100-TW femtosecond laser based on parametric amplification

In experiments on the parametrical amplification of femtosecond pulses in wide-aperture DKDP crystals, a power of more than 100 TW has been reached, which is much higher than the record level achieved in such lasers. The energy efficiency obtained for the parametric amplifier is equal to 27%. The energy of a 72-fs pulse is equal to 10 J.     

Headspace gas-chromatographic determination of formaldehyde in urine

A method is proposed for determining formaldehyde by headspace gas chromatography using an o-(2,3,4,5,6-pentafluorobenzyl)hydroxylamine (PFBHA) derivatizing agent. Formaldehyde in urine was derivatized to o-(pentafluorobenzyl)oxime and extracted by heating an urine sample with PFBHA in a sealed vial. Gas-chromatographic analysis of the headspace was performed in the temperature-programmed mode using an HP-5 capillary column with a flame ionization detector. The limit of detection is 3.5 μg/L. The accuracy of the procedure, equivalent to an extended relative uncertainty, does not exceed 21%. The examination of the procedure using urine samples of the population of the Irkutsk region has shown that the regional reference levels of formaldehyde concentration are in the range 44–83 μg/L.     

Nonlinear Equations of Motion of an Extensible Underground Pipeline: Derivation and Numerical Modeling

Slow motion of a pipeline modeled by a bent rod in a viscous medium is studied. It is assumed that the displacements of the axial line of the rod are finite and its strains are small. The mutual influence of the tensile axial force and transverse deflections is taken into account. Equations of motion are derived and some numerical examples are considered. An approximate estimate of stresses in the pipeline wall is given.     

Polarization modulation of light in an optical waveguide under lateral compression

It is shown that a lateral pressure applied to a circular single-mode optical waveguide changes the phase difference between two orthogonally polarized modes and thereby modulates the polarization state of light (elastooptic effect). The efficiency of polarization modulation is characterized by a strain-to-phase difference conversion factor as applied to polarization modes of the fiber. An expression relating the phase difference between the modes and the displacement of squeezing plates is obtained and checked in real experiments and numerically. The efficiency of conversion of lateral pressure to phase difference between the polarization modes is shown to be fairly high, on the order of 10⁴ rad/(μm m).     

Investigation of the turbulent mixing of thin layers of materials of different density during the laser acceleration of flat multilayer targets in the Iskra-4 facility

The results of the first experiments devised to investigate the mixing of thin layers of Al and Au during the laser acceleration of flat three-layer targets of Si (5 μm), Al (2 μm), and Au (0.05–0.26 μm) by radiation converted to the second harmonic from the Iskra-4 iodine laser with an intensity of 4×10¹³−7×10¹³ W/cm² (τ _0.5∼1 ns), which acts on the Si side of the target. A method for detecting the occurrence of mixing is developed. It is established that under the experimental conditions the thickness of the mixing region is at least ∼0.15 μm. The results of a theoretical analysis of the evolution of the disturbances leading to mixing are presented. Zh. éksp. Teor. Fiz. 111, 882–888 (March 1997) Deceased.     

Dynamics of a fluid-filled curvilinear pipeline

A mathematical model is presented, and numerical experiments are performed to describe the mechanics of the slow movement of a pipeline. The problem reduction algorithm to one-dimensional formulation is offered. Results of numerical experiment for the model problem are adduced. The proposed mathematical model is found to adequately describe the dynamics of known phenomena of pipes. The cross-sections of the extended curvilinear thin-walled pipeline are numerically demonstrated to experience warping, which has experimental confirmation in the literature.     

Numerical and Asymptotic Solution of the Equations of Propagation of Hydroelastic Vibrations in a Curved Pipe

A mathematical model for propagation of hydroelastic waves in a pipe is developed using the equations of motion of a shell and a fluid. A method for deriving two–dimensional equations is proposed, and asymptotic formulas for solutions of these equations are obtained. A model problem is solved numerically, and the results are compared with data obtained by others. The results obtained make it possible to calculate the propagation of pressure waves for an arbitrary (within the framework of the assumptions made) shape of the axial line of the pipe and can be used in designing systems for diagnostics of pipeline performance.     

New scheme of a petawatt laser based on nondegenerate parametric amplification of chirped pulses in DKDP crystals

The ultra-broadband phase matching was experimentally observed in a DKDP crystal upon parametric amplification of signal radiation with a wavelength of 911 nm in a pump field with a wavelength of 527 nm. The original scheme was used to excite the first parametric amplification stage by chirped pulses of idler radiation with a wavelength of 1250 nm. The saturated gain of a three-stage parametric amplifier was equal to 10⁸.     

On the isomorphic mapping of weighted spaces by an elliptic operator with degeneration on the domain boundary

We consider the first boundary value problem for a second-order elliptic equation with degeneration on the entire twice continuously differentiable boundary of a two-dimensional domain Ω; this problem has a generalized solution in the weighted space . We find conditions ensuring that the generalized solution belongs to the narrower space , which permits obtaining estimates for the convergence rate of an approximate finite-element solution to the exact solution in the norms of the spaces and L ₂(Ω).