Reactions of Acylpyruvic Acids and 2,3-Dihydrofuran-2,3-diones with 2,3-Diaminopyridine

Acylpyruvic acids readily react with 2,3-diaminopyridine to form (Z)-3-acylmethylene-1H-3,4-di- hydropyrido[2,3-b]pyrazin-2-ones. 5-Aryl-2,3-dihydrofuran-2,3-diones which can be regarded as lactones derived from -enolized aroylpyruvic acids react with 2,3-diaminopyridine under mild conditions, yielding regioisomeric (Z)-2-aroylmethylene-4H-1,2-dihydropyrido[2,3-b]pyrazin-3-ones. The structure of the products and reaction chemoselectivity are discussed.     

Maximum likelihood estimates in correlation acoustic thermotomography

Informative capabilities of active—passive acoustic thermotomography that allows a separate reconstruction of the local values of intrinsic and background temperature, absorption coefficient, and ultrasonic velocity are discussed. An iterative procedure based on the maximum likelihood method that provides unbiasedness of estimates is proposed for the correlation processing of a large body of experimental data. The sensitivity of a thermotomographic system is connected to the limitations imposed on the accumulation factor by actual experimental conditions. A sensitivity enhancement is possible at the cost of loosening the requirements on the resolution of the image under reconstruction. Results of numerical simulation of a thermotomographic experiment in narrowband and broadband modes of operation are presented.     

Angular Distributions of Radiation Polarization Components for A Charge Moving Along A Spiral

Russian Physics Journal - The angular distribution of polarization components of synchrotron radiation emitted by a charge moving along a spiral is investigated. The study is carried out within the...     

Reactions of 3-Aroylpyrrolo[1,2-<Emphasis Type="Italic">a</Emphasis>]quinoxaline-1,2,4(5<Emphasis Type="Italic">H</Emphasis>)-triones with 2,3-Dihydrofuran and 3,4-Dihydro-2<Emphasis Type="Italic">H</Emphasis>-pyran

3-Aroylpyrrolo[1,2-a]quinoxaline-1,2,4(5H)-triones reacted with 2,3-dihydrofuran and 3,4-dihydro-2H-pyran to give mixtures of the corresponding hetero-Diels–Alder (furo- and pyrano[3″,2″: 5′,6′]pyrano- [4′,3′: 2,3]pyrrolo[1,2-a]quinoxalines) and Michael adducts (furyl- and pyranylpyrrolo[1,2-a]quinoxalines).     

Hetero-Diels–Alder Reaction of Aroylpyrrolo[1,2-<Emphasis Type="Italic">a</Emphasis>]quinoxalinetriones with Styrene

Hetero-Diels–Alder reaction of 3-aroylpyrrolo[1,2-a]quinoxaline-1,2,4(5H)-triones with styrene afforded diastereoisomeric (5R*,6aR*)- and (5S*,6aR*)-3,5-diaryl-5,6-dihydropyrano[4′,3′:2,3]pyrrolo[1,2-a]-quinoxaline-1,2,7(8H)-triones.     

Cyclometallated Platinum(II) Complexes for Obtaining Phenyl-Containing Silicone Rubbers via Catalytic Hydrosilylation Reaction

Russian Journal of General Chemistry - C,N-Chelate deprotonated diaminecarbene platinum(II) complexes were studied as polysiloxane system hydrosilylation catalysts. Phenyl-containing silicone...     

One more puzzle of the Tunguska catastrophe?

Using the results of the dendrochronological analysis (68 tree-ring chronologies), it has been shown that the increase in the annual growth of trees after the Tunguska bolide explosion on June 30, 1908, is observed at a large distance (more than 1500 km) from the explosion site (61° N, 102° E) and covers a huge area of about 2 × 10⁶ km² (60°–75° N, 80°–110° E). The anomalous growth of the trees was previously reported only for the direct-destruction area (about 2000 km²). A similar result was obtained when analyzing changes in the annual growth at the time of the Chulym bolide explosion on February 26, 1984 (57.7° N, 85.1° E). A possible interpretation of the observed phenomenon is given. The results open new opportunities for using the dendrochronological method to solve the problems of asteroid-comet danger.     

Simulation of the tomographic reconstruction of thermoacoustic sources: Iteration-correlation methods

Schemes for improving the resolution of thermal tomographs using multielement receiving arrays are considered. Algorithms for processing the space-time correlation information are developed on the basis of the generalization of the high-resolution spectral analysis techniques in application to the problems of medical acoustic thermotomography in narrow-band and wide-band modes of operation. Special attention is given to Capon-type algorithms, which allow an increase in the spatial resolution of the fine structure of the power density distribution of thermoacoustic radiation sources.