Studies on haemoglobin from the Indian toad, Bufo melanostictus, by electron microscopy

Hæmoglobin from an amphibian, Bufo melanostictus, was studied by electron microscopy after metal shadowing and after negative staining with uranyl acetate. The effect of the electron stain on the protein was investigated by spectrophotometry. The sample was also characterized by alkali denaturation and sedimentation analysis. The results were compared to those of adult human hæmoglobin. Spectrophotometry of the sample showed characteristics similar to those of normal oxyhæmoglobin. The protein, like human adult hæmoglobin, was found to be completely alkali-labile. Ultracentrifugation of a freshly prepared sample showed a single symmetrical peak, an indication for the presence of a homogeneous component. The S⁰_20,W value (5.1) was found to be markedly higher than that of adult human hæmoglobin. With storage, however, the peak became asymmetrical suggesting the formation of a limited amount of a heavier component. The electron micrographs of the shadowed preparations revealed a characteristic shape and ultrastructure of the protein molecules and their average height was found to be 5.5 nm. The micrographs of the negatively stained samples showed many particles with a substructure similar to that of the shadowed molecules and a mean dimension of 6.1 nm, a number of dimers of average length 6.0 nm and overall width 3.6 nm, and many globules of average diameter 3.6 nm. These were interpreted as whole, half and quarter hæmoglobin molecules, respectively. Both techniques revealed at the most four subunits in a molecule. The structure of the subunits and their arrangement in the molecule were found to be essentially similar to those of normal human adult hæmoglobin, and could be interpreted in terms of the Perutz model. Spectrophotometry of the mixture of the protein and uranyl acetate showed that the protein becomes denatured with time and that the denaturation is due to the low pH (4.3) of the stain. Nevertheless, this study showed that by keeping the staining time very short, it is possible to obtain acceptable electron micrographs of small multi-unit protein molecules such as haemoglobin.     

Flow in the Ekman layer on an oscillating porous plate

Summary.  The Laplace transform technique is utilized to obtain the exact solution for thermally-induced wave propagation in a circular piezoelectric plate. The temperature is assumed to satisfy the one-dimensional heat conduction equation that includes a relaxation time. Displacement and electric potential functions are introduced in order to solve the equations of motion and electrodynamics. Numerical results obtained for both a PZT-5A plate and a non-piezoelectric plate illustrate the effects of relaxation time and piezoelasticity on displacement and stress histories. Received October 3, 2002 Published online: February 10, 2003     

Reliability evaluation of flow networks considering multistate modelling of network elements

This paper presents a simple method for evaluating the reliability of a multistate flow network. A system is considered reliable only if it successfully transmits at least the required system capacity from the transmitter to the receiver station. All successful states are obtained from the knowledge of the max-flow min-cuts of the system graph. Examples are solved to demonstrate the applicability of proposed method. It is observed that the method is simple, computationally fast and efficient.     

Surface microstructural modification and fracture behavior of tensile deformed polypropylene with different percentage crystallinity

Microstructural evolution during tensile deformation of injection molded polypropylene (PP) at the micro- and nano-scale level was studied using atomic force and scanning electron microscopy techniques. Atomic force microscopy (AFM) enabled microstructural changes of tensile deformed PPs with different percentage crystallinity to be captured. AFM of undeformed slow-cooled (SC-PP: high crystallinity) and water-quenched (WQ-PP: low crystallinity) PPs suggested that the fibrils are relatively more closely packed in the SC-PP with higher average surface height of 7.5 nm as compared to 5.4 nm in the case of WQ-PP. Tensile deformed SC-PP and WQ-PP at displacement rates of 125–500 mm/min (strain rates of 0.04 s⁻¹ to 0.16 s⁻¹) indicated that the fibrils/microfibrils are aligned along the tensile axis, with WQ-PP exhibiting enhanced stretching of fibrils/microfibrils/chain-folded lamellae in comparison to SC-PP. Three fracture morphologies were identified at different strain rates, and include crazing/tearing (C), brittle fracture in association with crazing/tearing (B1), and brittle fracture together with ductile pulling of ligaments (B2). The fracture morphology exhibited by both SC-PP and WQ-PP was similar, but the percent area fraction of the three identified morphologies varied. WQ-PP with lower crystallinity was characterized by a decrease in percent of crazing/tearing (C) and brittle+crazing/tearing (B1), and increase in brittle+ductile pulling of ligaments (B2). The fracture characteristics of PPs with differences in crystallinity was consistent with AFM observations.     

A new family of lipolytic plant enzymes with members in rice, arabidopsis and maize

We have noted a striking similarity between the sequences of proteins in a novel family of lipases we recently reported [Upton, C. and Buckley, J. T. (1995) Trends Biol. Sci. 20, 178-9] and more than 120 sequences from the database of Expressed Sequence Tags (dbEST) which correspond to at least 30 unique genes from arabidopsis, rice and maize. A cDNA (Arab-1) corresponding to one of these sequences was isolated, sequenced and translated. There was significant similarity to sequences in the new lipase family over the entire open reading frame of Arab-1 and when expressed in E. coli, the gene product was lipolytic. Arab-1 and genes for some of the other plant proteins appear to be differentially expressed. They may play a role in the regulation of lipid metabolism during plant development.     

Strain relaxation in SiGe due to process induced defects and their subsequent annealing behavior

Ion implantation and reactive ion etching are known to create defects in silicon which get cured during subsequent annealing operations. In this paper we have reported the annealing behavior of phosphorus implanted into strained SiGe layer at room temperature. The implantation was performed at 155 KeV with a dose of 1×10¹⁴/cm². Post implantation annealing was performed at 600, 700, 800 and 900°C for 10 s in a rapid thermal process furnace. Annealing behavior of defects generated as a consequence of dry etching is also reported. RTP annealing on reactive ion etching (RIE) etched samples were performed at 650, 700, 750 and 800 °C. I–V, C–V and DLTS measurements hint towards the presence of permanent dislocation loops created as a consequence of RIE and implantation causing strain relaxation.     

Rolling textures in nanoscale Cu/Nb multilayers

Rolling textures in nanoscale multilayered thin films are found to differ markedly from textures observed in bulk materials. Multilayered thin films consisting of alternating Cu and Nb layers with columnar grains were produced by magnetron sputtering, with individual layer thickness ranging from 4 μm to 75 nm and Cu/Nb interfaces locally satisfying the Kurdjumov–Sachs (K–S) orientation relations. After rolling to 80% effective strain, samples with a larger initial layer thickness develop a bulk rolling texture while those with a smaller initial layer thickness display co-rotation of Cu and Nb columnar grains about the interface normal, in order to preserve the K–S orientation relations. The resulting K–S texture has 0 0 1Nb parallel to and 1 1 0Cu approximately 5° from the rolling direction. A crystal plasticity model based on the Principle of Minimum Shear captures the K–S texture approximately and suggests that Nb drags Cu along in the rotation process.