Graphs With Least Eigenvalue —2: A New Proof of the 31 Forbidden Subgraphs Theorem

Generalized line graphs were introduced by Hoffman Proc. Calgary Internat. Conf. on Combinatorial Structures and their applications, Gordon and Breach, New York (1970); they were characterized in 1980 by a collection of 31 forbidden induced subgraphs, obtained independently by Cvetkovi et al., Comptes Rendus Math. Rep. Acad. Sci. Canada (1980) and S. B. Rao et al., Proc. Second Symp., Indian Statistical Institute, Calcutta, Lecture Notes in Math., (1981). Here a short new proof of this characterization theorem is given, based on an edge-colouring technique.     

Production and certification of “fresh” reference material for macronutrient analysis

Summary Reference materials for carrying out in-house quality assurance by food laboratories that analyse macronutrients have to date been inadequate. The freeze-dried, very specialized, materials that exist on the market are not always comparable with ordinary food products analysed at those laboratories.A homogeneous, fresh, canned meat material was produced by an ordinary cannery. The total amount of material (pork, nitrite salt and water) was 1700 kg. During production, the fat content was continuously analysed in the different sub-batches and combinations are made accordingly. The material was packed in tin cans containing 200 g, and tested for homogeneity. The shelf life is, by experience, at least five years. A large number of authorized public and industry laboratories participated in the certification procedure. For each constituent different types of standard analytical methods were used. The material is offered for sale together with a certificate, giving mean values for moisture, ash, fat, nitrogen, sodium, sodium chloride and hydroxyproline content. The uncertainty is given as standard deviations including the analytical error and the variations between laboratories, methods and units.     

Time-resolved saturated-absorption experiment. Effect of velocity-changing collisions upon non-thermal-equilibrium atomic velocities

Results obtained in a time-resolved study of atomic-velocities thermalization for the ¹D₂ metastable level of the barium transition 6 ¹P₁ → 5 ¹D₂ are presented. Time evolution of the absorption coefficient after saturation due to a strong monochromatic laser pulse is studied. The results are analyzed in the strong-collision model, including trapping effects in the ¹P₁ level. For barium and rare-gas mixtures the cross sections for strong elastic collisions are in agreement with the cross sections deduced from the kinetic theory.     

Semisynthetic 4-O-Methyl-ß-Rhodomycins: Synthesis and Structure-Activity Relationships

ABSTRACT

The synthesis of 7-O-α-L-daunosaminyl-4-O-methyl-β-rhodomycinone (3) and the determination of its cytotoxic potency compared to that of the natural 7-O-α-L-dau-nosaminyl-β-rhodomycinone (4) are described. Starting with natural β-rhodomycinone (7), trimethylsilyl protecting groups were attached to the hydroxy groups at position 7 and 10, and the 4-OH group was subsequently methylated (MeI/Cs₂CO₃), thus providing the 4-O-methyl-7, 10-bis-O-trimethylsilyl-β-rhodomycinone (10). The two TMS groups were then deblocked to give 4-O-methyl-β-rhodomycinone (12). In a 3-stage synthesis 12 was converted into 4-O-methyl-10-O-trifiuoroacetyl-ß-rhodomycinone (15) to which l, 4-bis-O-p-nitrobenzoyl-3-N-trifluoroacetyl-L-daunosamine 16 was selectively linked to afford the 7-O-α-glycoside 17. The acyl protective groups are removed by treatment with 1N NaOH to give 3.