A class of exact solutions to the force-free,axisymetric, stationary magnetosphere of a Kerr black hole

We analyze the constraint equation giving allowed solutions describing fields and currents in a force-free magnetosphere around a rotating black hole. Utilizing the divergence properties of the energy and angular-momentum fluxes, for physically allowed solutions with nonzero energy and angular momentum extraction, we conclude that poloidal surfaces are independent of the radial coordinate for large values of r. Imposing this requirement and the Znajek regularity condition, we explicitly derive all possible exact solutions admitted by the constraint equation for r independent poloidal surfaces which are given in terms of the electromagnetic angular velocity function , where a is the angular momentum per unit mass of the black hole. Further, we show that for the class of solutions we have developed there is no electromagnetic extraction of energy. G. M. acknowledges funding through a Troy University sabbatical. The work of C. D. D. is supported by the Office of Naval Research. This research was also supported through NASA GLAST Science Investigation No. DPR-S-1563-Y.     

N,N'-dimethylformamide-derived products from catalytic oxidation of 3-hydroxyflavone

The biomimetic conversion of 3-hydroxyflavone in the presence of a copper(II) catalyst, dioxygen, and N,N'-dimethylformamide to oxidation products as well as two previously unreported solvent-derived products is seen. The two solvent-derived products were characterized, and their crystal structures were determined.     

Characterization of the Mixing Layer Resulting from the Detonation of Heterogeneous Explosive Charges

A dense, two-phase numerical methodology is used to study the mixing layer developing behind the detonation of a heterogeneous explosive charge, i.e., a charge comprising of a high explosive with metal particles. The filtered Navier–Stokes equations are solved in addition to a sub-grid kinetic energy equation, along with a recently developed Eulerian–Lagrangian formulation to handle dense flow-fields. The mixing layer resulting from the post-detonation phase of the explosion of a nitromethane charge consisting of inert steel particles is of interest in this study. Significant mixing and turbulence effects are observed in the mixing layer, and the rms of the radial velocity component is found to be about 25% higher than that of the azimuthal and zenith velocity components due to the flow being primarily radial. The mean concentration profiles are self-similar in shape at different times, based on a scaling procedure used in the past for a homogeneous explosive charge. The peak rms of concentration profiles are 23–30% in intensity and decrease in magnitude with time. The behavior of concentration gradients in the mixing layer is investigated, and stretching along the radial direction is observed to decrease the concentration gradients along the azimuth and zenith directions faster than the radial direction. The mixing and turbulence effects in the mixing layer subsequent to the detonation of the heterogeneous explosive charge are superior to that of a homogeneous explosive charge containing the same amount of the high explosive, exemplifying the role played by the particles in perturbing the flow-field. The non-linear growth of the mixing layer width starts early for the heterogeneous explosive charge, and the rate is reduced during the implosion phase in comparison with the homogeneous charge. The turbulence intensities in the mixing layer for the heterogeneous explosive charge are found to be nearly independent of the particle size for two different sizes considered in the initial charge. Overall, this study has provided some useful insights on the mixing layer characteristics subsequent to the detonation of heterogeneous explosives, and has also demonstrated the efficacy of the dense, multiphase formulation for such applications.     

Model-independent data reductions of elastic proton–proton scattering

New developments in empirical analyses of the proton–proton differential cross section data at high energies are reported. Making use of an unconstrained model-independent parametrization for the scattering amplitude and two different fit procedures, all the experimental data in the center-of-mass energy interval 19.4–62.5 GeV are quite well described (optical point and data above the region of Coulomb-nuclear interference). The contributions from the real and imaginary parts of the amplitude beyond the forward direction are discussed and compared with the results from previous analyses and phenomenological models. Extracted overlap functions (impact parameter space) are outlined and a critical discussion on model-independent analyses and results are also presented.     

Preparation and characterization of multiwall carbon nanotube/polypyrrole coaxial fibrils

Multiwall carbon nanotube (MWNT)/polypyrrole (PPy) fibrils were fabricated by template-free in situ electrochemical deposition of PPy over MWNTs, and characterized by electron microscopy and electrical measurements. Scanning and transmission electron microscopy studies reveal that PPy coating on the surface of nanotube is quite uniform throughout the length, with the possibility of forming unique Y-junctions. Current (I)-voltage (V) characteristics at various temperatures show nonlinearity due to tunneling and hopping contributions to transport across the barriers. AC conductivity measurements (300-4.2 K) show that the onset frequency scales with temperature, and the nanoscale connectivity in MWNT/PPy fibrils decreases with the lowering of temperature.     

Molecular dynamics simulations of carbon nanotube/silicon interfacial thermal conductance

Using molecular dynamics simulations with Tersoff reactive many-body potential for Si-Si, Si-C, and C-C interactions, we have calculated the thermal conductance at the interfaces between carbon nanotube (CNT) and silicon at different applied pressures. The interfaces are formed by axially compressing and indenting capped or uncapped CNTs against 2 x 1 reconstructed Si surfaces. The results show an increase in the interfacial thermal conductance with applied pressure for interfaces with both capped and uncapped CNTs. At low applied pressure, the thermal conductance at interface with uncapped CNTs is found to be much higher than that at interface with capped CNTs. Our results demonstrate that the contact area or the number of bonds formed between the CNT and Si substrate is key to the interfacial thermal conductance, which can be increased by either applying pressure or by opening the CNT caps that usually form in the synthesis process. The temperature and size dependences of interfacial thermal conductance are also simulated. These findings have important technological implications for the application of vertically aligned CNTs as thermal interface materials.     

Microtubule dynamics regulated by stathmin

Microtubules perform a variety of functions which lead to the complex regulation of intracellular transport and cell division. However, the regulation of microtubule growth is not clearly known. Based on a recent experimental finding, we explore the possibility of spatial regulation of microtubule growth by stathmin–tubulin interaction gradients. Computer simulation of the model with stathmin–tubulin interaction gradients gave regulated growth as seen in experiments. In future, the stathmin–tubulin interaction gradients can be made dynamic and its impact on the microtubule growth can be explored.     

Electrochemical Fluorescence Switching from a Patternable Poly(1,3,4‐oxadiazole) Thin Film

A highly soluble poly(1,3,4‐oxadiazole) (POD) substituted with long alkyl chains was examined for electrochemical fluorescence switching. The high solubility of the polymers enabled a simple fabrication of an electrochemical cell, which showed reversible fluorescence switching between dark (n‐doping) and bright (neutral) states with a maximum on/off ratio of 2.5 and a cyclability longer than 1 000 cycles. Photochemical cleavage of the oxadiazole in POD allowed photo‐patterning of the POD film upon exposure to UV source. The patterned POD films displayed patterned image reversibly under a step potential of +1.8/−1.8 V.

     

Structural properties of metal-benzene, Mn(benzene)m, M=Ni, V complexes: an ab initio study

Interactions of Ni and V with benzene (Bz)-molecules are investigated using ab initio methods and tight-binding molecular dynamics (TBMD) simulations. The differences in the behavior for Ni and V is found to be consistent with their similar contrasting bonding behavior found in interactions with graphite, C₆₀ and carbon nanotubes.     

Curvature dependence of the metal catalyst atom interaction with carbon nanotubes walls

Interactions of the transition metal atoms with carbon nanotube walls are investigated using a tight-binding molecular dynamics method that allows for spin unrestricted geometry optimization. Comparison with the results for bonding on graphite indicates major differences in bonding sites, magnetic moments and the direction of charge transfer. The significant values of magnetic moments obtained for the metal atoms on nanotube walls is consistent with the recent experimental findings.