Pulse-width-dependent critical power for self-focusing of ultrashort laser pulses in bulk dielectrics.

Microscale filamentation of 0.25 NA-focused, linearly and circularly polarized 1030 nm and 515 nm ultrashort laser pulses of variable pulse widths in fused silica, fluorite, and natural and synthetic diamonds demonstrates the Raman-Kerr effect in the form of critical pulse power magnitudes, proportional to squared wavelength and inversely proportional to laser pulse width of 0.3-10 ps. The first trend represents the common spectral relationship between the quantities, while the second indicates its time-integrated inertial contribution of Raman-active lattice polarization, appearing in transmission spectra via ultrafast optical-phonon Raman scattering. The optical-phonon contribution to the nonlinear polarization could come from laser field-induced spontaneous/stimulated Raman scattering and coherent optical phonons generated by electron-hole plasma with its clamped density in the nonlinear focus. Almost constant product value of the (sub)picosecond laser pulse widths and corresponding critical pulse powers for self-focusing and filamentation in the dielectrics ("critical pulse energy") apparently implies constant magnitude of the nonlinear polarization and other "clamped" filamentation parameters at the given wavelength.

Kinetoplast DNA segments function as promoters in Escherichia coli cells.

By means of coupled transcription-translation in Escherichia coli cell-free system, an open reading frame was found in the Crithidia oncopelti maxi-circle kDNA segment cloned in the hybrid plasmid pCo1. Subfragments from this region were tested for their ability to function as promoters in E. coli cells. For this purpose the vector pVE8 was constructed using the aminoglycoside phosphotransferase II (APTII) gene from the Tn5 transposon, and the pHC79 cosmid. After cloning of Sau3A fragments of pCo1 by insertion into pVE8 three types of plasmids containing promoter sequences were obtained. Two of these plasmids displayed promoter strength in E. coli cells greater than that of the normal promoter of the APTII gene. However the promoters found are not necessary for the coupled transcription-translation of kDNA in the E. coli cell-free system.

Repeated sequences with unusual properties from the divergent region of Crithidia oncopelti maxicircle kinetoplast DNA.

The occurrence of bacterial promoter-like sequences was shown in the divergent region of Crithidia oncopelti maxicircular kinetoplast DNA. A promoter-cloning vector based on the neomycin phosphotransferase II (NPT II) gene was used to localize promoters in three homologous blocks of repeated sequences. The elements found displayed greater promoter strength in Escherichia coli than the normal promoter of the NPT II gene. Sequences of three promoter-containing inserts from different blocks were determined and typical prokaryotic promoter sequences were localized.