Effect of substrate roughness on growth of diamond by hot filament CVD

Polycrystalline diamond coatings are grown on Si (100) substrate by hot filament CVD technique. We investigate here the effect of substrate roughening on the substrate temperature and methane concentration required to maintain high quality, high growth rate and faceted morphology of the diamond coatings. It has been shown that as we increase the substrate roughness from 0.05 mu m to 0.91 mu m (centre line average or CLA) there is enhancement in deposited film quality (Raman peak intensity ratio of sp (3) to non-sp (3) content increases from 1.65 to 7.13) and the substrate temperature can be brought down to 640A degrees C without any additional substrate heating. The coatings grown at adverse conditions for sp (3) deposition has cauliflower morphology with nanocrystalline grains and coatings grown under favourable sp (3) condition gives clear faceted grains.

Effect of interface friction on the mechanics of indentation of a finite layer resting on a rigid substrate

Copper strips of 2.5 mm thickness resting on stainless steel anvils were normally indented by wedges under nominal plane strain conditions. Inflections in the hardness-penetration characteristics were identified. Inflections separate stages where each stage has typical mechanics of deformation. These are arrived at by studying the distortion of 0.125 mm spaced grids inscribed on the deformation plane of the strip. The sensitivity of hardness and deformation mechanics to wedge angle and the interfacial friction between strip and anvil were investigated within the framework of existing slip line field models of indentation of semi-infinite and finite blocks.

Structure of the putative mutarotase YeaD from Salmonella typhimurium in two different forms: in vivo binding of a sugar phosphate

Salmonella typhimurium YeaD (stYeaD), annotated as a putative aldose 1-epimerase, has a very low sequence identity to other well characterized mutarotases. Sequence analysis suggested that the catalytic residues and a few of the substrate-binding residues of galactose mutarotases (GalMs) are conserved in stYeaD. Determination of the crystal structure of stYeaD in an orthorhombic form at 1.9 angstrom resolution and in a monoclinic form at 2.5 angstrom resolution revealed this protein to adopt the beta-sandwich fold similar to GalMs. Structural comparison of stYeaD with GalMs has permitted the identification of residues involved in catalysis and substrate binding. In spite of the similar fold and conservation of catalytic residues, minor but significant differences were observed in the substrate- binding pocket. These analyses pointed out the possible role of Arg74 and Arg99, found only in YeaD-like proteins, in ligand anchoring and suggested that the specificity of stYeaD may be distinct from those of GalMs

Oestrogen-induced synthesis of thiamin-binding protein in immature chicks. Kinetics of induction, hormonal specificity and modulation

A specific radioimmunoassay procedure was developed to monitor the plasma concentrations of thiamin-binding protein, a minor yolk constituent of the chicken egg. By using this sensitive assay, the kinetics of oestrogen-induced elaboration of this specific protein in immature chicks was investigated. After a single injection of the steroid hormone, with an initial lag period of 4–5h the thiamin-binding protein rapidly accumulated in the plasma, attaining peak concentrations around 75h and declining thereafter. A 4-fold amplification of the response was noticed during the secondary stimulation, and this increased to 9-fold during the tertiary stimulation with the steroid hormone. The magnitude of the response was dependent on the hormone dose, and the initial latent period and the duration of the ascending phase of induction were unchanged for the hormonal doses tested during both the primary and secondary stimulations. The circulatory half-life of the protein was 6h as calculated from the measurement of the rate of disappearance of the exogenously administered 125I-labelled protein. Simultaneous administration of progesterone, dihydrotestosterone or corticosterone did not alter the pattern of induction. On the other hand, hyperthyroidism markedly decreased the oestrogenic response, whereas propylthiouracil-induced hypothyroidism had the opposite effect. The anti-oestrogen E- and Z-clomiphene citrates, administered 30min before oestrogen, effectively blocked the hormonal induction. a-Amanitin and cycloheximide administered along with or shortly after the sex steroid severely curtailed the protein elaboration. A comparison of the kinetics of induction of thiamin- and riboflavin-binding proteins by oestrogen revealed that, beneath an apparent similarity, a clear-cut difference exists between the two vitamin-binding proteins, particularly with regard to hormonal dose-dependent sensitivity of induction and the half-life in circulation. The steroid-mediated elaboration of the two yolk proteins thus appears to be not strictly co-ordinated, despite several common regulatory features underlying their induction.

Substrate-mediated purification and characterization of a 3-hydroxybenzoic acid-6-hydroxylase from Micrococcus

3-Hydroxybenzoic acid-6-hydroxylase from Micrococcus sp. was purified to homogeneity in a single step using the substrate-mediated interaction of the enzyme with blue-Sepharose. The enzyme was bound to the affinity matrix in the presence of 3-hydroxybenzoic acid and was eluted in its absence. The molecular weight of the purified enzyme is 70,000 with no subunit structure. The flavoenzyme required the exogenous addition of FAD for its complete activity and had a strict preference for NADH over NADPH. The activity of the enzyme was drastically inhibited by Cu2+ and Hg2+ and the inhibition was reversed by thiol reagents.

Effect of substrate temperature on the properties of ZrO2 films prepared by d.c. reactive magnetron sputtering

Studies of ZrO2 films prepared by d.c. reactive magnetron sputtering are described. The effects of substrate temperature on the packing density, refractive index, extinction coefficient and crystallinity phase have been investigated in the temperature range 25–450 °C. The refractive index varied from 1.84 to 1.95 and extinction coefficient from 2 × 10−3 to 9.6 × 10−3. This was explained on the basis of an increase in packing density from 0.686 to 0.813. The change in packing density has been attributed to a decrease in the oxygen condensation at higher temperatures. Annealing results in a decrease in refractive index and increase in extinction coefficient. The films deposited at 150 °C showed a monoclinic phase which transforms to a tetragonal phase at higher substrate temperatures.

Effect of Substrate and Annealing Temperatures on Mechanical Properties of Ti-rich NiTi Films

The effect of substrate and annealing temperatures on mechanical properties of Ti-rich NiTi films deposited on Si (100) substrates by DC magnetron sputtering was studied by nanoindentation. NiTi films were deposited at two substrate temperatures viz. 300 and 400 degrees C. NiTi films deposited at 300 degrees C were annealed for 4 h at four different temperatures, i.e. 300, 400, 500 and 600 degrees C whereas films deposited at 400 degrees C were annealed for 4 h at three different temperatures, i.e. 400, 500 and 600 degrees C. The elastic modulus and hardness of the films were found to be the same in the as-deposited as well as annealed conditions for both substrate temperatures. For a given substrate temperature, the hardness and elastic modulus were found to remain unchanged as long as the films were amorphous. However, both elastic modulus and hardness showed an increase with increasing annealing temperature as the films become crystalline. The results were explained on the basis of the change in microstructure of the film with change in annealing temperature.

Random sequential multilayer deposition of different‐sized k mers on a one dimensional infinite substrate

Kinetics of random sequential, irreversible multilayer deposition of macromolecules of two different sizes on a one dimensional infinite lattice is analyzed at the mean field level. A formal solution for the corresponding rate equation is obtained. The Jamming limits and the distribution of gaps of exact sizes are discussed. In the absence of screening, the jamming limits are shown to be the same for all the layers. A detailed analysis for the components differing by one monomer unit is presented. The small and large time behaviors and the dependence of the individual jamming limits of the k mers and (k−1) mers on k and the rate parameters are analyzed.

Specificity in the regulation of eukaryotic gene transcription

The regulation of eukaryotic gene transcription poses major challenges in terms of the innumerable protein factors required to ensure tissue or cell-type specificity. While this specificity is sought to be explained by the interaction of cis-acting DNA elements and thetrans-acting protein factor(s), considerable amount of degeneracy has been observed in this interaction. Immunoglobulin heavy chain gene expression in B cells and liver-specific gene expression are discussed as examples of this complexity in this article. Heterodimerization and post-translational modification of transcription factors and the organization of composite promoter elements are strategies by which diverse sets of genes can be regulated in a specific manner using a finite number of protein factors

Interaction of Sesbania Mosaic Virus Movement Protein with VPg and P10: Implication to Specificity of Genome Recognition

Sesbania mosaic virus (SeMV) is a single strand positive-sense RNA plant virus that belongs to the genus Sobemovirus. The mechanism of cell-to-cell movement in sobemoviruses has not been well studied. With a view to identify the viral encoded ancillary proteins of SeMV that may assist in cell-to-cell movement of the virus, all the proteins encoded by SeMV genome were cloned into yeast Matchmaker system 3 and interaction studies were performed. Two proteins namely, viral protein genome linked (VPg) and a 10-kDa protein (P10) c v gft encoded by OFR 2a, were identified as possible interacting partners in addition to the viral coat protein (CP). Further characterization of these interactions revealed that the movement protein (MP) recognizes cognate RNA through interaction with VPg, which is covalently linked to the 59 end of the RNA. Analysis of the deletion mutants delineated the domains of MP involved in the interaction with VPg and P10. This study implicates for the first time that VPg might play an important role in specific recognition of viral genome by MP in SeMV and shed light on the possible role of P10 in the viral movement.

Growth temperature induced effects in non-polar a-plane GaN on r-plane sapphire substrate by RF-MBE

Non-polar a-plane GaN films were grown on an r-plane sapphire substrate by plasma assisted molecular beam epitaxy (PAMBE). The effect of growth temperature on structural, morphological and optical properties has been studied. The growth of non-polar a-plane (1 1 - 2 0) orientation of the GaN epilayers were confirmed by high resolution X-ray diffraction (HRXRD) study. The X-ray rocking curve (XRC) full width at half maximum of the (1 1 - 2 0) reflection shows in-plane anisotropic behavior and found to decrease with increase in growth temperature. The atomic force micrograph (AFM) shows island-like growth for the film grown at a lower temperature. Surface roughness has been decreased with increase in growth temperature. Room temperature photoluminescence shows near band edge emission at 3.434-3.442 eV. The film grown at 800 degrees C shows emission at 2.2 eV, which is attributed to yellow luminescence along with near band edge emission. (C) 2010 Elsevier B.V. All rights reserved.