Reaction of 2-formyl-1,3-cyclohexanediones with cyanoacetamide

Chemistry of Heterocyclic Compounds -     

Optical separation of racemic 5-(p-hydroxyphenyl)-5-phenylhydantoin by reversed phase high-performance liquid chromatography using eluents containing beta-cyclodextrin.

Both S-(-)- and R-(+)-enantiomers of 5-(p-hydroxyphenyl)-5-phenylhydantoin (p-HPPH), a main oxidative metabolite of the achiral antiepileptic drug phenytoin, could be determined simply, sensitively and accurately using reversed phase high-performance liquid chromatography by using a methanol-monopotassium phosphate eluent containing beta-cyclodextrin. Using this assay procedure, it was determined that an S-(-)-enantiomer was formed predominantly by the oxidation of phenytoin in isolated rat hepatocytes.     

Temporal characteristics of picosecond stimulated Raman scattering in oxide crystals

The temporal characteristics of stimulated Raman scattering (SRS) under 22-ps laser excitation were studied in eight oxide crystals with a T ₂ optical-phonon dephasing time variable by up to two orders of magnitude. The measured SRS pulse width was shortened from 13.8 ps for Ba(NO₃)₂ (T ₂ = 26.5 ps) to 4 ps for the LiNbO₃ (T ₂ = 0.38 ps) crystal. The dependence of SRS pulse width on the dephasing time was analyzed in the framework of the known SRS theory.     

Temperature distribution in the bright spot of the optical discharge in an optical fiber

2D simulation of the optical discharge propagation in an optical fiber is performed. In contrast to the previous works, the temperature dependences of the transfer coefficient are taken into account for the bright-spot plasma. The results are compared with the recently published measurements of the spatial distribution of the bright-spot radiation intensity. Good agreement is obtained for the discharge propagation velocity and the dependence of the bright-spot size on the laser power.     

Minimax detection of a signal in the heteroscedastic Gaussian white noise

We consider the problem of signal detection in the heteroscedastic Gaussian white noise when the set of alternatives is essentially nonparametric. In this setting, we find a family of asymptotically minimax tests. The results are extended to the case of testing a parametric hypothesis against nonparametric sets of alternatives. Bibliography: 8 titles. __________ Translated from Zapiski Nauchnykh Seminarov POMI, Vol. 320, 2004, pp. 54–68.     

Ionization of Hydrogen and Helium Atoms in Collisions with Relativistic Structural Heavy Ions

Based on the eikonal approximation, cross sections for single and double ionization of hydrogen and helium atoms in collisions with structural multiply charged heavy ions moving with relativistic velocities are calculated. In the present paper, the structural ions are taken to mean the ions with partially filled electronic shells. It is demonstrated that a consideration of the ion charge extension may noticeably change the corresponding cross sections compared to the cross sections for ionization by point ions having the same charges and energies.