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Sample records for lattice block structures

  1. Superalloy Lattice Block Structures

    NASA Technical Reports Server (NTRS)

    Nathal, M. V.; Whittenberger, J. D.; Hebsur, M. G.; Kantzos, P. T.; Krause, D. L.

    2004-01-01

    Initial investigations of investment cast superalloy lattice block suggest that this technology will yield a low cost approach to utilize the high temperature strength and environmental resistance of superalloys in lightweight, damage tolerant structural configurations. Work to date has demonstrated that relatively large superalloy lattice block panels can be successfully investment cast from both IN-718 and Mar-M247. These castings exhibited mechanical properties consistent with the strength of the same superalloys measured from more conventional castings. The lattice block structure also accommodates significant deformation without failure, and is defect tolerant in fatigue. The potential of lattice block structures opens new opportunities for the use of superalloys in future generations of aircraft applications that demand strength and environmental resistance at elevated temperatures along with low weight.

  2. Superalloy Lattice Block Structures

    NASA Technical Reports Server (NTRS)

    Whittenberger, J. D.; Nathal, M. V.; Hebsur, M. G.; Kraus, D. L.

    2003-01-01

    In their simplest form, lattice block panels are produced by direct casting and result in lightweight, fully triangulated truss-like configurations which provide strength and stiffness [2]. The earliest realizations of lattice block were made from A1 and steels, primarily under funding from the US Navy [3]. This work also showed that the mechanical efficiency (eg., specific stiffness) of lattice block structures approached that of honeycomb structures [2]. The lattice architectures are also less anisotropic, and the investment casting route should provide a large advantage in cost and temperature capability over honeycombs which are limited to alloys that can be processed into foils. Based on this early work, a program was initiated to determine the feasibility of extending the high temperature superalloy lattice block [3]. The objective of this effort was to provide an alternative to intermetallics and composites in achieving a lightweight high temperature structure without sacrificing the damage tolerance and moderate cost inherent in superalloys. To establish the feasibility of the superalloy lattice block concept, work was performed in conjunction with JAMCORP, Inc. Billerica, MA, to produce a number of lattice block panels from both IN71 8 and Mar-M247.

  3. Determining the Mechanical Properties of Lattice Block Structures

    NASA Technical Reports Server (NTRS)

    Wilmoth, Nathan

    2013-01-01

    Lattice block structures and shape memory alloys possess several traits ideal for solving intriguing new engineering problems in industries such as aerospace, military, and transportation. Recent testing at the NASA Glenn Research Center has investigated the material properties of lattice block structures cast from a conventional aerospace titanium alloy as well as lattice block structures cast from nickel-titanium shape memory alloy. The lattice block structures for both materials were sectioned into smaller subelements for tension and compression testing. The results from the cast conventional titanium material showed that the expected mechanical properties were maintained. The shape memory alloy material was found to be extremely brittle from the casting process and only compression testing was completed. Future shape memory alloy lattice block structures will utilize an adjusted material composition that will provide a better quality casting. The testing effort resulted in baseline mechanical property data from the conventional titanium material for comparison to shape memory alloy materials once suitable castings are available.

  4. Mechanical Testing of IN718 Lattice Block Structures

    NASA Technical Reports Server (NTRS)

    Krause, David L.; Whittenberger, John D.; Kantzos, Pete T.; Hebsur, Mohan G.

    2002-01-01

    Lattice block construction produces a flat, structurally rigid panel composed of thin ligaments of material arranged in a three-dimensional triangulated truss-like structure. Low-cost methods of producing cast metallic lattice block panels are now available that greatly expand opportunities for using this unique material system in today's high-performance structures. Additional advances are being made in NASA's Ultra Efficient Engine Technology (UEET) program to extend the lattice block concept to superalloy materials. Advantages offered by this combination include high strength, light weight, high stiffness, and elevated temperature capabilities. Recently under UEET, the nickel-based superalloy Inconel 718 (IN718) was investment cast into lattice block panels with great success. To evaluate casting quality and lattice block architecture merit, individual ligaments, and structural subelement specimens were extracted from the panels. Tensile tests, structural compression, and bending strength tests were performed on these specimens. Fatigue testing was also completed for several bend test specimens. This paper first presents metallurgical and optical microscopy analysis of the castings. This is followed by mechanical test results for the tensile ligament tests and the subelement compression and bending strength tests, as well as for the fatigue tests that were performed. These tests generally showed comparable properties to base IN718 with the same heat treatment, and they underscored the benefits offered by lattice block materials. These benefits might be extended with improved architecture such as face sheets.

  5. Initial Mechanical Testing of Superalloy Lattice Block Structures Conducted

    NASA Technical Reports Server (NTRS)

    Krause, David L.; Whittenberger, J. Daniel

    2002-01-01

    The first mechanical tests of superalloy lattice block structures produced promising results for this exciting new lightweight material system. The testing was performed in-house at NASA Glenn Research Center's Structural Benchmark Test Facility, where small subelement-sized compression and beam specimens were loaded to observe elastic and plastic behavior, component strength levels, and fatigue resistance for hundreds of thousands of load cycles. Current lattice block construction produces a flat panel composed of thin ligaments arranged in a three-dimensional triangulated trusslike structure. Investment casting of lattice block panels has been developed and greatly expands opportunities for using this unique architecture in today's high-performance structures. In addition, advances made in NASA's Ultra-Efficient Engine Technology Program have extended the lattice block concept to superalloy materials. After a series of casting iterations, the nickel-based superalloy Inconel 718 (IN 718, Inco Alloys International, Inc., Huntington, WV) was successfully cast into lattice block panels; this combination offers light weight combined with high strength, high stiffness, and elevated-temperature durability. For tests to evaluate casting quality and configuration merit, small structural compression and bend test specimens were machined from the 5- by 12- by 0.5-in. panels. Linear elastic finite element analyses were completed for several specimen layouts to predict material stresses and deflections under proposed test conditions. The structural specimens were then subjected to room-temperature static and cyclic loads in Glenn's Life Prediction Branch's material test machine. Surprisingly, the test results exceeded analytical predictions: plastic strains greater than 5 percent were obtained, and fatigue lives did not depreciate relative to the base material. These assets were due to the formation of plastic hinges and the redundancies inherent in lattice block construction

  6. Structural Benchmark Testing of Superalloy Lattice Block Subelements Completed

    NASA Technical Reports Server (NTRS)

    2004-01-01

    Superalloy lattice block panels, which are produced directly by investment casting, are composed of thin ligaments arranged in three-dimensional triangulated trusslike structures (see the preceding figure). Optionally, solid panel face sheets can be formed integrally during casting. In either form, lattice block panels can easily be produced with weights less than 25 percent of the mass of a solid panel. Inconel 718 (IN 718) and MarM-247 superalloy lattice block panels have been developed under NASA's Ultra-Efficient Engine Technology Project and Higher Operating Temperature Propulsion Components Project to take advantage of the superalloys' high strength and elevated temperature capability with the inherent light weight and high stiffness of the lattice architecture (ref. 1). These characteristics are important in the future development of turbine engine components. Casting quality and structural efficiency were evaluated experimentally using small beam specimens machined from the cast and heat treated 140- by 300- by 11-mm panels. The matrix of specimens included samples of each superalloy in both open-celled and single-face-sheet configurations, machined from longitudinal, transverse, and diagonal panel orientations. Thirty-five beam subelements were tested in Glenn's Life Prediction Branch's material test machine at room temperature and 650 C under both static (see the following photograph) and cyclic load conditions. Surprisingly, test results exceeded initial linear elastic analytical predictions. This was likely a result of the formation of plastic hinges and redundancies inherent in lattice block geometry, which was not considered in the finite element models. The value of a single face sheet was demonstrated by increased bending moment capacity, where the face sheet simultaneously increased the gross section modulus and braced the compression ligaments against early buckling as seen in open-cell specimens. Preexisting flaws in specimens were not a

  7. Superalloy Lattice Block Developed for Use in Lightweight, High-Temperature Structures

    NASA Technical Reports Server (NTRS)

    Hebsur, Mohan G.; Whittenberger, J. Daniel; Krause, David L.

    2003-01-01

    Successful development of advanced gas turbine engines for aircraft will require lightweight, high-temperature components. Currently titanium-aluminum- (TiAl) based alloys are envisioned for such applications because of their lower density (4 g/cm3) in comparison to superalloys (8.5 g/cm3), which have been utilized for hot turbine engine parts for over 50 years. However, a recently developed concept (lattice block) by JAMCORP, Inc., of Willmington, Massachusetts, would allow lightweight, high-temperature structures to be directly fabricated from superalloys and, thus, take advantage of their well-known, characterized properties. In its simplest state, lattice block is composed of thin ligaments arranged in a three dimensional triangulated trusslike configuration that forms a structurally rigid panel. Because lattice block can be fabricated by casting, correctly sized hardware is produced with little or no machining; thus very low cost manufacturing is possible. Together, the NASA Glenn Research Center and JAMCORP have extended their lattice block methodology for lower melting materials, such as Al alloys, to demonstrate that investment casting of superalloy lattice block is possible. This effort required advances in lattice block pattern design and assembly, higher temperature mold materials and mold fabrication technology, and foundry practice suitable for superalloys (ref. 1). Lattice block panels have been cast from two different Ni-base superalloys: IN 718, which is the most commonly utilized superalloy and retains its strength up to 650 C; and MAR M247, which possesses excellent mechanical properties to at least 1100 C. In addition to the open-cell lattice block geometry, same-sized lattice block panels containing a thin (1-mm-thick) solid face on one side have also been cast from both superalloys. The elevated-temperature mechanical properties of the open cell and face-sheeted superalloy lattice block panels are currently being examined, and the

  8. Finite-difference lattice Boltzmann method with a block-structured adaptive-mesh-refinement technique.

    PubMed

    Fakhari, Abbas; Lee, Taehun

    2014-03-01

    An adaptive-mesh-refinement (AMR) algorithm for the finite-difference lattice Boltzmann method (FDLBM) is presented in this study. The idea behind the proposed AMR is to remove the need for a tree-type data structure. Instead, pointer attributes are used to determine the neighbors of a certain block via appropriate adjustment of its children identifications. As a result, the memory and time required for tree traversal are completely eliminated, leaving us with an efficient algorithm that is easier to implement and use on parallel machines. To allow different mesh sizes at separate parts of the computational domain, the Eulerian formulation of the streaming process is invoked. As a result, there is no need for rescaling the distribution functions or using a temporal interpolation at the fine-coarse grid boundaries. The accuracy and efficiency of the proposed FDLBM AMR are extensively assessed by investigating a variety of vorticity-dominated flow fields, including Taylor-Green vortex flow, lid-driven cavity flow, thin shear layer flow, and the flow past a square cylinder.

  9. Arbitrary lattice symmetries via block copolymer nanomeshes

    PubMed Central

    Majewski, Pawel W.; Rahman, Atikur; Black, Charles T.; Yager, Kevin G.

    2015-01-01

    Self-assembly of block copolymers is a powerful motif for spontaneously forming well-defined nanostructures over macroscopic areas. Yet, the inherent energy minimization criteria of self-assembly give rise to a limited library of structures; diblock copolymers naturally form spheres on a cubic lattice, hexagonally packed cylinders and alternating lamellae. Here, we demonstrate multicomponent nanomeshes with any desired lattice symmetry. We exploit photothermal annealing to rapidly order and align block copolymer phases over macroscopic areas, combined with conversion of the self-assembled organic phase into inorganic replicas. Repeated photothermal processing independently aligns successive layers, providing full control of the size, symmetry and composition of the nanoscale unit cell. We construct a variety of symmetries, most of which are not natively formed by block copolymers, including squares, rhombuses, rectangles and triangles. In fact, we demonstrate all possible two-dimensional Bravais lattices. Finally, we elucidate the influence of nanostructure on the electrical and optical properties of nanomeshes. PMID:26100566

  10. Processing of IN-718 Lattice Block Castings

    NASA Technical Reports Server (NTRS)

    Hebsur, Mohan G.

    2002-01-01

    Recently a low cost casting method known as lattice block casting has been developed by JAM Corporation, Wilmington, Massachusetts for engineering materials such as aluminum and stainless steels that has shown to provide very high stiffness and strength with only a fraction of density of the alloy. NASA Glenn Research Center has initiated research to investigate lattice block castings of high temperature Ni-base superalloys such as the model system Inconel-718 (IN-718) for lightweight nozzle applications. Although difficulties were encountered throughout the manufacturing process , a successful investment casting procedure was eventually developed. Wax formulation and pattern assembly, shell mold processing, and counter gravity casting techniques were developed. Ten IN-718 lattice block castings (each measuring 15-cm wide by 30-cm long by 1.2-cm thick) have been successfully produced by Hitchiner Gas Turbine Division, Milford, New Hampshire, using their patented counter gravity casting techniques. Details of the processing and resulting microstructures are discussed in this paper. Post casting processing and evaluation of system specific mechanical properties of these specimens are in progress.

  11. The packing of soft materials: Molecular asymmetry, geometric frustration and optimal lattices in block copolymer melts

    NASA Astrophysics Data System (ADS)

    Grason, Gregory M.

    Melts of block copolymers provide an ideal route to engineering well-controlled structures on nanometer length scales. Through the control of only a few thermodynamic parameters, these systems can be tuned to self-assemble into periodic structures of an astounding variety. It is known that geometry plays a particularly important role in determining equilibrium structure since phase behavior of copolymer melts is generically insensitive to detail at the monomeric scale. Here, we explore a particular way in which the geometry of packing objects in three dimensions frustrates the internal configurations of segregated block copolymer domains. In particular, we find that lattices of spherical micelles are sensitive to the periodic structure of the lattice arrangement because these micelles are forced to occupy the non-ideal, polyhedral unit cells of the lattice. By analyzing the energetics of block copolymer melts in the limit of strongly-segregated domains, we find that the interfaces which separate unlike polymer domains tend to adopt the polyhedral shape of the lattice unit cell, and this tendency is entirely controlled by the specific copolymer architecture. Furthermore, in the limit where interfaces are perfectly polyhedral, a remarkable simplicity emerges, and the relative stability of competing lattice arrangements of micelles can be assessed purely in terms of geometric measures of the two-dimensional lattice unit cell. From this analysis we predict the stability of a novel cubic arrangement spherical micelles in block copolymer melts, the A15 lattice. To corroborate our geometric arguments we develop and implement a numerical self-consistent field theory for melts of highly asymmetric block copolymers. This field theory allows us to systematically and efficiently explore the equilibrium phase behavior of asymmetric copolymer melts as a function of molecular architecture. These numerical results bear out the predictions of our geometric analysis and confirm that

  12. Optimal lattice-structured materials

    DOE PAGESBeta

    Messner, Mark C.

    2016-07-09

    This paper describes a method for optimizing the mesostructure of lattice-structured materials. These materials are periodic arrays of slender members resembling efficient, lightweight macroscale structures like bridges and frame buildings. Current additive manufacturing technologies can assemble lattice structures with length scales ranging from nanometers to millimeters. Previous work demonstrates that lattice materials have excellent stiffness- and strength-to-weight scaling, outperforming natural materials. However, there are currently no methods for producing optimal mesostructures that consider the full space of possible 3D lattice topologies. The inverse homogenization approach for optimizing the periodic structure of lattice materials requires a parameterized, homogenized material model describingmore » the response of an arbitrary structure. This work develops such a model, starting with a method for describing the long-wavelength, macroscale deformation of an arbitrary lattice. The work combines the homogenized model with a parameterized description of the total design space to generate a parameterized model. Finally, the work describes an optimization method capable of producing optimal mesostructures. Several examples demonstrate the optimization method. One of these examples produces an elastically isotropic, maximally stiff structure, here called the isotruss, that arguably outperforms the anisotropic octet truss topology.« less

  13. Lattice Structures For Aerospace Applications

    NASA Astrophysics Data System (ADS)

    Del Olmo, E.; Grande, E.; Samartin, C. R.; Bezdenejnykh, M.; Torres, J.; Blanco, N.; Frovel, M.; Canas, J.

    2012-07-01

    The way of mass reduction improving performances in the aerospace structures is a constant and relevant challenge in the space business. The designs, materials and manufacturing processes are permanently in evolution to explore and get mass optimization solutions at low cost. In the framework of ICARO project, EADS CASA ESPACIO (ECE) has designed, manufactured and tested a technology demonstrator which shows that lattice type of grid structures is a promising weight saving solution for replacing some traditional metallic and composite structures for space applications. A virtual testing methodology was used in order to support the design of a high modulus CFRP cylindrical lattice technology demonstrator. The manufacturing process, based on composite Automatic Fiber Placement (AFP) technology developed by ECE, allows obtaining high quality low weight lattice structures potentially applicable to a wide range of aerospace structures. Launcher payload adaptors, satellite platforms, antenna towers or instrument supports are some promising candidates.

  14. Hadron Structure on the Lattice

    NASA Astrophysics Data System (ADS)

    Can, K. U.; Kusno, A.; Mastropas, E. V.; Zanotti, J. M.

    The aim of these lectures will be to provide an introduction to some of the concepts needed to study the structure of hadrons on the lattice. Topics covered include the electromagnetic form factors of the nucleon and pion, the nucleon's axial charge and moments of parton and generalised parton distribution functions. These are placed in a phenomenological context by describing how they can lead to insights into the distribution of charge, spin and momentum amongst a hadron's partonic constituents. We discuss the techniques required for extracting the relevant matrix elements from lattice simulations and draw attention to potential sources of systematic error. Examples of recent lattice results are presented and are compared with results from both experiment and theoretical models.

  15. Lattice Truss Structural Response Using Energy Methods

    NASA Technical Reports Server (NTRS)

    Kenner, Winfred Scottson

    1996-01-01

    A deterministic methodology is presented for developing closed-form deflection equations for two-dimensional and three-dimensional lattice structures. Four types of lattice structures are studied: beams, plates, shells and soft lattices. Castigliano's second theorem, which entails the total strain energy of a structure, is utilized to generate highly accurate results. Derived deflection equations provide new insight into the bending and shear behavior of the four types of lattices, in contrast to classic solutions of similar structures. Lattice derivations utilizing kinetic energy are also presented, and used to examine the free vibration response of simple lattice structures. Derivations utilizing finite element theory for unique lattice behavior are also presented and validated using the finite element analysis code EAL.

  16. Localized structures in Kagome lattices

    SciTech Connect

    Saxena, Avadh B; Bishop, Alan R; Law, K J H; Kevrekidis, P G

    2009-01-01

    We investigate the existence and stability of gap vortices and multi-pole gap solitons in a Kagome lattice with a defocusing nonlinearity both in a discrete case and in a continuum one with periodic external modulation. In particular, predictions are made based on expansion around a simple and analytically tractable anti-continuum (zero coupling) limit. These predictions are then confirmed for a continuum model of an optically-induced Kagome lattice in a photorefractive crystal obtained by a continuous transformation of a honeycomb lattice.

  17. Recent lattice QCD results on nucleon structure

    SciTech Connect

    Konstantinos Orginos

    2006-06-25

    I review recent developments in lattice calculations of nucleon structure. In particular, I cover the calculations of nucleon matrix elements related to generalized parton distribution functions, structure functions and form factors.

  18. Recent lattice QCD results on nucleon structure

    SciTech Connect

    Konstantinos Orginos

    2006-07-01

    I review recent developments in lattice calculations of nucleon structure. In particular, I cover the calculations of nucleon matrix elements related to generalized parton distribution functions, structure functions and form factors.

  19. Vibration of prestressed periodic lattice structures

    NASA Technical Reports Server (NTRS)

    Anderson, M. S.

    1981-01-01

    Equations are developed for vibration of general lattice structures that have repetitive geometry. The method of solution is an extension of a previous paper for buckling of similar structures. The theory is based on representing each member of the structure with the exact dynamic stiffness matrix and taking advantage of the repetitive geometry to obtain an eigenvalue problem involving the degrees-of-freedom at a single node in the lattice. Results are given for shell-and beam-like lattice structures and for rings stiffened with tension cables and a central mast. The variation of frequency with external loading and the effect of local member vibration on overall modes is shown.

  20. Mesoscale Lattices Assembled from Charge-Tunable Block Copolymer Blends in Selective Solvents

    NASA Astrophysics Data System (ADS)

    Kim, Seyoung; Choi, Jewon; Choi, Soo-Hyung; Char, Kookheon

    Recent studies revealed that block copolymer (BCP) microdomains are capable of being organized into unusual symmetries such as the Frank-Casper phases. These unique structures result from a compromise between domain geometry and space-filling constraint; in other words, the deformability of soft matter. Our mesoscale micellar lattices co-assembled from the blends of oppositely charged BCPs demonstrate the nature of deformable soft materials in a distinctive way. The micellar structures and interactions of BCPs in selective solvents can be finely tuned by controlling the charge density such that the spherical micelles further assemble into hexagonal arrays. The micellar lattices show unconventional symmetry and sub-10 nm clean facet formation compared to hard-sphere counterparts reported so far. We attribute these novel phenomena to multi-compartment intrastructure of the micelles assembled and their strong interactions, since the crystalline symmetry disappears with a subtle control of solvency, mixing ratio of BCP blends, and micellar interactions. Analysis on the nucleation condition reveals that such deviation in the micellar lattices arises from the soft nature of BCP assemblies which can be readily deformed upon swelling.

  1. Microscopic Observation of Pauli Blocking in Degenerate Fermionic Lattice Gases

    NASA Astrophysics Data System (ADS)

    Hilker, Timon; Omran, Ahmed; Boll, Martin; Salomon, Guillaume; Bloch, Immanuel; Gross, Christian

    2016-05-01

    Ultracold atoms in optical lattices provide a powerful platform for the controlled study of quantum many-body physics. We present here the first studies with a new generation quantum gas microscope, which allows to observe the full atom number statistics on every site. The common problem of light induced losses during imaging is avoided by an additional small scale ``pinning lattice'' used for Raman sideband cooling in the imaging process. We report the local observation of the Pauli exclusion principle in a spin-polarized degenerate gas of 6 Li fermions in an optical lattice. In the band insulating regime, we measure a tenfold suppression of particle number fluctuations per site compared to classical particles. From the remaining fluctuations we extract a local entropy as low as 0.3 kB per atom. Our work opens an exciting avenue for studying local density and even magnetic correlations in fermionic quantum matter both in and out of equilibrium.

  2. Quaternionic Lattice Structures for Four-Channel Paraunitary Filter Banks

    NASA Astrophysics Data System (ADS)

    Parfieniuk, Marek; Petrovsky, Alexander

    2006-12-01

    A novel approach to the design and implementation of four-channel paraunitary filter banks is presented. It utilizes hypercomplex number theory, which has not yet been employed in these areas. Namely, quaternion multipliers are presented as alternative paraunitary building blocks, which can be regarded as generalizations of Givens (planar) rotations. The corresponding quaternionic lattice structures maintain losslessness regardless of coefficient quantization and can be viewed as extensions of the classic two-band lattice developed by Vaidyanathan and Hoang. Moreover, the proposed approach enables a straightforward expression of the one-regularity conditions. They are stated in terms of the lattice coefficients, and thus can be easily satisfied even in finite-precision arithmetic.

  3. Extension theorems for homogenization on lattice structures

    NASA Technical Reports Server (NTRS)

    Miller, Robert E.

    1992-01-01

    When applying homogenization techniques to problems involving lattice structures, it is necessary to extend certain functions defined on a perforated domain to a simply connected domain. This paper provides general extension operators which preserve bounds on derivatives of order l. Only the special case of honeycomb structures is considered.

  4. Nucleon Structure from Dynamical Lattice QCD

    SciTech Connect

    Huey-Wen Lin

    2007-06-01

    We present lattice QCD numerical calculations of hadronic structure functions and form factors from full-QCD lattices, with a chirally symmetric fermion action, domain-wall fermions, for the sea and valence quarks. The lattice spacing is about 0.12 fm with physical volume approximately (2 fm)3 for RBC 2-flavor ensembles and (3 fm)3 for RBC/UKQCD 2+1-flavor dynamical ones. The lightest sea quark mass is about 1/2 the strange quark mass for the former ensembles and 1/4 for the latter ones. Our calculations include: isovector vector- and axial-charge form factors and the first few moments of the polarized and unpolarized structure functions of the nucleon. Nonperturbative renormalization in RI/MOM scheme is applied.

  5. Nucleon Structure from Dynamical Lattice QCD

    SciTech Connect

    Lin, H.-W.

    2007-06-13

    We present lattice QCD numerical calculations of hadronic structure functions and form factors from full-QCD lattices, with a chirally symmetric fermion action, domain-wall fermions, for the sea and valence quarks. The lattice spacing is about 0.12 fm with physical volume approximately (2 fm)3 for RBC 2-flavor ensembles and (3 fm)3 for RBC/UKQCD 2+1-flavor dynamical ones. The lightest sea quark mass is about 1/2 the strange quark mass for the former ensembles and 1/4 for the latter ones. Our calculations include: isovector vector- and axial-charge form factors and the first few moments of the polarized and unpolarized structure functions of the nucleon. Nonperturbative renormalization in RI/MOM scheme is applied.

  6. Quantum Simulation with Circuit-QED Lattices: from Elementary Building Blocks to Many-Body Theory

    NASA Astrophysics Data System (ADS)

    Zhu, Guanyu

    Recent experimental and theoretical progress in superconducting circuits and circuit QED (quantum electrodynamics) has helped to develop high-precision techniques to control, manipulate, and detect individual mesoscopic quantum systems. A promising direction is hence to scale up from individual building blocks to form larger-scale quantum many-body systems. Although realizing a scalable fault-tolerant quantum computer still faces major barriers of decoherence and quantum error correction, it is feasible to realize scalable quantum simulators with state-of-the-art technology. From the technological point of view, this could serve as an intermediate stage towards the final goal of a large-scale quantum computer, and could help accumulating experience with the control of quantum systems with a large number of degrees of freedom. From the physical point of view, this opens up a new regime where condensed matter systems can be simulated and studied, here in the context of strongly correlated photons and two-level systems. In this thesis, we mainly focus on two aspects of circuit-QED based quantum simulation. First, we discuss the elementary building blocks of the quantum simulator, in particular a fluxonium circuit coupled to a superconducting resonator. We show the interesting properties of the fluxonium circuit as a qubit, including the unusual structure of its charge matrix elements. We also employ perturbation theory to derive the effective Hamiltonian of the coupled system in the dispersive regime, where qubit and the photon frequencies are detuned. The observables predicted with our theory, including dispersive shifts and Kerr nonlinearity, are compared with data from experiments, such as homodyne transmission and two-tone spectroscopy. These studies also relate to the problem of detection in a circuit-QED quantum simulator. Second, we study many-body physics of circuit-QED lattices, serving as quantum simulators. In particular, we focus on two different

  7. Naming Block Structures: A Multimodal Approach

    ERIC Educational Resources Information Center

    Cohen, Lynn; Uhry, Joanna

    2011-01-01

    This study describes symbolic representation in block play in a culturally diverse suburban preschool classroom. Block play is "multimodal" and can allow children to experiment with materials to represent the world in many forms of literacy. Combined qualitative and quantitative data from seventy-seven block structures were collected and analyzed.…

  8. Calculating Buckling And Vibrations Of Lattice Structures

    NASA Technical Reports Server (NTRS)

    Anderson, M. S.; Durling, B. J.; Herstrom, C. L.; Williams, F. W.; Banerjee, J. R.; Kennedy, D.; Warnaar, D. B.

    1989-01-01

    BUNVIS-RG computer program designed to calculate vibration frequencies or buckling loads of prestressed lattice structures used in outer space. For buckling and vibration problems, BUNVIS-RG calculates deadload axial forces caused in members by any combination of externally-applied static point forces and moments at nodes, axial preload or prestrain in members, and such acceleration loads as those due to gravity. BUNVIS-RG is FORTRAN 77 computer program implemented on CDC CYBER and VAX computer.

  9. Block structured dynamics and neuronal coding

    NASA Astrophysics Data System (ADS)

    González-Miranda, J. M.

    2005-11-01

    When certain control parameters of nervous cell models are varied, complex bifurcation structures develop in which the dynamical behaviors available appear classified in blocks, according to criteria of dynamical likelihood. This block structured dynamics may be a clue to understand how activated neurons encode information by firing spike trains of their action potentials.

  10. Some Poisson structures and Lax equations associated with the Toeplitz lattice and the Schur lattice

    NASA Astrophysics Data System (ADS)

    Lemarie, Caroline

    2016-01-01

    The Toeplitz lattice is a Hamiltonian system whose Poisson structure is known. In this paper, we unveil the origins of this Poisson structure and derive from it the associated Lax equations for this lattice. We first construct a Poisson subvariety H n of GL n (C), which we view as a real or complex Poisson-Lie group whose Poisson structure comes from a quadratic R-bracket on gl n (C) for a fixed R-matrix. The existence of Hamiltonians, associated to the Toeplitz lattice for the Poisson structure on H n , combined with the properties of the quadratic R-bracket allow us to give explicit formulas for the Lax equation. Then we derive from it the integrability in the sense of Liouville of the Toeplitz lattice. When we view the lattice as being defined over R, we can construct a Poisson subvariety H n τ of U n which is itself a Poisson-Dirac subvariety of GL n R (C). We then construct a Hamiltonian for the Poisson structure induced on H n τ , corresponding to another system which derives from the Toeplitz lattice the modified Schur lattice. Thanks to the properties of Poisson-Dirac subvarieties, we give an explicit Lax equation for the new system and derive from it a Lax equation for the Schur lattice. We also deduce the integrability in the sense of Liouville of the modified Schur lattice.

  11. Block copolymer structures in nano-pores

    NASA Astrophysics Data System (ADS)

    Pinna, Marco; Guo, Xiaohu; Zvelindovsky, Andrei

    2010-03-01

    We present results of coarse-grained computer modelling of block copolymer systems in cylindrical and spherical nanopores on Cell Dynamics Simulation. We study both cylindrical and spherical pores and systematically investigate structures formed by lamellar, cylinders and spherical block copolymer systems for various pore radii and affinity of block copolymer blocks to the pore walls. The obtained structures include: standing lamellae and cylinders, ``onions,'' cylinder ``knitting balls,'' ``golf-ball,'' layered spherical, ``virus''-like and mixed morphologies with T-junctions and U-type defects [1]. Kinetics of the structure formation and the differences with planar films are discussed. Our simulations suggest that novel porous nano-containers can be formed by confining block copolymers in pores of different geometries [1,2]. [4pt] [1] M. Pinna, X. Guo, A.V. Zvelindovsky, Polymer 49, 2797 (2008).[0pt] [2] M. Pinna, X. Guo, A.V. Zvelindovsky, J. Chem. Phys. 131, 214902 (2009).

  12. Modal analysis of kagome-lattice structures

    NASA Astrophysics Data System (ADS)

    Perez, H.; Blakley, S.; Zheltikov, A. M.

    2015-05-01

    The first few lowest order circularly symmetric electromagnetic eigenmodes of a full kagome lattice are compared to those of a kagome lattice with a hexagonal defect. This analysis offers important insights into the physics behind the waveguiding properties of hollow-core fibers with a kagome-lattice cladding.

  13. Buckling and vibration of periodic lattice structures

    NASA Technical Reports Server (NTRS)

    Anderson, M. S.

    1981-01-01

    Lattice booms and platforms composed of flexible members or large diameter rings which may be stiffened by cables in order to support membrane-like antennas or reflector surfaces are the main components of some large space structures. The nature of these structures, repetitive geometry with few different members, makes possible relatively simple solutions for buckling and vibration of a certain class of these structures. Each member is represented by a stiffness matrix derived from the exact solution of the beam column equation. This transcendental matrix gives the current member stiffness at any end load or frequency. Using conventional finite element techniques, equilibrium equations can be written involving displacements and rotations of a typical node and its neighbors. The assumptions of a simple trigonometric mode shape is found to satisfy these equations exactly; thus the entire problem is governed by just one 6 x 6 matrix equation involving the amplitude of the displacement and rotation mode shapes. The boundary conditions implied by this solution are simple supported ends for the column type configurations.

  14. Pawlak Algebra and Approximate Structure on Fuzzy Lattice

    PubMed Central

    Zhuang, Ying; Liu, Wenqi; Wu, Chin-Chia; Li, Jinhai

    2014-01-01

    The aim of this paper is to investigate the general approximation structure, weak approximation operators, and Pawlak algebra in the framework of fuzzy lattice, lattice topology, and auxiliary ordering. First, we prove that the weak approximation operator space forms a complete distributive lattice. Then we study the properties of transitive closure of approximation operators and apply them to rough set theory. We also investigate molecule Pawlak algebra and obtain some related properties. PMID:25152922

  15. Pawlak algebra and approximate structure on fuzzy lattice.

    PubMed

    Zhuang, Ying; Liu, Wenqi; Wu, Chin-Chia; Li, Jinhai

    2014-01-01

    The aim of this paper is to investigate the general approximation structure, weak approximation operators, and Pawlak algebra in the framework of fuzzy lattice, lattice topology, and auxiliary ordering. First, we prove that the weak approximation operator space forms a complete distributive lattice. Then we study the properties of transitive closure of approximation operators and apply them to rough set theory. We also investigate molecule Pawlak algebra and obtain some related properties.

  16. Concentration Dependent Structure of Block Copolymer Solutions

    NASA Astrophysics Data System (ADS)

    Choi, Soohyung; Bates, Frank S.; Lodge, Timothy P.

    2015-03-01

    Addition of solvent molecules into block copolymer can induce additional interactions between the solvent and both blocks, and therefore expands the range of accessible self-assembled morphologies. In particular, the distribution of solvent molecules plays a key role in determining the microstructure and its characteristic domain spacing. In this study, concentration dependent structures formed by poly(styrene-b-ethylene-alt-propylene) (PS-PEP) solution in squalane are investigated using small-angle X-ray scattering. This reveals that squalane is essentially completely segregated into the PEP domains. In addition, the conformation of the PS block changes from stretched to nearly fully relaxed (i.e., Gaussian conformation) as amounts of squalane increases. NRF

  17. Motifs and structural blocks retrieval by GHT

    NASA Astrophysics Data System (ADS)

    Cantoni, Virginio; Ferone, Alessio; Petrosino, Alfredo; Polat, Ozlem

    2014-06-01

    The structure of a protein gives more insight on the protein function than its amino acid sequence. Protein structure analysis and comparison are important for understanding the evolutionary relationships among proteins, predicting protein functions, and predicting protein folding. Proteins are formed by two basic regular 3D structural patterns, called Secondary Structures (SSs): helices and sheets. A structural motif is a compact 3D protein block referring to a small specific combination of secondary structural elements, which appears in a variety of molecules. In this paper we compare a few approaches for motif retrieval based on the Generalized Hough Transform (GHT). A primary technique is to adopt the single SS as structural primitives; alternatives are to adopt a SSs pair as primitive structural element, or a SSs triplet, and so on up-to an entire motif. The richer the primitive, the higher the time for pre-analysis and search, and the simpler the inspection process on the parameter space for analyzing the peaks. Performance comparisons, in terms of precision and computation time, are here presented considering the retrieval of motifs composed by three to five SSs for more than 15 million searches. The approach can be easily applied to the retrieval of greater blocks, up to protein domains, or even entire proteins.

  18. Bipart: Learning Block Structure for Activity Detection

    PubMed Central

    Mu, Yang; Lo, Henry Z.; Ding, Wei; Amaral, Kevin; Crouter, Scott E.

    2014-01-01

    Physical activity consists complex behavior, typically structured in bouts which can consist of one continuous movement (e.g. exercise) or many sporadic movements (e.g. household chores). Each bout can be represented as a block of feature vectors corresponding to the same activity type. This paper introduces a general distance metric technique to use this block representation to first predict activity type, and then uses the predicted activity to estimate energy expenditure within a novel framework. This distance metric, dubbed Bipart, learns block-level information from both training and test sets, combining both to form a projection space which materializes block-level constraints. Thus, Bipart provides a space which can improve the bout classification performance of all classifiers. We also propose an energy expenditure estimation framework which leverages activity classification in order to improve estimates. Comprehensive experiments on waist-mounted accelerometer data, comparing Bipart against many similar methods as well as other classifiers, demonstrate the superior activity recognition of Bipart, especially in low-information experimental settings. PMID:25328361

  19. Ab initio Hadron structure from lattice QCD

    SciTech Connect

    J.D. Bratt; R.G. Edwards; M. Engelhardt; G.T. Fleming; Ph. Hägler; B. Musch; J.W. Negele; K. Orginos; A.V. Pochinsky; D.B. Renner; D.G. Richards; W. Schroers

    2007-06-01

    Early scattering experiments revealed that the proton was not a point particle but a bound state of many quarks and gluons. Deep inelastic scattering (DIS) experiments have accurately determined the probability of struck quarks carrying a fraction of the proton's momentum. The current generation of experiments and Lattice QCD calculations will provide detailed multi-dimensional pictures of the distributions of quarks and gluons inside the proton.

  20. Large space erectable structures - building block structures study

    NASA Technical Reports Server (NTRS)

    Armstrong, W. H.; Skoumal, D. E.; Straayer, J. W.

    1977-01-01

    A modular planar truss structure and a long slender boom concept identified as building block approaches to construction of large spacecraft configurations are described. The concepts are compatible in weight and volume goals with the Space Transportation System, use standard structural units, and represent high on-orbit productivity in terms of structural area or beam length. Results of structural trade studies involving static and dynamic analyses of a single module and rigid body deployment analyses to assess kinetics and kinematics of automatic deployment of the building block modules are presented.

  1. Lattice instability in the AlMgB14 structure

    NASA Astrophysics Data System (ADS)

    Wan, L. F.; Beckman, S. P.

    2014-04-01

    The lattice dynamics of the AlMgB14 structure is characterized by phonon vibrational modes that are calculated from first-principles methods. The stoichiometric composition of AlMgB14 is found to have three soft phonon modes, which have displacements associated with metal atoms vibrating against the B lattice. This lattice instability is believed to be associated with the occupation of electronic states in the conduction bands. The off-stoichiometric occupation sweeps the Fermi level from the conduction band into the gap, and as a result the observed soft phonon modes are driven away. Based on a simple electron counting scheme, as also discussed by Mori [39], it is observed that stable XYB14 compounds have between 15 and 16 electrons contributed to the B-lattice from the metal species.

  2. Lattice Structure in Astrophysics: A reconsideration of White Dwarfs, Variables, and Wolf-Rayet Stars

    NASA Astrophysics Data System (ADS)

    Robitaille, Pierre-Marie

    2016-03-01

    Stars of the main sequence display a mass-luminosity relation which indicates that they share a common building block (hydrogen) and lattice structure (hexagonal planar) with the solar photosphere. White dwarfs however display very low luminosity in spite of their elevated color temperature. Rather than postulate that these stars represent degenerate matter, as Eddington and Chandrasekhar were forced to assume given their gaseous models, within the context of a Liquid Metallic Hydrogen Solar Model white dwarfs might simply be thought as possessing a different lattice structure (e.g. body centered cubic) and hence a lowered emissivity. They do not need to possess exceeding densities, reduced radii, and degeneracy in order to account for their lowered emissivity. Similarly, variable stars might well be oscillating between lattices types wherein the energy differences involved in the transformations are small. Other stars, such as Wolf-Rayet stars, which lack photospheric emission, might be too hot to enable a discrete lattice to form. Though condensed, the photosphere in that case would have a lattice which is so poorly organized that its emissivity is trivial. Nonetheless, the broad emission lines of Wolf-Rayet stars indicates that these objects are not breaking apart but rather, are important sites of condensation.

  3. Lattice-structures and constructs with designed thermal expansion coefficients

    DOEpatents

    Spadaccini, Christopher; Hopkins, Jonathan

    2014-10-28

    A thermal expansion-managed lattice structure having a plurality of unit cells each having flexure bearing-mounted tabs supported on a base and actuated by thermal expansion of an actuator having a thermal expansion coefficient greater than the base and arranged so that the tab is inwardly displaced into a base cavity. The flexure bearing-mounted tabs are connected to other flexure-bearing-mounted tabs of adjacent unit cells so that the adjacent unit cells are spaced from each other to accommodate thermal expansion of individual unit cells while maintaining a desired bulk thermal expansion coefficient of the lattice structure as a whole.

  4. Application of Transfer Matrix Approach to Modeling and Decentralized Control of Lattice-Based Structures

    NASA Technical Reports Server (NTRS)

    Cramer, Nick; Swei, Sean Shan-Min; Cheung, Kenny; Teodorescu, Mircea

    2015-01-01

    This paper presents a modeling and control of aerostructure developed by lattice-based cellular materials/components. The proposed aerostructure concept leverages a building block strategy for lattice-based components which provide great adaptability to varying ight scenarios, the needs of which are essential for in- ight wing shaping control. A decentralized structural control design is proposed that utilizes discrete-time lumped mass transfer matrix method (DT-LM-TMM). The objective is to develop an e ective reduced order model through DT-LM-TMM that can be used to design a decentralized controller for the structural control of a wing. The proposed approach developed in this paper shows that, as far as the performance of overall structural system is concerned, the reduced order model can be as e ective as the full order model in designing an optimal stabilizing controller.

  5. Lattice Boltzmann study of hydrodynamic effects in lamellar ordering process of two-dimensional quenched block copolymers.

    PubMed

    Song, Kai-Xu; Jia, Yu-Xi; Sun, Zhao-Yan; An, Li-Jia

    2008-10-14

    By incorporating self-consistent field theory with lattice Boltzmann method, a model for polymer melts is proposed. Compared with models based on Ginzburg-Landau free energy, our model does not employ phenomenological free energies to describe systems and can consider the chain topological details of polymers. We use this model to study the effects of hydrodynamic interactions on the dynamics of microphase separation for block copolymers. In the early stage of phase separation, an exponential growth predicted by Cahn-Hilliard treatment is found. Simulation results also show that the effect of hydrodynamic interactions can be neglected in the early stage. For the late stage of phase separation, it is easy to see the effects of hydrodynamic interactions on the ordering process of lamellae phase. From the analysis of structure factor curves, we find that the growth of domains is faster if hydrodynamic interactions are introduced. Furthermore, the scaling of the pattern dynamics is investigated for the late stage at zero thermal noise. By studying the behavior of scaling exponents of the structure factor and the nematic order-parameter correlation function C(nn), we can see that the effects of hydrodynamic interactions lead to bigger growth exponent for both functions. PMID:19045162

  6. PROCEEDINGS OF RIKEN BNL RESEARCH CENTER WORKSHOP, HADRON STRUCTURE FROM LATTICE QCD, MARCH 18 - 22, 2002, BROOKHAVEN NATIONAL LABORATORY.

    SciTech Connect

    BLUM, T.; BOER, D.; CREUTZ, M.; OHTA, S.; ORGINOS, K.

    2002-03-18

    The RIKEN BNL Research Center workshop on ''Hadron Structure from Lattice QCD'' was held at BNL during March 11-15, 2002. Hadron structure has been the subject of many theoretical and experimental investigations, with significant success in understanding the building blocks of matter. The nonperturbative nature of QCD, however, has always been an obstacle to deepening our understanding of hadronic physics. Lattice QCD provides the tool to overcome these difficulties and hence a link can be established between the fundamental theory of QCD and hadron phenomenology. Due to the steady progress in improving lattice calculations over the years, comparison with experimentally measured hadronic quantities has become important. In this respect the workshop was especially timely. By providing an opportunity for experts from the lattice and hadron structure communities to present their latest results, the workshop enhanced the exchange of knowledge and ideas. With a total of 32 registered participants and 26 talks, the interest of a growing community is clearly exemplified. At the workshop Schierholz and Negele presented the current status of lattice computations of hadron structure. Substantial progress has been made during recent years now that the quenched results are well under control and the first dynamical results have appeared. In both the dynamical and the quenched simulations the lattice results, extrapolated to lighter quark masses, seem to disagree with experiment. Melnitchouk presented a possible explanation (chiral logs) for this disagreement. It became clear from these discussions that lattice computations at significantly lighter quark masses need to be performed.

  7. Open-Lattice Composite Design Strengthens Structures

    NASA Technical Reports Server (NTRS)

    2007-01-01

    Advanced composite materials and designs could eventually be applied as the framework for spacecraft or extraterrestrial constructions for long-term space habitation. One such structure in which NASA has made an investment is the IsoTruss grid structure, an extension of a two-dimensional "isogrid" concept originally developed at McDonnell Douglas Astronautics Company, under contract to NASA's Marshall Space Flight Center in the early 1970s. IsoTruss is a lightweight and efficient alternative to monocoque composite structures, and can be produced in a manner that involves fairly simple techniques. The technology was developed with support from NASA to explore space applications, and is garnering global attention because it is extremely lightweight; as much as 12 times stronger than steel; inexpensive to manufacture, transport, and install; low-maintenance; and is fully recyclable. IsoTruss is expected to see application as utility poles and meteorological towers, for the aforementioned reasons and because its design offers superior wind resistance and is less susceptible to breaking and woodpeckers. Other applications, such as reinforcement for concrete structures, stand-alone towers, sign supports, prostheses, irrigation equipment, and sporting goods are being explored

  8. Lattice and off-lattice side chain models of protein folding: Linear time structure prediction better than 86% of optimal

    SciTech Connect

    Hart, W.E.; Istrail, S.

    1996-08-09

    This paper considers the protein structure prediction problem for lattice and off-lattice protein folding models that explicitly represent side chains. Lattice models of proteins have proven extremely useful tools for reasoning about protein folding in unrestricted continuous space through analogy. This paper provides the first illustration of how rigorous algorithmic analyses of lattice models can lead to rigorous algorithmic analyses of off-lattice models. The authors consider two side chain models: a lattice model that generalizes the HP model (Dill 85) to explicitly represent side chains on the cubic lattice, and a new off-lattice model, the HP Tangent Spheres Side Chain model (HP-TSSC), that generalizes this model further by representing the backbone and side chains of proteins with tangent spheres. They describe algorithms for both of these models with mathematically guaranteed error bounds. In particular, the authors describe a linear time performance guaranteed approximation algorithm for the HP side chain model that constructs conformations whose energy is better than 865 of optimal in a face centered cubic lattice, and they demonstrate how this provides a 70% performance guarantee for the HP-TSSC model. This is the first algorithm in the literature for off-lattice protein structure prediction that has a rigorous performance guarantee. The analysis of the HP-TSSC model builds off of the work of Dancik and Hannenhalli who have developed a 16/30 approximation algorithm for the HP model on the hexagonal close packed lattice. Further, the analysis provides a mathematical methodology for transferring performance guarantees on lattices to off-lattice models. These results partially answer the open question of Karplus et al. concerning the complexity of protein folding models that include side chains.

  9. Adaptive control of large space structures using recursive lattice filters

    NASA Technical Reports Server (NTRS)

    Sundararajan, N.; Goglia, G. L.

    1985-01-01

    The use of recursive lattice filters for identification and adaptive control of large space structures is studied. Lattice filters were used to identify the structural dynamics model of the flexible structures. This identification model is then used for adaptive control. Before the identified model and control laws are integrated, the identified model is passed through a series of validation procedures and only when the model passes these validation procedures is control engaged. This type of validation scheme prevents instability when the overall loop is closed. Another important area of research, namely that of robust controller synthesis, was investigated using frequency domain multivariable controller synthesis methods. The method uses the Linear Quadratic Guassian/Loop Transfer Recovery (LQG/LTR) approach to ensure stability against unmodeled higher frequency modes and achieves the desired performance.

  10. Adaptive control of large space structures using recursive lattice filters

    NASA Technical Reports Server (NTRS)

    Goglia, G. L.

    1985-01-01

    The use of recursive lattice filters for identification and adaptive control of large space structures was studied. Lattice filters are used widely in the areas of speech and signal processing. Herein, they are used to identify the structural dynamics model of the flexible structures. This identified model is then used for adaptive control. Before the identified model and control laws are integrated, the identified model is passed through a series of validation procedures and only when the model passes these validation procedures control is engaged. This type of validation scheme prevents instability when the overall loop is closed. The results obtained from simulation were compared to those obtained from experiments. In this regard, the flexible beam and grid apparatus at the Aerospace Control Research Lab (ACRL) of NASA Langley Research Center were used as the principal candidates for carrying out the above tasks. Another important area of research, namely that of robust controller synthesis, was investigated using frequency domain multivariable controller synthesis methods.

  11. Internal structure of hexagonal skyrmion lattices in cubic helimagnets

    NASA Astrophysics Data System (ADS)

    McGrouther, D.; Lamb, R. J.; Krajnak, M.; McFadzean, S.; McVitie, S.; Stamps, R. L.; Leonov, A. O.; Bogdanov, A. N.; Togawa, Y.

    2016-09-01

    We report the most precise observations to date concerning the spin structure of magnetic skyrmions in a nanowedge specimen of cubic B20 structured FeGe. Enabled by our development of advanced differential phase contrast (DPC) imaging (in a scanning transmission electron microscope (STEM)) we have obtained high spatial resolution quantitative measurements of skyrmion internal spin profile. For hexagonal skyrmion lattice cells, stabilised by an out-plane applied magnetic field, mapping of the in-plane component of magnetic induction has revealed precise spin profiles and that the internal structure possesses intrinsic six-fold symmetry. With increasing field strength, the diameter of skyrmion cores was measured to decrease and accompanied by a nonlinear variation of the lattice periodicity. Variations in structure for individual skyrmions across an area of the lattice were also studied utilising a new increased sensitivity DPC detection scheme and a variety of symmetry lowering distortions were observed. To provide insight into fundamental energetics we have constructed a phenomenological model, with which our experimental observations of spin profiles and field induced core diameter variation are in good agreement with predicted structure in the middle of the nanowedge crystal. In the vicinity of the crystal surfaces, our model predicts the existence of in-plane twisting distortions which our current experimental observations were not sensitive to. As an alternative to the requirement for as yet unidentified sources of magnetic anisotropy, we demonstrate that surface states could provide the energetic stabilisation needed for predomination over the conical magnetic phase.

  12. Structure and Properties of Block Copolymers of Polystyrene and Polybutadiene

    NASA Astrophysics Data System (ADS)

    Askadskii, Andrei A.; Andryushchenko, T. A.; Zubov, P. I.

    1984-08-01

    Recent studies of the structure and properties of block copolymers of polystyrene and polybutadiene are reviewed, with special emphasis on the effect of the structure and of the formation conditions for the samples on the interrelated physico-mechanical properties. Problems associated with the macro- and micro-layering of block copolymer solutions are examined in detail. Work on the analysis of block copolymer structures from measurements of sorption characteristics is reviewed in the light of an assumed relaxation mechanism for the sorption and swelling processes. The prospects of controlling the structure and properties of block copolymers are shown to be good. The bibliography contains 190 references.

  13. Symmetric blocking and renormalization in lattice N=4 super Yang-Mills

    NASA Astrophysics Data System (ADS)

    Giedt, Joel; Catterall, Simon

    2015-04-01

    The form of the long distance effective action of the twisted lattice N = 4 super Yang-Mills theory depends on having a real space renormalization group transformation that preserves the original lattice properties, both the symmetries and the geometric interpretation of the fields. We have found such a transformation and have exhibited its behavior through a preliminary Monte Carlo renormalization group calculation. Other results regarding the number of counterterms are also obtained by considering rescalings of the lattice fields. Supported by Department of Energy, Office of Science, Office of High Energy Physics Grants DE-FG02-08ER41575 and SC0009998.

  14. Ab initio nuclear structure from lattice effective field theory

    SciTech Connect

    Lee, Dean

    2014-11-11

    This proceedings article reviews recent results by the Nuclear Lattice EFT Collaboration on an excited state of the {sup 12}C nucleus known as the Hoyle state. The Hoyle state plays a key role in the production of carbon via the triple-alpha reaction in red giant stars. We discuss the structure of low-lying states of {sup 12}C as well as the dependence of the triple-alpha reaction on the masses of the light quarks.

  15. Transient response of lattice structures based on exact member theory

    NASA Technical Reports Server (NTRS)

    Anderson, Melvin S.

    1989-01-01

    The computer program BUNVIS-RG, which treats vibration and buckling of lattice structures using exact member stiffness matrices, has been extended to calculate the exact modal mass and stiffness quantities that can be used in a conventional transient response analysis based on modes. The exact nature of the development allows inclusion of local member response without introduction of any interior member nodes. Results are given for several problems in which significant interaction between local and global response occurs.

  16. Structure of Block Copolymer Hydrogel Formed by Complex Coacervate Process

    NASA Astrophysics Data System (ADS)

    Choi, Soohyung; Ortony, Julia; Krogstad, Daniel; Spruell, Jason; Lynd, Nathaniel; Han, Songi; Kramer, Edward

    2012-02-01

    Complex coacervation occurs when oppositely charged polyelectrolytes associate in solution, forming dense micron-sized droplets. Hydrogels with coacervate block domains were formed by mixing two ABA and A'BA' triblock copolymer solutions in water where the A and A' blocks are oppositely charged. Small-angle neutron scattering (SANS) was used to investigate the structure of hydrogels formed by ABA triblock copolymers (A block: poly(allyl glycidyl ether) functionalized with guanidinium (A) or sulfonate (A'), B block: poly(ethylene oxide)). By using an appropriate fitting model, structural information such as coacervate core block radius and water volume fraction w can be extracted from SANS data. The results reveal that w in the coacervate core block was significantly higher than in conventional triblock copolymer hydrogels where microphase separation is driven by the hydrophobicity of the core-forming blocks.

  17. First principles calculations of nucleon and pion form factors: understanding the building blocks of nuclear matter from lattice QCD

    SciTech Connect

    Constantia Alexandrou; Bojan Bistrovic; Robert Edwards; P de Forcrand; George Fleming; Philipp Haegler; John Negele; Konstantinos Orginos; Andrew Pochinsky; Dru Renner; David Richards; Wolfram Schroers; Antonios Tsapalis

    2005-10-01

    Lattice QCD is an essential complement to the current and anticipated DOE-supported experimental program in hadronic physics. In this poster we address several key questions central to our understanding of the building blocks of nuclear matter, nucleons and pions. Firstly, we describe progress at computing the electromagnetic form factors of the nucleon, describing the distribution of charge and current, before considering the role played by the strange quarks. We then describe the study of transition form factors to the Delta resonance. Finally, we present recent work to determine the pion form factor, complementary to the current JLab experimental determination and providing insight into the approach to asymptotic freedom.

  18. Nonequilibrium dynamics in lattice ecosystems: Chaotic stability and dissipative structures

    NASA Astrophysics Data System (ADS)

    Solé, Ricard V.; Bascompte, Jordi; Valls, Joaquim

    1992-07-01

    A generalized coupled map lattice (CML) model of ecosystem dynamics is presented. We consider the spatiotemporal behavior of a prey-predator map, a model of host-parasitoid interactions, and two-species competition. The latter model can show phase separation of domains (Turing-like structures) even when chaos is present. We also use this CML model to explore the time evolution and structural properties of ecological networks built with a set of N competing species. The May-Wigner criterion is applied as a measure of stability, and some regularities in the stable networks observed are discussed.

  19. From lattice Hamiltonians to tunable band structures by lithographic design

    NASA Astrophysics Data System (ADS)

    Tadjine, Athmane; Allan, Guy; Delerue, Christophe

    2016-08-01

    Recently, new materials exhibiting exotic band structures characterized by Dirac cones, nontrivial flat bands, and band crossing points have been proposed on the basis of effective two-dimensional lattice Hamiltonians. Here, we show using atomistic tight-binding calculations that these theoretical predictions could be experimentally realized in the conduction band of superlattices nanolithographed in III-V and II-VI semiconductor ultrathin films. The lithographed patterns consist of periodic lattices of etched cylindrical holes that form potential barriers for the electrons in the quantum well. In the case of honeycomb lattices, the conduction minibands of the resulting artificial graphene host several Dirac cones and nontrivial flat bands. Similar features, but organized in different ways, in energy or in k -space are found in kagome, distorted honeycomb, and Lieb superlattices. Dirac cones extending over tens of meV could be obtained in superlattices with reasonable sizes of the lithographic patterns, for instance in InAs/AlSb heterostructures. Bilayer artificial graphene could be also realized by lithography of a double quantum-well heterostructure. These new materials should be interesting for the experimental exploration of Dirac-based quantum systems, for both fundamental and applied physics.

  20. Nucleon Structure and hyperon form factors from lattice QCD

    SciTech Connect

    Lin, Huey-Wen

    2007-06-11

    In this work, I report the latest lattice QCD calculations of nucleon and hyperon structure from chiral fermions in 2+1-flavor dynamical simulations. All calculations are done with a chirally symmetric fermion action, domain-wall fermions, for valence quarks. I begin with the latest lattice results on the nucleon structure, focusing on results from RBC/UKQCD using 2+1-flavor chiral fermion actions. We find the chiral-extrapolated axial coupling constant at physical pion mass point to be 1.23(5), consistant with experimental value. The renormalization constants for the structure functions are obtained from RI/MOM-scheme non-perturbative renormalization. We find first moments of the polarized and unpolarized nucleon structure functions at zero transfer momentum to be 0.133(13) and 0.203(23) respectively, using continuum chiral extrapolation. These are consistent with the experimental values, unlike previous calculations which have been 50% larger. We also have a prediction for the transversity, which we find to be 0.56(4). The twist-3 matrix element is consistent with zero which agrees with the prediction of the Wandzura-Wilczek relation. In the second half of this work, I report an indirect dynamical estimation of the strangeness proton magnetic moments using mixed actions. With the analysis of hyperon form factors and using charge symmetry, the strangeness of proton is found to be -0.066(26), consistent with the Adelaide-JLab Collaboration's result. The hyperon Sigma and Xi axial coupling constants are also performed for the first time in a lattice calculation, g_SigmaSigma = 0.441(14) and g_XiXi = -0.277(11).

  1. Nucleon Structure and Hyperon Form Factors from Lattice QCD.

    SciTech Connect

    Lin,H.W.

    2007-06-11

    In this work, I report the latest lattice QCD calculations of nucleon and hyperon structure from chiral fermions in 2+1-flavor dynamical simulations. All calculations are done with a chirally symmetric fermion action, domain-wall fermions, for valence quarks. I begin with the latest lattice results on the nucleon structure, focusing on results from RBC/UKQCD using 2+1-flavor chiral fermion actions. We find the chiral-extrapolated axial coupling constant at physical pion mass point. to be 1.23(5), consistent with experimental value. The renormalization constants for the structure functions are obtained from RI/MOM-scheme non-perturbative renormalization. We find first moments of the polarized and unpolarized nucleon structure functions at zero transfer momentum to be 0.133(13) and 0.203(23) respectively, using continuum chiral extrapolation. These are consistent with the experimental values, unlike previous calculations which have been 50% larger. We also have a prediction for the transversity, which we find to be 0.56(4). The twist-3 matrix element is consistent with zero which agrees with the prediction of the Wandzura-Wilczek relation. In the second half of this work, I report an indirect dynamical estimation of the strangeness proton magnetic moments using mixed actions. With the analysis of hyperon form factors and using charge symmetry, the strangeness of proton is found to be -0.066(2G), consistent with the Adelaide-JLab Collaboration's result. The hyperon {Sigma} and {Xi} axial coupling constants are also performed for the first time in a lattice calculation, g{sub {Sigma}{Sigma}} = 0.441(14) and g{sub {Xi}{Xi}} = -0.277(11).

  2. Lattice investigation of nucleon structure at light quark masses

    SciTech Connect

    Zanotti, James M.

    2010-07-27

    Lattice simulations of hadronic structure are now reaching a level where they are able to not only complement, but also provide guidance to current and forthcoming experimental programmes at, e.g. Jefferson Lab, COMPASS/CERN and FAIR/GSI. By considering new simulations at low quark masses and on large volumes, we review the recent progress that has been made in this exciting area by the QCDSF/UKQCD collaboration. In particular, results obtained close to the physical point for several quantities, including electromagnetic form factors and moments of ordinary parton distribution functions, show some indication of approaching their phenomenological values.

  3. Continuum modeling of large lattice structures: Status and projections

    NASA Technical Reports Server (NTRS)

    Noor, Ahmed K.; Mikulas, Martin M., Jr.

    1988-01-01

    The status and some recent developments of continuum modeling for large repetitive lattice structures are summarized. Discussion focuses on a number of aspects including definition of an effective substitute continuum; characterization of the continuum model; and the different approaches for generating the properties of the continuum, namely, the constitutive matrix, the matrix of mass densities, and the matrix of thermal coefficients. Also, a simple approach is presented for generating the continuum properties. The approach can be used to generate analytic and/or numerical values of the continuum properties.

  4. High Velocity Impact Response of Composite Lattice Core Sandwich Structures

    NASA Astrophysics Data System (ADS)

    Wang, Bing; Zhang, Guoqi; Wang, Shixun; Ma, Li; Wu, Linzhi

    2014-04-01

    In this research, carbon fiber reinforced polymer (CFRP) composite sandwich structures with pyramidal lattice core subjected to high velocity impact ranging from 180 to 2,000 m/s have been investigated by experimental and numerical methods. Experiments using a two-stage light gas gun are conducted to investigate the impact process and to validate the finite element (FE) model. The energy absorption efficiency (EAE) in carbon fiber composite sandwich panels is compared with that of 304 stainless-steel and aluminum alloy lattice core sandwich structures. In a specific impact energy range, energy absorption efficiency in carbon fiber composite sandwich panels is higher than that of 304 stainless-steel sandwich panels and aluminum alloy sandwich panels owing to the big density of metal materials. Therefore, in addition to the multi-functional applications, carbon fiber composite sandwich panels have a potential advantage to substitute the metal sandwich panels as high velocity impact resistance structures under a specific impact energy range.

  5. Local atomic arrangements and lattice distortions in layered Ge-Sb-Te crystal structures

    NASA Astrophysics Data System (ADS)

    Lotnyk, Andriy; Ross, Ulrich; Bernütz, Sabine; Thelander, Erik; Rauschenbach, Bernd

    2016-05-01

    Insights into the local atomic arrangements of layered Ge-Sb-Te compounds are of particular importance from a fundamental point of view and for data storage applications. In this view, a detailed knowledge of the atomic structure in such alloys is central to understanding the functional properties both in the more commonly utilized amorphous–crystalline transition and in recently proposed interfacial phase change memory based on the transition between two crystalline structures. Aberration-corrected scanning transmission electron microscopy allows direct imaging of local arrangement in the crystalline lattice with atomic resolution. However, due to the non-trivial influence of thermal diffuse scattering on the high-angle scattering signal, a detailed examination of the image contrast requires comparison with theoretical image simulations. This work reveals the local atomic structure of trigonal Ge-Sb-Te thin films by using a combination of direct imaging of the atomic columns and theoretical image simulation approaches. The results show that the thin films are prone to the formation of stacking disorder with individual building blocks of the Ge2Sb2Te5, Ge1Sb2Te4 and Ge3Sb2Te6 crystal structures intercalated within randomly oriented grains. The comparison with image simulations based on various theoretical models reveals intermixed cation layers with pronounced local lattice distortions, exceeding those reported in literature.

  6. Local atomic arrangements and lattice distortions in layered Ge-Sb-Te crystal structures

    PubMed Central

    Lotnyk, Andriy; Ross, Ulrich; Bernütz, Sabine; Thelander, Erik; Rauschenbach, Bernd

    2016-01-01

    Insights into the local atomic arrangements of layered Ge-Sb-Te compounds are of particular importance from a fundamental point of view and for data storage applications. In this view, a detailed knowledge of the atomic structure in such alloys is central to understanding the functional properties both in the more commonly utilized amorphous–crystalline transition and in recently proposed interfacial phase change memory based on the transition between two crystalline structures. Aberration-corrected scanning transmission electron microscopy allows direct imaging of local arrangement in the crystalline lattice with atomic resolution. However, due to the non-trivial influence of thermal diffuse scattering on the high-angle scattering signal, a detailed examination of the image contrast requires comparison with theoretical image simulations. This work reveals the local atomic structure of trigonal Ge-Sb-Te thin films by using a combination of direct imaging of the atomic columns and theoretical image simulation approaches. The results show that the thin films are prone to the formation of stacking disorder with individual building blocks of the Ge2Sb2Te5, Ge1Sb2Te4 and Ge3Sb2Te6 crystal structures intercalated within randomly oriented grains. The comparison with image simulations based on various theoretical models reveals intermixed cation layers with pronounced local lattice distortions, exceeding those reported in literature. PMID:27220411

  7. Local atomic arrangements and lattice distortions in layered Ge-Sb-Te crystal structures.

    PubMed

    Lotnyk, Andriy; Ross, Ulrich; Bernütz, Sabine; Thelander, Erik; Rauschenbach, Bernd

    2016-05-25

    Insights into the local atomic arrangements of layered Ge-Sb-Te compounds are of particular importance from a fundamental point of view and for data storage applications. In this view, a detailed knowledge of the atomic structure in such alloys is central to understanding the functional properties both in the more commonly utilized amorphous-crystalline transition and in recently proposed interfacial phase change memory based on the transition between two crystalline structures. Aberration-corrected scanning transmission electron microscopy allows direct imaging of local arrangement in the crystalline lattice with atomic resolution. However, due to the non-trivial influence of thermal diffuse scattering on the high-angle scattering signal, a detailed examination of the image contrast requires comparison with theoretical image simulations. This work reveals the local atomic structure of trigonal Ge-Sb-Te thin films by using a combination of direct imaging of the atomic columns and theoretical image simulation approaches. The results show that the thin films are prone to the formation of stacking disorder with individual building blocks of the Ge2Sb2Te5, Ge1Sb2Te4 and Ge3Sb2Te6 crystal structures intercalated within randomly oriented grains. The comparison with image simulations based on various theoretical models reveals intermixed cation layers with pronounced local lattice distortions, exceeding those reported in literature.

  8. Credit BG. Southeast and northeast facades of concrete block structure ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    Credit BG. Southeast and northeast facades of concrete block structure built in the late 1960s. It is now used to store miscellaneous equipment - Edwards Air Force Base, North Base, Liquid Oxygen Storage Facility, Second Street, Boron, Kern County, CA

  9. Nanoscale Building Blocks and Nanoassembly of Structures

    NASA Astrophysics Data System (ADS)

    Ozkan, Cengiz

    2003-03-01

    Electronics and photonics industries are highly interested in developing new methods for nanofabrication in order to be able to continue their long-term trend of building ever smaller, faster and less expensive devices. Conventional patterning strategies must be augmented by new techniques in order to truly take advantage of the quantum nature of novel nanoscale devices. In our research, we are developing a bottom-up approach to fabricate building blocks, which can be used to assemble nanostructures and devices. This involves the assembly of atom- and molecule-like nanostructures into functional 2-D and 3-D units. This will take advantage of the unique optical, electronic, and size-tunable properties of nanostructures and permit the use of these properties for "real" applications in a larger system (> 10 nm and < 1 um). Here, we demonstrate a novel technique for the fabrication of nano-assemblies of carbon nanotubes (CNT) and quantum dots (QD) (CNT-QD conjugates) for the first time using a zero length cross-linker. CNT's are primarily functionalized with carboxylic end groups by oxidation in concentrated sulfuric acid. Thiol stabilized QD's in aqueous solution with amino end groups were prepared in the laboratory. The ethylene carbodiimide coupling reaction was used to achieve the CNT-QD conjugation. Sulfo-N-Hydroxysuccinimide (sulfo-NHS) was used to enhance this coupling procedure. We present EDS and FTIR data for the chemical modification and SEM images of the first nano-building blocks. Current work includes the more complex 3-D assembly of QD's and nanotubes on Anodized Aluminum Oxide (AAO) template for nanodevices. Potential future applications of our method include the fabrication of novel electronic and photonic devices, crystal displays and biosensors.

  10. Optical spectrum and local lattice structure for ruby

    NASA Astrophysics Data System (ADS)

    Wang, H.; Kuang, X.-Y.; Mao, A.-J.; Huang, X.-F.

    2007-01-01

    By diagonalizing the 120×120 complete energy matrices for d3 ion in trigonal crystal field, which contains the electrostatic interaction, the trigonal field as well as the spin-orbit interaction, the unified calculation of the whole optical and EPR spectra for ruby are made. And matrix elements of the Zeeman energy with the magnetic field parallel or perpendicular to the trigonal axis are introduced into the complete energy matrices for obtaining the g factors of the energy levels. It is concluded that zero-field splitting and optical spectra as well as g factors are in good agreement with the experimental data and the distorted local lattice structure is determined firstly results from a stretching of the O2- ions along the C3 axis. The pressure-induced shifts of energy levels, g factors and local lattice structure are also discussed. In particular, all the calculations are carried out successfully within the framework of the crystal-field model which is consistent with the opinion of Macfarlane and Sturge that if all terms within the d3 configuration are included, one need not go outside conventional crystal-field theory.

  11. Lattice dynamics of crystals having R2MX6 structure

    NASA Astrophysics Data System (ADS)

    Torres, D. I.; Freire, J. D.; Katiyar, R. S.

    1997-10-01

    The theory of lattice dynamics in the harmonic approximation using a rigid-ion model due to Born and Huang [Dynamical Theory of Crystal Lattices (Oxford University Press, New York, 1954)], is applied to ionic crystals of the R2MX6 type with antifluorite structure namely, K2SnCl6, K2PtBr6, Cs2SnBr6, and Rb2SnBr6 in the cubic phase. The model expresses the potential energy as the sum of long-range Coulomb interactions and repulsive short-range interactions between ions in the primitive cell. A function of axially symmetric type is used to approximate the short-range part, and the number of force constant parameters were reduced utilizing stability conditions in the manner described by Katiyar [J. Phys. C 3, 1087 (1970)]. The remaining constants were determined by a nonlinear least-squares analysis of some experimental frequencies at the critical point Γ. The long-range contributions were calculated using the Ewald transformation as described by Cowley [Acta Crystallogr. 15, 687 (1962)]. Phonon frequencies and the normal modes of vibrations at the zone center were obtained; of particular interest is the resulting lowest librational frequency for each crystal. We obtained excellent agreement between the calculated and the observed frequencies. The resulting effective charge parameters indicated that these crystals are partially ionic. In general, the results offered a better vision of the structural phase transition mechanism involving the rotational mode T1g.

  12. Block copolymer self-assembly fundamentals and applications in formulation of nano-structured fluids

    NASA Astrophysics Data System (ADS)

    Sarkar, Biswajit

    incorporation in the cylindrical lyotropic mesophase formed by hydrated PEO-PPO-PEO block copolymer. The amount of nanoparticle dispersed is limited to 10 wt% due to restrictions posed by a combination of thermodynamics and geometry. Incorporation of deprotonated nanoparticles by replacing equal mass of water did not affect the lattice parameter of the hexagonal lyotropic liquid crystalline structures formed by hydrated PEO-PPO-PEO block copolymer. The incorporation of protonated NPs resulted in an increase in the lattice parameter due to stronger nanoparticle-polymer enthalpic interactions. Two dimensional swelling exponent (d ˜ phipolymer -0.65) suggests that deprotonated nanoparticles are located inside the PEO-rich domains, away from PEO-PPO interfaces. The presence of organic solvents screen the effect of protonated NPs on the lattice parameter of the hexagonal lyotropic liquid crystalline structures formed by hydrated PEO-PPO-PEO block copolymer.

  13. Generating folded protein structures with a lattice chain growth algorithm

    NASA Astrophysics Data System (ADS)

    Gan, Hin Hark; Tropsha, Alexander; Schlick, Tamar

    2000-10-01

    We present a new application of the chain growth algorithm to lattice generation of protein structure and thermodynamics. Given the difficulty of ab initio protein structure prediction, this approach provides an alternative to current folding algorithms. The chain growth algorithm, unlike Metropolis folding algorithms, generates independent protein structures to achieve rapid and efficient exploration of configurational space. It is a modified version of the Rosenbluth algorithm where the chain growth transition probability is a normalized Boltzmann factor; it was previously applied only to simple polymers and protein models with two residue types. The independent protein configurations, generated segment-by-segment on a refined cubic lattice, are based on a single interaction site for each amino acid and a statistical interaction energy derived by Miyazawa and Jernigan. We examine for several proteins the algorithm's ability to produce nativelike folds and its effectiveness for calculating protein thermodynamics. Thermal transition profiles associated with the internal energy, entropy, and radius of gyration show characteristic folding/unfolding transitions and provide evidence for unfolding via partially unfolded (molten-globule) states. From the configurational ensembles, the protein structures with the lowest distance root-mean-square deviations (dRMSD) vary between 2.2 to 3.8 Å, a range comparable to results of an exhaustive enumeration search. Though the ensemble-averaged dRMSD values are about 1.5 to 2 Å larger, the lowest dRMSD structures have similar overall folds to the native proteins. These results demonstrate that the chain growth algorithm is a viable alternative to protein simulations using the whole chain.

  14. Dependency Parsing with Lattice Structures for Resource-Poor Languages

    NASA Astrophysics Data System (ADS)

    Sudprasert, Sutee; Kawtrakul, Asanee; Boitet, Christian; Berment, Vincent

    In this paper, we present a new dependency parsing method for languages which have very small annotated corpus and for which methods of segmentation and morphological analysis producing a unique (automatically disambiguated) result are very unreliable. Our method works on a morphosyntactic lattice factorizing all possible segmentation and part-of-speech tagging results. The quality of the input to syntactic analysis is hence much better than that of an unreliable unique sequence of lemmatized and tagged words. We propose an adaptation of Eisner's algorithm for finding the k-best dependency trees in a morphosyntactic lattice structure encoding multiple results of morphosyntactic analysis. Moreover, we present how to use Dependency Insertion Grammar in order to adjust the scores and filter out invalid trees, the use of language model to rescore the parse trees and the k-best extension of our parsing model. The highest parsing accuracy reported in this paper is 74.32% which represents a 6.31% improvement compared to the model taking the input from the unreliable morphosyntactic analysis tools.

  15. Nucleon Structure on a Lattice at the Physical Point

    NASA Astrophysics Data System (ADS)

    Syritsyn, Sergey

    2015-09-01

    We report initial nucleon structure results computed on lattices with 2+1 dynamical Mobius domain wall fermions at the physical point generated by the RBC and UKQCD collaborations. At this stage, we evaluate only connected quark contributions. In particular, we discuss the nucleon vector and axial-vector form factors, nucleon axial charge and the isovector quark momentum fraction. From currently available statistics, we estimate the stochastic accuracy of the determination of gA and u-d to be around 10%, and we expect to reduce that to 5% within the next year. To reduce the computational cost of our calculations, we extensively use acceleration techniques such as low-eigenmode deflation and all-mode-averaging (AMA). We present a method for choosing optimal AMA parameters.

  16. Spectral and structural stability properties of charged particle dynamics in coupled lattices

    SciTech Connect

    Qin, Hong; Chung, Moses; Davidson, Ronald C.; Burby, Joshua W.

    2015-05-15

    It has been realized in recent years that coupled focusing lattices in accelerators and storage rings have significant advantages over conventional uncoupled focusing lattices, especially for high-intensity charged particle beams. A theoretical framework and associated tools for analyzing the spectral and structural stability properties of coupled lattices are formulated in this paper, based on the recently developed generalized Courant-Snyder theory for coupled lattices. It is shown that for periodic coupled lattices that are spectrally and structurally stable, the matrix envelope equation must admit matched solutions. Using the technique of normal form and pre-Iwasawa decomposition, a new method is developed to replace the (inefficient) shooting method for finding matched solutions for the matrix envelope equation. Stability properties of a continuously rotating quadrupole lattice are investigated. The Krein collision process for destabilization of the lattice is demonstrated.

  17. Wave propagation in reconfigurable magneto-elastic kagome lattice structures

    NASA Astrophysics Data System (ADS)

    Schaeffer, Marshall; Ruzzene, Massimo

    2015-05-01

    The paper discusses the wave propagation characteristics of two-dimensional magneto-elastic kagome lattices. Mechanical instabilities caused by magnetic interactions are exploited in combination with particle contact to bring about changes in the topology and stiffness of the lattices. The analysis uses a lumped mass system of particles, which interact through axial and torsional elastic forces as well as magnetic forces. The propagation of in-plane waves is predicted by applying Bloch theorem to lattice unit cells with linearized interactions. Elastic wave dispersion in these lattices before and after topological changes is compared, and large differences are highlighted.

  18. Combined structures-controls optimization of lattice trusses

    NASA Technical Reports Server (NTRS)

    Balakrishnan, A. V.

    1991-01-01

    The role that distributed parameter model can play in CSI is demonstrated, in particular in combined structures controls optimization problems of importance in preliminary design. Closed form solutions can be obtained for performance criteria such as rms attitude error, making possible analytical solutions of the optimization problem. This is in contrast to the need for numerical computer solution involving the inversion of large matrices in traditional finite element model (FEM) use. Another advantage of the analytic solution is that it can provide much needed insight into phenomena that can otherwise be obscured or difficult to discern from numerical computer results. As a compromise in level of complexity between a toy lab model and a real space structure, the lattice truss used in the EPS (Earth Pointing Satellite) was chosen. The optimization problem chosen is a generic one: of minimizing the structure mass subject to a specified stability margin and to a specified upper bond on the rms attitude error, using a co-located controller and sensors. Standard FEM treating each bar as a truss element is used, while the continuum model is anisotropic Timoshenko beam model. Performance criteria are derived for each model, except that for the distributed parameter model, explicit closed form solutions was obtained. Numerical results obtained by the two model show complete agreement.

  19. Electronic state of a CoO2 layer with hexagonal structure: a Kagomé lattice structure in a triangular lattice.

    PubMed

    Koshibae, W; Maekawa, S

    2003-12-19

    The electronic state in layered cobalt oxides with a hexagonal structure is examined. We find that the electronic structure reflects the nature of the Kagomé lattice hidden in the CoO2 layer which consists of stacked triangular lattices of oxygen ions and of cobalt ions. A fundamental model for the electron system is proposed, and the mechanism of the unique transport and magnetic properties of the cobalt oxides are discussed in light of the model.

  20. Identifying block structure in the Pacific Northwest, USA

    USGS Publications Warehouse

    Savage, James C.; Wells, Ray E.

    2015-01-01

    We have identified block structure in the Pacific Northwest (west of 116°W between 38°N and 49°N) by clustering GPS stations so that the same Euler vector approximates the velocity of each station in a cluster. Given the total number k of clusters desired, the clustering procedure finds the best assignment of stations to clusters. Clustering is calculated for k= 2 to 14. In geographic space, cluster boundaries that remain relatively stable as k is increased are tentatively identified as block boundaries. That identification is reinforced if the cluster boundary coincides with a geologic feature. Boundaries identified in northern California and Nevada are the Central Nevada Seismic Belt, the west side of the Northern Walker Lane Belt, and the Bartlett Springs Fault. Three blocks cover all of Oregon and Washington. The principal block boundary there extends west-northwest along the Brothers Fault Zone, then north and northwest along the eastern boundary of Siletzia, the accreted oceanic basement of the forearc. East of this boundary is the Intermountain block, its eastern boundary undefined. A cluster boundary at Cape Blanco subdivides the forearc along the faulted southern margin of Siletzia. South of Cape Blanco the Klamath Mountains-Basin and Range block extends east to the Central Nevada Seismic Belt and south to the Sierra Nevada-Great Valley block. The Siletzia block north of Cape Blanco coincides almost exactly with the accreted Siletz terrane. The cluster boundary in the eastern Olympic Peninsula may mark permanent shortening of Siletzia against the Intermountain block.

  1. Identifying block structure in the Pacific Northwest, USA

    NASA Astrophysics Data System (ADS)

    Savage, J. C.; Wells, R. E.

    2015-11-01

    We have identified block structure in the Pacific Northwest (west of 116°W between 38°N and 49°N) by clustering GPS stations so that the same Euler vector approximates the velocity of each station in a cluster. Given the total number k of clusters desired, the clustering procedure finds the best assignment of stations to clusters. Clustering is calculated for k = 2-14. In geographic space, cluster boundaries that remain relatively stable as k is increased are tentatively identified as block boundaries. That identification is reinforced if the cluster boundary coincides with a geologic feature. Boundaries identified in Northern California and Nevada are the Central Nevada Seismic Belt, the west side of the Northern Walker Lane Belt, and the Bartlett Springs Fault. Three blocks cover all of Oregon and Washington. The principal block boundary there extends west-northwest along the Brothers Fault Zone, then north and northwest along the eastern boundary of Siletzia, the accreted oceanic basement of the forearc. East of this boundary is the Intermountain block; its eastern boundary undefined. A cluster boundary at Cape Blanco subdivides the forearc along the faulted southern margin of Siletzia. South of Cape Blanco, the Klamath Mountains-Basin and Range block, extends east to the Central Nevada Seismic Belt and south to the Sierra Nevada-Great Valley block. The Siletzia block, north of Cape Blanco, coincides almost exactly with the accreted Siletz terrane. The cluster boundary in the eastern Olympic Peninsula may mark permanent shortening of Siletzia against the Intermountain block.

  2. Investigation the effect of lattice angle on the band structure in 3D phononic crystals with rhombohedral(II) lattice

    NASA Astrophysics Data System (ADS)

    Aryadoust, M.; Salehi, H.

    2014-12-01

    In this paper, the propagation of acoustic waves in the phononic crystals (PC) of 3D with rhombohedral(II) lattice is studied theoretically. The PC are constituted of nickel spheres embedded in epoxy. The calculations of the band structure and density of states are performed with the plane wave expansion method in the irreducible part of the Brillouin zone (BZ). In this study, we analyze the dependence of the band structures inside (the complete band gap width) and outside the complete band gap (negative refraction of acoustic wave) on the lattice angle in the irreducible part of the first BZ. Also the effect of lattice angle has been analyzed on the band structure of the () and (122) planes. Then, the equifrequency surface is calculated for the high symmetry point in the [111] and [100] directions. The results show that the maximum width of AEBG (0.022) in the irreducible part of the BZ of RHL2 is formed for (105∘) and no AEBG is found for γ > 150∘. Also, the maximum of the first and second AEBG width are 0.1076 and 0.0523 for γ = 133∘ in the () plane and the maximum of the first and second AEBG width are 0.1446 and 0.0998 for γ = 113∘ in the (122) plane. In addition, we have found that frequencies in which negative refraction occurs is constant for all lattice angles.

  3. Block-structured grids for complex aerodynamic configurations: Current status

    NASA Technical Reports Server (NTRS)

    Vatsa, Veer N.; Sanetrik, Mark D.; Parlette, Edward B.

    1995-01-01

    The status of CFD methods based on the use of block-structured grids for analyzing viscous flows over complex configurations is examined. The objective of the present study is to make a realistic assessment of the usability of such grids for routine computations typically encountered in the aerospace industry. It is recognized at the very outset that the total turnaround time, from the moment the configuration is identified until the computational results have been obtained and postprocessed, is more important than just the computational time. Pertinent examples will be cited to demonstrate the feasibility of solving flow over practical configurations of current interest on block-structured grids.

  4. Thresholds of surface codes on the general lattice structures suffering biased error and loss

    SciTech Connect

    Tokunaga, Yuuki; Fujii, Keisuke

    2014-12-04

    A family of surface codes with general lattice structures is proposed. We can control the error tolerances against bit and phase errors asymmetrically by changing the underlying lattice geometries. The surface codes on various lattices are found to be efficient in the sense that their threshold values universally approach the quantum Gilbert-Varshamov bound. We find that the error tolerance of the surface codes depends on the connectivity of the underlying lattices; the error chains on a lattice of lower connectivity are easier to correct. On the other hand, the loss tolerance of the surface codes exhibits an opposite behavior; the logical information on a lattice of higher connectivity has more robustness against qubit loss. As a result, we come upon a fundamental trade-off between error and loss tolerances in the family of surface codes with different lattice geometries.

  5. Rapid manufacturing of lattice structures with selective laser melting

    NASA Astrophysics Data System (ADS)

    Rehme, Olaf; Emmelmann, Claus

    2006-02-01

    Since the development of layered freeform manufacturing processes some technologies have emerged such as the Selective Laser Melting process (SLM) which uses layers of metal powder to manufacture 3D-objects from CAD-data by melting targeted geometries. The main goal using this process is to obtain functional products from engineering materials that feature desired properties such as given strength, hardness, surface roughness and residual stress behaviour. Rapid production with short throughput times due to only few process steps, a high individuality and a high degree of geometric freedom are considered to be its major advantages. However one disadvantage to all laser-based freeform manufacturing is the immense consumption of time since only considerably small quantities of material can be processed per time unit. Therefore it is desirable to review oldfashioned engineering design rules and develop part geometries that allow for hollow shaped parts with interior lattice structures providing the part with virtually the same stiffness and strength. Thus the process cost could be massively cut down due to reduced production time and less need for costly powder material. The SLM-process is meeting the requirements to fulfil this intention. Based on using fiber laser technology that delivers high beam quality the process is capable of producing thin walled structures of high tensile strength. Here development, production and testing of such lightweight yet sustainable SLM-parts will be presented along with their possible applications.

  6. The probabilistic mechanism of formation of block structures

    NASA Astrophysics Data System (ADS)

    Ivanov, V. I.

    2012-03-01

    Questions on the formation of block structures are considered. It is shown that the block structure is characteristic of bodies in a wide range of scales from microscopic to astronomic and from the bodies of nonliving nature to living organisms and communities. A scheme of the mechanism of the probabilistic formation of block structures is suggested. The characteristics general for structures of all scales are revealed. Evidence is presented that the hierarchical pattern of element sizes is characteristic of natural structures in which the ratio of linear sizes of elements neighboring by hierarchy is 2-5, while the characteristic scale coefficient is √ N , where N is the total number of elements of which the system is formed. The block-probabilistic approach ensures knowledge of rare catastrophic events, including earthquakes, market crashes, floods, and industrial catastrophes, or creative events such as the formation of hypercomplex systems similar to organisms and communities. The statistics of rare events follows the power distribution (the distribution with a "heavy tail") rather than the exponential one and especially the Poisson distribution, the Gaussian distribution, or the distributions with "light tails" close to them. The expression for the factor of increasing the formation probability of the systems, which is of many orders of magnitude even for the simplest systems, is acquired.

  7. Adolescent Boys' and Girls' Block Constructions Differ in Structural Balance: A Block-Building Characteristic Related to Math Achievement

    ERIC Educational Resources Information Center

    Casey, Beth M.; Pezaris, Elizabeth E.; Bassi, Julie

    2012-01-01

    Two studies were conducted on block building in adolescents, assessing middle school (Study 1) and high school students (Study 2). Students were asked to build something interesting with blocks. In both samples, the same pattern of gender differences were found; boys built taller structures than girls, and balanced a larger number of blocks on a…

  8. Tailored complex 3D vortex lattice structures by perturbed multiples of three-plane waves.

    PubMed

    Xavier, Jolly; Vyas, Sunil; Senthilkumaran, Paramasivam; Joseph, Joby

    2012-04-20

    As three-plane waves are the minimum number required for the formation of vortex-embedded lattice structures by plane wave interference, we present our experimental investigation on the formation of complex 3D photonic vortex lattice structures by a designed superposition of multiples of phase-engineered three-plane waves. The unfolding of the generated complex photonic lattice structures with higher order helical phase is realized by perturbing the superposition of a relatively phase-encoded, axially equidistant multiple of three noncoplanar plane waves. Through a programmable spatial light modulator assisted single step fabrication approach, the unfolded 3D vortex lattice structures are experimentally realized, well matched to our computer simulations. The formation of higher order intertwined helices embedded in these 3D spiraling vortex lattice structures by the superposition of the multiples of phase-engineered three-plane waves interference is also studied.

  9. Block-Krylov component synthesis method for structural model reduction

    NASA Technical Reports Server (NTRS)

    Craig, Roy R., Jr.; Hale, Arthur L.

    1988-01-01

    A new analytical method is presented for generating component shape vectors, or Ritz vectors, for use in component synthesis. Based on the concept of a block-Krylov subspace, easily derived recurrence relations generate blocks of Ritz vectors for each component. The subspace spanned by the Ritz vectors is called a block-Krylov subspace. The synthesis uses the new Ritz vectors rather than component normal modes to reduce the order of large, finite-element component models. An advantage of the Ritz vectors is that they involve significantly less computation than component normal modes. Both 'free-interface' and 'fixed-interface' component models are derived. They yield block-Krylov formulations paralleling the concepts of free-interface and fixed-interface component modal synthesis. Additionally, block-Krylov reduced-order component models are shown to have special disturbability/observability properties. Consequently, the method is attractive in active structural control applications, such as large space structures. The new fixed-interface methodology is demonstrated by a numerical example. The accuracy is found to be comparable to that of fixed-interface component modal synthesis.

  10. Credit BG. Southwest and southeast facades of concrete block structure ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    Credit BG. Southwest and southeast facades of concrete block structure built in the late 1960s. Fire House No. 4 (Building 4456) appears in background at right - Edwards Air Force Base, North Base, Liquid Oxygen Repair Facility, Second Street, Boron, Kern County, CA

  11. PARTI primitives for unstructured and block structured problems

    NASA Technical Reports Server (NTRS)

    Sussman, Alan; Saltz, Joel; Das, Raja; Gupta, S.; Mavriplis, Dimitri; Ponnusamy, Ravi; Crowley, Kay

    1992-01-01

    Described here is a set of primitives (PARTI) developed to efficiently execute unstructured and block structured problems on distributed memory parallel machines. We present experimental data from a 3-D unstructured Euler solver run on the Intel Touchstone Delta to demonstrate the usefulness of our methods.

  12. Anisotropic Peak Effect due to Structural Phase Transition in the Vortex Lattice

    NASA Astrophysics Data System (ADS)

    Rosenstein, Baruch; Knigavko, Anton

    1999-07-01

    It is shown that the recently observed new peak effect in YBCO could be explained by the softening of the vortex lattice due to a structural phase transition in the vortex lattice. At this transition square lattice transforms into a distorted hexagonal one. While conventional peak effect is associated with the softening of shear modes (elastic modulus c66 vanishes) at melting, in this case the relevant mode is ``squash'' mode ( c11+c22-2c12 vanishes).

  13. Can we predict lattice energy from molecular structure?

    PubMed

    Ouvrard, Carole; Mitchell, John B O

    2003-10-01

    By using simply the numbers of occurrences of different atom types as descriptors, a conceptually transparent and remarkably accurate model for the prediction of the enthalpies of sublimation of organic compounds has been generated. The atom types are defined on the basis of atomic number, hybridization state and bonded environment. Models of this kind were applied firstly to aliphatic hydrocarbons, secondly to both aliphatic and aromatic hydrocarbons, thirdly to a wide range of non-hydrogen-bonding molecules, and finally to a set of 226 organic compounds including 70 containing hydrogen-bond donors and acceptors. The final model gives squared correlation coefficients of 0.925 for the 226 compounds in the training set and 0.937 for an independent test set of 35 compounds. The success of such a simple model implies that the enthalpy of sublimation can be predicted accurately without knowledge of the crystal packing. This hypothesis is in turn consistent with the idea that, rather than being determined by the particular features of the lowest-energy packing, the lattice energy is similar for a number of hypothetical alternative crystal structures of a molecule.

  14. Solubility of block copolymer surfactants in compressed CO{sub 2} using a lattice fluid hydrogen-bonding model

    SciTech Connect

    Takishima, Shigeki; O`Neill, M.L.; Johnston, K.P.

    1997-07-01

    Supercritical carbon dioxide (CO{sub 2}) is an environmentally benign alternative to organic solvents in chemical processing. The solubilities of the homopolymers poly(ethylene glycol), poly(ethylene glycol) dimethyl ether (PEGDME), and poly(propylene glycol) (PPG) in CO{sub 2} were correlated with a lattice fluid hydrogen-bonding (LFHB) model, which was then used to predict solubilities of Pluronic L (PEG-PPG-PEG) and Pluronic R (PPG-PEG-PPG) triblock copolymers. Simple averaging rules were developed to evaluate the physical properties of the copolymers without introducing any adjustable parameters. For a given average molecular weight, the predictions of the model were quite reasonable and in some cases perhaps more accurate than the data, due to the large polydispersity of the samples. The model predicts the effects of total molecular weight, PEG/PPG ratio, terminal functional groups, temperature, and density on solubility. The much higher solubility of PPG versus PEG is due primarily to steric hindrance from the methyl branch, which weakens segment-segment interactions, and to a lesser extent to the stronger hydrogen bond donor strength of a primary (in the case of PEG) versus a secondary (in the case of PPG) alcohol terminal group. Consequently, the predicted solubilities of Pluronic L surfactants, which have stronger hydrogen bond donors on the terminal groups, are not much smaller than those of Pluronic R surfactants for given molecular weights of the blocks.

  15. Distinct structural alterations in PCNA block DNA mismatch repair†

    PubMed Central

    Dieckman, Lynne M.; Boehm, Elizabeth M.; Hingorani, Manju M.; Washington, M. Todd

    2013-01-01

    During DNA replication, mismatches and small loops in the DNA resulting from insertions or deletions are repaired by the mismatch repair (MMR) machinery. Proliferating cell nuclear antigen (PCNA) plays an important role in both mismatch-recognition and resynthesis stages of MMR. Previously, two mutant forms of PCNA were identified that cause defects in MMR with little, if any, other defects. The C22Y mutant PCNA protein completely blocks MutSα-dependent MMR, and the C81R mutant PCNA protein partially blocks both MutSα-dependent and MutSβ-dependent MMR. In order to understand the structural and mechanistic basis by which these two amino acid substitutions in PCNA proteins block MMR, we solved the X-ray crystal structures of both mutant proteins and carried out further biochemical studies. We found that these amino acid substitutions lead to subtle, distinct structural changes in PCNA. The C22Y substitution alters the positions of the α-helices lining the central hole of the PCNA ring, whereas the C81R substitution creates a distortion in an extended loop near the PCNA subunit interface. We conclude that the structural integrity of the α-helices lining the central hole and this loop are both necessary to form productive complexes with MutS α and mismatch-containing DNA. PMID:23869605

  16. Adaptive bimaterial lattices to mitigate thermal expansion mismatch stresses in satellite structures

    NASA Astrophysics Data System (ADS)

    Toropova, Marina M.; Steeves, Craig A.

    2015-08-01

    Earth-orbiting satellites regularly pass from sunlight to shade and back; these transitions are typically accompanied by significant temperature changes. When adjoining parts of a satellite that are made of different materials are subjected to large temperature changes, thermal mismatch stresses arise that are a function of the temperature change and the difference in coefficients of thermal expansion (CTEs) between the two materials. These thermal stresses are linked to undesirable deformation and, through long-term cycling, fatigue and failure of the structure. This paper describes a type of anisotropic lattice that can serve as a stress-free adaptor between two materials, eliminating thermal mismatch stresses and their concomitant consequences. The lattices consist of planar nonidentical anisotropic bimaterial cells, each designed based on a virtual triangle. Physically the cells consist of a triangle made of material with higher CTE surrounded by a hexagon made of material with lower CTE. Different skew angles of the hexagon make a particular cell and the whole lattice anisotropic. The cells can be designed and combined in a lattice in such a way that one edge of the lattice has CTE that coincides with the CTE of the first part of the structure (substrate 1), while the other edge of the lattice has CTE equal to the CTE of the second part of the structure (substrate 2). If all joints between the parts of each cell, neighbouring cells, and the lattice and the substrates are pinned, the whole structure will be free of thermal stresses. This paper will discuss the fundamental principles governing such lattices, their refinement for special circumstances, and opportunities for improving the structural performance of the lattices. This will be presented coupled to a rational strategy for lattice design.

  17. Structure of characteristic Lyapunov vectors in anharmonic Hamiltonian lattices.

    PubMed

    Romero-Bastida, M; Pazó, Diego; López, Juan M; Rodríguez, Miguel A

    2010-09-01

    In this work we perform a detailed study of the scaling properties of Lyapunov vectors (LVs) for two different one-dimensional Hamiltonian lattices: the Fermi-Pasta-Ulam and Φ^{4} models. In this case, characteristic (also called covariant) LVs exhibit qualitative similarities with those of dissipative lattices but the scaling exponents are different and seemingly nonuniversal. In contrast, backward LVs (obtained via Gram-Schmidt orthonormalizations) present approximately the same scaling exponent in all cases, suggesting it is an artificial exponent produced by the imposed orthogonality of these vectors. We are able to compute characteristic LVs in large systems thanks to a "bit reversible" algorithm, which completely obviates computer memory limitations.

  18. SAXS studies of the structure of a BCC-ordered block copolymer melt subjected to uniaxial extensional flow

    NASA Astrophysics Data System (ADS)

    Burghardt, Wesley; McCready, Erica

    We report in situ small-angle x-ray scattering (SAXS) investigations of a spherically-ordered block copolymer melt with a low styrene content (13%) resulting in spherical polystyrene microdomains ordered in BCC lattice. Melt annealing after clearing above the ODT produces ordered samples that have a macroscopically random orientation distribution of BCC 'grains'. Melt samples are subjected to uniaxial extensional flow in a counter-rotating drum extensional flow fixture housed in an oven with synchrotron x-ray access. During flow, initially isotropic diffraction rings in SAXS patterns become deformed, reflecting distortion of the BCC lattice. Diffracted intensity also concentrates azimuthally, indicating macroscopic alignment of the BCC lattice. There is evidence that extensional flow leads to progressive disordering of the BCC structure, with loss of higher order peaks and the emergence of a diffuse 'halo' of scattering. While the primary diffraction peak is visible in directions parallel and perpendicular to the stretching direction, the deformation of the lattice d-spacing follows affine deformation. Indications of ordering persist to higher strains in samples stretched at higher extension rates, and evidence of affine lattice deformation persists to very high strains (Hencky

  19. Impact of lattice distortion and electron doping on α-MoO3 electronic structure

    PubMed Central

    Huang, Peng-Ru; He, Yao; Cao, Chao; Lu, Zheng-Hong

    2014-01-01

    Band structure of transition metal oxides plays a critical role in many applications such as photo-catalysis, photovoltaics, and electroluminescent devices. In this work we report findings that the band structure of MoO3 can be significantly altered by a distortion in the octahedral coordination structure. We discovered that, in addition to epitaxial type of structural strain, chemical force such as hydrogen inclusion can also cause extended lattice distortion. The lattice distortion in hydrogenated MoO3 led to a significant reduction of the energy gap, overshadowing the Moss-Burstein effect of band filling. Charge doping simulations revealed that filling of conduction band drives the lattice distortion. This suggests that any charge transfer or n-type electron doping could lead to lattice distortion and consequentially a reduction in energy gap. PMID:25410814

  20. Thin film structure of symmetric rod-coil block copolymers.

    SciTech Connect

    Olsen, B. D.; Li, X.; Wang, J.; Segalman, R. A.; Univ. of Califormia at Berkeley; LBNL

    2007-04-03

    Poly(alkoxyphenylenevinylene-b-isoprene) (PPV-b-PI) rod-coil block copolymers demonstrate novel structures due to the rodlike PPV block. Thin films of the polymers self-assemble into lamellar microphases upon thermal annealing with the lamellae oriented primarily parallel to the substrate. The parallel lamellae show symmetric wetting of PI at both the substrate and vacuum interfaces. Grains of lamellae with parallel orientation are characterized by irregular polygon shapes and are bounded by defect regions where the lamellae are oriented out of the plane of the film. Grazing-incidence small-angle X-ray scattering (GISAXS) shows that these out-of-plane lamellae are strongly oriented perpendicular to the film. The perpendicular lamellae are much straighter than those typically observed in coil-coil block copolymers due to the high bending energy of the liquid crystalline rod nanodomains. Islands or holes form in the films, and domain spacings estimated from the island/hole heights are equal to the bulk domain spacing. The perpendicular 'defect' lamellae mediate the change in thickness required to transition between islands or holes and the surrounding region. Increasing film thickness results in an increasing fraction of the surface covered by perpendicular lamellae, presumably due to limited penetration of the substrate orienting field into the film. At great enough thickness total reorientation of the lamellar structure from parallel to perpendicular orientation at the vacuum interface is observed.

  1. Hierarchical Structure of Lattices in Film Formation of Core-Shell Type Polymer Microspheres

    PubMed

    Saito; Sugita; Ishizu

    1997-03-15

    By adding polystyrene homopolymer in the solid state, super-lattice structures of poly(4-vinyl pyridine) core-polystyrene shell type polymer microspheres were hierarchically changed from a disordered state to a face-centered cubic via a body-centered cubic. The transition of the lattice structures was investigated from the view point of the excluded volume of the microsphere, which was controlled by a changing of the molecular weights and blend tarios of polystyrene homopolymers.

  2. Piezoelectricity and pyroelectricity in polyvinylidene fluoride - Influence of the lattice structure

    NASA Technical Reports Server (NTRS)

    Purvis, C. K.; Taylor, P. L.

    1983-01-01

    Piezoelectric and pyroelectric responses of beta-phase (Phase I) polyvinylidene fluoride are predicted for a model system of polarizable point dipoles. The model incorporates the influence of the orthorhombic crystal structure by including the dependence of the internal electric field on the lattice parameters. Strong anisotropy in the piezoelectric response under uniaxial stress is predicted as a consequence of the orthorhombic lattice structure. Predictions are found to be in reasonable agreement with room-temperature experimental data.

  3. Loading mode dependent effective properties of octet-truss lattice structures using 3D-printing

    NASA Astrophysics Data System (ADS)

    Challapalli, Adithya

    Cellular materials, often called lattice materials, are increasingly receiving attention for their ultralight structures with high specific strength, excellent impact absorption, acoustic insulation, heat dissipation media and compact heat exchangers. In alignment with emerging additive manufacturing (AM) technology, realization of the structural applications of the lattice materials appears to be becoming faster. Considering the direction dependent material properties of the products with AM, by directionally dependent printing resolution, effective moduli of lattice structures appear to be directionally dependent. In this paper, a constitutive model of a lattice structure, which is an octet-truss with a base material having an orthotropic material property considering AM is developed. In a case study, polyjet based 3D printing material having an orthotropic property with a 9% difference in the principal direction provides difference in the axial and shear moduli in the octet-truss by 2.3 and 4.6%. Experimental validation for the effective properties of a 3D printed octet-truss is done for uniaxial tension and compression test. The theoretical value based on the micro-buckling of truss member are used to estimate the failure strength. Modulus value appears a little overestimate compared with the experiment. Finite element (FE) simulations for uniaxial compression and tension of octettruss lattice materials are conducted. New effective properties for the octet-truss lattice structure are developed considering the observed behavior of the octet-truss structure under macroscopic compression and tension trough simulations.

  4. Mechanical and electrical strain response of a piezoelectric auxetic PZT lattice structure

    NASA Astrophysics Data System (ADS)

    Fey, Tobias; Eichhorn, Franziska; Han, Guifang; Ebert, Kathrin; Wegener, Moritz; Roosen, Andreas; Kakimoto, Ken-ichi; Greil, Peter

    2016-01-01

    A two-dimensional auxetic lattice structure was fabricated from a PZT piezoceramic. Tape casted and sintered sheets with a thickness of 530 μm were laser cut into inverted honeycomb lattice structure with re-entrant cell geometry (θ = -25°) and poling direction oriented perpendicular to the lattice plane. The in-plane strain response upon applying an uniaxial compression load as well as an electric field perpendicular to the lattice plane were analyzed by a 2D image data detection analysis. The auxetic lattice structure exhibits orthotropic deformation behavior with a negative in-plane Poisson’s ratio of -2.05. Compared to PZT bulk material the piezoelectric auxetic lattice revealed a strain amplification by a factor of 30-70. Effective transversal coupling coefficients {{d}al}31 of the PZT lattice exceeding 4 × 103 pm V-1 were determined which result in an effective hydrostatic coefficient {{d}al}h 66 times larger than that of bulk PZT.

  5. Observations of λ /4 structure in a low-loss radio-frequency-dressed optical lattice

    NASA Astrophysics Data System (ADS)

    Lundblad, N.; Ansari, S.; Guo, Y.; Moan, E.

    2014-11-01

    We load a Bose-Einstein condensate into a one-dimensional (1D) optical lattice altered through the use of radio-frequency (rf) dressing. The rf resonantly couples the three levels of the 87Rb F =1 manifold and combines with a spin-dependent "bare" optical lattice to result in adiabatic potentials of variable shape, depth, and spatial frequency content. We choose dressing parameters such that the altered lattice is stable over lifetimes exceeding tens of ms at higher depths than in previous work. We observe significant differences between the BEC momentum distributions of the dressed lattice as compared to the bare lattice, and find general agreement with a 1D band-structure calculation informed by the dressing parameters. Previous work using such lattices was limited by very shallow dressed lattices and strong Landau-Zener tunneling loss between adiabatic potentials, equivalent to failure of the adiabatic criterion. In this work we operate with significantly stronger rf coupling (increasing the avoided-crossing gap between adiabatic potentials), observing dressed lifetimes of interest for optical lattice-based analog solid-state physics.

  6. Modification of nanofibrillated cellulose using amphiphilic block-structured galactoglucomannans.

    PubMed

    Lozhechnikova, Alina; Dax, Daniel; Vartiainen, Jari; Willför, Stefan; Xu, Chunlin; Österberg, Monika

    2014-09-22

    Nanofibrillated cellulose (NFC) and hemicelluloses have shown to be highly promising renewable components both as barrier materials and in novel biocomposites. However, the hydrophilic nature of these materials restricts their use in some applications. In this work, the usability of modified O-acetyl galactoglucomannan (GGM) for modification of NFC surface properties was studied. Four GGM-block-structured, amphiphilic derivatives were synthesized using either fatty acids or polydimethylsiloxane as hydrophobic tails. The adsorption of these GGM derivatives was consecutively examined in aqueous solution using a quartz crystal microbalance with dissipation monitoring (QCM-D). It was found that the hydrophobic tails did not hinder adsorption of the GGM derivatives to cellulose, which was concluded to be due to the presence of the native GGM-block with high affinity to cellulose. The layer properties of the adsorbed block-co-polymers were discussed and evaluated. Self-standing NFC films were further prepared and coated with the GGM derivatives and the effect of the surface modification on wetting properties and oxygen permeability (OP) of the modified films was assessed. PMID:24906743

  7. Electrically Tunable Soft-Solid Block Copolymer Structural Color.

    PubMed

    Park, Tae Joon; Hwang, Sun Kak; Park, Sungmin; Cho, Sung Hwan; Park, Tae Hyun; Jeong, Beomjin; Kang, Han Sol; Ryu, Du Yeol; Huh, June; Thomas, Edwin L; Park, Cheolmin

    2015-12-22

    One-dimensional photonic crystals based on the periodic stacking of two different dielectric layers have been widely studied, but the fabrication of mechanically flexible polymer structural color (SC) films, with electro-active color switching, remains challenging. Here, we demonstrate free-standing electric field tunable ionic liquid (IL) swollen block copolymer (BCP) films. Placement of a polymer/ionic liquid film-reservoir adjacent to a self-assembled poly(styrene-block-quaternized 2-vinylpyridine) (PS-b-QP2VP) copolymer SC film allowed the development of red (R), green (G), and blue (B) full-color SC block copolymer films by swelling of the QP2VP domains by the ionic liquid associated with water molecules. The IL-polymer/BCP SC film is mechanically flexible with excellent color stability over several days at ambient conditions. The selective swelling of the QP2VP domains could be controlled by both the ratio of the IL to a polymer in the gel-like IL reservoir layer and by an applied voltage in the range of -3 to +6 V using a metal/IL reservoir/SC film/IL reservoir/metal capacitor type device.

  8. Apodized structures for the integration of defect sites into photonic lattices

    SciTech Connect

    Boguslawski, Martin Kelberer, Andreas; Rose, Patrick; Denz, Cornelia

    2014-09-15

    We introduce a versatile concept to optically induce photonic structures of local refractive index modulations as well as photonic lattices holding single defect sites. For a given structure, we develop a set of nondiffracting beams obtained by fractionalizing the corresponding spatial spectrum. By combining this set in a multiplexing procedure, we achieve an incoherent combination of all individual structures of the set resulting in a locally addressable refractive index manipulation. We exemplarily present experimental results for apodized, meaning locally confined index changes in a photorefractive crystal resembling a sixfold and a circular symmetric structure. By an additional multiplexing step, we furthermore create periodic photonic lattices featuring embedded defects.

  9. Anisotropic peak effect due to structural phase transition in the vortex lattice

    NASA Astrophysics Data System (ADS)

    Rosenstein, Baruch; Knigavko, Anton

    2000-05-01

    The recently observed new peak effect in YBCO is explained by softening of the vortex lattice (VL) due to a structural phase transition in the VL. At this transition, square lattice transforms into a distorted hexagonal one. While conventional peak effect is associated with softening of shear modes at melting, in this case the relevant mode is the point. The squash mode is highly anisotropic and we point out some peculiar effects associated with this feature.

  10. Dynamics of structure formation in crystallizable block copolymers

    SciTech Connect

    Rangarajan, P.; Register, R.A.; Adamson, D.H.

    1995-12-31

    Isothermal crystallization of polyolefin diblock copolymers from homogeneous and weakly segregated melts has been tracked using simultaneous, synchrotron-based small and wide-angle x-ray scattering (SAXS and WAXS). The polymers are prepared by hydrogenating polydiene diblocks, and contain crystallizable polyethylene ({open_quotes}E{close_quotes}; hydrogenated high 1,4-polybutadiene) blocks and a variety of amorphous polyolefin blocks. All polymers exhibit a well-ordered lamellar morphology at room temperature, as evidenced by 2-3 clear SAXS reflections, even for compositions containing as little as 12% E. In polymers crystallizing from homogeneous melts, the WAXS reflections from the E crystallites grow in parallel with the 3-4 SAXS reflections, so microphase separation is driven by crystallization. These structures, which are reminiscent of strong segregation (as indicated by the multiple SAXS reflections), are obtained by cooling only 20{degrees}C below the melting point. For a polymer having a weakly segregated melt, crystallization eradicates the melt morphology, but larger domain spacings were observed for higher crystallization temperatures, unlike the path-independent values obtained on crystallization from single-phase melts, suggesting that melt segregation hinders the development of the equilibrium crystallization-driven structure.

  11. Structural aspects of the relaxation process in spin crossover solids: Phase separation, mapping of lattice strain, and domain wall structure

    NASA Astrophysics Data System (ADS)

    Nicolazzi, W.; Pillet, S.

    2012-03-01

    We present a nonequilibrium study of the relaxation process in spin crossover solids using numerical simulations of a recently introduced two-variable elastic Ising-like model. We analyze the structural lattice distortions accompanying the relaxation from the metastable high-spin to the ground low-spin state as a function of cooperativity. In the highly cooperative case, a sigmoidal relaxation behavior of the high-spin fraction nHS is described, and it occurs jointly with a structural phase separation process. The mean lattice spacing follows a similar sigmoidal trend, owing to the interplay between electronic and lattice variables in the Hamiltonian. Weakly cooperative systems are characterized by single exponential relaxations of the high-spin fraction, the corresponding structural transformation proceeds homogeneously with a progressive relaxation of the mean lattice spacing. Long relaxation tail effects are also observed. We highlight the development of lattice strain accompanying the spin transition, and show that structural phase rebuilding proceeds in the late stage of the relaxation by releasing residual strain. Under specific conditions, a temporal decoupling between the electronic and lattice variables is observed, which may have direct applications for interpreting time-resolved spectroscopic or diffraction experiments and for elucidating unusual structural behaviors, such as the development of superstructures, modulated structures, or transient phases.

  12. Direct observation of Σ7 domain boundary core structure in magnetic skyrmion lattice.

    PubMed

    Matsumoto, Takao; So, Yeong-Gi; Kohno, Yuji; Sawada, Hidetaka; Ikuhara, Yuichi; Shibata, Naoya

    2016-02-01

    Skyrmions are topologically protected nanoscale magnetic spin entities in helical magnets. They behave like particles and tend to form hexagonal close-packed lattices, like atoms, as their stable structure. Domain boundaries in skyrmion lattices are considered to be important as they affect the dynamic properties of magnetic skyrmions. However, little is known about the fine structure of such skyrmion domain boundaries. We use differential phase contrast scanning transmission electron microscopy to directly visualize skyrmion domain boundaries in FeGe1-x Si x induced by the influence of an "edge" of a crystal grain. Similar to hexagonal close-packed atomic lattices, we find the formation of skyrmion "Σ7" domain boundary, whose orientation relationship is predicted by the coincidence site lattice theory to be geometrically stable. On the contrary, the skyrmion domain boundary core structure shows a very different structure relaxation mode. Individual skyrmions can flexibly change their size and shape to accommodate local coordination changes and free volumes formed at the domain boundary cores. Although atomic rearrangement is a common structural relaxation mode in crystalline grain boundaries, skyrmions show very unique and thus different responses to such local lattice disorders. PMID:26933690

  13. Direct observation of Σ7 domain boundary core structure in magnetic skyrmion lattice

    PubMed Central

    Matsumoto, Takao; So, Yeong-Gi; Kohno, Yuji; Sawada, Hidetaka; Ikuhara, Yuichi; Shibata, Naoya

    2016-01-01

    Skyrmions are topologically protected nanoscale magnetic spin entities in helical magnets. They behave like particles and tend to form hexagonal close-packed lattices, like atoms, as their stable structure. Domain boundaries in skyrmion lattices are considered to be important as they affect the dynamic properties of magnetic skyrmions. However, little is known about the fine structure of such skyrmion domain boundaries. We use differential phase contrast scanning transmission electron microscopy to directly visualize skyrmion domain boundaries in FeGe1−xSix induced by the influence of an “edge” of a crystal grain. Similar to hexagonal close-packed atomic lattices, we find the formation of skyrmion “Σ7” domain boundary, whose orientation relationship is predicted by the coincidence site lattice theory to be geometrically stable. On the contrary, the skyrmion domain boundary core structure shows a very different structure relaxation mode. Individual skyrmions can flexibly change their size and shape to accommodate local coordination changes and free volumes formed at the domain boundary cores. Although atomic rearrangement is a common structural relaxation mode in crystalline grain boundaries, skyrmions show very unique and thus different responses to such local lattice disorders. PMID:26933690

  14. Boron carbide: Consistency of components, lattice parameters, fine structure and chemical composition makes the complex structure reasonable

    NASA Astrophysics Data System (ADS)

    Werheit, Helmut

    2016-10-01

    The complex, highly distorted structure of boron carbide is composed of B12 and B11C icosahedra and CBC, CBB and B□B linear elements, whose concentration depends on the chemical composition each. These concentrations are shown to be consistent with lattice parameters, fine structure data and chemical composition. The respective impacts on lattice parameters are estimated and discussed. Considering the contributions of the different structural components to the energy of the overall structure makes the structure and its variation within the homogeneity range reasonable; in particular that of B4.3C representing the carbon-rich limit of the homogeneity range. Replacing in B4.3C virtually the B□B components by CBC yields the hypothetical moderately distorted B4.0C (structure formula (B11C)CBC). The reduction of lattice parameters related is compatible with recently reported uncommonly prepared single crystals, whose compositions deviate from B4.3C.

  15. The block structure and Quaternary strike-slip block rotation of central Japan

    NASA Astrophysics Data System (ADS)

    Kanaori, Yuji; Kawakami, Shin-Ichi; Yairi, Kenji

    1992-02-01

    Central Japan is situated on the inflection point of the bow-shaped Japanese islands. Numerous NW-SE trending active faults, arranged in parallel at intervals of 20 to 80 km are found in this area. These active faults are more than 30 km long with shattered zones from 30 to 300 m wide. Several active faults constitute a given block boundary, which serves as the dividing line for one of the four blocks that make up central Japan. The block boundaries require careful study since numerous historical earth-quakes have occurred along these lines. Offset measurements of basement rocks, created during the Quaternary period due to left-lateral faulting, amount to 1 to 7 km. Gravity lineaments, which link points of sudden change and saddles of Bouguer anomalies, are clearly found along the block boundaries. The NW-SE trending active faults appearing on the ground surface are associated with motions of the block boundaries. Block rotational movement, caused by left-lateral faulting, plays an important role in the crustal deformation of central Japan. Rotational angles of the blocks calculated from the amount of displacement of basement rocks, initiated during the Quaternary period, are estimated to be 3° to 7° in a clockwise manner.

  16. Efficient Multiplexer FPGA Block Structures Based on G4FETs

    NASA Technical Reports Server (NTRS)

    Vatan, Farrokh; Fijany, Amir

    2009-01-01

    Generic structures have been conceived for multiplexer blocks to be implemented in field-programmable gate arrays (FPGAs) based on four-gate field-effect transistors (G(sup 4)FETs). This concept is a contribution to the continuing development of digital logic circuits based on G4FETs and serves as a further demonstration that logic circuits based on G(sup 4)FETs could be more efficient (in the sense that they could contain fewer transistors), relative to functionally equivalent logic circuits based on conventional transistors. Results in this line of development at earlier stages were summarized in two previous NASA Tech Briefs articles: "G(sup 4)FETs as Universal and Programmable Logic Gates" (NPO-41698), Vol. 31, No. 7 (July 2007), page 44, and "Efficient G4FET-Based Logic Circuits" (NPO-44407), Vol. 32, No. 1 ( January 2008), page 38 . As described in the first-mentioned previous article, a G4FET can be made to function as a three-input NOT-majority gate, which has been shown to be a universal and programmable logic gate. The universality and programmability could be exploited to design logic circuits containing fewer components than are required for conventional transistor-based circuits performing the same logic functions. The second-mentioned previous article reported results of a comparative study of NOT-majority-gate (G(sup 4)FET)-based logic-circuit designs and equivalent NOR- and NAND-gate-based designs utilizing conventional transistors. [NOT gates (inverters) were also included, as needed, in both the G(sup 4)FET- and the NOR- and NAND-based designs.] In most of the cases studied, fewer logic gates (and, hence, fewer transistors), were required in the G(sup 4)FET-based designs. There are two popular categories of FPGA block structures or architectures: one based on multiplexers, the other based on lookup tables. In standard multiplexer- based architectures, the basic building block is a tree-like configuration of multiplexers, with possibly a few

  17. Structure and Interactions of Isolated Biomolecular Building Blocks.

    NASA Astrophysics Data System (ADS)

    de Vries, Mattanjah

    2006-03-01

    We investigate biomolecular building blocks and their clusters with each other and with water on a single molecular level. The motivation is the need to distinguish between intrinsic molecular properties and those that result from the biological environment. This is achieved by a combination of laser desorption and jet cooling, applied to aromatic amino acids, small peptides containing those, nucleobases and nucleosides. This approach is coupled with a number of laser spectroscopic techniques, including resonant multi-photon ionization, spectral hole burning and infra-red ion-dip spectroscopy. We will discuss examples illustrating how information can be obtained on spatial structure of individual biomolecules, including peptide conformations and details of DNA base-pairing.

  18. 2D Four-Channel Perfect Reconstruction Filter Bank Realized with the 2D Lattice Filter Structure

    NASA Astrophysics Data System (ADS)

    Sezen, S.; Ertüzün, A.

    2006-12-01

    A novel orthogonal 2D lattice structure is incorporated into the design of a nonseparable 2D four-channel perfect reconstruction filter bank. The proposed filter bank is obtained by using the polyphase decomposition technique which requires the design of an orthogonal 2D lattice filter. Due to constraint of perfect reconstruction, each stage of this lattice filter bank is simply parameterized by two coefficients. The perfect reconstruction property is satisfied regardless of the actual values of these parameters and of the number of the lattice stages. It is also shown that a separable 2D four-channel perfect reconstruction lattice filter bank can be constructed from the 1D lattice filter and that this is a special case of the proposed 2D lattice filter bank under certain conditions. The perfect reconstruction property of the proposed 2D lattice filter approach is verified by computer simulations.

  19. Vortex lattice structures in YNi{sub 2}B{sub 2}C

    SciTech Connect

    Yethiraj, M.; Paul, D.M.; Tomy, C.V.; Forgan, E.M.

    1997-12-01

    The authors observe a flux lattice with square symmetry in the superconductor YNi{sub 2}B{sub 2}C when the applied field is parallel to the c-axis of the crystal. A square lattice observed previously in the isostructural magnetic analog ErNi{sub 2}B{sub 2}C was attributed to the interaction between magnetic order in that system and the flux lattice. Since the Y-based compound does not order magnetically, it is clear that the structure of the flux lattice is unrelated to magnetic order. In fact, they show that the flux lines have a square cross-section when the applied field is parallel to the c-axis of the crystal, since the measured penetration depth along the 100 crystal direction is larger than the penetration depth along the 110 by approximately 60%. This is the likely reason for the square symmetry of the lattice. Although they find considerable disorder in the arrangement of the flux lines at 2.5T, no melting of the vortex lattice was observed.

  20. On complexity of trellis structure of linear block codes

    NASA Technical Reports Server (NTRS)

    Lin, Shu

    1990-01-01

    The trellis structure of linear block codes (LBCs) is discussed. The state and branch complexities of a trellis diagram (TD) for a LBC is investigated. The TD with the minimum number of states is said to be minimal. The branch complexity of a minimal TD for a LBC is expressed in terms of the dimensions of specific subcodes of the given code. Then upper and lower bounds are derived on the number of states of a minimal TD for a LBC, and it is shown that a cyclic (or shortened cyclic) code is the worst in terms of the state complexity among the LBCs of the same length and dimension. Furthermore, it is shown that the structural complexity of a minimal TD for a LBC depends on the order of its bit positions. This fact suggests that an appropriate permutation of the bit positions of a code may result in an equivalent code with a much simpler minimal TD. Boolean polynomial representation of codewords of a LBC is also considered. This representation helps in study of the trellis structure of the code. Boolean polynomial representation of a code is applied to construct its minimal TD. Particularly, the construction of minimal trellises for Reed-Muller codes and the extended and permuted binary primitive BCH codes which contain Reed-Muller as subcodes is emphasized. Finally, the structural complexity of minimal trellises for the extended and permuted, and double-error-correcting BCH codes is analyzed and presented. It is shown that these codes have relatively simple trellis structure and hence can be decoded with the Viterbi decoding algorithm.

  1. Structural, elastic, and lattice dynamic stability of yttrium selenide (YSe) under pressure: A first principle study

    SciTech Connect

    Sahoo, B. D. Joshi, K. D.; Gupta, Satish C.

    2014-11-21

    Structural, elastic, and lattice dynamical stability of YSe has been investigated as a function of pressure through first principles electronic band structure calculations. The comparison of enthalpies of rocksalt type (B1) and CsCl type cubic (B2) structures determined as a function of pressure suggests that the B1 phase will transform to B2 structure at ∼32 (30 GPa at 300 K obtained from comparison of Gibbs free energy at 300 K). The transition is identified to be of first order in nature with a volume discontinuity of ∼6.2% at the transition pressure. Furthermore, the theoretically determined equation of state has been utilized to derive various physical quantities, such as zero pressure equilibrium volume, bulk modulus, and pressure derivative of bulk modulus. The single crystal elastic constants have been predicted at various pressures for both the B1 and B2 structures using the energy strain method. The activation barrier between B1 and B2 phases calculated at transition point is ∼19.7mRy/formula unit. Our lattice dynamic calculations show that both the B1 as well as B2 structures are lattice dynamically stable not only at ambient pressure but also at transition pressure. The B1 phase becomes lattice dynamically unstable at ∼112 GPa, i.e., much beyond the transition pressure. The effect of temperature on volume and bulk modulus of the YSe in B1 phase has also been examined.

  2. Crystal lattice and band structure of the intermediate high-pressure phase of PbSe.

    PubMed

    Streltsov, S V; Manakov, A Yu; Vokhmyanin, A P; Ovsyannikov, S V; Shchennikov, V V

    2009-09-23

    In the present paper the results of fitting synchrotron diffraction data are obtained for the intermediate high-pressure phase (9.5 GPa) of the lead selenide based compound Pb(1-x)Sn(x)Se (x = 0.125)-an optoelectronic as well as a thermoelectric material-for two types of lattice symmetries Pnma (space group #62) and Cmcm (space group #63). Both lattice parameters and positions of atoms for the above mentioned structures have been used in calculations of the electron structure of high-pressure phases. The main difference between the electronic properties for Cmcm and Pnma structures established in electronic structure calculations is that in the first one the PbSe compound was found to be a metal, while in the second a small semiconductor gap (E(G) = 0.12 eV) was obtained. Moreover, the forces in the Cmcm structure are an order of magnitude larger than those calculated for the Pnma lattice. In the optimized, Pnma structure within a generalized gradient approximation (GGA), the band gap increases up to E(G) = 0.27 eV. The result coincides with the data on thermoelectric power and electrical resistance data pointing to a semiconductor gap of ∼0.2 eV at ∼9.5 GPa. Thus, the Pmna type of lattice seems to be a preferable version for the intermediate phase compared with the Cmcm one. PMID:21832372

  3. Atomic and electronic structures of lattice mismatched Cu2O/TiO2 interfaces

    NASA Astrophysics Data System (ADS)

    Wang, Shuzhi; Kavaipatti, Balasubramaniam; Kim, Sung-Joo; Pan, Xiaoqing; Ramesh, Ramamoorthy; Ager, Joel W.; Wang, Lin-Wang

    2014-05-01

    Heterojunction interfaces between metal oxides are often highly lattice mismatched. The atomic and electronic structures of such interfaces, however, are not well understood. We have synthesized Cu2O/TiO2 heterojunction thin films with 13% lattice mismatch and studied the interface via experimental methods and large-scale density function theory calculations of supercells containing ˜1300 atoms. We find that an interface of epitaxial quality is formed via a coincidence site lattice of 8 Cu2O unit cells matching 9 TiO2 unit cells. Calculations reveal the existence of a dislocation core of the O sublattices at the interface and a random arrangement of one layer of interfacial Cu atoms. The interfacial electronic structure is found to be mostly determined by the interfacial Cu distribution, rather than by the O dislocation core. The conduction band minimum and valence band maximum states are spatially separated, and there is no strongly localized state near the core.

  4. Progressive Fracture Analysis of Planar Lattices and Shape-Morphing Kagome Structure

    NASA Astrophysics Data System (ADS)

    Tserpes, Konstantinos I.

    The fracture behaviors of three defected planar lattices loaded in axial tension and the 3D shape-morphing Kagome structure loaded as a cantilever beam are explored by using finite element-based progressive fracture analysis. The assumed defects are in the form of symmetrical notches introduced in the lattices by removing the struts in single rows. Numerical results reveal that the presence of the notches significantly reduces the tensile strength of the lattices. On the other hand, with increasing the load in the Kagome structure, yielding and buckling of the struts in the core and yielding of the face-sheet appear consecutively inducing degradation of structure’s bending stiffness and large dips of the loaded end.

  5. Development of an Innovative Algorithm for Aerodynamics-Structure Interaction Using Lattice Boltzmann Method

    NASA Technical Reports Server (NTRS)

    Mei, Ren-Wei; Shyy, Wei; Yu, Da-Zhi; Luo, Li-Shi; Rudy, David (Technical Monitor)

    2001-01-01

    The lattice Boltzmann equation (LBE) is a kinetic formulation which offers an alternative computational method capable of solving fluid dynamics for various systems. Major advantages of the method are owing to the fact that the solution for the particle distribution functions is explicit, easy to implement, and the algorithm is natural to parallelize. In this final report, we summarize the works accomplished in the past three years. Since most works have been published, the technical details can be found in the literature. Brief summary will be provided in this report. In this project, a second-order accurate treatment of boundary condition in the LBE method is developed for a curved boundary and tested successfully in various 2-D and 3-D configurations. To evaluate the aerodynamic force on a body in the context of LBE method, several force evaluation schemes have been investigated. A simple momentum exchange method is shown to give reliable and accurate values for the force on a body in both 2-D and 3-D cases. Various 3-D LBE models have been assessed in terms of efficiency, accuracy, and robustness. In general, accurate 3-D results can be obtained using LBE methods. The 3-D 19-bit model is found to be the best one among the 15-bit, 19-bit, and 27-bit LBE models. To achieve desired grid resolution and to accommodate the far field boundary conditions in aerodynamics computations, a multi-block LBE method is developed by dividing the flow field into various blocks each having constant lattice spacing. Substantial contribution to the LBE method is also made through the development of a new, generalized lattice Boltzmann equation constructed in the moment space in order to improve the computational stability, detailed theoretical analysis on the stability, dispersion, and dissipation characteristics of the LBE method, and computational studies of high Reynolds number flows with singular gradients. Finally, a finite difference-based lattice Boltzmann method is

  6. Structure and Optimum Luminescence for Nearly Block-Like LaOCl:Eu3+ Nanoparticles.

    PubMed

    Lv, Li; Zhai, Hao; Liu, Xiaoqing; Su, Yiguo; Wang, Xiaojing

    2016-04-01

    In this work, we report a simple method for the synthesis of block-like Eu3+ doping LaOCl nanophosphors with different doping content. It was found that the average grain diameter of Eu3+ doping LaOCl samples decreased with increasing Eu3+ doping concentration. The lattice volume shrinked due to different response for different axial under high pressure that led to lower lattice symmetry of LaOCl:Eu3+. The emission of LaOCI:Eu3+ increased with the increasing Eu3+ concentration due to the lower local symmetry, which also led to a gradual reduction in lifetime. PMID:27451710

  7. Large-Scale, Exhaustive Lattice-Based Structural Auditing of SNOMED CT

    NASA Astrophysics Data System (ADS)

    Zhang, Guo-Qiang

    One criterion for the well-formedness of ontologies is that their hierarchical structure form a lattice. Formal Concept Analysis (FCA) has been used as a technique for assessing the quality of ontologies, but is not scalable to large ontologies such as SNOMED CT. We developed a methodology called Lattice-based Structural Auditing (LaSA), for auditing biomedical ontologies, implemented through automated SPARQL queries, in order to exhaustively identify all non-lattice pairs in SNOMED CT. The percentage of non-lattice pairs ranges from 0 to 1.66 among the 19 SNOMED CT hierarchies. Preliminary manual inspection of a limited portion of the 518K non-lattice pairs, among over 34 million candidate pairs, revealed inconsistent use of precoordination in SNOMED CT, but also a number of false positives. Our results are consistent with those based on FCA, with the advantage that the LaSA computational pipeline is scalable and applicable to ontological systems consisting mostly of taxonomic links. This work is based on collaboration with Olivier Bodenreider from the National Library of Medicine, Bethesda, USA.

  8. Magnetic structure of light nuclei from lattice QCD

    SciTech Connect

    Chang, Emmanuel; Detmold, William; Orginos, Kostas; Parreño, Assumpta; Savage, Martin J.; Tiburzi, Brian C.; Beane, Silas R.

    2015-12-09

    Lattice QCD with background magnetic fields is used to calculate the magnetic moments and magnetic polarizabilities of the nucleons and of light nuclei with $A\\le4$, along with the cross-section for the $M1$ transition $np\\rightarrow d\\gamma$, at the flavor SU(3)-symmetric point where the pion mass is $m_\\pi\\sim 806$ MeV. These magnetic properties are extracted from nucleon and nuclear energies in six uniform magnetic fields of varying strengths. The magnetic moments are presented in a recent Letter. For the charged states, the extraction of the polarizability requires careful treatment of Landau levels, which enter non-trivially in the method that is employed. The nucleon polarizabilities are found to be of similar magnitude to their physical values, with $\\beta_p=5.22(+0.66/-0.45)(0.23) \\times 10^{-4}$ fm$^3$ and $\\beta_n=1.253(+0.056/-0.067)(0.055) \\times 10^{-4}$ fm$^3$, exhibiting a significant isovector component. The dineutron is bound at these heavy quark masses and its magnetic polarizability, $\\beta_{nn}=1.872(+0.121/-0.113)(0.082) \\times 10^{-4}$ fm$^3$ differs significantly from twice that of the neutron. A linear combination of deuteron scalar and tensor polarizabilities is determined by the energies of the $j_z=\\pm 1$ deuteron states, and is found to be $\\beta_{d,\\pm 1}=4.4(+1.6/-1.5)(0.2) \\times 10^{-4}$ fm$^3$. The magnetic polarizabilities of the three-nucleon and four-nucleon systems are found to be positive and similar in size to those of the proton, $\\beta_{^{3}\\rm He}=5.4(+2.2/-2.1)(0.2) \\times 10^{-4}$ fm$^3$, $\\beta_{^{3}\\rm H}=2.6(1.7)(0.1) \\times 10^{-4}$ fm$^3$, $\\beta_{^{4}\\rm He}=3.4(+2.0/-1.9)(0.2) \\times 10^{-4}$ fm$^3$. Mixing between the $j_z=0$ deuteron state and the spin-singlet $np$ state induced by the background magnetic field is used to extract the short-distance two-nucleon counterterm, ${\\bar L}_1$, of the pionless effective theory for $NN$ systems (equivalent to the meson-exchange current

  9. Magnetic structure of light nuclei from lattice QCD

    DOE PAGESBeta

    Chang, Emmanuel; Detmold, William; Orginos, Kostas; Parreño, Assumpta; Savage, Martin J.; Tiburzi, Brian C.; Beane, Silas R.

    2015-12-09

    Lattice QCD with background magnetic fields is used to calculate the magnetic moments and magnetic polarizabilities of the nucleons and of light nuclei withmore » $$A\\le4$$, along with the cross-section for the $M1$ transition $$np\\rightarrow d\\gamma$$, at the flavor SU(3)-symmetric point where the pion mass is $$m_\\pi\\sim 806$$ MeV. These magnetic properties are extracted from nucleon and nuclear energies in six uniform magnetic fields of varying strengths. The magnetic moments are presented in a recent Letter. For the charged states, the extraction of the polarizability requires careful treatment of Landau levels, which enter non-trivially in the method that is employed. The nucleon polarizabilities are found to be of similar magnitude to their physical values, with $$\\beta_p=5.22(+0.66/-0.45)(0.23) \\times 10^{-4}$$ fm$^3$ and $$\\beta_n=1.253(+0.056/-0.067)(0.055) \\times 10^{-4}$$ fm$^3$, exhibiting a significant isovector component. The dineutron is bound at these heavy quark masses and its magnetic polarizability, $$\\beta_{nn}=1.872(+0.121/-0.113)(0.082) \\times 10^{-4}$$ fm$^3$ differs significantly from twice that of the neutron. A linear combination of deuteron scalar and tensor polarizabilities is determined by the energies of the $$j_z=\\pm 1$$ deuteron states, and is found to be $$\\beta_{d,\\pm 1}=4.4(+1.6/-1.5)(0.2) \\times 10^{-4}$$ fm$^3$. The magnetic polarizabilities of the three-nucleon and four-nucleon systems are found to be positive and similar in size to those of the proton, $$\\beta_{^{3}\\rm He}=5.4(+2.2/-2.1)(0.2) \\times 10^{-4}$$ fm$^3$, $$\\beta_{^{3}\\rm H}=2.6(1.7)(0.1) \\times 10^{-4}$$ fm$^3$, $$\\beta_{^{4}\\rm He}=3.4(+2.0/-1.9)(0.2) \\times 10^{-4}$$ fm$^3$. Mixing between the $j_z=0$ deuteron state and the spin-singlet $np$ state induced by the background magnetic field is used to extract the short-distance two-nucleon counterterm, $${\\bar L}_1$$, of the pionless effective theory for $NN$ systems (equivalent to the

  10. Surface structures of cerium oxide nanocrystalline particles from the size dependence of the lattice parameters

    NASA Astrophysics Data System (ADS)

    Tsunekawa, S.; Ito, S.; Kawazoe, Y.

    2004-10-01

    Cerium oxide nanocrystalline particles are synthesized and monodispersed in the size range from 2 to 8nm in diameter. The dependence of the lattice parameters on particle size is obtained by x-ray and electron diffraction analyses. The size dependence well coincides with the estimation based on the assumption that the surface is composed of one layer of Ce2O3 and the inside consists of CeO2. The effect of particle size on lattice parameters is discussed from the differences in the fabrication method and the surface structure.

  11. Adaptive identification and control of structural dynamics systems using recursive lattice filters

    NASA Technical Reports Server (NTRS)

    Sundararajan, N.; Montgomery, R. C.; Williams, J. P.

    1985-01-01

    A new approach for adaptive identification and control of structural dynamic systems by using least squares lattice filters thar are widely used in the signal processing area is presented. Testing procedures for interfacing the lattice filter identification methods and modal control method for stable closed loop adaptive control are presented. The methods are illustrated for a free-free beam and for a complex flexible grid, with the basic control objective being vibration suppression. The approach is validated by using both simulations and experimental facilities available at the Langley Research Center.

  12. Parallel Block Structured Adaptive Mesh Refinement on Graphics Processing Units

    SciTech Connect

    Beckingsale, D. A.; Gaudin, W. P.; Hornung, R. D.; Gunney, B. T.; Gamblin, T.; Herdman, J. A.; Jarvis, S. A.

    2014-11-17

    Block-structured adaptive mesh refinement is a technique that can be used when solving partial differential equations to reduce the number of zones necessary to achieve the required accuracy in areas of interest. These areas (shock fronts, material interfaces, etc.) are recursively covered with finer mesh patches that are grouped into a hierarchy of refinement levels. Despite the potential for large savings in computational requirements and memory usage without a corresponding reduction in accuracy, AMR adds overhead in managing the mesh hierarchy, adding complex communication and data movement requirements to a simulation. In this paper, we describe the design and implementation of a native GPU-based AMR library, including: the classes used to manage data on a mesh patch, the routines used for transferring data between GPUs on different nodes, and the data-parallel operators developed to coarsen and refine mesh data. We validate the performance and accuracy of our implementation using three test problems and two architectures: an eight-node cluster, and over four thousand nodes of Oak Ridge National Laboratory’s Titan supercomputer. Our GPU-based AMR hydrodynamics code performs up to 4.87× faster than the CPU-based implementation, and has been scaled to over four thousand GPUs using a combination of MPI and CUDA.

  13. Silicon network structure and 29Si spin-lattice relaxation in amorphous hydrogenated silicon

    NASA Astrophysics Data System (ADS)

    Cheung, Man Ken; Petrich, Mark A.

    1992-04-01

    We report a NMR study of amorphous hydrogenated silicon (a-Si:H) that measures the 29Si spin-lattice relaxation time T1. Measurements of 29Si T1 are useful in learning about the silicon network structure and the localized states within the mobility gap. Coupling to paramagnetic dangling bonds is the predominant 29Si spin-lattice relaxation mechanism in a-Si:H. Spin flipping of paramagnetic electrons, caused by coupling to the lattice, produces fluctuating local fields that stimulate nuclear spin-lattice relaxation. By comparing our experimental results with existing theory, we find that dangling bonds are randomly distributed in device-quality materials but are inhomogeneously distributed in non-device-quality materials. We also find that there are two simultaneously occurring dangling-bond spin-lattice relaxation mechanisms: one through the spin-orbit coupling modulated by thermal excitation of ``two-level systems,'' and the other through hopping conduction between localized states near the Fermi level. Simple chemical-shift measurements are also helpful in characterizing a-Si:H. We find that the 29Si resonance shifts upfield with increasing microstructure in the material.

  14. Strain-induced structural phase transition of a Ni lattice through dissolving Ta solute atoms

    NASA Astrophysics Data System (ADS)

    Zhang, Q.; Lai, W. S.; Liu, B. X.

    2001-06-01

    The structural phase transition of a single-crystal Ni lattice upon dissolving Ta solute atoms is investigated by means of molecular-dynamics simulations with a realistic n-body Ni-Ta potential. It is found that when the solute concentration is within 9-19 at. % of Ta, the accumulated strain results in a martensitic phase transition, i.e., face-centered-cubic (fcc) Ni transforms into a face-centered-orthorhombic-(fco) like structure through shearing, and that when the solute concentration is over 21 at. % of Ta, the Ni lattice collapses and turns into an amorphous state. Comparatively, for the case of an initial hcp Ni lattice, the same martensitic and amorphization transitions also take place. The former hcp-fco transition, however, is mainly through atomic rearrangement as well as readjustment of lattice parameters, and the resultant state is almost perfect single crystal with no shearing bands. Besides, the above structural transitions are frequently in association with a dramatic softening in shear elastic moduli.

  15. High-Pressure Crystal Structure, Lattice Vibrations, and Band Structure of BiSbO4.

    PubMed

    Errandonea, Daniel; Muñoz, Alfonso; Rodríguez-Hernández, Placida; Gomis, Oscar; Achary, S Nagabhusan; Popescu, Catalin; Patwe, Sadeque J; Tyagi, Avesh K

    2016-05-16

    The high-pressure crystal structure, lattice-vibrations, and electronic band structure of BiSbO4 were studied by ab initio simulations. We also performed Raman spectroscopy, infrared spectroscopy, and diffuse-reflectance measurements, as well as synchrotron powder X-ray diffraction. High-pressure X-ray diffraction measurements show that the crystal structure of BiSbO4 remains stable up to at least 70 GPa, unlike other known MTO4-type ternary oxides. These experiments also give information on the pressure dependence of the unit-cell parameters. Calculations properly describe the crystal structure of BiSbO4 and the changes induced by pressure on it. They also predict a possible high-pressure phase. A room-temperature pressure-volume equation of state is determined, and the effect of pressure on the coordination polyhedron of Bi and Sb is discussed. Raman- and infrared-active phonons were measured and calculated. In particular, calculations provide assignments for all the vibrational modes as well as their pressure dependence. In addition, the band structure and electronic density of states under pressure were also calculated. The calculations combined with the optical measurements allow us to conclude that BiSbO4 is an indirect-gap semiconductor, with an electronic band gap of 2.9(1) eV. Finally, the isothermal compressibility tensor for BiSbO4 is given at 1.8 GPa. The experimental (theoretical) data revealed that the direction of maximum compressibility is in the (0 1 0) plane at ∼33° (38°) to the c-axis and 47° (42°) to the a-axis. The reliability of the reported results is supported by the consistency between experiments and calculations.

  16. High-Pressure Crystal Structure, Lattice Vibrations, and Band Structure of BiSbO4.

    PubMed

    Errandonea, Daniel; Muñoz, Alfonso; Rodríguez-Hernández, Placida; Gomis, Oscar; Achary, S Nagabhusan; Popescu, Catalin; Patwe, Sadeque J; Tyagi, Avesh K

    2016-05-16

    The high-pressure crystal structure, lattice-vibrations, and electronic band structure of BiSbO4 were studied by ab initio simulations. We also performed Raman spectroscopy, infrared spectroscopy, and diffuse-reflectance measurements, as well as synchrotron powder X-ray diffraction. High-pressure X-ray diffraction measurements show that the crystal structure of BiSbO4 remains stable up to at least 70 GPa, unlike other known MTO4-type ternary oxides. These experiments also give information on the pressure dependence of the unit-cell parameters. Calculations properly describe the crystal structure of BiSbO4 and the changes induced by pressure on it. They also predict a possible high-pressure phase. A room-temperature pressure-volume equation of state is determined, and the effect of pressure on the coordination polyhedron of Bi and Sb is discussed. Raman- and infrared-active phonons were measured and calculated. In particular, calculations provide assignments for all the vibrational modes as well as their pressure dependence. In addition, the band structure and electronic density of states under pressure were also calculated. The calculations combined with the optical measurements allow us to conclude that BiSbO4 is an indirect-gap semiconductor, with an electronic band gap of 2.9(1) eV. Finally, the isothermal compressibility tensor for BiSbO4 is given at 1.8 GPa. The experimental (theoretical) data revealed that the direction of maximum compressibility is in the (0 1 0) plane at ∼33° (38°) to the c-axis and 47° (42°) to the a-axis. The reliability of the reported results is supported by the consistency between experiments and calculations. PMID:27128858

  17. Research of hail impact on aircraft wheel door with lattice hybrid structure

    NASA Astrophysics Data System (ADS)

    Li, Shengze; Jin, Feng; Zhang, Weihua; Meng, Xuanzhu

    2016-09-01

    Aimed at a long lasting issue of hail impact on aircraft structures and aviation safety due to its high speed, the resistance performance of hail impact on the wheel door of aircraft with lattice hybrid structure is investigated. The proper anti-hail structure can be designed both efficiency and precision based on this work. The dynamic responses of 8 different sandwich plates in diverse impact speed are measured. Smoothed Particle Hydrodynamic (SPH) method is introduced to mimic the speciality of solid-liquid mixture trait of hailstone during the impact process. The deformation and damage degree of upper and lower panel of sandwich plate are analysed. The application range and failure mode for the relevant structure, as well as the energy absorbing ratio between lattice structure and aluminium foam are summarized. Results show that the tetrahedral sandwich plate with aluminium foam core is confirmed the best for absorbing energy. Furthermore, the high absorption characteristics of foam material enhance the capability of the impact resistance for the composition with lattice structure without increasing the structure surface density. The results of study are of worth to provide a reliable basis for reduced weight aircraft wheel door.

  18. Observation of Nonlinear Looped Band Structure of Bose-Einstein condensates in an optical lattice

    NASA Astrophysics Data System (ADS)

    Goldschmidt, Elizabeth; Koller, Silvio; Brown, Roger; Wyllie, Robert; Wilson, Ryan; Porto, Trey

    2016-05-01

    We study experimentally the stability of excited, interacting states of bosons in a double-well optical lattice in regimes where the nonlinear interactions are expected to induce ``swallow-tail'' looped band structure. By carefully preparing different initial coherent states and observing their subsequent decay, we observe distinct decay rates, which provide direct evidence for multi-valued band structure. The double well lattice both stabilizes the looped band structure and allows for dynamic preparation of different initial states, including states within the loop structure. We confirm our state preparation procedure with dynamic Gross-Pitaevskii calculations. The excited loop states are found to be more stable than dynamically unstable ground states, but decay faster than expected based on a mean-field stability calculation, indicating the importance of correlations beyond a mean-field description. Now at Georgia Tech Research Institute.

  19. Lattice dynamics and electronic structure of mixed halofluoride scintillators under high pressure

    SciTech Connect

    Kanchana, V.; Yedukondalu, N.; Vaitheeswaran, G.

    2015-06-24

    We report the structural, lattice dynamics and electronic structure of mixed halo-fluoride scintillators MClF (M = Ca, Sr) based on density functional theory within generalized gradient approximation. The pressure dependent structural parameters and zone centered phonon frequencies are in reasonable agreement with the available experimental data. Both the structures are dynamically stable up to 50 GPa. MClF compounds are found to have a direct band gap along Γ−Γ direction at ambient as well as under pressure. It is found that these materials can serve as good storage phosphors in the low pressure region from the calculated electronic structure and optical spectra.

  20. Lattice QCD

    SciTech Connect

    Bornyakov, V.G.

    2005-06-01

    Possibilities that are provided by a lattice regularization of QCD for studying nonperturbative properties of QCD are discussed. A review of some recent results obtained from computer calculations in lattice QCD is given. In particular, the results for the QCD vacuum structure, the hadron mass spectrum, and the strong coupling constant are considered.

  1. Nebulisation on a disposable array structured with phononic lattices.

    PubMed

    Reboud, Julien; Wilson, Rab; Zhang, Yi; Ismail, Mohd H; Bourquin, Yannyk; Cooper, Jonathan M

    2012-04-01

    We demonstrate the use of a phononic crystal to enable the nebulisation of liquid droplets from low-cost disposable arrays, using surface acoustic waves (SAW). The SAWs were generated using interdigitated transducers (IDT) on a piezoelectric surface (LiNbO(3)) and the acoustic waves were coupled into a disposable phononic crystal structure, referred to as a superstrate. Using its excellent reflecting properties, the phononic structures confined the acoustic field within the superstrate, resulting in the concentration of the acoustic energy, in a manner controllable by the excitation frequency. We show that this capability mitigates against coupling losses incurred by the use of a disposable superstrate, greatly reducing the time needed to nebulise a drop of water with respect to an unstructured superstrate for a given power. We also demonstrate that by changing the excitation frequency, it is possible to change the spatial position at which the acoustic energy is concentrated, providing a means to specifically nebulise drops across an array. These results open up a promising future for the use of phonofluidics in high-throughput sample handling applications, such as drug delivery or the "soft" transfer of samples to a mass spectrometer in the field of proteomics. PMID:22327572

  2. Ferromagnetic resonance and resonance modes in kagome lattices: From an open to a closed kagome structure

    NASA Astrophysics Data System (ADS)

    Dubowik, J.; Kuświk, P.; Matczak, M.; Bednarski, W.; Stobiecki, F.; Aleshkevych, P.; Szymczak, H.; Kisielewski, M.; Kisielewski, J.

    2016-06-01

    We present ferromagnetic resonance (FMR) investigations of 20 nm thick permalloy (Ni80Fe20 ) elements (width W =200 nm, length L =470 nm, period a =500 nm) arranged in open and closed artificial kagome lattices. The measurements were done at 9.4 and 34 GHz to ensure a saturated or near-saturated magnetic state of the kagome structures. The FMR data are analyzed in the framework of an analytical macrospin model which grasps the essential features of the bulk and edge modes at these microwave frequencies and is in agreement with the results of micromagnetic simulations. Polar plots of the resonance fields versus the field angle made by the direction of the magnetic field with respect to the main symmetry directions of the kagome lattice are compared with the results of the analytical model. The measured FMR spectra with a sixfold rotational symmetry qualitatively reproduce the structure expected from the theory. Magnetic dipolar interactions between the elements of the kagome lattices result in the mixing of edge and bulklike excitations at 9.4 GHz and in a systematic deviation from the model, especially for the closed kagome lattice.

  3. Impact of internal crystalline boundaries on lattice thermal conductivity: Importance of boundary structure and spacing

    SciTech Connect

    Aghababaei, Ramin Anciaux, Guillaume; Molinari, Jean-François

    2014-11-10

    The low thermal conductivity of nano-crystalline materials is commonly explained via diffusive scattering of phonons by internal boundaries. In this study, we have quantitatively studied phonon-crystalline boundaries scattering and its effect on the overall lattice thermal conductivity of crystalline bodies. Various types of crystalline boundaries such as stacking faults, twins, and grain boundaries have been considered in FCC crystalline structures. Accordingly, the specularity coefficient has been determined for different boundaries as the probability of the specular scattering across boundaries. Our results show that in the presence of internal boundaries, the lattice thermal conductivity can be characterized by two parameters: (1) boundary spacing and (2) boundary excess free volume. We show that the inverse of the lattice thermal conductivity depends linearly on a non-dimensional quantity which is the ratio of boundary excess free volume over boundary spacing. This shows that phonon scattering across crystalline boundaries is mainly a geometrically favorable process rather than an energetic one. Using the kinetic theory of phonon transport, we present a simple analytical model which can be used to evaluate the lattice thermal conductivity of nano-crystalline materials where the ratio can be considered as an average density of excess free volume. While this study is focused on FCC crystalline materials, where inter-atomic potentials and corresponding defect structures have been well studied in the past, the results would be quantitatively applicable for semiconductors in which heat transport is mainly due to phonon transport.

  4. Detailed design of a lattice composite fuselage structure by a mixed optimization method

    NASA Astrophysics Data System (ADS)

    Liu, D.; Lohse-Busch, H.; Toropov, V.; Hühne, C.; Armani, U.

    2016-10-01

    In this article, a procedure for designing a lattice fuselage barrel is developed. It comprises three stages: first, topology optimization of an aircraft fuselage barrel is performed with respect to weight and structural performance to obtain the conceptual design. The interpretation of the optimal result is given to demonstrate the development of this new lattice airframe concept for the fuselage barrel. Subsequently, parametric optimization of the lattice aircraft fuselage barrel is carried out using genetic algorithms on metamodels generated with genetic programming from a 101-point optimal Latin hypercube design of experiments. The optimal design is achieved in terms of weight savings subject to stability, global stiffness and strain requirements, and then verified by the fine mesh finite element simulation of the lattice fuselage barrel. Finally, a practical design of the composite skin complying with the aircraft industry lay-up rules is presented. It is concluded that the mixed optimization method, combining topology optimization with the global metamodel-based approach, allows the problem to be solved with sufficient accuracy and provides the designers with a wealth of information on the structural behaviour of the novel anisogrid composite fuselage design.

  5. A firefly-inspired method for protein structure prediction in lattice models.

    PubMed

    Maher, Brian; Albrecht, Andreas A; Loomes, Martin; Yang, Xin-She; Steinhöfel, Kathleen

    2014-01-07

    We introduce a Firefly-inspired algorithmic approach for protein structure prediction over two different lattice models in three-dimensional space. In particular, we consider three-dimensional cubic and three-dimensional face-centred-cubic (FCC) lattices. The underlying energy models are the Hydrophobic-Polar (H-P) model, the Miyazawa-Jernigan (M-J) model and a related matrix model. The implementation of our approach is tested on ten H-P benchmark problems of a length of 48 and ten M-J benchmark problems of a length ranging from 48 until 61. The key complexity parameter we investigate is the total number of objective function evaluations required to achieve the optimum energy values for the H-P model or competitive results in comparison to published values for the M-J model. For H-P instances and cubic lattices, where data for comparison are available, we obtain an average speed-up over eight instances of 2.1, leaving out two extreme values (otherwise, 8.8). For six M-J instances, data for comparison are available for cubic lattices and runs with a population size of 100, where, a priori, the minimum free energy is a termination criterion. The average speed-up over four instances is 1.2 (leaving out two extreme values, otherwise 1.1), which is achieved for a population size of only eight instances. The present study is a test case with initial results for ad hoc parameter settings, with the aim of justifying future research on larger instances within lattice model settings, eventually leading to the ultimate goal of implementations for off-lattice models.

  6. Crystal structure of human CRMP-4: correction of intensities for lattice-translocation disorder

    SciTech Connect

    Ponnusamy, Rajesh; Lebedev, Andrey A.; Pahlow, Steffen; Lohkamp, Bernhard

    2014-06-01

    Crystals of human CRMP-4 showed severe lattice-translocation disorder. Intensities were demodulated using the so-called lattice-alignment method and a new more general method with simplified parameterization, and the structure is presented. Collapsin response mediator proteins (CRMPs) are cytosolic phosphoproteins that are mainly involved in neuronal cell development. In humans, the CRMP family comprises five members. Here, crystal structures of human CRMP-4 in a truncated and a full-length version are presented. The latter was determined from two types of crystals, which were either twinned or partially disordered. The crystal disorder was coupled with translational NCS in ordered domains and manifested itself with a rather sophisticated modulation of intensities. The data were demodulated using either the two-lattice treatment of lattice-translocation effects or a novel method in which demodulation was achieved by independent scaling of several groups of intensities. This iterative protocol does not rely on any particular parameterization of the modulation coefficients, but uses the current refined structure as a reference. The best results in terms of R factors and map correlation coefficients were obtained using this new method. The determined structures of CRMP-4 are similar to those of other CRMPs. Structural comparison allowed the confirmation of known residues, as well as the identification of new residues, that are important for the homo- and hetero-oligomerization of these proteins, which are critical to nerve-cell development. The structures provide further insight into the effects of medically relevant mutations of the DPYSL-3 gene encoding CRMP-4 and the putative enzymatic activities of CRMPs.

  7. Nucleon structure in lattice QCD with dynamical domain-wall fermions quarks

    SciTech Connect

    Huey-Wen Lin; Shigemi Ohta

    2006-07-23

    We report RBC and RBC/UKQCD lattice QCD numerical calculations of nucleon electroweak matrix elements with dynamical domain-wall fermions (DWF) quarks. The first, RBC, set of dynamical DWF ensembles employs two degenerate flavors of DWF quarks and the DBW2 gauge action. Three sea quark mass values of 0.04, 0.03 and 0.02 in lattice units are used with about 200 gauge configurations each. The lattice cutoff is about 1.7 GeV and the spatial volume is about (1.9 fm){sup 3}. Despite the small volume, the ratio of the isovector vector and axial charges g{sub A}/g{sub V} and that of structure function moments {sub u-d}/{sub {Delta} u - {Delta} d} are in agreement with experiment, and show only very mild quark mass dependence. The second, RBC/UK, set of ensembles employs one strange and two degenerate (up and down) dynamical DWF quarks and Iwasaki gauge action. The strange quark mass is set at 0.04, and three up/down mass values of 0.03, 0.02 and 0.01 in lattice units are used. The lattice cutoff is about 1.6 GeV and the spatial volume is about (3.0 fm){sup 3}. Even with preliminary statistics of 25-30 gauge configurations, the ratios g{sub A}/g{sub V} and {sub u-d}/{sub {Delta} u - {Delta} d} are consistent with experiment and show only very mild quark mass dependence. Another structure function moment, d{sub 1}, though yet to be renormalized, appears small in both sets.

  8. NUCLEON STRUCTURE IN LATTICE QCD WITH DYNAMICAL DOMAIN--WALL FERMIONS QUARKS.

    SciTech Connect

    LIN H.-W.; OHTA, S.

    2006-10-02

    We report RBC and RBC/UKQCD lattice QCD numerical calculations of nucleon electroweak matrix elements with dynamical domain-wall fermions (DWF) quarks. The first, RBC, set of dynamical DWF ensembles employs two degenerate flavors of DWF quarks and the DBW2 gauge action. Three sea quark mass values of 0.04, 0.03 and 0.02 in lattice units are used with 220 gauge configurations each. The lattice cutoff is a{sup -1} {approx} 1.7GeV and the spatial volume is about (1.9fm){sup 3}. Despite the small volume, the ratio of the isovector vector and axial charges g{sub A}/g{sub V} and that of structure function moments {sub u-d}/{sub {Delta}u-{Delta}d} are in agreement with experiment, and show only very mild quark mass dependence. The second, RBC/UK, set of ensembles employs one strange and two degenerate (up and down) dynamical DWF quarks and Iwasaki gauge action. The strange quark mass is set at 0.04, and three up/down mass values of 0.03, 0.02 and 0.01 in lattice units are used. The lattice cutoff is a{sup -1} {approx} 1.6GeV and the spatial volume is about (3.0fm){sup 3}. Even with preliminary statistics of 25-30 gauge configurations, the ratios g{sub A}/g{sub V} and {sub u-d}/{sub {Delta}u-{Delta}d} are consistent with experiment and show only very mild quark mass dependence. Another structure function moment, d{sub 1}, though yet to be renormalized, appears small in both sets.

  9. Thermodynamics of sublimation, crystal lattice energies, and crystal structures of racemates and enantiomers: (+)- and (+/-)-ibuprofen.

    PubMed

    Perlovich, German L; Kurkov, Sergey V; Hansen, Lars Kr; Bauer-Brandl, Annette

    2004-03-01

    Thermodynamic differences between ibuprofen (IBP) racemate and the (+)-enantiomer were studied by X-ray diffraction, thermoanalysis, and crystal energy calculations. The thermodynamic functions of sublimation (as a measure of crystal lattice energy) were obtained by the transpiration method. The sublimation enthalpies (DeltaH(sub)) of (+/-)-IBP and (+)-IBP are 115.8 +/- 0.6 and 107.4 +/- 0.5 kJ. mol(-1), respectively. Using the temperature dependency of the saturated vapor pressure, the relative fractions of enthalpy and entropy of the sublimation process were calculated, and the sublimation process for both the racemate and the enantiomer was found to be enthalpy driven (62%). Two different force fields, Mayo et al. (M) and Gavezzotti (G), were used for comparative analysis of crystal lattice energies. Both force fields revealed that the van der Waals term contributes more to the packing energy in (+)-IBP than in (+/-)-IBP. The hydrogen bonding energy, however, contributes at 29.7 and 32.3% to the total crystal lattice energy in (+)-IBP and (+/-)-IBP (M), respectively. Furthermore, different structure fragments of the IBP molecule were analyzed with respect to their contribution to nonbonded van der Waals interactions. The effect of the C-H distance on the van der Waals term of the crystal lattice energy was also studied.

  10. Enhanced hybrid search algorithm for protein structure prediction using the 3D-HP lattice model.

    PubMed

    Zhou, Changjun; Hou, Caixia; Zhang, Qiang; Wei, Xiaopeng

    2013-09-01

    The problem of protein structure prediction in the hydrophobic-polar (HP) lattice model is the prediction of protein tertiary structure. This problem is usually referred to as the protein folding problem. This paper presents a method for the application of an enhanced hybrid search algorithm to the problem of protein folding prediction, using the three dimensional (3D) HP lattice model. The enhanced hybrid search algorithm is a combination of the particle swarm optimizer (PSO) and tabu search (TS) algorithms. Since the PSO algorithm entraps local minimum in later evolution extremely easily, we combined PSO with the TS algorithm, which has properties of global optimization. Since the technologies of crossover and mutation are applied many times to PSO and TS algorithms, so enhanced hybrid search algorithm is called the MCMPSO-TS (multiple crossover and mutation PSO-TS) algorithm. Experimental results show that the MCMPSO-TS algorithm can find the best solutions so far for the listed benchmarks, which will help comparison with any future paper approach. Moreover, real protein sequences and Fibonacci sequences are verified in the 3D HP lattice model for the first time. Compared with the previous evolutionary algorithms, the new hybrid search algorithm is novel, and can be used effectively to predict 3D protein folding structure. With continuous development and changes in amino acids sequences, the new algorithm will also make a contribution to the study of new protein sequences. PMID:23824509

  11. Structure determination of the 1918 H1N1 neuraminidase from a crystal with lattice-translocation defects

    SciTech Connect

    Zhu, Xueyong; Xu, Xiaojin; Wilson, Ian A.

    2008-08-01

    The structure of the 1918 H1N1 neuraminidase was determined to 1.65 Å from crystals with a lattice-translocation defect using uncorrected, as well as corrected, diffraction data. Few examples of macromolecular crystals containing lattice-translocation defects have been published in the literature. Lattice translocation and twinning are believed to be two common but different crystal-growth anomalies. While the successful use of twinned data for structure determination has become relatively routine in recent years, structure determination of crystals with lattice-translocation defects has not often been reported. To date, only four protein crystal structures containing such a crystal defect have been determined, using corrected, but not uncorrected, intensity data. In this report, the crystallization, structure determination and refinement of N1 neuraminidase derived from the 1918 H1N1 influenza virus (18NA) at 1.65 Å resolution are described. The crystal was indexed in space group C222{sub 1}, with unit-cell parameters a = 117.7, b = 138.5, c = 117.9 Å, and the structure was solved by molecular replacement. The lattice-translocation vector in the 18NA crystal was (0, 1/2, 1/2) or its equivalent vector (1/2, 0, 1/2) owing to the C lattice symmetry. Owing to this special lattice-translocation vector in space group C222{sub 1}, structure refinement could be achieved in two different ways: using corrected or uncorrected diffraction data. In the refinement with uncorrected data, a composite model was built to represent the molecules in the translated and untranslated layers, respectively. This composite structure model provided a unique example to examine how the molecules were arranged in the two lattice domains resulting from lattice-translocation defects.

  12. Significant role of structural fractures in Ren-Qiu buried-block oil field, eastern China

    SciTech Connect

    Fei, Q.; Xie-Pei, W.

    1983-03-01

    Ren-qui oil field is in a buried block of Sinian (upper Proterozoic) rocks located in the Ji-zhong depression of the western Bohai Bay basin in eastern China. The main reservoir consists of Sinian dolomite rocks. It is a fault block with a large growth fault on the west side which trends north-northeast with throws of up to 1 km (0.6 mi) or more. The source rocks for the oil are Paleogene age and overlie the Sinian dolomite rocks. The structural fractures are the main factor forming the reservoir of the buried-block oil field. Three structural lines, trending northeast, north-northeast, and northwest, form the regional netted fracture system. The north-northeast growth fault controlled the structural development of the buried block. The block was raised and eroded before the Tertiary sediments were deposited. In the Eocene Epoch, the Ji-zhong depression subsided, but the deposition, faulting, and related uplift of the block happened synchronously as the block was gradually submerged. At the same time, several horizontal and vertical karst zones were formed by the karst water along the netted structural fractures. The Eocene oil source rocks lapped onto the block and so the buried block, with many developed karst fractures, was surrounded by a great thickness of source rocks. As the growth fault developed, the height of the block was increased from 400 m (1300 ft) before the Oligocene to 1300 m (4250 ft) after. As the petroleum was generated, it migrated immediately into the karst fractures of the buried block along the growth fault. The karst-fractured block reservoir has an 800-m (2600-ft) high oil-bearing closure and good connections developed between the karst fractures.

  13. Tunable Encapsulation Structure of Block Copolymer Coated Single-Walled Carbon Nanotubes in Aqueous Solution

    DOE PAGESBeta

    Han, Youngkyu; Ahn, Suk-Kyun; Zhang, Zhe; Smith, Gregory Scott; Do, Changwoo

    2015-05-15

    The nano-sized and shape-tunable molecular building blocks can provide great opportunities for the fabrication of precisely controlled nanostructures. In this work, we have fabricated a molecular building block of single-walled carbon nanotubes (SWNTs) coated by PPO-PEO-PPO block copolymers whose encapsulation structure can be controlled via temperature or addition of small molecules. The structure and optical properties of SWNT-block copolymers have been investigated by small angle neutron scattering (SANS), ultraviolet-visible (UV-vis) spectroscopy, atomic force microscopy (AFM), and molecular dynamics (MD) simulation. The structure of the hydrated block copolymer layer surrounding SWNT can be controlled reversibly by varying temperature as well asmore » by irreversibly adding 5-methylsalicylic acid (5MS). Increasing hydrophobicity of the polymers with temperature and strong tendency of 5MS to interact with both block copolymers and orbitals of the SWNTs are likely to be responsible for the significant structural change of the block copolymer encapsulation layer, from loose corona shell to tightly encapsulating compact shell. These result shows an efficient and simple way to fabricate and manipulate carbon-based nano building blocks in aqueous systems with tunable structure.« less

  14. Tunable Encapsulation Structure of Block Copolymer Coated Single-Walled Carbon Nanotubes in Aqueous Solution

    SciTech Connect

    Han, Youngkyu; Ahn, Suk-Kyun; Zhang, Zhe; Smith, Gregory Scott; Do, Changwoo

    2015-05-15

    The nano-sized and shape-tunable molecular building blocks can provide great opportunities for the fabrication of precisely controlled nanostructures. In this work, we have fabricated a molecular building block of single-walled carbon nanotubes (SWNTs) coated by PPO-PEO-PPO block copolymers whose encapsulation structure can be controlled via temperature or addition of small molecules. The structure and optical properties of SWNT-block copolymers have been investigated by small angle neutron scattering (SANS), ultraviolet-visible (UV-vis) spectroscopy, atomic force microscopy (AFM), and molecular dynamics (MD) simulation. The structure of the hydrated block copolymer layer surrounding SWNT can be controlled reversibly by varying temperature as well as by irreversibly adding 5-methylsalicylic acid (5MS). Increasing hydrophobicity of the polymers with temperature and strong tendency of 5MS to interact with both block copolymers and orbitals of the SWNTs are likely to be responsible for the significant structural change of the block copolymer encapsulation layer, from loose corona shell to tightly encapsulating compact shell. These result shows an efficient and simple way to fabricate and manipulate carbon-based nano building blocks in aqueous systems with tunable structure.

  15. On structural and lattice dynamic stability of LaF3 under high pressure: A first principle study

    NASA Astrophysics Data System (ADS)

    Sahoo, B. D.; Joshi, K. D.; Gupta, Satish C.

    2015-06-01

    Structural and lattice dynamical stability of the LaF3 has been analyzed as a function of hydrostatic compression through first principle electronic band structure calculations. The comparison of enthalpies of various plausible structures calculated at various pressures suggests a phase transition from ambient condition tysonite structure (space group P-3c1) to a primitive orthorhombic structure (space group Pmmn) at a pressure of ˜19.5 GPa, in line with the experimental value of 16 GPa. Further, it is predicted that this phase will remain stable up to 100 GPa (the maximum pressure up to which calculations have been performed in the present work). The theoretically determined equation of state displays a good agreement with experimental data. Various physical quantities such as zero pressure equilibrium volume, bulk modulus, and pressure derivative of bulk modulus have been derived from the theoretically determined equation of state and compared with the available experimental data. Our lattice dynamic calculations correctly demonstrate that at zero pressure the tysonite structure is lattice dynamically stable whereas the Pmmn structure is unstable lattice dynamically. Further, at transition pressure the theoretically calculated phonon spectra clearly show that the Pmmn phase emerges as lattice dynamically stable phase whereas the tysonite structure becomes unstable dynamically, supporting our static lattice calculations.

  16. On structural and lattice dynamic stability of LaF{sub 3} under high pressure: A first principle study

    SciTech Connect

    Sahoo, B. D. Joshi, K. D.; Gupta, Satish C.

    2015-06-24

    Structural and lattice dynamical stability of the LaF3 has been analyzed as a function of hydrostatic compression through first principle electronic band structure calculations. The comparison of enthalpies of various plausible structures calculated at various pressures suggests a phase transition from ambient condition tysonite structure (space group P-3c1) to a primitive orthorhombic structure (space group Pmmn) at a pressure of ∼19.5 GPa, in line with the experimental value of 16 GPa. Further, it is predicted that this phase will remain stable up to 100 GPa (the maximum pressure up to which calculations have been performed in the present work). The theoretically determined equation of state displays a good agreement with experimental data. Various physical quantities such as zero pressure equilibrium volume, bulk modulus, and pressure derivative of bulk modulus have been derived from the theoretically determined equation of state and compared with the available experimental data. Our lattice dynamic calculations correctly demonstrate that at zero pressure the tysonite structure is lattice dynamically stable whereas the Pmmn structure is unstable lattice dynamically. Further, at transition pressure the theoretically calculated phonon spectra clearly show that the Pmmn phase emerges as lattice dynamically stable phase whereas the tysonite structure becomes unstable dynamically, supporting our static lattice calculations.

  17. Effect of lattice defects on the electronic structures and floatability of pyrites

    NASA Astrophysics Data System (ADS)

    Xian, Yong-jun; Wen, Shu-ming; Chen, Xiu-ming; Deng, Jiu-shuai; Liu, Jian

    2012-12-01

    The electronic structures of three types of lattice defects in pyrites (i.e., As-substituted, Co-substituted, and intercrystalline Au pyrites) were calculated using the density functional theory (DFT). In addition, their band structures, density of states, and difference charge density were studied. The effect of the three types of lattice defects on the pyrite floatability was explored. The calculated results showed that the band-gaps of pyrites with Co-substitution and intercrystalline Au decreased significantly, which favors the oxidation of xanthate to dixanthogen and the adsorption of dixanthogen during pyrite flotation. The stability of the pyrites increased in the following order: As-substituted < perfect < Co-substituted < intercrystalline Au. Therefore, As-substituted pyrite is easier to be depressed by intensive oxidization compared to perfect pyrite in a strongly alkaline medium. However, Co-substituted and intercrystalline Au pyrites are more difficult to be depressed compared to perfect pyrite. The analysis of the Mulliken bond population and the electron density difference indicates that the covalence characteristic of the S-Fe bond is larger compared to the S-S bond in perfect pyrite. In addition, the presence of the three types of lattice defects in the pyrite bulk results in an increase in the covalence level of the S-Fe bond and a decrease in the covalence level of the S-S bond, which affect the natural floatability of the pyrites.

  18. Phonon modes of MgB2: super-lattice structures and spectral response.

    PubMed

    Alarco, Jose A; Chou, Alison; Talbot, Peter C; Mackinnon, Ian D R

    2014-11-28

    Micrometre-sized MgB2 crystals of varying quality, synthesized at low temperature and autogenous pressure, are compared using a combination of Raman and infra-red (IR) spectroscopy. These data, which include new peak positions in both spectroscopies for high quality MgB2, are interpreted using DFT calculations on phonon behaviour for symmetry-related structures. Raman and IR activity additional to that predicted by point group analyses of the P6/mmm symmetry are detected. These additional peaks, as well as the overall shapes of calculated phonon dispersion (PD) models are explained by assuming a double super-lattice, consistent with a lower symmetry structure for MgB2. A 2× super-lattice in the c-direction allows a simple correlation of the pair breaking energy and the superconducting gap by activation of corresponding acoustic frequencies. A consistent physical interpretation of these spectra is obtained when the position of a phonon anomaly defines a super-lattice modulation in the a-b plane.

  19. Di-hydrogen contact induced lattice instabilities and structural dynamics in complex hydride perovskites.

    PubMed

    Schouwink, P; Hagemann, H; Embs, J P; D'Anna, V; Černý, R

    2015-07-01

    The structural phase transitions occurring in a series of perovskite-type complex hydrides based on the tetrahydroborate anion BH4(-) are investigated by means of in situ synchrotron x-ray powder diffraction, vibrational spectroscopy, thermal methods and ab initio calculations in the solid state. Structural dynamics of the BH4 anion are followed with quasi-elastic neutron scattering. We show that unexpected temperature-induced lattice instabilities in perovskite-type ACa(BH4)3 (A = K, Rb, Cs) have their origin in close hydridic di-hydrogen contacts. The rich lattice dynamics lead to coupling between internal B-H vibrations and phonons, resulting in distortions in the high-temperature polymorph that are identical in symmetry to well-known instabilities in oxide perovskites, generally condensing at lower temperatures. It is found that anion-substitution BH4(-) <-> (X = Halide) can relax distortions in ACa(BH4)3 by eliminating coulomb repulsive H(-)···H(-) effects. The interesting nature of phase transition in ACa(BH4)3 enters an unexplored field of weak interactions in ceramic-like host lattices and is the principal motivation for this study. Close di-hydrogen contacts suggest new concepts to tailor crystal symmetries in complex hydride perovskites in the future. PMID:26076047

  20. Making waves round a structured cloak: lattices, negative refraction and fringes.

    PubMed

    Colquitt, D J; Jones, I S; Movchan, N V; Movchan, A B; Brun, M; McPhedran, R C

    2013-09-01

    Using the framework of transformation optics, this paper presents a detailed analysis of a non-singular square cloak for acoustic, out-of-plane shear elastic and electromagnetic waves. Analysis of wave propagation through the cloak is presented and accompanied by numerical illustrations. The efficacy of the regularized cloak is demonstrated and an objective numerical measure of the quality of the cloaking effect is provided. It is demonstrated that the cloaking effect persists over a wide range of frequencies. As a demonstration of the effectiveness of the regularized cloak, a Young's double slit experiment is presented. The stability of the interference pattern is examined when a cloaked and uncloaked obstacle are successively placed in front of one of the apertures. This novel link with a well-known quantum mechanical experiment provides an additional method through which the quality of cloaks may be examined. In the second half of the paper, it is shown that an approximate cloak may be constructed using a discrete lattice structure. The efficiency of the approximate lattice cloak is analysed and a series of illustrative simulations presented. It is demonstrated that effective cloaking may be obtained by using a relatively simple lattice structure, particularly, in the low-frequency regime.

  1. Making waves round a structured cloak: lattices, negative refraction and fringes

    PubMed Central

    Colquitt, D. J.; Jones, I. S.; Movchan, N. V.; Movchan, A. B.; Brun, M.; McPhedran, R. C.

    2013-01-01

    Using the framework of transformation optics, this paper presents a detailed analysis of a non-singular square cloak for acoustic, out-of-plane shear elastic and electromagnetic waves. Analysis of wave propagation through the cloak is presented and accompanied by numerical illustrations. The efficacy of the regularized cloak is demonstrated and an objective numerical measure of the quality of the cloaking effect is provided. It is demonstrated that the cloaking effect persists over a wide range of frequencies. As a demonstration of the effectiveness of the regularized cloak, a Young's double slit experiment is presented. The stability of the interference pattern is examined when a cloaked and uncloaked obstacle are successively placed in front of one of the apertures. This novel link with a well-known quantum mechanical experiment provides an additional method through which the quality of cloaks may be examined. In the second half of the paper, it is shown that an approximate cloak may be constructed using a discrete lattice structure. The efficiency of the approximate lattice cloak is analysed and a series of illustrative simulations presented. It is demonstrated that effective cloaking may be obtained by using a relatively simple lattice structure, particularly, in the low-frequency regime. PMID:24062625

  2. The Structural Disorder and Lattice Stability of (Ba,Sr)(Co,Fe)O3 Complex Perovskites

    SciTech Connect

    S.N.Rashkeev

    2011-05-01

    The structural disorder and lattice stability of complex perovskite (Ba,Sr)(Co,Fe)O3, a promising cathode material for solid oxide fuel cells and oxygen permeation membranes, is explored by means of first principles DFT calculations. It is predicted that Ba and Sr ions easily exchange their lattice positions (A-cation disorder) similarly to Co and Fe ions (B-cation disorder). The cation antisite defects (exchange of A- and B-type cations) have a relatively high formation energy. The BSCF is predicted to exist in an equilibrium mixture of several phases and can decompose exothermically into the Ba- and Co-rich hexagonal (Ba,Sr)CoO3 and Sr- and Fe-rich cubic (Ba,Sr)FeO3 perovskites.

  3. Block-copolymer-induced structure formation in microemulsions

    SciTech Connect

    Hilfiker, R.; Eicke, H.F.; Steeb, C.; Hofmeier, U. )

    1991-02-07

    Transient electric birefringence measurements were performed on water/AOT (sodium bis(2-ethylhexyl) sulfosuccinate)/isooctane microemulsions with various amounts of block-copoly(oxyethylene/isoprene/oxyethylene) added. The authors could show that addition of the copolymer leads to a formation of nanodroplet (ND)-copolymer-aggregates. The contributions of NDs and aggregates to the induced birefringence could easily be separated because the NDs exhibited a negative and the aggregates a positive induced birefringence and because the time scales corresponding to the two processes were different.

  4. Tunable multi-wavelength polymer laser based on a triangular-lattice photonic crystal structure

    NASA Astrophysics Data System (ADS)

    Huang, Wenbin; Pu, Donglin; Qiao, Wen; Wan, Wenqiang; Liu, Yanhua; Ye, Yan; Wu, Shaolong; Chen, Linsen

    2016-08-01

    A continuously tunable multi-wavelength polymer laser based on a triangular-lattice photonic crystal cavity is demonstrated. The triangular-lattice resonator was initially fabricated through multiple interference exposure and was then replicated into a low refractive index polymer via UV-nanoimprinting. The blend of a blue-emitting conjugated polymer and a red-emitting one was used as the gain medium. Three periods in the scalene triangular-lattice structure yield stable tri-wavelength laser emission (625.5 nm, 617.4 nm and 614.3 nm) in six different directions. A uniformly aligned liquid crystal (LC) layer was incorporated into the cavity as the top cladding layer. Upon heating, the orientation of LC molecules and thus the effective refractive index of the lasing mode changes which continuously shifts the lasing wavelength. A maximum tuning range of 12.2 nm was observed for the lasing mode at 625.5 nm. This tunable tri-wavelength polymer laser is simple constructed and cost-effective. It may find application in the fields of biosensors and photonic integrated circuits.

  5. Structure Determination of the 1918 H1N1 Neuraminidase From a Crystal With Lattice-Translocation Defects

    SciTech Connect

    Zhu, X.; Xu, X.; Wilson, I.A.

    2009-05-28

    Few examples of macromolecular crystals containing lattice-translocation defects have been published in the literature. Lattice translocation and twinning are believed to be two common but different crystal-growth anomalies. While the successful use of twinned data for structure determination has become relatively routine in recent years, structure determination of crystals with lattice-translocation defects has not often been reported. To date, only four protein crystal structures containing such a crystal defect have been determined, using corrected, but not uncorrected, intensity data. In this report, the crystallization, structure determination and refinement of N1 neuraminidase derived from the 1918 H1N1 influenza virus (18NA) at 1.65 {angstrom} resolution are described. The crystal was indexed in space group C222{sub 1}, with unit-cell parameters a = 117.7, b = 138.5, c = 117.9 {angstrom}, and the structure was solved by molecular replacement. The lattice-translocation vector in the 18NA crystal was (0, 1/2, 1/2) or its equivalent vector (1/2, 0, 1/2) owing to the C lattice symmetry. Owing to this special lattice-translocation vector in space group C222{sub 1}, structure refinement could be achieved in two different ways: using corrected or uncorrected diffraction data. In the refinement with uncorrected data, a composite model was built to represent the molecules in the translated and untranslated layers, respectively. This composite structure model provided a unique example to examine how the molecules were arranged in the two lattice domains resulting from lattice-translocation defects.

  6. Metal-oxide based nanoobjects: reactivity, building blocks for polymeric structures and structural variety

    NASA Astrophysics Data System (ADS)

    Müller, Achim; Roy, Soumyajit

    2002-12-01

    From the unique 'library' of molybdenum-oxide based building blocks/fragments under reducing conditions in aqueous solution a huge variety of nanoobjects, allowing specific reactions at well-defined positions, can be generated. This enables us to perform a new type of nanochemistry. Examples include the well-known molecular big-wheel of the type {Mo176} and big-ball of the type {Mo132} including their derivatives which are considered here. In addition, the by far largest structurally well-characterised cluster having 368 molybdenum atoms with the shape of a lemon is outlined and discussed. The bibliography includes 71 references.

  7. Structural Difference in Superconductive and Nonsuperconductive Bi-S Planes within Bi4O4Bi2S4 Blocks.

    PubMed

    Miura, Akira; Mizuguchi, Yoshikazu; Sugawara, Tsuyoshi; Wang, Yongming; Takei, Takahiro; Kumada, Nobuhiro; Magome, Eisuke; Moriyoshi, Chikako; Kuroiwa, Yoshihiro; Miura, Osuke; Tadanaga, Kiyoharu

    2015-11-01

    The relationship between the structure and superconductivity of Bi4O4S3 powders synthesized by heating under ambient and high pressures was investigated using synchrotron X-ray diffraction, Raman spectroscopy, and transmission electron microscopy (TEM) observation. The Bi4O4S3 powders synthesized under ambient pressure exhibited a strong superconductivity (diamagnetic) signal and zero resistivity below ∼4.5 K, while the Bi4O4S3 powder synthesized by the high-pressure method exhibited a low-intensity signal down to 2 K. Further annealing of the latter Bi4O4S3 powder under ambient pressure led to the development of a strong signal and zero resistivity. The crystal structures of all Bi4O4S3 phases consisted of Bi4O4Bi2S4 blocks including a Bi-S layer and anion(s) sandwiched between Bi4O4Bi2S4 blocks, but minor structural differences were detected. A comparison of the structures of the superconductive and nonsuperconductive Bi4O4S3 samples suggested that the superconductive Bi4O4S3 phases had slightly smaller lattice parameters. The average structures of the superconductive Bi4O4S3 phases were characterized by a slightly shorter and less bent Bi-S plane. Raman spectroscopy detected vibration of the S-O bonds, which can be attributed to sandwiched anion(s) such as SO4(2-). TEM observation showed stacking faults in the superconductive Bi4O4S3 phases, which indicated local fluctuation of the average structures. The observed superconductivity of Bi4O4S3 was discussed based on impurity phases, enhanced hybridization of the px and py orbitals of the Bi-S plane within Bi4O4Bi2S4 blocks, local fluctuation of the average structures, compositional deviation related to suspicious anion(s) sandwiched between Bi4O4Bi2S4 blocks, and the possibility of suppression of the charge-density-wave state by enriched carrier concentrations.

  8. Stability of the fcc structure in block copolymer systems.

    PubMed

    Nonomura, Makiko

    2008-11-19

    The stability of the face-centered cubic (fcc) structure in microphase separated copolymers is investigated by a coarse-grained approach. Direct simulations of the equation for the microphase separation in three dimensions indicate that there is a narrow area above a certain degree of segregation in the phase diagram, where the fcc structure is the most stable structure. By employing the mode expansion, we have confirmed that the fcc structure can form as a metastable structure even in the weak segregation regime.

  9. Limit Analysis for the Mechanical Structure of the ITER Neutron Shielding Block

    NASA Astrophysics Data System (ADS)

    Hao, Junchuan; Song, Yuntao; Du, Shuangsong; Wang, Zhongwei; Xu, Yang; Feng, Changle

    2013-04-01

    The ITER neutron shielding blocks are located between the inner shell and the outer shell of the vacuum vessel (VV) with the main function of providing neutron shielding. Considering the combined loads of the shielding blocks during the plasma operation of the ITER, limit analysis for one typical ferromagnetic (FM) shielding block has been performed and the structural design has been evaluated based on the American Society of Mechanical Engineers (ASME) criterion and European standards. Results show that the collapse load of this shielding block is three times the specified load, which is much higher than the design requirement of 1.25. The structure of this neutron shielding block has a sufficient safety margin.

  10. Thin Filament Structure and the Steric Blocking Model.

    PubMed

    Lehman, William

    2016-04-01

    By interacting with the troponin-tropomyosin complex on myofibrillar thin filaments, Ca2+ and myosin govern the regulatory switching processes influencing contractile activity of mammalian cardiac and skeletal muscles. A possible explanation of the roles played by Ca2+ and myosin emerged in the early 1970s when a compelling "steric model" began to gain traction as a likely mechanism accounting for muscle regulation. In its most simple form, the model holds that, under the control of Ca2+ binding to troponin and myosin binding to actin, tropomyosin strands running along thin filaments either block myosin-binding sites on actin when muscles are relaxed or move away from them when muscles are activated. Evidence for the steric model was initially based on interpretation of subtle changes observed in X-ray fiber diffraction patterns of intact skeletal muscle preparations. Over the past 25 years, electron microscopy coupled with three-dimensional reconstruction directly resolved thin filament organization under many experimental conditions and at increasingly higher resolution. At low-Ca2+, tropomyosin was shown to occupy a "blocked-state" position on the filament, and switched-on in a two-step process, involving first a movement of tropomyosin away from the majority of the myosin-binding site as Ca2+ binds to troponin and then a further movement to fully expose the site when small numbers of myosin heads bind to actin. In this contribution, basic information on Ca2+-regulation of muscle contraction is provided. A description is then given relating the voyage of discovery taken to arrive at the present understanding of the steric regulatory model. PMID:27065174

  11. Flow past an array of catalyst blocks with a honeycomb structure

    SciTech Connect

    Bespalov, A.V.

    1992-07-10

    There is interest in an organized stationary catalyst beds consisting of block catalysts with a honeycomb structure: The flow is directed between vertically positioned blocks, in which the through channels are oriented perpendicularly to the direction of the incident flow ({alpha} = 90{degrees}). Calculations of the flow past a single block of honey comb structure were performed for this case, and it has been shown that the surface of the through channel is accessible to the reaction flow. The authors continued this effort to quantitate the flow with honeycomb catalysts. 9 refs., 2 figs.

  12. Structure and lattice dynamics of PrFe3(BO3)4: Ab initio calculation

    NASA Astrophysics Data System (ADS)

    Chernyshev, V. A.; Nikiforov, A. E.; Petrov, V. P.

    2016-06-01

    The crystal structure and phonon spectrum of PrFe3(BO3)4 are ab initio calculated in the context of the density functional theory. The ion coordinates in the unit cell of a crystal and the lattice parameters are evaluated from the calculations. The types and frequencies of the fundamental vibrations, as well as the line intensities of the IR spectrum, are determined. The elastic constants of the crystal are calculated. A "seed" frequency of the vibration strongly interacting with the electron excitation on the praseodymium ion is obtained for low-frequency A 2 mode. The calculated results are in agreement with the known experimental data.

  13. Structural interpretation of the Chuan-Dian block and surrounding regions using discrete wavelet transform

    NASA Astrophysics Data System (ADS)

    Xuan, Songbai; Shen, Chongyang; Li, Hui; Tan, Hongbo

    2016-07-01

    The Chuan-Dian tectonic block is a transitional zone between the Tibetan Plateau and the South China block. The crustal structure in this region has been studied in several ways, and in this work we present Bouguer gravity anomaly data with which to investigate the Chuan-Dian block and surrounding regions. Regional and local anomalies are decomposed using a method of discrete wavelet transform (DWT), and furthermore, the relief of the Moho is inverted based on the regional anomalies. Results of the transform show that there is a distinct belt of regional anomalies on the east and southeast margins of the Tibetan Plateau. In addition, there are two distinct gradient belts evident in the maps of the local gravity anomalies. The first of these, in the western Indo-China block, has a north-south strike with high anomalies around this belt, and the second is along the Longmenshan fault zone in the eastern margin of the Tibetan Plateau. The Chuan-Dian block can be divided into two discrete parts, separated by a broad and indistinct boundary observed from the fifth-order DWT detail and Moho relief. The DWT details reveal that parallel anomalies existing in the Indo-China block region were induced by subduction of the Burmese block. We conclude that the clockwise rotation of the Chuan-Dian block was synthetically affected by the extrusion of the Tibetan lithosphere and subduction of the Burmese block.

  14. High-Q lattice mode matched structural resonances in terahertz metasurfaces

    NASA Astrophysics Data System (ADS)

    Xu, Ningning; Singh, Ranjan; Zhang, Weili

    2016-07-01

    The quality (Q) factor of metamaterial resonances is limited by the radiative and non-radiative losses. At terahertz frequencies, the dominant loss channel is radiative in nature since the non-radiative losses are low due to high conductivity of metals. Radiative losses could be suppressed by engineering the meta-atom structure. However, such suppression usually occurs at the fundamental resonance mode which is typically a closed mode resonance such as an inductive-capacitive resonance or a Fano resonance. Here, we report an order of magnitude enhancement in Q factor of all the structural eigenresonances of a split-ring resonator fueled by the lattice mode matching. We match the fundamental order diffractive mode to each of the odd and even eigenresonances, thus leading to a tremendous line-narrowing of all the resonances. Such precise tailoring and control of the structural resonances in a metasurface lattice could have potential applications in low-loss devices, sensing, and design of high-Q metamaterial cavities.

  15. The Calculation of the Band Structure in 3D Phononic Crystal with Hexagonal Lattice

    NASA Astrophysics Data System (ADS)

    Aryadoust, Mahrokh; Salehi, H.

    2015-12-01

    In this article, the propagation of acoustic waves in the phononic crystals (PCs) of three dimensions with the hexagonal (HEX) lattice is studied theoretically. The PCs are constituted of nickel (Ni) spheres embedded in epoxy. The calculations of the band structure and the density of states are performed using the plane wave expansion (PWE) method in the irreducible part of the Brillouin zone (BZ). In this study, we analyse the dependence of the band structures inside (the complete band gap width) on c/a and filling fraction in the irreducible part of the first BZ. Also, we have analysed the band structure of the ALHA and MLHKM planes. The results show that the maximum width of absolute elastic band gap (AEBG) (0.045) in the irreducible part of the BZ of HEX lattice is formed for c/a=6 and filling fraction equal to 0.01. In addition, the maximum of the first and second AEBG widths are 0.0884 and 0.0474, respectively, in the MLHKM plane, and the maximum of the first and second AEBG widths are 0.0851 and 0.0431, respectively, in the ALHA plane.

  16. Compressive behaviour of gyroid lattice structures for human cancellous bone implant applications.

    PubMed

    Yánez, A; Herrera, A; Martel, O; Monopoli, D; Afonso, H

    2016-11-01

    Electron beam melting (EBM) was used to fabricate porous titanium alloy structures. The elastic modulus of these porous structures was similar to the elastic modulus of the cancellous human bone. Two types of cellular lattice structures were manufactured and tested: gyroids and diamonds. The design of the gyroid structures was determined by the main angle of the struts with respect to the axial direction. Thus, structures with angles of between 19 and 68.5° were manufactured. The aim of the design was to reduce the amount of material needed to fabricate a structure with the desired angles to increase the range of stiffness of the scaffolds. Compression tests were conducted to obtain the elastic modulus and the strength. Both parameters increased as the angle decreased. Finally, the specific strength of the gyroid structures was compared with that of the diamond structures and other types of structures. It is shown that, for angles lower than 35°, the gyroid structures had a high strength to weight ratios. PMID:27524040

  17. Compressive behaviour of gyroid lattice structures for human cancellous bone implant applications.

    PubMed

    Yánez, A; Herrera, A; Martel, O; Monopoli, D; Afonso, H

    2016-11-01

    Electron beam melting (EBM) was used to fabricate porous titanium alloy structures. The elastic modulus of these porous structures was similar to the elastic modulus of the cancellous human bone. Two types of cellular lattice structures were manufactured and tested: gyroids and diamonds. The design of the gyroid structures was determined by the main angle of the struts with respect to the axial direction. Thus, structures with angles of between 19 and 68.5° were manufactured. The aim of the design was to reduce the amount of material needed to fabricate a structure with the desired angles to increase the range of stiffness of the scaffolds. Compression tests were conducted to obtain the elastic modulus and the strength. Both parameters increased as the angle decreased. Finally, the specific strength of the gyroid structures was compared with that of the diamond structures and other types of structures. It is shown that, for angles lower than 35°, the gyroid structures had a high strength to weight ratios.

  18. Optical generation of a spatially variant two-dimensional lattice structure by using a phase only spatial light modulator

    SciTech Connect

    Kumar, Manish Joseph, Joby

    2014-08-04

    We propose a simple and straightforward method to generate spatially variant lattice structures by optical interference lithography method. Using this method, it is possible to independently vary the orientation and period of the two-dimensional lattice. The method consists of two steps which are: numerical synthesis of corresponding phase mask by employing a two-dimensional integrated gradient calculations and experimental implementation of synthesized phase mask by making use of a phase only spatial light modulator in an optical 4f Fourier filtering setup. As a working example, we provide the experimental fabrication of a spatially variant square lattice structure which has the possibility to guide a Gaussian beam through a 90° bend by photonic crystal self-collimation phenomena. The method is digitally reconfigurable, is completely scalable, and could be extended to other kind of lattices as well.

  19. SFM-FDTD analysis of triangular-lattice AAA structure: Parametric study of the TEM mode

    NASA Astrophysics Data System (ADS)

    Hamidi, M.; Chemrouk, C.; Belkhir, A.; Kebci, Z.; Ndao, A.; Lamrous, O.; Baida, F. I.

    2014-05-01

    This theoretical work reports a parametric study of enhanced transmission through annular aperture array (AAA) structure arranged in a triangular lattice. The effect of the incidence angle in addition to the inner and outer radii values on the evolution of the transmission spectra is carried out. To this end, a 3D Finite-Difference Time-Domain code based on the Split Field Method (SFM) is used to calculate the spectral response of the structure for any angle of incidence. In order to work through an orthogonal unit cell which presents the advantage to reduce time and space of computation, special periodic boundary conditions are implemented. This study provides a new modeling of AAA structures useful for producing tunable ultra-compact devices.

  20. Crystalline Structure in Thin Films of DEH-PPV Homopolymer And PPV-B-PI Rod-Coil Block Copolymers

    SciTech Connect

    Olsen, B.D.; Alcazar, D.; Krikorian, V.; Toney, M.F.; Thomas, E.L.; Segalman, R.A.; /UC, Berkeley /LBL, Berkeley /MIT /SLAC, SSRL

    2009-04-30

    The rod orientation and crystalline packing of a model semiconducting rodlike polymer, poly(2,5-di(2{prime}-ethylhexyloxy)-1,4-phenylenevinylene) (DEH-PPV), is shown to affect the self-assembly of weakly segregated rod-coil block copolymers. The in-plane packing of DEH-PPV rods in lamellar poly(2,5-di(2{prime}-ethylhexyloxy)-1,4-phenylenevinylene-b-isoprene) (DEH-PPV-b-PI) diblock copolymers is nearly identical to that observed in DEH-PPV homopolymers for compositions ranging from 0.42 to 0.82 vol % coil block. The crystal structure of DEH-PPV, characterized by grazing incidence X-ray diffraction and electron diffraction, consists of a tetragonal unit cell having c = 0.665 nm with a = b = 1.348 nm. The polymer chain axis is aligned along the [001] direction, and the nearest neighbor rod-rod spacing along 110 is 1.0 nm. As-cast thin films of DEH-PPV homopolymer demonstrate chain alignment primarily perpendicular to the substrate in 5100 g/mol homopolymer, while for 3500 g/mol homopolymer the chains align both perpendicular and parallel to the substrate. For the DEH-PPV-b-PI block copolymers, a sharper 001 reflection is observed due to the effect of microphase separation, improving alignment and stacking of the rods. The lamellar phases have a smectic A-like packing structure with the rods oriented parallel to the lamellar normal regardless of coil fraction; however, at coil fractions above about 0.8 the crystalline lattice of the rods becomes rapidly disordered as evidenced by loss of all but the two strongest Bragg reflections. This suggests that the constraints of packing into the unit cell outweigh the chain stretching and segment-segment repulsion energies that are predicted to lead to a transition from normal (smectic A) to tilted (smectic C) rod orientation within the lamellae at high coil fraction; increasing coil fraction breaks apart the crystalline lattice rather than distorting it into a tilted polymorph.

  1. Columnar structured FePt films epitaxially grown on large lattice mismatched intermediate layer

    PubMed Central

    Dong, K. F.; Deng, J. Y.; Peng, Y. G.; Ju, G.; Chow, G. M.; Chen, J. S.

    2016-01-01

    The microstructure and magnetic properties of the FePt films grown on large mismatched ZrN (15.7%) intermediate layer were investigated. With using ZrN intermediate layer, FePt 10 nm films exhibited (001) texture except for some weaker FePt (110) texture. Good epitaxial relationships of FePt (001) <100>//ZrN (001) <100>//TiN (001) <100> among FePt and ZrN/TiN were revealed from the transmission electron microscopy (TEM) results. As compared with TiN intermediate layer, although FePt-SiO2-C films grown on ZrN/TiN intermediate layer showed isotropic magnetic properties, the large interfacial energy and lattice mismatch between FePt and ZrN would lead to form columnar structural FePt films with smaller grain size and improved isolation. By doping ZrN into the TiN layer, solid solution of ZrTiN was formed and the lattice constant is increased comparing with TiN and decreased comparing with ZrN. Moreover, FePt-SiO2-C films grown on TiN 2 nm-20 vol.% ZrN/TiN 3 nm intermediate layer showed an improved perpendicular magnetic anisotropy. Simultaneously, columnar structure with smaller grain size retained. PMID:27686046

  2. Spatially localized structures and oscillons in atomic Bose-Einstein condensates confined in optical lattices

    NASA Astrophysics Data System (ADS)

    Charukhchyan, M. V.; Sedov, E. S.; Arakelian, S. M.; Alodjants, A. P.

    2014-06-01

    We consider the problem of formation of small-amplitude spatially localized oscillatory structures for atomic Bose-Einstein condensates confined in two- and three-dimensional optical lattices, respectively. Our approach is based on applying the regions with different signs of atomic effective masses where an atomic system exhibits effective hyperbolic dispersion within the first Brillouin zone. By using the kp method we have demonstrated mapping of the initial Gross-Pitaevskii equation on nonlinear Klein-Gordon and/or Ginzburg-Landau-Higgs equations, which is inherent in matter fields within ϕ4-field theories. Formation of breatherlike oscillating localized states—atomic oscillons—as well as kink-shaped states have been predicted in this case. Apart from classical field theories atomic field oscillons occurring in finite lattice structures possess a critical number of particles for their formation. The obtained results pave the way to simulating some analogues of fundamental cosmological processes occurring during our Universe's evolution and to modeling nonlinear hyperbolic metamaterials with condensed matter (atomic) systems.

  3. Advanced thermoelectric materials with enhanced crystal lattice structure and methods of preparation

    NASA Technical Reports Server (NTRS)

    Fleurial, Jean-Pierre (Inventor); Caillat, Thierry F. (Inventor); Borshchevsky, Alexander (Inventor)

    1998-01-01

    New skutterudite phases including Ru.sub.0.5 Pd.sub.0.5 Sb.sub.3, RuSb.sub.2 Te, and FeSb.sub.2 Te, have been prepared having desirable thermoelectric properties. In addition, a novel thermoelectric device has been prepared using skutterudite phase Fe.sub.0.5 Ni.sub.0.5 Sb.sub.3. The skutterudite-type crystal lattice structure of these semiconductor compounds and their enhanced thermoelectric properties results in semiconductor materials which may be used in the fabrication of thermoelectric elements to substantially improve the efficiency of the resulting thermoelectric device. Semiconductor materials having the desired skutterudite-type crystal lattice structure may be prepared in accordance with the present invention by using powder metallurgy techniques. Measurements of electrical and thermal transport properties of selected semiconductor materials prepared in accordance with the present invention, demonstrated high Hall mobilities and good Seebeck coefficients. These materials have low thermal conductivity and relatively low electrical resistivity, and are good candidates for low temperature thermoelectric applications.

  4. Block-structured adaptive mesh refinement - theory, implementation and application

    SciTech Connect

    Deiterding, Ralf

    2011-01-01

    Structured adaptive mesh refinement (SAMR) techniques can enable cutting-edge simulations of problems governed by conservation laws. Focusing on the strictly hyperbolic case, these notes explain all algorithmic and mathematical details of a technically relevant implementation tailored for distributed memory computers. An overview of the background of commonly used finite volume discretizations for gas dynamics is included and typical benchmarks to quantify accuracy and performance of the dynamically adaptive code are discussed. Large-scale simulations of shock-induced realistic combustion in non-Cartesian geometry and shock-driven fluid-structure interaction with fully coupled dynamic boundary motion demonstrate the applicability of the discussed techniques for complex scenarios.

  5. Structure of the Dimerization Interface in the Mature HIV-1 Capsid Protein Lattice from Solid State NMR of Tubular Assemblies.

    PubMed

    Bayro, Marvin J; Tycko, Robert

    2016-07-13

    The HIV-1 capsid protein (CA) forms the capsid shell that encloses RNA within a mature HIV-1 virion. Previous studies by electron microscopy have shown that the capsid shell is primarily a triangular lattice of CA hexamers, with variable curvature that destroys the ideal symmetry of a planar lattice. The mature CA lattice depends on CA dimerization, which occurs through interactions between helix 9 segments of the C-terminal domain (CTD) of CA. Several high-resolution structures of the CTD-CTD dimerization interface have been reported, based on X-ray crystallography and multidimensional solution nuclear magnetic resonance (NMR), with significant differences in amino acid side chain conformations and helix 9-helix 9 orientations. In a structural model for tubular CA assemblies based on cryogenic electron microscopy (cryoEM) [Zhao et al. Nature, 2013, 497, 643-646], the dimerization interface is substantially disordered. The dimerization interface structure in noncrystalline CA assemblies and the extent to which this interface is structurally ordered within a curved lattice have therefore been unclear. Here we describe solid state NMR measurements on the dimerization interface in tubular CA assemblies, which contain the curved triangular lattice of a mature virion, including quantitative measurements of intermolecular and intramolecular distances using dipolar recoupling techniques, solid state NMR chemical shifts, and long-range side chain-side chain contacts. When combined with restraints on the distance and orientation between helix 9 segments from the cryoEM study, the solid state NMR data lead to a unique high-resolution structure for the dimerization interface in the noncrystalline lattice of CA tubes. These results demonstrate that CA lattice curvature is not dependent on disorder or variability in the dimerization interface. This work also demonstrates the feasibility of local structure determination within large noncrystalline assemblies formed by high

  6. A structured multi-block solution-adaptive mesh algorithm with mesh quality assessment

    NASA Technical Reports Server (NTRS)

    Ingram, Clint L.; Laflin, Kelly R.; Mcrae, D. Scott

    1995-01-01

    The dynamic solution adaptive grid algorithm, DSAGA3D, is extended to automatically adapt 2-D structured multi-block grids, including adaption of the block boundaries. The extension is general, requiring only input data concerning block structure, connectivity, and boundary conditions. Imbedded grid singular points are permitted, but must be prevented from moving in space. Solutions for workshop cases 1 and 2 are obtained on multi-block grids and illustrate both increased resolution of and alignment with the solution. A mesh quality assessment criteria is proposed to determine how well a given mesh resolves and aligns with the solution obtained upon it. The criteria is used to evaluate the grid quality for solutions of workshop case 6 obtained on both static and dynamically adapted grids. The results indicate that this criteria shows promise as a means of evaluating resolution.

  7. Temperature, pressure, and isotope effects on the structure and properties of liquid water: a lattice approach.

    PubMed

    Hakem, Ilhem F; Boussaid, Abdelhak; Benchouk-Taleb, Hafida; Bockstaller, Michael R

    2007-12-14

    We present a lattice model to describe the effect of isotopic replacement, temperature, and pressure changes on the formation of hydrogen bonds in liquid water. The approach builds upon a previously established generalized lattice theory for hydrogen bonded liquids [B. A. Veytsman, J. Phys. Chem. 94, 8499 (1990)], accounts for the binding order of 1/2 in water-water association complexes, and introduces the pressure dependence of the degree of hydrogen bonding (that arises due to differences between the molar volumes of bonded and free water) by considering the number of effective binding sites to be a function of pressure. The predictions are validated using experimental data on the temperature and pressure dependence of the static dielectric constant of liquid water. The model is found to correctly reproduce the experimentally observed decrease of the dielectric constant with increasing temperature without any adjustable parameters and by assuming values for the enthalpy and entropy of hydrogen bond formation as they are determined from the respective experiments. The pressure dependence of the dielectric constant of water is quantitatively predicted up to pressures of 2 kbars and exhibits qualitative agreement at higher pressures. Furthermore, the model suggests a--temperature dependent--decrease of hydrogen bond formation at high pressures. The sensitive dependence of the structure of water on temperature and pressure that is described by the model rationalizes the different solubilization characteristics that have been observed in aqueous systems upon change of temperature and pressure conditions. The simplicity of the presented lattice model might render the approach attractive for designing optimized processing conditions in water-based solutions or the simulation of more complex multicomponent systems.

  8. Design, fabrication, and characterization of lightweight and broadband microwave absorbing structure reinforced by two dimensional composite lattice

    NASA Astrophysics Data System (ADS)

    Chen, Mingji; Pei, Yongmao; Fang, Daining

    2012-07-01

    Microwave absorbing structures (MASs) reinforced by two dimensional (2D) composite lattice elements have been designed and fabricated. The density of these MASs is lower than 0.5 g/cm3. Experimental measurements show that the sandwich structure with glass fiber reinforced composite (GFRC) lattice core can serve as a broadband MAS with its reflectivity below -10 dB over the frequency range of 4-18 GHz. The low permittivity GFRC is indicated to be the proper material for both the structural element of the core and the transparent face sheet. Calculations by the periodic moment method (PMM) demonstrate that the 2D Kagome lattice performs better for microwave absorbing than the square one at relatively low frequencies. The volume fraction and cell size of the structural element are also revealed to be key factors for microwave absorbing performance.

  9. The Lattice Kinetic Monte Carlo Simulation of Atomic Diffusion and Structural Transition for Gold.

    PubMed

    He, Xiang; Cheng, Feng; Chen, Zhao-Xu

    2016-01-01

    For the kinetic simulation of metal nanoparticles, we developed a self-consistent coordination-averaged energies for Au atoms based on energy properties of gold bulk phases. The energy barrier of the atom pairing change is proposed and holds for the microscopic reversibility principle. By applying the lattice kinetic Monte Carlo simulation on gold films, we found that the atomic diffusion of Au on the Au(111) surface undergoes a late transition state with an energy barrier of about 0.2 eV and a prefactor between 40~50 Å(2)/ps. This study also investigates the structural transition from spherical to faceted gold nanoparticles upon heating. The temperatures of structural transition are in agreement with the experimental melting temperatures of gold nanoparticles with diameters ranging from 2 nm to 8 nm. PMID:27629538

  10. Effect of surface attractive strength on structural transitions of a confined HP lattice protein

    NASA Astrophysics Data System (ADS)

    Pattanasiri, Busara; Li, Ying Wai; Wust, Thomas; Landau, David P.

    2015-09-01

    We investigate the influence of surface attractive strength on structural transitions of a hydrophobic-polar (HP) lattice protein confined in a slit formed by two parallel, attractive walls. We apply Wang-Landau sampling together with efficient Monte Carlo updates to estimate the density of states of the system. The conformational transitions, namely, the debridging process and hydrophobic core formation, can be identified by analyzing the specific heat together with several structural observables, such as the numbers of surface contacts, the number of hydrophobic pairs, and radii of gyration in different directions. As temperature decreases, we find that the occurrence of the debridging process is conditional depending on the surface attractive strength. This, in turn, affects the nature of the hydrophobic core formation that takes place at a lower temperature. We illustrate these observations with the aid of a HP protein chain with 48 monomers.

  11. The Lattice Kinetic Monte Carlo Simulation of Atomic Diffusion and Structural Transition for Gold

    PubMed Central

    He, Xiang; Cheng, Feng; Chen, Zhao-Xu

    2016-01-01

    For the kinetic simulation of metal nanoparticles, we developed a self-consistent coordination-averaged energies for Au atoms based on energy properties of gold bulk phases. The energy barrier of the atom pairing change is proposed and holds for the microscopic reversibility principle. By applying the lattice kinetic Monte Carlo simulation on gold films, we found that the atomic diffusion of Au on the Au(111) surface undergoes a late transition state with an energy barrier of about 0.2 eV and a prefactor between 40~50 Å2/ps. This study also investigates the structural transition from spherical to faceted gold nanoparticles upon heating. The temperatures of structural transition are in agreement with the experimental melting temperatures of gold nanoparticles with diameters ranging from 2 nm to 8 nm. PMID:27629538

  12. QuaBingo: A Prediction System for Protein Quaternary Structure Attributes Using Block Composition.

    PubMed

    Tung, Chi-Hua; Chen, Chi-Wei; Guo, Ren-Chao; Ng, Hui-Fuang; Chu, Yen-Wei

    2016-01-01

    Background. Quaternary structures of proteins are closely relevant to gene regulation, signal transduction, and many other biological functions of proteins. In the current study, a new method based on protein-conserved motif composition in block format for feature extraction is proposed, which is termed block composition. Results. The protein quaternary assembly states prediction system which combines blocks with functional domain composition, called QuaBingo, is constructed by three layers of classifiers that can categorize quaternary structural attributes of monomer, homooligomer, and heterooligomer. The building of the first layer classifier uses support vector machines (SVM) based on blocks and functional domains of proteins, and the second layer SVM was utilized to process the outputs of the first layer. Finally, the result is determined by the Random Forest of the third layer. We compared the effectiveness of the combination of block composition, functional domain composition, and pseudoamino acid composition of the model. In the 11 kinds of functional protein families, QuaBingo is 23% of Matthews Correlation Coefficient (MCC) higher than the existing prediction system. The results also revealed the biological characterization of the top five block compositions. Conclusions. QuaBingo provides better predictive ability for predicting the quaternary structural attributes of proteins. PMID:27610389

  13. QuaBingo: A Prediction System for Protein Quaternary Structure Attributes Using Block Composition.

    PubMed

    Tung, Chi-Hua; Chen, Chi-Wei; Guo, Ren-Chao; Ng, Hui-Fuang; Chu, Yen-Wei

    2016-01-01

    Background. Quaternary structures of proteins are closely relevant to gene regulation, signal transduction, and many other biological functions of proteins. In the current study, a new method based on protein-conserved motif composition in block format for feature extraction is proposed, which is termed block composition. Results. The protein quaternary assembly states prediction system which combines blocks with functional domain composition, called QuaBingo, is constructed by three layers of classifiers that can categorize quaternary structural attributes of monomer, homooligomer, and heterooligomer. The building of the first layer classifier uses support vector machines (SVM) based on blocks and functional domains of proteins, and the second layer SVM was utilized to process the outputs of the first layer. Finally, the result is determined by the Random Forest of the third layer. We compared the effectiveness of the combination of block composition, functional domain composition, and pseudoamino acid composition of the model. In the 11 kinds of functional protein families, QuaBingo is 23% of Matthews Correlation Coefficient (MCC) higher than the existing prediction system. The results also revealed the biological characterization of the top five block compositions. Conclusions. QuaBingo provides better predictive ability for predicting the quaternary structural attributes of proteins.

  14. QuaBingo: A Prediction System for Protein Quaternary Structure Attributes Using Block Composition

    PubMed Central

    Tung, Chi-Hua; Chen, Chi-Wei; Guo, Ren-Chao; Ng, Hui-Fuang

    2016-01-01

    Background. Quaternary structures of proteins are closely relevant to gene regulation, signal transduction, and many other biological functions of proteins. In the current study, a new method based on protein-conserved motif composition in block format for feature extraction is proposed, which is termed block composition. Results. The protein quaternary assembly states prediction system which combines blocks with functional domain composition, called QuaBingo, is constructed by three layers of classifiers that can categorize quaternary structural attributes of monomer, homooligomer, and heterooligomer. The building of the first layer classifier uses support vector machines (SVM) based on blocks and functional domains of proteins, and the second layer SVM was utilized to process the outputs of the first layer. Finally, the result is determined by the Random Forest of the third layer. We compared the effectiveness of the combination of block composition, functional domain composition, and pseudoamino acid composition of the model. In the 11 kinds of functional protein families, QuaBingo is 23% of Matthews Correlation Coefficient (MCC) higher than the existing prediction system. The results also revealed the biological characterization of the top five block compositions. Conclusions. QuaBingo provides better predictive ability for predicting the quaternary structural attributes of proteins. PMID:27610389

  15. QuaBingo: A Prediction System for Protein Quaternary Structure Attributes Using Block Composition

    PubMed Central

    Tung, Chi-Hua; Chen, Chi-Wei; Guo, Ren-Chao; Ng, Hui-Fuang

    2016-01-01

    Background. Quaternary structures of proteins are closely relevant to gene regulation, signal transduction, and many other biological functions of proteins. In the current study, a new method based on protein-conserved motif composition in block format for feature extraction is proposed, which is termed block composition. Results. The protein quaternary assembly states prediction system which combines blocks with functional domain composition, called QuaBingo, is constructed by three layers of classifiers that can categorize quaternary structural attributes of monomer, homooligomer, and heterooligomer. The building of the first layer classifier uses support vector machines (SVM) based on blocks and functional domains of proteins, and the second layer SVM was utilized to process the outputs of the first layer. Finally, the result is determined by the Random Forest of the third layer. We compared the effectiveness of the combination of block composition, functional domain composition, and pseudoamino acid composition of the model. In the 11 kinds of functional protein families, QuaBingo is 23% of Matthews Correlation Coefficient (MCC) higher than the existing prediction system. The results also revealed the biological characterization of the top five block compositions. Conclusions. QuaBingo provides better predictive ability for predicting the quaternary structural attributes of proteins.

  16. Towards composite spheres as building blocks for structured molecules.

    PubMed

    Lee, Lloyd L; Pellicane, Giuseppe

    2016-10-19

    In order to design a flexible molecular model that mimics the chemical moieties of a polyatomic molecule, we propose the 'composite-sphere' model that can assemble the essential elements to produce the structure of the target molecule. This is likened to the polymerization process where monomers assemble to form the polymer. The assemblage is built into the pair interaction potentials which can 'react' (figuratively) with selective pieces into various bonds. In addition, we preserve the spherical symmetries of the individual pair potentials so that the isotropic Ornstein-Zernike equation (OZ) for multi-component mixtures can be used as a theoretical framework. We first test our approach on generating a dumbbell molecule. An equimolar binary mixture of hard spheres and square-well spheres are allowed to react to form a dimer. As the bond length shrinks to zero, we create a site-site model of a Janus-like molecule with a repulsive moiety and an attractive moiety. We employ the zero-separation (ZSEP) closure to solve the OZ equations. The structure and thermodynamic properties are calculated at three isotherms and at several densities and the results are compared with Monte Carlo simulations. The close agreement achieved demonstrates that the ZSEP closure is a reliable theory for this composite-sphere fluid model. PMID:27546819

  17. Towards composite spheres as building blocks for structured molecules

    NASA Astrophysics Data System (ADS)

    Lee, Lloyd L.; Pellicane, Giuseppe

    2016-10-01

    In order to design a flexible molecular model that mimics the chemical moieties of a polyatomic molecule, we propose the ‘composite-sphere’ model that can assemble the essential elements to produce the structure of the target molecule. This is likened to the polymerization process where monomers assemble to form the polymer. The assemblage is built into the pair interaction potentials which can ‘react’ (figuratively) with selective pieces into various bonds. In addition, we preserve the spherical symmetries of the individual pair potentials so that the isotropic Ornstein-Zernike equation (OZ) for multi-component mixtures can be used as a theoretical framework. We first test our approach on generating a dumbbell molecule. An equimolar binary mixture of hard spheres and square-well spheres are allowed to react to form a dimer. As the bond length shrinks to zero, we create a site-site model of a Janus-like molecule with a repulsive moiety and an attractive moiety. We employ the zero-separation (ZSEP) closure to solve the OZ equations. The structure and thermodynamic properties are calculated at three isotherms and at several densities and the results are compared with Monte Carlo simulations. The close agreement achieved demonstrates that the ZSEP closure is a reliable theory for this composite-sphere fluid model. Contribution to the George Stell Memorial Issue.

  18. Large band gaps in radial phononic crystal structure with round mass block

    NASA Astrophysics Data System (ADS)

    Gao, Nansha; Wu, Jiu Hui; Jing, Li; Lu, Kuan; Yu, Lie

    2016-06-01

    Using the finite element method, we theoretically study the vibration properties of radial phononic crystal (RPC) structure with round mass block. The band structures, transmission spectra, and displacement fields of eigenmode are given to estimate the starting and cut-off frequency of band gaps. Compared to the contrast structure, numerical calculation results show that RPC structure with round mass block can yield several band gaps below 150 kHz. The physical mechanism of band gaps are attributed to the coupling between the longitudinal vibration in round mass block and vibrations in outer frame or coating layer. By changing geometrical dimensions r of round mass block, we can shift the location and width of band gaps. Significantly, as the increase of geometric parameter ratio a1/a2, band width shifts and the more new band gaps appear; the more bands become flat at this moment because of the stronger multiple vibration coupling effect plays a more prominent role in the opening of band gaps. These vibration properties of RPC structure with round mass block can potentially be applied to optimize band gaps, generate filters, and design acoustic devices.

  19. Multiscale Control of Hierarchical Structure in Crystalline Block Copolymer Nanoparticles Using Microfluidics.

    PubMed

    Bains, Aman; Cao, Yimeng; Moffitt, Matthew G

    2015-11-01

    Hierarchical semicrystalline block copolymer nanoparticles are produced in a segmented gas-liquid microfluidic reactor with top-down control of multiscale structural features, including nanoparticle morphologies, sizes, and internal crystallinities. Control of multiscale structure on disparate length scales by a single control variable (flow rate) enables tailoring of drug delivery nanoparticle function including release rates.

  20. Simplicial lattices in classical and quantum gravity: Mathematical structure and application

    NASA Astrophysics Data System (ADS)

    Lafave, Norman Joseph

    1989-03-01

    Geometrodynamics can be understood more clearly in the language of geometry than in the language of differential equations. This is the primary motivation for the development of calculational schemes based on Regge Calculus as an alternative to those schemes based on Ricci Calculus. The mathematics of simplicial lattices were developed to the same level of sophistication as the mathematics of pseudo--Riemannian geometry for continuum manifolds. This involves the definition of the simplicial analogues of several concepts from differential topology and differential geometry-the concept of a point, tangent spaces, forms, tensors, parallel transport, covariant derivatives, connections, and curvature. These simplicial analogues are used to define the Einstein tensor and the extrinsic curvature on a simplicial geometry. This mathematical formalism was applied to the solution of several outstanding problems in the development of a Regge Calculus based computational scheme for general geometrodynamic problems. This scheme is based on a 3 + 1 splitting of spacetime within the Regge Calculus prescription known as Null-Strut Calculus (NSC). NSC describes the foliation of spacetime into spacelike hypersurfaces built of tetrahedra. These hypersurfaces are coupled by light rays (null struts) to past and future momentum-like structures, geometrically dual to the tetrahedral lattice of the hypersurface. Avenues of investigation for NSC in quantum gravity are described.

  1. Electronic structure of topological superconductors in the presence of a vortex lattice

    NASA Astrophysics Data System (ADS)

    Liu, Tianyu; Franz, M.

    2015-10-01

    Certain types of topological superconductors and superfluids are known to host protected Majorana zero modes in cores of Abrikosov vortices. When such vortices are arranged in a dense periodic lattice one expects zero modes from neighboring vortices to hybridize and form dispersing bands. Understanding the structure of these bands is essential for the schemes that aim to employ the zero modes in quantum computation applications and in studies of their strongly interacting phases. We investigate here the band formation phenomenon in two concrete models, describing a two-dimensional px+i py superconductor and a superconducting surface of a three-dimensional strong topological insulator (Fu-Kane model), using a combination of analytical and numerical techniques. We find that the physics of the Majorana bands is well described by tight-binding models of Majorana fermions coupled to a static Z2 gauge field with a nontrivial gauge flux through each plaquette, in accord with expectations based on very general arguments. In the case of the Fu-Kane model we also find that, irrespective of the lattice geometry, the Majorana band becomes completely flat at the so-called neutrality point (chemical potential coincident with the Dirac point) where the model exhibits an extra chiral symmetry. In this limit the low-energy physics will be dominated by four-fermion interaction terms which are permitted by symmetries and may arise from the Coulomb interaction between the constituent electron degrees of freedom.

  2. Structure and ionic conductivity of block copolymer electrolytes over a wide salt concentration range

    NASA Astrophysics Data System (ADS)

    Chintapalli, Mahati; Le, Thao; Venkatesan, Naveen; Thelen, Jacob; Rojas, Adriana; Balsara, Nitash

    Block copolymer electrolytes are promising materials for safe, long-lasting lithium batteries because of their favorable mechanical and ion transport properties. The morphology, phase behavior, and ionic conductivity of a block copolymer electrolyte, SEO mixed with LiTFSI was studied over a wide, previously unexplored salt concentration range using small angle X-ray scattering, differential scanning calorimetry and ac impedance spectroscopy, respectively. SEO exhibits a maximum in ionic conductivity at twice the salt concentration that PEO, the homopolymer analog of the ion-containing block, does. This finding is contrary to prior studies that examined a more limited range of salt concentrations. In SEO, the phase behavior of the PEO block and LiTFSI closely resembles the phase behavior of homopolymer PEO and LiTFSI. The grain size of the block copolymer morphology was found to decrease with increasing salt concentration, and the ionic conductivity of SEO correlates with decreasing grain size. Structural effects impact the ionic conductivity-salt concentration relationship in block copolymer electrolytes. SEO: polystyrene-block-poly(ethylene oxide); also PS-PEO LiTFSI: lithium bis(trifluoromethanesulfonyl imide

  3. Parallel architectures for iterative methods on adaptive, block structured grids

    NASA Technical Reports Server (NTRS)

    Gannon, D.; Vanrosendale, J.

    1983-01-01

    A parallel computer architecture well suited to the solution of partial differential equations in complicated geometries is proposed. Algorithms for partial differential equations contain a great deal of parallelism. But this parallelism can be difficult to exploit, particularly on complex problems. One approach to extraction of this parallelism is the use of special purpose architectures tuned to a given problem class. The architecture proposed here is tuned to boundary value problems on complex domains. An adaptive elliptic algorithm which maps effectively onto the proposed architecture is considered in detail. Two levels of parallelism are exploited by the proposed architecture. First, by making use of the freedom one has in grid generation, one can construct grids which are locally regular, permitting a one to one mapping of grids to systolic style processor arrays, at least over small regions. All local parallelism can be extracted by this approach. Second, though there may be a regular global structure to the grids constructed, there will be parallelism at this level. One approach to finding and exploiting this parallelism is to use an architecture having a number of processor clusters connected by a switching network. The use of such a network creates a highly flexible architecture which automatically configures to the problem being solved.

  4. Structural changes in block copolymer micelles induced by cosolvent mixtures

    SciTech Connect

    Kelley, Elizabeth G.; Smart, Thomas P.; Jackson, Andrew J.; Sullivan, Millicent O.; Epps, III, Thomas H.

    2012-11-26

    We investigated the influence of tetrahydrofuran (THF) addition on the structure of poly(1,2-butadiene-b-ethylene oxide) [PB-PEO] micelles in aqueous solution. Our studies showed that while the micelles remained starlike, the micelle core-corona interfacial tension and micelle size decreased upon THF addition. The detailed effects of the reduction in interfacial tension were probed using contrast variations in small angle neutron scattering (SANS) experiments. At low THF contents (high interfacial tensions), the SANS data were fit to a micelle form factor that incorporated a radial density distribution of corona chains to account for the starlike micelle profile. However, at higher THF contents (low interfacial tensions), the presence of free chains in solution affected the scattering at high q and required the implementation of a linear combination of micelle and Gaussian coil form factors. These SANS data fits indicated that the reduction in interfacial tension led to broadening of the core-corona interface, which increased the PB chain solvent accessibility at intermediate THF solvent fractions. We also noted that the micelle cores swelled with increasing THF addition, suggesting that previous assumptions of the micelle core solvent content in cosolvent mixtures may not be accurate. Control over the size, corona thickness, and extent of solvent accessible PB in these micelles can be a powerful tool in the development of targeting delivery vehicles.

  5. Fast sparse matrix-vector multiplication by exploiting variable block structure

    SciTech Connect

    Vuduc, R W; Moon, H

    2005-07-07

    We improve the performance of sparse matrix-vector multiply (SpMV) on modern cache-based superscalar machines when the matrix structure consists of multiple, irregularly aligned rectangular blocks. Matrices from finite element modeling applications often have this kind of structure. Our technique splits the matrix, A, into a sum, A{sub 1} + A{sub 2} + ... + A{sub s}, where each term is stored in a new data structure, unaligned block compressed sparse row (UBCSR) format . The classical alternative approach of storing A in a block compressed sparse row (BCSR) format yields limited performance gains because it imposes a particular alignment of the matrix non-zero structure, leading to extra work from explicitly padded zeros. Combining splitting and UBCSR reduces this extra work while retaining the generally lower memory bandwidth requirements and register-level tiling opportunities of BCSR. Using application test matrices, we show empirically that speedups can be as high as 2.1x over not blocking at all, and as high as 1.8x over the standard BCSR implementation used in prior work. When performance does not improve, split UBCSR can still significantly reduce matrix storage. Through extensive experiments, we further show that the empirically optimal number of splittings s and the block size for each matrix term A{sub i} will in practice depend on the matrix and hardware platform. Our data lay a foundation for future development of fully automated methods for tuning these parameters.

  6. Super-resolution microscopy reveals a preformed NEMO lattice structure that is collapsed in incontinentia pigmenti.

    PubMed

    Scholefield, Janine; Henriques, Ricardo; Savulescu, Anca F; Fontan, Elisabeth; Boucharlat, Alix; Laplantine, Emmanuel; Smahi, Asma; Israël, Alain; Agou, Fabrice; Mhlanga, Musa M

    2016-01-01

    The NF-κB pathway has critical roles in cancer, immunity and inflammatory responses. Understanding the mechanism(s) by which mutations in genes involved in the pathway cause disease has provided valuable insight into its regulation, yet many aspects remain unexplained. Several lines of evidence have led to the hypothesis that the regulatory/sensor protein NEMO acts as a biological binary switch. This hypothesis depends on the formation of a higher-order structure, which has yet to be identified using traditional molecular techniques. Here we use super-resolution microscopy to reveal the existence of higher-order NEMO lattice structures dependent on the presence of polyubiquitin chains before NF-κB activation. Such structures may permit proximity-based trans-autophosphorylation, leading to cooperative activation of the signalling cascade. We further show that NF-κB activation results in modification of these structures. Finally, we demonstrate that these structures are abrogated in cells derived from incontinentia pigmenti patients. PMID:27586688

  7. Structure of a turbulent crossbar near-wake studied by means of lattice Boltzmann simulation

    NASA Astrophysics Data System (ADS)

    Djenidi, Lyazid

    2008-03-01

    The turbulent near-wake of a crossbar is investigated numerically with the lattice Boltzmann method (LBM). The crossbar is made up of two perpendicular square bars arranged in a biplane configuration and is included in the computational domain. The Reynolds number based on a bar diameter is about 1600. The numerical results are first tested against results of both particle image velocimetry (PIV) and laser Doppler velocimetry (LDV). The LBM data compare well with the PIV and LDV data. In particular, the LBM reproduces the generation of vortical structures at the crossbar as observed in the PIV data. The numerical results reveal the presence of intermittent lateral motions along the span of the two bars, yielding fingerlike structures. It is argued that these motions contribute to the formation of streamwise vortical structures just behind the crossbar. These streamwise structures interlace with lateral structures also generated at the crossbar. The region over which this activity takes place is about four diameters. Within this region, the turbulent kinetic energy at the crossbar centerline increases and reaches a maximum at a distance of about three diameters. As the downstream distance increases, the individual wakes merge to form a single wake with features, for x/D≥20 , similar to those observed in grid-generated turbulence.

  8. Super-resolution microscopy reveals a preformed NEMO lattice structure that is collapsed in incontinentia pigmenti

    PubMed Central

    Scholefield, Janine; Henriques, Ricardo; Savulescu, Anca F.; Fontan, Elisabeth; Boucharlat, Alix; Laplantine, Emmanuel; Smahi, Asma; Israël, Alain; Agou, Fabrice; Mhlanga, Musa M.

    2016-01-01

    The NF-κB pathway has critical roles in cancer, immunity and inflammatory responses. Understanding the mechanism(s) by which mutations in genes involved in the pathway cause disease has provided valuable insight into its regulation, yet many aspects remain unexplained. Several lines of evidence have led to the hypothesis that the regulatory/sensor protein NEMO acts as a biological binary switch. This hypothesis depends on the formation of a higher-order structure, which has yet to be identified using traditional molecular techniques. Here we use super-resolution microscopy to reveal the existence of higher-order NEMO lattice structures dependent on the presence of polyubiquitin chains before NF-κB activation. Such structures may permit proximity-based trans-autophosphorylation, leading to cooperative activation of the signalling cascade. We further show that NF-κB activation results in modification of these structures. Finally, we demonstrate that these structures are abrogated in cells derived from incontinentia pigmenti patients. PMID:27586688

  9. Influence of crystal orientation on the formation of femtosecond laser-induced periodic surface structures and lattice defects accumulation

    SciTech Connect

    Sedao, Xxx; Garrelie, Florence Colombier, Jean-Philippe; Reynaud, Stéphanie; Pigeon, Florent; Maurice, Claire; Quey, Romain

    2014-04-28

    The influence of crystal orientation on the formation of femtosecond laser-induced periodic surface structures (LIPSS) has been investigated on a polycrystalline nickel sample. Electron Backscatter Diffraction characterization has been exploited to provide structural information within the laser spot on irradiated samples to determine the dependence of LIPSS formation and lattice defects (stacking faults, twins, dislocations) upon the crystal orientation. Significant differences are observed at low-to-medium number of laser pulses, outstandingly for (111)-oriented surface which favors lattice defects formation rather than LIPSS formation.

  10. Dynamic structure factor of a Fibonacci lattice: A renormalization-group approach

    NASA Astrophysics Data System (ADS)

    Karmakar, S. N.; Chakrabarti, Arunava; Moitra, R. K.

    1992-08-01

    We present a real-space renormalization-group method for evaluating the exact dynamic structure factor S(q,ω) of a quasiperiodic Fibonacci chain. Contrary to earlier work that takes account only of the global aspects of the symmetry of the chain, our method additionally takes care of the local environmental aspects of the symmetry by separating the original lattice into a finite number of self-similar interpenetrating sublattices, followed by elimination of the coupling between them. Our method also yields correctly the positions of the Bragg peaks of the Fibonacci chain. Moreover, the present method allows the sites of the chain to be grouped into classes following a ``genealogical'' classification, the members of a given class being equivalent up to a certain length scale. Based on this classification, the proof of the existence of a key site, which has only been conjectured in our earlier work using numerical search, has been given.

  11. Lattice dynamics and the nature of structural transitions in organolead halide perovskites

    DOE PAGESBeta

    Comin, Riccardo; Crawford, Michael K.; Said, Ayman H.; Herron, Norman; Guise, William E.; Wang, Xiaoping; Whitfield, Pamela S.; Jain, Ankit; Gong, Xiwen; McGaughey, Alan J. H.; et al

    2016-09-09

    Organolead halide perovskites are a family of hybrid organic-inorganic compounds whose remark- able optoelectronic properties have been under intensive scrutiny in recent years. Here we use inelastic X-ray scattering to study low-energy lattice excitations in single crystals of methylammonium lead iodide and bromide perovskites. Our ndings conrm the displacive nature of the cubic-to- tetragonal phase transition, which is further shown, using neutron and x-ray diraction, to be close to a tricritical point. The experimental sound speed, around 100-200 m/s, suggests that electron- phonon scattering is likely a limiting factor for further improvements in carrier mobility. Lastly, we detect quasistatic symmetry-breakingmore » nanodomains persisting well into the high-temperature cubic phase, possibly stabilized by local defects. These ndings reveal key structural properties of these materials, but also bear important implications for carrier dynamics across an extended temperature range relevant for photovoltaic applications.« less

  12. Effect of substrate rotation on domain structure and magnetic relaxation in magnetic antidot lattice arrays

    SciTech Connect

    Mallick, Sougata; Mallik, Srijani; Bedanta, Subhankar

    2015-08-28

    Microdimensional triangular magnetic antidot lattice arrays were prepared by varying the speed of substrate rotation. The pre-deposition patterning has been performed using photolithography technique followed by a post-deposition lift-off. Surface morphology taken by atomic force microscopy depicted that the growth mechanism of the grains changes from chain like formation to island structures due to the substrate rotation. Study of magnetization reversal via magneto optic Kerr effect based microscopy revealed reduction of uniaxial anisotropy and increase in domain size with substrate rotation. The relaxation measured under constant magnetic field becomes faster with rotation of the substrate during deposition. The nature of relaxation for the non-rotating sample can be described by a double exponential decay. However, the relaxation for the sample with substrate rotation is well described either by a double exponential or a Fatuzzo-Labrune like single exponential decay, which increases in applied field.

  13. Orbital thermal analysis of lattice structured spacecraft using color video display techniques

    NASA Technical Reports Server (NTRS)

    Wright, R. L.; Deryder, D. D.; Palmer, M. T.

    1983-01-01

    A color video display technique is demonstrated as a tool for rapid determination of thermal problems during the preliminary design of complex space systems. A thermal analysis is presented for the lattice-structured Earth Observation Satellite (EOS) spacecraft at 32 points in a baseline non Sun-synchronous (60 deg inclination) orbit. Large temperature variations (on the order of 150 K) were observed on the majority of the members. A gradual decrease in temperature was observed as the spacecraft traversed the Earth's shadow, followed by a sudden rise in temperature (100 K) as the spacecraft exited the shadow. Heating rate and temperature histories of selected members and color graphic displays of temperatures on the spacecraft are presented.

  14. Structure and lattice dynamics of rare-earth ferroborate crystals: Ab initio calculation

    NASA Astrophysics Data System (ADS)

    Chernyshev, V. A.; Nikiforov, A. E.; Petrov, V. P.; Serdtsev, A. V.; Kashchenko, M. A.; Klimin, S. A.

    2016-08-01

    The ab initio calculation of the crystal structure and the phonon spectrum of crystals RFe3(BO3)4 ( R = Pr, Nd, Sm) has been performed in the framework of the density functional theory. The ion coordinates in the unit cell, the lattice parameters, the frequencies and the types of fundamental vibrations, and also the intensities of lines in the Raman spectrum and infrared reflection spectra have been found. The elastic constants of the crystals have been calculated. For low-frequency A 2 mode in PrFe3(BO3)4, a "seed" vibration frequency that strongly interacts with the electronic excitation on a praseodymium ion was found. The calculation results satisfactory agree with the experimental data.

  15. The Lattice Structure of Connection Preserving Deformations for q-Painlevé Equations I

    NASA Astrophysics Data System (ADS)

    Ormerod, Christopher M.

    2011-05-01

    We wish to explore a link between the Lax integrability of the q-Painlevé equations and the symmetries of the q-Painlevé equations. We shall demonstrate that the connection preserving deformations that give rise to the q-Painlevé equations may be thought of as elements of the groups of Schlesinger transformations of their associated linear problems. These groups admit a very natural lattice structure. Each Schlesinger transformation induces a Bäcklund transformation of the q-Painlevé equation. Each translational Bäcklund transformation may be lifted to the level of the associated linear problem, effectively showing that each translational Bäcklund transformation admits a Lax pair. We will demonstrate this framework for the q-Painlevé equations up to and including q-PVI.

  16. Stochastic inflation lattice simulations - Ultra-large scale structure of the universe

    NASA Technical Reports Server (NTRS)

    Salopek, D. S.

    1991-01-01

    Non-Gaussian fluctuations for structure formation may arise in inflation from the nonlinear interaction of long wavelength gravitational and scalar fields. Long wavelength fields have spatial gradients, a (exp -1), small compared to the Hubble radius, and they are described in terms of classical random fields that are fed by short wavelength quantum noise. Lattice Langevin calculations are given for a toy model with a scalar field interacting with an exponential potential where one can obtain exact analytic solutions of the Fokker-Planck equation. For single scalar field models that are consistent with current microwave background fluctuations, the fluctuations are Gaussian. However, for scales much larger than our observable Universe, one expects large metric fluctuations that are non-Gaussian. This example illuminates non-Gaussian models involving multiple scalar fields which are consistent with current microwave background limits.

  17. Atomic structure and handedness of the building block of a biological assembly.

    PubMed

    Loquet, Antoine; Habenstein, Birgit; Chevelkov, Veniamin; Vasa, Suresh Kumar; Giller, Karin; Becker, Stefan; Lange, Adam

    2013-12-26

    Noncovalent supramolecular assemblies possess in general several unique subunit-subunit interfaces.The basic building block of such an assembly consists of several subunits and contains all unique interfaces. Atomic-resolution structures of monomeric subunits are typically accessed by crystallography or solution NMR and fitted into electron microscopy density maps. However, the structure of the intact building block in the assembled state remains unknown with this hybrid approach. Here, we present the solid-state NMR atomic structure of the building block of the type III secretion system needle. The building block structure consists of a homotetrameric subunit complex with three unique supramolecular interfaces. Side-chain positions at the interfaces were solved at atomic detail. The high-resolution structure reveals unambiguously the helical handedness of the assembly, determined to be right-handed for the type III secretion system needle.Additionally, the axial rise per subunit could be extracted from the tetramer structure and independently validated by mass-per-length measurements.

  18. Relationship between Structural and Stress Relaxation in a Block-Copolymer Melt

    SciTech Connect

    Patel, Amish J.; Narayanan, Suresh; Sandy, Alec; Mochrie, Simon G. J.; Garetz, Bruce A.; Watanabe, Hiroshi; Balsara, Nitash P.

    2006-06-30

    The relationship between structural relaxation on molecular length scales and macroscopic stress relaxation was explored in a disordered block-copolymer melt. Experiments show that the structural relaxation time, measured by x-ray photon correlation spectroscopy is larger than the terminal stress relaxation time, measured by rheology, by factors as large as 100. We demonstrate that the structural relaxation data are dominated by the diffusion of intact micelles while the stress relaxation data are dominated by contributions due to disordered concentration fluctuations.

  19. Thermal Analysis, Structural Studies and Morphology of Spider Silk-like Block Copolymers

    NASA Astrophysics Data System (ADS)

    Huang, Wenwen

    Spider silk is a remarkable natural block copolymer, which offers a unique combination of low density, excellent mechanical properties, and thermal stability over a wide range of temperature, along with biocompatibility and biodegrability. The dragline silk of Nephila clavipes, is one of the most well understood and the best characterized spider silk, in which alanine-rich hydrophobic blocks and glycine-rich hydrophilic blocks are linked together generating a functional block copolymer with potential uses in biomedical applications such as guided tissue repair and drug delivery. To provide further insight into the relationships among peptide amino acid sequence, block length, and physical properties, in this thesis, we studied synthetic proteins inspired by the genetic sequences found in spider dragline silks, and used these bioengineered spider silk block copolymers to study thermal, structural and morphological features. To obtain a fuller understanding of the thermal dynamic properties of these novel materials, we use a model to calculate the heat capacity of spider silk block copolymer in the solid or liquid state, below or above the glass transition temperature, respectively. We characterize the thermal phase transitions by temperature modulated differential scanning calorimetry (TMDSC) and thermogravimetric analysis (TGA). We also determined the crystallinity by TMDSC and compared the result with Fourier transform infrared spectroscopy (FTIR) and wide angle X-ray diffraction (WAXD). To understand the protein-water interactions with respect to the protein amino acid sequence, we also modeled the specific reversing heat capacity of the protein-water system, Cp(T), based on the vibrational, rotational and translational motions of protein amino acid residues and water molecules. Advanced thermal analysis methods using TMDSC and TGA show two glass transitions were observed in all samples during heating. The low temperature glass transition, Tg(1), is related to

  20. The Anopheles-midgut APN1 structure reveals a new malaria transmission-blocking vaccine epitope.

    PubMed

    Atkinson, Sarah C; Armistead, Jennifer S; Mathias, Derrick K; Sandeu, Maurice M; Tao, Dingyin; Borhani-Dizaji, Nahid; Tarimo, Brian B; Morlais, Isabelle; Dinglasan, Rhoel R; Borg, Natalie A

    2015-07-01

    Mosquito-based malaria transmission-blocking vaccines (mTBVs) target midgut-surface antigens of the Plasmodium parasite's obligate vector, the Anopheles mosquito. The alanyl aminopeptidase N (AnAPN1) is the leading mTBV immunogen; however, AnAPN1's role in Plasmodium infection of the mosquito and how anti-AnAPN1 antibodies functionally block parasite transmission have remained elusive. Here we present the 2.65-Å crystal structure of AnAPN1 and the immunoreactivity and transmission-blocking profiles of three monoclonal antibodies (mAbs) to AnAPN1, including mAb 4H5B7, which effectively blocks transmission of natural strains of Plasmodium falciparum. Using the AnAPN1 structure, we map the conformation-dependent 4H5B7 neoepitope to a previously uncharacterized region on domain 1 and further demonstrate that nonhuman-primate neoepitope-specific IgG also blocks parasite transmission. We discuss the prospect of a new biological function of AnAPN1 as a receptor for Plasmodium in the mosquito midgut and the implications for redesigning the AnAPN1 mTBV. PMID:26075520

  1. Learning to Lead: Self- and Peer Evaluation of Team Leaders in the Human Structure Didactic Block

    ERIC Educational Resources Information Center

    Chen, Laura P.; Gregory, Jeremy K.; Camp, Christopher L.; Juskewitch, Justin E.; Pawlina, Wojciech; Lachman, Nirusha

    2009-01-01

    Increasing emphasis on leadership in medical education has created a need for developing accurate evaluations of team leaders. Our study aimed to compare the accuracy of self- and peer evaluation of student leaders in the first-year Human Structure block (integrated gross anatomy, embryology, and radiology). Forty-nine first-year medical students…

  2. Two episodes of structural fractures and their stress field modeling in the Ordos Block, northern China

    NASA Astrophysics Data System (ADS)

    Zhao, Wentao; Hou, Guiting; Hari, K. R.

    2016-07-01

    The importance of the Ordos Block, which is surrounded by different Chinese continental blocks, is well documented, but the development of the structural fractures and the stress fields within the Late Mesozoic and Cenozoic eras in this stable block (dips of the Mesozoic and Cenozoic strata are less than 3°) have been poorly studied. In this paper, two dominant groups of structural fractures with NW to EW and NNE to ENE trends are identified through field measurements and imaging log observations. The maximum principal compressive stress magnitudes and stress trajectories are calculated employing 2D finite element models (2D-FEM). Based on the displacement fields, the rotation of the Ordos Block and comparisons between the measured and the calculated stresses, it can be deduced that there are two episodes of fracture formation in the Ordos Block. The calculated orientations of maximum compressive stress in the Late Mesozoic and the Cenozoic eras are found to be WNW and NE respectively, which imply that the NW to EW trending structural fractures were developed in a Late Mesozoic stress field whereas the NNE to ENE ones were developed in a Cenozoic stress field in the block. The change in stress fields may have resulted in the change in tectonic setting from the northwestward subduction of the Izanagi Plate in the Late Mesozoic to the collision between the Indian Plate and the Eurasian Plate in the Cenozoic. The change in the Mesozoic and Cenozoic stress fields is of great significance to the further fracture prediction in fractured reservoirs, basin analyses in the Ordos Basin and research on the geodynamics of the North China Craton.

  3. Lattice instability and competing spin structures in the double perovskite insulator Sr2FeOsO6.

    PubMed

    Paul, Avijit Kumar; Reehuis, Manfred; Ksenofontov, Vadim; Yan, Binghai; Hoser, Andreas; Többens, Daniel M; Abdala, Paula M; Adler, Peter; Jansen, Martin; Felser, Claudia

    2013-10-18

    The semiconductor Sr2FeOsO6, depending on temperature, adopts two types of spin structures that differ in the spin sequence of ferrimagnetic iron-osmium layers along the tetragonal c axis. Neutron powder diffraction experiments, 57Fe Mössbauer spectra, and density functional theory calculations suggest that this behavior arises because a lattice instability resulting in alternating iron-osmium distances fine-tunes the balance of competing exchange interactions. Thus, Sr2FeOsO6 is an example of a double perovskite, in which the electronic phases are controlled by the interplay of spin, orbital, and lattice degrees of freedom. PMID:24182298

  4. Nanoring structure, spacing, and local dielectric sensitivity for plasmonic resonances in Fano resonant square lattices.

    PubMed

    Forcherio, Gregory T; Blake, Phillip; DeJarnette, Drew; Roper, D Keith

    2014-07-28

    Lattices of plasmonic nanorings with particular geometries exhibit singular, tunable resonance features in the infrared. This work examined effects of nanoring inner radius, wall thickness, and lattice constant on the spectral response of single nanorings and in Fano resonant square lattices, combining use of the discrete and coupled dipole approximations. Increasing nanoring inner radius red-shifted and broadened the localized surface plasmon resonance (LSPR), while wall thickness modulated the LSPR wavelength and decreased absorption relative to scattering. The square lattice constant was tuned to observe diffractively-coupled lattice resonances, which increased resonant extinction 4.3-fold over the single-ring LSPR through Fano resonance. Refractive index sensitivities of 760 and 1075 nm RIU(-1) were computed for the plasmon and lattice resonances of an optimized nanoring lattice. Sensitivity of an optimal nanoring lattice to a local change in dielectric, useful for sensing applications, was 4 to 5 times higher than for isolated nanorings or non-coupling arrays. This was attributable to the Fano line-shape in far-field diffractive coupling with near-field LSPR.

  5. A lattice Boltzmann model for substrates with regularly structured surface roughness

    NASA Astrophysics Data System (ADS)

    Yagub, A.; Farhat, H.; Kondaraju, S.; Singh, T.

    2015-11-01

    Superhydrophobic surface characteristics are important in many industrial applications, ranging from the textile to the military. It was observed that surfaces fabricated with nano/micro roughness can manipulate the droplet contact angle, thus providing an opportunity to control the droplet wetting characteristics. The Shan and Chen (SC) lattice Boltzmann model (LBM) is a good numerical tool, which holds strong potentials to qualify for simulating droplets wettability. This is due to its realistic nature of droplet contact angle (CA) prediction on flat smooth surfaces. But SC-LBM was not able to replicate the CA on rough surfaces because it lacks a real representation of the physics at work under these conditions. By using a correction factor to influence the interfacial tension within the asperities, the physical forces acting on the droplet at its contact lines were mimicked. This approach allowed the model to replicate some experimentally confirmed Wenzel and Cassie wetting cases. Regular roughness structures with different spacing were used to validate the study using the classical Wenzel and Cassie equations. The present work highlights the strength and weakness of the SC model and attempts to qualitatively conform it to the fundamental physics, which causes a change in the droplet apparent contact angle, when placed on nano/micro structured surfaces.

  6. Turbulent boundary layer control through spanwise wall oscillation using Kagome lattice structures

    NASA Astrophysics Data System (ADS)

    Bird, James; Santer, Matthew; Morrison, Jonathan

    2015-11-01

    It is well established that a reduction in skin-friction and turbulence intensity can be achieved by applying in-plane spanwise forcing to a surface beneath a turbulent boundary layer. It has also been shown in DNS (M. Quadrio, P. Ricco, & C. Viotti; J. Fluid Mech; 627, 161, 2009), that this phenomenon is significantly enhanced when the forcing takes the form of a streamwise travelling wave of spanwise perturbation. In the present work, this type of forcing is generated by an active surface comprising a compliant structure, based on a Kagome lattice geometry, supporting a membrane skin. The structural design ensures negligible wall normal displacement while facilitating large in-plane velocities. The surface is driven pneumatically, achieving displacements of 3 mm approximately, at frequencies in excess of 70 Hz for a turbulent boundary layer at Reτ ~ 1000 . As the influence of this forcing on boundary layer is highly dependent on the wavenumber and frequency of the travelling wave, a flat surface was designed and optimised to allow these forcing parameters to be varied, without reconfiguration of the experiment. Simultaneous measurements of the fluid and surface motion are presented, and notable skin-friction drag reduction is demonstrated. Airbus support agreement IW202838 is gratefully acknowledged.

  7. Limited propagation of lattice distortion in trilayer Langmuir-Blodgett films: correlation with mesoscopic structure.

    PubMed

    Cantin, Sophie; Perrot, Françoise; Fontaine, Philippe; Goldmann, Michel

    2013-09-01

    The structure of trilayer Langmuir-Blodgett (LB) films on oxidized silicon wafers has been investigated using grazing incidence X-ray diffraction at various incidence angles and atomic force microscopy (AFM). These films are formed by two behenic acid (BA) layers and a third monolayer of amphiphilic molecules having different architectures. These molecules have the same polar head and differ from each other by the chain, either saturated or unsaturated hydrogenated or semi-fluorinated. The structure of the first BA monolayer appears as unchanged in all cases, whereas a condensation of the second BA monolayer is evidenced when the third layer is not formed with the saturated hydrogenated chain. We interpret this condensation as resulting from the mismatch between the lattices of the second BA layer and the external monolayer, possibly associated with the formation of a new monolayer-air interface creating line tension effects. Line tension estimation has also been made from the size of the holes observed in the different LB films.

  8. The choco block in the northwestern corner of South America: Structural, tectonostratigraphic, and paleogeographic implications

    NASA Astrophysics Data System (ADS)

    Duque-Caro, H.

    The Choco Block, located in the northwestern corner of South America, comprises the isthmus of Panama east of the Canal Zone and northwestern Colombia, including the westernmost flanks of the Cordillera Occidental above latitude 4°N. Three major structural and lithogenetic elements compose this terrain: the Dabeiba and Baudo Arches, the Atrato-Chucunaque Basins, and the Istmina Deformed Zone. The Dabeiba and Baudo Arches outline the external boundaries of the Choco Block and display similar characteristics: (a) mostly positive gravity anomalies and association of igneous bodies of oceanic origin with sedimentary suites, and (b) occurence of Upper Cretaceous to Miocene pelagic and hemipelagic and terrigenous strata in blocks of different ages and environments associated with mafic igneous rocks. The Dabeiba Arch exhibits a melange fabric, particularly at its eastern margin, in which disrupted strata and inclusions of Upper Cretaceous-Paleocene, Eocene-Oligocene, and Miocene exotic blocks are dispersed in a sheared pelitic matrix of middle Miocene age. The Atrato-Chucunaque Basins contain sedimentary fill exceeding 10 km in thickness. Two distinctive stratigraphic sequences comprise: (1) an outcropping and apparently continuous Oligocene to middle Miocene sequence composed mostly of pelagic and hemipelagic strata, overlain by hemipelagic and terrigenous strata of latest Middle Miocene to Pliocene age, and (2) an underlying middle Miocene and older sequence, composed mostly of turbidities, which has been recognized only in subsurface sections. An evaluation and synthesis of the structural and lithogenetic information of the Choco Block indicate the following conclusions. The Choco Block is an exotic terrane with no lithogenetic affinity with South America, accreted onto the northwestern flanks of the Cordillera Occidental during the middle Miocene. The occurence of exotic upper Paleocene planktic foraminiferal assemblages in the Dabeiba Arch suggests an origin for

  9. Algorithms for the automatic generation of 2-D structured multi-block grids

    NASA Technical Reports Server (NTRS)

    Schoenfeld, Thilo; Weinerfelt, Per; Jenssen, Carl B.

    1995-01-01

    Two different approaches to the fully automatic generation of structured multi-block grids in two dimensions are presented. The work aims to simplify the user interactivity necessary for the definition of a multiple block grid topology. The first approach is based on an advancing front method commonly used for the generation of unstructured grids. The original algorithm has been modified toward the generation of large quadrilateral elements. The second method is based on the divide-and-conquer paradigm with the global domain recursively partitioned into sub-domains. For either method each of the resulting blocks is then meshed using transfinite interpolation and elliptic smoothing. The applicability of these methods to practical problems is demonstrated for typical geometries of fluid dynamics.

  10. Entropy coding of syntax elements related to block structures and transform coefficient levels in HEVC

    NASA Astrophysics Data System (ADS)

    Nguyen, Tung; Helle, Philipp; Winken, Martin; Marpe, Detlev; Schwarz, Heiko; Wiegand, Thomas

    2012-10-01

    The most recent video compression technology is High Efficiency Video Coding (HEVC). This soon to be completed standard is a joint development by Video Coding Experts Group (VCEG) of ITU-T and Moving Picture Experts Group (MPEG) of ISO/IEC. As one of its major technical novelties, HEVC supports variable prediction and transform block sizes using the quadtree approach for block partitioning. In terms of entropy coding, the Draft International Standard (DIS) of HEVC specifies context-based adaptive binary arithmetic coding (CABAC) as the single mode of operation. In this paper, a description of the specific CABAC-based entropy coding part in HEVC is given that is related to block structures and transform coefficient levels. In addition, experimental results are presented that indicate the benefit of the transform-coefficient level coding design in HEVC in terms of improved coding performance and reduced complexity.

  11. Amphiphilic block copolymers in oil-water-surfactant mixtures: efficiency boosting, structure, phase behaviour and mechanism

    NASA Astrophysics Data System (ADS)

    Gompper, G.; Richter, D.; Strey, R.

    2001-10-01

    The effect of amphiphilic block copolymers on the phase behaviour and structure of ternary microemulsions in water, oil and non-ionic surfactant mixtures is reviewed. Recent experiments have revealed that the addition of small amounts of polyethylenepropylene-polyethyleneoxide block copolymer to the ternary systems leads to a dramatic increase in the volumes of oil and water solubilized into a bicontinuous microemulsion for a given surfactant volume fraction. While phase diagrams directly show the power of the amphiphilic block copolymers as efficiency boosters, the theoretical analysis in terms of bending energy discloses the mechanism for the efficiency boosting as due to the variation of the surfactant film curvature elasticity by tethered polymers in the form of mushrooms at the interface. Neutron scattering experiments employing a high-precision two-dimensional contrast variation technique confirm this picture and demonstrate that the polymer molecules uniformly decorate the surfactant film.

  12. Benchmarking DFT and semiempirical methods on structures and lattice energies for ten ice polymorphs

    NASA Astrophysics Data System (ADS)

    Brandenburg, Jan Gerit; Maas, Tilo; Grimme, Stefan

    2015-03-01

    Water in different phases under various external conditions is very important in bio-chemical systems and for material science at surfaces. Density functional theory methods and approximations thereof have to be tested system specifically to benchmark their accuracy regarding computed structures and interaction energies. In this study, we present and test a set of ten ice polymorphs in comparison to experimental data with mass densities ranging from 0.9 to 1.5 g/cm3 and including explicit corrections for zero-point vibrational and thermal effects. London dispersion inclusive density functionals at the generalized gradient approximation (GGA), meta-GGA, and hybrid level as well as alternative low-cost molecular orbital methods are considered. The widely used functional of Perdew, Burke and Ernzerhof (PBE) systematically overbinds and overall provides inconsistent results. All other tested methods yield reasonable to very good accuracy. BLYP-D3atm gives excellent results with mean absolute errors for the lattice energy below 1 kcal/mol (7% relative deviation). The corresponding optimized structures are very accurate with mean absolute relative deviations (MARDs) from the reference unit cell volume below 1%. The impact of Axilrod-Teller-Muto (atm) type three-body dispersion and of non-local Fock exchange is small but on average their inclusion improves the results. While the density functional tight-binding model DFTB3-D3 performs well for low density phases, it does not yield good high density structures. As low-cost alternative for structure related problems, we recommend the recently introduced minimal basis Hartree-Fock method HF-3c with a MARD of about 3%.

  13. Effect of implementation of a Bragg reflector in the photonic band structure of the Suzuki-phase photonic crystal lattice.

    PubMed

    Martinez, Luis Javier; Alija, Alfonso Rodriguez; Postigo, Pablo Aitor; Galisteo-López, J F; Galli, Matteo; Andreani, Lucio Claudio; Seassal, Christian; Viktorovitch, Pierre

    2008-06-01

    We investigate the change of the photonic band structure of the Suzuki-phase photonic crystal lattice when the horizontal mirror symmetry is broken by an underlying Bragg reflector. The structure consists of an InP photonic crystal slab including four InAsP quantum wells, a SiO(2) bonding layer, and a bottom high index contrast Si/SiO(2) Bragg mirror deposited on a Si wafer. Angle- and polarization-resolved photoluminescence spectroscopy has been used for measuring the photonic band structure and for investigating the coupling to a polarized plane wave in the far field. A drastic change in the k-space photonic dispersion between the structure with and without Bragg reflector is measured. An important enhancement on the photoluminescence emission up to seven times has been obtained for a nearly flat photonic band, which is characteristic of the Suzuki-phase lattice.

  14. On the Structure and Use of Linearized Block ADI and Related Schemes

    NASA Astrophysics Data System (ADS)

    Briley, W. R.; McDonald, H.

    1980-01-01

    The recent use of methods which may be termed "linearized block ADI methods" or more generally "consistently split linearized block implicit" methods has been a significant development in the efficient and noniterative solution of certain systems of coupled nonlinear multidimensional partial differential equations. Some observations on their structure, derivation, and use are given. Consistently split linearized block implicit (LBI) methods are unified here and are related to the earlier scalar ADI schemes, as well as to existing iterative and noniterative methods for solving both systems of nonlinear algebraic equations, and systems of nonlinear ordinary differential equations (including those having multipoint boundary conditions). It is shown that the method used by Lindemuth and Killeen and that of Briley and McDonald (utilizing a two-dimensional Crank-Nicolson formulation) are both consistently split block implicit schemes which differ in principle only with regard to implementation of the linearization technique. It is also observed that the first approximate factorization scheme of Beam and Warming utilizes a splitting due to D'Yakanov whose intermediate steps are inconsistent in the sense that they do not approximate the governing equations to within a truncation error which vanishes to some order for small Δt. Methods based on splittings which have inconsistent intermediate steps are placed in a separate category and are shown to present serious difficulties, which apparently have escaped notice, in treating derivative boundary conditions accurately. Although similar difficulties can arise in the transient with consistently split schemes, the consistent splitting normally provides one order of accuracy improvement. It is further demonstrated that the two-level version of the second and more recent "delta" form approximate factorization scheme of Warming and Beam and the earlier method of Briley and McDonald have identical linearized block implicit

  15. Swarm intelligence algorithm for interconnect model order reduction with sub-block structure preserving

    NASA Astrophysics Data System (ADS)

    Wang, Xinsheng; Wang, Chenxu; Yu, Mingyan

    2016-07-01

    In this paper, we propose a generalised sub-block structure preservation interconnect model order reduction (MOR) technique based on the swarm intelligence method, that is, particle swarm optimisation (PSO). The swarm intelligence-based structure preservation MOR can be used for a standard model as a criterion for different structure preservation interconnect MOR methods. In the proposed technique, the PSO method is used for predicting the unknown elements of structure-preserving reduced-order modelling of interconnect circuits. The prediction is based on minimising the difference of transform function between the original full-order and desired reduced-order systems maintaining the full-order structure in the reduced-order model. The proposed swarm-intelligence-based structure-preserving MOR method is compared with published work on structure preservation MOR SPRIM techniques. Simulation and synthesis results verify the accuracy and validity of the new structure-preserving MOR technique.

  16. Magnetic structure of Yb2Pt2Pb: Ising moments on the Shastry-Sutherland lattice

    DOE PAGESBeta

    Miiller, W.; Zaliznyak, I.; Wu, L. S.; Kim, M. S.; Orvis, T.; Simonson, J. W.; Gamza, M.; McNally, D. M.; Nelson, C. S.; Ehlers, G.; et al

    2016-03-22

    Neutron diffraction measurements were carried out on single crystals and powders of Yb2Pt2Pb, where Yb moments form two interpenetrating planar sublattices of orthogonal dimers, a geometry known as Shastry-Sutherland lattice, and are stacked along the c axis in a ladder geometry. Yb2Pt2Pb orders antiferromagnetically at TN=2.07K, and the magnetic structure determined from these measurements features the interleaving of two orthogonal sublattices into a 5×5×1 magnetic supercell that is based on stripes with moments perpendicular to the dimer bonds, which are along (110) and (–110). Magnetic fields applied along (110) or (–110) suppress the antiferromagnetic peaks from an individual sublattice, butmore » leave the orthogonal sublattice unaffected, evidence for the Ising character of the Yb moments in Yb2Pt2Pb that is supported by point charge calculations. Furthermore, specific heat, magnetic susceptibility, and electrical resistivity measurements concur with neutron elastic scattering results that the longitudinal critical fluctuations are gapped with ΔE≃0.07meV.« less

  17. Directional luminescence control of InGaN/GaN heterostructures using quantum structure lattice arrays

    SciTech Connect

    Wang, Y. L.; Chen, K. Y.; Yang, W. C.; Chiu, S. Y.; Cheng, K. Y.; Huang, H. H.; Hung, Y. C.

    2015-03-16

    The spontaneous surface luminescence properties of InGaN/GaN quantum structure lattice (QSL) are reported. The QSL consists of a two-dimensional array of InGaN/GaN quantum boxes (QBs) arranged in a rectangular pattern of 200 nm periodicity. The measured angular dependent photoluminescence (PL) spectra show a strong dependence on the in-plane Bragg diffractions between QBs. The maximum PL intensity of the InGaN/GaN QSL array that fulfill the Bragg condition points in the normal direction of the sample surface with a narrow radiation angle of ∼ ±12°. In addition, a small side lobe is also shown at ±40°. For the QSL sample that does not fulfill the Bragg diffraction condition, the radiation pattern shows a conventional cosine distribution. The finite-difference time-domain numerical analysis confirms that the lowest order and higher order Bragg diffractions between QBs determine the main and the small side lobe of the radiation pattern measured in QSLs, respectively.

  18. Dynamic and Structural Studies of Metastable Vortex Lattice Domains in MgB2

    NASA Astrophysics Data System (ADS)

    de Waard, E. R.; Kuhn, S. J.; Rastovski, C.; Eskildsen, M. R.; Leishman, A.; Dewhurst, C. D.; Debeer-Schmitt, L.; Littrell, K.; Karpinski, J.; Zhigadlo, N. D.

    Small-angle neutron scattering (SANS) studies of the vortex lattice (VL) in the type-II superconductor MgB2 have revealed an unprecedented degree of metastability that is demonstrably not due to vortex pinning, [C. Rastovski et al . , Phys. Rev. Lett. 111, 107002 (2013)]. The VL can be driven to the GS through successive application of an AC magnetic field. Here we report on detailed studies of the transition kinetics and structure of the VL domains. Stroboscopic studies of the transition revealed a stretched exponential decrease of the metastable volume fraction as a function of the number of applied AC cycles, with subtle differences depending on whether the AC field is oriented parallel or perpendicular to the DC field used to create the VL. We speculate the slower transition kinetics for the transverse AC field may be due to vortex cutting. Spatial studies include scanning SANS measurements showing the VL domain distribution within the MgB2 single crystal as well as measurements of VL correlation lengths. This work is supported by the U.S. Department of Energy, Office of Basic Energy Sciences under Award DE-FG02-10ER46783.

  19. Numerical simulation of the fatigue behavior of additive manufactured titanium porous lattice structures.

    PubMed

    Zargarian, A; Esfahanian, M; Kadkhodapour, J; Ziaei-Rad, S

    2016-03-01

    In this paper, the effects of cell geometry and relative density on the high-cycle fatigue behavior of Titanium scaffolds produced by selective laser melting and electron beam melting techniques were numerically investigated by finite element analysis. The regular titanium lattice samples with three different unit cell geometries, namely, diamond, rhombic dodecahedron and truncated cuboctahedron, and the relative density range of 0.1-0.3 were analyzed under uniaxial cyclic compressive loading. A failure event based algorithm was employed to simulate fatigue failure in the cellular material. Stress-life approach was used to model fatigue failure of both bulk (struts) and cellular material. The predicted fatigue life and the damage pattern of all three structures were found to be in good agreement with the experimental fatigue investigations published in the literature. The results also showed that the relationship between fatigue strength and cycles to failure obeyed the power law. The coefficient of power function was shown to depend on relative density, geometry and fatigue properties of the bulk material while the exponent was only dependent on the fatigue behavior of the bulk material. The results also indicated the failure surface at an angle of 45° to the loading direction. PMID:26706539

  20. Structural Studies of Metastable and Ground State Vortex Lattice Domains in MgB2

    NASA Astrophysics Data System (ADS)

    de Waard, E. R.; Kuhn, S. J.; Rastovski, C.; Eskildsen, M. R.; Leishman, A.; Dewhurst, C. D.; Debeer-Schmitt, L.; Littrell, K.; Karpinski, J.; Zhigadlo, N. D.

    2015-03-01

    Small-angle neutron scattering (SANS) studies of the vortex lattice (VL) in the type-II superconductor MgB2 have revealed an unprecedented degree of metastability that is demonstrably not due to vortex pinning, [C. Rastovski et al . , Phys. Rev. Lett. 111, 107002 (2013)]. Application of an AC magnetic field to drive the VL to the ground state revealed a two-step power law behavior, indicating a slow nucleation of ground state domains followed by a faster growth. The dependence on the number of applied AC cycles is reminiscent of jamming of soft, frictionless spheres. Here, we report on detailed structural studies of both metastable and ground state VL domains. These include measurements of VL correlation lengths as well as spatially resolved SANS measurements showing the VL domain distribution within the MgB2 single crystal. We discuss these results and how they may help to resolve the mechanism responsible for stabilizing the metastable VL phases. This work is supported by the U.S. Department of Energy, Office of Basic Energy Sciences under Award DE-FG02-10ER46783.

  1. Numerical simulation of the fatigue behavior of additive manufactured titanium porous lattice structures.

    PubMed

    Zargarian, A; Esfahanian, M; Kadkhodapour, J; Ziaei-Rad, S

    2016-03-01

    In this paper, the effects of cell geometry and relative density on the high-cycle fatigue behavior of Titanium scaffolds produced by selective laser melting and electron beam melting techniques were numerically investigated by finite element analysis. The regular titanium lattice samples with three different unit cell geometries, namely, diamond, rhombic dodecahedron and truncated cuboctahedron, and the relative density range of 0.1-0.3 were analyzed under uniaxial cyclic compressive loading. A failure event based algorithm was employed to simulate fatigue failure in the cellular material. Stress-life approach was used to model fatigue failure of both bulk (struts) and cellular material. The predicted fatigue life and the damage pattern of all three structures were found to be in good agreement with the experimental fatigue investigations published in the literature. The results also showed that the relationship between fatigue strength and cycles to failure obeyed the power law. The coefficient of power function was shown to depend on relative density, geometry and fatigue properties of the bulk material while the exponent was only dependent on the fatigue behavior of the bulk material. The results also indicated the failure surface at an angle of 45° to the loading direction.

  2. Local lattice distortions vs. structural phase transition in NdFeAsO1-xFx

    NASA Astrophysics Data System (ADS)

    Calamiotou, M.; Lampakis, D.; Zhigadlo, N. D.; Katrych, S.; Karpinski, J.; Fitch, A.; Tsiaklagkanos, P.; Liarokapis, E.

    2016-08-01

    The lattice properties at low temperatures of two samples of NdFeAsO1-xFx (x = 0.05 and 0.25) have been examined in order to investigate possible structural phase transition that may occur in the optimally doped superconducting sample with respect to the non-superconducting low-F concentration compound. In order to detect small modifications in the ion displacements with temperature micro-Raman and high resolution synchrotron powder diffraction measurements were carried out. No increase of the width of the (2 2 0) or (3 2 2) tetragonal diffraction peaks and microstrains could be found in the superconducting sample from synchrotron XRD measurements. On the other hand, the atomic displacement parameters deviate from the expected behavior, in agreement with modifications in the phonon width, as obtained by Raman scattering. These deviations occur around 150 K for both F dopings, with distinct differences among the two compounds, i.e., they decrease at low doping and increase for the superconducting sample. The data do not support a hidden phase transition to an orthorhombic phase in the superconducting compound, but point to an isostructural lattice deformation. Based on the absence of magnetic effects in this temperature range for the superconducting sample, we attribute the observed lattice anomalies to the formation of local lattice distortions that, being screened by the carriers, can only acquire long-range coherence by means of a structural phase transition at low doping levels.

  3. New Approach for IIR Adaptive Lattice Filter Structure Using Simultaneous Perturbation Algorithm

    NASA Astrophysics Data System (ADS)

    Martinez, Jorge Ivan Medina; Nakano, Kazushi; Higuchi, Kohji

    Adaptive infinite impulse response (IIR), or recursive, filters are less attractive mainly because of the stability and the difficulties associated with their adaptive algorithms. Therefore, in this paper the adaptive IIR lattice filters are studied in order to devise algorithms that preserve the stability of the corresponding direct-form schemes. We analyze the local properties of stationary points, a transformation achieving this goal is suggested, which gives algorithms that can be efficiently implemented. Application to the Steiglitz-McBride (SM) and Simple Hyperstable Adaptive Recursive Filter (SHARF) algorithms is presented. Also a modified version of Simultaneous Perturbation Stochastic Approximation (SPSA) is presented in order to get the coefficients in a lattice form more efficiently and with a lower computational cost and complexity. The results are compared with previous lattice versions of these algorithms. These previous lattice versions may fail to preserve the stability of stationary points.

  4. On the effects of geometry, defects, and material asymmetry on the mechanical response of shape memory alloy cellular lattice structures

    NASA Astrophysics Data System (ADS)

    Karamooz Ravari, M. R.; Nasr Esfahani, S.; Taheri Andani, M.; Kadkhodaei, M.; Ghaei, A.; Karaca, H.; Elahinia, M.

    2016-02-01

    Shape memory alloy (such as NiTi) cellular lattice structures are a new class of advanced materials with many potential applications. The cost of fabrication of these structures however is high. It is therefore necessary to develop modeling methods to predict the functional behavior of these alloys before fabrication. The main aim of the present study is to assess the effects of geometry, microstructural imperfections and material asymmetric response of dense shape memory alloys on the mechanical response of cellular structures. To this end, several cellular and dense NiTi samples are fabricated using a selective laser melting process. Both cellular and dense specimens were tested in compression in order to obtain their stress-strain response. For modeling purposes, a three -dimensional (3D) constitutive model based on microplane theory which is able to describe the material asymmetry was employed. Five finite element models based on unit cell and multi-cell methods were generated to predict the mechanical response of cellular lattices. The results show the considerable effects of the microstructural imperfections on the mechanical response of the cellular lattice structures. The asymmetric material response of the bulk material also affects the mechanical response of the corresponding cellular structure.

  5. First-Principles Study of Lattice Dynamics, Structural Phase Transition, and Thermodynamic Properties of Barium Titanate

    NASA Astrophysics Data System (ADS)

    Zhang, Huai-Yong; Zeng, Zhao-Yi; Zhao, Ying-Qin; Lu, Qing; Cheng, Yan

    2016-08-01

    Lattice dynamics, structural phase transition, and the thermodynamic properties of barium titanate (BaTiO3) are investigated by using first-principles calculations within the density functional theory (DFT). It is found that the GGA-WC exchange-correlation functional can produce better results. The imaginary frequencies that indicate structural instability are observed for the cubic, tetragonal, and orthorhombic phases of BaTiO3 and no imaginary frequencies emerge in the rhombohedral phase. By examining the partial phonon density of states (PDOSs), we find that the main contribution to the imaginary frequencies is the distortions of the perovskite cage (Ti-O). On the basis of the site-symmetry consideration and group theory, we give the comparative phonon symmetry analysis in four phases, which is useful to analyze the role of different atomic displacements in the vibrational modes of different symmetry. The calculated optical phonon frequencies at Γ point for the four phases are in good agreement with other theoretical and experimental data. The pressure-induced phase transition of BaTiO3 among four phases and the thermodynamic properties of BaTiO3 in rhombohedral phase have been investigated within the quasi-harmonic approximation (QHA). The sequence of the pressure-induced phase transition is rhombohedral→orthorhombic→tetragonal→cubic, and the corresponding transition pressure is 5.17, 5.92, 6.65 GPa, respectively. At zero pressure, the thermal expansion coefficient αV, heat capacity CV, Grüneisen parameter γ, and bulk modulus B of the rhombohedral phase BaTiO3 are estimated from 0 K to 200 K.

  6. Utilization of the Building-Block Approach in Structural Mechanics Research

    NASA Technical Reports Server (NTRS)

    Rouse, Marshall; Jegley, Dawn C.; McGowan, David M.; Bush, Harold G.; Waters, W. Allen

    2005-01-01

    In the last 20 years NASA has worked in collaboration with industry to develop enabling technologies needed to make aircraft safer and more affordable, extend their lifetime, improve their reliability, better understand their behavior, and reduce their weight. To support these efforts, research programs starting with ideas and culminating in full-scale structural testing were conducted at the NASA Langley Research Center. Each program contained development efforts that (a) started with selecting the material system and manufacturing approach; (b) moved on to experimentation and analysis of small samples to characterize the system and quantify behavior in the presence of defects like damage and imperfections; (c) progressed on to examining larger structures to examine buckling behavior, combined loadings, and built-up structures; and (d) finally moved to complicated subcomponents and full-scale components. Each step along the way was supported by detailed analysis, including tool development, to prove that the behavior of these structures was well-understood and predictable. This approach for developing technology became known as the "building-block" approach. In the Advanced Composites Technology Program and the High Speed Research Program the building-block approach was used to develop a true understanding of the response of the structures involved through experimentation and analysis. The philosophy that if the structural response couldn't be accurately predicted, it wasn't really understood, was critical to the progression of these programs. To this end, analytical techniques including closed-form and finite elements were employed and experimentation used to verify assumptions at each step along the way. This paper presents a discussion of the utilization of the building-block approach described previously in structural mechanics research and development programs at NASA Langley Research Center. Specific examples that illustrate the use of this approach are

  7. Choice of optimal properties of molding compounds for extrusion of block supports and catalysts with the honeycomb structure

    SciTech Connect

    Prokof`ev, V.Yu.; Il`in, A.P.; Shirokov, Yu.G.; Yurchenko, E.N.

    1995-09-20

    Properties of compounds for molding of block supports and catalysts with the honeycomb structure have been studied. The examples studied include ultraporcelain, alumina, titanium dioxide, clays, and graphite. The molding properties of these compounds are characterized by such parameters as the relationship between deformations, relaxation time, power for destruction of the coagulation structure, and flow index. For molding of blocks with the honeycomb structure compounds with enhanced plastic properties and a stable coagulation structure are suggested.

  8. Multiple magnetization plateaus and magnetic structures in the S =1/2 Heisenberg model on the checkerboard lattice

    NASA Astrophysics Data System (ADS)

    Morita, Katsuhiro; Shibata, Naokazu

    2016-10-01

    We study the ground state of the S =1/2 Heisenberg model on the checkerboard lattice in a magnetic field by the density matrix renormalization group method with the sine-square deformation. We obtain magnetization plateaus at M /Msat=0 ,1/4 ,3/8 ,1/2 , and 3/4 , where Msat is the saturated magnetization. The obtained 3/4 plateau state is consistent with the exact result, and the 1/2 plateau is found to have a four-spin resonating loop structure similar to the six-spin loop structure of the 1/3 plateau of the kagome lattice. Different four-spin loop structures are obtained in the 1/4 and 3/8 plateaus but no corresponding states exist in the kagome lattice. The 3/8 plateau has a unique magnetic structure of three types of four-spin local quantum states in a 4 √{2 }×2 √{2 } magnetic unit cell with a 16-fold degeneracy.

  9. The Brillouin zones and band gaps of a two-dimensional phononic crystal with parallelogram lattice structure

    NASA Astrophysics Data System (ADS)

    Hu, JiaGuang; Xu, Wen

    2014-06-01

    We present a detailed theoretical study on the acoustic band structure of two-dimensional (2D) phononic crystal. The 2D phononic crystal with parallelogram lattice structure is considered to be formed by rigid solid rods embedded in air. For the circular rods, some of the extrema of the acoustic bands appear in the usual high-symmetry points and, in contrast, we find that some of them are located in other specific lines. For the case of elliptic rods, our results indicate that it is necessary to study the whole first Brillouin zone to obtain rightly the band structure and corresponding band gaps. Furthermore, we evaluate the first and second band gaps using the plane wave expansion method and find that these gaps can be tuned by adjusting the side lengths ratio R, inclined angle θ and filling fraction F of the parallelogram lattice with circular rods. The results show that the largest value of the first band gap appears at θ=90° and F=0.7854. In contrast, the largest value of the second band gap is at θ=60° and F=0.9068. Our results indicate that the improvement of matching degree between scatterers and lattice pattern, rather than the reduction of structural symmetry, is mainly responsible for the enhancement of the band gaps in the 2D phononic crystal.

  10. Synthesis and Structure of Fully Conjugated Block Copolymers Utilized in Organic Photovoltaics

    NASA Astrophysics Data System (ADS)

    Lee, Youngmin; Aplan, Melissa; Wang, Qing; Gomez, Enrique D.

    2015-03-01

    Fully conjugated block copolymers have the potential to overcome many of the limitations of mixtures and blends as photoactive layers in solar cells; furthermore, they may serve as model systems to study fundamental questions regarding optoelectric properties and charge transfer. However, the synthesis of fully conjugated block copolymers remains a challenging issue in the fieldchallenge. We have optimized the two-step synthesis of P3HT-b-PFTBT, which is composed comprised of Grignard metathesis for polymerization of P3HT followed by chain extension through a Suzuki-Miyaura polycondenstation. We find that the concentration of the Grignard reagent is critical for end-group control such that P3HT is terminated by H at one end and Br at the other. Furthermore, we can utilize an asymmetric feed ratio of monomers for the Suzuki-Miyaura reaction to minimize the amount of uncoupled homopolymers and to control the molecular weight of the second block. We investigated the chemical composition, structure and electrical characteristics of the polymers prepared by the different synthetic methods, and demonstrate that we can utilize these strategies for the synthesis of block copolymers beyond P3HT-b-PFTBT.

  11. Structure of clusters and building blocks in amylopectin from African rice accessions.

    PubMed

    Gayin, Joseph; Abdel-Aal, El-Sayed M; Marcone, Massimo; Manful, John; Bertoft, Eric

    2016-09-01

    Enzymatic hydrolysis in combination with gel-permeation and anion-exchange chromatography techniques were employed to characterise the composition of clusters and building blocks of amylopectin from two African rice (Oryza glaberrima) accessions-IRGC 103759 and TOG 12440. The samples were compared with one Asian rice (Oryza sativa) sample (cv WITA 4) and one O. sativa×O. glaberrima cross (NERICA 4). The average DP of clusters from the African rice accessions (ARAs) was marginally larger (DP=83) than in WITA 4 (DP=81). However, regarding average number of chains, clusters from the ARAs represented both the smallest and largest clusters. Overall, the result suggested that the structure of clusters in TOG 12440 was dense with short chains and high degree of branching, whereas the situation was the opposite in NERICA 4. IRGC 103759 and WITA 4 possessed clusters with intermediate characteristics. The commonest type of building blocks in all samples was group 2 (single branched dextrins) representing 40.3-49.4% of the blocks, while groups 3-6 were found in successively lower numbers. The average number of building blocks in the clusters was significantly larger in NERICA 4 (5.8) and WITA 4 (5.7) than in IRGC 103759 and TOG 12440 (5.1 and 5.3, respectively). PMID:27185123

  12. Formation of 2D nanoparticles with block structure in simultaneous electric explosion of conductors

    SciTech Connect

    Kryzhevich, Dmitrij S. E-mail: kost@ispms.ru; Zolnikov, Konstantin P. E-mail: kost@ispms.ru; Abdrashitov, Andrei V.; Lerner, Marat I.; Psakhie, Sergey G.

    2014-11-14

    A molecular dynamics simulation of nanoparticle formation in simultaneous electric explosion of conductors is performed. Interatomic interaction is described using potentials calculated in the framework of the embedded atom method. High-rate heating results in failure of the conductors with the formation of nanoparticles. The influence of the heating rate, temperature distribution over the specimen cross-section and the distance between simultaneously exploded conductors on the structure of formed nanoparticles is studied. The calculation results show that the electric explosion of conductors allows the formation of nanoparticles with block structure.

  13. The structure of nanochannels formed by block copolymer solutions confined in nanotubes.

    PubMed

    Chen, Houyang; Ruckenstein, Eli

    2009-09-21

    Monte Carlo simulations are employed to obtain information about the radius and the roughness of the inner surface of the channels, which are generated by a family of block copolymer solutions confined in nanotubes. The fluctuations of the above quantities also have been calculated. The simulations have been carried out by varying the interactions between various kinds of segments and those between segments and the wall of the nanotubes, as well as the chemical structure of the copolymer and the nanotube diameter. The present simulations provide insight regarding the structure of ionic and water channels formed by protein in the phospholipid bilayers of the cell membrane.

  14. KIVA3. A KIVA Program With Block-Structured Mesh for Complex Geometries

    SciTech Connect

    Amsden, A.A.; Menon, R.G.

    1993-03-01

    KIVA3 is a computer program for the numerical calculation of transient, two and three-dimensional, chemically reactive flows with sprays. It is an extension of the earlier KIVA2, and uses the same numerical solution procedure and solves the same set of equations. KIVA3 differs in that it uses a block-structured mesh with connectivity defined through indirect addressing. The departure from a single rectangular structure in logical space allows complex geometries to be modeled with significantly greater efficiency because large regions of deactivated cells are no longer necessary. Cell-face boundary conditions permit greater flexibility and simplification in the application of boundary conditions.

  15. KIVA3. A KIVA Program with Block-Structured Mesh for Complex Geometries

    SciTech Connect

    Amsden, A.A.

    1993-03-01

    KIVA3 is a computer program for the numerical calculation of transient, two and three-dimensional, chemically reactive flows with sprays. It is an extension of the earlier KIVA2, and uses the same numerical solution procedure and solves the same set of equations. KIVA3 differs in that it uses a block-structured mesh with connectivity defined through indirect addressing. The departure from a single rectangular structure in logical space allows complex geometries to be modeled with significantly greater efficiency because large regions of deactivated cells are no longer necessary. Cell-face boundary conditions permit greater flexibility and simplification in the application of boundary conditions.

  16. "LPO Lite" : Representing Lattice Preferred Orientation and its Evolution Using Structured Basis Functions

    NASA Astrophysics Data System (ADS)

    Ribe, N. M.; Castelnau, O.

    2008-12-01

    Current methods for calculating the evolution of flow-induced seismic anisotropy in the upper mantle describe Lattice Preferred Orientation (LPO) using ensembles of 103-104 individual grains, and are nowaday too computationally expensive to be incorporated into three-dimensional time-dependent convection models. We propose a much faster (by a factor ~ 103) method wherein LPO is described by a small number of 'structured basis functions' (SBFs.) The number of SBFs required is equal to the number of active slip systems (= 3 for olivine), and each SBF represents the 'virtual' LPO that would be produced by the action of just one of those systems. Analytical expressions for the SBFs are obtained using a simple 'single-slip' (SS) model, and are then tested against the predictions of the second-order (SO) self-consistent model of Ponte-Castaneda (J. Mech. Phys. Solids 50, 737-757, 2002) in which several slip systems act simultaneously. Remarkably, the SS model reproduces exactly (99.9% variance reduction) the orientation- dependence of the slip rate ·γ predicted by the SO model for each active slip system, once the overall amplitude of the SS expression for ·γ has been determined by least-squares fitting to the SO prediction. Having thus demonstrated that the analytical SBFs are physically realistic, we develop a scheme for representing an arbitrary LPO as a superposition of the SBFs and for determining the evolution equations satisfied by the expansion coefficients. We illustrate the method both for simple uniform deformations (uniaxial compression, simple shear) and for more geophysically realistic nonuniform deformation histories.

  17. Towards a lattice-matching solid-state battery: synthesis of a new class of lithium-ion conductors with the spinel structure.

    PubMed

    Rosciano, Fabio; Pescarmona, Paolo P; Houthoofd, Kristof; Persoons, Andre; Bottke, Patrick; Wilkening, Martin

    2013-04-28

    Lithium ion batteries have conquered most of the portable electronics market and are now on the verge of deployment in large scale applications. To be competitive in the automotive and stationary sectors, however, they must be improved in the fields of safety and energy density (W h L(-1)). Solid-state batteries with a ceramic electrolyte offer the necessary advantages to significantly improve the current state-of-the-art technology. The major limit towards realizing a practical solid-state lithium-ion battery lies in the lack of viable ceramic ionic conductors. Only a few candidate materials are available, each carrying a difficult balance between advantages and drawbacks. Here we introduce a new class of possible solid-state lithium-ion conductors with the spinel structure. Such compounds could be coupled with spinel-type electrode materials to obtain a "lattice matching" solid device where low interfacial resistance could be achieved. Powders were prepared by wet chemistry, their structure was studied by means of diffraction techniques and magic angle spinning NMR, and Li(+) self-diffusion was estimated by static NMR line shape measurements. Profound differences in the Li(+) diffusion properties were observed depending on the composition, lithium content and cationic distribution. Local Li(+) hopping in the spinel materials is accompanied by a low activation energy of circa 0.35 eV being comparable with that of, e.g., LLZO-type garnets, which represent the current benchmark in this field. We propose these novel materials as a building block for a lattice-matching all-spinel solid-state battery with low interfacial resistance.

  18. Towards a lattice-matching solid-state battery: synthesis of a new class of lithium-ion conductors with the spinel structure.

    PubMed

    Rosciano, Fabio; Pescarmona, Paolo P; Houthoofd, Kristof; Persoons, Andre; Bottke, Patrick; Wilkening, Martin

    2013-04-28

    Lithium ion batteries have conquered most of the portable electronics market and are now on the verge of deployment in large scale applications. To be competitive in the automotive and stationary sectors, however, they must be improved in the fields of safety and energy density (W h L(-1)). Solid-state batteries with a ceramic electrolyte offer the necessary advantages to significantly improve the current state-of-the-art technology. The major limit towards realizing a practical solid-state lithium-ion battery lies in the lack of viable ceramic ionic conductors. Only a few candidate materials are available, each carrying a difficult balance between advantages and drawbacks. Here we introduce a new class of possible solid-state lithium-ion conductors with the spinel structure. Such compounds could be coupled with spinel-type electrode materials to obtain a "lattice matching" solid device where low interfacial resistance could be achieved. Powders were prepared by wet chemistry, their structure was studied by means of diffraction techniques and magic angle spinning NMR, and Li(+) self-diffusion was estimated by static NMR line shape measurements. Profound differences in the Li(+) diffusion properties were observed depending on the composition, lithium content and cationic distribution. Local Li(+) hopping in the spinel materials is accompanied by a low activation energy of circa 0.35 eV being comparable with that of, e.g., LLZO-type garnets, which represent the current benchmark in this field. We propose these novel materials as a building block for a lattice-matching all-spinel solid-state battery with low interfacial resistance. PMID:23503337

  19. Small angle x-ray diffraction through living muscle links the lattice structure to macroscopic material properties

    NASA Astrophysics Data System (ADS)

    Tune, Travis; Irving, Tom; Sponberg, Simon

    Muscle is a unique hierarchical material composed of millions of molecular motors arranged on filaments in a regular lattice structure. The macroscopic, material behavior of muscle can be characterized by its workloop, a periodically activated force-length curve. Muscle is capable of operating as a spring, motor, brake, or strut, defined by its workloop. We are interested in the multiscale physics of muscle that drive its ``energetic versatility'' - the ability of muscle to alter its function. Here we introduce a system of two muscles from the cockroach whose workloops are not explained by our current understanding of the determinants of workloop function (the classic force-length, force-velocity, and twitch response). Differences in material behavior may arise from structural differences in the muscle's active lattice. Using the BIOCat beam at the Advanced Photon Source at Argonne NL, we tested for differences in the two muscles' lattice structure. Small-angle x-ray scattering (SAXS) revealed a difference of 4-8

  20. Structure of human telomeric RNA (TERRA): stacking of two G-quadruplex blocks in K(+) solution.

    PubMed

    Martadinata, Herry; Phan, Anh Tuân

    2013-04-01

    Telomeric repeat-containing RNAs (TERRA) are transcription products of the telomeres. Human TERRA sequences containing UUAGGG repeats can form parallel-stranded G-quadruplexes. The stacking interaction of such structures was shown to be important for ligand targeting and higher-order arrangement of G-quadruplexes in long TERRA sequences. Here we report on the first high-resolution structure of a stacked G-quadruplex formed by the 10-nucleotide human TERRA sequence r(GGGUUAGGGU) in potassium solution. This structure comprises two dimeric three-layer parallel-stranded G-quadruplex blocks, which stack on each other at their 5'-ends. The adenine in each UUA loop is nearly coplanar with the 5'-end G-tetrad forming an A·(G·G·G·G)·A hexad, thereby increasing the stacking contacts between the two blocks. Interestingly, this stacking and loop conformation is different from all structures previously reported for the free human TERRA but resembles the structure previously determined for a complex between a human TERRA sequence and an acridine ligand. This stacking conformation is a potential target for drugs that recognize or induce the stacking interface.

  1. Lattice parameters and electronic structure of BeMgZnO quaternary solid solutions: Experiment and theory

    NASA Astrophysics Data System (ADS)

    Toporkov, M.; Demchenko, D. O.; Zolnai, Z.; Volk, J.; Avrutin, V.; Morkoç, H.; Özgür, Ü.

    2016-03-01

    BexMgyZn1-x-yO semiconductor solid solutions are attractive for UV optoelectronics and electronic devices owing to their wide bandgap and capability of lattice-matching to ZnO. In this work, a combined experimental and theoretical study of lattice parameters, bandgaps, and underlying electronic properties, such as changes in band edge wavefunctions in BexMgyZn1-x-yO thin films, is carried out. Theoretical ab initio calculations predicting structural and electronic properties for the whole compositional range of materials are compared with experimental measurements from samples grown by plasma assisted molecular beam epitaxy on (0001) sapphire substrates. The measured a and c lattice parameters for the quaternary alloys BexMgyZn1-x with x = 0-0.19 and y = 0-0.52 are within 1%-2% of those calculated using generalized gradient approximation to the density functional theory. Additionally, composition independent ternary BeZnO and MgZnO bowing parameters were determined for a and c lattice parameters and the bandgap. The electronic properties were calculated using exchange tuned Heyd-Scuseria-Ernzerhof hybrid functional. The measured optical bandgaps of the quaternary alloys are in good agreement with those predicted by the theory. Strong localization of band edge wavefunctions near oxygen atoms for BeMgZnO alloy in comparison to the bulk ZnO is consistent with large Be-related bandgap bowing of BeZnO and BeMgZnO (6.94 eV). The results in aggregate show that precise control over lattice parameters by tuning the quaternary composition would allow strain control in BexMgyZn1-x-yO/ZnO heterostructures with possibility to achieve both compressive and tensile strain, where the latter supports formation of two-dimensional electron gas at the interface.

  2. Free-energy derivatives and structure optimization within quasiharmonic lattice dynamics

    NASA Astrophysics Data System (ADS)

    Taylor, M. B.; Barrera, G. D.; Allan, N. L.; Barron, T. H. K.

    1997-12-01

    A method is presented for the calculation of the gradient of the free energy with respect to all the internal and external degrees of freedom of a periodic crystal. This gradient can be used in conjunction with a static-energy Hessian for efficient geometrical optimization of systems with large unit cells. The free energy is calculated using lattice statics and lattice dynamics in the quasiharmonic approximation, and its derivatives by means of first-order perturbation theory. In the present application of the method, particles are assumed to interact via arbitrary short-ranged spherically-symmetric pair potentials and long-ranged Coulomb forces, and polarizability effects are accounted for by use of the shell model. The method can be used directly as the basis for a computer program which makes efficient use of both storage and CPU time, especially for large unit cells. Detailed expressions for all the lattice sums are presented.

  3. Using a best-practice perioperative governance structure to implement better block scheduling.

    PubMed

    Heiser, Randy

    2013-01-01

    Achieving, developing, and maintaining a well-functioning OR scheduling system requires a well-designed perioperative governance structure. Traditional OR/surgery committees, consisting mainly of surgeons, have tried to provide this function but often have not succeeded. An OR governance model should be led by an OR executive committee that functions as a board of directors for the surgery program and works closely with the surgery department medical director and an OR advisory committee. Ideally, the OR executive committee should develop a block schedule that includes a mix of block, open, and urgent or emergent OR access, because this combination is most effective for improving OR use and adapting to changes in surgical procedure volume.

  4. LeuT-Desipramine Structure Reveals How Antidepressants Block Neurotransmitter Reuptake

    SciTech Connect

    Zhou,Z.; Zhen, J.; Karpowich, N.; Goetz, R.; Law, C.; Reith, M.; Wang, D.

    2007-01-01

    Tricyclic antidepressants exert their pharmacological effect -- inhibiting the reuptake of serotonin, norepinephrine, and dopamine -- by directly blocking neurotransmitter transporters (SERT, NET, and DAT, respectively) in the presynaptic membrane. The drug-binding site and the mechanism of this inhibition are poorly understood. We determined the crystal structure at 2.9 angstroms of the bacterial leucine transporter (LeuT), a homolog of SERT, NET, and DAT, in complex with leucine and the antidepressant desipramine. Desipramine binds at the inner end of the extracellular cavity of the transporter and is held in place by a hairpin loop and by a salt bridge. This binding site is separated from the leucine-binding site by the extracellular gate of the transporter. By directly locking the gate, desipramine prevents conformational changes and blocks substrate transport. Mutagenesis experiments on human SERT and DAT indicate that both the desipramine-binding site and its inhibition mechanism are probably conserved in the human neurotransmitter transporters.

  5. Prediction of RNA multiloop and pseudoknot conformations from a lattice-based, coarse-grain tertiary structure model

    NASA Astrophysics Data System (ADS)

    Jost, Daniel; Everaers, Ralf

    2010-03-01

    We present a semiquantitative lattice model of RNA folding, which is able to reproduce complex folded structures such as multiloops and pseudoknots without relying on the frequently employed ad hoc generalization of the Jacobson-Stockmayer loop entropy. We derive the model parameters from the Turner description of simple secondary structural elements and pay particular attention to the unification of mismatch and coaxial stacking parameters as well as of border and nonlocal loop parameters, resulting in a reduced, unified parameter set for simple loops of arbitrary type and size. For elementary structures, the predictive power of the model is comparable to the standard secondary structure approaches, from which its parameters are derived. For complex structures, our approach offers a systematic treatment of generic effects of chain connectivity as well as of excluded volume or attractive interactions between and within all elements of the secondary structure. We reproduce the native structures of tRNA multiloops and of viral frameshift signal pseudoknots.

  6. Comparison of Brazed Residual Stress and Thermal Deformation between X-Type and Pyramidal Lattice Truss Sandwich Structure: Neutron Diffraction Measurement and Simulation Study

    NASA Astrophysics Data System (ADS)

    Jiang, Wenchun; Wei, Zhiquan; Luo, Yun; Zhang, Weiya; Woo, Wanchuck

    2016-06-01

    This paper uses finite element method and neutron diffraction measurement to study the residual stress in lattice truss sandwich structure. A comparison of residual stress and thermal deformation between X-type and pyramidal lattice truss sandwich structure has been carried out. The residual stresses are concentrated in the middle joint and then decreases gradually to both the ends. The residual stresses in the X-type lattice truss sandwich structure are smaller than those in pyramidal structure. The maximum longitudinal and transverse stresses of pyramidal structure are 220 and 202 MPa, respectively, but they decrease to 190 and 145 MPa for X-type lattice truss sandwich structure, respectively. The thermal deformation for lattice truss sandwich panel structure is of wave shape. The X-type has a better resistance to thermal deformation than pyramidal lattice truss sandwich structure. The maximum wave deformation of pyramidal structure (0.02 mm) is about twice as that of X-type (0.01 mm) at the same brazing condition.

  7. Ground State of Magnetic Dipoles on a Two-Dimensional Lattice: Structural Phases in Complex Plasmas

    SciTech Connect

    Feldmann, J. D.; Kalman, G. J.; Hartmann, P.; Rosenberg, M.

    2008-02-29

    We study analytically and by molecular dynamics simulations the ground state configuration of a system of magnetic dipoles fixed on a two-dimensional lattice. We find different phases, in close agreement with previous results. Building on this result and on the minimum energy requirement we determine the equilibrium lattice configuration, the magnetic order (ferromagnetic versus antiferromagnetic), and the magnetic polarization direction of a system of charged mesoscopic particles with magnetic dipole moments, in the domain where the strong electrostatic coupling leads to a crystalline ground state. Orders of magnitudes of the parameters of the system relevant to possible future dusty plasma experiments are discussed.

  8. Relation between structure of blocked clusters and relaxation dynamics in kinetically constrained models

    NASA Astrophysics Data System (ADS)

    Teomy, Eial; Shokef, Yair

    In a liquid all the particles are mobile, while in a glass only some of them are mobile at any given time. Although overall the structure is amorphous in both cases, the difference is that in glasses there are local structures that inhibit the movement of particles inside them. We investigate the size of these structures by considering the minimum number of particles that need to move before a specific particle can move. In kinetically-constrained models this structural property, the mean culling time, is easy to find by iteratively culling mobile particles from a snapshot of the system. We use the Kob-Andersen, Fredrickson-Andersen, and the spiral models, which are either lattice gases in which a particle may hop to a nearby site if its local environment satisfies some constraint, or Ising-like models in which a spin, representing regions of high and low mobility, can flip if its environment satisfies some constraint. We compare these structural properties to the dynamics in these models by measuring the persistence time, which is the average time it takes a particle to move for the first time. We find an algebraic relation between the mean culling time and the persistence time, with a model-dependent exponent.

  9. Assessing Hydraulic Connections Across Structural Blocks, Pahute Mesa, Nevada—Detecting Distant Drawdowns

    NASA Astrophysics Data System (ADS)

    Garcia, C.; Fenelon, J. M.; Halford, K. J.; Sweetkind, D. S.

    2010-12-01

    Groundwater beneath Pahute Mesa flows through a complexly layered sequence of volcanic-rock aquifers and confining units that have been faulted into distinct structural blocks. Hydraulic properties of the rocks and structures in this aquifer system control radionuclide migration away from areas of underground testing. Detecting drawdowns in observation wells that penetrate a structural block different from the structural block intersected by the pumping well provides irrefutable evidence of a hydraulic connection. However, detecting these pumping-induced changes in water-level records typical of Pahute Mesa can be problematic because environmental noise frequently exceeds the pumping signal. Therefore, inherent noise must be removed from the water-level record systematically before pumping-induced drawdown and subsequent recovery can be quantified and analyzed. Successful applications of this approach on Pahute Mesa are illustrated using water-level records acquired during selected periods of recent drilling, development, testing, and pumping. Continuous monitoring of water level and air pressure changes in two dozen wells reveal moderate and high frequency stresses such as barometric pressure and earth tides along with gradual water-level changes induced by well drilling, development, and testing. At distances of nearly 4 km from pumping stresses, drawdown and recovery responses of less than 0.02 m can be detected using a synthetic water-level analysis. Synthetic water-levels are the summation of barometric, tidal, and pumping responses and water levels from background wells that are fit to measured water levels in remote observation wells. Pumping responses are simulated by superposition of Theis solutions. Differences between synthetic and measured water levels are minimized by adjusting the amplitude and phase of non-pumping components, while the transmissivity and storage coefficient are estimated from the pumping responses.

  10. Cooperativity in A-tract structure and bending properties of composite TnAn blocks.

    PubMed

    Haran, T E; Crothers, D M

    1989-04-01

    The existence of intrinsically curved DNA molecules incorporating short runs of adenines is undisputed, but none of the current models can explain the entire experimental data set. Recently, Burkhoff and Tullius [Burkhoff, A. M., & Tullius, T. D. (1988) Nature 331, 455-457] offered an explanation for Hagerman's observations on A4T4N2 vs T4A4N2 polymers [Hagerman, P. J. (1986) Nature 321, 449-450], which showed that A4T4N2 multimers migrate anomalously slowly on polyacrylamide gels and T4A4N2 multimers migrate normally. In A4T4N2 multimers Burkhoff and Tullius observe a hydroxy-radical cutting pattern associated with bent DNA and a B-like cutting pattern in T4A4N2. They attribute this difference in cutting pattern to a clash in the TA step of T4A4N2 and suggest that TA4N5 might already adopt an unbent B-DNA conformation [Tullius T. D., & Burkhoff, A. M. (1988) in Structure and Expression. Vol. 3: DNA Bending and Curvature (Olson, W. K., Sarma, M. H., Sarma, R. H., & Sundaralingam, M., Eds.) pp 77-85, Adenine Press, Guilderland, NY]. We show that the conformation adopted by TnAn blocks is similar to that of AnTn blocks. Two A-tract structures of opposite polarity coexist in both blocks. Moreover, we demonstrate a cooperative buildup of a T-tract structure adjacent to an A-tract structure that cannot be predicted by any of the current models. We conclude that AA steps do not assume the same conformation in long tracts of A's as in isolated AA steps. Therefore, the assumption of nearest-neighbor models, that global curvature is an additive phenomenon of local effects, is invalid. PMID:2742812

  11. Atomic and electronic structures of lattice mismatched Cu{sub 2}O/TiO{sub 2} interfaces

    SciTech Connect

    Wang, Shuzhi; Kavaipatti, Balasubramaniam; Ramesh, Ramamoorthy; Kim, Sung-Joo; Pan, Xiaoqing; Ager, Joel W.; Wang, Lin-Wang

    2014-05-26

    Heterojunction interfaces between metal oxides are often highly lattice mismatched. The atomic and electronic structures of such interfaces, however, are not well understood. We have synthesized Cu{sub 2}O/TiO{sub 2} heterojunction thin films with 13% lattice mismatch and studied the interface via experimental methods and large-scale density function theory calculations of supercells containing ∼1300 atoms. We find that an interface of epitaxial quality is formed via a coincidence site lattice of 8 Cu{sub 2}O unit cells matching 9 TiO{sub 2} unit cells. Calculations reveal the existence of a dislocation core of the O sublattices at the interface and a random arrangement of one layer of interfacial Cu atoms. The interfacial electronic structure is found to be mostly determined by the interfacial Cu distribution, rather than by the O dislocation core. The conduction band minimum and valence band maximum states are spatially separated, and there is no strongly localized state near the core.

  12. Simulation of Seismicity in the Block-structure Model of Italy and its Surroundings

    NASA Astrophysics Data System (ADS)

    Peresan, A.; Vorobieva, I.; Soloviev, A.; Panza, G. F.

    2007-12-01

    The numerical block-model of the lithosphere dynamics is used to simulate seismicity in Italy and its surroundings, based on the available structural and geodynamics information. The purpose of the study is to understand which are the tectonic processes that control the main features of the observed seismicity and the kinematics of the region. The influence of the rheology of the fault systems is studied as well. The model we use differs from other modeling approaches in that it simulates earthquakes and hence it possibly relates to seismicity and geodynamics. The model provides an effective capability to include the set of documented constraints supplied by widely available earthquake catalogs. This is done by means of the comparison of the GR relation, of the focal mechanisms and of the space distribution for observed and computed seismicity. The region is modeled as a system of perfectly rigid blocks, separated by infinitely thin fault planes, in viscoelastic interaction between themselves and with the underlying medium. The movement of the boundary blocks and of the underlying medium determines the motion of the blocks. The synthetic seismicity obtained with the defined block-model is similar to the observed one for the most seismically active areas. A linear frequency-magnitude (FM) relation (Gutenberg-Richter law) is obtained for synthetic earthquakes; the slope ( b-value) of the FM plot appears larger for the synthetic seismicity than for the observed one. Nevertheless, the b-value is essentially larger in northern and central Italy than that in southern Italy, both in the model and in the observations. The analysis of the source mechanisms of the synthetic earthquakes shows a good agreement with the observations. In the model normal faulting is typical for the Apennines, the eastern edge of Sicily and the Calabrian arc, while reverse faulting takes place at the northwestern boundary of the Adriatic Sea, in the southern Alps and along the eastern edge of the

  13. a Modal Expansion Analysis of Noise Transmission Through Circular Cylindrical Shell Structures with Blocking Masses

    NASA Astrophysics Data System (ADS)

    GARDONIO, P.; FERGUSON, N. S.; FAHY, F. J.

    2001-07-01

    This paper covers the development and application of a modal interaction analysis (MIA) to investigate the plane wave transmission characteristics of a circular cylindrical sandwich shell of the type used in the aerospace industry for satellite launch vehicles. The model is capable of handling many high order structural and acoustic modes, and can be used to investigate the sensitivity to different structural stiffness configurations, angles of incidence, damping and cavity absorption. The model has been developed to predict the structural response and transmitted noise when a number of discrete masses are applied to the shell. The study presented considers a set of cases where blocking masses, having a total weight equal to 8% of the cylinder weight, are attached to the cylinder. The simulations carried out show a substantial reduction of the sound transmission in many of the first 15 one-third octave frequency bands (frequency range 22·4-707 Hz). The blocking masses act on the shape of the cylinder normal modes and their orientations with respect to the plane of the incident wavenumber vector. In particular, the circumferential re-orientation reduces the coupling between the incident acoustic field and the structural modes of the cylinder. The modification of the structural mode shapes, both in axial and circumferential directions, also reduces the coupling between the cylinder modes and the acoustic modes of the interior.Simulations show the effect of the number of structural and acoustic modes included on the calculated frequency response, and indicate the number necessary for an accurate prediction of the resonant and non-resonant sound transmission through the structure. In particular, the effect of neglecting off-resonance acoustic and structural modes is investigated. It is shown that restricting the acoustic and structural modes to those having natural frequencies within an interval of ±40 and ±60 Hz, respectively, of the excitation frequency produces

  14. Structure-rheology relationship in weakly amphiphilic block copolymer Langmuir monolayers.

    PubMed

    Li Destri, Giovanni; Miano, Fausto; Marletta, Giovanni

    2014-04-01

    The linear viscoelastic behavior in the low-frequency regime at the water/air interface of three different polystyrene-b-poly(methyl methacrylate) (PS-b-PMMA) copolymer monolayers, with block length ratio varying from 66-33 to 50-50 and 25-75 in molecular units, was studied and related to the interfacial behavior, characterized by means of Langmuir isotherms, and their structure, characterized by means of the atomic force microscopy technique. The two monolayers with the highest PMMA amount showed a single phase transition at about 12 mN/m, the viscoelastic behavior changing from a predominantly elastic to a viscoelastic one. This change in the viscoelastic properties was ascribed to the beginning of entanglement among the PMMA coronas of the predominantly circular quasi-2D micelles formed by the two copolymer systems. Conversely, the polymer with the lowest PMMA amount, despite having the same PMMA block length of the PS-PMMA 50-50 block copolymer, was found to behave as a viscoelastic system at any surface pressure value. This characteristic behavior cannot therefore be simply related to the molecular weight difference, but it has been put in connection to the irregular micelle structure observed in this case, consisting of a mixture of spherical and wormlike micelles, and to the different conformation adopted by the PMMA block. By blending this copolymer with an immiscible elastic homopolymer, namely poly(2-vinylpyridine), it was possible to tune the micelle nanostructure, obtaining regular circular quasi-2D micelles, with viscoelastic properties as expected for the PMMA-rich copolymer monolayers. To the best of our knowledge, this study shows for the first time the explicit dependence upon the relative block length and, in turn, upon the nanostructure of the quasi-2D micelles, of the viscoelastic properties of Langmuir monolayers and suggests that molecular weight and intermolecular interactions are not the only parameters governing the polymer conformation and

  15. Patterns without patches: hierarchical self-assembly of complex structures from simple building blocks.

    PubMed

    Grünwald, Michael; Geissler, Phillip L

    2014-06-24

    Nanoparticles with "sticky patches" have long been proposed as building blocks for the self-assembly of complex structures. The synthetic realizability of such patchy particles, however, greatly lags behind predictions of patterns they could form. Using computer simulations, we show that structures of the same genre can be obtained from a solution of simple isotropic spheres, with control only over their sizes and a small number of binding affinities. In a first step, finite clusters of well-defined structure and composition emerge from natural dynamics with high yield. In effect a kind of patchy particle, these clusters can further assemble into a variety of complex superstructures, including filamentous networks, ordered sheets, and highly porous crystals.

  16. Hollow Block Copolymer Nanoparticles through a Spontaneous One-Step Structural Reorganization

    PubMed Central

    Petzetakis, Nikos; Robin, Mathew P.; Patterson, Joseph P.; Kelley, Elizabeth G.; Cotanda, Pepa; Bomans, Paul H. H.; Sommerdijk, Nico A. J. M.; Dove, Andrew P.; Epps, Thomas H.; O'Reilly, Rachel K.

    2013-01-01

    The spontaneous one-step synthesis of hollow nanocages and nanotubes from spherical and cylindrical micelles based on poly(acrylic acid)-b-polylactide (P(AA)-b-P(LA)) block copolymers (BCPs) has been achieved. This structural reorganization, which occurs simply upon drying of the samples, was elucidated by transmission electron microscopy (TEM) and atomic force microscopy (AFM). We show that it was necessary to use stain-free imaging to examine these nanoscale assemblies, as the hollow nature of the particles was obscured by application of a heavy metal stain. Additionally, the internal topology of the P(AA)-b-P(LA) particles could be tuned by manipulating the drying conditions to give solid or compartmentalized structures. Upon re-suspension, these reorganized nanoparticles retain their hollow structure and can be display significantly enhanced loading of a hydrophobic dye compared to the original cylinders. PMID:23391297

  17. Chemically directing d-block heterometallics to nanocrystal surfaces as molecular beacons of surface structure

    SciTech Connect

    Rosen, Evelyn L.; Gilmore, Keith; Sawvel, April M.; Hammack, Aaron T.; Doris, Sean E.; Aloni, Shaul; Altoe, Virginia; Nordlund, Dennis; Weng, Tsu -Chien; Sokaras, Dimosthenis; Cohen, Bruce E.; Urban, Jeffrey J.; Ogletree, D. Frank; Milliron, Delia J.; Prendergast, David; Helms, Brett A.

    2015-07-28

    Our understanding of structure and bonding in nanoscale materials is incomplete without knowledge of their surface structure. Needed are better surveying capabilities responsive not only to different atoms at the surface, but also their respective coordination environments. We report here that d-block organometallics, when placed at nanocrystal surfaces through heterometallic bonds, serve as molecular beacons broadcasting local surface structure in atomic detail. This unique ability stems from their elemental specificity and the sensitivity of their d-orbital level alignment to local coordination environment, which can be assessed spectroscopically. Re-surfacing cadmium and lead chalcogenide nanocrystals with iron- or ruthenium-based molecular beacons is readily accomplished with trimethylsilylated cyclopentadienyl metal carbonyls. For PbSe nanocrystals with iron-based beacons, we show how core-level X-ray spectroscopies and DFT calculations enrich our understanding of both charge and atomic reorganization at the surface when beacons are bound.

  18. Chemically directing d-block heterometallics to nanocrystal surfaces as molecular beacons of surface structure

    DOE PAGESBeta

    Rosen, Evelyn L.; Gilmore, Keith; Sawvel, April M.; Hammack, Aaron T.; Doris, Sean E.; Aloni, Shaul; Altoe, Virginia; Nordlund, Dennis; Weng, Tsu -Chien; Sokaras, Dimosthenis; et al

    2015-07-28

    Our understanding of structure and bonding in nanoscale materials is incomplete without knowledge of their surface structure. Needed are better surveying capabilities responsive not only to different atoms at the surface, but also their respective coordination environments. We report here that d-block organometallics, when placed at nanocrystal surfaces through heterometallic bonds, serve as molecular beacons broadcasting local surface structure in atomic detail. This unique ability stems from their elemental specificity and the sensitivity of their d-orbital level alignment to local coordination environment, which can be assessed spectroscopically. Re-surfacing cadmium and lead chalcogenide nanocrystals with iron- or ruthenium-based molecular beacons ismore » readily accomplished with trimethylsilylated cyclopentadienyl metal carbonyls. For PbSe nanocrystals with iron-based beacons, we show how core-level X-ray spectroscopies and DFT calculations enrich our understanding of both charge and atomic reorganization at the surface when beacons are bound.« less

  19. Patterns without Patches: Hierarchical Self-Assembly of Complex Structures from Simple Building Blocks

    PubMed Central

    2014-01-01

    Nanoparticles with “sticky patches” have long been proposed as building blocks for the self-assembly of complex structures. The synthetic realizability of such patchy particles, however, greatly lags behind predictions of patterns they could form. Using computer simulations, we show that structures of the same genre can be obtained from a solution of simple isotropic spheres, with control only over their sizes and a small number of binding affinities. In a first step, finite clusters of well-defined structure and composition emerge from natural dynamics with high yield. In effect a kind of patchy particle, these clusters can further assemble into a variety of complex superstructures, including filamentous networks, ordered sheets, and highly porous crystals. PMID:24816138

  20. Nanofabrication of Block Copolymer Bulk and Thin Films: Microdomain Structures as Templates

    NASA Astrophysics Data System (ADS)

    Hashimoto, Takeji; Fukunaga, Kenji

    In this chapter we shall discuss applications of block copolymers (bcps) to nanotechnologies and nanosciences. Our objectives here are to explore the methods and principles concerning fabrications of ordered structures of bcps having various symmetries with nano-sized periodicity to create new materials with interesting structures and properties. We define this kind of fabrication as nano-fabrication. In other words we aim to control or manipulate self- organized microdomain structures of bcps, in both nonequilibrium and equi- librium states, and utilize them as templates for further nano-fabrication to- ward advanced devices and materials, such as tunable photonic crystals [1-4], quantum dots and nanowires [5-9], nanohybrids with inorganic materials and nanometal particles [10-12], photovoltaics and photoluminescence [13-16], etc. We shall present the bcp templates in both bulk (Sect. 2) and thin films (Sect. 3).

  1. New Poly(dimethylsiloxane)/Poly(perfluorooctylethyl acrylate) Block Copolymers: Structure and Order Across Multiple Length Scales in Thin Films

    SciTech Connect

    E Martinelli; G Galli; S Krishnan; M Paik; C Ober; D Fischer

    2011-12-31

    Three sets of a new class of low surface tension block copolymers were synthesized consisting of a poly(dimethylsiloxane) (PDMS) block and a poly(perfluorooctylethyl acrylate) (AF8) block. The polymers were prepared using a bromo-terminated PDMS macroinitiator, to which was attached an AF8 block grown using atom transfer radical polymerization (ATRP) in such a designed way that the molecular weight and composition of the two polymer blocks were regularly varied. The interplay of both the phase separated microstructure and the mesomorphic character of the fluorinated domains with their effect on surface structure was evaluated using a suite of analytical tools. Surfaces of spin-coated and thermally annealed films were assessed using a combination of X-ray photoelectron spectroscopy (XPS) and near-edge X-ray absorption fine structure (NEXAFS) studies. Both atomic force microscopy (AFM) measurements and grazing incidence small angle X-ray scattering (GISAXS) studies were carried out to evaluate the microstructure of the thin films. Even in block copolymers in which the PDMS block was the majority component, a significant presence of the lower surface energy AF8 block was detected at the film surface. Moreover, the perfluorooctyl helices of the AF8 repeat units were highly oriented at the surface in an ordered, tilted smectic structure, which was compared with those of the bulk powder samples using wide-angle X-ray powder diffraction (WAXD) studies.

  2. Development of a block Lanczos algorithm for free vibration analysis of spinning structures

    NASA Technical Reports Server (NTRS)

    Gupta, K. K.; Lawson, C. L.

    1988-01-01

    This paper is concerned with the development of an efficient eigenproblem solution algorithm and an associated computer program for the economical solution of the free vibration problem of complex practical spinning structural systems. Thus, a detailed description of a newly developed block Lanczos procedure is presented in this paper that employs only real numbers in all relevant computations and also fully exploits sparsity of associated matrices. The procedure is capable of computing multiple roots and proves to be most efficient compared to other existing similar techniques.

  3. Block copolymer morphologies in dye-sensitized solar cells: probing the photovoltaic structure-function relation.

    PubMed

    Crossland, Edward J W; Nedelcu, Mihaela; Ducati, Caterina; Ludwigs, Sabine; Hillmyer, Marc A; Steiner, Ullrich; Snaith, Henry J

    2009-08-01

    We integrate mesostructured titania arrays into dye-sensitized solar cells by replicating ordered, oriented one-dimensional (1D) columnar and three-dimensional (3D) bicontinuous gyroid block copolymer phases. The solar cell performance, charge transport, and recombination are investigated. We observe faster charge transport in 1D "wires" than through 3D gyroid arrays. However, owing to their structural instability, the surface area of the wire arrays is low, inhibiting the solar cell performance. The gyroid morphology, on the other hand, outperforms the current state-of-the-art mesoporous nanoparticle films.

  4. X-Ray Structures of the Hexameric Building Block of the HIV Capsid

    SciTech Connect

    Pornillos, Owen; Ganser-Pornillos, Barbie K.; Kelly, Brian N.; Hua, Yuanzi; Whitby, Frank G.; Stout, C. David; Sundquist, Wesley I.; Hill, Christopher P.; Yeager, Mark

    2009-09-11

    The mature capsids of HIV and other retroviruses organize and package the viral genome and its associated enzymes for delivery into host cells. The HIV capsid is a fullerene cone: a variably curved, closed shell composed of approximately 250 hexamers and exactly 12 pentamers of the viral CA protein. We devised methods for isolating soluble, assembly-competent CA hexamers and derived four crystallographically independent models that define the structure of this capsid assembly unit at atomic resolution. A ring of six CA N-terminal domains form an apparently rigid core, surrounded by an outer ring of C-terminal domains. Mobility of the outer ring appears to be an underlying mechanism for generating the variably curved lattice in authentic capsids. Hexamer-stabilizing interfaces are highly hydrated, and this property may be key to the formation of quasi-equivalent interactions within hexamers and pentamers. The structures also clarify the molecular basis for capsid assembly inhibition and should facilitate structure-based drug design strategies.

  5. X-ray Structures of the Hexameric Building Block of the HIV Capsid

    PubMed Central

    Pornillos, Owen; Ganser-Pornillos, Barbie K.; Kelly, Brian N.; Hua, Yuanzi; Whitby, Frank G.; Stout, C. David; Sundquist, Wesley I.; Hill, Christopher P.; Yeager, Mark

    2010-01-01

    SUMMARY The mature capsids of HIV and other retroviruses organize and package the viral genome and its associated enzymes for delivery into host cells. The HIV capsid is a fullerene cone: a variably curved, closed shell composed of approximately 250 hexamers and exactly 12 pentamers of the viral CA protein. We devised methods for isolating soluble, assembly-competent CA hexamers and derived four crystallographically independent models that define the structure of this capsid assembly unit at atomic resolution. A ring of six CA N-terminal domains form an apparently rigid core, surrounded by an outer ring of C-terminal domains. Mobility of the outer ring appears to be an underlying mechanism for generating the variably curved lattice in authentic capsids. Hexamer-stabilizing interfaces are highly hydrated, and this property may be key to forming quasi-equivalent interactions within hexamers and pentamers. The structures also clarify the molecular basis for capsid assembly inhibition, and should facilitate structure-based drug design strategies. PMID:19523676

  6. Phase structure of the anisotropic antiferromagnetic Heisenberg model on a layered triangular lattice: Spiral state and deconfined spin liquid

    SciTech Connect

    Nakane, Kazuya; Kamijo, Takeshi; Ichinose, Ikuo

    2011-02-01

    In the present paper, we study a spin-1/2 antiferromagnetic (AF) Heisenberg model on layered anisotropic triangular lattice and obtain its phase structure. We use the Schwinger bosons for representing spin operators and also a coherent-state path integral for calculating physical quantities. Finite-temperature properties of the system are investigated by means of the numerical Monte-Carlo simulations. A detailed phase diagram of the system is obtained by calculating internal energy, specific heat, spin correlation functions, etc. There are AF Neel, paramagnetic, and spiral states. Turning on the plaquette term (i.e., the Maxwell term on a lattice) of an emergent U(1) gauge field that flips a pair of parallel spin-singlet bonds, we found that there appears a phase that is regarded as a deconfined spin-liquid state, though 'transition' to this phase from the paramagnetic phase is not of second order but a crossover. In that phase, the emergent gauge boson is a physical gapless excitation coupled with spinons. These results support our previous study on an AF Heisenberg model on a triangular lattice at vanishing temperature.

  7. Precise characterization of grain structures, stacking disorders, and lattice disorders of a close-packed colloidal crystal

    NASA Astrophysics Data System (ADS)

    Suzuki, Yoshihisa; Mori, Atsushi; Fujiwara, Takahisa; Tamura, Katsuhiro

    2011-05-01

    The perpendicular fracture surface of a dried colloidal crystal with pillar-like grains, obtained by centrifugation of a dispersion of polystyrene particles, was observed using a scanning electron microscope. Many grain boundaries on the fracture surface were observed at the particle level. Most of the particles on the surface showed a face-centered cubic (FCC) array. Although some grains were single FCC ones, other FCC grains contained some stacking disorders. Most of the surface was covered with such grains, and the grain boundaries formed a mosaic-like pattern. From these results, we confirmed that the colloidal crystals obtained by centrifugation formed a bundle structure of pillar-like FCC grains. A fracture surface adjacent to the side wall of the growth cell was also observed. The surface was composed of several layers. In the uppermost layer closest to the wall, numerous point defects and mismatches of triangular lattices between the neighboring two-dimensional islands were observed. These mismatches and point defects probably generated several lattice defects in the crystal. Similar generation of lattice defects probably occurred at the bottom of the container or the growth front of the crystals. Screw dislocations were also found in the layers, although they were not observed frequently. From these results, it was concluded that two-dimensional nucleation growth and spiral growth probably occurred on the crystal-dispersion interfaces of colloidal crystals as well as on the surface of atomic crystals.

  8. Textured and hierarchically structured calcium phosphate ceramic blocks through hydrothermal treatment.

    PubMed

    Galea, Laetitia; Alexeev, Dmitriy; Bohner, Marc; Doebelin, Nicola; Studart, André R; Aneziris, Christos G; Graule, Thomas

    2015-10-01

    Synthetic calcium phosphate bone graft substitutes are widely recognized for their biocompatibility and resorption characteristics in the treatment of large bone defects. However, due to their inherent brittleness, applications in load-bearing situations always require reinforcement by additional metallic implants. Improved mechanical stability would eliminate the need for non-resorbable metallic implants. In this context a new approach to obtain calcium phosphate scaffolds with improved mechanical stability by texturing the material in specific crystal orientations was evaluated. Texture and reduction of crystal size was achieved by recrystallizing α-TCP blocks into calcium deficient hydroxyapatite (CDHA) under hydrothermal conditions. SEM and XRD analysis revealed the formation of fine CDHA needles (diameter ≈ 0.1-0.5 μm), aligned over several hundreds of micrometers. The obtained microstructures were remarkably similar to the microstructures of the prismatic layer of mollusk shells or enamel, also showing organization at 5 hierarchical structure levels. Brazilian disc tests were used to determine the diametral tensile strength, σdts, and the work-of-fracture, WOF, of the textured materials. Hydrothermal incubation significantly increased σdts and WOF of the ceramic blocks as compared to sintered blocks. These improvements were attributed to the fine and entangled crystal structure obtained after incubation, which reduces the size of strength-determining critical defects and also leads to tortuous crack propagation. Rupture surfaces revealed intergranular tortuous crack paths, which dissipate much more energy than transgranular cracks as observed in the sintered samples. Hence, the refined and textured microstructure achieved through the proposed processing route is an effective way to improve the strength and particularly the toughness of calcium phosphate-based ceramics.

  9. Myofilament lattice structure in presence of a skeletal myopathy-related tropomyosin mutation.

    PubMed

    Ochala, Julien; Iwamoto, Hiroyuki

    2013-08-01

    Human tropomyosin mutations deregulate skeletal muscle contraction at the cellular level. One key feature is the slowing of the kinetics of force development. The aim of the present study was to characterize the potential underlying molecular mechanisms by recording and analyzing the X-ray diffraction patterns of human membrane-permeabilized muscle cells expressing a particular β-tropomyosin mutation (E41K). During resting conditions, the d1,0 lattice spacing, Δ1,0 and I1,1 to I1,0 ratio were not different from control values. These results suggest that, in presence of the E41K β-tropomyosin mutation, the myofilament lattice geometry is well maintained and therefore may not have any detrimental influence on the contraction mechanisms and thus, on the rate of force generation. PMID:23686574

  10. Engineering novel optical lattices.

    PubMed

    Windpassinger, Patrick; Sengstock, Klaus

    2013-08-01

    Optical lattices have developed into a widely used and highly recognized tool to study many-body quantum physics with special relevance for solid state type systems. One of the most prominent reasons for this success is the high degree of tunability in the experimental setups. While at the beginning quasi-static, cubic geometries were mainly explored, the focus of the field has now shifted toward new lattice topologies and the dynamical control of lattice structures. In this review we intend to give an overview of the progress recently achieved in this field on the experimental side. In addition, we discuss theoretical proposals exploiting specifically these novel lattice geometries. PMID:23828639

  11. Process optimization for lattice-selective wet etching of crystalline silicon structures

    NASA Astrophysics Data System (ADS)

    Dixson, Ronald G.; Guthrie, William F.; Allen, Richard A.; Orji, Ndubuisi G.; Cresswell, Michael W.; Murabito, Christine E.

    2016-01-01

    Lattice-selective etching of silicon is used in a number of applications, but it is particularly valuable in those for which the lattice-defined sidewall angle can be beneficial to the functional goals. A relatively small but important niche application is the fabrication of tip characterization standards for critical dimension atomic force microscopes (CD-AFMs). CD-AFMs are commonly used as reference tools for linewidth metrology in semiconductor manufacturing. Accurate linewidth metrology using CD-AFM, however, is critically dependent upon calibration of the tip width. Two national metrology institutes and at least two commercial vendors have explored the development of tip calibration standards using lattice-selective etching of crystalline silicon. The National Institute of Standards and Technology standard of this type is called the single crystal critical dimension reference material. These specimens, which are fabricated using a lattice-plane-selective etch on (110) silicon, exhibit near vertical sidewalls and high uniformity and can be used to calibrate CD-AFM tip width to a standard uncertainty of less than 1 nm. During the different generations of this project, we evaluated variations of the starting material and process conditions. Some of our starting materials required a large etch bias to achieve the desired linewidths. During the optimization experiment described in this paper, we found that for potassium hydroxide etching of the silicon features, it was possible to independently tune the target linewidth and minimize the linewidth nonuniformity. Consequently, this process is particularly well suited for small-batch fabrication of CD-AFM linewidth standards.

  12. An object-oriented approach for parallel self adaptive mesh refinement on block structured grids

    NASA Technical Reports Server (NTRS)

    Lemke, Max; Witsch, Kristian; Quinlan, Daniel

    1993-01-01

    Self-adaptive mesh refinement dynamically matches the computational demands of a solver for partial differential equations to the activity in the application's domain. In this paper we present two C++ class libraries, P++ and AMR++, which significantly simplify the development of sophisticated adaptive mesh refinement codes on (massively) parallel distributed memory architectures. The development is based on our previous research in this area. The C++ class libraries provide abstractions to separate the issues of developing parallel adaptive mesh refinement applications into those of parallelism, abstracted by P++, and adaptive mesh refinement, abstracted by AMR++. P++ is a parallel array class library to permit efficient development of architecture independent codes for structured grid applications, and AMR++ provides support for self-adaptive mesh refinement on block-structured grids of rectangular non-overlapping blocks. Using these libraries, the application programmers' work is greatly simplified to primarily specifying the serial single grid application and obtaining the parallel and self-adaptive mesh refinement code with minimal effort. Initial results for simple singular perturbation problems solved by self-adaptive multilevel techniques (FAC, AFAC), being implemented on the basis of prototypes of the P++/AMR++ environment, are presented. Singular perturbation problems frequently arise in large applications, e.g. in the area of computational fluid dynamics. They usually have solutions with layers which require adaptive mesh refinement and fast basic solvers in order to be resolved efficiently.

  13. Influence of lattice orientation on growth and structure of graphene on Cu(001)

    SciTech Connect

    Wofford, Joseph M.; Nie, Shu; Thürmer, Konrad; McCarty, Kevin F.; Dubon, Oscar D.

    2015-03-31

    We have used low-energy electron microscopy (LEEM) and diffraction (LEED) to examine the significance of lattice orientation in graphene growth on Cu(0 0 1). Individual graphene domains undergo anisotropic growth on the Cu surface, and develop into lens shapes with their long axes roughly aligned with Cu <1 0 0> in-plane directions. Furthermore, the long axis of a lens-shaped domain is only rarely oriented along a C <1 1> direction, suggesting that carbon attachment at “zigzag” graphene island edges is unfavorable. A kink-mediated adatom attachment process is consistent with the behavior observed here and reported in the literature. Likewise, the details of the ridged moiré pattern formed by the superposition of the graphene lattice on the (0 0 1) Cu surface also evolve with the graphene lattice orientation, and are predicted well by a simple geometric model. Managing the kink-mediated growth mode of graphene on Cu(0 0 1) will be necessary for the continued improvement of this graphene synthesis technique.

  14. Influence of lattice orientation on growth and structure of graphene on Cu(001)

    DOE PAGESBeta

    Wofford, Joseph M.; Nie, Shu; Thürmer, Konrad; McCarty, Kevin F.; Dubon, Oscar D.

    2015-03-31

    We have used low-energy electron microscopy (LEEM) and diffraction (LEED) to examine the significance of lattice orientation in graphene growth on Cu(0 0 1). Individual graphene domains undergo anisotropic growth on the Cu surface, and develop into lens shapes with their long axes roughly aligned with Cu <1 0 0> in-plane directions. Furthermore, the long axis of a lens-shaped domain is only rarely oriented along a C <1 1> direction, suggesting that carbon attachment at “zigzag” graphene island edges is unfavorable. A kink-mediated adatom attachment process is consistent with the behavior observed here and reported in the literature. Likewise, themore » details of the ridged moiré pattern formed by the superposition of the graphene lattice on the (0 0 1) Cu surface also evolve with the graphene lattice orientation, and are predicted well by a simple geometric model. Managing the kink-mediated growth mode of graphene on Cu(0 0 1) will be necessary for the continued improvement of this graphene synthesis technique.« less

  15. Two-Dimensional Pnictogen Honeycomb Lattice: Structure, On-Site Spin-Orbit Coupling and Spin Polarization

    PubMed Central

    Lee, Jason; Tian, Wen-Chuan; Wang, Wei-Liang; Yao, Dao-Xin

    2015-01-01

    Because of its novel physical properties, two-dimensional materials have attracted great attention. From first-principle calculations and vibration frequencies analysis, we predict a new family of two-dimensional materials based on the idea of octet stability: honeycomb lattices of pnictogens (N, P, As, Sb, Bi). The buckled structures of materials come from the sp3 hybridization. These materials have indirect band gap ranging from 0.43 eV to 3.7 eV. From the analysis of projected density of states, we argue that the s and p orbitals together are sufficient to describe the electronic structure under tight-binding model, and the tight-binding parameters are obtained by fitting the band structures to first-principle results. Surprisingly large on-site spin-orbit coupling is found for all the pnictogen lattices except nitrogen. Investigation on the electronic structures of both zigzag and armchair nanoribbons reveals the possible existence of spin-polarized ferromagnetic edge states in some cases, which are rare in one-dimensional systems. These edge states and magnetism may exist under the condition of high vacuum and low temperature. This new family of materials would have promising applications in electronics, optics, sensors, and solar cells. PMID:26122870

  16. Reliability study of Piezoelectric Structures Dedicated to Energy Harvesting by the Way of Blocking Force Investigation

    NASA Astrophysics Data System (ADS)

    Maaroufi, S.; Parrain, F.; Lefeuvre, E.; Boutaud, B.; Dal Molin, R.

    2015-12-01

    In this paper we propose an approach to study the reliability of piezoelectric structures and more precisely energy harvesting micro-devices dedicated to autonomous active medical implants (new generation pacemakers). The structure under test is designed as a bimorph piezoelectric cantilever with a seismic mass at its tip. Good understanding of material aging and mechanical failure is critical for this kind of system. To study the reliability and durability of the piezoelectric part we propose to establish a new accelerated methodology and an associated test bench where the environment and stimuli can be precisely controlled over a wide period of time. This will allow the identification of potential failure modes and the study of their impacts by the way of direct mechanical investigation based on stiffness and blocking force measurements performed periodically.

  17. Structural basis of open channel block in a prokaryotic pentameric ligand-gated ion channel.

    PubMed

    Hilf, Ricarda J C; Bertozzi, Carlo; Zimmermann, Iwan; Reiter, Alwin; Trauner, Dirk; Dutzler, Raimund

    2010-11-01

    The flow of ions through cation-selective members of the pentameric ligand-gated ion channel family is inhibited by a structurally diverse class of molecules that bind to the transmembrane pore in the open state of the protein. To obtain insight into the mechanism of channel block, we have investigated the binding of positively charged inhibitors to the open channel of the bacterial homolog GLIC by using X-ray crystallography and electrophysiology. Our studies reveal the location of two regions for interactions, with larger blockers binding in the center of the membrane and divalent transition metal ions binding to the narrow intracellular pore entry. The results provide a structural foundation for understanding the interactions of the channel with inhibitors that is relevant for the entire family.

  18. Polymer electrolyte membranes from fluorinated polyisoprene-block-sulfonated polystyrene: Structural evolution with hydration and heating

    SciTech Connect

    Sodeye, Akinbode; Huang, Tianzi; Gido, Samuel; Mays, Jimmy

    2011-01-01

    Small-angle neutron scattering (SANS) and ultra-small-angle X-ray scattering (USAXS) have been used to study the structural changes in fluorinated polyisoprene/sulfonated polystyrene (FISS) diblock copolymers as they evolved from the dry state to the water swollen state. A dilation of the nanometer-scale hydrophilic domains has been observed as hydration increased, with greater dilation occurring in the more highly sulfonated samples or upon hydration at higher temperatures. Furthermore, a decrease in the order in these phase separated structures is observed upon swelling. The glass transition temperatures of the fluorinated blocks have been observed to decrease upon hydration of these materials, and at the highest hydration levels, differential scanning calorimetry (DSC) has shown the presence of tightly bound water. A precipitous drop in the mechanical integrity of the 50% sulfonated materials is also observed upon exceeding the glass transition temperature (Tg), as measured by dynamic mechanical analysis (DMA).

  19. Fermi surface and order parameter driven vortex lattice structure transitions in twin-free YBa2Cu3O7.

    PubMed

    White, J S; Hinkov, V; Heslop, R W; Lycett, R J; Forgan, E M; Bowell, C; Strässle, S; Abrahamsen, A B; Laver, M; Dewhurst, C D; Kohlbrecher, J; Gavilano, J L; Mesot, J; Keimer, B; Erb, A

    2009-03-01

    We report on small-angle neutron scattering studies of the intrinsic vortex lattice (VL) structure in detwinned YBa2Cu3O7 at 2 K, and in fields up to 10.8 T. Because of the suppressed pinning to twin-domain boundaries, a new distorted hexagonal VL structure phase is stabilized at intermediate fields. It is separated from a low-field hexagonal phase of different orientation and distortion by a first-order transition at 2.0(2) T that is probably driven by Fermi surface effects. We argue that another first-order transition at 6.7(2) T, into a rhombic structure with a distortion of opposite sign, marks a crossover from a regime where Fermi surface anisotropy is dominant, to one where the VL structure and distortion is controlled by the order-parameter anisotropy. PMID:19392554

  20. Role of structural factors in formation of chiral magnetic soliton lattice in Cr1/3NbS2

    NASA Astrophysics Data System (ADS)

    Volkova, L. M.; Marinin, D. V.

    2014-10-01

    The sign and strength of magnetic interactions not only between nearest neighbors, but also for longer-range neighbors in the Cr1/3NbS2 intercalation compound have been calculated on the basis of structural data. It has been found that left-handed spin helices in Cr1/3NbS2 are formed from strength-dominant at low temperatures antiferromagnetic (AFM) interactions between triangular planes of Cr3+ ions through the plane of just one of two crystallographically equivalent diagonals of side faces of embedded into each other trigonal prisms building up the crystal lattice of magnetic Cr3+ ions. These helices are oriented along the c axis and packed into two-dimensional triangular lattices in planes perpendicular to these helices directions and lay one upon each other with a displacement. The competition of the above AFM helices with weaker inter-helix AFM interactions could promote the emergence of a long-period helical spin structure. One can assume that in this case, the role of Dzyaloshinskii-Moriya interaction consists of final ordering and stabilization of chiral spin helices into a chiral magnetic soliton lattice. The possibility of emergence of solitons in M1/3NbX2 and M1/3TaX2 (M = Cr, V, Ti, Rh, Ni, Co, Fe, and Mn; X = S and Se) intercalate compounds has been examined. Two important factors caused by the crystal structure (predominant chiral magnetic helices and their competition with weaker inter-helix interactions not destructing the system quasi-one-dimensional character) can be used for the crystal chemistry search of solitons.

  1. Determination of the fine structure constant based on BLOCH oscillations of ultracold atoms in a vertical optical lattice.

    PubMed

    Cladé, Pierre; de Mirandes, Estefania; Cadoret, Malo; Guellati-Khélifa, Saïda; Schwob, Catherine; Nez, François; Julien, Lucile; Biraben, François

    2006-01-27

    We report an accurate measurement of the recoil velocity of 87Rb atoms based on Bloch oscillations in a vertical accelerated optical lattice. We transfer about 900 recoil momenta with an efficiency of 99.97% per recoil. A set of 72 measurements of the recoil velocity, each one with a relative uncertainty of about 33 ppb in 20 min integration time, leads to a determination of the fine structure constant with a statistical relative uncertainty of 4.4 ppb. The detailed analysis of the different systematic errors yields to a relative uncertainty of 6.7 ppb. The deduced value of alpha-1 is 137.035 998 78(91).

  2. Crustal Structure across Rivera Plate and Jalisco Block (MEXICO): TsuJal Project

    NASA Astrophysics Data System (ADS)

    Nuñez-Cornu, F. J.; Nunez, D.; Barba, D. C., Sr.; Trejo, E.; Escalona, F.; Danobeitia, J.; Gutierrez Pena, Q. J.

    2015-12-01

    Located on the western margin of Mexico, the collision zone between Rivera, Cocos and North American plates is a complex tectonic collage with high seismic hazards and potential tsunamigenic sources. During the spring of 2014, within the framework of TSUJAL project, Spanish and Mexican scientists investigated this region with the main objective of defining the crustal architecture of this active margin and recognizing potential structural sources that can trigger earthquakes and tsunamis at the convergence between Rivera plate-Jalisco block with the North American Plate. To achieve these goals, a wide-ranging of geophysical data was acquired in this region both offshore and onshore. In this paper, we present the preliminary results obtained from this project about bathymetric, structural geology and wide-angle seismic data of the southern coast of Bahía de Banderas. A crustal P-wave velocity model for the southern coast of Bahía de Banderas was obtained using WAS data recorded by OBS and land seismic stations for more than 150 km across Rivera Plate and Jalisco Block. The thickness of the slab in this area is about 10 km and presents a dip angle about 8º. Continental crustal thickness below Puerto Vallarta is about 20 km, no evidence of continental Moho was found in this study. This model support that due to the convergence of Rivera Plate against Jalisco Block, the region of Bahía de Banderas is under strong crustal stresses that generate structural lineaments and have the same trends offshore and inland. Most of the seismicity reported can be associated to the main structural lineaments. The Banderas Canyon apparently is in an opening process from west to east, which seems to continue through the Rio Pitillal river valley. There is no seismic or morphological evidence to consider that the Banderas Canyon is a continuation of Vallarta Graben.South of María Cleofas Island, the SC marks the limit between RP and JB, possibly being the result of the RP against JB

  3. Semiexperimental equilibrium structures for building blocks of organic and biological molecules: the B2PLYP route.

    PubMed

    Penocchio, Emanuele; Piccardo, Matteo; Barone, Vincenzo

    2015-10-13

    The B2PLYP double hybrid functional, coupled with the correlation-consistent triple-ζ cc-pVTZ (VTZ) basis set, has been validated in the framework of the semiexperimental (SE) approach for deriving accurate equilibrium structures of molecules containing up to 15 atoms. A systematic comparison between new B2PLYP/VTZ results and several equilibrium SE structures previously determined at other levels, in particular B3LYP/SNSD and CCSD(T) with various basis sets, has put in evidence the accuracy and the remarkable stability of such model chemistry for both equilibrium structures and vibrational corrections. New SE equilibrium structures for phenylacetylene, pyruvic acid, peroxyformic acid, and phenyl radical are discussed and compared with literature data. Particular attention has been devoted to the discussion of systems for which lack of sufficient experimental data prevents a complete SE determination. In order to obtain an accurate equilibrium SE structure for these situations, the so-called templating molecule approach is discussed and generalized with respect to our previous work. Important applications are those involving biological building blocks, like uracil and thiouracil. In addition, for more general situations the linear regression approach has been proposed and validated.

  4. Structured nanoporous surfaces from hybrid block copolymer micelle films with metal ions

    NASA Astrophysics Data System (ADS)

    Kim, Minsoo P.; Kim, Hyeong Jun; Kim, Bumjoon J.; Yi, Gi-Ra

    2015-03-01

    We present a novel method for producing structured nanoporous thin films using block copolymer (BCP) micelles loaded with metallic ions. The BCP micellar thin films containing gold (Au) ions were prepared by spin-coating poly(styrene-block-4-vinylpyridine) (PS-b-P4VP) micelle solutions in which Au precursors (AuCl4-) were selectively loaded onto the P4VP core. When the micellar films were exposed to cetyltrimethylammonium bromide (CTAB) solutions, the Au precursors were selectively extracted from the P4VP domains due to their strong electrostatic interaction with CTAB, leading to the formation of pores in the micelles. Consequently, regularly patterned nanoporous surfaces were formed. By controlling the molecular weight (Mn) of PS-b-P4VP and the amount of Au precursors (λ) that were loaded in the P4VP domains, the pore size and depth could be tuned precisely. In particular, when a sufficient amount of Au precursors was loaded (λ ≥ 0.3), the porous surface nanostructure was well developed. In addition, the pore size and depth of the nanostructure increased as the λ value increased. For instance, when the λ value increased from 0.3 to 1.0, the pore size increased from 22.8 nm to 28.8 nm, and the pore depth increased from 2.1 nm to 3.2 nm. Interestingly, the transition from the nonporous structures to the porous structures in the micellar film could be reversibly controlled by adding and removing the Au precursors in the film. Moreover, our method for the preparation of nanoporous films can be extended to micellar film by incorporating other metal ions such as silver (Ag) and iron (Fe).

  5. Predicting epitaxial orientations and lattice structure in ultrathin magnetic thin films

    NASA Astrophysics Data System (ADS)

    Lu, Yong; Wang, Cuiping; Shi, Rongpei; Cui, Yuanyuan; Shi, Zhan; Yang, Shuiyuan; Cui, Yuwen; Liu, Xingjun

    2016-07-01

    Metastable phases, such as bcc Co or Ni and hcp Fe or Ni, reportedly possess extraordinary magnetic properties for epitaxial ultra-thin films. To understand phase stability of these epitaxy-oriented phases upon substrate lattices, we calculated novel phase diagrams of Co, Fe, and Ni ultrathin films by considering the chemical free energy, elastic strain energy, and surface energy. Verified by experimental data in the literatures, the stable epitaxy-oriented phases are readily identified from the phase diagrams. The stabilization of these metastable phases is determined by the interplay between orientation-dependent elastic strain energy and surface energy.

  6. Phase structure, magnetic monopoles, and vortices in the lattice Abelian Higgs model

    SciTech Connect

    Ranft, J.; Kripfganz, J.; Ranft, G.

    1983-07-15

    We present Monte Carlo calculations of lattice Abelian Higgs models in four dimensions and with charges of the Higgs particles equal to q = 1, 2, and 6. The phase transitions are studied in the plane of the two coupling constants considering separately average plaquette and average link expectation values. The density of topological excitations is studied. In the confinement phase we find finite densities of magnetic-monopole currents, electric currents, and vortex currents. The magnetic-monopole currents vanish exponentially in the Coulomb phase. The density of electric currents and vortex currents is finite in the Coulomb phase and vanishes exponentially in the Higgs phase.

  7. Sympatric speciation in an age-structured population living on a lattice

    NASA Astrophysics Data System (ADS)

    Sousa, A. O.

    2004-06-01

    A square lattice is introduced into the Penna model for biological aging in order to study the evolution of diploid sexual populations under certain conditions when one single locus in the individual’s genome is considered as identifier of species. The simulation results show, after several generations, the flourishing and coexistence of two separate species in the same environment, i.e., one original species splits up into two on the same territory (sympatric speciation). As well, the mortalities obtained are in a good agreement with the Gompertz law of exponential increase of mortality with age.

  8. Ice crystals growing on K-feldspar (microcline) have preferential orientation dictated by feldspar lattice structure

    NASA Astrophysics Data System (ADS)

    Kiselev, A. A.; Bachmann, F.; Pedevilla, P.; Cox, S.; Michaelides, A.

    2014-12-01

    Recently, we have conducted experiments on deposition nucleation and growth of ice on freshly cleaved natural K-feldspar (microcline) crystals exposed to water vapor in the Environmental Scanning Electron Microscope (ESEM, FEI Quanta 650 FEG). Independently adjusting the partial water vapor pressure in the sample chamber and the temperature of the substrate mounted on top of the double-stage Peltier element, deposition ice nucleation, growth, and sublimation can be studied within the temperature range from -5°C to -60°C. By using small crystal size and tilted geometry we have been able to record the video sequences of ice nucleation taking place on both 001 and 010 crystallographic planes simultaneously. Here, we report the following general features of ice nucleation and growth observed in these experiments: Nucleation of ice always starts before the water saturation is reached. Ice was preferentially nucleating on surface defects (steps, cracks, and pits) or on the debris particles scattered over the surface of feldspar crystal. Ice crystals grown via deposition at temperatures above -30°C on any of the feldspar crystal faces have shown the same directional and rotational orientation, with c-axis of ice aligned with the c-axis of microcline unit cell. Below -35°C no preferential orientation has been observed whatsoever. The majority of observed ice crystals exhibit the evaporation groove at the waist of hexagonal prism, indicting the presence of lattice dislocations in the crystal nucleation plane. We discuss a possible mechanism of crystal lattice alignment by considering layer of ordered water on the surface of feldspar crystal forming prior to ice nucleation. Using density functional theory we show how the mineral surface interacts with water, particularly addressing the interaction of surface cations and hydroxyl groups with a water overlayer. We argue that the misalignment of the 001 lattice planes for microcline and ice (inherently following from the

  9. Three-dimensional, off-lattice Monte-Carlo kinetics simulations of interstellar grain chemistry and ice structure

    SciTech Connect

    Garrod, Robin T.

    2013-12-01

    The first off-lattice Monte Carlo kinetics model of interstellar dust grain surface chemistry is presented. The positions of all surface particles are determined explicitly, according to the local potential minima resulting from the pair-wise interactions of contiguous atoms and molecules, rather than by a pre-defined lattice structure. The model is capable of simulating chemical kinetics on any arbitrary dust grain morphology, as determined by the user-defined positions of each individual dust grain atom. A simple method is devised for the determination of the most likely diffusion pathways and their associated energy barriers for surface species. The model is applied to a small, idealized dust grain, adopting various gas densities and using a small chemical network. Hydrogen and oxygen atoms accrete onto the grain to produce H{sub 2}O, H{sub 2}, O{sub 2}, and H{sub 2}O{sub 2}. The off-lattice method allows the ice structure to evolve freely; the ice mantle porosity is found to be dependent on the gas density, which controls the accretion rate. A gas density of 2 × 10{sup 4} cm{sup –3}, appropriate for dark interstellar clouds, is found to produce a fairly smooth and non-porous ice mantle. At all densities, H{sub 2} molecules formed on the grains collect within the crevices that divide nodules of ice and within micropores (whose extreme inward curvature produces strong local potential minima). The larger pores produced in the high-density models are not typically filled with H{sub 2}. Direct deposition of water molecules onto the grain indicates that amorphous ices formed in this way may be significantly more porous than interstellar ices that are formed by surface chemistry.

  10. Structure Activity Relationships of Monocyte Chemoattractant Proteins in Complex with a Blocking Antibody

    SciTech Connect

    Reid,C.; Rushe, M.; Jarpe, M.; Van Vlijmen, H.; Dolinski, B.; Qian, F.; Cachero, T.; Cuervo, H.; Yanachkova, M.; et al.

    2006-01-01

    Monocyte chemoattractant proteins (MCPs) are cytokines that direct immune cells bearing appropriate receptors to sites of inflammation or injury and are therefore attractive therapeutic targets for inhibitory molecules. 11K2 is a blocking mouse monoclonal antibody active against several human and murine MCPs. A 2.5 Angstroms structure of the Fab fragment of this antibody in complex with human MCP-1 has been solved. The Fab blocks CCR2 receptor binding to MCP-1 through an adjacent but distinct binding site. The orientation of the Fab indicates that a single MCP-1 dimer will bind two 11K2 antibodies. Several key residues on the antibody and on human MCPs were predicted to be involved in antibody selectivity. Mutational analysis of these residues confirms their involvement in the antibody- chemokine interaction. In addition to mutations that decreased or disrupted binding, one antibody mutation resulted in a 70-fold increase in affinity for human MCP-2. A key residue missing in human MCP-3, a chemokine not recognized by the antibody, was identified and engineering the preferred residue into the chemokine conferred binding to the antibody.

  11. Influencing the structure of block copolymer micelles with small molecule additives

    NASA Astrophysics Data System (ADS)

    Robertson, Megan; Singh, Avantika; Cooksey, Tyler; Kidd, Bryce; Piemonte, Rachele; Wang, Shu; Mai Le, Kim; Madsen, Louis

    Amphiphilic block copolymer micelles in water are under broad exploration for drug delivery applications due to their high loading capacity and targeted drug delivery. We aim to understand the kinetic and thermodynamic processes that underlie the self-assembly of diblock copolymer micelle systems. The present work focuses on diblock copolymers containing poly(ethylene oxide) (a hydrophilic polymer) and polycaprolactone (a hydrophobic polymer), which spontaneously self-assemble into spherical micelles in water. Addition of a common good solvent (a co-solvent) for both of the constituting blocks, such as tetrahydrofuran (THF), reduces the interfacial tension at the core-corona interface. We are currently investigating the effect of this phenomenon on the micelle structural properties, using small-angle scattering and nuclear magnetic resonance. We have characterized the hydrodynamic radius, core radius, corona thickness, aggregation number, degree of swelling of the micelle core with the co-solvent, and unimer (free chain) concentration, as a function of the co-solvent concentration. Fundamental knowledge from these studies will inform design of drug delivery systems by allowing us to tailor micelle properties for optimal cargo loading.

  12. Bragg spectroscopy of trapped one-dimensional strongly interacting bosons in optical lattices: Probing the cake structure

    NASA Astrophysics Data System (ADS)

    Pupillo, Guido; Rey, Ana Maria; Batrouni, Ghassan George

    2006-07-01

    We study Bragg spectroscopy of strongly interacting one-dimensional bosons loaded in an optical lattice plus an additional parabolic potential. We calculate the dynamic structure factor by using Monte Carlo simulations for the Bose-Hubbard Hamiltonian, exact diagonalizations and the results of a recently introduced extended fermionization model. We find that, due to the system’s inhomogeneity, the excitation spectrum exhibits a multibranched structure, whose origin is related to the presence of superfluid regions with different densities in the atomic distribution. We thus suggest that Bragg spectroscopy in the linear regime can be used as an experimental tool to unveil the shell structure of alternating Mott insulator and superfluid phases characteristic of trapped bosons.

  13. Bragg spectroscopy of trapped one-dimensional strongly interacting bosons in optical lattices: Probing the cake structure

    SciTech Connect

    Pupillo, Guido; Rey, Ana Maria; Batrouni, Ghassan George

    2006-07-15

    We study Bragg spectroscopy of strongly interacting one-dimensional bosons loaded in an optical lattice plus an additional parabolic potential. We calculate the dynamic structure factor by using Monte Carlo simulations for the Bose-Hubbard Hamiltonian, exact diagonalizations and the results of a recently introduced extended fermionization model. We find that, due to the system's inhomogeneity, the excitation spectrum exhibits a multibranched structure, whose origin is related to the presence of superfluid regions with different densities in the atomic distribution. We thus suggest that Bragg spectroscopy in the linear regime can be used as an experimental tool to unveil the shell structure of alternating Mott insulator and superfluid phases characteristic of trapped bosons.

  14. Computational analysis of triangular and honeycomb lattice-structured tapered nanoholes for enhanced light trapping in thin-film Si solar cells

    NASA Astrophysics Data System (ADS)

    Xavier, Jolly; Becker, Christiane

    2014-05-01

    For an optimized light harvesting while using diverse periodic photonic light-trapping architectures in low cost thin film crystalline silicon (c-Si) solar cells, it is also of prime importance to tune the features of their lattice point basis structure. In view of this, tapered nanoholes would be of importance for envisaged better light in-coupling due to graded index effect and also from the point of fabrication feasibility. Using a 3D finite element method based computational simulator, we investigate the basis structural influence of triangular as well as honeycomb lattice-structured experimentally feasible tapered air nanoholes in ~400 nm thick c-Si absorber on a glass substrate. We present a detailed convergence analysis of volume absorption in Si absorber with cylindrical as well as tapered nanoholes. For a wavelength rage of 300 nm to 1100 nm, we present the computed results on light absorption of the engineered Si nanoholes for a lattice periodicity of 600nm. In particular, we study the influence of tapering angle of engineered nano air holes in Si thin film for the absorption enhancement in photonic triangular and honeycomb lattice structured tapered nanoholes. Further we make a comparative analysis of cylindrical and tapered nanoholes for a range of light incident angles from 0° to 60°. For the presented triangular as well as honeycomb lattice structured nanoholes, we observe that in comparison to the cylindrical nanoholes, the tapered nanoholes perform better in terms of light trapping for enhanced light absorption in textured Si thin films even when the effective volume fraction of Si is lower in the absorber layer with tapered nanoholes in comparison to that of cylindrical ones. From the maximum achievable short circuit current density estimation in the present study, the performance of c-Si absorbing layer engineered with triangular lattice structured tapered air holes harvests light efficiently owing to its higher lattice symmetry among periodic

  15. High-performance microfluidic rectifier based on sudden expansion channel with embedded block structure.

    PubMed

    Tsai, Chien-Hsiung; Lin, Che-Hsin; Fu, Lung-Ming; Chen, Hui-Chun

    2012-06-01

    A high-performance microfluidic rectifier incorporating a microchannel and a sudden expansion channel is proposed. In the proposed device, a block structure embedded within the expansion channel is used to induce two vortex structures at the end of the microchannel under reverse flow conditions. The vortices reduce the hydraulic diameter of the microchannel and, therefore, increase the flow resistance. The rectification performance of the proposed device is evaluated by both experimentally and numerically. The experimental and numerical values of the rectification performance index (i.e., the diodicity, Di) are found to be 1.54 and 1.76, respectively. Significantly, flow rectification is achieved without the need for moving parts. Thus, the proposed device is ideally suited to the high pressure environment characteristic of most micro-electro-mechanical-systems (MEMS)-based devices. Moreover, the rectification performance of the proposed device is superior to that of existing valveless rectifiers based on Tesla valves, simple nozzle/diffuser structures, or cascaded nozzle/diffuser structures.

  16. High-performance microfluidic rectifier based on sudden expansion channel with embedded block structure

    PubMed Central

    Tsai, Chien-Hsiung; Lin, Che-Hsin; Fu, Lung-Ming; Chen, Hui-Chun

    2012-01-01

    A high-performance microfluidic rectifier incorporating a microchannel and a sudden expansion channel is proposed. In the proposed device, a block structure embedded within the expansion channel is used to induce two vortex structures at the end of the microchannel under reverse flow conditions. The vortices reduce the hydraulic diameter of the microchannel and, therefore, increase the flow resistance. The rectification performance of the proposed device is evaluated by both experimentally and numerically. The experimental and numerical values of the rectification performance index (i.e., the diodicity, Di) are found to be 1.54 and 1.76, respectively. Significantly, flow rectification is achieved without the need for moving parts. Thus, the proposed device is ideally suited to the high pressure environment characteristic of most micro-electro-mechanical-systems (MEMS)-based devices. Moreover, the rectification performance of the proposed device is superior to that of existing valveless rectifiers based on Tesla valves, simple nozzle/diffuser structures, or cascaded nozzle/diffuser structures. PMID:22655019

  17. Influences of salt structures on reservoir rocks in block L-2, Dutch continental shelf

    SciTech Connect

    Dronkert, H. ); Remmelts, G. )

    1993-09-01

    In the subsurface of the Netherlands Continental Shelf, thick layers of Zechstein salt have developed into salt domes and ridges that pierce through the overlying formations. To measure the range of lateral influence of the salt in these structures on the sandstone reservoir rocks of the Mesozoic sequence, a cementation model was developed. The target area, Block L-2, was chosen for the presence of salt domes, wells, and reservoir rocks. The L-2 case study has been performed on two Triassic sandstone intervals. The lower, Volpriehausen, sandstone showed halite cementation in one well, located within several 100 m from a salt dome. Four other wells, located more than 1.5 km from a salt structure, did not show any signs of halite cementation. Therefore, the lateral influence of salt domes on the surrounding reservoir rock is, in this case, limited to less than 1.5 km at 3-4 km depth. A slightly shallower Triassic sandstone (Detfurth) shows more frequent halite cementation. This cementation can be attributed to early seepage from overlying Rot salt brines.Triassic Rot salt is present above depletion areas of the Zechstein salt structures, and in such a way the seepage can be seen as an indirect influence of the salt structures.

  18. AFM study of excimer laser patterning of block-copolymer: Creation of ordered hierarchical, hybrid, or recessed structures

    NASA Astrophysics Data System (ADS)

    Švanda, Jan; Siegel, Jakub; Švorčík, Vaclav; Lyutakov, Oleksiy

    2016-05-01

    We report fabrication of the varied range of hierarchical structures by combining bottom-up self-assembly of block copolymer poly(styrene-block-vinylpyridine) (PS-b-P4VP) with top-down excimer laser patterning method. Different procedures were tested, where laser treatment was applied before phase separation and after phase separation or phase separation and surface reconstruction. Laser treatment was performed using either polarized laser light with the aim to create periodical pattern on polymer surface or non-polarized light for preferential removing of polystyrene (PS) part from PS-b-P4VP. Additionally, dye was introduced into one part of block copolymer (P4VP) with the aim to modify its response to laser light. Resulting structures were analyzed by XPS, UV-vis and AFM techniques. Application of polarized laser light leads to creation of structures with hierarchical, recessed or hybrid geometries. Non-polarized laser beam allows pronouncing the block copolymer phase separated structure. Tuning the order of steps or individual step conditions enables the efficient reorientation of block-copolymer domain at large scale, fabrication of hierarchical, hybrid or recessed structures. The obtained structures can find potential applications in nanotechnology, photonics, plasmonics, information storage, optical devices, sensors and smart surfaces.

  19. Baryon spin-flavor structure from an analysis of lattice QCD results of the baryon spectrum

    SciTech Connect

    Fernando, I. P.; Goity, J. L.

    2015-02-01

    The excited baryon masses are analyzed in the framework of the 1/Nc expansion using the available physical masses and also the masses obtained in lattice QCD for different quark masses. The baryon states are organized into irreducible representations of SU(6) x O(3), where the [56,lP=0⁺] ground state and excited baryons, and the [56,2+] and [70}},1-] excited states are analyzed. The analyses are carried out to order O(1/Nc) and first order in the quark masses. The issue of state identifications is discussed. Numerous parameter independent mass relations result at those orders, among them the well known Gell-Mann-Okubo and Equal Spacing relations, as well as additional relations involving baryons with different spins. It is observed that such relations are satisfied at the expected level of precision. The main conclusion of the analysis is that qualitatively the dominant physical effects are similar for the physical and the lattice QCD baryons.

  20. Baryon spin-flavor structure from an analysis of lattice QCD results of the baryon spectrum

    DOE PAGESBeta

    Fernando, I. P.; Goity, J. L.

    2015-02-01

    The excited baryon masses are analyzed in the framework of the 1/Nc expansion using the available physical masses and also the masses obtained in lattice QCD for different quark masses. The baryon states are organized into irreducible representations of SU(6) x O(3), where the [56,lP=0⁺] ground state and excited baryons, and the [56,2+] and [70}},1-] excited states are analyzed. The analyses are carried out to order O(1/Nc) and first order in the quark masses. The issue of state identifications is discussed. Numerous parameter independent mass relations result at those orders, among them the well known Gell-Mann-Okubo and Equal Spacing relations,more » as well as additional relations involving baryons with different spins. It is observed that such relations are satisfied at the expected level of precision. The main conclusion of the analysis is that qualitatively the dominant physical effects are similar for the physical and the lattice QCD baryons.« less

  1. Sparse Long Blocks and the Micro-structure of the Longuest Common Subsequences

    NASA Astrophysics Data System (ADS)

    Amsalu, S.; Houdré, C.; Matzinger, H.

    2014-03-01

    Consider two random strings having the same length and generated by an iid sequence taking its values uniformly in a fixed finite alphabet. Artificially place a long constant block into one of the strings, where a constant block is a contiguous substring consisting only of one type of symbol. The long block replaces a segment of equal size and its length is smaller than the length of the strings, but larger than its square-root. We show that for sufficiently long strings the optimal alignment (OA) corresponding to a longest common subsequence (LCS) treats the inserted block very differently depending on the size of the alphabet. For two-letter alphabets, the long constant block gets mainly aligned with the same symbol from the other string, while for three or more letters the opposite is true and the block gets mainly aligned with gaps. We further provide simulation results on the proportion of gaps in blocks of various lengths. In our simulations, the blocks are "regular blocks" in an iid sequence, and are not artificially inserted. Nonetheless, we observe for these natural blocks a phenomenon similar to the one shown in case of artificially-inserted blocks: with two letters, the long blocks get aligned with a smaller proportion of gaps; for three or more letters, the opposite is true. It thus appears that the microscopic nature of two-letter OAs and three-letter OAs are entirely different from each other.

  2. Comparison of Measured and Block Structured Simulations for the F-16XL Aircraft

    NASA Technical Reports Server (NTRS)

    Boelens, O. J.; Badcock, K. J.; Elmilgui, A.; Abdol-Hamid, K. S.; Massey, S. J.

    2008-01-01

    This article presents a comparison of the predictions of three RANS codes for flight conditions of the F-16XL aircraft which feature vortical flow. The three codes, ENSOLV, PMB and PAB3D, solve on structured multi-block grids. Flight data for comparison was available in the form of surface pressures, skin friction, boundary layer data and photographs of tufts. The three codes provided predictions which were consistent with expectations based on the turbulence modelling used, which was k- , k- with vortex corrections and an Algebraic Stress Model. The agreement with flight data was good, with the exception of the outer wing primary vortex strength. The confidence in the application of the CFD codes to complex fighter configurations increased significantly through this study.

  3. A comparison study on the electronic structures, lattice dynamics and thermoelectric properties of bulk silicon and silicon nanotubes

    NASA Astrophysics Data System (ADS)

    Lu, Peng-Xian; Qu, Ling-Bo; Cheng, Qiao-Huan

    2013-11-01

    In order to investigate the mechanism of the electron and phonon transport in a silicon nanotube (SiNT), the electronic structures, the lattice dynamics, and the thermoelectric properties of bulk silicon (bulk Si) and a SiNT have been calculated in this work using density functional theory and Boltzmann transport theory. Our results suggest that the thermal conductivity of a SiNT is reduced by a factor of 1, while its electrical conductivity is improved significantly, although the Seebeck coefficient is increased slightly as compared to those of the bulk Si. As a consequence, the figure of merit (ZT) of a SiNT at 1200 K is enhanced by 12 times from 0.08 for bulk Si to 1.10. The large enhancement in electrical conductivity originates from the largely increased density of states at the Fermi energy level and the obviously narrowed band gap. The significant reduction in thermal conductivity is ascribed to the remarkably suppressed phonon thermal conductivity caused by a weakened covalent bonding, a decreased phonon density of states, a reduced phonon vibration frequency, as well as a shortened mean free path of phonons. The other factors influencing the thermoelectric properties have also been studied from the perspective of electronic structures and lattice dynamics.

  4. A novel method for the generation of multi-block computational structured grids from medical imaging of arterial bifurcations.

    PubMed

    Makris, Evangelos; Neofytou, Panagiotis; Tsangaris, Sokrates; Housiadas, Christos

    2012-10-01

    In this study a description of a new approach, for the generation of multi-block structured computational grids on patient-specific bifurcation geometries is presented. The structured grid generation technique is applied to data obtained by medical imaging examination, resulting in a surface conforming, high quality, multi-block structured grid of the branching geometry. As a case study application a patient specific abdominal aorta bifurcation is selected. For the evaluation of the grid produced by the novel method, a grid convergence study and a comparison between the grid produced by the method and unstructured grids produced by commercial meshing software are carried out. PMID:22209311

  5. First-principles study of lattice dynamics of TiO2 in brookite and cotunnite structures

    NASA Astrophysics Data System (ADS)

    Shojaee, E.; Abbasnejad, M.; Saeedian, M.; Mohammadizadeh, M. R.

    2011-05-01

    The zone-center phonons and dielectric properties of orthorhombic brookite and cotunnite structures TiO2 were studied in the framework of density functional perturbative theory. The dielectric properties of brookite and anatase structures are similar. The calculated static dielectric permittivity of brookite is found to be slightly higher than that of anatase, but far lower than that of the rutile structure. This is in contrast with the recent experimental report on brookite flowers. Our study suggests that the static dielectric constant of cotunnite structure is smaller than those of rutile and brookite structures. We obtained the full phonon band structure and elastic properties of these structures. The bulk modulus and Debye temperature of brookite are intermediate between those of the anatase and rutile structures. The obtained value of 301 GPa for the bulk modulus of cotunnite is in good agreement with the stiffness of the material reported experimentally. Because of the similarity in z-direction packing of the TiO6 tetrahedron between brookite and rutile structures, the elastic constants associated with the z-polarized movement of atoms in brookite are similar to those of the rutile structure. The elastic constants of brookite associated with the movement of the atoms in x-y plane, are similar to the corresponding constants in anatase and rutile structures. This demonstrates the similarity between the packing character of the brookite structure with both anatase and rutile structures. So, the lattice dynamics of brookite is intermediate between those of anatase and rutile polymorphs. The calculated phonon density of states of cotunnite shows that it is stable at ambient pressure.

  6. Clues for a Tortonian reconstruction of the Gibraltar Arc: Structural pattern, deformation diachronism and block rotations

    NASA Astrophysics Data System (ADS)

    Crespo-Blanc, Ana; Comas, Menchu; Balanyá, Juan Carlos

    2016-06-01

    We proposed a reconstruction of one of the tightest orogenic arcs on Earth: the Gibraltar Arc System. This reconstruction, which includes onshore and offshore data, is completed for approximately 9 Ma. The clues that lead us to draw it are based on a review in terms of structures and age of the superposed deformational events that took place during Miocene, with special attention to the external zones. This review and new structural data presented in this paper permit us to constrain the timing of vertical axis-rotations evidenced by previously published paleomagnetic data, and to identify homogeneous domains in terms of relationships between timing of deformation events, (re)magnetization and rotations. In particular, remagnetization in the Betics took place after the main shortening which produced the external fold-and-thrust belts (pre-upper Miocene), but was mostly previous to a contractive reorganization that affected the whole area; it should have occurred during lower Tortonian (between 9.9 and 11 Ma). From Tortonian to Present, block-rotations as high as 53° took place. Together with plate convergence, they accommodated a tightening and lengthening of the Gibraltar Arc System and drastically altered its geometry. As the orientation and position of any pre-9 Ma kinematic indicator or structural element is also modified, our reconstruction should be used as starting point for any pre-Tortonian model of the westernmost orogenic segment of the Alpine-Mediterranean system.

  7. Smart Hydrogels with Inhomogeneous Structures Assembled Using Nanoclay-Cross-Linked Hydrogel Subunits as Building Blocks.

    PubMed

    Yao, Chen; Liu, Zhuang; Yang, Chao; Wang, Wei; Ju, Xiao-Jie; Xie, Rui; Chu, Liang-Yin

    2016-08-24

    A novel and facile assembly strategy has been successfully developed to construct smart nanocomposite (NC) hydrogels with inhomogeneous structures using nanoclay-cross-linked stimuli-responsive hydrogel subunits as building blocks via rearranged hydrogen bonding between polymers and clay nanosheets. The assembled thermoresponsive poly(N-isopropylacrylamide-co-acrylamide) (poly(NIPAM-co-AM)) hydrogels with various inhomogeneous structures exhibit excellent mechanical properties due to plenty of new hydrogen bonding interactions created at the interface for locking the NC hydrogel subunits, which are strong enough to tolerate external forces such as high levels of elongations and multicycles of swelling/deswelling operations. The proposed approach is featured with flexibility and designability to build assembled hydrogels with diverse architectures for achieving various responsive deformations, which are highly promising for stimuli-responsive manipulation such as actuation, encapsulation, and cargo transportation. Our assembly strategy creates new opportunities for further developing mechanically strong hydrogel systems with complex architectures that composed of diverse internal structures, multistimuli-responsive properties, and controllable shape deformation behaviors in the soft robots and actuators fields. PMID:27490585

  8. Investigations of the EPR Parameters and Local Lattice Structure for the Rhombic Cu2+ Centre in TZSH Crystal

    NASA Astrophysics Data System (ADS)

    Li, Chao-Ying; Liu, Shi-Fei; Fu, Jin-Xian

    2016-03-01

    The electron paramagnetic resonance (EPR) parameters [i.e. g factors gi (i=x, y, z) and hyperfine structure constants Ai] and the local lattice structure for the Cu2+ centre in Tl2Zn(SO4)2·6H2O (TZSH) crystal were theoretically investigated by utilising the perturbation formulae of these parameters for a 3d9 ion under rhombically elongated octahedra. In the calculations, the admixture of d orbitals in the ground state and the ligand orbital and spin-orbit coupling interactions are taken into account based on the cluster approach. The theoretical EPR parameters show good agreement with the observed values, and the Cu2+-H2O bond lengths are obtained as follows: Rx≈1.98 Å, Ry≈2.09 Å, Rz≈2.32 Å. The results are discussed.

  9. A first principles study of the lattice stability of diamond-structure semiconductors under intense laser irradiation

    SciTech Connect

    Feng Shiquan; Zhao Jianling; Cheng Xinlu

    2013-01-14

    Using density-functional linear-response theory, we calculated the phonon dispersion curves for the diamond structural elemental semiconductors of Ge, C and zinc-blende structure semiconductors of GaAs, InSb at different electronic temperatures. We found that the transverse-acoustic phonon frequencies of C and Ge become imaginary as the electron temperature is elevated, which means the lattices of C and Ge become unstable under intense laser irradiation. These results are very similar with previous theoretical and experimental results for Si. For GaAs and InSb, not only can be obtained the similar results for their transverse-acoustic modes, but also their LO-TO splitting gradually decreases as the electronic temperature is increased. It means that the electronic excitation weakens the strength of the ionicity of ionic crystal under intense laser irradiation.

  10. Crystal structure and lattice dynamics of Sr{sub 3}Y(BO{sub 3}){sub 3}

    SciTech Connect

    Maczka, M. Waskowska, A.; Majchrowski, A.; Kisielewski, J.; Szyrski, W.; Hanuza, J.

    2008-12-15

    X-ray, Raman and infrared (IR) studies of the Sr{sub 3}Y(BO{sub 3}){sub 3} (BOYS) single crystal grown by the Czochralski technique are presented. The crystal structure is trigonal, space group R3-bar (no. 148), and comprises six formula units in the unit cell with the hexagonal axes a=12.527(2) and c=9.280(2) A. The assignment of the observed vibrational modes is proposed on the basis of lattice dynamics calculations. The unusual large bandwidth of the internal modes and the enhancement of the principal mean square thermal displacements for BO{sub 3} and Y(1) indicate that some type of disorder is present in the studied crystal. - Graphical abstract: View of the crystal structure of BOYS along the c-axis.

  11. Pion Structure in Qcd: from Theory to Lattice to Experimental Data

    NASA Astrophysics Data System (ADS)

    Bakulev, A. P.; Mikhailov, S. V.; Pimikov, A. V.; Stefanis, N. G.

    We describe the present status of the pion distribution amplitude (DA) as it originates from several sources: (i) a nonperturbative approach based on QCD sum rules with nonlocal condensates, (ii) an O(as) QCD analysis of the CLEO data on Fgg*p(Q2) with asymptotic and renormalon models for higher twists and (iii) recent high-precision lattice QCD calculations of the second moment of the pion DA. We show predictions for the pion electromagnetic form factor, obtained in analytic QCD perturbation theory, and compare it with the JLab data on Fp(Q2). We also discuss in this context an improved model for nonlocal condensates in QCD and show its consequences for the pion DA and the gg*p transition form factor. We include a brief analysis of meson-induced massive lepton (muon) Drell-Yan production for the process p-Nm+m-X, considering both an unpolarized nucleon target and longitudinally polarized protons.

  12. Growth mechanisms and crystallographic structure of InP nanowires on lattice-mismatched substrates

    NASA Astrophysics Data System (ADS)

    Moewe, Michael; Chuang, Linus C.; Dubrovskii, Vladimir G.; Chang-Hasnain, Connie

    2008-08-01

    We present a growth model that predicts the growth phase and mechanism of InP nanowires (NWs) and the experimental verifications of the model. The NWs were grown on lattice-mismatched GaAs substrates using metal-organic chemical vapor deposition via Au nanodrop-assisted vapor-liquid-solid growth. Nanodrops with larger diameters are shown to grow longer NWs because growth is governed mainly by direct precursor impingement on the nanodrop surface. The theoretical and experimental results also show that growth phase is dependent on NW diameter. We show that InP NWs with a diameter less than a certain value exhibit coherent growth of a single crystalline wurtzite (WZ) phase, whereas larger diameter InP NWs often contain sequences of WZ and zincblende phases and stacking faults. These findings allow one to achieve coherent NW growth and WZ phases free from twinning if the NW diameter is below certain material-dependent critical diameters.

  13. An integrated runtime and compile-time approach for parallelizing structured and block structured applications

    NASA Technical Reports Server (NTRS)

    Agrawal, Gagan; Sussman, Alan; Saltz, Joel

    1993-01-01

    Scientific and engineering applications often involve structured meshes. These meshes may be nested (for multigrid codes) and/or irregularly coupled (called multiblock or irregularly coupled regular mesh problems). A combined runtime and compile-time approach for parallelizing these applications on distributed memory parallel machines in an efficient and machine-independent fashion was described. A runtime library which can be used to port these applications on distributed memory machines was designed and implemented. The library is currently implemented on several different systems. To further ease the task of application programmers, methods were developed for integrating this runtime library with compilers for HPK-like parallel programming languages. How this runtime library was integrated with the Fortran 90D compiler being developed at Syracuse University is discussed. Experimental results to demonstrate the efficacy of our approach are presented. A multiblock Navier-Stokes solver template and a multigrid code were experimented with. Our experimental results show that our primitives have low runtime communication overheads. Further, the compiler parallelized codes perform within 20 percent of the code parallelized by manually inserting calls to the runtime library.

  14. Theoretical studies on ultraviolet nearly lattice-matched BAlGaN/BAlGaN quantum well structures with quaternary BAlGaN barriers

    NASA Astrophysics Data System (ADS)

    Park, Seoung-Hwan; Ahn, Doyeol

    2016-07-01

    Light emission characteristics of B x Al y Ga1- x - y N/BAlGaN quantum well (QW) structures with quaternary BAlGaN barrier were investigated using the multiband effective-mass theory. The internal field in the BAlGaN well of the BAlGaN/AlN QW structure is shown to be large (˜10 MV/cm) under the lattice-matched condition (ɛ = 0.0%). On the other hand, the internal field is significantly reduced by using BAlGaN barrier and the peak intensity of the spontaneous emission coefficient of the lattice-matched BAlGaN/BAlGaN QW structure is comparable to that of the conventional BAlGaN/AlN QW structure. We observe that the light intensity of the lattice-matched BAlGaN/BAlGaN QW structure is comparable to that of the conventional BAlGaN/AlN QW structure. Also, we observe that the nearly lattice-matched BAlGaN/BAlGaN QW structure with small strain (0.5%) has about 3 times larger peak intensity than the conventional QW AlGaN/AlN structure. Hence, BAlGaN/BAlGaN QW system could be used as a UV light source with a higher light emission and a higher crystal quality, compared to conventional AlGaN/AlN QW structures with larger strain (1.78%).

  15. Structure-directing star-shaped block copolymers: supramolecular vesicles for the delivery of anticancer drugs.

    PubMed

    Yang, Chuan; Liu, Shao Qiong; Venkataraman, Shrinivas; Gao, Shu Jun; Ke, Xiyu; Chia, Xin Tian; Hedrick, James L; Yang, Yi Yan

    2015-06-28

    Amphiphilic polycarbonate/PEG copolymer with a star-like architecture was designed to facilitate a unique supramolecular transformation of micelles to vesicles in aqueous solution for the efficient delivery of anticancer drugs. The star-shaped amphipilic block copolymer was synthesized by initiating the ring-opening polymerization of trimethylene carbonate (TMC) from methyl cholate through a combination of metal-free organo-catalytic living ring-opening polymerization and post-polymerization chain-end derivatization strategies. Subsequently, the self-assembly of the star-like polymer in aqueous solution into nanosized vesicles for anti-cancer drug delivery was studied. DOX was physically encapsulated into vesicles by dialysis and drug loading level was significant (22.5% in weight) for DOX. Importantly, DOX-loaded nanoparticles self-assembled from the star-like copolymer exhibited greater kinetic stability and higher DOX loading capacity than micelles prepared from cholesterol-initiated diblock analogue. The advantageous disparity is believed to be due to the transformation of micelles (diblock copolymer) to vesicles (star-like block copolymer) that possess greater core space for drug loading as well as the ability of such supramolecular structures to encapsulate DOX. DOX-loaded vesicles effectively inhibited the proliferation of 4T1, MDA-MB-231 and BT-474 cells, with IC50 values of 10, 1.5 and 1.0mg/L, respectively. DOX-loaded vesicles injected into 4T1 tumor-bearing mice exhibited enhanced accumulation in tumor tissue due to the enhanced permeation and retention (EPR) effect. Importantly, DOX-loaded vesicles demonstrated greater tumor growth inhibition than free DOX without causing significant body weight loss or cardiotoxicity. The unique ability of the star-like copolymer emanating from the methyl cholate core provided the requisite modification in the block copolymer interfacial curvature to generate vesicles of high loading capacity for DOX with significant

  16. Structure-directing star-shaped block copolymers: supramolecular vesicles for the delivery of anticancer drugs.

    PubMed

    Yang, Chuan; Liu, Shao Qiong; Venkataraman, Shrinivas; Gao, Shu Jun; Ke, Xiyu; Chia, Xin Tian; Hedrick, James L; Yang, Yi Yan

    2015-06-28

    Amphiphilic polycarbonate/PEG copolymer with a star-like architecture was designed to facilitate a unique supramolecular transformation of micelles to vesicles in aqueous solution for the efficient delivery of anticancer drugs. The star-shaped amphipilic block copolymer was synthesized by initiating the ring-opening polymerization of trimethylene carbonate (TMC) from methyl cholate through a combination of metal-free organo-catalytic living ring-opening polymerization and post-polymerization chain-end derivatization strategies. Subsequently, the self-assembly of the star-like polymer in aqueous solution into nanosized vesicles for anti-cancer drug delivery was studied. DOX was physically encapsulated into vesicles by dialysis and drug loading level was significant (22.5% in weight) for DOX. Importantly, DOX-loaded nanoparticles self-assembled from the star-like copolymer exhibited greater kinetic stability and higher DOX loading capacity than micelles prepared from cholesterol-initiated diblock analogue. The advantageous disparity is believed to be due to the transformation of micelles (diblock copolymer) to vesicles (star-like block copolymer) that possess greater core space for drug loading as well as the ability of such supramolecular structures to encapsulate DOX. DOX-loaded vesicles effectively inhibited the proliferation of 4T1, MDA-MB-231 and BT-474 cells, with IC50 values of 10, 1.5 and 1.0mg/L, respectively. DOX-loaded vesicles injected into 4T1 tumor-bearing mice exhibited enhanced accumulation in tumor tissue due to the enhanced permeation and retention (EPR) effect. Importantly, DOX-loaded vesicles demonstrated greater tumor growth inhibition than free DOX without causing significant body weight loss or cardiotoxicity. The unique ability of the star-like copolymer emanating from the methyl cholate core provided the requisite modification in the block copolymer interfacial curvature to generate vesicles of high loading capacity for DOX with significant

  17. Determination of Paleoseismic Ground Motions from Inversion of Block Failures in Masonry Structures

    NASA Astrophysics Data System (ADS)

    Yagoda-Biran, G.; Hatzor, Y. H.

    2010-12-01

    Accurate estimation of ground motion parameters such as expected peak ground acceleration (PGA), predominant frequency and duration of motion in seismically active regions, is crucial for hazard preparedness and sound engineering design. The best way to estimate quantitatively these parameters would be to investigate long term recorded data of past strong earthquakes in a studied region. In some regions of the world however recorded data are scarce due to lack of seismic network infrastructure, and in all regions the availability of recorded data is restricted to the late 19th century and onwards. Therefore, existing instrumental data are hardly representative of the true seismicity of a region. When recorded data are scarce or not available, alternative methods may be applied, for example adopting a quantitative paleoseismic approach. In this research we suggest the use of seismically damaged masonry structures as paleoseismic indicators. Visitors to archeological sites all over the world are often struck by structural failure features which seem to be "seismically driven", particularly when inspecting old masonry structures. While it is widely accepted that no other loading mechanism can explain the preserved damage, the actual driving mechanism remains enigmatic even now. In this research we wish to explore how such failures may be triggered by earthquake induced ground motions and use observed block displacements to determine the characteristic parameters of the paleoseismic earthquake motion, namely duration, frequency, and amplitude. This is performed utilizing a 3D, fully dynamic, numerical analysis performed with the Discontinuous Deformation Analysis (DDA) method. Several case studies are selected for 3D numerical analysis. First we study a simple structure in the old city of L'Aquila, Italy. L'Aquila was hit by an earthquake on April 6th, 2009, with over 300 casualties and many of its medieval buildings damaged. This case study is an excellent opportunity

  18. Structural Evolution of Low-Molecular-Weight Poly(ethylene oxide)-block-polystyrene Diblock Copolymer Thin Film

    PubMed Central

    Huang, Xiaohua

    2013-01-01

    The structural evolution of low-molecular-weight poly(ethylene oxide)-block-polystyrene (PEO-b-PS) diblock copolymer thin film with various initial film thicknesses on silicon substrate under thermal annealing was investigated by atomic force microscopy, optical microscopy, and contact angle measurement. At film thickness below half of the interlamellar spacing of the diblock copolymer (6.2 nm), the entire silicon is covered by a polymer brush with PEO blocks anchored on the Si substrate due to the substrate-induced effect. When the film is thicker than 6.2 nm, a dense polymer brush which is equal to half of an interlamellar layer was formed on the silicon, while the excess material dewet this layer to form droplets. The droplet surface was rich with PS block and the PEO block crystallized inside the bigger droplet to form spherulite. PMID:24302862

  19. Structure of malaria invasion protein RH5 with erythrocyte basigin and blocking antibodies.

    PubMed

    Wright, Katherine E; Hjerrild, Kathryn A; Bartlett, Jonathan; Douglas, Alexander D; Jin, Jing; Brown, Rebecca E; Illingworth, Joseph J; Ashfield, Rebecca; Clemmensen, Stine B; de Jongh, Willem A; Draper, Simon J; Higgins, Matthew K

    2014-11-20

    Invasion of host erythrocytes is essential to the life cycle of Plasmodium parasites and development of the pathology of malaria. The stages of erythrocyte invasion, including initial contact, apical reorientation, junction formation, and active invagination, are directed by coordinated release of specialized apical organelles and their parasite protein contents. Among these proteins, and central to invasion by all species, are two parasite protein families, the reticulocyte-binding protein homologue (RH) and erythrocyte-binding like proteins, which mediate host-parasite interactions. RH5 from Plasmodium falciparum (PfRH5) is the only member of either family demonstrated to be necessary for erythrocyte invasion in all tested strains, through its interaction with the erythrocyte surface protein basigin (also known as CD147 and EMMPRIN). Antibodies targeting PfRH5 or basigin efficiently block parasite invasion in vitro, making PfRH5 an excellent vaccine candidate. Here we present crystal structures of PfRH5 in complex with basigin and two distinct inhibitory antibodies. PfRH5 adopts a novel fold in which two three-helical bundles come together in a kite-like architecture, presenting binding sites for basigin and inhibitory antibodies at one tip. This provides the first structural insight into erythrocyte binding by the Plasmodium RH protein family and identifies novel inhibitory epitopes to guide design of a new generation of vaccines against the blood-stage parasite. PMID:25132548

  20. Post-directed-self-assembly membrane fabrication for in situ analysis of block copolymer structures

    NASA Astrophysics Data System (ADS)

    Ren, J.; Ocola, L. E.; Divan, R.; Czaplewski, D. A.; Segal-Peretz, T.; Xiong, S.; Kline, R. J.; Arges, C. G.; Nealey, P. F.

    2016-10-01

    Full characterization of the three-dimensional structures resulting from the directed self-assembly (DSA) of block copolymers (BCP) remains a difficult challenge. Transmission electron microscope (TEM) tomography and resonant soft x-ray scattering have emerged as powerful and complementary methods for through-film characterization; both techniques require samples to be prepared on specialized membrane substrates. Here we report a generalizable process to implement BCP DSA with density multiplication on silicon nitride membranes. A key feature of the process developed here is that it does not introduce any artefacts or damage to the polymer assemblies as DSA is performed prior to back-etched membrane formation. Because most research and applications of BCP lithography are based on silicon substrates, process variations introduced by implementing DSA on a silicon nitride/silicon stack versus silicon were identified and mitigated. Using full-wafers, membranes were fabricated with different sizes and layouts to enable both TEM and x-ray characterization. Finally, both techniques were used to characterize structures resulting from the DSA of lamella-forming BCP with density multiplication.

  1. KIVA-3: A KIVA program with block-structured mesh for complex geometries

    SciTech Connect

    Amsden, A.A.

    1993-03-01

    This report describes the KIVA-3 computer program for numerical calculation of transient, two- and three-dimensional chemically reactive fluid flows with sprays. KIVA-3 is an extension of the earlier KIVA-II, uses the same numerical solution procedure, and solves the same set of equations. The full generality of KIVA-II has been retained; thus KIVA-3 is applicable to laminar or turbulent flows, subsonic or supersonic flows, and single-phase or dispersed two-phase flows. KIVA-3 differs from KIVA-11 in that it uses a block-structured mesh with connectivity defined through indirect addressing. The departure from a single rectangular structure in (i,j,k) logical space allows complex geometries to be modeled with significantly greater efficiency than was previously possible because large regions of deactivated cells are no longer necessary. Cell-face boundary conditions permit greater flexibility and simplification in the application of boundary conditions. This report discusses those features of KIVA-3 that differ from KIVA-II, the input required from a mesh generation preprocessor, and the output provided to a graphics postprocessor. Basic pre and post-processors are included in the KIVA-3 package, and are also described.

  2. Gravity And Seismic Data Set Constraint On The Crust Structure Of Liyue Block, Northeast Of Nansha Area

    NASA Astrophysics Data System (ADS)

    Sun, Z.

    2011-12-01

    The Liyue Block is composed of two parts: Reed Bank and Liyue Basin. It is separated by Zhongnan Fault in west, Palawan Trough in southeast and fault scarp in the north of Nansha area. We make a systematic investigation on major tectonic and crust structure units in the Liyue Block basing on gravity and seismic data set. Multichannel seismic data can help to know the stratum and fault structure that locating upon the sediment basement. In the Reed Bank composed of reefs, the faults are undeveloped and the stratum is flat. In basin area, the early faults are developed and there two kinds of structures: tilted fault block and low relief anticline. The thickness of the Mesozoic strata in basin area decreases from SW to NE. But the rifting strata increases from SW to NE, which indicates the fault activity strength in the rift period increased from southwest to northeast. We have performed gravity inversion to understand the geometry of the MOHO surface and the crustal thicknesses beneath this area. The region is characterized by large positive Bouguer gravity anomaly (60 to 140 mgal), and the MOHO depth generally varies from 16-27km.We calculate the stretching factor of the research area, which ranging from 1.3 to 2.0, that indicates the local region is lowly stretched. In general, we can distinguish the crustal structures of the study area into the thinned continental crust. Key words: Liyue Block; Mesozoic stratum; Gravity inversion; Seismic profile; Crust structure

  3. Molecular structure stability of short-chain chlorinated paraffins (SCCPs): Evidence from lattice compatibility and Simha-Somcynsky theories

    NASA Astrophysics Data System (ADS)

    Yumak, A.; Boubaker, K.; Petkova, P.; Yahsi, U.

    2015-10-01

    In is known that short-chain chlorinated paraffins (SCCPs) are highly complex technical mixtures of polychlorinated n-alkanes with single chlorine content. Due to their physical properties (viscosity, flame resistance) they are used in many different applications, such as lubricant additives, metal processing, leather fat-liquoring, plastics softening, PVC plasticizing and flame retardants in paints, adhesives and sealants. SCCPs are studied here in terms of processing-linked molecular structure stability, under Simha and Somcynsky-EOS theory calculations and elements from Simha-Somcynsky-related Lattice Compatibility Theory. Analyses were carried out on 1-chloropropane, 2-chloropropane, 1-chlorobutane, 2-chlorobutane, 1-chloro 2-methylane, and 2-chloro 2-methylane as (SCCPs) universal representatives. This paper gives evidence to this stability and reviews the current state of knowledge and highlights the need for further research in order to improve future (SCCPs) monitoring efforts.

  4. Additive lattice kirigami

    PubMed Central

    Castle, Toen; Sussman, Daniel M.; Tanis, Michael; Kamien, Randall D.

    2016-01-01

    Kirigami uses bending, folding, cutting, and pasting to create complex three-dimensional (3D) structures from a flat sheet. In the case of lattice kirigami, this cutting and rejoining introduces defects into an underlying 2D lattice in the form of points of nonzero Gaussian curvature. A set of simple rules was previously used to generate a wide variety of stepped structures; we now pare back these rules to their minimum. This allows us to describe a set of techniques that unify a wide variety of cut-and-paste actions under the rubric of lattice kirigami, including adding new material and rejoining material across arbitrary cuts in the sheet. We also explore the use of more complex lattices and the different structures that consequently arise. Regardless of the choice of lattice, creating complex structures may require multiple overlapping kirigami cuts, where subsequent cuts are not performed on a locally flat lattice. Our additive kirigami method describes such cuts, providing a simple methodology and a set of techniques to build a huge variety of complex 3D shapes. PMID:27679822

  5. Additive lattice kirigami

    PubMed Central

    Castle, Toen; Sussman, Daniel M.; Tanis, Michael; Kamien, Randall D.

    2016-01-01

    Kirigami uses bending, folding, cutting, and pasting to create complex three-dimensional (3D) structures from a flat sheet. In the case of lattice kirigami, this cutting and rejoining introduces defects into an underlying 2D lattice in the form of points of nonzero Gaussian curvature. A set of simple rules was previously used to generate a wide variety of stepped structures; we now pare back these rules to their minimum. This allows us to describe a set of techniques that unify a wide variety of cut-and-paste actions under the rubric of lattice kirigami, including adding new material and rejoining material across arbitrary cuts in the sheet. We also explore the use of more complex lattices and the different structures that consequently arise. Regardless of the choice of lattice, creating complex structures may require multiple overlapping kirigami cuts, where subsequent cuts are not performed on a locally flat lattice. Our additive kirigami method describes such cuts, providing a simple methodology and a set of techniques to build a huge variety of complex 3D shapes.

  6. SPIN ON THE LATTICE.

    SciTech Connect

    ORGINOS,K.

    2003-01-07

    I review the current status of hadronic structure computations on the lattice. I describe the basic lattice techniques and difficulties and present some of the latest lattice results; in particular recent results of the RBC group using domain wall fermions are also discussed. In conclusion, lattice computations can play an important role in understanding the hadronic structure and the fundamental properties of Quantum Chromodynamics (QCD). Although some difficulties still exist, several significant steps have been made. Advances in computer technology are expected to play a significant role in pushing these computations closer to the chiral limit and in including dynamical fermions. RBC has already begun preliminary dynamical domain wall fermion computations [49] which we expect to be pushed forward with the arrival of QCD0C. In the near future, we also expect to complete the non-perturbative renormalization of the relevant derivative operators in quenched QCD.

  7. Superradiance Lattice

    NASA Astrophysics Data System (ADS)

    Wang, Da-Wei; Liu, Ren-Bao; Zhu, Shi-Yao; Scully, Marlan O.

    2015-01-01

    We show that the timed Dicke states of a collection of three-level atoms can form a tight-binding lattice in momentum space. This lattice, coined the superradiance lattice (SL), can be constructed based on electromagnetically induced transparency (EIT). For a one-dimensional SL, we need the coupling field of the EIT system to be a standing wave. The detuning between the two components of the standing wave introduces an effective uniform force in momentum space. The quantum lattice dynamics, such as Bloch oscillations, Wannier-Stark ladders, Bloch band collapsing, and dynamic localization can be observed in the SL. The two-dimensional SL provides a flexible platform for Dirac physics in graphene. The SL can be extended to three and higher dimensions where no analogous real space lattices exist with new physics waiting to be explored.

  8. Investigation of the Effect of the Tortuous Pore Structure on Water Diffusion through a Polymer Film Using Lattice Boltzmann Simulations.

    PubMed

    Gebäck, Tobias; Marucci, Mariagrazia; Boissier, Catherine; Arnehed, Johan; Heintz, Alexei

    2015-04-23

    Understanding how the pore structure influences the mass transport through a porous material is important in several applications, not the least in the design of polymer film coatings intended to control drug release. In this study, a polymer film made of ethyl cellulose and hydroxypropyl cellulose was investigated. The 3D structure of the films was first experimentally characterized using confocal laser scanning microscopy data and then mathematically reconstructed for the whole film thickness. Lattice Boltzmann simulations were performed to compute the effective diffusion coefficient of water in the film and the results were compared to experimental data. The local porosities and pore sizes were also analyzed to determine how the properties of the internal film structure affect the water effective diffusion coefficient. The results show that the top part of the film has lower porosity, lower pore size, and lower connectivity, which results in a much lower effective diffusion coefficient in this part, largely determining the diffusion rate through the entire film. Furthermore, the local effective diffusion coefficients were not proportional to the local film porosity, indicating that the results cannot be explained by a single tortuosity factor. In summary, the proposed methodology of combining microscopy data, mass transport simulations, and pore space analysis can give valuable insights on how the film structure affects the mass transport through the film.

  9. Adaptation of Block-Structured Adaptive Mesh Refinement to Particle-In-Cell simulations

    NASA Astrophysics Data System (ADS)

    Vay, Jean-Luc; Colella, Phillip; McCorquodale, Peter; Friedman, Alex; Grote, Dave

    2001-10-01

    Particle-In-Cell (PIC) methods which solve the Maxwell equations (or a simplification) on a regular Cartesian grid are routinely used to simulate plasma and particle beam systems. Several techniques have been developed to accommodate irregular boundaries and scale variations. We describe here an ongoing effort to adapt the block-structured Adaptive Mesh Refinement (AMR) algorithm (http://seesar.lbl.gov/AMR/) to the Particle-In-Cell method. The AMR technique connects grids having different resolutions, using interpolation. Special care has to be taken to avoid the introduction of spurious forces close to the boundary of the inner, high-resolution grid, or at least to reduce such forces to an acceptable level. The Berkeley AMR library CHOMBO has been modified and coupled to WARP3d (D.P. Grote et al., Fusion Engineering and Design), 32-33 (1996), 193-200, a PIC code which is used for the development of high current accelerators for Heavy Ion Fusion. The methods and preliminary results will be presented.

  10. Using high-order methods on adaptively refined block-structured meshes - discretizations, interpolations, and filters.

    SciTech Connect

    Ray, Jaideep; Lefantzi, Sophia; Najm, Habib N.; Kennedy, Christopher A.

    2006-01-01

    Block-structured adaptively refined meshes (SAMR) strive for efficient resolution of partial differential equations (PDEs) solved on large computational domains by clustering mesh points only where required by large gradients. Previous work has indicated that fourth-order convergence can be achieved on such meshes by using a suitable combination of high-order discretizations, interpolations, and filters and can deliver significant computational savings over conventional second-order methods at engineering error tolerances. In this paper, we explore the interactions between the errors introduced by discretizations, interpolations and filters. We develop general expressions for high-order discretizations, interpolations, and filters, in multiple dimensions, using a Fourier approach, facilitating the high-order SAMR implementation. We derive a formulation for the necessary interpolation order for given discretization and derivative orders. We also illustrate this order relationship empirically using one and two-dimensional model problems on refined meshes. We study the observed increase in accuracy with increasing interpolation order. We also examine the empirically observed order of convergence, as the effective resolution of the mesh is increased by successively adding levels of refinement, with different orders of discretization, interpolation, or filtering.

  11. Block-structured adaptive meshes and reduced grids for atmospheric general circulation models.

    PubMed

    Jablonowski, Christiane; Oehmke, Robert C; Stout, Quentin F

    2009-11-28

    Adaptive mesh refinement techniques offer a flexible framework for future variable-resolution climate and weather models since they can focus their computational mesh on certain geographical areas or atmospheric events. Adaptive meshes can also be used to coarsen a latitude-longitude grid in polar regions. This allows for the so-called reduced grid setups. A spherical, block-structured adaptive grid technique is applied to the Lin-Rood finite-volume dynamical core for weather and climate research. This hydrostatic dynamics package is based on a conservative and monotonic finite-volume discretization in flux form with vertically floating Lagrangian layers. The adaptive dynamical core is built upon a flexible latitude-longitude computational grid and tested in two- and three-dimensional model configurations. The discussion is focused on static mesh adaptations and reduced grids. The two-dimensional shallow water setup serves as an ideal testbed and allows the use of shallow water test cases like the advection of a cosine bell, moving vortices, a steady-state flow, the Rossby-Haurwitz wave or cross-polar flows. It is shown that reduced grid configurations are viable candidates for pure advection applications but should be used moderately in nonlinear simulations. In addition, static grid adaptations can be successfully used to resolve three-dimensional baroclinic waves in the storm-track region.

  12. Finite Macro-Element Mesh Deformation in a Structured Multi-Block Navier-Stokes Code

    NASA Technical Reports Server (NTRS)

    Bartels, Robert E.

    2005-01-01

    A mesh deformation scheme is developed for a structured multi-block Navier-Stokes code consisting of two steps. The first step is a finite element solution of either user defined or automatically generated macro-elements. Macro-elements are hexagonal finite elements created from a subset of points from the full mesh. When assembled, the finite element system spans the complete flow domain. Macro-element moduli vary according to the distance to the nearest surface, resulting in extremely stiff elements near a moving surface and very pliable elements away from boundaries. Solution of the finite element system for the imposed boundary deflections generally produces smoothly varying nodal deflections. The manner in which distance to the nearest surface has been found to critically influence the quality of the element deformation. The second step is a transfinite interpolation which distributes the macro-element nodal deflections to the remaining fluid mesh points. The scheme is demonstrated for several two-dimensional applications.

  13. Molecular interactions and solubilization of structurally related meso-porphyrin photosensitizers by amphiphilic block copolymers (Pluronics).

    PubMed

    Sobczyński, Jan; Smistad, Gro; Hegge, Anne Bee; Kristensen, Solveig

    2015-01-01

    The influence of four Pluronics block copolymers (i.e. F68, P123, F127, and L44) on the aggregation and solubilization of five structurally related meso-tetraphenyl porphyrin photosensitizers (PS) as model compounds for use in Photodynamic Therapy of cancer (PDT) was evaluated. Interactions between the PSs and Pluronics were studied at micromolar concentration by means of UV-Vis absorption spectrometry and by kinematic viscosity (υ) and osmolarity measurements at millimolar concentrations. Pluronic micelles were characterized by size and zeta potential (ζ) measurements. The morphology of selected PS-Pluronic assemblies was studied by atomic force microscopy (AFM). While hydrophobic 5,10,15,20-Tetrakis(4-hydroxyphenyl) porphine (THPP) seemed to be solubilized in the Pluronic micellar cores, amphiphilic di(monoethanolammonium) meso-tetraphenyl porphine disulphonate (TPPS2a) was likely bound to the micellar palisade layer. Hydrophilic PSs like 5,10,15,20-Tetrakis (4-trimethylaniliniumphenyl) porphine (TAPP) seemed to form complexes with Pluronic unimers and to be distributed among the micellar coronas. TPPS2a aggregated into a network which could be broken at Pluronic concentration [Formula: see text] cmc, but would reconstitute in the presence of tonicity adjusting agents, e.g. sodium chloride (NaCl) or glucose. PMID:25027806

  14. Structural analysis of Anopheles midgut aminopeptidase N reveals a novel malaria transmission-blocking vaccine B-cell epitope

    PubMed Central

    Atkinson, Sarah C.; Armistead, Jennifer S.; Mathias, Derrick K.; Sandeu, Maurice M.; Tao, Dingyin; Borhani-Dizaji, Nahid; Tarimo, Brian B.; Morlais, Isabelle; Dinglasan, Rhoel R.; Borg, Natalie A.

    2015-01-01

    Mosquito-based malaria transmission-blocking vaccines (mTBVs) target midgut-surface antigens of the Plasmodium parasite's obligate vector, the Anopheles mosquito. The alanyl aminopeptidase N (AnAPN1) is the leading mTBV immunogen; however AnAPN1's role in Plasmodium infection of the mosquito and how anti-AnAPN1 antibodies functionally block parasite transmission remains elusive. Here we present the 2.65 Å crystal structure of AnAPN1 and the immunoreactivity and transmission-blocking profile of three AnAPN1 monoclonal antibodies (mAb), including mAb 4H5B7, which effectively block transmission of natural strains of Plasmodium falciparum. Utilizing the AnAPN1 structure we map the conformation-dependent 4H5B7 neo-epitope to a previously uncharacterized region on domain 1, and further demonstrate that non-human primate neo-epitope-specific IgG also block parasite transmission. We discuss the prospect of a novel biological function of AnAPN1 as a receptor for Plasmodium in the mosquito midgut and the implications for redesigning the AnAPN1 mTBV. PMID:26075520

  15. Anomalies, gauge field topology, and the lattice

    SciTech Connect

    Creutz, Michael

    2011-04-15

    Motivated by the connection between gauge field topology and the axial anomaly in fermion currents, I suggest that the fourth power of the naive Dirac operator can provide a natural method to define a local lattice measure of topological charge. For smooth gauge fields this reduces to the usual topological density. For typical gauge field configurations in a numerical simulation, however, quantum fluctuations dominate, and the sum of this density over the system does not generally give an integer winding. On cooling with respect to the Wilson gauge action, instanton like structures do emerge. As cooling proceeds, these objects tend shrink and finally 'fall through the lattice.' Modifying the action can block the shrinking at the expense of a loss of reflection positivity. The cooling procedure is highly sensitive to the details of the initial steps, suggesting that quantum fluctuations induce a small but fundamental ambiguity in the definition of topological susceptibility.

  16. The Effect of Block-Word Diagrams on the Structuring of Science Concepts as a Function of General Ability.

    ERIC Educational Resources Information Center

    Winn, William

    1980-01-01

    Examines the effectiveness of block-word diagrams in science instruction for ninth graders using directed graphs that express content structure as key concepts joined by arrows. Results include the finding that the effect of text-plus-diagram treatment compared to text-only treatment was different for learners of different ability. (CS)

  17. A Block-Structured KIVA Program for Engines with Vertical or Canted Valves

    1999-08-23

    KIVA3VRELEASE2 is a computer program for the numerical calculation of transient, two and three-dimensional, chemically reactive flows with sprays. It is a newer version of the earlier KIVA3 (1993) that has now been extended to model vertical of canted valves in the cylinder head of a gasoline or diesel engine. KIVA3, in turn, was based on the earlier KIVA2 (1989) and uses the same numerical solution procedure and solves the same sort of equations. KIVA3VRELEASE2more » uses a block-structured mesh with connectivity defined through indirect addressing. The departure from a single rectangular structure in logical space allows complex geometries to be modeled with significantly greater efficiency because large regions of deactivated cells are no longer necessary. Cell-face boundary conditions permit greater flexibility and simplification in the application of boundary conditions. KIVA3VRELEASE2 contains a number of significant changes. New features enhance the robustness, efficiency, and usefullness of the overall program for engine modeling. Automatic restart of the cycle with a reduced timestep in case of iteration limit or temperature overflow will reduce code crashes. A new option provides automatic deactivation of a port region when it is closed from the cylinder and reactivation when it communicates with the cylinder. Corrections in the code improve accuracy; extensions to the particle-based liquid wall film model makes the model more complete and a spli injection option has been added. A new subroutine monitors the liquid and gaseous fuel phases and energy balance data and emissions are monitored and printed. New features have been added to the grid generator K3PREP and the graphics post processor, K3POST.« less

  18. Molecular and structural basis of resting and use-dependent block of sodium current defined using disopyramide analogues.

    PubMed Central

    Yeh, J. Z.; TenEick, R. E.

    1987-01-01

    The effects of disopyramide (Norpace) and 14 closely related structural analogues on the Na current of voltage clamped squid axons were examined to determine which physico-chemical properties and which changes in the structure of the Norpace molecule can alter the nature of its sodium channel blocking actions. Conventional voltage clamp technique for internally perfused giant axons was used. Axons were exposed to 100 microM concentrations via the internal perfusion solution, and the actions of the 15 analogues to produce resting and use-dependent block of Na current were assessed. The roles of Na ions and the activation and inactivation processes in the development of and recovery from use-dependent block of Na current induced by the Norpace analogues were also examined. The results indicate that for both mono-tertiary and bis-tertiary amines the potency to produce use-dependent block was proportional to molecular weight, whereas the correlation between potency to produce resting block and molecular weight was significant only for bis-tertiary amines. The mono- were more potent than the bis-compounds. However, comparisons between compounds having similar molecular weights and/or pKa values indicate that other factors also can influence blocking potency. For compounds within each homologous mono- or bis-tertiary amine series, hydrophobicity as estimated from log P values (P = octanol/water partition coefficient) was found to influence the potency to produce use dependent block of Na current. Use-dependent block was extant in axons internally exposed to pronase to remove the inactivation process, which indicates that inactivation is not an obligate condition for development of use-dependent block of Na current. An important role for the activation process in the development of use-dependent block of Na current is suggested by the finding that, in general, the voltage dependence of Na current activation paralleled that of use-dependent block. However, the potential

  19. Structural investigation of InGaAsN films grown on pseudo-lattice-matched InGaAs substrates by metalorganic vapor phase epitaxy

    NASA Astrophysics Data System (ADS)

    Kongjaeng, Pornsiri; Sanorpim, Sakuntam; Yamamoto, Takahisa; Ono, Wataru; Nakajima, Fumio; Katayama, Ryuji; Onabe, Kentaro

    2007-01-01

    The use of the nearly lattice-matched In xGa 1-xAs pseudo-substrate has been explored for the growth of In xGa 1-xAs 1-yN y with higher In ( x) contents by metalorganic vapor phase epitaxy (MOVPE). As compared with the quality of high In-containing In 0.3Ga 0.7As 0.98N 0.02 films grown directly on GaAs substrates, the growth on In 0.2Ga 0.8As pseudo-lattice-matched substrates yielded good structural quality films. The number of misfit dislocations investigated by cross-sectional transmission electron microscopy was found to be reduced in the InGaAsN grown layer. Furthermore, higher optical quality In 0.3Ga 0.7As 0.98N 0.02 films with the bandgap of 1.01 eV were grown on the In 0.2Ga 0.8As pseudo-lattice-matched substrate. This study shows that the use of the In xGa 1-xAs pseudo-lattice-matched substrate is an effective method to fabricate a thick lattice-matched InGaAsN layers with higher optical and structural qualities necessary for the development of the multijunction (MJ) solar cells.

  20. Lattice-free prediction of three-dimensional structure of programmed DNA assemblies

    NASA Astrophysics Data System (ADS)

    Pan, Keyao; Kim, Do-Nyun; Zhang, Fei; Adendorff, Matthew R.; Yan, Hao; Bathe, Mark

    2014-12-01

    DNA can be programmed to self-assemble into high molecular weight 3D assemblies with precise nanometer-scale structural features. Although numerous sequence design strategies exist to realize these assemblies in solution, there is currently no computational framework to predict their 3D structures on the basis of programmed underlying multi-way junction topologies constrained by DNA duplexes. Here, we introduce such an approach and apply it to assemblies designed using the canonical immobile four-way junction. The procedure is used to predict the 3D structure of high molecular weight planar and spherical ring-like origami objects, a tile-based sheet-like ribbon, and a 3D crystalline tensegrity motif, in quantitative agreement with experiments. Our framework provides a new approach to predict programmed nucleic acid 3D structure on the basis of prescribed secondary structure motifs, with possible application to the design of such assemblies for use in biomolecular and materials science.

  1. Lattice-free prediction of three-dimensional structure of programmed DNA assemblies.

    PubMed

    Pan, Keyao; Kim, Do-Nyun; Zhang, Fei; Adendorff, Matthew R; Yan, Hao; Bathe, Mark

    2014-01-01

    DNA can be programmed to self-assemble into high molecular weight 3D assemblies with precise nanometer-scale structural features. Although numerous sequence design strategies exist to realize these assemblies in solution, there is currently no computational framework to predict their 3D structures on the basis of programmed underlying multi-way junction topologies constrained by DNA duplexes. Here, we introduce such an approach and apply it to assemblies designed using the canonical immobile four-way junction. The procedure is used to predict the 3D structure of high molecular weight planar and spherical ring-like origami objects, a tile-based sheet-like ribbon, and a 3D crystalline tensegrity motif, in quantitative agreement with experiments. Our framework provides a new approach to predict programmed nucleic acid 3D structure on the basis of prescribed secondary structure motifs, with possible application to the design of such assemblies for use in biomolecular and materials science. PMID:25470497

  2. Three-Dimensional Cellular Structures Enhanced By Shape Memory Alloys

    NASA Technical Reports Server (NTRS)

    Nathal, Michael V.; Krause, David L.; Wilmoth, Nathan G.; Bednarcyk, Brett A.; Baker, Eric H.

    2014-01-01

    This research effort explored lightweight structural concepts married with advanced smart materials to achieve a wide variety of benefits in airframe and engine components. Lattice block structures were cast from an aerospace structural titanium alloy Ti-6Al-4V and a NiTi shape memory alloy (SMA), and preliminary properties have been measured. A finite element-based modeling approach that can rapidly and accurately capture the deformation response of lattice architectures was developed. The Ti-6-4 and SMA material behavior was calibrated via experimental tests of ligaments machined from the lattice. Benchmark testing of complete lattice structures verified the main aspects of the model as well as demonstrated the advantages of the lattice structure. Shape memory behavior of a sample machined from a lattice block was also demonstrated.

  3. Lattice dynamics, electronic structure, and optical properties of LiBeSb: A hexagonal ABC-type hyperferroelectrics

    NASA Astrophysics Data System (ADS)

    Dai, Jian-Qing; Zhu, Jian-Hui; Xu, Jie-Wang

    2016-07-01

    The recently discovered hexagonal ABC-type hyperferroelectrics, in which the polarization persists in the presence of the depolarization filed, exhibit a variety of intriguing and potentially useful properties [Garrity et al., Phys. Rev. Lett. 112, 127601 (2014)]. For the existing prototype of LiBeSb, we present detailed first-principles calculations concerning the lattice dynamics, electronic structure, and optical properties. An unstable longitudinal optic mode in the high-symmetry structure and a large polarization of 0.5 C/m2 in the polar phase are reported, including the remarkable dependence of Born effective charges on structural distortion. Using the HSE06 hybrid functional, we predict that LiBeSb has a small band-gap of 1.5 eV and shows dominant asymmetric covalent bonding character. Importantly, we find that there are remarkable absorptions in the whole visible spectrum. These features, combined with the enhanced carrier mobility, make LiBeSb as well as the whole family of hexagonal ABC-type hyperferroelectrics as promising candidates for ferroelectric photovoltaic materials with large bulk photovoltaic effect in the visible spectrum.

  4. EB1 regulates attachment of Ska1 with microtubules by forming extended structures on the microtubule lattice

    PubMed Central

    Thomas, Geethu E.; Bandopadhyay, K.; Sutradhar, Sabyasachi; Renjith, M. R.; Singh, Puja; Gireesh, K. K.; Simon, Steny; Badarudeen, Binshad; Gupta, Hindol; Banerjee, Manidipa; Paul, Raja; Mitra, J.; Manna, Tapas K.

    2016-01-01

    Kinetochore couples chromosome movement to dynamic microtubules, a process that is fundamental to mitosis in all eukaryotes but poorly understood. In vertebrates, spindle-kinetochore-associated (Ska1–3) protein complex plays an important role in this process. However, the proteins that stabilize Ska-mediated kinetochore-microtubule attachment remain unknown. Here we show that microtubule plus-end tracking protein EB1 facilitates Ska localization on microtubules in vertebrate cells. EB1 depletion results in a significant reduction of Ska1 recruitment onto microtubules and defects in mitotic chromosome alignment, which is also reflected in computational modelling. Biochemical experiments reveal that EB1 interacts with Ska1, facilitates Ska1-microtubule attachment and together stabilizes microtubules. Structural studies reveal that EB1 either with Ska1 or Ska complex forms extended structures on microtubule lattice. Results indicate that EB1 promotes Ska association with K-fibres and facilitates kinetochore-microtubule attachment. They also implicate that in vertebrates, chromosome coupling to dynamic microtubules could be mediated through EB1-Ska extended structures. PMID:27225956

  5. Two spin-peierls-like compounds exhibiting divergent structural features, lattice compression, and expansion in the low- temperature phase.

    PubMed

    Tian, Zhengfang; Duan, Haibao; Ren, Xiaoming; Lu, Changsheng; Li, Yizhi; Song, You; Zhu, Huizhen; Meng, Qingjin

    2009-06-18

    Two quasi-one-dimensional (quasi-1D) compounds, [4'-CH(3)Bz-4-RPy][Ni(mnt)(2)] (mnt(2-) = maleonitriledithiolate), where 4'-CH(3)Bz-4-RPy(+) = 1-(4'-methylbenzyl)pyridinium (denoted as compound 1) and 1-(4'-methylbenzyl)-4-aminopyridinium (denoted as compound 2), show a spin-Peierls-like transition with T(C) approximately 182 K for 1 and T(C) approximately 155 K for 2. The enthalpy changes for the transition are estimated to be DeltaH = 316.6 J.mol(-1) for 1 and 1082.1 J.mol(-1) for 2. From fits to the magnetic susceptibility, the magnetic exchange constants in the gapless state are calculated to be J = 166(2) K with g = 2.020(23) for 1 versus J = 42(0) K with g = 2.056(5) for 2. In the high-temperature (HT) phase, 1 and 2 are isostructural and crystallize in the monoclinic space group P2(1)/c. The nonmagnetic cations and paramagnetic anions form segregated columns with regular anionic and cationic stacks. In the low-temperature (LT) phase, the crystals of the two compounds undergo a transformation to the triclinic space group P-1, and both anionic and cationic stacks dimerize. In the transformation from the HT to LT phases, the two compounds exhibit divergent structural features, with lattice compression for 1 but lattice expansion for 2, due to intermolecular slippage. Combined with our previous studies, it is also noted that the transition temperature, T(C), is qualitatively related to the cell volume in the HT phase for the series of compounds [1-(4'-R-benzylpyridinium][Ni(mnt)(2)] (where R represents the substituent). When there is a single substituent in the para position of benzene, giving a larger cell volume, the transition temperature increases.

  6. Al15Ge4Ni3: A new intergrowth structure with Cu3Au- and CaF2-type building blocks

    NASA Astrophysics Data System (ADS)

    Reichmann, Thomas L.; Jandl, Isabella; Effenberger, Herta S.; Herzig, Peter; Richter, Klaus W.

    2015-05-01

    The new ternary compound Al15Ge4Ni3 (τ2 in the system Al-Ge-Ni) was synthesized in single crystalline form by a special annealing procedure from samples located in the three phase fields [L+Al+τ2] and [L+Ge+τ2]. The crystal structure of Al15Ge4Ni3 was determined by single-crystal X-ray diffraction. The compound crystallizes in a new structure type in space group I4¯3m, Pearson Symbol cI88, cubic lattice parameter a=11.405(1) Å. Phase diagram investigations indicate stoichiometric composition without considerable homogeneity range; τ2 melts peritectically at T=444 °C. The crystal structure of Al15Ge4Ni3 shows a unique combination of simple Cu3Au- and CaF2-type building blocks: a three dimensional network of CaF2-type units, formed by Ni and Al atoms, is interspaced by clusters (Al6Ge8) resembling unit cells of the Cu3Au-type. Both structural motifs are connected by Al-Ge bonds. The ground state energy of the compound was obtained by DFT calculations and the densities of states were analyzed in detail. In addition, electron density maps were calculated in four different sections through the unit cell using the full potential linearized augmented plane-wave (FLAPW) method. The bonding situation in Al15Ge4Ni3 was discussed combining results from electronic calculations with the analysis of the coordination of atoms.

  7. Lattice Structures Manufactured by SLM: On the Effect of Geometrical Dimensions on Microstructure Evolution During Processing

    NASA Astrophysics Data System (ADS)

    Niendorf, Thomas; Brenne, Florian; Schaper, Mirko

    2014-08-01

    Employing selective laser melting direct microstructure manipulation is feasible through adjustment of thermal gradients and solidification velocity. Currently, the exposure strategy and laser energy have to be adapted in order to meet a processing window suited for introducing highly anisotropic microstructures. As selective laser melting allows for production of filigree complex structures, the impact of geometry on the microstructure evolution is investigated in the current study and it is shown that miniaturization of structures as well leads to the evolution of anisotropic microstructure.

  8. Petrology and structure of greenstone blocks encased in mud-matrix melange of the Franciscan complex near San Simeon, California

    SciTech Connect

    Davidsen, R.K.; Cloos, M.

    1985-01-01

    Greenstones comprise about 20% of all mappable (>1 m) blocks encased in blueschist-block-bearing mud-matrix melange exposed in a 10 km-length of sea cliffs near San Simeon. Field and petrographic analysis of 25 blocks show they vary from finely crystalline (<1 mm) locally porphyritic or amygdaloidal, volcanics to coarsely crystalline (1 to 5 mm) diabase. Some are in contact with bedded chert and two have relict pillows. However, most blocks are intensely deformed. Pinch-and-swell and boundinage are recognized on scales from cm to about 10 m. Distortion was accommodated by cataclasis to an aggregate of pieces from mm to m across. Generally, m-sized blocks are pervasively cataclastic whereas larger blocks are crosscut by cataclastic zones that emanate from pervasively cataclastic margins or necked regions of boudins. Discontinuous, cm-thick veins and cavities that are lined by quartz and clacite and rarely, laumontite, prehnite and aragonite locally crosscut all other structures. Relict igneous textures show the primary minerals are plagioclase and clinopyroxene. Abundant secondary minerals, particularly in cataclastic zones, are albite, chlorite, pumpellyite (some have high Al), and calcite. The metamorphic parageneses indicate relatively minor greenschist-facies, sea-floor-type alterations under static conditions followed by lower-temperature alterations synchronous with cataclasis and the development of boudinage. If the blocks are fragments of disrupted ophiolites, only the uppermost section of the suite are present within the mud-matrix melange near San Simeon. The simplest explanation for their crystallization, metamorphism and incorporation into the melange is that they are fragments of seamounts dismembered during subduction.

  9. Mixing Energy Models in Genetic Algorithms for On-Lattice Protein Structure Prediction

    PubMed Central

    Rashid, Mahmood A.; Newton, M. A. Hakim; Hoque, Md. Tamjidul; Sattar, Abdul

    2013-01-01

    Protein structure prediction (PSP) is computationally a very challenging problem. The challenge largely comes from the fact that the energy function that needs to be minimised in order to obtain the native structure of a given protein is not clearly known. A high resolution 20 × 20 energy model could better capture the behaviour of the actual energy function than a low resolution energy model such as hydrophobic polar. However, the fine grained details of the high resolution interaction energy matrix are often not very informative for guiding the search. In contrast, a low resolution energy model could effectively bias the search towards certain promising directions. In this paper, we develop a genetic algorithm that mainly uses a high resolution energy model for protein structure evaluation but uses a low resolution HP energy model in focussing the search towards exploring structures that have hydrophobic cores. We experimentally show that this mixing of energy models leads to significant lower energy structures compared to the state-of-the-art results. PMID:24224180

  10. Use of shock block transmitters in the structural rehabilitation of historical buildings in Calabria and Sicily

    SciTech Connect

    Bianco, Alessia; Candela, Michele; Fonti, Roberta

    2008-07-08

    Many old and historical masonry buildings, located in the Calabrian and Sicilian areas near the strait of Messina, are affected by typical pattern of cracks, which are not produced by previous earthquakes. These cracks in the masonry walls are characterized by a quasi-vertical trend with constant width. The careful examination of the crack distribution allows to clearly identify the diagnosis: the damage is caused by the sinking due to a horizontal movement of translation of the ground, which is an evident effect of creep phenomena in the soil, so-called 'solifluxion'. This paper, after showing this geological pathology, proposes an innovative strategy of intervention, which consists of the use of 'oleo-dynamic' devices, so-called shock block transmitters, providing different degrees of restraint, according to the loading conditions. In addition, in case of earthquake, an important part of the in-put seismic energy can be dissipated. The strategy of application of this system to the building consists of the subdivision of each masonry wall in two different parts, which are physically separated by the cracks. Each wall portion must be consolidated separately and the different parts of walls behave as statically independent each other, so that they can move independently during the serviceability conditions. The connection among the walls composing the whole structural organism is given by metal tie-rods equipped with 'oleo dynamic' devices, which allows, in a given range, the horizontal sliding in case of slow movement due to the phenomenon of 'solifluxion'. Contrary, in case of dynamic and fast movements, such as the ones produced by an earthquake, each 'oleo dynamic' device provides a fully restraint effect and, as a consequence, the tie-rods behave in the classical way.

  11. Structural influence of graft and block polycations on the adsorption of BSA.

    PubMed

    Zhang, Li; Jin, Fengmin; Zhang, Tingbin; Zhang, Ling; Xing, Jinfeng

    2016-04-01

    Protein adsorption is considered as an important factor for the low transfection efficiency of polycations in vivo. In this study, two typical polycations of equal molecular weight with different structures were chosen to investigate their adsorption on bovine serum albumin (BSA), including the block copolymer named poly (N-vinylpyrrolidone)-b-poly (2-dimethylaminoethyl methacrylate) (PVP-b-PDMAEMA, i.e. PbP) and graft copolymer named PVP-g-PDMAEMA (PgP), respectively. Fluorescence spectroscopy was used to confirm the binding constants and binding sites between polycations and BSA in static state. The binding constants were 4.1×10(4)M(-1) vs 8.3×10(4)M(-1) and binding sites were 0.3 vs 1.1 for PbP and PgP, respectively, indicating PgP had stronger binding affinity with BSA. Surface plasmon resonance (SPR) was used to study the dynamical non-specific interaction between BSA and polycations as well as the polyplexes. The numbers of both PbP and PgP adsorbed on BSA increased with concentration of polycations increasing, and the number of PgP adsorbed on BSA is higher compared with PbP when their concentration is low. When their concentration is high, the number of PbP adsorbed on BSA is more than that of PgP. However, PgP/DNA polyplexes showed higher adsorption amount compared with PbP/DNA polyplexes at different N/P ratios.

  12. Timing of amalgamation of the Alxa Block and the North China Block: Constraints based on detrital zircon U-Pb ages and sedimentologic and structural evidence

    NASA Astrophysics Data System (ADS)

    Zhang, Jin; Zhang, Beihang; Zhao, Heng

    2016-02-01

    Detrital zircon LA-ICP-MS U-Pb ages of the Paleozoic strata in the southeastern Alxa Block indicate that the primary provenance did not change between the Devonian and the Early Carboniferous. Except for a sample from the Cambrian strata, the Early Paleozoic North Qilian Orogenic Belt may have been a major source of Paleozoic sediments in the study area. The main source of Lower-Middle Devonian sediments was the Early Paleozoic North Qilian Orogenic Belt. The source of the Upper Devonian sediments was the Alxa Block, while the North China Block was a minor contributor. The deformation of the Cambrian and Devonian Systems in the southeastern Alxa Block indicates that a strong east-west compression event occurred in the study area before the Early Carboniferous. The paleocurrents of the Upper Devonian in the southeastern Alxa Block indicate that the source was located to the north and was not the North Qilian Orogenic Belt to the south. Moreover, the deposition of the Upper Devonian in the southeastern Alxa Block was a response to a strong deformation event that occurred along the eastern boundary of the Alxa Block during the Late Devonian and Early Carboniferous. The North China Block became the primary source during the Early Carboniferous, and the Alxa Block was a minor source. A regional stratigraphic comparison also indicates that similar depositional environments were present until the Carboniferous and Permian on the Alxa Block and North China Block. All of these data indicate that amalgamation of the Alxa Block and the North China Block occurred between the Late Devonian and the Early Carboniferous.

  13. Dynamic structure factor of a Bose-Einstein condensate in a one-dimensional optical lattice

    SciTech Connect

    Menotti, C.; Kraemer, M.; Stringari, S.; Pitaevskii, L.

    2003-05-01

    We study the effect of a one-dimensional periodic potential on the dynamic structure factor of an interacting Bose-Einstein condensate at zero temperature. We show that, due to phononic correlations, the excitation strength toward the first band develops a typical oscillating behavior as a function of the momentum transfer, and vanishes at even multiples of the Bragg momentum. The effects of interactions on the static structure factor are found to be significantly amplified by the presence of the optical potential. Our predictions can be tested in stimulated photon scattering experiments.

  14. Magnetophonon resonance in multimode lattices and two-dimensional structures (DQW)

    NASA Astrophysics Data System (ADS)

    Ploch, D.; Sheregii, E.; Marchewka, M.; Tomaka, G.

    2007-12-01

    The experimental results obtained for the magneto-transport in the InGaAs/InAlAs double quantum wells (DQW) structures of two different shapes of wells are reported. The Magnetophonon Resonance (MPR) o was observed for both types of the structures at 77-125K temperatures in the pulsed magnetic field. Four kinds of LO-phonons are taken into account to interpret the MPR oscillations in DQW. The particularity of MPR in DQW is the great number Landau levels caused by SAS-splitting all electron states.

  15. Computational studies of directed assembly and self assembly of building blocks and precise structures: From colloids to viruses

    NASA Astrophysics Data System (ADS)

    Chen, Ting

    The directed-assembly and self-assembly of building blocks are promising techniques to make structures with three-dimensional precision, which are important in many practical applications and may serve as a new generation of starting materials for novel superstructures. Experimental techniques have improved significantly to create building blocks out of diverse materials with varying properties and shapes, and allow site specific, selective functionalization of certain building blocks. The rational design and successful control of materials requires an unprecedented understanding of how building blocks assemble on the small scale. It is thus imperative to develop a systematic way to identify assembly principles and predict final structures for a given building block. The objective of this dissertation is to develop a general modeling and simulation approach to explore the governing principles underlying target directed-assembly and self-assembly. Exemplifying this approach, we use a "minimal model" approach, which contains a minimal set of parameters while still maintaining the key physics of the target problems to study selected assembly phenomena. We first examine polymer and biomolecule directed-assembly of nanoparticles, and find that despite the recognitive capability of linkers, fractal-like structures, instead of precise structures, are formed under the conditions studied. Further, we investigate the possibility of exploiting the anisotropic shapes and/or interactions of building blocks to assemble precise structures. We performed molecular simulations of the self-assembly of cone-shaped particles with specific attractions, and find that the cones self-assemble into a sequence of robust, precise clusters. We further show that this sequence is reproduced and is extended in simulations of two simple models of spheres self-assembling subject to convexity constraints. This sequence for small sizes is identical to those observed in evaporation-driven assembly of

  16. Insight into nucleon structure from lattice calculations of moments of parton and generalized parton distributions

    SciTech Connect

    J.W. Negele; R.C. Brower; P. Dreher; R. Edwards; G. Fleming; Ph. Hagler; U.M. Heller; Th. Lippert; A.V.Pochinsky; D.B. Renner; D. Richards; K. Schilling; W. Schroers

    2004-04-01

    This talk presents recent calculations in full QCD of the lowest three moments of generalized parton distributions and the insight they provide into the behavior of nucleon electromagnetic form factors, the origin of the nucleon spin, and the transverse structure of the nucleon. In addition, new exploratory calculations in the chiral regime of full QCD are discussed.

  17. Electronic structure and lattice dynamics at the interface of single layer FeSe and SrTiO3

    NASA Astrophysics Data System (ADS)

    Ahmed, Towfiq; Balatsky, Alexander; Zhu, Jian-Xin

    Recent discovery of high-temperature superconductivity with the superconducting energy gap opening at temperatures close to or above the liquid nitrogen boiling point in the single-layer FeSe grown on SrTiO3 has attracted significant interest. It suggests that the interface effects can be utilized to enhance the superconductivity. It has been shown recently that the coupling between the electrons in FeSe and vibrational modes at the interface play an important role. Here we report on a detailed study of electronic structure and lattice dynamics in the single-layer FeSe/SrTiO3 interface by using the state-of-art electronic structure method within the density functional theory. The nature of the vibrational modes at the interface and their coupling to the electronic degrees of freedom are analyzed. In addition, the effect of hole and electron doping in SrTiO3 on the electron-mode coupling strength is also considered. This work was carried out under the auspices of the National Nuclear Security Administration of the U.S. DOE at LANL under Contract No. DE-AC52-06NA25396, and was supported by the DOE Office of Basic Energy Sciences.

  18. Templated synthesis of porous particles with tunable pore structures from nanoscale building blocks

    NASA Astrophysics Data System (ADS)

    Wu, Zhiwang

    Porous silica, carbon, titania and carbon/silica composite micro- or nano-materials have been synthesized by the templated self-assembly approaches through an aerosol-assisted process or hydrothermal technique. Porous silica particles with controllable hierarchical pore structure (from hexagonal to lamellar or hierarchical) have been prepared through tuning the hydrophilic and hydrophobic balance among silicate, cetyltrimethylammonium bromide (CTAB), and hydrophobic poly(propylene oxide) (PPO, H[OCH(CH 3)CH2nOH) additives during a dynamic aerosol-assisted process. Aerosol-assisted self-assembly of hollow silica microspheres with microporous shell (HSMMS) are prepared by utilizing the block copolymer F127's aggregating behavior in basic solution and the self-assembly between silicate and amphiphilic tetrapropylammonium hydroxide (TPAOH) molecules. Interactions of TPAOH with both F127 and silicate are necessary for avoiding the phase separation between silicate and F127 aggregates because of the lack of hydrogen bonding interactions. Therefore, F127 aggregates with various sizes act as the core template while TPAOH molecules or TPAOH aggregates formed by excessive TPAOH molecules stay in the silica shell. Removal of F127 and TPAOH by solvent extraction results in the HSMMS materials. Mesoporous carbon/silica composite with both meso- and molecular ordering has been synthesized by carbonization of as-synthesized phenylene/silica/surfactant hybrid by co-assembly of BTEB and Pluronic surfactant P123. Removal of silica from carbon/silica composite results in the mesoporous carbon which retains some of the meso-ordering and has many worm-like pores due to silica dissolution. This mesoporous carbon has potential applications in such field as hydrogen storage, catalysis, and other areas. Hollow carbon microspheres with micropores in the shell and carbon nanotubes on the outer surface have been prepared using resols as the carbon precursor and hydrophobic PPO additives as

  19. Directed self-assembly of a colloidal kagome lattice.

    PubMed

    Chen, Qian; Bae, Sung Chul; Granick, Steve

    2011-01-20

    A challenging goal in materials chemistry and physics is spontaneously to form intended superstructures from designed building blocks. In fields such as crystal engineering and the design of porous materials, this typically involves building blocks of organic molecules, sometimes operating together with metallic ions or clusters. The translation of such ideas to nanoparticles and colloidal-sized building blocks would potentially open doors to new materials and new properties, but the pathways to achieve this goal are still undetermined. Here we show how colloidal spheres can be induced to self-assemble into a complex predetermined colloidal crystal-in this case a colloidal kagome lattice-through decoration of their surfaces with a simple pattern of hydrophobic domains. The building blocks are simple micrometre-sized spheres with interactions (electrostatic repulsion in the middle, hydrophobic attraction at the poles, which we call 'triblock Janus') that are also simple, but the self-assembly of the spheres into an open kagome structure contrasts with previously known close-packed periodic arrangements of spheres. This open network is of interest for several theoretical reasons. With a view to possible enhanced functionality, the resulting lattice structure possesses two families of pores, one that is hydrophobic on the rims of the pores and another that is hydrophilic. This strategy of 'convergent' self-assembly from easily fabricated colloidal building blocks encodes the target supracolloidal architecture, not in localized attractive spots but instead in large redundantly attractive regions, and can be extended to form other supracolloidal networks.

  20. Species coexistence in a lattice-structured habitat: effects of species dispersal and interactions.

    PubMed

    Ying, Zhixia; Liao, Jinbao; Wang, Shichang; Lu, Hui; Liu, Yongjie; Ma, Liang; Li, Zhenqing

    2014-10-21

    Opinions differ on how the spatial distribution of species over space affects species coexistence. Here, we constructed both mean-field and pair approximation (PA) models to explore the effects of interspecific and intraspecific interactions and dispersal modes on species coexistence. We found that spatial structure resulting from species dispersal traits and neighboring interactions in PA model did not promote coexistence if two species had the same traits, though it might intensify the contact frequency of intraspecific competition. If two species adopt different dispersal modes, the spatial structure in PA would make the coexistence or founder control less likely since it alters the species effective birth rate. This suggests that the spatial distribution caused by neighboring interactions and local dispersal does not affect species coexistence unless it adequately alters the effective birth rate for two species. Besides, we modeled how the initial densities and patterns affected population dynamics and revealed how the final spatial pattern was generated.

  1. Influence of carbon dopants on the structure, elasticity and lattice dynamics of Ti5Si3C x Nowotny phases

    NASA Astrophysics Data System (ADS)

    Wdowik, Urszula D.; Wasik, Magdalena; Twardowska, Agnieszka

    2016-02-01

    Density functional theory studies on the Ti5Si3C x systems with various concentrations of carbon impurities (x=0, 0.25, 0.50, 1.00 ) are reported. The effects of interstitial carbon atoms on crystal and electronic structures, and on the elastic and vibrational properties of the Ti5Si3C x compound are analysed and discussed. The results of the present investigations indicate not only strong bonding between carbon atoms and their neighbouring titanium atoms, but also the effects of carbon impurities on the atomic bonds beyond the immediate proximity of the dopants. These determine to a great extent the electron densities of states, and the structural and elastic properties of the Ti5Si3C x Nowotny phases. Although carbon atoms tend to stabilise Ti5Si3C x phases, they also have a negative effect on their ductile properties. The strong impact of carbon impurities on the lattice dynamics of Ti5Si3C x compounds is revealed by the phonon and Raman spectra, which remain sensitive to changes in the interatomic distances. In C-doped systems the phonon bands originating from the vibrations of carbon impurities appear at high frequencies and remain well-separated from the lower lying phonon bands dominated by the vibrations of Ti and Si sublattices. The lower frequency phonon bands also experience changes due to the incorporated dopants. Impurities occupying the interstitials of the Ti5Si3 lattice are responsible for the appearance of new infrared active and optically inactive modes of A 2u , E 1u and E 2u symmetries, leaving the number of Raman active modes unchanged. Modifications to the dynamical properties of ternary Ti5Si3C x phases manifest themselves via shifts and the suppression of phonon peaks as well as the emergence of new phonon peaks which are absent in the binary Ti5Si3 system. The observed effects become enhanced with an increased concentration of carbon impurities.

  2. A versatile building block: the structures and functions of negative-sense single-stranded RNA virus nucleocapsid proteins.

    PubMed

    Sun, Yuna; Guo, Yu; Lou, Zhiyong

    2012-12-01

    Nucleocapsid protein (NPs) of negative-sense single-stranded RNA (-ssRNA) viruses function in different stages of viral replication, transcription, and maturation. Structural investigations show that -ssRNA viruses that encode NPs preliminarily serve as structural building blocks that encapsidate and protect the viral genomic RNA and mediate the interaction between genomic RNA and RNA-dependent RNA polymerase. However, recent structural results have revealed other biological functions of -ssRNA viruses that extend our understanding of the versatile roles of virally encoded NPs. PMID:23136065

  3. Band structure properties of (BGa)P semiconductors for lattice matched integration on (001) silicon

    SciTech Connect

    Hossain, Nadir; Sweeney, Stephen; Hosea, Jeff; Liebich, Sven; Zimprich, Martin; Volz, Kerstin; Stolz, Wolfgang; Kunert, Bernerdette

    2013-12-04

    We report the band structure properties of (BGa)P layers grown on silicon substrate using metal-organic vapour-phase epitaxy. Using surface photo-voltage spectroscopy we find that both the direct and indirect band gaps of (BGa)P alloys (strained and unstrained) decrease with Boron content. Our experimental results suggest that the band gap of (BGa)P layers up to 6% Boron is large and suitable to be used as cladding and contact layers in GaP-based quantum well heterostructures on silicon substrates.

  4. Application of Powder Diffraction Methods to the Analysis of the Atomic Structure of Nanocrystals: The Concept of the Apparent Lattice Parameter (ALP)

    NASA Technical Reports Server (NTRS)

    Palosz, B.; Grzanka, E.; Gierlotka, S.; Stelmakh, S.; Pielaszek, R.; Bismayer, U.; Weber, H.-P.; Palosz, W.; Curreri, Peter A. (Technical Monitor)

    2002-01-01

    The applicability of standard methods of elaboration of powder diffraction data for determination of the structure of nano-size crystallites is analysed. Based on our theoretical calculations of powder diffraction data we show, that the assumption of the infinite crystal lattice for nanocrystals smaller than 20 nm in size is not justified. Application of conventional tools developed for elaboration of powder diffraction data, like the Rietveld method, may lead to erroneous interpretation of the experimental results. An alternate evaluation of diffraction data of nanoparticles, based on the so-called 'apparent lattice parameter' (alp) is introduced. We assume a model of nanocrystal having a grain core with well-defined crystal structure, surrounded by a surface shell with the atomic structure similar to that of the core but being under a strain (compressive or tensile). The two structural components, the core and the shell, form essentially a composite crystal with interfering, inseparable diffraction properties. Because the structure of such a nanocrystal is not uniform, it defies the basic definitions of an unambiguous crystallographic phase. Consequently, a set of lattice parameters used for characterization of simple crystal phases is insufficient for a proper description of the complex structure of nanocrystals. We developed a method of evaluation of powder diffraction data of nanocrystals, which refers to a core-shell model and is based on the 'apparent lattice parameter' methodology. For a given diffraction pattem, the alp values are calculated for every individual Bragg reflection. For nanocrystals the alp values depend on the diffraction vector Q. By modeling different a0tomic structures of nanocrystals and calculating theoretically corresponding diffraction patterns using the Debye functions we showed, that alp-Q plots show characteristic shapes which can be used for evaluation of the atomic structure of the core-shell system. We show, that using a simple

  5. Gd{sub 4}B{sub 4}O{sub 11}F{sub 2}: Synthesis and crystal structure of a rare-earth fluoride borate exhibiting a new 'fundamental building block' in borate chemistry

    SciTech Connect

    Haberer, Almut; Kaindl, Reinhard; Huppertz, Hubert

    2010-02-15

    A new gadolinium fluoride borate Gd{sub 4}B{sub 4}O{sub 11}F{sub 2} was yielded in a Walker-type multianvil apparatus at 7.5 GPa and 1100 deg. C. Gd{sub 4}B{sub 4}O{sub 11}F{sub 2} crystallizes monoclinically in the space group C2/c with the lattice parameters a=1361.3(3) pm, b=464.2(2) pm, c=1374.1(3) pm, and beta=91.32(3){sup o} (Z=4). The crystal structure exhibits a structural motif not yet reported from borate chemistry: two BO{sub 4}-tetrahedra (square) and two BO{sub 3}-groups (DELTA) are connected via common corners, leading to the fundamental building block 2DELTA2square:DELTAsquaresquareDELTA. In the two crystallographically identical BO{sub 4}-tetrahedra, a distortion resulting in a very long B-O-bond is found. - Graphical abstract: A new gadolinium fluoride borate Gd{sub 4}B{sub 4}O{sub 11}F{sub 2} could be synthesized via high-pressure/high-temperature synthesis (multianvil technique). The crystal structure exhibits a structural motif not yet reported from borate chemistry: two BO{sub 4}-tetrahedra (square) and two BO{sub 3}-groups (DELTA) are connected via common corners, leading to the fundamental building block 2DELTA2square:DELTAsquaresquareDELTA.

  6. Investigation of an investment casting method combined with additive manufacturing methods for manufacturing lattice structures

    NASA Astrophysics Data System (ADS)

    Kodira, Ganapathy D.

    Cellular metals exhibit combinations of mechanical, thermal and acoustic properties that provide opportunities for various implementations and applications; light weight aerospace and automobile structures, impact and noise absorption, heat dissipation, and heat exchange. Engineered cell topologies enable one to control mechanical, thermal, and acoustic properties of the gross cell structures. A possible way to manufacture complex 3D metallic cellular solids for mass production with a relatively low cost, the investment casting (IC) method may be used by combining the rapid prototyping (RP) of wax or injection molding. In spite of its potential to produce mass products of various 3D cellular metals, the method is known to have significant casting porosity as a consequence of the complex cellular topology which makes continuous fluid's access to the solidification interface difficult. The effects of temperature on the viscosity of the fluids were studied. A comparative cost analysis between AM-IC and additive manufacturing methods is carried out. In order to manufacture 3D cellular metals with various topologies for multi-functional applications, the casting porosity should be resolved. In this study, the relations between casting porosity and processing conditions of molten metals while interconnecting with complex cellular geometries are investigated. Temperature and pressure conditions on the rapid prototyping -- investment casting (RP-IC) method are reported, thermal stresses induced are also studied. The manufactured samples are compared with those made by additive manufacturing methods.

  7. Block Copolymer Templates for Optical Materials and Devices

    NASA Astrophysics Data System (ADS)

    Urbas, Augustine; Martin, Maldovan; Carter, W. C.; Thomas, E. L.; Fasolka, Michael; Fraser, Cassandra

    2002-03-01

    Block copolymers can act as super-lattices for creating novel optical structures. We have fabricated block copolymer photonic crystals from one, two and three dimensionally periodic systems and have enhanced their dielectric properties towards creating complete 3D band gaps. By using carefully selected blends of linear and star block copolymers, we are able to create hierarchical blends which exhibit precise molecular positioning of fluorescent molecules. We are exploring these unique patterning capabilities of block copolymer systems for the formation of ordered arrays of optically active components within a photonic crystal. Precise location of both fluorescent and nonlinear components within block copolymer photonic crystals affords new opportunities for creating low threshold, upconverting and array lasers as well as optical modulators and other photonic devices.

  8. Heart Block

    MedlinePlus

    ... Block Explore Heart Block What Is... Electrical System & EKG Results Types Causes Who Is at Risk Signs & ... heart block. Doctors use a test called an EKG (electrocardiogram) to help diagnose heart block. This test ...

  9. Three-dimensional bulk electronic structure of the Kondo lattice CeIn3 revealed by photoemission

    PubMed Central

    Zhang, Yun; Lu, Haiyan; Zhu, Xiegang; Tan, Shiyong; Liu, Qin; Chen, Qiuyun; Feng, Wei; Xie, Donghua; Luo, Lizhu; Liu, Yu; Song, Haifeng; Zhang, Zhengjun; Lai, Xinchun

    2016-01-01

    We show the three-dimensional electronic structure of the Kondo lattice CeIn3 using soft x-ray angle resolved photoemission spectroscopy in the paramagnetic state. For the first time, we have directly observed the three-dimensional topology of the Fermi surface of CeIn3 by photoemission. The Fermi surface has a complicated hole pocket centred at the Γ-Z line and an elliptical electron pocket centred at the R point of the Brillouin zone. Polarization and photon-energy dependent photoemission results both indicate the nearly localized nature of the 4f electrons in CeIn3, consistent with the theoretical prediction by means of the combination of density functional theory and single-site dynamical mean-field theory. Those results illustrate that the f electrons of CeIn3, which is the parent material of CeMIn5 compounds, are closer to the localized description than the layered CeMIn5 compounds. PMID:27641364

  10. Three-dimensional bulk electronic structure of the Kondo lattice CeIn3 revealed by photoemission.

    PubMed

    Zhang, Yun; Lu, Haiyan; Zhu, Xiegang; Tan, Shiyong; Liu, Qin; Chen, Qiuyun; Feng, Wei; Xie, Donghua; Luo, Lizhu; Liu, Yu; Song, Haifeng; Zhang, Zhengjun; Lai, Xinchun

    2016-01-01

    We show the three-dimensional electronic structure of the Kondo lattice CeIn3 using soft x-ray angle resolved photoemission spectroscopy in the paramagnetic state. For the first time, we have directly observed the three-dimensional topology of the Fermi surface of CeIn3 by photoemission. The Fermi surface has a complicated hole pocket centred at the Γ-Z line and an elliptical electron pocket centred at the R point of the Brillouin zone. Polarization and photon-energy dependent photoemission results both indicate the nearly localized nature of the 4f electrons in CeIn3, consistent with the theoretical prediction by means of the combination of density functional theory and single-site dynamical mean-field theory. Those results illustrate that the f electrons of CeIn3, which is the parent material of CeMIn5 compounds, are closer to the localized description than the layered CeMIn5 compounds. PMID:27641364

  11. Three-dimensional bulk electronic structure of the Kondo lattice CeIn3 revealed by photoemission

    NASA Astrophysics Data System (ADS)

    Zhang, Yun; Lu, Haiyan; Zhu, Xiegang; Tan, Shiyong; Liu, Qin; Chen, Qiuyun; Feng, Wei; Xie, Donghua; Luo, Lizhu; Liu, Yu; Song, Haifeng; Zhang, Zhengjun; Lai, Xinchun

    2016-09-01

    We show the three-dimensional electronic structure of the Kondo lattice CeIn3 using soft x-ray angle resolved photoemission spectroscopy in the paramagnetic state. For the first time, we have directly observed the three-dimensional topology of the Fermi surface of CeIn3 by photoemission. The Fermi surface has a complicated hole pocket centred at the Γ-Z line and an elliptical electron pocket centred at the R point of the Brillouin zone. Polarization and photon-energy dependent photoemission results both indicate the nearly localized nature of the 4f electrons in CeIn3, consistent with the theoretical prediction by means of the combination of density functional theory and single-site dynamical mean-field theory. Those results illustrate that the f electrons of CeIn3, which is the parent material of CeMIn5 compounds, are closer to the localized description than the layered CeMIn5 compounds.

  12. On the use of a hierarchical multi-level building block basis function scheme in periodic plasmonic structures

    NASA Astrophysics Data System (ADS)

    Zheng, X.; Valev, V. K.; Volskiy, V.; Vandenbosch, Guy A. E.; Moshchalkov, V. V.

    2014-05-01

    A Volumetric Method of Moments algorithm is applied to predict the plasmonic responses of chiral metamaterials. This algorithm is based on the use of a multi-level building block basis function scheme, in combination with a dedicated Kummer transformation in the calculation of periodic Green's functions. The validity of the algorithm is demonstrated by analyzing a Ninja Star periodic structure. A good agreement can be found between simulation and experiment.

  13. On the Grammar of Silence: The Structure of My Undocumented Immigrant Writer's Block

    ERIC Educational Resources Information Center

    Ledesma, Alberto

    2015-01-01

    In this reflective essay, Alberto Ledesma explores how being undocumented can produce a particular form of writer's block. He argues that there is a pattern of predictable silences and obfuscations inherent in all undocumented immigrant autobiographies that cannot be easily negotiated when undocumented students are asked to write about "their…

  14. Block Copolymer Modified Epoxy Amine System for Reactive Rotational Molding: Structures, Properties and Processability

    NASA Astrophysics Data System (ADS)

    Lecocq, Eva; Nony, Fabien; Tcharkhtchi, Abbas; Gérard, Jean-François

    2011-05-01

    Poly(styrene-butadiene-methylmethacrylate) (SBM) and poly(methylmethacrylate-butyle-acrylate-methylmethacrylate) (MAM) triblock copolymers have been dissolved in liquid DGEBA epoxy resin which is subsequently polymerized by meta-xylene diamine (MXDA) or Jeffamine EDR-148. A chemorheology study of these formulations by plate-plate rheology and by thermal analysis has allowed to conclude that the addition of these copolymer blocks improve the reactive rotational moulding processability without affecting the processing time. Indeed, it prevents the pooling of the formulation at the bottom of the mould and a too rapid build up of resin viscosity of these thermosetting systems. The morphology of the cured blends examined by scanning electron microscopy (SEM) shows an increase of fracture surface area and thereby a potential increase of the toughness with the modification of epoxy system. Dynamic mechanical spectroscopy (DMA) and opalescence of final material show that the block PMMA, initially miscible, is likely to induce phase separation from the epoxy-amine matrix. Thereby, the poor compatibilisation between the toughener and the matrix has a detrimental effect on the tensile mechanical properties. The compatibilisation has to be increased to improve in synergy the processability and the final properties of these block copolymer modified formulations. First attempts could be by adapting the length and ratio of each block.

  15. Testing and Estimation for Structures which are Circularly Symmetric in Blocks.

    ERIC Educational Resources Information Center

    Olkin, Ingram

    In this report, the circularly symmetric model is extended to the point where the symmetries are exhibited in blocks. In addition, it is shown how maximum likelihood estimators (MLEs) and likelihood ratio tests (LRTs) can be obtained. The circularly symmetric model is reviewed and it is shown how MLEs and LRTs can be obtained by reducing the model…

  16. Structure-property relationships in multilayered polymeric system and olefinic block copolymers

    NASA Astrophysics Data System (ADS)

    Khariwala, Devang

    diffusion. Subsequently, the oxygen permeability was directly related to the composition profile in each layer and changed as the interdiffusion proceeded. This methodology enabled the extraction of the mutual diffusion co-efficient, D, for the Nylon-6/EVOH system. The effect of comonomer content in EVOH on the mutual diffusion coefficient was also studied by comparing the kinetics of interdiffusion of Nylon-6 with two EVOHs containing 24 and 44 mole % ethylene. Chapter 3. Exciting new developments in polyolefin synthesis give rise to olefinic block copolymers with properties typical of thermoplastic elastomers. The block copolymers synthesized by chain shuttling technology consist of crystallizable ethylene-octene blocks with low comonomer content and high melting temperature (hard blocks), alternating with amorphous ethylene-octene blocks with high comonomer content and low glass transition temperature (soft blocks). This study describes the material science of these unique polymers as characterized by thermal analysis, X-ray diffraction, microscopy, and tensile deformation. The crystallizable blocks are long enough to form well-organized lamellar crystals with the orthorhombic unit cell and high melting temperature. The lamellae are organized into space-filling spherulites in all compositions even in copolymers with only 18 wt% hard block. The morphology is consistent with crystallization from a miscible melt. Crystallization of the hard blocks forces segregation of the noncrystallizable soft blocks into the interlamellar regions. Good separation of hard and soft blocks in the solid state is confirmed by distinct and separate beta- and alpha-relaxations in all the block copolymers. Compared to statistical ethylene-octene copolymers, the blocky architecture imparts a substantially higher crystallization temperature, a higher melting temperature and a better organized crystalline morphology, while maintaining a lower glass transition temperature. The differences between

  17. The Lattice As Allosteric Effector: Structural Studies of Alphabeta- And Gamma-Tubulin Clarify the Role of GTP in Microtubule Assembly

    SciTech Connect

    Rice, L.M.; Montabana, E.A.; Agard, D.A.

    2009-05-21

    GTP-dependent microtubule polymerization dynamics are required for cell division and are accompanied by domain rearrangements in the polymerizing subunit, alpha-tubulin. Two opposing models describe the role of GTP and its relationship to conformational change in alpha-tubulin. The allosteric model posits that unpolymerized alpha-tubulin adopts a more polymerization-competent conformation upon GTP binding. The lattice model posits that conformational changes occur only upon recruitment into the growing lattice. Published data support a lattice model, but are largely indirect and so the allosteric model has prevailed. We present two independent solution probes of the conformation of alpha-tubulin, the 2.3 A crystal structure of gamma-tubulin bound to GDP, and kinetic simulations to interpret the functional consequences of the structural data. These results (with our previous gamma-tubulin:GTPgammaS structure) support the lattice model by demonstrating that major domain rearrangements do not occur in eukaryotic tubulins in response to GTP binding, and that the unpolymerized conformation of alpha-tubulin differs significantly from the polymerized one. Thus, geometric constraints of lateral self-assembly must drive alpha-tubulin conformational changes, whereas GTP plays a secondary role to tune the strength of longitudinal contacts within the microtubule lattice. alpha-Tubulin behaves like a bent spring, resisting straightening until forced to do so by GTP-mediated interactions with the growing microtubule. Kinetic simulations demonstrate that resistance to straightening opposes microtubule initiation by specifically destabilizing early assembly intermediates that are especially sensitive to the strength of lateral interactions. These data provide new insights into the molecular origins of dynamic microtubule behavior.

  18. Effect of lattice anharmonicity in the structural phase transformation of Laves phase HfV2 alloy: A first-principles investigation

    SciTech Connect

    Krcmar, Maja; Fu, Chong Long

    2013-01-01

    First-principles theory was developed to study the structural phase transformations in the Laves phase HfV2 alloy. We explored the energy landscape and established the role of lattice anharmonicity underlying the structural phase transitions. Our approach is based on a phenomenological Landau theory for the structural phase transition and a mean-field approximation for the free energy. First-principles calculations were utilized to obtain the distortion energy as a function of relevant deformations, and to deduce parameters for constructing the free energy. Our result for the phase transition temperature of HfV2 is in good agreement with experiment. We find that the high-temperature cubic C15 phase is stabilized by the effect of lattice anharmonicity. The theory also predicts an anomalous increase in shear modulus with increasing temperature for systems where the anharmonicity is pronounced.

  19. Interplay of structural instability and lattice dynamics in Ni2MnAl

    NASA Astrophysics Data System (ADS)

    Mehaddene, Tarik; Neuhaus, Jürgen; Petry, Winfried; Hradil, Klaudia; Bourges, Philippe; Hiess, Arno

    2008-09-01

    We report on the structural instability of Ni2MnAl from calorimetry measurements and inelastic neutron scattering. The acoustic and optical phonon dispersions along the high-symmetry [ξ00] , [ξξ0] , and [ξξξ] directions have been interpolated from the normal modes of vibration using the Born von Kármán model. The tendency of Ni2MnAl to undergo a martensitic transformation shows up in the anomalous phonon softening of the particular TA2[ξξ0] phonons in the ξ range 0.1 0.25 rlu of two different crystals. The phonon frequencies of this branch scale inversely with the valence electron concentration in good agreement with ab initio calculations. Contrary to the prediction of first-principles calculations in the Heusler L21-Ni2MnAl , no anomaly is seen in the optical phonons measured in B2-Ni2MnAl . The anomalous TA2[ξξ0] phonon softening is not enhanced below room temperature when Ni2MnAl orders in the antiferromagnetic state.

  20. Lattice studies of baryons

    SciTech Connect

    David Richards

    2004-10-01

    This talk describes progress at understanding the properties of the nucleon and its excitations from lattice QCD. I begin with a review of recent lattice results for the lowest-lying states of the excited baryon spectrum. The need to approach physical values of the light quark masses is emphasized, enabling the effects of the pion cloud to be revealed. I then outline the development of techniques that will enable the extraction of the masses of the higher resonances, and describe how such calculations provide insight into the structure of the hadrons. Finally, I discuss direct probes of the quark and gluon structure of baryons through the lattice measurement of the moments of quark distributions and of Generalized Parton Distributions.

  1. Structural characteristic and origin of intra-continental fold belt in the eastern Sichuan basin, South China Block

    NASA Astrophysics Data System (ADS)

    Li, Chuanxin; He, Dengfa; Sun, Yanpeng; He, Jinyou; Jiang, Zaixing

    2015-11-01

    The fold-and-thrust belt in the eastern Sichuan basin is represented by a series of subparallel chevron anticlines. Under the orogenic tectonic setting within the South China Block in Meso-Cenozoic period and the influence of the multi-layer detachment fault, the deformation of the thrust belt exhibits remarkably layered and large-scale intracontinental thrusting structural characteristics. In this paper, we focus on the structural geometry and deformational mechanisms using the latest two-dimensional (2D) and three-dimensional (3D) seismic reflection data in combination with well and outcrop data. The multi-layer detachment faults, especially the upper gypsum-bearing detachment in the Middle Triassic Jialingjiang Formation and lower detachment with gypsum or shale in the Lower-Middle Cambrian system, directly control the deformational styles of the study area. Interpretation of seismic sections indicates that the fold-and-thrust belt has various deformational styles during folding, including fault-propagation fold, fault-bend fold, and detachment fold with box-fold or pop-up structural geometry. Regional location and structural boundaries play significant roles in controlling the deformational styles, and distinct differences exist among the different anticlines. The Huayingshan anticline located at the front of the thrust belt shows intense structural deformation with northwestward thrusting direction and a relatively weak opposite southeastward thrusting. In addition, the anticlines exhibit structural differences along strike and the fold-and-thrust belt in the northern segment is influenced by the North China Block.

  2. Multifunctional imine-POSS as uncommon 3D nanobuilding blocks for supramolecular hybrid materials: synthesis, structural characterization, and properties.

    PubMed

    Janeta, Mateusz; John, Łukasz; Ejfler, Jolanta; Lis, Tadeusz; Szafert, Sławomir

    2016-08-01

    In this article, we report on the chemistry and the spectroscopic properties of well-defined imino-functionalized polyoctahedral oligomeric silsesquioxanes (imine-POSS) with various substitutions. Our efforts were mainly focused on side chains with sizable aryl groups possessing hydroxyl, nitro, and halide moieties. Such a choice enabled us to track their reduction abilities to secondary amine-POSS, tautomerization effects, and thermal properties. We also report for the first time the solid-state structures of five imino-functionalized cage-like octasilsesquioxanes. These structures provide unique examples of the complexities of three-dimensional packing motifs and their relationship with the assembly of tunable materials from nanobuilding blocks.

  3. Adaptation of a Multi-Block Structured Solver for Effective Use in a Hybrid CPU/GPU Massively Parallel Environment

    NASA Astrophysics Data System (ADS)

    Gutzwiller, David; Gontier, Mathieu; Demeulenaere, Alain

    2014-11-01

    Multi-Block structured solvers hold many advantages over their unstructured counterparts, such as a smaller memory footprint and efficient serial performance. Historically, multi-block structured solvers have not been easily adapted for use in a High Performance Computing (HPC) environment, and the recent trend towards hybrid GPU/CPU architectures has further complicated the situation. This paper will elaborate on developments and innovations applied to the NUMECA FINE/Turbo solver that have allowed near-linear scalability with real-world problems on over 250 hybrid GPU/GPU cluster nodes. Discussion will focus on the implementation of virtual partitioning and load balancing algorithms using a novel meta-block concept. This implementation is transparent to the user, allowing all pre- and post-processing steps to be performed using a simple, unpartitioned grid topology. Additional discussion will elaborate on developments that have improved parallel performance, including fully parallel I/O with the ADIOS API and the GPU porting of the computationally heavy CPUBooster convergence acceleration module. Head of HPC and Release Management, Numeca International.

  4. Characterizing the Three-Dimensional Structure of Block Copolymers via Sequential Infiltration Synthesis and Scanning Transmission Electron Tomography.

    PubMed

    Segal-Peretz, Tamar; Winterstein, Jonathan; Doxastakis, Manolis; Ramírez-Hernández, Abelardo; Biswas, Mahua; Ren, Jiaxing; Suh, Hyo Seon; Darling, Seth B; Liddle, J Alexander; Elam, Jeffrey W; de Pablo, Juan J; Zaluzec, Nestor J; Nealey, Paul F

    2015-05-26

    Understanding and controlling the three-dimensional structure of block copolymer (BCP) thin films is critical for utilizing these materials for sub-20 nm nanopatterning in semiconductor devices, as well as in membranes and solar cell applications. Combining an atomic layer deposition (ALD)-based technique for enhancing the contrast of BCPs in transmission electron microscopy (TEM) together with scanning TEM (STEM) tomography reveals and characterizes the three-dimensional structures of poly(styrene-block-methyl methacrylate) (PS-b-PMMA) thin films with great clarity. Sequential infiltration synthesis (SIS), a block-selective technique for growing inorganic materials in BCPs films in an ALD tool and an emerging technique for enhancing the etch contrast of BCPs, was harnessed to significantly enhance the high-angle scattering from the polar domains of BCP films in the TEM. The power of combining SIS and STEM tomography for three-dimensional (3D) characterization of BCP films was demonstrated with the following cases: self-assembled cylindrical, lamellar, and spherical PS-b-PMMA thin films. In all cases, STEM tomography has revealed 3D structures that were hidden underneath the surface, including (1) the 3D structure of defects in cylindrical and lamellar phases, (2) the nonperpendicular 3D surface of grain boundaries in the cylindrical phase, and (3) the 3D arrangement of spheres in body-centered-cubic (BCC) and hexagonal-closed-pack (HCP) morphologies in the spherical phase. The 3D data of the spherical morphologies was compared to coarse-grained simulations and assisted in validating the simulations' parameters. STEM tomography of SIS-treated BCP films enables the characterization of the exact structure used for pattern transfer and can lead to a better understating of the physics that is utilized in BCP lithography.

  5. Heat flow, heat generation and crustal thermal structure of the northern block of the South Indian Craton

    NASA Technical Reports Server (NTRS)

    Gupta, Mohan L.; Sharma, S. R.; Sundar, A.

    1988-01-01

    Heat flow values and heat generation data calculated from the concentration of heat producing radioactive elements, U, Th and K in surface rocks were analyzed. The South Indian Craton according to Drury et al., can be divided into various blocks, separated by late Proterozoic shear belts. The northern block comprises Eastern and Western Dharwar Cratons of Rogers (1986), Naqvi and Rogers (1987) and a part of the South Indian granulite terrain up to a shear system occupying the Palghat-Cauvery low lands. The geothermal data analysis clearly demonstrates that the present thermal characteristics of the above two Archaean terrains of the Indian and Australian Shields are quite similar. Their crustal thermal structures are likely to be similar also.

  6. Core-shell structured square mixed-spin-2 and 3/2 Ising nanowire on the Bethe lattice: a Monte Carlo study

    NASA Astrophysics Data System (ADS)

    Masrour, R.; Jabar, A.; Hamedoun, M.; Benyoussef, A.

    2016-08-01

    The magnetic properties of square Ising nanowire on the Bethe lattice with core-shell structure consisting of spin-2 at the center and four spin-3/2 at the corners are studied by Monte Carlo simulation. The core-shell structured model is studied using exchange interactions between surface spins (Jss ), between core spins (J σσ ) and between surface and core spins (J S σ ) and crystal field interaction (Δ) at the sites of spin-2 and spin-3/2. The critical temperature is deduced for different layers (N) and different shell-shell exchange interactions. The variation of magnetization with the reduced crystal field and exchange interactions on square Ising nanowire on the Bethe lattice has been studied with effect of other physical parameters. The magnetic hysteresis cycle is studied with different parameters such as: temperature, crystal field and shell-shell exchange interactions. The multiple hysteresis cycles are found.

  7. Core–shell structured square mixed-spin-2 and 3/2 Ising nanowire on the Bethe lattice: a Monte Carlo study

    NASA Astrophysics Data System (ADS)

    Masrour, R.; Jabar, A.; Hamedoun, M.; Benyoussef, A.

    2016-08-01

    The magnetic properties of square Ising nanowire on the Bethe lattice with core–shell structure consisting of spin-2 at the center and four spin-3/2 at the corners are studied by Monte Carlo simulation. The core–shell structured model is studied using exchange interactions between surface spins (Jss ), between core spins (J σσ ) and between surface and core spins (J S σ ) and crystal field interaction (Δ) at the sites of spin-2 and spin-3/2. The critical temperature is deduced for different layers (N) and different shell–shell exchange interactions. The variation of magnetization with the reduced crystal field and exchange interactions on square Ising nanowire on the Bethe lattice has been studied with effect of other physical parameters. The magnetic hysteresis cycle is studied with different parameters such as: temperature, crystal field and shell–shell exchange interactions. The multiple hysteresis cycles are found.

  8. Structure and thermoelectric properties of the quaternary compound Cs2[PdCl4]I2 with ultralow lattice thermal conductivity

    NASA Astrophysics Data System (ADS)

    Li, Wenfeng; Yang, Gui

    2016-03-01

    We study the electronic structure and thermoelectric properties of Cs2[PdCl4]I2 with ultralow lattice thermal conductivity using first-principles calculations and the semi-classical Boltzmann transport theory. The coexistence of several ionic and covalent bonds in Cs2[PdCl4]I2 indicates a similar Zintl phase crystal structure. Cs2[PdCl4]I2 is an indirect-band semiconductor with high density of states near the valence band maximum, which leads to high Seebeck coefficients even at high carrier concentrations. The calculated transport properties of p-type Cs2[PdCl4]I2 are higher than that of the known high-performance thermoelectric material CuGaTe2. The combination of good transport properties and ultralow lattice thermal conductivity suggests that Cs2[PdCl4]I2 can be a promising p-type thermoelectric material.

  9. Rigidity of lattice domes

    NASA Technical Reports Server (NTRS)

    Savelyev, V. A.

    1979-01-01

    The means of ensuring total rigidity of lattice domes, using comparison with solid shells of 1-3 layers are discussed. Irregularities of manufacture, processing, and other factors are considered, as they relate to diminution of rigidity. The discussion uses the concepts of upper and lower critical loads on the structure in question.

  10. Progress in lattice QCD

    SciTech Connect

    Andreas S. Kronfeld

    2002-09-30

    After reviewing some of the mathematical foundations and numerical difficulties facing lattice QCD, I review the status of several calculations relevant to experimental high-energy physics. The topics considered are moments of structure functions, which may prove relevant to search for new phenomena at the LHC, and several aspects of flavor physics, which are relevant to understanding CP and flavor violation.

  11. Lateral variation of crustal structure and composition in the Cathaysia block of South China and its geodynamic implications

    NASA Astrophysics Data System (ADS)

    Xia, Shaohong; Sun, Jinlong; Xu, Huilong; Yin, Jianping; Cao, Jinhe

    2016-04-01

    To clarify lateral variations in the crustal structure and composition of the Cathaysia block in South China which was affected by extensive and intensive Mesozoic and Cenozoic tectono-magmatic activities, we study the crustal thickness and Poisson's ratio in this region using the H-κ stacking method of teleseismic receiver functions. Our results show that the Poisson's ratio varies between 0.20 and 0.29 and the crustal thickness ranges from 26 to 34 km in the Cathaysia block. The crustal thickness and Poisson's ratio show considerable differences across the Lishui-Haifeng Fault. The Southeast Coast Magmatic Belt is characterized by Poisson's ratios > 0.25 and the crustal thickness of 28-33 km, reflecting obviously intermediate to mafic compositions. The southwestern part of the Cathaysia Folded Belt exhibits the crustal thickness of 27-30 km and Poisson's ratios < 0.25, reflecting a more felsic crust. However, the northeastern part of the Cathaysia Folded Belt is characterized by an almost flat Moho at a depth of ~31 km and a strong variation of Poisson's ratio from 0.22 to 0.27. The ESE-WNW trending boundary between the southwestern and northeastern parts of the Cathaysia Folded Belt closely coincides with a geosuture between two Precambrian microcontinents which exhibit different patterns of crustal evolution revealed by geochemical studies. The lateral variations in the crustal structure and composition of the Cathaysia block may reflect not only the lithological variations of the primitive crustal rocks but also significant effects of tectonism and magmatism on the interior of the Cathaysia block during the Meso-Cenozoic.

  12. Structural and physicochemical properties of liquid Al-Zn alloys: A combined study based on molecular dynamics simulations and the quasi-lattice theory

    NASA Astrophysics Data System (ADS)

    Trybula, M.; Jakse, N.; Gasior, W.; Pasturel, A.

    2014-12-01

    Ordering phenomena have been investigated in liquid Al-Zn alloys performing molecular dynamics (MD) simulations using "empirical oscillating pair potentials." The local structural order is studied by computing two microscopic functions, namely, the concentration fluctuation function and the Warren-Cowley short-range order parameter. We also study the influence of ordering phenomena on transport properties like diffusivity and viscosity. The MD results are confronted to those determined from measurements and in the framework of the quasi-lattice theory.

  13. A new Kagomé lattice coordination polymer based on bismuth and pyridine-2,5-dicarboxylate: structure and photoluminescent properties.

    PubMed

    Wibowo, Arief C; Smith, Mark D; zur Loye, Hans-Conrad

    2011-07-14

    A new Kagomé lattice topology assembled from ML(4) metal-organic polyhedra prepared using bismuth nitrate and pyridine-2,5-dicarboxylate has been obtained via a solvo-thermal reaction. Bi(pydc)(2)·(H(3)O(+))(H(2)O)(0.83) is, to the best of our knowledge, the first example of a bismuth-based coordination polymer to form with a Kagomé topology. Its structure and photoluminescence properties are reported.

  14. Impact of Lattice Mismatch and Stoichiometry on the Structure and Bandgap of (Fe,Cr)2O3 Epitaxial Thin Films

    SciTech Connect

    Kaspar, Tiffany C.; Chamberlin, Sara E.; Bowden, Mark E.; Colby, Robert J.; Shutthanandan, V.; Manandhar, Sandeep; Wang, Yong; Sushko, Petr; Chambers, Scott A.

    2014-03-13

    The structural properties of high-quality epitaxial (Fe1-xCrx)2O3 thin films are investigated across the composition range. Epitaxial films are deposited on a-Al2O3(0001) substrates by oxygen-plasma-assisted molecular beam epitaxy. Corundum (Fe1-xCrx)2O3 supercells relaxed by density functional theory confirm that the non-linear behavior of the bulk lattice parameters originates in the magnetic structure of the alloy films. High-resolution x-ray diffraction reveals the degree of epitaxial strain relaxation in the films, with Cr-rich films remaining partially strained to the Al2O3 substrate. For intermediate compositions, a lattice expansion and non-Poisson-like tetragonal distortion are found. Scanning transmission electron microscopy and electron energy loss spectroscopy reveal a columnar grain structure in the films, with uniform mixing of cations on the nanometer scale. Oxygen non-stoichiometry is quantified by non-Rutherford resonant elastic scattering measurements utilizing 3.04 MeV He+. Intermediate-composition films are found to be slightly over-stoichiometric, resulting in the observed lattice expansion. Cr-rich films, in contrast, appear to be slightly oxygen deficient. A model is proposed to explain these results based on the energetics of oxygen defect formation and rate of oxygen diffusion in the corundum lattice. Compressive biaxial strain is found to reduce the bandgap of epitaxial Cr2O3 relative to the bulk value. The relationships which are elucidated between epitaxial film structure and optical properties can be applied to bandgap optimization in the (Fe,Cr)2O3 system.

  15. Asymmetric sound transmission in a passive non-blocking structure with multiple ports

    NASA Astrophysics Data System (ADS)

    Zhu, Yi-Fan; Gu, Zhong-Ming; Liang, Bin; Yang, Jing; Yang, Jun; Yin, Lei-lei; Cheng, Jian-Chun

    2016-09-01

    We present the mechanism for breaking the symmetry in sound transmission between any two neighboring ports in a passive multi-port system. Numerical simulations and experimental measurements verify that by using judiciously designed metastructures to provide an extra wavevector without blocking the sound path, the propagating wave will travel along a preset direction at each port instead of splitting to both directions. We have also demonstrated the flexibility of this scheme to adjust the location of each port. Our design advances further the concept of one-way manipulation in passive two-port systems and may enable novel sound-steering devices for more versatile applications.

  16. Structured block copolymer thin film composites for ultra-high energy density capacitors

    NASA Astrophysics Data System (ADS)

    Samant, Saumil; Hailu, Shimelis; Grabowski, Christopher; Durstock, Michael; Raghavan, Dharmaraj; Karim, Alamgir

    2014-03-01

    Development of high energy density capacitors is essential for future applications like hybrid vehicles and directed energy weaponry. Fundamentally, energy density is governed by product of dielectric permittivity ɛ and breakdown strength Vbd. Hence, improvements in energy density are greatly reliant on improving either ɛ or Vbd or a combination of both. Polymer films are widely used in capacitors due to high Vbd and low loss but they suffer from very low permittivities. Composite dielectrics offer a unique opportunity to combine the high ɛ of inorganic fillers with the high Vbd of a polymer matrix. For enhancement of dielectric properties, it is essential to improve matrix-filler interaction and control the spatial distribution of fillers for which nanostructured block copolymers BCP act as ideal templates. We use Directed Self-assembly of block copolymers to rapidly fabricate highly aligned BCP-TiO2 composite nanostructures in thin films under dynamic thermal gradient field to synergistically combine the high ɛ of functionalized TiO2 and high Vbd of BCP matrix. The results of impact of BCP morphology, processing conditions and concentration of TiO2 on capacitor performance will be reported. U.S. Air Force of Scientific Research under contract FA9550-12-1-0306

  17. Polymer electrolyte membranes from fluorinated polyisoprene-block-sulfonated polystyrene: Membrane structure and transport properties

    SciTech Connect

    Sodeye, Akinbode; Huang, Tianzi; Gido, Samuel; Mays, Jimmy

    2011-01-01

    With a view to optimizing morphology and ultimately properties, membranes have been cast from relatively inexpensive block copolymer ionomers of fluorinated polyisoprene-block-sulfonated polystyrene (FISS) with various sulfonation levels, in both the acid form and the cesium neutralized form. The morphology of these membranes was characterized by transmission electron microscopy and ultra-small angle X-ray scattering, as well as water uptake, proton conductivity and methanol permeability within the temperature range from 20 to 60 C. Random phase separated morphologies were obtained for all samples except the cesium sample with 50 mol% sulfonation. The transport properties increased with increasing degree of sulfonation and temperature for all samples. The acid form samples absorbed more water than the cesium samples with a maximum swelling of 595% recorded at 60 C for the acid sample having 50 mol% sulfonation. Methanol permeability for the latter sample was more than an order of magnitude less than for Nafion 112 but so was the proton conductivity within the plane of the membrane at 20 C. Across the plane of the membrane this sample had half the conductivity of Nafion 112 at 60 C.

  18. Domain modeling and grid generation for multi-block structured grids with application to aerodynamic and hydrodynamic configurations

    NASA Technical Reports Server (NTRS)

    Spekreijse, S. P.; Boerstoel, J. W.; Vitagliano, P. L.; Kuyvenhoven, J. L.

    1992-01-01

    About five years ago, a joint development was started of a flow simulation system for engine-airframe integration studies on propeller as well as jet aircraft. The initial system was based on the Euler equations and made operational for industrial aerodynamic design work. The system consists of three major components: a domain modeller, for the graphical interactive subdivision of flow domains into an unstructured collection of blocks; a grid generator, for the graphical interactive computation of structured grids in blocks; and a flow solver, for the computation of flows on multi-block grids. The industrial partners of the collaboration and NLR have demonstrated that the domain modeller, grid generator and flow solver can be applied to simulate Euler flows around complete aircraft, including propulsion system simulation. Extension to Navier-Stokes flows is in progress. Delft Hydraulics has shown that both the domain modeller and grid generator can also be applied successfully for hydrodynamic configurations. An overview is given about the main aspects of both domain modelling and grid generation.

  19. Quaternary polymethacrylate-sodium alginate films: effect of alginate block structures and use for sustained release tablets.

    PubMed

    Pongjanyakul, Thaned; Khuathan, Natnicha

    2016-01-01

    The objectives in this study were to characterize quaternary polymethacrylate-sodium alginate (QPM-SA) films prepared using high G block or high M block SA (GSA or MSA, respectively), and to investigate the effects of QPM-SA ratios, film-coating levels and SA block structures on propranolol HCl (PPN) released from coated tablets. The results demonstrated that GSA and MSA shared a similar interaction mechanism with QPM. The QPM-GSA films had higher puncture strength than the QPM-MSA films in dry and wet states, whereas the % elongations were not different. The drug permeability of the QPM-GSA films was lower than that of the QPM-MSA films in both acidic and neutral media, but higher water uptake of the QPM-GSA films was found at neutral pH. Moreover, the QPM-MSA-coated tablets had a greater PPN release rate than the QPM-GSA-coated tablets, and drug release was dependent on the film-coating levels. In addition, the QPM-SA films at a ratio of 4:0.5 produced a stronger film and could sustain PPN release. These results indicate that the QPM-GSA films had greater film strength and lower drug permeability than the QPM-MSA films. Additionally, the QPM-SA films have a strong potential for use in sustained-release tablets. PMID:25757646

  20. Characteristics of pore structures in Selma Chalk using dual FIB-SEM 3D imaging and Lattice Boltzmann Modeling

    NASA Astrophysics Data System (ADS)

    Yoon, H.; Dewers, T. A.

    2012-12-01

    Accurate prediction of coupled geophysical and chemical processes at the pore scale requires realistic representation of pore structures. This is especially true for chalk materials, where pore networks are small and complex, and often characterized at sub-micron scale. Common techniques such as X-ray microtomography, microscopic imaging, or mercury intrusion porosimetry often show a limit on determining pore throat distributions and seal analysis of such fine-grained rocks. Focused ion beam-scanning electron microscope (FIB-SEM) and laser scanning confocal microscopy methods are used for 3D imaging of nanometer-to-micron scale microcrack and pore distributions in samples of the Cretaceous Selma Group Chalk. The Selma Chalk is considered the seal for oil and gas fields in the Mississippi Interior Salt Basin and a proposed regional-scale seal identified for CO2 sequestration sites. A series of image analysis techniques is used to process raw images in order to recover both nano-scale pore structure and continuous fracture networks. We apply 3D imaging techniques in interpreting FIB-SEM binary data for characterizing geometric pore body and throat distributions and other topological properties, and lattice-Boltzmann method (LBM) for obtaining permeability at several different scales. In particular, comparison of primary flow paths obtained from 3D image analysis and LBM demonstrates that image analysis results may have too many equally plausible flow paths, compared to LBM results. Upscaling of permeability and LB multiphase flow results with image dataset will be discussed with emphasis on understanding microfracture-matrix interaction during multiphase flow, and seal analysis for geologic CO2 storage. This material is based upon work supported as part of the Center for Frontiers of Subsurface Energy Security, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Award Number DE-SC0001114

  1. High holding voltage segmentation stacking silicon-controlled-rectifier structure with field implant as body ties blocking layer

    NASA Astrophysics Data System (ADS)

    Yen, Shiang-Shiou; Cheng, Chun-Hu; Lan, Yu-Pin; Chiu, Yu-Chien; Fan, Chia-Chi; Hsu, Hsiao-Hsuan; Chang, Shao-Chin; Jiang, Zhe-Wei; Hung, Li-Yue; Tsai, Chi-Chung; Chang, Chun-Yen

    2016-04-01

    High electrostatic discharge (ESD) protection robustness and good transient-induced latchup immunity are two important issues for high voltage integrate circuit application. In this study, we report a high-voltage-n-type-field (HVNF) implantation to act as the body ties blocking layer in segmented topology silicon-controlled-rectifier (SCR) structure in 0.11 µm 32 V high voltage process. This body ties blocking layer eliminate the elevated triggered voltage in segmented technique. Using a large resistance as shunt resistor in resistor assisted triggered SCRs stacking structure, the double snapback phenomenon is eliminate. The series SCR could be decoupled a sufficient voltage drop to turned-on when a very low current flow through the shunt resistor. The holding voltage and the failure current of 22 V and 3.4 A are achieved in the best condition of segmented topology SCR stacking structure, respectively. It improves the latchup immunity at high voltage ICs application. On the other hand, the triggered voltage almost keep the same value which is identical to SCR single cell without using segmented topology.

  2. Block scheduling and science education: A case study of structure and culture in a rural Georgia high school

    NASA Astrophysics Data System (ADS)

    Jordan, Miriam Mcelheney

    The purpose of this study was to contribute to the documentation and analysis of the effects of block scheduling on science education. The foundation of this case study is the ongoing innovation program called the Block-8 Schedule at a rural Georgia High School. The research extended from 1994 through 1998, allowing the collection of data during the planning and early implementation of the program. The effects of the program that are related to science education are interpreted in the context of the entire school restructuring effort. The program was developed by the faculty of the school to meet the identified needs for scheduling and innovative instruction. The result was an alternating day block schedule that was supported by inservice prior to and during the implementation. The program was also supported by efforts of the leadership team, the school's version of shared school governance. The result was a program that was well received by the staff, students, and community. After four years, satisfaction was still evident. Gains in student achievement were moderate. Findings indicate that the success realized by the program were related to the structural and cultural support provided by the school. Changes in science instruction particularly benefited from the extended ninety minute classes. The changes that occurred in the science classrooms were consistent with the goals of the national science standards. Although the gains in achievement were small to moderate, the methods used in teaching were compatible with the teaching standards of National Science Education Standards. The need for finding a fit between the goals of a reform effort and the culture and structure of the school has been overlooked in much of the science reform movement. This local reform, The Block-8 Schedule, which took into account the existing culture and structure of the school, provides a model on which other efforts at implementing science education reform could be based. This reform

  3. The effects of molecular and lattice structures on thermotropic phase behaviour of zinc(II) undecanoate and isomeric zinc(II) undecynoates

    NASA Astrophysics Data System (ADS)

    Nelson, Peter N.; Taylor, Richard A.; Ellis, Henry A.

    2013-02-01

    Molecular structures, hydrocarbon chain packing, in the crystal lattice and their effects on the thermal behaviour of saturated and isomeric zinc(II) undecynoates have been investigated by a variety of physical methods. All the compounds crystallize in a monoclinic crystal system with a being the long axis. The hydrocarbon chains adopt the fully extended all-trans conformation and are arranged as methyl-methyl overlapping bilayers within a lamellar. Furthermore, in order to enhance lattice stability, hydrocarbon chains, from different layers in the lamellar are not in the same plane but are packed in an alternating spatial arrangement and are tilted at ca. 60° to the metal basal plane. In a molecule, four carbonyl groups bind to a zinc atom, in a bridging bidentate mode, to form a three dimensional polymeric network. At elevated temperatures a highly viscous phase, a polymeric ionic mesophase, possibly a smectic C phase, is observed for 10-undecynoate only, whereas two crystal-crystal and crystal-isotropic liquid transitions are observed for the undecanoate and 9-undecynoate, respectively. Though head group coordination is nearly iso-structural, differences in molecular symmetry and lattice packing are evident. These arise from differences in the spatial orientation of the high electron density hydrocarbon chains in the crystal lattice. Indeed, it is the relative balance between head group electrostatic and van der Waals interactions at elevated temperatures that accounts for formation of the mesophase. Surprisingly, all the freshly synthesized compounds are meta-stable, only achieving complete stability over several days. Furthermore, on heating and cooling the compounds, thermotropic behaviour is altered so that on re-heating, subtle changes in phase textures are observed.

  4. Fibonacci Optical Lattices

    NASA Astrophysics Data System (ADS)

    Singh, Kevin; Geiger, Zachary; Senaratne, Ruwan; Rajagopal, Shankari; Fujiwara, Kurt; Weld, David; Weld Group Team

    2015-05-01

    Quasiperiodicity is intimately involved in quantum phenomena from localization to the quantum Hall effect. Recent experimental investigation of quasiperiodic quantum effects in photonic and electronic systems have revealed intriguing connections to topological phenomena. However, such experiments have been limited by the absence of techniques for creating tunable quasiperiodic structures. We propose a new type of quasiperiodic optical lattice, constructed by intersecting a Gaussian beam with a 2D square lattice at an angle with an irrational tangent. The resulting potential, a generalization of the Fibonacci lattice, is a physical realization of the mathematical ``cut-and-project'' construction which underlies all quasiperiodic structures. Calculation of the energies and wavefunctions of atoms loaded into the proposed quasiperiodic lattice demonstrate a fractal energy spectrum and the existence of edge states. We acknowledge support from the ONR (award N00014-14-1-0805), the ARO and the PECASE program (award W911NF-14-1-0154), the AFOSR (award FA9550-12-1-0305), and the Alfred P. Sloan foundation (grant BR2013-110).

  5. Agar block smear preparation: a novel method of slide preparation for preservation of native fungal structures for microscopic examination and long-term storage.

    PubMed

    Woo, Patrick C Y; Ngan, Antonio H Y; Chui, Hon-Kit; Lau, Susanna K P; Yuen, Kwok-Yung

    2010-09-01

    We describe a novel method of fungal slide preparation named "agar block smear preparation." A total of 510 agar block smears of 25 fungal strains obtained from culture collections, 90 QC fungal strains, and 82 clinical fungal strains from our clinical microbiology laboratory, which included a total of 137 species of yeasts, molds, and thermal dimorphic fungi, were prepared and examined. In contrast to adhesive tape preparation, agar block smears preserved the native fungal structures, such as intact conidiophores of Aspergillus species and arrangements of conidia in Scopulariopsis brevicaulis. Furthermore, agar block smears allowed examination of fungal structures embedded in the agar, such as the ascomata with ascomal hairs in Chaetomium funicola; pycnidium of Phoma glomerata; the intercalary ovoidal chlamydospores arranged in chains of Fusarium dimerum; and the lateral, spherical chlamydospores arranged in pairs of Fusarium solani. After 1 year of storage, morphological integrity was found to have been maintained in 459 (90%) of the 510 agar block smears. After 3 years of storage, morphological integrity was found to have been maintained in 72 (71%) of the 102 smears prepared in 2006. Agar block smear preparation preserves the native fungal structures and allows long-term storage and examination of fungal structures embedded in the agar, hence overcoming the major drawbacks of adhesive tape preparation. The major roles of agar block smear should be diagnosis for difficult cases, accurate identification of fungal species for clinical management of patients and epidemiological studies, and long-term storage for transportation of slides and education purposes.

  6. Elimination of spurious lattice fermion solutions and noncompact lattice QCD

    SciTech Connect

    Lee, T.D.

    1997-09-22

    It is well known that the Dirac equation on a discrete hyper-cubic lattice in D dimension has 2{sup D} degenerate solutions. The usual method of removing these spurious solutions encounters difficulties with chiral symmetry when the lattice spacing l {ne} 0, as exemplified by the persistent problem of the pion mass. On the other hand, we recall that in any crystal in nature, all the electrons do move in a lattice and satisfy the Dirac equation; yet there is not a single physical result that has ever been entangled with a spurious fermion solution. Therefore it should not be difficult to eliminate these unphysical elements. On a discrete lattice, particle hop from point to point, whereas in a real crystal the lattice structure in embedded in a continuum and electrons move continuously from lattice cell to lattice cell. In a discrete system, the lattice functions are defined only on individual points (or links as in the case of gauge fields). However, in a crystal the electron state vector is represented by the Bloch wave functions which are continuous functions in {rvec {gamma}}, and herein lies one of the essential differences.

  7. Hands-On Exercise in Environmental Structural Geology Using a Fracture Block Model.

    ERIC Educational Resources Information Center

    Gates, Alexander E.

    2001-01-01

    Describes the use of a scale analog model of an actual fractured rock reservoir to replace paper copies of fracture maps in the structural geology curriculum. Discusses the merits of the model in enabling students to gain experience performing standard structural analyses. (DDR)

  8. Multifunctional imine-POSS as uncommon 3D nanobuilding blocks for supramolecular hybrid materials: synthesis, structural characterization, and properties.

    PubMed

    Janeta, Mateusz; John, Łukasz; Ejfler, Jolanta; Lis, Tadeusz; Szafert, Sławomir

    2016-08-01

    In this article, we report on the chemistry and the spectroscopic properties of well-defined imino-functionalized polyoctahedral oligomeric silsesquioxanes (imine-POSS) with various substitutions. Our efforts were mainly focused on side chains with sizable aryl groups possessing hydroxyl, nitro, and halide moieties. Such a choice enabled us to track their reduction abilities to secondary amine-POSS, tautomerization effects, and thermal properties. We also report for the first time the solid-state structures of five imino-functionalized cage-like octasilsesquioxanes. These structures provide unique examples of the complexities of three-dimensional packing motifs and their relationship with the assembly of tunable materials from nanobuilding blocks. PMID:27438046

  9. Predicting Human Preferences Using the Block Structure of Complex Social Networks

    PubMed Central

    Guimerà, Roger; Llorente, Alejandro; Moro, Esteban; Sales-Pardo, Marta

    2012-01-01

    With ever-increasing available data, predicting individuals' preferences and helping them locate the most relevant information has become a pressing need. Understanding and predicting preferences is also important from a fundamental point of view, as part of what has been called a “new” computational social science. Here, we propose a novel approach based on stochastic block models, which have been developed by sociologists as plausible models of complex networks of social interactions. Our model is in the spirit of predicting individuals' preferences based on the preferences of others but, rather than fitting a particular model, we rely on a Bayesian approach that samples over the ensemble of all possible models. We show that our approach is considerably more accurate than leading recommender algorithms, with major relative improvements between 38% and 99% over industry-level algorithms. Besides, our approach sheds light on decision-making processes by identifying groups of individuals that have consistently similar preferences, and enabling the analysis of the characteristics of those groups. PMID:22984533

  10. Electronic structure of lattice-mismatched superlattices: Si_n(SiO_x)m and (GaAs)_n(GaN)_1

    NASA Astrophysics Data System (ADS)

    Luo, Xuan; Wei, S.-H.; Zhang, S. B.

    2001-03-01

    Recent progress in optoelectronics requires materials by design: For example, a semiconductor lattice matched to Si with > 1.5-eV direct bandgap is ideal for optoelectronic integration. On the other hand, high efficiency multi junction III-V solar cell requires a material lattice matched to GaAs with 1-eV bandgap. We have carried out first-principles calculations to search for superlattices that satisfy these conditions. For Si_n(SiO_x)m (m = 1, 2) [1], our results suggest that oxygen atoms prefer the off-center sites between nearest-neighbor Si atoms. Depending on the O concentration, location, and Si layer thickness index n, the band gap can change to nearly zero or 1 eV larger than that of Si. For (GaAs)_n(GaN)_1, the GaN-layer causes the bandgap to decrease with decreasing n. For example, the equivalent bowing coefficient for n = 1 is 8.95, larger than the 50/50 bulk alloy (6.84) due to substrate constraint for lattice relaxation. This provides new opportunities for bandgap engineering by the growth of superlattice structures. [1] R. Tsu and J. C. Lofgren, ICPS-25 Abstract, p. 659 (Osaka, Japan, 2000).

  11. Computationally designed peptides for self-assembly of nanostructured lattices.

    PubMed

    Zhang, Huixi Violet; Polzer, Frank; Haider, Michael J; Tian, Yu; Villegas, Jose A; Kiick, Kristi L; Pochan, Darrin J; Saven, Jeffery G

    2016-09-01

    Folded peptides present complex exterior surfaces specified by their amino acid sequences, and the control of these surfaces offers high-precision routes to self-assembling materials. The complexity of peptide structure and the subtlety of noncovalent interactions make the design of predetermined nanostructures difficult. Computational methods can facilitate this design and are used here to determine 29-residue peptides that form tetrahelical bundles that, in turn, serve as building blocks for lattice-forming materials. Four distinct assemblies were engineered. Peptide bundle exterior amino acids were designed in the context of three different interbundle lattices in addition to one design to produce bundles isolated in solution. Solution assembly produced three different types of lattice-forming materials that exhibited varying degrees of agreement with the chosen lattices used in the design of each sequence. Transmission electron microscopy revealed the nanostructure of the sheetlike nanomaterials. In contrast, the peptide sequence designed to form isolated, soluble, tetrameric bundles remained dispersed and did not form any higher-order assembled nanostructure. Small-angle neutron scattering confirmed the formation of soluble bundles with the designed size. In the lattice-forming nanostructures, the solution assembly process is robust with respect to variation of solution conditions (pH and temperature) and covalent modification of the computationally designed peptides. Solution conditions can be used to control micrometer-scale morphology of the assemblies. The findings illustrate that, with careful control of molecular structure and solution conditions, a single peptide motif can be versatile enough to yield a wide range of self-assembled lattice morphologies across many length scales (1 to 1000 nm). PMID:27626071

  12. Computationally designed peptides for self-assembly of nanostructured lattices

    PubMed Central

    Zhang, Huixi Violet; Polzer, Frank; Haider, Michael J.; Tian, Yu; Villegas, Jose A.; Kiick, Kristi L.; Pochan, Darrin J.; Saven, Jeffery G.

    2016-01-01

    Folded peptides present complex exterior surfaces specified by their amino acid sequences, and the control of these surfaces offers high-precision routes to self-assembling materials. The complexity of peptide structure and the subtlety of noncovalent interactions make the design of predetermined nanostructures difficult. Computational methods can facilitate this design and are used here to determine 29-residue peptides that form tetrahelical bundles that, in turn, serve as building blocks for lattice-forming materials. Four distinct assemblies were engineered. Peptide bundle exterior amino acids were designed in the context of three different interbundle lattices in addition to one design to produce bundles isolated in solution. Solution assembly produced three different types of lattice-forming materials that exhibited varying degrees of agreement with the chosen lattices used in the design of each sequence. Transmission electron microscopy revealed the nanostructure of the sheetlike nanomaterials. In contrast, the peptide sequence designed to form isolated, soluble, tetrameric bundles remained dispersed and did not form any higher-order assembled nanostructure. Small-angle neutron scattering confirmed the formation of soluble bundles with the designed size. In the lattice-forming nanostructures, the solution assembly process is robust with respect to variation of solution conditions (pH and temperature) and covalent modification of the computationally designed peptides. Solution conditions can be used to control micrometer-scale morphology of the assemblies. The findings illustrate that, with careful control of molecular structure and solution conditions, a single peptide motif can be versatile enough to yield a wide range of self-assembled lattice morphologies across many length scales (1 to 1000 nm). PMID:27626071

  13. Computationally designed peptides for self-assembly of nanostructured lattices

    PubMed Central

    Zhang, Huixi Violet; Polzer, Frank; Haider, Michael J.; Tian, Yu; Villegas, Jose A.; Kiick, Kristi L.; Pochan, Darrin J.; Saven, Jeffery G.

    2016-01-01

    Folded peptides present complex exterior surfaces specified by their amino acid sequences, and the control of these surfaces offers high-precision routes to self-assembling materials. The complexity of peptide structure and the subtlety of noncovalent interactions make the design of predetermined nanostructures difficult. Computational methods can facilitate this design and are used here to determine 29-residue peptides that form tetrahelical bundles that, in turn, serve as building blocks for lattice-forming materials. Four distinct assemblies were engineered. Peptide bundle exterior amino acids were designed in the context of three different interbundle lattices in addition to one design to produce bundles isolated in solution. Solution assembly produced three different types of lattice-forming materials that exhibited varying degrees of agreement with the chosen lattices used in the design of each sequence. Transmission electron microscopy revealed the nanostructure of the sheetlike nanomaterials. In contrast, the peptide sequence designed to form isolated, soluble, tetrameric bundles remained dispersed and did not form any higher-order assembled nanostructure. Small-angle neutron scattering confirmed the formation of soluble bundles with the designed size. In the lattice-forming nanostructures, the solution assembly process is robust with respect to variation of solution conditions (pH and temperature) and covalent modification of the computationally designed peptides. Solution conditions can be used to control micrometer-scale morphology of the assemblies. The findings illustrate that, with careful control of molecular structure and solution conditions, a single peptide motif can be versatile enough to yield a wide range of self-assembled lattice morphologies across many length scales (1 to 1000 nm).

  14. Western closure of the Corinth Rift: Stratigraphy and structure of the Lakka fault block

    NASA Astrophysics Data System (ADS)

    Palyvos, Nikos; Ford, Mary; Mancini, Marco; Esu, Daniela; Girotti, Odoardo; Urban, Brigitte

    2013-04-01

    In the Corinth Gulf, seismicity is highest in the west, where the active Psathopyrgos-Neos Erineos-Aegion fault zone (PNEAFZ;30 km long, N dip) defines the south coast. To the south and SE the inactive early rift records N and NW migration of deformation since the Pliocene. When was the PNEAFZ initiated? How did it grow? What is the relevance of this fault zone within the full rift history? This paper presents new data for the onshore westernmost rift, indicating that it had a distinct early rifting history (Early to Middle Pleistocene) before being overprinted around 400 ka by the NW migrating Corinth rift. Two syn rift stratigraphic groups are recognised in the uplifted Lakka fault block in the footwall of the PNEAFZ. The youngest Galada group, comprises marine deposits and terraces that mainly document footwall uplift since initiation of the PNEAFZ at around 400-350 ka (Palyvos et al. 2010). The oldest sediments derived from the footwall of the Lakka fault are the 400-350 ka old Aravonitsa Gilbert delta (Palyvos et al. 2010), suggesting this fault is not significantly older than the PNEAFZ. The Galada group records a gradual eastward block tilting due to differential footwall uplift as the PNEAFZ propagated east. The underlying Profitis Ilias group, (pre 400 ka, < 600 m) is characterised by south and southeastward fining continental facies from coarse alluvial conglomerates in the immediate footwall of the Psathopyrgos fault (Rodini formation) passing east and south to fluvial sandstones and conglomerates (Salmoniko formation), to deltaic and shallow water sandstones interfingering with lacustrine marls, silts and fine sandstones with rare conglomerates and lignites (Synania formation). Faunal assemblages in the Synania formation indicate freshwater to brackish conditions with occasional marine levels and support an Early to Middle Pleistocene age. To the ESE, the Synania formation passes laterally and up into a 200 m succession of fine sandstones with rare

  15. Role of structural factors in formation of chiral magnetic soliton lattice in Cr{sub 1/3}NbS₂

    SciTech Connect

    Volkova, L. M.; Marinin, D. V.

    2014-10-07

    The sign and strength of magnetic interactions not only between nearest neighbors, but also for longer-range neighbors in the Cr{sub 1/3}NbS₂ intercalation compound have been calculated on the basis of structural data. It has been found that left-handed spin helices in Cr{sub 1/3}NbS₂ are formed from strength-dominant at low temperatures antiferromagnetic (AFM) interactions between triangular planes of Cr³⁺ ions through the plane of just one of two crystallographically equivalent diagonals of side faces of embedded into each other trigonal prisms building up the crystal lattice of magnetic Cr³⁺ ions. These helices are oriented along the c axis and packed into two-dimensional triangular lattices in planes perpendicular to these helices directions and lay one upon each other with a displacement. The competition of the above AFM helices with weaker inter-helix AFM interactions could promote the emergence of a long-period helical spin structure. One can assume that in this case, the role of Dzyaloshinskii-Moriya interaction consists of final ordering and stabilization of chiral spin helices into a chiral magnetic soliton lattice. The possibility of emergence of solitons in M{sub 1/3}NbX{sub 2} and M{sub 1/3}TaX₂ (M = Cr, V, Ti, Rh, Ni, Co, Fe, and Mn; X = S and Se) intercalate compounds has been examined. Two important factors caused by the crystal structure (predominant chiral magnetic helices and their competition with weaker inter-helix interactions not destructing the system quasi-one-dimensional character) can be used for the crystal chemistry search of solitons.

  16. Automated global structure extraction for effective local building block processing in XCS.

    PubMed

    Butz, Martin V; Pelikan, Martin; Llorà, Xavier; Goldberg, David E

    2006-01-01

    Learning Classifier Systems (LCSs), such as the accuracy-based XCS, evolve distributed problem solutions represented by a population of rules. During evolution, features are specialized, propagated, and recombined to provide increasingly accurate subsolutions. Recently, it was shown that, as in conventional genetic algorithms (GAs), some problems require efficient processing of subsets of features to find problem solutions efficiently. In such problems, standard variation operators of genetic and evolutionary algorithms used in LCSs suffer from potential disruption of groups of interacting features, resulting in poor performance. This paper introduces efficient crossover operators to XCS by incorporating techniques derived from competent GAs: the extended compact GA (ECGA) and the Bayesian optimization algorithm (BOA). Instead of simple crossover operators such as uniform crossover or one-point crossover, ECGA or BOA-derived mechanisms are used to build a probabilistic model of the global population and to generate offspring classifiers locally using the model. Several offspring generation variations are introduced and evaluated. The results show that it is possible to achieve performance similar to runs with an informed crossover operator that is specifically designed to yield ideal problem-dependent exploration, exploiting provided problem structure information. Thus, we create the first competent LCSs, XCS/ECGA and XCS/BOA, that detect dependency structures online and propagate corresponding lower-level dependency structures effectively without any information about these structures given in advance.

  17. Middle Jurassic Radiolaria from a siliceous argillite block in a structural melange zone near Viqueque, Timor Leste: Paleogeographic implications

    NASA Astrophysics Data System (ADS)

    Haig, David W.; Bandini, Alexandre Nicolas

    2013-10-01

    Thin-bedded siliceous argillite forming a large block within a structural melange zone at Viqueque, Timor Leste, has yielded a Middle Jurassic (late Bathonian-early Callovian) radiolarian assemblage belonging to Unitary Association Zone 7. Fifty-five species are recognized and illustrated, forming the most diverse radiolarian fauna yet documented from the Jurassic of Timor. The fauna shows little similarity in species content to the few other assemblages previously listed from the Middle or Late Jurassic of Timor, and also has few species in common with faunas known elsewhere in the region from Rotti, Sumatra, South Kalimantan, and Sula. Based on lithofacies similarities and age, the siliceous argillite succession in the melange block at Viqueque is included in the Noni Group originally described as the lower part of the Palelo Series in West Timor. In terms of lithofacies, the Noni Group is distinct from other stratigraphic units known in Timor. It may be associated with volcanic rocks but age relationships are uncertain, although some of the radiolarian cherts in the Noni Group in West Timor have been reported to include tuffaceous sediment. The deep-water character of the siliceous hemipelagite-pelagite facies, the probable volcanic association, and an age close to that of continental breakup in the region suggest deposition in a newly rifted Indian Ocean. In Timor's tectonostratigraphic classification scheme, the Noni Group is here placed in the "Indian Ocean Megasequence".

  18. Revisiting the microtrabecular lattice.

    PubMed

    Clegg, James S

    2010-11-01

    The 'microtrabecular lattice' (MTL) that Keith Porter described in the 1970s and 1980s is reconsidered as a proposed fundamental cytoplasmic structure of eukaryotic cells. Although considered to be an artefact by most cell biologists of his time (and probably ours), the case is made that something like the MTL may well exist, but in a much more dynamic form than images from electron microscopy imply and convey.

  19. An Electronic Structure Approach to Charge Transfer and Transport in Molecular Building Blocks for Organic Optoelectronics

    NASA Astrophysics Data System (ADS)

    Hendrickson, Heidi Phillips

    A fundamental understanding of charge separation in organic materials is necessary for the rational design of optoelectronic devices suited for renewable energy applications and requires a combination of theoretical, computational, and experimental methods. Density functional theory (DFT) and time-dependent (TD)DFT are cost effective ab-initio approaches for calculating fundamental properties of large molecular systems, however conventional DFT methods have been known to fail in accurately characterizing frontier orbital gaps and charge transfer states in molecular systems. In this dissertation, these shortcomings are addressed by implementing an optimally-tuned range-separated hybrid (OT-RSH) functional approach within DFT and TDDFT. The first part of this thesis presents the way in which RSH-DFT addresses the shortcomings in conventional DFT. Environmentally-corrected RSH-DFT frontier orbital energies are shown to correspond to thin film measurements for a set of organic semiconducting molecules. Likewise, the improved RSH-TDDFT description of charge transfer excitations is benchmarked using a model ethene dimer and silsesquioxane molecules. In the second part of this thesis, RSH-DFT is applied to chromophore-functionalized silsesquioxanes, which are currently investigated as candidates for building blocks in optoelectronic applications. RSH-DFT provides insight into the nature of absorptive and emissive states in silsesquioxanes. While absorption primarily involves transitions localized on one chromophore, charge transfer between chromophores and between chromophore and silsesquioxane cage have been identified. The RSH-DFT approach, including a protocol accounting for complex environmental effects on charge transfer energies, was tested and validated against experimental measurements. The third part of this thesis addresses quantum transport through nano-scale junctions. The ability to quantify a molecular junction via spectroscopic methods is crucial to their

  20. Protein based Block Copolymers

    PubMed Central

    Rabotyagova, Olena S.; Cebe, Peggy; Kaplan, David L.

    2011-01-01

    Advances in genetic engineering have led to the synthesis of protein-based block copolymers with control of chemistry and molecular weight, resulting in unique physical and biological properties. The benefits from incorporating peptide blocks into copolymer designs arise from the fundamental properties of proteins to adopt ordered conformations and to undergo self-assembly, providing control over structure formation at various length scales when compared to conventional block copolymers. This review covers the synthesis, structure, assembly, properties, and applications of protein-based block copolymers. PMID:21235251

  1. Directing Hybrid Structures by Combining Self-Assembly of Functional Block Copolymers and Atomic Layer Deposition: A Demonstration on Hybrid Photovoltaics.

    PubMed

    Moshonov, Moshe; Frey, Gitti L

    2015-11-24

    The simplicity and versatility of block copolymer self-assembly offers their use as templates for nano- and meso-structured materials. However, in most cases, the material processing requires multiple steps, and the block copolymer is a sacrificial building block. Here, we combine a self-assembled block copolymer template and atomic layer deposition (ALD) of a metal oxide to generate functional hybrid films in a simple process with no etching or burning steps. This approach is demonstrated by using the crystallization-induced self-assembly of a rod-coil block copolymer, P3HT-b-PEO, and the ALD of ZnO. The block copolymer self-assembles into fibrils, ∼ 20 nm in diameter and microns long, with crystalline P3HT cores and amorphous PEO corona. The affinity of the ALD precursors to the PEO corona directs the exclusive deposition of crystalline ZnO within the PEO domains. The obtained hybrid structure possesses the properties desired for photovoltaic films: donor-acceptor continuous nanoscale interpenetrated networks. Therefore, we integrated the films into single-layer hybrid photovoltaics devices, thus demonstrating that combining self-assembly of functional block copolymers and ALD is a simple approach to direct desired complex hybrid morphologies.

  2. Fermions on the low-buckled honey-comb structured lattice plane and classical Casimir-Polder force

    NASA Astrophysics Data System (ADS)

    Goswami, Partha

    2016-05-01

    We start with the well-known expression for the vacuum polarization and suitably modify it for 2+1-dimensional spin-orbit coupled (SOC) fermions on the low-buckled honey-comb structured lattice plane described by the low-energy Liu-Yao-Feng-Ezawa (LYFE) model Hamiltonian involving the Dirac matrices in the chiral representation obeying the Clifford algebra. The silicene and germanene fit this description suitably. They have the Dirac cones similar to those of graphene and SOC is much stronger. The system could be normal or ferromagnetic in nature. The silicene turns into the latter type if there is exchange field arising due to the proximity coupling to a ferromagnet (FM) such as depositing Fe atoms to the silicene surface. For the silicene, we find that the many-body effects considerably change the bare Coulomb potential by way of the dependence of the Coulomb propagator on the real-spin, iso-spin and the potential due to an electric field applied perpendicular to the silicene plane. The computation aspect of the Casimir-Polder force (CPF) needs to be investigated in this paper. An important quantity in this process is the dielectric response function (DRF) of the material. The plasmon branch was obtained by finding the zeros of DRF in the long-wavelength limit. This leads to the plasmon frequencies. We find that the collective charge excitations at zero doping, i.e., intrinsic plasmons, in this system, are absent in the Dirac limit. The valley-spin-split intrinsic plasmons, however, come into being in the case of the massive Dirac particles with characteristic frequency close to 10 THz. Our scheme to calculate the Casimir-Polder interaction (CPI) of a micro-particle with a sheet involves replacing the dielectric constant of the sample in the CPI expression obtained on the basis of the Lifshitz theory by the static DRF obtained using the expressions for the polarization function we started with. Though the approach replaces a macroscopic constant by a microscopic

  3. Blocking Phonon Transport by Structural Resonances in Alloy-Based Nanophononic Metamaterials Leads to Ultralow Thermal Conductivity.

    PubMed

    Xiong, Shiyun; Sääskilahti, Kimmo; Kosevich, Yuriy A; Han, Haoxue; Donadio, Davide; Volz, Sebastian

    2016-07-01

    Understanding the design rules to obtain materials that enable a tight control of phonon transport over a broad range of frequencies would aid major developments in thermoelectric energy harvesting, heat management in microelectronics, and information and communication technology. Using atomistic simulations we show that the metamaterials approach relying on localized resonances is very promising to engineer heat transport at the nanoscale. Combining designed resonant structures to alloying can lead to extremely low thermal conductivity in silicon nanowires. The hybridization between resonant phonons and propagating modes greatly reduces the group velocities and the phonon mean free paths in the low frequency acoustic range below 4 THz. Concurrently, alloy scattering hinders the propagation of high frequency thermal phonons. Our calculations establish a rationale between the size, shape, and period of the resonant structures, and the thermal conductivity of the nanowire, and demonstrate that this approach is even effective to block phonon transport in wavelengths much longer than the size and period of the surface resonant structures. A further consequence of using resonant structures is that they are not expected to scatter electrons, which is beneficial for thermoelectric applications. PMID:27447516

  4. Blocking Phonon Transport by Structural Resonances in Alloy-Based Nanophononic Metamaterials Leads to Ultralow Thermal Conductivity

    NASA Astrophysics Data System (ADS)

    Xiong, Shiyun; Sääskilahti, Kimmo; Kosevich, Yuriy A.; Han, Haoxue; Donadio, Davide; Volz, Sebastian

    2016-07-01

    Understanding the design rules to obtain materials that enable a tight control of phonon transport over a broad range of frequencies would aid major developments in thermoelectric energy harvesting, heat management in microelectronics, and information and communication technology. Using atomistic simulations we show that the metamaterials approach relying on localized resonances is very promising to engineer heat transport at the nanoscale. Combining designed resonant structures to alloying can lead to extremely low thermal conductivity in silicon nanowires. The hybridization between resonant phonons and propagating modes greatly reduces the group velocities and the phonon mean free paths in the low frequency acoustic range below 4 THz. Concurrently, alloy scattering hinders the propagation of high frequency thermal phonons. Our calculations establish a rationale between the size, shape, and period of the resonant structures, and the thermal conductivity of the nanowire, and demonstrate that this approach is even effective to block phonon transport in wavelengths much longer than the size and period of the surface resonant structures. A further consequence of using resonant structures is that they are not expected to scatter electrons, which is beneficial for thermoelectric applications.

  5. Blocking Phonon Transport by Structural Resonances in Alloy-Based Nanophononic Metamaterials Leads to Ultralow Thermal Conductivity.

    PubMed

    Xiong, Shiyun; Sääskilahti, Kimmo; Kosevich, Yuriy A; Han, Haoxue; Donadio, Davide; Volz, Sebastian

    2016-07-01

    Understanding the design rules to obtain materials that enable a tight control of phonon transport over a broad range of frequencies would aid major developments in thermoelectric energy harvesting, heat management in microelectronics, and information and communication technology. Using atomistic simulations we show that the metamaterials approach relying on localized resonances is very promising to engineer heat transport at the nanoscale. Combining designed resonant structures to alloying can lead to extremely low thermal conductivity in silicon nanowires. The hybridization between resonant phonons and propagating modes greatly reduces the group velocities and the phonon mean free paths in the low frequency acoustic range below 4 THz. Concurrently, alloy scattering hinders the propagation of high frequency thermal phonons. Our calculations establish a rationale between the size, shape, and period of the resonant structures, and the thermal conductivity of the nanowire, and demonstrate that this approach is even effective to block phonon transport in wavelengths much longer than the size and period of the surface resonant structures. A further consequence of using resonant structures is that they are not expected to scatter electrons, which is beneficial for thermoelectric applications.

  6. Structure and spectroscopy of two new bases for building block: Terpyridine derivatives

    NASA Astrophysics Data System (ADS)

    Toledo, Dominique; Baggio, Ricardo; Freire, Eleonora; Vega, Andrés; Pizarro, Nancy; Moreno, Yanko

    2015-12-01

    Two new terpyridine compounds are reported: 4‧-(3-methyl-2-thienyl)-4,2‧:6‧,4″-terpyridine, C20H15N3S, (I) and 4‧-(4-quinolinyl)-4,2‧:6‧,4″-terpyridine, C25H17Cl3N4, (II). Both structures crystallize in centrosymmetric space groups and present weak H-bonds, which gives greater stability to their structures. Light absorption by both molecules is firmly established on the experimental and the TDDFT analysis as coming from π → π* transitions. The fluorescence of both compounds has a small Stockes shift, which is also consistent with the emission from highly rigid molecules. Furthermore, the thermal stability observed for both compounds, until about 280 °C, making these molecules interesting candidates for use as complex ligands, which are obtained by means of solvothermal synthesis (technique with temperatures of about 150 °C).

  7. Structural hierarchies define toughness and defect-tolerance despite simple and mechanically inferior brittle building blocks

    PubMed Central

    Sen, Dipanjan; Buehler, Markus J.

    2011-01-01

    Mineralized biological materials such as bone, sea sponges or diatoms provide load-bearing and armor functions and universally feature structural hierarchies from nano to macro. Here we report a systematic investigation of the effect of hierarchical structures on toughness and defect-tolerance based on a single and mechanically inferior brittle base material, silica, using a bottom-up approach rooted in atomistic modeling. Our analysis reveals drastic changes in the material crack-propagation resistance (R-curve) solely due to the introduction of hierarchical structures that also result in a vastly increased toughness and defect-tolerance, enabling stable crack propagation over an extensive range of crack sizes. Over a range of up to four hierarchy levels, we find an exponential increase in the defect-tolerance approaching hundred micrometers without introducing additional mechanisms or materials. This presents a significant departure from the defect-tolerance of the base material, silica, which is brittle and highly sensitive even to extremely small nanometer-scale defects. PMID:22355554

  8. Structural hierarchies define toughness and defect-tolerance despite simple and mechanically inferior brittle building blocks.

    PubMed

    Sen, Dipanjan; Buehler, Markus J

    2011-01-01

    Mineralized biological materials such as bone, sea sponges or diatoms provide load-bearing and armor functions and universally feature structural hierarchies from nano to macro. Here we report a systematic investigation of the effect of hierarchical structures on toughness and defect-tolerance based on a single and mechanically inferior brittle base material, silica, using a bottom-up approach rooted in atomistic modeling. Our analysis reveals drastic changes in the material crack-propagation resistance (R-curve) solely due to the introduction of hierarchical structures that also result in a vastly increased toughness and defect-tolerance, enabling stable crack propagation over an extensive range of crack sizes. Over a range of up to four hierarchy levels, we find an exponential increase in the defect-tolerance approaching hundred micrometers without introducing additional mechanisms or materials. This presents a significant departure from the defect-tolerance of the base material, silica, which is brittle and highly sensitive even to extremely small nanometer-scale defects.

  9. Structural hierarchies define toughness and defect-tolerance despite simple and mechanically inferior brittle building blocks

    NASA Astrophysics Data System (ADS)

    Sen, Dipanjan; Buehler, Markus J.

    2011-07-01

    Mineralized biological materials such as bone, sea sponges or diatoms provide load-bearing and armor functions and universally feature structural hierarchies from nano to macro. Here we report a systematic investigation of the effect of hierarchical structures on toughness and defect-tolerance based on a single and mechanically inferior brittle base material, silica, using a bottom-up approach rooted in atomistic modeling. Our analysis reveals drastic changes in the material crack-propagation resistance (R-curve) solely due to the introduction of hierarchical structures that also result in a vastly increased toughness and defect-tolerance, enabling stable crack propagation over an extensive range of crack sizes. Over a range of up to four hierarchy levels, we find an exponential increase in the defect-tolerance approaching hundred micrometers without introducing additional mechanisms or materials. This presents a significant departure from the defect-tolerance of the base material, silica, which is brittle and highly sensitive even to extremely small nanometer-scale defects.

  10. Manipulation and control of a bichromatic lattice

    NASA Astrophysics Data System (ADS)

    Thomas, Claire; Barter, Thomas; Daiss, Severin; Leung, Zephy; Stamper-Kurn, Dan

    2015-05-01

    Recent experiments with ultracold atoms in optical lattices have had great success emulating the simple models of condensed matter systems. These experiments are typically performed with a single site per unit cell. We realize a lattice with up to four sites per unit cell by overlaying an attractive triangular lattice with a repulsive one at twice the wavelength. The relative displacement of the two lattices determines the particular structure. One available configuration is the kagome lattice, which has a flat energy band. In the flat band all kinetic energy states are degenerate, so we have the opportunity to explore a regime where interactions dominate. This bichromatic lattice requires careful stabilization, but offers an opportunity to manipulate the unit cell and band structure by perturbing the lattices relative to one another. I will discuss recent progress.

  11. Nano-spatial parameters from 3D to 2D lattice dimensionality by organic variant in [ZnCl4]- [R]+ hybrid materials: Structure, architecture-lattice dimensionality, microscopy, optical Eg and PL correlations

    NASA Astrophysics Data System (ADS)

    Kumar, Ajit; Verma, Sanjay K.; Alvi, P. A.; Jasrotia, Dinesh

    2016-04-01

    The nanospatial morphological features of [ZnCl]- [C5H4NCH3]+ hybrid derivative depicts 28 nm granular size and 3D spreader shape packing pattern as analyzed by FESEM and single crystal XRD structural studies. The organic moiety connect the inorganic components through N-H+…Cl- hydrogen bond to form a hybrid composite, the replacement of organic derivatives from 2-methylpyridine to 2-Amino-5-choloropyridine results the increase in granular size from 28nm to 60nm and unit cell packing pattern from 3D-2D lattice dimensionality along ac plane. The change in optical energy direct band gap value from 3.01eV for [ZnCl]- [C5H4NCH3]+ (HM1) to 3.42eV for [ZnCl]- [C5H5ClN2]+ (HM2) indicates the role of organic moiety in optical properties of hybrid materials. The photoluminescence emission spectra is observed in the wavelength range of 370 to 600 nm with maximum peak intensity of 9.66a.u. at 438 nm for (HM1) and 370 to 600 nm with max peak intensity of 9.91 a.u. at 442 nm for (HM2), indicating that the emission spectra lies in visible range. PL excitation spectra depicts the maximum excitation intensity [9.8] at 245.5 nm for (HM1) and its value of 9.9 a.u. at 294 nm, specify the excitation spectra lies in UV range. Photoluminescence excitation spectra is observed in the wavelength range of 280 to 350 nm with maximum peak intensity of 9.4 a.u. at 285.5 nm and 9.9 a.u. at 294 and 297 nm, indicating excitation in the UV spectrum. Single crystal growth process and detailed physiochemical characterization such as XRD, FESEM image analysis photoluminescence property reveals the structure stability with non-covalent interactions, lattice dimensionality (3D-2D) correlations interweaving into the design of inorganic-organic hybrid materials.

  12. Investigation of 2D laterally dispersive photonic crystal structures : LDRD 33602 final report.

    SciTech Connect

    Subramania,Ganapathi Subramanian; Vawter, Gregory Allen; Wendt, Joel Robert; Peake, Gregory Merwin; Guo, Junpeng; Peters, David William; Hadley, G. Ronald

    2003-12-01

    Artificially structured photonic lattice materials are commonly investigated for their unique ability to block and guide light. However, an exciting aspect of photonic lattices which has received relatively little attention is the extremely high refractive index dispersion within the range of frequencies capable of propagating within the photonic lattice material. In fact, it has been proposed that a negative refractive index may be realized with the correct photonic lattice configuration. This report summarizes our investigation, both numerically and experimentally, into the design and performance of such photonic lattice materials intended to optimize the dispersion of refractive index in order to realize new classes of photonic devices.

  13. Stable kagome lattices from group IV elements

    NASA Astrophysics Data System (ADS)

    Leenaerts, O.; Schoeters, B.; Partoens, B.

    2015-03-01

    A thorough investigation of three-dimensional kagome lattices of group IV elements is performed with first-principles calculations. The investigated kagome lattices of silicon and germanium are found to be of similar stability as the recently proposed carbon kagome lattice. Carbon and silicon kagome lattices are both direct-gap semiconductors but they have qualitatively different electronic band structures. While direct optical transitions between the valence and conduction bands are allowed in the carbon case, no such transitions can be observed for silicon. The kagome lattice of germanium exhibits semimetallic behavior but can be transformed into a semiconductor after compression.

  14. NMR sequential assignments and solution structure of chlorotoxin, a small scorpion toxin that blocks chloride channels.

    PubMed

    Lippens, G; Najib, J; Wodak, S J; Tartar, A

    1995-01-10

    The solution structure of chlorotoxin, a small toxin purified from the venom of the Leiurus quinquestriatus scorpion, has been determined using 2D 1H NMR spectroscopy. Analysis of the NMR data shows that the structure consists of a small three-stranded antiparallel beta-sheet packed against an alpha-helix, thereby adopting the same fold as charybdotoxin and other members of the short scorpion toxin family [Arseniev et al. (1984) FEBS Lett. 165, 57-62; Martins et al. (1990) FEBS Lett. 260, 249-253; Bontems et al. (1991) Science 254, 1521-1523]. Three disulfide bonds of chlorotoxin (Cys5-Cys28, Cys16-Cys33, and Cys20-Cys35), cross-linking the alpha-helix to the beta-sheet, follow the common pattern found in the other short scorpion toxins. The fourth disulfide bridge (Cys2-Cys19) links the small N-terminal beta strand to the rest of the molecule, in contrast to charybdotoxin where this disulfide bridge is absent and the first strand interacts with the rest of the molecule by several contacts between hydrophobic residues. Another structural difference between chlorotoxin and charybdotoxin is observed at the level of the alpha-beta turn. This difference is accompanied by a change in the electrostatic potential surface, which is largely positive at the level of this turn in chlorotoxin, whereas no such positive potential surface can be found at the same position in charybdotoxin. In the latter protein, the positive surface is formed by different charged residues situated on the solvent-exposed site of the C-terminal beta-sheet.(ABSTRACT TRUNCATED AT 250 WORDS)

  15. The defect structure and chemical lattice strain of the double perovskites Sr2BMoO6-δ (B = Mg, Fe).

    PubMed

    Tsvetkov, D S; Ivanov, I L; Malyshkin, D A; Steparuk, A S; Zuev, A Yu

    2016-08-01

    The defect structure of B-site ordered double perovskites Sr2BMoO6-δ was analyzed. The defect structure model was proposed and successfully verified using data on oxygen nonstoichiometry of Sr2MgMoO6-δ and Sr2FeMoO6-δ. As a result, equilibrium constants of the defect reactions involved were estimated. Fe and Mo in Sr2FeMoO6-δ were found to be in the mixed oxidation state close to +2.5 and +5.5, respectively. Chemical strain of the Sr2FeMoO6-δ double perovskite lattice was studied by in situ high temperature XRD at 1100 °C depending on pO2. Parameter a of the Sr2FeMoO6-δ cubic cell was found to increase with decreasing pO2 because of lattice chemical expansion. The tetragonal polymorph of Sr2FeMoO6-δ was shown to exhibit transversal isotropy with respect to chemical expansion. It was also found that its crystal lattice expands in the ab-plane and simultaneously contracts along the c-axis when the oxygen content in the double perovskite decreases. In order to describe the degree of anisotropy of chemical strain a new phenomenological coefficient was introduced. This coefficient was shown to affect both the magnitude and change direction of an oxide cell volume caused by its reduction/oxidation. Excellent agreement between the chemical expansion along the a-axis calculated for both polymorphs of Sr2FeMoO6-δ according to the model recently developed and that measured experimentally was shown. Chemical contraction observed along the c-axis with a decreasing oxygen content in the tetragonal polymorph was also found to coincide completely with that calculated using the approach developed in the present study. PMID:27476830

  16. The defect structure and chemical lattice strain of the double perovskites Sr2BMoO6-δ (B = Mg, Fe).

    PubMed

    Tsvetkov, D S; Ivanov, I L; Malyshkin, D A; Steparuk, A S; Zuev, A Yu

    2016-08-01

    The defect structure of B-site ordered double perovskites Sr2BMoO6-δ was analyzed. The defect structure model was proposed and successfully verified using data on oxygen nonstoichiometry of Sr2MgMoO6-δ and Sr2FeMoO6-δ. As a result, equilibrium constants of the defect reactions involved were estimated. Fe and Mo in Sr2FeMoO6-δ were found to be in the mixed oxidation state close to +2.5 and +5.5, respectively. Chemical strain of the Sr2FeMoO6-δ double perovskite lattice was studied by in situ high temperature XRD at 1100 °C depending on pO2. Parameter a of the Sr2FeMoO6-δ cubic cell was found to increase with decreasing pO2 because of lattice chemical expansion. The tetragonal polymorph of Sr2FeMoO6-δ was shown to exhibit transversal isotropy with respect to chemical expansion. It was also found that its crystal lattice expands in the ab-plane and simultaneously contracts along the c-axis when the oxygen content in the double perovskite decreases. In order to describe the degree of anisotropy of chemical strain a new phenomenological coefficient was introduced. This coefficient was shown to affect both the magnitude and change direction of an oxide cell volume caused by its reduction/oxidation. Excellent agreement between the chemical expansion along the a-axis calculated for both polymorphs of Sr2FeMoO6-δ according to the model recently developed and that measured experimentally was shown. Chemical contraction observed along the c-axis with a decreasing oxygen content in the tetragonal polymorph was also found to coincide completely with that calculated using the approach developed in the present study.

  17. Lattice gauge theory for QCD

    SciTech Connect

    DeGrand, T.

    1997-06-01

    These lectures provide an introduction to lattice methods for nonperturbative studies of Quantum Chromodynamics. Lecture 1: Basic techniques for QCD and results for hadron spectroscopy using the simplest discretizations; lecture 2: Improved actions--what they are and how well they work; lecture 3: SLAC physics from the lattice-structure functions, the mass of the glueball, heavy quarks and {alpha}{sub s} (M{sub z}), and B-{anti B} mixing. 67 refs., 36 figs.

  18. Population Blocks.

    ERIC Educational Resources Information Center

    Smith, Martin H.

    1992-01-01

    Describes an educational game called "Population Blocks" that is designed to illustrate the concept of exponential growth of the human population and some potential effects of overpopulation. The game material consists of wooden blocks; 18 blocks are painted green (representing land), 7 are painted blue (representing water); and the remaining…

  19. Comparison of different structures of niobium oxide blocking layer for dye-sensitized solar cells.

    PubMed

    Chun, Jae Hwan; Kim, Jong Sung

    2014-08-01

    In this study, four different types of Nb2O5 thin layers were prepared using sol-gel process to improve energy conversion efficiency of dye sensitized solar cells (DSSCs). Nb2O5 layer was prepared on the fluorine-doped tin oxide (FTO) layer, TiO2 electrode layer, and inside of TiO2 layer, respectively. The Nb2O5 layer was used to reduce the recombination of photo induced electrons and holes. The DSSCs were assembled with platinum (Pt) coated counter electrode, ruthenium dye, and iodine based electrolyte. The photocurrent-voltage (I-V) characteristics of DSSCs with different types of Nb2O5 were studied. The efficiency depends not only on the structure of DSSCs but also on the initial compositions for the preparation of Nb2O5.

  20. Crystal structures and magnetic properties of the honeycomb-lattice antiferromagnet M2(pymca)3(ClO4), (M = Fe, Co, Ni)

    NASA Astrophysics Data System (ADS)

    Honda, Zentaro; Kodama, Takafumi; Hagiwara, Masayuki; Kida, Takanori; Okutani, Akira; Sakai, Masamichi; Fukuda, Takeshi; Kamata, Norihiko

    2016-09-01

    We report on the syntheses, crystal structures, and magnetic properties of a series of transition metal coordination polymers M2(pymca)3(ClO4), (pymca = pyrimidine-2-carboxylic acid, M = Fe (1), Co (2), and Ni (3)). These compounds are found to crystallize in a trigonal crystal system, space group P31m, with the lattice constants a = 9.727 Å and c = 5.996 Å for 1, a = 9.608 Å and c = 5.996 Å for 2, and a = 9.477 Å and c = 5.958 Å for 3 at room temperature. In these compounds, each pymca ligand connects to two M2+ ions, forming a honeycomb network in the ab plane. The temperature dependences of magnetic susceptibilities in these compounds show broad maxima, indicating antiferromagnetic interactions within two-dimensional honeycomb layers. We also observed an antiferromagnetic phase transition at low temperatures by magnetic susceptibility and heat capacity measurements. From the crystal structures and magnetic properties, we conclude that the compounds 1, 2, and 3 are good realizations of honeycomb-lattice antiferromagnets.

  1. Local structure and lattice dynamics study of low dimensional materials using atomic pair distribution function and high energy resolution inelastic x-ray scattering

    NASA Astrophysics Data System (ADS)

    Shi, Chenyang

    Structure and dynamics lie at the heart of the materials science. A detailed knowledge of both subjects would be foundational in understanding the materials' properties and predicting their potential applications. However, the task becomes increasingly dicult as the particle size is reduced to the nanometer scale. For nanostructured materials their laboratory x-ray scattering patterns are overlapped and broadened, making structure determination impossible. Atomic pair distribution function technique based on either synchrotron x-ray or neutron scattering data is known as the tool of choice for probing local structures. However, to solve the "structure problem" in low-dimensional materials with PDF is still challenging. For example for 2D materials of interest in this thesis the crystallographic modeling approach often yields unphysical thermal factors along stacking direction where new chemical intuitions about their actual structures and new modeling methodology/program are needed. Beyond this, lattice dynamical investigations on nanosized particles are extremely dicult. Laboratory tools such as Raman and infra-red only probe phonons at Brillouin zone center. Although in literature there are a great number of theoretical studies of their vibrational properties based on either empirical force elds or density functional theory, various approximations made in theories make the theoretical predictions less reliable. Also, there lacks the direct experiment result to validate the theory against. In this thesis, we studied the structure and dynamics of a wide variety of technologically relevant low-dimensional materials through synchrotron based x-ray PDF and high energy resolution inelastic x-ray scattering (HERIX) techniques. By collecting PDF data and employing advanced modeling program such as DiPy-CMI, we successfully determined the atomic structures of (i) emerging Ti3C2, Nb4C3 MXenes (transition metal carbides and/or nitrides) that are promising for energy storage

  2. A Block-Structured KIVA Program for Engines with Vertical or Canted Valves

    SciTech Connect

    2007-04-16

    KIVA-4 is the latest version of the series of KIVA codes. While KIVA-4 maintains the full generality of KIVA-3V, it adds the capability of computing with unstructured grids. Unstructured grids can be generated more easily than structured grids for complex geometries. The unstructured grids can be composed of a variety of elements including hexahedra, prisms, pyramids, and tetrahedra. However the numerical accuracy is less when the grid is not composed of hexahedra. KIVA-4 was developed to work with the many geometries accommodated with KIVA-3V which include 2D axisymmetric, 2D planar, 3D axisymmetric sector geometries, and full 3D geometries. KIVA-4 also features a multicomponent fuel evaporation algorithm. Many of the numerical algorithms in KIVA-3V do generalize nicely to unstructured meshes. However fundamental changes were needed in the solution of the pressure equation and the fluxing of momentum. In addition, KIVA-4 loops over cell faces to compute diffusion terms. More details can be found in Torres, D.J. and Trujillo, M.F., KIVA-4: An unstructured ALE code for compressible gas flow with sprays, Journal of Computational Physics, 2006, vol. 219, pp. 943-975. PACKAGE TESTED USING LINUX OPERATING SYSTEM. MAY BE MODIFIED TO RUN USING UNIX OR WINDOWS.

  3. A Block-Structured KIVA Program for Engines with Vertical or Canted Valves

    2007-04-16

    KIVA-4 is the latest version of the series of KIVA codes. While KIVA-4 maintains the full generality of KIVA-3V, it adds the capability of computing with unstructured grids. Unstructured grids can be generated more easily than structured grids for complex geometries. The unstructured grids can be composed of a variety of elements including hexahedra, prisms, pyramids, and tetrahedra. However the numerical accuracy is less when the grid is not composed of hexahedra. KIVA-4 was developedmore » to work with the many geometries accommodated with KIVA-3V which include 2D axisymmetric, 2D planar, 3D axisymmetric sector geometries, and full 3D geometries. KIVA-4 also features a multicomponent fuel evaporation algorithm. Many of the numerical algorithms in KIVA-3V do generalize nicely to unstructured meshes. However fundamental changes were needed in the solution of the pressure equation and the fluxing of momentum. In addition, KIVA-4 loops over cell faces to compute diffusion terms. More details can be found in Torres, D.J. and Trujillo, M.F., KIVA-4: An unstructured ALE code for compressible gas flow with sprays, Journal of Computational Physics, 2006, vol. 219, pp. 943-975. PACKAGE TESTED USING LINUX OPERATING SYSTEM. MAY BE MODIFIED TO RUN USING UNIX OR WINDOWS.« less

  4. Al{sub 15}Ge{sub 4}Ni{sub 3}: A new intergrowth structure with Cu{sub 3}Au- and CaF{sub 2}-type building blocks

    SciTech Connect

    Reichmann, Thomas L.; Jandl, Isabella; Effenberger, Herta S.; Herzig, Peter; Richter, Klaus W.

    2015-05-15

    The new ternary compound Al{sub 15}Ge{sub 4}Ni{sub 3} (τ{sub 2} in the system Al–Ge–Ni) was synthesized in single crystalline form by a special annealing procedure from samples located in the three phase fields [L+Al+τ{sub 2}] and [L+Ge+τ{sub 2}]. The crystal structure of Al{sub 15}Ge{sub 4}Ni{sub 3} was determined by single-crystal X-ray diffraction. The compound crystallizes in a new structure type in space group I4-bar3m, Pearson Symbol cI88, cubic lattice parameter a=11.405(1) Å. Phase diagram investigations indicate stoichiometric composition without considerable homogeneity range; τ{sub 2} melts peritectically at T=444 °C. The crystal structure of Al{sub 15}Ge{sub 4}Ni{sub 3} shows a unique combination of simple Cu{sub 3}Au- and CaF{sub 2}-type building blocks: a three dimensional network of CaF{sub 2}-type units, formed by Ni and Al atoms, is interspaced by clusters (Al{sub 6}Ge{sub 8}) resembling unit cells of the Cu{sub 3}Au-type. Both structural motifs are connected by Al–Ge bonds. The ground state energy of the compound was obtained by DFT calculations and the densities of states were analyzed in detail. In addition, electron density maps were calculated in four different sections through the unit cell using the full potential linearized augmented plane-wave (FLAPW) method. The bonding situation in Al{sub 15}Ge{sub 4}Ni{sub 3} was discussed combining results from electronic calculations with the analysis of the coordination of atoms. - Graphical abstract: The new compound Al{sub 15}Ge{sub 4}Ni{sub 3} shows a unique combination of simple Cu{sub 3}Au- and CaF{sub 2}-type building blocks. - Highlights: • The crystal structure of Al{sub 15}Ge{sub 4}Ni{sub 3} (space group I4-bar3m) was determined. • It shows a unique combination of CaF{sub 2}- and Cu{sub 3}Au-type building blocks. • Electronic (DFT) calculations were performed to gain insight to chemical bonding.

  5. Engineered nonlinear lattices.

    PubMed

    Clausen, C B; Christiansen, P L; Torner, L; Gaididei, Y B

    1999-11-01

    We show that with the quasi-phase-matching technique it is possible to fabricate stripes of nonlinearity that trap and guide light like waveguides. We investigate an array of such stripes and find that when the stripes are sufficiently narrow, the beam dynamics is governed by a quadratic nonlinear discrete equation. The proposed structure therefore provides an experimental setting for exploring discrete effects in a controlled manner. In particular, we show propagation of breathers that are eventually trapped by discreteness. When the stripes are wide the beams evolve in a structure we term a quasilattice, which interpolates between a lattice system and a continuous system. PMID:11970457

  6. Geologic structures associated with the carbonate/hydrate mound in Mississippi Canyon Block 118, Gulf of Mexico

    NASA Astrophysics Data System (ADS)

    McGee, T. M.

    2009-12-01

    A carbonate/hydrate mound in Mississippi Canyon Block 118 has been chosen by the Gulf of Mexico Hydrates Research Consortium to be the site of a sea-floor observatory. It will include seismo-acoustic, geochemical and micro-biologic sensors to monitor ambient noise, fluid venting and environmental conditions. The observations are expected to promote a better understanding of how fluids migrate within the mound and affect the formation/dissociation of gas hydrates. A number of preliminary studies have been done in preparation for installing the observatory. The mound is approximately one kilometer in diameter and is located on the continental slope in about 900m of water. Its surface has been imaged by multi-beam bathymetric sonar from an AUV 40m above the sea floor and by cameras at, or a few meters above, the sea floor. Also, direct visual observations have been made from manned submersibles. The interior of the mound and the underlying hydrate stability zone have been imaged seismically, electromagnetically and by direct-current resistivity. Proprietary 3-D seismic volumes show nearly vertical normal faults that connect deep salt formations with soft fine-grained sediments near the sea floor. It is hypothesized that these faults act as conduits for brines and hydrocarbon fluids, including petroleum and natural gas, to migrate upward and form the carbonate and hydrate constituents of the mound. Gas samples have been collected from vents and outcropping hydrate. Chemical analyses show the vent gas to be thermogenic from deep hot source rocks and to average 95% methane, 3% ethane 1% propane with minor other gases. There is no significant biogenic component. The outcropping hydrate is Structure II with gas composition 70% methane, 7.5% ethane, 15.9% propane with minor other gases. The difference between gas compositions from vents and hydrate appears to be due to molecular fractionation during hydrate crystallization. Results of geochemical studies indicate that vents

  7. Syrbactin Structural Analog TIR-199 Blocks Proteasome Activity and Induces Tumor Cell Death.

    PubMed

    Bachmann, André S; Opoku-Ansah, John; Ibarra-Rivera, Tannya R; Yco, Lisette P; Ambadi, Sudhakar; Roberts, Christopher C; Chang, Chia-En A; Pirrung, Michael C

    2016-04-15

    Multiple myeloma is an aggressive hematopoietic cancer of plasma cells. The recent emergence of three effective FDA-approved proteasome-inhibiting drugs, bortezomib (Velcade®), carfilzomib (Kyprolis®), and ixazomib (Ninlaro®), confirms that proteasome inhibitors are therapeutically useful against neoplastic disease, in particular refractory multiple myeloma and mantle cell lymphoma. This study describes the synthesis, computational affinity assessment, and preclinical evaluation of TIR-199, a natural product-derived syrbactin structural analog. Molecular modeling and simulation suggested that TIR-199 covalently binds each of the three catalytic subunits (β1, β2, and β5) and revealed key interaction sites. In vitro and cell culture-based proteasome activity measurements confirmed that TIR-199 inhibits the proteasome in a dose-dependent manner and induces tumor cell death in multiple myeloma and neuroblastoma cells as well as other cancer types in the NCI-60 cell panel. It is particularly effective against kidney tumor cell lines, with >250-fold higher anti-tumor activities than observed with the natural product syringolin A. In vivo studies in mice revealed a maximum tolerated dose of TIR-199 at 25 mg/kg. The anti-tumor activity of TIR-199 was confirmed in hollow fiber assays in mice. Adverse drug reaction screens in a kidney panel revealed no off-targets of concern. This is the first study to examine the efficacy of a syrbactin in animals. Taken together, the results suggest that TIR-199 is a potent new proteasome inhibitor with promise for further development into a clinical drug for the treatment of multiple myeloma and other forms of cancer.

  8. Thermally actuated wedge block

    DOEpatents

    Queen, Jr., Charles C.

    1980-01-01

    This invention relates to an automatically-operating wedge block for maintaining intimate structural contact over wide temperature ranges, including cryogenic use. The wedging action depends on the relative thermal expansion of two materials having very different coefficients of thermal expansion. The wedge block expands in thickness when cooled to cryogenic temperatures and contracts in thickness when returned to room temperature.

  9. Magnetic Reversal of Electric Polarization with Fixed Chirality of Magnetic Structure in a Chiral-Lattice Helimagnet MnSb_{2}O_{6}.

    PubMed

    Kinoshita, M; Seki, S; Sato, T J; Nambu, Y; Hong, T; Matsuda, M; Cao, H B; Ishiwata, S; Tokura, Y

    2016-07-22

    The correlation between magnetic and dielectric properties has been investigated for the single crystal of the chiral triangular-lattice helimagnet MnSb_{2}O_{6}. We found that the spin-spiral plane in the ground state has a considerable tilting from the (110) plane and that the sign of the spin-spiral tilting angle is coupled to the clockwise or counterclockwise manner of spin rotation and accordingly to the sign of magnetically induced electric polarization. This leads to unique magnetoelectric responses such as the magnetic-field-induced selection of a single ferroelectric domain as well as the reversal of electric polarization just by a slight tilting of the magnetic field direction, where the chiral nature of the crystal structure plays a crucial role through the coupling of the chirality between the crystal and magnetic structures. Our results demonstrate that crystallographic chirality can be an abundant source of novel magnetoelectric functions with coupled internal degrees of freedom. PMID:27494497

  10. Lattice dynamics properties of XAs (X=Al, Ga and In) with zinc-blende structure from first-principle calculations

    NASA Astrophysics Data System (ADS)

    Li, Xingxiu; Tao, Xiaoma; Li, Ran; Chen, Hongmei; Ouyang, Yifang; Du, Yong

    2012-08-01

    Band structures, density of states, dielectric and vibrational properties of XAs (X=Al, Ga and In) alloys with zinc-blende structure have been studied using the density functional theory (DFT). The calculated lattice constants, band gap, static dielectric constants and phonon frequencies are all in good agreement with the available experimental data and other theoretical results. The calculated results show that Born effective charges ZB increase with cation mass. A similar tendency has been observed for phonon frequencies ωTO and ωLO. Calculation results prove that static dielectric constants ɛ(0) increase with atomic weight, i.e. in the sequences AlAs-GaAs-InAs, and show an inverse sequence for band gap.

  11. Magnetic Reversal of Electric Polarization with Fixed Chirality of Magnetic Structure in a Chiral-Lattice Helimagnet MnSb2 O6

    NASA Astrophysics Data System (ADS)

    Kinoshita, M.; Seki, S.; Sato, T. J.; Nambu, Y.; Hong, T.; Matsuda, M.; Cao, H. B.; Ishiwata, S.; Tokura, Y.

    2016-07-01

    The correlation between magnetic and dielectric properties has been investigated for the single crystal of the chiral triangular-lattice helimagnet MnSb2 O6 . We found that the spin-spiral plane in the ground state has a considerable tilting from the (110) plane and that the sign of the spin-spiral tilting angle is coupled to the clockwise or counterclockwise manner of spin rotation and accordingly to the sign of magnetically induced electric polarization. This leads to unique magnetoelectric responses such as the magnetic-field-induced selection of a single ferroelectric domain as well as the reversal of electric polarization just by a slight tilting of the magnetic field direction, where the chiral nature of the crystal structure plays a crucial role through the coupling of the chirality between the crystal and magnetic structures. Our results demonstrate that crystallographic chirality can be an abundant source of novel magnetoelectric functions with coupled internal degrees of freedom.

  12. Study of the phase structure of Abelian field theories through non-lattice, non-perturbative calculations

    SciTech Connect

    Karanikas, A.I.; Ktorides, C.N.; Mavromatos, N.E.

    1986-12-01

    A recently proposed approach to gauge field theories, by which one formulates them non-locally and subsequently approaches locality arbitrarily close, is applied to U(1) gauge theories. We test the possibility that the aformentioned methodology might introduce a measure in the functional integral which supports non-perturbative calculations in the continuum. In particular, we are able to carry relevant calculations pertaining to the expectation value of the Wilson's loop operator in 3+1, 2+1 and 1+1 dimensions. The results are similar to ones obtained through the lattice regularization of R(1) gauge theory, with the important difference that in our case they refer to continuum U(1) gauge theory, as a function of the bare coupling constant. We further solidify the validity of our approach by conducting a calculation referring to the 2-dimensional scalar Heisenberg model, remaining always in the continuum. copyright 1986 Academic Press, Inc.

  13. Suppression of the Structural Phase Transition and Lattice Softening in Slightly Underdoped Ba1−xKxFe2As2 with Electronic Phase Separation

    SciTech Connect

    Inosov, D.; Leineweber, A; Yang, X; Park, J; Christensen, N; Dinnebier, R; Sun, G; Niedermayer, C; Haug, H; et. al.

    2009-01-01

    We present x-ray powder diffraction (XRPD) and neutron-diffraction measurements on the slightly underdoped iron-pnictide superconductor Ba1-xKxFe2As2, Tc=32 K. Below the magnetic-transition temperature Tm=70 K, both techniques show an additional broadening of the nuclear Bragg peaks, suggesting a weak structural phase transition. However, macroscopically the system does not break its tetragonal symmetry down to 15 K. Instead, XRPD patterns at low temperature reveal an increase in the anisotropic microstrain proportionally in all directions. We associate this effect with the electronic phase separation previously observed in the same material and with the effect of lattice softening below the magnetic phase transition. We employ density-functional theory to evaluate the distribution of atomic positions in the presence of dopant atoms both in the normal and magnetic states and to quantify the lattice softening, showing that it can account for a major part of the observed increase in the microstrain.

  14. Tailoring the structure of two-dimensional self-assembled nanoarchitectures based on ni(ii) -salen building blocks.

    PubMed

    Viciano-Chumillas, Marta; Li, Dongzhe; Smogunov, Alexander; Latil, Sylvain; Dappe, Yannick J; Barreteau, Cyrille; Mallah, Talal; Silly, Fabien

    2014-10-13

    The synthesis of a series of Ni(II) -salen-based complexes with the general formula of [Ni(H2 L)] (H4 L=R(2) -N,N'-bis[R(1) -5-(4'-benzoic acid)salicylidene]; H4 L1: R(2) =2,3-diamino-2,3-dimethylbutane and R(1) =H; H4 L2: R(2) =1,2-diaminoethane and R(1) =tert-butyl and H4 L3: R(2) =1,2-diaminobenzene and R(1) =tert-butyl) is presented. Their electronic structure and self-assembly was studied. The organic ligands of the salen complexes are functionalized with peripheral carboxylic groups for driving molecular self-assembly through hydrogen bonding. In addition, other substituents, that is, tert-butyl and diamine bridges (2,3-diamino-2,3-dimethylbutane, 1,2-diaminobenzene or 1,2-diaminoethane), were used to tune the two-dimensional (2D) packing of these building blocks. Density functional theory (DFT) calculations reveal that the spatial distribution of the LUMOs is affected by these substituents, in contrast with the HOMOs, which remain unchanged. Scanning tunneling microscopy (STM) shows that the three complexes self-assemble into three different 2D nanoarchitectures at the solid-liquid interface on graphite. Two structures are porous and one is close-packed. These structures are stabilized by hydrogen bonds in one dimension, while the 2D interaction is governed by van der Waals forces and is tuned by the nature of the substituents, as confirmed by theoretical calculations. As expected, the total dipolar moment is minimized. PMID:25225027

  15. Oil migration in a major growth fault: Structural analysis of the Pathfinder core, South Eugene Island Block 330, offshore Louisiana

    SciTech Connect

    Losh, S.

    1998-09-01

    The Pathfinder core, collected in the South Eugene Island Block 330 field, offshore Louisiana, provides an outstanding sample of structures associated with a major growth fault that abuts a giant oil field and that is thought to have acted as a conduit for hydrocarbon migration into the producing reservoirs. The fault zone in the core consists of three structural domains, each characterized by a distinct rock type, distribution of fault dips and dip azimuths, and distribution of spacing between adjacent faults and fractures. Although all of the domains contain oil-bearing sands, only faults and fractures in the deepest domain contain oil, even though the oil-barren fault domains contain numerous faults and fractures that are parallel to those containing oil in the deepest domain. The deepest domain is also distinguished from the other two domains by a greater degree of structural complexity and by a well-defined power-law distribution of fault and fracture spacings. Even though oil is present in sands throughout the core, its restriction to faults and fractures in the youngest sampled portion of the fault zone implies that oil migrated only through that part of the fault that was active during the time when oil had access to it. The absence of oil in fractures or faults in the other, probably older, fault domains indicates that the oil was never sufficiently pressured to flow up the fault zone on its own, either by hydraulic fracture or by increased permeability as a result of decreased effective stress. Instead, fluid migration along faults and fractures in the Pathfinder core was enhanced by permeability created in response to relatively far-field stresses related to minibasin subsidence.

  16. Discrete fracture patterns of virus shells reveal mechanical building blocks.

    PubMed

    Ivanovska, Irena L; Miranda, Roberto; Carrascosa, Jose L; Wuite, Gijs J L; Schmidt, Christoph F

    2011-08-01

    Viral shells are self-assembled protein nanocontainers with remarkable material properties. They combine simplicity of construction with toughness and complex functionality. These properties make them interesting for bionanotechnology. To date we know little about how virus structure determines assembly pathways and shell mechanics. We have here used atomic force microscopy to study structural failure of the shells of the bacteriophage Φ29. We observed rigidity patterns following the symmetry of the capsid proteins. Under prolonged force exertion, we observed fracture along well-defined lines of the 2D crystal lattice. The mechanically most stable building block of the shells was a trimer. Our approach of "reverse engineering" the virus shells thus made it possible to identify stable structural intermediates. Such stable intermediates point to a hierarchy of interactions among equal building blocks correlated with distinct next-neighbor interactions. The results also demonstrate that concepts from macroscopic materials science, such as fracture, can be usefully employed in molecular engineering. PMID:21768340

  17. Optoelectronics using block copolymers.

    SciTech Connect

    Botiz, I.; Darling, S. B.; Center for Nanoscale Materials

    2010-05-01

    Block copolymers, either as semiconductors themselves or as structure directors, are emerging as a promising class of materials for understanding and controlling processes associated with both photovoltaic energy conversion and light emitting devices.

  18. Structural changes of block copolymers with bi-modal orientation under fast cyclical stretching as observed by synchrotron SAXS

    PubMed Central

    Brubert, J.; Serrani, M.; Talhat, A.; De Gaetano, F.; Costantino, M. L.; Moggridge, G. D.

    2015-01-01

    Load-bearing tissues are composite materials that depend strongly on anisotropic fibre arrangement to maximise performance. One such tissue is the heart valve, with orthogonally arranged fibrosa and ventricularis layers. Their function is to maintain mechanical stress while being resilient. It is postulated that while one layer bears the applied stress, the orthogonal layer helps to regenerate the microstructure when the load is released. The present paper describes changes in the microstructure of a block copolymer with cylindrical morphology, having a bio-inspired microstructure of anisotropic orthogonally oriented layers, under uniaxial strain. To allow structural observations during fast deformation, equivalent to the real heart valve operation, we used a synchrotron X-ray source and recorded 2D SAXS patterns in only 1 ms per frame. The deformation behaviour of the composite microstructure has been reported for two arrangements of the cylinders in skin and core layers. The behaviour is very different to that observed either for uniaxially oriented or isotropic samples. Deformation is far from being affine. Cylinders aligned in the direction of stretch show fragmentation, but complete recovery of the spacing between cylinders on removal of the load. Those oriented perpendicular to the direction of stretch incline at an angle of approximately 25° to their original direction during load. PMID:25781560

  19. Formation of sub-7 nm feature size PS-b-P4VP block copolymer structures by solvent vapour process

    NASA Astrophysics Data System (ADS)

    Chaudhari, Atul; Ghoshal, Tandra; Shaw, Matthew T.; Cummins, Cian; Borah, Dipu; Holmes, Justin D.; Morris, Michael A.

    2014-03-01

    The nanometer range structure produced by thin films of diblock copolymers makes them a great of interest as templates for the microelectronics industry. We investigated the effect of annealing solvents and/or mixture of the solvents in case of symmetric Poly (styrene-block-4vinylpyridine) (PS-b-P4VP) diblock copolymer to get the desired line patterns. In this paper, we used different molecular weights PS-b-P4VP to demonstrate the scalability of such high χ BCP system which requires precise fine-tuning of interfacial energies achieved by surface treatment and that improves the wetting property, ordering, and minimizes defect densities. Bare Silicon Substrates were also modified with polystyrene brush and ethylene glycol self-assembled monolayer in a simple quick reproducible way. Also, a novel and simple in situ hard mask technique was used to generate sub-7nm Iron oxide nanowires with a high aspect ratio on Silicon substrate, which can be used to develop silicon nanowires post pattern transfer.

  20. Hard X-ray polarizer to enable simultaneous three-dimensional nanoscale imaging of magnetic structure and lattice strain.

    PubMed

    Logan, Jonathan; Harder, Ross; Li, Luxi; Haskel, Daniel; Chen, Pice; Winarski, Robert; Fuesz, Peter; Schlagel, Deborah; Vine, David; Benson, Christa; McNulty, Ian

    2016-09-01

    Recent progress in the development of dichroic Bragg coherent diffractive imaging, a new technique for simultaneous three-dimensional imaging of strain and magnetization at the nanoscale, is reported. This progress includes the installation of a diamond X-ray phase retarder at beamline 34-ID-C of the Advanced Photon Source. The performance of the phase retarder for tuning X-ray polarization is demonstrated with temperature-dependent X-ray magnetic circular dichroism measurements on a gadolinium foil in transmission and on a Gd5Si2Ge2 crystal in diffraction geometry with a partially coherent, focused X-ray beam. Feasibility tests for dichroic Bragg coherent diffractive imaging are presented. These tests include (1) using conventional Bragg coherent diffractive imaging to determine whether the phase retarder introduces aberrations using a nonmagnetic gold nanocrystal as a control sample, and (2) collecting coherent diffraction patterns of a magnetic Gd5Si2Ge2 nanocrystal with left- and right-circularly polarized X-rays. Future applications of dichroic Bragg coherent diffractive imaging for the correlation of strain and lattice defects with magnetic ordering and inhomogeneities are considered. PMID:27577777

  1. Hard X-ray polarizer to enable simultaneous three-dimensional nanoscale imaging of magnetic structure and lattice strain

    PubMed Central

    Logan, Jonathan; Harder, Ross; Li, Luxi; Haskel, Daniel; Chen, Pice; Winarski, Robert; Fuesz, Peter; Schlagel, Deborah; Vine, David; Benson, Christa; McNulty, Ian

    2016-01-01

    Recent progress in the development of dichroic Bragg coherent diffractive imaging, a new technique for simultaneous three-dimensional imaging of strain and magnetization at the nanoscale, is reported. This progress includes the installation of a diamond X-ray phase retarder at beamline 34-ID-C of the Advanced Photon Source. The performance of the phase retarder for tuning X-ray polarization is demonstrated with temperature-dependent X-ray magnetic circular dichroism measurements on a gadolinium foil in transmission and on a Gd5Si2Ge2 crystal in diffraction geometry with a partially coherent, focused X-ray beam. Feasibility tests for dichroic Bragg coherent diffractive imaging are presented. These tests include (1) using conventional Bragg coherent diffractive imaging to determine whether the phase retarder introduces aberrations using a nonmagnetic gold nanocrystal as a control sample, and (2) collecting coherent diffraction patterns of a magnetic Gd5Si2Ge2 nanocrystal with left- and right-circularly polarized X-rays. Future applications of dichroic Bragg coherent diffractive imaging for the correlation of strain and lattice defects with magnetic ordering and inhomogeneities are considered. PMID:27577777

  2. Triple-barrel structure of inwardly rectifying K+ channels revealed by Cs+ and Rb+ block in guinea-pig heart cells.

    PubMed

    Matsuda, H; Matsuura, H; Noma, A

    1989-06-01

    1. The hypothesis that the inwardly rectifying K+ channel consists of a triple-barrel structure was investigated. Inward currents were recorded under the blocking effects of external Cs+ or Rb+ in the cell-attached configuration of the patch-clamp technique using single ventricular cells enzymatically isolated from guinea-pig hearts. 2. Cs+ (10-100 microM) or Rb+ (20-100 microM) added to the 150 mM-K+ pipette solution induced rapid open-blocked transitions in the inward open-channel currents. In about 20% of experiments the inward current showed two intermediate current levels equally spaced between the unit amplitude and the zero-conductance level. The current fluctuated between these four levels. In the remaining experiments no obvious sublevels were observed except spontaneous ones, whose amplitudes were not always equal to one-third or two-thirds of the unit amplitude. 3. In experiments showing sublevels, the probability that the open-channel current stayed at each level was measured at various concentrations of blockers and membrane potentials. In both Cs+ and Rb+ block, the distribution of the current levels showed reasonable agreement with the binomial theorem. This finding suggests that the inwardly rectifying K+ channel is composed of three equally conductive subunits and each subunit is independently blocked by Cs+ or Rb+. 4. The dwell-time histogram in each substate was well fitted with a single-exponential function. On the assumption of the binomial model, the blocking (mu) and unblocking (lambda) rate for Cs+ and Rb+ were calculated. The value of mu was linearly proportional to the concentration of the blocking ion at a given membrane potential and increased with hyperpolarization (e-fold increase with a change of -43.5 mV in the Cs+ block). lambda was almost independent of the concentration of the blocking ion and less dependent on the membrane potential than mu. 5. The open and blocked times were calculated in experiments showing no clear sublevels

  3. Chaotic and ballistic dynamics in time-driven quasiperiodic lattices

    NASA Astrophysics Data System (ADS)

    Wulf, Thomas; Schmelcher, Peter

    2016-04-01

    We investigate the nonequilibrium dynamics of classical particles in a driven quasiperiodic lattice based on the Fibonacci sequence. An intricate transient dynamics of extraordinarily long ballistic flights at distinct velocities is found. We argue how these transients are caused and can be understood by a hierarchy of block decompositions of the quasiperiodic lattice. A comparison to the cases of periodic and fully randomized lattices is performed.

  4. Chaotic and ballistic dynamics in time-driven quasiperiodic lattices.

    PubMed

    Wulf, Thomas; Schmelcher, Peter

    2016-04-01

    We investigate the nonequilibrium dynamics of classical particles in a driven quasiperiodic lattice based on the Fibonacci sequence. An intricate transient dynamics of extraordinarily long ballistic flights at distinct velocities is found. We argue how these transients are caused and can be understood by a hierarchy of block decompositions of the quasiperiodic lattice. A comparison to the cases of periodic and fully randomized lattices is performed. PMID:27176301

  5. Ionic Blocks

    ERIC Educational Resources Information Center

    Sevcik, Richard S.; Gamble, Rex; Martinez, Elizabet; Schultz, Linda D.; Alexander, Susan V.

    2008-01-01

    "Ionic Blocks" is a teaching tool designed to help middle school students visualize the concepts of ions, ionic compounds, and stoichiometry. It can also assist high school students in reviewing their subject mastery. Three dimensional blocks are used to represent cations and anions, with color indicating charge (positive or negative) and size…

  6. Modulating the self-assembly of amphiphilic X-shaped block copolymers with cyclodextrins: structure and mechanisms.

    PubMed

    González-Gaitano, Gustavo; Müller, Céline; Radulescu, Aurel; Dreiss, Cécile A

    2015-04-14

    Inclusion complexes between cyclodextrins and polymers-so-called pseudopolyrotaxanes (PPR)-are at the origin of fascinating supramolecular structures, which are finding increasing uses in biomedical and technological fields. Here we explore the impact of both native and a range of modified cyclodextrins (CD) on the self-assembly of X-shaped poly(ethylene oxide)-poly(propylene oxide) block copolymers, so-called Tetronics or poloxamines, by focusing on Tetronic 904 (T904, Mw 6700). The effects are markedly dependent on the type and arrangement of the substituents on the macrocycle. While native CDs drive the formation of a solid PPR, most substituted CDs induce micellar breakup, with dimethylated β-CD (DIMEB) having the strongest impact and randomly substituted CDs a much weaker disruptive effect. Using native α-CD as a "molecular trap", we perform competitive binding experiments-where two types of CDs thread together onto the polymer chains-to establish that DIMEB indeed has the highest propensity to form an inclusion complex with the polymer, while hydroxypropylated CDs do not thread. 1D (1)H NMR and ROESY experiments confirm the formation of a soluble PPR with DIMEB in which the CD binds preferentially to the PO units, thus providing the drive for the observed demicellization. A combination of dynamic light scattering (DLS) and small-angle neutron scattering (SANS) is used to extract detailed structural parameters on the micelles. A binding model is proposed, which exploits the chemical shifts of selected protons from the CD in conjunction with the Hill equation, to prove that the formation of the PPR is a negatively cooperative process, in which threaded DIMEBs hamper the entrance of subsequent macrocycles.

  7. Seismic structure of the southern Gulf of California from Los Cabos block to the East Pacific Rise

    NASA Astrophysics Data System (ADS)

    PáRamo, P.; Holbrook, W. S.; Brown, H. E.; Lizarralde, D.; Fletcher, J.; Umhoefer, P.; Kent, G.; Harding, A.; Gonzalez, A.; Axen, G.

    2008-03-01

    Multichannel reflection and coincident wide-angle seismic data collected during the 2002 Premier Experiment, Sea of Cortez, Addressing the Development of Oblique Rifting (PESCADOR) experiment provide the most detailed seismic structure to date of the southern Gulf of California. Multichannel seismic (MCS) data were recorded with a 6-km-long streamer, 480-channel, aboard the R/V Maurice Ewing, and wide-angle data was recorded by 19 instruments spaced every ˜12 km along the transect. The MCS and wide-angle data reveal the seismic structure across the continent-ocean transition of the rifted margin. Typical continental and oceanic crust are separated by a ˜75-km-wide zone of extended continental crust dominated by block-faulted basement. Little lateral variation in crustal thicknesses and seismic velocities is observed in the oceanic crust, suggesting a constant rate of magmatic productivity since seafloor spreading began. Oceanic crustal thickness and mean crustal velocities suggest normal mantle temperature (1300°C) and passive mantle upwelling at the early stages of seafloor spreading. The crustal thickness, width of extended continental crust, and predicted temperature conditions all indicate a narrow rift mode of extension. On the basis of upper and lower crust stretching factors, an excess of lower crust was found in the extended continental crust. Total extension along transect 5W is estimated to be ˜35 km. Following crustal extension, new oceanic crust ˜6.4-km-thick was formed at a rate of ˜48 mm a-1 to accommodate plate separation.

  8. Modulating the self-assembly of amphiphilic X-shaped block copolymers with cyclodextrins: structure and mechanisms.

    PubMed

    González-Gaitano, Gustavo; Müller, Céline; Radulescu, Aurel; Dreiss, Cécile A

    2015-04-14

    Inclusion complexes between cyclodextrins and polymers-so-called pseudopolyrotaxanes (PPR)-are at the origin of fascinating supramolecular structures, which are finding increasing uses in biomedical and technological fields. Here we explore the impact of both native and a range of modified cyclodextrins (CD) on the self-assembly of X-shaped poly(ethylene oxide)-poly(propylene oxide) block copolymers, so-called Tetronics or poloxamines, by focusing on Tetronic 904 (T904, Mw 6700). The effects are markedly dependent on the type and arrangement of the substituents on the macrocycle. While native CDs drive the formation of a solid PPR, most substituted CDs induce micellar breakup, with dimethylated β-CD (DIMEB) having the strongest impact and randomly substituted CDs a much weaker disruptive effect. Using native α-CD as a "molecular trap", we perform competitive binding experiments-where two types of CDs thread together onto the polymer chains-to establish that DIMEB indeed has the highest propensity to form an inclusion complex with the polymer, while hydroxypropylated CDs do not thread. 1D (1)H NMR and ROESY experiments confirm the formation of a soluble PPR with DIMEB in which the CD binds preferentially to the PO units, thus providing the drive for the observed demicellization. A combination of dynamic light scattering (DLS) and small-angle neutron scattering (SANS) is used to extract detailed structural parameters on the micelles. A binding model is proposed, which exploits the chemical shifts of selected protons from the CD in conjunction with the Hill equation, to prove that the formation of the PPR is a negatively cooperative process, in which threaded DIMEBs hamper the entrance of subsequent macrocycles. PMID:25785814

  9. Magnetic structure of the antiferromagnetic Kondo lattice compounds CeRhAl4Si2 and CeIrAl4Si2

    DOE PAGESBeta

    Ghimire, N. J.; Calder, S.; Janoschek, M.; Bauer, E. D.

    2015-06-01

    In this article, we have investigated the magnetic ground state of the antiferromagnetic Kondo-lattice compounds CeMAl4Si2(M = Rh, Ir) using neutron powder diffraction. Although both of these compounds show two magnetic transitions TN1 and TN2 in the bulk properties measurements, evidence for magnetic long-range order was only found below the lower transition TN2. Analysis of the diffraction profiles reveals a commensurate antiferromagnetic structure with a propagation vector k = (0, 0, 1/2). The magnetic moment in the ordered state of CeRhAl4Si2 and CeIrAl4Si2 were determined to be 1.14(2) and 1.41(3) μB/Ce, respectively, and are parallel to the crystallographic c-axis inmore » agreement with magnetic susceptibility measurements.« less

  10. Molecular beam epitaxy of high structural quality Bi{sub 2}Se{sub 3} on lattice matched InP(111) substrates

    SciTech Connect

    Schreyeck, S.; Tarakina, N. V.; Schumacher, C.; Borzenko, T.; Bruene, C.; Buhmann, H.; Gould, C.; Brunner, K.; Molenkamp, L. W.; Karczewski, G.

    2013-01-28

    Epitaxial layers of the topological insulator Bi{sub 2}Se{sub 3} have been grown by molecular beam epitaxy on laterally lattice-matched InP(111)B substrates. High resolution X-ray diffraction shows a significant improvement of Bi{sub 2}Se{sub 3} crystal quality compared to layers deposited on other substrates. The measured full width at half maximum of the rocking curve is {Delta}{omega}=13 arc sec, and the ({omega}-2{theta}) scans exhibit clear layer thickness fringes. Atomic force microscope images show triangular twin domains with sizes increasing with layer thickness. The structural quality of the domains is confirmed on the microscopic level by transmission electron microscopy.

  11. Micro-Raman study on the softening and stiffening of phonons in rutile titanium dioxide film: Competing effects of structural defects, crystallite size, and lattice strain

    SciTech Connect

    Gautam, Subodh K.; Singh, Fouran Sulania, I.; Kulriya, P. K.; Singh, R. G.; Pippel, E.

    2014-04-14

    Softening and stiffening of phonons in rutile titanium dioxide films are investigated by in situ micro-Raman studies during energetic ion irradiation. The in situ study minimized other possible mechanisms of phonon dynamics. Initial softening and broadening of Raman shift are attributed to the phonon confinement by structural defects and loss of stoichiometry. The stiffening of A{sub 1g} mode is ascribed to large distortion of TiO{sub 6} octahedra under the influence of lattice strain in the (110) plane, which gives rise to lengthening of equatorial Ti-O bond and shortening of apical Ti-O bond. The shortening of apical Ti-O bond induces stiffening of A{sub 1g} mode in the framework of the bond-order-length-strength correlation mechanism.

  12. The effects of annealing on the structural, optical, and vibrational properties of lattice-matched GaAsSbN /GaAs grown by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Bharatan, S.; Iyer, S.; Nunna, K.; Collis, W. J.; Matney, K.; Reppert, J.; Rao, A. M.; Kent, P. R. C.

    2007-07-01

    The structural, optical, and vibrational properties of a GaAsSbN epilayer lattice matched to GaAs with a band gap of 1eV have been investigated using a variety of characterization techniques. These layers have potential applications in GaAs based tandem solar cells that utilize the near infrared region of the solar spectrum. The epilayers were grown in an elemental solid source molecular beam epitaxy system with a rf plasma nitrogen source. The Sb and N compositions of the nearly lattice-matched layers are 6.8% and 2.6%, respectively, as determined by high resolution x-ray diffraction and secondary ion mass spectroscopy (SIMS) analysis. The high crystalline quality of the layers is attested by the presence of well resolved Pendellosung fringes on a triple axis (004) x-ray scan and dynamical truncation rods observed on the corresponding (004) reciprocal space map. The effects of in situ annealing in As ambient and ex situ annealing in N ambient on the low temperature photoluminescence (PL) characteristics are discussed. Ex situ (in situ) annealed samples display an 8K PL peak energy of 1eV with a full width at half maximum of 18meV (26meV). Raman spectral analysis, the temperature dependence of the PL peak energy, and SIMS profiles indicate that outdiffusions of N and As are suppressed in the in situ annealed samples and improvement in Ga-N bonding is observed, leading to higher PL intensities in these samples. In addition, indirect evidence of atomic scale ordering has been observed. The stability of these structures appears to be dependent on the annealing conditions.

  13. The effects of annealing on the structural, optical, and vibrational properties of lattice-matched GaAsSbN/GaAs grown by molecular beam epitaxy

    SciTech Connect

    Bharatan, S.; Iyer, Prof Shanthi; Nunna, K.; Collis, W J; Matney, K.; Reppert, J.; Rao, A. M.; Kent, Paul R

    2007-01-01

    The structural, optical, and vibrational properties of a GaAsSbN epilayer lattice matched to GaAs with a band gap of 1 eV have been investigated using a variety of characterization techniques. These layers have potential applications in GaAs based tandem solar cells that utilize the near infrared region of the solar spectrum. The epilayers were grown in an elemental solid source molecular beam epitaxy system with a rf plasma nitrogen source. The Sb and N compositions of the nearly lattice-matched layers are 6.8% and 2.6%, respectively, as determined by high resolution x-ray diffraction and secondary ion mass spectroscopy (SIMS) analysis. The high crystalline quality of the layers is attested by the presence of well resolved Pendellosung fringes on a triple axis (004) x-ray scan and dynamical truncation rods observed on the corresponding (004) reciprocal space map. The effects of in situ annealing in As ambient and ex situ annealing in N ambient on the low temperature photoluminescence (PL) characteristics are discussed. Ex situ (in situ) annealed samples display an 8 K PL peak energy of 1 eV with a full width at half maximum of 18 meV (26 meV). Raman spectral analysis, the temperature dependence of the PL peak energy, and SIMS profiles indicate that outdiffusions of N and As are suppressed in the in situ annealed samples and improvement in Ga-N bonding is observed, leading to higher PL intensities in these samples. In addition, indirect evidence of atomic scale ordering has been observed. The stability of these structures appears to be dependent on the annealing conditions.

  14. Structural and {sup 31}P NMR investigation of Bi(MM'){sub 2}PO{sub 6} statistic solid solutions: Deconvolution of lattice constraints and cationic influences

    SciTech Connect

    Colmont, Marie; Delevoye, Laurent; Ketatni, El Mostafa; Montagne, Lionel; Mentre, Olivier . E-mail: mentre@ensc-lille.fr

    2006-07-15

    Two solid solutions BiM{sub x} Mg{sub (2-x)}PO{sub 6} (with M {sup 2+}=Zn or Cd) have been studied through {sup 31}P MAS NMR. The analysis has been performed on the basis of refined crystal structures through X-ray diffraction and neutron diffraction. The BiZn {sub x} Mg{sub (2-x)}PO{sub 6} does not provide direct evidence for sensitive changes in the phosphorus local symmetry. This result is in good agreement with structural data which show nearly unchanged lattices and atomic separations through the Zn{sup 2+} for Mg{sup 2+} substitution. On the other hand, the Cd{sup 2+} for Mg{sup 2+} substitution behaves differently. Indeed, up to five resonances are observed, each corresponding to one of the five first-cationic neighbour distributions, i.e. 4Mg/0Cd, 3Mg/1Cd, 2Mg/2Cd, 1Mg/3Cd and 0Mg/4Cd. Their intensities match rather well the expected weight for each configuration of the statistical Cd{sup 2+}/Mg{sup 2+} mixed occupancy. The match is further improved when one takes into account the influence of the 2nd cationic sphere that is available from high-field NMR data (18.8 T). Finally, the fine examination of the chemical shift for each resonance versus x allows to de-convolute the mean Z/a {sup 2} effective field into two sub-effects: a lattice constraint-only term and a chemical-only term whose effects are directly quantifiable. - Graphical abstract: First (CdMg){sub 4} cationic sphere influence on the {sup 31}P NMR signal in Bi(Cd,Mg){sub 2}PO{sub 6}. Display Omitted.

  15. Calculated high-pressure structural properties, lattice dynamics and quasi particle band structures of perovskite fluorides KZnF3, CsCaF3 and BaLiF3

    NASA Astrophysics Data System (ADS)

    Vaitheeswaran, G.; Kanchana, V.; Zhang, Xinxin; Ma, Yanming; Svane, A.; Christensen, N. E.

    2016-08-01

    A detailed study of the high-pressure structural properties, lattice dynamics and band structures of perovskite structured fluorides KZnF3, CsCaF3 and BaLiF3 has been carried out by means of density functional theory. The calculated structural properties including elastic constants and equation of state agree well with available experimental information. The phonon dispersion curves are in good agreement with available experimental inelastic neutron scattering data. The electronic structures of these fluorides have been calculated using the quasi particle self-consistent GW approximation. The GW calculations reveal that all the fluorides studied are wide band gap insulators, and the band gaps are significantly larger than those obtained by the standard local density approximation, thus emphasizing the importance of quasi particle corrections in perovskite fluorides.

  16. Calculated high-pressure structural properties, lattice dynamics and quasi particle band structures of perovskite fluorides KZnF3, CsCaF3 and BaLiF3.

    PubMed

    Vaitheeswaran, G; Kanchana, V; Zhang, Xinxin; Ma, Yanming; Svane, A; Christensen, N E

    2016-08-10

    A detailed study of the high-pressure structural properties, lattice dynamics and band structures of perovskite structured fluorides KZnF3, CsCaF3 and BaLiF3 has been carried out by means of density functional theory. The calculated structural properties including elastic constants and equation of state agree well with available experimental information. The phonon dispersion curves are in good agreement with available experimental inelastic neutron scattering data. The electronic structures of these fluorides have been calculated using the quasi particle self-consistent [Formula: see text] approximation. The [Formula: see text] calculations reveal that all the fluorides studied are wide band gap insulators, and the band gaps are significantly larger than those obtained by the standard local density approximation, thus emphasizing the importance of quasi particle corrections in perovskite fluorides. PMID:27300494

  17. Enhancement of Hydrogen Storage Capacity in Hydrate Lattices

    SciTech Connect

    Yoo, Soohaeng; Xantheas, Sotiris S.

    2012-02-16

    First principles electronic structure calculations of the gas phase pentagonal dodecahedron (H2O)20 (D-cage) and tetrakaidecahedron (H2O)24 (T-cage), which are building blocks of structure I (sI) hydrate lattice, suggest that these can accommodate up to a maximum of 5 and 7 guest hydrogen molecules, respectively. For the pure hydrogen hydrate, Born-Oppenheimer Molecular Dynamics (BOMD) simulations of periodic (sI) hydrate lattices indicate that the guest molecules are released into the vapor phase via the hexagonal phases of the larger T-cages. An additional mechanism for the migration between neighboring D- and T-cages was found to occur through a shared pentagonal face via the breaking and reforming of a hydrogen bond. This molecular mechanism is also found for the expulsion of a CH4 molecule from the D-cage. The presence of methane in the larger T-cages was found to block this release, therefore suggesting possible scenarios for the stabilization of these mixed guest clathrate hydrates and the potential enhancement of their hydrogen storage capacity.

  18. Modeling of mass and charge transport in a solid oxide fuel cell anode structure by a 3D lattice Boltzmann approach

    NASA Astrophysics Data System (ADS)

    Paradis, Hedvig; Andersson, Martin; Sundén, Bengt

    2016-08-01

    A 3D model at microscale by the lattice Boltzmann method (LBM) is proposed for part of an anode of a solid oxide fuel cell (SOFC) to analyze the interaction between the transport and reaction processes and structural parameters. The equations of charge, momentum, heat and mass transport are simulated in the model. The modeling geometry is created with randomly placed spheres to resemble the part of the anode structure close to the electrolyte. The electrochemical reaction processes are captured at specific sites where spheres representing Ni and YSZ materials are present with void space. This work focuses on analyzing the effect of structural parameters such as porosity, and percentage of active reaction sites on the ionic current density and concentration of H2 using LBM. It is shown that LBM can be used to simulate an SOFC anode at microscale and evaluate the effect of structural parameters on the transport processes to improve the performance of the SOFC anode. It was found that increasing the porosity from 30 to 50 % decreased the ionic current density due to a reduction in the number of reaction sites. Also the consumption of H2 decreased with increasing porosity. When the percentage of active reaction sites was increased while the porosity was kept constant, the ionic current density increased. However, the H2 concentration was slightly reduced when the percentage of active reaction sites was increased. The gas flow tortuosity decreased with increasing porosity.

  19. A balance-evolution artificial bee colony algorithm for protein structure optimization based on a three-dimensional AB off-lattice model.

    PubMed

    Li, Bai; Chiong, Raymond; Lin, Mu

    2015-02-01

    Protein structure prediction is a fundamental issue in the field of computational molecular biology. In this paper, the AB off-lattice model is adopted to transform the original protein structure prediction scheme into a numerical optimization problem. We present a balance-evolution artificial bee colony (BE-ABC) algorithm to address the problem, with the aim of finding the structure for a given protein sequence with the minimal free-energy value. This is achieved through the use of convergence information during the optimization process to adaptively manipulate the search intensity. Besides that, an overall degradation procedure is introduced as part of the BE-ABC algorithm to prevent premature convergence. Comprehensive simulation experiments based on the well-known artificial Fibonacci sequence set and several real sequences from the database of Protein Data Bank have been carried out to compare the performance of BE-ABC against other algorithms. Our numerical results show that the BE-ABC algorithm is able to outperform many state-of-the-art approaches and can be effectively employed for protein structure optimization. PMID:25463349

  20. Low-cost spray-processed Ag{sub 1−x}Cu{sub x}InS{sub 2} nano-films: Structural and functional investigation within the Lattice Compatibility Theory framework

    SciTech Connect

    Gherouel, D.; Yumak, A.; Znaidi, M.; Bouzidi, A.; Boubaker, K.; Yacoubi, N.; Amlouk, M.

    2015-08-15

    Highlights: • Cu{sub x}Ag{sub 1−x}InS{sub 2} with a minimal lattice mismatch between absorbers and buffers. • The lattice compatibility for understanding silver–copper kinetics. • Controlled and enhanced spray pyrolisis method as a low-cost synthesis protocol. - Abstract: This work deals with some structural and optical investigations about Cu{sub x}Ag{sub 1−x}InS{sub 2} alloys sprayed films and the beneficial effect of copper incorporation in AgInS{sub 2} ternary matrices. The main purpose of this work is to obtain the band gap energy E{sub g} as well as different lattice parameters. The studied properties led to reaching minimum of lattice mismatch between absorber and buffer layers within solar cell devices. As a principal and original finding, the lattice compatibility between both silver and copper indium disulfide structures has been proposed as a guide for understanding kinetics of these materials crystallization.