Synthesis of oxacalothrixin B and its analogues involving iodine/TBHP-mediated electrocyclization

The total synthesis of oxacalothrixins, an isostere of biologically important carbazoloquinone alkaloid, calothrixin B was achieved from 2-acetyl-3-methylbenzofuran. An iodine/TBHP-mediated oxidative cyclization of benzofuranyl-enamine has been employed as a key step to synthesize, the crucial intermediate 1-hydroxy dibenzofurancarbaldehyde. The latter upon reductive cyclization followed by PIDA-mediated oxidation furnished oxacalothrixin B and its analogues.     

Bounds on an anomalous dijet resonance in W+jets production in pp collisions at √s = 1.96 TeV

We present a study of the dijet invariant mass spectrum in events with two jets produced in association with a W boson in data corresponding to an integrated luminosity of 4.3 fb(-1) collected with the D0 detector at √s = 1.96 TeV. We find no evidence for anomalous resonant dijet production and derive upper limits on the production cross section of an anomalous dijet resonance recently reported by the CDF Collaboration, investigating the range of dijet invariant mass from 110 to 170 GeV/c(2). The probability of the D0 data being consistent with the presence of a dijet resonance with 4 pb production cross section at 145 GeV/c(2) is 8×10(-6).     

Search for Resonant WW and WZ Production in pp collisions at √s=1.96 TeV

We search for resonant WW or WZ production by using up to 5.4 fb(-1) of integrated luminosity collected by the D0 experiment in run II of the Fermilab Tevatron Collider. The data are consistent with the standard model background expectation, and we set limits on a resonance mass by using the sequential standard model W' boson and the Randall-Sundrum model graviton G as benchmarks. We exclude a sequential standard model W' boson in the mass range 180-690 GeV and a Randall-Sundrum graviton in the range 300-754 GeV at 95% C.L.     

A simple technique for evaluation of transmission coefficient at the splice with angular offset and transverse offset for first higher mode propagation in graded index fibers

We present simple and accurate analytical expressions for transmission coefficient at the splice with angular offset and transverse offset in case of first higher mode propagation in graded index fibers. We employ the simple series expression for first higher order modal field for graded index fiber. The evaluation of the concerned parameters based on our formalism requires very little computations. Here, we show that our estimations match excellently well with the exact results in case of step and parabolic index fibers. Further, splice being highly tolerant for longitudinal separation, our analysis is judiciously restricted to the case of transverse and angular mismatches only. The analysis should find application in dual mode graded index fiber in all optical technology.     

Burstein–Moss shift and room temperature near-band-edge luminescence in lithium-doped zinc oxide

Nanopowders of pure and lithium-doped semiconducting ZnO (Zn_1−x Li _x O, where x= 0, 0.01, 0.03, 0.06, 0.09 and 0.15 in atomic percent (at.%)) are prepared by PEG-assisted low-temperature hydrothermal method. The average crystallite size is calculated using Debye–Scherrer formula and corrected for strain-induced broadening by Williamson–Hall (W–H) plot. The peak shift in XRD and the lattice constant of ZnO as a function of unit cell composition are predicted by Vegard’s law. The evolution of ZnO nanostructures from rod-shaped to particle nature is observed from TEM images and the influence of dopant on the morphology is investigated. The optical absorption measurement marks an indication that the incorporation of lithium ion into the lattice of ZnO widens the optical band gap energy from ∼2.60 to ∼3.20 eV. The near band edge (NBE) emission peak centered at ∼3.10 eV is considered to be the dominant emission peak in the PL spectra. Blue emission peak is not observed in doped ZnO, thus promoting defect-free nanoparticles. The Burstein–Moss shift serves as a qualitative tool to analyze the widening of the optical band gap and to study the shape of the NBE luminescence in doped ZnO nanopowders. FT-IR spectra are used to identify the strong metal–oxide (Zn–O) interaction.     

Structural and optical properties of RF magnetron sputtered aluminum nitride films without external substrate heating

We report structural and optical properties of aluminum nitride (AlN) thin films prepared by RF magnetron sputtering. A ceramic AlN target was used to sputter deposit AlN films without external substrate heating in Ar-N₂ (1:1) ambient. The X-ray diffraction and high resolution transmission electron microscopy results revealed that the films were preferentially oriented along c-axis. Cross-sectional imaging revealed columnar growth perpendicular to the substrate. The secondary ion mass spectroscopy analysis confirmed that aluminum and nitrogen distribution was uniform within the thickness of the film. The optical band gap of 5.3 eV was evaluated by UV-vis spectroscopy. Photo-luminescence broad band was observed in the range of 420-600 nm with two maxima, centered at 433 nm and 466 nm wavelengths related to the energy states originated during the film growth. A structural property correlation has been carried out to explore the possible application of such important well oriented nano-structured two-dimensional semiconducting objects.     

Approximating geometric bottleneck shortest paths

In a geometric bottleneck shortest path problem, we are given a set S of n points in the plane, and want to answer queries of the following type: given two points p and q of S and a real number L, compute (or approximate) a shortest path between p and q in the subgraph of the complete graph on S consisting of all edges whose lengths are less than or equal to L. We present efficient algorithms for answering several query problems of this type. Our solutions are based on Euclidean minimum spanning trees, spanners, and the Delaunay triangulation. A result of independent interest is the following. For any two points p and q of S, there is a path between p and q in the Delaunay triangulation, whose length is less than or equal to 2π/(3cos(π/6)) times the Euclidean distance |pq| between p and q, and all of whose edges have length at most |pq|.     

Elastic waves in a fiber-reinforced composite

The propagation of time-harmonic elastic waves in a fiber-reinforced composite is studied. The circular fibers are assumed to be parallel to each other and randomly distributed with a statistically uniform distribution. The direction of propagation and the associated particle motion are considered to be normal to the fibers. It is shown that the average waves in the composite separate into compressional and shear types. General formulae for the complex wave number giving the phase velocity and the damping are obtained. It is shown that these formulae lead to the Hashin-Rosen expressions for the transverse bulk modulus and the lower bound for the transverse rigidity, if the correlation in the positions of the fibers can be ignored. The correlation terms, for exponential correlation, are shown to have a significant effect on the damping property of the composite, especially at high frequencies and concentrations.     

Interaction of RuIII(EDTA) with cellular thiols and O2: biological implications thereof

Reaction of [Ru^III(EDTA)(CyS)]^2? (edta^4? = ethylenediaminetetraacetate; CySH = cysteine) with molecular oxygen (O₂) has been studied as a function of pH (4.0–8.0) and cysteine concentration (0.2–2.0 mM) at room temperature (25 °C). Biological activities of the [Ru(EDTA)]/CySH/O₂ system pertaining to cleavage of supercoiled plasmid DNA to its nicked open circular form has been explored in this work. Results are discussed in regard to the reaction of the ruthenium(III)-complex with molecular oxygen) and a working mechanism is proposed for the biological activities of the ruthenium(III)-complex in the presence of O₂.     

Planar solidification of a warm flowing-liquid under different boundary conditions

Planar solidification of a warm flowing liquid with the convective heat transfer to the growing solid layer, has been analysed for the boundary conditions of constant temperature, constant heat flux and convective heat flux at the surface respectively. The mathematical formulation of the problem resulted in a coupled set of two differential equations in temperature and solid thickness as function of position, time and the problem parameters. Analytical expressions for the temperature distribution within the growing solid layer, the rate of solidification and the solidification time are obtained. The perturbation techniques employed here is simple and straight forward in contrast with the earlier techniques. Good agreement between the experimental results and the present solutions is obtained for the convective heat flux boundary condition. The results of this analysis are useful in the design and analysis of experiments dealing with freezing/melting in one dimension. The role of the parameter Stefan number which is small for phase change materials, is discussed in context with the storage of thermal energy.