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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. 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

  7. 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.

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

    NASA Astrophysics Data System (ADS)

    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. A Block-Structured Adaptive Mesh Refinement Technique with a Finite-Difference-Based Lattice Boltzmann Method

    NASA Astrophysics Data System (ADS)

    Fakhari, Abbas; Lee, Taehun

    2013-11-01

    A novel adaptive mesh refinement (AMR) algorithm for the numerical solution of fluid flow problems is presented in this study. The proposed AMR algorithm can be used to solve partial differential equations including, but not limited to, the Navier-Stokes equations using an AMR technique. Here, the lattice Boltzmann method (LBM) is employed as a substitute of the nearly incompressible Navier-Stokes equations. Besides its simplicity, the proposed AMR algorithm is straightforward and yet efficient. The idea is to remove the need for a tree-type data structure by using the pointer attributes in a unique way, along with an appropriate adjustment of the child block's IDs, to determine the neighbors of a certain block. Thanks to the unique way of invoking pointers, there is no need to construct a quad-tree (in 2D) or oct-tree (in 3D) data structure for maintaining the connectivity data between different blocks. As a result, the memory and time required for tree traversal are completely eliminated, leaving us with a clean and efficient algorithm that is easier to implement and use on parallel machines. Several benchmark studies are carried out to assess the accuracy and efficiency of the proposed AMR-LBM, including lid-driven cavity flow, vortex shedding past a square cylinder, and Kelvin-Helmholtz instability for single-phase and multiphase fluids.

  11. 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.

  12. Modified block BiCGSTAB for lattice QCD

    NASA Astrophysics Data System (ADS)

    Nakamura, Y.; Ishikawa, K.-I.; Kuramashi, Y.; Sakurai, T.; Tadano, H.

    2012-01-01

    We present results for application of block BiCGSTAB algorithm modified by the QR decomposition and the SAP preconditioner to the Wilson-Dirac equation with multiple right-hand sides in lattice QCD on 32×64 and 64 4 lattices at almost physical quark masses. The QR decomposition improves convergence behaviors in the block BiCGSTAB algorithm suppressing deviation between true residual and recursive one. The SAP preconditioner applied to the domain-decomposed lattice helps us minimize communication overhead. We find remarkable cost reduction thanks to cache tuning and reduction of number of iterations.

  13. Optimal lattice-structured materials

    NASA Astrophysics Data System (ADS)

    Messner, Mark C.

    2016-11-01

    This work 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 describing 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.

  14. Optimal lattice-structured materials

    DOE PAGES

    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

  15. Optimal lattice-structured materials

    SciTech Connect

    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 describing 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.

  16. 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.

  17. Nucleon Structure from Lattice QCD

    SciTech Connect

    Haegler, Philipp

    2011-10-24

    Hadron structure calculations in lattice QCD have seen substantial progress during recent years. We illustrate the achievements that have been made by discussing latest lattice results for a limited number of important observables related to nucleon form factors and generalized parton distributions. A particular focus is placed on the decomposition of the nucleon spin 1/2 in terms of quark spin and orbital angular momentum contributions. Results and limitations of the necessary chiral extrapolations based on ChPT will be briefly discussed.

  18. Many-body lattice wave functions from conformal blocks

    NASA Astrophysics Data System (ADS)

    Montes, Sebastián; Rodríguez-Laguna, Javier; Tu, Hong-Hao; Sierra, Germán

    2017-02-01

    We introduce a general framework to construct many-body lattice wave functions starting from the conformal blocks (CBs) of rational conformal field theories (RCFTs). We discuss the different ways of encoding the physical degrees of freedom of the lattice system using both the internal symmetries of the theory and the fusion channels of the CBs. We illustrate this construction both by revisiting the known Haldane-Shastry model and by providing a novel implementation for the Ising RCFT. In the latter case, we find a connection to the Ising transverse field (ITF) spin chain via the Kramers-Wannier duality and the Temperley-Lieb-Jones algebra. We also find evidence that the ground state of the finite-size critical ITF Hamiltonian corresponds exactly to the wave function obtained from CBs of spin fields.

  19. Building block for an orthonormal-lattice-filter adaptive network

    NASA Astrophysics Data System (ADS)

    Gabriel, W. F.

    1980-07-01

    The recent algorithm for a multistage multichannel orthonormal lattice filter proposed by M. Aftab Alam is a welcome addition to the library of adaptive-processing algorithms and provides a flexible alternative to the conventional approach of an optimum Weiner filter. This algorithm is based on a Gram-Schmidt orthonormalization procedure which is similar to cascade adaptive processing techniques described in earlier works. One of the most desirable features of this type of processing network is that it can be implemented with simple one-stage orthogonal-filter building blocks which directly filter the input data samples. These building blocks are the major subject of this report, and a particular configuration is developed based on a modified version of the familiar Howells-Applebaum algorithm. It can be implemented in either analog or digital form, data storage is not required, it is unconditionally stable, speed of convergence is no longer a problem, and the design is simple. The performance characteristics of a complete orthogonal-lattice-filter network operating in the spacial domain were simulated for example cases of one, two, and three strong incoherent signal sources spaced within a beamwidth for a eight-element linear-array antenna. The adaptive spacial filter patterns and the transient responses demonstrate that the building block has sufficient transient-response speed and control to permit full use of the processing capabilities inherent in a Gram-Schmidt cascade network.

  20. 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.

  1. 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.

  2. Shock wave structure in a lattice gas

    NASA Astrophysics Data System (ADS)

    Broadwell, James E.; Han, Donghee

    2007-05-01

    The motion and structure of shock and expansion waves in a simple particle system, a lattice gas and cellular automaton, are determined in an exact computation. Shock wave solutions, also exact, of a continuum description, a model Boltzmann equation, are compared with the lattice results. The comparison demonstrates that, as proved by Caprino et al. ["A derivation of the Broadwell equation," Commun. Math. Phys. 135, 443 (1991)] only when the lattice processes are stochastic is the model Boltzmann description accurate. In the strongest shock wave, the velocity distribution function is the bimodal function proposed by Mott-Smith.

  3. Titanium-silicon carbide composite lattice structures

    NASA Astrophysics Data System (ADS)

    Moongkhamklang, Pimsiree

    Sandwich panel structures with stiff, strong face sheets and lightweight cellular cores are widely used for weight sensitive, bending dominated loading applications. The flexural stiffness and strength of a sandwich panel is determined by the stiffness, strength, thickness, and separation of the face sheets, and by the compressive and shear stiffness and strength of the cellular core. Panel performance can be therefore optimized using cores with high specific stiffness and strength. The specific stiffness and strength of all cellular materials depends upon the specific elastic modulus and strength of the material used to make the structure. The stiffest and strongest cores for ambient temperature applications utilize carbon fiber reinforced polymer (CFRP) honeycombs and lattice structures. Few options exist for lightweight sandwich panels intended for high temperature uses. High temperature alloys such as Ti-6A1-4V can be applied to SiC monofilaments to create very high specific modulus and strength fibers. These are interesting candidates for the cores of elevated temperature sandwich structures such as the skins of hypersonic vehicles. This dissertation explores the potential of sandwich panel concepts that utilize millimeter scale titanium matrix composite (TMC) lattice structures. A method has been developed for fabricating millimeter cell size cellular lattice structures with the square or diamond collinear truss topologies from 240 mum diameter Ti-6A1-4V coated SiC monofilaments (TMC monofilaments). Lattices with relative densities in the range 10% to 20% were manufactured and tested in compression and shear. Given the very high compressive strength of the TMC monofilaments, the compressive strengths of both the square and diamond lattices were dominated by elastic buckling of the constituent struts. However, under shear loading, some of the constituent struts of the lattices are subjected to tensile stresses and failure is then set by tensile failure of the

  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. 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.

  8. Advances in hadronic structure from Lattice QCD

    NASA Astrophysics Data System (ADS)

    Constantinou, Martha

    2017-01-01

    Understanding nucleon structure is considered a milestone of hadronic physics and new facilities are planned devoted to its study. A future Electron-Ion-Collider proposed by the scientific community will greatly deepen our knowledge on the fundamental constituents of the visible world. To achieve this goal, a synergy between the experimental and theoretical sectors is imperative, and Lattice QCD is in a unique position to provide input from first principle calculations. In this talk we will discuss recent progress in nucleon structure from Lattice QCD, focusing on the evaluation of matrix elements using state-of-the-art simulations with pion masses at their physical value. The axial form factors, electromagnetic radii, the quark momentum fraction and the spin content of the nucleon will be discussed. We will also highlight quantities that may guide New Physics searches, such as the scalar and tensor charges. Finally, we will give updates on a new direct approach to compute quark parton distributions functions on the lattice.

  9. 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.…

  10. Lattice QCD Calculation of Nucleon Structure

    SciTech Connect

    Liu, Keh-Fei; Draper, Terrence

    2016-08-30

    It is emphasized in the 2015 NSAC Long Range Plan that "understanding the structure of hadrons in terms of QCD's quarks and gluons is one of the central goals of modern nuclear physics." Over the last three decades, lattice QCD has developed into a powerful tool for ab initio calculations of strong-interaction physics. Up until now, it is the only theoretical approach to solving QCD with controlled statistical and systematic errors. Since 1985, we have proposed and carried out first-principles calculations of nucleon structure and hadron spectroscopy using lattice QCD which entails both algorithmic development and large-scale computer simulation. We started out by calculating the nucleon form factors -- electromagnetic, axial-vector, πNN, and scalar form factors, the quark spin contribution to the proton spin, the strangeness magnetic moment, the quark orbital angular momentum, the quark momentum fraction, and the quark and glue decomposition of the proton momentum and angular momentum. The first round of calculations were done with Wilson fermions in the `quenched' approximation where the dynamical effects of the quarks in the sea are not taken into account in the Monte Carlo simulation to generate the background gauge configurations. Beginning in 2000, we have started implementing the overlap fermion formulation into the spectroscopy and structure calculations. This is mainly because the overlap fermion honors chiral symmetry as in the continuum. It is going to be more and more important to take the symmetry into account as the simulations move closer to the physical point where the u and d quark masses are as light as a few MeV only. We began with lattices which have quark masses in the sea corresponding to a pion mass at ~ 300 MeV and obtained the strange form factors, charm and strange quark masses, the charmonium spectrum and the Ds meson decay constant fDs, the strangeness and charmness, the meson mass decomposition and the

  11. 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.

  12. 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).

  13. Chiral Block Copolymer Structures for Metamaterial Applications

    DTIC Science & Technology

    2015-01-27

    Final 3. DATES COVERED (From - To) 25-August-2011 to 24-August-2014 4. TITLE AND SUBTITLE Chiral Block Copolymer Structures for...researchers focused o synthesis and processing, morphology and physical characterization of chiral block copolymer (BCP) materials. Such materials a...valuable for both their optical and mechanical properties, particularly for their potential as chiral metamaterials and lightweig energy absorbing

  14. 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.

  15. Proton spin structure from lattice QCD

    SciTech Connect

    Fukugita, M.; Kuramashi, Y.; Okawa, M.; Ukawa, A. ||

    1995-09-11

    A lattice QCD calculation of the proton matrix element of the flavor singlet axial-vector current is reported. Both the connected and disconnected contributions are calculated, for the latter employing the variant method of wall source without gauge fixing. From simulations in quenched QCD with the Wilson quark action on a 16{sup 3}{times}20 lattice at {beta}=5.7 (the lattice spacing {ital a}{approx}0.14 fm), we find {Delta}{Sigma}={Delta}{ital u}+{Delta}{ital d}+{Delta}{ital s}=+0.638(54){minus}0.347(46){minus}0.109(30)=+0.18(10) with the disconnected contribution to {Delta}{ital u} and {Delta}{ital d} equal to {minus}0.119(44), which is reasonably consistent with the experiment.

  16. 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.

  17. Controlling Structure in Sulfonated Block Copolymer Membranes

    NASA Astrophysics Data System (ADS)

    Truong, Phuc; Stein, Gila; Strzalka, Joe

    2015-03-01

    In many ionic block copolymer systems, the strong incompatibility between ionic and non-ionic segments will trap non-equilibrium structures in the film, making it difficult to engineer the optimal domain sizes and transport pathways. The goal of this work is to establish a framework for controlling the solid-state structure of sulfonated pentablock copolymer membranes. They have ABCBA block sequence, where A is poly(t-butyl styrene), B is poly(hydrogenated isoprene), and C is poly(styrene sulfonate). To process into films, the polymer is dissolved in toluene/n-propanol solvent mixtures, where the solvent proportions and the polymer loading were both varied. Solution-state structure was measured with small angle X-ray scattering (SAXS). We detected micelles with radii that depend on the solvent composition and polymer loading. Film structure was measured with grazing-incidence SAXS, which shows (i) domain periodicity is constant throughout film thickness; (ii) domain periodicity depends on solvent composition and polymer loading, and approximately matches the micelle radii in solutions. The solid-state packing is consistent with a hard sphere structure factor. Results suggest that solid-state structure can be tuned by manipulating the solution-state self-assembly.

  18. 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.

  19. Modeling of Triangular Lattice Space Structures with Curved Battens

    NASA Technical Reports Server (NTRS)

    Chen, Tzikang; Wang, John T.

    2005-01-01

    Techniques for simulating an assembly process of lattice structures with curved battens were developed. The shape of the curved battens, the tension in the diagonals, and the compression in the battens were predicted for the assembled model. To be able to perform the assembly simulation, a cable-pulley element was implemented, and geometrically nonlinear finite element analyses were performed. Three types of finite element models were created from assembled lattice structures for studying the effects of design and modeling variations on the load carrying capability. Discrepancies in the predictions from these models were discussed. The effects of diagonal constraint failure were also studied.

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

    SciTech Connect

    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.

  1. Load-Adapted Design of Generative Manufactured Lattice Structures

    NASA Astrophysics Data System (ADS)

    Reinhart, Gunther; Teufelhart, Stefan

    Additive layer manufacturing offers many opportunities for the production of lightweight components, because of the high geometrical freedom that can be realized in comparison to conventional manufacturing processes. This potential gets demonstrated at the example of a bending beam. Therefore, a topology optimization is performed as well as the use of periodically arranged lattice structures. The latter ones show the constraint, that shear forces in the struts reduce the stiffness of the lattice. To avoid this, the structure has to be adapted to the flux of force. This thesis is supported by studies on a torqueloaded shaft.

  2. 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.

  3. 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.

  4. Nuclear structure and reactions using lattice effective field theory

    NASA Astrophysics Data System (ADS)

    Rupak, Gautam

    2016-09-01

    Effective field theory (EFT) formulated on a space-time lattice provides a model-independent framework for ab initio nuclear structure and reaction calculations. The EFT interactions are rooted in quantum chromodynamics through low energy symmetry constraints. In this talk I present several recent developments in lattice EFT, in particular I present the so called adiabatic projection method that enables elastic and in-elastic reaction calculations. Bound state properties of atomic nuclei such as carbon and oxygen will also be presented. Partial support from US National Science Foundation Grant PHY-1307453 is acknowledged.

  5. Electronic structure and energetics of graphene antidot lattice

    NASA Astrophysics Data System (ADS)

    Sakurai, Masahiro; Saito, Susumu; Takada, Yasutami

    2012-02-01

    We have made a systematic study of the electronic structure and the energetics of graphene with periodic array of vacancy clusters (graphene antidot lattice) in the framework of the density-functional theory (DFT). We find that the electronic property of the system is well controlled by its lattice periodicity. More specifically, this system can be either metallic or semiconducting, depending on its lattice geometry. Interestingly, some of them are predicted to be direct-gap semiconductors. For example, graphene sheet with high-symmetry arrangements of periodic circle-shape vacancies always has a direct fundamental gap [1]. The DFT total-energy calculations indicate that the geometry of hole edges plays an important role in determining its stability. [1] ``Electronic properties of graphene and boron-nitride based nanostructured materials'' M. Sakurai, Y. Sakai, and S. Saito, J. Phys.: Conf. Ser. 302 (2011) 012018.

  6. 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

  7. 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.

  8. 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.

  9. 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.

  10. Static Structural Analysis for a Neutron Shielding Block in ITER

    NASA Astrophysics Data System (ADS)

    Hao, Junchuan; Song, Yuntao; Wang, Xiaoyu; Ioki, K.; Du, Shuangsong; Ji, Xiang; Feng, Changle; Xu, Yang

    2013-02-01

    The ITER neutron shielding blocks are located between the outer shell and the inner shell of the vacuum vessel to provide neutron shielding. Considering the combined loads acting on the shielding blocks during ITER plasma operation, the structure of the shielding blocks must be evaluated. Using the finite element method with ANSYS analysis software, static structural analysis is performed, including elastic analysis and limit analysis for one typical shielding block. The evaluated results based on RCC-MR code show that the structure of this shielding block can meet the design requirement.

  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. 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.

  13. 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.

  14. An implicit block LU-SGS finite-volume lattice-Boltzmann scheme for steady flows on arbitrary unstructured meshes

    NASA Astrophysics Data System (ADS)

    Li, Weidong; Luo, Li-Shi

    2016-12-01

    This work proposes a fully implicit lattice Boltzmann (LB) scheme based on finite-volume (FV) discretization on arbitrary unstructured meshes. The linear system derived from the finite-volume lattice Boltzmann equation (LBE) is solved by the block lower-upper (BLU) symmetric-Gauss-Seidel (SGS) algorithm. The proposed implicit FV-LB scheme is efficient and robust, and has a low-storage requirement. The effectiveness and efficiency of the proposed implicit FV-LB scheme are validated and verified by the simulations of three test cases in two dimensions: (a) the laminar Blasius flow over a flat plate with Re =105; (b) the steady viscous flow past a circular cylinder with Re = 10, 20, and 40; and (c) the inviscid flow past a circular cylinder. The proposed implicit FV-LB scheme is shown to be not only effective and efficient for simulations of steady viscous flows, but also robust and efficient for simulations of inviscid flows in particular.

  15. Structure-property relationships in block copolymers

    NASA Technical Reports Server (NTRS)

    Mcgrath, J. E.

    1976-01-01

    Block copolymers are a class of relatively new materials which contain long sequences of two (or more) chemically different repeat units. Unlike random copolymers, each segment may retain some properties which are characteristic of its homopolymer. It is well known that most physical blends of two different homopolymers are incompatible on a macro-scale. By contrast most block copolymers display only a microphase (eg. 100-200 A domains) separation. Complete separation is restricted because of a loss in configurational entropy. The latter is due to presence of chemical bond(s) between the segments. Novel physical properties can be obtained because it is possible to prepare any desired combination of rubber-like, glassy, or crystalline blocks. The architecture and sequential arrangement of the segments can strongly influence mechanical behavior.

  16. 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.

  17. 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).

  18. 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).

  19. Efficient block rate structures: Rethinking conventional wisdom

    SciTech Connect

    Chamberlin, J.; Seiden, K.

    1993-12-01

    The supposed inefficiency of declining block rates is greatly exaggerated. In fact, evidence shows that rates that vary significantly from the cost of service - e.g., as they might for winter heating customers of a summer peaking utility - worsen economic efficiency.

  20. Creep Damage Analysis of a Lattice Truss Panel Structure

    NASA Astrophysics Data System (ADS)

    Jiang, Wenchun; Li, Shaohua; Luo, Yun; Xu, Shugen

    2017-01-01

    The creep failure for a lattice truss sandwich panel structure has been predicted by finite element method (FEM). The creep damage is calculated by three kinds of stresses: as-brazed residual stress, operating thermal stress and mechanical load. The creep damage at tensile and compressive loads have been calculated and compared. The creep rate calculated by FEM, Gibson-Ashby and Hodge-Dunand models have been compared. The results show that the creep failure is located at the fillet at both tensile and creep loads. The damage rate at the fillet at tensile load is 50 times as much as that at compressive load. The lattice truss panel structure has a better creep resistance to compressive load than tensile load, because the creep and stress triaxiality at the fillet has been decreased at compressive load. The maximum creep strain at the fillet and the equivalent creep strain of the panel structure increase with the increase of applied load. Compared with Gibson-Ashby model and Hodge-Dunand models, the modified Gibson-Ashby model has a good prediction result compared with FEM. However, a more accurate model considering the size effect of the structure still needs to be developed.

  1. Numerical Studies of Localized Vibrating Structures in Nonlinear Lattices

    DTIC Science & Technology

    1991-03-01

    unity, except in Chapter V, where nonuniformities are discussed. Thus, the lattice in each case is characterized by coupling and damping constants. The...with a simple lattice of point masses connected by massless springs. Except in Chapter V, this and all other lattices will be taken to consist of...next to last element and to the first element; this is essentially a finite ring lattice, except that all effects of curvature of such a ring lattice are

  2. 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.

  3. Vibration and buckling of general periodic lattice structures

    NASA Technical Reports Server (NTRS)

    Anderson, M. S.; Williams, F. W.

    1984-01-01

    A method is presented for vibration and buckling analysis of arbitrary lattice structures having repetitive geometry in any combination of coordinate directions. The approach is based on exact member theory for representing the stiffness of an individual member subject to axial load, and in the case of vibration, undergoing harmonic oscillation. The method is an extension of previous work that was limited to specific geometries. The resulting eigenvalue problem is of the size associated with the repeating element of the structure. A computer program has been developed incorporating the theory and results are given for vibration of rectangular platforms and a large antenna structure having rotational symmetry. Buckling and vibration results for cable-stiffened rings are also given.

  4. Basic Research on Lattice Structures Focused on the Strut Shape and Welding Beads

    NASA Astrophysics Data System (ADS)

    Kessler, Julia; Bâlc, Nicolae; Gebhardt, Andreas; Abbas, Karim

    This survey is about the requirements of lattice structures which are made by Selective Laser Melting. The process is based on Additive Manufacturing. It allows the generation of almost every shape. Even complex lattice structures can be manufactured using this technology. Moreover it is possible to integrate high performance lightweight structures into applications. Lattice structures are distinguished into periodic structures and stochastic cellular structures, each type with its individual properties. In a great field of applications periodic lattices are integrated. Because of the great demand for high performance applications, the industry has a big interest in lattice structures. A survey on this topic is indispensable. The main aim is to extract the most influencing process parameters that effect the properties of the structures and to create a construction guideline using the extracted results. Due to the fact that periodic lattices consist of struts, the basic research is focused on those.

  5. 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

  6. 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.

  7. 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.

  8. 23. VIEW SHOWING BROWN CONCRETE BLOCK STRUCTURES AND SOUTHERN EDGE ...

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

    23. VIEW SHOWING BROWN CONCRETE BLOCK STRUCTURES AND SOUTHERN EDGE OF RADAR SITE Everett Weinreb, photographer, March 1988 - Los Pinetos Nike Missile Site, Santa Clara Road, Los Angeles National Forest, Sylmar, Los Angeles County, CA

  9. 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

  10. Digital Morphing Wing: Active Wing Shaping Concept Using Composite Lattice-Based Cellular Structures.

    PubMed

    Jenett, Benjamin; Calisch, Sam; Cellucci, Daniel; Cramer, Nick; Gershenfeld, Neil; Swei, Sean; Cheung, Kenneth C

    2017-03-01

    We describe an approach for the discrete and reversible assembly of tunable and actively deformable structures using modular building block parts for robotic applications. The primary technical challenge addressed by this work is the use of this method to design and fabricate low density, highly compliant robotic structures with spatially tuned stiffness. This approach offers a number of potential advantages over more conventional methods for constructing compliant robots. The discrete assembly reduces manufacturing complexity, as relatively simple parts can be batch-produced and joined to make complex structures. Global mechanical properties can be tuned based on sub-part ordering and geometry, because local stiffness and density can be independently set to a wide range of values and varied spatially. The structure's intrinsic modularity can significantly simplify analysis and simulation. Simple analytical models for the behavior of each building block type can be calibrated with empirical testing and synthesized into a highly accurate and computationally efficient model of the full compliant system. As a case study, we describe a modular and reversibly assembled wing that performs continuous span-wise twist deformation. It exhibits high performance aerodynamic characteristics, is lightweight and simple to fabricate and repair. The wing is constructed from discrete lattice elements, wherein the geometric and mechanical attributes of the building blocks determine the global mechanical properties of the wing. We describe the mechanical design and structural performance of the digital morphing wing, including their relationship to wind tunnel tests that suggest the ability to increase roll efficiency compared to a conventional rigid aileron system. We focus here on describing the approach to design, modeling, and construction as a generalizable approach for robotics that require very lightweight, tunable, and actively deformable structures.

  11. Digital Morphing Wing: Active Wing Shaping Concept Using Composite Lattice-Based Cellular Structures

    PubMed Central

    Jenett, Benjamin; Calisch, Sam; Cellucci, Daniel; Cramer, Nick; Gershenfeld, Neil; Swei, Sean

    2017-01-01

    Abstract We describe an approach for the discrete and reversible assembly of tunable and actively deformable structures using modular building block parts for robotic applications. The primary technical challenge addressed by this work is the use of this method to design and fabricate low density, highly compliant robotic structures with spatially tuned stiffness. This approach offers a number of potential advantages over more conventional methods for constructing compliant robots. The discrete assembly reduces manufacturing complexity, as relatively simple parts can be batch-produced and joined to make complex structures. Global mechanical properties can be tuned based on sub-part ordering and geometry, because local stiffness and density can be independently set to a wide range of values and varied spatially. The structure's intrinsic modularity can significantly simplify analysis and simulation. Simple analytical models for the behavior of each building block type can be calibrated with empirical testing and synthesized into a highly accurate and computationally efficient model of the full compliant system. As a case study, we describe a modular and reversibly assembled wing that performs continuous span-wise twist deformation. It exhibits high performance aerodynamic characteristics, is lightweight and simple to fabricate and repair. The wing is constructed from discrete lattice elements, wherein the geometric and mechanical attributes of the building blocks determine the global mechanical properties of the wing. We describe the mechanical design and structural performance of the digital morphing wing, including their relationship to wind tunnel tests that suggest the ability to increase roll efficiency compared to a conventional rigid aileron system. We focus here on describing the approach to design, modeling, and construction as a generalizable approach for robotics that require very lightweight, tunable, and actively deformable structures. PMID:28289574

  12. DNA-controlled assembly of a NaTl lattice structure from gold nanoparticles and protein nanoparticles

    SciTech Connect

    Cigler, Petr; Lytton-Jean, Abigail K.R.; Anderson, Daniel G.; Finn, M.G.; Park, Sung Yong

    2010-11-03

    The formation of diamond structures from tailorable building blocks is an important goal in colloidal crystallization because the non-compact diamond lattice is an essential component of photonic crystals for the visible-light range. However, designing nanoparticle systems that self-assemble into non-compact structures has proved difficult. Although several methods have been proposed, single-component nanoparticle assembly of a diamond structure has not been reported. Binary systems, in which at least one component is arranged in a diamond lattice, provide alternatives, but control of interparticle interactions is critical to this approach. DNA has been used for this purpose in a number of systems. Here we show the creation of a non-compact lattice by DNA-programmed crystallization using surface-modified Q{beta} phage capsid particles and gold nanoparticles, engineered to have similar effective radii. When combined with the proper connecting oligonucleotides, these components form NaTl-type colloidal crystalline structures containing interpenetrating organic and inorganic diamond lattices, as determined by small-angle X-ray scattering. DNA control of assembly is therefore shown to be compatible with particles possessing very different properties, as long as they are amenable to surface modification.

  13. 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.

  14. Molecular modeling of micelle formation and solubilization in block copolymer micelles. 2. Lattice theory for monomers with internal degrees of freedom

    SciTech Connect

    Hurter, P.N.; Hatton, T.A. . Dept. of Chemical Engineering); Scheutjens, J.M.H.M. )

    1993-09-13

    A self-consistent mean-field lattice theory of the micellization and solubilization properties of poly(ethylene oxide)-poly(propylene oxide) block copolymers is described. The polymer segments are allowed to assume both polar and nonpolar conformations (corresponding to the gauche and trans rotations of the C-C and C-O bonds), which permits the dependence of the segment-segment interactions on temperature and composition to be accounted for in a physically realistic manner. The phase diagrams of poly(ethylene oxide) and poly(propylene oxide) in water, both of which exhibit lower critical solution temperatures, can be reproduced semiquantitatively. The predictions of the theory compare favorably with published light scattering results on the aggregation behavior of block copolymers and with the authors experimental results for the solubilization of naphthalene in these micelles as a function of polymer composition and molecular weight. The dependence of the micelle-water partition coefficient on polymer composition is not simply related to the proportion of the hydrophobic constituent but depends on the detailed micelle structure. The strong effect of the molecular weight and PPO content of the polymer on the amount of naphthalene solubilized observed experimentally was interpreted in terms of the model results.

  15. 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.

  16. The Structure of the Cubic Coincident Site Lattice Rotation Group

    SciTech Connect

    Reed, B W; Minich, R W; Rudd, R E; Kumar, M

    2004-01-13

    This work is intended to be a mathematical underpinning for the field of grain boundary engineering and its relatives. The interrelationships within the set of rotations producing coincident site lattices in cubic crystals are examined in detail. Besides combining previously established but widely scattered results into a unified context, the present work details newly developed representations of the group structure in terms of strings of generators (based on quaternionic number theory, and including uniqueness proofs and rules for algebraic manipulation) as well as an easily visualized topological network model. Important results that were previously obscure or not universally understood (e.g. the {Sigma} combination rule governing triple junctions) are clarified in these frameworks. The methods also facilitate several general observations, including the very different natures of twin-limited structures in two and three dimensions, the inadequacy of the {Sigma} combination rule to determine valid quadruple nodes, and a curious link between allowable grain boundary assignments and the four-color map theorem. This kind of understanding is essential to the generation of realistic statistical models of grain boundary networks (particularly in twin-dominated systems) and is especially applicable to the field of grain boundary engineering.

  17. 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.

  18. 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.

  19. 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.

  20. 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…

  1. 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.

  2. 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

  3. Chiral effective theory methods and their application to the structure of hadrons from lattice QCD

    NASA Astrophysics Data System (ADS)

    Shanahan, P. E.

    2016-12-01

    For many years chiral effective theory (ChEFT) has enabled and supported lattice QCD calculations of hadron observables by allowing systematic effects from unphysical lattice parameters to be controlled. In the modern era of precision lattice simulations approaching the physical point, ChEFT techniques remain valuable tools. In this review we discuss the modern uses of ChEFT applied to lattice studies of hadron structure in the context of recent determinations of important and topical quantities. We consider muon g-2, strangeness in the nucleon, the proton radius, nucleon polarizabilities, and sigma terms relevant to the prediction of dark-matter-hadron interaction cross-sections, among others.

  4. Nanostructured Block Copolymer Solutions and Composites: Mechanical and Structural Properties

    NASA Astrophysics Data System (ADS)

    Walker, Lynn

    2015-03-01

    Self-assembled block copolymer templates are used to control the nanoscale structure of materials that would not otherwise order in solution. In this work, we have developed a technique to use close-packed cubic and cylindrical mesophases of a thermoreversible block copolymer (PEO-PPO-PEO) to impart spatial order on dispersed nanoparticles. The thermoreversible nature of the template allows for the dispersion of particles synthesized outside the template. This feature extends the applicability of this templating method to many particle-polymer systems, including proteins, and also permits a systematic evaluation of the impact of design parameters on the structure and mechanical properties of the nanocomposites. The criteria for forming co-crystals have been characterized using small-angle scatting and the mechanical properties of these soft crystals determined. Numerous crystal structures have been reported for the block copolymer system and we have taken advantage of several to generate soft co-crystals. The result of this templating is spatially ordered nanoparticle arrays embedded within the block copolymer nanostructure. These soft materials can be shear aligned into crystals with long range order and this shear alignment is discussed. Finally, the dynamics of nanoparticles within the nanostructured material are characterized with fluorescence recovery after photobleaching (FRAP). The applications and general behavior of these nanostructured hydrogels are outlined.

  5. Crosstalk comparison of lattice-form optical interleaver with different coupler structures

    NASA Astrophysics Data System (ADS)

    Wan, Zhujun; Luo, Fengguang; Luo, Zhixiang

    2009-05-01

    Lattice circuit made from a cascade of couplers and delay-lines is a popular approach for optical interleaver based on planar lightwave circuit (PLC) technology. Different coupler structures can be employed in the lattice circuit, including 1-stage directional couplers (DCs), 4-stage DCs, and 2-stage multimode interference (MMI) couplers. We fabricated optical interleavers with above three coupler structures, respectively. The experimental results prove that the latter two coupler structures can help to reduce crosstalk, which meets the simulation results well.

  6. 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.

  7. 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.

  8. 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.

  9. Spring-Block Model Reveals Region-Like Structures

    PubMed Central

    Máté, Gabriell; Néda, Zoltán; Benedek, József

    2011-01-01

    A mechanical spring-block model is used for realizing an objective space partition of settlements from a geographic territory in region-like structures. The method is based on the relaxation-dynamics of the spring-block system and reveals in a hierarchical manner region-like entities at different spatial scales. It takes into account in an elegant manner both the spatiality of the elements and the connectivity relations among them. Spatiality is taken into account by using the geographic coordinates of the settlements, and by detecting the neighbors with the help of a Delaunay triangulation. Connectivity between neighboring settlements are quantified using a Pearson-like correlation for the relative variation of a relevant socio-economic parameter (population size, GDP, tax payed per inhabitant, etc.). The method is implemented in an interactive JAVA application and it is applied with success for an artificially generated society and for the case of USA, Hungary and Transylvania. PMID:21346819

  10. Spring-block model reveals region-like structures.

    PubMed

    Máté, Gabriell; Néda, Zoltán; Benedek, József

    2011-02-08

    A mechanical spring-block model is used for realizing an objective space partition of settlements from a geographic territory in region-like structures. The method is based on the relaxation-dynamics of the spring-block system and reveals in a hierarchical manner region-like entities at different spatial scales. It takes into account in an elegant manner both the spatiality of the elements and the connectivity relations among them. Spatiality is taken into account by using the geographic coordinates of the settlements, and by detecting the neighbors with the help of a Delaunay triangulation. Connectivity between neighboring settlements are quantified using a Pearson-like correlation for the relative variation of a relevant socio-economic parameter (population size, GDP, tax payed per inhabitant, etc.). The method is implemented in an interactive JAVA application and it is applied with success for an artificially generated society and for the case of USA, Hungary and Transylvania.

  11. Quantifying the Characteristics of Knowledge Structure Representations: A Lattice-Theoretic Framework.

    ERIC Educational Resources Information Center

    Young, Michael James

    This report shows how lattice theory can be used to develop quantitative measures of selected characteristics of knowledge structure representations and how these measures can be used to assess individual person's knowledge structure representations in a classroom setting. For a given set of concepts, a knowledge structure can be described by the…

  12. 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.

  13. 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.

  14. Active Faults, Modern Seismicity And Block Structure Of Eurasia

    NASA Astrophysics Data System (ADS)

    Gatinsky, Y.; Rundquist, D.

    2004-12-01

    The analysis of on active faults and seismicity shows that the only a northern part of Eurasia should be regarded as an indivisible lithosphere unit. We defined it as the North Eurasian plate (Gatinsky, Rundquist, 2004) unlike the Eurasian plate s.l., which can be used only for paleotectonic reconstructions. The North Eurasian plate is bordered by zones of seismic activity traced along the Gakkel ridge, the Chersky and Stanovoi ranges, the Baikal rift, Altai--Sayany region, northern Tien Shan, Pamir, Hindu Kush and Kopet Dagh, Great Caucasus, northern Anatolia, Rhodopes, Carpathians, eastern and central Alps. Relationships between this plate and Europe west of the Rhine grabens remain ambiguous. The satellite measurements for them seem to be similar (Nocquet, Calais, 2003), but structural and seismic evidences allow suggesting their incipient division. Wide zones between this plate and neighboring ones can be distinguished outside north Eurasia. These zones consist of numerous blocks of various sizes. Block boundaries are mainly characterized by the high seismicity and development of active wrench faults, thrusts or modern rifts. Some of such zones were named earlier as "diffuse plate boundaries" (Stein et al., 2002; Bird et al, 2003). We suggest to name them as "transit zones" because they are situated between large lithosphere plates and as if transfer the stress field of one of them to other. Blocks within the transit zones reveal local divergences in GPS vectors of their displacements in the ITRF system and especially with respect to fixed Eurasia. At the same time data of satellite measurements emphasize the unity of the North Eurasian plate, which moves eastward in absolute coordinates with some clockwise rotation. The stress distribution in inner parts of the continent is being affected by the interaction with different plates and blocks. It can be more effectively illustrated by a «triangle» of the maximal seismic activity of Eurasia in the central Asia

  15. The building block approach to airborne pod structures

    NASA Astrophysics Data System (ADS)

    Johansson, Jan D.

    2011-05-01

    The certification and testing of new airborne structures is a costly undertaking. This paper presents which measures can be taken to limit the cost and certification required in order to improve the capabilities of the current airborne as-sets, by applying a building block approach to the design and certification of airborne pod structures. A simple way of improving aircraft capabilities is by adding external pod structures, which has been performed for many applications over many years. However, this paper describes a truly modular approach, in which a typical airborne pod structure may be reconfigured to many various roles, with only limited re-certification requirements. Using existing or general aerodynamic shapes, the basic outer shape for the external store is defined, which is then combined with a modular substructure which can accommodate a large variety of electronic and/or optical sensors. This also allows the airborne pod structure to perform several intelligence collecting operations during the same sortie, thereby limiting the time spent near the danger area. The re-use of existing substructure modules reduces the cost and leadtime of the design phase allowing for a rapid entry into service. The modular design, relying on proven interface systems between the building blocks, significantly reduces risk involved in new programs. The certification process is also discussed in order to optimize the use of the pod structure modularity and certification requirements in order to simplify the certification task, by drawing similarity to existing designs. Finally the paper covers how modularity is implemented in new composite pod designs with stealth capabilities.

  16. Plasmonic emission and plasma lattice structures induced by pulsed laser in Purcell cavity on silicon

    NASA Astrophysics Data System (ADS)

    Huang, Wei-Qi; Huang, Zhong-Mei; Miao, Xin-Jian; Liu, Shi-Rong; Qin, Chao-Jian

    2015-10-01

    The lattice structure image of a plasma standing wave in a Purcell cavity of silicon is observed. The plasma wave produced by the pulsed laser could be used to fabricate the micro-nanostructure of silicon. The plasma lattice structures induced by the nanosecond pulsed laser in the cavity may be similar to the Wigner crystal structure. It is interesting that the beautiful diffraction pattern could be observed in the plasma lattice structure. The radiation lifetime could be shortened to the nanosecond range throughout the entire spectral range and the relaxation time could be lengthened for higher emission efficiency in the Purcell cavity, which results in the fact that the plasmonic emission is stronger and its threshold is lower. Project supported by the National Natural Science Foundation of China (Grant Nos. 11264007 and 61465003).

  17. 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

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

    PubMed

    Hart, W E; Istrail, S

    1997-01-01

    This paper considers the protein energy minimization problem for lattice and off-lattice protein folding models that explicitly represent side chains. Lattice models of proteins have proven 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. We consider two side chain models: a lattice model that generalizes the HP model (Dill, 1985) 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. We describe algorithms with mathematically guaranteed error bounds for both of these models. In particular, we describe a linear time performance guaranteed approximation algorithm for the HP side chain model that constructs conformations whose energy is better than 86% of optimal in a face-centered cubic lattice, and we demonstrate how this provides a better than 70% performance guarantee for the HP-TSSC model. Our analysis provides a mathematical methodology for transferring performance guarantees on lattices to off-lattice models. These results partially answer the open question of Ngo et al. (1994) concerning the complexity of protein folding models that include side chains.

  19. 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.

  20. Emergent structure in a dipolar Bose gas in a one-dimensional lattice

    SciTech Connect

    Wilson, Ryan M.; Bohn, John L.

    2011-02-15

    We consider an ultracold dipolar Bose gas in a one-dimensional lattice. For a sufficiently large lattice recoil energy, such a system becomes a series of nonoverlapping Bose-Einstein condensates that interact via the long-range dipole-dipole interaction (ddi). We model this system via a coupled set of nonlocal Gross-Pitaevskii equations (GPEs) for lattices of both infinite and finite extent. We find significantly modified stability properties in the lattice due to the softening of a discrete roton-like mode, as well as ''islands'' in parameter space where biconcave densities are predicted to exist and that only exist in the presence of the other condensates on the lattice. We solve for the elementary excitations of the system to check the dynamical stability of these solutions and to uncover the nature of their collapse. By solving a coupled set of GPEs exactly on a full numeric grid, we show that this emergent biconcave structure can be realized in a finite lattice with atomic {sup 52}Cr.

  1. Band-structural and Fourier-spectral properties of one-dimensional generalized Fibonacci lattices

    NASA Astrophysics Data System (ADS)

    Oh, G. Y.; Lee, M. H.

    1993-11-01

    We study the electronic and Fourier-spectral properties of one-dimensional generalized Fibonacci lattices generated by the stacking rule Sl+1=SnlSml-1 with positive integers n and m, where Sl is the lth generational binary sequence. After showing that, in the limit of the large potential strength, the energy spectrum of a lattice with certain specific n and m can be determined by the associated characteristic value τ(n,m), we investigate the relation between the electronic band structure and the Fourier spectrum. When the lattice possesses the Pisot-Vijayaraghavan (PV) property (i.e., when n+1>m), the Fourier spectrum is closely related to the electronic band structure; the location and the relative strength of the Fourier spectral peak is in agreement with the location and the relative width of the energy spectral gap. On the other hand, when the lattice possesses no PV property (i.e., when n+1<=m), the Fourier spectrum is not directly related to the electronic band structure; the strength of the Fourier spectral peak is irrelevant to the width of the energy spectral gap, while the location of the peak corresponds to that of the gap. We also study the dependence of the electronic and Fourier-spectral properties on the initial conditions of the stacking rule through detailed study of the copper mean lattice (n=1,m=2) with initial conditions S1=\\{A\\} and S2=\\{ABp\\}. It is found that the fractal structure of the energy spectrum is independent of the integer p, while some local electronic properties depend on p. It is also found that the global structure of the Fourier spectrum depends on p; it looks more blurred, and thus the aperiodic nature of the lattice becomes clearer with the increase of p.

  2. 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.

  3. 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

  4. 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

  5. s-Block amidoboranes: syntheses, structures, reactivity and applications.

    PubMed

    Stennett, Tom E; Harder, Sjoerd

    2016-02-21

    Metal amidoborane compounds of the alkali- and alkaline earth metals have in recent years found applications in diverse disciplines, notably as hydrogen storage materials, as reagents for the reduction of organic functional groups and as catalysts and intermediates in dehydrocoupling reactions. These functions are connected by the organometallic chemistry of the MNR2BH3 group. This review focusses on central aspects of the s-block amidoborane compounds - their syntheses, structures and reactivity. Well-defined amidoborane complexes of group 2 metals are now available by a variety of solution-phase routes, which has allowed a more detailed analysis of this functional group, which was previously largely confined to solid-state materials chemistry. Structures obtained from X-ray crystallography have begun to provide increased understanding of the fundamental steps of key processes, including amine-borane dehydrocoupling and hydrogen release from primary and secondary amidoboranes. We review structural parameters and reactivity to rationalise the effects of the metal, nitrogen substituents and supporting ligands on catalytic performance and dehydrogenative decomposition routes. Mechanistic features of key processes involving amidoborane compounds as starting materials or intermediates are discussed, alongside emerging applications such as the use of group 1 metal amidoboranes in synthesis. Finally, the future prospects of this vibrant branch of main group chemistry are evaluated.

  6. 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.

  7. Low-frequency photonic band structures in graphene-like triangular metallic lattice

    NASA Astrophysics Data System (ADS)

    Wang, Kang

    2016-11-01

    We study the low frequency photonic band structures in triangular metallic lattice, displaying Dirac points in the frequency spectrum, and constructed upon the lowest order regular polygonal tiles. We show that, in spite of the unfavourable geometrical conditions intrinsic to the structure symmetry, the lowest frequency photonic bands are formed by resonance modes sustained by local structure patterns, with the corresponding electric fields following a triangular distribution at low structure filling rate and a honeycomb distribution at high filling rate. For both cases, the lowest photonic bands, and thus the plasma gap, can be described in the framework of a tight binding model, and analysed in terms of local resonance modes and their mutual correlations. At high filling rate, the Dirac points and their movement following the structure deformation are described in the same framework, in relation with local structure patterns and their variations, as well as the particularity of the metallic lattice that enhances the topological anisotropy.

  8. Formation of limit-periodic structures by quadrupole particles confined to a triangular lattice

    NASA Astrophysics Data System (ADS)

    Rutkowski, David M.; Marcoux, Catherine; Socolar, Joshua E. S.; Hall, Carol K.

    2017-01-01

    We have performed Monte Carlo (MC) simulations on two-dimensional systems of quadrupole particles confined to a triangular lattice in order to determine the conditions that permit the formation of a limit-periodic phase. We have found that limit-periodic structures form only when the rotations of the particles are confined to a set of six orientations aligned with the lattice directions. Related structures including striped and unidirectional rattler phases form when π /π 6 rotations or continuous rotations are allowed. Order parameters signaling the formation of the limit-periodic structure and related structures are measured as a function of temperature. Our findings on the formation of the limit-periodic structure elucidate features relevant to the experimental creation of such a structure, which is expected to have interesting vibrational and electromagnetic modes.

  9. Chaos and band structure in a three-dimensional optical lattice.

    PubMed

    Boretz, Yingyue; Reichl, L E

    2015-04-01

    Classical chaos is known to affect wave propagation because it signifies the presence of broken symmetries. The effect of chaos has been observed experimentally for matter waves, electromagnetic waves, and acoustic waves. When these three types of waves propagate through a spatially periodic medium, the allowed propagation energies form bands. For energies in the band gaps, no wave propagation is possible. We show that optical lattices provide a well-defined system that allows a study of the effect of chaos on band structure. We have determined the band structure of a body-centered-cubic optical lattice for all theoretically possible couplings, and we find that the band structure for those lattices realizable in the laboratory differs significantly from that expected for the bands in an "empty" body-centered-cubic crystal. However, as coupling is increased, the lattice becomes increasingly chaotic and it becomes possible to produce band structure that has behavior qualitatively similar to the "empty" body-centered-cubic band structure, although with fewer degeneracies.

  10. Equivalent Continuum Finite Element Modelling of Plate-Like Space Lattice Structures.

    DTIC Science & Technology

    1985-08-01

    regulation cost of the structure as a function of the structural design parameters. A micropolar plate continuum model of large plate-like repetitive space...lattice structures with rigid joints is derived. A plate finite element is derived based on this continuum model with micropolar rotations and transverse...by rigid joints which makes use of the higher order micropolar beam continuum formulation. 8 Detailed Models For this research the baseline against

  11. Magnetic structure of light nuclei from lattice QCD

    DOE PAGES

    Chang, Emmanuel; Detmold, William; Orginos, Kostas; ...

    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

  12. 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

  13. Structure and flow properties of block copolyelectrolyte hydrogels

    NASA Astrophysics Data System (ADS)

    Srivastava, Samanvaya; Tirrell, Matthew

    2015-03-01

    Polyelectrolyte complexes (PEC) are dense, polymer-rich phases that form when oppositely charged polyelectrolyte chains spontaneously associate and phase separate in aqueous mediums. Bulk phase separation of the PECs can be evaded by combining one or both of the polyelectrolytes with a neutral polymer, thus engineering pathways for self-assembly of PEC based micelles and hydrogels with large-scale ordering of the nanoscale PEC domains. The PEC domains in these assemblies can encapsulate both hydrophobic and hydrophilic therapeutics and thus have tremendous potential in drug delivery, diagnostic and tissue engineering applications. This study will present insights on the equilibrium structure and self-assembly kinetics of PEC hybrid hydrogels through detailed rheology studies of self-assembled materials comprising of functionalized polyallyl glycidyl ethers (PAGE) connected to either single poly(ethylene glycol) (PEG) chain to form diblock copolymers or as functionalized end-groups on a triblock copolymer with a PEG midblock. The effect of key parameters such as polymer concentration, polymer block lengths, salt, ionic strength, and degree of charge mismatch on the equilibrium materials properties will be discussed, with a special emphasis on the temporal evolution of flow properties, and will lead to comparisons with the rheology models for associating polymers. Complementary studies with extensive static and dynamic light, X-ray and neutron scattering investigations will also be presented, thus providing a comprehensive structural description of these materials.

  14. 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.

  15. First Brillouin Polytope and Band Structure of Diamond Lattice in Four Dimensions

    NASA Astrophysics Data System (ADS)

    Kato, Yuichi; Yamanaka, Masanori

    2017-03-01

    We study the diamond lattice in four dimensions — a descendant of the three-dimensional diamond lattice. As a four-dimensional polytope, we determine the first Brillouin zone and draw the band structure of the corresponding tight-binding model on two-dimensional paper in the usual manner. In the polyhedral decomposition, we find the zone boundary of the first Brillouin zone in four dimensions to be the omnitruncated 5-cell, which comprises ten truncated octahedra glued to 20 hexagonal prisms. We find Dirac line nodes inside the hexagonal prisms.

  16. 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.

  17. Damage spreading on two-dimensional trivalent structures with Glauber dynamics: Hierarchical and random lattices

    NASA Astrophysics Data System (ADS)

    Guo, Z. Z.; Szeto, K. Y.; Fu, Xiujun

    2004-07-01

    The damage spreading of the Ising model on various two-dimensional trivalent structures with Glauber dynamics is investigated. It is shown that topology plays an important role in determining the damage spreading transition temperatures of the trivalent structures. When damage is considered in terms of only the topological properties of the cellular patterns, the transition temperature above which damage is saturated is found to be determined by the cells with the highest edge number. When the area of cells is also taken into account in the computation of damage, the damage spreading transition temperatures are all lowered. These results are verified by simulation on a set of hierarchical lattices constructed by recursive application of the star-triangle transformation on the vertices of the hexagonal structure, as well as soap froth and randomized lattice structures using Voronoi construction.

  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. 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.

  20. A Numerical Study of High-Speed Missile Configurations Using a Block- Structured Parallel Algorithm

    DTIC Science & Technology

    1993-12-01

    Transformation Calculation Subroutine ....................... 97 iv List of Figures Figure Page 1. Current and Projected Computational Requirements...B.3. Project Block Structure and Associated Block Table ......................... 68 B.4. Computational-to-Block Coordinate Transformation ...J, & unit vectors aligned along Cartesian xyz axes R position vector AdS surface vector U vector of conserved variables Kronecker Delta function J

  1. 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.

  2. 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.

  3. 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.

  4. Calcium sensitivity and myofilament lattice structure in titin N2B KO mice.

    PubMed

    Lee, Eun-Jeong; Nedrud, Joshua; Schemmel, Peter; Gotthardt, Michael; Irving, Thomas C; Granzier, Henk L

    2013-07-01

    The cellular basis of the Frank-Starling "Law of the Heart" is the length-dependence of activation, but the mechanisms by which the sarcomere detects length changes and converts this information to altered calcium sensitivity has remained elusive. Here the effect of titin-based passive tension on the length-dependence of activation (LDA) was studied by measuring the tension-pCa relation in skinned mouse LV muscle at two sarcomere lengths (SLs). N2B KO myocardium, where the N2B spring element in titin is deleted and passive tension is elevated, was compared to WT myocardium. Myofilament lattice structure was studied with low-angle X-ray diffraction; the myofilament lattice spacing (d1,0) was measured as well as the ratio of the intensities of the 1,1 and 1,0 diffraction peaks (I1,1/I1,0) as an estimate of the degree of association of myosin heads with the thin filaments. Experiments were carried out in skinned muscle in which the lattice spacing was reduced with Dextran-T500. Experiments with and without lattice compression were also carried out following PKA phosphorylation of the skinned muscle. Under all conditions that were tested, LDA was significantly larger in N2B KO myocardium compared to WT myocardium, with the largest differences following PKA phosphorylation. A positive correlation between passive tension and LDA was found that persisted when the myofilament lattice was compressed with Dextran and that was enhanced following PKA phosphorylation. Low-angle X-ray diffraction revealed a shift in mass from thin filaments to thick filaments as sarcomere length was increased. Furthermore, a positive correlation was obtained between myofilament lattice spacing and passive tension and the change in I1,1/I1,0 and passive tension and these provide possible explanations for how titin-based passive tension might regulate calcium sensitivity.

  5. A Firefly-Inspired Method for Protein Structure Prediction in Lattice Models

    PubMed Central

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

    2014-01-01

    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. PMID:24970205

  6. 3D lattice distortions and defect structures in ion-implanted nano-crystals

    DOE PAGES

    Hofmann, Felix; Robinson, Ian K.; Tarleton, Edmund; ...

    2017-04-06

    The ability of Focused Ion Beam (FIB) techniques to cut solid matter at the nano-scale revolutionized the study of material structure across the life-, earth- and material sciences. But a detailed understanding of the damage caused by the ion beam and its effect on material properties remains elusive. We examine this damage in 3D using coherent X-ray diffraction to measure the full lattice strain tensor in FIB-milled gold nano-crystals. We also found that even very low ion doses, previously thought to be negligible, cause substantial lattice distortions. At higher doses, extended self-organized defect structures appear. Combined with detailed numerical calculations,more » these observations allow fundamental insight into the nature of the damage created and the structural instabilities that lead to a surprisingly inhomogeneous morphology.« less

  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. Development of an Angular Distribution Function for the Study of Atomic Lattice Structures Used in Atomistic Simulation

    DTIC Science & Technology

    1991-03-01

    Structures Used in Atanistic Simulation 6. AUTHOR(S) David Wesley, Capt, USAF 7. PERFORMING ORGA1 NIZATION NAME(S) AND ADDRESS(ES) 8 . PERFORMING...42 7 Appendix A: Program Lattice for Generating Model Lattices ................ 43 8 Appendix B: RDF Fortran Programs...15 Figure 8 : Inner ADF’s for model systems .............................................. 16 Figure 9: Outer ADF’s for model systems

  10. Structural deformation of the S =1 kagome-lattice compound KV3Ge2O9

    NASA Astrophysics Data System (ADS)

    Takagi, Eigo; Aoyama, Takuya; Hara, Shigeo; Sato, Hirohiko; Kimura, Tsuyoshi; Wakabayashi, Yusuke

    2017-03-01

    The dielectric and structural properties of the S =1 kagome antiferromagnet KV3Ge2O9 are examined. The low-temperature structure below 50 K is orthorhombic with a typical correlation length of 8 nm. While the high-temperature hexagonal phase can be considered C -centered orthorhombic, the C -centered symmetry is broken below 50 K. The low-temperature symmetry does not support the simplex solid state, which is the theoretically expected ground state for the S =1 kagome lattice. Above 60 K, incommensurate lattice modulation is observed. The lock-in transition suggests that the origin of the orthorhombic deformation is the development of a short-range magnetic ordering.

  11. Adjoint design sensitivity analysis of reduced atomic systems using generalized Langevin equation for lattice structures

    SciTech Connect

    Kim, Min-Geun; Jang, Hong-Lae; Cho, Seonho

    2013-05-01

    An efficient adjoint design sensitivity analysis method is developed for reduced atomic systems. A reduced atomic system and the adjoint system are constructed in a locally confined region, utilizing generalized Langevin equation (GLE) for periodic lattice structures. Due to the translational symmetry of lattice structures, the size of time history kernel function that accounts for the boundary effects of the reduced atomic systems could be reduced to a single atom’s degrees of freedom. For the problems of highly nonlinear design variables, the finite difference method is impractical for its inefficiency and inaccuracy. However, the adjoint method is very efficient regardless of the number of design variables since one additional time integration is required for the adjoint GLE. Through numerical examples, the derived adjoint sensitivity turns out to be accurate and efficient through the comparison with finite difference sensitivity.

  12. Temperature effect on lattice and electronic structures of WTe2 from first-principles study

    NASA Astrophysics Data System (ADS)

    Liu, Gang; Liu, Huimei; Zhou, Jian; Wan, Xiangang

    2017-01-01

    Tungsten ditelluride (WTe2) exhibits extremely large and unsaturated magnetoresistance (MR). Due to the large spatial extensions of Te-5p and W-5d orbitals, the electronic properties of WTe2 are sensitive to the lattice structures, which can probably affect the strongly temperature dependent MR found in the experiment. Based on first-principle calculations, we investigate the temperature effect on the lattice and electronic structures of WTe2. Our numerical results show that the thermal expansion coefficients of WTe2 are highly anisotropic and considerably large. However, the temperature (less than 300 K) has an ignorable effect on the Fermi surface of WTe2. Our theoretical results clarify that the thermal expansion is not the main reason for the temperature-induced rapid decrease of magnetoresistance.

  13. Structure of critical lines in quenched lattice QCD with the Wilson quark action

    SciTech Connect

    Aoki, S.; Kaneda, T.; Ukawa, A.

    1997-08-01

    The structure of critical lines of a vanishing pion mass for the Wilson quark action is examined in quenched lattice QCD. Numerical evidence is presented that the critical lines spread into five branches beyond {beta}=5.6{endash}5.7 at zero temperature. It is also shown that the critical lines disappear in the deconfined phase for the case of finite temperatures. {copyright} {ital 1997} {ital The American Physical Society}

  14. Effect of Doping and Pressure on Magnetism and Lattice Structure of Fe-Based Superconductors

    DTIC Science & Technology

    2010-04-14

    ar X iv :1 00 4. 21 60 v1 [ co nd -m at .s up r- co n] 1 3 A pr 2 01 0 Effect of doping and pressure on magnetism and lattice structure of Fe...2010) Using first principles calculations, we analyze structural and magnetic trends as a function of charge doping and pressure in BaFe2As2, and...compare to experimentally established facts. We find that density functional theory, while accurately reproducing the structural and magnetic ordering at

  15. 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.

  16. 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.

  17. BGRID: A block-structured grid generation code for wing sections

    NASA Technical Reports Server (NTRS)

    Chen, H. C.; Lee, K. D.

    1981-01-01

    The operation of the BGRID computer program is described for generating block-structured grids. Examples are provided to illustrate the code input and output. The application of a fully implicit AF (approximation factorization)-based computer code, called TWINGB (Transonic WING), for solving the 3D transonic full potential equation in conservation form on block-structured grids is also discussed.

  18. Melt and Solid-State Structures of Polydisperse Polyolefin Block Copolymers

    NASA Astrophysics Data System (ADS)

    Register, Richard; Li, Sheng

    2013-03-01

    Recent developments in coordinative chain transfer polymerization have enabled the synthesis of ethylene-co-octene block copolymers, where the blocks are either crystallizable (an ethylene-co-octene random copolymer block with low octene content) or amorphous (analogous block with high octene content). With a suitable choice of catalyst type(s) and reactor train configuration, accessible chain architectures include diblock, where each block ideally has the most-probable distribution of chain lengths, and multiblock, where both the individual blocks and the number of blocks per chain follow the most-probable distribution. With a sufficiently large interblock octene differential, block copolymers of both architectures, containing roughly equal masses of the two types of block, self-assemble in the melt into well-ordered lamellar structures, despite the large polydispersity. Interblock mixing, induced by the modest Flory interaction parameter and the broad distribution of block lengths, yields an enormous domain spacing (> 100 nm) despite the relatively low average block molecular weights (< 50 kg/mol). Extensive interblock mixing also allows the polyethylene crystals to grow freely and nearly isotropically across the domain interfaces, while preserving the domain structure present in the melt; in the solid state, the optical and x-ray contrasts between dissimilar domains are greatly enhanced due to their different levels of crystallinity. (Work conducted in collaboration with Jeffrey Weinhold, Philip Hustad, and Brian Landes of Dow Chemical Core R&D.) Support from the NSF Polymers Program (DMR-1003942).

  19. 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.

  20. 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

  1. 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

    2013-09-08

    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.

  2. 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.

  3. 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.

  4. Effect of phonon confinement on lattice thermal conductivity of lead Telluride quantum well structure

    SciTech Connect

    Tripathi, Madhvendra Nath

    2014-04-24

    The paper examines the effect of spatial confinement of acoustic phonons on average group velocity and consequently the lattice thermal conductivity of a free-standing PbTe quantum well structure and their temperature dependence. The average group velocity at 100 Å decreases 30% to the bulk value and falls more rapidly on reducing the width of quantum well. Moreover, the lattice thermal conductivity of 100 Å wide PbTe quantum well with value of 0.60 W/mK shows considerable decrease of 70% compared to it’s bulk value. It is observed that the effect of reduction in well width is less pronounce as temperature increases. This appears mainly due to dominance of umklapp processes over the confinement effects.

  5. Large amplitude oscillatory shear of block copolymer spheres on a body-centered cubic lattice: are micelles like metals?

    PubMed

    Torija, Maria A; Choi, Soo-Hyung; Lodge, Timothy P; Bates, Frank S

    2011-05-19

    Small-angle X-ray diffraction experiments have uncovered a remarkable mechanism of grain alignment during plastic deformation of ordered sphere-forming diblock copolymer micelles when subjected to large amplitude dynamic shearing. A nearly monodisperse poly(styrene-b-ethylene-alt-propylene) (SEP) diblock copolymer with block molecular weights of 42,000 and 60,000 was mixed with squalane (C(30)H(62)), an EP selective solvent, at a concentration of 10 wt%. After high temperature annealing, the sample formed an ordered polydomain morphology containing glassy S cores at room temperature. SAXS powder patterns confirm body-centered cubic (BCC) symmetry and reveal the development of a complex array of two-dimensionally resolved Bragg reflections following the application, and cessation, of oscillatory shearing. These diffraction results are interpreted on the basis of the classic mechanism of crystalline slip, which accounts for plastic deformation of ductile materials such as metals. Four distinct slip systems are shown to be active in this work, suggesting a robust basis for deforming and mixing of soft ordered solids.

  6. 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.

  7. Gluon structure function of a color dipole in the light-cone limit of lattice QCD

    SciTech Connect

    Gruenewald, D.; Ilgenfritz, E.-M.; Pirner, H. J.

    2009-10-01

    We calculate the gluon structure function of a color dipole in near-light-cone SU(2) lattice QCD as a function of x{sub B}. The quark and antiquark are external nondynamical degrees of freedom which act as sources of the gluon string configuration defining the dipole. We compute the color dipole matrix element of transversal chromo-electric and chromo-magnetic field operators separated along a direction close to the light cone, the Fourier transform of which is the gluon structure function. As vacuum state in the pure glue sector, we use a variational ground state of the near-light-cone Hamiltonian. We derive a recursion relation for the gluon structure function on the lattice similar to the perturbative Dokshitzer-Gribov-Lipatov-Altarelli-Parisi equation. It depends on the number of transversal links assembling the Schwinger string of the dipole. Fixing the mean momentum fraction of the gluons to the 'experimental value' in a proton, we compare our gluon structure function for a dipole state with four links with the next-to-leading-order MRST 2002 and the CTEQ AB-0 parametrizations at Q{sup 2}=1.5 GeV{sup 2}. Within the systematic uncertainty we find rather good agreement. We also discuss the low x{sub B} behavior of the gluon structure function in our model calculation.

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

    DOE PAGES

    Han, Youngkyu; Ahn, Suk-Kyun; Zhang, Zhe; ...

    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

  9. 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.

  10. 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.

  11. 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.

  12. The topological structures in strongly coupled QGP with chiral fermions on the lattice

    NASA Astrophysics Data System (ADS)

    Sharma, Sayantan; Dick, Viktor; Karsch, Frithjof; Laermann, Edwin; Mukherjee, Swagato

    2016-12-01

    The nature of chiral phase transition for two flavor QCD is an interesting but unresolved problem. One of the most intriguing issues is whether or not the anomalous U(1) symmetry in the flavor sector is effectively restored along with the chiral symmetry. This may determine the universality class of the chiral phase transition. Since the physics near the chiral phase transition is essentially non-perturbative, we employ first principles lattice techniques to address this issue. We use overlap fermions, which have exact chiral symmetry on the lattice, to probe the anomalous U(1) symmetry violation of 2+1 flavor dynamical QCD configurations with domain wall fermions. The latter also optimally preserves chiral and flavor symmetries on the lattice, since it is known that the remnant chiral symmetry of the light quarks influences the scaling of the chiral condensate in the crossover transition region. We observe that the anomalous U(1) is not effectively restored in the chiral crossover region. We perform a systematic study of the finite size and cut-off effects since the signals of U(1) violation are sensitive to it. We also provide a glimpse of the microscopic topological structures of the QCD medium that are responsible for the strongly interacting nature of the quark gluon plasma phase. We study the effect of these microscopic constituents through our first calculations for the topological susceptibility of QCD at finite temperature, which could be a crucial input for the equation of state for anomalous hydrodynamics.

  13. Structure-Property Relationships in Polyolefin Block Copolymers

    NASA Astrophysics Data System (ADS)

    Mansour, Ameara Salah

    Poly(cyclohexylethylene) (PCHE for a homopolymer or C in a block copolymer) is created by hydrogenating polystyrene, and this polymer exhibits interesting properties, such as a high glass transition temperature (147 °C), high flexural modulus (2.8 GPa), low stress optical coefficient (-0.2 * 10-9 Pa-1), and low cost. However, the inherently brittle nature of PCHE prevents it from being used in applications that simultaneously require high modulus, ductility, thermal stability, and optical clarity. Previous research has shown that incorporating PCHE into a block copolymer with rubbery poly(ethylene-alt-propylene) (P) or poly(ethylethylene) (EE) or semicrystalline polyethylene (E) results in a tough material. In some cases, applications also require specific mechanical or optical properties. In order to tune these properties, this research examined tuning crystallinity using two methods: (1) by controlling the microstructure of the soft block by synthesizing a random copolymer of E and EE, and (2) by blending high C content pentablock copolymers with semicrystalline and rubbery minority components. In the first study, diblock copolymers of C(EcoEE) also were used to understand how the microstructure of the random copolymer affects the thermodynamics of the system. In the second study, CECEC and CPCPC, designed to form the same morphology (hexagonally packed cylinders with glassy C matrices), and have similar order-to-disorder transition temperatures and domain spacings, were blended together. Isothermal crystallization experiments were used to determine how the confining E and P in one domain affects the crystallization process. The effect of architecture, the state of the minority component, and the percent crystallinity on the mechanical properties of high glass content materials was also examined. These results were compared to the mechanical properties of homopolymer PCHE, polystyrene, and polycarbonate. The processing conditions needed to create smooth films of

  14. 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.

  15. The Fundamental Structure and the Reproduction of Spiral Wave in a Two-Dimensional Excitable Lattice

    PubMed Central

    Qian, Yu; Zhang, Zhaoyang

    2016-01-01

    In this paper we have systematically investigated the fundamental structure and the reproduction of spiral wave in a two-dimensional excitable lattice. A periodically rotating spiral wave is introduced as the model to reproduce spiral wave artificially. Interestingly, by using the dominant phase-advanced driving analysis method, the fundamental structure containing the loop structure and the wave propagation paths has been revealed, which can expose the periodically rotating orbit of spiral tip and the charity of spiral wave clearly. Furthermore, the fundamental structure is utilized as the core for artificial spiral wave. Additionally, the appropriate parameter region, in which the artificial spiral wave can be reproduced, is studied. Finally, we discuss the robustness of artificial spiral wave to defects. PMID:26900841

  16. The Fundamental Structure and the Reproduction of Spiral Wave in a Two-Dimensional Excitable Lattice.

    PubMed

    Qian, Yu; Zhang, Zhaoyang

    2016-01-01

    In this paper we have systematically investigated the fundamental structure and the reproduction of spiral wave in a two-dimensional excitable lattice. A periodically rotating spiral wave is introduced as the model to reproduce spiral wave artificially. Interestingly, by using the dominant phase-advanced driving analysis method, the fundamental structure containing the loop structure and the wave propagation paths has been revealed, which can expose the periodically rotating orbit of spiral tip and the charity of spiral wave clearly. Furthermore, the fundamental structure is utilized as the core for artificial spiral wave. Additionally, the appropriate parameter region, in which the artificial spiral wave can be reproduced, is studied. Finally, we discuss the robustness of artificial spiral wave to defects.

  17. A hierarchical lattice structure and formation mechanism of ZnO nano-tetrapods.

    PubMed

    Wu, Yaping; Zhang, Xian-Hua; Xu, Fuchun; Zheng, Lan-Sun; Kang, Junyong

    2009-08-12

    The existence of characteristic longitudinal optical and transverse optical phonons of cubic ZnO in ZnO nano-tetrapods is determined by Raman spectroscopy and first-principles calculations. Stacking sequence change at the boundary of the core and legs is also identified by high-resolution transmission electron microscopy. Based on this experimental and theoretical evidence, we demonstrate that the lattice structure of ZnO nano-tetrapods is hierarchical with a zinc blende core connecting to four wurtzite legs. Furthermore, we establish the atomic configuration and propose a formation mechanism induced by Laplace pressure in the initial growth stage of ZnO nano-tetrapods.

  18. 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.

  19. 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.

  20. 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.

  1. 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.

  2. 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.

  3. Surface adsorption of lattice HP proteins: Thermodynamics and structural transitions using Wang-Landau sampling

    NASA Astrophysics Data System (ADS)

    Li, Ying Wai; Wüst, Thomas; Landau, David P.

    2012-12-01

    Wang-Landau sampling has been applied to investigate the thermodynamics and structural properties of a lattice hydrophobic-polar heteropolymer (the HP protein model) interacting with an attractive substrate. For simplicity, we consider a short HP sequence consisting of only 36 monomers interacting with a substrate which attracts all monomers in the sequence. The conformational “phase transitions” have been identified by a canonical analysis of the specific heat and suitable structural observables. Three major “transitions”, namely, adsorption, hydrophobic core formation and “flattening” of adsorbed structures, are observed. Depending on the surface attractive strength relative to the intra-protein attraction among the H monomers, these processes take place in different sequences upon cooling.

  4. Spin structure factors of chiral quantum spin liquids on the kagome lattice

    NASA Astrophysics Data System (ADS)

    Halimeh, Jad C.; Punk, Matthias

    2016-09-01

    We calculate dynamical spin structure factors for gapped chiral spin liquid states in the spin-1/2 Heisenberg antiferromagnet on the kagome lattice using Schwinger-boson mean-field theory. In contrast to static (equal-time) structure factors, the dynamical structure factor shows clear signatures of time-reversal symmetry breaking for chiral spin liquid states. In particular, momentum inversion k →-k symmetry as well as the sixfold rotation symmetry around the Γ point are lost. We highlight other interesting features, such as a relatively flat onset of the two-spinon continuum for the cuboc1 state. Our work is based on the projective symmetry group classification of time-reversal symmetry breaking Schwinger-boson mean-field states by Messio, Lhuillier, and Misguich.

  5. 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.

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

    PubMed

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

    2016-09-30

    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.

  7. Passive damping augmentation of flexible beam-like lattice trusses for large space structures

    NASA Technical Reports Server (NTRS)

    Cohen, K.; Weller, T.

    1992-01-01

    A Timoshenko beam continuum model is developed to determine the transient response of a beam-like latticed large space structure, subjected to a unit impulse. It is demonstrated that an increase in diagonal stiffness, on account of the stiffness of the vertical girder, leads to a rise in the transverse shear rigidity. This results in higher natural frequencies and reduction in peak displacement. In addition, in an asymmetrical truss configuration, coupling between the extensional and shear modes raises the maximum peak displacement compared with that obtained for a symmetrical truss. The model is modified to investigate the introduction of passive damping in the form of several dynamic vibration absorbers. A unique absorber parameter optimization procedure, based on the classical steady-state criteria, is used to tune the absorbers, having a total allocated mass budget of 10%, to the first two frequencies of the latticed structure. It is found that inclusion of transverse shear rigidity as a design parameter in damping augmentation studies reduces settling time for predetermined maximum peak displacements.

  8. 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

  9. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2016-09-01

    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.

  11. 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

  12. 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.

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

    SciTech Connect

    Pattanasiri, Busara; Li, Ying Wai; Wuest, Thomas; Landau, David P

    2015-01-01

    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.

  14. 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

  15. Optimal sensor placement for spatial lattice structure based on genetic algorithms

    NASA Astrophysics Data System (ADS)

    Liu, Wei; Gao, Wei-cheng; Sun, Yi; Xu, Min-jian

    2008-10-01

    Optimal sensor placement technique plays a key role in structural health monitoring of spatial lattice structures. This paper considers the problem of locating sensors on a spatial lattice structure with the aim of maximizing the data information so that structural dynamic behavior can be fully characterized. Based on the criterion of optimal sensor placement for modal test, an improved genetic algorithm is introduced to find the optimal placement of sensors. The modal strain energy (MSE) and the modal assurance criterion (MAC) have been taken as the fitness function, respectively, so that three placement designs were produced. The decimal two-dimension array coding method instead of binary coding method is proposed to code the solution. Forced mutation operator is introduced when the identical genes appear via the crossover procedure. A computational simulation of a 12-bay plain truss model has been implemented to demonstrate the feasibility of the three optimal algorithms above. The obtained optimal sensor placements using the improved genetic algorithm are compared with those gained by exiting genetic algorithm using the binary coding method. Further the comparison criterion based on the mean square error between the finite element method (FEM) mode shapes and the Guyan expansion mode shapes identified by data-driven stochastic subspace identification (SSI-DATA) method are employed to demonstrate the advantage of the different fitness function. The results showed that some innovations in genetic algorithm proposed in this paper can enlarge the genes storage and improve the convergence of the algorithm. More importantly, the three optimal sensor placement methods can all provide the reliable results and identify the vibration characteristics of the 12-bay plain truss model accurately.

  16. 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.

  17. 3D lattice distortions and defect structures in ion-implanted nano-crystals

    PubMed Central

    Hofmann, Felix; Tarleton, Edmund; Harder, Ross J.; Phillips, Nicholas W.; Ma, Pui-Wai; Clark, Jesse N.; Robinson, Ian K.; Abbey, Brian; Liu, Wenjun; Beck, Christian E.

    2017-01-01

    Focussed Ion Beam (FIB) milling is a mainstay of nano-scale machining. By manipulating a tightly focussed beam of energetic ions, often gallium (Ga+), FIB can sculpt nanostructures via localised sputtering. This ability to cut solid matter on the nano-scale revolutionised sample preparation across the life, earth and materials sciences. Despite its widespread usage, detailed understanding of the FIB-induced structural damage, intrinsic to the technique, remains elusive. Here we examine the defects caused by FIB in initially pristine objects. Using Bragg Coherent X-ray Diffraction Imaging (BCDI), we are able to spatially-resolve the full lattice strain tensor in FIB-milled gold nano-crystals. We find that every use of FIB causes large lattice distortions. Even very low ion doses, typical of FIB imaging and previously thought negligible, have a dramatic effect. Our results are consistent with a damage microstructure dominated by vacancies, highlighting the importance of free-surfaces in determining which defects are retained. At larger ion fluences, used during FIB-milling, we observe an extended dislocation network that causes stresses far beyond the bulk tensile strength of gold. These observations provide new fundamental insight into the nature of the damage created and the defects that lead to a surprisingly inhomogeneous morphology. PMID:28383028

  18. Surface Structure and Lattice Dynamics of Alkali Halide Crystals Studied by High-Resolution Ion Scattering

    NASA Astrophysics Data System (ADS)

    Kido, Yoshiaki; Okazawa, Tetsuaki

    The rumpled surface structure and thermal lattice vibrations of KI(001) and RbI(001) were measured directly by high-resolution medium energy ion scattering (MEIS). The relaxation of interlayer distance between the top and second layer and the rumpling of the top and second layers were determined using the ion shadowing effect with an accuracy of 0.01 Å. From the displaced lattice positions determined above, we derived the dipole moments of the top- and second-layer ions self-consistently employing the polarizabilities estimated from the optical refractive index combined with the Clausius Mossotti relation. The balance between a short-range force and a long-range Coulombic one made it possible to judge the applicability of the short-range pair potentials proposed so far. We also determined the root-mean-square (rms) thermal vibration amplitudes of the bulk and the top-layer ions together with the correlations of the ions in the [001] and [101] strings by taking various kinds of scattering geometries. The results obtained were compared with those calculated from the molecular dynamics (MD) simulations based on a classical model using the dipole moments determined above and the Born Mayer type pair potential. The present MEIS results are in overall agreement with the MD simulations.

  19. 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.

  20. 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

  1. 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

  2. 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.

  3. The effect of RAFT-derived cationic block copolymer structure on gene silencing efficiency.

    PubMed

    Hinton, Tracey M; Guerrero-Sanchez, Carlos; Graham, Janease E; Le, Tam; Muir, Benjamin W; Shi, Shuning; Tizard, Mark L V; Gunatillake, Pathiraja A; McLean, Keith M; Thang, San H

    2012-10-01

    In this work a series of ABA tri-block copolymers was prepared from oligo(ethylene glycol) methyl ether methacrylate (OEGMA(475)) and N,N-dimethylaminoethyl methacrylate (DMAEMA) to investigate the effect of polymer composition on cell viability, siRNA uptake, serum stability and gene silencing. Reversible Addition-Fragmentation Chain Transfer (RAFT) polymerization was used as the method of polymer synthesis as this technique allows the preparation of well-defined block copolymers with low polydispersity. Eight block copolymers were prepared by systematically varying the central cationic block (DMAEMA) length from 38 to 192 monomer units and the outer hydrophilic block (OEGMA(475)) from 7 to 69 units. The polymers were characterized using size exclusion chromatography and (1)H NMR. Chinese Hamster Ovary-GFP and Human Embryonic Kidney 293 cells were used to assay cell viability while the efficiency of block copolymers to complex with siRNA was evaluated by agarose gel electrophoresis. The ability of the polymer-siRNA complexes to enter into cells and to silence the targeted reporter gene enhanced green fluorescent protein (EGFP) was measured by using a CHO-GFP silencing assay. The length of the central cationic block appears to be the key structural parameter that has a significant effect on cell viability and gene silencing efficiency with block lengths of 110-120 monomer units being the optimum. The ABA block copolymer architecture is also critical with the outer hydrophilic blocks contributing to serum stability and overall efficiency of the polymer as a delivery system.

  4. On linear structure and phase rotation invariant properties of block M-PSK modulation codes

    NASA Technical Reports Server (NTRS)

    Kasami, Tadao; Takata, Toyoo; Fujiwara, Toru; Lin, Shu

    1991-01-01

    Two important structural properties of block M(=2')-ary PSK modulation codes, linear structure and phase symmetry, are investigated. An M-ary modulation code is first represented as a code with symbols from the integer group S(MPSK) = (0,1,2,...M-1) under modulo-M addition. Then the linear structure of block MPSK modulation codes over S(M-PSK) with respect to modulo-M vector addition is defined, and conditions are derived under which a block MPSK modulation code is linear. Once the linear structure is developed, the phase symmetry of block M-PSK modulation codes is studied. In particular, a necessary and sufficient condition for a block MPSK modulation code that is linear as a binary code to be invariant under 2 h 180 deg/M phase rotation (for h = 1 to l) is derived. Finally, a list of short 8PSK and 16PSK modulation codes is given, together with their linear structure and the smallest phase rotation for which a code is invariant.

  5. 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.

  6. Asymmetric block copolymer membranes with ultrahigh porosity and hierarchical pore structure by plain solvent evaporation.

    PubMed

    Yu, H; Qiu, X; Behzad, A R; Musteata, V; Smilgies, D-M; Nunes, S P; Peinemann, K-V

    2016-10-04

    Membranes with a hierarchical porous structure could be manufactured from a block copolymer blend by pure solvent evaporation. Uniform pores in a 30 nm thin skin layer supported by a macroporous structure were formed. This new process is attractive for membrane production because of its simplicity and the lack of liquid waste.

  7. 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.

  8. 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.

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

    SciTech Connect

    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.; Sargent, Edward H.

    2016-09-09

    Organolead halide perovskites are a family of hybrid organic-inorganic compounds whose remarkable 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 findings confirm the displacive nature of the cubic-to-tetragonal phase transition, which is further shown, using neutron and x-ray diffraction, to be close to a tricritical point. Lastly, we detect quasistatic symmetry-breaking nanodomains persisting well into the high-temperature cubic phase, possibly stabilized by local defects. These findings reveal key structural properties of these materials, and also bear important implications for carrier dynamics across an extended temperature range relevant for photovoltaic applications.

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

    NASA Astrophysics Data System (ADS)

    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.; Sargent, Edward H.

    2016-09-01

    Organolead halide perovskites are a family of hybrid organic-inorganic compounds whose remarkable 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 findings confirm the displacive nature of the cubic-to-tetragonal phase transition, which is further shown, using neutron and x-ray diffraction, to be close to a tricritical point. Lastly, we detect quasistatic symmetry-breaking nanodomains persisting well into the high-temperature cubic phase, possibly stabilized by local defects. These findings reveal key structural properties of these materials, and also bear important implications for carrier dynamics across an extended temperature range relevant for photovoltaic applications.

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

    DOE PAGES

    Comin, Riccardo; Crawford, Michael K.; Said, Ayman H.; ...

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

    SciTech Connect

    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.; Sargent, Edward H.

    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-breaking 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.

  13. Flavor structure of Λ baryons from lattice QCD: From strange to charm quarks

    NASA Astrophysics Data System (ADS)

    Gubler, Philipp; Takahashi, Toru T.; Oka, Makoto

    2016-12-01

    We study Λ baryons of spin-parity 1/2± with either a strange or charm valence quark in full 2 +1 flavor lattice QCD. Multiple S U (3 ) singlet and octet operators are employed to generate the desired single baryon states on the lattice. Via the variational method, the couplings of these states to the different operators provide information about the flavor structure of the Λ baryons. We make use of the gauge configurations of the PACS-CS Collaboration and chirally extrapolate the results for the masses and S U (3 ) flavor components to the physical point. We furthermore gradually change the hopping parameter of the heaviest quark from strange to charm to study how the properties of the Λ baryons evolve as a function of the heavy quark mass. It is found that the baryon energy levels increase almost linearly with the quark mass. Meanwhile, the flavor structure of most of the states remains stable, with the exception of the lowest 1/2- state, which changes from a flavor singlet Λ to a Λc state with singlet and octet components of comparable size. Finally, we discuss whether our findings can be interpreted with the help of a simple quark model and find that the negative-parity Λc states can be naturally explained as diquark excitations of the light u and d quarks. On the other hand, the quark-model picture does not appear to be adequate for the negative-parity Λ states, suggesting the importance of other degrees of freedom to describe them.

  14. Surface grid generation for multi-block structured grids

    NASA Astrophysics Data System (ADS)

    Spekreijse, S. P.; Boerstoel, J. W.; Kuyvenhoven, J. L.; van der Marel, M. J.

    A new grid generation technique for the computation of a structured grid on a generally curved surface in 3D is discussed. The starting assumption is that the parameterization of the surface exists, i.e. a smooth geometrical shape function exists which maps the parametric space (the unit square) one-to-one on the surface. The grid generation system computes a grid on the surface with as boundary conditions the following data specified along the four edges of the surface: (1) the position of the boundary grid points, (2) the grid line slopes at the boundary grid points, (3) the first grid cell lengths at the boundary grid points. The fourth-order elliptic biharmonic equations are used to compute the two families of grid lines in the parametric space. After that, each grid point in the parametric space is found as the intersection point between two individual grid lines, one from each family. The grid points on the surface are finally found by mapping the grid points in the parametric space on the surface via the geometrical shape function. Results are shown for an O-type 2D Euler grid, a C-type 2D Navier-Stokes grid and on some curved surfaces in 3D space.

  15. 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.

  16. HAIM OMLET: An Expert System For Research In Orthomodular Lattices And Related Structures

    NASA Astrophysics Data System (ADS)

    Dankel, D. D.; Rodriguez, R. V.; Anger, F. D.

    1986-03-01

    This paper describes research towards the construction of an expert system combining the brute force power of algorithmic computation and the inductive reasoning power of a rule-based inference engine in the mathematical area of discrete structures. Little research has been conducted on extending existing expert systems' technology to computationally complex areas. This research addresses the extension of expert systems into areas such as these, where the process of inference by itself will not produce the proper results. Additionally, the research will demonstrate the benefits of combining inference engines and mathematical algorithms to attack computationally complex problems. The specific aim is to produce an expert system which embodies expert level knowledge of orthomodular lattices, graphs, structure spaces, boolean algebras, incidence relations, and projective configurations. The resulting system, implemented on a micro-computer, will provide researchers a powerful and accessible tool for exploring these discrete structures. The system's "shell" will provide a structure for developing other expert systems with similar capabilities in such related areas as coding theory, categories, monoids, automata theory, and non-standard logics.

  17. 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

  18. 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.

  19. Identification of the dynamics of a two-dimensional grid structure using least square lattice filters. [for large space structures

    NASA Technical Reports Server (NTRS)

    Montgomery, R. C.; Sundararajan, N.

    1984-01-01

    It is doubtful whether the dynamics of large space structures (LSS) can be predicted well enough for control system design applications. Hence, dynamic modeling from on-orbit measurements followed by a modification of the control system is of interest, taking into account the utilization of adaptive control concepts. The present paper is concerned with the model determination phase of the adaptive control problem. Using spectral decoupling to determine mode shapes, mode frequency and damping data can be obtained with the aid of an equation error parameter identification method. This method employs a second-order auto-regressive moving average (ARMA) model to represent the natural mode amplitudes. The discussed procedure involves an extension of the application of the least square lattice filter in system identification to a nonintegral, two-dimensional grid structure made of overlapping bars.

  20. Systematic study of the hybrid plasmonic-photonic band structure underlying lasing action of diffractive plasmon particle lattices

    NASA Astrophysics Data System (ADS)

    Schokker, A. Hinke; van Riggelen, Floor; Hadad, Yakir; Alù, Andrea; Koenderink, A. Femius

    2017-02-01

    We study lasing in distributed feedback lasers made from square lattices of silver particles in a dye-doped waveguide. We present a systematic analysis and experimental study of the band structure underlying the lasing process as a function of the detuning between the particle plasmon resonance and the lattice Bragg diffraction condition. To this end, as gain medium we use either a polymer doped with Rh6G only, or polymer doped with a pair of dyes (Rh6G and Rh700) that act as a Förster energy transfer (FRET) pair. This allows for gain, respectively, at 590 or 700 nm when pumped at 532 nm, compatible with the achievable size tunability of silver particles embedded in the polymer. By polarization-resolved spectroscopic Fourier microscopy, we are able to observe the plasmonic/photonic band structure of the array, unraveling both the stop gap width, as well as the loss properties of the four involved bands at fixed lattice Bragg diffraction condition and as a function of detuning of the plasmon resonance. To explain the measurements we derive an analytical model that sheds insights on the lasing process in plasmonic lattices, highlighting the interaction between two competing resonant processes, one localized at the particle level around the plasmon resonance, and one distributed across the lattice. Both are shown to contribute to the lasing threshold and the overall emission properties of the array.

  1. Thermodynamic and structural properties of finely discretized on-lattice hard-sphere fluids: Virial coefficients, free energies, and direct correlation functions.

    PubMed

    Siderius, Daniel W; Gelb, Lev D

    2009-08-28

    Using both molecular simulation and theory, we examine fluid-phase thermodynamic and structural properties of on-lattice hard-sphere fluids. Our purpose in this work is to provide reference data for on-lattice density functional theories [D. W. Siderius and L. D. Gelb, Langmuir 25, 1296 (2009)] and related perturbation theories. In this model, hard spheres are located at sites on a finely discretized cubic lattice where the spacing between lattice sites is between one-tenth and one-third the hard-sphere diameter. We calculate exactly the second, third, and fourth virial coefficients as functions of the lattice spacing. Via Monte Carlo simulation, we measure the excess chemical potential as a function of density for several lattice spacings. These results are then parametrized with a convenient functional form and can immediately be used in on-lattice density functional theories. Of particular interest is to identify those lattice spacings that yield properties similar to those of the off-lattice fluid. We find that the properties of the on-lattice fluid are strongly dependent on lattice spacing, generally approaching those of the off-lattice fluid with increasing lattice resolution, but not smoothly. These observations are consistent with results for larger lattice spacings [A. Z. Panagiotopoulos, J. Chem. Phys. 123, 104504 (2005)]. Certain lattice spacings are found to yield fluid properties in particularly good agreement with the off-lattice fluid. We also find that the agreement of many different on- and off-lattice hard-sphere fluid properties is predicted quite well by that of the virial coefficients, suggesting that they may be used to identify favorable lattice spacings. The direct correlation function at a few lattice spacings and a single density is obtained from simulation. The on-lattice fluid is structurally anisotropic, exhibiting spherical asymmetry in correlation functions. Interestingly, the anisotropies are properly captured in the Percus

  2. 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.

  3. Lattice instabilities and structural phase transformations in La sub 2 CuO sub 4 superconductors and insulators

    SciTech Connect

    Axe, J.D.

    1991-01-01

    Soft-mode structural phase transformations, common in many perovskite-based materials, are also found in La{sub 2}CuO{sub 4} and structurally related oxides. The resulting phase behavior is rather complex, but is a natural consequence of the degeneracy of the soft phonon order parameters. This paper reviews the structural and lattice-dynamical results and their interpretation based upon mean-field statistical mechanical models.

  4. Lattice instabilities and structural phase transformations in La{sub 2}CuO{sub 4} superconductors and insulators

    SciTech Connect

    Axe, J.D.

    1991-12-31

    Soft-mode structural phase transformations, common in many perovskite-based materials, are also found in La{sub 2}CuO{sub 4} and structurally related oxides. The resulting phase behavior is rather complex, but is a natural consequence of the degeneracy of the soft phonon order parameters. This paper reviews the structural and lattice-dynamical results and their interpretation based upon mean-field statistical mechanical models.

  5. Correlatively Dependent Lattice and Electronic Structural Evolutions in Compressed Monolayer Tungsten Disulfide.

    PubMed

    Han, Bo; Li, Fangfei; Li, Liang; Huang, Xiaoli; Gong, Yuanbo; Fu, Xinpeng; Gao, Hanxue; Zhou, Qiang; Cui, Tian

    2017-03-02

    Transition-metal dichalcogenides (TMDs) are promising materials for optoelectronic devices. Their lattice and electronic structural evolutions under high strain conditions and their relations remain open questions. We exert pressure on WS2 monolayers on different substrates, namely, Si/SiO2 substrate and diamond anvil surface up to ∼25 GPa. Structural distortions in various degree are disclosed based on the emergence of Raman-inactive B mode. Splits of out-of-plane B and A1' modes are only observed on Si/SiO2 substrate due to extra strain imported from volume decrease in Si and corrugation of SiO2 surface, and its photoluminescence (PL) quenches quickly because of decreased K-K transition by conspicuous distortion of Brillouin zone. While diamond anvil surface provides better hydrostatic environment, combined analysis of PL and absorption proves that pressure effectively tunes PL emission energy and enhances Coulomb interactions. Knowledge of these distinct pressure tunable characteristics of monolayer WS2 improves further understanding of structural and optical properties of TMDs.

  6. Reversal of lattice, electronic structure, and magnetism in epitaxial SrCoOx thin films

    NASA Astrophysics Data System (ADS)

    Jeen, H.; Choi, W. S.; Lee, J. H.; Cooper, V. R.; Lee, H. N.; Seo, S. S. A.; Rabe, K. M.

    2014-03-01

    SrCoOx (x = 2.5 - 3.0, SCO) is an ideal material to study the role of oxygen content for electronic structure and magnetism, since SCO has two distinct topotactic phases: the antiferromagnetic insulating brownmillerite SrCoO2.5 and the ferromagnetic metallic perovskite SrCoO3. In this presentation, we report direct observation of a reversible lattice and electronic structure evolution in SrCoOx epitaxial thin films as well as different magnetic and electronic ground states between the topotactic phases.[2] By magnetization measurements, optical absorption, and transport measurements drastically different electronic and magnetic ground states are found in the epitaxially grown SrCoO2.5 and SrCoO3 thin films by pulsed laser epitaxy. First-principles calculations confirm substantial, which originate from the modification in the Co valence states and crystallographic structures. By real-time spectroscopic ellipsometry, the two electronically and magnetically different phases can be reversibly changed by changing the ambient pressure at greatly reduced temperatures. Our finding provides an important pathway to understanding the novel oxygen-content-dependent phase transition uniquely found in multivalent transition metal oxides. The work was supported by the U.S. Department of Energy, Basic Energy Sciences, Materials Sciences and Engineering Division.

  7. Hierarchically structured materials from block polymer confinement within bicontinuous microemulsion-derived nanoporous polyethylene.

    PubMed

    Jones, Brad H; Lodge, Timothy P

    2011-11-22

    The self-assembly behavior of block polymers under strong two-dimensional and three-dimensional confinement has been well-studied in the past decade. Confinement effects enable access to a large suite of morphologies not typically observed in the bulk. We have used nanoporous polyethylene, derived from a polymeric bicontinuous microemulsion, as a novel template for the confinement of several different cylinder-forming block polymer systems: poly(isoprene-b-2-vinylpyridine), poly(styrene-b-isoprene), and poly(isoprene-b-dimethylsiloxane). The resultant materials exhibit unique hierarchical arrangements of structure with two distinct length scales. First, the polyethylene template imparts a disordered, microemulsion-like periodicity between bicontinuous polyethylene and block polymer networks with sizes on the order of 100 nm. Second, the block polymer networks display internal periodic arrangements produced by the spontaneous segregation of their incompatible constituents. The microphase-separated morphologies observed are similar to those previously reported for confinement of block polymers in cylindrical pores. However, at present, the morphologies are spatially variant in a complex manner, due to the three-dimensionally interconnected nature of the confining geometry and its distribution in pore sizes. We have further exploited the unique structure of the polyethylene template to generate new hierarchically structured porous monoliths. Poly(isoprene-b-2-vinylpyridine) is used as a model system in which the pyridine block is cross-linked, post-infiltration, and the polyethylene template is subsequently extracted. The resultant materials possess a three-dimensionally continuous pore network, of which the pore walls retain the unique, microphase-separated morphology of the confined block polymer.

  8. Electromagnetic fields generated by constrained rotation of structural blocks in the Earth’s crust

    NASA Astrophysics Data System (ADS)

    Losseva, T. V.; Kuzmicheva, M. Y.; Spivak, A. A.

    2009-12-01

    Specific features of low frequency electromagnetic impulses in the subsurface Earth’s crust with a low moisture content are defined by the tectonic activity of the region and its structure as well as the stressed-strained state. Electromagnetic effects related to seismic and deformation processes in rocks are very diverse and their physical nature is different. The electric polarization of rocks deserves special attention, since this mechanism is implied in an explosive loading of rocks or relaxation processes in any hierarchic block geophysical medium [1]. The amplitudes of electromagnetic pulses generated by electric currents in a relaxing block-structured stress-strained medium have been obtained by 3D numerical modeling. The source of currents is formed by electric polarization of solids filled inter-block gaps on the active face of a block which, in turn, rotates constrainedly under relaxation. The electric current impulse is defined by the shape of the seismic impulse of the block under relaxation. The block is embedded in the crust. The full system of Maxwell equations in a conductive medium has been solved. The numerical method used has been developed to describe properly the geometry of strain as well as impressed current and conductivity profiles at every time. The figure below presents the maximal amplitudes of electric fields Emax for different active block sizes L (curves 1, 2, 3) versus the relative distances from the source epicenter x/L. Here circles denote the experimental data obtained for the Kurai tectonic structure [1]. We see that the results of numerical simulations are in good agreement with the results of measurements. This proves the validity of our model for the estimation of electric effects in the low moisture rock medium. References: [1] S.P. Soloviev and A.A. Spivak, Doklady Earth Sciences, 2007, Vol. 417A, No. 9, pp. 1449-1453.

  9. Hierarchical assembly of micro-/nano-building blocks: bio-inspired rigid structural functional materials.

    PubMed

    Yao, Hong-Bin; Fang, Hai-Yu; Wang, Xiao-Han; Yu, Shu-Hong

    2011-07-01

    The huge diversity of hierarchical micro-/nano-rigid structures existing in biological systems is increasingly becoming a source of inspiration of materials scientists and engineers to create next-generation advanced functional materials. In the past decades, these multiscale hierarchical structures have been intensively investigated to show their contributions to high performance in mechanical properties. Recently, accompanied with the development of nanotechnology, some biologically hierarchical rigid structures have been duplicated and mimicked in artificial materials through hierarchical organization of micro-/nano-building blocks. In this critical review, we will present biological rigid structural models, functional micro-/nano-building blocks, and hierarchical assembly techniques for the manufacture of bio-inspired rigid structural functional materials (177 references).

  10. Thermally induced structural evolution and performance of mesoporous block copolymer-directed alumina perovskite solar cells.

    PubMed

    Tan, Kwan Wee; Moore, David T; Saliba, Michael; Sai, Hiroaki; Estroff, Lara A; Hanrath, Tobias; Snaith, Henry J; Wiesner, Ulrich

    2014-05-27

    Structure control in solution-processed hybrid perovskites is crucial to design and fabricate highly efficient solar cells. Here, we utilize in situ grazing incidence wide-angle X-ray scattering and scanning electron microscopy to investigate the structural evolution and film morphologies of methylammonium lead tri-iodide/chloride (CH3NH3PbI(3-x)Cl(x)) in mesoporous block copolymer derived alumina superstructures during thermal annealing. We show the CH3NH3PbI(3-x)Cl(x) material evolution to be characterized by three distinct structures: a crystalline precursor structure not described previously, a 3D perovskite structure, and a mixture of compounds resulting from degradation. Finally, we demonstrate how understanding the processing parameters provides the foundation needed for optimal perovskite film morphology and coverage, leading to enhanced block copolymer-directed perovskite solar cell performance.

  11. 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.

  12. Ultrafast Coupling between Light, Coherent Lattice Vibrations, and the Magnetic Structure of Semicovalent LaMnO3

    NASA Astrophysics Data System (ADS)

    Wall, S.; Prabhakaran, D.; Boothroyd, A. T.; Cavalleri, A.

    2009-08-01

    Coherent lattice vibrations are excited and probed with pulses of 10 fs duration in LaMnO3. The measured frequencies correspond to those of Jahn-Teller stretching and of out-of phase rotations of the oxygen octahedra. Surprisingly, the amplitude and damping rate of both modes exhibit a sharp discontinuity at the Néel temperature, highlighting nontrivial coupling between light, lattice, and magnetic structure. We explain this effect by applying the Goodenough-Kanamori rules to the excited state of LaMnO3, and note that charge transfer can invert the sign of the semicovalent exchange interaction, which in turn perturbs the equilibrium bond lengths.

  13. Ultrafast coupling between light, coherent lattice vibrations, and the magnetic structure of semicovalent LaMnO(3).

    PubMed

    Wall, S; Prabhakaran, D; Boothroyd, A T; Cavalleri, A

    2009-08-28

    Coherent lattice vibrations are excited and probed with pulses of 10 fs duration in LaMnO(3). The measured frequencies correspond to those of Jahn-Teller stretching and of out-of phase rotations of the oxygen octahedra. Surprisingly, the amplitude and damping rate of both modes exhibit a sharp discontinuity at the Néel temperature, highlighting nontrivial coupling between light, lattice, and magnetic structure. We explain this effect by applying the Goodenough-Kanamori rules to the excited state of LaMnO(3), and note that charge transfer can invert the sign of the semicovalent exchange interaction, which in turn perturbs the equilibrium bond lengths.

  14. Structural Color for Additive Manufacturing: 3D-Printed Photonic Crystals from Block Copolymers.

    PubMed

    Boyle, Bret M; French, Tracy A; Pearson, Ryan M; McCarthy, Blaine G; Miyake, Garret M

    2017-03-28

    The incorporation of structural color into 3D printed parts is reported, presenting an alternative to the need for pigments or dyes for colored parts produced through additive manufacturing. Thermoplastic build materials composed of dendritic block copolymers were designed, synthesized, and used to additively manufacture plastic parts exhibiting structural color. The reflection properties of the photonic crystals arise from the periodic nanostructure formed through block copolymer self-assembly during polymer processing. The wavelength of reflected light could be tuned across the visible spectrum by synthetically controlling the block copolymer molecular weight and manufacture parts that reflected violet, green, or orange light with the capacity to serve as selective optical filters and light guides.

  15. Shape transitions and lattice structuring of ceramide-enriched domains generated by sphingomyelinase in lipid monolayers.

    PubMed

    Härtel, Steffen; Fanani, María Laura; Maggio, Bruno

    2005-01-01

    Sphingomyelinases (SMases) hydrolyze the membrane constituent sphingomyelin (SM) to phosphocholine and ceramide (Cer). Growing evidence supports that SMase-induced SM-->Cer conversion leads to the formation of lateral Cer-enriched domains which drive structural reorganization in lipid membranes. We previously provided visual evidence in real-time for the formation of Cer-enriched domains in SM monolayers through the action of the neutral Bacillus cereus SMase. In this work, we disclose a succession of discrete morphologic transitions and lateral organization of Cer-enriched domains that underlay the SMase-generated surface topography. We further reveal how these structural parameters couple to the generation of two-dimensional electrostatic fields, based upon the specific orientation of the lipid dipole moments in the Cer-enriched domains. Advanced image processing routines in combination with time-resolved epifluorescence microscopy on Langmuir monolayers revealed: 1), spontaneous nucleation and circular growth of Cer-enriched domains after injection of SMase into the subphase of the SM monolayer; 2), domain-intrinsic discrete transitions from circular to periodically undulating shapes followed by a second transition toward increasingly branched morphologies; 3), lateral superstructure organization into predominantly hexagonal domain lattices; 4), formation of super-superstructures by the hexagonal lattices; and 5), rotationally and laterally coupled domain movement before domain border contact. All patterns proved to be specific for the SMase-driven system since they could not be observed with Cer-enriched domains generated by defined mixtures of SM/Cer in enzyme-free monolayers at the same surface pressure (pi = 10 mN/m). Following the theories of lateral shape transitions, dipolar electrostatic interactions of lipid domains, and direct determinations of the monolayer dipole potential, our data show that SMase induces a domain-specific packing and orientation of

  16. Random lattice structures. Modelling, manufacture and FEA of their mechanical response

    NASA Astrophysics Data System (ADS)

    Malians, G.; Sarafis, I. T.; Lazaridis, T.; Varoutoglou, A.; Tsakataras, G.

    2016-11-01

    The implementation of lightweight structures in various applications, especially in Aerospace/ Automotive industries and Orthopaedics, has become a necessity due to their exceptional mechanical properties with respect to reduced weight. In this work we present a Voronoi tessellation based algorithm, which has been developed for modelling stochastic lattice structures. With the proposed algorithm, is possible to generate CAD geometry with controllable structural parameters, such as porosity, cell number and strut thickness. The digital structures were transformed into physical objects through the combination of 3D printing technics and investment casting. This process was applied to check the mechanical behaviour of generated digital models. Until now, the only way to materialize such structures into physical objects, was feasible through 3D printing methods such as Selective Laser Sintering/ Melting (SLS/ SLM). Investment casting possesses numerous advantages against SLS or SLA, with the major one being the material variety. On the other hand, several trials are required in order to calibrate the process parameters to have successful castings, which is the major drawback of investment casting. The manufactured specimens were subjected to compression tests, where their mechanical response was registered in the form of compressive load - displacement curves. Also, a finite element model was developed, using the specimens’ CAD data and compression test parameters. The FE assisted calculation of specimen plastic deformation is identical with the one of the physical object, which validates the conclusions drawn from the simulation results. As it was observed, strut contact is initiated when specimen deformation is approximately 5mm. Although FE calculated compressive force follows the same trend for the first 3mm of compression, then diverges because of the elasto-plastic FE model type definition and the occurred remeshing steps.

  17. 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.

  18. 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

  19. Building block organisation of clusters in amylopectin from different structural types.

    PubMed

    Bertoft, Eric; Koch, Kristine; Aman, Per

    2012-06-01

    Clusters of chains consisting of tightly branched units of building blocks were isolated from 10 amylopectin samples possessing the 4 types of amylopectin with different internal unit chain profiles previously described. It was shown that clusters in types 1 and 2 amylopectins are larger than in types 3 and 4, but the average cluster size did not correspond to the ratio of short to long chains of the amylopectins. The size-distribution of the building blocks, having one or several branches, possessed generally only small differences between samples. However, the length of the interblock segments followed the type of amylopectin structure, so that type 1 amylopectins had shortest and type 4 the longest segments. The chains in the clusters were divided into characteristic groups probably being involved in the interconnection of two, three, and four - or more - building blocks. Long chains were typically found in high amounts in clusters from type 4 amylopectins, however, all cluster samples contained long chains. The results are discussed in terms of the building block structure of amylopectin, in which the blocks together with the interblock segments participate in a branched backbone building up the amorphous lamellae inside growth rings of the starch granules. In such a model, amylopectins with proportionally less long chains (types 1 and 2) possess a more extensively branched backbone compared to those with more long chains (types 3 and 4).

  20. Role of solution structure in self-assembly of conjugated block copolymer thin films

    DOE PAGES

    Brady, Michael A.; Ku, Sung -Yu; Perez, Louis A.; ...

    2016-10-24

    Conjugated block copolymers provide a pathway to achieve thermally stable nanostructured thin films for organic solar cells. We characterized the structural evolution of poly(3-hexylthiophene)-block-poly(diketopyrrolopyrrole–terthiophene) (P3HT-b-DPPT-T) from solution to nanostructured thin films. Aggregation of the DPPT-T block of P3HT-b-DPPT-T was found in solution by small-angle X-ray scattering with the P3HT block remaining well-solvated. The nanostructure in thin films was determined using a combination of wide and small-angle X-ray scattering techniques as a function of processing conditions. The structure in solution controlled the initial nanostructure in spin-cast thin films, allowing subsequent thermal annealing processes to further improve the ordering. In contrast tomore » the results for thin films, nanostructural ordering was not observed in the bulk samples by small-angle X-ray scattering. Finally, these results suggest the importance of controlling solvent induced aggregation in forming nanostructured thin films of conjugated block copolymers.« less

  1. Role of solution structure in self-assembly of conjugated block copolymer thin films

    SciTech Connect

    Brady, Michael A.; Ku, Sung -Yu; Perez, Louis A.; Cochran, Justin E.; Schmidt, Kristin; Weiss, Thomas M.; Toney, Michael F.; Ade, Harald; Hexemer, Alexander; Wang, Cheng; Hawker, Craig J.; Kramer, Edward J.; Chabinyc, Michael L.

    2016-10-24

    Conjugated block copolymers provide a pathway to achieve thermally stable nanostructured thin films for organic solar cells. We characterized the structural evolution of poly(3-hexylthiophene)-block-poly(diketopyrrolopyrrole–terthiophene) (P3HT-b-DPPT-T) from solution to nanostructured thin films. Aggregation of the DPPT-T block of P3HT-b-DPPT-T was found in solution by small-angle X-ray scattering with the P3HT block remaining well-solvated. The nanostructure in thin films was determined using a combination of wide and small-angle X-ray scattering techniques as a function of processing conditions. The structure in solution controlled the initial nanostructure in spin-cast thin films, allowing subsequent thermal annealing processes to further improve the ordering. In contrast to the results for thin films, nanostructural ordering was not observed in the bulk samples by small-angle X-ray scattering. Finally, these results suggest the importance of controlling solvent induced aggregation in forming nanostructured thin films of conjugated block copolymers.

  2. 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…

  3. Optical properties, lattice dynamics, and structural phase transition in hexagonal 2 H -BaMn O3 single crystals

    NASA Astrophysics Data System (ADS)

    Stanislavchuk, T. N.; Litvinchuk, A. P.; Hu, Rongwei; Jeon, Young Hun; Ji, Sung Dae; Cheong, S.-W.; Sirenko, A. A.

    2015-10-01

    Optical properties and lattice dynamics of hexagonal 2 H -BaMn O3 single crystals are studied experimentally in a wide temperature range by means of rotating analyzer ellipsometry and Raman scattering. The magnitude of the direct electronic band gap is found to be Eg=3.2 eV . At room temperature the far-infrared (IR) ellipsometry spectra reveal six IR-active phonons; two of them are polarized along the c axis and four are polarized within the a-b plane. Seven phonon modes are identified in the Raman scattering experiments. Group theoretical mode analysis and complementary density functional theory lattice dynamics calculations are consistent with the 2 H -BaMn O3 structure belonging to the polar P 63m c space group at room temperature. All observed vibrational modes are assigned to specific eigenmodes of the lattice. The neutron diffraction measurements reveal a structural phase transition upon cooling below TC=130 ±5 K , which is accompanied by a lattice symmetry change from P 63m c to P 63c m . Simultaneously, at temperatures below TC several additional IR- and Raman-active modes are detected in experimental spectra. This confirms the occurrence of a structural transition, which is possibly associated with the appearance of electrical polarization along the c axis and a previously known tripling of the primitive cell volume at low temperatures.

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

    PubMed

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

    2015-03-28

    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/cm(3) 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-D3(atm) 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%.

  5. 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%.

  6. Interdependence of modulated dispersion and tissue structure in the mechanism of unidirectional block.

    PubMed

    Laurita, K R; Rosenbaum, D S

    2000-11-10

    We previously showed that a premature stimulus can significantly alter vulnerability to arrhythmias by modulating spatial gradients of ventricular repolarization (ie, modulated dispersion). However, it is not clear if such changes in arrhythmia vulnerability can be attributed to the formation of an electrophysiological substrate for unidirectional block and what the potential role is of tissue structure in this process. Therefore, the main objective of the present study was to examine the concomitant effect repolarization gradients and tissue structure have on unidirectional block. Optical action potentials were recorded from 128 ventricular sites (1 cm(2)) in 8 Langendorff-perfused guinea pig hearts. Propagation was confined to the epicardial surface using an endocardial cryoablation procedure, and a 12-mm barrier with a 1.5-mm isthmus was etched with a laser onto the epicardium. A premature stimulus (S2) was delivered over a range of S1S2 coupling intervals to modulate repolarization gradients in a predictable fashion. When a second premature stimulus (S3) was delivered from the center of the isthmus, the occurrence and orientation of unidirectional block were highly dependent on repolarization gradients created by the S2 beat. In this model, a local repolarization gradient of 3.2 ms/mm was required for unidirectional block at this isthmus. In addition, the formation of unidirectional block was critically dependent on the presence of the source-sink mismatch imposed by the isthmus. These results may explain how the interplay between spatial heterogeneities of repolarization and tissue structure form a substrate for unidirectional block and reentry.

  7. Thinned crustal structure and tectonic boundary of the Nansha Block, southern South China Sea

    NASA Astrophysics Data System (ADS)

    Dong, Miao; Wu, Shi-Guo; Zhang, Jian

    2016-12-01

    The southern South China Sea margin consists of the thinned crustal Nansha Block and a compressional collision zone. The Nansha Block's deep structure and tectonic evolution contains critical information about the South China Sea's rifting. Multiple geophysical data sets, including regional magnetic, gravity and reflection seismic data, reveal the deep structure and rifting processes. Curie point depth (CPD), estimated from magnetic anomalies using a windowed wavenumber-domain algorithm, enables us to image thermal structures. To derive a 3D Moho topography and crustal thickness model, we apply Oldenburg algorithm to the gravity anomaly, which was extracted from the observed free air gravity anomaly data after removing the gravity effect of density variations of sediments, and temperature and pressure variations of the lithospheric mantle. We found that the Moho depth (20 km) is shallower than the CPD (24 km) in the Northwest Borneo Trough, possibly caused by thinned crust, low heat flow and a low vertical geothermal gradient. The Nansha Block's northern boundary is a narrow continent-ocean transition zone constrained by magnetic anomalies, reflection seismic data, gravity anomalies and an interpretation of Moho depth (about 13 km). The block extends southward beneath a gravity-driven deformed sediment wedge caused by uplift on land after a collision, with a contribution from deep crustal flow. Its southwestern boundary is close to the Lupar Line defined by a significant negative reduction to the pole (RTP) of magnetic anomaly and short-length-scale variation in crustal thickness, increasing from 18 to 26 km.

  8. COMPARISON OF DOUBLE BEND AND TRIPLE BEND ACHROMATIC LATTICE STRUCTURES AND NSLS-II.

    SciTech Connect

    KRAMER, S.L.; KRINSKY, S.; BENGTSSON, J.

    2006-06-26

    The Double Bend Achromatic (DBA) and the Triple Bend Achromatic (TBA) lattice have been studied rather extensively for use for the NSLS-II storage ring. The advantage of the TBA compared to the DBA in terms of emittance per period is well known. However, the DBA has the advantage of greater number of ID straight sections for the users and maybe easier to tune the dispersive section for reduced chromatic sextupole strength. We present a comparison of these lattices based on optimization of the non-linear driving terms using high order achromatic cancellation of driving terms of the nonlinear lattice.

  9. 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

  10. Structural transitions of the vortex lattice in anisotropic superconductors and fingering instability of electron droplets in an inhomogeneous magnetic field

    NASA Astrophysics Data System (ADS)

    Klironomos, Alexios

    I present a derivation of the nondispersive elastic moduli for the vortex lattice within the anisotropic Ginzburg-Landau model. I derive an extension of the virial theorem for superconductivity for anisotropic superconductors, with the anisotropy arising from s-d mixing or an anisotropic Fermi surface. The structural transition from rhombic to square vortex lattice is studied within this model along with the effects of thermal fluctuations on the structural transition. The reentrant transition from square to rhombic vortex lattice for high fields and the instability with respect to rigid rotations of the vortex lattice, predicted by calculations within the nonlocal London model, are also present in the anisotropic Ginzburg-Landau model. I also study the fingering of an electron droplet in a special Quantum Hall regime, where electrostatic forces are weak. Performing Monte Carlo simulations I study the growth and fingering of the electron droplet in an inhomogeneous magnetic field as the number of electrons is increased. I expand on recent theoretical results and find excellent agreement between my simulations and the theoretical predictions.

  11. 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.

  12. 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.

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

    DOE PAGES

    Miiller, W.; Zaliznyak, I.; Wu, L. S.; ...

    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

  14. 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.

  15. 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.

  16. Lattice Monte Carlo Simulation Study Atomic Structure of Alnico 5-7 Permanent Magnets

    NASA Astrophysics Data System (ADS)

    Nguyen, Manh Cuong; Zhao, Xin; Wang, Cai-Zhuang; Ho, Kai-Ming

    2015-03-01

    The fluctuations and increases in price and the issues in supply recently of rare earth metals re-heated the sought for non-rare earth permanent magnets. Alnico permanent magnets have been considered as promising replacements for rare earth-based permanent magnets due to the superiors in the magnetic performance at high temperature and the abundances of the constituent elements. Using lattice Monte Carlo simulation in combination with cluster expansion method we study the atomic structure of alnico 5-7 permanent magnets. We observed the phase separation into FeCo-rich and NiAl-rich phases in alnico 5-7 at low temperature, which is consistent with experiment. The phase boundary between these two phases is quite sharp. Both FeCo-rich and NiAl-rich phases are in B2 ordering with Fe and Al sitting on ?-site and Ni and Co sitting on ?-site. The degree of order of NiAl-rich phase is quite higher than that of FeCo-rich phase and it decreases with temperature slower than that of FeCo-rich phase. We also observed a small and increasing with annealing temperature magnetic moment in NiAl-rich phase, implying that the magnetic properties of alnico 5-7 could be improved by lowering annealing temperature to diminish the magnetism in NiAl-rich phase.

  17. 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.

  18. 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.

  19. Magnetic structure and local lattice distortion in giant negative thermal expansion material Mn3Cu1-xGexN

    NASA Astrophysics Data System (ADS)

    Iikubo, S.; Kodama, K.; Takenaka, K.; Takagi, H.; Shamoto, S.

    2010-11-01

    Magnetic and local structures in an antiperovskite system, Mn3Cu1-xGexN, with a giant negative thermal expansion have been studied by neutron powder diffraction measurement. We discuss (1) an importance of an averaged cubic crystal structure and a ΓG5g antiferromagnetic spin structure for the large magneto-volume effect (MVE) in this itinerant electron system, (2) an unique role of a local lattice distortion well described by the low temperature tetragonal structure of Mn3GeN for the broadening of MVE.

  20. 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.

  1. 2-D Hierarchical Structure of a Block Copolymer and Bio-nanoparticle Composites

    NASA Astrophysics Data System (ADS)

    Shin, Dongseok; Lin, Yao; Wang, Qian; Russell, Thomas

    2007-03-01

    2-dimensional hierarchical structures were generated by combining two different self assembling systems; block copolymer and bio-nanoparticle. For this study, a block copolymer having a positively charged component, i.e. poly (styrene-b-N-methyl-4-vinylpyridinium iodide), was used. Thin film composites of this block copolymer and bio-nanoparticles were fabricated by adsorbing bio-particles on the polymer film and subsequently annealing the sample under the presence of solvent vapor. 2-dimensional hierarchical structures, where block copolymer chains microphase separated inside of discrete grains surrounded by bio-nanoparticles, were obtained with rod- like bio-particles (tobacco mosaic virus and M13 phage) as well as with spherical one (ferritin). The pH effect on the assembly of rod-like bio-particles and the morphology of composites was investigated. When the pH of the solution used for the adsorption of bio-particles was low, the bio-molecules aggregated and formed large bundles, while they were dispersed well at high pH. This difference was reflected in the morphology of the resultant complexes.

  2. 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.

  3. 15 CFR 50.40 - Fee structure for statistics for city blocks in the 1980 Census of Population and Housing.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... 15 Commerce and Foreign Trade 1 2010-01-01 2010-01-01 false Fee structure for statistics for city... SERVICES AND STUDIES BY THE BUREAU OF THE CENSUS § 50.40 Fee structure for statistics for city blocks in... for each city block, drawn from the subjects which are being covered on a 100-percent basis. For...

  4. First-principles study of structure, initial lattice expansion, and pressure-composition-temperature hysteresis for substituted LaNi5 and TiMn2 alloys

    NASA Astrophysics Data System (ADS)

    Wong, D. F.; Young, K.; Ng, K. Y. S.

    2016-12-01

    The c/a unit-cell aspect ratios of CaCu5-structured AB5 and C14 Laves phase AB2 metal hydride alloy families are generally correlated to pressure-concentration-temperature hysteresis and degree of alloy pulverization. Structures of substituted LaNi4 X and C14 Ti4Mn7 X compositions and their hydrides in the α-phase were calculated by first principles using density functional theory to look at the c/a ratio and its relationship to initial lattice expansion. Lattice expansion with respect to the lattice parameters and lattice volume in the α-phase hydrides were analyzed, and a general trend in lattice expansion in the direction of higher resistance to elastic deformation was observed to correlate well to the trends in hysteresis measured in AB5 and C14 AB2 type alloys. Lattice expansion is noted to induce microstrains within the crystal lattice, and the anisotropy in the LaNi4 X and Ti4Mn7 X alloys played a role in determining the direction of higher resistance to deformation. Lattice expansions both measured and calculated have been linked to capacity degradation measurements as well as to hysteresis (a measure of irreversible energy losses due to lattice plastic deformation), which may be related to the dislocations and defects formed during hydrogenation.

  5. Robust metastable skyrmions and their triangular-square lattice structural transition in a high-temperature chiral magnet

    NASA Astrophysics Data System (ADS)

    Karube, K.; White, J. S.; Reynolds, N.; Gavilano, J. L.; Oike, H.; Kikkawa, A.; Kagawa, F.; Tokunaga, Y.; Rønnow, H. M.; Tokura, Y.; Taguchi, Y.

    2016-12-01

    Skyrmions, topologically protected nanometric spin vortices, are being investigated extensively in various magnets. Among them, many structurally chiral cubic magnets host the triangular-lattice skyrmion crystal (SkX) as the thermodynamic equilibrium state. However, this state exists only in a narrow temperature and magnetic-field region just below the magnetic transition temperature Tc, while a helical or conical magnetic state prevails at lower temperatures. Here we describe that for a room-temperature skyrmion material, β-Mn-type Co 8Zn 8Mn 4, a field-cooling via the equilibrium SkX state can suppress the transition to the helical or conical state, instead realizing robust metastable SkX states that survive over a very wide temperature and magnetic-field region. Furthermore, the lattice form of the metastable SkX is found to undergo reversible transitions between a conventional triangular lattice and a novel square lattice upon varying the temperature and magnetic field. These findings exemplify the topological robustness of the once-created skyrmions, and establish metastable skyrmion phases as a fertile ground for technological applications.

  6. Spontaneous structural distortion of the metallic Shastry-Sutherland system Dy B4 by quadrupole-spin-lattice coupling

    NASA Astrophysics Data System (ADS)

    Sim, Hasung; Lee, Seongsu; Hong, Kun-Pyo; Jeong, Jaehong; Zhang, J. R.; Kamiyama, T.; Adroja, D. T.; Murray, C. A.; Thompson, S. P.; Iga, F.; Ji, S.; Khomskii, D.; Park, Je-Geun

    2016-11-01

    Dy B4 has a two-dimensional Shastry-Sutherland (Sh-S) lattice with strong Ising character of the Dy ions. Despite the intrinsic frustrations, it undergoes two successive transitions: a magnetic ordering at TN=20 K and a quadrupole ordering at TQ=12.5 K . From high-resolution neutron and synchrotron x-ray powder diffraction studies, we have obtained full structural information on this material in all phases and demonstrate that structural modifications occurring at quadrupolar transition lead to the lifting of frustrations inherent in the Sh-S model. Our paper thus provides a complete experimental picture of how the intrinsic frustration of the Sh-S lattice can be lifted by the coupling to quadrupole moments. We show that two other factors, i.e., strong spin-orbit coupling and long-range Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction in metallic Dy B4 , play an important role in this behavior.

  7. Investigation of the Geometry-Dependent Anisotropic Material Behavior of Filigree Struts in ALM-Produced Lattice Structures

    NASA Astrophysics Data System (ADS)

    Reinhart, Gunther; Teufelhart, Stefan; Riss, Fabian

    Additive Layer Manufacturing (ALM) shows a great potential for the production of lightweight designed components. The use of lattice structures is one of the most common approaches for lightweight design in ALM because they show a high stiffness and strength combined with a small mass. To reach an optimum design, these structures should not have a periodical build up, but have to be optimized concerning their course and the strut's diameters. For the load dependent adaption of the diameters, the material properties of such filigree structures have to be known well. This geometry-dependent, anisotropic material behavior is described in the following paper.

  8. A lattice Boltzmann-finite element model for two-dimensional fluid-structure interaction problems involving shallow waters

    NASA Astrophysics Data System (ADS)

    De Rosis, Alessandro

    2014-03-01

    In this paper, a numerical method for the modeling of shallow waters interacting with slender elastic structures is presented. The fluid domain is modeled through the lattice Boltzmann method, while the solid domain is idealized by corotational beam finite elements undergoing large displacements. Structure dynamics is predicted by using the time discontinuous Galerkin method and the fluid-structure interface conditions are handled by the Immersed Boundary method. An explicit coupling strategy to combine the adopted numerical methods is proposed and its effectiveness is tested by computing the error in terms of the energy that is artificially introduced at the fluid-solid interface.

  9. 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

  10. 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.

  11. 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

  12. 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.

  13. Application of Force and Energy Approaches to the Problem of a One-Dimensional, Fully Connected, Nonlinear-Spring Lattice Structure

    DTIC Science & Technology

    2015-09-01

    Nonlinear-Spring Lattice Structure by Steven B Segletes Approved for public release; distribution is unlimited. NOTICES Disclaimers The findings in this...of a One-Dimensional, Fully Connected, Nonlinear-Spring Lattice Structure by Steven B Segletes Weapons and Materials Research Directorate, ARL... Structure Steven B Segletes ARL-MR-0900 Approved for public release; distribution is unlimited. June 2015 AH80 U.S. Army Research Laboratory ATTN: RDRL-WMP-C

  14. Intersubband transition in lattice-matched BGaN/AlN quantum well structures with high absorption coefficients.

    PubMed

    Park, Seoung-Hwan; Ahn, Doyeol; Park, Chan-Yong

    2017-02-20

    Intersubband absorption properties of lattice-matched BGaN/AlN quantum well (QW) structures grown on AlN substrate are theoretically investigated using an effective mass theory considering the nonparabolicity of the conduction band. These results are compared with those of GaN/AlN QW structures. The intersubband absorption coefficient of the BGaN/AlN QW structure is shown to be enhanced significantly, compared to that of the conventional GaN/AlN QW structure. This can be explained by the fact that the BGaN/AlN QW structure exhibits larger intersuband dipole moment and quasi-Fermi-level separation than the GaN/AlN QW structure, due to the increase in the carrier confinement by a larger internal field. We expect that the BGaN/AlN QW structure with a high absorption coefficient can be used for telecommunication applications at 1.55 µm under the lattice-matched condition, instead of the conventional GaN/AlN QW structure with the large strain.

  15. 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.

  16. Structure optimization in a three-dimensional off-lattice protein model.

    PubMed

    Huang, Wenqi; Liu, Jingfa

    2006-06-05

    We studied a three-dimensional off-lattice AB model with two species of monomers, hydrophobic (A) and hydrophilic (B), and present two optimization algorithms: face-centered-cubic (FCC)-lattice pruned-enriched-Rosenbluth method (PERM) and subsequent conjugate gradient (PERM++) minimization and heuristic conjugate gradient (HCG) simulation based on "off-trap" strategy. In PERM++, we apply the PERM to the FCC-lattice to produce the initial conformation, and conjugate gradient minimization is then used to reach the minimum energy state. Both algorithms have been tested in the three-dimensional AB model for all sequences with lengths 13 < or = n < or = 55. The numerical results show that the proposed methods are very promising for finding the ground states of proteins. In several cases, we renew the putative ground states energy values.

  17. Modulation of the photonic band structure topology of a honeycomb lattice in an atomic vapor

    SciTech Connect

    Zhang, Yiqi; Liu, Xing; Belić, Milivoj R.; Wu, Zhenkun; Zhang, Yanpeng

    2015-12-15

    In an atomic vapor, a honeycomb lattice can be constructed by utilizing the three-beam interference method. In the method, the interference of the three beams splits the dressed energy level periodically, forming a periodic refractive index modulation with the honeycomb profile. The energy band topology of the honeycomb lattice can be modulated by frequency detunings, thereby affecting the appearance (and disappearance) of Dirac points and cones in the momentum space. This effect can be usefully exploited for the generation and manipulation of topological insulators.

  18. Self-assembled ferromagnetic and superparamagnetic structures of hybrid Fe block copolymers

    NASA Astrophysics Data System (ADS)

    Sarantopoulou, E.; Kovač, J.; Pispas, S.; Kobe, S.; Kollia, Z.; Cefalas, A. C.

    2008-10-01

    Self-assembled 2D structures on thin films of block copolymers/Fe hybrid materials were fabricated on Si/Ta substrates, either by wet chemistry or laser irradiation at 157 nm. The polymer exhibits micelle-like structures with average dimensions of 5-10 nm and 30-50 nm for light and chemically reduced films respectively. For the laser processed films, SQUID measurements reveal a ferromagnetic response at 5 K, and 100 Oe coercivity was obtained for 2:1 iron concentration. For chemically reduced films, on the other hand, a superparamagnetic response with near zero coercivity at 5 K was obtained.

  19. Structural requirements for voltage-dependent block of muscle sodium channels by phenol derivatives

    PubMed Central

    Haeseler, G; Piepenbrink, A; Bufler, J; Dengler, R; Aronson, J K; Piepenbrock, S; Leuwer, M

    2001-01-01

    We have studied the effects of four different phenol derivatives, with methyl and halogen substituents, on heterologously expressed human skeletal muscle sodium channels, in order to find structural determinants of blocking potency.All compounds blocked skeletal muscle sodium channels in a concentration-dependent manner. The methylated phenol 3-methylphenol and the halogenated phenol 4-chlorophenol blocked sodium currents on depolarization from −100 mV to 0 mV with IC50 values of 2161 and 666 μM respectively. Methylation of the halogenated compound further increased potency, reducing the IC50 to 268 μM in 2-methyl-4-chlorophenol and to 150 μM in 3,5-dimethyl-4-chlorophenol.Membrane depolarization before the test depolarization increased sodium channel blockade. When depolarizations were started from −70 mV or when a 2.5 s prepulse was introduced before the test pulse inducing slow inactivation, the IC50 was reduced more than 3 fold in all compounds. The values of KD for the fast-inactivated state derived from drug-induced shifts in steady-state availability curves were 14 μM for 3,5-dimethyl-4-chlorophenol, 19 μM for 2-methyl-4-chlorophenol, 26 μM for 4-chlorophenol and 115 μM for 3-methylphenol.All compounds accelerated the current decay during depolarization and slowed recovery from fast inactivation. No relevant frequency-dependent block after depolarizing pulses applied at 10, 50 and 100 Hz was detected for any of the compounds.All the phenol derivatives that we examined are effective blockers of skeletal muscle sodium channels, especially in conditions that are associated with membrane depolarization. Blocking potency is increased by halogenation and by methylation with increasing numbers of methyl groups. PMID:11309264

  20. Perforated Layer Structures in Liquid Crystalline Rod-coil Block Copolymers

    SciTech Connect

    Tenneti,K.; Chen, X.; Li, C.; Tu, Y.; Wan, X.; Zhou, Q.; Sics, I.; Hsiao, B.

    2005-01-01

    We report a novel observation of the tetragonal perforated layer structures in a series of rod-coil liquid crystalline block copolymers (BCPs), poly(styrene-block-(2, 5-bis[4-methoxyphenyl]oxycarbonyl)styrene) (PS-b-PMPCS). PMPCS forms rigid rods while PS forms the coil block. Differential scanning calorimetry (DSC), polarized light microscopy (PLM), small-angle X-ray scattering (SAXS), wide-angle X-ray diffraction (WAXD), and transmission electron microscopy (TEM) techniques were used to investigate these rod-coil molecules, and a perforated layer structure was observed at {sup fPMPCS} {approx} 0.37 in relatively low molecular weight (M{sub w}) samples and {approx}0.5 in high M{sub w} PS-b-PMPCS. This substantial phase boundary shift was attributed to the rod-coil nature of the BCP. The perforation obeys a tetragonal instead of hexagonal symmetry. The 'onset' of perforation was also observed in real space in sample PS{sub 272}-b-PMPCS{sub 93} ({sup fPMPCS} {approx} 0.52), in which few PS chains punctuate PMPCS layers. A slight increase in f{sub PS}, by blending with PS homopolymer, led to a dramatic change in the BCP morphology, and uniform tetragonal perforations were observed at {sup fPMPCS} {approx} 0.48.

  1. 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.

  2. 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.

  3. LeuT-desipramine structure reveals how antidepressants block neurotransmitter reuptake.

    PubMed

    Zhou, Zheng; Zhen, Juan; Karpowich, Nathan K; Goetz, Regina M; Law, Christopher J; Reith, Maarten E A; Wang, Da-Neng

    2007-09-07

    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.

  4. First principle investigation of crystal lattice structure, thermodynamics and mechanical properties in ZnZrAl2 intermetallic compound

    NASA Astrophysics Data System (ADS)

    Wei, Zhenyi; Tou, Shushi; Wu, Bo; Bai, Kewu

    2016-12-01

    ZnZrAl2 is a kind of heterogeneous nucleation to promote the refine of grain of ZA43 alloy. ZnZrAl2 intermetallic is also considered as a candidate for superalloys. The crystal lattice structure, alloy thermodynamics and mechanical properties of ZnZrAl2 intermetallic compound were investigated by ab initio calculations based on density functional theory (DFT). In particular, the site preference of atoms in different sublattices was predicted based on alloy thermodynamics. At ground state, the most stable structure is L12 structure with sublattice model (Zn)1a(Zr0.3333Al0.6667)3c or (Zr)1a(Zn0.3333Al0.6667)3c, and the occupying preferences of Zn, Zr and Al atoms are independent with the increasing temperature. The bulk, shear, Young's modulus and the Poisson's ratio of the L12 structure ZnZrAl2 were calculated based on the site occupying configurations. The results show that ZnZrAl2 is a brittle material in nature. Electronic structures analysis revealed that Al-Zr atoms possess a covalent bonding character, while the Zn-Zr atoms have a metallic bonding character. ZnZrAl2 has stable mechanical properties at high temperature. The grain refinement effect of ZnZrAl2 precipitates in Zn-Al alloys were discussed based on crystal lattice match theory.

  5. Mantle heat flow and thermal structure of the northern block of Southern Granulite Terrain, India

    NASA Astrophysics Data System (ADS)

    Manglik, Ajay

    2006-07-01

    Continental shield regions are normally characterized by low-to-moderate mantle heat flow. Archaean Dharwar craton of the Indian continental shield also follows the similar global pattern. However, some recent studies have inferred significantly higher mantle heat flow for the Proterozoic northern block of Southern Granulite Terrain (SGT) in the immediate vicinity of the Dharwar craton by assuming that the radiogenic elements depleted exposed granulites constitute the 45-km-thick crust. In this study, we use four-layered model of the crustal structure revealed by integrated geophysical studies along a geo-transect in this region to estimate the mantle heat flow. The results indicate that: (i) the mantle heat flow of the northern block of SGT is 17 ± 2 mW/m 2, supporting the global pattern, and (ii) the lateral variability of 10-12 mW/m 2 in the surface heat flow within the block is of crustal origin. In terms of temperature, the Moho beneath the eastern Salem-Namakkal region appears to be at 80-100 °C higher temperature than that beneath the western Avinashi region.

  6. Electrically and chemically tunable soft-solid block copolymer structural color (Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Park, Cheolmin

    2016-09-01

    1D photonic crystals based on the periodic stacking of two different dielectric layers have been widely studied due to their potential use in low-power reflective mode displays, e-books and sensors, 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 swollen block copolymer films. Placement of a polymer/ionic liquid (IL) film-reservoir adjacent to a self-assembled poly(styrene-block-quaternized 2vinyl pyridine) (PS-b-QP2VP) copolymer SC film allowed the development of R, G and 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 -3V to +6V using a metal/IL reservoir/SC film/IL reservoir/metal capacitor type device.

  7. 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

  8. Structure in Photon Maps and Time Series: A New Approach to Bayesian Blocks

    NASA Astrophysics Data System (ADS)

    Scargle, J. D.; Norris, J. P.

    2000-10-01

    The Bayesian Blocks algorithm finds the most probable piecewise constant ("blocky") representation for time series in the form of binned, time-tagged, or time-to-spill photon counting data. In (Scargle, 1998, ApJ 504, 405) the number of blocks was determined in an ad hoc iterative procedure. Another approach maximizes the posterior -- after marginalizing all parameters except the number of blocks -- computed with Markov Chain Monte Carlo methods. A new, better algorithm starts with the Voronoi tessellation of the individual events in an arbitrary dimensioned data space. (This generalization allows solution of problems such as detection of clusters in high dimensional parameter spaces, and identification of structures in images.) In successive steps, these many cells are merged to form fewer, larger ones. The decision to merge two cells or keep them apart is based on comparison of the corresponding posterior probabilities. Let P(N,V) be the posterior for a Poisson model of a volume of size V containing N events, a function easily calculated explicitly. Then cells j and k are merged if $P( Nj + Nk, Vj + Vk ) > P( Nj, Vj ) P( Nk, Vk )$ and kept separate otherwise. When this criterion favors the merging of no further cells computation halts. Local structures ("shots") in the variability of Cygnus X-1 and RXTE 1118+480 were detected in this way, using time-tagged photon data from the USA X-ray Telescope. Since no time bins are invoked, the full sub-millisecond time resolution of the USA instrument is maintained. The method contains no parameters other than those defining prior probability distributions, and therefor yields objective structure estimates. For image data, the cells need not be restricted to be simply connected, e.g. in order to treat background regions surrounding sources. Partly funded by the NASA Applied Information Systems Research Program.

  9. Fractal Nature of the Electronic Structure of a Penrose Tiling Lattice in a Magnetic Field

    NASA Astrophysics Data System (ADS)

    Hatakeyama, Tetsuo; Kamimura, Hiroshi

    1989-01-01

    The one-electron energy spectrum of a Penrose tiling lattice in a magnetic field is studied with a tight-binding Hamiltonian. We show the following remarkable results characteristic of a Penrose lattice. (1) The density of states in a magnetic field has a central peak with zero width at zero energy. It is shown that the zero-energy states correspond to the ring states in which wavefunction has nonvanishing amplitudes only at the sites circling the origin. (2) The magnetic field dependence of the energy spectrum shows a butterfly shape caused by Landau quantization. (3) The magnetic field dependence of the energy spectrum also shows a fractal nature. In particular it is characterized by two periods whose ratio is equal to the golden mean (1+\\sqrt{5})/2, and two periods comprising a Fibonacci sequence. We have clarified the origin of this fractal behavior of the energy spectrum analytically.

  10. Local Lattice Structure and Dopant Occupancy of Doped Lithium Niobate Crystals

    NASA Astrophysics Data System (ADS)

    Zhang, Zhigang; Xue, Dongfeng

    We present a systematic study of the local distortions produced upon doping metal ions to lithium niobate (LiNbO3, LN) single crystals. The impurity bond length can be predicted by a radial force constant model, when the dopant ions substitute for Li+ or Nb5+ ions in the LN crystallographic frame. From the viewpoint of constituent chemical bonds, the lattice energy can be described as the function of bond valence on the basis of Born-Haber cycle for the formation of an ionic oxide MmOn. The dopant occupancy in the LN matrix can be determined by comparing the deviation of its lattice energy in different locations at both Li+ and Nb5+ sites, on the basis of the bond length relaxation of impurity ions, which can agree well with the experiment results. The effect of impurity ions on the property modification of LN crystals is also discussed according to our calculated results.

  11. 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.

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

    DOE PAGES

    Rosen, Evelyn L.; Gilmore, Keith; Sawvel, April M.; ...

    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

  13. Extended structure design with simple molybdenum oxide building blocks and urea as a directing agent.

    PubMed

    Veen, Sandra J; Roy, Soumyajit; Filinchuk, Yaroslav; Chernyshov, Dmitry; Petukhov, Andrei V; Versluijs-Helder, Marjan; Broersma, Alfred; Soulimani, Fouad; Visser, Tom; Kegel, Willem K

    2008-08-04

    We report here a simple one-pot directed synthesis of an oxomolybdate urea composite in which elementary molybdenum oxide building blocks are linked together with the aid of urea. This type of directed material design resulted in large rod-like crystals of an inorganic-organic hybrid extended structure of {MoO 3(NH 2-CO-NH 2)} infinity consisting of right- and left-handed helical units. In the crystal structure urea acts both as a glue that links the inorganic molybdenum units into a helix and as a supramolecular linker for the stabilization of the crystal structure as a whole. This type of molecular topology resulted in an unexpectedly high thermal stability.

  14. 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

  15. SVM-PB-Pred: SVM based protein block prediction method using sequence profiles and secondary structures.

    PubMed

    Suresh, V; Parthasarathy, S

    2014-01-01

    We developed a support vector machine based web server called SVM-PB-Pred, to predict the Protein Block for any given amino acid sequence. The input features of SVM-PB-Pred include i) sequence profiles (PSSM) and ii) actual secondary structures (SS) from DSSP method or predicted secondary structures from NPS@ and GOR4 methods. There were three combined input features PSSM+SS(DSSP), PSSM+SS(NPS@) and PSSM+SS(GOR4) used to test and train the SVM models. Similarly, four datasets RS90, DB433, LI1264 and SP1577 were used to develop the SVM models. These four SVM models developed were tested using three different benchmarking tests namely; (i) self consistency, (ii) seven fold cross validation test and (iii) independent case test. The maximum possible prediction accuracy of ~70% was observed in self consistency test for the SVM models of both LI1264 and SP1577 datasets, where PSSM+SS(DSSP) input features was used to test. The prediction accuracies were reduced to ~53% for PSSM+SS(NPS@) and ~43% for PSSM+SS(GOR4) in independent case test, for the SVM models of above two same datasets. Using our method, it is possible to predict the protein block letters for any query protein sequence with ~53% accuracy, when the SP1577 dataset and predicted secondary structure from NPS@ server were used. The SVM-PB-Pred server can be freely accessed through http://bioinfo.bdu.ac.in/~svmpbpred.

  16. Structure, Stability, and Reorganization of 0.5 L0 Topography in Block Copolymer Thin Films.

    PubMed

    Maher, Michael J; Self, Jeffrey L; Stasiak, Pawel; Blachut, Gregory; Ellison, Christopher J; Matsen, Mark W; Bates, Christopher M; Willson, C Grant

    2016-11-22

    The structure, stability, and reorganization of lamella-forming block copolymer thin film surface topography ("islands" and "holes") were studied under boundary conditions driving the formation of 0.5 L0 thick structures at short thermal annealing times. Self-consistent field theory predicts that the presence of one perfectly neutral surface renders 0.5 L0 topography thermodynamically stable relative to 1 L0 thick features, in agreement with previous experimental observations. The calculated through-film structures match cross-sectional scanning electron micrographs, collectively demonstrating the pinning of edge dislocations at the neutral surface. Remarkably, near-neutral surface compositions exhibit 0.5 L0 topography metastability upon extended thermal treatment, slowly transitioning to 1 L0 islands or holes as evidenced by optical and atomic force microscopy. Surface restructuring is rationalized by invoking commensurability effects imposed by slightly preferential surfaces. The results described herein clarify the impact of interfacial interactions on block copolymer self-assembly and solidify an understanding of 0.5 L0 topography, which is frequently used to determine neutral surface compositions of considerable importance to contemporary technological applications.

  17. 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.

  18. 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.

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

    DOE PAGES

    Wofford, Joseph M.; Nie, Shu; Thürmer, Konrad; ...

    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

  20. 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.

  1. Pair correlations and structure factor of the J1-J2 square lattice Ising model in an external field

    NASA Astrophysics Data System (ADS)

    Guerrero, Alejandra I.; Stariolo, Daniel A.

    2017-01-01

    We compute the structure factor of the J1-J2 Ising model in an external field on the square lattice within the Cluster Variation Method. We use a four point plaquette approximation, which is the minimal one able to capture phases with broken orientational order in real space, like the recently reported Ising-nematic phase in the model. The analysis of different local maxima in the structure factor allows us to track the different phases and phase transitions against temperature and external field. Although the nematic susceptibility is not directly related to the structure factor, we show that because of the close relationship between the nematic order parameter and the structure factor, the latter shows unambiguous signatures of the presence of a nematic phase, in agreement with results from direct minimization of a variational free energy. The disorder variety of the model is identified and the possibility that the CVM four point approximation be exact on the disorder variety is discussed.

  2. Structure of Bergman-type W-TiZrNi approximants to quasicrystal, analyzed by lattice inversion method

    NASA Astrophysics Data System (ADS)

    Huang, H.; Meng, D. Q.; Lai, X. C.; Liu, T. W.; Long, Y.; Hu, Q. M.

    2014-08-01

    The combined interatomic pair potentials of TiZrNi, including Morse and Inversion Gaussian, are successfully built by the lattice inversion method. Some experimental controversies on atomic occupancies of sites 6-8 in W-TiZrNi are analyzed and settled with these inverted potentials. According to the characteristics of composition and site preference occupancy of W-TiZrNi, two stable structural models of W-TiZrNi are proposed and the possibilities are partly confirmed by experimental data. The stabilities of W-TiZrNi mostly result from the contribution of Zr atoms to the phonon densities of states in lower frequencies.

  3. Structural deformations of the cubic lattice of the Zn1 - x Fe x Se ( x = 0.001) crystal

    NASA Astrophysics Data System (ADS)

    Maksimov, V. I.; Dubinin, S. F.; Sokolov, V. I.; Parkhomenko, V. D.

    2012-07-01

    The structural state of a Zn1 - x Fe x Se ( x = 0.001) crystal has been studied using thermal neutron diffraction. The diffraction patterns of the cubic crystal have been found to contain diffuse scattering regions concentrated in the vicinity of the strong Bragg reflections. It has been shown that the diffuse scattering effects are due to local transverse displacements of the crystal lattice atoms, and these displacements are induced by iron ions that demonstrate the static Jahn-Teller effect of the tetragonal type in the ZnSe compound.

  4. 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.

  5. Structure and impact of atmospheric blocking over the Euro-Atlantic region in present-day and future simulations

    NASA Astrophysics Data System (ADS)

    Masato, G.; Woollings, T.; Hoskins, B. J.

    2014-02-01

    The spatial structure of winter atmospheric blocking and its impact on the surface temperatures are analyzed for the current climate and a strong CO2 emission scenario over the Euro-Atlantic sector, using four different global circulation models. The models perform very well in describing the spatial pattern of meteorological fields associated with blocking, despite the well-known negative bias associated with the European blocking frequency. While a slight increase in the frequency of the Atlantic blocking is observed for the future climate, the European blocking frequency remains unchanged, with a net eastward shift apparent for the European warm blocking events. Under enhanced CO2 forcing, Atlantic blocking is associated with reduced amplitudes for positive and negative anomalies both in the geopotential height at 500 hPa and in the surface temperature, in particular for the latter. The anomalies associated with the occurrence of the two types of European blocking (those dominated by warm and cold air masses) exhibit changed shapes and locations in both the geopotential height and surface temperature fields, with only the cold cases leading to severe cold weather conditions over Europe and most of the polar region. Moreover, the eastward shift and amplification of the anticyclone associated with the warm events in the future is found to generate strong positive surface temperature anomalies over the entire polar cap. As a whole, the results show a marked increase in the sensitivity of Arctic temperatures to blocking in the future.

  6. 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.

  7. Lamellar structure of block copolymer poly(oxyethylene-oxypropylene-oxyethylene) in xylene/water mixtures

    SciTech Connect

    Wu, G; Ying, Q.; Chu, B. )

    1994-09-26

    Synchrotron small angle X-ray scattering (SAXS) was used to study the supramolecular structure formed by a block copolymer, Pluronic L64 (PEO[sub 13]PPO[sub 30]PEO[sub 13]), in xylene/water mixtures. Lamellar structure was observed at very high polymer concentrations (e.g., C[degree] > 0.53 g/ml). The lamellar spacing was determined by the amount of solubilized water and the copolymer concentration, with the amount of water playing a more important role on the lamellar spacing than the copolymer concentration. The lamellar spacing was almost independent of temperature. However the scattering peak became broader with increasing temperature, implying that the micellar size became smaller. Experimental data could be fitted by the Teubner-Strey model, and the resulting periodicity was in good agreement with the lamellar spacing derived by using the Bragg equation.

  8. 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).

  9. Stratigraphy and structure of the Hopewell fault block, Newark basin, NJ: Climatic and structural controls on sedimentation

    SciTech Connect

    Jones, B.D.; Schlische, R.W. . Dept. of Geological Sciences)

    1993-03-01

    The Hopewell fault, which generally strikes northeast and dips to the southeast, is a predominantly normal fault with a dip separation of 2-3 km located in the Newark rift basin of New Jersey. In order to define the geometry of the Hopewell fault and its associated structures as well as the extent to which those structures influenced sedimentation, a 14-km-wide area of the Hopewell fault and it hanging wall block was mapped. The deposits in this area belong mostly to the middle part of the Late Triassic-age Passaic Formation and have been continuously cored in the Titusville and Rutgers drill sites. As seen in core and outcrop, the middle Passaic Formation consists predominantly of red mudstone and minor sandstone (playa lacustrine deposits) cyclically alternating with purple, gray and black shale (deeper-water lacustrine deposits). The cyclical alternations were produced by fluctuating lake levels driven by climatic changes with Milankovitch periodicities. The non-red units are traceable across much of the study area, and their distribution within the hanging wall block of the Hopewell fault reveals three well-defined synclines separated by poorly defined anticlines, all of which plunge gently to the northwest (toward the Hopewell fault). The amplitude of folding decreases away from the fault, suggesting that the folds may have been at least partially controlled by the Hopewell fault. Some of the gray units are not laterally continuous across the entire mapped area, and many display along-strike facies and color changes, suggesting structural control on sedimentation. Minor faults within the Hopewell fault block strike northerly and east-southeasterly; the relative motion along these faults is uncertain. The most prominent extensional joint set in the mapped area strikes 040[degree], while a secondary set strikes 010[degree].

  10. 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.

  11. Finite-temperature phase structure of lattice QCD with Wilson quark action

    SciTech Connect

    Aoki, S.; Ukawa, A.; Umemura, T.

    1996-02-01

    The long-standing issue of the nature of the critical line of lattice QCD with the Wilson quark action at finite temperatures, defined to be the line of vanishing pion screening mass, and its relation to the line of finite-temperature chiral transition is examined. Presented are both analytical and numerical evidence that the critical line forms a cusp at a finite gauge coupling, and that the line of chiral transition runs past the tip of the cusp without touching the critical line. Implications on the continuum limit and the flavor dependence of chiral transition are discussed. {copyright} {ital 1996 The American Physical Society.}

  12. Nonequilibrium steady states in contact: approximate thermodynamic structure and zeroth law for driven lattice gases.

    PubMed

    Pradhan, Punyabrata; Amann, Christian P; Seifert, Udo

    2010-10-08

    We explore driven lattice gases for the existence of an intensive thermodynamic variable which could determine "equilibration" between two nonequilibrium steady-state systems kept in weak contact. In simulations, we find that these systems satisfy surprisingly simple thermodynamic laws, such as the zeroth law and the fluctuation-response relation between the particle-number fluctuation and the corresponding susceptibility remarkably well. However, at higher densities, small but observable deviations from these laws occur due to nontrivial contact dynamics and the presence of long-range spatial correlations.

  13. 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

  14. Crustal and Mantle Structure of the Jalisco Block of western Mexico from Surface Wave Tomography

    NASA Astrophysics Data System (ADS)

    Wang, X.; Niu, F.; Ni, J.; Grand, S.

    2008-12-01

    How a subduction system evolves to a transform system is a fundamental question in plate tectonics and is still not well understood. It is believed that fragmentation of both the subducting and overriding plates is one of the key steps of the evolution. Such a process is occurring in the Rivera subduction zone of the western Mexico. In this region, the Rivera plate detached from the Cocos plate a few million years ago and is presently subducting beneath the Jalisco block, which is separating from the North American plate along the Colima graben and Tepic-Zacoalco Rift to the east and north, respectively. Seismic imaging of the velocity structure and boundaries of the Rivera-Cocos-Jalisco microplate system is thus essential to understanding the regional tectonics as well as the broad question of subduction-to-transform transition. Fifty broadband seismic stations were temporarily deployed between January 2006 and June 2007 to explore the geodynamic processes of this plate boundary region under the MARS (MApping the Rivera Subduction zone) project. Here we present preliminary results on the crustal and upper mantle structure of the Jalisco block based on the analysis of surface waves recorded by the seismic array. Phase velocities at periods from 5 to 35 s were measured by cross correlating continuous records of two-station pairs. High SNR (signal-to-noise ratio) Green's functions were obtained along 474 ray paths and were inverted to generate the phase velocity map of the region. There is a good agreement between the phase velocity maps and the regional tectonic structure. The strongest low velocity anomaly is located beneath the Colima volcano system and is shown in all period bands. The NS trending Colima graben and the NW trending Tepic-Zacoalco Rift are also featured by distinct low velocity lineaments. We also analyzed the fundamental mode Rayleigh waves of 116 teleseismic Mw>6 events in the 20-100s period bands using the two-plane wave method. The resulting

  15. 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.

  16. 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.

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

    DOE PAGES

    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

  18. Fine structure of the spectra of the Kondo lattice model: Two-site cellular dynamical mean-field theory study

    NASA Astrophysics Data System (ADS)

    Osolin, Žiga; Žitko, Rok

    2017-01-01

    We study the antiferromagnetic and paramagnetic Kondo insulator phases of the Kondo lattice model on the cubic lattice at half filling using the cellular dynamical mean-field theory (CDMFT) with the numerical renormalization group (NRG) as the impurity solver, focusing on the fine details of the spectral function and self-energy. We find that the nonlocal correlations increase the gap in both the antiferromagnetic and Kondo insulator phases and shrink the extent of the antiferromagnetic phase in the phase diagram but do not alter any properties qualitatively. The agreement between the numerical CDMFT results and those within a simple hybridization picture, which adequately describes the overall band structure of the system but neglects all effects on the inelastic-scattering processes, is similar to that of the single-site DMFT results; there are deviations that are responsible for the additional fine structure, in particular for the asymmetric spectral resonances or dips that become more pronounced in the strong-coupling regime close to the antiferromagnet-paramagnetic quantum phase transition. These features appear broader in the CDMFT mostly due to numerical artifacts linked to more aggressive state truncation required in the NRG.

  19. Root lattices and quasicrystals

    NASA Astrophysics Data System (ADS)

    Baake, M.; Joseph, D.; Kramer, P.; Schlottmann, M.

    1990-10-01

    It is shown that root lattices and their reciprocals might serve as the right pool for the construction of quasicrystalline structure models. All noncrystallographic symmetries observed so far are covered in minimal embedding with maximal symmetry.

  20. Root lattices and quasicrystals

    NASA Astrophysics Data System (ADS)

    Baake, M.; Joseph, D.; Kramer, P.; Schlottmann, M.

    1990-10-01

    It is shown how root lattices and their reciprocals might serve as the right pool for the construction of quasicrystalline structure models. All non-periodic symmetries observed so far are covered in minimal embedding with maximal symmetry.

  1. Jammed lattice sphere packings

    NASA Astrophysics Data System (ADS)

    Kallus, Yoav; Marcotte, Étienne; Torquato, Salvatore

    2013-12-01

    We generate and study an ensemble of isostatic jammed hard-sphere lattices. These lattices are obtained by compression of a periodic system with an adaptive unit cell containing a single sphere until the point of mechanical stability. We present detailed numerical data about the densities, pair correlations, force distributions, and structure factors of such lattices. We show that this model retains many of the crucial structural features of the classical hard-sphere model and propose it as a model for the jamming and glass transitions that enables exploration of much higher dimensions than are usually accessible.

  2. Structure and Mechanical Behavior of Elastomeric Multiblock Terpolymers Containing Glassy, Rubbery, and Semicrystalline Blocks

    SciTech Connect

    Zuo, Feng; Alfonzo, C. Guillermo; Bates, Frank S.

    2012-11-14

    Multiblock copolymers containing glassy poly(cyclohexylethylene) (C), rubbery poly(ethylene-alt-propylene) (P), and semicrystalline poly(ethylene) (E) were synthesized by sequential anionic polymerization of styrene, isoprene, and butadiene followed by catalytic hydrogenation. The resulting CECPCEC (denoted XPX) and CECP (XP) multiblock copolymers each contain 50 vol % of P and equal amounts of C and E. These materials have been studied by dynamic mechanical spectroscopy (DMS), transmission electron microscopy (TEM), small- and wide-angle X-ray scattering (SAXS and WAXS), differential scanning calorimetry (DSC), and tensile deformation to characterize the morphology, phase behavior, and mechanical properties. Microphase separation in these compounds is induced by crystallization of E and/or chemical incompatibility between the three blocks, leading to a new type of morphology which contains continuous region of P and continuous region of microphase-separated X, resulting in mechanically resilient materials. High molecular weight block copolymers microphase separate with two different length scales associated with segregation between C and E and X and P. These structural features produce a nonclassical scaling relationship for the C-E domain spacing, d {approx} N{sup 0.31}, where N is the degree of polymerization of CEC portion. The role of semicrystalline E domains during uniaxial deformation has been exposed with WAXS experiments, which support a two-step mechanism involving recoverable and nonrecoverable deformation to different extents. Strain hardening is observed in double-anchored XPX, but not in single-anchored XP, at large tensile strains.

  3. 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.

  4. 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.

  5. Structure of a mutant form of proliferating cell nuclear antigen that blocks translesion DNA synthesis †

    PubMed Central

    Freudenthal, Bret D.; Ramaswamy, S.; Hingorani, Manju M.; Washington, M. Todd

    2009-01-01

    Proliferating cell nuclear antigen (PCNA) is a homotrimeric protein that functions as a sliding clamp during DNA replication. Several mutant forms of PCNA that block translesion DNA synthesis have been identified in genetic studies in yeast. One such mutant protein (encoded by the rev6-1 allele) is a glycine to serine substitution at residue 178, located at the subunit interface of PCNA. To better understand how this substitution interferes with translesion synthesis, we have determined the X-ray crystal structure of the G178S PCNA mutant protein. This substitution has little effect on the structure of the domain in which the substitution occurs. Instead, significant, local structural changes are observed in the adjacent subunit. The most notable difference between mutant and wild-type structures is in a single, extended loop (comprising amino acid residues 105-110), which we call loop J. In the mutant protein structure, loop J adopts a very different conformation in which the atoms of the protein backbone have moved by as much as 6.5 Å from their positions in the wild-type structure. To better understand the functional consequences of this structural change, we have examined the ability of this mutant protein to stimulate nucleotide incorporation by DNA polymerase eta (pol η). Steady state kinetic studies show that while wild-type PCNA stimulates incorporation by pol η opposite an abasic site, the mutant PCNA protein actually inhibits incorporation opposite this DNA lesion. These results show that the position of loop J in PCNA plays an essential role in facilitating translesion synthesis. PMID:19053247

  6. 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.

  7. Structure and Degeneracy of Vortex Lattice Domains in Pure Superconducting Niobium: A Small-Angle Neutron Scattering Study

    SciTech Connect

    Laver, M.; Bowell, C.; Forgan, E. M.; Abrahamsen, A. B.; Fort, D.; Dewhurst, C. D.; Muhlbauer, S.; Christen, David K; Kohlbrecher, J.; Cubitt, R.; Ramos, S.

    2009-01-01

    High-purity niobium exhibits a surprisingly rich assortment of vortex lattice (VL) structures for fields applied parallel to a fourfold symmetry axis, with all observed VL phases made up of degenerate domains that spontaneously break some crystal symmetry. Yet a single regular hexagonal VL domain is observed at all temperatures and fields parallel to a threefold symmetry axis. We report a detailed investigation of the transition between these lush and barren VL landscapes, discovering new VL structures and phase transitions at high fields. We show that the number and relative population of VL domains is intrinsically tied to the underlying crystal symmetry. We discuss how subtle anisotropies of the crystal may generate the remarkable VLs observed.

  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. Dual variables for lattice gauge theories and the phase structure of Z (N) systems

    SciTech Connect

    Ukawa, A.; Windey, P.; Guth, A.H.

    1980-02-15

    The 't Hooft disorder parameters are constructed within the framework of SU(N) lattice gauge theories in three or four dimensions. It is found that these operators arise naturally from a duality transformation which is similar to the standard transformation for Z (N) gauge theories. To illustrate the behavior of dual variables in a simpler context, we study the Villain form of the Z (N) gauge system in three and four dimensions. The techniques include duality, strong-coupling expansions, and the electrodynamic representation. In four dimensions it is found that for N>N/sub c/ approx. = 4, the system possesses at least three phases: a strong-coupling phase with electric confinement, a weak-coupling phase with magnetic confinement, and an intermediate phase which resembles QED, with a massless photon and no confinement. We also study an SU(N) -Higgs system, which interpolates between the Z (N) and SU(N) systems.

  11. 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.

  12. Structural features important for the biological activity of the potassium channel blocking dendrotoxins.

    PubMed

    Hollecker, M; Marshall, D L; Harvey, A L

    1993-10-01

    1. Dendrotoxins from mamba snake venoms are small proteins that block neuronal K+ channels. In order to investigate structural features associated with their biological activity, partially folded versions of dendrotoxins I and K from black mamba (Dendroaspis polylepis) were prepared by selectively reducing one or more of their three S-S bonds. 2. The modified toxins were tested for ability to compete with 125I-labelled native toxin I to high affinity binding sites on rat brain synaptosomal membranes and for the ability to increase acetylcholine release in a neuromuscular preparation. 3. Binding affinity increased progressively as the toxins folded to the native conformation and the most biologically active of the modified species were those in which only the disulphide bond between residues 14 and 38 was not formed. These intermediates had native-like conformations as determined by circular dichroism but still had about 5-10 times lower affinity than native toxins. 4. Addition of negatively charged groups to block the free sulthydryls at positions 14 and 38 caused a further, marked loss of activity. 5. The results are consistent with the existence of two important regions in the dendrotoxin molecules. The region containing two of the disulphide bonds (around Cys5-Cys55 and Cys30-Cys51) and much of the secondary structure is essential for the binding affinity of the toxins, while the region around Cys14 and Cys38, equivalent to part of the antiprotease site of the homologous protease inhibitor from bovine pancreas (BPTI), plays an important role in the potency of dendrotoxins.

  13. FaCSI: A block parallel preconditioner for fluid-structure interaction in hemodynamics

    NASA Astrophysics Data System (ADS)

    Deparis, Simone; Forti, Davide; Grandperrin, Gwenol; Quarteroni, Alfio

    2016-12-01

    Modeling Fluid-Structure Interaction (FSI) in the vascular system is mandatory to reliably compute mechanical indicators in vessels undergoing large deformations. In order to cope with the computational complexity of the coupled 3D FSI problem after discretizations in space and time, a parallel solution is often mandatory. In this paper we propose a new block parallel preconditioner for the coupled linearized FSI system obtained after space and time discretization. We name it FaCSI to indicate that it exploits the Factorized form of the linearized FSI matrix, the use of static Condensation to formally eliminate the interface degrees of freedom of the fluid equations, and the use of a SIMPLE preconditioner for saddle-point problems. FaCSI is built upon a block Gauss-Seidel factorization of the FSI Jacobian matrix and it uses ad-hoc preconditioners for each physical component of the coupled problem, namely the fluid, the structure and the geometry. In the fluid subproblem, after operating static condensation of the interface fluid variables, we use a SIMPLE preconditioner on the reduced fluid matrix. Moreover, to efficiently deal with a large number of processes, FaCSI exploits efficient single field preconditioners, e.g., based on domain decomposition or the multigrid method. We measure the parallel performances of FaCSI on a benchmark cylindrical geometry and on a problem of physiological interest, namely the blood flow through a patient-specific femoropopliteal bypass. We analyze the dependence of the number of linear solver iterations on the cores count (scalability of the preconditioner) and on the mesh size (optimality).

  14. Lightweight Structures

    NASA Technical Reports Server (NTRS)

    Whittenberger, J. Daniel

    2001-01-01

    Present structural concepts for hot static structures are conventional "sheet & stringer" or truss core construction. More weight-efficient concepts such as honeycomb and lattice block are being investigated, in combination with both conventional superalloys and TiAl. Development efforts for components made from TiAl sheet are centered on lower cost methods for sheet and foil production, plus alloy development for higher temperature capability. A low-cost casting technology recently developed for aluminum and steel lattice blocks has demonstrated the required higher strength and stiffness, with weight efficiency approach- ing honeycombs. The current effort is based on extending the temperature capability by developing lattice block materials made from IN-718 and Mar-M247.

  15. Surface structure and lattice dynamics of KI(001) studied by high-resolution ion scattering combined with molecular dynamics simulation

    NASA Astrophysics Data System (ADS)

    Okazawa, T.; Nishimura, T.; Kido, Y.

    2002-09-01

    The rumpled surface structure and thermal lattice vibrations of KI(001) were studied by high-resolution medium-energy ion scattering (MEIS) and molecular dynamics (MD) simulation. The relaxation of the interlayer distance between the top and second layer and the rumpling of the top and second layers were measured directly by MEIS with an accuracy of 0.01 Å. From the displaced lattice positions determined above, we derived the dipole moments of the top- and second-layer K+ and I- ions self-consistently using the polalizabilities estimated from the optical refractive index combined with the Clausius-Mossotti relation. The balance between a short-range force and a long-range Coulombic one made it possible to judge the applicability of the short-range pair potentials proposed so far. We also determined the root-mean-square thermal vibration amplitudes of the bulk and top-layer ions together with the correlations between the top- and second-layer ions by means of the ion shadowing effect applied to various kinds of scattering geometries. The results obtained were compared with those calculated from the MD simulations based on a semiclassical model using the dipole moments determined above and a Born-Mayer- or Hellmann-type pair potential. The present results are in overall agreement with the MD simulations employing the pair potential proposed by Catlow et al. [J. Phys. C 10, 1395 (1977)].

  16. Structural Influence on Superatomic Orbitals of Typical Gold Nanostructure Building Blocks

    NASA Astrophysics Data System (ADS)

    Jiang, Wanrun; Gao, Yang; Xu, Dexuan; Liu, Fang; Wang, Zhigang

    2016-10-01

    We compared superatomic orbitals mainly contributed by 6s atomic orbitals among spherical core-shell cluster Au13, hexagonal plane Au7 and a (5,5) nanotube segment Au35 through first-principles density functional theory calculations. The compatibility between geometry and orbital morphology influences both the presence and the energy level order of particular superatomic orbitals. Taking Au13 as a reference, which possesses a regular configuration of 1S 21P 61D 5, the hexagonal Au7 in 1S 21P 41D 1 lacks the 1P occupied superatomic orbital which is distributed out of the structural plane. Different from the nearly degenerated five occupied 1D orbitals in Au13, Au35 in 1S 21P 61D 101F 101G 61H 1 shows energy separations over 4.0 eV between split 1D regions and 1F regions according to the preference of tubular geometry to different orbital morphologies. The structural reliance of the electronic structure revealed by these typical building blocks might be informative for bottom-up design and fabrication of nanoscale devices based on a gold nanostructure and contributes to the variety and operability of nanoscale materials.

  17. 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.

  18. User manual for BUNVIS-RG: An exact buckling and vibration program for lattice structures, with repetitive geometry and substructuring options

    NASA Technical Reports Server (NTRS)

    Anderson, M. S.; Warnaar, D. B.; Ling, B. J. AEHERSTROM, C. l. afkennedy, d

    1986-01-01

    A computer program is described which is especially suited for making vibration and buckling calculations for prestressed lattice structures that might be used for space application. Structures having repetitive geometry are treated in a very efficient manner. Detailed instructions for data input are given along with several example problems illustrating the use and capability of the program.

  19. Electronic and lattice structures in SmFeAsO1-xFx probed by x-ray absorption spectroscopy

    NASA Astrophysics Data System (ADS)

    Zhang, C. J.; Oyanagi, H.; Sun, Z. H.; Kamihara, Y.; Hosono, H.

    2010-03-01

    Local lattice and electronic structures in the Fe-As layer of SmFeAsO1-xFx superconductors were studied by x-ray absorption spectroscopy, the FeK -edge and the AsK -edge extended x-ray absorption fine-structure, and x-ray absorption near-edge-structure experiments, respectively. Temperature-dependent local lattice distortions were observed in the Fe-As bond mean-square relative displacement of the superconducting samples. A strong coupling of the carrier-induced local lattice distortion (polaron) to the superconducting transition temperature in the oxypnictide superconductors is indicated. The near-edge spectra showed systematic temperature-dependent energy shifts, which indicate an intralayer electron redistribution from Fed states to Asp states due to orbital-selective band filling at low temperatures.

  20. 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.

  1. Quasicrystallography from Bn lattices

    NASA Astrophysics Data System (ADS)

    Koca, M.; Koca, N. O.; Al-Mukhaini, A.; Al-Qanabi, A.

    2014-11-01

    We present a group theoretical analysis of the hypercubic lattice described by the affine Coxeter-Weyl group Wa (Bn). An h-fold symmetric quasicrystal structure follows from the hyperqubic lattice whose point group is described by the Coxeter-Weyl group W (Bn) with the Coxeter number h=2n. Higher dimensional cubic lattices are explicitly constructed for n = 4,5,6 by identifying their rank-3 Coxeter subgroups and maximal dihedral subgroups. Decomposition of their Voronoi cells under the respective rank-3 subgroups W (A3), W (H2)×W (A1) and W (H3)lead to the rhombic dodecahedron, rhombic icosahedron and rhombic triacontahedron respectively. Projection of the lattice B4 describes a quasicrystal structure with 8-fold symmetry. The B5 lattice leads to quasicrystals with both 5fold and 10 fold symmetries. The lattice B6 projects on a 12-fold symmetric quasicrystal as well as a 3D icosahedral quasicrystal depending on the choice of subspace of projections. The projected sets of lattice points are compatible with the available experimental data.

  2. Embedded atom computer simulation of lattice distortion and dislocation core structure and mobility in Fe-Cr alloys

    SciTech Connect

    Farkas, D.; Schon, C.G.; Lima, M.S.F. de; Goldenstein, H.

    1996-01-01

    The atomistic structure of dislocation cores of <111> screw dislocations in disordered Fe-Cr b.c.c. alloys was simulated using embedded atom method potentials and molecular statics computer simulation. The mixed Fe-Cr interatomic potentials used were derived by fitting to the thermodynamic data of the disordered system and the measured lattice parameter changes of Fe upon Cr additions. The potentials predict phase separation as the most stable configuration for the central region of the phase diagram. The next most stable situation is the disordered b.c.c. phase. The structure of the screw 1/2 <111> dislocation core was studied using atomistic computer simulation and an improved visualization method for the representation of the resulting structures. The structure of the dislocation core is different from that typical of 1/2 <111> dislocations in pure b.c.c. materials. The core structure in the alloy tends to lose the threefold symmetry seen in pure b.c.c. materials and the stress necessary to initiate dislocation motion increases with Cr content. The mobility of kinks in these screw dislocations was also simulated and it was found that while the critical stress for kink motion in pure Fe is extremely low, it increases significantly with the addition of Cr. The implications of these differences for mechanical behavior are discussed.

  3. 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

  4. Additive lattice kirigami.

    PubMed

    Castle, Toen; Sussman, Daniel M; Tanis, Michael; Kamien, Randall D

    2016-09-01

    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.

  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. PMID:27679822

  6. 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.

  7. Crystal Structure, Lattice Vibrations,and Superconductivity of LaO1-xFxBiS2

    SciTech Connect

    Lee, Jooseop; Stone, Matthew B; Huq, Ashfia; Yildrim, Tanner; Ehlers, Georg; Mizuguchi, Y; Miura, O; Takano, Y; Demura, S; Lee, Seung Hyun

    2013-01-01

    Neutron scattering measurements have been performed on polycrystalline samples of the newly discovered layered superconductor LaO0:5F0:5BiS2, and its nonsuperconducting parent compound LaOBiS2. The crystal structures and vibrational modes have been examined. Upon F-doping, while the lattice contracts signicantly along c and expands slightly along a, the buckling of the BiS2 plane remains almost the same. In the inelastic measurements, a large dierence in the high energy phonon modes was observed upon F substitution. Alternatively, the low energy modes remain almost unchanged between non-superconducting and superconducting states either by F- doping or by cooling through the transition temperature. Using density functional perturbation theory we identify the phonon modes, and estimate the phonon density of states. We compare these calculations to the current measurements and other theoretical studies of this new superconducting material.

  8. Core-shell structured square mixed-spin 1 and 1/2 Ising nanowire on the Bethe lattice

    NASA Astrophysics Data System (ADS)

    Albayrak, Erhan

    2016-03-01

    The square Ising nanowire is constructed by adding square nanoparticles consisting of one spin-1 at the center and four spin-1/2 at the corners along a straight line in both directions. Therefore, this system may be taken to be equivalent to Bethe lattice of coordination number two and can be solved in terms of the exact recursion relations. This core-shell structured model is studied by using ferromagnetic exchange interactions between surface spins (Js), between core spins (Jc) and between surface and core spins (Jsc) and crystal field interaction (D) at the sites of spin-1. The phase diagrams of the model are obtained in terms of these parameters by varying the temperature on the possible planes. It is found that the model presents both second- and first-order phase transitions and tricritical points for the appropriate values of these parameters.

  9. 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.

  10. 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.

  11. Phyllotaxis of flux lattices in layered superconductors

    SciTech Connect

    Levitov, L.S. )

    1991-01-14

    The geometry of a flux lattice pinned by superconducting layers is studied. Under variation of magnetic field the lattice undergoes an infinite sequence of continuous transitions corresponding to different ways of selection of shortest distances. All possible lattices form a hierarchical structure identified as the hierarchy of Farey numbers. It is shown that dynamically accessible lattices are characterized by pairs of consecutive Fibonacci numbers.

  12. 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.

  13. 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.

  14. Enhancement of hydrogen storage capacity in hydrate lattices

    NASA Astrophysics Data System (ADS)

    Willow, Soohaeng Yoo; Xantheas, Sotiris S.

    2012-02-01

    First principles electronic structure calculations of the pentagonal dodecahedron (H2O)20 (D-cage) and tetrakaidecahedron (H2O)24 (T-cage), 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 faces of the larger T-cages. The presence of methane in the larger T-cages was found to block this release, therefore suggesting possible scenarios for the stabilization of these coated clathrate hydrates and the potential enhancement of their hydrogen storage capacity.

  15. Fabrication and characterisation of a fully auxetic 3D lattice structure via selective electron beam melting

    NASA Astrophysics Data System (ADS)

    Warmuth, Franziska; Osmanlic, Fuad; Adler, Lucas; Lodes, Matthias A.; Körner, Carolin

    2017-02-01

    A three-dimensional fully auxetic cellular structure with negative Poisson’s ratio is presented. Samples are fabricated from Ti6Al4V powder via selective electron beam melting. The influence of the strut thickness and the amplitude of the strut on the mechanical properties and the deformation behaviour of cellular structures is studied.

  16. 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.

  17. 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.

  18. Blocking anthrax lethal toxin at the protective antigen channel by using structure-inspired drug design.

    PubMed

    Karginov, Vladimir A; Nestorovich, Ekaterina M; Moayeri, Mahtab; Leppla, Stephen H; Bezrukov, Sergey M

    2005-10-18

    Bacillus anthracis secretes three polypeptides: protective antigen (PA), lethal factor (LF), and edema factor (EF), which interact at the surface of mammalian cells to form toxic complexes. LF and EF are enzymes that target substrates within the cytosol; PA provides a heptameric pore to facilitate LF and EF transport into the cytosol. Other than administration of antibiotics shortly after exposure, there is currently no approved effective treatment for inhalational anthrax. Here we demonstrate an approach to disabling the toxin: high-affinity blockage of the PA pore by a rationally designed low-molecular weight compound that prevents LF and EF entry into cells. Guided by the sevenfold symmetry and predominantly negative charge of the PA pore, we synthesized small cyclic molecules of sevenfold symmetry, beta-cyclodextrins chemically modified to add seven positive charges. By channel reconstitution and high-resolution conductance recording, we show that per-6-(3-aminopropylthio)-beta-cyclodextrin interacts strongly with the PA pore lumen, blocking PA-induced transport at subnanomolar concentrations (in 0.1 M KCl). The compound protected RAW 264.7 mouse macrophages from cytotoxicity of anthrax lethal toxin (= PA + LF). More importantly, it completely protected the highly susceptible Fischer F344 rats from lethal toxin. We anticipate that this approach will serve as the basis for a structure-directed drug discovery program to find new and effective treatments for anthrax.

  19. 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.

  20. 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.

  1. Investigation of defect structure of impurity-doped lithium niobate by combining thermodynamic constraints with lattice constant variations

    SciTech Connect

    Koyama, Chihiro; Nozawa, Jun Fujiwara, Kozo; Uda, Satoshi; Maeda, Kensaku

    2015-01-07

    The defect structures of impurity-doped congruent lithium niobates (c-LN) were determined for impurities with various valences, including divalent, trivalent, and tetravalent impurities, in a concentration range where antisite niobium (Nb{sub Li}) exists. On the basis of the “Li site vacancy model,” six kinds of defect structures in impurity-doped c-LN are possible. Using thermodynamic constraints, these can be narrowed down to two kinds. The first structure is that in which impurities, vacancies and Nb exist as defects in the Li site and no defects exist in the Nb site (structure A), described as ([Li{sub Li}] {sub 1-5x-jy}[Nb{sub Li}]{sub x}[M{sub Li}]{sub y}[V{sub Li}]{sub 4x+(j-1)y})[Nb{sub Nb}][O{sub O}] {sub 3} (V: vacancy, M: impurity, j: valence of impurity, x, y: compositional variable (≠0), Li/Nb = congruent ratio). ([Li{sub Li}{sup ×}] {sub 1-5x-2y}[Nb{sub Li}{sup ••••}]{sub x}[M{sub Li}{sup •}]{sub y}[V{sub Li}{sup ′}]{sub 4x+y})[Nb{sub Nb}{sup ×}][O{sub O}{sup ×}] {sub 3} is an example by the Kröger-Vink notation for divalent M. In the second structure, vacancies and Nb exist as defects in the Li site and impurities exist as defects in the Nb site (structure B), described as ([Li{sub Li}] {sub 1-5x-(j-5)y}[Nb{sub Li}]{sub x}[V{sub Li}]{sub 4x+(j-5)y})([Nb{sub Nb}] {sub 1-y}[M{sub Nb}]{sub y})[O{sub O}] {sub 3}. ([Li{sub Li}{sup ×}] {sub 1-5x+y}[Nb{sub Li}{sup ••••}]{sub x}[V{sub Li}{sup ′}]{sub 4x-y})([Nb{sub Nb}{sup ×}] {sub 1-y}[M{sub Nb}{sup ′}]{sub y})[O{sub O}{sup ×}] {sub 3} is an example for tetravalent M. Since the relationship between impurity concentration and lattice constants for structures A and B differs, the defect structures can be differentiated by analyzing lattice constant variations as a function of impurity concentration. The results show that the defect structure of divalent and trivalent impurity-doped c-LN is structure A and that of tetravalent impurity-doped c-LN is

  2. Mixing energy models in genetic algorithms for on-lattice protein structure prediction.

    PubMed

    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.

  3. 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

  4. Structure-property relationships of polyisobutylene- block-polyamide thermoplastic elastomers

    NASA Astrophysics Data System (ADS)

    Hooks, Edward T., Jr.

    Thermoplastic elastomers (TPEs) are a class of polymer fit for a wide variety of applications due to their customizability. In the synthesis of these types of materials, an elastically-performing polymer, deemed the "soft block," is combined with a stiffer "hard block" polymer, each of which can be selected based on their own specific properties in order to achieve desired material behavior in the final copolymer. Recently, the use of polyisobutylene as a soft block in combination with a polyamide hard block has been investigated for use in TPE synthesis. While the material showed some promising behavior, many properties were still below those of the commercially standard TPE material PebaxRTM. Polyisobutylene and polyamide samples of varying molecular weights and types were synthesized and combined in different ratios to form a variety of polyisobutylene-block-polyamide (PIB-PA) samples. Mechanical stirring as opposed to magnetic mixing and an increase in the soft block component of the copolymer were the most important adjustments made from previous PIB-PA syntheses. The effect of overall block length and the incorporation of a wider variety of polyamide (PA) types were also investigated. Mechanical stirring allowed for the achievement of higher molecular weights, and use of PA-6,6 as a hard block also produced a TPE with a markedly higher melting point than previously witnessed. Increasing the PIB content as well as using longer blocks of both precursors produced tougher copolymers, allowing them to undergo more mechanical deformation before failure as compared to previous PIB-PA formulations.

  5. Malakite: an automatic tool for characterisation of structure of reliable blocks in multiple alignments of protein sequences.

    PubMed

    Burkov, Boris; Nagaev, Boris; Spirin, Sergei; Alexeevski, Andrei

    2010-06-01

    It makes sense to speak of alignment of protein sequences only within the regions, where the sequences are related to each other. This simple consideration is often disregarded by programs of multiple alignment construction. A package for alignment analysis MAlAKiTE (Multiple Alignment Automatic Kinship Tiling Engine) is introduced. It aims to find the blocks of reliable alignment, which contain related regions only, within the whole alignment and allows for dealing with them. The validity of the detection of reliable blocks' was verified by comparison with structural data.

  6. Electronic structure, lattice dynamics, and magnetoelectric properties of double perovskite La2CuTiO6

    NASA Astrophysics Data System (ADS)

    Zinenko, V. I.; Pavlovskii, M. S.; Shinkorenko, A. S.

    2016-11-01

    The results of ab initio calculations of the electronic structure, vibrational properties, and the magnetoelectric effect in the La2CuTiO6 crystal with double perovskite structure are presented. The lattice dynamics calculation shows the presence of unstable modes in the phonon spectrum of the high-symmetry cubic phase with space group Fmoverline 3 m. Condensation of two most unstable modes belonging to the center and the boundary point X of the Brillouin zone leads to the formation of a nonpolar stable phase with space group P21/ n. The calculation taking into account spin polarization shows that the magnetic ground state is E*-type antiferromagnetic with doubled magnetic cell and with the two spin-up and two spin-down configuration of magnetic moments of copper ions along the [010] crystallographic direction. Such ordering of magnetic moments leads to polar space group and polarization formation. The polarization magnitude is estimated as 71 μC/m2.

  7. 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.

  8. Multilayer DNA Origami Packed on a Square Lattice

    PubMed Central

    Ke, Yonggang; Douglas, Shawn M.; Liu, Minghui; Sharma, Jaswinder; Cheng, Anchi; Leung, Albert; Liu, Yan; Shih, William M.; Yan, Hao

    2009-01-01

    Molecular self-assembly using DNA as a structural building block has proven to be an efficient route to the construction of nanoscale objects and arrays of increasing complexity. Using the remarkable “scaffolded DNA origami” strategy, Rothemund demonstrated that a long single-stranded DNA from a viral genome (M13) can be folded into a variety of custom two-dimensional (2D) shapes using hundreds of short synthetic DNA molecules as staple strands. More recently, we generalized a strategy to build custom-shaped, three-dimensional (3D) objects formed as pleated layers of helices constrained to a honeycomb lattice, with precisely controlled dimensions ranging from 10 to 100 nm. Here we describe a more compact design for 3D origami, with layers of helices packed on a square lattice, that can be folded successfully into structures of designed dimensions in a one-step annealing process, despite the increased density of DNA helices. A square lattice provides a more natural framework for designing rectangular structures, the option for a more densely packed architecture, and the ability to create surfaces that are more flat than is possible with the honeycomb lattice. Thus enabling the design and construction of custom 3D shapes from helices packed on a square lattice provides a general foundational advance for increasing the versatility and scope of DNA nanotechnology. PMID:19807088

  9. 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.

  10. 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.

  11. First principle calculation of structure and lattice dynamics of Lu2Si2O7

    NASA Astrophysics Data System (ADS)

    Nazipov, D. V.; Nikiforov, A. E.

    2016-12-01

    Ab initio calculations of crystal structure and Raman spectra has been performed for single crystal of lutetium pyrosilicate Lu2Si2O7. The types of fundamental vibrations, their frequencies and intensities in the Raman spectrum has been obtained for two polarizations. Calculations were made in the framework of density functional theory (DFT) with hybrid functionals. The isotopic substitution was calculated for all inequivalent ions in cell. The results in a good agreement with experimental data.

  12. Analysis of strategies to improve the directionality of square lattice band-edge photonic crystal structures.

    PubMed

    Hattori, Haroldo T; Schneider, Vitor M; Cazo, Rogério M; Barbosa, Carmem L

    2005-05-20

    Recently, photonic crystal band-edge structures have been analyzed in the literature. However, most devices that have been presented so far emit light in different directions. We present a modal analysis (no gain included) of a few schemes to improve the directionality of these devices, i.e., in such a way that light that exits from them will travel mainly in a certain direction, eventually coupling its energy to a wide waveguide.

  13. 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.

  14. Block-sparse reconstruction and imaging for Lamb wave structural health monitoring.

    PubMed

    Levine, Ross M; Michaels, Jennifer E

    2014-06-01

    A frequently investigated paradigm for monitoring the integrity of plate-like structures is a spatially-distributed array of piezoelectric transducers, with each array element capable of both transmitting and receiving ultrasonic guided waves. This configuration is relatively inexpensive and allows interrogation of defects from multiple directions over a relatively large area. Typically, full sets of pairwise transducer signals are acquired by exciting one transducer at a time in a round-robin fashion. Many algorithms that operate on such data use differential signals that are created by subtracting prerecorded baseline signals, leaving only signal differences introduced by scatterers. Analysis methods such as delay-and-sum imaging operate on these signals to detect and locate point-like defects, but such algorithms have limited performance and suffer when potential scatterers have high directionality or unknown phase-shifting behavior. Signal envelopes are commonly used to mitigate the effects of unknown phase shifts, but this further reduces performance. The blocksparse technique presented here uses a different principle to locate damage: each pixel is assumed to have a corresponding multidimensional linear scattering model, allowing any possible amplitude and phase shift for each transducer pair should a scatterer be present. By assuming that the differential signals are linear combinations of a sparse subset of these models, it is possible to split such signals into location-based components. Results are presented here for three experiments using aluminum and composite plates, each with a different type of scatterer. The scatterers in these images have smaller spot sizes than delay-and-sum imaging, and the images themselves have fewer artifacts. Although a propagation model is required, block-sparse imaging performs well even with a small number of transducers or without access to dispersion curves.

  15. Effect of doping and pressure on magnetism and lattice structure of iron-based superconductors

    NASA Astrophysics Data System (ADS)

    Johannes, M. D.; Mazin, I. I.; Parker, D. S.

    2010-07-01

    Using first-principles calculations, we analyze structural and magnetic trends as a function of charge doping and pressure in BaFe2As2 , and compare to experimentally established facts. We find that density-functional theory, while accurately reproducing the structural and magnetic ordering at ambient pressure, fails to reproduce some structural trends as pressure is increased. Most notably, the Fe-As bond length which is a gauge of the magnitude of the magnetic moment, μ , is rigid in experiment but soft in calculation, indicating residual local Coulomb interactions. By calculating the magnitude of the magnetic ordering energy, we show that the disruption of magnetic order as a function of pressure or doping can be qualitatively reproduced but that in calculation, it is achieved through diminishment of |μ| , and therefore likely does not reflect the same physics as detected in experiment. We also find that the strength of the stripe order as a function of doping is strongly site dependent: magnetism decreases monotonically with the number of electrons doped at the Fe site but increases monotonically with the number of electrons doped at the Ba site. Intraplanar magnetic ordering energy (the difference between checkerboard and stripe orderings) and interplanar coupling both follow a similar trend.

  16. Chromatin structural changes in synchronized cells blocked in early S phase by sequential use of isoleucine deprivation and hydroxyurea blockade

    SciTech Connect

    D'Anna, J.A.; Prentice, D.A.

    1983-01-01

    The authors have investigated the loss of histone H1 from chromatin and the structure of chromatin from Chinese hamster (line CHO) cells blocked in early S phase by sequential use of isoleucine deprivation G/sub 1/ block and 1 mM hydroxyurea (HU) blockade. Measurements of H1 content in the cell and histone turnover indicate that H1 is lost from the cell and that there is negligible replacement synthesis of H1 during the period of the S-phase block. As H1 is lost, chromatin appears to undergo structural change. After 10 h of HU block, the new deoxyribonucleic acid (DNA) and a portion of the old DNA have measured nucleosome repeat lengths (37/sup 0/C digestion). By 24 h of HU block, nearly all of the chromatin has assumed a pseudoimmature conformation in which the nucleosome cores appear to be more closely packed along the DNA chain, but the new DNA is slightly more resistant than old DNA to attack by micrococcal nuclease. Electrophoretic analysis of nucleoprotein particles produced by micrococcal nuclease digestion of nuclei indicates that: the distribution of mononucleosome species changes during Hu block and some mononucleosome species appear to be enriched in normally minor proteins which may determine the electrophoretic mobility of the nucleoprotein particles in agarose-acrylamide gels. The results raise the possibility that: during the early stages of replication (or prior to the passage of the replication fork), H1 is dissociated from initiated replicons and H1 does not reassociate in a concerted fashion with the H1-depleted chromatin until the replication fork has passed and, perhaps, a substantial portion of the replicon has been replicated.

  17. New data on the structure of the Kas Block in the basement of the West Siberian Plate

    NASA Astrophysics Data System (ADS)

    Kheraskova, T. N.; Kaplan, S. A.; Bubnov, V. P.; Galuev, V. I.

    2013-03-01

    A new concept concerning the structure and stages of evolution of the Kas Block of the West Siberian Plate is stated in this paper. The Kas Block is traditionally considered to be a subsided western margin of the Siberian Platform. The new concept is based on the results of the interpretation of the geophysical data recently obtained along the reference and regional profiles in this territory. The geological interpretation of the deep dynamic sections obtained by reprocessing of the CDP seismic reflection records has been performed for the first time. The structural features of the Kas Block, as well as the character of its junction with the Siberian Platform and the Paleozoic framework, are discussed. The tectonic scheme of the territory and the scheme of the pre-Late Devonian surface of the Kas Block have been compiled. The Baikalian age of the basement of the Kas Block is substantiated. The Salairian allochthonous ophiolite-basalt tectonic nappe is localized for the first time within the sedimentary cover of the Kas Block. The available information allowed us to reconstruct the development of the western margin of the Siberian continent in the Riphean and Early Paleozoic before and after the Baikalian Orogeny, respectively. The informational background of the geological and geophysical interpretation involves the results of the CDP seismic reflection profiling, including the deep dynamic seismic sections and parameters of the P-wave velocities along the reference 1-SB seismic line and the regional Vostok 10, 12, 15, and 16 seismic lines; the results of the deep seismic and magnetotelluric soundings; the gravity measurements; the magnetic exploration; and the new coherent physical geological models.

  18. Modelling of crystal structure of cis-1,2,3,6 and 3,4,5,6-tetrahydrophthalic anhydrides using lattice energy calculations.

    PubMed

    Fredj, A Ben; Day, G M

    2015-08-01

    Lattice energy calculations using a model potential were performed to model the crystal structures of cis-1,2,3,6- and 3,4,5,6-tetrahydrophthalic (THP) anhydrides. The optimized molecular models using the DFT method at the B3LYP/6-31G** level were found consistent with the available experimental evidence and allowed all differences observed in crystal packing between cis-1,2,3,6- and 3,4,5,6-THP anhydrides to be reproduced. Calculations provide evidence for the presence of dipole-dipole C=O⋯C=O intermolecular interactions and support the idea that the molecules distort from their ideal geometries, improving packing in both crystals. The search for minima in the lattice energy of both crystals amongst the more common space groups with Z' = 1, using a simulated annealing crystal structure prediction procedure followed by lattice energy minimization showed that the observed structure of 3,4,5,6-THP anhydride (Z' = 2) is the thermodynamically most stable, and allowed us to justify why 3,4,5,6-THP anhydride crystallizes in such a complex structure with 16 molecules in the unit cell. The computational model was successful in predicting the second observed form at 173 K for cis-1,2,3,6-THP anhydride as a polymorph, and could predict several hypothetical structures with Z' = 1 that appear competitive with the observed structures. The results of phonon estimates of zero point intermolecular vibrational energy and entropy suggest that crystal structures of cis-1,2,3,6-THP anhydride cannot be predicted solely on the basis of lattice energy; factors other than thermodynamics favor the observed structures.

  19. 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

  20. Structure and dynamics of the Lu2Si2O7 lattice: Ab initio calculation

    NASA Astrophysics Data System (ADS)

    Nazipov, D. V.; Nikiforov, A. E.

    2017-01-01

    The ab initio calculations have been carried out for the crystal structure and Raman spectrum of a single crystal of lutetium pyrosilicate Lu2Si2O7. The types of fundamental vibrations and their frequencies and intensities in the Raman spectrum for two polarizations of the crystal have been determined. The calculations have been performed within the framework of the density functional theory (DFT) using the hybrid functionals. The ions involved in the vibrations have been identified using the method of isotopic substitution. The results of the calculations are in good agreement with the experiment.

  1. Temperature effects on structural properties of pluronic P104 and F108 PEO-PPO-PEO block copolymer solutions

    SciTech Connect

    Alexandridis, P.; Nivaggioli, T.; Hatton, T.A.

    1995-05-01

    The effects of temperature on the micellization properties and the structure of the micelles for two poly(ethylene-oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide) (PEO-PPO-PEO) copolymers, having similar size hydrophobic (PPO) blocks and different size hydrophilic (PEO) blocks, are reported. Critical micellization concentration (CMC) and temperature (CMT) values for aqueous copolymer solutions were obtained from a dye solubilization method and corroborated with differential scanning calorimetry, surface tension, density, light scattering intensity, and fluorescence spectroscopy experiments; very good agreement among the different techniques is observed. The extraction of CMC and CMT values from the characteristic features of the data obtained from the various techniques is discussed. The hydrodynamic radii of the copolymer micelles, determined using dynamic light scattering, remained constant over the temperature range investigated; the polydispersity of the micelle size decreased with temperature. The micropolarity in aqueous copolymer solutions was probed as a function of temperature using the I{sub 1}/I{sub 3} intensity ratio of the pyrene vibrational fine structure recorded in fluorescence emission spectra. The decreasing values for the intensity ratio, following the formation of micelles, were considered to be a linear combination of the temperature effects on polarity observed in bulk PEO and PPO homopolymers, and in water. 59 refs., 10 figs., 2 tabs.

  2. Controlling the self-assembly structure of magnetic nanoparticles and amphiphilic block-copolymers: from micelles to vesicles.

    PubMed

    Hickey, Robert J; Haynes, Alyssa S; Kikkawa, James M; Park, So-Jung

    2011-02-09

    We report how to control the self-assembly of magnetic nanoparticles and a prototypical amphiphilic block-copolymer composed of poly(acrylic acid) and polystyrene (PAA-b-PS). Three distinct structures were obtained by controlling the solvent-nanoparticle and polymer-nanoparticle interactions: (1) polymersomes densely packed with nanoparticles (magneto-polymersomes), (2) core-shell type polymer assemblies where nanoparticles are radially arranged at the interface between the polymer core and the shell (magneto-core shell), and (3) polymer micelles where nanoparticles are homogeneously incorporated (magneto-micelles). Importantly, we show that the incorporation of nanoparticles drastically affects the self-assembly structure of block-copolymers by modifying the relative volume ratio between the hydrophobic block and the hydrophilic block. As a consequence, the self-assembly of micelle-forming block-copolymers typically produces magneto-polymersomes instead of magneto-micelles. On the other hand, vesicle-forming polymers tend to form magneto-micelles due to the solubilization of nanoparticles in polymer assemblies. The nanoparticle-polymer interaction also controls the nanoparticle arrangement in the polymer matrix. In N,N-dimethylformamide (DMF) where PS is not well-solvated, nanoparticles segregate from PS and form unique radial assemblies. In tetrahydrofuran (THF), which is a good solvent for both nanoparticles and PS, nanoparticles are homogeneously distributed in the polymer matrix. Furthermore, we demonstrated that the morphology of nanoparticle-encapsulating polymer assemblies significantly affects their magnetic relaxation properties, emphasizing the importance of the self-assembly structure and nanoparticle arrangement as well as the size of the assemblies.

  3. Lattice dynamics and electronic structure of cobalt-titanium spinel Co2TiO4

    NASA Astrophysics Data System (ADS)

    Prosnikov, M. A.; Molchanova, A. D.; Dubrovin, R. M.; Boldyrev, K. N.; Smirnov, A. N.; Davydov, V. Yu.; Balbashov, A. M.; Popova, M. N.; Pisarev, R. V.

    2016-12-01

    The results are presented on phonon excitations and the electronic structure of Co2TiO4 inverse spinel in which magnetically ordered cobalt ions Co2+ (3 d 7) are in equal amounts in tetrahedral and octahedral sublattices below T C = 56 K. Single crystals are studied using optical reflection and absorption in a wide spectral range, Raman scattering, and dielectric spectroscopy methods. The dynamics of infrared and Raman-active phonons are studied, and the features associated with disordering in tetrahedral sites are detected. The d-d electronic transitions recorded in the regions of 3800 and 6300 cm-1 confirm the coordination features of Co2+ ions. An increase in the permittivity in the temperature region below 130 K is detected.

  4. 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

  5. Static and dynamic analysis of periodic lattice structures with applications to acoustic cloaks of the pentamode type

    NASA Astrophysics Data System (ADS)

    Nagy, Adam Julius

    As a first step towards producing pentamode acoustic cloaks, so named for the type of elasticity required, periodic lattice structured materials are designed that mimic the acoustic properties of water. This material is termed Metal Water and is analyzed in detail. The requirements considered are matching of density and wave speed, this produces a type of metamaterial that couples acoustic wave energy from a background fluid into an elastic medium without reflection. General elastodynamic, scattering, and acoustic cloaking theories are reviewed. In application to scattering, a new method is developed for cylindrically layered elastic media, which combines impedance and matricant propagator matrices in a stable integration scheme. A variety of techniques are used to estimate and improve the homogenized material properties associated with Metal Water. Dispersion curves are found by the application of Bloch-Floquet theory where a new approach that utilizes Euler-Bernoulli beams is developed. Results are compared against finite element methods capable of more accurately determining homogenized properties. Several designs are proposed in two and three dimensions with detailed studies including dispersion curve analysis as well as statically determined properties.

  6. 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.

  7. Modified corrections for London forces in solid-state density functional theory calculations of structure and lattice dynamics of molecular crystals.

    PubMed

    King, Matthew D; Korter, Timothy M

    2012-06-28

    Dispersion forces are critical for defining the crystal structures and vibrational potentials of molecular crystals. It is, therefore, important to include corrections for these forces in periodic density functional theory (DFT) calculations of lattice vibrational frequencies. In this study, DFT was augmented with a correction term for London-type dispersion forces in the simulations of the structures and terahertz (THz) vibrational spectra of the dispersion-bound solids naphthalene and durene. The parameters of the correction term were modified to best reproduce the experimental crystal structures and THz spectra. It was found that the accurate reproduction of the lattice dimensions by adjusting the magnitude of the applied dispersion forces resulted in the highest-quality fit of the calculated vibrational modes with the observed THz absorptions. The method presented for the modification of the dispersion corrections provides a practical approach to accurately simulating the THz spectra of molecular crystals, accounting for inherent systematic errors imposed by computational and experimental factors.

  8. 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.

  9. 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.

  10. Anomalous lattice compression and magnetic ordering in CuO at high pressures: A structural study and first-principles calculations

    NASA Astrophysics Data System (ADS)

    Kozlenko, D. P.; DruŻbicki, K.; Kichanov, S. E.; Lukin, E. V.; Liermann, H.-P.; Glazyrin, K. V.; Savenko, B. N.

    2017-02-01

    The structural and magnetic properties of multiferroic CuO have been studied by means of neutron and x-ray powder diffraction at pressures up to 11 and 38 GPa, respectively, and by first-principles theoretical calculations. Anomalous lattice compression is observed, with enlargement of the lattice parameter a , reaching a maximum at P = 13 GPa , followed by its reduction at higher pressures. The lattice distortion of the monoclinic structure at high pressures is accompanied by a progressive change of the oxygen coordination around Cu atoms from the square fourfold towards the octahedral sixfold coordination. The pressure-induced evolution of the structural properties and electronic structure of CuO was successfully elucidated in the framework of full-electronic density functional theory calculations with range-separated HSE06, and meta-generalized gradient approximation hybrid M06 functionals. The antiferromagnetic (AFM) ground state with a propagation vector q = (0.5 , 0 , -0.5 ) remains stable in the studied pressure range. From the obtained structural parameters, the pressure dependencies of the principal superexchange magnetic interactions were analyzed, and the pressure behavior of the Néel temperature as well as the magnetic transition temperature from the intermediate incommensurate AFM multiferroic state to the commensurate AFM ground state were evaluated. The estimated upper limit of the Néel temperature at P = 38 GPa is about 260 K, not supporting the previously predicted existence of the multiferroic phase at room temperature and high pressure.

  11. Coherence and spectral weight transfer in the dynamic structure factor of cold lattice bosons

    NASA Astrophysics Data System (ADS)

    Zaleski, T. A.; Kopeć, T. K.

    2017-01-01

    Ultracold atoms have been used to create novel correlated quantum phases allowing to address many solid-state physics problems using the quasi-particle concept, which is the foundation of our understanding of many-body quantum systems. For bosons, the simplest kinds of excited states involve two particles and they are connected to the dynamic structure factor S (k , ω) , measured using Bragg spectroscopy, similarly to the angle-resolved photoemission spectroscopy (ARPES) in solid state physics - a major tool in the study of high-Tc cuprates. Calculation of S (k , ω) requires a significant numerical effort to determine multidimensional convolutions of momentum and frequency dependent constituents functions, which we achieve using parallelized fast Fourier transform. As a result, we are able to show that spectral weight transfer between low and high energies is an intrinsic property of the strongly correlated Bose system in close analogy to the doped Mott-Hubbard electronic insulator. Furthermore, the appearance of sharp coherence peaks in the superfluid phase of the cold bosons closely resembles the formation of sharply defined quasiparticle excitations below Tc in cuprates suggesting an intimate connection between the intrinsic nature of these seemingly different systems.

  12. A generalized diffraction approach to predict the coupling of interface structure and function with lattice displacements

    NASA Astrophysics Data System (ADS)

    Walker, F. J.; Reiner, J. W.; Kolpak, A. M.; Segal, Y.; Kumah, D.; Zhang, Z.; Ismail-Beigi, S.; Ahn, C. H.

    2010-03-01

    Abrupt changes in symmetry, bonding and structure strongly affect functional behavior at oxide-semiconductor interfaces. In this talk, we consider specific examples of crystalline BaO and SrTiO3 deposited on Si. Charge transfer at the interface between the oxide and semiconductor is found using synchrotron x-ray diffraction. This charge movement couples to optical modes in the BaO and SrTiO3 layers. This effect extends deep into the films because the polarization of the optical mode is not effectively screened in the insulating BaO and SrTiO3 layers. Differences in atomic displacements between the BaO and SrTiO3 thin films result in a polarization that alternates sign in the case of BaO, as opposed to a uniform polarization in SrTiO3. These differences impact on the electronic properties of the system, including how the semiconductor and oxide bands align.

  13. 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

  14. The Structure of the TANF Block Grant. Welfare Reform and Beyond. Policy Brief.

    ERIC Educational Resources Information Center

    Weaver, R. Kent

    The 1996 welfare reform legislation replaced the Aid to Families with Dependent Children (AFDC) program with a new Temporary Assistance for Needy Families (TANF) block grant. This new program has a fixed funding level that is not altered by inflation or economic cycles or caseload size. Individual states' shares are based on the amount they…

  15. 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.

  16. 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…

  17. Interaction of poloxamine block copolymers with lipid membranes: Role of copolymer structure and membrane cholesterol content.

    PubMed

    Sandez-Macho, Isabel; Casas, Matilde; Lage, Emilio V; Rial-Hermida, M Isabel; Concheiro, Angel; Alvarez-Lorenzo, Carmen

    2015-09-01

    Interactions of X-shaped poly(ethylene oxide)-poly(propylene oxide) (PEO-PPO) block copolymers with cell membranes were investigated recording the π-A isotherms of monolayer systems of dipalmitoylphosphatidylcholine (DPPC):cholesterol 100:0; 80:20 and 60:40 mol ratio and evaluating the capability of the copolymers to trigger haemolysis or to protect from haemolytic agents. Four varieties of poloxamine (Tetronic 904, 908, 1107 and 1307) were chosen in order to cover a wide range of EO and PO units contents and molecular weights, and compared to a variety of poloxamer (Pluronic P85). The π-A isotherms revealed that the greater the content in cholesterol, the stronger the interaction of the block copolymers with the lipids monolayer. The interactions were particularly relevant at low pressures and low lipid proportions, mimicking the conditions of damaged membranes. Relatively hydrophobic copolymers bearing short PEO blocks (e.g., T904 and P85) intercalated among the lipids expanding the surface area (ΔGexc) but not effectively sealing the pores. These varieties showed haemolytic behavior. Oppositely, highly hydrophilic copolymers bearing long PEO blocks (e.g., T908, T1107 and T1307) caused membrane contraction and outer leaflet sealing due to strong interactions of PEO with cholesterol and diamine core with phospholipids. These later varieties were not haemolytic and exerted a certain protective effect against spontaneous haemolysis for both intact erythrocytes and cholesterol-depleted erythrocytes.

  18. Lattice overview

    SciTech Connect

    Creutz, M.

    1984-01-01

    After reviewing some recent developments in supercomputer access, the author discusses a few areas where perturbation theory and lattice gauge simulations make contact. The author concludes with a brief discussion of a deterministic dynamics for the Ising model. This may be useful for numerical studies of nonequilibrium phenomena. 13 references.

  19. Playing with structures at the nanoscale: designing catalysts by manipulation of clusters and nanocrystals as building blocks.

    PubMed

    Cargnello, Matteo; Fornasiero, Paolo; Gorte, Raymond J

    2013-12-02

    The purpose of this Concept is to highlight some of the most recent and promising methods for the preparation of tailored catalysts by designing and preparing the component building blocks and by assembling them in a controlled fashion. We want to emphasize how rational design and synthesis of catalysts must be coupled to precise catalytic and structural characterization of the systems in an ideal feedback loop. New catalyst design and preparation techniques, dictated by information about the active sites that the specific application requires, are frequently available. The building blocks for developing these novel catalysts include colloidal methods for the preparation of uniform nanostructures, physical methods for rational assembly of the building blocks (Langmuir-Blodgett, liquid-air self-assembly), and development of rational interactions between the building blocks for enhanced activity of the assemblies. These methods, which apply techniques normally used in other fields of nanotechnology to catalysis, offer exciting opportunities to help improve currently available catalytic systems in terms of activity, stability and selectivity.

  20. 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.

  1. 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.

  2. 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.

  3. 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.

  4. Magnetic structure of the S =1/2 quasi-two-dimensional square-lattice Heisenberg antiferromagnet Sr2CuTeO6

    NASA Astrophysics Data System (ADS)

    Koga, Tomoyuki; Kurita, Nobuyuki; Avdeev, Maxim; Danilkin, Sergey; Sato, Taku J.; Tanaka, Hidekazu

    2016-02-01

    The magnetic structure of the double perovskite compound Sr2CuTeO6 was determined from neutron powder diffraction data. This material is magnetically described as an S =1 /2 quasi-two-dimensional square-lattice Heisenberg model with antiferromagnetic nearest-neighbor and next-nearest-neighbor interactions. Sr2CuTeO6 undergoes a magnetic phase transition at TN≃29 K. The spin structure below TN is Néel antiferromagnetic on the square lattice, which means that the nearest-neighbor interaction (J1) is stronger than the next-nearest-neighbor interaction (J2), in contrast to other isostructural compounds such as Ba2CuWO6 and Sr2CuWO6 , for which | J1|<| J2| is realized.

  5. Mechanically and structurally robust sulfonated block copolymer membranes for water purification applications

    NASA Astrophysics Data System (ADS)

    Yeo, J.; Kim, S. Y.; Kim, S.; Ryu, D. Y.; Kim, T.-H.; Park, M. J.

    2012-06-01

    The effective removal of ionic pollutants from contaminated water using negatively charged nanofiltration membranes is demonstrated. Block copolymers comprising polystyrene (PS) and partially hydrogenated polyisoprene (hPI) were synthesized by varying chain architectures. A one step procedure of cross-linking (hPI blocks) and sulfonation reactions (PS chains) was then carried out, which was revealed as an effective method to enhance mechanical integrity of membranes while hydrophilic sulfonated chains remain intact. In particular, the control of chain architecture allows us to create a synergetic effect on optimizing charge densities of the membrane, water permeability, and mechanical integrity under water purification conditions. The best performing membrane can almost completely (>99%) reject various divalent cations and also show NO3- rejection > 85% and Na+ rejection > 87%. Well defined nanostructures (tens of nanometers) as well as the periodically arranged water domains (a few nanometers) within hydrophilic phases of the hydrated membranes were confirmed by in situ neutron scattering experiments.

  6. Pluronic-P105 PEO-PPO-PEO block copolymer in aqueous urea solutions. Micelle formation, structure, and microenvironment

    SciTech Connect

    Alexandridis, P.; Athanassiou, V.; Hatton, T.A.

    1995-07-01

    The effects of urea on the micellization properties of a poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide) (PEO-PPO-PEO) copolymer (commercially available as Pluronic P105) and on the structure and microenvironment of the micelles are reported. Urea increased the critical micelle concentration (cmc) and critical micelle temperature (cmt) of the PEO-PPO-PEO copolymer; the effect of urea on the cmt was more pronounced at low copolymer concentrations and diminished at concentrations of nearly 2.5%. The surface activity and the partial specific volume of the block copolymer decreased with an increase in the urea concentration, whereas the hydrodynamic radii of the copolymer micelles, determined using dynamic light scattering, remained unaffected by the presence of 4 M urea in the solution. The micropolarity in copolymer solutions in urea/water was probed as a function of temperature using the I{sub 1}/I{sub 3} intensity ratio of the pyrene vibrational fine structure recorded in fluorescence emission spectra; a small decrease in the micropolarity of the micelle core was observed in the presence of urea. The microviscosity in the micelle interior, estimated from the intramolecular excimer fluorescence of the hydrophobic probe bis(1-pyrenylmethyl) ether (dipyme), also exhibited a small decrease with an increase in the urea concentration. 80 refs., 8 figs.

  7. On the efficiency of image completion methods for intra prediction in video coding with large block structures

    NASA Astrophysics Data System (ADS)

    Doshkov, Dimitar; Jottrand, Oscar; Wiegand, Thomas; Ndjiki-Nya, Patrick

    2013-02-01

    Intra prediction is a fundamental tool in video coding with hybrid block-based architecture. Recent investigations have shown that one of the most beneficial elements for a higher compression performance in high-resolution videos is the incorporation of larger block structures. Thus in this work, we investigate the performance of novel intra prediction modes based on different image completion techniques in a new video coding scheme with large block structures. Image completion methods exploit the fact that high frequency image regions yield high coding costs when using classical H.264/AVC prediction modes. This problem is tackled by investigating the incorporation of several intra predictors using the concept of Laplace partial differential equation (PDE), Least Square (LS) based linear prediction and the Auto Regressive model. A major aspect of this article is the evaluation of the coding performance in a qualitative (i.e. coding efficiency) manner. Experimental results show significant improvements in compression (up to 7.41 %) by integrating the LS-based linear intra prediction.

  8. Combining a popularity-productivity stochastic block model with a discriminative-content model for general structure detection

    NASA Astrophysics Data System (ADS)

    Chai, Bian-fang; Yu, Jian; Jia, Cai-yan; Yang, Tian-bao; Jiang, Ya-wen

    2013-07-01

    Latent community discovery that combines links and contents of a text-associated network has drawn more attention with the advance of social media. Most of the previous studies aim at detecting densely connected communities and are not able to identify general structures, e.g., bipartite structure. Several variants based on the stochastic block model are more flexible for exploring general structures by introducing link probabilities between communities. However, these variants cannot identify the degree distributions of real networks due to a lack of modeling of the differences among nodes, and they are not suitable for discovering communities in text-associated networks because they ignore the contents of nodes. In this paper, we propose a popularity-productivity stochastic block (PPSB) model by introducing two random variables, popularity and productivity, to model the differences among nodes in receiving links and producing links, respectively. This model has the flexibility of existing stochastic block models in discovering general community structures and inherits the richness of previous models that also exploit popularity and productivity in modeling the real scale-free networks with power law degree distributions. To incorporate the contents in text-associated networks, we propose a combined model which combines the PPSB model with a discriminative model that models the community memberships of nodes by their contents. We then develop expectation-maximization (EM) algorithms to infer the parameters in the two models. Experiments on synthetic and real networks have demonstrated that the proposed models can yield better performances than previous models, especially on networks with general structures.

  9. 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.

  10. Inelastic neutron scattering, lattice dynamics, and high-pressure phase stability of zircon-structured lanthanide orthophosphates

    SciTech Connect

    Bose, Preyoshi P.; Mittal, R; Chaplot, S L; Loong, C. K.; Boatner, Lynn A

    2010-01-01

    Inelastic neutron-scattering experiments and lattice-dynamical calculations are reported on a series of rareearth orthophosphates RPO4 R=Tm, Er, Ho, and Tb. The experimental phonon spectra for the compounds are in good agreement with our model calculations. The lattice-dynamical model is found useful for the calculation of various thermodynamic properties such as the lattice specific heat, thermal expansion, and equation of state of these compounds. The RPO4 compounds are known to transform to the scheelite body-centered tetragonal, I41 /a or monoclinic phase P21 /n at high pressures. Our calculations show that while the scheelite phase stabilizes at high pressure due to its lower volume, the monoclinic phase may occur as an intermediate phase depending on the ionic size of the R atom. The latter phase is stabilized at higher temperature at high pressure due to its high vibrational entropy. A pressure-temperature phase diagram is proposed.

  11. 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.

  12. The static structure and dynamics of cadmium sulfide nanoparticles within poly(styrene-block-isoprene) diblock copolymer melts

    DOE PAGES

    Jang, Woo -Sik; Koo, Peter; Bryson, Kyle; ...

    2015-12-20

    Here, the static structure and dynamic behavior of cadmium sulfide nanoparticles suspended in block copolymer matrix are investigated using transmission electron microscopy, small-angle X-ray scattering, and X-ray photon correlation spectroscopy. The transmission electron micro- scopy study shows that cadmium sulfide nanoparticles are preferentially segregated within the polyisoprene domain of a poly(styrene-block-isoprene) diblock copolymer. For the dynamics study, X-ray photon correlation spectroscopy captures the relaxation process of cadmium sulfide nanoparticles. The measured characteristic relaxation time reveals that the observed dynamics are hyperdiffusive. The characteristic velocity and corresponding activation energy, which are hallmarks of a hyperdiffusive system, are determined from the relationshipmore » between the characteristic relaxation time and the wavevector.« less

  13. The static structure and dynamics of cadmium sulfide nanoparticles within poly(styrene-block-isoprene) diblock copolymer melts

    SciTech Connect

    Jang, Woo -Sik; Koo, Peter; Bryson, Kyle; Narayanan, Suresh; Sandy, Alec R.; Russell, Thomas P.; Mochrie, Simon G.

    2015-12-20

    Here, the static structure and dynamic behavior of cadmium sulfide nanoparticles suspended in block copolymer matrix are investigated using transmission electron microscopy, small-angle X-ray scattering, and X-ray photon correlation spectroscopy. The transmission electron micro- scopy study shows that cadmium sulfide nanoparticles are preferentially segregated within the polyisoprene domain of a poly(styrene-block-isoprene) diblock copolymer. For the dynamics study, X-ray photon correlation spectroscopy captures the relaxation process of cadmium sulfide nanoparticles. The measured characteristic relaxation time reveals that the observed dynamics are hyperdiffusive. The characteristic velocity and corresponding activation energy, which are hallmarks of a hyperdiffusive system, are determined from the relationship between the characteristic relaxation time and the wavevector.

  14. Lattice fermions

    NASA Technical Reports Server (NTRS)

    Wilczek, Frank

    1987-01-01

    A simple heuristic proof of the Nielsen-Ninomaya theorem is given. A method is proposed whereby the multiplication of fermion species on a lattice is reduced to the minimal doubling, in any dimension, with retention of appropriate chiral symmetries. Also, it is suggested that use of spatially thinned fermion fields is likely to be a useful and appropriate approximation in QCD - in any case, it is a self-checking one.

  15. 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

  16. 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.

  17. Vibrational spectra and lattice thermal conductivity of kesterite-structured Cu2ZnSnS4 and Cu2ZnSnSe4

    NASA Astrophysics Data System (ADS)

    Skelton, Jonathan M.; Jackson, Adam J.; Dimitrievska, Mirjana; Wallace, Suzanne K.; Walsh, Aron

    2015-04-01

    Cu2ZnSnS4 (CZTS) is a promising material for photovoltaic and thermoelectric applications. Issues with quaternary semiconductors include chemical disorder (e.g., Cu-Zn antisites) and disproportionation into secondary phases (e.g., ZnS and Cu2SnS3). To provide a reference for the pure kesterite structure, we report the vibrational spectra—including both infra-red and Raman intensities—from lattice-dynamics calculations using first-principles force constants. Three-phonon interactions are used to estimate phonon lifetimes (spectral linewidths) and thermal conductivity. CZTS exhibits a remarkably low lattice thermal conductivity, competitive with high-performance thermoelectric materials. Transition from the sulfide to selenide (Cu2ZnSnSe4) results in softening of the phonon modes and an increase in phonon lifetimes.

  18. The structural defects and UV-VIS spectral characterization of TiO{sub 2} particles doped in the lattice with Cr{sup 3+} cations

    SciTech Connect

    Liu, Z.L.; Cui, Z.L.; Zhang, Z.K. . E-mail: zhangzk@public.qd.sd.cn

    2005-02-15

    Titania nanoparticles doped with Cr{sup 3+} (2% relative to molar quantity of titania) were prepared and examined by EDS, HRTEM, XRD, and UV-VIS analysis. HRTEM images showed the detailed atomic arrays and vacancy defects of the doped Titania nanocrystals and revealed that the implanted Cr element existed in titania mainly as Cr{sup 3+} ions which located at the lattice positions of Ti{sup 4+} ions. Compared with pure titania, the UV-VIS spectra of the Cr{sup 3+} doped titania show significantly increased absorbance in visible light region. This indicated that the presence of the Cr{sup 3+} ions affected the lattice structure of titania nanocrystals and plays an reformative role in spectral feature of titania.

  19. Long-Range Order of the Three-Sublattice Structure in theS=1 Heisenberg Antiferromagnet on a Spatially Anisotropic Triangular Lattice

    NASA Astrophysics Data System (ADS)

    Nakano, Hiroki; Todo, Synge; Sakai, Tôru

    2013-04-01

    We study the S=1 Heisenberg antiferromagnet on a spatially anisotropic triangular lattice by the numerical diagonalization method. We examine the stability of the long-range order of a three-sublattice structure observed in the isotropic system between the isotropic case and the case of isolated one-dimensional chains. It is found that the long-range-ordered ground state with this structure exists in the range of 0.7 \\simle J_2/J_1 \\le 1, where J_1 is the interaction amplitude along the chains and J_2 is the amplitude of other interactions.

  20. 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

  1. 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.

  2. Characterization of solution structure and its importance in thin film ordering of conjugated block copolymers for organic semiconductor devices

    NASA Astrophysics Data System (ADS)

    Brady, Michael; Ku, Sung-Yu; Cochran, Justin; Wang, Cheng; Hawker, Craig; Kramer, Edward; Chabinyc, Michael

    2014-03-01

    Fully conjugated diblock copolymers (CBCPs) form intriguing materials alternatives to polymer-small molecule blends for their control of mesoscopic order in low-cost organic semiconductor devices. In both bulk heterojunction (BHJ) photovoltaics, consisting of an interpenetrating network with high donor-acceptor interfacial area, and ambipolar transistors, the transport of charge carriers through continuous p- and n-type paths in thin films is a controlling factor in device performance. AFM, GIWAXS, NEXAFS spectroscopy, and RSoXS are used to probe the structure of films of CBCPs with a p-type P3HT block and an n-type DPP block. Thermal annealing in the P3HT melt after casting creates ordered domains with ~ 50 nm in-plane lamellar spacings, as confirmed with GISAXS and RSoXS. GIWAXS diffraction from the (h00) alkyl-stacking and (010) pi-stacking planes shows primarily edge-on orientation for crystals of both P3HT and DPP blocks. In addition, temperature-dependent solution SAXS and UV-Vis spectroscopy are used to probe the size and conformation of casting solution aggregates. Fibrillar DPP aggregates direct the crystallization of P3HT- b-DPP following film casting and enable the formation of wormlike domains after annealing and thus ideal morphologies for transport in organic devices.

  3. 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.

  4. Three-dimensional structure of kappa-conotoxin PVIIA, a novel potassium channel-blocking toxin from cone snails.

    PubMed

    Savarin, P; Guenneugues, M; Gilquin, B; Lamthanh, H; Gasparini, S; Zinn-Justin, S; Ménez, A

    1998-04-21

    kappa-Conotoxin PVIIA from the venom of Conus purpurascens is the first cone snail toxin that was described to block potassium channels. We synthesized chemically this toxin and showed that its disulfide bridge pattern is similar to those of omega- and delta-conotoxins. kappa-conotoxin competes with radioactive alpha-dendrotoxin for binding to rat brain synaptosomes, confirming its capacity to bind to potassium channels; however, it behaves as a weak competitor. The three-dimensional structure of kappa-conotoxin PVIIA, as elucidated by NMR spectroscopy and molecular modeling, comprises two large parallel loops stabilized by a triple-stranded antiparallel beta-sheet and three disulfide bridges. The overall fold of kappa-conotoxin is similar to that of calcium channel-blocking omega-conotoxins but differs from those of potassium channel-blocking toxins from sea anemones, scorpions, and snakes. Local topographies of kappa-conotoxin PVIIA that might account for its capacity to recognize Kv1-type potassium channels are discussed.

  5. 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.

  6. Structural and functional diversity among amyloid proteins: Agents of disease, building blocks of biology, and implications for molecular engineering.

    PubMed

    Bleem, Alissa; Daggett, Valerie

    2017-01-01

    Amyloids have long been associated with protein dysfunction and neurodegenerative diseases, but recent research has demonstrated that some organisms utilize the unique properties of the amyloid fold to create functional structures with important roles in biological processes. Additionally, new engineering approaches have taken advantage of amyloid structures for implementation in a wide variety of materials and devices. In this review, the role of amyloid in human disease is discussed and compared to the functional amyloids, which serve a largely structural purpose. We then consider the use of amyloid constructs in engineering applications, including their utility as building blocks for synthetic biology and molecular engineering. Biotechnol. Bioeng. 2017;114: 7-20. © 2016 Wiley Periodicals, Inc.

  7. 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.

  8. Gene structure variation in segmental duplication block C of human chromosome 7q 11.23 during primate evolution.

    PubMed

    Kim, Yun-Ji; Ahn, Kung; Gim, Jeong-An; Oh, Man Hwan; Han, Kyudong; Kim, Heui-Soo

    2015-12-01

    Segmental duplication, or low-copy repeat (LCR) event, occurs during primate evolution and is an important source of genomic diversity, including gain or loss of gene function. The human chromosome 7q 11.23 is related to the William-Beuren syndrome and contains large region-specific LCRs composed of blocks A, B, and C that have different copy numbers in humans and different primates. We analyzed the structure of POM121, NSUN5, FKBP6, and TRIM50 genes in the LCRs of block C. Based on computational analysis, POM121B created by a segmental duplication acquired a new exonic region, whereas NSUN5B (NSUN5C) showed structural variation by integration of HERV-K LTR after duplication from the original NSUN5 gene. The TRIM50 gene originally consists of seven exons, whereas the duplicated TRIM73 and TRIM74 genes present five exons because of homologous recombination-mediated deletion. In addition, independent duplication events of the FKBP6 gene generated two pseudogenes at different genomic locations. In summary, these clustered genes are created by segmental duplication, indicating that they show dynamic evolutionary events, leading to structure variation in the primate genome.

  9. 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).

  10. 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

  11. Structural differences between the western and eastern Qiongdongnan Basin: evidence of Indochina block extrusion and South China Sea seafloor spreading

    NASA Astrophysics Data System (ADS)

    Zhang, Cuimei; Wang, Zhenfeng; Sun, Zhipeng; Sun, Zhen; Liu, Jianbao; Wang, Zhangwen

    2013-12-01

    Located at the intersection between a NW-trending slip system and NE-trending rift system in the northern South China Sea, the Qiongdongnan Basin provides key clues for us to understand the proposed extrusion of the Indochina Block along with Red River Fault Zone and extensional margins. In this paper we for the first time systematically reveal the striking structural differences between the western and eastern sector of the Qiongdongnan Basin. Influenced by the NW-trending slip faults, the western Qiongdongnan Basin developed E-W-trending faults, and was subsequently inverted at 30-21 Ma. The eastern sector was dominated by faults with NE orientation before 30 Ma, and thereafter with various orientations from NE, to EW and NW during the period 30-21 Ma; rifting display composite symmetric graben instead of the composite half graben or asymmetric graben in the west. The deep and thermal structures in turn are invoked to account for such deformation differences. The lithosphere of the eastern Qiongdongnan Basin is very hot and thinned because of mantle upwelling and heating, composite symmetric grabens formed and the faults varied with the basal plate boundary. However, the Southern and Northern Uplift area and middle of the central depression is located on normal lithosphere and formed half grabens or simple grabens. The lithosphere in the western sector is transitional from very hot to normal. Eventually, the Paleogene tectonic development of the Qiongdongnan Basin may be summarized into three stages with dominating influences, the retreat of the West Pacific subduction zone (44-36 Ma), slow Indochina block extrusion together with slab-pull of the Proto-South China Sea (36-30 Ma), rapid Indochina block extrusion together with the South China Sea seafloor spreading (30-21 Ma).

  12. 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)

  13. Formation of undulated lamellar structure from ABC block terpolymer blends with different chain lengths

    NASA Astrophysics Data System (ADS)

    Matsushita, Yushu; Suzuki, Jiro; Izumi, Yuuki; Matsuoka, Kohei; Takahashi, Shuji; Aoyama, Yoshitaka; Mihira, Tomohiro; Takano, Atsushi

    2010-11-01

    The effect of molecular weight distribution of ABC linear terpolymers on the formation of periodic structures was investigated. Three poly(isoprene-b-styrene-b-2-vinylpridine) triblockterpolymers with molecular weights of 26k, 96k, and 150k were blended variously. Three-phase, four-layer lamellar structures were observed when polydispersity index (PDI) was low, but it has been found that simple lamellar structure with flat surface transforms into an undulated lamellar one, where two interfaces, i.e., I/S and S/P, are both undulated, and they are synchronizing each other if PDI exceeds the critical value. This new structure could be formed due to the periodic and "weak" localization of three chains along the domain interfaces, which produces periodic surfaces with nonconstant mean curvatures. With further increase of PDI, the blend macroscopically phase-separated into different microphase-separated structures.

  14. A first-principle study of the structural, elastic, lattice dynamical and thermodynamic properties of PrX (X=P, As)

    NASA Astrophysics Data System (ADS)

    Kocak, B.; Ciftci, Y. O.; Colakoglu, K.; Deligoz, E.

    2012-02-01

    The structural, phase transition, elastic, lattice dynamic and thermodynamic properties of rare-earth compounds PrP and PrAs with NaCl (B1), CsCl (B2), ZB (B3), WC (B h) and CuAu (L1 0) structures are investigated using the first principles calculations within the generalized gradient approximation (GGA). For the total-energy calculation, we have used the projected augmented plane-wave (PAW) implementation of the Vienna Ab-initio Simulation Package (VASP). Specifically, some basic physical parameters, e.g. lattice constants, bulk modulus, elastic constants, shear modulus, Young's modulus and Poison's ratio, are predicted. The obtained equilibrium structure parameters are in excellent agreement with the experimental and theoretical data. The temperature and pressure variations of the volume, bulk modulus, thermal expansion coefficient, heat capacity and Debye temperature are calculated in wide pressure and temperature ranges. The phonon dispersion curves and corresponding one-phonon density of states (DOS) for both compounds are also computed in the NaCl (B1) structure.

  15. BriX: a database of protein building blocks for structural analysis, modeling and design.

    PubMed

    Vanhee, Peter; Verschueren, Erik; Baeten, Lies; Stricher, Francois; Serrano, Luis; Rousseau, Frederic; Schymkowitz, Joost

    2011-01-01

    High-resolution structures of proteins remain the most valuable source for understanding their function in the cell and provide leads for drug design. Since the availability of sufficient protein structures to tackle complex problems such as modeling backbone moves or docking remains a problem, alternative approaches using small, recurrent protein fragments have been employed. Here we present two databases that provide a vast resource for implementing such fragment-based strategies. The BriX database contains fragments from over 7000 non-homologous proteins from the Astral collection, segmented in lengths from 4 to 14 residues and clustered according to structural similarity, summing up to a content of 2 million fragments per length. To overcome the lack of loops classified in BriX, we constructed the Loop BriX database of non-regular structure elements, clustered according to end-to-end distance between the regular residues flanking the loop. Both databases are available online (http://brix.crg.es) and can be accessed through a user-friendly web-interface. For high-throughput queries a web-based API is provided, as well as full database downloads. In addition, two exciting applications are provided as online services: (i) user-submitted structures can be covered on the fly with BriX classes, representing putative structural variation throughout the protein and (ii) gaps or low-confidence regions in these structures can be bridged with matching fragments.

  16. 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

  17. Predicting human preferences using the block structure of complex social networks.

    PubMed

    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.

  18. Chromatin structure is required to block transcription of the methylated herpes simplex virus thymidine kinase gene

    SciTech Connect

    Buschhausen, G.; Wittig, B.; Graessmann, M.; Graessmann, A.

    1987-03-01

    Inhibition of herpes simplex virus (HSV) thymidine kinase (TK) gene transcription (pHSV-106, pML-BPV-TK4) by DNA methylation is an indirect effect, which occurs with a latency period of approx. 8 hr microinjection of the DNA into TK/sup -/ rat 2 and mouse LTK/sup -/ cells. The authors have strong evidence that chromatin formation is critical for the transition of the injected DNA from methylation insensitivity to methylation sensitivity. Chromatin was reconstituted in vitro by using methylated and mock-methylated HSV TK DNA and purified chicken histone octamers. After microinjection, the methylated chromatin was always biologically inactive, as tested by autoradiography of the cells after incubation with (/sup 3/H)thymidine and by RNA dot blot analysis. However, in transformed cell lines, reactivation of the methylated chromatic occurred after treatment with 5-azacytidine. Furthermore, integration of the TK chromatin into the host genome is not required to block expression of the methylated TK gene. Mouse cells that contained the pML-BPV-TK4 chromatin permanently in an episomal state also did not support TK gene expression as long as the TK DNA remained methylated.

  19. 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.

  20. 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

  1. 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

  2. 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.

  3. Crustal-scale block tilting during Andean trench-parallel extension: Structural and geo-thermochronological insights

    NASA Astrophysics Data System (ADS)

    Noury, M.; Bernet, M.; Schildgen, T. F.; Simon-Labric, T.; Philippon, M.; Sempere, T.

    2016-09-01

    Despite a long history of plate convergence at the western margin of the South American plate that has been ongoing since at least the Early Paleozoic, the southern Peruvian fore-arc displays little to no evidence of shortening. In the light of this observation, we assess the deformation history of the southern Peruvian fore-arc and its geodynamic implications. To accomplish this, we present a new structural and geo-thermochronological data set (zircon U-Pb, mica 40Ar/39Ar, apatite and zircon fission-track and zircon (U-Th)/He analyses) for samples collected along a 400 km long transect parallel to the trench. Our results show that the Mesoproterozoic gneissic basement was mainly at temperatures ≤350°C since the Neoproterozoic and was later intruded by Jurassic volcanic arc plutons. Along the coast, a peculiar apatite fission-track age pattern, coupled with field observations and a synthesis of available geological maps, allows us to identify crustal-scale tilted blocks that span the coastal Peruvian fore-arc. These blocks, bounded by normal faults that are orthogonal to the trench, suggest post-60 Ma trench-parallel extension that potentially accommodated oroclinal bending in this region. Block tilting is consistent with the observed and previously described switch in the location of sedimentary sources in the fore-arc basin. Our data set allows us to estimate the cumulative slip on these faults to be less than 2 km and questions the large amount of trench-parallel extension suggested to have accommodated this bending.

  4. Two-dimensional electrostatic lattices for indirect excitons

    NASA Astrophysics Data System (ADS)

    Remeika, M.; Fogler, M. M.; Butov, L. V.; Hanson, M.; Gossard, A. C.

    2012-02-01

    We report on a method for the realization of two-dimensional electrostatic lattices for excitons using patterned interdigitated electrodes. Lattice structure is set by the electrode pattern and depth of the lattice potential is controlled by applied voltages. We demonstrate square, hexagonal, and honeycomb lattices created by this method.

  5. 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.

  6. Deep structures and surface boundaries among Proto-Tethyan micro-blocks: Constraints from seismic tomography and aeromagnetic anomalies in the Central China Orogen

    NASA Astrophysics Data System (ADS)

    Sun, Wenjun; Li, Sanzhong; Liu, Xin; Santosh, M.; Zhao, Shujuan; Guo, Lingli; Cao, Huahua; Yu, Shan; Dai, Liming; Zhang, Yong

    2015-09-01

    The Qinling-Qilian orogen preserves the records of Early Paleozoic convergence among the Proto-Tethyan micro-blocks. In this study, we analyze the seismic velocity structure and the aeromagnetic anomalies in the Qinling-Qilian orogen and its adjacent areas, showing that the northernmost boundaries of these Proto-Tethyan micro-blocks are defined by the Guyuan-Longshoushan Fault in the Qilian orogen and by the Luonan-Luanchuan Fault in the Qinling orogen, respectively. The lithosphere north of the Qinling-Qilian orogen subducted southward under the Qinling-Qilian orogen. The boundaries of the micro-blocks in the Qinling-Qilian orogen of the Proto-Tethys domain are mostly EW- or NE-trending. Combined with Early Paleozoic geological records, our results indicate that the south-dipping low-velocity anomaly under the Alxa block and the south-dipping high-velocity ones under the North Qilian orogen and the North China block might indicate that the Alxa block, the North Qilian Oceanic slab and the North China block subducted southward. The south-dipping high-velocity anomaly under the North Qilian orogen is interpreted as the remnant of the Proto-Tethys Ocean in that area. However, the north-dipping low-velocity anomaly under the South Qinling and the North Qinling orogens, the Qaidam block and the north-dipping high-velocity one under the Yangtze and the Bikou blocks suggest that the South Qinling and the North Qinling orogens, the Qaidam, the Yangtze and the Bikou blocks subducted northward. The present spatial framework of the Qinling-Qilian orogen is related to Early Paleozoic convergence among the Proto-Tethyan micro-blocks.

  7. Geometric requirements and examples of important structures in the assembly of square building blocks

    PubMed Central

    Eddaoudi, Mohamed; Kim, Jaheon; Vodak, David; Sudik, Andrea; Wachter, Joseph; O'Keeffe, Michael; Yaghi, Omar M.

    2002-01-01

    The basic structures for linking squares into polyhedra and networks (reticulation) are enumerated, and corresponding examples are described in which crystals were synthesized by linking paddle wheel (square) units into metal–organic frameworks (MOFs)—named MOF-102 to MOF-112. PMID:11959942

  8. 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

    2016-08-09

    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.

  9. 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".

  10. Band-edge electronic structure of β-In2S3: the role of s or p orbitals of atoms at different lattice positions.

    PubMed

    Zhao, Zongyan; Cao, Yuechan; Yi, Juan; He, Xijia; Ma, Chenshuo; Qiu, Jianbei

    2012-04-23

    As a promising solar-energy material, the electronic structure and optical properties of Beta phase indium sulfide (β-In(2)S(3)) are still not thoroughly understood. This paper devotes to solve these issues using density functional theory calculations. β-In(2)S(3) is found to be an indirect band gap semiconductor. The roles of its atoms at different lattice positions are not exactly identical because of the unique crystal structure. Additonally, a significant phenomenon of optical anisotropy was observed near the absorption edge. Owing to the low coordination numbers of the In3 and S2 atoms, the corresponding In3-5s states and S2-3p states are crucial for the composition of the band-edge electronic structure, leading to special optical properties and excellent optoelectronic performances.

  11. Reversal of the lattice structure in SrCoO(x) epitaxial thin films studied by real-time optical spectroscopy and first-principles calculations.

    PubMed

    Choi, Woo Seok; Jeen, Hyoungjeen; Lee, Jun Hee; Seo, S S Ambrose; Cooper, Valentino R; Rabe, Karin M; Lee, Ho Nyung

    2013-08-30

    Using real-time spectroscopic ellipsometry, we directly observed a reversible lattice and electronic structure evolution in SrCoO(x) (x=2.5-3) epitaxial thin films. Drastically different electronic ground states, which are extremely susceptible to the oxygen content x, are found in the two topotactic phases: i.e., the brownmillerite SrCoO2.5 and the perovskite SrCoO3. First-principles calculations confirmed substantial differences in the electronic structure, including a metal-insulator transition, which originate from the modification in the Co valence states and crystallographic structures. More interestingly, the two phases can be reversibly controlled by changing the ambient pressure at greatly reduced temperatures. Our finding provides an important pathway to understanding the novel oxygen-content-dependent phase transition uniquely found in multivalent transition metal oxides.

  12. 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

  13. 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

  14. 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.

  15. 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

  16. 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.

  17. 7-azabicyclo[2.2.1]heptane as a structural motif to block mutagenicity of nitrosamines.

    PubMed

    Ohwada, Tomohiko; Ishikawa, Satoko; Mine, Yusuke; Inami, Keiko; Yanagimoto, Takahiro; Karaki, Fumika; Kabasawa, Yoji; Otani, Yuko; Mochizuki, Masataka

    2011-04-15

    Nitrosamines are potent carcinogens and toxicants in the rat and potential genotoxins in humans. They are metabolically activated by hydroxylation at an α-carbon atom with respect to the nitrosoamino group, catalyzed by cytochrome P450. However, there has been little systematic investigation of the structure-mutagenic activity relationship of N-nitrosamines. Herein, we evaluated the mutagenicity of a series of 7-azabicyclo[2.2.1]heptane N-nitrosamines and related monocyclic nitrosamines by using the Ames assay. Our results show that the N-nitrosamine functionality embedded in the bicyclic 7-azabicylo[2.2.1]heptane structure lacks mutagenicity, that is, it is inert to α-hydroxylation, which is the trigger of mutagenic events. Further, the calculated α-C-H bond dissociation energies of the bicyclic nitrosamines are larger in magnitude than those of the corresponding monocyclic nitrosamines and N-nitrosodimethylamine by as much as 20-30 kcal/mol. These results are consistent with lower α-C-H bond reactivity of the bicyclic nitrosamines. Thus, the 7-azabicyclo[2.2.1]heptane structural motif may be useful for the design of nongenotoxic nitrosamine compounds with potential biological/medicinal applications.

  18. Combining a Ru(II) "Building Block" and Rapid Screening Approach to Identify DNA Structure-Selective "Light Switch" Compounds.

    PubMed

    Wachter, Erin; Moyá, Diego; Glazer, Edith C

    2017-02-13

    A chemically reactive Ru(II) "building block", able to undergo condensation reactions with substituted diamines, was utilized to create a small library of luminescent "light switch" dipyrido-[3,2-a:2',3'-c] phenazine (dppz) complexes. The impact of substituent identity, position, and the number of substituents on the light switch effect was investigated. An unbiased, parallel screening approach was used to evaluate the selectivity of the compounds for a variety of different biomolecules, including protein, nucleosides, single stranded DNA, duplex DNA, triplex DNA, and G-quadruplex DNA. Combining these two approaches allowed for the identification of hit molecules that showed different selectivities for biologically relevant DNA structures, particularly triplex and quadruplex DNA.

  19. 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

  20. Heart Block

    MedlinePlus

    ... not used to treat first-degree heart block. All types of heart block may increase your risk for other arrhythmias, such as atrial fibrillation (A-tre-al fih-brih-LA-shun). Talk with your doctor ...

  1. Building Block Approach' for Structural Analysis of Thermoplastic Composite Components for Automotive Applications

    NASA Astrophysics Data System (ADS)

    Carello, M.; Amirth, N.; Airale, A. G.; Monti, M.; Romeo, A.

    2017-02-01

    Advanced thermoplastic prepreg composite materials stand out with regard to their ability to allow complex designs with high specific strength and stiffness. This makes them an excellent choice for lightweight automotive components to reduce mass and increase fuel efficiency, while maintaining the functionality of traditional thermosetting prepreg (and mechanical characteristics) and with a production cycle time and recyclability suited to mass production manufacturing. Currently, the aerospace and automotive sectors struggle to carry out accurate Finite Elements (FE) component analyses and in some cases are unable to validate the obtained results. In this study, structural Finite Elements Analysis (FEA) has been done on a thermoplastic fiber reinforced component designed and manufactured through an integrated injection molding process, which consists in thermoforming the prepreg laminate and overmolding the other parts. This process is usually referred to as hybrid molding, and has the provision to reinforce the zones subjected to additional stresses with thermoformed themoplastic prepreg as required and overmolded with a shortfiber thermoplastic resin in single process. This paper aims to establish an accurate predictive model on a rational basis and an innovative methodology for the structural analysis of thermoplastic composite components by comparison with the experimental tests results.

  2. 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…

  3. 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.

  4. Planar nano-block structures Tin+1Al0.5Cn and Tin+1Cn (n = 1, and 2) from MAX phases: Structural, electronic properties and relative stability from first principles calculations

    NASA Astrophysics Data System (ADS)

    Shein, I. R.; Ivanovskii, A. L.

    2012-08-01

    Structural, electronic properties and relative stability of quasi-two-dimensional (2D) free-standing planar nano-block (NBs) structures Tin+1Al0.5Cn and Tin+1Cn (n = 1 and 2), which can be prepared using the recently developed procedure of exfoliation of corresponding NBs from MAX phases, were examined within first principles calculations in comparison with parent MAX phases Ti3AlC2 and Ti2AlC. We found that in general Tin+1Cn and Tin+1Al0.5Cn NBs retain the atomic geometries of the corresponding blocks of the MAX phases, but some structural distortions for the NBs occur owing to the lowering of the coordination number for atoms in the external Ti sheets of the nano-block structures. Our analysis based on their cohesive and formation energies reveals that the stability of the nano-block structures increases with index n (or, in other words, with a growth of the number of Ti-C bonds), the Al-containing NBs becoming more stable than the "pure" Ti-C NBs. Our data show that the magnetization of the simulated planar nano-block structures can be expected; so, for the Ti3C2 nano-block the most stable will be the spin configuration, where within each external Ti sheet the spins are coupled ferromagnetically together with antiferromagnetic ordering between opposite external titanium sheets of this nano-block.

  5. Manipulation of the crystal structure defects: An alternative route to the reduction in lattice thermal conductivity and improvement in thermoelectric performance of CuGaTe2

    NASA Astrophysics Data System (ADS)

    Wu, Wenchang; Li, Yapeng; Du, Zhengliang; Meng, Qingsen; Sun, Zheng; Ren, Wei; Cui, Jiaolin

    2013-07-01

    Here, we present the manipulation of the crystal structure defects: an alternative route to reduce the lattice thermal conductivity (κL) on an atomic scale and improve the thermoelectric performance of CuGaTe2. This semiconductor with defects, represented by anion position displacement (u) and tetragonal deformation (η), generally gives low κL values when u and η distinctly deviate from 0.25 and 1 in the ideal zinc-blende structure, respectively. However, this semiconductor will show high Seebeck coefficients and low electrical conductivities when u and η are close to 0.25 and 1, respectively, due to the electrical inactivity caused by an attractive interaction between donor-acceptor defect pairs (GaCu2+ + 2VCu-).

  6. The role of pre-existing tectonic structures and magma chamber shape on the geometry of resurgent blocks: Analogue models

    NASA Astrophysics Data System (ADS)

    Marotta, Enrica; de Vita, Sandro

    2014-02-01

    A set of analogue models has been carried out to understand the role of an asymmetric magma chamber on the resurgence-related deformation of a previously deformed crustal sector. The results are then compared with those of similar experiments, previously performed using a symmetric magma chamber. Two lines of experiments were performed to simulate resurgence in an area with a simple graben-like structure and resurgence in a caldera that collapsed within the previously generated graben-like structure. On the basis of commonly accepted scaling laws, we used dry-quartz sand to simulate the brittle behaviour of the crust and Newtonian silicone to simulate the ductile behaviour of the intruding magma. An asymmetric shape of the magma chamber was simulated by moulding the upper surface of the silicone. The resulting empty space was then filled with sand. The results of the asymmetric-resurgence experiments are similar to those obtained with symmetrically shaped silicone. In the sample with a simple graben-like structure, resurgence occurs through the formation of a discrete number of differentially displaced blocks. The most uplifted portion of the deformed depression floor is affected by newly formed, high-angle, inward-dipping reverse ring-faults. The least uplifted portion of the caldera is affected by normal faults with similar orientation, either newly formed or resulting from reactivation of the pre-existing graben faults. This asymmetric block resurgence is also observed in experiments performed with a previous caldera collapse. In this case, the caldera-collapse-related reverse ring-fault is completely erased along the shortened side, and enhances the effect of the extensional faults on the opposite side, so facilitating the intrusion of the silicone. The most uplifted sector, due to an asymmetrically shaped intrusion, is always in correspondence of the thickest overburden. These results suggest that the stress field induced by resurgence is likely dictated by

  7. 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.

  8. Adaptive comb filtering for motion artifact reduction from PPG with a structure of adaptive lattice IIR notch filter.

    PubMed

    Lee, Boreom; Kee, Youngwook; Han, Jonghee; Yi, Won Jin

    2011-01-01

    Photoplethysmographic (PPG) signal can provide important information about cardiovascular and respiratory conditions of individuals in a hospital or daily life. However, PPG can be distorted by motion artifacts significantly. Therefore, the reduction of the effects of motion artifacts is very important procedure for monitoring cardio-respiratory system by PPG. There have been many adaptive techniques to reduce motion artifacts from PPG signal including normalized least mean squares (NLMS) method, recursive least squares (RLS) filter, and Kalman filter. In the present study, we propose the adaptive comb filter (ACF) for reducing the effects of motion artifacts from PPG signal. ACF with adaptive lattice infinite impulse response (IIR) notch filter (ALNF) successfully reduced the motion artifacts from the quasi-periodic PPG signal.

  9. Rare-earth antisites in lutetium aluminum garnets: Influence on lattice parameter and Ce3+ multicenter structure

    NASA Astrophysics Data System (ADS)

    Przybylińska, H.; Wittlin, A.; Ma, Chong-Geng; Brik, M. G.; Kamińska, A.; Sybilski, P.; Zorenko, Yu.; Nikl, M.; Gorbenko, V.; Fedorov, A.; Kučera, M.; Suchocki, A.

    2014-07-01

    Low temperature, infrared transmission spectra of lutetium aluminum garnet (LuAG) bulk crystals and epitaxial layers doped with Ce are presented. In the region of intra-configurational 4f-4f transitions the spectra of the bulk LuAG crystal exhibit the signatures of several different Ce3+ related centers. Apart from the dominant center, associated with Ce substituting lutetium, at least six other centers are found, some of them attributed to so-called antisite locations of rare-earth ions in the garnet host, i.e., ions in the Al positions. X-ray diffraction data prove lattice expansion of bulk LuAG crystals due presence of rare-earth antisites.

  10. Multiple quasicrystal approximants with the same lattice parameters in Al-Cr-Fe-Si alloys

    PubMed Central

    He, Zhanbing; Li, Hua; Ma, Haikun; Li, Guowu

    2017-01-01

    By means of atomic-resolution high-angle annular dark-field scanning transmission electron microscopy, we found three types of giant approximants of decagonal quasicrystal in Al-Cr-Fe-Si alloys, where each type contains several structural variants possessing the same lattice parameters but different crystal structures. The projected structures of these approximants along the pseudo-tenfold direction were described using substructural blocks. Furthermore, the structural relationship and the plane crystallographic groups in the (a, c) plan of these structural variants was also discussed. The diversity of quasicrystal approximants with the same lattice parameters was shown to be closely related to the variety of shield-like tiles and their tiling patterns. PMID:28084405

  11. Multiple quasicrystal approximants with the same lattice parameters in Al-Cr-Fe-Si alloys

    NASA Astrophysics Data System (ADS)

    He, Zhanbing; Li, Hua; Ma, Haikun; Li, Guowu

    2017-01-01

    By means of atomic-resolution high-angle annular dark-field scanning transmission electron microscopy, we found three types of giant approximants of decagonal quasicrystal in Al-Cr-Fe-Si alloys, where each type contains several structural variants possessing the same lattice parameters but different crystal structures. The projected structures of these approximants along the pseudo-tenfold direction were described using substructural blocks. Furthermore, the structural relationship and the plane crystallographic groups in the (a, c) plan of these structural variants was also discussed. The diversity of quasicrystal approximants with the same lattice parameters was shown to be closely related to the variety of shield-like tiles and their tiling patterns.

  12. Ectopic A-lattice seams destabilize microtubules.

    PubMed

    Katsuki, Miho; Drummond, Douglas R; Cross, Robert A

    2014-01-01

    Natural microtubules typically include one A-lattice seam within an otherwise helically symmetric B-lattice tube. It is currently unclear how A-lattice seams influence microtubule dynamic instability. Here we find that including extra A-lattice seams in GMPCPP microtubules, structural analogues of the GTP caps of dynamic microtubules, destabilizes them, enhancing their median shrinkage rate by >20-fold. Dynamic microtubules nucleated by seeds containing extra A-lattice seams have growth rates similar to microtubules nucleated by B-lattice seeds, yet have increased catastrophe frequencies at both ends. Furthermore, binding B-lattice GDP microtubules to a rigor kinesin surface stabilizes them against shrinkage, whereas microtubules with extra A-lattice seams are stabilized only slightly. Our data suggest that introducing extra A-lattice seams into dynamic microtubules destabilizes them by destabilizing their GTP caps. On this basis, we propose that the single A-lattice seam of natural B-lattice MTs may act as a trigger point, and potentially a regulation point, for catastrophe.

  13. 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

  14. 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.

  15. Implementation of the equation of radiative transfer on block-structured grids for modeling light propagation in tissue.

    PubMed

    Montejo, Ludguier D; Klose, Alexander D; Hielscher, Andreas H

    2010-09-14

    We present the first algorithm for solving the equation of radiative transfer (ERT) in the frequency domain (FD) on three-dimensional block-structured Cartesian grids (BSG). This algorithm allows for accurate modeling of light propagation in media of arbitrary shape with air-tissue refractive index mismatch at the boundary at increased speed compared to currently available structured grid algorithms. To accurately model arbitrarily shaped geometries the algorithm generates BSGs that are finely discretized only near physical boundaries and therefore less dense than fine grids. We discretize the FD-ERT using a combination of the upwind-step method and the discrete ordinates (S(N)) approximation. The source iteration technique is used to obtain the solution. We implement a first order interpolation scheme when traversing between coarse and fine grid regions. Effects of geometry and optical parameters on algorithm performance are evaluated using numerical phantoms (circular, cylindrical, and arbitrary shape) and varying the absorption and scattering coefficients, modulation frequency, and refractive index. The solution on a 3-level BSG is obtained up to 4.2 times faster than the solution on a single fine grid, with minimal increase in numerical error (less than 5%).

  16. Sparse matrix multiplications for linear scaling electronic structure calculations in an atom-centered basis set using multiatom blocks.

    PubMed

    Saravanan, Chandra; Shao, Yihan; Baer, Roi; Ross, Philip N; Head-Gordon, Martin

    2003-04-15

    A sparse matrix multiplication scheme with multiatom blocks is reported, a tool that can be very useful for developing linear-scaling methods with atom-centered basis functions. Compared to conventional element-by-element sparse matrix multiplication schemes, efficiency is gained by the use of the highly optimized basic linear algebra subroutines (BLAS). However, some sparsity is lost in the multiatom blocking scheme because these matrix blocks will in general contain negligible elements. As a result, an optimal block size that minimizes the CPU time by balancing these two effects is recovered. In calculations on linear alkanes, polyglycines, estane polymers, and water clusters the optimal block size is found to be between 40 and 100 basis functions, where about 55-75% of the machine peak performance was achieved on an IBM RS6000 workstation. In these calculations, the blocked sparse matrix multiplications can be 10 times faster than a standard element-by-element sparse matrix package.

  17. Dynamic structure factor of one-dimensional lattice bosons in a disordered potential: a spectral fingerprint of the Bose-glass phase

    NASA Astrophysics Data System (ADS)

    Roux, Guillaume; Minguzzi, Anna; Roscilde, Tommaso

    2013-05-01

    We study the dynamic structure factor of a one-dimensional Bose gas confined in an optical lattice and modeled by the Bose-Hubbard Hamiltonian, using a variety of numerical and analytical approaches. The dynamic structure factor, experimentally measurable by Bragg spectroscopy, is studied in three relevant cases: in the clean regime, featuring either a superfluid or a Mott phase; and in the presence of two types of (quasi-)disordered external potentials: a quasi-periodic potential obtained from a bichromatic superlattice and a random box disorder—both featuring a Bose-glass phase. In the clean case, we show the emergence of a gapped doublon mode (corresponding to a repulsively bound state) for incommensurate filling, well separated from the low-energy acoustic mode. In the disordered case, we show that the dynamic structure factor provides direct insight into the spatial structure of the excitations, unveiling their localized nature, which represents a fundamental signature of the Bose-glass phase. Furthermore, it provides a clear fingerprint of the very nature of the localization mechanism which differs for the two kinds of disorder potentials we consider. In special cases, the dynamic structure factor may provide an estimate of the position of the localization transition from superfluid to Bose glass, in a complementary manner to the information deduced from the momentum distribution.

  18. 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.

  19. 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.

  20. 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

  1. 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.

  2. Hard X-ray polarizer to enable simultaneous three-dimensional nanoscale imaging of magnetic structure and lattice strain

    SciTech Connect

    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. Here, 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 Gd5Si2Ge2crystal 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 Gd5Si2Ge2nanocrystal 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.

  3. Hard X-ray polarizer to enable simultaneous three-dimensional nanoscale imaging of magnetic structure and lattice strain

    DOE PAGES

    Logan, Jonathan; Harder, Ross; Li, Luxi; ...

    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. Here, 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 Gd5Si2Ge2crystal 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)more » 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 Gd5Si2Ge2nanocrystal 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.« less

  4. Band lineup of lattice mismatched InSe/GaSe quantum well structures prepared by van der Waals epitaxy: Absence of interfacial dipoles

    NASA Astrophysics Data System (ADS)

    Lang, O.; Klein, A.; Pettenkofer, C.; Jaegermann, W.; Chevy, A.

    1996-10-01

    Epitaxial growth of the strongly lattice mismatched (6.5%) layered chalcogenides InSe and GaSe on each other is obtained with the concept of van der Waals epitaxy as proven by low-energy electron diffraction and scanning tunnel microscope. InSe/GaSe/InSe and GaSe/InSe/GaSe quantum well structures were prepared by molecular beam epitaxy and their interface properties were characterized by soft x-ray photoelectron spectroscopy. Valence and conduction band offsets are determined to be 0.1 and 0.9 eV, respectively, and do not depend on deposition sequence (commutativity). As determined from the measured work functions the interface dipole is 0.05 eV; the band lineup between the two materials is correctly predicted by the Anderson model (electron affinity rule).

  5. Design and optimization of 32-core rod/trench assisted square-lattice structured single-mode multi-core fiber.

    PubMed

    Xie, Xueqin; Tu, Jiajing; Zhou, Xian; Long, Keping; Saitoh, Kunimasa

    2017-03-06

    We propose and design a kind of heterogeneous rod-assisted and trench-assisted multi-core fiber (Hetero-RA-TA-MCF) with 32 cores arranged in square-lattice structure (SLS), and then we introduce the design method for Hetero-RA-TA-MCF. Simulation results show that the Hetero-RA-TA-32-Core-Fiber achieves average effective area (Aeff) of about 74 μm2, low crosstalk (XT) of about -31 dB/100km, threshold value of bending radius (Rpk) of 7.0 cm, relative core multiplicity factor (RCMF) of 8.74, and cable cutoff wavelength (λcc) of less than 1.53 μm.

  6. Magnetic structure of the antiferromagnetic Kondo lattice compounds CeRhAl4Si2 and CeIrAl4Si2

    DOE PAGES

    Ghimire, N. J.; Calder, S.; Janoschek, M.; ...

    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

  7. Structure and lattice dynamics of solid solutions (1 - x)BiFeO3- xANbO3 ( A = K, Na)

    NASA Astrophysics Data System (ADS)

    Teslenko, P. Yu.; Razumnaya, A. G.; Ponomarenko, V. O.; Rudskaya, A. G.; Nazarenko, A. V.; Anokhin, A. S.; Avramenko, M. V.; Levshov, D. I.; Kupriyanov, M. F.; Yuzyuk, Yu. I.

    2014-09-01

    The structures and the dynamic characteristics of the lattices of two compositions of solid solutions of multiferroic BiFeO3 with ferroelectric KNbO3 and antiferroelctric NaNbO3, namely, (1 - x)BiFeO3- xKNbO3 and (1 - x)BiFeO3- xNaNbO3, have been studied using X-ray powder diffraction and Raman spectroscopy. For these systems with x = 0.3, 0.5, and 0.7, the symmetry and unit cell parameters at room temperature have been determined. An analysis of the vibrational spectra has revealed sequences of rotational distortions with variations in the concentrations of components.

  8. 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.

  9. 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.

  10. 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.

  11. 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.

  12. 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.

  13. Conduction and block of inward rectifier K+ channels: predicted structure of a potent blocker of Kir2.1.

    PubMed

    Hilder, Tamsyn A; Chung, Shin-Ho

    2013-02-05

    Dysfunction of Kir2.1, thought to be the major component of inward currents, I(K1), in the heart, has been linked to various channelopathies, such as short Q-T syndrome. Unfortunately, currently no known blockers of Kir2.x channels exist. In contrast, Kir1.1b, predominantly expressed in the kidney, is potently blocked by an oxidation-resistant mutant of the honey bee toxin tertiapin (tertiapin-Q). Using various computational tools, we show that both channels are closed by a hydrophobic gating mechanism and inward rectification occurs in the absence of divalent cations and polyamines. We then demonstrate that tertiapin-Q binds to the external vestibule of Kir1.1b and Kir2.1 with K(d) values of 11.6 nM and 131 μM, respectively. We find that a single mutation of tertiapin-Q increases the binding affinity for Kir2.1 by 5 orders of magnitude (K(d) = 0.7 nM). This potent blocker of Kir2.1 may serve as a structural template from which potent compounds for the treatment of various diseases mediated by this channel subfamily, such as cardiac arrhythmia, can be developed.

  14. Crystal structure and anisotropic magnetic properties of new ferromagnetic Kondo lattice compound Ce(Cu,Al,Si)2

    NASA Astrophysics Data System (ADS)

    Maurya, A.; Thamizhavel, A.; Dhar, S. K.; Provino, A.; Pani, M.; Costa, G. A.

    2017-03-01

    Single crystals of the new compound CeCu0.18Al0.24Si1.58 have been grown by high-temperature solution growth method using a eutectic Al-Si mixture as flux. This compound is derived from the binary CeSi2 (tetragonal α-ThSi2-type, Pearson symbol tI12, space group I41/amd) obtained by partial substitution of Si by Cu and Al atoms but showing full occupation of the Si crystal site (8e). While CeSi2 is a well-known valence-fluctuating paramagnetic compound, the CeCu0.18Al0.24Si1.58 phase orders ferromagnetically at TC=9.3 K. At low temperatures the easy-axis of magnetization is along the a-axis, which re-orients itself along the c-axis above 30 K. The presence of hysteresis in the magnetization curve, negative temperature coefficient of resistivity at high temperatures, reduced jump in the heat capacity and a relatively lower entropy released up to the ordering temperature, and enhanced Sommerfeld coefficient (≈100 mJ/mol K2) show that CeCu0.18Al0.24Si1.58 is a Kondo lattice ferromagnetic, moderate heavy fermion compound. Analysis of the high temperature heat capacity data in the paramagnetic region lets us infer that the crystal electric field split doublet levels are located at 178 and 357 K, respectively, and Kondo temperature (8.4 K) is of the order of TC in CeCu0.18Al0.24Si1.58.

  15. Transmission Electron Microscope Measures Lattice Parameters

    NASA Technical Reports Server (NTRS)

    Pike, William T.

    1996-01-01

    Convergent-beam microdiffraction (CBM) in thermionic-emission transmission electron microscope (TEM) is technique for measuring lattice parameters of nanometer-sized specimens of crystalline materials. Lattice parameters determined by use of CBM accurate to within few parts in thousand. Technique developed especially for use in quantifying lattice parameters, and thus strains, in epitaxial mismatched-crystal-lattice multilayer structures in multiple-quantum-well and other advanced semiconductor electronic devices. Ability to determine strains in indivdual layers contributes to understanding of novel electronic behaviors of devices.

  16. Changes in histone H1 content and chromatin structure of cells blocked in early S phase by 5-fluorodeoxyuridine and aphidicolin

    SciTech Connect

    D'Anna, J.A.; Tobey, R.A.

    1984-01-01

    The authors have measured changes in histone H1 content and changes in chromatin structure of Chinese hamster (line CHO) cells blocked in early S phase by sequential use of isoleucine deprivation and blockade with 5-fluorodeoxyuridine or aphidicolin. Both the H1:core histone ratio in isolated nuclei and the H1 content of the cell are reduced 20-60%, depending on the duration of the block. The new deoxyribonucleic acid synthesized during S-phase block has a shorter nucleosome repeat length than that of bulk chromatin, but it is nearly equally resistant as bulk DNA to attack by micrococcal nuclease. During the time that H1 content is decreasing, bulk chromatin also undergoes structural changes so that its nucleosome cores appear to be more closely packed along the DNA chain. The losses in H1 content and changes in chromatin structure are similar to those reported for cells blocked in early S phase by hydroxyurea. The results suggest that losses of H1 and changes in chromatin structure are general events which occur when the elongation of initiated replicons or the joining of intermediate-sized DNA fragments is retarded during replication. They are consistent with the notions that (1) H1 is lost from initiated replicons and/or (2) the loss of H1 is part of an alarm response in the cell which might facilitate events leading to gene amplification. 39 references, 5 figures, 3 tables.

  17. 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…

  18. HREM study on the ledge structures, transient lattices and dislocation structures at the austenite-martensite and austenite-bainite interfaces in Fe-based alloys

    NASA Astrophysics Data System (ADS)

    Kajiwara, S.

    2003-10-01

    High-resolution electron microscopy (HREM) has been performed to know the atomic arrangement of the austenite-martensite interface and the austenite-bainite interface in Fe-based alloys. The alloys studied are Fe-23.0Ni-3.8Mn, Fe-8.8Cr-l.lC, Fe-30.5Ni-lOCo-3Ti (mass %) for martensitic transformation and Fe-2Si-1.4C (mass %) for bainitic transformation. These alloys have various transformation characteristics depending on the alloy; for martensitic transformation, athermal and isothermal kinetics, the Kurdjumow-Sachs (K-S) and Nishiyama (N) orientation relationships, reversible and irreversible movement of the interface, and for bainitic transformation, upper bainite and lower bainite. All the interfaces observed had to be limited to 112 (macroscopically 225) or very close to 112 because of the geometrical condition that the atom rows of <110>f, b and <100>b must be observed parallel to the interface, i.e., the edge-on orientation. The austenite-martensite interface is (121)f with the K-S orientation relationship of (lll)f//(011)b and [ bar{1}01] f//[ bar{1}bar{1}1] b, and the interface is basically composed of the terrace of (lll)f and the ledge of (010)f, which have the average ratio of 2:1 for the number of atom rows of [ bar{1}01] //[ bar{1}bar{1}1] b on these planes. This interface always accompanies the transient lattice region with the thickness of 0.4-1.0 nm, where the lattice changes continuously from fcc to bcc (or bct). No extra-half plane is observed at the (121)f interface over a large distance of 100-200 lattice planes. The interface for both the upper and lower bainites is close to (112)f with the N orientation relationship of (lll)f/(011)b and [ bar{1}bar{1}0] f//[ bar{1}00] b'. Contrary to the interface for martensite, this interface for bainite has many extra-half planes except when the interface is close to (112)f. The interface is basically made up of the terrace of (lll)f/(011)b and the ledge of (0bar{1}l)b'//(bar{1}bar{1}2)f, and the

  19. 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.

  20. Humanoid by ROBO-BLOCK

    NASA Astrophysics Data System (ADS)

    Niimi, Hirofumi; Koike, Minoru; Takeuchi, Seiichi; Douhara, Noriyoshi

    2007-12-01

    Humanoid by ROBO-BLOCK (robot block system) and the rational formula of robots were proposed. ROBO-BLOCK is composed of servo motors, the parts for servomotor rotor, the brackets for servomotor fixation, the board parts and the controllers. A robot can be assembled easily by ROBO-BLOCK. Meanwhile, it is convenient when the structure of the robot can be described easily as a character. The whole structure of the robot is expressed as rational formula of the robot to show molecule structure in chemistry. ROBO-BLOCK can be useful for not only the research but also the education. Creative student experiment was done in the college of industrial technology.

  1. The mystery of the fifteenth Bravais lattice

    NASA Astrophysics Data System (ADS)

    Nussbaum, Allen

    2000-10-01

    An understanding of the principles of crystal structure is necessary for the study of solids. There are contradictions in the literature dealing with the nature of crystal lattices, and there is also a miscounting of the number of possible lattices. This paper clarifies the situation in a systematic and simple way.

  2. Three-Dimensional Structure of Vertebrate Muscle Z-Band: The Small-Square Lattice Z-Band in Rat Cardiac Muscle.

    PubMed

    Burgoyne, Thomas; Morris, Edward P; Luther, Pradeep K

    2015-11-06

    The Z-band in vertebrate striated muscle crosslinks actin filaments of opposite polarity from adjoining sarcomeres and transmits tension along myofibrils during muscular contraction. It is also the location of a number of proteins involved in signalling and myofibrillogenesis; mutations in these proteins lead to myopathies. Understanding the high-resolution structure of the Z-band will help us understand its role in muscle contraction and the role of these proteins in the function of muscle. The appearance of the Z-band in transverse-section electron micrographs typically resembles a small-square lattice or a basketweave appearance. In longitudinal sections, the Z-band width varies more with muscle type than species: slow skeletal and cardiac muscles have wider Z-bands than fast skeletal muscles. As the Z-band is periodic, Fourier methods have previously been used for three-dimensional structural analysis. To cope with variations in the periodic structure of the Z-band, we have used subtomogram averaging of tomograms of rat cardiac muscle in which subtomograms are extracted and compared and similar ones are averaged. We show that the Z-band comprises four to six layers of links, presumably α-actinin, linking antiparallel overlapping ends of the actin filaments from the adjoining sarcomeres. The reconstruction shows that the terminal 5-7nm of the actin filaments within the Z-band is devoid of any α-actinin links and is likely to be the location of capping protein CapZ.

  3. Magnetic and electrode properties, structure and phase relations of the layered triangular-lattice tellurate Li{sub 4}NiTeO{sub 6}

    SciTech Connect

    Zvereva, Elena A.; Nalbandyan, Vladimir B.; Evstigneeva, Maria A.; Koo, Hyun-Joo; Whangbo, Myung-Hwan; Ushakov, Arseni V.; Medvedev, Boris S.; Medvedeva, Larisa I.; Gridina, Nelly A.; Yalovega, Galina E.; Churikov, Alexei V.; Vasiliev, Alexander N.; Büchner, Bernd

    2015-05-15

    We examined the magnetic properties of layered oxide Li{sub 4}NiTeO{sub 6} by magnetic susceptibility, magnetization and ESR measurements and density functional calculations, and characterized phase relations, crystal structure and electrochemical properties of Li{sub 4}NiTeO{sub 6}. The magnetization and ESR data indicate the absence of a long-range magnetic order down to 1.8 K, and the magnetic susceptibility data the presence of dominant antiferromagnetic interactions. These observations are well accounted for by density functional calculations, which show that the spin exchanges of the LiNiTeO{sub 6} layers in Li{sub 4}NiTeO{sub 6} are strongly spin frustrated. The electrochemical charging of Li{sub 4}NiTeO{sub 6} takes place at constant potential of ca. 4.2 V vs. Li/Li{sup +} indicating two-phase process as confirmed by X-rays. The starting phase is only partially recovered on discharge due to side reactions. - Graphical abstract: No long-range magnetic order due to frustration in 2D triangular lattice antiferromagnet Li{sub 4}NiTeO{sub 6}. - Highlights: • Li{sub 4}NiTeO{sub 6} is 2D triangular lattice magnet with no long-range order down to 1.8 K. • Intralayer exchange interactions are antiferromagnetic and strongly spin frustrated. • The electrochemical Li extraction proceeds in a two-phase mode at 4.2 V vs. Li/Li{sup +}. • The electrochemical charge–discharge is only partially reversible. • Li{sub 2}O–NiO{sub y}–TeO{sub x} phase relations are reported; Li{sub 4}NiTeO{sub 6} is essentially stoichiometric.

  4. [Relationship between the crystal lattice structure and the biological action of some agonists of amino acid receptors].

    PubMed

    Kertser, L S; Baev, K V

    1992-01-01

    The crystal structures of glycine, taurine, GABA, beta-alanine were compared. The quantity and the accuracy of distances coincidence between nitrogen and oxygen atoms were used as a criterion of similarity of the crystalline structures. The conclusion is made about a correlation between crystalline structure of agonists and their effect on amino acid receptors. It is assumed that in case of a cooperative effect of agonist on the receptor a mutual arrangement of molecules on the receptor surface is similar to their arrangement in the agonist crystal.

  5. Tetraquark states from lattice QCD

    SciTech Connect

    Mathur, Nilmani

    2011-10-24

    Recently there have been considerable interests in studying hadronic states beyond the usual two and three quark configurations. With the renewed experimental interests in {sigma}(600) and the inability of quark model to incorporate too many light scalar mesons, it is quite appropriate to study hadronic states with four quark configurations. Moreover, some of the newly observed charmed hadrons may well be described by four quark configurations. Lattice QCD is perhaps the most desirable tool to adjudicate the theoretical controversy of the scalar mesons and to interpret the structures of the newly observed charmed states. Here we briefly reviewed the lattice studies of four-quark hadrons.

  6. Chiral symmetry on the lattice

    SciTech Connect

    Creutz, M.

    1994-11-01

    The author reviews some of the difficulties associated with chiral symmetry in the context of a lattice regulator. The author discusses the structure of Wilson Fermions when the hopping parameter is in the vicinity of its critical value. Here one flavor contrasts sharply with the case of more, where a residual chiral symmetry survives anomalies. The author briefly discusses the surface mode approach, the use of mirror Fermions to cancel anomalies, and finally speculates on the problems with lattice versions of the standard model.

  7. Dynamic Behavior of Engineered Lattice Materials

    PubMed Central

    Hawreliak, J. A.; Lind, J.; Maddox, B.; Barham, M.; Messner, M.; Barton, N.; Jensen, B. J.; Kumar, M.

    2016-01-01

    Additive manufacturing (AM) is enabling the fabrication of materials with engineered lattice structures at the micron scale. These mesoscopic structures fall between the length scale associated with the organization of atoms and the scale at which macroscopic structures are constructed. Dynamic compression experiments were performed to study the emergence of behavior owing to the lattice periodicity in AM materials on length scales that approach a single unit cell. For the lattice structures, both bend and stretch dominated, elastic deflection of the structure was observed ahead of the compaction of the lattice, while no elastic deformation was observed to precede the compaction in a stochastic, random structure. The material showed lattice characteristics in the elastic response of the material, while the compaction was consistent with a model for compression of porous media. The experimental observations made on arrays of 4 × 4 × 6 lattice unit cells show excellent agreement with elastic wave velocity calculations for an infinite periodic lattice, as determined by Bloch wave analysis, and finite element simulations. PMID:27321697

  8. Reactive Orthotropic Lattice Diffuser for Noise Reduction

    NASA Technical Reports Server (NTRS)

    Khorrami, Mehdi R. (Inventor)

    2016-01-01

    An orthotropic lattice structure interconnects porous surfaces of the flap with internal lattice-structured perforations to equalize the steady pressure field on the flap surfaces adjacent to the end and to reduce the amplitude of the fluctuations in the flow field near the flap end. The global communication that exists within all of the perforations provides the mechanism to lessen the pressure gradients experienced by the end portion of the flap. In addition to having diffusive effects (diffusing the incoming flow), the three-dimensional orthogonal lattice structure is also reactive (acoustic wave phase distortion) due to the interconnection of the perforations.

  9. Evaluation of drug release profile from patches based on styrene-isoprene-styrene block copolymer: the effect of block structure and plasticizer.

    PubMed

    Wang, ChengXiao; Han, Wei; Tang, XiuZhen; Zhang, Hao

    2012-06-01

    We prepared pressure-sensitive adhesive (PSA) patches based on styrene-isoprene-styrene (SIS) thermoplastic elastomer using hot-melt coating method. The liquid paraffine is added in the PSA matrices as a plasticizer to moderate the PSA properties. Three drugs, methyl salicylate, capsaicin, and diphenhydramine hydrochloride are selected as model drugs. The Fourier transform infrared spectroscopy, differential scanning calorimetry test, and wide-angle X-ray diffraction test indicate a good compatibility between drugs and matrices. Peppas equation is used to describe drug release profile. Different drug-matrix absorption, as indicative of drug-matrix interaction, accounts for the variation in release profiles of different drugs. Furthermore, atomic force microscopy and rheological studies of the PSA samples are performed to investigate the effect of SIS structure and plasticizer of PSA on drug release behaviors. For methyl salicylate and capsaicin, drug diffusion in the PSA matrices is the main factor controlled by the release kinetic constant k. The high [SI] diblock content and high plasticizer amount in matrix provide the PSA with a homogeneous and soften microstructure, resulting in a high diffusion rate. But for water-soluble drugs such as diphenhydramine hydrochloride, the release rate is governed by water penetration with the competition from diffusion mechanisms.

  10. Exotic damping ring lattices

    SciTech Connect

    Palmer, R.B.

    1987-05-01

    This paper looks at, and compares three types of damping ring lattices: conventional, wiggler lattice with finite ..cap alpha.., wiggler lattice with ..cap alpha.. = 0, and observes the attainable equilibrium emittances for the three cases assuming a constraint on the attainable longitudinal impedance of 0.2 ohms. The emittance obtained are roughly in the ratio 4:2:1 for these cases.

  11. Solid state {sup 1}H spin-lattice relaxation and isolated-molecule and cluster electronic structure calculations in organic molecular solids: The relationship between structure and methyl group and t-butyl group rotation

    SciTech Connect

    Wang, Xianlong E-mail: pbeckman@brynmawr.edu; Mallory, Frank B.; Mallory, Clelia W.; Odhner, Hosanna R.; Beckmann, Peter A. E-mail: pbeckman@brynmawr.edu

    2014-05-21

    We report ab initio density functional theory electronic structure calculations of rotational barriers for t-butyl groups and their constituent methyl groups both in the isolated molecules and in central molecules in clusters built from the X-ray structure in four t-butyl aromatic compounds. The X-ray structures have been reported previously. We also report and interpret the temperature dependence of the solid state {sup 1}H nuclear magnetic resonance spin-lattice relaxation rate at 8.50, 22.5, and 53.0 MHz in one of the four compounds. Such experiments for the other three have been reported previously. We compare the computed barriers for methyl group and t-butyl group rotation in a central target molecule in the cluster with the activation energies determined from fitting the {sup 1}H NMR spin-lattice relaxation data. We formulate a dynamical model for the superposition of t-butyl group rotation and the rotation of the t-butyl group's constituent methyl groups. The four compounds are 2,7-di-t-butylpyrene, 1,4-di-t-butylbenzene, 2,6-di-t-butylnaphthalene, and 3-t-butylchrysene. We comment on the unusual ground state orientation of the t-butyl groups in the crystal of the pyrene and we comment on the unusually high rotational barrier of these t-butyl groups.

  12. Algebraic Lattices in QFT Renormalization

    NASA Astrophysics Data System (ADS)

    Borinsky, Michael

    2016-07-01

    The structure of overlapping subdivergences, which appear in the perturbative expansions of quantum field theory, is analyzed using algebraic lattice theory. It is shown that for specific QFTs the sets of subdivergences of Feynman diagrams form algebraic lattices. This class of QFTs includes the standard model. In kinematic renormalization schemes, in which tadpole diagrams vanish, these lattices are semimodular. This implies that the Hopf algebra of Feynman diagrams is graded by the coradical degree or equivalently that every maximal forest has the same length in the scope of BPHZ renormalization. As an application of this framework, a formula for the counter terms in zero-dimensional QFT is given together with some examples of the enumeration of primitive or skeleton diagrams.

  13. On the interaction structure of linear multi-input feedback control systems. M.S. Thesis; [problem solving, lattices (mathematics)

    NASA Technical Reports Server (NTRS)

    Wong, P. K.

    1975-01-01

    The closely-related problems of designing reliable feedback stabilization strategy and coordinating decentralized feedbacks are considered. Two approaches are taken. A geometric characterization of the structure of control interaction (and its dual) was first attempted and a concept of structural homomorphism developed based on the idea of 'similarity' of interaction pattern. The idea of finding classes of individual feedback maps that do not 'interfere' with the stabilizing action of each other was developed by identifying the structural properties of nondestabilizing and LQ-optimal feedback maps. Some known stability properties of LQ-feedback were generalized and some partial solutions were provided to the reliable stabilization and decentralized feedback coordination problems. A concept of coordination parametrization was introduced, and a scheme for classifying different modes of decentralization (information, control law computation, on-line control implementation) in control systems was developed.

  14. Broadband absorption enhancement of organic solar cells with interstitial lattice patterned metal nanoparticles

    NASA Astrophysics Data System (ADS)

    Chen, Luzhou; Choy, Wallace C. H.; Sha, Wei E. I.

    2013-06-01

    Light blocking induced by top patterned nanostructures is a fundamental limit in solar cells absorption. Here we propose an interstitial lattice patterned organic solar cell which can improve the light blocking of traditional square lattice and achieve broadband absorption enhancement. Compared to square lattice design, the plasmonic mode couplings between individual metallic nanoparticles in the interstitial lattice are more versatile and much stronger. Moreover, plasmonic modes can couple to the guided modes, resulting in large enhancement factor at some wavelengths. The interstitial lattice concept will be a broad interest and great help for high-performance photovoltaics.

  15. Subwavelength Lattice Optics by Evolutionary Design

    PubMed Central

    2015-01-01

    This paper describes a new class of structured optical materials—lattice opto-materials—that can manipulate the flow of visible light into a wide range of three-dimensional profiles using evolutionary design principles. Lattice opto-materials are based on the discretization of a surface into a two-dimensional (2D) subwavelength lattice whose individual lattice sites can be controlled to achieve a programmed optical response. To access a desired optical property, we designed a lattice evolutionary algorithm that includes and optimizes contributions from every element in the lattice. Lattice opto-materials can exhibit simple properties, such as on- and off-axis focusing, and can also concentrate light into multiple, discrete spots. We expanded the unit cell shapes of the lattice to achieve distinct, polarization-dependent optical responses from the same 2D patterned substrate. Finally, these lattice opto-materials can also be combined into architectures that resemble a new type of compound flat lens. PMID:25380062

  16. Impacts of core-shell structures on properties of lanthanide-based nanocrystals: crystal phase, lattice strain, downconversion, upconversion and energy transfer.

    PubMed

    Kar, Arik; Patra, Amitava

    2012-06-21

    This feature article highlights the new development and current status of rare-earth (RE) based core-shell nanocrystals, which is one of the new classes of hybrid nanostructures. Attractive properties of rare-earth based nanomaterials include extremely narrow emission bands, long lifetimes, large Stoke's shifts, photostability and absence of blinking that can be exploited for biophotonic and photonic applications. Core-shell nanostructures have been attracting a great deal of interest to improve the luminescence efficiency by the elimination of deleterious cross-relaxation. The main focus of this feature article is to address the impacts of core-shell structures on the properties of lanthanide based nanocrystals including crystal phase, lattice strain, downconversion emission, upconversion emission and energy transfer. We describe general synthetic methodologies to design core-shell nanostructure materials. An interesting finding reported is that the local environment of an ion in the core-shell structure significantly affects the modifications of radiative and nonradiative relaxation mechanisms. Finally, a tentative outlook on future developments of this research field is given. Here, we attempt to identify the critical parameters governing the design of luminescent lanthanide based core-shell nanostructures.

  17. Simulation-based optimization of lattice support structures for offshore wind energy converters with the simultaneous perturbation algorithm

    NASA Astrophysics Data System (ADS)

    Molde, H.; Zwick, D.; Muskulus, M.

    2014-12-01

    Support structures for offshore wind turbines are contributing a large part to the total project cost, and a cost saving of a few percent would have considerable impact. At present support structures are designed with simplified methods, e.g., spreadsheet analysis, before more detailed load calculations are performed. Due to the large number of loadcases only a few semimanual design iterations are typically executed. Computer-assisted optimization algorithms could help to further explore design limits and avoid unnecessary conservatism. In this study the simultaneous perturbation stochastic approximation method developed by Spall in the 1990s was assessed with respect to its suitability for support structure optimization. The method depends on a few parameters and an objective function that need to be chosen carefully. In each iteration the structure is evaluated by time-domain analyses, and joint fatigue lifetimes and ultimate strength utilization are computed from stress concentration factors. A pseudo-gradient is determined from only two analysis runs and the design is adjusted in the direction that improves it the most. The algorithm is able to generate considerably improved designs, compared to other methods, in a few hundred iterations, which is demonstrated for the NOWITECH 10 MW reference turbine.

  18. Light noble gas dissolution into ring structure-bearing materials and lattice influences on noble gas recycling

    NASA Astrophysics Data System (ADS)

    Jackson, Colin R. M.; Parman, Stephen W.; Kelley, Simon P.; Cooper, Reid F.

    2015-06-01

    Light noble gas (He-Ne-Ar) solubility has been experimentally determined in a range of materials with six-member, tetrahedral ring structures: beryl, cordierite, tourmaline, antigorite, muscovite, F-phlogopite, actinolite, and pargasite. Helium solubility in these materials is relatively high, 4 × 10-10 to 3 × 10-7 mol g-1 bar-1, which is ∼100 to 100,000× greater than He solubility in olivine, pyroxene, or spinel. Helium solubility broadly correlates with the topology of ring structures within different minerals. Distinctive He-Ne-Ar solubility patterns are associated with the different ring structure topologies. Combined, these observations suggest ring structures have a strong influence on noble gas solubility in materials and could facilitate the recycling of noble gases, along with other volatiles (i.e., water, chlorine, and fluorine), into the mantle. Measurements of Ne and Ar solubility in antigorite, however, are highly variable and correlated with each other, suggesting multiple factors contribute the solubility of noble gases in serpentine-rich materials.

  19. Collapse transitions in thermosensitive multi-block copolymers: A Monte Carlo study

    SciTech Connect

    Rissanou, Anastassia N.; Tzeli, Despoina S.; Anastasiadis, Spiros H.; Bitsanis, Ioannis A.

    2014-05-28

    Monte Carlo simulations are performed on a simple cubic lattice to investigate the behavior of a single linear multiblock copolymer chain of various lengths N. The chain of type (A{sub n}B{sub n}){sub m} consists of alternating A and B blocks, where A are solvophilic and B are solvophobic and N = 2nm. The conformations are classified in five cases of globule formation by the solvophobic blocks of the chain. The dependence of globule characteristics on the molecular weight and on the number of blocks, which participate in their formation, is examined. The focus is on relative high molecular weight blocks (i.e., N in the range of 500–5000 units) and very differing energetic conditions for the two blocks (very good—almost athermal solvent for A and bad solvent for B). A rich phase behavior is observed as a result of the alternating architecture of the multiblock copolymer chain. We trust that thermodynamic equilibrium has been reached for chains of N up to 2000 units; however, for longer chains kinetic entrapments are observed. The comparison among equivalent globules consisting of different number of B-blocks shows that the more the solvophobic blocks constituting the globule the bigger its radius of gyration and the looser its structure. Comparisons between globules formed by the solvophobic blocks of the multiblock copolymer chain and their homopolymer analogs highlight the important role of the solvophilic A-blocks.

  20. Influence of Solvent on the Structure of an Amphiphilic Block Copolymer in Solution and in Formation of an Integral Asymmetric Membrane.

    PubMed

    Radjabian, Maryam; Abetz, Clarissa; Fischer, Birgit; Meyer, Andreas; Abetz, Volker

    2017-02-15

    Nanoporous membranes with tailored size pores and multifunctionality derived from self-assembled block copolymers attract growing interest in ultrafiltration. The influence of the structure of block copolymer in the membrane casting solution on the formation of integral asymmetric isoporous block copolymer membranes using the nonsolvent induced phase separation process (NIPS) has been one of the long-standing questions in this research area. In this work we studied the principal role of the solvent on the micellization and self-assembly of asymmetric polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP) diblock copolymers by using a combination of dynamic light scattering (DLS) and small-angle X-ray scattering (SAXS). Our results indicate a significant effect of the solvent selectivity on the optimal casting concentration and solution structure. In addition, morphological characterization of the resulting membranes demonstrates considerable influence of the solvent system on the ordering and uniformity of the pores and pore characteristics in the separation layer as well as porous substructure of the final membranes.