Glycerin

Ohne Zusammenfassung     

Substituent effects on the mass spectra of substituted phenyl acetates

The mass spectra of a series of meta- and para-substituted phenyl acetates have been examined. Substituent effects have been correlated with Δ (AP-IP) values and by using the Harrison and Chin approach. The bond-cleavage and rearrangement reactions of phenyl accetates are compared with the corresponding reactions of acetanilides and the differences attributed to the degree of transmission of polar effects in the two systems.     

Dielectric properties of wool and horn containing absorbed water

Summary The dielectric properties of wool containing 0→30% H₂O have been examined for the temperature range −90→22 °C. An absorption peak due to the orientation of bound water molecules has been studied and found to be unlike ice or liquid water. Other absorption bands were found;Ω due to interfacial polarisation;α′ due to main chain motion;β due to localised chain motion andδ of unknown origin. For each of these bands the distribution of relaxation times and the activation enthalpies have been obtained.

---

Zusammenfassung Das dielektrische Verhalten von 0–30% Wasser enthaltender Wolle wurde zwischen −90 bis +22 °C untersucht. Ein Absorptionsmaximum, welches anhand der Orientierung der gebundenen Wassermoleküle bestehend, wurde eingehend untersucht und nicht als Eis oder (flüssiges) Wasser befunden. Weitere Absorptionsbanden wurden beobachtet;Ω von der Zwischenphasenpolarisation resultierend,α′ von der Hauptkettenbewegung,β von der Bewegung lokalisierter Ketten undσ von unbekannter Herkunft. Die Verteilung der Relaxationszeiten und die Aktivierungsenthalpie wurden für die einzelnen Banden erhalten.

     

Simultaneous analysis of hepatotoxic pyrrolizidine alkaloids and N-oxides in comfrey root by LC-ion trap mass spectrometry

The purpose of the current study was to develop a LC-MS(n) method for the analysis of pyrrolizidine alkaloids (PAs) in comfrey. Published data presents an extensive list of PAs and their N-oxides present in comfrey. However, standards are not commercially available for any of the PAs typically present in comfrey. Those PAs that are not stereoisomers were readily resolved on a C(18) column using a water-acetonitrile gradient as the mobile phase. The use of a selective technique, LC-MS/MS, allowed us to identify groups of PAs and their N-oxides, as well as identify the number of PAs present in each group, including those that were not completely resolved chromatographically.     

Right angle free subsets in the plane

In this paper we investigate the complexity of finding maximum right angle free subsets of a given set of points in the plane. For a set of rational pointsP in the plane, theright angle number (P) (respectivelyrectilinear right angle number _R (P)) ofP is the cardinality of a maximum subset ofP, no three members of which form a right angle triangle (respectively a right angle triangle with its side or base parallel to thex-axis). It is shown that both parameters areNP-hard to compute. The latter problem is also shown to be equivalent to finding a minimum dominating set in a bipartite graph. This is used to show that there is a polynomial algorithm for computing _R (P) whenP is a horizontally-convex subset of the lattice × (P ishorizontally-convex if for any pair of points inP which lie on a horizontal line, every lattice point between them is also inP). We then show that this algorithm yields a 1/2-approximate algorithm for the right angle number of a convex subregion of the lattice.     

A network penalty method

We consider the minimum cost network flow problem and describe how the non-linear penalty function methods of Conn and Bartels can be specialized to a combinatorial algorithm for this problem. We report on preliminary computational results which show that this method can require fewer pivots than the simplex method while the amount of work required for each pivot is comparable. The algorithm can be proven finite using a modification of Cunningham's strongly feasible basis pivoting rule.Supported by the Natural Sciences and Engineering Research Council of Canada, and the joint research project Combinatorial Optimization of the Natural Sciences and Engineering Research Council, Canada and the German Research Association (Deutsche Forschungsgemeinschaft, SFB 303).