Laser ablation of polytetrafluoroethylene

Anomalous behavior of polytetrafluoroethylene (PTFE) under the action of CO₂ laser radiation in vacuum is discussed. A feature of the ablation process is formation of polymer fibers which quantity depends on the target preliminary treatment and the ablation conditions. Experimental results are set out and possible mechanisms of the polymer fibering are discussed. A conclusion is made concerning two dynamic polymer components differ by the resistance to the laser beam action, appearing in the ablation crater. A method is proposed for producing unique fiber-porous polytetrafluoroethylene materials and other useful products as well as for the polytetrafluoroethylene wastes recycling. The results of industrial application of these new fiberporous materials are discussed.     

Neutron-scattering investigation of the excitation spectrum of liquid helium

The results of the investigation of the temperature evolution of the scattering law S(Q, ω) of superfluid helium measured in the wave-vector range 0.3 < Q < 0.8 Å^?1 and helium temperatures from 1.0 to 2.2 K are reported. The investigations have been performed on the high-flux reactor at the Institut Laue-Langevin (France) with the IN6 neutron inelastic-scattering spectrometer. The deviation of the experimental scattering law of liquid helium from the damping harmonic oscillator model, which was previously observed independently in the experiments with the IN6 spectrometer [1] and with the DIN-2PI spectrometer (at the IBR-2 reactor, Dubna, Russia) [2, 3] and were more recently called extrapeak, has been corroborated. The temperature dependence of the extrapeak parameters has been determined. This dependence makes it possible to propose hypotheses on the nature of the extrapeak.     

On the Reproduction of the Solar Activity Variations in the Range 2–40 Months in the Interplanetary Medium

Journal of Experimental and Theoretical Physics - We compare the quasi-biennial variations and Rieger-type variations (on a timescale of less than 1&nbsp;year) in solar activity, interplanetary...     

Influence of IR Laser Radiation on the Surface of Polytetrafluoroethylene Containing Small Amounts of Perfluoropropyl Vinyl Ether Units

High Energy Chemistry - The surface of chemically modified polytetrafluoroethylene, obtained by introducing 1 mol % perfluoropropyl vinyl ether in the polytetrafluoroethylene macromolecule chain,...     

Bragg Deflectors of Wave Fluxes for High-Power Relativistic Masers

Technical Physics - Quasi-optical Bragg structures that represent sections of planar waveguides with tilted (with respect to the beam propagation direction) corrugation are studied. It is shown...     

Experimental studies of the hydrolysis kinetics of aqueous-alkaline solutions of sodium borohydride

Experimental data were used to study the hydrolysis kinetics and construct an approximating expression for calculation of quasistationary hydrolysis constants for sodium borohydride in a wide range of alkali concentrations and temperatures.     

Wideband chaotic oscillators based on turbulent electron flows with internal electronic feedback

Wideband chaotic oscillators that operate on new physical principles, namely, using intense turbulent electron flows are studied. Various approaches to generating turbulent electron flows are considered, and the structure of the turbulent electron flow is experimentally investigated. Experimental results for oscillations generated by the suggested wideband microwave sources are reported. The generalization of analytical, numerical, and experimental data has made it possible to develop wideband chaotic oscillators based on commercial travelling-wave tubes.