The wear of high density polyethylene sliding against steel surfaces

The wear of high density polyethylene sliding against steel surfaces was studied with a pin-on-disc machine. The disc surfaces were finished by a turning operation on a lathe, changing the cutting conditions and tool geometries so as to provide varying surface finishes and different numbers of asperity peaks per unit distance. Optical and scanning electron microscopy were used to study the wear particles and the transfer films. It is found that a polymer film composed of layers about 500–1000 Å thick is formed on the metallic surfaces with sharp asperities. The size of the polymer wear particles decreases with increasing number of asperity peaks per unit distance and with decreasing asperity angle. The steady state wear rate increases rapidly with increasing polymer wear particle size. The wear for polymermetal sliding occurs by the mechanism of abrasion.     

Electron transport in non-crystalline garnet films

Thin films of yttrium iron garnet (yig) and Gd-substitutedyig of different thickness have been prepared by flash evaporation. The surfacedc andac electrical resistivity and thermopower in these films have been studied. The results are explained on the basis of Mott and Davis model in which narrow tails of localised states exist at the extreme valence and conduction bands and a band of localised levels near the middle of the gap. For the temperature range studied, the main conduction mechanism is on account of excitation of carriers into localised states at the band edges and hopping at energies close to the band tails.     

Mössbauer spectroscopy of titanium-substituted iron garnets

The Mössbauer spectroscopy of polycrystalline Y_3?x Ca _x Fe_5?x Ti _x O₁₂ (x=0·2, 0·5, 0·7) garnets has been studied at room temperature. The hyperfine fields both at the octahedral and tetrahedral sites decrease with increasing titanium content. The hyperfine fields both ata andd-sites are linearly proportional to magnetization. The quadrupole splitting fora-site shows no dependence on Ti content while the quadrupole splitting ford-site increases slightly withx. The results are explained on the basis of lattice distortion due to Ti substitution ona-site.     

Studies on viscosity of calcium soaps in aqueous methanol

Viscosity measurements of calcium soaps show that two kinds of micelles are formed in aqueous methanol mixtures. The change in the nature of micelles from hydrophilic oleomicelles to lipophilic hydromicelles occurs in solvents containing 40–50% (v/v) of methanol. The equations of Vand and Moulik are applicable only above the critical micelle concentration of the soaps. The parameters of the equations have been evaluated. These may be used to calculate the viscosity of soap solutions in the concentration range in which the equations hold good.     

Time-harmonic analysis of grounding system in horizontally stratified multilayer medium

This paper extends an electromagnetic model for time-harmonic analysis of grounding system in horizontally stratified multilayer medium which consists of air and arbitrary number of soil layers. Complete electromagnetic coupling between grounding system segments is taken into account. The model is based on applying the finite element technique to an integral equation formulation. Through an effective approximation of the attenuation and phase shift effects the computation of Sommerfeld integrals has been avoided, which considerably shortens the computational time. The treatment of non-horizontal segments of grounding grid conductors has been resolved by approximating the segment with five current point sources distributed along the segment length. An algorithm for scalar electric potential computation in any soil layers is presented and compared to published results. The effects of approximating a complex heterogeneous earth structure with a homogeneous earth is also analyzed and discussed.     

Taxonomic study of subfamily Nepetoideae (Lamiaceae) by polynomorphological approach

The present study is insight into pollen morphology for characterizing species and their utility in the taxonomic separation of certain taxa of subfamily Nepetoideae (Lamiaceae) from Pakistan. The pollen micromorphology of 11 species of the Nepetoideae was analyzed and documented using light microscopy and scanning electron microscopy (SEM) for both qualitative and quantitative characteristics. Most species have hexazonocolpate pollen grains but trizonocolpate and tetrazonocolpate pollen with circular and oval amb were also rarely observed in Mentha spicata. The basic pollen shape in most of the studied species was subspheroidal but prolate grains were also observed in M. spicata, S. coccinea, and S. plebeia. The exine sculpturing of Nepetoideae pollen was taxonomically very informative particularly at subfamily level. Observations of exine sculpturing with SEM revealed various types of pollen grains: reticulate, bireticulate, microreticulate, perforate, aerolate, and gammate. The bireticulate type further subdivided into three subtypes based on the number of secondary lumina in each primary lumen and is characterized by varying characteristics of the secondary reticulum and primary muri. A significant variation was observed in colpus surface ornamentation. The maximum polar diameter was found in O. americanum (58 ± 5.8 μm) and the maximum equatorial diameter observed in O. basilicum (50.25 ± 1.37 μm). Pollen features of the studied species were discussed and compared based on the current taxonomical concepts. The results showed that pollen traits of the subfamily Nepetoideae was found significant to classify the taxa. Furthermore, pollen features provide additional evidence to distinguish macromorphologically similar taxa from each other.