Time-delayed feedback control of coherence resonance near subcritical Hopf bifurcation: theory versus experiment

Using the model of a generalized Van der Pol oscillator in the regime of subcritical Hopf bifurcation we investigate the influence of time delay on noise-induced oscillations. It is shown that for appropriate choices of time delay either suppression or enhancement of coherence resonance can de achieved. Analytical calculations are combined with numerical simulations and experiments on an electronic circuit

Spreading Modes on Copper and Steel Surfaces

This work presents the experimental results of the studying the effect of surface roughness, microstructure and liquid flow rate on the dynamic contact angle during spreading of distilled nondeaerated water drop on a solid horizontal substrate. Copper and steel substrates with different roughness have been investigated. Three spreading modes were conventionally indicated. It was found that the spreading of drops on substrates made of different materials occurs in similar modes. However, the duration of each mode for substrates made of copper and steel are different. Spreading of a liquid above the asperities of a surface micro relief was observed to be dominant for large volumetric flow rates of drops (0.01 ml/s). Liquid was spreading inside the grooves of a rough substrate at low rates (0.005 ml/s)

Experimental Research of Thermophysical Processes in A Closed Two-Phase Thermosyphon

The temperature distribution in a thermosyphon was studied experimentally. To conduct the research, a closed two-phase thermosyphon was developed, which differs from the known by simple construction. The method of studying the rapid processes of conduction, convection and phase transitions was also developed. It will allow to highlight the operational modes of the thermosyphon, considering the load, cooling conditions of the condensation section, value of the heat supply. According to obtained results the instabilities of the temperature fields over the cross-section of the two-phase closed thermosyphon were observed by means of using the modern measuring equipment. It has been suggested that the instabilities can be caused by different modes of thermosyphon operation

Experimental Investigation of the Contact Angle at Wetting the Non-ferrous Metals

Experimental dependences on the effect of the drop volume from the contact angle under the conditions of the static three-phase contact line formation during wetting the non-ferrous metals (aluminium, magnalium, copper and brass) are presented in the work. The surface of the substrates was investigated by modern equipment (profilometer "Micro Measure 3D station" and microscope TM-3000). The drop was placed on the surface by the precision electronic single-channel pipette (Thermo scientific). Shadow method was used to obtain the drop profile; symmetry of the drop was controlled by Schlieren method. The comparison of the methods used to determine the contact angle on the image of the drop profile was executed. It was established that in spite of influencing the friction and gravity forces the structure of metal surfaces affects greatly the value of the contact angle

Reduction of Nitrogen Oxides Emissions from a Coal-Fired Boiler Unit

During combustion of fossil fuels a large amount of harmful substances are discharged into the atmospheres of cities by industrial heating boiler houses. The most harmful substances among them are nitrogen oxides. The paper presents one of the most effective technological solutions for suppressing nitrogen oxides; it is arrangement of circulation process with additional mounting of the nozzle directed into the bottom of the ash hopper. When brown high-moisture coals are burnt in the medium power boilers, generally fuel nitrogen oxides are produced. It is possible to reduce their production by two ways: lowering the temperature in the core of the torch or decreasing the excess-air factor in the boiler furnace. Proposed solution includes the arrangement of burning process with additional nozzle installed in the lower part of the ash hopper. Air supply from these nozzles creates vortex involving large unburned fuel particles in multiple circulations. Thereby time of their staying in the combustion zone is prolonging. The findings describe the results of the proposed solution; and recommendations for the use of this technological method are given for other boilers

Mechanism of Contact Line Movement of a Droplet Spreading Over a Solid Surface

The contact line movement, advancing and receding, of the distilled water droplet was studied on the polished and laser patterned aluminum surfaces. The obtained dependences of the dynamic contact angles on the contact line speed were fitted by the combined theory consisting of molecular-kinetic and hydrodynamic theories. Results obtained on laser patterned surface are found to fit better to the theory in comparison with polished surface. The assumption was made that this result is connected with the low contact angle hysteresis on the patterned surface compared to the polished one. It means that combined theory does not consider the contact angle hysteresis

Dynamic contact angle and three-phase contact line of water drop on copper surface

Nowadays there is a lack of experimental data describing the physical process of drop spreading on a solid metal surface for developing wetting and spreading theory. The experimental data obtained by using the high speed video-recording will allow to identify unknown previously spreading modes as well as the change of the dynamic contact angle and the three-phase contact line. The purpose of the work is to determine the effect of the drop growth rate and the copper substrate surface roughness on the dynamic contact angle and the three-phase contact line speed at distilled water drop spreading. Shadow and Schlieren methods are used to obtain experimental data. Three drop spreading modes on the rough surfaces were identified. Time dependences of the dynamic contact angle and contact line speed were obtained. Experimental results can be used for assessing the validity of the developed mathematical models of wetting and spreading processes in the field of micro- and nano-electronics, ink jet printing, thin-film coatings, spray cooling, and optoelectronics

Investigation of genetic structure in mesomorphic bluegrasses, Poa section Stenopoa dum, by using ISSR markers

A morphological and genetic analysis of five mesomorphic bluegrasses populations, Poa section Stenopoa, from a range of geographical locations were performed. We have established that all the populations have different level of the morphological and genetic diversity. A total of 79 DNA bands were obtained from six ISSR primers, including 61 polymorphic bands. Molecular data have shown no clear difference between morphologically homogeneous populations and hybrid populations P. palustris and P. nemoralis. This result may be due to the high genetic diversity of the populations studied