Constraint Programming Based Column Generation for Crew Assignment

Airline crew assignment problems are large-scale optimization problems which can be adequately solved by column generation. The subproblem is typically a so-called constrained shortest path problem and solved by dynamic programming. However, complex airline regulations arising frequently in European airlines cannot be expressed entirely in this framework and limit the use of pure column generation. In this paper, we formulate the subproblem as a constraint satisfaction problem, thus gaining high expressiveness. Each airline regulation is encoded by one or several constraints. An additional constraint which encapsulates a shortest path algorithm for generating columns with negative reduced costs is introduced. This constraint reduces the search space of the subproblem significantly. Resulting domain reductions are propagated to the other constraints which additionally reduces the search space. Numerical results based on data of a large European airline are presented and demonstrate the potential of our approach.     

A Review of Spectroscopic and Biophysical‐Chemical Studies of the Complex of Cyclobutane Pyrimidine Dimer Photolyase and Cryptochrome DASH with Substrate DNA

Cyclobutane pyrimidine dimer (CPD) photolyase (PL) is a structure‐specific DNA repair enzyme that uses blue light to repair CPD on DNA. Cryptochrome (CRY) DASH enzymes use blue light for the repair of CPD lesions on single‐stranded (ss) DNA, although some may also repair these lesions on double‐stranded (ds) DNA. In addition, CRY DASH may be involved in blue light signaling, similar to cryptochromes. The focus of this review is on spectroscopic and biophysical‐chemical experiments of the enzyme–substrate complex that have contributed to a more detailed understanding of all the aspects of the CPD repair mechanism of CPD photolyase and CRY DASH. This will be performed in the backdrop of the available X‐ray crystal structures of these enzymes bound to a CPD‐like lesion. These structures helped to confirm conclusions that were drawn earlier from spectroscopic and biophysical‐chemical experiments, and they have a critical function as a framework to design new experiments and to interpret new experimental data. This review will show the important synergy between X‐ray crystallography and spectroscopic/biophysical‐chemical investigations that is essential to obtain a sufficiently detailed picture of the overall mechanism of CPD photolyases and CRY DASH proteins.     

Insight into framework destruction in ultramarine pigments

We report key evidence on the framework destruction in ultramarine pigments upon color fading. Experiments on faded pigments in a fresco painting environment reveal that the paramagnetic chromophores are set free via sodalite framework destruction and are subsequently degraded. Fading in acidic media produces similar results, although a larger number of beta-cages appear to be destroyed, and H2S is released. The findings are further supported by studies on natural and synthetic ultramarine pigments of various shades via solid-state resonance-Raman spectroscopy, colorimentry, and solid-state 29Si and 27Al NMR spectroscopy. NMR parameters are shown to correlate well with the intensities of Raman signals corresponding to the S3(-*) chromophores. A further correlation is established between the colorimetric parameters, L* (lightness) and C* (chroma), and the paramagnetic shift and paramagnetic linebroadening in NMR spectra for both 27Al and 29Si.     

Resonance Raman spectroscopy of the neutral radical Trp306 in DNA photolyase

The resonance Raman spectrum of the tryptophan neutral radical in a protein, Escherichia coli photolyase, is reported for the first time. The data compare very well to a solution study and computational predictions, and tentative assignments are made for the observed vibrations. This important new result demonstrates the potential of time-resolved resonance Raman spectroscopy as a powerful tool to investigate these radicals in protein electron-transfer processes and in enzymatic reactions in real time.     

Bestimmung von Trialkylbleispecies in Urin

Zusammenfassung Für die Bestimmung von Trialkylbleispecies (Me₃Pb⁺ und Et₃Pb⁺) in Urin wird ein Analysenverfahren vorgestellt, das aus einem Anreicherungsschritt, einer hochdruckflüssigkeits-chromatographischen Trennung und dem Nachweis mit einem chemischen Reaktionsdetektor besteht. Die Anreicherung erfolgt aus der auf pH 10 eingestellten Urinprobe durch Adsorption an Kieselgel. Das Adsorbermaterial wird mit Borat-Puffer und Wasser gewaschen und die Bleispecies mit einem 10% Methanol enthaltenden Acetat-Puffer (pH 3,7) eluiert. Nach Verdünnen und gleichzeitigem Einstellen des Eluats auf pH 8 mit Borat-Puffer wird eine weitere Anreicherung auf einer Nucleosil 10-C₁₈ Vorsäule durchgeführt. Die Vorsäule ist in eine HPLC-Anlage so integriert, daß die Bleispecies durch eine Säulenschaltung im Backflush direkt auf die analytische Säule eluiert, getrennt und mit dem chemischen Reaktionsdetektor nachgewiesen werden können. Die Nachweisgrenzen für das gesamte Analysenverfahren betragen bei einem Probenvolumen von 50 ml Urin 150 pg/ml für Me₃Pb⁺ und 200 pg/ml für Et₃Pb⁺.

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Determination of trialkyllead species in urine

Summary An analytical method has been developed for the determination of trialkyllead species (Me₃Pb⁺ and Et₃Pb⁺) in urine. The procedure consists of an enrichment step, a separation by HPLC, and the detection by a chemical reaction detector. The urine sample is adjusted to pH 10 and the lead species are adsorbed on silica gel, washed with boratebuffer and water, and finally eluted with an acetate-buffer (pH 3.7) containing 10% of methanol. For further enrichment by a pre-column technique the eluate is diluted and simultaneously adjusted to pH 8 by a borate-buffer. This eluate is injected onto a Nucleosil 10-C₁₈ pre-column, which is integrated in a HPLC-system. The lead species are then eluted in a backflush mode onto the analytical column by column-switching. Separation takes place on a RP-C₁₈ stationary phase followed by the detection with an on-line coupled chemical reaction detector. Starting with 50 ml sample volume the limits of detection for the whole analytical procedure are 150 pg/ml for Me₃Pb⁺and 200 pg/ml for Et₃Pb⁺.

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Herrn Prof. Dr. H. Hartkamp zum 60. Geburtstag gewidmet

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Der Deutschen Forschungsgemeinschaft sind wir für die freundliche Unterstützung zu Dank verpflichtet (Ne 176-4).     

Spektroskopische und kristallographische Charakterisierung von [Cl3PNPCl3][MoOCl4] und die Kristallstruktur von [Cl3PNPCl3][MoCl6]

Spectroscopic and Crystallographic Characterization of [Cl₃PNPCl₃][MoOCl₄] and Crystal Structure of [Cl₃PNPCl₃][MoCl₆] [Cl₃PNPCl₃][MoCl₆] was obtained by reaction of MoCl₅ with [Cl₃PNPCl₃]Cl or [Cl₃PNPCl₃][PCl₆]. Its crystal was determined by X-ray diffraction (R = 0.072 for 889 observed reflexions). Lattice parameters: a = 811.9, b = 2086, c = 1016 pm, β = 101.7°, space group P2₁/c, Z = 4. The [Cl₃PNPCl₃]⁺ ions have a similar structure as in Cl₃PNPCl₃ [PCl₆] with PNP angles of 139°, but the crystal structures of the two compounds are not isotypic. Partial hydrolysis of [Cl₃PNPCl₃][MoCl₆] yields [Cl₃PNPCl₃][MoOCl₄] which forms green, very moisture sensitive crystals. X-ray diffraction patterns of [Cl₃PNPCl₃][MoOCl₄] single crystals exhibit planes of diffuse scattered radiation perpendicular to c^*, which show the presence of a two-dimensional disorder. Additional sharp reflexions correspond to an averaged structure with the lattice parameters a = 1598.4, b = 1141.2 and c = 415.1 pm, Z = 2, space group Pba2. Refinement of the averaged     

On the existence of a unipotent support for the irreducible characters of a finite group of Lie type

In 1980, Lusztig posed the problem of showing the existence of a unipotent support for the irreducible characters of a finite group of Lie type. This problem was solved by Lusztig in the case where the characteristic of the field over which the group is defined is large enough. The first named author extended this to the case where the characteristic is good. It is the purpose of this paper to remove this condition as well, so that the existence of unipotent supports is established in complete generality.

     

Effect of the cyclobutane cytidine dimer on the properties of Escherichia coli DNA photolyase

Cyclobutane pyrimidine dimer (CPD) photolyases are structure specific DNA-repair enzymes that specialize in the repair of CPDs, the major photoproducts that are formed upon irradiation of DNA with ultraviolet light. The purified enzyme binds a flavin adenine dinucleotide (FAD), which is in the neutral radical semiquinone (FADH(*)) form. The CPDs are repaired by a light-driven, electron transfer from the anionic hydroquinone (FADH(-)) singlet excited state to the CPD, which is followed by reductive cleavage of the cyclobutane ring and subsequent monomerization of the pyrimidine bases. CPDs formed between two adjacent thymidine bases (T< >T) are repaired with greater efficiency than those formed between two adjacent cytidine bases (C< >C). In this paper, we investigate the changes in Escherichia coli photolyase that are induced upon binding to DNA containing C< >C lesions using resonance Raman, UV-vis absorption, and transient absorption spectroscopies, spectroelectrochemistry, and computational chemistry. The binding of photolyase to a C< >C lesion modifies the energy levels of FADH(*), the rate of charge recombination between FADH(-) and Trp(306)(*), and protein-FADH(*) interactions differently than binding to a T< >T lesion. However, the reduction potential of the FADH(-)/FADH(*) couple is modified in the same way with both substrates. Our calculations show that the permanent electric dipole moment of C< >C is stronger (12.1 D) and oriented differently than that of T< >T (8.7 D). The possible role of the electric dipole moment of the CPD in modifying the physicochemical properties of photolyase as well as in affecting CPD repair will be discussed.