Sols containing core/shell CdS/ZnS semiconductor quantum dots are synthesized and their nonlinear properties, which are interesting for a large variety of applications in nanophotonics, are studied. The quantum dots produced are smaller in dimensions than the exciton Bohr radius and, therefore, exhibit a well-pronounced quantum-confinement effect. The nonlinear optical properties of low-concentration sols are studied upon exposure to laser pulses with an emission wavelength of 532 nm and a duration of 5 ns by the z-scan technique. The dependences of nonlinear optical coefficients on the concentration of CdS/ZnS quantum dots are obtained. The intensity dependence of two-photon absorption coefficients is presented. The dependence determines the boundary of the influence of high-order nonlinearities on the nonlinear transmittance of the samples. The mechanisms of optical limitation exhibited by sols, specifically, two-photon absorption, nonlinear refraction, and nonlinear scattering are discussed.

No abstract

No abstract

In the refractories industry, increasing use is now being made of a method of compacting the material on vibropercussive tables under a dynamic pressure of 1.5-2.0 MPa.An investigation of the process of vibropressing of shaped chamotte products revealed that to obtain a compact material it is necessary to exert a strong dynamic action (about I0 MPa or more). With this aim, at the All-Union Institute of Refractories (VIO) we have developed a method of vibropressing with a powerful dynamic action in a hydroinertial vibropercussive press [i]. A previous report [2] dealt with work on vibropressing of ladle parts of relatively simple shape.In this article we shall give the results of investigations of vibropressingof shaped refractory products made from semidry pastes of various degree of plasticity.In our investigation we used chamotte paste made at the Borovichi Refractories Combine and the Chasov-Yar Combine of Refractory Products, ready-mixed Dinas mixture made at the Krasnogorovka Refractories Works, and also a graphite--chamotte mixture made at the VIO.The graphite--chamotte and Chasov-Yar chamotte pastes were made in a blade-type mixer, which was also used to process the Dinas paste to break up lumps formed during transportation.The Borovichi chamotte paste was made in SM-21A edge runner mills.The specimens were pressed and their characteristics determined by a previously developed method [2]. The power parameters of the process were registered with the aid of tensometers and an N-105 oscillograph.All-Union Institute of Refractories.

The widely used method of making linings for induction furnaces by means of pneumatic rams is unproductive and laborious. The resulting crucibles have low density and strength and their density varies with height. The process of bringing these crucibles into operation after manufacture, including drying and firing during the first ungraded melt, is very laborious, requires large amounts of eleetrical power and metal burden, and constitutes an unproductive use of costly electrical equipment. The output of the furnace and the purity of the smelted metal depend on the stability of the refractory lining during vacuum induction melting [i-3].