Specific features of heat transfer at the stagnation point of an impact axisymmetric jet at low Reynolds numbers

The average and pulsating thermal characteristics at the stagnation point of a plate at inflow of an impact axisymmetric air jet have been studied. The influence of the Reynolds number (100 < Re < 12000) on heat transfer has been investigated for a jet flowing from a long tube (diameter d = 5 mm, relative length h/d = 200) with the output located at a distance h/d = 20 from the obstacle. The measurements have been carried out using a heat-flow sensor with high spatial and temporal resolutions. A nonmonotonic change in heat transfer having a maximum is found in the range Re < 4000 (in contrast to the known monotonic increase in heat transfer). A significant increase (200–600%) in the Nusselt number is observed for outflow from a tube in comparison with jet outflow from a nozzle. At Re > 4000, the difference in heat transfers for two cases of jet formation (from a tube and a nozzle) decreases asymptotically.     

Fullerenes in Russia

Abstract

Structure and main features of the Russian Research Program “Fullerenes and Atomic Clusters” are presented. Results of investigations in the framework of this Program in 1996 are briefly reviewed.     

Is there a ferroelectric diffuse phase transition in YBa2Cu3Ox?

Experimental results on ultrasonic attenuation in ceramic samples YBa₂Cu₃O_x are reported. The attenuation peaks near 150°C may be due either to a diffuse phase transition or to defects.     

Photogalvanic current in the incommensurate phase in Ba2NaNb5O15

The linear photogalvanic effect in the phase transition (commensurate tetragonal-to-in-commensurate) region has been studied in Ba₂NaNb₅O₁₅ crystal. The results show a strong correlation between the photogalvanic current and the modulation period of the incommensurate phase.     

Dielectric properties of planar structures based on ferroelectric Ba0.5Sr0.5TiO3 films

An experimental investigation has been made of the dielectric properties of planar Cu-Cr/Ba_0.5Sr_0.5TiO₃ and YBa₂Cu₃O_7−δ /Ba_0.5Sr_0.5TiO₃ structures in the temperature range 78–300 K. It is shown that the use of YBa₂Cu₃O_7−δ electrodes in Ba_0.5Sr_0.5TiO₃ film structures ensures that there is no dielectric hysteresis in the paraelectric phase. At the same time, the dielectric nonlinearity is preserved and the dielectric losses are reduced. Pis’ma Zh. Tekh. Fiz. 23, 46–52 (August 12, 1997)     

An experimental study of submerged jets at low reynolds numbers

Results of an experimental study of submerged subsonic air jets exiting from axially symmetric and plane channels in the Reynolds number range of 100–6000 are presented. Data on visualizing the flow picture and zone of the laminar-turbulent transition have been obtained. The measurement results are compared with well-known experimental data for gas macro- and microjets. The coordinate of the transition to the turbulence for microjets is shown to be able to reach high values, and a generalization of the experimental data is presented.     

Relaxor properties of single crystals of Na1/2Bi1/2TiO3-KTaO3 solid solutions

Single crystals of Na_1/2Bi_1/2TiO₃-KTaO₃ (NBT-KT) solid solutions have been grown for the first time. The elemental composition of as-grown single crystals determined by X-ray diffraction corresponds to 0.81 NBT-0.19 KT. Measurements of the temperature dependences of dielectric characteristics showed that the obtained NBT-KT crystals possess clearly pronounced relaxor properties.     

Nonlinear interaction of s.a.w.s in piezoelectric crystals with secondary electrons

Some new experimental results and a simple theoretical model of nonlinear interaction of s.a.w.s in piezoelectric crystals with electron beams are presented.     

Saw determination of D4h layer on the surface of SrTiO3

Velocity of bulk and surface acoustic waves with frequencies 38, 76 and 114 MHz was measured in SrTiO₃ crystals in the phase transition region. The difference in the temperature dependences of bulk and surface waves as well as strong dispersion for surface waves are explained in terms of existence of a thin surface layer with D_4h symmetry.