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Shell Systems (shell + system)
Selected AbstractsOne-Pot Synthesis of Catalytically Stable and Active Nanoreactors: Encapsulation of Size-Controlled Nanoparticles within a Hierarchically Macroporous Core@Ordered Mesoporous Shell SystemADVANCED MATERIALS, Issue 13 2009Xiao-Yu Yang Size-controlled, catalytically active nanoparticles are successfully encapsulated in a one-pot synthesis to form novel hierarchical macroporous core@mesoporous shell structures, where macroporous cores are connected by uniform and ordered mesoporous channels. Most importantly, the encapsulated nanoparticles can be used as "nanoreactors", with high activities and excellent long-term recycling stability. [source] Coarse-Grained Simulations of Elongational Viscosities, Superposition Rheology and Shear Banding in Model Core,Shell SystemsMACROMOLECULAR THEORY AND SIMULATIONS, Issue 8 2007A. van den Noort Abstract A recently developed coarse-grain model is used to investigate nonlinear rheological properties of model core,shell systems. The influence of several model parameters on the stresses and shear rates is investigated. Continuous planar elongational flow and superposition rheology are studied and compared to simple shear flow results. With particular values of the model parameters, an initially linear velocity profile splits into many bands with different shear rates and different densities, which finally merge into just two bands stacked along the gradient direction. With the box sizes used in our simulations, stick and Lees,Edwards boundary conditions lead to qualitatively similar results, with the stick boundary simulations showing better quantitative agreement with experiments. [source] Au@pNIPAM Thermosensitive Nanostructures: Control over Shell Cross-linking, Overall Dimensions, and Core GrowthADVANCED FUNCTIONAL MATERIALS, Issue 19 2009Rafael Contreras-Cáceres Abstract Thermoresponsive nanocomposites comprising a gold nanoparticle core and a poly(N -isopropylacrylamide) (pNIPAM) shell are synthesized by grafting the gold nanoparticle surface with polystyrene, which allows the coating of an inorganic core with an organic shell. Through careful control of the experimental conditions, the pNIPAM shell cross-linking density can be varied, and in turn its porosity and stiffness, as well as shell thickness from a few to a few hundred nanometers is tuned. The characterization of these core,shell systems is carried out by photon-correlation spectroscopy, transmission electron microscopy, and atomic force microscopy. Additionally, the porous pNIPAM shells are found to modulate the catalytic activity, which is demonstrated through the seeded growth of gold cores, either retaining the initial spherical shape or developing a branched morphology. The nanocomposites also present thermally modulated optical properties because of temperature-induced local changes of the refractive index surrounding the gold cores. [source] Nonlinear wave function expansions: A progress reportINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 15 2007Ron Shepard Abstract Some recent progress is reported for a novel nonlinear expansion form for electronic wave functions. This expansion form is based on spin eigenfunctions using the Graphical Unitary Group Approach and the wave function is expanded in a basis of product functions, allowing application to closed and open shell systems and to ground and excited electronic states. Each product basis function is itself a multiconfigurational expansion that depends on a relatively small number of nonlinear parameters called arc factors. Efficient recursive procedures for the computation of reduced one- and two-particle density matrices, overlap matrix elements, and Hamiltonian matrix elements result in a very efficient computational procedure that is applicable to very large configuration state function (CSF) expansions. A new energy-based optimization approach is presented based on product function splitting and variational recombination. Convergence of both valence correlation energy and dynamical correlation energy with respect to the product function basis dimension is examined. A wave function analysis approach suitable for very large CSF expansions is presented based on Shavitt graph node density and arc density. Some new closed-form expressions for various Shavitt Graph and Auxiliary Pair Graph statistics are presented. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2007 [source] DIESEL-MP2: A new program to perform large-scale multireference-MP2 computations,JOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 10 2006Patrick Musch Abstract This article presents a new MR-MP2 code (Multi- Reference Møller,Plesset 2nd order) suitable for the computation MR-MP2 energies of extended systems with strong near degeneracy effects (e.g., open shell systems). It is based on the DIESEL program package developed by Hanrath and Engels. Due to improved algorithms the new code is able to handle systems with 400,500 basis functions and more than 100 electrons. The code is made for parallel computers with distributed memory, but can also be run on local machines. It possesses two integral interfaces (MOLCAS, TURBOMOLE). The algorithms are briefly introduced and timings for the Neocarzinostatin chromophore are presented. The efficiencies of the codes obtained with Intel or GNU compilers are compared. © 2006 Wiley Periodicals, Inc. J Comput Chem 27: 1055,1062, 2006 [source] Coarse-Grained Simulations of Elongational Viscosities, Superposition Rheology and Shear Banding in Model Core,Shell SystemsMACROMOLECULAR THEORY AND SIMULATIONS, Issue 8 2007A. van den Noort Abstract A recently developed coarse-grain model is used to investigate nonlinear rheological properties of model core,shell systems. The influence of several model parameters on the stresses and shear rates is investigated. Continuous planar elongational flow and superposition rheology are studied and compared to simple shear flow results. With particular values of the model parameters, an initially linear velocity profile splits into many bands with different shear rates and different densities, which finally merge into just two bands stacked along the gradient direction. With the box sizes used in our simulations, stick and Lees,Edwards boundary conditions lead to qualitatively similar results, with the stick boundary simulations showing better quantitative agreement with experiments. [source] Thermal quenching of luminescence and isovalent trap model for rare-earth-ion-doped AlNPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 6 2007H. J. Lozykowski Abstract Investigations of the luminescent properties of Pr-, Eu-, Tb- and Tm-implanted AlN thin films at temperature in the range 9,830 K are reported. The temperature studies of photoluminescence and cathodoluminescence spectra revealed unexpectedly weak thermal quenching for all investigated rare earth (RE) ions. The maximum CL emission is observed from Eu (red) at 485 K, Tb (green) at 590 K and Tm (blue) at 530 K, respectively. For Tb- and Tm-doped AlN samples, temperature-dependent crossrelaxation processes were observed. Photoluminescence excitation spectra, obtained under UV excitation in the spectral range 200,400 nm, exhibit several bands. It is proposed that the RE ions exist in semiconductors as isolated ions (singlet), nearest-neighbor (nn) ion pairs (dimer), and three ions (trimer). The Koster,Slater and simple spherical potential-well models for RE-structured isovalent (RESI) hole trap are proposed. The exciton binding energies of RESI traps are calculated and compared with experimental thermal-quenching energies. The energy-transfer processes between the AlN host and the 4f-shell systems are emphasized as the main mechanisms for thermal-quenching processes rather than nonradiative decay of 4f transitions. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | |||||||||||||