Measurement of storage time, estimation of ion number and study of absorption line profile in a Paul trap

Europium (Eu⁺) ions were confined in a Paul trap and detected by non-destructive method. Storage time of Eu⁺ ions achieved in vacuum was improved by orders of magnitude employing buffer gas cooling. The experimentally detected signal was fitted to the ion response signal and the total number of ions trapped was estimated. It is found that the peak signal amplitude as well as the product of FWHM and the peak signal amplitude is proportional to the total number of trapped ions. The trapped ion secular frequency was swept at different rates and its effect on the absorption line profile was studied both experimentally and theoretically.     

Paramagnetic defects in BaTiO3 and their role in light-induced charge transport — Optical studies

On the basis of a previous identification of paramagnetic defects in nominally undoped as grown BaTiO₃ single crystals, we have investigated the changes of the concentrations of these centers and their optical absorptions under illumination with light of varying wavelengths. The most pronounced charge transfers occur by hole ionization of Fe⁴⁺ and — to a lesser extent — of Cr⁵⁺ and Cr⁴⁺. At low temperatures the created holes are trapped in the form of O^–-ions next to Al³⁺ or unknown acceptor defects. Corresponding Fe⁴⁺ and O^– absorptions have been identified.     

The course scheduling problem at Lufthansa Technical Training

Lufthansa Technical Training GmbH (LTT) performs training courses for Lufthansa Technik AG as well as for several other international airlines. Courses of about 670 different types are offered of which several hundred take place each year. The course scheduling problem faced by LTT is to construct a yearly schedule which maximizes the profit margin incurred while meeting a variety of complex precedence, temporal, and resource-related constraints. A “good” operational schedule should also meet a number of additional subordinate objectives. We formalize the problem and develop a heuristic scheme along with several priority rules, as well as a local search algorithm to determine well-suited weights for weighted composite rules. The operational planning situation of 1996 served as our major test instance; additional test instances were constructed by modifying this data. Several computational experiments were carried out to evaluate the performance of the algorithms. It turned out that the best so-found schedule is substantially better in terms of the profit margin incurred than the solution manually constructed by LTT.     

Zur Charakterisierung von Eigenschaften der versteiften dreizähnigen Aminophosphanliganden N,N'-Bis(diphenylphosphino)-2,6-diaminopyridin und N,N-Bis(diphenylphosphino)-2-aminopyridin mit Metallen der Chromgruppe

Inhaltsübersicht. Edukte von Typ M(CO)₆ (M = Cr, Mo,W), N,N'-Bis(diphenylphosphino)-2,6-diaminopyridin (PNP) und Trimethylaminoxid setzen sich bei Raumtemperatur nicht zu dem bekannten Verbindungstyp mer-M(CO)₃PNP, sondern zu Verbindungen der beiden Typen M(CO)₄(PNP=O) mit zweizähnig koordinierten Liganden PNP=O und M(CO)₅(NMe₃) um. Die zu Vergleichszwecken untersuchte Oxidation eines koordinierten PNP-Liganden von mer-Mo(CO)₃(PNP) in Tetramethylbenzollösung ergibt mit Luftsauerstoff bei 180°C eine Reaktion unter Spaltung der P–N-Bindung zur cubanartigen Verbindung Mo₄(μ₃-O)₄(μ-Ph₂PO₂)₄O₄ (Ausbeute 48%). In einem Glaseinschlußrohr reagiert der ambidente N,N-Bis(diphenyIphosphino)-2-nminopyridin-Ligand (NPP) mit den Hexacarbonylen M(CO)₆ in Toluollösung bei 140°C zu Verbindungen des Typs M(CO)₄(NPP) mit zweizähniger Verknüpfung des NPP-Liganden. Hierbei bilden die beiden P-Donoratome am Aminstickstoffatom einen MP₂N-Chelatvierring an Stelle des ebenfalls möglichen P, N_py-Chelatfünfrings. Der analoge Chelatvierring entsteht gleichfalls bei einer Ligandensubstitutions-reaktion zwischen Verbindungen des Zweikernkomplextyps MM′(CO)₈(μ-PPh₂)₂ (M = M′ = W; M = Mo, M′ = W) bzw. \V(CO)₄(μ-PPh₂)₂IrH(CO)(PPh₃) und NPP. Er bildet sich außerdem bei der Thermolyse von Mo(CO)₄(NPP) zu Mo₂(CO)₆(μ-PPh₂)₂(NPP). Die Identifizierung erfolgt im Falle der Verbindungen Mo(CO)₄(PNP=O), Mo₄(μ₃-O)₄(μ-Ph₂PO₂)₄O_4′ Mo₂(CO)₆(μ-PPh₂)₂(NPP) und W(CO)₄(μ-PPh₂)₂IrH(CO)(NPP) durch Einkristall-Röntgenstrukturanalysen. Alle isolierten Produkte werden durch spektroskopische Messungen insbesondere ³¹P-NMR-Daten charakterisiert. Characterization of Properties of the Rigid Tridentate Chelate Ligand N,N′-Bis(diphenylphosphino)-2,6-diaminopyridine and N,N-Bis(diphenylphosphino)-2-aminopyridine with Transition Metals of the Chromium Group Hexacarbonyls M(CO)₆ (M = Cr, Mo, W), N,N′-Bis(diphenylphosphino)-2,6-diaminopyridine (PNP) and trimethylamine oxide gave products of two types M(CO)₄(PNP=O) having a bidentate ligand PNP=O and M(CO)₅(NMe₃) instead of the desired mer-M(CO)₃PNP. For the purpose of a comparison, aerial oxidation of mer-Mo(CO)₃PNP in tetramethyl benzene solution at 180°C was examined which resulted a P–N bond rupture under formation of the cubane-like product Mo₄(μ₃-O)₄(μ-Ph₂PO₂C₄O₄){yield 48%). In sealed glass tubes the ambidentate ligand N,N-bis(diphenylphosphino)-2-aminopyridine (NPP) was reacted with the hexacarbonyls M(CO)₆ in toluene solution at 140°C to products of the type M(CO)₄NPP with NPP as bidentate ligand. Under this reaction conditions the four-membered chelate ring of the type MP₂N was formed with the two P donor atoms attached to the amine N atom instead of the possible competitive five-membered chelate ring formation with a P and pyridyl nitrogen. The analogous four-membered chelate ring was formed in ligand substitution reactions between the substance NPP and each of the dinuclear coordination compounds MM′(CO)₈(μ-PPh₂)₂ (M = M′ = W, M = Mo, M′ = W) including W(CO)₄(μ-PPh₂)₂IrH(CO)(PPh₃); Mo₂(CO)6(μ-PPh₂)₂(NPP) was obtained via thermolysis of Mo(CO)₄(PNP=O). The given structural identification of the compounds Mo(CO)₄(PNP=O), Mo₄(μ₃-O)₄(μ-Ph₂PO₂)₄O₄, Mo₂(CO)₆ (μ-PPh₂)₂(NPP) and W(CO)₄(μ-PPh₂)₂IrH(CO) (NPP) was done by single-crystal X-ray analysis. All seperated products have been characterized by means of spectroscopic measurements especially ³¹P n.m.r. data.     

Dithiol proteins as guardians of the intracellular redox milieu in parasites: old and new drug targets in trypanosomes and malaria-causing plasmodia

Parasitic diseases such as sleeping sickness, Chagas' heart disease, and malaria are major health problems in poverty-stricken areas. Antiparasitic drugs that are not only active but also affordable and readily available are urgently required. One approach to finding new drugs and rediscovering old ones is based on enzyme inhibitors that paralyze antioxidant systems in the pathogens. These antioxidant ensembles are essential to the parasites as they are attacked in the human host by strong oxidants such as peroxynitrite, hypochlorite, and H2O2. The pathogen-protecting system consists of some 20 thiol and dithiol proteins, which buffer the intraparasitic redox milieu at a potential of -250 mV. In trypanosomes and leishmania the network is centered around the unique dithiol trypanothione (N1,N8-bis(glutathionyl)spermidine). In contrast, malaria parasites have a more conservative dual antioxidative system based on glutathione and thioredoxin. Inhibitors of antioxidant enzymes such as trypanothione reductase are, indeed, parasiticidal but they can also delay or prevent resistance against a number of other antiparasitic drugs.     

Systematic optimisation of high-performance liquid chromatographic separation by varying the temperature, gradient, and stationary phase

Optimisation of the separation of a synthetic drug mixture by HPLC is performed by changing both continuous variables, i.e. mobile phase composition and temperature, and categorical variables, here the stationary phase. The retention of solutes is described on the basis of a general linear model in which the different columns are modelled by indicator variables. From the solute-specific retention models the global separation optimum is evaluated on the basis of multidimensional window diagrams using relative retentions of all peak pairs as the figure-of-merit.     

Ferrimagnetische Resonanz in Rotationsellipsoiden

Ferrimagnetic resonance at 9660 Mc/s in prolate spheroids (ratio of axes 1:5 to 1:1) of polycristalline ferrites has been investigated. The saturation magnetization between room temperature and the Curie point has been calculated from the displacement of the field needed for resonance in comparison to spherical samples. The halfwidth depends strongly on the ratio of axes and the orientation of the samples because the uniform precession is displaced in relation to the upper spin wave limit.