Une nouvelle famille de materiaux ferroelastiques-ferroelectriques oxyfluores de type chiolite

A new family of ferroelastic-ferroelectric materials has been prepared with the composition (Na_5?xNd_x) (W_3?2xNb_2x)O₉F₅ (0 ? x ? 1,50), and a related chiolite structure. The Curie temperature decreases as x increases.     

Stochastic behavior of a 2-unit standby redundant system with imperfect switchover and preventive maintenance

We discuss a 2-unit standby redundant system with imperfect switchover and preventive maintenance (PM). The switch assumes up and down states repeatedly, independently of the behavior of the main unit. We have the stochastic behavior of the system.     

Computer usage in developing countries: Case study Kuwait

This study is an examination of the position of computing technology in the developing country of Kuwait. The status of computer usage is described. These findings are assessed relative to technology trends, evolutionary computing stages, and/ or results reported in more developed countries; problems and concerns of computer users are identified; and factors potentially related to more successful computer utilization are explored. The following aspects of computer usage are analyzed: computing resources (hardware, software, staff, expenditure), application development methodologies, applications and evaluation. The study provides insight into the results of the transfer of computing technology to a developing country where computer usage is relatively widespread.     

Thermodynamic comparisons of methods for producing hot gases

We present a thermodynamic comparison of combustion processes for the production of high-temperature gases (2000–3100 °K) from methane. We compare:

1. (1) CH₄---O₂ mixtures, with oxygen added either in the gaseous or the liquid state,

2. (2) CH₄-enriched air systems, with enrichment by removal of gaseous nitrogen from air,

3. (3) CH₄-enriched air systems, with enrichment achieved by adding either pure gaseous or pure liquid oxygen to air, and

4. (4) CH₄-air electrically augmented systems, in which enriched air is produced in an air-separation plant and electrical augmentation is produced by applying strong electric fields between electrodes immersed in the flame gases.

Comparisons involve energy costing.     

An exact modelling for thermal diffusivities of solid objects exposed to heating

A new simple model for determining the thermal diffusivities of solid geometrical objects (i.e., infinite slab, infinite cylinder, and sphere) being heated in a heating medium is proposed. In the unsteady-state heat transfer modelling, the lag factor and heating coefficient for heating applications were well-defined as being in a cooling process. In addition, new characteristic equations for the case of 0 < Bi < 100 in the transient heat transfer were developed instead of the existing complicated equations, and these were employed. In order to test the present model, the literature heat transfer data were used as an example and the use of the model was described in detail. The results of this study indicate that the heating coefficient has a direct influence on the thermal diffusivity and that the present model permits the determination of the thermal diffusivity values of solid geometrical objects in a simple and accurate manner.     

Studies on the Vilsmeier-haack reaction. Part XIII: Novel heterocyclo-substituted 4,4′-bi-pyrazolyl dithiocarbamate derivatives

5-Imino-3-methyl-l-phenyl-2-pyrazoline-4-dithiocarbamic acid (I) underwent simultaneous formylation and dimerization reactions with the Vilsmeier reagent giving 4-[5′-imino-3-(1″-formyl-2″-dimethylaminoethenyl)-3′-methyl-1′-phenyl-1′H-pyrazolo-4′-dithiocarbamyl-2,4-dihydro-3-imino-5-methyl-2-phenyl-1-pyrazoline]dithiocarbamate (II) which hydrolysed with sodium hydroxide to give 4-[3′-(1″-formyl-2″-hydroxyethenyl)-3′-methyl-1-phenyl-1′-H-pyrazolo-4′-dithiocarbamyl-1′-pyrazoline]dithiocarbamate-5,5′-dione (IV). Treatment of II and/or IV with morpholine, piperidine, piperazine, hydroxylamine, hydrazine hydrate or phenylhydrazine afforded the corresponding dipyrazolo-4,4′-dithiocarbamate derivatives with different heterocyclic systems at the 3-position. The structures of these compounds were confirmed by microanalysis data, IR and ¹H-NMR spectrometry. All synthesized compounds have been screened in vitro against Gram-positive and Gram-negative bacteria, and fungi.     

Asymptotic stability for a class of linear discrete systems withbounded uncertainties

The problem of stabilizing linear discrete systems with additive-type bounded uncertainties is considered. It is established that when matching conditions hold, a two-part feedback control can be designed: a linear part to assign the eigenvalues within the unit cycle and a nonlinear part to ensure the uniform asymptotic stability for arbitrary initial conditions and bounded admissible uncertainties     

Solar radiation maps for Iraq

As measured solar radiation data for all parts of Iraq is not available, it has to be estimated using other weather variables. A number of correlations which use dry bulb temperature, relative humidity and sunshine duration were tried. Finally a correlation using sunshine duration was selected as it gave most accurate estimation of solar radiation. Constants for the correlation for three stations representing three climatic regions in Iraq were determined. Monthly and yearly solar radiation maps were drawn using sunshine duration data from 24 stations from all over the country.     

Characterization of polycyclohexene by high field 13C-NMR spectroscopy

Summary ¹³C NMR spectrum of polycyclohexene is recorded at 50.5 MHz and interpreted in terms of its different stereoisomers. The ratio of threo to erythro forms in the polymer is 21. The spectrum is also sensitive to tacticity of the polymer chain.