Effects of core turbulence on jet excitability

The effects of varying freestream core turbulence on the evolution of a circular jet with and without tonal excitation are examined. Measurements are made on an 8.8 cm diameter jet at a Mach number of 0.3. The jet is excitated by plane waves at Strouhal number 0.5. For the excited and unexcited cases the turbulence level is varied by screens and grids placed upstream of the nozzle exit. The experiment results are compared with a theoretical model which incorporates a variable core turbulence and considers the energy interactions between the mean flow, the turbulence and the forced component. Both data and theory indicate that increasing the freestream turbulence diminishes the excitability of the jet and reduces the effect of excitation on the spreading rate of the jet

Secular variations of the geomagnetic field and solar activity

An attempt was made to separate the secular fluctuations created by external sources, according to the observatories Nur Miyar Vee, Lervik, Leningrad, Nimek, Belsk, Hart Land, Kiev, Lviv, "Sham Bon-la-Foret", "Odessa", "Surlarly", "Coimbra". It is shown that there are three types of secular oscillations associated with external sources. Short-period oscillations (about 2 years) and fluctuations in the average periodicity (about 11 years) are well known. It is assumed that there is a long-term modulation of secular oscillations with a period of 80 years, which occurs in connection with changes in solar activity

Riglyne vir pleegouers by die bekendmaking van pediatriese MIV

Afrikaans textDie studie ondersoek die leemte aan teoreties gefundeerde riglyne om pleegouers in die bekendmakingsproses van hulle kind se MIV-positiewe status te ondersteun Die studie geskied binne die teoretiese raamwerk van ʼn intervensienavorsingsmodel. In die empiriese navorsing is die vrese en probleme van pleegouers by die bekendmakingsproses ondersoek. Daar is bevind dat hierdie vrese en probleme in ag geneem moet word in die beoogde riglyne. Die kognitiewe ontwikkeling van die kind is deur middel van ʼn literatuurstudie ondersoek om vas te stel watter kennis, denke en inligting die kind op verskillende ouderdomme begryp. Daar is bevind dat kinders wat MIV-positief is, moontlike agterstande ondervind en dat die riglyne gevolglik gebaseer moet word op die toenemende ontwikkeling van die kind, met begrip vir individuele ontwikkelingsverskille. Voorts is bevind dat pleegouers se eie gereedheid ʼn belangrike rol speel. Alhoewel die pleegouer die bekendmakingsproses self moet aanvoer en hanteer is dit belangrik dat die pleegouers deur ʼn interdissiplinêre span ondersteun en begelei sal word.This study investigates the absence of theoretical grounded guidelines to support foster parents when disclosing paediatric HIV. The study was done within the theoretical framework of an intervention research model. The empirical research investigated the fears and problems experienced by foster parents during the disclosure process. It was found that these fears and problems should be taken into account when compiling guidelines. The child‟s cognitive development was researched by way of a literary study in order to determine what knowledge, thoughts and information the child is able to grasp at different ages. It was found that children who are HIV positive could possibly lag behind and that the guidelines should therefore be based on the accumulative development of the child, with consideration given to individual developmental differences. Furthermore, it was established that foster parents‟ own readiness plays an important role. For this reason the foster parents should be supported and guided by an interdisciplinary team, but that they themselves should take care and execute the process of disclosure.Social WorkM. Diac. (Spelterapie

Phase development and its role on subharmonic control

The conditions for resonance interaction between two instability waves in an axisymmetric jet were investigated. Considerations of the energy equation of the wave resulting from the interaction indicate that the phase angle between the wave-induced stresses and the wave-induced strains plays a crucial role in the resonance interaction. This fact is demonstrated experimentally by exciting a jet at fundamental and subharmonic frequencies. The phase angle between the waves stresses and strains was varied by varying the initial phase-difference between the two excitation waves. The subharmonic resonance was found to be highly dependent on this angle. Favorable agreement was found between the phase angles predicted by a nonlinear theory and the measured ones. The theory is used to explain the subharmonic's resonance in terms of the phase-angles

Saturation and the limit of jet mixing enhancement by single frequency plane wave excitation: Experiment and theory

The limitations of single frequency plane wave excitation in mixing enhancement are investigated for a circular jet. Measurements made in an 8.8 cm diameter jet are compared with a theoretical model. The measurements are made to quantify mixing at excitation amplitudes up to 2 percent of the jet exit velocity. The initial boundary layer state, the exit mean and fluctuating velocity profiles and spectra are documented for all cases considered. The amplitude of the fundamental wave is recorded along the jet axis for various levels of excitation. As the amplitude of excitation is increased the jet spreading rate is increased, but beyond a saturation amplitude further increases have no effect on the spreading. The experimental results are compared with theoretical estimates. In the theory the flow is split into the mean flow, large scale motions, and fine scale turbulence. Shape assumptions for the mean flow, and fine scale turbulence along with the shape for the large scale motions obtained from a linear stability theory provide the closure. The experimental results compare reasonably well with predictions

Extracting Concrete Thermal Characteristics from Temperature Time History of RC Column Exposed to Standard Fire

A numerical method to identify thermal conductivity from time history of one-dimensional temperature variations in thermal unsteady-state is proposed. The numerical method considers the change of specific heat and thermal conductivity with respect to temperature. Fire test of reinforced concrete (RC) columns was conducted using a standard fire to obtain time history of temperature variations in the column section. A thermal equilibrium model in unsteady-state condition was developed. The thermal conductivity of concrete was then determined by optimizing the numerical solution of the model to meet the observed time history of temperature variations. The determined thermal conductivity with respect to temperature was then verified against standard thermal conductivity measurements of concrete bricks. It is concluded that the proposed method can be used to conservatively estimate thermal conductivity of concrete for design purpose. Finally, the thermal radiation properties of concrete for the RC column were estimated from the thermal equilibrium at the surface of the column. The radiant heat transfer ratio of concrete representing absorptivity to emissivity ratio of concrete during fire was evaluated and is suggested as a concrete criterion that can be used in fire safety assessment

Examining HIV and Tuberculosis Using a Decision Support Systems Computer Simulation Model: The Case of the Russian Federation

The aim of this paper is to describe the development and use of a computer simulation model that can be used as a Decision Support System (DSS) to tackle the critical public health issues of the chronic diseases, HIV and HIV related Tuberculosis in the Russian Federation. The model was developed to enable health officials and decision makers to determine the impact of policies to control the chronic diseases spread in an area of Russia. This area, like many others in Russia and elsewhere, have recently witnessed an explosion of HIV infections and a worrying spread of the Multi Drug Resistant form of Tuberculosis (MDRTB). The conclusions drawn is that a high population coverage with Highly Active Anti Retroviral Treatment (HAART) (75% or higher), allied with high MDRTB cure rates, reduces cumulative deaths by 60%, with limited impact below this level. The contributions that this research offers are the development of a simulation model that can be applied as a DSS by public health officials and managers in order to inform policy making. By doing so, ways of best controlling the spread of HIV and MDRTB and reduce the mortality rate from these serious public health threats is provided