A chemical method for preparation of cobalt oxide thin films

A very simple method has been developed for the preparation of cobalt oxides, CoO(OH) and Co₃O₄, thin films on glass substrates using cobalt(II) chloride and ammonia as reacting agents. These materials were characterized by optical and electrical measurements. CoO(OH) films are insulating and have DC dielectric breakdown at about 3700 V / mm when measurements are made using silver print electrodes placed at various spacings on the film. Electrical resistivity of Co₃O₄ is 2.5 ω m. Analysis of the absorption spectra shows that CoO(OH) and CO₃O₄ have optical band gaps of 2.36 eV and 1.65 eV respectively. Spectral variation of the optical constants of these materials have also been measured.     

Depth profiling of CdS homojunction using AES analysis

Top layer of spray pyrolyzedn-type CdS has been converted intop-type by diffusion of copper which resulted in the formation of homojunction. This is achieved by annealing CdS/Cu bilayer film. The nature of diffusion of copper atoms into CdS has been studied using auger electron spectroscopy (AES).     

Polymer–solvent interaction observed in rubbery plateau modulus

The conventional wisdom is that concentration dependence of the rubbery plateau modulus of polymer solutions is independent of the material. However, in industrial practice, sometimes a small addition of miscible liquid lowers the modulus significantly whilst at other times it hardly affects it. This work examines an example of the former case (nitrile rubber–plasticizer systems) and one of the latter (acrylic rubber–plasticizer systems). Two possible explanations are offered for the observed behaviour. One is a possible contribution of a polar association to the plateau modulus: when a solvent breaks the association it gives the former case and when it does not, it gives the latter. The other explanation is a possible contraction of polymer coils from unperturbed size giving the former case, and an expansion giving the latter. Changes of less than a few percent of the coil-radius are sufficient to explain the above behaviour © 1998 SCI.     

Rheological behavior of blends of natural rubber and styrene–butadiene rubber latices

The rheological behavior of blends of natural rubber (NR) and styrene–butadiene rubber (SBR) latices has been studied with reference to the effects of blend ratio, shear rate, surface-active agents (casein and sodium carboxymethyl cellulose), and temperature. When the SBR content was less than 50%, the viscosities of the blends appeared to be a nonadditive function of the viscosities of the constituent homopolymers; i.e., a positive deviation was observed. This was due to the structural buildup of the SBR domains. The SBR domains underwent agglomeration and consequently so-called microflocculation took place. The viscosities of all the blends were found to decrease with increase of temperature and shear rate. The increase in temperature and shear rate marginally weakened the structural buildup as evidenced by the lowering of viscosity. As the SBR content in the system increased, the pseudoplasticity of the blend increased. Even in the presence of surface-active agents the blends showed composition-dependent positive deviation. However, surface-active agents marginally reduced the extent of structural buildup by reducing the microflocculation behavior of SBR domains. © 1995 John Wiley & Sons, Inc.     

Isosorbide based chiral polyurethanes: optical and thermal studies

A new class of chiral polyurethanes containing amido linkages in the polymer backbone have been synthesized by reacting toluene diisocyanate with isosorbide (IS) chiral moiety and the chromophores [N,N′-ethane-1,2-diyl bis(6-hydroxy hexanamide), N,N′-butane-1,4-diyl bis(6-hydroxy hexanamide) and N,N′-hexane-1,6-diyl bis(6-hydroxy hexanamide)]. The corresponding chromophores were obtained by the aminolysis of ε-caprolactone by using the diamines, diaminoethane, diaminobutane and diaminohexane, respectively. All the polymers were synthesized according to the symmetry conditions so as to obtain the non-centrosymmetric environment. A series of polyurethanes were synthesized by varying the chiral–chromophore composition. The polyurethanes developed were characterized by optical and thermal methods.     

Measurement of insolation using CdS photoresistor

Utilizing a cadmium sulphide (CdS) photoresistor, the intensity of solar electromagnetic radiation (insolation) was investigated. Readings were taken daily and hourly at the Nsukka Campus of the University of Nigeria which lies on latitude 6.8° north and longitude 7.35° east. Our investigation spanned a period of 8 months (February–September). This was an extension of work done by E. Klugmann & O. E. Onyeogu who carried out a similar investigation, but for a shorter period, 4 months (October-January) and also their investigations took account of only the dry season and harmattan.

Our investigation took account of a very vital climatic period in Nigeria, namely the rainy season (March–September).

It was observed that with a cadmium sulphide photoresistor which has an average efficiency of 7%², the maximum average hourly insolation is roughly 63 W m⁻² which is equivalent to 900 Wm⁻² if cadmium sulphide were to be 100% efficient. Furthermore, it was consistently observed that the amount of solar intensity falling on our detector is always greater after the rains. Finally, our results are then compared with the modified empirical equations of Rapp & Hoffman and there is some times nice agreement between experimental and theoretical results of hourly insolation in Wm⁻², and sometimes there is sharp contrast between the two.     

Maternal health services in South Africa. During the 10th anniversary of the WHO 'Safe Motherhood' initiative

The tenth anniversary of the World Health Organisation's 'Safe Motherhood' initiative is being celebrated this year and the organisation is using the opportunity to assess critically its gains, its strengths and its weaknesses. South Africa has taken some bold steps to address maternal health services, specifically introducing free health care for pregnant women and children under 5. In this paper we explore what further steps are necessary to ensure improved health outcome for pregnant women. South African health care administrations are, in some cases, engaged in broad health systems interventions at provincial level. This approach to improving health services is nonetheless frustrated by programme-specific initiatives, such as the introduction of female condoms or other piecemeal additions. We argue that making the systems function is the essential, primary step in the success of any intervention. The case of maternal health is explored in this paper.