Influence of the Design of Metal Receivers of Slab Continuous-Casting Machines on the Motion of Flow in the Tundish in the Case of Deviations of the Metal Stream from the Required Position. Part II. Procedure of Simulation1

Refractories and Industrial Ceramics - We study the problem of evaluation of the influence of design of the metal receiver of a large-capacity tundish of slab continuous-casting machine on the...     

Study of the relaxation rate of photoexcited indole molecules by the interferometric pump-and-probe method at picosecond resolution

We present a new interferometric method that can be used for studying the dynamics of photoinduced processes in biologically important molecules at ultrahigh temporal resolution. The method is based upon the detection of changes in the refractive index of a substance excited by pulsed radiation of a femtosecond laser, which are measured by the pump-and-probe technique using time-delayed pulses of the same laser. The high sensitivity and stability of the interferometer allow this method to be used for monitoring variation of the concentration of short-lived excited states of biomolecules in solution. The proposed method has been verified by application to indole solutions in propylene glycol. The upper estimate of the lifetime of photoexcited indole molecules in solution amounted to about 40 ps.     

Atomic-absorption determination of aluminum in waters

The article investigated the impact of sodium salts of acylhydrazones of pyroracemic acid as modifiers of the matrix on the electrothermal atomic-absorption determination of aluminum. The technique has been developed for determination of aluminum in fresh waters with the detection limit 0.005 m/dm³.     

A study of epitaxially stacked tunnel-junction semiconductor lasers grown by MOCVD

Design parameters of epitaxially stacked tunnel-junction asymmetric separate-confinement laser heterostructures are chosen. Technological modes for fabrication of heterostructures of this kind by metal-organic chemical vapor deposition in the system of AlGaAs/GaAs/InGaAs solid solutions are found. It is demonstrated that high-efficiency GaAs:Si/GaAs:C tunnel stru ctures and asymmetric AlGaAs/GaAs/InGaAs laser heterostructures with low internal optical loss can be fabricated in a single technological process. Conditions are chosen in which a deep mesa can be formed for fabrication of mesa-stripe diode lasers based on epitaxially stacked tunnel-junction laser heterostructures. Mesa-stripe diode lasers with a 150 × 12-μm aperture have been manufactured on the basis of these structures. These samples have a threshold current density J _th of 96 A cm^-2, internal optical loss α_i of 0.82 cm^-1, and differential resistance R = 280 mΩ. Samples containing three laser structures have a slope efficiency of 3 W A^-1 and a maximum peak output power of 250 W in the pulsed operation mode (100 ns, 1 kHz).     

Comprehensive above-threshold analysis of antiresonant reflecting optical waveguide edge-emitting diode laser

A three-dimensional (3-D) above-threshold analysis has been performed for laterally antiguided laser structures of the antiresonant-reflecting-optical-waveguide type, of relatively large core width (/spl sim/ 10 /spl mu/m), for high-power, single-spatial-mode operation. A 3-D numerical code has been developed, which takes into account carrier diffusion in the quantum well as well as edge radiation losses. The laser characteristics are calculated as functions of the above-threshold drive level. Within the simulation, 3-5 higher order optical modes on a "frozen background" are computed by the Arnoldi algorithm. Because of the nonuniform gain saturation of the lasing mode, the modal gains for higher order modes increase with the drive current due to increasing overlap of their fields with the two-dimensional gain distribution. The onset of threshold for higher order modes puts an upper limit on the range for stable single-mode operation. The above-threshold analysis is done for various values of the width of the reflector region, below and above the lateral-antiresonance condition. It is found that the maximum intermodal discrimination, which in turn provides the maximum single-mode power, is obtained when the reflector-region width is /spl sim/25 % larger that its value at antiresonance. Then, for 10-/spl mu/m-core devices, stable, single-mode operation is found to occur to drive levels as high as 41 /spl times/ threshold, with single-mode output powers as high as 1.45 W.     

Effect of moisture content on the physicomechanical properties of polyamide yarns

Conclusions The effect of small amounts of moisture during a short interaction time (not over 2 sec) with undrawn Kapron fibre on its ability to undergo deformation and its structure is discussed.It has been found that applying an aqueous lubricant onto freshly spun yarn during the process of joint spinning and stretching leads to a rise in the stretching tension and an impairment in deformational ability as compared with the deformation of the dry yarn. This phenomenon is explained by a mechanism of the interaction of polyamides with water.Translated from Khimicheskie Volokna, No. 6, pp. 27–28, November–December, 1983.