Tunable device properties of free-standing inorganic/organic flexible hybrid structures obtained by exfoliation

We report the fabrication of free-standing flexible inorganic/organic hybrid structures by exfoliating ZnO nanostructured films from the flat indium tin oxide (ITO)/silicon/sapphire substrates using poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS). Strong interaction between ZnO and PEDOT: PSS and the thermomechanical response of PEDOT: PSS are the key issues for the exfoliation to prevail. The performance of the free-standing hybrid structures as rectifiers and photodetectors is better as compared to ITO supported hybrid structures. It is also shown that device properties of hybrid structures can be tuned by using different electrode materials. (C) 2012 American Institute of Physics. http://dx.doi.org/10.1063/1.4729550]

Conflict-Free Coloring for Rectangle Ranges Using O(n.382) Colors

Given a set of points P ⊆ R2, a conflict-free coloring of P w.r.t. rectangle ranges is an assignment of colors to points of P, such that each nonempty axisparallel rectangle T in the plane contains a point whose color is distinct from all other points in P ∩ T . This notion has been the subject of recent interest and is motivated by frequency assignment in wireless cellular networks: one naturally would like to minimize the number of frequencies (colors) assigned to base stations (points) such that within any range (for instance, rectangle), there is no interference. We show that any set of n points in R2 can be conflict-free colored with O(nβ∗+o(1)) colors in expected polynomial time, where β∗ = 3−√5 2 < 0.382.

Extracting Three Dimensional Surface Model of Human Kidney from the Visible Human Data Set using Free Software

Three dimensional digital model of a representative human kidney is needed for a surgical simulator that is capable of simulating a laparoscopic surgery involving kidney. Buying a three dimensional computer model of a representative human kidney, or reconstructing a human kidney from an image sequence using commercial software, both involve (sometimes significant amount of) money. In this paper, author has shown that one can obtain a three dimensional surface model of human kidney by making use of images from the Visible Human Data Set and a few free software packages (ImageJ, ITK-SNAP, and MeshLab in particular). Images from the Visible Human Data Set, and the software packages used here, both do not cost anything. Hence, the practice of extracting the geometry of a representative human kidney for free, as illustrated in the present work, could be a free alternative to the use of expensive commercial software or to the purchase of a digital model.

Characterization of structural and free energy properties of promoters associated with Primary and Operon TSS in Helicobacter pylori genome and their orthologs

Promoter regions in the genomes of all domains of life show similar trends in several structural properties such as stability, bendability, curvature, etc. In current study we analysed the stability and bendability of various classes of promoter regions (based on the recent identification of different classes of transcription start sites) of Helicobacter pylori 26695 strain. It is found that primary TSS and operon-associated TSS promoters show significantly strong features in their promoter regions. DNA free-energy-based promoter prediction tool PromPredict was used to annotate promoters of different classes, and very high recall values (similar to 80%) are obtained for primary TSS. Orthologous genes from other strains of H. pylori show conservation of structural properties in promoter regions as well as coding regions. PromPredict annotates promoters of orthologous genes with very high recall and precision.

Microstructure and Texture Evolution in Interstitial-free (IF) Steel processed by Multi-Axial Forging

In this study, severe plastic deformation (SPD) of Ti-bearing interstitial-free steel was carried out by multi-axial forging (MAF) technique. The grain refinement achieved was comparable to that by other SPD techniques. A considerable heterogeneity was observed in the microstructure and texture. Texture of multi-axially forged steels has been evaluated and reported for the first time. The material exhibited a six-fold increase in the yield strength after four cycles of MAF.

Maximum weight independent sets in hole- and dart-free graphs

The Maximum Weight Independent Set (MWIS) problem on graphs with vertex weights asks for a set of pairwise nonadjacent vertices of maximum total weight. The complexity of the MWIS problem for hole-free graphs is unknown. In this paper, we first prove that the MWIS problem for (hole, dart, gem)-free graphs can be solved in O(n(3))-time. By using this result, we prove that the MWIS problem for (hole, dart)-free graphs can be solved in O(n(4))-time. Though the MWIS problem for (hole, dart, gem)-free graphs is used as a subroutine, we also give the best known time bound for the solvability of the MWIS problem in (hole, dart, gem)-free graphs. (C) 2012 Elsevier B.V. All rights reserved.

Bromenium-Catalysed Tandem Ring Opening/Cyclisation of Vinylcyclopropanes and Vinylcyclobutanes: A Metal-Free 3+2+1]/4+2+1] Cascade for the Synthesis of Chiral Amidines and Computational Investigation

We present a detailed study of a 3+2+1] cascade cyclisation of vinylcyclopropanes (VCP) catalysed by a bromenium species (Brd+?Xd-) generated in situ, which results in the synthesis of chiral bicyclic amidines in a tandem one-pot operation. The formation of amidines involves the ring-opening of VCPs with Br?X, followed by a Ritter-type reaction with chloramine-T and a tandem cyclisation. The reaction has been further extended to vinylcyclobutane systems and involves a 4+2+1] cascade cyclisation with the same reagents. The versatility of the methodology has been demonstrated by careful choice of VCPs and VCBs to yield bicyclo4.3.0]-, -4.3.1]- and -4.4.0]amidines in enantiomerically pure form. On the basis of the experimental observations and DFT calculations, a reasonable mechanism has been put forth to account for the formation of the products and the observed stereoselectivity. We propose the existence of a p-stabilised homoallylic carbocation at the cyclopropane carbon as the reason for high stereoselectivity. DFT studies at B3LYP/6-311+G** and M06-2X/6-31+G* levels of theory in gas-phase calculations suggest the ring-opening of VCP is initiated at the p-complex stage (between the double bond and Br?X). This can be clearly perceived from the solution-phase (acetonitrile) calculations using the polarisable continuum model (PCM) solvation model, from which the extent of the ring opening of VCP was found to be noticeably high. Studies also show that the formation of zero-bridge bicyclic amidines is favoured over other bridged bicyclic amidines. The energetics of competing reaction pathways is compared to explain the product selectivity.

Size-dependent free flexural vibration behavior of functionally graded nanoplates

In this paper, size dependent linear free flexural vibration behavior of functionally graded (FG) nanoplates are investigated using the iso-geometric based finite element method. The field variables are approximated by non-uniform rational B-splines. The nonlocal constitutive relation is based on Eringen's differential form of nonlocal elasticity theory. The material properties are assumed to vary only in the thickness direction and the effective properties for the FG plate are computed using Mori-Tanaka homogenization scheme. The accuracy of the present formulation is demonstrated considering the problems for which solutions are available. A detailed numerical study is carried out to examine the effect of material gradient index, the characteristic internal length, the plate thickness, the plate aspect ratio and the boundary conditions on the global response of the FG nanoplate. From the detailed numerical study it is seen that the fundamental frequency decreases with increasing gradient index and characteristic internal length. (c) 2012 Elsevier B.V. All rights reserved.

Acyclic Edge Coloring of Triangle-Free Planar Graphs

An acyclic edge coloring of a graph is a proper edge coloring such that there are no bichromatic cycles. The acyclic chromatic index of a graph is the minimum number k such that there is an acyclic edge coloring using k colors and is denoted by a'(G). It was conjectured by Alon, Sudakov and Zaks (and much earlier by Fiamcik) that a'(G) ? ? + 2, where ? = ?(G) denotes the maximum degree of the graph. If every induced subgraph H of G satisfies the condition |E(H)| ? 2|V(H)|-1, we say that the graph G satisfies Property A. In this article, we prove that if G satisfies Property A, then a'(G) ? ? + 3. Triangle-free planar graphs satisfy Property A. We infer that a'(G) ? ? + 3, if G is a triangle-free planar graph. Another class of graph which satisfies Property A is 2-fold graphs (union of two forests). (C) 2011 Wiley Periodicals, Inc. J Graph Theory

Microwave-assisted, surfactant-free synthesis of air-stable copper nanostructures and their SERS study

A simple, rapid, and surfactant-free synthesis of crystalline copper nanostructures has been carried out through microwave irradiation of a solution of copper acetylacetonate in benzyl alcohol. The structures are found to be stable against oxidation in ambient air for several months. High-resolution electron microscopy (SEM and TEM) reveals that the copper samples comprise nanospheres measuring about 150 nm in diameter, each made of copper nanocrystals similar to 7 nm in extension. The nanocrystals are densely packed into spherical aggregates, the driving force being minimization of surface area and surface energy, and are thus immune to oxidation in ambient air. Such aggregates can also be adherently supported on SiO2 and Al2O3 when these substrates are immersed in the irradiated solution. The air-stable copper nanostructures exhibit surface enhanced Raman scattering, as evidenced by the detection of 4-mercaptobenzoic acid at 10(-6) M concentrations.

Magneto-Transport Study of Pure and Co Doped ZnO Thin Films

A detailed low temperature magneto-transport study is carried out to understand the transport mechanism in pure and Co doped ZnO thin films grown by pulsed laser deposition (PLD) technique. A negative transverse magneto-resistance (MR) (with a value similar to 4% at 4.5 K) which decreases monotonically with the increase in temperature, is observed for the undoped ZnO film. A competition between positive and negative MR is observed for the Co doped ZnO samples. In this case at higher field values negative MR contribution dominates over the positive MR, which gives rise to a slope change in the MR data. Our data for MR shows excellent agreement with the semi-empirical formula given by Khosla et al., which is originally proposed for the degenerate semiconductors. This formula incorporates the third order perturbation expansion of the s-d exchange scattering of the conduction electrons from the localised spins. We have also obtained the Hall mobility, carrier conc. and mean free path as function of temperature for the pure ZnO film.

Synthesis of free standing nanocrystalline Cu by ball milling at cryogenic temperature

This paper reports for the first time synthesis of free standing nano-crystalline copper crystals of a similar to 30-40 nm by ball milling of copper powder at 150 K under Argon atmosphere in a specially designed cryomill. The detailed characterization of these particles using multiple techniques that includes transmission electron microscopy confirms our conclusion. Careful analysis of the chemistry of these particles indicates that these particles are essentially contamination free. Through the analysis of existing models of grain size refinements during ball milling and low temperature deformation, we argue that the suppression of thermal processes and low temperature leads to formation of free nanoparticles as the process of fracture dominates over possible cold welding at low temperatures. (C) 2012 Elsevier B.V. All rights reserved.

Path-integral formulation for Levy flights: Evaluation of the propagator for free, linear, and harmonic potentials in the over- and underdamped limits

Levy flights can be described using a Fokker-Planck equation, which involves a fractional derivative operator in the position coordinate. Such an operator has its natural expression in the Fourier domain. Starting with this, we show that the solution of the equation can be written as a Hamiltonian path integral. Though this has been realized in the literature, the method has not found applications as the path integral appears difficult to evaluate. We show that a method in which one integrates over the position coordinates first, after which integration is performed over the momentum coordinates, can be used to evaluate several path integrals that are of interest. Using this, we evaluate the propagators for (a) free particle, (b) particle subjected to a linear potential, and (c) harmonic potential. In all the three cases, we have obtained results for both overdamped and underdamped cases. DOI: 10.1103/PhysRevE.86.061105

Perturbative expansion of the QCD Adler function improved by renormalization-group summation and analytic continuation in the Borel plane

We examine the large-order behavior of a recently proposed renormalization-group-improved expansion of the Adler function in perturbative QCD, which sums in an analytically closed form the leading logarithms accessible from renormalization-group invariance. The expansion is first written as an effective series in powers of the one-loop coupling, and its leading singularities in the Borel plane are shown to be identical to those of the standard ``contour-improved'' expansion. Applying the technique of conformal mappings for the analytic continuation in the Borel plane, we define a class of improved expansions, which implement both the renormalization-group invariance and the knowledge about the large-order behavior of the series. Detailed numerical studies of specific models for the Adler function indicate that the new expansions have remarkable convergence properties up to high orders. Using these expansions for the determination of the strong coupling from the hadronic width of the tau lepton we obtain, with a conservative estimate of the uncertainty due to the nonperturbative corrections, alpha(s)(M-tau(2)) = 0.3189(-0.0151)(+0.0173), which translates to alpha(s)(M-Z(2)) = 0.1184(-0.0018)(+0.0021). DOI: 10.1103/PhysRevD.87.014008

Numerical Investigation on Laminar Flow Due to Sudden Expansion Using Nanofluids

Laminar two-dimensional sudden expansion flow of different nanofluids is studied numerically. The governing equations are solved using stream function-vorticity method. The effect of volume fraction of the nanoparticles and type of nanoparticles on flow behaviour is examined and found significant impact. The flow response to Reynolds number in the presence of nanoparticles is examined. The presence of nanoparticles decreases the flow bifurcation Reynolds number. The size and the reattachment length of the bottom wall recirculation increase with increasing volume fraction and particle density. The effect of volume fraction and density of nanoparticles on friction factor is reported. The bottom wall recirculation strongly respond to the variation in volume faction and type of particles. However, weak response is observed for top wall recirculation.