Magnonic quantum spin Hall state in the zigzag and stripe phases of the antiferromagnetic honeycomb lattice

Science.gov (United States)

Lee, Ki Hoon; Chung, Suk Bum; Park, Kisoo; Park, Je-Geun

2018-05-01

We investigated the topological property of magnon bands in the collinear magnetic orders of zigzag and stripe phases for the antiferromagnetic honeycomb lattice and identified Berry curvature and symmetry constraints on the magnon band structure. Different symmetries of both zigzag and stripe phases lead to different topological properties, in particular, the magnon bands of the stripe phase being disentangled with a finite Dzyaloshinskii-Moriya (DM) term with nonzero spin Chern number. This is corroborated by calculating the spin Nernst effect. Our study establishes the existence of a nontrivial magnon band topology for all observed collinear antiferromagnetic honeycomb lattices in the presence of the DM term.

Nuclear design analysis of square-lattice honeycomb space nuclear rocket engine

International Nuclear Information System (INIS)

Widargo, Reza; Anghaie, Samim

1999-01-01

The square-lattice honeycomb reactor is designed based on a cylindrical core that is determined to have critical diameter and length of 0.50 m and 0.50 c, respectively. A 0.10-cm thick radial graphite reflector, in addition to a 0.20-m thick axial graphite reflector are used to reduce neutron leakage from the reactor. The core is fueled with solid solution of 93% enriched (U, Zr, Nb)C, which is one of several ternary uranium carbides that are considered for this concept. The fuel is to be fabricated as 2 mm grooved (U, Zr, Nb)C wafers. The fuel wafers are used to form square-lattice honeycomb fuel assemblies, 0.10 m in length with 30% cross-sectional flow area. Five fuel assemblies are stacked up axially to form the reactor core. Based on the 30% void fraction, the width of the square flow channel is about 1.3 mm. The hydrogen propellant is passed through these flow channels and removes the heat from the reactor core. To perform nuclear design analysis, a series of neutron transport and diffusion codes are used. The preliminary results are obtained using a simple four-group cross-section model. To optimize the nuclear design, the fuel densities are varied for each assembly. Tantalum, hafnium and tungsten are considered and used as a replacement for niobium in fuel material to provide water submersion sub-criticality for the reactor. Axial and radial neutron flux and power density distributions are calculated for the core. Results of the neutronic analysis indicate that the core has a relatively fast spectrum. From the results of the thermal hydraulic analyses, eight axial temperature zones are chosen for the calculation of group average cross-sections. An iterative process is conducted to couple the neutronic calculations with the thermal hydraulics calculations. Results of the nuclear design analysis indicate that a compact core can be designed based on ternary uranium carbide square-lattice honeycomb fuel. This design provides a relatively high thrust to weight

Unidirectional edge states in topological honeycomb-lattice membrane photonic crystals.

Science.gov (United States)

Anderson, P Duke; Subramania, Ganapathi

2017-09-18

Photonic analogs of electronic systems with topologically non-trivial behavior such as unidirectional scatter-free propagation has tremendous potential for transforming photonic systems. Like in electronics topological behavior can be observed in photonics for systems either preserving time-reversal (TR) symmetry or explicitly breaking it. TR symmetry breaking requires magneto-optic photonics crystals (PC) or generation of synthetic gauge fields. For on-chip photonics that operate at optical frequencies both are quite challenging because of poor magneto-optic response of materials or substantial nanofabrication challenges in generating synthetic gauge fields. A recent work by Ma, et al. [Phys. Rev. Lett.114, 223901 (2015)] based on preserving pseudo TR symmetry offers a promising design scheme for observing unidirectional edge states in a modified honeycomb photonic crystal (PC) lattice of circular rods that offers encouraging alternatives. Here we propose through bandstructure calculations the inverse system of modified honeycomb PC of circular holes in a dielectric membrane which is more attractive from fabrication standpoint for on-chip applications. We observe trivial and non-trivial bandgaps as well as unidirectional edge states of opposite helicity propagating in opposite directions at the interface of a trivial and non-trivial PC structures. Around 1550nm operating wavelength ~55nm of bandwidth is possible for practicable values of design parameters (lattice constant, hole radii, membrane thickness, scaling factor etc.) and robust to reasonable variations in those parameters.

Phase diagram of the Kondo-Heisenberg model on honeycomb lattice with geometrical frustration

Science.gov (United States)

Li, Huan; Song, Hai-Feng; Liu, Yu

2016-11-01

We calculated the phase diagram of the Kondo-Heisenberg model on a two-dimensional honeycomb lattice with both nearest-neighbor and next-nearest-neighbor antiferromagnetic spin exchanges, to investigate the interplay between RKKY and Kondo interactions in the presence of magnetic frustration. Within a mean-field decoupling technology in slave-fermion representation, we derived the zero-temperature phase diagram as a function of Kondo coupling J k and frustration strength Q. The geometrical frustration can destroy the magnetic order, driving the original antiferromagnetic (AF) phase to non-magnetic valence bond solids (VBS). In addition, we found two distinct VBS. As J k is increased, a phase transition from AF to Kondo paramagnetic (KP) phase occurs, without the intermediate phase coexisting AF order with Kondo screening found in square lattice systems. In the KP phase, the enhancement of frustration weakens the Kondo screening effect, resulting in a phase transition from KP to VBS. We also found a process to recover the AF order from VBS by increasing J k in a wide range of frustration strength. Our work may provide predictions for future experimental observation of new processes of quantum phase transitions in frustrated heavy-fermion compounds.

Short-range order in the quantum XXZ honeycomb lattice material BaCo2(PO4)2

Science.gov (United States)

Nair, Harikrishnan S.; Brown, J. M.; Coldren, E.; Hester, G.; Gelfand, M. P.; Podlesnyak, A.; Huang, Q.; Ross, K. A.

2018-04-01

We present observations of highly frustrated quasi-two-dimensional (2D) magnetic correlations in the honeycomb lattice layers of the Seff =1 /2 compound γ -BaCo2(PO4)2 (γ -BCPO). Specific heat shows a broad peak comprised of two weak kink features at TN 1˜6 K and TN 2˜3.5 K, the relative weights of which can be modified by sample annealing. Neutron powder diffraction measurements reveal short range quasi-2D order that is established below TN 1 and TN 2, at which two separate, incompatible, short range magnetic orders onset: commensurate antiferromagnetic correlations with correlation length ξc=60 ±2 Å (TN 1) and in quasi-2D helical domains with ξh=350 ±11 Å (TN 2). The ac magnetic susceptibility response lacks frequency dependence, ruling out spin freezing. Inelastic neutron scattering data on γ -BCPO is compared with linear spin wave theory, and two separate parameter regions of the XXZ J1-J2-J3 model with ferromagnetic nearest-neighbor exchange J1 are favored, both near regions of high classical degeneracy. High energy coherent excitations (˜10 meV) persist up to at least 40 K, suggesting strong in-plane correlations persist above TN. These data show that γ -BCPO is a rare highly frustrated, quasi-2D Seff =1 /2 honeycomb lattice material which resists long range magnetic order and spin freezing.

Analytic properties for the honeycomb lattice Green function at the origin

Science.gov (United States)

Joyce, G. S.

2018-05-01

The analytic properties of the honeycomb lattice Green function are investigated, where is a complex variable which lies in a plane. This double integral defines a single-valued analytic function provided that a cut is made along the real axis from w  =  ‑3 to . In order to analyse the behaviour of along the edges of the cut it is convenient to define the limit function where . It is shown that and can be evaluated exactly for all in terms of various hypergeometric functions, where the argument function is always real-valued and rational. The second-order linear Fuchsian differential equation satisfied by is also used to derive series expansions for and which are valid in the neighbourhood of the regular singular points and . Integral representations are established for and , where with . In particular, it is proved that where J 0(z) and Y 0(z) denote Bessel functions of the first and second kind, respectively. The results derived in the paper are utilized to evaluate the associated logarithmic integral where w lies in the cut plane. A new set of orthogonal polynomials which are connected with the honeycomb lattice Green function are also briefly discussed. Finally, a link between and the theory of Pearson random walks in a plane is established.

Design of Chern insulating phases in honeycomb lattices

Science.gov (United States)

Pickett, Warren E.; Lee, Kwan-Woo; Pentcheva, Rossitza

2018-06-01

The search for robust examples of the magnetic version of topological insulators, referred to as quantum anomalous Hall insulators or simply Chern insulators, so far lacks success. Our groups have explored two distinct possibilities based on multiorbital 3d oxide honeycomb lattices. Each has a Chern insulating phase near the ground state, but materials parameters were not appropriate to produce a viable Chern insulator. Further exploration of one of these classes, by substituting open shell 3d with 4d and 5d counterparts, has led to realistic prediction of Chern insulating ground states. Here we recount the design process, discussing the many energy scales that are active in participating (or resisting) the desired Chern insulator phase.

Detecting the BCS pairing amplitude via a sudden lattice ramp in a honeycomb lattice

Science.gov (United States)

Tiesinga, Eite; Nuske, Marlon; Mathey, Ludwig

2016-05-01

We determine the exact time evolution of an initial Bardeen-Cooper-Schrieffer (BCS) state of ultra-cold atoms in a hexagonal optical lattice. The dynamical evolution is triggered by ramping the lattice potential up, such that the interaction strength Uf is much larger than the hopping amplitude Jf. The quench initiates collective oscillations with frequency | Uf | /(2 π) in the momentum occupation numbers and imprints an oscillating phase with the same frequency on the order parameter Δ. The latter is not reproduced by treating the time evolution in mean-field theory. The momentum density-density or noise correlation functions oscillate at frequency | Uf | /(2 π) as well as its second harmonic. For a very deep lattice, with negligible tunneling energy, the oscillations of momentum occupation numbers are undamped. Non-zero tunneling after the quench leads to dephasing of the different momentum modes and a subsequent damping of the oscillations. This occurs even for a finite-temperature initial BCS state, but not for a non-interacting Fermi gas. We therefore propose to use this dephasing to detect a BCS state. Finally, we predict that the noise correlation functions in a honeycomb lattice will develop strong anti-correlations near the Dirac point. We acknowledge funding from the National Science Foundation.

Topological features of engineered arrays of adsorbates in honeycomb lattices

Energy Technology Data Exchange (ETDEWEB)

Gonzalez-Arraga, Luis A., E-mail: ludovici83@gmail.com [IMDEA Nanociencia, Calle de Faraday, 9, Cantoblanco, 28049 Madrid (Spain); Lado, J.L. [International Iberian Nanotechnology Laboratory (INL), Av. Mestre Jose Veiga, 4715-330 Braga (Portugal); Guinea, Francisco [IMDEA Nanociencia, Calle de Faraday, 9, Cantoblanco, 28049 Madrid (Spain); School of Physics and Astronomy, University of Manchester, Oxford Road, Manchester M13 9PL (United Kingdom)

2016-09-01

Hydrogen adatoms are one of the most the promising proposals for the functionalization of graphene. The adatoms induce narrow resonances near the Dirac energy, which lead to the formation of magnetic moments. Furthermore, they also create local lattice distortions which enhance the spin–orbit coupling. The combination of magnetism and spin–orbit coupling allows for a rich variety of phases, some of which have non-trivial topological features. We analyze the interplay between magnetism and spin–orbit coupling in ordered arrays of adsorbates on honeycomb lattice monolayers, and classify the different phases that may arise. We extend our model to consider arrays of adsorbates in graphene-like crystals with stronger intrinsic spin–orbit couplings. We also consider a regime away from half-filling in which the Fermi level is at the bottom of the conduction band, we find a Berry curvature distribution corresponding to a Valley–Hall effect.

Dirac and Chiral Quantum Spin Liquids on the Honeycomb Lattice in a Magnetic Field.

Science.gov (United States)

Liu, Zheng-Xin; Normand, B

2018-05-04

Motivated by recent experimental observations in α-RuCl_{3}, we study the K-Γ model on the honeycomb lattice in an external magnetic field. By a slave-particle representation and variational Monte Carlo calculations, we reproduce the phase transition from zigzag magnetic order to a field-induced disordered phase. The nature of this state depends crucially on the field orientation. For particular field directions in the honeycomb plane, we find a gapless Dirac spin liquid, in agreement with recent experiments on α-RuCl_{3}. For a range of out-of-plane fields, we predict the existence of a Kalmeyer-Laughlin-type chiral spin liquid, which would show an integer-quantized thermal Hall effect.

Dirac and Chiral Quantum Spin Liquids on the Honeycomb Lattice in a Magnetic Field

Science.gov (United States)

Liu, Zheng-Xin; Normand, B.

2018-05-01

Motivated by recent experimental observations in α -RuCl3 , we study the K -Γ model on the honeycomb lattice in an external magnetic field. By a slave-particle representation and variational Monte Carlo calculations, we reproduce the phase transition from zigzag magnetic order to a field-induced disordered phase. The nature of this state depends crucially on the field orientation. For particular field directions in the honeycomb plane, we find a gapless Dirac spin liquid, in agreement with recent experiments on α -RuCl3 . For a range of out-of-plane fields, we predict the existence of a Kalmeyer-Laughlin-type chiral spin liquid, which would show an integer-quantized thermal Hall effect.

Topological semimetal in honeycomb lattice LnSI

Science.gov (United States)

Nie, Simin; Xu, Gang; Prinz, Fritz B.; Zhang, Shou-cheng

2017-10-01

Recognized as elementary particles in the standard model, Weyl fermions in condensed matter have received growing attention. However, most of the previously reported Weyl semimetals exhibit rather complicated electronic structures that, in turn, may have raised questions regarding the underlying physics. Here, we report promising topological phases that can be realized in specific honeycomb lattices, including ideal Weyl semimetal structures, 3D strong topological insulators, and nodal-line semimetal configurations. In particular, we highlight a semimetal featuring both Weyl nodes and nodal lines. Guided by this model, we showed that GdSI, the long-perceived ideal Weyl semimetal, has two pairs of Weyl nodes residing at the Fermi level and that LuSI (YSI) is a 3D strong topological insulator with the right-handed helical surface states. Our work provides a mechanism to study topological semimetals and proposes a platform for exploring the physics of Weyl semimetals as well as related device designs.

Low crosstalk waveguide intersections in honeycomb lattice photonic crystals for TM-polarized light

International Nuclear Information System (INIS)

Ma, P; Jäckel, H

2011-01-01

We present the design of a low crosstalk, high throughput waveguide intersection for transverse-magnetic-polarized light. The design is based on two orthogonal photonic crystal waveguides and a resonant photonic crystal cavity in honeycomb lattice geometry. The results of our numerical simulation validate the concept of the design and demonstrate a crosstalk smaller than 0.1% and throughput transmission of more than 80% for both orthogonal waveguide branches

Fermionic quantum critical point of spinless fermions on a honeycomb lattice

International Nuclear Information System (INIS)

Wang, Lei; Corboz, Philippe; Troyer, Matthias

2014-01-01

Spinless fermions on a honeycomb lattice provide a minimal realization of lattice Dirac fermions. Repulsive interactions between nearest neighbors drive a quantum phase transition from a Dirac semimetal to a charge-density-wave state through a fermionic quantum critical point, where the coupling of the Ising order parameter to the Dirac fermions at low energy drastically affects the quantum critical behavior. Encouraged by a recent discovery (Huffman and Chandrasekharan 2014 Phys. Rev. B 89 111101) of the absence of the fermion sign problem in this model, we study the fermionic quantum critical point using the continuous-time quantum Monte Carlo method with a worm-sampling technique. We estimate the transition point V/t=1.356(1) with the critical exponents ν=0.80(3) and η=0.302(7). Compatible results for the transition point are also obtained with infinite projected entangled-pair states. (paper)

Correlated Dirac particles and superconductivity on the honeycomb lattice

Science.gov (United States)

Wu, Wei; Scherer, Michael M.; Honerkamp, Carsten; Le Hur, Karyn

2013-03-01

We investigate the properties of the nearest-neighbor singlet pairing and the emergence of d-wave superconductivity in the doped honeycomb lattice considering the limit of large interactions and the t-J1-J2 model. First, by applying a renormalized mean-field procedure as well as slave-boson theories which account for the proximity to the Mott-insulating state, we confirm the emergence of d-wave superconductivity, in agreement with earlier works. We show that a small but finite J2 spin coupling between next-nearest neighbors stabilizes d-wave symmetry compared to the extendeds-wave scenario. At small hole doping, to minimize the energy and to gap the whole Fermi surface or all the Dirac points, the superconducting ground state is characterized by a d+id singlet pairing assigned to one valley and a d-id singlet pairing to the other, which then preserves time-reversal symmetry. The slightly doped situation is distinct from the heavily doped case (around 3/8 and 5/8 filling) supporting a pure chiral d+id symmetry and breaking time-reversal symmetry. Then, we apply the functional renormalization group and study in more detail the competition between antiferromagnetism and superconductivity in the vicinity of half filling. We discuss possible applications to strongly correlated compounds with copper hexagonal planes such as In3Cu2VO9. Our findings are also relevant to the understanding of exotic superfluidity with cold atoms.

Infinite projected entangled-pair state algorithm for ruby and triangle-honeycomb lattices

Science.gov (United States)

Jahromi, Saeed S.; Orús, Román; Kargarian, Mehdi; Langari, Abdollah

2018-03-01

The infinite projected entangled-pair state (iPEPS) algorithm is one of the most efficient techniques for studying the ground-state properties of two-dimensional quantum lattice Hamiltonians in the thermodynamic limit. Here, we show how the algorithm can be adapted to explore nearest-neighbor local Hamiltonians on the ruby and triangle-honeycomb lattices, using the corner transfer matrix (CTM) renormalization group for 2D tensor network contraction. Additionally, we show how the CTM method can be used to calculate the ground-state fidelity per lattice site and the boundary density operator and entanglement entropy (EE) on an infinite cylinder. As a benchmark, we apply the iPEPS method to the ruby model with anisotropic interactions and explore the ground-state properties of the system. We further extract the phase diagram of the model in different regimes of the couplings by measuring two-point correlators, ground-state fidelity, and EE on an infinite cylinder. Our phase diagram is in agreement with previous studies of the model by exact diagonalization.

A first theoretical realization of honeycomb topological magnon insulator.

Science.gov (United States)

Owerre, S A

2016-09-28

It has been recently shown that in the Heisenberg (anti)ferromagnet on the honeycomb lattice, the magnons (spin wave quasipacticles) realize a massless two-dimensional (2D) Dirac-like Hamiltonian. It was shown that the Dirac magnon Hamiltonian preserves time-reversal symmetry defined with the sublattice pseudo spins and the Dirac points are robust against magnon-magnon interactions. The Dirac points also occur at nonzero energy. In this paper, we propose a simple realization of nontrivial topology (magnon edge states) in this system. We show that the Dirac points are gapped when the inversion symmetry of the lattice is broken by introducing a next-nearest neighbour Dzyaloshinskii-Moriya (DM) interaction. Thus, the system realizes magnon edge states similar to the Haldane model for quantum anomalous Hall effect in electronic systems. However, in contrast to electronic spin current where dissipation can be very large due to Ohmic heating, noninteracting topological magnons can propagate for a long time without dissipation as magnons are uncharged particles. We observe the same magnon edge states for the XY model on the honeycomb lattice. Remarkably, in this case the model maps to interacting hardcore bosons on the honeycomb lattice. Quantum magnetic systems with nontrivial magnon edge states are called topological magnon insulators. They have been studied theoretically on the kagome lattice and recently observed experimentally on the kagome magnet Cu(1-3, bdc) with three magnon bulk bands. Our results for the honeycomb lattice suggests an experimental procedure to search for honeycomb topological magnon insulators within a class of 2D quantum magnets and ultracold atoms trapped in honeycomb optical lattices. In 3D lattices, Dirac and Weyl points were recently studied theoretically, however, the criteria that give rise to them were not well-understood. We argue that the low-energy Hamiltonian near the Weyl points should break time-reversal symmetry of the pseudo spins

Iridium containing honeycomb Delafossites by topotactic cation exchange.

Science.gov (United States)

Roudebush, John H; Ross, K A; Cava, R J

2016-06-07

We report the structure and magnetic properties of two new iridium-based honeycomb Delafossite compounds, Cu3NaIr2O6 and Cu3LiIr2O6, formed by a topotactic cation exchange reaction. The starting materials Na2IrO3 and Li2IrO3, which are based on layers of IrO6 octahedra in a honeycomb lattice separated by layers of alkali ions, are transformed to the title compounds by a topotactic exchange reaction through heating with CuCl below 450 °C; higher temperature reactions cause decomposition. The new compounds display dramatically different magnetic behavior from their parent compounds - Cu3NaIr2O6 has a ferromagnetic like magnetic transition at 10 K, while Cu3LiIr2O6 retains the antiferromagnetic transition temperature of its parent compound but displays significantly stronger dominance of antiferromagnetic coupling between spins. These results reveal that a surprising difference in the magnetic interactions between the magnetic Ir ions has been induced by a change in the non-magnetic interlayer species. A combination of neutron and X-ray powder diffraction is used for the structure refinement of Cu3NaIr2O6 and both compounds are compared to their parent materials.

Two Topologically Distinct Dirac-Line Semimetal Phases and Topological Phase Transitions in Rhombohedrally Stacked Honeycomb Lattices

Science.gov (United States)

Hyart, T.; Ojajärvi, R.; Heikkilä, T. T.

2018-04-01

Three-dimensional topological semimetals can support band crossings along one-dimensional curves in the momentum space (nodal lines or Dirac lines) protected by structural symmetries and topology. We consider rhombohedrally (ABC) stacked honeycomb lattices supporting Dirac lines protected by time-reversal, inversion and spin rotation symmetries. For typical band structure parameters there exists a pair of nodal lines in the momentum space extending through the whole Brillouin zone in the stacking direction. We show that these Dirac lines are topologically distinct from the usual Dirac lines which form closed loops inside the Brillouin zone. In particular, an energy gap can be opened only by first merging the Dirac lines going through the Brillouin zone in a pairwise manner so that they turn into closed loops inside the Brillouin zone, and then by shrinking these loops into points. We show that this kind of topological phase transition can occur in rhombohedrally stacked honeycomb lattices by tuning the ratio of the tunneling amplitudes in the directions perpendicular and parallel to the layers. We also discuss the properties of the surface states in the different phases of the model.

Physical properties of the spin Hamiltonian on honeycomb lattice samples with Kekulé and vacuum polarization corrections

Science.gov (United States)

Martins, Ricardo Spagnuolo; Konstantinova, Elena; Belich, Humberto; Helayël-Neto, José Abdalla

2017-11-01

Magnetic and thermodynamical properties of a system of spins in a honeycomb lattice, such as magnetization, magnetic susceptibility and specific heat, in a low-temperature regime are investigated by considering the effects of a Kekulé scalar exchange and QED vacuum polarization corrections to the interparticle potential. The spin lattice calculations are carried out by means of Monte Carlo simulations. We present a number of comparative plots of all the physical quantities we have considered and a detailed analysis is presented to illustrate the main features and the variation profiles of the properties with the applied external magnetic field and temperature.

Topological magnon bands and unconventional thermal Hall effect on the frustrated honeycomb and bilayer triangular lattice.

Science.gov (United States)

Owerre, S A

2017-09-27

In the conventional ferromagnetic systems, topological magnon bands and thermal Hall effect are due to the Dzyaloshinskii-Moriya interaction (DMI). In principle, however, the DMI is either negligible or it is not allowed by symmetry in some quantum magnets. Therefore, we expect that topological magnon features will not be present in those systems. In addition, quantum magnets on the triangular-lattice are not expected to possess topological features as the DMI or spin-chirality cancels out due to equal and opposite contributions from adjacent triangles. Here, however, we predict that the isomorphic frustrated honeycomb-lattice and bilayer triangular-lattice antiferromagnetic system will exhibit topological magnon bands and topological thermal Hall effect in the absence of an intrinsic DMI. These unconventional topological magnon features are present as a result of magnetic-field-induced non-coplanar spin configurations with nonzero scalar spin chirality. The relevance of the results to realistic bilayer triangular antiferromagnetic materials are discussed.

Performance Assessment of Ordered Porous Electrospun Honeycomb Fibers for the Removal of Atmospheric Polar Volatile Organic Compounds

Directory of Open Access Journals (Sweden)

Yixin Wang

2018-05-01

Full Text Available This study explored a new facile method of preparing ordered porous electrospun honeycomb fibers to obtain the most promising composites for maximal adsorption of volatile organic compounds (VOCs. The self-assembly ordered porous material (OPM and polyacrylonitrile (PAN were formulated into a blend solution to prepare honeycomb fibers. SEM and TEM images showed that OPM was effectively bonded in PAN fibers because of the composite’s structure. Acetone was used as a model to assess the VOC adsorption performances of electrospun honeycomb fibers with different OPM contents. Experimental results revealed that the adsorption capacity of honeycomb fibers increased with the increase of loaded OPM within the PAN fibers. The highest adsorption capacity was 58.2 μg g−1 by the fibers containing with 60% OPM in weight. After several recycling times, the adsorption capacities of the reused honeycomb fibers were almost the same with the fresh fibers. This finding indicated that the electrospun honeycomb fibers have potential application in removing VOCs in the workplace, and promote the performance of masks for odor removal.

Chiral Spin-Density Wave, Spin-Charge-Chern Liquid, and d+id Superconductivity in 1/4-Doped Correlated Electronic Systems on the Honeycomb Lattice

Directory of Open Access Journals (Sweden)

Shenghan Jiang

2014-09-01

Full Text Available Recently, two interesting candidate quantum phases—the chiral spin-density wave state featuring anomalous quantum Hall effect and the d+id superconductor—were proposed for the Hubbard model on the honeycomb lattice at 1/4 doping. Using a combination of exact diagonalization, density matrix renormalization group, the variational Monte Carlo method, and quantum field theories, we study the quantum phase diagrams of both the Hubbard model and the t-J model on the honeycomb lattice at 1/4 doping. The main advantage of our approach is the use of symmetry quantum numbers of ground-state wave functions on finite-size systems (up to 32 sites to sharply distinguish different quantum phases. Our results show that for 1≲U/t<40 in the Hubbard model and for 0.1honeycomb lattice.

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

Science.gov (United States)

Garlea, Ovidiu

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

The Stability of New Single-Layer Combined Lattice Shell Based on Aluminum Alloy Honeycomb Panels

Directory of Open Access Journals (Sweden)

Caiqi Zhao

2017-11-01

Full Text Available This article proposes a new type of single-layer combined lattice shell (NSCLS; which is based on aluminum alloy honeycomb panels. Six models with initial geometric defect were designed and precision made using numerical control equipment. The stability of these models was tested. The results showed that the stable bearing capacity of NSCLS was approximately 16% higher than that of a lattice shell with the same span without a reinforcing plate. At the same time; the properties of the NSCLS were sensitive to defects. When defects were present; its stable bearing capacity was decreased by 12.3% when compared with the defect-free model. The model with random defects following a truncated Gaussian distribution could be used to simulate the distribution of defects in the NSCLS. The average difference between the results of the nonlinear analysis and the experimental results was 5.7%. By calculating and analyzing nearly 20,000 NSCLS; the suggested values of initial geometric defect were presented. The results of this paper could provide a theoretical basis for making and revising the design codes for this new combined lattice shell structure.

Effective-field theory of the Ising model with three alternative layers on the honeycomb and square lattices

Energy Technology Data Exchange (ETDEWEB)

Deviren, Bayram [Institute of Science, Erciyes University, Kayseri 38039 (Turkey); Canko, Osman [Department of Physics, Erciyes University, Kayseri 38039 (Turkey); Keskin, Mustafa [Department of Physics, Erciyes University, Kayseri 38039 (Turkey)], E-mail: keskin@erciyes.edu.tr

2008-09-15

The Ising model with three alternative layers on the honeycomb and square lattices is studied by using the effective-field theory with correlations. We consider that the nearest-neighbor spins of each layer are coupled ferromagnetically and the adjacent spins of the nearest-neighbor layers are coupled either ferromagnetically or anti-ferromagnetically depending on the sign of the bilinear exchange interactions. We investigate the thermal variations of the magnetizations and present the phase diagrams. The phase diagrams contain the paramagnetic, ferromagnetic and anti-ferromagnetic phases, and the system also exhibits a tricritical behavior.

Effective-field theory of the Ising model with three alternative layers on the honeycomb and square lattices

International Nuclear Information System (INIS)

Deviren, Bayram; Canko, Osman; Keskin, Mustafa

2008-01-01

The Ising model with three alternative layers on the honeycomb and square lattices is studied by using the effective-field theory with correlations. We consider that the nearest-neighbor spins of each layer are coupled ferromagnetically and the adjacent spins of the nearest-neighbor layers are coupled either ferromagnetically or anti-ferromagnetically depending on the sign of the bilinear exchange interactions. We investigate the thermal variations of the magnetizations and present the phase diagrams. The phase diagrams contain the paramagnetic, ferromagnetic and anti-ferromagnetic phases, and the system also exhibits a tricritical behavior

A bird’s eye view on the flat and conic band world of the honeycomb and Kagome lattices: towards an understanding of 2D metal-organic frameworks electronic structure

Science.gov (United States)

Barreteau, C.; Ducastelle, F.; Mallah, T.

2017-11-01

We present a thorough tight-binding analysis of the band structure of a wide variety of lattices belonging to the class of honeycomb and Kagome systems including several mixed forms combining both lattices. The band structure of these systems are made of a combination of dispersive and flat bands. The dispersive bands possess Dirac cones (linear dispersion) at the six corners (K points) of the Brillouin zone although in peculiar cases Dirac cones at the center of the zone (Γ point) appear. The flat bands can be of different nature. Most of them are tangent to the dispersive bands at the center of the zone but some, for symmetry reasons, do not hybridize with other states. The objective of our work is to provide an analysis of a wide class of so-called ligand-decorated honeycomb Kagome lattices that are observed in a 2D metal-organic framework where the ligand occupy honeycomb sites and the metallic atoms the Kagome sites. We show that the p x -p y graphene model is relevant in these systems and there exists four types of flat bands: Kagome flat (singly degenerate) bands, two kinds of ligand-centered flat bands (A2 like and E like, respectively doubly and singly degenerate) and metal-centered (three fold degenerate) flat bands.

Topological honeycomb magnon Hall effect: A calculation of thermal Hall conductivity of magnetic spin excitations

Energy Technology Data Exchange (ETDEWEB)

Owerre, S. A., E-mail: solomon@aims.ac.za [African Institute for Mathematical Sciences, 6 Melrose Road, Muizenberg, Cape Town 7945, South Africa and Perimeter Institute for Theoretical Physics, 31 Caroline St. N., Waterloo, Ontario N2L 2Y5 (Canada)

2016-07-28

Quite recently, the magnon Hall effect of spin excitations has been observed experimentally on the kagome and pyrochlore lattices. The thermal Hall conductivity κ{sup xy} changes sign as a function of magnetic field or temperature on the kagome lattice, and κ{sup xy} changes sign upon reversing the sign of the magnetic field on the pyrochlore lattice. Motivated by these recent exciting experimental observations, we theoretically propose a simple realization of the magnon Hall effect in a two-band model on the honeycomb lattice. The magnon Hall effect of spin excitations arises in the usual way via the breaking of inversion symmetry of the lattice, however, by a next-nearest-neighbour Dzyaloshinsky-Moriya interaction. We find that κ{sup xy} has a fixed sign for all parameter regimes considered. These results are in contrast to the Lieb, kagome, and pyrochlore lattices. We further show that the low-temperature dependence on the magnon Hall conductivity follows a T{sup 2} law, as opposed to the kagome and pyrochlore lattices. These results suggest an experimental procedure to measure thermal Hall conductivity within a class of 2D honeycomb quantum magnets and ultracold atoms trapped in a honeycomb optical lattice.

Influence of quantum phase transition on spin transport in the quantum antiferromagnet in the honeycomb lattice

Science.gov (United States)

Lima, L. S.

2017-06-01

We use the SU(3) Schwinger boson theory to study the spin transport properties of the two-dimensional anisotropic frustrated Heisenberg model in a honeycomb lattice at T = 0 with single ion anisotropy and third neighbor interactions. We have investigated the behavior of the spin conductivity for this model that presents exchange interactions J1 , J2 and J3 . We study the spin transport in the Bose-Einstein condensation regime where the bosons tz are condensed. Our results show an influence of the quantum phase transition point on the spin conductivity behavior. We also have made a diagrammatic expansion for the Green-function and did not obtain any significant change of the results.

Ground-state phases of the spin-1 J1-J2 Heisenberg antiferromagnet on the honeycomb lattice

Science.gov (United States)

Li, P. H. Y.; Bishop, R. F.

2016-06-01

We study the zero-temperature quantum phase diagram of a spin-1 Heisenberg antiferromagnet on the honeycomb lattice with both nearest-neighbor exchange coupling J1>0 and frustrating next-nearest-neighbor coupling J2≡κ J1>0 , using the coupled cluster method implemented to high orders of approximation, and based on model states with different forms of classical magnetic order. For each we calculate directly in the bulk thermodynamic limit both ground-state low-energy parameters (including the energy per spin, magnetic order parameter, spin stiffness coefficient, and zero-field uniform transverse magnetic susceptibility) and their generalized susceptibilities to various forms of valence-bond crystalline (VBC) order, as well as the energy gap to the lowest-lying spin-triplet excitation. In the range 0 κc 2=0.340 (5 ) . Two different paramagnetic phases are found to exist in the intermediate region. Over the range κc1<κ<κci=0.305 (5 ) we find a gapless phase with no discernible magnetic order, which is a strong candidate for being a quantum spin liquid, while over the range κci<κ <κc 2 we find a gapped phase, which is most likely a lattice nematic with staggered dimer VBC order that breaks the lattice rotational symmetry.

Mechanism for subgap optical conductivity in honeycomb Kitaev materials

Science.gov (United States)

Bolens, Adrien; Katsura, Hosho; Ogata, Masao; Miyashita, Seiji

2018-04-01

Motivated by recent terahertz absorption measurements in α -RuCl3 , we develop a theory for the electromagnetic absorption of materials described by the Kitaev model on the honeycomb lattice. We derive a mechanism for the polarization operator at second order in the nearest-neighbor hopping Hamiltonian. Using the exact results of the Kitaev honeycomb model, we then calculate the polarization dynamical correlation function corresponding to electric dipole transitions in addition to the spin dynamical correlation function corresponding to magnetic dipole transitions.

BCS @ 50: derivation of gap equations in different lattice geometries

International Nuclear Information System (INIS)

Saurabh Basu

2007-07-01

We rigorously derive BCS gap equations for a square, triangular and a honeycomb lattice using a two-dimensional t-J model. The gap equations in all the three lattice geometries look usual, with band indices appearing and a minor modification in the separable pair potential for the (two band) honeycomb lattice. In each case, the gap equation is solved (self consistently with the number equation) at low densities assuming singlet pairing. (author)

Multilayer DNA Origami Packed on Hexagonal and Hybrid Lattices

DEFF Research Database (Denmark)

Ke, Yonggang; Voigt, Niels Vinther; Shih, William M.

2012-01-01

“Scaffolded DNA origami” has been proven to be a powerful and efficient approach to construct two-dimensional or three-dimensional objects with great complexity. Multilayer DNA origami has been demonstrated with helices packing along either honeycomb-lattice geometry or square-lattice geometry....... Here we report successful folding of multilayer DNA origami with helices arranged on a close-packed hexagonal lattice. This arrangement yields a higher density of helical packing and therefore higher resolution of spatial addressing than has been shown previously. We also demonstrate hybrid multilayer...... DNA origami with honeycomb-lattice, square-lattice, and hexagonal-lattice packing of helices all in one design. The availability of hexagonal close-packing of helices extends our ability to build complex structures using DNA nanotechnology....

Multilayer DNA origami packed on hexagonal and hybrid lattices.

Science.gov (United States)

Ke, Yonggang; Voigt, Niels V; Gothelf, Kurt V; Shih, William M

2012-01-25

"Scaffolded DNA origami" has been proven to be a powerful and efficient approach to construct two-dimensional or three-dimensional objects with great complexity. Multilayer DNA origami has been demonstrated with helices packing along either honeycomb-lattice geometry or square-lattice geometry. Here we report successful folding of multilayer DNA origami with helices arranged on a close-packed hexagonal lattice. This arrangement yields a higher density of helical packing and therefore higher resolution of spatial addressing than has been shown previously. We also demonstrate hybrid multilayer DNA origami with honeycomb-lattice, square-lattice, and hexagonal-lattice packing of helices all in one design. The availability of hexagonal close-packing of helices extends our ability to build complex structures using DNA nanotechnology. © 2011 American Chemical Society

Unconventional spin dynamics in the honeycomb-lattice material α -RuCl3 : High-field electron spin resonance studies

Science.gov (United States)

Ponomaryov, A. N.; Schulze, E.; Wosnitza, J.; Lampen-Kelley, P.; Banerjee, A.; Yan, J.-Q.; Bridges, C. A.; Mandrus, D. G.; Nagler, S. E.; Kolezhuk, A. K.; Zvyagin, S. A.

2017-12-01

We present high-field electron spin resonance (ESR) studies of the honeycomb-lattice material α -RuCl3 , a prime candidate to exhibit Kitaev physics. Two modes of antiferromagnetic resonance were detected in the zigzag ordered phase, with magnetic field applied in the a b plane. A very rich excitation spectrum was observed in the field-induced quantum paramagnetic phase. The obtained data are compared with the results of recent numerical calculations, strongly suggesting a very unconventional multiparticle character of the spin dynamics in α -RuCl3 . The frequency-field diagram of the lowest-energy ESR mode is found consistent with the behavior of the field-induced energy gap, revealed by thermodynamic measurements.

Quantum Monte Carlo methods and strongly correlated electrons on honeycomb structures

Energy Technology Data Exchange (ETDEWEB)

Lang, Thomas C.

2010-12-16

In this thesis we apply recently developed, as well as sophisticated quantum Monte Carlo methods to numerically investigate models of strongly correlated electron systems on honeycomb structures. The latter are of particular interest owing to their unique properties when simulating electrons on them, like the relativistic dispersion, strong quantum fluctuations and their resistance against instabilities. This work covers several projects including the advancement of the weak-coupling continuous time quantum Monte Carlo and its application to zero temperature and phonons, quantum phase transitions of valence bond solids in spin-1/2 Heisenberg systems using projector quantum Monte Carlo in the valence bond basis, and the magnetic field induced transition to a canted antiferromagnet of the Hubbard model on the honeycomb lattice. The emphasis lies on two projects investigating the phase diagram of the SU(2) and the SU(N)-symmetric Hubbard model on the hexagonal lattice. At sufficiently low temperatures, condensed-matter systems tend to develop order. An exception are quantum spin-liquids, where fluctuations prevent a transition to an ordered state down to the lowest temperatures. Previously elusive in experimentally relevant microscopic two-dimensional models, we show by means of large-scale quantum Monte Carlo simulations of the SU(2) Hubbard model on the honeycomb lattice, that a quantum spin-liquid emerges between the state described by massless Dirac fermions and an antiferromagnetically ordered Mott insulator. This unexpected quantum-disordered state is found to be a short-range resonating valence bond liquid, akin to the one proposed for high temperature superconductors. Inspired by the rich phase diagrams of SU(N) models we study the SU(N)-symmetric Hubbard Heisenberg quantum antiferromagnet on the honeycomb lattice to investigate the reliability of 1/N corrections to large-N results by means of numerically exact QMC simulations. We study the melting of phases

[Study on formation process of honeycomb pattern in dielectric barrier discharge by optical emission spectrum].

Science.gov (United States)

Dong, Li-Fang; Zhu, Ping; Yang, Jing; Zhang, Yu

2014-04-01

The authors report on the first investigation of the variations in the plasma parameters in the formation process of the honeycomb pattern in a dielectric barrier discharge by optical emission spectrum in argon and air mixture. The discharge undergoes hexagonal lattice, concentric spot-ring pattern and honeycomb pattern with the applied voltage increasing. The molecular vibration temperature, electron excitation temperature and electronic density of the three kinds of patterns were investigated by the emission spectra of nitrogen band of second positive system (C3pi(u) --> B3 pi(g)), the relative intensity ratio method of spectral lines of Ar I 763.51 nm (2P(6) --> 1S(5)) and Ar I 772.42 nm (2P(2) -->1S(3)) and the broadening of spectral line 696.5 nm respectively. It was found that the molecular vibration temperature and electron excitation temperature of the honeycomb pattern are higher than those of the hexagonal lattice, but the electron density of the former is lower than that of the latter. The discharge powers of the patterns were also measured with the capacitance method. The discharge power of the honeycomb pattern is much higher than that of the hexagonal lattice. These results are of great importance to the formation mechanism of the patterns in dielectric barrier discharge.

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

Science.gov (United States)

Kim, Kwangmoo; Einstein, T. L.

2011-06-01

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

Topological magnon bands in ferromagnetic star lattice

International Nuclear Information System (INIS)

Owerre, S A

2017-01-01

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

Topological magnon bands in ferromagnetic star lattice.

Science.gov (United States)

Owerre, S A

2017-05-10

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

The quantum group, Harper equation and structure of Bloch eigenstates on a honeycomb lattice

International Nuclear Information System (INIS)

Eliashvili, M; Tsitsishvili, G; Japaridze, G I

2012-01-01

The tight-binding model of quantum particles on a honeycomb lattice is investigated in the presence of a homogeneous magnetic field. Provided the magnetic flux per unit hexagon is a rational of the elementary flux, the one-particle Hamiltonian is expressed in terms of the generators of the quantum group U q (sl 2 ). Employing the functional representation of the quantum group U q (sl 2 ), the Harper equation is rewritten as a system of two coupled functional equations in the complex plane. For the special values of quasi-momentum, the entangled system admits solutions in terms of polynomials. The system is shown to exhibit a certain symmetry allowing us to resolve the entanglement, and a basic single equation determining the eigenvalues and eigenstates (polynomials) is obtained. Equations specifying the locations of the roots of polynomials in the complex plane are found. Employing numerical analysis, the roots of polynomials corresponding to different eigenstates are solved and diagrams exhibiting the ordered structure of one-particle eigenstates are depicted. (paper)

Similarity between the superconductivity in the graphene with the spin transport in the two-dimensional antiferromagnet in the honeycomb lattice

Science.gov (United States)

Lima, L. S.

2017-02-01

We have used the Dirac's massless quasi-particles together with the Kubo's formula to study the spin transport by electrons in the graphene monolayer. We have calculated the electric conductivity and verified the behavior of the AC and DC currents of this system, that is a relativistic electron plasma. Our results show that the AC conductivity tends to infinity in the limit ω → 0 , similar to the behavior obtained for the spin transport in the two-dimensional frustrated antiferromagnet in the honeycomb lattice. We have made a diagrammatic expansion for the Green's function and we have not gotten significative change in the results.

Granular superconductor in a honeycomb lattice as a realization of bosonic Dirac material

Science.gov (United States)

Banerjee, S.; Fransson, J.; Black-Schaffer, A. M.; Ågren, H.; Balatsky, A. V.

2016-04-01

We examine the low-energy effective theory of phase oscillations in a two-dimensional granular superconducting sheet where the grains are arranged in a honeycomb lattice structure. Using the example of graphene, we present evidence for the engineered Dirac nodes in the bosonic excitations: the spectra of the collective bosonic modes cross at the K and K' points in the Brillouin zone and form Dirac nodes. We show how two different types of collective phase oscillations are obtained and that they are analogous to the Leggett and the Bogoliubov-Anderson-Gorkov modes in a two-band superconductor. We show that the Dirac node is preserved in the presence of an intergrain interaction, despite induced changes of the qualitative features of the two collective modes. Finally, breaking the sublattice symmetry by choosing different on-site potentials for the two sublattices leads to a gap opening near the Dirac node, in analogy with fermionic Dirac materials. The Dirac node dispersion of bosonic excitations is thus expanding the discussion of the conventional Dirac cone excitations to the case of bosons. We call this case as a representative of bosonic Dirac materials (BDM), similar to the case of Fermionic Dirac materials extensively discussed in the literature.

Role of spin-orbit coupling in the Kugel-Khomskii model on the honeycomb lattice

Science.gov (United States)

Koga, Akihisa; Nakauchi, Shiryu; Nasu, Joji

2018-03-01

We study the effective spin-orbital model for honeycomb-layered transition metal compounds, applying the second-order perturbation theory to the three-orbital Hubbard model with the anisotropic hoppings. This model is reduced to the Kitaev model in the strong spin-orbit coupling limit. Combining the cluster mean-field approximations with the exact diagonalization, we treat the Kugel-Khomskii type superexchange interaction and spin-orbit coupling on an equal footing to discuss ground-state properties. We find that a zigzag ordered state is realized in the model within nearest-neighbor interactions. We clarify how the ordered state competes with the nonmagnetic state, which is adiabatically connected to the quantum spin liquid state realized in a strong spin-orbit coupling limit. Thermodynamic properties are also addressed. The present paper should provide another route to account for the Kitaev-based magnetic properties in candidate materials.

Dimer coverings on random multiple chains of planar honeycomb lattices

International Nuclear Information System (INIS)

Ren, Haizhen; Zhang, Fuji; Qian, Jianguo

2012-01-01

We study dimer coverings on random multiple chains. A multiple chain is a planar honeycomb lattice constructed by successively fusing copies of a ‘straight’ condensed hexagonal chain at the bottom of the previous one in two possible ways. A random multiple chain is then generated by admitting the Bernoulli distribution on the two types of fusing, which describes a zeroth-order Markov process. We determine the expectation of the number of the pure dimer coverings (perfect matchings) over the ensemble of random multiple chains by the transfer matrix approach. Our result shows that, with only two exceptions, the average of the logarithm of this expectation (i.e., the annealed entropy per dimer) is asymptotically nonzero when the fusing process goes to infinity and the length of the hexagonal chain is fixed, though it is zero when the fusing process and the length of the hexagonal chain go to infinity simultaneously. Some numerical results are provided to support our conclusion, from which we can see that the asymptotic behavior fits well to the theoretical results. We also apply the transfer matrix approach to the quenched entropy and reveal that the quenched entropy of random multiple chains has a close connection with the well-known Lyapunov exponent of random matrices. Using the theory of Lyapunov exponents we show that, for some random multiple chains, the quenched entropy per dimer is strictly smaller than the annealed one when the fusing process goes to infinity. Finally, we determine the expectation of the free energy per dimer over the ensemble of the random multiple chains in which the three types of dimers in different orientations are distinguished, and specify a series of non-random multiple chains whose free energy per dimer is asymptotically equal to this expectation. (paper)

Localized structures in Kagome lattices

Energy Technology Data Exchange (ETDEWEB)

Saxena, Avadh B [Los Alamos National Laboratory; Bishop, Alan R [Los Alamos National Laboratory; Law, K J H [UNIV OF MASSACHUSETTS; Kevrekidis, P G [UNIV OF MASSACHUSETTS

2009-01-01

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

PREFACE: Ultrathin layers of graphene, h-BN and other honeycomb structures Ultrathin layers of graphene, h-BN and other honeycomb structures

Science.gov (United States)

Geber, Thomas; Oshima, Chuhei

2012-08-01

Since ancient times, pure carbon materials have been familiar in human society—not only diamonds in jewellery and graphite in pencils, but also charcoal and coal which have been used for centuries as fuel for living and industry. Carbon fibers are stronger, tougher and lighter than steel and increase material efficiency because of their lower weight. Today, carbon fibers and related composite materials are used to make the frames of bicycles, cars and even airplane parts. The two-dimensional allotrope, now called graphene, is just a single layer of carbon atoms, locked together in a strongly bonded honeycomb lattice. In plane, graphene is stiffer than diamond, but out-of-plane it is soft, like rubber. It is virtually invisible, may conduct electricity (heat) better than copper and weighs next to nothing. Carbon compounds with two carbon atoms as a base, such as graphene, graphite or diamond, have isoelectronic sister compounds made of boron-nitrogen pairs: hexagonal and cubic boron nitride, with almost the same lattice constant. Although the two 2D sisters, graphene and h-BN, have the same number of valence electrons, their electronic properties are very different: freestanding h-BN is an insulator, while charge carriers in graphene are highly mobile. The past ten years have seen a great expansion in studies of single-layer and few-layer graphene. This activity has been concerned with the π electron transport in graphene, in electric and magnetic fields. More than 30 years ago, however, single-layer graphene and h-BN on solid surfaces were widely investigated. It was noted that they drastically changed the chemical reactivity of surfaces, and they were known to 'poison' heterogeneous catalysts, to passivate surfaces, to prevent oxidation of surfaces and to act as surfactants. Also, it was realized that the controlled growth of h-BN and graphene on substrates yields the formation of mismatch driven superstructures with peculiar template functionality on the

Theory of a quantum spin liquid in the hydrogen-intercalated honeycomb iridate H3LiIr2O6

Science.gov (United States)

Slagle, Kevin; Choi, Wonjune; Chern, Li Ern; Kim, Yong Baek

2018-03-01

We propose a theoretical model for a gapless spin liquid phase that may have been observed in a recent experiment on H3LiIr2O6 . Despite the insulating and nonmagnetic nature of the material, the specific heat coefficient C /T ˜1 /√{T } in zero magnetic field and C /T ˜T /B3 /2 with finite magnetic field B have been observed. In addition, the NMR relaxation rate shows 1 /(T1T ) ˜(C/T ) 2 . Motivated by the fact that the interlayer/in-plane lattice parameters are reduced/elongated by the hydrogen intercalation of the parent compound Li2IrO3 , we consider four layers of the Kitaev honeycomb lattice model with additional interlayer exchange interactions. It is shown that the resulting spin liquid excitations reside mostly in the top and bottom layers of such a layered structure and possess a quartic dispersion. In an applied magnetic field, each quartic mode is split into four Majorana cones with the velocity v ˜B3 /4 . We suggest that the spin liquid phase in these "defect" layers, placed between different stacking patterns of the honeycomb layers, can explain the major phenomenology of the experiment, which can be taken as evidence that the Kitaev interaction plays the primary role in the formation of a quantum spin liquid in this material.

Local spin structure of the α -RuCl3 honeycomb-lattice magnet observed via muon spin rotation/relaxation

Science.gov (United States)

Yamauchi, Ichihiro; Hiraishi, Masatoshi; Okabe, Hirotaka; Takeshita, Soshi; Koda, Akihiro; Kojima, Kenji M.; Kadono, Ryosuke; Tanaka, Hidekazu

2018-04-01

We report a muon spin rotation/relaxation (μ SR ) study of single-crystalline samples of the α -RuCl3 honeycomb magnet, which is presumed to be a model compound for the Kitaev-Heisenberg interaction. It is inferred from magnetic susceptibility and specific-heat measurements that the present samples exhibit successive magnetic transitions at different critical temperatures TN with decreasing temperature, eventually falling into the TN=7 K antiferromagnetic (7 K) phase that has been observed in only single-crystalline specimens with the least stacking fault. Via μ SR measurements conducted under a zero external field, we show that such behavior originates from a phase separation induced by the honeycomb plane stacking fault, yielding multiple domains with different TN's. We also perform μ SR measurements under a transverse field in the paramagnetic phase to identify the muon site from the muon-Ru hyperfine parameters. Based on a comparison of the experimental and calculated internal fields at the muon site for the two possible spin structures inferred from neutron diffraction data, we suggest a modulated zigzag spin structure for the 7 K phase, with the amplitude of the ordered magnetic moment being significantly reduced from that expected for the orbital quenched spin-1/2 state.

The 3-edge-colouring problem on the 4–8 and 3–12 lattices

International Nuclear Information System (INIS)

Fjærestad, J O

2010-01-01

We consider the problem of counting the number of 3-colourings of the edges (bonds) of the 4–8 lattice and the 3–12 lattice. These lattices are Archimedean with coordination number 3, and can be regarded as decorated versions of the square and honeycomb lattice, respectively. We solve these edge-colouring problems in the infinite-lattice limit by mapping them to other models whose solution is known. The colouring problem on the 4–8 lattice is mapped to a completely packed loop model with loop fugacity n = 3 on the square lattice, which in turn can be mapped to a 6-vertex model. The colouring problem on the 3–12 lattice is mapped to the same problem on the honeycomb lattice. The 3-edge-colouring problems on the 4–8 and 3–12 lattices are equivalent to the 3-vertex-colouring problems (and thus to the zero-temperature 3-state antiferromagnetic Potts model) on the 'square kagome' ('squagome') and 'triangular kagome' lattices, respectively

Multilayer DNA Origami Packed on Hexagonal and Hybrid Lattices

OpenAIRE

Ke, Yonggang; Voigt, Niels V.; Gothelf, Kurt V.; Shih, William M.

2012-01-01

“Scaffolded DNA origami” has been proven to be a powerful and efficient approach to construct two-dimensional or three-dimensional objects with great complexity. Multilayer DNA origami has been demonstrated with helices packing along either honeycomb-lattice geometry or square-lattice geometry. Here we report successful folding of multilayer DNA origami with helices arranged on a close-packed hexagonal lattice. This arrangement yields a higher density of helical packing and therefore higher r...

Theoretical Predictions of Freestanding Honeycomb Sheets of Cadmium Chalcogenides

Energy Technology Data Exchange (ETDEWEB)

Zhou, Jia [ORNL; Huang, Jingsong [ORNL; Sumpter, Bobby G [ORNL; Kent, Paul R [ORNL; Xie, Yu [ORNL; Terrones Maldonado, Humberto [ORNL; Smith, Sean C [ORNL

2014-01-01

Two-dimensional (2D) nanocrystals of CdX (X = S, Se, Te) typically grown by colloidal synthesis are coated with organic ligands. Recent experimental work on ZnSe showed that the organic ligands can be removed at elevated temperature, giving a freestanding 2D sheet of ZnSe. In this theoretical work, freestanding single- to few-layer sheets of CdX, each possessing a pseudo honeycomb lattice, are considered by cutting along all possible lattice planes of the bulk zinc blende (ZB) and wurtzite (WZ) phases. Using density functional theory, we have systematically studied their geometric structures, energetics, and electronic properties. A strong surface distortion is found to occur for all of the layered sheets, and yet all of the pseudo honeycomb lattices are preserved, giving unique types of surface corrugations and different electronic properties. The energetics, in combination with phonon mode calculations and molecular dynamics simulations, indicate that the syntheses of these freestanding 2D sheets could be selective, with the single- to few-layer WZ110, WZ100, and ZB110 sheets being favored. Through the GW approximation, it is found that all single-layer sheets have large band gaps falling into the ultraviolet range, while thicker sheets in general have reduced band gaps in the visible and ultraviolet range. On the basis of the present work and the experimental studies on freestanding double-layer sheets of ZnSe, we envision that the freestanding 2D layered sheets of CdX predicted herein are potential synthesis targets, which may offer tunable band gaps depending on their structural features including surface corrugations, stacking motifs, and number of layers.

Topological quantum error correction in the Kitaev honeycomb model

Science.gov (United States)

Lee, Yi-Chan; Brell, Courtney G.; Flammia, Steven T.

2017-08-01

The Kitaev honeycomb model is an approximate topological quantum error correcting code in the same phase as the toric code, but requiring only a 2-body Hamiltonian. As a frustrated spin model, it is well outside the commuting models of topological quantum codes that are typically studied, but its exact solubility makes it more amenable to analysis of effects arising in this noncommutative setting than a generic topologically ordered Hamiltonian. Here we study quantum error correction in the honeycomb model using both analytic and numerical techniques. We first prove explicit exponential bounds on the approximate degeneracy, local indistinguishability, and correctability of the code space. These bounds are tighter than can be achieved using known general properties of topological phases. Our proofs are specialized to the honeycomb model, but some of the methods may nonetheless be of broader interest. Following this, we numerically study noise caused by thermalization processes in the perturbative regime close to the toric code renormalization group fixed point. The appearance of non-topological excitations in this setting has no significant effect on the error correction properties of the honeycomb model in the regimes we study. Although the behavior of this model is found to be qualitatively similar to that of the standard toric code in most regimes, we find numerical evidence of an interesting effect in the low-temperature, finite-size regime where a preferred lattice direction emerges and anyon diffusion is geometrically constrained. We expect this effect to yield an improvement in the scaling of the lifetime with system size as compared to the standard toric code.

The Kitaev honeycomb model on surfaces of genus g ≥ 2

Science.gov (United States)

Brennan, John; Vala, Jiří

2018-05-01

We present a construction of the Kitaev honeycomb lattice model on an arbitrary higher genus surface. We first generalize the exact solution of the model based on the Jordan–Wigner fermionization to a surface with genus g = 2, and then use this as a basic module to extend the solution to lattices of arbitrary genus. We demonstrate our method by calculating the ground states of the model in both the Abelian doubled {Z}}}2 phase and the non-Abelian Ising topological phase on lattices with the genus up to g = 6. We verify the expected ground state degeneracy of the system in both topological phases and further illuminate the role of fermionic parity in the Abelian phase.

The lattice dynamical studies of rare earth compounds: electron-phonon interactions

International Nuclear Information System (INIS)

Jha, Prafulla K.; Sanyal, Sankar P.; Singh, R.K.

2002-01-01

During the last two decades chalcogenides and pnictides of rare earth (RE) atoms have drawn considerable attention of the solid state physicists because of their peculiar electronic, magnetic, optical and phonon properties. Some of these compounds e.g. sulphides and selenides of cerium (Ce), samarium (Sm), yttrium (Y), ytterbium (Yb), europium (Eu) and thulium (Tm) and their alloys show nonintegral valence (between 2 and 3), arising due to f-d electron hybridization at ambient temperature and pressure. The rare earth mixed valence compounds (MVC) reviewed in this article crystallize in simple cubic structure. Most of these compounds show the existence of strong electron-phonon coupling at half way to the zone boundary. This fact manifests itself through softening of the longitudinal acoustic mode, negative value of elastic constant C 12 etc. The purpose of this contribution is to review some of the recent activities in the fields of lattice dynamics and allied properties of rare earth compounds. The present article is primarily devoted to review the effect of electron-phonon interactions on the dynamical properties of rare earth compounds by using the lattice dynamical model theories based on charged density deformations and long-range many body forces. While the long range charge transfer effect arises due to f-d hybridization of nearly degenerate 4f-5d bands of rare earth ions, the density deformation comes into the picture of breathing motion of electron shells. These effects of charge transfer and charge density deformation when considered in the lattice dynamical models namely the three body force rigid ion model (TRM) and breathing shell model (BSM) are quite successful in explaining the phonon anomalies in these compounds and undoubtedly unraveled many important physical process governing the phonon anomalies in rare earth compounds

Honeycomb metal panel

International Nuclear Information System (INIS)

1979-01-01

Product constituted by a honeycomb metal panel that can be employed to advantage for manufacturing lagging by sandwiching it between two plane sheets, utilized in particular in the nuclear industry where lagging has to have a very long life strength. The honeycomb metal panel is made of an expanded metal extrusion previously cut so as to form, after additional drawing, a honeycomb structure with square or rectangular cells with a plane surface [fr

Square lattice honeycomb tri-carbide fuels for 50 to 250 KN variable thrust NTP design

International Nuclear Information System (INIS)

Anghaie, Samim; Knight, Travis; Gouw, Reza; Furman, Eric

2001-01-01

Ultrahigh temperature solid solution of tri-carbide fuels are used to design an ultracompact nuclear thermal rocket generating 950 seconds of specific impulse with scalable thrust level in range of 50 to 250 kilo Newtons. Solid solutions of tri-carbide nuclear fuels such as uranium-zirconium-niobium carbide. UZrNbC, are processed to contain certain mixing ratio between uranium carbide and two stabilizing carbides. Zirconium or niobium in the tri-carbide could be replaced by tantalum or hafnium to provide higher chemical stability in hot hydrogen environment or to provide different nuclear design characteristics. Recent studies have demonstrated the chemical compatibility of tri-carbide fuels with hydrogen propellant for a few to tens of hours of operation at temperatures ranging from 2800 K to 3300 K, respectively. Fuel elements are fabricated from thin tri-carbide wafers that are grooved and locked into a square-lattice honeycomb (SLHC) shape. The hockey puck shaped SLHC fuel elements are stacked up in a grooved graphite tube to form a SLHC fuel assembly. A total of 18 fuel assemblies are arranged circumferentially to form two concentric rings of fuel assemblies with zirconium hydride filling the space between assemblies. For 50 to 250 kilo Newtons thrust operations, the reactor diameter and length including reflectors are 57 cm and 60 cm, respectively. Results of the nuclear design and thermal fluid analyses of the SLHC nuclear thermal propulsion system are presented

Maximum hardness and minimum polarizability principles through lattice energies of ionic compounds

International Nuclear Information System (INIS)

Kaya, Savaş; Kaya, Cemal; Islam, Nazmul

2016-01-01

The maximum hardness (MHP) and minimum polarizability (MPP) principles have been analyzed using the relationship among the lattice energies of ionic compounds with their electronegativities, chemical hardnesses and electrophilicities. Lattice energy, electronegativity, chemical hardness and electrophilicity values of ionic compounds considered in the present study have been calculated using new equations derived by some of the authors in recent years. For 4 simple reactions, the changes of the hardness (Δη), polarizability (Δα) and electrophilicity index (Δω) were calculated. It is shown that the maximum hardness principle is obeyed by all chemical reactions but minimum polarizability principles and minimum electrophilicity principle are not valid for all reactions. We also proposed simple methods to compute the percentage of ionic characters and inter nuclear distances of ionic compounds. Comparative studies with experimental sets of data reveal that the proposed methods of computation of the percentage of ionic characters and inter nuclear distances of ionic compounds are valid.

Maximum hardness and minimum polarizability principles through lattice energies of ionic compounds

Energy Technology Data Exchange (ETDEWEB)

Kaya, Savaş, E-mail: savaskaya@cumhuriyet.edu.tr [Department of Chemistry, Faculty of Science, Cumhuriyet University, Sivas 58140 (Turkey); Kaya, Cemal, E-mail: kaya@cumhuriyet.edu.tr [Department of Chemistry, Faculty of Science, Cumhuriyet University, Sivas 58140 (Turkey); Islam, Nazmul, E-mail: nazmul.islam786@gmail.com [Theoretical and Computational Chemistry Research Laboratory, Department of Basic Science and Humanities/Chemistry Techno Global-Balurghat, Balurghat, D. Dinajpur 733103 (India)

2016-03-15

The maximum hardness (MHP) and minimum polarizability (MPP) principles have been analyzed using the relationship among the lattice energies of ionic compounds with their electronegativities, chemical hardnesses and electrophilicities. Lattice energy, electronegativity, chemical hardness and electrophilicity values of ionic compounds considered in the present study have been calculated using new equations derived by some of the authors in recent years. For 4 simple reactions, the changes of the hardness (Δη), polarizability (Δα) and electrophilicity index (Δω) were calculated. It is shown that the maximum hardness principle is obeyed by all chemical reactions but minimum polarizability principles and minimum electrophilicity principle are not valid for all reactions. We also proposed simple methods to compute the percentage of ionic characters and inter nuclear distances of ionic compounds. Comparative studies with experimental sets of data reveal that the proposed methods of computation of the percentage of ionic characters and inter nuclear distances of ionic compounds are valid.

Extension theorems for homogenization on lattice structures

Science.gov (United States)

Miller, Robert E.

1992-01-01

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

Quantification of Honeycomb Number-Type Stacking Faults: Application to Na3Ni2BiO6 Cathodes for Na-Ion Batteries.

Science.gov (United States)

Liu, Jue; Yin, Liang; Wu, Lijun; Bai, Jianming; Bak, Seong-Min; Yu, Xiqian; Zhu, Yimei; Yang, Xiao-Qing; Khalifah, Peter G

2016-09-06

Ordered and disordered samples of honeycomb-lattice Na3Ni2BiO6 were investigated as cathodes for Na-ion batteries, and it was determined that the ordered sample exhibits better electrochemical performance, with a specific capacity of 104 mA h/g delivered at plateaus of 3.5 and 3.2 V (vs Na(+)/Na) with minimal capacity fade during extended cycling. Advanced imaging and diffraction investigations showed that the primary difference between the ordered and disordered samples is the amount of number-type stacking faults associated with the three possible centering choices for each honeycomb layer. A labeling scheme for assigning the number position of honeycomb layers is described, and it is shown that the translational shift vectors between layers provide the simplest method for classifying different repeat patterns. It is demonstrated that the number position of honeycomb layers can be directly determined in high-angle annular dark-field scanning transmission electron microscopy (STEM-HAADF) imaging studies. By the use of fault models derived from STEM studies, it is shown that both the sharp, symmetric subcell peaks and the broad, asymmetric superstructure peaks in powder diffraction patterns can be quantitatively modeled. About 20% of the layers in the ordered monoclinic sample are faulted in a nonrandom manner, while the disordered sample stacking is not fully random but instead contains about 4% monoclinic order. Furthermore, it is shown that the ordered sample has a series of higher-order superstructure peaks associated with 6-, 9-, 12-, and 15-layer periods whose existence is transiently driven by the presence of long-range strain that is an inherent consequence of the synthesis mechanism revealed through the present diffraction and imaging studies. This strain is closely associated with a monoclinic shear that can be directly calculated from cell lattice parameters and is strongly correlated with the degree of ordering in the samples. The present results are

Spin 1/2 Delafossite Honeycomb Compound Cu5SbO6

DEFF Research Database (Denmark)

Climent-Pascual, E.; Norby, Poul; Andersen, Niels Hessel

2012-01-01

Cu5SbO6 is found to have a monoclinic, Delafossite-derived structure consisting of alternating layers of O–Cu(I)–O sticks and magnetic layers of Jahn–Teller distorted Cu(II)O6 octahedra in an edge sharing honeycomb arrangement with Sb(V)O6 octahedra. This yields the structural formula Cu(I)3Cu(II...

Study of Cylindrical Honeycomb Solar Collector

Directory of Open Access Journals (Sweden)

Atish Mozumder

2014-01-01

Full Text Available We present the results of our investigation on cylindrical honeycomb solar collector. The honeycomb has been fabricated with transparent cellulose triacetate polymer sheets. Insulation characteristics of the honeycomb were studied by varying the separation between the honeycomb and the absorber plate. The optimal value of the separation was found to be 3.3 mm for which the heat transfer coefficient is 3.06 W m−2 K−1. This supports result of previous similar experiments. Further we test the honeycomb through a field experiment conducted in Delhi (28.6°N, 77°E and found that when the incident angle of the solar radiation is within 20° then the performance of the system with the honeycomb is better than the one without the honeycomb.

Dirac topological insulator in the dz2 manifold of a honeycomb oxide

Science.gov (United States)

Lado, J. L.; Pardo, V.

2016-09-01

We show by means of ab initio calculations and tight-binding modeling that an oxide system based on a honeycomb lattice can sustain topologically nontrivial states if a single orbital dominates the spectrum close to the Fermi level. In such a situation, the low-energy spectrum is described by two Dirac equations that become nontrivially gapped when spin-orbit coupling (SOC) is switched on. We provide one specific example but the recipe is general. We discuss a realization of this starting from a conventional spin-1/2 honeycomb antiferromagnet whose states close to the Fermi energy are dz2 orbitals. Switching off magnetism by atomic substitution and ensuring that the electronic structure becomes two-dimensional is sufficient for topologicality to arise in such a system. By deriving a tight-binding Wannier Hamiltonian, we find that the gap in such a model scales linearly with SOC, opposed to other oxide-based topological insulators, where smaller gaps tend to appear by construction of the lattice. We show that the quantum spin Hall state in this system survives in the presence of off-plane magnetism and the orbital magnetic field and we discuss its Landau level spectra, showing that our recipe provides a dz2 realization of the Kane-Mele model.

Effects of Edge on-Site Potential in a Honeycomb Topological Magnon Insulator

Science.gov (United States)

Pantaleón, Pierre A.; Xian, Yang

2018-06-01

While the deviation of the edge on-site potential from the bulk values in a magnonic topological honeycomb lattice leads to the formation of edge states in a bearded boundary, this is not the case for a zigzag termination, where no edge state is found. In a semi-infinite lattice, the intrinsic on-site interactions along the boundary sites generate an effective defect and this gives rise to Tamm-like edge states. If a nontrivial gap is induced, both Tamm-like and topologically protected edge states appear in the band structure. The effective defect can be strengthened by an external on-site potential, and the dispersion relation, velocity and magnon density of the edge states all become tunable.

Mechanical properties of additively manufactured octagonal honeycombs

Energy Technology Data Exchange (ETDEWEB)

Hedayati, R., E-mail: rezahedayati@gmail.com [Department of Mechanical Engineering, Amirkabir University of Technology (Tehran Polytechnic), Hafez Ave, Tehran (Iran, Islamic Republic of); Department of Biomechanical Engineering, Faculty of Mechanical, Maritime, and Materials Engineering, Delft University of Technology (TU Delft), Mekelweg 2, 2628 CD Delft (Netherlands); Sadighi, M.; Mohammadi-Aghdam, M. [Department of Mechanical Engineering, Amirkabir University of Technology (Tehran Polytechnic), Hafez Ave, Tehran (Iran, Islamic Republic of); Zadpoor, A.A. [Department of Biomechanical Engineering, Faculty of Mechanical, Maritime, and Materials Engineering, Delft University of Technology (TU Delft), Mekelweg 2, 2628 CD Delft (Netherlands)

2016-12-01

Honeycomb structures have found numerous applications as structural and biomedical materials due to their favourable properties such as low weight, high stiffness, and porosity. Application of additive manufacturing and 3D printing techniques allows for manufacturing of honeycombs with arbitrary shape and wall thickness, opening the way for optimizing the mechanical and physical properties for specific applications. In this study, the mechanical properties of honeycomb structures with a new geometry, called octagonal honeycomb, were investigated using analytical, numerical, and experimental approaches. An additive manufacturing technique, namely fused deposition modelling, was used to fabricate the honeycomb from polylactic acid (PLA). The honeycombs structures were then mechanically tested under compression and the mechanical properties of the structures were determined. In addition, the Euler-Bernoulli and Timoshenko beam theories were used for deriving analytical relationships for elastic modulus, yield stress, Poisson's ratio, and buckling stress of this new design of honeycomb structures. Finite element models were also created to analyse the mechanical behaviour of the honeycombs computationally. The analytical solutions obtained using Timoshenko beam theory were close to computational results in terms of elastic modulus, Poisson's ratio and yield stress, especially for relative densities smaller than 25%. The analytical solutions based on the Timoshenko analytical solution and the computational results were in good agreement with experimental observations. Finally, the elastic properties of the proposed honeycomb structure were compared to those of other honeycomb structures such as square, triangular, hexagonal, mixed, diamond, and Kagome. The octagonal honeycomb showed yield stress and elastic modulus values very close to those of regular hexagonal honeycombs and lower than the other considered honeycombs. - Highlights: • The octagonal

Dirac Cones, Topological Edge States, and Nontrivial Flat Bands in Two-Dimensional Semiconductors with a Honeycomb Nanogeometry

Directory of Open Access Journals (Sweden)

E. Kalesaki

2014-01-01

Full Text Available We study theoretically two-dimensional single-crystalline sheets of semiconductors that form a honeycomb lattice with a period below 10 nm. These systems could combine the usual semiconductor properties with Dirac bands. Using atomistic tight-binding calculations, we show that both the atomic lattice and the overall geometry influence the band structure, revealing materials with unusual electronic properties. In rocksalt Pb chalcogenides, the expected Dirac-type features are clouded by a complex band structure. However, in the case of zinc-blende Cd-chalcogenide semiconductors, the honeycomb nanogeometry leads to rich band structures, including, in the conduction band, Dirac cones at two distinct energies and nontrivial flat bands and, in the valence band, topological edge states. These edge states are present in several electronic gaps opened in the valence band by the spin-orbit coupling and the quantum confinement in the honeycomb geometry. The lowest Dirac conduction band has S-orbital character and is equivalent to the π-π^{⋆} band of graphene but with renormalized couplings. The conduction bands higher in energy have no counterpart in graphene; they combine a Dirac cone and flat bands because of their P-orbital character. We show that the width of the Dirac bands varies between tens and hundreds of meV. These systems emerge as remarkable platforms for studying complex electronic phases starting from conventional semiconductors. Recent advancements in colloidal chemistry indicate that these materials can be synthesized from semiconductor nanocrystals.

Spin-Orbit Coupled Quantum Magnetism in the 3D-Honeycomb Iridates

Science.gov (United States)

Kimchi, Itamar

In this doctoral dissertation, we consider the significance of spin-orbit coupling for the phases of matter which arise for strongly correlated electrons. We explore emergent behavior in quantum many-body systems, including symmetry-breaking orders, quantum spin liquids, and unconventional superconductivity. Our study is cemented by a particular class of Mott-insulating materials, centered around a family of two- and three-dimensional iridium oxides, whose honeycomb-like lattice structure admits peculiar magnetic interactions, the so-called Kitaev exchange. By analyzing recent experiments on these compounds, we show that this unconventional exchange is the key ingredient in describing their magnetism, and then use a combination of numerical and analytical techniques to investigate the implications for the phase diagram as well as the physics of the proximate three-dimensional quantum spin liquid phases. These long-ranged-entangled fractionalized phases should exhibit special features, including finite-temperature stability as well as unconventional high-Tc superconductivity upon charge-doping, which should aid future experimental searches for spin liquid physics. Our study explores the nature of frustration and fractionalization which can arise in quantum systems in the presence of strong spin-orbit coupling.

From lattice Hamiltonians to tunable band structures by lithographic design

Science.gov (United States)

Tadjine, Athmane; Allan, Guy; Delerue, Christophe

2016-08-01

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

Honeycomb technology materials, design, manufacturing, applications and testing

CERN Document Server

Bitzer, Tom

1997-01-01

Honeycomb Technology is a guide to honeycomb cores and honeycomb sandwich panels, from the manufacturing methods by which they are produced, to the different types of design, applications for usage and methods of testing the materials. It explains the different types of honeycomb cores available and provides tabulated data of their properties. The author has been involved in the testing and design of honeycomb cores and sandwich panels for nearly 30 years. Honeycomb Technology reflects this by emphasizing a `hands-on' approach and discusses procedures for designing sandwich panels, explaining the necessary equations. Also included is a section on how to design honeycomb energy absorbers and one full chapter discussing honeycomb core and sandwich panel testing. Honeycomb Technology will be of interest to engineers in the aircraft, aerospace and building industries. It will also be of great use to engineering students interested in basic sandwich panel design.

Competition between spin-orbit coupling, magnetism, and dimerization in the honeycomb iridates: α -Li2IrO3 under pressure

Science.gov (United States)

Hermann, V.; Altmeyer, M.; Ebad-Allah, J.; Freund, F.; Jesche, A.; Tsirlin, A. A.; Hanfland, M.; Gegenwart, P.; Mazin, I. I.; Khomskii, D. I.; Valentí, R.; Kuntscher, C. A.

2018-02-01

Single-crystal x-ray diffraction studies with synchrotron radiation on the honeycomb iridate α -Li2IrO3 reveal a pressure-induced structural phase transition with symmetry lowering from monoclinic to triclinic at a critical pressure of Pc=3.8 GPa. According to the evolution of the lattice parameters with pressure, the transition mainly affects the a b plane and thereby the Ir hexagon network, leading to the formation of Ir-Ir dimers. These observations are independently predicted and corroborated by our ab initio density functional theory calculations where we find that the appearance of Ir-Ir dimers at finite pressure is a consequence of a subtle interplay between magnetism, correlation, spin-orbit coupling, and covalent bonding. Our results further suggest that at Pc the system undergoes a magnetic collapse. Finally we provide a general picture of competing interactions for the honeycomb lattices A2M O3 with A =Li , Na and M =Ir , Ru.

Inserting Stress Analysis of Combined Hexagonal Aluminum Honeycombs

Directory of Open Access Journals (Sweden)

Xiangcheng Li

2016-01-01

Full Text Available Two kinds of hexagonal aluminum honeycombs are tested to study their out-of-plane crushing behavior. In the tests, honeycomb samples, including single hexagonal aluminum honeycomb (SHAH samples and two stack-up combined hexagonal aluminum honeycombs (CHAH samples, are compressed at a fixed quasistatic loading rate. The results show that the inserting process of CHAH can erase the initial peak stress that occurred in SHAH. Meanwhile, energy-absorbing property of combined honeycomb samples is more beneficial than the one of single honeycomb sample with the same thickness if the two types of honeycomb samples are completely crushed. Then, the applicability of the existing theoretical model for single hexagonal honeycomb is discussed, and an area equivalent method is proposed to calculate the crushing stress for nearly regular hexagonal honeycombs. Furthermore, a semiempirical formula is proposed to calculate the inserting plateau stress of two stack-up CHAH, in which structural parameters and mechanics properties of base material are concerned. The results show that the predicted stresses of three kinds of two stack-up combined honeycombs are in good agreement with the experimental data. Based on this study, stress-displacement curve of aluminum honeycombs can be designed in detail, which is very beneficial to optimize the energy-absorbing structures in engineering fields.

Low temperature anomalies in the lattice parameters of rare earth compounds and UPd3

International Nuclear Information System (INIS)

Pluemacher, D.

1980-01-01

Using a low temperature diffractometer, intermediate valence effects and crystal defects can be identified from the temperature dependence of the lattice parameters and the Debye-Waller factor. For polycrystalline powder samples the measuring error are too large. For intermediate valence systems the relative change in the 4f-level population probability can be calculated together with the anisotropic effects on the lattice parameters and on the unit cell colume. Pronounced effects on the lattice parameters can be observed in the case of RE Cu 2 Si 2 compounds with crystal fields. (DG) [de

Mechanical Properties of Additively Manufactured Thick Honeycombs

Directory of Open Access Journals (Sweden)

Reza Hedayati

2016-07-01

Full Text Available Honeycombs resemble the structure of a number of natural and biological materials such as cancellous bone, wood, and cork. Thick honeycomb could be also used for energy absorption applications. Moreover, studying the mechanical behavior of honeycombs under in-plane loading could help understanding the mechanical behavior of more complex 3D tessellated structures such as porous biomaterials. In this paper, we study the mechanical behavior of thick honeycombs made using additive manufacturing techniques that allow for fabrication of honeycombs with arbitrary and precisely controlled thickness. Thick honeycombs with different wall thicknesses were produced from polylactic acid (PLA using fused deposition modelling, i.e., an additive manufacturing technique. The samples were mechanically tested in-plane under compression to determine their mechanical properties. We also obtained exact analytical solutions for the stiffness matrix of thick hexagonal honeycombs using both Euler-Bernoulli and Timoshenko beam theories. The stiffness matrix was then used to derive analytical relationships that describe the elastic modulus, yield stress, and Poisson’s ratio of thick honeycombs. Finite element models were also built for computational analysis of the mechanical behavior of thick honeycombs under compression. The mechanical properties obtained using our analytical relationships were compared with experimental observations and computational results as well as with analytical solutions available in the literature. It was found that the analytical solutions presented here are in good agreement with experimental and computational results even for very thick honeycombs, whereas the analytical solutions available in the literature show a large deviation from experimental observation, computational results, and our analytical solutions.

Evidence for coexisting magnetic order in frustrated three-dimensional honeycomb iridates Li2IrO3

Science.gov (United States)

Breznay, Nicholas; Ruiz, Alejandro; Frano, Alex; Analytis, James

The search for unconventional magnetism has found a fertile hunting ground in 5d iridium oxide (iridate) materials. The competition between coulomb, spin-orbit, and crystal field energy scales in honeycomb iridates leads to a quantum magnetic system with localized spin-1/2 moments communicating through spin-anisotropic Kitaev exchange interactions. Although early and ongoing work has focused on layered two-dimensional honeycomb compounds such as Na2IrO3 and a 4d analog, RuCl3, recently discovered polytypes of Li2IrO3 take on three-dimensional honeycomb structures. Bulk thermodynamic studies, as well as recent resonant x-ray diffraction and absorption spectroscopy experiments, have uncovered a rich phase diagram for these three-dimensional honeycomb iridates. Low temperature incommensurate and commensurate magnetic orders can be stabilized by tuning the applied magnetic field, displaying a delicate coexistence that signals highly frustrated magnetism.

Freeform Honeycomb Structures

KAUST Repository

Jiang, Caigui

2014-07-01

Motivated by requirements of freeform architecture, and inspired by the geometry of hexagonal combs in beehives, this paper addresses torsion-free structures aligned with hexagonal meshes. Since repetitive geometry is a very important contribution to the reduction of production costs, we study in detail “honeycomb structures”, which are defined as torsion-free structures where the walls of cells meet at 120 degrees. Interestingly, the Gauss-Bonnet theorem is useful in deriving information on the global distribution of node axes in such honeycombs. This paper discusses the computation and modeling of honeycomb structures as well as applications, e.g. for shading systems, or for quad meshing. We consider this paper as a contribution to the wider topic of freeform patterns, polyhedral or otherwise. Such patterns require new approaches on the technical level, e.g. in the treatment of smoothness, but they also extend our view of what constitutes aesthetic freeform geometry.

Anti-ferromagnetic Heisenberg model on bilayer honeycomb

International Nuclear Information System (INIS)

Shoja, M.; Shahbazi, F.

2012-01-01

Recent experiment on spin-3/2 bilayer honeycomb lattice antiferromagnet Bi 3 Mn 4 O 12 (NO 3 ) shows a spin liquid behavior down to very low temperatures. This behavior can be ascribed to the frustration effect due to competitions between first and second nearest neighbour's antiferromagnet interaction. Motivated by the experiment, we study J 1 -J 2 Antiferromagnet Heisenberg model, using Mean field Theory. This calculation shows highly degenerate ground state. We also calculate the effect of second nearest neighbor through z direction and show these neighbors also increase frustration in these systems. Because of these degenerate ground state in these systems, spins can't find any ground state to be freeze in low temperatures. This behavior shows a novel spin liquid state down to very low temperatures.

Mechanical properties of additively manufactured thick honeycombs

NARCIS (Netherlands)

Hedayati, R.; Sadighi, M.; Mohammadi-Aghdam, M; Zadpoor, A.A.

2016-01-01

Honeycombs resemble the structure of a number of natural and biological materials such as cancellous bone, wood, and cork. Thick honeycomb could be also used for energy absorption applications. Moreover, studying the mechanical behavior of honeycombs under in-plane loading could help understanding

Systematic study of the lattice dynamics of the uranium rocksalt-structure compounds

International Nuclear Information System (INIS)

Jackman, J.A.; Holden, T.M.; Buyers, W.J.L.; DuPlessis, P. de V.; Vogt, O.; Genossar, J.

1986-01-01

The phonon-dispersion relations of USe and UTe have been determined by the inelastic scattering of thermal neutrons. All existing phonon measurements for the UX series, viz., UC, UN, UAs, USb, US, USe, and UTe, have been fitted to the rigid-ion and shell models and dispersion relations have been predicted for UP. The U-X force constants dominate the lattice dynamics and are nearly constant for the series, whereas the U-U force constants vary systematically from being large and positive for the compounds with the smallest lattice parameter to being negative for the chalcogenide series. The negative U-U force constant is identified with destabilizing f-d interactions. Elastic constants, derived from the slopes of the dispersion relations and from ultrasound velocity measurements, have been determined. The bulk modulus decreases unusually rapidly as the lattice parameter increases and is in fair agreement with band-structure calculations

Classical ground states of Heisenberg and X Y antiferromagnets on the windmill lattice

Science.gov (United States)

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.

Topological Valley Transport in Two-dimensional Honeycomb Photonic Crystals.

Science.gov (United States)

Yang, Yuting; Jiang, Hua; Hang, Zhi Hong

2018-01-25

Two-dimensional photonic crystals, in analogy to AB/BA stacking bilayer graphene in electronic system, are studied. Inequivalent valleys in the momentum space for photons can be manipulated by simply engineering diameters of cylinders in a honeycomb lattice. The inequivalent valleys in photonic crystal are selectively excited by a designed optical chiral source and bulk valley polarizations are visualized. Unidirectional valley interface states are proved to exist on a domain wall connecting two photonic crystals with different valley Chern numbers. With the similar optical vortex index, interface states can couple with bulk valley polarizations and thus valley filter and valley coupler can be designed. Our simple dielectric PC scheme can help to exploit the valley degree of freedom for future optical devices.

Quantitative neutron radiography using neutron absorbing honeycomb

International Nuclear Information System (INIS)

Tamaki, Masayoshi; Oda, Masahiro; Takahashi, Kenji; Ohkubo, Kohei; Tasaka, Kanji; Tsuruno, Akira; Matsubayashi, Masahito.

1993-01-01

This investigation concerns quantitative neutron radiography and computed tomography by using a neutron absorbing honeycomb collimator. By setting the neutron absorbing honeycomb collimator between object and imaging system, neutrons scattered in the object were absorbed by the honeycomb material and eliminated before coming to the imaging system, but the neutrons which were transmitted the object without interaction could reach the imaging system. The image by purely transmitted neutrons gives the quantitative information. Two honeycombs were prepared with coating of boron nitride and gadolinium oxide and evaluated for the quantitative application. The relation between the neutron total cross section and the attenuation coefficient confirmed that they were in a fairly good agreement. Application to quantitative computed tomography was also successfully conducted. The new neutron radiography method using the neutron-absorbing honeycomb collimator for the elimination of the scattered neutrons improved remarkably the quantitativeness of the neutron radiography and computed tomography. (author)

Analysis on High Temperature Aging Property of Self-brazing Aluminum Honeycomb Core at Middle Temperature

Directory of Open Access Journals (Sweden)

ZHAO Huan

2016-11-01

Full Text Available Tension-shear test was carried out on middle temperature self-brazing aluminum honeycomb cores after high temperature aging by micro mechanical test system, and the microstructure and component of the joints were observed and analyzed using scanning electron microscopy and energy dispersive spectroscopy to study the relationship between brazing seam microstructure, component and high temperature aging properties. Results show that the tensile-shear strength of aluminum honeycomb core joints brazed by 1060 aluminum foil and aluminum composite brazing plate after high temperature aging(200℃/12h, 200℃/24h, 200℃/36h is similar to that of as-welded joints, and the weak part of the joint is the base metal which is near the brazing joint. The observation and analysis of the aluminum honeycomb core microstructure and component show that the component of Zn, Sn at brazing seam is not much affected and no compound phase formed after high temperature aging; therefore, the main reason for good high temperature aging performance of self-brazing aluminum honeycomb core is that no obvious change of brazing seam microstructure and component occurs.

Prediction of Low-Thermal-Conductivity Compounds with First-Principles Anharmonic Lattice-Dynamics Calculations and Bayesian Optimization

Science.gov (United States)

Seko, Atsuto; Togo, Atsushi; Hayashi, Hiroyuki; Tsuda, Koji; Chaput, Laurent; Tanaka, Isao

2015-11-01

Compounds of low lattice thermal conductivity (LTC) are essential for seeking thermoelectric materials with high conversion efficiency. Some strategies have been used to decrease LTC. However, such trials have yielded successes only within a limited exploration space. Here, we report the virtual screening of a library containing 54 779 compounds. Our strategy is to search the library through Bayesian optimization using for the initial data the LTC obtained from first-principles anharmonic lattice-dynamics calculations for a set of 101 compounds. We discovered 221 materials with very low LTC. Two of them even have an electronic band gap <1 eV , which makes them exceptional candidates for thermoelectric applications. In addition to those newly discovered thermoelectric materials, the present strategy is believed to be powerful for many other applications in which the chemistry of materials is required to be optimized.

The growth of minicircle networks on regular lattices

International Nuclear Information System (INIS)

Diao, Y; Hinson, K; Arsuaga, J

2012-01-01

The mitochondrial DNA of trypanosomes is organized into a network of topologically linked minicircles. In order to investigate how key topological properties of the network change with minicircle density, the authors introduced, in an earlier study, a mathematical model in which randomly oriented minicircles were placed on the vertices of the simple square lattice. Using this model, the authors rigorously showed that when the density of minicircles increases, percolation clusters form. For higher densities, these percolation clusters are the backbones for networks of minicircles that saturate the entire lattice. An important relevant question is whether these findings are generally true. That is, whether these results are independent of the choice of the lattices on which the model is based. In this paper, we study two additional lattices (namely the honeycomb and the triangular lattices). These regular lattices are selected because they have been proposed for trypanosomes before and after replication. We compare our findings with our earlier results on the square lattice and show that the mathematical statements derived for the square lattice can be extended to these other lattices qualitatively. This finding suggests the universality of these properties. Furthermore, we performed a numerical study which provided data that are consistent with our theoretical analysis, and showed that the effect of the choice of lattices on the key network topological characteristics is rather small. (paper)

Quantum Monte Carlo Simulation of Frustrated Kondo Lattice Models

Science.gov (United States)

Sato, Toshihiro; Assaad, Fakher F.; Grover, Tarun

2018-03-01

The absence of the negative sign problem in quantum Monte Carlo simulations of spin and fermion systems has different origins. World-line based algorithms for spins require positivity of matrix elements whereas auxiliary field approaches for fermions depend on symmetries such as particle-hole symmetry. For negative-sign-free spin and fermionic systems, we show that one can formulate a negative-sign-free auxiliary field quantum Monte Carlo algorithm that allows Kondo coupling of fermions with the spins. Using this general approach, we study a half-filled Kondo lattice model on the honeycomb lattice with geometric frustration. In addition to the conventional Kondo insulator and antiferromagnetically ordered phases, we find a partial Kondo screened state where spins are selectively screened so as to alleviate frustration, and the lattice rotation symmetry is broken nematically.

Research on Shock Responses of Three Types of Honeycomb Cores

Science.gov (United States)

Peng, Fei; Yang, Zhiguang; Jiang, Liangliang; Ren, Yanting

2018-03-01

The shock responses of three kinds of honeycomb cores have been investigated and analyzed based on explicit dynamics analysis. According to the real geometric configuration and the current main manufacturing methods of aluminum alloy honeycomb cores, the finite element models of honeycomb cores with three different cellular configurations (conventional hexagon honeycomb core, rectangle honeycomb core and auxetic honeycomb core with negative Poisson’s ratio) have been established through FEM parametric modeling method based on Python and Abaqus. In order to highlight the impact response characteristics of the above three honeycomb cores, a 5 mm thick panel with the same mass and material was taken as contrast. The analysis results showed that the peak values of longitudinal acceleration history curves of the three honeycomb cores were lower than those of the aluminum alloy panel in all three reference points under the loading of a longitudinal pulse pressure load with the peak value of 1 MPa and the pulse width of 1 μs. It could be concluded that due to the complex reflection and diffraction of stress wave induced by shock in honeycomb structures, the impact energy was redistributed which led to a decrease in the peak values of the longitudinal acceleration at the measuring points of honeycomb cores relative to the panel.

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

Science.gov (United States)

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

2016-01-01

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

Investigation of the spin-1 honeycomb antiferromagnet BaNi2V2O8 with easy-plane anisotropy

Science.gov (United States)

Klyushina, E. S.; Lake, B.; Islam, A. T. M. N.; Park, J. T.; Schneidewind, A.; Guidi, T.; Goremychkin, E. A.; Klemke, B.; Mânsson, M.

2017-12-01

The magnetic properties of the two-dimensional, S =1 honeycomb antiferromagnet BaNi2V2O8 have been comprehensively studied using dc susceptibility measurements and inelastic neutron scattering techniques. The magnetic excitation spectrum is found to be dispersionless within experimental resolution between the honeycomb layers, while it disperses strongly within the honeycomb plane where it consists of two gapped spin-wave modes. The magnetic excitations are compared to linear spin-wave theory allowing the Hamiltonian to be determined. The first- and second-neighbor magnetic exchange interactions are antiferromagnetic and lie within the ranges 10.90 meV ≤Jn≤13.35 meV and 0.85 meV ≤Jn n≤1.65 meV, respectively. The interplane coupling Jout is four orders of magnitude weaker than the intraplane interactions, confirming the highly two-dimensional magnetic behavior of this compound. The sizes of the energy gaps are used to extract the magnetic anisotropies and reveal substantial easy-plane anisotropy and a very weak in-plane easy-axis anisotropy. Together these results reveal that BaNi2V2O8 is a candidate compound for the investigation of vortex excitations and Berezinsky-Kosterliz-Thouless phenomenon.

Sorption characteristics of honeycomb type sorption element composed of organic sorbent; Yukikei shuchakuzai wo tofushita honeycomb jo shuchaku element nio shuchaku tokuse

Energy Technology Data Exchange (ETDEWEB)

Inaba, H.; Horibe, A. [Okayama University, Okayama (Japan); Kida, T.; Kaneda, M. [Japan Exlan Co. Ltd., Osaka (Japan)

2000-12-25

This paper has dealt with the sorption characteristics of honeycomb shape type sorbent element composed of new organic sorbent which was composed of the bridged complex of sodium polyacrylate. The transient experiments in which the moist air was passed into the honeycomb type sorbent element were conducted under various conditions of air velocity, temperature, relative-humidity and honeycomb length. As a result, the effective mass transfer coefficient of the organic sorbent sorbing the water-vapor was non-dimensionalized as a function of Reynolds number, modified Stefan number and non-dimensional honeycomb length. (author)

Mechanic properties analysis of quasi-square honeycomb sandwich structure′s core

Directory of Open Access Journals (Sweden)

Guan TONG

2017-12-01

Full Text Available In order to illustrate the relationship between the quasi-square-honeycomb structure and the hexagonal honeycomb structure, after decomposing the quasi-square honeycomb sandwich structure into unique T-shaped cell, the equivalent elastic constants equations of T-shaped cell model are derived respectively by applying Euler beam theory and energy method. At the same time, the quasi-square honeycomb's characteristic structure parameters are substituted into the equivalent elastic constants equations which are derived by the classical method of a hexagonal honeycomb core, and the same results are obtained as that of the preceding both methods. It is proved that the quasi-square-honeycomb structure is an evolution of hexagonal honeycomb. The limitations and application scope of the two classical honeycomb formulas are pointed out. The research of the structural characteristics of the square-shaped honeycomb shows that the classical cellular theoretical formula are singular and inaccurate when the feature angle values equal to zero or near zero. This study has important reference value for the subsequent research and improvement of the theories about cellular structure mechanical properties.

The Honeycomb Strip Chamber

International Nuclear Information System (INIS)

Graaf, Harry van der; Buskens, Joop; Rewiersma, Paul; Koenig, Adriaan; Wijnen, Thei

1991-06-01

The Honeycomb Strip Chamber (HSC) is a new position sensitive detector. It consists of a stack of folded foils, forming a rigid honeycomb structure. In the centre of each hexagonal cell a wire is strung. Conducting strips on the foils, perpendicular to the wires, pick up the induced avalanche charge. Test results of a prototype show that processing the signals form three adjacent strips nearest to the track gives a spatial resolution better than 64 μm for perpendicular incident tracks. The chamber performance is only slightly affected by a magnetic field. (author). 25 refs.; 21 figs

The buckling transition of two-dimensional elastic honeycombs: numerical simulation and Landau theory

International Nuclear Information System (INIS)

Jagla, E A

2004-01-01

I study the buckling transition under compression of a two-dimensional, hexagonal, regular elastic honeycomb. Under isotropic compression, the system buckles to a configuration consisting of a unit cell containing four of the original hexagons. This buckling pattern preserves the sixfold rotational symmetry of the original lattice but is chiral, and can be described as a combination of three different elemental distortions in directions rotated by 2π/3 from each other. Non-isotropic compression may induce patterns consisting of a single elemental distortion or a superposition of two of them. The numerical results compare very well with the outcome of a Landau theory of second-order phase transitions

A comparison of mechanical properties of some foams and honeycombs

Science.gov (United States)

Bhat, Balakrishna T.; Wang, T. G.

1990-01-01

A comparative study is conducted of the mechanical properties of foam-core and honeycomb-core sandwich panels, using a normalizing procedure based on common properties of cellular solids and related properties of dense solids. Seven different honeycombs and closed-foam cells are discussed; of these, three are commercial Al alloy honeycombs, one is an Al-alloy foam, and two are polymeric foams. It is concluded that ideal, closed-cell foams may furnish compressive strengths which while isotropic can be fully comparable to the compressive strengths of honeycombs in the thickness direction. The shear strength of ideal closed-cell foams may be superior to the shear strength of honeycombs.

Mixed spin-((1)/(2)) and spin-1 Blume-Capel Ising ferrimagnetic system on the Bethe lattice

International Nuclear Information System (INIS)

Albayrak, Erhan; Keskin, Mustafa

2003-01-01

The mixed spin-((1)/(2)) and spin-1 Blume-Capel Ising ferrimagnetic system is studied on the Bethe lattice by using the exact recursion equations. Exact expressions for the magnetization, the quadrupolar moment, the Curie temperature and the free energy are found and the phase diagrams are constructed on the Bethe lattice with the coordination numbers q=3, 4, 5 and 6. The existence of a tricritical point is investigated for different values of q. The results are compared with those of other approximate methods and with the exact result on the Bethe lattice by using a discrete nonlinear map and also the exact results that are available for the case of the honeycomb lattice

Design of flexible skin based on a mixed cruciform honeycomb

Science.gov (United States)

Rong, Jiaxin; Zhou, Li

2017-04-01

As the covering of morphing wings, flexible skin is required to provide adequate cooperation deformation, keep the smoothness of the aerodynamic configuration and bear the air load. The non-deformation direction of flexible skin is required to be restrained to keep the smoothness during morphing. This paper studies the deformation mechanisms of a cruciform honeycomb under zero Poisson's ratio constraint. The morphing capacity and in-plane modulus of the cruciform honeycomb are improved by optimizing the shape parameters of honeycomb unit. To improve the out-of-plane bending capacity, a zero Poisson's ratio mixed cruciform honeycomb is proposed by adding ribs into cruciform honeycomb, which can be used as filling material of flexible skin. The mechanical properties of the mixed honeycomb are studied by theoretical analysis and simulation. The local deformation of flexible skin under air load is also analyzed. Targeting the situation of non-uniform air load, a gradient density design scheme is referred. According to the design requirements of the variable camber trailing edge wing flexible skin, the specific design parameters and performance parameters of the skin based on the mixed honeycomb are given. The results show that the zero Poisson's ratio mixed cruciform honeycomb has a large bending rigidity itself and can have a better deformation capacity in-plane and a larger bending rigidity out-of-plane by optimizing the shape parameters. Besides, the designed skin also has advantages in driving force, deformation capacity and quality compared with conventional skin.

Gauge field entanglement in Kitaev's honeycomb model

Science.gov (United States)

Dóra, Balázs; Moessner, Roderich

2018-01-01

A spin fractionalizes into matter and gauge fermions in Kitaev's spin liquid on the honeycomb lattice. This follows from a Jordan-Wigner mapping to fermions, allowing for the construction of a minimal entropy ground-state wave function on the cylinder. We use this to calculate the entanglement entropy by choosing several distinct partitionings. First, by partitioning an infinite cylinder into two, the -ln2 topological entanglement entropy is reconfirmed. Second, the reduced density matrix of the gauge sector on the full cylinder is obtained after tracing out the matter degrees of freedom. This allows for evaluating the gauge entanglement Hamiltonian, which contains infinitely long-range correlations along the symmetry axis of the cylinder. The matter-gauge entanglement entropy is (Ny-1 )ln2 , with Ny the circumference of the cylinder. Third, the rules for calculating the gauge sector entanglement of any partition are determined. Rather small correctly chosen gauge partitions can still account for the topological entanglement entropy in spite of long-range correlations in the gauge entanglement Hamiltonian.

Dirac Magnons in Honeycomb Ferromagnets

Directory of Open Access Journals (Sweden)

Sergey S. Pershoguba

2018-01-01

Full Text Available The discovery of the Dirac electron dispersion in graphene [A. H. Castro Neto, et al., The Electronic Properties of Graphene, Rev. Mod. Phys. 81, 109 (2009RMPHAT0034-686110.1103/RevModPhys.81.109] led to the question of the Dirac cone stability with respect to interactions. Coulomb interactions between electrons were shown to induce a logarithmic renormalization of the Dirac dispersion. With a rapid expansion of the list of compounds and quasiparticle bands with linear band touching [T. O. Wehling, et al., Dirac Materials, Adv. Phys. 63, 1 (2014ADPHAH0001-873210.1080/00018732.2014.927109], the concept of bosonic Dirac materials has emerged. We consider a specific case of ferromagnets consisting of van der Waals-bonded stacks of honeycomb layers, e.g., chromium trihalides CrX_{3} (X=F, Cl, Br and I, that display two spin wave modes with energy dispersion similar to that for the electrons in graphene. At the single-particle level, these materials resemble their fermionic counterparts. However, how different particle statistics and interactions affect the stability of Dirac cones has yet to be determined. To address the role of interacting Dirac magnons, we expand the theory of ferromagnets beyond the standard Dyson theory [F. J. Dyson, General Theory of Spin-Wave Interactions, Phys. Rev. 102, 1217 (1956PHRVAO0031-899X10.1103/PhysRev.102.1217, F. J. Dyson, Thermodynamic Behavior of an Ideal Ferromagnet, Phys. Rev. 102, 1230 (1956PHRVAO0031-899X10.1103/PhysRev.102.1230] to the case of non-Bravais honeycomb layers. We demonstrate that magnon-magnon interactions lead to a significant momentum-dependent renormalization of the bare band structure in addition to strongly momentum-dependent magnon lifetimes. We show that our theory qualitatively accounts for hitherto unexplained anomalies in nearly half-century-old magnetic neutron-scattering data for CrBr_{3} [W. B. Yelon and R. Silberglitt, Renormalization of Large-Wave-Vector Magnons in

Dirac Magnons in Honeycomb Ferromagnets

Science.gov (United States)

Pershoguba, Sergey S.; Banerjee, Saikat; Lashley, J. C.; Park, Jihwey; Ågren, Hans; Aeppli, Gabriel; Balatsky, Alexander V.

2018-01-01

The discovery of the Dirac electron dispersion in graphene [A. H. Castro Neto, et al., The Electronic Properties of Graphene, Rev. Mod. Phys. 81, 109 (2009), 10.1103/RevModPhys.81.109] led to the question of the Dirac cone stability with respect to interactions. Coulomb interactions between electrons were shown to induce a logarithmic renormalization of the Dirac dispersion. With a rapid expansion of the list of compounds and quasiparticle bands with linear band touching [T. O. Wehling, et al., Dirac Materials, Adv. Phys. 63, 1 (2014), 10.1080/00018732.2014.927109], the concept of bosonic Dirac materials has emerged. We consider a specific case of ferromagnets consisting of van der Waals-bonded stacks of honeycomb layers, e.g., chromium trihalides CrX3 (X =F , Cl, Br and I), that display two spin wave modes with energy dispersion similar to that for the electrons in graphene. At the single-particle level, these materials resemble their fermionic counterparts. However, how different particle statistics and interactions affect the stability of Dirac cones has yet to be determined. To address the role of interacting Dirac magnons, we expand the theory of ferromagnets beyond the standard Dyson theory [F. J. Dyson, General Theory of Spin-Wave Interactions, Phys. Rev. 102, 1217 (1956), 10.1103/PhysRev.102.1217, F. J. Dyson, Thermodynamic Behavior of an Ideal Ferromagnet, Phys. Rev. 102, 1230 (1956), 10.1103/PhysRev.102.1230] to the case of non-Bravais honeycomb layers. We demonstrate that magnon-magnon interactions lead to a significant momentum-dependent renormalization of the bare band structure in addition to strongly momentum-dependent magnon lifetimes. We show that our theory qualitatively accounts for hitherto unexplained anomalies in nearly half-century-old magnetic neutron-scattering data for CrBr3 [W. B. Yelon and R. Silberglitt, Renormalization of Large-Wave-Vector Magnons in Ferromagnetic CrBr3 Studied by Inelastic Neutron Scattering: Spin-Wave Correlation

The ferromagnetic Kondo-lattice compound SmFe sub 4 P sub 1 sub 2

CERN Document Server

Takeda, N

2003-01-01

We report on the magnetic properties of a filled skutterudite compound, SmFe sub 4 P sub 1 sub 2. Magnetic susceptibility and specific heat measurements revealed a ferromagnetic transition at 1.6 K. The temperature dependence of the electrical resistivity exhibits a Kondo-lattice behaviour and the electronic specific heat coefficient attains values as large as 370 mJ mol sup - sup 1 K sup - sup 2. This compound is thereby the first Sm-based heavy-fermion system found with a ferromagnetic ground state. The Kondo temperature is estimated to be about 30 K. (letter to the editor)

Lattice dynamics and electronic properties of superconducting Nbsub(x)Vsub(1-x)N compounds

International Nuclear Information System (INIS)

Geibel, C.; Rietschel, H.; Pelizzone, M.; Junod, A.; Muller, J.

1982-01-01

The Nbsub(x)Vsub(1-x)N-system presents a pronounced minimum in Tsub(c) at the composition Nbsub(0.5)Vsub(0.5)N. We investigated the structural, the electronic properties and the lattice dynamics of these compounds to study whether this minimum is induced by structural defects, a decrease of the electron-phonon-coupling or by spin fluctuations. (orig.)

Spot Welding of Honeycomb Structures

Science.gov (United States)

Cohal, V.

2017-08-01

Honeycomb structures are used to prepare meals water jet cutting machines for textile. These honeycomb structures are made of stainless steel sheet thickness of 0.1-0.2 mm. Corrugated sheet metal strips are between two gears with special tooth profile. Hexagonal cells for obtaining these strips are welded points between them. Spot welding device is three electrodes in the upper part, which carries three welding points across the width of the strip of corrugated sheet metal. Spot welding device filled with press and advance mechanisms. The paper presents the values of the regime for spot welding.

Lattice parameters and stability of the spinel compounds in relation to the ionic radii and electronegativities of constituting chemical elements.

Science.gov (United States)

Brik, Mikhail G; Suchocki, Andrzej; Kamińska, Agata

2014-05-19

A thorough consideration of the relation between the lattice parameters of 185 binary and ternary spinel compounds, on one side, and ionic radii and electronegativities of the constituting ions, on the other side, allowed for establishing a simple empirical model and finding its linear equation, which links together the above-mentioned quantities. The derived equation gives good agreement between the experimental and modeled values of the lattice parameters in the considered group of spinels, with an average relative error of about 1% only. The proposed model was improved further by separate consideration of several groups of spinels, depending on the nature of the anion (oxygen, sulfur, selenium/tellurium, nitrogen). The developed approach can be efficiently used for prediction of lattice constants for new isostructural materials. In particular, the lattice constants of new hypothetic spinels ZnRE2O4, CdRE2S4, CdRE2Se4 (RE = rare earth elements) are predicted in the present Article. In addition, the upper and lower limits for the variation of the ionic radii, electronegativities, and their certain combinations were established, which can be considered as stability criteria for the spinel compounds. The findings of the present Article offer a systematic overview of the structural properties of spinels and can serve as helpful guides for synthesis of new spinel compounds.

Signatures of lattice geometry in quantum and topological Hall effect

International Nuclear Information System (INIS)

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

2017-01-01

The topological Hall effect (THE) of electrons in skyrmion crystals (SkXs) is strongly related to the quantum Hall effect (QHE) on lattices. This relation suggests to revisit the QHE because its Hall conductivity can be unconventionally quantized. It exhibits a jump and changes sign abruptly if the Fermi level crosses a van Hove singularity. In this Paper, we investigate the unconventional QHE features by discussing band structures, Hall conductivities, and topological edge states for square and triangular lattices; their origin are Chern numbers of bands in the SkX (THE) or of the corresponding Landau levels (QHE). Striking features in the energy dependence of the Hall conductivities are traced back to the band structure without magnetic field whose properties are dictated by the lattice geometry. Based on these findings, we derive an approximation that allows us to determine the energy dependence of the topological Hall conductivity on any two-dimensional lattice. The validity of this approximation is proven for the honeycomb lattice. We conclude that SkXs lend themselves for experiments to validate our findings for the THE and—indirectly—the QHE. (paper)

Honeycombing on CT; its definition, pathologic correlation, and future direction of its diagnosis

Energy Technology Data Exchange (ETDEWEB)

Johkoh, Takeshi, E-mail: johkoht@aol.com [Department of Radiology, Kinki Central Hospital of Mutual Aid Association of Public School Teachers, 3-1 Kurumazuka, Itami, Hyogo, 664-8533 (Japan); Sakai, Fumikazu [Department of Diagnostic Radiology, Saitama International Medical Center, Saitama Medical University, Hidaka (Japan); Noma, Satoshi [Department of Radiology, Tenri Hospital, Tenri (Japan); Akira, Masanori [Department of Radiology, National Hospital Organization Kinki-Chuo Chest Medical Center, Sakai (Japan); Fujimoto, Kiminori [Department of Radiology and Center for Diagnostic Imaging, Kurume University School of Medicine, Kurume (Japan); Watadani, Takeyuki [Department of Radiology, University of Tokyo, Tokyo (Japan); Sugiyama, Yukihiko [Department of Internal Medicine, Jichi Medical University, Shimotsuke (Japan)

2014-01-15

Honeycombing on CT is the clue for the diagnosis of usual interstitial pneumonia (UIP) and its hallmark. According to the ATS-ERS-JRS-ALAT 2010 guideline, the patients with honeycombing on CT can be diagnosed as UIP without surgical biopsy. On CT scans, it is defined as clustered cystic airspaces, typically of comparable diameters of the order of 3–10 mm, which are usually subpleural and have well-defined walls. Pathologically, honeycombing consists of both collapsing of multiple fibrotic alveoli and dilation of alveolar duct and lumen Although the definition of honeycombing seems to be strict, recognition of honeycombing on CT is various among each observer Because typical honeycombing is frequently observed in the patients with UIP, we should judge clustered cysts as honeycombing when a diagnosis of UIP is suspected.

Neutron scattering in chemistry (scattering from layer lattices and their intercalation compounds - an illustration)

International Nuclear Information System (INIS)

White, J.W.

1983-01-01

Three cases of molecules on a free surface or inside layer lattice intercalation compounds are discussed to illustrate the use of neutron scattering techniques. The first is the second stage alkali metal-graphite intercalation compounds such as C 24 Cs which adsorb hydrogen, methane and other gases. The second case is methane physisorbed on the basal plane of graphite where the methane-methane interactions are relatively strong. Rotational tunnelling spectroscopy is sensitive to the parameters of the potential. The third case is that of water physisorbed on clay materials such as vermiculite or montmorillonite where the layer thickness can be changed from one to fifty layers. (UK)

Double-Lap Shear Test For Honeycomb Core

Science.gov (United States)

Nettles, Alan T.; Hodge, Andrew J.

1992-01-01

Double-lap test measures shear strength of panel made of honeycomb core with 8-ply carbon-fiber/epoxy face sheets. Developed to overcome three principal disadvantages of prior standard single-lap shear test: specimen had to be more than 17 in. long; metal face sheets had to be used; and test introduced torque, with consequent bending and peeling of face sheets and spurious tensile or compressive loading of honeycomb.

Directed self-assembly of large scaffold-free multi-cellular honeycomb structures

International Nuclear Information System (INIS)

Tejavibulya, Nalin; Youssef, Jacquelyn; Bao, Brian; Ferruccio, Toni-Marie; Morgan, Jeffrey R

2011-01-01

A significant challenge to the field of biofabrication is the rapid construction of large three-dimensional (3D) living tissues and organs. Multi-cellular spheroids have been used as building blocks. In this paper, we create large multi-cellular honeycomb building blocks using directed self-assembly, whereby cell-to-cell adhesion, in the context of the shape and obstacles of a micro-mold, drives the formation of a 3D structure. Computer-aided design, rapid prototyping and replica molding were used to fabricate honeycomb-shaped micro-molds. Nonadhesive hydrogels cast from these micro-molds were equilibrated in the cell culture medium and seeded with two types of mammalian cells. The cells settled into the honeycomb recess were unable to attach to the nonadhesive hydrogel and so cell-to-cell adhesion drove the self-assembly of a large multi-cellular honeycomb within 24 h. Distinct morphological changes occurred to the honeycomb and its cells indicating the presence of significant cell-mediated tension. Unlike the spheroid, whose size is constrained by a critical diffusion distance needed to maintain cell viability, the overall size of the honeycomb is not limited. The rapid production of the honeycomb building unit, with its multiple rings of high-density cells and open lumen spaces, offers interesting new possibilities for biofabrication strategies.

Active inflatable auxetic honeycomb structural concept for morphing wingtips

International Nuclear Information System (INIS)

Sun, Jian; Leng, Jinsong; Gao, Hongliang; Liu, Yanju; Scarpa, Fabrizio; Lira, Cristian

2014-01-01

This paper describes a new concept of an active honeycomb structure for morphing wingtip applications based on tubular inflatable systems and an auxetic cellular structure. A work-energy model to predict the output honeycomb displacement versus input pressure is developed together with a finite element formulation, and the results are compared with the data obtained from a small-scale example of an active honeycomb. An analysis of the hysteresis associated with multiple cyclic loading is also provided, and design considerations for a larger-scale wingtip demonstrator are made. (paper)

Mechanics and applications of pressure adaptive honeycomb

Science.gov (United States)

Vos, Roelof

A novel adaptive aerostructure is presented that relies on certified aerospace materials and can therefore be applied in conventional passenger aircraft. This structure consists of a honeycomb material which' cells extend over a significant length perpendicular to the plane of the cells. Each of the cells contains an inelastic pouch (or bladder) that forms a circular tube when the cell forms a perfect hexagon. By changing the cell differential pressure (CDP) the stiffness of the honeycomb can be altered. Using an external force or the elastic force within the honeycomb material, the honeycomb can be deformed such that the cells deviate from their perfect-hexagonal shape. It can be shown that by increasing the CDP, the structure eventually returns to a perfect hexagon. By doing so, a fully embedded pneumatic actuator is created that can perform work and substitute conventional low-bandwidth flight control actuators. It is shown that two approaches can be taken to regulate the stiffness of this embedded actuator: (1) The first approach relies on the pouches having a fixed amount of air in them and stiffness is altered by a change in ambient pressure. Coupled to the ambient pressure-altitude cycle that aircraft encounter during each flight, this approach yields a true adaptive aerostructure that operates independently of pilot input and is controlled solely by the altitude the aircraft is flying at. (2) The second approach relies on a controlled constant CDP. This CDP could be supplied from one of the compressor stages of the engine as a form of bleed air. Because of the air-tight pouches there would essentially be no mass flow, meaning engine efficiency would not be significantly affected due to this application. By means of a valve system the pilot could have direct control over the pressure and, consequently, the stiffness of the structure. This allows for much higher CDPs (on the order of 1MPa) than could physically be achieved by relying on the ambient pressure

Study of a zero Poisson’s ratio honeycomb used for flexible skin

Science.gov (United States)

Rong, Jiaxin; Zhou, Li

2017-04-01

Flexible skin used in morphing wings is required to provide adequate cooperation deformation as well as bear the air load. Besides, according to the requirement of smoothness, the non-deformation direction of flexible skin needs to be restrained. This paper studies the mechanical properties of a cruciform honeycomb under a zero Poisson’s ratio constraint. The in-plane morphing capacity of the honeycomb is improved by optimizing the shape parameters of the honeycomb unit. To improve the out-of-plane bending capacity, a zero Poisson’s ratio mixed cruciform honeycomb with additional ribs is proposed. The mechanical properties of the mixed honeycomb are studied by theoretical analysis and simulation. Based on the design requirements of variable-camber trailing-edge flexible skin, the specific design parameters and performance parameters of the skin based on the mixed honeycomb are given. The results show that the zero Poisson’s ratio mixed cruciform honeycomb has high bending rigidity itself and can have better deformation capacity in-plane and higher bending rigidity out-of-plane by optimizing the shape parameters. The designed skin also has advantages in driving force, deformation capacity and quality over conventional skin.

Modal analysis and acoustic transmission through offset-core honeycomb sandwich panels

Science.gov (United States)

Mathias, Adam Dustin

The work presented in this thesis is motivated by an earlier research that showed that double, offset-core honeycomb sandwich panels increased thermal resistance and, hence, decreased heat transfer through the panels. This result lead to the hypothesis that these panels could be used for acoustic insulation. Using commercial finite element modeling software, COMSOL Multiphysics, the acoustical properties, specifically the transmission loss across a variety of offset-core honeycomb sandwich panels, is studied for the case of a plane acoustic wave impacting the panel at normal incidence. The transmission loss results are compared with those of single-core honeycomb panels with the same cell sizes. The fundamental frequencies of the panels are also computed in an attempt to better understand the vibrational modes of these particular sandwich-structured panels. To ensure that the finite element analysis software is adequate for the task at hand, two relevant benchmark problems are solved and compared with theory. Results from these benchmark results compared well to those obtained from theory. Transmission loss results from the offset-core honeycomb sandwich panels show increased transmission loss, especially for large cell honeycombs when compared to single-core honeycomb panels.

Polarized-neutron investigation of magnetic ordering and spin dynamics in BaCo2(AsO42 frustrated honeycomb-lattice magnet

Directory of Open Access Journals (Sweden)

L.-P. Regnault

2018-01-01

Full Text Available The magnetic properties of the cobaltite BaCo2(AsO42, a good realization of the quasi two-dimensional frustrated honeycomb-lattice system with strong planar anisotropy, have been reinvestigated by means of spherical neutron polarimetry with CRYOPAD. From accurate measurements of polarization matrices both on elastic and inelastic contributions as a function of the scattering vector Q, we have been able to determine the low-temperature magnetic structure of BaCo2(AsO42 and reveal its puzzling in-plane spin dynamics. Surprisingly, the ground-state structure (described by an incommensurate propagation vector k1=(kx,0,kz, with kx=0.270±0.005 and kz≈−1.31 appears to be a quasi-collinear structure, and not a simple helix, as previously determined. In addition, our results have revealed the existence of a non-negligible out-of-plane moment component ≈0.25μB/Co2+, representing about 10% of the in-plane component, as demonstrated by the presence of finite off-diagonal elements Pyz and Pzy of the polarization matrix, both on elastic and inelastic magnetic contributions. Despite a clear evidence of the existence of a slightly inelastic contribution of structural origin superimposed to the magnetic excitations at the scattering vectors Q=(0.27,0,3.1 and Q=(0.73,0,0.8 (energy transfer ΔE≈2.3 meV, no strong inelastic nuclear-magnetic interference terms could be detected so far, meaning that the nuclear and magnetic degrees of freedom have very weak cross-correlations. The strong inelastic Pyz and Pzy matrix elements can be understood by assuming that the magnetic excitations in BaCo2(AsO42 are spin waves associated with trivial anisotropic precessions of the magnetic moments involved in the canted incommensurate structure.

Origin of honeycombs: Testing the hydraulic and case hardening hypotheses

Science.gov (United States)

Bruthans, Jiří; Filippi, Michal; Slavík, Martin; Svobodová, Eliška

2018-02-01

Cavernous weathering (cavernous rock decay) is a global phenomenon, which occurs in porous rocks around the world. Although honeycombs and tafoni are considered to be the most common products of this complex process, their origin and evolution are as yet not fully understood. The two commonly assumed formation hypotheses - hydraulic and case hardening - were tested to elucidate the origin of honeycombs on sandstone outcrops in a humid climate. Mechanical and hydraulic properties of the lips (walls between adjacent pits) and backwalls (bottoms of pits) of the honeycombs were determined via a set of established and novel approaches. While the case hardening hypothesis was not supported by the determinations of either tensile strength, drilling resistance or porosity, the hydraulic hypothesis was clearly supported by field measurements and laboratory tests. Fluorescein dye visualization of capillary zone, vapor zone, and evaporation front upon their contact, demonstrated that the evaporation front reaches the honeycomb backwalls under low water flow rate, while the honeycomb lips remain dry. During occasional excessive water flow events, however, the evaporation front may shift to the lips, while the backwalls become moist as a part of the capillary zone. As the zone of evaporation corresponds to the zone of potential salt weathering, it is the spatial distribution of the capillary and vapor zones which dictates whether honeycombs are created or the rock surface is smoothed. A hierarchical model of factors related to the hydraulic field was introduced to obtain better insights into the process of cavernous weathering.

Lattice dynamics of intercalation and layer compounds by 119Sn Moessbauer effect spectroscopy

International Nuclear Information System (INIS)

Herber, R.H.; Davis, R.F.

1976-01-01

Gamma ray resonance spectroscopy using the 28-keV radiation from 119 Sn was employed to study the lattice dynamics of layer compounds and their metal atom intercalates. It was found that in solids in which the ( 119 Sn) Moessbauer atom is held either as an ion or as an isolated atom in the structure, both the characteristic lattice temperature (THETA/sub M/) value calculated from the temperature dependence of the recoil-free fraction (evaluated in the high temperature limit where T is greater than THETA/2 and in the absence of significant anharmonic effects) and characteristic temperature (THETA/sub CT/) value calculated by the Craig-Taylor procedure give internally consistent values for the lattice temperature of the solid as probed by the Moessbauer atom. In cases where this probe atom is part of a covalently bonded structure, as for example in the extended polymeric SnS 2 , SnSe 2 and related solids, the difference between THETA/sub M/ and THETA/sub CT/ will be significant, and this difference should be useful in the elucidation of the intermolecular and bonding forces in such solids and their relationship to the solid state properties of these materials. It is noted that the experimental determination of a unique lattice temperature by Moessbauer spectroscopic methods provides the solid state physicist with an additional parameter which should be useful in the characterization of solids, and, more importantly, may serve as a diagnostic tool in the assessment of the effects of systematic changes (such as, for example, compositional variations, radiation damage effects, implantation, and intercalation consequences) brought about in such materials

Enhanced xylene removal by photocatalytic oxidation using fiber-illuminated honeycomb reactor at ppb level

International Nuclear Information System (INIS)

Wu, Yi-Ting; Yu, Yi-Hui; Nguyen, Van-Huy; Lu, Kung-Te; Wu, Jeffrey Chi-Sheng; Chang, Luh-Maan; Kuo, Chi-Wen

2013-01-01

Graphical abstract: We have designed a fiber-illuminated honeycomb reactor (FIHR) in which the removal efficiency of m-xylene is significantly enhanced to 96.5% as compared to 22.0% for UV irradiation only. The results indicate that photocatalysts not only play the role to substantially oxidize m-xylene, but also alter the chemical properties of xylene under UV illumination. -- Highlights: • The combination of optical fiber and honeycomb significantly enhanced the performance of VOCs photodegradation. • The removal efficiency of m-xylene is enhanced to 96.5% as compared to 22.0% for UV irradiation alone. • Fiber-illuminated honeycomb reactor is the first step toward an industrial-scale technology on the removal of xylene. -- Abstract: The removal of volatile organic compounds (VOCs) at ppb level is one of the most critical challenges in clean rooms for the semiconductor industry. Photocatalytic oxidation is an innovative and promising technology for ppb-level VOCs degradation. We have designed a fiber-illuminated honeycomb reactor (FIHR) in which the removal efficiency of m-xylene is significantly enhanced to 96.5% as compared to 22.0% for UV irradiation only. The results indicate that photocatalysts not only play the role to substantially oxidize m-xylene, but also alter the chemical properties of xylene under UV illumination. Using the FIHR with Mn-TiO 2 photocatalyst not only increased the m-xylene removal efficiency, but also increased the CO 2 selectivity. Interestingly, Mn-TiO 2 in FIHR also showed a very good reusability, 93% removal efficiency was still achieved in 72-h in reaction. Thus, the FIHR gave very high removal efficiency for xylene at ppb level under room temperature. The FIHR has great potential application in the clean room for the air purification system in the future

Enhanced xylene removal by photocatalytic oxidation using fiber-illuminated honeycomb reactor at ppb level

Energy Technology Data Exchange (ETDEWEB)

Wu, Yi-Ting [Department of Chemical Engineering, National Taiwan University, Taipei 10617, Taiwan (China); Yu, Yi-Hui [Department of Civil Engineering, National Taiwan University, Taipei 106, Taiwan (China); Nguyen, Van-Huy [Department of Chemical Engineering, National Taiwan University of Science and Technology, Taipei 10617, Taiwan (China); Lu, Kung-Te [Department of Chemical Engineering, National Taiwan University, Taipei 10617, Taiwan (China); Wu, Jeffrey Chi-Sheng, E-mail: cswu@ntu.edu.tw [Department of Chemical Engineering, National Taiwan University, Taipei 10617, Taiwan (China); Chang, Luh-Maan [Department of Civil Engineering, National Taiwan University, Taipei 106, Taiwan (China); Kuo, Chi-Wen [Taiwan Semiconductor Manufacturing Company, Hsinchu 30078, Taiwan (China)

2013-11-15

Graphical abstract: We have designed a fiber-illuminated honeycomb reactor (FIHR) in which the removal efficiency of m-xylene is significantly enhanced to 96.5% as compared to 22.0% for UV irradiation only. The results indicate that photocatalysts not only play the role to substantially oxidize m-xylene, but also alter the chemical properties of xylene under UV illumination. -- Highlights: • The combination of optical fiber and honeycomb significantly enhanced the performance of VOCs photodegradation. • The removal efficiency of m-xylene is enhanced to 96.5% as compared to 22.0% for UV irradiation alone. • Fiber-illuminated honeycomb reactor is the first step toward an industrial-scale technology on the removal of xylene. -- Abstract: The removal of volatile organic compounds (VOCs) at ppb level is one of the most critical challenges in clean rooms for the semiconductor industry. Photocatalytic oxidation is an innovative and promising technology for ppb-level VOCs degradation. We have designed a fiber-illuminated honeycomb reactor (FIHR) in which the removal efficiency of m-xylene is significantly enhanced to 96.5% as compared to 22.0% for UV irradiation only. The results indicate that photocatalysts not only play the role to substantially oxidize m-xylene, but also alter the chemical properties of xylene under UV illumination. Using the FIHR with Mn-TiO{sub 2} photocatalyst not only increased the m-xylene removal efficiency, but also increased the CO{sub 2} selectivity. Interestingly, Mn-TiO{sub 2} in FIHR also showed a very good reusability, 93% removal efficiency was still achieved in 72-h in reaction. Thus, the FIHR gave very high removal efficiency for xylene at ppb level under room temperature. The FIHR has great potential application in the clean room for the air purification system in the future.

3D Energy Absorption Diagram Construction of Paper Honeycomb Sandwich Panel

Directory of Open Access Journals (Sweden)

Dongmei Wang

2018-01-01

Full Text Available Paper honeycomb sandwich panel is an environment-sensitive material. Its cushioning property is closely related to its structural factors, the temperature and humidity, random shocks, and vibration events in the logistics environment. In order to visually characterize the cushioning property of paper honeycomb sandwich panel in different logistics conditions, the energy absorption equation of per unit volume of paper honeycomb sandwich panel was constructed by piecewise function. The three-dimensional (3D energy absorption diagram of paper honeycomb sandwich panel was constructed by connecting the inflexion of energy absorption curve. It takes into account the temperature, humidity, strain rate, and characteristics of the honeycomb structure. On the one hand, this diagram breaks through the limitation of the static compression curve of paper honeycomb sandwich panel, which depends on the test specimen and is applicable only to the standard condition. On the other hand, it breaks through the limitation of the conventional 2D energy absorption diagram which has less information. Elastic modulus was used to normalize the plateau stress and energy absorption per unit volume. This makes the 3D energy absorption diagram universal for different material sandwich panels. It provides a new theoretical basis for packaging optimized design.

Magnetization and vortex profiles in the honeycomb network of Pb

International Nuclear Information System (INIS)

Yoshikawa, Hirokazu; Noda, Hiroshi; Sato, Osamu; Kato, Masaru; Satoh, Kazuo; Yotsuya, Tsutomu; Ishida, Takekazu

2005-01-01

We have investigated a honeycomb microhole network of Pb film by a SQUID magnetometer and a SQUID microscope. A negative pattern of honeycomb network of photoresist has been fabricated by an electron beam lithography. A film of 200-nm thickness was prepared by the evaporation of Pb on the photoresist pattern, where the silicon substrate is 4 x 4 mm in size. The period of the network is 7.4 μm and line width is 1 μm. We found the matching effect in a M-H curve of the Pb honeycomb network by the SQUID magnetometer. The applied field ranges from -4.7 G to +4.7 G. Vortex configurations in the honeycomb network of the period 15 μm and line width 2 μm have also been observed by the SQUID microscope. We suggest that vortices form some local triangular configurations at lower temperatures

A Maximum Entropy Approach to Assess Debonding in Honeycomb aluminum Plates

Directory of Open Access Journals (Sweden)

Viviana Meruane

2014-05-01

Full Text Available Honeycomb sandwich structures are used in a wide variety of applications. Nevertheless, due to manufacturing defects or impact loads, these structures can be subject to imperfect bonding or debonding between the skin and the honeycomb core. The presence of debonding reduces the bending stiffness of the composite panel, which causes detectable changes in its vibration characteristics. This article presents a new supervised learning algorithm to identify debonded regions in aluminum honeycomb panels. The algorithm uses a linear approximation method handled by a statistical inference model based on the maximum-entropy principle. The merits of this new approach are twofold: training is avoided and data is processed in a period of time that is comparable to the one of neural networks. The honeycomb panels are modeled with finite elements using a simplified three-layer shell model. The adhesive layer between the skin and core is modeled using linear springs, the rigidities of which are reduced in debonded sectors. The algorithm is validated using experimental data of an aluminum honeycomb panel under different damage scenarios.

Design and analysis of adaptive honeycomb structure with pneumatic muscle fibers

Science.gov (United States)

Yin, Weilong; Tian, Dongkui; Chen, Yijin

2012-04-01

The adaptive honeycomb structure actuated by pneumatic muscle fibers is proposed in this paper. The FE model of adaptive honeycomb structure is developed by use of ANSYS software. The elastics modulus of the developed pneumatic muscle fibers is experimentally determined and their output force is tested. The results show that the contraction ratio of the pneumatic muscle fibers with inner diameter of 2mm could reach up to 26.8% and the force could reach to a value of 27N when the applied pressure is 0.4MPa and the contraction ratio is zero. When the adaptive honeycomb has a certain load and an effective output displacement, the applied force must be greater than a certain value. The adaptive honeycomb must be consumed extra energy when the output displacement and force are produced.

Polarized-neutron investigation of magnetic ordering and spin dynamics in BaCo2(AsO4)2 frustrated honeycomb-lattice magnet.

Science.gov (United States)

Regnault, L-P; Boullier, C; Lorenzo, J E

2018-01-01

The magnetic properties of the cobaltite BaCo 2 (AsO 4 ) 2 , a good realization of the quasi two-dimensional frustrated honeycomb-lattice system with strong planar anisotropy, have been reinvestigated by means of spherical neutron polarimetry with CRYOPAD. From accurate measurements of polarization matrices both on elastic and inelastic contributions as a function of the scattering vector Q , we have been able to determine the low-temperature magnetic structure of BaCo 2 (AsO 4 ) 2 and reveal its puzzling in-plane spin dynamics. Surprisingly, the ground-state structure (described by an incommensurate propagation vector [Formula: see text], with [Formula: see text] and [Formula: see text]) appears to be a quasi-collinear structure, and not a simple helix, as previously determined. In addition, our results have revealed the existence of a non-negligible out-of-plane moment component [Formula: see text]/Co 2+ , representing about 10% of the in-plane component, as demonstrated by the presence of finite off-diagonal elements [Formula: see text] and [Formula: see text] of the polarization matrix, both on elastic and inelastic magnetic contributions. Despite a clear evidence of the existence of a slightly inelastic contribution of structural origin superimposed to the magnetic excitations at the scattering vectors [Formula: see text] and [Formula: see text] (energy transfer [Formula: see text] meV), no strong inelastic nuclear-magnetic interference terms could be detected so far, meaning that the nuclear and magnetic degrees of freedom have very weak cross-correlations. The strong inelastic [Formula: see text] and [Formula: see text] matrix elements can be understood by assuming that the magnetic excitations in BaCo 2 (AsO 4 ) 2 are spin waves associated with trivial anisotropic precessions of the magnetic moments involved in the canted incommensurate structure.

Quantitative CT analysis of honeycombing area in idiopathic pulmonary fibrosis: Correlations with pulmonary function tests.

Science.gov (United States)

Nakagawa, Hiroaki; Nagatani, Yukihiro; Takahashi, Masashi; Ogawa, Emiko; Tho, Nguyen Van; Ryujin, Yasushi; Nagao, Taishi; Nakano, Yasutaka

2016-01-01

The 2011 official statement of idiopathic pulmonary fibrosis (IPF) mentions that the extent of honeycombing and the worsening of fibrosis on high-resolution computed tomography (HRCT) in IPF are associated with the increased risk of mortality. However, there are few reports about the quantitative computed tomography (CT) analysis of honeycombing area. In this study, we first proposed a computer-aided method for quantitative CT analysis of honeycombing area in patients with IPF. We then evaluated the correlations between honeycombing area measured by the proposed method with that estimated by radiologists or with parameters of PFTs. Chest HRCTs and pulmonary function tests (PFTs) of 36 IPF patients, who were diagnosed using HRCT alone, were retrospectively evaluated. Two thoracic radiologists independently estimated the honeycombing area as Identified Area (IA) and the percentage of honeycombing area to total lung area as Percent Area (PA) on 3 axial CT slices for each patient. We also developed a computer-aided method to measure the honeycombing area on CT images of those patients. The total honeycombing area as CT honeycombing area (HA) and the percentage of honeycombing area to total lung area as CT %honeycombing area (%HA) were derived from the computer-aided method for each patient. HA derived from three CT slices was significantly correlated with IA (ρ=0.65 for Radiologist 1 and ρ=0.68 for Radiologist 2). %HA derived from three CT slices was also significantly correlated with PA (ρ=0.68 for Radiologist 1 and ρ=0.70 for Radiologist 2). HA and %HA derived from all CT slices were significantly correlated with FVC (%pred.), DLCO (%pred.), and the composite physiologic index (CPI) (HA: ρ=-0.43, ρ=-0.56, ρ=0.63 and %HA: ρ=-0.60, ρ=-0.49, ρ=0.69, respectively). The honeycombing area measured by the proposed computer-aided method was correlated with that estimated by expert radiologists and with parameters of PFTs. This quantitative CT analysis of

The quantum anomalous Hall effect on a star lattice with spin-orbit coupling and an exchange field

International Nuclear Information System (INIS)

Chen Mengsu; Wan Shaolong

2012-01-01

We study a star lattice with Rashba spin-orbit coupling and an exchange field and find that there is a quantum anomalous Hall effect in this system, and that there are five energy gaps at Dirac points and quadratic band crossing points. We calculate the Berry curvature distribution and obtain the Hall conductivity (Chern number ν) quantized as integers, and find that ν =- 1,2,1,1,2 when the Fermi level lies in these five gaps. Our model can be viewed as a general quantum anomalous Hall system and, in limit cases, can give what the honeycomb lattice and kagome lattice give. We also find that there is a nearly flat band with ν = 1 which may provide an opportunity for realizing the fractional quantum anomalous Hall effect. Finally, the chiral edge states on a zigzag star lattice are given numerically, to confirm the topological property of this system. (paper)

Thermal behavior of laboratory models of honeycomb-covered solar ponds

Science.gov (United States)

Lin, E. I. H.

1983-01-01

Laboratory experiments were conducted to provide insight into the technical feasibility of honeycomb-covered solar ponds. Cooling tests using honeycomb panels of various materials and geometries showed that a 5.7-cm-thick one-tier panel insulated as effectively as a 10-cm fiberglass slab. Heating tests demonstrated that a model pond covered with a polycarbonate panel boiled upon 16 hours of continuous exposure to a 150-W spotlight. Analysis of the experimental data indicates positively that honeycomb-covered solar ponds can be expected to perform satisfactorily, and that larger-scale outdoor tests should be conducted to provide a more realistic assessment and a more refined performance estimate.

Crystal plasticity study of monocrystalline stochastic honeycombs under in-plane compression

International Nuclear Information System (INIS)

Ma, Duancheng; Eisenlohr, Philip; Epler, Eike; Volkert, Cynthia A.; Shanthraj, Pratheek; Diehl, Martin; Roters, Franz; Raabe, Dierk

2016-01-01

We present a study on the plastic deformation of single crystalline stochastic honeycombs under in-plane compression using a crystal plasticity constitutive description for face-centered cubic (fcc) materials, focusing on the very early stage of plastic deformation, and identifying the interplay between the crystallographic orientation and the cellular structure during plastic deformation. We observe that despite the stochastic structure, surprisingly, the slip system activations in the honeycombs are almost identical to their corresponding bulk single crystals at the early stage of the plastic deformation. On the other hand, however, the yield stresses of the honeycombs are nearly independent of their crystallographic orientations. Similar mechanical response is found in compression testing of nanoporous gold micro-pillars aligned with various crystallographic orientations. The macroscopic stress tensors of the honeycombs show the same anisotropy as their respective bulk single crystals. Locally, however, there is an appreciable fluctuation in the local stresses, which are even larger than for polycrystals. This explains why the Taylor/Schmid factor associated with the crystallographic orientation is less useful to estimate the yield stresses of the honeycombs than the bulk single crystals and polycrystals, and why the plastic deformation occurs at smaller strains in the honeycombs than their corresponding bulk single crystals. Besides these findings, the observations of the crystallographic reorientation suggest that conventional orientation analysis tools, such as inverse pole figure and related tools, would in general fail to study the plastic deformation mechanism of monocrystalline cellular materials.

Topotactic synthesis of the overlooked multilayer silicene intercalation compound SrSi2.

Science.gov (United States)

Tokmachev, A M; Averyanov, D V; Karateev, I A; Parfenov, O E; Vasiliev, A L; Yakunin, S N; Storchak, V G

2016-09-28

Silicene, a 2D honeycomb lattice of Si atoms similar to graphene, is expected to be a platform for nanoelectronics and home to novel quantum phenomena. Unlike graphene, free-standing silicene is notoriously difficult to stabilize, while strong hybridization of silicene with substrates destroys its desirable properties. On the other hand, Dirac cones of silicene are effectively realized in a bulk - stoichiometric ionic multilayer silicene intercalation compound CaSi2. Besides, a number of new 2D silicene-based materials are synthesized employing CaSi2 as a precursor. However, the rather complex atomic structure of CaSi2 and fresh opportunities of physical and chemical breakthroughs drive the search for alternative compounds with silicene networks. Here, a new polymorph of SrSi2 is synthesized, enjoying both the structure of intercalated multilayer silicene and the simplest possible stacking of silicene sheets. The MBE-quality synthesis accomplished on Si(001) and Si(111) surfaces leads to epitaxial films of SrSi2 with orientation controlled by the substrate, as revealed by XRD, RHEED and electron microscopy studies. The structural SrSi2/Si relation is mirrored in the transport properties of the films.

Density of states model for the lattice transformation in A-15 compounds

International Nuclear Information System (INIS)

Pietrass, B.; Handstein, A.; Behr, G.

1980-01-01

The cubic-tetragonal lattice transformation in A-15 compounds is described by an empirical model in which the density of states function near the Fermi energy is characterized by a two-parametric peak in addition to the constant part. Two types of peak splitting under tetragonal deformation are considered, leading to qualitatively different results about the phase transition. Results are given for the order parameter, the phase stability, the soft elastic modulus, and the paramagnetic spin susceptibility. Comparing with measurements of the magnetic susceptibility of V 3 Si single crystals near the phase transition a better agreement is obtained for a twofold degenerate density of states peak than for a threefold degenerate one. (author)

High-pressure versus isoelectronic doping effect on the honeycomb iridate Na2IrO3

Science.gov (United States)

Hermann, V.; Ebad-Allah, J.; Freund, F.; Pietsch, I. M.; Jesche, A.; Tsirlin, A. A.; Deisenhofer, J.; Hanfland, M.; Gegenwart, P.; Kuntscher, C. A.

2017-11-01

We study the effect of isoelectronic doping and external pressure in tuning the ground state of the honeycomb iridate Na2IrO3 by combining optical spectroscopy with synchrotron x-ray diffraction measurements on single crystals. The obtained optical conductivity of Na2IrO3 is discussed in terms of a Mott-insulating picture versus the formation of quasimolecular orbitals and in terms of Kitaev interactions. With increasing Li content x , (Na1 -xLix )2IrO3 moves deeper into the Mott-insulating regime, and there are indications that up to a doping level of 24% the compound comes closer to the Kitaev limit. The optical conductivity spectrum of single-crystalline α -Li2IrO3 does not follow the trends observed for the series up to x =0.24 . There are strong indications that α -Li2IrO3 is not as close to the Kitaev limit as Na2IrO3 and lies closer to the quasimolecular orbital picture instead. Except for the pressure-induced hardening of the phonon modes, the optical properties of Na2IrO3 seem to be robust against external pressure. Possible explanations of the unexpected evolution of the optical conductivity with isolectronic doping and the drastic change between x =0.24 and x =1 are given by comparing the pressure-induced changes of lattice parameters and the optical conductivity with the corresponding changes induced by doping.

Magnetic behaviour of the honeycomb antiferromagnet BaNi{sub 2}V{sub 2}O{sub 8}

Energy Technology Data Exchange (ETDEWEB)

Klyushina, Ekaterina; Lake, Bella [Helmholtz-Zentrum Berlin fuer Materialien und Energie, Berlin (Germany); Institut fuer Festkoerperphysik, Technische Universitaet Berlin, Berlin (Germany); Islam, Nazmul; Klemke, Bastian [Helmholtz-Zentrum Berlin fuer Materialien und Energie, Berlin (Germany); Schneidewind, Astrid; Park, Jitae [Heinz Maier-Leibnitz Zentrum, TU Muenchen, Garching (Germany); Mansson, Martin [Paul Scherrer Institute (Switzerland)

2016-07-01

Here we present our recent investigations of a spin-1 honeycomb antiferromagnetic BaNi{sub 2}V{sub 2}O{sub 8} which is a highly 2D antiferromagnet with XY anisotropy making this compound a potential candidate for the Berezinsky-Kosterliz-Thouless topological phase transition. Single crystal inelastic neutron scattering measurements in the honeycomb plane at 4 K reveal that the magnetic excitations extend from 0.3-26 meV and consist of two anisotropy-split gapped modes with gaps of 0.3 meV and 3.3 meV arising from the anisotropy within the a-b plane and XY anisotropy respectively. The excitations agree well with simulations based on linear spin - wave theory and are completely dispersionless in the out-of-plane direction suggesting negligible interplane coupling in spite of the long range magnetic order below T{sub N} = 48 K. A detailed investigation of the order parameter and correlation length are presented and compared to various theories.

Chronic interstitial pneumonia with honeycombing in coal workers

Energy Technology Data Exchange (ETDEWEB)

Brichet, A.; Tonnel, A.B.; Brambilla, E.; Devouassoux, G.; Remy-Jardin, M.; Copin, M.C.; Wallaert, B. [A. Calmette Hospital, Lille (France)

2002-10-01

Coal worker's pneumoconiosis (CWP) results from coal mine dust inhalation. The paper reports the presence of a chronic interstitial pneumonia (CIP) with honeycombing in 38 cases of coal miners, with or without CWP. The 38 patients were selected on the basis of clinical criteria which are unusual in CWP, i.e. fine inspiratory crackles and severe dyspnea. There were 37 men and one woman; mean age was 67.5 {+-} 9.1 years. Thirty-two were smokers. Duration of exposure was 26.7 {+-} 9.9 years. All the patients had clinical examination, chest radiography, computed tomography (CT), lung function, laboratory investigations, wedged fiberoptic bronchoscopy with bronchoalveolar lavage (BAL). In eight cases, lung specimens were obtained. Seventeen out of 38 had finger clubbing. 17 had radiological signs of CWP limited to the upper lobes or diffusely distributed. CT showed honeycombing (36 cases), and/or ground glass opacities (30 cases) with traction bronchiectasis (8 cases) predominant in the lower lobes. BAL analysis demonstrated an increased percentage of neutrophils (9.4% {+-} 6). Lung function showed a restrictive pattern associated with a decreased DLCO and hypoxemia. Lung specimens demonstrated in 2 cases a homogenous interstitial fibrosis of intra-alveolar septum with an accumulation of immune and inflammatory cells without temporal variation and with obvious honeycombing. The 6 other cases showed features of usual interstitial pneumonia. These cases, should alert other clinicians to a possible association between CIP with honeycombing and coal dust exposure, with or without associated CWP.

Program LATTICE for Calculation of Parameters of Targets with Heterogeneous (Lattice) Structure

CERN Document Server

Bznuni, S A; Soloviev, A G; Sosnin, A N

2002-01-01

Program LATTICE, with which help it is possible to describe lattice structure for the program complex CASCAD, is created in the C++ language. It is shown that for model-based electronuclear system on a basis of molten salt reactor with graphite moderator at transition from homogeneous structure to heterogeneous at preservation of a chemical compound there is a growth of k_{eff} by approximately 6 %.

Topology Design of Pressure Adaptive Honeycomb for a Morphing Fowler Flap

NARCIS (Netherlands)

Scheepstra, J.; Vos, R.; Barrett, R.

2011-01-01

A new method for designing a morphing Fowler flap based on pressure-adaptive honeycomb is detailed. Pressure adaptive honeycomb has been shown to be able to induce gross camber deformations in airfoil sections, such as a flap. However, due to the large amount of design variables the integration of

Topology optimization of pressure adaptive honeycomb for a morphing flap

Science.gov (United States)

Vos, Roelof; Scheepstra, Jan; Barrett, Ron

2011-03-01

The paper begins with a brief historical overview of pressure adaptive materials and structures. By examining avian anatomy, it is seen that pressure-adaptive structures have been used successfully in the Natural world to hold structural positions for extended periods of time and yet allow for dynamic shape changes from one flight state to the next. More modern pneumatic actuators, including FAA certified autopilot servoactuators are frequently used by aircraft around the world. Pneumatic artificial muscles (PAM) show good promise as aircraft actuators, but follow the traditional model of load concentration and distribution commonly found in aircraft. A new system is proposed which leaves distributed loads distributed and manipulates structures through a distributed actuator. By using Pressure Adaptive Honeycomb (PAH), it is shown that large structural deformations in excess of 50% strains can be achieved while maintaining full structural integrity and enabling secondary flight control mechanisms like flaps. The successful implementation of pressure-adaptive honeycomb in the trailing edge of a wing section sparked the motivation for subsequent research into the optimal topology of the pressure adaptive honeycomb within the trailing edge of a morphing flap. As an input for the optimization two known shapes are required: a desired shape in cruise configuration and a desired shape in landing configuration. In addition, the boundary conditions and load cases (including aerodynamic loads and internal pressure loads) should be specified for each condition. Finally, a set of six design variables is specified relating to the honeycomb and upper skin topology of the morphing flap. A finite-element model of the pressure-adaptive honeycomb structure is developed specifically tailored to generate fast but reliable results for a given combination of external loading, input variables, and boundary conditions. Based on two bench tests it is shown that this model correlates well

Simultaneous phosphate and CODcr removals for landfill leachate using modified honeycomb cinders as an adsorbent

International Nuclear Information System (INIS)

Yue Xiu; Li Xiaoming; Wang Dongbo; Shen Tingting; Liu Xian; Yang Qi; Zeng Guangming; Liao Dexiang

2011-01-01

In this study, honeycomb cinders were employed to remove phosphate and Chemical Oxygen Demand (COD cr ) simultaneously for landfill leachate treatment. Operating conditions of honeycomb cinders pretreatment, pH, temperature, honeycomb cinders dosage, reaction time, and settling time, were evaluated and optimized. The results revealed that the removal efficiencies of both phosphate and COD cr could be increased up to 99.9% and 66.7% under the optimal conditions, respectively. Moreover, the structures of raw/modified honeycomb cinders and resulting precipitates were detected by Scanning Electron Microscope (SEM), Energy Dispersive Spectrometers (EDS) analysis and X-ray Diffraction (XRD). The results suggested that the adsorption method using honeycomb cinders might be an effective strategy as a pretreatment technology for landfill leachate treatment.

Band structure engineering for ultracold quantum gases in optical lattices

International Nuclear Information System (INIS)

Weinberg, Malte

2014-01-01

the same system maps onto a quantum spin-1/2 XY model. Owing to the quantum nature of the pseudospins, geometrical frustration leads to a highly degenerate ground state which can result in exotic valence bond spin-liquid phases. First signatures of an order-by-disorder effect emerge in this regime. A complementary approach to the manipulation of the band structure is investigated in a honeycomb potential. By rotating the quantization field of the system, the statedependent energy offset between the twofold atomic basis of the hexagonal Bravais lattice can be adjusted. This purposeful breaking of inversion symmetry enables the continuous opening of an energy gap at the Dirac points of the honeycomb band structure. In addition, a striking influence of the band gap onto the lifetimes for atoms in the first excited energy band is observed. In the last part of the thesis, both experimental manipulation techniques are discussed with respect to future applications for ultracold quantum gases in non-cubic optical lattices.

Fermions on the low-buckled honey-comb structured lattice plane and classical Casimir-Polder force

Science.gov (United States)

Goswami, Partha

2016-05-01

We start with the well-known expression for the vacuum polarization and suitably modify it for 2+1-dimensional spin-orbit coupled (SOC) fermions on the low-buckled honey-comb structured lattice plane described by the low-energy Liu-Yao-Feng-Ezawa (LYFE) model Hamiltonian involving the Dirac matrices in the chiral representation obeying the Clifford algebra. The silicene and germanene fit this description suitably. They have the Dirac cones similar to those of graphene and SOC is much stronger. The system could be normal or ferromagnetic in nature. The silicene turns into the latter type if there is exchange field arising due to the proximity coupling to a ferromagnet (FM) such as depositing Fe atoms to the silicene surface. For the silicene, we find that the many-body effects considerably change the bare Coulomb potential by way of the dependence of the Coulomb propagator on the real-spin, iso-spin and the potential due to an electric field applied perpendicular to the silicene plane. The computation aspect of the Casimir-Polder force (CPF) needs to be investigated in this paper. An important quantity in this process is the dielectric response function (DRF) of the material. The plasmon branch was obtained by finding the zeros of DRF in the long-wavelength limit. This leads to the plasmon frequencies. We find that the collective charge excitations at zero doping, i.e., intrinsic plasmons, in this system, are absent in the Dirac limit. The valley-spin-split intrinsic plasmons, however, come into being in the case of the massive Dirac particles with characteristic frequency close to 10 THz. Our scheme to calculate the Casimir-Polder interaction (CPI) of a micro-particle with a sheet involves replacing the dielectric constant of the sample in the CPI expression obtained on the basis of the Lifshitz theory by the static DRF obtained using the expressions for the polarization function we started with. Though the approach replaces a macroscopic constant by a microscopic

Origin of the Giant Honeycomb Network of Quinones on Cu(111)

Science.gov (United States)

Einstein, T. L.; Kim, Kwangmoo; Wyrick, Jon; Cheng, Zhihai; Bartels, Ludwig; Berland, Kristian; Hyldgaard, Per

2011-03-01

We discuss the factors that lead to the amazing regular giant honeycomb network formed by quinones on Cu(111). Using a related lattice gas model with many characteristic energies, we can reproduce many experimental features. These models require a long-range attraction, which can be attributed to indirect interactions mediated by the Shockley surface state of Cu(111). However, Wyrick's preceding talk gave evidence that the network self-selects for the size of the pore rather than for the periodicity of the superstructure, suggesting that confined states are the key ingredient. We discuss this phenomenon in terms of the magic numbers of 2D quantum dots. We also report calculations of the effects of anthraquinones (AQ) in modifying the surface states by considering a superlattice of AQ chains with various separations. We discuss implications of these results for tuning the electronic states and, thence, superstructures. Supported by (TLE) NSF CHE 07-50334 & UMD MRSEC DMR 05-20471, (JW & LB) NSF CHE NSF CHE 07-49949, (KB & PH) Swedish Vetenskapsrådet VR 621-2008-4346.

Chirality-induced magnon transport in AA-stacked bilayer honeycomb chiral magnets.

Science.gov (United States)

Owerre, S A

2016-11-30

In this Letter, we study the magnetic transport in AA-stacked bilayer honeycomb chiral magnets coupled either ferromagnetically or antiferromagnetically. For both couplings, we observe chirality-induced gaps, chiral protected edge states, magnon Hall and magnon spin Nernst effects of magnetic spin excitations. For ferromagnetically coupled layers, thermal Hall and spin Nernst conductivities do not change sign as function of magnetic field or temperature similar to single-layer honeycomb ferromagnetic insulator. In contrast, for antiferromagnetically coupled layers, we observe a sign change in the thermal Hall and spin Nernst conductivities as the magnetic field is reversed. We discuss possible experimental accessible honeycomb bilayer quantum materials in which these effects can be observed.

The total hemispheric emissivity of painted aluminum honeycomb at cryogenic temperatures

Energy Technology Data Exchange (ETDEWEB)

Tuttle, J.; Canavan, E.; DiPirro, M.; Li, X. [NASA Goddard Space Flight Center, Code 552 Greenbelt, Maryland, 20771 (United States); Knollenberg, P. [Northrop Grumman Aerospace Systems Redondo Beach, CA 90278 (United States)

2014-01-29

NASA uses high-emissivity surfaces on deep-space radiators and thermal radiation absorbers in test chambers. Aluminum honeycomb core material, when coated with a high-emissivity paint, provides a lightweight, mechanically robust, and relatively inexpensive black surface that retains its high emissivity down to low temperatures. At temperatures below about 100 Kelvin, this material performs much better than the paint itself. We measured the total hemispheric emissivity of various painted honeycomb configurations using an adaptation of an innovative technique developed for characterizing thin black coatings. These measurements were performed from room temperature down to 30 Kelvin. We describe the measurement technique and compare the results with predictions from a detailed thermal model of each honeycomb configuration.

A stress field in the vortex lattice in the type-II superconductor

Directory of Open Access Journals (Sweden)

Maruszewski, Bogdan

2008-02-01

Full Text Available Magnetic flux can penetrate a type-II superconductor in the form of Abrikosov vortices (also called flux lines, flux tubes, or fluxons, each carrying a quantum of magnetic flux. These tiny vortices of supercurrent tend to arrange themselves in a triangular and/or quadratic flux-line lattice, which is more or less perturbed by material inhomogeneities that pin the flux lines. Pinning is caused by imperfections of the crystal lattice, such as dislocations, point defects, grain boundaries, etc. Hence, a honeycomb-like pattern of the vortex array presents some mechanical properties. If the Lorentz force of interactions between the vortices is much bigger than the pinning force, the vortex lattice behaves elastically. So we assume that the pinning force is negligible in the sequel and we deal with soft vortices. The vortex motion in the vortex lattice and/or creep of the vortices in the vortex fluid is accompanied by energy dissipation. Hence, except for the elastic properties, the vortex field is also of a viscous character. The main aim of the paper is a formulation of a thermoviscoelastic stress - strain constitutive law consisted of coexistence of the ordered and disordered states of the vortex field. Its form describes an auxetic-like thermomechanical (anomalous property of the vortex field.

Low-Velocity Impact Behavior of Sandwich Structures with Additively Manufactured Polymer Lattice Cores

Science.gov (United States)

Turner, Andrew J.; Al Rifaie, Mohammed; Mian, Ahsan; Srinivasan, Raghavan

2018-05-01

Sandwich panel structures are widely used in aerospace, marine, and automotive applications because of their high flexural stiffness, strength-to-weight ratio, good vibration damping, and low through-thickness thermal conductivity. These structures consist of solid face sheets and low-density cellular core structures, which are traditionally based upon honeycomb folded-sheet topologies. The recent advances in additive manufacturing (AM) or 3D printing process allow lattice core configurations to be designed with improved mechanical properties. In this work, the sandwich core is comprised of lattice truss structures (LTS). Two different LTS designs are 3D-printed using acrylonitrile butadiene styrene (ABS) and are tested under low-velocity impact loads. The absorption energy and the failure mechanisms of lattice cells under such loads are investigated. The differences in energy-absorption capabilities are captured by integrating the load-displacement curve found from the impact response. It is observed that selective placement of vertical support struts in the unit-cell results in an increase in the absorption energy of the sandwich panels.

Low-Velocity Impact Behavior of Sandwich Structures with Additively Manufactured Polymer Lattice Cores

Science.gov (United States)

Turner, Andrew J.; Al Rifaie, Mohammed; Mian, Ahsan; Srinivasan, Raghavan

2018-04-01

Sandwich panel structures are widely used in aerospace, marine, and automotive applications because of their high flexural stiffness, strength-to-weight ratio, good vibration damping, and low through-thickness thermal conductivity. These structures consist of solid face sheets and low-density cellular core structures, which are traditionally based upon honeycomb folded-sheet topologies. The recent advances in additive manufacturing (AM) or 3D printing process allow lattice core configurations to be designed with improved mechanical properties. In this work, the sandwich core is comprised of lattice truss structures (LTS). Two different LTS designs are 3D-printed using acrylonitrile butadiene styrene (ABS) and are tested under low-velocity impact loads. The absorption energy and the failure mechanisms of lattice cells under such loads are investigated. The differences in energy-absorption capabilities are captured by integrating the load-displacement curve found from the impact response. It is observed that selective placement of vertical support struts in the unit-cell results in an increase in the absorption energy of the sandwich panels.

Lattice constant changes leading to significant changes of the spin-gapless features and physical nature in a inverse Heusler compound Zr2MnGa

Science.gov (United States)

Wang, Xiaotian; Cheng, Zhenxiang; Khenata, Rabah; Wu, Yang; Wang, Liying; Liu, Guodong

2017-12-01

The spin-gapless semiconductors with parabolic energy dispersions [1-3] have been recently proposed as a new class of materials for potential applications in spintronic devices. In this work, according to the Slater-Pauling rule, we report the fully-compensated ferrimagnetic (FCF) behavior and spin-gapless semiconducting (SGS) properties for a new inverse Heusler compound Zr2MnGa by means of the plane-wave pseudo-potential method based on density functional theory. With the help of GGA-PBE, the electronic structures and the magnetism of Zr2MnGa compound at its equilibrium and strained lattice constants are systematically studied. The calculated results show that the Zr2MnGa is a new SGS at its equilibrium lattice constant: there is an energy gap between the conduction and valence bands for both the majority and minority electrons, while there is no gap between the majority electrons in the valence band and the minority electrons in the conduction band. Remarkably, not only a diverse physical nature transition, but also different types of spin-gapless features can be observed with the change of the lattice constants. Our calculated results of Zr2MnGa compound indicate that this material has great application potential in spintronic devices.

Simulated effect on the compressive and shear mechanical properties of bionic integrated honeycomb plates.

Science.gov (United States)

He, Chenglin; Chen, Jinxiang; Wu, Zhishen; Xie, Juan; Zu, Qiao; Lu, Yun

2015-05-01

Honeycomb plates can be applied in many fields, including furniture manufacturing, mechanical engineering, civil engineering, transportation and aerospace. In the present study, we discuss the simulated effect on the mechanical properties of bionic integrated honeycomb plates by investigating the compressive and shear failure modes and the mechanical properties of trabeculae reinforced by long or short fibers. The results indicate that the simulated effect represents approximately 80% and 70% of the compressive and shear strengths, respectively. Compared with existing bionic samples, the mass-specific strength was significantly improved. Therefore, this integrated honeycomb technology remains the most effective method for the trial manufacturing of bionic integrated honeycomb plates. The simulated effect of the compressive rigidity is approximately 85%. The short-fiber trabeculae have an advantage over the long-fiber trabeculae in terms of shear rigidity, which provides new evidence for the application of integrated bionic honeycomb plates. Copyright © 2015 Elsevier B.V. All rights reserved.

The relation between lattice parameters of NaCl type U, Np and Pu compounds and their magnetic and binding properties

International Nuclear Information System (INIS)

Ohmichi, Toshihiko; Arai, Yasuo

1992-01-01

The lattice parameters of NaCl type uranium, neptunium and plutonium compounds are analyzed using Pauling equation. The numbers of bonding electrons and localized electrons of the compounds are calculated using the single bond radius by Pauling for metalloids and assumed ones for the actinides. The number of bonding electrons per unit bonding length can be correlated linearly with the uranium compounds. The number of localized electrons is found to have a speculative relation with magnetic properties, in particular magnetic moments in ordered state; excluding some compounds, the magnetic moments increase at a gradient of 45 degrees with increasing localized electrons in the range up to about 2.5 and then decrease to zero value roughly at a same gradient with increasing localized electrons. (author)

Enhancement of cell growth on honeycomb-structured polylactide surface using atmospheric-pressure plasma jet modification

Energy Technology Data Exchange (ETDEWEB)

Cheng, Kuang-Yao; Chang, Chia-Hsing; Yang, Yi-Wei; Liao, Guo-Chun; Liu, Chih-Tung; Wu, Jong-Shinn, E-mail: chongsin@faculty.nctu.edu.tw

2017-02-01

Graphical abstract: Atmospheric-pressure plasma enhances cell growth on two different pore sizes of honeycomb pattern on polylactide surface. - Highlights: • Different pore sizes of honeycomb pattern on PLA film are created. • The two-step plasma treatment provided the oxygen- and nitrogen-containing functional groups that had a major impact on cell cultivation. • The plasma treatment had a significant effect for cell proliferation. • The surface structures are the main influence on cell cultivation, while plasma treatment can indeed improve the growth environment. - Abstract: In this paper, we compare the cell growth results of NIH-3T3 and Neuro-2A cells over 72 h on flat and honeycomb structured PLA films without and with a two-step atmospheric-pressure nitrogen-based plasma jet treatment. We developed a fabrication system used for forming of a uniform honeycomb structure on PLA surface, which can produce two different pore sizes, 3–4 μm and 7–8 μm, of honeycomb pattern. We applied a previously developed nitrogen-based atmospheric-pressure dielectric barrier discharge (DBD) jet system to treat the PLA film without and with honeycomb structure. NIH-3T3 and a much smaller Neuro-2A cells were cultivated on the films under various surface conditions. The results show that the two-step plasma treatment in combination with a honeycomb structure can enhance cell growth on PLA film, should the cell size be not too smaller than the pore size of honeycomb structure, e.g., NIH-3T3. Otherwise, cell growth would be better on flat PLA film, e.g., Neuro-2A.

Honeycomb surface-plasma negative-ion source

International Nuclear Information System (INIS)

Bel'chenko, Yu.I.

1983-01-01

A honeycomb surface-plasma source (SPS) of negative hydrogen ions the cathode of which consists of a great number of cells with spherical-concave surfaces, is described. Negative ions, knocked off the cathode by cesium-hydrogen discharge fast particles are accelerated in the near-cathode potential drop layer and focused geometrically on small emission apertures in the anode. Due to this, the gas and energy efficiency of the source is increased and the power density on the cathode is decreased. The H - yield is proportional to the number of celts. A pulse beam of negative ions with current up to 4 A is obtained and accelerated to 25 kV from the cathode effective area of 10.6 cm 2 through emission ports of 0.5 cm 2 total area. The honeycomb SPSs with a greater number of cells are promising as regards obtaining negative ion-beams with the current of scores of amperes

Stopping dynamics of ions passing through correlated honeycomb clusters

Science.gov (United States)

Balzer, Karsten; Schlünzen, Niclas; Bonitz, Michael

2016-12-01

A combined nonequilibrium Green functions-Ehrenfest dynamics approach is developed that allows for a time-dependent study of the energy loss of a charged particle penetrating a strongly correlated system at zero and finite temperatures. Numerical results are presented for finite inhomogeneous two-dimensional Fermi-Hubbard models, where the many-electron dynamics in the target are treated fully quantum mechanically and the motion of the projectile is treated classically. The simulations are based on the solution of the two-time Dyson (Keldysh-Kadanoff-Baym) equations using the second-order Born, third-order, and T -matrix approximations of the self-energy. As application, we consider protons and helium nuclei with a kinetic energy between 1 and 500 keV/u passing through planar fragments of the two-dimensional honeycomb lattice and, in particular, examine the influence of electron-electron correlations on the energy exchange between projectile and electron system. We investigate the time dependence of the projectile's kinetic energy (stopping power), the electron density, the double occupancy, and the photoemission spectrum. Finally, we show that, for a suitable choice of the Hubbard model parameters, the results for the stopping power are in fair agreement with ab initio simulations for particle irradiation of single-layer graphene.

Low frequency acoustic properties of a honeycomb-silicone rubber acoustic metamaterial

Science.gov (United States)

Gao, Nansha; Hou, Hong

2017-04-01

In order to overcome the influence of mass law on traditional acoustic materials and obtain a lightweight thin-layer structure which can effectively isolate the low frequency noises, a honeycomb-silicone rubber acoustic metamaterial was proposed. Experimental results show that the sound transmission loss (STL) of acoustic metamaterial in this paper is greatly higher than that of monolayer silicone rubber metamaterial. Based on the band structure, modal shapes, as well as the sound transmission simulation, the sound insulation mechanism of the designed honeycomb-silicone rubber structure was analyzed from a new perspective, which had been validated experimentally. Side length of honeycomb structure and thickness of the unit structure would affect STL in damping control zone. Relevant conclusions and design method provide a new concept for engineering noise control.

Comparison of phase boundaries between kagomé and honeycomb superconducting wire networks

Science.gov (United States)

Xiao, Yi; Huse, David A.; Chaikin, Paul M.; Higgins, Mark J.; Bhattacharya, Shobo; Spencer, David

2002-06-01

We measure resistively the mean-field superconducting-normal phase boundaries of both kagomé and honeycomb wire networks immersed in a transverse magnetic field. In addition to their agreement with theory about the overall shapes of phase diagrams, they show striking one-to-one correspondence between the cusps in the honeycomb phase boundary and those in the kagomé curve. This correspondence is due to their geometric arrangements and agrees with Lin and Nori's recent calculation. We also find that for the frustrated honeycomb network at f=1/2, the current patterns in the superconducting phase differ between the low-temperature London regime and the higher-temperature Ginzburg-Landau regime near Tc.

Gaussian quadrature and lattice discretization of the Fermi-Dirac distribution for graphene.

Science.gov (United States)

Oettinger, D; Mendoza, M; Herrmann, H J

2013-07-01

We construct a lattice kinetic scheme to study electronic flow in graphene. For this purpose, we first derive a basis of orthogonal polynomials, using as the weight function the ultrarelativistic Fermi-Dirac distribution at rest. Later, we use these polynomials to expand the respective distribution in a moving frame, for both cases, undoped and doped graphene. In order to discretize the Boltzmann equation and make feasible the numerical implementation, we reduce the number of discrete points in momentum space to 18 by applying a Gaussian quadrature, finding that the family of representative wave (2+1)-vectors, which satisfies the quadrature, reconstructs a honeycomb lattice. The procedure and discrete model are validated by solving the Riemann problem, finding excellent agreement with other numerical models. In addition, we have extended the Riemann problem to the case of different dopings, finding that by increasing the chemical potential the electronic fluid behaves as if it increases its effective viscosity.

The use of neutron imaging for the study of honeycomb structures in aircraft

International Nuclear Information System (INIS)

Hungler, P.C.; Bennett, L.G.I.; Lewis, W.J.; Brenizer, J.S.; Heller, A.K.

2009-01-01

Highly maneuverable aircraft, such as the CF188 Hornet, have several flight control surfaces on both the leading and the trailing edges of the wing surfaces. They are composed of composite panels constructed of aluminum honeycomb core usually covered with graphite epoxy skins. Although very light and structurally stiff, they are being compromised by water ingress. The trapped water degrades their structural integrity by interacting with the adhesive. Various studies are underway to understand the movement of water in the honeycomb core as well as to determine a method of removing the water. With a vertical neutron beam tube at Royal Military College (RMC), the component can be positioned horizontally and the pooled water in each honeycomb cell can be imaged. These images have been compared with those from a horizontal beam and thus vertical placement of the structure at Pennsylvania State University Radiation Science and Engineer Center's Breazeale reactor. Thereby, both the filet bond between the honeycomb and the skin as well as the node bond between the honeycomb cells can be studied to determine their contribution to the movement of water throughout the structure. Moreover, the exit path for water has been visualized as part of developing a drying procedure for these flight control surfaces.

Biomimetic honeycomb-patterned surface as the tunable cell adhesion scaffold.

Science.gov (United States)

Chen, Shuangshuang; Lu, Xuemin; Hu, Ying; Lu, Qinghua

2015-01-01

Inspired by the typically adhesive behaviors of fish skin and Parthenocissus tricuspidata, two different decorations of polystyrene honeycomb membrane (PSHCM) prepared by the breath figure approach were carried out with poly(N-(3-Sulfopropyl)-N-(methacryloxyethyl)-N,N-dimethylammonium betaine)(polySBMA) to explore controllable bioadhesive surfaces. Casting and dip-coating were employed to graft polySBMA onto the plasma treated PSHCM. The polySBMA casted PSHCM showed a uniform covering layer on the PSHCM similar to the mucus layer of fish skin, presenting excellent antifouling properties. On the contrary, a dip-coated one showed the polySBMA aggregating on the honeycomb pore walls forming a large number of sucking disks such as the adhesive disks of the tendrils of P. tricuspidata, which remarkably boosts cell adhesion on substrates. Thus, bioadhesion could be regulated as desired by tuning the distribution of zwitterionic polymer on the honeycomb surface. The results may provide a new approach for the design of biomaterial surfaces.

Mechanical properties of aluminium honeycomb impact limiters

International Nuclear Information System (INIS)

Maji, A.K.; Satpathi, D.; Donald, S.

1992-01-01

Aluminium honeycombs have been extensively used as impact limiters in nuclear waste transport casks. The mechanical behaviour of these shock absorbing materials was studied to develop an extensive experimental database. A series of tests were performed along various loading paths. Different densities of aluminium honeycombs were tested in different orientations. Static tests included uniaxial tension, uniaxial compression and torsion. Dynamic tests were conducted at different strain rates of up to 100 s -1 , to generate experimental data relevant to accident situations. Dynamic studies included the effects of specimen size and confinement. The purpose of using different loading paths was to generate an extensive experimental database which may also be used to develop constitutive models for these materials. Design charts were constructed which can be accessed by various cask designers to optimise and economise on cask development. (Author)

Aerodynamic effect of a honeycomb rotor tip shroud on a 50.8-centimeter-tip-diameter core turbine

Science.gov (United States)

Moffitt, T. P.; Whitney, W. J.

1983-01-01

A 50.8-cm-tip-diameter turbine equipped with a rotor tip shroud of hexagonal cell (or honeycomb) cross section has been tested in warm air (416 K) for a range of shroud coolant to primary flow rates. Test results were also obtained for the same turbine operated with a solid shroud for comparison. The results showed that the combined effect of the honeycomb shroud and the coolant flow was to cause a reduction of 2.8 points in efficiency at design speed, pressure ratio, and coolant flow rate. With the coolant system inactivated, the honeycomb shroud caused a decrease in efficiency of 2.3 points. These results and those obtained from a small reference turbine indicate that the dominant factor governing honeycomb tip shroud loss is the ratio of honeycomb depth to blade span. The loss results of the two shrouds could be correlated on this basis. The same honeycomb and coolant effects are expected to occur for the hot (2200 K) version of this turbine.

Combining aerogels with honeycombs – a new stiff and flexible superinsulation

OpenAIRE

Schwan, Marina; Ratke, Lorenz; Milow, Barbara

2014-01-01

Saving energy is the most important issue in the 21st century. New high qualitative thermal insulation materials are of critical importance to energy-efficient building design, transportation and aircraft industry. We propose to combine aramid honeycombs with aerogels to manufacture such new types of advanced insulation materials. Aramid honeycombs produced from aramid fibers by the expansion method possess extremely high stiffness-to-weight ratio and are heat-resisting up to 550°C. Aerogels ...

Radiative heat transfer in honeycomb structures-New simple analytical and numerical approaches

International Nuclear Information System (INIS)

Baillis, D; Coquard, R; Randrianalisoa, J

2012-01-01

Porous Honeycomb Structures present the interest of combining, at the same time, high thermal insulating properties, low density and sufficient mechanical resistance. However, their thermal properties remain relatively unexplored. The aim of this study is the modelling of the combined heat transfer and especially radiative heat transfer through this type of anisotropic porous material. The equivalent radiative properties of the material are determined using ray-tracing procedures inside the honeycomb porous structure. From computational ray-tracing results, simple new analytical relations have been deduced. These useful analytical relations permit to determine radiative properties such as extinction, absorption and scattering coefficients and phase function functions of cell dimensions and optical properties of cell walls. The radiative properties of honeycomb material strongly depend on the direction of propagation. From the radiative properties computed, we have estimated the radiative heat flux passing through slabs of honeycomb core materials submitted to a 1-D temperature difference between a hot and a cold plate. We have compared numerical results obtained from Discrete Ordinate Method with analytical results obtained from Rosseland-Deissler approximation. This approximation is usually used in the case of isotropic materials. We have extended it to anisotropic honeycomb materials. Indeed a mean over incident directions of Rosseland extinction coefficient is proposed. Results tend to show that Rosseland-Deissler extended approximation can be used as a first approximation. Deviation on radiative conductivity obtained from Rosseland-Deissler approximation and from the Discrete Ordinated Method are lower than 6.7% for all the cases studied.

Smart Kirigami open honeycombs in shape changing actuation and dynamics

Science.gov (United States)

Neville, R. M.; Scarpa, F.; Leng, J.

2017-04-01

Kirigami is the ancient Japanese art of cutting and folding paper, widespread in Asia since the 17th century. Kirigami offers a broader set of geometries and topologies than classical fold/valleys Origami, because of the presence of cuts. Moreover, Kirigami can be readily applied to a large set of composite and smart 2D materials, and can be used to up-scaled productions with modular molding. We describe the manufacturing and testing of a topology of Kirigami cellular structures defined as Open Honeycombs. Open Honeycombs (OHs) can assume fully closed shape and be alike classical hexagonal centresymmetric honeycombs, or can vary their morphology by tuning the opening angle and rotational stiffness of the folds. We show the performance of experimental PEEK OHs with cable actuation and morphing shape characteristics, and the analogous morphing behavior of styrene SMPs under combined mechanical and thermal loading. We also show the dynamic (modal analysis) behavior of OHs configurations parameterized against their geometry characteristics, and the controllable modal density characteristics that one could obtain by tuning the topology and folding properties.

Finite Element Analysis of Aluminum Honeycombs Subjected to Dynamic Indentation and Compression Loads

Directory of Open Access Journals (Sweden)

A.S.M. Ayman Ashab

2016-03-01

Full Text Available The mechanical behavior of aluminum hexagonal honeycombs subjected to out-of-plane dynamic indentation and compression loads has been investigated numerically using ANSYS/LS-DYNA in this paper. The finite element (FE models have been verified by previous experimental results in terms of deformation pattern, stress-strain curve, and energy dissipation. The verified FE models have then been used in comprehensive numerical analysis of different aluminum honeycombs. Plateau stress, σpl, and dissipated energy (EI for indentation and EC for compression have been calculated at different strain rates ranging from 102 to 104 s−1. The effects of strain rate and t/l ratio on the plateau stress, dissipated energy, and tearing energy have been discussed. An empirical formula is proposed to describe the relationship between the tearing energy per unit fracture area, relative density, and strain rate for honeycombs. Moreover, it has been found that a generic formula can be used to describe the relationship between tearing energy per unit fracture area and relative density for both aluminum honeycombs and foams.

Accordion-like honeycombs for tissue engineering of cardiac anisotropy

Science.gov (United States)

Engelmayr, George C.; Cheng, Mingyu; Bettinger, Christopher J.; Borenstein, Jeffrey T.; Langer, Robert; Freed, Lisa E.

2008-12-01

Tissue-engineered grafts may be useful in myocardial repair; however, previous scaffolds have been structurally incompatible with recapitulating cardiac anisotropy. Here, we use microfabrication techniques to create an accordion-like honeycomb microstructure in poly(glycerol sebacate), which yields porous, elastomeric three-dimensional (3D) scaffolds with controllable stiffness and anisotropy. Accordion-like honeycomb scaffolds with cultured neonatal rat heart cells demonstrated utility through: (1) closely matched mechanical properties compared to native adult rat right ventricular myocardium, with stiffnesses controlled by polymer curing time; (2) heart cell contractility inducible by electric field stimulation with directionally dependent electrical excitation thresholds (pthe formation of grafts with aligned heart cells and mechanical properties more closely resembling native myocardium.

Creating "hotels" for cells by electrospinning honeycomb-like polymeric structures.

Science.gov (United States)

Liang, T; Mahalingam, S; Edirisinghe, M

2013-10-01

It is well established that three-dimensional honeycomb-like nanofibrous structures enhance cell activity. In this work, we report that electrospun polymer nanofibres self-assemble into three-dimensional honeycomb-like structures. The underlying mechanism is studied by varying the polymer solution concentration, collecting substrates and working distance. The polymer solution concentration has a significant effect on the size of the electrospun nanofibres. The collection substrate and working distance affect the electric field strength, the evaporation of solvent and the discharging of nanofibres and consequently these two had a significant influence on the self-assembly of nanofibres. © 2013.

Absolute photonic band gap in 2D honeycomb annular photonic crystals

International Nuclear Information System (INIS)

Liu, Dan; Gao, Yihua; Tong, Aihong; Hu, Sen

2015-01-01

Highlights: • A two-dimensional honeycomb annular photonic crystal (PC) is proposed. • The absolute photonic band gap (PBG) is studied. • Annular PCs show larger PBGs than usual air-hole PCs for high refractive index. • Annular PCs with anisotropic rods show large PBGs for low refractive index. • There exist optimal parameters to open largest band gaps. - Abstract: Using the plane wave expansion method, we investigate the effects of structural parameters on absolute photonic band gap (PBG) in two-dimensional honeycomb annular photonic crystals (PCs). The results reveal that the annular PCs possess absolute PBGs that are larger than those of the conventional air-hole PCs only when the refractive index of the material from which the PC is made is equal to 4.5 or larger. If the refractive index is smaller than 4.5, utilization of anisotropic inner rods in honeycomb annular PCs can lead to the formation of larger PBGs. The optimal structural parameters that yield the largest absolute PBGs are obtained

Self-sustained oscillations in blood flow through a honeycomb capillary network.

Science.gov (United States)

Davis, J M; Pozrikidis, C

2014-09-01

Numerical simulations of unsteady blood flow through a honeycomb network originating at multiple inlets and terminating at multiple outlets are presented and discussed under the assumption that blood behaves as a continuum with variable constitution. Unlike a tree network, the honeycomb network exhibits both diverging and converging bifurcations between branching capillary segments. Numerical results based on a finite difference method demonstrate that as in the case of tree networks considered in previous studies, the cell partitioning law at diverging bifurcations is an important parameter in both steady and unsteady flow. Specifically, a steady flow may spontaneously develop self-sustained oscillations at critical conditions by way of a Hopf bifurcation. Contrary to tree-like networks comprised entirely of diverging bifurcations, the critical parameters for instability in honeycomb networks depend weakly on the system size. The blockage of one or more network segments due to the presence of large cells or the occurrence of capillary constriction may cause flow reversal or trigger a transition to unsteady flow.

Structure and magnetic ground states of spin-orbit coupled compound alpha-RuCl3

Science.gov (United States)

Banerjee, Arnab; Bridges, Craig; Yan, Jiaqiang; Mandrus, David; Stone, Matthew; Aczel, Adam; Li, Ling; Yiu, Yuen; Lumsden, Mark; Chakoumakos, Bryan; Tennant, Alan; Nagler, Stephen

2015-03-01

The layered material alpha-RuCl3 is composed of stacks of weakly coupled honeycomb lattices of octahedrally coordinated Ru3 + ions. The Ru ion ground state has 5 d electrons in the low spin state, with spin-orbit coupling very strong compared to other terms in the single ion Hamiltonian. The material is therefore an excellent candidate for investigating possible Heisenberg-Kitaev physics. In addition, this compound is very amenable to investigation by neutron scattering to explore the magnetic ground state and excitations in detail. In this talk, we discuss the synthesis of phase-pure alpha-RuCl3 and the characterization of the magnetization, susceptibility, and heat-capacity. We also report neutron diffraction on both powder and single crystal alpha-RuCl3, identifying the low temperature magnetic order observed in the material. The results, when compared to theoretical calculations, shed light on the relative importance of Kitaev and Heisenberg terms in the Hamiltonian. The research is supported by the DOE BES Scientific User Facility Division.

Increased power to weight ratio of piezoelectric energy harvesters through integration of cellular honeycomb structures

International Nuclear Information System (INIS)

Chandrasekharan, N; Thompson, L L

2016-01-01

The limitations posed by batteries have compelled the need to investigate energy harvesting methods to power small electronic devices that require very low operational power. Vibration based energy harvesting methods with piezoelectric transduction in particular has been shown to possess potential towards energy harvesters replacing batteries. Current piezoelectric energy harvesters exhibit considerably lower power to weight ratio or specific power when compared to batteries the harvesters seek to replace. To attain the goal of battery-less self-sustainable device operation the power to weight ratio gap between piezoelectric energy harvesters and batteries need to be bridged. In this paper the potential of integrating lightweight honeycomb structures with existing piezoelectric device configurations (bimorph) towards achieving higher specific power is investigated. It is shown in this study that at low excitation frequency ranges, replacing the solid continuous substrate of conventional bimorph with honeycomb structures of the same material results in a significant increase in power to weight ratio of the piezoelectric harvester. At higher driving frequency ranges it is shown that unlike the traditional piezoelectric bimorph with solid continuous substrate, the honeycomb substrate bimorph can preserve optimum global design parameters through manipulation of honeycomb unit cell parameters. Increased operating lifetime and design flexibility of the honeycomb core piezoelectric bimorph is demonstrated as unit cell parameters of the honeycomb structures can be manipulated to alter mass and stiffness properties of the substrate, resulting in unit cell parameter significantly influencing power generation. (paper)

Mould design and manufacturing considerations of honeycomb biocomposites with transverse fibre direction for aerospace application

Science.gov (United States)

Manan, N. H.; Majid, D. L.; Romli, F. I.

2016-10-01

Sandwich structures with honeycomb core are known to significantly improve stiffness at lower weight and possess high flexural rigidity. They have found wide applications in aerospace as part of the primary structures, as well as the interior paneling and floors. High performance aluminum and aramid are the typical materials used for the purpose of honeycomb core whereas in other industries, materials such as fibre glass, carbon fibre, Nomex and also Kevlar reinforced with polymer are used. Recently, growing interest in developing composite structures with natural fibre reinforcement has also spurred research in natural fibre honeycomb material. The majority of the researches done, however, have generally emphasized on the usage of random chopped fibre and only a few are reported on development of honeycomb structure using unidirectional fibre as the reinforcement. This is mainly due to its processing difficulties, which often involve several stages to account for the arrangement of fibres and curing. Since the use of unidirectional fibre supports greater strength compared to random chopped fibre, a single-stage process in conjunction with vacuum infusion is suggested with a mould design that supports fibre arrangement in the direction of honeycomb loading.

Atomic-scale observation of structural and electronic orders in the layered compound ?-RuCl3

OpenAIRE

Ziatdinov, M.; Banerjee, A.; Maksov, A.; Berlijn, T.; Zhou, W.; Cao, H. B.; Yan, J.-Q.; Bridges, C. A.; Mandrus, D. G.; Nagler, S. E.; Baddorf, A. P.; Kalinin, S. V.

2016-01-01

A pseudospin-1/2 Mott phase on a honeycomb lattice is proposed to host the celebrated two-dimensional Kitaev model which has an elusive quantum spin liquid ground state, and fascinating physics relevant to the development of future templates towards topological quantum bits. Here we report a comprehensive, atomically resolved real-space study by scanning transmission electron and scanning tunnelling microscopies on a novel layered material displaying Kitaev physics, ?-RuCl3. Our local crystal...

Competing anisotropies on 3d sub-lattice of YNi{sub 4–x}Co{sub x}B compounds

Energy Technology Data Exchange (ETDEWEB)

Caraballo Vivas, R. J.; Rocco, D. L.; Reis, M. S. [Instituto de Física, Universidade Federal Fluminense, Av. Gal. Milton Tavares de Souza s/n, 24210-346 Niterói, RJ (Brazil); Costa Soares, T. [Instituto de Física, Universidade Federal Fluminense, Av. Gal. Milton Tavares de Souza s/n, 24210-346 Niterói, RJ (Brazil); IF Sudeste MG Campus de Juiz de Fora-Núcleo de Física, 36080-001 Juiz de Fora, MG (Brazil); Caldeira, L. [IF Sudeste MG Campus de Juiz de Fora-Núcleo de Física, 36080-001 Juiz de Fora, MG (Brazil); Coelho, A. A. [Instituto de Física Gleb Wataghin, Universidade Estadual de Campinas-Unicamp, Caixa postal 6165, 13083-859 Campinas, SP (Brazil)

2014-08-14

The magnetic anisotropy of 3d sub-lattices has an important rule on the overall magnetic properties of hard magnets. Intermetallics alloys with boron (R-Co/Ni-B, for instance) belong to those hard magnets family and are useful objects to help to understand the magnetic behavior of 3d sub-lattice, specially when the rare earth ions R do not have magnetic nature, like YCo{sub 4}B ferromagnetic material. Interestingly, YNi{sub 4}B is a paramagnetic material and Ni ions do not contribute to the magnetic anisotropy. We focused therefore our attention to YNi{sub 4–x}Co{sub x}B series, with x = 0, 1, 2, 3, and 4. The magnetic anisotropy of these compounds is deeper described using statistical and preferential models of Co occupation among the possible Wyckoff positions into the CeCo{sub 4}B type hexagonal structure. We found that the preferential model is the most suitable to explain the magnetization experimental data.

Lattice anisotropy in uranium ternary compounds

DEFF Research Database (Denmark)

Maskova, S.; Adamska, A.M.; Havela, L.

2012-01-01

Several U-based intermetallic compounds (UCoGe, UNiGe with the TiNiSi structure type and UNiAl with the ZrNiAl structure type) and their hydrides were studied from the point of view of compressibility and thermal expansion. Confronted with existing data for the compounds with the ZrNiAl structure...

Synthesis of honeycomb MnO2 nanospheres/carbon nanoparticles/graphene composites as electrode materials for supercapacitors

Science.gov (United States)

Xiong, Yachao; Zhou, Min; Chen, Hao; Feng, Lei; Wang, Zhao; Yan, Xinzhu; Guan, Shiyou

2015-12-01

Improving the electrochemical performance of manganese dioxide (MnO2) electrodes is of great significance for supercapacitors. In this study, a novel honeycomb MnO2 nanospheres/carbon nanoparticles/graphene composites has been fabricated through freeze-drying method. The honeycomb MnO2 nanospheres are well inserted and dispersed on the graphene. Carbon nanoparticles in the composites act as spacers to effectively prevent graphene from restacking and agglomeration, construct efficient 3D conducting architecture with graphene for honeycomb MnO2 nanospheres, and alleviate the aggregation of honeycomb MnO2 nanospheres by separating them from each other. As a result, such honeycomb MnO2 nanospheres/carbon nanoparticles/graphene composites display much improved electrochemical capacitive performance of 255 F g-1 at a current density of 0.5 A g-1, outstanding rate capability (150 F g-1 remained at a current density of 20 A g-1) and good cycling stability (83% of the initial capacitance retained after 1000 charge/discharge cycles). The strategy for the synthesis of these composites is very effective.

Rhombohedral polytypes of the layered honeycomb delafossites with optical brilliance in the visible.

Science.gov (United States)

Roudebush, John H; Sahasrabudhe, Girija; Bergman, Susanna L; Cava, R J

2015-04-06

We report the synthesis of the Delafossite honeycomb compounds Cu3Ni2SbO6 and Cu3Co2SbO6 via a copper topotactic reaction from the layered α-NaFeO2-like precursors Na3Ni2SbO6 and Na3Co2SbO6. The low-temperature exchange reaction exclusively produces the rhombahedral 3R polytype subcell, whereas only the hexagonal 2H polytype subcell has been made by conventional synthesis. The thus-synthesized 3R variants are visually striking; they are bright lime-green (Ni variant) and terracotta-orange (Co variant), while both of the conventionally synthesized 2H variants have a burnt-red color. The new structures are characterized by powder X-ray diffraction and Rietveld analysis as well as magnetic susceptibility, X-ray photoelectron spectroscopy (XPS), and diffuse-reflectance optical spectroscopy. Using thermogravimetric analysis, we identify a second order 3R → 2H phase transition as well as a first-order structural transition associated with rearrangement of the honeycomb stacking layers. The optical absorbance spectra of the samples show discrete edges that correlate well to their visual colors. Exposing Cu3Ni2SbO6 to O2 and heat causes the sample to change color. XPS confirms the presence of Cu(2+) in these samples, which implies that the difference in color between the polytypes is due to oxygen intercalation resulting from their different synthetic routes.

A Fully Inkjet Printed 3D Honeycomb Inspired Patch Antenna

KAUST Repository

McKerricher, Garret

2015-07-16

The ability to inkjet print three-dimensional objects with integrated conductive metal provides many opportunities for fabrication of radio frequency electronics and electronics in general. Both a plastic material and silver conductor are deposited by inkjet printing in this work. This is the first demonstration of a fully 3D Multijet printing process with integrated polymer and metal. A 2.4 GHz patch antenna is successfully fabricated with good performance proving the viability of the process. The inkjet printed plastic surface is very smooth, with less than 100 nm root mean square roughness. The printed silver nanoparticles are laser sintered to achieve adequate conductivity of 1e6 S/m while keeping the process below 80oC and avoiding damage to the polymer. The antenna is designed with a honeycomb substrate which minimizes material consumption. This reduces the weight, dielectric constant and dielectric loss which are all around beneficial. The antenna is entirely inkjet printed including the ground plane conductor and achieves an impressive 81% efficiency. The honeycomb substrate weighs twenty times less than a solid substrate. For comparison the honeycomb antenna provides an efficiency nearly 15% greater than a similarly fabricated antenna with a solid substrate.

Phase diagram and quantum order by disorder in the Kitaev K1-K2 honeycomb magnet

Science.gov (United States)

Rousochatzakis, Ioannis; Reuther, Johannes; Thomale, Ronny; Rachel, Stephan; Perkins, Natalia

We show that the topological Kitaev spin liquid on the honeycomb lattice is extremely fragile against the second neighbor Kitaev coupling K2, which has been recently identified as the dominant perturbation away from the nearest neighbor model in iridate Na2IrO3, and may also play a role in α-RuCl3. This coupling explains naturally the zig-zag ordering and the special entanglement between real and spin space observed recently in Na2IrO3. The minimal K1-K2 model that we present here holds in addition the unique property that the classical and quantum phase diagrams and their respective order-by-disorder mechanisms are qualitatively different due to their fundamentally different symmetry structure. Nsf DMR-1511768; Freie Univ. Berlin Excellence Initiative of German Research Foundation; European Research Council, ERC-StG-336012; DFG-SFB 1170; DFG-SFB 1143, DFG-SPP 1666, and Helmholtz association VI-521.

Improved Electrochromic Characteristics of a Honeycomb-Structured Film Composed of NiO.

Science.gov (United States)

Yang, Hyeeun; Lee, Yulhee; Kim, Dong In; Seo, Hyeon Jin; Yu, Jung-Hoon; Nam, Sang-Hun; Boo, Jin-Hyo

2018-09-01

Color changes controlled by electronic energies have been studied for many years in order to fabricate energy-efficient smart windows. Reduction and oxidization of nickel oxide under the appropriate voltage can change the color of a window. For a superior nickel oxide (NiO) electrochromic device (ECD), it is important to control the chemical and physical characteristics of the surface. In this study, we applied polystyrene bead templates to nickel oxide films to fabricate a honeycomb-structured electrochromic (EC) layer. We synthesized uniform polystyrene beads using the chemical wet method and placed them on substrates to create honeycomb-structured NiO films. Then, the EC characteristics of the nickel oxide films with a honeycomb structure were evaluated with UV-Visible and cyclic voltammetry. FE-SEM and AFM were used to measure the morphologies of the nanostructures and the efficiencies of the redox reactions related to the specific surface area.

Lattice specific heat for the RMIn5 (R=Gd, La, Y; M=Co, Rh) compounds: Non-magnetic contribution subtraction

International Nuclear Information System (INIS)

Facio, Jorge I.; Betancourth, D.; Cejas Bolecek, N.R.; Jorge, G.A.; Pedrazzini, Pablo; Correa, V.F.; Cornaglia, Pablo S.; Vildosola, V.; García, D.J.

2016-01-01

We analyze theoretically a common experimental process used to obtain the magnetic contribution to the specific heat of a given magnetic material. In the procedure, the specific heat of a non-magnetic analog is measured and used to subtract the non-magnetic contributions, which are generally dominated by the lattice degrees of freedom in a wide range of temperatures. We calculate the lattice contribution to the specific heat for the magnetic compounds GdMIn 5 (M=Co, Rh) and for the non-magnetic YMIn 5 and LaMIn 5 (M=Co, Rh), using density functional theory based methods. We find that the best non-magnetic analog for the subtraction depends on the magnetic material and on the range of temperatures. While the phonon specific heat contribution of YRhIn 5 is an excellent approximation to the one of GdCoIn 5 in the full temperature range, for GdRhIn 5 we find a better agreement with LaCoIn 5 , in both cases, as a result of an optimum compensation effect between masses and volumes. We present measurements of the specific heat of the compounds GdMIn 5 (M=Co, Rh) up to room temperature where it surpasses the value expected from the Dulong–Petit law. We obtain a good agreement between theory and experiment when we include anharmonic effects in the calculations.

Classification of defects in honeycomb composite structure of helicopter rotor blades

International Nuclear Information System (INIS)

Balasko, M.; Svab, E.; Molnar, Gy.; Veres, I.

2005-01-01

The use of non-destructive testing methods to qualify the state of rotor blades with respect to their expected flight hours, with the aim to extend their lifetime without any risk of breakdown, is an important financial demand. In order to detect the possible defects in the composite structure of Mi-8 and Mi-24 type helicopter rotor blades used by the Hungarian Army, we have performed combined neutron- and X-ray radiography measurements at the Budapest Research Reactor. Several types of defects were detected, analysed and typified. Among the most frequent and important defects observed were cavities, holes and or cracks in the sealing elements on the interface of the honeycomb structure and the section boarders. Inhomogeneities of the resin materials (resin-rich or starved areas) at the core-honeycomb surfaces proved to be an other important point. Defects were detected at the adhesive filling, and water percolation was visualized at the sealing interfaces of the honeycomb sections. Corrosion effects, and metal inclusions have also been detected

Classification of defects in honeycomb composite structure of helicopter rotor blades

Science.gov (United States)

Balaskó, M.; Sváb, E.; Molnár, Gy.; Veres, I.

2005-04-01

The use of non-destructive testing methods to qualify the state of rotor blades with respect to their expected flight hours, with the aim to extend their lifetime without any risk of breakdown, is an important financial demand. In order to detect the possible defects in the composite structure of Mi-8 and Mi-24 type helicopter rotor blades used by the Hungarian Army, we have performed combined neutron- and X-ray radiography measurements at the Budapest Research Reactor. Several types of defects were detected, analysed and typified. Among the most frequent and important defects observed were cavities, holes and/or cracks in the sealing elements on the interface of the honeycomb structure and the section boarders. Inhomogeneities of the resin materials (resin-rich or starved areas) at the core-honeycomb surfaces proved to be an other important point. Defects were detected at the adhesive filling, and water percolation was visualized at the sealing interfaces of the honeycomb sections. Corrosion effects, and metal inclusions have also been detected.

Anomalous thermodynamic behaviour of novel compounds: inelastic neutron scattering and lattice dynamics studies

International Nuclear Information System (INIS)

Mittal, R.

2014-01-01

The understanding of the thermodynamic properties of solids has important applications in diverse areas like condensed matter physics, materials science, mineralogy, geophysics, etc. We have been extensively investigating anomalous thermodynamic properties of compounds using the techniques of inelastic neutron scattering and lattice dynamics. We would present some of the results from our recent studies. Studies of materials exhibiting anomalous thermal expansion are of interest due to their fundamental scientific importance and potential applications in ceramic, optical and electronic industry etc. We have studied the thermodynamic properties of negative thermal expansion (NTE) compounds ZrW 2 O 8 , HfW 2 O 8 , ZrMo 2 O 8 , ZrV 2 O 7 , HfV 2 O 7 , Zn(CN) 2 , Cu 2 O, Ag 2 O, Ag 3 Co(CN) 6 and Ag 3 Fe(CN) 6 . Our calculations predicted that large softening of the phonon spectrum involving librational and translational modes below 10 MeV would be responsible for anomalous thermal expansion behaviour. High pressure inelastic neutron scattering experiments carried by us on cubic ZrW 2 O 8 , ZrMo 2 O 8 and Zn(CN) 2 confirmed the phonon softening. Our studies indicate that unusual phonon softening of low energy modes is able to account for the thermal expansion behaviour in these compounds. Superionic conduction in fluorite-structured (anti-fluorite, Li 2 O) oxides (MO 2 , M= U, Th) have applications in energy storage, conversion and nuclear industry. The possible role of phonon in initiation of diffusion has been studied in Li 2 O. We found that in the superionic regime lithium atoms may exhibit macroscopic movement along (100) direction. The microscopic modeling or simulation is found to play a pivotal role in understanding the conduction processes at high temperatures in Li 2 O. We have also studied zircon structured compounds MSiO 4 (M=Zr, Hf, Th, U), RPO 4 , (R=rare earth atom). The compounds are known to transform to the scheelite (body centered tetragonal, I4 1 /a

Pressure dependence of the Curie temperature in the Kondo lattice compound YbNiSn

Energy Technology Data Exchange (ETDEWEB)

Sparn, G; Thompson, J D [Los Alamos National Lab., NM (United States); Hamzic, A [Dept. of Physics, Zagreb (Yugoslavia)

1992-04-03

We have measured the magnetic susceptibility (2 K < T < 300 K) and the electrical resistivity under pressure (1.2 K < T < 300 K; p < 20 kbar) of the Kondo lattice compound YbNiSn, which may be considered as the ''hole'' analogue of the isostructural compound CeNiSn. In contrast with CeNiSn, YbNiSn does not show an energy gap at low temperatures but instead undergoes a magnetic phase transition at T{sub M} = 5.5 K. The magnetic state might be either a weakly ferromagnetic or a complex antiferromagnetic state. By applying pressure the room temperature resistance {rho}{sub RT} decreases, while T{sub M} increases. This behavior can be interpreted with respect to Doniach's Kondo necklace model as a decrease in the local exchange coupling constant J with increasing pressure, which reduces Kondo spin compensation and favors long-range magnetic order. These results show that the idea that YbNiSn is the hole counterpart to CeNiSn holds well for the properties such as dT{sub M}/dP and d{rho}{sub RT}/dP but that it fails in more detailed aspects, such as the origin of the energy gap formation. (orig.).

The Honeycomb illusion: Uniform textures not perceived as such

Directory of Open Access Journals (Sweden)

Marco Bertamini

2016-07-01

Full Text Available We present a series of patterns, in which texture is perceived differently at fixation in comparison to the periphery, such that a physically uniform stimulus yields a nonuniform percept. We call this the Honeycomb illusion, and we discuss it in relation to the similar Extinction illusion (Ninio & Stevens, 2000. The effect remains strong despite multiple fixations, dynamic changes, and manipulations of the size of texture elements. We discuss the phenomenon in relation to how vision achieves a detailed and stable representation of the environment despite changes in retinal spatial resolution and dramatic changes across saccades. The Honeycomb illusion complements previous related observations in suggesting that this representation is not necessarily based on multiple fixations (i.e., memory or on extrapolation from information available to central vision.

Deformation behaviors of three-dimensional graphene honeycombs under out-of-plane compression: Atomistic simulations and predictive modeling

Science.gov (United States)

Meng, Fanchao; Chen, Cheng; Hu, Dianyin; Song, Jun

2017-12-01

Combining atomistic simulations and continuum modeling, a comprehensive study of the out-of-plane compressive deformation behaviors of equilateral three-dimensional (3D) graphene honeycombs was performed. It was demonstrated that under out-of-plane compression, the honeycomb exhibits two critical deformation events, i.e., elastic mechanical instability (including elastic buckling and structural transformation) and inelastic structural collapse. The above events were shown to be strongly dependent on the honeycomb cell size and affected by the local atomic bonding at the cell junction. By treating the 3D graphene honeycomb as a continuum cellular solid, and accounting for the structural heterogeneity and constraint at the junction, a set of analytical models were developed to accurately predict the threshold stresses corresponding to the onset of those deformation events. The present study elucidates key structure-property relationships of 3D graphene honeycombs under out-of-plane compression, and provides a comprehensive theoretical framework to predictively analyze their deformation responses, and more generally, offers critical new knowledge for the rational bottom-up design of 3D networks of two-dimensional nanomaterials.

Characterization of Thermal and Mechanical Impact on Aluminum Honeycomb Structures

Science.gov (United States)

Robinson, Christen M.

2013-01-01

This study supports NASA Kennedy Space Center's research in the area of intelligent thermal management systems and multifunctional thermal systems. This project addresses the evaluation of the mechanical and thermal properties of metallic cellular solid (MCS) materials; those that are lightweight; high strength, tunable, multifunctional and affordable. A portion of the work includes understanding the mechanical properties of honeycomb structured cellular solids upon impact testing under ambient, water-immersed, liquid nitrogen-cooled, and liquid nitrogen-immersed conditions. Additionally, this study will address characterization techniques of the aluminum honeycomb's ability to resist multiple high-rate loadings or impacts in varying environmental conditions, using various techniques for the quantitative and qualitative determination for commercial applicability.

Frustrated lattices of Ising chains

International Nuclear Information System (INIS)

Kudasov, Yurii B; Korshunov, Aleksei S; Pavlov, V N; Maslov, Dmitrii A

2012-01-01

The magnetic structure and magnetization dynamics of systems of plane frustrated Ising chain lattices are reviewed for three groups of compounds: Ca 3 Co 2 O 6 , CsCoCl 3 , and Sr 5 Rh 4 O 12 . The available experimental data are analyzed and compared in detail. It is shown that a high-temperature magnetic phase on a triangle lattice is normally and universally a partially disordered antiferromagnetic (PDA) structure. The diversity of low-temperature phases results from weak interactions that lift the degeneracy of a 2D antiferromagnetic Ising model on the triangle lattice. Mean-field models, Monte Carlo simulation results on the static magnetization curve, and results on slow magnetization dynamics obtained with Glauber's theory are discussed in detail. (reviews of topical problems)

Detection of honeycomb cell walls from measurement data based on Harris corner detection algorithm

Science.gov (United States)

Qin, Yan; Dong, Zhigang; Kang, Renke; Yang, Jie; Ayinde, Babajide O.

2018-06-01

A honeycomb core is a discontinuous material with a thin-wall structure—a characteristic that makes accurate surface measurement difficult. This paper presents a cell wall detection method based on the Harris corner detection algorithm using laser measurement data. The vertexes of honeycomb cores are recognized with two different methods: one method is the reduction of data density, and the other is the optimization of the threshold of the Harris corner detection algorithm. Each cell wall is then identified in accordance with the neighboring relationships of its vertexes. Experiments were carried out for different types and surface shapes of honeycomb cores, where the proposed method was proved effective in dealing with noise due to burrs and/or deformation of cell walls.

The use of paper honeycomb for prototype blade construction for small to medium-sized wind driven generators

Science.gov (United States)

Meyer, H.

1973-01-01

Paper honeycomb is used for the construction of conventional, propeller-type, windmill blades. Using fairly simple techniques and conventional power tools, it is possible to shape both simple foils and more complex foils with or without tapered plan forms and with or without varying profiles. A block of honeycomb, in its compressed form, is mounted on a wedge and run through a bandsaw with the table at an appropriate tilt angle. It is the combination of the wedge angle and the table angle that gives the tapered planform and profile shape. Next the honeycomb is expanded on the shaft and jigged to give the desired angles of attack. With the honeycomb fixed in position, the blade is covered with a fine weave fiberglass cloth. Any surface quality can then be achieved with filling and sanding.

Numerical Investigation on Dynamic Crushing Behavior of Auxetic Honeycombs with Various Cell-Wall Angles

Directory of Open Access Journals (Sweden)

Xin-chun Zhang

2015-02-01

Full Text Available Auxetic honeycombs have proven to be an attractive advantage in actual engineering applications owing to their unique mechanical characteristic and better energy absorption ability. The in-plane dynamic crushing behaviors of the honeycombs with various cell-wall angles are studied by means of explicit dynamic finite element simulation. The influences of the cell-wall angle, the impact velocity, and the edge thickness on the macro/microdeformation behaviors, the plateau stresses, and the specific energy absorption of auxetic honeycombs are discussed in detail. Numerical results show, that except for the impact velocity and the edge thickness, the in-plane dynamic performances of auxetic honeycombs also rely on the cell-wall angle. The “> <”-mode local deformation bands form under low- or moderate-velocity impacting, which results in lateral compression shrinkage and shows negative Poisson's ratio during the crushing. For the given impact velocity, the plateau stress at the proximal end and the energy-absorbed ability can be improved by increasing the negative cell angle, the relative density, the impact velocity, and the matrix material strength. When the microcell parameters are the constant, the plateau stresses are proportional to the square of impact velocity.

Mechanical analysis of an assembly box with honeycomb structure

International Nuclear Information System (INIS)

Herbell, Heiko; Himmel, Steffen; Schulenberg, Thomas

2008-01-01

Fuel assembly concepts for supercritical water cooled reactors have often been designed with assembly and moderator boxes to provide additional moderator water in the core in case of higher coolant temperatures. The fuel assembly considered here has been designed for the High Performance Light Water Reactor (HPLWR) with three succeeding heat up steps, one evaporator and two superheater steps. The high coolant pressure drop of such a core design causes, however, a higher pressure difference across the box walls than those typically occurring in boiling water reactors. Hot, superheated steam conditions, on the other hand, require thermally insulated box walls rather than solid box walls to reduce heating of the moderator water. In this paper an innovative design for moderator- and assembly boxes is investigated which consists of an alumina filled stainless steel honeycomb structure, built as a sandwich design between two stainless steel liners. The liners in contact with the colder moderator water are perforated to lower the pressure load on the honeycomb structure. As a consequence, the alumina will be soaked with supercritical water causing stagnant flow conditions in the honeycomb cells. In comparison to solid box walls, the use of the presented design can provide the same stiffness but with a drastic reduction of structural material and thus less neutron absorption. Finite Element Analyses are used to verify the required stiffness, to identify stress concentrations, and to optimize the design. (author)

Evaluation of thermal shock resistance of cordierite honeycombs

Indian Academy of Sciences (India)

A comparative study on thermal shock resistance (TSR) of extruded cordierite honeycombs is presented. TSR is an important property that predicts the life of these products in thermal environments used for automobile pollution control as catalytic converter or as diesel particulate filter. TSR was experimentally studied by ...

The Lattice Compatibility Theory LCT: Physical and Chemical Arguments from the Growth Behavior of Doped Compounds in terms of Bandgap Distortion and Magnetic Effects

Directory of Open Access Journals (Sweden)

K. Boubaker

2013-01-01

Full Text Available Physical and chemical arguments for the recently discussed materials-related Lattice Compatibility Theory are presented. The discussed arguments are based on some differences of Mn ions incorporation kinetics inside some compounds. These differences have been evaluated and quantified in terms of alteration of bandgap edges, magnetic patterns, and Faraday effect.

Flux lattice melting in high-Tc superconductors

International Nuclear Information System (INIS)

Houghton, A.; Pelcovits, R.A.; Sudbo, A.

1989-01-01

We derive the wave-vector-dependent elastic moduli for a flux line lattice in compounds with underlying tetragonal crystalline symmetry. We find that it is essential to retain wave-vector dependence of the moduli when dealing with compounds where κ is large, as it is in the high-T c materials. We use our results to establish a Lindemann criterion for flux lattice melting, which we then compare with experimental data on two materials, and find excellent agreement. The melting curves are suppressed well below the mean-field superconducting-normal transition line and are linear in temperature over a wide range of magnetic fields. The point H=0, T=T c is approached as 1-T/T c ∼H 1/2 . The degree of suppression of the melting curves among the different compounds is accounted for in the main by differences in mass anisotropy

Lattice dynamics of γ--Ce

International Nuclear Information System (INIS)

Gould, T.A.

1978-08-01

The phonon and magnetic measurements described in the thesis produced the following significant results concerning the lattice dynamical and magnetic properties of γ-Ce. The phonon spectrum is relatively soft, which is consistent with results obtained for CeSn 3 . The L [110] and T [111] branches of the dispersion curve are anomalous. The C 11 and C 44 elastic constants are quite close in value. No discrete magnetic excitations were observed. The magnetic scattering is qualitatively similar to the results from Ce 0 . 74 Th 0 . 26 , however, GAMMA/sub Ce/ less than GAMMA/sub Ce-Th/. The various lattice dynamical and magnetic similarities among γ-Ce, CeSn 3 , and Ce 0 . 74 Th 0 . 26 are mixed valence compounds. Therefore, a complete theoretical description of the observed properties of Ce and its compounds may provide a basis for understanding a whole class of mixed valence materials

The realization of Majorana fermions in Kitaev Quantum Spin Lattice

Science.gov (United States)

Do, Seung-Hwan; Park, Sang-Youn; Yoshitake, Junki; Nasu, Joji; Motome, Yukitoshi; Kwon, Y. S.; Adroja, D. T.; Voneshen, D.; Park, J.-H.; Choi, Kwang-Yong; Ji, Sungdae

The Kitaev honeycomb lattice is envisioned as an ideal host for Majorana fermions that are created out of the spin liquid background. Combining specific heat and neutron scattering experiments with theoretical calculations, here, we establish a hitherto unparalleled spin fractionalization to two species of Majorana fermions in the Kitaev material α-RuCl3. The specific heat data unveil a two-stage release of magnetic entropy by (R/2)ln2 and the T-linear dependence at intermediate temperatures. Our inelastic neutron scattering measurements further corroborate two distinct characters of fractionalized excitations: an Y-like, dispersive, magnetic continuum at higher energies and a dispersionless excitation at low energies around the Brillouin zone center. These dual features are well described by a Ferromagnetic Kitaev model, providing a smoking gun proof of the itinerant and localized Majorana fermions emergent in Kitaev magnets.

Possible bicollinear nematic state with monoclinic lattice distortions in iron telluride compounds

Energy Technology Data Exchange (ETDEWEB)

Bishop, Christopher B. [Univ. of Tennessee, Knoxville, TN (United States); Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Herbrych, Jacek W. [Univ. of Tennessee, Knoxville, TN (United States); Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Dagotto, Elbio R. [Univ. of Tennessee, Knoxville, TN (United States); Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Moreo, Adriana [Univ. of Tennessee, Knoxville, TN (United States); Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)

2017-07-15

Here, iron telluride (FeTe) is known to display bicollinear magnetic order at low temperatures together with a monoclinic lattice distortion. Because the bicollinear order can involve two different wave vectors (π/2,π/2) and (π/2,–π/2), symmetry considerations allow for the possible stabilization of a nematic state with short-range bicollinear order coupled to monoclinic lattice distortions at a T_S higher than the temperature T_N where long-range bicollinear order fully develops. As a concrete example, the three-orbital spin-fermion model for iron telluride is studied with an additional coupling ˜λ₁₂ between the monoclinic lattice strain and an orbital-nematic order parameter with B_2g symmetry. Monte Carlo simulations show that with increasing ˜λ₁₂ the first-order transition characteristic of FeTe splits and bicollinear nematicity is stabilized in a (narrow) temperature range. In this new regime, the lattice is monoclinically distorted and short-range spin and orbital order breaks rotational invariance. A discussion of possible realizations of this exotic state is provided.

Honeycomb-like graphitic ordered macroporous carbon prepared by pyrolysis of ammonium bicarbonate

Energy Technology Data Exchange (ETDEWEB)

Wang, Liancheng [Key Laboratory of Colloid and Interface Chemistry, Shandong University, Jinan, Shandong 250100 (China); Zhang, Junhao, E-mail: jhzhang6@mail.ustc.edu.cn [Key Laboratory of Colloid and Interface Chemistry, Shandong University, Jinan, Shandong 250100 (China); School of Biology and Chemical Engineering, Jiangsu University of Science and Technology, Zhenjiang, Jiangsu 212003 (China); Xu, Liqiang; Qian, Yitai [Key Laboratory of Colloid and Interface Chemistry, Shandong University, Jinan, Shandong 250100 (China)

2011-10-15

Graphical abstract: Honeycomb-like graphitic macroporous carbon (HGMC) with big pores centered at 1-3 {mu}m, has been prepared by controlling the reaction temperature and amount of NH{sub 4}HCO{sub 3} at 550 {sup o}C in a sealed reaction system. Possible formation processes of HGMC are discussed on the experimental results. It is believed that the in situ formed MgO microparticles play a template role during the preparation of HGMC. Highlights: {yields} Honeycomb-like graphitic carbon was synthesized at 550 {sup o}C. {yields} The honeycomb-like graphitic carbon is macroposous structures. {yields} The formed MgO microparticles play a template role during the HGMC formation. {yields} The method can be expended to synthesize other porous or hollow carbon material. -- Abstract: Honeycomb-like graphitic macroporous carbon (HGMC) was synthesized by means of pyrolysis of NH{sub 4}HCO{sub 3} using Mg powder as reductant in an autoclave at 550 {sup o}C. The characterization of structure and morphology was carried out by X-ray diffraction (XRD), Raman spectrum, field-emission scanning electron microscopy (FESEM), and (High-resolution) transmission electron microscope [(HR)TEM]. The results of nitrogen adsorption-desorption indicate that the products are macropore materials with the pore size of 1-3 {mu}m, and the Brunauer-Emett-Teller (BET) surface area was 14 m{sup 2}/g. As a typical morphology, the possible growth process of HGMC was also investigated and discussed. The experimental results show that the in situ formed MgO microparticles play a template role during the HGMC formation.

Honeycomb-like graphitic ordered macroporous carbon prepared by pyrolysis of ammonium bicarbonate

International Nuclear Information System (INIS)

Wang, Liancheng; Zhang, Junhao; Xu, Liqiang; Qian, Yitai

2011-01-01

Graphical abstract: Honeycomb-like graphitic macroporous carbon (HGMC) with big pores centered at 1-3 μm, has been prepared by controlling the reaction temperature and amount of NH 4 HCO 3 at 550 o C in a sealed reaction system. Possible formation processes of HGMC are discussed on the experimental results. It is believed that the in situ formed MgO microparticles play a template role during the preparation of HGMC. Highlights: → Honeycomb-like graphitic carbon was synthesized at 550 o C. → The honeycomb-like graphitic carbon is macroposous structures. → The formed MgO microparticles play a template role during the HGMC formation. → The method can be expended to synthesize other porous or hollow carbon material. -- Abstract: Honeycomb-like graphitic macroporous carbon (HGMC) was synthesized by means of pyrolysis of NH 4 HCO 3 using Mg powder as reductant in an autoclave at 550 o C. The characterization of structure and morphology was carried out by X-ray diffraction (XRD), Raman spectrum, field-emission scanning electron microscopy (FESEM), and (High-resolution) transmission electron microscope [(HR)TEM]. The results of nitrogen adsorption-desorption indicate that the products are macropore materials with the pore size of 1-3 μm, and the Brunauer-Emett-Teller (BET) surface area was 14 m 2 /g. As a typical morphology, the possible growth process of HGMC was also investigated and discussed. The experimental results show that the in situ formed MgO microparticles play a template role during the HGMC formation.

An examination of impact damage in glass-phenolic and aluminum honeycomb core composite panels

Science.gov (United States)

Nettles, A. T.; Lance, D. G.; Hodge, A. J.

1990-01-01

An examination of low velocity impact damage to glass-phenolic and aluminum core honeycomb sandwich panels with carbon-epoxy facesheets is presented. An instrumented drop weight impact test apparatus was utilized to inflict damage at energy ranges between 0.7 and 4.2 joules. Specimens were checked for extent of damage by cross sectional examination. The effect of core damage was assessed by subjecting impact-damaged beams to four-point bend tests. Skin-only specimens (facings not bonded to honeycomb) were also tested for comparison purposes. Results show that core buckling is the first damage mode, followed by delaminations in the facings, matrix cracking, and finally fiber breakage. The aluminum honeycomb panels exhibited a larger core damage zone and more facing delaminations than the glass-phenolic core, but could withstand more shear stress when damaged than the glass-phenolic core specimens.

Natural convection and radiation heat transfer in a vertical porous layer with a hexagonal honeycomb core. 2nd Report. Experiment on heat transfer; Honeycomb core de shikirareta enchoku takoshitsu sonai no shizen tairyu - fukusha fukugo netsu dentatsu. 2. Dennetsu jikken

Energy Technology Data Exchange (ETDEWEB)

Yamaguchi, Y; Asako, Y [Tokyo Metropolitan Univ., Tokyo (Japan). Faculty of Technology

1997-06-25

The combined natural convection and radiation heat transfer characteristics in a vertical porous layer with a hexagonal honeycomb core were investigate experimentally. The temperature distributions on the honeycomb core wall and the combined heat transfer rates through the porous layer were measured. The measurements of the heat transfer were accomplished using the guarded hot plate (GHP) method. The honeycomb core wall was made of paper and large mesh foamed resins were inserted into the honeycomb enclosures. The measurements were performed while varying the radiation parameters between 0.5 to 0.65, varying the temperature ratios between 0.01 to 0.1 and varying the Darcy-Rayleigh numbers between 5 to 80, and for a fixed aspect ratio of H/L=1. The experimental results for Nusselt numbers agreed well with our available numerical results. 9 refs., 8 figs.

Half-metallicity in 2D organometallic honeycomb frameworks

Science.gov (United States)

Sun, Hao; Li, Bin; Zhao, Jin

2016-10-01

Half-metallic materials with a high Curie temperature (T C) have many potential applications in spintronics. Magnetic metal free two-dimensional (2D) half-metallic materials with a honeycomb structure contain graphene-like Dirac bands with π orbitals and show excellent aspects in transport properties. In this article, by investigating a series of 2D organometallic frameworks with a honeycomb structure using first principles calculations, we study the origin of forming half-metallicity in this kind of 2D organometallic framework. Our analysis shows that charge transfer and covalent bonding are two crucial factors in the formation of half-metallicity in organometallic frameworks. (i) Sufficient charge transfer from metal atoms to the molecules is essential to form the magnetic centers. (ii) These magnetic centers need to be connected through covalent bonding, which guarantee the strong ferromagnetic (FM) coupling. As examples, the organometallic frameworks composed by (1,3,5)-benzenetricarbonitrile (TCB) molecules with noble metals (Au, Ag, Cu) show half-metallic properties with T C as high as 325 K. In these organometallic frameworks, the strong electronegative cyano-groups (CN groups) drive the charge transfer from metal atoms to the TCB molecules, forming the local magnetic centers. These magnetic centers experience strong FM coupling through the d-p covalent bonding. We propose that most of the 2D organometallic frameworks composed by molecule—CN—noble metal honeycomb structures contain similar half metallicity. This is verified by replacing TCB molecules with other organic molecules. Although the TCB-noble metal organometallic framework has not yet been synthesized, we believe the development of synthesizing techniques and facility will enable the realization of them. Our study provides new insight into the 2D half-metallic material design for the potential applications in nanotechnology.

Half-metallicity in 2D organometallic honeycomb frameworks

International Nuclear Information System (INIS)

Sun, Hao; Li, Bin; Zhao, Jin

2016-01-01

Half-metallic materials with a high Curie temperature (T C ) have many potential applications in spintronics. Magnetic metal free two-dimensional (2D) half-metallic materials with a honeycomb structure contain graphene-like Dirac bands with π orbitals and show excellent aspects in transport properties. In this article, by investigating a series of 2D organometallic frameworks with a honeycomb structure using first principles calculations, we study the origin of forming half-metallicity in this kind of 2D organometallic framework. Our analysis shows that charge transfer and covalent bonding are two crucial factors in the formation of half-metallicity in organometallic frameworks. (i) Sufficient charge transfer from metal atoms to the molecules is essential to form the magnetic centers. (ii) These magnetic centers need to be connected through covalent bonding, which guarantee the strong ferromagnetic (FM) coupling. As examples, the organometallic frameworks composed by (1,3,5)-benzenetricarbonitrile (TCB) molecules with noble metals (Au, Ag, Cu) show half-metallic properties with T C as high as 325 K. In these organometallic frameworks, the strong electronegative cyano-groups (CN groups) drive the charge transfer from metal atoms to the TCB molecules, forming the local magnetic centers. These magnetic centers experience strong FM coupling through the d – p covalent bonding. We propose that most of the 2D organometallic frameworks composed by molecule—CN—noble metal honeycomb structures contain similar half metallicity. This is verified by replacing TCB molecules with other organic molecules. Although the TCB-noble metal organometallic framework has not yet been synthesized, we believe the development of synthesizing techniques and facility will enable the realization of them. Our study provides new insight into the 2D half-metallic material design for the potential applications in nanotechnology. (paper)

Compressive failure modes and parameter optimization of the trabecular structure of biomimetic fully integrated honeycomb plates.

Science.gov (United States)

Chen, Jinxiang; Tuo, Wanyong; Zhang, Xiaoming; He, Chenglin; Xie, Juan; Liu, Chang

2016-12-01

To develop lightweight biomimetic composite structures, the compressive failure and mechanical properties of fully integrated honeycomb plates were investigated experimentally and through the finite element method. The results indicated that: fracturing of the fully integrated honeycomb plates primarily occurred in the core layer, including the sealing edge structure. The morphological failures can be classified into two types, namely dislocations and compactions, and were caused primarily by the stress concentrations at the interfaces between the core layer and the upper and lower laminations and secondarily by the disordered short-fiber distribution in the material; although the fully integrated honeycomb plates manufactured in this experiment were imperfect, their mass-specific compressive strength was superior to that of similar biomimetic samples. Therefore, the proposed bio-inspired structure possesses good overall mechanical properties, and a range of parameters, such as the diameter of the transition arc, was defined for enhancing the design of fully integrated honeycomb plates and improving their compressive mechanical properties. Copyright © 2016 Elsevier B.V. All rights reserved.

Post-Buckling Analysis of Curved Honeycomb Sandwich Panels Containing Interfacial Disbonds

Science.gov (United States)

Pineda, Evan J.; Bednarcyk, Brett A.; Krivanek, Thomas K.

2016-01-01

A numerical study on the effect of facesheet-core disbonds on the post-buckling response of curved honeycomb sandwich panels is presented herein. This work was conducted as part of the development of a damage tolerance plan for the next-generation Space Launch System heavy lift launch vehicle payload fairing. As such, the study utilized full-scale fairing barrel segments as the structure of interest. The panels were composed of carbon fiber reinforced polymer facesheets and aluminum honeycomb core. The panels were analyzed numerically using the finite element method incorporating geometric nonlinearity. In a predetermined circular region, facesheet and core nodes were detached to simulate a disbond, between the outer mold line facesheet and honeycomb core, induced via low-speed impact. Surface-to-surface contact in the disbonded region was invoked to prevent interpenetration of the facesheet and core elements and obtain realistic stresses in the core. The diameter of this disbonded region was varied and the effect of the size of the disbond on the post-buckling response was observed. Significant changes in the slope of the edge load-deflection response were used to determine the onset of global buckling and corresponding buckling load. Finally, several studies were conducted to determine the sensitivity of the numerical predictions to refinement in the finite element mesh.

Experimental and Analytical Evaluation of a Composite Honeycomb Deployable Energy Absorber

Science.gov (United States)

Jackson, Karen E.; Kellas, Sotiris; Horta, Lucas G.; Annett, Martin S.; Polanco, Michael A.; Littell, Justin D.; Fasanella, Edwin L.

2011-01-01

In 2006, the NASA Subsonic Rotary Wing Aeronautics Program sponsored the experimental and analytical evaluation of an externally deployable composite honeycomb structure that is designed to attenuate impact energy during helicopter crashes. The concept, which is designated the Deployable Energy Absorber (DEA), utilizes an expandable Kevlar honeycomb structure to dissipate kinetic energy through crushing. The DEA incorporates a unique flexible hinge design that allows the honeycomb to be packaged and stowed flat until needed for deployment. A variety of deployment options such as linear, radial, and/or hybrid methods can be used. Experimental evaluation of the DEA utilized a building block approach that included material characterization testing of its constituent, Kevlar -129 fabric/epoxy, and flexural testing of single hexagonal cells. In addition, the energy attenuation capabilities of the DEA were demonstrated through multi-cell component dynamic crush tests, and vertical drop tests of a composite fuselage section, retrofitted with DEA blocks, onto concrete, water, and soft soil. During each stage of the DEA evaluation process, finite element models of the test articles were developed and simulations were performed using the explicit, nonlinear transient dynamic finite element code, LS-DYNA. This report documents the results of the experimental evaluation that was conducted to assess the energy absorption capabilities of the DEA.

Mechanics of pressure-adaptive honeycomb and its application to wing morphing

International Nuclear Information System (INIS)

Vos, Roelof; Barrett, Ron

2011-01-01

Current, highly active classes of adaptive materials have been considered for use in many different aerospace applications. From adaptive flight control surfaces to wing surfaces, shape-memory alloy (SMA), piezoelectric and electrorheological fluids are making their way into wings, stabilizers and rotor blades. Despite the benefits which can be seen in many classes of aircraft, some profound challenges are ever present, including low power and energy density, high power consumption, high development and installation costs and outright programmatic blockages due to a lack of a materials certification database on FAR 23/25 and 27/29 certified aircraft. Three years ago, a class of adaptive structure was developed to skirt these daunting challenges. This pressure-adaptive honeycomb (PAH) is capable of extremely high performance and is FAA/EASA certifiable because it employs well characterized materials arranged in ways that lend a high level of adaptivity to the structure. This study is centered on laying out the mechanics, analytical models and experimental test data describing this new form of adaptive material. A directionally biased PAH system using an external (spring) force acting on the PAH bending structure was examined. The paper discusses the mechanics of pressure adaptive honeycomb and describes a simple reduced order model that can be used to simplify the geometric model in a finite element environment. The model assumes that a variable stiffness honeycomb results in an overall deformation of the honeycomb. Strains in excess of 50% can be generated through this mechanism without encountering local material (yield) limits. It was also shown that the energy density of pressure-adaptive honeycomb is akin to that of shape-memory alloy, while exhibiting strains that are an order of magnitude greater with an energy efficiency close to 100%. Excellent correlation between theory and experiment is demonstrated in a number of tests. A proof-of-concept wing section

Lattice specific heat for the RMIn{sub 5} (R=Gd, La, Y; M=Co, Rh) compounds: Non-magnetic contribution subtraction

Energy Technology Data Exchange (ETDEWEB)

Facio, Jorge I., E-mail: jorge.facio@cab.cnea.gov.ar [Centro Atómico Bariloche and Instituto Balseiro, CNEA, 8400 Bariloche (Argentina); Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET) (Argentina); Betancourth, D.; Cejas Bolecek, N.R. [Centro Atómico Bariloche and Instituto Balseiro, CNEA, 8400 Bariloche (Argentina); Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET) (Argentina); Jorge, G.A. [Instituto de Ciencias, Universidad Nacional de General Sarmiento, Buenos Aires (Argentina); Pedrazzini, Pablo; Correa, V.F.; Cornaglia, Pablo S. [Centro Atómico Bariloche and Instituto Balseiro, CNEA, 8400 Bariloche (Argentina); Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET) (Argentina); Vildosola, V. [Centro Atómico Constituyentes, CNEA, 1650 San Martín, Buenos Aires (Argentina); Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET) (Argentina); García, D.J. [Centro Atómico Bariloche and Instituto Balseiro, CNEA, 8400 Bariloche (Argentina); Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET) (Argentina)

2016-06-01

We analyze theoretically a common experimental process used to obtain the magnetic contribution to the specific heat of a given magnetic material. In the procedure, the specific heat of a non-magnetic analog is measured and used to subtract the non-magnetic contributions, which are generally dominated by the lattice degrees of freedom in a wide range of temperatures. We calculate the lattice contribution to the specific heat for the magnetic compounds GdMIn{sub 5} (M=Co, Rh) and for the non-magnetic YMIn{sub 5} and LaMIn{sub 5} (M=Co, Rh), using density functional theory based methods. We find that the best non-magnetic analog for the subtraction depends on the magnetic material and on the range of temperatures. While the phonon specific heat contribution of YRhIn{sub 5} is an excellent approximation to the one of GdCoIn{sub 5} in the full temperature range, for GdRhIn{sub 5} we find a better agreement with LaCoIn{sub 5}, in both cases, as a result of an optimum compensation effect between masses and volumes. We present measurements of the specific heat of the compounds GdMIn{sub 5} (M=Co, Rh) up to room temperature where it surpasses the value expected from the Dulong–Petit law. We obtain a good agreement between theory and experiment when we include anharmonic effects in the calculations.

Bondonic effects in group-IV honeycomb nanoribbons with Stone-Wales topological defects.

Science.gov (United States)

Putz, Mihai V; Ori, Ottorino

2014-04-03

This work advances the modeling of bondonic effects on graphenic and honeycomb structures, with an original two-fold generalization: (i) by employing the fourth order path integral bondonic formalism in considering the high order derivatives of the Wiener topological potential of those 1D systems; and (ii) by modeling a class of honeycomb defective structures starting from graphene, the carbon-based reference case, and then generalizing the treatment to Si (silicene), Ge (germanene), Sn (stannene) by using the fermionic two-degenerate statistical states function in terms of electronegativity. The honeycomb nanostructures present η-sized Stone-Wales topological defects, the isomeric dislocation dipoles originally called by authors Stone-Wales wave or SWw. For these defective nanoribbons the bondonic formalism foresees a specific phase-transition whose critical behavior shows typical bondonic fast critical time and bonding energies. The quantum transition of the ideal-to-defect structural transformations is fully described by computing the caloric capacities for nanostructures triggered by η-sized topological isomerisations. Present model may be easily applied to hetero-combinations of Group-IV elements like C-Si, C-Ge, C-Sn, Si-Ge, Si-Sn, Ge-Sn.

Bondonic Effects in Group-IV Honeycomb Nanoribbons with Stone-Wales Topological Defects

Directory of Open Access Journals (Sweden)

Mihai V. Putz

2014-04-01

Full Text Available This work advances the modeling of bondonic effects on graphenic and honeycomb structures, with an original two-fold generalization: (i by employing the fourth order path integral bondonic formalism in considering the high order derivatives of the Wiener topological potential of those 1D systems; and (ii by modeling a class of honeycomb defective structures starting from graphene, the carbon-based reference case, and then generalizing the treatment to Si (silicene, Ge (germanene, Sn (stannene by using the fermionic two-degenerate statistical states function in terms of electronegativity. The honeycomb nanostructures present η-sized Stone-Wales topological defects, the isomeric dislocation dipoles originally called by authors Stone-Wales wave or SWw. For these defective nanoribbons the bondonic formalism foresees a specific phase-transition whose critical behavior shows typical bondonic fast critical time and bonding energies. The quantum transition of the ideal-to-defect structural transformations is fully described by computing the caloric capacities for nanostructures triggered by η-sized topological isomerisations. Present model may be easily applied to hetero-combinations of Group-IV elements like C-Si, C-Ge, C-Sn, Si-Ge, Si-Sn, Ge-Sn.

Honeycomb supports with high thermal conductivity for the Tischer-Tropsch synthesis

Energy Technology Data Exchange (ETDEWEB)

Visconti, C.G.; Rronconi, E.; Groppi, G.; Lietti, L. [Politecnico di Milano (Italy). Dipt. di Energia; Iovane, M.; Rossini, S.; Zennaro, R. [Eni S.p.A., San Donato Milanese (Italy). Div. Exploration and Production

2011-07-01

The potential of multitubular reactors loaded with washcoated structured catalysts having highly conductive honeycomb supports is investigated herein in the low temperature Fischer- Tropsch synthesis by means of a theoretical investigation. Simulation results indicate that extruded aluminum honeycomb monoliths, washcoated with a Co-based catalyst, are promising for the application at the industrial scale, in particular when adopting supports with high cell densities and catalysts with high activity. Limited temperature gradients within the reactor are in fact possible even at extreme process conditions, thus leading to interesting volumetric reactor yields with negligible pressure drop. This result is achieved without the need of cofeeding to the reactor large amounts of liquid hydrocarbons to remove the reaction heat, as opposite to existing industrial Fischer-Tropsch packed-bed reactors. (orig.)

Inserts thermal coupling analysis in hexagonal honeycomb plates used for satellite structural design

International Nuclear Information System (INIS)

Boudjemai, A.; Mankour, A.; Salem, H.; Amri, R.; Hocine, R.; Chouchaoui, B.

2014-01-01

Mechanical joints and fasteners are essential elements in joining structural components in mechanical systems. The thermal coupling effect between the adjacent inserts depends to a great extent on the thermal properties of the inserts and the clearance. In this paper the Finite-Element Method (FEM) has been employed to study the insert thermal coupling behaviour of the hexagonal honeycomb panel. Fully coupled thermal analysis was conducted in order to predict thermal coupling phenomena caused by the adjacent inserts under extreme thermal loading conditions. Detailed finite elements models for a honeycomb panel are developed in this study including the insert joints. New approach of the adhesive joint is modelled. Thermal simulations showed that the adjacent inserts cause thermal interference and the adjacent inserts are highly sensitive to the effect of high temperatures. The clearance and thermal interference between the adjacent inserts have an important influence on the satellite equipments (such as the electronics box), which can cause the satellite equipments failures. The results of the model presented in this analysis are significant in the preliminary satellites structural dimensioning which present an effective approach of development by reducing the cost and the time of analysis. - Highlights: •In this work we perform thermal analysis of honeycomb plates using finite element method. •Detailed finite elements models for honeycomb panel are developed in this study including the insert joints. •New approach of the adhesive joint is modelled. •The adjacent inserts cause the thermal interference. •We conclude that this work will help in the analysis and the design of complex satellite structures

[Removal of toluene from waste gas by honeycomb adsorption rotor with modified 13X molecular sieves].

Science.gov (United States)

Wang, Jia-De; Zheng, Liang-Wei; Zhu, Run-Ye; Yu, Yun-Feng

2013-12-01

The removal of toluene from waste gas by Honeycomb Adsorption Rotor with modified 13X molecular sieves was systematically investigated. The effects of the rotor operating parameters and the feed gas parameters on the adsorption efficiency were clarified. The experimental results indicated that the honeycomb adsorption rotor had a good humidity resistance. The removal efficiency of honeycomb adsorption rotor achieved the maximal value with optimal rotor speed and optimal generation air temperature. Moreover, for an appropriate flow rate ratio the removal efficiency and energy consumption should be taken into account. When the recommended operating parameters were regeneration air temperature of 180 degrees C, rotor speed of 2.8-5 r x h(-1), flow rate ratio of 8-12, the removal efficiency kept over 90% for the toluene gas with concentration of 100 mg x m(-3) and inlet velocity of 2 m x s(-1). The research provided design experience and operating parameters for industrial application of honeycomb adsorption rotor. It showed that lower empty bed velocity, faster rotor speed and higher temperature were necessary to purify organic waste gases of higher concentrations.

Bond and flux-disorder effects on the superconductor-insulator transition of a honeycomb array of Josephson junctions

Science.gov (United States)

Granato, Enzo

2018-05-01

We study the effects of disorder on the zero-temperature quantum phase transition of a honeycomb array of Josephson junctions in a magnetic field with an average of fo flux quantum per plaquette. Bond disorder due to spatial variations in the Josephson couplings and magnetic flux disorder due to variations in the plaquette areas are considered. The model can describe the superconductor-insulator transition in ultra-thin films with a triangular pattern of nanoholes. Path integral Monte Carlo simulations of the equivalent (2 + 1)-dimensional classical model are used to study the critical behavior and estimate the universal resistivity at the transition. The results show that bond disorder leads to a rounding of the first-order phase transition for fo = 1 / 3 to a continuous transition. For integer fo, the decrease of the critical coupling parameter with flux disorder is significantly different from that of the same model defined on a square lattice. The results are compared with recent experimental observations on nanohole thin films with geometrical disorder and external magnetic field.

Relation between Kitaev magnetism and structure in $\\alpha$-RuCl$_3$

OpenAIRE

Glamazda, A.; Lemmens, P.; Do, S. -H.; Kwon, Y. S.; Choi, K. -Y.

2017-01-01

Raman scattering has been employed to investigate lattice and magnetic excitations of the honeycomb Kitaev material $\\alpha$-RuCl$_3$ and its Heisenberg counterpart CrCl$_3$. Our phonon Raman spectra give evidence for a first-order structural transition from a monoclinic to a rhombohedral structure for both compounds. Significantly, only $\\alpha$-RuCl$_3$ features a large thermal hysteresis, consistent with the formation of a wide phase of coexistence. In the related temperature interval of $...

Bifurcations of edge states—topologically protected and non-protected—in continuous 2D honeycomb structures

International Nuclear Information System (INIS)

Fefferman, C L; Lee-Thorp, J P; Weinstein, M I

2016-01-01

Edge states are time-harmonic solutions to energy-conserving wave equations, which are propagating parallel to a line-defect or ‘edge’ and are localized transverse to it. This paper summarizes and extends the authors’ work on the bifurcation of topologically protected edge states in continuous two-dimensional (2D) honeycomb structures. We consider a family of Schrödinger Hamiltonians consisting of a bulk honeycomb potential and a perturbing edge potential. The edge potential interpolates between two different periodic structures via a domain wall. We begin by reviewing our recent bifurcation theory of edge states for continuous 2D honeycomb structures (http://arxiv.org/abs/1506.06111). The topologically protected edge state bifurcation is seeded by the zero-energy eigenstate of a one-dimensional Dirac operator. We contrast these protected bifurcations with (more common) non-protected bifurcations from spectral band edges, which are induced by bound states of an effective Schrödinger operator. Numerical simulations for honeycomb structures of varying contrasts and ‘rational edges’ (zigzag, armchair and others), support the following scenario: (a) for low contrast, under a sign condition on a distinguished Fourier coefficient of the bulk honeycomb potential, there exist topologically protected edge states localized transverse to zigzag edges. Otherwise, and for general edges, we expect long lived edge quasi-modes which slowly leak energy into the bulk. (b) For an arbitrary rational edge, there is a threshold in the medium-contrast (depending on the choice of edge) above which there exist topologically protected edge states. In the special case of the armchair edge, there are two families of protected edge states; for each parallel quasimomentum (the quantum number associated with translation invariance) there are edge states which propagate in opposite directions along the armchair edge. (paper)

Bifurcations of edge states—topologically protected and non-protected—in continuous 2D honeycomb structures

Science.gov (United States)

Fefferman, C. L.; Lee-Thorp, J. P.; Weinstein, M. I.

2016-03-01

Edge states are time-harmonic solutions to energy-conserving wave equations, which are propagating parallel to a line-defect or ‘edge’ and are localized transverse to it. This paper summarizes and extends the authors’ work on the bifurcation of topologically protected edge states in continuous two-dimensional (2D) honeycomb structures. We consider a family of Schrödinger Hamiltonians consisting of a bulk honeycomb potential and a perturbing edge potential. The edge potential interpolates between two different periodic structures via a domain wall. We begin by reviewing our recent bifurcation theory of edge states for continuous 2D honeycomb structures (http://arxiv.org/abs/1506.06111). The topologically protected edge state bifurcation is seeded by the zero-energy eigenstate of a one-dimensional Dirac operator. We contrast these protected bifurcations with (more common) non-protected bifurcations from spectral band edges, which are induced by bound states of an effective Schrödinger operator. Numerical simulations for honeycomb structures of varying contrasts and ‘rational edges’ (zigzag, armchair and others), support the following scenario: (a) for low contrast, under a sign condition on a distinguished Fourier coefficient of the bulk honeycomb potential, there exist topologically protected edge states localized transverse to zigzag edges. Otherwise, and for general edges, we expect long lived edge quasi-modes which slowly leak energy into the bulk. (b) For an arbitrary rational edge, there is a threshold in the medium-contrast (depending on the choice of edge) above which there exist topologically protected edge states. In the special case of the armchair edge, there are two families of protected edge states; for each parallel quasimomentum (the quantum number associated with translation invariance) there are edge states which propagate in opposite directions along the armchair edge.

Improved electrochemical performance of natural honeycomb templated LiSbO3 as an anode in lithium-ion battery

International Nuclear Information System (INIS)

Kundu, M.; Mahanty, S.; Basu, R.N.

2011-01-01

Highlights: → LiSbO 3 powders are synthesized by using honeycomb from natural beehive as template. → Agglomeration-free morphology with discrete cubic shaped 40-80 nm particles. → Electrochemically active anode in lithium-ion coin cells. → Improved capacity retention and rate performance in templated LiSbO 3 . - Abstract: LiSbO 3 has been synthesized by wet-chemical route using natural honeycomb as template, followed by thermal treatment at 850 deg. C. X-ray powder diffraction (XRD) confirms a single phase material having an orthorhombic crystal structure with lattice parameters of a = 4.912 A, b = 8.679 A and c = 5.089 A. Field emission scanning electron microscopy (FESEM) revealed that while conventional LiSbO 3 synthesized without using any template (C-LiSbO 3 ) consists of softly agglomerated clusters of bar-shaped multifaceted micrometer-sized grains (0.5-4.0 μm long and 0.5-1.0 μm wide), templated LiSbO 3 (T-LiSbO 3 ) consists of an agglomeration-free morphology with discrete cubic shaped particles of sizes 40-80 nm. Electrochemical investigation in 2032 type coin cells vs Li/Li + shows that Li insertion in LiSbO 3 takes place at 0.78 V while Li extraction occurs in two stages at 1.1 and 1.4 V with initial capacities of 178 and 196 mAh g -1 for C-LiSbO 3 and T-LiSbO 3 respectively. While C-LiSbO 3 shows a drastic capacity fading retaining only 28% of initial capacity after 100 cycles, T-LiSbO 3 retains ∼48% of the initial capacity due to the faceted morphology of the nanoparticles.

Ballistic resistance of honeycomb sandwich panels under in-plane high-velocity impact.

Science.gov (United States)

Qi, Chang; Yang, Shu; Wang, Dong; Yang, Li-Jun

2013-01-01

The dynamic responses of honeycomb sandwich panels (HSPs) subjected to in-plane projectile impact were studied by means of explicit nonlinear finite element simulations using LS-DYNA. The HSPs consisted of two identical aluminum alloy face-sheets and an aluminum honeycomb core featuring three types of unit cell configurations (regular, rectangular-shaped, and reentrant hexagons). The ballistic resistances of HSPs with the three core configurations were first analyzed. It was found that the HSP with the reentrant auxetic honeycomb core has the best ballistic resistance, due to the negative Poisson's ratio effect of the core. Parametric studies were then carried out to clarify the influences of both macroscopic (face-sheet and core thicknesses, core relative density) and mesoscopic (unit cell angle and size) parameters on the ballistic responses of the auxetic HSPs. Numerical results show that the perforation resistant capabilities of the auxetic HSPs increase as the values of the macroscopic parameters increase. However, the mesoscopic parameters show nonmonotonic effects on the panels' ballistic capacities. The empirical equations for projectile residual velocities were formulated in terms of impact velocity and the structural parameters. It was also found that the blunter projectiles result in higher ballistic limits of the auxetic HSPs.

Anisotropic failure and size effects in periodic honeycomb materials: A gradient-elasticity approach

Science.gov (United States)

Réthoré, Julien; Dang, Thi Bach Tuyet; Kaltenbrunner, Christine

2017-02-01

This paper proposes a fracture mechanics model for the analysis of crack propagation in periodic honeycomb materials. The model is based on gradient-elasticity which enables us to account for the effect of the material structure at the macroscopic scale. For simulating the propagation of cracks along an arbitrary path, the numerical implementation is elaborated based on an extended finite element method with the required level of continuity. The two main features captured by the model are directionality and size effect. The numerical predictions are consistent with experimental results on honeycomb materials but also with results reported in the literature for microstructurally short cracks in metals.

Lattice anisotropy in uranium ternary compounds: UTX

International Nuclear Information System (INIS)

Mašková, S.; Adamska, A.M.; Havela, L.; Kim-Ngan, N.-T.H.; Przewoźnik, J.; Daniš, S.; Kothapalli, K.; Kolomiets, A.V.; Heathman, S.; Nakotte, H.; Bordallo, H.

2012-01-01

Highlights: ► Compressibility and thermal expansion of several U-based compounds were established. ► The direction of the U–U bonds is the “soft” crystallographic direction. ► Highest coefficient of linear thermal expansion is in the direction of the U–U bonds. ► The closer the U atoms are together the better they can be compressed together. - Abstract: Several U-based intermetallic compounds (UCoGe, UNiGe with the TiNiSi structure type and UNiAl with the ZrNiAl structure type) and their hydrides were studied from the point of view of compressibility and thermal expansion. Confronted with existing data for the compounds with the ZrNiAl structure type a common pattern emerges. The direction of the U–U bonds with participation of the 5f states is distinctly the “soft” crystallographic direction, exhibiting also the highest coefficient of linear thermal expansion. The finding leads to an apparent paradox: the closer the U atoms are together in a particular direction the better they can be additionally compressed together by applied hydrostatic pressure.

Application of sandwich honeycomb carbon/glass fiber-honeycomb composite in the floor component of electric car

Science.gov (United States)

Sukmaji, I. C.; Wijang, W. R.; Andri, S.; Bambang, K.; Teguh, T.

2017-01-01

Nowadays composite is a superior material used in automotive component due to its outstanding mechanical behavior. The sandwich polypropylene honeycomb core with carbon/glass fiber composite skin (SHCG) as based material in a floor component of electric car application is investigated in the present research. In sandwich structure form, it can absorb noise better compare with the conventional material [1]. Also in present paper, Finite Element Analysis (FEA) of SHCG as based material for floor component of the electric car is analyzed. The composite sandwich is contained with a layer uniform carbon fiber and mixing non-uniform carbon-glass fiber in upper and lower skin. Between skins of SHCG are core polypropylene honeycomb that it have good flexibility to form following dies profile. The variables of volume fraction ratio of carbon/glass fiber in SHCG skin are 20/80%, 30/70%, and 50/50%. The specimen of SHCG is tested using the universal testing machine by three points bending method refers to ASTM C393 and ASTM C365. The cross point between tensile strength to the volume fraction the mixing carbon/glass line and ratio cost line are the searched material with good mechanical performance and reasonable cost. The point is 30/70 volume fraction of carbon/glass fiber. The result of the testing experiment is become input properties of model structure sandwich in FEA simulation. FEA simulation approach is conducted to find critical strength and factor of complex safety geometry against varied distributed passenger loads of a floor component the electric car. The passenger loads variable are 80, 100, 150, 200, 250 and 300 kg.

Evaluation of a bi-directional aluminum honeycomb impact limiter design

International Nuclear Information System (INIS)

Doman, M.J.

1995-01-01

A 120 Ton shipping cask is being developed for the on-site shipment of dry spent fuel at the Idaho National Engineering Laboratory. Impact limiters were incorporated in the cask design to limit the inertial load of the package and its contents during the hypothetical 9-meter (30-foot) drop accident required by 10CFR71. The design process included: (1) a series of static and dynamic tests to determine the crush characteristics of the bi-directional aluminum honeycomb impact limiter material, (2) the development of an analytical model to predict the cask deceleration force as a function of impact limiter crush, and (3) a series of quarter scale model drop tests to qualify the analytical model. The scale model testing, performed at Sandia National Laboratory in Albuquerque, New Mexico, revealed several design aspects which should be considered in developing bi-directional aluminum honeycomb impact limiters and several other design aspects which should be considered for impact limiter designs in general

Investigation of structural imitation and lattice vibrations of Pr{sub 2}Fe{sub 17-} {sub x} Mn {sub x} compounds

Energy Technology Data Exchange (ETDEWEB)

Shen Jiang [Institute of Applied Physics, University of Science and Technology Beijing, 30 Xueyuou Road, HaiDian District, Beijing 100083 (China)]. E-mail: shenj@sas.ustb.edu.cn; Qian Ping [Institute of Applied Physics, University of Science and Technology Beijing, 30 Xueyuou Road, HaiDian District, Beijing 100083 (China); Chen Nanxian [Institute of Applied Physics, University of Science and Technology Beijing, 30 Xueyuou Road, HaiDian District, Beijing 100083 (China); Department of Physics, Tsinghua University, Beijing 100084 (China)

2005-03-15

We have investigated the structural properties of Pr{sub 2}Fe{sub 17-} {sub x} Mn {sub x} compounds by using quasi-ab initio pair potentials {phi} {sub Fe-Fe}(r), {phi} {sub Pr-Fe}(r), {phi} {sub Pr-Pr}(r), {phi} {sub Pr-Mn}(r), {phi} {sub Fe-Mn}(r) and {phi} {sub Mn-Mn}(r). In Pr{sub 2}Fe{sub 17-} {sub x} Mn {sub x} , the ternary elements Mn substitute for Fe atoms without changing the crystal structure. The calculated cohesive energy curves show that for all values of x, Mn preferentially substitutes for Fe in the 6c site and randomly substitutes for Fe in the 18f and 18h site. The calculated lattice constants coincide quite well with experimental values. Furthermore, the phonon density, specific heat and vibrational entropy of these compounds are also calculated. It is interesting that simple pair potentials can describe these extremely anisotropic materials.

Field emission characteristics of vertically aligned carbon nanotubes with honeycomb configuration grown onto glass substrate with titanium coating

Energy Technology Data Exchange (ETDEWEB)

Huang, Yung-Jui [Graduate Institute of Electro-Optical Engineering, National Taiwan University of Science and Technology, Taipei 10607, Taiwan (China); Chang, Hsin-Yueh; Chang, Hsuan-Chen [Department of Electronic and computer Engineering, National Taiwan University of Science and Technology, Taipei 10607, Taiwan (China); Shih, Yi-Ting; Su, Wei-Jhih [Graduate Institute of Electro-Optical Engineering, National Taiwan University of Science and Technology, Taipei 10607, Taiwan (China); Ciou, Chen-Hong [Department of Electronic and computer Engineering, National Taiwan University of Science and Technology, Taipei 10607, Taiwan (China); Chen, Yi-Ling [Graduate Institute of Electro-Optical Engineering, National Taiwan University of Science and Technology, Taipei 10607, Taiwan (China); Honda, Shin-ichi [Graduate School of Engineering, University of Hyogo, Himeji, Hyogo 671-2280 (Japan); Huang, Ying-Sheng [Graduate Institute of Electro-Optical Engineering, National Taiwan University of Science and Technology, Taipei 10607, Taiwan (China); Department of Electronic and computer Engineering, National Taiwan University of Science and Technology, Taipei 10607, Taiwan (China); Lee, Kuei-Yi, E-mail: kylee@mail.ntust.edu.tw [Graduate Institute of Electro-Optical Engineering, National Taiwan University of Science and Technology, Taipei 10607, Taiwan (China); Department of Electronic and computer Engineering, National Taiwan University of Science and Technology, Taipei 10607, Taiwan (China)

2014-03-15

Highlights: • We have successfully designed the honeycomb patterns on glass substrate by photolithography technique. • Honeycomb-VACNTs were synthesized successfully onto glass substrate by using thermal CVD and covered different Ti films on VACNTs by e-beam evaporation. • After coating the Ti films, the current density reached 7 mA/cm{sup 2} when the electric field was 2.5 V/μm. • The fluorescence of VACNTs with Ti 15 nm films exhibits the high brightness screen and emission uniformity. -- Abstract: Carbon nanotubes (CNTs) were grown successfully onto a glass substrate using thermal chemical vapor deposition (TCVD) with C{sub 2}H{sub 2} gas at 700 °C. The synthesized CNTs exhibited good crystallinity and a vertically aligned morphology. The vertically aligned CNTs (VACNTs) were patterned with a honeycomb configuration using photolithography and characterized using field emission (FE) applications. Owing to the electric field concentration, the FE current density of VACNTs with honeycomb configuration was higher than that of the un-patterned VACNTs. Ti was coated onto the VACNT surface utilizing the relatively lower work function property to enhance the FE current density. The FE current density reached up to 7.0 mA/cm{sup 2} at an applied electric field of 2.5 V/μm. A fluorescent screen was monitored to demonstrate uniform FE VACNTs with a honeycomb configuration. The designed field emitter provided an admirable example for FE applications.

Three-Dimensional Printing Hollow Polymer Template-Mediated Graphene Lattices with Tailorable Architectures and Multifunctional Properties.

Science.gov (United States)

Zhang, Qiangqiang; Zhang, Feng; Xu, Xiang; Zhou, Chi; Lin, Dong

2018-02-27

It is a significant challenge to concurrently achieve scalable fabrication of graphene aerogels with three-dimensional (3D) tailorable architectures (e.g., lattice structure) and controllable manipulation of microstructures on the multiscale. Herein, we highlight 3D graphene lattices (GLs) with complex engineering architectures that were delicately designed and manufactured via 3D stereolithography printed hollow polymer template-mediated hydrothermal process coupled with freeze-drying strategies. The resulting GLs with overhang beams and columns show a 3D geometric configuration with hollow-carved features at the macroscale, while the construction elements of graphene cellular on the microscale exhibit a well-ordered and honeycomb-like microstructure with high porosity. These GLs demonstrate multifunctional properties with robust structure, high electrical conductivity, low thermal conductivity, and superior absorption capacitance of organic solvents. Moreover, the GLs were utilized as a subtle sensor for the fast detection of chemical agents. Aforementioned superior properties of GLs confirm that the combination of 3D tailorable manipulation and self-organization design of structures on the multiscale is an effective strategy for the scalable fabrication of advanced multifunctional graphene monoliths, suggesting their promising applications as chemical detection sensors, environmental remediation absorbers, conductive electrodes, and engineering metamaterials.

Rolling Up the Sheet: Constructing Metal–Organic Lamellae and Nanotubes from a [{Mn 3 (propanediolato) 2 }(dicyanamide) 2 ] n Honeycomb Skeleton

KAUST Repository

Wu, Gang

2013-12-11

Target synthesis of metal-organic nanotubes (MONTs) through a classic "rolling-up" mechanism remains a big challenge for coordination chemists. In this work, we report three 2D lamellar compounds and one (4,0) zigzag MONT based on a common honeycomb coordination skeleton. Our synthetic strategy toward sheet/tube superstructure transformation is to asymmetrically modify the inter-layer interactions by gradually increasing the size of the amine templates. Eventually, to relieve the surface tension of individual layers and to enhance surface areas and optimize host-guest interactions to accommodate bigger guests, spontaneous rolling up to form a tubular structure was achieved. © 2013 American Chemical Society.

Vortex lattice structures in YNi2B2C

International Nuclear Information System (INIS)

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

1997-01-01

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

Magnetic resonance studies of intercalation compounds

International Nuclear Information System (INIS)

Miller, G.R.

1990-01-01

During the last three or four years, nearly tow hundred papers have been published that used NMR or ESR spectroscopy to study compounds formed by the intercalation of molecules or ions into the van der Waals gap of a layered hast compound. The host lattices have ranged from the simple, such as graphite, to the complex, such as clay. In many cases, magnetic resonance techniques now enable one to obtain quite detailed information on even fairly complex intercalated species, on the nature of the changes in the host lattice accompanying intercalation, and on the nature of the interactions between the intercalant species and the host lattice. Magnetic resonance is used in conunction with many other techniques to obtain a fuller picture of these interesting systems, but this review will limit its focus to the use of NMR and ESR techniques. (author). 51 refs

Response of Kondo lattice systems to pressure

International Nuclear Information System (INIS)

Thompson, J.D.; Borges, H.A.; Fisk, Z.; Horn, S.; Parks, R.D.; Wells, G.L.

1987-01-01

Yb-based Kondo lattice systems (YbAgCu 4 , YbCu 2 Si 2 , YbRh 2 Si 2 ) represent an interesting class of materials in which it is possible to study systematically the development of heavy electron behavior through the application of pressure. Certainly, additional experiments are required to determine to what extent Yb compounds are mirror images of their Ce counterparts. Finally, pressure reveals the presence of competing interactions for which a simple model exists that qualitatively accounts for the pressure response observed in a large number of Ce, U and Yb-based Kondo lattice systems

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

Energy Technology Data Exchange (ETDEWEB)

Maurya, A.; Thamizhavel, A.; Dhar, S.K. [Department of Condensed Matter Physics & Materials Science, Tata Institute of Fundamental Research, Homi Bhabha Road, Mumbai 400 005 (India); Provino, A.; Pani, M.; Costa, G.A. [Department of Chemistry, University of Genova, Via Dodecaneso 31, 16146 Genova (Italy); Institute SPIN-CNR, Corso Perrone 24, 16152 Genova (Italy)

2017-03-15

Single crystals of the new compound CeCu{sub 0.18}Al{sub 0.24}Si{sub 1.58} have been grown by high-temperature solution growth method using a eutectic Al-Si mixture as flux. This compound is derived from the binary CeSi{sub 2} (tetragonal α-ThSi{sub 2}-type, Pearson symbol tI12, space group I4{sub 1}/amd) obtained by partial substitution of Si by Cu and Al atoms but showing full occupation of the Si crystal site (8e). While CeSi{sub 2} is a well-known valence-fluctuating paramagnetic compound, the CeCu{sub 0.18}Al{sub 0.24}Si{sub 1.58} phase orders ferromagnetically at T{sub C}=9.3 K. At low temperatures the easy-axis of magnetization is along the a-axis, which re-orients itself along the c-axis above 30 K. The presence of hysteresis in the magnetization curve, negative temperature coefficient of resistivity at high temperatures, reduced jump in the heat capacity and a relatively lower entropy released up to the ordering temperature, and enhanced Sommerfeld coefficient (≈100 mJ/mol K{sup 2}) show that CeCu{sub 0.18}Al{sub 0.24}Si{sub 1.58} is a Kondo lattice ferromagnetic, moderate heavy fermion compound. Analysis of the high temperature heat capacity data in the paramagnetic region lets us infer that the crystal electric field split doublet levels are located at 178 and 357 K, respectively, and Kondo temperature (8.4 K) is of the order of T{sub C} in CeCu{sub 0.18}Al{sub 0.24}Si{sub 1.58}.

Lattice dynamical and thermodynamical properties of ReB2, RuB2, and OsB2 compounds in the ReB2 structure

International Nuclear Information System (INIS)

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

2012-01-01

Structural and lattice dynamical properties of ReB 2 , RuB 2 , and OsB 2 in the ReB 2 structure are studied in the framework of density functional theory within the generalized gradient approximation. The present results show that these compounds are dynamically stable for the considered structure. The temperature-dependent behaviors of thermodynamical properties such as internal energy, free energy, entropy, and heat capacity are also presented. The obtained results are in good agreement with the available experimental and theoretical data

Magnetic Excitations in α-RuCl3

Science.gov (United States)

Nagler, Stephen; Banerjee, Arnab; Bridges, Craig; Yan, Jiaqiang; Mandrus, David; Stone, Matthew; Aczel, Adam; Li, Ling; Yiu, Yuen; Lumsden, Mark; Knolle, Johannes; Moessner, Roderich; Tennant, Alan

2015-03-01

The layered material α-RuCl3 is composed of stacks of weakly coupled honeycomb lattices of octahedrally coordinated Ru3+ ions. The Ru ion ground state has 5 d electrons in the low spin state, with spin-orbit coupling very strong compared to other terms in the single ion Hamiltonian. The material is therefore an excellent candidate for investigating possible Heisenberg-Kitaev physics. In addition, this compound is very amenable to investigation by neutron scattering to explore the magnetic ground state and excitations in detail. Here we discuss new time-of-flight inelastic neutron scattering data on α-RuCl3. A high energy excitation near 200 meV is identified as a transition from the single ion J=1/2 ground state to the J=3/2 excited state, yielding a direct measurement of the spin orbit coupling energy. Higher resolution measurements reveal two collective modes at much lower energy scales. The results are compared with the theoretical expectations for excitations in the Heisenberg - Kitaev model on a honeycomb lattice, and show that Kitaev interactions are important. Research at SNS supported by the DOE BES Scientific User Facilities Division.

Ultrasonic, microwave, and millimeter wave inspection techniques for adhesively bonded stacked open honeycomb core composites

Science.gov (United States)

Thomson, Clint D.; Cox, Ian; Ghasr, Mohammad Tayeb Ahmed; Ying, Kuang P.; Zoughi, Reza

2015-03-01

Honeycomb sandwich composites are used extensively in the aerospace industry to provide stiffness and thickness to lightweight structures. A common fabrication method for thick, curved sandwich structures is to stack and bond multiple honeycomb layers prior to machining core curvatures. Once bonded, each adhesive layer must be inspected for delaminations and the presence of unwanted foreign materials. From a manufacturing and cost standpoint, it can be advantageous to inspect the open core prior to face sheet closeout in order to reduce end-article scrap rates. However, by nature, these honeycomb sandwich composite structures are primarily manufactured from low permittivity and low loss materials making detection of delamination and some of the foreign materials (which also are low permittivity and low loss) quite challenging in the microwave and millimeter wave regime. Likewise, foreign materials such as release film in adhesive layers can be sufficiently thin as to not cause significant attenuation in through-transmission ultrasonic signals, making them difficult to detect. This paper presents a collaborative effort intended to explore the efficacy of different non-contact NDI techniques for detecting flaws in a stacked open fiberglass honeycomb core panel. These techniques primarily included air-coupled through-transmission ultrasonics, single-sided wideband synthetic aperture microwave and millimeter-wave imaging, and lens-focused technique. The goal of this investigation has been to not only evaluate the efficacy of these techniques, but also to determine their unique advantages and limitations for evaluating parameters such as flaw type, flaw size, and flaw depth.

Lattice vibration spectra. 16

International Nuclear Information System (INIS)

Lutz, H.D.; Willich, P.

1977-01-01

The FIR absorption spectra of pyrite type compounds RuS 2 , RuSsub(2-x)Sesub(x), RuSe 2 , RuTe 2 , OsS 2 , OsSe 2 , and PtP 2 as well as loellingite type phosphides FeP 2 , RuP 2 , and OsP 2 are reported. For RuS 2 , RuSe 2 , RuTe 2 , OsS 2 , and PtP 2 all of the five infrared allowed modes (k = 0) are observed. As a first result of a numerical normal coordinate treatment vibration forms of pyrite structure are communicated. The spectra show that lattice forces of corresponding sulfides, tellurides, and phosphides are about the same strength, but increase strongly by substitution of iron by ruthenium and especially of ruthenium by osmium. The lattice constants of the RuSsub(2-x)Sesub(x) solid solution obey Vegard's rule. (author)

Honeycomb Actuators Inspired by the Unfolding of Ice Plant Seed Capsules.

Directory of Open Access Journals (Sweden)

Lorenzo Guiducci

Full Text Available Plant hydro-actuated systems provide a rich source of inspiration for designing autonomously morphing devices. One such example, the pentagonal ice plant seed capsule, achieves complex mechanical actuation which is critically dependent on its hierarchical organization. The functional core of this actuation system involves the controlled expansion of a highly swellable cellulosic layer, which is surrounded by a non-swellable honeycomb framework. In this work, we extract the design principles behind the unfolding of the ice plant seed capsules, and use two different approaches to develop autonomously deforming honeycomb devices as a proof of concept. By combining swelling experiments with analytical and finite element modelling, we elucidate the role of each design parameter on the actuation of the prototypes. Through these approaches, we demonstrate potential pathways to design/develop/construct autonomously morphing systems by tailoring and amplifying the initial material's response to external stimuli through simple geometric design of the system at two different length scales.

Percolation transitions in two dimensions

NARCIS (Netherlands)

Feng, X.; Deng, Y.; Blöte, H.W.J.

2008-01-01

We investigate bond- and site-percolation models on several two-dimensional lattices numerically, by means of transfer-matrix calculations and Monte Carlo simulations. The lattices include the square, triangular, honeycomb kagome, and diced lattices with nearest-neighbor bonds, and the square

Negative stiffness honeycombs as tunable elastic metamaterials

Science.gov (United States)

Goldsberry, Benjamin M.; Haberman, Michael R.

2018-03-01

Acoustic and elastic metamaterials are media with a subwavelength structure that behave as effective materials displaying atypical effective dynamic properties. These material systems are of interest because the design of their sub-wavelength structure allows for direct control of macroscopic wave dispersion. One major design limitation of most metamaterial structures is that the dynamic response cannot be altered once the microstructure is manufactured. However, the ability to modify wave propagation in the metamaterial with an external stimulus is highly desirable for numerous applications and therefore remains a significant challenge in elastic metamaterials research. In this work, a honeycomb structure composed of a doubly periodic array of curved beams, known as a negative stiffness honeycomb (NSH), is analyzed as a tunable elastic metamaterial. The nonlinear static elastic response that results from large deformations of the NSH unit cell leads to a large variation in linear elastic wave dispersion associated with infinitesimal motion superposed on the externally imposed pre-strain. A finite element model is utilized to model the static deformation and subsequent linear wave motion at the pre-strained state. Analysis of the slowness surface and group velocity demonstrates that the NSH exhibits significant tunability and a high degree of anisotropy which can be used to guide wave energy depending on static pre-strain levels. In addition, it is shown that partial band gaps exist where only longitudinal waves propagate. The NSH therefore behaves as a meta-fluid, or pentamode metamaterial, which may be of use for applications of transformation elastodynamics such as cloaking and gradient index lens devices.

Experimental research and use of finite elements method on mechanical behaviors of honeycomb structures assembled with epoxy-based adhesives reinforced with nanoparticles

Energy Technology Data Exchange (ETDEWEB)

Akkus, Harun [Technical Sciences Vocational School, Amasya University, Amasya (Turkmenistan); Duzcukoglu, Hayrettin; Sahin, Omer Sinan [Mechanical Engineering Department, Selcuk University, Selcuk (Turkmenistan)

2017-01-15

This study utilized experimental and finite element methods to investigate the mechanical behavior of aluminum honeycomb structures under compression. Aluminum honeycomb composite structures were subjected to pressing experiments according to the standard ASTM C365. Resistive forces in response to compression and maximum compressive force values were measured. Structural damage was observed. In the honeycomb structure, the cell width decreased as the compressive force increased. Results obtained with finite element models generated using ANSYS Workbench 15 were validated. Experimental results paralleled the finite element modeling results. The ANSYS results were approximately 85 % reliable.

Robust flat bands in RCo5 (R=rare earth) compounds

OpenAIRE

Ochi, Masayuki; Arita, Ryotaro; Matsumoto, Munehisa; Kino, Hiori; Miyake, Takashi

2014-01-01

The mechanism to realize the peculiar flat bands generally existing in RCo5 (R=rare earth) compounds is clarified by analyzing the first-principles band structures and the tight-binding model. These flat bands are constructed from the localized eigenstates, the existence of which is guaranteed by the partial cancelation between the intersite hopping amplitudes among the Co-3d states at the Kagome sites and those between the Kagome and honeycomb sites. Their relative positions to other bands c...

Simulation of the honeycomb construction process

International Nuclear Information System (INIS)

Zhang Yuanzhang

2010-01-01

The construction process of the honeycomb by bees is an astonishing process. The original structure which the bees built is nothing more than a lot of rough cylinders. But keeping the beeswax semi-flow for a certain time, those rough structures become perfect hexahedral columns. A modified, simplified particle method was used here to simulate the semi-flow state of the material. Although the parameters used here were still rather subjective, the simulation still could demonstrate some behavior of that sort of material like beeswax. And the method that the bees used to build their honey comb, could be an efficient method to imitate when we are trying to manufacture cellular materials.

Lattice parameters guide superconductivity in iron-arsenides

Science.gov (United States)

Konzen, Lance M. N.; Sefat, Athena S.

2017-03-01

The discovery of superconducting materials has led to their use in technological marvels such as magnetic-field sensors in MRI machines, powerful research magnets, short transmission cables, and high-speed trains. Despite such applications, the uses of superconductors are not widespread because they function much below room-temperature, hence the costly cooling. Since the discovery of Cu- and Fe-based high-temperature superconductors (HTS), much intense effort has tried to explain and understand the superconducting phenomenon. While no exact explanations are given, several trends are reported in relation to the materials basis in magnetism and spin excitations. In fact, most HTS have antiferromagnetic undoped ‘parent’ materials that undergo a superconducting transition upon small chemical substitutions in them. As it is currently unclear which ‘dopants’ can favor superconductivity, this manuscript investigates crystal structure changes upon chemical substitutions, to find clues in lattice parameters for the superconducting occurrence. We review the chemical substitution effects on the crystal lattice of iron-arsenide-based crystals (2008 to present). We note that (a) HTS compounds have nearly tetragonal structures with a-lattice parameter close to 4 Å, and (b) superconductivity can depend strongly on the c-lattice parameter changes with chemical substitution. For example, a decrease in c-lattice parameter is required to induce ‘in-plane’ superconductivity. The review of lattice parameter trends in iron-arsenides presented here should guide synthesis of new materials and provoke theoretical input, giving clues for HTS.

Electromechanical modeling of a honeycomb core integrated vibration energy converter with increased specific power for energy harvesting applications

Science.gov (United States)

Chandrasekharan, Nataraj

Innovation in integrated circuit technology along with improved manufacturing processes has resulted in considerable reduction in power consumption of electromechanical devices. Majority of these devices are currently powered by batteries. However, the issues posed by batteries, including the need for frequent battery recharge/replacement has resulted in a compelling need for alternate energy to achieve self-sufficient device operation or to supplement battery power. Vibration based energy harvesting methods through piezoelectric transduction provides with a promising potential towards replacing or supplementing battery power source. However, current piezoelectric energy harvesters generate low specific power (power-to-weight ratio) when compared to batteries that the harvesters seek to replace or supplement. In this study, the potential of integrating lightweight cellular honeycomb structures with existing piezoelectric device configurations (bimorph) to achieve higher specific power is investigated. It is shown in this study that at low excitation frequency ranges, replacing the solid continuous substrate of a conventional piezoelectric bimorph with honeycomb structures of the same material results in a significant increase in power-to-weight ratio of the piezoelectric harvester. In order to maximize the electrical response of vibration based power harvesters, the natural frequency of these harvesters is designed to match the input driving frequency. The commonly used technique of adding a tip mass is employed to lower the natural frequency (to match driving frequency) of both, solid and honeycomb substrate bimorphs. At higher excitation frequency, the natural frequency of the traditional solid substrate bimorph can only be altered (to match driving frequency) through a change in global geometric design parameters, typically achieved by increasing the thickness of the harvester. As a result, the size of the harvester is increased and can be disadvantageous

Effective Deffect Identifications in Honeycombs

Directory of Open Access Journals (Sweden)

Jarmila Dedkova

2008-01-01

Full Text Available The image reconstruction problem based on Electrical Impedance Tomography (EIT is an ill-posed inverse problem of finding such conductivity distribution that minimizes some optimisation criterion, which can be given by a suitable primal objective function. This paper describes new algorithms for the reconstruction of the surface conductivity distribution, which are based on stochastic methods to be used for the acquirement of more accurate reconstruction results and stable solution. The proposed methods are expected to non-destructive test of materials. There are shown examples of the identification of voids or cracks in special structures called honeycombs. Instead of the experimental data we used the phantom evaluated voltage values based on the application of finite element method. The results obtained by this new approach are compared with results from the known deterministic approach to the same image reconstruction

Behaviour of gaseous alkali compounds from coal gasification

International Nuclear Information System (INIS)

Nykaenen, J.

1996-01-01

In this project the behaviour of alkali compounds has been studied with a chemical equilibrium model. The goal is to evaluate the possibilities to remove the sodium and potassium compounds together with the fly ash particles by using a ceramic honeycomb filter. The studied processes include both CO 2 /O 2 - and air-blown gasification and combustion. The results show that the difference between the processes with flue gas recirculation and air-blown processes is small. This is due to that the equilibrium concentration of the dominant gaseous alkali compound, chloride, is more or less the same in both processes. This research project is closely connected to the EU-project coordinated by the Delft University of Technology (DUT). In that project alkali concentration of the fuel gas from a 1.6 MW pilot plant will be measured. During the next phase of this research the results from DUT will be compared with the results of this presentation. (author)

On Traveling Waves in Lattices: The Case of Riccati Lattices

Science.gov (United States)

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.

Nuclear spin-lattice relaxation in carbon nanostructures

Energy Technology Data Exchange (ETDEWEB)

Panich, A.M., E-mail: pan@bgu.ac.i [Department of Physics, Ben-Gurion University of the Negev, P.O. Box 653, Beer Sheva 84105 (Israel); Sergeev, N.A. [Institute of Physics, University of Szczecin, 70-451 Szczecin (Poland)

2010-04-15

Interpretation of nuclear spin-lattice relaxation data in the carbon nanostructures is usually based on the analysis of fluctuations of dipole-dipole interactions of nuclear spins and anisotropic electron-nuclear interactions responsible for chemical shielding, which are caused by molecular dynamics. However, many nanocarbon systems such as fullerene and nanotube derivatives, nanodiamonds and carbon onions reveal noticeable amount of paramagnetic defects with unpaired electrons originating from dangling bonds. The interaction between nuclear and electron spins strongly influences the nuclear spin-lattice relaxation, but usually is not taken into account, thus the relaxation data are not correctly interpreted. Here we report on the temperature dependent NMR spectra and spin-lattice relaxation measurements of intercalated fullerenes C{sub 60}(MF{sub 6}){sub 2} (M=As and Sb), where nuclear relaxation is caused by both molecular rotation and interaction between nuclei and unpaired electron spins. We present a detailed theoretical analysis of the spin-lattice relaxation data taking into account both these contributions. Good agreement between the experimental data and calculations is obtained. The developed approach would be useful in interpreting the NMR relaxation data in different nanostructures and their intercalation compounds.

LATTICE: an interactive lattice computer code

International Nuclear Information System (INIS)

Staples, J.

1976-10-01

LATTICE is a computer code which enables an interactive user to calculate the functions of a synchrotron lattice. This program satisfies the requirements at LBL for a simple interactive lattice program by borrowing ideas from both TRANSPORT and SYNCH. A fitting routine is included

Lattice Gas Model Based Optimization of Plasma-Surface Processes for GaN-Based Compound Growth

Science.gov (United States)

Nonokawa, Kiyohide; Suzuki, Takuma; Kitamori, Kazutaka; Sawada, Takayuki

2001-10-01

Progress of the epitaxial growth technique for GaN-based compounds makes these materials attractive for applications in high temperature/high-power electronic devices as well as in short-wavelength optoelectronic devices. For MBE growth of GaN epilayer, atomic nitrogen is usually supplied from ECR-plasma while atomic Ga is supplied from conventional K-cell. To grow high-quality epilayer, fundamental knowledge of the detailed atomic process, such as adsorption, surface migration, incorporation, desorption and so forth, is required. We have studied the influence of growth conditions on the flatness of the growth front surface and the growth rate using Monte Carlo simulation based on the lattice gas model. Under the fixed Ga flux condition, the lower the nitrogen flux and/or the higher the growth temperature, the better the flatness of the front surface at the sacrifice of the growth rate of the epilayer. When the nitrogen flux is increased, the growth rate reaches saturation value determined from the Ga flux. At a fixed growth temperature, increasing of nitrogen to Ga flux ratio results in rough surface owing to 3-dimensional island formation. Other characteristics of MBE-GaN growth using ECR-plasma can be well reproduced.

Thermo-plastic finite element analysis for metal honeycomb structure

Directory of Open Access Journals (Sweden)

Ji Zhanling

2013-01-01

Full Text Available This paper deals with thermal-plastic analysis for the metal honeycomb structure. The heat transfer equation and thermal elastoplastic constitutive equation of a multilayer panel are established and studied numerically using ANSYS software. The paper elucidates that only the outer skin produces easily plastic deformation, and the outer skin still exists some residual stress and residual deformation after cooling. The dynamic evolution of plastic deformation and material performance degradation under high energy thermal load are revealed.

Unconventional phases in quantum spin and pseudospin systems in two dimensional and three dimensional lattices

Science.gov (United States)

Xu, Cenke

Several examples of quantum spin systems and pseudo spin systems have been studied, and unconventional states of matters and phase transitions have been realized in all these systems under consideration. In the p +/- ip superconductor Josephson lattice and the p--band cold atomic system trapped in optical lattices, novel phases which behave similarly to 1+1 dimensional systems are realized, despite the fact that the real physical systems are in two or three dimensional spaces. For instance, by employing a spin-wave analysis together with a new duality transformation, we establish the existence and stability of a novel gapless "critical phase", which we refer to as a "bond algebraic liquid". This novel critical phase is analogous to the 1+1 dimensional algebraic boson liquid phase. The reason for the novel physics is that there is a quasilocal gauge symmetry in the effective low energy Hamiltonian. In a spin-1 system on the kagome lattice, and a hard-core boson system on the honeycomb lattice, the low energy physics is controlled by two components of compact U(1) gauge symmetries that emerge at low energy. Making use of the confinement nature of the 2+1 dimensional compact gauge theories and the powerful duality between gauge theories and height field theories, the crystalline phase diagrams are studied for both systems, and the transitions to other phases are also considered. These phase diagrams might be accessible in strongly correlated materials, or atomic systems in optical lattices. A novel quantum ground state of matter is realized in a bosonic model on three dimensional fcc lattice with emergent low energy excitations. The novel phase obtained is a stable gapless boson liquid phase, with algebraic boson density correlations. The stability of this phase is protected against the instanton effect and superfluidity by self-duality and large gauge symmetries on both sides of the duality. The gapless collective excitations of this phase closely resemble the

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

Science.gov (United States)

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

2017-11-01

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

A novel lattice energy calculation technique for simple inorganic crystals

Energy Technology Data Exchange (ETDEWEB)

Kaya, Cemal [Department of Chemistry, Faculty of Science, Cumhuriyet University, 58140 Sivas (Turkey); Kaya, Savaş, E-mail: savaskaya@cumhuriyet.edu.tr [Department of Chemistry, Faculty of Science, Cumhuriyet University, 58140 Sivas (Turkey); Banerjee, Priyabrata [Surface Engineering and Tribology Group, CSIR-Central Mechanical Engineering Research Institute, Mahatma Gandhi Avenue, Durgapur 713209 (India)

2017-01-01

In this pure theoretical study, a hitherto unexplored equation based on Shannon radii of the ions forming that crystal and chemical hardness of any crystal to calculate the lattice energies of simple inorganic ionic crystals has been presented. To prove the credibility of this equation, the results of the equation have been compared with experimental outcome obtained from Born-Fajans-Haber- cycle which is fundamentally enthalpy-based thermochemical cycle and prevalent theoretical approaches proposed for the calculation of lattice energies of ionic compounds. The results obtained and the comparisons made have demonstrated that the new equation is more useful compared to other theoretical approaches and allows to exceptionally accurate calculation of lattice energies of inorganic ionic crystals without doing any complex calculations.

Sublimation thermodynamics of four fluoroquinolone antimicrobial compounds

International Nuclear Information System (INIS)

Blokhina, Svetlana; Sharapova, Angelica; Ol’khovich, Marina; Perlovich, German

2017-01-01

Highlights: • The vapor pressures of ciprofloxacin, enrofloxacin, norfloxacin and levofloxacin were measured. • The values of enthalpies, entropies and Gibbs energies of sublimation were calculated at T = 298.15 K. • Thermophysical characteristics of the studied compounds were determined. • The influence hydrogen bonds in crystal lattices on the sublimation enthalpy was discussed. - Abstract: The transpiration method was used to measure the vapor pressures as a function of temperature of the following antimicrobial drugs: ciprofloxacin, enrofloxacin, norfloxacin and levofloxacin. Based on these results standard molar enthalpies, entropies and Gibbs energies of sublimation at T = 298.15 K were calculated and a correlation between the crystal lattice energy and the saturation vapor pressure in a number of fluoroquinolones was found. The thermophysical characteristics of the compounds studied were determined by DSC. The influence of different structural fragments of molecules substituents and the effects of hydrogen bonds in crystal lattices on the sublimation enthalpy was discussed.

Dynamical scaling analysis of the optical Hall conductivity in the graphene quantum Hall system with various types of disorder

International Nuclear Information System (INIS)

Morimoto, Takahiro; Aoki, Hideo; Avishai, Yshai

2011-01-01

Dynamical scaling of the optical Hall conductivity σ xy (ε F , ω) at the n = 0 Landau level in graphene is analyzed for the 2D effective Dirac fermion and honeycomb lattice models with various types of disorder. In the Dirac fermion model with potential disorder, σ xy (ε F , ω) obeys a well-defined dynamical scaling, characterized by the localization exponent ν and the dynamical critical exponent z. In sharp distinction, scaling behavior of σ xy (ε F , ω) in the honeycomb lattice model with bond disorder (preserving chiral symmetry), becomes anomalous.

Inner-Resonance Conditions for Honeycomb Paperboard Cushioning Packaging System with Critical Component

Directory of Open Access Journals (Sweden)

Jun Wang

2013-01-01

Full Text Available A dynamic model was proposed for a honeycomb paperboard cushioning packaging system with critical component. Then the coupled equations of the system were solved by the variational iteration method, from which the conditions for inner-resonance were obtained, which should be avoided in the cushioning packaging design.

Lattice QCD

International Nuclear Information System (INIS)

Hasenfratz, P.

1983-01-01

The author presents a general introduction to lattice gauge theories and discusses non-perturbative methods in the gauge sector. He then shows how the lattice works in obtaining the string tension in SU(2). Lattice QCD at finite physical temperature is discussed. Universality tests in SU(2) lattice QCD are presented. SU(3) pure gauge theory is briefly dealt with. Finally, fermions on the lattice are considered. (Auth.)

Metastable honeycomb SrTiO_3/SrIrO_3 heterostructures

International Nuclear Information System (INIS)

Anderson, T. J.; Ryu, S.; Podkaminer, J. P.; Ma, Y.; Eom, C. B.; Zhou, H.; Xie, L.; Irwin, J.; Rzchowski, M. S.; Pan, X. Q.

2016-01-01

Recent theory predictions of exotic band topologies in (111) honeycomb perovskite SrIrO_3 layers sandwiched between SrTiO_3 have garnered much attention in the condensed matter physics and materials communities. However, perovskite SrIrO_3 film growth in the (111) direction remains unreported, as efforts to synthesize pure SrIrO_3 on (111) perovskite substrates have yielded films with monoclinic symmetry rather than the perovskite structure required by theory predictions. In this study, we report the synthesis of ultra-thin metastable perovskite SrIrO_3 films capped with SrTiO_3 grown on (111) SrTiO_3 substrates by pulsed laser deposition. The atomic structure of the ultra-thin films was examined with scanning transmission electron microscopy (STEM), which suggests a perovskite layering distinct from the bulk SrIrO_3 monoclinic phase. In-plane 3-fold symmetry for the entire heterostructure was confirmed using synchrotron surface X-ray diffraction to measure symmetry equivalent crystal truncation rods. Our findings demonstrate the ability to stabilize (111) honeycomb perovskite SrIrO_3, which provides an experimental avenue to probe the phenomena predicted for this material system.

Interacting Fermi gases in disordered one-dimensional lattices

International Nuclear Information System (INIS)

Xianlong, Gao; Polini, M.; Tosi, M. P.; Tanatar, B.

2006-01-01

Interacting two-component Fermi gases loaded in a one-dimensional (1D) lattice and subject to harmonic trapping exhibit intriguing compound phases in which fluid regions coexist with local Mott-insulator and/or band-insulator regions. Motivated by experiments on cold atoms inside disordered optical lattices, we present a theoretical study of the effects of a random potential on these ground-state phases. Within a density-functional scheme we show that disorder has two main effects: (i) it destroys the local insulating regions if it is sufficiently strong compared with the on-site atom-atom repulsion, and (ii) it induces an anomaly in the compressibility at low density from quenching of percolation

Hyper thin 3D edge measurement of honeycomb core structures based on the triangular camera-projector layout & phase-based stereo matching.

Science.gov (United States)

Jiang, Hongzhi; Zhao, Huijie; Li, Xudong; Quan, Chenggen

2016-03-07

We propose a novel hyper thin 3D edge measurement technique to measure the profile of 3D outer envelope of honeycomb core structures. The width of the edges of the honeycomb core is less than 0.1 mm. We introduce a triangular layout design consisting of two cameras and one projector to measure hyper thin 3D edges and eliminate data interference from the walls. A phase-shifting algorithm and the multi-frequency heterodyne phase-unwrapping principle are applied for phase retrievals on edges. A new stereo matching method based on phase mapping and epipolar constraint is presented to solve correspondence searching on the edges and remove false matches resulting in 3D outliers. Experimental results demonstrate the effectiveness of the proposed method for measuring the 3D profile of honeycomb core structures.

Added value of prone CT in the assessment of honeycombing and classification of usual interstitial pneumonia pattern.

Science.gov (United States)

Kim, Minjae; Lee, Sang Min; Song, Jae-Woo; Do, Kyung-Hyun; Lee, Hyun Joo; Lim, Soyeoun; Choe, Jooae; Park, Kye Jin; Park, Hyo Jung; Kim, Hwa Jung; Seo, Joon Beom

2017-06-01

To retrospectively investigate whether prone CT improves identification of honeycombing and classification of UIP patterns in terms of interobserver agreement and accuracy using pathological results as a reference standard. Institutional review board approval with waiver of patients' informed consent requirement was obtained. HRCTs of 86 patients with pathologically proven UIP, NSIP and chronic HP between January 2011 and April 2015 were evaluated by 8 observers. Observers were asked to review supine only set and supine and prone combined set and determine the presence of honeycombing and UIP classification (UIP, possible UIP, inconsistent with UIP). The diagnosis was regarded as correct when UIP pattern on CT corresponded to pathological UIP. Interobserver agreement of honeycombing identification among radiologists was only fair on the supine and combined set (weighted κ=0.31 and 0.34). Additional review of prone images demonstrated a significant improvement in interobserver agreement (weighted κ) of UIP classification from 0.25 to 0.33. Prone CT conferred a significant improvement in interobserver agreement of UIP classification for trainee radiologists (from 0.10 to 0.34) while no improvement was found for board-certified radiologists (from 0.35 to 0.31). There were no significant differences in the accuracy of UIP pattern with reference to pathological results between the supine and combined set (78.8% (145/184) and 81.3% (179/220), P=0.612). Additional review of prone CT can improve overall interobserver agreement of UIP classification among radiologists with variable experiences, particularly for less experienced radiologists, while no improvement was found in honeycombing identification. Copyright © 2017 Elsevier B.V. All rights reserved.

Dynamic impact response of high-density square honeycombs made of TRIP steel and TRIP matrix composite material

Directory of Open Access Journals (Sweden)

Weigelt C.

2012-08-01

Full Text Available Two designs of square-celled metallic honeycomb structures fabricated by a modified extrusion technology based on a powder feedstock were investigated. The strength and ductility of these cellular materials are achieved by an austenitic CrNi (AISI 304 steel matrix particle reinforced by an MgO partially-stabilized zirconia building up their cell wall microstructure. Similar to the mechanical behaviour of the bulk materials, the strengthening mechanism and the martensitic phase transformations in the cell walls are affected by the deformation temperature and the nominal strain rate. The microstructure evolution during quasi-static and dynamic impact compression up to high strain rates of 103 1/s influences the buckling and failure behaviour of the honeycomb structures. In contrast to bending-dominated quasi-isotropic networks like open-celled metal foams, axial compressive loading to the honeycomb’s channels causes membrane stretching as well as crushing of the vertical cell node elements and cell walls. The presented honeycomb materials differ geometrically in their cell wall thickness-to-cell size-ratio. Therefore, the failure behaviour is predominantly controlled by global buckling and torsional-flexural buckling, respectively, accompanied by plastic matrix flow and strengthening of the cell wall microstructure.

A honeycomb sandwich structure vacuum jacket for cryogenic targets

International Nuclear Information System (INIS)

Harada, M.; Kasai, S.; Kato, S.

1988-11-01

Cryogenic targets (H 2 , D 2 and 4 He) have been built for use in the study of photonuclear reactions with π sr spectrometer, TAGX at the 1.3 GeV Tokyo electron synchrotron. A new type of vacuum jacket fabricated from plastic honeycomb core and Mylar skins has been used in the target system for more than 5000 hours. The average radiation thickness and the average density of this jacket are measured to be 3.3 x 10 -3 X 0 and 0.15 g/cm 3 , respectively. (author)

Sound transmission properties of honeycomb panels and double-walled structures

OpenAIRE

Ramanathan, Sathish Kumar

2012-01-01

Sandwich panels with aluminium face sheets and honeycomb core material have certain advantages over panels made of wood. Some of the advantages of these constructions are low weight, good moisture properties, fire resistance and high stiffness to-weight ratio etc. As product development is carried out in a fast pace today, there is a strong need for validated prediction tools to assist during early design stages. In this thesis, tools are developed for predicting the sound transmission throug...

SiC-SiC and C-SiC Honeycomb for Advanced Flight Structures, Phase II

Data.gov (United States)

National Aeronautics and Space Administration — The proposed project builds upon the work done in Phase I with the development of a C-SiC CMC honeycomb material that was successfully tested for mechanical...

Designing Kitaev Spin Liquids in Metal-Organic Frameworks

Science.gov (United States)

Yamada, Masahiko G.; Fujita, Hiroyuki; Oshikawa, Masaki

2017-08-01

Kitaev's honeycomb lattice spin model is a remarkable exactly solvable model, which has a particular type of spin liquid (Kitaev spin liquid) as the ground state. Although its possible realization in iridates and α -RuCl3 has been vigorously discussed recently, these materials have substantial non-Kitaev direct exchange interactions and do not have a spin liquid ground state. We propose metal-organic frameworks (MOFs) with Ru3 + (or Os3 + ), forming the honeycomb lattice as promising candidates for a more ideal realization of Kitaev-type spin models, where the direct exchange interaction is strongly suppressed. The great flexibility of MOFs allows generalization to other three-dimensional lattices for the potential realization of a variety of spin liquids, such as a Weyl spin liquid.

Facile synthesis of graphene-wrapped honeycomb MnO2 nanospheres and their application in supercapacitors.

Science.gov (United States)

Zhu, Jiayi; He, Junhui

2012-03-01

Graphene-wrapped MnO(2) nanocomposites were first fabricated by coassembly between honeycomb MnO(2) nanospheres and graphene sheets via electrostatic interaction. The materials were characterized by means of X-ray diffraction, scanning electron microscopy, transmission electron microscopy, atomic force microscopy, and thermogravimetric analysis. The novel MnO(2)/graphene hybrid materials were used for investigation of electrochemical capacitive behaviors. The hybrid materials displayed enhanced capacitive performance (210 F/g at 0.5 A/g). Additionally, over 82.4% of the initial capacitance was retained after repeating the cyclic voltammetry test for 1000 cycles. The improved electrochemical performance might be attributed to the combination of the pesudocapacitance of MnO(2) nanospheres with the honeycomb-like "opened" structure and good electrical conductivity of graphene sheets. © 2012 American Chemical Society

Energy gap formation mechanism through the interference phenomena of electrons in face-centered cubic elements and compounds with the emphasis on half-Heusler and Heusler compounds

Science.gov (United States)

Mizutani, U.; Sato, H.

2018-05-01

Many face-centred cubic elements and compounds with the number of atoms per unit cell N equal to 8, 12 and 16 are known to be stabilised by forming either a band gap or a pseudogap at the Fermi level. They are conveniently expressed as cF8, cF12 and cF16, respectively, in the Pearson symbol. From the cF8 family, we worked on three tetravalent elements C (diamond), Si and Ge, SZn-type AsGa compound and NaCl-type compounds like BiLu, AsSc, etc. From the cF12 family, more than 80 compounds were selected, with a particular emphasis on ABC- and half-Heusler-type ternary equiatomic compounds. Among cF16 compounds, both the Heusler compounds ABC2 and Zintl compounds were studied. We revealed that, regardless of whether or not the transition metal (TM) and/or rare-earth (RE) elements are involved as constituent elements, the energy gap formation mechanism for cF8, cF12 and cF16 compounds can be universally discussed in terms of interference phenomenon of itinerant electrons with set of reciprocal lattice planes with ? = 8, 11 and 12, where ? refers to square of the critical reciprocal of lattice vector of an fcc lattice. The number of itinerant electrons per unit cell, e/uc, for all these band gap/pseudogap-bearing compounds is found to fall on a universal line called "3/2-power law" when plotted against ? on a logarithmic scale. This proves the validity of the fulfilment of the interference condition ? in conformity with other pseudogap compounds with different crystal symmetries and different sizes of the unit cell reported in literature.

Salt or ice diapirism origin for the honeycomb terrain in Hellas basin, Mars?: Implications for the early martian climate

Science.gov (United States)

Weiss, David K.; Head, James W.

2017-03-01

The "honeycomb" terrain is a Noachian-aged cluster of ∼7 km wide linear cell-like depressions located on the northwestern floor of Hellas basin, Mars. A variety of origins have been proposed for the honeycomb terrain, including deformation rings of subglacial sediment, frozen convection cells from a Hellas impact melt sheet, a swarm of igneous batholiths, salt diapirism, and ice diapirism. Recent work has shown that the salt or ice diapirism scenarios appear to be most consistent with the morphology and morphometry of the honeycomb terrain. The salt and ice diapirism scenarios have different implications for the ancient martian climate and hydrological cycle, and so distinguishing between the two scenarios is critical. In this study, we specifically test whether the honeycomb terrain is consistent with a salt or ice diapir origin. We use thermal modeling to assess the stability limits on the thickness of an ice or salt diapir-forming layer at depth within the Hellas basin. We also apply analytical models for diapir formation to evaluate the predicted diapir wavelengths in order to compare with observations. Ice diapirism is generally predicted to reproduce the observed honeycomb wavelengths for ∼100 m to ∼1 km thick ice deposits. Gypsum and kieserite diapirism is generally predicted to reproduce the observed honeycomb wavelengths for ≥ 600-1000 m thick salt deposits, but only with a basaltic overburden. Halite diapirism generally requires approx. ≥ 1 km thick halite deposits in order to reproduce the observed honeycomb wavelengths. Hellas basin is a distinctive environment for diapirism on Mars due to its thin crust (which reduces surface heat flux), low elevation (which allows Hellas to act as a water/ice/sediment sink and increases the surface temperature), and location within the southern highlands (which may provide proximity to inflowing saline water or glacial ice). The plausibility of an ice diapir mechanism generally requires temperatures ≤ 250

pH-specific hydrothermal assembly of binary and ternary Pb(II)-(O,N-carboxylic acid) metal organic framework compounds: correlation of aqueous solution speciation with variable dimensionality solid-state lattice architecture and spectroscopic signatures.

Science.gov (United States)

Gabriel, C; Perikli, M; Raptopoulou, C P; Terzis, A; Psycharis, V; Mateescu, C; Jakusch, T; Kiss, T; Bertmer, M; Salifoglou, A

2012-09-03

Hydrothermal pH-specific reactivity in the binary/ternary systems of Pb(II) with the carboxylic acids N-hydroxyethyl-iminodiacetic acid (Heida), 1,3-diamino-2-hydroxypropane-N,N,N',N'-tetraacetic acid (Dpot), and 1,10-phenanthroline (Phen) afforded the new well-defined crystalline compounds [Pb(Heida)](n)·nH(2)O(1), [Pb(Phen)(Heida)]·4H(2)O(2), and [Pb(3)(NO(3))(Dpot)](n)(3). All compounds were characterized by elemental analysis, FT-IR, solution or/and solid-state NMR, and single-crystal X-ray diffraction. The structures in 1-2 reveal the presence of a Pb(II) center coordinated to one Heida ligand, with 1 exhibiting a two-dimensional (2D) lattice extending to a three-dimensional (3D) one through H-bonding interactions. The concurrent aqueous speciation study of the binary Pb(II)-Heida system projects species complementing the synthetic efforts, thereby lending credence to a global structural speciation strategy in investigating binary/ternary Pb(II)-Heida/Phen systems. The involvement of Phen in 2 projects the significance of nature and reactivity potential of N-aromatic chelators, disrupting the binary lattice in 1 and influencing the nature of the ultimately arising ternary 3D lattice. 3 is a ternary coordination polymer, where Pb(II)-Dpot coordination leads to a 2D metal-organic-framework material with unique architecture. The collective physicochemical properties of 1-3 formulate the salient features of variable dimensionality metal-organic-framework lattices in binary/ternary Pb(II)-(hydroxy-carboxylate) structures, based on which new Pb(II) materials with distinct architecture and spectroscopic signature can be rationally designed and pursued synthetically.

Lattice-induced nonadiabatic frequency shifts in optical lattice clocks

International Nuclear Information System (INIS)

Beloy, K.

2010-01-01

We consider the frequency shift in optical lattice clocks which arises from the coupling of the electronic motion to the atomic motion within the lattice. For the simplest of three-dimensional lattice geometries this coupling is shown to affect only clocks based on blue-detuned lattices. We have estimated the size of this shift for the prospective strontium lattice clock operating at the 390-nm blue-detuned magic wavelength. The resulting fractional frequency shift is found to be on the order of 10 -18 and is largely overshadowed by the electric quadrupole shift. For lattice clocks based on more complex geometries or other atomic systems, this shift could potentially be a limiting factor in clock accuracy.

Enhanced xylene removal by photocatalytic oxidation using fiber-illuminated honeycomb reactor at ppb level.

Science.gov (United States)

Wu, Yi-Ting; Yu, Yi-Hui; Nguyen, Van-Huy; Lu, Kung-Te; Wu, Jeffrey Chi-Sheng; Chang, Luh-Maan; Kuo, Chi-Wen

2013-11-15

The removal of volatile organic compounds (VOCs) at ppb level is one of the most critical challenges in clean rooms for the semiconductor industry. Photocatalytic oxidation is an innovative and promising technology for ppb-level VOCs degradation. We have designed a fiber-illuminated honeycomb reactor (FIHR) in which the removal efficiency of m-xylene is significantly enhanced to 96.5% as compared to 22.0% for UV irradiation only. The results indicate that photocatalysts not only play the role to substantially oxidize m-xylene, but also alter the chemical properties of xylene under UV illumination. Using the FIHR with Mn-TiO2 photocatalyst not only increased the m-xylene removal efficiency, but also increased the CO2 selectivity. Interestingly, Mn-TiO2 in FIHR also showed a very good reusability, 93% removal efficiency was still achieved in 72-h in reaction. Thus, the FIHR gave very high removal efficiency for xylene at ppb level under room temperature. The FIHR has great potential application in the clean room for the air purification system in the future. Copyright © 2013 Elsevier B.V. All rights reserved.

Finding New Thermoelectric Compounds Using Crystallographic Data: Atomic Displacement Parameters

International Nuclear Information System (INIS)

Chakoumakos, B.C.; Mandrus, D.G.; Sales, B.C.; Sharp, J.W.

1999-01-01

A new structure-property relationship is discussed which links atomic displacement parameters (ADPs) and the lattice thermal conductivity of clathrate-like compounds. For many clathrate-like compounds, in which one of the atom types is weakly bound and ''rattles'' within its atomic cage, room temperature ADP information can be used to estimate the room temperature lattice thermal conductivity, the vibration frequency of the ''rattler'', and the temperature dependence of the heat capacity. Neutron data and X-ray crystallography data, reported in the literature, are used to apply this analysis to several promising classes of thermoelectric materials

Lattice strings

International Nuclear Information System (INIS)

Thorn, C.B.

1988-01-01

The possibility of studying non-perturbative effects in string theory using a world sheet lattice is discussed. The light-cone lattice string model of Giles and Thorn is studied numerically to assess the accuracy of ''coarse lattice'' approximations. For free strings a 5 by 15 lattice seems sufficient to obtain better than 10% accuracy for the bosonic string tachyon mass squared. In addition a crude lattice model simulating string like interactions is studied to find out how easily a coarse lattice calculation can pick out effects such as bound states which would qualitatively alter the spectrum of the free theory. The role of the critical dimension in obtaining a finite continuum limit is discussed. Instead of the ''gaussian'' lattice model one could use one of the vertex models, whose continuum limit is the same as a gaussian model on a torus of any radius. Indeed, any critical 2 dimensional statistical system will have a stringy continuum limit in the absence of string interactions. 8 refs., 1 fig. , 9 tabs

Field induced phase transition in layered honeycomb spin system α-RuCl3 studied by thermal conductivity

Science.gov (United States)

Leahy, Ian; Bornstein, Alex; Choi, Kwang-Yong; Lee, Minhyea

α -RuCl3, a quasi -two-dimensional honeycomb lattice is known to be a candidate material to realize the Heisenberg-Kitaev spin model of a highly anisotropic bond-dependent exchange interaction. We investigate in-plane thermal conductivity (κ) as a function of temperature (T) and in-plane applied field (H). At H = 0 , the onset of a strong increase in κ marks the spontaneous long range ordering temperature, Tc = 6 . 5 K , corresponding to ``zigzag'' antiferromagnetic ordering. A broad peak appearing below Tc in κ was found to be suppressed significantly as H increases up to ~ 7 T , implying the system undergoes a field-induced transition from ordered to a new spin-disordered state analogous to the transverse-field Ising model. Further increasing H above 7 . 1 T , the large field seems to begin polarizing spins thus increasing the phonon mean free path, resulting in a significant rise in κ. This tendency is clearly shown in the field dependence of κ below Tc, which has a pronounced minimum at Hmin = 7 . 1 T . We will discuss our scaling analysis to characterize this field-induced phase transition and compare to the transverse-field Ising spin system. Work at the University of Colorado was supported by the US DOE Basic Energy Sciences under Award No. DE-SC0006888.

Pressure induced valence transitions in the Anderson lattice model

International Nuclear Information System (INIS)

Bernhard, B.H.; Coqblin, B.

2009-01-01

We apply the equation of motion method to the Anderson lattice model, which describes the physical properties of heavy fermion compounds. In particular, we focus here on the variation of the number of f electrons with pressure, associated to the crossover from the Kondo regime to the intermediate valence regime. We treat here the non-magnetic case and introduce an improved approximation, which consists of an alloy analogy based decoupling for the Anderson lattice model. It is implemented by partial incorporation of the spatial correlations contained in higher-order Green's functions involved in the problem that have been formerly neglected. As it has been verified in the framework of the Hubbard model, the alloy analogy avoids the breakdown of sum rules and is more appropriate to explore the asymmetric case of the periodic Anderson Hamiltonian. The densities of states for a simple cubic lattice are calculated for various values of the model parameters V, t, E f , and U.

The behaviour of gaseous alkali compounds in coal gasification

International Nuclear Information System (INIS)

Nykaenen, J.

1995-01-01

In this project the behaviour of alkali compounds emitting from CO 2 /O 2 -and air gasification will be studied by using an equilibrium model developed at the Aabo Akademi. This research project is closely connected to the EU-project coordinated by the Delft University of Technology (DUT). In that project alkali emissions from a 1.6 MW pilot plant are measured. The results from those measurements will be compared with the calculations performed in this LIEKKI 2 -project. Furthermore, in the project carried out at DUT the behaviour of a honeycomb-structured filter under CO 2 /O 2 -gasification environment is going to be studied. (author)

Lattice Vibrations in Chlorobenzenes:

DEFF Research Database (Denmark)

Reynolds, P. A.; Kjems, Jørgen; White, J. W.

1974-01-01

Lattice vibrational dispersion curves for the ``intermolecular'' modes in the triclinic, one molecule per unit cell β phase of p‐C6D4Cl2 and p‐C6H4Cl2 have been obtained by inelastic neutron scattering. The deuterated sample was investigated at 295 and at 90°K and a linear extrapolation to 0°K...... was applied in order to correct for anharmonic effects. Calculations based on the atom‐atom model for van der Waals' interaction and on general potential parameters for the aromatic compounds agree reasonably well with the experimental observations. There is no substantial improvement in fit obtained either...

Hybridization in Kondo lattice heavy fermions via quasiparticle scattering spectroscopy (QPS)

Science.gov (United States)

Narasiwodeyar, Sanjay; Dwyer, Matt; Greene, Laura; Park, Wan Kyu; Bauer, Eric; Tobash, Paul; Baumbach, Ryan; Ronning, Filip; Sarrao, John; Thompson, Joe; Canfield, Paul

2014-03-01

Band renormalization in a Kondo lattice via hybridization of the conduction band with localized states has been a hot topic over the last several years. In part, this has to do with recently reignited interest in the hidden order problem in URu2Si2. Despite recent developments regarding the electronic structure in this compound, it remains to be resolved whether the hidden order phase transition is related to the opening of a hybridization gap. Our quasiparticle scattering spectroscopy (QPS) has shown they are not related directly. This can be understood naturally since in principle band renormalization does not involve symmetry breaking. To deepen our understanding, we extend to other Kondo lattice compounds. For instance, when applied to YbAl3, a vegetable heavy-fermion system, QPS reveals conductance signatures for hybridization in a Kondo lattice such as asymmetric Fano background along with characteristic energy scales. Presenting new results on these materials, we will discuss a broader picture. The work at UIUC is supported by the NSF DMR 12-06766, the work at LANL is carried out under the auspices of the U.S. DOE, Office of Science, and the work done at Ames Lab. was supported under Contract No. DE-AC02-07CH11358.

Band structures of phononic crystal composed of lattices with different periodic constants

International Nuclear Information System (INIS)

Hu, Jia-Guang; Xu, Wen

2014-01-01

With a square lattice mercury and water system being as the model, the band structures of nesting and compound phononic crystals with two different lattice constants were investigated using the method of the supercell plane wave expansion. It was observed that large band gaps can be achieved in low frequency regions by adjusting one of the lattice constants. Meanwhile, effects similar to interstitial impurity defects can be achieved with the increase of lattice constant of the phononic crystal. The corresponding defect modes can be stimulated in band gaps. The larger the lattice constant, the stronger the localization effect of defect modes on the wave. In addition, the change of the filling fraction of impurity exerts great influence on the frequency and localization of defect modes. Furthermore, the change of the position of impurity has notable influence on the frequency of defect modes and their localization. However, the geometry structure and orientation of impurity have little effect on the frequency of defect modes and their localization in the band gap.

Spin and lattice structures of single-crystalline SrFe2As2

Science.gov (United States)

Zhao, Jun; Ratcliff, W., II; Lynn, J. W.; Chen, G. F.; Luo, J. L.; Wang, N. L.; Hu, Jiangping; Dai, Pengcheng

2008-10-01

We use neutron scattering to study the spin and lattice structure of single-crystal SrFe2As2 , the parent compound of the FeAs-based superconductor (Sr,K)Fe2As2 . We find that SrFe2As2 exhibits an abrupt structural phase transition at 220 K, where the structure changes from tetragonal with lattice parameters c>a=b to orthorhombic with c>a>b . At almost the same temperature, Fe spins develop a collinear antiferromagnetic structure along the orthorhombic a axis with spin direction parallel to this a axis. These results are consistent with earlier work on the RFeAsO ( R=rare earth) families of materials and on BaFe2As2 , and therefore suggest that static antiferromagnetic order is ubiquitous for the parent compounds of these FeAs-based high-transition temperature superconductors.

Strain-rate effect on initial crush stress of irregular honeycomb under dynamic loading and its deformation mechanism

Science.gov (United States)

Wang, Peng; Zheng, Zhijun; Liao, Shenfei; Yu, Jilin

2018-02-01

The seemingly contradictory understandings of the initial crush stress of cellular materials under dynamic loadings exist in the literature, and a comprehensive analysis of this issue is carried out with using direct information of local stress and strain. Local stress/strain calculation methods are applied to determine the initial crush stresses and the strain rates at initial crush from a cell-based finite element model of irregular honeycomb under dynamic loadings. The initial crush stress under constant-velocity compression is identical to the quasi-static one, but less than the one under direct impact, i.e. the initial crush stresses under different dynamic loadings could be very different even though there is no strain-rate effect of matrix material. A power-law relation between the initial crush stress and the strain rate is explored to describe the strain-rate effect on the initial crush stress of irregular honeycomb when the local strain rate exceeds a critical value, below which there is no strain-rate effect of irregular honeycomb. Deformation mechanisms of the initial crush behavior under dynamic loadings are also explored. The deformation modes of the initial crush region in the front of plastic compaction wave are different under different dynamic loadings.

Investigation of shape memory alloy honeycombs by means of a micromechanical analysis

International Nuclear Information System (INIS)

Freed, Yuval; Aboudi, Jacob; Gilat, Rivka

2008-01-01

Shape memory alloy (SMA) honeycombs are promising new smart materials which may be used for light-weight structures, biomedical implants, actuators and active structures. In this study, the behavior of several SMA honeycomb structures is investigated by means of a continuum-based thermomechanically coupled micromechanical analysis. To this end, macroscopic inelastic stress–strain responses of several topologies are investigated, both for pseudoelasticity and for shape memory effect. It was found that the triangular topology exhibits the best performance. In addition, the initial transformation surfaces are presented for all possible combinations of applied in-plane stresses. A special two-phase microstructure that is capable of producing an overall negative coefficient of thermal expansion is suggested and studied. In this configuration, in which one of the phases is a SMA, residual strains are being generated upon recovery. Here, the negative coefficient of thermal expansion appears to be associated with a larger amount of residual strain upon recovery. Furthermore, a two-dimensional SMA re-entrant topology that generates a negative in-plane Poisson's ratio is analyzed, and the effect of the full thermomechanical coupling is examined. Finally, the response of a particular three-dimensional microstructure is studied

Preparation and Application of Conductive Textile Coatings Filled with Honeycomb Structured Carbon Nanotubes

Directory of Open Access Journals (Sweden)

Filip Govaert

2014-01-01

Full Text Available Electrical conductive textile coatings with variable amounts of carbon nanotubes (CNTs are presented. Formulations of textile coatings were prepared with up to 15 wt % of CNT, based on the solid weight of the binder. The binders are water based polyacrylate dispersions. The CNTs were mixed into the binder dispersion starting from a commercially available aqueous CNT dispersion that is compatible with the binder dispersion. Coating formulations with variable CNT concentrations were applied on polyester and cotton woven and knitted fabrics by different textile coating techniques: direct coating, transfer coating, and screen printing. The coatings showed increasing electrical conductivity with increasing CNT concentration. The coatings can be regarded to be electrically conductive (sheet resistivity<103 Ohm/sq starting at 3 wt% CNT. The degree of dispersion of the carbon nanotubes particles inside the coating was visualized by scanning electron microscopy. The CNT particles form honeycomb structured networks in the coatings, proving a high degree of dispersion. This honeycomb structure of CNT particles is forming a conductive network in the coating leading to low resistivity values.

Finding New Thermoelectric Compounds Using Crystallographic Data: Atomic Displacement Parameters

Energy Technology Data Exchange (ETDEWEB)

Chakoumakos, B.C.; Mandrus, D.G.; Sales, B.C.; Sharp, J.W.

1999-08-29

A new structure-property relationship is discussed which links atomic displacement parameters (ADPs) and the lattice thermal conductivity of clathrate-like compounds. For many clathrate-like compounds, in which one of the atom types is weakly bound and ''rattles'' within its atomic cage, room temperature ADP information can be used to estimate the room temperature lattice thermal conductivity, the vibration frequency of the ''rattler'', and the temperature dependence of the heat capacity. Neutron data and X-ray crystallography data, reported in the literature, are used to apply this analysis to several promising classes of thermoelectric materials.

A S=1 underscreened Kondo lattice model

International Nuclear Information System (INIS)

Perkins, N.B.; Nunez-Regueiro, M.D.; Iglesias, J.R.; Coqblin, B.

2006-01-01

The underscreened Kondo lattice model presented here includes both an intra-site Kondo exchange interaction J K between the conduction band and localized 5f electrons described by S=1 spins, and an inter-site exchange f-f interaction J H . We write both localized and itinerant spins in a Fermionic representation, and then use a mean-field approximation. We obtain a coexistence of Kondo effect and magnetism which can account for the behavior of some Uranium compounds

Generalized isothermic lattices

International Nuclear Information System (INIS)

Doliwa, Adam

2007-01-01

We study multi-dimensional quadrilateral lattices satisfying simultaneously two integrable constraints: a quadratic constraint and the projective Moutard constraint. When the lattice is two dimensional and the quadric under consideration is the Moebius sphere one obtains, after the stereographic projection, the discrete isothermic surfaces defined by Bobenko and Pinkall by an algebraic constraint imposed on the (complex) cross-ratio of the circular lattice. We derive the analogous condition for our generalized isothermic lattices using Steiner's projective structure of conics, and we present basic geometric constructions which encode integrability of the lattice. In particular, we introduce the Darboux transformation of the generalized isothermic lattice and we derive the corresponding Bianchi permutability principle. Finally, we study two-dimensional generalized isothermic lattices, in particular geometry of their initial boundary value problem

Elimination of spurious lattice fermion solutions and noncompact lattice QCD

Energy Technology Data Exchange (ETDEWEB)

Lee, T.D.

1997-09-22

It is well known that the Dirac equation on a discrete hyper-cubic lattice in D dimension has 2{sup D} degenerate solutions. The usual method of removing these spurious solutions encounters difficulties with chiral symmetry when the lattice spacing l {ne} 0, as exemplified by the persistent problem of the pion mass. On the other hand, we recall that in any crystal in nature, all the electrons do move in a lattice and satisfy the Dirac equation; yet there is not a single physical result that has ever been entangled with a spurious fermion solution. Therefore it should not be difficult to eliminate these unphysical elements. On a discrete lattice, particle hop from point to point, whereas in a real crystal the lattice structure in embedded in a continuum and electrons move continuously from lattice cell to lattice cell. In a discrete system, the lattice functions are defined only on individual points (or links as in the case of gauge fields). However, in a crystal the electron state vector is represented by the Bloch wave functions which are continuous functions in {rvec {gamma}}, and herein lies one of the essential differences.

Lattice fermions

Energy Technology Data Exchange (ETDEWEB)

Randjbar-Daemi, S

1995-12-01

The so-called doubling problem in the lattice description of fermions led to a proof that under certain circumstances chiral gauge theories cannot be defined on the lattice. This is called the no-go theorem. It implies that if {Gamma}/sub/A is defined on a lattice then its infrared limit, which should correspond to the quantum description of the classical action for the slowly varying fields on lattice scale, is inevitably a vector like theory. In particular, if not circumvented, the no-go theorem implies that there is no lattice formulation of the Standard Weinberg-Salam theory or SU(5) GUT, even though the fermions belong to anomaly-free representations of the gauge group. This talk aims to explain one possible attempt at bypassing the no-go theorem. 20 refs.

Lattice fermions

International Nuclear Information System (INIS)

Randjbar-Daemi, S.

1995-12-01

The so-called doubling problem in the lattice description of fermions led to a proof that under certain circumstances chiral gauge theories cannot be defined on the lattice. This is called the no-go theorem. It implies that if Γ/sub/A is defined on a lattice then its infrared limit, which should correspond to the quantum description of the classical action for the slowly varying fields on lattice scale, is inevitably a vector like theory. In particular, if not circumvented, the no-go theorem implies that there is no lattice formulation of the Standard Weinberg-Salam theory or SU(5) GUT, even though the fermions belong to anomaly-free representations of the gauge group. This talk aims to explain one possible attempt at bypassing the no-go theorem. 20 refs

Fabrication of honeycomb-structured poly(ethylene glycol)-block-poly(lactic acid) porous films and biomedical applications for cell growth

Energy Technology Data Exchange (ETDEWEB)

Yao, Bingjian [Key Laboratory of Special Functional Aggregated Materials, Ministry of Education, School of Chemistry and Chemical Engineering, Shandong University, Jinan 250199 (China); College of chemistry, Chemical Engineering and Materials Science, Collaborative Innovation Center of Functionalized Probes for Chemical Imaging, Key Laboratory of Molecular and Nano Probes, Ministry of Education, Shandong Normal University, Jinan 250014 (China); Zhu, Qingzeng, E-mail: qzzhu@sdu.edu.cn [Key Laboratory of Special Functional Aggregated Materials, Ministry of Education, School of Chemistry and Chemical Engineering, Shandong University, Jinan 250199 (China); Yao, Linli [Key Laboratory of the Ministry of Education for Experimental Teratology, Department of Histology and Embryology, Shandong University School of Medicine, 250012 Jinan (China); Hao, Jingcheng [Key Laboratory of Special Functional Aggregated Materials, Ministry of Education, School of Chemistry and Chemical Engineering, Shandong University, Jinan 250199 (China)

2015-03-30

Graphical abstract: - Highlights: • Honeycomb-structured PEG-PLA porous films were fabricated. • The organization of pores depends on molecular weight ratio of PEG-to-PLA block. • The pores in the film were internally decorated with a layer of PEG. • The honeycomb-structured PEG-PLA film was suitable as a substrate for cell growth. - Abstract: A series of poly(ethylene glycol)-block-poly(lactic acid) (PEG-PLA) copolymers with a hydrophobic PLA block of different molecular weights and a fixed length hydrophilic PEG were synthesized successfully and characterized. These amphiphilic block copolymers were used to fabricate honeycomb-structured porous films using the breath figure (BF) templating technique. The surface topology and composition of the highly ordered pattern film were further characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and fluorescence microscopy. The results indicated that the PEG-to-PLA block molecular weight ratio influenced the BF film surface topology. The film with the best ordered pores was obtained with a PEG-to-PLA ratio of 2.0 × 10{sup 3}:3.0 × 10{sup 4}. The self-organization of the hydrophilic PEG chains within the pores was confirmed by XPS and fluorescence labeled PEG. A model is proposed to elucidate the stabilization process of the amphiphilic PEG-PLA aggregated architecture on the water droplet-based templates. In addition, GFP-U87 cell viability has been investigated by MTS test and the cell morphology on the honeycomb-structured PEG-PLA porous film has been evaluated using phase-contrast microscope. This porous film is shown to be suitable as a matrix for cell growth.

Fabrication of honeycomb-structured poly(ethylene glycol)-block-poly(lactic acid) porous films and biomedical applications for cell growth

International Nuclear Information System (INIS)

Yao, Bingjian; Zhu, Qingzeng; Yao, Linli; Hao, Jingcheng

2015-01-01

Graphical abstract: - Highlights: • Honeycomb-structured PEG-PLA porous films were fabricated. • The organization of pores depends on molecular weight ratio of PEG-to-PLA block. • The pores in the film were internally decorated with a layer of PEG. • The honeycomb-structured PEG-PLA film was suitable as a substrate for cell growth. - Abstract: A series of poly(ethylene glycol)-block-poly(lactic acid) (PEG-PLA) copolymers with a hydrophobic PLA block of different molecular weights and a fixed length hydrophilic PEG were synthesized successfully and characterized. These amphiphilic block copolymers were used to fabricate honeycomb-structured porous films using the breath figure (BF) templating technique. The surface topology and composition of the highly ordered pattern film were further characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and fluorescence microscopy. The results indicated that the PEG-to-PLA block molecular weight ratio influenced the BF film surface topology. The film with the best ordered pores was obtained with a PEG-to-PLA ratio of 2.0 × 10 3 :3.0 × 10 4 . The self-organization of the hydrophilic PEG chains within the pores was confirmed by XPS and fluorescence labeled PEG. A model is proposed to elucidate the stabilization process of the amphiphilic PEG-PLA aggregated architecture on the water droplet-based templates. In addition, GFP-U87 cell viability has been investigated by MTS test and the cell morphology on the honeycomb-structured PEG-PLA porous film has been evaluated using phase-contrast microscope. This porous film is shown to be suitable as a matrix for cell growth

Lattice and magnetic anisotropies in uranium intermetallic compounds

DEFF Research Database (Denmark)

Havela, L.; Mašková, S.; Adamska, A.

2013-01-01

Examples of UNiAlD and UCoGe illustrate that the soft crystallographic direction coincides quite generally with the shortest U-U links in U intermetallics. Added to existing experimental evidence on U compounds it leads to a simple rule, that the easy magnetization direction and the soft crystall...... crystallographic direction (in the sense of highest compressibility under hydrostatic pressure) must be mutually orthogonal....

Magnetoresistances and magnetic entropy changes associated with negative lattice expansions in NaZn13-type compounds LaFeCoSi

Science.gov (United States)

Hu, Feng-Xia; Qian, Xiao-Ling; Wang, Guang-Jun; Sun, Ji-Rong; Shen, Bao-Gen; Cheng, Zhao-Hua; Gao, Ju

2005-11-01

Magnetoresistances and magnetic entropy changes in NaZn13-type compounds La(Fe1-xCox)11.9Si1.1 (x=0.04, 0.06 and 0.08) with Curie temperatures of 243 K, 274 K and 301 K, respectively, are studied. The ferromagnetic ordering is accompanied by a negative lattice expansion. Large magnetic entropy changes in a wide temperature range from ~230 K to ~320 K are achieved. Raising Co content increases the Curie temperature but weakens the magnetovolume effect, thereby causing a decrease in magnetic entropy change. These materials exhibit a metallic character below TC, whereas the electrical resistance decreases abruptly and then recovers the metal-like behaviour above TC. Application of a magnetic field retains the transitions via increasing the ferromagnetic ordering temperature. An isothermal increase in magnetic field leads to an increase in electrical resistance at temperatures near but above TC, which is a consequence of the field-induced metamagnetic transition from a paramagnetic state to a ferromagnetic state.

Parametric study of self-forming ZnO Nanowall network with honeycomb structure by Pulsed Laser Deposition

KAUST Repository

El Zein, B.; Boulfrad, Samir; Jabbour, Ghassan E.; Doghè che, Elhadj Hadj

2014-01-01

The successful synthesis of catalyst free zinc oxide (ZnO) Nanowall networks with honeycomb like structure by Pulsed Laser Deposition (PLD) is demonstrated in this paper. The synthesis was conducted directly on Silicon (Si) (1 0 0) and Glass

The honeycomb strip chamber: A two coordinate and high precision muon detector

International Nuclear Information System (INIS)

Tolsma, H.P.T.

1996-01-01

This thesis describes the construction and performance of the Honeycomb Strip Chamber (HSC). The HSC offers several advantages with respect to classical drift chambers and drift tubes. The main features of the HSC are: -The detector offers the possibility of simultaneous readout of two orthogonal coordinates with approximately the same precision. - The HSC technology is optimised for mass production. This means that the design is modular (monolayers) and automisation of most of the production steps is possible (folding and welding machines). - The technology is flexible. The cell diameter can easily be changed from a few millimetres to at least 20 mm by changing the parameters in the computer programme of the folding machine. The number of monolayers per station can be chosen freely to the demands of the experiment. -The honeycomb structure gives the detector stiffness and makes it self supporting. This makes the technology a very transparent one in terms of radiation length which is important to prevent multiple scattering of high energetic muons. - The dimensions of the detector are defined by high precision templates. Those templates constrain for example the overall tolerance on the wire positions to 20 μm rms. Reproduction of the high precision assembly of the detector is thus guaranteed. (orig.)

The honeycomb strip chamber: A two coordinate and high precision muon detector

Energy Technology Data Exchange (ETDEWEB)

Tolsma, H P.T.

1996-04-19

This thesis describes the construction and performance of the Honeycomb Strip Chamber (HSC). The HSC offers several advantages with respect to classical drift chambers and drift tubes. The main features of the HSC are: -The detector offers the possibility of simultaneous readout of two orthogonal coordinates with approximately the same precision. - The HSC technology is optimised for mass production. This means that the design is modular (monolayers) and automisation of most of the production steps is possible (folding and welding machines). - The technology is flexible. The cell diameter can easily be changed from a few millimetres to at least 20 mm by changing the parameters in the computer programme of the folding machine. The number of monolayers per station can be chosen freely to the demands of the experiment. -The honeycomb structure gives the detector stiffness and makes it self supporting. This makes the technology a very transparent one in terms of radiation length which is important to prevent multiple scattering of high energetic muons. - The dimensions of the detector are defined by high precision templates. Those templates constrain for example the overall tolerance on the wire positions to 20 {mu}m rms. Reproduction of the high precision assembly of the detector is thus guaranteed. (orig.).

Intermediate honeycomb ordering to trigger oxygen redox chemistry in layered battery electrode.

Science.gov (United States)

Mortemard de Boisse, Benoit; Liu, Guandong; Ma, Jiangtao; Nishimura, Shin-ichi; Chung, Sai-Cheong; Kiuchi, Hisao; Harada, Yoshihisa; Kikkawa, Jun; Kobayashi, Yoshio; Okubo, Masashi; Yamada, Atsuo

2016-04-18

Sodium-ion batteries are attractive energy storage media owing to the abundance of sodium, but the low capacities of available cathode materials make them impractical. Sodium-excess metal oxides Na2MO3 (M: transition metal) are appealing cathode materials that may realize large capacities through additional oxygen redox reaction. However, the general strategies for enhancing the capacity of Na2MO3 are poorly established. Here using two polymorphs of Na2RuO3, we demonstrate the critical role of honeycomb-type cation ordering in Na2MO3. Ordered Na2RuO3 with honeycomb-ordered [Na(1/3)Ru(2/3)]O2 slabs delivers a capacity of 180 mAh g(-1) (1.3-electron reaction), whereas disordered Na2RuO3 only delivers 135 mAh g(-1) (1.0-electron reaction). We clarify that the large extra capacity of ordered Na2RuO3 is enabled by a spontaneously ordered intermediate Na1RuO3 phase with ilmenite O1 structure, which induces frontier orbital reorganization to trigger the oxygen redox reaction, unveiling a general requisite for the stable oxygen redox reaction in high-capacity Na2MO3 cathodes.

Development of an Automatic Testing Platform for Aviator’s Night Vision Goggle Honeycomb Defect Inspection

Directory of Open Access Journals (Sweden)

Bo-Lin Jian

2017-06-01

Full Text Available Due to the direct influence of night vision equipment availability on the safety of night-time aerial reconnaissance, maintenance needs to be carried out regularly. Unfortunately, some defects are not easy to observe or are not even detectable by human eyes. As a consequence, this study proposed a novel automatic defect detection system for aviator’s night vision imaging systems AN/AVS-6(V1 and AN/AVS-6(V2. An auto-focusing process consisting of a sharpness calculation and a gradient-based variable step search method is applied to achieve an automatic detection system for honeycomb defects. This work also developed a test platform for sharpness measurement. It demonstrates that the honeycomb defects can be precisely recognized and the number of the defects can also be determined automatically during the inspection. Most importantly, the proposed approach significantly reduces the time consumption, as well as human assessment error during the night vision goggle inspection procedures.

Lattice gauge theory

International Nuclear Information System (INIS)

Mack, G.

1982-01-01

After a description of a pure Yang-Mills theory on a lattice, the author considers a three-dimensional pure U(1) lattice gauge theory. Thereafter he discusses the exact relation between lattice gauge theories with the gauge groups SU(2) and SO(3). Finally he presents Monte Carlo data on phase transitions in SU(2) and SO(3) lattice gauge models. (HSI)

Band structure of semiconductor compounds of Mg sub 2 Si and Mg sub 2 Ge with strained crystal lattice

CERN Document Server

Krivosheeva, A V; Shaposhnikov, V L; Krivosheev, A E; Borisenko, V E

2002-01-01

The effect of isotopic and unaxial deformation of the crystal lattice on the electronic band structure of indirect band gap semiconductors Mg sub 2 Si and Mg sub 2 Ge has been simulated by means of the linear augmented plane wave method. The reduction of the lattice constant down to 95 % results in a linear increase of the direct transition in magnesium silicide by 48%. The stresses arising under unaxial deformation shift the bands as well as result in splitting of degenerated states. The dependence of the interband transitions on the lattice deformation is nonlinear in this case

Pd nanoparticles supported on ultrahigh surface area honeycomb-like carbon for alcohol electrooxidation

Energy Technology Data Exchange (ETDEWEB)

Yan, Zaoxue; He, Guoqiang; Zhang, Guanghui; Meng, Hui; Shen, Pei Kang [State Key Laboratory of Optoelectronic Materials and Technologies, School of Physics and Engineering, Sun Yat-Sen University, Guangzhou 510275 (China)

2010-04-15

The honeycomb-like porous carbon was prepared using glucose as carbon source and solid core mesoporous shell (SCMS) silica as templates. The material was characterized by physical and electrochemical methods. The results showed that the honeycomb-like porous carbon was consisted of hollow porous carbon (HPC) which gave an ultrahigh BET surface area of 1012.97 m{sup 2} g{sup -1} and pore volume of 2.19 cm{sup 3} g{sup -1}. The porous walls of the HPC were formed in the mesoporous shells of the silica templates. The HPC was used as the support to load Pd nanoparticles (Pd/HPC) for alcohol electrooxidation. It was highly active for methanol, ethanol and isopropanol electrooxidation. The peak current density for ethanol electrooxidation on Pd/HPC electrode was five times higher than that on Pd/C electrode at the same Pd loadings. The mass activity for ethanol electrooxidation was 4000 A g{sup -1} which is much higher compared to the data reported in the literature. The highly porous structure of such HPC can be widely used as support for uniform dispersing metal nanoparticles to increase their utilization as electrocatalysts. (author)

Elevated-Temperature Tests Under Static and Aerodynamic Conditions on Honeycomb-Core Sandwich Panels

Science.gov (United States)

Groen, Joseph M.; Johnson, Aldie E., Jr.

1959-01-01

Stainless-steel honeycomb-core sandwich panels which differed primarily in skin thicknesses were tested at elevated temperatures under static and aerodynamic conditions. The results of these tests were evaluated to determine the insulating effectiveness and structural integrity of the panels. The static radiant-heating tests were performed in front of a quartz-tube radiant heater at panel skin temperatures up to 1,5000 F. The aerodynamic tests were made in a Mach 1.4 heated blowdown wind tunnel. The tunnel temperature was augmented by additional heat supplied by a radiant heater which raised the panel surface temperature above 8000 F during air flow. Static radiant-heating tests of 2 minutes duration showed that all the panels protected the load-carrying structure about equally well. Thin-skin panels showed an advantage for this short-time test over thick-skin panels from a standpoint of weight against insulation. Permanent inelastic strains in the form of local buckles over each cell of the honeycomb core caused an increase in surface roughness. During the aero- dynamic tests all of the panels survived with little or no damage, and panel flutter did not occur.

Estimation of the Thermal Process in the Honeycomb Panel by a Monte Carlo Method

Science.gov (United States)

Gusev, S. A.; Nikolaev, V. N.

2018-01-01

A new Monte Carlo method for estimating the thermal state of the heat insulation containing honeycomb panels is proposed in the paper. The heat transfer in the honeycomb panel is described by a boundary value problem for a parabolic equation with discontinuous diffusion coefficient and boundary conditions of the third kind. To obtain an approximate solution, it is proposed to use the smoothing of the diffusion coefficient. After that, the obtained problem is solved on the basis of the probability representation. The probability representation is the expectation of the functional of the diffusion process corresponding to the boundary value problem. The process of solving the problem is reduced to numerical statistical modelling of a large number of trajectories of the diffusion process corresponding to the parabolic problem. It was used earlier the Euler method for this object, but that requires a large computational effort. In this paper the method is modified by using combination of the Euler and the random walk on moving spheres methods. The new approach allows us to significantly reduce the computation costs.

Spin-Lattice Coupling and Superconductivity in Fe Pnictides

Directory of Open Access Journals (Sweden)

T. Egami

2010-01-01

Full Text Available We consider strong spin-lattice and spin-phonon coupling in iron pnictides and discuss its implications on superconductivity. Strong magneto-volume effect in iron compounds has long been known as the Invar effect. Fe pnictides also exhibit this effect, reflected in particular on the dependence of the magnetic moment on the atomic volume of Fe defined by the positions of the nearest neighbor atoms. Through the phenomenological Landau theory, developed on the basis of the calculations by the density functional theory (DFT and the experimental results, we quantify the strength of the spin-lattice interaction as it relates to the Stoner criterion for the onset of magnetism. We suggest that the coupling between electrons and phonons through the spin channel may be sufficiently strong to be an important part of the superconductivity mechanism in Fe pnictides.

Charge-lattice interplay in layered cobaltates RBaCo2O5+x

Science.gov (United States)

Lavrov, A. N.; Kameneva, M. Yu.; Kozeeva, L. P.; Zhdanov, K. R.

2017-10-01

X-ray diffraction, electrical resistivity and thermal expansion measurements are used to study the interrelation between the structural, magnetic and electron-transport peculiarities in RBaCo2O5+x (R=Y, Gd) over a wide range of oxygen contents. We find that the anisotropic lattice strain caused by the oxygen chain ordering in these compounds favors the metallic state and is a necessary condition for the coupled insulator-to-metal and spin-state phase transitions to occur. The obtained data point to the key role of the crystal lattice in selecting the preferred spin and orbital states of cobalt ions.

Structure and lattice dynamics in non-centrosymmetric borates

International Nuclear Information System (INIS)

Stein, W.D.R.

2007-01-01

This thesis deals with a study of structural and lattice dynamical properties of some noncentrosymmetric borates with outstanding non-linear optical properties. The focus was on the compound bismuth triborate (BiB 3 O 6 ). The structure of the tetraborates MB 4 O 7 (M=Pb,Sr,Ba) was also investigated. The structural investigations in bismuth triborate include powder and single crystal diffraction experiments on X-ray and neutron sources. The crystal structure was under examination in the temperature range from 100 K to room temperature and the lattice constants in the temperature range from 20 K to 800 K. The lattice constants show a nearly linear dependency from temperature. Our observations are in good agreement with investigations of the thermal expansion, which shows a strong anisotropy within the layer-like structure of bismuth triborate. Within the borate layers, along the polar axis a strong positive and in the orthogonal direction a negative thermal expansion is observed. This effect can be explained by a zig-zag effect within the borate layers. The lone electron pair at the bismuth atom is discussed to be possibly the origin of the temperature dependency of the coordination environment of the bismuth atom. The influence of the lone electron pair on the crystal structure is raising by lowering the temperature. At the bismuth atom distinct anharmonic effects are observed, where the maximum points along the direction of the polar axis and therefore along the direction of the lone electron pair. The phonon dispersion of bismuth triborate has been investigated by inelastic neutron scattering. The low symmetry of the crystal structure depicts to be a special challenge. The dispersion was observed along the three reciprocal lattice constants. Along the polar axis the dispersion could be characterized to a maximum energy of 20 THz. The low energy acoustic branch along the polar axis shows a softening at the zone boundary. In the orthogonal directions the dispersion

Behaviour of gaseous alkali compounds from coal gasification; Kaasumaisten alkaliyhdisteiden kaeyttaeytyminen kivihiilen kaasutuksessa

Energy Technology Data Exchange (ETDEWEB)

Nykaenen, J. [Imatran Voima Oy, Vantaa (Finland)

1996-12-01

In this project the behaviour of alkali compounds has been studied with a chemical equilibrium model. The goal is to evaluate the possibilities to remove the sodium and potassium compounds together with the fly ash particles by using a ceramic honeycomb filter. The studied processes include both CO{sub 2}/O{sub 2}- and air-blown gasification and combustion. The results show that the difference between the processes with flue gas recirculation and air-blown processes is small. This is due to that the equilibrium concentration of the dominant gaseous alkali compound, chloride, is more or less the same in both processes. This research project is closely connected to the EU-project coordinated by the Delft University of Technology (DUT). In that project alkali concentration of the fuel gas from a 1.6 MW pilot plant will be measured. During the next phase of this research the results from DUT will be compared with the results of this presentation. (author)

Kitaev honeycomb model. Majorana fermion representation and disorder

International Nuclear Information System (INIS)

Zschocke, Fabian

2016-01-01

Many interesting phenomena in quantum physics arise through the quantum mechanical interaction of a large number of particles. In most cases describing the relevant physical properties is extremely difficult, because the complexity of the system increases exponentially with the number of interacting particles and solving the underlying Schroedinger equation becomes impossible. Nevertheless, our understanding of complex phenomena has progressed through some groundbreaking discoveries in the history of condensed matter physics. Examples include the development of Landau's theory of Fermi liquids, the BCS theory of superconductivity, the theory of superfluidity and the theory of the fractional quantum Hall effect. In all these cases a theoretical understanding was achieved with so-called quasi-particles. Instead of explaining a phenomenon through the behavior of fundamental particles, such as electrons, the corresponding properties can be described by the simple behavior of quasi-particles, which are themselves a result of the complex collective interaction. One of the rare examples, where a strongly correlated quantum mechanical problem can be solved analytical, is the Kitaev model. It describes interacting spins on a honeycomb lattice and exhibits a spin liquid ground state. Here the solution was achieved by means of certain quasi-particles, called Majorana fermions. However, it has not been possible to clearly identify such a spin liquid experimentally, because its defining feature is the absence of any conventional order, in particular magnetic order. In contrast, the observation of quasiparticle excitations may hint at the nature of the ground state. But also a definite detection of Majorana fermions in any kind of system remains one of the outstanding issues in modern condensed matter physics. Therefore this thesis is devoted to the question how such quasiparticles may be found experimentally. For this reason we study the influence of disorder on the states

Design, fabrication and test of a liquid hydrogen titanium honeycomb cryogenic test tank for use as a reusable launch vehicle main propellant tank

Science.gov (United States)

Stickler, Patrick B.; Keller, Peter C.

1998-01-01

Reusable Launch Vehicles (RLV's) utilizing LOX\\LH2 as the propellant require lightweight durable structural systems to meet mass fraction goals and to reduce overall systems operating costs. Titanium honeycomb sandwich with flexible blanket TPS on the windward surface is potentially the lightest-weight and most operable option. Light weight is achieved in part because the honeycomb sandwich tank provides insulation to its liquid hydrogen contents, with no need for separate cryogenic insulation, and in part because the high use temperature of titanium honeycomb reduces the required surface area of re-entry thermal protection systems. System operability is increased because TPS needs to be applied only to surfaces where temperatures exceed approximately 650 K. In order to demonstrate the viability of a titanium sandwich constructed propellant tank, a technology demonstration program was conducted including the design, fabrication and testing of a propellant tank-TPS system. The tank was tested in controlled as well as ambient environments representing ground hold conditions for a RLV main propellant tank. Data collected during each test run was used to validate predictions for air liquefaction, outside wall temperature, boil-off rates, frost buildup and its insulation effects, and the effects of placing a thermal protection system blanket on the external surface. Test results indicated that titanium honeycomb, when used as a RLV propellant tank material, has great promise as a light-weight structural system.

Area of Lattice Polygons

Science.gov (United States)

Scott, Paul

2006-01-01

A lattice is a (rectangular) grid of points, usually pictured as occurring at the intersections of two orthogonal sets of parallel, equally spaced lines. Polygons that have lattice points as vertices are called lattice polygons. It is clear that lattice polygons come in various shapes and sizes. A very small lattice triangle may cover just 3…

Auxiliary-Field Quantum Monte Carlo Simulations of Strongly-Correlated Systems, the Final Report

Energy Technology Data Exchange (ETDEWEB)

Chang, C. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)

2017-11-07

In this final report, we present preliminary results of ground state phases of interacting spinless Dirac fermions. The name "Dirac fermion" originates from the fact that low-energy excitations of electrons hopping on the honeycomb lattice are described by a relativistic Dirac equation. Dirac fermions have received much attention particularly after the seminal work of Haldale1 which shows that the quantum Hall physics can be realized on the honeycomb lattice without magnetic fields. Haldane's work later becomes the foundation of topological insulators (TIs). While the physics of TIs is based largely on spin-orbit coupled non-interacting electrons, it was conjectured that topological insulators can be induced by strong correlations alone.

Superhydrophilicity of anodic aluminum oxide films: From 'honeycomb' to 'bird's nest'

International Nuclear Information System (INIS)

Ye Jiaming; Yin Qiming; Zhou Yongliang

2009-01-01

An electrochemical method has been used to prepare different kinds of surfaces including 'honeycomb'-like and 'bird's nest'-like surfaces on anodic aluminum oxide (AAO) films. The relationship between the morphology and wettability of the AAO films was investigated by scanning electron microscopy and the measurement of water contact angles. The results show that the 'bird's nest'-like structure is necessary for superhydrophilic property, which provide direct experimental evidences for the 3D capillary theory concerning superhydrophilicity. It is expected that this investigation will be devoted to guiding the fabrication of superhydrophilic and superhydrophobic surfaces.

GA-4/GA-9 honeycomb impact limiter tests and analytical model

International Nuclear Information System (INIS)

Koploy, M.A.; Taylor, C.S.

1991-01-01

General Atomics (GA) has a test program underway to obtain data on the behavior of a honeycomb impact limiter. The program includes testing of small samples to obtain basic information, as well as testing of complete 1/4-scale impact limiters to obtain load-versus-deflection curves for different crush orientations. GA has used the test results to aid in the development of an analytical model to predict the impact limiter loads. The results also helped optimize the design of the impact limiters for the GA-4 and GA-9 Casks

Low-temperature field evaporation of Nb3Sn compound

International Nuclear Information System (INIS)

Ksenofontov, V.A.; Kul'ko, V.B.; Kutsenko, P.A.

1986-01-01

Investigation results on field evaporation of superconducting Nb 3 Sn compound wth A15 lattice are presented. Compound evaporation is shown to proceed in two stages. Evaporation field and ionic composition of evaporating material are determined. It is found out that in strong electric fields compound surface represents niobium skeleton, wich does not form regular image. Comparison of ion-microscopic and calculated images formed by low-temperature field evaporation indicates to possibility of sample surface reconstruction after preferable tin evaporation

A spin echo study of A15 intermetallic compounds

International Nuclear Information System (INIS)

Schoep, G.K.

1976-01-01

This thesis mainly concerns the measurement of spin-lattice relaxation times in intermetallic compounds of the bcc lattice structure, having the formula V 3 X (C = Pt, Ir, Os, Pd, Rh, Ni, Co, Au). When, in a spin echo experiment, a two-pulse sequence was applied, several quadrupolar echoes were observed. Special attention is given to the 'forbidden' echoes (absol.(Δm')GT1) in V 3 Au and V 3 Co. In relation to the V 3 X compounds, several characteristics are discussed including temperature dependence and concentration dependence of spin relaxation times, superconductivity and the importance of d-state electrons in determination of the spin relaxation times. Finally, the above characteristics were determined for 6 different samples of the vanadium-gold alloy, V 3 Au, specifically

New integrable lattice hierarchies

International Nuclear Information System (INIS)

Pickering, Andrew; Zhu Zuonong

2006-01-01

In this Letter we give a new integrable four-field lattice hierarchy, associated to a new discrete spectral problem. We obtain our hierarchy as the compatibility condition of this spectral problem and an associated equation, constructed herein, for the time-evolution of eigenfunctions. We consider reductions of our hierarchy, which also of course admit discrete zero curvature representations, in detail. We find that our hierarchy includes many well-known integrable hierarchies as special cases, including the Toda lattice hierarchy, the modified Toda lattice hierarchy, the relativistic Toda lattice hierarchy, and the Volterra lattice hierarchy. We also obtain here a new integrable two-field lattice hierarchy, to which we give the name of Suris lattice hierarchy, since the first equation of this hierarchy has previously been given by Suris. The Hamiltonian structure of the Suris lattice hierarchy is obtained by means of a trace identity formula

Structural and electronic properties of thallium compounds

International Nuclear Information System (INIS)

Paliwal, Neetu; Srivastava, Vipul

2016-01-01

The tight binding linear muffin-tin-orbital (TB-LMTO) method within the local density approximation (LDA has been used to calculate structural and electronic properties of thallium pnictides TlX (X=Sb, Bi) at high pressure. As a function of volume, the total energy is evaluated. Apart from this, the lattice parameter (a_0), bulk modulus (B_0), band structure (BS) and density of states (DOS) are calculated. From energy band diagram we observed metallic behaviour in TlSb and TlBi compounds. The values of equilibrium lattice constants and bulk modulus are agreed well with the available data.

Structural and electronic properties of thallium compounds

Energy Technology Data Exchange (ETDEWEB)

Paliwal, Neetu, E-mail: neetumanish@gmail.com [Department of Physics, AISECT University Bhopal, 464993 (India); Srivastava, Vipul [Department of Engineering Physics, NRI Institute of Research & Technology, Raisen Road, Bhopal, 462021 (India)

2016-05-06

The tight binding linear muffin-tin-orbital (TB-LMTO) method within the local density approximation (LDA has been used to calculate structural and electronic properties of thallium pnictides TlX (X=Sb, Bi) at high pressure. As a function of volume, the total energy is evaluated. Apart from this, the lattice parameter (a{sub 0}), bulk modulus (B{sub 0}), band structure (BS) and density of states (DOS) are calculated. From energy band diagram we observed metallic behaviour in TlSb and TlBi compounds. The values of equilibrium lattice constants and bulk modulus are agreed well with the available data.

Co-Fe-Si Aerogel Catalytic Honeycombs for Low Temperature Ethanol Steam Reforming

Directory of Open Access Journals (Sweden)

Montserrat Domínguez

2012-09-01

Full Text Available Cobalt talc doped with iron (Fe/Co~0.1 and dispersed in SiO2 aerogel was prepared from silica alcogel impregnated with metal nitrates by supercritical drying. Catalytic honeycombs were prepared following the same procedure, with the alcogel synthesized directly over cordierite honeycomb pieces. The composite aerogel catalyst was characterized by X-ray diffraction, scanning electron microscopy, focus ion beam, specific surface area and X-ray photoelectron spectroscopy. The catalytic layer is about 8 µm thick and adheres well to the cordierite support. It is constituted of talc layers of about 1.5 µm × 300 nm × 50 nm which are well dispersed and anchored in a SiO2 aerogel matrix with excellent mass-transfer properties. The catalyst was tested in the ethanol steam reforming reaction, aimed at producing hydrogen for on-board, on-demand applications at moderate temperature (573–673 K and pressure (1–7 bar. Compared to non-promoted cobalt talc, the catalyst doped with iron produces less methane as byproduct, which can only be reformed at high temperature, thereby resulting in higher hydrogen yields. At 673 K and 2 bar, 1.04 NLH2·mLEtOH(l−1·min−1 are obtained at S/C = 3 and W/F = 390 g·min·molEtOH−1.

Lattice gauge theories

International Nuclear Information System (INIS)

Creutz, M.

1983-04-01

In the last few years lattice gauge theory has become the primary tool for the study of nonperturbative phenomena in gauge theories. The lattice serves as an ultraviolet cutoff, rendering the theory well defined and amenable to numerical and analytical work. Of course, as with any cutoff, at the end of a calculation one must consider the limit of vanishing lattice spacing in order to draw conclusions on the physical continuum limit theory. The lattice has the advantage over other regulators that it is not tied to the Feynman expansion. This opens the possibility of other approximation schemes than conventional perturbation theory. Thus Wilson used a high temperature expansion to demonstrate confinement in the strong coupling limit. Monte Carlo simulations have dominated the research in lattice gauge theory for the last four years, giving first principle calculations of nonperturbative parameters characterizing the continuum limit. Some of the recent results with lattice calculations are reviewed

Parametric study of self-forming ZnO Nanowall network with honeycomb structure by Pulsed Laser Deposition

KAUST Repository

El Zein, B.

2014-02-01

The successful synthesis of catalyst free zinc oxide (ZnO) Nanowall networks with honeycomb like structure by Pulsed Laser Deposition (PLD) is demonstrated in this paper. The synthesis was conducted directly on Silicon (Si) (1 0 0) and Glass-ITO substrates without the intermediate of metal catalyst, template or chemical etching. Kinetic of growth and effects of gas pressure and substrate temperature were studied by depositing ZnO films on P type Si (1 0 0) substrates with different deposition parameters. The optimized growth parameters were found as: 10 mTorr oxygen pressure, 600 C substrate temperature, and deposition duration equal or higher than 10 min. X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM) and Photoluminescence (PL) measurements were used to investigate structural, microstructural and optical properties of ZnO Nanowall networks produced. They exhibit a non-uniform size high quality honeycomb structure with low deep level defects. © 2013 Elsevier B.V.

EXAFS investigations of Cu-Mg-O compound

CERN Document Server

Sidorenko, A F; Babanov, Y A; Naumov, S V; Samokhvalov, A A

2001-01-01

The interest to systems containing copper oxide is connected with the problem of high-temperature superconductivity because of the closeness of its basic physical properties and properties of superconductor mother Cu-compounds. In this work, EXAFS study of the Cu sub 0 sub . sub 2 Mg sub 0 sub . sub 8 O compound is presented. A new iterative algorithm of the solution of ill-posed problem on determining three partial pair correlation functions from one EXAFS-data set near the Cu K-edge is described. The results of X-ray scattering study of a given sample show a presence of a single phase with the MgO structure and a lattice parameter of 4.219 A instead of 4.208 A for pure MgO. From the EXAFS investigations, we find the local distortion of the lattice. We revealed that the short range order differs both from a hypothetical alloy with the MgO structure and from copper oxide.

Convection-diffusion lattice Boltzmann scheme for irregular lattices

NARCIS (Netherlands)

Sman, van der R.G.M.; Ernst, M.H.

2000-01-01

In this paper, a lattice Boltzmann (LB) scheme for convection diffusion on irregular lattices is presented, which is free of any interpolation or coarse graining step. The scheme is derived using the axioma that the velocity moments of the equilibrium distribution equal those of the

Advanced honeycomb adsorbent and scaling-up technique for thermal swing adsorptive VOC concentrator; Samarusuingu kyuchakushiki VOC noshuku sochiyo hanikamu kyuchakutai no kaizen to sukeru up gijutsu ni tsuite

Energy Technology Data Exchange (ETDEWEB)

Mitsuma, Y.; Kuwa, T.; Yamauchi, H. [Seibu Giken Co. Ltd., Fukuoka (Japan); Hirose, T. [Kumamoto Univ. (Japan). Faculty of Engineering

1998-03-01

On the honeycomb type adsorptive concentrator, a manufacturing method of the honeycomb adsorbent rotor, retention of mechanical strength corresponding with a large-scale processing and minimization of air leakage resulting in performance deterioration were technically examined. Honeycomb structure was formed from an alumina-silica fiber paper, and high silica-content zeolite was deposited in the fiber void of the matrix. The adsorbent rotor using sepiolite as an inorganic adhesive for honeycomb fabrication showed fracture strength of from 1.6 to 3.2 times the conventional adsorbent rotor. Two types of differently shaped fluorinated rubber seal were developed for the adsorbent rotor. Amount of air leakage from the seal between each zone as well as to outside was sufficiently small. A large-scale VOC concentrator with the 3950 mm diameter and 450 mm length was manufactured with the adsorbent rotor and seal structure in accordance with the aforementioned method. Results of the real machine operation showed same concentration performance at those of the small-scale experiment. 10 refs., 15 figs., 2 tabs.

Facile Synthesis of Hierarchical Mesoporous Honeycomb-like NiO for Aqueous Asymmetric Supercapacitors.

Science.gov (United States)

Ren, Xiaochuan; Guo, Chunli; Xu, Liqiang; Li, Taotao; Hou, Lifeng; Wei, Yinghui

2015-09-16

Three-dimensional (3D) hierarchical nanostructures have been demonstrated as one of the most ideal electrode materials in energy storage systems due to the synergistic combination of the advantages of both nanostructures and microstructures. In this study, the honeycomb-like mesoporous NiO microspheres as promising cathode materials for supercapacitors have been achieved using a hydrothermal reaction, followed by an annealing process. The electrochemical tests demonstrate the highest specific capacitance of 1250 F g(-1) at 1 A g(-1). Even at 5 A g(-1), a specific capacitance of 945 F g(-1) with 88.4% retention after 3500 cycles was obtained. In addition, the 3D porous graphene (reduced graphene oxide, rGO) has been prepared as an anode material for supercapacitors, which displays a good capacitance performance of 302 F g(-1) at 1 A g(-1). An asymmetric supercapacitor has been successfully fabricated based on the honeycomb-like NiO and rGO. The asymmetric supercapacitor achieves a remarkable performance with a specific capacitance of 74.4 F g(-1), an energy density of 23.25 Wh kg(-1), and a power density of 9.3 kW kg(-1), which is able to light up a light-emitting diode.

From two-dimensional graphene oxide to three-dimensional honeycomb-like Ni3S2@graphene oxide composite: insight into structure and electrocatalytic properties

Science.gov (United States)

Wei, Xinting; Li, Yueqiang; Xu, Wenli; Zhang, Kaixuan; Yin, Jie; Shi, Shaozhen; Wei, Jiazhen; Di, Fangfang; Guo, Junxue; Wang, Can; Chu, Chaofan; Sui, Ning; Chen, Baoli; Zhang, Yingtian; Hao, Hongguo; Zhang, Xianxi; Zhao, Jinsheng; Zhou, Huawei; Wang, Shuhao

2017-12-01

Three-dimensional (3D) graphene composites have drawn increasing attention in energy storage/conversion applications due to their unique structures and properties. Herein, we synthesized 3D honeycomb-like Ni3S2@graphene oxide composite (3D honeycomb-like Ni3S2@GO) by a one-pot hydrothermal method. We found that positive charges of Ni2+ and negative charges of NO3- in Ni(NO3)2 induced a transformation of graphene oxide with smooth surface into graphene oxide with wrinkled surface (w-GO). The w-GO in the mixing solution of Ni(NO3)2/thioacetamide/H2O evolved into 3D honeycomb-like Ni3S2@GO in solvothermal process. The GO effectively inhibited the aggregation of Ni3S2 nanoparticles. Photoelectrochemical cells based on 3D Ni3S2@GO synthesized at 60 mM l-1 Ni(NO3)2 exhibited the best energy conversion efficiency. 3D Ni3S2@GO had smaller charge transfer resistance and larger exchange current density than pure Ni3S2 for iodine reduction reaction. The cyclic stability of 3D honeycomb-like Ni3S2@GO was good in the iodine electrolyte. Results are of great interest for fundamental research and practical applications of 3D GO and its composites in solar water-splitting, artificial photoelectrochemical cells, electrocatalysts and Li-S or Na-S batteries.

Lattice disorder in strongly correlated lanthanide and actinide intermetallics

International Nuclear Information System (INIS)

Booth, C.H.; Bauer, E.D.; Maple, M.B.; Lawrence, J.M.; Kwei, G.H.; Sarrao, J.L.

2001-01-01

Lanthanide and actinide intermetallic compounds display a wide range of correlated-electron behavior, including ferromagnetism, antiferromagnetism, nonmagnetic (Kondo) ground states, and so-called 'non-Fermi liquid' (NFL) behavior. The interaction between f electrons and the conduction band is a dominant factor in determining the ground state of a given system. However, lattice disorder can create a distribution of interactions, generating unusual physical properties. These properties may include NFL behavior in many materials. In addition, lattice disorder can cause deviations from standard Kondo behavior that is less severe than NFL behavior. A review of the lattice disorder mechanism within a tight-binding model is presented, along with measurements of the YbBCu 4 and UPd x Cu 5-x systems, demonstrating the applicability of the model. These measurements indicate that while the YbBCu 4 system appears to be well ordered, both site interchange and continuous bond-length disorder occur in the UPd x Cu 5-x series. Nevertheless, the measured bond-length disorder in UPdCu 4 does not appear to be enough to explain the NFL properties simply with the Kondo disorder model. (au)

Ordered patterns and structures via interfacial self-assembly: superlattices, honeycomb structures and coffee rings.

Science.gov (United States)

Ma, Hongmin; Hao, Jingcheng

2011-11-01

Self-assembly is now being intensively studied in chemistry, physics, biology, and materials engineering and has become an important "bottom-up" approach to create intriguing structures for different applications. Self-assembly is not only a practical approach for creating a variety of nanostructures, but also shows great superiority in building hierarchical structures with orders on different length scales. The early work in self-assembly focused on molecular self-assembly in bulk solution, including the resultant dye aggregates, liposomes, vesicles, liquid crystals, gels and so on. Interfacial self-assembly has been a great concern over the last two decades, largely because of the unique and ingenious roles of this method for constructing materials at interfaces, such as self-assembled monolayers, Langmuir-Blodgett films, and capsules. Nanocrystal superlattices, honeycomb films and coffee rings are intriguing structural materials with more complex features and can be prepared by interfacial self-assembly on different length scales. In this critical review, we outline the recent development in the preparation and application of colloidal nanocrystal superlattices, honeycomb-patterned macroporous structures by the breath figure method, and coffee-ring-like patterns (247 references). This journal is © The Royal Society of Chemistry 2011

Inelastic neutron scattering and lattice dynamics studies of AlPO4 and GaPO4

International Nuclear Information System (INIS)

Mittal, R.; Chaplot, S.L.; Kolesnikov, A.I.; Loong, C.-K.; Jayakumar, O.D.; Kulshreshtha, S.K.

2006-01-01

The compounds AlPO 4 and GaPO 4 show phase transitions at high pressure depending on the compressibility of the constituent tetrahedra. Semi-empirical interatomic potentials are available for AlPO 4 and GaPO 4 . Molecular dynamics simulations have been reported using these potentials to understand the nature of phase transitions in different polymorphs of these compounds. In order to check these potentials we have carried out lattice dynamical studies for AlPO 4 and GaPO 4 . The phonon density of states measurements from the polycrystalline samples of low-cristobalite phase of AlPO 4 and GaPO 4 are carried out using High-Resolution Medium-Energy Chopper Spectrometer at ANL in the energy transfer range 0-160 meV. The calculated phonon spectra for both the compounds using the available potentials show fair agreement with the experimental data. However, the agreement between the two is improved by including the polarizibility of the oxygen atoms in the framework of the shell model. The lattice dynamical model is used for the calculation of specific heat and thermal expansion

Lattices with unique complements

CERN Document Server

Saliĭ, V N

1988-01-01

The class of uniquely complemented lattices properly contains all Boolean lattices. However, no explicit example of a non-Boolean lattice of this class has been found. In addition, the question of whether this class contains any complete non-Boolean lattices remains unanswered. This book focuses on these classical problems of lattice theory and the various attempts to solve them. Requiring no specialized knowledge, the book is directed at researchers and students interested in general algebra and mathematical logic.

Predictors of idiopathic pulmonary fibrosis in absence of radiologic honeycombing: A cross sectional analysis in ILD patients undergoing lung tissue sampling.

Science.gov (United States)

Salisbury, Margaret L; Xia, Meng; Murray, Susan; Bartholmai, Brian J; Kazerooni, Ella A; Meldrum, Catherine A; Martinez, Fernando J; Flaherty, Kevin R

2016-09-01

Idiopathic pulmonary fibrosis (IPF) can be diagnosed confidently and non-invasively when clinical and computed tomography (CT) criteria are met. Many do not meet these criteria due to absence of CT honeycombing. We investigated predictors of IPF and combinations allowing accurate diagnosis in individuals without honeycombing. We utilized prospectively collected clinical and CT data from patients enrolled in the Lung Tissue Research Consortium. Included patients had no honeycombing, no connective tissue disease, underwent diagnostic lung biopsy, and had CT pattern consistent with fibrosing ILD (n = 200). Logistic regression identified clinical and CT variables predictive of IPF. The probability of IPF was assessed at various cut-points of important clinical and CT variables. A multivariable model adjusted for age and gender found increasingly extensive reticular densities (OR 2.93, CI 95% 1.55-5.56, p = 0.001) predicted IPF, while increasing ground glass densities predicted a diagnosis other than IPF (OR 0.55, CI 95% 0.34-0.89, p = 0.02). The model-based probability of IPF was 80% or greater in patients with age at least 60 years and extent of reticular density one-third or more of total lung volume; for patients meeting or exceeding these clinical thresholds the specificity for IPF is 96% (CI 95% 91-100%) with 21 of 134 (16%) biopsies avoided. In patients with suspected fibrotic ILD and absence of CT honeycombing, extent of reticular and ground glass densities predict a diagnosis of IPF. The probability of IPF exceeds 80% in subjects over age 60 years with one-third of total lung having reticular densities. Copyright © 2016 Elsevier Ltd. All rights reserved.

Frontiers and critical expoents in percolation and Ising and Potts ferromagnets: renormalization group and others techniques

International Nuclear Information System (INIS)

Magalhaes, A.C.N. de.

1982-01-01

By using real space renormalization group methods, bond percolation on d-dimensional hypercubic (d = 2, 3, 4), first - and second - neighbour isotropic square, anisotropic square and 'inhomogeneous' 4-8 lattices is studied. Through some extrapolation methods, critical points and/or frontiers are obtained (as well as the critical exponent ν sub(p) in the isotropic cases) for these lattices that, or agree well with other available results, or are new as far as it is know (first - and second - neighbour isotropic square and 'inhomogeneous' 4-8 lattices). A conjecture concerning approximate (eventually exact) critical points and, in certain situations, critical frontiers of q-state Potts ferromagnets on d-dimensional lattices (d > 1) is formulated. This conjecture is verified within good accuracy for all the lattices whose critical points are known, and it allows the prediction of a great number of new results, some of them it is believed to be exact. Within a real space renomalization group framework, accurate approximations for the critical frontiers associated with the quenched bond-diluted first-neighbour spin-1/2 Ising ferromagnet on triangular and honeycomb lattices are calculated. The best numerical proposals lead, in both pure bond percolation (p = p sub(c)) and pure Ising (p = 1) limits, to the exact critical points and (dt 0 /dp) sub(p = p sub(c)) (where t 0 identical to tanh J/K sub(B) T), and to a 0.15% (0.96%) error in (dt 0 /dp) sub(p = 1) for the triangular (honeycomb) lattice; for p sub(c) 0 (for fixed p) of 0.27% (0.14%) is estimated for the triangular (honeycomb) lattice. It is exhibited, for many star-triangle graph pairs with any number of terminals and different sizes, that the exact q = 1, 2, 3, 4 critical points of Potts ferromagnets can aZZ of them, be obtained from any one of such graph pairs. (Author) [pt

Influence of Electrolyte Composition on the Calcium-Phosphorus compound Coating on Titanium Substrate by Micro-arc Oxidation

Institute of Scientific and Technical Information of China (English)

ZHU Xiu-hong; WANG Cong-zeng; KOU Bin-da; SU Xue-kuan; ZHANG Wen-quan

2004-01-01

The compound bioceramic coating containing calcium (Ca) and phosphorus (P) on titanium alloy substrate was prepared by means of micro-arc oxidation (MAO) treatment. The results show that under the different electrolyte the coating with the color of gray or black and surface morphology of cauliflower or honeycomb, where Ca content and P contain can attain 30% and 20% respectively, can be obtained. Meanwhile, the influences of electrolyte temperature, current density and discharge time on morphology and thickness of coating are also discussed here.

3D FDM production and mechanical behavior of polymeric sandwich specimens embedding classical and honeycomb cores

Science.gov (United States)

Brischetto, Salvatore; Ferro, Carlo Giovanni; Torre, Roberto; Maggiore, Paolo

2018-04-01

Desktop 3D FDM (Fused Deposition Modelling) printers are usually employed for the production of nonstructural objects. In recent years, the present authors tried to use this technology also to produce structural elements employed in the construction of small UAVs (Unmanned Aerial Vehicles). Mechanical stresses are not excessive for small multirotor UAVs. Therefore, the FDM technique combined with polymers, such as the ABS (Acrylonitrile Butadiene Styrene) and the PLA(Poly Lactic Acid), can be successfully employed to produce structural components. The present new work is devoted to the production and preliminary structural analysis of sandwich configurations. These new lamination schemes could lead to an important weight reduction without significant decreases of mechanical properties. Therefore, it could be possible, for the designed application (e.g., a multifunctional small UAV produced via FDM), to have stiffener and lighter structures easy to be manufactured with a low-cost 3D printer. The new sandwich specimens here proposed are PLA sandwich specimens embedding a PLA honeycomb core produced by means of the same extruder, multilayered specimens with ABS external layers and an internal homogeneous PLA core using different extruders for the two materials, sandwich specimens with external ABS skins and an internal PLA honeycomb core using different extruders for the two materials, and sandwich specimens where two different extruders have been employed for PLA material used for skins and for the internal honeycomb core. For all the proposed configurations, a detailed description of the production activity is given.Moreover, several preliminary results about three-point bending tests, different mechanical behaviors and relative delamination problems for each sandwich configuration will be discussed in depth.

Silicene on metal substrates: A first-principles study on the emergence of a hierarchy of honeycomb structures

International Nuclear Information System (INIS)

Kaltsas, D.; Tsetseris, L.; Dimoulas, A.

2014-01-01

Experimental studies have reported several types of Si monolayer structures that are formed on metal surfaces. These structures typically show the topology of a honeycomb bonding network, but differ in terms of corrugation and surface coverage. Using first-principles calculations, we identify atomic-scale mechanisms that underlie the appearance of different configurations as coverage increases during Si deposition on silver. The key point is that any extra Si adatoms that land on preformed silicene films can be incorporated in the honeycomb network and form bonds with underlying Ag atoms. As a result, the corrugation profile changes, giving rise to varying overlayer geometries. We also show that the same set of mechanisms control the appearance of silicene films on an iridium substrate. The results address available experimental data, but also probe the stability and properties of silicene wetting films that have not been observed yet.

The Lattice-Valued Turing Machines and the Lattice-Valued Type 0 Grammars

Directory of Open Access Journals (Sweden)

Juan Tang

2014-01-01

Full Text Available Purpose. The purpose of this paper is to study a class of the natural languages called the lattice-valued phrase structure languages, which can be generated by the lattice-valued type 0 grammars and recognized by the lattice-valued Turing machines. Design/Methodology/Approach. From the characteristic of natural language, this paper puts forward a new concept of the l-valued Turing machine. It can be used to characterize recognition, natural language processing, and dynamic characteristics. Findings. The mechanisms of both the generation of grammars for the lattice-valued type 0 grammar and the dynamic transformation of the lattice-valued Turing machines were given. Originality/Value. This paper gives a new approach to study a class of natural languages by using lattice-valued logic theory.

Additive lattice kirigami.

Science.gov (United States)

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

2016-09-01

Kirigami uses bending, folding, cutting, and pasting to create complex three-dimensional (3D) structures from a flat sheet. In the case of lattice kirigami, this cutting and rejoining introduces defects into an underlying 2D lattice in the form of points of nonzero Gaussian curvature. A set of simple rules was previously used to generate a wide variety of stepped structures; we now pare back these rules to their minimum. This allows us to describe a set of techniques that unify a wide variety of cut-and-paste actions under the rubric of lattice kirigami, including adding new material and rejoining material across arbitrary cuts in the sheet. We also explore the use of more complex lattices and the different structures that consequently arise. Regardless of the choice of lattice, creating complex structures may require multiple overlapping kirigami cuts, where subsequent cuts are not performed on a locally flat lattice. Our additive kirigami method describes such cuts, providing a simple methodology and a set of techniques to build a huge variety of complex 3D shapes.

Two iridates, two models, and two approaches: A comparative study on magnetism in three-dimensional honeycomb materials

Science.gov (United States)

Lee, Eric Kin-Ho; Rau, Jeffrey G.; Kim, Yong Baek

2016-05-01

Two recent theoretical works studied the role of Kitaev interactions in the newly observed incommensurate magnetic order in the hyper-honeycomb (β -Li2IrO3 ) and stripy-honeycomb (γ -Li2IrO3 ) iridates. Each of these works analyzed a different model (J K Γ versus coupled zigzag chain model) using a contrasting method (classical versus soft-spin analysis). The lack of commonality between these works precludes meaningful comparisons and a proper understanding of these unusual orderings. In this study, we complete the unfinished picture initiated by these two works by solving both models with both approaches for both three-dimensional (3D) honeycomb iridates. Through comparisons between all combinations of models, techniques, and materials, we find that the bond-isotropic J K Γ model consistently predicts the experimental phase of β -Li2IrO3 regardless of the method used, while the experimental phase of γ -Li2IrO3 can be generated by the soft-spin approach with eigenmode mixing irrespective of the model used. To gain further insights, we solve a one-dimensional (1D) quantum spin-chain model related to both 3D models using the density matrix renormalization group method to form a benchmark. We discover that in the 1D model, incommensurate correlations in the classical and soft-spin analysis survive in the quantum limit only in the presence of the symmetric-off-diagonal exchange Γ found in the J K Γ model. The relevance of these results to the real materials is also discussed.

Transport and magnetic properties of new heavy-fermion antiferromagnet YbNi{sub 3}Al{sub 9}

Energy Technology Data Exchange (ETDEWEB)

Ohara, S; Yamashita, T; Mori, Y; Sakamoto, I, E-mail: ohara.shigeo@nitech.ac.jp [Department of Engineering Physics, Electronics and Mechanics, Graduate School of Engineering, Nagoya Institute of Technology, Nagoya 466-8555 (Japan)

2011-01-01

We have synthesized a new Yb-based Kondo-lattice compound YbNi{sub 3}Al{sub 9}. This compound crystallizes in a trigonal ErNi{sub 3}Al{sub 9}-type structure (space group R32), in which the Yb-ion is arranged in a two-dimensional honey-comb lattice perpendicular to the c-axis. We report the first measurements of electrical resistivity and magnetization for single-crystalline samples of YbNi{sub 3}Al{sub 9}. The electrical resistivity of YbNi{sub 3}Al{sub 9} is characteristic of the typical properties of heavy-fermion antiferromagnets with a Neel temperature of T{sub N} = 3.4 K. The transport and magnetic properties exhibit large anisotropy in the low-temperature region owing to an interplay among the crystalline-electric-field effect, the Ruderman-Kittel-Kasuya-Yoshida interaction, and the Kondo effect. Below T{sub N}, the metamagnetic transition is observed at a very low magnetic field of around 1 kOe with the field applied along the a-axis. The magnetic structure of YbNi{sub 3}Al{sub 9} is highly sensitive to the applied magnetic field.

Half-Heusler compounds with a 1 eV (1.7 eV) direct band gap, lattice-matched to GaAs (Si), for solar cell application: A first-principles study

KAUST Repository

Belmiloud, N.

2016-01-10

A systematic theoretical study of the structural and electronic properties of new half-Heusler compounds is performed to find the appropriate target key physical parameters for photovoltaic application. As a result, five ternary half-Heusler compounds ScAgC, YCuC, CaZnC, NaAgO, and LiCuS are studied by density functional theory for potential applications in multi-junction solar cells. The calculated formation enthalpies indicate that these materials are thermodynamically stable. Using state-of-the-art modified Becke-Johnson exchange potential approximation, we find a direct band gap close to 1eV (∼1.88eV) for ScAgC, YCuC, CaZnC, NaAgO (LiCuS) being quasi-lattice matched to GaAs (Si). In addition, the band offsets between half-Heusler compounds and GaAs (Si) and their consequences for heterostructures are derived using the modified Tersoff method for the branch-point energy. Furthermore, the elastic constants and phonon dispersion curves are calculated. They indicate the respective mechanical and dynamical stability of these half-Heusler compounds. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Elastic properties of distorted triangular lattice KNiCl3-family compounds

International Nuclear Information System (INIS)

Nishiwaki, Yoichi; Hasegawa, Takumi; Machida, Kenichi; Takeuchi, Yoshio

2006-01-01

In order to discuss the condensation of the K 4 -mode in KNiCl 3 -family compounds, the temperature dependences of the elastic compliances of KNiCl 3 , RbMnBr 3 , RbFeBr 3 , and RbCoBr 3 were measured. In each compound, the temperature dependence of the elastic compliances s 33 showed a sharp discontinuity at the point of structural phase transition from a prototype P6 3 /mmc structure. The structural phase transitions of the KNiCl 3 -family compounds are induced by the condensation of the K 4 -mode at the Brilluoin zone boundary in the P6 3 /mmc structure. When the K 4 -mode is regarded as an order parameter η, the Landau free energy includes coupling term η 2 T 3 , where T 3 is an external stress. The experimental results were interpreted satisfactorily on the basis of a phenomenological Landau theory. (author)

Finite-lattice-spacing corrections to masses and g factors on a lattice

International Nuclear Information System (INIS)

Roskies, R.; Wu, J.C.

1986-01-01

We suggest an alternative method for extracting masses and g factors from lattice calculations. Our method takes account of more of the infrared and ultraviolet lattice effects. It leads to more reasonable results in simulations of QED on a lattice

Lattice distortion and spontaneous Γ5g ferro-quadrupole moment in phase IV of CexLa1-xB6

International Nuclear Information System (INIS)

Nemoto, Yuichi; Akatsu, Mitsuhiro; Goto, Terutaka; Suzuki, Osamu; Nakamura, Shintaro; Kunii, Satoru

2005-01-01

We have performed low-temperature thermal expansion measurements to investigate lattice effect of the phase IV in Ce x La 1-x B 6 , for x=0.75 and 0.70. In phase IV of both compounds, lattice length along the [111] direction shrinks notably, on the other hand length along the [001] direction expands. These results provide evidence that the spontaneous Γ 5g ferro-quadrupole moment yz >= zx >= xy > 0 is relevant in phase IV because the trigonal lattice distortion is described by the symmetry strain yz >= zx >= xy > 0 simultaneously

Lattices for laymen: a non-specialist's introduction to lattice gauge theory

International Nuclear Information System (INIS)

Callaway, D.J.E.

1985-01-01

The review on lattice gauge theory is based upon a series of lectures given to the Materials Science and Technology Division at Argonne National Laboratory. Firstly the structure of gauge theories in the continuum is discussed. Then the lattice formulation of these theories is presented, including quantum electrodynamics and non-abelian lattice gauge theories. (U.K.)

Lattice QCD on fine lattices

Energy Technology Data Exchange (ETDEWEB)

Schaefer, Stefan [DESY (Germany). Neumann Inst. for Computing

2016-11-01

These configurations are currently in use in many on-going projects carried out by researchers throughout Europe. In particular this data will serve as an essential input into the computation of the coupling constant of QCD, where some of the simulations are still on-going. But also projects computing the masses of hadrons and investigating their structure are underway as well as activities in the physics of heavy quarks. As this initial project of gauge field generation has been successful, it is worthwhile to extend the currently available ensembles with further points in parameter space. These will allow to further study and control systematic effects like the ones introduced by the finite volume, the non-physical quark masses and the finite lattice spacing. In particular certain compromises have still been made in the region where pion masses and lattice spacing are both small. This is because physical pion masses require larger lattices to keep the effects of the finite volume under control. At light pion masses, a precise control of the continuum extrapolation is therefore difficult, but certainly a main goal of future simulations. To reach this goal, algorithmic developments as well as faster hardware will be needed.

Twelve inequivalent Dirac cones in two-dimensional ${\mathrm{ZrB}}_2$

Energy Technology Data Exchange (ETDEWEB)

Lopez-Bezanilla, Alejandro

2018-01-01

Theoretical evidence of the existence of 12 inequivalent Dirac cones at the vicinity of the Fermi energy in monolayered ZrB2 is presented. Two-dimensional ZrB2 is a mechanically stable d- and p-orbital compound exhibiting a unique electronic structure with two Dirac cones out of high-symmetry points in the irreducible Brillouin zone with a small electron-pocket compensation. First-principles calculations demonstrate that while one of the cones is insensitive to lattice expansion, the second cone vanishes for small perturbation of the vertical Zr position. Internal symmetry breaking with external physical stimuli, along with the relativistic effect of spin-orbit coupling, is able to remove selectively the Dirac cones. A rational explanation in terms of d- and p-orbital mixing is provided to elucidate the origin of the infrequent Dirac cones in a flat structure. The versatility of transition-metal d orbitals combined with the honeycomb lattice provided by the B atoms yields particular features in a two-dimensional material.

Nonmonotonic and anisotropic magnetoresistance effect in antiferromagnet CaMn2Bi2

Science.gov (United States)

Kawaguchi, N.; Urata, T.; Hatano, T.; Iida, K.; Ikuta, H.

2018-04-01

We found a large and unique magnetoresistance (MR) effect for CaMn2Bi2 . When the magnetic field was applied along the crystallographic c axis at low temperatures, the resistivity increased with the magnetic field and the MR ratio reached several hundred percent, but then it decreased with further increasing the applied field. In addition, the angle dependence measurement revealed a strong anisotropy. This compound is an antiferromagnetic semiconductor with a narrow band gap, and Mn atoms form a corrugated honeycomb lattice. Therefore, a frustration among the magnetic moments is expected, and we propose that our observations can be understood by a nonmonotonic modulation of magnetic fluctuation under the magnetic field.

Single crystals of the anisotropic Kagome staircase compounds Ni3V2O8 and Co3V2O8

OpenAIRE

Balakrishnan, G.; Petrenko, O. A.; Lees, M. R.; Paul, D. McK.

2004-01-01

Compounds with a Kagome type lattice are known to exhibit magnetic frustration. Large single crystals of two compounds Ni3V2O8 and Co3V2O8, which are variants of a Kagome net lattice, have been grown successfully by the floating zone technique using an optical image furnace. The single crystals are of high quality and exhibit intriguing magnetic properties.

On singularities of lattice varieties

OpenAIRE

Mukherjee, Himadri

2013-01-01

Toric varieties associated with distributive lattices arise as a fibre of a flat degeneration of a Schubert variety in a minuscule. The singular locus of these varieties has been studied by various authors. In this article we prove that the number of diamonds incident on a lattice point $\\a$ in a product of chain lattices is more than or equal to the codimension of the lattice. Using this we also show that the lattice varieties associated with product of chain lattices is smooth.

Reducing Urban Heat Island Effect with Thermal Comfort Housing and Honeycomb Townships

DEFF Research Database (Denmark)

Davis, Mohd. Peter; Reimann, Gregers Peter; Ghazali, Mazlin

2005-01-01

Putra Malaysia can achieve almost passive thermal comfort without air-conditioning, even on the hottest days of the year. ‘Honeycomb townships’, a recent architectural invention by one of the authors, is a new method of subdividing land which saves greatly on roads, thereby permitting larger gardens...... consequences of urbanisation and can be corrected in Malaysia and avoided by other developing countries with a sensible application of the technologies outlined in this paper which prevent the thermal mass of houses and roads from absorbing solar radiation. ‘Cool House’ technology, developed at Universiti...

Formation of the honeycomb-like electrodes by the regime of pulsating overpotential in the second range

Directory of Open Access Journals (Sweden)

NEBOJŠA D. NIKOLIĆ

2012-03-01

Full Text Available In this study the honeycomb-like copper structures electrodeposited by the regime of pulsating overpotential in the second range were analyzed by the technique of scanning electron microscopy. The overpotential amplitude of 1000 mV, deposition pulse of 1 s, and pause durations of 1, 5, 10 and 15 s were selected for the production of this type of structures. The size of holes which remained upon detachment of hydrogen bubbles do not depend on the length of pause duration. On the other hand, the change in morphology of electrodeposited copper around holes from cauliflower-like agglomerates of copper grains to degenerated dendrites is observed when pause duration was increased. Effects of the application of the regime of pulsating overpotential in the second range on the formation of the honeycomb-like structures were less pronounced than the effects attained by the application of the same regime in the millisecond range. However, they were more pronounced than those attained by electrodeposition in the regime of constant potential.

Mean-field study of correlation-induced antisymmetric spin-orbit coupling in a two-orbital honeycomb model

Science.gov (United States)

Hayami, Satoru; Kusunose, Hiroaki; Motome, Yukitoshi

2018-05-01

We investigate a two-orbital Hubbard model on a honeycomb structure, with a special focus on the antisymmetric spin-orbit coupling (ASOC) induced by symmetry breaking in the electronic degrees of freedom. By investigating the ground-state phase diagram by the mean-field approximation in addition to the analysis in the strong correlation limit, we obtain a variety of symmetry-broken phases that induce different types of effective ASOCs by breaking of spatial inversion symmetry. We find several unusual properties emergent from the ASOCs, such as a linear magnetoelectric effect in a spin-orbital ordered phase at 1/4 filling and a spin splitting in the band structure in charge ordered phases at 1/4 and 1/2 fillings. We also show that a staggered potential on the honeycomb structure leads to another type of ASOC, which gives rise to a valley splitting in the band structure at 1/2 filling. We discuss the experimental relevance of our results to candidate materials including transition metal dichalcogenides and trichalcogenides.

Lattice and Valence Electronic Structures of Crystalline Octahedral Molybdenum Halide Clusters-Based Compounds, Cs2[Mo6X14] (X = Cl, Br, I), Studied by Density Functional Theory Calculations.

Science.gov (United States)

Saito, Norio; Cordier, Stéphane; Lemoine, Pierric; Ohsawa, Takeo; Wada, Yoshiki; Grasset, Fabien; Cross, Jeffrey S; Ohashi, Naoki

2017-06-05

The electronic and crystal structures of Cs 2 [Mo 6 X 14 ] (X = Cl, Br, I) cluster-based compounds were investigated by density functional theory (DFT) simulations and experimental methods such as powder X-ray diffraction, ultraviolet-visible spectroscopy, and X-ray photoemission spectroscopy (XPS). The experimentally determined lattice parameters were in good agreement with theoretically optimized ones, indicating the usefulness of DFT calculations for the structural investigation of these clusters. The calculated band gaps of these compounds reproduced those experimentally determined by UV-vis reflectance within an error of a few tenths of an eV. Core-level XPS and effective charge analyses indicated bonding states of the halogens changed according to their sites. The XPS valence spectra were fairly well reproduced by simulations based on the projected electron density of states weighted with cross sections of Al K α , suggesting that DFT calculations can predict the electronic properties of metal-cluster-based crystals with good accuracy.

Reactor lattice codes

International Nuclear Information System (INIS)

Kulikowska, T.

2001-01-01

The description of reactor lattice codes is carried out on the example of the WIMSD-5B code. The WIMS code in its various version is the most recognised lattice code. It is used in all parts of the world for calculations of research and power reactors. The version WIMSD-5B is distributed free of charge by NEA Data Bank. The description of its main features given in the present lecture follows the aspects defined previously for lattice calculations in the lecture on Reactor Lattice Transport Calculations. The spatial models are described, and the approach to the energy treatment is given. Finally the specific algorithm applied in fuel depletion calculations is outlined. (author)

Kitaev exchange and field-induced quantum spin-liquid states in honeycomb α-RuCl3

Science.gov (United States)

Yadav, Ravi; Bogdanov, Nikolay A.; Katukuri, Vamshi M.; Nishimoto, Satoshi; van den Brink, Jeroen; Hozoi, Liviu

2016-11-01

Large anisotropic exchange in 5d and 4d oxides and halides open the door to new types of magnetic ground states and excitations, inconceivable a decade ago. A prominent case is the Kitaev spin liquid, host of remarkable properties such as protection of quantum information and the emergence of Majorana fermions. Here we discuss the promise for spin-liquid behavior in the 4d5 honeycomb halide α-RuCl3. From advanced electronic-structure calculations, we find that the Kitaev interaction is ferromagnetic, as in 5d5 iridium honeycomb oxides, and indeed defines the largest superexchange energy scale. A ferromagnetic Kitaev coupling is also supported by a detailed analysis of the field-dependent magnetization. Using exact diagonalization and density-matrix renormalization group techniques for extended Kitaev-Heisenberg spin Hamiltonians, we find indications for a transition from zigzag order to a gapped spin liquid when applying magnetic field. Our results offer a unified picture on recent magnetic and spectroscopic measurements on this material and open new perspectives on the prospect of realizing quantum spin liquids in d5 halides and oxides in general.

Lattice topology dictates photon statistics.

Science.gov (United States)

Kondakci, H Esat; Abouraddy, Ayman F; Saleh, Bahaa E A

2017-08-21

Propagation of coherent light through a disordered network is accompanied by randomization and possible conversion into thermal light. Here, we show that network topology plays a decisive role in determining the statistics of the emerging field if the underlying lattice is endowed with chiral symmetry. In such lattices, eigenmode pairs come in skew-symmetric pairs with oppositely signed eigenvalues. By examining one-dimensional arrays of randomly coupled waveguides arranged on linear and ring topologies, we are led to a remarkable prediction: the field circularity and the photon statistics in ring lattices are dictated by its parity while the same quantities are insensitive to the parity of a linear lattice. For a ring lattice, adding or subtracting a single lattice site can switch the photon statistics from super-thermal to sub-thermal, or vice versa. This behavior is understood by examining the real and imaginary fields on a lattice exhibiting chiral symmetry, which form two strands that interleave along the lattice sites. These strands can be fully braided around an even-sited ring lattice thereby producing super-thermal photon statistics, while an odd-sited lattice is incommensurate with such an arrangement and the statistics become sub-thermal.

Void lattices

International Nuclear Information System (INIS)

Chadderton, L.T.; Johnson, E.; Wohlenberg, T.

1976-01-01

Void lattices in metals apparently owe their stability to elastically anisotropic interactions. An ordered array of voids on the anion sublattice in fluorite does not fit so neatly into this scheme of things. Crowdions may play a part in the formation of the void lattice, and stability may derive from other sources. (Auth.)

Lattice theory for nonspecialists

International Nuclear Information System (INIS)

Hari Dass, N.D.

1984-01-01

These lectures were delivered as part of the academic training programme at the NIKHEF-H. These lectures were intended primarily for experimentalists, and theorists not specializing in lattice methods. The goal was to present the essential spirit behind the lattice approach and consequently the author has concentrated mostly on issues of principle rather than on presenting a large amount of detail. In particular, the author emphasizes the deep theoretical infra-structure that has made lattice studies meaningful. At the same time, he has avoided the use of heavy formalisms as they tend to obscure the basic issues for people trying to approach this subject for the first time. The essential ideas are illustrated with elementary soluble examples not involving complicated mathematics. The following subjects are discussed: three ways of solving the harmonic oscillator problem; latticization; gauge fields on a lattice; QCD observables; how to solve lattice theories. (Auth.)

Role of elasticity forces in thermodynamics of intercalation compounds : Self-consistent mean-field theory and Monte Carlo simulations

NARCIS (Netherlands)

Kalikmanov, V.I.; De Leeuw, S.W.

2002-01-01

We propose a self-consistent mean-field lattice-gas theory of intercalation compounds based on effective interactions between interstitials in the presence of the host atoms. In addition to short-range screened Coulomb repulsions, usually discussed in the lattice gas models, the present theory takes

MEETING: Lattice 88

Energy Technology Data Exchange (ETDEWEB)

Mackenzie, Paul

1989-03-15

The forty-year dream of understanding the properties of the strongly interacting particles from first principles is now approaching reality. Quantum chromodynamics (QCD - the field theory of the quark and gluon constituents of strongly interacting particles) was initially handicapped by the severe limitations of the conventional (perturbation) approach in this picture, but Ken Wilson's inventions of lattice gauge theory and renormalization group methods opened new doors, making calculations of masses and other particle properties possible. Lattice gauge theory became a major industry around 1980, when Monte Carlo methods were introduced, and the first prototype calculations yielded qualitatively reasonable results. The promising developments over the past year were highlighted at the 1988 Symposium on Lattice Field Theory - Lattice 88 - held at Fermilab.

MEETING: Lattice 88

International Nuclear Information System (INIS)

Mackenzie, Paul

1989-01-01

The forty-year dream of understanding the properties of the strongly interacting particles from first principles is now approaching reality. Quantum chromodynamics (QCD - the field theory of the quark and gluon constituents of strongly interacting particles) was initially handicapped by the severe limitations of the conventional (perturbation) approach in this picture, but Ken Wilson's inventions of lattice gauge theory and renormalization group methods opened new doors, making calculations of masses and other particle properties possible. Lattice gauge theory became a major industry around 1980, when Monte Carlo methods were introduced, and the first prototype calculations yielded qualitatively reasonable results. The promising developments over the past year were highlighted at the 1988 Symposium on Lattice Field Theory - Lattice 88 - held at Fermilab

Fidelity susceptibility and long-range correlation in the Kitaev honeycomb model

Science.gov (United States)

Yang, Shuo; Gu, Shi-Jian; Sun, Chang-Pu; Lin, Hai-Qing

2008-07-01

We study exactly both the ground-state fidelity susceptibility and bond-bond correlation function in the Kitaev honeycomb model. Our results show that the fidelity susceptibility can be used to identify the topological phase transition from a gapped A phase with Abelian anyon excitations to a gapless B phase with non-Abelian anyon excitations. We also find that the bond-bond correlation function decays exponentially in the gapped phase, but algebraically in the gapless phase. For the former case, the correlation length is found to be 1/ξ=2sinh-1[2Jz-1/(1-Jz)] , which diverges around the critical point Jz=(1/2)+ .

Design considerations for application of metallic honeycomb as an energy absorber

International Nuclear Information System (INIS)

Lee, W.H.; Roemer, R.E.

1980-01-01

Design for postulated accidents in nuclear power plants often requires mitigation of impact to safety-related structures. Plastically designed, energy absorbing mechanisms are often used in the design of such mitigating structures. Metallic honeycomb is the most efficient, practical, energy-absorbing material currently in use. Recent tests indicate that its use in this application, however, presents some unique design and fabrication problems. The paper presents the results of static and dynamic crush tests concerned with the effect of impact velocity, material properties, cell density, loading configuration, and overall pad geometry. Specific design recommendations are made in each area, and suggestions are provided to improve fabrication techniques and minimize subsequent problems

Calculations of thermodynamic properties of PuO2 by the first-principles and lattice vibration

International Nuclear Information System (INIS)

Minamoto, Satoshi; Kato, Masato; Konashi, Kenji; Kawazoe, Yoshiyuki

2009-01-01

Plutonium dioxide (PuO 2 ) is a key compound of mixed oxide fuel (MOX fuel). To predict the thermal properties of PuO 2 at high temperature, it is important to understand the properties of MOX fuel. In this study, thermodynamic properties of PuO 2 were evaluated by coupling of first-principles and lattice dynamics calculation. Cohesive energy was estimated from first-principles calculations, and the contribution of lattice vibration to total energy was evaluated by phonon calculations. Thermodynamic properties such as volume thermal expansion, bulk modulus and specific heat of PuO 2 were investigated up to 1500 K

Perspectives from ab-initio and tight-binding: Applications to transition metal compounds and superlattices

Science.gov (United States)

Venkataraman, Vijay Shankar

The experimental and theoretical study of transition metal compounds have occupied condensed matter physicists for the best part of the last century. The rich variety of physical behaviour exhibited by these compounds owes its origin to the subtle balance of the energy scales at play for the d orbitals. In this thesis, we study three different systems comprised of transition metal atoms from the third, the fourth, and the fifth group of the periodic table using a combination of ab-initio density functional theory (DFT) computations and effective tight-binding models for the electronic properties. We first consider the electronic properties of artificially fabricated perovskite superlattices of the form [(SrIrO3)m / SrTiO3] with integer m denoting the number of layers of SrIrO3. After discussing the results of experiments undertaken by our collaborators, we present the results of our DFT calculations and build tight-binding models for the m = 1 and m = 2 superlattices. The active ingredient is found to be the 5d orbitals with significant spin-orbit coupling. We then study the energies of magnetic ground states within DFT and compare and contrast our results with those obtained for the bulk Ruddlesden-Popper iridates. Together with experimental measurements, our results suggest that these superlattices are an exciting venue to probe the magnetism and metal-insulator transitions that occur from the intricate balance of the spin-orbit coupling and electron interactions, as has been reported for their bulk counterparts. Next, we consider alpha-RuCl3, a honeycomb lattice compound. We first show using DFT calculations in conjunction with experiments performed by our collaborators, how spin-orbit coupling in the 4d orbitals of Ru is essential to understand the insulating state realized in this compound. Then, in the latter half of the chapter, we study the magnetic ground states of a two-dimensional analogue of alpha-RuCl3 in weak and strong-coupling regimes obtained from

Twisted mass lattice QCD

International Nuclear Information System (INIS)

Shindler, A.

2007-07-01

I review the theoretical foundations, properties as well as the simulation results obtained so far of a variant of the Wilson lattice QCD formulation: Wilson twisted mass lattice QCD. Emphasis is put on the discretization errors and on the effects of these discretization errors on the phase structure for Wilson-like fermions in the chiral limit. The possibility to use in lattice simulations different lattice actions for sea and valence quarks to ease the renormalization patterns of phenomenologically relevant local operators, is also discussed. (orig.)

Twisted mass lattice QCD

Energy Technology Data Exchange (ETDEWEB)

Shindler, A. [Deutsches Elektronen-Synchrotron (DESY), Zeuthen (Germany). John von Neumann-Inst. fuer Computing NIC

2007-07-15

I review the theoretical foundations, properties as well as the simulation results obtained so far of a variant of the Wilson lattice QCD formulation: Wilson twisted mass lattice QCD. Emphasis is put on the discretization errors and on the effects of these discretization errors on the phase structure for Wilson-like fermions in the chiral limit. The possibility to use in lattice simulations different lattice actions for sea and valence quarks to ease the renormalization patterns of phenomenologically relevant local operators, is also discussed. (orig.)

Lattice potential energies and thermochemical properties of triethylammonium halides (Et3NHX) (X = Cl, Br, and I)

International Nuclear Information System (INIS)

Liu Yupu; Tan Zhicheng; Di Youying; Xing Yiting; Zhang Peng

2012-01-01

Highlights: ► The crystal structures of (Et 3 NHX) (X = Cl, Br, and I) were determined. ► Lattice potential energies and ionic radius of the common cation were obtained. ► Molar enthalpies of dissolution at infinite dilution were derived. ► Relative partial molar enthalpies were derived. ► Hydration enthalpy of Et 3 NH + was calculated. - Abstract: A series of triethylammonium halides (Et 3 NHCl, Et 3 NHBr, and Et 3 NHI) was synthesized. The crystal structures of the three compounds were characterized by X-ray crystallography. The lattice potential energies and ionic radius of the common cation of the three compounds were obtained from crystallographic data. Molar enthalpies of dissolution of the compounds at various values of molality were measured in the double-distilled water at T = 298.150 K by means of an isoperibol solution-reaction calorimeter. According to Pitzer’s theory, the values of molar enthalpies of dissolution at infinite dilution and Pitzer’s parameters of the compounds were obtained. The values of apparent relative molar enthalpies, relative partial molar enthalpies of the solvent and the compounds at different molalities were derived from the experimental values of molar enthalpies of dissolution of the compounds. Finally, hydration enthalpy of the common cation Et 3 NH + was calculated to be ΔH + = −(150.386 ± 4.071) kJ · mol −1 by designing a thermochemical cycle.

Lattice regularized chiral perturbation theory

International Nuclear Information System (INIS)

Borasoy, Bugra; Lewis, Randy; Ouimet, Pierre-Philippe A.

2004-01-01

Chiral perturbation theory can be defined and regularized on a spacetime lattice. A few motivations are discussed here, and an explicit lattice Lagrangian is reviewed. A particular aspect of the connection between lattice chiral perturbation theory and lattice QCD is explored through a study of the Wess-Zumino-Witten term

Spectrum of a Dilated Honeycomb Network

Czech Academy of Sciences Publication Activity Database

Exner, Pavel; Turek, Ondřej

2015-01-01

Roč. 81, č. 4 (2015), s. 535-557 ISSN 0378-620X R&D Projects: GA ČR(CZ) GA14-06818S Institutional support: RVO:61389005 Keywords : quantum graphs * Hexagon lattice * Laplace operator * Vertex delta-coupling * spectrum Subject RIV: BE - Theoretical Physics Impact factor: 0.956, year: 2015

Lab-scale experiment of a closed thermochemical heat storage system including honeycomb heat exchanger

International Nuclear Information System (INIS)

Fopah-Lele, Armand; Rohde, Christian; Neumann, Karsten; Tietjen, Theo; Rönnebeck, Thomas; N'Tsoukpoe, Kokouvi Edem; Osterland, Thomas; Opel, Oliver

2016-01-01

A lab-scale thermochemical heat storage reactor was developed in the European project “thermal battery” to obtain information on the characteristics of a closed heat storage system, based on thermochemical reactions. The present type of storage is capable of re-using waste heat from cogeneration system to produce useful heat for space heating. The storage material used was SrBr 2 ·6H 2 O. Due to agglomeration or gel-like problems, a structural element was introduced to enhance vapour and heat transfer. Honeycomb heat exchanger was designed and tested. 13 dehydration-hydration cycles were studied under low-temperature conditions (material temperatures < 100 °C) for storage. Discharging was realized at water vapour pressure of about 42 mbar. Temperature evolution inside the reactor at different times and positions, chemical conversion, thermal power and overall efficiency were analysed for the selected cycles. Experimental system thermal capacity and efficiency of 65 kWh and 0.77 are respectively obtained with about 1 kg of SrBr 2 ·6H 2 O. Heat transfer fluid recovers heat at a short span of about 43 °C with an average of 22 °C during about 4 h, acceptable temperature for the human comfort (20 °C on day and 16 °C at night). System performances were obtained for a salt bed energy density of 213 kWh·m 3 . The overall heat transfer coefficient of the honeycomb heat exchanger has an average value of 147 W m −2  K −1 . Though promising results have been obtained, ameliorations need to be made, in order to make the closed thermochemical heat storage system competitive for space heating. - Highlights: • Lab-scale thermochemical heat storage is designed, constructed and tested. • The use of honeycomb heat exchanger as a heat and vapour process enhancement. • Closed system (1 kg SrBr 2 ·6H 2 O) able to give back 3/4 of initial thermal waste energy. • System storage capacity and thermal efficiency are respectively 65 kWh and 0.77. �

Supersymmetric lattices

International Nuclear Information System (INIS)

Catterall, Simon

2013-01-01

Discretization of supersymmetric theories is an old problem in lattice field theory. It has resisted solution until quite recently when new ideas drawn from orbifold constructions and topological field theory have been brought to bear on the question. The result has been the creation of a new class of lattice gauge theory in which the lattice action is invariant under one or more supersymmetries. The resultant theories are local and free of doublers and in the case of Yang-Mills theories also possess exact gauge invariance. In principle they form the basis for a truly non-perturbative definition of the continuum supersymmetric field theory. In this talk these ideas are reviewed with particular emphasis being placed on N = 4 super Yang-Mills theory.

Accidental degeneracy of double Dirac cones in a phononic crystal

KAUST Repository

Chen, Ze-Guo; Ni, Xu; Wu, Ying; He, Cheng; Sun, Xiao-Chen; Zheng, Li-Yang; Lu, Ming-Hui; Chen, Yan-Feng

2014-01-01

Artificial honeycomb lattices with Dirac cone dispersion provide a macroscopic platform to study the massless Dirac quasiparticles and their novel geometric phases. In this paper, a quadruple-degenerate state is achieved at the center of the Brillouin zone in a two-dimensional honeycomb lattice phononic crystal, which is a result of accidental degeneracy of two double-degenerate states. In the vicinity of the quadruple-degenerate state, the dispersion relation is linear. Such quadruple degeneracy is analyzed by rigorous representation theory of groups. Using method, a reduced Hamiltonian is obtained to describe the linear Dirac dispersion relations of this quadruple-degenerate state, which is well consistent with the simulation results. Near such accidental degeneracy, we observe some unique properties in wave propagating, such as defect-insensitive propagating character and the Talbot effect.

Accidental degeneracy of double Dirac cones in a phononic crystal

KAUST Repository

Chen, Ze-Guo

2014-04-09

Artificial honeycomb lattices with Dirac cone dispersion provide a macroscopic platform to study the massless Dirac quasiparticles and their novel geometric phases. In this paper, a quadruple-degenerate state is achieved at the center of the Brillouin zone in a two-dimensional honeycomb lattice phononic crystal, which is a result of accidental degeneracy of two double-degenerate states. In the vicinity of the quadruple-degenerate state, the dispersion relation is linear. Such quadruple degeneracy is analyzed by rigorous representation theory of groups. Using method, a reduced Hamiltonian is obtained to describe the linear Dirac dispersion relations of this quadruple-degenerate state, which is well consistent with the simulation results. Near such accidental degeneracy, we observe some unique properties in wave propagating, such as defect-insensitive propagating character and the Talbot effect.

Direct measurement of DX-centre related lattice relaxations in Al$_{x}$Ga$_{1-x}$As compounds

CERN Multimedia

2002-01-01

Donor impurities from elements of group IV and VI form localized electronic states, so-called DX-centers, in AlGaAs and other semiconductors. One of the well known effects related to DX-centers is the persistent photoconductivity. In spite of extensive studies, the microscopic structure of the DX-center is still a matter of controversy. The direct determination of the donor lattice sites and their microscopical surrounding is a crucial point in understanding the relation of microscopic structure to the localized electronic state of the DX-center.\\\\ It is proposed to implant radioactive group VI elements $^{73}$Se (from $^{73}$Br) and $^{118}$Te (from $^{118}$Xe) into Al$_{x}$Ga$_{1-x}$As of different mole fractions ${x}$ and to determine (i) the lattice site of Te and Se impurities by emission channeling of decay positrons and electrons (ii) the local structure of Se impurities using the perturbed $\\gamma$-$\\gamma$-angular correlation technique (PAC). The appearance of the DX-center shall be check...

Properties of 5052 Aluminum For Use as Honeycomb Core in Manned Spaceflight

Science.gov (United States)

Lerch, Bradley A.

2018-01-01

This work explains that the properties of Al 5052 material used commonly for honeycomb cores in sandwich panels are highly dependent on the tempering condition. It has not been common to specify the temper when ordering HC material nor is it common for the supplier to state what the temper is. For aerospace uses, a temper of H38 or H39 is probably recommended. This temper should be stated in the bill of material and should be verified upon receipt of the core. To this end some properties provided herein can aid as benchmark values.

The Relationship between Lattice Enthalpy and Melting Point in Magnesium and Aluminium Oxides. Science Notes

Science.gov (United States)

Talbot, Christopher; Yap, Lydia

2013-01-01

This "Science Note" presents a study by Christopher Talbot and Lydia Yap, who teach IB Chemistry at Anglo-Chinese School (Independent), Republic of Singapore, to pre-university students. Pre-university students may postulate the correlation between the magnitude of the lattice enthalpy compound and its melting point, since both…

Magnetic properties of Sm2Co17-xCrx (0 ≤ x ≤ 3.0) compounds

International Nuclear Information System (INIS)

Fuquan, B.; Wang, J.L.; Tegus, O.; Dagula, W.; Tang, N.; Wang, W.Q.; Yang, F.M.; Brueck, E.; Boer, F.R. de; Buschow, K.H.J.

2004-01-01

The structural and magnetic properties of Sm 2 Co 17-x Cr x (0≤x≤3.0) compounds have been investigated by means of X-ray diffraction and magnetization measurements. The powder X-ray diffraction patterns show that all samples crystallize as a single phase with the rhombohedral Th 2 Zn 17 -type structure. The lattice parameters a and V increase monotonically with increasing Cr content, but the lattice parameter c increases very slowly with increasing Cr content. The X-ray diffraction patterns of the aligned powder of the samples have confirmed that all the compounds investigated have uniaxial anisotropy. The Curie temperature of the compounds decreases rapidly the spontaneous magnetization M 0 , the anisotropy field B a , and the anisotropy constant K 1 of Sm 2 Co 17-x Cr x (0≤x≤3.0) compounds decrease strongly with increasing Cr content

Dirac cones in isogonal hexagonal metallic structures

Science.gov (United States)

Wang, Kang

2018-03-01

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

Vortex lattices in layered superconductors

International Nuclear Information System (INIS)

Prokic, V.; Davidovic, D.; Dobrosavljevic-Grujic, L.

1995-01-01

We study vortex lattices in a superconductor--normal-metal superlattice in a parallel magnetic field. Distorted lattices, resulting from the shear deformations along the layers, are found to be unstable. Under field variation, nonequilibrium configurations undergo an infinite sequence of continuous transitions, typical for soft lattices. The equilibrium vortex arrangement is always a lattice of isocell triangles, without shear

Magnetic behavior of binary intermetallic compound YPd{sub 3}

Energy Technology Data Exchange (ETDEWEB)

Pandey, Abhishek [S. N. Bose National Centre for Basic Sciences, Block-JD, Sector-III, Salt Lake, Kolkata 700098 (India); Saha Institute of Nuclear Physics, 1/AF Bidhannagar, Kolkata 700064 (India); Mazumdar, Chandan [Saha Institute of Nuclear Physics, 1/AF Bidhannagar, Kolkata 700064 (India)], E-mail: chandan.mazumdar@saha.ac.in; Ranganathan, R. [Saha Institute of Nuclear Physics, 1/AF Bidhannagar, Kolkata 700064 (India)

2009-05-12

We report the results of detailed magnetic studies on binary rare-earth-transition metal compound YPd{sub 3}. The results of temperature and magnetic field dependent DC-magnetic measurements along with the results of powder X-ray diffraction measurement and electrical transport have been discussed. The X-ray data suggest a well-defined ordered crystal lattice, free from any detectable impurity phase. Magnetization data exhibits predominant diamagnetic character at higher fields. However, the compound exhibits anomalous behavior at low fields.

Reactor lattice codes

International Nuclear Information System (INIS)

Kulikowska, T.

1999-01-01

The present lecture has a main goal to show how the transport lattice calculations are realised in a standard computer code. This is illustrated on the example of the WIMSD code, belonging to the most popular tools for reactor calculations. Most of the approaches discussed here can be easily modified to any other lattice code. The description of the code assumes the basic knowledge of reactor lattice, on the level given in the lecture on 'Reactor lattice transport calculations'. For more advanced explanation of the WIMSD code the reader is directed to the detailed descriptions of the code cited in References. The discussion of the methods and models included in the code is followed by the generally used homogenisation procedure and several numerical examples of discrepancies in calculated multiplication factors based on different sources of library data. (author)

Toward lattice fractional vector calculus

International Nuclear Information System (INIS)

Tarasov, Vasily E

2014-01-01

An analog of fractional vector calculus for physical lattice models is suggested. We use an approach based on the models of three-dimensional lattices with long-range inter-particle interactions. The lattice analogs of fractional partial derivatives are represented by kernels of lattice long-range interactions, where the Fourier series transformations of these kernels have a power-law form with respect to wave vector components. In the continuum limit, these lattice partial derivatives give derivatives of non-integer order with respect to coordinates. In the three-dimensional description of the non-local continuum, the fractional differential operators have the form of fractional partial derivatives of the Riesz type. As examples of the applications of the suggested lattice fractional vector calculus, we give lattice models with long-range interactions for the fractional Maxwell equations of non-local continuous media and for the fractional generalization of the Mindlin and Aifantis continuum models of gradient elasticity. (papers)

Toward lattice fractional vector calculus

Science.gov (United States)

Tarasov, Vasily E.

2014-09-01

An analog of fractional vector calculus for physical lattice models is suggested. We use an approach based on the models of three-dimensional lattices with long-range inter-particle interactions. The lattice analogs of fractional partial derivatives are represented by kernels of lattice long-range interactions, where the Fourier series transformations of these kernels have a power-law form with respect to wave vector components. In the continuum limit, these lattice partial derivatives give derivatives of non-integer order with respect to coordinates. In the three-dimensional description of the non-local continuum, the fractional differential operators have the form of fractional partial derivatives of the Riesz type. As examples of the applications of the suggested lattice fractional vector calculus, we give lattice models with long-range interactions for the fractional Maxwell equations of non-local continuous media and for the fractional generalization of the Mindlin and Aifantis continuum models of gradient elasticity.

Lattice gas cellular automata and lattice Boltzmann models an introduction

CERN Document Server

Wolf-Gladrow, Dieter A

2000-01-01

Lattice-gas cellular automata (LGCA) and lattice Boltzmann models (LBM) are relatively new and promising methods for the numerical solution of nonlinear partial differential equations. The book provides an introduction for graduate students and researchers. Working knowledge of calculus is required and experience in PDEs and fluid dynamics is recommended. Some peculiarities of cellular automata are outlined in Chapter 2. The properties of various LGCA and special coding techniques are discussed in Chapter 3. Concepts from statistical mechanics (Chapter 4) provide the necessary theoretical background for LGCA and LBM. The properties of lattice Boltzmann models and a method for their construction are presented in Chapter 5.

On the lattice stability of chromium, vanadium, niobium and tantalum

International Nuclear Information System (INIS)

Kaufman, L.

1994-01-01

In a recent review of the lattice stabilities of the elemental transition elements derived by ''ab initio'' and CALPHAD methods Watson et.al. noted that the ab initio values for the Nb-Mo-Tc-Ru-Rh group were 2 to 5 times larger in magnitude than those derived by Saunders et.al. which were in turn ''much larger in magnitude'' than those derived by the author. The implication of this observation is that some sign of coalescence of the ''ab initio'' and CALPHAD results is imminent. Unfortunately, this is not the case. This can be seen by extending the examination of the Au-V system first illustrated by Fernandez-Guillermet and Huang to the Au-Cr, Au-Nb and Au-Ta systems by taking advantage of the recent measurements of the heat of formation of compounds in this system by Fitzner, Selhaoui and Kleppa. The unanimity of opinion within the CALPHAD community on the lattice stability of fcc and bcc Au and Cr and the range of stability of the fee phase in these systems when coupled with the recent experimental results clearly shows how unreasonable the ''ab initio'' results for the lattice stabilities of fcc, Cr, V, Nb and Ta are

Electronic structure and simulated STM images of non-honeycomb phosphorene allotropes

Science.gov (United States)

Kaur, Sumandeep; Kumar, Ashok; Srivastava, Sunita; Tankeshwar, K.

2018-04-01

We have investigated the electronic structure and simulated STM images of various non-honeycomb allotropes of phosphorene namely ɛ - P, ζ - P, η - P and θ - P, within combined density functional theory and Tersoff-Hamman approach. All these allotropes are found to be energetically stable and electronically semiconductingwith bandgap ranging between 0.5-1.2 eV. Simulated STM images show distinctly different features in terms of the topography. Different maximas in the distance-height profile indicates the difference in buckling of atoms in these allotropes. Distinctly different images obtained in this study may be useful to differentiate various allotropes that can serve as fingerprints to identify various allotropes during the synthesis of phosphorene.

Lattice degeneracies of geometric fermions

International Nuclear Information System (INIS)

Raszillier, H.

1983-05-01

We give the minimal numbers of degrees of freedom carried by geometric fermions on all lattices of maximal symmetries in d = 2, 3, and 4 dimensions. These numbers are lattice dependent, but in the (free) continuum limit, part of the degrees of freedom have to escape to infinity by a Wilson mechanism built in, and 2sup(d) survive for any lattice. On self-reciprocal lattices we compare the minimal numbers of degrees of freedom of geometric fermions with the minimal numbers of naive fermions on these lattices and argue that these numbers are equal. (orig.)

Lattice gauge theory using parallel processors

International Nuclear Information System (INIS)

Lee, T.D.; Chou, K.C.; Zichichi, A.

1987-01-01

The book's contents include: Lattice Gauge Theory Lectures: Introduction and Current Fermion Simulations; Monte Carlo Algorithms for Lattice Gauge Theory; Specialized Computers for Lattice Gauge Theory; Lattice Gauge Theory at Finite Temperature: A Monte Carlo Study; Computational Method - An Elementary Introduction to the Langevin Equation, Present Status of Numerical Quantum Chromodynamics; Random Lattice Field Theory; The GF11 Processor and Compiler; and The APE Computer and First Physics Results; Columbia Supercomputer Project: Parallel Supercomputer for Lattice QCD; Statistical and Systematic Errors in Numerical Simulations; Monte Carlo Simulation for LGT and Programming Techniques on the Columbia Supercomputer; Food for Thought: Five Lectures on Lattice Gauge Theory

Electronic structure of disordered binary alloys with short range correlation in Bethe lattice

International Nuclear Information System (INIS)

Moreno, I.F.

1987-01-01

The determination of the electronic structure of a disordered material along the tight-binding model when applied to a Bethe lattice. The diagonal as well as off-diagonal disorder, are considered. The coordination number on the Bethe is fixed lattice to four (Z=4) that occurs in most compound semiconductors. The main proposal was to study the conditions under which a relatively simple model of a disordered material, i.e, a binary alloy, could account for the basic properties of transport or more specifically for the electronic states in such systems. By using a parametrization of the pair probability the behaviour of the electronic density of states (DOS) for different values of the short range order parameter, σ, which makes possible to treat the segregated, random and alternating cases, was analysed. In solving the problem via the Green function technique in the Wannier representation a linear chain of atoms was considered and using the solution of such a 1-D system the problem of the Bethe lattice which is constructed using such renormalized chains as elements, was solved. The results indicate that the obtained DOS are strongly dependent on the correlation assumed for the occupancy in the lattice. (author) [pt

Lattice degeneracies of fermions

International Nuclear Information System (INIS)

Raszillier, H.

1983-10-01

We present a detailed description of the minimal degeneracies of geometric (Kaehler) fermions on all the lattices of maximal symmetries in n = 1, ..., 4 dimensions. We also determine the isolated orbits of the maximal symmetry groups, which are related to the minimal numbers of ''naive'' fermions on the reciprocals of these lattices. It turns out that on the self-reciprocal lattices the minimal numbers of naive fermions are equal to the minimal numbers of degrees of freedom of geometric fermions. The description we give relies on the close connection of the maximal lattice symmetry groups with (affine) Weyl groups of root systems of (semi-) simple Lie algebras. (orig.)

Geometry of lattice field theory

International Nuclear Information System (INIS)

Honan, T.J.

1986-01-01

Using some tools of algebraic topology, a general formalism for lattice field theory is presented. The lattice is taken to be a simplicial complex that is also a manifold and is referred to as a simplicial manifold. The fields on this lattice are cochains, that are called lattice forms to emphasize the connections with differential forms in the continuum. This connection provides a new bridge between lattice and continuum field theory. A metric can be put onto this simplicial manifold by assigning lengths to every link or I-simplex of the lattice. Regge calculus is a way of defining general relativity on this lattice. A geometric discussion of Regge calculus is presented. The Regge action, which is a discrete form of the Hilbert action, is derived from the Hilbert action using distribution valued forms. This is a new derivation that emphasizes the underlying geometry. Kramers-Wannier duality in statistical mechanics is discussed in this general setting. Nonlinear field theories, which include gauge theories and nonlinear sigma models are discussed in the continuum and then are put onto a lattice. The main new result here is the generalization to curved spacetime, which consists of making the theory compatible with Regge calculus

Representation theory of lattice current algebras

International Nuclear Information System (INIS)

Alekseev, A.Yu.; Eidgenoessische Technische Hochschule, Zurich; Faddeev, L.D.; Froehlich, L.D.; Schomerus, V.; Kyoto Univ.

1996-04-01

Lattice current algebras were introduced as a regularization of the left-and right moving degrees of freedom in the WZNW model. They provide examples of lattice theories with a local quantum symmetry U q (G). Their representation theory is studied in detail. In particular, we construct all irreducible representations along with a lattice analogue of the fusion product for representations of the lattice current algebra. It is shown that for an arbitrary number of lattice sites, the representation categories of the lattice current algebras agree with their continuum counterparts. (orig.)

ISABELLE lattice

International Nuclear Information System (INIS)

Smith, L.

1975-01-01

An analysis is given of a number of variants of the basic lattice of the planned ISABELLE storage rings. The variants were formed by removing cells from the normal part of the lattice and juggling the lengths of magnets, cells, and insertions in order to maintain a rational relation of circumference to that of the AGS and approximately the same dispersion. Special insertions, correction windings, and the working line with nonlinear resonances are discussed

Atomic-scale observation of structural and electronic orders in the layered compound α-RuCl3

Science.gov (United States)

Ziatdinov, M.; Banerjee, A.; Maksov, A.; Berlijn, T.; Zhou, W.; Cao, H. B.; Yan, J.-Q.; Bridges, C. A.; Mandrus, D. G.; Nagler, S. E.; Baddorf, A. P.; Kalinin, S. V.

2016-12-01

A pseudospin-1/2 Mott phase on a honeycomb lattice is proposed to host the celebrated two-dimensional Kitaev model which has an elusive quantum spin liquid ground state, and fascinating physics relevant to the development of future templates towards topological quantum bits. Here we report a comprehensive, atomically resolved real-space study by scanning transmission electron and scanning tunnelling microscopies on a novel layered material displaying Kitaev physics, α-RuCl3. Our local crystallography analysis reveals considerable variations in the geometry of the ligand sublattice in thin films of α-RuCl3 that opens a way to realization of a spatially inhomogeneous magnetic ground state at the nanometre length scale. Using scanning tunnelling techniques, we observe the electronic energy gap of ~0.25 eV and intra-unit cell symmetry breaking of charge distribution in individual α-RuCl3 surface layer. The corresponding charge-ordered pattern has a fine structure associated with two different types of charge disproportionation at Cl-terminated surface.

Spin-orbit excitation energies, anisotropic exchange, and magnetic phases of honeycomb RuCl3

OpenAIRE

Yadav, Ravi; Bogdanov, Nikolay A.; Katukuri, Vamshi M.; Nishimoto, Satoshi; Brink, Jeroen van den; Hozoi, Liviu

2016-01-01

Large anisotropic exchange in 5d and 4d oxides and halides open the door to new types of magnetic ground states and excitations, inconceivable a decade ago. A prominent case is the Kitaev spin liquid, host of remarkable properties such as protection of quantum information and the emergence of Majorana fermions. Here we discuss the promise for spin-liquid behavior in the 4d 5 honeycomb halide ?-RuCl3. From advanced electronic-structure calculations, we find that the Kitaev interaction is ferro...

Mechanical Analysis of an Innovative Assembly Box with Honeycomb Structures Designed for a High Performance Light Water Reactor

International Nuclear Information System (INIS)

Herbell, Heiko; Himmel, Steffen; Schulenberg, Thomas

2008-01-01

The High Performance Light Water Reactor (HPLWR) is a water cooled reactor concept of the 4. generation, operated at a pressure beyond the critical point of water. Assemblies of this innovative reactor concept need to be built with assembly and moderator boxes, like boiling water reactors, to provide enough moderator water between them to compensate the low coolant density in the core. Hot, superheated steam conditions, on the other hand, require thermally insulated box walls rather than solid box walls to reduce the heat up of the moderator water. As a new an innovative approach, this paper describes moderator- and assembly boxes built from stainless steel honeycomb sandwich structures, in which the honeycomb cells are filled with alumina for thermal insulation. In comparison to solid box walls, the use of the presented design can provide the same stiffness but allows a drastic reduction of structural material and thus less neutron absorption. Finite element analyses are used to verify the required stiffness, to identify stress concentrations and to optimize the design. (authors)

Synthesis of honeycomb-like palladium nanostructures by using cucurbit[7]uril and their catalytic activities for reduction of 4-nitrophenol

Energy Technology Data Exchange (ETDEWEB)

Premkumar, Thathan [Department of Materials Science and Engineering, Gwangju Institute of Science and Technology (GIST), 1 Oryong-dong, Buk-gu, Gwangju 500-712 (Korea, Republic of); The University College/Department of Chemistry, Sungkyunkwan University, Suwon 440-746 (Korea, Republic of); Geckeler, Kurt E., E-mail: keg@gist.ac.kr [Department of Materials Science and Engineering, Gwangju Institute of Science and Technology (GIST), 1 Oryong-dong, Buk-gu, Gwangju 500-712 (Korea, Republic of); Department of Nanobio Materials and Electronics (WCU), Gwangju Institute of Science and Technology (GIST), 1 Oryong-dong, Buk-gu, Gwangju 500-712 (Korea, Republic of)

2014-12-15

An eco-friendly one-pot method to synthesize self-assembled palladium nanoclusters using a macrocycle, namely cucurbit[7]uril, in the alkaline medium without employing any special reducing or capping agents and/or external energy at room temperature is described. This greener approach, which utilizes water as a benign solvent and biocompatible cucurbit[7]uril as both reducing and protecting agents, can be applied to synthesize other noble metal nanoparticles such as gold, silver, and platinum. Owing to unique structural arrangement of cucurbit[7]uril, it was possible to prepare palladium nanoclusters of honeycomb-like structure irrespective of the reaction conditions. The honeycomb-like palladium nanoclusters were characterized using transmission electron microscopy (TEM), higher-resolution TEM (HR-TEM), X-ray diffraction (XRD), thermogravimetric analysis (TGA), UV–vis, and FT-IR spectroscopy. Significantly, the synthesized palladium nanoclusters exhibited catalytic activity for the reduction reaction of 4-nitrophenol at room temperature. The approach launched here is easy, green, and user-friendly in contrast to the conventional techniques using polymers or surfactants and harsh reductants. - Highlights: • A simple and one-pot method to synthesis palladium nanostructures with honey-comb like structure. • The strategy established here does not require any harsh and toxic reducing agents. • It has a potential to be a general method for the synthesis of metal nanoparticles in water medium. • Palladium nanoclusters can be used as catalyst for the reduction reaction of 4-nitrophenol. • This system makes a novel platform for industrial and biomedical applications.

Porous honeycomb structures formed from interconnected MnO2 sheets on CNT-coated substrates for flexible all-solid-state supercapacitors

Science.gov (United States)

Ko, Wen-Yin; Chen, You-Feng; Lu, Ke-Ming; Lin, Kuan-Jiuh

2016-01-01

The use of lightweight and easily-fabricated MnO2/carbon nanotube (CNT)-based flexible networks as binder-free electrodes and a polyvinyl alcohol/H2SO4 electrolyte for the formation of stretchable solid-state supercapacitors was examined. The active electrodes were fabricated from 3D honeycomb porous MnO2 assembled from cross-walled and interconnected sheet-architectural MnO2 on CNT-based plastic substrates (denoted as honeycomb MnO2/CNT textiles).These substrates were fabricated through a simple two-step procedure involving the coating of multi-walled carbon nanotubes (MWCNTs) onto commercial textiles by a dipping-drying process and subsequent electrodeposition of the interconnected MnO2 sheets onto the MWCNT-coated textile. With such unique MnO2 architectures integrated onto CNT flexible films, good performance was achieved with a specific capacitance of 324 F/g at 0.5 A/g. A maximum energy density of 7.2 Wh/kg and a power density as high as 3.3 kW/kg were exhibited by the honeycomb MnO2/CNT network device, which is comparable to the performance of other carbon-based and metal oxide/carbon-based solid-state supercapacitor devices. Specifically, the long-term cycling stability of this material is excellent, with almost no loss of its initial capacitance and good Coulombic efficiency of 82% after 5000 cycles. These impressive results identify these materials as a promising candidate for use in environmentally friendly, low-cost, and high-performance flexible energy-storage devices. PMID:26726724

Introduction to lattice gauge theory

International Nuclear Information System (INIS)

Gupta, R.

1987-01-01

The lattice formulation of Quantum Field Theory (QFT) can be exploited in many ways. We can derive the lattice Feynman rules and carry out weak coupling perturbation expansions. The lattice then serves as a manifestly gauge invariant regularization scheme, albeit one that is more complicated than standard continuum schemes. Strong coupling expansions: these give us useful qualitative information, but unfortunately no hard numbers. The lattice theory is amenable to numerical simulations by which one calculates the long distance properties of a strongly interacting theory from first principles. The observables are measured as a function of the bare coupling g and a gauge invariant cut-off ≅ 1/α, where α is the lattice spacing. The continuum (physical) behavior is recovered in the limit α → 0, at which point the lattice artifacts go to zero. This is the more powerful use of lattice formulation, so in these lectures the author focuses on setting up the theory for the purpose of numerical simulations to get hard numbers. The numerical techniques used in Lattice Gauge Theories have their roots in statistical mechanics, so it is important to develop an intuition for the interconnection between quantum mechanics and statistical mechanics. This will be the emphasis of the first lecture. In the second lecture, the author reviews the essential ingredients of formulating QCD on the lattice and discusses scaling and the continuum limit. In the last lecture the author summarizes the status of some of the main results. He also mentions the bottlenecks and possible directions for research. 88 refs

Basis reduction for layered lattices

NARCIS (Netherlands)

Torreão Dassen, Erwin

2011-01-01

We develop the theory of layered Euclidean spaces and layered lattices. We present algorithms to compute both Gram-Schmidt and reduced bases in this generalized setting. A layered lattice can be seen as lattices where certain directions have infinite weight. It can also be

Basis reduction for layered lattices

NARCIS (Netherlands)

E.L. Torreão Dassen (Erwin)

2011-01-01

htmlabstractWe develop the theory of layered Euclidean spaces and layered lattices. With this new theory certain problems that usually are solved by using classical lattices with a "weighting" gain a new, more natural form. Using the layered lattice basis reduction algorithms introduced here these

Local probe studies on lattice distortions and electronic correlations in manganites

CERN Document Server

lopes, Armandina; Correia, João Guilherme

This thesis presents an experimental study on lattice distortions and electronic correlations in colossal magnetoresistive magnetic oxides. The Perturbed Angular Correlation local probe technique is used to study selected manganite systems in order to obtain relevant insight into microscopic phenomena responsible for their macroscopic pr operties. Complementary structural, magnetic and electric characterization was performed. The work is focused on the following aspects: \\\\Lattice distortions and polaron clusters in LaMnO$_{3+ \\Delta}$ system. A study of the electric field gradi ent and magnetic hyperfine field was performed in representative samples of the LaMnO$_{3+ \\Delta}$ system, and correlated with macroscopic information obtained in the same samples. Particular attention was given to the LaMnO$_{3.12}$ sample since this compound is a prototype of a ferromagnetic-insulat or manganite, presenting a rhombohedric- orthorhombic structural phase transition near room temperature. We found that random distribu...

Lattice-Based Revocable Certificateless Signature

Directory of Open Access Journals (Sweden)

Ying-Hao Hung

2017-10-01

Full Text Available Certificateless signatures (CLS are noticeable because they may resolve the key escrow problem in ID-based signatures and break away the management problem regarding certificate in conventional signatures. However, the security of the mostly previous CLS schemes relies on the difficulty of solving discrete logarithm or large integer factorization problems. These two problems would be solved by quantum computers in the future so that the signature schemes based on them will also become insecure. For post-quantum cryptography, lattice-based cryptography is significant due to its efficiency and security. However, no study on addressing the revocation problem in the existing lattice-based CLS schemes is presented. In this paper, we focus on the revocation issue and present the first revocable CLS (RCLS scheme over lattices. Based on the short integer solution (SIS assumption over lattices, the proposed lattice-based RCLS scheme is shown to be existential unforgeability against adaptive chosen message attacks. By performance analysis and comparisons, the proposed lattice-based RCLS scheme is better than the previously proposed lattice-based CLS scheme, in terms of private key size, signature length and the revocation mechanism.

X-ray powder diffraction data on miscellaneous lanthanide compounds

International Nuclear Information System (INIS)

Ferguson, I.F.; Hughes, T.E.

1978-08-01

Recent work on neutron absorbing materials has produced various new X-ray diffraction powder patterns of compounds of the lanthanides. Various inconsistencies in previously published data have been noted, and accurate measurements have been made of the lattice parameters of the rare earth oxides Sm 2 0 3 , Eu 2 0 3 , Gd 2 0 3 which have the monoclinic rare earth type B- structure, as well as Eu0. These data are recorded for reference. The optimum conditions for obtaining X-ray powder diffraction data from europium compounds are also noted. (author)

Lattice Higgs models

International Nuclear Information System (INIS)

Jersak, J.

1986-01-01

This year has brought a sudden interest in lattice Higgs models. After five years of only modest activity we now have many new results obtained both by analytic and Monte Carlo methods. This talk is a review of the present state of lattice Higgs models with particular emphasis on the recent development

Nuclear lattice simulations

Directory of Open Access Journals (Sweden)

Epelbaum E.

2010-04-01

Full Text Available We review recent progress on nuclear lattice simulations using chiral effective field theory. We discuss lattice results for dilute neutron matter at next-to-leading order, three-body forces at next-to-next-toleading order, isospin-breaking and Coulomb effects, and the binding energy of light nuclei.

Three-dimensional hierarchical and interconnected honeycomb-like porous carbon derived from pomelo peel for high performance supercapacitors

Science.gov (United States)

Liu, Jingyuan; Li, Hongpeng; Zhang, Hongsen; Liu, Qi; Li, Rumin; Li, Bin; Wang, Jun

2018-01-01

The urgent need for sustainable development of human society has forced material scientists to explore novel materials starting from cheap natural precursors for next-generation energy storage devices by using environmentally friendly strategies. In this work, heteroatom-functionalized porous carbonaceous materials with 3D hierarchical and interconnected honeycomb-like structure have been successfully synthesized by using waste biomass pomelo peel as raw material through the combination of hydrothermal carbonization and followed KOH activation procedure. Benefiting from the unique honeycomb-like structure and high specific surface area, the as-obtained carbon material exhibits satisfactory capacitive behavior: 374 F/g at 0.1 A/g; excellent cycling stability of 92.5% capacitance retention over continuous 5000 cycles. More importantly, the as-assembled symmetric supercapacitors based on as-prepared electrode material can deliver high gravimetric and volumetric energy density of 20 W h/kg and 18.7 W h/L in 6 M KOH, respectively, as well as outstanding cycling stability. The obtained results demonstrate the possibility for taking full advantage of sustainable and large scale advanced carbon materials by choosing waste biomass, particularly the pomelo peel as a raw material.

Calculations of thermodynamic properties of PuO{sub 2} by the first-principles and lattice vibration

Energy Technology Data Exchange (ETDEWEB)

Minamoto, Satoshi [Energy and Industrial Systems Department, ITOCHU Techno-Solutions Corporation, Kasumigaseki 3-chome, Chiyoda-ku, Tokyo 100-6080 (Japan)], E-mail: satoshi.minamoto@ctc-g.co.jp; Kato, Masato [Japan Atomic Energy Agency, 4-33 Muramatsu, Tokai-mura, Naka-gun, Ibaraki 319-1194 (Japan); Konashi, Kenji [Institute for Materials Research, Tohoku University, 2145-2 Narita-chou, Oarai-chou, Ibaraki 311-1313 (Japan); Kawazoe, Yoshiyuki [Institute for Materials Research, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577 (Japan)

2009-03-15

Plutonium dioxide (PuO{sub 2}) is a key compound of mixed oxide fuel (MOX fuel). To predict the thermal properties of PuO{sub 2} at high temperature, it is important to understand the properties of MOX fuel. In this study, thermodynamic properties of PuO{sub 2} were evaluated by coupling of first-principles and lattice dynamics calculation. Cohesive energy was estimated from first-principles calculations, and the contribution of lattice vibration to total energy was evaluated by phonon calculations. Thermodynamic properties such as volume thermal expansion, bulk modulus and specific heat of PuO{sub 2} were investigated up to 1500 K.

Efficient decomposition of formaldehyde at room temperature over Pt/honeycomb ceramics with ultra-low Pt content.

Science.gov (United States)

Nie, Longhui; Zheng, Yingqiu; Yu, Jiaguo

2014-09-14

Pt/honeycomb ceramic (Pt/HC) catalysts with ultra-low Pt content (0.005-0.055 wt%) were for the first time prepared by an impregnation of honeycomb ceramics with Pt precursor and NaBH4-reduction combined method. The microstructures, morphologies and textural properties of the resulting samples were characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), and transmission electron microscopy (TEM). The obtained Pt/HC catalysts were used for catalytic oxidative decomposition of formaldehyde (HCHO) at room temperature. It was found that the as-prepared Pt/HC catalysts can efficiently decompose HCHO in air into CO2 and H2O at room temperature. The catalytic activity of the Pt/HC catalysts increases with increasing the Pt loading in the range of 0.005-0.013 wt%, and the further increase of the Pt loading does not obviously improve catalytic activity. From the viewpoint of cost and catalytic performance, 0.013 wt% Pt loading is the optimal Pt loading amount, and the Pt/HC catalyst with 0.013 wt% Pt loading also exhibited good catalytic stability. Considering practical applications, this work will provide new insights into the low-cost and large-scale fabrication of advanced catalytic materials for indoor air purification.

Controlled Bulk Properties of Composite Polymeric Solutions for Extensive Structural Order of Honeycomb Polysulfone Membranes.

Science.gov (United States)

Gugliuzza, Annarosa; Perrotta, Maria Luisa; Drioli, Enrico

2016-05-16

This work provides additional insights into the identification of operating conditions necessary to overcome a current limitation to the scale-up of the breath figure method, which is regarded as an outstanding manufacturing approach for structurally ordered porous films. The major restriction concerns, indeed, uncontrolled touching droplets at the boundary. Herein, the bulk of polymeric solutions are properly managed to generate honeycomb membranes with a long-range structurally ordered texture. Water uptake and dynamics are explored as chemical environments are changed with the intent to modify the hydrophilic/hydrophobic balance and local water floatation. In this context, a model surfactant such as the polyoxyethylene sorbitan monolaurate is used in combination with alcohols at different chain length extents and a traditional polymer such as the polyethersufone. Changes in the interfacial tension and kinematic viscosity taking place in the bulk of composite solutions are explored and examined in relation to competitive droplet nucleation and growth rate. As a result, extensive structurally ordered honeycomb textures are obtained with the rising content of the surfactant while a broad range of well-sized pores is targeted as a function of the hydrophilic-hydrophobic balance and viscosity of the composite polymeric mixture. The experimental findings confirm the consistency of the approach and are expected to give propulsion to the commercially production of breath figures films shortly.

Controlled Bulk Properties of Composite Polymeric Solutions for Extensive Structural Order of Honeycomb Polysulfone Membranes

Directory of Open Access Journals (Sweden)

Annarosa Gugliuzza

2016-05-01

Full Text Available This work provides additional insights into the identification of operating conditions necessary to overcome a current limitation to the scale-up of the breath figure method, which is regarded as an outstanding manufacturing approach for structurally ordered porous films. The major restriction concerns, indeed, uncontrolled touching droplets at the boundary. Herein, the bulk of polymeric solutions are properly managed to generate honeycomb membranes with a long-range structurally ordered texture. Water uptake and dynamics are explored as chemical environments are changed with the intent to modify the hydrophilic/hydrophobic balance and local water floatation. In this context, a model surfactant such as the polyoxyethylene sorbitan monolaurate is used in combination with alcohols at different chain length extents and a traditional polymer such as the polyethersufone. Changes in the interfacial tension and kinematic viscosity taking place in the bulk of composite solutions are explored and examined in relation to competitive droplet nucleation and growth rate. As a result, extensive structurally ordered honeycomb textures are obtained with the rising content of the surfactant while a broad range of well-sized pores is targeted as a function of the hydrophilic-hydrophobic balance and viscosity of the composite polymeric mixture. The experimental findings confirm the consistency of the approach and are expected to give propulsion to the commercially production of breath figures films shortly.

Computing the writhe on lattices

International Nuclear Information System (INIS)

Laing, C; Sumners, D W

2006-01-01

Given a polygonal closed curve on a lattice or space group, we describe a method for computing the writhe of the curve as the average of weighted projected writhing numbers of the polygon in a few directions. These directions are determined by the lattice geometry, the weights are determined by areas of regions on the unit 2-sphere, and the regions are formed by the tangent indicatrix to the polygonal curve. We give a new formula for the writhe of polygons on the face centred cubic lattice and prove that the writhe of polygons on the body centred cubic lattice, the hexagonal simple lattice, and the diamond space group is always a rational number, and discuss applications to ring polymers

Longitudinal disordering of vortex lattices in anisotropic superconductors

International Nuclear Information System (INIS)

Harshman, D.R.; Brandt, E.H.; Fiory, A.T.; Inui, M.; Mitzi, D.B.; Schneemeyer, L.F.; Waszczak, J.V.

1993-01-01

Vortex disordering in superconducting crystals is shown to be markedly sensitive to penetration-depth anisotropy. At low temperature and high magnetic field, the muon-spin-rotation spectra for the highly anisotropic Bi 2 Sr 2 CaCu 2 O 8+δ material are found to be anomalously narrow and symmetric about the applied field, in a manner consistent with a layered vortex sublattice structure with pinning-induced misalignment between layers. In contrast, spectra for the less-anisotropic YBa 2 Cu 3 O 7-δ compounds taken at comparable fields are broader and asymmetric, showing that the vortex lattices are aligned parallel to the applied-field direction

Hyper-lattice algebraic model for data warehousing

CERN Document Server

Sen, Soumya; Chaki, Nabendu

2016-01-01

This book presents Hyper-lattice, a new algebraic model for partially ordered sets, and an alternative to lattice. The authors analyze some of the shortcomings of conventional lattice structure and propose a novel algebraic structure in the form of Hyper-lattice to overcome problems with lattice. They establish how Hyper-lattice supports dynamic insertion of elements in a partial order set with a partial hierarchy between the set members. The authors present the characteristics and the different properties, showing how propositions and lemmas formalize Hyper-lattice as a new algebraic structure.

An overview of lattice QCD

International Nuclear Information System (INIS)

Woloshyn, R.M.

1988-03-01

The basic concepts of the Lagrangian formulation of lattice field theory are discussed. The Wilson and staggered schemes for dealing with fermions on the lattice are described. Some recent results for hadron masses and vector and axial vector current matrix elements in lattice QCD are reviewed. (Author) (118 refs., 16 figs.)

Polystyrene-template-assisted synthesis of Li3VO4/C/rGO ternary composite with honeycomb-like structure for durable high-rate lithium ion battery anode materials

International Nuclear Information System (INIS)

Yang, Yang; Li, Jiaqi; Huang, Jingxin; Huang, Jianxing; Zeng, Jing; Zhao, Jinbao

2017-01-01

Highlights: •Li 3 VO 4 /C/rGO ternary composite with honeycomb-like structure is prepared by taking advantage of spray drying method and polystyrene (PS) soft template. •Li 3 VO 4 /C/rGO composite electrode possesses rapid Li + ions intercalation kinetics and good structure integrity. •Li 3 VO 4 /C/rGO composite exhibits outstanding high-rate performance and long cycle-life (the high reversible capacity of 312 mAh g −1 can be maintained after 1000 cycles at 10C). -- Abstract: Li 3 VO 4 /C/rGO (HC-LVO/C/G) ternary composite with honeycomb-like structure is successfully prepared through a simple spray drying method with polystyrene (PS) microspheres as soft template. In this characteristic structure, carbon-coated Li 3 VO 4 nanoparticles are well wrapped by rGO sheets and uniformly distributed within the honeycomb-like micrometer-sized clusters. The double coating layers of amorphous carbon and rGO can avoid the direct exposure of Li 3 VO 4 nanoparticles to the electrolyte and enhance the electronic conductivity. Meanwhile, the honeycomb-like structure can shorten the diffusion paths of Li + ions and favors the relaxation of the strain/stress during cycling. The resultant HC-LVO/C/G composite exhibits significantly improved high-rate performance and long cycle-life (the high reversible capacity of 312 mAh g −1 can be maintained after 1000 cycles at 10 C) compared with the contrastive Li 3 VO 4 /C composite synthesized by a typical solid-state reaction method.

Hadron structure from lattice QCD

International Nuclear Information System (INIS)

Schaefer, Andreas

2008-01-01

Some elements and current developments of lattice QCD are reviewed, with special emphasis on hadron structure observables. In principle, high precision experimental and lattice data provide nowadays a very detailled picture of the internal structure of hadrons. However, to relate both, a very good controle of perturbative QCD is needed in many cases. Finally chiral perturbation theory is extremely helpful to boost the precision of lattice calculations. The mutual need and benefit of all four elements: experiment, lattice QCD, perturbative QCD and chiral perturbation theory is the main topic of this review

Lattice formulations of reggeon interactions

International Nuclear Information System (INIS)

Brower, R.C.; Ellis, J.; Savit, R.; Zinn-Justin, J.

1976-01-01

A class of lattice analogues to reggeon field theory is examined. First the transition from a continuum to a lattice field theory is discussed, emphasizing the necessity of a Wick rotation and the consideration of symmetry properties. Next the theory is transformed to a discrete system with two spins at each lattice site, and the problems of the triple-reggeon interaction and the reggeon energy gap are discussed. It is pointed out that transferring the theory from the continuum to a lattice necesarily introduces new relevant operators not normally present in reggeon field theory. (Auth.)

Irreversible stochastic processes on lattices

International Nuclear Information System (INIS)

Nord, R.S.

1986-01-01

Models for irreversible random or cooperative filling of lattices are required to describe many processes in chemistry and physics. Since the filling is assumed to be irreversible, even the stationary, saturation state is not in equilibrium. The kinetics and statistics of these processes are described by recasting the master equations in infinite hierarchical form. Solutions can be obtained by implementing various techniques: refinements in these solution techniques are presented. Programs considered include random dimer, trimer, and tetramer filling of 2D lattices, random dimer filling of a cubic lattice, competitive filling of two or more species, and the effect of a random distribution of inactive sites on the filling. Also considered is monomer filling of a linear lattice with nearest neighbor cooperative effects and solve for the exact cluster-size distribution for cluster sizes up to the asymptotic regime. Additionally, a technique is developed to directly determine the asymptotic properties of the cluster size distribution. Finally cluster growth is considered via irreversible aggregation involving random walkers. In particular, explicit results are provided for the large-lattice-size asymptotic behavior of trapping probabilities and average walk lengths for a single walker on a lattice with multiple traps. Procedures for exact calculation of these quantities on finite lattices are also developed

Non-Abelian vortex lattices

Science.gov (United States)

Tallarita, Gianni; Peterson, Adam

2018-04-01

We perform a numerical study of the phase diagram of the model proposed in [M. Shifman, Phys. Rev. D 87, 025025 (2013)., 10.1103/PhysRevD.87.025025], which is a simple model containing non-Abelian vortices. As per the case of Abrikosov vortices, we map out a region of parameter space in which the system prefers the formation of vortices in ordered lattice structures. These are generalizations of Abrikosov vortex lattices with extra orientational moduli in the vortex cores. At sufficiently large lattice spacing the low energy theory is described by a sum of C P (1 ) theories, each located on a vortex site. As the lattice spacing becomes smaller, when the self-interaction of the orientational field becomes relevant, only an overall rotation in internal space survives.

The ground-state phase diagrams of the spin-3/2 Ising model

International Nuclear Information System (INIS)

Canko, Osman; Keskin, Mustafa

2003-01-01

The ground-state spin configurations are obtained for the spin-3/2 Ising model Hamiltonian with bilinear and biquadratic exchange interactions and a single-ion crystal field. The interactions are assumed to be only between nearest-neighbors. The calculated ground-state phase diagrams are presented on diatomic lattices, such as the square, honeycomb and sc lattices, and triangular lattice in the (Δ/z vertical bar J vertical bar ,K/ vertical bar J vertical bar) and (H/z vertical bar J vertical bar, K/ vertical bar J vertical bar) planes

Artefacts in geometric phase analysis of compound materials

Energy Technology Data Exchange (ETDEWEB)

Peters, Jonathan J.P., E-mail: j.j.p.peters@warwick.ac.uk [Department of Physics, University of Warwick, Gibbet Hill Road, Coventry CV4 7AL (United Kingdom); Beanland, Richard; Alexe, Marin [Department of Physics, University of Warwick, Gibbet Hill Road, Coventry CV4 7AL (United Kingdom); Cockburn, John W.; Revin, Dmitry G.; Zhang, Shiyong Y. [Department of Physics and Astronomy, University of Sheffield, Hounsfield Road, Sheffield S3 7RH (United Kingdom); Sanchez, Ana M., E-mail: a.m.sanchez@warwick.ac.uk [Department of Physics, University of Warwick, Gibbet Hill Road, Coventry CV4 7AL (United Kingdom)

2015-10-15

The geometric phase analysis (GPA) algorithm is known as a robust and straightforward technique that can be used to measure lattice strains in high resolution transmission electron microscope (TEM) images. It is also attractive for analysis of aberration-corrected scanning TEM (ac-STEM) images that resolve every atom column, since it uses Fourier transforms and does not require real-space peak detection and assignment to appropriate sublattices. Here it is demonstrated that, in ac-STEM images of compound materials with compositionally distinct atom columns, an additional geometric phase is present in the Fourier transform. If the structure changes from one area to another in the image (e.g. across an interface), the change in this additional phase will appear as a strain in conventional GPA, even if there is no lattice strain. Strategies to avoid this pitfall are outlined. - Highlights: • GPA is shown to produce incorrect strains when applied to images of compound materials. • A mathematical description is laid out for why GPA can produce artefacts. • The artefact is demonstrated using experimental and simulated data. • A ‘rule’ is set to avoid this artefact in GPA.

Ionic self-assembly of surface functionalized metal-organic polyhedra nanocages and their ordered honeycomb architecture at the air/water interface.

Science.gov (United States)

Li, Yantao; Zhang, Daojun; Gai, Fangyuan; Zhu, Xingqi; Guo, Ya-nan; Ma, Tianliang; Liu, Yunling; Huo, Qisheng

2012-08-18

Metal-organic polyhedra (MOP) nanocages were successfully surface functionalized via ionic self-assembly and the ordered honeycomb architecture of the encapsulated MOP nanocages was also fabricated at the air/water surface. The results provide a novel synthetic method and membrane processing technique of amphiphilic MOP nanocages for various applications.

Superspace approach to lattice supersymmetry

International Nuclear Information System (INIS)

Kostelecky, V.A.; Rabin, J.M.

1984-01-01

We construct a cubic lattice of discrete points in superspace, as well as a discrete subgroup of the supersymmetry group which maps this ''superlattice'' into itself. We discuss the connection between this structure and previous versions of lattice supersymmetry. Our approach clarifies the mathematical problems of formulating supersymmetric lattice field theories and suggests new methods for attacking them

Dynamical lattice theory

International Nuclear Information System (INIS)

Chodos, A.

1978-01-01

A version of lattice gauge theory is presented in which the shape of the lattice is not assumed at the outset but is a consequence of the dynamics. Other related features which are not specified a priori include the internal and space-time symmetry groups and the dimensionality of space-time. The theory possesses a much larger invariance group than the usual gauge group on a lattice, and has associated with it an integer k 0 analogous to the topological quantum numer of quantum chromodynamics. Families of semiclassical solutions are found which are labeled by k 0 and a second integer x, but the analysis is not carried far enough to determine which space-time and internal symmetry groups characterize the lowest-lying states of the theory

Anisotropic lattice softening near the structural phase transition in the thermosalient crystal 1,2,4,5-tetrabromobenzene.

Science.gov (United States)

Zakharov, Boris A; Michalchuk, Adam A L; Morrison, Carole A; Boldyreva, Elena V

2018-03-28

The thermosalient effect (crystal jumping on heating) attracts much attention as both an intriguing academic phenomenon and in relation to its potential for the development of molecular actuators but its mechanism remains unclear. 1,2,4,5-Tetrabromobenzene (TBB) is one of the most extensively studied thermosalient compounds that has been shown previously to undergo a phase transition on heating, accompanied by crystal jumping and cracking. The difference in the crystal structures and intermolecular interaction energies of the low- and high-temperature phases is, however, too small to account for the large stress that arises over the course of the transformation. The energy is released spontaneously, and crystals jump across distances that exceed the crystal size by orders of magnitude. In the present work, the anisotropy of lattice strain is followed across the phase transition by single-crystal X-ray diffraction, focusing on the structural evolution from 273 to 343 K. A pronounced lattice softening is observed close to the transition point, with the structure becoming more rigid immediately after the phase transition. The diffraction studies are further supported by theoretical analysis of pairwise intermolecular energies and zone-centre lattice vibrations. Only three modes are found to monotonically soften up to the phase transition, with complex behaviour exhibited by the remaining lattice modes. The thermosalient effect is delayed with respect to the structural transformation itself. This can originate from the martensitic mechanism of the transformation, and the accumulation of stress associated with vibrational switching across the phase transition. The finding of this study sheds more light on the nature of the thermosalient effect in 1,2,4,5-tetrabromobenzene and can be applicable also to other thermosalient compounds.

Performance evaluation of RANS-based turbulence models in simulating a honeycomb heat sink

Science.gov (United States)

Subasi, Abdussamet; Ozsipahi, Mustafa; Sahin, Bayram; Gunes, Hasan

2017-07-01

As well-known, there is not a universal turbulence model that can be used to model all engineering problems. There are specific applications for each turbulence model that make it appropriate to use, and it is vital to select an appropriate model and wall function combination that matches the physics of the problem considered. Therefore, in this study, performance of six well-known Reynolds-Averaged Navier-Stokes ( RANS) based turbulence models which are the Standard k {{-}} ɛ, the Renormalized Group k- ɛ, the Realizable k- ɛ, the Reynolds Stress Model, the k- ω and the Shear Stress Transport k- ω and accompanying wall functions which are the standard, the non-equilibrium and the enhanced are evaluated via 3D simulation of a honeycomb heat sink. The CutCell method is used to generate grid for the part including heat sink called test section while a hexahedral mesh is employed to discretize to inlet and outlet sections. A grid convergence study is conducted for verification process while experimental data and well-known correlations are used to validate the numerical results. Prediction of pressure drop along the test section, mean base plate temperature of the heat sink and temperature at the test section outlet are regarded as a measure of the performance of employed models and wall functions. The results indicate that selection of turbulence models and wall functions has a great influence on the results and, therefore, need to be selected carefully. Hydraulic and thermal characteristics of the honeycomb heat sink can be determined in a reasonable accuracy using RANS- based turbulence models provided that a suitable turbulence model and wall function combination is selected.

Computing nucleon EDM on a lattice

Science.gov (United States)

Abramczyk, Michael; Aoki, Sinya; Blum, Tom; Izubuchi, Taku; Ohki, Hiroshi; Syritsyn, Sergey

2018-03-01

I will discuss briefly recent changes in the methodology of computing the baryon EDM on a lattice. The associated correction substantially reduces presently existing lattice values for the proton and neutron theta-induced EDMs, so that even the most precise previous lattice results become consistent with zero. On one hand, this change removes previous disagreements between these lattice results and the phenomenological estimates of the nucleon EDM. On the other hand, the nucleon EDM becomes much harder to compute on a lattice. In addition, I will review the progress in computing quark chromo-EDM-induced nucleon EDM using chiral quark action.

Computing nucleon EDM on a lattice

Energy Technology Data Exchange (ETDEWEB)

Abramczyk, Michael; Izubuchi, Taku

2017-06-18

I will discuss briefly recent changes in the methodology of computing the baryon EDM on a lattice. The associated correction substantially reduces presently existing lattice values for the proton and neutron theta-induced EDMs, so that even the most precise previous lattice results become consistent with zero. On one hand, this change removes previous disagreements between these lattice results and the phenomenological estimates of the nucleon EDM. On the other hand, the nucleon EDM becomes much harder to compute on a lattice. In addition, I will review the progress in computing quark chromo-EDM-induced nucleon EDM using chiral quark action.

Cold collisions in dissipative optical lattices

International Nuclear Information System (INIS)

Piilo, J; Suominen, K-A

2005-01-01

The invention of laser cooling methods for neutral atoms allows optical and magnetic trapping of cold atomic clouds in the temperature regime below 1 mK. In the past, light-assisted cold collisions between laser cooled atoms have been widely studied in magneto-optical atom traps (MOTs). We describe here theoretical studies of dynamical interactions, specifically cold collisions, between atoms trapped in near-resonant, dissipative optical lattices. The extension of collision studies to the regime of optical lattices introduces several complicating factors. For the lattice studies, one has to account for the internal substates of atoms, position-dependent matter-light coupling, and position-dependent couplings between the atoms, in addition to the spontaneous decay of electronically excited atomic states. The developed one-dimensional quantum-mechanical model combines atomic cooling and collision dynamics in a single framework. The model is based on Monte Carlo wavefunction simulations and is applied when the lattice-creating lasers have frequencies both below (red-detuned lattice) and above (blue-detuned lattice) the atomic resonance frequency. It turns out that the radiative heating mechanism affects the dynamics of atomic cloud in a red-detuned lattice in a way that is not directly expected from the MOT studies. The optical lattice and position-dependent light-matter coupling introduces selectivity of collision partners. The atoms which are most mobile and energetic are strongly favoured to participate in collisions, and are more often ejected from the lattice, than the slow ones in the laser parameter region selected for study. Consequently, the atoms remaining in the lattice have a smaller average kinetic energy per atom than in the case of non-interacting atoms. For blue-detuned lattices, we study how optical shielding emerges as a natural part of the lattice and look for ways to optimize the effect. We find that the cooling and shielding dynamics do not mix

Magnon edge states in the hardcore- Bose-Hubbard model.

Science.gov (United States)

Owerre, S A

2016-11-02

Quantum Monte Carlo (QMC) simulation has uncovered nonzero Berry curvature and bosonic edge states in the hardcore-Bose-Hubbard model on the gapped honeycomb lattice. The competition between the chemical potential and staggered onsite potential leads to an interesting quantum phase diagram comprising the superfluid phase, Mott insulator, and charge density wave insulator. In this paper, we present a semiclassical perspective of this system by mapping to a spin-1/2 quantum XY model. We give an explicit analytical origin of the quantum phase diagram, the Berry curvatures, and the edge states using semiclassical approximations. We find very good agreement between the semiclassical analyses and the QMC results. Our results show that the topological properties of the hardcore-Bose-Hubbard model are the same as those of magnon in the corresponding quantum spin system. Our results are applicable to systems of ultracold bosonic atoms trapped in honeycomb optical lattices.

Introduction to lattice gauge theories

International Nuclear Information System (INIS)

La Cock, P.

1988-03-01

A general introduction to Lattice Gauge Theory (LGT) is given. The theory is discussed from first principles to facilitate an understanding of the techniques used in LGT. These include lattice formalism, gauge invariance, fermions on the lattice, group theory and integration, strong coupling methods and mean field techniques. A review of quantum chromodynamics on the lattice at finite temperature and density is also given. Monte Carlo results and analytical methods are discussed. An attempt has been made to include most relevant data up to the end of 1987, and to update some earlier reviews existing on the subject. 224 refs., 33 figs., 14 tabs

Angles in hyperbolic lattices

DEFF Research Database (Denmark)

Risager, Morten S.; Södergren, Carl Anders

2017-01-01

It is well known that the angles in a lattice acting on hyperbolic n -space become equidistributed. In this paper we determine a formula for the pair correlation density for angles in such hyperbolic lattices. Using this formula we determine, among other things, the asymptotic behavior of the den......It is well known that the angles in a lattice acting on hyperbolic n -space become equidistributed. In this paper we determine a formula for the pair correlation density for angles in such hyperbolic lattices. Using this formula we determine, among other things, the asymptotic behavior...... of the density function in both the small and large variable limits. This extends earlier results by Boca, Pasol, Popa and Zaharescu and Kelmer and Kontorovich in dimension 2 to general dimension n . Our proofs use the decay of matrix coefficients together with a number of careful estimates, and lead...

Working Group Report: Lattice Field Theory

Energy Technology Data Exchange (ETDEWEB)

Blum, T.; et al.,

2013-10-22

This is the report of the Computing Frontier working group on Lattice Field Theory prepared for the proceedings of the 2013 Community Summer Study ("Snowmass"). We present the future computing needs and plans of the U.S. lattice gauge theory community and argue that continued support of the U.S. (and worldwide) lattice-QCD effort is essential to fully capitalize on the enormous investment in the high-energy physics experimental program. We first summarize the dramatic progress of numerical lattice-QCD simulations in the past decade, with some emphasis on calculations carried out under the auspices of the U.S. Lattice-QCD Collaboration, and describe a broad program of lattice-QCD calculations that will be relevant for future experiments at the intensity and energy frontiers. We then present details of the computational hardware and software resources needed to undertake these calculations.

Magnetic order and Kondo effect in the Anderson-lattice model

International Nuclear Information System (INIS)

Bernhard, B.H.; Aguiar, C.; Kogoutiouk, I.; Coqblin, B.

2007-01-01

The Anderson-lattice model has been extensively developed to account for the properties of many anomalous rare-earth compounds and in particular for the competition between the Kondo effect and an antiferromagnetic (AF) phase in a cubic lattice. Here we apply the higher-order decoupling of the equations of motion for the Green Functions (GF) introduced in [H.G. Luo, S.J. Wang, Phys. Rev. B 62 (2000) 1485]. We obtain an improved description of the phase diagram, where the AF phase subsists in a smaller range of the model parameters. As higher-order GF are included in the chain of equations, we are able to calculate directly the local spin-flip correlation function † ↓ d † ↑ f ↑ d ↓ >. As a further improvement to the previous approximation of [B.H. Bernhard, C. Aguiar, B. Coqblin, Physica B 378-380 (2006) 712], we obtain a reduced range of existence for the AF phase for the symmetric half-filled case and then we discuss the competition between the AF order and the Kondo effect as a function of the band filling

Ising antiferromagnet on the Archimedean lattices

Science.gov (United States)

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.

Removal of H₂S from Biogas by Iron (Fe³⁺ Doped MgO on Ceramic Honeycomb Catalyst using Double Packed Columns System

Directory of Open Access Journals (Sweden)

Juntima Chungsiriporn

2010-03-01

Full Text Available Hydrogen sulfide is a toxic and corrosive in nature, gas should be safely removed from the biogas streams before subjecting into the fuel cell. Fe3+ doped magnesium oxide was synthesized using sol-gel technique and dip coating process of Fe3+ doped MgO on foam ceramic honeycomb. XRD and SEM indicate that Fe3+ in Fe3+ doped MgO on foam ceramic honeycomb catalyst is finely dispersed in the MgO support. Performance of the synthesized Fe3+ doped magnesium oxide on the honeycomb catalyst was examined for hydrogen sulfide (H2S oxidation by double packed column scrubbers. The absorption column was used for H2S scrubbing from biogas by deionized water absorption and catalytic column was used as catalyst bed for degradation of absorbed H2S in scrubbing water. In the catalytic column, counter current flow of the scrubbing water and air through the catalyst pack was performed for H2S oxidation accompany with catalyst regeneration. System capacity for H2S removal from gas stream showed 98% constant along 3 hr testing time at room temperature.

Statistical hydrodynamics of lattice-gas automata

OpenAIRE

Grosfils, Patrick; Boon, Jean-Pierre; Brito López, Ricardo; Ernst, M. H.

1993-01-01

We investigate the space and time behavior of spontaneous thermohydrodynamic fluctuations in a simple fluid modeled by a lattice-gas automaton and develop the statistical-mechanical theory of thermal lattice gases to compute the dynamical structure factor, i.e., the power spectrum of the density correlation function. A comparative analysis of the theoretical predictions with our lattice gas simulations is presented. The main results are (i) the spectral function of the lattice-gas fluctuation...

Standard enthalpies of formation of selected Rh2YZ Heusler compounds

International Nuclear Information System (INIS)

Yin, Ming; Nash, Philip

2015-01-01

The standard enthalpies of formation (Δ f H°) of selected ternary Rh-based Rh 2 YZ (Y = Cu, Fe, Mn, Ni, Ru, Ti, V; Z = Al, Ga, In, Si, Ge, Sn) compounds were measured using high temperature direct reaction calorimetry. The measured standard enthalpies of formation (in kJ/mol of atoms) are, for the Heusler compound Rh 2 MnSn (−40.1 ± 3.6), for the B2-structured compounds: Rh 2 FeAl (−48.5 ± 2.9); Rh 2 MnAl (−72.4 ± 2.7); Rh 2 MnGa (−55.3 ± 2.0); Rh 2 MnIn (−35.3 ± 1.9), for the tetragonal compounds: Rh 2 FeSn (−28.9 ± 1.3); Rh 2 TiAl (−97.6 ± 2.2); Rh 2 TiGa (−79.0 ± 1.8); Rh 2 TiSn (−74.7 ± 3.1). Values are compared with those from first principles calculations in published papers and the Open Quantum Materials Database (OQMD). Lattice parameters of these compounds are determined using X-ray diffraction analysis (XRD). Microstructures were characterized using scanning electron microscopy (SEM) and Energy Dispersive Spectroscopy (EDS). - Highlights: • Standard enthalpies of formation of Rh 2 YZ were measured using a drop calorimeter. • Measured enthalpies agree with first principles data in general. • Lattice parameters and related phase relationships were consistent with literature data. • Rh 2 TiSn of tI8 structure were reported for the first time.

The Effect of Face and Adhesive Types on Mechanical Properties of Sandwich Panels Made from Honeycomb Paper

Directory of Open Access Journals (Sweden)

Mohsen Saffari

2013-11-01

Full Text Available Sandwich panels are new kind of layered composites that usually are composed of three layers and their core layer's thickness is higher and the outer layers are determinative in determination of the products strength and stiffness. The core layer is commonly made of honeycomb paper, corrugated paper and polyurethane etc. In this study, effects of face and adhesive types on mechanical properties of sandwich panels made from honeycomb paper were investigated. The variables included three types; beech face, poplar face and hardboard (S2S face, veneer less and adhesive type (two types; epoxy and PVA. Out of experimental panels specimens were cut and tested according to DIN E 326-1 standard. Mechanical properties of panels, included modulus of elasticity as well as modulus of rupture at the edge and surface (based on DIN EN 310 standard and Impact Bending Strength (IBS of the panels (based on ASTM D 3499 standard were measured. The gathered data were analyzed as completely randomized factorial design. Highest mechanical properties were reported for panels glued with epoxy resin and containing fiberboard at the middle. According to results, optimum condition of producing sandwich panels was observed in uses of epoxy resin and fiberboard S2S face, veneer less at the middle.

On the performance of 1-level LDPC lattices

OpenAIRE

Sadeghi, Mohammad-Reza; Sakzad, Amin

2013-01-01

The low-density parity-check (LDPC) lattices perform very well in high dimensions under generalized min-sum iterative decoding algorithm. In this work we focus on 1-level LDPC lattices. We show that these lattices are the same as lattices constructed based on Construction A and low-density lattice-code (LDLC) lattices. In spite of having slightly lower coding gain, 1-level regular LDPC lattices have remarkable performances. The lower complexity nature of the decoding algorithm for these type ...

Critical properties of the Kitaev-Heisenberg Model

Science.gov (United States)

Sizyuk, Yuriy; Price, Craig; Perkins, Natalia

2013-03-01

Collective behavior of local moments in Mott insulators in the presence of strong spin-orbit coupling is one of the most interesting questions in modern condensed matter physics. Here we study the finite temperature properties of the Kitaev-Heisenberg model which describe the interactions between the pseudospin J = 1 / 2 iridium moments on the honeycomb lattice. This model was suggested as a possible model to explain low-energy physics of AIr2O3 compounds. In our study we show that the Kitaev-Heisenberg model may be mapped into the six state clock model with an intermediate power-law phase at finite temperatures. In the framework of the Ginsburg-Landau theory, we provide an analysis of the critical properties of the finite-temperature ordering transitions. NSF grant DMR-1005932

Relation between Kitaev magnetism and structure in α -RuCl3

Science.gov (United States)

Glamazda, A.; Lemmens, P.; Do, S.-H.; Kwon, Y. S.; Choi, K.-Y.

2017-05-01

Raman scattering has been employed to investigate lattice and magnetic excitations of the honeycomb Kitaev material α -RuCl3 and its Heisenberg counterpart CrCl3. Our phonon Raman spectra give evidence for a first-order structural transition from a monoclinic to a rhombohedral structure for both compounds. Significantly, only α -RuCl3 features a large thermal hysteresis, consistent with the formation of a wide phase of coexistence. In the related temperature interval of 70 -170 K, we observe a hysteretic behavior of magnetic excitations as well. The stronger magnetic response in the rhombohedral compared to the monoclinic phase evidences a coupling between the crystallographic structure and low-energy magnetic response. Our results demonstrate that the Kitaev magnetism concomitant with fractionalized excitations is susceptible to small variations of bonding geometry.

Spatial classification with fuzzy lattice reasoning

NARCIS (Netherlands)

Mavridis, Constantinos; Athanasiadis, I.N.

2017-01-01

This work extends the Fuzzy Lattice Reasoning (FLR) Classifier to manage spatial attributes, and spatial relationships. Specifically, we concentrate on spatial entities, as countries, cities, or states. Lattice Theory requires the elements of a Lattice to be partially ordered. To match such

Fuel lattice design using heuristics and new strategies

Energy Technology Data Exchange (ETDEWEB)

Ortiz S, J. J.; Castillo M, J. A.; Torres V, M.; Perusquia del Cueto, R. [ININ, Carretera Mexico-Toluca s/n, Ocoyoacac 52750, Estado de Mexico (Mexico); Pelta, D. A. [ETS Ingenieria Informatica y Telecomunicaciones, Universidad de Granada, Daniel Saucedo Aranda s/n, 18071 Granada (Spain); Campos S, Y., E-mail: juanjose.ortiz@inin.gob.m [IPN, Escuela Superior de Fisica y Matematicas, Unidad Profesional Adolfo Lopez Mateos, Edif. 9, 07738 Mexico D. F. (Mexico)

2010-10-15

This work show some results of the fuel lattice design in BWRs when some allocation pin rod rules are not taking into account. Heuristics techniques like Path Re linking and Greedy to design fuel lattices were used. The scope of this work is to search about how do classical rules in design fuel lattices affect the heuristics techniques results and the fuel lattice quality. The fuel lattices quality is measured by Power Peaking Factor and Infinite Multiplication Factor at the beginning of the fuel lattice life. CASMO-4 code to calculate these parameters was used. The analyzed rules are the following: pin rods with lowest uranium enrichment are only allocated in the fuel lattice corner, and pin rods with gadolinium cannot allocated in the fuel lattice edge. Fuel lattices with and without gadolinium in the main diagonal were studied. Some fuel lattices were simulated in an equilibrium cycle fuel reload, using Simulate-3 to verify their performance. So, the effective multiplication factor and thermal limits can be verified. The obtained results show a good performance in some fuel lattices designed, even thought, the knowing rules were not implemented. A fuel lattice performance and fuel lattice design characteristics analysis was made. To the realized tests, a dell workstation was used, under Li nux platform. (Author)

Fuel lattice design using heuristics and new strategies

International Nuclear Information System (INIS)

Ortiz S, J. J.; Castillo M, J. A.; Torres V, M.; Perusquia del Cueto, R.; Pelta, D. A.; Campos S, Y.

2010-10-01

This work show some results of the fuel lattice design in BWRs when some allocation pin rod rules are not taking into account. Heuristics techniques like Path Re linking and Greedy to design fuel lattices were used. The scope of this work is to search about how do classical rules in design fuel lattices affect the heuristics techniques results and the fuel lattice quality. The fuel lattices quality is measured by Power Peaking Factor and Infinite Multiplication Factor at the beginning of the fuel lattice life. CASMO-4 code to calculate these parameters was used. The analyzed rules are the following: pin rods with lowest uranium enrichment are only allocated in the fuel lattice corner, and pin rods with gadolinium cannot allocated in the fuel lattice edge. Fuel lattices with and without gadolinium in the main diagonal were studied. Some fuel lattices were simulated in an equilibrium cycle fuel reload, using Simulate-3 to verify their performance. So, the effective multiplication factor and thermal limits can be verified. The obtained results show a good performance in some fuel lattices designed, even thought, the knowing rules were not implemented. A fuel lattice performance and fuel lattice design characteristics analysis was made. To the realized tests, a dell workstation was used, under Li nux platform. (Author)

Physics in graphene & quantum rings : from mesoscopic device fabrication to measurement in high magnetic fields

NARCIS (Netherlands)

Giesbers, A.J.M.

2010-01-01

New materials often lead to spectacular discoveries. A prominenent example is graphene, a single layer of carbon atoms arranged in a honeycomb lattice. This one atom thick carbon sheet has a high crystal quality and remarkable electronic properties. The charge carriers in graphene behave as

The dilute spin-one Ising model with both bilinear and biquadratic exchange interactions

International Nuclear Information System (INIS)

Saber, M.

1987-08-01

The influence of bond and site dilution on the two-dimensional spin-one Ising model on a honeycomb lattice is investigated. Temperature-concentration phase diagrams for fixed values of the ratio of bilinear and biquadratic exchange interactions are determined. (author). 7 refs, 3 figs

Quantum transport in d -dimensional lattices

International Nuclear Information System (INIS)

Manzano, Daniel; Chuang, Chern; Cao, Jianshu

2016-01-01

We show that both fermionic and bosonic uniform d -dimensional lattices can be reduced to a set of independent one-dimensional chains. This reduction leads to the expression for ballistic energy fluxes in uniform fermionic and bosonic lattices. By the use of the Jordan–Wigner transformation we can extend our analysis to spin lattices, proving the coexistence of both ballistic and non-ballistic subspaces in any dimension and for any system size. We then relate the nature of transport to the number of excitations in the homogeneous spin lattice, indicating that a single excitation always propagates ballistically and that the non-ballistic behaviour of uniform spin lattices is a consequence of the interaction between different excitations. (paper)

Intercalation compounds of vanadium(5) phosphates with glycerol

International Nuclear Information System (INIS)

Yakovleva, T.N.; Vykhodtseva, K.I.; Tarasova, D.V.; Soderzhinova, M.M.

1997-01-01

Interaction products of glycerol aqueous solutions with vanadium(5) phosphates were investigated by the methods of ESR, X-ray phase and thermal analyses. It is shown that glycerol molecules enter the interlayer space of VOPO 4 · 2H 2 O lattice with formation of disordered intercalated compounds with glycerol on the basis of partially reduced vanadium phosphate form when using α-VOPO 4 . 16 refs., 4 figs., 1 tab

Embedded Lattice and Properties of Gram Matrix

Directory of Open Access Journals (Sweden)

Futa Yuichi

2017-03-01

Full Text Available In this article, we formalize in Mizar [14] the definition of embedding of lattice and its properties. We formally define an inner product on an embedded module. We also formalize properties of Gram matrix. We formally prove that an inverse of Gram matrix for a rational lattice exists. Lattice of Z-module is necessary for lattice problems, LLL (Lenstra, Lenstra and Lov´asz base reduction algorithm [16] and cryptographic systems with lattice [17].

Transmission Electron Microscope Measures Lattice Parameters

Science.gov (United States)

Pike, William T.

1996-01-01

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

Magnetoelastic couplings in the distorted diamond-chain compound azurite

Science.gov (United States)

Cong, Pham Thanh; Wolf, Bernd; Manna, Rudra Sekhar; Tutsch, Ulrich; de Souza, Mariano; Brühl, Andreas; Lang, Michael

2014-05-01

We present results of ultrasonic measurements on a single crystal of the distorted diamond-chain compound azurite Cu3(CO3)2(OH)2. Pronounced elastic anomalies are observed in the temperature dependence of the longitudinal elastic mode c22 which can be assigned to the relevant magnetic interactions in the system and their couplings to the lattice degrees of freedom. From a semiquantitative analysis of the magnetic contribution to c22 the magnetoelastic coupling G =∂J2/∂ɛb can be estimated, where J2 is the intradimer coupling constant and ɛb the strain along the intrachain b axis. We find an exceptionally large coupling constant of |G |˜ 3650 K highlighting an extraordinarily strong sensitivity of J2 against changes of the b-axis lattice parameter. These results are complemented by measurements of the hydrostatic pressure dependence of J2 by means of thermal expansion and magnetic susceptibility measurements performed both at ambient and finite hydrostatic pressure. We propose that a structural peculiarity of this compound, in which Cu2O6 dimer units are incorporated in an unusually stretched manner, is responsible for the anomalously large magnetoelastic coupling.

Lattice vibrations in α-boron

International Nuclear Information System (INIS)

Richter, W.

1976-01-01

α-rhombohedral boron is the simplest boron modification, with only 12 atoms per unit cell. The boron atoms are arranged in B 12 icosahedra, which are centered at the lattice points of a primitive rhombohedral lattice. The icosahedra are slightly deformed, as the five-fold symmetry of the ideal icosahedron is incompatible with any crystal structure. The lattice dynamics of α-boron are discussed in terms of the model developed by Weber and Thorpe. (Auth.)

Galilean invariant lattice Boltzmann scheme for natural convection on square and rectangular lattices

NARCIS (Netherlands)

Sman, van der R.G.M.

2006-01-01

In this paper we present lattice Boltzmann (LB) schemes for convection diffusion coupled to fluid flow on two-dimensional rectangular lattices. Via inverse Chapman-Enskog analysis of LB schemes including source terms, we show that for consistency with physics it is required that the moments of the

Flexural Behavior of Aluminum Honeycomb Core Sandwich Structure

Science.gov (United States)

Matta, Vidyasagar; Kumar, J. Suresh; Venkataraviteja, Duddu; Reddy, Guggulla Bharath Kumar

2017-05-01

This project is concerned with the fabrication and flexural testing of aluminium honey comb sandwich structure which is a special case of composite materials that is fabricated by attaching two thin but stiff skins to a light weight but thick core. The core material is normally low density material but its high thickness provide the sandwich composite with high bonding stiffness. Honeycomb core are classified into two types based on the materials and structures. Hexagonal shape has a unique properties i.e has more bonding strength and less formation time based on the cell size and sheet thickness. Sandwich structure exhibit different properties such as high load bearing capacity at low weight and has excellent thermal insulation. By considering the above properties it has tendency to minimize the structural problem. So honey comb sandwich structure is choosed. The core structure has a different applications such as aircraft, ship interiors, construction industries. As there is no proper research on strength characteristics of sandwich structure. So, we use light weight material to desire the strength. There are different parameters involved in this structure i.e cell size, sheet thickness and core height. In this project we considered 3 level of comparison among the 3 different parameters cell size of 4, 6 and 8 mm, sheet thickness of 0.3, 0.5 and 0.7 mm, and core height of 20,25 and 30 mm. In order to reduce the number of experiment we use taguchi design of experiment, and we select the L8 orthogonal array is the best array for this type of situation, which clearly identifies the parameters by independent of material weight to support this we add the minitab software, to identify the main effective plots and regression equation which involves the individual response and corresponding parameters. Aluminium material is used for the fabrication of Honeycomb sandwich structure among the various grades of aluminium we consider the AL6061 which is light weight material

Magnetic re-entrance in intermediate valence compounds

International Nuclear Information System (INIS)

Allub, R.; Machiavelli, O.; Balseiro, C.; Alascio, B.

1980-01-01

The possibility is explored of magnetic re-entrance in intermediate valence compounds. Using a simplified Anderson-Lattice model the pressure-temperature magnetic phase diagram is obtained. This diagram shows that for some value of the microscopic parameters the temperature induced two transitions (non-magnetic to magnetically ordered to paramagnetic). The magnetization and the average occupation number of the localized state are calculated. Estimations of the observability of the effect in systems like CeAl 2 are made. (author)

Modeling the rubbing contact in honeycomb seals

Science.gov (United States)

Fischer, Tim; Welzenbach, Sarah; Meier, Felix; Werner, Ewald; kyzy, Sonun Ulan; Munz, Oliver

2018-03-01

Metallic honeycomb labyrinth seals are commonly used as sealing systems in gas turbine engines. Because of their capability to withstand high thermo-mechanical loads and oxidation, polycrystalline nickel-based superalloys, such as Hastelloy X and Haynes 214, are used as sealing material. In addition, these materials must exhibit a tolerance against rubbing between the rotating part and the stationary seal component. The tolerance of the sealing material against rubbing preserves the integrity of the rotating part. In this article, the rubbing behavior at the rotor-stator interface is considered numerically. A simulation model is incorporated into the commercial finite element code ABAQUS/explicit and is utilized to simulate a simplified rubbing process. A user-defined interaction routine between the contact surfaces accounts for the thermal and mechanical interfacial behavior. Furthermore, an elasto-plastic constitutive material law captures the extreme temperature conditions and the damage behavior of the alloys. To validate the model, representative quantities of the rubbing process are determined and compared with experimental data from the literature. The simulation results correctly reproduce the observations made on a test rig with a reference stainless steel material (AISI 304). A parametric study using the nickel-based superalloys reveals a clear dependency of the rubbing behavior on the sliding and incursion velocity. Compared to each other, the two superalloys studied exhibit a different rubbing behavior.

Spin structures of S = 5/2 antiferromagnetic triangular lattices: AAg{sub 2}M[VO{sub 4}]{sub 2}

Energy Technology Data Exchange (ETDEWEB)

Moeller, Angela; Amuneke, Ngozi E.; Tapp, Joshua [Department of Chemistry and TcSUH, University of Houston (United States); Cruz, Clarina R. de la [Quantum Condensed Matter Division, ORNL, Oak Ridge (United States)

2015-07-01

The AAg{sub 2}M[VO{sub 4}]{sub 2} compounds present a unique series for studying structure-property relationships. The size of the A cation (Ba{sup 2+}, K{sup +}, Rb{sup +}, or Ag{sup +}) controls (i) the inter-layer distances between the magnetic triangular lattices (M, here Mn{sup 2+} or Fe{sup 3+}) and (ii) the distortion of the non-magnetic vanadate units. The crystal and magnetic structures were refined from neutron diffraction data under applied fields (ORNL, HB2A) and reveal the complex magnetic phase diagrams of frustrated S=5/2 triangular lattices with axial and XY-anisotropy, respectively.

Prepreg effects on honeycomb composite manufacturing

Science.gov (United States)

Martin, Cary Joseph

Fiber reinforced composites offer many advantages over traditional materials and are widely utilized in aerospace applications. Advantages include a high stiffness to weight ratio and excellent fatigue resistance. However, the pace of new implementation is slow. The manufacturing processes used to transform composite intermediates into final products are poorly understood and are a source of much variability. This limits new implementation and increases the manufacturing costs of existing designs. One such problem is honeycomb core crush, in which a core-stiffened structure collapses during autoclave manufacture, making the structure unusable and increasing the overall manufacturing cost through increased scrap rates. Consequently, the major goal of this research was to investigate the scaling of core crush from prepreg process-structure-property relations to commercial composite manufacture. The material dependent nature of this defect was of particular interest. A methodology and apparatus were developed to measure the frictional resistance of prepreg materials under typical processing conditions. Through a characterization of commercial and experimental prepregs, it was found that core crush behavior was the result of differences in prepreg frictional resistance. This frictional resistance was related to prepreg morphology and matrix rheology and elasticity. Resin composition and prepreg manufacturing conditions were also found to affect manufacturing behavior. Mechanical and dimensional models were developed and demonstrated utility for predicting this crushing behavior. Collectively, this work explored and identified the process-structure-property relations as they relate to the manufacture of composite materials and suggested several avenues by which manufacturing-robust materials may be developed.

Automated laser-based barely visible impact damage detection in honeycomb sandwich composite structures

International Nuclear Information System (INIS)

Girolamo, D.; Yuan, F. G.; Girolamo, L.

2015-01-01

Nondestructive evaluation (NDE) for detection and quantification of damage in composite materials is fundamental in the assessment of the overall structural integrity of modern aerospace systems. Conventional NDE systems have been extensively used to detect the location and size of damages by propagating ultrasonic waves normal to the surface. However they usually require physical contact with the structure and are time consuming and labor intensive. An automated, contactless laser ultrasonic imaging system for barely visible impact damage (BVID) detection in advanced composite structures has been developed to overcome these limitations. Lamb waves are generated by a Q-switched Nd:YAG laser, raster scanned by a set of galvano-mirrors over the damaged area. The out-of-plane vibrations are measured through a laser Doppler Vibrometer (LDV) that is stationary at a point on the corner of the grid. The ultrasonic wave field of the scanned area is reconstructed in polar coordinates and analyzed for high resolution characterization of impact damage in the composite honeycomb panel. Two methodologies are used for ultrasonic wave-field analysis: scattered wave field analysis (SWA) and standing wave energy analysis (SWEA) in the frequency domain. The SWA is employed for processing the wave field and estimate spatially dependent wavenumber values, related to discontinuities in the structural domain. The SWEA algorithm extracts standing waves trapped within damaged areas and, by studying the spectrum of the standing wave field, returns high fidelity damage imaging. While the SWA can be used to locate the impact damage in the honeycomb panel, the SWEA produces damage images in good agreement with X-ray computed tomographic (X-ray CT) scans. The results obtained prove that the laser-based nondestructive system is an effective alternative to overcome limitations of conventional NDI technologies

Fabrication and characterization of porous-core honeycomb bandgap THz fibers

DEFF Research Database (Denmark)

Bao, Hualong; Nielsen, Kristian; Rasmussen, Henrik K.

We have fabricated a porous-core honeycomb fiber in the cyclic olefin copolymer (COC) Topas® by drill-draw technology [1]. A cross-sectional image of the fabricated fiber is shown in the left Panel of Fig. 1. Simulation of the electromagnetic properties of the fiber shows two wide bandgaps within......-TDS system (Picometrix T-Ray 4000). The reference pulse before coupling into the fiber is shown in Fig. 1(a) and the time trace of the THz pulse after propagation through a 5-cm long segment of fiber is shown in Fig. 1(b) (blue curve). After adding some water on the outside of the fiber surface......, the transmitted pulse experiences less pronounced oscillations at times later than 20 ps ( red curve in Fig. 1(b)). Figs. 1(c) and (d) show the short-time Fourier transforms of the two time-domain traces in Fig. 1(b), overlaid with the calculated group delay in the two bandgaps (black squares). The frequencies...

Elastic lattice in an incommensurate background

International Nuclear Information System (INIS)

Dickman, R.; Chudnovsky, E.M.

1995-01-01

We study a harmonic triangular lattice, which relaxes in the presence of an incommensurate short-wavelength potential. Monte Carlo simulations reveal that the elastic lattice exhibits only short-ranged translational correlations, despite the absence of defects in either lattice. Extended orientational order, however, persists in the presence of the background. Translational correlation lengths exhibit approximate power-law dependence upon cooling rate and background strength. Our results may be relevant to Wigner crystals, atomic monolayers on crystals surfaces, and flux-line and magnetic bubble lattices

Lattice gravity near the continuum limit

International Nuclear Information System (INIS)

Feinberg, G.; Friedberg, R.; Lee, T.D.; Ren, H.C.

1984-01-01

We prove that the lattice gravity always approaches the usual continuum limit when the link length l -> 0, provided that certain general boundary conditions are satisfied. This result holds for any lattice, regular or irregular. Furthermore, for a given lattice, the deviation from its continuum limit can be expressed as a power series in l 2 . General formulas for such a perturbative calculation are given, together with a number of illustrative examples, including the graviton propagator. The lattice gravity satisfies all the invariance properties of Einstein's theory of general relativity. In addition, it is symmetric under a new class of transformations that are absent in the usual continuum theory. The possibility that the lattice theory (with a nonzero l) may be more fundamental is discussed. (orig.)

Lattices for the TRIUMF KAON factory

International Nuclear Information System (INIS)

Servranckx, R.V.; Craddock, M.K.

1989-09-01

Separated-function racetrack lattices have been developed for the KAON Factory accelerators that have more flexibility than the old circular lattices. The arcs of the large rings have a regular FODO structure with a superimposed six-fold symmetric modulation of the betafunction in order to raise γ t to infinity. Straight sections with zero dispersion are provided for rf cavities and fast injection and extraction, and with controlled dispersion for H - injection and slow extraction. For the small rings, sixfold symmetric circular lattices with high γ t are retained. In the Accumulator lattice, a straight section with double waist and controlled η function allows for H - injection and phase-space painting. The ion-optical properties of the lattices and the results from tracking studies are discussed

Dip coating of air purifier ceramic honeycombs with photocatalytic TiO₂ nanoparticles: A case study for occupational exposure

DEFF Research Database (Denmark)

Koivisto, Antti Joonas; Kling, Kirsten Inga; Fonseca, Ana Sofia

2018-01-01

Nanoscale TiO2 (nTiO2) is manufactured in high volumes and is of potential concern in occupational health. Here, we measured workers exposure levels while ceramic honeycombs were dip coated with liquid photoactive nanoparticle suspension and dried with an air blade. The measured nTiO2 concentrati...

Buckling Testing and Analysis of Honeycomb Sandwich Panel Arc Segments of a Full-Scale Fairing Barrel: Comparison of In- and Out-of-Autoclave Facesheet Configurations

Science.gov (United States)

Pineda, Evan Jorge; Myers, David E.; Kosareo, Daniel N.; Zalewski, Bart F.; Kellas, Sotiris; Dixon, Genevieve D.; Krivanek, Thomas M.; Gyekenyesi, Thomas G.

2014-01-01

Four honeycomb sandwich panels, representing 1/16th arc segments of a 10-m diameter barrel section of the Heavy Lift Launch Vehicle, were manufactured and tested under the NASA Composites for Exploration and the NASA Constellation Ares V programs. Two configurations were chosen for the panels: 6-ply facesheets with 1.125 in. honeycomb core and 8-ply facesheets with 1.0 in. honeycomb core. Additionally, two separate carbon fiber/epoxy material systems were chosen for the facesheets: in-autoclave IM7/977-3 and out-of-autoclave T40-800b/5320-1. Smaller 3 ft. by 5 ft. panels were cut from the 1/16th barrel sections and tested under compressive loading. Furthermore, linear eigenvalue and geometrically nonlinear finite element analyses were performed to predict the compressive response of each 3 ft. by 5 ft. panel. To improve the robustness of the geometrically nonlinear finite element model, measured surface imperfections were included in the geometry of the model. Both the linear and nonlinear models yielded good qualitative and quantitative predictions. Additionally, it was correctly predicted that the panel would fail in buckling prior to failing in strength. Furthermore, several imperfection studies were performed to investigate the influence of geometric imperfections, fiber angle misalignments, and three-dimensional effects on the compressive response of the panel.

Permutohedral Lattice CNNs

OpenAIRE

Kiefel, Martin; Jampani, Varun; Gehler, Peter V.

2014-01-01

This paper presents a convolutional layer that is able to process sparse input features. As an example, for image recognition problems this allows an efficient filtering of signals that do not lie on a dense grid (like pixel position), but of more general features (such as color values). The presented algorithm makes use of the permutohedral lattice data structure. The permutohedral lattice was introduced to efficiently implement a bilateral filter, a commonly used image processing operation....

On the hierarchical lattices approximation of Bravais lattices: Specific heat and correlation length

International Nuclear Information System (INIS)

Tsallis, C.

1984-01-01

Certain types of real-space renormalization groups (which essentially approximate Bravais lattices through hierarchical ones) do not preserve standard thermodynamic convexity properties. It is pointed out that this serious defect is not intrinsic to any real-space renormalization. It can be avoided if form-invariance (under uniform translation of the energy scale) of the equation connecting the Bravais lattice (which is intended to study) to the hierarchical one (which approximates it) is demanded. In addition to that expressions for the critical exponentes ν and α corresponding to hierarchical lattices are analysed; these are consistent with Melrose recent analysis of the fractal intrinsic dimensionality. (Author) [pt

Aliasing modes in the lattice Schwinger model

International Nuclear Information System (INIS)

Campos, Rafael G.; Tututi, Eduardo S.

2007-01-01

We study the Schwinger model on a lattice consisting of zeros of the Hermite polynomials that incorporates a lattice derivative and a discrete Fourier transform with many properties. Such a lattice produces a Klein-Gordon equation for the boson field and the exact value of the mass in the asymptotic limit if the boundaries are not taken into account. On the contrary, if the lattice is considered with boundaries new modes appear due to aliasing effects. In the continuum limit, however, this lattice yields also a Klein-Gordon equation with a reduced mass

Lattice distortion and spontaneous {gamma}{sub 5g} ferro-quadrupole moment in phase IV of Ce{sub x}La{sub 1-x}B{sub 6}

Energy Technology Data Exchange (ETDEWEB)

Nemoto, Yuichi [Graduate School of Science and Technology, Niigata University, Niigata 950-2181 (Japan)]. E-mail: nemoto@phys.sc.niigata-u.ac.jp; Akatsu, Mitsuhiro [Graduate School of Science and Technology, Niigata University, Niigata 950-2181 (Japan); Goto, Terutaka [Graduate School of Science and Technology, Niigata University, Niigata 950-2181 (Japan); Suzuki, Osamu [National Institute for Materials Science, Tukuba 305-0003 (Japan); Nakamura, Shintaro [Center for Low Temperature Science, Tohoku University, Sendai 980-8577 (Japan); Kunii, Satoru [Department of Physics, Graduate School of Science, Tohoku University, Sendai 980-8578 (Japan)

2005-04-30

We have performed low-temperature thermal expansion measurements to investigate lattice effect of the phase IV in Ce{sub x}La{sub 1-x}B{sub 6}, for x=0.75 and 0.70. In phase IV of both compounds, lattice length along the [111] direction shrinks notably, on the other hand length along the [001] direction expands. These results provide evidence that the spontaneous {gamma}{sub 5g} ferro-quadrupole moment ==<>0 is relevant in phase IV because the trigonal lattice distortion is described by the symmetry strain <{epsilon}{sub yz}>=<{epsilon}{sub zx}>=<{epsilon}{sub xy}><>0 simultaneously.

Racetrack lattices for the TRIUMF KAON factory

International Nuclear Information System (INIS)

Servranckx, R.V.; Wienands, U.; Craddock, M.K.; Rees, G.H.

1989-03-01

Separated-function racetrack lattices have been developed for the KAON Factory accelerators that have more flexibility than the old circular lattices. Straight sections with zero dispersion are provided for rf cavities and fast injection and extraction, and with controlled dispersion for H - injection and slow extraction. In addition the new lattices have fewer depolarizing resonances than the old circular lattices

Lattice-Like Total Perfect Codes

Directory of Open Access Journals (Sweden)

Araujo Carlos

2014-02-01

Full Text Available A contribution is made to the classification of lattice-like total perfect codes in integer lattices Λn via pairs (G, Φ formed by abelian groups G and homomorphisms Φ: Zn → G. A conjecture is posed that the cited contribution covers all possible cases. A related conjecture on the unfinished work on open problems on lattice-like perfect dominating sets in Λn with induced components that are parallel paths of length > 1 is posed as well.

Buckling Testing and Analysis of Honeycomb Sandwich Panel Arc Segments of a Full-Scale Fairing Barrel. Part 3; 8-ply Out-of-Autoclave Facesheets

Science.gov (United States)

Pineda, Evan J.; Myers, David E.; Kosareo, Daniel N.; Kellas, Sotiris

2014-01-01

Four honeycomb sandwich panels, representing 1/16th arc segments of a 10 m diameter barrel section of the heavy lift launch vehicle, were manufactured under the NASA Composites for Exploration program and the NASA Constellation Ares V program. Two configurations were chosen for the panels: 6-ply facesheets with 1.125 in. honeycomb core and 8-ply facesheets with 1.000 in. honeycomb core. Additionally, two separate carbon fiber/epoxy material systems were chosen for the facesheets: inautoclave IM7/977-3 and out-of-autoclave T40-800B/5320-1. Smaller 3- by 5-ft panels were cut from the 1/16th barrel sections. These panels were tested under compressive loading at the NASA Langley Research Center. Furthermore, linear eigenvalue and geometrically nonlinear finite element analyses were performed to predict the compressive response of the 3- by 5-ft panels. This manuscript summarizes the experimental and analytical modeling efforts pertaining to the panel composed of 8-ply, T40-800B/5320-1 facesheets (referred to as Panel C). To improve the robustness of the geometrically nonlinear finite element model, measured surface imperfections were included in the geometry of the model. Both the linear and nonlinear, two-dimensional (2-D) and three-dimensional (3-D), models yield good qualitative and quantitative predictions. Additionally, it was predicted correctly that the panel would fail in buckling prior to failing in strength.