Ising antiferromagnet on a finite triangular lattice with free boundary conditions

NASA Astrophysics Data System (ADS)

Kim, Seung-Yeon

2015-11-01

The exact integer values for the density of states of the Ising model on an equilateral triangular lattice with free boundary conditions are evaluated up to L = 24 spins on a side for the first time by using the microcanonical transfer matrix. The total number of states is 2 N s = 2300 ≈ 2.037 × 1090 for L = 24, where N s = L( L+1)/2 is the number of spins. Classifying all 2300 spin states according to their energy values is an enormous work. From the density of states, the exact partition function zeros in the complex temperature plane of the triangular-lattice Ising model are evaluated. Using the density of states and the partition function zeros, we investigate the properties of the triangularlattice Ising antiferromagnet. The scaling behavior of the ground-state entropy and the form of the correlation length at T = 0 are studied for the triangular-lattice Ising antiferromagnet with free boundary conditions. Also, the scaling behavior of the Fisher edge singularity is investigated.

High magnetic field magnetization of a new triangular lattice antiferromagnet

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhou, H. D.; Stritzinger, Laurel Elaine Winter; Harrison, Neil

2017-03-23

In CsV(MoO 4) 2, the magnetic V 3+ ions with octahedral oxygen-coordination form a geometrically frustrated triangular lattice. So fare, there is no magnetic properties reported on it. Recently, we successfully grew single crystals of CsV(MoO 4) 2 by using flux method. The susceptibility shows a sharp drop around 24 K, representing a long range magnetic ordering. To understand the physical properties of this new triangular lattice antiferromagnet (TLAF), we pursued high field magnetization measurements to answer two questions: (i) what is the saturation field, which will be very useful to calculate the exchange interaction of the system? (ii) Willmore » it exhibit spin state transition, such as the up up down phase with 1/3-saturation moment as other TLAFs? Recently, we performed VSM measurements in Cell 8, Tallahassee, NHMFL, the results show that the magnetization reaches 0.38 MuB at 34 T, which is just 19% of the full moment of 2 MuB for V 3+ (3d 2) ions. Apparently we need higher field to reach 1/3 value or full moment.« less

Yu-Shiba-Rusinov states of impurities in a triangular lattice of NbSe2 with spin-orbit coupling

NASA Astrophysics Data System (ADS)

Ptok, Andrzej; Głodzik, Szczepan; Domański, Tadeusz

2017-11-01

We study the topography of the spin-polarized bound states of magnetic impurities embedded in a triangular lattice of a superconducting host. Such states have been observed experimentally in 2 H -NbSe2 crystal [G. C. Ménard et al., Nat. Phys. 11, 1013 (2015), 10.1038/nphys3508], and they revealed oscillating particle-hole asymmetry extending to tens of nanometers. Using the Bogoliubov-de Gennes approach, we explore the Yu-Shiba-Rusinov states in the presence of spin-orbit interaction. We also study the bound states of double impurities for several relative positions in a triangular lattice.

Spin Structures and Phase Diagrams of Extended Spatially Completely Anisotropic Triangular Lattice Antiferromagnets

NASA Astrophysics Data System (ADS)

Sakakida, Keishiro; Shimahara, Hiroshi

2017-12-01

Motivated by recently discovered organic antiferromagnets, we examine an extended triangular lattice that consists of two types of triangles of bonds with exchange coupling constants Jℓ and J'ℓ (ℓ= 1, 2, and 3), respectively. The simplified system with Jℓ = J'ℓ > 0 is the spatially completely anisotropic triangular lattice (SCATL) antiferromagnet examined previously. The extended system, which we call an extended SCATL (ESCATL), has two different spatial anisotropy parameters J3/J2 and J'3/J'2 when J1 = J'1 is assumed. We derive classical phase diagrams and spin structures. It is found that the ESCATL antiferromagnet exhibits two up-up-down-down (uudd) phases when the imbalance of the anisotropy parameters is significant, in addition to the three Néel phases that occur in the SCATL. When the model parameters vary, these collinear phases are continuously connected by the spiral-spin phase. Using the available model parameters for the organic compounds λ-(BETS)2XCl4 (X = Fe and Ga), we examine the stabilities of the spin structures of the independent π-electron system, which is considered to primarily sustain the magnetic order, where BETS represents bis(ethylenedithio)tetraselenafulvalene. It is found that one of the uudd phases has an energy close to the ground-state energy for λ-(BETS)2FeCl4. We discuss the relevance of the magnetic anion FeCl4 and the quantum fluctuation to the magnetism of these compounds. When J'3 = 0, the system is reduced to a trellis lattice antiferromagnet. The system exhibits a stripe spiral-spin phase, which comprises one-dimensional spiral-spin states stacked alternately.

A nonlinear mechanics model of bio-inspired hierarchical lattice materials consisting of horseshoe microstructures

PubMed Central

Ma, Qiang; Cheng, Huanyu; Jang, Kyung-In; Luan, Haiwen; Hwang, Keh-Chih; Rogers, John A.; Huang, Yonggang; Zhang, Yihui

2016-01-01

Development of advanced synthetic materials that can mimic the mechanical properties of non-mineralized soft biological materials has important implications in a wide range of technologies. Hierarchical lattice materials constructed with horseshoe microstructures belong to this class of bio-inspired synthetic materials, where the mechanical responses can be tailored to match the nonlinear J-shaped stress-strain curves of human skins. The underlying relations between the J-shaped stress-strain curves and their microstructure geometry are essential in designing such systems for targeted applications. Here, a theoretical model of this type of hierarchical lattice material is developed by combining a finite deformation constitutive relation of the building block (i.e., horseshoe microstructure), with the analyses of equilibrium and deformation compatibility in the periodical lattices. The nonlinear J-shaped stress-strain curves and Poisson ratios predicted by this model agree very well with results of finite element analyses (FEA) and experiment. Based on this model, analytic solutions were obtained for some key mechanical quantities, e.g., elastic modulus, Poisson ratio, peak modulus, and critical strain around which the tangent modulus increases rapidly. A negative Poisson effect is revealed in the hierarchical lattice with triangular topology, as opposed to a positive Poisson effect in hierarchical lattices with Kagome and honeycomb topologies. The lattice topology is also found to have a strong influence on the stress-strain curve. For the three isotropic lattice topologies (triangular, Kagome and honeycomb), the hierarchical triangular lattice material renders the sharpest transition in the stress-strain curve and relative high stretchability, given the same porosity and arc angle of horseshoe microstructure. Furthermore, a demonstrative example illustrates the utility of the developed model in the rapid optimization of hierarchical lattice materials for reproducing the desired stress-strain curves of human skins. This study provides theoretical guidelines for future designs of soft bio-mimetic materials with hierarchical lattice constructions. PMID:27087704

A nonlinear mechanics model of bio-inspired hierarchical lattice materials consisting of horseshoe microstructures

NASA Astrophysics Data System (ADS)

Ma, Qiang; Cheng, Huanyu; Jang, Kyung-In; Luan, Haiwen; Hwang, Keh-Chih; Rogers, John A.; Huang, Yonggang; Zhang, Yihui

2016-05-01

Development of advanced synthetic materials that can mimic the mechanical properties of non-mineralized soft biological materials has important implications in a wide range of technologies. Hierarchical lattice materials constructed with horseshoe microstructures belong to this class of bio-inspired synthetic materials, where the mechanical responses can be tailored to match the nonlinear J-shaped stress-strain curves of human skins. The underlying relations between the J-shaped stress-strain curves and their microstructure geometry are essential in designing such systems for targeted applications. Here, a theoretical model of this type of hierarchical lattice material is developed by combining a finite deformation constitutive relation of the building block (i.e., horseshoe microstructure), with the analyses of equilibrium and deformation compatibility in the periodical lattices. The nonlinear J-shaped stress-strain curves and Poisson ratios predicted by this model agree very well with results of finite element analyses (FEA) and experiment. Based on this model, analytic solutions were obtained for some key mechanical quantities, e.g., elastic modulus, Poisson ratio, peak modulus, and critical strain around which the tangent modulus increases rapidly. A negative Poisson effect is revealed in the hierarchical lattice with triangular topology, as opposed to a positive Poisson effect in hierarchical lattices with Kagome and honeycomb topologies. The lattice topology is also found to have a strong influence on the stress-strain curve. For the three isotropic lattice topologies (triangular, Kagome and honeycomb), the hierarchical triangular lattice material renders the sharpest transition in the stress-strain curve and relative high stretchability, given the same porosity and arc angle of horseshoe microstructure. Furthermore, a demonstrative example illustrates the utility of the developed model in the rapid optimization of hierarchical lattice materials for reproducing the desired stress-strain curves of human skins. This study provides theoretical guidelines for future designs of soft bio-mimetic materials with hierarchical lattice constructions.

A nonlinear mechanics model of bio-inspired hierarchical lattice materials consisting of horseshoe microstructures.

PubMed

Ma, Qiang; Cheng, Huanyu; Jang, Kyung-In; Luan, Haiwen; Hwang, Keh-Chih; Rogers, John A; Huang, Yonggang; Zhang, Yihui

2016-05-01

Development of advanced synthetic materials that can mimic the mechanical properties of non-mineralized soft biological materials has important implications in a wide range of technologies. Hierarchical lattice materials constructed with horseshoe microstructures belong to this class of bio-inspired synthetic materials, where the mechanical responses can be tailored to match the nonlinear J-shaped stress-strain curves of human skins. The underlying relations between the J-shaped stress-strain curves and their microstructure geometry are essential in designing such systems for targeted applications. Here, a theoretical model of this type of hierarchical lattice material is developed by combining a finite deformation constitutive relation of the building block (i.e., horseshoe microstructure), with the analyses of equilibrium and deformation compatibility in the periodical lattices. The nonlinear J-shaped stress-strain curves and Poisson ratios predicted by this model agree very well with results of finite element analyses (FEA) and experiment. Based on this model, analytic solutions were obtained for some key mechanical quantities, e.g., elastic modulus, Poisson ratio, peak modulus, and critical strain around which the tangent modulus increases rapidly. A negative Poisson effect is revealed in the hierarchical lattice with triangular topology, as opposed to a positive Poisson effect in hierarchical lattices with Kagome and honeycomb topologies. The lattice topology is also found to have a strong influence on the stress-strain curve. For the three isotropic lattice topologies (triangular, Kagome and honeycomb), the hierarchical triangular lattice material renders the sharpest transition in the stress-strain curve and relative high stretchability, given the same porosity and arc angle of horseshoe microstructure. Furthermore, a demonstrative example illustrates the utility of the developed model in the rapid optimization of hierarchical lattice materials for reproducing the desired stress-strain curves of human skins. This study provides theoretical guidelines for future designs of soft bio-mimetic materials with hierarchical lattice constructions.

Quantum fluctuations in anisotropic triangular lattices with ferromagnetic and antiferromagnetic exchange

NASA Astrophysics Data System (ADS)

Schmidt, Burkhard; Thalmeier, Peter

2014-05-01

The Heisenberg model on a triangular lattice is a prime example of a geometrically frustrated spin system. However most experimentally accessible compounds have spatially anisotropic exchange interactions. As a function of this anisotropy, ground states with different magnetic properties can be realized. Motivated by recent experimental findings on Cs2CuCl4-xBrx, we discuss the full phase diagram of the anisotropic model with two exchange constants J1 and J2, including possible ferromagnetic exchange. Furthermore a comparison with the related square lattice model is carried out. We discuss the zero-temperature phase diagram, ordering vector, ground-state energy, and ordered moment on a classical level and investigate the effect of quantum fluctuations within the framework of spin-wave theory. The field dependence of the ordered moment is shown to be nonmonotonic with field and control parameter.

Magnetic order in a frustrated two-dimensional atom lattice at a semiconductor surface.

PubMed

Li, Gang; Höpfner, Philipp; Schäfer, Jörg; Blumenstein, Christian; Meyer, Sebastian; Bostwick, Aaron; Rotenberg, Eli; Claessen, Ralph; Hanke, Werner

2013-01-01

Two-dimensional electron systems, as exploited for device applications, can lose their conducting properties because of local Coulomb repulsion, leading to a Mott-insulating state. In triangular geometries, any concomitant antiferromagnetic spin ordering can be prevented by geometric frustration, spurring speculations about 'melted' phases, known as spin liquid. Here we show that for a realization of a triangular electron system by epitaxial atom adsorption on a semiconductor, such spin disorder, however, does not appear. Our study compares the electron excitation spectra obtained from theoretical simulations of the correlated electron lattice with data from high-resolution photoemission. We find that an unusual row-wise antiferromagnetic spin alignment occurs that is reflected in the photoemission spectra as characteristic 'shadow bands' induced by the spin pattern. The magnetic order in a frustrated lattice of otherwise non-magnetic components emerges from longer-range electron hopping between the atoms. This finding can offer new ways of controlling magnetism on surfaces.

Field-controlled ultrafast magnetization dynamics in two-dimensional nanoscale ferromagnetic antidot arrays

PubMed Central

De, Anulekha; Mondal, Sucheta; Sahoo, Sourav; Barman, Saswati; Otani, Yoshichika; Mitra, Rajib Kumar

2018-01-01

Ferromagnetic antidot arrays have emerged as a system of tremendous interest due to their interesting spin configuration and dynamics as well as their potential applications in magnetic storage, memory, logic, communications and sensing devices. Here, we report experimental and numerical investigation of ultrafast magnetization dynamics in a new type of antidot lattice in the form of triangular-shaped Ni80Fe20 antidots arranged in a hexagonal array. Time-resolved magneto-optical Kerr effect and micromagnetic simulations have been exploited to study the magnetization precession and spin-wave modes of the antidot lattice with varying lattice constant and in-plane orientation of the bias-magnetic field. A remarkable variation in the spin-wave modes with the orientation of in-plane bias magnetic field is found to be associated with the conversion of extended spin-wave modes to quantized ones and vice versa. The lattice constant also influences this variation in spin-wave spectra and spin-wave mode profiles. These observations are important for potential applications of the antidot lattices with triangular holes in future magnonic and spintronic devices. PMID:29719763

Dirac fermions and pseudomagnetic fields in two-dimensional electron gases with triangular antidot lattices

NASA Astrophysics Data System (ADS)

Li, Yun-Mei; Zhou, Xiaoying; Zhang, Yan-Yang; Zhang, Dong; Chang, Kai

2017-07-01

We investigate theoretically the electronic properties of two-dimensional electron gases (2DEGs) with regular and distorted triangular antidot lattices. We show that the triangular antidot lattices embedded in 2DEGs behave like artificial graphene and host Dirac fermions. By introducing the Wannier representation, we obtain a tight-binding Hamiltonian including the second-nearest-neighboring hopping, which agrees well with the numerically exact solutions. Based on the tight-binding model, we find that spatially nonuniform distortions of the antidot lattices strongly modify the electronic structures, generate pseudomagnetic fields and the well-defined Landau levels. In contrast to graphene, we can design the nonuniform distortions to generate various configurations of pseudomagnetic fields. We show that the snake orbital states arise by designing the ±B pseudomagnetic field configuration. We find that the disorders of antidot lattices during fabrication would not affect the basic feature of the Dirac electrons, but they lead to a reduction in conductance in strong disorder cases.

Triangular lattice atomic layer of Sn(1 × 1) at graphene/SiC(0001) interface

NASA Astrophysics Data System (ADS)

Hayashi, Shingo; Visikovskiy, Anton; Kajiwara, Takashi; Iimori, Takushi; Shirasawa, Tetsuroh; Nakastuji, Kan; Miyamachi, Toshio; Nakashima, Shuhei; Yaji, Koichiro; Mase, Kazuhiko; Komori, Fumio; Tanaka, Satoru

2018-01-01

Sn atomic layers attract considerable interest owing to their spin-related physical properties caused by their strong spin-orbit interactions. We performed Sn intercalation into the graphene/SiC(0001) interface and found a new type of Sn atomic layer. Sn atoms occupy on-top sites of Si-terminated SiC(0001) with in-plane Sn-Sn bondings, resulting in a triangular lattice. Angle-resolved photoemission spectroscopy revealed characteristic dispersions at \\bar{\\text{K}} and \\bar{\\text{M}} points, which agreed well with density functional theory calculations. The Sn triangular lattice atomic layer at the interface showed no oxidation upon exposure to air, which is useful for characterization and device fabrication ex situ.

One-dimensional magnetic fluctuations in the spin-2 triangular lattice alpha-NaMnO2.

PubMed

Stock, C; Chapon, L C; Adamopoulos, O; Lappas, A; Giot, M; Taylor, J W; Green, M A; Brown, C M; Radaelli, P G

2009-08-14

The S=2 anisotropic triangular lattice alpha-NaMnO2 is studied by neutron inelastic scattering. Antiferromagnetic order occurs at T< or =45 K with opening of a spin gap. The spectral weight of the magnetic dynamics above the gap (Delta approximately equal to 7.5 meV) has been analyzed by the single-mode approximation. Excellent agreement with the experiment is achieved when a dominant exchange interaction (|J|/k(B) approximately 73 K), along the monoclinic b axis and a sizable easy-axis magnetic anisotropy (|D|/k(B) approximately 3 K) are considered. Despite earlier suggestions for two-dimensional spin interactions, the dynamics illustrate strongly coupled antiferromagnetic S=2 chains and cancellation of the interchain exchange due to the lattice topology. alpha-NaMnO2 therefore represents a model system where the geometric frustration is resolved through the lowering of the dimensionality of the spin interactions.

Simultaneous breaking of lattice symmetry and spin frustration in triangular lattice antiferromagnet CuFeO2

NASA Astrophysics Data System (ADS)

Ren, Y.; Ye, F.; Huang, Q.; Fernandez-Baca, J. A.; Dai, Pengcheng; Lynn, J. W.; Kimura, T.

2006-03-01

We use high resolution synchrotron X-ray and neutron diffraction to study the geometrically frustrated triangular lattice antiferromagnet (TLA) CuFeO2. We show that the occurrence of the two magnetic transitions, at 14 K and 11 K, respectively is accompanied simultaneously by a second-and first- order structural phase transitions from a hexagonal structure to a monoclinic form. This is the first observation of two successive spin-driven structural transitions directly coupled with incommensurate and commensurate magnetic orderings in frustrated TLA systems. This work is supported by the U. S. NSF DMR-0453804 and DOE Nos. DE-FG02-05ER46202 and DE-AC05-00OR22725 with UT/Battelle LLC. Use of the Advanced Photon Source was supported by the U. S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. W-31-109-Eng-38.

Symmetry-protected gapless Z2 spin liquids

NASA Astrophysics Data System (ADS)

Lu, Yuan-Ming

2018-03-01

Despite rapid progress in understanding gapped topological states, much less is known about gapless topological phases of matter, especially in strongly correlated electrons. In this work, we discuss a large class of robust gapless quantum spin liquids in frustrated magnets made of half-integer spins, which are described by gapless fermionic spinons coupled to dynamical Z2 gauge fields. Requiring U(1 ) spin conservation, time-reversal, and certain space-group symmetries, we show that certain spinon symmetry fractionalization class necessarily leads to a gapless spectrum. These gapless excitations are stable against any perturbations, as long as the required symmetries are preserved. Applying these gapless criteria to spin-1/2 systems on square, triangular, and kagome lattices, we show that all gapped symmetric Z2 spin liquids in Abrikosov-fermion representation can also be realized in Schwinger-boson representation. This leads to 64 gapped Z2 spin liquids on square lattice, and 8 gapped states on both kagome and triangular lattices.

Jamming and percolation in random sequential adsorption of straight rigid rods on a two-dimensional triangular lattice

NASA Astrophysics Data System (ADS)

Perino, E. J.; Matoz-Fernandez, D. A.; Pasinetti, P. M.; Ramirez-Pastor, A. J.

2017-07-01

Monte Carlo simulations and finite-size scaling analysis have been performed to study the jamming and percolation behavior of linear k-mers (also known as rods or needles) on a two-dimensional triangular lattice of linear dimension L, considering an isotropic RSA process and periodic boundary conditions. Extensive numerical work has been done to extend previous studies to larger system sizes and longer k-mers, which enables the confirmation of a nonmonotonic size dependence of the percolation threshold and the estimation of a maximum value of k from which percolation would no longer occur. Finally, a complete analysis of critical exponents and universality has been done, showing that the percolation phase transition involved in the system is not affected, having the same universality class of the ordinary random percolation.

Magnetic Interaction in the Geometrically Frustrated Triangular LatticeAntiferromagnet CuFeO2

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ye, Feng; Fernandez-Baca, Jaime A; Fishman, Randy Scott

2007-01-01

The spin wave excitations of the geometrically frustrated triangular lattice antiferromagnet (TLA) CuFeO2 have been measured using high resolution inelastic neutron scattering. Antiferromagnetic interactions up to third nearest neighbors in the ab plane (J1, J2, J3, with J2=J1 0:44 and J3=J1 0:57), as well as out-of-plane coupling (Jz, with Jz=J1 0:29) are required to describe the spin wave dispersion relations, indicating a three dimensional character of the magnetic interactions. Two energy deeps in the spin wave dispersion occur at the incommensurate wavevectors associated with multiferroic phase, and can be interpreted as dynamic precursors to the magnetoelectric behavior in this system.

Topological color codes on Union Jack lattices: a stable implementation of the whole Clifford group

DOE Office of Scientific and Technical Information (OSTI.GOV)

Katzgraber, Helmut G.; Theoretische Physik, ETH Zurich, CH-8093 Zurich; Bombin, H.

We study the error threshold of topological color codes on Union Jack lattices that allow for the full implementation of the whole Clifford group of quantum gates. After mapping the error-correction process onto a statistical mechanical random three-body Ising model on a Union Jack lattice, we compute its phase diagram in the temperature-disorder plane using Monte Carlo simulations. Surprisingly, topological color codes on Union Jack lattices have a similar error stability to color codes on triangular lattices, as well as to the Kitaev toric code. The enhanced computational capabilities of the topological color codes on Union Jack lattices with respectmore » to triangular lattices and the toric code combined with the inherent robustness of this implementation show good prospects for future stable quantum computer implementations.« less

The Rényi entanglement entropy of a general quantum dimer model at the RK point: a highly efficient algorithm.

PubMed

Pei, Jiquan; Han, Steve; Liao, Haijun; Li, Tao

2014-01-22

A highly efficient and simple-to-implement Monte Carlo algorithm is proposed for the evaluation of the Rényi entanglement entropy (REE) of the quantum dimer model (QDM) at the Rokhsar-Kivelson (RK) point. It makes possible the evaluation of REE at the RK point to the thermodynamic limit for a general QDM. We apply the algorithm to a QDM defined on the triangular and the square lattice in two dimensions and the simple and the face centered cubic (fcc) lattice in three dimensions. We find the REE on all these lattices follows perfect linear scaling in the thermodynamic limit, apart from an even-odd oscillation in the case of the square lattice. We also evaluate the topological entanglement entropy (TEE) with both a subtraction and an extrapolation procedure. We find the QDMs on both the triangular and the fcc lattice exhibit robust Z2 topological order. The expected TEE of ln2 is clearly demonstrated in both cases. Our large scale simulation also proves the recently proposed extrapolation procedure in cylindrical geometry to be a highly reliable way to extract the TEE of a topologically ordered system.

Complete band gaps of phononic crystal plates with square rods.

PubMed

El-Naggar, Sahar A; Mostafa, Samia I; Rafat, Nadia H

2012-04-01

Much of previous work has been devoted in studying complete band gaps for bulk phononic crystal (PC). In this paper, we theoretically investigate the existence and widths of these gaps for PC plates. We focus our attention on steel rods of square cross sectional area embedded in epoxy matrix. The equations for calculating the dispersion relation for square rods in a square or a triangular lattice have been derived. Our analysis is based on super cell plane wave expansion (SC-PWE) method. The influence of inclusions filling factor and plate thickness on the existence and width of the phononic band gaps has been discussed. Our calculations show that there is a certain filling factor (f=0.55) below which arrangement of square rods in a triangular lattice is superior to the arrangement in a square lattice. A comparison between square and circular cross sectional rods reveals that the former has superior normalized gap width than the latter in case of a square lattice. This situation is switched in case of a triangular lattice. Moreover, a maximum normalized gap width of 0.7 can be achieved for PC plate of square rods embedded in a square lattice and having height 90% of the lattice constant. Copyright © 2011 Elsevier B.V. All rights reserved.

Bold Diagrammatic Monte Carlo for Fermionic and Fermionized Systems

NASA Astrophysics Data System (ADS)

Svistunov, Boris

2013-03-01

In three different fermionic cases--repulsive Hubbard model, resonant fermions, and fermionized spins-1/2 (on triangular lattice)--we observe the phenomenon of sign blessing: Feynman diagrammatic series features finite convergence radius despite factorial growth of the number of diagrams with diagram order. Bold diagrammatic Monte Carlo technique allows us to sample millions of skeleton Feynman diagrams. With the universal fermionization trick we can fermionize essentially any (bosonic, spin, mixed, etc.) lattice system. The combination of fermionization and Bold diagrammatic Monte Carlo yields a universal first-principle approach to strongly correlated lattice systems, provided the sign blessing is a generic fermionic phenomenon. Supported by NSF and DARPA

Spin liquid state in the disordered triangular lattice Sc 2Ga 2CuO 7 revealed by NMR

DOE PAGES

Khuntia, P.; Kumar, R.; Mahajan, A. V.; ...

2016-04-18

We present microscopic magnetic properties of a two-dimensional triangular lattice Sc 2Ga 2CuO 7, consisting of single and double triangular Cu planes. An antiferromagnetic (AFM) exchange interaction J/k B ≈ 35 K between Cu 2+ (S = 1/2) spins in the triangular biplane is obtained from the analysis of intrinsic magnetic susceptibility data. The intrinsic magnetic susceptibility, extracted from 71Ga NMR shift data, displays the presence of AFM short range spin correlations and remains finite down to 50 mK, suggesting a nonsinglet ground state. The nuclear spin-lattice relaxation rate (1/T 1) reveals a slowing down of Cu 2+ spin fluctuationsmore » with decreasing T down to 100 mK. Magnetic specific heat (C m) and 1/T 1 exhibit power law behavior at low temperatures, implying the gapless nature of the spin excitation spectrum. The absence of long range magnetic ordering down to ~J/700, nonzero spin susceptibility at low T, and the power law behavior of C m and 1/T 1 suggest a gapless quantum spin liquid (QSL) state. Our results demonstrate that persistent spin dynamics induced by frustration maintain a quantum-disordered state at T → 0 in this triangular lattice antiferromagnet. Furthermore, this suggests that the low energy modes are dominated by spinon excitations in the QSL state due to randomness engendered by disorder and frustration.« less

Investigation of a Structural Phase Transition and Magnetic Structure of Na 2BaFe(VO 4) 2: A Triangular Magnetic Lattice with a Ferromagnetic Ground State

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sanjeewa, Liurukara D.; Garlea, Vasile O.; McGuire, Michael A.

The structural and magnetic properties of a glaserite-type Na 2BaFe(VO 4) 2 compound, featuring a triangular magnetic lattice of Fe 2+ (S = 2), are reported. Temperature dependent X-ray single crystal studies indicate that at room temperature the system adopts a trigonal Pmore » $$\\bar{3}$$ m1 structure and undergoes a structural phase transition to a C2/c monoclinic phase slightly below room temperature (T s = 288 K). This structural transition involves a tilting of Fe–O–V bond angles and strongly influences the magnetic correlation within the Fe triangular lattice. The magnetic susceptibility measurements reveal a ferromagnetic transition near 7 K. Single crystal neutron diffraction confirms the structural distortion and the ferromagnetic spin ordering in Na 2BaFe(VO 4) 2. The magnetic structure of the ordered state is modeled in the magnetic space group C2'/c' that implies a ferromagnetic order of the a and c moment components and antiferromagnetic arrangement for the b components. Altogether, the Fe magnetic moments form ferromagnetic layers that are stacked along the c-axis, where the spins point along one of the (111) facets of the FeO 6 octahedron.« less

Absence of Long-Range Order in a Triangular Spin System with Dipolar Interactions

NASA Astrophysics Data System (ADS)

Keleş, Ahmet; Zhao, Erhai

2018-05-01

The antiferromagnetic Heisenberg model on the triangular lattice is perhaps the best known example of frustrated magnets, but it orders at low temperatures. Recent density matrix renormalization group (DMRG) calculations find that the next nearest neighbor interaction J2 enhances the frustration, and it leads to a spin liquid for J2/J1∈(0.08 ,0.15 ). In addition, a DMRG study of a dipolar Heisenberg model with longer range interactions gives evidence for a spin liquid at a small dipole tilting angle θ ∈[0 ,1 0 ° ). In both cases, the putative spin liquid region appears to be small. Here, we show that for the triangular lattice dipolar Heisenberg model, a robust quantum paramagnetic phase exists in a surprisingly wide region, θ ∈[0 ,5 4 ° ) , for dipoles tilted along the lattice diagonal direction. We obtain the phase diagram of the model by functional renormalization group (RG), which treats all magnetic instabilities on equal footing. The quantum paramagnetic phase is characterized by a smooth continuous flow of vertex functions and spin susceptibility down to the lowest RG scale, in contrast to the apparent breakdown of RG flow in phases with stripe or spiral order. Our finding points to a promising direction to search for quantum spin liquids in ultracold dipolar molecules.

Investigation of a Structural Phase Transition and Magnetic Structure of Na 2BaFe(VO 4) 2: A Triangular Magnetic Lattice with a Ferromagnetic Ground State

DOE PAGES

Sanjeewa, Liurukara D.; Garlea, Vasile O.; McGuire, Michael A.; ...

2017-12-07

The structural and magnetic properties of a glaserite-type Na 2BaFe(VO 4) 2 compound, featuring a triangular magnetic lattice of Fe 2+ (S = 2), are reported. Temperature dependent X-ray single crystal studies indicate that at room temperature the system adopts a trigonal Pmore » $$\\bar{3}$$ m1 structure and undergoes a structural phase transition to a C2/c monoclinic phase slightly below room temperature (T s = 288 K). This structural transition involves a tilting of Fe–O–V bond angles and strongly influences the magnetic correlation within the Fe triangular lattice. The magnetic susceptibility measurements reveal a ferromagnetic transition near 7 K. Single crystal neutron diffraction confirms the structural distortion and the ferromagnetic spin ordering in Na 2BaFe(VO 4) 2. The magnetic structure of the ordered state is modeled in the magnetic space group C2'/c' that implies a ferromagnetic order of the a and c moment components and antiferromagnetic arrangement for the b components. Altogether, the Fe magnetic moments form ferromagnetic layers that are stacked along the c-axis, where the spins point along one of the (111) facets of the FeO 6 octahedron.« less

Properties of spin-1/2 triangular-lattice antiferromagnets CuY2Ge2O8 and CuLa2Ge2O8

NASA Astrophysics Data System (ADS)

Cho, Hwanbeom; Kratochvílová, Marie; Sim, Hasung; Choi, Ki-Young; Kim, Choong Hyun; Paulsen, Carley; Avdeev, Maxim; Peets, Darren C.; Jo, Younghun; Lee, Sanghyun; Noda, Yukio; Lawler, Michael J.; Park, Je-Geun

2017-04-01

We found new two-dimensional (2D) quantum (S =1 /2 ) antiferromagnetic systems: Cu R E2G e2O8 (R E =Y and La). According to our analysis of high-resolution x-ray and neutron diffraction experiments, the Cu network of Cu R E2G e2O8 (R E =Y and La) exhibits a 2D triangular lattice linked via weak bonds along the perpendicular b axis. Our bulk characterizations from 0.08 to 400 K show that they undergo a long-range order at 0.51(1) and 1.09(4) K for the Y and La systems, respectively. Interestingly, they also exhibit field induced phase transitions. For theoretical understanding, we carried out the density functional theory (DFT) band calculations to find that they are typical charge-transfer-type insulators with a gap of Eg≅2 eV . Taken together, our observations make Cu R E2G e2O8 (R E =Y and La) additional examples of low-dimensional quantum spin triangular antiferromagnets with the low-temperature magnetic ordering.

Spin Bose-metal phase in a spin- (1)/(2) model with ring exchange on a two-leg triangular strip

NASA Astrophysics Data System (ADS)

Sheng, D. N.; Motrunich, Olexei I.; Fisher, Matthew P. A.

2009-05-01

Recent experiments on triangular lattice organic Mott insulators have found evidence for a two-dimensional (2D) spin liquid in close proximity to the metal-insulator transition. A Gutzwiller wave function study of the triangular lattice Heisenberg model with a four-spin ring exchange term appropriate in this regime has found that the projected spinon Fermi sea state has a low variational energy. This wave function, together with a slave particle-gauge theory analysis, suggests that this putative spin liquid possesses spin correlations that are singular along surfaces in momentum space, i.e., “Bose surfaces.” Signatures of this state, which we will refer to as a “spin Bose metal” (SBM), are expected to manifest in quasi-one-dimensional (quasi-1D) ladder systems: the discrete transverse momenta cut through the 2D Bose surface leading to a distinct pattern of 1D gapless modes. Here, we search for a quasi-1D descendant of the triangular lattice SBM state by exploring the Heisenberg plus ring model on a two-leg triangular strip (zigzag chain). Using density matrix renormalization group (DMRG) supplemented by variational wave functions and a bosonization analysis, we map out the full phase diagram. In the absence of ring exchange the model is equivalent to the J1-J2 Heisenberg chain, and we find the expected Bethe-chain and dimerized phases. Remarkably, moderate ring exchange reveals a new gapless phase over a large swath of the phase diagram. Spin and dimer correlations possess singular wave vectors at particular “Bose points” (remnants of the 2D Bose surface) and allow us to identify this phase as the hoped for quasi-1D descendant of the triangular lattice SBM state. We use bosonization to derive a low-energy effective theory for the zigzag spin Bose metal and find three gapless modes and one Luttinger parameter controlling all power law correlations. Potential instabilities out of the zigzag SBM give rise to other interesting phases such as a period-3 valence bond solid or a period-4 chirality order, which we discover in the DMRG. Another interesting instability is into a spin Bose-metal phase with partial ferromagnetism (spin polarization of one spinon band), which we also find numerically using the DMRG.

Fermionic Symmetry-Protected Topological Phase in a Two-Dimensional Hubbard Model

DOE PAGES

Chen, Cheng-Chien; Muechler, Lukas; Car, Roberto; ...

2016-08-25

We study the two-dimensional (2D) Hubbard model using exact diagonalization for spin-1/2 fermions on the triangular and honeycomb lattices decorated with a single hexagon per site. In certain parameter ranges, the Hubbard model maps to a quantum compass model on those lattices. On the triangular lattice, the compass model exhibits collinear stripe antiferromagnetism, implying d-density wave charge order in the original Hubbard model. On the honeycomb lattice, the compass model has a unique, quantum disordered ground state that transforms nontrivially under lattice reflection. The ground state of the Hubbard model on the decorated honeycomb lattice is thus a 2D fermionicmore » symmetry-protected topological phase. This state—protected by time-reversal and reflection symmetries—cannot be connected adiabatically to a free-fermion topological phase.« less

Competing spin fluctuations and trace of vortex dynamics in the two-dimensional triangular-lattice antiferromagnet AgCrS2

NASA Astrophysics Data System (ADS)

Gao, Wenshuai; Shi, Liran; Ouyang, Zhongwen; Xia, Zhengcai; Wang, Zhe; Liu, Bingjie; Li, Hexuan; Zou, Youming; Yu, Lu; Zhang, Lei; Pi, Li; Qu, Zhe; Zhang, Yuheng

2018-07-01

The spin dynamics of the two-dimensional triangular-lattice antiferromagnet AgCrS2 is investigated by electron spin resonance (ESR) spectroscopy. The g-factor is found to show an unusual non-monotonously temperature dependent behavior, which, along with the super-Curie behavior observed in the ESR intensity data, provides clear evidence for the competition between ferromagnetic and antiferromagnetic fluctuations at temperatures well above T N. On approaching the Néel temperature T N from above, the linewidth is found to diverge. Such a divergent behavior could be well described by the Kawamura–Miyashita model due to Z2 type magnetic vortex–antivortex pairing, which is consistent with the expectation for a 2D Heisenberg magnetic system.

Pressure effects on the magnetoelectric properties of a multiferroic triangular-lattice antiferromagnet CuCrO2

NASA Astrophysics Data System (ADS)

Aoyama, Takuya; Miyake, Atsushi; Kagayama, Tomoko; Shimizu, Katsuya; Kimura, Tsuyoshi

2013-03-01

Effects of high pressure exceeding 10 GPa on spin-driven ferroelectricity were investigated for a multiferroic, triangular-lattice antiferromagnet (TLA), CuCrO2. For this purpose, we developed a system which enables us to measure ferroelectric polarization under a pressure of 10 GPa by using a diamond anvil cell. We found that the magnetic transition temperature accompanying the ferroelectric one in CuCrO2 was remarkably enhanced by applying pressure. The result is simply explained by considering the pressure-induced enhancement of inter- and/or intralayer magnetic interaction due to the compression of the lattice. In addition, the coercive electric field for the polarization reversal was also increased with increasing pressure, while the amplitude of the ferroelectric polarization was steeply suppressed at around 8 GPa. A possible origin of the observed pressure effects on the ferroelectric property in the multiferroic TLA is discussed in terms of a ferroelectric-antiferroelectric transition and structural domain rearrangement by uniaxial stress.

Spin-Chirality-Driven Ferroelectricity on a Perfect Triangular Lattice Antiferromagnet

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mitamura, H.; Watanuki, R.; Kaneko, Koji

Magnetic field (B) variation of the electrical polarization P c ( ∥c) of the perfect triangular lattice antiferromagnet RbFe(MoO 4) 2 is examined up to the saturation point of the magnetization for B⊥c. P c is observed only in phases for which chirality is predicted in the in-plane magnetic structures. No strong anomaly is observed in P c at the field at which the spin modulation along the c axis, and hence the spin helicity, exhibits a discontinuity to the commensurate state. These results indicate that the ferroelectricity in this compound originates predominantly from the spin chirality, the explanation ofmore » which would require a new mechanism for magnetoferroelectricity. Lastly, the obtained field-temperature phase diagrams of ferroelectricity well agree with those theoretically predicted for the spin chirality of a Heisenberg spin triangular lattice antiferromagnet.« less

Spin-Chirality-Driven Ferroelectricity on a Perfect Triangular Lattice Antiferromagnet

DOE PAGES

Mitamura, H.; Watanuki, R.; Kaneko, Koji; ...

2014-10-01

Magnetic field (B) variation of the electrical polarization P c ( ∥c) of the perfect triangular lattice antiferromagnet RbFe(MoO 4) 2 is examined up to the saturation point of the magnetization for B⊥c. P c is observed only in phases for which chirality is predicted in the in-plane magnetic structures. No strong anomaly is observed in P c at the field at which the spin modulation along the c axis, and hence the spin helicity, exhibits a discontinuity to the commensurate state. These results indicate that the ferroelectricity in this compound originates predominantly from the spin chirality, the explanation ofmore » which would require a new mechanism for magnetoferroelectricity. Lastly, the obtained field-temperature phase diagrams of ferroelectricity well agree with those theoretically predicted for the spin chirality of a Heisenberg spin triangular lattice antiferromagnet.« less

Anisotropic magnetic properties of the triangular plane lattice material TmMgGaO 4

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cevallos, F. Alex; Stolze, Karoline; Kong, Tai

Here, the crystal growth, structure, and basic magnetic properties of TmMgGaO 4 are reported. The Tm ions are located in a planar triangular lattice consisting of distorted TmO6 octahedra, while the Mg and Ga atoms randomly occupy intermediary bilayers of M-O triangular bipyramids. The Tm ions are positionally disordered. The material displays an antiferromagnetic Curie Weiss theta of ~ -20 -25 K, with no clear ordering visible in the magnetic susceptibility down to 1.8 K; the structure and magnetic properties suggest that ordering of the magnetic moments is frustrated by both structural disorder and the triangular magnetic motif. Single crystalmore » magnetization measurements indicate that the magnetic properties are highly anisotropic, with large moments measured perpendicular to the triangular planes. At 2 K, a broad step-like feature is seen in the field-dependent magnetization perpendicular to the plane on applied field near 2 Tesla.« less

Anisotropic magnetic properties of the triangular plane lattice material TmMgGaO 4

DOE PAGES

Cevallos, F. Alex; Stolze, Karoline; Kong, Tai; ...

2018-04-30

Here, the crystal growth, structure, and basic magnetic properties of TmMgGaO 4 are reported. The Tm ions are located in a planar triangular lattice consisting of distorted TmO6 octahedra, while the Mg and Ga atoms randomly occupy intermediary bilayers of M-O triangular bipyramids. The Tm ions are positionally disordered. The material displays an antiferromagnetic Curie Weiss theta of ~ -20 -25 K, with no clear ordering visible in the magnetic susceptibility down to 1.8 K; the structure and magnetic properties suggest that ordering of the magnetic moments is frustrated by both structural disorder and the triangular magnetic motif. Single crystalmore » magnetization measurements indicate that the magnetic properties are highly anisotropic, with large moments measured perpendicular to the triangular planes. At 2 K, a broad step-like feature is seen in the field-dependent magnetization perpendicular to the plane on applied field near 2 Tesla.« less

Limitation of optical properties through porous silicon photonic crystals influenced by porosity and lattice dynamic

NASA Astrophysics Data System (ADS)

Amedome Min-Dianey, Kossi Aniya; Zhang, Hao-Chun; M'Bouana, Noé Landry Privace; Kougblenou, Komi; Xia, Xinlin

2018-01-01

Finite differential time domain (FDTD) tools were applied to simulate the optical properties characteristics' through square and triangular lattices of porous silicon (pSi) photonic crystals (PhCs); which consisted of periodical patterns of circular air holes built into the pSi material. This was used to investigate the influence of porosity and lattice dynamic on the reflection, transmission and absorption characteristics through unit cell pSi PhC in the visible wavelength domain (400 nm - 700 nm). The numerical simulation was achieved using FDTD Lumerical solutions with periodic boundary conditions (PBC) and perfectly matched layers (PML) as the appropriate boundary conditions. The results revealed that the limitation of optical properties is dependent on porosity and the lattice dynamic in pSi PhC. This was presented by the trend; the higher the reflection the higher the porosity and a decrease in porosity led to an increase in absorption in both lattice considerations. It was discovered that attaining optimum properties for triangular lattice will entail considering porosities less than 50% and hole radius r to the lattice constant a ratio (r / a) above 0.3 for the absorption characteristic and below 0.3 for the transmission characteristic. Triangular lattice can be adapted to improve the optical pattern through the PhC. In addition, the optimisation of these properties through pSi PhCs was achieved by controlling porosity and the ratio r / a .

Structure and Reversibility of 2D von Neumann Cellular Automata Over Triangular Lattice

NASA Astrophysics Data System (ADS)

Uguz, Selman; Redjepov, Shovkat; Acar, Ecem; Akin, Hasan

2017-06-01

Even though the fundamental main structure of cellular automata (CA) is a discrete special model, the global behaviors at many iterative times and on big scales could be a close, nearly a continuous, model system. CA theory is a very rich and useful phenomena of dynamical model that focuses on the local information being relayed to the neighboring cells to produce CA global behaviors. The mathematical points of the basic model imply the computable values of the mathematical structure of CA. After modeling the CA structure, an important problem is to be able to move forwards and backwards on CA to understand their behaviors in more elegant ways. A possible case is when CA is to be a reversible one. In this paper, we investigate the structure and the reversibility of two-dimensional (2D) finite, linear, triangular von Neumann CA with null boundary case. It is considered on ternary field ℤ3 (i.e. 3-state). We obtain their transition rule matrices for each special case. For given special triangular information (transition) rule matrices, we prove which triangular linear 2D von Neumann CAs are reversible or not. It is known that the reversibility cases of 2D CA are generally a much challenged problem. In the present study, the reversibility problem of 2D triangular, linear von Neumann CA with null boundary is resolved completely over ternary field. As far as we know, there is no structure and reversibility study of von Neumann 2D linear CA on triangular lattice in the literature. Due to the main CA structures being sufficiently simple to investigate in mathematical ways, and also very complex to obtain in chaotic systems, it is believed that the present construction can be applied to many areas related to these CA using any other transition rules.

Thermodynamics of Ising spins on the triangular kagome lattice: Exact analytical method and Monte Carlo simulations

NASA Astrophysics Data System (ADS)

Loh, Y. L.; Yao, D. X.; Carlson, E. W.

2008-04-01

A new class of two-dimensional magnetic materials Cu9X2(cpa)6ṡxH2O ( cpa=2 -carboxypentonic acid; X=F,Cl,Br ) was recently fabricated in which Cu sites form a triangular kagome lattice (TKL). As the simplest model of geometric frustration in such a system, we study the thermodynamics of Ising spins on the TKL using exact analytic method as well as Monte Carlo simulations. We present the free energy, internal energy, specific heat, entropy, sublattice magnetizations, and susceptibility. We describe the rich phase diagram of the model as a function of coupling constants, temperature, and applied magnetic field. For frustrated interactions in the absence of applied field, the ground state is a spin liquid phase with residual entropy per spin s0/kB=(1)/(9)ln72≈0.4752… . In weak applied field, the system maps to the dimer model on a honeycomb lattice, with residual entropy 0.0359 per spin and quasi-long-range order with power-law spin-spin correlations that should be detectable by neutron scattering. The power-law correlations become exponential at finite temperatures, but the correlation length may still be long.

Instability of a triangular Abrikosov lattice at values of the Ginzburg–Landau parameter κ close to unity

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ovchinnikov, Yu. N., E-mail: ovc@itp.ac.ru; Sigal, I. M.

2016-07-15

The “soft” transverse mode of gapless excitations related to the deformation of a triangular Abrikosov lattice with a single flux quantum per unit cell at an arbitrary value of the Ginzburg–Landau parameter κ is investigated. An Abrikosov lattice with the angle φ = π/3 between the unit cell vectors is shown to be unstable in a narrow range of values, 1 < κ < 1.000634. The excitation spectrum of the mode under consideration at low values of the momentum k (in the k{sup 2} approximation) is isotropic at k lying in a plane perpendicular to the magnetic field.

Large-N solution of the Sp(N) Heisenberg quantum antiferromagnet on the anisotropic triangular lattice in a magnetic field.

NASA Astrophysics Data System (ADS)

Chung, Chung-Hou; Marston, Brad

2002-03-01

We study the Sp(N) generalization of the physical Sp(1) \\cong SU(2) Heisenberg antiferromagnet on the anisotropic triangular lattice( C. H. Chung, J. B. Marston and R. H. McKenzie, Journal of Physics: Condensed Matter 13), 5159 (2001). in a magnetic field. The model is relevant for describing recent experiments on the magnetic phases of the quasi-2D system Cs_2CuCl4 in a magnetic field(R. Coldea, D. A. Tennant, A. M. Tsvelik, and Z. Tylczynski, Phys. Rev. Lett. 86), 1335 (2001).. We solve the model in the large-N limit and study the effect of a magnetic field on the incommensurate magnetic order. Below a critical field the spins form a ``cone'' of polarization, in apparent agreement with neutron scattering experiments when the magnetic field is oriented perpendicular to the lattice. The incommensuration increases with increasing field strength. Above the critical field the spins are fully polarized. We have difficulty treating Dzyaloshinskii-Moriya interactions which are believed to be important for in-plane fields.

Phase transitions and critical properties in the antiferromagnetic Ising model on a layered triangular lattice with allowance for intralayer next-nearest-neighbor interactions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Badiev, M. K., E-mail: m-zagir@mail.ru; Murtazaev, A. K.; Ramazanov, M. K.

2016-10-15

The phase transitions (PTs) and critical properties of the antiferromagnetic Ising model on a layered (stacked) triangular lattice have been studied by the Monte Carlo method using a replica algorithm with allowance for the next-nearest-neighbor interactions. The character of PTs is analyzed using the histogram technique and the method of Binder cumulants. It is established that the transition from the disordered to paramagnetic phase in the adopted model is a second-order PT. Static critical exponents of the heat capacity (α), susceptibility (γ), order parameter (β), and correlation radius (ν) and the Fischer exponent η are calculated using the finite-size scalingmore » theory. It is shown that (i) the antiferromagnetic Ising model on a layered triangular lattice belongs to the XY universality class of critical behavior and (ii) allowance for the intralayer interactions of next-nearest neighbors in the adopted model leads to a change in the universality class of critical behavior.« less

Critical behavior of a chiral superfluid in a bipartite square lattice

NASA Astrophysics Data System (ADS)

Okamoto, Junichi; Huang, Wen-Min; Höppner, Robert; Mathey, Ludwig

2018-01-01

We study the critical behavior of Bose-Einstein condensation in the second band of a bipartite optical square lattice in a renormalization group framework at one-loop order. Within our field theoretical representation of the system, we approximate the system as a two-component Bose gas in three dimensions. We demonstrate that the system is in a different universality class than the previously studied condensation in a frustrated triangular lattice due to an additional Umklapp scattering term, which stabilizes the chiral superfluid order at low temperatures. We derive the renormalization group flow of the system and show that this order persists in the low energy limit. Furthermore, the renormalization flow suggests that the phase transition from the thermal phase to the chiral superfluid state is first order.

Multiferroicity in the generic easy-plane triangular lattice antiferromagnet RbFe(MoO4)2

NASA Astrophysics Data System (ADS)

White, J. S.; Niedermayer, Ch.; Gasparovic, G.; Broholm, C.; Park, J. M. S.; Shapiro, A. Ya.; Demianets, L. A.; Kenzelmann, M.

2013-08-01

RbFe(MoO4)2 is a quasi-two-dimensional (quasi-2D) triangular lattice antiferromagnet (TLA) that displays a zero-field magnetically driven multiferroic phase with a chiral spin structure. By inelastic neutron scattering, we determine quantitatively the spin Hamiltonian. We show that the easy-plane anisotropy is nearly 1/3 of the dominant spin exchange, making RbFe(MoO4)2 an excellent system for studying the physics of the model 2D easy-plane TLA. Our measurements demonstrate magnetic-field-induced fluctuations in this material to stabilize the generic finite-field phases of the 2D XY TLA. We further explain how Dzyaloshinskii-Moriya interactions can generate ferroelectricity only in the zero-field phase. Our conclusion is that multiferroicity in RbFe(MoO4)2, and its absence at high fields, results from the generic properties of the 2D XY TLA.

Emergent properties of magnetic materials

NASA Astrophysics Data System (ADS)

Ratcliff, William Davis, II

In Tolstoy's War and Peace, history is presented as a tapestry spun from the daily interactions of large numbers of individuals. Even if one understands individuals, it is very difficult to predict history. Similarly, the interactions of large numbers of electrons give rise to properties that one would not initially guess from their microscopic interactions. During the course of my dissertation, I have explored emergent phenomena in a number of contexts. In ZnCr2O4, geometric frustration gives rise to a plethora of equivalent ground states. From these, a lower dimensional set of collinear spins on hexagons are selected to form the building blocks of the lattice. In MgTi2O4, quantum spins dimerize and form a unique chiral ordering pattern on the spinel lattice. Descending into two dimensions, differences in size and charge give rise to an ordering between triangular layers of magnetic and nonmagnetic ions. This triangular lattice allows for the possibility of observing the RVB spin liquid state, or perhaps a valence bond crystal and initial measurements are promising. Also, on the spinel lattice, ionic ordering gives rise to one dimensional chains with their own interesting physics. Finally, in the SrCoxTi1-x O3, system we find that upon reduction, tiny clusters of Co metal precipitate out and chemical inhomogeneity on the microscale may determine much of the physics. This has relevance to a number of recent claims of room temperature ferromagnism in dilute magnetic systems. In all of these systems, complex behavior emerges from well understood microscopic behavior. For me, this is the fascination of strongly correlated electronic systems.

2-D modeling of dual-mode acoustic phonon excitation of a triangular nanoplate

NASA Astrophysics Data System (ADS)

Tai, Po-Tse; Yu, Pyng; Tang, Jau

2010-08-01

In this theoretical work, we investigated coherent phonon excitation of a triangular nanoplate based on 2-D Fermi-Pasta-Ulam lattice model. Based on the two-temperature model commonly used in description of laser heating of metals, we considered two kinds of forces related to electronic and lattice stresses. Based on extensive simulation and analysis, we identified two major planar phonon modes, namely, a standing wave mode related to the triangle bisector and another mode corresponding to half of the side length. This work elucidates the roles of laser-induced electronic stress and lattice stress in controlling the initial phase and the amplitude ratio between these two phonon modes.

Exact ground states for the nearest neighbor quantum XXZ model on the kagome and other lattices with triangular motifs at Jz /Jxy = - 1 / 2

NASA Astrophysics Data System (ADS)

Changlani, Hitesh; Kumar, Krishna; Kochkov, Dmitrii; Fradkin, Eduardo; Clark, Bryan

We report the existence of a quantum macroscopically degenerate ground state manifold on the nearest neighbor XXZ model on the kagome lattice at the point Jz /Jxy = - 1 / 2 . On many lattices with triangular motifs (including the kagome, sawtooth, icosidodecahedron and Shastry-Sutherland lattice for a certain choice of couplings) this Hamiltonian is found to be frustration-free with exact ground states which correspond to three-colorings of these lattices. Several results also generalize to the case of variable couplings and to other motifs (albeit with possibly more complex Hamiltonians). The degenerate manifold on the kagome lattice corresponds to a ''many-body flat band'' of interacting hard-core bosons; and for the one boson case our results also explain the well-known non-interacting flat band. On adding realistic perturbations, state selection in this manifold of quantum many-body states is discussed along with the implications for the phase diagram of the kagome lattice antiferromagnet. supported by DE-FG02-12ER46875, DMR 1408713, DE-FG02-08ER46544.

Quantum Statistical Mechanics on a Quantum Computer

NASA Astrophysics Data System (ADS)

Raedt, H. D.; Hams, A. H.; Michielsen, K.; Miyashita, S.; Saito, K.

We describe a quantum algorithm to compute the density of states and thermal equilibrium properties of quantum many-body systems. We present results obtained by running this algorithm on a software implementation of a 21-qubit quantum computer for the case of an antiferromagnetic Heisenberg model on triangular lattices of different size.

Role-separating ordering in social dilemmas controlled by topological frustration

NASA Astrophysics Data System (ADS)

Amaral, Marco A.; Perc, Matjaž; Wardil, Lucas; Szolnoki, Attila; da Silva Júnior, Elton J.; da Silva, Jafferson K. L.

2017-03-01

``Three is a crowd" is an old proverb that applies as much to social interactions as it does to frustrated configurations in statistical physics models. Accordingly, social relations within a triangle deserve special attention. With this motivation, we explore the impact of topological frustration on the evolutionary dynamics of the snowdrift game on a triangular lattice. This topology provides an irreconcilable frustration, which prevents anticoordination of competing strategies that would be needed for an optimal outcome of the game. By using different strategy updating protocols, we observe complex spatial patterns in dependence on payoff values that are reminiscent to a honeycomb-like organization, which helps to minimize the negative consequence of the topological frustration. We relate the emergence of these patterns to the microscopic dynamics of the evolutionary process, both by means of mean-field approximations and Monte Carlo simulations. For comparison, we also consider the same evolutionary dynamics on the square lattice, where of course the topological frustration is absent. However, with the deletion of diagonal links of the triangular lattice, we can gradually bridge the gap to the square lattice. Interestingly, in this case the level of cooperation in the system is a direct indicator of the level of topological frustration, thus providing a method to determine frustration levels in an arbitrary interaction network.

Role-separating ordering in social dilemmas controlled by topological frustration.

PubMed

Amaral, Marco A; Perc, Matjaž; Wardil, Lucas; Szolnoki, Attila; da Silva Júnior, Elton J; da Silva, Jafferson K L

2017-03-01

''Three is a crowd" is an old proverb that applies as much to social interactions as it does to frustrated configurations in statistical physics models. Accordingly, social relations within a triangle deserve special attention. With this motivation, we explore the impact of topological frustration on the evolutionary dynamics of the snowdrift game on a triangular lattice. This topology provides an irreconcilable frustration, which prevents anticoordination of competing strategies that would be needed for an optimal outcome of the game. By using different strategy updating protocols, we observe complex spatial patterns in dependence on payoff values that are reminiscent to a honeycomb-like organization, which helps to minimize the negative consequence of the topological frustration. We relate the emergence of these patterns to the microscopic dynamics of the evolutionary process, both by means of mean-field approximations and Monte Carlo simulations. For comparison, we also consider the same evolutionary dynamics on the square lattice, where of course the topological frustration is absent. However, with the deletion of diagonal links of the triangular lattice, we can gradually bridge the gap to the square lattice. Interestingly, in this case the level of cooperation in the system is a direct indicator of the level of topological frustration, thus providing a method to determine frustration levels in an arbitrary interaction network.

Discrete cosine and sine transforms generalized to honeycomb lattice

NASA Astrophysics Data System (ADS)

Hrivnák, Jiří; Motlochová, Lenka

2018-06-01

The discrete cosine and sine transforms are generalized to a triangular fragment of the honeycomb lattice. The honeycomb point sets are constructed by subtracting the root lattice from the weight lattice points of the crystallographic root system A2. The two-variable orbit functions of the Weyl group of A2, discretized simultaneously on the weight and root lattices, induce a novel parametric family of extended Weyl orbit functions. The periodicity and von Neumann and Dirichlet boundary properties of the extended Weyl orbit functions are detailed. Three types of discrete complex Fourier-Weyl transforms and real-valued Hartley-Weyl transforms are described. Unitary transform matrices and interpolating behavior of the discrete transforms are exemplified. Consequences of the developed discrete transforms for transversal eigenvibrations of the mechanical graphene model are discussed.

Mean-field scaling of the superfluid to Mott insulator transition in a 2D optical superlattice.

NASA Astrophysics Data System (ADS)

Okano, Masayuki; Thomas, Claire; Barter, Thomas; Leung, Tsz-Him; Jo, Gyu-Boong; Guzman, Jennie; Kimchi, Itamar; Vishwanath, Ashvin; Stamper-Kurn, Dan

2017-04-01

Quantum gases within optical lattices provide a nearly ideal experimental representation of the Bose-Hubbard model. The mean-field treatment of this model predicts properties of non-zero temperature lattice-trapped gasses to be insensitive to the specific lattice geometry once system energies are scaled by the lattice coordination number z. We examine an ultracold Bose gas of rubidium atoms prepared within a two-dimensional lattice whose geometry can be tuned between two configurations, triangular and kagome, for which z varies from six to four, respectively. Measurements of the coherent fraction of the gas thereby provide a quantitative test of the mean-field scaling prediction. We observe the suppression of superfluidity upon decreasing z, and find our results to be consistent with the predicted mean-field scaling. These optical lattice systems can offer a way to study paradigmatic solid-state phenomena in highly controlled crystal structures. This work was supported by the NSF and by the Army Research Office with funding from the DARPA OLE program.

Critical frontier of the Potts and percolation models on triangular-type and kagome-type lattices. II. Numerical analysis

NASA Astrophysics Data System (ADS)

Ding, Chengxiang; Fu, Zhe; Guo, Wenan; Wu, F. Y.

2010-06-01

In the preceding paper, one of us (F. Y. Wu) considered the Potts model and bond and site percolation on two general classes of two-dimensional lattices, the triangular-type and kagome-type lattices, and obtained closed-form expressions for the critical frontier with applications to various lattice models. For the triangular-type lattices Wu’s result is exact, and for the kagome-type lattices Wu’s expression is under a homogeneity assumption. The purpose of the present paper is twofold: First, an essential step in Wu’s analysis is the derivation of lattice-dependent constants A,B,C for various lattice models, a process which can be tedious. We present here a derivation of these constants for subnet networks using a computer algorithm. Second, by means of a finite-size scaling analysis based on numerical transfer matrix calculations, we deduce critical properties and critical thresholds of various models and assess the accuracy of the homogeneity assumption. Specifically, we analyze the q -state Potts model and the bond percolation on the 3-12 and kagome-type subnet lattices (n×n):(n×n) , n≤4 , for which the exact solution is not known. Our numerical determination of critical properties such as conformal anomaly and magnetic correlation length verifies that the universality principle holds. To calibrate the accuracy of the finite-size procedure, we apply the same numerical analysis to models for which the exact critical frontiers are known. The comparison of numerical and exact results shows that our numerical values are correct within errors of our finite-size analysis, which correspond to 7 or 8 significant digits. This in turn infers that the homogeneity assumption determines critical frontiers with an accuracy of 5 decimal places or higher. Finally, we also obtained the exact percolation thresholds for site percolation on kagome-type subnet lattices (1×1):(n×n) for 1≤n≤6 .

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lu, Yuan; Zuo, Xu, E-mail: xzuo@nankai.edu.cn; Feng, Min

Motivated by recent theoretical predications for Dirac cone in two-dimensional (2D) triangular lattice [H. Ishizuka, Phys. Rev. Lett. 109, 237207 (2012)], first-principles studies are performed to predict Dirac cones in artificial structures of 3d transitional-metals (TM = Ti, V, Cr, Mn, Fe, Co, Ni, and Cu) doped Mg-Al spinels. In investigated artificial structures, TM dopants substitute specific positions of the B sub-lattice in Mg-Al spinel, and form a quasi-2D triangular lattice in the a-b plane. Calculated results illustrate the existence of the spin-polarized Dirac cones formed in d-wave bands at (around) the K-point in the momentum space. The study provides a promisingmore » route for engineering Dirac physics in condensed matters.« less

Quantum phase transition in strongly correlated systems

NASA Astrophysics Data System (ADS)

Jiang, Longhua

In this thesis, we investigated the strongly correlated phenomena in bilayer quantum Hall effect, inhomogeneous superconductivity and Boson Hubbard model. Bilayer quantum Hall system is studied in chapter 2. By using the Composite Boson (CB) theory developed by J. Ye, we derive the ground state, quasihole and a quasihole-pair wave functions from the CB theory and its dual action. We find that the ground state wave function is the product of two parts, one in the charge sector which is the well known Halperin's (111) wave function and the other in the spin sector which is non-trivial at any finite d due to the gapless mode. So the total groundstate wave function differs from the well known (111) wave function at any finite d. In addition to commonly known multiplicative factors, the quasihole and quasihole-pair wave functions also contain non-trivial normalization factors multiplying the correct ground state wave function. Then we continue to study the quantum phase transition from the excitonic superfluid (ESF) to a possible pseudo-spin density wave (PSDW) at some intermediate distances driven by the magneto-roton minimum collapsing at a finite wavevector. We analyze the properties of the PSDW and explicitly show that a square lattice is the favored lattice. We suggest that correlated hopping of vacancies in the active and passive layers in the PSDW state leads to very large and temperature-dependent drag, consistent with the experimental data. Comparisons with previous microscopic numerical calculations are made. Further experimental implications are given. In chapter 3, we investigate inhomogeneous superconductivity. Starting from the Ginzburg-Landau free energy describing the normal state to Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state transition, we evaluate the free energy of seven most common lattice structures: stripe, square, triangular, Simple Cubic (SC), Face centered Cubic (FCC), Body centered Cubic (BCC) and Quasicrystal (QC). We find that the stripe phase, which is the original LO state, is the most stable phase. This result may be relevant to the detection of the FFLO state in some heavy fermion compounds and the pairing lattice structure of fermions with unequal populations on the BCS side of the Feshbach resonance in ultra-cold atoms. In chapter 4, the Boson Hubbard model is studied by duality transformation. Interacting bosons at filling factor f = p/q hopping on a lattice can be mapped to interacting vortices hopping on the dual lattice subject to a fluctuating dual " magnetic field" whose average strength through a dual plaquette is equal to the boson density f = p/q. So the kinetic term of the vortices is the same as the Hofstadter problem of electrons moving in a lattice in the presence of f = p/q flux per plaquette. Motivated by this mapping, we study the Hofstadter bands of vortices hopping in the presence of magnetic flux f = p/q per plaquette on the 5 most common bipartite and frustrated lattices namely square, honeycomb, triangular, dice and kagome lattices. We count the total number of bands and determine the number of minima in the lowest band and their locations. We also numerically calculate the bandwidths of the lowest Hofstadter bands in these lattices, which directly measure the mobility of the dual vortices. The less mobile the dual vortices are, the more likely the bosons are in a superfluid state. We find that, except for the kagome lattice at odd q, they all satisfy the exponential decay law W = Ae-cq even at the smallest q. At given q, the bandwidth W decreases in the order: triangle, square and honeycomb lattice. This indicates that the domain of the superfluid state of the original bosons increases in the order of the corresponding direct lattices: honeycome, square and triangular. When q = 2, we find that the lowest Hofstadter band is completely flat for both kagome and dice lattices. There is a gap on the kagome lattice, but no gap on dice lattice. This indicates that the boson ground state at half filling with nearest neighbor hopping on kagome lattice is always a superfluid state. The superfluid state remains stable slightly away from half filling. Our results show that the behaviors of bosons at or near half filling on kagome lattice are quite distinct from those on square, honeycomb and triangular lattices studied previously.

Universal quantum computing using (Zd) 3 symmetry-protected topologically ordered states

NASA Astrophysics Data System (ADS)

Chen, Yanzhu; Prakash, Abhishodh; Wei, Tzu-Chieh

2018-02-01

Measurement-based quantum computation describes a scheme where entanglement of resource states is utilized to simulate arbitrary quantum gates via local measurements. Recent works suggest that symmetry-protected topologically nontrivial, short-ranged entangled states are promising candidates for such a resource. Miller and Miyake [npj Quantum Inf. 2, 16036 (2016), 10.1038/npjqi.2016.36] recently constructed a particular Z2×Z2×Z2 symmetry-protected topological state on the Union Jack lattice and established its quantum-computational universality. However, they suggested that the same construction on the triangular lattice might not lead to a universal resource. Instead of qubits, we generalize the construction to qudits and show that the resulting (d -1 ) qudit nontrivial Zd×Zd×Zd symmetry-protected topological states are universal on the triangular lattice, for d being a prime number greater than 2. The same construction also holds for other 3-colorable lattices, including the Union Jack lattice.

Continuous excitations of the triangular-lattice quantum spin liquid YbMgGaO 4

DOE PAGES

Paddison, Joseph A. M.; Daum, Marcus; Dun, Zhiling; ...

2016-12-05

A quantum spin liquid (QSL) is an exotic state of matter in which electrons’ spins are quantum entangled over long distances, but do not show magnetic order in the zero-temperature limit. The observation of QSL states is a central aim of experimental physics, because they host collective excitations that transcend our knowledge of quantum matter; however, examples in real materials are scarce. We report neutron-scattering experiments on YbMgGaO 4, a QSL candidate in which Yb 3+ ions with effective spin-1/2 occupy a triangular lattice. Furthermore, our measurements reveal a continuum of magnetic excitations—the essential experimental hallmark of a QSL7—at verymore » low temperature (0.06 K). The origin of this peculiar excitation spectrum is a crucial question, because isotropic nearest-neighbour interactions do not yield a QSL ground state on the triangular lattice. In using measurements the field-polarized state, we identify antiferromagnetic next-nearest-neighbour interactions spin-space anisotropies and chemical disorder between the magnetic layers as key ingredients in YbMgGaO 4.« less

Quantum phases of dipolar rotors on two-dimensional lattices

NASA Astrophysics Data System (ADS)

Abolins, B. P.; Zillich, R. E.; Whaley, K. B.

2018-03-01

The quantum phase transitions of dipoles confined to the vertices of two-dimensional lattices of square and triangular geometry is studied using path integral ground state quantum Monte Carlo. We analyze the phase diagram as a function of the strength of both the dipolar interaction and a transverse electric field. The study reveals the existence of a class of orientational phases of quantum dipolar rotors whose properties are determined by the ratios between the strength of the anisotropic dipole-dipole interaction, the strength of the applied transverse field, and the rotational constant. For the triangular lattice, the generic orientationally disordered phase found at zero and weak values of both dipolar interaction strength and applied field is found to show a transition to a phase characterized by net polarization in the lattice plane as the strength of the dipole-dipole interaction is increased, independent of the strength of the applied transverse field, in addition to the expected transition to a transverse polarized phase as the electric field strength increases. The square lattice is also found to exhibit a transition from a disordered phase to an ordered phase as the dipole-dipole interaction strength is increased, as well as the expected transition to a transverse polarized phase as the electric field strength increases. In contrast to the situation with a triangular lattice, on square lattices, the ordered phase at high dipole-dipole interaction strength possesses a striped ordering. The properties of these quantum dipolar rotor phases are dominated by the anisotropy of the interaction and provide useful models for developing quantum phases beyond the well-known paradigms of spin Hamiltonian models, implementing in particular a novel physical realization of a quantum rotor-like Hamiltonian that possesses an anisotropic long range interaction.

Multiorbital kinetic effects on charge ordering of frustrated electrons on the triangular lattice

NASA Astrophysics Data System (ADS)

Février, C.; Fratini, S.; Ralko, A.

2015-06-01

The role of the multiorbital effects on the emergence of frustrated electronic orders on the triangular lattice at half filling is investigated through an extended spinless fermion Hubbard model. By using two complementary approaches, unrestricted Hartree-Fock and exact diagonalizations, we unravel a very rich phase diagram controlled by the strength of both local and off-site Coulomb interactions and by the interorbital hopping anisotropy ratio t'/t . Three robust unconventional electronic phases, a pinball liquid, an inverse pinball liquid, and a large-unit-cell √{12 }×√{12 } droplet phase, are found to be generic in the triangular geometry, being controlled by the band structure parameters. The latter are also stabilized in the isotropic limit of our microscopic model, which recovers the standard SU(2) spinful extended single-band Hubbard model.

Berezinskii-Kosterlitz-Thouless phase transition for the dilute planar rotator model on a triangular lattice

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sun Yunzhou; Yi Lin; Wysin, G. M.

2008-10-15

The Berezinskii-Kosterlitz-Thouless (BKT) phase transition for the dilute planar rotator model on a triangular lattice is studied by using a hybrid Monte Carlo method. The phase-transition temperatures for different nonmagnetic impurity densities are obtained by three approaches: finite-size scaling of plane magnetic susceptibility, helicity modulus, and Binder's fourth cumulant. It is found that the phase-transition temperature decreases with increasing impurity density {rho} and the BKT phase transition vanishes when the magnetic occupancy falls to the site percolation threshold: 1-{rho}{sub c}=p{sub c}=0.5.

Thermodynamics of dilute 3He-4He solid solutions with hcp structure

NASA Astrophysics Data System (ADS)

Chishko, K. A.

2018-02-01

To interpret the anomalies in heat capacity CV(T) and temperature-dependent pressure P(T) of solid hexagonal close-packed (hcp) 4He we exploit the model of hcp crystalline polytype with specific lattice degrees of freedom and describe the thermodynamics of impurity-free 4He solid as superposition of phononic and polytypic contributions. The hcp-based polytype is a stack of 2D basal atomic monolayers on triangular lattice packed with arbitrary long (up to infinity) spatial period along the hexagonal c axis perpendicular to the basal planes. It is a crystal with perfect ordering along the layers, but without microscopic translational symmetry in perpendicular direction (which remains, nevertheless, the rotational crystallographic axis of third order, so that the polytype can be considered as semidisordered system). Each atom of the hcp polytype has twelve crystallographic neighbors in both first and second coordination spheres at any arbitrary packing order. It is shown that the crystal of such structure behaves as anisotropic elastic medium with specific dispersion law of phonon excitations along c axis. The free energy and the heat capacity consist of two terms: one of them is a normal contribution [with CV(T) ˜ T3] from phonon excitations in an anisotropic lattice of hexagonal symmetry, and another term (an "excessive" heat) is a contribution resulted by packing entropy from quasi-one-dimensional system of 2D basal planes on triangular lattice stacked randomly along c axis without braking the closest pack between neighboring atomic layers. The excessive part of the free energy has been treated within 1D quasi-Ising (lattice gas) model using the transfer matrix approach. This model makes us possible to interpret successfully the thermodynamic anomaly (heat capacity peak in hcp 4He) observed experimentally.

Dirac cones in artificial structures of 3d transitional-metals doped Mg-Al spinels

NASA Astrophysics Data System (ADS)

Lu, Yuan; Feng, Min; Shao, Bin; Zuo, Xu

2014-05-01

Motivated by recent theoretical predications for Dirac cone in two-dimensional (2D) triangular lattice [H. Ishizuka, Phys. Rev. Lett. 109, 237207 (2012)], first-principles studies are performed to predict Dirac cones in artificial structures of 3d transitional-metals (TM = Ti, V, Cr, Mn, Fe, Co, Ni, and Cu) doped Mg-Al spinels. In investigated artificial structures, TM dopants substitute specific positions of the B sub-lattice in Mg-Al spinel, and form a quasi-2D triangular lattice in the a-b plane. Calculated results illustrate the existence of the spin-polarized Dirac cones formed in d-wave bands at (around) the K-point in the momentum space. The study provides a promising route for engineering Dirac physics in condensed matters.

Thermodynamic and critical properties of an antiferromagnetically stacked triangular Ising antiferromagnet in a field

NASA Astrophysics Data System (ADS)

Žukovič, M.; Borovský, M.; Bobák, A.

2018-05-01

We study a stacked triangular lattice Ising model with both intra- and inter-plane antiferromagnetic interactions in a field, by Monte Carlo simulation. We find only one phase transition from a paramagnetic to a partially disordered phase, which is of second order and 3D XY universality class. At low temperatures we identify two highly degenerate phases: at smaller (larger) fields the system shows long-range ordering in the stacking direction (within planes) but not in the planes (stacking direction). Nevertheless, crossovers to these phases do not have a character of conventional phase transitions but rather linear-chain-like excitations.

Quantum electric-dipole liquid on a triangular lattice.

PubMed

Shen, Shi-Peng; Wu, Jia-Chuan; Song, Jun-Da; Sun, Xue-Feng; Yang, Yi-Feng; Chai, Yi-Sheng; Shang, Da-Shan; Wang, Shou-Guo; Scott, James F; Sun, Young

2016-02-04

Geometric frustration and quantum fluctuations may prohibit the formation of long-range ordering even at the lowest temperature, and therefore liquid-like ground states could be expected. A good example is the quantum spin liquid in frustrated magnets. Geometric frustration and quantum fluctuations can happen beyond magnetic systems. Here we propose that quantum electric-dipole liquids, analogues of quantum spin liquids, could emerge in frustrated dielectrics where antiferroelectrically coupled electric dipoles reside on a triangular lattice. The quantum paraelectric hexaferrite BaFe12O19 with geometric frustration represents a promising candidate for the proposed electric-dipole liquid. We present a series of experimental lines of evidence, including dielectric permittivity, heat capacity and thermal conductivity measured down to 66 mK, to reveal the existence of an unusual liquid-like quantum phase in BaFe12O19, characterized by itinerant low-energy excitations with a small gap. The possible quantum liquids of electric dipoles in frustrated dielectrics open up a fresh playground for fundamental physics.

Deconfined quantum critical point on the triangular lattice

NASA Astrophysics Data System (ADS)

Jian, Chao-Ming; Thomson, Alex; Rasmussen, Alex; Bi, Zhen; Xu, Cenke

2018-05-01

In this work we propose a theory for the deconfined quantum critical point (DQCP) for spin-1/2 systems on a triangular lattice, which is a direct unfine-tuned quantum phase transition between the standard "√{3 }×√{3 } " noncollinear antiferromagnetic order (or the so-called 120∘ state) and the "√{12 }×√{12 } " valence solid bond (VBS) order, both of which are very standard ordered phases often observed in numerical simulations. This transition is beyond the standard Landau-Ginzburg paradigm and is also fundamentally different from the original DQCP theory on the square lattice due to the very different structures of both the magnetic and VBS order on frustrated lattices. We first propose a topological term in the effective-field theory that captures the "intertwinement" between the √{3 }×√{3 } antiferromagnetic order and the √{12 }×√{12 } VBS order. Then using a controlled renormalization-group calculation, we demonstrate that an unfine-tuned direct continuous DQCP exists between the two ordered phases mentioned above. This DQCP is described by the Nf=4 quantum electrodynamics (QED) with an emergent PSU(4)=SU(4)/Z4 symmetry only at the critical point. The aforementioned topological term is also naturally derived from the Nf=4 QED. We also point out that physics around this DQCP is analogous to the boundary of a 3 d bosonic symmetry- protected topological state with only on-site symmetries.

Nonlinear integrable model of Frenkel-like excitations on a ribbon of triangular lattice

NASA Astrophysics Data System (ADS)

Vakhnenko, Oleksiy O.

2015-03-01

Following the considerable progress in nanoribbon technology, we propose to model the nonlinear Frenkel-like excitations on a triangular-lattice ribbon by the integrable nonlinear ladder system with the background-controlled intersite resonant coupling. The system of interest arises as a proper reduction of first general semidiscrete integrable system from an infinite hierarchy. The most significant local conservation laws related to the first general integrable system are found explicitly in the framework of generalized recursive approach. The obtained general local densities are equally applicable to any general semidiscrete integrable system from the respective infinite hierarchy. Using the recovered second densities, the Hamiltonian formulation of integrable nonlinear ladder system with background-controlled intersite resonant coupling is presented. In doing so, the relevant Poisson structure turns out to be essentially nontrivial. The Darboux transformation scheme as applied to the first general semidiscrete system is developed and the key role of Bäcklund transformation in justification of its self-consistency is pointed out. The spectral properties of Darboux matrix allow to restore the whole Darboux matrix thus ensuring generation one more soliton as compared with a priori known seed solution of integrable nonlinear system. The power of Darboux-dressing method is explicitly demonstrated in generating the multicomponent one-soliton solution to the integrable nonlinear ladder system with background-controlled intersite resonant coupling.

Strong-coupling analysis of two-dimensional O({ital N}) {sigma} models with {ital N}{le}2 on square, triangular, and honeycomb lattices

DOE Office of Scientific and Technical Information (OSTI.GOV)

Campostrini, M.; Pelissetto, A.; Rossi, P.

1996-09-01

The critical behavior of two-dimensional (2D) O({ital N}) {sigma} models with {ital N}{le}2 on square, triangular, and honeycomb lattices is investigated by an analysis of the strong-coupling expansion of the two-point fundamental Green{close_quote}s function {ital G}({ital x}), calculated up to 21st order on the square lattice, 15th order on the triangular lattice, and 30th order on the honeycomb lattice. For {ital N}{lt}2 the critical behavior is of power-law type, and the exponents {gamma} and {nu} extracted from our strong-coupling analysis confirm exact results derived assuming universality with solvable solid-on-solid models. At {ital N}=2, i.e., for the 2D {ital XY} model,more » the results from all lattices considered are consistent with the Kosterlitz-Thouless exponential approach to criticality, characterized by an exponent {sigma}=1/2, and with universality. The value {sigma}=1/2 is confirmed within an uncertainty of few percent. The prediction {eta}=1/4 is also roughly verified. For various values of {ital N}{le}2, we determine some ratios of amplitudes concerning the two-point function {ital G}({ital x}) in the critical limit of the symmetric phase. This analysis shows that the low-momentum behavior of {ital G}({ital x}) in the critical region is essentially Gaussian at all values of {ital N}{le}2. Exact results for the long-distance behavior of {ital G}({ital x}) when {ital N}=1 (Ising model in the strong-coupling phase) confirm this statement. {copyright} {ital 1996 The American Physical Society.}« less

Nonlinear dust-lattice waves: a modified Toda lattice

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cramer, N. F.

Charged dust grains in a plasma interact with a Coulomb potential, but also with an exponential component to the potential, due to Debye shielding in the background plasma. Here we investigate large-amplitude oscillations and waves in dust-lattices, employing techniques used in Toda lattice analysis. The lattice consists of a linear chain of particles, or a periodic ring as occurs in experimentally observed dust particle clusters. The particle motion has a triangular waveform, and chaotic motion for large amplitude motion of a grain.

Matter-wave propagation in optical lattices: geometrical and flat-band effects

DOE PAGES

Metcalf, Mekena; Chern, Gia-Wei; Di Ventra, Massimiliano; ...

2016-03-17

Here we report that the geometry of optical lattices can be engineered allowing the study of atomic transport along paths arranged in patterns that are otherwise difficult to probe in the solid state. A question feasible to atomic systems is related to the speed of propagation of matter-waves as a function of the lattice geometry. To address this issue, we have investigated theoretically the quantum transport of non-interacting and weakly-interacting ultracold fermionic atoms in several 2D optical lattice geometries. We find that the triangular lattice has a higher propagation velocity compared to the square lattice, and the cross-linked square latticemore » has an even faster propagation velocity. The increase results from the mixing of the momentum states which leads to different group velocities in quantum systems. Standard band theory provides an explanation and allows for a systematic way to search and design systems with controllable matter-wave propagation. Moreover, the presence of a flat band such as in a two-leg ladder geometry leads to a dynamical density discontinuity due to its localized atoms. Lastly, we discuss possible realizations of those dynamical phenomena.« less

H-T Magnetic Phase Diagram of a Frustrated Triangular Lattice Antiferromagnet CuFeO 2

NASA Astrophysics Data System (ADS)

Mitsuda, Setsuo; Mase, Motoshi; Uno, Takahiro; Kitazawa, Hideaki; Katori, Hiroko

2000-01-01

By magnetization and specific heat measurements in an applied magnetic field up to 12 T, we obtained the magnetic field (H) versus temperature (T) phase diagram of a frustrated triangular lattice antiferromagnet (TLA), CuFeO2, where a partially disordered phase typical to Ising TLA exists as a thermally induced state for the 4-sublattice ground state as well as for the first-field-induced 5-sublattice-like state. The experimentally obtained H-T magnetic phase diagram is compared with that from Monte-Carlo simulation of a 2D Ising TLA model with competing exchange interactions up to 3rd neighbors.

Evidence for a spinon Fermi surface in a triangular-lattice quantum-spin-liquid candidate

DOE PAGES

Shen, Yao; Li, Yao-Dong; Wo, Hongliang; ...

2016-12-05

A quantum spin liquid is an exotic quantum state of matter in which spins are highly entangled and remain disordered down to zero temperature. Such a state of matter is potentially relevant to high-temperature superconductivity and quantum-information applications, and experimental identification of a quantum spin liquid state is of fundamental importance for our understanding of quantum matter. Theoretical studies have proposed various quantum-spin-liquid ground states, most of which are characterized by exotic spin excitations with fractional quantum numbers (termed ‘spinons’). In this paper, we report neutron scattering measurements of the triangular-lattice antiferromagnet YbMgGaO 4 that reveal broad spin excitations coveringmore » a wide region of the Brillouin zone. The observed diffusive spin excitation persists at the lowest measured energy and shows a clear upper excitation edge, consistent with the particle–hole excitation of a spinon Fermi surface. Finally, our results therefore point to the existence of a quantum spin liquid state with a spinon Fermi surface in YbMgGaO 4, which has a perfect spin-1/2 triangular lattice as in the original proposal of quantum spin liquids.« less

One dimensionalization in the spin-1 Heisenberg model on the anisotropic triangular lattice

NASA Astrophysics Data System (ADS)

Gonzalez, M. G.; Ghioldi, E. A.; Gazza, C. J.; Manuel, L. O.; Trumper, A. E.

2017-11-01

We investigate the effect of dimensional crossover in the ground state of the antiferromagnetic spin-1 Heisenberg model on the anisotropic triangular lattice that interpolates between the regime of weakly coupled Haldane chains (J'≪J ) and the isotropic triangular lattice (J'=J ). We use the density-matrix renormalization group (DMRG) and Schwinger boson theory performed at the Gaussian correction level above the saddle-point solution. Our DMRG results show an abrupt transition between decoupled spin chains and the spirally ordered regime at (J'/J) c˜0.42 , signaled by the sudden closing of the spin gap. Coming from the magnetically ordered side, the computation of the spin stiffness within Schwinger boson theory predicts the instability of the spiral magnetic order toward a magnetically disordered phase with one-dimensional features at (J'/J) c˜0.43 . The agreement of these complementary methods, along with the strong difference found between the intra- and the interchain DMRG short spin-spin correlations for sufficiently large values of the interchain coupling, suggests that the interplay between the quantum fluctuations and the dimensional crossover effects gives rise to the one-dimensionalization phenomenon in this frustrated spin-1 Hamiltonian.

Monte Carlo Study of the Fish-like Patterns of Anthracenes on Cu(111)

NASA Astrophysics Data System (ADS)

Kim, Kwangmoo; Einstein, T. L.; Sun, Dezheng; Kim, Dae-Ho; Bartels, Ludwig

2011-03-01

Using Monte Carlo calculations of the two-dimensional triangular lattice with a 2-component 3-state Potts model, we demonstrate a mechanism for the spontaneous formation of fish-like patterns of anthracene (AC) molecules on Cu(111) by sputtering and annealing, then cooling to ~ 80 K. The two components are an AC on a hollow site and another on a bridge site of Cu(111). The liquid crystal model with two separate parts, positional and orientational, only explains a part of the fish-like pattern, not the whole regular pattern. Our model fixes the positional order of AC's into the triangular lattice and the orientational order into three angles as observed in the experiments. The variation of the coverages of AC's is reflected in the change of the ratio of two components in our model. We also try to understand the compression of AC's with the introduction of Gaussian dispersion of AC's about their triangular lattice sites. Supported primarily by NSF Grants CHE 07-50334 with a secondary support from NSF-MRSEC at the University of Maryland, DMR05-20471. Work at UCR supported primarily by NSF CHE 07-49949.

Hofstadter butterfly evolution in the space of two-dimensional Bravais lattices

NASA Astrophysics Data System (ADS)

Yılmaz, F.; Oktel, M. Ö.

2017-06-01

The self-similar energy spectrum of a particle in a periodic potential under a magnetic field, known as the Hofstadter butterfly, is determined by the lattice geometry as well as the external field. Recent realizations of artificial gauge fields and adjustable optical lattices in cold-atom experiments necessitate the consideration of these self-similar spectra for the most general two-dimensional lattice. In a previous work [F. Yılmaz et al., Phys. Rev. A 91, 063628 (2015), 10.1103/PhysRevA.91.063628], we investigated the evolution of the spectrum for an experimentally realized lattice which was tuned by changing the unit-cell structure but keeping the square Bravais lattice fixed. We now consider all possible Bravais lattices in two dimensions and investigate the structure of the Hofstadter butterfly as the lattice is deformed between lattices with different point-symmetry groups. We model the optical lattice with a sinusoidal real-space potential and obtain the tight-binding model for any lattice geometry by calculating the Wannier functions. We introduce the magnetic field via Peierls substitution and numerically calculate the energy spectrum. The transition between the two most symmetric lattices, i.e., the triangular and the square lattices, displays the importance of bipartite symmetry featuring deformation as well as closing of some of the major energy gaps. The transitions from the square to rectangular lattice and from the triangular to centered rectangular lattices are analyzed in terms of coupling of one-dimensional chains. We calculate the Chern numbers of the major gaps and Chern number transfer between bands during the transitions. We use gap Chern numbers to identify distinct topological regions in the space of Bravais lattices.

Realization of a Hole-Doped Mott Insulator on a Triangular Silicon Lattice

NASA Astrophysics Data System (ADS)

Ming, Fangfei; Johnston, Steve; Mulugeta, Daniel; Smith, Tyler S.; Vilmercati, Paolo; Lee, Geunseop; Maier, Thomas A.; Snijders, Paul C.; Weitering, Hanno H.

2017-12-01

The physics of doped Mott insulators is at the heart of some of the most exotic physical phenomena in materials research including insulator-metal transitions, colossal magnetoresistance, and high-temperature superconductivity in layered perovskite compounds. Advances in this field would greatly benefit from the availability of new material systems with a similar richness of physical phenomena but with fewer chemical and structural complications in comparison to oxides. Using scanning tunneling microscopy and spectroscopy, we show that such a system can be realized on a silicon platform. The adsorption of one-third monolayer of Sn atoms on a Si(111) surface produces a triangular surface lattice with half filled dangling bond orbitals. Modulation hole doping of these dangling bonds unveils clear hallmarks of Mott physics, such as spectral weight transfer and the formation of quasiparticle states at the Fermi level, well-defined Fermi contour segments, and a sharp singularity in the density of states. These observations are remarkably similar to those made in complex oxide materials, including high-temperature superconductors, but highly extraordinary within the realm of conventional s p -bonded semiconductor materials. It suggests that exotic quantum matter phases can be realized and engineered on silicon-based materials platforms.

Quasi-two-dimensional spin correlations in the triangular lattice bilayer spin glass LuCoGaO 4

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fritsch, Katharina; Ross, Kathyrn A.; Granroth, Garrett E.

Here we present a single-crystal time-of-flight neutron scattering study of the static and dynamic spin correlations in LuCoGaO 4, a quasi-two-dimensional dilute triangular lattice antiferromagnetic spin-glass material. This system is based on Co 2+ ions that are randomly distributed on triangular bilayers within the YbFe 2O 4 type, hexagonal crystal structure. Antiferromagnetic short-range two-dimensional correlations at wave vectors Q = (1/3,1/3, L) develop within the bilayers at temperatures as high as |Θ CW| ~100 K and extend over roughly five unit cells at temperatures below T g = 19 K. These two-dimensional static correlations are observed as diffuse rods ofmore » neutron scattering intensity along c * and display a continuous spin freezing process in their energy dependence. Aside from exhibiting these typical spin-glass characteristics, this insulating material reveals a novel gapped magnetic resonant spin excitation at ΔE ~12 meV localized around Q = (1 / 3, 1 / 3,L) . The temperature dependence of the spin gap associated with this two-dimensional excitation correlates with the evolution of the static correlations into the spin-glass state ground state. Lastly, we associate it with the effect of the staggered exchange field acting on the S eff = 1/2 Ising-like doublet of the Co 2+ moments.« less

Quasi-two-dimensional spin correlations in the triangular lattice bilayer spin glass LuCoGaO 4

DOE PAGES

Fritsch, Katharina; Ross, Kathyrn A.; Granroth, Garrett E.; ...

2017-09-13

Here we present a single-crystal time-of-flight neutron scattering study of the static and dynamic spin correlations in LuCoGaO 4, a quasi-two-dimensional dilute triangular lattice antiferromagnetic spin-glass material. This system is based on Co 2+ ions that are randomly distributed on triangular bilayers within the YbFe 2O 4 type, hexagonal crystal structure. Antiferromagnetic short-range two-dimensional correlations at wave vectors Q = (1/3,1/3, L) develop within the bilayers at temperatures as high as |Θ CW| ~100 K and extend over roughly five unit cells at temperatures below T g = 19 K. These two-dimensional static correlations are observed as diffuse rods ofmore » neutron scattering intensity along c * and display a continuous spin freezing process in their energy dependence. Aside from exhibiting these typical spin-glass characteristics, this insulating material reveals a novel gapped magnetic resonant spin excitation at ΔE ~12 meV localized around Q = (1 / 3, 1 / 3,L) . The temperature dependence of the spin gap associated with this two-dimensional excitation correlates with the evolution of the static correlations into the spin-glass state ground state. Lastly, we associate it with the effect of the staggered exchange field acting on the S eff = 1/2 Ising-like doublet of the Co 2+ moments.« less

Itinerant fermions on a triangular lattice: Unconventional magnetism and other ordered states

NASA Astrophysics Data System (ADS)

Ye, Mengxing; Chubukov, Andrey V.

2018-06-01

We consider a system of 2D fermions on a triangular lattice with well separated electron and hole pockets of similar sizes, centered at certain high-symmetry points in the Brillouin zone. We first analyze Stoner-type spin-density-wave (SDW) magnetism. We show that SDW order is degenerate at the mean-field level. Beyond mean-field, the degeneracy is lifted and is either 120∘ "triangular" order (same as for localized spins), or a collinear order with antiferromagnetic spin arrangement on two-thirds of sites, and nonmagnetic on the rest of sites. We also study a time-reversal symmetric directional spin bond order, which emerges when some interactions are repulsive and some are attractive. We show that this order is also degenerate at a mean-field level, but beyond mean-field the degeneracy is again lifted. We next consider the evolution of a magnetic order in a magnetic field starting from an SDW state in zero field. We show that a field gives rise to a canting of an SDW spin configuration. In addition, it necessarily triggers the directional bond order, which, we argue, is linearly coupled to the SDW order in a finite field. We derive the corresponding term in the free energy. Finally, we consider the interplay between an SDW order and superconductivity and charge order. For this, we analyze the flow of the couplings within parquet renormalization group (pRG) scheme. We show that magnetism wins if all interactions are repulsive and there is little energy space for pRG to develop. However, if system parameters are such that pRG runs over a wide range of energies, the system may develop either superconductivity or an unconventional charge order, which breaks time-reversal symmetry.

Spin-Glass Ground State in a Triangular-Lattice Compound YbZnGaO4

NASA Astrophysics Data System (ADS)

Ma, Zhen; Wang, Jinghui; Dong, Zhao-Yang; Zhang, Jun; Li, Shichao; Zheng, Shu-Han; Yu, Yunjie; Wang, Wei; Che, Liqiang; Ran, Kejing; Bao, Song; Cai, Zhengwei; Čermák, P.; Schneidewind, A.; Yano, S.; Gardner, J. S.; Lu, Xin; Yu, Shun-Li; Liu, Jun-Ming; Li, Shiyan; Li, Jian-Xin; Wen, Jinsheng

2018-02-01

We report on comprehensive results identifying the ground state of a triangular-lattice structured YbZnGaO4 as a spin glass, including no long-range magnetic order, prominent broad excitation continua, and the absence of magnetic thermal conductivity. More crucially, from the ultralow-temperature ac susceptibility measurements, we unambiguously observe frequency-dependent peaks around 0.1 K, indicating the spin-glass ground state. We suggest this conclusion holds also for its sister compound YbMgGaO4 , which is confirmed by the observation of spin freezing at low temperatures. We consider disorder and frustration to be the main driving force for the spin-glass phase.

Quantum gap and spin-wave excitations in the Kitaev model on a triangular lattice

NASA Astrophysics Data System (ADS)

Avella, Adolfo; Di Ciolo, Andrea; Jackeli, George

2018-05-01

We study the effects of quantum fluctuations on the dynamical generation of a gap and on the evolution of the spin-wave spectra of a frustrated magnet on a triangular lattice with bond-dependent Ising couplings, analog of the Kitaev honeycomb model. The quantum fluctuations lift the subextensive degeneracy of the classical ground-state manifold by a quantum order-by-disorder mechanism. Nearest-neighbor chains remain decoupled and the surviving discrete degeneracy of the ground state is protected by a hidden model symmetry. We show how the four-spin interaction, emergent from the fluctuations, generates a spin gap shifting the nodal lines of the linear spin-wave spectrum to finite energies.

Supersolid-like magnetic states in a mixed honeycomb-triangular lattice system.

NASA Astrophysics Data System (ADS)

Garlea, Ovidiu

Field-induced magnetic states that occur in layered triangular antiferromagnets have been of broad interest due to the emergence of new exotic phases, such as topologically ordered states and supersolids. Experimental realization of the supersolid states where spin components break simultaneously the translational and rotational symmetries remains scarce. In this context, the mixed vanadate -carbonate K2Mn3(VO4)2CO3 is a very promising system. This compound contains two types of two-dimensional layers alternately stacked along the crystallographic c-axis: one layer consists of a honeycomb web structure made of edge sharing MnO6 octahedra, while the other consists of MnO5 trigonal bipyramids linked by [CO3] triangles to form a triangular magnetic lattice. Magnetization and heat capacity measurements reveal a complex magnetic phase diagram that includes three phase transition associated with sequential long range magnetic ordering of the different sublattices. The lowest temperature state resembles a supersolid state that was predicted to occur in two-dimensional frustrated magnet with easy axis anisotropy. Such a supersolid phase is defined by a commensurate √3× √3 magnetic superlattice, where two thirds of the spins are canted away from the easy axis direction. Applied magnetic field destabilizes this ordered state and induces a cascade of new exotic magnetic ground states. The nature of these field-induced magnetic states is evaluated by using neutron scattering techniques. Work at the Oak Ridge National Laboratory was sponsored by the US Department of Energy, Office of Science, Basic Energy Sciences, Scientific User Facilities Division and Materials Sciences and Engineering Division.

Phase diagram of the quantum Ising model with long-range interactions on an infinite-cylinder triangular lattice

NASA Astrophysics Data System (ADS)

Saadatmand, S. N.; Bartlett, S. D.; McCulloch, I. P.

2018-04-01

Obtaining quantitative ground-state behavior for geometrically-frustrated quantum magnets with long-range interactions is challenging for numerical methods. Here, we demonstrate that the ground states of these systems on two-dimensional lattices can be efficiently obtained using state-of-the-art translation-invariant variants of matrix product states and density-matrix renormalization-group algorithms. We use these methods to calculate the fully-quantitative ground-state phase diagram of the long-range interacting triangular Ising model with a transverse field on six-leg infinite-length cylinders and scrutinize the properties of the detected phases. We compare these results with those of the corresponding nearest neighbor model. Our results suggest that, for such long-range Hamiltonians, the long-range quantum fluctuations always lead to long-range correlations, where correlators exhibit power-law decays instead of the conventional exponential drops observed for short-range correlated gapped phases. Our results are relevant for comparisons with recent ion-trap quantum simulator experiments that demonstrate highly-controllable long-range spin couplings for several hundred ions.

Vortex lattices in binary mixtures of repulsive superfluids

NASA Astrophysics Data System (ADS)

Mingarelli, Luca; Keaveny, Eric E.; Barnett, Ryan

2018-04-01

We present an extension of the framework introduced in previous work [L. Mingarelli, E. E. Keaveny, and R. Barnett, J. Phys.: Condens. Matter 28, 285201 (2016), 10.1088/0953-8984/28/28/285201] to treat multicomponent systems, showing that new degrees of freedom are necessary in order to obtain the desired boundary conditions. We then apply this extended framework to the coupled Gross-Pitaevskii equations to investigate the ground states of two-component systems with equal masses, thereby extending previous work in the lowest Landau limit [E. J. Mueller and T.-L. Ho, Phys. Rev. Lett. 88, 180403 (2002), 10.1103/PhysRevLett.88.180403] to arbitrary interactions within Gross-Pitaevskii theory. We show that away from the lowest Landau level limit, the predominant vortex lattice consists of two interlaced triangular lattices. Finally, we derive a linear relation which accurately describes the phase boundaries in the strong interacting regimes.

Effective Hubbard model for Helium atoms adsorbed on a graphite

NASA Astrophysics Data System (ADS)

Motoyama, Yuichi; Masaki-Kato, Akiko; Kawashima, Naoki

Helium atoms adsorbed on a graphite is a two-dimensional strongly correlated quantum system and it has been an attractive subject of research for a long time. A helium atom feels Lennard-Jones like potential (Aziz potential) from another one and corrugated potential from the graphite. Therefore, this system may be described by a hardcore Bose Hubbard model with the nearest neighbor repulsion on the triangular lattice, which is the dual lattice of the honeycomb lattice formed by carbons. A Hubbard model is easier to simulate than the original problem in continuous space, but we need to know the model parameters of the effective model, hopping constant t and interaction V. In this presentation, we will present an estimation of the model parameters from ab initio quantum Monte Carlo calculation in continuous space in addition to results of quantum Monte Carlo simulation for an obtained discrete model.

Infinite lattices of vortex molecules in Rabi-coupled condensates

NASA Astrophysics Data System (ADS)

Mencia Uranga, B.; Lamacraft, Austen

2018-04-01

Vortex molecules can form in a two-component superfluid when a Rabi field drives transitions between the two components. We study the ground state of an infinite system of vortex molecules in two dimensions, using a numerical scheme which makes no use of the lowest Landau level approximation. We find the ground state lattice geometry for different values of intercomponent interactions and strength of the Rabi field. In the limit of large field when molecules are tightly bound, we develop a complementary analytical description. The energy governing the alignment of molecules on a triangular lattice is found to correspond to that of an infinite system of two-dimensional quadrupoles, which may be written in terms of an elliptic function Q (zi j;ω1,ω2) . This allows for a numerical evaluation of the energy which enables us to find the ground state configuration of the molecules.

Frustrated Magnetism of Dipolar Molecules on a Square Optical Lattice: Prediction of a Quantum Paramagnetic Ground State

NASA Astrophysics Data System (ADS)

Zou, Haiyuan; Zhao, Erhai; Liu, W. Vincent

2017-08-01

Motivated by the experimental realization of quantum spin models of polar molecule KRb in optical lattices, we analyze the spin 1 /2 dipolar Heisenberg model with competing anisotropic, long-range exchange interactions. We show that, by tilting the orientation of dipoles using an external electric field, the dipolar spin system on square lattice comes close to a maximally frustrated region similar, but not identical, to that of the J1-J2 model. This provides a simple yet powerful route to potentially realize a quantum spin liquid without the need for a triangular or kagome lattice. The ground state phase diagrams obtained from Schwinger-boson and spin-wave theories consistently show a spin disordered region between the Néel, stripe, and spiral phase. The existence of a finite quantum paramagnetic region is further confirmed by an unbiased variational ansatz based on tensor network states and a tensor renormalization group.

Ising antiferromagnet on the Archimedean lattices.

PubMed

Yu, Unjong

2015-06-01

Geometric frustration effects were studied systematically with the Ising antiferromagnet on the 11 Archimedean lattices using the Monte Carlo methods. The Wang-Landau algorithm for static properties (specific heat and residual entropy) and the Metropolis algorithm for a freezing order parameter were adopted. The exact residual entropy was also found. Based on the degree of frustration and dynamic properties, ground states of them were determined. The Shastry-Sutherland lattice and the trellis lattice are weakly frustrated and have two- and one-dimensional long-range-ordered ground states, respectively. The bounce, maple-leaf, and star lattices have the spin ice phase. The spin liquid phase appears in the triangular and kagome lattices.

Ising antiferromagnet on the Archimedean lattices

NASA Astrophysics Data System (ADS)

Yu, Unjong

2015-06-01

Geometric frustration effects were studied systematically with the Ising antiferromagnet on the 11 Archimedean lattices using the Monte Carlo methods. The Wang-Landau algorithm for static properties (specific heat and residual entropy) and the Metropolis algorithm for a freezing order parameter were adopted. The exact residual entropy was also found. Based on the degree of frustration and dynamic properties, ground states of them were determined. The Shastry-Sutherland lattice and the trellis lattice are weakly frustrated and have two- and one-dimensional long-range-ordered ground states, respectively. The bounce, maple-leaf, and star lattices have the spin ice phase. The spin liquid phase appears in the triangular and kagome lattices.

Statistical transmutation in doped quantum dimer models.

PubMed

Lamas, C A; Ralko, A; Cabra, D C; Poilblanc, D; Pujol, P

2012-07-06

We prove a "statistical transmutation" symmetry of doped quantum dimer models on the square, triangular, and kagome lattices: the energy spectrum is invariant under a simultaneous change of statistics (i.e., bosonic into fermionic or vice versa) of the holes and of the signs of all the dimer resonance loops. This exact transformation enables us to define the duality equivalence between doped quantum dimer Hamiltonians and provides the analytic framework to analyze dynamical statistical transmutations. We investigate numerically the doping of the triangular quantum dimer model with special focus on the topological Z(2) dimer liquid. Doping leads to four (instead of two for the square lattice) inequivalent families of Hamiltonians. Competition between phase separation, superfluidity, supersolidity, and fermionic phases is investigated in the four families.

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

NASA Astrophysics Data System (ADS)

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

2014-05-01

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

Partially Disordered Phase in Frustrated Triangular Lattice Antiferromagnet CuFeO 2

NASA Astrophysics Data System (ADS)

Mitsuda, Setsuo; Kasahara, Noriaki; Uno, Takahiro; Mase, Motoshi

1998-12-01

We reinvestigated successive magnetic phase transitions (T N1˜14.0 K, T N2˜10.5 K) in a frustrated triangular lattice antiferromagnet (TLA) CuFeO2 by neutron diffraction measurements using single crystals. The magnetic structure of the intermediate-temperature phase between T N1 and T N2 is found to be a quasi-long range ordered sinusoidally amplitude-modulated structure with a temperature dependent propagation wave vector (q q 0). These features of successive phase transitions are well explained by reinvestigated Monte-Carlo simulation of a 2D Ising TLA with competing exchange interactions up to 3rd neighbors, in spite of the Heisenberg spin character of orbital singlet Fe3+ magnetic ions.

Field-Induced Magnetic Phase Transitions in a Triangular Lattice Antiferromagnet CuFeO 2 up to 14.5 T

NASA Astrophysics Data System (ADS)

Mitsuda, Setsuo; Mase, Motoshi; Prokes, K.; Kitazawa, Hideaki; Katori, H.

2000-11-01

Neutron diffraction studies on a frustrated triangular lattice antiferromagnet (TLA) CuFeO2 have been performed under an applied magnetic field up to 14.5 T. The first-field-induced state was found to be not the commensurate 5-sublattice (↑↑↑↓↓) magnetic state but rather an incommensurate complex helical state reflecting the Heisenberg spin character of orbital singlet Fe3+ magnetic ions. In contrast, the second-field-induced state was found to be the 5-sublattice (↑↑↑↓↓) magnetic state predicted by the two-dimensional (2D) Ising spin TLA model with competing exchange interactions up to the 3rd neighbors.

Simulation of Molecular Transport in Systems Containing Mobile Obstacles.

PubMed

Polanowski, Piotr; Sikorski, Andrzej

2016-08-04

In this paper, we investigate the movement of molecules in crowded environments with obstacles undergoing Brownian motion by means of extensive Monte Carlo simulations. Our investigations were performed using the dynamic lattice liquid model, which was based on the cooperative movement concept and allowed to mimic systems at high densities where the motion of all elements (obstacles as well as moving particles) were highly correlated. The crowded environments are modeled on a two-dimensional triangular lattice containing obstacles (particles whose mobility was significantly reduced) moving by a Brownian motion. The subdiffusive motion of both elements in the system was analyzed. It was shown that the percolation transition does not exist in such systems in spite of the cooperative character of the particles' motion. The reduction of the obstacle mobility leads to the longer caging of liquid particles by mobile obstacles.

Tricriticality of the Blume-Emery-Griffiths model in thin films of stacked triangular lattices

NASA Astrophysics Data System (ADS)

El Hog, Sahbi; Diep, H. T.

2016-03-01

We study in this paper the Blume-Emery-Griffiths model in a thin film of stacked triangular lattices. The model is described by three parameters: bilinear exchange interaction between spins J, quadratic exchange interaction K and single-ion anisotropy D. The spin Si at the lattice site i takes three values (-1, 0, +1). This model can describe the mixing phase of He-4 (Si = +1,-1) and He-3 (Si = 0) at low temperatures. Using Monte Carlo simulations, we show that there exists a critical value of D below (above) which the transition is of second-(first-)order. In general, the temperature dependence of the concentrations of He-3 is different from layer by layer. At a finite temperature in the superfluid phase, the film surface shows a deficit of He-4 with respect to interior layers. However, effects of surface interaction parameters can reverse this situation. Effects of the film thickness on physical properties will be also shown as functions of temperature.

Magnetic excitations in the spin-1/2 triangular-lattice antiferromagnet Cs 2CuBr 4

DOE PAGES

Zvyagin, S. A.; Ozerov, M.; Kamenskyi, D.; ...

2015-11-27

We present on high- field electron spin resonance (ESR) studies of magnetic excitations in the spin- 1/2 triangular-lattice antiferromagnet Cs 2CuBr 4. Frequency- field diagrams of ESR excitations are measured for different orientations of magnetic fields up to 25 T. We show that the substantial zero- field energy gap, Δ ≈ 9.5 K, observed in the low-temperature excitation spectrum of Cs 2CuBr 4 [Zvyagin et al:, Phys. Rev. Lett. 112, 077206 (2014)], is present well above T N. Noticeably, the transition into the long-range magnetically ordered phase does not significantly affect the size of the gap, suggesting that even belowmore » T N the high-energy spin dynamics in Cs 2CuBr 4 is determined by short-range-order spin correlations. The experimental data are compared with results of model spin-wave-theory calculations for spin-1/2 triangle-lattice antiferromagnet.« less

Spin frustration and magnetic ordering in triangular lattice antiferromagnet Ca3CoNb2O9

NASA Astrophysics Data System (ADS)

Dai, Jia; Zhou, Ping; Wang, Peng-Shuai; Pang, Fei; Munsie, Tim J.; Luke, Graeme M.; Zhang, Jin-Shan; Yu, Wei-Qiang

2015-12-01

We synthesized a quasi-two-dimensional distorted triangular lattice antiferromagnet Ca3CoNb2O9, in which the effective spin of Co2+ is 1/2 at low temperatures, whose magnetic properties were studied by dc susceptibility and magnetization techniques. The x-ray diffraction confirms the quality of our powder samples. The large Weiss constant θCW˜ -55 K and the low Neel temperature TN˜ 1.45 K give a frustration factor f = | θCW/TN | ≈ 38, suggesting that Ca3CoNb2O9 resides in strong frustration regime. Slightly below TN, deviation between the susceptibility data under zero-field cooling (ZFC) and field cooling (FC) is observed. A new magnetic state with 1/3 of the saturate magnetization Ms is suggested in the magnetization curve at 0.46 K. Our study indicates that Ca3CoNb2O9 is an interesting material to investigate magnetism in triangular lattice antiferromagnets with weak anisotropy. Project supported by the National Natural Science Foundation of China (Grant Nos. 11374364 and 11222433), the National Basic Research Program of China (Grant No. 2011CBA00112). Research at McMaster University supported by the Natural Sciences and Engineering Research Council. Work at North China Electric Power University supported by the Scientific Research Foundation for the Returned Overseas Chinese Scholars, State Education Ministry.

Muon spin rotation study of spin dimers on a triangular lattice in Ba3 MRu2 O9

NASA Astrophysics Data System (ADS)

Ziat, Djamel; Verrier, Aimé; Quilliam, Jeffrey; Aczel, Adam; Sinclair, Ryan; Chen, Qiang; Zhou, Haidong

The family of hexagonal perovskites, Ba3 MA2 O9 has recently been proven to be fertile ground for the discovery of new, exotic magnetic phases, including several quantum spin liquid candidates. The 6H-perovskites can also accommodate spin dimers on a triangular lattice, as in the ruthenate materials Ba3MRu2O9. We will present measurements on materials containing M3 + (M = Y, La, Lu, In), which give rise to mixed valence Ru4.5 + ions wherein the orbital and charge degrees of freedom must also be considered. In particular, muon spin rotation (µSR) experiments, have allowed us to probe the nature of the magnetically ordered ground state of these materials at low temperatures.

Critical anisotropies of a geometrically frustrated triangular-lattice antiferromagnet

NASA Astrophysics Data System (ADS)

Swanson, M.; Haraldsen, J. T.; Fishman, R. S.

2009-05-01

This work examines the critical anisotropy required for the local stability of the collinear ground states of a geometrically frustrated triangular-lattice antiferromagnet (TLA). Using a Holstein-Primakoff expansion, we calculate the spin-wave frequencies for the one-, two-, three-, four-, and eight-sublattice (SL) ground states of a TLA with up to third neighbor interactions. Local stability requires that all spin-wave frequencies are real and positive. The two-, four-, and eight-SL phases break up into several regions where the critical anisotropy is a different function of the exchange parameters. We find that the critical anisotropy is a continuous function everywhere except across the two-SL/three-SL and three-SL/four-SL phase boundaries, where the three-SL phase has the higher critical anisotropy.

Critical Anisotropies of a Geometrically-Frustrated Triangular-Lattice

DOE Office of Scientific and Technical Information (OSTI.GOV)

Swanson, Mason R; Haraldsen, Jason T; Fishman, Randy Scott

2009-01-01

This work examines the critical anisotropy required for the local stability of the collinear ground states of a geometrically-frustrated triangular-lattice antiferromagnet (TLA). Using a Holstein-Primakoff expansion, we calculate the spin-wave frequencies for the 1, 2, 3, 4, and 8-sublattice (SL) ground states of a TLA with up to third neighbor interactions. Local stability requires that all spin-wave frequencies are real and positive. The 2, 4, and 8-SL phases break up into several regions where the critical anisotropy is a different function of the exchange parameters. We find that the critical anisotropy is a continuous function everywhere except across the 2-SL/3-SLmore » and 3-SL/4-SL phase boundaries, where the 3-SL phase has the higher critical anisotropy.« less

The nature of turbulence in a triangular lattice gas automaton

NASA Astrophysics Data System (ADS)

Duong-Van, Minh; Feit, M. D.; Keller, P.; Pound, M.

1986-12-01

Power spectra calculated from the coarse-graining of a simple lattice gas automaton, and those of time averaging other stochastic times series that we have investigated, have exponents in the range -1.6 to -2, consistent with observation of fully developed turbulence. This power spectrum is a natural consequence of coarse-graining; the exponent -2 represents the continuum limit.

Frustrated spin- 1 2 molecular magnetism in the mixed-valence antiferromagnets Ba 3 M Ru 2 O 9 ( M = In , Y, Lu)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ziat, D.; Aczel, Adam A.; Sinclair, R.

We have performed magnetic susceptibility, heat capacity, muon spin relaxation, and neutron-scattering measurements on three members of the family Ba 3MRu 2O 9, where M=In, Y, and Lu. These systems consist of mixed-valence Ru dimers on a triangular lattice with antiferromagnetic interdimer exchange. Although previous work has argued that charge order within the dimers or intradimer double exchange plays an important role in determining the magnetic properties, our results suggest that the dimers are better described as molecular units due to significant orbital hybridization, resulting in one spin-1/2 moment distributed equally over the two Ru sites. These molecular building blocksmore » form a frustrated, quasi-two-dimensional triangular lattice. Our zero- and longitudinal-field μSR results indicate that the molecular moments develop a collective, static magnetic ground state, with oscillations of the zero-field muon spin polarization indicative of long-range magnetic order in the Lu sample. In conclusion, the static magnetism is much more disordered in the Y and In samples, but they do not appear to be conventional spin glasses.« less

Frustrated spin- 1 2 molecular magnetism in the mixed-valence antiferromagnets Ba 3 M Ru 2 O 9 ( M = In , Y, Lu)

DOE PAGES

Ziat, D.; Aczel, Adam A.; Sinclair, R.; ...

2017-05-22

We have performed magnetic susceptibility, heat capacity, muon spin relaxation, and neutron-scattering measurements on three members of the family Ba 3MRu 2O 9, where M=In, Y, and Lu. These systems consist of mixed-valence Ru dimers on a triangular lattice with antiferromagnetic interdimer exchange. Although previous work has argued that charge order within the dimers or intradimer double exchange plays an important role in determining the magnetic properties, our results suggest that the dimers are better described as molecular units due to significant orbital hybridization, resulting in one spin-1/2 moment distributed equally over the two Ru sites. These molecular building blocksmore » form a frustrated, quasi-two-dimensional triangular lattice. Our zero- and longitudinal-field μSR results indicate that the molecular moments develop a collective, static magnetic ground state, with oscillations of the zero-field muon spin polarization indicative of long-range magnetic order in the Lu sample. In conclusion, the static magnetism is much more disordered in the Y and In samples, but they do not appear to be conventional spin glasses.« less

Response properties in the adsorption-desorption model on a triangular lattice

NASA Astrophysics Data System (ADS)

Šćepanović, J. R.; Stojiljković, D.; Jakšić, Z. M.; Budinski-Petković, Lj.; Vrhovac, S. B.

2016-06-01

The out-of-equilibrium dynamical processes during the reversible random sequential adsorption (RSA) of objects of various shapes on a two-dimensional triangular lattice are studied numerically by means of Monte Carlo simulations. We focused on the influence of the order of symmetry axis of the shape on the response of the reversible RSA model to sudden perturbations of the desorption probability Pd. We provide a detailed discussion of the significance of collective events for governing the time coverage behavior of shapes with different rotational symmetries. We calculate the two-time density-density correlation function C(t ,tw) for various waiting times tw and show that longer memory of the initial state persists for the more symmetrical shapes. Our model displays nonequilibrium dynamical effects such as aging. We find that the correlation function C(t ,tw) for all objects scales as a function of single variable ln(tw) / ln(t) . We also study the short-term memory effects in two-component mixtures of extended objects and give a detailed analysis of the contribution to the densification kinetics coming from each mixture component. We observe the weakening of correlation features for the deposition processes in multicomponent systems.

Ordering of two-dimensional crystals confined in strips of finite width

NASA Astrophysics Data System (ADS)

Ricci, A.; Nielaba, P.; Sengupta, S.; Binder, K.

2007-01-01

Monte Carlo simulations are used to study the effect of confinement on a crystal of point particles interacting with an inverse power law potential ∝r-12 in d=2 dimensions. This system can describe colloidal particles at the air-water interface, a model system for experimental study of two-dimensional melting. It is shown that the state of the system (a strip of width D ) depends very sensitively on the precise boundary conditions at the two “walls” providing the confinement. If one uses a corrugated boundary commensurate with the order of the bulk triangular crystalline structure, both orientational order and positional order is enhanced, and such surface-induced order persists near the boundaries also at temperatures where the system in the bulk is in its fluid state. However, using smooth repulsive boundaries as walls providing the confinement, only the orientational order is enhanced, but positional (quasi-)long range order is destroyed: The mean-square displacement of two particles n lattice parameters apart in the y direction along the walls then crosses over from the logarithmic increase (characteristic for d=2 ) to a linear increase with n (characteristic for d=1 ). The strip then exhibits a vanishing shear modulus. These results are interpreted in terms of a phenomenological harmonic theory. Also the effect of incommensurability of the strip width D with the triangular lattice structure is discussed, and a comparison with surface effects on phase transitions in simple Ising and XY models is made.

Phase transitions in a system of hard Y-shaped particles on the triangular lattice

NASA Astrophysics Data System (ADS)

Mandal, Dipanjan; Nath, Trisha; Rajesh, R.

2018-03-01

We study the different phases and the phase transitions in a system of Y-shaped particles, examples of which include immunoglobulin-G and trinaphthylene molecules, on a triangular lattice interacting exclusively through excluded volume interactions. Each particle consists of a central site and three of its six nearest neighbors chosen alternately, such that there are two types of particles which are mirror images of each other. We study the equilibrium properties of the system using grand canonical Monte Carlo simulations that implement an algorithm with cluster moves that is able to equilibrate the system at densities close to full packing. We show that, with increasing density, the system undergoes two entropy-driven phase transitions with two broken-symmetry phases. At low densities, the system is in a disordered phase. As intermediate phases, there is a solidlike sublattice phase in which one type of particle is preferred over the other and the particles preferentially occupy one of four sublattices, thus breaking both particle symmetry as well as translational invariance. At even higher densities, the phase is a columnar phase, where the particle symmetry is restored, and the particles preferentially occupy even or odd rows along one of the three directions. This phase has translational order in only one direction, and breaks rotational invariance. From finite-size scaling, we demonstrate that both the transitions are first order in nature. We also show that the simpler system with only one type of particle undergoes a single discontinuous phase transition from a disordered phase to a solidlike sublattice phase with an increasing density of particles.

Anisotropic quantum quench in the presence of frustration or background gauge fields: A probe of bulk currents and topological chiral edge modes

NASA Astrophysics Data System (ADS)

Killi, Matthew; Trotzky, Stefan; Paramekanti, Arun

2012-12-01

Bosons and fermions, in the presence of frustration or background gauge fields, can form many-body ground states that support equilibrium charge or spin currents. Motivated by the experimental creation of frustration or synthetic gauge fields in ultracold atomic systems, we propose a general scheme by which making a sudden anisotropic quench of the atom tunneling across the lattice and tracking the ensuing density modulations provides a powerful and gauge-invariant route to probing diverse equilibrium current patterns. Using illustrative examples of trapped superfluid Bose and normal Fermi systems in the presence of artificial magnetic fluxes on square lattices, and frustrated bosons in a triangular lattice, we show that this scheme to probe equilibrium bulk current order works independent of particle statistics. We also show that such quenches can detect chiral edge modes in gapped topological states, such as quantum Hall or quantum spin Hall insulators.

Simulations of water nano-confined between corrugated planes

NASA Astrophysics Data System (ADS)

Zubeltzu, Jon; Artacho, Emilio

2017-11-01

Water confined to nanoscale widths in two dimensions between ideal planar walls has been the subject of ample study, aiming at understanding the intrinsic response of water to confinement, avoiding the consideration of the chemistry of actual confining materials. In this work, we study the response of such nanoconfined water to the imposition of a periodicity in the confinement by means of computer simulations, both using empirical potentials and from first-principles. For that we propose a periodic confining potential emulating the atomistic oscillation of the confining walls, which allows varying the lattice parameter and amplitude of the oscillation. We do it for a triangular lattice, with several values of the lattice parameter: one which is ideal for commensuration with layers of Ih ice and other values that would correspond to more realistic substrates. For the former, the phase diagram shows an overall rise of the melting temperature. The liquid maintains a bi-layer triangular structure, however, despite the fact that it is not favoured by the external periodicity. The first-principles liquid is significantly affected by the modulation in its layering and stacking even at relatively small amplitudes of the confinement modulation. Beyond some critical modulation amplitude, the hexatic phase present in flat confinement is replaced by a trilayer crystalline phase unlike any of the phases encountered for flat confinement. For more realistic lattice parameters, the liquid does not display higher tendency to freeze, but it clearly shows inhomogeneous behaviour as the strength of the rugosity increases. In spite of this expected inhomogeneity, the structural and dynamical response of the liquid is surprisingly insensitive to the external modulation. Although the first-principles calculations give a more triangular liquid than the one observed with empirical potentials (TIP4P/2005), both agree remarkably well for the main conclusions of the study.

Solutions for correlations along the coexistence curve and at the critical point of a kagomé lattice gas with three-particle interactions

NASA Astrophysics Data System (ADS)

Barry, J. H.; Muttalib, K. A.; Tanaka, T.

2008-01-01

We consider a two-dimensional (d=2) kagomé lattice gas model with attractive three-particle interactions around each triangular face of the kagomé lattice. Exact solutions are obtained for multiparticle correlations along the liquid and vapor branches of the coexistence curve and at criticality. The correlation solutions are also determined along the continuation of the curvilinear diameter of the coexistence region into the disordered fluid region. The method generates a linear algebraic system of correlation identities with coefficients dependent only upon the interaction parameter. Using a priori knowledge of pertinent solutions for the density and elementary triplet correlation, one finds a closed and linearly independent set of correlation identities defined upon a spatially compact nine-site cluster of the kagomé lattice. Resulting exact solution curves of the correlations are plotted and discussed as functions of the temperature and are compared with corresponding results in a traditional kagomé lattice gas having nearest-neighbor pair interactions. An example of application for the multiparticle correlations is demonstrated in cavitation theory.

Optimum Laser Beam Characteristics for Achieving Smoother Ablations in Laser Vision Correction.

PubMed

Verma, Shwetabh; Hesser, Juergen; Arba-Mosquera, Samuel

2017-04-01

Controversial opinions exist regarding optimum laser beam characteristics for achieving smoother ablations in laser-based vision correction. The purpose of the study was to outline a rigorous simulation model for simulating shot-by-shot ablation process. The impact of laser beam characteristics like super Gaussian order, truncation radius, spot geometry, spot overlap, and lattice geometry were tested on ablation smoothness. Given the super Gaussian order, the theoretical beam profile was determined following Lambert-Beer model. The intensity beam profile originating from an excimer laser was measured with a beam profiler camera. For both, the measured and theoretical beam profiles, two spot geometries (round and square spots) were considered, and two types of lattices (reticular and triangular) were simulated with varying spot overlaps and ablated material (cornea or polymethylmethacrylate [PMMA]). The roughness in ablation was determined by the root-mean-square per square root of layer depth. Truncating the beam profile increases the roughness in ablation, Gaussian profiles theoretically result in smoother ablations, round spot geometries produce lower roughness in ablation compared to square geometry, triangular lattices theoretically produce lower roughness in ablation compared to the reticular lattice, theoretically modeled beam profiles show lower roughness in ablation compared to the measured beam profile, and the simulated roughness in ablation on PMMA tends to be lower than on human cornea. For given input parameters, proper optimum parameters for minimizing the roughness have been found. Theoretically, the proposed model can be used for achieving smoothness with laser systems used for ablation processes at relatively low cost. This model may improve the quality of results and could be directly applied for improving postoperative surface quality.

Bose and Fermi Gases of Ultracold Ytterbium in a Triangular Optical Lattice

NASA Astrophysics Data System (ADS)

Thobe, Alexander; Doerscher, Soeren; Hundt, Bastian; Kochanke, Andre; Becker, Christoph; Sengstock, Klaus

2013-05-01

Quantum gases of alkaline-earth like atoms such as Calcium, Strontium and Ytterbium (Yb) open up exciting new possibilities for the study of many body physics in optical lattices, ranging from SU(N) symmetric spin Hamiltonians to the Kondo Lattice Model. Here, we present experimental studies of ultracold bosonic and fermionic Yb quantum gases. Unlike other experiments studying ultracold alkaline earth-like atoms, we have implemented a 2D-MOT instead of a Zeeman slower as a source of cold atoms. From the 2D-MOT, operating on the broad 1S0 -->1P1 transtition, the atoms are directly loaded into the 3D-MOT operating on a narrow intercombination line. The atoms are then evaporatively cooled to quantum degeneracy in a crossed optical dipole trap. With this setup we routinely produce BECs and degenerate Fermi gases of different Yb isotopes. Moreover, we present first results on spectroscopy of an interacting fermi gas on the ultranarrow 1S0 -->3P0 clock transition in a magic wavelength optical lattice. In future experiments, this spectroscopy will serve as a versatile tool for interaction sensing and selective addressing of atoms in a wavelength tunable, state dependent, triangular optical lattice, which we are currently implementing. This work is supported by DFG within SFB 925 and GrK 1355, as well as EU FETOpen (iSense).

Optimal design for crosstalk analysis in 12-core 5-LP mode homogeneous multicore fiber for different lattice structure

NASA Astrophysics Data System (ADS)

Kumar, Dablu; Ranjan, Rakesh

2018-03-01

12-Core 5-LP mode homogeneous multicore fibers have been proposed for analysis of inter-core crosstalk and dispersion, with four different lattice structures (circular, 2-ring, square lattice, and triangular lattice) having cladding diameter of 200 μm and a fixed cladding thickness of 35 μm. The core-to-core crosstalk impact has been studied numerically with respect to bending radius, core pitch, transmission distance, wavelength, and core diameter for all 5-LP modes. In anticipation of further reduction in crosstalk levels, the trench-assisted cores have been incorporated for all respective designs. Ultra-low crosstalk (-138 dB/100 km) has been achieved through the triangular lattice arrangement, with trench depth Δ2 = -1.40% for fundamental (LP01) mode. It has been noted that the impact of mode polarization on crosstalk behavior is minor, with difference in crosstalk levels between two polarized spatial modes as ≤0.2 dB. Moreover, the optimized cladding diameter has been obtained for all 5-LP modes for a target value of crosstalk of -50 dB/100 km, with all the core arrangements. The dispersion characteristic has also been analyzed with respect to wavelength, which is nearly 2.5 ps/nm km at operating wavelength 1550 nm. The relative core multiplicity factor (RCMF) for the proposed design is obtained as 64.

Magnetic dipole interactions in crystals

NASA Astrophysics Data System (ADS)

Johnston, David C.

2016-01-01

The influence of magnetic dipole interactions (MDIs) on the magnetic properties of local-moment Heisenberg spin systems is investigated. A general formulation is presented for calculating the eigenvalues λ and eigenvectors μ ̂ of the MDI tensor of the magnetic dipoles in a line (one dimension, 1D), within a circle (2D) or a sphere (3D) of radius r surrounding a given moment μ⃗i for given magnetic propagation vectors k for collinear and coplanar noncollinear magnetic structures on both Bravais and non-Bravais spin lattices. Results are calculated for collinear ordering on 1D chains, 2D square and simple-hexagonal (triangular) Bravais lattices, 2D honeycomb and kagomé non-Bravais lattices, and 3D cubic Bravais lattices. The λ and μ ̂ values are compared with previously reported results. Calculations for collinear ordering on 3D simple tetragonal, body-centered tetragonal, and stacked triangular and honeycomb lattices are presented for c /a ratios from 0.5 to 3 in both graphical and tabular form to facilitate comparison of experimentally determined easy axes of ordering on these Bravais lattices with the predictions for MDIs. Comparisons with the easy axes measured for several illustrative collinear antiferromagnets (AFMs) are given. The calculations are extended to the cycloidal noncollinear 120∘ AFM ordering on the triangular lattice where λ is found to be the same as for collinear AFM ordering with the same k. The angular orientation of the ordered moments in the noncollinear coplanar AFM structure of GdB4 with a distorted stacked 3D Shastry-Sutherland spin-lattice geometry is calculated and found to be in disagreement with experimental observations, indicating the presence of another source of anisotropy. Similar calculations for the undistorted 2D and stacked 3D Shastry-Sutherland lattices are reported. The thermodynamics of dipolar magnets are calculated using the Weiss molecular field theory for quantum spins, including the magnetic transition temperature Tm and the ordered moment, magnetic heat capacity, and anisotropic magnetic susceptibility χ versus temperature T . The anisotropic Weiss temperature θp in the Curie-Weiss law for T >Tm is calculated. A quantitative study of the competition between FM and AFM ordering on cubic Bravais lattices versus the demagnetization factor in the absence of FM domain effects is presented. The contributions of Heisenberg exchange interactions and of the MDIs to Tm and to θp are found to be additive, which simplifies analysis of experimental data. Some properties in the magnetically-ordered state versus T are presented, including the ordered moment and magnetic heat capacity and, for AFMs, the dipolar anisotropy of the free energy and the perpendicular critical field. The anisotropic χ for dipolar AFMs is calculated both above and below the Néel temperature TN and the results are illustrated for a simple tetragonal lattice with c /a >1 , c /a =1 (cubic), and c /a <1 , where a change in sign of the χ anisotropy is found at c /a =1 . Finally, following the early work of Keffer [Phys. Rev. 87, 608 (1952), 10.1103/PhysRev.87.608], the dipolar anisotropy of χ above TN=69 K of the prototype collinear Heisenberg-exchange-coupled tetragonal compound MnF2 is calculated and found to be in excellent agreement with experimental single-crystal literature data above 130 K, where the smoothly increasing deviation of the experimental data from the theory on cooling from 130 K to TN is deduced to arise from dynamic short-range collinear c -axis AFM ordering in this temperature range driven by the exchange interactions.

Towards the simplest hydrodynamic lattice-gas model.

PubMed

Boghosian, Bruce M; Love, Peter J; Meyer, David A

2002-03-15

It has been known since 1986 that it is possible to construct simple lattice-gas cellular automata whose hydrodynamics are governed by the Navier-Stokes equations in two dimensions. The simplest such model heretofore known has six bits of state per site on a triangular lattice. In this work, we demonstrate that it is possible to construct a model with only five bits of state per site on a Kagome lattice. Moreover, the model has a simple, deterministic set of collision rules and is easily implemented on a computer. In this work, we derive the equilibrium distribution function for this lattice-gas automaton and carry out the Chapman-Enskog analysis to determine the form of the Navier-Stokes equations.

On Born's Conjecture about Optimal Distribution of Charges for an Infinite Ionic Crystal

NASA Astrophysics Data System (ADS)

Bétermin, Laurent; Knüpfer, Hans

2018-04-01

We study the problem for the optimal charge distribution on the sites of a fixed Bravais lattice. In particular, we prove Born's conjecture about the optimality of the rock salt alternate distribution of charges on a cubic lattice (and more generally on a d-dimensional orthorhombic lattice). Furthermore, we study this problem on the two-dimensional triangular lattice and we prove the optimality of a two-component honeycomb distribution of charges. The results hold for a class of completely monotone interaction potentials which includes Coulomb-type interactions for d≥3 . In a more general setting, we derive a connection between the optimal charge problem and a minimization problem for the translated lattice theta function.

Magnetic and magnetocaloric properties of the exactly solvable mixed-spin Ising model on a decorated triangular lattice in a magnetic field

NASA Astrophysics Data System (ADS)

Gálisová, Lucia; Strečka, Jozef

2018-05-01

The ground state, zero-temperature magnetization process, critical behaviour and isothermal entropy change of the mixed-spin Ising model on a decorated triangular lattice in a magnetic field are exactly studied after performing the generalized decoration-iteration mapping transformation. It is shown that both the inverse and conventional magnetocaloric effect can be found near the absolute zero temperature. The former phenomenon can be found in a vicinity of the discontinuous phase transitions and their crossing points, while the latter one occurs in some paramagnetic phases due to a spin frustration to be present at zero magnetic field. The inverse magnetocaloric effect can also be detected slightly above continuous phase transitions following the power-law dependence | - ΔSisomin | ∝hn, where n depends basically on the ground-state spin ordering.

Transition-metal oxides with triangular lattices: generation of new magnetic and electronic properties.

PubMed

Maignan, A; Kobayashi, W; Hébert, S; Martinet, G; Pelloquin, D; Bellido, N; Simon, Ch

2008-10-06

The search for multifunctional materials as multiferroics to be applied in microelectronic or for new, chemically stable and nontoxic, thermoelectric materials to recover waste heat is showing a common interest in the oxides whose structures contain a triangular network of transition-metal cations. To illustrate this point, two ternary systems, Ba-Co-O and Ca-Co-O, have been chosen. It is shown that new phases with a complex triangular structure can be discovered, for instance, by introduction of Ga (3+) into the Ba-Co-O system to stabilize Ba 6Ga 2Co 11O 26 and Ba 2GaCo 8O 14, which both belong to a large family of compounds with formula [Ba(Co,Ga)O 3-delta] n [BaCo 8O 11]. In the latter, both sublattices contain triangular networks derived from the hexagonal perovskite and the spinel structure. Among the hexagonal perovskite, the Ca 3Co 2O 6 crystals give clear evidence where the coupling of charges and spins is at the origin of a magnetocapacitance effect. In particular, the ferrimagnetic to ferromagnetic transition, with a one-third plateau on the M( H) curve characteristic of triangular magnetism, is accompanied by a peak in the dielectric constant. A second class of cobaltites is the focus of much interest. Their 2D structure, containing CoO 2 planes isostructural to a CdI 2 slice that are stacked in an incommensurate way with rock salt type layers, is referred to misfit cobaltite. The 2D triangular network of edge-shared CoO 6 octahedra is believed to be responsible for large values of the Seebeck coefficient and low electrical resistivity. A clear relationship between the structuresincommensurability ratiosand the electronic properties is evidenced, showing that the charge carrier concentration can be tuned via the control of the ionic radius of the cations in the separating layers.

Comparison of different models of motion in a crowded environment: a Monte Carlo study.

PubMed

Polanowski, P; Sikorski, A

2017-02-22

In this paper we investigate the motion of molecules in crowded environments for two dramatically different types of molecular transport. The first type is realized by the dynamic lattice liquid model, which is based on a cooperative movement concept and thus, the motion of molecules is highly correlated. The second one corresponds to a so-called motion of a single agent where the motion of molecules is considered as a random walk without any correlation with other moving elements. The crowded environments are modeled as a two-dimensional triangular lattice with fixed impenetrable obstacles. Our simulation results indicate that the type of transport has an impact on the dynamics of the system, the percolation threshold, critical exponents, and on molecules' trajectories.

Phase-space networks of geometrically frustrated systems.

PubMed

Han, Yilong

2009-11-01

We illustrate a network approach to the phase-space study by using two geometrical frustration models: antiferromagnet on triangular lattice and square ice. Their highly degenerated ground states are mapped as discrete networks such that the quantitative network analysis can be applied to phase-space studies. The resulting phase spaces share some comon features and establish a class of complex networks with unique Gaussian spectral densities. Although phase-space networks are heterogeneously connected, the systems are still ergodic due to the random Poisson processes. This network approach can be generalized to phase spaces of some other complex systems.

Static and dynamical properties of the spin-1/2 equilateral triangular-lattice antiferromagnet Ba 3CoSb 2O 9

DOE PAGES

Ma, Jie; Kamiya, Yoshitomo; Hong, Tao; ...

2016-02-24

We present single-crystal neutron scattering measurements of the spin-1/2 equilateral triangular-lattice antiferromagnet Ba 3CoSb 2O 9. Besides confirming that the Co 2+ magnetic moments lie in the ab plane for zero magnetic field and then determining all the exchange parameters of the minimal quasi-2D spin Hamiltonian, we provide conclusive experimental evidence of magnon decay through observation of intrinsic line broadening. Through detailed comparisons with the linear and nonlinear spin-wave theories, we also point out that the large-S approximation, which is conventionally employed to predict magnon decay in noncollinear magnets, is inadequate to explain our experimental observation. Hence, our results callmore » for a new theoretical framework for describing excitation spectra in low-dimensional frustrated magnets under strong quantum effects.« less

Anomalous matching effect and attractive vortex interaction in 7.5-/μm triangular microhole lattice on Pb film

NASA Astrophysics Data System (ADS)

Ishida, Takekazu; Yoshida, Masaaki; Nakata, Shin'ichiro; Koyama, Tomio

2002-10-01

It is considerably exciting to explore the novel vortex physics in multiply connected superconductors. We prepare triangular microhole lattice on Pb film (TriMHoLP) by evaporation of a type-I superconductor Pb upon a capillary plate (6-μm hole and 7.5-μm pitch) in vacuum. We measure the magnetization of TriMHoLP in the RSO mode under low fields (| H|⩽4.7 G). The polarity of magnetization peaks is identical against the field reversal. The magnetization curves as a function of temperature taken in a field-cooling mode of RSO are always positive irrelevant to the field polarity. We show that a vortex-vortex interaction is not always repulsive in a low- κ superconductor. We consider that a spontaneous magnetization and an anomalous matching effect near Tc are relevant to the attractive interaction between vortices.

Internal Magnetic Field on the Two-Dimensional Triangular Lattice Formed by Mo3O8 Trimers

NASA Astrophysics Data System (ADS)

Sugiyama, Jun; Nozaki, Hiroshi; Umegaki, Izumi; Haraguchi, Yuya; Michioka, Chishiro; Ueda, Hiroaki; Yoshimura, Kazuyoshi; Sassa, Yasmine; Forslund, Ola Kenji; Andreica, Daniel; Goko, Tatsuo; Amato, Alex; Månsson, Martin

In order to elucidate the magnetic ground state of the cluster magnets with a half filled triangular lattice, we have recorded zero field (ZF-) and weak transverse field (wTF-) μ+SR spectra using powder samples of Li2InMo3O8 and Li2ScMo3O8 down to 1.9 K. The ZF measurements at 1.9 K demonstrated the presence of static magnetic order in Li2InMo3O8, whereas paramagnetic nature in Li2ScMo3O8. The wTF measurements clarified that the magnetic transition occurs at around 11 K (= TN) in Li2InMo3O8. However, for Li2ScMo3O8, there is no detectable change in the ZF- and wTF-μ+SR fit-parameters in the temperature range between 60 and 1.9 K.

Optical devices combining an organic semiconductor crystal with a two-dimensional inorganic diffraction grating

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kitazawa, Takenori; Yamao, Takeshi, E-mail: yamao@kit.ac.jp; Hotta, Shu

2016-02-01

We have fabricated optical devices using an organic semiconductor crystal as an emission layer in combination with a two-dimensional (2D) inorganic diffraction grating used as an optical cavity. We formed the inorganic diffraction grating by wet etching of aluminum-doped zinc oxide (AZO) under a 2D cyclic olefin copolymer (COC) diffraction grating used as a mask. The COC diffraction grating was fabricated by nanoimprint lithography. The AZO diffraction grating was composed of convex prominences arranged in a triangular lattice. The organic crystal placed on the AZO diffraction grating indicated narrowed peaks in its emission spectrum under ultraviolet light excitation. These aremore » detected parallel to the crystal plane. The peaks were shifted by rotating the optical devices around the normal to the crystal plane, which reflected the rotational symmetries of the triangular lattice through 60°.« less

Frustrated magnetism in doped quasi-triangular lattice materials, Cu2(1-x)Zn2x(OH)3NO3/(C7H15COO)

NASA Astrophysics Data System (ADS)

Wu, Jian; Werner, Fletcher; Gangopadhyay, Anup K.; Solin, S. A.

2010-03-01

We have performed DC and AC magnetic susceptibility measurements on the spin S=1/2 quasi-triangular lattice materials Cu2(1-x)Zn2x(OH)3NO3/(C7H15COO). The X-ray diffraction experiments reveal that this class of materials has a crystal structure in P21/m space group, in which Cu^2+ and Zn^2+ ions are arranged on a slightly distorted triangular lattice [1]. Cu2(1-)Zn2x(OH)3NO3 with a short inorganic intercalation NO3 group, have a long-range antiferromagnetic order at low temperature. The Neel temperature TN decreases from 11K to 5.6K while the Curie-Weiss temperature increases from -5.1K to +2.8K as the Zn concentration increases from 0 to 65%. After a longer alkanecarboxylate C7H15COO group was introduced into the interlayer space, a spin-glass like behavior in magnetic properties was observed [2]. The value |θcw /TN| is approximately 20, indicating the materials are in a medium level frustrated state. The onset of a ferromagnetic correlation was found in both DC and AC susceptibility data. The interplay of geometrical frustration and the coexistence of ferromagnetic and antiferromagnetic couplings has driven the materials into a glassy ground state. [1] G. Linder, et al., Journal of Solid State Chemistry (1995) [2] M. A. Girtu et al, Phys Rev B 61,4117(2000).

Strong Cosserat Elasticity in a Transversely Isotropic Polymer Lattice

NASA Astrophysics Data System (ADS)

Rueger, Z.; Lakes, R. S.

2018-02-01

Large size effects are experimentally measured in lattices of triangular unit cells: about a factor of 36 in torsion rigidity and 29 in bending rigidity. This nonclassical phenomenon is consistent with Cosserat elasticity, which allows for the rotation of points and distributed moments in addition to the translation of points and force stress of classical elasticity. The Cosserat characteristic length for torsion is ℓt=9.4 mm ; for bending, it is ℓb=8.8 mm ; these values are comparable to the cell size. Nonclassical effects are much stronger than in stretch-dominated lattices with uniform straight ribs. The lattice structure provides a path to the attainment of arbitrarily large effects.

Carbon kagome lattice and orbital-frustration-induced metal-insulator transition for optoelectronics.

PubMed

Chen, Yuanping; Sun, Y Y; Wang, H; West, D; Xie, Yuee; Zhong, J; Meunier, V; Cohen, Marvin L; Zhang, S B

2014-08-22

A three-dimensional elemental carbon kagome lattice, made of only fourfold-coordinated carbon atoms, is proposed based on first-principles calculations. Despite the existence of 60° bond angles in the triangle rings, widely perceived to be energetically unfavorable, the carbon kagome lattice is found to display exceptional stability comparable to that of C(60). The system allows us to study the effects of triangular frustration on the electronic properties of realistic solids, and it demonstrates a metal-insulator transition from that of graphene to a direct gap semiconductor in the visible blue region. By minimizing s-p orbital hybridization, which is an intrinsic property of carbon, not only the band edge states become nearly purely frustrated p states, but also the band structure is qualitatively different from any known bulk elemental semiconductors. For example, the optical properties are similar to those of direct-gap semiconductors GaN and ZnO, whereas the effective masses are comparable to or smaller than those of Si.

Pair correlation functions for identifying spatial correlation in discrete domains

NASA Astrophysics Data System (ADS)

Gavagnin, Enrico; Owen, Jennifer P.; Yates, Christian A.

2018-06-01

Identifying and quantifying spatial correlation are important aspects of studying the collective behavior of multiagent systems. Pair correlation functions (PCFs) are powerful statistical tools that can provide qualitative and quantitative information about correlation between pairs of agents. Despite the numerous PCFs defined for off-lattice domains, only a few recent studies have considered a PCF for discrete domains. Our work extends the study of spatial correlation in discrete domains by defining a new set of PCFs using two natural and intuitive definitions of distance for a square lattice: the taxicab and uniform metric. We show how these PCFs improve upon previous attempts and compare between the quantitative data acquired. We also extend our definitions of the PCF to other types of regular tessellation that have not been studied before, including hexagonal, triangular, and cuboidal. Finally, we provide a comprehensive PCF for any tessellation and metric, allowing investigation of spatial correlation in irregular lattices for which recognizing correlation is less intuitive.

Topological magnon bands in ferromagnetic star lattice.

PubMed

Owerre, S A

2017-05-10

The experimental observation of topological magnon bands and thermal Hall effect in a kagomé lattice ferromagnet Cu(1-3, bdc) has inspired the search for topological magnon effects in various insulating ferromagnets that lack an inversion center allowing a Dzyaloshinskii-Moriya (DM) spin-orbit interaction. The star lattice (also known as the decorated honeycomb lattice) ferromagnet is an ideal candidate for this purpose because it is a variant of the kagomé lattice with additional links that connect the up-pointing and down-pointing triangles. This gives rise to twice the unit cell of the kagomé lattice, and hence more interesting topological magnon effects. In particular, the triangular bridges on the star lattice can be coupled either ferromagnetically or antiferromagnetically which is not possible on the kagomé lattice ferromagnets. Here, we study DM-induced topological magnon bands, chiral edge modes, and thermal magnon Hall effect on the star lattice ferromagnet in different parameter regimes. The star lattice can also be visualized as the parent material from which topological magnon bands can be realized for the kagomé and honeycomb lattices in some limiting cases.

Linear flavor-wave theory for fully antisymmetric SU(N ) irreducible representations

NASA Astrophysics Data System (ADS)

Kim, Francisco H.; Penc, Karlo; Nataf, Pierre; Mila, Frédéric

2017-11-01

The extension of the linear flavor-wave theory to fully antisymmetric irreducible representations (irreps) of SU (N ) is presented in order to investigate the color order of SU (N ) antiferromagnetic Heisenberg models in several two-dimensional geometries. The square, triangular, and honeycomb lattices are considered with m fermionic particles per site. We present two different methods: the first method is the generalization of the multiboson spin-wave approach to SU (N ) which consists of associating a Schwinger boson to each state on a site. The second method adopts the Read and Sachdev bosons which are an extension of the Schwinger bosons that introduces one boson for each color and each line of the Young tableau. The two methods yield the same dispersing modes, a good indication that they properly capture the semiclassical fluctuations, but the first one leads to spurious flat modes of finite frequency not present in the second one. Both methods lead to the same physical conclusions otherwise: long-range Néel-type order is likely for the square lattice for SU(4) with two particles per site, but quantum fluctuations probably destroy order for more than two particles per site, with N =2 m . By contrast, quantum fluctuations always lead to corrections larger than the classical order parameter for the tripartite triangular lattice (with N =3 m ) or the bipartite honeycomb lattice (with N =2 m ) for more than one particle per site, m >1 , making the presence of color very unlikely except maybe for m =2 on the honeycomb lattice, for which the correction is only marginally larger than the classical order parameter.

Graphical Representations and Cluster Algorithms for Ice Rule Vertex Models.

NASA Astrophysics Data System (ADS)

Shtengel, Kirill; Chayes, L.

2002-03-01

We introduce a new class of polymer models which is closely related to loop models, recently a topic of intensive studies. These particular models arise as graphical representations for ice-rule vertex models. The associated cluster algorithms provide a unification and generalisation of most of the existing algorithms. For many lattices, percolation in the polymer models evidently indicates first order phase transitions in the vertex models. Critical phases can be understood as being susceptible to colour symmetry breaking in the polymer models. The analysis includes, but is certainly not limited to the square lattice six-vertex model. In particular, analytic criteria can be found for low temperature phases in other even coordinated 2D lattices such as the triangular lattice, or higher dimensional lattices such as the hyper-cubic lattices of arbitrary dimensionality. Finally, our approach can be generalised to the vertex models that do not obey the ice rule, such as the eight-vertex model.

Modeling of Triangular Lattice Space Structures with Curved Battens

NASA Technical Reports Server (NTRS)

Chen, Tzikang; Wang, John T.

2005-01-01

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

Mermin-Wagner physics, (H ,T ) phase diagram, and candidate quantum spin-liquid phase in the spin-1/2 triangular-lattice antiferromagnet Ba8CoNb6O24

NASA Astrophysics Data System (ADS)

Cui, Y.; Dai, J.; Zhou, P.; Wang, P. S.; Li, T. R.; Song, W. H.; Wang, J. C.; Ma, L.; Zhang, Z.; Li, S. Y.; Luke, G. M.; Normand, B.; Xiang, T.; Yu, W.

2018-04-01

Ba8CoNb6O24 presents a system whose Co2 + ions have an effective spin 1/2 and construct a regular triangular-lattice antiferromagnet (TLAFM) with a very large interlayer spacing, ensuring purely two-dimensional character. We exploit this ideal realization to perform a detailed experimental analysis of the S =1 /2 TLAFM, which is one of the keystone models in frustrated quantum magnetism. We find strong low-energy spin fluctuations and no magnetic ordering, but a diverging correlation length down to 0.1 K, indicating a Mermin-Wagner trend toward zero-temperature order. Below 0.1 K, however, our low-field measurements show an unexpected magnetically disordered state, which is a candidate quantum spin liquid. We establish the (H ,T ) phase diagram, mapping in detail the quantum fluctuation corrections to the available theoretical analysis. These include a strong upshift in field of the maximum ordering temperature, qualitative changes to both low- and high-field phase boundaries, and an ordered regime apparently dominated by the collinear "up-up-down" state. Ba8CoNb6O24 , therefore, offers fresh input for the development of theoretical approaches to the field-induced quantum phase transitions of the S =1 /2 Heisenberg TLAFM.

Magnetic dipole interactions in crystals

DOE PAGES

Johnston, David

2016-01-13

The influence of magnetic dipole interactions (MDIs) on the magnetic properties of local-moment Heisenberg spin systems is investigated. A general formulation is presented for calculating the eigenvalues λ and eigenvectors μ ˆ of the MDI tensor of the magnetic dipoles in a line (one dimension, 1D), within a circle (2D) or a sphere (3D) of radius r surrounding a given moment μ → i for given magnetic propagation vectors k for collinear and coplanar noncollinear magnetic structures on both Bravais and non-Bravais spin lattices. Results are calculated for collinear ordering on 1D chains, 2D square and simple-hexagonal (triangular) Bravaismore » lattices, 2D honeycomb and kagomé non-Bravais lattices, and 3D cubic Bravais lattices. The λ and μ ˆ values are compared with previously reported results. Calculations for collinear ordering on 3D simple tetragonal, body-centered tetragonal, and stacked triangular and honeycomb lattices are presented for c/a ratios from 0.5 to 3 in both graphical and tabular form to facilitate comparison of experimentally determined easy axes of ordering on these Bravais lattices with the predictions for MDIs. Comparisons with the easy axes measured for several illustrative collinear antiferromagnets (AFMs) are given. The calculations are extended to the cycloidal noncollinear 120 ° AFM ordering on the triangular lattice where λ is found to be the same as for collinear AFM ordering with the same k. The angular orientation of the ordered moments in the noncollinear coplanar AFM structure of GdB 4 with a distorted stacked 3D Shastry-Sutherland spin-lattice geometry is calculated and found to be in disagreement with experimental observations, indicating the presence of another source of anisotropy. Similar calculations for the undistorted 2D and stacked 3D Shastry-Sutherland lattices are reported. The thermodynamics of dipolar magnets are calculated using the Weiss molecular field theory for quantum spins, including the magnetic transition temperature T m and the ordered moment, magnetic heat capacity, and anisotropic magnetic susceptibility χ versus temperature T . The anisotropic Weiss temperature θ p in the Curie-Weiss law for T>T m is calculated. A quantitative study of the competition between FM and AFM ordering on cubic Bravais lattices versus the demagnetization factor in the absence of FM domain effects is presented. The contributions of Heisenberg exchange interactions and of the MDIs to T m and to θ p are found to be additive, which simplifies analysis of experimental data. Some properties in the magnetically-ordered state versus T are presented, including the ordered moment and magnetic heat capacity and, for AFMs, the dipolar anisotropy of the free energy and the perpendicular critical field. The anisotropic χ for dipolar AFMs is calculated both above and below the Néel temperature T N and the results are illustrated for a simple tetragonal lattice with c/a>1, c/a=1 (cubic), and c/a<1 , where a change in sign of the χ anisotropy is found at c/a=1 . Finally, following the early work of Keffer [Phys. Rev. 87, 608 (1952)], the dipolar anisotropy of χ above T N =69 K of the prototype collinear Heisenberg-exchange-coupled tetragonal compound MnF 2 is calculated and found to be in excellent agreement with experimental single-crystal literature data above 130 K, where the smoothly increasing deviation of the experimental data from the theory on cooling from 130 K to T N is deduced to arise from dynamic short-range collinear c -axis AFM ordering in this temperature range driven by the exchange interactions.« less

3D printed hierarchical honeycombs with shape integrity under large compressive deformations

DOE PAGES

Chen, Yanyu; Li, Tiantian; Jia, Zian; ...

2017-10-12

Here, we describe the in-plane compressive performance of a new type of hierarchical cellular structure created by replacing cell walls in regular honeycombs with triangular lattice configurations. The fabrication of this relatively complex material architecture with size features spanning from micrometer to centimeter is facilitated by the availability of commercial 3D printers. We apply to these hierarchical honeycombs a thermal treatment that facilitates the shape preservation and structural integrity of the structures under large compressive loading. The proposed hierarchical honeycombs exhibit a progressive failure mode, along with improved stiffness and energy absorption under uniaxial compression. High energy dissipation and shapemore » integrity at large imposed strains (up to 60%) have also been observed in these hierarchical honeycombs under cyclic loading. Experimental and numerical studies suggest that these anomalous mechanical behaviors are attributed to the introduction of a structural hierarchy, intrinsically controlled by the cell wall slenderness of the triangular lattice and by the shape memory effect induced by the thermal and mechanical compressive treatment.« less

3D printed hierarchical honeycombs with shape integrity under large compressive deformations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen, Yanyu; Li, Tiantian; Jia, Zian

Here, we describe the in-plane compressive performance of a new type of hierarchical cellular structure created by replacing cell walls in regular honeycombs with triangular lattice configurations. The fabrication of this relatively complex material architecture with size features spanning from micrometer to centimeter is facilitated by the availability of commercial 3D printers. We apply to these hierarchical honeycombs a thermal treatment that facilitates the shape preservation and structural integrity of the structures under large compressive loading. The proposed hierarchical honeycombs exhibit a progressive failure mode, along with improved stiffness and energy absorption under uniaxial compression. High energy dissipation and shapemore » integrity at large imposed strains (up to 60%) have also been observed in these hierarchical honeycombs under cyclic loading. Experimental and numerical studies suggest that these anomalous mechanical behaviors are attributed to the introduction of a structural hierarchy, intrinsically controlled by the cell wall slenderness of the triangular lattice and by the shape memory effect induced by the thermal and mechanical compressive treatment.« less

Spin-dependent excitation of plasma modes in non-neutral ion plasmas

NASA Astrophysics Data System (ADS)

Sawyer, Brian C.; Britton, Joe W.; Bollinger, John J.

2011-10-01

We report on a new technique for exciting and sensitively detecting plasma modes in small, cold non-neutral ion plasmas. The technique uses an optical dipole force generated from laser beams to excite plasma modes. By making the force spin- dependent (i.e. depend on the internal state of the atomic ion) very small mode excitations (<100 nm) can be detected through spin-motion entanglement. Even when the optical dipole force is homogeneous throughout the plasma, short wavelength modes on the order of the interparticle spacing can in principle be excited and detected through the spin dependence of the force. We use this technique to study the drumhead modes of single plane triangular arrays of a few hundred Be+ ions. Spin-dependent mode excitation is interesting in this system because it provides a means of engineering an Ising interaction on a 2-D triangular lattice. For the case of an anti-ferromagnetic interaction, this system exhibits spin frustration on a scale that is at present computationally intractable. Work supported by the DARPA OLE program and NIST.

Ultrasmall multi-channel resonant-tunneling filter using mode gap of width-tuned photonic-crystal waveguide.

PubMed

Shinya, Akihiko; Mitsugi, Satoshi; Kuramochi, Eiichi; Notomi, Masaya

2005-05-30

We have devised an ultra-small multi-channel drop filter based on a two-port resonant tunneling system in a two-dimensional photonic crystal with a triangular air-hole lattice. This filter does not require careful consideration of the interference process to achieve a high dropping efficiency. First we develop three-port systems based on a two-port resonant tunneling filter. Next we devise a multi-port channel drop filter by cascading these three-port systems. In this paper, we demonstrate a ten-channel drop filter with an 18 mum device size by 2D-FDTD calculation, and a three-port resonant tunneling filter with 65+/- 20 % dropping efficiency by experiment.

Pinning, flux diodes and ratchets for vortices interacting with conformal pinning arrays

DOE PAGES

Olson Reichhardt, C. J.; Wang, Y. L.; Xiao, Z. L.; ...

2016-05-31

A conformal pinning array can be created by conformally transforming a uniform triangular pinning lattice to produce a new structure in which the six-fold ordering of the original lattice is conserved but where there is a spatial gradient in the density of pinning sites. Here we examine several aspects of vortices interacting with conformal pinning arrays and how they can be used to create a flux flow diode effect for driving vortices in different directions across the arrays. Under the application of an ac drive, a pronounced vortex ratchet effect occurs where the vortices flow in the easy direction ofmore » the array asymmetry. When the ac drive is applied perpendicular to the asymmetry direction of the array, it is possible to realize a transverse vortex ratchet effect where there is a generation of a dc flow of vortices perpendicular to the ac drive due to the creation of a noise correlation ratchet by the plastic motion of the vortices. We also examine vortex transport in experiments and compare the pinning effectiveness of conformal arrays to uniform triangular pinning arrays. In conclusion, we find that a triangular array generally pins the vortices more effectively at the first matching field and below, while the conformal array is more effective at higher fields where interstitial vortex flow occurs.« less

Two-dimensional Magnetism in Arrays of Superconducting Rings

NASA Astrophysics Data System (ADS)

Reich, Daniel H.

1996-03-01

An array of superconducting rings in an applied field corresponding to a flux of Φ0 /2 per ring behaves like a 2D Ising antiferromagnet. Each ring has two energetically equivalent states with equal and opposite magnetic moments due to fluxoid quantization, and the dipolar coupling between rings favors antiparallel alignment of the moments. Using SQUID magnetometry and scanning Hall probe microscopy, we have studied the dynamics and magnetic configurations of micron-size aluminum rings on square, triangular, honeycomb, and kagomé lattices. We have found that there are significant antiferromagnetic correlations between rings, and that effects of geometrical frustration can be observed on the triangular and kagomé lattices. Long range correlations on the other lattices are suppressed by the analog of spin freezing that locks the rings in metastable states at low temperatures, and by quenched disorder due to imperfections in the fabrication. This disorder produces a roughly 1% variation in the rings' areas, which translates into an effective random field on the spins. The ring arrays are thus an extremely good realization of the 2D random-field Ising model. (Performed in collaboration with D. Davidović, S. Kumar, J. Siegel, S. B. Field, R. C. Tiberio, R. Hey, and K. Ploog.) (Supported by NSF grants DMR-9222541, and DMR-9357518, and by the David and Lucile Packard Foundation.)

Spontaneous magnetization and anomalous Hall effect in an emergent Dice lattice

PubMed Central

Dutta, Omjyoti; Przysiężna, Anna; Zakrzewski, Jakub

2015-01-01

Ultracold atoms in optical lattices serve as a tool to model different physical phenomena appearing originally in condensed matter. To study magnetic phenomena one needs to engineer synthetic fields as atoms are neutral. Appropriately shaped optical potentials force atoms to mimic charged particles moving in a given field. We present the realization of artificial gauge fields for the observation of anomalous Hall effect. Two species of attractively interacting ultracold fermions are considered to be trapped in a shaken two dimensional triangular lattice. A combination of interaction induced tunneling and shaking can result in an emergent Dice lattice. In such a lattice the staggered synthetic magnetic flux appears and it can be controlled with external parameters. The obtained synthetic fields are non-Abelian. Depending on the tuning of the staggered flux we can obtain either anomalous Hall effect or its quantized version. Our results are reminiscent of Anomalous Hall conductivity in spin-orbit coupled ferromagnets. PMID:26057635

Magnetic assembly and annealing of colloidal lattices and superlattices.

PubMed

Tierno, Pietro

2014-07-08

The ability to assemble mesoscopic colloidal lattices above a surface is important for fundamental studies related with nucleation and crystallization but also for a variety of technological applications in photonics and microengineering. Current techniques based on particle sedimentation above a lithographic template are limited by a slow deposition process and by the use of static templates, which make difficult to implement fast annealing procedures. Here it is demonstrated a method to realize and anneal a series of colloidal lattices displaying triangular, honeycomb, or kagome-like symmetry above a structure magnetic substrate. By using a binary mixture of particles, superlattices can be realized increasing further the variety and complexity of the colloidal patterns which can be produced.

Geometrically frustrated GdInO3: An exotic system to study negative thermal expansion and spin-lattice coupling

NASA Astrophysics Data System (ADS)

Paul, Barnita; Chatterjee, Swastika; Roy, Anushree; Midya, A.; Mandal, P.; Grover, Vinita; Tyagi, A. K.

2017-02-01

In this article, we report negative thermal expansion and spin frustration in hexagonal GdInO3. Rietveld refinements of the x-ray diffraction patterns reveal that the negative thermal expansion in the temperature range of 50-100 K stems from the triangular lattice of Gd3 + ions. The downward deviation of the low-temperature inverse susceptibility (χ-1) versus T plot from the Curie-Weiss law and the large value of the ratio, | θCW|/ TN>28 , where θCW and TN are respectively Curie-Weiss and Neel temperature, indicate a strong spin frustration, which inhibits long-range magnetic ordering down to 1.8 K. Magnetostriction measurements clearly demonstrate a spin-lattice coupling in the system. Low-temperature anomalous phonon softening, as obtained from temperature-dependent Raman measurements, also reveals the same. Our experimental observations are supported by first-principles density functional theory calculations of the electronic and phonon dispersion in GdInO3. The calculations suggest that the GdInO3 lattice is highly frustrated at low temperature. Further, the calculated normal mode frequencies of the Gd-related Γ point phonon modes reveal significant magnetoelastic coupling in this system. The competitive role of magnetic interaction energy and thermal stabilization energy in determining the change in interatomic distances is the possible origin for the negative thermal expansion in GdInO3 over a limited range of temperature.

Reconfigurable lattice mesh designs for programmable photonic processors.

PubMed

Pérez, Daniel; Gasulla, Ivana; Capmany, José; Soref, Richard A

2016-05-30

We propose and analyse two novel mesh design geometries for the implementation of tunable optical cores in programmable photonic processors. These geometries are the hexagonal and the triangular lattice. They are compared here to a previously proposed square mesh topology in terms of a series of figures of merit that account for metrics that are relevant to on-chip integration of the mesh. We find that that the hexagonal mesh is the most suitable option of the three considered for the implementation of the reconfigurable optical core in the programmable processor.

Application of the DMRG in two dimensions: a parallel tempering algorithm

NASA Astrophysics Data System (ADS)

Hu, Shijie; Zhao, Jize; Zhang, Xuefeng; Eggert, Sebastian

The Density Matrix Renormalization Group (DMRG) is known to be a powerful algorithm for treating one-dimensional systems. When the DMRG is applied in two dimensions, however, the convergence becomes much less reliable and typically ''metastable states'' may appear, which are unfortunately quite robust even when keeping a very high number of DMRG states. To overcome this problem we have now successfully developed a parallel tempering DMRG algorithm. Similar to parallel tempering in quantum Monte Carlo, this algorithm allows the systematic switching of DMRG states between different model parameters, which is very efficient for solving convergence problems. Using this method we have figured out the phase diagram of the xxz model on the anisotropic triangular lattice which can be realized by hardcore bosons in optical lattices. SFB Transregio 49 of the Deutsche Forschungsgemeinschaft (DFG) and the Allianz fur Hochleistungsrechnen Rheinland-Pfalz (AHRP).

A principle of economy predicts the functional architecture of grid cells.

PubMed

Wei, Xue-Xin; Prentice, Jason; Balasubramanian, Vijay

2015-09-03

Grid cells in the brain respond when an animal occupies a periodic lattice of 'grid fields' during navigation. Grids are organized in modules with different periodicity. We propose that the grid system implements a hierarchical code for space that economizes the number of neurons required to encode location with a given resolution across a range equal to the largest period. This theory predicts that (i) grid fields should lie on a triangular lattice, (ii) grid scales should follow a geometric progression, (iii) the ratio between adjacent grid scales should be √e for idealized neurons, and lie between 1.4 and 1.7 for realistic neurons, (iv) the scale ratio should vary modestly within and between animals. These results explain the measured grid structure in rodents. We also predict optimal organization in one and three dimensions, the number of modules, and, with added assumptions, the ratio between grid periods and field widths.

Modified spin-wave theory with ordering vector optimization: spatially anisotropic triangular lattice and J1J2J3 model with Heisenberg interactions

NASA Astrophysics Data System (ADS)

Hauke, Philipp; Roscilde, Tommaso; Murg, Valentin; Cirac, J. Ignacio; Schmied, Roman

2011-07-01

We study the ground-state phases of the S=1/2 Heisenberg quantum antiferromagnet on the spatially anisotropic triangular lattice (SATL) and on the square lattice with up to next-next-nearest-neighbor coupling (the J1J2J3 model), making use of Takahashi's modified spin-wave (MSW) theory supplemented by ordering vector optimization. We compare the MSW results with exact diagonalization and projected-entangled-pair-states calculations, demonstrating their qualitative and quantitative reliability. We find that the MSW theory correctly accounts for strong quantum effects on the ordering vector of the magnetic phases of the models under investigation: in particular, collinear magnetic order is promoted at the expense of non-collinear (spiral) order, and several spiral states that are stable at the classical level disappear from the quantum phase diagram. Moreover, collinear states and non-collinear ones are never connected continuously, but they are separated by parameter regions in which the MSW theory breaks down, signaling the possible appearance of a non-magnetic ground state. In the case of the SATL, a large breakdown region appears also for weak couplings between the chains composing the lattice, suggesting the possible occurrence of a large non-magnetic region continuously connected with the spin-liquid state of the uncoupled chains. This shows that the MSW theory is—despite its apparent simplicity—a versatile tool for finding candidate regions in the case of spin-liquid phases, which are among prime targets for relevant quantum simulations.

Integrable Seven-Point Discrete Equations and Second-Order Evolution Chains

NASA Astrophysics Data System (ADS)

Adler, V. E.

2018-04-01

We consider differential-difference equations defining continuous symmetries for discrete equations on a triangular lattice. We show that a certain combination of continuous flows can be represented as a secondorder scalar evolution chain. We illustrate the general construction with a set of examples including an analogue of the elliptic Yamilov chain.

Phase diagram of the triangular-lattice Potts antiferromagnet

DOE PAGES

Jacobsen, Jesper Lykke; Salas, Jesus; Scullard, Christian R.

2017-07-28

Here, we study the phase diagram of the triangular-lattice Q-state Potts model in the realmore » $(Q, v)$ -plane, where $$v={\\rm e}^J-1$$ is the temperature variable. Our first goal is to provide an obviously missing feature of this diagram: the position of the antiferromagnetic critical curve. This curve turns out to possess a bifurcation point with two branches emerging from it, entailing important consequences for the global phase diagram. We have obtained accurate numerical estimates for the position of this curve by combining the transfer-matrix approach for strip graphs with toroidal boundary conditions and the recent method of critical polynomials. The second goal of this work is to study the corresponding $$A_{p-1}$$ RSOS model on the torus, for integer $$p=4, 5, \\ldots, 8$$ . We clarify its relation to the corresponding Potts model, in particular concerning the role of boundary conditions. For certain values of p, we identify several new critical points and regimes for the RSOS model and we initiate the study of the flows between the corresponding field theories.« less

Magnetic phase diagram and multiferroicity of Ba 3 MnNb 2 O 9 : A spin - 5 2 triangular lattice antiferromagnet with weak easy-axis anisotropy

DOE PAGES

Lee, M.; Choi, E. S.; Huang, X.; ...

2014-12-01

Here we have performed magnetic, electric, thermal and neutron powder diffraction (NPD) experiments as well as density functional theory (DFT) calculations on Ba 3MnNb 2 O 9. All results suggest that Ba 3MnNb 2 O 9 is a spin-5/2 triangular lattice antiferromagnet (TLAF) with weak easy-axis anisotropy. At zero field, we observed a narrow two-step transition at T N1 = 3.4 K and T N2 = 3.0 K. The neutron diffraction measurement and the DFT calculation indicate a 120 spin structure in ab plane with out-of-plane canting at low temperatures. With increasing magnetic field, the 120 spin structure evolves intomore » up-up-down (uud) and oblique phases showing successive magnetic phase transitions, which fits well to the theoretical prediction for the 2D Heisenberg TLAF with classical spins. Ultimately, multiferroicity is observed when the spins are not collinear but suppressed in the uud and oblique phases.« less

Uniaxial compression on the superconductivity of β-BDA-TTP salts

NASA Astrophysics Data System (ADS)

Ito, Hiroshi; Ishihara, Tetsuo; Tanaka, Hisaaki; Kuroda, Shin-ichi; Yamada, Jun-ichi

2008-10-01

The β-type BDA-TTP superconductors attract attention due to the high transition temperature Tc at ambient pressure for organic superconductors. In order to get insight into the superconductivity in terms of the dimerized anisotropic triangular lattice model, Tc of β-(BDA-TTP)2X [X = SbF6, X = AsF6] is studied under uniaxial compression by resistivity measurements. Under compression parallel to the donor stack, Tc increases gradually up to 3 (X = SbF6), 5 (X = AsF6) kbar, and decreases under further piston pressure. Under compression perpendicular to the donor stack, Tc decreases gradually up to 2.5 (X = SbF6), 4 (X = AsF6) kbar and then decreases rapidly under further pressure. Only for X = AsF6, a Tc minimum at 3 kbar is found for both direction. These trends in Tc are understood as an interplay between the enhancement of antiferromagnetic spin fluctuation and frustration on the triangular lattice. By the interplane compression, Tc increased by 0.5 K up to 2 kbar for both salts, demonstrating the importance of the interlayer interaction.

Ising lattices with +/-J second-nearest-neighbor interactions

NASA Astrophysics Data System (ADS)

Ramírez-Pastor, A. J.; Nieto, F.; Vogel, E. E.

1997-06-01

Second-nearest-neighbor interactions are added to the usual nearest-neighbor Ising Hamiltonian for square lattices in different ways. The starting point is a square lattice where half the nearest-neighbor interactions are ferromagnetic and the other half of the bonds are antiferromagnetic. Then, second-nearest-neighbor interactions can also be assigned randomly or in a variety of causal manners determined by the nearest-neighbor interactions. In the present paper we consider three causal and three random ways of assigning second-nearest-neighbor exchange interactions. Several ground-state properties are then calculated for each of these lattices:energy per bond ɛg, site correlation parameter pg, maximal magnetization μg, and fraction of unfrustrated bonds hg. A set of 500 samples is considered for each size N (number of spins) and array (way of distributing the N spins). The properties of the original lattices with only nearest-neighbor interactions are already known, which allows realizing the effect of the additional interactions. We also include cubic lattices to discuss the distinction between coordination number and dimensionality. Comparison with results for triangular and honeycomb lattices is done at specific points.

Hydration of an apolar solute in a two-dimensional waterlike lattice fluid

NASA Astrophysics Data System (ADS)

Buzano, C.; de Stefanis, E.; Pretti, M.

2005-05-01

In a previous work, we investigated a two-dimensional lattice-fluid model, displaying some waterlike thermodynamic anomalies. The model, defined on a triangular lattice, is now extended to aqueous solutions with apolar species. Water molecules are of the “Mercedes Benz” type, i.e., they possess a D3 (equilateral triangle) symmetry, with three equivalent bonding arms. Bond formation depends both on orientation and local density. The insertion of inert molecules displays typical signatures of hydrophobic hydration: large positive transfer free energy, large negative transfer entropy (at low temperature), strong temperature dependence of the transfer enthalpy and entropy, i.e., large (positive) transfer heat capacity. Model properties are derived by a generalized first order approximation on a triangle cluster.

Hydration of an apolar solute in a two-dimensional waterlike lattice fluid.

PubMed

Buzano, C; De Stefanis, E; Pretti, M

2005-05-01

In a previous work, we investigated a two-dimensional lattice-fluid model, displaying some waterlike thermodynamic anomalies. The model, defined on a triangular lattice, is now extended to aqueous solutions with apolar species. Water molecules are of the "Mercedes Benz" type, i.e., they possess a D3 (equilateral triangle) symmetry, with three equivalent bonding arms. Bond formation depends both on orientation and local density. The insertion of inert molecules displays typical signatures of hydrophobic hydration: large positive transfer free energy, large negative transfer entropy (at low temperature), strong temperature dependence of the transfer enthalpy and entropy, i.e., large (positive) transfer heat capacity. Model properties are derived by a generalized first order approximation on a triangle cluster.

Geometric magnetic frustration in RE{sub 2}O{sub 2}S oxysulfides (RE = Sm, Eu and Gd)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Biondo, V.; Sarvezuk, P.W.C.; Ivashita, F.F.

2014-06-01

Graphical abstract: Stacked planes in the <001> direction of an oxysulfide structure, showing the triangular nets formed by rare earth cations, which moments present geometric magnetic frustration. - Highlights: • We prepared monophasic RE{sub 2}O{sub 2}S Oxysulfides (RE = Sm, Eu and Gd). • RE{sub 2}O{sub 2}S compounds were characterized regarding structural and magnetic properties. • Mössbauer spectra were obtained for Eu{sub 2}O{sub 2}S and Gd{sub 2}O{sub 2}S at different temperatures. • Oxysulfides present geometric magnetic frustration of the rare-earth sublattice. - Abstract: RE{sub 2}O{sub 2}S oxysulfides (with RE = Sm, Eu and Gd) were prepared and characterized regarding theirmore » structural and magnetic properties. The compounds crystallized in the trigonal symmetry (space group P-3m/D{sub 3}{sup 3}d), with the lattice parameter varying linearly with the ionic radius of the RE cation. All these oxysulfides are magnetically frustrated and only the gadolinium sample showed magnetic order down to 3 K. The magnetic frustration is attributed to the spatial distribution of cations over the lattice, where the RE’s magnetic moments occupy the sites forming a triangular plane lattice, perpendicular to the direction. This geometric magnetic frustration was firstly recognized for these oxysulfides.« less

Still states of bistable lattices, compatibility, and phase transition

NASA Astrophysics Data System (ADS)

Cherkaev, Andrej; Kouznetsov, Andrei; Panchenko, Alexander

2010-09-01

We study a two-dimensional triangular lattice made of bistable rods. Each rod has two equilibrium lengths, and thus its energy has two equal minima. A rod undergoes a phase transition when its elongation exceeds a critical value. The lattice is subject to a homogeneous strain and is periodic with a sufficiently large period. The effective strain of a periodic element is defined. After phase transitions, the lattice rods are in two different states and lattice strain is inhomogeneous, the Cauchy-Born rule is not applicable. We show that the lattice has a number of deformed still states that carry no stresses. These states densely cover a neutral region in the space of entries of effective strains. In this region, the minimal energy of the periodic lattice is asymptotically close to zero. When the period goes to infinity, the effective energy of such lattices has the “flat bottom” which we explicitly describe. The compatibility of the partially transited lattice is studied. We derive compatibility conditions for lattices and demonstrate a family of compatible lattices (strips) that densely covers the flat bottom region. Under an additional assumption of the small difference of two equilibrium lengths, we demonstrate that the still structures continuously vary with the effective strain and prove a linear dependence of the average strain on the concentration of transited rods.

Impact of ultrasonic assisted triangular lattice like arranged dispersion of nanoparticles on physical and mechanical properties of epoxy-TiO2 nanocomposites.

PubMed

Goyat, M S; Ghosh, P K

2018-04-01

Emerging ex-situ technique, ultrasonic dual mixing (UDM) offers unique and hitherto unapproachable opportunities to alter the physical and mechanical properties of polymer nanocomposites. In this study, triangular lattice-like arranged dispersion of TiO 2 nanoparticles (average size ∼ 48 nm) in the epoxy polymer has been attained via concurrent use of a probe ultra-sonicator and 4 blades pitched impeller which collectively named as UDM technique. The UDM processing of neat epoxy reveals the generation of triangular lattice-like arranged nanocavities with nanoscale inter-cavity spacing. The UDM processing of epoxy-TiO 2 nanocomposites reveals two unique features such as partial and complete entrapping of the nanoparticles by the nanocavities leading the arranged dispersion of particles in the epoxy matrix. Pristine TiO 2 nanoparticles were dispersed in the epoxy polymer at loading fractions of up to 20% by weight. The results display that the arranged dispersion of nanoparticles is very effective at enhancing the glass transition temperature (T g ) and tensile properties of the epoxy at loading fractions of 10 wt%. We quantify a direct relationship among three important parameters such as nanoparticle content, cluster size, and inter-particle spacing. Our results offer a novel understanding of these parameters on the T g and tensile properties of the epoxy nanocomposites. The tensile fracture surfaces revealed several toughening mechanisms such as particle pull-out, plastic void growth, crack deflection, crack bridging and plastic deformation. We show that a strong nanoparticle-matrix interface led to the enhanced mechanical properties due to leading toughening mechanisms such as crack deflection, plastic deformation and particle pull-out. We showed that the UDM has an inordinate prospective to alter the dispersion state of nanoparticles in viscous polymer matrices. Copyright © 2017 Elsevier B.V. All rights reserved.

Phase Transitions in a Model of Y-Molecules Abstract

NASA Astrophysics Data System (ADS)

Holz, Danielle; Ruth, Donovan; Toral, Raul; Gunton, James

Immunoglobulin is a Y-shaped molecule that functions as an antibody to neutralize pathogens. In special cases where there is a high concentration of immunoglobulin molecules, self-aggregation can occur and the molecules undergo phase transitions. This prevents the molecules from completing their function. We used a simplified model of 2-Dimensional Y-molecules with three identical arms on a triangular lattice with 2-dimensional Grand Canonical Ensemble. The molecules were permitted to be placed, removed, rotated or moved on the lattice. Once phase coexistence was found, we used histogram reweighting and multicanonical sampling to calculate our phase diagram.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kishino, Katsumi, E-mail: kishino@sophia.ac.jp; Sophia Nanotechnology Research Center, Sophia University, 7-1 Kioi-cho, Chiyoda-ku, Tokyo 102-8554; Ishizawa, Shunsuke

Bottom-up grown structurally graded InGaN-based nanocolumn photonic crystals, in which nanocolumns were arranged in triangular lattice and the nanocolumn diameter changed one-dimensionally from 93 to 213 nm with a fixed lattice constant of 250 nm, were fabricated. The spatial distribution of the diameter resulted in random-laser-like operation under optical excitation. A broad multi-wavelength lasing spectrum with more than 10 peaks was obtained with a full width at half maximum of 27 nm at 505 nm wavelength as well as lowering of the polarization degree, which is expected to be suitable for speckle contrast reduction in laser projection display applications.

Semi-analytical solution for the generalized absorbing boundary condition in molecular dynamics simulations

NASA Astrophysics Data System (ADS)

Lee, Chung-Shuo; Chen, Yan-Yu; Yu, Chi-Hua; Hsu, Yu-Chuan; Chen, Chuin-Shan

2017-07-01

We present a semi-analytical solution of a time-history kernel for the generalized absorbing boundary condition in molecular dynamics (MD) simulations. To facilitate the kernel derivation, the concept of virtual atoms in real space that can conform with an arbitrary boundary in an arbitrary lattice is adopted. The generalized Langevin equation is regularized using eigenvalue decomposition and, consequently, an analytical expression of an inverse Laplace transform is obtained. With construction of dynamical matrices in the virtual domain, a semi-analytical form of the time-history kernel functions for an arbitrary boundary in an arbitrary lattice can be found. The time-history kernel functions for different crystal lattices are derived to show the generality of the proposed method. Non-equilibrium MD simulations in a triangular lattice with and without the absorbing boundary condition are conducted to demonstrate the validity of the solution.

Finite element method analysis of band gap and transmission of two-dimensional metallic photonic crystals at terahertz frequencies.

PubMed

Degirmenci, Elif; Landais, Pascal

2013-10-20

Photonic band gap and transmission characteristics of 2D metallic photonic crystals at THz frequencies have been investigated using finite element method (FEM). Photonic crystals composed of metallic rods in air, in square and triangular lattice arrangements, are considered for transverse electric and transverse magnetic polarizations. The modes and band gap characteristics of metallic photonic crystal structure are investigated by solving the eigenvalue problem over a unit cell of the lattice using periodic boundary conditions. A photonic band gap diagram of dielectric photonic crystal in square lattice array is also considered and compared with well-known plane wave expansion results verifying our FEM approach. The photonic band gap designs for both dielectric and metallic photonic crystals are consistent with previous studies obtained by different methods. Perfect match is obtained between photonic band gap diagrams and transmission spectra of corresponding lattice structure.

Flipping Triangles!

ERIC Educational Resources Information Center

Zucker, Marc

2009-01-01

We introduce a simple game made up of a board of coins on a triangular lattice. We then study the possibility of turning the board from one pattern of heads and tails to some other pattern. Given that a solution exists we find a precise answer to the number of solutions possible. We then generalize this to more complex boards with coins of many…

The A{sup 2+}Mn{sub 5}(SO{sub 4}){sub 6} family of triangular lattice, ferrimagnetic sulfates

DOE Office of Scientific and Technical Information (OSTI.GOV)

West, D.V., E-mail: barelytone@gmail.co; McQueen, T.M.; Posen, I.D.

2009-06-15

A new family of anhydrous sulfates, A{sup 2+}Mn{sub 5}(SO{sub 4}){sub 6} (A=Pb, Ba, Sr) is reported. The crystal structures of PbMn{sub 5}(SO{sub 4}){sub 6} and SrMn{sub 5}(SO{sub 4}){sub 6} are solved by powder X-ray and neutron diffraction. BaMn{sub 5}(SO{sub 4}){sub 6} is isostructural. PbMn{sub 5}(SO{sub 4}){sub 6} crystallizes with P3-bar symmetry and unit cell parameters of a=14.551(1) A and c=7.535(1) A. The structure has rich features, including dimers of face-sharing MnO{sub 6} octahedra, and two complementary triangular layers of Mn atoms. All compounds undergo a magnetic ordering transition at 10 K, below which, the magnetic susceptibility of the compounds variesmore » systematically with the radius of the non-magnetic cation. Low temperature neutron diffraction shows that the complementary triangular layers result in a ferrimagnet with a net moment corresponding to one high spin Mn{sup 2+} per unit cell, correlating well with the magnetization data. The non-magnetic variant PbMg{sub 5}(SO{sub 4}){sub 6} is also reported. - Graphical abstract: A new family sulfates, A{sup 2+}Mn{sub 5}(SO{sub 4}){sub 6} (A=Pb, Ba, Sr) is reported. Structures are solved by powder neutron diffraction. PbMn{sub 5}(SO{sub 4}){sub 6} is trigonal with lattice parameters of a=14.551(1) A and c=7.535(1) A. The structure has dimers of face-sharing MnO{sub 6} octahedra, and two complementary triangular layers of Mn atoms that result in a ferrimagnet. All compounds magnetically order at 10 K. Low field susceptibility varies systematically with non-magnetic cation radius.« less

Triangular Quantum Loop Topography for Machine Learning

NASA Astrophysics Data System (ADS)

Zhang, Yi; Kim, Eun-Ah

Despite rapidly growing interest in harnessing machine learning in the study of quantum many-body systems there has been little success in training neural networks to identify topological phases. The key challenge is in efficiently extracting essential information from the many-body Hamiltonian or wave function and turning the information into an image that can be fed into a neural network. When targeting topological phases, this task becomes particularly challenging as topological phases are defined in terms of non-local properties. Here we introduce triangular quantum loop (TQL) topography: a procedure of constructing a multi-dimensional image from the ''sample'' Hamiltonian or wave function using two-point functions that form triangles. Feeding the TQL topography to a fully-connected neural network with a single hidden layer, we demonstrate that the architecture can be effectively trained to distinguish Chern insulator and fractional Chern insulator from trivial insulators with high fidelity. Given the versatility of the TQL topography procedure that can handle different lattice geometries, disorder, interaction and even degeneracy our work paves the route towards powerful applications of machine learning in the study of topological quantum matters.

Diophantine Approach to the Classification of Two-Dimensional Lattices: Surfaces of Face-Centered Cubic Materials.

PubMed

Jenkins, Stephen J

2018-04-03

The long-range periodic order of a crystalline surface is generally represented by means of a two-dimensional Bravais lattice, of which only five symmetrically distinct types are possible. Here, we explore the circumstances under which each type may or may not be found at the surfaces of face-centered cubic materials and provide means by which the type of lattice may be determined with reference only to the Miller indices of the surface; the approach achieves formal rigor by focusing on the number theory of integer variables rather than directly upon real geometry. We prove that the {100} and {111} surfaces are, respectively, the only exemplars of square and triangular lattices. For surfaces exhibiting a single mirror plane, we not only show that rectangular and rhombic lattices are the only two possibilities, but also capture their alternation in terms of the parity of the indices. In the case of chiral surfaces, oblique lattices predominate, but rectangular and rhombic cases are also possible and arise according to well-defined rules, here partially recounted.

Three-dimensional periodic dielectric structures having photonic Dirac points

DOEpatents

Bravo-Abad, Jorge; Joannopoulos, John D.; Soljacic, Marin

2015-06-02

The dielectric, three-dimensional photonic materials disclosed herein feature Dirac-like dispersion in quasi-two-dimensional systems. Embodiments include a face-centered cubic (fcc) structure formed by alternating layers of dielectric rods and dielectric slabs patterned with holes on respective triangular lattices. This fcc structure also includes a defect layer, which may comprise either dielectric rods or a dielectric slab with patterned with holes. This defect layer introduces Dirac cone dispersion into the fcc structure's photonic band structure. Examples of these fcc structures enable enhancement of the spontaneous emission coupling efficiency (the .beta.-factor) over large areas, contrary to the conventional wisdom that the .beta.-factor degrades as the system's size increases. These results enable large-area, low-threshold lasers; single-photon sources; quantum information processing devices; and energy harvesting systems.

Two-dimensional lattice-fluid model with waterlike anomalies.

PubMed

Buzano, C; De Stefanis, E; Pelizzola, A; Pretti, M

2004-06-01

We investigate a lattice-fluid model defined on a two-dimensional triangular lattice, with the aim of reproducing qualitatively some anomalous properties of water. Model molecules are of the "Mercedes Benz" type, i.e., they possess a D3 (equilateral triangle) symmetry, with three bonding arms. Bond formation depends both on orientation and local density. We work out phase diagrams, response functions, and stability limits for the liquid phase, making use of a generalized first order approximation on a triangle cluster, whose accuracy is verified, in some cases, by Monte Carlo simulations. The phase diagram displays one ordered (solid) phase which is less dense than the liquid one. At fixed pressure the liquid phase response functions show the typical anomalous behavior observed in liquid water, while, in the supercooled region, a reentrant spinodal is observed.

Coherent, atomically thin transition-metal dichalcogenide superlattices with engineered strain

NASA Astrophysics Data System (ADS)

Xie, Saien; Tu, Lijie; Han, Yimo; Huang, Lujie; Kang, Kibum; Lao, Ka Un; Poddar, Preeti; Park, Chibeom; Muller, David A.; DiStasio, Robert A.; Park, Jiwoong

2018-03-01

Epitaxy forms the basis of modern electronics and optoelectronics. We report coherent atomically thin superlattices in which different transition metal dichalcogenide monolayers—despite large lattice mismatches—are repeated and laterally integrated without dislocations within the monolayer plane. Grown by an omnidirectional epitaxy, these superlattices display fully matched lattice constants across heterointerfaces while maintaining an isotropic lattice structure and triangular symmetry. This strong epitaxial strain is precisely engineered via the nanoscale supercell dimensions, thereby enabling broad tuning of the optical properties and producing photoluminescence peak shifts as large as 250 millielectron volts. We present theoretical models to explain this coherent growth and the energetic interplay governing the ripple formation in these strained monolayers. Such coherent superlattices provide building blocks with targeted functionalities at the atomically thin limit.

Topological modes bound to dislocations in mechanical metamaterials

NASA Astrophysics Data System (ADS)

Paulose, Jayson; Chen, Bryan Gin-Ge; Vitelli, Vincenzo

2015-02-01

Mechanical metamaterials are artificial structures with unusual properties, such as negative Poisson ratio, bistability or tunable vibrational properties, that originate in the geometry of their unit cell. Often at the heart of such unusual behaviour is a soft mode: a motion that does not significantly stretch or compress the links between constituent elements. When activated by motors or external fields, soft modes become the building blocks of robots and smart materials. Here, we demonstrate the existence of topological soft modes that can be positioned at desired locations in a metamaterial while being robust against a wide range of structural deformations or changes in material parameters. These protected modes, localized at dislocations in deformed kagome and square lattices, are the mechanical analogue of topological states bound to defects in electronic systems. We create physical realizations of the topological modes in prototypes of kagome lattices built out of rigid triangular plates. We show mathematically that they originate from the interplay between two Berry phases: the Burgers vector of the dislocation and the topological polarization of the lattice. Our work paves the way towards engineering topologically protected nanomechanical structures for molecular robotics or information storage and read-out.

Nuclear core and fuel assemblies

DOEpatents

Downs, Robert E.

1981-01-01

A fast flux nuclear core of a plurality of rodded, open-lattice assemblies having a rod pattern rotated relative to a rod support structure pattern. Elongated fuel rods are oriented on a triangular array and laterally supported by grid structures positioned along the length of the assembly. Initial inter-assembly contact is through strongbacks at the corners of the support pattern and peripheral fuel rods between adjacent assemblies are nested so as to maintain a triangular pitch across a clearance gap between the other portions of adjacent assemblies. The rod pattern is rotated relative to the strongback support pattern by an angle .alpha. equal to sin .sup.-1 (p/2c), where p is the intra-assembly rod pitch and c is the center-to-center spacing among adjacent assemblies.

On the Wiener Polarity Index of Lattice Networks.

PubMed

Chen, Lin; Li, Tao; Liu, Jinfeng; Shi, Yongtang; Wang, Hua

2016-01-01

Network structures are everywhere, including but not limited to applications in biological, physical and social sciences, information technology, and optimization. Network robustness is of crucial importance in all such applications. Research on this topic relies on finding a suitable measure and use this measure to quantify network robustness. A number of distance-based graph invariants, also known as topological indices, have recently been incorporated as descriptors of complex networks. Among them the Wiener type indices are the most well known and commonly used such descriptors. As one of the fundamental variants of the original Wiener index, the Wiener polarity index has been introduced for a long time and known to be related to the cluster coefficient of networks. In this paper, we consider the value of the Wiener polarity index of lattice networks, a common network structure known for its simplicity and symmetric structure. We first present a simple general formula for computing the Wiener polarity index of any graph. Using this formula, together with the symmetric and recursive topology of lattice networks, we provide explicit formulas of the Wiener polarity index of the square lattices, the hexagonal lattices, the triangular lattices, and the 33 ⋅ 42 lattices. We also comment on potential future research topics.

Engineered long-range interactions on a 2D array of trapped ions

NASA Astrophysics Data System (ADS)

Britton, Joseph W.; Sawyer, Brian C.; Bollinger, John J.; Freericks, James K.

2014-03-01

Ising interactions are one paradigm used to model quantum magnetism in condensed matter systems. At NIST Boulder we confine and Doppler laser cool hundreds of 9Be+ ions in a Penning trap. The valence electron of each ion behaves as an ideal spin-1/2 particle and, in the limit of weak radial confinement relative to axial confinement, the ions naturally form a two-dimensional triangular lattice. A variable-range anti-ferromagnetic Ising interaction is engineered with a spin-dependent optical dipole force (ODF) through spin-dependent excitation of collective modes of ion motion. We have also exploited this spin-dependent force to perform spectroscopy and thermometry of the normal modes of the trapped ion crystal. The high spin-count and long-range spin-spin couplings achievable in the NIST Penning trap brings within reach simulation of computationally intractable problems in quantum magnetism. Examples include modeling quantum magnetic phase transitions and propagation of spin correlations resulting from a quantum quench. The Penning system may also be amenable to observation of spin-liquid behavior thought to arise in systems where the underlying lattice structure can frustrate long-range ordering. Supported by DARPA OLE and NIST.

Wavelength-scale Microlasers based on VCSEL-Photonic Crystal Architecture

DTIC Science & Technology

2015-01-20

molecular beam epitaxy , MBE). We will also assume the triangular lattice of air...Abbreviations, and Acronyms InP: indium phosphide InGaAsP: indium gallium arsenide phosphide MBE: molecular beam epiitaxy VCSEL : vertical cavity...substrates and were grown by MBE. Electron beam lithography and reactive ion etching was used to deep‐etch the holes of the PhC‐ VCSELS ,

Strong and weak second-order topological insulators with hexagonal symmetry and ℤ3 index

NASA Astrophysics Data System (ADS)

Ezawa, Motohiko

2018-06-01

We propose second-order topological insulators (SOTIs) whose lattice structure has a hexagonal symmetry C6. We start with a three-dimensional weak topological insulator constructed on a stacked triangular lattice, which has only side topological surface states. We then introduce an additional mass term which gaps out the side surface states but preserves the hinge states. The resultant system is a three-dimensional SOTI. The bulk topological quantum number is shown to be the Z3 index protected by inversion time-reversal symmetry I T and rotoinversion symmetry I C6 . We obtain three phases: trivial, strong, and weak SOTI phases. We argue the origin of these two types of SOTIs. A hexagonal prism is a typical structure respecting these symmetries, where six topological hinge states emerge at the side. The building block is a hexagon in two dimensions, where topological corner states emerge at the six corners in the SOTI phase. Strong and weak SOTIs are obtained when the interlayer hopping interaction is strong and weak, respectively.

A principle of economy predicts the functional architecture of grid cells

PubMed Central

Wei, Xue-Xin; Prentice, Jason; Balasubramanian, Vijay

2015-01-01

Grid cells in the brain respond when an animal occupies a periodic lattice of ‘grid fields’ during navigation. Grids are organized in modules with different periodicity. We propose that the grid system implements a hierarchical code for space that economizes the number of neurons required to encode location with a given resolution across a range equal to the largest period. This theory predicts that (i) grid fields should lie on a triangular lattice, (ii) grid scales should follow a geometric progression, (iii) the ratio between adjacent grid scales should be √e for idealized neurons, and lie between 1.4 and 1.7 for realistic neurons, (iv) the scale ratio should vary modestly within and between animals. These results explain the measured grid structure in rodents. We also predict optimal organization in one and three dimensions, the number of modules, and, with added assumptions, the ratio between grid periods and field widths. DOI: http://dx.doi.org/10.7554/eLife.08362.001 PMID:26335200

Magnetic structure of the swedenborgite CaBa (Co3Fe ) O7 derived by unpolarized neutron diffraction and spherical neutron polarimetry

NASA Astrophysics Data System (ADS)

Qureshi, N.; Díaz, M. T. Fernández; Chapon, L. C.; Senyshyn, A.; Schweika, W.; Valldor, M.

2018-02-01

We present a study that combines polarized and unpolarized neutrons to derive the magnetic structure of the swedenborgite compound CaBa (Co3Fe ) O7. Integrated intensities from a standard neutron diffraction experiment and polarization matrices from spherical neutron polarimetry have been simultaneously analyzed revealing a complex order, which differs from the usual spin configurations on a kagome lattice. We find that the magnetic structure is well described by a combination of two one-dimensional representations corresponding to the magnetic superspace symmetry P 21' , and it consists of spins rotating around an axis close to the [110] direction. Due to the propagation vector q =(1/3 00 ) , this modulation has cycloidal and helicoidal character rendering this system a potential multiferroic. The resulting spin configuration can be mapped onto the classical √{3 }×√{3 } structure of a kagome lattice, and it indicates an important interplay between the kagome and the triangular layers of the crystal structure.

Microwave (EPR) measurements of the penetration depth measurements of high-Tc superconductors

NASA Technical Reports Server (NTRS)

Dalal, N. S.; Rakvin, B.; Mahl, T. A.; Bhalla, A. S.; Sheng, Z. Z.

1991-01-01

The use is discussed of electron paramagnetic resonance (EPR) as a quick and easily accessible method for measuring the London penetration depth, lambda for the high T sub c superconductors. The method uses the broadening of the EPR signal, due to the emergence of the magnetic flux lattice, of a free radical adsorbed on the surface of the sample. The second moment, of the EPR signal below T sub c is fitted to the Brandt equation for a simple triangular lattice. The precision of this method compares quite favorably with those of the more standard methods such as micro sup(+)SR, neutron scattering, and magnetic susceptibility.

An EPR methodology for measuring the London penetration depth for the ceramic superconductors

NASA Technical Reports Server (NTRS)

Rakvin, B.; Mahl, T. A.; Dalal, N. S.

1990-01-01

The use is discussed of electron paramagnetic resonance (EPR) as a quick and easily accessible method for measuring the London penetration depth, lambda for the high T(sub c) superconductors. The method utilizes the broadening of the EPR signal, due to the emergence of the magnetic flux lattice, of a free radical adsorbed on the surface of the sample. The second moment, of the EPR signal below T(sub c) is fitted to the Brandt equation for a simple triangular lattice. The precision of this method compares quite favorably with those of the more standard methods such as micro sup(+)SR, Neutron scattering, and magnetic susceptibility.

Competition between dynamic and structural disorder in a doped triangular antiferromagnet RbFe(MoO4)2

NASA Astrophysics Data System (ADS)

Smirnov, A. I.; Soldatov, T. A.; Petrenko, O. A.; Takata, A.; Kida, T.; Hagiwara, M.; Zhitomirsky, M. E.; Shapiro, A. Ya

2018-03-01

Magnetisation measurements and electron spin resonance (ESR) spectra of a doped quasi two dimensional (2D) antiferromagnet on a triangular lattice Rb1 ‑ x K x Fe(MoO4)2 reveal a crucial change of the ground state spin configuration and a disappearance of a characteristic 1/3-magnetisation plateau at x = 0.15. According to theory for triangular antiferromagnets with a weak random modulation of the exchange bonds, this is a result of the competition between the structural and dynamic disorders. The dynamic zero-point or thermal fluctuations are known to lift the degeneracy of the mean field ground state of a triangular antiferromagnet and cause the spin configuration to be the most collinear, while the static disorder provides another selection of the ground state, with the least collinear structure. Low-level doping (x ≤ 0.15) was found to decrease the Néel temperature and saturation field by only few percent, while the magnetisation plateau disappears completely and the spin configuration is drastically changed. ESR spectra confirm an impurity-induced change of the so-called Y-type structure to an inverted Y-structure for x = 0.15. For x = 0.075 the intermediate regime with the decrease of width and weakening of flattening of 1/3-plateau was found.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Platero-Prats, Ana E.; Li, Zhanyong; Gallington, Leighanne C.

Here, we explore the dynamic structure and reactivity of Cu species supported on NU-1000. By combining pair distribution function (PDF) analysis and difference envelope density (DED) analysis ofin situsynchrotron-based X-ray scattering data, we simultaneously probe the local structure of supported Cu-species, their distribution within NU-1000 and distortions of the NU-1000 lattice under conditions relevant to catalysis and catalyst activation. Our analyses show that atomic layer deposition (ALD) of Cu in NU-1000 (Cu-AIM) leads to the formation of Cu-oxo clusters within the small pores that connect the triangular and hexagonal channels. Exposure of Cu-AIM to a reducing atmosphere at 200 °Cmore » produces metallic Cu 0of two distinct particle sizes: ~4 nm nanoparticles and small sub-nanometer clusters. The size of these nanoparticles appears to be constrained by NU-1000 pore dimensions, with evidence of the sub-nanometer clusters being bound within the triangular channels flanked by pyrene rings. This supported Cu 0–NU-1000 system is catalytically active for gas-phase ethylene hydrogenation. Exposure of the catalyst to oxidative atmosphere re-oxidises the Cu species to a Cu 2O cuprite phase. The dynamic restructuring of the system in different chemical environments underscores the importance of probing these systemsin situ.« less

Two-dimensional lattice-fluid model with waterlike anomalies

NASA Astrophysics Data System (ADS)

Buzano, C.; de Stefanis, E.; Pelizzola, A.; Pretti, M.

2004-06-01

We investigate a lattice-fluid model defined on a two-dimensional triangular lattice, with the aim of reproducing qualitatively some anomalous properties of water. Model molecules are of the “Mercedes Benz” type, i.e., they possess a D3 (equilateral triangle) symmetry, with three bonding arms. Bond formation depends both on orientation and local density. We work out phase diagrams, response functions, and stability limits for the liquid phase, making use of a generalized first order approximation on a triangle cluster, whose accuracy is verified, in some cases, by Monte Carlo simulations. The phase diagram displays one ordered (solid) phase which is less dense than the liquid one. At fixed pressure the liquid phase response functions show the typical anomalous behavior observed in liquid water, while, in the supercooled region, a reentrant spinodal is observed.

Hidden symmetries of the extended Kitaev-Heisenberg model: Implications for the honeycomb-lattice iridates A2IrO3

NASA Astrophysics Data System (ADS)

Chaloupka, Jiří; Khaliullin, Giniyat

2015-07-01

We have explored the hidden symmetries of a generic four-parameter nearest-neighbor spin model, allowed in honeycomb-lattice compounds under trigonal compression. Our method utilizes a systematic algorithm to identify all dual transformations of the model that map the Hamiltonian on itself, changing the parameters and providing exact links between different points in its parameter space. We have found the complete set of points of hidden SU(2) symmetry at which a seemingly highly anisotropic model can be mapped back on the Heisenberg model and inherits therefore its properties such as the presence of gapless Goldstone modes. The procedure used to search for the hidden symmetries is quite general and may be extended to other bond-anisotropic spin models and other lattices, such as the triangular, kagome, hyperhoneycomb, or harmonic-honeycomb lattices. We apply our findings to the honeycomb-lattice iridates Na2IrO3 and Li2IrO3 , and illustrate how they help to identify plausible values of the model parameters that are compatible with the available experimental data.

Addressing the characterisation challenge to understand catalysis in MOFs: the case of nanoscale Cu supported in NU-1000.

PubMed

Platero-Prats, Ana E; Li, Zhanyong; Gallington, Leighanne C; Peters, Aaron W; Hupp, Joseph T; Farha, Omar K; Chapman, Karena W

2017-09-01

We explore the dynamic structure and reactivity of Cu species supported on NU-1000. By combining pair distribution function (PDF) analysis and difference envelope density (DED) analysis of in situ synchrotron-based X-ray scattering data, we simultaneously probe the local structure of supported Cu-species, their distribution within NU-1000 and distortions of the NU-1000 lattice under conditions relevant to catalysis and catalyst activation. These analyses show that atomic layer deposition (ALD) of Cu in NU-1000 (Cu-AIM) leads to the formation of Cu-oxo clusters within the small pores that connect the triangular and hexagonal channels. Exposure of Cu-AIM to a reducing atmosphere at 200 °C produces metallic Cu 0 of two distinct particle sizes: ∼4 nm nanoparticles and small sub-nanometer clusters. The size of these nanoparticles appears to be constrained by NU-1000 pore dimensions, with evidence of the sub-nanometer clusters being bound within the triangular channels flanked by pyrene rings. This supported Cu 0 -NU-1000 system is catalytically active for gas-phase ethylene hydrogenation. Exposure of the catalyst to oxidative atmosphere re-oxidises the Cu species to a Cu 2 O cuprite phase. The dynamic restructuring of the system in different chemical environments underscores the importance of probing these systems in situ.

Tiling a figure using a height in a tree

DOE Office of Scientific and Technical Information (OSTI.GOV)

Remila, E.

1996-12-31

We first give a new presentation of an algorithm from Thurston of tiling with lozenges formed from two cells of the triangular lattice A. Secondly we extend the method to get a linear algorithm of tiling with leaning dominoes (parallelograms formed from four cells of {Lambda}) and triangles (formed from four cells of {Lambda}). Thirdly, we produce a quadratic algorithm of tiling with leaning dominoes.

ACOSS Eleven (Active Control of Space Structures). Volume 1

DTIC Science & Technology

1983-12-01

Influence Function ................. 19 3.4 Mirror Deformations. ........................... o............. 23 3.5 Selection of Point Objects...to simulate errors in the knowledge of influence function . 5) The influence function for edge actuators may be different from that for interior... Influence Function Each of the three mirrors has 37 actuators distributed on an equi- lateral triangular lattice as shown in Figure 3-3. In consultation with

Computing Trimmed, Mean-Camber Surfaces At Minimum Drag

NASA Technical Reports Server (NTRS)

Lamar, John E.; Hodges, William T.

1995-01-01

VLMD computer program determines subsonic mean-camber surfaces of trimmed noncoplanar planforms with minimum vortex drag at specified lift coefficient. Up to two planforms designed together. Method used that of subsonic vortex lattice method of chord loading specification, ranging from rectangular to triangular, left specified by user. Program versatile and applied to isolated wings, wing/canard configurations, tandem wing, and wing/-winglet configuration. Written in FORTRAN.

Dynamics of the Spin Liquid Phase of Cs2CuCl4

NASA Astrophysics Data System (ADS)

Ma, Ookie; Vachon, Marc-Andre; Mitrovi{Ć}, Vesna F.; Marston, Brad

2008-03-01

The dynamics of a spin-liquid phase of an antiferromagnet on the anisotropic triangular lattice and in a magnetic field are studied with a combination of Gutzwiller-projected wavefunctions and mean-field theory. Candidate ground states that support fermionic gapless spinon excitations include four different U(1) spin liquidsootnotetextY. Zhou, X. G. Wen, cond-mat/0210662 (2003).. The lattice and the states interpolate between limiting cases of 1D decoupled chains (J/J^' = 0) and the isotropic 2D square lattice (J/J^'= ∞). Parameters of the mean field theory are chosen to minimize the ground state energy of the corresponding Gutzwiller-projected wavefunction. The spin-lattice relaxation rate 1/T1, calculated within the mean-field approximation, is compared to NMR measurementsootnotetextM. A. Vachon, O. Ma, J. B. Marston, V. F. Mitrovi'c, unpublished (2007). in the spin liquid phase of Cs2CuCl4ootnotetextY. Tokiwa, T. Radu, R. Coldea, H. Wilhelm, Z. Tylczynski, F. Steglich, PRB 73, 134414 (2006)..

Quantum Information Processing in the Wall of Cytoskeletal Microtubules

PubMed Central

Qiu, Xijun; Wu, Tongcheng; Li, Ruxin

2006-01-01

Microtubules (MT) are composed of 13 protofilaments, each of which is a series of two-state tubulin dimers. In the MT wall, these dimers can be pictured as “lattice” sites similar to crystal lattices. Based on the pseudo-spin model, two different location states of the mobile electron in each dimer are proposed. Accordingly, the MT wall is described as an anisotropic two-dimensional (2D) pseudo-spin system considering a periodic triangular “lattice”. Because three different “spin-spin” interactions in each cell exist periodically in the whole MT wall, the system may be shown to be an array of three types of two-pseudo-spin-state dimers. For the above-mentioned condition, the processing of quantum information is presented by using the scheme developed by Lloyd. PMID:19669447

Spins Dynamics in a Dissipative Environment: Hierarchal Equations of Motion Approach Using a Graphics Processing Unit (GPU).

PubMed

Tsuchimoto, Masashi; Tanimura, Yoshitaka

2015-08-11

A system with many energy states coupled to a harmonic oscillator bath is considered. To study quantum non-Markovian system-bath dynamics numerically rigorously and nonperturbatively, we developed a computer code for the reduced hierarchy equations of motion (HEOM) for a graphics processor unit (GPU) that can treat the system as large as 4096 energy states. The code employs a Padé spectrum decomposition (PSD) for a construction of HEOM and the exponential integrators. Dynamics of a quantum spin glass system are studied by calculating the free induction decay signal for the cases of 3 × 2 to 3 × 4 triangular lattices with antiferromagnetic interactions. We found that spins relax faster at lower temperature due to transitions through a quantum coherent state, as represented by the off-diagonal elements of the reduced density matrix, while it has been known that the spins relax slower due to suppression of thermal activation in a classical case. The decay of the spins are qualitatively similar regardless of the lattice sizes. The pathway of spin relaxation is analyzed under a sudden temperature drop condition. The Compute Unified Device Architecture (CUDA) based source code used in the present calculations is provided as Supporting Information .

On the Wiener Polarity Index of Lattice Networks

PubMed Central

Chen, Lin; Li, Tao; Liu, Jinfeng; Shi, Yongtang; Wang, Hua

2016-01-01

Network structures are everywhere, including but not limited to applications in biological, physical and social sciences, information technology, and optimization. Network robustness is of crucial importance in all such applications. Research on this topic relies on finding a suitable measure and use this measure to quantify network robustness. A number of distance-based graph invariants, also known as topological indices, have recently been incorporated as descriptors of complex networks. Among them the Wiener type indices are the most well known and commonly used such descriptors. As one of the fundamental variants of the original Wiener index, the Wiener polarity index has been introduced for a long time and known to be related to the cluster coefficient of networks. In this paper, we consider the value of the Wiener polarity index of lattice networks, a common network structure known for its simplicity and symmetric structure. We first present a simple general formula for computing the Wiener polarity index of any graph. Using this formula, together with the symmetric and recursive topology of lattice networks, we provide explicit formulas of the Wiener polarity index of the square lattices, the hexagonal lattices, the triangular lattices, and the 33 ⋅ 42 lattices. We also comment on potential future research topics. PMID:27930705

Classical Magnetic Frustration

NASA Astrophysics Data System (ADS)

Tsao, Eugene; Henriksen, Erik

We report on studies of classical magnetic frustration, inspired by Mellado et al., by studying an ensemble of freely rotating magnets, made of 1'' rare-earth bar magnets press-fit into polypropylene spheres floating on air bearings. The magnets can be arranged in any configuration to study frustration in 1, 2, or 3 dimensions. For instance, arranged in a Kagome lattice the magnets show an absence of high-energy in-in-in and out-out-out states; the presence of multiple ground states is indicative of macroscopic frustration. We also observe classical ``magnon'' transport in a one-dimensional chain. We will report on progress made in exploring the behavior of these magnets in triangular, Kagome, and honeycomb lattice configurations.

Computing arbitrary defect structures on arbitrary lattices on arbitrary geometries from arbitrary energies

NASA Astrophysics Data System (ADS)

Allen, Brian; Travesset, Alex

2004-03-01

Dislocations and disclinations play a fundamental role in the properties of two dimensional crystals. In this talk, it will be shown that a general computational framework can be developed by combining previous work of Seung and Nelson* and modern advances in objected oriented design. This allows separating the problem into independent classes such as: geometry (sphere, plane, torus..), lattice (triangular, square, etc..), type of defect (dislocation, disclinations, etc..), boundary conditions, type of order (crystalline, hexatic) or energy functional. As applications, the ground state of crystals in several geometries will be discussed. Experimental examples with colloidal particles will be shown. *S. Seung and D. Nelson, Phys. Rev. A 38, 1005 (1988)

An effective lattice Boltzmann flux solver on arbitrarily unstructured meshes

NASA Astrophysics Data System (ADS)

Wu, Qi-Feng; Shu, Chang; Wang, Yan; Yang, Li-Ming

2018-05-01

The recently proposed lattice Boltzmann flux solver (LBFS) is a new approach for the simulation of incompressible flow problems. It applies the finite volume method (FVM) to discretize the governing equations, and the flux at the cell interface is evaluated by local reconstruction of lattice Boltzmann solution from macroscopic flow variables at cell centers. In the previous application of the LBFS, the structured meshes have been commonly employed, which may cause inconvenience for problems with complex geometries. In this paper, the LBFS is extended to arbitrarily unstructured meshes for effective simulation of incompressible flows. Two test cases, the lid-driven flow in a triangular cavity and flow around a circular cylinder, are carried out for validation. The obtained results are compared with the data available in the literature. Good agreement has been achieved, which demonstrates the effectiveness and reliability of the LBFS in simulating flows on arbitrarily unstructured meshes.

Geometry, bonding and magnetism in planar triangulene graphene molecules with D3h symmetry: Zigzag Cm∗∗2+4m+1H3m+3 (m = 2, …, 15)

NASA Astrophysics Data System (ADS)

Philpott, Michael R.; Cimpoesu, Fanica; Kawazoe, Yoshiyuki

2008-12-01

Ab initio plane wave based all valence electron DFT calculations with geometry optimization are reported for the electronic structure of planar zigzag edged triangular shaped graphene molecules CH where the zigzag ring number m = 2, …, 15. The largest molecule C 286H 48 has a 3.8 nm side length and retains D3h symmetric geometry. The zone in the middle of the molecules, where the geometry and electronic properties resemble infinite single sheet graphite (graphene), expands with increasing ring number m, driving deviations in geometry, charge and spin to the perimeter. If a molecule is viewed as a set of nested triangular rings of carbon, then the zone where the lattice resembles an infinite sheet of graphene with CC = 142 pm, extends to the middle of the penultimate ring. The radial bonds joining the perimeter carbon atoms to the interior are long CC = 144 pm, except near the three apexes where the bonds are shorter. Isometric surfaces of the total charge density show that the two bonds joined at the apex have the highest valence charge. The perimeter CC bonds establish a simple pattern as the zigzag number increases, which shares some features with the zigzag edges in the D2h linear acenes C 4m+2H 2m+4 and the D6h hexangulenes CH6m but not the D6h symmetric annulenes (CH). The two CC bonds forming each apex are short (≈139 pm), next comes one long bond CC ≈ 142 pm and a middle region where all the CC bonds have length ≈141 pm. The homo-lumo gap declines from 0.53 eV at m = 2 to approximately 0.29 V at m = 15, the latter being larger than found for linear or hexagonal shaped graphenes with comparable edge lengths. Across the molecule the charge on the carbon atoms undergoes a small oscillation following the bipartite lattice. The magnitude of the charge in the same nested triangle decreases monotonically with the distance of the row from the center of the molecule. These systems are predicted to have spin polarized ground states with S = ½( m - 1), in accord with the theorems of Lieb for a bipartite lattice with unequal numbers of sub-lattice carbon atoms. The magnitude of the spin on the atoms increases monotonically from the center to the edges, this effect being greatest on the majority A-sub lattice atoms. The spins are delocalized, not confined to specific atoms as might result in geometries stabilized by islands of aromatic resonance. In the largest systems the magnetic non-bonding levels (NBL) occur as a narrowly distributed set of homos close to the Fermi level, separated from the lower lying valence bond manifold by a gap of about 1 eV. The NBL are a set of disjoint radical orbitals having charge only on atoms belonging to the A-lattice and this charge is concentrated on the perimeter and penultimate row atoms.

Quantifying and tuning entanglement for quantum systems

NASA Astrophysics Data System (ADS)

Xu, Qing

A 2D Ising model with transverse field on a triangular lattice is studied using exact diagonalization. The quantum entanglement of the system is quantified by the entanglement of formation. The ground state property of the system is studied and the quantified entanglement is shown to be closely related to the ground state wavefunction while the singularity in the entanglement as a function of the transverse field is a reasonable indicator of the quantum phase transition. In order to tune the entanglement, one can either include an impurity in the otherwise homogeneous system whose strength is tunable, or one can vary the external transverse field as a tuner. The latter kind of tuning involves complicated dynamical properties of the system. From the study of the dynamics on a comparatively smaller system, we provide ways to tune the entanglement without triggering any decoherence. The finite temperature effect is also discussed. Besides showing above physical results, the realization of the trace-minimization method in our system is provided; the scalability of such method to larger systems is argued.

Bursting at the Seams: Rippled Monolayer Bismuth on NbSe 2

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fang, Alan; Adamo, Carolina; Jia, Shuang

Bismuth, one of the heaviest semimetals in nature, ignited the interest of the materials-physics community for its potential impact on topological quantum-material systems that utilize its strong spin-orbit coupling (SOC) and unique orbital hybridization. In particular, recent theoretical predictions of unique topological and superconducting properties of thin bismuth films and interfaces prompted intense research on the growth of sub- to a few monolayers of bismuth on different substrates. Similar to bulk rhombohedral bismuth, the initial growth of bismuth films on most substrates results in buckled bilayers that either grow in the (111) or (110) directions, with a lattice constant closemore » to that of bulk Bi. By contrast, in this paper we show a new growth pattern for bismuth monolayers on NbSe 2. We find that the initial growth of Bi can form a strongly bonded commensurate layer, resulting in a compressively strained two-dimensional triangular lattice. A unique pattern of 1D ripples and domain walls is observed. The single layer of bismuth also introduces strong marks on the electronic properties at the surface.« less

Confinement-Driven Phase Separation of Quantum Liquid Mixtures

NASA Astrophysics Data System (ADS)

Prisk, T. R.; Pantalei, C.; Kaiser, H.; Sokol, P. E.

2012-08-01

We report small-angle neutron scattering studies of liquid helium mixtures confined in Mobil Crystalline Material-41 (MCM-41), a porous silica glass with narrow cylindrical nanopores (d=3.4nm). MCM-41 is an ideal model adsorbent for fundamental studies of gas sorption in porous media because its monodisperse pores are arranged in a 2D triangular lattice. The small-angle scattering consists of a series of diffraction peaks whose intensities are determined by how the imbibed liquid fills the pores. Pure He4 adsorbed in the pores show classic, layer-by-layer film growth as a function of pore filling, leaving the long range symmetry of the system intact. In contrast, the adsorption of He3-He4 mixtures produces a structure incommensurate with the pore lattice. Neither capillary condensation nor preferential adsorption of one helium isotope to the pore walls can provide the symmetry-breaking mechanism. The scattering is consistent with the formation of randomly distributed liquid-liquid microdomains ˜2.3nm in size, providing evidence that confinement in a nanometer scale capillary can drive local phase separation in quantum liquid mixtures.

Electrodynamics of quantum spin liquids

NASA Astrophysics Data System (ADS)

Dressel, Martin; Pustogow, Andrej

2018-05-01

Quantum spin liquids attract great interest due to their exceptional magnetic properties characterized by the absence of long-range order down to low temperatures despite the strong magnetic interaction. Commonly, these compounds are strongly correlated electron systems, and their electrodynamic response is governed by the Mott gap in the excitation spectrum. Here we summarize and discuss the optical properties of several two-dimensional quantum spin liquid candidates. First we consider the inorganic material herbertsmithite ZnCu3(OH)6Cl2 and related compounds, which crystallize in a kagome lattice. Then we turn to the organic compounds -EtMe3Sb[Pd(dmit)2]2, κ-(BEDT-TTF)2Ag2(CN)3 and κ-(BEDT-TTF)2Cu2(CN)3, where the spins are arranged in an almost perfect triangular lattice, leading to strong frustration. Due to differences in bandwidth, the effective correlation strength varies over a wide range, leading to a rather distinct behavior as far as the electrodynamic properties are concerned. We discuss the spinon contributions to the optical conductivity in comparison to metallic quantum fluctuations in the vicinity of the Mott transition.

Bursting at the Seams: Rippled Monolayer Bismuth on NbSe 2

DOE PAGES

Fang, Alan; Adamo, Carolina; Jia, Shuang; ...

2018-04-13

Bismuth, one of the heaviest semimetals in nature, ignited the interest of the materials-physics community for its potential impact on topological quantum-material systems that utilize its strong spin-orbit coupling (SOC) and unique orbital hybridization. In particular, recent theoretical predictions of unique topological and superconducting properties of thin bismuth films and interfaces prompted intense research on the growth of sub- to a few monolayers of bismuth on different substrates. Similar to bulk rhombohedral bismuth, the initial growth of bismuth films on most substrates results in buckled bilayers that either grow in the (111) or (110) directions, with a lattice constant closemore » to that of bulk Bi. By contrast, in this paper we show a new growth pattern for bismuth monolayers on NbSe 2. We find that the initial growth of Bi can form a strongly bonded commensurate layer, resulting in a compressively strained two-dimensional triangular lattice. A unique pattern of 1D ripples and domain walls is observed. The single layer of bismuth also introduces strong marks on the electronic properties at the surface.« less

Thermal algebraic-decay charge liquid driven by competing short-range Coulomb repulsion

NASA Astrophysics Data System (ADS)

Kaneko, Ryui; Nonomura, Yoshihiko; Kohno, Masanori

2018-05-01

We explore the possibility of a Berezinskii-Kosterlitz-Thouless-like critical phase for the charge degrees of freedom in the intermediate-temperature regime between the charge-ordered and disordered phases in two-dimensional systems with competing short-range Coulomb repulsion. As the simplest example, we investigate the extended Hubbard model with on-site and nearest-neighbor Coulomb interactions on a triangular lattice at half filling in the atomic limit by using a classical Monte Carlo method, and find a critical phase, characterized by algebraic decay of the charge correlation function, belonging to the universality class of the two-dimensional XY model with a Z6 anisotropy. Based on the results, we discuss possible conditions for the critical phase in materials.

Addressing the characterisation challenge to understand catalysis in MOFs: the case of nanoscale Cu supported in NU-1000

DOE PAGES

Platero-Prats, Ana E.; Li, Zhanyong; Gallington, Leighanne C.; ...

2017-04-03

Here, we explore the dynamic structure and reactivity of Cu species supported on NU-1000. By combining pair distribution function (PDF) analysis and difference envelope density (DED) analysis ofin situsynchrotron-based X-ray scattering data, we simultaneously probe the local structure of supported Cu-species, their distribution within NU-1000 and distortions of the NU-1000 lattice under conditions relevant to catalysis and catalyst activation. Our analyses show that atomic layer deposition (ALD) of Cu in NU-1000 (Cu-AIM) leads to the formation of Cu-oxo clusters within the small pores that connect the triangular and hexagonal channels. Exposure of Cu-AIM to a reducing atmosphere at 200 °Cmore » produces metallic Cu 0of two distinct particle sizes: ~4 nm nanoparticles and small sub-nanometer clusters. The size of these nanoparticles appears to be constrained by NU-1000 pore dimensions, with evidence of the sub-nanometer clusters being bound within the triangular channels flanked by pyrene rings. This supported Cu 0–NU-1000 system is catalytically active for gas-phase ethylene hydrogenation. Exposure of the catalyst to oxidative atmosphere re-oxidises the Cu species to a Cu 2O cuprite phase. The dynamic restructuring of the system in different chemical environments underscores the importance of probing these systemsin situ.« less

Noncircular skyrmion and its anisotropic response in thin films of chiral magnets under a tilted magnetic field

DOE PAGES

Lin, Shi-Zeng; Saxena, Avadh

2015-11-03

Here we study the equilibrium and dynamical properties of skyrmions in thin films of chiral magnets with oblique magnetic field. The shape of an individual skyrmion is non-circular and the skyrmion density decreases with the tilt angle from the normal of films. As a result, the interaction between two skyrmions depends on the relative angle between them in addition to their separation. The triangular lattice of skyrmions under a perpendicular magnetic field is distorted into a centered rectangular lattice for a tilted magnetic field. For a low skyrmion density, skyrmions form a chain like structure. Lastly, the dynamical response ofmore » the non-circular skyrmions depends on the direction of external currents.« less

Dirac cones in isogonal hexagonal metallic structures

NASA Astrophysics Data System (ADS)

Wang, Kang

2018-03-01

A honeycomb hexagonal metallic lattice is equivalent to a triangular atomic one and cannot create Dirac cones in its electromagnetic wave spectrum. We study in this work the low-frequency electromagnetic band structures in isogonal hexagonal metallic lattices that are directly related to the honeycomb one and show that such structures can create Dirac cones. The band formation can be described by a tight-binding model that allows investigating, in terms of correlations between local resonance modes, the condition for the Dirac cones and the consequence of the third structure tile sustaining an extra resonance mode in the unit cell that induces band shifts and thus nonlinear deformation of the Dirac cones following the wave vectors departing from the Dirac points. We show further that, under structure deformation, the deformations of the Dirac cones result from two different correlation mechanisms, both reinforced by the lattice's metallic nature, which directly affects the resonance mode correlations. The isogonal structures provide new degrees of freedom for tuning the Dirac cones, allowing adjustment of the cone shape by modulating the structure tiles at the local scale without modifying the lattice periodicity and symmetry.

Structural disorder and elementary magnetic properties of triangular lattice ErMgGaO 4 single crystals

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cevallos, F. Alex; Stolze, Karoline; Cava, Robert J.

The single crystal growth, structure, and basic magnetic properties of ErMgGaO 4 are reported. The structure consists of triangular layers of magnetic ErO 6 octahedra separated by a double layer of randomly occupied non-magnetic (Ga,Mg)O 5 bipyramids. The Er atoms are positionally disordered. Magnetic measurements parallel and perpendicular to the c axis of a single crystal reveal dominantly antiferromagnetic interactions, with a small degree of magnetic anisotropy. A weighted average of the directional data suggests an antiferromagnetic Curie Weiss temperature of approximately -30 K. Below 10 K the temperature dependences of the inverse susceptibilities in the in-plane and perpendicular-to planemore » directions are parallel, indicative of an isotropic magnetic moment at low temperatures. In conclusion, no sign of magnetic ordering is observed above 1.8 K, suggesting that ErMgGaO 4 is a geometrically frustrated magnet.« less

Structural disorder and elementary magnetic properties of triangular lattice ErMgGaO 4 single crystals

DOE PAGES

Cevallos, F. Alex; Stolze, Karoline; Cava, Robert J.

2018-03-23

The single crystal growth, structure, and basic magnetic properties of ErMgGaO 4 are reported. The structure consists of triangular layers of magnetic ErO 6 octahedra separated by a double layer of randomly occupied non-magnetic (Ga,Mg)O 5 bipyramids. The Er atoms are positionally disordered. Magnetic measurements parallel and perpendicular to the c axis of a single crystal reveal dominantly antiferromagnetic interactions, with a small degree of magnetic anisotropy. A weighted average of the directional data suggests an antiferromagnetic Curie Weiss temperature of approximately -30 K. Below 10 K the temperature dependences of the inverse susceptibilities in the in-plane and perpendicular-to planemore » directions are parallel, indicative of an isotropic magnetic moment at low temperatures. In conclusion, no sign of magnetic ordering is observed above 1.8 K, suggesting that ErMgGaO 4 is a geometrically frustrated magnet.« less

Quantum Phase Transition and Local Entanglement in Extended Hubbard Model on Anisotropic Triangular Lattices

NASA Astrophysics Data System (ADS)

Gao, Ji-Ming; Tang, Rong-An; Zhang, Zheng-Mei; Xue, Ju-Kui

2016-11-01

Using a mean-field theory based upon Hartree—Fock approximation, we theoretically investigate the competition between the metallic conductivity, spin order and charge order phases in a two-dimensional half-filled extended Hubbard model on anisotropic triangular lattice. Bond order, double occupancy, spin and charge structure factor are calculated, and the phase diagram of the extended Hubbard model is presented. It is found that the interplay of strong interaction and geometric frustration leads to exotic phases, the charge fluctuation is enhanced and three kinds of charge orders appear with the introduction of the nearest-neighbor interaction. Moreover, for different frustrations, it is also found that the antiferromagnetic insulating phase and nonmagnetic insulating phase are rapidly suppressed, and eventually disappeared as the ratio between the nearest-neighbor interaction and on-site interaction increases. This indicates that spin order is also sensitive to the nearest-neighbor interaction. Finally, the single-site entanglement is calculated and it is found that a clear discontinuous of the single-site entanglement appears at the critical points of the phase transition. Supported by National Natural Science Foundation of China under Grant Nos.11274255, 11475027 and 11305132, Specialized Research Fund for the Doctoral Program of Higher Education of China under Grant No. 20136203110001, and Technology of Northwest Normal University, China under Grants No. NWNU-LKQN-11-26

Exact Solution of the Classical Dimer Model on a Triangular Lattice: Monomer-Monomer Correlations

NASA Astrophysics Data System (ADS)

Basor, Estelle; Bleher, Pavel

2017-12-01

We obtain an asymptotic formula, as {n\\to∞}, for the monomer-monomer correlation function {K_2(n)} in the classical dimer model on a triangular lattice, with the horizontal and vertical weights {w_h=w_v=1} and the diagonal weight {w_d=t > 0}, between two monomers at vertices q and r that are n spaces apart in adjacent rows. We find that {t_c=1/2} is a critical value of t. We prove that in the subcritical case, {0 < t < 1/2}, as {n\\to∞, K_2(n)=K_2(∞)[1-e^{-n/ξ}/n \\Big(C_1+C_2(-1)^n+ O(n^{-1})\\Big) ]}, with explicit formulae for {K_2(∞), ξ, C_1}, and {C_2}. In the supercritical case, {1/2 < t < 1}, we prove that as {n\\to∞, K_2(n)=K_2(∞)\\Bigg[1-e^{-n/ξ}/n \\Big(C_1 cos(ω n+φ_1)+C_2(-1)^n cos(ω n+φ_2)+ C_3+C_4(-1)^n + O(n^{-1})\\Big)\\Bigg]}, with explicit formulae for {K_2(∞), ξ,ω}, and {C_1, C_2, C_3, C_4, φ_1, φ_2}. The proof is based on an extension of the Borodin-Okounkov-Case-Geronimo formula to block Toeplitz determinants and on an asymptotic analysis of the Fredholm determinants in hand.

A neutron diffraction study of the magnetic phases of CsCuCl3 for in-plane fields up to 17 T

NASA Astrophysics Data System (ADS)

Stüßer, N.; Schotte, U.; Hoser, A.; Meschke, M.; Meißner, M.; Wosnitza, J.

2002-05-01

Neutron diffraction investigations have been performed to study the magnetization process of CsCuCl3 with the magnetic field aligned within the ab-plane. In zero field the stacked, triangular-lattice antiferromagnet (TLA) CsCuCl3 has a helical structure incommensurate in the chain direction normal to the ab-plane. The magnetic phase diagram was investigated from 2 K up to TN in fields up to 17 T. The phase line for the expected incommensurate-commensurate (IC-C) phase transition could be determined throughout the whole phase diagram. At low temperature the IC-C transition is roughly at half the saturation field HS. The neutron diffraction patterns were found to be well described by a sinusoidally modulated spiral in fields up to HS/3. The initial increase of the scattering intensity in rising field indicates a continuous reduction of the spin frustration on the triangular lattice. Between HS/3 and HS/2 a new phase occurs where the spiral vector has a plateau in its field dependence. Close to the IC-C transition a growing asymmetry of magnetic satellite-peak intensities indicates domain effects which are related to the lifting of the chiral degeneracy in the ab-plane in rising field. The phase diagram obtained has some similarities with those calculated for stacked TLAs by considering the effects of quantum and thermal fluctuations.

Ordering phenomena in a heterostructure of frustrated and unfrustrated triangular-lattice Ising layers

NASA Astrophysics Data System (ADS)

Žukovič, Milan; Tomita, Yusuke; Kamiya, Y.

2017-07-01

We study critical and magnetic properties of a bilayer Ising system consisting of two triangular planes A and B, with the antiferromagnetic (AF) coupling JA and the ferromagnetic (FM) one JB for the respective layers, which are coupled by the interlayer interaction JAB by using Monte Carlo simulations. When JA and JB are of the same order, the unfrustrated FM plane orders first at a high temperature Tc 1˜JB . The spontaneous FM order then exerts influence on the other frustrated AF plane as an effective magnetic field, which subsequently induces a ferrimagnetic order in this plane at low temperatures below Tc 2. When short-range order is developed in the AF plane while the influence of the FM plane is still small, there appears a preemptive Berezinskii-Kosterlitz-Thouless-type pseudocritical crossover regime just above the ferrimagnetic phase transition point, where the short-distance behavior up to a rather large length scale exponentially diverging in ∝JA/T is controlled by a line of Gaussian fixed points at T =0 . In the crossover region, a continuous variation in the effective critical exponent 4/9 ≲ηeff≲1/2 is observed. The phase diagram by changing the ratio JA/JB is also investigated.

Melting of Pb Charge Glass and Simultaneous Pb-Cr Charge Transfer in PbCrO 3 as the Origin of Volume Collapse

DOE PAGES

Yu, Runze; Hojo, Hajime; Watanuki, Tetsu; ...

2015-09-15

A metal to insulator transition in integer or half integer charge systems can be regarded as crystallization of charges. The insulating state tends to have a glassy nature when randomness or geometrical frustration exists. In this paper, we report that the charge glass state is realized in a perovskite compound PbCrO 3, which has been known for almost 50 years, without any obvious inhomogeneity or triangular arrangement in the charge system. PbCrO 3 has a valence state of Pb 2+ 0.5Pb 4+ 0.5Cr 3+O 3 with Pb 2+–Pb 4+ correlation length of three lattice-spacings at ambient condition. A pressure inducedmore » melting of charge glass and simultaneous Pb–Cr charge transfer causes an insulator to metal transition and ~10% volume collapse.« less

Magnetic inhomogeneity on a triangular lattice: the magnetic-exchange versus the elastic energy and the role of disorder

PubMed Central

Zorko, A.; Kokalj, J.; Komelj, M.; Adamopoulos, O.; Luetkens, H.; Arčon, D.; Lappas, A.

2015-01-01

Inhomogeneity in the ground state is an intriguing, emergent phenomenon in magnetism. Recently, it has been observed in the magnetostructural channel of the geometrically frustrated α-NaMnO2, for the first time in the absence of active charge degrees of freedom. Here we report an in-depth numerical and local-probe experimental study of the isostructural sister compound CuMnO2 that emphasizes and provides an explanation for the crucial differences between the two systems. The experimentally verified, much more homogeneous, ground state of the stoichiometric CuMnO2 is attributed to the reduced magnetoelastic competition between the counteracting magnetic-exchange and elastic-energy contributions. The comparison of the two systems additionally highlights the role of disorder and allows the understanding of the puzzling phenomenon of phase separation in uniform antiferromagnets. PMID:25786810

Shear localization in three-dimensional amorphous solids.

PubMed

Dasgupta, Ratul; Gendelman, Oleg; Mishra, Pankaj; Procaccia, Itamar; Shor, Carmel A B Z

2013-09-01

In this paper we extend the recent theory of shear localization in two-dimensional (2D) amorphous solids to three dimensions. In two dimensions the fundamental instability of shear localization is related to the appearance of a line of displacement quadrupoles that makes an angle of 45^{∘} with the principal stress axis. In three dimensions the fundamental plastic instability is also explained by the formation of a lattice of anisotropic elastic inclusions. In the case of pure external shear stress, we demonstrate that this is a 2D triangular lattice of similar elementary events. It is shown that this lattice is arranged on a plane that, similarly to the 2D case, makes an angle of 45^{∘} with the principal stress axis. This solution is energetically favorable only if the external strain exceeds a yield-strain value that is determined by the strain parameters of the elementary events and the Poisson ratio. The predictions of the theory are compared to numerical simulations and very good agreement is observed.

Adaptive non-predictor control of lower triangular uncertain nonlinear systems with an unknown time-varying delay in the input

NASA Astrophysics Data System (ADS)

Koo, Min-Sung; Choi, Ho-Lim

2018-01-01

In this paper, we consider a control problem for a class of uncertain nonlinear systems in which there exists an unknown time-varying delay in the input and lower triangular nonlinearities. Usually, in the existing results, input delays have been coupled with feedforward (or upper triangular) nonlinearities; in other words, the combination of lower triangular nonlinearities and input delay has been rare. Motivated by the existing controller for input-delayed chain of integrators with nonlinearity, we show that the control of input-delayed nonlinear systems with two particular types of lower triangular nonlinearities can be done. As a control solution, we propose a newly designed feedback controller whose main features are its dynamic gain and non-predictor approach. Three examples are given for illustration.

Improved methods of estimating critical indices via fractional calculus

NASA Astrophysics Data System (ADS)

Bandyopadhyay, S. K.; Bhattacharyya, K.

2002-05-01

Efficiencies of certain methods for the determination of critical indices from power-series expansions are shown to be considerably improved by a suitable implementation of fractional differentiation. In the context of the ratio method (RM), kinship of the modified strategy with the ad hoc `shifted' RM is established and the advantages are demonstrated. Further, in the course of the estimation of critical points, significant betterment of convergence properties of diagonal Padé approximants is observed on several occasions by invoking this concept. Test calculations are performed on (i) various Ising spin-1/2 lattice models for susceptibility series attended with a ferromagnetic phase transition, (ii) complex model situations involving confluent and antiferromagnetic singularities and (iii) the chain-generating functions for self-avoiding walks on triangular, square and simple cubic lattices.

Fault-tolerance in Two-dimensional Topological Systems

NASA Astrophysics Data System (ADS)

Anderson, Jonas T.

This thesis is a collection of ideas with the general goal of building, at least in the abstract, a local fault-tolerant quantum computer. The connection between quantum information and topology has proven to be an active area of research in several fields. The introduction of the toric code by Alexei Kitaev demonstrated the usefulness of topology for quantum memory and quantum computation. Many quantum codes used for quantum memory are modeled by spin systems on a lattice, with operators that extract syndrome information placed on vertices or faces of the lattice. It is natural to wonder whether the useful codes in such systems can be classified. This thesis presents work that leverages ideas from topology and graph theory to explore the space of such codes. Homological stabilizer codes are introduced and it is shown that, under a set of reasonable assumptions, any qubit homological stabilizer code is equivalent to either a toric code or a color code. Additionally, the toric code and the color code correspond to distinct classes of graphs. Many systems have been proposed as candidate quantum computers. It is very desirable to design quantum computing architectures with two-dimensional layouts and low complexity in parity-checking circuitry. Kitaev's surface codes provided the first example of codes satisfying this property. They provided a new route to fault tolerance with more modest overheads and thresholds approaching 1%. The recently discovered color codes share many properties with the surface codes, such as the ability to perform syndrome extraction locally in two dimensions. Some families of color codes admit a transversal implementation of the entire Clifford group. This work investigates color codes on the 4.8.8 lattice known as triangular codes. I develop a fault-tolerant error-correction strategy for these codes in which repeated syndrome measurements on this lattice generate a three-dimensional space-time combinatorial structure. I then develop an integer program that analyzes this structure and determines the most likely set of errors consistent with the observed syndrome values. I implement this integer program to find the threshold for depolarizing noise on small versions of these triangular codes. Because the threshold for magic-state distillation is likely to be higher than this value and because logical CNOT gates can be performed by code deformation in a single block instead of between pairs of blocks, the threshold for fault-tolerant quantum memory for these codes is also the threshold for fault-tolerant quantum computation with them. Since the advent of a threshold theorem for quantum computers much has been improved upon. Thresholds have increased, architectures have become more local, and gate sets have been simplified. The overhead for magic-state distillation has been studied, but not nearly to the extent of the aforementioned topics. A method for greatly reducing this overhead, known as reusable magic states, is studied here. While examples of reusable magic states exist for Clifford gates, I give strong reasons to believe they do not exist for non-Clifford gates.

Monte Carlo renormalization-group study of the Baxter-Wu model

DOE Office of Scientific and Technical Information (OSTI.GOV)

Novotny, M.A.; Landau, D.P.; Swendsen, R.H.

1982-07-01

The effectiveness of a Monte Carlo renormalization-group method is studied by applying it to the Baxter-Wu model (Ising spins on a triangular lattice with three-spin interactions). The calculations yield three relevent eigenvalues in good agreement with exact or conjectured results. We demonstrate that the method is capable of distinguishing between models expected to be in the same universality class, when one of them (four-state Potts) exhibits logarithmic corrections to the usual power-law singularities and the other (Baxter-Wu) does not.

Disorder-induced losses in photonic crystal waveguides with line defects.

PubMed

Gerace, Dario; Andreani, Lucio Claudio

2004-08-15

A numerical analysis of extrinsic diffraction losses in two-dimensional photonic crystal slabs with line defects is reported. To model disorder, a Gaussian distribution of hole radii in the triangular lattice of airholes is assumed. The extrinsic losses below the light line increase quadratically with the disorder parameter, decrease slightly with increasing core thickness, and depend weakly on the hole radius. For typical values of the disorder parameter the calculated loss values of guided modes below the light line compare favorably with available experimental results.

Effect of background dielectric on TE-polarized photonic bandgap of metallodielectric photonic crystals using Dirichlet-to-Neumann map method.

PubMed

Sedghi, Aliasghar; Rezaei, Behrooz

2016-11-20

Using the Dirichlet-to-Neumann map method, we have calculated the photonic band structure of two-dimensional metallodielectric photonic crystals having the square and triangular lattices of circular metal rods in a dielectric background. We have selected the transverse electric mode of electromagnetic waves, and the resulting band structures showed the existence of photonic bandgap in these structures. We theoretically study the effect of background dielectric on the photonic bandgap.

Magnetic Correlations in the Triangular Antiferromagnet TbInO3

NASA Astrophysics Data System (ADS)

Sala, Gabriele; Clark, Lucy; Maharaj, Dalini; Stone, Matthew B.; Knight, Kevin S.; Cheong, Sang-Wook; Gaulin, Bruce D.

TbInO3 crystallizes with a hexagonal P63 cm structure in which layers of edge-sharing triangles of magnetic Tb3+ ions are separated by non-magnetic [InO5]7- units. TbInO3, therefore, realizes an excellent opportunity to explore the behavior of a two-dimensional magnetic triangular lattice, a canonical model of geometric frustration. Here we present our study of a polycrystalline sample of TbInO3. Our high resolution powder neutron diffraction data (HRPD, ISIS) of TbInO3 confirm that the triangular layers of Tb3+ remain undistorted to at least 0 . 46 K. Magnetic susceptibility data follow Curie-Weiss behavior over a wide range of T with θ = - 17 . 19 (3) K indicating the dominance of antiferromagnetic correlations. The susceptibility data also show an absence of conventional long-range spin order down to at least 0 . 55 K, reflecting the frustrated nature of TbInO3. Elastic magnetic diffuse neutron scattering (SEQUOIA, SNS) is observed below ~ 15 K, due to the presence of static two-dimensional spin correlations. The spectrum of crystal field excitations in TbInO3 appears to have an exotic form due to the existence of two crystallographically distinct Tb3+ sites and leads to a strong Ising anisotropy of the spin symmetry.

Design of Mott and topological phases on buckled 3d-oxide honeycomb lattices

NASA Astrophysics Data System (ADS)

Pentcheva, Rossitza

The honeycomb lattice, as realized e.g. in graphene, has rendered a robust platform for innovative science and potential applications. A much richer generalization of this lattice arises in (111)-oriented bilayers of perovskites, adding the complexity of the strongly correlated, multiorbital nature of electrons in transition metal oxides. Based on first principles calculations with an on-site Coulomb repulsion, here we provide trends in the evolution of ground states versus band filling in (111)-oriented (La XO3)2 /(LaAlO3)4 superlattices, with X spanning the entire 3d transition metal series. The competition between local quasi-cubic and global triangular symmetry triggers unanticipated broken symmetry phases, with mechanisms ranging from Jahn-Teller distortion, to charge-, spin-, and orbital-ordering. LaMnO3 and LaCoO3 bilayers, where spin-orbit coupling opens a sizable gap in the Dirac-point Fermi surface, emerge as much desired oxide-based Chern insulators, the latter displaying a gap capable of supporting room-temperature applications Further realizations of the honeycomb lattice and geometry patterns beyond the perovskite structure will be addressed. Research supported by the DFG, SFB/TR80.

Finite-temperature behavior of a classical spin-orbit-coupled model for YbMgGaO4 with and without bond disorder

NASA Astrophysics Data System (ADS)

Parker, Edward; Balents, Leon

2018-05-01

We present the results of finite-temperature classical Monte Carlo simulations of a strongly spin-orbit-coupled nearest-neighbor triangular-lattice model for the candidate U (1 ) quantum spin liquid YbMgGaO4 at large system sizes. We find a single continuous finite-temperature stripe-ordering transition with slowly diverging heat capacity that completely breaks the sixfold ground-state degeneracy, despite the absence of a known conformal field theory describing such a transition. We also simulate the effect of random-bond disorder in the model, and find that even weak bond disorder destroys the transition by fragmenting the system into very large domains—possibly explaining the lack of observed ordering in the real material. The Imry-Ma argument only partially explains this fragility to disorder, and we extend the argument with a physical explanation for the preservation of our system's time-reversal symmetry even under a disorder model that preserves the same symmetry.

Elastic constants from microscopic strain fluctuations

PubMed

Sengupta; Nielaba; Rao; Binder

2000-02-01

Fluctuations of the instantaneous local Lagrangian strain epsilon(ij)(r,t), measured with respect to a static "reference" lattice, are used to obtain accurate estimates of the elastic constants of model solids from atomistic computer simulations. The measured strains are systematically coarse-grained by averaging them within subsystems (of size L(b)) of a system (of total size L) in the canonical ensemble. Using a simple finite size scaling theory we predict the behavior of the fluctuations as a function of L(b)/L and extract elastic constants of the system in the thermodynamic limit at nonzero temperature. Our method is simple to implement, efficient, and general enough to be able to handle a wide class of model systems, including those with singular potentials without any essential modification. We illustrate the technique by computing isothermal elastic constants of "hard" and "soft" disk triangular solids in two dimensions from Monte Carlo and molecular dynamics simulations. We compare our results with those from earlier simulations and theory.

Collocation of equilibria in gravitational field of triangular body via mass redistribution

NASA Astrophysics Data System (ADS)

Burov, Alexander A.; Guerman, Anna D.; Nikonov, Vasily I.

2018-05-01

We consider a gravitating system with triangular mass distribution that can be used as approximation of gravitational field for small irregular celestial bodies. In such system, the locations of equilibrium points, that is, the points where the gravitational forces are balanced, are analyzed. The goal is to find the mass distribution which provides equilibrium in a pre-assigned location near the triangular system, and to study the stability of this equilibrium.

Zero-field random-field effect in diluted triangular lattice antiferromagnet CuFe1-xAlxO2

NASA Astrophysics Data System (ADS)

Nakajima, T.; Mitsuda, S.; Kitagawa, K.; Terada, N.; Komiya, T.; Noda, Y.

2007-04-01

We performed neutron scattering experiments on a diluted triangular lattice antiferromagnet (TLA), CuFe1-xAlxO2 with x = 0.10. The detailed analysis of the scattering profiles revealed that the scattering function of magnetic reflection is described as the sum of a Lorentzian term and a Lorentzian-squared term with anisotropic width. The Lorentzian-squared term dominating at low temperature is indicative of the domain state in the prototypical random-field Ising model. Taking account of the sinusoidally amplitude-modulated magnetic structure with incommensurate wavenumber in CuFe1-xAlxO2 with x = 0.10, we conclude that the effective random field arises even at zero field, owing to the combination of site-random magnetic vacancies and the sinusoidal structure that is regarded as a partially disordered (PD) structure in a wide sense, as reported in the typical three-sublattice PD phase of a diluted Ising TLA, CsCo0.83Mg0.17Br3 (van Duijn et al 2004 Phys. Rev. Lett. 92 077202). While the previous study revealed the existence of a domain state in CsCo0.83Mg0.17Br3 by detecting magnetic reflections specific to the spin configuration near the domain walls, our present study revealed the existence of a domain state in CuFe1-xAlxO2 (x = 0.10) by determination of the functional form of the scattering function.

Evolution of domain walls in the early universe. Ph.D. Thesis - Chicago Univ.

NASA Technical Reports Server (NTRS)

Kawano, Lawrence

1989-01-01

The evolution of domain walls in the early universe is studied via 2-D computer simulation. The walls are initially configured on a triangular lattice and then released from the lattice, their evolution driven by wall curvature and by the universal expansion. The walls attain an average velocity of about 0.3c and their surface area per volume (as measured in comoving coordinates) goes down with a slope of -1 with respect to conformal time, regardless of whether the universe is matter or radiation dominated. The additional influence of vacuum pressure causes the energy density to fall away from this slope and steepen, thus allowing a situation in which domain walls can constitute a significant portion of the energy density of the universe without provoking an unacceptably large perturbation upon the microwave background.

Dirac Fermions in Borophene

NASA Astrophysics Data System (ADS)

Feng, Baojie; Sugino, Osamu; Liu, Ro-Ya; Zhang, Jin; Yukawa, Ryu; Kawamura, Mitsuaki; Iimori, Takushi; Kim, Howon; Hasegawa, Yukio; Li, Hui; Chen, Lan; Wu, Kehui; Kumigashira, Hiroshi; Komori, Fumio; Chiang, Tai-Chang; Meng, Sheng; Matsuda, Iwao

2017-03-01

Honeycomb structures of group IV elements can host massless Dirac fermions with nontrivial Berry phases. Their potential for electronic applications has attracted great interest and spurred a broad search for new Dirac materials especially in monolayer structures. We present a detailed investigation of the β12 sheet, which is a borophene structure that can form spontaneously on a Ag(111) surface. Our tight-binding analysis revealed that the lattice of the β12 sheet could be decomposed into two triangular sublattices in a way similar to that for a honeycomb lattice, thereby hosting Dirac cones. Furthermore, each Dirac cone could be split by introducing periodic perturbations representing overlayer-substrate interactions. These unusual electronic structures were confirmed by angle-resolved photoemission spectroscopy and validated by first-principles calculations. Our results suggest monolayer boron as a new platform for realizing novel high-speed low-dissipation devices.

Phyllotactic transformations as plastic deformations of tubular crystals with defects

NASA Astrophysics Data System (ADS)

Beller, Daniel; Nelson, David

Tubular crystals are 2D lattices in cylindrical topologies, which could be realized as assemblies of colloidal particles, and occur naturally in biological microtubules and in single-walled carbon nanotubes. Their geometry can be understood in the language of phyllotaxis borrowed from botany. We study the mechanics of plastic deformations in tubular crystals in response to tensile stress, as mediated by the formation and separation of dislocation pairs in a triangular lattice. Dislocation motion allows the growth of one phyllotactic arrangement at the expense of another, offering a low-energy, stepwise mode of plastic deformation in response to external stresses. Through theory and simulation, we examine how the tube's radius and helicity affects, and is in turn altered by, dislocation glide. The crystal's bending modulus is found to produce simple but important corrections to the tube's deformation mechanics.

Frustrated quantum magnetism in the Kondo lattice on the zigzag ladder

NASA Astrophysics Data System (ADS)

Peschke, Matthias; Rausch, Roman; Potthoff, Michael

2018-03-01

The interplay between the Kondo effect, indirect magnetic interaction, and geometrical frustration is studied in the Kondo lattice on the one-dimensional zigzag ladder. Using the density-matrix renormalization group, the ground-state and various short- and long-range spin- and density-correlation functions are calculated for the model at half filling as a function of the antiferromagnetic Kondo interaction down to J =0.3 t , where t is the nearest-neighbor hopping on the zigzag ladder. Geometrical frustration is shown to lead to at least two critical points: Starting from the strong-J limit, where almost local Kondo screening dominates and where the system is a nonmagnetic Kondo insulator, antiferromagnetic correlations between nearest-neighbor and next-nearest-neighbor local spins become stronger and stronger, until at Jcdim≈0.89 t frustration is alleviated by a spontaneous breaking of translational symmetry and a corresponding transition to a dimerized state. This is characterized by antiferromagnetic correlations along the legs and by alternating antiferro- and ferromagnetic correlations on the rungs of the ladder. A mechanism of partial Kondo screening that has been suggested for the Kondo lattice on the two-dimensional triangular lattice is not realized in the one-dimensional case. Furthermore, within the symmetry-broken dimerized state, there is a magnetic transition to a 90∘ quantum spin spiral with quasi-long-range order at Jcmag≈0.84 t . The quantum-critical point is characterized by a closure of the spin gap (with decreasing J ) and a divergence of the spin-correlation length and of the spin-structure factor S (q ) at wave vector q =π /2 . This is opposed to the model on the one-dimensional bipartite chain, which is known to have a finite spin gap for all J >0 at half filling.

Modulation transfer function of a triangular pixel array detector.

PubMed

Karimzadeh, Ayatollah

2014-07-01

The modulation transfer function (MTF) is the main parameter that is used to evaluate image quality in electro-optical systems. Detector sampling MTF in most electro-optical systems determines the cutoff frequency of the system. The MTF of the detector depends on its pixel shape. In this work, we calculated the MTF of a detector with an equilateral triangular pixel shape. Some new results were found in deriving the MTF for the equilateral triangular pixel shape.

New similarity of triangular fuzzy number and its application.

PubMed

Zhang, Xixiang; Ma, Weimin; Chen, Liping

2014-01-01

The similarity of triangular fuzzy numbers is an important metric for application of it. There exist several approaches to measure similarity of triangular fuzzy numbers. However, some of them are opt to be large. To make the similarity well distributed, a new method SIAM (Shape's Indifferent Area and Midpoint) to measure triangular fuzzy number is put forward, which takes the shape's indifferent area and midpoint of two triangular fuzzy numbers into consideration. Comparison with other similarity measurements shows the effectiveness of the proposed method. Then, it is applied to collaborative filtering recommendation to measure users' similarity. A collaborative filtering case is used to illustrate users' similarity based on cloud model and triangular fuzzy number; the result indicates that users' similarity based on triangular fuzzy number can obtain better discrimination. Finally, a simulated collaborative filtering recommendation system is developed which uses cloud model and triangular fuzzy number to express users' comprehensive evaluation on items, and result shows that the accuracy of collaborative filtering recommendation based on triangular fuzzy number is higher.

Fluctuation in the Intermediate Magnetic Phase of Triangular Ising Antiferromagnet (CeS)1.16[Fe0.33(NbS2)2

NASA Astrophysics Data System (ADS)

Michioka, Chishiro; Suzuki, Kazuya; Mibu, Ko

2002-10-01

We applied 57Fe Mössbauer spectroscopy for investigating the Ising spin triangular lattice antiferromagnet (TLA) (CeS)1.16[Fe0.33(NbS2)2] between 2 and 300 K. The spectra revealed that the relaxation time of the hyperfine field markedly changes in the intermediate phase between TN1=22 K and TN2=15 K due to strong spin fluctuation. The relaxation of the hyperfine field is not sufficiently fast as a paramagnet even at 77 K, which is much higher than TN1, and the inverse susceptibility of (LaS)1.14[Fe0.33(NbS2)2] deviates from the Curie-Weiss law below 100 K. These results indicate that an unusual short-range order exists above TN1. The temperature dependence of the Mössbauer spectra can be explained by phase transition of the three-dimensional TLA model with weak interlayer exchange interactions.

Unconventional topological Hall effect in skyrmion crystals caused by the topology of the lattice

NASA Astrophysics Data System (ADS)

Göbel, Börge; Mook, Alexander; Henk, Jürgen; Mertig, Ingrid

2017-03-01

The hallmark of a skyrmion crystal (SkX) is the topological Hall effect (THE). In this article we predict and explain an unconventional behavior of the topological Hall conductivity in SkXs. In simple terms, the spin texture of the skyrmions causes an inhomogeneous emergent magnetic field whose associated Lorentz force acts on the electrons. By making the emergent field homogeneous, the THE is mapped onto the quantum Hall effect (QHE). Consequently, each electronic band of the SkX is assigned to a Landau level. This correspondence of THE and QHE allows us to explain the unconventional behavior of the THE of electrons in SkXs. For example, a skyrmion crystal on a triangular lattice exhibits a quantized topological Hall conductivity with steps of 2 .e2/h below and with steps of 1 .e2/h above the van Hove singularity. On top of this, the conductivity shows a prominent sign change at the van Hove singularity. These unconventional features are deeply connected to the topology of the structural lattice.

An existence criterion for low-dimensional materials

NASA Astrophysics Data System (ADS)

Chen, Jiapeng; Wang, Biao; Hu, Yangfan

2017-10-01

The discovery of graphene and other two-dimensional (2-D) materials has stimulated a general interest in low-dimensional (low-D) materials. Whereas long time ago, Peierls (1935) and Landau's (1937) theoretical work demonstrated that any one- and two-dimensional materials could not exist in any finite temperature environment. Then, two basic issues became a central concern for many researchers: How can stable low-D materials exist? What kind of low-D materials are stable? Here, we establish an energy stability criterion for low-D materials, which seeks to provide a clear answer to these questions. For a certain kind of element, the stability of its specific low-D structure is determined by several derivatives of its interatomic potential. This atomistic-based approach is then applied to study any straight/planar, low-D, equal-bond-length elemental materials. We found that 1-D monatomic chains, 2-D honeycomb lattices, square lattices, and triangular lattices are the only four permissible structures, and the stability of these structures can only be understood by assuming multi-body interatomic potentials. Using this approach, the stable existence of graphene, silicene and germanene can be explained.

Simulations to Predict the Phase Behavior and Structure of Multipolar Colloidal Particles

NASA Astrophysics Data System (ADS)

Rutkowski, David Matthew

Colloidal particles with anisotropic charge distributions can assemble into a number of interesting structures including chains, lattices and micelles that could be useful in biotechnology, optics and electronics. The goal of this work is to understand how the properties of the colloidal particles, such as their charge distribution or shape, affect the selfassembly and phase behavior of collections of such particles. The specific aim of this work is to understand how the separation between a pair of oppositely signed charges affects the phase behavior and structure of assemblies of colloidal particles. To examine these particles, we have used both discontinuous molecular dynamics (DMD) and Monte Carlo (MC) simulation techniques. In our first study of colloidal particles with finite charge separation, we simulate systems of 2-D colloidal rods with four possible charge separations. Our simulations show that the charge separation does indeed have a large effect on the phase behavior as can be seen in the phase diagrams we construct for these four systems in the area fraction-reduced temperature plane. The phase diagrams delineate the boundaries between isotropic fluid, string-fluid and percolated fluid for all systems considered. In particular, we find that coarse gel-like structures tend to form at large charge separations while denser aggregates form at small charge separations, suggesting a route to forming low volume gels by focusing on systems with large charge separations. Next we examine systems of circular particles with four embedded charges of alternating sign fixed to a triangular lattice. This system is found to form a limit periodic structure, a theoretical structure with an infinite number of phase transitions, under specific conditions. The limit-periodic structure only forms when the rotation of the particles in the system is restricted to increments of pi/3. When the rotation is restricted to increments of th/6 or the rotation is continuous, related structures form including a striped phase and a phase with nematic order. Neither the distance from the point charges to the center of the particle nor the angle between the charges influences whether the system forms a limit-periodic structure, suggesting that point quadrupoles may also be able to form limit-periodic structures. Results from these simulations will likely aid in the quest to find an experimental realization of a limit-periodic structure. Next we examine the effect of charge separation on the self-assembly of systems of 2-D colloidal particles with off-center extended dipoles. We simulate systems with both small and large charge separations for a set of displacements of the dipole from the particle center. Upon cooling, these particles self-assemble into closed, cyclic structures at large displacements including dimers, triangular shapes and square shapes, and chain-like structures at small displacements. At extremely low temperatures, the cyclic structures form interesting lattices with particles of similar chirality grouped together. Results from this work could aid in the experimental construction of open lattice-like structures that could find use in photonic applications. Finally, we present work in collaboration with Drs. Bhuvnesh Bharti and Orlin Velev in which we investigate how the surface coverage affects the self-assembly of systems of Janus particles coated with both an iron oxide and fatty acid chain layer. We model these particles by decorating a sphere with evenly dispersed points that interact with points on other spheres through square-well interactions. The interactions are designed to mimic specific coverage values for the iron oxide/fatty acid chain layer. Structures similar to those found in experiment form readily in the simulations. The number of clusters formed as a function of surface coverage agrees well with experiment. The aggregation behavior of these novel particles can therefore, be described by a relatively simple model.

Method and apparatus for enhancing vortex pinning by conformal crystal arrays

DOEpatents

Janko, Boldizsar; Reichhardt, Cynthia; Reichhardt, Charles; Ray, Dipanjan

2015-07-14

Disclosed is a method and apparatus for strongly enhancing vortex pinning by conformal crystal arrays. The conformal crystal array is constructed by a conformal transformation of a hexagonal lattice, producing a non-uniform structure with a gradient where the local six-fold coordination of the pinning sites is preserved, and with an arching effect. The conformal pinning arrays produce significantly enhanced vortex pinning over a much wider range of field than that found for other vortex pinning geometries with an equivalent number of vortex pinning sites, such as random, square, and triangular.

Multiwavelength ultralow-threshold lasing in quantum dot photonic crystal microcavities.

PubMed

Chakravarty, S; Bhattacharya, P; Chakrabarti, S; Mi, Z

2007-05-15

We demonstrate multiwavelength lasing of resonant modes in linear (L3) microcavities in a triangular-lattice 2D photonic crystal (PC) slab. The broad spontaneous emission spectrum from coupled quantum dots, modified by the PC microcavity, is studied as a function of the intensity of incident optical excitation. We observe lasing with an ultralow-threshold power of approximately 600 nW and an output efficiency of approximately 3% at threshold. Two other resonant modes exhibit weaker turnon characteristics and thresholds of approximately 2.5 and 200 microW, respectively.

Image transfer by cascaded stack of photonic crystal and air layers.

PubMed

Shen, C; Michielsen, K; De Raedt, H

2006-01-23

We demonstrate image transfer by a cascaded stack consisting of two and three triangular-lattice photonic crystal slabs separated by air. The quality of the image transfered by the stack is sensitive to the air/photonic crystal interface termination and the frequency. Depending on the frequency and the surface termination, the image can be transfered by the stack with very little deterioration of the resolution, that is the resolution of the final image is approximately the same as the resolution of the image formed behind one single photonic crystal slab.

Etched distributed Bragg reflectors as three-dimensional photonic crystals: photonic bands and density of states.

PubMed

Pavarini, E; Andreani, L C

2002-09-01

The photonic band dispersion and density of states (DOS) are calculated for the three-dimensional (3D) hexagonal structure corresponding to a distributed Bragg reflector patterned with a 2D triangular lattice of circular holes. Results for the Si/SiO(2) and GaAs/Al(x)Ga(1-x)As systems determine the optimal parameters for which a gap in the 2D plane occurs and overlaps the 1D gap of the multilayer. The DOS is considerably reduced in correspondence with the overlap of 2D and 1D gaps. Also, the local density of states (i.e., the DOS weighted with the squared electric field at a given point) has strong variations depending on the position. Both results imply substantial changes of spontaneous emission rates and patterns for a local emitter embedded in the structure and make this system attractive for the fabrication of a 3D photonic crystal with controlled radiative properties.

Spin wave Feynman diagram vertex computation package

NASA Astrophysics Data System (ADS)

Price, Alexander; Javernick, Philip; Datta, Trinanjan

Spin wave theory is a well-established theoretical technique that can correctly predict the physical behavior of ordered magnetic states. However, computing the effects of an interacting spin wave theory incorporating magnons involve a laborious by hand derivation of Feynman diagram vertices. The process is tedious and time consuming. Hence, to improve productivity and have another means to check the analytical calculations, we have devised a Feynman Diagram Vertex Computation package. In this talk, we will describe our research group's effort to implement a Mathematica based symbolic Feynman diagram vertex computation package that computes spin wave vertices. Utilizing the non-commutative algebra package NCAlgebra as an add-on to Mathematica, symbolic expressions for the Feynman diagram vertices of a Heisenberg quantum antiferromagnet are obtained. Our existing code reproduces the well-known expressions of a nearest neighbor square lattice Heisenberg model. We also discuss the case of a triangular lattice Heisenberg model where non collinear terms contribute to the vertex interactions.

Predictive wind turbine simulation with an adaptive lattice Boltzmann method for moving boundaries

NASA Astrophysics Data System (ADS)

Deiterding, Ralf; Wood, Stephen L.

2016-09-01

Operating horizontal axis wind turbines create large-scale turbulent wake structures that affect the power output of downwind turbines considerably. The computational prediction of this phenomenon is challenging as efficient low dissipation schemes are necessary that represent the vorticity production by the moving structures accurately and that are able to transport wakes without significant artificial decay over distances of several rotor diameters. We have developed a parallel adaptive lattice Boltzmann method for large eddy simulation of turbulent weakly compressible flows with embedded moving structures that considers these requirements rather naturally and enables first principle simulations of wake-turbine interaction phenomena at reasonable computational costs. The paper describes the employed computational techniques and presents validation simulations for the Mexnext benchmark experiments as well as simulations of the wake propagation in the Scaled Wind Farm Technology (SWIFT) array consisting of three Vestas V27 turbines in triangular arrangement.

Evidence of benzenoid domains in nanographenes.

PubMed

Baldoni, Matteo; Mercuri, Francesco

2015-01-21

Calculations based on density functional theory demonstrate the occurrence of local deformations of the perfect honeycomb lattice in nanographenes to form arrangements, with triangular symmetry, composed of six-membered ring patterns. The formation of these locally regular superstructures, which can be considered as benzenoid-like domains on the 2D graphene lattice, is ascribed to the gain in resonance energy deriving from aromaticity. The relationship between the atomic morphology of nanographenes and details of the relaxed structure is rationalized in terms of Clar's theory of the aromatic sextet and by extending concepts borrowed from valence bond theory to 2D carbon nanostructures. Namely, two regular arrangements can be evidenced, defined as Clar (fully benzenoid) and Kekulé domains, which correspond to two different regular bond patterns in sets of adjacent six-membered rings. Our findings are compatible with recent experiments and have potentially relevant consequences in the development of novel electronic devices based on graphene materials.

Diffusive and martensitic nucleation kinetics in solid-solid transitions of colloidal crystals

NASA Astrophysics Data System (ADS)

Peng, Yi; Li, Wei; Wang, Feng; Still, Tim; Yodh, Arjun G.; Han, Yilong

2017-05-01

Solid-solid transitions between crystals follow diffusive nucleation, or various diffusionless transitions, but these kinetics are difficult to predict and observe. Here we observed the rich kinetics of transitions from square lattices to triangular lattices in tunable colloidal thin films with single-particle dynamics by video microscopy. Applying a small pressure gradient in defect-free regions or near dislocations markedly transform the diffusive nucleation with an intermediate-stage liquid into a martensitic generation and oscillation of dislocation pairs followed by a diffusive nucleus growth. This transformation is neither purely diffusive nor purely martensitic as conventionally assumed but a combination thereof, and thus presents new challenges to both theory and the empirical criterion of martensitic transformations. We studied how pressure, density, grain boundary, triple junction and interface coherency affect the nucleus growth, shape and kinetic pathways. These novel microscopic kinetics cast new light on control solid-solid transitions and microstructural evolutions in polycrystals.

Magnetic Property in Large Array Niobium Antidot Thin Films

NASA Astrophysics Data System (ADS)

Tinghui, Chen; Hsiang-Hsi, Kung; Wei-Li, Lee; Institute of Physics, Academia Sinica, Taipei, Taiwan Team

2014-03-01

In a superconducting ring, the total flux inside the ring is required to be an integer number of the flux quanta. Therefore, a supercurrent current can appear within the ring in order to satisfy this quantization rule, which gives rise to certain magnetic response. By using a special monolayer polymer/nanosphere hybrid we developed previously, we fabricated a series of superconducting niobium antidot thin films with different antidot diameters. The antidots form well-ordered triangular lattice with a lattice spacing about 200 nm and extend over an area larger than 1 cm2, which enables magnetic detections simply by a SQUID magnetometer. We observed magnetization oscillation with external magnetic field due to the supercurrent screening effect, where different features for large and small antidot thin films were found. Detailed size and temperature dependencies of the magnetization in niobium antidot nanostructures will be presented.

Emergence of chiral spin liquids via quantum melting of noncoplanar magnetic orders

DOE PAGES

Hickey, Ciarán; Cincio, Lukasz; Papić, Zlatko; ...

2017-09-11

Quantum spin liquids (QSLs) are highly entangled states of quantum magnets which lie beyond the Landau paradigm of classifying phases of matter via broken symmetries. A physical route to arriving at QSLs is via frustration-induced quantum melting of ordered states such as valence bond crystals or magnetic orders. Using extensive exact diagonalization (ED) and density-matrix renormalization group (DMRG)we show studies of concrete S U ( 2 ) invariant spin models on honeycomb, triangular, and square lattices, that chiral spin liquids (CSLs) emerge as descendants of triple- Q spin crystals with tetrahedral magnetic order and a large scalar spin chirality. Suchmore » ordered-to-CSL melting transitions may yield lattice realizations of effective Chern-Simons-Higgs field theories. We provides a distinct unifying perspective on the emergence of CSLs and suggests that materials with certain noncoplanar magnetic orders might provide a good starting point to search for CSLs.« less

Emergence of chiral spin liquids via quantum melting of noncoplanar magnetic orders

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hickey, Ciarán; Cincio, Lukasz; Papić, Zlatko

Quantum spin liquids (QSLs) are highly entangled states of quantum magnets which lie beyond the Landau paradigm of classifying phases of matter via broken symmetries. A physical route to arriving at QSLs is via frustration-induced quantum melting of ordered states such as valence bond crystals or magnetic orders. Using extensive exact diagonalization (ED) and density-matrix renormalization group (DMRG)we show studies of concrete S U ( 2 ) invariant spin models on honeycomb, triangular, and square lattices, that chiral spin liquids (CSLs) emerge as descendants of triple- Q spin crystals with tetrahedral magnetic order and a large scalar spin chirality. Suchmore » ordered-to-CSL melting transitions may yield lattice realizations of effective Chern-Simons-Higgs field theories. We provides a distinct unifying perspective on the emergence of CSLs and suggests that materials with certain noncoplanar magnetic orders might provide a good starting point to search for CSLs.« less

Diffusive and martensitic nucleation kinetics in solid-solid transitions of colloidal crystals

PubMed Central

Peng, Yi; Li, Wei; Wang, Feng; Still, Tim; Yodh, Arjun G.; Han, Yilong

2017-01-01

Solid–solid transitions between crystals follow diffusive nucleation, or various diffusionless transitions, but these kinetics are difficult to predict and observe. Here we observed the rich kinetics of transitions from square lattices to triangular lattices in tunable colloidal thin films with single-particle dynamics by video microscopy. Applying a small pressure gradient in defect-free regions or near dislocations markedly transform the diffusive nucleation with an intermediate-stage liquid into a martensitic generation and oscillation of dislocation pairs followed by a diffusive nucleus growth. This transformation is neither purely diffusive nor purely martensitic as conventionally assumed but a combination thereof, and thus presents new challenges to both theory and the empirical criterion of martensitic transformations. We studied how pressure, density, grain boundary, triple junction and interface coherency affect the nucleus growth, shape and kinetic pathways. These novel microscopic kinetics cast new light on control solid–solid transitions and microstructural evolutions in polycrystals. PMID:28504246

Triangular-shaped landforms reveal subglacial drainage routes in SW Finland

NASA Astrophysics Data System (ADS)

Mäkinen, J.; Kajuutti, K.; Palmu, J.-P.; Ojala, A.; Ahokangas, E.

2017-05-01

The aim of this study is to present the first evidence of triangular-shaped till landforms and related erosional features indicative of subglacial drainage within the ice stream bed of the Scandinavian ice sheet in Finland. Previously unidentified grouped patterns of Quaternary deposits with triangular landforms can be recognized from LiDAR-based DEMs. The triangular landforms occur as segments within geomorphologically distinguishable routes that are associated with eskers. The morphological and sedimentological characteristics as well as the distribution of the triangular landforms are interpreted to involve the creep of saturated deforming till, flow and pressure fluctuations of subglacial meltwater associated with meltwater erosion. There are no existing models for the formation of this kind of large-scale drainage systems, but we claim that they represent an efficient drainage system for subglacial meltwater transfer under high pressure conditions. Our hypothesis is that the routed, large-scale subglacial drainage systems described herein form a continuum between channelized (eskers) and more widely spread small-scale distributed subglacial drainage. Moreover, the transition from the conduit dominated drainage to triangular-shaped subglacial landforms takes place about 50-60 km from the ice margin. We provide an important contribution towards a more realistic representation of ice sheet hydrological drainage systems that could be used to improve paleoglaciological models and to simulate likely responses of ice sheets to increased meltwater production.

Frustrated Magnetism in Low-Dimensional Lattices

NASA Astrophysics Data System (ADS)

Tovar, Mayra

2011-12-01

In this dissertation we present the results of a theoretical investigation of spin models on two-dimensional and quasi one-dimensional lattices, all unified under the concept of quantum frustrated antiferromagnetism, and all discussing various aspects of the antiferromagnetic Heisenberg model on the kagome lattice. In the Introduction (Chapter 1), we discuss at some length such concepts as frustration and superexchange, among others, which are of common relevance in the rest of the chapters. In Chapter 2, we study the effect of Dzyaloshinskii-Moriya (DM) interactions on the zero-temperature magnetic susceptibility of systems whose low energy can be described by short-range valence bond states. Our work shows that this treatment is consistent with the experimentally observed non-vanishing susceptibility---in the specified temperature limit---of the spin-1/2 kagome antiferromagnetic compound ZnCu3(OH)6Cl2, also known as herbertsmithite. Although the objective of this work is explaining the aforementioned characteristic of the experimental system, our methods are more general and we apply them to the checkerboard and Shastry-Sutherland lattices as well. In Chapter 3, we discuss our findings in the study of ghost-mediated domain wall interactions in the diamondback ladder. These domain walls are the the spin excitations---the kinks and the antikinks---separating the ground states along one chain of the ladder. While as individual entities an antikink is energy costly and a kink energy free, our study finds that both interact via the ghosts that they produce in the opposite side of the ladder from where they are located. Through the study of these ghosts, we find that domain walls proliferate in the system above a critical value of the system's coupling constants. It is this proliferation that makes their treatment as free, non-interacting particles impossible, so we study here their interactions both quantitatively and qualitatively, in a region where the latter are yet not very strong, namely below the critical point. Based on the calculated two-body interaction potential, domain walls interact attractively (repulsively) when separated at even (odd) distances, with a strength that decays as 1/sp, where s is their separation and p<1. We also consider higher-order interactions. In the last chapter, Chapter 4, we present our study of the spin-1 kagome Heisenberg antiferromagnet. Our approach is to first consider an SU(2)-symmetric parent Hamiltonian with known ground states on the S=1 kagome lattice, in which nearest-neighbor Heisenberg interactions are already present. We then enhance these interactions by an additional Heisenberg term added perturbatively in order to move the system closer to a pure Heisenberg antiferromagnet. The results of this enhancement is obtaining a description of the system in terms of an effective Hamiltonian, namely a transverse field Ising AF on the triangular lattice. Based on the particular values of this effective Hamiltonian, our system is found to be in the order-by-disorder phase.

Itinerant electrons in the Coulomb phase

NASA Astrophysics Data System (ADS)

Jaubert, L. D. C.; Piatecki, Swann; Haque, Masudul; Moessner, R.

2012-02-01

We study the interplay between magnetic frustration and itinerant electrons. For example, how does the coupling to mobile charges modify the properties of a spin liquid, and does the underlying frustration favor insulating or conducting states? Supported by Monte Carlo simulations, our goal is in particular to provide an analytical picture of the mechanisms involved. The models under consideration exhibit Coulomb phases in two and three dimensions, where the itinerant electrons are coupled to the localized spins via double exchange interactions. Because of the Hund coupling, magnetic loops naturally emerge from the Coulomb phase and serve as conducting channels for the mobile electrons, leading to doping-dependent rearrangements of the loop ensemble in order to minimize the electronic kinetic energy. At low electron density ρ, the double exchange coupling mainly tends to segment the very long loops winding around the system into smaller ones while it gradually lifts the extensive degeneracy of the Coulomb phase with increasing ρ. For higher doping, the results are strongly lattice dependent, displaying loop crystals with a given loop length for some specific values of ρ. By varying ρ, they can melt into different mixtures of these loop crystals, recovering extensive degeneracy in the process. Finally, we contrast this to the qualitatively different behavior of analogous models on kagome or triangular lattices.

Tunable Quantum Spin Liquidity in Mo3O13 Cluster Mott Insulators

NASA Astrophysics Data System (ADS)

Akbari-Sharbaf, Arash; Ziat, Djamel; Verrier, Aime; Quilliam, Jeffrey A.; Sinclair, Ryan; Zhou, Haidong D.; Sun, Xuefeng F.

A study of a tunable quantum spin liquid (QSL) phase in the compound Li2In1- x ScxMo3O8 (x = 0.2, 0.4, 0.6, 0.8, 1) will be presented. Crystal structure of these compounds can be viewed as Mo ions arranged on an asymmetric Kagome lattice (KL), with two different Mo-Mo bond lengths, separated by nonmagnetic layers composed of Li, In, and Sc ions. Using X-ray diffraction spectroscopy, muon spin relaxation spectroscopy, bulk magnetic susceptibility and specific heat measurements we show that by changing the composition of the nonmagnetic layers we can drive the system from an ordered antiferromagnetic state to a quantum spin liquid state. The mechanism responsible for the tunability of the magnetic phase in this class of materials may be associated with the degree of asymmetry of the KL controlled by the composition of the nonmagnetic layers. For high degree of asymmetry the constraint on the electronic distribution leads to a configuration of Mo3O8 clusters with net spin-1/2 per cluster arrange on a triangular lattice and long range antiferromagnetic order. For low degree of asymmetry the electronic distribution leads to a magnetic phase with QSL character. We acknowledge support from NSERC and CFREF.

Entanglement entropy of critical spin liquids.

PubMed

Zhang, Yi; Grover, Tarun; Vishwanath, Ashvin

2011-08-05

Quantum spin liquids are phases of matter whose internal structure is not captured by a local order parameter. Particularly intriguing are critical spin liquids, where strongly interacting excitations control low energy properties. Here we calculate their bipartite entanglement entropy that characterizes their quantum structure. In particular we calculate the Renyi entropy S(2) on model wave functions obtained by Gutzwiller projection of a Fermi sea. Although the wave functions are not sign positive, S(2) can be calculated on relatively large systems (>324 spins) using the variational Monte Carlo technique. On the triangular lattice we find that entanglement entropy of the projected Fermi sea state violates the boundary law, with S(2) enhanced by a logarithmic factor. This is an unusual result for a bosonic wave function reflecting the presence of emergent fermions. These techniques can be extended to study a wide class of other phases.

Glide dislocation nucleation from dislocation nodes at semi-coherent {111} Cu–Ni interfaces

DOE PAGES

Shao, Shuai; Wang, Jian; Beyerlein, Irene J.; ...

2015-07-23

Using atomistic simulations and dislocation theory on a model system of semi-coherent {1 1 1} interfaces, we show that misfit dislocation nodes adopt multiple atomic arrangements corresponding to the creation and redistribution of excess volume at the nodes. We identified four distinctive node structures: volume-smeared nodes with (i) spiral or (ii) straight dislocation patterns, and volume-condensed nodes with (iii) triangular or (iv) hexagonal dislocation patterns. Volume-smeared nodes contain interfacial dislocations lying in the Cu–Ni interface but volume-condensed nodes contain two sets of interfacial dislocations in the two adjacent interfaces and jogs across the atomic layer between the two adjacent interfaces.more » Finally, under biaxial tension/compression applied parallel to the interface, we show that the nucleation of lattice dislocations is preferred at the nodes and is correlated with the reduction of excess volume at the nodes.« less

Spin nematics next to spin singlets

NASA Astrophysics Data System (ADS)

Yokoyama, Yuto; Hotta, Chisa

2018-05-01

We provide a route to generate nematic order in a spin-1/2 system. Unlike the well-known magnon-binding mechanism, our spin nematics requires neither the frustration effect nor spin polarization in a high field or in the vicinity of a ferromagnet, but instead appears next to the spin singlet phase. We start from a state consisting of a quantum spin-1/2 singlet dimer placed on each site of a triangular lattice, and show that interdimer ring exchange interactions efficiently dope the SU(2) triplets that itinerate and interact, easily driving a stable singlet state to either Bose-Einstein condensates or a triplet crystal, some hosting a spin nematic order. A variety of roles the ring exchange serves includes the generation of a bilinear-biquadratic interaction between nearby triplets, which is responsible for the emergent nematic order separated from the singlet phase by a first-order transition.

Systematic approaches to layered materials with strong electron correlations

NASA Astrophysics Data System (ADS)

Chung, Chung-Hou

I present systematic large-N approaches to study the ground state magnetic orderings and charge transport of layered materials with strong electron correlations, including the organic material kappa-(BEDT-TTF)2X, and the antiferromagnetic insulators Cs2CuCl4 and SrCu2(BO3) 2. I model the electronic properties of the organic materials kappa-(BEDT-TTF) 2X with a fermionic SU(N) Hubbard-Heisenberg model on an anisotropic triangular lattice. The ground state phase diagram shows a metal-insulator transition and a depression of the density of states in the metallic phase which are consistent with the experiments. The magnetic properties of kappa-(BEDT-TTF) 2X are modeled by a bosonic Sp(N) quantum Heisenberg antiferromagnet on the same lattice. The phase diagram consists of five different phases as a function of the size of the spin and the degree of frustration: the Neel ordered phase, a (pi, pi) short-range-order (SRO) phase, an incommensurate (q, q) long-range-order (LRO) phase, a (q, q) SRO phase, and a decoupled chain phase. I apply the same Sp(N) approach on the same triangular lattice to model the magnetic properties of Cs2CuCl 4 both with and without a magnetic field. At zero field, I find the ground state either exhibits incommensurate spin order, or is in a quantum disordered phase with deconfined spin-1/2 excitations and topological order. The Sp(N) calculation of spin excitation spectrum shows a large upward quantum renormalization consistent with that seen in experiments. For fields perpendicular to the plane of spin rotation, I find that the spins form an incommensurate "cone" of polarization up to a saturation field where all spins are fully polarized. There is a large quantum renormalization of the zero-field incommensuration. The results are in apparent agreement with neutron scattering experiments. Finally, the magnetic properties of the insulator SrCu2(BO 3)2 is modeled by the Sp(N) quantum antiferromagnet on the Shastry-Sutherland lattice. In addition to the familiar Neel and dimer phases, I find a confining phase with plaquette order, and a topologically ordered phase with deconfined S = 1/2 spinons and helical spin correlations. The deconfined phase is contiguous to the dimer phase, and in a regime of couplings close to those appropriate for the material.

Tool calibration system for micromachining system

DOEpatents

Miller, Donald M.

1979-03-06

A tool calibration system including a tool calibration fixture and a tool height and offset calibration insert for calibrating the position of a tool bit in a micromachining tool system. The tool calibration fixture comprises a yokelike structure having a triangular head, a cavity in the triangular head, and a port which communicates a side of the triangular head with the cavity. Yoke arms integral with the triangular head extend along each side of a tool bar and a tool head of the micromachining tool system. The yoke arms are secured to the tool bar to place the cavity around a tool bit which may be mounted to the end of the tool head. Three linear variable differential transformer's (LVDT) are adjustably mounted in the triangular head along an X axis, a Y axis, and a Z axis. The calibration insert comprises a main base which can be mounted in the tool head of the micromachining tool system in place of a tool holder and a reference projection extending from a front surface of the main base. Reference surfaces of the calibration insert and a reference surface on a tool bar standard length are used to set the three LVDT's of the calibration fixture to the tool reference position. These positions are transferred permanently to a mastering station. The tool calibration fixture is then used to transfer the tool reference position of the mastering station to the tool bit.

Localized states in a triangular set of linearly coupled complex Ginzburg-Landau equations.

PubMed

Sigler, Ariel; Malomed, Boris A; Skryabin, Dmitry V

2006-12-01

We introduce a pattern-formation model based on a symmetric system of three linearly coupled cubic-quintic complex Ginzburg-Landau equations, which form a triangular configuration. This is the simplest model of a multicore fiber laser. We identify stability regions for various types of localized patterns possible in this setting, which include stationary and breathing triangular vortices.

Pairing from strong repulsion in triangular lattice Hubbard model

NASA Astrophysics Data System (ADS)

Zhang, Shang-Shun; Zhu, Wei; Batista, Cristian D.

2018-04-01

We propose a pairing mechanism between holes in the dilute limit of doped frustrated Mott insulators. Hole pairing arises from a hole-hole-magnon three-body bound state. This pairing mechanism has its roots on single-hole kinetic energy frustration, which favors antiferromagnetic (AFM) correlations around the hole. We demonstrate that the AFM polaron (hole-magnon bound state) produced by a single hole propagating on a field-induced polarized background is strong enough to bind a second hole. The effective interaction between these three-body bound states is repulsive, implying that this pairing mechanism is relevant for superconductivity.

d +i d chiral superconductivity in a triangular lattice from trigonal bipyramidal complexes

NASA Astrophysics Data System (ADS)

Lu, Chen; Zhang, Li-Da; Wu, Xianxin; Yang, Fan; Hu, Jiangping

2018-04-01

We model the newly predicted high-Tc superconducting candidates constructed by corner-shared trigonal bipyramidal complexes with an effective three-orbital tight-binding Hamiltonian and investigate the pairing symmetry of their superconducting states driven by electron-electron interactions. Our combined weak- and strong-coupling-based calculations consistently identify the chiral d +i d superconductivity as the leading pairing symmetry in a wide doping range with realistic interaction parameters. This pairing state has a nontrivial topological Chern number and can host gapless chiral edge modes, and the vortex cores under magnetic field can carry Majorana zero modes.

Nanolattices: An Emerging Class of Mechanical Metamaterials.

PubMed

Bauer, Jens; Meza, Lucas R; Schaedler, Tobias A; Schwaiger, Ruth; Zheng, Xiaoyu; Valdevit, Lorenzo

2017-10-01

In 1903, Alexander Graham Bell developed a design principle to generate lightweight, mechanically robust lattice structures based on triangular cells; this has since found broad application in lightweight design. Over one hundred years later, the same principle is being used in the fabrication of nanolattice materials, namely lattice structures composed of nanoscale constituents. Taking advantage of the size-dependent properties typical of nanoparticles, nanowires, and thin films, nanolattices redefine the limits of the accessible material-property space throughout different disciplines. Herein, the exceptional mechanical performance of nanolattices, including their ultrahigh strength, damage tolerance, and stiffness, are reviewed, and their potential for multifunctional applications beyond mechanics is examined. The efficient integration of architecture and size-affected properties is key to further develop nanolattices. The introduction of a hierarchical architecture is an effective tool in enhancing mechanical properties, and the eventual goal of nanolattice design may be to replicate the intricate hierarchies and functionalities observed in biological materials. Additive manufacturing and self-assembly techniques enable lattice design at the nanoscale; the scaling-up of nanolattice fabrication is currently the major challenge to their widespread use in technological applications. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Two-dimensional triangular lattice and its application to lithium-intercalated layered compounds

NASA Astrophysics Data System (ADS)

Decerqueira, R. O.

1982-08-01

Good rechargeable batteries are being searched for use in electric vehicles and in energy storage during off-peak consumption periods and from solar sources. The interest in lithium intercalation compounds has been recently enhanced by the search for such batteries. The process of intercalation of lithium in several transition metal dichalcogenides can provide an emf of several volts. The progress achieved in the last decade in the investigation of these intercalates has been facilitated by the availability of the dichalcogenides as single crystals and by their chemical stability. The transition-metal dichalcogenides and their Li-intercalates are studied, with emphasis on the Li/su xTa/sub yTi/sub l-y/S2 series. The interactions between the Li atoms and the applicability of a lattice gas model to the problem of ordering of these atoms is discussed. A formulation is presented of the cluster-variation aproximation to the lattice gas problem. The single-site and the nearest-neighbor triangle basic clusters are considered as models for Li/sub x TiS2. Also a theory is presented for the effects of a random distribution of different species of host atoms, as in Ta/sub y/Ti/sub l-y/S2.

Global phase diagram and quantum spin liquids in a spin- 1 2 triangular antiferromagnet

DOE PAGES

Gong, Shou-Shu; Zhu, Wei; Zhu, Jianxin; ...

2017-08-09

For this research, we study the spin-1/2 Heisenberg model on the triangular lattice with the nearest-neighbor J 1 > 0 , the next-nearest-neighobr J 2 > 0 Heisenberg interactions, and the additional scalar chiral interaction Jχ (more » $$\\vec{S}$$ i × $$\\vec{S}$$ j ) · $$\\vec{S}$$ k for the three spins in all the triangles using large-scale density matrix renormalization group calculation on cylinder geometry. With increasing J 2 (J 2 / J 1 ≤ 0.3 ) and Jχ (Jχ / J 1 ≤ 1.0 ) interactions, we establish a quantum phase diagram with the magnetically ordered 120°, stripe, and noncoplanar tetrahedral phase. In between these magnetic order phases, we find a chiral spin liquid (CSL) phase, which is identified as a ν = 1/2 bosonic fractional quantum Hall state with possible spontaneous rotational symmetry breaking. By switching on the chiral interaction, we find that the previously identified spin liquid in the J 1 - J 2 triangular model (0.08 ≲ J 2 / J 1 ≲ 0.15) shows a phase transition to the CSL phase at very small Jχ. We also compute the spin triplet gap in both spin liquid phases, and our finite-size results suggest a large gap in the odd topological sector but a small or vanishing gap in the even sector. Lastly, we discuss the implications of our results on the nature of the spin liquid phases.« less

Charge-patterning phase transition on a surface lattice of titratable sites adjacent to an electrolyte solution

NASA Astrophysics Data System (ADS)

Shore, Joel; Thurston, George

We discuss a model for a charge-patterning phase transition on a two-dimensional square lattice of titratable sites, here regarded as protonation sites, placed on a square lattice in a dielectric medium just below the planar interface between this medium and an aqueous salt solution. Within Debye-Huckel theory, the analytical form of the electrostatic repulsion between protonated sites exhibits an approximate inverse cubic power-law decrease beyond short distances. The problem can thus be mapped onto the two-dimensional antiferromagnetic Ising model with this longer-range interaction, which we study with Monte Carlo simulations. As we increase pH, the occupation probability of a site decreases from 1 at low pH to 0 at high pH. For sufficiently-strong interaction strengths, a phase transition occurs as the occupation probability of 1/2 is approached: the charges arrange themselves into a checkerboard pattern. This ordered phase persists over a range of pH until a transition occurs back to a disordered state. This state is the analogue of the Neel state in the antiferromagnetic Ising spin model. More complicated ordered phases are expected for sufficiently strong interactions (with occupation probabilities of 1/4 and 3/4) and if the lattice is triangular rather than square. This work was supported by NIH EY018249 (GMT).

Singular ferromagnetic susceptibility of the transverse-field Ising antiferromagnet on the triangular lattice

NASA Astrophysics Data System (ADS)

Biswas, Sounak; Damle, Kedar

2018-02-01

A transverse magnetic field Γ is known to induce antiferromagnetic three-sublattice order of the Ising spins σz in the triangular lattice Ising antiferromagnet at low enough temperature. This low-temperature order is known to melt on heating in a two-step manner, with a power-law ordered intermediate temperature phase characterized by power-law correlations at the three-sublattice wave vector Q : <σz(R ⃗) σz(0 ) > ˜cos(Q .R ⃗) /|R⃗| η (T ) with the temperature-dependent power-law exponent η (T )∈(1 /9 ,1 /4 ) . Here, we use a quantum cluster algorithm to study the ferromagnetic easy-axis susceptibility χu(L ) of an L ×L sample in this power-law ordered phase. Our numerical results are consistent with a recent prediction of a singular L dependence χu(L ) ˜L2 -9 η when η (T ) is in the range (1 /9 ,2 /9 ) . This finite-size result implies, via standard scaling arguments, that the ferromagnetic susceptibility χu(B ) to a uniform field B along the easy axis is singular at intermediate temperatures in the small B limit, χu(B ) ˜|B| -4/-18 η 4 -9 η for η (T )∈(1 /9 ,2 /9 ) , although there is no ferromagnetic long-range order in the low temperature state. Additionally we establish similar two-step melting behavior (via a study of the order parameter susceptibility χQ) in the case of the ferrimagnetic three-sublattice ordered phase which is stabilized by ferromagnetic next-neighbor couplings (J2) and confirm that the ferromagnetic susceptibility obeys the predicted singular form in the associated power-law ordered phase.

Spin-1/2 Heisenberg antiferromagnet on an anisotropic triangular lattice

NASA Astrophysics Data System (ADS)

Starykh, Oleg

2007-03-01

The Triangular lattice spin-1/2 Heisenberg AntiFerromagnet (TAF) is a prototypical model of frustrated quantum magnetism. While it is believed to exhibit long-range order in the isotropic limit, changes such as spatial anisotropy can alter the delicate balance amongst competing ground states. I will describe the static and dynamic properties of the spatially anisotropic TAF, with inter-chain diagonal exchange J' much weaker than the intrachain exchange J. Treating J' as a perturbation of decoupled Heisenberg spin-1/2 chains, I find that the ground state is spontaneously dimerized in a four-fold degenerate zig-zag pattern. This dimerization instability is driven by quantum fluctuations, which are dramatically enhanced here by the frustrated nature of inter-chain exchange. A magnetic field partially relieves frustration, by canting the spins along the field direction, and causes a quantum phase transition into a magnetically-ordered spin-density-wave phase. This is followed by cone and, finally, fully polarized (saturated) phases, as a function of increasing magnetic field. I show that many of these features are in fact observed in experiments on the celebrated material Cs2CuCl4 (J'/J =1/3). I will also discuss the significant modification of the phase diagram by symmetry-breaking anisotropic Dzyaloshinskii-Moriya (DM) interactions, present in this interesting magnet. In addition to static and thermodynamic properties, the proposed ``one-dimensional'' approach offers a compelling explanation of the unusual experimentally measured dynamical structure factor of Cs2CuCl4 in terms of descendants of one-dimensional spinons. Quite generally, I find characteristic features of a momentum-dependent spinon bound state and a dispersing incoherent excitation in the structure factor, in agreement with experiments.

Polarized neutron scattering studies of chiral criticality, and new universality classes of phase transitions

NASA Astrophysics Data System (ADS)

Plakhty, V. P.; Wosnitza, J.; Kulda, J.; Brückel, Th.; Schweika, W.; Visser, D.; Gavrilov, S. V.; Moskvin, E. V.; Kremer, R. K.; Banks, M. G.

2006-11-01

Using a novel polarised neutron scattering technique, the critical exponents for the spin chirality and chiral susceptibility are determined for the triangular lattice antiferromagnet (TLA) CsMnBr 3 in the ranges of reduced temperature τ>10 -3 and τ>7×10 -3, respectively. Their values, βC=0.44(2) and γC=0.85(3), together with the scaling relation α+2β+γ=2.13(9), including the critical exponent where α for the specific heat, prove that the spin-ordering transition belongs to the XY chiral universality class. In the case of helimagnet Ho, it is found that β-2β=0.14(4), where β is the staggered magnetisation exponent. The scaling relation α+2β+γ=2 could be fulfilled with a reasonable α=0.23(4), although for the chiral critical exponents βC=0.90(2) and γC=0.69(5) one needs α=-0.49(5) in contradiction with any experimental data. As the scaling relation always holds, we assume that the spin-ordering transition in Ho is of the first order. In the quantum antiferromagnet CsCuCl 3, a triangular spin order coexists with a long-period Dzyaloshinskii helix. The Dzyaloshinskii axial vector should remove the helix chiral degeneracy, which has not been observed in reality. The critical exponent β=0.22(2) is found to be in agreement with the XY chiral scenario for a TLA. Chiral scattering above TN is very weak, probably being masked by zero-point quantum fluctuations. A modulation of the crystal structure with the periodicity of the helix is observed, indicating strong coupling of the Dzyaloshinskii-Moriya interaction with the lattice.

2d affine XY-spin model/4d gauge theory duality and deconfinement

NASA Astrophysics Data System (ADS)

Anber, Mohamed M.; Poppitz, Erich; Ünsal, Mithat

2012-04-01

We introduce a duality between two-dimensional XY-spin models with symmetry-breaking perturbations and certain four-dimensional SU(2) and SU(2)/ {{Z}_2} gauge theories, compactified on a small spatial circle {{R}^{{^{{{1},{2}}}}}} × {{S}^{{^{{1}}}}} , and considered at temperatures near the deconfinement transition. In a Euclidean set up, the theory is defined on {{R}^{{^{{2}}}}} × {{T}^{{^{{2}}}}} . Similarly, thermal gauge theories of higher rank are dual to new families of "affine" XY-spin models with perturbations. For rank two, these are related to models used to describe the melting of a 2d crystal with a triangular lattice. The connection is made through a multi-component electric-magnetic Coulomb gas representation for both systems. Perturbations in the spin system map to topological defects in the gauge theory, such as monopole-instantons or magnetic bions, and the vortices in the spin system map to the electrically charged W-bosons in field theory (or vice versa, depending on the duality frame). The duality permits one to use the two-dimensional technology of spin systems to study the thermal deconfinement and discrete chiral transitions in four-dimensional SU( N c ) gauge theories with n f ≥1 adjoint Weyl fermions.

Efficient ICCG on a shared memory multiprocessor

NASA Technical Reports Server (NTRS)

Hammond, Steven W.; Schreiber, Robert

1989-01-01

Different approaches are discussed for exploiting parallelism in the ICCG (Incomplete Cholesky Conjugate Gradient) method for solving large sparse symmetric positive definite systems of equations on a shared memory parallel computer. Techniques for efficiently solving triangular systems and computing sparse matrix-vector products are explored. Three methods for scheduling the tasks in solving triangular systems are implemented on the Sequent Balance 21000. Sample problems that are representative of a large class of problems solved using iterative methods are used. We show that a static analysis to determine data dependences in the triangular solve can greatly improve its parallel efficiency. We also show that ignoring symmetry and storing the whole matrix can reduce solution time substantially.

Optimal parallel solution of sparse triangular systems

NASA Technical Reports Server (NTRS)

Alvarado, Fernando L.; Schreiber, Robert

1990-01-01

A method for the parallel solution of triangular sets of equations is described that is appropriate when there are many right-handed sides. By preprocessing, the method can reduce the number of parallel steps required to solve Lx = b compared to parallel forward or backsolve. Applications are to iterative solvers with triangular preconditioners, to structural analysis, or to power systems applications, where there may be many right-handed sides (not all available a priori). The inverse of L is represented as a product of sparse triangular factors. The problem is to find a factored representation of this inverse of L with the smallest number of factors (or partitions), subject to the requirement that no new nonzero elements be created in the formation of these inverse factors. A method from an earlier reference is shown to solve this problem. This method is improved upon by constructing a permutation of the rows and columns of L that preserves triangularity and allow for the best possible such partition. A number of practical examples and algorithmic details are presented. The parallelism attainable is illustrated by means of elimination trees and clique trees.

Nearest-neighbor Kitaev exchange blocked by charge order in electron-doped α -RuCl3

NASA Astrophysics Data System (ADS)

Koitzsch, A.; Habenicht, C.; Müller, E.; Knupfer, M.; Büchner, B.; Kretschmer, S.; Richter, M.; van den Brink, J.; Börrnert, F.; Nowak, D.; Isaeva, A.; Doert, Th.

2017-10-01

A quantum spin liquid might be realized in α -RuCl3 , a honeycomb-lattice magnetic material with substantial spin-orbit coupling. Moreover, α -RuCl3 is a Mott insulator, which implies the possibility that novel exotic phases occur upon doping. Here, we study the electronic structure of this material when intercalated with potassium by photoemission spectroscopy, electron energy loss spectroscopy, and density functional theory calculations. We obtain a stable stoichiometry at K0.5RuCl3 . This gives rise to a peculiar charge disproportionation into formally Ru2 + (4 d6 ) and Ru3 + (4 d5 ). Every Ru 4 d5 site with one hole in the t2 g shell is surrounded by nearest neighbors of 4 d6 character, where the t2 g level is full and magnetically inert. Thus, each type of Ru site forms a triangular lattice, and nearest-neighbor interactions of the original honeycomb are blocked.

Coherent-Anomaly Method in Self-Avoiding Walk Problems

NASA Astrophysics Data System (ADS)

Hu, Xiao; Suzuki, Masuo

Self-avoiding walk (SAW), being a nonequilibrium cooperative phenomenon, is investigated with a finite-order-restricted-walk (finite-ORW or FORW) coherent-anomaly method (CAM). The coefficient β1r in the asymptotic form Cnr ≃ βlrλn1r for the total number Cnr of r-ORW's with respect to the step number n is investigated for the first time. An asymptotic form for SAW's is thus obtained from the series of FORW approximants, Cnr ≃ brgμ(1 + a/r)n, as the envelope curve Cn ≃ b(ae/g)gμnng. Numerical results are given by Cn ≃ 1.424n0.27884.1507n and Cn ≃ 1.179n0.158710.005n for the plane triangular lattice and f.c.c. lattice, respectively. A good coincidence of the total numbers estimated from the above simple formulae with exact enumerations for finite-step SAW's implies that the essential nature of SAW (non-Markov process) can be understood from FORW (Markov process) in the CAM framework.

Mechanism of Superconductivity in Quasi-Two-Dimensional Organic Conductor β-(BDA-TTP) Salts

NASA Astrophysics Data System (ADS)

Nonoyama, Yoshito; Maekawa, Yukiko; Kobayashi, Akito; Suzumura, Yoshikazu; Ito, Hiroshi

2008-09-01

We investigate theoretically the superconductivity of two-dimensional organic conductors, β-(BDA-TTP)2SbF6 and β-(BDA-TTP)2AsF6, to understand the role of the spin and charge fluctuations. The transition temperature is estimated by applying random phase approximation to an extended Hubbard model wherein realistic transfer energies are estimated by extended Hückel calculation. We find a gapless superconducting state with a dxy-like symmetry, which is consistent with the experimental results obtained by specific heat and scanning tunneling microscope. In the present model with an effectively half-filled triangular lattice, spin fluctuation competes with charge fluctuation as a mechanism of pairing interaction since both fluctuations have the same characteristic momentum q=(π,0) for V being smaller than U. This is in contrast to a model with a quarter-filled square lattice, wherein both fluctuations contribute cooperatively to pairing interaction due to fluctuations having different characteristic momenta. The resultant difference in the superconductivity of these two materials is also discussed.

Rotational Symmetry Breaking in a Trigonal Superconductor Nb-doped Bi 2 Se 3

DOE Office of Scientific and Technical Information (OSTI.GOV)

Asaba, Tomoya; Lawson, B. J.; Tinsman, Colin

2017-01-27

The search for unconventional superconductivity has been focused on materials with strong spin-orbit coupling and unique crystal lattices. Doped bismuth selenide (Bi 2Se 3) is a strong candidate, given the topological insulator nature of the parent compound and its triangular lattice. The coupling between the physical properties in the superconducting state and its underlying crystal symmetry is a crucial test for unconventional superconductivity. In this paper, we report direct evidence that the superconducting magnetic response couples strongly to the underlying trigonal crystal symmetry in the recently discovered superconductor with trigonal crystal structure, niobium (Nb)-doped Bi 2Se 3. As a result,more » the in-plane magnetic torque signal vanishes every 60°. More importantly, the superconducting hysteresis loop amplitude is enhanced along one preferred direction, spontaneously breaking the rotational symmetry. This observation indicates the presence of nematic order in the superconducting ground state of Nb-doped Bi 2Se 3.« less

Controlled calculation of the thermal conductivity for a spinon Fermi surface coupled to a U(1) gauge field

DOE Office of Scientific and Technical Information (OSTI.GOV)

Freire, Hermann, E-mail: hfreire@mit.edu

2014-10-15

Motivated by recent transport measurements on the candidate spin-liquid phase of the organic triangular lattice insulator EtMe{sub 3}Sb[Pd(dmit){sub 2}]{sub 2}, we perform a controlled calculation of the thermal conductivity at intermediate temperatures in a spin liquid system where a spinon Fermi surface is coupled to a U(1) gauge field. The present computation builds upon the double expansion approach developed by Mross et al. (2010) for small ϵ=z{sub b}−2 (where z{sub b} is the dynamical critical exponent of the gauge field) and large number of fermionic species N. Using the so-called memory matrix formalism that most crucially does not assume the existencemore » of well-defined quasiparticles at low energies in the system, we calculate the temperature dependence of the thermal conductivity κ of this model due to non-critical Umklapp scattering of the spinons for a finite N and small ϵ. Then we discuss the physical implications of such theoretical result in connection with the experimental data available in the literature.« less

Molecular dynamics for dense matter

NASA Astrophysics Data System (ADS)

Maruyama, Toshiki; Watanabe, Gentaro; Chiba, Satoshi

2012-08-01

We review a molecular dynamics method for nucleon many-body systems called quantum molecular dynamics (QMD), and our studies using this method. These studies address the structure and the dynamics of nuclear matter relevant to neutron star crusts, supernova cores, and heavy-ion collisions. A key advantage of QMD is that we can study dynamical processes of nucleon many-body systems without any assumptions about the nuclear structure. First, we focus on the inhomogeneous structures of low-density nuclear matter consisting not only of spherical nuclei but also of nuclear "pasta", i.e., rod-like and slab-like nuclei. We show that pasta phases can appear in the ground and equilibrium states of nuclear matter without assuming nuclear shape. Next, we show our simulation of compression of nuclear matter which corresponds to the collapsing stage of supernovae. With the increase in density, a crystalline solid of spherical nuclei changes to a triangular lattice of rods by connecting neighboring nuclei. Finally, we discuss fragment formation in expanding nuclear matter. Our results suggest that a generally accepted scenario based on the liquid-gas phase transition is not plausible at lower temperatures.

Towards atomic scale engineering of rare-earth-doped SiAlON ceramics through aberration-corrected scanning transmission electron microscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yurdakul, Hilmi; Idrobo Tapia, Juan C; Pennycook, Stephen J

2011-01-01

Direct visualization of rare earths in {alpha}- and {beta}-SiAlON unit-cells is performed through Z-contrast imaging technique in an aberration-corrected scanning transmission electron microscope. The preferential occupation of Yb and Ce atoms in different interstitial locations of {beta}-SiAlON lattice is demonstrated, yielding higher solubility for Yb than Ce. The triangular-like host sites in {alpha}-SiAlON unit cell accommodate more Ce atoms than hexagonal sites in {beta}-SiAlON. We think that our results will be applicable as guidelines for many kinds of rare-earth-doped materials.

Spin correlated dielectric memory and rejuvenation in multiferroic CuCrS{sub 2}

DOE Office of Scientific and Technical Information (OSTI.GOV)

Karmakar, A.; Dey, K.; Majumdar, S.

We report a rare consequence of memory effect in dielectric response (ϵ) and magnetic field induced rejuvenation in a relaxor-type multiferroic chalcogenide, CuCrS{sub 2}. Despite reasonably high conductivity, we are able to detect significant spontaneous polarization using an improvised technique verifying ferroelectric (FE) order. Concomitant appearance of both FE and antiferromagnetic orders authenticates multiferroicity. A smeared out FE transition and strong frequency dependence of the broadened peak in ϵ obeying Dynamical scaling law signify relaxor properties. We discuss the role of geometrical frustration in the antiferromagnetically coupled layered triangular lattice and metal ligand hybridization for these unusual properties.

Asymmetric Quintuplet Condensation in the Frustrated S=1 Spin Dimer Compound Ba3Mn2O8

NASA Astrophysics Data System (ADS)

Samulon, E. C.; Kohama, Y.; McDonald, R. D.; Shapiro, M. C.; Al-Hassanieh, K. A.; Batista, C. D.; Jaime, M.; Fisher, I. R.

2009-07-01

Ba3Mn2O8 is a spin-dimer compound based on pairs of S=1, 3d2, Mn5+ ions arranged on a triangular lattice. Antiferromagnetic intradimer exchange leads to a singlet ground state in zero field, with excited triplet and quintuplet states at higher energy. High field thermodynamic measurements are used to establish the phase diagram, revealing a substantial asymmetry of the quintuplet condensate. This striking effect, all but absent for the triplet condensate, is due to a fundamental asymmetry in quantum fluctuations of the paramagnetic phases near the various critical fields.

Effects of Shannon entropy and electric field on polaron in RbCl triangular quantum dot

NASA Astrophysics Data System (ADS)

M, Tiotsop; A, J. Fotue; S, C. Kenfack; N, Issofa; H, Fotsin; L, C. Fai

2016-04-01

In this paper, the time evolution of the quantum mechanical state of a polaron is examined using the Pekar type variational method on the condition of the electric-LO-phonon strong-coupling and polar angle in RbCl triangular quantum dot. We obtain the eigenenergies, and the eigenfunctions of the ground state, and the first excited state respectively. This system in a quantum dot can be treated as a two-level quantum system qubit and the numerical calculations are performed. The effects of Shannon entropy and electric field on the polaron in the RbCl triangular quantum dot are also studied.

Experimental realization of two-dimensional boron sheets

NASA Astrophysics Data System (ADS)

Feng, Baojie; Zhang, Jin; Zhong, Qing; Li, Wenbin; Li, Shuai; Li, Hui; Cheng, Peng; Meng, Sheng; Chen, Lan; Wu, Kehui

2016-06-01

A variety of two-dimensional materials have been reported in recent years, yet single-element systems such as graphene and black phosphorus have remained rare. Boron analogues have been predicted, as boron atoms possess a short covalent radius and the flexibility to adopt sp2 hybridization, features that favour the formation of two-dimensional allotropes, and one example of such a borophene material has been reported recently. Here, we present a parallel experimental work showing that two-dimensional boron sheets can be grown epitaxially on a Ag(111) substrate. Two types of boron sheet, a β12 sheet and a χ3 sheet, both exhibiting a triangular lattice but with different arrangements of periodic holes, are observed by scanning tunnelling microscopy. Density functional theory simulations agree well with experiments, and indicate that both sheets are planar without obvious vertical undulations. The boron sheets are quite inert to oxidization and interact only weakly with their substrate. We envisage that such boron sheets may find applications in electronic devices in the future.

Evidence for intertwined superfluid and density wave order in two dimensional 4He

NASA Astrophysics Data System (ADS)

Saunders, John

2015-03-01

We report the identification of a new state of quantum matter with intertwined superfluid and density wave order in a system of two dimensional bosons subject to a triangular lattice potential. Using a torsional oscillator we have measured the response of the second atomic layer of 4He adsorbed on the surface of graphite over a wide temperature range down to 2 mK. Superfluidity is observed over a narrow range of film densities, emerging suddenly and collapsing towards a quantum critical point, near to layer completion where a Mott insulating phase is predicted to form. The unusual temperature dependence of the superfluid density in the T --> 0 limit and the absence of a clear superfluid onset temperature are explained, self-consistently, by an ansatz for the excitation spectrum, reflecting density wave order, and a quasi-condensate wavefunction breaking both gauge and translational symmetry. In collaboration with Jan Nyeki, Anastasia Phillis, Andrew Ho, Derek Lee, Piers Coleman, Jeevak Parpia, Brian Cowan. Supported by EPSRC (U.K) EP/H048375/1.

Merging of the Dirac points in electronic artificial graphene

NASA Astrophysics Data System (ADS)

Feilhauer, J.; Apel, W.; Schweitzer, L.

2015-12-01

Theory predicts that graphene under uniaxial compressive strain in an armchair direction should undergo a topological phase transition from a semimetal into an insulator. Due to the change of the hopping integrals under compression, both Dirac points shift away from the corners of the Brillouin zone towards each other. For sufficiently large strain, the Dirac points merge and an energy gap appears. However, such a topological phase transition has not yet been observed in normal graphene (due to its large stiffness) neither in any other electronic system. We show numerically and analytically that such a merging of the Dirac points can be observed in electronic artificial graphene created from a two-dimensional electron gas by application of a triangular lattice of repulsive antidots. Here, the effect of strain is modeled by tuning the distance between the repulsive potentials along the armchair direction. Our results show that the merging of the Dirac points should be observable in a recent experiment with molecular graphene.

Ground-state and magnetocaloric properties of a coupled spin-electron double-tetrahedral chain (exact study at the half filling)

NASA Astrophysics Data System (ADS)

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.

The Position Control of the Surface Motor with the Poles Distribution of Triangular Lattice

NASA Astrophysics Data System (ADS)

Watada, Masaya; Katsuyama, Norikazu; Ebihara, Daiki

Recently, as for the machine tools or industrial robots, high performance, accuracy, etc. are demanded. Generally, when drive of many degrees of freedom is required in the machine tools or industrial robots, it has realized by using two or more motors. For example, two-dimensional positioning stages such as the X-Y plotter or the X-Y stage are enabling the two-dimensional drive by using each one motor in the direction of x, y. In order to use plural motors, these, however, have problems that equipment becomes large and complicate control system. From such problems, the Surface Motor (SFM) that can drive two directions by only one motor is researched. Authors have proposed SFM that considered wide range movement and the application to a curved surface. In this paper, the characteristics of the micro step drive by the open loop control are showed. Introduction of closed loop control for highly accurate positioning, moreover, is examined. The drive characteristics by each control are compared.

Quasi-continuous transition from a Fermi liquid to a spin liquid in κ-(ET)2Cu2(CN)3.

PubMed

Furukawa, Tetsuya; Kobashi, Kazuhiko; Kurosaki, Yosuke; Miyagawa, Kazuya; Kanoda, Kazushi

2018-01-22

The Mott metal-insulator transition-a manifestation of Coulomb interactions among electrons-is known as a discontinuous transition. Recent theoretical studies, however, suggest that the transition is continuous if the Mott insulator carries a spin liquid with a spinon Fermi surface. Here, we demonstrate the case of a quasi-continuous Mott transition from a Fermi liquid to a spin liquid in an organic triangular-lattice system κ-(ET) 2 Cu 2 (CN) 3 . Transport experiments performed under fine pressure tuning have found that as the Mott transition is approached, the Fermi liquid coherence temperature continuously falls to the scale of kelvins, with a divergent quasi-particle decay rate on the metal side, and the charge gap continuously closes on the insulator side. A Clausius-Clapeyron analysis provides thermodynamic evidence for the extremely weak first-order nature of the transition. These results provide additional support for the existence of a spinon Fermi surface, which becomes an electron Fermi surface when charges are delocalized.

Classification of ulnar triangular fibrocartilage complex tears. A treatment algorithm for Palmer type IB tears.

PubMed

Atzei, A; Luchetti, R; Garagnani, L

2017-05-01

The classical definition of 'Palmer Type IB' triangular fibrocartilage complex tear, includes a spectrum of clinical conditions. This review highlights the clinical and arthroscopic criteria that enable us to categorize five classes on a treatment-oriented classification system of triangular fibrocartilage complex peripheral tears. Class 1 lesions represent isolated tears of the distal triangular fibrocartilage complex without distal radio-ulnar joint instability and are amenable to arthroscopic suture. Class 2 tears include rupture of both the distal triangular fibrocartilage complex and proximal attachments of the triangular fibrocartilage complex to the fovea. Class 3 tears constitute isolated ruptures of the proximal attachment of the triangular fibrocartilage complex to the fovea; they are not visible at radio-carpal arthroscopy. Both Class 2 and Class 3 tears are diagnosed with a positive hook test and are typically associated with distal radio-ulnar joint instability. If required, treatment is through reattachment of the distal radio-ulnar ligament insertions to the fovea. Class 4 lesions are irreparable tears due to the size of the defect or to poor tissue quality and, if required, treatment is through distal radio-ulnar ligament reconstruction with tendon graft. Class 5 tears are associated with distal radio-ulnar joint arthritis and can only be treated with salvage procedures. This subdivision of type IB triangular fibrocartilage complex tear provides more insights in the pathomechanics and treatment strategies. II.

Two-dimensional liquid crystalline growth within a phase-field-crystal model.

PubMed

Tang, Sai; Praetorius, Simon; Backofen, Rainer; Voigt, Axel; Yu, Yan-Mei; Wang, Jincheng

2015-07-01

By using a two-dimensional phase-field-crystal (PFC) model, the liquid crystalline growth of the plastic triangular phase is simulated with emphasis on crystal shape and topological defect formation. The equilibrium shape of a plastic triangular crystal (PTC) grown from an isotropic phase is compared with that grown from a columnar or smectic-A (CSA) phase. While the shape of a PTC nucleus in the isotropic phase is almost identical to that of the classical PFC model, the shape of a PTC nucleus in CSA is affected by the orientation of stripes in the CSA phase, and irregular hexagonal, elliptical, octagonal, and rectangular shapes are obtained. Concerning the dynamics of the growth process, we analyze the topological structure of the nematic order, which starts from nucleation of +1/2 and -1/2 disclination pairs at the PTC growth front and evolves into hexagonal cells consisting of +1 vortices surrounded by six satellite -1/2 disclinations. It is found that the orientational and the positional order do not evolve simultaneously; the orientational order evolves behind the positional order, leading to a large transition zone, which can span over several lattice spacings.

Thermoviscoplastic analysis of fibrous periodic composites using triangular subvolumes

NASA Technical Reports Server (NTRS)

Walker, Kevin P.; Freed, Alan D.; Jordan, Eric H.

1993-01-01

The nonlinear viscoplastic behavior of fibrous periodic composites is analyzed by discretizing the unit cell into triangular subvolumes. A set of these subvolumes can be configured by the analyst to construct a representation for the unit cell of a periodic composite. In each step of the loading history, the total strain increment at any point is governed by an integral equation which applies to the entire composite. A Fourier series approximation allows the incremental stresses and strains to be determined within a unit cell of the periodic lattice. The nonlinearity arising from the viscoplastic behavior of the constituent materials comprising the composite is treated as fictitious body force in the governing integral equation. Specific numerical examples showing the stress distributions in the unit cell of a fibrous tungsten/copper metal matrix composite under viscoplastic loading conditions are given. The stress distribution resulting in the unit cell when the composite material is subjected to an overall transverse stress loading history perpendicular to the fibers is found to be highly heterogeneous, and typical homogenization techniques based on treating the stress and strain distributions within the constituent phases as homogeneous result in large errors under inelastic loading conditions.

Thermoviscoplastic analysis of fibrous periodic composites by the use of triangular subvolumes

NASA Technical Reports Server (NTRS)

Walker, Kevin P.; Freed, Alan D.; Jordan, Eric H.

1994-01-01

The non-linear viscoplastic behavior of fibrous periodic composites is analyzed by discretizing the unit cell into triangular subvolumes. A set of these subvolumes can be configured by the analyst to construct a representation for the unit cell of a periodic composite. In each step of the loading history the total strain increment at any point is governed by an integral equation which applies to the entire composite. A Fourier series approximation allows the incremental stresses and strains to be determined within a unit cell of the periodic lattice. The non-linearity arising from the viscoplastic behavior of the constituent materials comprising the composite is treated as a fictitious body force in the governing integral equation. Specific numerical examples showing the stress distributions in the unit cell of a fibrous tungsten/copper metal-matrix composite under viscoplastic loading conditions are given. The stress distribution resulting in the unit cell when the composite material is subjected to an overall transverse stress loading history perpendicular to the fibers is found to be highly heterogeneous, and typical homogenization techniques based on treating the stress and strain distributions within the constituent phases as homogeneous result in large errors under inelastic loading conditions.

Anomalous critical behavior in the polymer collapse transition of three-dimensional lattice trails.

PubMed

Bedini, Andrea; Owczarek, Aleksander L; Prellberg, Thomas

2012-07-01

Trails (bond-avoiding walks) provide an alternative lattice model of polymers to self-avoiding walks, and adding self-interaction at multiply visited sites gives a model of polymer collapse. Recently a two-dimensional model (triangular lattice) where doubly and triply visited sites are given different weights was shown to display a rich phase diagram with first- and second-order collapse separated by a multicritical point. A kinetic growth process of trails (KGTs) was conjectured to map precisely to this multicritical point. Two types of low-temperature phases, a globule phase and a maximally dense phase, were encountered. Here we investigate the collapse properties of a similar extended model of interacting lattice trails on the simple cubic lattice with separate weights for doubly and triply visited sites. Again we find first- and second-order collapse transitions dependent on the relative sizes of the doubly and triply visited energies. However, we find no evidence of a low-temperature maximally dense phase with only the globular phase in existence. Intriguingly, when the ratio of the energies is precisely that which separates the first-order from the second-order regions anomalous finite-size scaling appears. At the finite-size location of the rounded transition clear evidence exists for a first-order transition that persists in the thermodynamic limit. This location moves as the length increases, with its limit apparently at the point that maps to a KGT. However, if one fixes the temperature to sit at exactly this KGT point, then only a critical point can be deduced from the data. The resolution of this apparent contradiction lies in the breaking of crossover scaling and the difference in the shift and transition width (crossover) exponents.

Striped, honeycomb, and twisted moiré patterns in surface adsorption systems with highly degenerate commensurate ground states

NASA Astrophysics Data System (ADS)

Elder, K. R.; Achim, C. V.; Granato, E.; Ying, S. C.; Ala-Nissila, T.

2017-11-01

Atomistically thin adsorbate layers on surfaces with a lattice mismatch display complex spatial patterns and ordering due to strain-driven self-organization. In this work, a general formalism to model such ultrathin adsorption layers that properly takes into account the competition between strain and adhesion energy of the layers is presented. The model is based on the amplitude expansion of the two-dimensional phase field crystal (PFC) model, which retains atomistic length scales but allows relaxation of the layers at diffusive time scales. The specific systems considered here include cases where both the film and the adsorption potential can have either honeycomb (H) or triangular (T) symmetry. These systems include the so-called (1 ×1 ) , (√{3 }×√{3 }) R 30∘ , (2 ×2 ) , (√{7 }×√{7 }) R 19 .1∘ , and other higher order states that can contain a multitude of degenerate commensurate ground states. The relevant phase diagrams for many combinations of the H and T systems are mapped out as a function of adhesion strength and misfit strain. The coarsening patterns in some of these systems is also examined. The predictions are in good agreement with existing experimental data for selected strained ultrathin adsorption layers.

Effects on the Distal Radioulnar Joint of Ablation of Triangular Fibrocartilage Complex Tears With Radiofrequency Energy.

PubMed

Huber, Michaela; Loibl, Markus; Eder, Christoph; Kujat, Richard; Nerlich, Michael; Gehmert, Sebastian

2016-11-01

This cadaver study investigated the temperature profile in the wrist joint and distal radioulnar joint (DRUJ) during radiofrequency energy (RFE) application for triangular fibrocartilage complex resection. An arthroscopic partial resection of the triangular fibrocartilage complex using monopolar and bipolar RFE was simulated in 14 cadaver limbs. The temperature was recorded simultaneously in the DRUJ and at 6 other anatomic locations of the wrist during RFE application. The mean temperature in the DRUJ was 43.3 ± 8.2°C for the bipolar system in the ablation mode (60 W) and 30.4 ± 3.4°C for the monopolar system in the cut mode (20 W) after 30 seconds. The highest measured temperature in the DRUJ was 54.3°C for the bipolar system and 68.1°C for the monopolar system. The application of RFE for debridement or resection of the triangular fibrocartilage complex in a clinical setting can induce peak temperatures that might cause damage to the cartilage of the DRUJ. Bipolar systems produce higher mean temperatures than monopolar devices. RFE application increases the mean temperature in the DRUJ after 30 seconds to a level that may jeopardize cartilage tissue. Copyright © 2016 American Society for Surgery of the Hand. Published by Elsevier Inc. All rights reserved.

Field-design optimization with triangular heliostat pods

NASA Astrophysics Data System (ADS)

Domínguez-Bravo, Carmen-Ana; Bode, Sebastian-James; Heiming, Gregor; Richter, Pascal; Carrizosa, Emilio; Fernández-Cara, Enrique; Frank, Martin; Gauché, Paul

2016-05-01

In this paper the optimization of a heliostat field with triangular heliostat pods is addressed. The use of structures which allow the combination of several heliostats into a common pod system aims to reduce the high costs associated with the heliostat field and therefore reduces the Levelized Cost of Electricity value. A pattern-based algorithm and two pattern-free algorithms are adapted to handle the field layout problem with triangular heliostat pods. Under the Helio100 project in South Africa, a new small-scale Solar Power Tower plant has been recently constructed. The Helio100 plant has 20 triangular pods (each with 6 heliostats) whose positions follow a linear pattern. The obtained field layouts after optimization are compared against the reference field Helio100.

Mitigating crack propagation in a highly maneuverable flight vehicle using life extending control logic

NASA Astrophysics Data System (ADS)

Elshabasy, Mohamed Mostafa Yousef Bassyouny

In this research, life extending control logic is proposed to reduce the cost of treating the aging problem of military aircraft structures and to avoid catastrophic failures and fatal accidents due to undetected cracks in the airframe components. The life extending control logic is based on load tailoring to facilitate a desired stress sequence that prolongs the structural life of the cracked airframe components by exploiting certain nonlinear crack retardation phenomena. The load is tailored to include infrequent injections of a single-cycle overload or a single-cycle overload and underload. These irregular loadings have an anti-intuitive but beneficial effect, which has been experimentally validated, on the extension of the operational structural life of the aircraft. A rigid six-degree-of freedom dynamic model of a highly maneuverable air vehicle coupled with an elastic dynamic wing model is used to generate the stress history at the lower skin of the wing. A three-dimensional equivalent plate finite element model is used to calculate the stress in the cracked skin. The plate is chosen to be of uniform chord-wise and span-wise thickness where the mechanical properties are assigned using an ad-hoc approach to mimic the full scale wing model. An in-extensional 3-node triangular element is used as the gridding finite element while the aerodynamic load is calculated using the vortex-lattice method where each lattice is laid upon two triangular finite elements with common hypotenuse. The aerodynamic loads, along with the base-excitation which is due to the motion of the rigid aircraft model, are the driving forces acting on the wing finite element model. An aerodynamic control surface is modulated based on the proposed life extending control logic within an existing flight control system without requiring major modification. One of the main goals of life extending control logic is to enhance the aircraft's service life, without incurring significant loss of vehicle dynamic performance. The value of the control-surface deflection angle is modulated so that the created overstress is sufficiently below the yield stress of the panel material. The results show that extension in crack length was reduced by 40% to 75% with an absence of damage mitigation logic. Moreover, the desired structural integrity is satisfied without affecting the air vehicle dynamic performance.

Optical fabrication of large area photonic microstructures by spliced lens

NASA Astrophysics Data System (ADS)

Jin, Wentao; Song, Meng; Zhang, Xuehua; Yin, Li; Li, Hong; Li, Lin

2018-05-01

We experimentally demonstrate a convenient approach to fabricate large area photorefractive photonic microstructures by a spliced lens device. Large area two-dimensional photonic microstructures are optically induced inside an iron-doped lithium niobate crystal. The experimental setups of our method are relatively compact and stable without complex alignment devices. It can be operated in almost any optical laboratories. We analyze the induced triangular lattice microstructures by plane wave guiding, far-field diffraction pattern imaging and Brillouin-zone spectroscopy. By designing the spliced lens appropriately, the method can be easily extended to fabricate other complex large area photonic microstructures, such as quasicrystal microstructures. Induced photonic microstructures can be fixed or erased and re-recorded in the photorefractive crystal.

Buffering capability and limitations in low dispersion photonic crystal waveguides with elliptical airholes.

PubMed

Long, Fang; Tian, Huiping; Ji, Yuefeng

2010-09-01

A low dispersion photonic crystal waveguide with triangular lattice elliptical airholes is proposed for compact, high-performance optical buffering applications. In the proposed structure, we obtain a negligible-dispersion bandwidth with constant group velocity ranging from c/41 to c/256, by optimizing the major and minor axes of bulk elliptical holes and adjusting the position and the hole size of the first row adjacent to the defect. In addition, the limitations of buffer performance in a dispersion engineering waveguide are well studied. The maximum buffer capacity and the maximum data rate can reach as high as 262bits and 515 Gbits/s, respectively. The corresponding delay time is about 255.4ps.

Direct writing of tunable multi-wavelength polymer lasers on a flexible substrate.

PubMed

Zhai, Tianrui; Wang, Yonglu; Chen, Li; Zhang, Xinping

2015-08-07

Tunable multi-wavelength polymer lasers based on two-dimensional distributed feedback structures are fabricated on a transparent flexible substrate using interference ablation. A scalene triangular lattice structure was designed to support stable tri-wavelength lasing emission and was achieved through multiple exposure processes. Three wavelengths were controlled by three periods of the compound cavity. Mode competition among different cavity modes was observed by changing the pump fluence. Both a redshift and blueshift of the laser wavelength could be achieved by bending the soft substrate. These results not only provide insight into the physical mechanisms behind co-cavity polymer lasers but also introduce new laser sources and laser designs for white light lasers.

Design of a compact polarizing beam splitter based on a photonic crystal ring resonator with a triangular lattice.

PubMed

Yu, Tianbao; Huang, Jiehui; Liu, Nianhua; Yang, Jianyi; Liao, Qinghua; Jiang, Xiaoqing

2010-04-10

We propose and simulate a new kind of compact polarizing beam splitter (PBS) based on a photonic crystal ring resonator (PCRR) with complete photonic bandgaps. The two polarized states are separated far enough by resonant and nonresonant coupling between the waveguide modes and the microring modes. Some defect holes are utilized to control the beam propagation. The simulated results obtained by the finite-difference time-domain method show that high transmission (over 95%) is obtained and the polarization separation is realized with a length as short as 3.1 microm. The design of the proposed PBS can be flexible, thanks to the advantages of PCRRs.

Adaptive neural control of MIMO nonlinear systems with a block-triangular pure-feedback control structure.

PubMed

Chen, Zhenfeng; Ge, Shuzhi Sam; Zhang, Yun; Li, Yanan

2014-11-01

This paper presents adaptive neural tracking control for a class of uncertain multiinput-multioutput (MIMO) nonlinear systems in block-triangular form. All subsystems within these MIMO nonlinear systems are of completely nonaffine pure-feedback form and allowed to have different orders. To deal with the nonaffine appearance of the control variables, the mean value theorem is employed to transform the systems into a block-triangular strict-feedback form with control coefficients being couplings among various inputs and outputs. A systematic procedure is proposed for the design of a new singularity-free adaptive neural tracking control strategy. Such a design procedure can remove the couplings among subsystems and hence avoids the possible circular control construction problem. As a consequence, all the signals in the closed-loop system are guaranteed to be semiglobally uniformly ultimately bounded. Moreover, the outputs of the systems are ensured to converge to a small neighborhood of the desired trajectories. Simulation studies verify the theoretical findings revealed in this paper.

Stability of triangular lagrangian points in elliptical restricted three body problem under the radiating binary systems

NASA Astrophysics Data System (ADS)

Narayan, A.; Singh, Nutan

2014-10-01

This paper studies the stability of Triangular Lagrangian points in the model of elliptical restricted three body problem, under the assumption that both the primaries are radiating. The model proposed is applicable to the well known binary systems Achird, Luyten, αCen AB, Kruger-60, Xi-Bootis. Conditional stability of the motion around the triangular points exists for 0≤ μ≤ μ ∗, where μ is the mass ratio. The method of averaging due to Grebenikov has been exploited throughout the analysis of stability of the system. The critical mass ratio depends on the combined effects of radiation of both the primaries and eccentricity of this orbit. It is found by adopting the simulation technique that the range of stability decreases as the radiation pressure parameter increases.

Solution of Volterra and Fredholm Classes of Equations via Triangular Orthogonal Function (A Combination of Right Hand Triangular Function and Left Hand Triangular Function) and Hybrid Orthogonal Function (A Combination of Sample Hold Function and Right Hand Triangular Function)

NASA Astrophysics Data System (ADS)

Mukhopadhyay, Anirban; Ganguly, Anindita; Chatterjee, Saumya Deep

2018-04-01

In this paper the authors have dealt with seven kinds of non-linear Volterra and Fredholm classes of equations. The authors have formulated an algorithm for solving the aforementioned equation types via Hybrid Function (HF) and Triangular Function (TF) piecewise-linear orthogonal approach. In this approach the authors have reduced integral equation or integro-differential equation into equivalent system of simultaneous non-linear equation and have employed either Newton's method or Broyden's method to solve the simultaneous non-linear equations. The authors have calculated the L2-norm error and the max-norm error for both HF and TF method for each kind of equations. Through the illustrated examples, the authors have shown that the HF based algorithm produces stable result, on the contrary TF-computational method yields either stable, anomalous or unstable results.

A programmable nanoreplica molding for the fabrication of nanophotonic devices.

PubMed

Liu, Longju; Zhang, Jingxiang; Badshah, Mohsin Ali; Dong, Liang; Li, Jingjing; Kim, Seok-min; Lu, Meng

2016-03-01

The ability to fabricate periodic structures with sub-wavelength features has a great potential for impact on integrated optics, optical sensors, and photovoltaic devices. Here, we report a programmable nanoreplica molding process to fabricate a variety of sub-micrometer periodic patterns using a single mold. The process utilizes a stretchable mold to produce the desired periodic structure in a photopolymer on glass or plastic substrates. During the replica molding process, a uniaxial force is applied to the mold and results in changes of the periodic structure, which resides on the surface of the mold. Direction and magnitude of the force determine the array geometry, including the lattice constant and arrangement. By stretching the mold, 2D arrays with square, rectangular, and triangular lattice structures can be fabricated. As one example, we present a plasmonic crystal device with surface plasmon resonances determined by the force applied during molding. In addition, photonic crystal slabs with different array patterns are fabricated and characterized. This unique process offers the capability of generating various periodic nanostructures rapidly and inexpensively.

Coherent-anomaly method in self-avoiding walk problems

NASA Astrophysics Data System (ADS)

Hu, Xiao; Suzuki, Masuo

1988-06-01

Self-avoiding walk (SAW), being a nonequilibrium cooperative phenomenon, is investigated with a finite-order-restricted-walk (finite-ORW or FORW) coherent-anomaly method (CAM). The coefficient β 1 r in the asymptotic form C nr≅ β 1 r λ n1 r for the total number C nr of r- ORW's with respect to the step number n is investigated for the first time. An asymptotic form for SAW's is thus obtained form the series of FORW approximants, C nr≅ brgμ n(1 + a/r) n, as the envelope curve C n≅b(ae/g) gμ nn g. Numerical results are given by C n≅1.424 n0.27884.1507 n and C n≅1.179 n0.158710.005 n for the plane triangular lattice and f.c.c. lattice, respectively. A good coincidence of the total numbers estimated from the above simple formulae with exact enumerations for finite-step SAW's implies that the essential nature of SAW (non-Markov process) can be understood from FORW (Markov process) in the CAM framework.

A programmable nanoreplica molding for the fabrication of nanophotonic devices

PubMed Central

Liu, Longju; Zhang, Jingxiang; Badshah, Mohsin Ali; Dong, Liang; Li, Jingjing; Kim, Seok-min; Lu, Meng

2016-01-01

The ability to fabricate periodic structures with sub-wavelength features has a great potential for impact on integrated optics, optical sensors, and photovoltaic devices. Here, we report a programmable nanoreplica molding process to fabricate a variety of sub-micrometer periodic patterns using a single mold. The process utilizes a stretchable mold to produce the desired periodic structure in a photopolymer on glass or plastic substrates. During the replica molding process, a uniaxial force is applied to the mold and results in changes of the periodic structure, which resides on the surface of the mold. Direction and magnitude of the force determine the array geometry, including the lattice constant and arrangement. By stretching the mold, 2D arrays with square, rectangular, and triangular lattice structures can be fabricated. As one example, we present a plasmonic crystal device with surface plasmon resonances determined by the force applied during molding. In addition, photonic crystal slabs with different array patterns are fabricated and characterized. This unique process offers the capability of generating various periodic nanostructures rapidly and inexpensively. PMID:26925828

Magnetic phase diagram of Ba3CoSb2O9 as determined by ultrasound velocity measurements

NASA Astrophysics Data System (ADS)

Quirion, G.; Lapointe-Major, M.; Poirier, M.; Quilliam, J. A.; Dun, Z. L.; Zhou, H. D.

2015-07-01

Using high-resolution sound velocity measurements we have obtained a very precise magnetic phase diagram of Ba3CoSb2O9 , a material that is considered to be an archetype of the spin-1/2 triangular-lattice antiferromagnet. Results obtained for the field parallel to the basal plane (up to 18 T) show three phase transitions, consistent with predictions based on simple two-dimensional isotropic Heisenberg models and previous experimental investigations. The phase diagram obtained for the field perpendicular to the basal plane clearly reveals an easy-plane character of this compound and, in particular, our measurements show a single first-order phase transition at Hc 1=12.0 T which can be attributed to a spin flop between an umbrella-type configuration and a coplanar V -type order where spins lie in a plane perpendicular to the a b plane. At low temperatures, softening of the lattice within some of the ordered phases is also observed and may be a result of residual spin fluctuations.

A novel analytical model for scattering limited electron transport in nano-dimensional InAlAs/InGaAs heterostructure for cryogenic applications

NASA Astrophysics Data System (ADS)

Sharma, Neetika; Verma, Neha; Jogi, Jyotika

2017-11-01

This paper models the scattering limited electron transport in a nano-dimensional In0.52Al0.48As/In0.53Ga0.47As/InP heterostructure. An analytical model for temperature dependent sheet carrier concentration and carrier mobility in a two dimensional electron gas, confined in a triangular potential well has been developed. The model accounts for all the major scattering process including ionized impurity scattering and lattice scattering. Quantum mechanical variational technique is employed for studying the intrasubband scattering mechanism in the two dimensional electron gas. Results of various scattering limited structural parameters such as energy band-gap and functional parameters such as sheet carrier concentration, scattering rate and mobility are presented. The model corroborates the dominance of ionized impurity scattering mechanism at low temperatures and that of lattice scattering at high temperatures, both in turn limiting the carrier mobility. Net mobility obtained taking various scattering mechanisms into account has been found in agreement with earlier reported results, thus validating the model.

Anisotropy and multiband superconductivity in Sr 2 RuO 4 determined by small-angle neutron scattering studies of the vortex lattice [Anisotropy and multiband superconductivity in Sr 2 RuO 4

DOE PAGES

Kuhn, S. J.; Morgenlander, W.; Louden, E. R.; ...

2017-11-14

Despite numerous studies the exact nature of the order parameter in superconducting Sr 2RuO 4 remains unresolved. We have extended previous small-angle neutron scattering studies of the vortex lattice in this material to a wider field range, higher temperatures, and with the field applied close to both the <100> and <110> basal plane directions. Measurements at high field were made possible by the use of both spin polarization and analysis to improve the signal-to-noise ratio. Rotating the field towards the basal plane causes a distortion of the square vortex lattice observed for H // <001> and also a symmetry changemore » to a distorted triangular symmetry for fields close to <100>.The vortex lattice distortion allows us to determine the intrinsic superconducting anisotropy between the c axis and the Ru-O basal plane, yielding a value of ~60 at low temperature and low to intermediate fields. This greatly exceeds the upper critical field anisotropy of ~20 at low temperature, reminiscent of Pauli limiting. Indirect evidence for Pauli paramagnetic effects on the unpaired quasiparticles in the vortex cores are observed, but a direct detection lies below the measurement sensitivity. The superconducting anisotropy is found to be independent of temperature but increases for fields > 1 T, indicating multiband superconductvity in Sr 2RuO 4. Lastly, the temperature dependence of the scattered intensity provides further support for gap nodes or deep minima in the superconducting gap.« less

Anisotropy and multiband superconductivity in Sr 2 RuO 4 determined by small-angle neutron scattering studies of the vortex lattice [Anisotropy and multiband superconductivity in Sr 2 RuO 4

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kuhn, S. J.; Morgenlander, W.; Louden, E. R.

Despite numerous studies the exact nature of the order parameter in superconducting Sr 2RuO 4 remains unresolved. We have extended previous small-angle neutron scattering studies of the vortex lattice in this material to a wider field range, higher temperatures, and with the field applied close to both the <100> and <110> basal plane directions. Measurements at high field were made possible by the use of both spin polarization and analysis to improve the signal-to-noise ratio. Rotating the field towards the basal plane causes a distortion of the square vortex lattice observed for H // <001> and also a symmetry changemore » to a distorted triangular symmetry for fields close to <100>.The vortex lattice distortion allows us to determine the intrinsic superconducting anisotropy between the c axis and the Ru-O basal plane, yielding a value of ~60 at low temperature and low to intermediate fields. This greatly exceeds the upper critical field anisotropy of ~20 at low temperature, reminiscent of Pauli limiting. Indirect evidence for Pauli paramagnetic effects on the unpaired quasiparticles in the vortex cores are observed, but a direct detection lies below the measurement sensitivity. The superconducting anisotropy is found to be independent of temperature but increases for fields > 1 T, indicating multiband superconductvity in Sr 2RuO 4. Lastly, the temperature dependence of the scattered intensity provides further support for gap nodes or deep minima in the superconducting gap.« less

Magnetic-field-induced vortex-lattice transition in HgBa 2 CuO 4 + δ

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lee, Jeongseop A.; Xin, Yizhou; Stolt, I.

Measurements of the 17O nuclear magnetic resonance (NMR) quadrupolar spectrum of apical oxygen in HgBa 2CuO 4+δ were performed over a range of magnetic fields from 6.4–30 T in the superconducting state. Oxygen-isotope-exchanged single crystals were investigated with doping corresponding to superconducting transition temperatures from 74 K underdoped, to 78 K overdoped. The apical oxygen site was chosen since its NMR spectrum has narrow quadrupolar satellites that are well separated from any other resonance. Nonvortex contributions to the spectra can be deconvolved in the time domain to determine the local magnetic field distribution from the vortices. Numerical analysis using Brandt'smore » Ginzburg-Landau theory was used to find structural parameters of the vortex lattice, penetration depth, and coherence length as a function of magnetic field in the vortex solid phase. From this analysis we report a vortex structural transition near 15 T from an oblique lattice with an opening angle of 73° at low magnetic fields to a triangular lattice with 60° stabilized at high field. The temperature for onset of vortex dynamics has been identified from spin-spin relaxation. This is independent of the magnetic field at sufficiently high magnetic field similar to that reported for YBa 2Cu 3O 7 and Bi 2Sr 2CaCu 2O 8+δ and is correlated with mass anisotropy of the material. Here, this behavior is accounted for theoretically only in the limit of very high anisotropy.« less

3D Spin-Liquid State in an Organic Hyperkagome Lattice of Mott Dimers

NASA Astrophysics Data System (ADS)

Mizuno, Asato; Shuku, Yoshiaki; Matsushita, Michio M.; Tsuchiizu, Masahisa; Hara, Yuuki; Wada, Nobuo; Shimizu, Yasuhiro; Awaga, Kunio

2017-08-01

We report the first 3D spin liquid state of isotropic organic spins. Structural analysis, and magnetic and heat-capacity measurements were carried out for a chiral organic radical salt, (TBA) 1.5[(-)-NDI -Δ ] (TBA denotes tetrabutylammonium and NDI denotes naphthalene diimide), in which (-)-NDI -Δ forms a K4 structure due to its triangular molecular structure and an intermolecular π -π overlap between the NDI moieties. This lattice was identical to the hyperkagome lattice of S =1 /2 Mott dimers, and should exhibit 3D spin frustration. In fact, even though the high-temperature magnetic susceptibility followed the Curie-Weiss law with a negative Weiss constant of θ =-15 K , the low-temperature magnetic measurements revealed no long-range magnetic ordering down to 70 mK, and suggested the presence of a spin liquid state with a large residual paramagnetism χ0 of 8.5 ×10-6 emu g-1 at the absolute zero temperature. This was supported by the N 14 NMR measurements down to 0.38 K. Further, the low-temperature heat capacities cp down to 68 mK clearly indicated the presence of cp for the spin liquid state, which can be fitted to the power law of T0.62 in the wide temperature range 0.07-4.5 K.

Half-magnetization plateau in a Heisenberg antiferromagnet on a triangular lattice

NASA Astrophysics Data System (ADS)

Ye, Mengxing; Chubukov, Andrey V.

2017-10-01

We present the phase diagram of a 2D isotropic triangular Heisenberg antiferromagnet in a magnetic field. We consider spin-S model with nearest-neighbor (J1) and next-nearest-neighbor (J2) interactions. We focus on the range of 1 /8

Mechanics of evolving thin film structures

NASA Astrophysics Data System (ADS)

Liang, Jim

In the Stranski-Krastanov system, the lattice mismatch between the film and the substrate causes the film to break into islands. During annealing, both the surface energy and the elastic energy drive the islands to coarsen. Motivated by several related studies, we suggest that stable islands should form when a stiff ceiling is placed at a small gap above the film. We show that the role of elasticity is reversed: with the ceiling, the total elastic energy stored in the system increases as the islands coarsen laterally. Consequently, the islands select an equilibrium size to minimize the combined elastic energy and surface energy. In lithographically-induced self-assembly, when a two-phase fluid confined between parallel substrates is subjected to an electric field, one phase can self-assemble into a triangular lattice of islands in another phase. We describe a theory of the stability of the island lattice. The islands select the equilibrium diameter to minimize the combined interface energy and electrostatic energy. Furthermore, we study compressed SiGe thin film islands fabricated on a glass layer, which itself lies on a silicon wafer. Upon annealing, the glass flows, and the islands relax. A small island relaxes by in-plane expansion. A large island, however, wrinkles at the center before the in-plane relaxation arrives. The wrinkles may cause significant tensile stress in the island, leading to fracture. We model the island by the von Karman plate theory and the glass layer by the Reynolds lubrication theory. Numerical simulations evolve the in-plane expansion and the wrinkles simultaneously. We determine the critical island size, below which in-plane expansion prevails over wrinkling. Finally, in devices that integrate dissimilar materials in small dimensions, crack extension in one material often accompanies inelastic deformation in another. We analyze a channel crack advancing in an elastic film under tension, while an underlayer creeps. We use a two-dimensional shear lag model to approximate the three-dimensional fracture process. Based on the computational results, we propose new experiments to measure fracture toughness and creep laws in small structures. Similarly, we study delayed crack initiation, steady crack growth, and transient crack growth when the underlayer is viscoelastic.

Evolution of triangular topographic facets along active normal faults

NASA Astrophysics Data System (ADS)

Balogun, A.; Dawers, N. H.; Gasparini, N. M.; Giachetta, E.

2011-12-01

Triangular shaped facets, which are generally formed by the erosion of fault - bounded mountain ranges, are arguably one of the most prominent geomorphic features on active normal fault scarps. Some previous studies of triangular facet development have suggested that facet size and slope exhibit a strong linear dependency on fault slip rate, thus linking their growth directly to the kinematics of fault initiation and linkage. Other studies, however, generally conclude that there is no variation in triangular facet geometry (height and slope) with fault slip rate. The landscape of the northeastern Basin and Range Province of the western United States provides an opportunity for addressing this problem. This is due to the presence of well developed triangular facets along active normal faults, as well as spatial variations in fault scale and slip rate. In addition, the Holocene climatic record for this region suggests a dominant tectonic regime, as the faulted landscape shows little evidence of precipitation gradients associated with tectonic uplift. Using GIS-based analyses of USGS 30 m digital elevation data (DEMs) for east - central Idaho and southwestern Montana, we analyze triangular facet geometries along fault systems of varying number of constituent segments. This approach allows us to link these geometries with established patterns of along - strike slip rate variation. For this study, we consider major watersheds to include only catchments with upstream and downstream boundaries extending from the drainage divide to the mapped fault trace, respectively. In order to maintain consistency in the selection criteria for the analyzed triangular facets, only facets bounded on opposite sides by major watersheds were considered. Our preliminary observations reflect a general along - strike increase in the surface area, average slope, and relief of triangular facets from the tips of the fault towards the center. We attribute anomalies in the along - strike geometric measurements of the triangular facets to represent possible locations of fault segment linkage associated with normal fault evolution.

Adaptive Neural Output-Feedback Control for a Class of Nonlower Triangular Nonlinear Systems With Unmodeled Dynamics.

PubMed

Wang, Huanqing; Liu, Peter Xiaoping; Li, Shuai; Wang, Ding

2017-08-29

This paper presents the development of an adaptive neural controller for a class of nonlinear systems with unmodeled dynamics and immeasurable states. An observer is designed to estimate system states. The structure consistency of virtual control signals and the variable partition technique are combined to overcome the difficulties appearing in a nonlower triangular form. An adaptive neural output-feedback controller is developed based on the backstepping technique and the universal approximation property of the radial basis function (RBF) neural networks. By using the Lyapunov stability analysis, the semiglobally and uniformly ultimate boundedness of all signals within the closed-loop system is guaranteed. The simulation results show that the controlled system converges quickly, and all the signals are bounded. This paper is novel at least in the two aspects: 1) an output-feedback control strategy is developed for a class of nonlower triangular nonlinear systems with unmodeled dynamics and 2) the nonlinear disturbances and their bounds are the functions of all states, which is in a more general form than existing results.

An analytical design procedure for the determination of effective leading edge extensions on thick delta wings

NASA Technical Reports Server (NTRS)

Ghaffari, F.; Chaturvedi, S. K.

1984-01-01

An analytical design procedure for leading edge extensions (LEE) was developed for thick delta wings. This LEE device is designed to be mounted to a wing along the pseudo-stagnation stream surface associated with the attached flow design lift coefficient of greater than zero. The intended purpose of this device is to improve the aerodynamic performance of high subsonic and low supersonic aircraft at incidences above that of attached flow design lift coefficient, by using a vortex system emanating along the leading edges of the device. The low pressure associated with these vortices would act on the LEE upper surface and the forward facing area at the wing leading edges, providing an additional lift and effective leading edge thrust recovery. The first application of this technique was to a thick, round edged, twisted and cambered wing of approximately triangular planform having a sweep of 58 deg and aspect ratio of 2.30. The panel aerodynamics and vortex lattice method with suction analogy computer codes were employed to determine the pseudo-stagnation stream surface and an optimized LEE planform shape.

Controlling the energy of defects and interfaces in the amplitude expansion of the phase-field crystal model

NASA Astrophysics Data System (ADS)

Salvalaglio, Marco; Backofen, Rainer; Voigt, Axel; Elder, Ken R.

2017-08-01

One of the major difficulties in employing phase-field crystal (PFC) modeling and the associated amplitude (APFC) formulation is the ability to tune model parameters to match experimental quantities. In this work, we address the problem of tuning the defect core and interface energies in the APFC formulation. We show that the addition of a single term to the free-energy functional can be used to increase the solid-liquid interface and defect energies in a well-controlled fashion, without any major change to other features. The influence of the newly added term is explored in two-dimensional triangular and honeycomb structures as well as bcc and fcc lattices in three dimensions. In addition, a finite-element method (FEM) is developed for the model that incorporates a mesh refinement scheme. The combination of the FEM and mesh refinement to simulate amplitude expansion with a new energy term provides a method of controlling microscopic features such as defect and interface energies while simultaneously delivering a coarse-grained examination of the system.

Highly birefringent large negative dispersion-flattened photonic crystal fibre for broadband residual dispersion compensation

NASA Astrophysics Data System (ADS)

Faisal, Mohammad; Bala, Animesh; Roy Chowdhury, Kanan; Mia, Md. Borhan

2018-07-01

A triangular lattice photonic crystal fibre is presented in this paper for residual dispersion compensation. The fibre exhibits a flattened negative dispersion of -992.01 ± 6.93 ps/(nm-km) over S+C+L wavelength bands and -995.83 ± 0.42 ps/(nm-km) over C-band. The birefringence is about 4.4 × 10-2 at the excitation wavelength of 1550 nm which is also very high. Full vector finite element method (FEM) with a perfectly matched absorbing layer (PML) boundary condition is applied to numerically investigate the guiding properties of this PCF. The fibre operates at fundamental mode only. All these properties endorse this fibre as a suitable candidate for compensating residual dispersion and polarization maintaining applications.

Roles of spin fluctuation and frustration in the superconductivity of β-(BDA-TTP)2X (X=SbF6,AsF6) under uniaxial compression

NASA Astrophysics Data System (ADS)

Ito, Hiroshi; Ishihara, Tetsuo; Tanaka, Hisaaki; Kuroda, Shin-Ichi; Suzuki, Takeo; Onari, Seiichiro; Tanaka, Yukio; Yamada, Jun-Ichi; Kikuchi, Koichi

2008-11-01

β -type BDA-TTP [ BDA-TTP=2,5 -bis(1,3-dithian-2-ylidene)-1,3,4,6-tetrathiapentalene] salts possess high transition temperatures TC reaching 7 K among organic superconductors. TC of β-(BDA-TTP)2X (X=SbF6,AsF6) is studied by resistive measurements under uniaxial compression. TC once increases and takes a maximum under compression parallel to the donor stack while it decreases under compression perpendicular to the donor stack. These results are in agreement with the half-filled Hubbard model on the triangular lattice in which the compression controls the spin fluctuation and frustration in the weak pressure region.

Inhomogeneous field induced magnetoelectric effect in Mott insulators

DOE Office of Scientific and Technical Information (OSTI.GOV)

Boulaevskii, Lev N; Batista, Cristian D

2008-01-01

We consider a Mott insulator like HoMnO{sub 3} whose magnetic lattice is geometrically frustrated and comprises a 3D array of triangular layers with magnetic moments ordered in a 120{sup o} structure. We show that the effect of a uniform magnetic field gradient, {gradient}H, is to redistribute the electronic charge of the magnetically ordered phase leading to a unfirom electric field gradient. The resulting voltage difference between the crystal edges is proportional to the square of the crystal thickness, or inter-edge distance, L. It can reach values of several volts for |{gradient}H| {approx} 0.01 T/cm and L {approx_equal} 1mm, as longmore » as the crystal is free of antiferromagnetic domain walls.« less

Nonlinear vibrations of thin arbitrarily laminated composite plates subjected to harmonic excitations using DKT elements

NASA Astrophysics Data System (ADS)

Chiang, C. K.; Xue, David Y.; Mei, Chuh

1993-04-01

A finite element formulation is presented for determining the large-amplitude free and steady-state forced vibration response of arbitrarily laminated anisotropic composite thin plates using the Discrete Kirchhoff Theory (DKT) triangular elements. The nonlinear stiffness and harmonic force matrices of an arbitrarily laminated composite triangular plate element are developed for nonlinear free and forced vibration analyses. The linearized updated-mode method with nonlinear time function approximation is employed for the solution of the system nonlinear eigenvalue equations. The amplitude-frequency relations for convergence with gridwork refinement, triangular plates, different boundary conditions, lamination angles, number of plies, and uniform versus concentrated loads are presented.

Nonlinear vibrations of thin arbitrarily laminated composite plates subjected to harmonic excitations using DKT elements

NASA Technical Reports Server (NTRS)

Chiang, C. K.; Xue, David Y.; Mei, Chuh

1993-01-01

A finite element formulation is presented for determining the large-amplitude free and steady-state forced vibration response of arbitrarily laminated anisotropic composite thin plates using the Discrete Kirchhoff Theory (DKT) triangular elements. The nonlinear stiffness and harmonic force matrices of an arbitrarily laminated composite triangular plate element are developed for nonlinear free and forced vibration analyses. The linearized updated-mode method with nonlinear time function approximation is employed for the solution of the system nonlinear eigenvalue equations. The amplitude-frequency relations for convergence with gridwork refinement, triangular plates, different boundary conditions, lamination angles, number of plies, and uniform versus concentrated loads are presented.

Comparison of two-transsacral-screw fixation versus triangular osteosynthesis for transforaminal sacral fractures.

PubMed

Min, Kyong S; Zamorano, David P; Wahba, George M; Garcia, Ivan; Bhatia, Nitin; Lee, Thay Q

2014-09-01

Transforaminal pelvic fractures are high-energy injuries that are translationally and rotationally unstable. This study compared the biomechanical stability of triangular osteosynthesis vs 2-transsacral-screw fixation in the repair of a transforaminal pelvic fracture model. A transforaminal fracture model was created in 10 cadaveric lumbopelvic specimens. Five of the specimens were stabilized with triangular osteosynthesis, which consisted of unilateral L5-to-ilium lumbopelvic fixation and ipsilateral iliosacral screw fixation. The remaining 5 were stabilized with a 2-transsacral-screw fixation technique that consisted of 2 transsacral screws inserted across S1. All specimens were loaded cyclically and then loaded to failure. Translation and rotation were measured using the MicroScribe 3D digitizing system (Revware Inc, Raleigh, North Carolina). The 2-transsacral-screw group showed significantly greater stiffness than the triangular osteosynthesis group (2-transsacral-screw group, 248.7 N/mm [standard deviation, 73.9]; triangular osteosynthesis group, 125.0 N/mm [standard deviation, 66.9]; P=.02); however, ultimate load and rotational stiffness were not statistically significant. Compared with triangular osteosynthesis fixation, the use of 2 transsacral screws provides a comparable biomechanical stability profile in both translation and rotation. This newly revised 2-transsacral-screw construct offers the traumatologist an alternative method of repair for vertical shear fractures that provides biplanar stability. It also offers the advantage of percutaneous placement in either the prone or supine position. Copyright 2014, SLACK Incorporated.

Measurements of Elliptic and Triangular Flow in High-Multiplicity 3He+Au Collisions at √(s(NN))=200 GeV.

PubMed

Adare, A; Afanasiev, S; Aidala, C; Ajitanand, N N; Akiba, Y; Akimoto, R; Al-Bataineh, H; Alexander, J; Alfred, M; Al-Ta'ani, H; Andrews, K R; Angerami, A; Aoki, K; Apadula, N; Aphecetche, L; Appelt, E; Aramaki, Y; Armendariz, R; Aronson, S H; Asai, J; Asano, H; Aschenauer, E C; Atomssa, E T; Averbeck, R; Awes, T C; Azmoun, B; Babintsev, V; Bai, M; Baksay, G; Baksay, L; Baldisseri, A; Bandara, N S; Bannier, B; Barish, K N; Barnes, P D; Bassalleck, B; Basye, A T; Bathe, S; Batsouli, S; Baublis, V; Baumann, C; Bazilevsky, A; Beaumier, M; Beckman, S; Belikov, S; Belmont, R; Ben-Benjamin, J; Bennett, R; Berdnikov, A; Berdnikov, Y; Bhom, J H; Bickley, A A; Blau, D S; Boissevain, J G; Bok, J S; Borel, H; Boyle, K; Brooks, M L; Broxmeyer, D; Bryslawskyj, J; Buesching, H; Bumazhnov, V; Bunce, G; Butsyk, S; Camacho, C M; Campbell, S; Caringi, A; Castera, P; Chang, B S; Chang, W C; Charvet, J-L; Chen, C-H; Chernichenko, S; Chi, C Y; Chiba, J; Chiu, M; Choi, I J; Choi, J B; Choudhury, R K; Christiansen, P; Chujo, T; Chung, P; Churyn, A; Chvala, O; Cianciolo, V; Citron, Z; Cleven, C R; Cole, B A; Comets, M P; Conesa del Valle, Z; Connors, M; Constantin, P; Csanád, M; Csörgő, T; Dahms, T; Dairaku, S; Danchev, I; Danley, D; Das, K; Datta, A; Daugherity, M S; David, G; Dayananda, M K; Deaton, M B; DeBlasio, K; Dehmelt, K; Delagrange, H; Denisov, A; d'Enterria, D; Deshpande, A; Desmond, E J; Dharmawardane, K V; Dietzsch, O; Dion, A; Diss, P B; Do, J H; Donadelli, M; D'Orazio, L; Drapier, O; Drees, A; Drees, K A; Dubey, A K; Durham, J M; Durum, A; Dutta, D; Dzhordzhadze, V; Edwards, S; Efremenko, Y V; Egdemir, J; Ellinghaus, F; Emam, W S; Engelmore, T; Enokizono, A; En'yo, H; Esumi, S; Eyser, K O; Fadem, B; Feege, N; Fields, D E; Finger, M; Finger, M; Fleuret, F; Fokin, S L; Fraenkel, Z; Frantz, J E; Franz, A; Frawley, A D; Fujiwara, K; Fukao, Y; Fusayasu, T; Gadrat, S; Gal, C; Gallus, P; Garg, P; Garishvili, I; Ge, H; Giordano, F; Glenn, A; Gong, H; Gong, X; Gonin, M; Gosset, J; Goto, Y; Granier de Cassagnac, R; Grau, N; Greene, S V; Grim, G; Grosse Perdekamp, M; Gu, Y; Gunji, T; Guo, L; Gustafsson, H-Å; Hachiya, T; Hadj Henni, A; Haegemann, C; Haggerty, J S; Hahn, K I; Hamagaki, H; Hamblen, J; Hamilton, H F; Han, R; Han, S Y; Hanks, J; Harada, H; Harper, C; Hartouni, E P; Haruna, K; Hasegawa, S; Haseler, T O S; Hashimoto, K; Haslum, E; Hayano, R; He, X; Heffner, M; Hemmick, T K; Hester, T; Hiejima, H; Hill, J C; Hobbs, R; Hohlmann, M; Hollis, R S; Holzmann, W; Homma, K; Hong, B; Horaguchi, T; Hori, Y; Hornback, D; Hoshino, T; Hotvedt, N; Huang, J; Huang, S; Ichihara, T; Ichimiya, R; Iinuma, H; Ikeda, Y; Imai, K; Imrek, J; Inaba, M; Inoue, Y; Iordanova, A; Isenhower, D; Isenhower, L; Ishihara, M; Isobe, T; Issah, M; Isupov, A; Ivanishchev, D; Iwanaga, Y; Jacak, B V; Jezghani, M; Jia, J; Jiang, X; Jin, J; Jinnouchi, O; John, D; Johnson, B M; Jones, T; Joo, K S; Jouan, D; Jumper, D S; Kajihara, F; Kametani, S; Kamihara, N; Kamin, J; Kanda, S; Kaneta, M; Kaneti, S; Kang, B H; Kang, J H; Kang, J S; Kanou, H; Kapustinsky, J; Karatsu, K; Kasai, M; Kawall, D; Kawashima, M; Kazantsev, A V; Kempel, T; Key, J A; Khachatryan, V; Khanzadeev, A; Kijima, K M; Kikuchi, J; Kim, A; Kim, B I; Kim, C; Kim, D H; Kim, D J; Kim, E; Kim, E-J; Kim, G W; Kim, M; Kim, S H; Kim, Y-J; Kim, Y K; Kimelman, B; Kinney, E; Kiriluk, K; Kiss, Á; Kistenev, E; Kitamura, R; Kiyomichi, A; Klatsky, J; Klay, J; Klein-Boesing, C; Kleinjan, D; Kline, P; Koblesky, T; Kochenda, L; Kochetkov, V; Komkov, B; Konno, M; Koster, J; Kotchetkov, D; Kotov, D; Kozlov, A; Král, A; Kravitz, A; Kubart, J; Kunde, G J; Kurihara, N; Kurita, K; Kurosawa, M; Kweon, M J; Kwon, Y; Kyle, G S; Lacey, R; Lai, Y S; Lajoie, J G; Layton, D; Lebedev, A; Lee, D M; Lee, J; Lee, K B; Lee, K S; Lee, M K; Lee, S; Lee, S H; Lee, S R; Lee, T; Leitch, M J; Leite, M A L; Lenzi, B; Li, X; Lichtenwalner, P; Liebing, P; Lim, S H; Linden Levy, L A; Liška, T; Litvinenko, A; Liu, H; Liu, M X; Love, B; Lynch, D; Maguire, C F; Makdisi, Y I; Makek, M; Malakhov, A; Malik, M D; Manion, A; Manko, V I; Mannel, E; Mao, Y; Mašek, L; Masui, H; Matathias, F; McCumber, M; McGaughey, P L; McGlinchey, D; McKinney, C; Means, N; Meles, A; Mendoza, M; Meredith, B; Miake, Y; Mibe, T; Mignerey, A C; Mikeš, P; Miki, K; Miller, T E; Milov, A; Mioduszewski, S; Mishra, D K; Mishra, M; Mitchell, J T; Mitrovski, M; Miyachi, Y; Miyasaka, S; Mizuno, S; Mohanty, A K; Montuenga, P; Moon, H J; Moon, T; Morino, Y; Morreale, A; Morrison, D P; Motschwiller, S; Moukhanova, T V; Mukhopadhyay, D; Murakami, T; Murata, J; Mwai, A; Nagamiya, S; Nagashima, K; Nagata, Y; Nagle, J L; Naglis, M; Nagy, M I; Nakagawa, I; Nakagomi, H; Nakamiya, Y; Nakamura, K R; Nakamura, T; Nakano, K; Nam, S; Nattrass, C; Netrakanti, P K; Newby, J; Nguyen, M; Nihashi, M; Niida, T; Nishimura, S; Norman, B E; Nouicer, R; Novak, T; Novitzky, N; Nyanin, A S; Oakley, C; O'Brien, E; Oda, S X; Ogilvie, C A; Ohnishi, H; Oka, M; Okada, K; Omiwade, O O; Onuki, Y; Orjuela Koop, J D; Osborn, J D; Oskarsson, A; Ouchida, M; Ozawa, K; Pak, R; Pal, D; Palounek, A P T; Pantuev, V; Papavassiliou, V; Park, B H; Park, I H; Park, J; Park, J S; Park, S; Park, S K; Park, W J; Pate, S F; Patel, L; Patel, M; Pei, H; Peng, J-C; Pereira, H; Perepelitsa, D V; Perera, G D N; Peresedov, V; Peressounko, D Yu; Perry, J; Petti, R; Pinkenburg, C; Pinson, R; Pisani, R P; Proissl, M; Purschke, M L; Purwar, A K; Qu, H; Rak, J; Rakotozafindrabe, A; Ramson, B J; Ravinovich, I; Read, K F; Rembeczki, S; Reuter, M; Reygers, K; Reynolds, D; Riabov, V; Riabov, Y; Richardson, E; Rinn, T; Roach, D; Roche, G; Rolnick, S D; Romana, A; Rosati, M; Rosen, C A; Rosendahl, S S E; Rosnet, P; Rowan, Z; Rubin, J G; Rukoyatkin, P; Ružička, P; Rykov, V L; Sahlmueller, B; Saito, N; Sakaguchi, T; Sakai, S; Sakashita, K; Sakata, H; Sako, H; Samsonov, V; Sano, S; Sarsour, M; Sato, S; Sato, T; Savastio, M; Sawada, S; Schaefer, B; Schmoll, B K; Sedgwick, K; Seele, J; Seidl, R; Semenov, A Yu; Semenov, V; Sen, A; Seto, R; Sett, P; Sexton, A; Sharma, D; Shein, I; Shevel, A; Shibata, T-A; Shigaki, K; Shim, H H; Shimomura, M; Shoji, K; Shukla, P; Sickles, A; Silva, C L; Silvermyr, D; Silvestre, C; Sim, K S; Singh, B K; Singh, C P; Singh, V; Skutnik, S; Slunečka, M; Snowball, M; Sodre, T; Soldatov, A; Soltz, R A; Sondheim, W E; Sorensen, S P; Sourikova, I V; Staley, F; Stankus, P W; Stenlund, E; Stepanov, M; Ster, A; Stoll, S P; Sugitate, T; Suire, C; Sukhanov, A; Sumita, T; Sun, J; Sziklai, J; Tabaru, T; Takagi, S; Takagui, E M; Takahara, A; Taketani, A; Tanabe, R; Tanaka, Y; Taneja, S; Tanida, K; Tannenbaum, M J; Tarafdar, S; Taranenko, A; Tarján, P; Tennant, E; Themann, H; Thomas, D; Thomas, T L; Tieulent, R; Timilsina, A; Todoroki, T; Togawa, M; Toia, A; Tojo, J; Tomášek, L; Tomášek, M; Tomita, Y; Torii, H; Towell, C L; Towell, R; Towell, R S; Tram, V-N; Tserruya, I; Tsuchimoto, Y; Utsunomiya, K; Vale, C; Valle, H; van Hecke, H W; Vazquez-Zambrano, E; Veicht, A; Velkovska, J; Vértesi, R; Vinogradov, A A; Virius, M; Vossen, A; Vrba, V; Vznuzdaev, E; Wagner, M; Walker, D; Wang, X R; Watanabe, D; Watanabe, K; Watanabe, Y; Watanabe, Y S; Wei, F; Wei, R; Wessels, J; White, A S; White, S N; Winter, D; Woody, C L; Wright, R M; Wysocki, M; Xia, B; Xie, W; Xue, L; Yalcin, S; Yamaguchi, Y L; Yamaura, K; Yang, R; Yanovich, A; Yasin, Z; Ying, J; Yokkaichi, S; Yoo, J H; Yoo, J S; Yoon, I; You, Z; Young, G R; Younus, I; Yu, H; Yushmanov, I E; Zajc, W A; Zaudtke, O; Zelenski, A; Zhang, C; Zhou, S; Zimamyi, J; Zolin, L; Zou, L

2015-10-02

We present the first measurement of elliptic (v(2)) and triangular (v(3)) flow in high-multiplicity (3)He+Au collisions at √(s(NN))=200  GeV. Two-particle correlations, where the particles have a large separation in pseudorapidity, are compared in (3)He+Au and in p+p collisions and indicate that collective effects dominate the second and third Fourier components for the correlations observed in the (3)He+Au system. The collective behavior is quantified in terms of elliptic v(2) and triangular v(3) anisotropy coefficients measured with respect to their corresponding event planes. The v(2) values are comparable to those previously measured in d+Au collisions at the same nucleon-nucleon center-of-mass energy. Comparisons with various theoretical predictions are made, including to models where the hot spots created by the impact of the three (3)He nucleons on the Au nucleus expand hydrodynamically to generate the triangular flow. The agreement of these models with data may indicate the formation of low-viscosity quark-gluon plasma even in these small collision systems.

Measurements of Elliptic and Triangular Flow in High-Multiplicity 3He +Au Collisions at √{sN N }=200 GeV

NASA Astrophysics Data System (ADS)

Adare, A.; Afanasiev, S.; Aidala, C.; Ajitanand, N. N.; Akiba, Y.; Akimoto, R.; Al-Bataineh, H.; Alexander, J.; Alfred, M.; Al-Ta'Ani, H.; Andrews, K. R.; Angerami, A.; Aoki, K.; Apadula, N.; Aphecetche, L.; Appelt, E.; Aramaki, Y.; Armendariz, R.; Aronson, S. H.; Asai, J.; Asano, H.; Aschenauer, E. C.; Atomssa, E. T.; Averbeck, R.; Awes, T. C.; Azmoun, B.; Babintsev, V.; Bai, M.; Baksay, G.; Baksay, L.; Baldisseri, A.; Bandara, N. S.; Bannier, B.; Barish, K. N.; Barnes, P. D.; Bassalleck, B.; Basye, A. T.; Bathe, S.; Batsouli, S.; Baublis, V.; Baumann, C.; Bazilevsky, A.; Beaumier, M.; Beckman, S.; Belikov, S.; Belmont, R.; Ben-Benjamin, J.; Bennett, R.; Berdnikov, A.; Berdnikov, Y.; Bhom, J. H.; Bickley, A. A.; Blau, D. S.; Boissevain, J. G.; Bok, J. S.; Borel, H.; Boyle, K.; Brooks, M. L.; Broxmeyer, D.; Bryslawskyj, J.; Buesching, H.; Bumazhnov, V.; Bunce, G.; Butsyk, S.; Camacho, C. M.; Campbell, S.; Caringi, A.; Castera, P.; Chang, B. S.; Chang, W. C.; Charvet, J.-L.; Chen, C.-H.; Chernichenko, S.; Chi, C. Y.; Chiba, J.; Chiu, M.; Choi, I. J.; Choi, J. B.; Choudhury, R. K.; Christiansen, P.; Chujo, T.; Chung, P.; Churyn, A.; Chvala, O.; Cianciolo, V.; Citron, Z.; Cleven, C. R.; Cole, B. A.; Comets, M. P.; Conesa Del Valle, Z.; Connors, M.; Constantin, P.; Csanád, M.; Csörgő, T.; Dahms, T.; Dairaku, S.; Danchev, I.; Danley, D.; Das, K.; Datta, A.; Daugherity, M. S.; David, G.; Dayananda, M. K.; Deaton, M. B.; Deblasio, K.; Dehmelt, K.; Delagrange, H.; Denisov, A.; D'Enterria, D.; Deshpande, A.; Desmond, E. J.; Dharmawardane, K. V.; Dietzsch, O.; Dion, A.; Diss, P. B.; Do, J. H.; Donadelli, M.; D'Orazio, L.; Drapier, O.; Drees, A.; Drees, K. A.; Dubey, A. K.; Durham, J. M.; Durum, A.; Dutta, D.; Dzhordzhadze, V.; Edwards, S.; Efremenko, Y. V.; Egdemir, J.; Ellinghaus, F.; Emam, W. S.; Engelmore, T.; Enokizono, A.; En'yo, H.; Esumi, S.; Eyser, K. O.; Fadem, B.; Feege, N.; Fields, D. E.; Finger, M.; Finger, M.; Fleuret, F.; Fokin, S. L.; Fraenkel, Z.; Frantz, J. E.; Franz, A.; Frawley, A. D.; Fujiwara, K.; Fukao, Y.; Fusayasu, T.; Gadrat, S.; Gal, C.; Gallus, P.; Garg, P.; Garishvili, I.; Ge, H.; Giordano, F.; Glenn, A.; Gong, H.; Gong, X.; Gonin, M.; Gosset, J.; Goto, Y.; Granier de Cassagnac, R.; Grau, N.; Greene, S. V.; Grim, G.; Grosse Perdekamp, M.; Gu, Y.; Gunji, T.; Guo, L.; Gustafsson, H.-Å.; Hachiya, T.; Hadj Henni, A.; Haegemann, C.; Haggerty, J. S.; Hahn, K. I.; Hamagaki, H.; Hamblen, J.; Hamilton, H. F.; Han, R.; Han, S. Y.; Hanks, J.; Harada, H.; Harper, C.; Hartouni, E. P.; Haruna, K.; Hasegawa, S.; Haseler, T. O. S.; Hashimoto, K.; Haslum, E.; Hayano, R.; He, X.; Heffner, M.; Hemmick, T. K.; Hester, T.; Hiejima, H.; Hill, J. C.; Hobbs, R.; Hohlmann, M.; Hollis, R. S.; Holzmann, W.; Homma, K.; Hong, B.; Horaguchi, T.; Hori, Y.; Hornback, D.; Hoshino, T.; Hotvedt, N.; Huang, J.; Huang, S.; Ichihara, T.; Ichimiya, R.; Iinuma, H.; Ikeda, Y.; Imai, K.; Imrek, J.; Inaba, M.; Inoue, Y.; Iordanova, A.; Isenhower, D.; Isenhower, L.; Ishihara, M.; Isobe, T.; Issah, M.; Isupov, A.; Ivanishchev, D.; Iwanaga, Y.; Jacak, B. V.; Jezghani, M.; Jia, J.; Jiang, X.; Jin, J.; Jinnouchi, O.; John, D.; Johnson, B. M.; Jones, T.; Joo, K. S.; Jouan, D.; Jumper, D. S.; Kajihara, F.; Kametani, S.; Kamihara, N.; Kamin, J.; Kanda, S.; Kaneta, M.; Kaneti, S.; Kang, B. H.; Kang, J. H.; Kang, J. S.; Kanou, H.; Kapustinsky, J.; Karatsu, K.; Kasai, M.; Kawall, D.; Kawashima, M.; Kazantsev, A. V.; Kempel, T.; Key, J. A.; Khachatryan, V.; Khanzadeev, A.; Kijima, K. M.; Kikuchi, J.; Kim, A.; Kim, B. I.; Kim, C.; Kim, D. H.; Kim, D. J.; Kim, E.; Kim, E.-J.; Kim, G. W.; Kim, M.; Kim, S. H.; Kim, Y.-J.; Kim, Y. K.; Kimelman, B.; Kinney, E.; Kiriluk, K.; Kiss, Á.; Kistenev, E.; Kitamura, R.; Kiyomichi, A.; Klatsky, J.; Klay, J.; Klein-Boesing, C.; Kleinjan, D.; Kline, P.; Koblesky, T.; Kochenda, L.; Kochetkov, V.; Komkov, B.; Konno, M.; Koster, J.; Kotchetkov, D.; Kotov, D.; Kozlov, A.; Král, A.; Kravitz, A.; Kubart, J.; Kunde, G. J.; Kurihara, N.; Kurita, K.; Kurosawa, M.; Kweon, M. J.; Kwon, Y.; Kyle, G. S.; Lacey, R.; Lai, Y. S.; Lajoie, J. G.; Layton, D.; Lebedev, A.; Lee, D. M.; Lee, J.; Lee, K. B.; Lee, K. S.; Lee, M. K.; Lee, S.; Lee, S. H.; Lee, S. R.; Lee, T.; Leitch, M. J.; Leite, M. A. L.; Lenzi, B.; Li, X.; Lichtenwalner, P.; Liebing, P.; Lim, S. H.; Linden Levy, L. A.; Liška, T.; Litvinenko, A.; Liu, H.; Liu, M. X.; Love, B.; Lynch, D.; Maguire, C. F.; Makdisi, Y. I.; Makek, M.; Malakhov, A.; Malik, M. D.; Manion, A.; Manko, V. I.; Mannel, E.; Mao, Y.; Mašek, L.; Masui, H.; Matathias, F.; McCumber, M.; McGaughey, P. L.; McGlinchey, D.; McKinney, C.; Means, N.; Meles, A.; Mendoza, M.; Meredith, B.; Miake, Y.; Mibe, T.; Mignerey, A. C.; Mikeš, P.; Miki, K.; Miller, T. E.; Milov, A.; Mioduszewski, S.; Mishra, D. K.; Mishra, M.; Mitchell, J. T.; Mitrovski, M.; Miyachi, Y.; Miyasaka, S.; Mizuno, S.; Mohanty, A. K.; Montuenga, P.; Moon, H. J.; Moon, T.; Morino, Y.; Morreale, A.; Morrison, D. P.; Motschwiller, S.; Moukhanova, T. V.; Mukhopadhyay, D.; Murakami, T.; Murata, J.; Mwai, A.; Nagamiya, S.; Nagashima, K.; Nagata, Y.; Nagle, J. L.; Naglis, M.; Nagy, M. I.; Nakagawa, I.; Nakagomi, H.; Nakamiya, Y.; Nakamura, K. R.; Nakamura, T.; Nakano, K.; Nam, S.; Nattrass, C.; Netrakanti, P. K.; Newby, J.; Nguyen, M.; Nihashi, M.; Niida, T.; Nishimura, S.; Norman, B. E.; Nouicer, R.; Novak, T.; Novitzky, N.; Nyanin, A. S.; Oakley, C.; O'Brien, E.; Oda, S. X.; Ogilvie, C. A.; Ohnishi, H.; Oka, M.; Okada, K.; Omiwade, O. O.; Onuki, Y.; Orjuela Koop, J. D.; Osborn, J. D.; Oskarsson, A.; Ouchida, M.; Ozawa, K.; Pak, R.; Pal, D.; Palounek, A. P. T.; Pantuev, V.; Papavassiliou, V.; Park, B. H.; Park, I. H.; Park, J.; Park, J. S.; Park, S.; Park, S. K.; Park, W. J.; Pate, S. F.; Patel, L.; Patel, M.; Pei, H.; Peng, J.-C.; Pereira, H.; Perepelitsa, D. V.; Perera, G. D. N.; Peresedov, V.; Peressounko, D. Yu.; Perry, J.; Petti, R.; Pinkenburg, C.; Pinson, R.; Pisani, R. P.; Proissl, M.; Purschke, M. L.; Purwar, A. K.; Qu, H.; Rak, J.; Rakotozafindrabe, A.; Ramson, B. J.; Ravinovich, I.; Read, K. F.; Rembeczki, S.; Reuter, M.; Reygers, K.; Reynolds, D.; Riabov, V.; Riabov, Y.; Richardson, E.; Rinn, T.; Roach, D.; Roche, G.; Rolnick, S. D.; Romana, A.; Rosati, M.; Rosen, C. A.; Rosendahl, S. S. E.; Rosnet, P.; Rowan, Z.; Rubin, J. G.; Rukoyatkin, P.; Ružička, P.; Rykov, V. L.; Sahlmueller, B.; Saito, N.; Sakaguchi, T.; Sakai, S.; Sakashita, K.; Sakata, H.; Sako, H.; Samsonov, V.; Sano, S.; Sarsour, M.; Sato, S.; Sato, T.; Savastio, M.; Sawada, S.; Schaefer, B.; Schmoll, B. K.; Sedgwick, K.; Seele, J.; Seidl, R.; Semenov, A. Yu.; Semenov, V.; Sen, A.; Seto, R.; Sett, P.; Sexton, A.; Sharma, D.; Shein, I.; Shevel, A.; Shibata, T.-A.; Shigaki, K.; Shim, H. H.; Shimomura, M.; Shoji, K.; Shukla, P.; Sickles, A.; Silva, C. L.; Silvermyr, D.; Silvestre, C.; Sim, K. S.; Singh, B. K.; Singh, C. P.; Singh, V.; Skutnik, S.; Slunečka, M.; Snowball, M.; Sodre, T.; Soldatov, A.; Soltz, R. A.; Sondheim, W. E.; Sorensen, S. P.; Sourikova, I. V.; Staley, F.; Stankus, P. W.; Stenlund, E.; Stepanov, M.; Ster, A.; Stoll, S. P.; Sugitate, T.; Suire, C.; Sukhanov, A.; Sumita, T.; Sun, J.; Sziklai, J.; Tabaru, T.; Takagi, S.; Takagui, E. M.; Takahara, A.; Taketani, A.; Tanabe, R.; Tanaka, Y.; Taneja, S.; Tanida, K.; Tannenbaum, M. J.; Tarafdar, S.; Taranenko, A.; Tarján, P.; Tennant, E.; Themann, H.; Thomas, D.; Thomas, T. L.; Tieulent, R.; Timilsina, A.; Todoroki, T.; Togawa, M.; Toia, A.; Tojo, J.; Tomášek, L.; Tomášek, M.; Tomita, Y.; Torii, H.; Towell, C. L.; Towell, R.; Towell, R. S.; Tram, V.-N.; Tserruya, I.; Tsuchimoto, Y.; Utsunomiya, K.; Vale, C.; Valle, H.; van Hecke, H. W.; Vazquez-Zambrano, E.; Veicht, A.; Velkovska, J.; Vértesi, R.; Vinogradov, A. A.; Virius, M.; Vossen, A.; Vrba, V.; Vznuzdaev, E.; Wagner, M.; Walker, D.; Wang, X. R.; Watanabe, D.; Watanabe, K.; Watanabe, Y.; Watanabe, Y. S.; Wei, F.; Wei, R.; Wessels, J.; White, A. S.; White, S. N.; Winter, D.; Woody, C. L.; Wright, R. M.; Wysocki, M.; Xia, B.; Xie, W.; Xue, L.; Yalcin, S.; Yamaguchi, Y. L.; Yamaura, K.; Yang, R.; Yanovich, A.; Yasin, Z.; Ying, J.; Yokkaichi, S.; Yoo, J. H.; Yoo, J. S.; Yoon, I.; You, Z.; Young, G. R.; Younus, I.; Yu, H.; Yushmanov, I. E.; Zajc, W. A.; Zaudtke, O.; Zelenski, A.; Zhang, C.; Zhou, S.; Zimamyi, J.; Zolin, L.; Zou, L.; Phenix Collaboration

2015-10-01

We present the first measurement of elliptic (v2) and triangular (v3) flow in high-multiplicity 3He +Au collisions at √{sN N }=200 GeV . Two-particle correlations, where the particles have a large separation in pseudorapidity, are compared in 3He +Au and in p +p collisions and indicate that collective effects dominate the second and third Fourier components for the correlations observed in the 3He +Au system. The collective behavior is quantified in terms of elliptic v2 and triangular v3 anisotropy coefficients measured with respect to their corresponding event planes. The v2 values are comparable to those previously measured in d +Au collisions at the same nucleon-nucleon center-of-mass energy. Comparisons with various theoretical predictions are made, including to models where the hot spots created by the impact of the three 3He nucleons on the Au nucleus expand hydrodynamically to generate the triangular flow. The agreement of these models with data may indicate the formation of low-viscosity quark-gluon plasma even in these small collision systems.

Investigation of thermal conduction in symmetric and asymmetric nanoporous structures

NASA Astrophysics Data System (ADS)

Yu, Ziqi; Ferrer-Argemi, Laia; Lee, Jaeho

2017-12-01

Nanoporous structures with a critical dimension comparable to or smaller than the phonon mean free path have demonstrated significant thermal conductivity reductions that are attractive for thermoelectric applications, but the presence of various geometric parameters complicates the understanding of governing mechanisms. Here, we use a ray tracing technique to investigate phonon boundary scattering phenomena in Si nanoporous structures of varying pore shapes, pore alignments, and pore size distributions, and identify mechanisms that are primarily responsible for thermal conductivity reductions. Our simulation results show that the neck size, or the smallest distance between nearest pores, is the key parameter in understanding nanoporous structures of varying pore shapes and the same porosities. When the neck size and the porosity are both identical, asymmetric pore shapes provide a lower thermal conductivity compared with symmetric pore shapes, due to localized heat fluxes. Asymmetric nanoporous structures show possibilities of realizing thermal rectification even with fully diffuse surface boundaries, in which optimal arrangements of triangular pores show a rectification ratio up to 13 when the injection angles are optimally controlled. For symmetric nanoporous structures, hexagonal-lattice pores achieve larger thermal conductivity reductions than square-lattice pores due to the limited line of sight for phonons. We also show that nanoporous structures of alternating pore size distributions from large to small pores yield a lower thermal conductivity compared with those of uniform pore size distributions in the given porosity. These findings advance the understanding of phonon boundary scattering phenomena in complex geometries and enable optimal designs of artificial nanostructures for thermoelectric energy harvesting and solid-state cooling systems.

Investigations of surface structural, dynamical, and magnetic properties of systems exhibiting multiferroicity, and topological phases by helium scattering spectroscopies

DOE Office of Scientific and Technical Information (OSTI.GOV)

El-Batanouny, Maged

2015-08-03

We propose to investigate the surface structural, dynamics and magnetic properties of the novel class of topological insulator crystals, as well as crystals that exhibit multiferroicity, magnetoelectricity and thermoelectricity. Topological insulators (TIs) are a new class of insulators in which a bulk gap for electronic excitations is generated because of the strong spin-orbit coupling inherent to these systems. These materials are distinguished from ordinary insulators by the presence of gapless metallic surface states, resembling chiral edge modes in quantum Hall systems, but with unconventional spin textures. These exotic metallic states are formed by topological conditions that also render the electrons travelling on such surfaces insensitive to scattering by impurities. The electronic quasi-particles populating the topological surface state are Dirac fermions; they have a linear dispersion and thus are massless just like photons. We propose to investigate the interaction of these massless Dirac fermions with the massive lattice in the newly discovered crystals, Bi2Se3, Bi2Te3 and Sb2Te3. We shall use inelastic helium beam scattering from surfaces to search for related signatures in surface phonon dispersions mappings that cover the entire surface Brillouin zone of these materials. Our recent investigations of the (001) surface of the multiferroic crystals (Li/Na)Cu2O2 revealed an anomalous surface structural behavior where surface Cumore » $$^{2+}$$ row rise above the surface plane as the crystal was cooled. Subsequent worming revealed the onset of a thermally activated incommensurate surface phase, driven by the elevated rows. We are currently investigating the structure of the magnetic phases in these quasi-one-dimensional magnetic rows. Multiferroics are excellent candidates for large magnetoelectric response. We propose to extend this investigation to the class of delafossites which are also multiferroics and have been investigated as good candidates for thermoelectric power devices. They are also typical triangular lattice antiferromagnets with geometric magnetic frustration that leads to helimagnetic structures.« less

Vehicle antenna for the mobile satellite experiment

NASA Technical Reports Server (NTRS)

Peng, Sheng Y.; Chung, H. H.; Leggiere, D.; Foy, W.; Schaffner, G.; Nelson, J.; Pagels, W.; Vayner, M.; Faller, H. L.; Messer, L.

1988-01-01

A low profile, low cost, printed circuit, electronically steered, right hand circularly polarized phase array antenna system has been developed for the Mobile Satellite Experiment (MSAT-X) Program. The success of this antenna is based upon the development of a crossed-slot element array and detailed trade-off analyses for both the phased array and pointing system design. The optimized system provides higher gain at low elevation angles (20 degrees above the horizon) and broader frequency coverage (approximately 8 1/2 percent bandwidth) than is possible with a patch array. Detailed analysis showed that optimum performance could be achieved with a 19 element array of a triangular lattice geometry of 3.9 inch element spacing. This configuration has the effect of minimizing grating lobes at large scan angles plus it improves the intersatellite isolation. The array has an aperture 20 inches in diameter and is 0.75 inch thick overall, exclusive of the RF and power connector. The pointing system employs a hybrid approach that operates with both an external rate sensor and an internal error signal as a means of fine tuning the beam acquisition and track. Steering the beam is done electronically via 18, 3-bit diode phase shifters. A nineteenth phase shifter is not required as the center element serves as a reference only. Measured patterns and gain show that the array meets the stipulated performance specifications everywhere except at some low elevation angles.

S/sub n/ analysis of the TRX metal lattices with ENDF/B version III data

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wheeler, F.J.; Pearlstein, S.

1975-03-01

Two critical assemblies, designated as thermal-reactor benchmarks TRX-1 and TRX-2 for ENDF/B data testing, were analyzed using the one-dimensional S/sub n/-theory code SCAMP. The two assemblies were simple lattices of aluminum-clad, uranium-metal fuel rods in triangular arrays with D$sub 2$O as moderator and reflector. The fuel was low-enriched (1.3 percent $sup 235$U), 0.387-inch in diameter and had an active height of 48 inches. The volume ratio of water to uranium was 2.35 for the TRX-1 lattice and 4.02 for TRX-2. Full-core S/sub n/ calculations based on Version III data were performed for these assemblies and the results obtained were comparedmore » with the measured values of the multiplication factors, the ratio of epithermal-to-thermal neutron capture in $sup 238$U, the ratio of epithermal-to-thermal fission in $sup 235$U, the ratio of $sup 238$U fission to $sup 235$U fission, and the ratio of capture in $sup 238$U to fission in $sup 235$U. Reaction rates were obtained from a central region of the full- core problems. Multigroup cross sections for the reactor calculation were obtained from S/sub n/ cell calculations with resonance self-shielding calculated using the RABBLE treatment. The results of the analyses are generally consistent with results obtained by other investigators. (auth)« less

P13631-E002PF: Pulsed field magnetostriction of Ba 2CoTeO 6

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tanaka, H.; Kurita, N.; Koike, M.

Ba 2CoTeO 6 is an insulating material consisting of two magnetic subsystems referred as A and B build of S=1/2 spins. Subsystem A is considered to be a Heisenberg-like antiferromagnet (AFM) on a triangular lattice and subsystem B is a J 1-J 2 Ising-like AFM on a honey-comb lattice. The magnetic phase transitions are observed at T N1 = 12 K and T N2=3K for A and B respectively. The application of magnetic fields unveils a rich phase diagram that varies depending on the direction of the applied field for either H ll c or H perp c. To datemore » the phase diagram has been investigated by means of specific heat measurement up to 9T and susceptibility measurements with a SQUID magnetometer up to 7T. Magnetization measured in pulsed magnetic fields up to 60T at 1.3K and 4.2K reveal several steps and plateaux occurring at varying critical fields depending on the crystallographic direction. Common to the magnetization parallel c and perpendicular c is the saturation above 40T.« less

Supersymmetrical bounding of asymmetric states and quantum phase transitions by anti-crossing of symmetric states

PubMed Central

Afzal, Muhammad Imran; Lee, Yong Tak

2016-01-01

Von Neumann and Wigner theorized the bounding and anti-crossing of eigenstates. Experiments have demonstrated that owing to anti-crossing and similar radiation rates, the graphene-like resonance of inhomogeneously strained photonic eigenstates can generate a pseudomagnetic field, bandgaps and Landau levels, whereas exponential or dissimilar rates induce non-Hermicity. Here, we experimentally demonstrate higher-order supersymmetry and quantum phase transitions by resonance between similar one-dimensional lattices. The lattices consisted of inhomogeneous strain-like phases of triangular solitons. The resonance created two-dimensional, inhomogeneously deformed photonic graphene. All parent eigenstates were annihilated. Eigenstates of mildly strained solitons were annihilated at similar rates through one tail and generated Hermitian bounded eigenstates. The strongly strained solitons with positive phase defects were annihilated at exponential rates through one tail, which bounded eigenstates through non-Hermitianally generated exceptional points. Supersymmetry was evident, with preservation of the shapes and relative phase differences of the parent solitons. Localizations of energies generated from annihilations of mildly and strongly strained soliton eigenstates were responsible for geometrical (Berry) and topological phase transitions, respectively. Both contributed to generating a quantum Zeno phase, whereas only strong twists generated topological (Anderson) localization. Anti-bunching-like condensation was also observed. PMID:27966596

Correlated impurities and intrinsic spin-liquid physics in the kagome material herbertsmithite

DOE PAGES

Han, Tian-Heng; Norman, M. R.; Wen, J. -J.; ...

2016-08-18

Low energy inelastic neutron scattering on single crystals of the kagome spin-liquid compound ZnCu 3(OD) 6Cl 2 (herbertsmithite) reveals in this paper antiferromagnetic correlations between impurity spins for energy transfers h(with stroke)ω < 0.8 meV (~ J/20). The momentum dependence differs significantly from higher energy scattering which arises from the intrinsic kagome spins. The low energy fluctuations are characterized by diffuse scattering near wave vectors (100) and (00 3/2), which is consistent with antiferromagnetic correlations between pairs of nearest-neighbor Cu impurities on adjacent triangular (Zn) interlayers. The corresponding impurity lattice resembles a simple cubic lattice in the dilute limit belowmore » the percolation threshold. Such an impurity model can describe prior neutron, NMR, and specific heat data. The low energy neutron data are consistent with the presence of a small spin gap (Δ ~ 0.7 meV) in the kagome layers, similar to that recently observed by NMR. Finally, the ability to distinguish the scattering due to Cu impurities from that of the planar kagome Cu spins provides an important avenue for probing intrinsic spin-liquid physics.« less

Discovering phases, phase transitions, and crossovers through unsupervised machine learning: A critical examination

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hu, Wenjian; Singh, Rajiv R. P.; Scalettar, Richard T.

Here, we apply unsupervised machine learning techniques, mainly principal component analysis (PCA), to compare and contrast the phase behavior and phase transitions in several classical spin models - the square and triangular-lattice Ising models, the Blume-Capel model, a highly degenerate biquadratic-exchange spin-one Ising (BSI) model, and the 2D XY model, and examine critically what machine learning is teaching us. We find that quantified principal components from PCA not only allow exploration of different phases and symmetry-breaking, but can distinguish phase transition types and locate critical points. We show that the corresponding weight vectors have a clear physical interpretation, which ismore » particularly interesting in the frustrated models such as the triangular antiferromagnet, where they can point to incipient orders. Unlike the other well-studied models, the properties of the BSI model are less well known. Using both PCA and conventional Monte Carlo analysis, we demonstrate that the BSI model shows an absence of phase transition and macroscopic ground-state degeneracy. The failure to capture the 'charge' correlations (vorticity) in the BSI model (XY model) from raw spin configurations points to some of the limitations of PCA. Finally, we employ a nonlinear unsupervised machine learning procedure, the 'antoencoder method', and demonstrate that it too can be trained to capture phase transitions and critical points.« less

Discovering phases, phase transitions, and crossovers through unsupervised machine learning: A critical examination

DOE PAGES

Hu, Wenjian; Singh, Rajiv R. P.; Scalettar, Richard T.

2017-06-19

Here, we apply unsupervised machine learning techniques, mainly principal component analysis (PCA), to compare and contrast the phase behavior and phase transitions in several classical spin models - the square and triangular-lattice Ising models, the Blume-Capel model, a highly degenerate biquadratic-exchange spin-one Ising (BSI) model, and the 2D XY model, and examine critically what machine learning is teaching us. We find that quantified principal components from PCA not only allow exploration of different phases and symmetry-breaking, but can distinguish phase transition types and locate critical points. We show that the corresponding weight vectors have a clear physical interpretation, which ismore » particularly interesting in the frustrated models such as the triangular antiferromagnet, where they can point to incipient orders. Unlike the other well-studied models, the properties of the BSI model are less well known. Using both PCA and conventional Monte Carlo analysis, we demonstrate that the BSI model shows an absence of phase transition and macroscopic ground-state degeneracy. The failure to capture the 'charge' correlations (vorticity) in the BSI model (XY model) from raw spin configurations points to some of the limitations of PCA. Finally, we employ a nonlinear unsupervised machine learning procedure, the 'antoencoder method', and demonstrate that it too can be trained to capture phase transitions and critical points.« less

Discovering phases, phase transitions, and crossovers through unsupervised machine learning: A critical examination

NASA Astrophysics Data System (ADS)

Hu, Wenjian; Singh, Rajiv R. P.; Scalettar, Richard T.

2017-06-01

We apply unsupervised machine learning techniques, mainly principal component analysis (PCA), to compare and contrast the phase behavior and phase transitions in several classical spin models—the square- and triangular-lattice Ising models, the Blume-Capel model, a highly degenerate biquadratic-exchange spin-1 Ising (BSI) model, and the two-dimensional X Y model—and we examine critically what machine learning is teaching us. We find that quantified principal components from PCA not only allow the exploration of different phases and symmetry-breaking, but they can distinguish phase-transition types and locate critical points. We show that the corresponding weight vectors have a clear physical interpretation, which is particularly interesting in the frustrated models such as the triangular antiferromagnet, where they can point to incipient orders. Unlike the other well-studied models, the properties of the BSI model are less well known. Using both PCA and conventional Monte Carlo analysis, we demonstrate that the BSI model shows an absence of phase transition and macroscopic ground-state degeneracy. The failure to capture the "charge" correlations (vorticity) in the BSI model (X Y model) from raw spin configurations points to some of the limitations of PCA. Finally, we employ a nonlinear unsupervised machine learning procedure, the "autoencoder method," and we demonstrate that it too can be trained to capture phase transitions and critical points.

Raman scattering of IrTe2

NASA Astrophysics Data System (ADS)

Lee, Alexander; Thorsmolle, Verner; Artyukhin, Sergey; Yang, Jun; Cheong, Sang-Wook; Blumberg, Girsh

2014-03-01

IrTe2 presents a layered compound with a triangular lattice. It is known to exhibit a first order structural phase transition at approximately 260 K which is of a first order, corresponding to a formation of a superstructure with a period of five unit cells. Using polarized Raman spectroscopy we have studied the temperature dependence of 14 observed Raman allowed phononic modes. These phonons couple strongly to this transition and one additional first order transition at approximately 170 K. In the high-temperature phase only 3 modes are observed, while below approximately 280 K all 14 modes become visible. Below approximately 170 K only 11 modes are observed. Our results shed light on the possible mechanism driving the transitions. ACL, VKT and GB acknowledge support by NSF DMR-1104884.

Elastic Backbone Defines a New Transition in the Percolation Model

NASA Astrophysics Data System (ADS)

Sampaio Filho, Cesar I. N.; Andrade, José S.; Herrmann, Hans J.; Moreira, André A.

2018-04-01

The elastic backbone is the set of all shortest paths. We found a new phase transition at peb above the classical percolation threshold at which the elastic backbone becomes dense. At this transition in 2D, its fractal dimension is 1.750 ±0.003 , and one obtains a novel set of critical exponents βeb=0.50 ±0.02 , γeb=1.97 ±0.05 , and νeb=2.00 ±0.02 , fulfilling consistent critical scaling laws. Interestingly, however, the hyperscaling relation is violated. Using Binder's cumulant, we determine, with high precision, the critical probabilities peb for the triangular and tilted square lattice for site and bond percolation. This transition describes a sudden rigidification as a function of density when stretching a damaged tissue.

Ab initio density functional theory investigation of crystalline bundles of polygonized single-walled silicon carbide nanotubes

NASA Astrophysics Data System (ADS)

Moradian, Rostam; Behzad, Somayeh; Chegel, Raad

2008-11-01

By using ab initio density functional theory, the structural characterizations and electronic properties of two large-diameter (13, 13) and (14, 14) armchair silicon carbide nanotube (SiCNT) bundles are investigated. Full structural optimizations show that the cross sections of these large-diameter SiCNTs in the bundles have a nearly hexagonal shape. The effects of inter-tube coupling on the electronic dispersions of large-diameter SiCNT bundles are demonstrated. By comparing the band structures of the triangular lattices of (14, 14) SiCNTs with nearly hexagonal and circular cross sections we found that the polygonization of the tubes in the bundle leads to a further dispersion of the occupied bands and an increase in the bandgap by 0.18 eV.

Ab initio density functional theory investigation of crystalline bundles of polygonized single-walled silicon carbide nanotubes.

PubMed

Moradian, Rostam; Behzad, Somayeh; Chegel, Raad

2008-11-19

By using ab initio density functional theory, the structural characterizations and electronic properties of two large-diameter (13, 13) and (14, 14) armchair silicon carbide nanotube (SiCNT) bundles are investigated. Full structural optimizations show that the cross sections of these large-diameter SiCNTs in the bundles have a nearly hexagonal shape. The effects of inter-tube coupling on the electronic dispersions of large-diameter SiCNT bundles are demonstrated. By comparing the band structures of the triangular lattices of (14, 14) SiCNTs with nearly hexagonal and circular cross sections we found that the polygonization of the tubes in the bundle leads to a further dispersion of the occupied bands and an increase in the bandgap by 0.18 eV.

Monte Carlo study of the honeycomb structure of anthraquinone molecules on Cu(111)

NASA Astrophysics Data System (ADS)

Kim, Kwangmoo; Einstein, T. L.

2011-06-01

Using Monte Carlo calculations of the two-dimensional (2D) triangular lattice gas model, we demonstrate a mechanism for the spontaneous formation of honeycomb structure of anthraquinone (AQ) molecules on a Cu(111) plane. In our model long-range attractions play an important role, in addition to the long-range repulsions and short-range attractions proposed by Pawin, Wong, Kwon, and Bartels [ScienceSCIEAS0036-807510.1126/science.1129309 313, 961 (2006)]. We provide a global account of the possible combinations of long-range attractive coupling constants which lead to a honeycomb superstructure. We also provide the critical temperature of disruption of the honeycomb structure and compare the critical local coverage rate of AQ’s where the honeycomb structure starts to form with the experimental observations.

Tunable Transmission and Deterministic Interface states in Double-zero-index Acoustic Metamaterials.

PubMed

Zhao, Wei; Yang, Yuting; Tao, Zhi; Hang, Zhi Hong

2018-04-20

Following the seminal work by Dubois et al. (Nat. Commun. 8, 14871 (2017)), we study a double-zero-index acoustic metamaterial with triangular lattice. By varying the height and diameter of air scatterers inside a parallel-plate acoustic waveguide, acoustic dispersion of the first-order waveguide mode can be manipulated and various interesting properties are explored. With accidental degeneracy of monopolar and dipolar modes, we numerically prove the double-zero-index properties of this novel acoustic metamaterial. Acoustic waveguides with tunable and asymmetric transmission are realized with this double-zero-index acoustic metamaterial embedded. Band inversion occurs if the bulk acoustic band diagram of this acoustic metamaterial is tuned. Deterministic interface states are found to exist on the interface between two acoustic metamaterials with inverted band diagrams.

Investigation of magnetic properties on spin-ordering effects of FeGa2S4 and FeIn2S4

NASA Astrophysics Data System (ADS)

Myoung, Bo Ra; Lim, Jung Tae; Kim, Chul Sung

2017-09-01

We have studied crystal and magnetic properties of chalcogenides FeGa2S4 and FeIn2S4 with X-ray diffractometer (XRD), magnetic property measurement system (MPMS), magnetometer, physical property measurement system (PPMS), and Mössbauer spectrometer. The crystal structure has 2-dimension triangular lattice structure with P-3m1 of FeGa2S4, while FeIn2S4 has inverse spinel with space group Fd3m. The AC magnetic susceptibility measurements show that FeGa2S4 is an insulating spin glass material, exhibiting geometrical frustration, unlike in the antiferromagnetic [AFM] metallic spin glass FeIn2S4. From hysteresis (M-H) curves at 4.2 K, FeGa2S4 has spin-flop behavior with an angle of 120° of triangle, as against linear slope of FeIn2S4 due to anti-parallel spin. The gap energy by splitting of 5T2g, Δ1 and electric quadrupole splitting ΔEQ of FeIn2S4 are much higher than that of FeGa2S4 at 4.2 K because FeGa2S4 is geometrically frustrated magnet having degenerate ground state at low temperature.

3D animation of facial plastic surgery based on computer graphics

NASA Astrophysics Data System (ADS)

Zhang, Zonghua; Zhao, Yan

2013-12-01

More and more people, especial women, are getting desired to be more beautiful than ever. To some extent, it becomes true because the plastic surgery of face was capable in the early 20th and even earlier as doctors just dealing with war injures of face. However, the effect of post-operation is not always satisfying since no animation could be seen by the patients beforehand. In this paper, by combining plastic surgery of face and computer graphics, a novel method of simulated appearance of post-operation will be given to demonstrate the modified face from different viewpoints. The 3D human face data are obtained by using 3D fringe pattern imaging systems and CT imaging systems and then converted into STL (STereo Lithography) file format. STL file is made up of small 3D triangular primitives. The triangular mesh can be reconstructed by using hash function. Top triangular meshes in depth out of numbers of triangles must be picked up by ray-casting technique. Mesh deformation is based on the front triangular mesh in the process of simulation, which deforms interest area instead of control points. Experiments on face model show that the proposed 3D animation facial plastic surgery can effectively demonstrate the simulated appearance of post-operation.

Stability of triangular points in the elliptic restricted three-body problem with oblateness up to zonal harmonic J4 of both primaries

NASA Astrophysics Data System (ADS)

Singh, Jagadish; Tyokyaa, Richard K.

2016-10-01

In this paper, we study the locations and stability of triangular points in the elliptic restricted three-body problem when both primaries are taken as oblate spheroids with oblateness up to J4. The positions of the triangular points are seen to be affected by oblateness of the primaries and the eccentricity of their orbits. The triangular points are conditionally stable for 0<μ<μc0<μ<μc and unstable for μc≤μ≤12μc≤μ≤12, where μcμc is the critical mass parameter depending on the oblateness coefficients J2iJ2i (i =1,2) and the eccentricity of the orbits. We further observe that both coefficients J2 and J4, semi-major axis and the eccentricity have destabilizing tendencies resulting in a decrease in the size of the region of stability with an increase in the parameters involved. Knowing that, in general, the triangular equilibrium points are stable for 0<μ<μc0<μ<μc, in particular systems (Alpha Centauri, X1X1 Bootis, Sirius and Kruger 60) this does not hold and such points are unstable.

Efficient computer algebra algorithms for polynomial matrices in control design

NASA Technical Reports Server (NTRS)

Baras, J. S.; Macenany, D. C.; Munach, R.

1989-01-01

The theory of polynomial matrices plays a key role in the design and analysis of multi-input multi-output control and communications systems using frequency domain methods. Examples include coprime factorizations of transfer functions, cannonical realizations from matrix fraction descriptions, and the transfer function design of feedback compensators. Typically, such problems abstract in a natural way to the need to solve systems of Diophantine equations or systems of linear equations over polynomials. These and other problems involving polynomial matrices can in turn be reduced to polynomial matrix triangularization procedures, a result which is not surprising given the importance of matrix triangularization techniques in numerical linear algebra. Matrices with entries from a field and Gaussian elimination play a fundamental role in understanding the triangularization process. In the case of polynomial matrices, matrices with entries from a ring for which Gaussian elimination is not defined and triangularization is accomplished by what is quite properly called Euclidean elimination. Unfortunately, the numerical stability and sensitivity issues which accompany floating point approaches to Euclidean elimination are not very well understood. New algorithms are presented which circumvent entirely such numerical issues through the use of exact, symbolic methods in computer algebra. The use of such error-free algorithms guarantees that the results are accurate to within the precision of the model data--the best that can be hoped for. Care must be taken in the design of such algorithms due to the phenomenon of intermediate expressions swell.

Complex Ordered Patterns in Mechanical Instability Induced Geometrically Frustrated Triangular Cellular Structures

NASA Astrophysics Data System (ADS)

Kang, Sung Hoon; Shan, Sicong; Košmrlj, Andrej; Noorduin, Wim L.; Shian, Samuel; Weaver, James C.; Clarke, David R.; Bertoldi, Katia

2014-03-01

Geometrical frustration arises when a local order cannot propagate throughout the space because of geometrical constraints. This phenomenon plays a major role in many systems leading to disordered ground-state configurations. Here, we report a theoretical and experimental study on the behavior of buckling-induced geometrically frustrated triangular cellular structures. To our surprise, we find that buckling induces complex ordered patterns which can be tuned by controlling the porosity of the structures. Our analysis reveals that the connected geometry of the cellular structure plays a crucial role in the generation of ordered states in this frustrated system.

In-plane crashworthiness of bio-inspired hierarchical honeycombs

DOE PAGES

Yin, Hanfeng; Huang, Xiaofei; Scarpa, Fabrizio; ...

2018-03-13

Biological tissues like bone, wood, and sponge possess hierarchical cellular topologies, which are lightweight and feature an excellent energy absorption capability. Here we present a system of bio-inspired hierarchical honeycomb structures based on hexagonal, Kagome, and triangular tessellations. The hierarchical designs and a reference regular honeycomb configuration are subjected to simulated in-plane impact using the nonlinear finite element code LS-DYNA. The numerical simulation results show that the triangular hierarchical honeycomb provides the best performance compared to the other two hierarchical honeycombs, and features more than twice the energy absorbed by the regular honeycomb under similar loading conditions. We also proposemore » a parametric study correlating the microstructure parameters (hierarchical length ratio r and the number of sub cells N) to the energy absorption capacity of these hierarchical honeycombs. The triangular hierarchical honeycomb with N = 2 and r = 1/8 shows the highest energy absorption capacity among all the investigated cases, and this configuration could be employed as a benchmark for the design of future safety protective systems.« less

In-plane crashworthiness of bio-inspired hierarchical honeycombs

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yin, Hanfeng; Huang, Xiaofei; Scarpa, Fabrizio

Biological tissues like bone, wood, and sponge possess hierarchical cellular topologies, which are lightweight and feature an excellent energy absorption capability. Here we present a system of bio-inspired hierarchical honeycomb structures based on hexagonal, Kagome, and triangular tessellations. The hierarchical designs and a reference regular honeycomb configuration are subjected to simulated in-plane impact using the nonlinear finite element code LS-DYNA. The numerical simulation results show that the triangular hierarchical honeycomb provides the best performance compared to the other two hierarchical honeycombs, and features more than twice the energy absorbed by the regular honeycomb under similar loading conditions. We also proposemore » a parametric study correlating the microstructure parameters (hierarchical length ratio r and the number of sub cells N) to the energy absorption capacity of these hierarchical honeycombs. The triangular hierarchical honeycomb with N = 2 and r = 1/8 shows the highest energy absorption capacity among all the investigated cases, and this configuration could be employed as a benchmark for the design of future safety protective systems.« less

Quantum simulations of the Ising model with trapped ions: Devil's staircase and arbitrary lattice proposal

NASA Astrophysics Data System (ADS)

Korenblit, Simcha

A collection of trapped atomic ions represents one of the most attractive platforms for the quantum simulation of interacting spin networks and quantum magnetism. Spin-dependent optical dipole forces applied to an ion crystal create long-range effective spin-spin interactions and allow the simulation of spin Hamiltonians that possess nontrivial phases and dynamics. We trap linear chains of 171Yb+ ions in a Paul trap, and constrain the occupation of energy levels to the ground hyperne clock-states, creating a qubit or pseudo-spin 1/2 system. We proceed to implement spin-spin couplings between two ions using the far detuned Molmer-Sorenson scheme and perform adiabatic quantum simulations of Ising Hamiltonians with long-range couplings. We then demonstrate our ability to control the sign and relative strength of the interaction between three ions. Using this control, we simulate a frustrated triangular lattice, and for the first time establish an experimental connection between frustration and quantum entanglement. We then scale up our simulation to show phase transitions from paramagnetism to ferromagnetism for nine ions, and to anti-ferromagnetism for sixteen ions. The experimental work culminates with our most complicated Hamiltonian---a long range anti-ferromagnetic Ising interaction between 10 ions with a biasing axial field. Theoretical work presented in this thesis shows how the approach to quantum simulation utilized in this thesis can be further extended and improved. It is shown how appropriate design of laser fields can provide for arbitrary multidimensional spin-spin interaction graphs even for the case of a linear spatial array of ions. This scheme uses currently existing trap technology and is scalable to levels where classical methods of simulation are intractable.

Cascaded chirped narrow bandpass filter with flat-top based on two-dimensional photonic crystals.

PubMed

Zhuang, Yuyang; Chen, Heming; Ji, Ke

2017-05-10

We propose a structure of a cascaded chirped narrow bandpass filter with a flat-top based on two-dimensional (2D) photonic crystals (PhCs). The filter discussed here consists of three filter units, each with a resonator and two reflectors. Coupled mode theory and transfer matrix method are methodologies applied in the analysis of the features. The calculations show that the bandwidth of the filter can be adjusted by changing the distances between resonators and reflectors, and based on this, a flat-top response can be achieved by chirped-cascading the filter units. According to the theoretical model, we design a narrow bandpass filter based on 2D PhCs with a triangular lattice of air holes, the parameters of which are calculated using the finite element method. The simulation results show that the filter has a center frequency of 193.40 THz, an insertion loss of 0.18 dB, a flat bandwidth of 40 GHz, and ripples of about 0.2 dB in the passband. The filter is suitable for dense-wavelength-division-multiplexed optical communication systems with 100 GHz channel spacing.

Emergent structures and dynamics in suspensions of self-phoretic colloids

NASA Astrophysics Data System (ADS)

Scagliarini, Andrea; Pagonabarraga, Ignacio

2013-11-01

Active fluids, such as suspensions of self-propelled particles , are a fascinating example of Soft Matter displaying complex collective behaviours which provide challenges in non-equilibrium Statistical Physics. The recent development of techniques to assemble miniaturized devices has led to a growing interest for micro and nanoscale engines that can perform autonomous motion (``microrobots''), as, for instance, self-phoretic colloids, for which the propulsion is induced by the generation of a chemical species in a reaction catalyzed at the particle surface. We perform a mesoscopic numerical study of suspensions of self-phoretic colloids. We show that, at changing the sign of the phoretic mobility (which accounts for the colloid-solute interactions), the system switches from a cluster phase to a state with slowed dynamics. We find that the cluster size distribution follows an exponential behaviour, with a characteristic size growing linearly with the colloid activity, while the density fluctuations grow as a power-law with an exponent depending on the cluster fractal dimension.We single out hydrodynamic interactions, showing that their effect is to work against cluster formation. For positive μ, we observe that colloids tend to reach an ordered state on a triangular lattice.

Doping effects on the relaxation of frustration and magnetic properties of YMn0.9Cu0.1O3

NASA Astrophysics Data System (ADS)

Xiao, L. X.; Xia, Z. C.; Wang, X.; Ni, Y.; Yu, W.; Shi, L. R.; Jin, Z.; Xiao, G. L.

2017-12-01

The crystal structure and magnetic properties of hexagonal YMn0.9Cu0.1O3 single crystal are systematically investigated. The refinement results of XRD show the lattice constant decreases, which is unusually due to the doped Cu2+ ion has a larger ionic radius than the Mn3+ ions. The XPS results show that the coexistence of Mn2+, Mn3+ and Mn4+ ions in YMn0.9Cu0.1O3 single crystal. Magnetization measurements show that Cu doped YMn0.9Cu0.1O3 and parent YMnO3 have almost the same antiferromagnetic transition temperature TN, which indicates the AFM interaction is robust in the geometry frustrated system. Because doping directly destroy some of the Mn3+ ions nets, the relaxation of frustration of Mn in-plane 2D triangular geometry network leads to the significantly decrease of Mn3+ ions AFM interaction. In addition, the coexistence and competition between the ferromagnetic and antiferromagnetic interactions among the Mn2+, Mn3+ and Mn4+ ions lead to a complicated and irreversible magnetization behavior in YMn0.9Cu0.1O3 single crystal.

Strings on plane-waves and spin chains on orbifolds

NASA Astrophysics Data System (ADS)

Sadri, Darius

This thesis covers a number of topics in string theory focusing on various aspects of the AdS/CFT duality in various guises and regimes. In the first chapter we present a self-contained review of the Plane-wave/super-Yang-Mills duality. This duality is a specification of the usual AdS/CFT correspondence in the "Penrose limit". In chapter two we study the most general parallelizable pp-wave backgrounds which are non-dilatonic solutions in the NS-NS sector of type IIA and IIB string theories. We demonstrate that parallelizable pp-wave backgrounds are necessarily homogeneous plane-waves, and that a large class of homogeneous plane-waves are parallelizable, stating the necessary conditions. Quantization of string modes, their compactification and behaviour under T-duality are also studied, as are BPS Dp-branes on such backgrounds. In chapter three we consider giant gravitons on the maximally supersymmetric plane-wave background. We deduce the low energy effective light-cone Hamiltonian of the three-sphere giant graviton, and place sources in this effective gauge theory. Although non-vanishing net electric charge configurations are disallowed by Gauss' law, electric dipoles can be formed. From the string theory point of view these dipoles can be understood as open strings piercing the three-sphere, giving a two dimensional (worldsheet) description of giant gravitons. Chapter four presents some new ideas regarding the relation between super-conformal gauge theories and string theories with three-dimensional target spaces, possible relations of these systems to Hamiltonian lattice gauge theories, and integrable spin chains. We consider N = 1, D = 4 superconformal SU( N)px q Yang-Mills theories dual to AdS5 x S5/Zp x Zq orbifolds. We show that a specific sector of this dilatation operator can be thought of as the transfer matrix for a three-dimensional statistical mechanical system, which in turn is equivalent to a 2 + 1-dimensional string theory where the spatial slices are discretized on a triangular lattice, and comment on the integrability of this N = 1 gauge theory, its connection to three-dimensional lattice gauge theories, extensions to six-dimensional string theories, AdS/CFT type dualities and finally their construction via orbifolds and brane-box models. In the process we discover a new class of almost-BPS BMN type operators with large engineering dimensions but controllably small anomalous corrections.

An algorithm for propagating the square-root covariance matrix in triangular form

NASA Technical Reports Server (NTRS)

Tapley, B. D.; Choe, C. Y.

1976-01-01

A method for propagating the square root of the state error covariance matrix in lower triangular form is described. The algorithm can be combined with any triangular square-root measurement update algorithm to obtain a triangular square-root sequential estimation algorithm. The triangular square-root algorithm compares favorably with the conventional sequential estimation algorithm with regard to computation time.

Transformation matrices between non-linear and linear differential equations

NASA Technical Reports Server (NTRS)

Sartain, R. L.

1983-01-01

In the linearization of systems of non-linear differential equations, those systems which can be exactly transformed into the second order linear differential equation Y"-AY'-BY=0 where Y, Y', and Y" are n x 1 vectors and A and B are constant n x n matrices of real numbers were considered. The 2n x 2n matrix was used to transform the above matrix equation into the first order matrix equation X' = MX. Specially the matrix M and the conditions which will diagonalize or triangularize M were studied. Transformation matrices P and P sub -1 were used to accomplish this diagonalization or triangularization to return to the solution of the second order matrix differential equation system from the first order system.

Triangular arbitrage in the foreign exchange market

NASA Astrophysics Data System (ADS)

Aiba, Yukihiro; Hatano, Naomichi

2004-12-01

We first review our previous work, showing what is the triangular arbitrage transaction and how to quantify the triangular arbitrage opportunity. Next we explain that the correlation of the foreign exchange rates can appear without actual triangular arbitrage transaction.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xu, Shao-Gang; Liao, Ji-Hai; Zhao, Yu-Jun

The unique electronic property induced diversified structure of boron (B) cluster has attracted much interest from experimentalists and theorists. B{sub 30–40} were reported to be planar fragments of triangular lattice with proper concentrations of vacancies recently. Here, we have performed high-throughput screening for possible B clusters through the first-principles calculations, including various shapes and distributions of vacancies. As a result, we have determined the structures of B{sub n} clusters with n = 30–51 and found a stable planar cluster of B{sub 49} with a double-hexagon vacancy. Considering the 8-electron rule and the electron delocalization, a concise model for the distributionmore » of the 2c–2e and 3c–2e bonds has been proposed to explain the stability of B planar clusters, as well as the reported B cages.« less

Ashkin-Teller criticality and weak first-order behavior of the phase transition to a fourfold degenerate state in two-dimensional frustrated Ising antiferromagnets

NASA Astrophysics Data System (ADS)

Liu, R. M.; Zhuo, W. Z.; Chen, J.; Qin, M. H.; Zeng, M.; Lu, X. B.; Gao, X. S.; Liu, J.-M.

2017-07-01

We study the thermal phase transition of the fourfold degenerate phases (the plaquette and single-stripe states) in the two-dimensional frustrated Ising model on the Shastry-Sutherland lattice using Monte Carlo simulations. The critical Ashkin-Teller-like behavior is identified both in the plaquette phase region and the single-stripe phase region. The four-state Potts critical end points differentiating the continuous transitions from the first-order ones are estimated based on finite-size-scaling analyses. Furthermore, a similar behavior of the transition to the fourfold single-stripe phase is also observed in the anisotropic triangular Ising model. Thus, this work clearly demonstrates that the transitions to the fourfold degenerate states of two-dimensional Ising antiferromagnets exhibit similar transition behavior.

A photonic crystal waveguide with silicon on insulator in the near-infrared band

NASA Astrophysics Data System (ADS)

Tang, Hai-Xia; Zuo, Yu-Hua; Yu, Jin-Zhong; Wang, Qi-Ming

2007-07-01

A two-dimensional (2D) photonic crystal waveguide in the Γ-K direction with triangular lattice on a silicon-on-insulator (SOI) substrate in the near-infrared band is fabricated by the combination of electron beam lithography and inductively coupled plasma etching. Its transmission characteristics are analysed from the stimulated band diagram by the effective index and the 2D plane wave expansion (PWE) methods. In the experiment, the transmission band edge in a longer wavelength of the photonic crystal waveguide is about 1590 nm, which is in good qualitative agreement with the simulated value. However, there is a disagreement between the experimental and the simulated results when the wavelength ranges from 1607 to 1630 nm, which can be considered as due to the unpolarized source used in the transmission measurement.

Node degree distribution in spanning trees

NASA Astrophysics Data System (ADS)

Pozrikidis, C.

2016-03-01

A method is presented for computing the number of spanning trees involving one link or a specified group of links, and excluding another link or a specified group of links, in a network described by a simple graph in terms of derivatives of the spanning-tree generating function defined with respect to the eigenvalues of the Kirchhoff (weighted Laplacian) matrix. The method is applied to deduce the node degree distribution in a complete or randomized set of spanning trees of an arbitrary network. An important feature of the proposed method is that the explicit construction of spanning trees is not required. It is shown that the node degree distribution in the spanning trees of the complete network is described by the binomial distribution. Numerical results are presented for the node degree distribution in square, triangular, and honeycomb lattices.

Strain-induced phase transition and electron spin-polarization in graphene spirals

PubMed Central

Zhang, Xiaoming; Zhao, Mingwen

2014-01-01

Spin-polarized triangular graphene nanoflakes (t-GNFs) serve as ideal building blocks for the long-desired ferromagnetic graphene superlattices, but they are always assembled to planar structures which reduce its mechanical properties. Here, by joining t-GNFs in a spiral way, we propose one-dimensional graphene spirals (GSs) with superior mechanical properties and tunable electronic structures. We demonstrate theoretically the unique features of electron motion in the spiral lattice by means of first-principles calculations combined with a simple Hubbard model. Within a linear elastic deformation range, the GSs are nonmagnetic metals. When the axial tensile strain exceeds an ultimate strain, however, they convert to magnetic semiconductors with stable ferromagnetic ordering along the edges. Such strain-induced phase transition and tunable electron spin-polarization revealed in the GSs open a new avenue for spintronics devices. PMID:25027550

Strain-induced phase transition and electron spin-polarization in graphene spirals.

PubMed

Zhang, Xiaoming; Zhao, Mingwen

2014-07-16

Spin-polarized triangular graphene nanoflakes (t-GNFs) serve as ideal building blocks for the long-desired ferromagnetic graphene superlattices, but they are always assembled to planar structures which reduce its mechanical properties. Here, by joining t-GNFs in a spiral way, we propose one-dimensional graphene spirals (GSs) with superior mechanical properties and tunable electronic structures. We demonstrate theoretically the unique features of electron motion in the spiral lattice by means of first-principles calculations combined with a simple Hubbard model. Within a linear elastic deformation range, the GSs are nonmagnetic metals. When the axial tensile strain exceeds an ultimate strain, however, they convert to magnetic semiconductors with stable ferromagnetic ordering along the edges. Such strain-induced phase transition and tunable electron spin-polarization revealed in the GSs open a new avenue for spintronics devices.

WOLF: a computer code package for the calculation of ion beam trajectories

DOE Office of Scientific and Technical Information (OSTI.GOV)

Vogel, D.L.

1985-10-01

The WOLF code solves POISSON'S equation within a user-defined problem boundary of arbitrary shape. The code is compatible with ANSI FORTRAN and uses a two-dimensional Cartesian coordinate geometry represented on a triangular lattice. The vacuum electric fields and equipotential lines are calculated for the input problem. The use may then introduce a series of emitters from which particles of different charge-to-mass ratios and initial energies can originate. These non-relativistic particles will then be traced by WOLF through the user-defined region. Effects of ion and electron space charge are included in the calculation. A subprogram PISA forms part of this codemore » and enables optimization of various aspects of the problem. The WOLF package also allows detailed graphics analysis of the computed results to be performed.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Brummer, Gordie, E-mail: gbrummer@bu.edu; Photonics Center, Boston University, Boston, Massachusetts 02215; Nothern, Denis

Distributed Bragg reflectors (DBRs) with peak reflectivity at approximately 280 nm, based on compositionally graded Al{sub x}Ga{sub 1−x}N alloys, were grown on 6H-SiC substrates by plasma-assisted molecular beam epitaxy. DBRs with square, sinusoidal, triangular, and sawtooth composition profiles were designed with the transfer matrix method. The crystal structure of these DBRs was studied with high-resolution x-ray diffraction of the (1{sup ¯}015) reciprocal lattice point. The periodicity of the DBR profiles was confirmed with cross-sectional Z-contrast scanning transmission electron microscopy. The peak reflectance of these DBRs with 15.5 periods varies from 77% to 56% with corresponding full width at half maximum ofmore » 17–14 nm. Coupled mode analysis was used to explain the dependence of the reflectivity characteristics on the profile of the graded composition.« less

Double level selection in a constitutional dynamic library of coordination driven supramolecular polygons.

PubMed

Rancan, Marzio; Tessarolo, Jacopo; Casarin, Maurizio; Zanonato, Pier Luigi; Quici, Silvio; Armelao, Lidia

2014-07-21

A constitutional dynamic library (CDL) of Cu(II) metallo-supramolecular polygons has been studied as a bench test to examine an interesting selection case based on molecular recognition. Sorting of the CDL polygons is achieved through a proper guest that is hosted into the triangular metallo-macrocycle constituent. Two selection mechanisms are observed, a guest induced path and a guest templated self-assembly (virtual library approach). Remarkably, the triangular host can accommodate several guests with a degree of selectivity ranging from ∼1 to ∼10(4) for all possible guest pairs. A double level selection operates: guests drive the CDL toward the triangular polygon, and, at the same time, this is able to pick a specific guest from a set of competitive molecules, according to a selectivity-affinity correlation. Association constants of the host-guest systems have been determined. Guest competition and exchange studies have been analyzed through variable temperature UV-Vis absorption spectroscopy and single crystal X-ray diffraction studies. Molecular structures and electronic properties of the triangular polygon and of the host-guest systems also have been studied by means of all electrons density functional theory (DFT) and time-dependent density functional theory (TDDFT) calculations including dispersive contributions. DFT outcomes ultimately indicate the dispersive nature of the host-guest interactions, while TDDFT results allow a thorough assignment of the host and host-guests spectral features.

Phase transitions in Ising models on directed networks

NASA Astrophysics Data System (ADS)

Lipowski, Adam; Ferreira, António Luis; Lipowska, Dorota; Gontarek, Krzysztof

2015-11-01

We examine Ising models with heat-bath dynamics on directed networks. Our simulations show that Ising models on directed triangular and simple cubic lattices undergo a phase transition that most likely belongs to the Ising universality class. On the directed square lattice the model remains paramagnetic at any positive temperature as already reported in some previous studies. We also examine random directed graphs and show that contrary to undirected ones, percolation of directed bonds does not guarantee ferromagnetic ordering. Only above a certain threshold can a random directed graph support finite-temperature ferromagnetic ordering. Such behavior is found also for out-homogeneous random graphs, but in this case the analysis of magnetic and percolative properties can be done exactly. Directed random graphs also differ from undirected ones with respect to zero-temperature freezing. Only at low connectivity do they remain trapped in a disordered configuration. Above a certain threshold, however, the zero-temperature dynamics quickly drives the model toward a broken symmetry (magnetized) state. Only above this threshold, which is almost twice as large as the percolation threshold, do we expect the Ising model to have a positive critical temperature. With a very good accuracy, the behavior on directed random graphs is reproduced within a certain approximate scheme.

Possible nodal vortex state in CeRu2

NASA Astrophysics Data System (ADS)

Kadono, R.; Higemoto, W.; Koda, A.; Ohishi, K.; Yokoo, T.; Akimitsu, J.; Hedo, M.; Inada, Y.; O¯nuki, Y.; Yamamoto, E.; Haga, Y.

2001-06-01

The microscopic property of magnetic vortices in the mixed state of a high-quality CeRu2 crystal has been studied by muon spin rotation. We have found that the spatial distribution of magnetic induction B(r) probed by muons is perfectly described by the London model for the triangular vortex lattice with appropriate modifications to incorporate the high-field cutoff around the vortex core and the effect of long-range defects in the vortex lattice structure at lower fields. The vortex core radius is proportional to H(β-1)/2 with β~=0.53 (H being the magnetic field), which is in good agreement with the recently observed nonlinear field dependence of the electronic specific heat coefficient γ~Hβ. In particular, the anomalous increase of magnetic penetration depth in accordance with the peak effect in dc magnetization (>=H*~=3 T at 2.0 K) has been confirmed; this cannot be explained by the conventional pair-breaking effect due to magnetic field. In addition, the spontaneous enhancement of flux pinning, which is also associated with the peak effect, has been demonstrated microscopically. These results strongly suggest the onset of collective pinning induced by a new vortex state having an anomalously enhanced quasiparticle density of states for H>=H*.

Slip-flow in complex porous media as determined by a multi-relaxation-time lattice Boltzmann model

NASA Astrophysics Data System (ADS)

Landry, C. J.; Prodanovic, M.; Eichhubl, P.

2014-12-01

The pores and throats of shales and mudrocks are predominantly found within a range of 1-100 nm, within this size range the flow of gas at reservoir conditions will fall within the slip-flow and low transition-flow regime (0.001 < Kn < 0.5). Currently, the study of slip-flows is for the most part limited to simple tube and channel geometries, however, the geometry of mudrock pores is often sponge-like (organic matter) and/or platy (clays). Molecular dynamics (MD) simulations can be used to predict slip-flow in complex geometries, but due to prohibitive computational demand are generally limited to small volumes (one to several pores). Here we present a multi-relaxation-time lattice Boltzmann model (LBM) parameterized for slip-flow (Guo et al. 2008) and adapted here to complex geometries. LBMs are inherently parallelizable, such that flow in complex geometries of significant (near REV-scale) volumes can be readily simulated at a fraction of the computational cost of MD simulations. At the macroscopic-scale the LBM is parameterized with local effective viscosities at each node to capture the variance of the mean-free-path of gas molecules in a bounded system. The corrected mean-free-path for each lattice node is determined using the mean distance of the node to the pore-wall and Stop's correction for mean-free-paths in an infinite parallel-plate geometry. At the microscopic-scale, a combined bounce-back specular-reflection boundary condition is applied to the pore-wall nodes to capture Maxwellian-slip. The LBM simulation results are first validated in simple tube and channel geometries, where good agreement is found for Knudsen numbers below 0.1, and fair agreement is found for Knudsen numbers between 0.1 and 0.5. More complex geometries are then examined including triangular-ducts and ellipsoid-ducts, both with constant and tapering/expanding cross-sections, as well as a clay pore-network imaged from a hydrocarbon producing shale by sequential focused ion-beam scanning electron microscopy. These results are analyzed to determine grid-independent resolutions, and used to explore the relationship between effective permeability and Knudsen number in complex geometries.

On some labelings of triangular snake and central graph of triangular snake graph

NASA Astrophysics Data System (ADS)

Agasthi, P.; Parvathi, N.

2018-04-01

A Triangular snake Tn is obtained from a path u 1 u 2 … u n by joining ui and u i+1 to a new vertex wi for 1≤i≤n‑1. A Central graph of Triangular snake C(T n ) is obtained by subdividing each edge of Tn exactly once and joining all the non adjacent vertices of Tn . In this paper the ways to construct square sum, square difference, Root Mean square, strongly Multiplicative, Even Mean and Odd Mean labeling for Triangular Snake and Central graph of Triangular Snake graphs are reported.

One-Pot Polyol Synthesis of Pt/CeO2 and Au/CeO2 Nanopowders as Catalysts for CO Oxidation.

PubMed

Pilger, Frank; Testino, Andrea; Lucchini, Mattia Alberto; Kambolis, Anastasios; Tarik, Mohammed; El Kazzi, Mario; Arroyo, Yadira; Rossell, Marta D; Ludwig, Christian

2015-05-01

The facile one-pot synthesis of CeO2-based catalysts has been developed to prepare a relatively large amount of nanopowders with relevant catalytic activity towards CO oxidation. The method consists of a two-steps process carried out in ethylene glycol: in the first step, 5 nm well-crystallized pure CeO2 is prepared. In a subsequent second step, a salt of a noble metal is added to the CeO2 suspension and the deposition of the noble metal on the nanocrystalline CeO2 is induced by heating. Two catalysts were prepared: Pt/CeO2 and Au/CeO2. The as-prepared catalysts, the thermally treated catalysts, as well as the pure CeO2, are characterized by XRD, TGA, XPS, FTIR, HR-TEM, STEM, particle size distribution, and N2-physisorption. In spite of the identical preparation protocol, Au and Pt behave in a completely different way: Au forms rather large particles, most of them with triangular shape, easily identifiable and dispersed in the CeO2 matrix. In contrast, Pt was not identified as isolated particles. The high resolution X-ray diffraction carried out on the Pt/CeO2 thermally treated sample (500 degrees C for 1 h) shows a significant CeO2 lattice shrinkage, which can be interpreted as an at least partial incorporation of Pt into the CeO2 crystal lattice. Moreover, only Pt2+ and Pt4+ species were identified by XPS. In literature, the incorporation of Pt into the CeO2 lattice is supported by first-principle calculations and experimentally demonstrated only by combustion synthesis methods. To the best of our knowledge this is the first report where ionically dispersed Pt into the CeO2 lattice is obtained via a liquid synthesis method. The thermally treated Pt/CeO2 sample revealed good activity with 50% CO conversion at almost room temperature.

System and Method for Generating a Frequency Modulated Linear Laser Waveform

NASA Technical Reports Server (NTRS)

Pierrottet, Diego F. (Inventor); Petway, Larry B. (Inventor); Amzajerdian, Farzin (Inventor); Barnes, Bruce W. (Inventor); Lockard, George E. (Inventor); Hines, Glenn D. (Inventor)

2017-01-01

A system for generating a frequency modulated linear laser waveform includes a single frequency laser generator to produce a laser output signal. An electro-optical modulator modulates the frequency of the laser output signal to define a linear triangular waveform. An optical circulator passes the linear triangular waveform to a band-pass optical filter to filter out harmonic frequencies created in the waveform during modulation of the laser output signal, to define a pure filtered modulated waveform having a very narrow bandwidth. The optical circulator receives the pure filtered modulated laser waveform and transmits the modulated laser waveform to a target.

System and Method for Generating a Frequency Modulated Linear Laser Waveform

NASA Technical Reports Server (NTRS)

Pierrottet, Diego F. (Inventor); Petway, Larry B. (Inventor); Amzajerdian, Farzin (Inventor); Barnes, Bruce W. (Inventor); Lockard, George E. (Inventor); Hines, Glenn D. (Inventor)

2014-01-01

A system for generating a frequency modulated linear laser waveform includes a single frequency laser generator to produce a laser output signal. An electro-optical modulator modulates the frequency of the laser output signal to define a linear triangular waveform. An optical circulator passes the linear triangular waveform to a band-pass optical filter to filter out harmonic frequencies created in the waveform during modulation of the laser output signal, to define a pure filtered modulated waveform having a very narrow bandwidth. The optical circulator receives the pure filtered modulated laser waveform and transmits the modulated laser waveform to a target.

Structural models of inorganic fullerene-like structures

NASA Astrophysics Data System (ADS)

Ascencio, J. A.; Perez-Alvarez, M.; Molina, L. M.; Santiago, P.; José-Yacaman, M.

2003-03-01

In the study of fullerene-like structures, some of the more interesting systems are the inorganic cages, made of MoS 2 (usually named inorganic fullerenes), which have many important potential applications as lubricant and catalysts. In the present work, we report calculations for structural models of closed cage of inorganic fullerene-like structures for MoS 2 system. Three cage shapes were found to be the most stable: triangular pyramid, octahedron and dodecahedron. High resolution TEM images of MoS 2 cages structures were calculated to be compared with experimental data. Some examples of triangular pyramid and polyhedron in experimental MoS 2 samples are presented.

Spin and charge controlled by antisymmetric spin-orbit coupling in a triangular-triple-quantum-dot Kondo system

NASA Astrophysics Data System (ADS)

Koga, M.; Matsumoto, M.; Kusunose, H.

2018-05-01

We study a local antisymmetric spin-orbit (ASO) coupling effect on a triangular-triple-quantum-dot (TTQD) system as a theoretical proposal for a new application of the Kondo physics to nanoscale devices. The electric polarization induced by the Kondo effect is strongly correlated with the spin configurations and molecular orbital degrees of freedom in the TTQD. In particular, an abrupt sign reversal of the emergent electric polarization is associated with a quantum critical point in a magnetic field, which can also be controlled by the ASO coupling that changes the mixing weight of different orbital components in the TTQD ground state.

Recent Topics of Organic Superconductors

NASA Astrophysics Data System (ADS)

Ardavan, Arzhang; Brown, Stuart; Kagoshima, Seiichi; Kanoda, Kazushi; Kuroki, Kazuhiko; Mori, Hatsumi; Ogata, Masao; Uji, Shinya; Wosnitza, Jochen

2012-01-01

Recent developments in research into superconductivity in organic materials are reviewed. In the epoch-defining quasi-one-dimensional TMTSF superconductors with Tc ˜ 1 K, Tc decreases monotonically with increasing pressure, as do signatures of spin fluctuations in the normal state, providing good evidence for magnetically-mediated pairing. Upper critical fields exceed the Zeeman-limiting field by several times, suggesting triplet pairing or a transition to an inhomogeneous superconducting state at high magnetic fields, while triplet pairing is ruled out at low fields by NMR Knight-shift measurements. Evidence for a spatially inhomogeneous superconducting state, Fulde--Ferrel--Larkin--Ovchinnikov state, which has long been sought in various superconducting systems, is now captured by thermodynamic and transport measurements for clean and highly two-dimensional BEDT-TTF and BETS superconductors. Some of the layered superconductors also serve as model systems for Mott physics on anisotropic triangular lattice. For example, the Nernst effect and the pseudo-gap behavior in NMR relaxation are enhanced near to the Mott transition. In the case of increasing spin frustration, the superconducting transition temperature is depressed, and antiferromagnetic ordering is eliminated altogether in the adjacent Mott insulating phase. There is an increasing number of materials exhibiting superconductivity in competition or cooperation with charge order. Theoretical studies shed light on the role of spin and/or charge fluctuations for superconductivity appearing under conditions close to those of correlation-induced insulating phases in the diversity of organic materials.

Stabilizers as a design tool for new forms of the Lechner-Hauke-Zoller annealer

PubMed Central

Rocchetto, Andrea; Benjamin, Simon C.; Li, Ying

2016-01-01

In a recent paper, Lechner, Hauke, and Zoller (LHZ) described a means to translate a Hamiltonian of N spin-1/2 particles with “all-to-all” interactions into a larger physical lattice with only on-site energies and local parity constraints. LHZ used this mapping to propose a novel form of quantum annealing. We provide a stabilizer-based formulation within which we can describe both this prior approach and a wide variety of variants. Examples include a triangular array supporting all-to-all connectivity as well as arrangements requiring only 2N or N log N spins but providing interesting bespoke connectivities. Further examples show that arbitrarily high-order logical terms can be efficiently realized, even in a strictly two-dimensional layout. Our stabilizers can correspond to either even-parity constraints, as in the LHZ proposal, or odd-parity constraints. Considering the latter option applied to the original LHZ layout, we note that it may simplify the physical realization because the required ancillas are only spin-1/2 systems (that is, qubits rather than qutrits); moreover, the interactions are very simple. We make a preliminary assessment of the impact of these design choices by simulating small (few-qubit) systems; we find some indications that the new variant may maintain a larger minimum energy gap during the annealing process. PMID:27819050

Balanced Central Schemes for the Shallow Water Equations on Unstructured Grids

NASA Technical Reports Server (NTRS)

Bryson, Steve; Levy, Doron

2004-01-01

We present a two-dimensional, well-balanced, central-upwind scheme for approximating solutions of the shallow water equations in the presence of a stationary bottom topography on triangular meshes. Our starting point is the recent central scheme of Kurganov and Petrova (KP) for approximating solutions of conservation laws on triangular meshes. In order to extend this scheme from systems of conservation laws to systems of balance laws one has to find an appropriate discretization of the source terms. We first show that for general triangulations there is no discretization of the source terms that corresponds to a well-balanced form of the KP scheme. We then derive a new variant of a central scheme that can be balanced on triangular meshes. We note in passing that it is straightforward to extend the KP scheme to general unstructured conformal meshes. This extension allows us to recover our previous well-balanced scheme on Cartesian grids. We conclude with several simulations, verifying the second-order accuracy of our scheme as well as its well-balanced properties.

Hierarchically triangular prism structured Co3O4: Self-supported fabrication and photocatalytic property

EPA Science Inventory

The formation of ammonium cobalt (II) phosphate was utilized to synthesize unprecedented 3D structures of Co3O4, triangular prisms and trunk-like structures, via a self-supported and organics-free method. The length of a triangular side of the prepared 3D triangular prisms is ~1...

Instrument Landing System performance prediction

DOT National Transportation Integrated Search

1974-01-01

Further achievements made in fiscal year 1973 on the development : of an Instrument Landing System (ILS) performance prediction model : are reported. These include (ILS) localizer scattering from generalized : slanted rectangular, triangular and cyli...

Measurements of elliptic and triangular flow in high-multiplicity 3He+Au collisions at √s NN=200 GeV

DOE PAGES

Adare, A.

2015-09-28

We present the first measurement of elliptic (v 2) and triangular (v 3) flow in high-multiplicity 3He+Aucollisions at √s NN=200 GeV. Two-particle correlations, where the particles have a large separation in pseudorapidity, are compared in 3He+Au and in p+p collisions and indicate that collective effects dominate the second and third Fourier components for the correlations observed in the 3He+Ausystem. The collective behavior is quantified in terms of elliptic v 2 and triangular v 3 anisotropy coefficients measured with respect to their corresponding event planes. The v 2 values are comparable to those previously measured in d+Au collisions at the samemore » nucleon-nucleon center-of-mass energy. Comparisons with various theoretical predictions are made, including to models where the hot spots created by the impact of the three 3He nucleons on the Au nucleus expand hydrodynamically to generate the triangular flow. The agreement of these models with data may indicate the formation of low-viscosity quark-gluon plasma even in these small collision systems.« less

Geometric Triangular Chiral Hexagon Crystal-Like Complexes Organization in Pathological Tissues Biological Collision Order

PubMed Central

Díaz, Jairo A.; Jaramillo, Natalia A.; Murillo, Mauricio F.

2007-01-01

The present study describes and documents self-assembly of geometric triangular chiral hexagon crystal like complex organizations (GTCHC) in human pathological tissues.The authors have found this architectural geometric expression at macroscopic and microscopic levels mainly in cancer processes. This study is based essentially on macroscopic and histopathologic analyses of 3000 surgical specimens: 2600 inflammatory lesions and 400 malignant tumours. Geometric complexes identified photographically at macroscopic level were located in the gross surgical specimen, and these areas were carefully dissected. Samples were taken to carry out histologic analysis. Based on the hypothesis of a collision genesis mechanism and because it is difficult to carry out an appropriate methodological observation in biological systems, the authors designed a model base on other dynamic systems to obtain indirect information in which a strong white flash wave light discharge, generated by an electronic device, hits over the lines of electrical conductance structured in helicoidal pattern. In their experimental model, the authors were able to reproduce and to predict polarity, chirality, helicoid geometry, triangular and hexagonal clusters through electromagnetic sequential collisions. They determined that similar events among constituents of extracelular matrix which drive and produce piezoelectric activity are responsible for the genesis of GTCHC complexes in pathological tissues. This research suggests that molecular crystals represented by triangular chiral hexagons derived from a collision-attraction event against collagen type I fibrils emerge at microscopic and macroscopic scales presenting a lateral assembly of each side of hypertrophy helicoid fibers, that represent energy flow in cooperative hierarchically chiral electromagnetic interaction in pathological tissues and arises as a geometry of the equilibrium in perturbed biological systems. Further interdisciplinary studies must be carried out to reproduce, manipulate and amplify their activity and probably use them as a base to develop new therapeutic strategies in cancer. PMID:18074008

A microcomputer program for energy assessment and aggregation using the triangular probability distribution

USGS Publications Warehouse

Crovelli, R.A.; Balay, R.H.

1991-01-01

A general risk-analysis method was developed for petroleum-resource assessment and other applications. The triangular probability distribution is used as a model with an analytic aggregation methodology based on probability theory rather than Monte-Carlo simulation. Among the advantages of the analytic method are its computational speed and flexibility, and the saving of time and cost on a microcomputer. The input into the model consists of a set of components (e.g. geologic provinces) and, for each component, three potential resource estimates: minimum, most likely (mode), and maximum. Assuming a triangular probability distribution, the mean, standard deviation, and seven fractiles (F100, F95, F75, F50, F25, F5, and F0) are computed for each component, where for example, the probability of more than F95 is equal to 0.95. The components are aggregated by combining the means, standard deviations, and respective fractiles under three possible siutations (1) perfect positive correlation, (2) complete independence, and (3) any degree of dependence between these two polar situations. A package of computer programs named the TRIAGG system was written in the Turbo Pascal 4.0 language for performing the analytic probabilistic methodology. The system consists of a program for processing triangular probability distribution assessments and aggregations, and a separate aggregation routine for aggregating aggregations. The user's documentation and program diskette of the TRIAGG system are available from USGS Open File Services. TRIAGG requires an IBM-PC/XT/AT compatible microcomputer with 256kbyte of main memory, MS-DOS 3.1 or later, either two diskette drives or a fixed disk, and a 132 column printer. A graphics adapter and color display are optional. ?? 1991.

On the estimation of sound speed in two-dimensional Yukawa fluids

DOE Office of Scientific and Technical Information (OSTI.GOV)

Semenov, I. L., E-mail: Igor.Semenov@dlr.de; Thomas, H. M.; Khrapak, S. A.

2015-11-15

The longitudinal sound speed in two-dimensional Yukawa fluids is estimated using the conventional hydrodynamic expression supplemented by appropriate thermodynamic functions proposed recently by Khrapak et al. [Phys. Plasmas 22, 083706 (2015)]. In contrast to the existing approaches, such as quasi-localized charge approximation (QLCA) and molecular dynamics simulations, our model provides a relatively simple estimate for the sound speed over a wide range of parameters of interest. At strong coupling, our results are shown to be in good agreement with the results obtained using the QLCA approach and those derived from the phonon spectrum for the triangular lattice. On the othermore » hand, our model is also expected to remain accurate at moderate values of the coupling strength. In addition, the obtained results are used to discuss the influence of the strong coupling effects on the adiabatic index of two-dimensional Yukawa fluids.« less

Membrane potential dynamics of grid cells

PubMed Central

Domnisoru, Cristina; Kinkhabwala, Amina A.; Tank, David W.

2014-01-01

During navigation, grid cells increase their spike rates in firing fields arranged on a strikingly regular triangular lattice, while their spike timing is often modulated by theta oscillations. Oscillatory interference models of grid cells predict theta amplitude modulations of membrane potential during firing field traversals, while competing attractor network models predict slow depolarizing ramps. Here, using in-vivo whole-cell recordings, we tested these models by directly measuring grid cell intracellular potentials in mice running along linear tracks in virtual reality. Grid cells had large and reproducible ramps of membrane potential depolarization that were the characteristic signature tightly correlated with firing fields. Grid cells also exhibited intracellular theta oscillations that influenced their spike timing. However, the properties of theta amplitude modulations were not consistent with the view that they determine firing field locations. Our results support cellular and network mechanisms in which grid fields are produced by slow ramps, as in attractor models, while theta oscillations control spike timing. PMID:23395984

Ultrabroadband polarization splitter based on three-core photonic crystal fiber with a modulation core.

PubMed

Zhao, Tongtong; Lou, Shuqin; Wang, Xin; Zhou, Min; Lian, Zhenggang

2016-08-10

We design an ultrabroadband polarization splitter based on three-core photonic crystal fiber (PCF). A modulation core and two fluorine-doped cores are introduced to achieve an ultrawide bandwidth. The properties of three-core PCF are modeled by using the full-vector finite element method along with the full-vector beam propagation method. Numerical results demonstrate that an ultrabroadband splitter with 320 nm bandwidth with an extinction ratio as low as -20  dB can be achieved by using 52.8 mm long three-core PCF. This splitter also has high compatibility with standard single-mode fibers as the input and output ports due to low splicing loss of 0.02 dB. All the air holes in the proposed structure are circular holes and arranged in a triangular lattice that makes it easy to fabricate.

Reconfigurable all-optical NOT, XOR, and NOR logic gates based on two dimensional photonic crystals

NASA Astrophysics Data System (ADS)

Parandin, Fariborz; Malmir, M. Reza; Naseri, Mosayeb; Zahedi, Abdulhamid

2018-01-01

Photonic crystals can be considered as one of the most important basis for designing optical devices. In this research, using two-dimensional photonic crystals with triangular lattices, ultra-compact logic gates are designed and simulated. The intended structure has the capability to be used as three logical gates (NOT, XOR, and NOR). The designed structures not only have characteristics of small dimensions which make them suitable for integrated optical circuits, but also exhibit very low power transfer delay which makes it possible to design high speed gates. On comparison with the previous works, our simulations show that at a wavelength of 1.55 μm , the gates indicate a time delay of about 0.1 ps and the contrast ratio for the XOR gate is about 30 dB, i.e., the proposed structures are more applicable in designing low error optical logic gates.

Distortion of 3D SU8 photonic structures fabricated by four-beam holographic lithography withumbrella configuration.

PubMed

Zhu, Xuelian; Xu, Yongan; Yang, Shu

2007-12-10

We present a quantitative study of the distortion from a threeterm diamond-like structure fabricated in SU8 polymer by four-beam holographic lithography. In the study of the refraction effect, theory suggests that the lattice in SU8 should be elongated in the [111] direction but have no distortion in the (111) plane, and each triangular-like hole array in the (111) plane would rotate by ~30 degrees away from that in air. Our experiments agree with the prediction on the periodicity in the (111) plane and the rotation due to refraction effect, however, we find that the film shrinkage during lithographic process has nearly compensated the predicted elongation in the [111] direction. In study of photonic bandgap (PBG) properties of silicon photonic crystals templated by the SU8 structure, we find that the distortion has decreased quality of PBG.

Experimental observation of wave localization at the Dirac frequency in a two-dimensional photonic crystal microcavity.

PubMed

Hu, Lei; Xie, Kang; Hu, Zhijia; Mao, Qiuping; Xia, Jiangying; Jiang, Haiming; Zhang, Junxi; Wen, Jianxiang; Chen, Jingjing

2018-04-02

Trapping light within cavities or waveguides in photonic crystals is an effective technology in modern integrated optics. Traditionally, cavities rely on total internal reflection or a photonic bandgap to achieve field confinement. Recent investigations have examined new localized modes that occur at a Dirac frequency that is beyond any complete photonic bandgap. We design Al 2 O 3 dielectric cylinders placed on a triangular lattice in air, and change the central rod size to form a photonic crystal microcavity. It is predicted that waves can be localized at the Dirac frequency in this device without photonic bandgaps or total internal reflections. We perform a theoretical analysis of this new wave localization and verify it experimentally. This work paves the way for exploring localized defect modes at the Dirac point in the visible and infrared bands, with potential applicability to new optical devices.

Layered copper hydroxide n-alkylsulfonate salts: synthesis, characterization, and magnetic behaviors in relation to the basal spacing.

PubMed

Park, Seong-Hun; Lee, Cheol Eui

2005-01-27

A series of hybrid inorganic-organic copper(II) hydroxy n-alkylsulfonate with a triangular lattice, Cu(2)(OH)(3)(C(n)H(2)(n)(+1)SO(3)) (n = 6, 8, 10), are prepared by anion exchange, starting from copper hydroxy nitrate Cu(2)(OH)(3)NO(3). These compounds show a layered structure as determined by X-ray diffraction, with interlayer distances of 14.3-34.8 A in alternation with interdigitated bilayer packing. Magnetic properties have been investigated by means of dc and ac measurements. All the compounds show similar metamagnet behaviors, with a Neel temperature of about 11 K. A subtle difference in the ac magnetic susceptibility among the compounds is understood by the existence of hydrogen bonding between the sulfonate headgroup and the hydroxide anion. A detailed molecular structure of the alkyl chains incorporated to the inorganic copper hydroxide layer is also discussed from the FTIR data.

Upon Generating Discrete Expanding Integrable Models of the Toda Lattice Systems and Infinite Conservation Laws

NASA Astrophysics Data System (ADS)

Zhang, Yufeng; Zhang, Xiangzhi; Wang, Yan; Liu, Jiangen

2017-01-01

With the help of R-matrix approach, we present the Toda lattice systems that have extensive applications in statistical physics and quantum physics. By constructing a new discrete integrable formula by R-matrix, the discrete expanding integrable models of the Toda lattice systems and their Lax pairs are generated, respectively. By following the constructing formula again, we obtain the corresponding (2+1)-dimensional Toda lattice systems and their Lax pairs, as well as their (2+1)-dimensional discrete expanding integrable models. Finally, some conservation laws of a (1+1)-dimensional generalised Toda lattice system and a new (2+1)-dimensional lattice system are generated, respectively.

Design of Miniaturized Double-Negative Material for Specific Absorption Rate Reduction in Human Head

PubMed Central

Faruque, Mohammad Rashed Iqbal; Islam, Mohammad Tariqul

2014-01-01

In this study, a double-negative triangular metamaterial (TMM) structure, which exhibits a resounding electric response at microwave frequency, was developed by etching two concentric triangular rings of conducting materials. A finite-difference time-domain method in conjunction with the lossy-Drude model was used in this study. Simulations were performed using the CST Microwave Studio. The specific absorption rate (SAR) reduction technique is discussed, and the effects of the position of attachment, the distance, and the size of the metamaterials on the SAR reduction are explored. The performance of the double-negative TMMs in cellular phones was also measured in the cheek and the tilted positions using the COMOSAR system. The TMMs achieved a 52.28% reduction for the 10 g SAR. These results provide a guideline to determine the triangular design of metamaterials with the maximum SAR reducing effect for a mobile phone. PMID:25350398

Design of miniaturized double-negative material for specific absorption rate reduction in human head.

PubMed

Faruque, Mohammad Rashed Iqbal; Islam, Mohammad Tariqul

2014-01-01

In this study, a double-negative triangular metamaterial (TMM) structure, which exhibits a resounding electric response at microwave frequency, was developed by etching two concentric triangular rings of conducting materials. A finite-difference time-domain method in conjunction with the lossy-Drude model was used in this study. Simulations were performed using the CST Microwave Studio. The specific absorption rate (SAR) reduction technique is discussed, and the effects of the position of attachment, the distance, and the size of the metamaterials on the SAR reduction are explored. The performance of the double-negative TMMs in cellular phones was also measured in the cheek and the tilted positions using the COMOSAR system. The TMMs achieved a 52.28% reduction for the 10 g SAR. These results provide a guideline to determine the triangular design of metamaterials with the maximum SAR reducing effect for a mobile phone.

High-Order Residual-Distribution Schemes for Discontinuous Problems on Irregular Triangular Grids

NASA Technical Reports Server (NTRS)

Mazaheri, Alireza; Nishikawa, Hiroaki

2016-01-01

In this paper, we develop second- and third-order non-oscillatory shock-capturing hyperbolic residual distribution schemes for irregular triangular grids, extending our second- and third-order schemes to discontinuous problems. We present extended first-order N- and Rusanov-scheme formulations for hyperbolic advection-diffusion system, and demonstrate that the hyperbolic diffusion term does not affect the solution of inviscid problems for vanishingly small viscous coefficient. We then propose second- and third-order blended hyperbolic residual-distribution schemes with the extended first-order Rusanov-scheme. We show that these proposed schemes are extremely accurate in predicting non-oscillatory solutions for discontinuous problems. We also propose a characteristics-based nonlinear wave sensor for accurately detecting shocks, compression, and expansion regions. Using this proposed sensor, we demonstrate that the developed hyperbolic blended schemes do not produce entropy-violating solutions (unphysical stocks). We then verify the design order of accuracy of these blended schemes on irregular triangular grids.

Existence and instability of steady states for a triangular cross-diffusion system: A computer-assisted proof

NASA Astrophysics Data System (ADS)

Breden, Maxime; Castelli, Roberto

2018-05-01

In this paper, we present and apply a computer-assisted method to study steady states of a triangular cross-diffusion system. Our approach consist in an a posteriori validation procedure, that is based on using a fixed point argument around a numerically computed solution, in the spirit of the Newton-Kantorovich theorem. It allows to prove the existence of various non homogeneous steady states for different parameter values. In some situations, we obtain as many as 13 coexisting steady states. We also apply the a posteriori validation procedure to study the linear stability of the obtained steady states, proving that many of them are in fact unstable.

Algorithms for solving large sparse systems of simultaneous linear equations on vector processors

NASA Technical Reports Server (NTRS)

David, R. E.

1984-01-01

Very efficient algorithms for solving large sparse systems of simultaneous linear equations have been developed for serial processing computers. These involve a reordering of matrix rows and columns in order to obtain a near triangular pattern of nonzero elements. Then an LU factorization is developed to represent the matrix inverse in terms of a sequence of elementary Gaussian eliminations, or pivots. In this paper it is shown how these algorithms are adapted for efficient implementation on vector processors. Results obtained on the CYBER 200 Model 205 are presented for a series of large test problems which show the comparative advantages of the triangularization and vector processing algorithms.

Heteroclinic, Homoclinic Connections Between the Sun-Earth Triangular Points and Quasi-Satellite Orbits for Solar Observations

NASA Technical Reports Server (NTRS)

Llanos, Pedro J.; Hintz, Gerald R.; Lo, Martin W.; Miller, James K.

2013-01-01

Investigation of new orbit geometries exhibits a very attractive behavior for a spacecraft to monitor space weather coming from the Sun. Several orbit transfer mechanisms are analyzed as potential alternatives to monitor solar activity such as a sub-solar orbit or quasi-satellite orbit and short and long heteroclinic and homoclinic connections between the triangular points L(sub 4) and L(sub 5) and the collinear point L(sub 3) of the Circular Restricted Three-Body Problem (CRTBP) in the Sun-Earth system.

New method for propagating the square root covariance matrix in triangular form. [using Kalman-Bucy filter

NASA Technical Reports Server (NTRS)

Choe, C. Y.; Tapley, B. D.

1975-01-01

A method proposed by Potter of applying the Kalman-Bucy filter to the problem of estimating the state of a dynamic system is described, in which the square root of the state error covariance matrix is used to process the observations. A new technique which propagates the covariance square root matrix in lower triangular form is given for the discrete observation case. The technique is faster than previously proposed algorithms and is well-adapted for use with the Carlson square root measurement algorithm.

The correlation of initial radiographic characteristics of distal radius fractures and injuries of the triangular fibrocartilage complex.

PubMed

Kasapinova, K; Kamiloski, V

2016-06-01

Our purpose was to determine the correlation of initial radiographic parameters of a distal radius fracture with an injury of the triangular fibrocartilage complex. In a prospective study, 85 patients with surgically treated distal radius fractures were included. Wrist arthroscopy was used to identify and classify triangular fibrocartilage complex lesions. The initial radial length and angulation, dorsal angulation, ulnar variance and distal radioulnar distance were measured. Wrist arthroscopy identified a triangular fibrocartilage complex lesion in 45 patients. Statistical analysis did not identify a correlation with any single radiographic parameter of the distal radius fractures with the associated triangular fibrocartilage complex injuries. The initial radiograph of a distal radius fracture does not predict a triangular fibrocartilage complex injury. III. © The Author(s) 2016.

Hesitant triangular fuzzy information aggregation operators based on Bonferroni means and their application to multiple attribute decision making.

PubMed

Wang, Chunyong; Li, Qingguo; Zhou, Xiaoqiang; Yang, Tian

2014-01-01

We investigate the multiple attribute decision-making (MADM) problems with hesitant triangular fuzzy information. Firstly, definition and some operational laws of hesitant triangular fuzzy elements are introduced. Then, we develop some hesitant triangular fuzzy aggregation operators based on Bonferroni means and discuss their basic properties. Some existing operators can be viewed as their special cases. Next, we apply the proposed operators to deal with multiple attribute decision-making problems under hesitant triangular fuzzy environment. Finally, an illustrative example is given to show the developed method and demonstrate its practicality and effectiveness.

Hesitant Triangular Fuzzy Information Aggregation Operators Based on Bonferroni Means and Their Application to Multiple Attribute Decision Making

PubMed Central

Zhou, Xiaoqiang; Yang, Tian

2014-01-01

We investigate the multiple attribute decision-making (MADM) problems with hesitant triangular fuzzy information. Firstly, definition and some operational laws of hesitant triangular fuzzy elements are introduced. Then, we develop some hesitant triangular fuzzy aggregation operators based on Bonferroni means and discuss their basic properties. Some existing operators can be viewed as their special cases. Next, we apply the proposed operators to deal with multiple attribute decision-making problems under hesitant triangular fuzzy environment. Finally, an illustrative example is given to show the developed method and demonstrate its practicality and effectiveness. PMID:25140338

Series of Reciprocal Triangular Numbers

ERIC Educational Resources Information Center

Bruckman, Paul; Dence, Joseph B.; Dence, Thomas P.; Young, Justin

2013-01-01

Reciprocal triangular numbers have appeared in series since the very first infinite series were summed. Here we attack a number of subseries of the reciprocal triangular numbers by methodically expressing them as integrals.

A Generalization of the Formula for the Triangular Number of the Sum and Product of Natural Numbers

ERIC Educational Resources Information Center

Asiru, M. A.

2008-01-01

This note generalizes the formula for the triangular number of the sum and product of two natural numbers to similar results for the triangular number of the sum and product of "r" natural numbers. The formula is applied to derive formula for the sum of an odd and an even number of consecutive triangular numbers.

Quantum oscillations in insulators with neutral Fermi surfaces

NASA Astrophysics Data System (ADS)

Sodemann, Inti; Chowdhury, Debanjan; Senthil, T.

2018-02-01

We develop a theory of quantum oscillations in insulators with an emergent Fermi sea of neutral fermions minimally coupled to an emergent U(1 ) gauge field. As pointed out by Motrunich [Phys. Rev. B 73, 155115 (2006), 10.1103/PhysRevB.73.155115], in the presence of a physical magnetic field the emergent magnetic field develops a nonzero value leading to Landau quantization for the neutral fermions. We focus on the magnetic field and temperature dependence of the analog of the de Haas-van Alphen effect in two and three dimensions. At temperatures above the effective cyclotron energy, the magnetization oscillations behave similarly to those of an ordinary metal, albeit in a field of a strength that differs from the physical magnetic field. At low temperatures, the oscillations evolve into a series of phase transitions. We provide analytical expressions for the amplitude and period of the oscillations in both of these regimes and simple extrapolations that capture well their crossover. We also describe oscillations in the electrical resistivity of these systems that are expected to be superimposed with the activated temperature behavior characteristic of their insulating nature and discuss suitable experimental conditions for the observation of these effects in mixed-valence insulators and triangular lattice organic materials.

Dynamic nuclear polarization using frequency modulation at 3.34 T.

PubMed

Hovav, Y; Feintuch, A; Vega, S; Goldfarb, D

2014-01-01

During dynamic nuclear polarization (DNP) experiments polarization is transferred from unpaired electrons to their neighboring nuclear spins, resulting in dramatic enhancement of the NMR signals. While in most cases this is achieved by continuous wave (cw) irradiation applied to samples in fixed external magnetic fields, here we show that DNP enhancement of static samples can improve by modulating the microwave (MW) frequency at a constant field of 3.34 T. The efficiency of triangular shaped modulation is explored by monitoring the (1)H signal enhancement in frozen solutions containing different TEMPOL radical concentrations at different temperatures. The optimal modulation parameters are examined experimentally and under the most favorable conditions a threefold enhancement is obtained with respect to constant frequency DNP in samples with low radical concentrations. The results are interpreted using numerical simulations on small spin systems. In particular, it is shown experimentally and explained theoretically that: (i) The optimal modulation frequency is higher than the electron spin-lattice relaxation rate. (ii) The optimal modulation amplitude must be smaller than the nuclear Larmor frequency and the EPR line-width, as expected. (iii) The MW frequencies corresponding to the enhancement maxima and minima are shifted away from one another when using frequency modulation, relative to the constant frequency experiments. Copyright © 2013 Elsevier Inc. All rights reserved.

Effect of triangular texture on the tribological performance of die steel with TiN coatings under lubricated sliding condition

NASA Astrophysics Data System (ADS)

Chen, Ping; Xiang, Xin; Shao, Tianmin; La, Yingqian; Li, Junling

2016-12-01

The friction and wear of stamping die surface can affect the service life of stamping die and the quality of stamping products. Surface texturing and surface coating have been widely used to improve the tribological performance of mechanical components. This study experimentally investigated the effect of triangular surface texture on the friction and wear properties of the die steel substrate with TiN coatings under oil lubrication. TiN coatings were deposited on a die steel (50Cr) substrate through a multi-arc ion deposition system, and then triangular surface texturing was fabricated by a laser surface texturing. The friction and wear test was conducted by a UMT-3 pin-on-disk tribometer under different sliding speeds and different applied loads, respectively. The adhesion test was performed to evaluate the effectiveness of triangular texturing on the interfacial bonding strength between the TiN coating and the die steel substrate. Results show that the combination method of surface texturing process and surface coating process has excellent tribological properties (the lowest frictional coefficient and wear volume), compared with the single texturing process or the single coating process. The tribological performance is improved resulting from the high hardness and low elastic modulus of TiN coatings, and the generation of hydrodynamic pressure, function of micro-trap for wear debris and micro-reservoirs for lubricating oil of the triangular surface texture. In addition, the coating bonding strength of the texturing sample is 3.63 MPa, higher than that of the single coating sample (3.48 MPa), but the mechanisms remain to be further researched.

An Evaluation of Fractal Surface Measurement Methods for Characterizing Landscape Complexity from Remote-Sensing Imagery

NASA Technical Reports Server (NTRS)

Lam, Nina Siu-Ngan; Qiu, Hong-Lie; Quattrochi, Dale A.; Emerson, Charles W.; Arnold, James E. (Technical Monitor)

2001-01-01

The rapid increase in digital data volumes from new and existing sensors necessitates the need for efficient analytical tools for extracting information. We developed an integrated software package called ICAMS (Image Characterization and Modeling System) to provide specialized spatial analytical functions for interpreting remote sensing data. This paper evaluates the three fractal dimension measurement methods: isarithm, variogram, and triangular prism, along with the spatial autocorrelation measurement methods Moran's I and Geary's C, that have been implemented in ICAMS. A modified triangular prism method was proposed and implemented. Results from analyzing 25 simulated surfaces having known fractal dimensions show that both the isarithm and triangular prism methods can accurately measure a range of fractal surfaces. The triangular prism method is most accurate at estimating the fractal dimension of higher spatial complexity, but it is sensitive to contrast stretching. The variogram method is a comparatively poor estimator for all of the surfaces, particularly those with higher fractal dimensions. Similar to the fractal techniques, the spatial autocorrelation techniques are found to be useful to measure complex images but not images with low dimensionality. These fractal measurement methods can be applied directly to unclassified images and could serve as a tool for change detection and data mining.

Suitable configurations for triangular formation flying about collinear libration points under the circular and elliptic restricted three-body problems

NASA Astrophysics Data System (ADS)

Ferrari, Fabio; Lavagna, Michèle

2018-06-01

The design of formations of spacecraft in a three-body environment represents one of the most promising challenges for future space missions. Two or more cooperating spacecraft can greatly answer some very complex mission goals, not achievable by a single spacecraft. The dynamical properties of a low acceleration environment such as the vicinity of libration points associated to a three-body system, can be effectively exploited to design spacecraft configurations able of satisfying tight relative position and velocity requirements. This work studies the evolution of an uncontrolled formation orbiting in the proximity of periodic orbits about collinear libration points under the Circular and Elliptic Restricted Three-Body Problems. A three spacecraft triangularly-shaped formation is assumed as a representative geometry to be investigated. The study identifies initial configurations that provide good performance in terms of formation keeping, and investigates key parameters that control the relative dynamics between the spacecraft within the three-body system. Formation keeping performance is quantified by monitoring shape and size changes of the triangular formation. The analysis has been performed under five degrees of freedom to define the geometry, the orientation and the location of the triangle in the synodic rotating frame.

An algorithmic approach to solving polynomial equations associated with quantum circuits

NASA Astrophysics Data System (ADS)

Gerdt, V. P.; Zinin, M. V.

2009-12-01

In this paper we present two algorithms for reducing systems of multivariate polynomial equations over the finite field F 2 to the canonical triangular form called lexicographical Gröbner basis. This triangular form is the most appropriate for finding solutions of the system. On the other hand, the system of polynomials over F 2 whose variables also take values in F 2 (Boolean polynomials) completely describes the unitary matrix generated by a quantum circuit. In particular, the matrix itself can be computed by counting the number of solutions (roots) of the associated polynomial system. Thereby, efficient construction of the lexicographical Gröbner bases over F 2 associated with quantum circuits gives a method for computing their circuit matrices that is alternative to the direct numerical method based on linear algebra. We compare our implementation of both algorithms with some other software packages available for computing Gröbner bases over F 2.

Adaptive output feedback NN control of a class of discrete-time MIMO nonlinear systems with unknown control directions.

PubMed

Li, Yanan; Yang, Chenguang; Ge, Shuzhi Sam; Lee, Tong Heng

2011-04-01

In this paper, adaptive neural network (NN) control is investigated for a class of block triangular multiinput-multioutput nonlinear discrete-time systems with each subsystem in pure-feedback form with unknown control directions. These systems are of couplings in every equation of each subsystem, and different subsystems may have different orders. To avoid the noncausal problem in the control design, the system is transformed into a predictor form by rigorous derivation. By exploring the properties of the block triangular form, implicit controls are developed for each subsystem such that the couplings of inputs and states among subsystems have been completely decoupled. The radial basis function NN is employed to approximate the unknown control. Each subsystem achieves a semiglobal uniformly ultimately bounded stability with the proposed control, and simulation results are presented to demonstrate its efficiency.

Quantum behaviour of pumped and damped triangular Bose-Hubbard systems

NASA Astrophysics Data System (ADS)

Chianca, C. V.; Olsen, M. K.

2017-12-01

We propose and analyse analogs of optical cavities for atoms using three-well Bose-Hubbard models with pumping and losses. We consider triangular configurations. With one well pumped and one damped, we find that both the mean-field dynamics and the quantum statistics show a quantitative dependence on the choice of damped well. The systems we analyse remain far from equilibrium, preserving good coherence between the wells in the steady-state. We find quadrature squeezing and mode entanglement for some parameter regimes and demonstrate that the trimer with pumping and damping at the same well is the stronger option for producing non-classical states. Due to recent experimental advances, it should be possible to demonstrate the effects we investigate and predict.

Mathematical model of parking space unit for triangular parking area

NASA Astrophysics Data System (ADS)

Syahrini, Intan; Sundari, Teti; Iskandar, Taufiq; Halfiani, Vera; Munzir, Said; Ramli, Marwan

2018-01-01

Parking space unit (PSU) is an effective measure for the area size of a vehicle, including the free space and the width of the door opening of the vehicle (car). This article discusses a mathematical model for parking space of vehicles in triangular shape area. An optimization model for triangular parking lot is developed. Integer Linear Programming (ILP) method is used to determine the maximum number of the PSU. The triangular parking lot is in isosceles and equilateral triangles shape and implements four possible rows and five possible angles for each field. The vehicles which are considered are cars and motorcycles. The results show that the isosceles triangular parking area has 218 units of optimal PSU, which are 84 units of PSU for cars and 134 units of PSU for motorcycles. Equilateral triangular parking area has 688 units of optimal PSU, which are 175 units of PSU for cars and 513 units of PSU for motorcycles.

A novel method of the image processing on irregular triangular meshes

NASA Astrophysics Data System (ADS)

Vishnyakov, Sergey; Pekhterev, Vitaliy; Sokolova, Elizaveta

2018-04-01

The paper describes a novel method of the image processing based on irregular triangular meshes implementation. The triangular mesh is adaptive to the image content, least mean square linear approximation is proposed for the basic interpolation within the triangle. It is proposed to use triangular numbers to simplify using of the local (barycentric) coordinates for the further analysis - triangular element of the initial irregular mesh is to be represented through the set of the four equilateral triangles. This allows to use fast and simple pixels indexing in local coordinates, e.g. "for" or "while" loops for access to the pixels. Moreover, representation proposed allows to use discrete cosine transform of the simple "rectangular" symmetric form without additional pixels reordering (as it is used for shape-adaptive DCT forms). Furthermore, this approach leads to the simple form of the wavelet transform on triangular mesh. The results of the method application are presented. It is shown that advantage of the method proposed is a combination of the flexibility of the image-adaptive irregular meshes with the simple form of the pixel indexing in local triangular coordinates and the using of the common forms of the discrete transforms for triangular meshes. Method described is proposed for the image compression, pattern recognition, image quality improvement, image search and indexing. It also may be used as a part of video coding (intra-frame or inter-frame coding, motion detection).

Evolution of silver/gold triangular nanoframes from prismatic silver/gold core/shell nanostructures and their SERS properties

NASA Astrophysics Data System (ADS)

Parthiban, P.; Sakar, M.; Balakumar, S.

2013-02-01

We report the evolution of Ag/Au triangular nanoframes from nano core/shell of Ag/Au and their surface enhanced Raman scattering (SERS) properties. The Ag/Au prismatic core/shell nanostructures were synthesized using chemical reduction method. It was observed that, on the addition of excess gold chloride (HAuCl4) solution, the morphology of nano core/shell was changed to alloy like triangular nanoframes. Accordingly, a shift was found towards higher wavelengths in the UV-Visible absorption peaks of Ag/Au nanoframes compare to Ag/Au nano core/shell. Consequently, the SERS effect of these Ag/Au anisotropic nanostructures were studied on methylene blue. The Ag/Au alloy like prismatic nanoframes showed improved SERS effect than that of prismatic core/shell nanostructures. The experimental findings were revealed that the improved SERS effect could be resulted from the enhanced surface plasmon resonance (SPR) due to the alloy like construction of Ag/Au system.

Triangular Libration Points in the CR3BP with Radiation, Triaxiality and Potential from a Belt

NASA Astrophysics Data System (ADS)

Singh, Jagadish; Taura, Joel John

2017-07-01

In this paper the equations of motion of the circular restricted three body problem is modified to include radiation of the bigger primary, triaxiality of the smaller primary; and gravitational potential created by a belt. We have obtained that due to the perturbations, the locations of the triangular libration points and their linear stability are affected. The points move towards the bigger primary due to the resultant effect of the perturbations. Triangular libration points are stable for 0<μ<μc0<μ<μc and unstable for μc≤μ≤12μc≤μ≤12, where μcμc is the critical mass ratio affected by the perturbations. The radiation of the bigger primary and triaxiality of the smaller primary have destabilizing propensities, whereas the potential created by the belt has stabilizing propensity. This model could be applied in the study of the motion of a dust particle near radiating -triaxial binary system surrounded by a belt.

Geometric Magnetic Frustration in Li3Mg2OsO6 Studied with Muon Spin Relaxation

NASA Astrophysics Data System (ADS)

Carlo, J. P.; Derakhshan, S.; Greedan, J. E.

Geometric frustration manifests when the spatial arrangement of ions inhibits magnetic order. Typically associated with antiferromagnetically (AF)-correlated moments on triangular or tetrahedral lattices, frustration occurs in a variety of structures and systems, resulting in rich phase diagrams and exotic ground states. As a window to exotic physics revealed by the cancellation of normally dominant interactions, the research community has taken great interest in frustrated systems. One family of recent interest are the rock-salt ordered oxides A5BO6, in which the B sites are occupied by magnetic ions comprising a network of interlocked tetrahedra, and nonmagnetic ions on the A sites control the B oxidation state through charge neutrality. Here we will discuss studies of Li3Mg2OsO6 using muon spin relaxation (μSR), a highly sensitive local probe of magnetism. Previous studies of this family included Li5OsO6, which exhibits AF order below 50K with minimal evidence for frustration, and Li4MgReO6, which exhibits glassy magnetism. Li3Mg2RuO6, meanwhile, exhibits long-range AF, with the ordering temperature suppressed by frustration. But its isoelectronic twin, Li3Mg2OsO6 (5d3 vs. 4d3) exhibits very different behavior, revealed by μSR to be a glassy ground state below 12K. Understanding why such similar systems exhibit diverse ground-state behavior is key to understanding the nature of geometric magnetic frustration. Financial support from the Research Corporation for Science Advancement.

Characterization of Martian Rock Shape for MER Airbag Drop Tests

NASA Astrophysics Data System (ADS)

Dimaggio, E. N.; Schroeder, R.; Castle, N.; Golombek, M.

2002-12-01

Rock distributions for the final platforms used in airbag drop tests are currently being designed for the Mars Exploration Rovers (MER) scheduled to launch in 2003. Like Mars Pathfinder (MPF), launched in 1996, MER will use a series of airbags to cushion its landing on the surface of Mars. Previous MER airbag drop tests have shown that sharp, angular (triangular) rocks >20 cm high may be hazardous. To aid in defining the rock distributions for the final airbag tests, images from the Viking Landers 1 and 2 and MPF were used to identify rocks that are >20 cm high, and characterize them as triangular, square or round. Approximately 33% of all rocks analyzed are triangular. Of the rocks analyzed that are ~20-60 cm high, ~14% are triangular. Most of these triangular rocks are small, ~20-30 cm high. Rock distributions of previous airbag platforms were similarly classified and show a greater percentage of triangular and square rocks that are ~20-60 cm high than at the landing sites. The burial of a rock (perched, partially buried or buried) was also considered because perched rocks may pose less of a threat to the airbags than those buried because perched rocks can be dislodged and roll during impact. Approximately 19% of all rocks analyzed, and ~19% of rocks that are ~20-60 cm high, are triangular and partially buried or buried. These data suggest that the platform rock distributions appropriately represented the risks to the airbags associated with triangular rocks. A similar percentage of >20 cm high triangular rocks will be added to the drop test platforms to represent landing site rock distributions.

Magnetoresistance measurement of permalloy thin film rings with triangular fins

NASA Astrophysics Data System (ADS)

Lai, Mei-Feng; Hsu, Chia-Jung; Liao, Chun-Neng; Chen, Ying-Jiun; Wei, Zung-Hang

2010-01-01

Magnetization reversals in permalloy rings controlled by nucleation sites using triangular fins at the same side and diagonal with respect to the field direction are demonstrated by magnetoresistance measurement and micromagnetic simulation. In the ring with triangular fins at the same side, there exists two-step reversal from onion to flux-closure state (or vortex state) and then from flux-closure (or vortex state) to reverse onion state; in the ring with diagonal triangular fins, one-step reversal occurs directly from onion to reverse onion state. The reversal processes are repeatable and controllable in contrast to an ideal ring without triangular fins where one-step and two-step reversals occur randomly in sweep-up and sweep-down processes.

Benchmarks of simple, generic, shaped plates for validation of low-frequency electromagnetic computational codes

NASA Technical Reports Server (NTRS)

Deshpande, M. D.; Cockrell, C. R.; Beck, F. B.; Nguyen, T. X.

1993-01-01

The validation of low-frequency measurements and electromagnetic (EM) scattering computations for several simple, generic shapes, such as an equilateral-triangular plate, an equilateral-triangular plate with a concentric equilateral-triangular hole, and diamond- and hexagonal-shaped plates, is discussed. The plates were constructed from a thin aluminum sheet with a thickness of 0.08 cm. EM scattering by the planar plates was measured in the experimental test range (ETR) facility of NASA Langley Research Center. The dimensions of the plates were selected such that, over the frequency range of interest, the dimensions were in the range of lambda0 to 3(lambda0). In addition, the triangular plate with a triangular hole was selected to study internal-hole resonances.

Temperature-dependent errors in nuclear lattice simulations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lee, Dean; Thomson, Richard

2007-06-15

We study the temperature dependence of discretization errors in nuclear lattice simulations. We find that for systems with strong attractive interactions the predominant error arises from the breaking of Galilean invariance. We propose a local 'well-tempered' lattice action which eliminates much of this error. The well-tempered action can be readily implemented in lattice simulations for nuclear systems as well as cold atomic Fermi systems.

Nonautonomous ultradiscrete hungry Toda lattice and a generalized box-ball system

NASA Astrophysics Data System (ADS)

Maeda, Kazuki

2017-09-01

A nonautonomous version of the ultradiscrete hungry Toda lattice with a finite lattice boundary condition is derived by applying reduction and ultradiscretization to a nonautonomous two-dimensional discrete Toda lattice. It is shown that the derived ultradiscrete system has a direct connection to the box-ball system with many kinds of balls and finite carrier capacity. Particular solutions to the ultradiscrete system are constructed by using the theory of some sort of discrete biorthogonal polynomials.

Study of propellant dynamics in a shuttle type launch vehicle

NASA Technical Reports Server (NTRS)

Jones, C. E.; Feng, G. C.

1972-01-01

A method and an associated digital computer program for evaluating the vibrational characteristics of large liquid-filled rigid wall tanks of general shape are presented. A solution procedure was developed in which slosh modes and frequencies are computed for systems mathematically modeled as assemblages of liquid finite elements. To retain sparsity in the assembled system mass and stiffness matrices, a compressible liquid element formulation was incorporated in the program. The approach taken in the liquid finite element formulation is compatible with triangular and quadrilateral structural finite elements so that the analysis of liquid motion can be coupled with flexible tank wall motion at some future time. The liquid element repertoire developed during the course of this study consists of a two-dimensional triangular element and a three-dimensional tetrahedral element.

Comparative Analysis of Membership Function on Mamdani Fuzzy Inference System for Decision Making

NASA Astrophysics Data System (ADS)

harliana, Putri; Rahim, Robbi

2017-12-01

Membership function is a curve that shows mapping the input data points into the value or degree of membership which has an interval between 0 and 1. One way to get membership value is through a function approach. There are some membership functions can be used on mamdani fuzzy inference system. They are triangular, trapezoid, singleton, sigmoid, Gaussian, etc. In this paper only discuss three membership functions, are triangular, trapezoid and Gaussian. These three membership functions will be compared to see the difference in parameter values and results obtained. For case study in this paper is admission of students at popular school. There are three variable can be used, they are students’ report, IQ score and parents’ income. Which will then be created if-then rules.

Antiferromagnetic Ordering in Quasi-Triangular Localized Spin System, β'-Et2Me2P[Pd(dmit)2]2, Studied by 13C NMR

NASA Astrophysics Data System (ADS)

Otsuka, Kei; Iikubo, Hideaki; Kogure, Takayuki; Takano, Yoshiki; Hiraki, Ko-ichi; Takahashi, Toshihiro; Cui, Hengbo; Kato, Reizo

2014-05-01

We performed 13C NMR measurements of a selectively 13C isotope-labeled single-crystal sample of a frustrated spin system, β'-Et2Me2P[Pd(dmit)2]2. A long-range antiferromagnetic (AF) ordering below 17 K was confirmed by the observation of NMR spectrum broadening and well split resonance lines at lower temperatures. NMR spectra in the AF state can be well explained by a two sublattice model. From the analysis of the angular dependence of the NMR spectrum, we clarified the magnetic structure in the AF state, where the easy and hard axes are the crystallographic c*- and b-axes, respectively, and the effective localized moments are quite small, ˜0.28 μB/dimer. This suggests a strong quantum fluctuation effect due to magnetic frustrations in a quasi-triangular spin-1/2 system.

7 CFR 810.1002 - Definition of other terms.

Code of Federal Regulations, 2014 CFR

2014-01-01

... seeds. All matter that passes through a 5/64 triangular-hole sieve after sieving according to procedures..., rye, safflower, sorghum, soybeans, spelt, sunflower seed, sweet corn, triticale, and wheat. (e) Sieves—(1) 5/64 triangular-hole sieve. A metal sieve 0.032 inch thick with equilateral triangular...

7 CFR 810.1002 - Definition of other terms.

Code of Federal Regulations, 2012 CFR

2012-01-01

... seeds. All matter that passes through a 5/64 triangular-hole sieve after sieving according to procedures..., rye, safflower, sorghum, soybeans, spelt, sunflower seed, sweet corn, triticale, and wheat. (e) Sieves—(1) 5/64 triangular-hole sieve. A metal sieve 0.032 inch thick with equilateral triangular...

7 CFR 810.1002 - Definition of other terms.

Code of Federal Regulations, 2013 CFR

2013-01-01

... seeds. All matter that passes through a 5/64 triangular-hole sieve after sieving according to procedures..., rye, safflower, sorghum, soybeans, spelt, sunflower seed, sweet corn, triticale, and wheat. (e) Sieves—(1) 5/64 triangular-hole sieve. A metal sieve 0.032 inch thick with equilateral triangular...

Triangular osteosynthesis of vertically unstable sacrum fractures: a new concept allowing early weight-bearing.

PubMed

Schildhauer, T A; Josten, Ch; Muhr, G

2006-01-01

Presentation of a new triangular osteosynthesis technique that permits early weight-bearing in vertically unstable sacral fractures. : Retrospective evaluation of a consecutive series. Level I trauma center. Thirty-four patients, twenty-eight of whom were poly-traumatized, all with vertically unstable sacral fractures. This group included eight women and twenty-six men, with a mean age of thirty-five years. Average time between trauma and definite operation was thirteen days (range 0 to 28 days). All patients underwent triangular osteosynthesis using a combination of a vertical vertebro-pelvic distraction osteosynthesis (pedicle screw system) and a transverse fixation of the sacrum fracture with either iliosacral screws or trans-sacral plating. Immediate postoperative weight-bearing was permitted postoperatively. Nineteen patients were treated with early progressive weight-bearing and advanced to full weight-bearing, on average, after twenty-three days (range 8 to 70 days). Three of the thirty-four patients (9 percent) experienced loosening of hardware, including two patients (6 percent) who required secondary intervention because of loss of the original reduction. Further complications included one pulmonary embolism (3 percent), one iatrogenic nerve lesion (3 percent), one wound necrosis (3 percent), and two local infections (6 percent). Triangular osteosynthesis is a demanding procedure that can be performed on vertically unstable sacral fractures to allow early progressive weight-bearing with an acceptable complication rate.

Ternary and Quaternary Composition Diagrams: An Overview of the Subject.

ERIC Educational Resources Information Center

MacCarthy, Patrick

1983-01-01

Reviews graphical methods for representing ternary and quaternary systems, focusing on use of triangular composition diagrams. Examines some of the relevant geometry of triangles in general, showing that right isosceles triangles possess some very advantageous features for representing ternary systems. (JN)

Triangular Diagrams Teach Steady and Dynamic Behaviour of Catalytic Reactions.

ERIC Educational Resources Information Center

Klusacek, K.; And Others

1989-01-01

Illustrates how triangular diagrams can aid in presenting some of the rather complex transient interactions that occur among gas and surface species during heterogeneous catalytic reactions. The basic equations and numerical examples are described. Classroom use of the triangular diagram is discussed. Several diagrams and graphs are provided. (YP)

On Certain Topological Indices of Boron Triangular Nanotubes

NASA Astrophysics Data System (ADS)

Aslam, Adnan; Ahmad, Safyan; Gao, Wei

2017-08-01

The topological index gives information about the whole structure of a chemical graph, especially degree-based topological indices that are very useful. Boron triangular nanotubes are now replacing usual carbon nanotubes due to their excellent properties. We have computed general Randić (Rα), first Zagreb (M1) and second Zagreb (M2), atom-bond connectivity (ABC), and geometric-arithmetic (GA) indices of boron triangular nanotubes. Also, we have computed the fourth version of atom-bond connectivity (ABC4) and the fifth version of geometric-arithmetic (GA5) indices of boron triangular nanotubes.

Structural Performance of a Hybrid FRP-Aluminum Modular Triangular Truss System Subjected to Various Loading Conditions

PubMed Central

Zhang, Dongdong; Huang, Yaxin; Zhao, Qilin; Li, Fei; Gao, Yifeng

2014-01-01

A novel hybrid FRP-aluminum truss system has been employed in a two-rut modular bridge superstructure composed of twin inverted triangular trusses. The actual flexural behavior of a one-rut truss has been previously investigated under the on-axis loading test; however, the structural performance of the one-rut truss subjected to an off-axis load is still not fully understood. In this paper, a geometrical linear finite element model is introduced and validated by the on-axis loading test; the structural performance of the one-rut truss subjected to off-axis load was numerically obtained; the dissimilarities of the structural performance between the two different loading cases are investigated in detail. The results indicated that (1) the structural behavior of the off-axis load differs from that of the on-axis load, and the off-axis load is the critical loading condition controlling the structural performance of the triangular truss; (2) under the off-axis load, the FRP trussed members and connectors bear certain out-of-plane bending moments and are subjected to a complicated stress state; and (3) the stress state of these members does not match that of the initial design, and optimization for the redesign of these members is needed, especially for the pretightened teeth connectors. PMID:25254254

Numerical investigation of Al2O3/water nanofluid laminar convective heat transfer through triangular ducts

NASA Astrophysics Data System (ADS)

Zeinali Heris, Saeed; Noie, Seyyed Hossein; Talaii, Elham; Sargolzaei, Javad

2011-12-01

In this article, laminar flow-forced convective heat transfer of Al2O3/water nanofluid in a triangular duct under constant wall temperature condition is investigated numerically. In this investigation, the effects of parameters, such as nanoparticles diameter, concentration, and Reynolds number on the enhancement of nanofluids heat transfer is studied. Besides, the comparison between nanofluid and pure fluid heat transfer is achieved in this article. Sometimes, because of pressure drop limitations, the need for non-circular ducts arises in many heat transfer applications. The low heat transfer rate of non-circular ducts is one the limitations of these systems, and utilization of nanofluid instead of pure fluid because of its potential to increase heat transfer of system can compensate this problem. In this article, for considering the presence of nanoparticl: es, the dispersion model is used. Numerical results represent an enhancement of heat transfer of fluid associated with changing to the suspension of nanometer-sized particles in the triangular duct. The results of the present model indicate that the nanofluid Nusselt number increases with increasing concentration of nanoparticles and decreasing diameter. Also, the enhancement of the fluid heat transfer becomes better at high Re in laminar flow with the addition of nanoparticles.

Macro and micro rate zonal analytical centrifugation of polydisperse and slowly diffusing sedimenting systems in isovolumetric density gradients. Application to cartilage proteoglycans.

PubMed

Müller, F J; Pezon, C F; Pita, J C

1989-06-13

A method to study the polydispersity of zonally sedimenting and slowly diffusing macromolecules or particles in isokinetic or isovolumetric density gradients is presented. First, a brief theory is given for predicting the zonal profile after a "triangular" (or "inverse") zone is centrifuged. This type of zone is essential to preserve hydrodynamic stability of the very slowly diffusing polydisperse solutes. It is proven, both by semitheoretical considerations and by computer calculations, that the resulting concentration profile of macrosolute is almost identical with that obtainable with a rectangular zone coextensive with the triangular one and carrying the same total mass. Next, practical procedures are described for the convectionless layering of very small triangular zones (50 microL or less). The linearity and stability of the zones are experimentally tested and verified. Finally, the method is applied to cartilage proteoglycan preparations that included either the monomeric molecules only or both the monomeric and the aggregated ones. The zonal results are compared with those obtained by using conventional boundary sedimentation. The two sets of results are seen to coincide fairly well, thus proving that the present technique can add to preparative zonal centrifugation the analytical precision of boundary sedimentation. A multimodal polydisperse system is suggested to describe the aggregated proteoglycan macromolecules.

A parallel finite element procedure for contact-impact problems using edge-based smooth triangular element and GPU

NASA Astrophysics Data System (ADS)

Cai, Yong; Cui, Xiangyang; Li, Guangyao; Liu, Wenyang

2018-04-01

The edge-smooth finite element method (ES-FEM) can improve the computational accuracy of triangular shell elements and the mesh partition efficiency of complex models. In this paper, an approach is developed to perform explicit finite element simulations of contact-impact problems with a graphical processing unit (GPU) using a special edge-smooth triangular shell element based on ES-FEM. Of critical importance for this problem is achieving finer-grained parallelism to enable efficient data loading and to minimize communication between the device and host. Four kinds of parallel strategies are then developed to efficiently solve these ES-FEM based shell element formulas, and various optimization methods are adopted to ensure aligned memory access. Special focus is dedicated to developing an approach for the parallel construction of edge systems. A parallel hierarchy-territory contact-searching algorithm (HITA) and a parallel penalty function calculation method are embedded in this parallel explicit algorithm. Finally, the program flow is well designed, and a GPU-based simulation system is developed, using Nvidia's CUDA. Several numerical examples are presented to illustrate the high quality of the results obtained with the proposed methods. In addition, the GPU-based parallel computation is shown to significantly reduce the computing time.

MR Imaging of the Triangular Fibrocartilage Complex.

PubMed

Cody, Michael E; Nakamura, David T; Small, Kirstin M; Yoshioka, Hiroshi

2015-08-01

MR imaging has emerged as the mainstay in imaging internal derangement of the soft tissues of the musculoskeletal system largely because of superior contrast resolution. The complex geometry and diminutive size of the triangular fibrocartilage complex (TFCC) and its constituent structures can make optimal imaging of the TFCC challenging; therefore, production of clinically useful images requires careful optimization of image acquisition parameters. This article provides a foundation for advanced TFCC imaging including factors to optimize magnetic resonance images, arthrography, detailed anatomy, and classification of injury. In addition, clinical presentations and treatments for TFCC injury are briefly considered. Copyright © 2015 Elsevier Inc. All rights reserved.

The Traumatized TFCC: An Illustrated Review of the Anatomy and Injury Patterns of the Triangular Fibrocartilage Complex.

PubMed

Skalski, Matthew R; White, Eric A; Patel, Dakshesh B; Schein, Aaron J; RiveraMelo, Hector; Matcuk, George R

2016-01-01

The triangular fibrocartilage complex (TFCC) plays an important role in wrist biomechanics and is prone to traumatic and degenerative injury, making it a common source of ulnar-sided wrist pain. Because of this, the TFCC is frequently imaged, and a detailed understanding of its anatomy and injury patterns is critical in generating an accurate report to help guide treatment. In this review, we provide a detailed overview of TFCC anatomy, its normal appearance on magnetic resonance imaging, the spectrum of TFCC injuries based on the Palmer classification system, and pitfalls in accurate assessment. Copyright © 2015 Mosby, Inc. All rights reserved.

Face Centered Cubic and Hexagonal Close Packed Skyrmion Crystals in Centrosymmetric Magnets

NASA Astrophysics Data System (ADS)

Lin, Shi-Zeng; Batista, Cristian D.

2018-02-01

Skyrmions are disklike objects that typically form triangular crystals in two-dimensional systems. This situation is analogous to the so-called pancake vortices of quasi-two-dimensional superconductors. The way in which Skyrmion disks or "pancake Skyrmions" pile up in layered centrosymmetric materials is dictated by the interlayer exchange. Unbiased Monte Carlo simulations and simple stabilization arguments reveal face centered cubic and hexagonal close packed Skyrmion crystals for different choices of the interlayer exchange, in addition to the conventional triangular crystal of Skyrmion lines. Moreover, an inhomogeneous current induces a sliding motion of pancake Skyrmions, indicating that they behave as effective mesoscale particles.

Linear beam raster magnet driver based on H-bridge technique

DOEpatents

Sinkine, Nikolai I.; Yan, Chen; Apeldoorn, Cornelis; Dail, Jeffrey Glenn; Wojcik, Randolph Frank; Gunning, William

2006-06-06

An improved raster magnet driver for a linear particle beam is based on an H-bridge technique. Four branches of power HEXFETs form a two-by-two switch. Switching the HEXFETs in a predetermined order and at the right frequency produces a triangular current waveform. An H-bridge controller controls switching sequence and timing. The magnetic field of the coil follows the shape of the waveform and thus steers the beam using a triangular rather than a sinusoidal waveform. The system produces a raster pattern having a highly uniform raster density distribution, eliminates target heating from non-uniform raster density distributions, and produces higher levels of beam current.

Nonequilibrium relaxations within the ground-state manifold in the antiferromagnetic Ising model on a triangular lattice.

PubMed

Kim, Eunhye; Lee, Sung Jong; Kim, Bongsoo

2007-02-01

We present an extensive Monte Carlo simulation study on the nonequilibrium kinetics of triangular antiferromagnetic Ising model within the ground state ensemble which consists of sectors, each of which is characterized by a unique value of the string density p through a dimer covering method. Building upon our recent work [Phys. Rev. E 68, 066127 (2003)] where we considered the nonequilibrium relaxation observed within the dominant sector with p=2/3, we here focus on the nonequilibrium kinetics within the minor sectors with p<2/3. The initial configurations are chosen as those in which the strings are straight and evenly distributed. In the minor sectors, we observe a characteristic spatial anisotropy in both equilibrium and nonequilibrium spatial correlations. We observe emergence of a critical relaxation region (in the spatial and temporal domain) which grows as p deviates from p=2/3. Spatial anisotropy appears in the equilibrium spatial correlation with the characteristic length scale xi(e,V)(p) diverging with vanishing string density as xi(e,V)(p) approximately p(-2) along the vertical direction, while along the horizontal direction the spatial length scale diverges as xi(e,H) approximately p(-1). Analytic forms for the anisotropic equilibrium correlation functions are given. We also find that the spin autocorrelation function A(t) shows a simple scaling behavior A(t)=A(t/tau(A)(p)), where the time scale tau(A)(p) shows a power-law divergence with vanishing p as tau(A)(p) approximately p(-phi) with phi approximately or equal to 4. These features can be understood in terms of random walk nature of the fluctuations of the strings within the typical separation between neighboring strings.

Oversized 250 GHz Traveling Wave Tube with a Photonic Band-Gap Structure

NASA Astrophysics Data System (ADS)

Rosenzweig, Guy; Shapiro, Michael A.; Temkin, Richard J.

2017-10-01

The challenge in manufacturing traveling wave tubes (TWTs) at high frequencies is that the sizes of the structures scale with, and are much smaller than, the wavelength. We have designed and are building a 250 GHz TWT that uses an oversized structure to overcome fabrication and power handling issues that result from the small dimensions. Using a photonic band-gap (PBG) structure, we succeeded to design the TWT with a beam tunnel diameter of 0.72 mm. The circuit consists of metal plates with the beam tunnel drilled down their center. Twelve posts are protruding on one side of each plate in a triangular array and corresponding sockets are drilled on the other side. The posts of each plate are inserted into the sockets of an adjacent plate, forming a PBG lattice. The vacuum spacing between adjacent plates forms the `PBG cavity''. The full structure is a series of PBG coupled cavities, with microwave power coupling through the beam tunnel. The PBG lattice provides confinement of microwave power in each of the cavities and can be tuned to give the right amount of diffraction per cavity so that no sever is needed to suppress oscillations in the operating mode. CST PIC simulations predict over 38 dB gain with 67 W peak power, using a 30 kV, 310 mA electron beam, 0.6 mm in diameter. Research supported by the AFOSR Program on Plasma and Electro-Energetic Physics and by the NIH National Institute of Biomedical Imaging and Bioengineering.

Regular Deployment of Wireless Sensors to Achieve Connectivity and Information Coverage

PubMed Central

Cheng, Wei; Li, Yong; Jiang, Yi; Yin, Xipeng

2016-01-01

Coverage and connectivity are two of the most critical research subjects in WSNs, while regular deterministic deployment is an important deployment strategy and results in some pattern-based lattice WSNs. Some studies of optimal regular deployment for generic values of rc/rs were shown recently. However, most of these deployments are subject to a disk sensing model, and cannot take advantage of data fusion. Meanwhile some other studies adapt detection techniques and data fusion to sensing coverage to enhance the deployment scheme. In this paper, we provide some results on optimal regular deployment patterns to achieve information coverage and connectivity as a variety of rc/rs, which are all based on data fusion by sensor collaboration, and propose a novel data fusion strategy for deployment patterns. At first the relation between variety of rc/rs and density of sensors needed to achieve information coverage and connectivity is derived in closed form for regular pattern-based lattice WSNs. Then a dual triangular pattern deployment based on our novel data fusion strategy is proposed, which can utilize collaborative data fusion more efficiently. The strip-based deployment is also extended to a new pattern to achieve information coverage and connectivity, and its characteristics are deduced in closed form. Some discussions and simulations are given to show the efficiency of all deployment patterns, including previous patterns and the proposed patterns, to help developers make more impactful WSN deployment decisions. PMID:27529246

Multicomponent Supramolecular Systems: Self-Organization in Coordination-Driven Self-Assembly

PubMed Central

Zheng, Yao-Rong; Yang, Hai-Bo; Ghosh, Koushik; Zhao, Liang; Stang, Peter J.

2009-01-01

The self-organization of multicomponent supramolecular systems involving a variety of two-dimensional (2-D) polygons and three-dimensional (3-D) cages is presented. Nine self-organizing systems, SS1–SS9, have been studied. Each involving the simultaneous mixing of organoplatinum acceptors and pyridyl donors of varying geometry and their selective self-assembly into three to four specific 2-D (rectangular, triangular, and rhomboid) and/or 3-D (triangular prism and distorted and nondistorted trigonal bipyramidal) supramolecules. The formation of these discrete structures is characterized using NMR spectroscopy and electrospray ionization mass spectrometry (ESI-MS). In all cases, the self-organization process is directed by: (1) the geometric information encoded within the molecular subunits and (2) a thermodynamically driven dynamic self-correction process. The result is the selective self-assembly of multiple discrete products from a randomly formed complex. The influence of key experimental variables – temperature and solvent – on the self-correction process and the fidelity of the resulting self-organization systems is also described. PMID:19544512

New drilling rigs

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tubb, M.

1983-03-01

Petronas recently commissioned its first offshore jack-up drilling rig at Promet, Singapore. The $49 million jack-up Parameswara will undertake both exploration and development activities in Petronas Carigali's exploration block off the eastern coast of Malaysia. The block measures 19,800 sq. km. Initially, the rig will be located at the Duyong gas field. Based on Baker Marine Corporation's BMC 300 design, the 65 X 64 X 8 m rig is capable of working in water depths of up to 91.4 m and is able to drill to a depth of 7,600 m. It has three triangular open-lattice truss-type legs, each 131more » m long. Prominent features include four-tier living quarters which can house 90 men, three cranes of boom length 30.48 m each, a helideck, mess hall, galley, and recreation room. The rig is built to American Bureau of Shipping standards. This paper describes the transport, installation and ballast operations involved in situating the Petronas rig in the Duyong field.« less

Frozen State and Spin Liquid Physics in Na_{4}Ir_{3}O_{8}: An NMR Study.

PubMed

Shockley, A C; Bert, F; Orain, J-C; Okamoto, Y; Mendels, P

2015-07-24

Na_{4}Ir_{3}O_{8} is a unique case of a hyperkagome 3D corner sharing triangular lattice that can be decorated with quantum spins. It has spurred a lot of theoretical interest as a spin liquid candidate. We present a comprehensive set of NMR data taken on both the ^{23}Na and ^{17}O sites. We show that disordered magnetic freezing of all Ir sites sets in below T_{f}~7 K, well below J=300 K, with a drastic slowing down of fluctuations to a static state revealed by our T_{1} measurements. Above typically 2T_{f}, physical properties are relevant to the spin liquid state induced by this exotic geometry. While the shift data show that the susceptibility levels off below 80 K, 1/T_{1} has little variation from 300 K to 2T_{f}. We discuss the implication of our results in the context of published experimental and theoretical work.

Self-assembly and electrostriction of arrays and chains of hopfion particles in chiral liquid crystals

PubMed Central

Ackerman, Paul J.; van de Lagemaat, Jao; Smalyukh, Ivan I.

2015-01-01

Some of the most exotic condensed matter phases, such as twist grain boundary and blue phases in liquid crystals and Abrikosov phases in superconductors, contain arrays of topological defects in their ground state. Comprised of a triangular lattice of double-twist tubes of magnetization, the so-called ‘A-phase’ in chiral magnets is an example of a thermodynamically stable phase with topologically nontrivial solitonic field configurations referred to as two-dimensional skyrmions, or baby-skyrmions. Here we report that three-dimensional skyrmions in the form of double-twist tori called ‘hopfions’, or ‘torons’ when accompanied by additional self-compensating defects, self-assemble into periodic arrays and linear chains that exhibit electrostriction. In confined chiral nematic liquid crystals, this self-assembly is similar to that of liquid crystal colloids and originates from long-range elastic interactions between particle-like skyrmionic torus knots of molecular alignment field, which can be tuned from isotropic repulsive to weakly or highly anisotropic attractive by low-voltage electric fields. PMID:25607778

Tunable two-dimensional photonic crystals using liquid crystal infiltration

NASA Astrophysics Data System (ADS)

Leonard, S. W.; Mondia, J. P.; van Driel, H. M.; Toader, O.; John, S.; Busch, K.; Birner, A.; Gösele, U.; Lehmann, V.

2000-01-01

The photonic band gap of a two-dimensional photonic crystal is continuously tuned using the temperature dependent refractive index of a liquid crystal. Liquid crystal E7 was infiltrated into the air pores of a macroporous silicon photonic crystal with a triangular lattice pitch of 1.58 μm and a band gap wavelength range of 3.3-5.7 μm. After infiltration, the band gap for the H polarized field shifted dramatically to 4.4-6.0 μm while that of the E-polarized field collapsed. As the sample was heated to the nematic-isotropic phase transition temperature of the liquid crystal (59 °C), the short-wavelength band edge of the H gap shifted by as much as 70 nm while the long-wavelength edge was constant within experimental error. Band structure calculations incorporating the temperature dependence of the liquid crystal birefringence can account for our results and also point to an escaped-radial alignment of the liquid crystal in the nematic phase.

Atomic density functional and diagram of structures in the phase field crystal model

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ankudinov, V. E., E-mail: vladimir@ankudinov.org; Galenko, P. K.; Kropotin, N. V.

2016-02-15

The phase field crystal model provides a continual description of the atomic density over the diffusion time of reactions. We consider a homogeneous structure (liquid) and a perfect periodic crystal, which are constructed from the one-mode approximation of the phase field crystal model. A diagram of 2D structures is constructed from the analytic solutions of the model using atomic density functionals. The diagram predicts equilibrium atomic configurations for transitions from the metastable state and includes the domains of existence of homogeneous, triangular, and striped structures corresponding to a liquid, a body-centered cubic crystal, and a longitudinal cross section of cylindricalmore » tubes. The method developed here is employed for constructing the diagram for the homogeneous liquid phase and the body-centered iron lattice. The expression for the free energy is derived analytically from density functional theory. The specific features of approximating the phase field crystal model are compared with the approximations and conclusions of the weak crystallization and 2D melting theories.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jacobsen, Jesper Lykke; Salas, Jesus; Scullard, Christian R.

Here, we study the phase diagram of the triangular-lattice Q-state Potts model in the realmore » $(Q, v)$ -plane, where $$v={\\rm e}^J-1$$ is the temperature variable. Our first goal is to provide an obviously missing feature of this diagram: the position of the antiferromagnetic critical curve. This curve turns out to possess a bifurcation point with two branches emerging from it, entailing important consequences for the global phase diagram. We have obtained accurate numerical estimates for the position of this curve by combining the transfer-matrix approach for strip graphs with toroidal boundary conditions and the recent method of critical polynomials. The second goal of this work is to study the corresponding $$A_{p-1}$$ RSOS model on the torus, for integer $$p=4, 5, \\ldots, 8$$ . We clarify its relation to the corresponding Potts model, in particular concerning the role of boundary conditions. For certain values of p, we identify several new critical points and regimes for the RSOS model and we initiate the study of the flows between the corresponding field theories.« less

Crystal structure and crystal growth of the polar ferrimagnet CaBaFe4O7

NASA Astrophysics Data System (ADS)

Perry, R. S.; Kurebayashi, H.; Gibbs, A.; Gutmann, M. J.

2018-05-01

Magnetic materials are a cornerstone for developing spintronic devices for the transport of information via magnetic excitations. To date, relatively few materials have been investigated for the purpose of spin transport, mostly due to the paucity of suitable candidates as these materials are often chemically complex and difficult to synthesize. We present the crystal growth and a structure solution on the high-temperature crystal structure of the layered, polar ferrimagnet CaBaFe4O7 , which is a possible new contender for spintronics research. The space group is identified as P 3 by refinement of single crystal and powder neutron diffraction data. At 400 K, the trigonal lattice parameters are a =11.0114 (11 )Å and c =10.330 (3 )Å . The structure is similar to the low-temperature phase with alternating layers of triangular and Kagome-arranged Fe-O tetrahedra. We also present details of the crystal growth by traveling solvent method.

First-Principles Prediction of New Electrides with Nontrivial Band Topology Based on One-Dimensional Building Blocks

NASA Astrophysics Data System (ADS)

Park, Changwon; Kim, Sung Wng; Yoon, Mina

2018-01-01

We introduce a new class of electrides with nontrivial band topology by coupling materials database searches and first-principles-calculations-based analysis. Cs3O and Ba3N are for the first time identified as a new class of electrides, consisting of one-dimensional (1D) nanorod building blocks. Their crystal structures mimic β -TiCl3 with the position of anions and cations exchanged. Unlike the weakly coupled nanorods of β -TiCl3 , Cs3O and Ba3N retain 1D anionic electrons along the hollow interrod sites; additionally, a strong interrod interaction in C3O and Ba3N induces band inversion in a 2D superatomic triangular lattice, resulting in Dirac-node lines. The new class of electrides can serve as a prototype for new electrides with a large cavity space that can be utilized for various applications such as gas storage, ion transport, and metal intercalation.

Simulations of vortices in a star-shaped plate with an artificial pin

NASA Astrophysics Data System (ADS)

Miyoshi, Hiroki; Ito, Atsuki; Dang, Vu The; Thanh Huy, Ho; Hayashi, Masahiko; Kato, Masaru; Ishida, Takekazu

2017-07-01

Although a triangular vortex lattice is stable in a bulk type-II superconductor, exotic vortex configurations are expected to appear in a small superconducting plate. Theoretical calculations on vortex structures in a star-shaped superconducting plate have been given in our preceding work. In this work, we extended our theoretical studies to the case of having an artificial pin. We performed the Ginzburg-Landau (GL) calculations systematically to compare with the pin-free case by using the finite element method. We found that a vortex tends to accommodate preferentially in an aritificial pin in the star-shaped plate. We found a systematic evolution of vortex structure with increaseing magnetic field. We compare our theoretical calculations with vortices in a star-shaped Mo80Ge20 plate with an artificial pin and without an artificial pin obtained by a scanning SQUID microscope. We reconstructed the vortex image on the sample surface by using the inverse Biot-Savart law and the Fourier transformation.

Atom-Dependent Edge-Enhanced Second-Harmonic Generation on MoS2 Monolayers.

PubMed

Lin, Kuang-I; Ho, Yen-Hung; Liu, Shu-Bai; Ciou, Jian-Jhih; Huang, Bo-Ting; Chen, Christopher; Chang, Han-Ching; Tu, Chien-Liang; Chen, Chang-Hsiao

2018-02-14

Edge morphology and lattice orientation of single-crystal molybdenum disulfide (MoS 2 ) monolayers, a transition metal dichalcogenide (TMD), possessing a triangular shape with different edges grown by chemical vapor deposition are characterized by atomic force microscopy and transmission electron microscopy. Multiphoton laser scanning microscopy is utilized to study one-dimensional atomic edges of MoS 2 monolayers with localized midgap electronic states, which result in greatly enhanced optical second-harmonic generation (SHG). Microscopic S-zigzag edge and S-Mo Klein edge (bare Mo atoms protruding from a S-zigzag edge) terminations and the edge-atom dependent resonance energies can therefore be deduced based on SHG images. Theoretical calculations based on density functional theory clearly explain the lower energy of the S-zigzag edge states compared to the corresponding S-Mo Klein edge states. Characterization of the atomic-scale variation of edge-enhanced SHG is a step forward in this full-optical and high-yield technique of atomic-layer TMDs.

Magnetization plateau as a result of the uniform and gradual electron doping in a coupled spin-electron double-tetrahedral chain

NASA Astrophysics Data System (ADS)

Gálisová, Lucia

2017-11-01

The double-tetrahedral chain in a longitudinal magnetic field, whose nodal lattice sites occupied by the localized Ising spins regularly alternate with triangular plaquettes with the dynamics described by the Hubbard model, is rigorously investigated. It is demonstrated that the uniform change of electron concentration controlled by the chemical potential in a combination with the competition between model parameters and the external magnetic field leads to the formation of one chiral and seven nonchiral phases at the absolute zero temperature. Rational plateaux at one-third and one-half of the saturation magnetization can also be identified in the low-temperature magnetization curves. On the other hand, the gradual electron doping results in 11 different ground-state regions that distinguish from each other by the evolution of the electron distribution during this process. Several doping-dependent magnetization plateaux are observed in the magnetization process as a result of the continuous change of electron content in the model.

Molecular dynamics simulations for mechanical properties of borophene: parameterization of valence force field model and Stillinger-Weber potential

PubMed Central

Zhou, Yu-Ping; Jiang, Jin-Wu

2017-01-01

While most existing theoretical studies on the borophene are based on first-principles calculations, the present work presents molecular dynamics simulations for the lattice dynamical and mechanical properties in borophene. The obtained mechanical quantities are in good agreement with previous first-principles calculations. The key ingredients for these molecular dynamics simulations are the two efficient empirical potentials developed in the present work for the interaction of borophene with low-energy triangular structure. The first one is the valence force field model, which is developed with the assistance of the phonon dispersion of borophene. The valence force field model is a linear potential, so it is rather efficient for the calculation of linear quantities in borophene. The second one is the Stillinger-Weber potential, whose parameters are derived based on the valence force field model. The Stillinger-Weber potential is applicable in molecular dynamics simulations of nonlinear physical or mechanical quantities in borophene. PMID:28349983

Self-assembly of triangular particles via capillary interactions

NASA Astrophysics Data System (ADS)

Bedi, Deshpreet; Zhou, Shangnan; Ferrar, Joseph; Solomon, Michael; Mao, Xiaoming

Colloidal particles adsorbed to a fluid interface deform the interface around them, resulting in either attractive or repulsive forces mediated by the interface. In particular, particle shape and surface roughness can produce an undulating contact line, such that the particles will assume energetically-favorable relative orientations and inter-particle distances to minimize the excess interfacial surface area. By expediently selecting specific particle shapes and associated design parameters, capillary interactions can be utilized to promote self-assembly of these particles into extended regular open structures, such as the kagome lattice, which have novel mechanical properties. We present the results of numerical simulations of equilateral triangle microprisms at an interface, including individually and in pairs. We show how particle bowing can yield two distinct binding events and connect it to theory in terms of a capillary multipole expansion and also to experiment, as presented in an accompanying talk. We also discuss and suggest design principles that can be used to create desirable open structures.

Self-assembly of thin, triangular prisms into open networks at a flat air-water interface

NASA Astrophysics Data System (ADS)

Solomon, Michael; Ferrar, Joseph; Bedi, Deshpreet; Zhou, Shangnan; Mao, Xiaoming

We observe capillary-driven binding between thin, equilateral triangle microprisms at a flat air-water interface. The triangles are fabricated from epoxy resin via SU-8 photolithography. For small thickness to length (T/L) ratios, two distinct pairwise particle-particle binding events occur with roughly equal frequency, and optical and environmental scanning electron microscopy (eSEM) demonstrate that these two distinct binding events are driven by the specific manner in which the interface is pinned to the particle surface. Additionally, particle bending is observed for the lowest T/L ratios, which leads to enhanced interface curvature and thus enhanced strength of capillary-driven attractions, and may also play a pivotal role in the dichotomy in particle-particle binding. Dichotomy in particle-particle binding is not observed at thicker T/L ratios, although capillary-driven binding still occurs. Ultimately, the particles self-assemble into space-spanning open networks, and the results suggest design parameters for the fabrication of building blocks of ordered open structures, such as the Kagome lattice.

Numerical analysis of light extraction enhancement of GaN-based thin-film flip-chip light-emitting diodes with high-refractive-index buckling nanostructures

NASA Astrophysics Data System (ADS)

Yue, Qing-Yang; Yang, Yang; Cheng, Zhen-Jia; Guo, Cheng-Shan

2018-06-01

In this work, the light extraction efficiency enhancement of GaN-based thin-film flip-chip (TFFC) light-emitting diodes (LEDs) with high-refractive-index (TiO2) buckling nanostructures was studied using the three-dimensional finite difference time domain method. Compared with 2-D photonic crystals, the buckling structures have the advantages of a random directionality and a broad distribution in periodicity, which can effectively extract the guided light propagating in all azimuthal directions over a wide spectrum. Numerical studies revealed that the light extraction efficiency of buckling-structured LEDs reaches 1.1 times that of triangular lattice photonic crystals. The effects of the buckling structure feature sizes and the thickness of the N-GaN layer on the light extraction efficiency for TFFC LEDs were also investigated systematically. With optimized structural parameters, a significant light extraction enhancement of about 2.6 times was achieved for TiO2 buckling-structured TFFC LEDs compared with planar LEDs.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ackerman, P. J.; van de Lagemaat, J.; Smalyukh, I. I.

Some of the most exotic condensed matter phases, such as twist grain boundary and blue phases in liquid crystals and Abrikosov phases in superconductors, contain arrays of topological defects in their ground state. Comprised of a triangular lattice of double-twist tubes of magnetization, the so-called ‘A-phase’ in chiral magnets is an example of a thermodynamically stable phase with topologically nontrivial solitonic field configurations referred to as two-dimensional skyrmions, or baby-skyrmions. Here we report that three-dimensional skyrmions in the form of double-twist tori called ‘hopfions’, or ‘torons’ when accompanied by additional self-compensating defects, self-assemble into periodic arrays and linear chains thatmore » exhibit electrostriction. In confined chiral nematic liquid crystals, this self-assembly is similar to that of liquid crystal colloids and originates from long-range elastic interactions between particle-like skyrmionic torus knots of molecular alignment field, which can be tuned from isotropic repulsive to weakly or highly anisotropic attractive by low-voltage electric fields.« less

Self-arraying of charged levitating droplets.

PubMed

Kauffmann, Paul; Nussbaumer, Jérémie; Masse, Alain; Jeandey, Christian; Grateau, Henri; Pham, Pascale; Reyne, Gilbert; Haguet, Vincent

2011-06-01

Diamagnetic levitation of water droplets in air is a promising phenomenon to achieve contactless manipulation of chemical or biochemical samples. This noncontact handling technique prevents contaminations of samples as well as provides measurements of interaction forces between levitating reactors. Under a nonuniform magnetic field, diamagnetic bodies such as water droplets experience a repulsive force which may lead to diamagnetic levitation of a single or few micro-objects. The levitation of several repulsively charged picoliter droplets was successfully performed in a ~1 mm(2) adjustable flat magnetic well provided by a centimeter-sized cylindrical permanent magnet structure. Each droplet position results from the balance between the centripetal diamagnetic force and the repulsive Coulombian forces. Levitating water droplets self-organize into satellite patterns or thin clouds, according to their charge and size. Small triangular lattices of identical droplets reproduce magneto-Wigner crystals. Repulsive forces and inner charges can be measured in the piconewton and the femtocoulomb ranges, respectively. Evolution of interaction forces is accurately followed up over time during droplet evaporation.

7 CFR 810.802 - Definition of other terms.

Code of Federal Regulations, 2012 CFR

2012-01-01

... and fines. All matter other than whole flaxseed that passes through a 5/64 triangular-hole sieve, and... established under the Act, that are materially discolored and damaged by heat. (e) Sieve— 5/64 triangular-hole sieve. A metal sieve 0.032 inch thick with equilateral triangular perforations the inscribed circles of...

7 CFR 810.802 - Definition of other terms.

Code of Federal Regulations, 2013 CFR

2013-01-01

... and fines. All matter other than whole flaxseed that passes through a 5/64 triangular-hole sieve, and... established under the Act, that are materially discolored and damaged by heat. (e) Sieve— 5/64 triangular-hole sieve. A metal sieve 0.032 inch thick with equilateral triangular perforations the inscribed circles of...

7 CFR 810.802 - Definition of other terms.

Code of Federal Regulations, 2011 CFR

2011-01-01

... and fines. All matter other than whole flaxseed that passes through a 5/64 triangular-hole sieve, and... established under the Act, that are materially discolored and damaged by heat. (e) Sieve— 5/64 triangular-hole sieve. A metal sieve 0.032 inch thick with equilateral triangular perforations the inscribed circles of...

7 CFR 810.802 - Definition of other terms.

Code of Federal Regulations, 2014 CFR

2014-01-01

... and fines. All matter other than whole flaxseed that passes through a 5/64 triangular-hole sieve, and... established under the Act, that are materially discolored and damaged by heat. (e) Sieve— 5/64 triangular-hole sieve. A metal sieve 0.032 inch thick with equilateral triangular perforations the inscribed circles of...

Sorption of Triangular Silver Nanoplates on Polyurethane Foam

NASA Astrophysics Data System (ADS)

Furletov, A. A.; Apyari, V. V.; Garshev, A. V.; Volkov, P. A.; Tolmacheva, V. V.; Dmitrienko, S. G.

2018-02-01

The sorption of triangular silver nanoplates on polyurethane foam is investigated as a procedure for creating a nanocomposite sensing material for subsequent use in optical means of chemical analysis. Triangular silver nanoplates are synthesized and characterized, and a simple sorption technique for the formation of a composite material based on these nanoplates is proposed.

Properties of plane discrete Poisson-Voronoi tessellations on triangular tiling formed by the Kolmogorov-Johnson-Mehl-Avrami growth of triangular islands

NASA Astrophysics Data System (ADS)

Korobov, A.

2011-08-01

Discrete uniform Poisson-Voronoi tessellations of two-dimensional triangular tilings resulting from the Kolmogorov-Johnson-Mehl-Avrami (KJMA) growth of triangular islands have been studied. This shape of tiles and islands, rarely considered in the field of random tessellations, is prompted by the birth-growth process of Ir(210) faceting. The growth mode determines a triangular metric different from the Euclidean metric. Kinetic characteristics of tessellations appear to be metric sensitive, in contrast to area distributions. The latter have been studied for the variant of nuclei growth to the first impingement in addition to the conventional case of complete growth. Kiang conjecture works in both cases. The averaged number of neighbors is six for all studied densities of random tessellations, but neighbors appear to be mainly different in triangular and Euclidean metrics. Also, the applicability of the obtained results for simulating birth-growth processes when the 2D nucleation and impingements are combined with the 3D growth in the particular case of similar shape and the same orientation of growing nuclei is briefly discussed.

Properties of plane discrete Poisson-Voronoi tessellations on triangular tiling formed by the Kolmogorov-Johnson-Mehl-Avrami growth of triangular islands.

PubMed

Korobov, A

2011-08-01

Discrete uniform Poisson-Voronoi tessellations of two-dimensional triangular tilings resulting from the Kolmogorov-Johnson-Mehl-Avrami (KJMA) growth of triangular islands have been studied. This shape of tiles and islands, rarely considered in the field of random tessellations, is prompted by the birth-growth process of Ir(210) faceting. The growth mode determines a triangular metric different from the Euclidean metric. Kinetic characteristics of tessellations appear to be metric sensitive, in contrast to area distributions. The latter have been studied for the variant of nuclei growth to the first impingement in addition to the conventional case of complete growth. Kiang conjecture works in both cases. The averaged number of neighbors is six for all studied densities of random tessellations, but neighbors appear to be mainly different in triangular and Euclidean metrics. Also, the applicability of the obtained results for simulating birth-growth processes when the 2D nucleation and impingements are combined with the 3D growth in the particular case of similar shape and the same orientation of growing nuclei is briefly discussed.

A Ranking Analysis/An Interlinking Approach of New Triangular Fuzzy Cognitive Maps and Combined Effective Time Dependent Matrix

NASA Astrophysics Data System (ADS)

Adiga, Shreemathi; Saraswathi, A.; Praveen Prakash, A.

2018-04-01

This paper aims an interlinking approach of new Triangular Fuzzy Cognitive Maps (TrFCM) and Combined Effective Time Dependent (CETD) matrix to find the ranking of the problems of Transgenders. Section one begins with an introduction that briefly describes the scope of Triangular Fuzzy Cognitive Maps (TrFCM) and CETD Matrix. Section two provides the process of causes of problems faced by Transgenders using Fuzzy Triangular Fuzzy Cognitive Maps (TrFCM) method and performs the calculations using the collected data among the Transgender. In Section 3, the reasons for the main causes for the problems of the Transgenders. Section 4 describes the Charles Spearmans coefficients of rank correlation method by interlinking of Triangular Fuzzy Cognitive Maps (TrFCM) Method and CETD Matrix. Section 5 shows the results based on our study.

Experimental evidence for the lattice instability of Bi-based superconducting systems

NASA Astrophysics Data System (ADS)

Yusheng, He; Jiong, Xiang; Hsin, Wang; Aisheng, He; Jincang, Zhang; Fanggao, Chang

1989-11-01

Ultrasonic measurements, specific heat and thermal analysis experiments, X-ray diffraction study and infrared investigation revealed that there are anomalous structural changes or lattice instabilities near 200 K in single 2212 or 2223 phase samples of Bi(Pb)-Sr-Ca-Cu-O system. Detailed study showed that anomalous changes or lattice instabilities are isothermal-like processes and have the characteristics of a structural phase transition, accompanying with increases in lattice constants. Possible mechanism for this lattice instability is discussed.

A fast direct method for block triangular Toeplitz-like with tri-diagonal block systems from time-fractional partial differential equations

NASA Astrophysics Data System (ADS)

Ke, Rihuan; Ng, Michael K.; Sun, Hai-Wei

2015-12-01

In this paper, we study the block lower triangular Toeplitz-like with tri-diagonal blocks system which arises from the time-fractional partial differential equation. Existing fast numerical solver (e.g., fast approximate inversion method) cannot handle such linear system as the main diagonal blocks are different. The main contribution of this paper is to propose a fast direct method for solving this linear system, and to illustrate that the proposed method is much faster than the classical block forward substitution method for solving this linear system. Our idea is based on the divide-and-conquer strategy and together with the fast Fourier transforms for calculating Toeplitz matrix-vector multiplication. The complexity needs O (MNlog2 ⁡ M) arithmetic operations, where M is the number of blocks (the number of time steps) in the system and N is the size (number of spatial grid points) of each block. Numerical examples from the finite difference discretization of time-fractional partial differential equations are also given to demonstrate the efficiency of the proposed method.

ASICs Approach for the Implementation of a Symmetric Triangular Fuzzy Coprocessor and Its Application to Adaptive Filtering

NASA Technical Reports Server (NTRS)

Starks, Scott; Abdel-Hafeez, Saleh; Usevitch, Bryan

1997-01-01

This paper discusses the implementation of a fuzzy logic system using an ASICs design approach. The approach is based upon combining the inherent advantages of symmetric triangular membership functions and fuzzy singleton sets to obtain a novel structure for fuzzy logic system application development. The resulting structure utilizes a fuzzy static RAM to store the rule-base and the end-points of the triangular membership functions. This provides advantages over other approaches in which all sampled values of membership functions for all universes must be stored. The fuzzy coprocessor structure implements the fuzzification and defuzzification processes through a two-stage parallel pipeline architecture which is capable of executing complex fuzzy computations in less than 0.55us with an accuracy of more than 95%, thus making it suitable for a wide range of applications. Using the approach presented in this paper, a fuzzy logic rule-base can be directly downloaded via a host processor to an onchip rule-base memory with a size of 64 words. The fuzzy coprocessor's design supports up to 49 rules for seven fuzzy membership functions associated with each of the chip's two input variables. This feature allows designers to create fuzzy logic systems without the need for additional on-board memory. Finally, the paper reports on simulation studies that were conducted for several adaptive filter applications using the least mean squared adaptive algorithm for adjusting the knowledge rule-base.

Neutron diffraction study and theoretical analysis of the antiferromagnetic order and the diffuse scattering in the layered kagome system CaBaCo2Fe2O7

NASA Astrophysics Data System (ADS)

Reim, J. D.; Rosén, E.; Zaharko, O.; Mostovoy, M.; Robert, J.; Valldor, M.; Schweika, W.

2018-04-01

The hexagonal swedenborgite, CaBaCo2Fe2O7 , is a chiral frustrated antiferromagnet, in which magnetic ions form alternating kagome and triangular layers. We observe a long-range √{3 }×√{3 } antiferromagnetic order setting in below TN=160 K by neutron diffraction on single crystals of CaBaCo2Fe2O7 . Both magnetization and polarized neutron single crystal diffraction measurements show that close to TN spins lie predominantly in the a b plane, while upon cooling the spin structure becomes increasingly canted due to Dzyaloshinskii-Moriya interactions. The ordered structure can be described and refined within the magnetic space group P 31 m' . Diffuse scattering between the magnetic peaks reveals that the spin order is partial. Monte Carlo simulations based on a Heisenberg model with two nearest-neighbor exchange interactions show a similar diffuse scattering and coexistence of the √{3 }×√{3 } order with disorder. The coexistence can be explained by the freedom to vary spins without affecting the long-range order, which gives rise to ground-state degeneracy. Polarization analysis of the magnetic peaks indicates the presence of long-period cycloidal spin correlations resulting from the broken inversion symmetry of the lattice, in agreement with our symmetry analysis.

Design considerations for lunar base photovoltaic power systems

NASA Technical Reports Server (NTRS)

Hickman, J. Mark; Curtis, Henry B.; Landis, Geoffrey A.

1990-01-01

A survey was made of factors that may affect the design of photovoltaic arrays for a lunar base. These factors, which include the lunar environment and system design criteria, are examined. A photovoltaic power system design with a triangular array geometry is discussed and compared to a nuclear reactor power systems and a power system utilizing both nuclear and solar power sources.

Triangular Arbitrage as an Interaction in Foreign Exchange Markets

NASA Astrophysics Data System (ADS)

Aiba, Yukihiro; Hatano, Naomichi

Analyzing correlation in financial time series is a topic of considerable interest [1]-[17]. In the foreign exchange market, a correlation among the exchange rates can be generated by a triangular arbitrage transaction. The purpose of this article is to review our recent study [18]-[23] on modeling the interaction generated by the triangular arbitrage.

Glancing angle deposition of Fe triangular nanoprisms consisting of vertically-layered nanoplates

NASA Astrophysics Data System (ADS)

Li, Jianghao; Li, Liangliang; Ma, Lingwei; Zhang, Zhengjun

2016-10-01

Fe triangular nanoprisms consisting of vertically-layered nanoplates were synthesized on Si substrate by glancing angle deposition (GLAD) with an electron beam evaporation system. It was found that Fe nanoplates with a crystallographic plane index of BCC (110) were stacked vertically to form triangular nanoprisms and the axial direction of the nanoprisms, BCC <001>, was normal to the substrate. The effects of experimental parameters of GLAD on the growth and morphology of Fe nanoprisms were systematically studied. The deposition rate played an important role in the morphology of Fe nanoprisms at the same length, the deposition angle just affected the areal density of nanoprisms, and the rotation speed of substrate had little influence within the parameter range we investigated. In addition, the crystal growth mechanism of Fe nanoprisms was explained with kinetically-controlled growth mechanism and zone model theory. The driving force of crystal growth was critical to the morphology and microstructure of Fe nanoprisms deposited by GLAD. Our work introduced an oriented crystal structure into the nanomaterials deposited by GLAD, which provided a new approach to manipulate the properties and functions of nanomaterials.

Investigation of a driven fermionic system and detecting chiral edge modes in an optical lattice

NASA Astrophysics Data System (ADS)

Görg, Frederik; Messer, Michael; Jotzu, Gregor; Sandholzer, Kilian; Desbuquois, Rémi; Goldman, Nathan; Esslinger, Tilman

2017-04-01

Periodically driven systems of ultracold fermions in optical lattices allow to implement a large variety of effective Hamiltonians through Floquet engineering. An important question is whether this method can be extended to interacting systems. We investigate driven two-body systems in an array of double wells and measure the double occupancy and the spin-spin correlator in the large frequency limit and when driving resonantly to an energy scale of the underlying static Hamiltonian. We analyze whether the emerging states of the driven system can be adiabatically connected to states in the unshaken lattice. In addition, we measure the amplitude of the micromotion which describes the short time dynamics of the system and compare it directly to theory. In another context we propose a method to create topological interfaces and detect chiral edge modes in a two dimensional optical lattice. We illustrate this through an optical lattice realization of the Haldane model for cold atoms, where an additional spatially-varying lattice potential induces distinct topological phases in separated regions of space.

Variation in shape of the lingula in the adult human mandible

PubMed Central

TULI, A.; CHOUDHRY, R.; CHOUDHRY, S.; RAHEJA, S.; AGARWAL, S.

2000-01-01

The lingulae of both sides of 165 dry adult human mandibles, 131 males and 34 females of Indian origin, were classified by their shape into 4 types: 1, triangular; 2, truncated; 3, nodular; and 4, assimilated. Triangular lingulae were found in 226 (68.5%) sides, truncated in 52 (15.8%), nodular in 36 (10.9%) and assimilated in 16 (4.8%) sides. Triangular lingulae were found bilaterally in 110, truncated in 23, nodular in 17 and assimilated in 7 mandibles. Of the remaining 8 mandibles with different appearances on the 2 sides, 6 had a combination of triangular and truncated and 2 had nodular and assimilated. The incidence of triangular and assimilated types in the male and female mandibles are almost equal. In the truncated type it was double in the male mandibles while the nodular type was a little less than double in the female mandibles. PMID:11005723

Facile synthesis of microporous SiO2/triangular Ag composite nanostructures for photocatalysis

NASA Astrophysics Data System (ADS)

Sirohi, Sidhharth; Singh, Anandpreet; Dagar, Chakit; Saini, Gajender; Pani, Balaram; Nain, Ratyakshi

2017-11-01

In this article, we present a novel fabrication of microporous SiO2/triangular Ag nanoparticles for dye (methylene blue) adsorption and plasmon-mediated degradation. Microporous SiO2 nanoparticles with pore size <2 nm were synthesized using cetyltrimethylammonium bromide as a structure-directing agent and functionalized with APTMS ((3-aminopropyl) trimethoxysilane) to introduce amine groups. Amine-functionalized microporous silica was used for adsorption of triangular silver (Ag) nanoparticles. The synthesized microporous SiO2 nanostructures were investigated for adsorption of different dyes including methylene blue, congo red, direct green 26 and curcumin crystalline. Amine-functionalized microporous SiO2/triangular Ag nanostructures were used for plasmon-mediated photocatalysis of methylene blue. The experimental results revealed that the large surface area of microporous silica facilitated adsorption of dye. Triangular Ag nanoparticles, due to their better charge carrier generation and enhanced surface plasmon resonance, further enhanced the photocatalysis performance.

Application of cylindrical, triangular and hemispherical dimples in the film cooling technology

NASA Astrophysics Data System (ADS)

Khalatov, A. A.; Panchenko, N. A.; Severin, S. D.

2017-11-01

The results of film cooling numerical simulation over a flat plate with coolant supply through a single span-wise array of inclined (α = 30°) holes arranged inside cylindrical, triangular, and hemispherical dimples are represented in the paper. Such configurations are of a great practical interest for application in advanced blade cooling systems of high-performance gas turbines. The schemes with coolant supply into triangular and hemispherical dimples were first proposed and patented by the IET of the NAS of Ukraine. For numerical simulation the ANSYS CFX 14 commercial code was used. Numerical simulation were carried out in a wide range of the blowing ratio parameter varied from 0.5 to 2.0. For low blowing ratio parameter (m = 0.5) the laterally averaged film cooling efficiency is actually the same for all investigated schemes over the main film cooling area. In this area, the most simple in terms of the film cooling production technology configuration can be used. At the medium and high blowing ratios (m = 1.0 or higher) all investigated film cooling schemes allow to increase the laterally averaged film cooling efficiency in comparison with the traditional cooling scheme with single row of incline holes. In this case the configuration with coolant supply into triangular dimples of the «crater» type demonstrates the best film cooling efficiency due to significant reduction in the intensity and scale of the “kidney” vortex beyond configuration, as well as due to decrease in the coolant blowing non-uniformity factor.

Indications, techniques, and outcomes of arthroscopic repair of scapholunate ligament and triangular fibrocartilage complex.

PubMed

Mathoulin, C L

2017-07-01

This review includes updated understanding of the roles of intrinsic and extrinsic carpal ligaments in scapholunate instability and details the author's experience of indications, arthroscopic repair methods, and outcomes of treating the instability. A classification on triangular fibrocartilage complex injuries is reviewed, followed by author's indications, methods, and outcomes of arthroscopic repair of triangular fibrocartilage complex injuries.

26 CFR 1.367(b)-14T - Acquisition of parent stock for property in triangular reorganizations (temporary).

Code of Federal Regulations, 2010 CFR

2010-04-01

... 26 Internal Revenue 4 2010-04-01 2010-04-01 false Acquisition of parent stock for property in triangular reorganizations (temporary). 1.367(b)-14T Section 1.367(b)-14T Internal Revenue INTERNAL REVENUE... § 1.367(b)-14T Acquisition of parent stock for property in triangular reorganizations (temporary). (a...

The generation of piezoelectricity and flexoelectricity in graphene by breaking the materials symmetries.

PubMed

Javvaji, Brahmanandam; He, Bo; Zhuang, Xiaoying

2018-06-01

Graphene is a non-piezoelectric material. Engineering the piezoelectricity in graphene is possible with the help of impurities, defects and structural modifications. This study reports the mechanism of strain induced polarization and the estimation of piezoelectric and flexoelectric coefficients for graphene system. The combination of charge-dipole potential and the strong many-body potential is employed for describing the inter-atomic interactions. The breaking of symmetry in graphene material is utilized to generate the polarization. Pristine graphene, graphene with circular defect, graphene with triangular defect and trapezium-shaped graphene are considered. Molecular dynamics simulations are performed for straining the graphene atomic systems. The optimization of charge-dipole potential functions measure the polarization for these systems. Pristine and circular defect graphene systems show a constant polarization with strain. The polarization is varying with strain for a triangular defected and trapezium-shaped graphene system. The local atomic deformation produces a change in polarization with respect to the strain gradient. Estimated piezo and flexo coefficients motivate the usage of graphene in electro-mechanical devices.

GPU surface extraction using the closest point embedding

NASA Astrophysics Data System (ADS)

Kim, Mark; Hansen, Charles

2015-01-01

Isosurface extraction is a fundamental technique used for both surface reconstruction and mesh generation. One method to extract well-formed isosurfaces is a particle system; unfortunately, particle systems can be slow. In this paper, we introduce an enhanced parallel particle system that uses the closest point embedding as the surface representation to speedup the particle system for isosurface extraction. The closest point embedding is used in the Closest Point Method (CPM), a technique that uses a standard three dimensional numerical PDE solver on two dimensional embedded surfaces. To fully take advantage of the closest point embedding, it is coupled with a Barnes-Hut tree code on the GPU. This new technique produces well-formed, conformal unstructured triangular and tetrahedral meshes from labeled multi-material volume datasets. Further, this new parallel implementation of the particle system is faster than any known methods for conformal multi-material mesh extraction. The resulting speed-ups gained in this implementation can reduce the time from labeled data to mesh from hours to minutes and benefits users, such as bioengineers, who employ triangular and tetrahedral meshes

The generation of piezoelectricity and flexoelectricity in graphene by breaking the materials symmetries

NASA Astrophysics Data System (ADS)

Javvaji, Brahmanandam; He, Bo; Zhuang, Xiaoying

2018-06-01

Graphene is a non-piezoelectric material. Engineering the piezoelectricity in graphene is possible with the help of impurities, defects and structural modifications. This study reports the mechanism of strain induced polarization and the estimation of piezoelectric and flexoelectric coefficients for graphene system. The combination of charge-dipole potential and the strong many-body potential is employed for describing the inter-atomic interactions. The breaking of symmetry in graphene material is utilized to generate the polarization. Pristine graphene, graphene with circular defect, graphene with triangular defect and trapezium-shaped graphene are considered. Molecular dynamics simulations are performed for straining the graphene atomic systems. The optimization of charge-dipole potential functions measure the polarization for these systems. Pristine and circular defect graphene systems show a constant polarization with strain. The polarization is varying with strain for a triangular defected and trapezium-shaped graphene system. The local atomic deformation produces a change in polarization with respect to the strain gradient. Estimated piezo and flexo coefficients motivate the usage of graphene in electro-mechanical devices.

Comparative analysis of film cooling efficiency at coolant supply into a single array of triangular dimples

NASA Astrophysics Data System (ADS)

Khalatov, A. A.; Petliak, O. O.; Severin, S. D.; Panchenko, N. A.

2018-03-01

The purpose of this work is a comparative study of the physical structure and film cooling efficiency of the single array of inclined holes, placed in triangular dimples and in a trench. The software package ANSYS CFX 17.0 was used along with RANS SST turbulence model. Calculations were made in a wide range of the blowing ratio ranging from 0.5 to 2.0. Results of modeling have shown high efficiency of triangular film cooling configuration. At m ≥ 1.5, the triangular configuration is comparable with the trench configuration in terms of the film cooling efficiency.

Nonzero θ13 from the Triangular Ansatz and Leptogenesis

NASA Astrophysics Data System (ADS)

Benaoum, H. B.

2012-08-01

Recent experiments indicate a departure from the exact tri-bimaximal mixing by measure ring definitive nonzero value of θ13. Within the framework of type I seesaw mechanism, we reconstruct the triangular Dirac neutrino mass matrix from the μ - τ symmetric mass matrix. The deviation from μ - τ symmetry is then parametrized by adding dimensionless parameters yi in the triangular mass matrix. In this parametrization of the neutrino mass matrix, the nonzero value θ13 is controlled by Δy = y4 - y6. We also calculate the resulting leptogenesis and show that the triangular texture can generate the observed baryon asymmetry in the universe via leptogenesis scenario.

Influence of two different flap designs on the sequelae of mandibular third molar surgery.

PubMed

Erdogan, Ozgür; Tatlı, Ufuk; Ustün, Yakup; Damlar, Ibrahim

2011-09-01

The aim of this study was to compare the influence of triangular and envelope flaps on trismus, pain, and facial swelling after mandibular third molar surgery. Twenty healthy patients with bilateral, symmetrically impacted mandibular third molars were included in this double-blinded, prospective, cross-over, randomized study. The patients were operated with envelope flap on one side and triangular flap on the other side. Trismus was determined by measuring maximum interincisal opening, and facial swelling was evaluated using a tape measuring method. Pain was determined using visual analog scale (VAS) and recording the number of pain pills taken. The facial swelling measurements and VAS scores were lower in the envelope flap group compared to the triangular flap group. There was no significant difference between the two flap designs in operation time, maximum interincisal opening, and the number of analgesics taken. Envelope flap yields to less facial swelling and reduced VAS scores in comparison to triangular flap. There is no clinical difference in trismus between the two flap designs. Despite the higher VAS scores with triangular flap, no additional doses of analgesics were required in triangular flap.