Search for efficient,near UV lasing dyes. III. Monocyclic and miscellaneous dyes

A potential new class of “monocyclic” lasing dyes is discussed and four families out of nine within the class are examined. The 2,6-diaminopyridines in acid are found to lase under flashlamp excitation but show low slope efficiencies and lower stabilities than the “bicyclic” dyes described previously. Other, miscellaneous dyes show oxygen quenching of laser action rather than enhancement and the best of these produces short pulses under long pulse excitation. This study was supported under contract SANL 284 from the Lawrence Livermore Laboratory.     

Reactions of cyclo-octatetraene and its derivatives—VIII: 1,2,3,8- And 1,2,3,4-tetrachlorocyclo-octatetraene

Earlier attempts to synthesize 1,2,3,8-tetrachlorocyclo-octatetraene 4 are described. A ca. 2:1 mixture of 1,2,3,8- and 1,2,3,4-tetrachlorocyclo-octatetraene was finally obtained by hydrolysis (using 96% trifluoroacetic acid) of the ketal 15 followed by thermal decarbonylation of the product. Reaction of the mixture of cyclo-octatetraenes with bromine gave the (separable) dibromo-derivatives 17 and 18. On attempted debromination with zinc, the dibromodiene 17 formed the benzocyclobutadiene dimer 12, together with the benzobiphenylene 13; these compounds were also produced directly from the cyclo-octatetraene mixture by the action of zinc. In contrast, similar treatment of the dibromodiene 18 led to the E-bromostyrene 22. The mixture of cyclo-octatetraenes reacted with maleic anhydride to give the adduct 27, whereas with acenaphthylene the adduct 28 was obtained.     

Search for efficient,near UV lasing dyes. II. Aza substitution in bicyclic dyes

Two new families of lasing dyes, the 8-azacoumarins and the 8-azaquinolones are described and are found to operate blue-shifted from the coumarins and quinolones. Like the quinolones, they have higher thresholds and lower slope efficiencies than the coumarins. All have yielded long output pulses on long pulse excitation. This study was supported under contract SANL 284 from the Lawrence Livermore Laboratory.     

New laser dyes with blue-green emission

Several new derivatives of 7-amino coumarin and 7-amino-(2)-quinolone were synthesized and tested for lasing performance. Relative output, stability and lasing wavelength for these dyes are reported.     

Laser performance and stability of fluorinated coumarin dyes

Several new coumarin derivatives are reported and their relative photochemical stability under flash and cw excitation is investigated. There seems to be no simple relation between the cw bleaching rate and the number of laser shots obtainable from any particular dye solution.     

Horizon Valuations for Mathematical Programming in Financial Planning

Using a linear programming model for the financial planning of an organization requires the specification of a horizon date and a valuation of the firm at that date. Given perfect information about future opportunities, an exact valuation procedure should lead to the same optimal solution of the model regardless of the choice of horizon date. Even in the absence of perfect information, conventional valuations fall far shorter of this ideal than they need to. It is shown that for a modest increase in the size of the linear programme, better valuations can be achieved and, most importantly, valuations which consider the impact on the value of the firm of post horizon constraints and liabilities as well as post-horizon opportunities.     

Coupling p-multigrid to geometric multigrid for discontinuous Galerkin formulations of the convection–diffusion equation

An improved p-multigrid algorithm for discontinuous Galerkin (DG) discretizations of convection–diffusion problems is presented. The general p  -multigrid algorithm for DG discretizations involves a restriction from the p=1$p=1$ to p=0$p=0$ discontinuous polynomial solution spaces. This restriction is problematic and has limited the efficiency of the p  -multigrid method. For purely diffusive problems, Helenbrook and Atkins have demonstrated rapid convergence using a method that restricts from a discontinuous to continuous polynomial solution space at p=1$p=1$. It is shown that this method is not directly applicable to the convection–diffusion (CD) equation because it results in a central-difference discretization for the convective term. To remedy this, ideas from the streamwise upwind Petrov–Galerkin (SUPG) formulation are used to devise a transition from the discontinuous to continuous space at p=1$p=1$ that yields an upwind discretization. The results show that the new method converges rapidly for all Peclet numbers.