GOSAC: global optimization with surrogate approximation of constraints

We introduce GOSAC, a global optimization algorithm for problems with computationally expensive black-box constraints and computationally cheap objective functions. The variables may be continuous, integer, or mixed-integer. GOSAC uses a two-phase optimization approach. The first phase aims at finding a feasible point by solving a multi-objective optimization problem in which the constraints are minimized simultaneously. The second phase aims at improving the feasible solution. In both phases, we use cubic radial basis function surrogate models to approximate the computationally expensive constraints. We iteratively select sample points by minimizing the computationally cheap objective function subject to the constraint function approximations. We assess GOSAC’s efficiency on computationally cheap test problems with integer, mixed-integer, and continuous variables and two environmental applications. We compare GOSAC to NOMAD and a genetic algorithm (GA). The results of the numerical experiments show that for a given budget of allowed expensive constraint evaluations, GOSAC finds better feasible solutions more efficiently than NOMAD and GA for most benchmark problems and both applications. GOSAC finds feasible solutions with a higher probability than NOMAD and GOSAC.     

Karminsäure

Carminic acid was isolated from dried Dactylopius coccus Costa (Dactylopiidae) and chromatographically purified. All analytical spectra were recorded and are reproduced either in the main part or in the supplementary material. The NMR‐ and mass‐spectra have been interpreted and compared with theoretical calculations of the ¹³C chemical shifts. The project is a follow up of the recent book “Classics in Spectroscopy” by S. Berger und D. Sicker (Wiley‐VCH 2009).     

Formation of Schottky-type metal/SrTiO3 junctions and their resistive properties

Motivated by the successful use of strontium titanate with different doping metals for memory cells on the basis of resistive switching and the recent findings on the major importance of oxygen vacancy redistribution in this compound, the present work shows the possibility of a non-volatile resistance change memory based on vacancy-doped SrTiO₃. The formation of corresponding metal/SrTiO_3−δ junctions (δ>0) in an electric field will be discussed as well as the switching between ohmic and Schottky-type contact behavior. A notable hysteresis in the current–voltage characteristics is used to carry out Write, Read, and Erase operations exemplifying the memory cell properties of such junctions. But whereas the electric field-induced formation of Schottky-type junctions is explainable by oxygen vacancy redistribution, the resistive switching needs to be discussed in terms of vacancies serving as electron trap states at the metal/oxide interface.     

Carbon ceramic electrodes modified with mixed oxides SiO<Subscript>2</Subscript>/SnO<Subscript>2</Subscript> for determination of levofloxacin

The preparation of a carbon ceramic electrode modified with SnO₂ (CCE/SnO₂) using tin dibutyl diacetate as precursor was optimized by a 2³ factorial design. The factors analyzed were catalyst (HCl), graphite/organic precursor ratio, and inorganic precursor (dibutyltin diacetate). The statistical treatment of the data showed that only the second-order interaction effect, catalyst × inorganic precursor, was significant at 95% confidence level, for the electrochemical response of the system. The obtained material was characterized by scanning electron microscopy (MEV), X-ray diffraction (XRD), RAMAN spectroscopy, XPS spectra, and voltammetric techniques. From the XPS spectra, it was confirmed the formation of the Si–O–Sn bond by the shift in the binding energy values referred to Sn 3d3/2 due to the interaction of Sn with SiOH species. The incorporation of SnO₂ provided an increment of the electrode response for levofloxacin, with Ipa = 147.0 μA for the ECC and Ipa = 228.8 μA for ECC/SnO₂, indicating that SnO₂ when incorporated into the silica network enhances the electron transfer process. Under the optimized working conditions, the peak current increased linearly with the levofloxacin concentration in the range from 6.21×10^?5 to 6.97×10^?4 mol L^?1 with quantification and detection limits of 3.80×10^?5 mol L^?1 (14.07 mg L^?1) and 1.13×10^?5 mol L^?1 (4.18 mg L^?1), respectively.     

Sr5Al5+xSi21−xN35−xO2+x:Eu2+ (x≈0)—A Novel Green Phosphor for White‐Light pcLEDs with Disordered Intergrowth Structure

A novel sialon phosphor is characterized by an unusual silicate framework, built up of edge‐ and vertex‐sharing tetrahedra (orange and green). Owing to pronounced pseudotranslations, the compound is highly disordered. It was investigated in detail by X‐ray diffraction and electron microscopy. Despite the disorder, all Sr atoms (yellow spheres) exhibit very similar coordination spheres, and doping with Eu²⁺ results in efficient green luminescence (see inset; Em.=emission, Exc.=excitation, Refl.=reflection).

     

Similarity of High-Resolution Tandem Mass Spectrometry Spectra of Structurally Related Micropollutants and Transformation Products

High-resolution tandem mass spectrometry (HRMS2) with electrospray ionization is frequently applied to study polar organic molecules such as micropollutants. Fragmentation provides structural information to confirm structures of known compounds or propose structures of unknown compounds. Similarity of HRMS2 spectra between structurally related compounds has been suggested to facilitate identification of unknown compounds. To test this hypothesis, the similarity of reference standard HRMS2 spectra was calculated for 243 pairs of micropollutants and their structurally related transformation products (TPs); for comparison, spectral similarity was also calculated for 219 pairs of unrelated compounds. Spectra were measured on Orbitrap and QTOF mass spectrometers and similarity was calculated with the dot product. The influence of different factors on spectral similarity [e.g., normalized collision energy (NCE), merging fragments from all NCEs, and shifting fragments by the mass difference of the pair] was considered. Spectral similarity increased at higher NCEs and highest similarity scores for related pairs were obtained with merged spectra including measured fragments and shifted fragments. Removal of the monoisotopic peak was critical to reduce false positives. Using a spectral similarity score threshold of 0.52, 40% of related pairs and 0% of unrelated pairs were above this value. Structural similarity was estimated with the Tanimoto coefficient and pairs with higher structural similarity generally had higher spectral similarity. Pairs where one or both compounds contained heteroatoms such as sulfur often resulted in dissimilar spectra. This work demonstrates that HRMS2 spectral similarity may indicate structural similarity and that spectral similarity can be used in the future to screen complex samples for related compounds such as micropollutants and TPs, assisting in the prioritization of non-target compounds.

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Graphical Abstract ?

     

Templated Generation of a Bcl-xL Inhibitor by Isomer-Free SPAAC Based on Azacyclonon-5-yne

High-affinity inhibitors of large protein–protein interactions often have a high molecular weight, which compromises their cell permeability and oral bioavailability. We recently presented isomer-free, strain-promoted azide-alkyne cycloaddition (iSPAAC) as a method by which to generate large, chemically uniform bioactive molecules inside living cells from two smaller components with higher cell permeability. Here, we present the synthesis of Fmoc-protected azacyclonon-5-yne (Fmoc-ACN) as the first cyclononyne suitable for iSPAAC. ACN facilitated the structure-guided development of a single-digit micromolar triazole inhibitor of the protein–protein interaction domain of the antiapoptotic protein Bcl-x_L. Inhibitor formation in aqueous buffer at 37 °C, templated by the target protein Bcl-x_L, proceeded 2800 times faster than the reaction between Fmoc-ACN and benzyl azide under standard conditions in acetonitrile. Our data demonstrate the utility of cyclononynes for iSPAAC and their potential for achieving vastly accelerated templated reactions in aqueous environments.     

In situ investigations of the thermal fatigue behaviour of hot pressed Si3N4 by laser shock loading inside an SEM

The influence of both material microstructure and chemical composition of the grain boundary phase on subcritical crack growth under cyclic heat loading of hot pressed Si₃N₄ ceramics was investigated. The samples were locally irradiated by Nd : YAG high power laser pulses in front of a saw notch, in order to generate high temperature gradients. By combination of the laser with an SEM, material damage such as crack initiation and growth at the surface could be characterised with high lateral resolution and depth of focus. The relevance of high temperature processes like viscous flow of the grain boundary phase to material damage can be deduced from the analysis of subcritical crack growth. On the basis of experimental results a damage model is developed for the high temperature range. Received: 30 July 1997 / Revised: 13 March 1998 / Accepted: 20 March 1998     

Bemerkung über Faltungspotenzen eines Wahrscheinlichkeitsmaßes auf kompakten Gruppen

Ohne Zusammenfassung     

Local damage of HT-materials by laser irradiation in the SEM

By using a pulsed Nd:YAG laser the high temperature materials zirconium oxide, fine grain graphite and silicon nitride were rapidly irradiated (heating thermal shock) and their damage behavior was investigated. The laser beam parameters at sample surface were detected by a laser beam analyzing system and correlated with the local damage mechanisms of the materials as erosion, crack formation and solid-solid phase transformation. For the investigations image analysis, localized x-ray analysis, and the ion beam slope cutting technique were applied. The temperature field in the material was simulated by using temperature dependent material parameters for different laser beam parameters. The results illustrate both the strong influence of the temporal and spatial laser energy profile and the materials properties to the material damage.Dedicated to Professor Dr. rer. nat. Dr. h.c. Hubertus Nickel on the occasion of his 65th birthday