Stereoelectronic control of Cope rearrangement energetics through remote double bonds in novel, rigid polycyclic frames

The presence and orientation of remote double bonds are shown to completely alter the shapes of Cope rearrangement energy profiles in a heptacyclic system.

Structure and properties of Tl0.5Pb0.5Sr2Gd2−xCexCu2O9−δ

A systematic study of the Tl0.5Pb0.5Sr2Gd2−xCexCu2O9−δ system has revealed the existence of a pure phase in the compositional. range 0.0≤x≤0.6 crystalizzing in the 1222 structure. It has an intersheet distance of approximately 6 Å, a value much higher than those found in other cuprates with double CuO2 sheets interleaved by a single fluorite layer. Superconductivity has been observed in the range 0.1≤x≤0.4 with a Tc of 45 K and a superconductive volume fraction up to 20% for the optimal composition. An interesting variation of the superconducting properties of the above system with the composition, i.e. cerium content, has also been noticed. A possible dependence of superconductivity on the coupling between CuO2 sheets in the layered cuprates has been pointed out to bring out a correlation between structure and properties.

Interior Photon Absorption Based Adaptive Regularization Improves Diffuse Optical Tomography

An adaptive regularization algorithm that combines elementwise photon absorption and data misfit is proposed to stabilize the non-linear ill-posed inverse problem. The diffuse photon distribution is low near the target compared to the normal region. A Hessian is proposed based on light and tissue interaction, and is estimated using adjoint method by distributing the sources inside the discretized domain. As iteration progresses, the photon absorption near the inhomogeneity becomes high and carries more weightage to the regularization matrix. The domain's interior photon absorption and misfit based adaptive regularization method improves quality of the reconstructed Diffuse Optical Tomographic images.

The impact of ultra thin silicon nitride buffer layer on GaN growth on Si (1 1 1) by RF-MBE

Ultra thin films of pure silicon nitride were grown on a Si (1 1 1) surface by exposing the surface to radio-frequency (RF) nitrogen plasma with a high content of nitrogen atoms. The effect of annealing of silicon nitride surface was investigated with core-level photoelectron spectroscopy. The Si 2p photoelectron spectra reveals a characteristic series of components for the Si species, not only in stoichiometric Si3N4 (Si4+) but also in the intermediate nitridation states with one (Si1+) or three (Si3+) nitrogen nearest neighbors. The Si 2p core-level shifts for the Si1+, Si3+, and Si4+ components are determined to be 0.64, 2.20, and 3.05 eV, respectively. In annealed sample it has been observed that the Si4+ component in the Si 2p spectra is significantly improved, which clearly indicates the crystalline nature of silicon nitride. The high resolution X-ray diffraction (HRXRD), scanning electron microscopy (SEM) and photoluminescence (PL) studies showed a significant improvement of the crystalline qualities and enhancement of the optical properties of GaN grown on the stoichiometric Si3N4 by molecular beam epitaxy (MBE). (C) 2010 Elsevier B.V. All rights reserved.

Tuning the electronic effective mass in double-doped SrTiO3

We elucidate the relationship between effective mass and carrier concentration in an oxide semiconductor controlled by a double-doping mechanism. In this model oxide system, Sr1-xLaxTiO3-delta, we can tune the effective mass ranging from 6 to 20m(e) as a function of filling (carrier concentration) and the scattering mechanism, which are dependent on the chosen lanthanum-and oxygen-vacancy concentrations. The effective mass values were calculated from the Boltzmann transport equation using the measured transport properties of thin films of Sr1-xLaxTiO3-delta. We show that the effective mass decreases with carrier concentration in this large-band-gap, low-mobility oxide, and this behavior is contrary to the traditional high-mobility, small-effective-mass semiconductors.

Pulsed laser deposition film of a donor-acceptor-donor polymer as possible active layer in devices

A molecule having a ketone group between two thiophene groups was synthesized. Presence of alternating electron donating and accepting moieties gives this material a donor-acceptor-donor (DAD) architecture. PolyDAD was synthesized from DAD monomer by oxidative polymerization. Device quality films of polyDAD were fabricated using pulsed laser deposition technique. X-ray photoelectron spectroscopy (XPS) and fourier transform infrared spectra (FTIR) data of both as synthesized and film indicate the material does not degrade during ablation. Optical band gap was determined to be about 1.45 eV. Four orders of magnitude increase in conductivity was observed from as synthesized to pulsed laser deposition (PLD) fabricated film of polyDAD. Annealing of polyDAD films increase conductivity, indicating better ordering of the molecules upon heating. Rectifying devices were fabricated from polyDAD, and preliminary results are discussed.

Accelerating frequency-domain diffuse optical tomographic image reconstruction using graphics processing units

Diffuse optical tomographic image reconstruction uses advanced numerical models that are computationally costly to be implemented in the real time. The graphics processing units (GPUs) offer desktop massive parallelization that can accelerate these computations. An open-source GPU-accelerated linear algebra library package is used to compute the most intensive matrix-matrix calculations and matrix decompositions that are used in solving the system of linear equations. These open-source functions were integrated into the existing frequency-domain diffuse optical image reconstruction algorithms to evaluate the acceleration capability of the GPUs (NVIDIA Tesla C 1060) with increasing reconstruction problem sizes. These studies indicate that single precision computations are sufficient for diffuse optical tomographic image reconstruction. The acceleration per iteration can be up to 40, using GPUs compared to traditional CPUs in case of three-dimensional reconstruction, where the reconstruction problem is more underdetermined, making the GPUs more attractive in the clinical settings. The current limitation of these GPUs in the available onboard memory (4 GB) that restricts the reconstruction of a large set of optical parameters, more than 13, 377. (C) 2010 Society of Photo-Optical Instrumentation Engineers. DOI: 10.1117/1.3506216]

3-Dimensional laminar boundary-layer in a constant-pressure diverging

larity solution is obtained for laminar 3D constant pressure flow with lateral streamline divergence. The similarity solution is shown to reduce to a Blasius solution for 2D flow over a flat plate. Measurements of velocity profiles are made to compare the similarity solution and are found to be in excellent agreement with the prediction

A note on the slow rotation of a disc in a bounded fluid with a surfactant surface layer

A method involving eigenfunction expansion and collocation is employed to solve the axisymmetric problem of a slowly and steadily rotating circular disc in a fluid of finite extent whose surface is covered with a surfactant film. The present method (originally described by Wang (Acta Mech. 94, 97, 1992)) is observed to produce results of practical importance associated with the problem more quickly and more easily than the one used earlier by Shail and Gooden (Int. J. Multiphase Flow 7, 245, 1992). (C) 1994 Academic Press, Inc.

A novel double friedel-crafts reaction: A new entry into bicyclo[3.2.2]nonane system

A novel synthesis of dibenzobicyclo[3.2.2]nonane systems is described through a double Friedel-Crafts reaction.

Electrochemical preparation of few layer-graphene nanosheets via reduction of oriented exfoliated graphene oxide thin films in acetamide-urea-ammonium nitrate melt under ambient conditions

Electrochemical reduction of exfoliated graphene oxide, prepared from pre-exfoliated graphite, in acetamide-urea-ammonium nitrate ternary eutectic melt results in few layer-graphene thin films. Negatively charged exfoliated graphene oxide is attached to positively charged cystamine monolyer self-assembled on a gold surface. Electrochemical reduction of the oriented graphene oxide film is carried out in a room temperature, ternary molten electrolyte. The reduced film is characterized by atomic force microscopy (AFM), conductive AFM, Fourier-transform infrared spectroscopy and Raman spectroscopy. Ternary eutectic melt is found to be a suitable medium for the regulated reduction of graphene oxide to reduced graphene oxide-based sheets on conducting surfaces. (C) 2010 Elsevier B.V. All rights reserved.

Accelerated gradient based diffuse optical tomographic image reconstruction

Purpose: Fast reconstruction of interior optical parameter distribution using a new approach called Broyden-based model iterative image reconstruction (BMOBIIR) and adjoint Broyden-based MOBIIR (ABMOBIIR) of a tissue and a tissue mimicking phantom from boundary measurement data in diffuse optical tomography (DOT). Methods: DOT is a nonlinear and ill-posed inverse problem. Newton-based MOBIIR algorithm, which is generally used, requires repeated evaluation of the Jacobian which consumes bulk of the computation time for reconstruction. In this study, we propose a Broyden approach-based accelerated scheme for Jacobian computation and it is combined with conjugate gradient scheme (CGS) for fast reconstruction. The method makes explicit use of secant and adjoint information that can be obtained from forward solution of the diffusion equation. This approach reduces the computational time many fold by approximating the system Jacobian successively through low-rank updates. Results: Simulation studies have been carried out with single as well as multiple inhomogeneities. Algorithms are validated using an experimental study carried out on a pork tissue with fat acting as an inhomogeneity. The results obtained through the proposed BMOBIIR and ABMOBIIR approaches are compared with those of Newton-based MOBIIR algorithm. The mean squared error and execution time are used as metrics for comparing the results of reconstruction. Conclusions: We have shown through experimental and simulation studies that Broyden-based MOBIIR and adjoint Broyden-based methods are capable of reconstructing single as well as multiple inhomogeneities in tissue and a tissue-mimicking phantom. Broyden MOBIIR and adjoint Broyden MOBIIR methods are computationally simple and they result in much faster implementations because they avoid direct evaluation of Jacobian. The image reconstructions have been carried out with different initial values using Newton, Broyden, and adjoint Broyden approaches. These algorithms work well when the initial guess is close to the true solution. However, when initial guess is far away from true solution, Newton-based MOBIIR gives better reconstructed images. The proposed methods are found to be stable with noisy measurement data. (C) 2011 American Association of Physicists in Medicine. DOI: 10.1118/1.3531572]