Experimental study of photonic crystal triangular lattices
NASA Astrophysics Data System (ADS)
Qin, Ruhu; Qin, Bo; Jin, Chongjun
1999-06-01
Triangular lattice photonic crystal behaving in the electromagnetic zones constructed from fused silica cylinders in styrofoam is fabricated. The transmission spectra of the photonic crystal with and without defects are measured. On this basis, the defect modes of photonic crystal were studied, and the potential applications of the photonic crystal are discussed.
Maximum independent set on diluted triangular lattices
NASA Astrophysics Data System (ADS)
Fay, C. W., IV; Liu, J. W.; Duxbury, P. M.
2006-05-01
Core percolation and maximum independent set on random graphs have recently been characterized using the methods of statistical physics. Here we present a statistical physics study of these problems on bond diluted triangular lattices. Core percolation critical behavior is found to be consistent with the standard percolation values, though there are strong finite size effects. A transfer matrix method is developed and applied to find accurate values of the density and degeneracy of the maximum independent set on lattices of limited width but large length. An extrapolation of these results to the infinite lattice limit yields high precision results, which are tabulated. These results are compared to results found using both vertex based and edge based local probability recursion algorithms, which have proven useful in the analysis of hard computational problems, such as the satisfiability problem.
Thermodynamic Properties in Triangular-Lattice Superconductors
NASA Astrophysics Data System (ADS)
Ma, Xixiao; Qin, Ling; Zhao, Huaisong; Lan, Yu; Feng, Shiping
2016-06-01
The study of superconductivity arising from doping a Mott insulator has become a central issue in the area of superconductivity. Within the framework of the kinetic-energy-driven superconducting (SC) mechanism, we discuss the thermodynamic properties in the triangular-lattice cobaltate superconductors. It is shown that a sharp peak in the specific heat appears at the SC transition temperature T_c, and then the specific heat varies exponentially as a function of temperature for temperatures T
Coupled-wave model for triangular-lattice photonic crystal with transverse electric polarization.
Sakai, Kyosuke; Yue, Jianglin; Noda, Susumu
2008-04-28
We present a coupled-wave model for a triangular-lattice two-dimensional (2D) photonic crystal (PC) with a transverse electric (TE) polarization and derive a set of coupled-wave equations. We use these equations to obtain analytic expressions that describe the relations between the resonant mode frequencies and the coupling constants. We calculate the resonant mode frequencies for a PC composed of circular holes. These agree well with the frequencies calculated using the 2D plane wave expansion method. We also evaluate the coupling constants of fabricated samples using their measured resonant mode frequencies. Our analytic expressions allow the design and evaluation of feedback strength in triangular-lattice 2D PC cavities.
Magnetization Process of Spin-1/2 Heisenberg Antiferromagnets on a Layered Triangular Lattice
NASA Astrophysics Data System (ADS)
Yamamoto, Daisuke; Marmorini, Giacomo; Danshita, Ippei
2016-02-01
We study the magnetization process of the spin-1/2 antiferromagnetic Heisenberg model on a layered triangular lattice by means of a numerical cluster mean-field method with a scaling scheme (CMF+S). It has been known that antiferromagnetic spins on a two-dimensional (2D) triangular lattice with quantum fluctuations exhibit a one-third magnetization plateau in the magnetization curve under magnetic field. We demonstrate that the CMF+S quantitatively reproduces the magnetization curve including the stabilization of the plateau. We also discuss the effects of a finite interlayer coupling, which is unavoidable in real quasi-2D materials. It has been recently argued for a model of the layered-triangular-lattice compound Ba3CoSb2O9 that such interlayer coupling can induce an additional first-order transition at a strong field. We present the detailed CMF+S results for the magnetization and susceptibility curves of the fundamental Heisenberg Hamiltonian in the presence of magnetic field and weak antiferromagnetic interlayer coupling. The extra first-order transition appears as a quite small jump in the magnetization curve and a divergence in the susceptibility at a strong magnetic field ˜0.712 of the saturation field.
Grid Cell Responses in 1D Environments Assessed as Slices through a 2D Lattice.
Yoon, KiJung; Lewallen, Sam; Kinkhabwala, Amina A; Tank, David W; Fiete, Ila R
2016-03-01
Grid cells, defined by their striking periodic spatial responses in open 2D arenas, appear to respond differently on 1D tracks: the multiple response fields are not periodically arranged, peak amplitudes vary across fields, and the mean spacing between fields is larger than in 2D environments. We ask whether such 1D responses are consistent with the system's 2D dynamics. Combining analytical and numerical methods, we show that the 1D responses of grid cells with stable 1D fields are consistent with a linear slice through a 2D triangular lattice. Further, the 1D responses of comodular cells are well described by parallel slices, and the offsets in the starting points of the 1D slices can predict the measured 2D relative spatial phase between the cells. From these results, we conclude that the 2D dynamics of these cells is preserved in 1D, suggesting a common computation during both types of navigation behavior. PMID:26898777
Mott Insulating Ground State on a Triangular Surface Lattice
Weitering, H.; Shi, X.; Weitering, H.; Johnson, P.; Chen, J.; DiNardo, N.; DiNardo, N.; Kempa, K.
1997-02-01
Momentum-resolved direct and inverse photoemission spectra of the K/Si(111)-({radical}(3){times}{radical}(3))R30{degree}-B interface reveals the presence of strongly localized surface states. The K overlayer remains nonmetallic up to the saturation coverage. This system most likely presents the first experimental realization of a frustrated spin 1/2 Heisenberg antiferromagnet on a two-dimensional triangular lattice. {copyright} {ital 1997} {ital The American Physical Society}
Effective-medium theory of a filamentous triangular lattice.
Mao, Xiaoming; Stenull, Olaf; Lubensky, T C
2013-04-01
We present an effective-medium theory that includes bending as well as stretching forces, and we use it to calculate the mechanical response of a diluted filamentous triangular lattice. In this lattice, bonds are central-force springs, and there are bending forces between neighboring bonds on the same filament. We investigate the diluted lattice in which each bond is present with a probability p. We find a rigidity threshold p(b) which has the same value for all positive bending rigidity and a crossover characterizing bending, stretching, and bend-stretch coupled elastic regimes controlled by the central-force rigidity percolation point at p(CF)=/~2/3 of the lattice when fiber bending rigidity vanishes. PMID:23679437
Effective-medium theory of a filamentous triangular lattice
NASA Astrophysics Data System (ADS)
Mao, Xiaoming; Stenull, Olaf; Lubensky, T. C.
2013-04-01
We present an effective-medium theory that includes bending as well as stretching forces, and we use it to calculate the mechanical response of a diluted filamentous triangular lattice. In this lattice, bonds are central-force springs, and there are bending forces between neighboring bonds on the same filament. We investigate the diluted lattice in which each bond is present with a probability p. We find a rigidity threshold pb which has the same value for all positive bending rigidity and a crossover characterizing bending, stretching, and bend-stretch coupled elastic regimes controlled by the central-force rigidity percolation point at pCF≃2/3 of the lattice when fiber bending rigidity vanishes.
Dynamical polarizability of the 2D pseudospin-1 dice lattice
NASA Astrophysics Data System (ADS)
Malcolm, John; Nicol, Elisabeth
The two-dimensional dice lattice is composed of three triangular sublattices whose low-energy excitation spectrum consists of Dirac-Weyl fermions with pseudospin-1. The energy dispersion has two Dirac cones, like the pseudospin-1/2 two-triangular-sublattice graphene, with an additional third band exactly at zero energy. We present theoretical results for the electronic dynamical polarization function in the material. This is a fundamental entity in many-body physics, renormalizing the Coulomb interaction through the dielectric function. From the polarization function we also obtain the Lindhard function, the plasmon branch, and can discuss other screening effects. These are constrasted with those of graphene.
Frustration and correlations in stacked triangular-lattice Ising antiferromagnets
NASA Astrophysics Data System (ADS)
Burnell, F. J.; Chalker, J. T.
2015-12-01
We study multilayer triangular-lattice Ising antiferromagnets with interlayer interactions that are weak and frustrated in an abc stacking. By analyzing a coupled height model description of these systems, we show that they exhibit a classical spin liquid regime at low temperature, in which both intralayer and interlayer correlations are strong but there is no long-range order. Diffuse scattering in this regime is concentrated on a helix in reciprocal space, as observed for charge ordering in the materials LuFe2O4 and YbFe2O4 .
Chiral Bosonic Mott Insulator on the Frustrated Triangular Lattice
NASA Astrophysics Data System (ADS)
Parameswaran, Siddharth; Zaletel, Michael; Rüegg, Andreas; Altman, Ehud
2014-03-01
We study the superfluid and insulating phases of interacting bosons on the triangular lattice with an inverted dispersion, corresponding to frustrated hopping between sites. The resulting single-particle dispersion has multiple minima at nonzero wavevectors in momentum space, in contrast to the unique zero-wavevector minimum of the unfrustrated problem. As a consequence, the superfluid phase is unstable against developing additional chiral order that breaks time reversal (T) and parity (P) symmetries by forming a condensate at nonzero wavevector. We demonstrate that the loss of superfluidity can lead to an even more exotic phase, the chiral Mott insulator, with nontrivial current order that breaks T, P. These results are obtained via variational estimates, as well as a combination of bosonization and DMRG of triangular ladders, which taken together permit a fairly complete characterization of the phase diagram. We discuss the relevance of these phases to optical lattice experiments, as well as signatures of chiral symmetry breaking in time-of-flight images. We acknowledge support from NSF Grants 1066293 (SP, EA) and DGE-1106400 (MPZ), the Simons Foundation (SP), the Swiss National Science Foundation (AR), the ISF, BSF, ERC Synergy UQUAM program and the Miller Institute at UC Berkeley (EA).
Chiral bosonic Mott insulator on the frustrated triangular lattice
NASA Astrophysics Data System (ADS)
Zaletel, Michael P.; Parameswaran, S. A.; Rüegg, Andreas; Altman, Ehud
2014-04-01
We study the superfluid and insulating phases of interacting bosons on the triangular lattice with an inverted dispersion, corresponding to frustrated hopping between sites. The resulting single-particle dispersion has multiple minima at nonzero wave vectors in momentum space, in contrast to the unique zero-wave-vector minimum of the unfrustrated problem. As a consequence, the superfluid phase is unstable against developing additional chiral order that breaks time-reversal (T) and parity (P) symmetries by forming a condensate at nonzero wave vector. We demonstrate that the loss of superfluidity can lead to an even more exotic phase, the chiral Mott insulator, with nontrivial current order that breaks T ,P. These results are obtained via variational estimates, as well as a combination of bosonization and density-matrix renormalization group of triangular ladders, which, taken together, permit a fairly complete characterization of the phase diagram. We discuss the relevance of these phases to optical lattice experiments, as well as signatures of chiral symmetry breaking in time-of-flight images.
Low-cost Triangular Lattice Towers for Small Wind Turbines
NASA Astrophysics Data System (ADS)
Adhikari, Ram Chandra
This thesis focuses on the study of low-cost steel and bamboo triangular lattice towers for small wind turbines. The core objective is to determine the material properties of bamboo and assess the feasibility of bamboo towers. Using the experimentally determined buckling resistance, elastic modulus, and Poisson's ratio, a 12 m high triangular lattice tower for a 500W wind turbine has been modeled as a tripod to formulate the analytical solutions for the stresses and tower deflections, which enables design of the tower based on buckling strength of tower legs. The tripod formulation combines the imposed loads, the base distance between the legs and tower height, and cross-sectional dimensions of the tower legs. The tripod model was used as a reference for the initial design of the bamboo tower and extended to finite element analysis. A 12 m high steel lattice tower was also designed for the same turbine to serve as a comparison to the bamboo tower. The primary result of this work indicates that bamboo is a valid structural material. The commercial software package ANSYS APDL was used to carry out the tower analysis, evaluate the validity of the tripod model, and extend the analysis for the tower design. For this purpose, a 12 m high steel lattice tower for a 500 W wind turbine was examined. Comparison of finite element analysis and analytical solution has shown that tripod model can be accurately used in the design of lattice towers. The tower designs were based on the loads and safety requirements of international standard for small wind turbine safety, IEC 61400-2. For connecting the bamboo sections in the lattice tower, a steel-bamboo adhesive joint combined with conventional lashing has been proposed. Also, considering the low durability of bamboo, periodic replacement of tower members has been proposed. The result of this study has established that bamboo could be used to construct cost-effective and lightweight lattice towers for wind turbines of 500 Watt
Resistance calculation of three-dimensional triangular and hexagonal prism lattices
NASA Astrophysics Data System (ADS)
Owaidat, M. Q.; Asad, J. H.
2016-09-01
The resistance between two arbitrary lattice sites in infinite three-dimensional triangular and hexagonal prism lattice networks of equal resistances, that have not been studied before, is computed by using lattice Green's function technique. For large separation between lattice points we numerically calculate the asymptotic value of the resistance for these lattices.
Beam-Plasma Instabilities in a 2D Yukawa Lattice
Kyrkos, S.; Kalman, G. J.; Rosenberg, M.
2009-06-05
We consider a 2D Yukawa lattice of grains, with a beam of other charged grains moving in the lattice plane. In contrast to Vlasov plasmas, where the electrostatic instability excited by the beam is only longitudinal, here both longitudinal and transverse instabilities of the lattice phonons can develop. We determine and compare the transverse and longitudinal growth rates. The growth rate spectrum in wave number space exhibits remarkable gaps where no instability can develop. Depending on the system parameters, the transverse instability can be selectively excited.
2D Four-Channel Perfect Reconstruction Filter Bank Realized with the 2D Lattice Filter Structure
NASA Astrophysics Data System (ADS)
Sezen, S.; Ertüzün, A.
2006-12-01
A novel orthogonal 2D lattice structure is incorporated into the design of a nonseparable 2D four-channel perfect reconstruction filter bank. The proposed filter bank is obtained by using the polyphase decomposition technique which requires the design of an orthogonal 2D lattice filter. Due to constraint of perfect reconstruction, each stage of this lattice filter bank is simply parameterized by two coefficients. The perfect reconstruction property is satisfied regardless of the actual values of these parameters and of the number of the lattice stages. It is also shown that a separable 2D four-channel perfect reconstruction lattice filter bank can be constructed from the 1D lattice filter and that this is a special case of the proposed 2D lattice filter bank under certain conditions. The perfect reconstruction property of the proposed 2D lattice filter approach is verified by computer simulations.
Quantum Paramagnet in a π Flux Triangular Lattice Hubbard Model.
Rachel, Stephan; Laubach, Manuel; Reuther, Johannes; Thomale, Ronny
2015-04-24
We propose the π flux triangular lattice Hubbard model (π THM) as a prototypical setup to stabilize magnetically disordered quantum states of matter in the presence of charge fluctuations. The quantum paramagnetic domain of the π THM that we identify for intermediate Hubbard U is framed by a Dirac semimetal for weak coupling and by 120° Néel order for strong coupling. Generalizing the Klein duality from spin Hamiltonians to tight-binding models, the π THM maps to a Hubbard model which corresponds to the (J_{H},J_{K})=(-1,2) Heisenberg-Kitaev model in its strong coupling limit. The π THM provides a promising microscopic testing ground for exotic finite-U spin liquid ground states amenable to numerical investigation. PMID:25955072
Field-induced decays in XXZ triangular-lattice antiferromagnets
NASA Astrophysics Data System (ADS)
Maksimov, P. A.; Zhitomirsky, M. E.; Chernyshev, A. L.
2016-10-01
We investigate field-induced transformations in the dynamical response of the XXZ model on the triangular lattice that are associated with the anharmonic magnon coupling and decay phenomena. Detailed theoretical predictions are made for Ba3CoSb2O9 , which provides a close realization of the spin-1/2 XXZ model. We demonstrate that dramatic modifications in the magnon spectrum must occur in low out-of-plane fields that are easily achievable for this material. The hallmark of the effect is a coexistence of the clearly distinct well-defined magnon excitations with significantly broadened ones in different regions of the k -ω space. The field-induced decays are generic for this class of models and become more prominent at larger anisotropies and in higher fields.
Spin Fluctuations from Hertz to Terahertz on a Triangular Lattice.
Nambu, Yusuke; Gardner, Jason S; MacLaughlin, Douglas E; Stock, Chris; Endo, Hitoshi; Jonas, Seth; Sato, Taku J; Nakatsuji, Satoru; Broholm, Collin
2015-09-18
The temporal magnetic correlations of the triangular-lattice antiferromagnet NiGa_{2}S_{4} are examined through 13 decades (10^{-13}-1 sec) using ultrahigh-resolution inelastic neutron scattering, muon spin relaxation, and ac and nonlinear susceptibility measurements. Unlike the short-ranged spatial correlations, the temperature dependence of the temporal correlations show distinct anomalies. The spin fluctuation rate decreases precipitously upon cooling towards T^{*}=8.5 K, but fluctuations on the microsecond time scale then persist in an anomalous dynamical regime for 4 K
Simulations of Quantum Spin Models on 2D Frustrated Lattices
NASA Astrophysics Data System (ADS)
Melko, Roger
2006-03-01
Algorithmic advances in quantum Monte Carlo techniques have opened up the possibility of studying models in the general class of the S=1/2 XXZ model (equivalent to hard-core bosons) on frustrated lattices. With an antiferromagnetic diagonal interaction (Jz), these models can be solved exactly with QMC, albeit with some effort required to retain ergodicity in the near-degenerate manifold of states that exists for large Jz. The application of the quantum (ferromagnetic off-diagonal) interaction to this classically degenerate manifold produces a variety of intriguing physics, including an order-by-disorder supersolid phase, novel insulating states, and possible exotic quantum critical phenomena. We discuss numerical results for the triangular and kagome lattices with nearest and next-nearest neighbor exchange interactions, and focus on the relevance of the simulations to related areas of physics, such as experiments of cold trapped atomic gasses and the recent theory of deconfined quantum criticality.
Wang, Y.; Wang, X.; Rybczynski, J.; Wang, D.Z.; Kempa, K.; Ren, Z.F.
2005-04-11
Self-assembly of polystyrene microspheres has been utilized in a two-step masking technique to prepare triangular lattices of catalytic nanodots at low cost. Subsequent triangular lattices of aligned carbon nanotubes on a silicon substrate are achieved by plasma-enhanced chemical vapor deposition. Nickel is used both in the nanodots and in the secondary mask. The triangular lattices of carbon nanotube arrays as two-dimensional photonic crystals show higher geometrical symmetry than the hexagonal lattices previously reported, enabling broader applications including negative index of refraction and subwavelength lensing effect.
2D photonic crystals on the Archimedean lattices (tribute to Johannes Kepler (1571 1630))
NASA Astrophysics Data System (ADS)
Gajić, R.; class="cross-out">D. Jovanović,
2008-03-01
Results of our research on 2D Archemedean lattice photonic crystals are presented. This involves the calculations of the band structures, band-gap maps, equifrequency contours and FDTD simulations of electromagnetic propagation through the structures as well as an experimental verification of negative refraction at microwaves. The band-gap dependence on dielectric contrast is established both for dielectric rods in air and air-holes in dielectric materials. A special emphasis is placed on possibilities of negative refraction and left-handedness in these structures. Together with the familiar Archimedean lattices like square, triangular, honeycomb and Kagome' ones, we consider also, the less known, (3 2, 4, 3, 4) (ladybug) and (3, 4, 6, 4) (honeycomb-ring) structures.
Quantum electric-dipole liquid on a triangular lattice
NASA Astrophysics Data System (ADS)
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
2016-02-01
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.
Quantum electric-dipole liquid on a triangular lattice.
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
2016-01-01
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. PMID:26843363
Agglomerative percolation on the Bethe lattice and the triangular cactus
NASA Astrophysics Data System (ADS)
Chae, Huiseung; Yook, Soon-Hyung; Kim, Yup
2013-08-01
Agglomerative percolation (AP) on the Bethe lattice and the triangular cactus is studied to establish the exact mean-field theory for AP. Using the self-consistent simulation method based on the exact self-consistent equations, the order parameter P∞ and the average cluster size S are measured. From the measured P∞ and S, the critical exponents βk and γk for k = 2 and 3 are evaluated. Here, βk and γk are the critical exponents for P∞ and S when the growth of clusters spontaneously breaks the Zk symmetry of the k-partite graph. The obtained values are β2 = 1.79(3), γ2 = 0.88(1), β3 = 1.35(5) and γ3 = 0.94(2). By comparing these exponents with those for ordinary percolation (β∞ = 1 and γ∞ = 1), we also find β∞ < β3 < β2 and γ∞ > γ3 > γ2. These results quantitatively verify the conjecture that the AP model belongs to a new universality class if the Zk symmetry is broken spontaneously, and the new universality class depends on k.
Quantum electric-dipole liquid on a triangular lattice
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
2016-01-01
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. PMID:26843363
Quantum electric-dipole liquid on a triangular lattice.
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.
Superconducting correlations and thermodynamic properties in 2D square and triangular t-J model
NASA Astrophysics Data System (ADS)
Ogata, Masao
2006-03-01
Equal-time superconducting correlation functions of the two-dimensional t-J model on the square lattice are studied using high-temperature expansion method.[1] The sum of the pairing correlation, its spatial dependence and correlation length are obtained down to T ˜0.2t. By comparison of single-particle contributions in the correlation functions, we find effective attractive interactions between quasi-particles in dx^2-y^2-wave channel. It is shown that d-wave correlation grows rapidly at low temperatures for the doping 0.1 < δ< 0.5. The temperature for this growth is roughly scaled by J/2. This is in sharp contrast to the Hubbard model in a weak or intermediate coupling region, where there are few numerical evidences of superconductivity. We also study the possible d- and f-wave pairing in the triangular t-J model.[2] When t>0 with hole doping, a rapid growth of effective d-wave paring interaction is found that indicates the resonating-valence-bond superconductivity. In contrast, when t<0, where the ferromagnetic- and antiferromagnetic correlation compete, correlation lengths of the f-wave triplet paring tends to diverge around δ=0.6, although its effective interaction is small. This result is compared and discussed with the recently discovered superconductor, NaxCoO2.yH2O, where Co atoms form a triangular lattice. Specific heat in low temperatures are also obtained in the high-temperature expansion method. We will discuss that the doping dependence of the specific heat coefficient, γ, agrees with experimental data. [1] T. Koretsune and M. Ogata, J. Phys. Soc. Japan 74, 1390 (2005). [2] T. Koretsune and M. Ogata, Phys. Rev. Lett. 89, 116401 (2002), and Phys. Rev. B72, 134513 (2005).
Extended particle swarm optimisation method for folding protein on triangular lattice.
Guo, Yuzhen; Wu, Zikai; Wang, Ying; Wang, Yong
2016-02-01
In this study, the authors studied the protein structure prediction problem by the two-dimensional hydrophobic-polar model on triangular lattice. Particularly the non-compact conformation was modelled to fold the amino acid sequence into a relatively larger triangular lattice, which is more biologically realistic and significant than the compact conformation. Then protein structure prediction problem was abstracted to match amino acids to lattice points. Mathematically, the problem was formulated as an integer programming and they transformed the biological problem into an optimisation problem. To solve this problem, classical particle swarm optimisation algorithm was extended by the single point adjustment strategy. Compared with square lattice, conformations on triangular lattice are more flexible in several benchmark examples. They further compared the authors' algorithm with hybrid of hill climbing and genetic algorithm. The results showed that their method was more effective in finding solution with lower energy and less running time.
Extended particle swarm optimisation method for folding protein on triangular lattice.
Guo, Yuzhen; Wu, Zikai; Wang, Ying; Wang, Yong
2016-02-01
In this study, the authors studied the protein structure prediction problem by the two-dimensional hydrophobic-polar model on triangular lattice. Particularly the non-compact conformation was modelled to fold the amino acid sequence into a relatively larger triangular lattice, which is more biologically realistic and significant than the compact conformation. Then protein structure prediction problem was abstracted to match amino acids to lattice points. Mathematically, the problem was formulated as an integer programming and they transformed the biological problem into an optimisation problem. To solve this problem, classical particle swarm optimisation algorithm was extended by the single point adjustment strategy. Compared with square lattice, conformations on triangular lattice are more flexible in several benchmark examples. They further compared the authors' algorithm with hybrid of hill climbing and genetic algorithm. The results showed that their method was more effective in finding solution with lower energy and less running time. PMID:26816397
Temperley's triangular lattice compact cluster model: exact solution in terms of the q series
NASA Astrophysics Data System (ADS)
Glasser, M. L.; Privman, V.; Svrakic, N. M.
1987-12-01
Temperley's model (1952) of self-supporting stackings of circles in a triangular lattice array against a line wall is solved exactly in terms of q hypergeometric functions. For N circles, the number of different configurations is described by the large-N asymptotic law A lambda N, with A=0.312 36. . . and lambda =1.735 66. . . .
NASA Astrophysics Data System (ADS)
Ducatman, Samuel; Perkins, Natalia
2013-03-01
While it is well known that the ground state of the isotropic Heisenberg model on a triangular lattice is the so called 120° structure, its appearance on the distorted triangular lattice is rather unusual. This case has been recently observed in the distorted triangular lattice antiferromagnet α-CaCr2O4 [S. Toth et al, PRB 84, 054452 (2011)] which shows the onset of the 120° long-range magnetic order below TN = 42 . 6 K . Recent neutron scattering experiments also revealed that this compound has unusual magnetic excitations with a dispersion with roton-like minima at momenta different from those corresponding to its 120°-magnetic order [S. Toth et al, PRL 109, 127203 (2012)]. Motivated by these experimental findings, we calculate a magnetic phase diagram and excitation spectrum of anisotropic Heisenberg Hamiltonian on triangular lattice. We showed that at the parameters characterizing α-CaCr2O4 compound, the ground state is indeed the 120°-structure, however, other possible magnetic orderings are very close in energy. We compute the dispersion of magnetic excitations to order 1/S and compare it with the neutron scattering data. supported by the grant NSF-DMR-0844115
Agarwala, R.; Batzoglou, S.; Dancik, V.
1997-06-01
We consider the problem of determining the three-dimensional folding of a protein given its one-dimensional amino acid sequence. We use the HP model for protein folding proposed by Dill, which models protein as a chain of amino acid residues that are either hydrophobic or polar, and hydrophobic interactions are the dominant initial driving force for the protein folding. Hart and Istrail gave approximation algorithms for folding proteins on the cubic lattice under HP model. In this paper, we examine the choice of a lattice by considering its algorithmic and geometric implications and argue that triangular lattice is a more reasonable choice. We present a set of folding rules for a triangular lattice and analyze the approximation ratio which they achieve. In addition, we introduce a generalization of the HP model to account for residues having different levels of hydrophobicity. After describing the biological foundation for this generalization, we show that in the new model we are able to achieve similar constant factor approximation guarantees on the triangular lattice as were achieved in the standard HP model. While the structures derived from our folding rules are probably still far from biological reality, we hope that having a set of folding rules with different properties will yield more interesting folds when combined.
Spin-Chirality-Driven Ferroelectricity on a Perfect Triangular Lattice Antiferromagnet
Mitamura, H.; Watanuki, R.; Kaneko, Koji; Onozaki, N.; Amou, Y.; Kittaka, S.; Kobayashi, Riki; Shimura, Y.; Yamamoto, I.; Suzuki, K.; et al
2014-10-01
Magnetic field (B) variation of the electrical polarization Pc ( ∥c) of the perfect triangular lattice antiferromagnet RbFe(MoO4)2 is examined up to the saturation point of the magnetization for B⊥c. Pc is observed only in phases for which chirality is predicted in the in-plane magnetic structures. No strong anomaly is observed in Pc 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 of which would require a newmore » 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
Mitamura, H.; Watanuki, R.; Kaneko, Koji; Onozaki, N.; Amou, Y.; Kittaka, S.; Kobayashi, Riki; Shimura, Y.; Yamamoto, I.; Suzuki, K.; Chi, Songxue; Sakakibara, T.
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 of 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.
Lattice Boltzmann Equation On a 2D Rectangular Grid
NASA Technical Reports Server (NTRS)
Bouzidi, MHamed; DHumieres, Dominique; Lallemand, Pierre; Luo, Li-Shi; Bushnell, Dennis M. (Technical Monitor)
2002-01-01
We construct a multi-relaxation lattice Boltzmann model on a two-dimensional rectangular grid. The model is partly inspired by a previous work of Koelman to construct a lattice BGK model on a two-dimensional rectangular grid. The linearized dispersion equation is analyzed to obtain the constraints on the isotropy of the transport coefficients and Galilean invariance for various wave propagations in the model. The linear stability of the model is also studied. The model is numerically tested for three cases: (a) a vortex moving with a constant velocity on a mesh periodic boundary conditions; (b) Poiseuille flow with an arbitrasy inclined angle with respect to the lattice orientation: and (c) a cylinder &symmetrically placed in a channel. The numerical results of these tests are compared with either analytic solutions or the results obtained by other methods. Satisfactory results are obtained for the numerical simulations.
Tunable multi-wavelength polymer laser based on a triangular-lattice photonic crystal structure
NASA Astrophysics Data System (ADS)
Huang, Wenbin; Pu, Donglin; Qiao, Wen; Wan, Wenqiang; Liu, Yanhua; Ye, Yan; Wu, Shaolong; Chen, Linsen
2016-08-01
A continuously tunable multi-wavelength polymer laser based on a triangular-lattice photonic crystal cavity is demonstrated. The triangular-lattice resonator was initially fabricated through multiple interference exposure and was then replicated into a low refractive index polymer via UV-nanoimprinting. The blend of a blue-emitting conjugated polymer and a red-emitting one was used as the gain medium. Three periods in the scalene triangular-lattice structure yield stable tri-wavelength laser emission (625.5 nm, 617.4 nm and 614.3 nm) in six different directions. A uniformly aligned liquid crystal (LC) layer was incorporated into the cavity as the top cladding layer. Upon heating, the orientation of LC molecules and thus the effective refractive index of the lasing mode changes which continuously shifts the lasing wavelength. A maximum tuning range of 12.2 nm was observed for the lasing mode at 625.5 nm. This tunable tri-wavelength polymer laser is simple constructed and cost-effective. It may find application in the fields of biosensors and photonic integrated circuits.
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.
Destruction of spin-nematic order on randomly depleted triangular lattices
NASA Astrophysics Data System (ADS)
Lovell, Simon; Demidio, Jonathan; Kaul, Ribhu
2015-03-01
We consider the spin-1 Heisenberg model with biquadratic interactions on a 2-dimensional triangular lattice with random site dilution. It has been shown for this model that the ground state on a clean lattice exhibits spin nematic order. Using the stochastic series expansion (SSE) quantum Monte Carlo (QMC) algorithm, we study the nature of the order-disorder transition in the thermodynamic limit by extrapolating the ground state nematic order averaged over disorder realizations. This research was partially financially supported by NSF DMR-1056536.
Magnetic correlations in the Hubbard model on triangular and Kagomé lattices.
Bulut, N; Koshibae, W; Maekawa, S
2005-07-15
In order to study the magnetic properties of frustrated metallic systems, we present, for the first time, quantum Monte Carlo data on the magnetic susceptibility of the Hubbard model on triangular and kagomé lattices. We show that the underlying lattice structure determines the nature and the doping dependence of the magnetic fluctuations. In particular, in the doped kagomé case we find strong short-range magnetic correlations, which makes the metallic kagomé systems a promising field for studies of superconductivity.
Spontaneous formation of kagome network and Dirac half-semimetal on a triangular lattice
NASA Astrophysics Data System (ADS)
Akagi, Yutaka; Motome, Yukitoshi
2015-04-01
In spin-charge coupled systems, geometrical frustration of underlying lattice structures can give rise to nontrivial magnetic orders and electronic states. Here we explore such a possibility in the Kondo lattice model with classical localized spins on a triangular lattice by using a variational calculation and simulated annealing. We find that the system exhibits a four-sublattice collinear ferrimagnetic phase at 5/8 filling for a large Hund's-rule coupling. In this state, the system spontaneously differentiates into the up-spin kagome network and the isolated down-spin sites, which we call the kagome network formation. In the kagome network state, the system becomes Dirac half-semimetallic: The electronic structure shows a massless Dirac node at the Fermi level, and the Dirac electrons are almost fully spin polarized due to the large Hund's-rule coupling. We also study the effect of off-site Coulomb repulsion in the kagome network phase where the system is effectively regarded as a 1/3-filling spinless fermion system on the kagome lattice. We find that, at the level of the mean-field approximation, a √{3 }×√{3 } -type charge order occurs in the kagome network state, implying the possibility of fractional charge excitations in this triangular lattice system. Moreover, we demonstrate that the kagome network formation with fully polarized Dirac electrons are controllable by an external magnetic field.
Lattice Formulation of 2D SQCD with exact supersymmetry
Sugino, Fumihiko
2008-11-23
We construct a lattice model for two-dimensional N = (2,2) supersymmetric QCD (SQCD), with the matter multiplets belonging to the fundamental or anti-fundamental representation of the gauge group U(N) or SU(N). The construction is based on the topological field theory (twisted supercharge) formulation and exactly preserves one supercharge. In order to avoid the species doublers of the matter multiplets, we introduce the Wilson terms and the model is defined for the case of the number of the fundamental matters (n{sub +}) equal to that of the anti-fundamental matters (n{sub -}). If some of the matter multiplets decouple from the theory by sending the corresponding anti-holomorphic twisted masses to the infinity, we can analyze the general n{sub +}{ne}n{sub -} case, although the lattice model is defined for n{sub +} = n{sub -}. By computing the anomaly of the U(1){sub A} R-symmetry in the lattice perturbation, we see that the decoupling is achieved and the anomaly for n{sub +}{ne}n{sub -} is correctly obtained.
Quantum spin Hall phase in 2D trigonal lattice.
Wang, Z F; Jin, Kyung-Hwan; Liu, Feng
2016-01-01
The quantum spin Hall (QSH) phase is an exotic phenomena in condensed-matter physics. Here we show that a minimal basis of three orbitals (s, px, py) is required to produce a QSH phase via nearest-neighbour hopping in a two-dimensional trigonal lattice. Tight-binding model analyses and calculations show that the QSH phase arises from a spin-orbit coupling (SOC)-induced s-p band inversion or p-p bandgap opening at Brillouin zone centre (Γ point), whose topological phase diagram is mapped out in the parameter space of orbital energy and SOC. Remarkably, based on first-principles calculations, this exact model of QSH phase is shown to be realizable in an experimental system of Au/GaAs(111) surface with an SOC gap of ∼73 meV, facilitating the possible room-temperature measurement. Our results will extend the search for substrate supported QSH materials to new lattice and orbital types. PMID:27599580
Quantum spin Hall phase in 2D trigonal lattice
NASA Astrophysics Data System (ADS)
Wang, Z. F.; Jin, Kyung-Hwan; Liu, Feng
2016-09-01
The quantum spin Hall (QSH) phase is an exotic phenomena in condensed-matter physics. Here we show that a minimal basis of three orbitals (s, px, py) is required to produce a QSH phase via nearest-neighbour hopping in a two-dimensional trigonal lattice. Tight-binding model analyses and calculations show that the QSH phase arises from a spin-orbit coupling (SOC)-induced s-p band inversion or p-p bandgap opening at Brillouin zone centre (Γ point), whose topological phase diagram is mapped out in the parameter space of orbital energy and SOC. Remarkably, based on first-principles calculations, this exact model of QSH phase is shown to be realizable in an experimental system of Au/GaAs(111) surface with an SOC gap of ~73 meV, facilitating the possible room-temperature measurement. Our results will extend the search for substrate supported QSH materials to new lattice and orbital types.
Quantum spin Hall phase in 2D trigonal lattice
Wang, Z. F.; Jin, Kyung-Hwan; Liu, Feng
2016-01-01
The quantum spin Hall (QSH) phase is an exotic phenomena in condensed-matter physics. Here we show that a minimal basis of three orbitals (s, px, py) is required to produce a QSH phase via nearest-neighbour hopping in a two-dimensional trigonal lattice. Tight-binding model analyses and calculations show that the QSH phase arises from a spin–orbit coupling (SOC)-induced s–p band inversion or p–p bandgap opening at Brillouin zone centre (Γ point), whose topological phase diagram is mapped out in the parameter space of orbital energy and SOC. Remarkably, based on first-principles calculations, this exact model of QSH phase is shown to be realizable in an experimental system of Au/GaAs(111) surface with an SOC gap of ∼73 meV, facilitating the possible room-temperature measurement. Our results will extend the search for substrate supported QSH materials to new lattice and orbital types. PMID:27599580
Percolation in random sequential adsorption of extended objects on a triangular lattice
NASA Astrophysics Data System (ADS)
Budinski-Petković, Lj.; Lončarević, I.; Petković, M.; Jakšić, Z. M.; Vrhovac, S. B.
2012-06-01
The percolation aspect of random sequential adsorption of extended objects on a triangular lattice is studied by means of Monte Carlo simulations. The depositing objects are formed by self-avoiding lattice steps on the lattice. Jamming coverage θjam, percolation threshold θp*, and their ratio θp*/θjam are determined for objects of various shapes and sizes. We find that the percolation threshold θp* may decrease or increase with the object size, depending on the local geometry of the objects. We demonstrate that for various objects of the same length, the threshold θp* of more compact shapes exceeds the θp* of elongated ones. In addition, we study polydisperse mixtures in which the size of line segments making up the mixture gradually increases with the number of components. It is found that the percolation threshold decreases, while the jamming coverage increases, with the number of components in the mixture.
Modeling of 2D photonic bandgap structures using a triangular mesh finite difference method
NASA Astrophysics Data System (ADS)
Hadley, G. Ronald
2001-10-01
A numerical model is presented for computing the out-of- plane losses of a general class of row-defect waveguides formed by the superposition of a 2D photonic crystal onto a slab confinement structure. The usefulness of this model is demonstrated here by calculating the propagation loss of a single-row-defect waveguide composed of hexagonal air holes etched into two different slab structures. The results are interpreted in terms of a simple coupled-mode-theory picture in which loss is due to coupling by the waveguide corrugation between the fundamental and certain radiative slab modes. These calculations show that low-loss photonic crystal waveguides should be possible by carefully engineering the radiation modes of the slab waveguide.
Relaxation properties in a diffusive model of extended objects on a triangular lattice
NASA Astrophysics Data System (ADS)
Šćepanović, J. R.; Budinski-Petković, Lj.; Lončarević, I.; Petković, M.; Jakšić, Z. M.; Vrhovac, S. B.
2013-03-01
In a preceding paper, Šćepanović et al. [J.R. Šćepanović, I. Lončarević, Lj. Budinski-Petković, Z.M. Jakšić, S.B. Vrhovac, Phys. Rev. E 84 (2011) 031109. http://dx.doi.org/10.1103/PhysRevE.84.031109] studied the diffusive motion of k-mers on the planar triangular lattice. Among other features of this system, we observed that the suppression of rotational motion results in a subdiffusive dynamics on intermediate length and time scales. We also confirmed that systems of this kind generally exhibit heterogeneous dynamics. Here we extend this analysis to objects of various shapes that can be made by self-avoiding random walks on a triangular lattice. We start by studying the percolation properties of random sequential adsorption of extended objects on a triangular lattice. We find that for various objects of the same length, the threshold ρp∗ of more compact shapes exceeds the ρp∗ of elongated ones. At the lower densities of ρp∗, the long-time decay of the self-intermediate scattering function (SISF) is characterized by the Kohlrausch-Williams-Watts law. It is found that near the percolation threshold ρp∗, the decay of SISF to zero occurs via the power-law for sufficiently low wave-vectors. Our results establish that power-law divergence of the relaxation time τ as a function of density ρ occurs at a shape-dependent critical density ρc above the percolation threshold ρp∗. In the case of k-mers, the critical density ρc cannot be distinguished from the closest packing limit ρ⪅1. For other objects, the critical density ρc is usually below the jamming limit ρ.
NASA Astrophysics Data System (ADS)
Anastasiou, K.; Chan, C. T.
1997-06-01
A 2D, depth-integrated, free surface flow solver for the shallow water equations is developed and tested. The solver is implemented on unstructured triangular meshes and the solution methodology is based upon a Godunov-type second-order upwind finite volume formulation, whereby the inviscid fluxes of the system of equations are obtained using Roes flux function. The eigensystem of the 2D shallow water equations is derived and is used for the construction of Roes matrix on an unstructured mesh. The viscous terms of the shallow water equations are computed using a finite volume formulation which is second-order-accurate. Verification of the solution technique for the inviscid form of the governing equations as well as for the full system of equations is carried out by comparing the model output with documented published results and very good agreement is obtained. A numerical experiment is also conducted in order to evaluate the performance of the solution technique as applied to linear convection problems. The presented results show that the solution technique is robust.
Phase Diagram of the Antiferromagnetic Blume-Capel Model on Triangular Lattice
NASA Astrophysics Data System (ADS)
Park, Sojeong; Kwak, Wooseop
2016-08-01
We perform Monte-Carlo simulations of the anti-ferromagnetic (AF) spin-1 Blume- Capel (BC) model and the AF Ising model on triangular lattice. We estimate the exact critical magnetic fields for both models at zero temperature using the Wang-Landau sampling method. We also show the phase diagrams and the critical lines for the models using the joint density functions. We find that the shapes of critical lines for the models are identical, but the phase transitions across the critical lines are different.
NASA Astrophysics Data System (ADS)
Hu, Wenjun; Gong, Shoushu; Sheng, Donna; Donna Sheng Team
We investigate the Heisenberg model with chiral coupling on the triangular lattice by using Gutzwiller projected fermionic states and the variational Monte Carlo technique. As the chiral coupling grows, a gapped spin liquid with non-trivial magnetic fluxes and nonzero chiral order is stabilized. Furthermore, we calculate the topological Chern number and the degeneracy of the ground state, both of which lead us to identify this flux state as the chiral spin liquid with C = 1 / 2 fractionalized Chern number. Finally, we add spatial anisotropy in the model to study the effects for the chiral order.
Quantum phases of Bose-Bose mixtures on a triangular lattice
NASA Astrophysics Data System (ADS)
He, Liang; Li, Yongqiang; Altman, Ehud; Hofstetter, Walter
2012-10-01
We investigate the zero-temperature quantum phases of a Bose-Bose mixture on a triangular lattice using the bosonic dynamical mean-field theory (BDMFT). We consider the case of total filling where geometric frustration arises for asymmetric hopping. We map out a rich ground-state phase diagram including xy-ferromagnetic, spin-density wave, superfluid, and supersolid phases. In particular, we identify a stripe spin-density wave phase for highly asymmetric hopping. On top of the spin-density wave, we find that the system generically shows weak charge (particle) density wave order.
Ffrench, P A; Zeidler, J H; Ku, W H
1997-01-01
Two-dimensional (2-D) adaptive filtering is a technique that can be applied to many image processing applications. This paper will focus on the development of an improved 2-D adaptive lattice algorithm (2-D AL) and its application to the removal of correlated clutter to enhance the detectability of small objects in images. The two improvements proposed here are increased flexibility in the calculation of the reflection coefficients and a 2-D method to update the correlations used in the 2-D AL algorithm. The 2-D AL algorithm is shown to predict correlated clutter in image data and the resulting filter is compared with an ideal Wiener-Hopf filter. The results of the clutter removal will be compared to previously published ones for a 2-D least mean square (LMS) algorithm. 2-D AL is better able to predict spatially varying clutter than the 2-D LMS algorithm, since it converges faster to new image properties. Examples of these improvements are shown for a spatially varying 2-D sinusoid in white noise and simulated clouds. The 2-D LMS and 2-D AL algorithms are also shown to enhance a mammogram image for the detection of small microcalcifications and stellate lesions.
NASA Astrophysics Data System (ADS)
Pasrija, Kanika; Kumar, Sanjeev
2016-05-01
Motivated by the importance of noncollinear and noncoplanar magnetic phases in determining various electrical properties in magnets, we investigate the magnetic phase diagram of the extended Hubbard model on an anisotropic triangular lattice. We map out the ground-state phase diagram within a mean-field scheme that treats collinear, noncollinear, and noncoplanar phases on equal footing. In addition to the standard ferromagnet and 120∘ antiferromagnet states, we find the four-sublattice flux, the 3Q noncoplanar, and the noncollinear charge-ordered states to be stable at specific values of filling fraction n . Inclusion of a nearest-neighbor Coulomb repulsion leads to intriguing spin-charge-ordered phases. The most notable of these are the collinear and noncollinear magnetic states at n =2 /3 , which occur together with a pinball-liquid-like charge order. Our results demonstrate that the elementary single-orbital extended Hubbard model on a triangular lattice hosts unconventional spin-charge ordered phases, which are similar to those reported in more complex and material-specific electronic Hamiltonians.
Bound states and Cooper pairs of molecules in 2D optical lattices bilayer
NASA Astrophysics Data System (ADS)
Camacho-Guardian, A.; Domínguez-Castro, G. A.; Paredes, R.
2016-08-01
We investigate the formation of Cooper pairs, bound dimers and the dimer-dimer elastic scattering of ultra- cold dipolar Fermi molecules confined in a 2D optical lattice bilayer configuration. While the energy and their associated bound states are determined in a variational way, the correlated two-molecule pair is addressed as in the original Cooper formulation. We demonstrate that the 2D lattice confinement favors the formation of zero center mass momentum bound states. Regarding the Cooper pairs binding energy, this depends on the molecule populations in each layer. Maximum binding energies occur for non-zero (zero) pair momentum when the Fermi system is polarized (unpolarized). We find an analytic expression for the dimer-dimer effective interaction in the deep BEC regime. The present analysis represents a route for addressing the BCS-BEC crossover superfluidity in dipolar Fermi gases confined in 2D optical lattices within the current experimental panorama.
NASA Astrophysics Data System (ADS)
Thesberg, Mischa; Sørensen, Erik S.
2014-10-01
Ground- and excited-state quantum fidelities in combination with generalized quantum fidelity susceptibilites, obtained from exact diagonalizations, are used to explore the phase diagram of the anisotropic next-nearest-neighbour triangular Heisenberg model. Specifically, the J‧ - J2 plane of this model, which connects the J1 - J2 chain and the anisotropic triangular lattice Heisenberg model, is explored using these quantities. Through the use of a quantum fidelity associated with the first excited-state, in addition to the conventional ground-state fidelity, the BKT-type transition and Majumdar-Ghosh point of the J1 - J2 chain (J‧ = 0) are found to extend into the J‧ - J2 plane and connect with points on the J2 = 0 axis thereby forming bounded regions in the phase diagram. These bounded regions are then explored through the generalized quantum fidelity susceptibilities χρ, χ120\\circ , χD and χCAF which are associated with the spin stiffness, 120° spiral order parameter, dimer order parameter and collinear antiferromagnetic order parameter respectively. These quantities are believed to be extremely sensitive to the underlying phase and are thus well suited for finite-size studies. Analysis of the fidelity susceptibilities suggests that the J‧, J2 ≪ J phase of the anisotropic triangular model is either a collinear antiferromagnet or possibly a gapless disordered phase that is directly connected to the Luttinger phase of the J1 - J2 chain. Furthermore, the outer region is dominated by incommensurate spiral physics as well as dimer order.
NASA Astrophysics Data System (ADS)
Hu, Wen-Jun; Gong, Shou-Shu; Sheng, D. N.
2016-08-01
By using Gutzwiller projected fermionic wave functions and variational Monte Carlo technique, we study the spin-1 /2 Heisenberg model with the first-neighbor (J1), second-neighbor (J2), and additional scalar chiral interaction JχSi.(Sj×Sk) on the triangular lattice. In the nonmagnetic phase of the J1-J2 triangular model with 0.08 ≲J2/J1≲0.16 , recent density-matrix renormalization group (DMRG) studies [Zhu and White, Phys. Rev. B 92, 041105(R) (2015), 10.1103/PhysRevB.92.041105 and Hu, Gong, Zhu, and Sheng, Phys. Rev. B 92, 140403(R) (2015), 10.1103/PhysRevB.92.140403] find a possible gapped spin liquid with the signal of a competition between a chiral and a Z2 spin liquid. Motivated by the DMRG results, we consider the chiral interaction JχSi.(Sj×Sk) as a perturbation for this nonmagnetic phase. We find that with growing Jχ, the gapless U(1) Dirac spin liquid, which has the best variational energy for Jχ=0 , exhibits the energy instability towards a gapped spin liquid with nontrivial magnetic fluxes and nonzero chiral order. We calculate topological Chern number and ground-state degeneracy, both of which identify this flux state as the chiral spin liquid with fractionalized Chern number C =1 /2 and twofold topological degeneracy. Our results indicate a positive direction to stabilize a chiral spin liquid near the nonmagnetic phase of the J1-J2 triangular model.
NASA Astrophysics Data System (ADS)
Budinski-Petković, Lj.; Lončarević, I.; Jakšić, Z. M.; Vrhovac, S. B.; Švrakić, N. M.
2011-11-01
The properties of the anisotropic random sequential adsorption (RSA) of objects of various shapes on a two-dimensional triangular lattice are studied numerically by means of Monte Carlo simulations. The depositing objects are formed by self-avoiding lattice steps, whereby the first step determines the orientation of the object. Anisotropy is introduced by positing unequal probabilities for orientation of depositing objects along different directions of the lattice. This probability is equal p or (1-p)/2, depending on whether the randomly chosen orientation is horizontal or not, respectively. Approach of the coverage θ(t) to the jamming limit θjam is found to be exponential θjam-θ(t)∝exp(-t/σ), for all probabilities p. It was shown that the relaxation time σ increases with the degree of anisotropy in the case of elongated and asymmetrical shapes. However, for rounded and symmetrical shapes, values of σ and θjam are not affected by the presence of anisotropy. We finally analyze the properties of the anisotropic RSA of polydisperse mixtures of k-mers. Strong dependencies of the parameter σ and the jamming coverage θjam on the degree of anisotropy are obtained. It is found that anisotropic constraints lead to the increased contribution of the longer k-mers in the total coverage fraction of the mixture.
Theory of a competitive spin liquid state for weak Mott insulators on the triangular lattice.
Mishmash, Ryan V; Garrison, James R; Bieri, Samuel; Xu, Cenke
2013-10-11
We propose a novel quantum spin liquid state that can explain many of the intriguing experimental properties of the low-temperature phase of the organic spin liquid candidate materials κ-(BEDT-TTF)2Cu2(CN)3 and EtMe3Sb[Pd(dmit)2]2. This state of paired fermionic spinons preserves all symmetries of the system, and it has a gapless excitation spectrum with quadratic bands that touch at momentum k[over →]=0. This quadratic band touching is protected by symmetries. Using variational Monte Carlo techniques, we show that this state has highly competitive energy in the triangular lattice Heisenberg model supplemented with a realistically large ring-exchange term.
Ground state pairing correlation competes in the doped triangular lattice Hubbard model
NASA Astrophysics Data System (ADS)
Cheng, Shuai; Wang, Xin; Liu, Suhang; Ma, Tianxing
2014-11-01
By using the constrained path quantum Monte carlo method, we study the ground state paring correlations in the t - U - V Hubbard model on the triangular lattice. It is shown that pairings with various symmetries dominate in different electron filling regions. The pairing correlation with fn-wave symmetry dominates over other pairings around half fillings, and as the electron filling decreases away from the half filling, the d + id-wave pairing correlation tends to dominate. As the electron filling is bellow the Van Hove singularity, the f-wave pairing dominates. These crossovers are due to the interplay of electronic correlation and geometric frustration, associating with the competition between the antiferromagnetic correlations and ferromagnetic fluctuations. Our findings reveal the possible magnetic origin of superconductivity, and also provide useful information for the understanding of superconductivity in NaxCoO2·H2O and the organic compounds.
Order by disorder in the antiferromagnetic Ising model on an elastic triangular lattice
Shokef, Yair; Souslov, Anton; Lubensky, T. C.
2011-01-01
Geometrically frustrated materials have a ground-state degeneracy that may be lifted by subtle effects, such as higher-order interactions causing small energetic preferences for ordered structures. Alternatively, ordering may result from entropic differences between configurations in an effect termed order by disorder. Motivated by recent experiments in a frustrated colloidal system in which ordering is suspected to result from entropy, we consider in this paper the antiferromagnetic Ising model on a deformable triangular lattice. We calculate the displacements exactly at the microscopic level and, contrary to previous studies, find a partially disordered ground state of randomly zigzagging stripes. Each such configuration is deformed differently and thus has a unique phonon spectrum with distinct entropy, lifting the degeneracy at finite temperature. Nonetheless, due to the free-energy barriers between the ground-state configurations, the system falls into a disordered glassy state. PMID:21730164
Frustrated Ising chains on the triangular lattice in Sr3NiIrO6
NASA Astrophysics Data System (ADS)
Toth, S.; Wu, W.; Adroja, D. T.; Rayaprol, S.; Sampathkumaran, E. V.
2016-05-01
Inelastic neutron scattering study on the spin-chain compound Sr3NiIrO6 reveals gapped quasi-1D magnetic excitations. The observed one-magnon band between 29.5 and 39 meV consists of magnon modes of the Ni2 + ions. The fitting of the spin wave spectrum reveals strongly coupled Ising-like chains along the c axis that are weakly coupled into a frustrated triangular lattice in the a b plane. The magnetic excitations survive up to 200 K well above the magnetic ordering temperature of TN˜75 K, also indicating a quasi-1D nature of the magnetic interactions in Sr3NiIrO6 . Our microscopic model is in agreement with ab initio electronic structure calculations and explains the giant spin-flip field observed in bulk magnetization measurements.
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.
XY ring exchange model with frustrated Ising coupling on the triangular lattice
NASA Astrophysics Data System (ADS)
Owerre, S. A.
2016-07-01
We investigate the nature of a Z2-invariant XY ring-exchange interaction with a frustrated Ising coupling on the triangular lattice. Within the limits of pure XY ring-exchange interaction, we show that the classical ground state is degenerate resulting from the Z2-invariance of the Hamiltonian. Quantum fluctuations lift these classical degenerate ground states and produce an unusual state whose excitation spectrum exhibits a gapped maximum quadratic dispersion near k = 0 and vanishes at the midpoints of each side of the Brillouin zone. This result is in contrast to a gapless quadratic dispersion near k = 0 in the U(1)-invariant counterpart. We also study the effects of frustration when competing with a classically frustrated Ising interaction. We provide a glimpse into the possible quantum phases that could emerge. A comprehensive understanding of this Hamiltonian, however, cannot be elucidated analytically and requires an explicit numerical simulation.
Spin superfluidity in the anisotropic XY model in the triangular lattice
NASA Astrophysics Data System (ADS)
Lima, L. S.
2016-07-01
We use the SU(3) Schwinger's boson theory to study the spin transport properties in the two-dimensional anisotropic frustrated Heisenberg model in the triangular lattice at T=0. We have investigated the behavior of the spin conductivity for this model which presents an single-ion anisotropy. We study the spin transport in the Bose-Einstein condensation regime where we have that the tz bosons are condensed and the following condition is valid:
Magnetic Interaction in the Geometrically Frustrated Triangular LatticeAntiferromagnet CuFeO2
Ye, Feng; Fernandez-Baca, Jaime A; Fishman, Randy Scott; Ren, Y.; Kang, H. J.; Qiu, Y.; Kimura, T.
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.
Hydration-induced spin-glass state in a frustrated Na-Mn-O triangular lattice
NASA Astrophysics Data System (ADS)
Bakaimi, Ioanna; Brescia, Rosaria; Brown, Craig M.; Tsirlin, Alexander A.; Green, Mark A.; Lappas, Alexandros
2016-05-01
Birnessite compounds are stable across a wide range of compositions that produces a remarkable diversity in their physical, electrochemical, and functional properties. These are hydrated analogs of the magnetically frustrated, mixed-valent manganese oxide structures, with general formula, N axMn O2 . Here we demonstrate that the direct hydration of layered rock-salt type α-NaMn O2 , with the geometrically frustrated triangular lattice topology, yields the birnessite type oxide, N a0.36Mn O2.0.2 H2O , transforming its magnetic properties. This compound has a much-expanded interlayer spacing compared to its parent α-NaMn O2 compound. We show that while the parent α-NaMn O2 possesses a Néel temperature of 45 K as a result of broken symmetry in the M n3 + sublattice, the hydrated derivative undergoes collective spin freezing at 29 K within the M n3 +/M n4 + sublattice. Scaling-law analysis of the frequency dispersion of the ac susceptibility, as well as the temperature-dependent, low-field dc magnetization confirm a cooperative spin-glass state of strongly interacting spins. This is supported by complementary spectroscopic analysis [high-angle annular dark-field scanning transmission electron miscroscopy (TEM), energy-dispersive x-ray spectroscopy, and electron energy-loss spectroscopy] as well as by a structural investigation (high-resolution TEM, x-ray, and neutron powder diffraction) that yield insights into the chemical and atomic structure modifications. We conclude that the spin-glass state in birnessite is driven by the spin frustration imposed by the underlying triangular lattice topology that is further enhanced by the in-plane bond-disorder generated by the mixed-valent character of manganese in the layers.
Shuaibu, A.; Rahman, M. M.
2014-03-05
We study the low temperature behavior of a triangular lattice quantum spin-1 Heisenberg antiferromagnet with single-site anisotropy by using coordinate Bethe ansatz method. We compute the standard two-particle Hermitian Hamiltonian, and obtain the eigenfunctions and eigenvalue of the system. The obtained results show a number of advantages in comparison with many results.
Koshibae, W; Maekawa, S
2003-12-19
The electronic state in layered cobalt oxides with a hexagonal structure is examined. We find that the electronic structure reflects the nature of the Kagomé lattice hidden in the CoO2 layer which consists of stacked triangular lattices of oxygen ions and of cobalt ions. A fundamental model for the electron system is proposed, and the mechanism of the unique transport and magnetic properties of the cobalt oxides are discussed in light of the model.
Frustrated mixed spin-1/2 and spin-1 Ising ferrimagnets on a triangular lattice
NASA Astrophysics Data System (ADS)
Žukovič, M.; Bobák, A.
2015-05-01
Mixed spin-1/2 and spin-1 Ising ferrimagnets on a triangular lattice with sublattices A, B, and C are studied for two spin-value distributions (SA,SB,SC) =(1 /2 ,1 /2 ,1 ) and (1 /2 ,1 ,1 ) by Monte Carlo simulations. The nonbipartite character of the lattice induces geometrical frustration in both systems, which leads to the critical behavior rather different from their ferromagnetic counterparts. We confirm second-order phase transitions belonging to the standard Ising universality class occurring at higher temperatures, however, in both models these change at tricritical points (TCP) to first-order transitions at lower temperatures. In the model (1 /2 ,1 /2 ,1 ) , TCP occurs on the boundary between paramagnetic and ferrimagnetic (±1 /2 ,±1 /2 ,∓1 ) phases. The boundary between two ferrimagnetic phases (±1 /2 ,±1 /2 ,∓1 ) and (±1 /2 ,∓1 /2 ,0 ) at lower temperatures is always first order and it is joined by a line of second-order phase transitions between the paramagnetic and the ferrimagnetic (±1 /2 ,∓1 /2 ,0 ) phases at a critical endpoint. The tricritical behavior is also confirmed in the model (1 /2 ,1 ,1 ) on the boundary between the paramagnetic and ferrimagnetic (0 ,±1 ,∓1 ) phases.
Superglass Phase of Interaction-Blockaded Gases on a Triangular Lattice
NASA Astrophysics Data System (ADS)
Angelone, Adriano; Mezzacapo, Fabio; Pupillo, Guido
2016-04-01
We investigate the quantum phases of monodispersed bosonic gases confined to a triangular lattice and interacting via a class of soft-shoulder potentials. The latter correspond to soft-core potentials with an additional hard-core onsite interaction. Using exact quantum Monte Carlo simulations, we show that the low temperature phases for weak and strong interactions following a temperature quench are a homogeneous superfluid and a glass, respectively. The latter is an insulating phase characterized by inhomogeneity in the density distribution and structural disorder. Remarkably, we find that for intermediate interaction strengths a superglass occurs in an extended region of the phase diagram, where glassy behavior coexists with a sizable finite superfluid fraction. This glass phase is obtained in the absence of geometrical frustration or external disorder and is a result of the competition of quantum fluctuations and cluster formation in the corresponding classical ground state. For high enough temperature, the glass and superglass turn into a floating stripe solid and a supersolid, respectively. Given the simplicity and generality of the model, these phases should be directly relevant for state-of-the-art experiments with Rydberg-dressed atoms in optical lattices.
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.
Geometric frustration on a 1/9th site depleted triangular lattice
NASA Astrophysics Data System (ADS)
Hopkinson, John; Beck, Jarrett
2013-03-01
In the searches both for new spin liquid and spin ice (artificial and macroscopic) candidates, geometrically frustrated two-dimensional spin systems have played a prominent role. Here we present a study of the classical antiferromagnetic Ising (AFI) model on the sorrel net, a 1/9th site depleted and 1/7th bond depleted triangular lattice. The AFI model on this corner-shared triangle net is found to have a large residual entropy per spin S/N = 0 . 48185 +/- 0 . 00008 , indicating the sorrel net is highly geometrically frustrated. Anticipating that it may be difficult to achieve perfect bond depletion, we investigate the physics resulting from turning back on the depleted bonds (J2). We present the phase diagram, analytic expressions for the long range partially ordered ground state spin structure for antiferromagnetic J2 and the short range ordered ground state spin structure for ferromagnetic J2, the magnetic susceptibility and the static structure factor. We briefly comment on the possibility that artificial spin ice on the sorrel lattice could by made, and on a recent report [T. D. Keene et al., Dalton Trans. 40 2983 (2011)] of the creation of a 1/9th depleted cobalt hydroxide oxalate. This work was supported by NSERC (JMH) and NSERC USRA (JJB)
NASA Astrophysics Data System (ADS)
Celi, Alessio; Grass, Tobias; Ferris, Andrew J.; Padhi, Bikash; Raventós, David; Simonet, Juliette; Sengstock, Klaus; Lewenstein, Maciej
2016-08-01
Ultracold bosons in a triangular lattice are a promising candidate for observing quantum spin liquid behavior. Here we investigate, for such system, the role of a harmonic trap giving rise to an inhomogeneous density. We construct a modified spin-wave theory for arbitrary filling and predict the breakdown of order for certain values of the lattice anisotropy. These regimes, identified with the spin liquid phases, are found to be quite robust upon changes in the filling factor. This result is backed by an exact diagonalization study on a small lattice.
Spin liquid state in the disordered triangular lattice Sc2Ga2CuO7 revealed by NMR
NASA Astrophysics Data System (ADS)
Khuntia, P.; Kumar, R.; Mahajan, A. V.; Baenitz, M.; Furukawa, Y.
2016-04-01
We present microscopic magnetic properties of a two-dimensional triangular lattice Sc2Ga2CuO7 , consisting of single and double triangular Cu planes. An antiferromagnetic (AFM) exchange interaction J /kB≈35 K between Cu2 + (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 /T1 ) reveals a slowing down of Cu2 + spin fluctuations with decreasing T down to 100 mK. Magnetic specific heat (Cm) and 1 /T1 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 Cm and 1 /T1 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. This suggests that the low energy modes are dominated by spinon excitations in the QSL state due to randomness engendered by disorder and frustration.
Spin liquid state in the disordered triangular lattice Sc2Ga2CuO7 revealed by NMR
Khuntia, P.; Kumar, R.; Mahajan, A. V.; Baenitz, M.; Furukawa, Y.
2016-04-18
We present microscopic magnetic properties of a two-dimensional triangular lattice Sc2Ga2CuO7, consisting of single and double triangular Cu planes. An antiferromagnetic (AFM) exchange interaction J/kB ≈ 35 K between Cu2+ (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/T1) reveals a slowing down of Cu2+ spin fluctuations with decreasing T down to 100 mK.more » Magnetic specific heat (Cm) and 1/T1 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 Cm and 1/T1 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
Nonlinear propagating localized modes in a 2D hexagonal crystal lattice
NASA Astrophysics Data System (ADS)
Bajars, Janis; Eilbeck, J. Chris; Leimkuhler, Benedict
2015-05-01
In this paper we consider a 2D hexagonal crystal lattice model first proposed by Marín, Eilbeck and Russell in 1998. We perform a detailed numerical study of nonlinear propagating localized modes, that is, propagating discrete breathers and kinks. The original model is extended to allow for arbitrary atomic interactions, and to allow atoms to travel out of the unit cell. A new on-site potential is considered with a periodic smooth function with hexagonal symmetry. We are able to confirm the existence of long-lived propagating discrete breathers. Our simulations show that, as they evolve, breathers appear to localize in frequency space, i.e. the energy moves from sidebands to a main frequency band. Our numerical findings shed light on the open question of whether exact moving breather solutions exist in 2D hexagonal layers in physical crystal lattices.
A 2D DNA lattice as an ultrasensitive detector for beta radiations.
Dugasani, Sreekantha Reddy; Kim, Jang Ah; Kim, Byeonghoon; Joshirao, Pranav; Gnapareddy, Bramaramba; Vyas, Chirag; Kim, Taesung; Park, Sung Ha; Manchanda, Vijay
2014-02-26
There is growing demand for the development of efficient ultrasensitive radiation detectors to monitor the doses administered to individuals during therapeutic nuclear medicine which is often based on radiopharmaceuticals, especially those involving beta emitters. Recently biological materials are used in sensors in the nanobio disciplines due to their abilities to detect specific target materials or sites. Artificially designed two-dimensional (2D) DNA lattices grown on a substrate were analyzed after exposure to pure beta emitters, (90)Sr-(90)Y. We studied the Raman spectra and reflected intensities of DNA lattices at various distances from the source with different exposure times. Although beta particles have very low linear energy transfer values, the significant physical and chemical changes observed throughout the extremely thin, ∼0.6 nm, DNA lattices suggested the feasibility of using them to develop ultrasensitive detectors of beta radiations.
Influence of lattice defects on the ferromagnetic resonance behaviour of 2D magnonic crystals
Manzin, Alessandra; Barrera, Gabriele; Celegato, Federica; Coïsson, Marco; Tiberto, Paola
2016-01-01
This paper studies, from a modelling point of view, the influence of randomly distributed lattice defects (non-patterned areas and variable hole size) on the ferromagnetic resonance behaviour and spin wave mode profiles of 2D magnonic crystals based on Ni80Fe20 antidot arrays with hexagonal lattice. A reference sample is first defined via the comparison of experimental and simulated hysteresis loops and magnetoresistive curves of patterned films, prepared by self-assembly of polystyrene nanospheres. Second, a parametric analysis of the dynamic response is performed, investigating how edge, quasi-uniform and localized modes are affected by alterations of the lattice geometry and bias field amplitude. Finally, some results about the possible use of magnetic antidot arrays in frequency-based sensors for magnetic bead detection are presented, highlighting the need for an accurate control of microstructural features. PMID:26911336
Semiclassical theory of the magnetization process of the triangular lattice Heisenberg model
NASA Astrophysics Data System (ADS)
Coletta, Tommaso; Tóth, Tamás A.; Penc, Karlo; Mila, Frédéric
2016-08-01
Motivated by the numerous examples of 1/3 magnetization plateaux in the triangular-lattice Heisenberg antiferromagnet with spins ranging from 1/2 to 5/2, we revisit the semiclassical calculation of the magnetization curve of that model, with the aim of coming up with a simple method that allows one to calculate the full magnetization curve and not just the critical fields of the 1/3 plateau. We show that it is actually possible to calculate the magnetization curve including the first quantum corrections and the appearance of the 1/3 plateau entirely within linear spin-wave theory, with predictions for the critical fields that agree to order 1 /S with those derived a long time ago on the basis of arguments that required going beyond linear spin-wave theory. This calculation relies on the central observation that there is a kink in the semiclassical energy at the field where the classical ground state is the collinear up-up-down structure and that this kink gives rise to a locally linear behavior of the energy with the field when all semiclassical ground states are compared to each other for all fields. The magnetization curves calculated in this way for spin 1/2, 1, and 5/2 are shown to be in good agreement with available experimental data.
Yamamoto, Daisuke; Marmorini, Giacomo; Danshita, Ippei
2015-01-16
Magnetization processes of spin-1/2 layered triangular-lattice antiferromagnets (TLAFs) under a magnetic field H are studied by means of a numerical cluster mean-field method with a scaling scheme. We find that small antiferromagnetic couplings between the layers give rise to several types of extra quantum phase transitions among different high-field coplanar phases. Especially, a field-induced first-order transition is found to occur at H≈0.7H_{s}, where H_{s} is the saturation field, as another common quantum effect of ideal TLAFs in addition to the well-established one-third plateau. Our microscopic model calculation with appropriate parameters shows excellent agreement with experiments on Ba_{3}CoSb_{2}O_{9} [T. Susuki et al., Phys. Rev. Lett. 110, 267201 (2013)]. Given this fact, we suggest that the Co^{2+}-based compounds may allow for quantum simulations of intriguing properties of this simple frustrated model, such as quantum criticality and supersolid states. PMID:25635561
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.
NASA Astrophysics Data System (ADS)
Lee, Taejin
2016-09-01
We study the dissipative Hofstadter model on a triangular lattice, making use of the O(2, 2; R) T-dual transformation of string theory. The O(2, 2; R) dual transformation transcribes the model in a commutative basis into the model in a noncommutative basis. In the zero-temperature limit, the model exhibits an exact duality, which identifies equivalent points on the two-dimensional parameter space of the model. The exact duality also defines magic circles on the parameter space, where the model can be mapped onto the boundary sine-Gordon on a triangular lattice. The model describes the junction of three quantum wires in a uniform magnetic field background. An explicit expression of the equivalence relation, which identifies the points on the two-dimensional parameter space of the model by the exact duality, is obtained. It may help us to understand the structure of the phase diagram of the model.
Quantum Monte Carlo study of long-range transverse-field Ising models on the triangular lattice
NASA Astrophysics Data System (ADS)
Humeniuk, Stephan
2016-03-01
Motivated by recent experiments with a Penning ion trap quantum simulator, we perform numerically exact Stochastic Series Expansion quantum Monte Carlo simulations of long-range transverse-field Ising models on a triangular lattice for different decay powers α of the interactions. The phase boundary for the ferromagnet is obtained as a function of α . For antiferromagnetic interactions, there is strong indication that the transverse field stabilizes a clock ordered phase with sublattice magnetization (M ,-M/2 ,-M/2 ) with unsaturated M <1 in a process known as "order by disorder" similar to the nearest-neighbor antiferromagnet on the triangular lattice. Connecting the known limiting cases of nearest-neighbor and infinite-range interactions, a semiquantitative phase diagram is obtained. Magnetization curves for the ferromagnet for experimentally relevant system sizes and with open boundary conditions are presented.
Ma, J; Kamiya, Y; Hong, Tao; Cao, H B; Ehlers, G; Tian, W; Batista, C D; Dun, Z L; Zhou, H D; Matsuda, M
2016-02-26
We present single-crystal neutron scattering measurements of the spin-1/2 equilateral triangular-lattice antiferromagnet Ba_{3}CoSb_{2}O_{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. Thus, our results call for a new theoretical framework for describing excitation spectra in low-dimensional frustrated magnets under strong quantum effects. PMID:26967439
Ma, Jie; Kamiya, Yoshitomo; Hong, Tao; Cao, H. B.; Ehlers, Georg; Tian, Wei; Batista, C. D.; Dun, Z. L.; Zhou, H. D.; Matsuda, Masaaki
2016-02-24
We present single-crystal neutron scattering measurements of the spin-1/2 equilateral triangular-lattice antiferromagnet Ba3CoSb2O9. Besides confirming that the Co2+ 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 call for a new theoreticalmore » framework for describing excitation spectra in low-dimensional frustrated magnets under strong quantum effects.« less
NASA Technical Reports Server (NTRS)
Baskaran, G.
1989-01-01
Using a nonmean-field approach the triangular-lattice S = 1/2 Heisenberg antiferromagnet with nearest- and next-nearest-neighbor couplings is shown undergo an Ising-type phase transition into a chiral-symmetry-broken phase (Kalmeyer-Laughlin-like state) at small T. Removal of next-nearest-neighbor coupling introduces a local Z2 symmetry, thereby suppressing any finite-T chiral order.
A topological semimetal model with f-wave symmetry in a non-Abelian triangular optical lattice
NASA Astrophysics Data System (ADS)
Li, Ling; Bai, Zhiming; Hao, Ningning; Liu, Guocai
2016-08-01
We demonstrate that an chiral f-wave topological semimetal can be induced in a non-Abelian triangular optical lattice. We show that the f-wave symmetry topological semimetal is characterized by the topological invariant, i.e., the winding number W, with W=3 and is different from the semimetal with W=1 and 2 which have the p-wave and d-wave symmetry, respectively.
Zvereva, Elena A.; Nalbandyan, Vladimir B.; Evstigneeva, Maria A.; Koo, Hyun-Joo; Whangbo, Myung-Hwan; Ushakov, Arseni V.; Medvedev, Boris S.; Medvedeva, Larisa I.; Gridina, Nelly A.; Yalovega, Galina E.; Churikov, Alexei V.; Vasiliev, Alexander N.; Büchner, Bernd
2015-05-15
We examined the magnetic properties of layered oxide Li{sub 4}NiTeO{sub 6} by magnetic susceptibility, magnetization and ESR measurements and density functional calculations, and characterized phase relations, crystal structure and electrochemical properties of Li{sub 4}NiTeO{sub 6}. The magnetization and ESR data indicate the absence of a long-range magnetic order down to 1.8 K, and the magnetic susceptibility data the presence of dominant antiferromagnetic interactions. These observations are well accounted for by density functional calculations, which show that the spin exchanges of the LiNiTeO{sub 6} layers in Li{sub 4}NiTeO{sub 6} are strongly spin frustrated. The electrochemical charging of Li{sub 4}NiTeO{sub 6} takes place at constant potential of ca. 4.2 V vs. Li/Li{sup +} indicating two-phase process as confirmed by X-rays. The starting phase is only partially recovered on discharge due to side reactions. - Graphical abstract: No long-range magnetic order due to frustration in 2D triangular lattice antiferromagnet Li{sub 4}NiTeO{sub 6}. - Highlights: • Li{sub 4}NiTeO{sub 6} is 2D triangular lattice magnet with no long-range order down to 1.8 K. • Intralayer exchange interactions are antiferromagnetic and strongly spin frustrated. • The electrochemical Li extraction proceeds in a two-phase mode at 4.2 V vs. Li/Li{sup +}. • The electrochemical charge–discharge is only partially reversible. • Li{sub 2}O–NiO{sub y}–TeO{sub x} phase relations are reported; Li{sub 4}NiTeO{sub 6} is essentially stoichiometric.
Magnetism and multiferroicity of an isosceles triangular lattice antiferromagnet Sr3NiNb2O9.
Lee, M; Choi, E S; Ma, J; Sinclair, R; Dela Cruz, C R; Zhou, H D
2016-11-30
Various experimental measurements were performed to complete the phase diagram of a weakly distorted triangular lattice system, Sr3NiNb2O9 with Ni(2+) , spin-1 magnetic ions. This compound possesses an isosceles triangular lattice with two shorter bonds and one longer bond. It shows a two-step magnetic phase transition at [Formula: see text] K and [Formula: see text] K at zero magnetic field, characteristic of an easy-axis anisotropy. In the magnetization curves, a series of magnetic phase transitions was observed such as an up-up-down phase at [Formula: see text] T with 1/3 of the saturation magnetization (M sat) and an oblique phase at [Formula: see text] T with [Formula: see text]/3 M sat. Intriguingly, the magnetic phase transition below T N2 is in tandem with the ferroelectricity, which demonstrates multiferroic behaviors. Moreover, the multiferroic phase persists in all magnetically ordered phases regardless of the spin structure. The comparison between the phase diagrams of Sr3NiNb2O9 and its sister compound with an equilateral triangular lattice antiferromagnet Ba3NiNb2O9 (Hwang et al 2012 Phys. Rev. Lett. 109 257205), illustrates how a small imbalance among exchange interactions change the magnetic ground states of the TLAFs. PMID:27661860
Magnetism and multiferroicity of an isosceles triangular lattice antiferromagnet Sr3NiNb2O9.
Lee, M; Choi, E S; Ma, J; Sinclair, R; Dela Cruz, C R; Zhou, H D
2016-11-30
Various experimental measurements were performed to complete the phase diagram of a weakly distorted triangular lattice system, Sr3NiNb2O9 with Ni(2+) , spin-1 magnetic ions. This compound possesses an isosceles triangular lattice with two shorter bonds and one longer bond. It shows a two-step magnetic phase transition at [Formula: see text] K and [Formula: see text] K at zero magnetic field, characteristic of an easy-axis anisotropy. In the magnetization curves, a series of magnetic phase transitions was observed such as an up-up-down phase at [Formula: see text] T with 1/3 of the saturation magnetization (M sat) and an oblique phase at [Formula: see text] T with [Formula: see text]/3 M sat. Intriguingly, the magnetic phase transition below T N2 is in tandem with the ferroelectricity, which demonstrates multiferroic behaviors. Moreover, the multiferroic phase persists in all magnetically ordered phases regardless of the spin structure. The comparison between the phase diagrams of Sr3NiNb2O9 and its sister compound with an equilateral triangular lattice antiferromagnet Ba3NiNb2O9 (Hwang et al 2012 Phys. Rev. Lett. 109 257205), illustrates how a small imbalance among exchange interactions change the magnetic ground states of the TLAFs.
Magnetism and multiferroicity of an isosceles triangular lattice antiferromagnet Sr3NiNb2O9
NASA Astrophysics Data System (ADS)
Lee, M.; Choi, E. S.; Ma, J.; Sinclair, R.; Dela Cruz, C. R.; Zhou, H. D.
2016-11-01
Various experimental measurements were performed to complete the phase diagram of a weakly distorted triangular lattice system, Sr3NiNb2O9 with Ni2+ , spin-1 magnetic ions. This compound possesses an isosceles triangular lattice with two shorter bonds and one longer bond. It shows a two-step magnetic phase transition at {{T}\\text{N1}}∼ 5.1 K and {{T}\\text{N2}}∼ 5.5 K at zero magnetic field, characteristic of an easy-axis anisotropy. In the magnetization curves, a series of magnetic phase transitions was observed such as an up-up-down phase at {μ0}{{H}c1}∼ 10.5 T with 1/3 of the saturation magnetization (M sat) and an oblique phase at {μ0}{{H}c2}∼ 16 T with \\sqrt{3} /3 M sat. Intriguingly, the magnetic phase transition below T N2 is in tandem with the ferroelectricity, which demonstrates multiferroic behaviors. Moreover, the multiferroic phase persists in all magnetically ordered phases regardless of the spin structure. The comparison between the phase diagrams of Sr3NiNb2O9 and its sister compound with an equilateral triangular lattice antiferromagnet Ba3NiNb2O9 (Hwang et al 2012 Phys. Rev. Lett. 109 257205), illustrates how a small imbalance among exchange interactions change the magnetic ground states of the TLAFs.
Kaul, Ribhu K
2015-10-01
We introduce a simple model of SO(N) spins with two-site interactions which is amenable to quantum Monte Carlo studies without a sign problem on nonbipartite lattices. We present numerical results for this model on the two-dimensional triangular lattice where we find evidence for a spin nematic at small N, a valence-bond solid at large N, and a quantum spin liquid at intermediate N. By the introduction of a sign-free four-site interaction, we uncover a rich phase diagram with evidence for both first-order and exotic continuous phase transitions. PMID:26550748
Self-Assembly of Cubes into 2D Hexagonal and Honeycomb Lattices by Hexapolar Capillary Interactions
NASA Astrophysics Data System (ADS)
Soligno, Giuseppe; Dijkstra, Marjolein; van Roij, René
2016-06-01
Particles adsorbed at a fluid-fluid interface induce capillary deformations that determine their orientations and generate mutual capillary interactions which drive them to assemble into 2D ordered structures. We numerically calculate, by energy minimization, the capillary deformations induced by adsorbed cubes for various Young's contact angles. First, we show that capillarity is crucial not only for quantitative, but also for qualitative predictions of equilibrium configurations of a single cube. For a Young's contact angle close to 90°, we show that a single-adsorbed cube generates a hexapolar interface deformation with three rises and three depressions. Thanks to the threefold symmetry of this hexapole, strongly directional capillary interactions drive the cubes to self-assemble into hexagonal or graphenelike honeycomb lattices. By a simple free-energy model, we predict a density-temperature phase diagram in which both the honeycomb and hexagonal lattice phases are present as stable states.
Self-Assembly of Cubes into 2D Hexagonal and Honeycomb Lattices by Hexapolar Capillary Interactions.
Soligno, Giuseppe; Dijkstra, Marjolein; van Roij, René
2016-06-24
Particles adsorbed at a fluid-fluid interface induce capillary deformations that determine their orientations and generate mutual capillary interactions which drive them to assemble into 2D ordered structures. We numerically calculate, by energy minimization, the capillary deformations induced by adsorbed cubes for various Young's contact angles. First, we show that capillarity is crucial not only for quantitative, but also for qualitative predictions of equilibrium configurations of a single cube. For a Young's contact angle close to 90°, we show that a single-adsorbed cube generates a hexapolar interface deformation with three rises and three depressions. Thanks to the threefold symmetry of this hexapole, strongly directional capillary interactions drive the cubes to self-assemble into hexagonal or graphenelike honeycomb lattices. By a simple free-energy model, we predict a density-temperature phase diagram in which both the honeycomb and hexagonal lattice phases are present as stable states. PMID:27391753
Identifying topological edge states in 2D optical lattices using light scattering
NASA Astrophysics Data System (ADS)
Goldman, Nathan; Beugnon, Jérôme; Gerbier, Fabrice
2013-02-01
We recently proposed in a Letter [Phys. Rev. Lett. 108, 255303] a novel scheme to detect topological edge states in an optical lattice, based on a generalization of Bragg spectroscopy. The scope of the present article is to provide a more detailed and pedagogical description of the system - the Hofstadter optical lattice - and probing method. We first show the existence of topological edge states, in an ultra-cold gas trapped in a 2D optical lattice and subjected to a synthetic magnetic field. The remarkable robustness of the edge states is verified for a variety of external confining potentials. Then, we describe a specific laser probe, made from two lasers in Laguerre-Gaussian modes, which captures unambiguous signatures of these edge states. In particular, the resulting Bragg spectra provide the dispersion relation of the edge states, establishing their chiral nature. In order to make the Bragg signal experimentally detectable, we introduce a "shelving method", which simultaneously transfers angular momentum and changes the internal atomic state. This scheme allows to directly visualize the selected edge states on a dark background, offering an instructive view on topological insulating phases, not accessible in solid-state experiments.
Nakane, Kazuya; Kamijo, Takeshi; Ichinose, Ikuo
2011-02-01
In the present paper, we study a spin-1/2 antiferromagnetic (AF) Heisenberg model on layered anisotropic triangular lattice and obtain its phase structure. We use the Schwinger bosons for representing spin operators and also a coherent-state path integral for calculating physical quantities. Finite-temperature properties of the system are investigated by means of the numerical Monte-Carlo simulations. A detailed phase diagram of the system is obtained by calculating internal energy, specific heat, spin correlation functions, etc. There are AF Neel, paramagnetic, and spiral states. Turning on the plaquette term (i.e., the Maxwell term on a lattice) of an emergent U(1) gauge field that flips a pair of parallel spin-singlet bonds, we found that there appears a phase that is regarded as a deconfined spin-liquid state, though 'transition' to this phase from the paramagnetic phase is not of second order but a crossover. In that phase, the emergent gauge boson is a physical gapless excitation coupled with spinons. These results support our previous study on an AF Heisenberg model on a triangular lattice at vanishing temperature.
NASA Astrophysics Data System (ADS)
Yamamoto, Daisuke; Marmorini, Giacomo; Danshita, Ippei
2014-03-01
A triangular-lattice spin system is a fundamental model of geometric frustration. Recent experimental developments in magnetic materials synthesis and in frustrated optical lattices of ultracold atoms have renewed interest in studying magnetic properties of ideal two-dimensional frustrated systems over wide range of external field and anisotropy. We study the spin structures of S = 1/2 antiferromagnets on a triangular lattice using a large-size cluster mean-field method combined with a scaling scheme. We determine the ground-state phase diagram of the spin model in the plane of magnetic field and XXZ anisotropy, and compare it with the classical counterpart in order to discuss the quantum effects. We find that a nontrivial continuous degeneracy existing in the classical model is broken up into two first-order phase transitions between which a non-classical phase emerges as a result of the selection by quantum fluctuations. We also use the dilute Bose gas expansion in the vicinity of the saturation field and interpret one of the first-order transitions as the 0- π transition of the relative phase between two magnon Bose-Einstein condensates. We suggest that the quantum phase transitions can be observed in current or near-future experiments. G.M. is supported by a RIKEN FPR fellowship. I.D. is supported by KAKENHI from JSPS Grants No. 25800228 and No. 25220711.
All optical active high decoder using integrated 2D square lattice photonic crystals
NASA Astrophysics Data System (ADS)
Moniem, Tamer A.
2015-11-01
The paper introduces a novel all optical active high 2 × 4 decoder based on 2D photonic crystals (PhC) of silicon rods with permittivity of ε = 10.1 × 10-11 farad/m. The main structure of optical decoder is designed using a combination of five nonlinear photonic crystal ring resonator, set of T-type waveguide, and line defect of Y and T branch splitters. The proposed structure has two logic input ports, four output ports, and one bias input port. The total size of the proposed 2 × 4 decoder is equal to 40 μm × 38 μm. The PhC structure has a square lattice of silicon rod with refractive index of 3.39 in air. The overall design and the results are discussed through the realization and the numerically simulation to confirm its operation and feasibility.
NASA Astrophysics Data System (ADS)
Masrour, R.; Jabar, A.
2016-07-01
Mixed-spin-1 and spin-3/2 Ising model on the decorated triangular lattice is studied by the use of Monte Carlo simulation. Within this approach, the results for the ground-state of the antiferromagnetic and ferromagnetic of decorated triangular lattice are obtained. The reduced transition temperature of each sublattice are obtained. The reduced temperature of compensation is also obtained. The thermal total ratio of magnetic susceptibilities of sublattices is given. The effect of crystal field and exchange interactions on the magnetization of the system are detailed. The magnetic hysteresis cycles are found for different values of exchanges interactions between the same lattice and the two sublattices different, for different crystal filed and temperatures. In addition, very weak exchange interactions and for a higher temperatures and a higher crystal filed values the decorated triangular lattice has been exhibited the superparamagnetic behavior.
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 .
Electronic and geometrical properties of monoatomic and diatomic 2D honeycomb lattices. A DFT study
NASA Astrophysics Data System (ADS)
Rojas, Ángela; Rey, Rafael; Fonseca, Karen; Grupo de Óptica e Información Cuántica Team
Since the discovery of graphene by Geim and Novoselov at 2004, several analogous systems have been theoretically and experimentally studied, due to their technological interest. Both monoatomic lattices, such as silicine and germanene, and diatomic lattices (h-GaAs and h-GaN) have been studied. Using Density Functional Theory we obtain and confirm the chemical stability of these hexagonal 2D systems through the total energy curves as a function of interatomic distance. Unlike graphene, silicine and germanene, gapless materials, h-GaAs and h-GaN exhibit electronic gaps, different from that of the bulk, which could be interesting for the industry. On the other hand, the ab initio band structure calculations for graphene, silicene and germanene show a non-circular cross section around K points, at variance with the prediction of usual Tight-binding models. In fact, we have found that Dirac cones display a dihedral group symmetry. This implies that Fermi speed can change up to 30 % due to the orientation of the wave vector, for both electrons and holes. Traditional analytic studies use the Dirac equation for the electron dynamics at low energies. However, this equation assumes an isotropic, homogeneous and uniform space. Authors would like to thank the División de Investigación Sede Bogotá for their financial support at Universidad Nacional de Colombia. A. M. Rojas-Cuervo would also like to thank the Colciencias, Colombia.
NASA Astrophysics Data System (ADS)
Nishimoto, Satoshi; Katukuri, Vamshi M.; Yushankhai, Viktor; Stoll, Hermann; Rößler, Ulrich K.; Hozoi, Liviu; Rousochatzakis, Ioannis; van den Brink, Jeroen
2016-01-01
Iridium oxides with a honeycomb lattice have been identified as platforms for the much anticipated Kitaev topological spin liquid: the spin-orbit entangled states of Ir4+ in principle generate precisely the required type of anisotropic exchange. However, other magnetic couplings can drive the system away from the spin-liquid phase. With this in mind, here we disentangle the different magnetic interactions in Li2IrO3, a honeycomb iridate with two crystallographically inequivalent sets of adjacent Ir sites. Our ab initio many-body calculations show that, while both Heisenberg and Kitaev nearest-neighbour couplings are present, on one set of Ir-Ir bonds the former dominates, resulting in the formation of spin-triplet dimers. The triplet dimers frame a strongly frustrated triangular lattice and by exact cluster diagonalization we show that they remain protected in a wide region of the phase diagram.
Nishimoto, Satoshi; Katukuri, Vamshi M; Yushankhai, Viktor; Stoll, Hermann; Rößler, Ulrich K; Hozoi, Liviu; Rousochatzakis, Ioannis; van den Brink, Jeroen
2016-01-01
Iridium oxides with a honeycomb lattice have been identified as platforms for the much anticipated Kitaev topological spin liquid: the spin-orbit entangled states of Ir(4+) in principle generate precisely the required type of anisotropic exchange. However, other magnetic couplings can drive the system away from the spin-liquid phase. With this in mind, here we disentangle the different magnetic interactions in Li2IrO3, a honeycomb iridate with two crystallographically inequivalent sets of adjacent Ir sites. Our ab initio many-body calculations show that, while both Heisenberg and Kitaev nearest-neighbour couplings are present, on one set of Ir-Ir bonds the former dominates, resulting in the formation of spin-triplet dimers. The triplet dimers frame a strongly frustrated triangular lattice and by exact cluster diagonalization we show that they remain protected in a wide region of the phase diagram. PMID:26776664
Nishimoto, Satoshi; Katukuri, Vamshi M.; Yushankhai, Viktor; Stoll, Hermann; Rößler, Ulrich K.; Hozoi, Liviu; Rousochatzakis, Ioannis; van den Brink, Jeroen
2016-01-01
Iridium oxides with a honeycomb lattice have been identified as platforms for the much anticipated Kitaev topological spin liquid: the spin-orbit entangled states of Ir4+ in principle generate precisely the required type of anisotropic exchange. However, other magnetic couplings can drive the system away from the spin-liquid phase. With this in mind, here we disentangle the different magnetic interactions in Li2IrO3, a honeycomb iridate with two crystallographically inequivalent sets of adjacent Ir sites. Our ab initio many-body calculations show that, while both Heisenberg and Kitaev nearest-neighbour couplings are present, on one set of Ir–Ir bonds the former dominates, resulting in the formation of spin-triplet dimers. The triplet dimers frame a strongly frustrated triangular lattice and by exact cluster diagonalization we show that they remain protected in a wide region of the phase diagram. PMID:26776664
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.
NASA Astrophysics Data System (ADS)
Yoshida, Tempei; Hotta, Chisa
2014-12-01
We study the interplay of correlation and thermal fluctuation in a system consisting of two species of classical particles with up and down spin on a geometrically frustrated anisotropic triangular lattice, described by an extended four-state Potts model. The model corresponds to the strong coupling limit of the extended Hubbard model at quarter-filling, which is known to host several competing charge ordered phases as well as an exotic quantum state called pinball liquid. The frustrated intersite Coulomb interactions together with the on-site Coulomb interaction generate macroscopically degenerate manifolds of low-energy states. They compete entropically at finite temperature and two characteristic states emerge; a threefold periodic charge ordered state and a quasi-one-dimensionally disordered state called "good defect state" characterized by the systematic generation of ferroelectric bonds. The two states show good correspondence with the threefold charge order and the pinball liquid in the extended Hubbard model, and are separated by the partial Mott transition taking place on one of the three sublattices of the triangular lattice.
Magnetic excitations in the spin-1/2 triangular-lattice antiferromagnet Cs2CuBr4
NASA Astrophysics Data System (ADS)
Zvyagin, S. A.; Ozerov, M.; Kamenskyi, D.; Wosnitza, J.; Krzystek, J.; Yoshizawa, D.; Hagiwara, M.; Hu, Rongwei; Ryu, Hyejin; Petrovic, C.; Zhitomirsky, M. E.
2015-11-01
We report on high-field electron spin resonance (ESR) studies of magnetic excitations in the spin-1/2 triangular-lattice antiferromagnet Cs2CuBr4. 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 Cs2CuBr4, (Zvyagin et al 2014 Phys. Rev. Lett.112 077206) is present well above TN. Noticeably, the transition into the long-range magnetically ordered phase does not significantly affect the size of the gap, suggesting that even below TN the high-energy spin dynamics in Cs2CuBr4 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 triangular-lattice antiferromagnet.
NASA Astrophysics Data System (ADS)
Budinski-Petković, Lj; Lončarević, I.; Jakšić, Z. M.; Vrhovac, S. B.
2016-05-01
Random sequential adsorption (RSA) on a triangular lattice with defects is studied by Monte Carlo simulations. The lattice is initially randomly covered by point-like impurities at a certain concentration p. The deposited objects are formed by self-avoiding random walks on the lattice. Jamming coverage {θ\\text{jam}} and percolation threshold θ \\text{p}\\ast are determined for a wide range of impurity concentrations p for various object shapes. Rapidity of the approach to the jamming state is found to be independent on the impurity concentration. The jamming coverage {θ\\text{jam}} decreases with the impurity concentration p and this decrease is more prominent for objects of larger size. For a certain defect concentration, decrease of the jamming coverage with the length of the walk \\ell making the object is found to obey an exponential law, {θ\\text{jam}}={θ0}+{θ1}{{\\text{e}}-\\ell /r} . The results for RSA of polydisperse mixtures of objects of various sizes suggest that, in the presence of impurities, partial jamming coverage of small objects can have even larger values than in the case of an ideal lattice. Percolation in the presence of impurities is also studied and it is found that the percolation threshold θ \\text{p}\\ast is practically insensitive to the concentration of point defects p. Percolation can be reached at highest impurity concentrations with angled objects, and the critical defect concentration p c is lowest for the most compact objects.
NASA Astrophysics Data System (ADS)
Guillamon, I.; Vieira, S.; Suderow, H.; Cordoba, R.; Sese, J.; de Teresa, J. M.; Ibarra, R.
In two dimensional (2D) systems, theory has proposed that random disorder destroys long range correlations driving a transition to a glassy state. Here, I will discuss new insights into this issue obtained through the direct visualization of the critical behaviour of a 2D superconducting vortex lattice formed in a thin film with a smooth 1D thickness modulation. Using scanning tunneling microscopy at 0.1K, we have tracked the modification in the 2D vortex arrangements induced by the 1D thickness modulation while increasing the vortex density by three orders of magnitude. Upon increasing the field, we observed a two-step order-disorder transition in the 2D vortex lattice mediated by the appearance of dislocations and disclinations and accompanied by an increase in the local vortex density fluctuations. Through a detailed analysis of correlation functions, we find that the transition is driven by the incommensurate 1D thickness modulation. We calculate the critical points and exponents and find that they are well above theoretical expectation for random disorder. Our results show that long range 1D correlations in random potentials enhance the stability range of the ordered phase in a 2D vortex lattice. Work supported by Spanish MINECO, CIG Marie Curie Grant, Axa Research Fund and FBBVA.
Lee, M.; Choi, E. S.; Huang, X.; Ma, J.; Dela Cruz, C. R.; Matsuda, M.; Tian, W.; Dun, Z. L.; Dong, S.; Zhou, H. D.
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 Ba3MnNb2 O9. All results suggest that Ba3MnNb2 O9 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 TN1 = 3.4 K and TN2 = 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 into up-up-down (uud) and oblique phases showing successive magneticmore » 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
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.
Chen, J; Zhuo, W Z; Qin, M H; Dong, S; Zeng, M; Lu, X B; Gao, X S; Liu, J-M
2016-09-01
In this work, we study the magnetization behaviors of the classical Ising model on the triangular lattice using Monte Carlo simulations, and pay particular attention to the effect of further-neighbor interactions. Several fascinating spin states are identified to be stabilized in certain magnetic field regions, respectively, resulting in the magnetization plateaus at 2/3, 5/7, 7/9 and 5/6 of the saturation magnetization M S, in addition to the well-known plateaus at 0, 1/3 and 1/2 of M S. The stabilization of these interesting orders can be understood as the consequence of the competition between Zeeman energy and exchange energy. PMID:27356040
NASA Astrophysics Data System (ADS)
Chen, J.; Zhuo, W. Z.; Qin, M. H.; Dong, S.; Zeng, M.; Lu, X. B.; Gao, X. S.; Liu, J.-M.
2016-09-01
In this work, we study the magnetization behaviors of the classical Ising model on the triangular lattice using Monte Carlo simulations, and pay particular attention to the effect of further-neighbor interactions. Several fascinating spin states are identified to be stabilized in certain magnetic field regions, respectively, resulting in the magnetization plateaus at 2/3, 5/7, 7/9 and 5/6 of the saturation magnetization M S, in addition to the well-known plateaus at 0, 1/3 and 1/2 of M S. The stabilization of these interesting orders can be understood as the consequence of the competition between Zeeman energy and exchange energy.
NASA Astrophysics Data System (ADS)
Murtazaev, Akai K.; Babaev, Albert B.; Magomedov, Magomed A.; Kassan-Ogly, Felix A.; Proshkin, Alexey I.
2016-11-01
Using Monte Carlo simulations, we investigated phase transitions and frustrations in the three-state Potts model on a triangular lattice with allowance for antiferromagnetic exchange interactions between nearest-neighbors J1 and next-nearest-neighbors J2. The ratio of the next-nearest-neighbor and nearest-neighbor exchange constants r=J2/J1 is chosen within the range of 0≤r≤2. Based on the analysis of the entropy, specific heat, system state density function, and fourth order Binder cumulants, the phase transitions in the Potts model with interactions J1<0 and J2<0 are shown to be found in value ranges of 0≤r<0.2 and 1.25≤r≤2.0. In an intermediate range of 0.2≤r≤1.0 the phase transition fails and the frustrations are revealed.
Rare-Earth Triangular Lattice Spin Liquid: A Single-Crystal Study of YbMgGaO4.
Li, Yuesheng; Chen, Gang; Tong, Wei; Pi, Li; Liu, Juanjuan; Yang, Zhaorong; Wang, Xiaoqun; Zhang, Qingming
2015-10-16
YbMgGaO4, a structurally perfect two-dimensional triangular lattice with an odd number of electrons per unit cell and spin-orbit entangled effective spin-1/2 local moments for the Yb(3+) ions, is likely to experimentally realize the quantum spin liquid ground state. We report the first experimental characterization of single-crystal YbMgGaO4 samples. Because of the spin-orbit entanglement, the interaction between the neighboring Yb(3+) moments depends on the bond orientations and is highly anisotropic in the spin space. We carry out thermodynamic and the electron spin resonance measurements to confirm the anisotropic nature of the spin interaction as well as to quantitatively determine the couplings. Our result is a first step towards the theoretical understanding of the possible quantum spin liquid ground state in this system and sheds new light on the search for quantum spin liquids in strong spin-orbit coupled insulators.
Agarwala, R.; Batzoglou, S.; Dancik, V.
1997-12-01
A long standing problem in molecular biology is to determine the three-dimensional structure of a protein, given its amino acid sequence. A variety of simplifying models have been proposed abstracting only the {open_quotes}essential physical properties{close_quotes} of real proteins. In these models, the three dimensional space is often represented by a lattice. Residues which are adjacent in the primary sequence (i.e. covalently linked) must be placed at adjacent points in the lattice. A conformation of a protein is simply a self-avoiding walk along the lattice. The protein folding problem STRING-FOLD is that of finding a conformation of the protein sequence on the lattice such that the overall energy is minimized, for some reasonable definition of energy. This formulation leaves open the choices of a lattice and an energy function. Once these choices are made, one may then address the algorithmic complexity of optimizing the energy function for the lattice. For a variety of such simple models, this minimization problem is in fact NP-hard. In this paper, we consider the Hydrophobic-Polar (HP) Model introduced by Dill. The HP model abstracts the problem by grouping the 20 amino acids into two classes: hydrophobic (or non-polar) residues and hydrophilic (or polar) residues. For concreteness, we will take our input to be a string from (H,P){sup +}, where P represents polar residues, and H represents hydrophobic residues. Dill et.al. survey the literature analyzing this model. 8 refs., 2 figs., 1 tab.
NASA Astrophysics Data System (ADS)
Xavier, Jolly; Becker, Christiane
2014-05-01
For an optimized light harvesting while using diverse periodic photonic light-trapping architectures in low cost thin film crystalline silicon (c-Si) solar cells, it is also of prime importance to tune the features of their lattice point basis structure. In view of this, tapered nanoholes would be of importance for envisaged better light in-coupling due to graded index effect and also from the point of fabrication feasibility. Using a 3D finite element method based computational simulator, we investigate the basis structural influence of triangular as well as honeycomb lattice-structured experimentally feasible tapered air nanoholes in ~400 nm thick c-Si absorber on a glass substrate. We present a detailed convergence analysis of volume absorption in Si absorber with cylindrical as well as tapered nanoholes. For a wavelength rage of 300 nm to 1100 nm, we present the computed results on light absorption of the engineered Si nanoholes for a lattice periodicity of 600nm. In particular, we study the influence of tapering angle of engineered nano air holes in Si thin film for the absorption enhancement in photonic triangular and honeycomb lattice structured tapered nanoholes. Further we make a comparative analysis of cylindrical and tapered nanoholes for a range of light incident angles from 0° to 60°. For the presented triangular as well as honeycomb lattice structured nanoholes, we observe that in comparison to the cylindrical nanoholes, the tapered nanoholes perform better in terms of light trapping for enhanced light absorption in textured Si thin films even when the effective volume fraction of Si is lower in the absorber layer with tapered nanoholes in comparison to that of cylindrical ones. From the maximum achievable short circuit current density estimation in the present study, the performance of c-Si absorbing layer engineered with triangular lattice structured tapered air holes harvests light efficiently owing to its higher lattice symmetry among periodic
Lattice Boltzmann simulation of a fluid flow around a triangular unit of three isothermal cylinders
NASA Astrophysics Data System (ADS)
Alinejad, J.
2016-01-01
The lattice Boltzmann method is employed to simulate heat transfer in the flow past three arrangements of elliptical and circular cylinders under an isothermal boundary condition. The lattice Boltzmann equations and the Bhatnagar-Gross-Krook model are used to simulate two-dimensional forced convection at 30 ≤ Re ≤ 100 and Pr = 0.71. Pressure distributions, isotherms, and streamlines are obtained. Vortex shedding maps are observed in detail for several cases. The present results are in good agreement with available experimental and numerical data.
NASA Astrophysics Data System (ADS)
Nataf, Pierre; Lajkó, Miklós; Wietek, Alexander; Penc, Karlo; Mila, Frédéric; Läuchli, Andreas M.
2016-10-01
We show that, in the presence of a π /2 artificial gauge field per plaquette, Mott insulating phases of ultracold fermions with SU (N ) symmetry and one particle per site generically possess an extended chiral phase with intrinsic topological order characterized by an approximate ground space of N low-lying singlets for periodic boundary conditions, and by chiral edge states described by the SU(N ) 1 Wess-Zumino-Novikov-Witten conformal field theory for open boundary conditions. This has been achieved by extensive exact diagonalizations for N between 3 and 9, and by a parton construction based on a set of N Gutzwiller projected fermionic wave functions with flux π /N per triangular plaquette. Experimental implications are briefly discussed.
Orso, G.; Stringari, S.; Menotti, C.
2006-11-10
We use Bogoliubov theory to calculate the beyond mean field correction to the equation of state of a weakly interacting Bose gas in the presence of a tight 2D optical lattice. We show that the lattice induces a characteristic 3D to 1D crossover in the behavior of quantum fluctuations. Using the hydrodynamic theory of superfluids, we calculate the corresponding shift of the collective frequencies of a harmonically trapped gas. We find that this correction can be of the order of a few percent and hence easily measurable in current experiments. The behavior of the quantum depletion of the condensate is also discussed.
Magnetic excitations in the spin-1/2 triangular-lattice antiferromagnet Cs2CuBr4
Zvyagin, S. A.; Ozerov, M.; Kamenskyi, D.; Wosnitza, J.; Krzystek, J.; Yoshizawa, D.; Hagiwara, M.; Hu, Rongwei; Ryu, Hyejin; Petrovic, C.; et al
2015-11-27
We present on high- field electron spin resonance (ESR) studies of magnetic excitations in the spin- 1/2 triangular-lattice antiferromagnet Cs2CuBr4. 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 Cs2CuBr4 [Zvyagin et al:, Phys. Rev. Lett. 112, 077206 (2014)], is present well above TN. Noticeably, the transition into the long-range magnetically ordered phase does not significantly affect the size of the gap, suggesting that even below TN the high-energy spin dynamicsmore » in Cs2CuBr4 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
Critical behavior of a triangular lattice Ising AF/FM bilayer
NASA Astrophysics Data System (ADS)
Žukovič, M.; Bobák, A.
2016-03-01
We study a bilayer Ising spin system consisting of antiferromagnetic (AF) and ferromagnetic (FM) triangular planes, coupled by ferromagnetic exchange interaction, by standard Monte Carlo and parallel tempering methods. The AF/FM bilayer is found to display the critical behavior completely different from both the single FM and AF constituents as well as the FM/FM and AF/AF bilayers. Namely, by finite-size scaling (FSS) analysis we identify at the same temperature a standard Ising transition from the paramagnetic to FM state in the FM plane that induces a ferrimagnetic state with a finite net magnetic moment in the AF plane. At lower temperatures there is another phase transition, that takes place only in the AF plane, to different ferrimagnetic state with spins on two sublattices pointing parallel and on one sublattice antiparallel to the spins on the FM plane. FSS indicates that the corresponding critical exponents are close to the two-dimensional three-state ferromagnetic Potts model values.
Metastable States of a Gas of Dipolar Bosons in a 2D Optical Lattice
Menotti, C.; Trefzger, C.; Lewenstein, M.
2007-06-08
We investigate the physics of dipolar bosons in a two-dimensional optical lattice. It is known that due to the long-range character of dipole-dipole interaction, the ground state phase diagram of a gas of dipolar bosons in an optical lattice presents novel quantum phases, like checkerboard and supersolid phases. In this Letter, we consider the properties of the system beyond its ground state, finding that it is characterized by a multitude of almost degenerate metastable states, often competing with the ground state. This makes dipolar bosons in a lattice similar to a disordered system and opens possibilities of using them as quantum memories.
NASA Astrophysics Data System (ADS)
Seabra, Luis; Shannon, Nic
2011-04-01
The majority of magnetic materials possess some degree of magnetic anisotropy, either at the level of a single ion, or in the exchange interactions between different magnetic ions. Where these exchange interactions are also frustrated, the competition between them and anisotropy can stabilize a wide variety of new phases in applied magnetic field. Motivated by the hexagonal delafossite 2H-AgNiO2, we study the Heisenberg antiferromagnet on a layered triangular lattice with competing first- and second-neighbor interactions and single-ion easy-axis anisotropy. Using a combination of classical Monte Carlo simulation, mean-field analysis, and Landau theory, we establish the magnetic phase diagram of this model as a function of temperature and magnetic field for a fixed ratio of exchange interactions, but with values of easy-axis anisotropy D extending from the Heisenberg (D=0) to the Ising (D=∞) limits. We uncover a rich variety of different magnetic phases. These include several phases which are magnetic supersolids (in the sense of Matsuda and Tsuneto or Liu and Fisher), one of which may already have been observed in AgNiO2. We explore how this particular supersolid arises through the closing of a gap in the spin-wave spectrum, and how it competes with rival collinear phases as the easy-axis anisotropy is increased. The finite temperature properties of this phase are found to be different from those of any previously studied magnetic supersolid.
Rare-Earth Triangular Lattice Spin Liquid: A Single-Crystal Study of YbMgGaO4.
Li, Yuesheng; Chen, Gang; Tong, Wei; Pi, Li; Liu, Juanjuan; Yang, Zhaorong; Wang, Xiaoqun; Zhang, Qingming
2015-10-16
YbMgGaO4, a structurally perfect two-dimensional triangular lattice with an odd number of electrons per unit cell and spin-orbit entangled effective spin-1/2 local moments for the Yb(3+) ions, is likely to experimentally realize the quantum spin liquid ground state. We report the first experimental characterization of single-crystal YbMgGaO4 samples. Because of the spin-orbit entanglement, the interaction between the neighboring Yb(3+) moments depends on the bond orientations and is highly anisotropic in the spin space. We carry out thermodynamic and the electron spin resonance measurements to confirm the anisotropic nature of the spin interaction as well as to quantitatively determine the couplings. Our result is a first step towards the theoretical understanding of the possible quantum spin liquid ground state in this system and sheds new light on the search for quantum spin liquids in strong spin-orbit coupled insulators. PMID:26550899
Interferometric approach to measuring band topology in 2D optical lattices.
Abanin, Dmitry A; Kitagawa, Takuya; Bloch, Immanuel; Demler, Eugene
2013-04-19
Recently, optical lattices with nonzero Berry's phases of Bloch bands have been realized. New approaches for measuring Berry's phases and topological properties of bands with experimental tools appropriate for ultracold atoms need to be developed. In this Letter, we propose an interferometric method for measuring Berry's phases of two-dimensional Bloch bands. The key idea is to use a combination of Ramsey interference and Bloch oscillations to measure Zak phases, i.e., Berry's phases for closed trajectories corresponding to reciprocal lattice vectors. We demonstrate that this technique can be used to measure the Berry curvature of Bloch bands, the π Berry's phase of Dirac points, and the first Chern number of topological bands. We discuss several experimentally feasible realizations of this technique, which make it robust against low-frequency magnetic noise.
Spin frustration in 2D kagomé lattices: a problem for inorganic synthetic chemistry.
Nocera, Daniel G; Bartlett, Bart M; Grohol, Daniel; Papoutsakis, Dimitris; Shores, Matthew P
2004-08-20
A kagomé antiferromagnet presents an ideal construct for studying the unusual physics that result from the placement of magnetically frustrated spins on a low-dimensional lattice. Jarosites are the prototype for a spin-frustrated magnetic structure, because these materials are composed exclusively of kagomé layers. Notwithstanding, jarosite-type materials have escaped precise magnetic characterization over the past three decades, because they are notoriously difficult to prepare in pure and single-crystal forms. These hurdles have been overcome with the development of redox-based hydrothermal methods. Armed with pure and crystalline materials, several perplexing issues surrounding the magnetic properties of the jarosites have been resolved, yielding a detailed and comprehensive picture of the ground-state physics of this kagomé lattice.
Lattice Boltzmann methods for some 2-D nonlinear diffusion equations:Computational results
Elton, B.H.; Rodrigue, G.H. . Dept. of Applied Science Lawrence Livermore National Lab., CA ); Levermore, C.D. . Dept. of Mathematics)
1990-01-01
In this paper we examine two lattice Boltzmann methods (that are a derivative of lattice gas methods) for computing solutions to two two-dimensional nonlinear diffusion equations of the form {partial derivative}/{partial derivative}t u = v ({partial derivative}/{partial derivative}x D(u){partial derivative}/{partial derivative}x u + {partial derivative}/{partial derivative}y D(u){partial derivative}/{partial derivative}y u), where u = u({rvec x},t), {rvec x} {element of} R{sup 2}, v is a constant, and D(u) is a nonlinear term that arises from a Chapman-Enskog asymptotic expansion. In particular, we provide computational evidence supporting recent results showing that the methods are second order convergent (in the L{sub 1}-norm), conservative, conditionally monotone finite difference methods. Solutions computed via the lattice Boltzmann methods are compared with those computed by other explicit, second order, conservative, monotone finite difference methods. Results are reported for both the L{sub 1}- and L{sub {infinity}}-norms.
Metal-dielectric photonic crystal superlattice: 1D and 2D models and empty lattice approximation
NASA Astrophysics Data System (ADS)
Kichin, G.; Weiss, T.; Gao, H.; Henzie, J.; Odom, T. W.; Tikhodeev, S. G.; Giessen, H.
2012-10-01
Periodic nanostructures are one of the main building blocks in modern nanooptics. They are used for constructing photonic crystals and metamaterials and provide optical properties that can be changed by adjusting the geometrical parameters of the structures. In this paper the optical properties of a photonic crystal slab with a 2D superlattice are discussed. The structure consists of a gold layer with a finite periodic pattern of air holes that is itself repeated periodically with a larger superperiod. We propose simplified 1D and 2D models to understand the physical nature of Wood's anomalies in the optical spectra of the investigated structure. The latter are attributed to the Rayleigh anomalies, surface plasmon Bragg resonances and the hole-localized plasmons.
Yang Xuefeng; Cui Jian; Zhang Yuan; Liu Yue
2012-07-15
The dispersion relations of the externally and thermally (naturally) excited dust lattice modes (both longitudinal and transverse) in two-dimensional Debye-Yukawa complex plasma crystals are investigated. The dispersion relations are calculated numerically by taking the neutral gas damping effects into account and the numerical results are in agreement with the experimental data given by Nunomura et al.[Phys. Rev. E 65, 066402 (2002)]. It is found that for the mode excited by an external disturbance with a real frequency, the dispersion properties are changed at a critical frequency near where the group velocity of the mode goes to zero. Therefore, the high frequency branch with negative dispersion cannot be reached. In contrast, for the thermally excited mode, the dispersion curve can extend all the way to the negative dispersion region, while a 'cut-off' wave number exists at the long wavelength end of the dispersion in the transverse mode.
Kondo lattice on the edge of a 2D topological insulator
NASA Astrophysics Data System (ADS)
Maciejko, Joseph
2012-02-01
Much attention has been devoted recently to the experimental and theoretical study of the effect of magnetic impurities on the stability of the gapless boundary modes of topological insulators. When the quantum dynamics of the impurities is considered, those boundary modes constitute novel types of fermionic baths which may affect the nature of possible impurity phases and phase transitions. We study a regular one-dimensional array of quantum magnetic impurities interacting with the helical edge liquid of a two-dimensional time-reversal invariant topological insulator. Exact solutions at the special Toulouse and Luther-Emery points as well as a renormalization group analysis àla Anderson-Yuval allow us to construct a phase diagram in the space of Kondo coupling, electron-electron interaction strength, and electron density. We point out similarities and differences with the Kondo lattice in a ordinary one-dimensional electron gas.
A hydrodynamically-consistent MRT lattice Boltzmann model on a 2D rectangular grid
NASA Astrophysics Data System (ADS)
Peng, Cheng; Min, Haoda; Guo, Zhaoli; Wang, Lian-Ping
2016-12-01
A multiple-relaxation time (MRT) lattice Boltzmann (LB) model on a D2Q9 rectangular grid is designed theoretically and validated numerically in the present work. By introducing stress components into the equilibrium moments, this MRT-LB model restores the isotropy of diffusive momentum transport at the macroscopic level (or in the continuum limit), leading to moment equations that are fully consistent with the Navier-Stokes equations. The model is derived by an inverse design process which is described in detail. Except one moment associated with the energy square, all other eight equilibrium moments can be theoretically and uniquely determined. The model is then carefully validated using both the two-dimensional decaying Taylor-Green vortex flow and lid-driven cavity flow, with different grid aspect ratios. The corresponding results from an earlier model (Bouzidi et al. (2001) [28]) are also presented for comparison. The results of Bouzidi et al.'s model show problems associated with anisotropy of viscosity coefficients, while the present model exhibits full isotropy and is accurate and stable.
Adiabatic and Hamiltonian computing on a 2D lattice with simple two-qubit interactions
NASA Astrophysics Data System (ADS)
Lloyd, Seth; Terhal, Barbara M.
2016-02-01
We show how to perform universal Hamiltonian and adiabatic computing using a time-independent Hamiltonian on a 2D grid describing a system of hopping particles which string together and interact to perform the computation. In this construction, the movement of one particle is controlled by the presence or absence of other particles, an effective quantum field effect transistor that allows the construction of controlled-NOT and controlled-rotation gates. The construction translates into a model for universal quantum computation with time-independent two-qubit ZZ and XX+YY interactions on an (almost) planar grid. The effective Hamiltonian is arrived at by a single use of first-order perturbation theory avoiding the use of perturbation gadgets. The dynamics and spectral properties of the effective Hamiltonian can be fully determined as it corresponds to a particular realization of a mapping between a quantum circuit and a Hamiltonian called the space-time circuit-to-Hamiltonian construction. Because of the simple interactions required, and because no higher-order perturbation gadgets are employed, our construction is potentially realizable using superconducting or other solid-state qubits.
A hierarchical lattice spring model to simulate the mechanics of 2-D materials-based composites
NASA Astrophysics Data System (ADS)
Brely, Lucas; Bosia, Federico; Pugno, Nicola
2015-07-01
In the field of engineering materials, strength and toughness are typically two mutually exclusive properties. Structural biological materials such as bone, tendon or dentin have resolved this conflict and show unprecedented damage tolerance, toughness and strength levels. The common feature of these materials is their hierarchical heterogeneous structure, which contributes to increased energy dissipation before failure occurring at different scale levels. These structural properties are the key to exceptional bioinspired material mechanical properties, in particular for nanocomposites. Here, we develop a numerical model in order to simulate the mechanisms involved in damage progression and energy dissipation at different size scales in nano- and macro-composites, which depend both on the heterogeneity of the material and on the type of hierarchical structure. Both these aspects have been incorporated into a 2-dimensional model based on a Lattice Spring Model, accounting for geometrical nonlinearities and including statistically-based fracture phenomena. The model has been validated by comparing numerical results to continuum and fracture mechanics results as well as finite elements simulations, and then employed to study how structural aspects impact on hierarchical composite material properties. Results obtained with the numerical code highlight the dependence of stress distributions on matrix properties and reinforcement dispersion, geometry and properties, and how failure of sacrificial elements is directly involved in the damage tolerance of the material. Thanks to the rapidly developing field of nanocomposite manufacture, it is already possible to artificially create materials with multi-scale hierarchical reinforcements. The developed code could be a valuable support in the design and optimization of these advanced materials, drawing inspiration and going beyond biological materials with exceptional mechanical properties.
NASA Astrophysics Data System (ADS)
Ranjith, K. M.; Nath, R.; Majumder, M.; Kasinathan, D.; Skoulatos, M.; Keller, L.; Skourski, Y.; Baenitz, M.; Tsirlin, A. A.
2016-07-01
We report the thermodynamic properties, magnetic ground state, and microscopic magnetic model of the spin-1 frustrated antiferromagnet Li2NiW2O8 , showing successive transitions at TN 1≃18 K and TN 2≃12.5 K in zero field. Nuclear magnetic resonance and neutron diffraction reveal collinear and commensurate magnetic order with the propagation vector k =(1/2 ,0 ,1/2 ) below TN 2. The ordered moment of 1.8 μB at 1.5 K is directed along [0.89 (9 ),-0.10 (5 ),-0.49 (6 )] and matches the magnetic easy axis of spin-1 Ni2 + ions, which is determined by the scissor-like distortion of the NiO6 octahedra. Incommensurate magnetic order, presumably of spin-density-wave type, is observed in the region between TN 2 and TN 1. Density-functional band-structure calculations put forward a three-dimensional spin lattice with spin-1 chains running along the [01 1 ¯] direction and stacked on a spatially anisotropic triangular lattice in the a b plane. We show that the collinear magnetic order in Li2NiW2O8 is incompatible with the triangular lattice geometry and thus driven by a pronounced easy-axis single-ion anisotropy of Ni2 +.
NASA Astrophysics Data System (ADS)
Liu, Ya-Zhao; Liu, Rong-Juan; Feng, Shuai; Ren, Cheng; Yang, Hai-Fang; Zhang, Dao-Zhong; Li, Zhi-Yuan
2008-12-01
We demonstrate the design, fabrication, and characterization of a multichannel filter in a two-dimensional triangular-lattice photonic crystal slab. The output signal channel, which directs in the Γ-M crystalline direction, is orthogonal to the input signal channel that directs in the Γ-K crystalline direction. In each channel, the filtering function is guaranteed by the indirect resonant coupling between the waveguide and the cavity. Four resonant cavities with different sizes provide the mechanism of finely tuning the output wavelength. Our experimental results are in good agreement with simulations.
Li, Juan; Wang, Yi-Fei; Gong, Chang-De
2011-04-20
We consider the tight-binding models of electrons on a two-dimensional triangular lattice and kagomé lattice under staggered modulated magnetic fields. Such fields have two components: a uniform-flux part with strength φ, and a staggered-flux part with strength Δφ. Various properties of the Hall conductances and Hofstadter butterflies are studied. When φ is fixed, variation of Δφ leads to the quantum Hall transitions and Chern numbers of Landau subbands being redistributed between neighboring pairs. The energy spectra with nonzero Δφs have similar fractal structures but quite different energy gaps compared with the original Hofstadter butterflies of Δφ = 0. Moreover, the fan-like structure of Landau levels in the low magnetic field region is also modified appreciably by Δφ.
An exact and efficient first passage time algorithm for reaction-diffusion processes on a 2D-lattice
NASA Astrophysics Data System (ADS)
Bezzola, Andri; Bales, Benjamin B.; Alkire, Richard C.; Petzold, Linda R.
2014-01-01
We present an exact and efficient algorithm for reaction-diffusion-nucleation processes on a 2D-lattice. The algorithm makes use of first passage time (FPT) to replace the computationally intensive simulation of diffusion hops in KMC by larger jumps when particles are far away from step-edges or other particles. Our approach computes exact probability distributions of jump times and target locations in a closed-form formula, based on the eigenvectors and eigenvalues of the corresponding 1D transition matrix, maintaining atomic-scale resolution of resulting shapes of deposit islands. We have applied our method to three different test cases of electrodeposition: pure diffusional aggregation for large ranges of diffusivity rates and for simulation domain sizes of up to 4096×4096 sites, the effect of diffusivity on island shapes and sizes in combination with a KMC edge diffusion, and the calculation of an exclusion zone in front of a step-edge, confirming statistical equivalence to standard KMC simulations. The algorithm achieves significant speedup compared to standard KMC for cases where particles diffuse over long distances before nucleating with other particles or being captured by larger islands.
An exact and efficient first passage time algorithm for reaction–diffusion processes on a 2D-lattice
Bezzola, Andri; Bales, Benjamin B.; Alkire, Richard C.; Petzold, Linda R.
2014-01-01
We present an exact and efficient algorithm for reaction–diffusion–nucleation processes on a 2D-lattice. The algorithm makes use of first passage time (FPT) to replace the computationally intensive simulation of diffusion hops in KMC by larger jumps when particles are far away from step-edges or other particles. Our approach computes exact probability distributions of jump times and target locations in a closed-form formula, based on the eigenvectors and eigenvalues of the corresponding 1D transition matrix, maintaining atomic-scale resolution of resulting shapes of deposit islands. We have applied our method to three different test cases of electrodeposition: pure diffusional aggregation for large ranges of diffusivity rates and for simulation domain sizes of up to 4096×4096 sites, the effect of diffusivity on island shapes and sizes in combination with a KMC edge diffusion, and the calculation of an exclusion zone in front of a step-edge, confirming statistical equivalence to standard KMC simulations. The algorithm achieves significant speedup compared to standard KMC for cases where particles diffuse over long distances before nucleating with other particles or being captured by larger islands.
NASA Astrophysics Data System (ADS)
Shimokawa, Tokuro; Watanabe, Ken; Kawamura, Hikaru
2015-10-01
Inspired by the recent theoretical suggestion that the random-bond S =1 /2 antiferromagnetic Heisenberg model on the triangular and the kagome lattices might exhibit a randomness-induced quantum spin liquid (QSL) behavior when the strength of the randomness exceeds a critical value, and that this "random-singlet state" might be relevant to the QSL behaviors experimentally observed in triangular organic salts κ -(ET) 2Cu2(CN) 3 and EtMe3Sb [Pd(dmit)2] 2 and in kagome herbertsmithite ZnCu3(OH) 6Cl2 , we further investigate the nature of the static and the dynamical spin correlations of these models. We compute the static and the dynamical spin structure factors, S (q ) and S (q ,ω ) , by means of an exact diagonalization method. In both triangular and kagome models, the computed S (q ,ω ) in the random-singlet state depends on the wave vector q only weakly, robustly exhibiting gapless behaviors accompanied by the broad distribution extending to higher energy ω . Especially in the strongly random kagome model, S (q ,ω ) hardly depends on q , and exhibits an almost flat distribution for a wide range of ω , together with a ω =0 peak. These features agree semiquantitatively with the recent neutron-scattering data on a single-crystal herbertsmithite. Furthermore, the computed magnetization curve agrees almost quantitatively with the experimental one recently measured on a single-crystal herbertsmithite. These results suggest that the QSL state observed in herbertsmithite might indeed be the randomness-induced QSL state, i.e., the random-singlet state.
Kumar, Sant Maitra, Tulika; Singh, Ishwar; Yadav, Umesh K.
2015-06-24
Ground state magnetic properties are studied by incorporating the super-exchange interaction (J{sub se}) in the spin-dependent Falicov-Kimball model (FKM) between localized (f-) electrons on a triangular lattice for half filled case. Numerical diagonalization and Monte-Carlo simulation are used to study the ground state magnetic properties. We have found that the magnetic moment of (d-) and (f-) electrons strongly depend on the value of Hund’s exchange (J), super-exchange interaction (J{sub se}) and also depends on the number of (d-) electrons (N{sub d}). The ground state changes from antiferromagnetic (AFM) to ferromagnetic (FM) state as we decrease (N{sub d}). Also the density of d electrons at each site depends on the value of J and J{sub se}.
NASA Astrophysics Data System (ADS)
Shimizu, Yasuhiro; Hiramatsu, Takaaki; Maesato, Mitsuhiko; Otsuka, Akihiro; Yamochi, Hideki; Ono, Akihiro; Itoh, Masayuki; Yoshida, Makoto; Takigawa, Masashi; Yoshida, Yukihiro; Saito, Gunzi
2016-09-01
The effects of pressure on a quantum spin liquid are investigated in an organic Mott insulator κ -(ET )2Ag2 (CN )3 with a spin-1 /2 triangular lattice. The application of negative chemical pressure to κ -(ET )2Cu2 (CN )3 , which is a well-known sister Mott insulator, allows for extensive tuning of antiferromagnetic exchange coupling, with J /kB=175 - 310 K , under hydrostatic pressure. Based on 13C nuclear magnetic resonance measurements under pressure, we uncover universal scaling in the static and dynamic spin susceptibilities down to low temperatures ˜0.1 kBT /J . The persistent fluctuations and residual specific heat coefficient are consistent with the presence of gapless low-lying excitations. Our results thus demonstrate the fundamental finite-temperature properties of a quantum spin liquid in a wide parameter range.
Shimizu, Yasuhiro; Hiramatsu, Takaaki; Maesato, Mitsuhiko; Otsuka, Akihiro; Yamochi, Hideki; Ono, Akihiro; Itoh, Masayuki; Yoshida, Makoto; Takigawa, Masashi; Yoshida, Yukihiro; Saito, Gunzi
2016-09-01
The effects of pressure on a quantum spin liquid are investigated in an organic Mott insulator κ-(ET)_{2}Ag_{2}(CN)_{3} with a spin-1/2 triangular lattice. The application of negative chemical pressure to κ-(ET)_{2}Cu_{2}(CN)_{3}, which is a well-known sister Mott insulator, allows for extensive tuning of antiferromagnetic exchange coupling, with J/k_{B}=175-310 K, under hydrostatic pressure. Based on ^{13}C nuclear magnetic resonance measurements under pressure, we uncover universal scaling in the static and dynamic spin susceptibilities down to low temperatures ∼0.1k_{B}T/J. The persistent fluctuations and residual specific heat coefficient are consistent with the presence of gapless low-lying excitations. Our results thus demonstrate the fundamental finite-temperature properties of a quantum spin liquid in a wide parameter range. PMID:27636491
NASA Astrophysics Data System (ADS)
Ito, Hiroshi; Asai, Takayuki; Shimizu, Yasuhiro; Hayama, Hiromi; Yoshida, Yukihiro; Saito, Gunzi
2016-07-01
We report an antiferromagnetic (AF) ordering at ambient pressure and a superconducting transition under pressure for κ - (ET) 2C F3S O3 [ ET =bis (ethylenedithio)tetrathiafulvalene], which has a two-dimensional electronic system with quasi-one-dimensional triangular spin lattice. At ambient pressure, AF ordering was detected at TN=2.5 K by 1H NMR, subsequent to two structural phase transitions at 230 and 190 K. Under hydrostatic pressures, metallic behavior appeared above ˜1.1 GPa, and a superconducting transition (maximum onset Tc=4.8 K at ˜1.3 GPa) was observed up to 2.2 GPa. Superconductivity was also found under c -axis strain, which reduced t'/t , but was absent under b -axis strain which increased t'/t .
NASA Astrophysics Data System (ADS)
Bouchiat, Marie-Anne; Bouchiat, Claude
2012-10-01
lattice from the dressed atom instability. The geometric field B3(r) is computed analytically in terms of the Euler angles. The magnitude of the second-order corrections due to the transverse fields can be reduced to the per cent level by a choice of light intensity that keeps the dressed atom loss rate ⩽5 s-1. A second optical lattice can be designed to confine the atoms inside 2D domains where {\\mathbf {B}}_3({\\mathbf {r}})\\,{\\bm\\cdot}\\, \\hat{z}\\ge 0. We extend our analysis to the case of a triangular lattice.
Yang, Ming; Zhang, Su-Yun; Guo, Wen-Bin; Tang, Ying-Ying; He, Zhang-Zhen
2015-09-21
A novel copper compound, Cu13(VO4)4(OH)10F4, featuring two types of two-dimensional extended kagome-like and triangular lattices, exhibits long-range antiferromagnetic ordering at ∼3 K, a strong spin-frustration effect with f = 21 and a spin-flop transition at 5 T.
Static magnetic order on the metallic triangular lattice in CrSe2 detected by μ <>SR
NASA Astrophysics Data System (ADS)
Sugiyama, Jun; Nozaki, Hiroshi; Umegaki, Izumi; Uyama, Takeshi; Miwa, Kazutoshi; Brewer, Jess H.; Kobayashi, Shintaro; Michioka, Chishiro; Ueda, Hiroaki; Yoshimura, Kazuyoshi
2016-07-01
The magnetic nature of a metallic two-dimensional triangular compound, CrSe2, has been investigated by muon spin rotation and relaxation (μ <>SR ) measurements using both powder and single crystal samples. It is found that CrSe2 enters into a static antiferromagnetic (AF) ordered state below 157 K (=TN ). Furthermore, the AF state is slightly changed below around 20 K (=TN 2 ). Based on the analysis of the internal magnetic fields at the muon sites predicted with DFT calculations, collinear AF and helical 120° AF are clearly eliminated for the ground state of CrSe2. The most probable one is an incommensurate spin density wave order.
Antiferromagnetism in 2D arrays of superconducting rings
NASA Astrophysics Data System (ADS)
Davidović, D.; Kumar, S.; Reich, D. H.; Siegel, J.; Field, S. B.; Tiberio, R. C.; Hey, R.; Ploog, K.
1996-03-01
An array of isolated superconducting rings at Φ_0/2 applied flux is equivalent to a 2D random field Ising antiferromagnet. The quantized magnetic moments of the rings play the role of Ising spins, and small variations in the rings' areas lead to a Gaussian random field. Using SQUID magnetometry and scanning Hall probe microscopy, we studied the dynamics and antiferromagnetic correlations of arrays of micron-size Al rings, arranged on square, honeycomb, triangular, and kagomé lattices. All the arrays exhibit short range antiferromagnetic order. Spin freezing at low temperatures and the random field prevent the development of long range correlations on bipartite lattices. Effects of geometrical frustration on the triangular and kagomé lattices were also observed.
Magnetic excitations in the spin-1/2 triangular-lattice antiferromagnet Cs_{2}CuBr_{4}
Zvyagin, S. A.; Ozerov, M.; Kamenskyi, D.; Wosnitza, J.; Krzystek, J.; Yoshizawa, D.; Hagiwara, M.; Hu, Rongwei; Ryu, Hyejin; Petrovic, C.; Zhitomirsky, M. E.
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_{2}CuBr_{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_{2}CuBr_{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 below T_{N} the high-energy spin dynamics in Cs_{2}CuBr_{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.
Liu, Meifeng; Zhang, Huimin; Huang, Xin; Ma, Chunyang; Dong, Shuai; Liu, Jun-Ming
2016-03-21
We report the low-temperature characterizations on structural, specific heat, magnetic, and ferroelectric behaviors of transition metal oxide compound Sr3NiTa2O9. It is suggested that Sr3NiTa2O9 is a spin-1 triangular lattice Heisenberg quantum antiferromagnet which may have weak easy-axis anisotropy. At zero magnetic field, a two-step transition sequence at T(N1) = 3.35 K and T(N2) = 2.74 K, respectively, is observed, corresponding to the up-up-down (uud) spin ordering and 120° spin ordering, respectively. The two transition points shift gradually with increasing magnetic field toward the low temperature, accompanying an evolution from the 120° spin structure (phase) to the normal oblique phases. Ferroelectricity in the 120° phase is clearly identified. The first-principles calculations confirm the 120° phase as the ground state whose ferroelectricity originates mainly from the electronic polarization. PMID:26934503
NASA Astrophysics Data System (ADS)
Wu, Jian; Werner, Fletcher; Wildeboer, Julia S.; Seidel, Alexander; Nussinov, Zohar; Solin, S. A.
2011-03-01
We discuss the magnetic properties of a class of spin S = 1 / 2 antiferromagnetic quasi-triangular lattice materials, both in the clean limit and in the presence of non-magnetic Zn impurities. These systems are long organic chain intercalated derivatives of copper hydroxy nitrate, with a very large c-axis separation of 24Å. In these compounds, we find that a spin glass phase is universally preceded by two different power law regimes in the temperature dependence of the DC magnetic susceptibility, separated by a sharp crossover. This is seen both in the presence as well as in the absence of non-magnetic Zn impurities, where the power law exponents are surprisingly unperturbed by the compositional disorder. We argue that these findings may be consistent with a picture based on a self-generated spin glass in the clean undoped compound, where frustration is the driving mechanism of the glassiness rather than disorder. While AC measurements and time dependent magnetization follow traditional spin glass paradigms, the power law structure found in the DC susceptibility is argued to deviate in various ways from scenarios expected based on Griffiths type physics, and may call for new explanations.
NASA Astrophysics Data System (ADS)
Murray, Benjamin; Salzmann, Christoph; Heymsfield, Andrew; Neely, Ryan
2014-05-01
We are all familiar with the hexagonal form of snow crystals and it is well established that this shape is derived from the arrangement of water molecules in the crystal lattice. However, crystals with a triangular form are often found in the Earth's atmosphere and the reason for this non-hexagonal shape has remained elusive. Recent laboratory work has shed light on why ice crystals should take on this triangular or three-fold scalene habit. Studies of the crystal structure of ice have shown that ice which initially crystallises can be made of up of hexagonal layers which are interlaced with cubic layers to produce a 'stacking disordered ice'. The degree of stacking disorder can vary from crystals which are dominantly hexagonal with a few cubic stacking faults, through to ice where the cubic and hexagonal sequences are fully randomised. The introduction of stacking disorder to ice crystals reduces the symmetry of the crystal from 6-fold (hexagonal) to 3-fold (triangular); this offers an explanation for the long standing problem of why some atmospheric ice crystals have a triangular habit. We discuss the implications of triangular crystals for halos, radiative properties, and also discuss the implications for our understanding of the nucleation and early stages of ice crystal growth for ice crystals in the atmosphere.
NASA Astrophysics Data System (ADS)
Amaya-Ventura, Gilberto; Rodríguez-Romo, Suemi
2011-09-01
This paper deals with the computational simulation of the reaction-diffusion-advection phenomena emerging in Rayleigh-Bénard (RB) and Poiseuille-Bénard reactive convection systems. We use the Boussinesq's approximation for buoyancy forces and the Lattice Boltzmann method (LBM). The first kinetic mesoscopic model proposed here is based on the discrete Boltzmann equation needed to solve the momentum balance coupled with buoyancy forces. Then, a second lattice Boltzmann algorithm is applied to solve the reaction-diffusion-advection equation to calculate the evolution of the chemical species concentration. We use a reactive system composed by nitrous oxide (so call laughing gas) in air as an example; its spatio-temporal decomposition is calculated. Two cases are considered, a rectangular enclosed cavity and an open channel. The simulations are performed at low Reynolds numbers and in a steady state between the first and second thermo-hydrodynamic instabilities. The results presented here, for the thermo-hydrodynamic behavior, are in good agreement with experimental data; while our| chemical kinetics simulation yields expected results. Some applications of our approach are related to chemical reactors and atmospheric phenomena, among others.
NASA Astrophysics Data System (ADS)
Yang, PeiPei; Wen, Zhi; Dou, RuiFeng; Liu, Xunliang
2016-08-01
Flow and heat transfer through a 2D random porous medium are studied by using the lattice Boltzmann method (LBM). For the random porous medium, the influence of disordered cylinder arrangement on permeability and Nusselt number are investigated. Results indicate that the permeability and Nusselt number for different cylinder locations are unequal even with the same number and size of cylinders. New correlations for the permeability and coefficient b‧Den of the Forchheimer equation are proposed for random porous medium composed of Gaussian distributed circular cylinders. Furthermore, a general set of heat transfer correlations is proposed and compared with existing experimental data and empirical correlations. Our results show that the Nu number increases with the increase of the porosity, hence heat transfer is found to be accurate considering the effect of porosity.
Xu, Zhenfeng; Wang, Jiangang; He, Qingsheng; Cao, Liangcai; Su, Ping; Jin, Guofan
2005-07-25
A coupler-type optical filter in 2D photonic crystal (PhC) with square lattice of dielectric rods in air is presented. The reduced-index and increased-index waveguides of filter have dispersion curves with opposite slopes to realize contra-directional coupling, and the point of anti-crossing is designed below the light line to avoid vertical radiation. The filter has a broad operable bandwidth due to the absence of mini stop bands. The transmission properties are analyzed using coupled modes theory (CMT) and simulated using the finite-difference time-domain (FDTD) method. The results show that a filtering bandwidth of 4 nm can be achieved in the range of 1500~1600 nm, and over 83% drop coefficient is obtained.
Neutron Scattering Studies of the S=1/2 Triangular Lattice Magnets NaNiO2 and LiNiO2
NASA Astrophysics Data System (ADS)
Clancy, J. Patrick
2011-03-01
NaNi O2 and LiNi O2 are isostructural quantum magnets based on a stacked triangular lattice in which magnetism arises from S=1/2 magnetic moments carried by Ni 3+ ions. Surprisingly, while these compounds are structurally and electronically very similar, the magnetic properties they exhibit are dramatically different. NaNi O2 undergoes a cooperative Jahn-Teller phase transition at 480K and magnetically orders below TN ~ 23 K, adopting a structure which consists of ferromagnetic sheets of S=1/2 moments stacked in an antiferromagnetic fashion. In contrast, LiNi O2 undergoes a spin glass transition at Tg ~ 9 K and remains disordered down to the lowest measured temperatures. Understanding the absence of long-range magnetic order in LiNi O2 is a problem which has attracted considerable interest for more than twenty five years. Among many potential explanations, the answer has most notably been attributed to geometric frustration caused by inherent mixing of the Li and Ni sublattices, or orbital degeneracy resulting from the lack of a coherent Jahn-Teller distortion. In this talk I will describe time-of-flight neutron scattering measurements performed on polycrystalline samples of NaNi O2 and LiNi O2 using the wide Angular-Range Chopper Spectrometer (ARCS) at ORNL and the Disk Chopper Spectrometer (DCS) at NIST. These measurements provide a thorough characterization of the excitation spectra for these two compounds, probing the inelastic scattering over energy scales ranging from ~ 0.1 meV to 1.5 eV. In NaNi O2 , our measurements reveal two sets of well-defined spin excitations, which we associate with ferromagnetic spin waves mediated by in-plane interactions and antiferromagnetic spin waves mediated by out-of-plane interactions. In LiNi O2 , we observe similar, albeit much broader, excitations consistent with short-range two-dimensional magnetic correlations. In the case of NaNi O2 , we have developed a simple linear spin wave theory model to describe these excitations
Two Spin Liquid phases in the anisotropic triangular Heisenberg model
NASA Astrophysics Data System (ADS)
Sorella, Sandro
2005-03-01
Recently there have been rather clean experimental realizations of the quantum spin 1/2 Heisenberg Hamiltonian on a 2D triangular lattice geometry in systems like Cs2Cu Cl4 and organic compounds like k-(ET)2Cu2(CN)3. These materials are nearly two dimensional and are characterized by an anisotropic antiferromagnetic superexchange. The strength of the spatial anisotropy can increase quantum fluctuations and can destabilize the magnetically ordered state leading to non conventional spin liquid phases. In order to understand these interesting phenomena we have studied, by Quantum Monte Carlo methods, the triangular lattice Heisenberg model as a function of the strength of this anisotropy, represented by the ratio r between the intra-chain nearest neighbor coupling J' and the inter-chain one J. We have found evidence of two spin liquid regions, well represented by projected BCS wave functions[1,2] of the type proposed by P. W. Anderson at the early stages of High temperature superconductivity [3]. The first spin liquid phase is stable for small values of the coupling r 0.6 and appears gapless and fractionalized, whereas the second one is a more conventional spin liquid, very similar to the one realized in the quantum dimer model in the triangular lattice[4]. It is characterized by a spin gap and a finite correlation length, and appears energetically favored in the region 0.6 r 0.9. The various phases are in good agreement with the experimental findings and supports the existence of spin liquid phases in 2D quantum spin-half systems. %%%%%%%%%%%%%%%%%% 1cm *[1] L. Capriotti F. Becca A. Parola and S. Sorella , Phys. Rev. Letters 87, 097201 (2001). *[2] S. Yunoki and S. Sorella Phys. Rev. Letters 92, 15003 (2004). *[3] P. W. Anderson, Science 235, 1186 (1987). *[4] P. Fendley, R. Moessner, and S. L. Sondhi Phys. Rev. B 66, 214513 (2002).
Kobayashi, Shintaro; Ueda, Hiroaki; Michioka, Chishiro; Yoshimura, Kazuyoshi
2016-08-01
Physical properties of new S = 3/2 triangular-lattice compounds LiCrSe2, LiCrTe2, and NaCrTe2 have been investigated by X-ray diffraction and magnetic measurements. These compounds crystallize in the ordered NiAs-type structure, where alkali metal ions and Cr atoms stack alternately. Despite their isomorphic structures, magnetic properties of these three compounds are different; NaCrTe2 has an A-type spin structure with ferromagnetic layers, LiCrTe2 is likely to exhibit a helical spin structure, and LiCrSe2 shows a first-order-like phase transition from the paramagnetic trigonal phase to the antiferromagnetic monoclinic phase. In these compounds and the other chromium chalcogenides with a triangular lattice, we found a general relationship between the Curie-Weiss temperature and magnetic structures. This relation indicates that the competition between the antiferromagnetic direct d-d exchange interaction and the ferromagnetic superexchange interaction plays an important role in determining the ground state of chromium chalcogenides. PMID:27400024
NASA Astrophysics Data System (ADS)
Chetverikov, A. P.; Ebeling, W.; Velarde, M. G.
2016-09-01
We present computational evidence of the possibility of fast, supersonic or subsonic, nearly loss-free ballistic-like transport of electrons bound to lattice solitons (a form of electron surfing on acoustic waves) along crystallographic axes in two-dimensional anharmonic crystal lattices. First we study the structural changes a soliton creates in the lattice and the time lapse of recovery of the lattice. Then we study the behavior of one electron in the polarization field of one and two solitons with crossing pathways with suitably monitored delay. We show how an electron surfing on a lattice soliton may switch to surf on the second soliton and hence changing accordingly the direction of its path. Finally we discuss the possibility to control the way an excess electron proceeds from a source at a border of the lattice to a selected drain at another border by following appropriate straight pathways on crystallographic axes.
Dea-Ayuela, María Auxiliadora; Pérez-Castillo, Yunierkis; Meneses-Marcel, Alfredo; Ubeira, Florencio M; Bolas-Fernández, Francisco; Chou, Kuo-Chen; González-Díaz, Humberto
2008-08-15
The toxicity and inefficacy of actual organic drugs against Leishmaniosis justify research projects to find new molecular targets in Leishmania species including Leishmania infantum (L. infantum) and Leishmaniamajor (L. major), both important pathogens. In this sense, quantitative structure-activity relationship (QSAR) methods, which are very useful in Bioorganic and Medicinal Chemistry to discover small-sized drugs, may help to identify not only new drugs but also new drug targets, if we apply them to proteins. Dyneins are important proteins of these parasites governing fundamental processes such as cilia and flagella motion, nuclear migration, organization of the mitotic splinde, and chromosome separation during mitosis. However, despite the interest for them as potential drug targets, so far there has been no report whatsoever on dyneins with QSAR techniques. To the best of our knowledge, we report here the first QSAR for dynein proteins. We used as input the Spectral Moments of a Markov matrix associated to the HP-Lattice Network of the protein sequence. The data contain 411 protein sequences of different species selected by ClustalX to develop a QSAR that correctly discriminates on average between 92.75% and 92.51% of dyneins and other proteins in four different train and cross-validation datasets. We also report a combined experimental and theoretic study of a new dynein sequence in order to illustrate the utility of the model to search for potential drug targets with a practical example. First, we carried out a 2D-electrophoresis analysis of L. infantum biological samples. Next, we excised from 2D-E gels one spot of interest belonging to an unknown protein or protein fragment in the region M<20,200 and pI<4. We used MASCOT search engine to find proteins in the L. major data base with the highest similarity score to the MS of the protein isolated from L. infantum. We used the QSAR model to predict the new sequence as dynein with probability of 99.99% without
NASA Astrophysics Data System (ADS)
Kumar, Ajit; Verma, Sanjay K.; Alvi, P. A.; Jasrotia, Dinesh
2016-04-01
The nanospatial morphological features of [ZnCl]- [C5H4NCH3]+ hybrid derivative depicts 28 nm granular size and 3D spreader shape packing pattern as analyzed by FESEM and single crystal XRD structural studies. The organic moiety connect the inorganic components through N-H+…Cl- hydrogen bond to form a hybrid composite, the replacement of organic derivatives from 2-methylpyridine to 2-Amino-5-choloropyridine results the increase in granular size from 28nm to 60nm and unit cell packing pattern from 3D-2D lattice dimensionality along ac plane. The change in optical energy direct band gap value from 3.01eV for [ZnCl]- [C5H4NCH3]+ (HM1) to 3.42eV for [ZnCl]- [C5H5ClN2]+ (HM2) indicates the role of organic moiety in optical properties of hybrid materials. The photoluminescence emission spectra is observed in the wavelength range of 370 to 600 nm with maximum peak intensity of 9.66a.u. at 438 nm for (HM1) and 370 to 600 nm with max peak intensity of 9.91 a.u. at 442 nm for (HM2), indicating that the emission spectra lies in visible range. PL excitation spectra depicts the maximum excitation intensity [9.8] at 245.5 nm for (HM1) and its value of 9.9 a.u. at 294 nm, specify the excitation spectra lies in UV range. Photoluminescence excitation spectra is observed in the wavelength range of 280 to 350 nm with maximum peak intensity of 9.4 a.u. at 285.5 nm and 9.9 a.u. at 294 and 297 nm, indicating excitation in the UV spectrum. Single crystal growth process and detailed physiochemical characterization such as XRD, FESEM image analysis photoluminescence property reveals the structure stability with non-covalent interactions, lattice dimensionality (3D-2D) correlations interweaving into the design of inorganic-organic hybrid materials.
Continuum Nonsimple Loops and 2D Critical Percolation
NASA Astrophysics Data System (ADS)
Camia, Federico; Newman, Charles M.
2004-08-01
Substantial progress has been made in recent years on the 2D critical percolation scaling limit and its conformal invariance properties. In particular, chordal SLE 6(the Stochastic Loewner Evolution with parameter κ=6) was, in the work of Schramm and of Smirnov, identified as the scaling limit of the critical percolation "exploration process." In this paper we use that and other results to construct what we argue is the fullscaling limit of the collection of allclosed contours surrounding the critical percolation clusters on the 2D triangular lattice. This random process or gas of continuum nonsimple loops in Bbb R2is constructed inductively by repeated use of chordal SLE 6. These loops do not cross but do touch each other—indeed, any two loops are connected by a finite "path" of touching loops.
Murtazaev, A. K.; Ramazanov, M. K. Badiev, V. K.
2012-08-15
The critical behavior of the three-dimensional antiferromagnetic Heisenberg model with nearest-neighbor (J) and next-to-nearest-neighbor (J{sub 1}) interactions is studied by the replica Monte Carlo method. The first-order phase transition and pseudouniversal critical behavior of this model are established for a small lattice in the interval R = vertical bar J{sub 1}/J vertical bar = 0-0.115. A complete set of the main static magnetic and chiral critical indices is calculated in this interval using the finite-dimensional scaling theory.
NASA Astrophysics Data System (ADS)
Yamamoto, Takashi; Tamura, Masafumi; Yakushi, Kyuya; Kato, Reizo
2016-10-01
We have carried out the complete analyses of the C=C stretching modes in the vibrational spectra in the triangular lattice of β'-Cs[Pd(dmit)2]2 in order to solve the puzzling phenomenon that the ground state is neither spin frustration nor anti-ferromagnetic state but octamerization. We found that both charge-rich and charge-poor dimers are non-centrosymmetric dimers with the inhomogeneous charges. Because the energy levels of HOMO and LUMO are interchanged due to the tight dimerization, the cooperative interaction between the inter-site Coulomb repulsions and the valence-bond formation operates within and between dimers, those which contribute to the inter-dimer and intra-dimer charge separations, respectively. Octamer is the minimal unit under both cooperative interactions. In the high-temperature phase of β'-Cs[Pd(dmit)2]2, the competition between octamerization and tetramerization is observed because of the suppression of the intra-dimer cooperative interaction. The competition between two different states indicates the degree of freedom characteristic of the molecular orbital due to the tight dimerization. The cooperative interactions of the various X[Pd(dmit)2]2 salts are quantitatively evaluated from the C=C stretching modes.
NASA Astrophysics Data System (ADS)
Dey, K.; Karmakar, A.; Majumdar, S.; Giri, S.
2013-03-01
This work reports an experimental study on the temperature dependence of the structural parameters of LiCrO2 (LCO) and Li0.99Cu0.01CrO2 (LCCO) by using a synchrotron x-ray diffraction technique. A significant magnetoelastic coupling is revealed by the anomalies observed in lattice parameters at the magnetic and electric phase transitions, apparent as steplike features in both Cr-O and Li-O bond lengths, as well as in O-Cr-O bond angles. Magnetic, dielectric, and electric polarization measurements reveal the antiferromagnetic and antiferroelectric (AFE) ordering at 119 and 61 K, respectively, for LCCO. Interestingly, a fairly large uncompensated spontaneous electric polarization appears for LCCO in contrast to nearly compensated polarization value for LCO below the AFE ordering. This is correlated to the structurally driven enhancement (˜4 times) of the interlayer Cr-O-Li/Cu-O-Cr superexchange interaction for LCCO. We argue that strong magnetoelastic coupling holds the key for the observed uncompensated spontaneous electric polarization in LCCO.
Lee, M.; Choi, E. S.; Huang, X.; Ma, J.; Dela Cruz, C. R.; Matsuda, M.; Tian, W.; Dun, Z. L.; Dong, S.; Zhou, H. D.
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_{3}MnNb_{2} O_{9}. All results suggest that Ba_{3}MnNb_{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 into 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.
Takagawa, Yousuke; Ogawa, Shinpei; Kimata, Masafumi
2015-01-01
Wavelength-selective uncooled infrared (IR) sensors are highly promising for a wide range of applications, such as fire detection, gas analysis and biomedical analysis. We have recently developed wavelength-selective uncooled IR sensors using square lattice two-dimensional plasmonic absorbers (2-D PLAs). The PLAs consist of a periodic 2-D lattice of Au-based dimples, which allow photons to be manipulated using surface plasmon modes. In the present study, a detailed investigation into control of the detection wavelength was conducted by varying the PLA lattice structure. A comparison was made between wavelength-selective uncooled IR sensors with triangular and square PLA lattices that were fabricated using complementary metal oxide semiconductor and micromachining techniques. Selective enhancement of the responsivity could be achieved, and the detection wavelength for the triangular lattice was shorter than that for the square lattice. The results indicate that the detection wavelength is determined by the reciprocal-lattice vector for the PLAs. The ability to control the detection wavelength in this manner enables the application of such PLAs to many types of thermal IR sensors. The results obtained here represent an important step towards multi-color imaging in the IR region. PMID:26067198
Takagawa, Yousuke; Ogawa, Shinpei; Kimata, Masafumi
2015-06-10
Wavelength-selective uncooled infrared (IR) sensors are highly promising for a wide range of applications, such as fire detection, gas analysis and biomedical analysis. We have recently developed wavelength-selective uncooled IR sensors using square lattice two-dimensional plasmonic absorbers (2-D PLAs). The PLAs consist of a periodic 2-D lattice of Au-based dimples, which allow photons to be manipulated using surface plasmon modes. In the present study, a detailed investigation into control of the detection wavelength was conducted by varying the PLA lattice structure. A comparison was made between wavelength-selective uncooled IR sensors with triangular and square PLA lattices that were fabricated using complementary metal oxide semiconductor and micromachining techniques. Selective enhancement of the responsivity could be achieved, and the detection wavelength for the triangular lattice was shorter than that for the square lattice. The results indicate that the detection wavelength is determined by the reciprocal-lattice vector for the PLAs. The ability to control the detection wavelength in this manner enables the application of such PLAs to many types of thermal IR sensors. The results obtained here represent an important step towards multi-color imaging in the IR region.
Gao, Song; Fan, Rui Qing; Wang, Xin Ming; Wei, Li Guo; Song, Yang; Du, Xi; Xing, Kai; Wang, Ping; Yang, Yu Lin
2016-07-28
In this work, a rare 2D → 3D single-crystal-to-single-crystal transformation (SCSC) is observed in metal-organic coordination complexes, which is triggered by thermal treatment. The 2D two-fold interpenetrating square lattice layer [Cd(IBA)2]n (1) is irreversibly converted into a 3D four-fold interpenetrating diamond framework {[Cd(IBA)2(H2O)]·2.5H2O}n (2) (HIBA = 4-(1H-imidazol-1-yl)benzoic acid). Consideration is given to these two complexes with different interpenetrating structures and dimensionality, and their influence on photovoltaic properties are studied. Encouraged by the UV-visible absorption and HOMO-LUMO energy states matched for sensitizing TiO2, the two complexes are employed in combination with N719 in dye-sensitized solar cells (DSSCs) to compensate absorption in the ultraviolet and blue-violet region, offset competitive visible light absorption of I3(-) and reducing charge the recombination of injected electrons. After co-sensitization with 1 and 2, the device co-sensitized by 1/N719 and 2/N719 to yield overall efficiencies of 7.82% and 8.39%, which are 19.94% and 28.68% higher than that of the device sensitized only by N719 (6.52%). Consequently, high dimensional interpenetrating complexes could serve as excellent co-sensitizers and have application in DSSCs. PMID:27356177
Gao, Song; Fan, Rui Qing; Wang, Xin Ming; Wei, Li Guo; Song, Yang; Du, Xi; Xing, Kai; Wang, Ping; Yang, Yu Lin
2016-07-28
In this work, a rare 2D → 3D single-crystal-to-single-crystal transformation (SCSC) is observed in metal-organic coordination complexes, which is triggered by thermal treatment. The 2D two-fold interpenetrating square lattice layer [Cd(IBA)2]n (1) is irreversibly converted into a 3D four-fold interpenetrating diamond framework {[Cd(IBA)2(H2O)]·2.5H2O}n (2) (HIBA = 4-(1H-imidazol-1-yl)benzoic acid). Consideration is given to these two complexes with different interpenetrating structures and dimensionality, and their influence on photovoltaic properties are studied. Encouraged by the UV-visible absorption and HOMO-LUMO energy states matched for sensitizing TiO2, the two complexes are employed in combination with N719 in dye-sensitized solar cells (DSSCs) to compensate absorption in the ultraviolet and blue-violet region, offset competitive visible light absorption of I3(-) and reducing charge the recombination of injected electrons. After co-sensitization with 1 and 2, the device co-sensitized by 1/N719 and 2/N719 to yield overall efficiencies of 7.82% and 8.39%, which are 19.94% and 28.68% higher than that of the device sensitized only by N719 (6.52%). Consequently, high dimensional interpenetrating complexes could serve as excellent co-sensitizers and have application in DSSCs.
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.
2-d Finite Element Code Postprocessor
1996-07-15
ORION is an interactive program that serves as a postprocessor for the analysis programs NIKE2D, DYNA2D, TOPAZ2D, and CHEMICAL TOPAZ2D. ORION reads binary plot files generated by the two-dimensional finite element codes currently used by the Methods Development Group at LLNL. Contour and color fringe plots of a large number of quantities may be displayed on meshes consisting of triangular and quadrilateral elements. ORION can compute strain measures, interface pressures along slide lines, reaction forcesmore » along constrained boundaries, and momentum. ORION has been applied to study the response of two-dimensional solids and structures undergoing finite deformations under a wide variety of large deformation transient dynamic and static problems and heat transfer analyses.« less
Sharma, Subash; Kalita, Golap; Vishwakarma, Riteshkumar; Zulkifli, Zurita; Tanemura, Masaki
2015-01-01
In-plane heterostructure of monolayer hexagonal boron nitride (h-BN) and graphene is of great interest for its tunable bandgap and other unique properties. Here, we reveal a H2-induced etching process to introduce triangular hole in triangular-shaped chemical vapor deposited individual h-BN crystal. In this study, we synthesized regular triangular-shaped h-BN crystals with the sizes around 2-10 μm on Cu foil by chemical vapor deposition (CVD). The etching behavior of individual h-BN crystal was investigated by annealing at different temperature in an H2:Ar atmosphere. Annealing at 900 °C, etching of h-BN was observed from crystal edges with no visible etching at the center of individual crystals. While, annealing at a temperature ≥950 °C, highly anisotropic etching was observed, where the etched areas were equilateral triangle-shaped with same orientation as that of original h-BN crystal. The etching process and well-defined triangular hole formation can be significant platform to fabricate planar heterostructure with graphene or other two-dimensional (2D) materials. PMID:25994455
Adaptive triangular mesh generation
NASA Technical Reports Server (NTRS)
Erlebacher, G.; Eiseman, P. R.
1984-01-01
A general adaptive grid algorithm is developed on triangular grids. The adaptivity is provided by a combination of node addition, dynamic node connectivity and a simple node movement strategy. While the local restructuring process and the node addition mechanism take place in the physical plane, the nodes are displaced on a monitor surface, constructed from the salient features of the physical problem. An approximation to mean curvature detects changes in the direction of the monitor surface, and provides the pulling force on the nodes. Solutions to the axisymmetric Grad-Shafranov equation demonstrate the capturing, by triangles, of the plasma-vacuum interface in a free-boundary equilibrium configuration.
Yang, Li-Ming; Dornfeld, Matthew; Frauenheim, Thomas; Ganz, Eric
2015-10-21
We predict a highly stable and robust atomically thin gold monolayer with a hexagonal close packed lattice stabilized by metallic bonding with contributions from strong relativistic effects and aurophilic interactions. We have shown that the framework of the Au monolayer can survive 10 ps MD annealing simulations up to 1400 K. The framework is also able to survive large motions out of the plane. Due to the smaller number of bonds per atom in the 2D layer compared to the 3D bulk we observe significantly enhanced energy per bond (0.94 vs. 0.52 eV per bond). This is similar to the increase in bond strength going from 3D diamond to 2D graphene. It is a non-magnetic metal, and was found to be the global minima in the 2D space. Phonon dispersion calculations demonstrate high kinetic stability with no negative modes. This 2D gold monolayer corresponds to the top monolayer of the bulk Au(111) face-centered cubic lattice. The close-packed lattice maximizes the aurophilic interactions. We find that the electrons are completely delocalized in the plane and behave as 2D nearly free electron gas. We hope that the present work can inspire the experimental fabrication of novel free standing 2D metal systems.
NASA Astrophysics Data System (ADS)
Venderbos, J. W. F.
2016-03-01
In this work we introduce a symmetry classification for electronic density waves which break translational symmetry due to commensurate wave-vector modulations. The symmetry classification builds on the concept of extended point groups: symmetry groups which contain, in addition to the lattice point group, translations that do not map the enlarged unit cell of the density wave to itself, and become "nonsymmorphic"-like elements. Multidimensional representations of the extended point group are associated with degenerate wave vectors. Electronic properties such as (nodal) band degeneracies and topological character can be straightforwardly addressed, and often follow directly. To further flesh out the idea of symmetry, the classification is constructed so as to manifestly distinguish time-reversal invariant charge (i.e., site and bond) order, and time-reversal breaking flux order. For the purpose of this work, we particularize to spin-rotation invariant density waves. As a first example of the application of the classification we consider the density waves of a simple single- and two-orbital square lattice model. The main objective, however, is to apply the classification to two-dimensional (2D) hexagonal lattices, specifically the triangular and the honeycomb lattices. The multicomponent density waves corresponding to the commensurate M -point ordering vectors are worked out in detail. To show that our results generally apply to 2 D hexagonal lattices, we develop a general low-energy SU(3 ) theory of (spinless) saddle-point electrons.
Complete band gaps and deaf bands of triangular and honeycomb water-steel phononic crystals
NASA Astrophysics Data System (ADS)
Hsiao, Fu-Li; Khelif, Abdelkrim; Moubchir, Hanane; Choujaa, Abdelkrim; Chen, Chii-Chang; Laude, Vincent
2007-02-01
Phononic crystals with triangular and honeycomb lattices are investigated experimentally and theoretically. They are composed of arrays of steel cylinders immersed in water. The measured transmission spectra reveal the existence of complete band gaps but also of deaf bands. Band gaps and deaf bands are identified by comparing band structure computations, obtained by a periodic-boundary finite element method, with transmission simulations, obtained using the finite difference time domain method. The appearance of flat bands and the polarization of the associated eigenmodes is also discussed. Triangular and honeycomb phononic crystals with equal cylinder diameter and smallest spacing are compared. As previously obtained with air-solid phononic crystals, it is found that the first complete band gap opens for the honeycomb lattice but not for the triangular lattice, thanks to symmetry reduction.
NASA Astrophysics Data System (ADS)
Yan, Weigen; Zhang, Zuhe
2009-04-01
The energy of a simple graph G arising in chemical physics, denoted by E(G), is defined as the sum of the absolute values of eigenvalues of G. As the dimer problem and spanning trees problem in statistical physics, in this paper we propose the energy per vertex problem for lattice systems. In general for a type of lattice in statistical physics, to compute the entropy constant with toroidal, cylindrical, Mobius-band, Klein-bottle, and free boundary conditions are different tasks with different hardness and may have different solutions. We show that the energy per vertex of plane lattices is independent of the toroidal, cylindrical, Mobius-band, Klein-bottle, and free boundary conditions. In particular, the asymptotic formulae of energies of the triangular, 33.42, and hexagonal lattices with toroidal, cylindrical, Mobius-band, Klein-bottle, and free boundary conditions are obtained explicitly.
Dynamic optical lattices: two-dimensional rotating and accordion lattices for ultracold atoms.
Williams, R A; Pillet, J D; Al-Assam, S; Fletcher, B; Shotter, M; Foot, C J
2008-10-13
We demonstrate a novel experimental arrangement which can rotate a 2D optical lattice at frequencies up to several kilohertz. Ultracold atoms in such a rotating lattice can be used for the direct quantum simulation of strongly correlated systems under large effective magnetic fields, allowing investigation of phenomena such as the fractional quantum Hall effect. Our arrangement also allows the periodicity of a 2D optical lattice to be varied dynamically, producing a 2D accordion lattice.
2005-07-01
Aniso2d is a two-dimensional seismic forward modeling code. The earth is parameterized by an X-Z plane in which the seismic properties Can have monoclinic with x-z plane symmetry. The program uses a user define time-domain wavelet to produce synthetic seismograms anrwhere within the two-dimensional media.
NASA Astrophysics Data System (ADS)
Jang, Hyun-Sook; Yu, Changqian; Hayes, Robert; Granick, Steve
2015-03-01
Polymer vesicles (``polymersomes'') are an intriguing class of soft materials, commonly used to encapsulate small molecules or particles. Here we reveal they can also effectively incorporate nanoparticles inside their polymer membrane, leading to novel ``2D nanocomposites.'' The embedded nanoparticles alter the capacity of the polymersomes to bend and to stretch upon external stimuli.
Vortex lattice disorder in pseudorandom potential in rotating Bose-Einstein condensate
NASA Astrophysics Data System (ADS)
Mithun, T.; Porsezian, K.; Dey, Bishwajyoti
2016-05-01
We numerically study the vortex lattice dynamics in presence of pseudorandom potential in rotating Bose-Einstein condensate. The rotating condensate displays highly ordered triangular vortex lattice. In presence of pseudorandom potential the vortex lattice gets distorted. The histogram of the distances between each pair of the vortices shows how the long-range order of the triangular vortex lattice is destroyed in presence of pseudorandom potential.
Matter-wave propagation in optical lattices: geometrical and flat-band effects
NASA Astrophysics Data System (ADS)
Metcalf, Mekena; Chern, Gia-Wei; Di Ventra, Massimiliano; Chien, Chih-Chun
2016-04-01
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 matter-wave propagation as a function of the lattice geometry. To address this issue, we investigated, theoretically, the quantum transport of noninteracting 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 lattice 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. Possible realizations of those dynamical phenomena are discussed.
MAGNUM-2D computer code: user's guide
England, R.L.; Kline, N.W.; Ekblad, K.J.; Baca, R.G.
1985-01-01
Information relevant to the general use of the MAGNUM-2D computer code is presented. This computer code was developed for the purpose of modeling (i.e., simulating) the thermal and hydraulic conditions in the vicinity of a waste package emplaced in a deep geologic repository. The MAGNUM-2D computer computes (1) the temperature field surrounding the waste package as a function of the heat generation rate of the nuclear waste and thermal properties of the basalt and (2) the hydraulic head distribution and associated groundwater flow fields as a function of the temperature gradients and hydraulic properties of the basalt. MAGNUM-2D is a two-dimensional numerical model for transient or steady-state analysis of coupled heat transfer and groundwater flow in a fractured porous medium. The governing equations consist of a set of coupled, quasi-linear partial differential equations that are solved using a Galerkin finite-element technique. A Newton-Raphson algorithm is embedded in the Galerkin functional to formulate the problem in terms of the incremental changes in the dependent variables. Both triangular and quadrilateral finite elements are used to represent the continuum portions of the spatial domain. Line elements may be used to represent discrete conduits. 18 refs., 4 figs., 1 tab.
2011-12-31
Mesh2d is a Fortran90 program designed to generate two-dimensional structured grids of the form [x(i),y(i,j)] where [x,y] are grid coordinates identified by indices (i,j). The x(i) coordinates alone can be used to specify a one-dimensional grid. Because the x-coordinates vary only with the i index, a two-dimensional grid is composed in part of straight vertical lines. However, the nominally horizontal y(i,j0) coordinates along index i are permitted to undulate or otherwise vary. Mesh2d also assignsmore » an integer material type to each grid cell, mtyp(i,j), in a user-specified manner. The complete grid is specified through three separate input files defining the x(i), y(i,j), and mtyp(i,j) variations.« less
Subjectivity, objectivity, and triangular space.
Britton, Ronald
2004-01-01
The author reviews his ideas on subjectivity, objectivity, and the third position in the psychoanalytic encounter, particularly in clinical work with borderline and narcissistic patients. Using the theories of Melanie Klein and Wilfred Bion as a basis, the author describes his concept of triangular space. A case presentation of a particular type of narcissistic patient illustrates the principles discussed.
Building Buildings with Triangular Numbers
ERIC Educational Resources Information Center
Pagni, David L.
2006-01-01
Triangular numbers are used to unravel a new sequence of natural numbers here-to-fore not appearing on the Encyclopedia of Integer Sequences website. Insight is provided on the construction of the sequence using "buildings" as a viewable model of the sequence entries. A step-by-step analysis of the sequence pattern reveals a method for generating…
Subjectivity, objectivity, and triangular space.
Britton, Ronald
2004-01-01
The author reviews his ideas on subjectivity, objectivity, and the third position in the psychoanalytic encounter, particularly in clinical work with borderline and narcissistic patients. Using the theories of Melanie Klein and Wilfred Bion as a basis, the author describes his concept of triangular space. A case presentation of a particular type of narcissistic patient illustrates the principles discussed. PMID:14750465
Slow light with large group index - bandwidth product in lattice-shifted photonic crystal waveguides
NASA Astrophysics Data System (ADS)
Tang, Jian; Li, Wenhui; Wu, Jun; Xu, Zhonghui
2016-10-01
This study presents a systematic optimization procedure to generate slow light with large group index, wideband, and low dispersion in an lattice-shifted photonic crystal waveguide. The waveguide is based on triangular lattice photonic crystal imposed by selectively altering the locations of the holes adjacent to the line defect. Under a constant group index criterion of ± 10% variation, when group indices are nearly constants of 24, 33, 46, 57, and 66, their corresponding bandwidths of flat band reach 24.2, 17.6, 12.8, 10.1 and 8.6 nm around 1550 nm, respectively. A nearly constant large group index - bandwidth product (GBP) of 0.37 is achieved for all cases. Low dispersion slow light propagation is confirmed by studying the relative temporal pulse-width spreading with the 2-D finite-difference time-domain method.
Nonlinear dust-lattice waves: a modified Toda lattice
Cramer, N. F.
2008-09-07
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.
ORION96. 2-d Finite Element Code Postprocessor
Sanford, L.A.; Hallquist, J.O.
1992-02-02
ORION is an interactive program that serves as a postprocessor for the analysis programs NIKE2D, DYNA2D, TOPAZ2D, and CHEMICAL TOPAZ2D. ORION reads binary plot files generated by the two-dimensional finite element codes currently used by the Methods Development Group at LLNL. Contour and color fringe plots of a large number of quantities may be displayed on meshes consisting of triangular and quadrilateral elements. ORION can compute strain measures, interface pressures along slide lines, reaction forces along constrained boundaries, and momentum. ORION has been applied to study the response of two-dimensional solids and structures undergoing finite deformations under a wide variety of large deformation transient dynamic and static problems and heat transfer analyses.
Realistic and efficient 2D crack simulation
NASA Astrophysics Data System (ADS)
Yadegar, Jacob; Liu, Xiaoqing; Singh, Abhishek
2010-04-01
Although numerical algorithms for 2D crack simulation have been studied in Modeling and Simulation (M&S) and computer graphics for decades, realism and computational efficiency are still major challenges. In this paper, we introduce a high-fidelity, scalable, adaptive and efficient/runtime 2D crack/fracture simulation system by applying the mathematically elegant Peano-Cesaro triangular meshing/remeshing technique to model the generation of shards/fragments. The recursive fractal sweep associated with the Peano-Cesaro triangulation provides efficient local multi-resolution refinement to any level-of-detail. The generated binary decomposition tree also provides efficient neighbor retrieval mechanism used for mesh element splitting and merging with minimal memory requirements essential for realistic 2D fragment formation. Upon load impact/contact/penetration, a number of factors including impact angle, impact energy, and material properties are all taken into account to produce the criteria of crack initialization, propagation, and termination leading to realistic fractal-like rubble/fragments formation. The aforementioned parameters are used as variables of probabilistic models of cracks/shards formation, making the proposed solution highly adaptive by allowing machine learning mechanisms learn the optimal values for the variables/parameters based on prior benchmark data generated by off-line physics based simulation solutions that produce accurate fractures/shards though at highly non-real time paste. Crack/fracture simulation has been conducted on various load impacts with different initial locations at various impulse scales. The simulation results demonstrate that the proposed system has the capability to realistically and efficiently simulate 2D crack phenomena (such as window shattering and shards generation) with diverse potentials in military and civil M&S applications such as training and mission planning.
High precision triangular waveform generator
Mueller, Theodore R.
1983-01-01
An ultra-linear ramp generator having separately programmable ascending and descending ramp rates and voltages is provided. Two constant current sources provide the ramp through an integrator. Switching of the current at current source inputs rather than at the integrator input eliminates switching transients and contributes to the waveform precision. The triangular waveforms produced by the waveform generator are characterized by accurate reproduction and low drift over periods of several hours. The ascending and descending slopes are independently selectable.
Synthetic magnetic fluxes on the honeycomb lattice
Gorecka, Agnieszka; Gremaud, Benoit; Miniatura, Christian
2011-08-15
We devise experimental schemes that are able to mimic uniform and staggered magnetic fluxes acting on ultracold two-electron atoms, such as ytterbium atoms, propagating in a honeycomb lattice. The atoms are first trapped into two independent state-selective triangular lattices and then further exposed to a suitable configuration of resonant Raman laser beams. These beams induce hops between the two triangular lattices and make atoms move in a honeycomb lattice. Atoms traveling around each unit cell of this honeycomb lattice pick up a nonzero phase. In the uniform case, the artificial magnetic flux sustained by each cell can reach about two flux quanta, thereby realizing a cold-atom analog of the Harper model with its notorious Hofstadter's butterfly structure. Different condensed-matter phenomena such as the relativistic integer and fractional quantum Hall effects, as observed in graphene samples, could be targeted with this scheme.
Luther, Pradeep K.; Squire, John M.
2014-01-01
Myosin filaments in vertebrate striated muscle have a long roughly cylindrical backbone with cross-bridge projections on the surfaces of both halves except for a short central bare zone. In the middle of this central region the filaments are cross-linked by the M-band which holds them in a well-defined hexagonal lattice in the muscle A-band. During muscular contraction the M-band-defined rotation of the myosin filaments around their long axes influences the interactions that the cross-bridges can make with the neighbouring actin filaments. We can visualise this filament rotation by electron microscopy of thin cross-sections in the bare-region immediately adjacent to the M-band where the filament profiles are distinctly triangular. In the muscles of teleost fishes, the thick filament triangular profiles have a single orientation giving what we call the simple lattice. In other vertebrates, for example all the tetrapods, the thick filaments have one of two orientations where the triangles point in opposite directions (they are rotated by 60° or 180°) according to set rules. Such a distribution cannot be developed in an ordered fashion across a large 2D lattice, but there are small domains of superlattice such that the next-nearest neighbouring thick filaments often have the same orientation. We believe that this difference in the lattice forms can lead to different contractile behaviours. Here we provide a historical review, and when appropriate cite recent work related to the emergence of the simple and superlattice forms by examining the muscles of several species ranging back to primitive vertebrates and we discuss the functional differences that the two lattice forms may have. PMID:25478994
Luther, Pradeep K; Squire, John M
2014-01-01
Myosin filaments in vertebrate striated muscle have a long roughly cylindrical backbone with cross-bridge projections on the surfaces of both halves except for a short central bare zone. In the middle of this central region the filaments are cross-linked by the M-band which holds them in a well-defined hexagonal lattice in the muscle A-band. During muscular contraction the M-band-defined rotation of the myosin filaments around their long axes influences the interactions that the cross-bridges can make with the neighbouring actin filaments. We can visualise this filament rotation by electron microscopy of thin cross-sections in the bare-region immediately adjacent to the M-band where the filament profiles are distinctly triangular. In the muscles of teleost fishes, the thick filament triangular profiles have a single orientation giving what we call the simple lattice. In other vertebrates, for example all the tetrapods, the thick filaments have one of two orientations where the triangles point in opposite directions (they are rotated by 60° or 180°) according to set rules. Such a distribution cannot be developed in an ordered fashion across a large 2D lattice, but there are small domains of superlattice such that the next-nearest neighbouring thick filaments often have the same orientation. We believe that this difference in the lattice forms can lead to different contractile behaviours. Here we provide a historical review, and when appropriate cite recent work related to the emergence of the simple and superlattice forms by examining the muscles of several species ranging back to primitive vertebrates and we discuss the functional differences that the two lattice forms may have. PMID:25478994
Matter-wave propagation in optical lattices: geometrical and flat-band effects
Metcalf, Mekena; Chern, Gia-Wei; Di Ventra, Massimiliano; Chien, Chih-Chun
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
Chern-Simons theory for Heisenberg spins on the Kagome Lattice
NASA Astrophysics Data System (ADS)
Kumar, Krishna; Sun, Kai; Fradkin, Eduardo
2015-03-01
We study the problem of Heisenberg spins on the frustrated Kagome lattice using a 2D Jordan-Wigner transformation that maps the spins (hard-core bosons) onto a system of (interacting) fermions coupled to a Chern-Simons gauge field. This mapping requires us to define a discretized version of the Chern-Simons term on the lattice. Using a recently developed result on how to define Chern-Simons theories on a class of planar lattices, we can consistently study spin models beyond the mean-field level and include the effects of fluctuations, which are generally strong in frustrated systems. Here, we apply these results to study magnetization plateau type states on the Kagome lattice in the regime of XY anisotropy. We find that the 1/3 and 2/3 magnetization plateaus are chiral spin liquid states equivalent to a primary Laughlin fractional quantum Hall state of bosons with (spin) Hall conductivity 1/2 1/4 π and semionic excitations. The 5/9 plateau is a chiral spin liquid equivalent to the first Jain descendant. We also consider the spin-1/2 Heisenberg model on the Kagome lattice with a chirality-breaking term on the triangular plaquettes. This situation also leads to a primary Laughlin bosonic fractional quantum Hall type state with filling fraction 1 / 2 .
Quantum information experiments with 2D arrays of hundreds of trapped ions
NASA Astrophysics Data System (ADS)
Gilmore, Kevin; Bohnet, Justin; Sawyer, Brian; Britton, Joseph; Wall, Michael; Foss-Feig, Michael; Rey, Ana Maria; Bollinger, John
2016-05-01
We summarize recent experimental work with 2D arrays of hundreds of trapped 9 Be+ ions stored in a Penning trap. Penning traps utilize static magnetic and electric fields to confine ions, and enable the trapping and laser cooling of ion crystals larger than typically possible in RF ion traps. We work with single-plane ion crystals where the ions form a triangular lattice through minimization of their Coulomb potential energy. The crystals rotate, and we present numerical studies that determine optimal operating parameters for producing low temperature, stable 2-dimensional crystals with Doppler laser cooling and a rotating wall potential. Our qubit is the electron spin-flip transition in the ground state of 9 Be+ and is sensitive to magnetic field fluctuations. Through mitigation of part-per-billion, vibration-induced magnetic field fluctuations we demonstrate T2 coherence times longer than 50 ms. We engineer long-range Ising interactions with spin-dependent optical dipole forces, and summarize recent measurements that characterize the entanglement generated through single-axis twisting. Supported by: JILA-NSF-PFC-1125844, NSF-PHY-1521080, ARO, AFOSR, AFOSR-MURI.
2d Affine XY-Spin Model/4d Gauge Theory Duality and Deconfinement
Anber, Mohamed M.; Poppitz, Erich; Unsal, Mithat; /SLAC /Stanford U., Phys. Dept. /San Francisco State U.
2012-08-16
We introduce a duality between two-dimensional XY-spin models with symmetry-breaking perturbations and certain four-dimensional SU(2) and SU(2) = Z{sub 2} gauge theories, compactified on a small spatial circle R{sup 1,2} x S{sup 1}, and considered at temperatures near the deconfinement transition. In a Euclidean set up, the theory is defined on R{sup 2} x T{sup 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{sub c}) gauge theories with n{sub f} {ge} 1 adjoint Weyl fermions.
2D hexagonal quaternion Fourier transform in color image processing
NASA Astrophysics Data System (ADS)
Grigoryan, Artyom M.; Agaian, Sos S.
2016-05-01
In this paper, we present a novel concept of the quaternion discrete Fourier transform on the two-dimensional hexagonal lattice, which we call the two-dimensional hexagonal quaternion discrete Fourier transform (2-D HQDFT). The concept of the right-side 2D HQDFT is described and the left-side 2-D HQDFT is similarly considered. To calculate the transform, the image on the hexagonal lattice is described in the tensor representation when the image is presented by a set of 1-D signals, or splitting-signals which can be separately processed in the frequency domain. The 2-D HQDFT can be calculated by a set of 1-D quaternion discrete Fourier transforms (QDFT) of the splitting-signals.
Coupled spin-charge order in frustrated itinerant triangular magnets
NASA Astrophysics Data System (ADS)
Reja, Sahinur; Ray, Rajyavardhan; van den Brink, Jeroen; Kumar, Sanjeev
2015-04-01
We uncover four spin-charge ordered ground states in the strong coupling limit of the Kondo lattice model on triangular geometry. The results are obtained using Monte Carlo simulations, with a classical treatment of localized moments. Two of the states at one-third electronic filling (n =1 /3 ) consist of decorated ferromagnetic chains coupled antiferromagnetically with the neighboring chains. The third magnetic ground state is noncollinear, consisting of antiferromagnetic chains separated by a pair of canted ferromagnetic chains. An even more unusual magnetic ground state, a variant of the 120∘ Yafet-Kittel phase, is discovered at n =2 /3 . These magnetic orders are stabilized by opening a gap in the electronic spectrum: a "band effect." All the phases support modulations in the electronic charge density due to the presence of magnetically inequivalent sites. In particular, the charge ordering pattern found at n =2 /3 is observed in various triangular lattice systems, such as 2 H -AgNiO2, 3 R -AgNiO2, and NaxCoO2 .
Magnetic phase diagram of the coupled triangular spin tubes for CsCrF4
NASA Astrophysics Data System (ADS)
Seki, Kouichi; Okunishi, Kouichi
2015-06-01
Using Monte Carlo simulations, we explore the magnetic phase diagram of triangular spin tubes coupled with a ferromagnetic intertube interaction for CsCrF4. The planar structure of the coupled tubes is topologically equivalent to the kagome-triangular lattice, which induces nontrivial frustration effects in the system. We particularly find that, depending on the intertube coupling, various ordered phases are actually realized, such as incommensurate order, ferromagnetic order, and cuboc order, which is characterized by the noncoplanar spin structure of the 12 sublattices accompanying the spin chirality breaking. We also discuss the relevance of the results to recent experiments on CsCrF4.
Finite-temperature mechanical instability in disordered lattices.
Zhang, Leyou; Mao, Xiaoming
2016-02-01
Mechanical instability takes different forms in various ordered and disordered systems and little is known about how thermal fluctuations affect different classes of mechanical instabilities. We develop an analytic theory involving renormalization of rigidity and coherent potential approximation that can be used to understand finite-temperature mechanical stabilities in various disordered systems. We use this theory to study two disordered lattices: a randomly diluted triangular lattice and a randomly braced square lattice. These two lattices belong to two different universality classes as they approach mechanical instability at T=0. We show that thermal fluctuations stabilize both lattices. In particular, the triangular lattice displays a critical regime in which the shear modulus scales as G∼T(1/2), whereas the square lattice shows G∼T(2/3). We discuss generic scaling laws for finite-T mechanical instabilities and relate them to experimental systems. PMID:26986291
Manipulation and control of a bichromatic lattice
NASA Astrophysics Data System (ADS)
Thomas, Claire; Barter, Thomas; Daiss, Severin; Leung, Zephy; Stamper-Kurn, Dan
2015-05-01
Recent experiments with ultracold atoms in optical lattices have had great success emulating the simple models of condensed matter systems. These experiments are typically performed with a single site per unit cell. We realize a lattice with up to four sites per unit cell by overlaying an attractive triangular lattice with a repulsive one at twice the wavelength. The relative displacement of the two lattices determines the particular structure. One available configuration is the kagome lattice, which has a flat energy band. In the flat band all kinetic energy states are degenerate, so we have the opportunity to explore a regime where interactions dominate. This bichromatic lattice requires careful stabilization, but offers an opportunity to manipulate the unit cell and band structure by perturbing the lattices relative to one another. I will discuss recent progress.
NASA Astrophysics Data System (ADS)
Wang, Jin; Ma, Jianyong; Zhou, Changhe
2014-11-01
A 3×3 high divergent 2D-grating with period of 3.842μm at wavelength of 850nm under normal incidence is designed and fabricated in this paper. This high divergent 2D-grating is designed by the vector theory. The Rigorous Coupled Wave Analysis (RCWA) in association with the simulated annealing (SA) is adopted to calculate and optimize this 2D-grating.The properties of this grating are also investigated by the RCWA. The diffraction angles are more than 10 degrees in the whole wavelength band, which are bigger than the traditional 2D-grating. In addition, the small period of grating increases the difficulties of fabrication. So we fabricate the 2D-gratings by direct laser writing (DLW) instead of traditional manufacturing method. Then the method of ICP etching is used to obtain the high divergent 2D-grating.
Chemical compounds isolated from Talinum triangulare (Portulacaceae).
de Oliveira Amorim, Ana Paula; de Carvalho, Almir Ribeiro; Lopes, Norberto Peporine; Castro, Rosane Nora; de Oliveira, Marcia Cristina Campos; de Carvalho, Mário Geraldo
2014-10-01
This first phytochemical study of Talinum triangulare Leach (Portulacaceae), also known as 'cariru', which is a commonly consumed food in Northern Brazil, allowed the isolation and structural determination of four new compounds: one acrylamide, 3-N-(acryloyl, N-pentadecanoyl) propanoic acid (5), and three new phaeophytins named (15(1)S, 17R, 18R)-Ficuschlorin D acid (3(1),3(2)-didehydro-7-oxo-17(3)-O-phytyl-rhodochlorin-15-acetic acid), (13), Talichorin A (17R, 18R)-phaeophytin b-15(1)-hidroxy, 15(2),15(3)-acetyl-13(1)-carboxilic acid (14), and (15(1)S, 17R, 18R)-phaeophytin b peroxylactone or (15(1)S, 17R, 18R)-hydroperoxy-ficuschlorin D (16), together with twelve known compounds, including four phaeophytins (11,12, 15 and 17). The structures of the compounds were established on the basis of 1D and 2D NMR, IR, HRESI-MS spectra, including GC-MS, and HPLC-UV analysis, as well as comparisons with the literature data. The CD spectra data analysis were used to define the absolute configuration of phaeophytins 12 (13(2)R, 17R, 18R)-13(2)-hydroxyphaeophytin a, 13 and 16, 15 (15(1)S, 17R, 18R)-3(1),3(2)-didehydro-15(1)-hydroxyrhodochlorin-15-acetic acid δ-lactone-15(2)-methyl-17(3)-phytyl ester and 17 (17R, 18R)-purpurin 18-phytyl ester. PMID:24799228
Ding, Jian-Jiun; Huang, Ying-Wun; Lin, Pao-Yen; Pei, Soo-Chang; Chen, Hsin-Hui; Wang, Yu-Hsiang
2013-09-01
In the conventional JPEG algorithm, an image is divided into eight by eight blocks and then the 2-D DCT is applied to encode each block. In this paper, we find that, in addition to rectangular blocks, the 2-D DCT is also orthogonal in the trapezoid and triangular blocks. Therefore, instead of eight by eight blocks, we can generalize the JPEG algorithm and divide an image into trapezoid and triangular blocks according to the shapes of objects and achieve higher compression ratio. Compared with the existing shape adaptive compression algorithms, as we do not try to match the shape of each object exactly, the number of bytes used for encoding the edges can be less and the error caused from the high frequency component at the boundary can be avoided. The simulations show that, when the bit rate is fixed, our proposed algorithm can achieve higher PSNR than the JPEG algorithm and other shape adaptive algorithms. Furthermore, in addition to the 2-D DCT, we can also use our proposed method to generate the 2-D complete and orthogonal sine basis, Hartley basis, Walsh basis, and discrete polynomial basis in a trapezoid or a triangular block.
Longhi, Stefano; Dreisow, Felix; Heinrich, Matthias; Pertsch, Thomas; Tuennermann, Andreas; Nolte, Stefan; Szameit, Alexander
2010-11-15
Polychromatic dynamic localization in tight-binding lattices with long-range interaction is theoretically proposed and experimentally demonstrated in curved-waveguide photonic lattices. Efficient suppression of discrete diffraction over the whole white-light spectral region (450-750 nm) has been demonstrated in femtosecond-laser-written triangular-waveguide lattices with first- and second-order coupling.
Monte Carlo studies of a driven lattice gas. I. Growth and asymmetry during phase segregation
Alexander, F.J.; Laberge, C.A.; Lebowitz, J.L.
1996-02-01
We investigate the effects of an external field on the kinetics of phase segregation in systems with conservative diffusive dynamics. We find that, in contrast to the situation without a field, there are now qualitative differences between the results of microscopic simulations of a 2D lattice model with biased Kawasaki exchanges and those obtained from various modifications of the macroscopic Cahn-Hilliard equation (mCH). While both microscopic simulations and numerical solutions of MCH yield triangular domains, we find that in the former the triangles mainly point opposite to the field, while in the latter and in new calculations with the mCH they point along the field. On the other hand, the rate of growth of the clusters and their final state, bands parallel to the field, are similar. This issue and the question of the mesoscopic behavior of cell dynamical systems is discussed but not resolved.
Baiz, Carlos R.; Schach, Denise; Tokmakoff, Andrei
2014-01-01
We describe a microscope for measuring two-dimensional infrared (2D IR) spectra of heterogeneous samples with μm-scale spatial resolution, sub-picosecond time resolution, and the molecular structure information of 2D IR, enabling the measurement of vibrational dynamics through correlations in frequency, time, and space. The setup is based on a fully collinear “one beam” geometry in which all pulses propagate along the same optics. Polarization, chopping, and phase cycling are used to isolate the 2D IR signals of interest. In addition, we demonstrate the use of vibrational lifetime as a contrast agent for imaging microscopic variations in molecular environments. PMID:25089490
Experimental Realization of a Quantum Pentagonal Lattice
Yamaguchi, Hironori; Okubo, Tsuyoshi; Kittaka, Shunichiro; Sakakibara, Toshiro; Araki, Koji; Iwase, Kenji; Amaya, Naoki; Ono, Toshio; Hosokoshi, Yuko
2015-01-01
Geometric frustration, in which competing interactions give rise to degenerate ground states, potentially induces various exotic quantum phenomena in magnetic materials. Minimal models comprising triangular units, such as triangular and Kagome lattices, have been investigated for decades to realize novel quantum phases, such as quantum spin liquid. A pentagon is the second-minimal elementary unit for geometric frustration. The realization of such systems is expected to provide a distinct platform for studying frustrated magnetism. Here, we present a spin-1/2 quantum pentagonal lattice in the new organic radical crystal α-2,6-Cl2-V [=α-3-(2,6-dichlorophenyl)-1,5-diphenylverdazyl]. Its unique molecular arrangement allows the formation of a partially corner-shared pentagonal lattice (PCPL). We find a clear 1/3 magnetization plateau and an anomalous change in magnetization in the vicinity of the saturation field, which originate from frustrated interactions in the PCPL. PMID:26468930
Experimental Realization of a Quantum Pentagonal Lattice.
Yamaguchi, Hironori; Okubo, Tsuyoshi; Kittaka, Shunichiro; Sakakibara, Toshiro; Araki, Koji; Iwase, Kenji; Amaya, Naoki; Ono, Toshio; Hosokoshi, Yuko
2015-01-01
Geometric frustration, in which competing interactions give rise to degenerate ground states, potentially induces various exotic quantum phenomena in magnetic materials. Minimal models comprising triangular units, such as triangular and Kagome lattices, have been investigated for decades to realize novel quantum phases, such as quantum spin liquid. A pentagon is the second-minimal elementary unit for geometric frustration. The realization of such systems is expected to provide a distinct platform for studying frustrated magnetism. Here, we present a spin-1/2 quantum pentagonal lattice in the new organic radical crystal α-2,6-Cl2-V [=α-3-(2,6-dichlorophenyl)-1,5-diphenylverdazyl]. Its unique molecular arrangement allows the formation of a partially corner-shared pentagonal lattice (PCPL). We find a clear 1/3 magnetization plateau and an anomalous change in magnetization in the vicinity of the saturation field, which originate from frustrated interactions in the PCPL. PMID:26468930
Experimental Realization of a Quantum Pentagonal Lattice
NASA Astrophysics Data System (ADS)
Yamaguchi, Hironori; Okubo, Tsuyoshi; Kittaka, Shunichiro; Sakakibara, Toshiro; Araki, Koji; Iwase, Kenji; Amaya, Naoki; Ono, Toshio; Hosokoshi, Yuko
2015-10-01
Geometric frustration, in which competing interactions give rise to degenerate ground states, potentially induces various exotic quantum phenomena in magnetic materials. Minimal models comprising triangular units, such as triangular and Kagome lattices, have been investigated for decades to realize novel quantum phases, such as quantum spin liquid. A pentagon is the second-minimal elementary unit for geometric frustration. The realization of such systems is expected to provide a distinct platform for studying frustrated magnetism. Here, we present a spin-1/2 quantum pentagonal lattice in the new organic radical crystal α-2,6-Cl2-V [=α-3-(2,6-dichlorophenyl)-1,5-diphenylverdazyl]. Its unique molecular arrangement allows the formation of a partially corner-shared pentagonal lattice (PCPL). We find a clear 1/3 magnetization plateau and an anomalous change in magnetization in the vicinity of the saturation field, which originate from frustrated interactions in the PCPL.
Molecular rectification in triangularly shaped graphene nanoribbons.
Liu, Hongmei; Wang, Hongbo; Zhao, Jianwei; Kiguchi, Manabu
2013-02-15
We present a theoretical study of electron transport in tailored zigzag graphene nanoribbons (ZGNRs) with triangular structure using density functional theory together with the nonequilibrium Green's function formalism. We find significant rectification with a favorite electron transfer direction from the vertex to the right edge. The triangular ZGNR connecting to the electrode with one thiol group at each terminal shows an average rectification ratio of 8.4 over the bias range from -1.0 to 1.0 V. This asymmetric electron transport property originates from nearly zero band gap of triangular ZGNR under negative bias, whereas a band gap opens under positive bias. When the molecule is connected to the electrode by multithiol groups, the current is enhanced due to strong interfacial coupling; however, the rectification ratio decreases. The simulation results indicate that the unique electronic states of triangular ZGNR are responsible for rectification, rather than the asymmetric anchoring groups.
Triangular spectral elements for incompressible fluid flow
NASA Technical Reports Server (NTRS)
Mavriplis, C.; Vanrosendale, John
1993-01-01
We discuss the use of triangular elements in the spectral element method for direct simulation of incompressible flow. Triangles provide much greater geometric flexibility than quadrilateral elements and are better conditioned and more accurate when small angles arise. We employ a family of tensor product algorithms for triangles, allowing triangular elements to be handled with comparable arithmetic complexity to quadrilateral elements. The triangular discretizations are applied and validated on the Poisson equation. These discretizations are then applied to the incompressible Navier-Stokes equations and a laminar channel flow solution is given. These new triangular spectral elements can be combined with standard quadrilateral elements, yielding a general and flexible high order method for complex geometries in two dimensions.
RF MEMS reconfigurable triangular patch antenna.
Nordquist, Christopher Daniel; Christodoulou, Christos George; Feldner, Lucas Matthew
2005-01-01
A Ka-band RF MEMS enabled frequency reconfigurable triangular microstrip patch antenna has been designed for monolithic integration with RF MEMS phase shifters to demonstrate a low-cost monolithic passive electronically scanned array (PESA). This paper introduces our first prototype reconfigurable triangular patch antenna currently in fabrication. The aperture coupled patch antenna is fabricated on a dual-layer quartz/alumina substrate using surface micromachining techniques.
RF MEMS reconfigurable triangular patch antenna.
Christodoulou, Christos George; Nordquist, Christopher Daniel; Feldner, Lucas Matthew
2005-07-01
A Ka-band RF MEMS enabled frequency reconfigurable triangular microstrip patch antenna has been designed for monolithic integration with RF MEMS phase shifters to demonstrate a low-cost monolithic passive electronically scanned array (PESA). This paper introduces our first prototype reconfigurable triangular patch antenna currently in fabrication. The aperture coupled patch antenna is fabricated on a dual-layer quartz/alumina substrate using surface micromachining techniques.
2004-08-01
AnisWave2D is a 2D finite-difference code for a simulating seismic wave propagation in fully anisotropic materials. The code is implemented to run in parallel over multiple processors and is fully portable. A mesh refinement algorithm has been utilized to allow the grid-spacing to be tailored to the velocity model, avoiding the over-sampling of high-velocity materials that usually occurs in fixed-grid schemes.
Honeycomb and triangular domain wall networks in heteroepitaxial systems
NASA Astrophysics Data System (ADS)
Elder, K. R.; Chen, Z.; Elder, K. L. M.; Hirvonen, P.; Mkhonta, S. K.; Ying, S.-C.; Granato, E.; Huang, Zhi-Feng; Ala-Nissila, T.
2016-05-01
A comprehensive study is presented for the influence of misfit strain, adhesion strength, and lattice symmetry on the complex Moiré patterns that form in ultrathin films of honeycomb symmetry adsorbed on compact triangular or honeycomb substrates. The method used is based on a complex Ginzburg-Landau model of the film that incorporates elastic strain energy and dislocations. The results indicate that different symmetries of the heteroepitaxial systems lead to distinct types of domain wall networks and phase transitions among various surface Moiré patterns and superstructures. More specifically, the results show a dramatic difference between the phase diagrams that emerge when a honeycomb film is adsorbed on substrates of honeycomb versus triangular symmetry. It is also shown that in the small deformation limit, the complex Ginzburg-Landau model reduces to a two-dimensional sine-Gordon free energy form. This free energy can be solved exactly for one dimensional patterns and reveals the role of domains walls and their crossings in determining the nature of the phase diagrams.
New mechanism of chaos in triangular billiards
NASA Astrophysics Data System (ADS)
Naydenov, S. V.; Naplekov, D. M.; Yanovsky, V. V.
2013-12-01
A new mechanism of weak chaos in triangular billiards has been proposed owing to the effect of cutting of beams of rays. A similar mechanism is also implemented in other polygonal billiards. Cutting of beams results in the separation of initially close rays at a finite angle by jumps in the process of reflections of beams at the vertices of a billiard. The opposite effect of joining of beams of rays occurs in any triangular billiard along with cutting. It has been shown that the cutting of beams has an absolute character and is independent of the form of a triangular billiard or the parameters of a beam. On the contrary, joining has a relative character and depends on the commensurability of the angles of the triangle with π. Joining always suppresses cutting in triangular billiards whose angles are commensurable with π. For this reason, their dynamics cannot be chaotic. In triangular billiards whose angles are rationally incommensurable with π, cutting always dominates, leading to weak chaos. The revealed properties are confirmed by numerical experiments on the phase portraits of typical triangular billiards.
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.
Castle, Toen; Sussman, Daniel M.; Tanis, Michael; Kamien, Randall D.
2016-01-01
Kirigami uses bending, folding, cutting, and pasting to create complex three-dimensional (3D) structures from a flat sheet. In the case of lattice kirigami, this cutting and rejoining introduces defects into an underlying 2D lattice in the form of points of nonzero Gaussian curvature. A set of simple rules was previously used to generate a wide variety of stepped structures; we now pare back these rules to their minimum. This allows us to describe a set of techniques that unify a wide variety of cut-and-paste actions under the rubric of lattice kirigami, including adding new material and rejoining material across arbitrary cuts in the sheet. We also explore the use of more complex lattices and the different structures that consequently arise. Regardless of the choice of lattice, creating complex structures may require multiple overlapping kirigami cuts, where subsequent cuts are not performed on a locally flat lattice. Our additive kirigami method describes such cuts, providing a simple methodology and a set of techniques to build a huge variety of complex 3D shapes. PMID:27679822
Castle, Toen; Sussman, Daniel M.; Tanis, Michael; Kamien, Randall D.
2016-01-01
Kirigami uses bending, folding, cutting, and pasting to create complex three-dimensional (3D) structures from a flat sheet. In the case of lattice kirigami, this cutting and rejoining introduces defects into an underlying 2D lattice in the form of points of nonzero Gaussian curvature. A set of simple rules was previously used to generate a wide variety of stepped structures; we now pare back these rules to their minimum. This allows us to describe a set of techniques that unify a wide variety of cut-and-paste actions under the rubric of lattice kirigami, including adding new material and rejoining material across arbitrary cuts in the sheet. We also explore the use of more complex lattices and the different structures that consequently arise. Regardless of the choice of lattice, creating complex structures may require multiple overlapping kirigami cuts, where subsequent cuts are not performed on a locally flat lattice. Our additive kirigami method describes such cuts, providing a simple methodology and a set of techniques to build a huge variety of complex 3D shapes.
Wave propagation in fractal-inspired self-similar beam lattices
Lim, Qi Jian; Wang, Pai; Koh, Soo Jin Adrian; Khoo, Eng Huat; Bertoldi, Katia
2015-11-30
We combine numerical analysis and experiments to investigate the effect of hierarchy on the propagation of elastic waves in triangular beam lattices. While the response of the triangular lattice is characterized by a locally resonant band gap, both Bragg-type and locally resonant gaps are found for the hierarchical lattice. Therefore, our results demonstrate that structural hierarchy can be exploited to introduce an additional type of band gaps, providing a robust strategy for the design of lattice-based metamaterials with hybrid band gap properties (i.e., possessing band gaps that arises from both Bragg scattering and localized resonance)
NASA Astrophysics Data System (ADS)
Tomita, Takahiro; Nambu, Yusuke; Nakatsuji, Satoru; Koeda, Shinji; Hedo, Masato; Uwatoko, Yoshiya
2009-09-01
NiGa2S4, FeGa2S4, and Fe2Ga2S5 are layered triangular lattice antiferromagnets. Although the single-layer systems NiGa2S4 with S=1 and FeGa2S4 with S=2 are both insulators and have two-dimensional (2D) spin-disordered states, the bilayer system Fe2Ga2S5, which has an effective buckled honeycomb lattice of S=2, is a semiconductor and exhibits an antiferromagnetic long-range order at 110 K. Here, we present our results of the resistivity measurements of single crystals of FeGa2S4 and Fe2Ga2S5 under pressures of up to 8 GPa. We have observed a kink in the temperature dependence of the resistivity ρ(T) of FeGa2S4 under a pressure of 8 GPa, which is attributable to a transition from a 2D frozen spin-disordered state to a three-dimensional (3D) spin-ordered state. In either FeGa2S4 or Fe2Ga2S5, we have observed no transition into a metallic state within pressure range of up to 8 GPa, despite the fact that the resistivities of both FeGa2S4 and Fe2Ga2S5 show decreases with an increase in pressure at room temperature. The energy gap of FeGa2S4 estimated from the temperature dependences of the resistivities show negative pressure dependences.
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.
DYNA2D96. Explicit 2-D Hydrodynamic FEM Program
Whirley, R.G.
1992-04-01
DYNA2D is a vectorized, explicit, two-dimensional, axisymmetric and plane strain finite element program for analyzing the large deformation dynamic and hydrodynamic response of inelastic solids. DYNA2D contains 13 material models and 9 equations of state (EOS) to cover a wide range of material behavior. The material models implemented in all machine versions are: elastic, orthotropic elastic, kinematic/isotropic elastic plasticity, thermoelastoplastic, soil and crushable foam, linear viscoelastic, rubber, high explosive burn, isotropic elastic-plastic, temperature-dependent elastic-plastic. The isotropic and temperature-dependent elastic-plastic models determine only the deviatoric stresses. Pressure is determined by one of 9 equations of state including linear polynomial, JWL high explosive, Sack Tuesday high explosive, Gruneisen, ratio of polynomials, linear polynomial with energy deposition, ignition and growth of reaction in HE, tabulated compaction, and tabulated.
A TVD-type method for 2D scalar Hamilton-Jacobi equations on unstructured meshes
NASA Astrophysics Data System (ADS)
Tang, Lingyan; Song, Songhe
2006-10-01
In this paper, a TVD-type difference scheme which satisfies maximum principle is developed for 2D scalar Hamilton-Jacobi equations on unstructured triangular meshes. The main ideas are node-based approximations and derivative-limited reconstruction with quadratic interpolation polynomial. The solution's slope satisfies maximum principle. Numerical experiments are performed to demonstrate high-order accuracy in smooth fields and good resolution of derivative singularities. The new method is simpler than WENO.
Localized lasing modes of triangular organic microlasers.
Lafargue, C; Lebental, M; Grigis, A; Ulysse, C; Gozhyk, I; Djellali, N; Zyss, J; Bittner, S
2014-11-01
We investigated experimentally the ray-wave correspondence in organic microlasers of various triangular shapes. Triangular billiards are of interest since they are the simplest cases of polygonal billiards and the existence and properties of periodic orbits in triangles are not yet fully understood. The microlasers with symmetric shapes that were investigated exhibited states localized on simple periodic orbits, and their lasing characteristics like spectra and far-field distributions could be well explained by the properties of the periodic orbits. Furthermore, asymmetric triangles that do not feature simple periodic orbits were studied. Their lasing properties were found to be more complicated and could not be explained by periodic orbits.
Reducing quasilinear systems to block triangular form
Tunitsky, Dmitry V
2013-03-31
The paper is concerned with systems of n quasilinear partial differential equations of the first order with 2 independent variables. Using a geometric formalism for such equations, which goes back to Riemann, it is possible to assign a field of linear operators on an appropriate vector bundle to this type of quasilinear system. Several tests for a quasilinear system to be reducible to triangular or block triangular form are obtained in terms of this field; they supplement well known results on diagonalization and block diagonalization due to Haantjes and Bogoyavlenskij. Bibliography: 10 titles.
Ultrahigh-Q modes in anisotropic 2D photonic crystal
NASA Astrophysics Data System (ADS)
Bouleghlimat, Oussama; Hocini, Abdesselam
2014-10-01
In this work, we design a two-dimensional photonic crystal cavity made with a substrate of an anisotropic material. We consider triangular lattice photonic crystal made from air holes in tellurium. The cavity itself is then created by three missing holes in the centre. Using the three-dimensional finite-difference time-domain simulation and optimization of the geometrical parameters and the symmetric displacement of the edge air holes on the quality factor, the cavity’s structural parameters yield an ultrahigh-Q mode cavity with quality factor Q = 2.95 × 1011 for a filling factor r/a = 0.45 and lateral displacement of 10 nm. This shows great enhancement compared with previous studies in which silicon material has been used. The designed structure can be helpful in a number of applications associated with photonic crystal cavities, including quantum information processing, filters, and nanoscale sensors.
2001-01-31
This software reduces the data from two-dimensional kSA MOS program, k-Space Associates, Ann Arbor, MI. Initial MOS data is recorded without headers in 38 columns, with one row of data per acquisition per lase beam tracked. The final MOSS 2d data file is reduced, graphed, and saved in a tab-delimited column format with headers that can be plotted in any graphing software.
Robust band gap and half-metallicity in graphene with triangular perforations
NASA Astrophysics Data System (ADS)
Gregersen, Søren Schou; Power, Stephen R.; Jauho, Antti-Pekka
2016-06-01
Ideal graphene antidot lattices are predicted to show promising band gap behavior (i.e., EG≃500 meV) under carefully specified conditions. However, for the structures studied so far this behavior is critically dependent on superlattice geometry and is not robust against experimentally realistic disorders. Here we study a rectangular array of triangular antidots with zigzag edge geometries and show that their band gap behavior qualitatively differs from the standard behavior which is exhibited, e.g., by rectangular arrays of armchair-edged triangles. In the spin unpolarized case, zigzag-edged antidots give rise to large band gaps compared to armchair-edged antidots, irrespective of the rules which govern the existence of gaps in armchair-edged antidot lattices. In addition the zigzag-edged antidots appear more robust than armchair-edged antidots in the presence of geometrical disorder. The inclusion of spin polarization within a mean-field Hubbard approach gives rise to a large overall magnetic moment at each antidot due to the sublattice imbalance imposed by the triangular geometry. Half-metallic behavior arises from the formation of spin-split dispersive states near the Fermi energy, reducing the band gaps compared to the unpolarized case. This behavior is also found to be robust in the presence of disorder. Our results highlight the possibilities of using triangular perforations in graphene to open electronic band gaps in systems with experimentally realistic levels of disorder, and furthermore, of exploiting the strong spin dependence of the system for spintronic applications.
Metrology for graphene and 2D materials
NASA Astrophysics Data System (ADS)
Pollard, Andrew J.
2016-09-01
The application of graphene, a one atom-thick honeycomb lattice of carbon atoms with superlative properties, such as electrical conductivity, thermal conductivity and strength, has already shown that it can be used to benefit metrology itself as a new quantum standard for resistance. However, there are many application areas where graphene and other 2D materials, such as molybdenum disulphide (MoS2) and hexagonal boron nitride (h-BN), may be disruptive, areas such as flexible electronics, nanocomposites, sensing and energy storage. Applying metrology to the area of graphene is now critical to enable the new, emerging global graphene commercial world and bridge the gap between academia and industry. Measurement capabilities and expertise in a wide range of scientific areas are required to address this challenge. The combined and complementary approach of varied characterisation methods for structural, chemical, electrical and other properties, will allow the real-world issues of commercialising graphene and other 2D materials to be addressed. Here, examples of metrology challenges that have been overcome through a multi-technique or new approach are discussed. Firstly, the structural characterisation of defects in both graphene and MoS2 via Raman spectroscopy is described, and how nanoscale mapping of vacancy defects in graphene is also possible using tip-enhanced Raman spectroscopy (TERS). Furthermore, the chemical characterisation and removal of polymer residue on chemical vapour deposition (CVD) grown graphene via secondary ion mass spectrometry (SIMS) is detailed, as well as the chemical characterisation of iron films used to grow large domain single-layer h-BN through CVD growth, revealing how contamination of the substrate itself plays a role in the resulting h-BN layer. In addition, the role of international standardisation in this area is described, outlining the current work ongoing in both the International Organization of Standardization (ISO) and the
Optimizing triangular mesh generation from range images
NASA Astrophysics Data System (ADS)
Lu, Tianyu; Yun, David Y.
2000-03-01
An algorithm for the automatic reconstruction of triangular mesh surface model form range images is presented. The optimal piecewise linear surface approximation problem is defined as: given a set S of points uniformly sampled from a vibrate function f(x,y) on a rectangular grid of dimension W X H, find a minimum triangular mesh approximating the surface with vertices anchored at a subset S' of S, such that the deviation at any sample point is within a given bound of (epsilon) > 0. The algorithm deploys a multi- agent resource planning approach to achieve adaptive, accurate and concise piecewise linear approximation using the L-(infinity) norm. The resulting manifold triangular mesh can be directly used as 3D rendering model for visualization with controllable and guaranteed quality. Due to this dual optimality, the algorithm achieves both storage efficiency and visual quality. The error control scheme further facilitates the construction of models in multiple levels of details, which is desirable in animation and virtual reality moving scenes. Experiments with various benchmark range images form smooth functional surfaces to satellite terrain images yield succinct, accurate and visually pleasant triangular meshes. Furthermore, the independence and multiplicity of agents suggest a natural parallelism for triangulation computation, which provides a promising solution for the real-time exploration of large data sets.
Basic Employability Skills: A Triangular Design Approach
ERIC Educational Resources Information Center
Rosenberg, Stuart; Heimler, Ronald; Morote, Elsa-Sofia
2012-01-01
Purpose: This paper seeks to examine the basic employability skills needed for job performance, the reception of these skills in college, and the need for additional training in these skills after graduation. Design/methodology/approach: The research was based on a triangular design approach, in which the attitudes of three distinct groups--recent…
Solutions to the Triangular Bicycle Flags Problem
ERIC Educational Resources Information Center
Hartweg, Kim
2005-01-01
Students in a fifth-grade general education class and a second-grade gifted class participated in the Triangular Bicycle Flags problem. The results indicated that providing students with geometric experiences at the correct van Hiele level is necessary for helping students move from one level of understanding to the next.
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.
Transport Code for Regular Triangular Geometry
1993-06-09
DIAMANT2 solves the two-dimensional static multigroup neutron transport equation in planar regular triangular geometry. Both regular and adjoint, inhomogeneous and homogeneous problems subject to vacuum, reflective or input specified boundary flux conditions are solved. Anisotropy is allowed for the scattering source. Volume and surface sources are allowed for inhomogeneous problems.
Assembling Fibonacci anyons from a Z3 parafermion lattice model
NASA Astrophysics Data System (ADS)
Stoudenmire, E. M.; Clarke, David J.; Mong, Roger S. K.; Alicea, Jason
2015-06-01
Recent concrete proposals suggest it is possible to engineer a two-dimensional bulk phase supporting non-Abelian Fibonacci anyons out of Abelian fractional quantum Hall systems. The low-energy degrees of freedom of such setups can be modeled as Z3 parafermions "hopping" on a two-dimensional lattice. We use the density matrix renormalization group to study a model of this type interpolating between the decoupled-chain, triangular-lattice, and square-lattice limits. The results show clear evidence of the Fibonacci phase over a wide region of the phase diagram, most notably including the isotropic triangular-lattice point. We also study the broader phase diagram of this model and show that elsewhere it supports an Abelian state with semionic excitations.
A transient, quadratic nodal method for triangular-Z geometry
DeLorey, T.F.
1993-06-01
Many systematically-derived nodal methods have been developed for Cartesian geometry due to the extensive interest in Light Water Reactors. These methods typically model the transverse-integrated flux as either an analytic or low order polynomial function of position within the node. Recently, quadratic nodal methods have been developed for R-Z and hexagonal geometry. A static and transient quadratic nodal method is developed for triangular-Z geometry. This development is particularly challenging because the quadratic expansion in each node must be performed between the node faces and the triangular points. As a consequence, in the 2-D plane, the flux and current at the points of the triangles must be treated. Quadratic nodal equations are solved using a non-linear iteration scheme, which utilizes the corrected, mesh-centered finite difference equations, and forces these equations to match the quadratic equations by computing discontinuity factors during the solution. Transient nodal equations are solved using the improved quasi-static method, which has been shown to be a very efficient solution method for transient problems. Several static problems are used to compare the quadratic nodal method to the Coarse Mesh Finite Difference (CMFD) method. The quadratic method is shown to give more accurate node-averaged fluxes. However, it appears that the method has difficulty predicting node leakages near reactor boundaries and severe material interfaces. The consequence is that the eigenvalue may be poorly predicted for certain reactor configurations. The transient methods are tested using a simple analytic test problem, a heterogeneous heavy water reactor benchmark problem, and three thermal hydraulic test problems. Results indicate that the transient methods have been implemented correctly.
Collisional diffusion in toroidal plasmas with elongation and triangularity
Martin, P.; Castro, E.; Haines, M. G.
2007-05-15
Collisional diffusion is analyzed for plasma tokamaks with different ellipticities and triangularities. Improved nonlinear equations for the families of magnetic surfaces are used here. Dimensionless average velocities are calculated as a function of the inductive electric field, elongation, triangularity, and Shafranov shift. Confinement has been found to depend significantly on triangularity.
Bornyakov, V.G.
2005-06-01
Possibilities that are provided by a lattice regularization of QCD for studying nonperturbative properties of QCD are discussed. A review of some recent results obtained from computer calculations in lattice QCD is given. In particular, the results for the QCD vacuum structure, the hadron mass spectrum, and the strong coupling constant are considered.
NASA Astrophysics Data System (ADS)
Wang, Da-Wei; Liu, Ren-Bao; Zhu, Shi-Yao; Scully, Marlan O.
2015-01-01
We show that the timed Dicke states of a collection of three-level atoms can form a tight-binding lattice in momentum space. This lattice, coined the superradiance lattice (SL), can be constructed based on electromagnetically induced transparency (EIT). For a one-dimensional SL, we need the coupling field of the EIT system to be a standing wave. The detuning between the two components of the standing wave introduces an effective uniform force in momentum space. The quantum lattice dynamics, such as Bloch oscillations, Wannier-Stark ladders, Bloch band collapsing, and dynamic localization can be observed in the SL. The two-dimensional SL provides a flexible platform for Dirac physics in graphene. The SL can be extended to three and higher dimensions where no analogous real space lattices exist with new physics waiting to be explored.
Tomographic particle image velocimetry over a triangular prism in unidirectional flows
NASA Astrophysics Data System (ADS)
Sou, In Mei; Calantoni, Joseph
2011-11-01
Using tomographic particle image velocimetry (Tomo-PIV), the full three-dimensional-three-component (3D-3C) flow structure and turbulence characteristics over a triangular prism in a recirculating water tunnel were investigated. Here we present preliminary results from a new Tomo-PIV system for subcritical Froude number flows. Large-scale vortex shedding from the tip of the triangular prism is observed. Results of coherent structure organization analyzed by 3D vorticity calculation will be presented. Using the full 3D-3C instantaneous velocity field, turbulent kinetic energy is directly evaluated without any of the assumptions often needed for 2D PIV measurements. Details of the experimental setup including a unique device designed to perform our Tomo-PIV volume calibration will be discussed. We perform an in-depth turbulent kinetic energy budget and explore the feasibility of extending the measurement technique to other complex flows.
NASA Astrophysics Data System (ADS)
Singh, Kevin; Geiger, Zachary; Senaratne, Ruwan; Rajagopal, Shankari; Fujiwara, Kurt; Weld, David; Weld Group Team
2015-05-01
Quasiperiodicity is intimately involved in quantum phenomena from localization to the quantum Hall effect. Recent experimental investigation of quasiperiodic quantum effects in photonic and electronic systems have revealed intriguing connections to topological phenomena. However, such experiments have been limited by the absence of techniques for creating tunable quasiperiodic structures. We propose a new type of quasiperiodic optical lattice, constructed by intersecting a Gaussian beam with a 2D square lattice at an angle with an irrational tangent. The resulting potential, a generalization of the Fibonacci lattice, is a physical realization of the mathematical ``cut-and-project'' construction which underlies all quasiperiodic structures. Calculation of the energies and wavefunctions of atoms loaded into the proposed quasiperiodic lattice demonstrate a fractal energy spectrum and the existence of edge states. We acknowledge support from the ONR (award N00014-14-1-0805), the ARO and the PECASE program (award W911NF-14-1-0154), the AFOSR (award FA9550-12-1-0305), and the Alfred P. Sloan foundation (grant BR2013-110).
Georgi, Howard; Kats, Yevgeny
2008-09-26
We discuss what can be learned about unparticle physics by studying simple quantum field theories in one space and one time dimension. We argue that the exactly soluble 2D theory of a massless fermion coupled to a massive vector boson, the Sommerfield model, is an interesting analog of a Banks-Zaks model, approaching a free theory at high energies and a scale-invariant theory with nontrivial anomalous dimensions at low energies. We construct a toy standard model coupling to the fermions in the Sommerfield model and study how the transition from unparticle behavior at low energies to free particle behavior at high energies manifests itself in interactions with the toy standard model particles.
NASA Astrophysics Data System (ADS)
Barrios-Vargas, Eduardo; Naumis, Gerardo G.
2014-03-01
An intuitive explanation of the increase in localization observed near the Dirac point in doped graphene is presented. To do this, we renormalize the tight binding Hamiltonian in such a way that the honeycomb lattice maps into a triangular one. Then, we investigate the frustration effects that emerge in this Hamiltonian. In this doped triangular lattice, the eigenstates have a bonding and antibonding contribution near the Dirac point, and thus there is a kind of Lifshitz tail. The increase in frustration is related to an increase in localization, since the number of frustrated bonds decreases with disorder, while the frustration contribution raises. Then we show that states have a multifractal nature, with a fractal spectrum that approaches freezing as disorder increases. We compute exacty the first spectral moments of the DOS using statistical averages and counting paths. Finally, the number of states at the Dirac point is obtained using a configurational counting. Apdo. Postal 20-364, 01000, México DF.
Triangular springs for modeling nonlinear membranes.
Delingette, Hervé
2008-01-01
This paper provides a formal connexion between springs and continuum mechanics in the context of one-dimensional and two-dimensional elasticity. In a first stage, the equivalence between tensile springs and the finite element discretization of stretching energy on planar curves is established. Furthermore, when considering a quadratic strain function of stretch, we introduce a new type of springs called tensile biquadratic springs. In a second stage, we extend this equivalence to non-linear membranes (St Venant-Kirchhoff materials) on triangular meshes leading to triangular biquadratic and quadratic springs. Those tensile and angular springs produce isotropic deformations parameterized by Young modulus and Poisson ratios on unstructured meshes in an efficient and simple way. For a specific choice of the Poisson ratio, 0.3, we show that regular spring-mass models may be used realistically to simulate a membrane behavior. Finally, the different spring formulations are tested in pure traction and cloth simulation experiments.
Efficient triangular adaptive meshes for tsunami simulations
NASA Astrophysics Data System (ADS)
Behrens, J.
2012-04-01
With improving technology and increased sensor density for accurate determination of tsunamogenic earthquake source parameters and consecutively uplift distribution, real-time simulations of even near-field tsunami hazard appears feasible in the near future. In order to support such efforts a new generation of tsunami models is currently under development. These models comprise adaptively refined meshes, in order to save computational resources (in areas of low wave activity) and still represent the inherently multi-scale behavior of a tsunami approaching coastal waters. So far, these methods have been based on oct-tree quadrilateral refinement. The method introduced here is based on binary tree refinement on triangular grids. By utilizing the structure stemming from the refinement strategy, a very efficient method can be achieved, with a triangular mesh, able to accurately represent complex boundaries.
Lattice Green's functions in all dimensions
NASA Astrophysics Data System (ADS)
Guttmann, Anthony J.
2010-07-01
We give a systematic treatment of lattice Green's functions (LGF) on the d-dimensional diamond, simple cubic, body-centred cubic and face-centred cubic lattices for arbitrary dimensionality d >= 2 for the first three lattices, and for 2 <= d <= 5 for the hyper-fcc lattice. We show that there is a close connection between the LGF of the d-dimensional hyper-cubic lattice and that of the (d - 1)-dimensional diamond lattice. We give constant-term formulations of LGFs for each of these lattices in all dimensions. Through a still under-developed connection with Mahler measures, we point out an unexpected connection between the coefficients of the sc, bcc and diamond LGFs and some Ramanujan-type formulae for 1/π.
High-precision triangular-waveform generator
Mueller, T.R.
1981-11-14
An ultra-linear ramp generator having separately programmable ascending and decending ramp rates and voltages is provided. Two constant current sources provide the ramp through an integrator. Switching of the current at current source inputs rather than at the integrator input eliminates switching transients and contributes to the waveform precision. The triangular waveforms produced by the waveform generator are characterized by accurate reproduction and low drift over periods of several hours. The ascending and descending slopes are independently selectable.
Finite volume TVD formulation of lattice Boltzmann simulation on unstructured mesh
NASA Astrophysics Data System (ADS)
Patil, Dhiraj V.; Lakshmisha, K. N.
2009-08-01
A numerical scheme is presented for accurate simulation of fluid flow using the lattice Boltzmann equation (LBE) on unstructured mesh. A finite volume approach is adopted to discretize the LBE on a cell-centered, arbitrary shaped, triangular tessellation. The formulation includes a formal, second order discretization using a Total Variation Diminishing (TVD) scheme for the terms representing advection of the distribution function in physical space, due to microscopic particle motion. The advantage of the LBE approach is exploited by implementing the scheme in a new computer code to run on a parallel computing system. Performance of the new formulation is systematically investigated by simulating four benchmark flows of increasing complexity, namely (1) flow in a plane channel, (2) unsteady Couette flow, (3) flow caused by a moving lid over a 2D square cavity and (4) flow over a circular cylinder. For each of these flows, the present scheme is validated with the results from Navier-Stokes computations as well as lattice Boltzmann simulations on regular mesh. It is shown that the scheme is robust and accurate for the different test problems studied.
Analysis and Improvement of Upwind and Centered Schemes on Quadrilateral and Triangular Meshes
NASA Technical Reports Server (NTRS)
Huynh, H. T.
2003-01-01
Second-order accurate upwind and centered schemes are presented in a framework that facilitates their analysis and comparison. The upwind scheme employed consists of a reconstruction step (MUSCL approach) followed by an upwind step (Roe's flux-difference splitting). The two centered schemes are of Lax-Friedrichs (L-F) type. They are the nonstaggered versions of the Nessyahu-Tadmor (N-T) scheme and the CE/SE method with epilson = 1/2. The upwind scheme is extended to the case of two spatial dimensions (2D) in a straightforward manner. The N-T and CE/SE schemes are extended in a manner similar to the 2D extensions of the CE/SE scheme by Wang and Chang for a triangular mesh and by Zhang, Yu, and Chang for a quadrilateral mesh. The slope estimates, however, are simplified. Fourier stability and accuracy analyses are carried out for these schemes for the standard 1D and the 2D quadrilateral mesh cases. In the nonstandard case of a triangular mesh, the triangles must be paired up when analyzing the upwind and N-T schemes. An observation resulting in an extended N-T scheme which is faster and uses only one-third of the storage for flow data compared with the CE/SE method is presented. Numerical results are shown. Other improvements to the schemes are discussed.
NASA Astrophysics Data System (ADS)
Hayward, A. L. C.; Martin, A. M.
2016-02-01
We investigate the ground-state behavior of Jaynes-Cummings-Hubbard lattices in the presence of a synthetic magnetic field, via a Gutzwiller ansatz. Specifically, we study the superfluid-Mott transition and the formation of vortex lattices in the superfluid regime. We find a suppression of the superfluid fraction due to the frustration induced by the incommensurate magnetic and spacial lattice lengths. We also predict the formation of triangular vortex lattices inside the superfluid regime.
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.
Vortex structure and dynamics in kagome and triangular pinning potentials
Laguna, M. F.; Balseiro, C. A.; Dominguez, D.; Nori, Franco
2001-09-01
We study the dynamics of thermally driven superconducting vortices in two types of periodic pinning potentials: kagome and triangular. For the first, second, and third matching fields, we obtain the corresponding ground-state vortex configurations and their phase diagrams. We analyze the system properties by looking at the vortex trajectories and the structure factor, as well as the linear and angular diffusion. The temperature versus pinning force phase diagram is analyzed in detail for each matching field. When the temperature is varied, we observe several stages of lattice pinning and melting. In most of the cases we find, for decreasing temperature, first a pinning of vortices and afterwards a freezing transition of the interstitial vortices. The intermediate regime corresponds to interstitial vortices in a confined liquidlike state and pinned vortices. The kagome pinning potential shows interesting behavior at low temperatures: there is a phase with rotating vortex triangles caged by kagome hexagons (''cooperative ring elementary excitations''), and there is geometric frustration for T{yields}0 with a nearly degenerate ground state.
Vertex-Atom-Dependent Rectification in Triangular h-BNC/Triangular Graphene Heterojunctions
NASA Astrophysics Data System (ADS)
Wang, Lihua; Zhao, Jianguo; Zhang, Zizhen; Ding, Bingjun; Guo, Yong
2016-08-01
First-principles calculations have shown dramatically unexpected rectifying regularities in particular heterojunction configurations with triangular hexagonal boron-nitride-carbon ( h-BNC) and triangular graphene (TG) sandwiched between two armchair graphene nanoribbon electrodes. When the triangular h-BNC and TG are linked by vertex atoms of nitrogen and carbon (boron and carbon), forward (reverse) rectifying performance can be observed. Moreover, for a certain linking mode, the larger the elemental proportion p (where p = N_{{{boron}} + {{nitrogen}}} /N_{{{boron}} + {{nitrogen}} + {{carbon}}} ) in the h-BNC, the larger the ratio for forward (reverse) rectification. A mechanism for these rectification behaviors is suggested. The findings provide insights into control of rectification behaviors in TG-based nanodevices.
FRANC2D: A two-dimensional crack propagation simulator. Version 2.7: User's guide
NASA Technical Reports Server (NTRS)
Wawrzynek, Paul; Ingraffea, Anthony
1994-01-01
FRANC 2D (FRacture ANalysis Code, 2 Dimensions) is a menu driven, interactive finite element computer code that performs fracture mechanics analyses of 2-D structures. The code has an automatic mesh generator for triangular and quadrilateral elements. FRANC2D calculates the stress intensity factor using linear elastic fracture mechanics and evaluates crack extension using several methods that may be selected by the user. The code features a mesh refinement and adaptive mesh generation capability that is automatically developed according to the predicted crack extension direction and length. The code also has unique features that permit the analysis of layered structure with load transfer through simulated mechanical fasteners or bonded joints. The code was written for UNIX workstations with X-windows graphics and may be executed on the following computers: DEC DecStation 3000 and 5000 series, IBM RS/6000 series, Hewlitt-Packard 9000/700 series, SUN Sparc stations, and most Silicon Graphics models.
Subwavelength Lattice Optics by Evolutionary Design
2015-01-01
This paper describes a new class of structured optical materials—lattice opto-materials—that can manipulate the flow of visible light into a wide range of three-dimensional profiles using evolutionary design principles. Lattice opto-materials are based on the discretization of a surface into a two-dimensional (2D) subwavelength lattice whose individual lattice sites can be controlled to achieve a programmed optical response. To access a desired optical property, we designed a lattice evolutionary algorithm that includes and optimizes contributions from every element in the lattice. Lattice opto-materials can exhibit simple properties, such as on- and off-axis focusing, and can also concentrate light into multiple, discrete spots. We expanded the unit cell shapes of the lattice to achieve distinct, polarization-dependent optical responses from the same 2D patterned substrate. Finally, these lattice opto-materials can also be combined into architectures that resemble a new type of compound flat lens. PMID:25380062
Solution of an associating lattice-gas model with density anomaly on a Husimi lattice
NASA Astrophysics Data System (ADS)
Oliveira, Tiago J.; Stilck, Jürgen F.; Barbosa, Marco Aurélio A.
2010-11-01
We study a model of a lattice gas with orientational degrees of freedom which resemble the formation of hydrogen bonds between the molecules. In this model, which is the simplified version of the Henriques-Barbosa model, no distinction is made between donors and acceptors in the bonding arms. We solve the model in the grand-canonical ensemble on a Husimi lattice built with hexagonal plaquettes with a central site. The ground state of the model, which was originally defined on the triangular lattice, is exactly reproduced by the solution on this Husimi lattice. In the phase diagram, one gas and two liquid [high density liquid (HDL) and low density liquid (LDL)] phases are present. All phase transitions (GAS-LDL, GAS-HDL, and LDL-HDL) are discontinuous, and the three phases coexist at a triple point. A line of temperatures of maximum density in the isobars is found in the metastable GAS phase, as well as another line of temperatures of minimum density appears in the LDL phase, part of it in the stable region and another in the metastable region of this phase. These findings are at variance with simulational results for the same model on the triangular lattice, which suggested a phase diagram with two critical points. However, our results show very good quantitative agreement with the simulations, both for the coexistence loci and the densities of particles and of hydrogen bonds. We discuss the comparison of the simulations with our results.
Solution of an associating lattice-gas model with density anomaly on a Husimi lattice.
Oliveira, Tiago J; Stilck, Jürgen F; Barbosa, Marco Aurélio A
2010-11-01
We study a model of a lattice gas with orientational degrees of freedom which resemble the formation of hydrogen bonds between the molecules. In this model, which is the simplified version of the Henriques-Barbosa model, no distinction is made between donors and acceptors in the bonding arms. We solve the model in the grand-canonical ensemble on a Husimi lattice built with hexagonal plaquettes with a central site. The ground state of the model, which was originally defined on the triangular lattice, is exactly reproduced by the solution on this Husimi lattice. In the phase diagram, one gas and two liquid [high density liquid (HDL) and low density liquid (LDL)] phases are present. All phase transitions (GAS-LDL, GAS-HDL, and LDL-HDL) are discontinuous, and the three phases coexist at a triple point. A line of temperatures of maximum density in the isobars is found in the metastable GAS phase, as well as another line of temperatures of minimum density appears in the LDL phase, part of it in the stable region and another in the metastable region of this phase. These findings are at variance with simulational results for the same model on the triangular lattice, which suggested a phase diagram with two critical points. However, our results show very good quantitative agreement with the simulations, both for the coexistence loci and the densities of particles and of hydrogen bonds. We discuss the comparison of the simulations with our results.
Anisotropic spin model of strong spin-orbit-coupled triangular antiferromagnets
NASA Astrophysics Data System (ADS)
Li, Yao-Dong; Wang, Xiaoqun; Chen, Gang
2016-07-01
Motivated by the recent experimental progress on the strong spin-orbit-coupled rare-earth triangular antiferromagnet, we analyze the highly anisotropic spin model that describes the interaction between the spin-orbit-entangled Kramers' doublet local moments on the triangular lattice. We apply the Luttinger-Tisza method, the classical Monte Carlo simulation, and the self-consistent spin wave theory to analyze the anisotropic spin Hamiltonian. The classical phase diagram includes the 120∘ state and two distinct stripe-ordered phases. The frustration is very strong and significantly suppresses the ordering temperature in the regimes close to the phase boundary between two ordered phases. Going beyond the semiclassical analysis, we include the quantum fluctuations of the spin moments within a self-consistent Dyson-Maleev spin-wave treatment. We find that the strong quantum fluctuations melt the magnetic order in the frustrated regions. We explore the magnetic excitations in the three different ordered phases as well as in strong magnetic fields. Our results provide a guidance for the future theoretical study of the generic model and are broadly relevant for strong spin-orbit-coupled triangular antiferromagnets such as YbMgGaO4, RCd3P3 , RZn3P3 , RCd3As3 , RZn3As3 , and R2O2CO3 .
Duality analysis on random planar lattices.
Ohzeki, Masayuki; Fujii, Keisuke
2012-11-01
The conventional duality analysis is employed to identify a location of a critical point on a uniform lattice without any disorder in its structure. In the present study, we deal with the random planar lattice, which consists of the randomized structure based on the square lattice. We introduce the uniformly random modification by the bond dilution and contraction on a part of the unit square. The random planar lattice includes the triangular and hexagonal lattices in extreme cases of a parameter to control the structure. A modern duality analysis fashion with real-space renormalization is found to be available for estimating the location of the critical points with a wide range of the randomness parameter. As a simple test bed, we demonstrate that our method indeed gives several critical points for the cases of the Ising and Potts models and the bond-percolation thresholds on the random planar lattice. Our method leads to not only such an extension of the duality analyses on the classical statistical mechanics but also a fascinating result associated with optimal error thresholds for a class of quantum error correction code, the surface code on the random planar lattice, which is known as a skillful technique to protect the quantum state.
Duality analysis on random planar lattices
NASA Astrophysics Data System (ADS)
Ohzeki, Masayuki; Fujii, Keisuke
2012-11-01
The conventional duality analysis is employed to identify a location of a critical point on a uniform lattice without any disorder in its structure. In the present study, we deal with the random planar lattice, which consists of the randomized structure based on the square lattice. We introduce the uniformly random modification by the bond dilution and contraction on a part of the unit square. The random planar lattice includes the triangular and hexagonal lattices in extreme cases of a parameter to control the structure. A modern duality analysis fashion with real-space renormalization is found to be available for estimating the location of the critical points with a wide range of the randomness parameter. As a simple test bed, we demonstrate that our method indeed gives several critical points for the cases of the Ising and Potts models and the bond-percolation thresholds on the random planar lattice. Our method leads to not only such an extension of the duality analyses on the classical statistical mechanics but also a fascinating result associated with optimal error thresholds for a class of quantum error correction code, the surface code on the random planar lattice, which is known as a skillful technique to protect the quantum state.
Micropolar modeling of planar orthotropic rectangular chiral lattices
NASA Astrophysics Data System (ADS)
Chen, Yi; Liu, Xiaoning; Hu, Gengkai
2014-05-01
Rectangular chiral lattices possess a two-fold symmetry; in order to characterize the overall behavior of such lattices, a two-dimensional orthotropic chiral micropolar theory is proposed. Eight additional material constants are necessary to represent the anisotropy in comparison with triangular ones, four of which are devoted to chirality. Homogenization procedures are also developed for the chiral lattice with rigid or deformable circles, all material constants in the developed micropolar theory are derived analytically for the case of the rigid circles and numerically for the case of the deformable circles. The dependences of these material constants and of wave propagation on the microstructural parameters are also examined.
Spangolite: an s = 1/2 maple leaf lattice antiferromagnet?
NASA Astrophysics Data System (ADS)
Fennell, T.; Piatek, J. O.; Stephenson, R. A.; Nilsen, G. J.; Rønnow, H. M.
2011-04-01
Spangolite, Cu6Al(SO4)(OH)12Cl·3H2O, is a hydrated layered copper sulfate mineral. The Cu2 + ions of each layer form a systematically depleted triangular lattice which approximates a maple leaf lattice. We present details of the crystal structure, which suggest that in spangolite this lattice actually comprises two species of edge linked trimers with different exchange parameters. However, magnetic susceptibility measurements show that despite the structural trimers, the magnetic properties are dominated by dimerization. The high temperature magnetic moment is strongly reduced below that expected for the six s = 1/2 in the unit cell.
Geometric Frustration of Colloidal Dimers on a Honeycomb Magnetic Lattice
NASA Astrophysics Data System (ADS)
Tierno, Pietro
2016-01-01
We study the phase behavior and the collective dynamics of interacting paramagnetic colloids assembled above a honeycomb lattice of triangular shaped magnetic minima. A frustrated colloidal molecular crystal is realized when filling these potential minima with exactly two particles per pinning site. External in-plane rotating fields are used to anneal the system into different phases, including long range ordered stripes, random fully packed loops, labyrinth and disordered states. At a higher amplitude of the annealing field, the dimer lattice displays a two-step melting transition where the initially immobile dimers perform first localized rotations and later break up by exchanging particles across consecutive lattice minima.
Interfacing graphene and related 2D materials with the 3D world.
Tománek, David
2015-04-10
An important prerequisite to translating the exceptional intrinsic performance of 2D materials such as graphene and transition metal dichalcogenides into useful devices precludes their successful integration within the current 3D technology. This review provides theoretical insight into nontrivial issues arising from interfacing 2D materials with 3D systems including epitaxy and ways to accommodate lattice mismatch, the key role of contact resistance and the effect of defects in electrical and thermal transport.
Two-dimensional surface emitting photonic crystal laser with hybrid triangular-graphite structure.
Martínez, Luis Javier; Alén, Benito; Prieto, Ivan; Galisteo-López, J F; Galli, Matteo; Andreani, Lucio Claudio; Seassal, Christian; Viktorovitch, Pierre; Postigo, Pablo Aitor
2009-08-17
We present laser emission of a compact surface-emitting micro laser, optical pumped and operating at 1.5 microm at room temperature. A two-dimensional photonic crystal lattice conformed in a hybrid triangular-graphite configuration is designed for vertical emission. The structures have been fabricated in an InP slab, including four InAsP quantum wells as active layer, on the top of a Si substrate SiO(2) wafer bonded. Laser emission with thresholds around 70 microW and quality factors (Qs) up to 12000 have been measured. The Bloch mode selected for the emission keeps a high Q (>or= 2 x 10(5)) around the Gamma point for a wide range of in-plane values k(||)
Emergent Power-Law Phase in the 2D Heisenberg Windmill Antiferromagnet: A Computational Experiment
NASA Astrophysics Data System (ADS)
Jeevanesan, Bhilahari; Chandra, Premala; Coleman, Piers; Orth, Peter P.
2015-10-01
In an extensive computational experiment, we test Polyakov's conjecture that under certain circumstances an isotropic Heisenberg model can develop algebraic spin correlations. We demonstrate the emergence of a multispin U(1) order parameter in a Heisenberg antiferromagnet on interpenetrating honeycomb and triangular lattices. The correlations of this relative phase angle are observed to decay algebraically at intermediate temperatures in an extended critical phase. Using finite-size scaling we show that both phase transitions are of the Berezinskii-Kosterlitz-Thouless type, and at lower temperatures we find long-range Z6 order.
Emergent Power-Law Phase in the 2D Heisenberg Windmill Antiferromagnet: A Computational Experiment.
Jeevanesan, Bhilahari; Chandra, Premala; Coleman, Piers; Orth, Peter P
2015-10-23
In an extensive computational experiment, we test Polyakov's conjecture that under certain circumstances an isotropic Heisenberg model can develop algebraic spin correlations. We demonstrate the emergence of a multispin U(1) order parameter in a Heisenberg antiferromagnet on interpenetrating honeycomb and triangular lattices. The correlations of this relative phase angle are observed to decay algebraically at intermediate temperatures in an extended critical phase. Using finite-size scaling we show that both phase transitions are of the Berezinskii-Kosterlitz-Thouless type, and at lower temperatures we find long-range Z(6) order.
NASA Astrophysics Data System (ADS)
Ryu, Gyeong Hee; Park, Hyo Ju; Ryou, Junga; Park, Jinwoo; Lee, Jongyeong; Kim, Gwangwoo; Shin, Hyeon Suk; Bielawski, Christopher W.; Ruoff, Rodney S.; Hong, Suklyun; Lee, Zonghoon
2015-06-01
The production of holes by electron beam irradiation in hexagonal boron nitride (hBN), which has a lattice similar to that of graphene, is monitored over time using atomic resolution transmission electron microscopy. The holes appear to be initiated by the formation of a vacancy of boron and grow in a manner that retains an overall triangular shape. The hole growth process involves the formation of single chains of B and N atoms and is accompanied by the ejection of atoms and bundles of atoms along the hole edges, as well as atom migration. These observations are compared to density functional theory calculations and molecular dynamics simulations.The production of holes by electron beam irradiation in hexagonal boron nitride (hBN), which has a lattice similar to that of graphene, is monitored over time using atomic resolution transmission electron microscopy. The holes appear to be initiated by the formation of a vacancy of boron and grow in a manner that retains an overall triangular shape. The hole growth process involves the formation of single chains of B and N atoms and is accompanied by the ejection of atoms and bundles of atoms along the hole edges, as well as atom migration. These observations are compared to density functional theory calculations and molecular dynamics simulations. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr01473e
Graphene Triangular Ballistic Rectifier: Fabrication and Characterisation
NASA Astrophysics Data System (ADS)
Auton, Gregory; Kumar, Roshan Krishna; Hill, Ernie; Song, Aimin
2016-09-01
It has been shown that graphene can demonstrate ballistic transport at room temperature. This opens up a range of practical applications that do not require graphene to have a band gap, which is one of the most significant challenges for its use in the electronics industry. Here, the very latest high mobility graphene (>100,000 cm2 V-1 s-1) fabrication techniques will be demonstrated so that one such device, called the triangular ballistic rectifier (TBR), can be characterised. The TBR is a four-terminal device with a triangular anti-dot at their intersection; two sides of the triangle are positioned and angled such that ballistic carriers from the two input electrodes are redirected like billiard balls to one of the two output contacts irrespective of the instantaneous polarity of the input. A responsivity of 2400 mV mW-1 is demonstrated at room temperature from a low-frequency input signal. The ballistic nature of the device is justified and explained in more detail with low-temperature measurements.
Kondo effects in triangular triple quantum dots
NASA Astrophysics Data System (ADS)
Oguri, Akira; Numata, Takahide; Nisikawa, Yunori; Hewson, A. C.
2009-03-01
We study the conductance through a triangular triple quantum dot, which is connected to two noninteracting leads, using the numerical renormalization group (NRG). It is found that the system shows a variety of Kondo effects depending on the filling of the triangle. The SU(4) Kondo effect occurs at half-filling, and a sharp conductance dip due to a phase lapse appears in the gate-voltage dependence. Furthermore, when four electrons occupy the three sites on average, a local S=1 moment, which is caused by the Nagaoka mechanism, is induced along the triangle. The temperature dependence of the entropy and spin susceptibility of the triangle shows that this moment is screened by the conduction electrons via two separate stages at different temperatures. The two-terminal and four-terminal conductances show a clear difference at the gate voltages, where the SU(4) or the S=1 Kondo effects occur[1]. We will also discuss effects of deformations of the triangular configuration, caused by the inhomogeneity in the inter-dot couplings and in the gate voltages. [4pt] [1] T.Numata, Y.Nisikawa, A.Oguri, and A.C.Hewson: arXiv:0808.3496.
NASA Astrophysics Data System (ADS)
Li, Shuai; Qiu, Wen-Xuan; Gao, Jin-Hua
2016-06-01
Recently, a new kind of artificial two dimensional (2D) electron lattice on the nanoscale, i.e. molecular graphene, has drawn a lot of interest, where the metal surface electrons are transformed into a honeycomb lattice via absorbing a molecular lattice on the metal surface [Gomes et al., Nature, 2012, 438, 306; Wang et al., Phys. Rev. Lett., 2014, 113, 196803]. In this work, we theoretically demonstrate that this technique can be readily used to build other complex 2D electron lattices on a metal surface, which are of high interest in the field of condensed matter physics. The main challenge to build a complex 2D electron lattice is that this is a quantum antidot system, where the absorbed molecule normally exerts a repulsive potential on the surface electrons. Thus, there is no straightforward corresponding relation between the molecular lattice pattern and the desired 2D lattice of surface electrons. Here, we give an interesting example about the Kagome lattice, which has exotic correlated electronic states. We design a special molecular pattern and show that this molecular lattice can transform the surface electrons into a Kagome-like lattice. The numerical simulation is conducted using a Cu(111) surface and CO molecules. We first estimate the effective parameters of the Cu/CO system by fitting experimental data of the molecular graphene. Then, we calculate the corresponding energy bands and LDOS of the surface electrons in the presence of the proposed molecular lattice. Finally, we interpret the numerical results by the tight binding model of the Kagome lattice. We hope that our work can stimulate further theoretical and experimental interest in this novel artificial 2D electron lattice system.
Li, Shuai; Qiu, Wen-Xuan; Gao, Jin-Hua
2016-07-01
Recently, a new kind of artificial two dimensional (2D) electron lattice on the nanoscale, i.e. molecular graphene, has drawn a lot of interest, where the metal surface electrons are transformed into a honeycomb lattice via absorbing a molecular lattice on the metal surface [Gomes et al., Nature, 2012, 438, 306; Wang et al., Phys. Rev. Lett., 2014, 113, 196803]. In this work, we theoretically demonstrate that this technique can be readily used to build other complex 2D electron lattices on a metal surface, which are of high interest in the field of condensed matter physics. The main challenge to build a complex 2D electron lattice is that this is a quantum antidot system, where the absorbed molecule normally exerts a repulsive potential on the surface electrons. Thus, there is no straightforward corresponding relation between the molecular lattice pattern and the desired 2D lattice of surface electrons. Here, we give an interesting example about the Kagome lattice, which has exotic correlated electronic states. We design a special molecular pattern and show that this molecular lattice can transform the surface electrons into a Kagome-like lattice. The numerical simulation is conducted using a Cu(111) surface and CO molecules. We first estimate the effective parameters of the Cu/CO system by fitting experimental data of the molecular graphene. Then, we calculate the corresponding energy bands and LDOS of the surface electrons in the presence of the proposed molecular lattice. Finally, we interpret the numerical results by the tight binding model of the Kagome lattice. We hope that our work can stimulate further theoretical and experimental interest in this novel artificial 2D electron lattice system. PMID:27279292
Perspectives for spintronics in 2D materials
NASA Astrophysics Data System (ADS)
Han, Wei
2016-03-01
The past decade has been especially creative for spintronics since the (re)discovery of various two dimensional (2D) materials. Due to the unusual physical characteristics, 2D materials have provided new platforms to probe the spin interaction with other degrees of freedom for electrons, as well as to be used for novel spintronics applications. This review briefly presents the most important recent and ongoing research for spintronics in 2D materials.
Yaqi Wang; Jean C. Ragusa
2011-02-01
Standard and goal-oriented adaptive mesh refinement (AMR) techniques are presented for the linear Boltzmann transport equation. A posteriori error estimates are employed to drive the AMR process and are based on angular-moment information rather than on directional information, leading to direction-independent adapted meshes. An error estimate based on a two-mesh approach and a jump-based error indicator are compared for various test problems. In addition to the standard AMR approach, where the global error in the solution is diminished, a goal-oriented AMR procedure is devised and aims at reducing the error in user-specified quantities of interest. The quantities of interest are functionals of the solution and may include, for instance, point-wise flux values or average reaction rates in a subdomain. A high-order (up to order 4) Discontinuous Galerkin technique with standard upwinding is employed for the spatial discretization; the discrete ordinates method is used to treat the angular variable.
Quantitative 2D liquid-state NMR.
Giraudeau, Patrick
2014-06-01
Two-dimensional (2D) liquid-state NMR has a very high potential to simultaneously determine the absolute concentration of small molecules in complex mixtures, thanks to its capacity to separate overlapping resonances. However, it suffers from two main drawbacks that probably explain its relatively late development. First, the 2D NMR signal is strongly molecule-dependent and site-dependent; second, the long duration of 2D NMR experiments prevents its general use for high-throughput quantitative applications and affects its quantitative performance. Fortunately, the last 10 years has witnessed an increasing number of contributions where quantitative approaches based on 2D NMR were developed and applied to solve real analytical issues. This review aims at presenting these recent efforts to reach a high trueness and precision in quantitative measurements by 2D NMR. After highlighting the interest of 2D NMR for quantitative analysis, the different strategies to determine the absolute concentrations from 2D NMR spectra are described and illustrated by recent applications. The last part of the manuscript concerns the recent development of fast quantitative 2D NMR approaches, aiming at reducing the experiment duration while preserving - or even increasing - the analytical performance. We hope that this comprehensive review will help readers to apprehend the current landscape of quantitative 2D NMR, as well as the perspectives that may arise from it.
Cold atoms in a rotating optical lattice
NASA Astrophysics Data System (ADS)
Foot, Christopher J.
2009-05-01
We have demonstrated a novel experimental arrangement which can rotate a two-dimensional optical lattice at frequencies up to several kilohertz. Our arrangement also allows the periodicity of the optical lattice to be varied dynamically, producing a 2D ``accordion lattice'' [1]. The angles of the laser beams are controlled by acousto-optic deflectors and this allows smooth changes with little heating of the trapped cold (rubidium) atoms. We have loaded a BEC into lattices with periodicities ranging from 1.8μm to 18μm, observing the collapse and revival of the diffraction orders of the condensate over a large range of lattice parameters as recently reported by a group in NIST [2]. We have also imaged atoms in situ in a 2D lattice over a range of lattice periodicities. Ultracold atoms in a rotating lattice can be used for the direct quantum simulation of strongly correlated systems under large effective magnetic fields, i.e. the Hamiltonian of the atoms in the rotating frame resembles that of a charged particle in a strong magnetic field. In the future, we plan to use this to investigate a range of phenomena such as the analogue of the fractional quantum Hall effect. [4pt] [1] R. A. Williams, J. D. Pillet, S. Al-Assam, B. Fletcher, M. Shotter, and C. J. Foot, ``Dynamic optical lattices: two-dimensional rotating and accordion lattices for ultracold atoms,'' Opt. Express 16, 16977-16983 (2008) [0pt] [2] J. H. Huckans, I. B. Spielman, B. Laburthe Tolra, W. D. Phillips, and J. V. Porto, Quantum and Classical Dynamics of a BEC in a Large-Period Optical Lattice, arXiv:0901.1386v1
Photonic crystal based 2D integrating cell for sensing applications
NASA Astrophysics Data System (ADS)
Fohrmann, Lena Simone; Petrov, Alexander Y.; Sommer, Gerrit; Krauss, Thomas; Eich, Manfred
2016-04-01
We present a concept of a silicon slab based 2D integrating cell where photonic crystal (PhC) reflectors are used in order to confine light in a two-dimensional area to acquire a long propagation length. The evanescent field of the guided wave can be used for sensing applications. We use FDTD simulations to investigate the dependence of the reflectivity of photonic crystal mirrors with a hexagonal lattice. The reflectivity in ΓM direction demonstrates reduced vertical losses compared to the ΓK direction and can be further improved by adiabatically tapering the hole radii of the photonic crystal. A small hexagonal 2D integrating cell was studied with PhC boundaries oriented in ΓM and ΓK direction. It is shown that average reflectivities of 99% can be obtained in a rectangular 2D cell with optimized reflector design, limited only by residual vertical scattering losses at the PhC boundary. This reflectivity is already comparable to the best metallic reflectors.
Laminar natural convection in right triangular enclosures
NASA Astrophysics Data System (ADS)
Fuad Kent, E.; Asmaz, E.; Ozerbay, S.
2007-12-01
In this study, natural convection in non-rectangular enclosures is analyzed numerically. Streamlines and isotherms are presented for different triangular enclosures with different boundary conditions and Rayleigh numbers. Mean Nusselt numbers on hot walls are also calculated in order to make comparisons between different cases. The solutions are obtained for different aspect ratios where boundary conditions represent the wintertime heating of an attic space. This made possible to investigate the effect of aspect ratio on natural convection. In this study, quarter circular enclosure, which is very similar to right triangles, is also examined. Consequently, we had the opportunity to analyze how shape changes affect the flow pattern. The results of the calculations are compared with the similar enclosures and boundary conditions.
Efficiency considerations in triangular adaptive mesh refinement.
Behrens, Jörn; Bader, Michael
2009-11-28
Locally or adaptively refined meshes have been successfully applied to simulation applications involving multi-scale phenomena in the geosciences. In particular, for situations with complex geometries or domain boundaries, meshes with triangular or tetrahedral cells demonstrate their superior ability to accurately represent relevant realistic features. On the other hand, these methods require more complex data structures and are therefore less easily implemented, maintained and optimized. Acceptance in the Earth-system modelling community is still low. One of the major drawbacks is posed by indirect addressing due to unstructured or dynamically changing data structures and correspondingly lower efficiency of the related computations. In this paper, we will derive several strategies to circumvent the mentioned efficiency constraint. In particular, we will apply recent computational sciences methods in combination with results of classical mathematics (space-filling curves) in order to linearize the complex data and access structure.
Triangular model integrating clinical teaching and assessment.
Abdelaziz, Adel; Koshak, Emad
2014-01-01
Structuring clinical teaching is a challenge facing medical education curriculum designers. A variety of instructional methods on different domains of learning are indicated to accommodate different learning styles. Conventional methods of clinical teaching, like training in ambulatory care settings, are prone to the factor of coincidence in having varieties of patient presentations. Accordingly, alternative methods of instruction are indicated to compensate for the deficiencies of these conventional methods. This paper presents an initiative that can be used to design a checklist as a blueprint to guide appropriate selection and implementation of teaching/learning and assessment methods in each of the educational courses and modules based on educational objectives. Three categories of instructional methods were identified, and within each a variety of methods were included. These categories are classroom-type settings, health services-based settings, and community service-based settings. Such categories have framed our triangular model of clinical teaching and assessment.
Biological synthesis of triangular gold nanoprisms
NASA Astrophysics Data System (ADS)
Shankar, S. Shiv; Rai, Akhilesh; Ankamwar, Balaprasad; Singh, Amit; Ahmad, Absar; Sastry, Murali
2004-07-01
The optoelectronic and physicochemical properties of nanoscale matter are a strong function of particle size. Nanoparticle shape also contributes significantly to modulating their electronic properties. Several shapes ranging from rods to wires to plates to teardrop structures may be obtained by chemical methods; triangular nanoparticles have been synthesized by using a seeded growth process. Here, we report the discovery that the extract from the lemongrass plant, when reacted with aqueous chloroaurate ions, yields a high percentage of thin, flat, single-crystalline gold nanotriangles. The nanotriangles seem to grow by a process involving rapid reduction, assembly and room-temperature sintering of 'liquid-like' spherical gold nanoparticles. The anisotropy in nanoparticle shape results in large near-infrared absorption by the particles, and highly anisotropic electron transport in films of the nanotriangles.
Coherent transfer by adiabatic passage in two-dimensional lattices
Longhi, Stefano
2014-09-15
Coherent tunneling by adiabatic passage (CTAP) is a well-established technique for robust spatial transport of quantum particles in linear chains. Here we introduce two exactly-solvable models where the CTAP protocol can be extended to two-dimensional lattice geometries. Such bi-dimensional lattice models are synthesized from time-dependent second-quantization Hamiltonians, in which the bosonic field operators evolve adiabatically like in an ordinary three-level CTAP scheme thus ensuring adiabatic passage in Fock space. - Highlights: • New ways of coherent transport by adiabatic passage (CTAP) in 2D lattices. • Synthesis of exactly-solvable 2D lattices from a simple three-well model. • CTAP in 2D lattices can be exploited for quantum state transfer.
NASA Astrophysics Data System (ADS)
Buchheim, Jakob; Wyss, Roman M.; Shorubalko, Ivan; Park, Hyung Gyu
2016-04-01
We report experimentally and theoretically the behavior of freestanding graphene subjected to bombardment of energetic ions, investigating the capability of large-scale patterning of freestanding graphene with nanometer sized features by focused ion beam technology. A precise control over the He+ and Ga+ irradiation offered by focused ion beam techniques enables investigating the interaction of the energetic particles and graphene suspended with no support and allows determining sputter yields of the 2D lattice. We found a strong dependency of the 2D sputter yield on the species and kinetic energy of the incident ion beams. Freestanding graphene shows material semi-transparency to He+ at high energies (10-30 keV) allowing the passage of >97% He+ particles without creating destructive lattice vacancy. Large Ga+ ions (5-30 keV), in contrast, collide far more often with the graphene lattice to impart a significantly higher sputter yield of ~50%. Binary collision theory applied to monolayer and few-layer graphene can successfully elucidate this collision mechanism, in great agreement with experiments. Raman spectroscopy analysis corroborates the passage of a large fraction of He+ ions across graphene without much damaging the lattice whereas several colliding ions create single vacancy defects. Physical understanding of the interaction between energetic particles and suspended graphene can practically lead to reproducible and efficient pattern generation of unprecedentedly small features on 2D materials by design, manifested by our perforation of sub-5 nm pore arrays. This capability of nanometer-scale precision patterning of freestanding 2D lattices shows the practical applicability of focused ion beam technology to 2D material processing for device fabrication and integration.We report experimentally and theoretically the behavior of freestanding graphene subjected to bombardment of energetic ions, investigating the capability of large-scale patterning of
Mirror effects and optical meta-surfaces in 2d atomic arrays
NASA Astrophysics Data System (ADS)
Shahmoon, Ephraim; Wild, Dominik; Lukin, Mikhail; Yelin, Susanne
2016-05-01
Strong optical response of natural and artificial (meta-) materials typically relies on the fact that the lattice constant that separates their constituent particles (atoms or electromagnetic resonators, respectively) is much smaller than the optical wavelength. Here we consider a single layer of a 2d atom array with a lattice constant on the order of an optical wavelength, which can be thought of as a highly dilute 2d metamaterial (meta-surface). Our theoretical analysis shows how strong scattering of resonant incoming light off the array can be controlled by choosing its lattice constant, e.g. allowing the array to operate as a perfect mirror or a retro-reflector for most incident angles of the incoming light. We discuss the prospects for quantum metasurfaces, i.e. the ability to shape the output quantum state of light by controlling the atomic states, and the possible generality of our results as a universal wave phenomena.
Psyplot: Visualizing rectangular and triangular Climate Model Data with Python
NASA Astrophysics Data System (ADS)
Sommer, Philipp
2016-04-01
The development and use of climate models often requires the visualization of geo-referenced data. Creating visualizations should be fast, attractive, flexible, easily applicable and easily reproducible. There is a wide range of software tools available for visualizing raster data, but they often are inaccessible to many users (e.g. because they are difficult to use in a script or have low flexibility). In order to facilitate easy visualization of geo-referenced data, we developed a new framework called "psyplot," which can aid earth system scientists with their daily work. It is purely written in the programming language Python and primarily built upon the python packages matplotlib, cartopy and xray. The package can visualize data stored on the hard disk (e.g. NetCDF, GeoTIFF, any other file format supported by the xray package), or directly from the memory or Climate Data Operators (CDOs). Furthermore, data can be visualized on a rectangular grid (following or not following the CF Conventions) and on a triangular grid (following the CF or UGRID Conventions). Psyplot visualizes 2D scalar and vector fields, enabling the user to easily manage and format multiple plots at the same time, and to export the plots into all common picture formats and movies covered by the matplotlib package. The package can currently be used in an interactive python session or in python scripts, and will soon be developed for use with a graphical user interface (GUI). Finally, the psyplot framework enables flexible configuration, allows easy integration into other scripts that uses matplotlib, and provides a flexible foundation for further development.
Staring 2-D hadamard transform spectral imager
Gentry, Stephen M.; Wehlburg, Christine M.; Wehlburg, Joseph C.; Smith, Mark W.; Smith, Jody L.
2006-02-07
A staring imaging system inputs a 2D spatial image containing multi-frequency spectral information. This image is encoded in one dimension of the image with a cyclic Hadamarid S-matrix. The resulting image is detecting with a spatial 2D detector; and a computer applies a Hadamard transform to recover the encoded image.
Buchheim, Jakob; Wyss, Roman M; Shorubalko, Ivan; Park, Hyung Gyu
2016-04-21
We report experimentally and theoretically the behavior of freestanding graphene subjected to bombardment of energetic ions, investigating the capability of large-scale patterning of freestanding graphene with nanometer sized features by focused ion beam technology. A precise control over the He(+) and Ga(+) irradiation offered by focused ion beam techniques enables investigating the interaction of the energetic particles and graphene suspended with no support and allows determining sputter yields of the 2D lattice. We found a strong dependency of the 2D sputter yield on the species and kinetic energy of the incident ion beams. Freestanding graphene shows material semi-transparency to He(+) at high energies (10-30 keV) allowing the passage of >97% He(+) particles without creating destructive lattice vacancy. Large Ga(+) ions (5-30 keV), in contrast, collide far more often with the graphene lattice to impart a significantly higher sputter yield of ∼50%. Binary collision theory applied to monolayer and few-layer graphene can successfully elucidate this collision mechanism, in great agreement with experiments. Raman spectroscopy analysis corroborates the passage of a large fraction of He(+) ions across graphene without much damaging the lattice whereas several colliding ions create single vacancy defects. Physical understanding of the interaction between energetic particles and suspended graphene can practically lead to reproducible and efficient pattern generation of unprecedentedly small features on 2D materials by design, manifested by our perforation of sub-5 nm pore arrays. This capability of nanometer-scale precision patterning of freestanding 2D lattices shows the practical applicability of focused ion beam technology to 2D material processing for device fabrication and integration.
The effective half-filled band model is inappropriate for the dimerized 2D organic superconductors
NASA Astrophysics Data System (ADS)
Gomes, Niladri; Clay, R. Torsten; Mazumdar, Sumit
2013-03-01
The antiferromagnetism in κ-(ET)2X can be understood within the effective 1/2-filled band anisotropic triangular lattice Hubbard Hamiltonian for strong anisotropy. DMFT theories have claimed antiferromagnetic-to-superconductor transition within the same model, as the anistropy is reduced. In previous work we have shown the absence of superconductivity within the triangular lattice 1/2-filled band Hubbard model for any Hubbard U and any anisotropy. Other DMFT approaches theories have claimed superconductivity within the so-called Hubbard-Heisenberg model, which incorporates an additional antiferromagnetic spin-exchange over and above that due to the Hubbard U. Very recent work has also claimed a valence-bond solid (VBS) phase within the Hubbard-Heisenberg model, which would seemingly explain the observed VBS phase in EtMe3P[Pd(dmit)2]2. We report exact calculations that show that neither the VBS nor the superconducting phase occur within the Hubbard-Heisenberg model, showing clearly that the effective 1/2-filled band model is unsuitable for describing the complete phase space of the κ-(ET)2X. Our work raises serious doubts about the DMFT theories of superconductivity of metal intercalated C60 and picene. Supported by DOE Grant Number: DE-FG02-06ER46315
2D materials for nanophotonic devices
NASA Astrophysics Data System (ADS)
Xu, Renjing; Yang, Jiong; Zhang, Shuang; Pei, Jiajie; Lu, Yuerui
2015-12-01
Two-dimensional (2D) materials have become very important building blocks for electronic, photonic, and phononic devices. The 2D material family has four key members, including the metallic graphene, transition metal dichalcogenide (TMD) layered semiconductors, semiconducting black phosphorous, and the insulating h-BN. Owing to the strong quantum confinements and defect-free surfaces, these atomically thin layers have offered us perfect platforms to investigate the interactions among photons, electrons and phonons. The unique interactions in these 2D materials are very important for both scientific research and application engineering. In this talk, I would like to briefly summarize and highlight the key findings, opportunities and challenges in this field. Next, I will introduce/highlight our recent achievements. We demonstrated atomically thin micro-lens and gratings using 2D MoS2, which is the thinnest optical component around the world. These devices are based on our discovery that the elastic light-matter interactions in highindex 2D materials is very strong. Also, I would like to introduce a new two-dimensional material phosphorene. Phosphorene has strongly anisotropic optical response, which creates 1D excitons in a 2D system. The strong confinement in phosphorene also enables the ultra-high trion (charged exciton) binding energies, which have been successfully measured in our experiments. Finally, I will briefly talk about the potential applications of 2D materials in energy harvesting.
Internal Photoemission Spectroscopy of 2-D Materials
NASA Astrophysics Data System (ADS)
Nguyen, Nhan; Li, Mingda; Vishwanath, Suresh; Yan, Rusen; Xiao, Shudong; Xing, Huili; Cheng, Guangjun; Hight Walker, Angela; Zhang, Qin
Recent research has shown the great benefits of using 2-D materials in the tunnel field-effect transistor (TFET), which is considered a promising candidate for the beyond-CMOS technology. The on-state current of TFET can be enhanced by engineering the band alignment of different 2D-2D or 2D-3D heterostructures. Here we present the internal photoemission spectroscopy (IPE) approach to determine the band alignments of various 2-D materials, in particular SnSe2 and WSe2, which have been proposed for new TFET designs. The metal-oxide-2-D semiconductor test structures are fabricated and characterized by IPE, where the band offsets from the 2-D semiconductor to the oxide conduction band minimum are determined by the threshold of the cube root of IPE yields as a function of photon energy. In particular, we find that SnSe2 has a larger electron affinity than most semiconductors and can be combined with other semiconductors to form near broken-gap heterojunctions with low barrier heights which can produce a higher on-state current. The details of data analysis of IPE and the results from Raman spectroscopy and spectroscopic ellipsometry measurements will also be presented and discussed.
Frustrated Cooper pairing and f-wave supersolidity in cold-atom optical lattices
Hung, Hsiang-Hsuan; Lee, Wei-Cheng; Wu Congjun
2011-04-01
Geometric frustration in quantum magnetism refers to the fact that magnetic interactions on different bonds cannot be simultaneously minimized. The usual Cooper pairing systems favor uniform spatial distributions of pairing phases among different lattice sites without frustration. In contrast, we propose ''frustrated Cooper pairing'' in non-bipartite lattices which leads to supersolid states of Cooper pairs. Not only the amplitudes of the pairing order parameter but also its signs vary from site to site. This exotic pairing state naturally occurs in the p-orbital bands in optical lattices with ultracold spinless fermions. In the triangular lattice, it exhibits an unconventional supersolid state with the f-wave symmetry.
Unusual dimensionality effects and surface charge density in 2D Mg(OH)2
Suslu, Aslihan; Wu, Kedi; Sahin, Hasan; Chen, Bin; Yang, Sijie; Cai, Hui; Aoki, Toshihiro; Horzum, Seyda; Kang, Jun; Peeters, Francois M.; Tongay, Sefaattin
2016-01-01
We present two-dimensional Mg(OH)2 sheets and their vertical heterojunctions with CVD-MoS2 for the first time as flexible 2D insulators with anomalous lattice vibration and chemical and physical properties. New hydrothermal crystal growth technique enabled isolation of environmentally stable monolayer Mg(OH)2 sheets. Raman spectroscopy and vibrational calculations reveal that the lattice vibrations of Mg(OH)2 have fundamentally different signature peaks and dimensionality effects compared to other 2D material systems known to date. Sub-wavelength electron energy-loss spectroscopy measurements and theoretical calculations show that Mg(OH)2 is a 6 eV direct-gap insulator in 2D, and its optical band gap displays strong band renormalization effects from monolayer to bulk, marking the first experimental confirmation of confinement effects in 2D insulators. Interestingly, 2D-Mg(OH)2 sheets possess rather strong surface polarization (charge) effects which is in contrast to electrically neutral h-BN materials. Using 2D-Mg(OH)2 sheets together with CVD-MoS2 in the vertical stacking shows that a strong change transfer occurs from n-doped CVD-MoS2 sheets to Mg(OH)2, naturally depleting the semiconductor, pushing towards intrinsic doping limit and enhancing overall optical performance of 2D semiconductors. Results not only establish unusual confinement effects in 2D-Mg(OH)2, but also offer novel 2D-insulating material with unique physical, vibrational, and chemical properties for potential applications in flexible optoelectronics. PMID:26846617
Unusual dimensionality effects and surface charge density in 2D Mg(OH)2
NASA Astrophysics Data System (ADS)
Suslu, Aslihan; Wu, Kedi; Sahin, Hasan; Chen, Bin; Yang, Sijie; Cai, Hui; Aoki, Toshihiro; Horzum, Seyda; Kang, Jun; Peeters, Francois M.; Tongay, Sefaattin
2016-02-01
We present two-dimensional Mg(OH)2 sheets and their vertical heterojunctions with CVD-MoS2 for the first time as flexible 2D insulators with anomalous lattice vibration and chemical and physical properties. New hydrothermal crystal growth technique enabled isolation of environmentally stable monolayer Mg(OH)2 sheets. Raman spectroscopy and vibrational calculations reveal that the lattice vibrations of Mg(OH)2 have fundamentally different signature peaks and dimensionality effects compared to other 2D material systems known to date. Sub-wavelength electron energy-loss spectroscopy measurements and theoretical calculations show that Mg(OH)2 is a 6 eV direct-gap insulator in 2D, and its optical band gap displays strong band renormalization effects from monolayer to bulk, marking the first experimental confirmation of confinement effects in 2D insulators. Interestingly, 2D-Mg(OH)2 sheets possess rather strong surface polarization (charge) effects which is in contrast to electrically neutral h-BN materials. Using 2D-Mg(OH)2 sheets together with CVD-MoS2 in the vertical stacking shows that a strong change transfer occurs from n-doped CVD-MoS2 sheets to Mg(OH)2, naturally depleting the semiconductor, pushing towards intrinsic doping limit and enhancing overall optical performance of 2D semiconductors. Results not only establish unusual confinement effects in 2D-Mg(OH)2, but also offer novel 2D-insulating material with unique physical, vibrational, and chemical properties for potential applications in flexible optoelectronics.
Vortex lattices in theory and practice
Capmbell, Laurence J.
1988-01-01
The formal simplicity of ideal point vortex systems in two dimensions has long attracted interest in both their exact solutions and in their capacity to simulate physical processes. Attention here is focused on infinite, two-fold periodic vortex arrays, including an expression for the energy density of an arbitrary vortex lattice (i.e., an arbitrary number of vortices with arbitrary strengths in a unit cell parallelogram of arbitrary shape). For the case of two vortices per unit cell, the morphology of stable lattices can be described completely. A non-trivial physical realization of such lattices is a rotating mixture of /sup 3/He and /sup 4/He at temperatures so low that both isotopic components are superfluid. The structure of the expected lattices is quite different from the usual triangular structure. Magnetic flux lines in high-temperature superconductors show a one-parameter family of degenerate ground state of the lattice due to the anisotropy of the vortex--vortex interaction. A final topic, closely related to Josephson-junction arrays, is the case of vortices confined to a grid. That is, the vortices interact pair-wise in the usual manner but are constrained to occupy only locations on an independent periodic grid. By using vortex relaxation methods in the continuum and then imposing the grid it is possible to find low-lying states extremely rapidly compared to previous Monte Carlo calculations. 11 refs., 8 figs.
2D materials: to graphene and beyond.
Mas-Ballesté, Rubén; Gómez-Navarro, Cristina; Gómez-Herrero, Julio; Zamora, Félix
2011-01-01
This review is an attempt to illustrate the different alternatives in the field of 2D materials. Graphene seems to be just the tip of the iceberg and we show how the discovery of alternative 2D materials is starting to show the rest of this iceberg. The review comprises the current state-of-the-art of the vast literature in concepts and methods already known for isolation and characterization of graphene, and rationalizes the quite disperse literature in other 2D materials such as metal oxides, hydroxides and chalcogenides, and metal-organic frameworks.
Ginsparg, P.
1991-01-01
These are introductory lectures for a general audience that give an overview of the subject of matrix models and their application to random surfaces, 2d gravity, and string theory. They are intentionally 1.5 years out of date.
Ginsparg, P.
1991-12-31
These are introductory lectures for a general audience that give an overview of the subject of matrix models and their application to random surfaces, 2d gravity, and string theory. They are intentionally 1.5 years out of date.
Brittle damage models in DYNA2D
Faux, D.R.
1997-09-01
DYNA2D is an explicit Lagrangian finite element code used to model dynamic events where stress wave interactions influence the overall response of the system. DYNA2D is often used to model penetration problems involving ductile-to-ductile impacts; however, with the advent of the use of ceramics in the armor-anti-armor community and the need to model damage to laser optics components, good brittle damage models are now needed in DYNA2D. This report will detail the implementation of four brittle damage models in DYNA2D, three scalar damage models and one tensor damage model. These new brittle damage models are then used to predict experimental results from three distinctly different glass damage problems.
Coherently Tunable Triangular Trefoil Phaseonium Metamaterial
NASA Astrophysics Data System (ADS)
Nguyen, D. M.; Soci, Cesare; Ooi, C. H. Raymond
2016-02-01
Phaseonium is a three-level Λ quantum system, in which a coherent microwave and an optical control (pump) beams can be used to actively modulate the dielectric response. Here we propose a new metamaterial structure comprising of a periodic array of triangular phaseonium metamolecules arranged as a trefoil. We present a computational study of the spatial distribution of magnetic and electric fields of the probe light and the corresponding transmission and reflection, for various parameters of the optical and microwave beams. For specific values of the probing frequencies and control fields, the phaseonium can display either metallic or dielectric optical response. We find that, in the metallic regime, the phaseonium metamaterial structure supports extremely large transmission, with optical amplification at large enough intensity of the microwave thanks to strong surface plasmon coupling; while, in the dielectric regime without microwave excitation, the transmission bandwidth can be tuned by varying the control beam intensity. Implementation of such phaseonium metamaterial structure in solid-state systems, such as patterned crystals doped with rare-earth elements or dielectric matrices embedded with quantum dots, could enable a new class of actively tunable quantum metamaterials.
Coherently Tunable Triangular Trefoil Phaseonium Metamaterial
Nguyen, D. M.; Soci, Cesare; Ooi, C. H. Raymond
2016-01-01
Phaseonium is a three-level Λ quantum system, in which a coherent microwave and an optical control (pump) beams can be used to actively modulate the dielectric response. Here we propose a new metamaterial structure comprising of a periodic array of triangular phaseonium metamolecules arranged as a trefoil. We present a computational study of the spatial distribution of magnetic and electric fields of the probe light and the corresponding transmission and reflection, for various parameters of the optical and microwave beams. For specific values of the probing frequencies and control fields, the phaseonium can display either metallic or dielectric optical response. We find that, in the metallic regime, the phaseonium metamaterial structure supports extremely large transmission, with optical amplification at large enough intensity of the microwave thanks to strong surface plasmon coupling; while, in the dielectric regime without microwave excitation, the transmission bandwidth can be tuned by varying the control beam intensity. Implementation of such phaseonium metamaterial structure in solid-state systems, such as patterned crystals doped with rare-earth elements or dielectric matrices embedded with quantum dots, could enable a new class of actively tunable quantum metamaterials. PMID:26879520
Chemical Approaches to 2D Materials.
Samorì, Paolo; Palermo, Vincenzo; Feng, Xinliang
2016-08-01
Chemistry plays an ever-increasing role in the production, functionalization, processing and applications of graphene and other 2D materials. This special issue highlights a selection of enlightening chemical approaches to 2D materials, which nicely reflect the breadth of the field and convey the excitement of the individuals involved in it, who are trying to translate graphene and related materials from the laboratory into a real, high-impact technology. PMID:27478083
Chemical Approaches to 2D Materials.
Samorì, Paolo; Palermo, Vincenzo; Feng, Xinliang
2016-08-01
Chemistry plays an ever-increasing role in the production, functionalization, processing and applications of graphene and other 2D materials. This special issue highlights a selection of enlightening chemical approaches to 2D materials, which nicely reflect the breadth of the field and convey the excitement of the individuals involved in it, who are trying to translate graphene and related materials from the laboratory into a real, high-impact technology.
NASA Astrophysics Data System (ADS)
Potasz, P.; Güçlü, A. D.; Wójs, A.; Hawrylak, P.
2012-02-01
We present a theory of electronic properties of gated triangular graphene quantum dots with zigzag edges as a function of size and carrier density. We focus on electronic correlations, spin, and geometrical effects using a combination of atomistic tight-binding, Hartree-Fock, and configuration interaction methods (TB + HF + CI), including long-range Coulomb interactions. The single-particle energy spectrum of triangular dots with zigzag edges exhibits a degenerate shell at the Fermi level with a degeneracy Nedge proportional to the edge size. We determine the effect of the electron-electron interactions on the ground state, the total spin, and the excitation spectrum as a function of a shell filling and the degeneracy of the shell using TB + HF + CI for Nedge<12 and approximate CI method for Nedge⩾12. For a half-filled neutral shell we find spin-polarized ground state for structures up to N=500 atoms in agreement with previous ab initio and mean-field calculations and in agreement with Lieb's theorem for a Hubbard model on a bipartite lattice. Adding a single electron leads to the complete spin depolarization for Nedge⩽9. For larger structures, the spin depolarization is shown to occur at different filling factors. Away from half-fillings excess electrons(holes) are shown to form Wigner-like spin-polarized triangular molecules corresponding to large gaps in the excitation spectrum. The validity of conclusions is assessed by a comparison of results obtained from different levels of approximations. While for the charge-neutral system all methods give qualitatively similar results, away from the charge neutrality an inclusion of all Coulomb scattering terms is necessary to produce results presented here.
2d index and surface operators
NASA Astrophysics Data System (ADS)
Gadde, Abhijit; Gukov, Sergei
2014-03-01
In this paper we compute the superconformal index of 2d (2, 2) supersymmetric gauge theories. The 2d superconformal index, a.k.a. flavored elliptic genus, is computed by a unitary matrix integral much like the matrix integral that computes the 4d superconformal index. We compute the 2d index explicitly for a number of examples. In the case of abelian gauge theories we see that the index is invariant under flop transition and under CY-LG correspondence. The index also provides a powerful check of the Seiberg-type duality for non-abelian gauge theories discovered by Hori and Tong. In the later half of the paper, we study half-BPS surface operators in = 2 super-conformal gauge theories. They are engineered by coupling the 2d (2, 2) supersymmetric gauge theory living on the support of the surface operator to the 4d = 2 theory, so that different realizations of the same surface operator with a given Levi type are related by a 2d analogue of the Seiberg duality. The index of this coupled system is computed by using the tools developed in the first half of the paper. The superconformal index in the presence of surface defect is expected to be invariant under generalized S-duality. We demonstrate that it is indeed the case. In doing so the Seiberg-type duality of the 2d theory plays an important role.
Quantum Phase Transitions of Hard-Core Bosons on the Kagome Lattice
NASA Astrophysics Data System (ADS)
Isakov, S. V.; Melko, R. G.; Sengupta, K.; Wessel, S.; Kim, Yong Baek
2006-03-01
We study hard-core bosons with nearest-neighbor repulsion on the kagome lattice at different filling factors using quantum Monte Carlo simulations and a dual vortex theory. At half-filling, the ground state of the system is always a uniform superfluid in contrast to the case of the triangular lattice. There exists a quantum phase transition from a superfluid to a valence bond solid phase away from half-filling. The possibility of unusual quantum criticality is investigated.
Interior, detail at rear of theater showing partition with triangular ...
Interior, detail at rear of theater showing partition with triangular roof projections. Doors lead to lobby. - Fitzsimons General Hospital, Theater, Northwest Corner of East McAfee Avenue & South Page Street, Aurora, Adams County, CO
7. NORTH EXTERIOR SIDE SHOWING TRIANGULAR KNEE BRACE SUPPORTS AND ...
7. NORTH EXTERIOR SIDE SHOWING TRIANGULAR KNEE BRACE SUPPORTS AND ENCLOSED PORCH SCREENED WINDOWS. VIEW TO SOUTH. - Big Creek Hydroelectric System, Powerhouse 8, Operator Cottage, Big Creek, Big Creek, Fresno County, CA
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.
The Centre of Mass of a Triangular Plate
ERIC Educational Resources Information Center
Slusarenko, Viktor; Rojas, Roberto; Fuster, Gonzalo
2008-01-01
We present a derivation for the coordinates of the centre of mass--or centre of gravity--of a homogeneous triangular plate by using scaling and symmetry. We scale the triangular plate by a factor of 2 and divide its area into four plates identical to the original. By symmetry, we assert that the centre of mass of two identical masses lies at the…
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.
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.
Free Vibration of Shear-Deformable General Triangular Plates
NASA Astrophysics Data System (ADS)
Karunasena, W.; Kitipornchai, S.
1997-01-01
An analysis of free vibration of shear-deformable general triangular plates with arbitrary combinations of boundary conditions is presented. The Reissner-Mindlin plate theory is used to incorporate shear deformation effects in the analysis. The triangular plate is first mapped onto a basic square plate. The Rayleigh-Ritz method with an admissible displacement function expressed as a product of a two-dimensional simple polynomial and a basic function is then used to obtain the governing eigenvalue equation. The basic function is chosen as the product of boundary expressions of the basic square plate, each raised to an appropriate power to satisfy the various geometric boundary conditions of the actual triangular plate Gaussian quadrature is used for numerical evaluation of stiffness and mass matrices. The natural frequencies of general triangular Mindlin plates with different combinations of free, simply supported and clamped conditions are determined. Wherever possible, the results are verified by comparison with existing published solutions. A comprehensive parametric study of natural frequencies of general triangular plates with all three edges clamped is presented graphically. No previous results are known to exist for general triangular Mindlin plates having arbitrary combinations of boundary conditions.
The triangular maps with closed sets of periodic points
NASA Astrophysics Data System (ADS)
Kupka, Jiri
2006-07-01
In a recent paper we provided a characterization of triangular maps of the square, i.e., maps given by F(x,y)=(f(x),gx(y)), satisfying condition (P1) that any chain recurrent point is periodic. For continuous maps of the interval, there is a list of 18 other conditions equivalent to (P1), including (P2) that there is no infinite [omega]-limit set, (P3) that the set of periodic points is closed and (P4) that any regularly recurrent point is periodic, for instance. We provide an almost complete classification among these conditions for triangular maps, improve a result given by C. Arteaga [C. Arteaga, Smooth triangular maps of the square with closed set of periodic points, J. Math. Anal. Appl. 196 (1995) 987-997] and state an open problem concerning minimal sets of the triangular maps. The paper solves partially a problem formulated by A.N. Sharkovsky in the eighties. The mentioned open problem, the validity of (P4) => (P3), is related to the question whether some regularly recurrent point lies in the fibres over an f-minimal set possessing a regularly recurrent point. We answered this question in the positive for triangular maps with nondecreasing fiber maps. Consequently, the classification is completed for monotone triangular maps.
Quantum phases and phase transitions of frustrated hard-core bosons on a triangular ladder
NASA Astrophysics Data System (ADS)
Mishra, Tapan; Pai, Ramesh V.; Mukerjee, Subroto; Paramekanti, Arun
2013-05-01
Kinetically frustrated bosons at half filling in the presence of a competing nearest-neighbor repulsion support a wide supersolid regime on the two-dimensional triangular lattice. We study this model on a two-leg ladder using the finite-size density-matrix renormalization-group method, obtaining a phase diagram which contains three phases: a uniform superfluid (SF), an insulating charge density wave (CDW) crystal, and a bond ordered insulator (BO). We show that the transitions from SF to CDW and SF to BO are continuous in nature, with critical exponents varying continuously along the phase boundaries, while the transition from CDW to BO is found to be first order. The phase diagram is also found to contain an exactly solvable Majumdar Ghosh point, and reentrant SF to CDW phase transitions.
Magnetic soft modes in the distorted triangular antiferromagnet -CaCr2O4
Toth, Sandor; Lake, Bella; Hradil, Klaudia; Rule, K; Stone, Matthew B; Islam, A. T. M. N.
2012-01-01
-CaCr2O4 is a spin-3/2, distorted triangular lattice antiferromagnet with a simple 120 spin structure that masks the complex pattern of exchange interactions. The magnetic excitation spectrum has been measured using inelastic neutron scattering on powder and single crystal samples. It reveals unusual low energy modes which can be explained by linear spin-wave theory assuming nearest and next-nearest neighbor interactions. The mode softening is due to the next-nearest neighbor interactions and indicates a new magnetic phase nearby as revealed by the phase diagram constructed for this system. The extracted direct exchange interactions correlate well with the Cr3+{Cr3+ distances and are in agreement with other chromium oxide delafossite compounds.
Controlling Orientational Order in 1-D Assemblies of Multivalent Triangular Prisms.
Kohlstedt, Kevin L; Olvera de la Cruz, Monica; Schatz, George C
2013-01-01
Multivalent nanostructures are becoming an increasingly important player in the self-assembly of supramolecular lattices. Understanding the role that shape plays in the coordination of the assemblies is crucial for the functional response of the material. We develop a simple design rule for the assembly of multivalent Au triangular nanoprisms into 1-D ordered arrays based on both the length of the valent DNA and the aspect ratio of the prism. Using MD simulations, we describe an order parameter that captures the short-range order of the assembly controlled by the design parameters. The order parameter shows that even short chains (N = 4) of prisms have a high degree of orientational order that transitions to no orientational order when the DNA length is similar to the prism length. Unlike isotropic polyvalent assemblies, we find that the highly oriented chains of prisms lose orientational order in discrete steps during melting as the prisms in the arrays dissociate.
NASA Astrophysics Data System (ADS)
Chen, Hui; Chen, Albert; Jie Sun, Wei; Sun, Zhen Dong; Yeow, John TW
2016-01-01
This article presents the development and implementation of a robust nonlinear control scheme for a 2-D micromirror-based laser scanning microscope system. The presented control scheme, built around sliding mode control approach and augmented an adaptive algorithm, is proposed to improve the tracking accuracy in presence of cross-axis effect. The closed-loop controlled imaging system is developed through integrating a 2-D micromirror with sidewall electrodes (SW), a laser source, NI field-programmable gate array (FPGA) hardware, the optics, position sensing detector (PSD) and photo detector (PD). The experimental results demonstrated that the proposed scheme is able to achieve accurate tracking of a reference triangular signal. Compared with open-loop control, the scanning performance is significantly improved, and a better 2-D image is obtained using the micromirror with the proposed scheme.
Simulations of two-particle interactions with 2D quantum walks in time
Schreiber, A.; Laiho, K.; Silberhorn, C.; Rohde, P. P.; Štefaňak, M.; Potoček, V.; Hamilton, C.; Jex, I.
2014-12-04
We present the experimental implementation of a quantum walk on a two-dimensional lattice and show how to employ the optical system to simulate the quantum propagation of two interacting particles. Our quantum walk in time transfers the spatial spread of a quantum walk into the time domain, which guarantees a high stability and scalability of the setup. We present with our device quantum walks over 12 steps on a 2D lattice. By changing the properties of the driving quantum coin, we investigate different kinds of two-particle interactions and reveal their impact on the occurring quantum propagation.
A 2-D Model to Predict Time Development of Scour below Pipelines with Spoiler
NASA Astrophysics Data System (ADS)
Alam, M. S.; Cheng, Liang
2010-05-01
A lattice Boltzmann 2-D scour model is developed in order to predict time development of scour around offshore pipelines with spoiler. The fluid flow is captured employing Lattice Boltzmann method and the scour model is designed with the combination of multi-particle Cellular Automata technique and threshold of sediment entrainment technique available in literature. It is revealed that the proposed hybrid model is robust enough to predict evolution of bed profiles for flow and scour underneath offshore pipelines considering various orientation and length of spoiler attached.
Construction of 2D atomic crystals on transition metal surfaces: graphene, silicene, and hafnene.
Pan, Yi; Zhang, Lizhi; Huang, Li; Li, Linfei; Meng, Lei; Gao, Min; Huan, Qing; Lin, Xiao; Wang, Yeliang; Du, Shixuan; Freund, Hans-Joachim; Gao, Hong-Jun
2014-06-12
The synthesis and structures of graphene on Ru(0001) and Pt(111), silicene on Ag(111) and Ir(111) and the honeycomb hafnium lattice on Ir(111) are reviewed. Epitaxy on a transition metal (TM) substrate is a pro-mising method to produce a variety of two dimensional (2D) atomic crystals which potentially can be used in next generation electronic devices. This method is particularly valuable in the case of producing 2D materials that do not exist in 3D forms, for instance, silicene. Based on the intensive investigations of epitaxial graphene on TM in recent years, it is known that the quality of graphene is affected by many factors, including the interaction between the 2D material overlayer and the substrate, the lattice mismatch, the nucleation density at the early stage of growth. It is found that these factors also apply to many other epitaxial 2D crystals on TM. The knowledge from the reviewed systems will shine light on the design and synthesis of new 2D crystals with novel properties.
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
Feature edge extraction from 3D triangular meshes using a thinning algorithm
NASA Astrophysics Data System (ADS)
Nomura, Masaru; Hamada, Nozomu
2001-11-01
Highly detailed geometric models, which are represented as dense triangular meshes are becoming popular in computer graphics. Since such 3D meshes often have huge information, we require some methods to treat them efficiently in the 3D mesh processing such as, surface simplification, subdivision surface, curved surface approximation and morphing. In these applications, we often extract features of 3D meshes such as feature vertices and feature edges in preprocessing step. An automatic extraction method of feature edges is treated in this study. In order to realize the feature edge extraction method, we first introduce the concavity and convexity evaluation value. Then the histogram of the concavity and convexity evaluation value is used to separate the feature edge region. We apply a thinning algorithm, which is used in 2D binary image processing. It is shown that the proposed method can extract appropriate feature edges from 3D meshes.
Orthotropic Piezoelectricity in 2D Nanocellulose
NASA Astrophysics Data System (ADS)
García, Y.; Ruiz-Blanco, Yasser B.; Marrero-Ponce, Yovani; Sotomayor-Torres, C. M.
2016-10-01
The control of electromechanical responses within bonding regions is essential to face frontier challenges in nanotechnologies, such as molecular electronics and biotechnology. Here, we present Iβ-nanocellulose as a potentially new orthotropic 2D piezoelectric crystal. The predicted in-layer piezoelectricity is originated on a sui-generis hydrogen bonds pattern. Upon this fact and by using a combination of ab-initio and ad-hoc models, we introduce a description of electrical profiles along chemical bonds. Such developments lead to obtain a rationale for modelling the extended piezoelectric effect originated within bond scales. The order of magnitude estimated for the 2D Iβ-nanocellulose piezoelectric response, ~pm V‑1, ranks this material at the level of currently used piezoelectric energy generators and new artificial 2D designs. Such finding would be crucial for developing alternative materials to drive emerging nanotechnologies.
Orthotropic Piezoelectricity in 2D Nanocellulose
García, Y.; Ruiz-Blanco, Yasser B.; Marrero-Ponce, Yovani; Sotomayor-Torres, C. M.
2016-01-01
The control of electromechanical responses within bonding regions is essential to face frontier challenges in nanotechnologies, such as molecular electronics and biotechnology. Here, we present Iβ-nanocellulose as a potentially new orthotropic 2D piezoelectric crystal. The predicted in-layer piezoelectricity is originated on a sui-generis hydrogen bonds pattern. Upon this fact and by using a combination of ab-initio and ad-hoc models, we introduce a description of electrical profiles along chemical bonds. Such developments lead to obtain a rationale for modelling the extended piezoelectric effect originated within bond scales. The order of magnitude estimated for the 2D Iβ-nanocellulose piezoelectric response, ~pm V−1, ranks this material at the level of currently used piezoelectric energy generators and new artificial 2D designs. Such finding would be crucial for developing alternative materials to drive emerging nanotechnologies. PMID:27708364
2D microwave imaging reflectometer electronics
Spear, A. G.; Domier, C. W. Hu, X.; Muscatello, C. M.; Ren, X.; Luhmann, N. C.; Tobias, B. J.
2014-11-15
A 2D microwave imaging reflectometer system has been developed to visualize electron density fluctuations on the DIII-D tokamak. Simultaneously illuminated at four probe frequencies, large aperture optics image reflections from four density-dependent cutoff surfaces in the plasma over an extended region of the DIII-D plasma. Localized density fluctuations in the vicinity of the plasma cutoff surfaces modulate the plasma reflections, yielding a 2D image of electron density fluctuations. Details are presented of the receiver down conversion electronics that generate the in-phase (I) and quadrature (Q) reflectometer signals from which 2D density fluctuation data are obtained. Also presented are details on the control system and backplane used to manage the electronics as well as an introduction to the computer based control program.
Optical modulators with 2D layered materials
NASA Astrophysics Data System (ADS)
Sun, Zhipei; Martinez, Amos; Wang, Feng
2016-04-01
Light modulation is an essential operation in photonics and optoelectronics. With existing and emerging technologies increasingly demanding compact, efficient, fast and broadband optical modulators, high-performance light modulation solutions are becoming indispensable. The recent realization that 2D layered materials could modulate light with superior performance has prompted intense research and significant advances, paving the way for realistic applications. In this Review, we cover the state of the art of optical modulators based on 2D materials, including graphene, transition metal dichalcogenides and black phosphorus. We discuss recent advances employing hybrid structures, such as 2D heterostructures, plasmonic structures, and silicon and fibre integrated structures. We also take a look at the future perspectives and discuss the potential of yet relatively unexplored mechanisms, such as magneto-optic and acousto-optic modulation.
Tunable Lattice-Induced Opacity for Matter Wave Transport
NASA Astrophysics Data System (ADS)
Zhang, Chen; Greene, Chris H.
2014-03-01
We describe the novel phenomena of lattice-induced opacity in the process of matter wave scattering from a two dimensional atomic lattice. As an analogue to the confinement-induced resonance, the two dimensional atomic lattice can be tuned to complete opacity to a normally incident low energy matter wave, by changing the s-wave scattering length between the matter wave and the atoms in the lattice. A scheme for a matter wave transistor is proposed based on the transmission-reflection properties of the matter wave through the atomic lattice. We also propose a matter wave cavity, constructed by two parallel 2D atomic lattices that are both opaque to the matter wave. In higher kinetic energy regimes of the matter wave, the two dimensional atomic lattice is shown to be a matter wave beam splitter and wave plate, with tunable peak intensity into different directions.
Inkjet printing of 2D layered materials.
Li, Jiantong; Lemme, Max C; Östling, Mikael
2014-11-10
Inkjet printing of 2D layered materials, such as graphene and MoS2, has attracted great interests for emerging electronics. However, incompatible rheology, low concentration, severe aggregation and toxicity of solvents constitute critical challenges which hamper the manufacturing efficiency and product quality. Here, we introduce a simple and general technology concept (distillation-assisted solvent exchange) to efficiently overcome these challenges. By implementing the concept, we have demonstrated excellent jetting performance, ideal printing patterns and a variety of promising applications for inkjet printing of 2D layered materials. PMID:25169938
Inkjet printing of 2D layered materials.
Li, Jiantong; Lemme, Max C; Östling, Mikael
2014-11-10
Inkjet printing of 2D layered materials, such as graphene and MoS2, has attracted great interests for emerging electronics. However, incompatible rheology, low concentration, severe aggregation and toxicity of solvents constitute critical challenges which hamper the manufacturing efficiency and product quality. Here, we introduce a simple and general technology concept (distillation-assisted solvent exchange) to efficiently overcome these challenges. By implementing the concept, we have demonstrated excellent jetting performance, ideal printing patterns and a variety of promising applications for inkjet printing of 2D layered materials.
Parallel stitching of 2D materials
Ling, Xi; Wu, Lijun; Lin, Yuxuan; Ma, Qiong; Wang, Ziqiang; Song, Yi; Yu, Lili; Huang, Shengxi; Fang, Wenjing; Zhang, Xu; et al
2016-01-27
Diverse parallel stitched 2D heterostructures, including metal–semiconductor, semiconductor–semiconductor, and insulator–semiconductor, are synthesized directly through selective “sowing” of aromatic molecules as the seeds in the chemical vapor deposition (CVD) method. Lastly, the methodology enables the large-scale fabrication of lateral heterostructures, which offers tremendous potential for its application in integrated circuits.
Parallel Stitching of 2D Materials.
Ling, Xi; Lin, Yuxuan; Ma, Qiong; Wang, Ziqiang; Song, Yi; Yu, Lili; Huang, Shengxi; Fang, Wenjing; Zhang, Xu; Hsu, Allen L; Bie, Yaqing; Lee, Yi-Hsien; Zhu, Yimei; Wu, Lijun; Li, Ju; Jarillo-Herrero, Pablo; Dresselhaus, Mildred; Palacios, Tomás; Kong, Jing
2016-03-23
Diverse parallel stitched 2D heterostructures, including metal-semiconductor, semiconductor-semiconductor, and insulator-semiconductor, are synthesized directly through selective "sowing" of aromatic molecules as the seeds in the chemical vapor deposition (CVD) method. The methodology enables the large-scale fabrication of lateral heterostructures, which offers tremendous potential for its application in integrated circuits.
Computational study of acoustic solitary waves in 2D complex plasma
NASA Astrophysics Data System (ADS)
Garee, M. J.; Sheridan, T. E.
2008-03-01
A one-dimensional, nonlinear model has been developed for dust-acoustic (DA) waves in a two-dimensional complex plasma. In our model, identical charged dust particles reside on a periodic triangular lattice with lattice constant a. These particles are constrained to move in one dimension, and interact with each other via a screened Coulomb force with Debye length λD. The model is used to compute the dependence of the DA wave speed on the screening parameter κ=a/λD. Computed wave speeds show excellent agreement with theoretical predictions, thereby verifying the model. Total energy is also conserved, as it should be. Localized velocity perturbations are found to evolve into compressive solitary waves and to propagate through the lattice with speeds greater than the DA wave speed. Rarefactive solitary waves are not observed. We intend to characterize overtaking collisions of solitary waves in this system to determine if the phase shift predicted by Korteweg--deVries (KdV) theory occurs, and to compare computed solitary wave widths, amplitudes and speeds to the scalings predicted for KdV solitons.
Emergent Honeycomb Lattice in LiZn2Mo3O8
NASA Astrophysics Data System (ADS)
Flint, Rebecca; Lee, Patrick A.
2013-11-01
We introduce the idea of emergent lattices, where a simple lattice decouples into two weakly coupled lattices as a way to stabilize spin liquids. In LiZn2Mo3O8, the disappearance of 2/3 of the spins at low temperatures suggests that its triangular lattice decouples into an emergent honeycomb lattice weakly coupled to the remaining spins, and we suggest several ways to test this proposal. We show that these orphan spins act to stabilize the spin liquid in the J1-J2 honeycomb model and also discuss a possible 3D analogue, Ba2MoYO6 that may form a “depleted fcc lattice.”
Application of 2D Non-Graphene Materials and 2D Oxide Nanostructures for Biosensing Technology
Shavanova, Kateryna; Bakakina, Yulia; Burkova, Inna; Shtepliuk, Ivan; Viter, Roman; Ubelis, Arnolds; Beni, Valerio; Starodub, Nickolaj; Yakimova, Rositsa; Khranovskyy, Volodymyr
2016-01-01
The discovery of graphene and its unique properties has inspired researchers to try to invent other two-dimensional (2D) materials. After considerable research effort, a distinct “beyond graphene” domain has been established, comprising the library of non-graphene 2D materials. It is significant that some 2D non-graphene materials possess solid advantages over their predecessor, such as having a direct band gap, and therefore are highly promising for a number of applications. These applications are not limited to nano- and opto-electronics, but have a strong potential in biosensing technologies, as one example. However, since most of the 2D non-graphene materials have been newly discovered, most of the research efforts are concentrated on material synthesis and the investigation of the properties of the material. Applications of 2D non-graphene materials are still at the embryonic stage, and the integration of 2D non-graphene materials into devices is scarcely reported. However, in recent years, numerous reports have blossomed about 2D material-based biosensors, evidencing the growing potential of 2D non-graphene materials for biosensing applications. This review highlights the recent progress in research on the potential of using 2D non-graphene materials and similar oxide nanostructures for different types of biosensors (optical and electrochemical). A wide range of biological targets, such as glucose, dopamine, cortisol, DNA, IgG, bisphenol, ascorbic acid, cytochrome and estradiol, has been reported to be successfully detected by biosensors with transducers made of 2D non-graphene materials. PMID:26861346
Application of 2D Non-Graphene Materials and 2D Oxide Nanostructures for Biosensing Technology.
Shavanova, Kateryna; Bakakina, Yulia; Burkova, Inna; Shtepliuk, Ivan; Viter, Roman; Ubelis, Arnolds; Beni, Valerio; Starodub, Nickolaj; Yakimova, Rositsa; Khranovskyy, Volodymyr
2016-01-01
The discovery of graphene and its unique properties has inspired researchers to try to invent other two-dimensional (2D) materials. After considerable research effort, a distinct "beyond graphene" domain has been established, comprising the library of non-graphene 2D materials. It is significant that some 2D non-graphene materials possess solid advantages over their predecessor, such as having a direct band gap, and therefore are highly promising for a number of applications. These applications are not limited to nano- and opto-electronics, but have a strong potential in biosensing technologies, as one example. However, since most of the 2D non-graphene materials have been newly discovered, most of the research efforts are concentrated on material synthesis and the investigation of the properties of the material. Applications of 2D non-graphene materials are still at the embryonic stage, and the integration of 2D non-graphene materials into devices is scarcely reported. However, in recent years, numerous reports have blossomed about 2D material-based biosensors, evidencing the growing potential of 2D non-graphene materials for biosensing applications. This review highlights the recent progress in research on the potential of using 2D non-graphene materials and similar oxide nanostructures for different types of biosensors (optical and electrochemical). A wide range of biological targets, such as glucose, dopamine, cortisol, DNA, IgG, bisphenol, ascorbic acid, cytochrome and estradiol, has been reported to be successfully detected by biosensors with transducers made of 2D non-graphene materials.
2D to 3D transition of polymeric carbon nitride nanosheets
Chamorro-Posada, Pedro; Vázquez-Cabo, José; Martín-Ramos, Pablo; Martín-Gil, Jesús; Navas-Gracia, Luis M.; Dante, Roberto C.
2014-11-15
The transition from a prevalent turbostratic arrangement with low planar interactions (2D) to an array of polymeric carbon nitride nanosheets with stronger interplanar interactions (3D), occurring for samples treated above 650 °C, was detected by terahertz-time domain spectroscopy (THz-TDS). The simulated 3D material made of stacks of shifted quasi planar sheets composed of zigzagged polymer ribbons, delivered a XRD simulated pattern in relatively good agreement with the experimental one. The 2D to 3D transition was also supported by the simulation of THz-TDS spectra obtained from quantum chemistry calculations, in which the same broad bands around 2 THz and 1.5 THz were found for 2D and 3D arrays, respectively. This transition was also in accordance with the tightening of the interplanar distance probably due to an interplanar π bond contribution, as evidenced also by a broad absorption around 2.6 eV in the UV–vis spectrum, which appeared in the sample treated at 650 °C, and increased in the sample treated at 700 °C. The band gap was calculated for 1D and 2D cases. The value of 3.374 eV for the 2D case is, within the model accuracy and precision, in a relative good agreement with the value of 3.055 eV obtained from the experimental results. - Graphical abstract: 2D lattice mode vibrations and structural changes correlated with the so called “2D to 3D transition”. - Highlights: • A 2D to 3D transition has been detected for polymeric carbon nitride. • THz-TDS allowed us to discover and detect the 2D to 3D transition of polymeric carbon nitride. • We propose a structure for polymeric carbon nitride confirming it with THz-TDS.
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.
Synthesis of triangular Au core-Ag shell nanoparticles
Rai, Akhilesh; Chaudhary, Minakshi; Ahmad, Absar; Bhargava, Suresh; Sastry, Murali . E-mail: msastry@tatachemicals.com
2007-07-03
In this paper, we demonstrate a simple and reproducible method for the synthesis of triangular Au core-Ag shell nanoparticles. The triangular gold core is obtained by the reduction of gold ions by lemongrass extract. Utilizing the negative charge on the gold nanotriangles, silver ions are bound to their surface and thereafter reduced by ascorbic acid under alkaline conditions. The thickness of the silver shell may be modulated by varying the pH of the reaction medium. The formation of the Au core-Ag shell triangular nanostructures has been followed by UV-vis-NIR Spectroscopy, X-ray photoelectron spectroscopy, transmission electron microscopy (TEM) and atomic force microscopy (AFM) measurements. The sharp vertices of the triangles coupled with the core-shell structure is expected to have potential for application in surface enhanced Raman spectroscopy and in the sensitive detection of biomolecules.
Magnetic properties in kagomé lattice with RKKY interaction: A Monte Carlo study
NASA Astrophysics Data System (ADS)
Masrour, R.; Jabar, A.; Benyoussef, A.; Hamedoun, M.
2016-03-01
The magnetic properties of the kagomé lattice have been studied with Ruderman-Kittel-Kasuya-Yosida (RKKY) exchange interactions in a spin-7/2 Ising model using Monte Carlo simulations. The RKKY interaction between the two magnetic layers is considered for different distances. The magnetizations and magnetic susceptibilities of this lattice are given for different triquadratic interactions around each triangular face. The critical temperature is obtained for a fixed size. The magnetic hysteresis cycle of kagomé lattice with RKKY interactions is obtained for different temperatures and for different crystal field with a fixed size of nonmagnetic layer.
A depth-averaged 2-D model of flow and sediment transport in coastal waters
NASA Astrophysics Data System (ADS)
Sanchez, Alejandro; Wu, Weiming; Beck, Tanya M.
2016-11-01
A depth-averaged 2-D model has been developed to simulate unsteady flow and nonuniform sediment transport in coastal waters. The current motion is computed by solving the phase-averaged 2-D shallow water flow equations reformulated in terms of total-flux velocity, accounting for the effects of wave radiation stresses and general diffusion or mixing induced by current, waves, and wave breaking. The cross-shore boundary conditions are specified by assuming fully developed longshore current and wave setup that are determined using the reduced 1-D momentum equations. A 2-D wave spectral transformation model is used to calculate the wave height, period, direction, and radiation stresses, and a surface wave roller model is adopted to consider the effects of surface roller on the nearshore currents. The nonequilibrium transport of nonuniform total-load sediment is simulated, considering sediment entrainment by current and waves, the lag of sediment transport relative to the flow, and the hiding and exposure effect of nonuniform bed material. The flow and sediment transport equations are solved using an implicit finite volume method on a variety of meshes including nonuniform rectangular, telescoping (quadtree) rectangular, and hybrid triangular/quadrilateral meshes. The flow and wave models are integrated through a carefully designed steering process. The model has been tested in three field cases, showing generally good performance.
Sparse and incomplete factorial matrices to screen membrane protein 2D crystallization.
Lasala, R; Coudray, N; Abdine, A; Zhang, Z; Lopez-Redondo, M; Kirshenbaum, R; Alexopoulos, J; Zolnai, Z; Stokes, D L; Ubarretxena-Belandia, I
2015-02-01
Electron crystallography is well suited for studying the structure of membrane proteins in their native lipid bilayer environment. This technique relies on electron cryomicroscopy of two-dimensional (2D) crystals, grown generally by reconstitution of purified membrane proteins into proteoliposomes under conditions favoring the formation of well-ordered lattices. Growing these crystals presents one of the major hurdles in the application of this technique. To identify conditions favoring crystallization a wide range of factors that can lead to a vast matrix of possible reagent combinations must be screened. However, in 2D crystallization these factors have traditionally been surveyed in a relatively limited fashion. To address this problem we carried out a detailed analysis of published 2D crystallization conditions for 12 β-barrel and 138 α-helical membrane proteins. From this analysis we identified the most successful conditions and applied them in the design of new sparse and incomplete factorial matrices to screen membrane protein 2D crystallization. Using these matrices we have run 19 crystallization screens for 16 different membrane proteins totaling over 1300 individual crystallization conditions. Six membrane proteins have yielded diffracting 2D crystals suitable for structure determination, indicating that these new matrices show promise to accelerate the success rate of membrane protein 2D crystallization.
Sparse and incomplete factorial matrices to screen membrane protein 2D crystallization
Lasala, R.; Coudray, N.; Abdine, A.; Zhang, Z.; Lopez-Redondo, M.; Kirshenbaum, R.; Alexopoulos, J.; Zolnai, Z.; Stokes, D.L.; Ubarretxena-Belandia, I.
2014-01-01
Electron crystallography is well suited for studying the structure of membrane proteins in their native lipid bilayer environment. This technique relies on electron cryomicroscopy of two-dimensional (2D) crystals, grown generally by reconstitution of purified membrane proteins into proteoliposomes under conditions favoring the formation of well-ordered lattices. Growing these crystals presents one of the major hurdles in the application of this technique. To identify conditions favoring crystallization a wide range of factors that can lead to a vast matrix of possible reagent combinations must be screened. However, in 2D crystallization these factors have traditionally been surveyed in a relatively limited fashion. To address this problem we carried out a detailed analysis of published 2D crystallization conditions for 12 β-barrel and 138 α-helical membrane proteins. From this analysis we identified the most successful conditions and applied them in the design of new sparse and incomplete factorial matrices to screen membrane protein 2D crystallization. Using these matrices we have run 19 crystallization screens for 16 different membrane proteins totaling over 1,300 individual crystallization conditions. Six membrane proteins have yielded diffracting 2D crystals suitable for structure determination, indicating that these new matrices show promise to accelerate the success rate of membrane protein 2D crystallization. PMID:25478971
Sparse and incomplete factorial matrices to screen membrane protein 2D crystallization.
Lasala, R; Coudray, N; Abdine, A; Zhang, Z; Lopez-Redondo, M; Kirshenbaum, R; Alexopoulos, J; Zolnai, Z; Stokes, D L; Ubarretxena-Belandia, I
2015-02-01
Electron crystallography is well suited for studying the structure of membrane proteins in their native lipid bilayer environment. This technique relies on electron cryomicroscopy of two-dimensional (2D) crystals, grown generally by reconstitution of purified membrane proteins into proteoliposomes under conditions favoring the formation of well-ordered lattices. Growing these crystals presents one of the major hurdles in the application of this technique. To identify conditions favoring crystallization a wide range of factors that can lead to a vast matrix of possible reagent combinations must be screened. However, in 2D crystallization these factors have traditionally been surveyed in a relatively limited fashion. To address this problem we carried out a detailed analysis of published 2D crystallization conditions for 12 β-barrel and 138 α-helical membrane proteins. From this analysis we identified the most successful conditions and applied them in the design of new sparse and incomplete factorial matrices to screen membrane protein 2D crystallization. Using these matrices we have run 19 crystallization screens for 16 different membrane proteins totaling over 1300 individual crystallization conditions. Six membrane proteins have yielded diffracting 2D crystals suitable for structure determination, indicating that these new matrices show promise to accelerate the success rate of membrane protein 2D crystallization. PMID:25478971
NASA Astrophysics Data System (ADS)
Jeromin, A.; Schaffarczyk, A. P.; Puczylowski, J.; Peinke, J.; Hölling, M.
2014-12-01
For the investigation of atmospheric turbulent flows on small scales a new anemometer was developed, the so-called 2d-Atmospheric Laser Cantilever Anemometer (2d-ALCA). It performs highly resolved measurements with a spatial resolution in millimeter range and temporal resolution in kHz range, thus detecting very small turbulent structures. The anemometer is a redesign of the successfully operating 2d-LCA for laboratory application. The new device was designed to withstand hostile operating environments (rain and saline, humid air). In February 2012, the 2d-ALCA was used for the first time in a test field. The device was mounted in about 53 m above ground level on a lattice tower near the German North Sea coast. Wind speed was measured by the 2d-ALCA at 10 kHz sampling rate and by cup anemometers at 1 Hz. The instantaneous wind speed ranged from 8 m/s to 19 m/s at an average turbulence level of about 7 %. Wind field characteristics were analyzed based on cup anemometer as well as 2d-ALCA. The combination of both devices allowed the study of atmospheric turbulence over several magnitudes in turbulent scales.
Stochastic Inversion of 2D Magnetotelluric Data
Chen, Jinsong
2010-07-01
The algorithm is developed to invert 2D magnetotelluric (MT) data based on sharp boundary parametrization using a Bayesian framework. Within the algorithm, we consider the locations and the resistivity of regions formed by the interfaces are as unknowns. We use a parallel, adaptive finite-element algorithm to forward simulate frequency-domain MT responses of 2D conductivity structure. Those unknown parameters are spatially correlated and are described by a geostatistical model. The joint posterior probability distribution function is explored by Markov Chain Monte Carlo (MCMC) sampling methods. The developed stochastic model is effective for estimating the interface locations and resistivity. Most importantly, it provides details uncertainty information on each unknown parameter. Hardware requirements: PC, Supercomputer, Multi-platform, Workstation; Software requirements C and Fortan; Operation Systems/version is Linux/Unix or Windows
Explicit 2-D Hydrodynamic FEM Program
1996-08-07
DYNA2D* is a vectorized, explicit, two-dimensional, axisymmetric and plane strain finite element program for analyzing the large deformation dynamic and hydrodynamic response of inelastic solids. DYNA2D* contains 13 material models and 9 equations of state (EOS) to cover a wide range of material behavior. The material models implemented in all machine versions are: elastic, orthotropic elastic, kinematic/isotropic elastic plasticity, thermoelastoplastic, soil and crushable foam, linear viscoelastic, rubber, high explosive burn, isotropic elastic-plastic, temperature-dependent elastic-plastic. Themore » isotropic and temperature-dependent elastic-plastic models determine only the deviatoric stresses. Pressure is determined by one of 9 equations of state including linear polynomial, JWL high explosive, Sack Tuesday high explosive, Gruneisen, ratio of polynomials, linear polynomial with energy deposition, ignition and growth of reaction in HE, tabulated compaction, and tabulated.« less
Stochastic Inversion of 2D Magnetotelluric Data
2010-07-01
The algorithm is developed to invert 2D magnetotelluric (MT) data based on sharp boundary parametrization using a Bayesian framework. Within the algorithm, we consider the locations and the resistivity of regions formed by the interfaces are as unknowns. We use a parallel, adaptive finite-element algorithm to forward simulate frequency-domain MT responses of 2D conductivity structure. Those unknown parameters are spatially correlated and are described by a geostatistical model. The joint posterior probability distribution function ismore » explored by Markov Chain Monte Carlo (MCMC) sampling methods. The developed stochastic model is effective for estimating the interface locations and resistivity. Most importantly, it provides details uncertainty information on each unknown parameter. Hardware requirements: PC, Supercomputer, Multi-platform, Workstation; Software requirements C and Fortan; Operation Systems/version is Linux/Unix or Windows« less
Static & Dynamic Response of 2D Solids
1996-07-15
NIKE2D is an implicit finite-element code for analyzing the finite deformation, static and dynamic response of two-dimensional, axisymmetric, plane strain, and plane stress solids. The code is fully vectorized and available on several computing platforms. A number of material models are incorporated to simulate a wide range of material behavior including elasto-placicity, anisotropy, creep, thermal effects, and rate dependence. Slideline algorithms model gaps and sliding along material interfaces, including interface friction, penetration and single surfacemore » contact. Interactive-graphics and rezoning is included for analyses with large mesh distortions. In addition to quasi-Newton and arc-length procedures, adaptive algorithms can be defined to solve the implicit equations using the solution language ISLAND. Each of these capabilities and more make NIKE2D a robust analysis tool.« less
Static & Dynamic Response of 2D Solids
Lin, Jerry
1996-07-15
NIKE2D is an implicit finite-element code for analyzing the finite deformation, static and dynamic response of two-dimensional, axisymmetric, plane strain, and plane stress solids. The code is fully vectorized and available on several computing platforms. A number of material models are incorporated to simulate a wide range of material behavior including elasto-placicity, anisotropy, creep, thermal effects, and rate dependence. Slideline algorithms model gaps and sliding along material interfaces, including interface friction, penetration and single surface contact. Interactive-graphics and rezoning is included for analyses with large mesh distortions. In addition to quasi-Newton and arc-length procedures, adaptive algorithms can be defined to solve the implicit equations using the solution language ISLAND. Each of these capabilities and more make NIKE2D a robust analysis tool.
Explicit 2-D Hydrodynamic FEM Program
Lin, Jerry
1996-08-07
DYNA2D* is a vectorized, explicit, two-dimensional, axisymmetric and plane strain finite element program for analyzing the large deformation dynamic and hydrodynamic response of inelastic solids. DYNA2D* contains 13 material models and 9 equations of state (EOS) to cover a wide range of material behavior. The material models implemented in all machine versions are: elastic, orthotropic elastic, kinematic/isotropic elastic plasticity, thermoelastoplastic, soil and crushable foam, linear viscoelastic, rubber, high explosive burn, isotropic elastic-plastic, temperature-dependent elastic-plastic. The isotropic and temperature-dependent elastic-plastic models determine only the deviatoric stresses. Pressure is determined by one of 9 equations of state including linear polynomial, JWL high explosive, Sack Tuesday high explosive, Gruneisen, ratio of polynomials, linear polynomial with energy deposition, ignition and growth of reaction in HE, tabulated compaction, and tabulated.
2D photonic-crystal optomechanical nanoresonator.
Makles, K; Antoni, T; Kuhn, A G; Deléglise, S; Briant, T; Cohadon, P-F; Braive, R; Beaudoin, G; Pinard, L; Michel, C; Dolique, V; Flaminio, R; Cagnoli, G; Robert-Philip, I; Heidmann, A
2015-01-15
We present the optical optimization of an optomechanical device based on a suspended InP membrane patterned with a 2D near-wavelength grating (NWG) based on a 2D photonic-crystal geometry. We first identify by numerical simulation a set of geometrical parameters providing a reflectivity higher than 99.8% over a 50-nm span. We then study the limitations induced by the finite value of the optical waist and lateral size of the NWG pattern using different numerical approaches. The NWG grating, pierced in a suspended InP 265-nm thick membrane, is used to form a compact microcavity involving the suspended nanomembrane as an end mirror. The resulting cavity has a waist size smaller than 10 μm and a finesse in the 200 range. It is used to probe the Brownian motion of the mechanical modes of the nanomembrane. PMID:25679837
Compact 2-D graphical representation of DNA
NASA Astrophysics Data System (ADS)
Randić, Milan; Vračko, Marjan; Zupan, Jure; Novič, Marjana
2003-05-01
We present a novel 2-D graphical representation for DNA sequences which has an important advantage over the existing graphical representations of DNA in being very compact. It is based on: (1) use of binary labels for the four nucleic acid bases, and (2) use of the 'worm' curve as template on which binary codes are placed. The approach is illustrated on DNA sequences of the first exon of human β-globin and gorilla β-globin.
2D materials: Graphene and others
NASA Astrophysics Data System (ADS)
Bansal, Suneev Anil; Singh, Amrinder Pal; Kumar, Suresh
2016-05-01
Present report reviews the recent advancements in new atomically thick 2D materials. Materials covered in this review are Graphene, Silicene, Germanene, Boron Nitride (BN) and Transition metal chalcogenides (TMC). These materials show extraordinary mechanical, electronic and optical properties which make them suitable candidates for future applications. Apart from unique properties, tune-ability of highly desirable properties of these materials is also an important area to be emphasized on.
Layer Engineering of 2D Semiconductor Junctions.
He, Yongmin; Sobhani, Ali; Lei, Sidong; Zhang, Zhuhua; Gong, Yongji; Jin, Zehua; Zhou, Wu; Yang, Yingchao; Zhang, Yuan; Wang, Xifan; Yakobson, Boris; Vajtai, Robert; Halas, Naomi J; Li, Bo; Xie, Erqing; Ajayan, Pulickel
2016-07-01
A new concept for junction fabrication by connecting multiple regions with varying layer thicknesses, based on the thickness dependence, is demonstrated. This type of junction is only possible in super-thin-layered 2D materials, and exhibits similar characteristics as p-n junctions. Rectification and photovoltaic effects are observed in chemically homogeneous MoSe2 junctions between domains of different thicknesses. PMID:27136275
Strain-displacement relations for strain engineering in single-layer 2d materials
NASA Astrophysics Data System (ADS)
Midtvedt, Daniel; Lewenkopf, Caio H.; Croy, Alexander
2016-03-01
We investigate the electromechanical coupling in single-layer 2d materials. For non-Bravais lattices, we find important corrections to the standard macroscopic strain-microscopic atomic-displacement theory. We put forward a general and systematic approach to calculate strain-displacement relations for several classes of 2d materials. We apply our findings to graphene as a study case, by combining a tight binding and a valence force-field model to calculate electronic and mechanical properties of graphene nanoribbons under strain. The results show good agreement with the predictions of the Dirac equation coupled to continuum mechanics. For this long wave-limit effective theory, we find that the strain-displacement relations lead to a renormalization correction to the strain-induced pseudo-magnetic fields. A similar renormalization is found for the strain-induced band-gap of black phosphorous. Implications for nanomechanical properties and electromechanical coupling in 2d materials are discussed.
Quantum Diffusion on Molecular Tubes: Universal Scaling of the 1D to 2D Transition
NASA Astrophysics Data System (ADS)
Chuang, Chern; Lee, Chee Kong; Moix, Jeremy M.; Knoester, Jasper; Cao, Jianshu
2016-05-01
The transport properties of disordered systems are known to depend critically on dimensionality. We study the diffusion coefficient of a quantum particle confined to a lattice on the surface of a tube, where it scales between the 1D and 2D limits. It is found that the scaling relation is universal and independent of the temperature, disorder, and noise parameters, and the essential order parameter is the ratio between the localization length in 2D and the circumference of the tube. Phenomenological and quantitative expressions for transport properties as functions of disorder and noise are obtained and applied to real systems: In the natural chlorosomes found in light-harvesting bacteria the exciton transfer dynamics is predicted to be in the 2D limit, whereas a family of synthetic molecular aggregates is found to be in the homogeneous limit and is independent of dimensionality.
Quantum Diffusion on Molecular Tubes: Universal Scaling of the 1D to 2D Transition.
Chuang, Chern; Lee, Chee Kong; Moix, Jeremy M; Knoester, Jasper; Cao, Jianshu
2016-05-13
The transport properties of disordered systems are known to depend critically on dimensionality. We study the diffusion coefficient of a quantum particle confined to a lattice on the surface of a tube, where it scales between the 1D and 2D limits. It is found that the scaling relation is universal and independent of the temperature, disorder, and noise parameters, and the essential order parameter is the ratio between the localization length in 2D and the circumference of the tube. Phenomenological and quantitative expressions for transport properties as functions of disorder and noise are obtained and applied to real systems: In the natural chlorosomes found in light-harvesting bacteria the exciton transfer dynamics is predicted to be in the 2D limit, whereas a family of synthetic molecular aggregates is found to be in the homogeneous limit and is independent of dimensionality. PMID:27232033
2D Spinodal Decomposition in Forced Turbulence
NASA Astrophysics Data System (ADS)
Fan, Xiang; Diamond, Patrick; Chacon, Luis; Li, Hui
2015-11-01
Spinodal decomposition is a second order phase transition for binary fluid mixture, from one thermodynamic phase to form two coexisting phases. The governing equation for this coarsening process below critical temperature, Cahn-Hilliard Equation, is very similar to 2D MHD Equation, especially the conserved quantities have a close correspondence between each other, so theories for MHD turbulence are used to study spinodal decomposition in forced turbulence. Domain size is increased with time along with the inverse cascade, and the length scale can be arrested by a forced turbulence with direct cascade. The two competing mechanisms lead to a stabilized domain size length scale, which can be characterized by Hinze Scale. The 2D spinodal decomposition in forced turbulence is studied by both theory and simulation with ``pixie2d.'' This work focuses on the relation between Hinze scale and spectra and cascades. Similarities and differences between spinodal decomposition and MHD are investigated. Also some transport properties are studied following MHD theories. This work is supported by the Department of Energy under Award Number DE-FG02-04ER54738.
Engineering light outcoupling in 2D materials.
Lien, Der-Hsien; Kang, Jeong Seuk; Amani, Matin; Chen, Kevin; Tosun, Mahmut; Wang, Hsin-Ping; Roy, Tania; Eggleston, Michael S; Wu, Ming C; Dubey, Madan; Lee, Si-Chen; He, Jr-Hau; Javey, Ali
2015-02-11
When light is incident on 2D transition metal dichalcogenides (TMDCs), it engages in multiple reflections within underlying substrates, producing interferences that lead to enhancement or attenuation of the incoming and outgoing strength of light. Here, we report a simple method to engineer the light outcoupling in semiconducting TMDCs by modulating their dielectric surroundings. We show that by modulating the thicknesses of underlying substrates and capping layers, the interference caused by substrate can significantly enhance the light absorption and emission of WSe2, resulting in a ∼11 times increase in Raman signal and a ∼30 times increase in the photoluminescence (PL) intensity of WSe2. On the basis of the interference model, we also propose a strategy to control the photonic and optoelectronic properties of thin-layer WSe2. This work demonstrates the utilization of outcoupling engineering in 2D materials and offers a new route toward the realization of novel optoelectronic devices, such as 2D LEDs and solar cells.
Adaptive reorganization of 2D molecular nanoporous network induced by coadsorbed guest molecule.
Zheng, Qing-Na; Wang, Lei; Zhong, Yu-Wu; Liu, Xuan-He; Chen, Ting; Yan, Hui-Juan; Wang, Dong; Yao, Jian-Nian; Wan, Li-Jun
2014-03-25
The ordered array of nanovoids in nanoporous networks, such as honeycomb, Kagome, and square, provides a molecular template for the accommodation of "guest molecules". Compared with the commonly studied guest molecules featuring high symmetry evenly incorporated into the template, guest molecules featuring lower symmetry are rare to report. Herein, we report the formation of a distinct patterned superlattice of guest molecules by selective trapping of guest molecules into the honeycomb network of trimesic acid (TMA). Two distinct surface patterns have been achieved by the guest inclusion induced adaptive reconstruction of a 2D molecular nanoporous network. The honeycomb networks can synergetically tune the arrangement upon inclusion of the guest molecules with different core size but similar peripherals groups, resulting in a trihexagonal Kagome or triangular patterns.
The simulation of 3D mass models in 2D digital mammography and breast tomosynthesis
Shaheen, Eman De Keyzer, Frederik; Bosmans, Hilde; Ongeval, Chantal Van; Dance, David R.; Young, Kenneth C.
2014-08-15
Purpose: This work proposes a new method of building 3D breast mass models with different morphological shapes and describes the validation of the realism of their appearance after simulation into 2D digital mammograms and breast tomosynthesis images. Methods: Twenty-five contrast enhanced MRI breast lesions were collected and each mass was manually segmented in the three orthogonal views: sagittal, coronal, and transversal. The segmented models were combined, resampled to have isotropic voxel sizes, triangularly meshed, and scaled to different sizes. These masses were referred to as nonspiculated masses and were then used as nuclei onto which spicules were grown with an iterative branching algorithm forming a total of 30 spiculated masses. These 55 mass models were projected into 2D projection images to obtain mammograms after image processing and into tomographic sequences of projection images, which were then reconstructed to form 3D tomosynthesis datasets. The realism of the appearance of these mass models was assessed by five radiologists via receiver operating characteristic (ROC) analysis when compared to 54 real masses. All lesions were also given a breast imaging reporting and data system (BIRADS) score. The data sets of 2D mammography and tomosynthesis were read separately. The Kendall's coefficient of concordance was used for the interrater observer agreement assessment for the BIRADS scores per modality. Further paired analysis, using the Wilcoxon signed rank test, of the BIRADS assessment between 2D and tomosynthesis was separately performed for the real masses and for the simulated masses. Results: The area under the ROC curves, averaged over all observers, was 0.54 (95% confidence interval [0.50, 0.66]) for the 2D study, and 0.67 (95% confidence interval [0.55, 0.79]) for the tomosynthesis study. According to the BIRADS scores, the nonspiculated and the spiculated masses varied in their degrees of malignancy from normal (BIRADS 1) to highly
Antiferromagnetic Ground States in Some Commonly Known Lattices
NASA Astrophysics Data System (ADS)
Bayri, Ali
1997-01-01
Antiferromagnetism is a very interesting behaviours in some real materials and their alloys. It is important in high Tc materials as well. The main reasons for antiferromagnetism are the kinetic exchange[1,2]. In this study, I will consider commonly known lattices in two or three dimensions. Using the Heisenberg model I will show that there are two systems: Frustrated and unfrustrated. In unfrustrated case the spin structure is unique and it involves ferromagnetism as well. However, in frustrated case the spin structure is not unique and it gives more than one spin orderings. This behaviours is very interesting since it causes a first order magnetic phase transition[3,4]. Finally, I will summarize that the simplier lattice (the square, the S.C. and B.C.C.) are unfrustrated and the complicated lattices (triangular, F.C.C. and H.C.P.) are frustrated.
Topological spin liquids in the ruby lattice with anisotropic Kitaev interactions
NASA Astrophysics Data System (ADS)
Jahromi, Saeed S.; Kargarian, Mehdi; Masoudi, S. Farhad; Langari, Abdollah
2016-09-01
The ruby lattice is a four-valent lattice interpolating between honeycomb and triangular lattices. In this work we investigate the topological spin-liquid phases of a spin Hamiltonian with Kitaev interactions on the ruby lattice using exact diagonalization and perturbative methods. The latter interactions combined with the structure of the lattice yield a model with Z2×Z2 gauge symmetry. We mapped out the phase diagram of the model and found gapped and gapless spin-liquid phases. While the low-energy sector of the gapped phase corresponds to the well-known topological color code model on a honeycomb lattice, the low-energy sector of the gapless phases is described by an effective spin model with three-body interactions on a triangular lattice. A gap is opened in the spectrum in small magnetic fields, where we showed that the ground state has a finite topological entanglement entropy. We argue that the gapped phases could be possibly described by exotic excitations, and their corresponding spectrum is richer than the Ising phase of the Kitaev model.
GBL-2D Version 1.0: a 2D geometry boolean library.
McBride, Cory L. (Elemental Technologies, American Fort, UT); Schmidt, Rodney Cannon; Yarberry, Victor R.; Meyers, Ray J.
2006-11-01
This report describes version 1.0 of GBL-2D, a geometric Boolean library for 2D objects. The library is written in C++ and consists of a set of classes and routines. The classes primarily represent geometric data and relationships. Classes are provided for 2D points, lines, arcs, edge uses, loops, surfaces and mask sets. The routines contain algorithms for geometric Boolean operations and utility functions. Routines are provided that incorporate the Boolean operations: Union(OR), XOR, Intersection and Difference. A variety of additional analytical geometry routines and routines for importing and exporting the data in various file formats are also provided. The GBL-2D library was originally developed as a geometric modeling engine for use with a separate software tool, called SummitView [1], that manipulates the 2D mask sets created by designers of Micro-Electro-Mechanical Systems (MEMS). However, many other practical applications for this type of software can be envisioned because the need to perform 2D Boolean operations can arise in many contexts.
Spin liquid nature in the Heisenberg J1-J2 triangular antiferromagnet
NASA Astrophysics Data System (ADS)
Iqbal, Yasir; Hu, Wen-Jun; Thomale, Ronny; Poilblanc, Didier; Becca, Federico
2016-04-01
We investigate the spin-1/2 Heisenberg model on the triangular lattice in the presence of nearest-neighbor J1 and next-nearest-neighbor J2 antiferromagnetic couplings. Motivated by recent findings from density-matrix renormalization group (DMRG) claiming the existence of a gapped spin liquid with signatures of spontaneously broken lattice point group symmetry [Zhu and White, Phys. Rev. B 92, 041105 (2015), 10.1103/PhysRevB.92.041105 and Hu, Gong, Zhu, and Sheng, Phys. Rev. B 92, 140403 (2015), 10.1103/PhysRevB.92.140403], we employ the variational Monte Carlo (VMC) approach to analyze the model from an alternative perspective that considers both magnetically ordered and paramagnetic trial states. We find a quantum paramagnet in the regime 0.08 ≲J2/J1≲0.16 , framed by 120∘ coplanar (stripe collinear) antiferromagnetic order for smaller (larger) J2/J1 . By considering the optimization of spin-liquid wave functions of a different gauge group and lattice point group content as derived from Abrikosov mean-field theory, we obtain the gapless U(1 ) Dirac spin liquid as the energetically most preferable state in comparison to all symmetric or nematic gapped Z2 spin liquids so far advocated by DMRG. Moreover, by the application of few Lanczos iterations, we find the energy to be the same as the DMRG result within error bars. To further resolve the intriguing disagreement between VMC and DMRG, we complement our methodological approach by the pseudofermion functional renormalization group (PFFRG) to compare the spin structure factors for the paramagnetic regime calculated by VMC, DMRG, and PFFRG. This model promises to be an ideal test bed for future numerical refinements in tracking the long-range correlations in frustrated magnets.
14. INTERIOR, IN TRIANGULAR STORAGE AREA, IN SOUTHEAST AREA OF ...
14. INTERIOR, IN TRIANGULAR STORAGE AREA, IN SOUTHEAST AREA OF BUILDING (EAST OF LOCKER/OFFICE/HEAD AREA), LOOKING EAST-NORTHEAST. - Oakland Naval Supply Center, Pier Transit Shed, South of D Street between First & Second Streets, Oakland, Alameda County, CA
View of the demilune, a triangular piece of land that ...
View of the demilune, a triangular piece of land that protected the rear of gorge wall of the fort. After the civil war, large earthen mounds were built in the demilune area. These mounds overlay four powder magazines and passageways to several gun emplacements. - Fort Pulaski, Cockspur Island, Savannah, Chatham County, GA
Triangular Numbers, Gaussian Integers, and KenKen
ERIC Educational Resources Information Center
Watkins, John J.
2012-01-01
Latin squares form the basis for the recreational puzzles sudoku and KenKen. In this article we show how useful several ideas from number theory are in solving a KenKen puzzle. For example, the simple notion of triangular number is surprisingly effective. We also introduce a variation of KenKen that uses the Gaussian integers in order to…
Triangular congenital cataract morphology associated with prenatal methamphetamine exposure.
Clarke, Michael E; Schloff, Susan; Bothun, Erick D
2009-08-01
Bilateral congenital cataracts are often characterized by morphology, etiology, and related conditions. We report a case of unique congenital cataracts with triangular morphology and associated prenatal methamphetamine exposure. Although this association is likely coincidental, the cataract's morphology in light of the specific timing of prenatal drug use deserves reporting.
Middle Passage in the Triangular Slave Trade: The West Indies
ERIC Educational Resources Information Center
Sawh, Ruth; Scales, Alice M.
2006-01-01
Our narrative focuses on the middle passage of the slave trade in the West Indies. Herein we describe why more men, women, and children were imported in the West Indies than other islands. Specifically, our aim was to address how slaves in the middle passage of the triangular slave trade were treated, how they sustained themselves, and how they…
6. SOUTH EXTERIOR SIDE SHOWING TRIANGULAR KNEE BRACE SUPPORTS AND ...
6. SOUTH EXTERIOR SIDE SHOWING TRIANGULAR KNEE BRACE SUPPORTS AND ENCLOSED PORCH SCREENED WINDOWS. ON BASIC FLOOR-PLAN FOR THE SIX-ROOM HOUSE THIS END WAS THE FRONT ENTRANCE. VIEW TO NORTH. - Big Creek Hydroelectric System, Powerhouse 8, Operator Cottage, Big Creek, Big Creek, Fresno County, CA
Periodically sheared 2D Yukawa systems
Kovács, Anikó Zsuzsa; Hartmann, Peter; Donkó, Zoltán
2015-10-15
We present non-equilibrium molecular dynamics simulation studies on the dynamic (complex) shear viscosity of a 2D Yukawa system. We have identified a non-monotonic frequency dependence of the viscosity at high frequencies and shear rates, an energy absorption maximum (local resonance) at the Einstein frequency of the system at medium shear rates, an enhanced collective wave activity, when the excitation is near the plateau frequency of the longitudinal wave dispersion, and the emergence of significant configurational anisotropy at small frequencies and high shear rates.
ENERGY LANDSCAPE OF 2D FLUID FORMS
Y. JIANG; ET AL
2000-04-01
The equilibrium states of 2D non-coarsening fluid foams, which consist of bubbles with fixed areas, correspond to local minima of the total perimeter. (1) The authors find an approximate value of the global minimum, and determine directly from an image how far a foam is from its ground state. (2) For (small) area disorder, small bubbles tend to sort inwards and large bubbles outwards. (3) Topological charges of the same sign repel while charges of opposite sign attract. (4) They discuss boundary conditions and the uniqueness of the pattern for fixed topology.
Quantum Simulation with 2D Arrays of Trapped Ions
NASA Astrophysics Data System (ADS)
Richerme, Philip
2016-05-01
The computational difficulty of solving fully quantum many-body spin problems is a significant obstacle to understanding the behavior of strongly correlated quantum matter. This work proposes the design and construction of a 2D quantum spin simulator to investigate the physics of frustrated materials, highly entangled states, mechanisms potentially underpinning high-temperature superconductivity, and other topics inaccessible to current 1D systems. The effective quantum spins will be encoded within the well-isolated electronic levels of trapped ions, confined in a two-dimensional planar geometry, and made to interact using phonon-mediated optical dipole forces. The system will be scalable to 100+ quantum particles, far beyond the realm of classical intractability, while maintaining individual-ion control, long quantum coherence times, and site-resolved projective spin measurements. Once constructed, the two-dimensional quantum simulator will implement a broad range of spin models on a variety of reconfigurable lattices and characterize their behavior through measurements of spin-spin correlations and entanglement. This versatile tool will serve as an important experimental resource for exploring difficult quantum many-body problems in a regime where classical methods fail.
Duality Between Spin Networks and the 2D Ising Model
NASA Astrophysics Data System (ADS)
Bonzom, Valentin; Costantino, Francesco; Livine, Etera R.
2016-06-01
The goal of this paper is to exhibit a deep relation between the partition function of the Ising model on a planar trivalent graph and the generating series of the spin network evaluations on the same graph. We provide respectively a fermionic and a bosonic Gaussian integral formulation for each of these functions and we show that they are the inverse of each other (up to some explicit constants) by exhibiting a supersymmetry relating the two formulations. We investigate three aspects and applications of this duality. First, we propose higher order supersymmetric theories that couple the geometry of the spin networks to the Ising model and for which supersymmetric localization still holds. Secondly, after interpreting the generating function of spin network evaluations as the projection of a coherent state of loop quantum gravity onto the flat connection state, we find the probability distribution induced by that coherent state on the edge spins and study its stationary phase approximation. It is found that the stationary points correspond to the critical values of the couplings of the 2D Ising model, at least for isoradial graphs. Third, we analyze the mapping of the correlations of the Ising model to spin network observables, and describe the phase transition on those observables on the hexagonal lattice. This opens the door to many new possibilities, especially for the study of the coarse-graining and continuum limit of spin networks in the context of quantum gravity.
Cooperative dynamics in ultrasoft 2D crystals
NASA Astrophysics Data System (ADS)
Sprakel, Joris; van der Meer, Berend; Dijkstra, Marjolein; van der Gucht, Jasper
2015-03-01
The creation, annihilation, and diffusion of defects in crystal lattices play an important role during crystal melting and deformation. Although it is well understood how defects form and react when crystals are subjected to external stresses, it remains unclear how crystals cope with internal stresses. We report a study in which we create a highly localized internal stress, by means of optical tweezing, in a crystal formed from micrometer-sized colloidal spheres and directly observe how the solid reacts using microscopy. We find that, even though the excitation is highly localized, a collective dance of colloidal particles results; these collective modes take the form of closed rings or open-ended strings, depending on the sequence of events which nucleate the rearrangements. Surprisingly, we find from Brownian Dynamics simulations that these cooperative dynamics are thermally-activated modes inherent to the crystal, and can even occur through a single, sufficiently large thermal fluctuation, resulting in the irreversible displacement of 100s of particles from their lattice sites.
Superfluid density through 2D superconductor junctions
NASA Astrophysics Data System (ADS)
Nam, Hyoungdo; Shih, Chih-Kang
As S. Qin et al. reported, two monolayer (2 ML) lead film on a silicon (111) substrate has one of two different atomic structures on the silicon substrate: the unstrained 1x1 and the psedumorphically strained √3x √3 (i.e. the same lattice constant as the Si √3x √3 lattice). Most interestingly, although these two different regions show the same quantum well state features, they have different Tc's (5 K and 4 K). These two different regions of 2 ML film naturally form superconductor-superconductor (SS or SS') junctions along silicon step edges. Physical connection of the junction is only 1 ML thickness because of the step height difference of substrate. We will present this study of SS (or SS') junction system using scanning tunneling microscopy/spectroscopy and in-situ double-coil mutual inductance measurement. The transition of superconducting gaps across either SS or SS' junctions should show how to locally affect each other. Double coil measurement show a global Tc close to the lower Tc region with sizable superfluid density. We will discuss the phase rigidity and its relationship to the superfluid density in this ultra-thin Pb film that is only 2 ML thick.
Nieber, J.L.; Friedel, M.J.; Munir, H.M.
1994-01-01
This information circular describes a computer program called VARSAT2D, a comprehensive unsaturated fluid flow simulator developed by the U.S. Bureau of Mines. VARSAT2D solves for either a vertical or horizontal, transient or steady-state solution in variably saturated, heterogeneous, anisotropic porous media using the Galerkin finite-element approach. Simplex triangular elements are used. Moisture retention characteristics are described by specifying either the Brooks and Corey, Brutsaert, or Van Genuchten power functions, with hysteresis described using the Maulem independent domain model. Boundary conditions may include any combination of time-varying seepage, pressure along solution domain boundaries and/or at internal node points, unit hydraulic gradient at the lower boundary, and a uniform source and/or sink. The program should be a welcome addition for mining and environmental hydrologists, researchers, and engineers interested in modeling unsaturated fluid flow.
WFR-2D: an analytical model for PWAS-generated 2D ultrasonic guided wave propagation
NASA Astrophysics Data System (ADS)
Shen, Yanfeng; Giurgiutiu, Victor
2014-03-01
This paper presents WaveFormRevealer 2-D (WFR-2D), an analytical predictive tool for the simulation of 2-D ultrasonic guided wave propagation and interaction with damage. The design of structural health monitoring (SHM) systems and self-aware smart structures requires the exploration of a wide range of parameters to achieve best detection and quantification of certain types of damage. Such need for parameter exploration on sensor dimension, location, guided wave characteristics (mode type, frequency, wavelength, etc.) can be best satisfied with analytical models which are fast and efficient. The analytical model was constructed based on the exact 2-D Lamb wave solution using Bessel and Hankel functions. Damage effects were inserted in the model by considering the damage as a secondary wave source with complex-valued directivity scattering coefficients containing both amplitude and phase information from wave-damage interaction. The analytical procedure was coded with MATLAB, and a predictive simulation tool called WaveFormRevealer 2-D was developed. The wave-damage interaction coefficients (WDICs) were extracted from harmonic analysis of local finite element model (FEM) with artificial non-reflective boundaries (NRB). The WFR-2D analytical simulation results were compared and verified with full scale multiphysics finite element models and experiments with scanning laser vibrometer. First, Lamb wave propagation in a pristine aluminum plate was simulated with WFR-2D, compared with finite element results, and verified by experiments. Then, an inhomogeneity was machined into the plate to represent damage. Analytical modeling was carried out, and verified by finite element simulation and experiments. This paper finishes with conclusions and suggestions for future work.
Microwave Assisted 2D Materials Exfoliation
NASA Astrophysics Data System (ADS)
Wang, Yanbin
Two-dimensional materials have emerged as extremely important materials with applications ranging from energy and environmental science to electronics and biology. Here we report our discovery of a universal, ultrafast, green, solvo-thermal technology for producing excellent-quality, few-layered nanosheets in liquid phase from well-known 2D materials such as such hexagonal boron nitride (h-BN), graphite, and MoS2. We start by mixing the uniform bulk-layered material with a common organic solvent that matches its surface energy to reduce the van der Waals attractive interactions between the layers; next, the solutions are heated in a commercial microwave oven to overcome the energy barrier between bulk and few-layers states. We discovered the minutes-long rapid exfoliation process is highly temperature dependent, which requires precise thermal management to obtain high-quality inks. We hypothesize a possible mechanism of this proposed solvo-thermal process; our theory confirms the basis of this novel technique for exfoliation of high-quality, layered 2D materials by using an as yet unknown role of the solvent.
Multienzyme Inkjet Printed 2D Arrays.
Gdor, Efrat; Shemesh, Shay; Magdassi, Shlomo; Mandler, Daniel
2015-08-19
The use of printing to produce 2D arrays is well established, and should be relatively facile to adapt for the purpose of printing biomaterials; however, very few studies have been published using enzyme solutions as inks. Among the printing technologies, inkjet printing is highly suitable for printing biomaterials and specifically enzymes, as it offers many advantages. Formulation of the inkjet inks is relatively simple and can be adjusted to a variety of biomaterials, while providing nonharmful environment to the enzymes. Here we demonstrate the applicability of inkjet printing for patterning multiple enzymes in a predefined array in a very straightforward, noncontact method. Specifically, various arrays of the enzymes glucose oxidase (GOx), invertase (INV) and horseradish peroxidase (HP) were printed on aminated glass surfaces, followed by immobilization using glutardialdehyde after printing. Scanning electrochemical microscopy (SECM) was used for imaging the printed patterns and to ascertain the enzyme activity. The successful formation of 2D arrays consisting of enzymes was explored as a means of developing the first surface confined enzyme based logic gates. Principally, XOR and AND gates, each consisting of two enzymes as the Boolean operators, were assembled, and their operation was studied by SECM. PMID:26214072
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...
NASA Astrophysics Data System (ADS)
Kuramashi, Yoshinobu
2007-12-01
Preface -- Fixed point actions, symmetries and symmetry transformations on the lattice / P. Hasenfratz -- Algorithms for dynamical fennions / A. D. Kennedy -- Applications of chiral perturbation theory to lattice QCD / Stephen R. Sharpe -- Lattice QCD with a chiral twist / S. Sint -- Non-perturbative QCD: renormalization, O(A) - Improvement and matching to Heavy Quark effective theory / Rainer Sommer.
2-D or not 2-D, that is the question: A Northern California test
Mayeda, K; Malagnini, L; Phillips, W S; Walter, W R; Dreger, D
2005-06-06
Reliable estimates of the seismic source spectrum are necessary for accurate magnitude, yield, and energy estimation. In particular, how seismic radiated energy scales with increasing earthquake size has been the focus of recent debate within the community and has direct implications on earthquake source physics studies as well as hazard mitigation. The 1-D coda methodology of Mayeda et al. has provided the lowest variance estimate of the source spectrum when compared against traditional approaches that use direct S-waves, thus making it ideal for networks that have sparse station distribution. The 1-D coda methodology has been mostly confined to regions of approximately uniform complexity. For larger, more geophysically complicated regions, 2-D path corrections may be required. The complicated tectonics of the northern California region coupled with high quality broadband seismic data provides for an ideal ''apples-to-apples'' test of 1-D and 2-D path assumptions on direct waves and their coda. Using the same station and event distribution, we compared 1-D and 2-D path corrections and observed the following results: (1) 1-D coda results reduced the amplitude variance relative to direct S-waves by roughly a factor of 8 (800%); (2) Applying a 2-D correction to the coda resulted in up to 40% variance reduction from the 1-D coda results; (3) 2-D direct S-wave results, though better than 1-D direct waves, were significantly worse than the 1-D coda. We found that coda-based moment-rate source spectra derived from the 2-D approach were essentially identical to those from the 1-D approach for frequencies less than {approx}0.7-Hz, however for the high frequencies (0.7{le} f {le} 8.0-Hz), the 2-D approach resulted in inter-station scatter that was generally 10-30% smaller. For complex regions where data are plentiful, a 2-D approach can significantly improve upon the simple 1-D assumption. In regions where only 1-D coda correction is available it is still preferable over 2
Classical ground states of Heisenberg and X Y antiferromagnets on the windmill lattice
NASA Astrophysics Data System (ADS)
Jeevanesan, Bhilahari; Orth, Peter P.
2014-10-01
We investigate the classical Heisenberg and planar (X Y ) spin models on the windmill lattice. The windmill lattice is formed out of two widely occurring lattice geometries: a triangular lattice is coupled to its dual honeycomb lattice. Using a combination of iterative minimization, heat-bath Monte Carlo simulations, and analytical calculations, we determine the complete ground-state phase diagram of both models and find the exact energies of the phases. The phase diagram shows a rich phenomenology due to competing interactions and hosts, in addition to collinear and various coplanar phases, also intricate noncoplanar phases. We briefly outline different paths to an experimental realization of these spin models. Our extensive study provides a starting point for the investigation of quantum and thermal fluctuation effects.
Emergent Criticality and Ricci Flow in a 2D Frustrated Heisenberg Model
NASA Astrophysics Data System (ADS)
Orth, Peter P.
2014-03-01
In most systems that exhibit order at low temperatures, the order occurs in the elementary degrees of freedom such as spin or charge. Prominent examples are magnetic or superconducting states of matter. In contrast, emergent order describes the phenomenon where composite objects exhibit longer range correlations. Such emergent order has been suspected to occur in a range of correlated materials. One specific example are spin systems with competing interactions, where long-range discrete order in the relative orientation of spins may occur. Interestingly, this order parameter may induce other phase transitions as is the case for the nematic transition in the iron pnictides. In this talk, we introduce and discuss a system with emergent Z6 symmetry, a two-dimensional frustrated Heisenberg antiferromagnet on the windmill lattice consisting of interpenetrating honeycomb and triangular lattices. The multiple spin stiffnesses can be captured in terms of a four-dimensional metric tensor, and the renormalization group flow of the stiffnesses is described by the Ricci flow of the metric tensor. The key result is a decoupling of an emergent collective degree of freedom given by the relative phase of spins on different sublattices. In particular, our results reveal a sequence of two Berezinskii-Kosterlitz-Thouless phase transitions that bracket a critical phase.
Canard configured aircraft with 2-D nozzle
NASA Technical Reports Server (NTRS)
Child, R. D.; Henderson, W. P.
1978-01-01
A closely-coupled canard fighter with vectorable two-dimensional nozzle was designed for enhanced transonic maneuvering. The HiMAT maneuver goal of a sustained 8g turn at a free-stream Mach number of 0.9 and 30,000 feet was the primary design consideration. The aerodynamic design process was initiated with a linear theory optimization minimizing the zero percent suction drag including jet effects and refined with three-dimensional nonlinear potential flow techniques. Allowances were made for mutual interference and viscous effects. The design process to arrive at the resultant configuration is described, and the design of a powered 2-D nozzle model to be tested in the LRC 16-foot Propulsion Wind Tunnel is shown.
2D Electrostatic Actuation of Microshutter Arrays
NASA Technical Reports Server (NTRS)
Burns, Devin E.; Oh, Lance H.; Li, Mary J.; Kelly, Daniel P.; Kutyrev, Alexander S.; Moseley, Samuel H.
2015-01-01
Electrostatically actuated microshutter arrays consisting of rotational microshutters (shutters that rotate about a torsion bar) were designed and fabricated through the use of models and experiments. Design iterations focused on minimizing the torsional stiffness of the microshutters, while maintaining their structural integrity. Mechanical and electromechanical test systems were constructed to measure the static and dynamic behavior of the microshutters. The torsional stiffness was reduced by a factor of four over initial designs without sacrificing durability. Analysis of the resonant behavior of the microshutters demonstrates that the first resonant mode is a torsional mode occurring around 3000 Hz. At low vacuum pressures, this resonant mode can be used to significantly reduce the drive voltage necessary for actuation requiring as little as 25V. 2D electrostatic latching and addressing was demonstrated using both a resonant and pulsed addressing scheme.
2D Electrostatic Actuation of Microshutter Arrays
NASA Technical Reports Server (NTRS)
Burns, Devin E.; Oh, Lance H.; Li, Mary J.; Jones, Justin S.; Kelly, Daniel P.; Zheng, Yun; Kutyrev, Alexander S.; Moseley, Samuel H.
2015-01-01
An electrostatically actuated microshutter array consisting of rotational microshutters (shutters that rotate about a torsion bar) were designed and fabricated through the use of models and experiments. Design iterations focused on minimizing the torsional stiffness of the microshutters, while maintaining their structural integrity. Mechanical and electromechanical test systems were constructed to measure the static and dynamic behavior of the microshutters. The torsional stiffness was reduced by a factor of four over initial designs without sacrificing durability. Analysis of the resonant behavior of the microshutter arrays demonstrates that the first resonant mode is a torsional mode occurring around 3000 Hz. At low vacuum pressures, this resonant mode can be used to significantly reduce the drive voltage necessary for actuation requiring as little as 25V. 2D electrostatic latching and addressing was demonstrated using both a resonant and pulsed addressing scheme.
2D quantum gravity from quantum entanglement.
Gliozzi, F
2011-01-21
In quantum systems with many degrees of freedom the replica method is a useful tool to study the entanglement of arbitrary spatial regions. We apply it in a way that allows them to backreact. As a consequence, they become dynamical subsystems whose position, form, and extension are determined by their interaction with the whole system. We analyze, in particular, quantum spin chains described at criticality by a conformal field theory. Its coupling to the Gibbs' ensemble of all possible subsystems is relevant and drives the system into a new fixed point which is argued to be that of the 2D quantum gravity coupled to this system. Numerical experiments on the critical Ising model show that the new critical exponents agree with those predicted by the formula of Knizhnik, Polyakov, and Zamolodchikov.
Graphene suspensions for 2D printing
NASA Astrophysics Data System (ADS)
Soots, R. A.; Yakimchuk, E. A.; Nebogatikova, N. A.; Kotin, I. A.; Antonova, I. V.
2016-04-01
It is shown that, by processing a graphite suspension in ethanol or water by ultrasound and centrifuging, it is possible to obtain particles with thicknesses within 1-6 nm and, in the most interesting cases, 1-1.5 nm. Analogous treatment of a graphite suspension in organic solvent yields eventually thicker particles (up to 6-10 nm thick) even upon long-term treatment. Using the proposed ink based on graphene and aqueous ethanol with ethylcellulose and terpineol additives for 2D printing, thin (~5 nm thick) films with sheet resistance upon annealing ~30 MΩ/□ were obtained. With the ink based on aqueous graphene suspension, the sheet resistance was ~5-12 kΩ/□ for 6- to 15-nm-thick layers with a carrier mobility of ~30-50 cm2/(V s).
Some properties of correlations of quantum lattice systems in thermal equilibrium
Fröhlich, Jürg; Ueltschi, Daniel
2015-05-15
Simple proofs of uniqueness of the thermodynamic limit of KMS states and of the decay of equilibrium correlations are presented for a large class of quantum lattice systems at high temperatures. New quantum correlation inequalities for general Heisenberg models are described. Finally, a simplified derivation of a general result on power-law decay of correlations in 2D quantum lattice systems with continuous symmetries is given, extending results of McBryan and Spencer for the 2D classical XY model.
Gaedigk, Andrea; Bradford, L Dianne; Alander, Sarah W; Leeder, J Steven
2006-04-01
Unexplained cases of CYP2D6 genotype/phenotype discordance continue to be discovered. In previous studies, several African Americans with a poor metabolizer phenotype carried the reduced function CYP2D6*10 allele in combination with a nonfunctional allele. We pursued the possibility that these alleles harbor either a known sequence variation (i.e., CYP2D6*36 carrying a gene conversion in exon 9 along the CYP2D6*10-defining 100C>T single-nucleotide polymorphism) or novel sequences variation(s). Discordant cases were evaluated by long-range polymerase chain reaction (PCR) to test for gene rearrangement events, and a 6.6-kilobase pair PCR product encompassing the CYP2D6 gene was cloned and entirely sequenced. Thereafter, allele frequencies were determined in different study populations comprising whites, African Americans, and Asians. Analyses covering the CYP2D7 to 2D6 gene region established that CYP2D6*36 did not only exist as a gene duplication (CYP2D6*36x2) or in tandem with *10 (CYP2D6*36+*10), as previously reported, but also by itself. This "single" CYP2D6*36 allele was found in nine African Americans and one Asian, but was absent in the whites tested. Ultimately, the presence of CYP2D6*36 resolved genotype/phenotype discordance in three cases. We also discovered an exon 9 conversion-positive CYP2D6*4 gene in a duplication arrangement (CYP2D6*4Nx2) and a CYP2D6*4 allele lacking 100C>T (CYP2D6*4M) in two white subjects. The discovery of an allele that carries only one CYP2D6*36 gene copy provides unequivocal evidence that both CYP2D6*36 and *36x2 are associated with a poor metabolizer phenotype. Given a combined frequency of between 0.5 and 3% in African Americans and Asians, genotyping for CYP2D6*36 should improve the accuracy of genotype-based phenotype prediction in these populations.
Vortex Lattices in Rotating Atomic Bose Gases with Dipolar Interactions
Cooper, N.R.; Rezayi, E.H.; Simon, S.H.
2005-11-11
We show that dipolar interactions have dramatic effects on the ground states of rotating atomic Bose gases in the weak-interaction limit. With increasing dipolar interaction (relative to the net contact interaction), the mean field, or high filling factor, ground state undergoes a series of transitions between vortex lattices of different symmetries: triangular, square, 'stripe', and 'bubble' phases. We also study the effects of dipolar interactions on the quantum fluids at low filling factors. We show that the incompressible Laughlin state at filling factor {nu}=1/2 is replaced by compressible stripe and bubble phases.
NASA Astrophysics Data System (ADS)
Yan, Bo; Li, Yuguo; Liu, Ying
2016-07-01
In this paper, we present an adaptive finite element (FE) algorithm for direct current (DC) resistivity modeling in 2-D generally anisotropic conductivity structures. Our algorithm is implemented on an unstructured triangular mesh that readily accommodates complex structures such as topography and dipping layers and so on. We implement a self-adaptive, goal-oriented grid refinement algorithm in which the finite element analysis is performed on a sequence of refined grids. The grid refinement process is guided by an a posteriori error estimator. The problem is formulated in terms of total potentials where mixed boundary conditions are incorporated. This type of boundary condition is superior to the Dirichlet type of conditions and improves numerical accuracy considerably according to model calculations. We have verified the adaptive finite element algorithm using a two-layered earth with azimuthal anisotropy. The FE algorithm with incorporation of mixed boundary conditions achieves high accuracy. The relative error between the numerical and analytical solutions is less than 1% except in the vicinity of the current source location, where the relative error is up to 2.4%. A 2-D anisotropic model is used to demonstrate the effects of anisotropy upon the apparent resistivity in DC soundings.
Highly efficient reflective Dammann grating with a triangular structure.
Wang, Jin; Zhou, Changhe; Ma, Jianyong; Zong, Yonghong; Jia, Wei
2016-07-01
A highly efficient reflective Dammann grating with a triangular structure operating at 1064 nm wavelength under normal incidence for TE polarization is designed and fabricated. Rigorous coupled wave analysis and particle swarm optimization algorithms are adopted to design and analyze the properties. The triangular reflective grating could cancel the 0th order, and the mechanism is clarified by the simplified modal method. The gratings are fabricated by direct laser writing lithography. The diffraction efficiency of fabricated grating is more than 86% at 1064 nm wavelength (97.6% in theory). This reflective grating should be a useful optical element in the field of high-power lasers as well as other reflective applications. PMID:27409211
A Novel Triangular Shaped UWB Fractal Antenna Using Circular Slot
NASA Astrophysics Data System (ADS)
Shahu, Babu Lal; Pal, Srikanta; Chattoraj, Neela
2016-03-01
The article presents the design of triangular shaped fractal based antenna with circular slot for ultra wideband (UWB) application. The antenna is fed using microstrip line and has overall dimension of 24×24×1.6 mm3. The proposed antenna is covering the wide frequency bandwidth of 2.99-11.16 GHz and is achieved using simple fractal based triangular-circular geometries and asymmetrical ground plane. The antenna is designed and parametrical studies are performed using method of moment (MOM) based Full Wave Electromagnetic (EM) software Simulator Zeland IE3D. The prototype of proposed antenna is fabricated and tested to compare the simulated and measured results of various antenna parameters. The antenna has good impedance bandwidth, nearly constant gain and stable radiation pattern. Measured return loss shows fair agreement with simulated one. Also measured group delay variation obtained is less than 1.0 ns, which proves good time domain behavior of the proposed antenna.
Three-dimensional vibrations of cantilevered right triangular plates
NASA Astrophysics Data System (ADS)
McGee, O. G.; Giaimo, G. T.
1992-12-01
The first known three-dimensional continuum vibration solutions for cantilevered right triangular plates with variable thickness are obtained using the Ritz method. Assumed displacement functions are in the form of algebraic polynomials, which satisfy the fixed face conditions exactly, and which are mathematically complete. Reasonably accurate natural frequencies are calculated for low aspect ratio, right triangular thin plates having arbitrary values of thickness taper ratios in the spanwise direction. Detailed numerical studies show that a three-dimensional analysis is essential to monitoring coupled-mode sensitivities in the variation of non-dimensional natural frequencies with increasing thickness taper ratio. Upper bound results, obtained using the present method, are compared with those obtained by other investigators using ordinary beam theories, two-dimensional finite element and finite difference procedures, and experimental methods. This unified comparison of upper and lower bound solutions is presented here with the aim of 'bracketing' the exact analytical solution of the subject problem.
The free vibration of isotropic and specially orthotropic triangular plates
NASA Astrophysics Data System (ADS)
Kim, C. S.
1991-05-01
A relatively simple Rayleigh Ritz solution, with simple polynomials as the admissible functions, was given for the free vibration analysis of thin, isotropic and orthotropic, right triangular plates. Numerical results were obtained for plates of various aspect ratios and having all combinations of the classical free, simply supported and clamped boundary conditions. In the present paper, the method is extended to apply to plates of general triangular planform. The analysis remains relatively simple and the computational work remains less than that required when using the methods described in most eariler studies, whilst the accuracy is comparable. Sample studies illustrating the convergence of the solution are given and comparison with results available from the literature show the validity of the approach. Natural frequency parameters and nodal patterns have been determined for a fairly comprehensive selection of particular plates, a few of these results being reported here.
Self-Avoiding Walks over Adaptive Triangular Grids
NASA Technical Reports Server (NTRS)
Heber, Gerd; Biswas, Rupak; Gao, Guang R.; Saini, Subhash (Technical Monitor)
1998-01-01
In this paper, we present a new approach to constructing a "self-avoiding" walk through a triangular mesh. Unlike the popular approach of visiting mesh elements using space-filling curves which is based on a geometric embedding, our approach is combinatorial in the sense that it uses the mesh connectivity only. We present an algorithm for constructing a self-avoiding walk which can be applied to any unstructured triangular mesh. The complexity of the algorithm is O(n x log(n)), where n is the number of triangles in the mesh. We show that for hierarchical adaptive meshes, the algorithm can be easily parallelized by taking advantage of the regularity of the refinement rules. The proposed approach should be very useful in the run-time partitioning and load balancing of adaptive unstructured grids.
Two-dimensional B-C-O alloys: a promising class of 2D materials for electronic devices.
Zhou, Si; Zhao, Jijun
2016-04-28
Graphene, a superior 2D material with high carrier mobility, has limited application in electronic devices due to zero band gap. In this regard, boron and nitrogen atoms have been integrated into the graphene lattice to fabricate 2D semiconducting heterostructures. It is an intriguing question whether oxygen can, as a replacement of nitrogen, enter the sp2 honeycomb lattice and form stable B-C-O monolayer structures. Here we explore the atomic structures, energetic and thermodynamic stability, and electronic properties of various 2D B-C-O alloys using first-principles calculations. Our results show that oxygen can be stably incorporated into the graphene lattice by bonding with boron. The B and O species favor forming alternate patterns into the chain- or ring-like structures embedded in the pristine graphene regions. These B-C-O hybrid sheets can be either metals or semiconductors depending on the B : O ratio. The semiconducting (B2O)nCm and (B6O3)nCm phases exist under the B- and O-rich conditions, and possess a tunable band gap of 1.0-3.8 eV and high carrier mobility, retaining ∼1000 cm2 V(-1) s(-1) even for half coverage of B and O atoms. These B-C-O alloys form a new class of 2D materials that are promising candidates for high-speed electronic devices.
A new inversion method for (T2, D) 2D NMR logging and fluid typing
NASA Astrophysics Data System (ADS)
Tan, Maojin; Zou, Youlong; Zhou, Cancan
2013-02-01
One-dimensional nuclear magnetic resonance (1D NMR) logging technology has some significant limitations in fluid typing. However, not only can two-dimensional nuclear magnetic resonance (2D NMR) provide some accurate porosity parameters, but it can also identify fluids more accurately than 1D NMR. In this paper, based on the relaxation mechanism of (T2, D) 2D NMR in a gradient magnetic field, a hybrid inversion method that combines least-squares-based QR decomposition (LSQR) and truncated singular value decomposition (TSVD) is examined in the 2D NMR inversion of various fluid models. The forward modeling and inversion tests are performed in detail with different acquisition parameters, such as magnetic field gradients (G) and echo spacing (TE) groups. The simulated results are discussed and described in detail, the influence of the above-mentioned observation parameters on the inversion accuracy is investigated and analyzed, and the observation parameters in multi-TE activation are optimized. Furthermore, the hybrid inversion can be applied to quantitatively determine the fluid saturation. To study the effects of noise level on the hybrid method and inversion results, the numerical simulation experiments are performed using different signal-to-noise-ratios (SNRs), and the effect of different SNRs on fluid typing using three fluid models are discussed and analyzed in detail.
Incommensurate lattice modulations in Potassium Vanadate
NASA Astrophysics Data System (ADS)
Chakoumakos, Bryan; Banerjee, Arnab; Mark, Lumsden; Cao, Huibo; Kim, Jong-Woo; Hoffman, Christina; Wang, Xiaoping
Potassium Vanadate (K2V3O8) is an S = 1/2 2D square lattice antiferromagnet that shows spin reorientation indicating a strong coupling between the magnetism and its dielectric properties with a promise of rich physics that promises multiferroicity. These tangible physical properties are strongly tied through a spin-lattice coupling to the underlying lattice and superlattice behavior. It has a superlattice (SL) onsetting below Tc = 115 K with an approximate [3 x 3 x 2] modulation. Here we present our recent experiments at TOPAZ beamline at SNS which for the first time proves conclusively that the lattice modulations are incommensurate, with an in-plane Q of 0.315. We will also show our attempts to refine the data using JANA which requires a redefinition of the lattice, as well as the temperature and Q dependence of the superlattice modulation measured using neutrons at HFIR and synchrotron x-rays at APS. Our results are not only relevant for the ongoing search of multifunctional behavior in K2V3O8 but also generally for the superlattice modulations observed in a large family of fresnoites. Work performed at ORNL and ANL is supported by U.S. Dept. of Energy, Office of Basic Energy Sciences and Office of User Facilities Division.
New triangular and quadrilateral plate-bending finite elements
NASA Technical Reports Server (NTRS)
Narayanaswami, R.
1974-01-01
A nonconforming plate-bending finite element of triangular shape and associated quadrilateral elements are developed. The transverse displacement is approximated within the element by a quintic polynomial. The formulation takes into account the effects of transverse shear deformation. Results of the static and dynamic analysis of a square plate, with edges simply supported or clamped, are compared with exact solutions. Good accuracy is obtained in all calculations.
A Step-Wise Approach to Elicit Triangular Distributions
NASA Technical Reports Server (NTRS)
Greenberg, Marc W.
2013-01-01
Adapt/combine known methods to demonstrate an expert judgment elicitation process that: 1.Models expert's inputs as a triangular distribution, 2.Incorporates techniques to account for expert bias and 3.Is structured in a way to help justify expert's inputs. This paper will show one way of "extracting" expert opinion for estimating purposes. Nevertheless, as with most subjective methods, there are many ways to do this.
Development of Negative Triangularity Plasmas in DIII-D
NASA Astrophysics Data System (ADS)
Walker, M. L.
2015-11-01
We report on development of DIII-D electron cyclotron heated discharges with controlled negative triangularity plasma shapes, to evaluate the effect on electron heat transport in L-mode plasmas, as reported on TCV. Analysis of TCV data found that negative triangularity exerts a stabilizing influence on the trapped electron mode, the dominant instability in the conditions of those experiments. Major objectives of the DIII-D development are producing complementary plasmas, one with negative and one with positive triangularity, approximately symmetric in major radial coordinate and having similar density and current profiles. Major constraints include selection of plasma parameters and toroidal field to optimize fluctuation diagnostic measurements while preventing transition from L- to H-mode and deposition of EC heating power near the q=1 surface to limit sawteeth. Issues discussed are definition of control scenarios by which the pair of shapes are accessed and their resulting controllability under the constraints imposed by DIII-D shaping control. Supported by US DOE under DE-FC02-04ER54698.
Natural convection in asymmetric triangular enclosures heated from below
NASA Astrophysics Data System (ADS)
Kamiyo, O. M.; Angeli, D.; Barozzi, G. S.; Collins, M. W.
2014-11-01
Triangular enclosures are typical configurations of attic spaces found in residential as well as industrial pitched-roof buildings. Natural convection in triangular rooftops has received considerable attention over the years, mainly on right-angled and isosceles enclosures. In this paper, a finite volume CFD package is employed to study the laminar air flow and temperature distribution in asymmetric rooftop-shaped triangular enclosures when heated isothermally from the base wall, for aspect ratios (AR) 0.2 <= AR <= 1.0, and Rayleigh number (Ra) values 8 × 105 <= Ra <= 5 × 107. The effects of Rayleigh number and pitch angle on the flow structure and temperature distributions within the enclosure are analysed. Results indicate that, at low pitch angle, the heat transfer between the cold inclined and the hot base walls is very high, resulting in a multi-cellular flow structure. As the pitch angle increases, however, the number of cells reduces, and the total heat transfer rate progressively reduces, even if the Rayleigh number, being based on the enclosure height, rapidly increases. Physical reasons for the above effect are inspected.
Parabolic similariton Yb-fiber laser with triangular pulse evolution
NASA Astrophysics Data System (ADS)
Wang, Sijia; Wang, Lei
2016-04-01
We propose a novel mode-locked fiber laser design which features a passive nonlinear triangular pulse formation and self-similar parabolic pulse amplification intra cavity. Attribute to the nonlinear reshaping progress in the passive fiber, a triangular-profiled pulse with negative-chirp is generated and paved the way for rapid and efficient self-similar parabolic evolution in a following short-length high-gain fiber. In the meanwhile, the accompanied significantly compressed narrow spectrum from this passive nonlinear reshaping also gives the promise of pulse stabilization and gain-shaping robustness without strong filtering. The resulting short average intra-cavity pulse duration, low amplified spontaneous emission (ASE) and low intra-cavity power loss are essential for the low-noise operation. Simulations predict this modelocked fiber laser allows for high-energy ultra-short transform-limited pulse generation exceeding the gain bandwidth. The output pulse has a de-chirped duration (full-width at half maximum, FWHM) of 27 fs. In addition to the ultrafast laser applications, the proposed fiber laser scheme can support low-noise parabolic and triangular pulse trains at the same time, which are also attractive in optical pulse shaping, all-optical signal processing and high-speed communication applications.
NASA Astrophysics Data System (ADS)
Cheng, Chingyun; Kangara, Jayampathi; Arakelyan, Ilya; Thomas, John
2016-05-01
We tune the dimensionality of a strongly interacting degenerate 6 Li Fermi gas from 2D to quasi-2D, by adjusting the radial confinement of pancake-shaped clouds to control the radial chemical potential. In the 2D regime with weak radial confinement, the measured pair binding energies are in agreement with 2D-BCS mean field theory, which predicts dimer pairing energies in the many-body regime. In the qausi-2D regime obtained with increased radial confinement, the measured pairing energy deviates significantly from 2D-BCS theory. In contrast to the pairing energy, the measured radii of the cloud profiles are not fit by 2D-BCS theory in either the 2D or quasi-2D regimes, but are fit in both regimes by a beyond mean field polaron-model of the free energy. Supported by DOE, ARO, NSF, and AFOSR.
A lattice-Boltzmann scheme of the Navier-Stokes equations on a 3D cuboid lattice
NASA Astrophysics Data System (ADS)
Min, Haoda; Peng, Cheng; Wang, Lian-Ping
2015-11-01
The standard lattice-Boltzmann method (LBM) for fluid flow simulation is based on a square (in 2D) or cubic (in 3D) lattice grids. Recently, two new lattice Boltzmann schemes have been developed on a 2D rectangular grid using the MRT (multiple-relaxation-time) collision model, by adding a free parameter in the definition of moments or by extending the equilibrium moments. Here we developed a lattice Boltzmann model on 3D cuboid lattice, namely, a lattice grid with different grid lengths in different spatial directions. We designed our MRT-LBM model by matching the moment equations from the Chapman-Enskog expansion with the Navier-Stokes equations. The model guarantees correct hydrodynamics. A second-order term is added to the equilibrium moments in order to restore the isotropy of viscosity on a cuboid lattice. The form and the coefficients of the extended equilibrium moments are determined through an inverse design process. An additional benefit of the model is that the viscosity can be adjusted independent of the stress-moment relaxation parameter, thus improving the numerical stability of the model. The resulting cuboid MRT-LBM model is then validated through benchmark simulations using laminar channel flow, turbulent channel flow, and the 3D Taylor-Green vortex flow.
Competing coexisting phases in 2D water
Zanotti, Jean-Marc; Judeinstein, Patrick; Dalla-Bernardina, Simona; Creff, Gaëlle; Brubach, Jean-Blaise; Roy, Pascale; Bonetti, Marco; Ollivier, Jacques; Sakellariou, Dimitrios; Bellissent-Funel, Marie-Claire
2016-01-01
The properties of bulk water come from a delicate balance of interactions on length scales encompassing several orders of magnitudes: i) the Hydrogen Bond (HBond) at the molecular scale and ii) the extension of this HBond network up to the macroscopic level. Here, we address the physics of water when the three dimensional extension of the HBond network is frustrated, so that the water molecules are forced to organize in only two dimensions. We account for the large scale fluctuating HBond network by an analytical mean-field percolation model. This approach provides a coherent interpretation of the different events experimentally (calorimetry, neutron, NMR, near and far infra-red spectroscopies) detected in interfacial water at 160, 220 and 250 K. Starting from an amorphous state of water at low temperature, these transitions are respectively interpreted as the onset of creation of transient low density patches of 4-HBonded molecules at 160 K, the percolation of these domains at 220 K and finally the total invasion of the surface by them at 250 K. The source of this surprising behaviour in 2D is the frustration of the natural bulk tetrahedral local geometry and the underlying very significant increase in entropy of the interfacial water molecules. PMID:27185018
Phase Engineering of 2D Tin Sulfides.
Mutlu, Zafer; Wu, Ryan J; Wickramaratne, Darshana; Shahrezaei, Sina; Liu, Chueh; Temiz, Selcuk; Patalano, Andrew; Ozkan, Mihrimah; Lake, Roger K; Mkhoyan, K A; Ozkan, Cengiz S
2016-06-01
Tin sulfides can exist in a variety of phases and polytypes due to the different oxidation states of Sn. A subset of these phases and polytypes take the form of layered 2D structures that give rise to a wide host of electronic and optical properties. Hence, achieving control over the phase, polytype, and thickness of tin sulfides is necessary to utilize this wide range of properties exhibited by the compound. This study reports on phase-selective growth of both hexagonal tin (IV) sulfide SnS2 and orthorhombic tin (II) sulfide SnS crystals with diameters of over tens of microns on SiO2 substrates through atmospheric pressure vapor-phase method in a conventional horizontal quartz tube furnace with SnO2 and S powders as the source materials. Detailed characterization of each phase of tin sulfide crystals is performed using various microscopy and spectroscopy methods, and the results are corroborated by ab initio density functional theory calculations. PMID:27099950
Phase Engineering of 2D Tin Sulfides.
Mutlu, Zafer; Wu, Ryan J; Wickramaratne, Darshana; Shahrezaei, Sina; Liu, Chueh; Temiz, Selcuk; Patalano, Andrew; Ozkan, Mihrimah; Lake, Roger K; Mkhoyan, K A; Ozkan, Cengiz S
2016-06-01
Tin sulfides can exist in a variety of phases and polytypes due to the different oxidation states of Sn. A subset of these phases and polytypes take the form of layered 2D structures that give rise to a wide host of electronic and optical properties. Hence, achieving control over the phase, polytype, and thickness of tin sulfides is necessary to utilize this wide range of properties exhibited by the compound. This study reports on phase-selective growth of both hexagonal tin (IV) sulfide SnS2 and orthorhombic tin (II) sulfide SnS crystals with diameters of over tens of microns on SiO2 substrates through atmospheric pressure vapor-phase method in a conventional horizontal quartz tube furnace with SnO2 and S powders as the source materials. Detailed characterization of each phase of tin sulfide crystals is performed using various microscopy and spectroscopy methods, and the results are corroborated by ab initio density functional theory calculations.
Competing coexisting phases in 2D water
NASA Astrophysics Data System (ADS)
Zanotti, Jean-Marc; Judeinstein, Patrick; Dalla-Bernardina, Simona; Creff, Gaëlle; Brubach, Jean-Blaise; Roy, Pascale; Bonetti, Marco; Ollivier, Jacques; Sakellariou, Dimitrios; Bellissent-Funel, Marie-Claire
2016-05-01
The properties of bulk water come from a delicate balance of interactions on length scales encompassing several orders of magnitudes: i) the Hydrogen Bond (HBond) at the molecular scale and ii) the extension of this HBond network up to the macroscopic level. Here, we address the physics of water when the three dimensional extension of the HBond network is frustrated, so that the water molecules are forced to organize in only two dimensions. We account for the large scale fluctuating HBond network by an analytical mean-field percolation model. This approach provides a coherent interpretation of the different events experimentally (calorimetry, neutron, NMR, near and far infra-red spectroscopies) detected in interfacial water at 160, 220 and 250 K. Starting from an amorphous state of water at low temperature, these transitions are respectively interpreted as the onset of creation of transient low density patches of 4-HBonded molecules at 160 K, the percolation of these domains at 220 K and finally the total invasion of the surface by them at 250 K. The source of this surprising behaviour in 2D is the frustration of the natural bulk tetrahedral local geometry and the underlying very significant increase in entropy of the interfacial water molecules.
Magnetic order in a frustrated two-dimensional atom lattice at a semiconductor surface.
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.
Magnetic order in a frustrated two-dimensional atom lattice at a semiconductor surface.
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. PMID:23535641
Magnetic vortex lattice in HgBa2CuO4+δ observed by small-angle neutron scattering
NASA Astrophysics Data System (ADS)
Li, Yuan; Egetenmeyer, N.; Gavilano, J. L.; Barišić, N.; Greven, M.
2011-02-01
We report the direct observation of the magnetic vortex lattice in the model high-temperature superconductor HgBa2CuO4+δ. Using small-angle neutron scattering on high-quality crystals, we observe two equal domains of undistorted triangular vortex lattices well aligned with the tetragonal crystallographic axes. The signal decreases rapidly with increasing magnetic field and vanishes above 0.4 T, which we attribute to a crossover from a three-dimensional to a two-dimensional vortex system, similar to previous results for the more anisotropic compound Bi2.15Sr1.95CaCu2O8+δ. Our result indicates that a triangular vortex lattice (with or without distortion) at low magnetic fields is a generic property of cuprates with critical temperatures above 80 K.
Holographic method for site-resolved detection of a 2D array of ultracold atoms
NASA Astrophysics Data System (ADS)
Hoffmann, Daniel Kai; Deissler, Benjamin; Limmer, Wolfgang; Hecker Denschlag, Johannes
2016-08-01
We propose a novel approach to site-resolved detection of a 2D gas of ultracold atoms in an optical lattice. A near-resonant laser beam is coherently scattered by the atomic array, and after passing a lens its interference pattern is holographically recorded by superimposing it with a reference laser beam on a CCD chip. Fourier transformation of the recorded intensity pattern reconstructs the atomic distribution in the lattice with single-site resolution. The holographic detection method requires only about two hundred scattered photons per atom in order to achieve a high reconstruction fidelity of 99.9 %. Therefore, additional cooling during detection might not be necessary even for light atomic elements such as lithium. Furthermore, first investigations suggest that small aberrations of the lens can be post-corrected in imaging processing.
Phase diagram of the spin-1/2 triangular J1-J2 Heisenberg model on a three-leg cylinder
NASA Astrophysics Data System (ADS)
Saadatmand, S. N.; Powell, B. J.; McCulloch, I. P.
2015-06-01
We study the phase diagram of the frustrated Heisenberg model on the triangular lattice with nearest- and next-nearest-neighbor spin-exchange coupling, on three-leg ladders. Using the density-matrix renormalization-group method, we obtain the complete phase diagram of the model, which includes quasi-long-range 120∘ and columnar order, and a Majumdar-Ghosh phase with short-ranged correlations. All these phases are nonchiral and planar. We also identify the nature of phase transitions.
Electrochemical fabrication of 2D and 3D nickel nanowires using porous anodic alumina templates
NASA Astrophysics Data System (ADS)
Mebed, A. M.; Abd-Elnaiem, Alaa M.; Al-Hosiny, Najm M.
2016-06-01
Mechanically stable nickel (Ni) nanowires array and nanowires network were synthesized by pulse electrochemical deposition using 2D and 3D porous anodic alumina (PAA) templates. The structures and morphologies of as-prepared films were characterized by X-ray diffraction and scanning electron microscopy, respectively. The grown Ni nanowire using 3D PAA revealed more strength and larger surface area than has grown Ni use 2D PAA template. The prepared nanowires have a face-centered cubic crystal structure with average grain size 15 nm, and the preferred orientation of the nucleation of the nanowires is (111). The diameter of the nanowires is about 50-70 nm with length 3 µm. The resulting 3D Ni nanowire lattice, which provides enhanced mechanical stability and an increased surface area, benefits energy storage and many other applications which utilize the large surface area.
2-D Animation's Not Just for Mickey Mouse.
ERIC Educational Resources Information Center
Weinman, Lynda
1995-01-01
Discusses characteristics of two-dimensional (2-D) animation; highlights include character animation, painting issues, and motion graphics. Sidebars present Silicon Graphics animations tools and 2-D animation programs for the desktop computer. (DGM)
NASA Astrophysics Data System (ADS)
Yue, Yang-Yang; Lu, Rong-er; Yang, Bo; Huang, Huang; Hong, Xu-Hao; Zhang, Chao; Qin, Yi-Qiang; Zhu, Yong-Yuan
2016-10-01
We take a theoretical investigation on the reciprocal property of a class of 2D nonlinear photonic quasicrystal proposed by Lifshitz et al. in PRL 95, 133901 (2005). Using the rectangular projection method, the analytical expression for the Fourier spectrum of the quasicrystal structure is obtained explicitly. It is interesting to find that the result has a similar form to the corresponding expression of the well-known 1D Fibonacci lattice. In addition, we predict a further extension of the result to higher dimensions. This work is of practical importance for the photonic device design in nonlinear optical conversion progresses.
Canonical vs. micro-canonical sampling methods in a 2D Ising model
Kepner, J.
1990-12-01
Canonical and micro-canonical Monte Carlo algorithms were implemented on a 2D Ising model. Expressions for the internal energy, U, inverse temperature, Z, and specific heat, C, are given. These quantities were calculated over a range of temperature, lattice sizes, and time steps. Both algorithms accurately simulate the Ising model. To obtain greater than three decimal accuracy from the micro-canonical method requires that the more complicated expression for Z be used. The overall difference between the algorithms is small. The physics of the problem under study should be the deciding factor in determining which algorithm to use. 13 refs., 6 figs., 2 tabs.
Zhang, Zi-Xuan; Ding, Ni-Ni; Zhang, Wen-Hua; Chen, Jin-Xiang; Young, David J; Hor, T S Andy
2014-04-25
A 2D coordination polymer prepared with bulky diethylformamide solvates exhibits channels which allow dipyridyl bridging ligands to diffuse into the crystal lattice. The absorbed dipyridyls thread through the pores of one layer and substitute the surface diethylformamide molecules on the neighboring layers to stitch alternate layers to form flexible interpenetrated metal-orgaic frameworks. The threading process also results in exchange of the bulky diethylformamide solvates for aqua to minimize congestion and, more strikingly, forces the slippage of two-dimensional layers, while still maintaining crystallinity. PMID:24692130
On Traveling Waves in Lattices: The Case of Riccati Lattices
NASA Astrophysics Data System (ADS)
Dimitrova, Zlatinka
2012-09-01
The method of simplest equation is applied for analysis of a class of lattices described by differential-difference equations that admit traveling-wave solutions constructed on the basis of the solution of the Riccati equation. We denote such lattices as Riccati lattices. We search for Riccati lattices within two classes of lattices: generalized Lotka-Volterra lattices and generalized Holling lattices. We show that from the class of generalized Lotka-Volterra lattices only the Wadati lattice belongs to the class of Riccati lattices. Opposite to this many lattices from the Holling class are Riccati lattices. We construct exact traveling wave solutions on the basis of the solution of Riccati equation for three members of the class of generalized Holling lattices.
NASA Astrophysics Data System (ADS)
Goździewski, Krzysztof
2003-01-01
In papers (Goździewski and Maciejewski, 1998a, b, 1999), we investigate unrestricted, planar problem of a dynamically symmetric rigid body and a sphere. Following the original statement of the problem by Kokoriev and Kirpichnikov (1988), we assume that the potential of the rigid body is approximated by the gravitational field of a dumb-bell. The model is described in terms of a 2D Hamiltonian depending on three parameters. In this paper, we investigate the stability of triangular equilibria permissible by the dynamics of the model, under the assumption of low-order resonances. We analyze all resonances of order smaller than four, and we examine the stability with application of theorems by Markeev and Sokolsky. These are the possible following cases: the non-diagonal resonance of the first order with two null characteristic frequencies (unstable); resonances of the first order with one nonzero frequency (diagonal and non-diagonal, stable and unstable); the second-order resonance, which is non-diagonal and stable, and the third-order resonance which is generically unstable, except for three points in the parameters' space, corresponding to stable equilibria. We discuss a perturbed version of Kokoriev and Kirpichnikov model, and we find that if the perturbation is small and depends on the coordinates only, the triangular equilibria persist, except if for the unperturbed equilibria the first-order resonance occurs. We show that the resonances of the order higher than two are also preserved if the perturbation acts.
Generates 2D Input for DYNA NIKE & TOPAZ
Hallquist, J. O.; Sanford, Larry
1996-07-15
MAZE is an interactive program that serves as an input and two-dimensional mesh generator for DYNA2D, NIKE2D, TOPAZ2D, and CHEMICAL TOPAZ2D. MAZE also generates a basic template for ISLAND input. MAZE has been applied to the generation of input data to study the response of two-dimensional solids and structures undergoing finite deformations under a wide variety of large deformation transient dynamic and static problems and heat transfer analyses.
MAZE96. Generates 2D Input for DYNA NIKE & TOPAZ
Sanford, L.; Hallquist, J.O.
1992-02-24
MAZE is an interactive program that serves as an input and two-dimensional mesh generator for DYNA2D, NIKE2D, TOPAZ2D, and CHEMICAL TOPAZ2D. MAZE also generates a basic template for ISLAND input. MAZE has been applied to the generation of input data to study the response of two-dimensional solids and structures undergoing finite deformations under a wide variety of large deformation transient dynamic and static problems and heat transfer analyses.
Spin-lattice coupling in iron jarosite
Buurma, A.J.C.; Handayani, I.P.; Mufti, N.; Blake, G.R.; Loosdrecht, P.H.M. van; Palstra, T.T.M.
2012-11-15
We have studied the magnetoelectric coupling of the frustrated triangular antiferromagnet iron jarosite using Raman spectroscopy, dielectric measurements and specific heat. Temperature dependent capacitance measurements show an anomaly in the dielectric constant at T{sub N}. Specific heat data indicate the presence of a low frequency Einstein mode at low temperature. Raman spectroscopy confirms the presence of a new mode below T{sub N} that can be attributed to folding of the Brillouin zone. This mode shifts and sharpens below T{sub N}. We evaluate the strength of the magnetoelectric coupling using the symmetry unrestricted biquadratic magnetoelectric terms in the free energy. - Graphical abstract: Sketch of two connected triangles formed by Fe{sup 3+} spins (red arrows) in the hexagonal basal plane of potassium iron jarosite. An applied magnetic field (H) below the antiferromagnetic ordering temperature induces shifts of the hydroxy ligands, giving rise to local electrical dipole moments (blue arrows). These electric displacements cancel out in pairwise fashion by symmetry. Ligand shifts are confined to the plane and shown by shadowing. Highlights: Black-Right-Pointing-Pointer Evidence has been found for spin-lattice coupling in iron jarosite. Black-Right-Pointing-Pointer A new optical Raman mode appears below T{sub N} and shifts with temperature. Black-Right-Pointing-Pointer The magnetodielectric coupling is mediated by superexchange. Black-Right-Pointing-Pointer Symmetry of Kagome magnetic lattice causes local electrical dipole moments to cancel.
NASA Astrophysics Data System (ADS)
Franz, Silvio; Gradenigo, Giacomo; Spigler, Stefano
2016-03-01
We study how the thermodynamic properties of the triangular plaquette model (TPM) are influenced by the addition of extra interactions. The thermodynamics of the original TPM is trivial, while its dynamics is glassy, as usual in kinetically constrained models. As soon as we generalize the model to include additional interactions, a thermodynamic phase transition appears in the system. The additional interactions we consider are either short ranged, forming a regular lattice in the plane, or long ranged of the small-world kind. In the case of long-range interactions we call the new model the random-diluted TPM. We provide arguments that the model so modified should undergo a thermodynamic phase transition, and that in the long-range case this is a glass transition of the "random first-order" kind. Finally, we give support to our conjectures studying the finite-temperature phase diagram of the random-diluted TPM in the Bethe approximation. This corresponds to the exact calculation on the random regular graph, where free energy and configurational entropy can be computed by means of the cavity equations.
Franz, Silvio; Gradenigo, Giacomo; Spigler, Stefano
2016-03-01
We study how the thermodynamic properties of the triangular plaquette model (TPM) are influenced by the addition of extra interactions. The thermodynamics of the original TPM is trivial, while its dynamics is glassy, as usual in kinetically constrained models. As soon as we generalize the model to include additional interactions, a thermodynamic phase transition appears in the system. The additional interactions we consider are either short ranged, forming a regular lattice in the plane, or long ranged of the small-world kind. In the case of long-range interactions we call the new model the random-diluted TPM. We provide arguments that the model so modified should undergo a thermodynamic phase transition, and that in the long-range case this is a glass transition of the "random first-order" kind. Finally, we give support to our conjectures studying the finite-temperature phase diagram of the random-diluted TPM in the Bethe approximation. This corresponds to the exact calculation on the random regular graph, where free energy and configurational entropy can be computed by means of the cavity equations. PMID:27078408
Engineering novel optical lattices.
Windpassinger, Patrick; Sengstock, Klaus
2013-08-01
Optical lattices have developed into a widely used and highly recognized tool to study many-body quantum physics with special relevance for solid state type systems. One of the most prominent reasons for this success is the high degree of tunability in the experimental setups. While at the beginning quasi-static, cubic geometries were mainly explored, the focus of the field has now shifted toward new lattice topologies and the dynamical control of lattice structures. In this review we intend to give an overview of the progress recently achieved in this field on the experimental side. In addition, we discuss theoretical proposals exploiting specifically these novel lattice geometries. PMID:23828639
Electrostatic 2D assembly of bionanoparticles on a cationic lipid monolayer.
NASA Astrophysics Data System (ADS)
Kewalramani, Sumit; Wang, Suntao; Fukuto, Masafumi; Yang, Lin; Niu, Zhongwei; Nguyen, Giang; Wang, Qian
2010-03-01
We present a grazing-incidence small-angle X-ray scattering (GISAXS) study on 2D assembly of cowpea mosaic virus (CPMV) under a mixed cationic-zwitterionic (DMTAP^+-DMPC) lipid monolayer at the air-water interface. The inter-particle and particle-lipid electrostatic interactions were varied by controlling the subphase pH and the membrane charge density. GISAXS data show that 2D crystals of CPMV are formed above a threshold membrane charge density and only in a narrow pH range just above CPMV's isoelectric point, where the charge on CPMV is expected to be weakly negative. The particle density for the 2D crystals is similar to that for the densest lattice plane in the 3D crystals of CPMV. The results show that the 2D crystallization is achieved in the part of the phase space where the electrostatic interactions are expected to maximize the adsorption of CPMV onto the lipid membrane. This electrostatics-based strategy for controlling interfacial nanoscale assembly should be generally applicable to other nanoparticles.
Fractal properties of the lattice Lotka-Volterra model.
Tsekouras, G A; Provata, A
2002-01-01
The lattice Lotka-Volterra (LLV) model is studied using mean-field analysis and Monte Carlo simulations. While the mean-field phase portrait consists of a center surrounded by an infinity of closed trajectories, when the process is restricted to a two-dimensional (2D) square lattice, local inhomogeneities/fluctuations appear. Spontaneous local clustering is observed on lattice and homogeneous initial distributions turn into clustered structures. Reactions take place only at the interfaces between different species and the borders adopt locally fractal structure. Intercluster surface reactions are responsible for the formation of local fluctuations of the species concentrations. The box-counting fractal dimension of the LLV dynamics on a 2D support is found to depend on the reaction constants while the upper bound of fractality determines the size of the local oscillators. Lacunarity analysis is used to determine the degree of clustering of homologous species. Besides the spontaneous clustering that takes place on a regular 2D lattice, the effects of fractal supports on the dynamics of the LLV are studied. For supports of dimensionality D(s)<2 the lattice can, for certain domains of the reaction constants, adopt a poisoned state where only one of the species survives. By appropriately selecting the fractal dimension of the substrate, it is possible to direct the system into a poisoned or oscillatory steady state at will.
2d PDE Linear Symmetric Matrix Solver
1983-10-01
ICCG2 (Incomplete Cholesky factorized Conjugate Gradient algorithm for 2d symmetric problems) was developed to solve a linear symmetric matrix system arising from a 9-point discretization of two-dimensional elliptic and parabolic partial differential equations found in plasma physics applications, such as resistive MHD, spatial diffusive transport, and phase space transport (Fokker-Planck equation) problems. These problems share the common feature of being stiff and requiring implicit solution techniques. When these parabolic or elliptic PDE''s are discretized withmore » finite-difference or finite-element methods,the resulting matrix system is frequently of block-tridiagonal form. To use ICCG2, the discretization of the two-dimensional partial differential equation and its boundary conditions must result in a block-tridiagonal supermatrix composed of elementary tridiagonal matrices. The incomplete Cholesky conjugate gradient algorithm is used to solve the linear symmetric matrix equation. Loops are arranged to vectorize on the Cray1 with the CFT compiler, wherever possible. Recursive loops, which cannot be vectorized, are written for optimum scalar speed. For matrices lacking symmetry, ILUCG2 should be used. Similar methods in three dimensions are available in ICCG3 and ILUCG3. A general source containing extensions and macros, which must be processed by a pre-compiler to obtain the standard FORTRAN source, is provided along with the standard FORTRAN source because it is believed to be more readable. The pre-compiler is not included, but pre-compilation may be performed by a text editor as described in the UCRL-88746 Preprint.« less
2d PDE Linear Asymmetric Matrix Solver
1983-10-01
ILUCG2 (Incomplete LU factorized Conjugate Gradient algorithm for 2d problems) was developed to solve a linear asymmetric matrix system arising from a 9-point discretization of two-dimensional elliptic and parabolic partial differential equations found in plasma physics applications, such as plasma diffusion, equilibria, and phase space transport (Fokker-Planck equation) problems. These equations share the common feature of being stiff and requiring implicit solution techniques. When these parabolic or elliptic PDE''s are discretized with finite-difference or finite-elementmore » methods, the resulting matrix system is frequently of block-tridiagonal form. To use ILUCG2, the discretization of the two-dimensional partial differential equation and its boundary conditions must result in a block-tridiagonal supermatrix composed of elementary tridiagonal matrices. A generalization of the incomplete Cholesky conjugate gradient algorithm is used to solve the matrix equation. Loops are arranged to vectorize on the Cray1 with the CFT compiler, wherever possible. Recursive loops, which cannot be vectorized, are written for optimum scalar speed. For problems having a symmetric matrix ICCG2 should be used since it runs up to four times faster and uses approximately 30% less storage. Similar methods in three dimensions are available in ICCG3 and ILUCG3. A general source, containing extensions and macros, which must be processed by a pre-compiler to obtain the standard FORTRAN source, is provided along with the standard FORTRAN source because it is believed to be more readable. The pre-compiler is not included, but pre-compilation may be performed by a text editor as described in the UCRL-88746 Preprint.« less
Position control using 2D-to-2D feature correspondences in vision guided cell micromanipulation.
Zhang, Yanliang; Han, Mingli; Shee, Cheng Yap; Ang, Wei Tech
2007-01-01
Conventional camera calibration that utilizes the extrinsic and intrinsic parameters of the camera and the objects has certain limitations for micro-level cell operations due to the presence of hardware deviations and external disturbances during the experimental process, thereby invalidating the extrinsic parameters. This invalidation is often neglected in macro-world visual servoing and affects the visual image processing quality, causing deviation from the desired position in micro-level cell operations. To increase the success rate of vision guided biological micromanipulations, a novel algorithm monitoring the changing image pattern of the manipulators including the injection micropipette and cell holder is designed and implemented based on 2 dimensional (2D)-to 2D feature correspondences and can adjust the manipulator and perform position control simultaneously. When any deviation is found, the manipulator is retracted to the initial focusing plane before continuing the operation.
Lattice thermal conductance of quantum wires with disorder
NASA Astrophysics Data System (ADS)
Vyhmeister, Erik; Hershfield, Selman
We model the lattice thermal conductance in long quantum wires connected to two large heat baths at different temperatures in the harmonic approximation. The thermal conductance is computed with the Landauer formula for phonons, where it is related to the sum over all transmission probabilities for phonons through the wire. The net transmission probability is computed using a recursive Green function technique, which allows one to study long wires efficiently. We consider several different kinds of disorder to reduce the lattice thermal conductivity: periodic rectangular holes of varying sizes and shapes, periodic triangular holes, and narrow bands, averaged over randomness to account for variance in manufacturing. Depending on the model, the thermal conductance was reduced by 80 percent or more from the perfectly ordered wire case. Funded by NSF grant DMR-1461019.
Two-dimensional lattice-fluid model with waterlike anomalies.
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.
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.
Two-dimensional lattice-fluid model with waterlike anomalies.
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. PMID:15244571
NASA Astrophysics Data System (ADS)
Gibanov, N. S.; Sheremet, M. A.
2016-04-01
Numerical analysis of laminar natural convection inside a cubical cavity with a local heat source of triangular cross-section has been conducted. The mathematical model formulated in dimensionless variables such as "vector potential functions - vorticity vector" has been solved by the finite difference method of the second order accuracy. The three-dimensional temperature fields, 2D streamlines and isotherms in a wide range of the Rayleigh number from 104 to 106 have been presented illustrating variations of the fluid flow and heat transfer.
A Planar Quantum Transistor Based on 2D-2D Tunneling in Double Quantum Well Heterostructures
Baca, W.E.; Blount, M.A.; Hafich, M.J.; Lyo, S.K.; Moon, J.S.; Reno, J.L.; Simmons, J.A.; Wendt, J.R.
1998-12-14
We report on our work on the double electron layer tunneling transistor (DELTT), based on the gate-control of two-dimensional -- two-dimensional (2D-2D) tunneling in a double quantum well heterostructure. While previous quantum transistors have typically required tiny laterally-defined features, by contrast the DELTT is entirely planar and can be reliably fabricated in large numbers. We use a novel epoxy-bond-and-stop-etch (EBASE) flip-chip process, whereby submicron gating on opposite sides of semiconductor epitaxial layers as thin as 0.24 microns can be achieved. Because both electron layers in the DELTT are 2D, the resonant tunneling features are unusually sharp, and can be easily modulated with one or more surface gates. We demonstrate DELTTs with peak-to-valley ratios in the source-drain I-V curve of order 20:1 below 1 K. Both the height and position of the resonant current peak can be controlled by gate voltage over a wide range. DELTTs with larger subband energy offsets ({approximately} 21 meV) exhibit characteristics that are nearly as good at 77 K, in good agreement with our theoretical calculations. Using these devices, we also demonstrate bistable memories operating at 77 K. Finally, we briefly discuss the prospects for room temperature operation, increases in gain, and high-speed.
'Brukin2D': a 2D visualization and comparison tool for LC-MS data
Tsagkrasoulis, Dimosthenis; Zerefos, Panagiotis; Loudos, George; Vlahou, Antonia; Baumann, Marc; Kossida, Sophia
2009-01-01
Background Liquid Chromatography-Mass Spectrometry (LC-MS) is a commonly used technique to resolve complex protein mixtures. Visualization of large data sets produced from LC-MS, namely the chromatogram and the mass spectra that correspond to its compounds is the focus of this work. Results The in-house developed 'Brukin2D' software, built in Matlab 7.4, which is presented here, uses the compound data that are exported from the Bruker 'DataAnalysis' program, and depicts the mean mass spectra of all the chromatogram compounds from one LC-MS run, in one 2D contour/density plot. Two contour plots from different chromatograph runs can then be viewed in the same window and automatically compared, in order to find their similarities and differences. The results of the comparison can be examined through detailed mass quantification tables, while chromatogram compound statistics are also calculated during the procedure. Conclusion 'Brukin2D' provides a user-friendly platform for quick, easy and integrated view of complex LC-MS data. The software is available at . PMID:19534737
Inhibition of human cytochrome P450 2D6 (CYP2D6) by methadone.
Wu, D; Otton, S V; Sproule, B A; Busto, U; Inaba, T; Kalow, W; Sellers, E M
1993-01-01
1. In microsomes prepared from three human livers, methadone competitively inhibited the O-demethylation of dextromethorphan, a marker substrate for CYP2D6. The apparent Ki value of methadone ranged from 2.5 to 5 microM. 2. Two hundred and fifty-two (252) white Caucasians, including 210 unrelated healthy volunteers and 42 opiate abusers undergoing treatment with methadone were phenotyped using dextromethorphan as the marker drug. Although the frequency of poor metabolizers was similar in both groups, the extensive metabolizers among the opiate abusers tended to have higher O-demethylation metabolic ratios and to excrete less of the dose as dextromethorphan metabolites than control extensive metabolizer subjects. These data suggest inhibition of CYP2D6 by methadone in vivo as well. 3. Because methadone is widely used in the treatment of opiate abuse, inhibition of CYP2D6 activity in these patients might contribute to exaggerated response or unexpected toxicity from drugs that are substrates of this enzyme. PMID:8448065
Umeokoli, Blessing O; Muharini, Rini; Okoye, Festus B; Ajiwe, Vincent I; Akpuaka, Mabel U; Lin, Wenhan; Liu, Zhen; Proksch, Peter
2016-03-01
The first chemical examination of roots of the traditionally used medicinal plant Talinum triangulare (Portulacaceae) from Nigeria led to the isolation of two new C-methylated flavonoids, 5,6-dimethoxy-7-hydroxy-8-methyl-flavone (1), 5,6-dimethoxy-8-methyl-2-phenyl-7H-1-benzopyran-7-one (2), and one new α-pyrone derivative, 4-methoxy-6-(2-hydroxy-4-phenylbutyl)-2H-pyran-2-one (3), along with thirteen known compounds, including nine amides (4-12), indole-3-carboxylic acid (13), p-hydroxy benzoic acid (14), and two steroids (15-16). Their structures were elucidated by extensive spectroscopic measurements including 1D, 2D NMR, MS, and by comparison with the literature. All isolated compounds were screened for their cytotoxic and antifungal activities. However, none of them showed significant activity. PMID:26773210
NASA Astrophysics Data System (ADS)
Ii, Satoshi; Xie, Bin; Xiao, Feng
2014-02-01
A novel interface-capturing method is proposed to compute moving interfaces on unstructured grids with triangular (2D) and tetrahedral (3D) elements. Different from the conventional VOF (volume of fluid) method which involves geometric reconstructions of the interface, the present method is based on the algebraic reconstruction approach originally developed in the THINC (tangent of hyperbola interface capturing) scheme by Xiao et al. (2005) [17]. A continuous multidimensional hyperbolic tangent function is employed for retrieving the jump-like distribution of the indicator function, which avoids the explicit geometric representation of the interface and thus substantially reduces the algorithmic complexity in unstructured grids. Numerical diffusion and smearing are effectively eliminated, and the compact thickness of the jump transition layer in the volume fraction is retained throughout the computation even for largely deformed interface. The solution quality of the present scheme is comparable to the VOF method with PLIC (piecewise linear interface calculation) algorithm.
Correlated Electron Phenomena in 2D Materials
NASA Astrophysics Data System (ADS)
Lambert, Joseph G.
In this thesis, I present experimental results on coherent electron phenomena in layered two-dimensional materials: single layer graphene and van der Waals coupled 2D TiSe2. Graphene is a two-dimensional single-atom thick sheet of carbon atoms first derived from bulk graphite by the mechanical exfoliation technique in 2004. Low-energy charge carriers in graphene behave like massless Dirac fermions, and their density can be easily tuned between electron-rich and hole-rich quasiparticles with electrostatic gating techniques. The sharp interfaces between regions of different carrier densities form barriers with selective transmission, making them behave as partially reflecting mirrors. When two of these interfaces are set at a separation distance within the phase coherence length of the carriers, they form an electronic version of a Fabry-Perot cavity. I present measurements and analysis of multiple Fabry-Perot modes in graphene with parallel electrodes spaced a few hundred nanometers apart. Transition metal dichalcogenide (TMD) TiSe2 is part of the family of materials that coined the term "materials beyond graphene". It contains van der Waals coupled trilayer stacks of Se-Ti-Se. Many TMD materials exhibit a host of interesting correlated electronic phases. In particular, TiSe2 exhibits chiral charge density waves (CDW) below TCDW ˜ 200 K. Upon doping with copper, the CDW state gets suppressed with Cu concentration, and CuxTiSe2 becomes superconducting with critical temperature of T c = 4.15 K. There is still much debate over the mechanisms governing the coexistence of the two correlated electronic phases---CDW and superconductivity. I will present some of the first conductance spectroscopy measurements of proximity coupled superconductor-CDW systems. Measurements reveal a proximity-induced critical current at the Nb-TiSe2 interfaces, suggesting pair correlations in the pure TiSe2. The results indicate that superconducting order is present concurrently with CDW in
NASA Astrophysics Data System (ADS)
Bergner, Georg; Catterall, Simon
2016-08-01
We discuss the motivations, difficulties and progress in the study of supersymmetric lattice gauge theories focusing in particular on 𝒩 = 1 and 𝒩 = 4 super-Yang-Mills in four dimensions. Brief reviews of the corresponding lattice formalisms are given and current results are presented and discussed. We conclude with a summary of the main aspects of current work and prospects for the future.
Laterally closed lattice homomorphisms
NASA Astrophysics Data System (ADS)
Toumi, Mohamed Ali; Toumi, Nedra
2006-12-01
Let A and B be two Archimedean vector lattices and let be a lattice homomorphism. We call that T is laterally closed if T(D) is a maximal orthogonal system in the band generated by T(A) in B, for each maximal orthogonal system D of A. In this paper we prove that any laterally closed lattice homomorphism T of an Archimedean vector lattice A with universal completion Au into a universally complete vector lattice B can be extended to a lattice homomorphism of Au into B, which is an improvement of a result of M. Duhoux and M. Meyer [M. Duhoux and M. Meyer, Extended orthomorphisms and lateral completion of Archimedean Riesz spaces, Ann. Soc. Sci. Bruxelles 98 (1984) 3-18], who established it for the order continuous lattice homomorphism case. Moreover, if in addition Au and B are with point separating order duals (Au)' and B' respectively, then the laterally closedness property becomes a necessary and sufficient condition for any lattice homomorphism to have a similar extension to the whole Au. As an application, we give a new representation theorem for laterally closed d-algebras from which we infer the existence of d-algebra multiplications on the universal completions of d-algebras.
Spontaneous magnetization and anomalous Hall effect in an emergent Dice lattice
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
NASA Astrophysics Data System (ADS)
Weinberg, M.; Staarmann, C.; Ölschläger, C.; Simonet, J.; Sengstock, K.
2016-06-01
Here, we present the application of a novel method for controlling the geometry of a state-dependent honeycomb lattice: the energy offset between the two sublattices of the honeycomb structure can be adjusted by rotating the atomic quantization axis. This enables us to continuously tune between a homogeneous graphene-like honeycomb lattice and a triangular lattice and to open an energy gap at the characteristic Dirac points. We probe the symmetry of the lattice with microwave spectroscopy techniques and investigate the behavior of atoms excited to the second energy band. We find a striking influence of the energy gap at the Dirac cones onto the lifetimes of bosonic atoms in the excited band.
Spontaneous magnetization and anomalous Hall effect in an emergent Dice lattice
NASA Astrophysics Data System (ADS)
Dutta, Omjyoti; Przysiężna, Anna; Zakrzewski, Jakub
2015-06-01
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.
CYP2D7 Sequence Variation Interferes with TaqMan CYP2D6*15 and *35 Genotyping
Riffel, Amanda K.; Dehghani, Mehdi; Hartshorne, Toinette; Floyd, Kristen C.; Leeder, J. Steven; Rosenblatt, Kevin P.; Gaedigk, Andrea
2016-01-01
TaqMan™ genotyping assays are widely used to genotype CYP2D6, which encodes a major drug metabolizing enzyme. Assay design for CYP2D6 can be challenging owing to the presence of two pseudogenes, CYP2D7 and CYP2D8, structural and copy number variation and numerous single nucleotide polymorphisms (SNPs) some of which reflect the wild-type sequence of the CYP2D7 pseudogene. The aim of this study was to identify the mechanism causing false-positive CYP2D6*15 calls and remediate those by redesigning and validating alternative TaqMan genotype assays. Among 13,866 DNA samples genotyped by the CompanionDx® lab on the OpenArray platform, 70 samples were identified as heterozygotes for 137Tins, the key SNP of CYP2D6*15. However, only 15 samples were confirmed when tested with the Luminex xTAG CYP2D6 Kit and sequencing of CYP2D6-specific long range (XL)-PCR products. Genotype and gene resequencing of CYP2D6 and CYP2D7-specific XL-PCR products revealed a CC>GT dinucleotide SNP in exon 1 of CYP2D7 that reverts the sequence to CYP2D6 and allows a TaqMan assay PCR primer to bind. Because CYP2D7 also carries a Tins, a false-positive mutation signal is generated. This CYP2D7 SNP was also responsible for generating false-positive signals for rs769258 (CYP2D6*35) which is also located in exon 1. Although alternative CYP2D6*15 and *35 assays resolved the issue, we discovered a novel CYP2D6*15 subvariant in one sample that carries additional SNPs preventing detection with the alternate assay. The frequency of CYP2D6*15 was 0.1% in this ethnically diverse U.S. population sample. In addition, we also discovered linkage between the CYP2D7 CC>GT dinucleotide SNP and the 77G>A (rs28371696) SNP of CYP2D6*43. The frequency of this tentatively functional allele was 0.2%. Taken together, these findings emphasize that regardless of how careful genotyping assays are designed and evaluated before being commercially marketed, rare or unknown SNPs underneath primer and/or probe regions can impact
CYP2D7 Sequence Variation Interferes with TaqMan CYP2D6 (*) 15 and (*) 35 Genotyping.
Riffel, Amanda K; Dehghani, Mehdi; Hartshorne, Toinette; Floyd, Kristen C; Leeder, J Steven; Rosenblatt, Kevin P; Gaedigk, Andrea
2015-01-01
TaqMan™ genotyping assays are widely used to genotype CYP2D6, which encodes a major drug metabolizing enzyme. Assay design for CYP2D6 can be challenging owing to the presence of two pseudogenes, CYP2D7 and CYP2D8, structural and copy number variation and numerous single nucleotide polymorphisms (SNPs) some of which reflect the wild-type sequence of the CYP2D7 pseudogene. The aim of this study was to identify the mechanism causing false-positive CYP2D6 (*) 15 calls and remediate those by redesigning and validating alternative TaqMan genotype assays. Among 13,866 DNA samples genotyped by the CompanionDx® lab on the OpenArray platform, 70 samples were identified as heterozygotes for 137Tins, the key SNP of CYP2D6 (*) 15. However, only 15 samples were confirmed when tested with the Luminex xTAG CYP2D6 Kit and sequencing of CYP2D6-specific long range (XL)-PCR products. Genotype and gene resequencing of CYP2D6 and CYP2D7-specific XL-PCR products revealed a CC>GT dinucleotide SNP in exon 1 of CYP2D7 that reverts the sequence to CYP2D6 and allows a TaqMan assay PCR primer to bind. Because CYP2D7 also carries a Tins, a false-positive mutation signal is generated. This CYP2D7 SNP was also responsible for generating false-positive signals for rs769258 (CYP2D6 (*) 35) which is also located in exon 1. Although alternative CYP2D6 (*) 15 and (*) 35 assays resolved the issue, we discovered a novel CYP2D6 (*) 15 subvariant in one sample that carries additional SNPs preventing detection with the alternate assay. The frequency of CYP2D6 (*) 15 was 0.1% in this ethnically diverse U.S. population sample. In addition, we also discovered linkage between the CYP2D7 CC>GT dinucleotide SNP and the 77G>A (rs28371696) SNP of CYP2D6 (*) 43. The frequency of this tentatively functional allele was 0.2%. Taken together, these findings emphasize that regardless of how careful genotyping assays are designed and evaluated before being commercially marketed, rare or unknown SNPs underneath primer
BERG,J.S.; RUGGIERO, A.; MACHIDA, S.; KOSCIELNIAK, S.
2007-06-25
EMMA is a 10 to 20 MeV electron ring designed to test our understanding of beam dynamics in a relativistic linear non-scaling fixed field alternating gradient accelerator (FFAG). This paper describes the design of the EMMA lattice. We begin with a summary of the experimental goals that impact the lattice design, and then outline what motivated the choice for the basic lattice parameters, such as the type of cells, the number of cells, and the RF frequency. We next list the different configurations that we wish to operate the machine in so as to accomplish our experimental goals. Finally, we enumerate the detailed lattice parameters, showing how these parameters result from the various lattice configurations.
Lei, Shengbin; Surin, Mathieu; Tahara, Kazukuni; Adisoejoso, Jinne; Lazzaroni, Roberto; Tobe, Yoshito; De Feyter, Steven
2008-08-01
Recognition and selection are of fundamental importance for the hierarchical assembly of supramolecular systems. Coronene induces the formation of a hydrogen-bonded isophthalic acid supramolecular macrocycle, and this well-defined heterocluster forces, in its turn, DBA1 to form a van der Waals stabilized honeycomb lattice, leading to a three-component 2D crystal containing nine molecules in the unit cell. The recognition and selection events enable efficient error correction and healing in redundant mixtures.
Modelling of Motion of Bodies Near Triangular Lagrangian Points
NASA Astrophysics Data System (ADS)
Bobrov, O. A.
In this paper, we consider a system of three bodies connected by gravity, two of which are of comparable mass (the Sun and Jupiter), and the third is negligible and it is located in one of the triangular Lagrange points (restricted 3 - body problem). We used the equations of motion in a planar coordinate system that rotates together with massive bodies. Several programs have been written in the programming environment Pascal ABC, in order to build the trajectory of a small body, to indicate the osculating orbit around a massive body, to display equipotential surfaces.
INTEGRATING A LINEAR INTERPOLATION FUNCTION ACROSS TRIANGULAR CELL BOUNDARIES
J. R. WISEMAN; J. S. BROCK
2000-04-01
Computational models of particle dynamics often exchange solution data with discretized continuum-fields using interpolation functions. These particle methods require a series expansion of the interpolation function for two purposes: numerical analysis used to establish the model's consistency and accuracy, and logical-coordinate evaluation used to locate particles within a grid. This report presents discrete-expansions for a linear interpolation function commonly used within triangular cell geometries. Discrete-expansions, unlike a Taylor's series, account for interpolation discontinuities across cell boundaries and, therefore, are valid throughout a discretized domain. Verification of linear discrete-expansions is demonstrated on a simple test problem.
A triangular element based on generalized potential energy concepts
NASA Technical Reports Server (NTRS)
Thomas, G. R.; Gallagher, R. H.
1976-01-01
Stiffness equations are formulated for a doubly-curved triangular thin shell finite element. The strain energy component of the potential energy is first expressed in terms of displacements and displacement gradients with the aid of consistent deep shell strain-displacement equations. The element in-plane and normal displacement fields are approximated by complete cubic polynomials. These functions do not satisfy the interelement displacement admissibility conditions. Satisfaction is forced by the imposition of constraint conditions on the interelement boundaries; the constraints represent the modification of the potential energy. Some numerical results for a pinched cylinder, a cylindrical sphere, and a pinched sphere are examined.
Triangular preconditioners for saddle point problems with a penalty term
Klawonn, A.
1996-12-31
Triangular preconditioners for a class of saddle point problems with a penalty term are considered. An important example is the mixed formulation of the pure displacement problem in linear elasticity. It is shown that the spectrum of the preconditioned system is contained in a real, positive interval, and that the interval bounds can be made independent of the discretization and penalty parameters. This fact is used to construct bounds of the convergence rate of the GMRES method used with an energy norm. Numerical results are given for GMRES and BI-CGSTAB.
Low lattice thermal conductivity of stanene.
Peng, Bo; Zhang, Hao; Shao, Hezhu; Xu, Yuchen; Zhang, Xiangchao; Zhu, Heyuan
2016-02-03
A fundamental understanding of phonon transport in stanene is crucial to predict the thermal performance in potential stanene-based devices. By combining first-principle calculation and phonon Boltzmann transport equation, we obtain the lattice thermal conductivity of stanene. A much lower thermal conductivity (11.6 W/mK) is observed in stanene, which indicates higher thermoelectric efficiency over other 2D materials. The contributions of acoustic and optical phonons to the lattice thermal conductivity are evaluated. Detailed analysis of phase space for three-phonon processes shows that phonon scattering channels LA + LA/TA/ZA ↔ TA/ZA are restricted, leading to the dominant contributions of high-group-velocity LA phonons to the thermal conductivity. The size dependence of thermal conductivity is investigated as well for the purpose of the design of thermoelectric nanostructures.
Low lattice thermal conductivity of stanene
Peng, Bo; Zhang, Hao; Shao, Hezhu; Xu, Yuchen; Zhang, Xiangchao; Zhu, Heyuan
2016-01-01
A fundamental understanding of phonon transport in stanene is crucial to predict the thermal performance in potential stanene-based devices. By combining first-principle calculation and phonon Boltzmann transport equation, we obtain the lattice thermal conductivity of stanene. A much lower thermal conductivity (11.6 W/mK) is observed in stanene, which indicates higher thermoelectric efficiency over other 2D materials. The contributions of acoustic and optical phonons to the lattice thermal conductivity are evaluated. Detailed analysis of phase space for three-phonon processes shows that phonon scattering channels LA + LA/TA/ZA ↔ TA/ZA are restricted, leading to the dominant contributions of high-group-velocity LA phonons to the thermal conductivity. The size dependence of thermal conductivity is investigated as well for the purpose of the design of thermoelectric nanostructures. PMID:26838731
Mechanical cloak design by direct lattice transformation.
Bückmann, Tiemo; Kadic, Muamer; Schittny, Robert; Wegener, Martin
2015-04-21
Spatial coordinate transformations have helped simplifying mathematical issues and solving complex boundary-value problems in physics for decades already. More recently, material-parameter transformations have also become an intuitive and powerful engineering tool for designing inhomogeneous and anisotropic material distributions that perform wanted functions, e.g., invisibility cloaking. A necessary mathematical prerequisite for this approach to work is that the underlying equations are form invariant with respect to general coordinate transformations. Unfortunately, this condition is not fulfilled in elastic-solid mechanics for materials that can be described by ordinary elasticity tensors. Here, we introduce a different and simpler approach. We directly transform the lattice points of a 2D discrete lattice composed of a single constituent material, while keeping the properties of the elements connecting the lattice points the same. After showing that the approach works in various areas, we focus on elastic-solid mechanics. As a demanding example, we cloak a void in an effective elastic material with respect to static uniaxial compression. Corresponding numerical calculations and experiments on polymer structures made by 3D printing are presented. The cloaking quality is quantified by comparing the average relative SD of the strain vectors outside of the cloaked void with respect to the homogeneous reference lattice. Theory and experiment agree and exhibit very good cloaking performance. PMID:25848021
Phonons and elasticity in critically coordinated lattices
NASA Astrophysics Data System (ADS)
Lubensky, T. C.; Kane, C. L.; Mao, Xiaoming; Souslov, A.; Sun, Kai
2015-07-01
Much of our understanding of vibrational excitations and elasticity is based upon analysis of frames consisting of sites connected by bonds occupied by central-force springs, the stability of which depends on the average number of neighbors per site z. When z < zc ≈ 2d, where d is the spatial dimension, frames are unstable with respect to internal deformations. This pedagogical review focuses on the properties of frames with z at or near zc, which model systems like randomly packed spheres near jamming and network glasses. Using an index theorem, N0 -NS = dN -NB relating the number of sites, N, and number of bonds, NB, to the number, N0, of modes of zero energy and the number, NS, of states of self stress, in which springs can be under positive or negative tension while forces on sites remain zero, it explores the properties of periodic square, kagome, and related lattices for which z = zc and the relation between states of self stress and zero modes in periodic lattices to the surface zero modes of finite free lattices (with free boundary conditions). It shows how modifications to the periodic kagome lattice can eliminate all but trivial translational zero modes and create topologically distinct classes, analogous to those of topological insulators, with protected zero modes at free boundaries and at interfaces between different topological classes.
Mechanical cloak design by direct lattice transformation
Bückmann, Tiemo; Kadic, Muamer; Schittny, Robert; Wegener, Martin
2015-01-01
Spatial coordinate transformations have helped simplifying mathematical issues and solving complex boundary-value problems in physics for decades already. More recently, material-parameter transformations have also become an intuitive and powerful engineering tool for designing inhomogeneous and anisotropic material distributions that perform wanted functions, e.g., invisibility cloaking. A necessary mathematical prerequisite for this approach to work is that the underlying equations are form invariant with respect to general coordinate transformations. Unfortunately, this condition is not fulfilled in elastic–solid mechanics for materials that can be described by ordinary elasticity tensors. Here, we introduce a different and simpler approach. We directly transform the lattice points of a 2D discrete lattice composed of a single constituent material, while keeping the properties of the elements connecting the lattice points the same. After showing that the approach works in various areas, we focus on elastic–solid mechanics. As a demanding example, we cloak a void in an effective elastic material with respect to static uniaxial compression. Corresponding numerical calculations and experiments on polymer structures made by 3D printing are presented. The cloaking quality is quantified by comparing the average relative SD of the strain vectors outside of the cloaked void with respect to the homogeneous reference lattice. Theory and experiment agree and exhibit very good cloaking performance. PMID:25848021
Kinetics of largely lattice-mismatch epitaxy
Chen, Yong |
1997-12-31
The kinetics of island nucleation, growth, and dislocation formation in largely lattice-mismatch heteroepitaxy are analyzed theoretically. It is shown that 2D platelets tend to transform to 3D islands as they exceed a certain critical size. During island growth, the increase of the strain concentration at the island edge makes it increasingly difficult for adatoms to reach the island, which leads to the formation of homogeneously sized islands. The high strain concentration at the island edge is eventually relieved by growing-in dislocations.
Mechanical characterization of 2D, 2D stitched, and 3D braided/RTM materials
NASA Technical Reports Server (NTRS)
Deaton, Jerry W.; Kullerd, Susan M.; Portanova, Marc A.
1993-01-01
Braided composite materials have potential for application in aircraft structures. Fuselage frames, floor beams, wing spars, and stiffeners are examples where braided composites could find application if cost effective processing and damage tolerance requirements are met. Another important consideration for braided composites relates to their mechanical properties and how they compare to the properties of composites produced by other textile composite processes being proposed for these applications. Unfortunately, mechanical property data for braided composites do not appear extensively in the literature. Data are presented in this paper on the mechanical characterization of 2D triaxial braid, 2D triaxial braid plus stitching, and 3D (through-the-thickness) braid composite materials. The braided preforms all had the same graphite tow size and the same nominal braid architectures, (+/- 30 deg/0 deg), and were resin transfer molded (RTM) using the same mold for each of two different resin systems. Static data are presented for notched and unnotched tension, notched and unnotched compression, and compression after impact strengths at room temperature. In addition, some static results, after environmental conditioning, are included. Baseline tension and compression fatigue results are also presented, but only for the 3D braided composite material with one of the resin systems.
Courant, E.D.; Garren, A.A.
1985-10-01
A realistic, distributed interaction region (IR) lattice has been designed that includes new components discussed in the June 1985 lattice workshop. Unlike the test lattices, the lattice presented here includes utility straights and the mechanism for crossing the beams in the experimental straights. Moreover, both the phase trombones and the dispersion suppressors contain the same bending as the normal cells. Vertically separated beams and 6 Tesla, 1-in-1 magnets are assumed. Since the cells are 200 meters long, and have 60 degree phase advance, this lattice has been named RLD1, in analogy with the corresponding test lattice, TLD1. The quadrupole gradient is 136 tesla/meter in the cells, and has similar values in other quadrupoles except in those in the IR`s, where the maximum gradient is 245 tesla/meter. RLD1 has distributed IR`s; however, clustered realistic lattices can easily be assembled from the same components, as was recently done in a version that utilizes the same type of experimental and utility straights as those of RLD1.
Superalloy Lattice Block Structures
NASA Technical Reports Server (NTRS)
Whittenberger, J. D.; Nathal, M. V.; Hebsur, M. G.; Kraus, D. L.
2003-01-01
In their simplest form, lattice block panels are produced by direct casting and result in lightweight, fully triangulated truss-like configurations which provide strength and stiffness [2]. The earliest realizations of lattice block were made from A1 and steels, primarily under funding from the US Navy [3]. This work also showed that the mechanical efficiency (eg., specific stiffness) of lattice block structures approached that of honeycomb structures [2]. The lattice architectures are also less anisotropic, and the investment casting route should provide a large advantage in cost and temperature capability over honeycombs which are limited to alloys that can be processed into foils. Based on this early work, a program was initiated to determine the feasibility of extending the high temperature superalloy lattice block [3]. The objective of this effort was to provide an alternative to intermetallics and composites in achieving a lightweight high temperature structure without sacrificing the damage tolerance and moderate cost inherent in superalloys. To establish the feasibility of the superalloy lattice block concept, work was performed in conjunction with JAMCORP, Inc. Billerica, MA, to produce a number of lattice block panels from both IN71 8 and Mar-M247.
Triangular Black Phosphorus Atomic Layers by Liquid Exfoliation.
Seo, Soonjoo; Lee, Hyun Uk; Lee, Soon Chang; Kim, Yooseok; Kim, Hyeran; Bang, Junhyeok; Won, Jonghan; Kim, Youngjun; Park, Byoungnam; Lee, Jouhahn
2016-01-01
Few-layer black phosphorus (BP) is the most promising material among the two-dimensional materials due to its layered structure and the excellent semiconductor properties. Currently, thin BP atomic layers are obtained mostly by mechanical exfoliation of bulk BP, which limits applications in thin-film based electronics due to a scaling process. Here we report highly crystalline few-layer black phosphorus thin films produced by liquid exfoliation. We demonstrate that the liquid-exfoliated BP forms a triangular crystalline structure on SiO2/Si (001) and amorphous carbon. The highly crystalline BP layers are faceted with a preferred orientation of the (010) plane on the sharp edge, which is an energetically most favorable facet according to the density functional theory calculations. Our results can be useful in understanding the triangular BP structure for large-area applications in electronic devices using two-dimensional materials. The sensitivity and selectivity of liquid-exfoliated BP to gas vapor demonstrate great potential for practical applications as sensors. PMID:27026070
Triangular covariance factorizations for. Ph.D. Thesis. - Calif. Univ.
NASA Technical Reports Server (NTRS)
Thornton, C. L.
1976-01-01
An improved computational form of the discrete Kalman filter is derived using an upper triangular factorization of the error covariance matrix. The covariance P is factored such that P = UDUT where U is unit upper triangular and D is diagonal. Recursions are developed for propagating the U-D covariance factors together with the corresponding state estimate. The resulting algorithm, referred to as the U-D filter, combines the superior numerical precision of square root filtering techniques with an efficiency comparable to that of Kalman's original formula. Moreover, this method is easily implemented and involves no more computer storage than the Kalman algorithm. These characteristics make the U-D method an attractive realtime filtering technique. A new covariance error analysis technique is obtained from an extension of the U-D filter equations. This evaluation method is flexible and efficient and may provide significantly improved numerical results. Cost comparisons show that for a large class of problems the U-D evaluation algorithm is noticeably less expensive than conventional error analysis methods.
Triangular Black Phosphorus Atomic Layers by Liquid Exfoliation
Seo, Soonjoo; Lee, Hyun Uk; Lee, Soon Chang; Kim, Yooseok; Kim, Hyeran; Bang, Junhyeok; Won, Jonghan; Kim, Youngjun; Park, Byoungnam; Lee, Jouhahn
2016-01-01
Few-layer black phosphorus (BP) is the most promising material among the two-dimensional materials due to its layered structure and the excellent semiconductor properties. Currently, thin BP atomic layers are obtained mostly by mechanical exfoliation of bulk BP, which limits applications in thin-film based electronics due to a scaling process. Here we report highly crystalline few-layer black phosphorus thin films produced by liquid exfoliation. We demonstrate that the liquid-exfoliated BP forms a triangular crystalline structure on SiO2/Si (001) and amorphous carbon. The highly crystalline BP layers are faceted with a preferred orientation of the (010) plane on the sharp edge, which is an energetically most favorable facet according to the density functional theory calculations. Our results can be useful in understanding the triangular BP structure for large-area applications in electronic devices using two-dimensional materials. The sensitivity and selectivity of liquid-exfoliated BP to gas vapor demonstrate great potential for practical applications as sensors. PMID:27026070
Triangular Black Phosphorus Atomic Layers by Liquid Exfoliation.
Seo, Soonjoo; Lee, Hyun Uk; Lee, Soon Chang; Kim, Yooseok; Kim, Hyeran; Bang, Junhyeok; Won, Jonghan; Kim, Youngjun; Park, Byoungnam; Lee, Jouhahn
2016-03-30
Few-layer black phosphorus (BP) is the most promising material among the two-dimensional materials due to its layered structure and the excellent semiconductor properties. Currently, thin BP atomic layers are obtained mostly by mechanical exfoliation of bulk BP, which limits applications in thin-film based electronics due to a scaling process. Here we report highly crystalline few-layer black phosphorus thin films produced by liquid exfoliation. We demonstrate that the liquid-exfoliated BP forms a triangular crystalline structure on SiO2/Si (001) and amorphous carbon. The highly crystalline BP layers are faceted with a preferred orientation of the (010) plane on the sharp edge, which is an energetically most favorable facet according to the density functional theory calculations. Our results can be useful in understanding the triangular BP structure for large-area applications in electronic devices using two-dimensional materials. The sensitivity and selectivity of liquid-exfoliated BP to gas vapor demonstrate great potential for practical applications as sensors.
Triangular Black Phosphorus Atomic Layers by Liquid Exfoliation
NASA Astrophysics Data System (ADS)
Seo, Soonjoo; Lee, Hyun Uk; Lee, Soon Chang; Kim, Yooseok; Kim, Hyeran; Bang, Junhyeok; Won, Jonghan; Kim, Youngjun; Park, Byoungnam; Lee, Jouhahn
2016-03-01
Few-layer black phosphorus (BP) is the most promising material among the two-dimensional materials due to its layered structure and the excellent semiconductor properties. Currently, thin BP atomic layers are obtained mostly by mechanical exfoliation of bulk BP, which limits applications in thin-film based electronics due to a scaling process. Here we report highly crystalline few-layer black phosphorus thin films produced by liquid exfoliation. We demonstrate that the liquid-exfoliated BP forms a triangular crystalline structure on SiO2/Si (001) and amorphous carbon. The highly crystalline BP layers are faceted with a preferred orientation of the (010) plane on the sharp edge, which is an energetically most favorable facet according to the density functional theory calculations. Our results can be useful in understanding the triangular BP structure for large-area applications in electronic devices using two-dimensional materials. The sensitivity and selectivity of liquid-exfoliated BP to gas vapor demonstrate great potential for practical applications as sensors.
RKKY interaction in triangular MoS2 nanoflakes
NASA Astrophysics Data System (ADS)
Mastrogiuseppe, Diego; Avalos-Ovando, Oscar; Ulloa, Sergio
Transition-metal dichalcogenides (TMDs), such as MoS2, possess unique electronic and optical properties, making them promising for optospintronics. Exfoliation and CVD growth processes produce nanoflakes of different shapes, often triangular with zigzag edges. Magnetic impurities in this material interact indirectly through the TMD conduction electrons/holes. Using an effective 3-orbital tight-binding model, we study the Ruderman-Kittel-Kasuya-Yosida interaction between magnetic impurities in p-doped triangular flakes with zigzag termination. We analyze the interaction as function of impurity separation along high symmetry directions in the nanoflake, considering hybridization to different Mo orbitals, and different fillings. The interaction is anisotropic for impurities in the interior of the flake. However, when impurities lie on the edges of the crystallite, the effective exchange is Ising-like, reflecting the presence of z2-orbitals associated with edge states. Other interactions are possible by selecting impurity positions and orbital character of the states in their neighborhood. Our results can be tested with local probes, such as spin-polarized STM Supported by NSF DMR-1508325.
SHIFT: a distributed runoff model using irregular triangular facets*1
NASA Astrophysics Data System (ADS)
Palacios-Vélez, Oscar Luis; Cuevas-Renaud, Baltasar
1992-06-01
SHIFT (Sistema HIdrológico de Facetas Triangulares) is a computational system that allows for the: (1) creation, editing and visualization of a watershed Digital Elevation Model (DEM), based on the Triangular Irregular Network (TIN) concepts; (2) input and interpolation of soil, river-bed, and rainfall data; and (3) calculation and routing of runoff in all the facets and reaches. The TIN DEM model is constructed from a set of points, where the slope changes abruptly. Afterwards, the drainage network is automatically identified and an interactive editor allows the addition or deletion of points to eliminate network discontinuities. Rainfall data are interpolated by means of a procedure based on the minimization of the bending energy of a thin plate. In order to calculate and route the runoff, the system determines the routing sequence of river segments and for each one: identifies the facets forming the contributing area; and determines a cascade of overland flow planes. Then, for each element and time interval, the system calculates the infiltration and routes the resultant runoff by a numerical solution of the kinematic wave equations. This information is saved and the user can see the hydrograph for any facet or reach.
Local Scale Transformations on the Lattice with Tensor Network Renormalization.
Evenbly, G; Vidal, G
2016-01-29
Consider the partition function of a classical system in two spatial dimensions, or the Euclidean path integral of a quantum system in two space-time dimensions, both on a lattice. We show that the tensor network renormalization algorithm [G. Evenbly and G. Vidal Phys. Rev. Lett. 115, 180405 (2015)] can be used to implement local scale transformations on these objects, namely, a lattice version of conformal maps. Specifically, we explain how to implement the lattice equivalent of the logarithmic conformal map that transforms the Euclidean plane into a cylinder. As an application, and with the 2D critical Ising model as a concrete example, we use this map to build a lattice version of the scaling operators of the underlying conformal field theory, from which one can extract their scaling dimensions and operator product expansion coefficients.
Local Scale Transformations on the Lattice with Tensor Network Renormalization
NASA Astrophysics Data System (ADS)
Evenbly, G.; Vidal, G.
2016-01-01
Consider the partition function of a classical system in two spatial dimensions, or the Euclidean path integral of a quantum system in two space-time dimensions, both on a lattice. We show that the tensor network renormalization algorithm [G. Evenbly and G. Vidal Phys. Rev. Lett. 115, 180405 (2015)] can be used to implement local scale transformations on these objects, namely, a lattice version of conformal maps. Specifically, we explain how to implement the lattice equivalent of the logarithmic conformal map that transforms the Euclidean plane into a cylinder. As an application, and with the 2D critical Ising model as a concrete example, we use this map to build a lattice version of the scaling operators of the underlying conformal field theory, from which one can extract their scaling dimensions and operator product expansion coefficients.
Computational Screening of 2D Materials for Photocatalysis.
Singh, Arunima K; Mathew, Kiran; Zhuang, Houlong L; Hennig, Richard G
2015-03-19
Two-dimensional (2D) materials exhibit a range of extraordinary electronic, optical, and mechanical properties different from their bulk counterparts with potential applications for 2D materials emerging in energy storage and conversion technologies. In this Perspective, we summarize the recent developments in the field of solar water splitting using 2D materials and review a computational screening approach to rapidly and efficiently discover more 2D materials that possess properties suitable for solar water splitting. Computational tools based on density-functional theory can predict the intrinsic properties of potential photocatalyst such as their electronic properties, optical absorbance, and solubility in aqueous solutions. Computational tools enable the exploration of possible routes to enhance the photocatalytic activity of 2D materials by use of mechanical strain, bias potential, doping, and pH. We discuss future research directions and needed method developments for the computational design and optimization of 2D materials for photocatalysis.
Coherent matter waves of a dipolar condensate in two-dimensional optical lattices
Zhang Aixia; Xue Jukui
2010-07-15
The coherent matter waves of a dipolar condensate in deep two-dimensional (2D) tilted and nontilted optical lattices are studied both analytically and numerically. It is shown that, in tilted lattices, by properly designing the sign and the magnitude of the contact interaction and the dipolar interaction, it is possible to control the decoherence of Bloch oscillations. Contrary to the usual short-range interacting Bose system, long-lived Bloch oscillations of the dipolar condensate are achieved when the dipolar interaction, the contact interaction, and the lattice dimension satisfy an analytical condition. Furthermore, we predict that, in untilted lattices, stable coherent 2D moving soliton and breather states of the dipolar condensate exist. This fact is very different from the purely short-range interacting Bose system (where the moving soliton cannot be stabilized in high-dimensional lattices). The dipolar interaction can lead to some novel phenomena that can not appear in short-range interacting BEC system.
Savara, Aditya
2016-08-15
The paper by Campbell et al. was recently brought to my attention. This comment is written to provide greater clarity to the community to prevent misconceptions regarding the entropies being discussed in that work and to clarify the differences between the adsorbate standard states suggested by Campbell and by Savara.
Kornilovitch, P E; Hague, J P
2015-02-25
Both FeSe and cuprate superconductors are quasi 2D materials with high transition temperatures and local fermion pairs. Motivated by such systems, we investigate real space pairing of fermions in an anisotropic lattice model with intersite attraction, V, and strong local Coulomb repulsion, U, leading to a determination of the optimal conditions for superconductivity from Bose-Einstein condensation. Our aim is to gain insight as to why high temperature superconductors tend to be quasi 2D. We make both analytically and numerically exact solutions for two body local pairing applicable to intermediate and strong V. We find that the Bose-Einstein condensation temperature of such local pairs pairs is maximal when hopping between layers is intermediate relative to in-plane hopping, indicating that the quasi 2D nature of unconventional superconductors has an important contribution to their high transition temperatures. PMID:25629425
Synthetic Covalent and Non-Covalent 2D Materials.
Boott, Charlotte E; Nazemi, Ali; Manners, Ian
2015-11-16
The creation of synthetic 2D materials represents an attractive challenge that is ultimately driven by their prospective uses in, for example, electronics, biomedicine, catalysis, sensing, and as membranes for separation and filtration. This Review illustrates some recent advances in this diverse field with a focus on covalent and non-covalent 2D polymers and frameworks, and self-assembled 2D materials derived from nanoparticles, homopolymers, and block copolymers.
Color generation and refractive index sensing using diffraction from 2D silicon nanowire arrays.
Walia, Jaspreet; Dhindsa, Navneet; Khorasaninejad, Mohammadreza; Saini, Simarjeet Singh
2014-01-15
Tunable structural color generation from vertical silicon nanowires arranged in different square lattices is demonstrated. The generated colors are adjustable using well-defined Bragg diffraction theory, and only depend on the lattice spacing and angles of incidence. Vivid colors spanning from bright red to blue are easily achieved. In keeping with this, a single square lattice of silicon nanowires is also able to produce different colors spanning the entire visible range. It is also shown that the 2D gratings also have a third grating direction when rotated 45 degrees. These simple and elegant solutions to color generation from silicon are used to demonstrate a cost-effective refractive index sensor. The sensor works by measuring color changes resulting from changes in the refractive index of the medium surrounding the nanowires using a trichromatic RGB decomposition. Moreover, the sensor produces linear responses in the trichromatic decomposition values versus the surrounding medium index. An index resolution of 10(-4) is achieved by performing basic image processing on the collected images, without the need for a laser or a spectrometer. Spectral analysis enables an increase in the index resolution of the sensor to a value of 10(-6) , with a sensitivity of 400 nm/RIU. PMID:23784866
All-optical digital 4 × 2 encoder based on 2D photonic crystal ring resonators
NASA Astrophysics Data System (ADS)
Moniem, Tamer A.
2016-04-01
The photonic crystals draw significant attention to build all-optical logic devices and are considered one of the solutions for the opto-electronic bottleneck via speed and size. The paper presents a novel optical 4 × 2 encoder based on 2D square lattice photonic crystals of silicon rods. The main realization of optical encoder is based on the photonic crystal ring resonator NOR gates. The proposed structure has four logic input ports, two output ports, and two bias input port. The photonic crystal structure has a square lattice of silicon rods with a refractive index of 3.39 in air. The structure has lattice constant 'a' equal to 630 nm and bandgap range from 0.32 to 044. The total size of the proposed 4 × 2 encoder is equal to 35 μm × 35 μm. The simulation results using the dimensional finite difference time domain and Plane Wave Expansion methods confirm the operation and the feasibility of the proposed optical encoder for ultrafast optical digital circuits.
Ruzmetov, Dmitry; Zhang, Kehao; Stan, Gheorghe; Kalanyan, Berc; Bhimanapati, Ganesh R; Eichfeld, Sarah M; Burke, Robert A; Shah, Pankaj B; O'Regan, Terrance P; Crowne, Frank J; Birdwell, A Glen; Robinson, Joshua A; Davydov, Albert V; Ivanov, Tony G
2016-03-22
When designing semiconductor heterostructures, it is expected that epitaxial alignment will facilitate low-defect interfaces and efficient vertical transport. Here, we report lattice-matched epitaxial growth of molybdenum disulfide (MoS2) directly on gallium nitride (GaN), resulting in high-quality, unstrained, single-layer MoS2 with strict registry to the GaN lattice. These results present a promising path toward the implementation of high-performance electronic devices based on 2D/3D vertical heterostructures, where each of the 3D and 2D semiconductors is both a template for subsequent epitaxial growth and an active component of the device. The MoS2 monolayer triangles average 1 μm along each side, with monolayer blankets (merged triangles) exhibiting properties similar to that of single-crystal MoS2 sheets. Photoluminescence, Raman, atomic force microscopy, and X-ray photoelectron spectroscopy analyses identified monolayer MoS2 with a prominent 20-fold enhancement of photoluminescence in the center regions of larger triangles. The MoS2/GaN structures are shown to electrically conduct in the out-of-plane direction, confirming the potential of directly synthesized 2D/3D semiconductor heterostructures for vertical current flow. Finally, we estimate a MoS2/GaN contact resistivity to be less than 4 Ω·cm(2) and current spreading in the MoS2 monolayer of approximately 1 μm in diameter. PMID:26866442
Ruzmetov, Dmitry; Zhang, Kehao; Stan, Gheorghe; Kalanyan, Berc; Bhimanapati, Ganesh R; Eichfeld, Sarah M; Burke, Robert A; Shah, Pankaj B; O'Regan, Terrance P; Crowne, Frank J; Birdwell, A Glen; Robinson, Joshua A; Davydov, Albert V; Ivanov, Tony G
2016-03-22
When designing semiconductor heterostructures, it is expected that epitaxial alignment will facilitate low-defect interfaces and efficient vertical transport. Here, we report lattice-matched epitaxial growth of molybdenum disulfide (MoS2) directly on gallium nitride (GaN), resulting in high-quality, unstrained, single-layer MoS2 with strict registry to the GaN lattice. These results present a promising path toward the implementation of high-performance electronic devices based on 2D/3D vertical heterostructures, where each of the 3D and 2D semiconductors is both a template for subsequent epitaxial growth and an active component of the device. The MoS2 monolayer triangles average 1 μm along each side, with monolayer blankets (merged triangles) exhibiting properties similar to that of single-crystal MoS2 sheets. Photoluminescence, Raman, atomic force microscopy, and X-ray photoelectron spectroscopy analyses identified monolayer MoS2 with a prominent 20-fold enhancement of photoluminescence in the center regions of larger triangles. The MoS2/GaN structures are shown to electrically conduct in the out-of-plane direction, confirming the potential of directly synthesized 2D/3D semiconductor heterostructures for vertical current flow. Finally, we estimate a MoS2/GaN contact resistivity to be less than 4 Ω·cm(2) and current spreading in the MoS2 monolayer of approximately 1 μm in diameter.
Room temperature quantum spin Hall insulators with a buckled square lattice.
Luo, Wei; Xiang, Hongjun
2015-05-13
Two-dimensional (2D) topological insulators (TIs), also known as quantum spin Hall (QSH) insulators, are excellent candidates for coherent spin transport related applications because the edge states of 2D TIs are robust against nonmagnetic impurities since the only available backscattering channel is forbidden. Currently, most known 2D TIs are based on a hexagonal (specifically, honeycomb) lattice. Here, we propose that there exists the quantum spin Hall effect (QSHE) in a buckled square lattice. Through performing global structure optimization, we predict a new three-layer quasi-2D (Q2D) structure, which has the lowest energy among all structures with the thickness less than 6.0 Å for the BiF system. It is identified to be a Q2D TI with a large band gap (0.69 eV). The electronic states of the Q2D BiF system near the Fermi level are mainly contributed by the middle Bi square lattice, which are sandwiched by two inert BiF2 layers. This is beneficial since the interaction between a substrate and the Q2D material may not change the topological properties of the system, as we demonstrate in the case of the NaF substrate. Finally, we come up with a new tight-binding model for a two-orbital system with the buckled square lattice to explain the low-energy physics of the Q2D BiF material. Our study not only predicts a QSH insulator for realistic room temperature applications but also provides a new lattice system for engineering topological states such as quantum anomalous Hall effect.
A Geometric Boolean Library for 2D Objects
2006-01-05
The 2D Boolean Library is a collection of C++ classes -- which primarily represent 2D geometric data and relationships, and routines -- which contain algorithms for 2D geometric Boolean operations and utility functions. Classes are provided for 2D points, lines, arcs, edgeuses, loops, surfaces and mask sets. Routines are provided that incorporate the Boolean operations Union(OR), XOR, Intersection and Difference. Various analytical geometry routines and routines for importing and exporting the data in various filemore » formats, are also provided in the library.« less
VizieR Online Data Catalog: The 2dF Galaxy Redshift Survey (2dFGRS) (2dFGRS Team, 1998-2003)
NASA Astrophysics Data System (ADS)
Colless, M.; Dalton, G.; Maddox, S.; Sutherland, W.; Norberg, P.; Cole, S.; Bland-Hawthorn, J.; Bridges, T.; Cannon, R.; Collins, C.; Couch, W.; Cross, N.; Deeley, K.; de Propris, R.; Driver, S. P.; Efstathiou, G.; Ellis, R. S.; Frenk, C. S.; Glazebrook, K.; Jackson, C.; Lahav, O.; Lewis, I.; Lumsden, S.; Madgwick, D.; Peacock, J. A.; Peterson, B. A.; Price, I.; Seaborne, M.; Taylor, K.
2007-11-01
The 2dF Galaxy Redshift Survey (2dFGRS) is a major spectroscopic survey taking full advantage of the unique capabilities of the 2dF facility built by the Anglo-Australian Observatory. The 2dFGRS is integrated with the 2dF QSO survey (2QZ, Cat. VII/241). The 2dFGRS obtained spectra for 245591 objects, mainly galaxies, brighter than a nominal extinction-corrected magnitude limit of bJ=19.45. Reliable (quality>=3) redshifts were obtained for 221414 galaxies. The galaxies cover an area of approximately 1500 square degrees selected from the extended APM Galaxy Survey in three regions: a North Galactic Pole (NGP) strip, a South Galactic Pole (SGP) strip, and random fields scattered around the SGP strip. Redshifts are measured from spectra covering 3600-8000 Angstroms at a two-pixel resolution of 9.0 Angstrom and a median S/N of 13 per pixel. All redshift identifications are visually checked and assigned a quality parameter Q in the range 1-5; Q>=3 redshifts are 98.4% reliable and have an rms uncertainty of 85 km/s. The overall redshift completeness for Q>=3 redshifts is 91.8% but this varies with magnitude from 99% for the brightest galaxies to 90% for objects at the survey limit. The 2dFGRS data base is available on the World Wide Web at http://www.mso.anu.edu.au/2dFGRS/. (6 data files).
Superalloy Lattice Block Structures
NASA Technical Reports Server (NTRS)
Nathal, M. V.; Whittenberger, J. D.; Hebsur, M. G.; Kantzos, P. T.; Krause, D. L.
2004-01-01
Initial investigations of investment cast superalloy lattice block suggest that this technology will yield a low cost approach to utilize the high temperature strength and environmental resistance of superalloys in lightweight, damage tolerant structural configurations. Work to date has demonstrated that relatively large superalloy lattice block panels can be successfully investment cast from both IN-718 and Mar-M247. These castings exhibited mechanical properties consistent with the strength of the same superalloys measured from more conventional castings. The lattice block structure also accommodates significant deformation without failure, and is defect tolerant in fatigue. The potential of lattice block structures opens new opportunities for the use of superalloys in future generations of aircraft applications that demand strength and environmental resistance at elevated temperatures along with low weight.