Computing ray class groups, conductors and discriminants

We use the algorithmic computation of exact sequences of Abelian groups to compute the complete structure of for an ideal of a number field , as well as ray class groups of number fields, and conductors and discriminants of the corresponding Abelian extensions. As an application we give several number fields with discriminants less than previously known ones.

     

Harmonization of methods for analysis of cholesterol oxides in foods--the first portion of a long road toward standardization: interlaboratory study

A compilation of literature data on the content of cholesterol oxidation products (COP) in various food products and in blood demonstrates a large variation in content in products or tissues of very similar nature when analyzed in different laboratories according to a large number of methods. The lack of validated, internationally recognized methodology with published accuracy and precision has so far hindered such assessments. Hence an interlaboratory comparision of methodologies of COP analysis was undertaken on egg yolk powders (EYP), whole milk powders (WMP), skim milk powders (SMP), and lard (L). Each product type had one fresh sample (low) and one aged (high) in COP contents. A total of 17 sets of results on WMP, 15 on SMP and EYP, and 13 on L were compared. Overall results (mg/kg sample) varied extensively: Fresh EYP 0.72-265, aged EYP 2.51-361; fresh WMP 0.02-18.1, aged WMP 0.02-26.9; fresh SMP 0.02-6.51, aged SMP <0.01-6.51; fresh L 0.18-97, aged L 4.15-452. Some results were questioned, viz., those from laboratories not indicating substantial differences between samples "low" and "high" in total COP. Others were excluded because of lack of verification of identity of gas chromatographic peaks by mass spectrometry. Then a more narrow range of core results (mg/kg sample) was observed: Fresh EYP 5.69-29.5 sample, aged EYP 11.8-79.0; fresh WMP 0.12-1.76, aged WMP 1.17-13.7; fresh SMP <0.30-<1.21, aged SMP 0.30-2.26; fresh L 0.18-5.07, aged L 94.4-231. At a workshop discussing the results, numerous recommendations were made toward more reliable methodology for determination of COP in foods.     

Effect of Iron Substitution on the Structural, Electric, and Magnetic Properties inR-Type PbFexV6−xO11, a Frustrated System

Single-phase material of the solid solution PbFe_xV_6−xO₁₁was prepared by solid-state reaction over the range 1≤x≤1.75. Powder preparations of PbV₆O₁₁, however, were always accompanied by a small amount of impurity. The noncentrosymmetric space groupP6₃mcof PbV₆O₁₁, which has anR-block structure, remains unchanged with iron substitution. The crystal structure of PbFe_1.75V_4.25O₁₁was refined from single-crystal X-ray data toR=0.049. The iron atoms are located preferentially in specific crystallographic sites. The triangular–bipyramidal site is completely occupied by Fe³⁺while the interstices of the central octahedral layer are solely occupied by the vanadium V(1) atoms. The other two crystallographic sites have mixed Fe/V occupancies. Magnetic measurements performed on nearly single-phase PbV₆O₁₁and the iron substituted phases reveal a spin-glass-type behavior with freezing temperaturesT_fof 50 and 65 K, respectively.T_fis independent of the iron ratio. This spin-disordered system is attributed to strong frustration occuring in thea–bplane because of the existence of V(1) trimers providing alternatively long and short V–V distances along theaaxis. Resistance and Seebeck coefficient measurements indicatep-type conduction aboveT_fwhile the system becomes an insulator belowT_f. Fe³⁺ions do not participate in the hopping process, and they block conduction parallel to thecaxis because of their location in the bridging dimeric octahedral and bipyramidal sites.     

Synthesis,structure and reactivity of imidazo[1,2-a][1,8]naphthyridines

The synthesis and reactivity of imidazo[1,2-a][1,8]naphthyridines are reported. Electrophilic substitution reactions were studied and the site of the reaction was established with the aid of high-field ¹H and ¹³C nmr spectra. The experimental C-1 position reaction was correlated with a CNDO/2 calculations.     

Toward the synthesis of spirastrellolide A: construction of two C1-C25 diastereomers containing the BC-spiroacetal

[reaction: see text] Stereo-controlled syntheses of two possible C1-C25 diastereomers of spirastrellolide A containing the cis-disubstituted tetrahydropyran and [6,6]-spiroacetal are reported, exploiting boron-mediated asymmetric aldol and allylation methodology.     

Ensemble methods for classification in cheminformatics

We describe the application of ensemble methods to binary classification problems on two pharmaceutical compound data sets. Several variants of single and ensembles models of k-nearest neighbors classifiers, support vector machines (SVMs), and single ridge regression models are compared. All methods exhibit robust classification even when more features are given than observations. On two data sets dealing with specific properties of drug-like substances (cytochrome P450 inhibition and "Frequent Hitters", i.e., unspecific protein inhibition), we achieve classification rates above 90%. We are able to reduce the cross-validated misclassification rate for the Frequent Hitters problem by a factor of 2 compared to previous results obtained for the same data set with different modeling techniques.     

Verfahren zur Bestimmung von Quecksilberspuren durch flammenlose Atomabsorption

Zusammenfassung Beschrieben wird die Bestimmung von Spuren Quecksilber nach Reduktion mit, Zinn(II)-chlorid in Lösung. Das nach der Reduktion in elementarer Form vorliegende Quecksilber wird mit einem Luftstrom in eine Meßküvette überführt, die sich im Strahlengang einer Hohlkathodenlampe oder eines Niederdruckbrenners befindet. Die Energieabnahme bei 254 nm ist ein Maß für die vorhandene Quecksilbermenge.Verfahren zur Probenaufbereitung von Gasen, Wasser, Natronlauge, Urin, Pyrokohlensäurediäthylester und weiteren organischen Substanzen werden beschrieben.Nach dieser Methode lassen sich noch 0,2 ppb Quecksilber sicher bestimmen. Im Vergleich zur Atomabsorptionsanalyse mit Flamme ist damit eine Empfindlichkeitssteigerung um den Faktor 10⁴ erreicht worden. Die Methode eignet sich für anorganisch und organisch gebundenes Quecksilber und läßt sich auf alle Probleme anwenden, soweit eine geeignete Probenaufbereitung gefunden werden kann.Durch ein Kompensationsverfahren (Deuteriumkompensator) sind Störungen durch andere im ultravioletten Bereich absorbierende Substanzen weitgehend ausgeschaltet.

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Method for the determination of traces of mercury by flameless atomic absorption

The determination of traces of mercury after reduction by stannous chloride in solution is described. The reduced elementary mercury is transported by an air stream into an absorption cell placed in the beam of a hollow cathode lamp or a low pressure burner. The energy decrease at 254 nm is a measure for the mercury present. Methods for sample preparation of gases, water, soda licquor, urine, diethyl pyrocarbonate and other organic materials are described.By that method 0.2 ppb of mercury are exactly determined. Compared to flame atomic absorption there is an increase in sensitivity by 10⁴. The method is suitable for inorganic and organic bound mercury and is applicable for all problems, if a suitable sample preparation is possible.By a compensation method (deuterium arc background corrector) interferences by other UV-absorbing substances are largely eliminated.

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An dieser Stelle sei Herrn Dr. von Falkai, dem Leiter des Wissenschaftlichen Laboratoriums der Farbenfabriken Bayer AG, Werk Dormagen, für seine Unterstützung gedankt.

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Den Herren K. Schumann und G. Mausbach danke ich für ihre sorgfältige experimentelle Mitarbeit.     

Polarization effects on the hyper-Raman spectra of carbon tetrachloride: a joint experimental-theoretical study

Hyper-Raman spectra of pure carbon tetrachloride in the liquid phase are recorded for different combinations of the polarizations of the incident and scattered lights and are compared to ab initio time-dependent Hartree-Fock simulations. Both the calculated intensities of the Raman and hyper-Raman spectra give indeed a quite satisfactory agreement with polarized experimental spectra.     

Synthesis and biological testing of 3‐phenyloctahydro‐pyrimido[1,2‐a]‐s‐triazine derivatives

A series of 46 3‐phenyloctahydropyrimido[1,2‐a]‐s–triazine derivatives were synthesized. This synthesis was performed via iminodimethylation of dialkylated 2‐aminopyrimidinedione synthons by substituted primary arylamines. In vitro pharmacological evaluation of these compounds is reported. One of them exhibited antifungal activity against Microsporum canis (10^?6₅₀10^?5 mol/L), and another showed affinity for serotoninergic 5‐HT_1A and 5‐HT_2b receptors (10^?8₅₀10^?7 mol/L).     

Dependence on sampling rates of Radiello((R)) diffusion sampler for BTEX measurements with the concentration level and exposure time

Radiello^® diffusive samplers filled with a thermally desorbable adsorbent (graphitised charcoal Carbograph 4) have been tested for the monitoring of BTEX. The sampling rates have been estimated under various controlled atmospheres in order to evaluate the effects of two factors (exposure time, concentration levels and their interaction) on the performances of the Radiello^® sampler. Experiments have been carried out under various atmospheres in exposure chamber. A total of 174 Radiello^® samplers were exposed while varying two conditions: exposure time (1, 3, 7 and 14 days) and BTEX concentrations (low, medium and high levels). The results show that the sampling rates of benzene and toluene decrease for exposure of 14 days and especially for high concentration levels: decrease of 30% at 10 μg m⁻³ for benzene and 14% at 30 μg m⁻³ for toluene.

To try to explain the variations of these sampling rates, the breakthrough volumes (V_B) of BTEX on Carbograph 4 have been determined at different temperature and concentration conditions in order to evaluate the Langmuir parameters and their adsorption enthalpy (−ΔH_ads) using the Van’t Hoff equation. With regard to these adsorption characteristics, the dependence of sampling rates with concentration level and exposure time were analysed and discussed.