Showing papers by "Indian Institute of Science published in 1992"

Hairpin and parallel quartet structures for telomeric sequences

Abstract: The role of thymine residues in the formation of G-quartet structures for telomeric sequences has been investigated using model oligonucleotides of the type d(G4TnG4), with n = 1-4. Sequences d(G4T3G4) and d(G4T4G4) adopt a G-quartet structure formed by hairpin dimerization in 70 mM NaCl as judged by a characteristic circular dichroism signature with a 295 nm positive and 265 nm negative bands while d(G4TG4) adopts a parallel G-quartet structure like d(G12) which exhibits a strong positive band at 260 nm and a negative band at 240 nm. The sequence d(G4T2G4) exhibits a mixture of both conformations. The stability of hairpin G-quartet structures decreases with decrease in the number of intervening thymine residues. Potassium permanganate, a single strand specific probe has been used to establish the presence of loops composed of T residues in the hairpin G quartet structures formed by the oligonucleotides d(G4TnG4) with n = 2-4 in 70 mM NaCl. The formation of hairpin G quartet structure for the above sequences is further supported by the enhanced electrophoretic mobility observed on non-denaturing polyacrylamide gels. Human telomeric sequence d(TTAGGG)4 which showed enhanced electrophoretic mobility like Tetrahymena telomeric sequence d(T2G4)4 also exhibited a characteristic CD spectrum for a folded-back G-quartet structure. A detailed model for G-quartet structure involving hairpin dimer with alternating syn-anti-syn-anti conformation for the guanine residues both along the chain as well as around the G tetrad with at least two thymine residues in the loop is proposed. Intermolecular association of short telomeric sequences reported here provides a possible model for chromosomal pairing.

Performance Modeling Of Automated Manufacturing Systems

Abstract: (1993). Performance Modeling of Automated Manufacturing Systems. Technometrics: Vol. 35, No. 4, pp. 456-456.

Magnetism in the layered transition-metal thiophosphates M PS 3 ( M =Mn, Fe, and Ni)

Abstract: Anisotropic magnetic susceptibilities of single crystals of the layered transition-metal thiophosphates ${\mathrm{MnPS}}_{3}$, ${\mathrm{FePS}}_{3}$, and ${\mathrm{NiPS}}_{3}$ have been measured as a function of temperature. The materials order antiferromagnetically at low temperatures, the N\'eel temperatures being 78, 123, and 155 K, respectively. In the ordered state, the magnetization axis lies perpendicular to the layers for ${\mathrm{MnPS}}_{3}$ and ${\mathrm{FePS}}_{3}$, while for ${\mathrm{NiPS}}_{3}$ it lies in the layer. In the paramagnetic regime, the anisotropies of these compounds are different; while the susceptibility for ${\mathrm{MnPS}}_{3}$ is isotropic and that for ${\mathrm{NiPS}}_{3}$ shows only a weak ansiotropy, ${\mathrm{FePS}}_{3}$ exhibits highly anisotropic susceptibility. The anisotropic susceptibilities have been analyzed to obtain information on the state of the magnetic ions and the nature of magnetic interactions between them. The results show that ${\mathrm{MnPS}}_{3}$, ${\mathrm{FePS}}_{3}$, and ${\mathrm{NiPS}}_{3}$ form a unique class of compounds. Although all three compounds are isostructural with the magnetic lattice being the two-dimensional honeycomb, the spin dimensionalities for the three are different. While ${\mathrm{MnPS}}_{3}$ is best described by the isotropic Heisenberg Hamiltonian, ${\mathrm{FePS}}_{3}$ is most effectively treated by the Ising model and ${\mathrm{NiPS}}_{3}$ by the anisotropic Heisenberg Hamiltonian. The origin of the anisotropy in these compounds has been discussed, and it is shown how it arises from a combination of spin-orbit coupling and the trigonal distortion of the M${\mathrm{S}}_{6}$ octahedra. The magnetic exchange constant, J and the zero-field splitting energies of the ground state of the transition-metal ion have been evaluated from the anisotropic paramagnetic susceptibilities.

Performance modeling of automated manufacturing systems

Abstract: (1993). Performance Modeling of Automated Manufacturing Systems. Technometrics: Vol. 35, No. 4, pp. 456-456.

Electron-spectroscopy study of the semiconductor-metal transition in La1-xSrxCoO3.

Abstract: A study of the semiconductor-metal transition in the series ${\mathrm{La}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Sr}}_{\mathit{x}}$${\mathrm{CoO}}_{3}$, x=0.0--0.4, using electron-spectroscopy techniques is presented. The results show that the ground state of ${\mathrm{LaCoO}}_{3}$ has strongly mixed character. From the experiments we estimate the on-site Coulomb correlation energies ${\mathit{U}}_{\mathit{d}\mathit{d}}$ and ${\mathit{U}}_{\mathit{p}\mathit{p}}$ to be 3.4 and 6.7 eV, respectively, while the (${\mathit{pd}}_{\mathrm{\ensuremath{\sigma}}}$) interaction strength is 2.2 eV. A comparison of the experiment with the results of a model many-body cluster calculation for the Co 2p spectra indicates a low-spin state of Co in ${\mathrm{LaCoO}}_{3}$. The band gap of ${\mathrm{LaCoO}}_{3}$ is estimated to be about 0.6 eV from ultraviolet photoemission spectroscopy and bremsstrahlung isochromat spectroscopy measurements. The semiconductor-metal transition results from overlap of doped hole states with the valence band for x\ensuremath{\ge}0.2.

Combustion Synthesis of Metal Chromite Powders

Abstract: Fine-particle metal chromites (MCr2O4, where M = Mg, Ca, Mn, Fe, Co, Ni, Cu, and Zn) have been prepared by the combustion of aqueous solutions containing the respective metal nitrate, chromium(III) nitrate, and urea in stoichiometric amounts. The mixtures, when rapidly heated to 350°C, ignite and yield voluminous chromites with surface areas ranging from 5 to 25 m2/g. MgCr2O4, sintered in air at 1500°C for 5 h, has a density of 4.0 g/cm3.

Extended hypercube: a hierarchical interconnection network of hypercubes

Abstract: A new interconnection topology-the extended hypercube-consisting of an interconnection network of k-cubes is discussed. The extended hypercube is a hierarchical, expansive, recursive structure with a constant predefined building block. The extended hypercube retains the positive features of the k-cube at different levels of hierarchy and at the same time has some additional advantages like reduced diameter and constant degree of a node. The paper presents an introduction to the topology of the extended hypercube and analyzes its architectural potential in terms of message routing and executing a class of highly parallel algorithms. Topological properties and performance studies of the extended hypercube are presented. >

An application of functional dependencies to the topological analysis of protection schemes

Abstract: The concept of functional dependency is applied to the problem of relay coordination in protection systems. An algorithm is developed for the identification of a minimal break point set (BPS) of relays of a protection topology. This algorithm is an improvement over existing algorithms in that it identifies a minimal BPS within a time period that is a polynomial function of the number of relays, while the earlier algorithms had exponential time behavior. In the case of large protection schemes, the saving in computation costs is considerable. An algorithm is developed for the selection of a relative sequence matrix; this algorithm also has polynomial time complexity. The functional dependency approach is seen to be more flexible and more powerful than the graph theoretic schemes, and holds out much promise for the development of efficient computer-aided design tools for the protection engineer. >

Solid state amorphization in binary Ti-Ni, Ti-Cu and ternary Ti-Ni-Cu system by mechanical alloying

Abstract: An amorphous phase has been synthesized by mechanical alloying in a planetary mill over a nickel content range of 10–70 at.% in the TiNi system and a copper content range of 10–50 at.% in the TiCu system. In the case of ternary TiNiCu alloys the glass-forming composition range has been found to be given by x = 10–20 for Ti60Ni40 − xCux, x = 10 – 30 for Ti50Ni50 − xCux and x = 10 – 40 for Ti40Ni60 − xCux alloys. The difficulty in the amorphization of copper-rich compositions is explained in the light of enthalpy composition diagrams calculated for the ternary solid solution and the amorphous phase.

Long-term contraceptive efficacy of vaccine of ovine follicle-stimulating hormone in male bonnet monkeys (Macaca radiata).

Abstract: A group of ten healthy fertile adult male bonnet monkeys were actively immunized using procedures acceptable for human use with pure follicle-stimulating hormone (oFSH) isolated from sheep pituitaries. The vaccine elicited an immunogenic response in all ten monkeys; the antibody-binding capacity, determined by Scatchard analysis, varied from 3 to 18 micrograms $oFSH ml^{-1}$, the binding affinity ranging from $0.13 to 2.0 \times 10(10) mol^{-1}$. A substantial population of antibodies against oFSH crossreacted with 125I-labelled human (h) FSH, used here as a representative ligand of primate FSH. The bioneutralization activity of the antisera assessed by a specific bioassay in vitro, when the antibody titre was high, was 6.9 $\pm$ 0.18 micrograms $hFSH ml^{-1}$. Immunization for 4.7-5.7 years did not affect the health and libido of the animals. Concentration of testosterone in serum remained normal throughout the study, but, within 150 days of immunization, there was a marked decrease (75-100%) in the number of spermatozoa in seminal ejaculates. Oligospermic status interspersed with azoospermia was maintained by periodic boosting. The fertility of these animals was monitored between 6 months and 2 years after primary immunization. All the ten animals proved infertile in repeated mating experiments with females of proven fertility. After stopping booster injections, nine of ten animals regained fertility, but the time taken for this depended upon the rate of decline of antibody titres. Re-boosting these monkeys with 100 micrograms oFSH after confirming that recovery had occurred revealed prompt increases in antibody titres followed once again by onset of oligo-azoospermia and infertility, underscoring the specificity of immunization effect. The immunized monkeys, apart from being acutely oligospermic, ejaculated spermatozoa that were markedly deficient in key acrosomal enzymes, such as acrosin and hyaluronidase, and motility as well as in their ability to penetrate a gel in vitro, suggesting that the infertility observed was due to gross reductions in the numbers of spermatozoa that could effectively interact with the oocyte and cause successful fertilization.

Temperature dependence of the c-axis resistivity of high-T c layered oxides

Abstract: Electrical transport along the c axis of high-${\mathit{T}}_{\mathit{c}}$ layered oxides is pictured as a coherent interplanar tunneling between neighboring layers blocked by repeated intraplanar incoherent scatterings. This gives the same temperature dependence for the c-axis resistivity as that for the in-plane resistivity. Additional temperature dependence can arise from the temperature-dependent renormalization of the tunneling matrix element by an ohmic coupling to adiabatic phonons because of the large effective electron mass along the c axis. Our calculation is consistent with recent experimental results on single crystals, and makes some definite predictions that can be put to test.

Analysis of ECG from pole-zero models

Abstract: A complete solution for the delineation of the ECG signal into its component waves is proposed from a system theoretic point of view. The discrete cosine transform (DCT) of a bell-shaped biphasic function is approximated mathematically by a system function with two poles and two zeros, i.e., of order

Intraseasonal Variation of the Summer Monsoon I:Observational Aspects

Abstract: Within the summer monsoon, the circulation and rainfall over the Indian region exhibit large variations over the synoptic scale of 3-7 days and the supersynoptic scales of 10 days and longer. In this paper we discuss some facets of intraseasonal variation on the supersynoptic scale on the basis of existing observational studies and some new analysis. The major variation of the summer monsoon rainfall on this scale is the active-break cycle. The deep convection over the Indian region on a typical day in the active phase is organized over thousands of kilometers in the zonal direction and is associated with a tropical convergence zone (TCZ). The intraseasonal variations on the supersynoptic scale are also coherent on these scales and are related to the space-time variation of the large-scale TCZ. The latitudinal distribution of the occurrence of the TCZ is bimodal with the primary mode over the heated continent and a secondary mode over the ocean. The variation of the continental TCZ is generally out of phase with that of the oceanic TCZ. During the active spells, the TCZ persists over the continent in the monsoon zone. The revival from breaks occurs either by northward propagation of the TCZ over the equatorial Indian Ocean or by genesis of a disturbance in the monsoon zone (often as a result of westward propagations from W. Pacific). The mechanisms governing the fluctuation between active spells and breaks, the interphase transition and the complex interactions of the TCZ over the Indian subcontinent with the TCZ over the equatorial Indian Ocean and the W. Pacific, have yet to be completely understood.

Electroless nickel hydroxide: synthesis and characterization

Abstract: An electroless method of nickel hydroxide synthesis through the complexation-precipitation route which yields a fine particle material having a specific surface area of 178 m2 g−1 has been described. The morphology of this material as revealed by electron microscopy is distinctly different from the turbostratic nature of electrosynthesized nickel hydroxide. While the long range structure as shown by the X-ray diffraction pattern is similar to that of β-Ni(OH)2, the short range structure as revealed by infrared spectroscopy incorporates characteristics similar to that of α-Ni(OH)2. Cyclic voltammetry studies show that the electroless nickel hydroxide has a higher coulombic efficiency (>90%), a more anodic reversible potential and a higher degree of reversibility compared to the electrosynthesized nickel hydroxide and conventionally prepared nickel hydroxide.

Circuit definitions of nondeterministic complexity classes

Abstract: We consider restictions on Boolean circuits and use them to obtain new uniform circuit characterizations of nondeterministic space and time classes. We also obtain characterizations of counting classes based on nondeterministic time bounded computations on the arithmetic circuit model. It is shown how the notion of semiunboundedness unifies the definitions of many natural complexity classes.

Phase separation in binary nearly-hard-sphere colloids : evidence for the depletion force

Abstract: A binary aqueous suspension of large (L) and small (S) nearly-hard-sphere colloidal polystyrene spheres is shown to segregate spontaneously into L-rich and S-rich regions for suitable choices of volume fraction and size ratio. This is the first observation of such purely entropic phase separation of chemically identical species in which at least one component remains fluid. Simple theoretical arguments are presented to make this effect plausible.

In vitro micropropagation of elite rosewood (Dalbergia latifolia Roxb.)

Abstract: Induction of single and multiple shoots was obtained from nodal expiants of 60-80 year-old elite trees of rosewood on Murashige and Skoog's basal medium supplemented with 6-benzylaminopurine (1.0 mg 1(-1)) and δ -Naphthalene acetic acid (0.05 mg 1(-1)) or indole acetic acid (0.5 mg 1(-1)). Multiplication of shoots was obtained on MS (reduced major elements) or Woody Plant Medium supplemented with 6-benzylaminopurine (1.0 mg 1(-1)) and kinetin (0.5-1.0 mg 1(-1)). Excised shoots were rooted on half-strength MS with IBA (2.0 mg 1(-1)) to obtain complete plantlets. The regenerated plantlets have been acclimatized and successfully transferred to the soil.

The properties of ion channels formed by zervamicins

Abstract: The zervamicins (Zrv) are a family of 16 residue peptaibol channel formers, related to the 20 residue peptaibol alamethicin (Alm), but containing a higher proportion of polar sidechains. Zrv-IIB forms multi-level channels in planar lipid (diphytanoyl phosphatidyl- choline) bilayers in response to cis positive voltages. Analysis of the voltage and concentration dependence of macroscopic conductances induced by Zrv-IIB suggests that, on average, channels contain ca. 13 peptide monomers. Analysis of single channel conductance levels suggests a similar value. The pattern of successive conductance levels is consistent with a modified helix bundle model in which the higher order bundle are distorted within the plane of the bilayer towards a "torpedo" shaped cross-section, The kinetics of intra-burst switching between adjacent conductance levels are shown to be approximately an order of magnitude faster for Zrv-IIB than for Ahn. The channel forming properties of the related naturally occurring peptaibols, Zrv-Leu and Zrv-IC, have also been demonstrated, as have those of the synthetic apolar analogue Zrv-Al-16. The experimental studies on channel formation are combined with the known crystallographic structures of Zrv-Al-16 and Zrv- Leu to develop a molecular model of Zrv-IIB channels.