature, P=excitation probability, and E=incidence energy of translation).     

Molecular orientation of terephthalic acid assembly on epitaxial graphene: NEXAFS and XPS study

The adsorption of terephthalic acid molecules [C(6)H(4)(COOH)(2)), TPA] on a single layer of graphene grown epitaxially on Ni(111) has been investigated by means of near-edge X-ray absorption fine structure (NEXAFS) spectroscopy and X-ray photoelectron spectroscopy (XPS) at room temperature. The assignment of the NEXAFS resonances was aided by ab initio calculations for the free TPA molecule. For coverages up to a monolayer the molecular plane of TPA adopts a parallel orientation with regard to the epitaxial graphene (EG) layer. Deprotonation of TPA molecules at one monolayer coverage can be excluded. For TPA multilayers, the molecular plane is tilted on average by approximately 45° with respect to the sample surface.     

Circular grating waveguide structures for intracavity generation of azimuthal polarization in a thin-disk laser

We report on the generation of beams with azimuthal polarization using resonant grating waveguide structures (GWSs) inside an Yb:YAG thin-disk laser (TDL) oscillator. Two different GWS concepts were used to select the polarization of the emitted beam. The first uses the resonant reflection principle, and the second is based on the leaky-mode approach already reported in our previous work. Up to 93 W and 103 W of output power were extracted from a TDL with an optical efficiency, η(oo), of 36.2% and 40.1% using the first and the second approaches, respectively. In both cases, a pure azimuthal polarization and a beam quality factor, M2, of about 2.2 were measured. The design, fabrication, and different experimental results, as well as the laser performances for both GWSs, are discussed in the present Letter.     

Redox mediation enabled by immobilised centres in the pores of a metal-organic framework grown by liquid phase epitaxy

A layer of a metal-organic framework (SURMOF) was prepared on a thiol monolayer on Au. Charge transport across the insulating membrane could be established by using ferrocene as an immobilised redox mediator. Reversibility of the immobilisation and its role in the electrode kinetics are discussed.     

SQP-methods for solving optimal control problems with control and state constraints: adjoint variables, sensitivity analysis and real-time control

Parametric nonlinear optimal control problems subject to control and state constraints are studied. Two discretization methods are discussed that transcribe optimal control problems into nonlinear programming problems for which SQP-methods provide efficient solution methods. It is shown that SQP-methods can be used also for a check of second-order sufficient conditions and for a postoptimal calculation of adjoint variables. In addition, SQP-methods lead to a robust computation of sensitivity differentials of optimal solutions with respect to perturbation parameters. Numerical sensitivity analysis is the basis for real-time control approximations of perturbed solutions which are obtained by evaluating a first-order Taylor expansion with respect to the parameter. The proposed numerical methods are illustrated by the optimal control of a low-thrust satellite transfer to geosynchronous orbit and a complex control problem from aquanautics. The examples illustrate the robustness, accuracy and efficiency of the proposed numerical algorithms.     

Modelling and Optimization of Cogeneration Plants

Cogeneration plants have a long tradition in Germany and are used to transfrom a given energy into various destination energies, e.g. natural gas into mechanical, electrical and heat energy. In this paper a cogeneration plant composed of several components like gas turbines, waste heat boilers, steam turbines, etc, is modelled in steady state. The thermo-dynamic behaviour of the plant is determined by a set of measured data, which is used to adopt the mathematical model to the real plant. By defining a suitable objective function incorporating e.g. emission trading, an appropriate NLP-solver can be used to solve the generated model which includes several nonlinear constraints. Solutions for different environmental and business conditions are presented, to demonstrate the enormous potential of the proposed method for energy suppliers. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Real-Time Solution of Bi-Level Optimal Control Problems

Bi-level optimal control problems are presented as an extension to classical optimal control problems. Hereby, additional constraints for the primary problem are considered, which depend on the optimal solution of a secondary optimal control problem. A demanding problem is the numerical complexity, since at any point in time the solution of the optimal control problem as well as a complete solution of the secondary problem have to be determined. Hence we deal with two dependent variables in time. The numerical solution of the bi-level problem is illustrated by an application of a container crane. Jerk and energy optimal trajectories with free final time are calculated under the terminal condition that the crane system comes to be at rest at a predefined location. In enlargement additional constraints are investigated to ensure that the crane system can be brought to a rest position by a safety stop at a free but admissible location in minimal time from any state of the trajectory. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Polyketide Cyclizations for the Synthesis of Polyaromatics

The folding and cyclization of poly‐β‐carbonyl chains controlled by the intricate enzymatic polyketide synthase machinery results in a remarkable diversity of aromatic natural products. Synthetic methods that allow for the preparation of highly reactive polyketide chains while governing their folding in ensuing cyclizations likewise lead to versatile divergent preparations of aromatic scaffolds valuable for numerous applications. Although biomimetic polyketide cyclizations have repeatedly been applied in the total synthesis of polyphenol natural products, their utility for the preparation of the broad range of polyaromatic architectures has yet to reach its full potential. This Minireview highlights some of the virtues of applying polyketide logic to the retrosynthetic analysis of polycyclic aromatic scaffolds, the increasing accessibility of precursors, and the potential of small‐molecule catalysts for controlling polyketide cyclizations to provide polyaromatic scaffolds.