CW and Q-switched diode-pumped laser operation of Yb3+:NaLa(MoO4)2

Continuous wave (CW) and Q-switched diode-pumped laser operation of Yb³⁺:NaLa(MoO₄)₂ single crystal was to our knowledge, demonstrated for the first time. A CW output power of 220 mW and slope efficiency of 46% were obtained. Q-switched laser operation was achieved with a pulse duration of 60 ns average output power of 70 mW and slope efficiency of 22%. PACS 42.55.Xi; 42.60.Pk; 42.60.Gd.     

Condensed Isoquinolines. 10. Borohydride Reduction in the 5H-Isoquino[2,3-a]quinazolin-5-one Series

Borohydride reduction in a series of 7-benzyl- and newly synthesized 7-arylmethylene-7,12-dihydro-5H-isoquino[2,3-a]quinazolin-5-ones leads stereoselectively to erythro-7-benzyl-6,6a,7,12-tetrahydro-5H-isoquino[2,3-a]quinazolin-5-ones. 7,7-Disubstituted 7,12-dihydro-5H-isoquino[2,3-a]quinazolin-5-ones are inert to the action of sodium borohydride, but spiro[5H-isoquino[2,3-a]quinazolin-7(12H),2'-indane]-5-one is reduced under rigid conditions to 6,6a-dihydrospiro[5H-isoquino[2,3-a]quinazolin-7(12H),2'-indan]-5-one. 7-Acetyl- and 7-benzoyl-6,11-dihydro-5H-isoquino[2,3-a]quinazolin-5-ones are converted in an aqueous alcoholic solution of sodium borohydride to the previously described 6,6a,7,12-tetrahydro-5H-isoquino[2,3-a]quinazolin-5-one. The structure and special features of the conformational behavior of the reduction products obtained were demonstrated by ¹H NMR spectroscopy.!     

Glycoside bond cleavage in the radiolysis of aqueous solutions of methylglycosides and disaccharides

The kinetics of formation of methylglycoside and disaccharide radiolysis products resulting from the O-glycoside bond cleavage was studied, and the yields of these products were determined. It was found that oxygen inhibits these processes. The findings suggest that the fragmentation reaction of C’₂ radicals plays an important role in the formation of carbohydrate degradation products in the radiolysis of aqueous carbohydrate solutions.     

Synthesis and properties of novel dibenz[b,f]azocines

5-Acetyl- and 5-trifluoroacetyl-12-hydroxy-11-cyano-5,6-dihydrodibenz[b,f]azocines have been synthesized by intramolecular cyclocondensation of ethyl N-acetyl and N-trifluoroacetyl-N-[1-(cyanomethyl)benzyl]-anthranilates. Spectral data show that the hydroxyl group in 5-acetyl-12-hydroxy-11-cyano-5,6-dihydrodibenz[b,f]azocine takes part in transannular hydrogen bond formation with the acetamide group carbonyl oxygen. A study of the chemical properties of this compound has shown that its alkylation by p, -dibromoacetophenone is accompanied by a Thorpe reaction to form 11-amino-5-acetyl-12-(p-bromo-bemoyl)-5,6-dihydro[b,f]dibenzofuro[2,3-d]azocine.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 109–113, January, 1991.     

Condensed Isoquinolines. 15. Synthesis of 5,10-Dihydro[1,2,4]triazolo[1,5-b]isoquinolines and Related Spiranes

Condensation of o-bromomethylphenylacetonitrile with arylcarbohydrazides gave, depending on the reaction conditions, 2-arylcarboxamido-1,4-dihydroisoquinoline-3(2H)-imine hydrobromides or 2-aryl-5,10-dihydro[1,2,4]triazolo[1,5-b]isoquinolines. Analogous condensation of 4-(2-bromomethylphenyl)tetrahydro-2H-pyran-4-carbonitrile and 1-(2-bromomethylphenyl)-1-cyclopentanecarbonitrile with arylcarbohydrazides gave respectively 2-aryl-2,3,5,6-tetrahydrospiro[4H-pyran-4,10'(5'H)-[1,2,4]triazolo[1,5-b]isoquinolines and 2-arylspiro[1,2,4]triazolo[1,5,b]isoquinoline-10(5'H)-1'-cyclopentanes, derivatives of new spirane heterocycles. The reaction with condensing agents of 3-imino-2,2',3,3'5',6'-hexahydrospiro[isoquinoline-4(1H),4'-4H-pyran]-2-amine and 3-imino-2,3-dihydrospiro[isoquinoline-4(1H),1'-cyclopentane]-2-amine hydrobromides, synthesized from the corresponding bromo nitriles and hydrazine, may serve as an alternative route for the synthesis of these compounds. The structure of obtained triazoloisoquinolines was established from IR, ¹H and ¹³C NMR spectra. An X-ray crystallographic study of 2-phenylspiro[1,2,4]triazolo[1,5-b]isoquinoline-10(5H),1'-cyclopentane was carried out.     

The Malthusian parameter in microbial ecology and evolution: An optimal control treatment

There is a consensus among evolutionary microbiologists that the (quasi-)instantaneous specific rate of proliferation is a good measure for fitness. On the other hand, it is well known in evolutionary theory that the appropriate fitness measure is generally dependent on ecotype. We consider two ecotypes: one in which the instantaneous specific growth rate, discounted into the future, is an appropriate measure of fitness, and one in which fitness is measured as “ burst fitness” under intermittently favorable conditions. Our analysis is based on a standard model of microbial growth, the Droop Quota model, which we have extended with a variable balance between assimilation and proliferation, since this balance constitutes an important regulatory choice. We evaluate optimal allocation regimes and contrast these to control regimes based on maximization of the instantaneous specific growth rate.     

Spectroscopy and femtosecond laser performance of Yb3+ :Gd0.64Y0.36VO4 crystal

We report for the first time on the efficient continuous-wave and mode-locked laser operation of a diode-pumped Yb:Gd_0.64Y_0.36VO₄ laser. cw output power of 855 mW with a slope efficiency of 45% with respect to the absorbed pump power was demonstrated for the 2.1%-doped crystal. In mode-locked regime with SESAM as passive shutter pulses as short as 100 fs were obtained. PACS 42.55.Xi; 42.65.Re; 42.70.Hj     

Spectroscopy and laser properties of Tm<Superscript>3+</Superscript>:KY(WO<Subscript>4</Subscript>)<Subscript>2</Subscript> crystal

The polarized absorption spectra of Tm³⁺-doped potassium yttrium tungstate (Tm:KY(WO₄)₂) crystal at room temperature were measured. The emission spectrum and lifetime of the ³ F ₄ excited state were determined. Using standard and modified Judd–Ofelt theories, the intensity parameters and the radiative lifetimes were calculated and good agreement with the experimental results was obtained for both theories. Continuous-wave laser operation in Tm:KYW crystal under laser diode pumping at 802 nm and 1750 nm was demonstrated with slope efficiency of 53% and 28% and output power of about 555 mW and 86 mW, respectively. PACS 42.55.Xi; 42.60.Pk; 42.70.Hj