A suitable low-order, eight-node tetrahedral finite element for solids
Energy Technology Data Exchange (ETDEWEB)
Key, S.W.; Heinstein, M.S.; Stone, C.M.; Mello, F.J.; Blanford, M.L.; Budge, K.G.
1998-03-01
To use the all-tetrahedral mesh generation existing today, the authors have explored the creation of a computationally efficient eight-node tetrahedral finite element (a four-node tetrahedral finite element enriched with four mid-face nodal points). The derivation of the element`s gradient operator, studies in obtaining a suitable mass lumping, and the element`s performance in applications are presented. In particular they examine the eight-node tetrahedral finite element`s behavior in longitudinal plane wave propagation, in transverse cylindrical wave propagation, and in simulating Taylor bar impacts. The element samples only constant strain states and, therefore, has 12 hour-glass modes. In this regard it bears similarities to the eight-node, mean-quadrature hexahedral finite element. Comparisons with the results obtained from the mean-quadrature eight-node hexahedral finite element and the four-node tetrahedral finite element are included. Given automatic all-tetrahedral meshing, the eight-node, constant-strain tetrahedral finite element is a suitable replacement for the eight-node hexahedral finite element in those cases where mesh generation requires an inordinate amount of user intervention and direction to obtain acceptable mesh properties.
Energy Technology Data Exchange (ETDEWEB)
Dohrmann, C.R.; Heinstein, M.W.; Jung, J.; Key, S.W.
1999-01-01
This report documents a collection of papers on a family of uniform strain tetrahedral finite elements and their connection to different element types. Also included in the report are two papers which address the general problem of connecting dissimilar meshes in two and three dimensions. Much of the work presented here was motivated by the development of the tetrahedral element described in the report "A Suitable Low-Order, Eight-Node Tetrahedral Finite Element For Solids," by S. W. Key {ital et al.}, SAND98-0756, March 1998. Two basic issues addressed by the papers are: (1) the performance of alternative tetrahedral elements with uniform strain and enhanced uniform strain formulations, and (2) the proper connection of tetrahedral and other element types when two meshes are "tied" together to represent a single continuous domain.
Binary Tetrahedral Flavor Symmetry
Eby, David A
2013-01-01
A study of the T' Model and its variants utilizing Binary Tetrahedral Flavor Symmetry. We begin with a description of the historical context and motivations for this theory, together with some conceptual background for added clarity, and an account of our theory's inception in previous works. Our model endeavors to bridge two categories of particles, leptons and quarks, a unification made possible by the inclusion of additional Higgs particles, shared between the two fermion sectors and creating a single coherent system. This is achieved through the use of the Binary Tetrahedral symmetry group and an investigation of the Tribimaximal symmetry evidenced by neutrinos. Our work details perturbations and extensions of this T' Model as we apply our framework to neutrino mixing, quark mixing, unification, and dark matter. Where possible, we evaluate model predictions against experimental results and find excellent matching with the atmospheric and reactor neutrino mixing angles, an accurate prediction of the Cabibb...
TETRAHEDRAL Cm INTERPOLATION BY RATIONAL FUNCTIONS
Institute of Scientific and Technical Information of China (English)
Guo-liang Xu; Chuan I Chu; Wei-min Xue
2001-01-01
A general local Cm(m ≥ 0) tetrahedral interpolation scheme bypolynomials of degree 4m + l plus low order rational functions from the given data is proposed. The scheme can have either 4m + l order algebraic precision if C2m data at vertices and Cm data on faces are given or k + E[k/3] + 1 order algebraic precision if Ck (k ≤ 2m) data are given at vertices. The resulted interpolant and its partial derivatives of up to order m are polynomials on the boundaries of the tetrahedra.
Purely tetrahedral quadruple systems
Institute of Scientific and Technical Information of China (English)
JI Lijun
2006-01-01
An oriented tetrahedron is a set of four vertices and four cyclic triples with the property that any ordered pair of vertices is contained in exactly one of the cyclic triples. A tetrahedral quadruple system of order n (briefly TQS(n)) is a pair (X,B), where X is an nelement set and B is a set of oriented tetrahedra such that every cyclic triple on X is contained in a unique member of B. A TQS(n) (X, B) is pure if there do not exist two oriented tetrahedra with the same vertex set. In this paper, we show that there is a pure TQS(n) if and only if n≡2,4(mod 6),n＞4,or n≡1,5(mod 12). One corollary is that there is a simple two-fold quadruple system of order n if and only if n≡2,4 (mod 6) and n＞4, or n≡1, 5 (mod 12).Another corollary is that there is an overlarge set of pure Mendelsohn triple systems of order n for n≡1,3(mod 6),n＞3, or n≡0,4 (mod 12).
Tetrahedral Order in Liquid Crystals
Pleiner, Harald; Brand, Helmut R.
2016-10-01
We review the impact of tetrahedral order on the macroscopic dynamics of bent-core liquid crystals. We discuss tetrahedral order comparing with other types of orientational order, like nematic, polar nematic, polar smectic, and active polar order. In particular, we present hydrodynamic equations for phases, where only tetrahedral order exists or tetrahedral order is combined with nematic order. Among the latter, we discriminate between three cases, where the nematic director (a) orients along a fourfold, (b) along a threefold symmetry axis of the tetrahedral structure, or (c) is homogeneously uncorrelated with the tetrahedron. For the optically isotropic T d phase, which only has tetrahedral order, we focus on the coupling of flow with, e.g., temperature gradients and on the specific orientation behavior in external electric fields. For the transition to the nematic phase, electric fields lead to a temperature shift that is linear in the field strength. Electric fields induce nematic order, again linear in the field strength. If strong enough, electric fields can change the tetrahedral structure and symmetry leading to a polar phase. We briefly deal with the T phase that arises when tetrahedral order occurs in a system of chiral molecules. To case (a), defined above, belong (i) the non-polar, achiral, optically uniaxial D2d phase with ambidextrous helicity (due to a linear gradient free energy contribution) and with orientational frustration in external fields, (ii) the non-polar tetragonal S4 phase, (iii) the non-polar, orthorhombic D2 phase that is structurally chiral featuring ambidextrous chirality, (iv) the polar orthorhombic C2v phase, and (v) the polar, structurally chiral, monoclinic C2 phase. Case (b) results in a trigonal C3v phase that behaves like a biaxial polar nematic phase. An example for case (c) is a splay bend phase, where the ground state is inhomogeneous due to a linear gradient free energy contribution. Finally, we discuss some experiments
An Improved Linear Tetrahedral Element for Plasticity
Energy Technology Data Exchange (ETDEWEB)
Puso, M
2005-04-25
A stabilized, nodally integrated linear tetrahedral is formulated and analyzed. It is well known that linear tetrahedral elements perform poorly in problems with plasticity, nearly incompressible materials, and acute bending. For a variety of reasons, linear tetrahedral elements are preferable to quadratic tetrahedral elements in most nonlinear problems. Whereas, mixed methods work well for linear hexahedral elements, they don't for linear tetrahedrals. On the other hand, automatic mesh generation is typically not feasible for building many 3D hexahedral meshes. A stabilized, nodally integrated linear tetrahedral is developed and shown to perform very well in problems with plasticity, nearly incompressible materials and acute bending. Furthermore, the formulation is analytically and numerically shown to be stable and optimally convergent. The element is demonstrated to perform well in several standard linear and nonlinear benchmarks.
Tetrahedral Units: For Dodecahedral Super-Structures
Ortiz, Y; Liebman, J F
2016-01-01
Different novel organic-chemical possibilities for tetrahedral building units are considered, with attention to their utility in constructing different super-structures. As a representative construction we consider the use of sets of 20 such identical tetrahedral units to form a super-dodecahedron.
Building Tetrahedral Kites. Grades 6-8.
Rushton, Erik; Ryan, Emily; Swift, Charles
Working in teams of four, students build a tetrahedral kite following a specific set of directions and using specific provided materials. Students use basic processes of manufacturing systems-- cutting, shaping, forming, conditioning, assembling, joining, finishing, and quality control--to manufacture a complete tetrahedral kite within a given…
NEW RSW & Wall Medium Fully Tetrahedral Grid
National Aeronautics and Space Administration — New Medium Fully Tetrahedral RSW Grid with viscous wind tunnel wall at the root. This grid is for a node-based unstructured solver. Medium Tet: Quad Surface Faces= 0...
NEW RSW & Wall Fine Fully Tetrahedral Grid
National Aeronautics and Space Administration — NEW RSW Fine Fully Tetrahedral Grid with Viscous Wind Tunnel wall at the root. This grid is for a node-based unstructured solver. Note that the CGNS file is very...
On local cohomology of a tetrahedral curve
Giang, Do Hoang
2009-01-01
It is shown that the diameter $\\diam (H^1_\\mfr(R/I))$ of the first local cohomology module of a tetrahedral curve $C= C(a_1,...,a_6)$ can be explicitly expressed in terms of the $a_i$ and is the smallest non-negative integer $k$ such that $\\mfr^k H^1_\\mfr(R/I)=0$. From that one can describe all arithmetically Cohen-Macaulay or Buchsbaum tetrahedral curves.
Tetrahedrality and hydrogen bonds in water
Székely, Eszter; Varga, Imre K.; Baranyai, András
2016-06-01
We carried out extensive calculations of liquid water at different temperatures and pressures using the BK3 model suggested recently [P. T. Kiss and A. Baranyai, J. Chem. Phys. 138, 204507 (2013)]. In particular, we were interested in undercooled regions to observe the propensity of water to form tetrahedral coordination of closest neighbors around a central molecule. We compared the found tetrahedral order with the number of hydrogen bonds and with the partial pair correlation functions unfolded as distributions of the closest, the second closest, etc. neighbors. We found that contrary to the number of hydrogen bonds, tetrahedrality changes substantially with state variables. Not only the number of tetrahedral arrangements increases with lowering the pressure, the density, and the temperature but the domain size of connecting tetrahedral structures as well. The difference in tetrahedrality is very pronounced between the two sides of the Widom line and even more so between the low density amorphous (LDA) and high density amorphous (HDA) phases. We observed that in liquid water and in HDA, the 5th water molecule, contrary to ice and LDA, is positioned between the first and the second coordination shell. We found no convincing evidence of structural heterogeneity or regions referring to structural transition.
NEW METHOD FOR LOW ORDER SPECTRAL MODEL AND ITS APPLICATION
Institute of Scientific and Technical Information of China (English)
无
2006-01-01
In order to overcome the deficiency in classical method of low order spectral model, a new method for low order spectral model was advanced. Through calculating the multiple correlation coefficients between combinations of different functions and the recorded data under the least square criterion, the truncated functions which can mostly reflect the studied physical phenomenon were objectively distilled from these data. The new method overcomes the deficiency of artificially selecting the truncated functions in the classical low order spectral model. The new method being applied to study the inter-annual variation of summer atmospheric circulation over Northern Hemisphere, the truncated functions were obtained with the atmospheric circulation data of June 1994 and June 1998. The mechanisms for the two-summer atmospheric circulation variations over Northern Hemisphere were obtained with two-layer quasi-geostrophic baroclinic equation.
Search for Tetrahedral Symmetry in 70Ge
Le, Khanh; Haring-Kaye, R. A.; Elder, R. M.; Jones, K. D.; Morrow, S. I.; Tabor, S. L.; Tripathi, V.; Bender, P. C.; Allegro, P. R. P.; Medina, N. H.; Oliveira, J. R. B.; Doring, J.
2014-09-01
The even-even Ge isotopes have recently become an active testing ground for a variety of exotic structural characteristics, including the existence of tetrahedral symmetry (pyramid-like shapes). Although theoretical shape calculations predict the onset of tetrahedral symmetry near 72Ge, the experimental signatures (including vanishing quadrupole moments within high-spin bands) remain elusive. This study searched for possible experimental evidence of tetrahedral symmetry in 70Ge. Excited states in 70Ge were populated at Florida State University using the 55Mn(18O,p2n) fusion-evaporation reaction at 50 MeV. Prompt γ- γ coincidences were measured with a Compton-suppressed Ge array consisting of three Clover detectors and seven single-crystal detectors. The existing level scheme was enhanced through the addition of 20 new transitions and the rearrangement of five others based on the measured coincidence relations and relative intensities. Lifetimes of 24 states were measured using the Doppler-shift attenuation method, from which transition quadrupole moments were inferred. These results will be compared with those obtained from cranked Woods-Saxon calculations. The even-even Ge isotopes have recently become an active testing ground for a variety of exotic structural characteristics, including the existence of tetrahedral symmetry (pyramid-like shapes). Although theoretical shape calculations predict the onset of tetrahedral symmetry near 72Ge, the experimental signatures (including vanishing quadrupole moments within high-spin bands) remain elusive. This study searched for possible experimental evidence of tetrahedral symmetry in 70Ge. Excited states in 70Ge were populated at Florida State University using the 55Mn(18O,p2n) fusion-evaporation reaction at 50 MeV. Prompt γ- γ coincidences were measured with a Compton-suppressed Ge array consisting of three Clover detectors and seven single-crystal detectors. The existing level scheme was enhanced through the addition
On the accuracy of low-order projection methods
Paul Pichler
2007-01-01
We use low-order projection methods to compute numerical solutions of the basic neoclassical stochastic growth model. We assess the quality of the obtained solutions, and compare them to numerical approximations derived with first and second-order perturbation techniques. We show that projection methods perform surprisingly poor when the degree of approximation is very low, and we provide some intuition behind this finding.
Low-order modelling of droplets on hydrophobic surfaces
Matar, Omar; Wray, Alex; Kahouadji, Lyes; Davis, Stephen
2015-11-01
We consider the behaviour of a droplet deposited onto a hydrophobic substrate. This and associated problems have garnered a wide degree of attention due to their significance in industrial and experimental settings, such as the post-rupture dewetting problem. These problems have generally defied low-order analysis due to the multi-valued nature of the interface, but we show here how to overcome this in this instance. We first discuss the static problem: when the droplet is stationary, its shape is prescribed by an ordinary differential equation (ODE) given by balancing gravitational and capillary stresses at the interface. This is dependent on the contact angle, the Bond number and the volume of the drop. In the high Bond number limit, we derive several low-order models of varying complexity to predict the shape of such drops. These are compared against numerical calculations of the ODE. We then approach the dynamic problem: in this case, the full Stokes equations throughout the drop must be considered. A low-order approach is used by solving the biharmonic equation in a coordinate system naturally mapping to the droplet shape. The results are compared against direct numerical simulations. EPSRC Programme Grant, MEMPHIS, EP/K0039761/1, EPSRC Doctoral Prize Fellowship (AWW).
A Low Order Theory of Arctic Sea Ice Stability
Moon, W
2011-01-01
We analyze the stability of a low-order coupled sea ice and climate model and extract the essential physics governing the time scales of response as a function of greenhouse gas forcing. Under present climate conditions the stability is controlled by longwave radiation driven heat conduction. However, as greenhouse gas forcing increases and the ice cover decays, the destabilizing influence of ice-albedo feedback acts on equal footing with longwave stabilization. Both are seasonally out of phase and as the system warms towards a seasonal ice state these effects, which underlie the bifurcations between climate states, combine to extend the intrinsic relaxation time scale from ~ 2 yr to 5 yr.
Transport of phase space densities through tetrahedral meshes using discrete flow mapping
Bajars, Janis; Chappell, David J.; Søndergaard, Niels; Tanner, Gregor
2017-01-01
Discrete flow mapping was recently introduced as an efficient ray based method determining wave energy distributions in complex built up structures. Wave energy densities are transported along ray trajectories through polygonal mesh elements using a finite dimensional approximation of a ray transfer operator. In this way the method can be viewed as a smoothed ray tracing method defined over meshed surfaces. Many applications require the resolution of wave energy distributions in three-dimensional domains, such as in room acoustics, underwater acoustics and for electromagnetic cavity problems. In this work we extend discrete flow mapping to three-dimensional domains by propagating wave energy densities through tetrahedral meshes. The geometric simplicity of the tetrahedral mesh elements is utilised to efficiently compute the ray transfer operator using a mixture of analytic and spectrally accurate numerical integration. The important issue of how to choose a suitable basis approximation in phase space whilst maintaining a reasonable computational cost is addressed via low order local approximations on tetrahedral faces in the position coordinate and high order orthogonal polynomial expansions in momentum space.
ALGORITHMS FOR TETRAHEDRAL NETWORK (TEN) GENERATION
Institute of Scientific and Technical Information of China (English)
无
2000-01-01
The Tetrahedral Network(TEN) is a powerful 3-D vector structure in GIS, which has a lot of advantages such as simple structure, fast topological relation processing and rapid visualization. The difficulty of TEN application is automatic creating data structure. Al though a raster algorithm has been introduced by some authors, the problems in accuracy, memory requirement, speed and integrity are still existent. In this paper, the raster algorithm is completed and a vector algorithm is presented after a 3-D data model and structure of TEN have been introducted. Finally, experiment, conclusion and future work are discussed.
Multiscale high-order/low-order (HOLO) algorithms and applications
Chacón, L.; Chen, G.; Knoll, D. A.; Newman, C.; Park, H.; Taitano, W.; Willert, J. A.; Womeldorff, G.
2017-02-01
We review the state of the art in the formulation, implementation, and performance of so-called high-order/low-order (HOLO) algorithms for challenging multiscale problems. HOLO algorithms attempt to couple one or several high-complexity physical models (the high-order model, HO) with low-complexity ones (the low-order model, LO). The primary goal of HOLO algorithms is to achieve nonlinear convergence between HO and LO components while minimizing memory footprint and managing the computational complexity in a practical manner. Key to the HOLO approach is the use of the LO representations to address temporal stiffness, effectively accelerating the convergence of the HO/LO coupled system. The HOLO approach is broadly underpinned by the concept of nonlinear elimination, which enables segregation of the HO and LO components in ways that can effectively use heterogeneous architectures. The accuracy and efficiency benefits of HOLO algorithms are demonstrated with specific applications to radiation transport, gas dynamics, plasmas (both Eulerian and Lagrangian formulations), and ocean modeling. Across this broad application spectrum, HOLO algorithms achieve significant accuracy improvements at a fraction of the cost compared to conventional approaches. It follows that HOLO algorithms hold significant potential for high-fidelity system scale multiscale simulations leveraging exascale computing.
Correction of low order aberrations using continuous deformable mirrors.
Vdovin, Gleb; Soloviev, Oleg; Samokhin, Alexander; Loktev, Mikhail
2008-03-03
By analyzing the Poisson equation describing the static behavior of membrane and bimorph deformable mirrors and biharmonic equation describing the continuous facesheet mirror with push-pull actuators, we found that to achieve a high quality correction of low-order aberrations these mirrors should have sufficient number of actuators positioned outside the correction aperture. In particular, any deformable mirror described by the Poisson equation requires at least two actuators to be placed outside the working aperture per period of the azimuthal aberration of the highest expected order. Any deformable mirror described by the biharmonic equation, such as a continuous facesheet mirror with push-pull actuators, requires at least four actuators to be placed outside the working aperture per period of the azimuthal aberration of the highest expected order, and these actuators should not be positioned on a single circle.
Phase diagram of a truncated tetrahedral model
Krcmar, Roman; Gendiar, Andrej; Nishino, Tomotoshi
2016-08-01
Phase diagram of a discrete counterpart of the classical Heisenberg model, the truncated tetrahedral model, is analyzed on the square lattice, when the interaction is ferromagnetic. Each spin is represented by a unit vector that can point to one of the 12 vertices of the truncated tetrahedron, which is a continuous interpolation between the tetrahedron and the octahedron. Phase diagram of the model is determined by means of the statistical analog of the entanglement entropy, which is numerically calculated by the corner transfer matrix renormalization group method. The obtained phase diagram consists of four different phases, which are separated by five transition lines. In the parameter region, where the octahedral anisotropy is dominant, a weak first-order phase transition is observed.
ENHANCING ADHESION OF TETRAHEDRAL AMORPHOUS CARBON FILMS
Institute of Scientific and Technical Information of China (English)
Zhao Yuqing; Lin Yi; Wang Xiaoyan; Wang Yanwu; Wei Xinyu
2005-01-01
Objective The high energy ion bombardment technique is applied to enhancing the adhesion of the tetrahedral amorphous carbon (TAC) films deposited by the filtered cathode vacuum arc (FCVA). Methods The abrasion method, scratch method, heating and shaking method as well as boiling salt solution method is used to test the adhesion of the TAC films on various material substrates. Results The test results show that the adhesion is increased as the ion bombardment energy increases. However, if the bombardment energy were over the corresponding optimum value, the adhesion would be enhanced very slowly for the harder material substrates and drops quickly, for the softer ones. Conclusion The optimum values of the ion bombardment energy are larger for the harder materials than that for the softer ones.
Nonperturbative Quantum Physics from Low-Order Perturbation Theory.
Mera, Héctor; Pedersen, Thomas G; Nikolić, Branislav K
2015-10-02
The Stark effect in hydrogen and the cubic anharmonic oscillator furnish examples of quantum systems where the perturbation results in a certain ionization probability by tunneling processes. Accordingly, the perturbed ground-state energy is shifted and broadened, thus acquiring an imaginary part which is considered to be a paradigm of nonperturbative behavior. Here we demonstrate how the low order coefficients of a divergent perturbation series can be used to obtain excellent approximations to both real and imaginary parts of the perturbed ground state eigenenergy. The key is to use analytic continuation functions with a built-in singularity structure within the complex plane of the coupling constant, which is tailored by means of Bender-Wu dispersion relations. In the examples discussed the analytic continuation functions are Gauss hypergeometric functions, which take as input fourth order perturbation theory and return excellent approximations to the complex perturbed eigenvalue. These functions are Borel consistent and dramatically outperform widely used Padé and Borel-Padé approaches, even for rather large values of the coupling constant.
Optimal image interpolation using local low-order surfaces
Gustafson, Steven C.; Claypoole, Roger L., Jr.; Magee, Eric P.; Loomis, John S.
2002-05-01
Desirable features of any digital image resolution- enhancement algorithm include exact interpolation (for 'distortionless' or 'lossless' processing) adjustable resolution, adjustable smoothness, and ease of computation. A given low-order polynomial surface (linear, quadratic, cubic, etc.) optimally fit by least squares to a given local neighborhood of a pixel to be interpolated can enable all of these features. For example, if the surface is cubic, if a pixel and the 5-by-5 pixel array surrounding it are selected, and if interpolation of this pixel must yield a 4- by-4 array of sub-pixels, then the 10 coefficients that define the surface may be determined by the constrained least squares solution of 25 linear equations in 10 unknowns, where each equation sets the surface value at a pixel center equal to the pixel gray value and where the constraint is that the mean of the surface values at the sub-pixel centers equals the gray value of the interpolated pixel. Note that resolution is adjustable because the interpolating surface for each pixel may be subdivided arbitrarily, that smoothness is adjustable (within each pixel) because the polynomial order and number neighboring pixels may be selected, and that the most computationally demanding operation is solving a relatively small number of simultaneous linear equations for each pixel.
Low-Order GAM Admire System in Landing Preparation Phase
Directory of Open Access Journals (Sweden)
Ionel IORGA
2011-09-01
Full Text Available In this paper the symbolic and numeric computations for the simplified GAM (Generic Aerodynamic Model Admire system are presented . The numeric computations were performed into the MatLab environment with the aim of presenting to the reader the details of the preparation for landing of the airplane generic model. Regarding the symbolic computations that have been made it's worth to mention here the fact that they concerned the issues of stability in the manner that the trim point for the low order non-linear system was computed and an analysis of the eigenvalues of the Jacobian matrix associated to the system, which has been evaluated in the trim point, was performed. The case of the stable longitudinal level descending flight and the case of transition to a state appropriate for the touch-down are presented. It is shown the fact that the plane can regain stability if the real moment for touch-down is missed by reentering into the stable longitudinal level descending flight (by usage of the control e.
Streaming Compression of Tetrahedral Volume Meshes
Energy Technology Data Exchange (ETDEWEB)
Isenburg, M; Lindstrom, P; Gumhold, S; Shewchuk, J
2005-11-21
Geometry processing algorithms have traditionally assumed that the input data is entirely in main memory and available for random access. This assumption does not scale to large data sets, as exhausting the physical memory typically leads to IO-inefficient thrashing. Recent works advocate processing geometry in a 'streaming' manner, where computation and output begin as soon as possible. Streaming is suitable for tasks that require only local neighbor information and batch process an entire data set. We describe a streaming compression scheme for tetrahedral volume meshes that encodes vertices and tetrahedra in the order they are written. To keep the memory footprint low, the compressor is informed when vertices are referenced for the last time (i.e. are finalized). The compression achieved depends on how coherent the input order is and how many tetrahedra are buffered for local reordering. For reasonably coherent orderings and a buffer of 10,000 tetrahedra, we achieve compression rates that are only 25 to 40 percent above the state-of-the-art, while requiring drastically less memory resources and less than half the processing time.
Details of tetrahedral anisotropic mesh adaptation
Jensen, Kristian Ejlebjerg; Gorman, Gerard
2016-04-01
We have implemented tetrahedral anisotropic mesh adaptation using the local operations of coarsening, swapping, refinement and smoothing in MATLAB without the use of any for- N loops, i.e. the script is fully vectorised. In the process of doing so, we have made three observations related to details of the implementation: 1. restricting refinement to a single edge split per element not only simplifies the code, it also improves mesh quality, 2. face to edge swapping is unnecessary, and 3. optimising for the Vassilevski functional tends to give a little higher value for the mean condition number functional than optimising for the condition number functional directly. These observations have been made for a uniform and a radial shock metric field, both starting from a structured mesh in a cube. Finally, we compare two coarsening techniques and demonstrate the importance of applying smoothing in the mesh adaptation loop. The results pertain to a unit cube geometry, but we also show the effect of corners and edges by applying the implementation in a spherical geometry.
Computer model of tetrahedral amorphous diamond
Djordjević, B. R.; Thorpe, M. F.; Wooten, F.
1995-08-01
We computer generate a model of amorphous diamond using the Wooten-Weaire method, with fourfold coordination everywhere. We investigate two models: one where four-membered rings are allowed and the other where the four-membered rings are forbidden; each model consisting of 4096 atoms. Starting from the perfect diamond crystalline structure, we first randomize the structure by introducing disorder through random bond switches at a sufficiently high temperature. Subsequently, the temperature is reduced in stages, and the topological and geometrical relaxation of the structure takes place using the Keating potential. After a long annealing process, a random network of comparatively low energy is obtained. We calculate the pair distribution function, mean bond angle, rms angular deviation, rms bond length, rms bond-length deviation, and ring statistics for the final relaxed structures. We minimize the total strain energy by adjusting the density of the sample. We compare our results with similar computer-generated models for amorphous silicon, and with experimental measurement of the structure factor for (predominantly tetrahedral) amorphous carbon.
Relativistic theory of the Jahn-Teller effect: p-orbitals in tetrahedral and trigonal systems
Domcke, Wolfgang; Opalka, Daniel; Poluyanov, Leonid V.
2016-03-01
A relativistic generalization of Jahn-Teller theory is presented which includes spin-orbit coupling effects beyond low-order Taylor expansions in vibrational coordinates. For the example of a p-electron in tetrahedral and trigonal environments, the matrix elements of the Breit-Pauli spin-orbit-coupling operator are expressed in terms of the matrix elements of the electrostatic electronic potential. Employing expansions of the latter in invariant polynomials in symmetry-adapted nuclear coordinates, the spin-orbit induced Jahn-Teller coupling terms are derived for the T2 × (t2 + e) and (E + A) × (e + a) Jahn-Teller problems up to arbitrarily high orders. The linear G3/2 × (t2 + e) Jahn-Teller Hamiltonian of Moffitt and Thorson [Phys. Rev. 108, 1251 (1957)] for tetrahedral systems is generalized to higher orders in vibrational displacements. The Jahn-Teller Hamiltonians derived in the present work are useful for the interpolation and extrapolation of Jahn-Teller distorted potential-energy surfaces of molecules and complexes with heavy elements as well as for the calculation of vibronic spectra of such systems.
A geometric toolbox for tetrahedral finite element partitions
Brandts, J.; Korotov, S.; Křížek, M.; Axelsson, O.; Karátson, J.
2011-01-01
In this work we present a survey of some geometric results on tetrahedral partitions and their refinements in a unified manner. They can be used for mesh generation and adaptivity in practical calculations by the finite element method (FEM), and also in theoretical finite element (FE) analysis. Spec
Is there tetrahedral Fe/sup 3 +/ in biotite
Energy Technology Data Exchange (ETDEWEB)
Dyar, M.D.; Burns, R.G.; Rossman, G.R.
1985-01-01
Tetrahedral Fe/sup 3 +/ has been observed in Moessbauer and optical studies of Al-deficient micas, including synthetic ferri-annites, annites from banded iron formations and phlogopites from deep-seated rocks. In such samples Si + Al < 4 (per 11 0), and 0.10-0.67 formula units of Fe/sup 3 +/ fill the tetrahedral sites in the structure. The authors also discovered several Al-rich biotites which contain small amounts of Fe/sub tet//sup 3 +/ based on their spectroscopic data. Fe/sup 3 +/ appears to be displacing some of the Al/sup 3 +/ into the octahedral site. Examination of the literature shows nine other cases of Fe/sub tet//sup 3 +/ in trioctahedral 1M micas where Si + Al > 4. Traditionally, the effects of cation substitutions on the physical properties have been considered to be dependent on the size difference between the octahedral and tetrahedral layers of the structure. Much attention has focused on the substitution of the larger Fe/sup 2 +/ for Mg/sup 2 +/ and other cations in the octahedra of relatively simple synthetic compositions. However, in the natural micas studied here high fO/sub 2/ and high proportions of Al/sup 3 +/, Fe/sup 3 +/, and Ti/sup 4 +/ in the compositions raise the issue of structural readjustments based on substitution of small cations into the structure. In our samples, the average octahedral cation size is 0.67 A. If many small octahedral cations are incorporated into the structure during biotite formation, considerable octahedral flattening and (in response) tetrahedral rotation must occur to stabilize the mica. Perhaps the high degree of tetrahedral rotation allows accommodation of the larger Fe/sub tet//sup 3 +/ instead of Al/sub tet//sup 3 +/.
A LOW ORDER NONCONFORMING ANISOTROPIC FINITE ELEMENT APPROXIMATION TO PARABOLIC PROBLEM
Institute of Scientific and Technical Information of China (English)
Dongyang SHI; Wei GONG
2009-01-01
A low order nonconforming finite element is applied to the parabolic problem with anisotropic meshes. Both the semidiscrete and fully discrete forms are studied. Some superclose properties and superconvergence are obtained through some novel approaches and techniques.
Low-order aeroelastic models of wind turbines for controller design
DEFF Research Database (Denmark)
Sønderby, Ivan Bergquist
Wind turbine controllers are used to optimize the performance of wind turbines such as to reduce power variations and fatigue and extreme loads on wind turbine components. Accurate tuning and design of modern controllers must be done using low-order models that accurately captures the aeroelastic...... response of the wind turbine. The purpose of this thesis is to investigate the necessary model complexity required in aeroelastic models used for controller design and to analyze and propose methods to design low-order aeroelastic wind turbine models that are suited for model-based control design......-frequency non-minimum phase zeros. To correctly predict the non-minimum phase zeros, it is shown to be essential to include lateral tower and blade flap degrees of freedom. The thesis describes and analyzes various methods to design low-order aeroelastic models of wind turbines. Low-order models are designed...
Motion Planning of Kinematically Redundant 12-tetrahedral Rolling Robot
Directory of Open Access Journals (Sweden)
Xingbo Wang
2016-02-01
Full Text Available The 12-tetrahedral robot is an addressable reconfigurable technology (ART-based variable geometry truss mechanism with 26 extensible struts and nine nodes arranged in a tetrahedral mesh. The robot has the capability of configuring its shape to adapt to environmental requirements, which makes it suitable for space exploration. This paper considers the motion planning problem for the robot in terms of gait planning and trajectory planning. First, a gait planning method is developed that limits the forward falling angles to only 25 degrees. Then, according to the given gait, the jerk-bounded method and inverse kinematics are utilized to calculate the trajectories of the nodes and the struts, respectively. A robot system model was built in ADAMS and simulations were conducted to demonstrate the feasibility of the motion planning method.
A computational study of nodal-based tetrahedral element behavior.
Energy Technology Data Exchange (ETDEWEB)
Gullerud, Arne S.
2010-09-01
This report explores the behavior of nodal-based tetrahedral elements on six sample problems, and compares their solution to that of a corresponding hexahedral mesh. The problems demonstrate that while certain aspects of the solution field for the nodal-based tetrahedrons provide good quality results, the pressure field tends to be of poor quality. Results appear to be strongly affected by the connectivity of the tetrahedral elements. Simulations that rely on the pressure field, such as those which use material models that are dependent on the pressure (e.g. equation-of-state models), can generate erroneous results. Remeshing can also be strongly affected by these issues. The nodal-based test elements as they currently stand need to be used with caution to ensure that their numerical deficiencies do not adversely affect critical values of interest.
Quality Tetrahedral Mesh Smoothing via Boundary-Optimized Delaunay Triangulation.
Gao, Zhanheng; Yu, Zeyun; Holst, Michael
2012-12-01
Despite its great success in improving the quality of a tetrahedral mesh, the original optimal Delaunay triangulation (ODT) is designed to move only inner vertices and thus cannot handle input meshes containing "bad" triangles on boundaries. In the current work, we present an integrated approach called boundary-optimized Delaunay triangulation (B-ODT) to smooth (improve) a tetrahedral mesh. In our method, both inner and boundary vertices are repositioned by analytically minimizing the error between a paraboloid function and its piecewise linear interpolation over the neighborhood of each vertex. In addition to the guaranteed volume-preserving property, the proposed algorithm can be readily adapted to preserve sharp features in the original mesh. A number of experiments are included to demonstrate the performance of our method.
Tetrahedral meshing via maximal Poisson-disk sampling
Guo, Jianwei
2016-02-15
In this paper, we propose a simple yet effective method to generate 3D-conforming tetrahedral meshes from closed 2-manifold surfaces. Our approach is inspired by recent work on maximal Poisson-disk sampling (MPS), which can generate well-distributed point sets in arbitrary domains. We first perform MPS on the boundary of the input domain, we then sample the interior of the domain, and we finally extract the tetrahedral mesh from the samples by using 3D Delaunay or regular triangulation for uniform or adaptive sampling, respectively. We also propose an efficient optimization strategy to protect the domain boundaries and to remove slivers to improve the meshing quality. We present various experimental results to illustrate the efficiency and the robustness of our proposed approach. We demonstrate that the performance and quality (e.g., minimal dihedral angle) of our approach are superior to current state-of-the-art optimization-based approaches.
Single-laser, one beam, tetrahedral magneto-optical trap.
Vangeleyn, Matthieu; Griffin, Paul F; Riis, Erling; Arnold, Aidan S
2009-08-03
We have realized a 4-beam pyramidal magneto-optical trap ideally suited for future microfabrication. Three mirrors split and steer a single incoming beam into a tripod of reflected beams, allowing trapping in the four-beam overlap volume. We discuss the influence of mirror angle on cooling and trapping, finding optimum efficiency in a tetrahedral configuration. We demonstrate the technique using an ex-vacuo mirror system to illustrate the previously inaccessible supra-plane pyramid MOT configuration. Unlike standard pyramidal MOTs both the pyramid apex and its mirror angle are non-critical and our MOT offers improved molasses free from atomic shadows in the laser beams. The MOT scheme naturally extends to a 2-beam refractive version with high optical access. For quantum gas experiments, the mirror system could also be used for a stable 3D tetrahedral optical lattice.
Dynamic components of linear stable mixtures from fractional low order moments
DEFF Research Database (Denmark)
Fabricius, Thomas; Kidmose, Preben; Hansen, Lars Kai
2001-01-01
The second moment-based independent component analysis scheme of Molgedey and Schuster (1994) is generalized to fractional low-order moments, relevant for linear mixtures of heavy tail stable processes. The Molgedey-Schuster algorithm stands out by allowing explicitly construction of the independ...... of the independent components. Surprisingly, this turns out to be possible also for decorrelation based on fractional low-order moments....
Search for Fingerprints of Tetrahedral Symmetry in $^{156}Gd$
Doan, Q T; Stezowski, O; Dudek, J; Mazurek, K; Gózdz, A; Piot, J; Duchêne, G; Gall, B; Molique, H; Richet, M; Medina, P; Guinet, D; Redon, N; Schmitt, C; Jones, P; Julin, R; Peura, P; Ketelhut, S; Nyman, M; Jakobsson, U; Maj, A; Zuber, K; Bednarczyk, P; Schunck, N; Dobaczewski, J; Astier, A; Deloncle, I; Verney, D; De Angelis, G; Gerl, J
2008-01-01
Theoretical predictions suggest the presence of tetrahedral symmetry as an explanation for the vanishing intra-band E2-transitions at the bottom of the odd-spin negative parity band in $^{156}Gd$. The present study reports on experiment performed to address this phenomenon. It allowed to determine the intra-band E2 transitions and branching ratios B(E2)/B(E1) of two of the negative-parity bands in $^{156}Gd$.
Building dynamic thermal simulation of low-order multi-dimensional heat transfer
Institute of Scientific and Technical Information of China (English)
高岩; 范蕊; 张群力
2014-01-01
Multi-dimensional heat transfers modeling is crucial for building simulations of insulated buildings, which are widely used and have multi-dimensional heat transfers characteristics. For this work, state-model-reduction techniques were used to develop a reduced low-order model of multi-dimensional heat transfers. With hot box experiment of hollow block wall, heat flow relative errors between experiment and low-order model predication were less than 8%and the largest errors were less than 3%. Also, frequency responses of five typical walls, each with different thermal masses or insulation modes, the low-order model and the complete model showed that the low-order model results agree very well in the lower excitation frequency band with deviations appearing only at high frequency. Furthermore, low-order model was used on intersection thermal bridge of a floor slab and exterior wall. Results show that errors between the two models are very small. This low-order model could be coupled with most existing simulation software for different thermal mass envelope analyses to make up for differences between the multi-dimensional and one-dimensional models, simultaneously simplifying simulation calculations.
Tetrahedral gray code for visualization of genome information.
Ichinose, Natsuhiro; Yada, Tetsushi; Gotoh, Osamu
2014-01-01
We propose a tetrahedral Gray code that facilitates visualization of genome information on the surfaces of a tetrahedron, where the relative abundance of each [Formula: see text]-mer in the genomic sequence is represented by a color of the corresponding cell of a triangular lattice. For biological significance, the code is designed such that the [Formula: see text]-mers corresponding to any adjacent pair of cells differ from each other by only one nucleotide. We present a simple procedure to draw such a pattern on the development surfaces of a tetrahedron. The thus constructed tetrahedral Gray code can demonstrate evolutionary conservation and variation of the genome information of many organisms at a glance. We also apply the tetrahedral Gray code to the honey bee (Apis mellifera) genome to analyze its methylation structure. The results indicate that the honey bee genome exhibits CpG overrepresentation in spite of its methylation ability and that two conserved motifs, CTCGAG and CGCGCG, in the unmethylated regions are responsible for the overrepresentation of CpG.
Tetrahedral gray code for visualization of genome information.
Directory of Open Access Journals (Sweden)
Natsuhiro Ichinose
Full Text Available We propose a tetrahedral Gray code that facilitates visualization of genome information on the surfaces of a tetrahedron, where the relative abundance of each [Formula: see text]-mer in the genomic sequence is represented by a color of the corresponding cell of a triangular lattice. For biological significance, the code is designed such that the [Formula: see text]-mers corresponding to any adjacent pair of cells differ from each other by only one nucleotide. We present a simple procedure to draw such a pattern on the development surfaces of a tetrahedron. The thus constructed tetrahedral Gray code can demonstrate evolutionary conservation and variation of the genome information of many organisms at a glance. We also apply the tetrahedral Gray code to the honey bee (Apis mellifera genome to analyze its methylation structure. The results indicate that the honey bee genome exhibits CpG overrepresentation in spite of its methylation ability and that two conserved motifs, CTCGAG and CGCGCG, in the unmethylated regions are responsible for the overrepresentation of CpG.
Termination shock thermal processes as a possible source for the CMB low-order multipole anomalies
2009-01-01
We discuss the possibility that the observed low-order multipole features of the cosmic microwave background radiation (CMB) all originate in the termination shock (TS) region of the heliosheath that surrounds the solar system. If the intrinsic CMB spectrum is assumed to be a pure monopole (2.73K) then thermodynamic processes occurring within the plasma region of the TS could imprint the observed power spectrum of the low-order multipoles and their alignment (the so-called "axis of evil") ont...
Crossover between tetrahedral and hexagonal structures in liquid water
Energy Technology Data Exchange (ETDEWEB)
Chara, Osvaldo [Instituto de Fisica de Liquidos y Sistemas Biologicos (IFLYSIB), CONICET - Universidad Nacional de La Plata (Argentina); McCarthy, Andres N., E-mail: amccarthy@iflysib.unlp.edu.a [Instituto de Fisica de Liquidos y Sistemas Biologicos (IFLYSIB), CONICET - Universidad Nacional de La Plata (Argentina); Grigera, J. Raul [Instituto de Fisica de Liquidos y Sistemas Biologicos (IFLYSIB), CONICET - Universidad Nacional de La Plata (Argentina)
2011-01-17
It is widely accepted that liquid water structure is comprised of two closely interweaved components; i.e. tetrahedral (low density) and hexagonal (high density) structures. The relative amount of these components is temperature and pressure dependent. We propose an order parameter, based on the radial distribution function, that quantifies the relative structural composition at any defined temperature and pressure, thus establishing the crossover point in structural dominance. At 300 K this point lies close to 2 kbar, pressure at which water looses most of its 'anomalous' properties.
Stable Tetrahedral Aluminum Sites in Hexagonal Mesoporous Aluminosilicates
Institute of Scientific and Technical Information of China (English)
韩宇; 刘宪春; 等
2002-01-01
A unique templating approach for the synthesis of hexagonal mesoporous aluminosilicates via self-assembly of pre-formed aluminosilcate nacoclusters with the templating micella formed by cetyltrimethylammonium bromide (CTAB) is described ,The obtained materials of MAS-5 are hydrothermally stable,which is shown by X-ray diffraction (XRD) analysis,Further-more,as charaacterized by NMR technique ,MAS-5 has taable tetrahedral aluminum sites that is the major contributions to the acidity of aluminosilicate molecular sieve ,and on non-frame-work aluminium species in the saples was observed.
Practical implementation of tetrahedral mesh reconstruction in emission tomography
Boutchko, R.; Sitek, A.; Gullberg, G. T.
2013-05-01
This paper presents a practical implementation of image reconstruction on tetrahedral meshes optimized for emission computed tomography with parallel beam geometry. Tetrahedral mesh built on a point cloud is a convenient image representation method, intrinsically three-dimensional and with a multi-level resolution property. Image intensities are defined at the mesh nodes and linearly interpolated inside each tetrahedron. For the given mesh geometry, the intensities can be computed directly from tomographic projections using iterative reconstruction algorithms with a system matrix calculated using an exact analytical formula. The mesh geometry is optimized for a specific patient using a two stage process. First, a noisy image is reconstructed on a finely-spaced uniform cloud. Then, the geometry of the representation is adaptively transformed through boundary-preserving node motion and elimination. Nodes are removed in constant intensity regions, merged along the boundaries, and moved in the direction of the mean local intensity gradient in order to provide higher node density in the boundary regions. Attenuation correction and detector geometric response are included in the system matrix. Once the mesh geometry is optimized, it is used to generate the final system matrix for ML-EM reconstruction of node intensities and for visualization of the reconstructed images. In dynamic PET or SPECT imaging, the system matrix generation procedure is performed using a quasi-static sinogram, generated by summing projection data from multiple time frames. This system matrix is then used to reconstruct the individual time frame projections. Performance of the new method is evaluated by reconstructing simulated projections of the NCAT phantom and the method is then applied to dynamic SPECT phantom and patient studies and to a dynamic microPET rat study. Tetrahedral mesh-based images are compared to the standard voxel-based reconstruction for both high and low signal-to-noise ratio
Search for Fingerprints of Tetrahedral Symmetry in ^{156}Gd
Energy Technology Data Exchange (ETDEWEB)
Doan, Q. T. [Universite Lyon 1, Villeurbanne, France; Curien, D. [CNRS, Strasbourg, France; Stezowski, O. [Universite Lyon 1, Villeurbanne, France; Dudek, J. [CNRS, Strasbourg, France; Mazurek, K. [H. Niewodniczanski Institute of Nuclear Physics (INP), Krakow, Poland; Gozdz, A. [Maria Curie-Sklodowskiej, Lublin, Poland; Piot, J. [CNRS, Strasbourg, France; Duchene, G. [CNRS, Strasbourg, France; Gall, B. [CNRS, Strasbourg, France; Molique, H. [CNRS, Strasbourg, France; Richet, M. [CNRS, Strasbourg, France; Guinet, D. [Universite Lyon 1, Villeurbanne, France; Redon, N. [Universite Lyon 1, Villeurbanne, France; Schmitt, Ch. [Universite Lyon 1, Villeurbanne, France; Jones, P. [University of Jyvaskyla; Peura, P. [University of Jyvaskyla; Ketelhut, S. [University of Jyvaskyla; Nyman, M. [University of Jyvaskyla; Jakobsson, U. [University of Jyvaskyla; Greenlees, P. T. [University of Jyvaskyla; Julin, R. [University of Jyvaskyla; Juutinen, S. [University of Jyvaskyla; Rahkila, P. [University of Jyvaskyla; Maj, A. [H. Niewodniczanski Institute of Nuclear Physics (INP), Krakow, Poland; Zuber, K. [H. Niewodniczanski Institute of Nuclear Physics (INP), Krakow, Poland; Bednarczyk, P. [H. Niewodniczanski Institute of Nuclear Physics (INP), Krakow, Poland; Schunck, N. [Oak Ridge National Laboratory (ORNL); Dobaczewski, J. [Warsaw University; Astier, A. [CNRS, Orsay, France; Deloncle, I. [CNRS, Orsay, France; Verney, D. [CNRS/IN2P3, Orsay, France; De Angelis, G. [INFN, Laboratori Nazionali di Legnaro, Italy; Gerl, J. [Gesellschaft fur Schwerionenforschung (GSI), Germany
2009-01-01
Theoretical predictions suggest the presence of tetrahedral symmetry as an explanation for the vanishing intra-band E2 transitions at the bottom of the odd-spin negative-parity band in ^{156}Gd. The present study reports on experiment performed to address this phenomenon. It allowed to remove certain ambiguities related to the intra-band E2 transitions in the negative-parity bands to determine the new inter-band transitions and reduced probability ratios B(E2)/B(E1) and, for the first time, to determine the experimental uncertainties related to the latter observable.
Stable Tetrahedral Aluminum Sites in Hexagonal Mesoporous Aluminosilicates
Institute of Scientific and Technical Information of China (English)
HAN,Yu(韩宇); YU,Yi(于沂); XU,Xian-Zhu(许宪祝); XIAO,Feng-Shou(肖丰收); LIU,Xian-Chun(刘宪春); HAN,Xiu-Wen(韩秀文); BAO,Xin-He(包信和)
2002-01-01
A unique templating approach for the synthesis of hexagonal mesoporous aluminosilicates via self-assembly of pre-formed aluminosilcate nanoclusters with the templating micella formed by cetyltrimethylammonium bromide (CTAB) is described.The obtained materials of MAS-5 are hydrothermally stable,which is shown by X-ray diffraction (XRD) analysis. Furthermore, as characterized by NMR technique, MAS-5 has stable tetrahedral aluminum sites that is the major contributions to the acidity of aluminosilicate molecular sieve, and on non-framework aluminium species in the samples was observed.
SHAPE OF POLYMER CHAINS ON A TETRAHEDRAL LATTICE
Institute of Scientific and Technical Information of China (English)
Jian-hua Huang; Me+ng-bo Luo; Wen-hua Jiang; Shi-jun Han
2000-01-01
The shape of unperturbed polymer chains was studied using the Monte Carlo technique on a tetrahedral lattice.The asphericity A, the ratios / and / were calculated for different values of polymer chain length n,conformational energy ε (ε≥ 0) and temperature T. The asphericity A decreases with the increase of chain length and tends to reach its limiting value rapidly with the decrease of γ (γ = ε/kBT). For large n, A is about 0.525 ± 0.005, the ratios/ and / are about 2.7 and 12.0, respectively, and are almost independent of γ, but for short chains, they depend on γ.
Development of a Low-Order Model of an X-Wing Aircraft by System Identification.
1982-02-01
The original purpose of this contract was to prepare a flight test plan for the proposed X-wing demonstrator using system identification to extract...demonstration of the feasibility of using system identification techniques to extract low-order math models from time history data from a detailed X-wing rotor simulation (REXOR).
Termination shock thermal processes as a possible source for the CMB low-order multipole anomalies
Sharpe, H N
2009-01-01
We discuss the possibility that the observed low-order multipole features of the cosmic microwave background radiation (CMB) all originate in the termination shock (TS) region of the heliosheath that surrounds the solar system. If the intrinsic CMB spectrum is assumed to be a pure monopole (2.73K) then thermodynamic processes occurring within the plasma region of the TS could imprint the observed power spectrum of the low-order multipoles and their alignment (the so-called "axis of evil") onto this background isotropic CMB. Conditions are outlined for the geometric shape of the TS region. A key requirement of this model is that the TS plasma be characterized as an optically thin graybody with non-LTE perturbations. Data from the ongoing Voyager missions is critical to this study.
Electron dynamics from low-order harmonics generated by short laser pulses
Xiong, Wei-Hao; Gong, Qihuang; Peng, Liang-You
2017-08-01
Recently, low-order harmonics have gained much attention due to their applications as coherent light sources with a high repetition rate. In addition, the generation process is highly related to the bound electrons and can thus be applied to detect the dynamics of these electrons. In this work, we theoretically investigate the low-order harmonics below the first excited state, produced by a single-cycle optical pulse. We numerically solve the three-dimensional time-dependent Schrödinger equation (TDSE) to calculate the harmonic spectrum. With the help of a perturbation model, we can transparently understand the generation process of the spectrum. The results indicate that the harmonic spectrum can be sensitively influenced by the frequency component of the driving field. We find that the carrier envelope phase (CEP) dependence of low-order-harmonic generation originates from the interference of different harmonic orders. For these harmonics, the CEP effects can only be observed when the spectrum of the driving laser is extremely wide, which corresponds to the very short driving pulse. From the CEP-dependent interference structure, the phase relation of the third and the fifth harmonic can be extracted. The extracted information indicates that the atomic response induces a positive chirp for the emitted low-order harmonics. In addition, we investigated the harmonic phase calculated from the TDSE results. The harmonic phase is different from the phase predicted by the adiabatic model, and this phase difference can be related to the time delay of the electronic response. We extract the time delay from the harmonic phase and explore the CEP and intensity dependence of this time delay.
Testbed Demonstration of Low Order Wavefront Sensing and Control Technology for WFIRST Coronagraph
Shi, Fang; Balasubramanian, K.; Cady, E.; Kern, B.; Lam, R.; Mandic, M.; Patterson, K.; Poberezhskiy, I.; Shields, J.; Seo, J.; Tang, H.; Truong, T.; Wilson, D.
2017-01-01
NASA’s WFIRST-AFTA Coronagraph will be capable of directly imaging and spectrally characterizing giant exoplanets similar to Neptune and Jupiter, and possibly even super-Earths, around nearby stars. To maintain the required coronagraph performance in a realistic space environment, a Low Order Wavefront Sensing and Control (LOWFS/C) subsystem is necessary. The LOWFS/C will use the rejected stellar light to sense and suppress the telescope pointing drift and jitter as well as low order wavefront errors due to the changes in thermal loading of the telescope and the rest of the observatory. The LOWFS/C uses a Zernike phase contrast wavefront sensor with the phase shifting disk combined with the stellar light rejecting occulting mask, a key concept to minimize the non-common path error. Developed as a part of the Dynamic High Contrast Imaging Testbed (DHCIT), the LOWFS/C subsystem also consists of an Optical Telescope Assembly Simulator (OTA-S) to generate the realistic line-of-sight (LoS) drift and jitter as well as low order wavefront error from WFIRST-AFTA telescope’s vibration and thermal drift. The entire LOWFS/C subsystem have been integrated, calibrated, and tested in the Dynamic High Contrast Imaging Testbed. In this presentation we will show the results of LOWFS/C performance during the dynamic coronagraph tests in which we have demonstrated that LOWFS/C is able to maintain the coronagraph contrast with the presence of WFIRST like line-of-sight drift and jitter as well as low order wavefront drifts.
A radiative model of quark masses with binary tetrahedral symmetry
Natale, Alexander
2017-01-01
A radiative model of quark and lepton masses utilizing the binary tetrahedral (T‧) flavor symmetry, or horizontal symmetry, is proposed which produces the first two generation of quark masses through their interactions with vector-like quarks that carry charges under an additional U (1). By softly-breaking the T‧ to a residual Z4 through the vector-like quark masses, a CKM mixing angle close to the Cabibbo angle is produced. In order to generate the cobimaximal neutrino oscillation pattern (θ13 ≠ 0 ,θ23 = π / 4 ,δCP = ± π / 2) and protect the horizontal symmetry from arbitrary corrections in the lepton sector, there are automatically two stabilizing symmetries in the dark sector. Several benchmark cases where the correct relic density is achieved in a multi-component DM scenario, as well as the potential collider signatures of the vector-like quarks are discussed.
Nuclear tetrahedral symmetry: possibly present throughout the periodic table.
Dudek, J; Goźdź, A; Schunck, N; Miśkiewicz, M
2002-06-24
More than half a century after the fundamental, spherical shell structure in nuclei had been established, theoretical predictions indicated that the shell gaps comparable or even stronger than those at spherical shapes may exist. Group-theoretical analysis supported by realistic mean-field calculations indicate that the corresponding nuclei are characterized by the TD(d) ("double-tetrahedral") symmetry group. Strong shell-gap structure is enhanced by the existence of the four-dimensional irreducible representations of TD(d); it can be seen as a geometrical effect that does not depend on a particular realization of the mean field. Possibilities of discovering the TD(d) symmetry in experiment are discussed.
Mechanical dissipation at elevated temperatures in tetrahedral amorphous carbon.
Energy Technology Data Exchange (ETDEWEB)
Sullivan, John P.; Friedmann, Thomas Aquinas; Czaplewski, David A.; Wendt, Joel Robert
2005-05-01
We have measured the temperature dependence of mechanical dissipation in tetrahedral amorphous carbon flexural and torsional resonators over the temperature range from 300 to 1023 K. The mechanical dissipation was found to be controlled by defects within the material, and the magnitude and temperature dependence of the dissipation were found to depend on whether flexural or torsional vibrational modes were excited. The defects that were active under flexural stresses have a relatively flat concentration from 0.4 to 0.7 eV with an ever increasing defect concentration up to 1.9 eV. Under shear stresses (torsion), the defect activation energies increase immediately beginning at 0.4 eV, with increasing defect concentration at higher energies.
Optimal tetrahedral mesh generation for three-dimensional point set
Institute of Scientific and Technical Information of China (English)
秦开怀; 吴边; 关右江; 葛振州
1997-01-01
Three-dimensional (3D) tnangulation is a basic topic in computer graphics. It is considered very difficult to obtain the global optimal 3D triangulatlon, such as the triangulation which satisfies the max-min solid angle criterion A new method called genetic tetrahedral mesh generation algorithm (GTMGA for short) is presented. GT-MGA is based on the principle of genetic algorithm and aims at the global optimal triangulation. With a multi-objective fitness function, GTMGA is able to perform optimizations for different requirements. New crossover operator and mutation operator, polyhedron crossover and polyhedron mutation, are used in GTMGA. It is shown by the experimental results that GTMGA works better than both the 3D Delaunay triangulation and the algorithm based on local transformations.
Photoconductive detection of tetrahedrally coordinated hydrogen in ZnO.
Koch, S G; Lavrov, E V; Weber, J
2012-04-20
In this Letter we apply an innovative experimental approach, which allows us to improve the sensitivity of detecting local vibrational modes (LVMs) even in highly absorbing spectral regions. This photoconductive technique allowed us to confirm a recent suggestion of a new multicenter bond for hydrogen in ZnO [A. Janotti and C. G. Van de Walle, Nature Mater. 6, 44 (2007)]. The two LVMs of the hydrogen substituting oxygen in ZnO are identified at 742 and 792 cm(-1). The modes belong to a nondegenerated A(1) and a twofold degenerated E representations of the C(3v) point group. The tetrahedral coordination of the hydrogen atom is the result of a newly detected multicenter bond for defects in solids.
Low-order models of the motion of sessile droplets on highly hydrophobic surfaces
Wray, Alex; Kahouadji, Lyes; Matar, Omar; Davis, Stephen
2016-11-01
We consider the behaviour of a droplet deposited onto a hydroophobic substrate. This and associated problems have received attention due to their significance in a wide array of experimental and industrial contexts, such as the post-rupture wetting problem is of importance to coating flow applications. Such systems have typically defied low-order analysis due to the multi-valued nature of the interface, but we demonstrate how to resolve this issue in this instance. We begin by analysing the static case. We find that the system is governed by the Young-Laplace equation with the equilbrium shape depending on the Bond number, the contact angle and the volume of the droplet. We solve the system numerically, and use these results to validate a variety of low-order models. We then solve the dynamic problem using both direct numerical simulations and a low-order model based on conservation of energy. EPSRC UK platform Grant MACIPh (EP/L020564/1) and programme Grant MEMPHIS (EP/K003976/1).
UNIFORM SUPERAPPROXIMATION OF THE DERIVATIVE OF TETRAHEDRAL QUADRATIC FINITE ELEMENT APPROXIMATION
Institute of Scientific and Technical Information of China (English)
Jing-hong Liu; Qi-ding Zhu
2005-01-01
In this paper,we will prove the derivative of tetrahedral quadratic finite element approximation is superapproximate to the derivative of the quadratic Lagrange interpolant of the exact solution in the L∞-norm, which can be used to enhance the accuracy of the derivative of tetrahedral quadratic finite element approximation to the derivative of the exact solution.
An 8-node tetrahedral finite element suitable for explicit transient dynamic simulations
Energy Technology Data Exchange (ETDEWEB)
Key, S.W.; Heinstein, M.W.; Stone, C.M. [Sandia National Labs., Albuquerque, NM (United States)
1997-12-31
Considerable effort has been expended in perfecting the algorithmic properties of 8-node hexahedral finite elements. Today the element is well understood and performs exceptionally well when used in modeling three-dimensional explicit transient dynamic events. However, the automatic generation of all-hexahedral meshes remains an elusive achievement. The alternative of automatic generation for all-tetrahedral finite element is a notoriously poor performer, and the 10-node quadratic tetrahedral finite element while a better performer numerically is computationally expensive. To use the all-tetrahedral mesh generation extant today, the authors have explored the creation of a quality 8-node tetrahedral finite element (a four-node tetrahedral finite element enriched with four midface nodal points). The derivation of the element`s gradient operator, studies in obtaining a suitable mass lumping and the element`s performance in applications are presented. In particular, they examine the 80node tetrahedral finite element`s behavior in longitudinal plane wave propagation, in transverse cylindrical wave propagation, and in simulating Taylor bar impacts. The element only samples constant strain states and, therefore, has 12 hourglass modes. In this regard, it bears similarities to the 8-node, mean-quadrature hexahedral finite element. Given automatic all-tetrahedral meshing, the 8-node, constant-strain tetrahedral finite element is a suitable replacement for the 8-node hexahedral finite element and handbuilt meshes.
Why Is the Tetrahedral Bond Angle 109 Degrees? The Tetrahedron-in-a-Cube
Lim, Kieran F.
2012-01-01
The common question of why the tetrahedral angle is 109.471 degrees can be answered using a tetrahedron-in-a-cube, along with some Year 10 level mathematics. The tetrahedron-in-a-cube can also be used to demonstrate the non-polarity of tetrahedral molecules, the relationship between different types of lattice structures, and to demonstrate that…
Automatic low-order aberration correction based on geometry optics: simulations
Yu, Xin; Dong, Lizhi; Liu, Yong; Yang, Ping; Tang, Guomao; Xu, Bing
2016-10-01
The slab laser is a promising architecture to achieve high beam quality and high power. By propagating the laser beams in zigzag geometries, the temperature gradient in the gain medium can be well averaged, and the beam quality in this direction can be excellent. However, the temperature gradient in the non-zigzag direction is not compensated, resulting in aberrations in this direction which lead to poorer beam quality. Among the overall aberrations, the main contributors are two low-order aberrations: astigmatism and defocus. These aberrations will magnify beam divergence angle and degrade beam quality. If the beam divergence angles in both directions are almost zero, the astigmatism and defocus are well corrected. Besides, the output beams of slab lasers are generally in a rectangular aperture with high aspect ratio (normally 1:10), which need to be reshaped into square in many applications. In this paper, a new method is proposed to correct low-order aberrations and reshape the beams of slab lasers. Three lenses are adapted, one is a spherical lens and the others are cylindrical lenses. These lenses work as a beam shaping system, which converts the beam from rectangular into square and the low-order aberrations are compensated simultaneously. Two wavefront sensors are used to detect input and output beam parameters. The initial size of the beam is 4mm×20mm, and peak to valley (PV) value of the wavefront is several tens of microns. Simulation results show that after correction, the dimension becomes 40mm×40mm, and peak to valley (PV) value of the wavefront is less than 1microns.
Low order p-modes in a bipolytropic model of the Sun
Pinzon, G A
2001-01-01
Based on the Solar Standard Model we developed a solar model in hydrostatic equilibrium using two polytropes that describes both the "radiative" and "convective" zones of the solar interior. Then we apply small periodic and adiabatic perturbations on this bipolytropic model in order to obtain proper frequencies and proper functions. The frequencies obtained are in the "p-modes" range of low order l<20 which agrees with the observational data, particularly with the so called five minutes solar oscillations. Key Words: Solar Standard Model, Lane-Emden, Non Radial Oscillations, p-modes.
Unified description of low-order above-threshold ionization on and off axis
Becker, W.; Milošević, D. B.
2016-02-01
A recently developed unified description of low-order above-threshold ionization (Becker et al 2014 J. Phys. B: At. Mol. Opt. Phys. 47 204022; 2015 J. Phys. B: At. Mol. Opt. Phys. 48 151001) is revisited and extended. By considering the rescattering electron energies and angles at the classical cutoffs and the contributions of particular quantum-orbit solutions, it is shown that summing both the backward- and the forward-scattering contributions, within the low-frequency approximation, it is possible to reproduce the observed features of the ATI spectra both for low and high energies and both on and off the laser-polarization axis in the momentum plane.
Polymer gratings based on photopolymerization for low-order distributed feedback polymer lasers
Institute of Scientific and Technical Information of China (English)
Xuanke Zhao; Qingwu Zhao; Qinghua Zhang
2008-01-01
Novel polymer distributed feedback(DFB)gratings are fabricated based on photopolymerization to reduce lasing threshold of polymer lasers.A photopolymer formulation sensitive to 355-nm ultraviolet(UV)light is proposed for the fabrication of polymer gratings and it can be used to form polymer films by spin-coating process.A very low surface-relief depth ranging from 12.5 to about 1.0 nm has been demonstrated with a refractive-index modulation of about 0.012.The experimental results indicate that such polymer gratings have promising potentials for the fabrication of low-order DFB organic semiconductor lasers.
Experimental Verification of Sparse Aperture Mask for Low Order Wavefront Sensing
Subedi, Hari; Kasdin, N. Jeremy
2017-01-01
To directly image exoplanets, future space-based missions are equipped with coronagraphs which manipulate the diffraction of starlight and create regions of high contrast called dark holes. Theoretically, coronagraphs can be designed to achieve the high level of contrast required to image exoplanets, which are billions of times dimmer than their host stars, however the aberrations caused by optical imperfections and thermal fluctuations cause the degradation of contrast in the dark holes. Focal plane wavefront control (FPWC) algorithms using deformable mirrors (DMs) are used to mitigate the quasi-static aberrations caused by optical imperfections. Although the FPWC methods correct the quasi-static aberrations, they are blind to dynamic errors caused by telescope jitter and thermal fluctuations. At Princeton's High Contrast Imaging Lab we have developed a new technique that integrates a sparse aperture mask with the coronagraph to estimate these low-order dynamic wavefront errors. This poster shows the effectiveness of a SAM Low-Order Wavefront Sensor in estimating and correcting these errors via simulation and experiment and compares the results to other methods, such as the Zernike Wavefront Sensor planned for WFIRST.
Directory of Open Access Journals (Sweden)
Ying Li
2017-01-01
Full Text Available Ultrasonic guided waves have recently been used in fracture evaluation and fracture healing monitoring. An axial transmission technique has been used to quantify the impact of the gap breakage width and fracture angle on the amplitudes of low order guided wave modes S0 and A0 under a 100 kHz narrowband excitation. In our two dimensional finite-difference time-domain (2D-FDTD simulation, the long bones are modeled as three layers with a soft tissue overlay and marrow underlay. The simulations of the transversely and obliquely fractured long bones show that the amplitudes of both S0 and A0 decrease as the gap breakage widens. Fixing the crack width, the increase of the fracture angle relative to the cross section perpendicular to the long axis enhances the amplitude of A0, while the amplitude of S0 shows a nonmonotonic trend with the decrease of the fracture angle. The amplitude ratio between the S0 and A0 modes is used to quantitatively evaluate the fracture width and angles. The study suggests that the low order guided wave modes S0 and A0 have potentials for transverse and oblique bone fracture evaluation and fracture healing monitoring.
Low order modelling for feedback control of fluid flows around complex geometries
Dellar, Oliver; Jones, Bryn; Department of Automatic Control; Systems Engineering Collaboration
2015-11-01
The majority of goods transportation vehicles' power is consumed in overcoming aerodynamic drag. Reduction in pressure drag via feedback control could have significant economic and environmental effects on CO2 emissions, and reduce fatigue on the body by suppressing vortex shedding. The difficulty in designing such controllers lies in obtaining models suited to modern control design methods, which are necessarily of much lesser complexity than typical Computational Fluid Dynamics (CFD) models, or models derived from immediate spatial discretisation of the Navier-Stokes equations. This work develops an approach for modelling fluid flows using frequency response data generated for individual computational node sub-systems that result from a CFD type spatial discretisation of the governing equations. Input-to-sensor frequency response data for the overall system are then computed by forming interconnections between adjacent nodes via a Redheffer Star Product operation, from which one typically observes low-order dynamics. With this data, a low-order model can be identified and used for controller design. This method avoids manipulating large matrices and is therefore computationally efficient and numerically well-conditioned. It can be readily applied to complex geometry flows.
First Experimental Results Using Sparse Aperture Mask for Low Order Wavefront Sensing
Subedi, Hari; Zimmerman, Neil T.; Kasdin, N. Jeremy; Eldorado Riggs, A. J.
2016-01-01
We can determine the existence of life outside of earth by analyzing the spectra of exoplanets. Such direct imaging will provide the capability to thoroughly characterize an exoplanet's atmosphere. Direct imaging of exoplanets, however, has many technical challenges and difficulties: scattering and diffraction of light and the large difference in contrast, which is the ratio of brightness between the bright star and the dimmer planet. A coronagraph is an optical device that manipulates the diffraction of starlight and creates a region of high contrast (dark hole) where the dimmer planets can be seen. While in principle the level of contrast required for direct imaging of exoplanets can be achieved by stellar coronagraphic imaging, the resulting dark hole is highly sensitive to phase aberrations. In order to effectively suppress starlight for exoplanet imaging applications, low-order wavefront aberrations entering a coronagraph such as tip-tilt, defocus and coma must be determined and compensated for. A sparse-aperture mask (SAM) can be integrated in the telescopic imaging system to make precise estimate of low-order wavefront aberrations. In this technique, the starlight rejected by the coronagraph's focal plane stop is collimated to a relay pupil, where the mask forms an interference fringe pattern on a detector and the phase aberrations are inferred from this fringe pattern. At Princeton's High Contrast Imaging Lab (HCIL), we have numerically proved this concept and we are currently working on verifying it experimentally.
Shamoon, D.; Lasquellec, S.; Brosseau, C.
2017-07-01
Understanding the collective, low-frequency dielectric properties of heterostructures is a major goal in condensed matter. In 1935, Bruggeman [Ann. Phys. Lpz. 24, 636 (1935)] conceived the concept of an effective medium approximation (EMA) involving a decoupling between the low-order statistics of the electric field fluctuations and the characteristic length scales. We report on and characterize, via finite element studies, the low-order statistics effective permittivity of two-phase 2D and 3D random and deterministic heterostructures as geometry, phase permittivity contrast, and inclusion content are varied. Since EMA analytical expressions become cumbersome even for simple shapes and arrangements, numerical approaches are more suitable for studying heterostructures with complex shapes and topologies. Our numerical study verifies the EMA analytic predictions when the scales are well-separated. Our numerical study compares two approaches for calculating effective permittivity by explicit calculations of local average fields and energy as geometry, phase permittivity contrast, and inclusion content are varied. We study the conditions under which these approaches give a reliable estimate of permittivity by comparing with 2D/3D EMA analytical models and duality relation. By considering 2D checkerboards which consist of a multitude of contiguous N × N square cells, the influence of the internal length scale (i.e., N) on permittivity is discussed.
Connectivity, dynamics, and structure in a tetrahedral network liquid.
Roldán-Vargas, Sándalo; Rovigatti, Lorenzo; Sciortino, Francesco
2017-01-04
We report a detailed computational study by Brownian dynamics simulations of the structure and dynamics of a liquid of patchy particles which forms an amorphous tetrahedral network upon decreasing the temperature. The highly directional particle interactions allow us to investigate the system connectivity by discriminating the total set of particles into different populations according to a penta-modal distribution of bonds per particle. With this methodology we show how the particle bonding process is not randomly independent but it manifests clear bond correlations at low temperatures. We further explore the dynamics of the system in real space and establish a clear relation between particle mobility and particle connectivity. In particular, we provide evidence of anomalous diffusion at low temperatures and reveal how the dynamics is affected by the short-time hopping motion of the weakly bounded particles. Finally we widely investigate the dynamics and structure of the system in Fourier space and identify two quantitatively similar length scales, one dynamic and the other static, which increase upon cooling the system and reach distances of the order of few particle diameters. We summarize our findings in a qualitative picture where the low temperature regime of the viscoelastic liquid is understood in terms of an evolving network of long time metastable cooperative domains of particles.
Tetrahedral Arrangements of Perylene Bisimide Columns via Supramolecular Orientational Memory.
Sahoo, Dipankar; Peterca, Mihai; Aqad, Emad; Partridge, Benjamin E; Heiney, Paul A; Graf, Robert; Spiess, Hans W; Zeng, Xiangbing; Percec, Virgil
2017-01-24
Chiral, shape, and liquid crystalline memory effects are well-known to produce commercial macroscopic materials with important applications as springs, sensors, displays, and memory devices. A supramolecular orientational memory effect that provides complex nanoscale arrangements was only recently reported. This supramolecular orientational memory was demonstrated to preserve the molecular orientation and packing within supramolecular units of a self-assembling cyclotriveratrylene crown at the nanoscale upon transition between its columnar hexagonal and Pm3̅n cubic periodic arrays. Here we report the discovery of supramolecular orientational memory in a dendronized perylene bisimide (G2-PBI) that self-assembles into tetrameric crowns and subsequently self-organizes into supramolecular columns and spheres. This supramolecular orientation memory upon transition between columnar hexagonal and body-centered cubic (BCC) mesophases preserves the 3-fold cubic [111] orientations rather than the 4-fold [100] axes, generating an unusual tetrahedral arrangement of supramolecular columns. These results indicate that the supramolecular orientational memory concept may be general for periodic arrays of self-assembling dendrons and dendrimers as well as for other periodic and quasiperiodic nanoscale organizations comprising supramolecular spheres, generated from other organized complex soft matter including block copolymers and surfactants.
Dynamics and predictability of a low-order wind-driven ocean - atmosphere model
Vannitsem, Stéphane
2013-04-01
The dynamics of a low order coupled wind-driven Ocean-Atmosphere (OA) system is investigated with emphasis on its predictability properties. The low-order coupled deterministic system is composed of a baroclinic atmosphere for which 12 dominant dynamical modes are only retained (Charney and Straus, 1980) and a wind-driven, quasi-geostrophic and reduced-gravity shallow ocean whose field is truncated to four dominant modes able to reproduce the large scale oceanic gyres (Pierini, 2011). The two models are coupled through mechanical forcings only. The analysis of its dynamics reveals first that under aperiodic atmospheric forcings only dominant single gyres (clockwise or counterclockwise) appear. This feature is expected to be related with the specific domain choice over which the coupled system is defined. Second the dynamical quantities characterizing the short-term predictability (Lyapunov exponents, Lyapunov dimension, Kolmogorov-Sinaï (KS) entropy) displays a complex dependence as a function of the key parameters of the system, namely the coupling strength and the external thermal forcing. In particular, the KS-entropy is increasing as a function of the coupling in most of the experiments, implying an increase of the rate of loss of information about the localization of the system on his attractor. Finally the dynamics of the error is explored and indicates, in particular, a rich variety of short term behaviors of the error in the atmosphere depending on the (relative) amplitude of the initial error affecting the ocean, from polynomial (at2 + bt3 + ct4) up to purely exponential evolutions. These features are explained and analyzed in the light of the recent findings on error growth (Nicolis et al, 2009). References Charney J G, Straus DM (1980) Form-Drag Instability, Multiple Equilibria and Propagating Planetary Waves in Baroclinic, Orographically Forced, Planetary Wave Systems. J Atmos Sci 37: 1157-1176. Nicolis C, Perdigao RAP, Vannitsem S (2009) Dynamics of
Energy Technology Data Exchange (ETDEWEB)
Hong, J.H. [Kyungwon University, Songnam (Korea, Republic of)
1995-07-01
This paper describes a method of obtaining transmission network equivalents from the network`s response to a impulse excitation signal. Proposed method is based on the modal decomposition representation for the large-scale interconnected system. For this framework we use Prony analysis to identify the network function of the system and to decompose the large system into a parallel combination of simple first-order systems. As a result, rational network function of optimal low order can be obtained in a direct and simple way. And Thevenin-type of discrete-time filter model can be generated. It can reproduce the driving-point impedance characteristic of the network. Furthermore proposed model can be implemented into the EMTP in a direct manner. The simulation results with the full system representation and the developed equivalent system showed a good agreement. (author). 14 refs., 11 figs.
Low-Order Modeling of Internal Heat Transfer in Biomass Particle Pyrolysis
Energy Technology Data Exchange (ETDEWEB)
Wiggins, Gavin M.; Ciesielski, Peter N.; Daw, C. Stuart
2016-06-16
We present a computationally efficient, one-dimensional simulation methodology for biomass particle heating under conditions typical of fast pyrolysis. Our methodology is based on identifying the rate limiting geometric and structural factors for conductive heat transport in biomass particle models with realistic morphology to develop low-order approximations that behave appropriately. Comparisons of transient temperature trends predicted by our one-dimensional method with three-dimensional simulations of woody biomass particles reveal good agreement, if the appropriate equivalent spherical diameter and bulk thermal properties are used. We conclude that, for particle sizes and heating regimes typical of fast pyrolysis, it is possible to simulate biomass particle heating with reasonable accuracy and minimal computational overhead, even when variable size, aspherical shape, anisotropic conductivity, and complex, species-specific internal pore geometry are incorporated.
A Low Order Model for Analyzing effects of Blade Fatigue Load Control
DEFF Research Database (Denmark)
Kallesøe, Bjarne Skovmose
2006-01-01
, and torsional blade oscillations, and rotor speed). The aerodynamics is described by a model of unsteady aerodynamic. The equations of motion are derived in nonlinear and linear form. The linear equations of motion are used for stability analysis and control design. The nonlinear equations of motion are used...... for time simulations to evaluate control performance. The stability analysis shows that the model is capable of predicting classical flutter, and stall-induced vibrations. The results from the stability analysis are compared with known results, showing good agreement. The model is used to compare......A new low order mathematical model is introduced to analyse blade dynamics and blade load reducing control strategies for wind turbines. The model consists of a typical wing section model combined with a rotor speed model, leading to four structural degrees of freedom (flapwise, edgewise...
Extrusion induced low-order starch matrices: Enzymic hydrolysis and structure.
Zhang, Bin; Dhital, Sushil; Flanagan, Bernadine M; Luckman, Paul; Halley, Peter J; Gidley, Michael J
2015-12-10
Waxy, normal and highwaymen maize starches were extruded with water as sole plasticizer to achieve low-order starch matrices. Of the three starches, we found that only high-amylose extrudate showed lower digestion rate/extent than starches cooked in excess water. The ordered structure of high-amylose starches in cooked and extruded forms was similar, as judged by NMR, XRD and DSC techniques, but enzyme resistance was much greater for extruded forms. Size exclusion chromatography suggested that longer chains were involved in enzyme resistance. We propose that the local molecular density of packing of amylose chains can control the digestion kinetics rather than just crystallinity, with the principle being that density sufficient to either prevent/limit binding and/or slow down catalysis can be achieved by dense amorphous packing.
Historic human impact on low order mountain streams - what role did the dams play?
Larsen, Annegret; Fuelling, Alexander; Wilder, Nicole; Bork, Hans-Rudolf; Larsen, Joshua R.
2014-05-01
The historic damming of central European rivers is extensive, with the highest density concentrated on low-order streams. Construction of dams started mostly in medieval times (~ 1200 years ago) and peaked in the early nineteenth century, resulting in shifting dam densities with different ages and types. Early dams were mainly build for energy , but later their primary purpose shifted to floodplain irrigation . This legacy highlights the intense alteration of small streams by humans in a short time period relative to their Holocene evolution. However, our understanding of the impact of such high number of dams on the ecology, river morphology and sediment storage over longer time periods remains very limited. This knowledge gap becomes critical to address as dam removal and river restoration expands under the implementation of the Water Framework Directive, a European-wide legislative framework. In order to explore the possible effects of this framework on small order streams, we examine the changes that have occurred to a fluvial system since the onset of historic dam building. We combine the analysis of historic maps, chrono-stratigraphy and hydraulic modeling to understand the influence of the large number of dams along the low-order streams in two representative mountain catchments of 3rd and 4th order streams (Elsava and Sinn river in the Spessart and Rhön mountains, Germany). The datings and stratigraphical analysis indicate that the rivers were likely influenced by valley bottom damming before hillslope agriculture caused erosion and an increase of sediment delivery to the streams. Future work will examine the hydraulic behavior of the streams with and without dams in order to better understand their role in floodplain development.
Low-Order Modeling of Dynamic Stall on Airfoils in Incompressible Flow
Narsipur, Shreyas
Unsteady aerodynamics has been a topic of research since the late 1930's and has increased in popularity among researchers studying dynamic stall in helicopters, insect/bird flight, micro air vehicles, wind-turbine aerodynamics, and ow-energy harvesting devices. Several experimental and computational studies have helped researchers gain a good understanding of the unsteady ow phenomena, but have proved to be expensive and time-intensive for rapid design and analysis purposes. Since the early 1970's, the push to develop low-order models to solve unsteady ow problems has resulted in several semi-empirical models capable of effectively analyzing unsteady aerodynamics in a fraction of the time required by high-order methods. However, due to the various complexities associated with time-dependent flows, several empirical constants and curve fits derived from existing experimental and computational results are required by the semi-empirical models to be an effective analysis tool. The aim of the current work is to develop a low-order model capable of simulating incompressible dynamic-stall type ow problems with a focus on accurately modeling the unsteady ow physics with the aim of reducing empirical dependencies. The lumped-vortex-element (LVE) algorithm is used as the baseline unsteady inviscid model to which augmentations are applied to model unsteady viscous effects. The current research is divided into two phases. The first phase focused on augmentations aimed at modeling pure unsteady trailing-edge boundary-layer separation and stall without leading-edge vortex (LEV) formation. The second phase is targeted at including LEV shedding capabilities to the LVE algorithm and combining with the trailing-edge separation model from phase one to realize a holistic, optimized, and robust low-order dynamic stall model. In phase one, initial augmentations to theory were focused on modeling the effects of steady trailing-edge separation by implementing a non-linear decambering
Dynamical Instability Causes the Demise of a Supercooled Tetrahedral Liquid
Gautam, Arvind Kumar; Pingua, Nandlal; Goyal, Aashish; Apte, Pankaj A.
2017-09-01
We investigate the relaxation mechanism of a supercooled tetrahedral liquid at its limit of stability using isothermal isobaric ( NPT) Monte Carlo simulations. In similarity with systems which are far from equilibrium but near the onset of jamming (O'Hern et al. in Phys Rev Lett 93:165702, 2004), we find that the relaxation is characterized by two time-scales: the decay of long-wavelength (slow) fluctuations of potential energy is controlled by the slope [partial (G/N)/partial φ ] of the Gibbs free energy ( G) at a unique value of per particle potential energy φ = φ _{{\\tiny mid}}. The short-wavelength (fast) fluctuations are controlled by the bath temperature T. The relaxation of the supercooled liquid is initiated with a dynamical crossover after which the potential energy fluctuations are biased towards values progressively lesser than φ _{{\\tiny mid}}. The dynamical crossover leads to the change of time-scale, i.e., the decay of long-wavelength potential energy fluctuations (intermediate stage of relaxation). Because of the condition [partial ^2 (G/N)/partial φ ^2 = 0] at φ = φ _{{\\tiny mid}}, the slope [partial (G/N)/partial φ ] has a unique value and governs the intermediate stage of relaxation, which ends just after the crossover. In the subsequent stage, there is a relatively rapid crystallization due to lack of long-wavelength fluctuations and the instability at φ _{{\\tiny mid}}, i.e., the condition that G decreases as configurations with potential energies lower than φ _{{\\tiny mid}} are accessed. The dynamical crossover point and the associated change in the time-scale of fluctuations is found to be consistent with the previous studies.
Institute of Scientific and Technical Information of China (English)
Xin Yi ZHU; Wei Qiang ZHANG; Yu Hua ZHANG; Li Ren CHEN; Yong Min LI
2003-01-01
A series of novel chiral tetrahedral heterometal clusters have firstly been separated oncellulose tris-(3,5-dimethylphenylcarbamate) stationary phase by high performance liquid chrom-atography, using hexane as the mobile phase with various alcohols as modifiers.
Lattice Cleaving: Conforming Tetrahedral Meshes of Multimaterial Domains with Bounded Quality.
Bronson, Jonathan R; Levine, Joshua A; Whitaker, Ross T
2013-01-01
We introduce a new algorithm for generating tetrahedral meshes that conform to physical boundaries in volumetric domains consisting of multiple materials. The proposed method allows for an arbitrary number of materials, produces high-quality tetrahedral meshes with upper and lower bounds on dihedral angles, and guarantees geometric fidelity. Moreover, the method is combinatoric so its implementation enables rapid mesh construction. These meshes are structured in a way that also allows grading, in order to reduce element counts in regions of homogeneity.
Arita, Ken-ichiro
2014-01-01
Shell structures in single-particle energy spectra are investigated against regular tetrahedral type deformation using radial power-law potential model. Employing a natural way of shape parametrization which interpolate sphere and regular tetrahedron, we find prominent shell effects at rather large tetrahedral deformations, which bring about shell energies much larger than the cases of spherical and quadrupole type shapes. We discuss the semiclassical origin of these anomalous shell structures using periodic orbit theory.
Low-order dynamical system model of a fully developed turbulent channel flow
Hamilton, Nicholas; Tutkun, Murat; Cal, Raúl Bayoán
2017-06-01
A reduced order model of a turbulent channel flow is composed from a direct numerical simulation database hosted at the Johns Hopkins University. Snapshot proper orthogonal decomposition (POD) is used to identify the Hilbert space from which the reduced order model is obtained, as the POD basis is defined to capture the optimal energy content by mode. The reduced order model is defined by coupling the evolution of the dynamic POD mode coefficients through their respective time derivative with a least-squares polynomial fit of terms up to third order. Parameters coupling the dynamics of the POD basis are defined in analog to those produced in the classical Galerkin projection. The resulting low-order dynamical system is tested for a range of basis modes demonstrating that the non-linear mode interactions do not lead to a monotonic decrease in error propagation. A basis of five POD modes accounts for 50% of the integrated turbulence kinetic energy but captures only the largest features of the turbulence in the channel flow and is not able to reflect the anticipated flow dynamics. Using five modes, the low-order model is unable to accurately reproduce Reynolds stresses, and the root-mean-square error of the predicted stresses is as great as 30%. Increasing the basis to 28 modes accounts for 90% of the kinetic energy and adds intermediate scales to the dynamical system. The difference between the time derivatives of the random coefficients associated with individual modes and their least-squares fit is amplified in the numerical integration leading to unstable long-time solutions. Periodic recalibration of the dynamical system is undertaken by limiting the integration time to the range of the sampled data and offering the dynamical system new initial conditions. Renewed initial conditions are found by pushing the mode coefficients in the end of the integration time toward a known point along the original trajectories identified through a least-squares projection. Under
Shape effects on the random-packing density of tetrahedral particles.
Zhao, Jian; Li, Shuixiang; Jin, Weiwei; Zhou, Xuan
2012-09-01
Regular tetrahedra have been demonstrated recently giving high packing density in random configurations. However, it is unknown whether the random-packing density of tetrahedral particles with other shapes can reach an even higher value. A numerical investigation on the random packing of regular and irregular tetrahedral particles is carried out. Shape effects of rounded corner, eccentricity, and height on the packing density of tetrahedral particles are studied. Results show that altering the shape of tetrahedral particles by rounding corners and edges, by altering the height of one vertex, or by lateral displacement of one vertex above its opposite face, all individually have the effect of reducing the random-packing density. In general, the random-packing densities of irregular tetrahedral particles are lower than that of regular tetrahedra. The ideal regular tetrahedron should be the shape which has the highest random-packing density in the family of tetrahedra, or even among convex bodies. An empirical formula is proposed to describe the rounded corner effect on the packing density, and well explains the density deviation of tetrahedral particles with different roundness ratios. The particles in the simulations are verified to be randomly packed by studying the pair correlation functions, which are consistent with previous results. The spherotetrahedral particle model with the relaxation algorithm is effectively applied in the simulations.
List-mode image reconstruction for positron emission tomography using tetrahedral voxels
Gillam, John E.; Angelis, Georgios I.; Meikle, Steven R.
2016-09-01
Image space decomposition based on tetrahedral voxels are interesting candidates for use in emission tomography. Tetrahedral voxels provide many of the advantages of point clouds with irregular spacing, such as being intrinsically multi-resolution, yet they also serve as a volumetric partition of the image space and so are comparable to more standard cubic voxels. Additionally, non-rigid displacement fields can be applied to the tetrahedral mesh in a straight-forward manner. So far studies incorporating tetrahedral decomposition of the image space have concentrated on pre-calculated, node-based, system matrix elements which reduces the flexibility of the tetrahedral approach and the capacity to accurately define regions of interest. Here, a list-mode on-the-fly calculation of the system matrix elements is described using a tetrahedral decomposition of the image space and volumetric elements—voxels. The algorithm is demonstrated in the context of awake animal PET which may require both rigid and non-rigid motion compensation, as well as quantification within small regions of the brain. This approach allows accurate, event based, motion compensation including non-rigid deformations.
Tadepalli, Srinivas C; Erdemir, Ahmet; Cavanagh, Peter R
2011-08-11
Finite element analysis has been widely used in the field of foot and footwear biomechanics to determine plantar pressures as well as stresses and strains within soft tissue and footwear materials. When dealing with anatomical structures such as the foot, hexahedral mesh generation accounts for most of the model development time due to geometric complexities imposed by branching and embedded structures. Tetrahedral meshing, which can be more easily automated, has been the approach of choice to date in foot and footwear biomechanics. Here we use the nonlinear finite element program Abaqus (Simulia, Providence, RI) to examine the advantages and disadvantages of tetrahedral and hexahedral elements under compression and shear loading, material incompressibility, and frictional contact conditions, which are commonly seen in foot and footwear biomechanics. This study demonstrated that for a range of simulation conditions, hybrid hexahedral elements (Abaqus C3D8H) consistently performed well while hybrid linear tetrahedral elements (Abaqus C3D4H) performed poorly. On the other hand, enhanced quadratic tetrahedral elements with improved stress visualization (Abaqus C3D10I) performed as well as the hybrid hexahedral elements in terms of contact pressure and contact shear stress predictions. Although the enhanced quadratic tetrahedral element simulations were computationally expensive compared to hexahedral element simulations in both barefoot and footwear conditions, the enhanced quadratic tetrahedral element formulation seems to be very promising for foot and footwear applications as a result of decreased labor and expedited model development, all related to facilitated mesh generation.
Dynamics and predictability of a low-order wind-driven ocean-atmosphere coupled model
Vannitsem, Stéphane
2014-04-01
The dynamics of a low-order coupled wind-driven ocean-atmosphere system is investigated with emphasis on its predictability properties. The low-order coupled deterministic system is composed of a baroclinic atmosphere for which 12 dominant dynamical modes are only retained (Charney and Straus in J Atmos Sci 37:1157-1176, 1980) and a wind-driven, quasi-geostrophic and reduced-gravity shallow ocean whose field is truncated to four dominant modes able to reproduce the large scale oceanic gyres (Pierini in J Phys Oceanogr 41:1585-1604, 2011). The two models are coupled through mechanical forcings only. The analysis of its dynamics reveals first that under aperiodic atmospheric forcings only dominant single gyres (clockwise or counterclockwise) appear, while for periodic atmospheric solutions the double gyres emerge. In the present model domain setting context, this feature is related to the level of truncation of the atmospheric fields, as indicated by a preliminary analysis of the impact of higher wavenumber ("synoptic" scale) modes on the development of oceanic gyres. In the latter case, double gyres appear in the presence of a chaotic atmosphere. Second the dynamical quantities characterizing the short-term predictability (Lyapunov exponents, Lyapunov dimension, Kolmogorov-Sinaï (KS) entropy) displays a complex dependence as a function of the key parameters of the system, namely the coupling strength and the external thermal forcing. In particular, the KS-entropy is increasing as a function of the coupling in most of the experiments, implying an increase of the rate of loss of information about the localization of the system on its attractor. Finally the dynamics of the error is explored and indicates, in particular, a rich variety of short term behaviors of the error in the atmosphere depending on the (relative) amplitude of the initial error affecting the ocean, from polynomial ( at 2 + bt 3 + ct 4) up to exponential-like evolutions. These features are explained
Hamilton, Nicholas; Tutkun, Murat; Cal, Raúl Bayoán
2017-01-01
Proper orthogonal decomposition (POD) is applied to distinct data sets in order to characterize the propagation of error arising from basis truncation in the description of turbulence. Experimental data from stereo particle image velocimetry measurements in a wind turbine array and direct numerical simulation data from a fully developed channel flow are used to illustrate dependence of the anisotropy tensor invariants as a function of POD modes used in low-order descriptions. In all cases, ensembles of snapshots illuminate a variety of anisotropic states of turbulence. In the near wake of a model wind turbine, the turbulence field reflects the periodic interaction between the incoming flow and rotor blade. The far wake of the wind turbine is more homogenous, confirmed by the increased magnitude of the anisotropy factor. By contrast, the channel flow exhibits many anisotropic states of turbulence. In the inner layer of the wall-bounded region, one observes one-component turbulence at the wall; immediately above, the turbulence is dominated by two components, with the outer layer showing fully three-dimensional turbulence, conforming to theory for wall-bounded turbulence. The complexity of flow descriptions resulting from truncated POD bases can be greatly mitigated by severe basis truncations. However, the current work demonstrates that such simplification necessarily exaggerates the anisotropy of the modeled flow and, in extreme cases, can lead to the loss of three-dimensionality. Application of simple corrections to the low-order descriptions of the Reynolds stress tensor significantly reduces the residual root-mean-square error. Similar error reduction is seen in the anisotropy tensor invariants. Corrections of this form reintroduce three-dimensionality to severe truncations of POD bases. A threshold for truncating the POD basis based on the equivalent anisotropy factor for each measurement set required many more modes than a threshold based on energy. The mode
Development of a Low-order Adaptive Optics System at Udaipur Solar Observatory
Indian Academy of Sciences (India)
A. R. Bayanna; B. Kumar; R. E. Louis; P. Venkatakrishnan; S. K. Mathew
2008-03-01
A low-order Adaptive Optics (AO) system is being developed at the Udaipur Solar Observatory and we present in this paper the status of the project, which includes the image stabilization system and calibration of wavefront sensor and deformable mirror. The image stabilization system comprises of a piezo driven tip-tilt mirror, a high speed camera (955 fps), a frame grabber system for sensing the overall tilt and a Linux based Intel Pentium 4 control computer with Red Hat Linux OS. The system operates under PID control. In the closed loop, an rms image motion of 0.1–0.2 arcsec was observed with the improvement factor varying from 10–20 depending on the external conditions. Error rejection bandwidth of the system at 0 dB is 80–100 Hz. In addition to that, we report the on-going efforts in the calibration of lenslet array and deformable mirror for sensing and correcting the local tilt of the wavefront.
Wind farm density and harvested power in very large wind farms: A low-order model
Cortina, G.; Sharma, V.; Calaf, M.
2017-07-01
In this work we create new understanding of wind turbine wakes recovery process as a function of wind farm density using large-eddy simulations of an atmospheric boundary layer diurnal cycle. Simulations are forced with a constant geostrophic wind and a time varying surface temperature extracted from a selected period of the Cooperative Atmospheric Surface Exchange Study field experiment. Wind turbines are represented using the actuator disk model with rotation and yaw alignment. A control volume analysis around each turbine has been used to evaluate wind turbine wake recovery and corresponding harvested power. Results confirm the existence of two dominant recovery mechanisms, advection and flux of mean kinetic energy, which are modulated by the background thermal stratification. For the low-density arrangements advection dominates, while for the highly loaded wind farms the mean kinetic energy recovers through fluxes of mean kinetic energy. For those cases in between, a smooth balance of both mechanisms exists. From the results, a low-order model for the wind farms' harvested power as a function of thermal stratification and wind farm density has been developed, which has the potential to be used as an order-of-magnitude assessment tool.
Different coupled atmosphere-recharge oscillator Low Order Models for ENSO: a projection approach.
Bianucci, Marco; Mannella, Riccardo; Merlino, Silvia; Olivieri, Andrea
2016-04-01
El Ninõ-Southern Oscillation (ENSO) is a large scale geophysical phenomenon where, according to the celebrated recharge oscillator model (ROM), the Ocean slow variables given by the East Pacific Sea Surface Temperature (SST) and the average thermocline depth (h), interact with some fast "irrelevant" ones, representing mostly the atmosphere (the westerly wind burst and the Madden-Julian Oscillation). The fast variables are usually inserted in the model as an external stochastic forcing. In a recent work (M. Bianucci, "Analytical probability density function for the statistics of the ENSO phenomenon: asymmetry and power law tail" Geophysical Research Letters, under press) the author, using a projection approach applied to general deterministic coupled systems, gives a physically reasonable explanation for the use of stochastic models for mimicking the apparent random features of the ENSO phenomenon. Moreover, in the same paper, assuming that the interaction between the ROM and the fast atmosphere is of multiplicative type, i.e., it depends on the SST variable, an analytical expression for the equilibrium density function of the anomaly SST is obtained. This expression fits well the data from observations, reproducing the asymmetry and the power law tail of the histograms of the NINÕ3 index. Here, using the same theoretical approach, we consider and discuss different kind of interactions between the ROM and the other perturbing variables, and we take into account also non linear ROM as a low order model for ENSO. The theoretical and numerical results are then compared with data from observations.
Dynamical system analysis of a low-order tropical cyclone model
Directory of Open Access Journals (Sweden)
Daria Schönemann
2012-02-01
Full Text Available Tropical cyclone dynamics is investigated by means of a conceptual box model. The tropical cyclone (TC is divided into three regions, the eye, eyewall and ambient region. The model forms a low-order dynamical system of three ordinary differential equations. These are based on entropy budget equations comprising processes of surface enthalpy transfer, entropy advection, convection and radiative cooling. For tropical ocean parameter settings, the system possesses four non-trivial steady state solutions when the sea surface temperature (SST is above a critical value. Two steady states are unstable while the two remaining states are stable. Bifurcation diagrams provide an explanation why only finite-amplitude perturbations above a critical SST can transform into TCs. Besides SST, relative humidity of the ambient region forms an important model parameter. The surfaces that describe equilibria as a function of SST and relative humidity reveal a cusp-catastrophe where the two non-trivial equilibria split into four. Within the model regime of four equilibria, cyclogenesis becomes very unlikely due to the repelling and attracting effects of the two additional equilibria. The results are in qualitative agreement with observations and evince the relevance of the simple model approach to the dynamics of TC formation and its maximum potential intensity.
Stochastic modelling and predictability: analysis of a low-order coupled ocean-atmosphere model.
Vannitsem, Stéphane
2014-06-28
There is a growing interest in developing stochastic schemes for the description of processes that are poorly represented in atmospheric and climate models, in order to increase their variability and reduce the impact of model errors. The use of such noise could however have adverse effects by modifying in undesired ways a certain number of moments of their probability distributions. In this work, the impact of developing a stochastic scheme (based on stochastic averaging) for the ocean is explored in the context of a low-order coupled (deterministic) ocean-atmosphere system. After briefly analysing its variability, its ability in predicting the oceanic flow generated by the coupled system is investigated. Different phases in the error dynamics are found: for short lead times, an initial overdispersion of the ensemble forecast is present while the ensemble mean follows a dynamics reminiscent of the combined amplification of initial condition and model errors for deterministic systems; for longer lead times, a reliable diffusive ensemble spread is observed. These different phases are also found for ensemble-oriented skill measures like the Brier score and the rank histogram. The implications of these features on building stochastic models are then briefly discussed.
Directory of Open Access Journals (Sweden)
Agapov Vladimir Pavlovich
2013-03-01
Full Text Available Solid eight-node finite elements are widely used in practical design in spite of the fact that numerous curvilinear finite elements having multiple nodes are developed. This element is suitable for nonlinear calculations if characteristics of a structure are subject to numerous alterations. Therefore, it is preferable that all calculations were simple. An eight-node element meets this requirement. A standard linear shape function is used by many software programmes to construct this element. Strains and stresses remain constant within the limits of the above element.The authors have developed and implemented a solid eight-node isoparametric finite element using PRINS software. The element developed by the authors has improved bending properties. A quadratic out-of-node shape function was used to improve the bending properties of the element. Principal formulas and testing results are provided. Numerical results confirm the accuracy and effectiveness of the element developed by the authors.Описан разработанный авторами и реализованный в вычислительном комплексе ПРИНС восьмиузловой изопараметрический конечный элемент сплошной среды с улучшенными изгибными свойствами. В качестве базового использован известный восьмиузловой конечный элемент с линейными функциями формы. Для улучшения изгибных свойств элемента введены квадратичные внеузловые функции формы. Приведены основные расчетные формулы и результаты решения тестовых задач.
Discovery of a low order drug-cell response surface for applications in personalized medicine
Ding, Xianting; Liu, Wenjia; Weiss, Andrea; Li, Yiyang; Wong, Ieong; Griffioen, Arjan W.; van den Bergh, Hubert; Xu, Hongquan; Nowak-Sliwinska, Patrycja; Ho, Chih-Ming
2014-12-01
The cell is a complex system involving numerous components, which may often interact in a non-linear dynamic manner. Diseases at the cellular level are thus likely to involve multiple cellular constituents and pathways. As some drugs, or drug combinations, may act synergistically on these multiple pathways, they might be more effective than the respective single target agents. Optimizing a drug mixture for a given disease in a particular patient is particularly challenging due to both the difficulty in the selection of the drug mixture components to start out with, and the all-important doses of these drugs to be applied. For n concentrations of m drugs, in principle, nm combinations will have to be tested. As this may lead to a costly and time-consuming investigation for each individual patient, we have developed a Feedback System Control (FSC) technique which can rapidly select the optimal drug-dose combination from the often millions of possible combinations. By testing this FSC technique in a number of experimental systems representing different disease states, we found that the response of cells to multiple drugs is well described by a low order, rather smooth, drug-mixture-input/drug-effect-output multidimensional surface. The main consequences of this are that optimal drug combinations can be found in a surprisingly small number of tests, and that translation from in vitro to in vivo is simplified. This points to the possibility of personalized optimal drug mixtures in the near future. This unexpectedly simple input-output relationship may also lead to a simple solution for handling the issue of human diversity in cancer therapeutics.
Ngo, Phong D; Mansoorabadi, Steven O; Frey, Perry A
2016-08-04
Peptide boronic acids and peptidyl trifluoromethyl ketones (TFKs) inhibit serine proteases by forming monoanionic, tetrahedral adducts to serine in the active sites. Investigators regard these adducts as analogs of monoanionic, tetrahedral intermediates. Density functional theory (DFT) calculations and fractional charge analysis show that tetrahedral adducts of model peptidyl TFKs are structurally and electrostatically very similar to corresponding tetrahedral intermediates. In contrast, the DFT calculations show the structures and electrostatic properties of analogous peptide boronate adducts to be significantly different. The peptide boronates display highly electrostatically positive boron, with correspondingly negative ligands in the tetrahedra. In addition, the computed boron-oxygen and boron-carbon bond lengths in peptide boronates (which are identical or very similar to the corresponding bonds in a peptide boronate adduct of α-lytic protease determined by X-ray crystallography at subangstrom resolution) are significantly longer than the corresponding bond lengths in model tetrahedral intermediates. Since protease-peptidyl TFKs incorporate low-barrier hydrogen bonds (LBHBs) between an active site histidine and aspartate, while the protease-peptide boronates do not, these data complement the spectroscopic and chemical evidence for the participation of LBHBs in catalysis by serine proteases. Moreover, while the potency of these classes of inhibitors can be correlated to the structures of the peptide moieties, the present results indicate that the strength of their bonds to serine contribute significantly to their inhibitory properties.
Implementation of tetrahedral-mesh geometry in Monte Carlo radiation transport code PHITS
Furuta, Takuya; Sato, Tatsuhiko; Han, Min Cheol; Yeom, Yeon Soo; Kim, Chan Hyeong; Brown, Justin L.; Bolch, Wesley E.
2017-06-01
A new function to treat tetrahedral-mesh geometry was implemented in the particle and heavy ion transport code systems. To accelerate the computational speed in the transport process, an original algorithm was introduced to initially prepare decomposition maps for the container box of the tetrahedral-mesh geometry. The computational performance was tested by conducting radiation transport simulations of 100 MeV protons and 1 MeV photons in a water phantom represented by tetrahedral mesh. The simulation was repeated with varying number of meshes and the required computational times were then compared with those of the conventional voxel representation. Our results show that the computational costs for each boundary crossing of the region mesh are essentially equivalent for both representations. This study suggests that the tetrahedral-mesh representation offers not only a flexible description of the transport geometry but also improvement of computational efficiency for the radiation transport. Due to the adaptability of tetrahedrons in both size and shape, dosimetrically equivalent objects can be represented by tetrahedrons with a much fewer number of meshes as compared its voxelized representation. Our study additionally included dosimetric calculations using a computational human phantom. A significant acceleration of the computational speed, about 4 times, was confirmed by the adoption of a tetrahedral mesh over the traditional voxel mesh geometry.
Low order climate models as a tool for cross-disciplinary collaboration
Newton, R.; Pfirman, S. L.; Tremblay, B.; Schlosser, P.
2014-12-01
Human impacts on climate are pervasive and significant and project future states cannot be projected without taking human influence into account. We recently helped convene a meeting of climatologists, policy analysts, lawyers and social scientists to discuss the dramatic loss in Arctic summer sea ice. A dialogue emerged around distinct time scales in the integrated human/natural climate system. Climate scientists tended to discuss engineering solutions as though they could be implemented immediately, whereas lags of 2 or more decades were estimated by social scientists for societal shifts and similar lags were cited for deployment by the engineers. Social scientists tended to project new climate states virtually overnight, while climatologists described time scales of decades to centuries for the system to respond to changes in forcing functions. For the conversation to develop, the group had to come to grips with an increasingly complex set of transient effect time scales and lags between decisions, changes in forcing, and system outputs. We use several low-order dynamical system models to explore mismatched timescales, ranges of lags, and uncertainty in cost estimates on climate outcomes, focusing on Arctic-specific issues. In addition to lessons regarding what is/isn't feasible from a policy and engineering perspective, these models provide a useful tool to concretize cross-disciplinary thinking. They are fast and easy to iterate through a large region of the problem space, while including surprising complexity in their evolution. Thus they are appropriate for investigating the implications of policy in an efficient, but not unrealistic physical setting. (Earth System Models, by contrast, can be too resource- and time-intensive for iteratively testing "what if" scenarios in cross-disciplinary collaborations.) Our runs indicate, for example, that the combined social, engineering and climate physics lags make it extremely unlikely that an ice-free summer ecology
Dudek, Jerzy; Rouvel, David; Mazurek, Katarzyna; Shimizu, Yoshifumi; Tagami, Shingo
2014-01-01
We discuss the predictions of the large scale calculations using the realistic realisation of the phenomenological nuclear mean-field theory. Calculations indicate that certain Zirconium nuclei are tetrahedral-symmetric in their ground-states. After a short overview of the research of the nuclear tetrahedral symmetry in the past we analyse the predictive capacities of the method and focus on the $^{96}$Zr nucleus expected to be tetrahedral in its ground-state.
Mielke, S L; Ryan, R E; Hilgeman, T; Lesyna, L; Madonna, R G; Van Nostrand, W C
1997-11-01
A simple technique based on a Fizeau interferometer to measure the absolute phase shift on reflection for a Fabry-Perot interferometer dielectric stack mirror is described. Excellent agreement between the measured and predicted phase shift on reflection was found. Also described are the salient features of low-order Fabry-Perot interferometers and the demonstration of a near ideal low-order (1-10) Fabry-Perot interferometer through minimizing the phase dispersion on reflection of the dielectric stack. This near ideal performance of a low-order Fabry-Perot interferometer should enable several applications such as compact spectral imagers for solid and gas detection. The large free spectral range of such systems combined with an active control system will also allow simple interactive tuning of wavelength agile laser sources such as CO(2) lasers, external cavity diode lasers, and optical parametric oscillators.
Presentation, calibration and validation of the low-order, DCESS Earth System Model (Version 1
Directory of Open Access Journals (Sweden)
J. O. Pepke Pedersen
2008-11-01
Full Text Available A new, low-order Earth System Model is described, calibrated and tested against Earth system data. The model features modules for the atmosphere, ocean, ocean sediment, land biosphere and lithosphere and has been designed to simulate global change on time scales of years to millions of years. The atmosphere module considers radiation balance, meridional transport of heat and water vapor between low-mid latitude and high latitude zones, heat and gas exchange with the ocean and sea ice and snow cover. Gases considered are carbon dioxide and methane for all three carbon isotopes, nitrous oxide and oxygen. The ocean module has 100 m vertical resolution, carbonate chemistry and prescribed circulation and mixing. Ocean biogeochemical tracers are phosphate, dissolved oxygen, dissolved inorganic carbon for all three carbon isotopes and alkalinity. Biogenic production of particulate organic matter in the ocean surface layer depends on phosphate availability but with lower efficiency in the high latitude zone, as determined by model fit to ocean data. The calcite to organic carbon rain ratio depends on surface layer temperature. The semi-analytical, ocean sediment module considers calcium carbonate dissolution and oxic and anoxic organic matter remineralisation. The sediment is composed of calcite, non-calcite mineral and reactive organic matter. Sediment porosity profiles are related to sediment composition and a bioturbated layer of 0.1 m thickness is assumed. A sediment segment is ascribed to each ocean layer and segment area stems from observed ocean depth distributions. Sediment burial is calculated from sedimentation velocities at the base of the bioturbated layer. Bioturbation rates and oxic and anoxic remineralisation rates depend on organic carbon rain rates and dissolved oxygen concentrations. The land biosphere module considers leaves, wood, litter and soil. Net primary production depends on atmospheric carbon dioxide concentration and
Presentation, calibration and validation of the low-order, DCESS Earth System Model
Directory of Open Access Journals (Sweden)
J. O. P. Pedersen
2008-06-01
Full Text Available A new, low-order Earth system model is described, calibrated and tested against Earth system data. The model features modules for the atmosphere, ocean, ocean sediment, land biosphere and lithosphere and has been designed to simulate global change on time scales of years to millions of years. The atmosphere module considers radiation balance, meridional transport of heat and water vapor between low-mid latitude and high latitude zones, heat and gas exchange with the ocean and sea ice and snow cover. Gases considered are carbon dioxide and methane for all three carbon isotopes, nitrous oxide and oxygen. The ocean module has 100 m vertical resolution, carbonate chemistry and prescribed circulation and mixing. Ocean biogeochemical tracers are phosphate, dissolved oxygen, dissolved inorganic carbon for all three carbon isotopes and alkalinity. Biogenic production of particulate organic matter in the ocean surface layer depends on phosphate availability but with lower efficiency in the high latitude zone, as determined by model fit to ocean data. The calcite to organic carbon rain ratio depends on surface layer temperature. The semi-analytical, ocean sediment module considers calcium carbonate dissolution and oxic and anoxic organic matter remineralisation. The sediment is composed of calcite, non-calcite mineral and reactive organic matter. Sediment porosity profiles are related to sediment composition and a bioturbated layer of 0.1 m thickness is assumed. A sediment segment is ascribed to each ocean layer and segment area stems from observed ocean depth distributions. Sediment burial is calculated from sedimentation velocities at the base of the bioturbated layer. Bioturbation rates and oxic and anoxic remineralisation rates depend on organic carbon rain rates and dissolved oxygen concentrations. The land biosphere module considers leaves, wood, litter and soil. Net primary production depends on atmospheric carbon dioxide concentration and
On the relation between hydrogen bonds, tetrahedral order and molecular mobility in model water
Pereyra, R G; Malaspina, D C; Carignano, M A
2013-01-01
We studied by molecular dynamics simulations the relation existing between the lifetime of hydrogen bonds, the tetrahedral order and the diffusion coefficient of model water. We tested four different models: SPC/E, TIP4P-Ew, TIP5P-Ew and Six-site, these last two having sites explicitly resembling the water lone pairs. While all the models perform reasonably well at ambient conditions, their behavior is significantly different for temperatures below 270 K. The models with explicit lone-pairs have a longer hydrogen bond lifetime, a better tetrahedral order and a smaller diffusion coefficient than the models without them.
Institute of Scientific and Technical Information of China (English)
陈刚; 冯民富; 何银年
2013-01-01
A unified analysis is presented for the stabilized methods including the pres-sure projection method and the pressure gradient local projection method of conforming and nonconforming low-order mixed finite elements for the stationary Navier-Stokes equa-tions. The existence and uniqueness of the solution and the optimal error estimates are proved.
Mankbadi, M. R.; Georgiadis, N. J.; DeBonis, J. R.
2015-01-01
The objective of this work is to compare a high-order solver with a low-order solver for performing large-eddy simulations (LES) of a compressible mixing layer. The high-order method is the Wave-Resolving LES (WRLES) solver employing a Dispersion Relation Preserving (DRP) scheme. The low-order solver is the Wind-US code, which employs the second-order Roe Physical scheme. Both solvers are used to perform LES of the turbulent mixing between two supersonic streams at a convective Mach number of 0.46. The high-order and low-order methods are evaluated at two different levels of grid resolution. For a fine grid resolution, the low-order method produces a very similar solution to the high-order method. At this fine resolution the effects of numerical scheme, subgrid scale modeling, and filtering were found to be negligible. Both methods predict turbulent stresses that are in reasonable agreement with experimental data. However, when the grid resolution is coarsened, the difference between the two solvers becomes apparent. The low-order method deviates from experimental results when the resolution is no longer adequate. The high-order DRP solution shows minimal grid dependence. The effects of subgrid scale modeling and spatial filtering were found to be negligible at both resolutions. For the high-order solver on the fine mesh, a parametric study of the spanwise width was conducted to determine its effect on solution accuracy. An insufficient spanwise width was found to impose an artificial spanwise mode and limit the resolved spanwise modes. We estimate that the spanwise depth needs to be 2.5 times larger than the largest coherent structures to capture the largest spanwise mode and accurately predict turbulent mixing.
Haussaire, Jean-Matthieu; Bocquet, Marc
2016-04-01
Atmospheric chemistry models are becoming increasingly complex, with multiphasic chemistry, size-resolved particulate matter, and possibly coupled to numerical weather prediction models. In the meantime, data assimilation methods have also become more sophisticated. Hence, it will become increasingly difficult to disentangle the merits of data assimilation schemes, of models, and of their numerical implementation in a successful high-dimensional data assimilation study. That is why we believe that the increasing variety of problems encountered in the field of atmospheric chemistry data assimilation puts forward the need for simple low-order models, albeit complex enough to capture the relevant dynamics, physics and chemistry that could impact the performance of data assimilation schemes. Following this analysis, we developped a low-order coupled chemistry meteorology model named L95-GRS [1]. The advective wind is simulated by the Lorenz-95 model, while the chemistry is made of 6 reactive species and simulates ozone concentrations. With this model, we carried out data assimilation experiments to estimate the state of the system as well as the forcing parameter of the wind and the emissions of chemical compounds. This model proved to be a powerful playground giving insights on the hardships of online and offline estimation of atmospheric pollution. Building on the results on this low-order model, we test advanced data assimilation methods on a state-of-the-art chemical transport model to check if the conclusions obtained with our low-order model still stand. References [1] Haussaire, J.-M. and Bocquet, M.: A low-order coupled chemistry meteorology model for testing online and offline data assimilation schemes, Geosci. Model Dev. Discuss., 8, 7347-7394, doi:10.5194/gmdd-8-7347-2015, 2015.
Tetrahedral symmetry in Zr nuclei: Calculations of low-energy excitations with Gogny interaction
Tagami, Shingo; Dudek, Jerzy
2014-01-01
We report on the results of the calculations of the low energy excitation patterns for three Zirconium isotopes, viz. $^{80}$Zr$_{40}$, $^{96}$Zr$_{56}$ and $^{110}$Zr$_{70}$, reported by other authors to be doubly-magic tetrahedral nuclei (with tetrahedral magic numbers $Z$=40 and $N$=40, 56 and 70). We employ the realistic Gogny effective interactions using three variants of their parametrisation and the particle-number, parity and the angular-momentum projection techniques. We confirm quantitatively that the resulting spectra directly follow the pattern expected from the group theory considerations for the tetrahedral symmetric quantum objects. We also find out that, for all the nuclei studied, the correlation energy obtained after the angular momentum projection is very large for the tetrahedral deformation as well as other octupole deformations. The lowering of the energies of the resulting configurations is considerable, i.e. by about 10 MeV or even more, once again confirming the significance of the an...
A review of defects and disorder in multinary tetrahedrally bonded semiconductors
Baranowski, Lauryn L.; Zawadzki, Pawel; Lany, Stephan; Toberer, Eric S.; Zakutayev, Andriy
2016-12-01
Defects are critical to understanding the electronic properties of semiconducting compounds, for applications such as light-emitting diodes, transistors, photovoltaics, and thermoelectrics. In this review, we describe our work investigating defects in tetrahedrally bonded, multinary semiconductors, and discuss the place of our research within the context of publications by other groups. We applied experimental and theory techniques to understand point defects, structural disorder, and extended antisite defects in one semiconductor of interest for photovoltaic applications, Cu2SnS3. We contrast our findings on Cu2SnS3 with other chemically related Cu-Sn-S compounds, as well as structurally related compounds such as Cu2ZnSnS4 and Cu(In,Ga)Se2. We find that evaluation of point defects alone is not sufficient to understand defect behavior in multinary tetrahedrally bonded semiconductors. In the case of Cu2SnS3 and Cu2ZnSnS4, structural disorder and entropy-driven cation clustering can result in nanoscale compositional inhomogeneities which detrimentally impact the electronic transport. Therefore, it is not sufficient to assess only the point defect behavior of new multinary tetrahedrally bonded compounds; effects such as structural disorder and extended antisite defects must also be considered. Overall, this review provides a framework for evaluating tetrahedrally bonded semiconducting compounds with respect to their defect behavior for photovoltaic and other applications, and suggests new materials that may not be as prone to such imperfections.
Fostering Teacher Development to a Tetrahedral Orientation in the Teaching of Chemistry
Lewthwaite, Brian; Wiebe, Rick
2011-01-01
This paper reports on the initial outcomes from the end of the fourth year of a 5 year research and professional development project to improve chemistry teaching among three cohorts of chemistry teachers in Manitoba, Canada. The project responds to a new curriculum introduction advocating a tetrahedral orientation (Mahaffy, "Journal of…
A Review of Defects and Disorder in Multinary Tetrahedrally Bonded Semiconductors
Energy Technology Data Exchange (ETDEWEB)
Baranowski, Lauryn L.; Zawadzki, Pawel; Lany, Stephan; Toberer, Eric S.; Zakutayev, Andriy
2016-12-01
Defects are critical to understanding the electronic properties of semiconducting compounds, for applications such as light-emitting diodes, transistors, photovoltaics, and thermoelectrics. In this review, we describe our work investigating defects in tetrahedrally bonded, multinary semiconductors, and discuss the place of our research within the context of publications by other groups. We applied experimental and theory techniques to understand point defects, structural disorder, and extended antisite defects in one semiconductor of interest for photovoltaic applications, Cu2SnS3. We contrast our findings on Cu2SnS3 with other chemically related Cu-Sn-S compounds, as well as structurally related compounds such as Cu2ZnSnS4 and Cu(In,Ga)Se2. We find that evaluation of point defects alone is not sufficient to understand defect behavior in multinary tetrahedrally bonded semiconductors. In the case of Cu2SnS3 and Cu2ZnSnS4, structural disorder and entropy-driven cation clustering can result in nanoscale compositional inhomogeneities which detrimentally impact the electronic transport. Therefore, it is not sufficient to assess only the point defect behavior of new multinary tetrahedrally bonded compounds; effects such as structural disorder and extended antisite defects must also be considered. Overall, this review provides a framework for evaluating tetrahedrally bonded semiconducting compounds with respect to their defect behavior for photovoltaic and other applications, and suggests new materials that may not be as prone to such imperfections.
Effect of Substrate Bias on Microstructure and Properties of Tetrahedral Amorphous Carbon Films
Institute of Scientific and Technical Information of China (English)
Jiaqi ZHU; Jiecai HAN; Songhe MENG; Qiang LI; Manlin TAN
2003-01-01
The microstructure and properties of tetrahedral amorphous carbon (ta-C) films deposited by the filtered cathodic vacuum arc technology has been investigated by visible Raman spectroscopy, AFM and Nano-indentor. The Raman spectra have been fitted with a s
Mixed-metal chalcogenide tetrahedral clusters with an exo-polyhedral metal fragment.
Yuvaraj, K; Roy, Dipak Kumar; Anju, V P; Mondal, Bijnaneswar; Varghese, Babu; Ghosh, Sundargopal
2014-12-07
The reaction of metal carbonyl compounds with group 6 and 8 metallaboranes led us to report the synthesis and structural characterization of several novel mixed-metal chalcogenide tetrahedral clusters. Thermolysis of arachno-[(Cp*RuCO)2B2H6], 1, and [Os3(CO)12] in the presence of 2-methylthiophene yielded [Cp*Ru(CO)2(μ-H){Os3(CO)9}S], 3, and [Cp*Ru(μ-H){Os3(CO)11}], 4. In a similar fashion, the reaction of [(Cp*Mo)2B5H9], 2, with [Ru3(CO)12] and 2-methylthiophene yielded [Cp*Ru(CO)2(μ-H){Ru3(CO)9}S], 5, and conjuncto-[(Cp*Mo)2B5H8(μ-H){Ru3(CO)9}S], 6. Both compounds 3 and 5 can be described as 50-cve (cluster valence electron) mixed-metal chalcogenide clusters, in which a sulfur atom replaces one of the vertices of the tetrahedral core. Compounds 3 and 5 possess a [M3S] tetrahedral core, in which the sulfur is attached to an exo-metal fragment, unique in the [M3S] metal chalcogenide tetrahedral arrangements. All the compounds have been characterized by mass spectrometry, IR, and (1)H, (11)B and (13)C NMR spectroscopy in solution, and the solid state structures were unequivocally established by crystallographic analysis of compounds 3, 5 and 6.
A tetrahedral mesh generation approach for 3D marine controlled-source electromagnetic modeling
Um, Evan Schankee; Kim, Seung-Sep; Fu, Haohuan
2017-03-01
3D finite-element (FE) mesh generation is a major hurdle for marine controlled-source electromagnetic (CSEM) modeling. In this paper, we present a FE discretization operator (FEDO) that automatically converts a 3D finite-difference (FD) model into reliable and efficient tetrahedral FE meshes for CSEM modeling. FEDO sets up wireframes of a background seabed model that precisely honors the seafloor topography. The wireframes are then partitioned into multiple regions. Outer regions of the wireframes are discretized with coarse tetrahedral elements whose maximum size is as large as a skin depth of the regions. We demonstrate that such coarse meshes can produce accurate FE solutions because numerical dispersion errors of tetrahedral meshes do not accumulate but oscillates. In contrast, central regions of the wireframes are discretized with fine tetrahedral elements to describe complex geology in detail. The conductivity distribution is mapped from FD to FE meshes in a volume-averaged sense. To avoid excessive mesh refinement around receivers, we introduce an effective receiver size. Major advantages of FEDO are summarized as follow. First, FEDO automatically generates reliable and economic tetrahedral FE meshes without adaptive meshing or interactive CAD workflows. Second, FEDO produces FE meshes that precisely honor the boundaries of the seafloor topography. Third, FEDO derives multiple sets of FE meshes from a given FD model. Each FE mesh is optimized for a different set of sources and receivers and is fed to a subgroup of processors on a parallel computer. This divide and conquer approach improves the parallel scalability of the FE solution. Both accuracy and effectiveness of FEDO are demonstrated with various CSEM examples.
Singh, Garima; Guyon, Olivier; Baudoz, Pierre; Jovanovic, Nemanja; Martinache, Frantz; Kudo, Tomoyuki; Serabyn, Eugene; Kuhn, Jonas
2015-01-01
The ability to characterize exoplanets by spectroscopy of their atmospheres requires direct imaging techniques to isolate planet signal from the bright stellar glare. One of the limitations with the direct detection of exoplanets, either with ground- or space-based coronagraphs, is pointing errors and other low-order wavefront aberrations. The coronagraphic detection sensitivity at the diffraction limit therefore depends on how well low-order aberrations upstream of the focal plane mask are corrected. To prevent starlight leakage at the inner working angle of a phase mask coronagraph, we have introduced a Lyot-based low-order wavefront sensor (LLOWFS), which senses aberrations using the rejected starlight diffracted at the Lyot plane. In this paper, we present the implementation, testing and results of LLOWFS on the Subaru Coronagraphic Extreme Adaptive Optics system (SCExAO) at the Subaru Telescope. We have controlled thirty-five Zernike modes of a H-band vector vortex coronagraph in the laboratory and ten Z...
Selective formation of tetrahedral Pt nanocrystals from K2PtCl6/PVP
Institute of Scientific and Technical Information of China (English)
YU Yingtao; XU Boqing
2003-01-01
Tetrahedral platinum (Pt) nanocrystals (3-8 nm) are synthesized in high selectivity (ca. 80%) from hydrogen reduction of aqueous K2PtCl6 by using polyvinylpyrrolidone (PVP: Mw≈360000) as a protector. Morphology (TEM) measurements of the metal colloids and UV-Vis absorption of the colloidal solution are employed to monitor the tetrahedron formation during the syntheses with varying K2PtCl6/PVP ratios. The results clearly show a two-stage process for the selective formation of tetrahedral nanocrystals. Rapid nucleation and crystal formation at the early stage result in round-like crystallites and the external facet evolution in thereafter slow crystal growth leads selectively to the formation of the tetrahedrons.
Fostering Teacher Development to a Tetrahedral Orientation in the Teaching of Chemistry
Lewthwaite, Brian; Wiebe, Rick
2011-11-01
This paper reports on the initial outcomes from the end of the fourth year of a 5 year research and professional development project to improve chemistry teaching among three cohorts of chemistry teachers in Manitoba, Canada. The project responds to a new curriculum introduction advocating a tetrahedral orientation (Mahaffy, Journal of Chemical Education 83(1), 49-55, 2006) to the teaching of chemistry. The project in its entirety is based upon several theoretical models in fostering chemistry teacher development (in particular Bronfenbrenner's bio-ecological model). These models are described, as is the progress made by teachers based upon the use of a Chemistry Teacher Inventory and associated teacher responses. Overall, statistical analysis of perceptions of their own teaching and comments made by teachers suggests they are showing limited development towards a tetrahedral orientation, albeit in a manner consistent with the curriculum. Ongoing research-based activities in this project are also described.
Transport of phase space densities through tetrahedral meshes using discrete flow mapping
Bajars, Janis; Sondergaard, Niels; Tanner, Gregor
2016-01-01
Discrete flow mapping was recently introduced as an efficient ray based method determining wave energy distributions in complex built up structures. Wave energy densities are transported along ray trajectories through polygonal mesh elements using a finite dimensional approximation of a ray transfer operator. In this way the method can be viewed as a smoothed ray tracing method defined over meshed surfaces. Many applications require the resolution of wave energy distributions in three-dimensional domains, such as in room acoustics, underwater acoustics and for electromagnetic cavity problems. In this work we extend discrete flow mapping to three-dimensional domains by propagating wave energy densities through tetrahedral meshes. The geometric simplicity of the tetrahedral mesh elements is utilised to efficiently compute the ray transfer operator using a mixture of analytic and spectrally accurate numerical integration. The important issue of how to choose a suitable basis approximation in phase space whilst m...
3D level set methods for evolving fronts on tetrahedral meshes with adaptive mesh refinement
Morgan, Nathaniel R.; Waltz, Jacob I.
2017-05-01
The level set method is commonly used to model dynamically evolving fronts and interfaces. In this work, we present new methods for evolving fronts with a specified velocity field or in the surface normal direction on 3D unstructured tetrahedral meshes with adaptive mesh refinement (AMR). The level set field is located at the nodes of the tetrahedral cells and is evolved using new upwind discretizations of Hamilton-Jacobi equations combined with a Runge-Kutta method for temporal integration. The level set field is periodically reinitialized to a signed distance function using an iterative approach with a new upwind gradient. The details of these level set and reinitialization methods are discussed. Results from a range of numerical test problems are presented.
Miao, Peng; Wang, Bidou; Chen, Xifeng; Li, Xiaoxi; Tang, Yuguo
2015-03-25
MicroRNAs are not only important regulators of a wide range of cellular processes but are also identified as promising disease biomarkers. Due to the low contents in serum, microRNAs are always difficult to detect accurately . In this study, an electrochemical biosensor for ultrasensitive detection of microRNA based on tetrahedral DNA nanostructure is developed. Four DNA single strands are engineered to form a tetrahedral nanostructure with a pendant stem-loop and modified on a gold electrode surface, which largely enhances the molecular recognition efficiency. Moreover, taking advantage of strand displacement polymerization, catalytic recycling of microRNA, and silver nanoparticle-based solid-state Ag/AgCl reaction, the proposed biosensor exhibits high sensitivity with the limit of detection down to 0.4 fM. This biosensor shows great clinical value and may have practical utility in early diagnosis and prognosis of certain diseases.
Pleiner, Harald; Brand, Helmut R
2014-02-01
We discuss the symmetry properties as well as the dynamic behavior of various non-polar nematic liquid crystal phases with tetrahedral order. We concentrate on systems that show biaxial nematic order coexisting with octupolar (tetrahedral) order. Non-polar examples are phases with D2 and S4 symmetries, which can be characterized as biaxial nematics lacking inversion symmetry. It is this combination that allows for new features in the statics and dynamics of these phases. The D2-symmetric phase is chiral, even for achiral molecules, and shows ambidextrous chirality in all three preferred directions. The achiral S4-symmetric phase allows for ambidextrous helicity, similar to the higher-symmetric D2d-symmetric phase. Such phases are candidates for nematic phases made from banana-shaped molecules.
A study of pH-dependence of shrink and stretch of tetrahedral DNA nanostructures.
Wang, Ping; Xia, Zhiwei; Yan, Juan; Liu, Xunwei; Yao, Guangbao; Pei, Hao; Zuo, Xiaolei; Sun, Gang; He, Dannong
2015-04-21
We monitored the shrink and stretch of the tetrahedral DNA nanostructure (TDN) and the i-motif connected TDN structure at pH 8.5 and pH 4.5, and we found that not only the i-motif can change its structure when the pH changes, but also the TDN and the DNA double helix change their structures when the pH changes.
A Novel Tetrahedral Mesh Generation Method for Rotating Machines Including End-Coil Region
Yamashita, Hideo; Yamaji, Akihisa; Cingoski, Vlatko; Kaneda, Kazufumi
1996-01-01
In this paper, a novel method for generating tetrahedral finite-element meshes suitable for 3-D finite element analysis of rotating machines is presented. The proposed method enables the easy development of 3-D meshes for various rotating machines, especially in the end-coil region and the surrounding air region. Tessellation of the 3-D region is made possible by simple extension of a previously generated 2-D triangular mesh, used as a model mesh, into the third dimension.
An Efficient Optimization Procedure for Tetrahedral Meshes by Chaos Search Algorithm
Institute of Scientific and Technical Information of China (English)
SUN ShuLi (孙树立); LIU JianFei (刘剑飞)
2003-01-01
A simple and efficient local optimization-based procedure for node repositioning/smoothing of three-dimensional tetrahedral meshes is presented. The initial tetrahedral mesh is optimized with respect to a specified element shape measure by chaos search algorithm, which is very effective for the optimization problems with only a few design variables. Examples show that the presented smoothing procedure can provide favorable conditions for local transformation approach and the quality of mesh can be significantly improved by the combination of these two procedures with respect to a specified element shape measure. Meanwhile, several commonly used shape measures for tetrahedral element, which are considered to be equivalent in some weak sense over a long period of time, are briefly re-examined in this paper. Preliminary study indicates that using different measures to evaluate the change of element shape will probably lead to inconsistent result for both well shaped and poorly shaped elements. The proposed smoothing approach can be utilized as an appropriate and effective tool for evaluating element shape measures and their influence on mesh optimization process and optimal solution.
A FAST ITERATIVE METHOD FOR SOLVING THE EIKONAL EQUATION ON TETRAHEDRAL DOMAINS.
Fu, Zhisong; Kirby, Robert M; Whitaker, Ross T
2013-01-01
Generating numerical solutions to the eikonal equation and its many variations has a broad range of applications in both the natural and computational sciences. Efficient solvers on cutting-edge, parallel architectures require new algorithms that may not be theoretically optimal, but that are designed to allow asynchronous solution updates and have limited memory access patterns. This paper presents a parallel algorithm for solving the eikonal equation on fully unstructured tetrahedral meshes. The method is appropriate for the type of fine-grained parallelism found on modern massively-SIMD architectures such as graphics processors and takes into account the particular constraints and capabilities of these computing platforms. This work builds on previous work for solving these equations on triangle meshes; in this paper we adapt and extend previous two-dimensional strategies to accommodate three-dimensional, unstructured, tetrahedralized domains. These new developments include a local update strategy with data compaction for tetrahedral meshes that provides solutions on both serial and parallel architectures, with a generalization to inhomogeneous, anisotropic speed functions. We also propose two new update schemes, specialized to mitigate the natural data increase observed when moving to three dimensions, and the data structures necessary for efficiently mapping data to parallel SIMD processors in a way that maintains computational density. Finally, we present descriptions of the implementations for a single CPU, as well as multicore CPUs with shared memory and SIMD architectures, with comparative results against state-of-the-art eikonal solvers.
Tetrahedral Element Shape Optimization via the Jacobian Determinant and Condition Number
Energy Technology Data Exchange (ETDEWEB)
FREITAG,LORI A.; KNUPP,PATRICK
1999-09-27
We present a new shape measure for tetrahedral elements that is optimal in the sense that it gives the distance of a tetrahedron from the set of inverted elements. This measure is constructed from the condition number of the linear transformation between a unit equilateral tetrahedron and any tetrahedron with positive volume. We use this shape measure to formulate two optimization objective functions that are differentiated by their goal: the first seeks to improve the average quality of the tetrahedral mesh; the second aims to improve the worst-quality element in the mesh. Because the element condition number is not defined for tetrahedral with negative volume, these objective functions can be used only when the initial mesh is valid. Therefore, we formulate a third objective function using the determinant of the element Jacobian that is suitable for mesh untangling. We review the optimization techniques used with each objective function and present experimental results that demonstrate the effectiveness of the mesh improvement and untangling methods. We show that a combined optimization approach that uses both condition number objective functions obtains the best-quality meshes.
Tetrahedral element shape optimization via the Jacobian determinant and condition number.
Energy Technology Data Exchange (ETDEWEB)
Freitag, L. A.; Knupp, P. M.
1999-07-30
We present a new shape measure for tetrahedral elements that is optimal in the sense that it gives the distance of a tetrahedron from the set of inverted elements. This measure is constructed from the condition number of the linear transformation between a unit equilateral tetrahedron and any tetrahedron with positive volume. We use this shape measure to formulate two optimization objective functions that are differentiated by their goal: the first seeks to improve the average quality of the tetrahedral mesh; the second aims to improve the worst-quality element in the mesh. Because the element condition number is not defined for tetrahedral with negative volume, these objective functions can be used only when the initial mesh is valid. Therefore, we formulate a third objective function using the determinant of the element Jacobian that is suitable for mesh untangling. We review the optimization techniques used with each objective function and present experimental results that demonstrate the effectiveness of the mesh improvement and untangling methods. We show that a combined optimization approach that uses both condition number objective functions obtains the best-quality meshes.
Richard, Jacques C.
1995-01-01
This paper presents a dynamic model of an internal combustion engine coupled to a variable pitch propeller. The low-order, nonlinear time-dependent model is useful for simulating the propulsion system of general aviation single-engine light aircraft. This model is suitable for investigating engine diagnostics and monitoring and for control design and development. Furthermore, the model may be extended to provide a tool for the study of engine emissions, fuel economy, component effects, alternative fuels, alternative engine cycles, flight simulators, sensors, and actuators. Results show that the model provides a reasonable representation of the propulsion system dynamics from zero to 10 Hertz.
A three-dimensional tetrahedral-shaped conjugated small molecule for organic solar cells
Directory of Open Access Journals (Sweden)
QIN Yang
2014-04-01
Full Text Available We report the synthesis of a novel three-dimensional tetrahedral-shaped small molecule,SO,containing a tetraphenylsilane core and cyanoester functionalized terthiophene arms.A deep lying HOMO energy level of -5.3 eV and a narrow bandgap of 1.9 eV were obtained from cyclic voltammetry measurements.Absorption,X-ray scattering and differential scanning calorimetry experiments all indicate high crystallinity of this compound.Solar cells employing SO were fabricated and evaluated.The relatively low performance was mainly ascribed to lack of appreciable phase separation,which is confirmed by optical microscopy.
Raman spectra of nitrogen-doped tetrahedral amorphous carbon from first principles
Institute of Scientific and Technical Information of China (English)
NIU Li; ZHU JiaQi; GAO Wei; HAN Xiao; DU ShanYi
2009-01-01
The non-resonant vibrational Raman spectra of nitrogen-doped tetrahedral amorphous carbon have been calculated from first principles, including the generation of s structural model, and the calculation of vibrational frequencies, vibrational eigenmodes and Raman coupling tensors. The calculated Raman spectra are in good agreement with the experimental results. The broad band at around 500 cm~(-1) arises from mixed bonds. The T peak originates from the vibrations of sp~3 carbon and the G peak comes from the stretching vibrations of sp~2-type bonding of C=C and C=N. The simulation results indicate the direct contribution of N vibrations to Raman spectra.
Experimental evidence of tetrahedral interstitial and bond-centered Er in Ge
Decoster, S; Wahl, U; Correia, J G; Vantomme, A
2008-01-01
We report on an emission channeling study of the lattice site location of implanted Er in Ge together with its thermal stability. We found direct experimental evidence of Er atoms located on the tetrahedral (T) interstitial site and on the bond-centered (BC) site, with a maximum total occupancy after annealing at 400 °C. Whereas Er is expected to occupy the T site in a diamond crystal structure, the observation of BC Er in Ge is more surprising and believed to be related to the Er-vacancy defect in the split-vacancy complex configuration.
Tetrahedral-Mesh Simulation of Turbulent Flows with the Space-Time Conservative Schemes
Chang, Chau-Lyan; Venkatachari, Balaji; Cheng, Gary C.
2015-01-01
Direct numerical simulations of turbulent flows are predominantly carried out using structured, hexahedral meshes despite decades of development in unstructured mesh methods. Tetrahedral meshes offer ease of mesh generation around complex geometries and the potential of an orientation free grid that would provide un-biased small-scale dissipation and more accurate intermediate scale solutions. However, due to the lack of consistent multi-dimensional numerical formulations in conventional schemes for triangular and tetrahedral meshes at the cell interfaces, numerical issues exist when flow discontinuities or stagnation regions are present. The space-time conservative conservation element solution element (CESE) method - due to its Riemann-solver-free shock capturing capabilities, non-dissipative baseline schemes, and flux conservation in time as well as space - has the potential to more accurately simulate turbulent flows using unstructured tetrahedral meshes. To pave the way towards accurate simulation of shock/turbulent boundary-layer interaction, a series of wave and shock interaction benchmark problems that increase in complexity, are computed in this paper with triangular/tetrahedral meshes. Preliminary computations for the normal shock/turbulence interactions are carried out with a relatively coarse mesh, by direct numerical simulations standards, in order to assess other effects such as boundary conditions and the necessity of a buffer domain. The results indicate that qualitative agreement with previous studies can be obtained for flows where, strong shocks co-exist along with unsteady waves that display a broad range of scales, with a relatively compact computational domain and less stringent requirements for grid clustering near the shock. With the space-time conservation properties, stable solutions without any spurious wave reflections can be obtained without a need for buffer domains near the outflow/farfield boundaries. Computational results for the
Tetrahedral 1B4Sb nanoclusters in GaP:(B, Sb)
Energy Technology Data Exchange (ETDEWEB)
Elyukhin, V A, E-mail: elyukhin@cinvestav.m [Departamento de Ingenieria Electrica-SEES, CINVESTAV-IPN, Avenida IPN 2508, Col. San Pedro Zacatenco, C. P. 07360, Mexico, D. F. (Mexico)
2009-05-01
Self-assembling conditions of 1B4Sb tetrahedral nanoclusters in GaP doped with boron and Sb isoelectronic impurities are represented in the ultradilute and dilute limits of the boron and Sb contents, respectively. The fulfilled estimates demonstrated the preferential complete or almost complete allocation of boron atoms in 1B4Sb nanoclusters at temperatures of 500 {sup 0}C and 900 {sup 0}C, respectively. The significant decrease of the sum of the free energies of the constituent compounds is the main origin of self-assembling. The reduction of the strain energy is the additional cause of this phenomenon.
Palmesi, Pietro; Bruckner, Florian; Abert, Claas; Suess, Dieter
2016-01-01
The long-range magnetic field is the most time-consuming part in micromagnetic simulations. Improvements both on a numerical and computational basis can relief problems related to this bottleneck. This work presents an efficient implementation of the Fast Multipole Method [FMM] for the magnetic scalar potential as used in micromagnetics. We assume linearly magnetized tetrahedral sources, treat the near field directly and use analytical integration on the multipole expansion in the far field. This approach tackles important issues like the vectorial and continuous nature of the magnetic field. By using FMM the calculations scale linearly in time and memory.
Neyrinck, Mark C
2015-01-01
We discuss an idealized model of halo formation, in which a collapsing halo node is tetrahedral, with a filament extruding from each of its four faces, and with a wall connecting each pair of filaments. In the model, filaments generally spin when they form, and the halo spins if and only if there is some rotation in filaments. This is the simplest-possible fully three-dimensional halo collapse in the 'origami approximation,' in which voids are irrotational, and the dark-matter sheet out of which dark-matter structures form is allowed to fold in position-velocity phase space, but not stretch (i.e., it cannot vary in density along a stream). Up to an overall scaling, the four filament directions, and only three other quantities, such as filament spins, suffice to determine all of the collapse's properties: the shape, mass, and spin of the halo; the densities per unit length and spins of all filaments; and masses per unit area of the walls. If the filaments are arranged regular-tetrahedrally, filament properties...
Neyrinck, Mark C.
2016-07-01
We discuss an idealized model of halo formation, in which a collapsing halo node is tetrahedral, with a filament extruding from each of its four faces, and with a wall connecting each pair of filaments. In the model, filaments generally spin when they form, and the halo spins if and only if there is some rotation in filaments. This is the simplest possible fully three-dimensional halo collapse in the `origami approximation', in which voids are irrotational, and the dark-matter sheet out of which dark-matter structures form is allowed to fold in position-velocity phase space, but not stretch (i.e. it cannot vary in density along a stream). Up to an overall scaling, the four filament directions, and only three other quantities, such as filament spins, suffice to determine all of the collapse's properties: the shape, mass, and spin of the halo; the densities per unit length and spins of all filaments; and masses per unit area of the walls. If the filaments are arranged regular-tetrahedrally, filament properties obey simple laws, reminiscent of angular-momentum conservation. The model may be most useful in understanding spin correlations between neighbouring galaxies joined by filaments; these correlations would give intrinsic alignments between galaxies, essential to understand for accurate cosmological weak-lensing measurements.
Homemdemello, Luiz S.
1992-01-01
An assembly planner for tetrahedral truss structures is presented. To overcome the difficulties due to the large number of parts, the planner exploits the simplicity and uniformity of the shapes of the parts and the regularity of their interconnection. The planning automation is based on the computational formalism known as production system. The global data base consists of a hexagonal grid representation of the truss structure. This representation captures the regularity of tetrahedral truss structures and their multiple hierarchies. It maps into quadratic grids and can be implemented in a computer by using a two-dimensional array data structure. By maintaining the multiple hierarchies explicitly in the model, the choice of a particular hierarchy is only made when needed, thus allowing a more informed decision. Furthermore, testing the preconditions of the production rules is simple because the patterned way in which the struts are interconnected is incorporated into the topology of the hexagonal grid. A directed graph representation of assembly sequences allows the use of both graph search and backtracking control strategies.
Energy Technology Data Exchange (ETDEWEB)
Rojas, Onofre, E-mail: ors@dex.ufla.br [Departamento de Ciencias Exatas, Universidade Federal de Lavras, 37200-000, Lavras-MG (Brazil); Strečka, Jozef [Department of Theoretical Physics and Astrophysics, Faculty of Science, P.J. Šafárik University, Park Angelinum 9, 040 01 Košice (Slovakia); Lyra, Marcelo L. [Instituto de Física, Universidade Federal de Alagoas, 57072-970, Maceio-AL (Brazil)
2013-05-03
The spin-1/2 Ising–Heisenberg tetrahedral chain is exactly solved using its local gauge symmetry (the total spin of the Heisenberg bonds is locally conserved) and the transfer-matrix approach. Exact results derived for spin–spin correlation functions are employed to obtain the frustration temperature. In addition, we have exactly calculated a concurrence quantifying thermal entanglement. It is shown that the frustration and threshold temperature coincide at sufficiently low temperatures, while they exhibit a very different behavior in the high-temperature region when tending towards completely different asymptotic limits. The threshold temperature additionally shows a notable reentrant behavior when it extends over a narrow temperature region above the classical ground state without any quantum correlations. -- Highlights: ► Using local gauge symmetry we solved the spin-1/2 Ising–Heisenberg tetrahedral chain. ► The frustration temperature was calculated using the correlation functions. ► Thermal entanglement, concurrence and threshold temperature were analyzed. ► The zero-field specific heat was exactly calculated and discussed.
Tetrahedral shape and surface density wave of $^{16}$O caused by $\\alpha$-cluster correlations
Kanada-En'yo, Yoshiko
2016-01-01
$\\alpha$-cluster correlations in the $0^+_1$ and $3^-_1$ states of $^{12}$C and $^{16}$O are studied using the method of antisymmetrized molecular dynamics, with which nuclear structures are described from nucleon degrees of freedom without assuming existence of clusters. The intrinsic states of $^{12}$C and $^{16}$O have triangle and tetrahedral shapes, respectively, because of the $\\alpha$-cluster correlations. These shapes can be understood as spontaneous symmetry breaking of rotational invariance, and the resultant surface density oscillation is associated with density wave (DW) caused by the instability of Fermi surface with respect to particle-hole correlations with the wave number $\\lambda=3$. $^{16}$O($0^+_1$) and $^{16}$O($3^-_1$) are regarded as a set of parity partners constructed from the rigid tetrahedral intrinsic state, whereas $^{12}$C($0^+_1$) and $^{12}$C($3^-_1$) are not good parity partners as they have triangle intrinsic states of different sizes with significant shape fluctuation because...
Coupled atmosphere-ocean data assimilation experiments with a low-order model and CMIP5 model data
Tardif, Robert; Hakim, Gregory J.; Snyder, Chris
2015-09-01
Coupled atmosphere-ocean data assimilation (DA) experiments are performed for estimating the Atlantic meridional overturning circulation (AMOC). Recovery of the AMOC with an ensemble Kalman filter is assessed for a range of experiments over observation availability (atmosphere, upper and deep ocean) and for assimilating high-frequency observations compared to time averages. For an idealised low-order coupled climate model, the traditional DA approach using an ensemble of model trajectories to estimate covariances is compared to a simplified "no-cycling" approach involving climatological covariances derived from a single long model integration. Robustness of the no-cycling method is also tested on data from a millennial-scale simulation of a comprehensive coupled atmosphere-ocean climate model. Results show that the no-cycling approach provides a good approximation to the traditional approach, and that assimilation of time-averaged observations improves AMOC recovery using drastically smaller ensembles than would be required for the case of instantaneous observations. Even in the limit of no ocean observations, the no-cycling approach is capable of recovering the low-frequency AMOC with time-averaged observations; assimilation of noisy instantaneous atmospheric observations fails to recover decadal-scale AMOC variability.
Directory of Open Access Journals (Sweden)
Marek Svitok
2014-05-01
Full Text Available Only little attention has been paid to the impact of acid mine drainages (AMD on aquatic ecosystems in Central Europe. In this study, we investigate the physico-chemical properties of low-order streams and the response of benthic invertebrates to AMD pollution in the Banská Štiavnica mining region (Slovakia. The studied streams showed typical signs of mine drainage pollution: higher conductivity, elevated iron, aluminum, zinc and copper loads and accumulations of ferric precipitates. Electric conductivity correlated strongly with most of the investigated elements (weighted mean absolute correlation = 0.95 and, therefore, can be recommended as a good proxy indicator for rapid AMD pollution assessments. The diversity and composition of invertebrate assemblages was related to water chemistry. Taxa richness decreased significantly along an AMD-intensity gradient. While moderately affected sites supported relatively rich assemblages, the harshest environmental conditions (pH < 2.5 were typical for the presence of a limited number of very tolerant taxa, such as Oligochaeta and some Diptera (Limnophyes, Forcipomyiinae. The trophic guild structure correlated significantly with AMD chemistry, whereby predators completely disappeared under the most severe AMD conditions. We also provide a brief review of the AMD literature and outline the needs for future detailed studies involving functional descriptors of the impact of AMD on aquatic ecosystems.
Low-frequency variability and heat transport in a low-order nonlinear coupled ocean-atmosphere model
Vannitsem, Stéphane; De Cruz, Lesley; Ghil, Michael
2014-01-01
We formulate and study a low-order nonlinear coupled ocean-atmosphere model with an emphasis on the impact of radiative and heat fluxes and of the frictional coupling between the two components. This model version extends a previous 24-variable version by adding a dynamical equation for the passive advection of temperature in the ocean, together with an energy balance model. The bifurcation analysis and the numerical integration of the model reveal the presence of low-frequency variability (LFV) concentrated on and near a long-periodic, attracting orbit. This orbit combines atmospheric and oceanic modes, and it arises for large values of the meridional gradient of radiative input and of frictional coupling. Chaotic behavior develops around this orbit as it loses its stability; this behavior is still dominated by the LFV on decadal and multi-decadal time scales that is typical of oceanic processes. Atmospheric diagnostics also reveals the presence of predominant low- and high-pressure zones, as well as of a su...
Adjoint-based sensitivity analysis of low-order thermoacoustic networks using a wave-based approach
Aguilar, José G.; Magri, Luca; Juniper, Matthew P.
2017-07-01
Strict pollutant emission regulations are pushing gas turbine manufacturers to develop devices that operate in lean conditions, with the downside that combustion instabilities are more likely to occur. Methods to predict and control unstable modes inside combustion chambers have been developed in the last decades but, in some cases, they are computationally expensive. Sensitivity analysis aided by adjoint methods provides valuable sensitivity information at a low computational cost. This paper introduces adjoint methods and their application in wave-based low order network models, which are used as industrial tools, to predict and control thermoacoustic oscillations. Two thermoacoustic models of interest are analyzed. First, in the zero Mach number limit, a nonlinear eigenvalue problem is derived, and continuous and discrete adjoint methods are used to obtain the sensitivities of the system to small modifications. Sensitivities to base-state modification and feedback devices are presented. Second, a more general case with non-zero Mach number, a moving flame front and choked outlet, is presented. The influence of the entropy waves on the computed sensitivities is shown.
Institute of Scientific and Technical Information of China (English)
李萍; 熊勇; 芶清泉; 张建平
2002-01-01
We propose the formation mechanism of the body-centred regular tetrahedral structure of the He+5 cluster. The total energy curve for this structure has been calculated by using a modified arrangement channel quantum mechanics method. The result shows that a minimal energy of -13.9106 a.u. occurs at a separation of 1.14a0 between the nucleus at the centre and nuclei at the apexes. Therefore we obtain the binding energy of 0.5202 a.u. for this structure. This means that the He+5 cluster may be stable with a high binding energy in a body-centred regular tetrahedral structure.
Energy Technology Data Exchange (ETDEWEB)
N' Diaye, Mamadou; Pueyo, Laurent; Soummer, Rémi, E-mail: mamadou@stsci.edu [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States)
2015-02-01
The Apodized Pupil Lyot Coronagraph (APLC) is a diffraction suppression system installed in the recently deployed instruments Palomar/P1640, Gemini/GPI, and VLT/SPHERE to allow direct imaging and spectroscopy of circumstellar environments. Using a prolate apodization, the current implementations offer raw contrasts down to 10{sup –7} at 0.2 arcsec from a star over a wide bandpass (20%), in the presence of central obstruction and struts, enabling the study of young or massive gaseous planets. Observations of older or lighter companions at smaller separations would require improvements in terms of the inner working angle (IWA) and contrast, but the methods originally used for these designs were not able to fully explore the parameter space. We propose a novel approach to improve the APLC performance. Our method relies on the linear properties of the coronagraphic electric field with the apodization at any wavelength to develop numerical solutions producing coronagraphic star images with high-contrast region in broadband light. We explore the parameter space by considering different aperture geometries, contrast levels, dark-zone sizes, bandpasses, and focal plane mask sizes. We present an application of these solutions to the case of Gemini/GPI with a design delivering a 10{sup –8} raw contrast at 0.19 arcsec and offering a significantly reduced sensitivity to low-order aberrations compared to the current implementation. Optimal solutions have also been found to reach 10{sup –10} contrast in broadband light regardless of the aperture shape, with effective IWA in the 2-3.5 λ/D range, therefore making the APLC a suitable option for the future exoplanet direct imagers on the ground or in space.
Using a low-order model to detect and characterize intense vortices in multiple-Doppler radar data
Potvin, Corey Keith
A new multiple-Doppler radar analysis technique is presented for the objective detection and characterization of intense vortices. The technique consists of fitting radial wind data from two or more radars to a simple analytical model of a vortex and its near-environment. The model combines a uniform flow, linear shear flow, linear divergence flow (all of which comprise a broadscale flow), and modified combined Rankine vortex. The vortex and its environment are allowed to translate. A cost-function accounting for the discrepancy between the model and observed radial winds is evaluated over space and time so that observations can be used at the actual times and locations they were acquired. The parameters in the low-order model are determined by minimizing this cost function. The development of the method is initially guided by emulated radial velocity observations of analytical vortices. A high-resolution Advanced Regional Prediction System (ARPS) simulation of a supercellular tornado is then used to generate more realistic pseudo-observations. Finally, the technique is tested using real dual-Doppler tornado and mesocyclone observations from a variety of radar platforms including Weather Surveillance Radar - 1988 Doppler (WSR-88D), Terminal Doppler Weather Radar (TDWR), Shared Mobile Atmospheric Research and Teaching Radar (SMART-R), and Doppler on Wheels (DOW). The technique shows skill in detecting intense vortices and, when the vortex is well-resolved, in retrieving key model parameters including vortex location, translational velocity, radius and maximum tangential wind speed. In cases where the vortex is not well-resolved, additional vortex characteristics computed from the retrieved model parameters and verified against radial velocity observations can still provide useful information about vortex size and strength.
Yu, Tianliang; Lesieutre, George A.; Griffin, Steven F.; Brzozowski, Daniel P.; Sassoon, Aaron M.
2017-04-01
Synthetic jet actuators are of interest for potential applications to active flow control and thermal management. Resonant piezoelectric-diaphragm-type configurations are commonly considered. Modeling of such actuators remains a challenge due to complexities associated with both electro-elastic and fluid-structure coupling, as well as potential non-linearities in both. A key metric for synthetic jet performance is the time-averaged jet momentum. Linear lumped-element modeling is an approach that has demonstrated the ability to predict jet momentum in terms of input frequency and voltage; however, it neglects nonlinearity and increasing losses at high amplitude. Full electro-elastic-fluidic finite element modeling makes the most accurate prediction but is computationally expensive for design and optimization purposes. The assumed-modes method provides an energy-based low-order model which captures electro-elastic and acoustic-structure couplings with adequate accuracy. Tri-laminar circular plates under clamped boundary conditions were modeled using the assumed-modes method. Maximization of jet momentum is considered via the maximization of surrogate device metrics: free volume displacement, effective blocking pressure, strain energy, and device coupling coefficient. The driving frequency of the actuator is treated as a constraint in the optimization which nominally matches the fundamental acoustic natural frequency of the cylindrical cavity. Device configurations were obtained for various polycrystalline and single crystal piezoelectric materials, driven at 10% of their coercive fields in the model. The optimal configurations approximate a simply-supported circular plate with complete piezo coverage. The relative merits of individual materials were also discerned from the optimization results. The low mechanical loss factor of PZT8 enables high output at resonance, while high loss factor and low stiffness limit the utility of PVDF in this application. Due to a
Hedayatrasa, Saeid; Abhary, Kazem; Uddin, Mohammad
2015-03-01
The optimum topology of bimaterial phononic crystal (PhCr) plates with one-dimensional (1D) periodicity to attain maximum relative bandgap width of low order Lamb waves is computationally investigated. The evolution of optimized topology with respect to filling fraction of constituents, alternatively stiff scattering inclusion, is explored. The underlying idea is to develop PhCr plate structures with high specific bandgap efficiency at particular filling fraction, or further with multiscale functionality through gradient of optimized PhCr unitcell all over the lattice array. Multiobjective genetic algorithm (GA) is employed in this research in conjunction with finite element method (FEM) for topology optimization of silicon-tungsten PhCr plate unitcells. A specialized FEM model is developed and verified for dispersion analysis of plate waves and calculation of modal response. Modal band structure of regular PhCr plate unitcells with centric scattering layer is studied as a function of aspect ratio and filling fraction. Topology optimization is then carried out for a few aspect ratios, with and without prescribed symmetry, over various filling fractions. The efficiency of obtained solutions is verified as compared to corresponding regular centric PhCr plate unitcells. Moreover, being inspired by the obtained optimum topologies, definite and easy to produce topologies are proposed with enhanced bandgap efficiency as compared to centric unitcells. Finally a few cases are introduced to evaluate the frequency response of finite PhCr plate structures produced by achieved topologies and also to confirm the reliability of calculated modal band structures. Cases made by consecutive unitcells of different filling fraction are examined in order to attest the bandgap efficiency and multiscale functionality of such graded PhCr plate structures. Crown Copyright © 2014. Published by Elsevier B.V. All rights reserved.
Open Volumetric Mesh-An Efficient Data Structure for Tetrahedral and Hexa-hedral Meshes
Institute of Scientific and Technical Information of China (English)
XIAN Chu-hua; LI Gui-qing; GAO Shu-ming
2013-01-01
This work introduces a scalable and efficient topological structure for tetrahedral and hexahedral meshes. The design of the data structure aims at maximal flexibility and high performance. It provides a high scalability by using hierarchical representa-tions of topological elements. The proposed data structure is array-based, and it is a compact representation of the half-edge data structure for volume elements and half-face data structure for volumetric meshes. This guarantees constant access time to the neighbors of the topological elements. In addition, an open-source implementation named Open Volumetric Mesh (OVM) of the pro-posed data structure is written in C++using generic programming concepts.
Supported Tetrahedral Oxo-Sn Catalyst: Single Site, Two Modes of Catalysis
Energy Technology Data Exchange (ETDEWEB)
Beletskiy, Evgeny V.; Hou, Xianliang; Shen, Zhongliang; Gallagher, James R.; Miller, Jeffrey T.; Wu, Yuyang; Li, Tiehu; Kung, Mayfair C.; Kung, Harold H.
2016-03-17
Mild calcination in ozone of a (POSS)-Sn- (POSS) complex grafted on silica generated a heterogenized catalyst that mostly retained the tetrahedral coordination of its homogeneous precursor, as evidenced by spectroscopic characterizations using EXAFS, NMR, UV-vis, and DRIFT. The Sn centers are accessible and uniform and can be quantified by stoichiometric pyridine poisoning. This Sn-catalyst is active in hydride transfer reactions as a typical solid Lewis acid. However, the Sn centers can also create Brønsted acidity with alcohol by binding the alcohol strongly as alkoxide and transferring the hydroxyl H to the neighboring Sn-O-Si bond. The resulting acidic silanol is active in epoxide ring opening and acetalization reactions.
A Parallel Algorithm for Adaptive Local Refinement of Tetrahedral Meshes Using Bisection
Institute of Scientific and Technical Information of China (English)
LinBo Zhang
2009-01-01
Local mesh refinement is one of the key steps in the implementations of adaptive finite element methods. This paper presents a parallel algorithm for distributed memory parallel computers for adaptive local refinement of tetrahedral meshes using bisection. This algorithm is used in PHG, Parallel Hierarchical Grid (http: //lsec. cc. ac. cn/phg/J, a toolbox under active development for parallel adaptive finite element solutions of partial differential equations. The algorithm proposed is characterized by allowing simultaneous refinement of submeshes to arbitrary levels before synchronization between submeshes and without the need of a central coordinator process for managing new vertices. Using the concept of canonical refinement, a simple proof of the independence of the resulting mesh on the mesh partitioning is given, which is useful in better understanding the behaviour of the bisectioning refinement procedure.AMS subject classifications: 65Y05, 65N50
Dabiri, Zohreh; Kazempour, Ali; Sadeghzadeh, Mohammad Ali
2016-11-01
The strength of phonon anharmonicity is investigated in the framework of the Density Functional Perturbation Theory via an applied constant electric field. In contrast to routine approaches, we have employed the electric field as an effective probe to quest after the quasi-harmonic and anharmonic effects. Two typical tetrahedral semiconductors (diamond and silicon) have been selected to test the efficiency of this approach. In this scheme the applied field is responsible for establishing the perturbation and also inducing the anharmonicity in systems. The induced polarization is a result of changing the electronic density while ions are located at their ground state coordinates or at a specified strain. Employing this method, physical quantities of the semiconductors are calculated in presence of the electron-phonon interaction directly and, phonon-phonon interaction, indirectly. The present approach, which is in good agreement with previous theoretical and experimental studies, can be introduced as a benchmark to simply investigate the anharmonicity and pertinent consequences in materials.
Filgueiras, Carlos A. L.; Carazza, Fernando
1980-01-01
Discusses procedures, theoretical considerations, and results of an experiment involving the preparation of a tetrahedral nickel(II) complex and its transformation into an octahedral species. Suggests that fundamental aspects of coordination chemistry can be demonstrated by simple experiments performed in introductory level courses. (Author/JN)
Schoedel, Alexander
2013-02-10
The self-assembly of triangular, tetrahedral, and trigonal-prismatic molecular building blocks affords the first example of a trinodal family of metal-organic materials. Four examples of isoreticular expanded and functionalized frameworks are detailed. Gas adsorption experiments validated the permanent porosity of the parent structure. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
The role of fcc tetrahedral subunits in the phase behavior of medium sized Lennard-Jones clusters.
Saika-Voivod, Ivan; Poon, Louis; Bowles, Richard K
2010-08-21
The free energy of a 600-atom Lennard-Jones cluster is calculated as a function of surface and bulk crystallinity in order to study the structural transformations that occur in the core of medium sized clusters. Within the order parameter range studied, we find the existence of two free energy minima at temperatures near freezing. One minimum, at low values of both bulk and surface order, belongs to the liquid phase. The second minimum exhibits a highly ordered core with a disordered surface and is related to structures containing a single fcc-tetrahedral subunit, with an edge length of seven atoms (l=7), located in the particle core. At lower temperatures, a third minimum appears at intermediate values of the bulk order parameter which is shown to be related to the formation of multiple l=6 tetrahedra in the core of the cluster. We also use molecular dynamics simulations to follow a series of nucleation events and find that the clusters freeze to structures containing l=5, 6, 7, and 8 sized tetrahedra as well as those containing no tetrahedral units. The structural correlations between bulk and surface order with the size of the tetrahedral units in the cluster core are examined. Finally, the relationships between the formation of fcc tetrahedral subunits in the core, the phase behavior of medium sized clusters and the nucleation of noncrystalline global structures such as icosahedra and decahedra are discussed.
Orbital Calculations of Kaolinite Surface:on Substitution of Al3+ for Si4+ in the Tetrahedral Sites
Institute of Scientific and Technical Information of China (English)
无
2007-01-01
The surface properties of kaolinite were determined using density functional theory discrete variational method (DFT-DVM) and Gaussian 03 program. A SiO4 tetrahedral hexagonal ring with two Al octahedra was chosen to model the kaolinite crystal. The total density of states of the kaolinite cluster are located near the Fermi level at both sides of the Fermi level. Both the highest occupied molecular orbit(HOMO) and the lowest unoccupied molecular orbit (LUMO) of kaolinite indicate that kaolinite system can not only readily interact with electron-acceptor species, but also readily interact with electron-donor species on the edge surface and the gibbsite layer surface, and thus, shows amphoteric behavior. Substitution of Al3+ for Si4+ in the tetrahedral site linking the vacant Al3+ octahedra does not increase the surface chemical reactivity of kaolinite, while substitution of Al3+ for Si4+ in the tetrahedral site with the apex O linking Al3+ octahedra increase the surface chemical reactivity of the siloxane surface of kaolinite, especially acting as electron donors.Additionally, substitution of Al3+ for Si4+ in the tetrahedral site results in the re-balance of charges, leading to the increase of negative charge of the coordinated O atoms of the AlO4 tetrahedra, and therefore favoring the formation of ionic bonds between cations and the surface O atoms in the basal plane.
Indian Academy of Sciences (India)
Jun-bo Li; Xiang-Lin Yu; Jing Fu; Xiwen Liu; Yang Zeng
2010-11-01
In this study, a novel tetrahedral molecule TPPY was successfully designed and synthesized. The self-assembly of TPPY with gold nanoparticles (Au NPs) in toluene has also been investigated. The aggregation morphologies of Au NPs can be controlled to produce different aggregate structures by changing the concentration of ligand TPPY.
Slow magnetic relaxation at zero field in the tetrahedral complex [Co(SPh)4]2-.
Zadrozny, Joseph M; Long, Jeffrey R
2011-12-28
The Ph(4)P(+) salt of the tetrahedral complex [Co(SPh)(4)](2-), possessing an S = (3)/(2) ground state with an axial zero-field splitting of D = -70 cm(-1), displays single-molecule magnet behavior in the absence of an applied magnetic field. At very low temperatures, ac magnetic susceptibility data show the magnetic relaxation time, τ, to be temperature-independent, while above 2.5 K thermally activated Arrhenius behavior is apparent with U(eff) = 21(1) cm(-1) and τ(0) = 1.0(3) × 10(-7) s. Under an applied field of 1 kOe, τ more closely approximates Arrhenius behavior over the entire temperature range. Upon dilution of the complex within a matrix of the isomorphous compound (Ph(4)P)(2)[Zn(SPh)(4)], ac susceptibility data reveal the molecular nature of the slow magnetic relaxation and indicate that the quantum tunneling pathway observed at low temperatures is likely mediated by intermolecular dipolar interactions.
Energy Technology Data Exchange (ETDEWEB)
Prehna,G.; Stebbins, E.
2007-01-01
The Rho family of small GTPases represent well characterized signaling molecules that regulate many cellular functions such as actin cytoskeletal arrangement and the cell cycle by acting as molecular switches. A Rac1-GDP-Zn complex has been crystallized in space group P3{sub 2}21 and its crystal structure has been solved at 1.9 {angstrom} resolution. These trigonal crystals reveal the unexpected ability of Rac1 to coordinate Zn atoms in a tetrahedral fashion by use of its biologically relevant switch I and switch II regions. Upon coordination of zinc, the switch I region is stabilized in the GDP-bound conformation and contributes to a Rac1 trimer in the asymmetric unit. Zinc coordination causes switch II to adopt a novel conformation with a symmetry-related molecule. Additionally, zinc was found to displace magnesium from its octahedral coordination at switch I, although GDP binding remained stable. This structure represents the first reported Rac1-GDP-Zn complex, which further underscores the conformational flexibility and versatility of the small GTPase switch regions.
Energy Technology Data Exchange (ETDEWEB)
Prehna, G.; Stebbins, C
2007-01-01
The Rho family of small GTPases represent well characterized signaling molecules that regulate many cellular functions such as actin cytoskeletal arrangement and the cell cycle by acting as molecular switches. A Rac1-GDP-Zn complex has been crystallized in space group P3221 and its crystal structure has been solved at 1.9 {angstrom} resolution. These trigonal crystals reveal the unexpected ability of Rac1 to coordinate Zn atoms in a tetrahedral fashion by use of its biologically relevant switch I and switch II regions. Upon coordination of zinc, the switch I region is stabilized in the GDP-bound conformation and contributes to a Rac1 trimer in the asymmetric unit. Zinc coordination causes switch II to adopt a novel conformation with a symmetry-related molecule. Additionally, zinc was found to displace magnesium from its octahedral coordination at switch I, although GDP binding remained stable. This structure represents the first reported Rac1-GDP-Zn complex, which further underscores the conformational flexibility and versatility of the small GTPase switch regions.
Tetrahedral homonuclear organoelement clusters and subhalides of aluminium, gallium and indium
Uhl, Werner
This review is focused on the synthesis and the reactivity of tetrahedral organoelement clusters of the heavier elements of third main-group aluminium, gallium, and indium, which have been known for about a decade. They possess the elements in an unusually low oxidation state of +1 and have direct element-element interactions between their four constituents. Each cluster atom is further attached to one terminal and in most cases a bulky organic substituent, which prevents disproportionation by steric shielding. The synthesis of these compounds succeeds by different methods such as the reduction of suitable organoelement(III) halides with alkali metals and magnesium or the treatment of element(I) halides with lithium organyls. They are deeply coloured, and their bonding situation may best be described by delocalized molecular orbitals. They show a singular chemical reactivity, which results in the formation of many secondary products possessing unprecedented structures and properties. The synthesis of organoelement subhalides still containing the elements in low oxidation states is discussed in more detail in the second part of this review. These compounds are easily accessible by the careful oxidation of the clusters with halogen donors such as hexachloroethane or with AlX3/X2 mixtures. They produce dimers via halogen bridges, but in certain cases monomers were observed even for the solid state. They are very effective starting compounds for secondary reactions and the generation of new products containing the elements in unusual oxidation states by salt-elimination reactions, for instance.
Vibrations of tetrahedral Co and Cu clusters on a Cu(111) surface
Energy Technology Data Exchange (ETDEWEB)
Borisova, Svetlana D.; Rusina, Galina G. [Institute of Strength Physics and Materials Science SB RAS, pr. Akademichesky 2/4, 634021 Tomsk (Russian Federation); Eremeev, Sergey V. [Institute of Strength Physics and Materials Science SB RAS, pr. Akademichesky 2/4, 634021 Tomsk (Russian Federation); Tomsk State University, pr. Lenina 36, 634050 Tomsk (Russian Federation); Donostia International Physics Center (DIPC), Paseo Manuel de Lardizabal, 4, 20018 San Sebastian/Donostia (Spain); Chulkov, Evgueni V. [Donostia International Physics Center (DIPC), Paseo Manuel de Lardizabal, 4, 20018 San Sebastian/Donostia (Spain); Depto. de Fisica de Materiales and Centro de Fisica de Materiales - CFM (CSIS-UPV/EHU), Facultad de Ciencias Quimicas, Universidad del Pais Vasco/Euskal Herriko Unibertsitatea, Apdo. 1072, 20018 San Sebastian/Donostia (Spain)
2010-11-15
Vibrational properties of tetrahedral clusters of Cu and Co on the Cu(111) surface are studied by using interatomic interaction potentials constructed within tight-binding second moment approximation. It was shown that interaction of the Co{sub 4} and Cu{sub 4} clusters with the substrate leads to arising of frustrated translation and frustrated rotation in-plane polarized vibrational modes localized on the cluster atoms. The vibrational modes of the free Cu{sub 4} cluster upon its adsorption on the Cu(111) surface mix with Cu bulk phonons and become almost delocalized. Contrary to that, in the Co{sub 4} cluster on the surface the high frequency modes remain strongly localized and mixed with the nearest neighbor atoms vibrations. The highest frequency vibration of the Co{sub 4} cluster splits due to different interaction with certain groups of nearest neighbor atoms (copyright 2010 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)
Birnbaum, G.; Borysow, A.; Buechele, A.
1993-01-01
The far infrared absorption of a CH4-N2 mixture was measured at 297, 195, and 162 K from 30 to 650/cm. The spectral invariants gamma1 and alpha1, proportional, respectively, to the zeroth and first spectral moments, due to bimolecular collisions between CH4 and N2 were obtained from these data and compared with theoretical values. The theory for collision-induced dipoles between a tetrahedral and a diatomic or symmetrical linear molecule includes contributions not previously considered. Whereas the theoretical values of gamma1 are only somewhat greater than experiment at all temperatures, the theoretical values of alpha1 are significantly lower than the experimental values. From the theoretical spectral moments for the various induced dipole components, the parameters of the BC shape were computed, and theoretical spectra were constructed. Good agreement was obtained at the lower frequencies, but with increasing frequencies the theoretical spectra were increasingly less intense than the experimental spectra. Although the accuracy of the theoretical results may suffer from the lack of a reliable potential function, it does not appear that this high frequency discrepancy can be removed by any conceivable modification in the potential.
Energy Technology Data Exchange (ETDEWEB)
Boutchko, Rostyslav; Reutter, Bryan; Gullberg, Grant T. [Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States)
2011-07-01
Irregular tetrahedral meshes based on adaptively distributed point clouds are used as the object space data representation method to reconstruct SPECT images in pinhole geometry. In the object space, a tetrahedron is defined by the positions and intensities of its four vertices; image intensity inside a tetrahedron is a linear combination of the vertex intensities. For the parallel projection geometry, the projection of a tetrahedron is conveniently expressed in terms of an integral that is solved analytically. For the pinhole case, the vertices are first projected onto the detector plane and the geometric magnification factor is computed. Then, a virtual tetrahedron is formed in the detector space and projected onto the detector using exact analytical formulae developed for the parallel geometry. In order to compute the system matrix, point cloud geometry and acquisition geometry is adjusted using geometric calibration expressed in terms of 24 parameters determined from a special calibration study. The 3D images are reconstructed using a standard MLEM algorithm. Initial reconstruction is performed on a uniform finely-spaced cloud. Then, the points are adaptively removed or merged in constant intensity regions and moved to better outline the boundaries. The density of the point cloud is adjusted adaptively after each reconstruction so that the number of unknowns in the inverse problem is reduced by an order of magnitude. (orig.)
Lu, Qingzhang; Shen, Guoli; Yu, Ruqin
2002-11-15
The chaotic dynamical system is introduced in genetic algorithm to train ANN to formulate the CGANN algorithm. Logistic mapping as one of the most important chaotic dynamic mappings provides each new generation a high chance to hold GA's population diversity. This enhances the ability to overcome overfitting in training an ANN. The proposed CGANN has been used for QSAR studies to predict the tetrahedral modes (nu(1)(A1) and nu(2)(E)) of halides [MX(4)](epsilon). The frequencies predicted by QSAR were compared with those calculated by quantum chemistry methods including PM3, AM1, and MNDO/d. The possibility of improving the predictive ability of QSAR by including quantum chemistry parameters as feature variables has been investigated using tetrahedral tetrahalide examples.
Energy Technology Data Exchange (ETDEWEB)
Gálisová, Lucia, E-mail: galisova.lucia@gmail.com [Department of Applied Mathematics and Informatics, Faculty of Mechanical Engineering, Technical University, Letná 9, 042 00 Košice (Slovakia); Strečka, Jozef, E-mail: jozef.strecka@upjs.sk [Department of Theoretical Physics and Astrophysics, Faculty of Science, P.J. Šafárik University, Park Angelinum 9, 040 01 Košice (Slovakia)
2015-10-16
Magnetocaloric effect in a double-tetrahedral chain, in which nodal lattice sites occupied by the localized Ising spins regularly alternate with three equivalent lattice sites available for mobile electrons, is exactly investigated by considering the one-third electron filling and the ferromagnetic Ising exchange interaction between the mobile electrons and their nearest Ising neighbours. The entropy and the magnetic Grüneisen parameter, which closely relate to the magnetocaloric effect, are exactly calculated in order to investigate the relation between the ground-state degeneracy and the cooling efficiency of the hybrid spin–electron system during the adiabatic demagnetization. - Highlights: • A double-tetrahedral chain of mobile electrons and localized Ising spins is studied. • Magnetic Grüneisen parameter for the system is exactly derived. • Macroscopically degenerate phases FRU and FM constitute the ground state. • MCE is three times higher nearby FRU–FM transition than in FRU phase at small fields.
Synthesis of tetrahedral quasi-type-II CdSe-CdS core-shell quantum dots.
Sugunan, Abhilash; Zhao, Yichen; Mitra, Somak; Dong, Lin; Li, Shanghua; Popov, Sergei; Marcinkevicius, Saulius; Toprak, Muhammet S; Muhammed, Mamoun
2011-10-21
Synthesis of colloidal nanocrystals of II-VI semiconductor materials has been refined in recent decades and their size dependent optoelectronic properties have been well established. Here we report a facile synthesis of CdSe-CdS core-shell heterostructures using a two-step hot injection process. Red-shifts in absorption and photoluminescence spectra show that the obtained quantum dots have quasi-type-II alignment of energy levels. The obtained nanocrystals have a heterostructure with a large and highly faceted tetrahedral CdS shell grown epitaxially over a spherical CdSe core. The obtained morphology as well as high resolution electron microscopy confirms that the tetrahedral shell have a zinc blende crystal structure. A phenomenological mechanism for the growth and morphology of the nanocrystals is discussed.
Directory of Open Access Journals (Sweden)
Anke Kelchtermans
2015-01-01
Full Text Available Nanocrystalline ZnO:Al nanoparticles are suitable building blocks for transparent conductive layers. As the concentration of substitutional tetrahedral Al is an important factor for improving conductivity, here we aim to increase the fraction of substitutional Al. To this end, synthesis parameters of a solvothermal reaction yielding ZnO:Al nanorods were varied. A unique set of complementary techniques was combined to reveal the exact position of the aluminium ions in the ZnO lattice and demonstrated its importance in order to evaluate the potential of ZnO:Al nanocrystals as optimal building blocks for solution deposited transparent conductive oxide layers. Both an extension of the solvothermal reaction time and stirring during solvothermal treatment result in a higher total tetrahedral aluminium content in the ZnO lattice. However, only the longer solvothermal treatment effectively results in an increase of the substitutional positions aimed for.
Directory of Open Access Journals (Sweden)
Iain eHepburn
2013-10-01
Full Text Available We describe a novel method for calculating the quasi-static electrical potential on tetrahedral meshes, which we call E-Field. The E-Field method is implemented in STEPS, which performs stochastic spatial reaction-diffusion computations in tetrahedral-based cellular geometry reconstructions. This provides a level of integration between electrical excitability and spatial molecular dynamics in realistic cellular morphology not previously achievable. Deterministic solutions are also possible. By performing the Rallpack tests we demonstrate the accuracy of the E-Field method. Efficient node ordering is an important practical consideration, and we find that a breadth-first search provides the best solutions, although principal axis ordering suffices for some geometries. We discuss potential applications and possible future directions, and predict that the E-Field implementation in STEPS will play an important role in the future of multiscale neural simulations.
Venkatachari, Balaji Shankar; Chang, Chau-Lyan
2016-11-01
The focus of this study is scale-resolving simulations of the canonical normal shock- isotropic turbulence interaction using unstructured tetrahedral meshes and the space-time conservation element solution element (CESE) method. Despite decades of development in unstructured mesh methods and its potential benefits of ease of mesh generation around complex geometries and mesh adaptation, direct numerical or large-eddy simulations of turbulent flows are predominantly carried out using structured hexahedral meshes. This is due to the lack of consistent multi-dimensional numerical formulations in conventional schemes for unstructured meshes that can resolve multiple physical scales and flow discontinuities simultaneously. The CESE method - due to its Riemann-solver-free shock capturing capabilities, non-dissipative baseline schemes, and flux conservation in time as well as space - has the potential to accurately simulate turbulent flows using tetrahedral meshes. As part of the study, various regimes of the shock-turbulence interaction (wrinkled and broken shock regimes) will be investigated along with a study on how adaptive refinement of tetrahedral meshes benefits this problem. The research funding for this paper has been provided by Revolutionary Computational Aerosciences (RCA) subproject under the NASA Transformative Aeronautics Concepts Program (TACP).
Energy Technology Data Exchange (ETDEWEB)
Gong K.; Vukmirovic M.B.; Ma C.; Zhu Y.; Adzic R.R.
2011-11-01
We synthesized the Pt monolayer shell-Pd tetrahedral core electrocatalysts that are notable for their high activity and stable performance. A small number of low-coordination sites and defects, and high content of the (1 1 1)-oriented facets on Pd tetrahedron makes them a suitable support for a Pt monolayer to obtain an active O{sub 2} reduction reaction (ORR) electrocatalyst. The surfactants, used to control size and shape of Pd tetrahedral nanoparticles, are difficult to remove and cause adverse effects on the ORR. We describe a simple and noninvasive method to synthesize high-purity tetrahedral Pd nanocrystals (TH Pd) by combining a hydrothermal route and CO adsorption-induced removal of surfactants. Poly(vinylpyrrolidone) (PVP), used as a protecting and reducing agent in hydrothermal reactions, is strongly bonded to the surface of the resulting nanocrystals. We demonstrate that PVP was displaced efficiently by adsorbed CO. A clean surface was achieved upon CO stripping at a high potential (1.0 V vs RHE). It played a decisive role in improving the activity of the Pt monolayer/TH Pd electrocatalyst for the ORR. Furthermore, the results demonstrate a versatile method for removal of surfactants from various nanoparticles that severely limited their applications.
Institute of Scientific and Technical Information of China (English)
LI Yang-xue; XUE Ming; GUO Li-jia; HUANG Lin; CHEN Si-ru; QIU Shi-lun
2013-01-01
Multifunctional lanthanide metal-organic frameworks(MOFs),M(H4TCPS)(H2O)1.5[M=Tb(JUC-95a),Er(JUC-95b),Dy(JUC-95c),Tm(JUC-95d),Y(JUC-95e) and Pr(JUC-95f); H4TCPS=tetrakis(4-carboxyphenyl)silane] were synthesized via the reaction of the lanthanide metal ions(Ln3) with a rigid silicon-centered tetrahedral carboxylate ligand H4TCPS via a hydrothermal synthesis method.X-Ray diffraction(XRD) analyses reveal that they are extremely similar in structure and crystallized in a monoclinic system with space group C2/c.Two eight-coordinated metal centers and four tetrahedral H4TCPS groups constructed a paddle-wheel building block.The paddle-wheel building blocks assembled with each other via one oxygen bridge from a water molecule to lead to a 1D infinite inorganic rod-shaped chain,—Y—O—C—O—Y—,along the [001] direction.These 1D inorganic rod-shaped chains linked with the phenyl groups of the tetrahedral H4TCPS ligand to form a 3D framework.In addition,the luminescent and magnetic properties of these compounds show that they could be potential antiferromagnetic and fluorescent materials.
Han, Yifeng; Ye, Xuanhong; Zhu, Hong; Li, Yuexiang; Kuang, Xiaojun
2017-03-01
Ba6Na2M2Mn2O17 (M=Nb, Ta) oxides were synthesized by high-temperature solid-state reaction. The compounds adopt 6-layer perovskite-related structure (referred to as 6C) in P 3 ̅m1, analogous to Ba6Na2Nb2P2O17. The 6C structure consists of cubic (c) BaO3 layers and pseudo-cubic (c') oxygen-vacancy-ordered BaO2 layers stacked according to a sequence of c'ccccc. Ordering of oxygen vacancies in oxygen-deficient c'-BaO2 layers leads to two successive isolated tetrahedral layers, which stabilize an unusual +5 oxidation state for Mn cations in the tetrahedral sites. In Ba6Na2M2Mn2O17, these two Mn5+O4 layers are sandwiched by two single octahedral NaO6 layers that connected by two successive octahedral NbO6 layers, forming alternative 2:1-ordered (Ba3NaM2O9)- and (Ba3NaMn2O8)+ perovskite-like units along the stacking direction. The Mn5+O4 tetrahedral units act as a turquoise chromophore in Ba6Na2M2Mn2O17, making these two compounds potential turquoise-coloring materials for the cool pigments.
Zhao, Jie; Zhao, En-Guang; Zhou, Shan-Gui
2016-01-01
We develop a multidimensionally-constrained relativistic Hartree-Bogoliubov (MDC-RHB) model in which the pairing correlations are taken into account by making the Bogoliubov transformation. In this model, the nuclear shape is assumed to be invariant under the reversion of $x$ and $y$ axes, i.e., the intrinsic symmetry group is $V_4$ and all shape degrees of freedom $\\beta_{\\lambda\\mu}$ with even $\\mu$ are included self-consistently. The RHB equation is solved in an axially deformed harmonic oscillator basis. A separable pairing force of finite range is adopted in the MDC-RHB model. The potential energy curves of neutron-rich even-even Zr isotopes are calculated. The ground state shapes of $^{108-112}$Zr are predicted to be tetrahedral with both functionals DD-PC1 and PC-PK1 and $^{106}$Zr is also predicted to have a tetrahedral ground state with the functional PC-PK1. The tetrahedral ground states are caused by large energy gaps at $Z=40$ and $N=70$ when $\\beta_{32}$ deformation is included. Although the incl...
Peltola, Emilia; Wester, Niklas; Holt, Katherine B; Johansson, Leena-Sisko; Koskinen, Jari; Myllymäki, Vesa; Laurila, Tomi
2017-02-15
We hypothesize that by using integrated carbon nanostructures on tetrahedral amorphous carbon (ta-C), it is possible to take the performance and characteristics of these bioelectrodes to a completely new level. The integrated carbon electrodes were realized by combining nanodiamonds (NDs) with ta-C thin films coated on Ti-coated Si-substrates. NDs were functionalized with mixture of carboxyl and amine groups NDandante or amine NDamine, carboxyl NDvox or hydroxyl groups NDH and drop-casted or spray-coated onto substrate. By utilizing these novel structures we show that (i) the detection limit for dopamine can be improved by two orders of magnitude [from 10µM to 50nM] in comparison to ta-C thin film electrodes and (ii) the coating method significantly affects electrochemical properties of NDs and (iii) the ND coatings selectively promote cell viability. NDandante and NDH showed most promising electrochemical properties. The viability of human mesenchymal stem cells and osteoblastic SaOS-2 cells was increased on all ND surfaces, whereas the viability of mouse neural stem cells and rat neuroblastic cells was improved on NDandante and NDH and reduced on NDamine and NDvox. The viability of C6 cells remained unchanged, indicating that these surfaces will not cause excess gliosis. In summary, we demonstrated here that by using functionalized NDs on ta-C thin films we can significantly improve sensitivity towards dopamine as well as selectively promote cell viability. Thus, these novel carbon nanostructures provide an interesting concept for development of various in vivo targeted sensor solutions.
Importance of Tetrahedral Iron during Microbial Reduction of Clay Mineral NAu-2
Shi, B.; Wu, L.; Liu, K.; Smeaton, C. M.; Li, W.; Beard, B. L.; Johnson, C.; Roden, E. E.; Van Cappellen, P.
2015-12-01
Transformations between Fe(II) and Fe(III) in ferruginous clay minerals significantly impact the physicochemical properties of soils and sediments, such as the ion exchange capacity and redox potential. An increasing number of studies have focused on clay minerals that undergo redox changes, however, none have so far addressed Fe isotope fractionation during these processes. In this study, Fe isotope fractionations were determined during microbial reduction of Fe(III) in nontronite NAu-2 with different concentrations of lactate. No secondary Fe-bearing minerals, including Fe oxides, were detected by SEM in over 100 days of incubation, suggesting that the measured fractionations only reflected the net isotope effect associated with the clay minerals. The initial reduction likely started from edge sites, and the reductive dissolution released aqueous Fe(II). Basal plane sorbed Fe(II) was detectable after the extent of Fe reduction exceeded 5% and extensive electron transfer and isotope exchange had occurred between basal plane sorbed Fe(II) and structural Fe(III). With lower concentrations of the lactate(40 mM), the maximum Fe isotope fractionation was larger (∆56Febasal Fe(II)-structure Fe(III)= -4.37‰), consistent with greater adsorption than in systems with more lactate. After the Fe in reactive sites was all reduced, isotope exchange between Fe(II) and structural Fe(III) was inhibited due to blockage of electron transfer pathways by the collapse of the clay layers. The results agree with another study in our group on microbial reduction of NAu-1, despite both the smaller extent of reduction (~10% vs. 22% max bioreduction for NAu-1 and NAu-2, respectively) and smaller isotope fractionation factor than for NAu-2. We speculate that tetrahedral Fe in NAu-2 may have accelerated the electron transfer between Fe atoms, thus inducing a higher extent of reduction and a larger Fe isotope fractionation compared to NAu-1.
Energy Technology Data Exchange (ETDEWEB)
Pascucci, V
2004-02-18
This paper presents a simple approach for rendering isosurfaces of a scalar field. Using the vertex programming capability of commodity graphics cards, we transfer the cost of computing an isosurface from the Central Processing Unit (CPU), running the main application, to the Graphics Processing Unit (GPU), rendering the images. We consider a tetrahedral decomposition of the domain and draw one quadrangle (quad) primitive per tetrahedron. A vertex program transforms the quad into the piece of isosurface within the tetrahedron (see Figure 2). In this way, the main application is only devoted to streaming the vertices of the tetrahedra from main memory to the graphics card. For adaptively refined rectilinear grids, the optimization of this streaming process leads to the definition of a new 3D space-filling curve, which generalizes the 2D Sierpinski curve used for efficient rendering of triangulated terrains. We maintain the simplicity of the scheme when constructing view-dependent adaptive refinements of the domain mesh. In particular, we guarantee the absence of T-junctions by satisfying local bounds in our nested error basis. The expensive stage of fixing cracks in the mesh is completely avoided. We discuss practical tradeoffs in the distribution of the workload between the application and the graphics hardware. With current GPU's it is convenient to perform certain computations on the main CPU. Beyond the performance considerations that will change with the new generations of GPU's this approach has the major advantage of avoiding completely the storage in memory of the isosurface vertices and triangles.
Do the Kontsevich tetrahedral flows preserve or destroy the space of Poisson bi-vectors?
Bouisaghouane, Anass; Kiselev, Arthemy V.
2017-01-01
From the paper “Formality Conjecture” (Ascona 1996): I am aware of only one such a class, it corresponds to simplest good graph, the complete graph with 4 vertices (and 6 edges). This class gives a remarkable vector field on the space of bi-vector fields on ℝd . The evolution with respect to the time t is described by the following non-linear partial differential equation: …, where α = ∑i,j αij∂ / ∂ xi ∧ ∂ / ∂ xj is a bi-vector field on ℝd. It follows from general properties of cohomology that 1) this evolution preserves the class of ( real-analytic ) Poisson structures , … In fact, I cheated a little bit. In the formula for the vector field on the space of bivector fields which one get from the tetrahedron graph, an additional term is present. … It is possible to prove formally that if α is a Poisson bracket, i.e. if [α, α] = 0 ∈ T2(ℝ d ), then the additional term shown above vanishes . By using twelve Poisson structures with high-degree polynomial coefficients as explicit counter-examples, we show that both the above claims are false: neither does the first flow preserve the property of bi-vectors to be Poisson nor does the second flow vanish identically at Poisson bi-vectors. The counterexamples at hand suggest a correction to the formula for the “exotic” flow on the space of Poisson bi-vectors; in fact, this flow is encoded by the balanced sum involving both the Kontsevich tetrahedral graphs (that give rise to the flows mentioned above). We reveal that it is only the balance 1 : 6 for which the flow does preserve the space of Poisson bi-vectors.
The stability of a crystal with diamond structure for patchy particles with tetrahedral symmetry.
Noya, Eva G; Vega, Carlos; Doye, Jonathan P K; Louis, Ard A
2010-06-21
The phase diagram of model anisotropic particles with four attractive patches in a tetrahedral arrangement has been computed at two different values of the range of the potential, with the aim of investigating the conditions under which a diamond crystal can be formed. We find that the diamond phase is never stable for our longer-ranged potential. At low temperatures and pressures, the fluid freezes into a body-centered-cubic solid that can be viewed as two interpenetrating diamond lattices with a weak interaction between the two sublattices. Upon compression, an orientationally ordered face-centered-cubic crystal becomes more stable than the body-centered-cubic crystal, and at higher temperatures, a plastic face-centered-cubic phase is stabilized by the increased entropy due to orientational disorder. A similar phase diagram is found for the shorter-ranged potential, but at low temperatures and pressures, we also find a region over which the diamond phase is thermodynamically favored over the body-centered-cubic phase. The higher vibrational entropy of the diamond structure with respect to the body-centered-cubic solid explains why it is stable even though the enthalpy of the latter phase is lower. Some preliminary studies on the growth of the diamond structure starting from a crystal seed were performed. Even though the diamond phase is never thermodynamically stable for the longer-ranged model, direct coexistence simulations of the interface between the fluid and the body-centered-cubic crystal and between the fluid and the diamond crystal show that at sufficiently low pressures, it is quite probable that in both cases the solid grows into a diamond crystal, albeit involving some defects. These results highlight the importance of kinetic effects in the formation of diamond crystals in systems of patchy particles.
Sapaev, Usman; Husakou, Anton; Herrmann, Joachim
2013-10-21
We study numerically low-order harmonic generation in noble gases pumped by intense femtosecond laser pulses in the tunneling ionization regime. We analyze the influence of the phase-mismatching on this process, caused by the generated plasma, and study in dependence on the pump intensity the origin of harmonic generation arising either from the bound-electron nonlinearity or the tunnel-ionization current. It is shown that in argon the optimum pump intensity of about 100 TW/cm² leads to the maximum efficiency, where the main contribution to low-order harmonics originates from the bound-electron third and fifth order susceptibilities, while for intensities higher than 300 TW/cm² the tunnel-ionization current plays the dominant role. Besides, we predict that VUV pulses at 133 nm can be generated with relatively high efficiency of about 1.5 × 10⁻³ by 400 nm pump pulses.
Sapaev, U; Herrmann, J
2013-01-01
We study numerically low-order harmonic generation in noble gases pumped by intense femtosecond laser pulses in the tunneling ionization regime. We analyze the influence of the phase-mismatching on this process, caused by the generated plasma, and study in dependence on the pump intensity the origin of harmonic generation arising either from the bound-electron nonlinearity or the tunnel-ionization current. It is shown that in argon the optimum pump intensity of about 100 TW/cm$^2$ leads to the maximum efficiency, where the main contribution to low-order harmonics originates from the bound-electron third and fifth order susceptibilities, while for intensities higher than 300 TW/cm$^2$ the tunnel-ionization current plays the dominant role. Besides, we predict that VUV pulses at 133 nm can be generated with relatively high efficiency of about $1.5\\times10^{-3}$ by 400 nm pump pulses.
Stacy, Erin Michele
2012-01-01
Soil erosion can alter the mechanisms of organic matter (OM) storage and persistence in soil, including aggregation, burial, and organo-mineral associations. I studied how extended transport of topsoil and associated OM alters OM stabilization mechanisms by comparing soil from different landform positions with sediment exported from eight, low-order watersheds in the Sierra Nevada, California. To assess the relative importance of different stabilization mechanisms, I separated free, unprotect...
Directory of Open Access Journals (Sweden)
Ole A. Solheim
1980-10-01
Full Text Available This paper describes a method for designing optimal feedback controllers with stability requirements using low-order Riccati equations. For originally stable systems the Riccati equation will be of first or second order, depending upon whether the eigenvalues are real or complex. For originally unstable systems the order of the Riccati equation will be equal to the number of eigenvalues with positive real part.
Ding, Jiao; Jiang, Yuan; Liu, Qi; Hou, Zhaojiang; Liao, Jianyu; Fu, Lan; Peng, Qiuzhi
2016-05-01
Understanding the relationships between land use patterns and water quality in low-order streams is useful for effective landscape planning to protect downstream water quality. A clear understanding of these relationships remains elusive due to the heterogeneity of land use patterns and scale effects. To better assess land use influences, we developed empirical models relating land use patterns to the water quality of low-order streams at different geomorphic regions across multi-scales in the Dongjiang River basin using multivariate statistical analyses. The land use pattern was quantified in terms of the composition, configuration and hydrological distance of land use types at the reach buffer, riparian corridor and catchment scales. Water was sampled under summer base flow at 56 low-order catchments, which were classified into two homogenous geomorphic groups. The results indicated that the water quality of low-order streams was most strongly affected by the configuration metrics of land use. Poorer water quality was associated with higher patch densities of cropland, orchards and grassland in the mountain catchments, whereas it was associated with a higher value for the largest patch index of urban land use in the plain catchments. The overall water quality variation was explained better by catchment scale than by riparian- or reach-scale land use, whereas the spatial scale over which land use influenced water quality also varied across specific water parameters and the geomorphic basis. Our study suggests that watershed management should adopt better landscape planning and multi-scale measures to improve water quality.
Institute of Scientific and Technical Information of China (English)
Shuang-suo Zhao; Zhang-hua Luo; Guo-feng Zhang
2000-01-01
This paper presents optimum an one-parameter iteration (OOPI) method and a multi-parameter iteration direct (MPID) method for efficiently solving linear algebraic systems with low order matrix A and high order matrix B: Y = (A B)Y +Ф. On parallel computers (also on serial computer) the former will be efficient, even very efficient under certain conditions, the latter will be universally very efficient.
Natural off-stoichiometry causes carrier doping in half-Heusler filled tetrahedral structures
Yu, Yonggang G.; Zhang, Xiuwen; Zunger, Alex
2017-02-01
The half-Heusler filled tetrahedral structures (FTSs) are zinc-blende-like compounds, where an additional atom is filling its previously empty interstitial site. The FTSs having 18 valence electrons per formula unit are an emerging family of functional materials, whose intrinsic doping trends underlying a wide range of electronic functionalities are yet to be understood. Interestingly, even pristine compounds without any attempt at impurity/chemical doping exhibit intriguing trends in the free carriers they exhibit. Applying the first principles theory of doping to a few prototype compounds in the AIVBXCIV and AIVBIXCV groups, we describe the key ingredients controlling the materials' propensity for both intrinsic and extrinsic doping: (a) The spontaneous deviations from 1:1:1 stoichiometry reflect predictable thermodynamic stability of specific competing phases. (b) Bulk ABC compounds containing 3 d elements in the B position (ZrNiSn and ZrCoSb) are predicted to be naturally 3 d rich. The B =3 d interstitials are the prevailing shallow donors, whereas the potential acceptors (e.g., Zr vacancy and Sn-on-Zr antisite) are ineffective electron killers, resulting in an overall uncompensated n -type character, even without any chemical doping. In these materials, the band edges are "natural impurity bands" due to non-Daltonian off-stoichiometry, such as B interstitials, not intrinsic bulk controlled states as in a perfect crystal. (c) Bulk ABC compounds containing 5 d elements in the B position (ZrPtSn, ZrIrSb, and TaIrGe) are predicted to be naturally C rich and A poor. This promotes the hole-producing C -on-A antisite defects rather than B -interstitial donors. The resultant p -type character (without chemical doping) therein is "latent" for C =Sn and Sb; however, as the C -on-A hole-producing acceptors are rather deep and p typeness is manifest only at high temperature or via impurity doping. In contrast, in TaIrGe (B =Ir , 5 d ) , the prevailing hole-producing Ge
Stoddard, Mary Caswell; Prum, Richard O
2008-06-01
We use a tetrahedral color space to describe and analyze male plumage color variation and evolution in a clade of New World buntings--Cyanocompsa and Passerina (Aves: Cardinalidae). The Goldsmith color space models the relative stimulation of the four retinal cones, using the integrals of the product of plumage reflectance spectra and cone sensitivity functions. A color is represented as a vector defined by the relative stimulation of the four cone types--ultraviolet, blue, green, and red. Color vectors are plotted in a tetrahedral, or quaternary, plot with the achromatic point at the origin and the ultraviolet/violet channel along the Z-axis. Each color vector is specified by the spherical coordinates theta, phi, and r. Hue is given by the angles theta and phi. Chroma is given by the magnitude of r, the distance from the achromatic origin. Color vectors of all distinct patches in a plumage characterize the plumage color phenotype. We describe the variation in color space occupancy of male bunting plumages, using various measures of color contrast, hue contrast and diversity, and chroma. Comparative phylogenetic analyses using linear parsimony (in MacClade) and generalized least squares (GLS) models (in CONTINUOUS) with a molecular phylogeny of the group document that plumage color evolution in the clade has been very dynamic. The single best-fit GLS evolutionary model of plumage color variation over the entire clade is a directional change model with no phylogenetic correlation among species. However, phylogenetic innovations in feather color production mechanisms--derived pheomelanin and carotenoid expression in two lineages--created new opportunities to colonize novel areas of color space and fostered the explosive differentiation in plumage color. Comparison of the tetrahedral color space of Goldsmith with that of Endler and Mielke demonstrates that both provide essentially identical results. Evolution of avian ultraviolet/violet opsin sensitivity in relation
Rustad, James R.
2016-01-01
Molecular dynamics calculations are carried out on pure, Al-substituted, and In-substituted LLZO. The calculations show that the tendency of Al to occupy the 24d sites in LLZO lithium ion conductors is hypothesized here to negatively impact ionic conductivity. The room-temperature ionic conductivity of In-LLZO, in which the In resides at the 48g sites, is predicted to be an order of magnitude higher than Al-LLZO. Consideration of the simple tetrahedral topology of the lithium ion conduction n...
Sapaev, U; Husakou, A.; Herrmann, J.
2013-01-01
We study numerically low-order harmonic generation in noble gases pumped by intense femtosecond laser pulses in the tunneling ionization regime. We analyze the influence of the phase-mismatching on this process, caused by the generated plasma, and study in dependence on the pump intensity the origin of harmonic generation arising either from the bound-electron nonlinearity or the tunnel-ionization current. It is shown that in argon the optimum pump intensity of about 100 TW/cm$^2$ leads to th...
Yang, Xingyi
Tetrahedral amorphous carbon (ta-C) is a diamond-like carbon (DLC) material comprised of a mixture of sp2 (˜40%) and sp3-bonded (˜60%) carbon domains. The physicochemical structure and electrochemical properties depend strongly on the sp2/sp3 bonding ratio as well as the incorporation of impurities, such as hydrogen or nitrogen. The ability to grow ta-C films at lower temperatures (25-100 °C) on a wider variety of substrates is a potential advantage of these materials as compared with diamond films. In this project, the basic structural and electrochemical properties of nitrogen-incorporated ta-C thin films will be discussed. The major goal of this work was to determine if the ta-C:N films exhibit electrochemical properties more closely aligned with those of boron-doped diamond (sp 3 carbon) or glassy carbon (amorphous sp2 carbon). Much like diamond, ta-C:N thin-film electrodes are characterized by a low background voltammetric current, a wide working potential window, relatively rapid electron-transfer kinetics for aqueous redox systems, such as Fe(CN) 6-3/-4 and Ru(NH3)6+3/+2 , and weak adsorption of polar molecules from solution. For example, negligible adsorption of methylene blue was found on the ta-C:N films in contrast to glassy carbon; a surface on which this molecule strongly adsorbs. The film microstructure was studied with x-ray photoelectron microscopy (XPS), visible Raman spectroscopy and electron-energy loss spectroscopy (EELS); all of which revealed the sp2-bonded carbon content increased with increasing nitrogen. The electrical properties of ta-C:N films were studied by four-point probe resistance measurement and conductive-probe AFM (CP-AFM). The incorporation of nitrogen into ta-C films increased the electrical conductivity primarily by increasing the sp2-bonded carbon content. CP-AFM showed the distribution of the conductive sp2-carbon on the film surface was not uniform. These films have potential to be used in field emission area. The
Jenkins, D. M.; Lei, J.
2013-12-01
The sodium content in the M4 site of amphibole (BNa) was calibrated by Brown (1977, J Petrol, 18, 53-72) in a study that continues to be highly cited to this day. This study, based on empirical observations of amphibole compositional changes in the presence of the buffering assemblage plagioclase, chlorite, epidote, iron oxide, and water, demonstrated a systematic variation in the BNa and tetrahedral Al (TAl) content with pressure. Recent experimental work in this lab aimed at defining the extent of miscibility along the tremolite-glaucophane and hornblende-glaucophane joins in the Na2O-CaO-MgO-Al2O3-SiO2-H2O system has provided some additional information on the cation mixing along these joins. These joins also serve as the chemically-simplified framework of the BNa versus TAl correlation reported by Brown (1977). There are now sufficient, though still a bare minimum, of experimentally-confirmed mixing data for sodium-rich amphiboles to test this correlation and for quantifying the pressure-temperature (P-T) dependence of amphibole compositions in metamafic rocks relevant to subduction zones. From experimental results obtained over the range of 500-800°C, 1.5-2.0 GPa, and using a variety of amphibole synthesis and re-equilibration methods, the following set of asymmetric formalism (ASF) macroscopic interaction and mixing parameters have been derived that can be used with THERMOCALC dataset 55: Wtrgl = 70 kJ, Wglts = Wtrts =20 kJ, α(tr) = 1.0, α(ts) = 1.2, and α(gl) = 0.52. Using a fixed MORB bulk composition, the composition of amphiboles within the P-T stability field of the buffering assemblage were calculated for the above chemical system with FeO added (i.e., NCFMASH) over the range of 0.2 - 2.0 GPa and 400 - 700°C. The following main observations can be made. First, the empirical amphibole compositions at low TAl and high BNa contents are well modeled by the miscibility gap in the amphibole ternary sub-system tremolite
Lee, Okkyun; Kappler, Steffen; Polster, Christoph; Taguchi, Katsuyuki
2016-10-26
Photon counting detector (PCD)-based computed tomography exploits spectral information from a transmitted x-ray spectrum to estimate basis line-integrals. The recorded spectrum, however, is distorted and deviates from the transmitted spectrum due to spectral response effect (SRE). Therefore, the SRE needs to be compensated for when estimating basis lineintegrals. One approach is to incorporate the SRE model with an incident spectrum into the PCD measurement model and the other approach is to perform a calibration process that inherently includes both the SRE and the incident spectrum. A maximum likelihood estimator can be used to the former approach, which guarantees asymptotic optimality; however, a heavy computational burden is a concern. Calibration-based estimators are a form of the latter approach. They can be very efficient; however, a heuristic calibration process needs to be addressed. In this paper, we propose a computationally efficient three-step estimator for the former approach using a low-order polynomial approximation of x-ray transmittance. The low-order polynomial approximation can change the original non-linear estimation method to a two-step linearized approach followed by an iterative bias correction step. We show that the calibration process is required only for the bias correction step and prove that it converges to the unbiased solution under practical assumptions. Extensive simulation studies validate the proposed method and show that the estimation results are comparable to those of the ML estimator while the computational time is reduced substantially.
Haussaire, J.-M.; Bocquet, M.
2016-01-01
Bocquet and Sakov (2013) introduced a low-order model based on the coupling of the chaotic Lorenz-95 (L95) model, which simulates winds along a mid-latitude circle, with the transport of a tracer species advected by this zonal wind field. This model, named L95-T, can serve as a playground for testing data assimilation schemes with an online model. Here, the tracer part of the model is extended to a reduced photochemistry module. This coupled chemistry meteorology model (CCMM), the L95-GRS (generic reaction set) model, mimics continental and transcontinental transport and the photochemistry of ozone, volatile organic compounds and nitrogen oxides. Its numerical implementation is described. The model is shown to reproduce the major physical and chemical processes being considered. L95-T and L95-GRS are specifically designed and useful for testing advanced data assimilation schemes, such as the iterative ensemble Kalman smoother (IEnKS), which combines the best of ensemble and variational methods. These models provide useful insights prior to the implementation of data assimilation methods into larger models. We illustrate their use with data assimilation schemes on preliminary yet instructive numerical experiments. In particular, online and offline data assimilation strategies can be conveniently tested and discussed with this low-order CCMM. The impact of observed chemical species concentrations on the wind field estimate can be quantitatively assessed. The impacts of the wind chaotic dynamics and of the chemical species non-chaotic but highly nonlinear dynamics on the data assimilation strategies are illustrated.
Directory of Open Access Journals (Sweden)
Frank J Brooks
Full Text Available There is increasing interest in applying image texture quantifiers to assess the intra-tumor heterogeneity observed in FDG-PET images of various cancers. Use of these quantifiers as prognostic indicators of disease outcome and/or treatment response has yielded inconsistent results. We study the general applicability of some well-established texture quantifiers to the image data unique to FDG-PET.We first created computer-simulated test images with statistical properties consistent with clinical image data for cancers of the uterine cervix. We specifically isolated second-order statistical effects from low-order effects and analyzed the resulting variation in common texture quantifiers in response to contrived image variations. We then analyzed the quantifiers computed for FIGOIIb cervical cancers via receiver operating characteristic (ROC curves and via contingency table analysis of detrended quantifier values.We found that image texture quantifiers depend strongly on low-effects such as tumor volume and SUV distribution. When low-order effects are controlled, the image texture quantifiers tested were not able to discern only the second-order effects. Furthermore, the results of clinical tumor heterogeneity studies might be tunable via choice of patient population analyzed.Some image texture quantifiers are strongly affected by factors distinct from the second-order effects researchers ostensibly seek to assess via those quantifiers.
Kim, Cheolmin; Yoon, Min-Ju; Hong, Seok Hee; Park, Minjoon; Park, Kwangyong; Kim, Soo Young
2016-05-01
Tetrahedral structures comprising Sn-cored materials with five different types of substituents were synthesized. For the substituents, we employed methyl and tert-butyl as aliphatic groups, and naphthyl and phenyl as aromatic groups. The bandgap is in the range of 3.28 - 3.56 eV. The All the compounds with substituents showed bathochromical photoluminescence characteristics and exhibited aggregation-induced emission characteristics. Specifically, the compounds with aromatic substituents prohibited side-chain packing and π-π stacking. The energy levels of the highest occupied and lowest unoccupied molecular orbitals were measured to be 5.5 - 5.75 and 2.0 - 2.37 eV, respectively. The maximum luminance efficiencies and power efficiencies of the Sn-cored compound-based organic light-emitting diodes (OLEDs) were 0.38 - 0.71 cd/A and 0.15 - 0.28 lm/W. Therefore, it is expected that Sn-cored compounds with a tetrahedral structure, especially those containing aromatic substituents, can be used as an active material in blue OLEDs for prohibiting side-chain packing and π-π stacking. [Figure not available: see fulltext.
Chang, Chau-Lyan; Venkatachari, Balaji
2016-11-01
Flow physics near the viscous wall is intrinsically anisotropic in nature, namely, the gradient along the wall normal direction is much larger than that along the other two orthogonal directions parallel to the surface. Accordingly, high aspect ratio meshes are employed near the viscous wall to capture the physics and maintain low grid count. While such arrangement works fine for structured-grid based methods with dimensional splitting that handles derivatives in each direction separately, similar treatments often lead to numerical instability for unstructured-mesh based methods when triangular or tetrahedral meshes are used. The non-splitting treatment of near-wall gradients for high-aspect ratio triangular or tetrahedral elements results in an ill-conditioned linear system of equations that is closely related to the numerical instability. Altering the side lengths of the near wall tetrahedrons in the gradient calculations would make the system less unstable but more dissipative. This research presents recent progress in applying numerical dissipation control in the space-time conservation element solution element (CESE) method to reduce or alleviate the above-mentioned instability while maintaining reasonable solution accuracy.
Directory of Open Access Journals (Sweden)
Klaus Oehr
2014-11-01
Full Text Available We hypothesize a mechanistic model of how negatively-charged exclusion zones (EZs are created. While the growth of EZs is known to be associated with the absorption of ambient photonic energy, the molecular dynamics giving rise to this process need greater elucidation. We believe they arise due to the formation of oxy-subhydride structures (OH−(H2O4 with a tetrahedral (sp3 (OH−(H2O3 core. Five experimental data sets derived by previous researchers were assessed in this regard: (1 water-derived EZ light absorbance at specific infrared wavelengths, (2 EZ negative potential in water and ethanol, (3 maximum EZ light absorbance at 270 nm ultraviolet wavelength, (4 ability of dimethyl sulphoxide but not ether to form an EZ, and (5 transitory nature of melting ice derived EZs. The proposed tetrahedral oxy-subhydride structures (TOSH appear to adequately account for all of the experimental evidence derived from water or other polar solvents.
Energy Technology Data Exchange (ETDEWEB)
Zhang, Xin; Zhang, Xu; Johnson, Jacob A.; Chen, Yu-Sheng; Zhang, Jian
2016-06-24
Two non-interpenetrated zirconium metal–organic frameworks (Zr-MOFs), NPF-200 and NPF-201, were synthesized via the assembly of elongated tetrahedral linkers with Zr_{6} and Zr_{8} clusters. They represent the first examples of MOFs to have the β-UH_{3}-like, 4,12,12T1 topology. Upon activation, NPF-200 exhibits the largest BET surface area (5463 m^{2} g^{–1}) and void volume (81.6%) among all MOFs formed from tetrahedral ligands. Composed of negative-charged boron-centered tetrahedral linkers, NPF-201 is an anionic Zr-MOF which selectively uptakes photoactive [Ru(bpy)_{3}]^{2+} for heterogeneous photo-oxidation of thioanisole.
Matausek, M R; Ribić, A I
2009-10-01
This paper presents an effective design and robust tuning method for the control structure based on a series PD controller and a simple Disturbance Observer. All elements of the proposed controller are directly obtained from the low-order Integrating First-Order Plus Dead-Time (IFOPDT) model, used to approximate essential dynamic characteristics of lag-dominant stable, integrating and unstable plants. The structure of the proposed controller is an effective, easy to implement and tune, extension of the series PID controller. For the same robustness, a better disturbance rejection response is obtained by the proposed controller than that of the PID, by adjusting only two parameters with a clear meaning. A comparison with well-tuned PIDs, done by simulations, and the experimental results, obtained on a real thermal power plant, confirm that high performance and robustness are obtained, for dynamic characteristics common to industrial processes.
Venkatachari, Balaji Shankar; Streett, Craig L.; Chang, Chau-Lyan; Friedlander, David J.; Wang, Xiao-Yen; Chang, Sin-Chung
2016-01-01
Despite decades of development of unstructured mesh methods, high-fidelity time-accurate simulations are still predominantly carried out on structured, or unstructured hexahedral meshes by using high-order finite-difference, weighted essentially non-oscillatory (WENO), or hybrid schemes formed by their combinations. In this work, the space-time conservation element solution element (CESE) method is used to simulate several flow problems including supersonic jet/shock interaction and its impact on launch vehicle acoustics, and direct numerical simulations of turbulent flows using tetrahedral meshes. This paper provides a status report for the continuing development of the space-time conservation element solution element (CESE) numerical and software framework under the Revolutionary Computational Aerosciences (RCA) project. Solution accuracy and large-scale parallel performance of the numerical framework is assessed with the goal of providing a viable paradigm for future high-fidelity flow physics simulations.
Morra, Elena; Giamello, Elio; Chiesa, Mario
2014-06-10
Transition-metal ions with open-shell configurations hold promise in the development of novel coordination chemistry and potentially unprecedented redox catalysis. Framework-substituted Ti(3+) ions with tetrahedral coordination are generated by reductive activation of titanium silicalite-1 with triethylaluminum, an indispensable co-catalyst for heterogeneous Ziegler-Natta polymerization catalysts. Continuous-wave and pulse electron paramagnetic resonance methods are applied to unravel details on the local environment of the reduced transition metal-ions, which are shown to be part of the silica framework by detection of (29)Si hyperfine interactions. The chemical accessibility of the reduced sites is probed using ammonia as probe molecule. Evidence is found for the coordination of a single ammonia molecule. Comparison to similar systems, such as TiAlPO-5, reveals clear differences in the coordination chemistry of the reduced Ti sites in the two solids, which may be understood considering the different electronic properties of the solid frameworks.
Interacting spin-1/2 tetrahedral system Cu2Te2O5X2 (X = Cl, Br)
DEFF Research Database (Denmark)
Jensen, Jens
2009-01-01
, 064422 (2006)]. The calculated excitation spectra show many similarities with the experimental neutron-scattering results. Close to a magnetic Bragg point at 2 K, the theory predicts the presence of a quasielastic phason mode and an inelastic amplitude mode at about 0.6 meV. This is in qualitative...... agreement with experimental observations of Prša et al., but the amplitude mode is observed at the much higher energy of about 2.5 meV. This discrepancy is puzzling since the tetrahedral Cu-spin system, in any other respect, behaves as a system of large local spins coupled with each other in a three......-dimensional fashion. Preliminary model calculations for the Cu2Te2O5Br2 system lead to the same conclusion. Udgivelsesdato: 7. Januar...
Vaidya, Shefali; Tewary, Subrata; Singh, Saurabh Kumar; Langley, Stuart K; Murray, Keith S; Lan, Yanhua; Wernsdorfer, Wolfgang; Rajaraman, Gopalan; Shanmugam, Maheswaran
2016-10-03
A family of mononuclear tetrahedral cobalt(II) thiourea complexes, [Co(L1)4](NO3)2 (1) and [Co(Lx)4](ClO4)2 where x = 2 (2), 3 (3), 4 (4) (where L1 = thiourea, L2 = 1,3-dibutylthiourea, L3 = 1,3-phenylethylthiourea, and L4 = 1,1,3,3-tetramethylthiourea), has been synthesized using a rationally designed synthetic approach, with the aim of stabilizing an Ising-type magnetic anisotropy (-D). On the basis of direct-current, alternating-current, and hysteresis magnetic measurements and theoretical calculations, we have identified the factors that govern the sign and magnitude of D and ultimately the ability to design a single-ion magnet for a tetrahedral cobalt(II) ion. To better understand the magnetization relaxation dynamics, particularly for complexes 1 and 2, dilution experiments were performed using their diamagnetic analogues, which are characterized by single-crystal X-ray diffraction with the general molecular formulas of [Zn(L1)4](NO3)2 (5) and [Zn(L2)4](ClO4)2 (6). Interestingly, intermolecular interactions are shown to play a role in quenching the quantum tunneling of magnetization in zero field, as evidenced in the hysteresis loop of 1. Complex 2 exhibits the largest Ueff value of 62 cm(-1) and reveals open hysteresis loops below 4 K. Furthermore, the influence of the hyperfine interaction on the magnetization relaxation dynamics is witnessed in the hysteresis loops, allowing us to determine the electron/nuclear spin S(Co) = (3)/2/I(Co) = (7)/2 hyperfine coupling constant of 550 MHz, a method ideally suited to determine the hyperfine coupling constant of highly anisotropic metal ions stabilized with large D value, which are otherwise hard to determine by conventional methods such as electron paramagnetic resonance.
Jing, Longfei; Jiang, Shaoen; Kuang, Longyu; Zhang, Lu; Li, Liling; Lin, Zhiwei; Li, Hang; Zheng, Jianhua; Hu, Feng; Huang, Yunbao; Huang, Tianxuan; Ding, Yongkun
2017-04-01
A tetrahedral hohlraum with four half-cylindrical cavities (FHCH) is proposed to balance tradeoffs among the drive symmetry, coupling efficiency, and plasma filling of the hohlraum performance for indirectly driven inertial confinement fusion. The peak drive symmetry in the FHCH with a cavity-to-capsule ratio (CCR) of 2.2 is comparable to those in the spherical hohlraum of CCR = 4.5 with six laser entrance holes (6LEHs-Sph.) ((Lan et al 2014 Phys. Plasmas 21 010704) and three-axis cylindrical hohlraum (6LEHs-Cyls.) of CCR = 2.0 (Kuang et al 2016 Sci. Rep. 6 34636), and the filling time of plasma is close to the ones in the 6LEHs-Cyls. and the ignition target Rev5-CH of the national ignition campaign, and about half of that in the 6LEHs-Sph. In particular, the coupling efficiency is about 19% and 16% higher than those of the 6LEHs-Sph. and 6LEHs-Cyls., respectively. Besides, preliminary study indicates that the FHCH has a robust symmetry to uncertainties of power imbalance and pointing errors of laser beams. Furthermore, utilizing the FHCH, the feasibility of a tetrahedral indirect drive approach on the national ignition facility and hybrid indirect–direct drive approach with the laser arrangement designed specially for 6LEHs-Sph. or 6LEHs-Cyls., is also envisioned. Therefore, the proposed hohlraum configuration merits consideration as an alternative route to indirect-drive ignition.
Strečka, Jozef; Rojas, Onofre; Verkholyak, Taras; Lyra, Marcelo L
2014-02-01
The frustrated spin-1/2 Ising-Heisenberg ladder with Heisenberg intra-rung and Ising inter-rung interactions is exactly solved in a longitudinal magnetic field by taking advantage of the local conservation of the total spin on each rung and the transfer-matrix method. We have rigorously calculated the ground-state phase diagram, magnetization process, magnetocaloric effect, and basic thermodynamic quantities for the model, which can be alternatively viewed as an Ising-Heisenberg tetrahedral chain. It is demonstrated that a stepwise magnetization curve with an intermediate plateau at half of the saturation magnetization is also reflected in respective stepwise changes of the concurrence serving as a measure of bipartite entanglement. The ground-state phase diagram and zero-temperature magnetization curves of the Ising-Heisenberg tetrahedral chain are contrasted with the analogous results of the purely quantum Heisenberg tetrahedral chain, which have been obtained through density-matrix renormalization group (DMRG) calculations. While both ground-state phase diagrams fully coincide in the regime of weak inter-rung interaction, the purely quantum Heisenberg tetrahedral chain develops Luttinger spin-liquid and Haldane phases for strongly coupled rungs, which are absent in the Ising-Heisenberg counterpart model.
Richardson, Robert R.; Zhao, Shi; Howey, David A.
2016-09-01
Estimating the temperature distribution within Li-ion batteries during operation is critical for safety and control purposes. Although existing control-oriented thermal models - such as thermal equivalent circuits (TEC) - are computationally efficient, they only predict average temperatures, and are unable to predict the spatially resolved temperature distribution throughout the cell. We present a low-order 2D thermal model of a cylindrical battery based on a Chebyshev spectral-Galerkin (SG) method, capable of predicting the full temperature distribution with a similar efficiency to a TEC. The model accounts for transient heat generation, anisotropic heat conduction, and non-homogeneous convection boundary conditions. The accuracy of the model is validated through comparison with finite element simulations, which show that the 2-D temperature field (r, z) of a large format (64 mm diameter) cell can be accurately modelled with as few as 4 states. Furthermore, the performance of the model for a range of Biot numbers is investigated via frequency analysis. For larger cells or highly transient thermal dynamics, the model order can be increased for improved accuracy. The incorporation of this model in a state estimation scheme with experimental validation against thermocouple measurements is presented in the companion contribution (http://www.sciencedirect.com/science/article/pii/S0378775316308163).
Chang, J.-C.; Shen, S.-M.; Liu, Y.-S.
2003-04-01
The Taiwan Island, located at the collision boundary of the Eurasia Plate and the Philippine Sea Plate, is characterized by intensive weathering, frequent landslides and debris flows. The latter, however, had never been regarded as a serious threat until the extensive debris flows, induced by Typhoon Herb in 1996 and/or Typhoon Toraji in 2001, caused unprecedented hazardous damages in many low-order streams, especially in the Chenyulan river basin, central Taiwan. Certain streams that remained intact in 1996 experienced dramatic change in 2001. For a better understanding of the historical records of the debris flow, a thorough examination of 17~29 versions of aerial photographs (ranging from 1951 to 2000) of four selected small catchments, which are located in the northern part of the Chenyulan basin, were conducted. The result shows that the Fengchiu stream has experienced six debris flow events over last 50 years and stands for the most vulnerable group in the basin. Statistically, the accumulation rainfall amount of an individual typhoon over 200 mm may trigger debris flow in this stream. During the same period, the other three streams did not experience any dramatic change Typhoon Toraji (>400 mm / 12 hrs). The devastating earthquake (magnitude 7.3), which occurred in 1999 and caused extensive landslides and rockfalls, is also believed playing an important role.
Kortan, Victoria Ramaker
It has become increasingly apparent that the future of electronic devices can and will rely on the functionality provided by single or few dopant atoms. The most scalable physical system for quantum technologies, i.e. sensing, communication and computation, are spins in crystal lattices. Diamond is an excellent host crystal offering long room temperature spin coherence times and there has been exceptional experimental work done with the nitrogen vacancy center in diamond demonstrating many forms of spin control. Transition metal dopants have additional advantages, large spin-orbit interaction and internal core levels, that are not present in the nitrogen vacancy center. This work explores the implications of the internal degrees of freedom associated with the core d levels using a tight-binding model and the Koster-Slater technique. The core d levels split into two separate symmetry states in tetrahedral bonding environments and result in two levels with different wavefunction spatial extents. For 4 d semiconductors, e.g. GaAs, this is reproduced in the tight-binding model by adding a set of d orbitals on the location of the transition metal impurity and modifying the hopping parameters from impurity to its nearest neighbors. This model does not work in the case of 3d semiconductors, e.g. diamond, where there is no physical reason to drastically alter the hopping from 3 d dopant to host and the difference in wavefunction extent is not as pronounced. In the case of iron dopants in gallium arsenide the split symmetry levels in the band gap are responsible for a decrease in tunneling current when measured with a scanning tunneling microscope due to interference between two elastic tunneling paths and comparison between wavefunction measurements and tight-binding calculations provides information regarding material parameters. In the case of transition metal dopants in diamond there is less distinction between the symmetry split d levels. When considering pairs of
Institute of Scientific and Technical Information of China (English)
Tun Seng Herng[1,2; Wen Xiao[1; Sock Mui Poh[2,3; Feizhou He[5; Ronny Sutarto[5; Xiaojian Zhu[6; Runwei Li[6; Xinmao Yin[2,3,4; Caozheng Diao[2; Yang Yang[1; Xuelian Huang[1; Xiaojiang Yu[2; Yuan Ping Feng[4; AndrivoRusydi[2,3,4; Jun Ding[1
2015-01-01
Magnetite Fe304 （ferrite） has attracted considerable interest for its exceptional physical properties： It is predicted to be a semimetallic ferromagnetic with a high Curie temperature, it displays a metal-insulator transition, and has potential oxide-electronics applications. Here, we fabricate a high-magnetization （〉 1 Tesla） high-resistance （-0.1 Ωcm） sub-nanostructured （grain size 〈 3 nm） Fe304 film via grain-size control and nano-engineering. We report a new phenomenon of spin- flipping of the valence-spin tetrahedral FeB＊ in the sub-nanostructured Fe304 film, which produces the high magnetization. Using soft X-ray magnetic circular dichroism and soft X-ray absorption, both at the Fe L3,2- and O K-edges, and supported by first-principles and charge-transfer multiple calculations, we observe an anomalous enhancement of double exchange, accompanied by a suppression of the superexchange interactions because of the spin-flipping mechanism via oxygen at the grain boundaries. Our result may open avenues for developing spin- manipulated giant magnetic Fe304-based compounds via nano-grain size control.
Energy Technology Data Exchange (ETDEWEB)
Nikitin, A. V., E-mail: avn@lts.iao.ru [Laboratory of Theoretical Spectroscopy, V.E. Zuev Institute of Atmospheric Optics, SB RAS, 1, Academician Zuev square, 634021 Tomsk (Russian Federation); Tomsk State University, 36 Lenin Avenue, 634050 Tomsk (Russian Federation); Rey, M.; Tyuterev, Vl. G. [Groupe de Spectrométrie Moléculaire et Atmosphérique, UMR CNRS 7331, Université de Reims, U.F.R. Sciences, B.P. 1039, 51687 Cedex 2 Reims (France)
2015-03-07
A simultaneous use of the full molecular symmetry and of an exact kinetic energy operator (KEO) is of key importance for accurate predictions of vibrational levels at a high energy range from a potential energy surface (PES). An efficient method that permits a fast convergence of variational calculations would allow iterative optimization of the PES parameters using experimental data. In this work, we propose such a method applied to tetrahedral AB{sub 4} molecules for which a use of high symmetry is crucial for vibrational calculations. A symmetry-adapted contracted angular basis set for six redundant angles is introduced. Simple formulas using this basis set for explicit calculation of the angular matrix elements of KEO and PES are reported. The symmetric form (six redundant angles) of vibrational KEO without the sin(q){sup −2} type singularity is derived. The efficient recursive algorithm based on the tensorial formalism is used for the calculation of vibrational matrix elements. A good basis set convergence for the calculations of vibrational levels of the CH{sub 4} molecule is demonstrated.
Energy Technology Data Exchange (ETDEWEB)
Wang Guigen, E-mail: wanggghit@yahoo.com [Shenzhen Graduate School, Harbin Institute of Technology, Shenzhen 518055 (China); Kuang Xuping; Zhang Huayu; Zhu Can [Shenzhen Graduate School, Harbin Institute of Technology, Shenzhen 518055 (China); Han Jiecai [Shenzhen Graduate School, Harbin Institute of Technology, Shenzhen 518055 (China); Center for Composite Materials, Harbin Institute of Technology, Harbin 150080 (China); Zuo Hongbo [Center for Composite Materials, Harbin Institute of Technology, Harbin 150080 (China); Ma Hongtao [SAE Technologies Development (Dongguan) Co., Ltd., Dongguan 523087 (China)
2011-12-15
Highlights: Black-Right-Pointing-Pointer The ultra-thin carbon films with different silicon nitride (Si-N) film underlayers were prepared. Black-Right-Pointing-Pointer It highlighted the influences of Si-N underlayers. Black-Right-Pointing-Pointer The carbon films with Si-N underlayers obtained by nitriding especially at the substrate bias of -150 V, can exhibit better corrosion protection properties - Abstract: There are higher technical requirements for protection overcoat of magnetic recording slider used in high-density storage fields for the future. In this study, silicon nitride (Si-N) composition-gradient films were firstly prepared by nitriding of silicon thin films pre-sputtered on silicon wafers and magnetic recording sliders, using microwave electron cyclotron resonance plasma source. The ultra-thin tetrahedral amorphous carbon films were then deposited on the Si-N films by filtered cathodic vacuum arc method. Compared with amorphous carbon overcoats with conventional silicon underlayers, the overcoats with Si-N underlayers obtained by plasma nitriding especially at the substrate bias of -150 V, can provide better corrosion protection for high-density magnetic recording sliders.
Liang, Le; Li, Jiang; Li, Qian; Huang, Qing; Shi, Jiye; Yan, Hao; Fan, Chunhai
2014-07-21
DNA is typically impermeable to the plasma membrane due to its polyanionic nature. Interestingly, several different DNA nanostructures can be readily taken up by cells in the absence of transfection agents, which suggests new opportunities for constructing intelligent cargo delivery systems from these biocompatible, nonviral DNA nanocarriers. However, the underlying mechanism of entry of the DNA nanostructures into the cells remains unknown. Herein, we investigated the endocytotic internalization and subsequent transport of tetrahedral DNA nanostructures (TDNs) by mammalian cells through single-particle tracking. We found that the TDNs were rapidly internalized by a caveolin-dependent pathway. After endocytosis, the TDNs were transported to the lysosomes in a highly ordered, microtubule-dependent manner. Although the TDNs retained their structural integrity within cells over long time periods, their localization in the lysosomes precludes their use as effective delivery agents. To modulate the cellular fate of the TDNs, we functionalized them with nuclear localization signals that directed their escape from the lysosomes and entry into the cellular nuclei. This study improves our understanding of the entry into cells and transport pathways of DNA nanostructures, and the results can be used as a basis for designing DNA-nanostructure-based drug delivery nanocarriers for targeted therapy.
Energy Technology Data Exchange (ETDEWEB)
Panwar, O.S., E-mail: ospanwar@mail.nplindia.ernet.in [Plasma Processed Materials Group, National Physical Laboratory (CSIR), Dr. K.S. Krishnan Road, New Delhi 110012 (India); Khan, Mohd Alim [Plasma Processed Materials Group, National Physical Laboratory (CSIR), Dr. K.S. Krishnan Road, New Delhi 110012 (India); Satyanarayana, B.S. [40, Sreeniketan, NDSE 24, New Delhi 110096 (India); Kumar, Sushil; Ishpal [Plasma Processed Materials Group, National Physical Laboratory (CSIR), Dr. K.S. Krishnan Road, New Delhi 110012 (India)
2010-04-15
This paper reports the electrical, mechanical, structural and field emission properties of as grown and also boron and phosphorous incorporated tetrahedral amorphous carbon (ta-C) films, deposited using a filtered cathodic vacuum arc process. The effect of varying boron and phosphorous content (up to 2.0 at.% in to ta-C) on the conductivity ({sigma}{sub D}), activation energy ({Delta}E{sub 1}), hardness, microstructure, emission threshold (E{sub turn-ON}) and emission current density (J) at 12.5 V/{mu}m of ta-C: B and ta-C: P films deposited at a high negative substrate bias of -300 V are reported. It is observed that both boron and phosphorous incorporation leads to a nearly an order increase in {sigma}{sub D} and corresponding decrease in {Delta}E{sub 1} and a slight increase in hardness as compared to as grown ta-C films. In the case of field assisted electron emission, it is observed that E{sub turn-ON} increases and J decreases. The changes are attributed to the changes in the sp{sup 3}/sp{sup 2} ratio of the films due to boron and phosphorous incorporation. The effect of boron on ta-C is to give a p-type effect whereas the effect of phosphorous gives n-type doping effect.
Nikitin, A V; Rey, M; Tyuterev, Vl G
2015-03-07
A simultaneous use of the full molecular symmetry and of an exact kinetic energy operator (KEO) is of key importance for accurate predictions of vibrational levels at a high energy range from a potential energy surface (PES). An efficient method that permits a fast convergence of variational calculations would allow iterative optimization of the PES parameters using experimental data. In this work, we propose such a method applied to tetrahedral AB4 molecules for which a use of high symmetry is crucial for vibrational calculations. A symmetry-adapted contracted angular basis set for six redundant angles is introduced. Simple formulas using this basis set for explicit calculation of the angular matrix elements of KEO and PES are reported. The symmetric form (six redundant angles) of vibrational KEO without the sin(q)(-2) type singularity is derived. The efficient recursive algorithm based on the tensorial formalism is used for the calculation of vibrational matrix elements. A good basis set convergence for the calculations of vibrational levels of the CH4 molecule is demonstrated.
Energy Technology Data Exchange (ETDEWEB)
Wang, Z J
2012-12-06
The overriding objective for this project is to develop an efficient and accurate method for capturing strong discontinuities and fine smooth flow structures of disparate length scales with unstructured grids, and demonstrate its potentials for problems relevant to DOE. More specifically, we plan to achieve the following objectives: 1. Extend the SV method to three dimensions, and develop a fourth-order accurate SV scheme for tetrahedral grids. Optimize the SV partition by minimizing a form of the Lebesgue constant. Verify the order of accuracy using the scalar conservation laws with an analytical solution; 2. Extend the SV method to Navier-Stokes equations for the simulation of viscous flow problems. Two promising approaches to compute the viscous fluxes will be tested and analyzed; 3. Parallelize the 3D viscous SV flow solver using domain decomposition and message passing. Optimize the cache performance of the flow solver by designing data structures minimizing data access times; 4. Demonstrate the SV method with a wide range of flow problems including both discontinuities and complex smooth structures. The objectives remain the same as those outlines in the original proposal. We anticipate no technical obstacles in meeting these objectives.
Energy Technology Data Exchange (ETDEWEB)
Wu, Z. [Laboratoire Pierre Sue, CEA-CNRS CE Saclay, Gif-sur Yvette (France)]|[INFN, Laboratori Nazionali di Frascati, Rome (Italy); Romano, C. [Rome, Univ. `Roma Tre` (Italy). Dip di Scienze Geologiche]|[Univ. Bayreuth (Germany). Bayerishes Geoinstitut; Marcelli, A.; Cibin, G. [INFN, Laboratori Nazionali di Frascati, Rome (Italy); Mottana, A.; Della Ventura, G. [Rome, Univ. `Roma Tre` (Italy). Dip di Scienze Geologiche]|[INFN, Laboratori Nazionali di Frascati, Rome (Italy); Giuli, G. [Florence Univ. (Italy). Dip. Scienze Mineralogiche; Courtial, P.; Dinwell, D.B. [Univ. Bayreuth (Germany). Bayerishes Geoinstitut
1998-11-01
The structure of aluminosilicate melts/glasses plays a key role in Earth Sciences for the understanding of rock-forming igneous processes, as well as in the Materials Sciences for their technical applications. In particular, the alkaline earth aluminosilicate glasses are an extremely important group of materials, with a wide range of commercial application, as well as serving as analogue for natural basaltic melts. However, definition of their structure and properties is still controversial, and in particular the role and effect of Al has long been a subject of debate. The paper reports a series of experimental x-ray absorption near-edge structure (XANES) spectra at the Al K edge on a series of synthetic glasses of peralkaline composition in the CaO-Al{sub 2}O{sub 3}-SiO{sub 2} system, together with a general theoretical framework for data analysis based on an ab initio full multiple scattering (MS) theory. It`s proposed an Al/Si tetrahedral network model for aluminosilicate glasses based on distorted polyhedra, with varying both the T-O (T=Al or Si) bond lengths and the T-O-T angles, and with different Al/Si composition. This model achieves a significant agreement between experiments and simulations. in these glasses, experimental data and theoretical results concur to support a model in which Al is network-former with a comparatively well ordered local medium-range order (up to 5 A).
Optical Study of Filled Tetrahedral Compounds Li3AlN2 and Li3GaN2
Dadsetani, M.; Namjoo, S.; Nejati, H.
2010-08-01
A detailed analysis of the optical properties of filled tetrahedral semiconductors Li3AlN2 and Li3GaN2 has been performed, using the full potential linearized augmented plane wave method within the density functional theory. The real and imaginary parts of the dielectric function ɛ( ω), the optical absorption coefficient I( ω), the reflectivity R( ω), and the electron energy loss function are calculated within the random phase approximation. The interband transitions responsible for the structures in the spectra are specified. Looking at optical matrix element, we note that the major peaks are dominated by transition from metal s, N 2 p states to N 2 p, Ga 3 d states. The theoretical calculated optical properties and electron energy loss spectrum yield a static dielectric constant of 5.34 and a plasmon energy of 19.47 eV for Li3GaN2. In the Li3AlN2 compound, the static dielectric constant decreases to 4.75 and yields a plasmon energy of 18.5 eV. The effect of spin-orbit coupling on the optical properties is also investigated and found to be quite small, especially in the low-energy region. In order to check the reliability of our calculations, analogous results obtained for Be3N2 in the same structure [space group Ia3(206)] are included in this work.
Xu, Zhijun; Schneeloch, J. A.; Wen, Jinsheng; Božin, E. S.; Granroth, G. E.; Winn, B. L.; Feygenson, M.; Birgeneau, R. J.; Gu, Genda; Zaliznyak, I. A.; Tranquada, J. M.; Xu, Guangyong
2016-03-01
It has recently been demonstrated that dynamical magnetic correlations measured by neutron scattering in iron chalcogenides can be described with models of short-range correlations characterized by particular choices of four-spin plaquettes, where the appropriate choice changes as the parent material is doped towards superconductivity. Here we apply such models to describe measured maps of magnetic scattering as a function of two-dimensional wave vectors obtained for optimally superconducting crystals of FeTe1 -xSex . We show that the characteristic antiferromagnetic wave vector evolves from that of the bicollinear structure found in underdoped chalcogenides (at high temperature) to that associated with the stripe structure of antiferromagnetic iron arsenides (at low temperature); these can both be described with the same local plaquette, but with different interplaquette correlations. While the magnitude of the low-energy magnetic spectral weight is substantial at all temperatures, it actually weakens somewhat at low temperature, where the charge carriers become more itinerant. The observed change in spin correlations is correlated with the dramatic drop in the electronic scattering rate and the growth of the bulk nematic response upon cooling. Finally, we also present powder neutron diffraction results for lattice parameters in FeTe1 -xSex indicating that the tetrahedral bond angle tends to increase towards the ideal value upon cooling, in agreement with the increased screening of the crystal field by more itinerant electrons and the correspondingly smaller splitting of the Fe 3 d orbitals.
Zhao, Nan
2017-01-01
The origin of winter Northern Hemispheric low-frequency variability (hereafter, LFV) is regarded to be related to the coupled earth-atmosphere system characterized by the interaction of the jet stream with mid-latitude mountain ranges. On the other hand, observed LFV usually appears as transitions among multiple planetary-scale flow regimes of Northern Hemisphere like NAO + , AO +, AO - and NAO - . Moreover, the interaction between synoptic-scale eddies and the planetary-scale disturbance is also inevitable in the origin of LFV. These raise a question regarding how to incorporate all these aspects into just one framework to demonstrate (1) a planetary-scale dynamics of interaction of the jet stream with mid-latitude mountain ranges can really produce LFV, (2) such a dynamics can be responsible for the existence of above multiple flow regimes, and (3) the role of interaction with eddy is also clarified. For this purpose, a hierarchy of low-order stochastic dynamical models of the coupled earth-atmosphere system derived empirically from different timescale ranges of indices of Arctic Oscillation (AO), North Atlantic Oscillation (NAO), Pacific/North American (PNA), and length of day (LOD) and related probability density function (PDF) analysis are employed in this study. The results seem to suggest that the origin of LFV cannot be understood completely within the planetary-scale dynamics of the interaction of the jet stream with mid-latitude mountain ranges, because (1) the existence of multiple flow regimes such as NAO+, AO+, AO- and NAO- resulted from processes with timescales much longer than LFV itself, which may have underlying dynamics other than topography-jet stream interaction, and (2) we find LFV seems not necessarily to come directly from the planetary-scale dynamics of the interaction of the jet stream with mid-latitude mountain, although it can produce similar oscillatory behavior. The feedback/forcing of synoptic-scale eddies on the planetary
Dzwigaj, S; Che, M
2006-06-29
A CoSiBEA zeolite is prepared by a two-step postsynthesis method that consists of first creating vacant T-sites with associated silanol groups by dealumination of TEABEA zeolite with nitric acid and then impregnating the resulting SiBEA zeolite with an aqueous solution of Co(NO3)2. The incorporation of Co into lattice sites of SiBEA is evidenced by XRD. The consumption of OH groups is monitored by FTIR. The presence of Co in its II oxidation state and in tetrahedral coordination is evidenced by diffuse reflectance UV-vis and EPR spectroscopy. The very high reduction temperature (1120 K) of cobalt in CoSiBEA zeolite determined by TPR confirms that Co interacts strongly with the zeolite support, consistent with lattice tetrahedral (T(d)) coordination.
Energy Technology Data Exchange (ETDEWEB)
Bianconi, A.; Fritsch, E.; Calas, G.; Petiau, J.
1985-09-15
The x-ray-absorption near-edge structure (XANES) of transition elements in tetrahedral coordination in crystals and glasses has been studied. We have identified the XANES features in the continuum that can be assigned to multiple scattering within the first coordination shell. The energy positions E/sub r/ of the XANES peaks in the continuum follow the rule (E/sub r/-E/sub b/)d/sup 2/ = const, where E/sub b/ is the energy of the prepeak, defined as the first core excitation to the bound antibonding state of T/sub 2/ symmetry, and d is the interatomic distance. This plot allows us to determine the tetrahedral coordination of a vanadium impurity in a SiO/sub 2/ glass and to get an estimation of the vanadium-oxygen distance (1.77 +- 0.05 A).
Bianconi, A.; Fritsch, E.; Calas, G.; Petiau, J.
1985-09-01
The x-ray-absorption near-edge structure (XANES) of transition elements in tetrahedral coordination in crystals and glasses has been studied. We have identified the XANES features in the continuum that can be assigned to multiple scattering within the first coordination shell. The energy positions Er of the XANES peaks in the continuum follow the rule (Er-Eb)d2= const, where Eb is the energy of the prepeak, defined as the first core excitation to the bound antibonding state of T2 symmetry, and d is the interatomic distance. This plot allows us to determine the tetrahedral coordination of a vanadium impurity in a SiO2 glass and to get an estimation of the vanadium-oxygen distance (1.77+/-0.05 Å).
Biryukov, V. A.; Muratov, M. V.; Petrov, I. B.; Sannikov, A. V.; Favorskaya, A. V.
2015-10-01
Seismic responses from fractured geological layers are mathematically simulated by applying the grid-characteristic method on unstructured tetrahedral meshes with the use of high-performance computer systems. The method is intended for computing complicated spatial dynamical processes in complex heterogeneous media and is characterized by exact formulation of contact conditions. As a result, it can be applied to the simulation of seismic exploration problems, including in regions with a large number of inhomogeneities, examples of which are fractured structures. The use of unstructured tetrahedral meshes makes it possible to specify geological cracks of various shapes and spatial orientations. As a result, problems are solved in a formulation maximally close to an actual situation. A cluster of computers is used to improve the accuracy of the computation by optimizing its duration.
Institute of Scientific and Technical Information of China (English)
LI,Wen-Zhi(李文智); WANG,Xia(王霞); ZHANG,Wei-Qiang(张伟强); CHEN Li-Ren(陈立仁); LI,Yong-Min(李永民); MA,Chun-Lin(马春林); YIN,Yuan-Qi(殷元骐)
2004-01-01
Amylose tris(3,5-dimethylphenylcarbamate) (ADMPC) coated on a kind of small particle silica gel was prepared. On this ADMPC chiral stationary phase (CSP), the direct enantiomeric separation of six novel chiral transition metal tetrahedral clusters has firstly been achieved using n-hexane as the mobile phase containing various alcohols as modifiers. The effect of mobile phase modifiers and the structural variation of the solutes on their retention factors (k′) and resolutions (Rs) were investigated. The result suggests that not only the structure and concentration of alcohol in mobile phase, but also the structural differences in racemates can have a pronounced effect on enantiomeric separation. ADMPC-CSP is a suitable CSP for the optical resolution of chiral tetrahedral cluster by HPLC.
Stühler, Sven; Fleissner, Florian; Eberhard, Peter
2016-11-01
We present an extended particle model for the discrete element method that on the one hand is tetrahedral in shape and on the other hand is capable to describe deformations. The deformations of the tetrahedral particles require a framework to interrelate the particle strains and resulting stresses. Hence, adaptations from the finite element method were used. This allows to link the two methods and to adequately describe material and simulation parameters separately in each scope. Due to the complexity arising of the non-spherical tetrahedral geometry, all possible contact combinations of vertices, edges, and surfaces must be considered by the used contact detection algorithm. The deformations of the particles make the contact evaluation even more challenging. Therefore, a robust contact detection algorithm based on an optimization approach that exploits temporal coherence is presented. This algorithm is suitable for general {R}^{{n}} simplices. An evaluation of the robustness of this algorithm is performed using a numerical example. In order to create complex geometries, bonds between these deformable particles are introduced. This coupling via the tetrahedra faces allows the simulation bonding of deformable bodies composed of several particles. Numerical examples are presented and validated with results that are obtained by the same simulation setup modeled with the finite element method. The intention of using these bonds is to be able to model fracture and material failure. Therefore, the bonds between the particles are not lasting and feature a release mechanism based on a predefined criterion.
Energy Technology Data Exchange (ETDEWEB)
Li, Xin; Miller, Eric L.; Rappaport, Carey; Silevich, Michael
2000-04-11
A common problem in signal processing is to estimate the structure of an object from noisy measurements linearly related to the desired image. These problems are broadly known as inverse problems. A key feature which complicates the solution to such problems is their ill-posedness. That is, small perturbations in the data arising e.g. from noise can and do lead to severe, non-physical artifacts in the recovered image. The process of stabilizing these problems is known as regularization of which Tikhonov regularization is one of the most common. While this approach leads to a simple linear least squares problem to solve for generating the reconstruction, it has the unfortunate side effect of producing smooth images thereby obscuring important features such as edges. Therefore, over the past decade there has been much work in the development of edge-preserving regularizers. This technique leads to image estimates in which the important features are retained, but computationally the y require the solution of a nonlinear least squares problem, a daunting task in many practical multi-dimensional applications. In this thesis we explore low-order models for reducing the complexity of the re-construction process. Specifically, B-Splines are used to approximate the object. If a ''proper'' collection B-Splines are chosen that the object can be efficiently represented using a few basis functions, the dimensionality of the underlying problem will be significantly decreased. Consequently, an optimum distribution of splines needs to be determined. Here, an adaptive refining and pruning algorithm is developed to solve the problem. The refining part is based on curvature information, in which the intuition is that a relatively dense set of fine scale basis elements should cluster near regions of high curvature while a spares collection of basis vectors are required to adequately represent the object over spatially smooth areas. The pruning part is a greedy
Pelties, Christian
2012-02-18
Accurate and efficient numerical methods to simulate dynamic earthquake rupture and wave propagation in complex media and complex fault geometries are needed to address fundamental questions in earthquake dynamics, to integrate seismic and geodetic data into emerging approaches for dynamic source inversion, and to generate realistic physics-based earthquake scenarios for hazard assessment. Modeling of spontaneous earthquake rupture and seismic wave propagation by a high-order discontinuous Galerkin (DG) method combined with an arbitrarily high-order derivatives (ADER) time integration method was introduced in two dimensions by de la Puente et al. (2009). The ADER-DG method enables high accuracy in space and time and discretization by unstructured meshes. Here we extend this method to three-dimensional dynamic rupture problems. The high geometrical flexibility provided by the usage of tetrahedral elements and the lack of spurious mesh reflections in the ADER-DG method allows the refinement of the mesh close to the fault to model the rupture dynamics adequately while concentrating computational resources only where needed. Moreover, ADER-DG does not generate spurious high-frequency perturbations on the fault and hence does not require artificial Kelvin-Voigt damping. We verify our three-dimensional implementation by comparing results of the SCEC TPV3 test problem with two well-established numerical methods, finite differences, and spectral boundary integral. Furthermore, a convergence study is presented to demonstrate the systematic consistency of the method. To illustrate the capabilities of the high-order accurate ADER-DG scheme on unstructured meshes, we simulate an earthquake scenario, inspired by the 1992 Landers earthquake, that includes curved faults, fault branches, and surface topography. Copyright 2012 by the American Geophysical Union.
Institute of Scientific and Technical Information of China (English)
李一良; 李玉芝; 等
1998-01-01
It is well known that in pyroxene structure,there are two metal sites,M1 and M2.Generally speaking,Ferrous iron in each of these sites would normally be expected to give rise to a doublet,However,anomalies have been found in the relative areas of the peaks in the room temperature spectra of some clinopyroxene(CPX)when the above assignment is followed.According to the calculation of Next Nearest Neighbor configurations of divalent cations in M1,we found that the four configurations of M1 can be divided into two groups.One group is 3Ca configuration that increases with the content of Ca(p.f.u);the other group is made up of three No-3Ca configurations that decrease with the content of Ca.The two groups contribute to the spectrum structure of M1.so in this study we fit two doublets for ferrous iron in M1.Though there were several reports on Fe3+ in tetrahedral site previously,it was not sure that Fe3+ occupies the T site is a universal fact in CPX,despite of the content of Al.We found that the Fe3+ in the T site fitted by Moessbauer spectroscopy is negatively correlated to the Si content in the T site and positively correlated to the Fe3+ in the T site estimated on the supposition that Fe3+ and Al occupy the T site randomly.If it is true.it is important in the modeling of ion exchange geobarometries and geothermomeries.
Energy Technology Data Exchange (ETDEWEB)
Panwar, O.S. [Plasma Processed Materials Group, National Physical Laboratory, Dr. K.S. Krishnan Road, New Delhi-110 012 (India)], E-mail: ospanwar@mail.nplindia.ernet.in; Khan, Mohd. Alim [Plasma Processed Materials Group, National Physical Laboratory, Dr. K.S. Krishnan Road, New Delhi-110 012 (India); Kumar, Mahesh; Shivaprasad, S.M. [Surface Physics and Nanostructures Group, National Physical Laboratory, Dr. K.S. Krishnan Road, New Delhi-110 012 (India); Satyanarayana, B.S. [MIT Innovation Centre and Electronics and Communication Department, Manipal Institute of Technology, Manipal-579104 (India); Dixit, P.N. [Plasma Processed Materials Group, National Physical Laboratory, Dr. K.S. Krishnan Road, New Delhi-110 012 (India); Bhattacharyya, R. [Emeritus Scientist, National Physical Laboratory, New Delhi-110012 (India); Khan, M.Y. [Department of Physics, Jamia Millia Islamia, Central University, New Delhi-110025 (India)
2008-02-29
The application of a sufficiently high negative substrate bias, during the growth of tetrahedral amorphous carbon (ta-C), is usually associated with low sp{sup 3} bonding configuration and stressed films. However, in an effort to understand and utilize the higher pseudo thermo dynamical conditions during the film growth, at high negative substrate bias (- 300 V), reported here is a study on ta-C films grown under different hydrogen and nitrogen concentration. As grown ta-C films were studied under different negative substrate bias conditions. The variation of the sp{sup 3} content and sp{sup 3}/sp{sup 2} ratio in the ta-C films exhibits a trend similar to those reported in literature, with a subtle variation in this report being the substrate bias voltage, which was observed to be around - 200 V, for obtaining the highest sp{sup 3} (80%) bonding and sp{sup 3}/sp{sup 2} (3.95) ratio. The hydrogen and nitrogen incorporated ta-C films studied, at a bias of - 300 V, show an increase in sp{sup 3} (87-91%) bonding and sp{sup 3}/sp{sup 2} (7-10) ratio in the range of studies reported. The inference is drawn on the basis of the set of data obtained from measurements carried out using X-ray photoelectron spectroscopy, X-ray induced Auger electron spectroscopy and Raman spectroscopy of as grown and hydrogen and nitrogen incorporated ta-C films deposited using an S bend filtered cathodic vacuum arc system. The study indicates the possibility of further tailoring ta-C film properties and also extending capabilities of the cathodic arc system for developing carbon based films for electronics and tribological applications.
Usui, Yoshiya; Ogawa, Yasuo; Aizawa, Koki; Kanda, Wataru; Hashimoto, Takeshi; Koyama, Takao; Yamaya, Yusuke; Kagiyama, Tsuneomi
2017-03-01
Asama Volcano is an andesitic composite volcano and one of the most active volcanoes in Japan. In order to reveal electrical resistivity structure beneath the volcano accurately, we performed a 3-D inversion of dense magnetotelluric survey data. In order to prevent misinterpretation of the subsurface resistivity due to the steep topography around Asama Volcano, we used an unstructured tetrahedral mesh to represent the topography. Furthermore, we reduced the calculation time by transforming the inverse problem from the model space into the data space. Comparison of the new data-space method to the original model-space method showed that the calculation time required to update the model parameters was reduced as a result of the transformation, whereas the resistivity structure obtained remained unchanged. In the subsurface resistivity structure around Asama Volcano that was estimated from the inversion, resistive bodies were discovered to be located under the old eruption centres. In particular, under the 24 ka collapse caldera to the west of the presently active crater, a spherical resistive body was found to exist in isolation. In addition, there was a widespread conductive layer below the resistive surface layer. By comparison with previous hydrological and geochemical studies, the conductive layer was interpreted as being a high-water-content layer and an overlying layer rich in altered clay minerals. Because the western part of the volcanic conduit was considered to be the resistive area, which is inferred to consist of unfractured rocks with lower permeability than their surroundings, it would appear that the area obstructs the westward flow of the hydrothermal fluid beneath the summit, thereby contributing to higher concentrations of SO42- and Cl- in the spring water at the northern and eastern feet as well as the uneven location of a diffuse CO2 anomaly.
Gavette, Jesse V; Klug, Christina M; Zakharov, Lev N; Shores, Matthew P; Haley, Michael M; Johnson, Darren W
2014-07-11
A bipyridyl-based anion receptor is utilized as a ligand in a tetrahedral FeCl2 complex and demonstrates secondary coordination sphere influence through intramolecular hydrogen bonding to the chloride ligands as evidenced by X-ray crystallography.
Krauser, J.; Gehrke, H.-G.; Hofsäss, H.; Amani, J.; Trautmann, C.; Weidinger, A.
2015-12-01
This paper gives an extended overview of the electrical properties of ion tracks in hydrogen-free tetrahedral amorphous carbon (ta-C) with a sp3 bond fraction of about 80%. The films were grown by mass selected ion beam deposition of 100 eV 12C+ ions. The ion tracks are generated by irradiation of ta-C films with uranium ions of 1 GeV kinetic energy. Along the ion path a conversion from diamond-like (sp3) carbon to graphite-like (sp2) carbon takes place. Topography and current measurements of individual ion tracks were performed by atomic force microscopy at ambient temperature. The temperature dependence of the electric conductivity was studied between 15 and 390 K by means of 0.28 mm2 large contact pads averaging over about 107 tracks. For each sample and at each temperature the conductivity as a function of the applied electrical field (non-ohmic behaviour) was measured separately and the data were extrapolated to field zero. In this way, the zero-field conductivity was determined independent from the field dependence. In spite of large differences in the absolute values, the temperature dependence of the zero-field conductivities is found to be very similar in shape for all samples. The conductivities follow a {T}-{1/4} law up to temperatures slightly below room temperature. At higher temperatures a transport mechanism based on over-barrier hopping dominates with an activation energy of about 220 meV for tracks and 260 meV for the ta-C matrix. The field dependence measurements show that the deviation of the I-V characteristics from ohmic behaviour decreases with increasing zero-field conductivity. We also tested Cu-doped ta-C samples and found that they conduct significantly better than pure ta-C. However, the doping also increases the zero-field conductivity resulting in a weaker contrast between the track and matrix. The data are interpreted within the so-called ‘barrier model’ where the electrons are assumed to move fairly freely in well-conducting sp2
Electronic spectrum of non-tetrahedral acceptors in CdTe:Cl and CdTe:Bi,Cl single crystals
Energy Technology Data Exchange (ETDEWEB)
Krivobok, V. S., E-mail: krivobok@lebedev.ru [P.N. Lebedev Physical Institute, Russian Academy of Sciences, Moscow (Russian Federation); Moscow Institute of Physics and Technology (State University), Dolgoprudny, Moscow Region (Russian Federation); Nikolaev, S. N.; Bagaev, V. S.; Pruchkina, A. A.; Onishchenko, E. E.; Kolosov, S. A.; Klevkov, Yu. V.; Skorikov, M. L. [P.N. Lebedev Physical Institute, Russian Academy of Sciences, Moscow (Russian Federation)
2016-02-07
The electronic spectra of complex acceptors in compensated CdTe:Cl, CdTe:Ag,Cl, and CdTe:Bi,Cl single crystals are studied using low-temperature photoluminescence (PL) measurements under both nonresonant and resonant excitation of distant donor–acceptor pairs (DAP). The wavelength modulation of the excitation source combined with the analysis of the differential PL signal is used to enhance narrow spectral features obscured because of inhomogeneous line broadening and/or excitation transfer for selectively excited DAPs. For the well-known tetrahedral (T{sub D}) Ag{sub Cd} acceptor, the energies of four excited states are measured, and the values obtained are shown to be in perfect agreement with the previous data. Moreover, splitting between the 2P{sub 3/2} (Γ{sub 8}) and 2S{sub 3/2} (Γ{sub 8}) states is clearly observed for Ag{sub Cd} centers located at a short distance (5–7 nm) from a hydrogen-like donor (Cl{sub Te}). This splitting results from the reduction of the T{sub D} symmetry taking place when the acceptor is a member of a donor–acceptor pair. For the Cl-related complex acceptor with an activation energy of ∼121 meV (A-center), the energies of eight excited states are measured. It is shown that this defect produces low-symmetry central-cell correction responsible for the strong splitting of S-like T{sub D} shells. The energy spectrum of the Bi-related shallow acceptor with an activation energy of ∼36 meV is measured as well. The spectrum obtained differs drastically from the hydrogen-like set of levels, which indicates the existence of repulsive low-symmetry perturbation of the hydrogen-like Coulomb potential. It is also shown that the spectra of selectively excited PL recorded for a macroscopic ensemble of distant donor–acceptor pairs allow one to detect the low symmetry of acceptors of a given type caused by their complex nature or by the Jahn–Teller distortion. This method does not require any additional (external) field and is
Dong, Shibiao; Zhao, Rongtao; Zhu, Jiangong; Lu, Xiao; Li, Yang; Qiu, Shaofu; Jia, Leili; Jiao, Xiong; Song, Shiping; Fan, Chunhai; Hao, RongZhang; Song, HongBin
2015-04-29
A DNA tetrahedral nanostructure-based electrochemical biosensor was developed to detect avian influenza A (H7N9) virus through recognizing a fragment of the hemagglutinin gene sequence. The DNA tetrahedral probe was immobilized onto a gold electrode surface based on self-assembly between three thiolated nucleotide sequences and a longer nucleotide sequence containing complementary DNA to hybridize with the target single-stranded (ss)DNA. The captured target sequence was hybridized with a biotinylated-ssDNA oligonucleotide as a detection probe, and then avidin-horseradish peroxidase was introduced to produce an amperometric signal through the interaction with 3,3',5,5'-tetramethylbenzidine substrate. The target ssDNA was obtained by asymmetric polymerase chain reaction (PCR) of the cDNA template, reversely transcribed from the viral lysate of influenza A (H7N9) virus in throat swabs. The results showed that this electrochemical biosensor could specifically recognize the target DNA fragment of influenza A (H7N9) virus from other types of influenza viruses, such as influenza A (H1N1) and (H3N2) viruses, and even from single-base mismatches of oligonucleotides. Its detection limit could reach a magnitude of 100 fM for target nucleotide sequences. Moreover, the cycle number of the asymmetric PCR could be reduced below three with the electrochemical biosensor still distinguishing the target sequence from the negative control. To the best of our knowledge, this is the first report of the detection of target DNA from clinical samples using a tetrahedral DNA probe functionalized electrochemical biosensor. It displays that the DNA tetrahedra has a great potential application as a probe of the electrochemical biosensor to detect avian influenza A (H7N9) virus and other pathogens at the gene level, which will potentially aid the prevention and control of the disease caused by such pathogens.
Lobach, K. A.; Ovchinnikov, S. G.; Ovchinnikova, T. M.
2015-01-01
For Mott insulators with tetrahedral environment, the effective Hubbard parameter U eff is obtained as a function of pressure. This function is not universal. For crystals with d 5 configuration, the spin crossover suppresses electron correlations, while for d 4 configurations, the parameter U eff increases after a spin crossover. For d 2 and d 7 configurations, U eff increases with pressure in the high-spin (HS) state and is saturated after the spin crossover. Characteristic features of the insulator-metal transition are considered as pressure increases; it is shown that there may exist cascades of several transitions for various configurations.
Bavec, Aljoša; Knez, Damijan; Makovec, Tomaž; Stojan, Jure; Gobec, Stanislav; Goličnik, Marko
2014-11-01
Although a recent study of Debord et al. in Biochimie (2014; 97:72-77) described the thermodynamics of the catalysed hydrolysis of phenyl acetate by human paraoxonase-1, the mechanistic details along the reaction route of this enzyme remain unclear. Therefore, we briefly present the solvent kinetic isotope effects on the phenyl acetate esterase activity of paraoxonase-1 and its inhibition with the phenyl methylphosphonate anion, which is a stable isosteric analogue that mimics the high-energy tetrahedral intermediate on the hydroxide-promoted hydrolysis pathway. The data show normal isotope effects, while proton inventory analysis indicates that two protons contribute to the kinetic isotope effect. Coherently, moderate competitive inhibition with the phenyl methylphosphonate anion reveals that the rate-limiting transition state suboptimally resembles the tetrahedral intermediate. The implications of these findings can be attributed to two possible reaction mechanisms that might occur during the paraoxonase-1-catalysed hydrolysis of phenyl acetate. Copyright © 2014 Elsevier B.V. and Société française de biochimie et biologie Moléculaire (SFBBM). All rights reserved.
Energy Technology Data Exchange (ETDEWEB)
Mantovani, M. [Instituto de Ciencia de Materiales de Sevilla, Departamento de Quimica Inorganica (CSIC-US) Avda. Americo Vespucio, s/n. 41092 Sevilla (Spain); Escudero, A. [Bayerisches Geoinstitut, Universitaet Bayreuth, Bayeruth 95440 (Germany); Alba, M.D. [Instituto de Ciencia de Materiales de Sevilla, Departamento de Quimica Inorganica (CSIC-US) Avda. Americo Vespucio, s/n. 41092 Sevilla (Spain); Becerro, A.I., E-mail: anieto@icmse.csic.es [Instituto de Ciencia de Materiales de Sevilla, Departamento de Quimica Inorganica (CSIC-US) Avda. Americo Vespucio, s/n. 41092 Sevilla (Spain)
2009-07-15
This paper presents the results of a comprehensive investigation of the interaction of layered silicates with Ca(OH){sub 2} in hydrothermal conditions. The study is intended to evaluate the stability of the clay buffer in radioactive waste repositories, at the intermediate stages of concrete leaching, when the pH is controlled by the dissolution of portlandite. The influence of layer nature, octahedral occupation, presence of tetrahedral Al and degree of crystallinity will be assessed by analysing the behaviour of a set of well-selected phyllosilicates and using the combined capabilities of {sup 29}Si and {sup 27}Al MAS-NMR spectroscopy, powder X-ray diffraction and SEM/EDX. The results show that the main factor affecting the stability of the clay is the octahedral occupation, so that trioctahedral phyllosilicates are much more stable than dioctahedral ones. The nature and expandability of the layer does not seem to much influence the stability of the clay, so that a 2:1 expandable phyllosilicate shows the same stability as a chemically analogous 1:1 non-expandable phyllosilicate. However other factors like the poor crystallinity of the starting material or the presence of Al in the tetrahedral sheet of trioctahedral phyllosilicates weaken the clay structure in alkaline conditions and favour the transformation towards other phases.
Institute of Scientific and Technical Information of China (English)
LI Yang-xue; XUE Ming; HUANG Lin; CHEN Si-ru; QIU Shi-lun
2013-01-01
Two 3D multifunctional lanthanide metal-organic frameworks(MOFs),Pr(HTCPS)(H2O)·2DMF·C2H5OH·5H2O(JUC-93) and Pr3(TCPS)2(NO3)(H2O)4(DMA)2·2DMA·C2H5OH·3H2(JUC-94)[H4TCPS=tetrakis(4-carboxyphenyl)-silane,DMF=N,N'-dimethylformamide,DMA=N,N'-dimethylacetamide and JUC=Jilin University China] were synthesized by the self-assembly of a rigid silicon-centered tetrahedral carboxylate ligand H4TCPS and Pr(Ⅲ) ions in different solvothermal reactions.X-Ray crystallography revealed that they exhibited a rare CaF2 topology framework,constructed from the 4-connected tetrahedral TCPS unit with the 8-connected dinuclear praseodymium cluster unit and trinuclear praseodymium cluster unit,respectively.In addition,the luminescent and magnetic properties of the two compounds were investigated.
Directory of Open Access Journals (Sweden)
Stan Schein
2016-08-01
Full Text Available The Goldberg construction of symmetric cages involves pasting a patch cut out of a regular tiling onto the faces of a Platonic host polyhedron, resulting in a cage with the same symmetry as the host. For example, cutting equilateral triangular patches from a 6.6.6 tiling of hexagons and pasting them onto the full triangular faces of an icosahedron produces icosahedral fullerene cages. Here we show that pasting cutouts from a 6.6.6 tiling onto the full hexagonal and triangular faces of an Archimedean host polyhedron, the truncated tetrahedron, produces two series of tetrahedral (Td fullerene cages. Cages in the first series have 28n2 vertices (n ≥ 1. Cages in the second (leapfrog series have 3 × 28n2. We can transform all of the cages of the first series and the smallest cage of the second series into geometrically convex equilateral polyhedra. With tetrahedral (Td symmetry, these new polyhedra constitute a new class of “convex equilateral polyhedra with polyhedral symmetry”. We also show that none of the other Archimedean polyhedra, six with octahedral symmetry and six with icosahedral, can host full-face cutouts from regular tilings to produce cages with the host’s polyhedral symmetry.
一种新的基于四面体的体细分方法%A New Volumetric Subdivision Scheme of Tetrahedral Meshes
Institute of Scientific and Technical Information of China (English)
张华; 潘日晶
2012-01-01
A new subdivision scheme for tetrahedral meshes is proposed. Previous tetra-hedral subdivision schemes encoded directional preferences, or subdivided a tetrahedron into tetrahedrons and octahedrons, which result increased complexity in representation and operation to the meshes. The proposed method solves the problems to a certain extent. For the volumetric meshes of tetrahedron, the inners of the meshes are subdivided by using the volumetric subdivision, and the surfaces of the meshes are subdivided by using a quasi-Loop surface subdivision with a parameter to control the shapes of the solids.%提出了一种新的四面体网格细分方法,之前的体细分方法存在着对角线选择或者四面体细分成四面体和八面体的问题,增加了表示和处理的复杂性.新方法较好地解决了上述问题,对一个由四面体单元组成的网格实体,体内进行体细分,细分后的体网格全部由四面体单元组成,而实体的表面,采用一种带参数的类Loop曲面细分,用于控制实体的形状.
Tavelli, Maurizio; Dumbser, Michael
2016-08-01
In this paper we propose a novel arbitrary high order accurate semi-implicit space-time discontinuous Galerkin method for the solution of the three-dimensional incompressible Navier-Stokes equations on staggered unstructured curved tetrahedral meshes. As is typical for space-time DG schemes, the discrete solution is represented in terms of space-time basis functions. This allows to achieve very high order of accuracy also in time, which is not easy to obtain for the incompressible Navier-Stokes equations. Similarly to staggered finite difference schemes, in our approach the discrete pressure is defined on the primary tetrahedral grid, while the discrete velocity is defined on a face-based staggered dual grid. While staggered meshes are state of the art in classical finite difference schemes for the incompressible Navier-Stokes equations, their use in high order DG schemes is still quite rare. A very simple and efficient Picard iteration is used in order to derive a space-time pressure correction algorithm that achieves also high order of accuracy in time and that avoids the direct solution of global nonlinear systems. Formal substitution of the discrete momentum equation on the dual grid into the discrete continuity equation on the primary grid yields a very sparse five-point block system for the scalar pressure, which is conveniently solved with a matrix-free GMRES algorithm. From numerical experiments we find that the linear system seems to be reasonably well conditioned, since all simulations shown in this paper could be run without the use of any preconditioner, even up to very high polynomial degrees. For a piecewise constant polynomial approximation in time and if pressure boundary conditions are specified at least in one point, the resulting system is, in addition, symmetric and positive definite. This allows us to use even faster iterative solvers, like the conjugate gradient method. The flexibility and accuracy of high order space-time DG methods on curved
Ba3(P1−MnO4)2 : Blue/green inorganic materials based on tetrahedral Mn(V)
Indian Academy of Sciences (India)
Sourav Laha; Rohit Sharma; S V Bhat; M L P Reddy; J Gopalakrishnan; S Natarajan
2011-10-01
We describe a blue/green inorganic material, Ba3(P1−MnO4)2 (I) based on tetrahedral MnO$^{3-}_{4}$ :32 chromophore. The solid solutions (I) which are sky-blue and turquoise-blue for ≤ 0.25 and dark green for ≥ 0.50, are readily synthesized in air from commonly available starting materials, stabilizing the MnO$^{3-}_{4}$ chromophore in an isostructural phosphate host. We suggest that the covalency/ionicity of P–O/Mn–O bonds in the solid solutions tunes the crystal field strength around Mn(V) such that a blue colour results for materials with small values of . The material could serve as a nontoxic blue/green inorganic pigment.
Energy Technology Data Exchange (ETDEWEB)
Lobach, K. A., E-mail: ks-ad@yandex.ru; Ovchinnikov, S. G., E-mail: sgo@iph.krasn.ru [Siberian Federal University (Russian Federation); Ovchinnikova, T. M. [Russian Academy of Sciences, Sukachev Institute of Forest, Siberian Branch (Russian Federation)
2015-01-15
For Mott insulators with tetrahedral environment, the effective Hubbard parameter U{sub eff} is obtained as a function of pressure. This function is not universal. For crystals with d{sup 5} configuration, the spin crossover suppresses electron correlations, while for d{sup 4} configurations, the parameter U{sub eff} increases after a spin crossover. For d{sup 2} and d{sup 7} configurations, U{sub eff} increases with pressure in the high-spin (HS) state and is saturated after the spin crossover. Characteristic features of the insulator-metal transition are considered as pressure increases; it is shown that there may exist cascades of several transitions for various configurations.
Jensen, J.; Lemmens, P.; Gros, C.
2003-12-01
Raman light-scattering experiments in the antiferromagnetic phase of the Cu2Te2O5(Br1 - xClx)2 compounds are analyzed in terms of a dimerized spin model for the tetrahedral Cu-clusters. It is shown that the longitudinal magnetic excitation in the pure Br system hybridizes with a localized singlet excitation due to the presence of a Dzyaloshinskii-Moriya anisotropy term. The drastic change of the magnetic scattering intensities observed when a proportion of Br is replaced by Cl ions, is proposed to be caused by a change of the magnetic order parameter. Instead of being parallel/antiparallel with each other, the spins in the two pairs of spin-½ order perpendicular to each other, when the composition x is larger than about 0.25.
Tanaka, Masashi; Zhang, Shuai; Inumaru, Kei; Yamanaka, Shoji
2013-05-20
The Zintl compound CaAl2Si2 peritectically decomposes to a new ternary cubic Laves phase Ca(Al,Si)2 and an Al-Si eutectic at temperatures above 750 °C under a pressure of 13 GPa. The ternary Laves phase compound can also be prepared as solid solutions Ca(Al(1-x)Si(x))2 (0.35 ≤ x ≤ 0.75) directly from the ternary mixtures under high-pressure and high-temperature conditions. The cubic Laves phase structure can be regarded as a type of clathrate compound composed of face-sharing truncated tetrahedral cages with Ca atoms at the center, Ca@(Al,Si)12. The compound with a stoichiometric composition CaAlSi exhibits superconductivity with a transition temperature of 2.6 K. This is the first superconducting Laves phase compound composed solely of commonly found elements.
Directory of Open Access Journals (Sweden)
JONG WOON KIM
2014-04-01
In this paper, we introduce a modified scattering kernel approach to avoid the unnecessarily repeated calculations involved with the scattering source calculation, and used it with parallel computing to effectively reduce the computation time. Its computational efficiency was tested for three-dimensional full-coupled photon-electron transport problems using our computer program which solves the multi-group discrete ordinates transport equation by using the discontinuous finite element method with unstructured tetrahedral meshes for complicated geometrical problems. The numerical tests show that we can improve speed up to 17∼42 times for the elapsed time per iteration using the modified scattering kernel, not only in the single CPU calculation but also in the parallel computing with several CPUs.
Abshire, J. B.
1984-01-01
The paper computes direct detection laser communications receiver performance when using avalanche photodiode (APD) detectors. The performances are compared in terms of bit error probability vs average signal required per bit when the transmitter uses either on-off keying (OOK) or low-order PPM formats. It is shown that QPPM requires 3 dB less signal than OOK, while BPPM requires the same or slightly more than OOK for the same performance. Optimum APD gain values range from 200 to 400. When using QPPM, k(eff) = 0.006, and optimum gain, 60 signal counts/bit are required at 500 Mbits/s for a 0.000001 bit error probability. It is concluded that QPPM may be an attractive signaling format for some fiber or free space laser communication applications.
Institute of Scientific and Technical Information of China (English)
潘晓春
2012-01-01
It is necessary to describe the statistical properties of wind speed using three-parameter Weibull distribution for offshore wind energy resource assessment and utilization.According to the functional relation between parameters and probability-weighted moments（PWM）,the functions were fitted with the shape parameter and PWM using logistic curve.Two formulae of parameter estimation were studied out based on low-order insufficient and exceeding PWM.Accuracy test results show that these formulae had higher precision in large-scale range.Through comparative analysis with high-order PWM method for example,the author believes the low-order PWM methods in this paper are worth popularizing.%为便于进行海上风能资源评估与利用,采用三参数Weibull分布来描述风的统计特性是必要的。根据Weibull分布的三参数与概率权重矩（probability-weighted moment,PWM）的关系,应用罗吉斯蒂曲线拟合形状参数与PWM的函数关系,提出低阶不及PWM和超过PWM 2种参数估计方法。精度检验显示,文中方法在较大范围内均具有较高的精度。通过算例分析比较,认为提出的低阶PWM法值得推广使用。
Energy Technology Data Exchange (ETDEWEB)
Lin, Qisheng, E-mail: qslin@ameslab.gov [Division of Materials Sciences and Engineering, Ames Laboratory, US-DOE, Ames, IA 50011 (United States); Taufour, Valentin [Division of Materials Sciences and Engineering, Ames Laboratory, US-DOE, Ames, IA 50011 (United States); Department of Physics and Astronomy, Iowa State University, Ames, IA 50011 (United States); Zhang, Yuemei [Department of Chemistry, Iowa State University, Ames, IA 50011 (United States); Wood, Max; Drtina, Thomas; Bud’ko, Sergey L.; Canfield, Paul C. [Division of Materials Sciences and Engineering, Ames Laboratory, US-DOE, Ames, IA 50011 (United States); Department of Physics and Astronomy, Iowa State University, Ames, IA 50011 (United States); Miller, Gordon J. [Division of Materials Sciences and Engineering, Ames Laboratory, US-DOE, Ames, IA 50011 (United States); Department of Chemistry, Iowa State University, Ames, IA 50011 (United States)
2015-09-15
Single crystals of Nd{sub 4}FeOS{sub 6} were grown from an Fe–S eutectic solution. Single crystal X-ray diffraction analysis revealed a Nd{sub 4}MnOSe{sub 6}-type structure (P6{sub 3}mc, a=9.2693(1) Å, c=6.6650(1)Å, V=495.94(1) Å{sup 3}, Z=2), featuring parallel chains of face-sharing [FeS{sub 6×1/2}]{sup 4−} trigonal antiprisms and interlinked [Nd{sub 4}OS{sub 3}]{sup 4+} cubane-like clusters. Oxygen atoms were found to be trapped by Nd{sub 4} clusters in the [Nd{sub 4}OS{sub 3}]{sup 4{sub +}} chains. Structural differences among Nd{sub 4}MnOSe{sub 6}-type Nd{sub 4}FeOS{sub 6} and the related La{sub 3}CuSiS{sub 7}− and Pr{sub 8}CoGa{sub 3}-type structures have been described. Magnetic susceptibility measurements on Nd{sub 4}FeOS{sub 6} suggested the dominance of antiferromagnetic interactions at low temperature, but no magnetic ordering down to 2 K was observed. Spin-polarized electronic structure calculations revealed magnetic frustration with dominant antiferromagnetic interactions. - Graphical abstract: Trapping of oxygen in Nd{sub 4} tetrahedral clusters results in the formation of the Nd{sub 4}MnOSe{sub 6}-type Nd{sub 4}FeOS{sub 6}, in contrast to the La{sub 3}CuSiS{sub 7}-type oxygen-free Nd{sub 4}FeS{sub 7} and related Pr{sub 8}CoGa{sub 3}-type structures. Complex magnetic frustration inhibits magnetic ordering at low temperature. - Highlights: • Single crystals of Nd{sub 4}FeOS{sub 6} were grown using self-flux method. • Oxygen was found trapped by Nd{sub 4} tetrahedral clusters. • Comparison with two closely related structural types were discussed. • Magnetic measurements revealed antiferromagnetic (AFM) interaction. • VASP calculations confirmed strong magnetic frustration in AFM model.
Wendt, O F; Deeth, R J; Elding, L I
2000-11-13
The substitution kinetics of Me2PhP in cis-Pt(SiMePh2)2(PMe2Ph)2 (1) by the chelating ligand bis(diphenylphosphino)ethane has been followed at 25.0 degrees C in dichloromethane by stopped-flow spectrophotometry. Addition of the leaving ligand causes mass-law retardation compatible with a dissociative process via a three-coordinate transition state or intermediate. Exchange of Me2PhP in 1 has been studied by variable-temperature magnetization transfer 1H NMR in toluene-d8, giving kex326 = 1.76 +/- 0.12 s-1, delta H++ = 117.8 +/- 2.1 kJ mol-1, and delta S++ = 120 +/- 7 J K-1 mol-1. An exchange rate constant independent of the concentrations of free phosphine, a strongly positive delta S++, and nearly equal exchange and ligand dissociation rate constants also support a dissociative process. Density functional theory (DFT) calculations for a dissociative process give an estimate for the Pt-P bond energy of 98 kJ mol-1 for R = R' = Me, which is in reasonable agreement with the experimental activation energy given the differences between the substituents used in the calculation and those employed experimentally. DFT calculations on cis-Pt(PR3)2(SiR'3)2 (R = H, CH3; R' = H, CH3) are consistent with the experimental molecular structure and show that methyl substituents on the Si donors are sufficient to induce the observed tetrahedral twist. The optimized Si-Pt-Si angle in cis-Pt(SiH3)2(PH3)2 is not significantly altered by changing the P-Pt-P angle from its equilibrium value of 104 degrees to 80 degrees or 120 degrees. The origin of the tetrahedral twist is therefore not steric but electronic. The Si-Pt-Si angle is consistently less than 90 degrees, but the Si-Si distance is still too long to support an incipient reductive elimination reaction with its attendant Si-Si bonding interaction. Instead, it appears that four tertiary ligands introduce a steric strain which can be decreased by a twist of two of the ligands out of the plane; this twist is only possible when two
Gálisová, Lucia; Jakubczyk, Dorota
2017-01-01
Ground-state and magnetocaloric properties of a double-tetrahedral chain, in which nodal lattice sites occupied by the localized Ising spins regularly alternate with triangular clusters half filled with mobile electrons, are exactly investigated by using the transfer-matrix method in combination with the construction of the Nth tensor power of the discrete Fourier transformation. It is shown that the ground state of the model is formed by two non-chiral phases with the zero residual entropy and two chiral phases with the finite residual entropy S = NkB ln 2. Depending on the character of the exchange interaction between the localized Ising spins and mobile electrons, one or three magnetization plateaus can be observed in the magnetization process. Their heights basically depend on the values of Landé g-factors of the Ising spins and mobile electrons. It is also evidenced that the system exhibits both the conventional and inverse magnetocaloric effect depending on values of the applied magnetic field and temperature.
Schmittel, Michael; He, Bice; Fan, Jian; Bats, Jan W; Engeser, Marianne; Schlosser, Marc; Deiseroth, Hans-Jörg
2009-09-07
The tetrahedral [Cu(phenAr(2))(py)(2)](+) coordination motif (phen = 1,10-phenanthroline; py = pyridine) conceived on the basis of the HETPYP concept (heteroleptic pyridyl and phenanthroline metal complexes) is a versatile dynamic unit for constructing various heteroleptic metallosupramolecular pseudo-1D, 2D, and 3D structures, both in solution and the solid state. The 2,9-diaryl substituted phenanthroline (phenAr(2)) serves as a capping ligand for copper(I) ions, as its bulky nature prevents formation of the homoleptic complex [Cu(phenAr(2))(2)](+). Combination of the dynamic and concave metal ligand building block [Cu(phenAr(2))](+) with various pyridine (py) ligands, such as bi-, tri-, and tetra-pyridines, opened the way to infinite 1D helicates, 2D networks, and discrete 3D hexanuclear cages, whereas spatial integration of both phenAr(2) and py units into a single ligand resulted in the formation of a Borromean-ring-type hexanuclear cage.
Dileep, K.; Loukya, B.; Silwal, P.; Gupta, A.; Datta, R.
2014-10-01
High resolution electron energy loss spectroscopy (HREELS) is utilized to probe the optical band gaps at the nanoscale in epitaxial NiCo2O4 (NCO) thin films with different structural order (cation/charge). The structure of NCO deviates from the ideal inverse spinel (non-magnetic and insulating) for films grown at higher temperatures (>500 °C) towards a mixed cation structure (magnetic with metallic conductivity) at lower deposition temperatures (<450 °C). This significantly modifies the electronic structure as well as the nature of the band gap of the material. Nanoscale regions with unoccupied tetrahedral A site cations are additionally observed in all the samples and direct measurement from such areas reveals considerably lower band gap values as compared to the ideal inverse spinel and mixed cation configurations. Experimental values of band gaps have been found to be in good agreement with the theoretical mBJLDA exchange potential based calculated band gaps for various cation ordering and consideration of A site cation vacancy defects. The origin of rich variation in cation ordering observed in this system is discussed.
Energy Technology Data Exchange (ETDEWEB)
Gong, Kuanping [Brookhaven National Lab. (BNL), Upton, NY (United States); Choi, YongMan [Brookhaven National Lab. (BNL), Upton, NY (United States); Vukmirovic, Miomir B. [Brookhaven National Lab. (BNL), Upton, NY (United States); Liu, Ping [Brookhaven National Lab. (BNL), Upton, NY (United States); Ma, Chao [Brookhaven National Lab. (BNL), Upton, NY (United States); Su, Dong [Brookhaven National Lab. (BNL), Upton, NY (United States); Adzic, Radoslav R. [Brookhaven National Lab. (BNL), Upton, NY (United States)
2012-10-01
The recent availability of tetrahedral palladium (PdTH) nanocrystals with cleaned surfaces allowed us to evaluate their facet-specific electrochemical properties as a new support of platinum monolayer (PtML) catalysts. The Pd–PtML core-shell electrocatalyst was examined by combining structural analyses and Density Functional Theory (DFT) with electrochemical techniques. The surfaces of the PdTH core are composed of (111) facets wherein the Pd atoms are highly coordinated and have low surface energy. Our results revealed that in comparison with sphere Pd (PdSP)-supported PtML or pure Pt, the PdTH-supported PtML features more surface contraction and a downshift of d-band relative to the Fermi level. These geometric- and electronic-effects determine the higher activity of PtML/PdTH/C for the oxygen reduction reaction (ORR) compared to that of PtML/PdSP/C. This shape-property interdependence illuminated new approaches to basic- and applied- research on Pt-based ORR electrocatalysts of significant importance to the widespread use of fuel cells.
Shi, Sirong; Peng, Qiang; Shao, Xiaoru; Xie, Jing; Lin, Shiyu; Zhang, Tao; Li, Qianshun; Li, Xiaolong; Lin, Yunfeng
2016-08-03
Self-assembled tetrahedral DNA nanostructures (TDNs) with precise sizes have been extensively applied in various fields owing to their exceptional mechanical rigidity, structural stability, and modification versatility. In addition, TDNs can be internalized by mammalian cells and remain mainly intact within the cytoplasm by escaping degradation by nucleases. Here, we studied the effects of TDNs on cell migration and the underlying molecular mechanisms. TDNs remarkably enhanced the migration of rat adipose-derived stem cells and down-regulated the long noncoding RNA (lncRNA) XLOC 010623 to activate the mRNA expression of Tiam1 and Rac1. Furthermore, TDNs highly up-regulated the mRNA and protein expression of RHOA, ROCK2, and VCL. These results indicate that TDNs suppressed the transcription of lncRNA XLOC 010623 and activated the TIAM1/RAC1 and RHOA/ROCK2 signaling pathways to promote cell migration. On the basis of these findings, TDNs show a high potential for application in tissue repair and regenerative medicine as a functional three-dimensional DNA nanomaterial.
Structural instability of the CoO{sub 4} tetrahedral chain in SrCoO{sub 3−δ} thin films
Energy Technology Data Exchange (ETDEWEB)
Glamazda, A.; Choi, K.-Y. [Department of Physics, Chung-Ang University, Seoul 156-756 (Korea, Republic of); Lemmens, P. [Institute for Condensed Matter Physics, TU Braunschweig, D-38106 Braunschweig, Germany and Laboratory for Emerging Nanometrology, TU Braunschweig, Braunschweig (Germany); Choi, Woo Seok [Department of Physics, Sungkyunkwan University, Suwon 440-746 (Korea, Republic of); Jeen, Hyoungjeen [Department of Physics, Pusan National University, Busan 609-735 (Korea, Republic of); Meyer, Tricia L.; Lee, Ho Nyung [Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831 (United States)
2015-08-28
Raman scattering experiments together with detailed lattice dynamic calculations are performed to elucidate crystallographic and electronic peculiarities of SrCoO{sub 3−δ} films. We observe that the 85 cm{sup −1} phonon mode involving the rotation of a CoO{sub 4} tetrahedron undergoes a huge hardening by 21 cm{sup −1} with decreasing temperature. In addition, new phonon modes appear at 651.5 and 697.6 cm{sup −1}. The latter modes are attributed to the Jahn-Teller activated modes. Upon cooling from room temperature, all phonons exhibit an exponential-like increase of intensity with a characteristic energy of about 103–107 K. We attribute this phenomenon to an instability of the CoO{sub 4} tetrahedral chain structure, which constitutes a key ingredient to understand the electronic and structural properties of the brownmillerite SrCoO{sub 2.5}.
Institute of Scientific and Technical Information of China (English)
Jianguo Xin; Nailong Guo; Wei Cai
2011-01-01
A partially orthonormal basis is constructed with better conditioning properties for tetrahedral H(curl)-conforming Nédélec elements.The shape functions are classified into several categories with respect to their topological entities on the reference 3-simplex.The basis functions in each category are constructed to achieve maximum orthogonality.The numerical study on the matrix conditioning shows that for the mass and quasi-stiffness matrices,and in a logarithmic scale the condition number grows linearly vs. order of approximation up to order three.For each order of approximation,the condition number of the quasi-stiffness matrix is about one order less than the corresponding one for the mass matrix.Also,up to order six of approximation the conditioning of the mass and quasistiffness matrices with the proposed basis is better than the corresponding one with the Ainsworth-Coyle basis Internat.J.Numer.Methods.Engrg.,58:2103-2130,2003.except for order four with the quasi-stiffness matrix.Moreover,with the new basis the composite matrix μM + S has better conditioning than the Ainsworth-Coyle basis for a wide range of the parameter μ.
Energy Technology Data Exchange (ETDEWEB)
Murata, T.; Kawatani, R. [Nagaoka University of Technology, Nagaoka (Japan)
1998-01-31
This paper proposes one design method of low order controllers using a loop shaping design procedure (LSDP). The order of a controller using the central solution of LSDP becomes the sum of the order of a design model and 2 times the order of a weight transfer function, while that using this method becomes the sum of 1 and the order of a weight transfer function. Since this method uses no approximation in order reduction, the proper shaping performance of LSDP is retained. This method was applied to the stabilizing control problem of a two-wheeled vehicle as typical unstable mechanical system to verify its effectiveness. Measured tilt angles to a floor and truck positions of a two-wheeled vehicle are inputted into a computer, and calculated control inputs are sent to the servo module of a speed control system through a D/A convertor. The DC motor-driven truck of a two- wheeled vehicle thus moves in a direction to stabilize a two- wheeled vehicle. A good agreement was obtained between the simulation and experimental results of this design. 8 refs., 10 figs.
Energy Technology Data Exchange (ETDEWEB)
Carlisle, John A. (Argonne National Laboratory, Argonne, IL); Moldovan, N. (Northwestern University, Evanston, IL); Xiao, Xingcheng (Argonne National Laboratory, Argonne, IL); Zorman, C. A. (Case Western Reserve University, Cleveland, OH); Mancini, D. C. (Argonne National Laboratory, Argonne, IL); Peng, B. (Northwestern University, Evanston, IL); Espinosa, H. D. (Northwestern University, Evanston, IL); Friedmann, Thomas Aquinas; Auciello, Orlando, (Argonne National Laboratory, Argonne, IL)
2004-06-01
Many MEMS devices are based on polysilicon because of the current availability of surface micromachining technology. However, polysilicon is not the best choice for devices where extensive sliding and/or thermal fields are applied due to its chemical, mechanical and tribological properties. In this work, we investigated the mechanical properties of three new materials for MEMS/NEMS devices: silicon carbide (SiC) from Case Western Reserve University (CWRU), ultrananocrystalline diamond (UNCD) from Argonne National Laboratory (ANL), and hydrogen-free tetrahedral amorphous carbon (ta-C) from Sandia National Laboratories (SNL). Young's modulus, characteristic strength, fracture toughness, and theoretical strength were measured for these three materials using only one testing methodology - the Membrane Deflection Experiment (MDE) developed at Northwestern University. The measured values of Young's modulus were 430GPa, 960GPa, and 800GPa for SiC, UNCD, and ta-C, repectively. Fracture toughness measurments resulted in values of 3.2, 4.5, and 6.2 MPa x m{sup 1/2}, respectively. The strengths were found to follow a Weibull distribution but their scaling was found to be controlled by different specimen size parameters. Therefore, a cross comparison of the strengths is not fully meaningful. We instead propose to compare their theoretical strengths as determined by employing Novozhilov fracture criterion. The estimated theoretical strength for SiC is 10.6GPa at a characteristic length of 58nm, for UNCD is 18.6GPa at a characteristic length of 37nm, and for ta-C is 25.4GPa at a characteristic length of 38nm. The techniques used to obtained these results as well as microscopic fractographic analyses are summarized in the article. We also highlight the importance of characterizing mechanical properties of MEMS materials by means of only one simple and accurate experimental technique.
Enamullah, Mohammed; Makhloufi, Gamall; Ahmed, Rifat; Joy, Baitul Alif; Islam, Mohammad Ariful; Padula, Daniele; Hunter, Howard; Pescitelli, Gennaro; Janiak, Christoph
2016-07-01
Bidentate enantiopure Schiff base ligands, (R or S)-N-1-(Ar)ethyl-2-oxo-1-naphthaldiminate (R- or S-N^O), diastereoselectively provide Λ- or Δ-chiral-at-metal four-coordinated Zn(R- or S-N^O)2 {Ar = C6H5; Zn-1R or Zn-1S and p-C6H4OMe; Zn-2R or Zn-2S}. Two R- or S-N^O-chelate ligands coordinate to the zinc(II) in a tetrahedral mode and induce Λ- or Δ-configuration at the zinc metal center. In the solid state, the R- or S-ligand diastereoselectively gives Λ- or Δ-Zn configuration, respectively, and forms enantiopure crystals. Single crystal structure determinations show two symmetry-independent molecules (A and B) in each asymmetric unit to give Z' = 2 structures. Electronic circular dichroism (ECD) spectra show the expected mirror image relationship resulting from diastereomeric excess toward the Λ-Zn for R-ligands and Δ-Zn for S-ligands in solution. ECD spectra are well reproduced by TDDFT calculations, while the application of the exciton chirality method, in the common point-dipole approximation, predicts the wrong sign for the long-wavelength couplet. A dynamic diastereomeric equilibrium (Λ vs Δ) prevails for both R- and S-ligand-metal complexes in solution, respectively, evidenced by (1)H NMR spectroscopy. Variable temperature (1)H NMR spectra show a temperature-dependent shift of the diastereomeric equilibrium and confirm Δ-Zn configuration (for S-ligand) to be the most stable one and favored at low temperature. DSC analyses provide quantitative diastereomeric excess in the solid state for Zn-2R and Zn-2S, which is comparable to the results of solution studies.
Optimal Reconfiguration of Tetrahedral Formations
Huntington, Geoffrey; Rao, Anil V.; Hughes, Steven P.
2004-01-01
The problem of minimum-fuel formation reconfiguration for the Magnetospheric Multi-Scale (MMS) mission is studied. This reconfiguration trajectory optimization problem can be posed as a nonlinear optimal control problem. In this research, this optimal control problem is solved using a spectral collocation method called the Gauss pseudospectral method. The objective of this research is to provide highly accurate minimum-fuel solutions to the MMS formation reconfiguration problem and to gain insight into the underlying structure of fuel-optimal trajectories.
Directory of Open Access Journals (Sweden)
Jennifer A. Cleary
2016-03-01
Full Text Available New trypsin inhibitors Z-Lys-COCHO and Z-Lys-H have been synthesised. Ki values for Z-Lys-COCHO, Z-Lys-COOH, Z-Lys-H and Z-Arg-COOH have been determined. The glyoxal group (–COCHO of Z-Lys-COCHO increases binding ~300 fold compared to Z-Lys-H. The α-carboxylate of Z-Lys-COOH has no significant effect on inhibitor binding. Z-Arg-COOH is shown to bind ~2 times more tightly than Z-Lys-COOH. Both Z-Lys-13COCHO and Z-Lys-CO13CHO have been synthesized. Using Z-Lys-13COCHO we have observed a signal at 107.4 ppm by 13C NMR which is assigned to a terahedral adduct formed between the hydroxyl group of the catalytic serine residue and the 13C-enriched keto-carbon of the inhibitor glyoxal group. Z-Lys-CO13CHO has been used to show that in this tetrahedral adduct the glyoxal aldehyde carbon is not hydrated and has a chemical shift of 205.3 ppm. Hemiketal stabilization is similar for trypsin, chymotrypsin and subtilisin Carlsberg. For trypsin hemiketal formation is optimal at pH 7.2 but decreases at pHs 5.0 and 10.3. The effective molarity of the active site serine hydroxyl group of trypsin is shown to be 25300 M. At pH 10.3 the free glyoxal inhibitor rapidly (t1/2=0.15 h forms a Schiff base while at pH 7 Schiff base formation is much slower (t1/2=23 h. Subsequently a free enol species is formed which breaks down to form an alcohol product. These reactions are prevented in the presence of trypsin and when the inhibitor is bound to trypsin it undergoes an internal Cannizzaro reaction via a C2 to C1 alkyl shift producing an α-hydroxycarboxylic acid.
Ibrahim, Masooma; Mal, Sib Sankar; Bassil, Bassem S; Banerjee, Abhishek; Kortz, Ulrich
2011-02-01
The yttrium(III)-containing tungstoantimonate(III) [{Y(α-SbW(9)O(31)(OH)(2))(CH(3)COO)(H(2)O)}(3)(WO(4))](17-) (1) has been synthesized in a simple one-pot reaction of Y(3+) ions with [α-SbW(9)O(33)](9-) and WO(4)(2-) in a 3:3:1 molar ratio in 1 M LiOAc/AcOH buffer at pH 5.3. Polyanion 1 is composed of three (α-SbW(9)O(33)) units linked by three Y(3+) ions and a capping, tetrahedral WO(4)(2-) capping unit, resulting in an assembly with C(3v) symmetry. The hydrated ammonium-sodium salt of 1 was investigated in the solid state by single-crystal XRD, FT-IR spectroscopy, thermogravimetric and elemental analyses, and in solution by multinuclear NMR spectroscopy.
Zwijnenburg, Martijn A; Corà, Furio; Bell, Robert G
2008-08-20
We employ periodic density functional theory calculations to compare the structural chemistry of silicon chalcogenides (silica, silicon sulfide) and anhydrous tetrahedral halides (beryllium fluoride, beryllium chloride). Despite the different formal oxidation states of the elements involved, the divalent halides are known experimentally to form crystal structures similar to known SiX2 frameworks; the rich polymorphic chemistry of SiO2 is however not matched by divalent halides, for which a very limited number of polymorphs are currently known. The calculated energy landscapes yield a quantitative match between the relative polymorphic stability in the SiO2/BeF2 pair, and a semiquantitative match for the SiS2/BeCl2 pair. The experimentally observed polymorphs are found to lie lowest in energy for each composition studied. For the two BeX2 compounds studied, polymorphs not yet synthesized are predicted to lie very low in energy, either slightly above or even in between the energy of the experimentally observed polymorphs. The experimental lack of polymorphism for tetrahedral halide materials thus does not appear to stem from a lack of low-energy polymorphs but more likely is the result of a lack of experimental exploration. Our calculations further indicate that the rich polymorphic chemistry of SiO2 can be potentially matched, if not extended, by BeF2, provided that milder synthetic conditions similar to those employed in zeolite synthesis are developed for BeF2. Finally, our work demonstrates that both classes of materials show the same behavior upon replacement of the 2p anion with the heavier 3p anion from the same group; the thermodynamic preference shifts from structures with large rings to structures with larger fractions of small two and three membered rings.
Time scale interaction in low-order climate models
Veen, Lennaert van
2002-01-01
Over the last decades, the study of climate variability has attracted ample attention. The observation of structural climatic change has led to questions about the causes and the mechanisms involved. The task to understand interactions in the complex climate system is particularly di±cult because of
Low-order models of biogenic ocean mixing
Dabiri, J. O.; Rosinelli, D.; Koumoutsakos, P.
2009-12-01
Biogenic ocean mixing, the process whereby swimming animals may affect ocean circulation, has primarily been studied using order-of-magnitude theoretical estimates and a small number of field observations. We describe numerical simulations of arrays of simplified animal shapes migrating in inviscid fluid and at finite Reynolds numbers. The effect of density stratification is modeled in the fluid dynamic equations of motion by a buoyancy acceleration term, which arises due to perturbations to the density field by the migrating bodies. The effects of fluid viscosity, body spacing, and array configuration are investigated to identify scenarios in which a meaningful contribution to ocean mixing by swimming animals is plausible.
A low order adaptive control scheme for hydraulic servo systems
DEFF Research Database (Denmark)
Andersen, Torben Ole; Pedersen, Henrik Clemmensen; Bech, Michael Møller;
2015-01-01
This paper deals with high-performance position control of hydraulics servo systems in general. The hydraulic servo system used is a two link robotic manipulator actuated by two hydraulic servo cylinders. A non-linear model of the hydraulic system and a Newton-Euler based model of the mechanical...... system were constructed and linearized. Controllers are implemented and tested on the manipulator. Pressure feedback was found to greatly improve system stability margins. Passive gain feedforward shows improved tracking performance for small changes in load pressure. For large changes in load pressure......, active gain feedforward shows a slightly improved performance. Computed-Torque Control shows better performance, but requires a well described system for best performance. A novel Adaptive Inverse Dynamics Controller was tested and the performance was found to be similar to that of Computed...
Low Order Empirical Galerkin Models for Feedback Flow Control
Tadmor, Gilead; Noack, Bernd
2005-11-01
Model-based feedback control restrictions on model order and complexity stem from several generic considerations: real time computation, the ability to either measure or reliably estimate the state in real time and avoiding sensitivity to noise, uncertainty and numerical ill-conditioning are high on that list. Empirical POD Galerkin models are attractive in the sense that they are simple and (optimally) efficient, but are notoriously fragile, and commonly fail to capture transients and control effects. In this talk we review recent efforts to enhance empirical Galerkin models and make them suitable for feedback design. Enablers include `subgrid' estimation of turbulence and pressure representations, tunable models using modes from multiple operating points, and actuation models. An invariant manifold defines the model's dynamic envelope. It must be respected and can be exploited in observer and control design. These ideas are benchmarked in the cylinder wake system and validated by a systematic DNS investigation of a 3-dimensional Galerkin model of the controlled wake.
Joint importance sampling of low-order volumetric scattering
DEFF Research Database (Denmark)
Georgiev, Iliyan; Křivánek, Jaroslav; Hachisuka, Toshiya
2013-01-01
Central to all Monte Carlo-based rendering algorithms is the construction of light transport paths from the light sources to the eye. Existing rendering approaches sample path vertices incrementally when constructing these light transport paths. The resulting probability density is thus a product...... of the conditional densities of each local sampling step, constructed without explicit control over the form of the final joint distribution of the complete path. We analyze why current incremental construction schemes often lead to high variance in the presence of participating media, and reveal...... that such approaches are an unnecessary legacy inherited from traditional surface-based rendering algorithms. We devise joint importance sampling of path vertices in participating media to construct paths that explicitly account for the product of all scattering and geometry terms along a sequence of vertices instead...
Low-order invariant solutions in plane Couette flow
Ahmed, Muhammad; Sharma, Ati
2016-11-01
Ten new equilibrium solutions of the Navier-Stokes equations in plane Couette flow are presented. The new solutions add to the inventory of known equilibria in plane Couette flow found by Nagata JFM 1990, Gibson JFM 2008, 2009, and Halcrow JFM 2008, who together found 13. These new solutions elucidate the low-dimensional nature of exact coherent structures, which are essential to defining simplified mechanisms that explain the self-sustaining nature of wall-bounded flows. In particular, one of the solutions found has a one-dimensional unstable manifold in the symmetry-invariant subspace and otherwise, like the lower branch equilibrium solution found by Nagata JFM 1990. A new method for generating initial guesses for Newton-Krylov-hookstep (NKH) searches is also presented. This method allows the NKH algorithm to find equilibrium solutions that are derived from previous solutions. Air Force Office of Scientific Research (European Office of Aerospace Research and Development) under award FA9550-14-1-0042.
Wachhold, Michael; Kasthuri Rangan, K.; Lei, Ming; Thorpe, M. F.; Billinge, Simon J. L.; Petkov, Valeri; Heising, Joy; Kanatzidis, Mercouri G.
2000-06-01
The polymerization of [Ge4S10]4- and [Ge4Se10]4- unit clusters with the divalent metal ions Zn2+, Cd2+, Hg2+, Ni2+, and Co2+ in the presence of various surfactant cations leads to novel mesostructured phases. The surfactants are the quaternary ammonium salts C12H25NMe3Br, C14H29NMe3Br, C16H33NMe3Br, and C18H37NMe3Br, which play the role of templates, helping to assemble a three-dimensional mesostructured metal-germanium chalcogenide framework. These materials are stoichiometric in nature and have the formula of (R-NMe3)2[MGe4Q10] (Q=S, Se). The local atomic structure was probed by X-ray diffuse scattering and pair distribution function analysis methods and indicates that the adamantane clusters stay intact while the linking metal atoms possess a tetrahedral coordination environment. A model can be derived, from the comparison of measured and simulated X-ray powder diffraction patterns, describing the structure as an amorphous three-dimensional framework consisting of adamantane [Ge4Q10]4- units that are bridged by tetrahedral coordinated M2+ cations. The network structures used in the simulations were derived from corresponding disordered structures developed for amorphous silicon. The frameworks in (R-NMe3)2[MGe4Q10] are perforated with worm hole-like tunnels, occupied by the surfactant cations, which show no long-range order. This motif is supported by transmission electron microscopy images of these materials. The pore sizes of these channels were estimated to lie in the range of 20-30 Å, depending on the appointed surfactant cation length. The framework wall thickness of ca. 10 Å is thereby independent from the surfactant molecules used. Up to 80% of the surfactant molecules can be removed by thermal degradation under vacuum without loss of mesostructural integrity. Physical, chemical, and spectroscopic properties of these materials are discussed.
Boldog, Ishtvan; Domasevitch, Konstantin V; Sanchiz, Joaquín; Mayer, Peter; Janiak, Christoph
2014-09-07
1,3,5,7-Tetrakis(tetrazol-5-yl)-adamantane (H4L) was probed as a building block for the synthesis of tetrazolato/halido coordination polymers with open-network structures. MCl2 (M = Cu, Cd, Zn, Mn) was reacted with H4L in DMF at 70 °C to yield [Cu4Cl4L(DMF)5]·DMF, ; [Cd4Cl4L(DMF)7]·DMF, ; [Zn3Cl2L(DMF)4]·2DMF, and [Mn2L(DMF)2(MeOH)4]·DMF·2MeOH·2H2O, . and (Fddd) are nearly isostructural and have zeolitic structures with a {4(3)·6(2)·8}, gis or gismondine underlying net, where the role of the tetrahedral nodes is served by the coordination bonded clusters and the adamantane moiety. (P21/n) has a porous structure composed of coordination bonded layers with a (4·8(2)) fes topology joined via trans-{Zn(tetrazolate)2(DMF)4} pillars with an overall topology of {4·6(2)}{4·6(6)·8(3)}, fsc-3,5-Cmce-2. (Pca21) is composed of stacked {Mn2L} hexagonal networks. In and the ligand fulfills a symmetric role of a tetrahedral building block, while in and it fulfills rather a role of an effective trigonal unit. Methanol-exchanged and activated displayed an unusual type IV isotherm with H2 type hysteresis for N2 sorption with an expected uptake at high P/P0, but with a smaller SBET = 505.5 m(2) g(-1) compared to the calculated 1789 m(2) g(-1), which is a possible result of the framework's flexibility. For H2 sorption 0.79 wt% (1 bar, 77 K) and 0.06 wt% (1 bar, RT) uptake and Qst = -7.2 kJ mol(-1) heat of adsorption (77 K) were recorded. Weak antiferromagnetic interactions were found in and with J1 = -9.60(1), J2 = -17.2(2), J3 = -2.28(10) cm(-1) and J = -0.76 cm(-1) respectively. The formation of zeolitic structures in and , the concept of structural 'imprinting' of rigid building blocks, and design opportunities suggested as a potential hexafunctionalized biadamantane building block.
Energy Technology Data Exchange (ETDEWEB)
Bouhemadou, A., E-mail: a_bouhemadou@yahoo.fr [Laboratory for Developing New Materials and their Characterization, University of Setif 1, Setif 19000 (Algeria); Bin-Omran, S. [Department of Physics and Astronomy, College of Science, King Saud University, P.O. Box 2455, Riyadh 11451 (Saudi Arabia); Department of Physics, Faculty of Science & Humanitarian Studies, Salman Bin Abdalaziz University, Alkharj 11942 (Saudi Arabia); Allali, D. [Laboratory for Developing New Materials and their Characterization, University of Setif 1, Setif 19000 (Algeria); Al-Otaibi, S.M. [Department of Physics and Astronomy, College of Science, King Saud University, P.O. Box 2455, Riyadh 11451 (Saudi Arabia); Khenata, R. [Laboratoire de Physique Quantique et de Modélisation Mathématique (LPQ3M), Département de Technologie, Université de Mascara, Mascara 29000 (Algeria); Al-Douri, Y. [Institute of Nano Electronic Engineering, Universiti Malaysia Perlis, Kangar, Perlis 01000 (Malaysia); Chegaar, M. [Department of Physics, Faculty of Science, University of Setif 1, Setif 19000 (Algeria); Reshak, A.H. [New Technologies-Research Center, University of West Bohemia, Univerzitni 8, Pilson 306 14 (Czech Republic); Center of Excellence Geopolymer and Green Technology, School of Material Engineering, University Malaysia Perlis, Kangar, Perlis 01007 (Malaysia)
2015-04-15
Highlights: • Electronic and optical properties of the LiCdX compounds have been predicted. • Tran–Blaha-modified Becke–Johnson functional significantly improves the band gap. • We predict a direct band gap in all of the considered LiCdX compounds. • Origin of the peaks in the optical spectra is determined. - Abstract: The structural, electronic and optical properties of the LiCdN, LiCdP, LiCdAs and LiCdSb filled-tetrahedral compounds have been explored from first-principles. The calculated structural parameters are consistent with the available experimental results. Since DFT with the common LDA and GGA underestimates the band gap, we use a new developed functional able to accurately describe the electronic structure of semiconductors, namely the Tran–Blaha-modified Becke–Johnson potential. The four investigated compounds demonstrate semiconducting behavior with direct band gap ranging from about 0.32 to 1.65 eV. The charge-carrier effective masses are evaluated at the topmost valence band and at the bottommost conduction band. The evolution of the value and nature of the energy band gap under pressure effect is also investigated. The frequency-dependent complex dielectric function and some macroscopic optical constants are estimated. The microscopic origins of the structures in the optical spectra are determined in terms of the calculated energy band structures.
Kempgens, Pierre; Rosé, Jacky
2011-03-01
Two-dimensional ⁵⁹Co correlation spectroscopy (COSY) and double-quantum-filtered (DQF) COSY NMR experiments are reported for the tetrahedral mixed-metal cluster HFeCo₃(CO)₁₀(PCyH₂)(PPh₂[CH₂C(O)Ph]), which consists from the point of view of ⁵⁹Co NMR spectroscopy, of an AMX system of three-spin S=7/2. Both 2D NMR spectra prove the existence of a J scalar coupling constant between non-equivalent ⁵⁹Co nuclei. By contrast to what happens with the conventional 2D ⁵⁹Co COSY NMR spectrum, it was possible to simulate the 2D ⁵⁹Co DQF-COSY NMR spectrum by density matrix calculations in order to extract the values of the ¹J(⁵⁹Co-⁵⁹Co) coupling constants. The comparison between experimental and theoretical 2D NMR spectra gives spin-couplings constants of several hundreds Hertz for this cluster. Copyright © 2010 Elsevier Inc. All rights reserved.
Sarkar, Mrinal; Clérac, Rodolphe; Mathonière, Corine; Hearns, Nigel G R; Bertolasi, Valerio; Ray, Debashis
2011-05-02
[Cu(2)(μ(4)-O)Cu(2)] and [Cu(2)(μ(1,1)-N(3))(4)Cu(2)] geometrical arrangements are found in a new family of tetranuclear copper(II) complexes: [Cu(4)(μ(4)-O)(μ-cip)(2)Cl(4)] (1), [Cu(4)(μ(4)-O)(μ-cip)(2)(μ(1,3)-O(2)CPh)(4)]·2CH(3)OH (2·2CH(3)OH), and [Cu(4)(μ(1,1)-N(3))(4)(μ-cip)(2)(N(3))(2)]·DMF (3·DMF) [Hcip = 2,6-bis(cyclohexyliminomethylene)-4-methylphenol; CH(3)OH = methanol; DMF = dimethylformamide]. These complexes have been characterized by X-ray crystallography, and their magnetic properties have been studied. 1 and 2 form quasi-tetrahedral [Cu(4)(μ(4)-O)] complexes, and 3 is the first example of a rhomboidal [Cu(4)(μ(1,1)-N(3))] compound. Formation of the [Cu(4)] compounds is achieved via ligand-exchange reactions. The relative binding strength of the three ancillary ligands as N(3)(-) > PhCO(2)(-) > Cl(-) has been demonstrated from the core-conversion and peripheral ligand-exchange reactions. For the three complexes, the magnetic susceptibility measurements in the range of 1.8-300 K have been performed and modeled using two isolated S = (1)/(2) dimers based on the spin Hamiltonian H = -2J{S(Cu,1)·S(Cu,2)} with J/k(B) = -513, -340, and -315 K for 1-3, respectively (where J is the exchange constant through the oxido-phenoxido and azido-phenoxido bridges, respectively). © 2011 American Chemical Society
Hermann, Johannes C.; Pradon, Juliette; Harvey, Jeremy N.; Mulholland, Adrian J.
2009-09-01
The breakdown of β-lactam antibiotics by β-lactamases is the most important resistance mechanism of Gram negative bacteria against these drugs. The reaction mechanism of class A β-lactamases, the most widespread family of these enzymes, consists of two main steps: acylation of an active site serine by the antibiotic, followed by deacylation and release of the cleaved compound. We have investigated the first step in acylation (the formation of the tetrahedral intermediate) for the reaction of benzylpenicillin in the TEM-1 enzyme using high level combined quantum mechanics/molecular mechanics (QM/MM) methods. Structures were optimized at the B3LYP/6-31+G(d)/CHARMM27 level, with energies for key points calculated up to the ab initio SCS-MP2/aug-cc-pVTZ/CHARMM27 level. The results support a mechanism in which Glu166 removes a proton (via an intervening water molecule) from Ser70, which in turn attacks the β-lactam of the antibiotic. Depending on the method used, the calculated barriers range from 3 to 12 kcal mol-1 for this step, consistent with experimental data. We have also modeled this reaction step in a model of the K73A mutant enzyme. The barrier to reaction in this mutant model is found to be slightly higher: the results indicate that Lys73 stabilizes the transition state, in particular deprotonated Ser70, lowering the barrier by about 1.7 kcal mol-1. This finding may help to explain the conservation of Lys73, in addition to the role we have previously found for it in the later stages of the reaction ( Hermann et al. Org. Biomol. Chem. 2006, 4, 206 - 210 ).
Planet map generation by tetrahedral subdivision
DEFF Research Database (Denmark)
Mogensen, Torben Ægidius
2010-01-01
We present a method for generating pseudo-random, zoomable planet maps for games and art. The method is based on spatial subdivision using tetrahedrons. This ensures planet maps without discontinuities caused by mapping a flat map onto a sphere. We compare the method to other map...
Theoretical Studies of Defects in Tetrahedral Semiconductors.
1980-08-01
within 5(E)=-tan-lf ImD(E) ReDE )l . 18) the band continua, we write Eq. (8) in the form It follows that ,5rE) goes through an odd multiple 1- 6 1(E...an atom from "h. The use of the FHT resulted in a very accurate determination of the Green’s-function matrix ele- _____- ments on an energy mesh ...spaced by 0.07 eV. This ,, mesh was found dense enough to allow interpolation , I ’or intermediate energy values when needed. The 2:- / Green’s-function
Adaptive refinement tools for tetrahedral unstructured grids
Pao, S. Paul (Inventor); Abdol-Hamid, Khaled S. (Inventor)
2011-01-01
An exemplary embodiment providing one or more improvements includes software which is robust, efficient, and has a very fast run time for user directed grid enrichment and flow solution adaptive grid refinement. All user selectable options (e.g., the choice of functions, the choice of thresholds, etc.), other than a pre-marked cell list, can be entered on the command line. The ease of application is an asset for flow physics research and preliminary design CFD analysis where fast grid modification is often needed to deal with unanticipated development of flow details.
ENHANCING ADHESION OF TETRAHEDRAL AMORPHOUS CARBON FILMS
Institute of Scientific and Technical Information of China (English)
赵玉清; 林毅; 王晓艳; 王炎武; 魏新宇
2005-01-01
TheperformanceoftheTACfilmsdeposited bytheFCVAisbetterthanthatofthediamond like carbonfilms[1,2],becausetheformerisofhigher hardnessandtransparency,smallerfriction coefficientandabsorbingtheultravioletraymore easily,etc.[3].Thesecharacteristicsaresimilarto thoseofthenaturaldiamond.Therefore,theTAC filmdepositedonawindowmaterialcanraisethe operatinglifegreatly.TheTACfilmisanideal protectivematerialforvariouskindsofwatch glassesandcameralenses. Metalandpotteryareoftenusedasthe substratesfordepositingtheTACfil...
Planet Map Generation by Tetrahedral Subdivision
DEFF Research Database (Denmark)
Mogensen, Torben Ægidius
2010-01-01
We present a method for generating pseudo-random, zoomable planet maps for games and art. The method is based on spatial subdivision using tetrahedrons. This ensures planet maps without discontinuities caused by mapping a flat map onto a sphere. We compare the method to other map...
A comparison of tetrahedral mesh improvement techniques
Energy Technology Data Exchange (ETDEWEB)
Freitag, L.A.; Ollivier-Gooch, C. [Argonne National Lab., IL (United States). Mathematics and Computer Science Div.
1996-12-01
Automatic mesh generation and adaptive refinement methods for complex three-dimensional domains have proven to be very successful tools for the efficient solution of complex applications problems. These methods can, however, produce poorly shaped elements that cause the numerical solution to be less accurate and more difficult to compute. Fortunately, the shape of the elements can be improved through several mechanisms, including face-swapping techniques that change local connectivity and optimization-based mesh smoothing methods that adjust grid point location. The authors consider several criteria for each of these two methods and compare the quality of several meshes obtained by using different combinations of swapping and smoothing. Computational experiments show that swapping is critical to the improvement of general mesh quality and that optimization-based smoothing is highly effective in eliminating very small and very large angles. The highest quality meshes are obtained by using a combination of swapping and smoothing techniques.
Inherent properties of binary tetrahedral semiconductors
Verma, A. S.; Sarkar, B. K.; Jindal, V. K.
2010-04-01
A new approach utilising the concept of ionic charge theory has been used to explain the inherent properties such as lattice thermal conductivity and bulk modulus of A IIIB V and A IIB VI semiconductors. The lattice thermal conductivity ( K) of these semiconductors exhibit a linear relationship when plotted on a log-log scale against the nearest neighbour distance d (Å), but fall on two straight lines according to the product of the ionic charge of the compounds. On the basis of this result a simple lattice thermal conductivity-bulk modulus relationship is proposed and used to estimate the bulk modulus of these semiconductors. A fairly good agreement has been found between the experimental and calculated values of these parameters for zinc blende structured solids.
Energy Technology Data Exchange (ETDEWEB)
Mobarak, H.M., E-mail: mobarak.ho31@yahoo.com; Masjuki, H.H.; Mohamad, E. Niza, E-mail: edzrol@um.edu.my; Kalam, M.A.; Rashedul, H.K.; Rashed, M.M.; Habibullah, M.
2014-10-30
Highlights: • We tested a-C:H and ta-C DLC coatings as a function of temperature. • Jatropha oil contains large amounts of polar components that enhanced the lubricity of coatings. • CoF decreases with increasing temperature for both contacts. • Wear rate increases with increasing temperature in a-C:H and decreases in ta-C DLC. • At high temperature, ta-C coatings confer more protection than a-C:H coatings. - Abstract: The application of diamond-like carbon (DLC) coatings on automotive components is emerging as a favorable strategy to address the recent challenges in the industry. DLC coatings can effectively lower the coefficient of friction (CoF) and wear rate of engine components, thereby improving their fuel efficiency and durability. The lubrication of ferrous materials can be enhanced by a large amount of unsaturated and polar components of oils. Therefore, the interaction between nonferrous coatings (e.g., DLC) and vegetable oil should be investigated. A ball-on-plate tribotester was used to run the experiments. Stainless steel plates coated with amorphous hydrogenated (a-C:H) DLC and hydrogen-free tetrahedral (ta-C) DLC that slide against 440C stainless steel ball were used to create a ball-on-plate tribotester. The wear track was investigated through scanning electron microscopy. Energy dispersive and X-ray photoelectron spectroscopies were used to analyze the tribofilm inside the wear track. Raman analysis was performed to investigate the structural changes in the coatings. At high temperatures, the CoF in both coatings decreased. The wear rate, however, increased in the a-C:H but decreased in the ta-C DLC-coated plates. The CoF and the wear rate (coated layer and counter surface) were primarily influenced by the graphitization of the coating. Tribochemical films, such as polyphosphate glass, were formed in ta-C and acted as protective layers. Therefore, the wear rate of the ta-C DLC was lower than that of the-C:H DLC.
Beckett, John R.
2002-01-01
Activity coefficients of oxide components in the system CaO-MgO-Al 2O 3-SiO 2 (CMAS) were calculated with the model of Berman (Berman R. G., "A thermodynamic model for multicomponent melts with application to the system CaO-MgO-Al 2O 3-SiO 2," Ph.D. dissertation, University of British Columbia, 1983) and used to explore large-scale relationships among these variables and between them and the liquid composition. On the basis of Berman's model, the natural logarithm of the activity coefficient of MgO, ln(γ MgOLiq), and ln(γ MgOLiq/γ SiO 2Liq) are nearly linear functions of ln(γ CaOLiq). All three of these variables are simple functions of the optical basicity Λ with which they display minima near Λ ˜ 0.54 that are generated by liquids with low ratios of nonbridging to tetrahedral oxygens (NBO/T) (factor in determining the thermodynamic properties of aluminosilicate liquids. For a constant NBO/T, ln(γ CaOLiq/γ Al 2O 3Liq) and ln(γ MgOLiqγ Al 2O 3Liq) form curves in terms of X SiO 2Liq/X Al 2O 3Liq. The same liquids that generate minima in the Λ plots are also associated with minima in ln(γ CaOLiqγ Al 2O 3Liq) and ln(γ MgOLiqγ Al 2O 3Liq) as a function of X SiO 2Liq/X Al 2O 3Liq. In addition, there are maxima or sharp changes in slope for NBO/T > 0.3, which occur for X SiO 2Liq/X Al 2O 3Liq ranging from ˜0 to ˜6 and increase with increasing NBO/T. The systematic variations in activity coefficients as a function of composition and optical basicity reflect underlying shifts in speciation as the composition of the liquid is changed. On the basis of correlations among the activity coefficients, it is likely that the use of CaO, an exchange component such as SiMg -1 and two of MgO, CaAl 2O 4, or MgAl 2O 4 would yield significant savings in the number of parameters required to model the excess free energy surface of liquids over large portions of CMAS relative to the use of oxide end members. Systematic behavior of thermodynamic properties extends to small
Institute of Scientific and Technical Information of China (English)
李晓伟; 周毅; 孙丽丽; 汪爱英
2012-01-01
Tetrahedral amorphous carbon (ta-C) films under different substrate negative bias are prepared by a home developed filtered cathodic vacuum arc (FCVA) technology with double bend shape. The film thickness is measured by a combined spectrophotometry and spectroscopic ellipsometry (SE) approach; the chemical bonds including sp2C and sp3C are gained by the fitted ellipsometry method. Furthermore,the accuracy of ellipsometry results is evaluated by comparing with those of X-ray photoelectron spectroscopy (XPS) and Raman spectra. The results indicate that the minimum thickness of ta-C film of 33. 9 nm is obtained when the bias voltage is -100 V; with the increase of bias voltage,the optical gaps and the content of sp3C atomic bond decrease,while the sp2C content increases correspondingly. By comparison with the results of XPS and Raman spectra,it is found that when the optical constants of sp2C model are represented by the glassy carbon and the fitting wavelength ranges are chosen from 250 to 1700 nm,the best fitting result of atomic bonds of ta-C films can be deduced by the ellipsometry method. Therefore,it could be said that the elliposometry method is a quite promising method to characterize the atomic bonds of ta-C films including sp2C and sp3C,as a new nondestructive,fast,quantitative and easy way.%采用自主研制的双弯曲磁过滤阴极真空电弧(FCVA)技术,在不同衬底负偏压下制备了四面体非晶碳(ta-C)薄膜.通过分光光度计和椭偏(SE)联用技术精确测量了薄膜厚度,重点采用椭偏法对不同偏压下制备的ta-C薄膜sp3C键和sp2C键结构进行了拟合表征,并与X射线光电子能谱(XPS)和拉曼光谱的实验结果相对比,分析了非晶碳结构的椭偏拟合新方法可靠性.结果表明,在-100 V偏压时薄膜厚度最小,为33.9 nm;随着偏压的增加,薄膜中的sp2C含量增加,sp3C含量减小,光学带隙下降.对比结果发现,椭偏法作为一种无损、简易、快速的表征
Seth, Michael; Ziegler, Tom
2005-10-08
A method for calculating the UV-vis spectra of molecules with spatially degenerate ground states using time-dependent density-functional theory (TDDFT) is proposed. The new transformed reference via an intermediate configuration Kohn-Sham TDDFT (TRICKS-TDDFT) method avoids the difficulties caused by the multireference nature of spatially degenerate states by rather than utilizing the ground state instead taking a nondegenerate excited state with desirable properties as the reference for the TDDFT calculation. The scope and practical application of the method are discussed. Like all open-shell TDDFT calculations this method at times suffers from the inability to produce transitions to states that are eigenfunctions of the total spin operator. A technique for alleviating this difficulty to some extent is proposed. The applicability and accuracy of the TRICKS-TDDFT method is demonstrated through example calculations of several d(1) and d(2) transition metal complexes with tetrahedral and octahedral symmetries. For the most part, the results of these calculations are similar in quality to to those obtained from standard TDDFT calculations.
Institute of Scientific and Technical Information of China (English)
梁士金; Tatsuya Banno; Yutaka Mera; Masahiro Kitajima; Kunie Ishioka; Yoshihisa Harada; Yoshinori Kitajima; Shik Shin; Koji Maeda
2008-01-01
对渗气阴极真空电弧法制备的四而体非晶炭(ta-c)膜实施氧等离子体刻蚀,消除其表面石墨层后,发现:原沉积膜中ta-C石墨表层的消除会影响其受激电子的石墨建序化.应用发射电子能耗谱,表面增强拉曼光谱和表面敏化X光吸收光谱等测量方法,测定了其表层的淌除(程度).样品的氧等离子体刻蚀阻迟了受激电子的石墨化作用,可能归因于多相成核过程中石墨晶核的缺失之故.%Electron-stimulated graphitic ordering in tetrahedral amorphous carbon (ta-C) films was found to be affected by the removal of the graphitic surface layer present in as-deposited films. To remove the graphitic layer on ta-C films fabricated by the filtered cathodic vacuum are method, the sample was etched with oxygen plasma. The removal of the surface layer was examined by transmission electron energy loss spectroscopy, surface-enhanced Raman spectroscopy,and surface-sensitive X-ray absorption spectroscopic measurements. The electron-stimulated graphitization was retarded in oxygen plasma etched samples presumably owing to the lack of graphitic nuclei for heterogeneous nucleation.
Low order anti-aliasing ﬁlters for sparse signals in embedded applications
Indian Academy of Sciences (India)
J V Satyanarayana; A G Ramakrishnan
2013-06-01
Major emphasis, in compressed sensing (CS) research, has been on the acquisition of sub-Nyquist number of samples of a signal that has a sparse representation on some tight frame or an orthogonal basis, and subsequent reconstruction of the original signal using a plethora of recovery algorithms. In this paper, we present compressed sensing data acquisition from a different perspective, wherein a set of signals are reconstructed at a sampling rate which is a multiple of the sampling rate of the ADCs that are used to measure the signals. We illustrate how this can facilitate usage of anti-aliasing ﬁlters with relaxed frequency speciﬁcations and, consequently, of lower order.
Solitary attractors and low-order filamentation in anisotropic self-focusing media
DEFF Research Database (Denmark)
Zozulya, A.A.; Anderson, D.Z.; Mamaev, A.V.
1998-01-01
We present a detailed theoretical analysis of the properties and formation of single solitons and higher-order bound dipole pairs in media with anisotropic nonlocal photorefractive material response. The single solitons are elliptical beams, whereas the dipole pairs are formed by a pair of displa......We present a detailed theoretical analysis of the properties and formation of single solitons and higher-order bound dipole pairs in media with anisotropic nonlocal photorefractive material response. The single solitons are elliptical beams, whereas the dipole pairs are formed by a pair...... concentrates on the region further away in parameter space, where complex spatial oscillations, including asymmetric filamentation into several beamlets, occurs. [S1050-2947(97)03011-4]....
A global low order spectral model designed for climate sensitivity studies
Hanna, A. F.; Stevens, D. E.
1984-01-01
A two level, global, spectral model using pressure as a vertical coordinate is developed. The system of equations describing the model is nonlinear and quasi-geostrophic. A moisture budget is calculated in the lower layer only with moist convective adjustment between the two layers. The mechanical forcing of topography is introduced as a lower boundary vertical velocity. Solar forcing is specified assuming a daily mean zenith angle. On land and sea ice surfaces a steady state thermal energy equation is solved to calculate the surface temperature. Over the oceans the sea surface temperatures are prescribed from the climatological average of January. The model is integrated to simulate the January climate.
On-sky low order non-common path correction of the GPI Calibration Unit
Hartung, Markus; Langlois, Paul; Sadakuni, Naru; Gavel, Don; Wallace, J Kent; Palmer, Dave; Poyneer, Lisa; Savransky, Dmitry; Thomas, Sandrine; Dillon, Darren; Dunn, Jennifer; Hibon, Pascal; Rantakyro, Fredrik; Goodsell, Stephen
2014-01-01
The Gemini Planet Imager (GPI) entered on-sky commissioning phase, and had its First Light at the Gemini South telescope in November 2013. Meanwhile, the fast loops for atmospheric correction of the Extreme Adaptive Optics (XAO) system have been closed on many dozen stars at different magnitudes (I=4-8), elevation angles and a variety of seeing conditions, and a stable loop performance was achieved from the beginning. Ultimate contrast performance requires a very low residual wavefront error (design goal 60 nm RMS), and optimization of the planet finding instrument on different ends has just begun to deepen and widen its dark hole region. Laboratory raw contrast benchmarks are in the order of 10^-6 or smaller. In the telescope environment and in standard operations new challenges are faced (changing gravity, temperature, vibrations) that are tackled by a variety of techniques such as Kalman filtering, open-loop models to keep alignment to within 5 mas, speckle nulling, and a calibration unit (CAL). The CAL un...
High power low-order modes operation of a multimode fiber laser
Institute of Scientific and Technical Information of China (English)
Libo Li; Qihong Lou; Jun Zhou; Jingxing Dong; Yunrong Wei; Jinyan Li
2007-01-01
Coiling technique is used to suppress high-order modes of a large mode area (LMA) double clad multimode fiber. Output powers and beam quality factors M2 are measured under two different coiling radii. 217 W with M2 of 2.96 can be obtained for coiling radius of 165 mm and 160 W with M2 of 1.38 for 52 mm. The corresponding slope efficiencies are 60% and 48%. With smaller coiling radius, the brightness is 3.4 times as high as that of the larger one.
Optimized low-order explicit Runge-Kutta schemes for high- order spectral difference method
Parsani, Matteo
2012-01-01
Optimal explicit Runge-Kutta (ERK) schemes with large stable step sizes are developed for method-of-lines discretizations based on the spectral difference (SD) spatial discretization on quadrilateral grids. These methods involve many stages and provide the optimal linearly stable time step for a prescribed SD spectrum and the minimum leading truncation error coefficient, while admitting a low-storage implementation. Using a large number of stages, the new ERK schemes lead to efficiency improvements larger than 60% over standard ERK schemes for 4th- and 5th-order spatial discretization.
2015-08-07
relativistic corrections comprise of Schwarzschild terms, Lense- Thirring precession (frame-dragging), and de Sitter ( geodesic ) precession. The Schwarzschild...Lense-Thirring, and de Sitter terms can be seen on lines 1, 2, and 3 respectively in Equation 1.13 ∆ −→̈ r = GME c2r3 {[ 2(β + γ) GME r − γ−→̇r · −→̇r...satellite. Figure 3. RSS Position Differences for Various Lunar Gravity Field Model Solutions It can be seen that all four lines representing each RSS
2010-06-07
7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) Iris AO, Inc. 2680 Bancroft Way Berkeley, CA 04704 8...aberration theory. 15. SUBJECT TERMS Nodal Aberration Theory, James Webb Space Telescope, Misalignment, Segmented , Mirror, Adaptive Optics, Coma...NOT field quadratic K. P. Thompson, “Description of the third-order optical aberrations of near-circular pupil optical systems without symmetry,” J
Global solutions for the generalized Boussinesq equation in low-order Sobolev spaces
Farah, Luiz Gustavo
2010-01-01
We show that the Cauchy problem for the defocusing generalized Boussinesq equation $u_{tt}-u_{xx}+u_{xxxx}-(|u|^{2k}u)_{xx}=0$, $k\\geq1$, on the real line is globally well-posed in $H^{s}(\\R)$ for $s>1-({1}/{3k})$. We use the "$I$-method" to define a modification of the energy functional that is "almost conserved" in time. Our result extends the previous one obtained by Farah and Linares (2010 \\textit{J. London Math. Soc.} \\textbf{81} 241-254) when $k=1$.
Detection of Low-order Curves in Images using Biologically-plausible Hardware
2012-09-29
saveacc(struct param *); void clparse(int ,char *[],struct clp *); void zap (IFSIMG); void zapacc(float **,struct param *); void clparse(int,char *[],struct...int HighPassFilter(struct param *p,int iteration) { void zap (IFSIMG); int ifnullimage(IFSIMG,float); switch...iteration) 87 { case 1: zap (p->y); zap (p->xnm1);flcp(p->retina,p->xn); // initialization return 0; break; case 2: flcp(p->xn,p->y); flcp(p->xn,p->xnm1
Four-quadrant propeller modeling: A low-order harmonic approximation
Digital Repository Service at National Institute of Oceanography (India)
Haeusler, A.J.; Saccon, A.; Hauser, J.; Pascoal, A.M.; Aguiar, A.P.
We propose a four-quadrant propeller model suitable for energy-efficient motion planning of autonomous marine vehicles. The model can be used to capturethe main features of experimental thrust and torque curves by using a small number of parameters...
A low order viscoplasticity of transversely isotropic quasi-rate independent materials
Directory of Open Access Journals (Sweden)
Mićunović Milan
2014-01-01
Full Text Available As found by experiments quasi rate independent materials (QRI describe very well behavior of steels in very wide range of strains and strain rates ([3],[4]. This property has been combined with tensor representation modeling using a generalized associative flow rule based not on the yield function but on a more general loading function. Seemingly rate independent QRI producing incremental evolution equations show rate sensitivity by means of variability of yield stress with stress rate. On the other hand transverse isotropy appears in metal forming issues like in rolled car body sheets [18]. Here an extension of tensor generators and invariants is needed to include the preferred anisotropy direction. Such a procedure has been made here. In addition we believe that the results of this paper are applicable to dynamic deformation of orthogneiss rocks treated recently in [5].
Postglacial adjustment of steep, low-order drainage basins, Canadian Rocky Mountains
Hoffmann, T.; Müller, T.; Johnson, E. A.; Martin, Y. E.
2013-12-01
is generally argued that Pleistocene glaciation results in increased sediment flux in mountain systems. An important, but not well constrained, aspect of Pleistocene glacial erosion is the geomorphic decoupling of cirque basins from main river systems. This study provides a quantitative link between glacier-induced basin morphology, postglacial erosion, and sediment delivery for mountain headwaters (with basin area cirque glaciers, which we classify into headwater basins with either cirque or noncirque morphology. Despite steeper slope gradients in cirque basins, higher-mean postglacial erosion rates in basins with noncirque morphology (0.43-0.6 mm a-1) compared to those in cirques (0.19-0.39 mm a-1) suggest a more complex relationship between hillslope erosion and slope gradient in calcareous mountain environments than implied by the threshold hillslope concept. Higher values of channel profile concavity and lower channel gradients in cirques imply lower transport capacities and, thus, lower sediment delivery ratios (SDR). These results are supported by (i) postglacial SDR values for cirques and noncirque basins of 28%, respectively, and (ii) larger fan sizes at outlets of noncirque basins compared to cirques. Although small headwater basins represent the steepest part of mountain environments and erode significant postglacial sediment, the majority of sediment remains in storage under interglacial climatic conditions and does not affect large-scale mountain river systems.
Seismic-Acoustic Active Range Monitoring for Characterizing Low-Order Ordnance Detonation
2006-04-01
The artillery fire included both air-disbursed para- chute munitions and high-explosive ground impact rounds. Figure 4. Artillery used in...Between 7 and 28 m deep, the sediments are mostly gravel with some sug- gestions of boulders. From 28 to over 65 m deep, the sediments are pre
Presentation, calibration and validation of the low-order, DCESS Earth System Model
DEFF Research Database (Denmark)
Shaffer, G.; Olsen, S. Malskaer; Pedersen, Jens Olaf Pepke
2008-01-01
for the period 1765 to 2000, as forced by prescribed anthropogenic greenhouse gas inputs and other anthropogenic and natural forcing. Long term, transient model behavior is studied with a set of 100 000 year simulations, forced by a slow, 5000 GtC input of CO2 to the atmosphere, and with a 1.5 million year...... constrain sediment module parameters. Carbon isotopic data and carbonate vs silicate weathering fractions are used to estimate initial lithosphere outgassing and rock weathering rates. Model performance is tested by simulating atmospheric greenhouse gas increases, global warming and model tracer evolution....... The atmosphere module considers radiation balance, meridional transport of heat and water vapor between low-mid latitude and high latitude zones, heat and gas exchange with the ocean and sea ice and snow cover. Gases considered are carbon dioxide and methane for all three carbon isotopes, nitrous oxide...
Low order H∞ optimal control for ACFA blended wing body aircraft
Haniš, T.; Kucera, V.; Hromčík, M.
2013-12-01
Advanced nonconvex nonsmooth optimization techniques for fixed-order H∞ robust control are proposed in this paper for design of flight control systems (FCS) with prescribed structure. Compared to classical techniques - tuning of and successive closures of particular single-input single-output (SISO) loops like dampers, attitude stabilizers, etc. - all loops are designed simultaneously by means of quite intuitive weighting filters selection. In contrast to standard optimization techniques, though (H2, H∞ optimization), the resulting controller respects the prescribed structure in terms of engaged channels and orders (e. g., proportional (P), proportional-integral (PI), and proportional-integralderivative (PID) controllers). In addition, robustness with regard to multimodel uncertainty is also addressed which is of most importance for aerospace applications as well. Such a way, robust controllers for various Mach numbers, altitudes, or mass cases can be obtained directly, based only on particular mathematical models for respective combinations of the §ight parameters.
Stock sheets of polycarbonate as inexpensive low-order optical wave plates
Kavanaugh, James; Green, Adam
2008-04-01
We show that commercially available transparent polycarbonate sheets often have linear retardances in the quarter- to half-wave range for visible light. Sheets with thicknesses from 1/16'' to 3/16'' act as zero- to third-order retarders that are modestly stable with temperature and uniform with position. By adjusting the sheets' tilt and orientation angles, they can be tuned to desired retardances, although they are not as sensitive to these parameters as are higher-order wave plates. Since they are readily available and inexpensive, these sheets make good candidates as easily machined, large-aperture wave plates for general laboratory use.
Rad-Hydro with a High-Order, Low-Order Method
Energy Technology Data Exchange (ETDEWEB)
Wollaber, Allan Benton [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Park, HyeongKae [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Lowrie, Robert Byron [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Rauenzahn, Rick M. [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Cleveland, Mathew Allen [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
2015-08-04
Moment-based acceleration via the development of “high-order, low-order” (HO-LO) algorithms has provided substantial accuracy and efficiency enhancements for solutions of the nonlinear, thermal radiative transfer equations by CCS-2 and T-3 staff members. Accuracy enhancements over traditional, linearized methods are obtained by solving a nonlinear, timeimplicit HO-LO system via a Jacobian-free Newton Krylov procedure. This also prevents the appearance of non-physical maximum principle violations (“temperature spikes”) associated with linearization. Efficiency enhancements are obtained in part by removing “effective scattering” from the linearized system. In this highlight, we summarize recent work in which we formally extended the HO-LO radiation algorithm to include operator-split radiation-hydrodynamics.
LOW ORDER NONCONFORMING RECTANGULAR FINITE ELEMENT METHODS FOR DARCY-STOKES PROBLEMS
Institute of Scientific and Technical Information of China (English)
Shiquan Zhang; Xiaoping Xie; Yumei Chen
2009-01-01
In this paper, we consider lower order rectangular finite element methods for the singularly perturbed Stokes problem. The model problem reduces to a linear Stokes problem when the perturbation parameter is large and degenerates to a mixed formulation of Poisson's equation as the perturbation parameter tends to zero. We propose two 2D and two 3D nonconforming rectangular finite elements, and derive robust discretization error estimates. Numerical experiments are carried out to verify the theoretical results.
Multivariable low order structured-controller design by frequency response approximation
Directory of Open Access Journals (Sweden)
J.O. Trierweiler
2000-12-01
Full Text Available The method presented here offers an effective and time saving tool for multivariable controller design. The relation between controller complexity and closed loop performance can easily be evaluated. The method consists of five steps: 1. A desired behavior of the closed loop system is specified. Considering the nonminimum phase part of the process model the closed loop attainable performance is determined. 2. The process model and the attainable performance are scaled by the RPN-scaling procedure. 3. This defines an "ideal" scaled controller, which is usually too complex to be realized. 4. The frequency response of the ideal scaled compensator is approximated by a simpler one with structure and order chosen by the user. 5. Since the approximation in frequency response is performed with the scaled system, it is necessary to return to the original system’s units.
In-Situ Landmine Neutralization Using Chemicals to Initiate Low Order Burning of Main Charge
2006-01-01
of the gun tube. Once the squib is fired, it produces gas pressure, driving a hammer to impact a firing pin , which in turn fires a cartridge. The...Large Reactive Mine Clearance-II (REMIC-II) The large REMIC-II body is cast in two identical polyurethane halves, connected by four small pins ... four prototype chemical delivery systems. Two systems use diethylene triamine (DETA), which is hypergolic with TNT, Tetryl and TNT based
Parallel and Low-Order Scaling Implementation of Hartree-Fock Exchange Using Local Density Fitting.
Köppl, Christoph; Werner, Hans-Joachim
2016-07-12
Calculations using modern linear-scaling electron-correlation methods are often much faster than the necessary reference Hartree-Fock (HF) calculations. We report a newly implemented HF program that speeds up the most time-consuming step, namely, the evaluation of the exchange contributions to the Fock matrix. Using localized orbitals and their sparsity, local density fitting (LDF), and atomic orbital domains, we demonstrate that the calculation of the exchange matrix scales asymptotically linearly with molecular size. The remaining parts of the HF calculation scale cubically but become dominant only for very large molecular sizes or with many processing cores. The method is well parallelized, and the speedup scales well with up to about 100 CPU cores on multiple compute nodes. The effect of the local approximations on the accuracy of computed HF and local second-order Møller-Plesset perturbation theory energies is systematically investigated, and default values are established for the parameters that determine the domain sizes. Using these values, calculations for molecules with hundreds of atoms in combination with triple-ζ basis sets can be carried out in less than 1 h, with just a few compute nodes. The method can also be used to speed up density functional theory calculations with hybrid functionals that contain HF exchange.
Erem, B; Stovicek, P; Brooks, D H
2012-07-12
The dynamical structure of electrical recordings from the heart or torso surface is a valuable source of information about cardiac physiological behavior. In this paper, we use an existing data-driven technique for manifold identification to reveal electrophysiologically significant changes in the underlying dynamical structure of these signals. Our results suggest that this analysis tool characterizes and differentiates important parameters of cardiac bioelectric activity through their dynamic behavior, suggesting the potential to serve as an effective dynamic constraint in the context of inverse solutions.
Low Order Semi-simple Nelson Algebras%低阶半单Nelson代数
Institute of Scientific and Technical Information of China (English)
李鹏; 张小红
2009-01-01
给出半单Nelson代数的一些新性质,证明了全序半单Nelson代数只存在二阶和三阶的,四阶及以上的有限全序半单Nelson代数不存在.同时,借助数学软件Mathematica得到阶数不超过9的全部(同构意义下)半单Nelson代数.
On the efficient numerical solution of lattice systems with low-order couplings
Ammon, A; Hartung, T; Jansen, K; Leövey, H; Volmer, J
2015-01-01
We apply the Quasi Monte Carlo (QMC) and recursive numerical integration methods to evaluate the Euclidean, discretized time path-integral for the quantum mechanical anharmonic oscillator and a topological quantum mechanical rotor model. For the anharmonic oscillator both methods outperform standard Markov Chain Monte Carlo methods and show a significantly improved error scaling. For the quantum mechanical rotor we could, however, not find a successful way employing QMC. On the other hand, the recursive numerical integration method works extremely well for this model and shows an at least exponentially fast error scaling.
On the efficient numerical solution of lattice systems with low-order couplings
Ammon, A.; Genz, A.; Hartung, T.; Jansen, K.; Leövey, H.; Volmer, J.
2016-01-01
We apply the Quasi Monte Carlo (QMC) and recursive numerical integration methods to evaluate the Euclidean, discretized time path-integral for the quantum mechanical anharmonic oscillator and a topological quantum mechanical rotor model. For the anharmonic oscillator both methods outperform standard Markov Chain Monte Carlo methods and show a significantly improved error scaling. For the quantum mechanical rotor we could, however, not find a successful way employing QMC. On the other hand, the recursive numerical integration method works extremely well for this model and shows an at least exponentially fast error scaling.
M-Adapting Low Order Mimetic Finite Differences for Dielectric Interface Problems
Energy Technology Data Exchange (ETDEWEB)
McGregor, Duncan A. [Oregon State Univ., Corvallis, OR (United States); Gyrya, Vitaliy [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Manzini, Gianmarco [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
2016-03-07
We consider a problem of reducing numerical dispersion for electromagnetic wave in the domain with two materials separated by a at interface in 2D with a factor of two di erence in wave speed. The computational mesh in the homogeneous parts of the domain away from the interface consists of square elements. Here the method construction is based on m-adaptation construction in homogeneous domain that leads to fourth-order numerical dispersion (vs. second order in non-optimized method). The size of the elements in two domains also di ers by a factor of two, so as to preserve the same value of Courant number in each. Near the interface where two meshes merge the mesh with larger elements consists of degenerate pentagons. We demonstrate that prior to m-adaptation the accuracy of the method falls from second to rst due to breaking of symmetry in the mesh. Next we develop m-adaptation framework for the interface region and devise an optimization criteria. We prove that for the interface problem m-adaptation cannot produce increase in method accuracy. This is in contrast to homogeneous medium where m-adaptation can increase accuracy by two orders.
Batch distillation column low-order models for quality program control
Betlem, B.H.L.
2000-01-01
For batch distillation, the dynamic composition behaviour can be described by the dominant time constant and the bottom exhaustion. Its magnitude is determined by the change of the composition distribution and is maximal when the inflection point of the molar fraction profile is located in the middl
Computer program for fitting low-order polynomial splines by method of least squares
Smith, P. J.
1972-01-01
FITLOS is computer program which implements new curve fitting technique. Main program reads input data, calls appropriate subroutines for curve fitting, calculates statistical analysis, and writes output data. Method was devised as result of need to suppress noise in calibration of multiplier phototube capacitors.
Explicit calibration and simulation of stochastic fields by low-order ARMA processes
DEFF Research Database (Denmark)
Krenk, Steen
2011-01-01
to the process via an extension to autoregressive moving average (ARMA) processes. The ARMA format incorporates a more detailed correlation structure by including previous values of the simulated process. Alternatively, a more detailed correlation structure can be obtained by including additional 'state...
On the efficient numerical solution of lattice systems with low-order couplings
Energy Technology Data Exchange (ETDEWEB)
Ammon, A. [OAKLABS GmbH, Hennigsdorf (Germany); Genz, A. [Washington State Univ., Pullman, WA (United States). Dept. of Mathematics; Hartung, T. [King' s College London (United Kingdom). Dept. of Mathematics; Jansen, K.; Volmer, J. [DESY Zeuthen (Germany). NIC; Leoevey, H. [Humboldt Univ. Berlin (Germany). Inst. fuer Mathematik
2015-10-15
We apply the Quasi Monte Carlo (QMC) and recursive numerical integration methods to evaluate the Euclidean, discretized time path-integral for the quantum mechanical anharmonic oscillator and a topological quantum mechanical rotor model. For the anharmonic oscillator both methods outperform standard Markov Chain Monte Carlo methods and show a significantly improved error scaling. For the quantum mechanical rotor we could, however, not find a successful way employing QMC. On the other hand, the recursive numerical integration method works extremely well for this model and shows an at least exponentially fast error scaling.
Explicit calibration and simulation of stochastic fields by low-order ARMA processes
DEFF Research Database (Denmark)
Krenk, Steen
2011-01-01
A simple framework for autoregressive simulation of stochastic fields is presented. The autoregressive format leads to a simple exponential correlation structure in the time-dimension. In the case of scalar processes a more detailed correlation structure can be obtained by adding memory to the pr......A simple framework for autoregressive simulation of stochastic fields is presented. The autoregressive format leads to a simple exponential correlation structure in the time-dimension. In the case of scalar processes a more detailed correlation structure can be obtained by adding memory......-space' variables in the simulation. For a scalar process this would imply an increase of the dimension of the process to be simulated. In the case of a stochastic field the correlation in the time-dimension is represented, although indirectly, in the simultaneous spatial correlation. The model with the shortest...... memory -the single-step autoregressive model - is analyzed in detail, and an efficient multi-step calibration procedure is developed. The calibration makes direct use of conditional correlations and means, expressed explicitly in terms of the zero and k-step correlation matrices of the stochastic field...
A low-order model for flow control studies in cylinder wakes
Balasubramanian, Ganapathi; Olinger, David J.; Demetriou, Michael
1998-11-01
Control of three-dimensional wake structures behind circular cylinders is investigated using a previously developed coupled map lattice. The map consists of circle map oscillators along the cylinder span coupled by a diffusion model. Our goal is to develop an efficient model for flow control studies in cylinder wakes. Complex vortex shedding patterns, such as vortex dislocations and frequency cells, are observed behind vibrating cables in uniform freestream flows and stationary cylinders in sheared flows. These structures are controlled by the addition of periodic control signals to the forcing term in the map. Discontinuous nonlinear control theory is used to derive the control laws. Parallel shedding is realized for the case of uniform flow and oblique shedding is achieved for sheared inflows. The effectiveness of the discontinuous nonlinear control theory is compared with the previous application of chaos control theory to the coupled map lattice.
Analysis of leading edge separation using a low order panel method
Sandlin, Doral R.
1989-01-01
An examination of the potential flow computer code VSAERO to model leading edge separation over a delta wing is examined. Recent improvements to the code suggest that it may be capable of predicting pressure coefficients on the body. Investigation showed that although that code does predict the vortex roll-up, the pressure coefficients have significant error. The program is currently unsatisfactory, but with some additional development it may become a useful tool for this application.
Intermediate order in tetrahedrally coordinated silicon: evidence for chainlike objects
Energy Technology Data Exchange (ETDEWEB)
Tsu, D.V.; Chao, B.S.; Jones, S.J. [Energy Conversion Devices, Rochester Hills, MI (United States)
2003-07-01
In this report, we describe the nature of intermediate order in silicon as determined by recent measurements on thin films using transmission electron microscopy (TEM) and Raman scattering. The TEM images show in addition to the expected continuous random network (CRN), the presence of highly ordered quasi-one-dimensional ''chain-like objects'' (CLOs) that are 1-2 nm wide and tens of nm long that meander and show some evidence of cross-linking with each other. The presence of these objects correlate to a Raman feature centered at 490 cm{sup -1} whose width is 35-40 cm{sup -1}, and is used to quantify the heterogeneity in terms of the CLO and CRN (=475 cm{sup -1} scattering) concentrations. The 490 and 35 cm{sup -1} values are consistent with bond angle deviations approaching 0{sup o}, and thus reinforces an association with the CLOs. We find that in reference quality a-Si:H (made using pure SiH{sub 4}), the CLO concentration is about 5 vol%, while in state-of-the-art material using high H{sub 2} levels of dilution during processing, it increases to about 15%. Increased stability of such material to light-soaking is thus not mediated by a direct volumetric replacement of poor with high-quality components. Rather, an important characteristic of intermediate order in silicon is the low-dimensional aspect of its order, which allows it to influence more total volume than which it is itself composed. Consistent with these and other recent findings, we propose a tensegrity model of amorphous silicon. (author)
Anomalous Magnetic Excitations of Cooperative Tetrahedral Spin Clusters
DEFF Research Database (Denmark)
Prsa, K.; Rønnow, H.M.; Zaharko, O.;
2009-01-01
An inelastic neutron scattering study of Cu2Te2O5X2 (X=Cl, Br) shows strong dispersive modes with large energy gaps persisting far above T-N, notably in Cu2Te2O5Br2. The anomalous features: a coexisting unusually weak Goldstone-like mode observed in Cu2Te2O5Cl2 and the size of the energy gaps can...
Flavor from the double tetrahedral group without supersymmetry
Carone, Christopher D; Vasquez, Savannah
2016-01-01
We consider a class of flavor models proposed by Aranda, Carone and Lebed, relaxing the assumption of supersymmetry and allowing the flavor scale to float anywhere between the weak and Planck scales. We perform global fits to the charged fermion masses and CKM angles, and consider the dependence of the results on the unknown mass scale of the flavor sector. We find that the typical Yukawa textures in these models provide a good description of the data over a wide range of flavor scales, with a preference for those that approach the lower bounds allowed by flavor-changing-neutral-current constraints. Nevertheless, the possibility that the flavor scale and Planck scale are identified remains viable. We present models that demonstrate how the assumed textures can arise most simply in a non-supersymmetric framework.
Tetrahedral Mn{sub i4} cluster in silicon
Energy Technology Data Exchange (ETDEWEB)
Wedekind, J.; Vollmer, H.; Labusch, R.
2001-06-15
Mn{sub i4}{sup 0} clusters were investigated by electron paramagnetic resonance in silicon specimens with initial doping concentrations between 1.5{times}10{sup 15} Pcm{sup {minus}3} and 5{times}10{sup 16} Bcm{sup {minus}3}. In n-type samples and in intrinsic samples, we obtained the EPR spectrum of the well-known Mn{sub i4}{sup 0} cluster, whereas in p-type material we observed an unknown EPR spectrum of cubic symmetry which we attribute to a Mn{sub i4}{sup +} cluster. This spectrum is highly light sensitive. Its +/0 level was found near midgap by photo-EPR. In highly doped p-type material we could prove the presence of a Mn{sub i4}{sup 2+} center which shows no EPR spectrum, but is transformed into Mn{sub i4}{sup +} under illumination.
New nuclear stability islands of octahedral and tetrahedral shapes
Energy Technology Data Exchange (ETDEWEB)
Mazurek, Katarzyna; Kmiecik, Maria; Maj, Adam [Niewodniczanski Institute of Nuclear Physics - PAN, ul. Radzikowskiego 152, PL-31-342 Krakow (Poland); Dudek, Jerzy; Curien, Dominique [Institut de Recherches Subatomiques, Universite Louis Pasteur, F-67037 Strasbourg Cedex 2 (France); Gozdz, Andrzej [Zaklad Fizyki Matematycznej, Uniwersytet Marii Curie-Sklodowskiej, pl. Marii Curie-Sklodowskiej 1, PL-20031 Lublin (Poland)
2009-07-01
Large scale calculations based on the microscopic-macroscopic method with Woods- Saxon single particle potential guided by the use of the discrete point group symmetries allow us to find the new islands of nuclear stability. These new stability regions are the consequence of particularly strong shell effects which are obtained in the calculations when the nuclear mean field is allowed to deform by respecting some special the so called high-rank symmetry-point groups. The underlying mechanism is illustrated together with the full chain of the symmetry-associated magic numbers.
Non-Centrosymmetric Homochiral Supramolecular Polymers of Tetrahedral Subphthalocyanine Molecules
Guilleme, Julia; Mayoral, María J.; Calbo, Joaquín; Aragó, Juan; Viruela, Pedro M.; Ortí, Enrique; Torres, Tomás; González-Rodríguez, David
2015-01-01
This is the peer reviewed version of the following article: Angewandte Chemie - International Edition 54.8 (2015): 2543-2547, which has been published in final form at http://dx.doi.org/10.1002/anie.201411272. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving A combination of spectroscopy (UV/Vis absorption, emission, and circular dichroism), microscopy (AFM and TEM), and computational studies reveal the formation of non-c...
Neutrino mixing from the double tetrahedral group $T^{\\prime}$
Aranda, Alfredo
2007-01-01
It is shown that it is possible to create successful models of flavor for both quarks and leptons using the discrete non-abelian group $T^{\\prime}$ by itself. Two simple realizations are presented that can be used as the starting point for more general scenarios. In addition to the Minimal Supersymmetric Standard Model particle content, the models include three generations of right handed neutrinos and four scalar flavon fields. Three of the flavons are needed in the quark and charged lepton sector of the models and the fourth flavon participates only in the neutrino sector.
The Magnetic Shielding Polarizabilities of Some Tetrahedral Molecules
Directory of Open Access Journals (Sweden)
Paul Chittenden
2000-09-01
Full Text Available TMS is the commonest standard reference for both protons and 13C NMR spectroscopy. The Magnetic Shielding and its Polarizabilities, plus the static polarizability have been calculated for TMS, tetramethyl ammonium cation and 2,2-dimethylpropane. An investigation of continuum solvation effects on these highly symmetrical molecules, whose first surviving electric moment is the octopole, showed interaction with solvent makes little change to these magnetic properties. This small change is however consistent with both the high symmetry of the molecules and the available extensive experimental data for TMS. A rationalization of the signs and magnitudes of A in a sequence of related molecules has been suggested.
Mitchell, K. E.; Dutton, J. A.
1981-01-01
The considered investigation is concerned with periodic solutions in the context of a forced, dissipative, barotropic spectral model truncated to three complex coefficients with constant forcing on only the intermediate scale. It is found that determining a periodic solution of this three-coefficient model also reduces to finding the algebraic roots of a real polynomial. In the derivation of this polynomial, a class of hydrodynamic spectral systems is described for which a periodic solution might be similarly specified. The existence of periodic solutions of the three-coefficient model is controlled by the roots of the stability polynomial of the basic stationary solution, which represents the simplest response to the constant forcing. When the forcing exceeds a critical value, the basic solution becomes unstable. Owing to the nature of the roots of the stability polynomial at critical forcing, bifurcation theory guarantees the existence of a periodic solution.
Larsen, A.; Bork, H.; Larsen, J.
2013-12-01
Historic dams of mostly unknown ages are a widespread feature within low (1st to 3rd) order streams in central Germany. Within many of these catchments, floodplain compilation studies have found increases in aggradation rates during medieval times, suggesting this was due to deforestation and agricultural land use causing widespread slope instability. However, this process only explains the delivery of sediment to these rivers, and we suggest that the construction of valley bottom dams was also critical to this process through the effective trapping of the increased sediment. Dams were built for multiple purposes from the beginning of human occupation in central Europe, culminating in very high dam densities of many ages and levels of operation. Dam construction probably peaked first during medieval times and again around 1830 AD, when new methods of river engineering were introduced. Preliminary results show an increased floodplain sedimentation rate at ~ 900 AD, which coincides with the earliest written sources from the area and represents the onset of human impact on riverscapes. As a result of these impacts on the flow regime and sediment load, some rivers experienced morphological changes and shifted from multithread to meandering. This is most pronounced where rapid floodplain sedimentation buried wetland soils, therefore altering both river morphology and ecosystem function. In order to test what role dams have played in morphological change and floodplain aggradation, we compiled historic maps and high resolution Lidar data for backwater modelling. In addition, extensive field and lab data are used to check the stratigraphy and age of the alluvial sequences.
2011-12-01
in the structural response of the panel. The damping comes from different sources, such as from the boundary conditions in the form of frictional ...exhaust nozzle due to the limited amount of working space between the nozzle and the facility exhaust duct. An overhead chain hoist as well as an...additional horizontally mounted come-along hoist were required to move the test article into place on the test fixture. The installation/removal set-up is
N'Diaye, Mamadou; Soummer, Rémi
2014-01-01
The Apodized Pupil Lyot Coronagraph (APLC) is a diffraction suppression system installed in the recently deployed instruments Palomar/P1640, Gemini/GPI, and VLT/SPHERE to allow direct imaging and spectroscopy of circumstellar environments. Using a prolate apodization, the current implementations offer raw contrasts down to $10^{-7}$ at 0.2 arcsec from a star over a wide bandpass (20\\%), in the presence of central obstruction and struts, enabling the study of young or massive gaseous planets. Observations of older or lighter companions at smaller separations would require improvements in terms of inner working angle (IWA) and contrast, but the methods originally used for these designs were not able to fully explore the parameter space. We here propose a novel approach to improve the APLC performance. Our method relies on the linear properties of the coronagraphic electric field with the apodization at any wavelength to develop numerical solutions producing coronagraphic star images with high-contrast region in...
Flockerzi, Dietrich; Heineken, Wolfram
2006-12-01
It is claimed by Rhodes, Morari, and Wiggins [Chaos 9, 108-123 (1999)] that the projection algorithm of Maas and Pope [Combust. Flame 88, 239-264 (1992)] identifies the slow invariant manifold of a system of ordinary differential equations with time-scale separation. A transformation to Fenichel normal form serves as a tool to prove this statement. Furthermore, Rhodes, Morari, and Wiggins [Chaos 9, 108-123 (1999)] conjectured that away from a slow manifold, the criterion of Maas and Pope will never be fulfilled. We present two examples that refute the assertions of Rhodes, Morari, and Wiggins. In the first example, the algorithm of Maas and Pope leads to a manifold that is not invariant but close to a slow invariant manifold. The claim of Rhodes, Morari, and Wiggins that the Maas and Pope projection algorithm is invariant under a coordinate transformation to Fenichel normal form is shown to be not correct in this case. In the second example, the projection algorithm of Maas and Pope leads to a manifold that lies in a region where no slow manifold exists at all. This rejects the conjecture of Rhodes, Morari, and Wiggins mentioned above.
Rhodes, Carl; Morari, Manfred; Wiggins, Stephen
2006-12-01
Flockerzi and Heineken [Chaos 16, 048101 (2006)] present two examples with the goal of elucidating issues related to the Maas and Pope method for identifying low dimensional "slow" manifolds in systems with a time-scale separation. The goal of their first example is to show that the result claimed by Rhodes et al. [Chaos 9, 108-123 (1999)] that the Maas and Pope algorithm identifies the slow invariant manifold in the situation in which there is finite time-scale separation is incorrect. We show that their arguments result from an incomplete understanding of the situation and that, in fact, their example supports, and is completely consistent with, the result in Rhodes et al.. Their second example claims to be a counterexample to a conjecture in Rhodes et al. that away from the slow manifold the criterion of Maas and Pope [Combust. Flame 88, 239-264 (1992)] will never be fulfilled. While this conjecture may indeed be false, we argue that it is not clear that the example presented by Flockerzi and Heineken is indeed a counterexample.
Crass, Jonathan; Femenia, Bruno; King, David L; Mackay, Craig D; Rebolo-López, Rafael; Labadie, Lucas; Garrido, Antonio Pérez; Balcells, Marc; Sánchez, Anastasio Díaz; Fuensalida, Jesús Jimenez; Lopez, Roberto L; Oscoz, Alejandro; Prieto, Jorge A Pérez; Rodríguez-Ramos, Luis F; Villó, Isidro
2012-01-01
The Adaptive Optics Lucky Imager (AOLI) is a new instrument under development to demonstrate near diffraction limited imaging in the visible on large ground-based telescopes. We present the adaptive optics system being designed for the instrument comprising a large stroke deformable mirror, fixed component non-linear curvature wavefront sensor and photon-counting EMCCD detectors. We describe the optical design of the wavefront sensor where two photoncounting CCDs provide a total of four reference images. Simulations of the optical characteristics of the system are discussed, with their relevance to low and high order AO systems. The development and optimisation of high-speed wavefront reconstruction algorithms are presented. Finally we discuss the results of simulations to demonstrate the sensitivity of the system.
Carver, Daniel P.; Beeton, Jared M.
2014-09-01
This geoarcheological study investigates soil stratigraphy and geochronology of alluvial deposits to determine Holocene landscape evolution within the Hot Creek, La Jara Creek, and Alamosa River drainage basins in the San Juan Mountains of Colorado. Geomorphic mapping and radiocarbon dating indicate synchronicity in patterns of erosion, deposition, and stability between drainage basins. In all three basins, the maximum age of mapped alluvial terraces and fans is ~ 3300 cal yr BP. A depositional period seen at both Hot Creek and the Alamosa River begins ~ 3300 to 3200 cal yr BP. Based on soil development, short periods of stability followed by alluvial fan aggradation occur in the Alamosa River basin ~ 2200 cal yr BP. A period of landscape stability at Hot Creek before ~ 1100 cal yr BP is followed by a period of rapid aggradation within all three drainages between ~ 1100 and 850 cal yr BP. A final aggradation event occurred between ~ 630 and 520 cal yr BP at La Jara Creek. These patterns of landscape evolution over the past ~ 3300 yr provide the framework for an archeological model that predicts the potential for buried and surficial cultural materials in the research area.
Li, Wei; Xiao, Chuan; Liu, Yaduo
2013-12-01
Audio identification via fingerprint has been an active research field for years. However, most previously reported methods work on the raw audio format in spite of the fact that nowadays compressed format audio, especially MP3 music, has grown into the dominant way to store music on personal computers and/or transmit it over the Internet. It will be interesting if a compressed unknown audio fragment could be directly recognized from the database without decompressing it into the wave format at first. So far, very few algorithms run directly on the compressed domain for music information retrieval, and most of them take advantage of the modified discrete cosine transform coefficients or derived cepstrum and energy type of features. As a first attempt, we propose in this paper utilizing compressed domain auditory Zernike moment adapted from image processing techniques as the key feature to devise a novel robust audio identification algorithm. Such fingerprint exhibits strong robustness, due to its statistically stable nature, against various audio signal distortions such as recompression, noise contamination, echo adding, equalization, band-pass filtering, pitch shifting, and slight time scale modification. Experimental results show that in a music database which is composed of 21,185 MP3 songs, a 10-s long music segment is able to identify its original near-duplicate recording, with average top-5 hit rate up to 90% or above even under severe audio signal distortions.
A spectral approach to compute the mean performance measures of the queue with low-order BMAP input
Directory of Open Access Journals (Sweden)
Ho Woo Lee
2003-01-01
Full Text Available This paper targets engineers and practitioners who want a simple procedure to compute the mean performance measures of the Batch Markovian Arrival process (BMAP/G/1 queueing system when the parameter matrices order is very low. We develop a set of system equations and derive the vector generating function of the queue length. Starting from the generating function, we propose a spectral approach that can be understandable to those who have basic knowledge of M/G/1 queues and eigenvalue algebra.
Yang, Jun
2014-01-01
In the spirit of minimal modeling of complex systems, we develop an idealized two-column model to investigate the climate of tidally locked terrestrial planets with Earth-like atmospheres in the habitable zone of M-dwarf stars. The model is able to approximate the fundamental features of the climate obtained from three-dimensional (3D) atmospheric general circulation model (GCM) simulations. One important reason for the two-column model's success is that it reproduces the high cloud albedo of the GCM simulations, which reduces the planet's temperature and delays the onset of a runaway greenhouse state. The two-column model also clearly illustrates a secondary mechanism for determining the climate: the nightside acts as a ``radiator fin'' through which infrared energy can be lost to space easily. This radiator fin is maintained by a temperature inversion and dry air on the nightside, and plays a similar role to the subtropics on modern Earth. Since 1D radiative-convective models cannot capture the effects of t...
Energy Technology Data Exchange (ETDEWEB)
Yang, Jun; Abbot, Dorian S., E-mail: junyang28@uchicago.edu [Department of the Geophysical Sciences, University of Chicago, 5734 South Ellis Avenue, Chicago, IL 60637 (United States)
2014-04-01
In the spirit of minimal modeling of complex systems, we develop an idealized two-column model to investigate the climate of tidally locked terrestrial planets with Earth-like atmospheres in the habitable zone of M-dwarf stars. The model is able to approximate the fundamental features of the climate obtained from three-dimensional (3D) atmospheric general circulation model (GCM) simulations. One important reason for the two-column model's success is that it reproduces the high cloud albedo of the GCM simulations, which reduces the planet's temperature and delays the onset of a runaway greenhouse state. The two-column model also clearly illustrates a secondary mechanism for determining the climate: the nightside acts as a 'radiator fin' through which infrared energy can be lost to space easily. This radiator fin is maintained by a temperature inversion and dry air on the nightside, and plays a similar role to the subtropics on modern Earth. Since one-dimensional radiative-convective models cannot capture the effects of the cloud albedo and radiator fin, they are systematically biased toward a narrower habitable zone. We also show that cloud parameters are the most important in the two-column model for determining the day-night thermal emission contrast, which decreases and eventually reverses as the stellar flux increases. This reversal is important because it could be detected by future extrasolar planet characterization missions, which would suggest that the planet has Earth-like water clouds and is potentially habitable.
Lemoult, Grégoire; Aider, Jean-Luc; Wesfreid, José Eduardo
2013-01-01
We present new experimental results on the development of turbulent spots in channel flow. The internal structure of a turbulent spot is measured, with Time Resolved Stereoscopic Particle Image Velocimetry. We report the observation of travelling-wave-like structures at the trailing edge of the turbulent spot. Special attention is paid to the large-scale flow surrounding the spot. We show that this large-scale flow is an asymmetric quadrupole centred on the spot. We measure the time evolution of the turbulent fluctuations and the mean flow distortions and compare these with the predictions of a nonlinear reduced order model predicting the main features of subcritical transition to turbulence.
Directory of Open Access Journals (Sweden)
Raisa Valdivé Lunar
2012-12-01
Full Text Available The work presented shows the simulated values of the temperatures experimentally un-dertaken in [1] and [11] during friction stir welding (FSW of AA 1100-0 aluminum plates. This is done using the finite element method (FEM. We studied the behavior of temperature by applying MEF to the heat transfer equation used by [9]. The methodology used allowed modeling the problem using the software ABAQUS /CAE v6.7-1 with elements hexahedral of eight nodes and tetrahedral of four nodes. The simulation of the AA 1100-0 aluminum FSW reported a temperature difference of 80.3 C compared to the maximum value obtained experimentally by [1]. The result shows that the process modeling allows to predict the thermal behavior of the weld. // RESUMEN: The work presented shows the simulated values of the temperatures experimentally un-dertaken in [1] and [11] during friction stir welding (FSW of AA 1100-0 aluminum plates. This is done using the finite element method (FEM. We studied the behavior of temperature by applying MEF to the heat transfer equation used by [9]. The methodology used allowed modeling the problem using the software ABAQUS /CAE v6.7-1 with elements hexahedral of eight nodes and tetrahedral of four nodes. The simulation of the AA 1100-0 aluminum FSW reported a temperature difference of 80.3 C compared to the maximum value obtained experimentally by [1]. The result shows that the process modeling allows to predict the thermal behavior of the weld.
Electronic Structures of the Filled Tetrahedral Semiconductor Li3AlN2
Institute of Scientific and Technical Information of China (English)
MA Chun-Lan; PAN Tao
2006-01-01
The first-principles total energy calculations with the local density approximation (LDA) and the plane wave pseudopotential method are employed to investigate the structural properties and electronic structures of Li3AlN2. The calculated lattice constants and internal coordination of atoms agree well with the experimental results. Detailed studies of the electronic structure and the charge-density redistribution reveal the features of the strong ionicity bonding of Al-N and Al-Li, and strong hybridizations between Li and N in Li3AlN2. Our band structure calculation verifies Li3AlN2 is a direct gap semiconductor with the LDA gap value of about 2.97eV and transition at Γ.
Competing ordered structures formed by particles with a regular tetrahedral patch decoration.
Doppelbauer, Günther; Noya, Eva G; Bianchi, Emanuela; Kahl, Gerhard
2012-07-18
We study the ordered equilibrium structures of patchy particles where the patches are located on the surface of the colloid such that they form a regular tetrahedron. Using optimization techniques based on ideas of evolutionary algorithms we identify possible candidate structures. We retain not only the energetically most favourable lattices but also include a few energetically less favourable particle arrangements (i.e., local minima on the enthalpy landscape). Using suitably developed Monte Carlo based simulation techniques in an NPT ensemble we evaluate the thermodynamic properties of these candidate structures along selected isobars and isotherms and identify thereby the respective ranges of stability. We demonstrate on a quantitative level that the equilibrium structures at a given state point result from a delicate compromise between entropy, energy (i.e., the lattice sum) and packing.
Periodic model of LTA framework containing various non-tetrahedral cations
Koleżyński, A.; Mikuła, A.; Król, M.
2016-03-01
A simplified periodic model of Linde Type A zeolite (LTA) structure with various selected mono- and di-valent extra-framework cations was formulated. Ab initio calculations (geometry optimization and vibrational spectra calculations) using the proposed model were carried out by means of Crystal09 program. The resulting structures and simulated spectra were analyzed in detail and compared with the experimental ones. The presented results show that in most cases the proposed model agrees well with experimental results. Individual bands were assigned to respective normal modes of vibration and the changes resulting from the selective substitution of extra framework cations were described and explained.
Electron Spin Resonance of Tetrahedral Transition Metal Oxyanions (MO4n-) in Solids.
Greenblatt, M.
1980-01-01
Outlines general principles in observing sharp electron spin resonance (ESR) lines in the solid state by incorporating the transition metal ion of interest into an isostructural diamagnetic host material in small concentration. Examples of some recent studies are described. (CS)
Triedman, John K.; Jolley, Matthew; Stinstra, Jeroen; Brooks, Dana H.; MacLeod, Rob
2008-01-01
ICD implants may be complicated by body size and anatomy. One approach to this problem has been the adoption of creative, extracardiac implant strategies using standard ICD components. Because data on safety or efficacy of such ad hoc implant strategies is lacking, we have developed image-based finite element models (FEMs) to compare electric fields and expected defibrillation thresholds (DFTs) using standard and novel electrode locations. In this paper, we review recently published studies by our group using such models, and progress in meshing strategies to improve efficiency and visualization. Our preliminary observations predict that they may be large changes in DFTs with clinically relevant variations of electrode placement. Extracardiac ICDs of various lead configurations are predicted to be effective in both children and adults. This approach may aid both ICD development and patient-specific optimization of electrode placement, but the simplified nature of current models dictates further development and validation prior to clinical or industrial utilization. PMID:18817926
Structural and Thermal Properties of Elementary and Binary Tetrahedral Semiconductor Nanoparticles
Omar, M. S.
2016-01-01
We report an equation free from fitting parameters as a direct calculation of size-dependent mean bond length for group IV and compounds from the III-V and II-VI binary groups. Size-dependent melting temperature and thermal expansion are also investigated for some materials forming the groups mentioned above. The empirical relation, which is obtained from fitting experimental data of melting enthalpy, is used to recalculate their values as well as entropy. The nanosize dependence of lattice thermal expansion for elements forming group IV is analyzed according to the hard sphere model, while mean ionicity is used for groups III-V and II-VI.
Periodic model of LTA framework containing various non-tetrahedral cations.
Koleżyński, A; Mikuła, A; Król, M
2016-03-15
A simplified periodic model of Linde Type A zeolite (LTA) structure with various selected mono- and di-valent extra-framework cations was formulated. Ab initio calculations (geometry optimization and vibrational spectra calculations) using the proposed model were carried out by means of Crystal09 program. The resulting structures and simulated spectra were analyzed in detail and compared with the experimental ones. The presented results show that in most cases the proposed model agrees well with experimental results. Individual bands were assigned to respective normal modes of vibration and the changes resulting from the selective substitution of extra framework cations were described and explained.
Electron doping through lithium intercalation to interstitial channels in tetrahedrally bonded SiC
Energy Technology Data Exchange (ETDEWEB)
Sakai, Yuki [Department of Applied Physics, The University of Tokyo, 7-3-1, Hongo, Bunkyo-ku, Tokyo 113-8656 (Japan); Center for Computational Materials, Institute for Computational Engineering and Sciences, The University of Texas at Austin, Austin, Texas 78712 (United States); Oshiyama, Atsushi [Department of Applied Physics, The University of Tokyo, 7-3-1, Hongo, Bunkyo-ku, Tokyo 113-8656 (Japan)
2015-11-07
We report on first-principles calculations that clarify the effect of lithium atom intercalation into zinc blende 3C-silicon carbide (3C-SiC) on electronic and structural properties. Lithium atoms inside 3C-SiC are found to donate electrons to 3C-SiC that is an indication of a new way of electron doping through the intercalation. The electrons doped into the conduction band interact with lithium cations and reduce the band spacing between the original valence and conduction bands. We have also found that a silicon monovacancy in 3C-SiC promotes the lithium intercalation, showing that the vacancy generation makes SiC as a possible anode material for lithium-ion battery.
Probing the Intact Cluster Catalysis Concept by Tetrahedral Clusters With Framework Chirality
Institute of Scientific and Technical Information of China (English)
G. Süss-Fink; L. Vieille-Petit
2005-01-01
@@ 1Results and Discussion In order to bring evidence for or against the hypothesis of catalytic hydrogenation by intact trinuclear arene ruthenium clusters containing an oxo cap, the substrate being hydrogenated inside the hydrophobic pocket spanned by the three arene ligands ("supramolecular cluster catalysis")[1], we synthesized cationic Ru3O clusters (See Fig. 1) with three different arene ligands (intrinsically chiral tetrahedra).
The Tetrahedral Zamolodchikov Algebra and the {AdS_5× S^5} S-matrix
Mitev, Vladimir; Staudacher, Matthias; Tsuboi, Zengo
2017-08-01
The S-matrix of the {AdS_5× S^5} string theory is a tensor product of two centrally extended su{(2|2)\\ltimes R^2 S-matrices, each of which is related to the R-matrix of the Hubbard model. The R-matrix of the Hubbard model was first found by Shastry, who ingeniously exploited the fact that, for zero coupling, the Hubbard model can be decomposed into two XX models. In this article, we review and clarify this construction from the AdS/CFT perspective and investigate the implications this has for the {AdS_5× S^5} S-matrix.
Directory of Open Access Journals (Sweden)
Mauro Massayoshi Sakamoto
2008-01-01
Full Text Available In this work, a software package based on the Delaunay´s algorithm is described. The main feature of this package is the capability in applying discretization in geometric domains of teeth taking into account their complex inner structures and the materials with different hardness. Usually, the mesh generators reported in literature treat molars and other teeth by using simplified geometric models, or even considering the teeth as homogeneous structures.
Hepburn, I.; Chen, W.; De Schutter, E.
2016-08-01
Spatial stochastic molecular simulations in biology are limited by the intense computation required to track molecules in space either in a discrete time or discrete space framework, which has led to the development of parallel methods that can take advantage of the power of modern supercomputers in recent years. We systematically test suggested components of stochastic reaction-diffusion operator splitting in the literature and discuss their effects on accuracy. We introduce an operator splitting implementation for irregular meshes that enhances accuracy with minimal performance cost. We test a range of models in small-scale MPI simulations from simple diffusion models to realistic biological models and find that multi-dimensional geometry partitioning is an important consideration for optimum performance. We demonstrate performance gains of 1-3 orders of magnitude in the parallel implementation, with peak performance strongly dependent on model specification.
Swift heavy ion irradiation of metal containing tetrahedral amorphous carbon films
Karaseov, P. A.; Protopopova, V. S.; Karabeshkin, K. V.; Shubina, E. N.; Mishin, M. V.; Koskinen, J.; Mohapatra, S.; Tripathi, A.; Avasthi, D. K.; Titov, A. I.
2016-07-01
Thin carbon films were grown at room temperature on (0 0 1) n-Si substrate using dual cathode filtered vacuum arc deposition system. Graphite was used as a source of carbon atoms and separate metallic electrode was simultaneously utilized to introduce Ni or Cu atoms. Films were irradiated by 100 MeV Ag7+ ions to fluences in the range 1 × 1010-3 × 1011 cm-2. Rutherford backscattering spectroscopy, Raman scattering, scanning electron microscopy and atomic force microscopy in conductive mode were used to investigate film properties and structure change under irradiation. Some conductive channels having metallic conductivity type were found in the films. Number of such channels is less than number of impinged ions. Presence of Ni and Cu atoms increases conductivity of those conductive channels. Fluence dependence of all properties studied suggests different mechanisms of swift heavy ion irradiation-induced transformation of carbon matrix due to different chemical effect of nickel and copper atoms.
Dune-CurvilinearGrid: Parallel Dune Grid Manager for Unstructured Tetrahedral Curvilinear Meshes
Fomins, Aleksejs; Oswald, Benedikt
2016-01-01
We introduce the dune-curvilineargrid module. The module provides the self-contained, parallel grid manager, as well as the underlying elementary curvilinear geometry module dune-curvilineargeometry. This work is motivated by the need for reliable and scalable electromagnetic design of nanooptical devices. Curvilinear geometries improve both the accuracy of modeling smooth material boundaries, and the h/p-convergence rate of PDE solutions, reducing the necessary computational effort. dune-cur...
Swift heavy ion irradiation of metal containing tetrahedral amorphous carbon films
Energy Technology Data Exchange (ETDEWEB)
Karaseov, P.A., E-mail: platon.karaseov@spbstu.ru [Peter the Great St. Petersburg Polytechnic University, St. Petersburg (Russian Federation); Protopopova, V.S. [Aalto University, Espoo (Finland); Karabeshkin, K.V.; Shubina, E.N.; Mishin, M.V. [Peter the Great St. Petersburg Polytechnic University, St. Petersburg (Russian Federation); Koskinen, J. [Aalto University, Espoo (Finland); Mohapatra, S. [Guru Gobind Singh Indraprastha University, New Delhi (India); Tripathi, A. [Inter University Accelerator Center, New Delhi (India); Avasthi, D.K. [Amity University, Noida 201313, Uttar Pradesh (India); Titov, A.I. [Peter the Great St. Petersburg Polytechnic University, St. Petersburg (Russian Federation)
2016-07-15
Highlights: • ta-C films with Ni and Cu doping were grown using dual cathode filtered vacuum arc deposition. • Conductive channels were found in the films by C-AFM after irradiation with 100 MeV Ag ions. • SEM contrast found after irradiation strongly depends on kind of metal impurity in the film. • Different chemical effect of Ni and Cu on transformation of carbon matrix under irradiation was revealed. - Abstract: Thin carbon films were grown at room temperature on (0 0 1) n-Si substrate using dual cathode filtered vacuum arc deposition system. Graphite was used as a source of carbon atoms and separate metallic electrode was simultaneously utilized to introduce Ni or Cu atoms. Films were irradiated by 100 MeV Ag{sup 7+} ions to fluences in the range 1 × 10{sup 10}–3 × 10{sup 11} cm{sup −2}. Rutherford backscattering spectroscopy, Raman scattering, scanning electron microscopy and atomic force microscopy in conductive mode were used to investigate film properties and structure change under irradiation. Some conductive channels having metallic conductivity type were found in the films. Number of such channels is less than number of impinged ions. Presence of Ni and Cu atoms increases conductivity of those conductive channels. Fluence dependence of all properties studied suggests different mechanisms of swift heavy ion irradiation-induced transformation of carbon matrix due to different chemical effect of nickel and copper atoms.
Kobayashi, Tsuyoshi
2012-01-01
We provide a detailed proof of the following folklore theorem: Let mu > 0 be a Margulis constant for 3-dimensional hyperbolic space. Then for any d>0 there exists a constant K>0, depending on mu and d, so that for any complete finite volume hyperbolic 3-manifold M, the d-neighborhood of the mu-thick part of M can be triangulated using at most K Vol(M) tetrahedra; here Vol is the hyperbolic volume function. As a corollary, we obtain the following topological interpretation of the volume: the minimal number of tetrahedra required to triangulate a link exterior in M is linearly equivalent to Vol(M); for a precise statement see Corollary 1.3.
Tobias, C.; Böhlke, J.K.
2011-01-01
Movement of dissolved inorganic carbon (DIC) through the hydrologic cycle is an important component of global carbon budgets, but there is considerable uncertainty about the controls of DIC transmission from landscapes to streams, and through river networks to the oceans. In this study, diel measurements of DIC, ??13C-DIC, dissolved oxygen (O2), ??18O-O2, alkalinity, pH, and other parameters were used to assess the relative magnitudes of biological and geochemical controls on DIC cycling and flux in a nutrient-rich, net autotrophic stream. Rates of photosynthesis (P), respiration (R), groundwater discharge, air-water exchange of CO2, and carbonate precipitation/dissolution were quantified through a time-stepping chemical/isotope (12C and 13C, 16O and 18O) mass balance model. Groundwater was the major source of DIC to the stream. Primary production and carbonate precipitation were equally important sinks for DIC removed from the water column. The stream was always super-saturated with respect to carbonate minerals, but carbonate precipitation occurred mainly during the day when P increased pH. We estimated more than half (possibly 90%) of the carbonate precipitated during the day was retained in the reach under steady baseflow conditions. The amount of DIC removed from the overlying water through carbonate precipitation was similar to the amount of DIC generated from R. Air-water exchange of CO2 was always from the stream to the atmosphere, but was the smallest component of the DIC budget. Overall, the in-stream DIC reactions reduced the amount of CO2 evasion and the downstream flux of groundwater-derived DIC by about half relative to a hypothetical scenario with groundwater discharge only. Other streams with similar characteristics are widely distributed in the major river basins of North America. Data from USGS water quality monitoring networks from the 1960s to the 1990s indicated that 40% of 652 stream monitoring stations in the contiguous USA were at or above the equilibrium saturation state for calcite, and 77% of all stations exhibited apparent increases in saturation state from the 1960/70s to the 1980/90s. Diel processes including partially irreversible carbonate precipitation may affect net carbon fluxes from many such watersheds. ?? 2010 Elsevier B.V.
Paisani, Julio Cesar; Pontelli, Marga Eliz; Osterrieth, Margarita Luisa; Paisani, Sani Daniela Lopes; Fachin, Andressa; Guerra, Simone; Oliveira, Leandro
2014-10-01
The Araucaria Plateau is a geomorphological unit that occupies approximately three-quarters of the terrain in the southern region of Brazil. The plateau displays different altitudinal levels (600 to S8-S1). These surfaces are maintained by basic (S3-S8) and acidic (S1 and S2) volcanic flows from the Neocretaceous period of the Paraná Basin. The largest extent of this plateau is located in a humid subtropical climate zone. Colluvial, colluvial-alluvial, alluvial sediments and paleosols (Ab diagnostic horizons) occur predominantly in S2. The paleosols are located in low-hierarchical-order fossil valleys (first- to fourth-order in Strahler's stream classification) and valley heads, which are referred to as paleovalleys in this paper. We employed these paleosols as stratigraphic level markers of the pedogenesis of the regional Upper Quaternary and propose their importance as records of the paleoenvironmental conditions of the Araucaria Plateau in areas above 1200 m a.s.l. These paleosols were dated by 14C and show ages between 23.8 ± 0.05 kyr BP (28.06-29.08 kyr cal. BP) and 41.16 ± 0.48 kyr BP (44.13-45.58 kyr cal. BP). The calibrated ages are related to Marine Isotope Stage 3 (MIS 3), in which the last period of global warming occurred (approximately 60-25 kyr cal. BP). We integrated the morphological, pedogeochemical, clay fraction mineralogy, micromorphological and δC-13 analyses of five paleosols from S2 to verify the paleoenvironmental conditions of the Araucaria Plateau and its correspondence with the paleoclimatic phenomena that were identified on a global scale during MIS 3 in the Southern Hemisphere. We obtained the following conclusions: a) the properties of paleosols reflect pedological processes that are adjusted to the paleoenvironmental conditions at the end of MIS 3 and the transition to MIS 2 (Last Glacial Maximum); b) aplasmogenic partial acidolysis was the predominant pedogeochemical process during MIS 3; c) during this period, the water regime was sufficiently humid to develop hydromorphic horizons in the valley bottoms of the entire drainage network to the valley heads; d) regional change toward a drier hydric regime occurred in MIS 2, when erosion of the paleosols predominated; and e) in MIS 1 (current Holocene interglacial), burial of the paleosols and relief inversion occurred, which resulted in fossilization of the valleys.
Institute of Scientific and Technical Information of China (English)
李俊昌; 马琨; 樊则宾
2002-01-01
The vertical excitation axial-flux kilowatt CO2 laser is an equipment widely used in the high-power laser heat treatment industrial applications. The experimental measurements indicate that the power density distribution of laser beam is generally of ring distribution with a sunken at the center, therefore the laser beam cannot be simply regarded as base mode Gaussian beam. In this paper, such laser beam is regarded as the non-interference superposition of TEM00 and TEM01 mode beams, the method to determine the simulation parameters is discussed, and the relevant heat effect calculation equation is deduced.
Cocho, Germinal; Miramontes, Pedro; Mansilla, Ricardo; Li, Wentian
2014-12-01
We examine the relationship between exponential correlation functions and Markov models in a bacterial genome in detail. Despite the well known fact that Markov models generate sequences with correlation function that decays exponentially, simply constructed Markov models based on nearest-neighbor dimer (first-order), trimer (second-order), up to hexamer (fifth-order), and treating the DNA sequence as being homogeneous all fail to predict the value of exponential decay rate. Even reading-frame-specific Markov models (both first- and fifth-order) could not explain the fact that the exponential decay is very slow. Starting with the in-phase coding-DNA-sequence (CDS), we investigated correlation within a fixed-codon-position subsequence, and in artificially constructed sequences by packing CDSs with out-of-phase spacers, as well as altering CDS length distribution by imposing an upper limit. From these targeted analyses, we conclude that the correlation in the bacterial genomic sequence is mainly due to a mixing of heterogeneous statistics at different codon positions, and the decay of correlation is due to the possible out-of-phase between neighboring CDSs. There are also small contributions to the correlation from bases at the same codon position, as well as by non-coding sequences. These show that the seemingly simple exponential correlation functions in bacterial genome hide a complexity in correlation structure which is not suitable for a modeling by Markov chain in a homogeneous sequence. Other results include: use of the (absolute value) second largest eigenvalue to represent the 16 correlation functions and the prediction of a 10-11 base periodicity from the hexamer frequencies.
Szomborg, Katarzyna; Jongekrijg, Fleur; Gilchrist, Elizabeth; Webb, Tony; Wood, Dan; Barron, Leon
2013-12-10
A quantitative study of common forensic evidence collection devices for the recovery of low-explosive residues from non-porous glass and plastic is presented herein. Swabbing materials including cotton, rayon, Nomex(®) (poly(isophthaloylchloride/m-phenylenediamine)), Teflon/Teflon-coated fibreglass (polytetrafluoroethylene) and adhesive-coated tapes were used to collect known quantities of up to 14 forensically relevant inorganic and organic anion and cation species from both surfaces. Analysis was performed using two validated ion chromatography methods. This study revealed that all swabs and surfaces contributed highly variable levels of interfering ionic species and that swabbing materials showed variance in the quantities and total number of analytes recovered from both surfaces. Teflon and Nomex(®) materials demonstrated the most promise due to their ability to collect and release analytes into simple extraction solvents as well as displaying relatively low endogenous interference. In parallel, the ability to extract residue directly from both surfaces via the addition of a suitable extraction solvent was investigated instead of swabbing. This work highlights that direct solvent extraction from a surface should be considered as an alternative approach, especially for small areas or objects. To the best of our knowledge, this work represents the most comprehensive study of the efficiencies of sample collection technologies for low-explosive residues prior to analysis by ion chromatography.
Sundararajan, Mahesh; Ganyushin, Dmitry; Ye, Shengfa; Neese, Frank
2009-08-14
A newly developed multireference (MR) ab initio method for the calculation of magnetic circular dichroism (MCD) spectra was calibrated through the calculation of the ground- and excited state properties of seven high-spin (S = 3/2) Co(II) complexes. The MCD spectra were computed by the explicit treatment of spin-orbit coupled (SOC) and spin-spin coupled (SSC) N-electron states. For the complexes studied in this work, we found that the SOC is more important than the SSC for determining the ground state zero field splitting (ZFS). Our computed ZFS parameter D for the [Co(PPh(3))(2)Cl(2)] model complex is -17.6 cm(-1), which is reasonably close to the experimental value of -14.8 cm(-1). Generally, the computed absorption and MCD spectra are in fair agreement with experiment for all investigated complexes. Thus, reliable electronic structure and spectroscopic predictions for medium sized transition metal complexes are feasible on the basis of this methodology. This characterizes the presented method as a promising tool for MCD spectra interpretations of transition metal complexes in a variety of areas of chemistry and biology.
Thermoelectric transport properties of diamond-like Cu1-xFe1+xS2 tetrahedral compounds
Li, Yulong; Zhang, Tiansong; Qin, Yuting; Day, Tristan; Jeffrey Snyder, G.; Shi, Xun; Chen, Lidong
2014-11-01
Polycrystalline samples with the composition of Cu1-xFe1+xS2 (x = 0, 0.01, 0.03, 0.05, 0.1) were synthesized by a melting-annealing-sintering process. X-ray powder diffraction reveals all the samples are phase pure. The backscattered electron image and X-ray map indicate that all elements are distributed homogeneously in the matrix. The measurements of Hall coefficient, electrical conductivity, and Seebeck coefficient show that Fe is an effective n-type dopant in CuFeS2. The electron carrier concentration of Cu1-xFe1+xS2 is tuned within a wide range leading to optimized power factors. The lattice phonons are also strongly scattered by the substitution of Fe for Cu, leading to reduced thermal conductivity. We use Debye approximation to model the low temperature lattice thermal conductivity. It is found that the large strain field fluctuation introduced by the disordered Fe ions generates extra strong phonon scatterings for lowered lattice thermal conductivity.
Alzamly, Ahmed; Gambarotta, Sandro; Korobkov, Ilia; Murugesu, Muralee; Le Roy, Jennifer J H; Budzelaar, Peter H M
2014-06-16
A chromium complex [2-(NHCH2PPh2)C5H4N]CrCl3·THF2 (1) of the ligand PyNHCH2PPh2 has been synthesized, characterized, and examined for its catalytic behavior toward ethylene oligomerization. When complex 1 was treated with (i-Bu)3Al, an unprecedented divalent polyhydride chromium cluster μ,κ(1),κ(2),κ(3)-N,N,P-{[2-(NCH2PPh2)C5H4N]Cr(μ-H)}4[(μ-Cl)Cr(μ-Cl)Al(i-Bu)2Cl]2 (2) was obtained. The complex contains a Cr4H4 core, which is expected to be diamagnetic, and which remains coordinated to two additional divalent high-spin Cr atoms via bridging interactions. Two aluminate residues remain bonded to the peripheral chromium atoms. The structure, magnetism, and electronic configuration are herein discussed.
Sarı, Nurşen; Şahin, Songül Çiğdem; Öğütcü, Hatice; Dede, Yavuz; Yalcin, Soydan; Altundaş, Aliye; Doğanay, Kadir
2013-04-01
A new amine containing selenium and their five imine, (SeSchX)(X: -H, F, Cl, Br, CH3), and Ni (II) complexes, [Ni(SeSchX)(H2O)2]Cl/[Ni(SeSchCl)(H2O)Cl], were synthesized. The compounds were characterized by means of elemental analyses, 13C and 1H NMR (for imine), FT-IR, UV-Visible spectroscopy, TGA/DTA and elemental analyses. [Ni(SeSchCl)(H2O)Cl] complex from Ni(II) complexes changes color from yellow to orange in the range pH 5-7. [Ni(SeSchCl)(H2O)Cl] complex has ligand-to-metal charge-transfer (LMCT) transitions in the basic medium. Excitation characteristics and energetic of [Ni(SeSchCl)(H2O)Cl] complex, examined via TD-DFT calculations, reveals transitions of LMCT and π → π* character that matches the experimental values. [Ni(SeSchCl)(H2O)Cl] complex showed the highest antibacterial activity when compared to other complexes reported in this work.
DEFF Research Database (Denmark)
Møgelhøj, Andreas; Kelkkanen, Kari André; Wikfeldt, K Thor
2011-01-01
The structure of liquid water at ambient conditions is studied in ab initio molecular dynamics simulations in the NVE ensemble using van der Waals (vdW) density-functional theory, i.e., using the new exchange-correlation functionals optPBE-vdW and vdW-DF2, where the latter has softer nonlocal...... shows some resemblance with experiment for high-density water ( Soper , A. K. and Ricci , M. A. Phys. Rev. Lett. 2000 , 84 , 2881 ), but not directly with experiment for ambient water. Considering the accuracy of the new functionals for interaction energies, we investigate whether the simulation...... protocol could cause the deviation. An O-O PCF consisting of a linear combination of 70% from vdW-DF2 and 30% from low-density liquid water, as extrapolated from experiments, reproduces near-quantitatively the experimental O-O PCF for ambient water. This suggests the possibility that the new functionals...
Tujunen, Noora; Kaivosoja, Emilia; Protopopova, Vera; Valle-Delgado, Juan José; Österberg, Monika; Koskinen, Jari; Laurila, Tomi
2015-10-01
Hydrogen peroxide is the product of various enzymatic reactions, and is thus typically utilized as the analyte in biosensors. However, its detection with conventional materials, such as noble metals or glassy carbon, is often hindered by slow kinetics and biofouling of the electrode. In this study electrochemical properties and suitability to peroxide detection as well as ability to resist biofouling of Pt-doped ta-C samples were evaluated. Pure ta-C and pure Pt were used as references. According to the results presented here it is proposed that combining ta-C with Pt results in good electrocatalytic activity towards H2O2 oxidation with better tolerance towards aqueous environment mimicking physiological conditions compared to pure Pt. In biofouling experiments, however, both the hybrid material and Pt were almost completely blocked after immersion in protein-containing solutions and did not produce any peaks for ferrocenemethanol oxidation or reduction. On the contrary, it was still possible to obtain clear peaks for H2O2 oxidation with them after similar treatment. Moreover, quartz crystal microbalance experiment showed less protein adsorption on the hybrid sample compared to Pt which is also supported by the electrochemical biofouling experiments for H2O2 detection.
Directory of Open Access Journals (Sweden)
B. A. Golodenko
2013-01-01
Full Text Available The technique and results of an experimental research of power conditions of amorphous alloy hydrogenated carbide silicon is described. Application of power spectra of a silicon valence zone for definition phase structure of its amorphous hydrogenated carbide is shown. Quantitative dependence of a share carbide phases of silicon in structure of its alloy from the maintenance of methane in an initial gas mix is established.
Mollemans, W.; Schutyser, F.; Nadjmi, N.; Maes, F.; Suetens, P.
2006-03-01
In this paper we present an extensive quantitative validation on 3D facial soft tissue simulation for maxillofacial surgery planning. The study group contained 10 patients. In previous work we presented a new Mass Tensor Model to simulate the new facial appearance after maxillofacial surgery in a fast way. 10 patients were preoperatively CT-scanned and the surgical intervention was planned. 4 months after surgery, a post-operative control CT was acquired. In this study, the simulated facial outlook is compared with post-operative image data. After defining corresponding points between the predicted and actual post-operative facial skin surface, using a variant of the non-rigid TPS-RPM algorithm, distances between these correspondences are quantified and visualized in 3D. As shown, the average median distance measures only 0.60 mm and the average 90% percentile stays below 1.5 mm. We can conclude that our model clearly provides an accurate prediction of the real post-operative outcome and is therefore suitable for use in clinical practice.
Institute of Scientific and Technical Information of China (English)
孙林
2002-01-01
提出了一种利用干涉级较低的牛顿环条纹测平凸透镜的曲面半径的新方法,以相同的明暗边界作为依据,由干涉条纹的宽度及高度差即可求出平凸透镜的曲率半径.
Alternative quadratic programming for non-negative matrix low-order factorization%非负矩阵低秩分解的交替二次规划算法
Institute of Scientific and Technical Information of China (English)
阳明盛; 刘力军
2014-01-01
非负矩阵分解算法有多种，但都存在着各自的缺陷。在现有工作的基础上，将非负矩阵分解(NMF)模型转化为一组(两个)二次凸规划模型，利用二次凸规划有解的充分必要条件推导出迭代公式，进行交替迭代，可求出问题的解。得到的解不仅具有某种最优性、稀疏性，还避免了约束非线性规划求解的复杂过程和大量的计算。证明了迭代的收敛性，且收敛速度快于已知的方法，对于大规模数据模型尤能显示出其优越性。%Many algorithms are available for solving the problem of non-negative matrix factorization (NMF)despite respective shortcomings.Based on existing works,NMF model is transformed into one group of (two ) convex quadratic programming model. Using the sufficient and necessary conditions for quadratic programming problems,iteration formula for NMF is obtained by which the problem is solved after alternative iteration process.The obtained solution reaches its optimality and sparseness while avoiding computational burden and complexity for solving constrained nonlinear programming problems.The iteration convergence can be proved easily and its speed is faster than that of existing approaches.The proposed approach has its superority for large-scale data model.
Energy Technology Data Exchange (ETDEWEB)
Brun, J. F., E-mail: brun@cnrs-orleans.fr [CNRS, UPR 3079 CEMHTI, Orléans 45071 (France); UFR Collégium Sciences et Techniques, Université d' Orléans, Orléans 45067 (France); Campo, L. del; De Sousa Meneses, D. [CNRS, UPR 3079 CEMHTI, Orléans 45071 (France); Polytech' Orléans, Université d' Orléans, 45072 Orléans (France); Echegut, P. [CNRS, UPR 3079 CEMHTI, Orléans 45071 (France)
2013-12-14
The normal spectral emittance of α-Al{sub 2}O{sub 3} single crystal has been measured from room temperature up to the liquid state and from 20 cm{sup −1} up to 10 000 cm{sup −1}, in two polarization configurations. The spectra were fitted with a semi-quantum dielectric function model. AlO{sub 4} structure units are revealed within the phonon spectral range more than a hundred degrees below the melting point when heating from the solid state. In parallel, the anomalous increase of emittance observed within the transparency spectral range with the approach to melting appears strongly correlated. Implications on the electronic structure are discussed: the existence of small polaron conduction is suggested which has never been mentioned before.
Energy Technology Data Exchange (ETDEWEB)
Li, Yulong; Qin, Yuting [State Key Laboratory of High Performance Ceramics and Superfine Microstructure, Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai 200050 (China); CAS Key Laboratory of Materials for Energy Conversion, Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai 200050 (China); University of Chinese Academy of Sciences, Beijing 100049 (China); Zhang, Tiansong; Shi, Xun, E-mail: xshi@mail.sic.ac.cn, E-mail: cld@mail.sic.ac.cn; Chen, Lidong, E-mail: xshi@mail.sic.ac.cn, E-mail: cld@mail.sic.ac.cn [State Key Laboratory of High Performance Ceramics and Superfine Microstructure, Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai 200050 (China); CAS Key Laboratory of Materials for Energy Conversion, Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai 200050 (China); Day, Tristan; Jeffrey Snyder, G. [Department of Materials Science, California Institute of Technology, Pasadena, California 91125 (United States)
2014-11-28
Polycrystalline samples with the composition of Cu{sub 1−x}Fe{sub 1+x}S{sub 2} (x = 0, 0.01, 0.03, 0.05, 0.1) were synthesized by a melting-annealing-sintering process. X-ray powder diffraction reveals all the samples are phase pure. The backscattered electron image and X-ray map indicate that all elements are distributed homogeneously in the matrix. The measurements of Hall coefficient, electrical conductivity, and Seebeck coefficient show that Fe is an effective n-type dopant in CuFeS{sub 2}. The electron carrier concentration of Cu{sub 1−x}Fe{sub 1+x}S{sub 2} is tuned within a wide range leading to optimized power factors. The lattice phonons are also strongly scattered by the substitution of Fe for Cu, leading to reduced thermal conductivity. We use Debye approximation to model the low temperature lattice thermal conductivity. It is found that the large strain field fluctuation introduced by the disordered Fe ions generates extra strong phonon scatterings for lowered lattice thermal conductivity.
Energy Technology Data Exchange (ETDEWEB)
Li, Linping [Xinjiang Key Laboratory of Electronic Information Material and Devices, Xinjiang Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, 40-1 South Beijing Road, Urumqi 830011 (China); School of Physics Science and Technology, Xinjiang University, Urumqi 830046 (China); Jing, Qun; Yang, Zhihua, E-mail: zhyang@ms.xjb.ac.cn, E-mail: zhj@xju.edu.cn; Su, Xin; Lei, Bing-Hua; Pan, Shilie; Zhang, Fangfang [Xinjiang Key Laboratory of Electronic Information Material and Devices, Xinjiang Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, 40-1 South Beijing Road, Urumqi 830011 (China); Zhang, Jun, E-mail: zhyang@ms.xjb.ac.cn, E-mail: zhj@xju.edu.cn [School of Physics Science and Technology, Xinjiang University, Urumqi 830046 (China)
2015-09-21
As potential candidates for deep-UV nonlinear optical (NLO) crystals, borosilicates and borogermanates, which contain NLO-active groups such as B-O, Si-O, and Ge-O groups, have fascinated many material scientists' research enthusiasm. In this paper, the electronic structures and optical properties of two isostructural noncentrosymmetric crystals LaBRO{sub 5} (R = Si and Ge) have been studied by the first-principles method. Combined with the analyses of the SHG-density and the localized electron-density difference, contributions of the constituent tetrahedra to the total NLO responses are investigated. Eventually, BO{sub 4} and GeO{sub 4} groups give nearly equal contributions to the SHG effect of LaBGeO{sub 5}, but for LaBSiO{sub 5}, SiO{sub 4} groups express stronger SHG response than that of BO{sub 4}. Such interesting conclusion is consistent with the distortion index analyses and dipole moment.
Energy Technology Data Exchange (ETDEWEB)
Goldberg, A.; El-Batanouny, M.; Wooten, F.
1982-12-15
The phonon dispersion curves and phonon density of states for silicon in the BC-8 structure have been calculated with the use of Weber's adiabatic-bond-charge model. All parameters were scaled in an unambiguous physical manner from Weber's values for silicon in the diamond structure. The frequency values at GAMMA agree to within 10% of those values available from Raman spectroscopy. The GAMMA/sub 1//sup -/ mode is compatible with a transformation from the BC-8 structure to the wurtzite structure, a transformation that takes place upon heating the BC-8 polymorph.
Goldberg, A.; El-Batanouny, M.; Wooten, F.
1982-12-01
The phonon dispersion curves and phonon density of states for silicon in the BC-8 structure have been calculated with the use of Weber's adiabatic-bond-charge model. All parameters were scaled in an unambiguous physical manner from Weber's values for silicon in the diamond structure. The frequency values at Γ agree to within 10% of those values available from Raman spectroscopy. The Γ-1 mode is compatible with a transformation from the BC-8 structure to the wurtzite structure, a transformation that takes place upon heating the BC-8 polymorph.
Laha, Sourav; Tamilarasan, Subramani; Natarajan, Srinivasan; Gopalakrishnan, Jagannatha
2016-04-04
An experimental investigation of the stabilization of the turquoise-colored chromophore Mn(5+)O4 in various oxide hosts, viz., A3(VO4)2 (A = Ba, Sr, Ca), YVO4, and Ba2MO4 (M = Ti, Si), has been carried out. The results reveal that substitution of Mn(5+)O4 occurs in Ba3(VO4)2 forming the entire solid solution series Ba3(V1-xMnxO4)2 (0 concept, we synthesized new turquoise-colored Mn(5+)O4 materials, Ba5(BO3)(MnO4)2Cl and Ba5(BO3)(PO4)(MnO4)Cl, based on the apatite-Ba5(PO4)3Cl-structure.
基于LEPP递变的四面体网格自适应剖分算法%Adaptive Tetrahedral Mesh Generation Based on LEPP Algorithm
Institute of Scientific and Technical Information of China (English)
刘君; 朱善安; HE B
2008-01-01
为了更合理地进行四面体网格剖分,提出了一种根据待剖分对象形态不同进行网格密度自适应调整的四面体网格削分方法.该方法首先采用BCC(body-centered cubic)网格初始化网格空间,并根据表面曲率的大小以及距离物体表面的远近,采用LEPP(logest edge propagation path)算法由外至内对初始化后的网格空间进行不同尺度的细分;然后对横跨表面的网格进行调整,以形成对象的表面形态;最后采用以质量函数引导的拉普拉斯平滑与棱边收缩(edge collapse)的方法对网格的质量进行优化来最终得到待剖分对象的四面体网格.结果表明,该方法所生成的网格不仅具有自适应的网格密度,而且网格质量比常用的Advancing Front算法也有所提高.对于基于3维断层图像或表面模型进行有限元建模,该方法不失为一种行之有效的好方法.
Nolas, George S.; Hassan, M. Shafiq; Dong, Yongkwan; Martin, Joshua
2016-10-01
Quaternary chalcogenides form a large class of materials that continue to be of interest for energy-related applications. Certain compositions have recently been identified as possessing good thermoelectric properties however these materials typically have the kesterite structure type with limited variation in composition. In this study we report on the structural, optical and electrical properties of the quaternary chalcogenides CuZn2InTe4 and CuCd2InTe4 which crystallize in the modified zinc-blende crystal structure, and compare their properties with that of CuZn2InSe4. These p-type semiconductors have direct band gaps of about 1 eV resulting in relatively high Seebeck coefficient and resistivity values. This work expands on the research into quaternary chalcogenides with new compositions and structure types in order to further the fundamental investigation of multinary chalcogenides for potential thermoelectrics applications.
根据STL文件生成三维四面体网格%Generation of 3-D Tetrahedral Mesh from Stereolithography(STL) Files
Institute of Scientific and Technical Information of China (English)
李海生; 杨钦; 陈其明
2003-01-01
STL文件通过记录一系列的三角形集合信息表示实体的边界几何信息.给出了一种从STL文件生成实体的边界一致的符合Delaunay准则的四面体网格的方法,并对生成的四面体网格进行尺度控制及质量优化,从而得到适合于有限元分析的四面体网格.该方法为CAD/CAE的集成提供了一种思路.
Welsch, Stefan; Lescop, Christophe; Balazs, Gabor; Réau, Régis; Scheer, Manfred
2011-08-08
The reaction of the [{CpMo(CO)(2)}(2)(μ,η(2):η(2)-P(2))] (Cp=cyclopentadienyl) metallo-ligand 2 with pre-organized Cu(I) bi- and trimetallic precursors afforded new coordination complexes with unprecedented coordination modes for a Mo(2)P(2) complex. Variable-temperature solution and solid-state (31)P NMR spectroscopy measurements were performed and X-ray diffraction studies revealed an η(2):η(1) coordination mode for the Mo(2)P(2) unit of 2 in the Cu(I) bimetallic complexes 3 and 4. DFT calculations were carried out to highlight the bonding situation of this unprecedented coordination mode in the Cu(I) bimetallic compound 3. It is built up from a side-on coordination of the P-P σ bond to one copper ion and from the interaction of the lone pair of one phosphorus atom with the second copper ion. The remaining available lone pair of the second phosphorus atom can be involved as well to interact with an additional metal centre, as evidenced in the Cu(I) trimetallic compound 5 in which an η(2):η(1):η(1) coordination mode of the ligand 2 is observed. Derivative 3 can be used as a molecular clip to obtain discrete π-stacked dimers through a ligand exchange reaction between acetonitrile ligands and cyano-capped π-conjugated systems, indicating the stability of the new η(2):η(1) coordination mode. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Structure characterization for the geopolymer of sodium silicate and metakaolin
Institute of Scientific and Technical Information of China (English)
CAO De-guang; SU Da-gen
2005-01-01
Geopolymers of metakaolin and sodium silicate were synthesized respectively with the ratios of the amount of SiO2 in the sodium silica solution to that of Al2O3 in metakaolinite equal to 1.0, and 0.66. The geopolymeric structures of the products were investigated by 27Al and 29Si solid-state nuclear magnetic resonances with magic-angle spinning (MAS NMR), Fourier transform infrared spectroscopy (FTIR), X-ray powder diffraction (XRD), differential scanning colorimetry (DSC) and scanning electron microscopy (SEM). The reaction of the Al-O sheet in meakaolinite with low-order polymerized Si-O tetrahedral units such as monomer of SiO4 yields three-dimensional structures with the Q3 Si-O tetrahedral structure and the coordination of Al(IV) in the Al-O tetrahedral structure. The geopolymers are essentially X-ray amorphous. The assays by 27Al and 29Si NMR, FTIR confirm that the active structure in the metakaolinite is the sheet of Al-O with three coordination states.
Institute of Scientific and Technical Information of China (English)
万敏; 苏毅; 向汝建
2001-01-01
The residual phase error after correction for turbulence-induced phase aberrations by a partially compensating adaptive optics system (with temporal lag and limited space resolution) is computed by using the phase expansion on the Zernike polynomials in this paper. The computation can be used to derive the maximum order of aberration to be corrected to get the most from the compensation. The partially compensating adaptive optics system with Rayleigh beacon or sodium beacon as reference is computed also in this paper. The results show, the system with sodium beacon requires higher space frequency than the system with Rayleigh beacon. And the off-axis anisoplanatism effect due to the angular separation between the object and the beacon or the system temporal lag is more serious for the system with sodium beacon. The correction for high order aberration is more suitable for the system with sodium beacon than the system with Rayleigh beacon.%在对大气湍流相位扰动进行Zernike多项式展开的基础上，通过对信标和目标光的Zernike系数相关因子的推导,得到了实际自适应光学系统（系统存在时间滞后和有限的空间分辨率）对相位扰动各阶像差的校正残差公式。同时结合实际，对瑞利导星以及钠导星自适应光学系统补偿大气湍流各阶像差的能力进行了计算和分析，为实际自适应光学系统的设计提供了理论参考。
Directory of Open Access Journals (Sweden)
EVELYN HABIT
2003-03-01
Full Text Available RESUMEN El estero Nonguén (orden 3, tributario de la zona inferior del río Andalién (región del Bío-Bío, presenta una marcada diferencia entre su parte alta ritral, bien conservada y con un bosque secundario de Nothofagus, y su parte baja potamal, de uso urbano y de aguas con contaminación orgánica. Este contraste podría implicar la alteración de los patrones normales detectados en la ictiofauna chilena descritos para diversos sistemas fluviales. Tales patrones consisten en un aumento del número de especies, individuos y diversidad en el sentido de la corriente, así como en un incremento de las tallas corporales de los individuos que habitan las zonas bajas. Se estudió la composición específica de peces del estero Nonguén y sus patrones comunitarios a lo largo del sistema fluvial en un ciclo anual. Se encontró un incremento en la riqueza específica, desde cuatro especies en el ritrón a diez en el sector de desembocadura. Tanto la diversidad, abundancia y distribución de los peces varió según la época del año, reflejando los desplazamientos asociados a la ontogenia, reproducción y alimentación de la fauna íctica. Las estaciones de la zona media y baja del estero presentaron un ensamble con individuos de menor tamaño que los que se encuentran en la cabecera, consistentemente con la dominancia de salmónidos de mayor talla en la parte alta. Los resultados sugieren que: (i la alteración del área potamal no modifica significativamente los patrones característicos de la ictiofauna de sistemas fluviales, y que (ii el estero Nonguén es un sistema de reproducción y crianza de juveniles de especies nativas e introducidas, las cuales conforman asociaciones permanentes en este sistema fluvial.ABSTRACT The Nonguén stream (order 3 is a lower zone tributary of the Andalién river coastal mountain basin (Bio-Bío region which displays a marked difference between its rithral sector (well-conserved and with a secondary Nothofagus forest and its potamal area (urbanly-used and organically polluted waters. This contrast could imply an alteration in the normal pattern of Chilean ichthyofauna, as described for a variety of fluvial systems in the country: a downstream increase in numbers of species, individuals, and diversity downstream, as well as increased corporal sizes of individuals in the lower zones of the river. Species composition of fishes of the Nonguén stream and their community patterns along the fluvial system within an annual cycle have been studied. The results show a high number of species in the lower parts, i.e. four species in the rithron and ten in the river mouth. The diversity, abundance and distribution of the fishes varied according to the season of the year, reflecting displacements associated with the fauna's ontogeny, reproduction and feeding. The sampling stations of the middle and lower zones of the river presented an assemblage with smaller individuals than those found at the head of the river, with the consistent dominance of larger salmonidae in the upper zone. Accordingly, it is suggested that: (i the alteration of the potamal area does not significantly modify the characteristic patterns of ichthyofauna in fluvial systems, and (ii the Nonguén stream is a reproduction and growth system for juveniles of both native and introduced species which make up permanent associations in the fluvial system.
Stegemann, Frank; Benndorf, Christopher; Zhang, Yuemei; Bartsch, Manfred; Zacharias, Helmut; Fokwa, Boniface P T; Eckert, Hellmut; Janka, Oliver
2017-02-20
Na2Au3Al, the first experimentally prepared compound in the ternary Na-Au-Al system, crystallizes in the cubic crystal system with space group P4132 (a = 771.42(2) pm). It can be described as a P-centered ternary ordered variant of the F-centered Laves phase MgCu2 and is isostructural to Mo3Al2C. A phase width was found for the series Na2Au4-xAlx allowing a successive substitution of Au by Al. The primitive structure forms for x ≥ 0.5. Na2Au3Al is diamagnetic at room temperature but metallic in nature, as seen from susceptibility and electrical resistivity measurements. Band structure calculations and X-ray photoelectron spectroscopy confirm the metallic nature of the title compound as states are found at the Fermi level of the DOS, along with its "auride" character. (23)Na and (27)Al solid-state-NMR investigations show the existence of both a disordered (x = 0.5 and 0.75) and a fully ordered (x = 1.0) representative within this series. Both COHP and Bader charge analyses suggest the presence of strong Au-Al interactions forming an anionic [Au3Al](δ-) network, with the Na cations occupying the cavities.
Pothoczki, Sz.; Temleitner, L.; Jóvári, P.; Kohara, S.; Pusztai, L.
2009-02-01
Neutron and x-ray weighted total scattering structure factors of liquid carbon, silicon, germanium, and tin tetrachlorides, CCl4, SiCl4, GeCl4, and SnCl4, have been interpreted by means of reverse Monte Carlo modeling. For each material the two sets of diffraction data were modeled simultaneously, thus providing sets of particle coordinates that were consistent with two experimental structure factors within errors. From these particle configurations, partial radial distribution functions, as well as correlation functions characterizing mutual orientations of molecules as a function of distance between molecular centers were calculated. Via comparison with reference systems, obtained by hard sphere Monte Carlo simulations, we demonstrate that orientational correlations characterizing these liquids are much longer ranged than expected, particularly in carbon tetrachloride.
Pothoczki, Sz; Temleitner, L; Jóvári, P; Kohara, S; Pusztai, L
2009-02-14
Neutron and x-ray weighted total scattering structure factors of liquid carbon, silicon, germanium, and tin tetrachlorides, CCl(4), SiCl(4), GeCl(4), and SnCl(4), have been interpreted by means of reverse Monte Carlo modeling. For each material the two sets of diffraction data were modeled simultaneously, thus providing sets of particle coordinates that were consistent with two experimental structure factors within errors. From these particle configurations, partial radial distribution functions, as well as correlation functions characterizing mutual orientations of molecules as a function of distance between molecular centers were calculated. Via comparison with reference systems, obtained by hard sphere Monte Carlo simulations, we demonstrate that orientational correlations characterizing these liquids are much longer ranged than expected, particularly in carbon tetrachloride.
Distorted Tetrahedral CoII in K5H[CoW12O40]·xH2O Probed by 2p3d Resonant Inelastic X-ray Scattering
Liu, LIU BY; Wang, Ru Pan; Glass, Elliot N.; Hill, Craig L.; Cuk, Tanja; Okamoto, Jun; Huang, Di Jing; Van Schooneveld, Matti M.; De Groot, Frank M F
2016-01-01
The Co 2p3/2 X-ray absorption spectroscopy and high-energy-resolution (∼0.09 eV fwhm) 2p3d resonant inelastic X-ray scattering (RIXS) spectra of the single-cobalt-centered polyoxometalate K5H[CoW12O40]·xH2O were measured. The low-energy dd transition features at 0.55 eV, unmeasurable with
Energy Technology Data Exchange (ETDEWEB)
Collis, W.J.
1995-06-01
This research program was originally defined to investigate the deposition of semiconductor and dielectric thin films using a low pressure remote plasma chemical vapor deposition system incorporating a process for etching the films. This etching was to be performed in a periodic fashion during the deposition process to remove defect regions in the film being deposited. The goal was to remove voids and other defects which are characteristic of low temperature deposition processes. While the original research proposal suggested that the studies include the amorphous alloys (Si/C):H and (Si/Ge):H, subsequent funding reductions limited the work to the deposition of an amorphous silicon alloy material (a-Si:H). Intrinsic and doped forms of these materials have applications in the fabrication of single and multi-junction thin film solar cells.
DEFF Research Database (Denmark)
Nielsen, Bo Bjerregaard; Nielsen, Martin S.; Santos, Ilmar
2017-01-01
) is presented. The developed element is based on a purely mechanical eight-node isoparametric layered element for a double curved shell, utilizing first-order shear deformation theory. The electromechanical coupling of piezoelectric material is added to all elements, but can also be excluded by setting...
Performance evaluation of lightweight piezocomposite curved actuator
Goo, Nam Seo; Kim, Cheol; Park, Hoon C.; Yoon, Kwang J.
2001-07-01
A numerical method for the performance evaluation of LIPCA actuators is proposed using a finite element method. Fully-coupled formulations for piezo-electric materials are introduced and eight-node incompatible elements used. After verifying the developed code, the behavior of LIPCA actuators is investigated.
Ring-element analysis of layered orthotropic bodies
DEFF Research Database (Denmark)
Jørgensen, O.
1993-01-01
to be determined in the finite element analysis. The element chosen is an eight node isoparametric element of the serendipity family. The Fourier series show very high rate of convergence for the problems solved. The investigation shows that the computational work is remarkably reduced in relation...
Firefighting Agent Research, Phase I
2007-04-01
Beowulf Linux cluster from Aspen Systems, Inc. This system contains eight nodes, each node having two 2.8 GHz processors and 2GB of memory, as... Clusters ........................................................................................................... 15 Aqueous Salts...14 Figure 11: A cluster of PFOA molecules solvated by water molecules. .......................... 14 Figure 18: Plots of temperature and
Liu, Ying-Ya; Grzywa, Maciej; Weil, Matthias; Volkmer, Dirk
2010-01-01
A novel metal-organic framework (MOF) based on a tetranuclear copper cluster and a linear organic ligand formulated as [Cu 4OCl 6(DABCO) 2] ·0.5DABCO ·4CH 3OH (denoted as MFU-5, MFU=Metal-Organic Framework, Ulm University; DABCO=1,4-diazabicyclo[2.2.2]octane), was prepared via solvothermal synthesis. In contrast with common MOF synthesis strategies, MFU-5 is assembled from pre-defined molecular secondary building units, i.e. {Cu 4OCl 6} moieties, which become the nodes of the coordination framework. The title compound was characterized by single crystal X-ray diffraction, variable temperature powder diffraction (VT-XRPD), thermal analysis, as well as IR- and UV/Vis spectroscopy. Crystal data for MFU-5: hexagonal, P6/ mcc (no. 192), a=25.645(9), c=17.105(11) Å, V=9742(8) Å 3, Z=12, 1690 structure factors, R[ F2>2 σ( F2)]=0.049. MFU-5 is a 3D metal-organic framework with 1D channels running along the c-axis hosting DABCO and methanol solvent molecules. The framework displays a zeolite-like structure constructed from mso cages, which represents the composite building units in the zeolites SSF, MSO and SZR. Two-fold interpenetration is observed between these building units. TG/DTA-MS and VT-XRPD characterization reveal a stepwise release of methanol and DABCO molecules upon heating, eventually resulting in a structural change into a non-porous material.
Energy Technology Data Exchange (ETDEWEB)
Schroeder, B.; Oechsner, H.
1998-07-31
In a comprehensive study we have investigated the effect of the most important deposition parameters on the electronic and microstructural properties of a-Si:H films, deposited by the thermocatalytic CVD, also called hot wire (HW) CVD. This method was found to be an attractive alternative to the plasma enhanced CVD realizing the deposition of amorphous and microcrystalline semiconductor films for solar cell application. Using relatively simple equipment device quality material can be deposited with high rates and large flexibility. Due to results obtained by thin film growth investigations employing the in-situ ellipsometry the material quality could be optimized in terms of microstructural properties. With the invention of a special process control, the microstructural interface engineering, the thermocatalytic CVD a-Si:H material was integrated in solar cells with a conversion efficiency of up to 10.2%. This value was obtained without using highly reflecting rear contacts and, even more, two until now unavoidable `air breaks`. The knowledge about the relationship between microstructure and stability, which was gained during the investigation within the project, enabled us to open up new ways to reduce the degradation of solar cells containing HW-a-Si:H. In that way solar cells with the same initial conversion efficiency but improved stability have been produced, depositing the HW-a-Si:H i-layer with moderate H-dilution. Also {mu}c-Si:H, a-SiGe:H, and a-Ge:H films could be deposited with large rates and high quality applying the TCCVD method. These materials which are important for stacked cell application could be integrated with good (a-SiGe:H) and less good effort ({mu}c-Si:H, a-Ge:H) into solar cell structures. (orig.) [Deutsch] Intensive und grundlegende Untersuchungen im Rahmen dieses Vorhabens haben ergeben, dass sog. `Hot wire (HW)` oder `thermokatalytische (TC)` CVD-Verfahren eine aeusserst attraktive Alternative zur Abscheidung von amorphem und mikrokristallinem Halbleitermaterial fuer Duennschicht-Solarzellen auf der Basis von Silizium darstellt. Mit diesem Verfahren, das mit einfacher apparativer Ausruestung eine schnelle und flexible Abscheidung von Schichten erlaubt, kann nicht nur hochwertiges (device grade) Material hergestellt, sondern dieses Material kann mit dieser Methode auch optimal in das Bauelement Solarzelle integriert werden. Aufgrund der Erkenntnisse aus in-situ ellipsometrischen Untersuchungen konnte das Wachstum der HW-a-Si:H-Schichten so optimiert werden, dass insbesondere die wichtigen Grenzflaechen aber auch das Volumenmaterial fuer Solarzellen mit einer geeigneten Mikrostruktur hergestellt werden kann. Der Wirkungsgrad von pin-Solarzellen, die diese HW-a-Si:H-Schichten enthalten, konnte so bereits auf Werte {eta}>10% gesteigert werden, obwohl noch Potential (besserer Rueckkontakt, keine Zwischenbelueftungen) fuer weitere Verbesserungen besteht. Das Verstaendnis des Zusammenhanges zwischen Mikrostruktur und Stabilitaet eroeffnet neue Wege zur Verringerung der Degradation von Solarzellen mit HW-a-Si:H. Erste Solarzellen, die mit moderater Wasserstoffverduennung hergestellt werden, weisen bei Ausgangswerten von {eta}>10% deutlich hoehere Stabilitaet auf ({eta}{sub stab}>7%). Auch mikrokristalline Silizium-({mu}c-Si:H)-, a-SiGe:H und a-Ge:H-Schichten koennen mit dem thermokatalytischen CVD-Verfahren in guter Qualitaet hergestellt werden. Diese fuer Stapelzellen wichtigen Materialien konnten bisher mit gutem (a-SiGe:H) und weniger gutem Erfolg ({mu}c-Si:H, a-Ge:H) in Solarzellen integriert werden. (orig.)
Bayesian Identification of a Cracked Plate using a Population-Based Markov Chain Monte Carlo Method
2011-01-01
serendipity elements, with nodes at each corner and at the middle of each side. Adjacent to the crack tip the eight-noded quads are modified as...noise variance) have been Fig. 4. (a) Nodal configuration of the Mindlin serendipity element, (b) resulting interpolation functions, (c) schematic of...repeated iterations of the forward model, great care was taken in developing an efficient model. This was accomplished by using tailored ‘‘ serendipity
A mixed formulation finite element for linear thin shell analysis
Lee, S. W.; Wong, S. C.
1982-01-01
An eight node curved thin shell slement was tested. The element is based on the degenerate solid concept and the mixed formulation with the independent inplane and transverse shear strains. The number of unknown parameters in the assumed strains is chosen to alleviate the spurious constaining or locking effect. It is indicated that for a pinched cylindrical shell with diaphragmed ends and fixed ends the present element shows good performance.
Studies on the solid-state ion exchange of nickel ions into zeolites using DRS technique
Zanjanchi, M. A.; Ebrahimian, A.
2004-05-01
The coordination of Ni 2+ ions in the dehydrated nickel-exchanged zeolites was investigated from the analysis of diffuse reflectance spectra. Solid-state ion exchange method was used to prepare nickel-containing mordenite, Y, L and mazzite zeolites. In the dehydrated mordenite and zeolite Y, nickel cations are presented in both forms of tetrahedral and distorted tetrahedral symmetries. The relative amount of tetrahedral and distorted tetrahedral nickel species are related to the heating temperature and heating time used for calcinations. In the dehydrated zeolite L and mazzite, Ni 2+ ions are mainly in the distorted octahedral symmetries.
Structures of d4 MH3X: a computational study of the influence of the metal and the ligands.
Poblador-Bahamonde, Amalia I; Raynaud, Christophe; Eisenstein, Odile
2012-05-21
Density functional theory (DFT, PBE0, and range separated DFT, RSH + MP2) and coupled-cluster with single and double and perturbative triple excitations (CCSD(T)) calculations have been used to probe the structural preference of d(4) MH(3)X(q) (M = Ru, Os, Rh(+), Ir(+), and Re(-); X = H, F, CH(3), CF(3), SiH(3), and SiF(3)) and of MX(4) (M = Ru; X = H, F, CH(3), CF(3), SiH(3), and SiF(3)). Landis et al. have shown that complexes in which the metal is sd(3) hybridized have tetrahedral and non-tetrahedral structures with shapes of an umbrella or a 4-legged piano stool. In this article, the influence of the metal and ligands on the energies of the three isomeric structures of d(4) MH(3)X and MX(4) is established and rationalized. Fluoride and alkyl ligands stabilize the tetrahedral relative to non-tetrahedral structures while hydride and silyl ligands stabilize the non-tetrahedral structures. For given ligands and charge, 4d metal favors more the non-tetrahedral structures than 5d metals. A positive charge increases the preference for the non-tetrahedral structures while a negative charge increases the preference for the tetrahedral structure. The factors that determine these energy patterns are discussed by means of a molecular orbital analysis, based on Extended Hückel (EHT) calculations, and by means of Natural Bond Orbital (NBO) analyses of charges and resonance structures (NRT analysis). These analyses show the presence of through-space interactions in the non-tetrahedral structures that can be sufficiently stabilizing, for specific metals and ligands, to stabilize the non-tetrahedral structures relative to the tetrahedral isomer.
Algarra, Andrés G; Basallote, Manuel G; Fernández-Trujillo, María J; Hernández-Molina, Rita; Safont, Vicent S
2007-08-07
Kinetic and DFT studies indicate that the stabilization of a single pyramidal H(3)PO(2) molecule at the M' site of [Mo(3)S(4)M'] clusters requires the participation of two tetrahedral H(3)PO(2) molecules, the role of the second one being assisting tautomerization of a previously coordinated tetrahedral H(3)PO(2).
Double-bond defect modelling in As-S glasses
Energy Technology Data Exchange (ETDEWEB)
Boyko, V; Shpotyuk, O; Hyla, M, E-mail: shpotyuk@novas.lviv.ua
2010-11-15
Ab initio calculations with the RHF/6-311G* basis set are used for geometrical optimization of regular pyramidal and defect quasi-tetrahedral clusters in binary As-S glasses. It is shown that quasi-tetrahedral S=AsS{sub 3/2} structural units are impossible as main network-building blocks in these glasses.
Buiochi, F.; Kiyono, C. Y.; Peréz, N.; Adamowski, J. C.; Silva, E. C. N.
A new systematic and efficient algorithm to obtain the ten complex constants of piezoelectric materials belonging to the 6 mm symmetry class was developed. A finite element method routine was implemented in Matlab using eight-node axisymmetric elements. The algorithm raises the electrical conductance and resistance curves and calculates the quadratic difference between the experimental and numerical curves. Finally, to minimize the difference, an optimization algorithm based on the "Method of Moving Asymptotes" (MMA) is used. The algorithm is able to adjust the curves over a wide frequency range obtaining the real and imaginary parts of the material properties simultaneously.
Static shape control of a flat shell structure
Institute of Scientific and Technical Information of China (English)
无
2006-01-01
The eight-node and forty-DOF piezoelectric shell element were applied to shape control of a flat shell structure. By the direct and converse effects, a distributed piezoelectric sensor layer was used to monitor the shape deformation and a distributed actuator layer was used to suppresse the deflection. A finite element model was for static response of laminated shell with piezoelectric sensors/actuators was derived. The model was verified by calculating piezoelectric polymeric PVDF bimorph beam. The results are in good agreement with those obtained by theoretical analysis of Tzou[1] and Hwang[2]. A case study of the static shape control of a flat shell structure is presented.
Energy Technology Data Exchange (ETDEWEB)
Juliachs, M
2004-07-01
In this state of the art on parallel scientific visualization applications on PC clusters, we deal with both surface and volume rendering approaches. We first analyze available PC cluster configurations and existing parallel rendering software components for parallel graphics rendering. CEA/DIF has been studying cluster visualization since 2001. This report is part of a study to set up a new visualization research platform. This platform consisting of an eight-node PC cluster under Linux and a tiled display was installed in collaboration with Versailles-Saint-Quentin University in August 2003. (author)
Perspective on the structure of liquid water
Energy Technology Data Exchange (ETDEWEB)
Nilsson, A., E-mail: nilsson@slac.stanford.edu [Stanford Synchrotron Radiation Lightsource, P.O. Box 20450, Stanford, CA 94309 (United States); Department of Physics, AlbaNova University Center, Stockholm University, S-106 91 Stockholm (Sweden); Pettersson, L.G.M. [Department of Physics, AlbaNova University Center, Stockholm University, S-106 91 Stockholm (Sweden)
2011-11-07
Graphical abstract: Liquid water can be described in a fluctuating inhomogeneous picture with two local structural motifs that are spatially separated. At ambient temperatures most molecules favor a closer packing than tetrahedral, with strongly distorted hydrogen bonds giving higher density (yellow), which allows the quantized librational modes to be excited and contribute to the entropy, but with enthalpically favored tetrahedrally bonded water patches appearing as fluctuations (blue), i.e. a competition between entropy and enthalpy. Upon cooling water the amount of molecules participating in tetrahedral structures and the size of the tetrahedral patches increase. Highlights: Black-Right-Pointing-Pointer Two components maximizing either enthalpy (tetrahedral, low-density) or entropy (non-specific H-bonding, higher density). Black-Right-Pointing-Pointer Interconvert discontinuously and ratio depends on temperature. Black-Right-Pointing-Pointer Density fluctuations on 1 nm length scale. Black-Right-Pointing-Pointer Increasing size in supercooled region. Black-Right-Pointing-Pointer Connection to Widom line and 2nd critical point. - Abstract: We present a picture that combines discussions regarding the thermodynamic anomalies in ambient and supercooled water with recent interpretations of X-ray spectroscopy and scattering data of water in the ambient regime. At ambient temperatures most molecules favor a closer packing than tetrahedral, with strongly distorted hydrogen bonds, which allows the quantized librational modes to be excited and contribute to the entropy, but with enthalpically favored tetrahedrally bonded water patches appearing as fluctuations, i.e. a competition between entropy and enthalpy. Upon cooling water the amount of molecules participating in tetrahedral structures and the size of the tetrahedral patches increase. The two local structures are connected to the liquid-liquid critical point hypothesis in supercooled water corresponding to high
Tejedor-Tejedor, M. Isabel; Anderson, Marc A.; Herbillon, Adrien J.
1983-11-01
Visible region reflectance spectroscopy and nonlinear regression analysis of spectral data have been used to present qualitative and semiquantitative evidence that some tetrahedral Ni 2+ is present in all six phyllosilicates examined. Highly crystalline willemseite and chrysotile, poorly crystalline nepouite as well as two natural minerals, and a mixture of poorly crystalline nepouite and nickel hydroxide all showed the presence of tetrahedral Ni 2+ as well as octahedral nickel. Chemical analysis of willemseite confirmed quantitatively the presence of excess Ni lending further support for the presence of tetrahedral nickel.
Pressure induced elastic softening in framework aluminosilicate- albite (NaAlSi3O8)
Mookherjee, Mainak; Mainprice, David; Maheshwari, Ketan; Heinonen, Olle; Patel, Dhenu; Hariharan, Anant
2016-10-01
Albite (NaAlSi3O8) is an aluminosilicate mineral. Its crystal structure consists of 3-D framework of Al and Si tetrahedral units. We have used Density Functional Theory to investigate the high-pressure behavior of the crystal structure and how it affects the elasticity of albite. Our results indicate elastic softening between 6-8 GPa. This is observed in all the individual elastic stiffness components. Our analysis indicates that the softening is due to the response of the three-dimensional tetrahedral framework, in particular by the pressure dependent changes in the tetrahedral tilts. At pressure Mohorovicic discontinuity in thickened continental crustal regions.
Electron Density Determination, Bonding and Properties of Tetragonal Ferromagnetic Intermetallics
Energy Technology Data Exchange (ETDEWEB)
Wiezorek, Jorg [Univ. of Pittsburgh, PA (United States)
2016-09-01
. This implies that onsite Coulomb repulsion effects become non-negligible as the d-orbitals fill. The use of now easily measured low-order structure factors as an additional experimental metric in validation of DFT calculation of electronic structures of crystals offers potential to capture better both total energy related properties and details of the interatomic bonding in system with d-electron orbital contributions. This effort advanced the state of the art in quantitative TEM experimentation, provides original experimental data uniquely suited for new validation approaches of DFT calculations of d-electron affected transition metals and intermetallics.
Energy Technology Data Exchange (ETDEWEB)
Dobrev, Veselin A. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Kolev, Tzanio V. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Rieben, Robert N. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
2012-09-20
-grid hydrodynamics (SGH) approach and we show that under specific low-order assumptions, we exactly recover the classical SGH method. We also present numerical results from an extensive series of verification tests that demonstrate several important practical advantages of using high-order finite elements in this context.
Study on Destructuring effect of trehalose on water by neutron diffraction
Branca, C; Migliardo, F; Magazù, V; Soper, A K
2002-01-01
In this work results on trehalose/water solutions by neutron diffraction are reported. The study of the partial structure factors and spatial distribution functions gives evidence of a decreasing tetrahedrality degree of water and justifies its cryoprotectant effectiveness. (orig.)
RSW Fully Tet Medium Cell-Centered Mesh
National Aeronautics and Space Administration — This is the RSW Fully tetrahedral medium cell-centered unstructured grid with a viscous wall. UG3 : Grid File Name = rsw_med_tetcc.b8.ugrid UG3 : Quad Surface Faces=...
Deformations of crystal frameworks
Borcea, Ciprian S
2011-01-01
We apply our deformation theory of periodic bar-and-joint frameworks to tetrahedral crystal structures. The deformation space is investigated in detail for frameworks modelled on quartz, cristobalite and tridymite.
National Aeronautics and Space Administration — Model with Tetrahedral elements includes wing, balance, exciter and modelcart Some files were too large and had to be split into parts. To combine the parts, use cat...
Dicyclohexyl[4-(dimethylaminophenyl]phosphine selenide
Directory of Open Access Journals (Sweden)
Zanele H Phasha
2012-01-01
Full Text Available In the title molecule, C20H32NPSe, the P atom has a distorted tetrahedral environment resulting in an effective cone angle of 172°. Weak intermolecular C—H...Se interactions are observed.
RSW Fully Tet Coarse Cell-Centered Mesh
National Aeronautics and Space Administration — This is the RSW fully tetrahedral unstructured mesh dataset for a cell-centered code, including the viscous wind tunnel wall. UG3 : Grid File Name =...
NEW THIO S2- ADDUCTS WITH ANTIMONY (III AND V HALIDE: SYNTHESIS AND INFRARED STUDY
Directory of Open Access Journals (Sweden)
HASSAN ALLOUCH
2013-12-01
Full Text Available Five new S2- adducts with SbIII and SbV halides have been synthesized and studied by infrared. Discrete structures have been suggested, the environment around the antimony being tetrahedral, trigonal bipyramidal or octahedral.
RSW Fully Tet Cell-Centered Fine Mesh
National Aeronautics and Space Administration — This is the RSW dataset for a fine fully tetrahedral grid designed for a cell-centered unstructured solver. UG3 : Grid File Name = rsw_fine_tetcc.b8.ugrid UG3 : Quad...
CHEMICAL REACTION: DIAGNOSIS AND TOWARDS REMEDY OF ...
African Journals Online (AJOL)
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subscripts in a chemical reaction a new teaching-learning strategy is suggested: Tetrahedral. - in - Zone .... Approaches from Pedagogy and Psychology. According .... matching pedagogical strategies to the learning styles of students. It maps ...
Polymer-Dependent Layer Structures in Montmorillonite Nanocomposites
Directory of Open Access Journals (Sweden)
Justyna Strankowska
2011-12-01
Full Text Available We have studied structural differences among tetrahedral and octahedral sodium Montmorillonite layer arrangements in naturally occurring and synthetic montmorillonite clay minerals, as well as their poly(ethylene oxide and poly(ε-coprolatone polymer nanocomposites.
Fundamentals of semiconductors physics and materials properties
Yu, Peter Y
2005-01-01
Provides detailed explanations of the electronic, vibrational, transport, and optical properties of semiconductors. This textbook emphasizes understanding the physical properties of Si and similar tetrahedrally coordinated semiconductors and features an extensive collection of tables of material parameters, figures, and problems.
Architecture of Platonic and Archimedean polyhedral links
Institute of Scientific and Technical Information of China (English)
无
2008-01-01
A new methodology for understanding the construction of polyhedral links has been developed on the basis of the Platonic and Archimedean solids by using our method of the 'three-cross-curve and doubletwist-line covering'. There are five classes of polyhedral links that can be explored: the tetrahedral and truncated tetrahedral links; the hexahedral and truncated hexahedral links; the dodecahedral and truncated dodecahedral links; the truncated octahedral and icosahedral links. Our results show that the tetrahedral and truncated tetrahedral links have T symmetry; the hexahedral and truncated hexahedral links, as well as the truncated octahedral links, O symmetry; the dodecahedral and truncated dodecahedral links, as well as the truncated icosahedral links, I symmetry, respectively. This study provides further insight into the molecular design, as well as theoretical characterization, of the DNA and protein catenanes.
Architecture of Platonic and Archimedean polyhedral links
Institute of Scientific and Technical Information of China (English)
2008-01-01
A new methodology for understanding the construction of polyhedral links has been developed on the basis of the Platonic and Archimedean solids by using our method of the ‘three-cross-curve and dou- ble-twist-line covering’. There are five classes of polyhedral links that can be explored: the tetrahedral and truncated tetrahedral links; the hexahedral and truncated hexahedral links; the dodecahedral and truncated dodecahedral links; the truncated octahedral and icosahedral links. Our results show that the tetrahedral and truncated tetrahedral links have T symmetry; the hexahedral and truncated hexahedral links, as well as the truncated octahedral links, O symmetry; the dodecahedral and truncated dodeca- hedral links, as well as the truncated icosahedral links, I symmetry, respectively. This study provides further insight into the molecular design, as well as theoretical characterization, of the DNA and protein catenanes.
Directed flexibility: self-assembly of a supramolecular tetrahedron.
Ludlow, James M; Xie, Tingzheng; Guo, Zaihong; Guo, Kai; Saunders, Mary Jane; Moorefield, Charles N; Wesdemiotis, Chrys; Newkome, George R
2015-03-01
Self-assembly of a tribenzo-27-crown-9 ether functionalized with six terpyridines generated (85%) an expanded tetrahedral structure comprised of four independent triangular surfaces interlinked by crown ether vertices.
Triplet correlation functions in liquid water
Energy Technology Data Exchange (ETDEWEB)
Dhabal, Debdas; Chakravarty, Charusita, E-mail: charus@chemistry.iitd.ac.in [Department of Chemistry, Indian Institute of Technology-Delhi, New Delhi 110016 (India); Singh, Murari [School of Physical Sciences, Jawaharlal Nehru University, New Delhi 110067 (India); Wikfeldt, Kjartan Thor [Science Institute, University of Iceland, 107 Reykjavik (Iceland)
2014-11-07
Triplet correlations have been shown to play a crucial role in the transformation of simple liquids to anomalous tetrahedral fluids [M. Singh, D. Dhabal, A. H. Nguyen, V. Molinero, and C. Chakravarty, Phys. Rev. Lett. 112, 147801 (2014)]. Here we examine triplet correlation functions for water, arguably the most important tetrahedral liquid, under ambient conditions, using configurational ensembles derived from molecular dynamics (MD) simulations and reverse Monte Carlo (RMC) datasets fitted to experimental scattering data. Four different RMC data sets with widely varying hydrogen-bond topologies fitted to neutron and x-ray scattering data are considered [K. T. Wikfeldt, M. Leetmaa, M. P. Ljungberg, A. Nilsson, and L. G. M. Pettersson, J. Phys. Chem. B 113, 6246 (2009)]. Molecular dynamics simulations are performed for two rigid-body effective pair potentials (SPC/E and TIP4P/2005) and the monatomic water (mW) model. Triplet correlation functions are compared with other structural measures for tetrahedrality, such as the O–O–O angular distribution function and the local tetrahedral order distributions. In contrast to the pair correlation functions, which are identical for all the RMC ensembles, the O–O–O triplet correlation function can discriminate between ensembles with different degrees of tetrahedral network formation with the maximally symmetric, tetrahedral SYM dataset displaying distinct signatures of tetrahedrality similar to those obtained from atomistic simulations of the SPC/E model. Triplet correlations from the RMC datasets conform closely to the Kirkwood superposition approximation, while those from MD simulations show deviations within the first two neighbour shells. The possibilities for experimental estimation of triplet correlations of water and other tetrahedral liquids are discussed.
Bis[1,3-bis(diphenylphosphanylpropane]copper(I tetrachloridogallate(III
Directory of Open Access Journals (Sweden)
Nian-Nian Wang
2012-07-01
Full Text Available In the title compound, [Cu(C27H26P22][GaCl4], the CuI atom in the complex cation is P,P′-chelated by two 1,3-bis(diphenylphosphanylpropane ligands in a distorted tetrahedral geometry, while the GaIII cation is coordinated by four chloride anions in a distorted tetrahedral geometry. In the crystal, weak C—H...π interactions occur between adjacent complex cations.
Coordination chemistry of iron in glasses contributing to remote-sensed spectra of the moon
Dyar, M. D.; Burns, R. G.
1982-01-01
Ferric iron and tetrahedrally coordinated Fe(2+) ions are identified using Moessbauer and electronic absorption spectroscopic measurements of synthetic glasses equilibrated at P(O2) less than 10 to the -11 atm, simulating the Luna 24 brown glass and Apollo 15 green glass compositions. The presence of 10-20% ferric iron in these low Ti glasses is a result of the absence of Ti(3+) ions. In the brown glass absorption spectra, tetrahedral Fe(3+) and Fe(2+) ions induce an extension of the oxygen-metal charge transfer band into the visible region further than in the green glass containing predominantly octahedral Fe(2+) and Fe(3+) ions. Whereas the glass one-micron band originates from crystal field transitions in octahedral Fe(2+), the glass two-micron band is now positively correlated with tetrahedral Fe(2+) rather than with Fe(2+) ions in pyroxene M2-like sites in the glass structure. The tetrahedral Fe(2+) do not, however, substitute for Si(4+) in glass network-forming sites, instead occurring as network modifiers in larger tetrahedral interstices. The effect of temperature is to induce a pronounced red-shift of the oxygen-iron charge transfer absorption edge, especially for the brown glass, and to intensify significantly the tetrahedral Fe(2+) crystal field two micron band.
Lambert, Michael D.
2011-12-01
The stress and strength behavior of cylindrical tubular adhesive joints composed of dissimilar materials was explored. This was accomplished with the finite element method (FEM) and stress-based failure theories. Also, it was shown how a design of experiments (DOE) based method can be used to objectively organize the process of optimizing joint strength by using stress-based failure criteria. The finite element program used in this work was written in-house from scratch to implement the FEM for the purpose of solving both axisymmetric and three-dimensional linear elastic governing equations of static equilibrium. The formulation of the three-dimensional model is presented, and the required operations to arrive to the axisymmetric model are also presented. The axisymmetric model is two dimensional, capable of using four and eight node quadrilateral elements. However, only four node elements are used because a mesh of eight node elements requires more memory and increased mesh refinement. The three-dimensional model is capable of using eight and twenty node brick elements, but only eight node brick elements are used for the same reason. Both of the axisymmetric and three-dimensional models calculate the nodal displacements, strains, stress values for each material, and strength values for each material. The external static loads can be individually applied, or coupled together. The outputs seem to be most useful for interpretation when plotted through-the-thickness (TTT) and along-the-length (ATL) of the joint or tube. Outputs are valid only for materials that behave linearly elastic up to (or near) failure, and the stress-based failure criteria are used to define that limit. A small laboratory-sized joint was modeled to look at the theoretical stress and strength distributions plotted along-the-length of the joint at different radial locations. These stress and strength distributions can be correlated to the type of load being applied because of unique or prominent
Energy Technology Data Exchange (ETDEWEB)
Singh, Santosh Kumar; Kiran, S. Roopas; Murthy, V.R.K., E-mail: vrkm@iitm.ac.in
2013-09-16
Li{sub 2}Zn{sub (1−x)}Ni{sub x}Ti{sub 3}O{sub 8} (x = 0, 0.1, 0.2, 0.4 and 1.0) microwave dielectric ceramics were studied with the help of powder X-ray diffraction and Raman spectroscopic measurements. These ceramic materials were synthesized by conventional solid state reaction method and observed to crystallize in cubic crystal system with P4{sub 3}32 space group. The cation's occupancies in tetrahedral and octahedral sites were quantified by performing Rietveld refinement. The occupancy of the Li{sup 1+} and Ni{sup 2+} in the respective tetrahedral and octahedral sites were found to increase, whereas occupancy of Zn{sup 2+} in tetrahedral site was observed to decrease with increase in Ni substitution. This decrease in occupancy of Zn{sup 2+} in tetrahedral site increased the AC conductivity by allowing the migration path 8c-12d-8c, which in turn increases the dielectric loss in these compounds. Dielectric constant and observed ionic polarizability were linearly decreased by increasing the Ni substitution. Raman spectra revealed that the shift in A{sub 1g} mode of ZnO{sub 4} tetrahedra to higher wavenumber side was due to increase of Li{sup 1+} at tetrahedral site and narrower FWHM of symmetric stretching mode of Zn–O corresponded to the higher quality factor. - Highlights: • Li{sub 2}Zn{sub (1−x)}Ni{sub x}Ti{sub 3}O{sub 8} compounds were synthesized by solid state reaction method. • Tetrahedral occupancy of different cations was obtained by Rietveld refinement. • The variation of Q × f with tetrahedral occupancy of Zn{sup 2+} was studied. • Raman spectroscopy also revealed the variation of AC conductivity with occupancy.
Carneiro, José Walkimar de M; Cruz, Maurício T de M
2008-09-25
B3LYP/LANL2DZ and B3LYP/6-31G(d)-restricted and -unrestricted calculations are employed to calculate energies and adsorption forms of formaldehyde adsorbed on planar and on tetrahedral Pd4 clusters and on a Pd4 cluster supported on Al10O15. Formaldehyde adsorbs on planar Pd4 in the eta(2)(C,O)-di-sigma adsorption mode, while on tetrahedral Pd4, it adsorbs in the eta(2)(C,O)-pi adsorption mode. The adsorption energy on planar Pd4 is -21.4 kcal x mol(-1), whereas for the tetrahedral Pd4 cluster, the adsorption energy is -13.2 kcal x mol(-1). The latter value is close to experimental findings (-12 to -14 kcal x mol(-1)). Adsorption of formaldehyde on Pd4 supported on an Al10O15 cluster leads essentially to the same result as that found for adsorption on the tetrahedral Pd4 cluster. Charge density analysis for the interaction between formaldehyde and the Pd4 clusters indicates strong backdonation in the eta(2) adsorption mode, leading to positive charge on the Pd4 cluster. NBO analysis shows that the highly coordinated octahedral aluminum atoms of Al10O15 donate electron density to the supported Pd4 cluster, while tetrahedral aluminum atoms with lower coordination number have acidic nature and therefore act as electron acceptors.
Spatial Convergence of Three Dimensional Turbulent Flows
Park, Michael A.; Anderson, W. Kyle
2016-01-01
Finite-volume and finite-element schemes, both implemented within the FUN3D flow solver, are evaluated for several test cases described on the Turbulence-Modeling Resource (TMR) web site. The cases include subsonic flow over a hemisphere cylinder, subsonic flow over a swept bump configuration, and supersonic flow in a square duct. The finite- volume and finite-element schemes are both used to obtain solutions for the first two cases, whereas only the finite-volume scheme is used for the supersonic duct. For the hemisphere cylinder, finite-element solutions obtained on tetrahedral meshes are compared with finite- volume solutions on mixed-element meshes. For the swept bump, finite-volume solutions have been obtained for both hexahedral and tetrahedral meshes and are compared with finite-element solutions obtained on tetrahedral meshes. For the hemisphere cylinder and the swept bump, solutions are obtained on a series of meshes with varying grid density and comparisons are made between drag coefficients, pressure distributions, velocity profiles, and profiles of the turbulence working variable. The square duct shows small variation due to element type or the spatial accuracy of turbulence model convection. It is demonstrated that the finite-element scheme on tetrahedral meshes yields similar accuracy as the finite- volume scheme on mixed-element and hexahedral grids, and demonstrates less sensitivity to the mesh topology (biased tetrahedral grids) than the finite-volume scheme.
Zaki, H. M.; Al-Heniti, S.; Al Shehri, N.
2014-03-01
MgAlxFe2-xO4 (x=0.0 up to 1 step 0.2) was prepared using co-precipitation method. The value of lattice constant is found to decrease with increasing Al3+ concentration. The particle size of the samples calculated using the Sherrer formula was obtained in the range of 15-28 nm. The two main bands corresponding to tetrahedral and octahedral sites were observed to be around 600 cm-1 and 450 cm-1, respectively. These bands are shifted to high frequencies with more doping of Al3+ ions which may be attributed to the decrease in the mean radius of the tetrahedral and octahedral sites. The threshold frequency (νth) for the electronic transition decreases with increasing the Al3+content. The tetrahedral force constant (KT) increases continuously with Al3+ concentration.The bandwidth of the tetrahedral site is found to increase gradually with the Al3+ content. The validity of the proposed cation distribution is confirmed by considering the X-ray intensity ratios of diffraction lines sensitive to the tetrahedral and octahedral sites. DC conductivity measurements exhibited metallic and semiconductor-like behavior with temperature for all compositions. The decrease of Curie temperature with the increase of non-magnetic ions of aluminum indicates their preference to the octahedral sites as well and confirms the validity of the cation distribution.
Diffusivity anomaly in modified Stillinger-Weber liquids
Sengupta, Shiladitya; Vasisht, Vishwas V.; Sastry, Srikanth
2014-01-01
By modifying the tetrahedrality (the strength of the three body interactions) in the well-known Stillinger-Weber model for silicon, we study the diffusivity of a series of model liquids as a function of tetrahedrality and temperature at fixed pressure. Previous work has shown that at constant temperature, the diffusivity exhibits a maximum as a function of tetrahedrality, which we refer to as the diffusivity anomaly, in analogy with the well-known anomaly in water upon variation of pressure at constant temperature. We explore to what extent the structural and thermodynamic changes accompanying changes in the interaction potential can help rationalize the diffusivity anomaly, by employing the Rosenfeld relation between diffusivity and the excess entropy (over the ideal gas reference value), and the pair correlation entropy, which provides an approximation to the excess entropy in terms of the pair correlation function. We find that in the modified Stillinger-Weber liquids, the Rosenfeld relation works well above the melting temperatures but exhibits deviations below, with the deviations becoming smaller for smaller tetrahedrality. Further we find that both the excess entropy and the pair correlation entropy at constant temperature go through maxima as a function of the tetrahedrality, thus demonstrating the close relationship between structural, thermodynamic, and dynamical anomalies in the modified Stillinger-Weber liquids.
Diffusivity anomaly in modified Stillinger-Weber liquids
Energy Technology Data Exchange (ETDEWEB)
Sengupta, Shiladitya [TIFR Centre for Interdisciplinary Sciences, 21 Brundavan Colony, Narsingi, Hyderabad 500089 (India); Vasisht, Vishwas V. [Theoretical Sciences Unit, Jawaharlal Nehru Centre for Advanced Scientific Research, Jakkur Campus, Bangalore 560064 (India); Sastry, Srikanth [TIFR Centre for Interdisciplinary Sciences, 21 Brundavan Colony, Narsingi, Hyderabad 500089 (India); Theoretical Sciences Unit, Jawaharlal Nehru Centre for Advanced Scientific Research, Jakkur Campus, Bangalore 560064 (India)
2014-01-28
By modifying the tetrahedrality (the strength of the three body interactions) in the well-known Stillinger-Weber model for silicon, we study the diffusivity of a series of model liquids as a function of tetrahedrality and temperature at fixed pressure. Previous work has shown that at constant temperature, the diffusivity exhibits a maximum as a function of tetrahedrality, which we refer to as the diffusivity anomaly, in analogy with the well-known anomaly in water upon variation of pressure at constant temperature. We explore to what extent the structural and thermodynamic changes accompanying changes in the interaction potential can help rationalize the diffusivity anomaly, by employing the Rosenfeld relation between diffusivity and the excess entropy (over the ideal gas reference value), and the pair correlation entropy, which provides an approximation to the excess entropy in terms of the pair correlation function. We find that in the modified Stillinger-Weber liquids, the Rosenfeld relation works well above the melting temperatures but exhibits deviations below, with the deviations becoming smaller for smaller tetrahedrality. Further we find that both the excess entropy and the pair correlation entropy at constant temperature go through maxima as a function of the tetrahedrality, thus demonstrating the close relationship between structural, thermodynamic, and dynamical anomalies in the modified Stillinger-Weber liquids.
A hybrid-stress solid-shell element for non-linear analysis of piezoelectric structures
Institute of Scientific and Technical Information of China (English)
SZE; K; Y
2009-01-01
This paper presents eight-node solid-shell elements for geometric non-linear analyze of piezoelectric structures. To subdue shear, trapezoidal and thickness locking, the assumed natural strain method and an ad hoc modified generalized laminate stiffness matrix are employed. With the generalized stresses arising from the modified generalized laminate stiffness matrix assumed to be independent from the ones obtained from the displacement, an extended Hellinger-Reissner functional can be derived. By choosing the assumed generalized stresses similar to the assumed stresses of a previous solid ele- ment, a hybrid-stress solid-shell element is formulated. The presented finite shell element is able to model arbitrary curved shell structures. Non-linear numerical examples demonstrate the ability of the proposed model to analyze nonlinear piezoelectric devices.
Implementation of a strain energy-based nonlinear finite element in the object-oriented environment
Wegner, Tadeusz; Pęczak, Andrzej
2010-03-01
The objective of the paper is to describe a novel finite element computational method based on a strain energy density function and to implement it in the object-oriented environment. The original energy-based finite element was put into the known standard framework of classes and handled in a different manner. The nonlinear properties of material are defined with a modified strain energy density function. The local relaxation procedure proposed as a method used to resolve a nonlinear problem is implemented in C++ language. The hexahedral element with eight nodes as well as the adaptation of the nonlinear finite element is introduced. The chosen numerical model is made of nearly incompressible hyperelastic material. The application of the proposed element is shown on the example of a rectangular parallelepiped with a hollow port.
RBFNN Model for Predicting Nonlinear Response of Uniformly Loaded Paddle Cantilever
Directory of Open Access Journals (Sweden)
Abdullah H. Abdullah
2009-01-01
Full Text Available The Radial basis Function neural network (RBFNN model has been developed for the prediction of nonlinear response for paddle Cantilever with built-in edges and different sizes, thickness and uniform loads. Learning data was performed by using a nonlinear finite element program, incremental stages of the nonlinear finite element analysis were generated by using 25 schemes of built paddle Cantilevers with different thickness and uniform distributed loads. The neural network model has 5 input nodes representing the uniform distributed load and paddle size, length, width and thickness, eight nodes at hidden layer and one output node representing the max. deflection response (1500×1 represent the deflection response of load. Regression analysis between finite element results and values predicted by the neural network model shows the least error.
Energy Technology Data Exchange (ETDEWEB)
Biffle, J.H.
1993-02-01
JAC3D is a three-dimensional finite element program designed to solve quasi-static nonlinear mechanics problems. A set of continuum equations describes the nonlinear mechanics involving large rotation and strain. A nonlinear conjugate gradient method is used to solve the equation. The method is implemented in a three-dimensional setting with various methods for accelerating convergence. Sliding interface logic is also implemented. An eight-node Lagrangian uniform strain element is used with hourglass stiffness to control the zero-energy modes. This report documents the elastic and isothermal elastic-plastic material model. Other material models, documented elsewhere, are also available. The program is vectorized for efficient performance on Cray computers. Sample problems described are the bending of a thin beam, the rotation of a unit cube, and the pressurization and thermal loading of a hollow sphere.
Failure analysis of multiple delaminated composite plates due to bending and impact
Indian Academy of Sciences (India)
P K Parhi; S K Bhattacharyya; P K Sinha
2001-04-01
The present work aims at the first ply failure analysis of laminated composite plates with arbitrarily located multiple delaminations subjected to transverse static load as well as impact. The theoretical formulation is based on a simple multiple delamination model. Conventional first order shear deformation is assumed using eight-noded isoparametric quadratic elements to develop the finite element analysis procedure. Composite plates are assumed to contain both single and multiple delaminations. For the case of impact, Newmark time integration algorithm is employed for solving the time dependent multiple equations of the plate and the impactor. Tsai-Wu failure criterion is used to check for failure of the laminate for both the cases. To investigate the first ply failure, parametric studies are made for different cases by varying the size and number of delaminations as well as the stacking sequences and boundary conditions.
Dynamic simulation of viscoelastic soft tissues in harmonic motion imaging application.
Shan, Baoxiang; Kogit, Megan L; Pelegri, Assimina A
2008-10-20
A finite element model was built to simulate the dynamic behavior of soft tissues subjected to sinusoidal excitation during harmonic motion imaging. In this study, soft tissues and tissue-like phantoms were modeled as isotropic, viscoelastic, and nearly incompressible media. A 3D incompressible mixed u-p element of eight nodes, S1P0, was developed to accurately calculate the stiffness matrix for soft tissues. The finite element equations of motion were solved using the Newmark method. The Voigt description for tissue viscosity was applied to estimate the relative viscous coefficient from the phase shift between the response and excitation in a harmonic case. After validating our model via ANSYS simulation and experiments, a MATLAB finite element program was then employed to explore the effect of excitation location, viscosity, and multiple frequencies on the dynamic displacement at the frequency of interest.
Mallikarjuna; Kant, T.; Fafard, M.
1992-09-01
The first-order Reissner-Mindlin shear deformation theory is employed to investigate the transient response of isotropic, layered orthotropic and anisotropic composite and sandwich shells. The eight-noded Serendipity and nine-noded Lagrangian quadrilateral superparametric shell elements are used. Numerical convergence and stability of the elements are established using an explicit central difference technique with a special mass matrix diagonalization scheme. The effects of transverse shear modulii of stiff layers, length/thickness and radius/length ratios, time step, finite element mesh, orientation of fibers and degree of orthotropy on the transient response of shells are studied. The variety of results presented here, based on realistic material properties of more commonly used advanced laminated composite shells, should serve as references for future investigations.
Large rotation FE transient analysis of piezolaminated thin-walled smart structures
Zhang, S. Q.; Schmidt, R.
2013-10-01
A geometrically nonlinear large rotation shell theory is proposed for dynamic finite element (FE) analysis of piezoelectric integrated thin-walled smart structures. The large rotation theory, which has six independent kinematic parameters but expressed by five nodal degrees of freedom (DOFs), is based on first-order shear deformation (FOSD) hypothesis. The two-dimensional (2D) FE model is constructed using eight-node quadrilateral shell elements with five mechanical DOFs per node and one electrical DOF per piezoelectric material layer with linear constitutive equations. The linear and nonlinear dynamic responses are determined by the central difference algorithm (CDA) and the Newmark method. The results are compared with those obtained by simplified nonlinear theories, as well as those reported in the literature. It is shown that the present large rotation theory yields considerable improvement if the structures undergo large displacements and rotations.
Free vibration of laminated composite stiffened hyperbolic paraboloid shell panel with cutout
Sahoo, Sarmila
2016-08-01
Composite shell structures are extensively used in aerospace, civil, marine and other engineering applications. In practical civil engineering applications, the necessity of covering large column free open areas is often an issue and hyperbolic paraboloid shells are used as roofing units. Quite often, to save weight and also to provide a facility for inspection, cutouts are provided in shell panels. The paper considers free vibration characteristics of stiffened composite hyperbolic paraboloid shell panel with cutout in terms of natural frequency and mode shapes. A finite element code is developed for the purpose by combining an eight noded curved shell element with a three noded curved beam element. The size of the cutouts and their positions with respect to the shell centre are varied for different edge conditions to arrive at a set of inferences of practical engineering significances.
Decentralized Control of Dynamic Routing with a Neural Network Algorithm
Institute of Scientific and Technical Information of China (English)
无
2000-01-01
A state-dependent routing algorithm based on the neural network model, which takes advantage of other dynamic routing algorithm for circuit-switched network, is given in [1]. But, the Algorithm in [1] is a centralized control model with complex O (N7), therefore, is difficult to realize by hardware. A simplified algorithm is put forward in this paper, in which routing can be controlled decentralizedly, and its complexity is reduced to O (10N3). Computer simulations are made in a fully connected test network with eight nodes. The results show that the centralized control model has very effective performance that can match RTNR, and the centralized control model is not as good as the centralized one but better than DAR-1.
MSAProbs-MPI: parallel multiple sequence aligner for distributed-memory systems.
González-Domínguez, Jorge; Liu, Yongchao; Touriño, Juan; Schmidt, Bertil
2016-12-15
MSAProbs is a state-of-the-art protein multiple sequence alignment tool based on hidden Markov models. It can achieve high alignment accuracy at the expense of relatively long runtimes for large-scale input datasets. In this work we present MSAProbs-MPI, a distributed-memory parallel version of the multithreaded MSAProbs tool that is able to reduce runtimes by exploiting the compute capabilities of common multicore CPU clusters. Our performance evaluation on a cluster with 32 nodes (each containing two Intel Haswell processors) shows reductions in execution time of over one order of magnitude for typical input datasets. Furthermore, MSAProbs-MPI using eight nodes is faster than the GPU-accelerated QuickProbs running on a Tesla K20. Another strong point is that MSAProbs-MPI can deal with large datasets for which MSAProbs and QuickProbs might fail due to time and memory constraints, respectively.
Directory of Open Access Journals (Sweden)
Sarmila Sahoo
2013-01-01
Full Text Available Dynamic characteristics of stiffened composite conoidal shells with cutout are analyzed in terms of the natural frequency and mode shapes. A finite element code is developed for the purpose by combining an eight-noded curved shell element with a three-noded curved beam element. The code is validated by solving benchmark problems available in the literature and comparing the results. The size of the cutouts and their positions with respect to the shell centre are varied for different edge constraints of cross-ply and angle-ply laminated composite conoids. The effects of these parametric variations on the fundamental frequencies and mode shapes are considered in details. The results furnished here may be readily used by practicing engineers dealing with stiffened composite conoids with cutouts central or eccentric.
A Simulation Method for High-Cycle Fatigue-Driven Delamination using a Cohesive Zone Model
DEFF Research Database (Denmark)
Bak, Brian Lau Verndal; Turon, A.; Lindgaard, Esben;
2016-01-01
on parameter fitting of any kind. The method has been implemented as a zero-thickness eight-node interface element for Abaqus and as a spring element for a simple finite element model in MATLAB. The method has been validated in simulations of mode I, mode II, and mixed-mode crack loading for both self......A novel computational method for simulating fatigue-driven mixed-mode delamination cracks in laminated structures under cyclic loading is presented. The proposed fatigue method is based on linking a cohesive zone model for quasi-static crack growth and a Paris' law-like model described......-similar and non-self-similar crack propagation. The method produces highly accurate results compared with currently available methods and is capable of simulating general mixed-mode non-self-similar crack growth problems....
Karlovitz, L. A.; Atluri, S. N.; Xue, W.-M.
1985-01-01
The extensions of Reissner's two-field (stress and displacement) principle to the cases wherein the displacement field is discontinuous and/or the stress field results in unreciprocated tractions, at a finite number of surfaces ('interelement boundaries') in a domain (as, for instance, when the domain is discretized into finite elements), is considered. The conditions for the existence, uniqueness, and stability of mixed-hybrid finite element solutions based on such discontinuous fields, are summarized. The reduction of these global conditions to local ('element') level, and the attendant conditions on the ranks of element matrices, are discussed. Two examples of stable, invariant, least-order elements - a four-node square planar element and an eight-node cubic element - are discussed in detail.
Free Vibration of Laminated Composite Hypar Shell Roofs with Cutouts
Directory of Open Access Journals (Sweden)
Sarmila Sahoo
2011-01-01
Full Text Available Use of laminated composites in civil engineering structural components including shell roofs is increasing day by day due to their light weight, high specific strength, and stiffness properties. In the present paper, laminated composite hypar shell (hyperbolic paraboloidal shells bounded by straight edges roofs with cutouts are analyzed for their free vibration characteristics using finite element method. An eight-noded curved shell element is used for modeling the shell. Specific numerical problems of earlier investigators are solved to compare their results with the present formulation. A number of problems are further solved where the size of the cutouts and their positions with respect to the shell centre are varied for different edge constraints. The results are furnished in the form of figures and tables. The results are examined thoroughly to arrive at some meaningful conclusions useful to designers.
Konyakhin, Igor; Molev, Fedor; Konyakhin, Alexey; Li, Renpu
2015-02-01
The improved autocollimators for measuring angular deformations of the large constructions as support tube of mirror and elevation axle of the radio telescopes are analyzed. Two new types of the reflector for autocollimator are researched. The first type of the reflectors is the tetrahedral reflector with flat reflecting sides and invariant axis. The autocollimator with tetrahedral reflector is used for the measuring 3-D deformations as roll, pitch and yaw angular deviations. The second type of the reflector is the composition of the anamorphic wedge system and ordinary cube-corner retroreflector. This reflector generates the narrow beam, as result the work distance and the range of measurement of the roll angle increase. Technical characteristics of the experimental setups of new reflectors are presented. Features of the tetrahedral reflector and anamorphic system as the reflectors for multipurpose autocollimator are discussed.
Temperature dependence of the electronic gaps of semiconductors
Energy Technology Data Exchange (ETDEWEB)
Cardona, M.; Kremer, R.K.
2014-11-28
Understanding the temperature dependence of the direct and indirect gaps is indispensable for optimizing the applications of semiconductors. Experimentally, this temperature dependence can be very precisely determined by ellipsometry, by absorption or by luminescence spectroscopy. We have re-analyzed the temperature dependence of the direct and indirect gaps of some prominent tetrahedral semiconductors and improved available fits by applying a simple modified approach which uses statistical factors and the knowledge of prominent transverse-acoustic and transverse-optical bands in the measured or calculated phonon density of states of the semiconductors under consideration. - Highlights: • Re-analysis of the temperature dependence of the gaps of tetrahedral semiconductors • Modeling of the temperature dependence of the gaps of tetrahedral semiconductors • Simplified modeling using statistical factors and prominent phonon bands.
Adaptive and Unstructured Mesh Cleaving
Bronson, Jonathan R.; Sastry, Shankar P.; Levine, Joshua A.; Whitaker, Ross T.
2015-01-01
We propose a new strategy for boundary conforming meshing that decouples the problem of building tetrahedra of proper size and shape from the problem of conforming to complex, non-manifold boundaries. This approach is motivated by the observation that while several methods exist for adaptive tetrahedral meshing, they typically have difficulty at geometric boundaries. The proposed strategy avoids this conflict by extracting the boundary conforming constraint into a secondary step. We first build a background mesh having a desired set of tetrahedral properties, and then use a generalized stenciling method to divide, or “cleave”, these elements to get a set of conforming tetrahedra, while limiting the impacts cleaving has on element quality. In developing this new framework, we make several technical contributions including a new method for building graded tetrahedral meshes as well as a generalization of the isosurface stuffing and lattice cleaving algorithms to unstructured background meshes. PMID:26137171
Cation distribution in Ni{sub 1−x}Zn{sub x}Fe{sub 2}O{sub 4} using X-ray absorption spectroscopy
Energy Technology Data Exchange (ETDEWEB)
Yadav, A. K., E-mail: akyadav@barc.gov.in; Jha, S. N.; Bhattacharyya, D.; Sahoo, N. K. [Atomic and Molecular Physics Division, Bhabha Atomic Research Centre, Mumbai - 400094 (India); Jadhav, J.; Biswas, S. [Department of Physics, The LNM Institute of Information Technology, Jaipur-302031 (India)
2014-04-24
Spinel ferrite samples of Ni{sub 1−x}Zn{sub x}Fe{sub 2}O{sub 4} (for x=0.2, 0.4, 0.5, 0.6 and 0.8) nanoparticles prepared by a novel chemical synthesis method have been characterized by X-ray Absorption Spectroscopy (XAS) technique to investigate the distribution of cations in the unit cell. XANES region clearly shows that as Ni concentration increases, the pre-edge feature, which is a characteristic of tetrahedral coordination of Fe, is enhanced. A quantitative determination of the relative occupancy of iron cation in the octahedral and tetrahedral sites of the spinel structure was obtained from EXAFS data analysis. It has been found that as atomic fraction of Ni is increased from 0.2 to 0.8, Fe occupancy at tetrahedral to octahedral sites is increased from 13:87 and to 39:61.
Re4As6S3, a thio-spinel-related cluster system
DEFF Research Database (Denmark)
Besnard, Celine; Svensson, Christer; Ståhl, Kenny
2003-01-01
We have synthesized a new compound with formula Re4As6S3 and characterized its crystal structure by Rietveld powder diffraction methods. Re4As6S3 crystallizes in an face-centered cubic unit cell, space group F (4) over bar 3m (no. 216), with lattice constant a = 9.8608(1) Angstrom and Z = 4....... The rhenium atoms form tetrahedral clusters linked via tetrahedral arsenic clusters to produce an NaCl-type arrangement. The oxidation state of rhenium is IV and the number of electrons shared by the rhenium atoms in the cluster is 12. The structure is based on an ordered defect thio-spinel A((1-x))B(2)X(4......) where the B-type atoms form tetrahedral clusters....
Symmetry-Guided Synthesis of Highly Porous Metal-Organic Frameworks with Fluorite Topology
Energy Technology Data Exchange (ETDEWEB)
Zhang, MW; Chen, YP; Bosch, M; Gentle, T; Wang, KC; Feng, DW; Wang, ZYU; Zhou, HC
2013-11-11
Two stable, non-interpenetrated MOFs, PCN-521 and PCN-523, were synthesized by a symmetry-guided strategy. Augmentation of the 4-connected nodes in the fluorite structure with a rigid tetrahedral ligand and substitution of the 8-connected nodes by the Zr/Hf clusters yielded MOFs with large octahedral interstitial cavities. They are the first examples of Zr/Hf MOFs with tetrahedral linkers. PCN-521 has the largest BET surface area (3411 m(2) g(-1)), pore size (20.5 x 20.5 x 37.4 angstrom) and void volume (78.5%) of MOFs formed from tetrahedral ligands. This work not only demonstrates a successful implementation of rational design of MOFs with desired topology, but also provides a systematic way of constructing non-interpenetrated MOFs with high porosity.
Van der Waals epitaxial growth of MoS2 on SiO2/Si by chemical vapor deposition
Cheng, Yingchun
2013-01-01
Recently, single layer MoS2 with a direct band gap of 1.9 eV has been proposed as a candidate for two dimensional nanoelectronic devices. However, the synthetic approach to obtain high-quality MoS2 atomic thin layers is still problematic. Spectroscopic and microscopic results reveal that both single layers and tetrahedral clusters of MoS2 are deposited directly on the SiO2/Si substrate by chemical vapor deposition. The tetrahedral clusters are mixtures of 2H- and 3R-MoS2. By ex situ optical analysis, both the single layers and tetrahedral clusters can be attributed to van der Waals epitaxial growth. Due to the similar layered structures we expect the same growth mechanism for other transition-metal disulfides by chemical vapor deposition. © 2013 The Royal Society of Chemistry.
Enhanced coherence of a quantum doublet coupled to Tomonaga-Luttinger liquid leads
Energy Technology Data Exchange (ETDEWEB)
Cirillo, Antonio, E-mail: antonio.cirillo@fisica.unipg.it [Dipartimento di Fisica, Universita di Perugia, Via A. Pascoli, I-06123, Perugia (Italy); I.N.F.N., Sezione di Perugia, Via A. Pascoli, I-06123, Perugia (Italy); Mancini, Matteo, E-mail: matteo.mancini@fisica.unipg.it [Dipartimento di Fisica, Universita di Perugia, Via A. Pascoli, I-06123, Perugia (Italy); I.N.F.N., Sezione di Perugia, Via A. Pascoli, I-06123, Perugia (Italy); Giuliano, Domenico, E-mail: domenico.giuliano@fis.unical.it [Dipartimento di Fisica, Universita della Calabria, Arcavacata di Rende I-87036, Cosenza (Italy); I.N.F.N., Gruppo Collegato di Cosenza, Arcavacata di Rende I-87036, Cosenza (Italy); Sodano, Pasquale, E-mail: pasquale.sodano@pg.infn.it [Perimeter Institute for Theoretical Physics, 31 Caroline St. N, Waterloo ON, N2L 2Y5 (Canada); Dipartimento di Fisica, Universita di Perugia, Via A. Pascoli, I-06123, Perugia (Italy); I.N.F.N., Sezione di Perugia, Via A. Pascoli, I-06123, Perugia (Italy)
2011-11-01
We use boundary field theory to describe the phases accessible to a tetrahedral qubit coupled to Josephson junction chains acting as Tomonaga-Luttinger liquid leads. We prove that, in a pertinent range of the fabrication and control parameters, an attractive finite coupling fixed point emerges due to the geometry of the composite Josephson junction network. We show that this new stable phase is characterized by the emergence of a quantum doublet which is robust not only against the noise in the external control parameters (magnetic flux, gate voltage) but also against the decoherence induced by the coupling of the tetrahedral qubit with the superconducting leads. We provide protocols allowing to read and to manipulate the state of the emerging quantum doublet and argue that a tetrahedral Josephson junction network operating near the new finite coupling fixed point may be fabricated with today's technologies.
Molecular-dynamics study of amorphous SiO{sub 2} relaxation
Energy Technology Data Exchange (ETDEWEB)
Fadhilah, Irfan Muhammad, E-mail: irfanmuhammadf@ymail.com [Department of Physics, Universitas Padjadjaran, Jatinangor, Sumedang 45363 (Indonesia); Rosandi, Yudi, E-mail: rosandi@geophys.unpad.ac.id [Theoretical and Computational Geophysics Laboratory, Department of Physics, Universitas Padjadjaran, Jatinangor, Sumedang 45363 (Indonesia)
2015-09-30
Using Molecular-Dynamics simulation we observed the generation of amorphous SiO{sub 2} target from a randomly distributed Si and O atoms. We applied a sequence of annealing of the target with various temperature and quenching to room temperature. The relaxation time required by the system to form SiO{sub 4} tetrahedral mesh after a relatively long simulation time, is studied. The final amorphous target was analyzed using the radial distribution function method, which can be compared with the available theoretical and experimental data. We found that up to 70% of the target atoms form the tetrahedral SiO{sub 4} molecules. The number of formed tetrahedral increases following the growth function and the rate of SiO{sub 4} formation follows Arrhenius law, depends on the annealing temperature. The local structure of amorphous SiO{sub 2} after this treatment agrees well with those reported in some literatures.
Identification of the interstitial Mn site in ferromagnetic (Ga,Mn)As
AUTHOR|(CDS)2093111; Wahl, Ulrich; Augustyns, Valerie; Silva, Daniel; Granadeiro Costa, Angelo Rafael; Houben, K; Edmonds, Kevin W; Gallagher, BL; Campion, RP; Van Bael, MJ; Castro Ribeiro Da Silva, Manuel; Martins Correia, Joao; Esteves De Araujo, Araujo Joao Pedro; Temst, Kristiaan; Vantomme, André; Da Costa Pereira, Lino Miguel
2015-01-01
We determined the lattice location of Mn in ferromagnetic (Ga,Mn)As using the electron emission channeling technique. We show that interstitial Mn occupies the tetrahedral site with As nearest neighbors (TAs) both before and after thermal annealing at 200 °C, whereas the occupancy of the tetrahedral site with Ga nearest neighbors (TGa) is negligible. TAs is therefore the energetically favorable site for interstitial Mn in isolated form as well as when forming complexes with substitutional Mn. These results shed new light on the long standing controversy regarding TAs versus TGa occupancy of interstitial Mn in (Ga,Mn)As.
Trivariate Local Lagrange Interpolation and Macro Elements of Arbitrary Smoothness
Matt, Michael Andreas
2012-01-01
Michael A. Matt constructs two trivariate local Lagrange interpolation methods which yield optimal approximation order and Cr macro-elements based on the Alfeld and the Worsey-Farin split of a tetrahedral partition. The first interpolation method is based on cubic C1 splines over type-4 cube partitions, for which numerical tests are given. The second is the first trivariate Lagrange interpolation method using C2 splines. It is based on arbitrary tetrahedral partitions using splines of degree nine. The author constructs trivariate macro-elements based on the Alfeld split, where each tetrahedron
Photonic Band Gaps in 3D Network Structures with Short-range Order
Liew, Seng Fatt; Noh, Heeso; Schreck, Carl F; Dufresne, Eric R; O'Hern, Corey S; Cao, Hui
2011-01-01
We present a systematic study of photonic band gaps (PBGs) in three-dimensional (3D) photonic amorphous structures (PAS) with short-range order. From calculations of the density of optical states (DOS) for PAS with different topologies, we find that tetrahedrally connected dielectric networks produce the largest isotropic PBGs. Local uniformity and tetrahedral order are essential to the formation of PBGs in PAS, in addition to short-range geometric order. This work demonstrates that it is possible to create broad, isotropic PBGs for vector light fields in 3D PAS without long-range order.
Energy Technology Data Exchange (ETDEWEB)
Pennington, C.H.; Hahm, C.; Stenger, V.A.; Gorny, K.; Recchia, C.H.; Martindale, J.A. [Department of Physics, The Ohio State University, 174 West 18th Avenue, Columbus, Ohio 43210 (United States); Buffinger, D.R.; Ziebarth, R.P. [Department of Chemistry, The Ohio State University, 120 West 18th Avenue, Columbus, Ohio 43210 (United States)
1996-09-01
The {sup 87}Rb NMR line shape of the Rb{sub 3}C{sub 60} superconductor contains three distinct peaks: one associated with octahedrally coordinated Rb in the fcc lattice of C{sub 60} molecules and two others, labeled {ital T} and {ital T}{sup {prime}}, both associated with tetrahedrally coordinated Rb. This contrasts with the accepted crystal structure, in which all tetrahedral Rb sites are equivalent. We report multinuclear single and double resonance NMR experiments which probe for effects which could lead to the unexpected splitting, and discuss implications for electronic structure. {copyright} {ital 1996 The American Physical Society.}
High-pressure synthesis of a La orthosilicate and Nd, Gd, and Dy disilicates
Liu, Xiaoyang; Fleet, Michael E.
2002-11-01
Several rare-earth silicates have been synthesized at 10 GPa and 1600-1700 °C: a La orthosilicate (La4Si3O12) with a defect Ba3(PO4)2-type, a new structure type (K) for Nd and Gd disilicates (Nd2Si2O7 and Gd2Si2O7) with a diorthosilicate structure, and a new structure type (L) for Dy disilicate (Dy2Si2O7) with a structure containing linear triple tetrahedral groups [Si3O10], but having one in six atoms distributed with 50% occupancy over two tetrahedral positions.
Zaręba, Jan K; Białek, Michał J; Janczak, Jan; Nyk, Marcin; Zoń, Jerzy; Samoć, Marek
2015-11-16
Powder second-harmonic generation (SHG) efficiencies are usually measured at single wavelengths. In the present work, we provide a proof of concept of spectrally resolved powder SHG measured for a newly obtained series of three non-centrosymmetric coordination polymers (CPs). CPs are constructed from tetrahedral linker-tetraphenylmethane-based tetraphosphonate octaethyl ester and cobalt(II) ions of mixed, octahedral (Oh), and tetrahedral (Td), geometries and different sets of donors (CoO6 vs CoX3O). Isostructurality of the obtained materials allowed for the determination of anion-dependent tunability of SHG optical spectra and their relationship with solid-state absorption spectra.
Mössbauer studies of Sn4+/Nb5+ substituted Mn–Zn ferrites
Indian Academy of Sciences (India)
A D P Rao; S B Raju; S R Vadera; D R Sharma
2003-08-01
At room temperature, Mössbauer spectra of Sn4+/Nb5+ substituted Mn–Zn ferrites have been taken to understand the site occupancy of substituted ions. The results indicate that both the substituted ions occupy tetrahedral (A) site only at lower concentration of substitution while at higher concentration they occupy both tetrahedral and octahedral sites. At higher concentration of Nb substitution a doublet has been observed besides sextets. The possibility of canting existence on octahedral sites has been discussed. The observed variations of the hyperfine fields, isomer shift, line widths and B/A peak area ratio with the ferrite composition are interpreted.
ADAPTIVITY IN SPACE AND TIME FOR MAGNETOQUASISTATICS
Institute of Scientific and Technical Information of China (English)
Markus Clemens; Jens Lang; Delia Teleaga; Georg Wimmer
2009-01-01
This paper addresses fully space-time adaptive magnetic field computations. We de-scribe an adaptive Whitney finite element method for solving the magnetoquasistatic for-mulation of Maxwell's equations on unstructured 3D tetrahedral grids. Spatial mesh re-finement and coarsening are based on hierarchical error estimators especially designed for combining tetrahedral H (curl)-conforming edge elements in space with linearly implicit Rosenbrock methods in time. An embedding technique is applied to get efficiency in time through variable time steps. Finally, we present numerical results for the magnetic recording write head benchmark problem proposed by the Storage Research Consortium in Japan.
Lactam hydrolysis catalyzed by mononuclear metallo-beta-lactamases: A density functional study
DEFF Research Database (Denmark)
Hemmingsen, Lars Bo Stegeager; Olsen, L.; Antony, J.
2003-01-01
coordinating to the zinc ion. Potential proton shuttles from the second (unoccupied) metal-binding site (water, Asp, or Cys) are included in some calculations. The calculated reaction barrier for formation of the tetrahedral intermediate is 13 kcal/mol, close to what is observed experimentally for the rate....... For most studied systems, the tetrahedral structure is a stable intermediate. Moreover, the C-N bond in the lactam ring is intact in this intermediate, as well as in the following transition state-its cleavage is induced by proton transfer to the nitrogen atom in the lactam ring. However, for the model...
Hex-dominant mesh generation using 3D constrained triangulation
Energy Technology Data Exchange (ETDEWEB)
OWEN,STEVEN J.
2000-05-30
A method for decomposing a volume with a prescribed quadrilateral surface mesh, into a hexahedral-dominated mesh is proposed. With this method, known as Hex-Morphing (H-Morph), an initial tetrahedral mesh is provided. Tetrahedral are transformed and combined starting from the boundary and working towards the interior of the volume. The quadrilateral faces of the hexahedra are treated as internal surfaces, which can be recovered using constrained triangulation techniques. Implementation details of the edge and face recovery process are included. Examples and performance of the H-Morph algorithm are also presented.
Energy Technology Data Exchange (ETDEWEB)
Usov, V.A.; Timokhina, L.V.; Turchaninov, V.K.; Taryashinov, D.S.D.; Voronkov, M.G.
1987-11-10
Experimental evidence has been obtained indicating the existence of a netral intermediate with tetrahedral structure in the aminolysis of 2-alkoxy- and 3-alkylthio-2-cyclohexene-1-thiones. As in the aminolysis of alkylthiothioketone, the structure of the product of the 1,2-addition of the amine cannot be assigned to the tetrahedral intermediate in this reaction. This is indicated by the reaction of alkylthioketone with N-deuterated dimethylamine which gives only enaminothioketone without a trace of its C/sup 2/-deuterated analog as indicated by /sup 1/H NMR spectroscopy.
DEFF Research Database (Denmark)
Kelley, Matthew S.; Shelby, Megan L.; Mara, Michael W.
2017-01-01
have the general formula [Cu(I)(R)2]+, where R = 2,9-dimethyl-1,10-phenanthroline (dmp) and 2,9-diphenyl-1,10-phenanthroline disulfonic acid disodium salt (dpps). [Cu(I)(dmp)2]+ has methyl groups at the 2,9 positions of phenanthroline (phen) and adopts a pseudo-tetrahedral geometry. In contrast, [Cu......(I)(dpps)2]+ possesses two bulky phenyl-sulfonate groups attached to each phen ligand that force the molecule to adopt a flattened tetrahedral geometry in the ground state. Previously, optical transient absorption (OTA) and synchrotron based XTA experiments with 100 ps time resolution have been employed...
The γ-polymorph of AgZnPO4 with an ABW zeolite-type framework topology
Abderrazzak Assani; Mohamed Saadi; Lahcen El Ammari
2010-01-01
The γ-polymorph of the title compound, silver zinc orthophosphate, was synthesized under hydrothermal conditions. The structure consists of ZnO4, PO4 and AgO4 units. The coordination spheres of ZnII and PV are tetrahedral, whereas the AgI atom is considerably distorted from a tetrahedral coordination. Each O atom is linked to each of the three cations. An elliptic eight-membered ring system is formed by corner-sharing of alternating PO4 and ZnO4 tetrahedra, leading to a framework wit...
Hydrogen diffusion in doped and undoped α-Ti: An ab-initio investigation
Spiridonova, T. I.
2016-11-01
The projector augmented wave method within the density functional theory is used for calculation of the hydrogen diffusion paths in α-Ti. It is shown that the indirect mechanism of hydrogen diffusion between octahedral sites through a tetrahedral interstitial is more preferable than the direct path in the basal plane. In spite of that the lowest energy barrier of 0.1 eV is found between the tetrahedral sites along the c axis, this path is only a part of more complex path and a hydrogen atom can only oscillate between these positions. The influence of substitutional impurities on the main barriers is discussed.
Bordiga, S.; Scarano, D.; Lamberti, C; Zecchina, A.; Geobaldo, F.; Vlaic, G.; Buzzoni, R.; Tozzola, G.; Petrini, G.
1997-01-01
We report a XAFS study of the Fe3+ local environment in Fe-silicalite as a function of the template burning temperature. We investigate the structural changes of the zeolitic structure, upon thermal treatments and interaction with NH3. Our XAFS results show that, before template burning, Fe3+ are in tetrahedral symmetry with 4 oxygens at 1.85 Å, while after template removal and in vacuum conditions, they exhibit a distorted tetrahedral symmetry with 3 oxygens at 1.87 Å, and one at 2.10 Å ; do...
Compressibility and thermal expansion of cubic silicon nitride
DEFF Research Database (Denmark)
Jiang, Jianzhong; Lindelov, H.; Gerward, Leif
2002-01-01
The compressibility and thermal expansion of the cubic silicon nitride (c-Si3N4) phase have been investigated by performing in situ x-ray powder-diffraction measurements using synchrotron radiation, complemented with computer simulations by means of first-principles calculations. The bulk...... compressibility of the c-Si3N4 phase originates from the average of both Si-N tetrahedral and octahedral compressibilities where the octahedral polyhedra are less compressible than the tetrahedral ones. The origin of the unit cell expansion is revealed to be due to the increase of the octahedral Si-N and N-N bond...
Optical and electronic properties of some binary semiconductors from energy gaps
Tripathy, Sunil K
2015-01-01
II-VI and III-V tetrahedral semiconductors have significant potential for novel optoelectronic applications. In the present work, some of the optical and electronic properties of these groups of semiconductors have been studied using a recently proposed empirical relationship for refractive index from energy gap. The calculated values of these properties are also compared with those calculated from some well known relationships. From an analysis of the calculated electronic polarisability of these tetrahedral binary semiconductors from different formulations, we have proposed an empirical relation for its calculation. The predicted values of electronic polarisability of these semiconductors agree fairly well with the known values over a wide range of energy gap.
(μ-2,3-Dihydroxybutane-1,4-dithiolatobis[triphenyltin(IV
Directory of Open Access Journals (Sweden)
Cuiping Li
2010-02-01
Full Text Available In the title compound, [Sn2(C6H56(C4H8O2S2], the geometry around the Sn atoms is distorted tetrahedral. The hydroxy groups are involved in O—H...O hydrogen bonding, which connects molecules into centrosymmetric dimers.
Inertial confinement fusion quarterly report, October-December 1996
Energy Technology Data Exchange (ETDEWEB)
Hammer, J.
1997-01-01
The articles in this issue report progress on: Supernova Hydrodynamics Experiments on the Nova Laser; Characterization of Laser-Driven Shock Waves Using Interferometry; Absolute Equation of State Measurements of Compressed Liquid Deuterium Using Nova; Low-Density-Foam Shells; Tetrahedral Hohlraums; The Rosseland Mean Opacity of a Composite Material at High Temperatures.
Koningsberger, D.C.; Bokhoven, J.A. van; Kunkeler, P.J.; Bekkum, H. van
2002-01-01
The effect of steam activation on the aluminum coordination in zeolite NH{4}-beta was investigated by means of quantitative analysis of Al K edge XANES spectra. Framework tetrahedral aluminum is converted to octahedral aluminum after calcination and steaming, a process that, at the same time,
Water in a Soft Confinement: Structure of Water in Amorphous Sorbitol.
Shalaev, Evgenyi; Soper, Alan K
2016-07-28
The structure of water in 70 wt % sorbitol-30 wt % water mixture is investigated by wide-angle neutron scattering (WANS) as a function of temperature. WANS data are analyzed using empirical potential structure refinement to obtain the site-site radial distribution functions (RDFs). Orientational structure of water is represented using OW-OW-OW triangles distributions and a tetrahedrality parameter, q, while water-water correlation function is used to estimate size of water clusters. Water structure in the sorbitol matrix is compared with that of water confined in nanopores of MCM41. The results indicate the existence of voids in the sorbitol matrix with the length scale of approximately 5 Å, which are filled by water. At 298 K, positional water structure in these voids is similar to that of water in MCM41, whereas there is a difference in the tetrahedral (orientational) arrangement. Cooling to 213 K strengthens tetrahedrality, with the orientational order of water in sorbitol becoming similar to that of confined water in MCM41 at 210 K, whereas further cooling to 100 K does not introduce any additional changes in the tetrahedrality. The results obtained allow us to propose, for the first time, that such confinement of water in a sorbitol matrix is the main reason for the lack of ice formation in this system.
A Comparison of Inexact Newton and Coordinate Descent Meshoptimization Technqiues
Energy Technology Data Exchange (ETDEWEB)
Diachin, L F; Knupp, P; Munson, T; Shontz, S
2004-07-08
We compare inexact Newton and coordinate descent methods for optimizing the quality of a mesh by repositioning the vertices, where quality is measured by the harmonic mean of the mean-ratio metric. The effects of problem size, element size heterogeneity, and various vertex displacement schemes on the performance of these algorithms are assessed for a series of tetrahedral meshes.
DeGrand, Michael J.; Abrams, M. Leigh; Jenkins, Judith L.; Welch, Lawrence E.
2011-01-01
By adding a large quantity of Cl[superscript -] to an aqueous solution of CoCl[subscript 2][multiplied by]6H[subscript 2]O, a mixture containing a red octahedral cobalt complex and a blue tetrahedral complex is produced. When the solution temperature is modified, the equilibrium constant, K[subscript eq], of the complexation reaction is shifted…
A unified multigrid solver for the Navier-Stokes equations on mixed element meshes
Mavriplis, D. J.; Venkatakrishnan, V.
1995-01-01
A unified multigrid solution technique is presented for solving the Euler and Reynolds-averaged Navier-Stokes equations on unstructured meshes using mixed elements consisting of triangles and quadrilaterals in two dimensions, and of hexahedra, pyramids, prisms, and tetrahedra in three dimensions. While the use of mixed elements is by no means a novel idea, the contribution of the paper lies in the formulation of a complete solution technique which can handle structured grids, block structured grids, and unstructured grids of tetrahedra or mixed elements without any modification. This is achieved by discretizing the full Navier-Stokes equations on tetrahedral elements, and the thin layer version of these equations on other types of elements, while using a single edge-based data-structure to construct the discretization over all element types. An agglomeration multigrid algorithm, which naturally handles meshes of any types of elements, is employed to accelerate convergence. An automatic algorithm which reduces the complexity of a given triangular or tetrahedral mesh by merging candidate triangular or tetrahedral elements into quadrilateral or prismatic elements is also described. The gains in computational efficiency afforded by the use of non-simplicial meshes over fully tetrahedral meshes are demonstrated through several examples.
OVERVIEW AND CLASSIFICATION OF PERMANENT OFFSHORE PLATFORMS FOR WORKING IN ICE CONDITIONS
Mr. Nikolay A. Taranukha; Mr Andrey S. Mironov
2016-01-01
This article is dedicated to permanent offshore platforms for working in ice conditions. The authors focus on creating constructions for working in ice conditions. The article presents drawings of ice-resistant permanent offshore platforms according to their attachment to the seabed. The article also describes the scheme of the general arrangement of the ice-resistant tetrahedral permanent offshore platforms.
Intemann, Julia; Spielmann, Jan; Sirsch, Peter; Harder, Sjoerd
A new tetranuclear magnesium hydride cluster, [{NN-(MgH)2}2], which was based on a NN-coupled bis--diketiminate ligand (NN2-), was obtained from the reaction of [{NN-(MgnBu)2}2] with PhSiH3. Its crystal structure reveals an almost-tetrahedral arrangement of Mg atoms and two different sets of hydride
Mahlmoodite, FeZr(PO4).4H2O, a new iron zirconium phosphate mineral from Wilson Springs, Arkansas
Milton, C.; McGee, J.J.; Evans, H.T.
1993-01-01
Small (phosphate tetrahedrate, FeZr(PO4)2.4H2O. This new mineral, named mahlmoodite, occurs as spherules of radiating fibers usually perched on crystals of pyroxene in vugs. The optical and crystallographic properties of mahlmoodite are described. -after Authors
A Comparison of Continuous Mass-lumped Finite Elements and Finite Differences for 3D
Zhebel, E.; Minisini, S.; Kononov, A.; Mulder, W.A.
2012-01-01
The finite-difference method is widely used for time-domain modelling of the wave equation because of its ease of implementation of high-order spatial discretization schemes, parallelization and computational efficiency. However, finite elements on tetrahedral meshes are more accurate in complex geo
(2,2′-Dimethyl-4,4′-bi-1,3-thiazole-κ2N,N′bis(thiocyanato-κSmercury(II
Directory of Open Access Journals (Sweden)
Nasser Safari
2009-04-01
Full Text Available The HgII atom in the title compound, [Hg(SCN2(C8H8N2S2], is chelated by the bidentate heterocycle through the N atoms and is coordinated by the S atoms of two thiocyanate anions, resulting in a considerably distorted tetrahedral coordination geometry.
Dichloridobis[1-(2-methylbenzimidazol-1-ylmethyl-κN3benzotriazole]mercury(II
Directory of Open Access Journals (Sweden)
Jie Wu
2009-07-01
Full Text Available In the title compound, [HgCl2(C15H13N52], the HgII atom is located on a twofold rotation axis and resides in a distorted tetrahedral coordination environment composed of two Cl atoms and two N atoms from two 1-(2-methylbenzimidazol-1-ylmethylbenzotriazole ligands.
motivated particularly by the special conditions and considerations of importance to molecular beam epitaxial ( MBE ) growth of interfaces between tetrahedrally...presentation of a conceptual framework for MBE growth . This coherent presentation unfolds several kinetic aspects and their finer considerations which may by...defects and impurities, the surface migration kinetics, etc. in MBE growth . (Reprints)
Formation of global energy minimim structures in the growth process of Lennard-Jones clusters
DEFF Research Database (Denmark)
Solov'yov, Ilia; Koshelev, Andrey; Shutovich, Andrey
2003-01-01
We present a new theoretical framework for modelling the cluster growing process. Starting from the initial tetrahedral cluster configuration, adding new atoms to the system and absorbing its energy at each step, we find cluster growing paths up to the cluster sizes of 150 atoms. We demonstrate t...
Hartree-Fock Cluster Study of Interstitial Transition Metals in Silicon
Broer, R.; Aissing, G.; Nieuwpoort, W.C.; Feiner, L.F.
1986-01-01
Results are presented of a Hartree-Fock cluster study of interstitial Ti, V, Cr, and Mn impurities in silicon. A Si10 cluster models the nearest Si atoms around a tetrahedral interstitial site in crystalline Si. The dangling bonds of the Si atoms are saturated by hydrogens. The effect of the Si core
V-shaped nematogens with the "magic bent angle".
Seltmann, Jens; Müller, Kathrin; Klein, Susanne; Lehmann, Matthias
2011-06-21
V-shaped nematogens 1a-c and 2a-b with benzodithiophene bending units have been synthesised. The derivatives 1a-c comprise a flat core with a bending angle of 109°, which is almost the tetrahedral angle proposed to be optimal in the realization of mesogens forming a biaxial nematic thermotropic mesophase.
Activation of CO2 by phosphinoamide hafnium complexes.
Sgro, Michael J; Stephan, Douglas W
2013-04-04
Hf-phosphinoamide cation complexes behave as metal-based frustrated Lewis pairs and bind one or two equivalent of CO2 and in as well can activate CO2 in a bimetallic fashion to give a pseudo-tetrahedral P2CO2 fragment linking two Hf centres.