International Nuclear Information System (INIS)
Guo Fengyun; Lue Qiang; Sun Liang; Li Hongtao; Zhen Xihe; Xu Yuheng; Zhao Liancheng
2006-01-01
A series of the double doped lithium niobate (LiNbO 3 , LN) single crystals had been grown by Czochralski method. The Curie temperatures of various concentrations doped or [Li]/[Nb] ratio LN crystals measured by differential thermal analysis (DTA) were discussed to investigate their defect structures with Safaryan et al. new approach about LN lattice defect structure using Curie temperatures calculated. Infrared transmission spectra of various concentrations doped were used to compare the investigation above. The results show that the lithium vacancy model is the more probable to describe the lattice defect structure of the doped LN single crystal
Energy Technology Data Exchange (ETDEWEB)
Sedao, Xxx; Garrelie, Florence, E-mail: florence.garrelie@univ-st-etienne.fr; Colombier, Jean-Philippe; Reynaud, Stéphanie; Pigeon, Florent [Université de Lyon, CNRS, UMR5516, Laboratoire Hubert Curien, Université de Saint Etienne, Jean Monnet, F-42023 Saint-Etienne (France); Maurice, Claire; Quey, Romain [Ecole Nationale Supérieure des Mines de Saint-Etienne, CNRS, UMR5307, Laboratoire Georges Friedel, F-42023 Saint-Etienne (France)
2014-04-28
The influence of crystal orientation on the formation of femtosecond laser-induced periodic surface structures (LIPSS) has been investigated on a polycrystalline nickel sample. Electron Backscatter Diffraction characterization has been exploited to provide structural information within the laser spot on irradiated samples to determine the dependence of LIPSS formation and lattice defects (stacking faults, twins, dislocations) upon the crystal orientation. Significant differences are observed at low-to-medium number of laser pulses, outstandingly for (111)-oriented surface which favors lattice defects formation rather than LIPSS formation.
Fang, C.M.; Wijs, G.A. de
2004-01-01
The phonon spectrum Of C3N4 with defect zincblende-type structure (deltaC(3)N(4)) was calculated by density functional theory (DFT) techniques. The results permit an assessment of important mechanical and thermodynamical properties such as the bulk modulus, lattice specific heat, vibration energy,
Neutron diffraction and lattice defects
International Nuclear Information System (INIS)
Hamaguchi, Yoshikazu
1974-01-01
Study on lattice defects by neutron diffraction technique is described. Wave length of neutron wave is longer than that of X-ray, and absorption cross-section is small. Number of defects observed by ESR is up to several defects, and the number studied with electron microscopes is more than 100. Information obtained by neutron diffraction concerns the number of defects between these two ranges. For practical analysis, several probable models are selected from the data of ESR or electron microscopes, and most probable one is determined by calculation. Then, defect concentration is obtained from scattering cross section. It is possible to measure elastic scattering exclusively by neutron diffraction. Minimum detectable concentration estimated is about 0.5% and 10 20 - 10 21 defects per unit volume. A chopper and a time of flight system are used as a measuring system. Cold neutrons are obtained from the neutron sources inserted into reactors. Examples of measurements by using similar equipments to PTNS-I system of Japan Atomic Energy Research Institute are presented. Interstitial concentration in the graphite irradiated by fast neutrons is shown. Defects in irradiated MgO were also investigated by measuring scattering cross section. Study of defects in Ge was made by measuring total cross section, and model analysis was performed in comparison with various models. (Kato, T.)
How to 'visualize' lattice defects
International Nuclear Information System (INIS)
Doi, Kenji
1974-01-01
Methods to recognize objects are discussed. In case of optics, lenses are used, and light from objects passing through the lenses focuses on focal planes. The amplitude of light on the focal planes in given as a function of the structure factor of scattering light from objects, images of objects are made on image planes. In case of X-ray or neutron diffraction, lenses which make images by X-ray or neutrons can not be made, accordingly images cannot be obtained. Images can be seen with electron microscopes. By X-ray or thermal neutron diffraction, intensity on focal planes in observed, and the defects to be studied are recognized as diffuse scattering. Since it is necessary to minimize aberration in case of image observation with electron microscopes, slits are used to utilize electron beam near optical axis exclusively. Therefore large resolving power cannot be expected. The information concerning structure obtained from focal planes is of statistical nature, and that from image planes is local information. The principle of neutron topography, by which the informations concerning local points are obtained, is explained. A photograph of LiF irradiated by 0.5 MeV proton beam was taken by the topographic method, and shown in this paper. (Kato, T.)
International Nuclear Information System (INIS)
Ravari, M R Karamooz; Kadkhodaei, M; Ghaei, A; Esfahani, S Nasr; Andani, M Taheri; Elahinia, M; Karaca, H
2016-01-01
Shape memory alloy (such as NiTi) cellular lattice structures are a new class of advanced materials with many potential applications. The cost of fabrication of these structures however is high. It is therefore necessary to develop modeling methods to predict the functional behavior of these alloys before fabrication. The main aim of the present study is to assess the effects of geometry, microstructural imperfections and material asymmetric response of dense shape memory alloys on the mechanical response of cellular structures. To this end, several cellular and dense NiTi samples are fabricated using a selective laser melting process. Both cellular and dense specimens were tested in compression in order to obtain their stress–strain response. For modeling purposes, a three -dimensional (3D) constitutive model based on microplane theory which is able to describe the material asymmetry was employed. Five finite element models based on unit cell and multi-cell methods were generated to predict the mechanical response of cellular lattices. The results show the considerable effects of the microstructural imperfections on the mechanical response of the cellular lattice structures. The asymmetric material response of the bulk material also affects the mechanical response of the corresponding cellular structure. (paper)
International Nuclear Information System (INIS)
Liu, Z.L.; Cui, Z.L.; Zhang, Z.K.
2005-01-01
Titania nanoparticles doped with Cr 3+ (2% relative to molar quantity of titania) were prepared and examined by EDS, HRTEM, XRD, and UV-VIS analysis. HRTEM images showed the detailed atomic arrays and vacancy defects of the doped Titania nanocrystals and revealed that the implanted Cr element existed in titania mainly as Cr 3+ ions which located at the lattice positions of Ti 4+ ions. Compared with pure titania, the UV-VIS spectra of the Cr 3+ doped titania show significantly increased absorbance in visible light region. This indicated that the presence of the Cr 3+ ions affected the lattice structure of titania nanocrystals and plays an reformative role in spectral feature of titania
Lattice defects in LPE InP-InGaAsP-InGaAs structure epitaxial layers on InP substrates
International Nuclear Information System (INIS)
Ishida, K.; Matsumoto, Y.; Taguchi, K.
1982-01-01
Lattice defects generated during LPE growth of InP-InGaAsP-InGaAs structure epitaxial layers on InP substrates are studied. Two different kinds of dislocations are observed at the two interfaces of the epitaxial layers; at the InP-InGaAsP interface, misfit dislocations are generated in the InP layer by carry over of InGaAsP melt into the InP one and at the InGaAs-InP interface, V-shaped dislocations are generated in the InGaAs layer. It is shown that the critical amount of lattice mismatch to suppress generation of misfit dislocations in InP is about two times smaller than that of other III-V compound semiconductors. Conditions to suppress the generation of these dislocations are clarified. (author)
Multiscale Modeling of Point and Line Defects in Cubic Lattices
National Research Council Canada - National Science Library
Chung, P. W; Clayton, J. D
2007-01-01
.... This multiscale theory explicitly captures heterogeneity in microscopic atomic motion in crystalline materials, attributed, for example, to the presence of various point and line lattice defects...
Lattice defects as Lotka-Volterra societies
Energy Technology Data Exchange (ETDEWEB)
Yost, F.G.
1995-07-01
Since the early part of this century the Lotka-Volterra or predator-prey equations have been known to simulate the stability, instability, and persistent oscillations observed in many biological and ecological societies. These equations have been modified in many ways and have been used to model phenomena as varied as childhood epidemics, enzyme reactions, and conventional warfare. In the work to be described, similarities are drawn between various lattice defects and Lotka-Volterra (LV) societies. Indeed, grain boundaries are known to ``consume`` dislocations, inclusions ``infect`` grain boundaries, and dislocations ``annihilate`` dislocations. Several specific cases of lattice defect interaction kinetics models are drawn from the materials science literature to make these comparisons. Each model will be interpreted as if it were a description of a biological system. Various approaches to the modification of this class of interaction kinetics will be presented and discussed. The earliest example is the Damask-Dienes treatment of vacancy-divacancy annealing kinetics. This historical model will be modified to include the effects of an intermediate species and the results will be compared with the original model. The second example to be examined is the Clark-Alden model for deformation-enhanced grain growth. Dislocation kinetics will be added to this model and results will be discussed considering the original model. The third example to be presented is the Ananthakrishna-Sahoo model of the Portevin-Le Chatelier effect that was offered in 1985 as an extension of the classical Cottrell atmosphere explanation. Their treatment will be modified by inclusion of random interference from a pesky but peripheral species and by allowing a rate constant to be a function of time.
Vydyanath, H. R.; Donovan, J. D.; Nelson, D. A.
1981-01-01
Hall effect measurements were carried out on undoped Hg0.6Cd0.4Te crystals quenched to room temperature subsequent to equilibration at temperatures varying from 450 to 720 C under various partial pressures of Hg. The variation of the hole concentration as a function of the partial pressure of Hg indicates that the native acceptor defects are doubly ionized. Native donor defects are found to be negligible in concentration and the p-type to n-type conversion is shown to be due to residual donors and not due to native donor defects. Thermodynamic constant for the incorporation of the doubly ionized native acceptor defect has been established.
Designed defects in 2D antidot lattices for quantum information processing
DEFF Research Database (Denmark)
Pedersen, Jesper Goor; Flindt, Christian; Mortensen, Niels Asger
2008-01-01
We propose a new physical implementation of spin qubits for quantum information processing, namely defect states in antidot lattices defined in the two-dimensional electron gas (2DEG) at a semiconductor heterostructure. Calculations of the band structure of a periodic antidot lattice are presented...
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
Nucleon structure from lattice QCD
Energy Technology Data Exchange (ETDEWEB)
Dinter, Simon
2012-11-13
In this thesis we compute within lattice QCD observables related to the structure of the nucleon. One part of this thesis is concerned with moments of parton distribution functions (PDFs). Those moments are essential elements for the understanding of nucleon structure and can be extracted from a global analysis of deep inelastic scattering experiments. On the theoretical side they can be computed non-perturbatively by means of lattice QCD. However, since the time lattice calculations of moments of PDFs are available, there is a tension between these lattice calculations and the results from a global analysis of experimental data. We examine whether systematic effects are responsible for this tension, and study particularly intensively the effects of excited states by a dedicated high precision computation. Moreover, we carry out a first computation with four dynamical flavors. Another aspect of this thesis is a feasibility study of a lattice QCD computation of the scalar quark content of the nucleon, which is an important element in the cross-section of a heavy particle with the nucleon mediated by a scalar particle (e.g. Higgs particle) and can therefore have an impact on Dark Matter searches. Existing lattice QCD calculations of this quantity usually have a large error and thus a low significance for phenomenological applications. We use a variance-reduction technique for quark-disconnected diagrams to obtain a precise result. Furthermore, we introduce a new stochastic method for the calculation of connected 3-point correlation functions, which are needed to compute nucleon structure observables, as an alternative to the usual sequential propagator method. In an explorative study we check whether this new method is competitive to the standard one. We use Wilson twisted mass fermions at maximal twist in all our calculations, such that all observables considered here have only O(a{sup 2}) discretization effects.
Nucleon structure from lattice QCD
International Nuclear Information System (INIS)
Dinter, Simon
2012-01-01
In this thesis we compute within lattice QCD observables related to the structure of the nucleon. One part of this thesis is concerned with moments of parton distribution functions (PDFs). Those moments are essential elements for the understanding of nucleon structure and can be extracted from a global analysis of deep inelastic scattering experiments. On the theoretical side they can be computed non-perturbatively by means of lattice QCD. However, since the time lattice calculations of moments of PDFs are available, there is a tension between these lattice calculations and the results from a global analysis of experimental data. We examine whether systematic effects are responsible for this tension, and study particularly intensively the effects of excited states by a dedicated high precision computation. Moreover, we carry out a first computation with four dynamical flavors. Another aspect of this thesis is a feasibility study of a lattice QCD computation of the scalar quark content of the nucleon, which is an important element in the cross-section of a heavy particle with the nucleon mediated by a scalar particle (e.g. Higgs particle) and can therefore have an impact on Dark Matter searches. Existing lattice QCD calculations of this quantity usually have a large error and thus a low significance for phenomenological applications. We use a variance-reduction technique for quark-disconnected diagrams to obtain a precise result. Furthermore, we introduce a new stochastic method for the calculation of connected 3-point correlation functions, which are needed to compute nucleon structure observables, as an alternative to the usual sequential propagator method. In an explorative study we check whether this new method is competitive to the standard one. We use Wilson twisted mass fermions at maximal twist in all our calculations, such that all observables considered here have only O(a 2 ) discretization effects.
Solitons in a linear lattice with a defect
International Nuclear Information System (INIS)
Viswanathan, K.S.; Venugopal, C.
1989-01-01
For a lattice in which the neighbouring atoms interact through an anharmonic Morse potential, the equations of motion are shown to lead to the Korteweg-deVries equation. At the site of the defect atom the first non-vanishing term in the equation of motion in terms of the ordering parameter ε are of order ε 3 and it is shown that a localized mode appears at this site. Additional solitons are also generated at the site of the defect atom. (author). 11 refs
Lattice defects in rutile, TiO2
International Nuclear Information System (INIS)
Nakagawa, M.; Itoh, H.; Nakanishi, S.; Kondo, K.; Okada, M.; Atobe, K.
1991-01-01
Rutile, TiO 2 , having a relatively high melting point exhibits strong optical absorption after neutron irradiation (8 x 10 16 n f /cm 2 ) at 15K. The band peak is located near 0.96 μ, having a FWHM of 0.87 eV (at liquid nitrogen temperature). After inverse recovery at 120K, lattice defects due probably to F centers are annealed out at about 220K. (author)
Insulating Behavior in Graphene with Irradiation-induced Lattice Defects
Chen, Jian-Hao; Williams, Ellen; Fuhrer, Michael
2010-03-01
We irradiated cleaned graphene on silicon dioxide in ultra-high vacuum with low energy inert gas ions to produce lattice defects [1], and investigated in detail the transition from metallic to insulating temperature dependence of the conductivity as a function of defect density. We measured the low field magnetoresistance and temperature-dependent resistivity in situ and find that weak localization can only account for a small correction of the resistivity increase with decreasing temperature. We will discuss possible origins of the insulating temperature dependent resistivity in defected graphene in light of our recent experiments. [4pt] [1] Jian-Hao Chen, W. G. Cullen, C. Jang, M. S. Fuhrer, E. D. Williams, PRL 102, 236805 (2009)
Spin helical states and spin transport of the line defect in silicene lattice
Energy Technology Data Exchange (ETDEWEB)
Yang, Mou; Chen, Dong-Hai; Wang, Rui-Qiang [Laboratory of Quantum Engineering and Quantum Materials, School of Physics and Telecommunication Engineering, South China Normal University, Guangzhou 510006 (China); Bai, Yan-Kui, E-mail: ykbai@semi.ac.cn [College of Physical Science and Information Engineering and Hebei Advance Thin Films Laboratory, Hebei Normal University, Shijiazhuang, Hebei 050024 (China)
2015-02-06
We investigated the electronic structure of a silicene-like lattice with a line defect under the consideration of spin–orbit coupling. In the bulk energy gap, there are defect related bands corresponding to spin helical states localized beside the defect line: spin-up electrons flow forward on one side near the line defect and move backward on the other side, and vice versa for spin-down electrons. When the system is subjected to random distribution of spin-flipping scatterers, electrons suffer much less spin-flipped scattering when they transport along the line defect than in the bulk. An electric gate above the line defect can tune the spin-flipped transmission, which makes the line defect as a spin-controllable waveguide. - Highlights: • Band structure of silicene with a line defect. • Spin helical states around the line defect and their probability distribution features. • Spin transport along the line defect and that in the bulk silicene.
Nucleon Structure from Lattice QCD
International Nuclear Information System (INIS)
Zanotti, J. M.
2011-01-01
Lattice simulations of hadronic structure are now reaching a level where they are able to not only complement, but also provide guidance to current and forthcoming experimental programmes.By considering new simulations at low quark masses and on large volumes, we review the recent progress that has been made in this area by the QCDSF/UKQCD collaboration. In particular, results obtained close to the physical point for several quantities, including electromagnetic form factors and moments of parton distribution functions, show some indication of approaching their phenomenological values.
Vetrov, S Y
2001-01-01
The properties of the localized electromagnetic modes in the one-dimensional photon crystal with a structural defective layer are studied. The anisotropic layer of the nematic liquid layer is considered as the defect. It is shown that the frequency and coefficient of the defective modes attenuation essentially depend on the defective layer thickness and nematic optical axis orientation. The spectrum of the photon crystal transmittance with one or two defects in the lattice is studied. The possibility of controlling the the photon crystal transmittance spectrum on the count of changing the orientation of the nematic optical axis, for example, through the external electric field is shown with an account of strong anisotropy of the dielectric permittivity
Lyu, Dandan; Li, Shaofan
2017-10-01
Crystal defects have microstructure, and this microstructure should be related to the microstructure of the original crystal. Hence each type of crystals may have similar defects due to the same failure mechanism originated from the same microstructure, if they are under the same loading conditions. In this work, we propose a multiscale crystal defect dynamics (MCDD) model that models defects by considering its intrinsic microstructure derived from the microstructure or material genome of the original perfect crystal. The main novelties of present work are: (1) the discrete exterior calculus and algebraic topology theory are used to construct a scale-up (coarse-grained) dual lattice model for crystal defects, which may represent all possible defect modes inside a crystal; (2) a higher order Cauchy-Born rule (up to the fourth order) is adopted to construct atomistic-informed constitutive relations for various defect process zones, and (3) an hierarchical strain gradient theory based finite element formulation is developed to support an hierarchical multiscale cohesive (process) zone model for various defects in a unified formulation. The efficiency of MCDD computational algorithm allows us to simulate dynamic defect evolution at large scale while taking into account atomistic interaction. The MCDD model has been validated by comparing of the results of MCDD simulations with that of molecular dynamics (MD) in the cases of nanoindentation and uniaxial tension. Numerical simulations have shown that MCDD model can predict dislocation nucleation induced instability and inelastic deformation, and thus it may provide an alternative solution to study crystal plasticity.
Directory of Open Access Journals (Sweden)
Jeffrey Lutkenhaus
2016-04-01
Full Text Available We report the holographic fabrication of designed defect lines in photonic crystal lattices through phase engineering using a spatial light modulator (SLM. The diffracted beams from the SLM not only carry the defect’s content but also the defect related phase-shifting information. The phase-shifting induced lattice shifting in photonic lattices around the defects in three-beam interference is less than the one produced by five-beam interference due to the alternating shifting in lattice in three beam interference. By designing the defect line at a 45 degree orientation and using three-beam interference, the defect orientation can be aligned with the background photonic lattice, and the shifting is only in one side of the defect line, in agreement with the theory. Finally, a new design for the integration of functional defect lines in a background phase pattern reduces the relative phase shift of the defect and utilizes the different diffraction efficiency between the defect line and background phase pattern. We demonstrate that the desired and functional defect lattice can be registered into the background lattice through the direct imaging of designed phase patterns.
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.
Vydyanath, H. R.
1981-01-01
Hall effect and mobility measurements were conducted on undoped Hg(0.8)Cd(0.2)Te crystals which were quenched to room temperature after being subjected to equilibration at temperatures ranging from 400 to 655 C in various Hg atmospheres. The variation of the hole concentration in the cooled crystals at 77 K as a function of Hg's partial pressure at the equilibration temperature, together with a comparison of the hole mobility in the undoped samples with that in copper-doped ones, yields a defect model for the undoped crystals according to which they are intrinsic at the equilibration temperatures and the native acceptor defects are doubly ionized. In the second part of this paper, the effects of indium doping are considered. The concentration of electrons obtained in the cooled crystals was found to be lower than the intrinsic carrier concentration at the equilibration temperatures. A defect model is proposed according to which most of the indium is incorporated as In2Te3(s) dissolved in the crystal, with only a small fraction of indium acting as single donors occupying Hg lattice sites.
Synthesizing lattice structures in phase space
International Nuclear Information System (INIS)
Guo, Lingzhen; Marthaler, Michael
2016-01-01
In one dimensional systems, it is possible to create periodic structures in phase space through driving, which is called phase space crystals (Guo et al 2013 Phys. Rev. Lett. 111 205303). This is possible even if for particles trapped in a potential without periodicity. In this paper we discuss ultracold atoms in a driven optical lattice, which is a realization of such a phase space crystals. The corresponding lattice structure in phase space is complex and contains rich physics. A phase space lattice differs fundamentally from a lattice in real space, because its coordinate system, i.e., phase space, has a noncommutative geometry, which naturally provides an artificial gauge (magnetic) field. We study the behavior of the quasienergy band structure and investigate the dissipative dynamics. Synthesizing lattice structures in phase space provides a new platform to simulate the condensed matter phenomena and study the intriguing phenomena of driven systems far away from equilibrium. (paper)
Function of TiO2 Lattice Defects toward Photocatalytic Processes: View of Electronic Driven Force
Directory of Open Access Journals (Sweden)
Huanan Cui
2013-01-01
Full Text Available Oxygen vacancies and Ti-related defects (OTDs are the main lattice defects of TiO2, which have great influence on its photocatalytic activity. To understand the relationship between the defects and photocatalytic activities, detailed discussions based on the electronic driven force provided by these defects are carried out during the three commonly accepted processes in photocatalytic reactions. It is found that these defects inevitably (i influence the energy structure of the pristine TiO2 as the isolate acceptor/donor level or hybrid with the original orbital, (ii provide a disordered short-range force that confuses the charge carriers transferring to surface active sites, (iii act not only as the surface active sites for trapping the charge carriers but also as the main chemisorption sites for O2, H2O, and organic species. These effects of the defects make them one of the key factors that determine the efficiency of heterogeneous photocatalysis. Clarifying the role of the defects will further facilitate the exploration and the construction of high-performance photocatalysts for practical applications.
Directory of Open Access Journals (Sweden)
R.S. Khymyn
2014-09-01
Full Text Available The regular array of magnetic particles (magnetic dots of the form of a two-dimensional triangular lattice in the presence of external magnetic field demonstrates complicated magnetic structures. The magnetic symmetry of the ground state for such a system is lower than that for the underlying lattice. Long range dipole-dipole interaction leads to a specific antiferromagnetic order in small fields, whereas a set of linear topological defects appears with the growth of the magnetic field. Self-organization of such defects determines the magnetization process for a system within a wide range of external magnetic fields.
Exotic Non-Abelian Topological Defects in Lattice Fractional Quantum Hall States
Liu, Zhao; Möller, Gunnar; Bergholtz, Emil J.
2017-09-01
We investigate extrinsic wormholelike twist defects that effectively increase the genus of space in lattice versions of multicomponent fractional quantum Hall systems. Although the original band structure is distorted by these defects, leading to localized midgap states, we find that a new lowest flat band representing a higher genus system can be engineered by tuning local single-particle potentials. Remarkably, once local many-body interactions in this new band are switched on, we identify various Abelian and non-Abelian fractional quantum Hall states, whose ground-state degeneracy increases with the number of defects, i.e, with the genus of space. This sensitivity of topological degeneracy to defects provides a "proof of concept" demonstration that genons, predicted by topological field theory as exotic non-Abelian defects tied to a varying topology of space, do exist in realistic microscopic models. Specifically, our results indicate that genons could be created in the laboratory by combining the physics of artificial gauge fields in cold atom systems with already existing holographic beam shaping methods for creating twist defects.
Baryon structure from lattice QCD
International Nuclear Information System (INIS)
Alexandrou, C.
2009-01-01
We present recent lattice results on the baryon spectrum, nucleon electromagnetic and axial form factors, nucleon to Δ transition form factors as well as the Δ electromagnetic form factors. The masses of the low lying baryons and the nucleon form factors are calculated using two degenerate flavors of twisted mass fermions down to pion mass of about 270 MeV. We compare to the results of other collaborations. The nucleon to Δ transition and Δ form factors are calculated in a hybrid scheme, which uses staggered sea quarks and domain wall valence quarks. The dominant magnetic dipole nucleon to Δ transition form factor is also evaluated using dynamical domain wall fermions. The transverse density distributions of the Δ in the infinite momentum frame are extracted using the form factors determined from lattice QCD. (author)
Energy Technology Data Exchange (ETDEWEB)
Verma, Kuldeep Chand, E-mail: dkuldeep.physics@gmail.com [Department of Physics, Panjab University, Chandigarh 160014 (India); Kotnala, R.K., E-mail: rkkotnala@gmail.com [CSIR-National Physical Laboratory, New Delhi 110012 (India)
2017-02-15
Future spintronics technologies based on diluted magnetic semiconductors (DMS) will rely heavily on a sound understanding of the microscopic origins of ferromagnetism in such materials. It remains unclear, however, whether the ferromagnetism in DMS is intrinsic - a precondition for spintronics - or due to dopant clustering. For this, we include a simultaneous doping from transition metal (Ni, Cu) and rare earth (Ce) ions in ZnO nanoparticles that increase the antiferromagnetic ordering to achieve high-T{sub c} ferromagnetism. Rietveld refinement of XRD patterns indicate that the dopant ions in ZnO had a wurtzite structure and the dopants, Ni{sup 2+}, Cu{sup 2+}, Ce{sup 3+} ions, are highly influenced the lattice constants to induce lattice defects. The Ni, Cu, Ce ions in ZnO have nanoparticles formation than nanorods was observed in pure sample. FTIR involve some organic groups to induce lattice defects and the metal-oxygen bonding of Zn, Ni, Cu, Ce and O atoms to confirm wurtzite structure. Raman analysis evaluates the crystalline quality, structural disorder and defects in ZnO lattice with doping. Photoluminescence spectra have strong near-band-edge emission and visible emission bands responsible for defects due to oxygen vacancies. The energy band gap is calculated using Tauc relation. Room temperature ferromagnetism has been described due to bound magnetic polarons formation with Ni{sup 2+}, Cu{sup 2+}, Ce{sup 3+} ions in ZnO via oxygen vacancies. The zero field and field cooling SQUID measurement confirm the strength of antiferromagnetism in ZnO. The field cooling magnetization is studied by Curie-Weiss law that include antiferromagnetic interactions up to low temperature. The XPS spectra have involve +3/+4 oxidation states of Ce ions to influence the observed ferromagnetism. - Graphical abstract: The lattice defects/vacancies attributed by Ni and Ce ions in the wurtzite ZnO structure are responsible in high T{sub c} -ferromagnetism due to long-range magnetic
Computer code for the atomistic simulation of lattice defects and dynamics
International Nuclear Information System (INIS)
Schiffgens, J.O.; Graves, N.J.; Oster, C.A.
1980-04-01
The computer code COMENT used to simulate the effect of temperature, impurities, and pre-existing defects on radiation-induced defect production mechanisms, defect properties, defect migration, and defect stability. This report documents Version IV of COMENT (models, methods, and implementation) and defines current code options. Version IV of COMENT generates only face-centered-cubic (fcc) crystal lattices. However, an effort was made to structure COMENT to allow addition of new options with a minimum of change in the existing version of the code. This document describes the calling program and thirty-two user-defined subroutines. Fourteen subroutines (ALOYORD, DASPKA, DFCT, DSLOAN, DSLOIN, EXPAND, POT1, POT2, POT3, POT4, POT5, POT6, POT7, and THRMAL) are associated with the selection of program options; only a few of these are used in any given analysis. Seven of the other subroutines (CRYSTL, IEAF, INCBOX, LABLE, MINILAT, SPEFORS, and SQUEZ are used to establish a variety of arrays and conditions required for each analysis; most of them are used once in a given calculation. The remaining eleven subroutines (DAMP, DIRECT, IDDEF, NEAF, INBIN, FILBIN, FTBIN, PAC3, UNPAC3, PACF, and UNPACF) are used many times in each calculation; the last eight of these are used many times in each time step during the integration and, therefore, are written in COMPASS (CDC assembly language). The COMPASS subroutines are described in sufficient detail to permit easy conversion to some other assembly language or to FORTRAN
Pion structure from lattice QCD
Energy Technology Data Exchange (ETDEWEB)
Javadi Motaghi, Narjes
2015-05-12
In this thesis we use lattice QCD to compute the second Mellin moments of pion generalized parton distributions and pion electromagnetic form factors. For our calculations we are able to analyze a large set of gauge configurations with 2 dynamical flavours using non-perturbatively the improved Wilson-Sheikholeslami-Wohlert fermionic action pion masses ranging down to 151 MeV. By employing improved smearing we were able to suppress excited state contamination. However, our data in the physical quark mass limit show that some excited state contamination remains. We show the non-zero sink momentum is optimal for the computation of the electromagnetic form factors and generalized form factors at finite momenta.
The role of diffusion measurements in the study of crystal lattice defects
Energy Technology Data Exchange (ETDEWEB)
Kidson, G V
1965-07-15
Measurements of atomic mobility in solids are frequently of direct interest to those concerned with the design, development and utilization of materials in engineering. Increasing attention, however, is currently devoted to an under standing of such properties in terms of the occurrence and nature of point and line defects in the crystals. This paper reviews some recent diffusion studies conducted at C.R,N.L. that provide, in addition to data of interest in nuclear technology, a means of gaining some insight into the more fundamental nature of the lattice defects occurring in the materials. The systems discussed are (i) self diffusion in the high temperature phase of pure zirconium (ii) solute diffusion in lead and (iii) interdiffusion of aluminum and zirconium The unusual and at present incompletely understood results described in (i) are briefly reviewed. Evidence is given to suggest that diffusion occurs either through a dense dislocation network produced as a result of a martensitic phase transformation, or, alternatively, by excess vacancies introduced into the crystal by impurities. In (ii) the extraordinarily rapid diffusion of noble metal solutes in high purity lead single crystals will be discussed n terms of the state of solution of the solute atoms. It will be shown that their diffusion behaviour can be understood by assuming that a fraction f{sub i} of the dissolved solute atoms occupy interstitial sites, The measured diffusion coefficient D{sub m} is related to the interstitial diffusion coefficient by D{sub m} = f{sub i} D{sub i}. In (iii) the formation and rapid growth of single intermetallic compound ZrAl{sub 3} in the diffusion zone formed between pure zirconium and pure aluminum is described and the diffusion mechanism is interpreted in terms of the structure of the compound lattice. The results indicate that ZrAl{sub 3} forms a defect lattice, leading to the relatively rapid migration of aluminum atoms. (author)
Extension theorems for homogenization on lattice structures
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.
Defect structure in proton-irradiated copper and nickel
International Nuclear Information System (INIS)
Tsukuda, Noboru; Ehrhart, P.; Jaeger, W.; Schilling, W.; Dworschak, F.; Gadalla, A.A.
1987-01-01
This single crystals of copper or nickel with a thickness of about 10 μm are irradiated with 3 MeV protons at room temperature and the structures of resultant defects are investigated based on measurements of the effects of irradiation on the electrical resistivity, length, lattice constants, x-ray diffraction line profile and electron microscopic observations. The measurements show that the electrical resistivity increases with irradiation dose, while leveling off at high dose due to overlapping of irradiation cascades. The lattice constants decreases, indicating that many vacancies still remain while most of the interstitial stoms are eliminated, absorbed or consumed for dislocation loop formation. The x-ray line profile undergoes broadening, which is the result of dislocation loops, dislocation networks and SFT's introduced by the proton irradiation. Various defects have different effects though they cannot be identified separately from the profile alone. A satellite peak appears at a low angle, which seems to arise from periodic defect structures that are found in electron microscopic observations. In both copper and nickel, such periodic defect structures are seen over a wide range from high to low dose. Defect-free and defect-rich domains (defect walls), 0.5 to several μm in size, are alingned parallel to the {001} plane at intervals of 60 nm. The defect walls, which consist of dislocations, dislocation loops and SFT's, is 20 - 40 nm thick. (Nogami, K.)
Lattice strain in irradiated materials unveils a prevalent defect evolution mechanism
Debelle, Aurélien; Crocombette, Jean-Paul; Boulle, Alexandre; Chartier, Alain; Jourdan, Thomas; Pellegrino, Stéphanie; Bachiller-Perea, Diana; Carpentier, Denise; Channagiri, Jayanth; Nguyen, Tien-Hien; Garrido, Frédérico; Thomé, Lionel
2018-01-01
Modification of materials using ion beams has become a widespread route to improve or design materials for advanced applications, from ion doping for microelectronic devices to emulation of nuclear reactor environments. Yet, despite decades of studies, major issues regarding ion/solid interactions are not solved, one of them being the lattice-strain development process in irradiated crystals. In this work, we address this question using a consistent approach that combines x-ray diffraction (XRD) measurements with both molecular dynamics (MD) and rate equation cluster dynamics (RECD) simulations. We investigate four distinct materials that differ notably in terms of crystalline structure and nature of the atomic bonding. We demonstrate that these materials exhibit a common behavior with respect to the strain development process. In fact, a strain build-up followed by a strain relaxation is observed in the four investigated cases. The strain variation is unambiguously ascribed to a change in the defect configuration, as revealed by MD simulations. Strain development is due to the clustering of interstitial defects into dislocation loops, while the strain release is associated with the disappearance of these loops through their integration into a network of dislocation lines. RECD calculations of strain depth profiles, which are in agreement with experimental data, indicate that the driving force for the change in the defect nature is the defect clustering process. This study paves the way for quantitative predictions of the microstructure changes in irradiated materials.
Directory of Open Access Journals (Sweden)
Chollet Mélanie
2017-01-01
Full Text Available Fission gas behavior within the fuel structure plays a major role for the safety of nuclear fuels during operation in the nuclear power plant. Fission gas distribution and retention is determined by both, micro- and lattice-structure of the fuel matrix. The ADOPT (Advanced Doped Pellet Technology fuel, containing chromium and aluminum additives, shows larger grain sizes than standard (undoped UO2 fuel, enhancing the fission gas retention properties of the matrix. However, the additions of such trivalent cations shall also induce defects in the lattice. In this study, we investigated the microstructure of such doped fuels as well as a reference standard UO2 by positron annihilation spectroscopy (PAS. Although this technique is particularly sensitive to lattice point defects in materials, a wider application in the UO2 research is still missing. The PAS-lifetime components were measured in the hotlab facility of PSI using a 22Na source sandwiched between two 500-μm-thin sample discs. The values of lifetime at the center and the rim of both samples, examined to check at the radial homogeneity of the pellets, are not significantly different. The mean lifetimes were found to be longer in the ADOPT material, 220 ps, than in standard UO2, 190 ps, which indicates a larger presence of additional defects, presumably generated by the dopants. While two-component decomposition (bulk + one defect component could be performed for the standard material, only one lifetime component was found in the doped material. The absence of the bulk component in the ADOPT sample refers to a saturated positron trapping (i.e., all positrons are trapped at defects. In order to associate a type of lattice defect to each PAS component, interpretation of the PAS experimental observations was conducted with respect to existing experimental and modeling studies. This work has shown the efficiency of PAS to detect lattice point defects in UO2 produced by Cr and Al oxides
Kosevich, Yu. A.; Strelnikov, I. A.
2018-02-01
Destructive quantum interference between the waves propagating through laterally inhomogeneous layer can result in their total reflection, which in turn reduces energy flux carried by these waves. We consider the systems of Ge atoms, which fully or partly, in the chequer-wise order, fill a crystal plane in diamond-like Si lattice. We have revealed that a single type of the atomic defects, which are placed in identical positions in different unit cells in the defect crystal plane, can result in double transmission antiresonances of phonon wave packets. This new effect we relate with the complex structure of the diamond-like unit cell, which comprises two atoms in different positions and results in two distinct vibration resonances in two interfering phonon paths. We also consider the propagation of phonon wave packets in the superlatticies made of the defect planes, half-filled in the chequer-wise order with Ge atoms. We have revealed relatively broad phonon stop bands with center frequencies at the transmission antiresonances. We elaborate the equivalent analytical quasi-1D lattice model of the two phonon paths through the complex planar defect in the diamond-like lattice and describe the reduction of phonon heat transfer through the atomic-scale planar defects.
The influence of coordinated defects on inhomogeneous broadening in cubic lattices
Energy Technology Data Exchange (ETDEWEB)
Matheson, P. L., E-mail: phil.matheson@uvu.edu; Sullivan, Francis P.; Evenson, William E. [Utah Valley University, Department of Physics (United States)
2016-12-15
The joint probability distribution function (JPDF) of electric field gradient (EFG) tensor components in cubic materials is dominated by coordinated pairings of defects in shells near probe nuclei. The contributions from these inner shell combinations and their surrounding structures contain the essential physics that determine the PAC-relevant quantities derived from them. The JPDF can be used to predict the nature of inhomogeneous broadening (IHB) in perturbed angular correlation (PAC) experiments by modeling the G{sub 2} spectrum and finding expectation values for V{sub zz} and η. The ease with which this can be done depends upon the representation of the JPDF. Expanding on an earlier work by Czjzek et al. (Hyperfine Interact. 14, 189–194, 1983), Evenson et al. (Hyperfine Interact. 237, 119, 2016) provide a set of coordinates constructed from the EFG tensor invariants they named W{sub 1} and W{sub 2}. Using this parameterization, the JPDF in cubic structures was constructed using a point charge model in which a single trapped defect (TD) is the nearest neighbor to a probe nucleus. Individual defects on nearby lattice sites pair with the TD to provide a locus of points in the W{sub 1}−W{sub 2} plane around which an amorphous-like distribution of probability density grows. Interestingly, however, marginal, separable PDFs appear adequate to model IHB relevant cases. We present cases from simulations in cubic materials illustrating the importance of these near-shell coordinations.
Interatomic potentials and the simulation of lattice defects in metals
International Nuclear Information System (INIS)
Heugten, W.F.W.M. van.
1979-01-01
The computer simulation technique is applied to investigate the properties of point defects and line defects in metals. For that purpose crystallites are constructed in which these defects are simulated. In the case of line defects (dislocations) the initial positions of the atoms, surrounding the dislocations, are determined using the elastic theory of anisotropic media. Hereafter the atoms in such crystallites are allowed to relax to there minimum potential energy positions under the influence of the interatomic forces. These forces are derived from interatomic interaction potentials. These potentials are together with the boundary conditions of the simulated crystallite the main input data in these computer simulation models. The metals considered include molybdenum, tungsten and tantalum. (Auth.)
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.
Elastic interaction energies of defect structures
International Nuclear Information System (INIS)
Seitz, E.; de Fontaine, D.
1976-01-01
The elastic strain energy between point defects and small disk-shaped clusters of defects are calculated to determine stable configurations. A distortion tensor of tetragonal symmetry is assigned to each impurity atom. The tetragonality ratio t is varied to cover needle-type (t greater than 1), spherical (t = 1) and disk-type (t less than 0) strain fields. To vary the elastic properties of the host material, Fe, Cu, Al, and V were chosen as examples. Computer calculations are based on the microscopic theory of elasticity which emphasizes calculations in discrete Fourier space. Pairs of point defects order along [001] for t less than 1 and along (001) for t = 1 for all host elements. For t greater than 1 fcc lattices and bcc lattices behave differently. It is shown that only certain three dimensional periodic arrangements of parallel and perpendicular disk-like defect clusters are realized for given tetragonality ratio t and host element
Influence of lattice defects on criticality of Potts ferromagnet
International Nuclear Information System (INIS)
Souza Costa, U.M. de.
1985-01-01
The critical properties of the q-state Potts ferromagnet and the anisotropic Heisenberg model on hypercubic lattices (d = 2,3); emphasis is given to the free surface and the interface effects, the Real Space Renormalization Group approach. The criticality of the quenched bond-mixed q-state Potts ferromagnet on square lattice is discussed. It is shown that, the crossover from the pure fixed point to the random one occurs, while q increases, through a pitchfork bifurcation; the relation-ship with the Harris criterion is analyzed. High precision numerical values for the critical temperatures corresponding to arbitrary concentrations of the coupling constants J sub(1) and J sub(2), and arbitrary ratios J sub(1)/J sub(2) are presented.(author)
Electrons in feldspar I: On the wavefunction of electrons trapped at simple lattice defects
DEFF Research Database (Denmark)
Poolton, H.R.J.; Wallinga, J.; Murray, A.S.
2002-01-01
The purpose of this article is to make an initial consideration of the physical properties of electrons trapped at classic hydrogenic lattice defects in feldspar. We are particularly interested to determine the radial extent of the electron wavefunctions in the ground and excited states. It is sh......The purpose of this article is to make an initial consideration of the physical properties of electrons trapped at classic hydrogenic lattice defects in feldspar. We are particularly interested to determine the radial extent of the electron wavefunctions in the ground and excited states...
DFT computations of the lattice constant, stable atomic structure and ...
African Journals Online (AJOL)
This paper presents the most stable atomic structure and lattice constant of Fullerenes (C60). FHI-aims DFT code was used to predict the stable structure and the computational lattice constant of C60. These were compared with known experimental structures and lattice constants of C60. The results obtained showed that ...
Transfer-matrix approach for modulated structures with defects
International Nuclear Information System (INIS)
Kostyrko, T.
2000-01-01
We consider scattering of electrons by defects in a periodically modulated, quasi-one-dimensional structure, within a tight-binding model. Combining a transfer matrix method and a Green function method we derive a formula for a Landauer conductance and show its equivalence to the result of Kubo linear response theory. We obtain explicitly unperturbed lattice Green functions from their equations of motion, using the transfer matrices. We apply the presented formalism in computations of the conductance of several multiband modulated structures with defects: (a) carbon nanotubes (b) two-dimensional (2D) superlattice (c) modulated leads with 1D wire in the tunneling regime. (c) 2000 The American Physical Society
Packing defects into ordered structures
DEFF Research Database (Denmark)
Bechstein, R.; Kristoffersen, Henrik Høgh; Vilhelmsen, L.B.
2012-01-01
. With the help of density functional theory calculations we develop a complete structural model for the entire strand and demonstrate these adstructures to be more stable than an equivalent amount of bulk defects such as Ti interstitials. We argue that strands can form particularly easy on stepped surfaces......We have studied vicinal TiO2(110) surfaces by high-resolution scanning tunneling microscopy and density functional theory calculations. On TiO2 surfaces characterized by a high density of ⟨11̅ 1⟩ steps, scanning tunneling microscopy reveals a high density of oxygen-deficient strandlike adstructures...
Lattice QCD Calculation of Nucleon Structure
International Nuclear Information System (INIS)
Liu, Keh-Fei; Draper, Terrence
2016-01-01
It is emphasized in the 2015 NSAC Long Range Plan that 'understanding the structure of hadrons in terms of QCD's quarks and gluons is one of the central goals of modern nuclear physics.' Over the last three decades, lattice QCD has developed into a powerful tool for ab initio calculations of strong-interaction physics. Up until now, it is the only theoretical approach to solving QCD with controlled statistical and systematic errors. Since 1985, we have proposed and carried out first-principles calculations of nucleon structure and hadron spectroscopy using lattice QCD which entails both algorithmic development and large-scale computer simulation. We started out by calculating the nucleon form factors -- electromagnetic, axial-vector, ?NN, and scalar form factors, the quark spin contribution to the proton spin, the strangeness magnetic moment, the quark orbital angular momentum, the quark momentum fraction, and the quark and glue decomposition of the proton momentum and angular momentum. The first round of calculations were done with Wilson fermions in the 'quenched' approximation where the dynamical effects of the quarks in the sea are not taken into account in the Monte Carlo simulation to generate the background gauge configurations. Beginning in 2000, we have started implementing the overlap fermion formulation into the spectroscopy and structure calculations. This is mainly because the overlap fermion honors chiral symmetry as in the continuum. It is going to be more and more important to take the symmetry into account as the simulations move closer to the physical point where the u and d quark masses are as light as a few MeV only. We began with lattices which have quark masses in the sea corresponding to a pion mass at ~ 300 MeV and obtained the strange form factors, charm and strange quark masses, the charmonium spectrum and the D_s meson decay constant f_D__s, the strangeness and charmness, the meson mass decomposition and the strange quark spin from the
Lattice QCD Calculation of Nucleon Structure
Energy Technology Data Exchange (ETDEWEB)
Liu, Keh-Fei [University of Kentucky, Lexington, KY (United States). Dept. of Physics and Astronomy; Draper, Terrence [University of Kentucky, Lexington, KY (United States). Dept. of Physics and Astronomy
2016-08-30
It is emphasized in the 2015 NSAC Long Range Plan that "understanding the structure of hadrons in terms of QCD's quarks and gluons is one of the central goals of modern nuclear physics." Over the last three decades, lattice QCD has developed into a powerful tool for ab initio calculations of strong-interaction physics. Up until now, it is the only theoretical approach to solving QCD with controlled statistical and systematic errors. Since 1985, we have proposed and carried out first-principles calculations of nucleon structure and hadron spectroscopy using lattice QCD which entails both algorithmic development and large-scale computer simulation. We started out by calculating the nucleon form factors -- electromagnetic, axial-vector, πNN, and scalar form factors, the quark spin contribution to the proton spin, the strangeness magnetic moment, the quark orbital angular momentum, the quark momentum fraction, and the quark and glue decomposition of the proton momentum and angular momentum. The first round of calculations were done with Wilson fermions in the `quenched' approximation where the dynamical effects of the quarks in the sea are not taken into account in the Monte Carlo simulation to generate the background gauge configurations. Beginning in 2000, we have started implementing the overlap fermion formulation into the spectroscopy and structure calculations. This is mainly because the overlap fermion honors chiral symmetry as in the continuum. It is going to be more and more important to take the symmetry into account as the simulations move closer to the physical point where the u and d quark masses are as light as a few MeV only. We began with lattices which have quark masses in the sea corresponding to a pion mass at ~ 300 MeV and obtained the strange form factors, charm and strange quark masses, the charmonium spectrum and the D_{s} meson decay constant f_{Ds}, the strangeness and charmness, the meson mass
Transmutation doping and lattice defects in degenerate InSb
International Nuclear Information System (INIS)
Gerstenberg, H.; Glaeser, W.
1990-01-01
n-type InSb single crystals were irradiated with thermal neutrons below T = 6 K. The Shubnikov-de Haas effect and the resistivity ρ(T = 4.6 K) were measured as a function of the neutron dose and the holding temperature of a subsequent annealing program. The results are discussed in terms of the transport scattering rate and the lifetime of the Landau-levels. They have to be interpreted by means of n-doping due to nuclear reactions and irradiation induced negatively charged defects. Almost complete annealing of the transport parameters can be achieved by heating the samples to T A = 400 K. (author)
Decelerating defects and non-ergodic critical behaviour in a unidirectionally coupled map lattice
International Nuclear Information System (INIS)
Ashwin, Peter; Sturman, Rob
2003-01-01
We examine a coupled map lattice (CML) consisting of an infinite chain of logistic maps coupled in one direction by inhibitory coupling. We find that for sufficiently strong coupling strength there are dynamical states with 'decelerating defects', where defects between stable patterns (with chaotic temporal evolution and average spatial period two) slow down but never stop. These defects annihilate each other when they meet. We show for certain states that this leads to a lack of convergence (non-ergodicity) of averages taken from observables in the system and conjecture that this is typical for the system
Defect solitons in saturable nonlinearity media with parity-time symmetric optical lattices
Energy Technology Data Exchange (ETDEWEB)
Hu, Sumei [Department of Physics, Guangdong University of Petrochemical Technology, Maoming 525000 (China); Laboratory of Nanophotonic Functional Materials and Devices, South China Normal University, Guangzhou 510631 (China); Hu, Wei, E-mail: huwei@scnu.edu.cn [Laboratory of Nanophotonic Functional Materials and Devices, South China Normal University, Guangzhou 510631 (China)
2013-11-15
We reported the existence and stability of defect solitons in saturable nonlinearity media with parity-time (PT) symmetric optical lattices. Families of fundamental and dipole solitons are found in the semi-infinite gap and the first gap. The power of solitons increases with the increasing of the propagation constant and saturation parameter. The existence areas of fundamental and dipole solitons shrink with the growth of saturation parameter. The instability of dipole solitons for positive and no defect induced by the imaginary part of PT symmetric potentials can be suppressed by the saturation nonlinearity, but for negative defect it cannot be suppressed by the saturation nonlinearity.
Thin-walled reinforcement lattice structure for hollow CMC buckets
de Diego, Peter
2017-06-27
A hollow ceramic matrix composite (CMC) turbine bucket with an internal reinforcement lattice structure has improved vibration properties and stiffness. The lattice structure is formed of thin-walled plies made of CMC. The wall structures are arranged and located according to high stress areas within the hollow bucket. After the melt infiltration process, the mandrels melt away, leaving the wall structure to become the internal lattice reinforcement structure of the bucket.
Computer code for the atomistic simulation of lattice defects and dynamics
International Nuclear Information System (INIS)
Schiffgens, J.O.; Graves, N.J.; Oster, C.A.
1980-04-01
This document has been prepared to satisfy the need for a detailed, up-to-date description of a computer code that can be used to simulate phenomena on an atomistic level. COMENT was written in FORTRAN IV and COMPASS (CDC assembly language) to solve the classical equations of motion for a large number of atoms interacting according to a given force law, and to perform the desired ancillary analysis of the resulting data. COMENT is a dual-purpose intended to describe static defect configurations as well as the detailed motion of atoms in a crystal lattice. It can be used to simulate the effect of temperature, impurities, and pre-existing defects on radiation-induced defect production mechanisms, defect migration, and defect stability
Computer code for the atomistic simulation of lattice defects and dynamics. [COMENT code
Energy Technology Data Exchange (ETDEWEB)
Schiffgens, J.O.; Graves, N.J.; Oster, C.A.
1980-04-01
This document has been prepared to satisfy the need for a detailed, up-to-date description of a computer code that can be used to simulate phenomena on an atomistic level. COMENT was written in FORTRAN IV and COMPASS (CDC assembly language) to solve the classical equations of motion for a large number of atoms interacting according to a given force law, and to perform the desired ancillary analysis of the resulting data. COMENT is a dual-purpose intended to describe static defect configurations as well as the detailed motion of atoms in a crystal lattice. It can be used to simulate the effect of temperature, impurities, and pre-existing defects on radiation-induced defect production mechanisms, defect migration, and defect stability.
The ambivalent effect of lattice structure on a spatial game
Zhang, Hui; Gao, Meng; Li, Zizhen; Maa, Zhihui; Wang, Hailong
2011-06-01
The evolution of cooperation is studied in lattice-structured populations, in which each individual who adopts one of the following strategies ‘always defect' (ALLD), ‘tit-for-tat' (TFT), and ‘always cooperate' (ALLC) plays the repeated Prisoner's Dilemma game with its neighbors according to an asynchronous update rule. Computer simulations are applied to analyse the dynamics depending on major parameters. Mathematical analyses based on invasion probability analysis, mean-field approximation, as well as pair approximation are also used. We find that the lattice structure promotes the evolution of cooperation compared with a non-spatial population, this is also confirmed by invasion probability analysis in one dimension. Meanwhile, it also inhibits the evolution of cooperation due to the advantage of being spiteful, which indicates the key role of specific life-history assumptions. Mean-field approximation fails to predict the outcome of computer simulations. Pair approximation is accurate in two dimensions but fails in one dimension.
Lattice defects in ion-implanted aluminium studied by means of perturbed angular correlations. Pt. 1
International Nuclear Information System (INIS)
Pleiter, F.; Prasad, K.G.
1984-01-01
Migration and clustering of lattice defects after implantation of 111 In in Al and subsequent annealing at temperatures in the range from 80 to 800 K were investigated applying the DPAC technique. The effects of implantation dose, implantation temperature, laser irradiation, and plastic deformation were studied. The measurements on plastically deformed Al were complemented by positron lifetime measurements. Four In-defect clusters were observed that can be flagged by well-defined hyperfine interaction parameters, and their symmetry properties were determined by using single-crystal samples. Important conclusions are: (i) monovacancies are not trapped by In-atoms, (ii) small In-defect clusters are formed by direct trapping of divacancies and/or trivacancies, and (iii) extended In-defect clusters are very stable and anneal in the temperature range 600-700 K. Consequences for the interpretation of other measurements on dilute Al(In) alloys are discussed. (Auth.)
Ganesan, K; Ghosh, Subrata; Gopala Krishna, Nanda; Ilango, S; Kamruddin, M; Tyagi, A K
2016-08-10
Defects in planar and vertically oriented nanographitic structures (NGSs) synthesized by plasma enhanced chemical vapor deposition (PECVD) have been investigated using Raman and X-ray photoelectron spectroscopy. While Raman spectra reveal the dominance of vacancy and boundary type defects respectively in vertical and planar NGSs, XPS provides additional information on vacancy related defect peaks in the C 1s spectrum, which originate from non-conjugated carbon atoms in the hexagonal lattice. Although an excellent correlation prevails between these two techniques, our results show that estimation of surface defects by XPS is more accurate than Raman analysis. Nuances of these techniques are discussed in the context of assessing defects in nanographitic structures.
Energy Technology Data Exchange (ETDEWEB)
Schmidt, R.
2007-03-15
The present work is addressed to defects and boundaries in quantum field theory considering the application to AdS/CFT correspondence. We examine interactions of fermions with spins localised on these boundaries. Therefore, an algebra method is emphasised adding reflection and transmission terms to the canonical quantisation prescription. This method has already been applied to bosons in two space-time dimensions before. We show the possibilities of such reflection-transmission algebras in two, three, and four dimensions. We compare with models of solid state physics as well as with the conformal field theory approach to the Kondo effect. Furthermore, we discuss ansatzes of extensions to lattice structures. (orig.)
Energy Technology Data Exchange (ETDEWEB)
Arroyo Rojas Dasilva, Yadira; Kozak, Roksolana; Erni, Rolf; Rossell, Marta D., E-mail: marta.rossell@empa.ch
2017-05-15
The development of new electro-optical devices and the realization of novel types of transistors require a profound understanding of the structural characteristics of new semiconductor heterostructures. This article provides a concise review about structural defects which occur in semiconductor heterostructures on the basis of micro-patterned Si substrates. In particular, one- and two-dimensional crystal defects are being discussed which are due to the plastic relaxation of epitaxial strain caused by the misfit of crystal lattices. Besides a few selected examples from literature, we treat in particular crystal defects occurring in GaAs/Si, Ge/Si and β-SiC/Si structures which are studied by high-resolution annular dark-field scanning transmission electron microscopy. The relevance of this article is twofold; firstly, it should provide a collection of data which are of help for the identification and characterization of defects in cubic semiconductors by means of atomic-resolution imaging, and secondly, the experimental data shall provide a basis for advancing the understanding of device characteristics with the aid of theoretical modelling by considering the defective nature of strained semiconductor heterostructures. - Highlights: • The heterogeneous integration of high-quality compound semiconductors remains a challenge. • Lattice defects cause severe degradation of the semiconductor device performances. • Aberration-corrected HAADF-STEM allows atomic-scale characterization of defects. • An overview of lattice defects found in cubic semiconductors is presented. • Theoretical modelling and calculations are needed to determine the defect properties.
Program LATTICE for Calculation of Parameters of Targets with Heterogeneous (Lattice) Structure
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 %.
Determining the Mechanical Properties of Lattice Block Structures
Wilmoth, Nathan
2013-01-01
Lattice block structures and shape memory alloys possess several traits ideal for solving intriguing new engineering problems in industries such as aerospace, military, and transportation. Recent testing at the NASA Glenn Research Center has investigated the material properties of lattice block structures cast from a conventional aerospace titanium alloy as well as lattice block structures cast from nickel-titanium shape memory alloy. The lattice block structures for both materials were sectioned into smaller subelements for tension and compression testing. The results from the cast conventional titanium material showed that the expected mechanical properties were maintained. The shape memory alloy material was found to be extremely brittle from the casting process and only compression testing was completed. Future shape memory alloy lattice block structures will utilize an adjusted material composition that will provide a better quality casting. The testing effort resulted in baseline mechanical property data from the conventional titanium material for comparison to shape memory alloy materials once suitable castings are available.
Defect structure of electrodeposited chromium layers
International Nuclear Information System (INIS)
Marek, T.; Suevegh, K.; Vertes, A.; El-Sharif, M.; McDougall, J.; Chisolm, C.U.
2000-01-01
Positron annihilation spectroscopy was applied to study the effects of pre-treatment and composition of substrates on the quality and defect structure of electrodeposited thick chromium coatings. The results show that both parameters are important, and a scenario is proposed why the mechanically polished substrate gives more defective film than the electro polished one.
Defect structure of electrodeposited chromium layers
Energy Technology Data Exchange (ETDEWEB)
Marek, T. E-mail: marek@para.chem.elte.hu; Suevegh, K.; Vertes, A.; El-Sharif, M.; McDougall, J.; Chisolm, C.U
2000-06-01
Positron annihilation spectroscopy was applied to study the effects of pre-treatment and composition of substrates on the quality and defect structure of electrodeposited thick chromium coatings. The results show that both parameters are important, and a scenario is proposed why the mechanically polished substrate gives more defective film than the electro polished one.
Pawlak algebra and approximate structure on fuzzy lattice.
Zhuang, Ying; Liu, Wenqi; Wu, Chin-Chia; Li, Jinhai
2014-01-01
The aim of this paper is to investigate the general approximation structure, weak approximation operators, and Pawlak algebra in the framework of fuzzy lattice, lattice topology, and auxiliary ordering. First, we prove that the weak approximation operator space forms a complete distributive lattice. Then we study the properties of transitive closure of approximation operators and apply them to rough set theory. We also investigate molecule Pawlak algebra and obtain some related properties.
Dislocations and related defects in niobium oxide structures
Energy Technology Data Exchange (ETDEWEB)
Anderson, J S; Hutchinson, J L; Lincoln, F J [Oxford Univ. (UK). Inorganic Chemistry Lab.
1977-01-07
Lattice images of the niobium oxides, structures based on the linkage of octahedral groups in continuous networks, occasionally contain features recognizable as dislocations. Since lattice imaging enables the microstructure to be resolved in greater detail, at the level of local structural organization, it is possible to determine the configuration, and also to infer the chemical composition, of dislocated areas. By treating the niobium oxide 'block' structures as superstructures of the ReO/sub 3/ (DO/sub 9/) type, the topology of dislocations can be expressed by relations between the insertion (or deletion) of one or more half-planes of cations, or of oxygen atoms only, changes in the number of crystallographic shear plane interfaces between blocks or columns, changes in (idealized) dimensions and any requisite distortion in the third dimension. Mapping the structure around a dislocation, from the lattice image, is directly equivalent to plotting the Burgers' circuit. In this way, the precise nature of a dislocating perturbation and its implications for the local chemical composition of the crystal can be directly identified. The method is exemplified by analysis of dislocations and of related extended defects of several types, associated with twinning phenomena, semicoherent intergrowth between different ReO/sub 3/-type superstructures and arrays building up a low angle boundary. The essential features of the analysis are not restricted to structures of the niobium oxide type, but can be extended to other types of polyhedron networks.
X-ray three beam cases and the influence of lattice defects
International Nuclear Information System (INIS)
Scherz, W.; Hildebrandt, G.
1981-01-01
The three beam cases (111 anti 111; 200) (Case I) and (111, anti 1anti 11; 220) (Case II) in germanium were examined with CuKα 1 radiation from a bent quartz monochromator crystal. For the intensity relation Isub(O)/(Isub(L) + Isub(M)), excellent agreement with precious measurements (Uebach) resulted for Case I; small deviations from a calculated value could be explained by theoretical arguments, considering the crystal as slightly imperfect. In Case II, which reacted more sensitively upon lattice defects, these deviations were much larger and in an unexpexted direction. A first attempt of a 'Three Beam Lang Topography' is reported. (orig.)
Atomistic observations and analyses of lattice defects in transmission electron microscopes
Abe, H
2003-01-01
The transmission electron microscope (TEM) -accelerators was developed. TEM-Accelerator made possible to observe in situ experiments of ion irradiation and implantation. The main results are the experimental proof of new lattice defects by irradiation, the formation process and synthesized conditions of carbon onion by ion implantation, the microstructure and phase transformation conditions of graphite by ion irradiated phase transformation, the irradiation damage formation process by simultaneous irradiation of electron and ion and behavior of fullerene whisker under irradiation. The microstructural evolution of defect clusters in copper irradiated with 240-keV Cu sup + ions and a high resolution electron micrograph of carbon onions synthesized by ion implantation are explained as the examples of recent researches. (S.Y.)
The Developement of A Lattice Structured Database
DEFF Research Database (Denmark)
Bruun, Hans
In this project we have investigated the possibilities to make a system based on the concept algebra described in [3], [4] and [5]. The concept algebra is used for ontology specification and knowledge representation. It is a distributive lattice extended with attribution operations. One of the main...... ideas in this work is to use Birkhoff's representation theorem, so we represent distributive lattices using its dual representation: the partial order of join irreducibles. We show how to construct a concept algebra satisfying a given set of equations. The universal/initial algebra is usually too big...
Lattice Modeling of Early-Age Behavior of Structural Concrete
Pan, Yaming; Prado, Armando; Porras, Roc?o; Hafez, Omar M.; Bolander, John E.
2017-01-01
The susceptibility of structural concrete to early-age cracking depends on material composition, methods of processing, structural boundary conditions, and a variety of environmental factors. Computational modeling offers a means for identifying primary factors and strategies for reducing cracking potential. Herein, lattice models are shown to be adept at simulating the thermal-hygral-mechanical phenomena that influence early-age cracking. In particular, this paper presents a lattice-based ap...
Designing lattice structures with maximal nearest-neighbor entanglement
Energy Technology Data Exchange (ETDEWEB)
Navarro-Munoz, J C; Lopez-Sandoval, R [Instituto Potosino de Investigacion CientIfica y Tecnologica, Camino a la presa San Jose 2055, 78216 San Luis Potosi (Mexico); Garcia, M E [Theoretische Physik, FB 18, Universitaet Kassel and Center for Interdisciplinary Nanostructure Science and Technology (CINSaT), Heinrich-Plett-Str.40, 34132 Kassel (Germany)
2009-08-07
In this paper, we study the numerical optimization of nearest-neighbor concurrence of bipartite one- and two-dimensional lattices, as well as non-bipartite two-dimensional lattices. These systems are described in the framework of a tight-binding Hamiltonian while the optimization of concurrence was performed using genetic algorithms. Our results show that the concurrence of the optimized lattice structures is considerably higher than that of non-optimized systems. In the case of one-dimensional chains, the concurrence increases dramatically when the system begins to dimerize, i.e., it undergoes a structural phase transition (Peierls distortion). This result is consistent with the idea that entanglement is maximal or shows a singularity near quantum phase transitions. Moreover, the optimization of concurrence in two-dimensional bipartite and non-bipartite lattices is achieved when the structures break into smaller subsystems, which are arranged in geometrically distinguishable configurations.
Electronic structure of point defects in semiconductors
International Nuclear Information System (INIS)
Bruneval, Fabien
2014-01-01
This 'Habilitation a diriger des Recherches' memoir presents most of my scientific activities during the past 7 years, in the field of electronic structure calculations of defects in solids. Point defects (vacancies, interstitials, impurities) in functional materials are a key parameter to determine if these materials will actually fill the role they have been assigned or not. Indeed, the presence of defects cannot be avoided when the temperature is increased or when the material is subjected to external stresses, such as irradiation in the nuclear reactors and in artificial satellites with solar radiations. However, in many cases, defects are introduced in the materials on purpose to tune the electronic transport, optical or even magnetic properties. This procedure is called the doping of semiconductors, which is the foundation technique for transistors, diodes, or photovoltaic cells. However, doping is not always straightforward and unexpected features may occur, such as doping asymmetry or Fermi level pinning, which can only be explained by complex phenomena involving different types of defects or complexes of defects. In this context, the calculations of electronic structure ab initio is an ideal tool to complement the experimental observations, to gain the understanding of phenomena at the atomic level, and even to predict the properties of defects. The power of the ab initio calculations comes from their ability to describe any system of electrons and nuclei without any specific adjustment. But although there is a strong need for numerical simulations in this field, the ab initio calculations for defects are still under development as of today. The work presented in this memoir summarizes my contributions to methodological developments on this subject. These developments have followed two main tracks. The first topic is the better understanding of the unavoidable finite size effects. Indeed, defects in semiconductors or insulators are generally present in
Hattori, M.; Suzuki, H.; Seko, Y.; Takai, K.
2017-08-01
Studies to date have not completely determined the factors influencing hydrogen embrittlement of ferrite/bainite X80 pipeline steel. Hydrogen embrittlement susceptibility was evaluated based on fracture strain in tensile testing. We conducted a thermal desorption analysis to measure the amount of tracer hydrogen corresponding to that of lattice defects. Hydrogen embrittlement susceptibility and the amount of tracer hydrogen significantly increased with decreasing crosshead speed. Additionally, a significant increase in the formation of hydrogen-enhanced strain-induced lattice defects was observed immediately before the final fracture. In contrast to hydrogen-free specimens, the fracture surface of the hydrogen-charged specimens exhibited shallower dimples without nuclei, such as secondary phase particles. These findings indicate that the presence of hydrogen enhanced the formation of lattice defects, particularly just prior to the occurrence of final fracture. This in turn enhanced the formation of shallower dimples, thereby potentially causing premature fracture of X80 pipeline steel at lower crosshead speeds.
Electronic structure of defects in semiconductor heterojunctions
International Nuclear Information System (INIS)
Haussy, Bernard; Ganghoffer, Jean Francois
2002-01-01
Full text.heterojunctions and semiconductors and superlattices are well known and well used by people interested in optoelectronics communications. Components based on the use of heterojunctions are interesting for confinement of light and increase of quantum efficiency. An heterojunction is the contact zone between two different semiconductors, for example GaAs and Ga 1-x Al x As. Superlattices are a succession of heterojunctions (up to 10 or 20). These systems have been the subjects of many experiments ao analyse the contact between semiconductors. They also have been theoretically studied by different types of approach. The main result of those studies is the prediciton of band discontinuities. Defects in heterojunctions are real traps for charge carriers; they can affect the efficiency of the component decreasing the currents and the fluxes in it. the knowledge of their electronic structure is important, a great density of defects deeply modifies the electronic structure of the whole material creating real new bands of energy in the band structure of the component. in the first part of this work, we will describe the heterostructure and the defect in terms of quantum wells and discrete levels. This approach allows us to show the role of the width of the quantum well describing the structure but induces specific behaviours due to the one dimensional modelling. Then a perturbative treatment is proposed using the Green's functions formalism. We build atomic chains with different types of atoms featuring the heterostructure and the defect. Densities of states of a structure with a defect and levels associated to the defect are obtained. Results are comparable with the free electrons work, but the modelling do not induce problems due to a one dimensional approach. To extend our modelling, a three dimensions approach, based on a cavity model, is investigated. The influence of the defect, - of hydrogenoid type - introduced in the structure, is described by a cavity
Energy Technology Data Exchange (ETDEWEB)
Xu Xixiang, E-mail: xu_xixiang@hotmail.co [College of Science, Shandong University of Science and Technology, Qingdao, 266510 (China)
2010-01-04
An integrable coupling family of Merola-Ragnisco-Tu lattice systems is derived from a four-by-four matrix spectral problem. The Hamiltonian structure of the resulting integrable coupling family is established by the discrete variational identity. Each lattice system in the resulting integrable coupling family is proved to be integrable discrete Hamiltonian system in Liouville sense. Ultimately, a nonisospectral integrable lattice family associated with the resulting integrable lattice family is constructed through discrete zero curvature representation.
International Nuclear Information System (INIS)
Xu Xixiang
2010-01-01
An integrable coupling family of Merola-Ragnisco-Tu lattice systems is derived from a four-by-four matrix spectral problem. The Hamiltonian structure of the resulting integrable coupling family is established by the discrete variational identity. Each lattice system in the resulting integrable coupling family is proved to be integrable discrete Hamiltonian system in Liouville sense. Ultimately, a nonisospectral integrable lattice family associated with the resulting integrable lattice family is constructed through discrete zero curvature representation.
Investigation of defect structures in solids
Energy Technology Data Exchange (ETDEWEB)
Dienel, G; Hubrig, W H; Schenk, M; Syhre, H [Zentralinstitut fuer Kernforschung, Rossendorf bei Dresden (German Democratic Republic)
1976-01-01
Some central points of interest of research in the field of defect structures in solids dealt with at the Central Institute of Nuclear Research at Rossendorf in the last years are presented. Studies on f.c.c. and b.c.c. metals, radiation-induced phase transitions in perovskites and ion-implanted silicon are described in some detail.
International Nuclear Information System (INIS)
Kuramoto, E.; Nakamura, Y.; Tsutsumi, T.
1993-01-01
The interaction between an extended dislocation and a radiation-induced defect, especially, a self-interstitial atom (SIA), has been investigated in the model fcc lattice by computer simulation technique. An SIA was absorbed into the core of one of the two partial dislocations of the extended screw dislocation as a crowdion which extends along the dislocation line. Under the applied shear stress this crowdion acted as a pinning point, resulting in irradiation hardening. On the other hand, an SIA was absorbed at the jog site of the extended edge dislocation (at one of the two jog sites on two partial dislocations) and after some relaxation the total jog was shifted to one atomic distance through the spreading out of the strain due to an SIA from one partial side to the other side. (orig.)
A model for the formation of lattice defects at silicon oxide precipitates in silicon
International Nuclear Information System (INIS)
Vanhellemont, J.; Gryse, O. de; Clauws, P.
2003-01-01
The critical size of silicon oxide precipitates and the formation of lattice defects by the precipitates are discussed. An expression is derived allowing estimation of self-interstitial emission by spherical precipitates as well as strain build-up during precipitate growth. The predictions are compared with published experimental data. A model for stacking fault nucleation at oxide precipitates is developed based on strain and self-interstitial accumulation during the thermal history of the wafer. During a low-temperature treatment high levels of strain develop. During subsequent high-temperature treatment, excess strain energy in the precipitate is released by self-interstitial emission leading to favourable conditions for stacking fault nucleation
Superalloy Lattice Block Developed for Use in Lightweight, High-Temperature Structures
Hebsur, Mohan G.; Whittenberger, J. Daniel; Krause, David L.
2003-01-01
Successful development of advanced gas turbine engines for aircraft will require lightweight, high-temperature components. Currently titanium-aluminum- (TiAl) based alloys are envisioned for such applications because of their lower density (4 g/cm3) in comparison to superalloys (8.5 g/cm3), which have been utilized for hot turbine engine parts for over 50 years. However, a recently developed concept (lattice block) by JAMCORP, Inc., of Willmington, Massachusetts, would allow lightweight, high-temperature structures to be directly fabricated from superalloys and, thus, take advantage of their well-known, characterized properties. In its simplest state, lattice block is composed of thin ligaments arranged in a three dimensional triangulated trusslike configuration that forms a structurally rigid panel. Because lattice block can be fabricated by casting, correctly sized hardware is produced with little or no machining; thus very low cost manufacturing is possible. Together, the NASA Glenn Research Center and JAMCORP have extended their lattice block methodology for lower melting materials, such as Al alloys, to demonstrate that investment casting of superalloy lattice block is possible. This effort required advances in lattice block pattern design and assembly, higher temperature mold materials and mold fabrication technology, and foundry practice suitable for superalloys (ref. 1). Lattice block panels have been cast from two different Ni-base superalloys: IN 718, which is the most commonly utilized superalloy and retains its strength up to 650 C; and MAR M247, which possesses excellent mechanical properties to at least 1100 C. In addition to the open-cell lattice block geometry, same-sized lattice block panels containing a thin (1-mm-thick) solid face on one side have also been cast from both superalloys. The elevated-temperature mechanical properties of the open cell and face-sheeted superalloy lattice block panels are currently being examined, and the
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
Nucleon structure functions from lattice operator product expansion
Energy Technology Data Exchange (ETDEWEB)
Chambers, A.J.; Somfleth, K.; Young, R.D.; Zanotti, J.M. [Adelaide Univ., SA (Australia). CSSM, Dept. of Physics; Horsley, R. [Edinburgh Univ. (United Kingdom). School of Physics and Astronomy; Nakamura, Y. [RIKEN Advanced Institute for Computational Science, Kobe (Japan); Perlt, H.; Schiller, A. [Leipzig Univ. (Germany). Inst. fuer Theoretische Physik; Rakow, P.E.L. [Liverpool Univ. (United Kingdom). Theoretical Physics Div.; Schierholz, G. [Deutsches Elektronen-Synchrotron (DESY), Hamburg (Germany)
2017-03-15
Deep-inelastic scattering, in the laboratory and on the lattice, is most instructive for understanding how the nucleon is built from quarks and gluons. The long-term goal is to compute the associated structure functions from first principles. So far this has been limited to model calculations. In this Letter we propose a new method to compute the structure functions directly from the virtual, all-encompassing Compton amplitude, utilizing the operator product expansion. This overcomes issues of renormalization and operator mixing, which so far have hindered lattice calculations of power corrections and higher moments.
Initial Mechanical Testing of Superalloy Lattice Block Structures Conducted
Krause, David L.; Whittenberger, J. Daniel
2002-01-01
The first mechanical tests of superalloy lattice block structures produced promising results for this exciting new lightweight material system. The testing was performed in-house at NASA Glenn Research Center's Structural Benchmark Test Facility, where small subelement-sized compression and beam specimens were loaded to observe elastic and plastic behavior, component strength levels, and fatigue resistance for hundreds of thousands of load cycles. Current lattice block construction produces a flat panel composed of thin ligaments arranged in a three-dimensional triangulated trusslike structure. Investment casting of lattice block panels has been developed and greatly expands opportunities for using this unique architecture in today's high-performance structures. In addition, advances made in NASA's Ultra-Efficient Engine Technology Program have extended the lattice block concept to superalloy materials. After a series of casting iterations, the nickel-based superalloy Inconel 718 (IN 718, Inco Alloys International, Inc., Huntington, WV) was successfully cast into lattice block panels; this combination offers light weight combined with high strength, high stiffness, and elevated-temperature durability. For tests to evaluate casting quality and configuration merit, small structural compression and bend test specimens were machined from the 5- by 12- by 0.5-in. panels. Linear elastic finite element analyses were completed for several specimen layouts to predict material stresses and deflections under proposed test conditions. The structural specimens were then subjected to room-temperature static and cyclic loads in Glenn's Life Prediction Branch's material test machine. Surprisingly, the test results exceeded analytical predictions: plastic strains greater than 5 percent were obtained, and fatigue lives did not depreciate relative to the base material. These assets were due to the formation of plastic hinges and the redundancies inherent in lattice block construction
Modeling of Triangular Lattice Space Structures with Curved Battens
Chen, Tzikang; Wang, John T.
2005-01-01
Techniques for simulating an assembly process of lattice structures with curved battens were developed. The shape of the curved battens, the tension in the diagonals, and the compression in the battens were predicted for the assembled model. To be able to perform the assembly simulation, a cable-pulley element was implemented, and geometrically nonlinear finite element analyses were performed. Three types of finite element models were created from assembled lattice structures for studying the effects of design and modeling variations on the load carrying capability. Discrepancies in the predictions from these models were discussed. The effects of diagonal constraint failure were also studied.
Nucleon structure functions from lattice operator product expansion
International Nuclear Information System (INIS)
Chambers, A.J.; Somfleth, K.; Young, R.D.; Zanotti, J.M.; Perlt, H.; Schiller, A.
2017-03-01
Deep-inelastic scattering, in the laboratory and on the lattice, is most instructive for understanding how the nucleon is built from quarks and gluons. The long-term goal is to compute the associated structure functions from first principles. So far this has been limited to model calculations. In this Letter we propose a new method to compute the structure functions directly from the virtual, all-encompassing Compton amplitude, utilizing the operator product expansion. This overcomes issues of renormalization and operator mixing, which so far have hindered lattice calculations of power corrections and higher moments.
Nucleon Structure Functions from Operator Product Expansion on the Lattice.
Chambers, A J; Horsley, R; Nakamura, Y; Perlt, H; Rakow, P E L; Schierholz, G; Schiller, A; Somfleth, K; Young, R D; Zanotti, J M
2017-06-16
Deep-inelastic scattering, in the laboratory and on the lattice, is most instructive for understanding how the nucleon is built from quarks and gluons. The long-term goal is to compute the associated structure functions from first principles. So far this has been limited to model calculations. In this Letter we propose a new method to compute the structure functions directly from the virtual, all-encompassing Compton amplitude, utilizing the operator product expansion. This overcomes issues of renormalization and operator mixing, which so far have hindered lattice calculations of power corrections and higher moments.
Plain defects and their vortex configuration in dilute Mo-B alloys in dissipative structure
International Nuclear Information System (INIS)
Sofronova, R.M.
1992-01-01
Electron microscopic study of single crystal of Mo-0.003 mas.% B alloy after zone melting and annealing at 2373 K was conducted to reveal the nature of planar defects and the role of boron in their formation. It was shown that planar defects should be considered as preprecipitations of MoB nonequilibrous phase out of molybdenum base solid solution. A planar defect was found to constitute a monolayer of boron atoms which consisted of B-B zigzag-like chains. Inturn the chains were surrounded by Mo atoms which formed hexagonal prism. The coherency of planar defects with matrix was due to close lattice parameters of Mo, β-MoB and δ-MoB. The planar defects in molybdenum base alloy were considered as elements of dissipative structure. They determined formation of supercellular dislocation structure under deformation
Defect luminescence and lattice strain in Mn{sup 2+} doped ZnGa{sub 2}O{sub 4}
Energy Technology Data Exchange (ETDEWEB)
Somasundaram, K.; Abhilash, K.P. [Department of Physics, Nallamuthu Gounder Mahalingam College, Pollachi, 642001 Coimbatore (India); Sudarsan, V., E-mail: vsudar@barc.gov.in [Chemistry Division, Bhabha Atomic Research Centre, Trombay, Mumbai 400085 (India); Christopher Selvin, P., E-mail: pcsphyngmc@rediffmail.com [Department of Physics, Nallamuthu Gounder Mahalingam College, Pollachi, 642001 Coimbatore (India); Kadam, R.M. [Radiochemistry Division, Bhabha Atomic Research Centre, Trombay, Mumbai 400085 (India)
2016-06-15
Undoped and Mn{sup 2+} doped ZnGa{sub 2}O{sub 4} phosphors were prepared by solution combustion method and characterized by XRD, SEM, luminescence and electron paramagnetic resonance (EPR) techniques. Based on XRD results, it is inferred that, strain in ZnGa{sub 2}O{sub 4} host lattice increases with incorporation of Mn{sup 2+} ions in the lattice. Mn{sup 2+} doping at concentration levels investigated, lead to significant reduction in the defect emission and this has been attributed to the formation of higher oxidation states of Mn ions in the lattice. Electron Paramagnetic Resonance studies confirmed that majority of Mn ions exist as Mn{sup 2+} species and they occupy tetrahedral Zn{sup 2+} site in ZnGa{sub 2}O{sub 4} lattice with an average hyperfine coupling constant, A{sub iso}∼82 G.
The electronic structure of the F-center in alkali-halides-The Bethe cluster - lattice
International Nuclear Information System (INIS)
Queiroz, S.L.A. de.
1977-07-01
The electronic structure of the F-center in alkali-halides with the NaCl structure has been studied using the Bethe Cluster lattice method. The central cluster has been taken as constituted by the vacancy and the nearest- and second-neighbors to it, respectively cations and anions. The optical transitions have been calculated and compared to experimental data on the location of the peak of the F-absorption band. The agreement obtained indicates that this method may be used to study properties of this defect in alkali halides. (Author) [pt
X-ray Tomography Characterisation of Lattice Structures Processed by Selective Electron Beam Melting
Directory of Open Access Journals (Sweden)
Everth Hernández-Nava
2017-08-01
Full Text Available Metallic lattice structures intentionally contain open porosity; however, they can also contain unwanted closed porosity within the structural members. The entrained porosity and defects within three different geometries of Ti-6Al-4V lattices, fabricated by Selective Electron Beam Melting (SEBM, is assessed from X-ray computed tomography (CT scans. The results suggest that horizontal struts that are built upon loose powder show particularly high (~20 × 10−3 vol % levels of pores, as do nodes at which many (in our case 24 struts meet. On the other hand, for struts more closely aligned (0° to 54° to the build direction, the fraction of porosity appears to be much lower (~0.17 × 10−3% arising mainly from pores contained within the original atomised powder particles.
A conceivable lattice structure of the Coulomb law
International Nuclear Information System (INIS)
Papp, E.; Santilli, R.M.
1983-01-01
A few heuristic remarks on recent extensions of the Coulomb law via effective potentials and other means, which appear to admit a lattice structure in time and space whose spacing are given by the characteristic period of the elctron and its Compton wave-length, respectively, are presented
Some recent work on lattice structures for digital signal processing
Indian Academy of Sciences (India)
Digital signal processing (DSP); lattice structures; finite impulse ... fascinated this author for a long time, and for the known non-canonical ...... where M
The fixed point structure of lattice field theories
International Nuclear Information System (INIS)
Baier, R.; Reusch, H.J.; Lang, C.B.
1989-01-01
Monte-Carlo renormalization group methods allow to analyze lattice regularized quantum field theories. The properties of the quantized field theory in the continuum may be recovered at a critical point of the lattice model. This requires a study of the phase diagram and the renormalization flow structure of the coupling constants. As an example the authors discuss the results of a recent MCRG investigation of the SU(2) adjoint Higgs model, where they find evidence for the existence of a tricritical point at finite values of the inverse gauge coupling β
Polarized and unpolarized nucleon structure functions from lattice QCD
International Nuclear Information System (INIS)
Goeckeler, M.; Technische Hochschule Aachen; Horsley, R.; Humboldt-Universitaet, Berlin; Ilgenfritz, E.M.; Perlt, H.; Rakow, P.; Schierholz, G.; Forschungszentrum Juelich GmbH; Schiller, A.
1995-06-01
We report on a high statistics quenched lattice QCD calculation of the deep-inelastic structure functions F 1 , F 2 , g 1 and g 2 of the proton and neutron. The theoretical basis for the calculation is the operator product expansion. We consider the moments of the leading twist operators up to spin four. Using Wilson fermions the calculation is done for three values of K, and we perform the extrapolation to the chiral limit. The renormalization constants, which lead us from lattice to continuum operators, are calculated in perturbation theory to one loop order. (orig.)
Many-beam effects in electron microscope images of lattice defects
International Nuclear Information System (INIS)
Izui, Kazuhiko; Nishida, Takahiko; Furuno, Shigemi; Otsu, Hitoshi
1974-01-01
Multi-beam effects in electron microscopic images were investigated. A computation program was developed on the basis of a matrix theory of the multi-beam effects. The matrix theory for a perfect crystal and an imperfect crystal is described, and expression for absorption coefficient is presented. The amplitude of electron wave penetrating through lattice defects is expressed by using scattering matrices which correspond to crystal slices. Calculation of extinction distance was performed, and compared with experimental results. In case of systematic reflection, the difference between two beams and from four to eight beams approximation was small, while a large effect was seen in case of accidental reflection. The intensity profile of bend contour was calculated for silicon and copper-aluminum alloy. Distance between submaxima becomes short with increase of thickness. The change in stacking fault fringes with diffraction condition was investigated. Samples were copper-aluminum alloy. Systematic behavior of the fringes was obtained, and the calculated results reproduced experimental ones. (Kato, T.)
Lattice shear distortions in fluorite structure oxides
International Nuclear Information System (INIS)
Faber, J. Jr.; Mueller, M.H.; Hitterman, R.L.
1979-01-01
Crystallographic shear distortions have been observed in fluorite structure, single crystals of UO 2 and Zr(Ca)O 2 /sub-x/ by neutron-diffraction techniques. These distortions localize on the oxygen sublattice and do not require the presence of an external strain. The internal rearrangement mode in UO 2 is a transverse, zone boundary q vector = 2π/a (0.5, 0.0) deformation with amplitude 0.014 A. In Zr(Ca)O/sub 2-x/, the mode is a longitudinal, q vector = 2-/a (0,0,0.5) deformation with amplitude 0.23 A. Cation-anion elastic interactions dominate in selecting the nature of the internal distortion
On the structure of Lattice code WIMSD-5B
International Nuclear Information System (INIS)
Kim, Won Young; Min, Byung Joo
2004-03-01
The WIMS-D code is a freely available thermal reactor physics lattice code used widely for thermal research and power reactor calculation. Now the code WIMS-AECL, developed on the basis of WIMS-D, has been used as one of lattice codes for the cell calculation in Canada and also, in 1998, the latest version WIMSD-5B is released for OECD/NEA Data Bank. While WIMS-KAERI was developed and has been used, originated from WIMS-D, in Korea, it was adjusted for the cell calculation of research reactor HANARO and so it has no confirmaty to CANDU reactor. Therefore, the code development applicable to cell calculation of CANDU reactor is necessary not only for technological independence and but also for the establishment of CANDU safety analysis system. A lattice code WIMSD-5B was analyzed in order to set the system of reactor physics computer codes, to be used in the assessment of void reactivity effect. In order to improve and validate WIMSD-5B code, the analysis of the structure of WIMSD-5B lattice code was made and so its structure, algorithm and the subroutines of WIMSD-5B were presented for the cluster type and the pij method modelling the CANDU-6 fuel
Investigation of hadronic structure by solving QCD on a lattice
International Nuclear Information System (INIS)
Grandy, J.M.
1992-01-01
Various aspects of hadronic structure are investigated by means of lattice calculations. The measurements focus on equal-time quark wavefunctions, correlations of density operators, and vacuum correlators of hadronic currents, with additional measurements of Wilson loops and hadron masses as a consistency check. The wavefunctions are shown to be consistent with a confinement model prediction. The effect of hyperfine splitting on the wavefunctions is shown to agree closely with the quark model prediction. The computed quark density correlations for the pion, rho, and proton at long range are compared with the expected asymptotic behavior. The density correlation also provides a basis for comparing the spatial extent of quark pairs surrounding the hadron with the extent of the valence quark wavefunction. Vacuum correlation functions of hadronic currents are compared with phenomenological fits to experimental data and sum rule calculations. Hadronic observable calculations are performed by evaluating path integrals in imaginary time using a Monte Carlo technique. Lattices with 16 points in the time direction and spatial volume of 12 3 and 16 3 points are used. The physical lattice spacing is 0.2 fm, and the physical volume of the lattice is large enough that the effect of spatial boundary conditions on the long range structure of the particles can be corrected in a linear fashion
Fractional vortex lattice structures in spin-triplet superconductors
International Nuclear Information System (INIS)
Chung, Suk Bum; Agterberg, Daniel F; Kim, Eun-A
2009-01-01
Motivated by recent interest in spin-triplet superconductors, we investigate the vortex lattice structures for this class of unconventional superconductors. We discuss how the order parameter symmetry can give rise to U(1)xU(1) symmetry in the same sense as in spinor condensates, making half-quantum vortices (HQVs) topologically stable. We then calculate the vortex lattice structure of HQVs, with particular attention on the roles of the crystalline lattice, the Zeeman coupling and Meissner screening, all absent in spinor condensates. Finally, we consider how spin-orbit coupling leads to a breakdown of the U(1)xU(1) symmetry in free energy and whether the HQV lattice survives this symmetry breaking. As examples, we examine simpler spin-triplet models proposed in the context of Na x CoO 2 ·yH 2 O and Bechgaard salts, as well as the better known and more complex model for Sr 2 RuO 4 .
Lattice defects of ZnO and hybrids with GO: Characterization, EPR and optoelectronic properties
Ahmed, Gulzar; Hanif, Muddasir; Mahmood, Khalid; Yao, Rihui; Ning, Honglong; jiao, Dongling; Wu, Mingmei; Khan, Javid; Liu, Zhongwu
2018-02-01
We have prepared and combined ZnO nanoparticles (ZnO-NPs) with different graphene oxide (GO) contents (10%, 20% and 30%) via microwave processing. The procedure provided well-dispersed ZnO-NPs between and onto the rGO layers (GZCs). The annealing temperature and graphene oxide contents affected the UV-Vis absorption, PL emission, defect-states of the ZnO, EPR signals, photo-electrochemical response and charge transfer properties. The HRTEM microscopy images of the GZCs showed interpenetrating structures and clearly visible vacancy defects. The results indicated that the defect sites (Zn interstitials, oxygen vacancy, ionized zinc vacancy and oxygen interstitials) significantly decreased after hybridization with GO. The photo-conversion efficiency of the GZC-10% (η = 13.1 x 10-3%), is 13 times higher than the ZnO-NPs (η = 1.02 x 10-3%) illustrating higher exciton production and separation efficiency of the GZCs under photo-excitation. The GZC-10% has lower (8-15 Ω) charge transfer resistance (Rct) compared to all the GZCs under same experimental conditions, therefore an important reason of better performance of the GZC 10%. The EPR spectra showed presence of radicals in all the samples with GZC 10% most intense signal among the different GZCs.
Lattice defects of ZnO and hybrids with GO: Characterization, EPR and optoelectronic properties
Directory of Open Access Journals (Sweden)
Gulzar Ahmed
2018-02-01
Full Text Available We have prepared and combined ZnO nanoparticles (ZnO-NPs with different graphene oxide (GO contents (10%, 20% and 30% via microwave processing. The procedure provided well-dispersed ZnO-NPs between and onto the rGO layers (GZCs. The annealing temperature and graphene oxide contents affected the UV-Vis absorption, PL emission, defect-states of the ZnO, EPR signals, photo-electrochemical response and charge transfer properties. The HRTEM microscopy images of the GZCs showed interpenetrating structures and clearly visible vacancy defects. The results indicated that the defect sites (Zn interstitials, oxygen vacancy, ionized zinc vacancy and oxygen interstitials significantly decreased after hybridization with GO. The photo-conversion efficiency of the GZC-10% (η = 13.1 x 10-3%, is 13 times higher than the ZnO-NPs (η = 1.02 x 10-3% illustrating higher exciton production and separation efficiency of the GZCs under photo-excitation. The GZC-10% has lower (8-15 Ω charge transfer resistance (Rct compared to all the GZCs under same experimental conditions, therefore an important reason of better performance of the GZC 10%. The EPR spectra showed presence of radicals in all the samples with GZC 10% most intense signal among the different GZCs.
Nucleon structure by Lattice QCD computations with twisted mass fermions
International Nuclear Information System (INIS)
Harraud, P.A.
2010-11-01
Understanding the structure of the nucleon from quantum chromodynamics (QCD) is one of the greatest challenges of hadronic physics. Only lattice QCD allows to determine numerically the values of the observables from ab-initio principles. This thesis aims to study the nucleon form factors and the first moments of partons distribution functions by using a discretized action with twisted mass fermions. As main advantage, the discretization effects are suppressed at first order in the lattice spacing. In addition, the set of simulations allows a good control of the systematical errors. After reviewing the computation techniques, the results obtained for a wide range of parameters are presented, with lattice spacings varying from 0.0056 fm to 0.089 fm, spatial volumes from 2.1 up to 2.7 fm and several pion masses in the range of 260-470 MeV. The vector renormalization constant was determined in the nucleon sector with improved precision. Concerning the electric charge radius, we found a finite volume effect that provides a key towards an explanation of the chiral dependence of the physical point. The results for the magnetic moment, the axial charge, the magnetic and axial charge radii, the momentum and spin fractions carried by the quarks show no dependence on the lattice spacing nor volume. In our range of pion masses, their values show a deviation from the experimental values. Their chiral behaviour do not exhibit the curvature predicted by the chiral perturbation theory which could explain the apparent discrepancy. (author)
The gluon structure of hadrons and nuclei from lattice QCD
Energy Technology Data Exchange (ETDEWEB)
Shanahan, Phiala A. [College of William and Mary, Williamsburg, VA (United States); Thomas Jefferson National Accelerator Facility (TJNAF), Newport News, VA (United States); Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States)
2018-04-01
I discuss recent lattice QCD studies of the gluon structure of hadrons and light nuclei. After very briefly highlighting new determinations of the gluon contributions to the nucleon's momentum and spin, presented by several collaborations over the last year, I describe first calculations of gluon generalised form factors. The generalised transversity gluon distributions are of particular interest since they are purely gluonic; they do not mix with quark distributions at leading twist. In light nuclei they moreover provide a clean signature of non-nucleonic gluon degrees of freedom, and I present the first evidence for such effects, based on lattice QCD calculations. The planned Electron-Ion Collider, designed to access gluon structure quantities, will have the capability to test this prediction, and measure a range of gluon observables including generalised gluon distributions and transverse momentum dependent gluon distributions, within the next decade.
The gluon structure of hadrons and nuclei from lattice QCD
Shanahan, Phiala
2018-03-01
I discuss recent lattice QCD studies of the gluon structure of hadrons and light nuclei. After very briefly highlighting new determinations of the gluon contributions to the nucleon's momentum and spin, presented by several collaborations over the last year, I describe first calculations of gluon generalised form factors. The generalised transversity gluon distributions are of particular interest since they are purely gluonic; they do not mix with quark distributions at leading twist. In light nuclei they moreover provide a clean signature of non-nucleonic gluon degrees of freedom, and I present the first evidence for such effects, based on lattice QCD calculations. The planned Electron-Ion Collider, designed to access gluon structure quantities, will have the capability to test this prediction, and measure a range of gluon observables including generalised gluon distributions and transverse momentum dependent gluon distributions, within the next decade.
Fine defective structure of silicon carbide powders obtained from different starting materials
Directory of Open Access Journals (Sweden)
Tomila T.V.
2006-01-01
Full Text Available The fine defective structure of silicon carbide powders obtained from silicic acid-saccharose, aerosil-saccharose, aerosil-carbon black, and hydrated cellulose-silicic acid gel systems was investigated. The relation between IR absorption characteristics and the microstructure of SiC particles obtained from different starting materials was established. The numerical relationship between the lattice parameter a and the frequency νTO is presented.
Study of defects and vacancies in structural properties of Mn, co-doped oxides: ZnO
Kumar, Harish; Kaushik, A.; Alvi, P. A.; Dalela, B.; Dalela, S.
2018-05-01
The paper deals with the Structural properties on Mn, Co doped oxides ZnO samples using XRD, Positron Annihilation Lifetime (PAL) Spectra and Raman Spectra. The Mn, Co doped ZnO samples crystallize in a wurtzite structure without any impurity phases in XRD Spectra. The defect state of these samples has been investigated by using positron annihilation lifetime (PAL) spectroscopy technique in which all the relevant lifetime parameters are measured for all the spectra. The results are explained in the direction of doping concentration in these samples in terms of defects structure on Zn lattice site VZn and oxygen defects Vo.
Charged Semiconductor Defects Structure, Thermodynamics and Diffusion
Seebauer, Edmund G
2009-01-01
The technologically useful properties of a solid often depend upon the types and concentrations of the defects it contains. Not surprisingly, defects in semiconductors have been studied for many years, in many cases with a view towards controlling their behavior through various forms of "defect engineering." For example, in the bulk, charging significantly affects the total concentration of defects that are available to mediate phenomena such as solid-state diffusion. Surface defects play an important role in mediating surface mass transport during high temperature processing steps such as epitaxial film deposition, diffusional smoothing in reflow, and nanostructure formation in memory device fabrication. Charged Semiconductor Defects details the current state of knowledge regarding the properties of the ionized defects that can affect the behavior of advanced transistors, photo-active devices, catalysts, and sensors. Features: Group IV, III-V, and oxide semiconductors; Intrinsic and extrinsic defects; and, P...
Hornfeck, W.; Harbrecht, B.
2009-11-01
An analysis of certain types of multiplicative congruential generators - otherwise known for their application to the sequential generation of pseudo-random numbers - reveals their relation to lattice-sublattice transformations and the coordinate description of crystal structures.
Qian, Yu; Zhang, Zhaoyang
2016-01-01
In this paper we have systematically investigated the fundamental structure and the reproduction of spiral wave in a two-dimensional excitable lattice. A periodically rotating spiral wave is introduced as the model to reproduce spiral wave artificially. Interestingly, by using the dominant phase-advanced driving analysis method, the fundamental structure containing the loop structure and the wave propagation paths has been revealed, which can expose the periodically rotating orbit of spiral tip and the charity of spiral wave clearly. Furthermore, the fundamental structure is utilized as the core for artificial spiral wave. Additionally, the appropriate parameter region, in which the artificial spiral wave can be reproduced, is studied. Finally, we discuss the robustness of artificial spiral wave to defects.
Butler, Christopher John; Yang, Po-Ya; Sankar, Raman; Lien, Yen-Neng; Lu, Chun-I; Chang, Luo-Yueh; Chen, Chia-Hao; Wei, Ching-Ming; Chou, Fang-Cheng; Lin, Minn-Tsong
2016-09-28
Observations of quasiparticle interference have been used in recent years to examine exotic carrier behavior at the surfaces of emergent materials, connecting carrier dispersion and scattering dynamics to real-space features with atomic resolution. We observe quasiparticle interference in the strongly Rashba split 2DEG-like surface band found at the tellurium termination of BiTeBr and examine two mechanisms governing quasiparticle scattering: We confirm the suppression of spin-flip scattering by comparing measured quasiparticle interference with a spin-dependent elastic scattering model applied to the calculated spectral function. We also use atomically resolved STM maps to identify point defect lattice sites and spectro-microscopy imaging to discern their varying scattering strengths, which we understand in terms of the calculated orbital characteristics of the surface band. Defects on the Bi sublattice cause the strongest scattering of the predominantly Bi 6p derived surface band, with other defects causing nearly no scattering near the conduction band minimum.
Structural evolution of defective graphene under heat treatment and gamma irradiation
Zhang, Yifei; Shi, Jie; Chen, Cheng; Li, Nan; Xu, Zhiwei; Liu, Liangsen; Zhao, Lihuan; Li, Jing; Jing, Miaolei
2018-03-01
We have studied the structural change of defective graphene built by annealing in different temperature under the condition of gamma irradiation. Firstly, we found the heat treatment not only reduced but also striped the graphene. This behavior made defects become more firstly and then become less with the increase of temperature. And then gamma irradiation removed some oxygen-containing groups, by a simultaneous changed over carbon in the graphitic lattice from sp3 to sp2. Also, the gamma irradiation decreased the interlayer spacing between graphene lowest to 3.391 Å and made a crosslink which resulting in the size of the ordered gaining. A variation was detected by Raman spectroscopy that the amorphous carbon was declined after gamma irradiation. Furtherly we found the degree of this decline raised first and then diminished with the increase in the number of defects. The change in repair capacity of gamma irradiation presented a strategy for repairing the defects of graphene.
Quark structure from the lattice operator product expansion
International Nuclear Information System (INIS)
Bietenholz, W.; Cundy, N.; Goeckeler, M.
2009-11-01
We have reported elsewhere in this conference on our continuing project to determine nonperturbative Wilson coefficients on the lattice, as a step towards a completely non-perturbative determination of the nucleon structure. In this talk we discuss how these Wilson coefficients can be used to extract Nachtmann moments of structure functions, using the case of off-shell Landau-gauge quarks as a first simple example. This work is done using overlap fermions, because their improved chiral properties reduce the difficulties due to operator mixing. (orig.)
Energy Technology Data Exchange (ETDEWEB)
Dietrich, Jens; Boit, Christian [Department of Semiconductor Devices, Berlin University of Technology, Einsteinufer 19, 10587 Berlin (Germany); Abou-Ras, Daniel; Rissom, Thorsten; Unold, Thomas; Schock, Hans-Werner [Helmholtz-Zentrum Berlin fuer Materialien und Energie, Hahn-Meitner-Platz 1, 14109 Berlin (Germany)
2011-07-01
Cu(In,Ga)Se{sub 2} absorber layers used in thin-film solar cells exhibit, when grown in a multi-stage process, compositional gradients of gallium and indium, dependent on process parameters such as the Ga content. The high lateral resolution of transmission electron microscopy (TEM) imaging and energy-dispersive X-ray spectroscopy (EDX) allows the determination of lattice defects and the elemental concentrations at identical sample positions. Cross-sectional TEM samples of ZnO/CdS/Cu(In,Ga)Se{sub 2}/Mo/glass stacks were prepared with varying [Ga]/([In]+[Ga]) ratio in the absorber. The shape of the Ga distribution was measured by means of EDX and differs for the various [Ga]/([In]+[Ga]) ratios. Linear (dislocations) and planar defects (stacking faults, microtwins) were studied by means of TEM bright field and dark field images along the lengths of the Cu(In,Ga)Se{sub 2} layers. Strong Ga compositional gradients were found even within individual grains. It appears that these Ga gradients correlate with the occurrence of dislocation networks in large grains (diameter > 1 {mu}m). We assume that these dislocations compensate for lattice mismatch due to the change in composition in this area of the lattice.
Defect Structure of Localized Excitons in a WSe2 Monolayer
Zhang, Shuai
2017-07-26
The atomic and electronic structure of intrinsic defects in a WSe2 monolayer grown on graphite was revealed by low temperature scanning tunneling microscopy and spectroscopy. Instead of chalcogen vacancies that prevail in other transition metal dichalcogenide materials, intrinsic defects in WSe2 arise surprisingly from single tungsten vacancies, leading to the hole (p-type) doping. Furthermore, we found these defects to dominate the excitonic emission of the WSe2 monolayer at low temperature. Our work provided the first atomic-scale understanding of defect excitons and paved the way toward deciphering the defect structure of single quantum emitters previously discovered in the WSe2 monolayer.
From lattice Hamiltonians to tunable band structures by lithographic design
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.
Nucleon Structure and Hyperon Form Factors from Lattice QCD.
Energy Technology Data Exchange (ETDEWEB)
Lin,H.W.
2007-06-11
In this work, I report the latest lattice QCD calculations of nucleon and hyperon structure from chiral fermions in 2+1-flavor dynamical simulations. All calculations are done with a chirally symmetric fermion action, domain-wall fermions, for valence quarks. I begin with the latest lattice results on the nucleon structure, focusing on results from RBC/UKQCD using 2+1-flavor chiral fermion actions. We find the chiral-extrapolated axial coupling constant at physical pion mass point. to be 1.23(5), consistent with experimental value. The renormalization constants for the structure functions are obtained from RI/MOM-scheme non-perturbative renormalization. We find first moments of the polarized and unpolarized nucleon structure functions at zero transfer momentum to be 0.133(13) and 0.203(23) respectively, using continuum chiral extrapolation. These are consistent with the experimental values, unlike previous calculations which have been 50% larger. We also have a prediction for the transversity, which we find to be 0.56(4). The twist-3 matrix element is consistent with zero which agrees with the prediction of the Wandzura-Wilczek relation. In the second half of this work, I report an indirect dynamical estimation of the strangeness proton magnetic moments using mixed actions. With the analysis of hyperon form factors and using charge symmetry, the strangeness of proton is found to be -0.066(2G), consistent with the Adelaide-JLab Collaboration's result. The hyperon {Sigma} and {Xi} axial coupling constants are also performed for the first time in a lattice calculation, g{sub {Sigma}{Sigma}} = 0.441(14) and g{sub {Xi}{Xi}} = -0.277(11).
Nucleon Structure and hyperon form factors from lattice QCD
Energy Technology Data Exchange (ETDEWEB)
Lin, Huey-Wen
2007-06-11
In this work, I report the latest lattice QCD calculations of nucleon and hyperon structure from chiral fermions in 2+1-flavor dynamical simulations. All calculations are done with a chirally symmetric fermion action, domain-wall fermions, for valence quarks. I begin with the latest lattice results on the nucleon structure, focusing on results from RBC/UKQCD using 2+1-flavor chiral fermion actions. We find the chiral-extrapolated axial coupling constant at physical pion mass point to be 1.23(5), consistant with experimental value. The renormalization constants for the structure functions are obtained from RI/MOM-scheme non-perturbative renormalization. We find first moments of the polarized and unpolarized nucleon structure functions at zero transfer momentum to be 0.133(13) and 0.203(23) respectively, using continuum chiral extrapolation. These are consistent with the experimental values, unlike previous calculations which have been 50% larger. We also have a prediction for the transversity, which we find to be 0.56(4). The twist-3 matrix element is consistent with zero which agrees with the prediction of the Wandzura-Wilczek relation. In the second half of this work, I report an indirect dynamical estimation of the strangeness proton magnetic moments using mixed actions. With the analysis of hyperon form factors and using charge symmetry, the strangeness of proton is found to be -0.066(26), consistent with the Adelaide-JLab Collaboration's result. The hyperon Sigma and Xi axial coupling constants are also performed for the first time in a lattice calculation, g_SigmaSigma = 0.441(14) and g_XiXi = -0.277(11).
Moessbauer study of solute interactions with the lattice defect and grain boundary
International Nuclear Information System (INIS)
Ishida, Y.
1979-10-01
Moessbauer effect was used in the investigations of defect structures of Al- 57 Co alloys introduced by electron irradiation and grain boundary embrittlement in binary iron alloys containing sup(119m)Sn nuclei. The behaviour of tin during aging of Al-Cu-Sn alloys was examined by Moessbauer spectra during isothermal annealing of the samples at various temperatures. Similar investigations were conducted for polycrystalline and bicrystalline silver foils containing sup(119m)Sn sandwiched in the boundary. The binding state of tin atoms segregated at the grain boundary of fine grained iron and iron alloys provided the clues for the embrittlement of iron alloys. The inhibiting effect of Ti, V, and Mo can be explained by the usurpation of the electrons in the tin atoms to the 3d shell of iron. Moessbauer effect was extensively applied in studying the aging behaviour of aluminium alloys in quenching, ion-implantation and electron irradiation processes
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
International Nuclear Information System (INIS)
Shunkeev, K.; Sagimbaeva, Sh.; Shunkeev, S.
2007-01-01
Effect of auto-localized excitons (ALE) luminescence strengthening is conditioned by two mechanisms: either decrease of potential barrier divided of quasi-free states and auto-localized states or decrease of emission-less channel effectiveness of exciton decay on primary radiation defects. In considered range (80 K) all excitons are only in auto-localized state. Therefore a realization of the first mechanism is improbable, For instant, in KI crystal at 80-100 K luminescence of free exciton is completely putting out, and ALE luminescence has maximal intensity. It is known that in the temperature range when ALE luminescence putting out is beginning an effectiveness of radiation defects is beginning to grow. This effect is related with predominating at that time emission-less exciton decay on radiation defects (F-H pairs). Experimentally by luminescence spectroscopy method activation energy of temperature putting out of ALE in AHC under uniaxial deformation. It is revealed, that increase of activation energy value has observed in a number of crystals: KBr→NaCl→KI→Na Br→CsBr→RbI. It is concluded, that effect of ALE intensity building-up and decrease of effectiveness of radiation defect formation are interpreted by growth of potential barrier of ALE decay into radiation defects under low symmetry of AHC lattice of low-temperature uniaxial deformation
Lattice investigation of nucleon structure at light quark masses
International Nuclear Information System (INIS)
Zanotti, James M.
2010-01-01
Lattice simulations of hadronic structure are now reaching a level where they are able to not only complement, but also provide guidance to current and forthcoming experimental programmes at, e.g. Jefferson Lab, COMPASS/CERN and FAIR/GSI. By considering new simulations at low quark masses and on large volumes, we review the recent progress that has been made in this exciting area by the QCDSF/UKQCD collaboration. In particular, results obtained close to the physical point for several quantities, including electromagnetic form factors and moments of ordinary parton distribution functions, show some indication of approaching their phenomenological values.
One-dimensional map lattices: Synchronization, bifurcations, and chaotic structures
DEFF Research Database (Denmark)
Belykh, Vladimir N.; Mosekilde, Erik
1996-01-01
The paper presents a qualitative analysis of coupled map lattices (CMLs) for the case of arbitrary nonlinearity of the local map and with space-shift as well as diffusion coupling. The effect of synchronization where, independently of the initial conditions, all elements of a CML acquire uniform...... dynamics is investigated and stable chaotic time behaviors, steady structures, and traveling waves are described. Finally, the bifurcations occurring under the transition from spatiotemporal chaos to chaotic synchronization and the peculiarities of CMLs with specific symmetries are discussed....
Band structure engineering for ultracold quantum gases in optical lattices
International Nuclear Information System (INIS)
Weinberg, Malte
2014-01-01
The energy band structure fundamentally influences the physical properties of a periodic system. It may give rise to highly exotic phenomena in yet uncharted physical regimes. Ultracold quantum gases in optical lattices provide an ideal playground for the investigation of a large variety of such intriguing effects. Experiments presented here address several issues that require the systematic manipulation of energy band structures in optical lattices with diverse geometries. These artificial crystals of light, generated by interfering laser beams, allow for an unprecedented degree of control over a wide range of parameters. A major part of this thesis employs time-periodic driving to engineer tunneling matrix elements and, thus, the dispersion relation for bosonic quantum gases in optical lattices. Resonances emerging in the excitation spectrum due to the particularly strong forcing can be attributed to multi-photon transitions that are investigated systematically. By changing the sign of the tunneling, antiferromagnetic spin-spin interactions can be emulated. In a triangular lattice this leads to geometrical frustration with a doubly degenerate ground state as the simultaneous minimization of competing interactions is inhibited. Moreover, complex-valued tunneling matrix elements can be generated with a suitable breaking of time-reversal symmetry in the driving scheme. The associated Peierls phases mimic the presence of an electromagnetic vector gauge potential acting on charged particles. First proof-of-principle experiments reveal an excellent agreement with theoretical calculations. In the weakly interacting superfluid regime, these artificial gauge fields give rise to an Ising-XY model with tunable staggered magnetic fluxes and a complex interplay between discrete and continuous symmetries. A thermal phase transition from an ordered ferromagnetic- to an unordered paramagnetic state could be observed. In the opposite hard-core boson limit of strong interactions
The behavior of lattice defects produced in Al2O3 irradiated by neutrons at high temperatures
International Nuclear Information System (INIS)
Atobe, K.; Koizumi, T.; Okada, M.
2003-01-01
Single crystals of α-Al 2 O 3 were irradiated by the two reactors, KUR and JMTR, at three different temperatures. Lattice defects produced by irradiation were studied by esr (electron spin resonance). Three kinds of esr spectram, which are denoted as A, B and C spectram, are observed. The spectram A was observed at three different irradiation temperatures and was ascribed to oxygen vacancies. The spectram B showed no angular dependence for the rotation of external magnetic field to the crystal axis, and the defect density of this spectram decreased with an increase of annealing temperature. When the specimen was annealed at 400 degC after irradiation at 200 degC, the spectram C was observed and was presumed to be due to Al-colloids. (Y. Kazumata)
Investigation of the crystal lattice defects by means of the positrons annihilations
International Nuclear Information System (INIS)
Dryzek, J.
1994-01-01
In this report the positrons annihilation methods as a tool for the crystal defects studies is presented. The short description of the positron - crystal interactions and different positron capture models are discussed. 192 refs, 67 figs, 6 tabs
Nucleon Structure on a Lattice at the Physical Point
International Nuclear Information System (INIS)
Syritsyn, Sergey
2015-01-01
We report initial nucleon structure results computed on lattices with 2+1 dynamical Mobius domain wall fermions at the physical point generated by the RBC and UKQCD collaborations. At this stage, we evaluate only connected quark contributions. In particular, we discuss the nucleon vector and axial-vector form factors, nucleon axial charge and the isovector quark momentum fraction. From currently available statistics, we estimate the stochastic accuracy of the determination of g A and 〈x〉 u-d to be around 10%, and we expect to reduce that to 5% within the next year. To reduce the computational cost of our calculations, we extensively use acceleration techniques such as low-eigenmode deflation and all-mode-averaging (AMA). We present a method for choosing optimal AMA parameters. (paper)
International Nuclear Information System (INIS)
Doshida, Tomoki; Takai, Kenichi
2014-01-01
The effects of the hydrogen state, temperature, strain rate and hydrogen content on hydrogen embrittlement susceptibility and hydrogen-induced lattice defects were evaluated for cold-drawn pearlitic steel that absorbed hydrogen in two trapping states. Firstly, tensile tests were carried out under various conditions to evaluate hydrogen embrittlement susceptibility. The results showed that peak 2 hydrogen, desorbed at temperatures above 200 °C as determined by thermal desorption analysis (TDA), had no significant effect on hydrogen embrittlement susceptibility. In contrast, hydrogen embrittlement susceptibility increased in the presence of peak 1 hydrogen, desorbed from room temperature to 200 °C as determined by TDA, at temperatures higher than −30 °C, at lower strain rates and with higher hydrogen content. Next, the same effects on hydrogen-induced lattice defects were also evaluated by TDA using hydrogen as a probe. Peak 2 hydrogen showed no significant effect on either hydrogen-induced lattice defects or hydrogen embrittlement susceptibility. It was found that hydrogen-induced lattice defects formed under the conditions where hydrogen embrittlement susceptibility increased. This relationship indicates that hydrogen embrittlement susceptibility was higher under the conditions where the formation of hydrogen-induced lattice defects tended to be enhanced. Since hydrogen-induced lattice defects formed by the interaction between hydrogen and strain were annihilated by annealing at a temperature of 200 °C, they were presumably vacancies or vacancy clusters. One of the common atomic-level changes that occur in cold-drawn pearlitic steel showing higher hydrogen embrittlement susceptibility is the formation of vacancies and vacancy clusters
Energy Technology Data Exchange (ETDEWEB)
Kaczmarczyk, G.
2006-07-01
The group III-nitrides and zinc oxide are in the focus of material research because of their high application potential. The presentation of the first UV laser diode as well as blue light emitting diodes were the preliminary highlights. Although of all technological progress many physical questions are still open. In this work some of these questions are examined experimentally with Raman-scattering and theoretically with valence-force calculations. Many physical properties such as strain and doping concentration affect the lattice dynamics. As a start the phonons of the center of the Brillouin-zone in GaN, AlN, InN and ZnO are studied with first-order Raman-scattering. These results are the basis for advanced investigations. The acoustical and optical modes at the zone boundary and their combinations and overtones are determinated from the second-order Raman-scattering. Using the valence-force calculations the experimental frequencies are assigned to particular phonon branches or points of the Brillouin zone. The second part of this work treats systematically the physics of local vibrational modes. They occur due to intrinsic defects or impurities in the semiconductors. They are investigated with respect to the vibrational properties of the unperturbed crystals. In order to assign new experimentally found structures, calculations of local vibrational modes in GaN:Mg, GaN:As and ZnO:N systems were carried out. Furthermore, the calculations in Si- and C-doped hexagonal GaN suggest the frequency range for local vibrational modes. In the last section the influence of external parameters such as temperature or strain on the phonon frequency is analyzed. It is shown, that the influence on the temperature dependence of host phonons and local vibrational modes are dominated through different effects. In case of the host phonons it is mainly due to the volume effect whereas the local modes are highly affected by the anharmonic decay. Moreover, the calculations verified
International Nuclear Information System (INIS)
Tournarie, Max
1959-01-01
The total diffusing power for a crystallite of any form containing a centrosymmetric defect has been established. The antisymmetrical part of the deformation potential only contributes very slightly to the primary dissymmetry. We then go on to study the case of a group of defects of the same type. The calculation converges sufficiently to describe the thermal agitation of an infinite crystal. Reprint of a paper published in 'Comptes Rendus des Seances de l'Academie des Sciences', t. 248, p. 2103-2105, sitting of April 6, 1959 [fr
International Nuclear Information System (INIS)
Huang Feng; Wang Xue-Jin; Liu Yan-Hong; Ye Mao-Fu; Wang Long
2010-01-01
Structures and dynamics of two-dimensional dust lattices with and without Coulomb molecules in plasmas are investigated. The experimental results show that the lattices have the crystal-like hexagonal structures, i.e. most particles have six nearest-neighboring particles. However, the lattice points can be occupied by the individual particles or by a pair of particles called Coulomb molecules. The pair correlation function is used to compare the structures between the lattices with or without the Coulomb molecules. In the experiments, the Coulomb molecules can also decompose and recombine with another individual particle to form a new molecule. (physics of gases, plasmas, and electric discharges)
Liu, Lu; Kamm, Paul; García-Moreno, Francisco; Banhart, John; Pasini, Damiano
2017-10-01
This paper examines three-dimensional metallic lattices with regular octet and rhombicuboctahedron units fabricated with geometric imperfections via Selective Laser Sintering. We use X-ray computed tomography to capture morphology, location, and distribution of process-induced defects with the aim of studying their role in the elastic response, damage initiation, and failure evolution under quasi-static compression. Testing results from in-situ compression tomography show that each lattice exhibits a distinct failure mechanism that is governed not only by cell topology but also by geometric defects induced by additive manufacturing. Extracted from X-ray tomography images, the statistical distributions of three sets of defects, namely strut waviness, strut thickness variation, and strut oversizing, are used to develop numerical models of statistically representative lattices with imperfect geometry. Elastic and failure responses are predicted within 10% agreement from the experimental data. In addition, a computational study is presented to shed light into the relationship between the amplitude of selected defects and the reduction of elastic properties compared to their nominal values. The evolution of failure mechanisms is also explained with respect to strut oversizing, a parameter that can critically cause failure mode transitions that are not visible in defect-free lattices.
Band Structure Characteristics of Nacreous Composite Materials with Various Defects
Yin, J.; Zhang, S.; Zhang, H. W.; Chen, B. S.
2016-06-01
Nacreous composite materials have excellent mechanical properties, such as high strength, high toughness, and wide phononic band gap. In order to research band structure characteristics of nacreous composite materials with various defects, supercell models with the Brick-and-Mortar microstructure are considered. An efficient multi-level substructure algorithm is employed to discuss the band structure. Furthermore, two common systems with point and line defects and varied material parameters are discussed. In addition, band structures concerning straight and deflected crack defects are calculated by changing the shear modulus of the mortar. Finally, the sensitivity of band structures to the random material distribution is presented by considering different volume ratios of the brick. The results reveal that the first band gap of a nacreous composite material is insensitive to defects under certain conditions. It will be of great value to the design and synthesis of new nacreous composite materials for better dynamic properties.
Zillner, E.; Paul, A.; Jutimoosik, J.; Chandarak, S.; Monnor, T.; Rujirawat, S.; Yimnirun, R.; Lin, X. Z.; Ennaoui, A.; Dittrich, Th.; Lux-Steiner, M.
2013-06-01
Lattice positions of Sn in kesterite Cu2ZnSnS4 and Cu2SnS3 nanoparticles and thin films were investigated by XANES (x-ray absorption near edge structure) analysis at the S K-edge. XANES spectra were analyzed by comparison with simulations taking into account anti-site defects and vacancies. Annealing of Cu2ZnSnS4 nanoparticle thin films led to a decrease of Sn at its native and defect sites. The results show that XANES analysis at the S K-edge is a sensitive tool for the investigation of defect sites, being critical in kesterite thin film solar cells.
Cellular structure formed by ion-implantation-induced point defect
International Nuclear Information System (INIS)
Nitta, N.; Taniwaki, M.; Hayashi, Y.; Yoshiie, T.
2006-01-01
The authors have found that a cellular defect structure is formed on the surface of Sn + ion implanted GaSb at a low temperature and proposed its formation mechanism based on the movement of the induced point defects. This research was carried out in order to examine the validity of the mechanism by clarifying the effect of the mobility of the point defects on the defect formation. The defect structure on the GaSb surfaces implanted at cryogenic temperature and room temperature was investigated by scanning electron microscopy (SEM) and cross-sectional transmission electron microscopy (TEM) observation. In the sample implanted at room temperature, the sponge-like structure (a pileup of voids) was formed and the cellular structure, as observed at a low temperature, did not develop. This behavior was explained by the high mobility of the vacancies during implantation at room temperature, and the proposed idea that the defect formation process is dominated by the induced point defects was confirmed
Graphene materials having randomly distributed two-dimensional structural defects
Kung, Harold H; Zhao, Xin; Hayner, Cary M; Kung, Mayfair C
2013-10-08
Graphene-based storage materials for high-power battery applications are provided. The storage materials are composed of vertical stacks of graphene sheets and have reduced resistance for Li ion transport. This reduced resistance is achieved by incorporating a random distribution of structural defects into the stacked graphene sheets, whereby the structural defects facilitate the diffusion of Li ions into the interior of the storage materials.
Thresholds of surface codes on the general lattice structures suffering biased error and loss
International Nuclear Information System (INIS)
Tokunaga, Yuuki; Fujii, Keisuke
2014-01-01
A family of surface codes with general lattice structures is proposed. We can control the error tolerances against bit and phase errors asymmetrically by changing the underlying lattice geometries. The surface codes on various lattices are found to be efficient in the sense that their threshold values universally approach the quantum Gilbert-Varshamov bound. We find that the error tolerance of the surface codes depends on the connectivity of the underlying lattices; the error chains on a lattice of lower connectivity are easier to correct. On the other hand, the loss tolerance of the surface codes exhibits an opposite behavior; the logical information on a lattice of higher connectivity has more robustness against qubit loss. As a result, we come upon a fundamental trade-off between error and loss tolerances in the family of surface codes with different lattice geometries
Thresholds of surface codes on the general lattice structures suffering biased error and loss
Energy Technology Data Exchange (ETDEWEB)
Tokunaga, Yuuki [NTT Secure Platform Laboratories, NTT Corporation, 3-9-11 Midori-cho, Musashino, Tokyo 180-8585, Japan and Japan Science and Technology Agency, CREST, 5 Sanban-cho, Chiyoda-ku, Tokyo 102-0075 (Japan); Fujii, Keisuke [Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka 560-8531 (Japan)
2014-12-04
A family of surface codes with general lattice structures is proposed. We can control the error tolerances against bit and phase errors asymmetrically by changing the underlying lattice geometries. The surface codes on various lattices are found to be efficient in the sense that their threshold values universally approach the quantum Gilbert-Varshamov bound. We find that the error tolerance of the surface codes depends on the connectivity of the underlying lattices; the error chains on a lattice of lower connectivity are easier to correct. On the other hand, the loss tolerance of the surface codes exhibits an opposite behavior; the logical information on a lattice of higher connectivity has more robustness against qubit loss. As a result, we come upon a fundamental trade-off between error and loss tolerances in the family of surface codes with different lattice geometries.
Phase structure of lattice QCD for general number of flavors
International Nuclear Information System (INIS)
Iwasaki, Y.; Kanaya, K.; Yoshie, T.; Kaya, S.; Sakai, S.
2004-01-01
We investigate the phase structure of lattice QCD for the general number of flavors in the parameter space of gauge coupling constant and quark mass, employing the one-plaquette gauge action and the standard Wilson quark action. Performing a series of simulations for the number of flavors N F =6-360 with degenerate-mass quarks, we find that when N F ≥7 there is a line of a bulk first order phase transition between the confined phase and a deconfined phase at a finite current quark mass in the strong coupling region and the intermediate coupling region. The massless quark line exists only in the deconfined phase. Based on these numerical results in the strong coupling limit and in the intermediate coupling region, we propose the following phase structure, depending on the number of flavors whose masses are less than Λ d which is the physical scale characterizing the phase transition in the weak coupling region: When N F ≥17, there is only a trivial IR fixed point and therefore the theory in the continuum limit is free. On the other hand, when 16≥N F ≥7, there is a nontrivial IR fixed point and therefore the theory is nontrivial with anomalous dimensions, however, without quark confinement. Theories which satisfy both quark confinement and spontaneous chiral symmetry breaking in the continuum limit exist only for N F ≤6
Fe and Cu in Si: Lattice sites and trapping at implantation-related defects
International Nuclear Information System (INIS)
Wahl, U.; Correia, J.G.; Rita, E.; Araujo, J.P.; Soares, J.C.
2006-01-01
We have used the emission channeling technique in order to study the lattice sites of radioactive 59 Fe and 67 Cu following 60 keV ion implantation into Si single crystals at fluences around 10 12 -10 14 cm -2 . We find that in the room temperature as-implanted state in high-resistivity Si both Fe and Cu occupy mainly lattice sites displaced around 0.05 nm (0.5 A) from substitutional positions. Both are released from these positions during annealing at temperatures between 300 deg. C and 600 deg. C. Fe is then found mainly on near-tetrahedral interstitial sites and further annealing causes it to be increasingly incorporated on ideal substitutional sites, on which it is stable to around 800 deg. C. We have strong indications that during annealing around 600 deg. C, along with the dominance of interstitial Fe, a redistribution towards the surface takes place, suggesting that the subsequent formation of ideal substitutional Fe may be related to the trapping of Fe at R p /2, half of its implanted depth. Possible R p /2 trapping might also have taken place in our Cu experiments but appears to be less efficient since Cu tended to escape to the bulk of the samples
International Nuclear Information System (INIS)
Schroers, W.
2007-01-01
This review focuses on the discussion of three key results of nucleon structure calculations on the lattice. These three results are the quark contribution to the nucleon spin, J q , the nucleon-Δ transition form factors, and the nucleon axial coupling, g A . The importance for phenomenology and experiment is discussed and the requirements for future simulations are pointed out. (orig.)
Dynamic structure factor for liquid He4 and quantum lattice model
International Nuclear Information System (INIS)
Lee, M.H.
1975-01-01
It has been realized for some time now that the quantum lattice model (or the anisotropic Heisenberg antiferromagnetic model) is a useful model for studying the properties of quantum liquids especially near the lambda transition. The static critical values calculated from the quantum lattice model are in good agreement with the observed values. Furthermore, it was shown recently that there are collective modes in the quantum lattice model which are equivalent to the plasmons. Hence, it would seem to be interesting to study the dynamic structure factor for the quantum lattice model and to make a comparison with experiment. Work on the dynamic structure factor is reported here. (Auth.)
Topology Optimization of Lightweight Lattice Structural Composites Inspired by Cuttlefish Bone
Hu, Zhong; Gadipudi, Varun Kumar; Salem, David R.
2018-03-01
Lattice structural composites are of great interest to various industries where lightweight multifunctionality is important, especially aerospace. However, strong coupling among the composition, microstructure, porous topology, and fabrication of such materials impedes conventional trial-and-error experimental development. In this work, a discontinuous carbon fiber reinforced polymer matrix composite was adopted for structural design. A reliable and robust design approach for developing lightweight multifunctional lattice structural composites was proposed, inspired by biomimetics and based on topology optimization. Three-dimensional periodic lattice blocks were initially designed, inspired by the cuttlefish bone microstructure. The topologies of the three-dimensional periodic blocks were further optimized by computer modeling, and the mechanical properties of the topology optimized lightweight lattice structures were characterized by computer modeling. The lattice structures with optimal performance were identified.
Tarasevich, Yuri Yu.; Laptev, Valeri V.; Goltseva, Valeria A.; Lebovka, Nikolai I.
2017-07-01
The effect of defects on the behaviour of electrical conductivity, σ, in a monolayer produced by the random sequential adsorption of linear k-mers (particles occupying k adjacent sites) onto a square lattice is studied by means of a Monte Carlo simulation. The k-mers are deposited on the substrate until a jamming state is reached. The presence of defects in the lattice (impurities) and of defects in the k-mers with concentrations of dl and dk, respectively, is assumed. The defects in the lattice are distributed randomly before deposition and these lattice sites are forbidden for the deposition of k-mers. The defects of the k-mers are distributed randomly on the deposited k-mers. The sites filled with k-mers have high electrical conductivity, σk, whereas the empty sites, and the sites filled by either types of defect have a low electrical conductivity, σl, i.e., a high-contrast, σk /σl ≫ 1, is assumed. We examined isotropic (both the possible x and y orientations of a particle are equiprobable) and anisotropic (all particles are aligned along one given direction, y) deposition. To calculate the effective electrical conductivity, the monolayer was presented as a random resistor network and the Frank-Lobb algorithm was used. The effects of the concentrations of defects dl and dk on the electrical conductivity for the values of k =2n, where n = 1 , 2 , … , 5, were studied. Increase of both the dl and dk parameters values resulted in decreases in the value of σ and the suppression of percolation. Moreover, for anisotropic deposition the electrical conductivity along the y direction was noticeably larger than in the perpendicular direction, x. Phase diagrams in the (dl ,dk)-plane for different values of k were obtained.
Extracting and identifying concrete structural defects in GPR images
Ye, Qiling; Jiao, Liangbao; Liu, Chuanxin; Cao, Xuehong; Huston, Dryver; Xia, Tian
2018-03-01
Traditionally most GPR data interpretations are performed manually. With the advancement of computing technologies, how to automate GPR data interpretation to achieve high efficiency and accuracy has become an active research subject. In this paper, analytical characterizations of major defects in concrete structures, including delamination, air void and moisture in GPR images, are performed. In the study, the image features of different defects are compared. Algorithms are developed for defect feature extraction and identification. For validations, both simulation results and field test data are utilized.
Electron-lattice Interaction and Nonlinear Excitations in Cuprate Structures
International Nuclear Information System (INIS)
Paulsen, J.; Eschrig, H.; Drechsler, S.L.; Malek, J.
1995-01-01
A low temperature lattice modulation of the chains of the YBa 2 Cu 3 O 7 is considered by deriving a Hamiltonian of electron-lattice interaction from density-functional calculations for deformed lattice and solving it for the groundstate. Hubbard-type Coulomb interaction is included. The obtained groundstate is a charge-density-wave state with a pereodicity of four lattice constants and a gap for one-electron excitations of about 1eV, sensitively depending on parameters of the Hamiltonian. There are lots of polaronic and solitonic excitations with formation energies deep in the gap, which can pin the Fermi level and thus produce again metallicity of the chain. They might also contribute to pairing of holes in adjacent CuO 2 -planes. (author)
Vortex structure in abelian-projected lattice gauge theory
International Nuclear Information System (INIS)
Ambjoern, J.; Giedt, J.; Greensite, J.
2000-01-01
We report on a breakdown of both monopole dominance and positivity in abelian-projected lattice Yang-Mills theory. The breakdown is associated with observables involving two units of the abelian charge. We find that the projected lattice has at most a global Z 2 symmetry in the confined phase, rather than the global U(1) symmetry that might be expected in a dual superconductor or monopole Coulomb gas picture. Implications for monopole and center vortex theories of confinement are discussed
Diffusion Mechanisms and Lattice Locations of Thermal-Equilibrium Defects in Si-Ge Alloys
Lyutovich, K; Touboltsev, V; Laitinen, P O; Strohm, A
2002-01-01
It is generally accepted that Ge and Si differ considerably with respect to intrinsic-point-defect-mediated diffusion. In Ge, the native point defects dominating under thermal-equilibium conditions at all solid-state temperatures accessible in diffusion experiments are vacancies, and therefore Ge self-diffusion is vacancy-controlled. In Si, by contrast, self-interstitials and vacancies co-exist in thermal equilibrium. Whereas in the most thoroughly investigated temperature regime above about 1000$^\\circ$C Si self-diffusion is self-interstitial-controlled, it is vacancy-controlled at lower temperatures. According to the scenario displayed above, self-diffusion in Si-Ge alloys is expected to change from an interstitialcy mechanism on the Si side to a vacancy mechanism on the Ge side. Therefore, $^{71}$Ge self-diffusion experiments in Si$_{1- \\it y}$Ge$_{\\it y}$ as a function of composition Y are highly interesting. In a first series of experiments the diffusion of Ge in 0.4 to 10 $\\mu$m thick, relaxed, low-disl...
Production defects in marine composite structures
DEFF Research Database (Denmark)
Hayman, Brian; Berggreen, Christian; Tsouvalis, Nicholas G.
2007-01-01
Composite structures are often used when there is a requirement for low weight. Then a key aspect is to be able to take full advantage of the material and utilise it to its limits. To do this it is important to achieve as low a variability as possible in the manufacture of such structures...
DEFF Research Database (Denmark)
Mahshid, Rasoul; Hansen, Hans Nørgaard; Loft Højbjerre, Klaus
2016-01-01
in injection molding tools and lattice structures. This research examines the effect of cellular lattice structures on the strength of workpieces additively manufactured from ultra high-strength steel powder. Two commercial SLM machines are used to fabricate cellular samples based on four architectures— solid...... with experimental data and it is shown that they agree well. The results from this research show that using lattice structures significantly reduces the strength of material with respect to solid samples while indicating no serious increase of strength compared to hollow structures. In combination with an analysis...
International Nuclear Information System (INIS)
Schafler, E.; Steiner, G.; KEXrber, M.; Zehetbauer, M.J.; Korznikova, E.
2005-01-01
Full text: Cu rods have been deformed by Equal Channel Angular Pressing (ECAP) up to shear strains γ ∼ 5 while applying various deformation paths A, B c and C. ECAP processed materials show a microstructure with grain sizes in the nanometer range and a high density of lattice defects. X-ray Bragg Profile Analyses (XPA), Differential Scanning Calorimetry (DSC) as well as Residual Electrical Resistivity (RER) measurements have been performed, in order to detect the densities of various deformation induced lattice defects and/or their arrangements. The results have been analyzed in terms of annealing of deformation induced dislocations and vacancies (vacancy agglomerates). Compared to conventional cold work procedures, deformation by ECAP achieves a strongly enhanced concentration of vacancy type defects. (author)
International Nuclear Information System (INIS)
Ryan, K M; McGrath, J P; Farrell, R A; O'Neill, W M; Barnes, C J; Morris, M A
2003-01-01
Conventionally, the addition of sesquioxide cation dopants to ceria has been thought of as a class of almost model systems. The most important defect mechanism involves simple anion vacancy charge compensation with those vacancy defects associating themselves with the trivalent cation and being distributed randomly through the lattice. However, this simple model has been significantly challenged in recent years and it seems possible that these associated defects might cluster in ordered arrangements. Whilst evidence has been provided by theoretical work, only limited experimental data are available. This letter reports the first observation of local ordering in these systems as observed by careful powder x-ray diffraction studies. In detail, it is shown that measurements of the lattice parameter do not vary monotonically with dopant concentration. It is also shown that far from being ideal systems with very high dopant solubilities and true solid-state solutions, these systems have complex solubility. (letter to the editor)
Local structure theory: calculation on hexagonal arrays, and interaction of rule and lattice
International Nuclear Information System (INIS)
Gutowitz, H.A.; Victor, J.D.
1989-01-01
Local structure theory calculations are applied to the study of cellular automata on the two-dimensional hexagonal lattice. A particular hexagonal lattice rule denoted (3422) is considered in detail. This rule has many features in common with Conway's Life. The local structure theory captures many of the statistical properties of this rule; this supports hypotheses raised by a study of Life itself. As in Life, the state of a cell under (3422) depends only on the state of the cell itself and the sum of states in its neighborhood at the previous time step. This property implies that evolution rules which operate in the same way can be studied on different lattices. The differences between the behavior of these rules on different lattices are dramatic. The mean field theory cannot reflect these differences. However, a generalization of the mean field theory, the local structure theory, does account for the rule-lattice interaction
Mechanical properties of regular hexahedral lattice structure formed by selective laser melting
International Nuclear Information System (INIS)
Sun, Jianfeng; Yang, Yongqiang; Wang, Di
2013-01-01
The Ti–6Al–4V lattice structure is widely used in the aerospace field. This research first designs a regular hexahedral unit, processes the lattice structure composed of the Ti–6Al–4V units by selective laser melting technology, obtains the experimental fracture load and the compression deformation of them through compression tests, then conducts a simulation of the unit and the lattice structure through ANSYS to analyze the failure point. Later, according to the force condition of the point, the model of maximum load is built, through which the analytical formula of the fracture load of the unit and the lattice structure are obtained. The results of groups of experiments demonstrate that there exists an exponential relationship between the practical fracture load and the porosity of the lattice structure. There also exists a trigonometric function relationship between the compression deformation and the porosity of the lattice structure. The fracture analysis indicates that fracture of the units and lattice structure is brittle fracture due to cleavage fracture. (paper)
Electronic structure properties of deep defects in hBN
Dev, Pratibha; Prdm Collaboration
In recent years, the search for room-temperature solid-state qubit (quantum bit) candidates has revived interest in the study of deep-defect centers in semiconductors. The charged NV-center in diamond is the best known amongst these defects. However, as a host material, diamond poses several challenges and so, increasingly, there is an interest in exploring deep defects in alternative semiconductors such as hBN. The layered structure of hBN makes it a scalable platform for quantum applications, as there is a greater potential for controlling the location of the deep defect in the 2D-matrix through careful experiments. Using density functional theory-based methods, we have studied the electronic and structural properties of several deep defects in hBN. Native defects within hBN layers are shown to have high spin ground states that should survive even at room temperature, making them interesting solid-state qubit candidates in a 2D matrix. Partnership for Reduced Dimensional Material (PRDM) is part of the NSF sponsored Partnerships for Research and Education in Materials (PREM).
Structure Transformation and Coherent Interface in Large Lattice-Mismatched Nanoscale Multilayers
Directory of Open Access Journals (Sweden)
J. Y. Xie
2013-01-01
Full Text Available Nanoscale Al/W multilayers were fabricated by DC magnetron sputtering and characterized by transmission electron microscopy and high-resolution electron microscopy. Despite the large lattice mismatch and significantly different lattice structures between Al and W, a structural transition from face-centered cubic to body-centered cubic in Al layers was observed when the individual layer thickness was reduced from 5 nm to 1 nm, forming coherent Al/W interfaces. For potential mechanisms underlying the observed structure transition and forming of coherent interfaces, it was suggested that the reduction of interfacial energy and high stresses induced by large lattice-mismatch play a crucial role.
International Nuclear Information System (INIS)
Okada, Moritami; Atobe, Kozo; Nakagawa, Masuo
2004-01-01
Temperature dependence of production efficiency of irradiation-induced defects in neutron-irradiated oxides has been investigated. Some oxide single crystals, MgO, α-Al 2 O 3 (sapphire) and TiO 2 (rutile), were irradiated at several controlled temperatures, 10, 20, 50, 100, 150 and 200 K, using the low-temperature irradiation facility of Kyoto University Reactor (KUR-LTL), and at ambient temperature (∼370 K) in the same facility. Irradiation temperature dependence of production efficiency of a 1 μm band in TiO 2 differs greatly from that of anion vacancy (F-type centers) in MgO and α-Al 2 O 3 . Results for MgO and α-Al 2 O 3 show steep negative gradients from 10 to 370 K, whereas that for TiO 2 includes a valley between 40 and 60 K and a hump at about 130 K, and then disappear at about 200 K. In MgO and α-Al 2 O 3 , this behavior can be explained by the recombination of Frenkel pairs, which is activated at higher temperature. In TiO 2 , in addition to the recombination mechanism, a covalent bonding property is thought to be exerted strong influence, and it is suggested that a disappearance of the 1 μm band at above 200 K is due to the recombination process of Frenkel pairs which is caused by the irradiation-induced crystallization
DEFF Research Database (Denmark)
Mahshid, Rasoul; Hansen, Hans Nørgaard; Loft Højbjerre, Klaus
2016-01-01
Additive manufacturing is rapidly developing and gaining popularity for direct metal fabrication systems like selective laser melting (SLM). The technology has shown significant improvement for high-quality fabrication of lightweight design-efficient structures such as conformal cooling channels...... in injection molding tools and lattice structures. This research examines the effect of cellular lattice structures on the strength of workpieces additively manufactured from ultra high-strength steel powder. Two commercial SLM machines are used to fabricate cellular samples based on four architectures— solid......, hollow, lattice structure and rotated lattice structure. Compression test is applied to the specimens while they are deformed. The analytical approach includes finite element (FE), geometrical and mathematical models for prediction of collapse strength. The results from the the models are verified...
Directory of Open Access Journals (Sweden)
Jing Chenchen
2017-01-01
Full Text Available Lattice structure with high strength and low mass using selective laser melting (SLM has been a hot topic. However, there are some problems in the fabrication of lattice structure by SLM. Rod unit is the basic component of lattice structure and its performance affects the whole structure. It is necessary to investigate the influence of selective laser melting on rod unit’s mechanical properties. A series of rod units with different inclination angle and diameter were fabricated by SLM in this research. And the mechanical properties of these units were measured by tensile test. The results show that the rod units with different diameters and inclination angles have good mechanical properties and show no difference. It is a good news for lattice structure designing for there is no necessary to consider the mechanical properties’ anisotropy of rod units.
Energy Technology Data Exchange (ETDEWEB)
Okada, Moritami [Research Reactor Institute, Kyoto University, Kumatori-cho, Sennan-gun, Osaka 5900494 (Japan)]. E-mail: okada@rri.kyoto-u.ac.jp; Atobe, Kozo [Faculty of Science, Naruto University of Education, Naruto, Tokushima 7728502 (Japan); Nakagawa, Masuo [Faculty of Education, Kagawa University, Takamatsu, Kagawa 7608522 (Japan)
2004-11-01
Temperature dependence of production efficiency of irradiation-induced defects in neutron-irradiated oxides has been investigated. Some oxide single crystals, MgO, {alpha}-Al{sub 2}O{sub 3} (sapphire) and TiO{sub 2} (rutile), were irradiated at several controlled temperatures, 10, 20, 50, 100, 150 and 200 K, using the low-temperature irradiation facility of Kyoto University Reactor (KUR-LTL), and at ambient temperature ({approx}370 K) in the same facility. Irradiation temperature dependence of production efficiency of a 1 {mu}m band in TiO{sub 2} differs greatly from that of anion vacancy (F-type centers) in MgO and {alpha}-Al{sub 2}O{sub 3}. Results for MgO and {alpha}-Al{sub 2}O{sub 3} show steep negative gradients from 10 to 370 K, whereas that for TiO{sub 2} includes a valley between 40 and 60 K and a hump at about 130 K, and then disappear at about 200 K. In MgO and {alpha}-Al{sub 2}O{sub 3}, this behavior can be explained by the recombination of Frenkel pairs, which is activated at higher temperature. In TiO{sub 2}, in addition to the recombination mechanism, a covalent bonding property is thought to be exerted strong influence, and it is suggested that a disappearance of the 1 {mu}m band at above 200 K is due to the recombination process of Frenkel pairs which is caused by the irradiation-induced crystallization.
International Nuclear Information System (INIS)
Mercer, Michael P.; Finnigan, Sophie; Kramer, Denis; Richards, Daniel; Hoster, Harry E.
2017-01-01
In-situ diagnostic tools have become established to as a means to understanding the aging processes that occur during charge/discharge cycles in Li-ion batteries (LIBs). One electrochemical thermodynamic technique that can be applied to this problem is known as entropy profiling. Entropy profiles are obtained by monitoring the variation in the open circuit potential as a function of temperature. The peaks in these profiles are related to phase transitions, such as order/disorder transitions, in the lattice. In battery aging studies of cathode materials, the peaks become suppressed but the mechanism by which this occurs is currently poorly understood. One suggested mechanism is the formation of point defects. Intentional modifications of LIB electrodes may also lead to the introduction of point defects. To gain quantitative understanding of the entropy profile changes that could be caused by point defects, we have performed Monte Carlo simulations on lattices of variable defect content. As a model cathode, we have chosen manganese spinel, which has a well-described order-disorder transition when it is half filled with Li. We assume, in the case of trivalent defect substitution (M = Cr,Co) that each defect M permanently pins one Li atom. This assumption is supported by Density Functional Theory (DFT) calculations. Assuming that the distribution of the pinned Li sites is completely random, we observe the same trend in the change in partial molar entropy with defect content as observed in experiment: the peak amplitudes become increasing suppressed as the defect fraction is increased. We also examine changes in the configurational entropy itself, rather than the entropy change, as a function of the defect fraction and analyse these results with respect to the ones expected for an ideal solid solution. We discuss the implications of the quantitative differences between some of the results obtained from the model and the experimentally observed ones.
Chen, Yuntian; Zhang, Yan; Femius Koenderink, A
2017-09-04
We study semi-analytically the light emission and absorption properties of arbitrary stratified photonic structures with embedded two-dimensional magnetoelectric point scattering lattices, as used in recent plasmon-enhanced LEDs and solar cells. By employing dyadic Green's function for the layered structure in combination with the Ewald lattice summation to deal with the particle lattice, we develop an efficient method to study the coupling between planar 2D scattering lattices of plasmonic, or metamaterial point particles, coupled to layered structures. Using the 'array scanning method' we deal with localized sources. Firstly, we apply our method to light emission enhancement of dipole emitters in slab waveguides, mediated by plasmonic lattices. We benchmark the array scanning method against a reciprocity-based approach to find that the calculated radiative rate enhancement in k-space below the light cone shows excellent agreement. Secondly, we apply our method to study absorption-enhancement in thin-film solar cells mediated by periodic Ag nanoparticle arrays. Lastly, we study the emission distribution in k-space of a coupled waveguide-lattice system. In particular, we explore the dark mode excitation on the plasmonic lattice using the so-called array scanning method. Our method could be useful for simulating a broad range of complex nanophotonic structures, i.e., metasurfaces, plasmon-enhanced light emitting systems and photovoltaics.
Moments of unpolarized nucleon structure functions in chirally improved lattice QCD
Energy Technology Data Exchange (ETDEWEB)
Goeckeler, Meinulf; Maurer, Thilo; Schaefer, Andreas [University of Regensburg (Germany); Lang, Christian B.; Limmer, Markus [University of Graz (Austria)
2008-07-01
We present our results for the lowest moments of unpolarized nucleon structure functions at leading twist. We employ lattice quantum chromodynamics using chirally improved fermions in quenched as well as dynamical simulations.
Defects and defect generation in oxide layer of ion implanted silicon-silicon dioxide structures
Baraban, A P
2002-01-01
One studies mechanism of generation of defects in Si-SiO sub 2 structure oxide layer as a result of implantation of argon ions with 130 keV energy and 10 sup 1 sup 3 - 3.2 x 10 sup 1 sup 7 cm sup - sup 2 doses. Si-SiO sub 2 structures are produced by thermal oxidation of silicon under 950 deg C temperature. Investigations were based on electroluminescence technique and on measuring of high-frequency volt-farad characteristics. Increase of implantation dose was determined to result in spreading of luminosity centres and in its maximum shifting closer to boundary with silicon. Ion implantation was shown, as well, to result in increase of density of surface states at Si-SiO sub 2 interface. One proposed model of defect generation resulting from Ar ion implantation into Si-SiO sub 2
Piezoelectricity and pyroelectricity in polyvinylidene fluoride - Influence of the lattice structure
Purvis, C. K.; Taylor, P. L.
1983-01-01
Piezoelectric and pyroelectric responses of beta-phase (Phase I) polyvinylidene fluoride are predicted for a model system of polarizable point dipoles. The model incorporates the influence of the orthorhombic crystal structure by including the dependence of the internal electric field on the lattice parameters. Strong anisotropy in the piezoelectric response under uniaxial stress is predicted as a consequence of the orthorhombic lattice structure. Predictions are found to be in reasonable agreement with room-temperature experimental data.
Ignatenko, A. N.; Irkhin, V. Yu.
2016-01-01
We have studied the Heisenberg antiferromagnets characterized by the magnetic structures with the periods being two times larger than the lattice period. We have considered all the types of the Bravais lattices (simple cubic, bcc and fcc) and divided all these antiferromagnets into 7 classes i.e. 3 plus 4 classes denoted with symbols A and B correspondingly. The order parameter characterizing the degeneracies of the magnetic structures is an ordinary Neel vector for A classes and so-called 4-...
Status and prospects for the calculation of hadron structure from lattice QCD
International Nuclear Information System (INIS)
Renner, Dru B.
2010-02-01
Lattice QCD calculations of hadron structure are a valuable complement to many experimental programs as well as an indispensable tool to understand the dynamics of QCD. I present a focused review of a few representative topics chosen to illustrate both the challenges and advances of our community: the momentum fraction, axial charge and charge radius of the nucleon. I will discuss the current status of these calculations and speculate on the prospects for accurate calculations of hadron structure from lattice QCD. (orig.)
Fracture Resistance, Surface Defects and Structural Strength of Glass
Rodichev, Y.M.; Veer, F.A.
2010-01-01
This paper poses the theory that the fracture resistance of basic float glass is dependent on it physicochemical properties and the surface defects fonned under the float glass production, glass processing and handling at the service conditions compose the aggregate basis for structural glass
Structure defects in malachite revealed by positron annihilation
International Nuclear Information System (INIS)
Geffroy, B.; Diallo, I.; Paulin, R.
1984-01-01
Positron lifetime is measured between 77 and 400 K in two malachite samples with different mineralogical structures. The complex spectrum found in zoned malachite reveals a microporosity which remains stable in this range of temperature. Besides, above 200 K, equilibrium defects appear. Their formation energy is estimated to be Esub(f) = 0.27 +- 0.02 eV [fr
Structure defects in malachite revealed by positron annihilation
Energy Technology Data Exchange (ETDEWEB)
Geffroy, B; Diallo, I; Paulin, R [Institut National des Sciences et Techniques Nucleaires, CEN/Saclay, 91 - Gif-sur-Yvette (France)
1984-01-01
Positron lifetime is measured between 77 and 400 K in two malachite samples with different mineralogical structures. The complex spectrum found in zoned malachite reveals a microporosity which remains stable in this range of temperature. Besides, above 200 K, equilibrium defects appear. Their formation energy is estimated to be Esub(f) = 0.27 +- 0.02 eV.
Influence of structural defects on excitonic photoluminescence of pentacene
International Nuclear Information System (INIS)
Piryatins'kij, Yu.P.; Kurik, M.V.
2011-01-01
The exciton reflection, absorption, and photoluminescence spectra for single crystals and polycrystalline films have been studied in the temperature range of 4.2-296 K. A significant influence of structural defects arising during phase transitions on the exciton spectra of pentacene has been detected. The mechanisms of photoluminescence in single crystals and crystalline films of pentacene have been considered.
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.
Loading mode dependent effective properties of octet-truss lattice structures using 3D-printing
Challapalli, Adithya
Cellular materials, often called lattice materials, are increasingly receiving attention for their ultralight structures with high specific strength, excellent impact absorption, acoustic insulation, heat dissipation media and compact heat exchangers. In alignment with emerging additive manufacturing (AM) technology, realization of the structural applications of the lattice materials appears to be becoming faster. Considering the direction dependent material properties of the products with AM, by directionally dependent printing resolution, effective moduli of lattice structures appear to be directionally dependent. In this paper, a constitutive model of a lattice structure, which is an octet-truss with a base material having an orthotropic material property considering AM is developed. In a case study, polyjet based 3D printing material having an orthotropic property with a 9% difference in the principal direction provides difference in the axial and shear moduli in the octet-truss by 2.3 and 4.6%. Experimental validation for the effective properties of a 3D printed octet-truss is done for uniaxial tension and compression test. The theoretical value based on the micro-buckling of truss member are used to estimate the failure strength. Modulus value appears a little overestimate compared with the experiment. Finite element (FE) simulations for uniaxial compression and tension of octettruss lattice materials are conducted. New effective properties for the octet-truss lattice structure are developed considering the observed behavior of the octet-truss structure under macroscopic compression and tension trough simulations.
Mechanical and electrical strain response of a piezoelectric auxetic PZT lattice structure
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.
Interactions of structural defects with metallic impurities in multicrystalline silicon
International Nuclear Information System (INIS)
McHugo, S.A.; Thompson, A.C.; Hieslmair, H.
1997-01-01
Multicrystalline silicon is one of the most promising materials for terrestrial solar cells. It is critical to getter impurities from the material as well as inhibit contamination during growth and processing. Standard processing steps such as, phosphorus in-diffusion for p-n junction formation and aluminum sintering for backside ohmic contact fabrication, intrinsically possess gettering capabilities. These processes have been shown to improve L n values in regions of multicrystalline silicon with low structural defect densities but not in highly dislocated regions. Recent Deep Level Transient Spectroscopy (DLTS) results indirectly reveal higher concentrations of iron in highly dislocated regions while further work suggests that the release of impurities from structural defects, such as dislocations, is the rate limiting step for gettering in multicrystalline silicon. The work presented here directly demonstrates the relationship between metal impurities, structural defects and solar cell performance in multicrystalline silicon. Edge-defined Film-fed Growth (EFG) multicrystalline silicon in the as-grown state and after full solar cell processing was used in this study. Standard solar cell processing steps were carried out at ASE Americas Inc. Metal impurity concentrations and distributions were determined by use of the x-ray fluorescence microprobe (beamline 10.3.1) at the Advanced Light Source, Lawrence Berkeley National Laboratory. The sample was at atmosphere so only elements with Z greater than silicon could be detected, which includes all metal impurities of interest. Structural defect densities were determined by preferential etching and surface analysis using a Scanning Electron Microscope (SEM) in secondary electron mode. Mapped areas were exactly relocated between the XRF and SEM to allow for direct comparison of impurity and structural defect distributions
Magnetic structure and resonance properties of hexagonal antidot lattice
International Nuclear Information System (INIS)
Marchenko, A.I.; Krivoruchko, V.N.
2012-01-01
Static and resonance properties of ferromagnetic films with an antidot lattice (pores in the film) are studied. The description of the system is based on micromagnetic modeling and analytical solution of the Landau-Lifshitz equation. The dependences of ferromagnetic resonance spectra on the in-plane direction of applied magnetic field and on the lattice parameters are investigated. The dependences of a dynamic system response on frequency at fixed magnetic field and on field at fixed frequency, when the field changes cause the static magnetic order to change are explored. It is found that the specific peculiarities of the system dynamics leave unchange for both of these experimental conditions. Namely, for low damping the resonance spectra contain three quasi-homogeneous modes which are due to the resonance of different regions (domains) of the antidot lattice cell. It is shown the angular field dependences of each mode are characterized by a twofold symmetry and the related easy axes are mutually rotated by 60 degrees. As the result, a hexagonal symmetry of the system static and dynamic magnetic characteristics is realized. The existence in the resonance spectrum of several quasi-homogeneous modes related to different regions of the unit cell could be fundamental for working elements of magnonic devices.
High resolution electron microscopy. Visualization of crystal lattices and of their defects
International Nuclear Information System (INIS)
Desseaux, J.
1981-10-01
A great number of fault characterization results may be obtained without calculations simply by observing the pictures: determination of Burgers' vector of dislocations, dissociation of the dislocations, presence of precipitates in the heart of the dislocations, presence of micro-twin-crystals, phase boundaries, etc. Determining the position of the atoms will be facilitated if the phase system approximation can be applied. In those cases where it is necessary to use the calculated image-experimental image comparison, it is fundamental to check the parameters on which the image depends. For the simplicity of the interpretation it is always necessary to obtain images taken in conditions where the structure is the most directly projected and where the image contrast is as stable as possible for a small variation in the parameters: thickness, focusing and crystalline parameters. A few examples are given on silicon [fr
Diffusive, Structural, Optical, and Electrical Properties of Defects in Semiconductors
Wagner, F E
2002-01-01
Electronic properties of semiconductors are extremely sensitive to defects and impurities that have localized electronic states with energy levels in the band gap of the semiconductor. Spectroscopic techniques like photoluminescence (PL), deep level transient spectroscopy (DLTS), or Hall effect, that are able to detect and characterize band gap states do not reveal direct information about their microscopic origin. To overcome this chemical "blindness", the present approach is to use radioactive isotopes as a tracer. Moreover, the recoil energies involved in $\\beta$ and $\\gamma$-decays can be used to create intrinsic isolated point defects (interstitials, vacancies) in a controlled way. A microscopic insight into the structure and the thermodynamic properties of complexes formed by interacting defects can be gained by detecting the hyperfine interaction between the nuclear moments of radioactive dopants and the electromagnetic fields present at the site of the radioactive nucleus. The understanding and the co...
Complete flexural vibration band gaps in membrane-like lattice structures
International Nuclear Information System (INIS)
Yu Dianlong; Liu Yaozong; Qiu Jing; Wang Gang; Zhao Honggang
2006-01-01
The propagation of flexural vibration in the periodical membrane-like lattice structure is studied. The band structure calculated with the plane wave expansion method indicates the existence of complete gaps. The frequency response function of a finite periodic structure is simulated with finite element method. Frequency ranges with vibration attenuation are in good agreement with the gaps found in the band structure. Much larger attenuations are found in the complete gaps comparing to those directional ones. The existence of complete flexural vibration gaps in such a lattice structure provides a new idea for vibration control of thin plates
Directory of Open Access Journals (Sweden)
A-F. Obaton
2017-08-01
Full Text Available Several cylindrical specimens and dental implants, presenting diagonal lattice structures with different cell sizes (600, 900 and 1200 μm were additively manufactured by selective laser melting process. Then they were implanted for two months in a sheep. After removal, they were studied by Archimedes’ method as well as X-ray computed tomography in order to assess the penetration of bone into the lattice. We observed that the additive manufactured parts were geometrically conformed to the theoretical specifications. However, several particles were left adhering to the surface of the lattice, thereby partly or entirely obstructing the cells. Nevertheless, bone penetration was clearly visible. We conclude that the 900 μm lattice cell size is more favourable to bone penetration than the 1200 μm lattice cell size, as the bone penetration is 84% for 900 μm against 54% for 1200 μm cell structures. The lower bone penetration value for the 1200 μm lattice cell could possibly be attributed to the short residence time in the sheep. Our results lead to the conclusion that lattice implants additively manufactured by selective laser melting enable better bone integration.
International Nuclear Information System (INIS)
He Heming; Qin, Z.; Shoesmith, D.W.
2010-01-01
The ability of the UO 2 fluorite structure to accommodate large amounts of interstitial oxygen in various lattice sites leads to the formation of hyper-stoichiometric phases. The defect structures occurring in hyper-stoichiometric UO 2+x over the range 0.02 ≤ x ≤ 0.1 have been characterized by SEM/EDX and Raman analyses. The results demonstrate that as the nominal stoichiometry increases from 2.002 to 2.1, the diversity of defective structures existing on the UO 2+ surface also increases. Scanning electrochemical microscopy (SECM) measurements combined with a theoretical model were used to determine the rate constant for the reduction of the redox mediator ferrocene methanol, acting as a cathodic oxidant to corrode the four UO 2+x specimens. The rate constant was found to vary with location on the surface. Stoichiometric locations, with a well defined fluorite structure, exhibited very low corrosion rates. Higher rates were observed at more non-stoichiometric locations with the highest rates being obtained on locations exhibiting tetragonal distortions as their composition approached UO 2.33 . The distribution of rates increases with the degree of nominal non-stoichiometry as the diversity of microstructures existing on the UO 2+x surface increases.
On the topological structure of the vacuum in SU(2) and SU(3) lattice gauge theories
International Nuclear Information System (INIS)
Ishikawa, K.; Schierholz, G.; Schneider, H.; Teper, M.
1983-01-01
We present Monte Carlo measurements of the net topological charge of the vacuum in SU(2) and SU(3) lattice gauge theories. In both cases there is no evidence of any topological structure, and the values obtained are a factor of 0(100) smaller than expectations based on analyses of the U(1) problem. Moreover we find a strong sensitivity to the lattice size and to the boundary conditions imposed on the lattice. We comment on the physical significance of these results, establish criteria for the reliable performance of such calculations, and remark on the possibly detrimental impact of these findings on the calculation of hadron spectra
Physical content of preparation-question structures and Brouwer-Zadeh lattices
Cattaneo, Gianpiero; Nisticó, Giuseppe
1992-10-01
We give a criterion to compare the physical content of different mathematical structures derived from a preparation-question structure. Then this criterion is used in order to compare the physical content of the (Jauch-Piron's) property lattice with the physical content of the poset of testable properties. We prove that for complete preparation-question structures these two structures carry the same physical content; moreover the set of testable properties has the algebraic structure of the Brouwer-Zadeh lattice. For more general preparation-question structures the physical content of the poset of testable property can be larger than that of the property lattice. Physically relevant examples of the possible cases are given.
Emergent dynamic structures and statistical law in spherical lattice gas automata
Yao, Zhenwei
2017-12-01
Various lattice gas automata have been proposed in the past decades to simulate physics and address a host of problems on collective dynamics arising in diverse fields. In this work, we employ the lattice gas model defined on the sphere to investigate the curvature-driven dynamic structures and analyze the statistical behaviors in equilibrium. Under the simple propagation and collision rules, we show that the uniform collective movement of the particles on the sphere is geometrically frustrated, leading to several nonequilibrium dynamic structures not found in the planar lattice, such as the emergent bubble and vortex structures. With the accumulation of the collision effect, the system ultimately reaches equilibrium in the sense that the distribution of the coarse-grained speed approaches the two-dimensional Maxwell-Boltzmann distribution despite the population fluctuations in the coarse-grained cells. The emergent regularity in the statistical behavior of the system is rationalized by mapping our system to a generalized random walk model. This work demonstrates the capability of the spherical lattice gas automaton in revealing the lattice-guided dynamic structures and simulating the equilibrium physics. It suggests the promising possibility of using lattice gas automata defined on various curved surfaces to explore geometrically driven nonequilibrium physics.
Emergent dynamic structures and statistical law in spherical lattice gas automata.
Yao, Zhenwei
2017-12-01
Various lattice gas automata have been proposed in the past decades to simulate physics and address a host of problems on collective dynamics arising in diverse fields. In this work, we employ the lattice gas model defined on the sphere to investigate the curvature-driven dynamic structures and analyze the statistical behaviors in equilibrium. Under the simple propagation and collision rules, we show that the uniform collective movement of the particles on the sphere is geometrically frustrated, leading to several nonequilibrium dynamic structures not found in the planar lattice, such as the emergent bubble and vortex structures. With the accumulation of the collision effect, the system ultimately reaches equilibrium in the sense that the distribution of the coarse-grained speed approaches the two-dimensional Maxwell-Boltzmann distribution despite the population fluctuations in the coarse-grained cells. The emergent regularity in the statistical behavior of the system is rationalized by mapping our system to a generalized random walk model. This work demonstrates the capability of the spherical lattice gas automaton in revealing the lattice-guided dynamic structures and simulating the equilibrium physics. It suggests the promising possibility of using lattice gas automata defined on various curved surfaces to explore geometrically driven nonequilibrium physics.
Structural and optical investigations of oxygen defects in zinc oxide nanoparticles
International Nuclear Information System (INIS)
Sahai, Anshuman; Goswami, Navendu
2015-01-01
ZnO nanoparticles (NPs) were prepared implementing chemical precipitation method. Structural and optical characterizations of synthesized ZnO NPs were thoroughly probed applying X-ray diffraction (XRD), transmission electron microscope (TEM), energy dispersive X-ray (EDX) analysis, X-ray photoelectron spectroscopy (XPS), UV- Visible absorption and fluorescence (FL) spectroscopy. The XRD and TEM analyses revealed hexagonal wurtzite phase with 25-30 nm size. EDX analysis indicated oxygen (O) rich composition of nanoparticles. In accordance with EDX, XPS analysis verifies O i rich stoichiometry of prepared NPs. Furthermore, concurrence of lattice oxygen (O L ), interstitial oxygen (O i ) and oxygen vacancy (V O ) in ZnO NPs was demonstrated through XPS analysis. Size quantization of nanoparticles is evident by blue shift of UV-Visible absorption energy. The FL spectroscopic investigations ascertain the existence of several discrete and defect states and radiative transitions occurring therein. Display of visible emission from oxygen defect states and most importantly, excess of O i defects in prepared ZnO nanoparticles, was well established through FL study
Additive-manufactured sandwich lattice structures: A numerical and experimental investigation
Fergani, Omar; Tronvoll, Sigmund; Brøtan, Vegard; Welo, Torgeir; Sørby, Knut
2017-10-01
The utilization of additive-manufactured lattice structures in engineered products is becoming more and more common as the competitiveness of AM as a production technology has increased during the past several years. Lattice structures may enable important weight reductions as well as open opportunities to build products with customized functional properties, thanks to the flexibility of AM for producing complex geometrical configurations. One of the most critical aspects related to taking AM into new application areas—such as safety critical products—is currently the limited understanding of the mechanical behavior of sandwich-based lattice structure mechanical under static and dynamic loading. In this study, we evaluate manufacturability of lattice structures and the impact of AM processing parameters on the structural behavior of this type of sandwich structures. For this purpose, we conducted static compression testing for a variety of geometry and manufacturing parameters. Further, the study discusses a numerical model capable of predicting the behavior of different lattice structure. A reasonably good correlation between the experimental and numerical results was observed.
Fracture Resistance, Surface Defects and Structural Strength of Glass
Rodichev, Y.M.; Veer, F.A.
2010-01-01
This paper poses the theory that the fracture resistance of basic float glass is dependent on it physicochemical properties and the surface defects fonned under the float glass production, glass processing and handling at the service conditions compose the aggregate basis for structural glass strength assessment. The effect of loading conditions, constructional and technological factors on the engineering strength of glass can be evaluated in certain cases using fracture mechanics with inform...
Fine structure and analytical quantum-defect wave functions
International Nuclear Information System (INIS)
Kostelecky, V.A.; Nieto, M.M.; Truax, D.R.
1988-01-01
We investigate the domain of validity of previously proposed analytical wave functions for atomic quantum-defect theory. This is done by considering the fine-structure splitting of alkali-metal and singly ionized alkaline-earth atoms. The Lande formula is found to be naturally incorporated. A supersymmetric-type integer is necessary for finite results. Calculated splittings correctly reproduce the principal features of experimental values for alkali-like atoms
Defect-induced magnetic structure of CuMnSb
Czech Academy of Sciences Publication Activity Database
Máca, František; Kudrnovský, Josef; Drchal, Václav; Turek, I.; Stelmakhovych, O.; Beran, Přemysl; Llobet, A.; Martí, Xavier
2016-01-01
Roč. 94, č. 9 (2016), 1-9, č. článku 094407. ISSN 2469-9950 R&D Projects: GA ČR GB14-37427G Institutional support: RVO:68378271 ; RVO:61389005 Keywords : CuMnSb * electronic structure * defects * magnetic order * ab initio calculations * neutron diffraction analysis Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 3.836, year: 2016
Probing defect and magnetic structures on the nanoscale
Kallis, Alexis
2010-01-01
This thesis reports on experimental research on structural defects and magnetic species on the nanoscale. The latter project involved considerable development work on the production of a spin-polarised mono-energetic positron beam. The construction of the system is described through various trial steps with emphasis on the methods of maximum practical polarization of the positron beam and of electrons in the sample with the smallest possible loss of beam intensity. A new sodium-22 source caps...
The defect structure of ceramic high Tc superconductors
International Nuclear Information System (INIS)
Van Tendeloo, G.; Amelinckx, S.; Zandbergen, H.W.; Verwerft, M.
1989-01-01
In this paper an overview is given of electron microscopy studies on the different ceramic superconductors: YBa 2 Cu 3 O 7 , Bi(Tl)-Sr(Ba)- Ca-Cu-O and Pb 2 Sr 2 Y 0.5 Ca 0.5 Cu 3 O x . Planar defects in these materials play an important role in the superconducting properties. Their structural characteristics are discussed
Structural defects in electrodeposited Ni studied by positron annihilation
International Nuclear Information System (INIS)
Vertes, A.; Szeles, C.; Czako-Nagy, I.; Lakatos-Varsanyi, M.
1982-01-01
Structural investigation of electrodeposited Ni was carried out by positron annihilation (PA) technique. Additional Moessbauer effect and X-ray diffraction measurements were also performed. The samples were produced under different plating conditions resulting in stress in the range -100 to +600 N/mm 2 . From the positron lifetime measurements it seems that the defect pattern of electrodeposited Ni samples might be substantially different from sample to sample with different deposition and plating conditions. (Auth.)
Vacuum structure of pure gauge theories on the lattice
International Nuclear Information System (INIS)
Haymaker, R.W.; Singh, V.; Browne, D.; Wosiek, J.; Max-Planck-Institut fuer Physik und Astrophysik, Muenchen
1992-01-01
Results from simulations on two aspects of quark confinement in the pure gauge sector are presented. First is the calculation of the profile of the flux tube connecting a static q bar q pair in SU(2). By use of the Michael sum rules as a constraint, evidence is set forth that the energy density at the center of the flux tube goes to a constant as a function of quark- separation. Slow variation of the width and energy density is not ruled out. Secondly in the confined phase of lattice U(l), the curl of the magnetic monopole current is calculated, and it is shown that the dual London equation is satisfied and that the electric fluxoid is quantized
Rapid characterization of a nanomaterial structure using X-ray reciprocal-lattice-space imaging
International Nuclear Information System (INIS)
Sakata, Osami; Yoshimoto, Mamoru; Miki, Kazushi
2006-01-01
The X-ray reciprocal-lattice-space imaging method is able to record the reciprocal-lattice-space of nanostructure by sample-and-detector fixed geometry. This method was developed by the surface structure analysis beam line BL13XU of SPring-8. Outline of the X-ray diffraction method and basic principles of the X-ray reciprocal-lattice-space imaging method, and application examples are stated. The method is able to find out the Bragg conditions of nanostructure of surface in the atmosphere. The reciprocal-lattice of the embedded trace atomic wires was observed. The trace atoms of Bi atomic wires embedded in silicone showed the diffraction signal and image by a short exposure time. This method is useful at rapid non-destructive measurement of nanostructure. (S.Y.)
Coustaty, M; Bertet, K; Visani, M; Ogier, J
2011-08-01
In this paper, we propose a new approach for symbol recognition using structural signatures and a Galois lattice as a classifier. The structural signatures are based on topological graphs computed from segments which are extracted from the symbol images by using an adapted Hough transform. These structural signatures-that can be seen as dynamic paths which carry high-level information-are robust toward various transformations. They are classified by using a Galois lattice as a classifier. The performance of the proposed approach is evaluated based on the GREC'03 symbol database, and the experimental results we obtain are encouraging.
Characterization of the structure and chemistry of defects in materials
International Nuclear Information System (INIS)
Larson, B.C.; Ruehle, M.; Seidman, D.N.
1988-01-01
Research programs, presented at the materials research symposium, on defects in materials are presented. Major areas include: point defects, defect aggregates, and ordering; defects in non-metals and semiconductors; atomic resolution imaging of defects; and gain boundaries, interfaces, and layered materials. Individual projects are processed separately for the data bases
Directory of Open Access Journals (Sweden)
2016-01-01
Full Text Available Lattice composite fuselage structures are developed as an alternative to conventional composite structures based on laminated skin and stiffeners. Structure layout of lattice structures allows to realize advantages of current composite materials to a maximal extent, at the same time minimizing their main shortcomings, that allows to provide higher weight efficiency for these structures in comparison with conventional analogues.Development and creation of lattice composite structures requires development of novel methods of strength anal- ysis, as conventional methods, as a rule, are aiming to strength analysis of thin-walled elements and do not allow to get confident estimation of local strength of high-loaded unidirectional composite ribs.In the present work the method of operative strength analysis of lattice composite structure is presented, based onspecialized FE-models of unidirectional composite ribs and their intersections. In the frames of the method, every rib is modeled by a caisson structure, consisting of arbitrary number of flanges and webs, modeled by membrane finite elements. Parameters of flanges and webs are calculated automatically from the condition of stiffness characteristics equality of real rib and the model. This method allows to perform local strength analysis of high-loaded ribs of lattice structure without use of here-dimensional finite elements, that allows to shorten time of calculations and sufficiently simplify the procedure of analysis of results of calculations.For validation of the suggested method, the results of experimental investigations of full-scale prototype of shell of lattice composite fuselage section have been used. The prototype of the lattice section was manufactured in CRISM and tested in TsAGI within the frames of a number of Russian and International scientific projects. The results of validation have shown that the suggested method allows to provide high operability of strength analysis, keeping
Structures of single vortex and vortex lattice in a d-wave superconductor
International Nuclear Information System (INIS)
Xu, J.; Ren, Y.; Ting, C.
1996-01-01
The structures of a single vortex and vortex lattice in a superconductor with d x 2 -y 2 symmetry are studied self-consistently employing a recently developed Ginzburg-Landau theory. Near a single vortex, we found that an s-wave component of the order parameter is always induced, and it causes the local magnetic-field distribution and the d-wave order parameter to have a fourfold anisotropy. It is shown that there is a strong correlation between the structure of a single vortex and the shape of the vortex lattice. Our numerical calculation indicates that the structure of the vortex lattice is always oblique except for temperatures very close to T c where it becomes triangular. The possible connection of the result with experiment is also discussed. copyright 1996 The American Physical Society
International Nuclear Information System (INIS)
Khodos, M.Ya.; Belysheva, G.M.; Brajnina, Kh.Z.
1986-01-01
Effect of iso- and heterovalent substitution in the structure of alkaline earth metal ortho-vanadates and synthesis conditions, simulating the definite type of their crystal lattice disordering, on the character of potentiodynamic anodic-cathodic curves has been investigated by the method of cyclic voltammetry. Correlation between signals observed and the defect structure of oxide compounds is refined. Oxygen chemisorption is shown to be determined by concentration of nonequilibrium oxygen vacancies, which formation is accompanied by appearance of quasi-free electrons
International Nuclear Information System (INIS)
Pietsch, U.; Borchard, W.
1987-01-01
The sensitivity of measurements of the lattice-parameter difference in monocrystalline heterostructures can be enhanced by use of an extremely asymmetrical diffraction geometry. If the angle of incidence is somewhat higher than the critical angle for total external reflection, the Bragg peak is shifted from the position calculated by kinematic theory. The amount of shift depends on the angle of incidence as well as on the mass density of the material used. For heteroepitaxial structures both the layer and the substrate peaks are shifted but by different amounts. Therefore it becomes possible to characterize layers of totally lattice-matched structures also. (orig.)
Understanding the defect structure of solution grown zinc oxide
Energy Technology Data Exchange (ETDEWEB)
Liew, Laura-Lynn [Institute of Materials Research and Engineering, Agency for Science, Technology and Research (A-STAR), 3 Research Link, Singapore 117602 (Singapore); School of Materials Science and Engineering, Nanyang Technological University, Block N4.1 Nanyang Avenue, Singapore 639798 (Singapore); Sankar, Gopinathan, E-mail: g.sankar@ucl.ac.uk [Department of Chemistry, University College London, 20 Gordon Street, London WC1H 0AJ (United Kingdom); Handoko, Albertus D. [Institute of Materials Research and Engineering, Agency for Science, Technology and Research (A-STAR), 3 Research Link, Singapore 117602 (Singapore); Goh, Gregory K.L., E-mail: g-goh@imre.a-star.edu.sg [Institute of Materials Research and Engineering, Agency for Science, Technology and Research (A-STAR), 3 Research Link, Singapore 117602 (Singapore); School of Materials Science and Engineering, Nanyang Technological University, Block N4.1 Nanyang Avenue, Singapore 639798 (Singapore); Kohara, Shinji [Japan Synchrotron Radiation Research Institute (JASRI), Mikazuki, Sayo, Hyogo 679-5198 (Japan)
2012-05-15
Zinc oxide (ZnO) is a wide bandgap semiconducting oxide with many potential applications in various optoelectronic devices such as light emitting diodes (LEDs) and field effect transistors (FETs). Much effort has been made to understand the ZnO structure and its defects. However, one major issue in determining whether it is Zn or O deficiency that provides ZnO its unique properties remains. X-ray absorption spectroscopy (XAS) is an ideal, atom specific characterization technique that is able to probe defect structure in many materials, including ZnO. In this paper, comparative studies of bulk and aqueous solution grown ({<=}90 Degree-Sign C) ZnO powders using XAS and x-ray pair distribution function (XPDF) techniques are described. The XAS Zn-Zn correlation and XPDF results undoubtedly point out that the solution grown ZnO contains Zn deficiency, rather than the O deficiency that were commonly reported. This understanding of ZnO short range order and structure will be invaluable for further development of solid state lighting and other optoelectronic device applications. - Graphical abstract: Highlights: Black-Right-Pointing-Pointer ZnO powders have been synthesized through an aqueous solution method. Black-Right-Pointing-Pointer Defect structure studied using XAS and XPDF. Black-Right-Pointing-Pointer Zn-Zn correlations are less in the ZnO powders synthesized in solution than bulk. Black-Right-Pointing-Pointer Zn vacancies are present in the powders synthesized. Black-Right-Pointing-Pointer EXAFS and XPDF, when used complementary, are useful characterization techniques.
International Nuclear Information System (INIS)
Fenwick, D.M.
1990-09-01
Our motivation for studying the effect of lattice defects on sintering kinetics came from a theory by Searcy concerning surface melting of solids. Surface melting has been shown to occur in ice, argon, and lead at temperatures below the melting point. While surface melting of this sort is an equilibrium phenomenon, Searcy has predicted that surface melting may also occur in a non-equilibrium situation -- when a solid is being rapidly heated and has a below-equilibrium concentration of vacancies for the temperature reached. To test the surface melting theory we have compared the density changes of two different types of powder compacts of lithium fluoride after subjecting both to the same fast-firing heat treatment. One type of compact consisted of powder originating from a crystal which he had quenched from a high temperature, and the other consisted of powder from a crystal which we had annealed at a lower temperature. When calcite is decomposed in vacuum, CaO is sometimes found in two distinguishable layers. Both layers are comprised of fairly uniformly sized, cylindrical rods on the order of 10 nm in diameter with the normal NaCl-type crystal structure. The outer layer consists of ∼1 μm diameter bundles of rods separated by ∼1 μm wide cracks. The second layer, adjacent to any undecomposed calcite -- the ''intermediate layer'' -- probably consists of rods which are relatively evenly spaced. Because sintering is negligible when calcite decomposition occurs below 700 degree C in a vacuum of 10 -3 torr or less, the outer layer is probably formed by a diffusionless, cooperative re-packing of CaO rods first formed with the uniform spacing characteristic of the intermediate layer. 35 refs., 25 figs., 6 tabs
Energy Technology Data Exchange (ETDEWEB)
Hu, P.P. [Institute of Modern Physics, Chinese Academy of Sciences (CAS), Lanzhou 730000 (China); University of Chinese Academy of Sciences (UCAS), Beijing 100049 (China); Liu, J., E-mail: J.Liu@impcas.ac.cn [Institute of Modern Physics, Chinese Academy of Sciences (CAS), Lanzhou 730000 (China); Zhang, S.X. [Institute of Modern Physics, Chinese Academy of Sciences (CAS), Lanzhou 730000 (China); University of Chinese Academy of Sciences (UCAS), Beijing 100049 (China); Maaz, K. [Institute of Modern Physics, Chinese Academy of Sciences (CAS), Lanzhou 730000 (China); Nanomaterials Research Group, Physics Division, PINSTECH, Nilore, 45650 Islamabad (Pakistan); Zeng, J. [Institute of Modern Physics, Chinese Academy of Sciences (CAS), Lanzhou 730000 (China); Guo, H. [Institute of Modern Physics, Chinese Academy of Sciences (CAS), Lanzhou 730000 (China); University of Chinese Academy of Sciences (UCAS), Beijing 100049 (China); Zhai, P.F.; Duan, J.L.; Sun, Y.M.; Hou, M.D. [Institute of Modern Physics, Chinese Academy of Sciences (CAS), Lanzhou 730000 (China)
2016-04-01
InP crystals and GaN films were irradiated by swift heavy ions {sup 86}Kr and {sup 209}Bi with kinetic energies of 25 and 9.5 MeV per nucleon and ion fluence in the range 5 × 10{sup 10} to 3.6 × 10{sup 12} ions/cm{sup 2}. The characteristic optical bands were studied by Raman spectroscopy to reveal the disorder and defects induced in the samples during the irradiation process. The crystallinity of InP and GaN was found to be deteriorated after irradiation by the swift heavy ions and resulted in the amorphous nature of the samples along the ion tracks. The amorphous tracks observed by transmission electron microscopy (TEM) images confirmed the formation of lattice defects. In typical F{sub 2}(LO) mode, in case of InP, the spectra shifted towards the lower wavenumbers with a maximum shift of 7.6 cm{sup −1} induced by 1030 MeV Bi ion irradiation. While in case of GaN, the typical E{sub 2}(high) mode shifted towards the higher wavenumbers, with maximum shift of 5.4 cm{sup −1} induced by 760 MeV Bi ion irradiation at ion fluence of 1 × 10{sup 12} ions/cm{sup 2}. The observed Raman shifts reveal the presence of lattice defects and disorder induced in the samples after irradiation by the swift heavy ions. This irradiation also generated lattice stress in the samples, which has been investigated and discussed in detail in this work.
Large-Scale, Exhaustive Lattice-Based Structural Auditing of SNOMED CT
Zhang, Guo-Qiang
One criterion for the well-formedness of ontologies is that their hierarchical structure form a lattice. Formal Concept Analysis (FCA) has been used as a technique for assessing the quality of ontologies, but is not scalable to large ontologies such as SNOMED CT. We developed a methodology called Lattice-based Structural Auditing (LaSA), for auditing biomedical ontologies, implemented through automated SPARQL queries, in order to exhaustively identify all non-lattice pairs in SNOMED CT. The percentage of non-lattice pairs ranges from 0 to 1.66 among the 19 SNOMED CT hierarchies. Preliminary manual inspection of a limited portion of the 518K non-lattice pairs, among over 34 million candidate pairs, revealed inconsistent use of precoordination in SNOMED CT, but also a number of false positives. Our results are consistent with those based on FCA, with the advantage that the LaSA computational pipeline is scalable and applicable to ontological systems consisting mostly of taxonomic links. This work is based on collaboration with Olivier Bodenreider from the National Library of Medicine, Bethesda, USA.
Structural defects in laser- and electron-beam annealed silicon
International Nuclear Information System (INIS)
Narayan, J.
1979-01-01
Laser and electron beam pulses provide almost an ideal source of heat by which thin layers of semiconductors can be rapidly melted and solidified with heating and cooling rates exceeding 10 80 C/sec. Microstructural modifications obtained as a function of laser parameters are examined and it is shown that both laser and electron beam pulses can be used to remove displacement damage, dislocations, dislocation loops and precipitates. Annealing of defects underneath the oxide layers in silicon is possible within a narrow energy window. The formation of cellular structure provides a rather clear evidence of melting which leads to segregation and supercooling, and subsequent cell formation
International Nuclear Information System (INIS)
Kwok, W.K.; Fendrich, J.; Fleshler, S.; Welp, U.; Downey, J.; Crabtree, G.W.; Giapintzakis, J.
1994-01-01
The vortex melting transition T m in several untwinned and twinned crystals is measured resistively in fields up to 8T. A Lindemann criterion for vortex lattice melting is obtained in addition to a sharp hysteresis in the magnetoresistance at B m supporting a first-order phase transition. The anisotropy of twin boundary pinning and its reduction of the 'kink' in ρ(T) associated with the first-order melting transition is discussed in samples with very dilute twin boundaries. We also report on the direct suppression of the the melting transition by intrinsic pinning for H parallel ab and by electron-irradiation-induced point defects. (orig.)
International Nuclear Information System (INIS)
Kwok, W.K.; Fleshler, S.; Welp, U.; Downey, J.; Crabtree, G.W.; Fendrich, J. Giapintzakis, J.
1993-08-01
The vortex melting transition T m in several untwinned and twinned crystals measured resistively in fields up to 8 Tesla. A Lindemann criterion for vortex lattice melting is obtained in addition to a sharp hysteresis in the magnetoresistance at B m supporting a first order phase transition. The anisotropy of twin boundary pinning and its reduction of the ''kink'' in ρ(T) associated with the first order melting transition is discussed in samples with very dilute twin boundaries. We also report on direct suppression of melting transition by intrinsic pinning for H parallel ab and by electron-irradiation-induced point defects
Relations between anisotropic defects, structural evolution, and van der Waals bonding in 2H-NbSe2
International Nuclear Information System (INIS)
Gavarri, J.R.; Mokrani, R.; Boulesteix, C.; Vacquier, G.
1988-01-01
Correlations between anisotropic defects and van der Waals interactions have been established for the layer compound 2H-NbSe 2 which is investigated by low temperature X-ray diffraction techniques. Thermal expansion coefficients and anisotropic Debye temperatures are determined. A diffraction profile analysis reveals the existence of lattice distortions independent of the temperature. They are due to layer defects. To interpret the structural evolution data, the thermal expansion functions, α a (T) and α c (T) are simulated in the low temperature range which yield the elastic constants and the Grueneisen parameters. Using bond energy models, the Van der Waals nature of interlayer Se-Se interactions is confirmed by a model of thermal expansion of bonds and connected with the C 13 component of the elastic tensor. Such interactions can explain the presence of some layer defects that can be 4H-NbSe 2 nuclei in the 2H host lattice. In addition, no strong change in the Grueneisen parameters is clearly shown to occur at the 35 K transition of 2H-NbSe 2 . (author)
Lattice instabilities and structural phase transformations in La2CuO4 superconductors and insulators
International Nuclear Information System (INIS)
Axe, J.D.
1991-01-01
Soft-mode structural phase transformations, common in many perovskite-based materials, are also found in La 2 CuO 4 and structurally related oxides. The resulting phase behavior is rather complex, but is a natural consequence of the degeneracy of the soft phonon order parameters. This paper reviews the structural and lattice-dynamical results and their interpretation based upon mean-field statistical mechanical models
Energy Technology Data Exchange (ETDEWEB)
Atobe, K.; Koizumi, T. [Naruto Univ. of Education, Tokushima (Japan); Okada, M. [Kyoto Univ., Research Reactor Inst., Kumatori, Osaka (Japan)
2003-01-01
Single crystals of {alpha}-Al{sub 2}O{sub 3} were irradiated by the two reactors, KUR and JMTR, at three different temperatures. Lattice defects produced by irradiation were studied by esr (electron spin resonance). Three kinds of esr spectram, which are denoted as A, B and C spectram, are observed. The spectram A was observed at three different irradiation temperatures and was ascribed to oxygen vacancies. The spectram B showed no angular dependence for the rotation of external magnetic field to the crystal axis, and the defect density of this spectram decreased with an increase of annealing temperature. When the specimen was annealed at 400 degC after irradiation at 200 degC, the spectram C was observed and was presumed to be due to Al-colloids. (Y. Kazumata)
International Nuclear Information System (INIS)
Norgett, M.J.
1980-01-01
Calculations, drawing principally on developments at AERE Harwell, of the relaxation about lattice defects are reviewed with emphasis on the techniques required for such calculations. The principles of defect modelling are outlined and various programs developed for defect simulations are discussed. Particular calculations for metals, ionic crystals and oxides, are considered. (UK)
Towards a lattice calculation of the nucleon structure functions
International Nuclear Information System (INIS)
Goeckeler, M.; Ilgenfritz, M.; Perlt, H.; Rakow, P.; Schierholz, G.; Forschungszentrum Juelich GmbH; Schiller, A.
1994-12-01
We have initiated a programme to compute the lower moments of the unpolarised and polarised deep inelastic structure functions of the nucleon in the quenched approxiation. We review our progress to date. (orig.)
q-deformed phase-space and its lattice structure
International Nuclear Information System (INIS)
Wess, J.
1998-01-01
Quantum groups lead to an algebraic structure that can be realized on quantum spaces. These are non-commutative spaces that inherit a well-defined mathematical structure from the quantum group symmetry. In turn, such quantum spaces can be interpreted as non-commutative configuration spaces for physical systems. We study the non-commutative Euclidean space that is based on the quantum group SO q (3)
Phase structure of lattice gauge theories for non-abelian subgroups of SU(3)
International Nuclear Information System (INIS)
Grosse, H.; Kuehnelt, H.
1981-01-01
The authors study the phase structure of Euclidean lattice gauge theories in four dimensions for certain non-abelian subgroups of SU(3) by using Monte-Carlo simulations and strong coupling expansions. As the order of the group increases a splitting of one phase transition into two is observed. (Auth.)
AACSD: An atomistic analyzer for crystal structure and defects
Liu, Z. R.; Zhang, R. F.
2018-01-01
We have developed an efficient command-line program named AACSD (Atomistic Analyzer for Crystal Structure and Defects) for the post-analysis of atomic configurations generated by various atomistic simulation codes. The program has implemented not only the traditional filter methods like the excess potential energy (EPE), the centrosymmetry parameter (CSP), the common neighbor analysis (CNA), the common neighborhood parameter (CNP), the bond angle analysis (BAA), and the neighbor distance analysis (NDA), but also the newly developed ones including the modified centrosymmetry parameter (m-CSP), the orientation imaging map (OIM) and the local crystallographic orientation (LCO). The newly proposed OIM and LCO methods have been extended for all three crystal structures including face centered cubic, body centered cubic and hexagonal close packed. More specially, AACSD can be easily used for the atomistic analysis of metallic nanocomposite with each phase to be analyzed independently, which provides a unique pathway to capture their dynamic evolution of various defects on the fly. In this paper, we provide not only a throughout overview on various theoretical methods and their implementation into AACSD program, but some critical evaluations, specific testing and applications, demonstrating the capability of the program on each functionality.
The equivalent thermal conductivity of lattice core sandwich structure: A predictive model
International Nuclear Information System (INIS)
Cheng, Xiangmeng; Wei, Kai; He, Rujie; Pei, Yongmao; Fang, Daining
2016-01-01
Highlights: • A predictive model of the equivalent thermal conductivity was established. • Both the heat conduction and radiation were considered. • The predictive results were in good agreement with experiment and FEM. • Some methods for improving the thermal protection performance were proposed. - Abstract: The equivalent thermal conductivity of lattice core sandwich structure was predicted using a novel model. The predictive results were in good agreement with experimental and Finite Element Method results. The thermal conductivity of the lattice core sandwich structure was attributed to both core conduction and radiation. The core conduction caused thermal conductivity only relied on the relative density of the structure. And the radiation caused thermal conductivity increased linearly with the thickness of the core. It was found that the equivalent thermal conductivity of the lattice core sandwich structure showed a highly dependent relationship on temperature. At low temperatures, the structure exhibited a nearly thermal insulated behavior. With the temperature increasing, the thermal conductivity of the structure increased owing to radiation. Therefore, some attempts, such as reducing the emissivity of the core or designing multilayered structure, are believe to be of benefit for improving the thermal protection performance of the structure at high temperatures.
Directory of Open Access Journals (Sweden)
J. Piątkowski
2009-07-01
Full Text Available Adding high-melting point elements (Mo, Nb, Ni, Ti, W to complex silumins results in hardening of the latter ones, owing to the formation of new intermetallic phases of the AlxMey type, with refinement of dendrites in α solution and crystals in β phase. The hardening is also due to the effect of various inoculants. An addition of the inoculant is expected to form substrates, the crystal lattice of which, or some (privileged lattice planes and interatomic spaces should bear a strong resemblance to the crystal nucleus. To verify this statement, using binary phase equilibria systems, the coefficient of crystal lattice matching, being one of the measures of the crystallographic similarity, was calculated. A compatibility of this parameter (up to 20% may decide about the structure compatibility between the substrate and crystal which, in turn, is responsible for the effectiveness of alloy modification. Investigations have proved that, given the temperature range of their formation, the density, the lattice type, and the lattice parameter, some intermetallic phases of the AlxMey type can act as substrates for the crystallisation of aluminium and silicon, and some of the silumin hardening phases.
Phase structure of thermal lattice QCD with N{sub f} = 2 twisted mass Wilson fermions
Energy Technology Data Exchange (ETDEWEB)
Ilgenfritz, E.M. [Humboldt-Universitaet, Berlin (Germany). Inst. fuer Physik; Heidelberg Univ. (Germany). Inst. fuer Theoretische Physik; Jansen, K. [Deutsches Elektronen-Synchrotron (DESY), Zeuthen (Germany); Lombardo, M. P. [INFN, Laboratori Nazionali di Frascati (Italy); Mueller-Preussker, M.; Petschlies, M. [Humboldt-Universitaet, Berlin (Germany). Inst. fuer Physik; Philipsen, O.; Zeidlewicz, L. [Inst. fuer Theoretische Physik, Wilhelms-Univ. Muenster (Germany)
2009-09-15
We present numerical results for the phase diagram of lattice QCD at finite temperature in the formulation with twisted mass Wilson fermions and a tree-level Symanzik-improved gauge action. Our simulations are performed on lattices with temporal extent N{sub {tau}}=8, and lattice coupling {beta} ranging from strong coupling to the scaling domain. Covering a wide range in the space spanned by the lattice coupling {beta} and the hopping and twisted mass parameters {kappa} and {mu}, respectively, we obtain a comprehensive picture of the rich phase structure of the lattice theory. In particular, we verify the existence of an Aoki phase in the strong coupling region and the realisation of the Sharpe-Singleton scenario at intermediate couplings. In the weak coupling region we identify the phase boundary for the physical finite temperature phase transition/crossover. Its shape in the three-dimensional parameter space is consistent with Creutz's conjecture of a cone-shaped thermal transition surface. (orig.)
Study of the tunneling effect within lattices with cubic structure on varying temperature
International Nuclear Information System (INIS)
Frisone, F.
2008-01-01
In this theoretical study, it is underlined that the presence of micro-cracks in the lattice structure increases the probability of tunneling effect between two deuterons by some orders of magnitude with respect to non-deformed lattices. We have derived an expression to compute the tunneling probability within a micro-crack, and hypothesized a D + 2 -D + 2 binding mechanism. Finally, the overall indications provided by these theoretical simulations appear to suggest that the deformation of the crystalline lattice, at varying temperature, seems able to influence the process of tunneling between the deuterons in the metal, while the forced loading with D 2 has, in general, no evident positive effects in pure metals, but in some cases could, on the contrary, condition the phenomenon negatively. (authors)
International Nuclear Information System (INIS)
Yu, Z.G.; Smith, D.L.; Saxena, A.; Bishop, A.R.
1997-01-01
The electronic transmission across metal/conjugated-oligomer/metal structures in the presence of lattice fluctuations is studied for short oligomer chains. The lattice fluctuations are approximated by static white noise disorder. Resonant transmission occurs when the energy of an incoming electron coincides with a discrete electronic level of the oligomer. The corresponding transmission peak diminishes in intensity with increasing disorder strength. Because of disorder there is an enhancement of the electronic transmission for energies that lie within the electronic gap of the oligomer. If fluctuations are sufficiently strong, a transmission peak within the gap is found at the midgap energy E=0 for degenerate conjugated oligomers (e.g., trans-polyacetylene) and E≠0 for AB-type degenerate oligomers. These results can be interpreted in terms of soliton-antisoliton states created by lattice fluctuations. copyright 1997 The American Physical Society
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
Magnetic structure and lattice deformation in UO/sub 2/
Energy Technology Data Exchange (ETDEWEB)
Aksenov, V L; Frauenheim, T; Sikora, V [Joint Inst. for Nuclear Research, Dubna (USSR)
1981-12-21
The magnetic phase transition in UO/sub 2/ is studied by means of a group theoretical analysis and the admitted symmetry groups in the low temperature phase are determined. With the help of the neutron diffraction data of Faber and Lander a three-arm magnetic and crystallographic structure with two types of translational domains is found and a new interpretation of the experiment of Faber and Lander is given.
Spin and lattice structures of single-crystalline SrFe2As2
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.
Kadioglu, Yelda; Kilic, Sevket Berkay; Demirci, Salih; Aktürk, O. Üzengi; Aktürk, Ethem; Ciraci, Salim
2017-12-01
This paper reveals how the electronic structure, magnetic structure, and topological phase of two-dimensional (2D), single-layer structures of bismuth are modified by point defects. We first showed that a free-standing, single-layer, hexagonal structure of bismuth, named h-bismuthene, exhibits nontrivial band topology. We then investigated interactions between single foreign adatoms and bismuthene structures, which comprise stability, bonding, electronic structure, and magnetic structures. Localized states in diverse locations of the band gap and resonant states in band continua of bismuthene are induced upon the adsorption of different adatoms, which modify electronic and magnetic properties. Specific adatoms result in reconstruction around the adsorption site. Single vacancies and divacancies can form readily in bismuthene structures and remain stable at high temperatures. Through rebondings, Stone-Whales-type defects are constructed by divacancies, which transform into a large hole at high temperature. Like adsorbed adatoms, vacancies induce also localized gap states, which can be eliminated through rebondings in divacancies. We also showed that not only the optical and magnetic properties, but also the topological features of pristine h-bismuthene can be modified by point defects. The modification of the topological features depends on the energies of localized states and also on the strength of coupling between point defects.
Defect structure of ultrafine MgB2 nanoparticles
International Nuclear Information System (INIS)
Bateni, Ali; Somer, Mehmet; Repp, Sergej; Erdem, Emre; Thomann, Ralf; Acar, Selçuk
2014-01-01
Defect structure of MgB 2 bulk and ultrafine particles, synthesized by solid state reaction route, have been investigated mainly by the aid of X-band electron paramagnetic resonance spectrometer. Two different amorphous Boron (B) precursors were used for the synthesis of MgB 2 , namely, boron 95 (purity 95%–97%, <1.5 μm) and nanoboron (purity >98.5%, <250 nm), which revealed bulk and nanosized MgB 2 , respectively. Scanning and transmission electron microscopy analysis demonstrate uniform and ultrafine morphology for nanosized MgB 2 in comparison with bulk MgB 2 . Powder X-ray diffraction data show that the concentration of the by-product MgO is significantly reduced when nanoboron is employed as precursor. It is observed that a significant average particle size reduction for MgB 2 can be achieved only by using B particles of micron or nano size. The origin and the role of defect centers were also investigated and the results proved that at nanoscale MgB 2 material contains Mg vacancies. Such vacancies influence the connectivity and the conductivity properties which are crucial for the superconductivity applications
Manipulation and quantification of microtubule lattice integrity
Directory of Open Access Journals (Sweden)
Taylor A. Reid
2017-08-01
Full Text Available Microtubules are structural polymers that participate in a wide range of cellular functions. The addition and loss of tubulin subunits allows the microtubule to grow and shorten, as well as to develop and repair defects and gaps in its cylindrical lattice. These lattice defects act to modulate the interactions of microtubules with molecular motors and other microtubule-associated proteins. Therefore, tools to control and measure microtubule lattice structure will be invaluable for developing a quantitative understanding of how the structural state of the microtubule lattice may regulate its interactions with other proteins. In this work, we manipulated the lattice integrity of in vitro microtubules to create pools of microtubules with common nucleotide states, but with variations in structural states. We then developed a series of novel semi-automated analysis tools for both fluorescence and electron microscopy experiments to quantify the type and severity of alterations in microtubule lattice integrity. These techniques will enable new investigations that explore the role of microtubule lattice structure in interactions with microtubule-associated proteins.
Compressive behaviour of gyroid lattice structures for human cancellous bone implant applications
International Nuclear Information System (INIS)
Yánez, A.; Herrera, A.; Martel, O.; Monopoli, D.; Afonso, H.
2016-01-01
Electron beam melting (EBM) was used to fabricate porous titanium alloy structures. The elastic modulus of these porous structures was similar to the elastic modulus of the cancellous human bone. Two types of cellular lattice structures were manufactured and tested: gyroids and diamonds. The design of the gyroid structures was determined by the main angle of the struts with respect to the axial direction. Thus, structures with angles of between 19 and 68.5° were manufactured. The aim of the design was to reduce the amount of material needed to fabricate a structure with the desired angles to increase the range of stiffness of the scaffolds. Compression tests were conducted to obtain the elastic modulus and the strength. Both parameters increased as the angle decreased. Finally, the specific strength of the gyroid structures was compared with that of the diamond structures and other types of structures. It is shown that, for angles lower than 35°, the gyroid structures had a high strength to weight ratios. - Highlights: • Gyroid and diamond lattice structures were fabricated by electron beam melting. • Compression tests were conducted to obtain the elastic modulus and the strength. • Some gyroid structures show a higher specific strength than other types of structures.
Compressive behaviour of gyroid lattice structures for human cancellous bone implant applications
Energy Technology Data Exchange (ETDEWEB)
Yánez, A., E-mail: alejandro.yanez@ulpgc.es [Department of Mechanical Engineering, University of Las Palmas de Gran Canaria (Spain); Herrera, A. [Julius Wolff Institute, Berlin (Germany); Martel, O. [Department of Mechanical Engineering, University of Las Palmas de Gran Canaria (Spain); Monopoli, D.; Afonso, H. [Department of Mechanical Engineering, Instituto Tecnológico de Canarias (Spain)
2016-11-01
Electron beam melting (EBM) was used to fabricate porous titanium alloy structures. The elastic modulus of these porous structures was similar to the elastic modulus of the cancellous human bone. Two types of cellular lattice structures were manufactured and tested: gyroids and diamonds. The design of the gyroid structures was determined by the main angle of the struts with respect to the axial direction. Thus, structures with angles of between 19 and 68.5° were manufactured. The aim of the design was to reduce the amount of material needed to fabricate a structure with the desired angles to increase the range of stiffness of the scaffolds. Compression tests were conducted to obtain the elastic modulus and the strength. Both parameters increased as the angle decreased. Finally, the specific strength of the gyroid structures was compared with that of the diamond structures and other types of structures. It is shown that, for angles lower than 35°, the gyroid structures had a high strength to weight ratios. - Highlights: • Gyroid and diamond lattice structures were fabricated by electron beam melting. • Compression tests were conducted to obtain the elastic modulus and the strength. • Some gyroid structures show a higher specific strength than other types of structures.
Energy Technology Data Exchange (ETDEWEB)
Dryzek, J [Institute of Nuclear Physics, Cracow (Poland)
1994-12-31
In this report the positrons annihilation methods as a tool for the crystal defects studies is presented. The short description of the positron - crystal interactions and different positron capture models are discussed. 192 refs, 67 figs, 6 tabs.
Detailed design of a lattice composite fuselage structure by a mixed optimization method
Liu, D.; Lohse-Busch, H.; Toropov, V.; Hühne, C.; Armani, U.
2016-10-01
In this article, a procedure for designing a lattice fuselage barrel is developed. It comprises three stages: first, topology optimization of an aircraft fuselage barrel is performed with respect to weight and structural performance to obtain the conceptual design. The interpretation of the optimal result is given to demonstrate the development of this new lattice airframe concept for the fuselage barrel. Subsequently, parametric optimization of the lattice aircraft fuselage barrel is carried out using genetic algorithms on metamodels generated with genetic programming from a 101-point optimal Latin hypercube design of experiments. The optimal design is achieved in terms of weight savings subject to stability, global stiffness and strain requirements, and then verified by the fine mesh finite element simulation of the lattice fuselage barrel. Finally, a practical design of the composite skin complying with the aircraft industry lay-up rules is presented. It is concluded that the mixed optimization method, combining topology optimization with the global metamodel-based approach, allows the problem to be solved with sufficient accuracy and provides the designers with a wealth of information on the structural behaviour of the novel anisogrid composite fuselage design.
Cramer, Nick; Swei, Sean Shan-Min; Cheung, Kenny; Teodorescu, Mircea
2015-01-01
This paper presents a modeling and control of aerostructure developed by lattice-based cellular materials/components. The proposed aerostructure concept leverages a building block strategy for lattice-based components which provide great adaptability to varying ight scenarios, the needs of which are essential for in- ight wing shaping control. A decentralized structural control design is proposed that utilizes discrete-time lumped mass transfer matrix method (DT-LM-TMM). The objective is to develop an e ective reduced order model through DT-LM-TMM that can be used to design a decentralized controller for the structural control of a wing. The proposed approach developed in this paper shows that, as far as the performance of overall structural system is concerned, the reduced order model can be as e ective as the full order model in designing an optimal stabilizing controller.
Energy Technology Data Exchange (ETDEWEB)
Capaz, Rodrigo B. [Instituto de Física, Universidade Federal do Rio de Janeiro, Caixa Postal 68528, Rio de Janeiro, RJ 21941-972 (Brazil); ElMassalami, M., E-mail: massalam@if.ufrj.br [Instituto de Física, Universidade Federal do Rio de Janeiro, Caixa Postal 68528, Rio de Janeiro, RJ 21941-972 (Brazil); Terrazos, L.A. [Centro de Educação e Saúde, Universidade Federal de Campina Grande, Cuité, PB 58175-000 (Brazil); Elhadi, M. [Instituto de Física, Universidade Federal do Rio de Janeiro, Caixa Postal 68528, Rio de Janeiro, RJ 21941-972 (Brazil); Takeya, H. [National Institute for Materials Science, 1-2-1, Sengen, Tsukuba, 305-0047 (Japan); Ghivelder, L. [Instituto de Física, Universidade Federal do Rio de Janeiro, Caixa Postal 68528, Rio de Janeiro, RJ 21941-972 (Brazil)
2016-06-05
Using a combination of theoretical (first-principles total-energy and electronic structure calculations) as well as experimental (structural, thermodynamics) techniques, we systematically investigated the influence of B incorporation on the structural, electronic and thermodynamic properties of a series of technologically-important B-containing AlNi matrix. Special attention was paid to calculating the energy cost of placing B at various sites within the cubic unit cell. The most energetically favorable defects were identified to be, depending on initial stoichiometry, substitutional B at Al site (B{sub Al}), Ni vacancy (V{sub Ni}), or Ni antisite (Ni{sub Al}). We show that the induced variation in the lattice parameters can be correlated with the type and concentration of the involved defects: e.g. the surge of V{sub Ni} defects leads to a stronger lattice-parameter reduction, that of Ni{sub Al} ones to a relatively weaker reduction while that of B{sub Al} defects to a much weaker influence. Both electronic band structure calculations as well as thermodynamics measurements indicate that the 3d bands of Ni are fully occupied and magnetically unpolarized and that the resulting N(E{sub F}) is very small: all studied compounds are normal conductors with no trace of superconductivity or magnetic polarization.
Crystal structure of human CRMP-4: correction of intensities for lattice-translocation disorder
Energy Technology Data Exchange (ETDEWEB)
Ponnusamy, Rajesh [Universidade Nova de Lisboa, Avenida da República, EAN, 2781-901 Oeiras (Portugal); Lebedev, Andrey A. [Research Complex at Harwell, STFC Rutherford Appleton Laboratory, Didcot OX11 0FA (United Kingdom); Pahlow, Steffen [University of Hamburg, Ohnhorststrasse 18, 22609 Hamburg (Germany); Lohkamp, Bernhard, E-mail: bernhard.lohkamp@ki.se [Karolinska Institutet, Tomtebodavägen 6, 4tr, 17177 Stockholm (Sweden); Universidade Nova de Lisboa, Avenida da República, EAN, 2781-901 Oeiras (Portugal)
2014-06-01
Crystals of human CRMP-4 showed severe lattice-translocation disorder. Intensities were demodulated using the so-called lattice-alignment method and a new more general method with simplified parameterization, and the structure is presented. Collapsin response mediator proteins (CRMPs) are cytosolic phosphoproteins that are mainly involved in neuronal cell development. In humans, the CRMP family comprises five members. Here, crystal structures of human CRMP-4 in a truncated and a full-length version are presented. The latter was determined from two types of crystals, which were either twinned or partially disordered. The crystal disorder was coupled with translational NCS in ordered domains and manifested itself with a rather sophisticated modulation of intensities. The data were demodulated using either the two-lattice treatment of lattice-translocation effects or a novel method in which demodulation was achieved by independent scaling of several groups of intensities. This iterative protocol does not rely on any particular parameterization of the modulation coefficients, but uses the current refined structure as a reference. The best results in terms of R factors and map correlation coefficients were obtained using this new method. The determined structures of CRMP-4 are similar to those of other CRMPs. Structural comparison allowed the confirmation of known residues, as well as the identification of new residues, that are important for the homo- and hetero-oligomerization of these proteins, which are critical to nerve-cell development. The structures provide further insight into the effects of medically relevant mutations of the DPYSL-3 gene encoding CRMP-4 and the putative enzymatic activities of CRMPs.
Crystal structure of human CRMP-4: correction of intensities for lattice-translocation disorder
International Nuclear Information System (INIS)
Ponnusamy, Rajesh; Lebedev, Andrey A.; Pahlow, Steffen; Lohkamp, Bernhard
2014-01-01
Crystals of human CRMP-4 showed severe lattice-translocation disorder. Intensities were demodulated using the so-called lattice-alignment method and a new more general method with simplified parameterization, and the structure is presented. Collapsin response mediator proteins (CRMPs) are cytosolic phosphoproteins that are mainly involved in neuronal cell development. In humans, the CRMP family comprises five members. Here, crystal structures of human CRMP-4 in a truncated and a full-length version are presented. The latter was determined from two types of crystals, which were either twinned or partially disordered. The crystal disorder was coupled with translational NCS in ordered domains and manifested itself with a rather sophisticated modulation of intensities. The data were demodulated using either the two-lattice treatment of lattice-translocation effects or a novel method in which demodulation was achieved by independent scaling of several groups of intensities. This iterative protocol does not rely on any particular parameterization of the modulation coefficients, but uses the current refined structure as a reference. The best results in terms of R factors and map correlation coefficients were obtained using this new method. The determined structures of CRMP-4 are similar to those of other CRMPs. Structural comparison allowed the confirmation of known residues, as well as the identification of new residues, that are important for the homo- and hetero-oligomerization of these proteins, which are critical to nerve-cell development. The structures provide further insight into the effects of medically relevant mutations of the DPYSL-3 gene encoding CRMP-4 and the putative enzymatic activities of CRMPs
Energy Technology Data Exchange (ETDEWEB)
Zhao, Jun [College of Physical Science and Technology, Yangtze University, Jingzhou, Hubei 434023 (China); Zeng, Hui, E-mail: zenghui@yangtzeu.edu.cn [College of Physical Science and Technology, Yangtze University, Jingzhou, Hubei 434023 (China); Wei, Jianwei [College of Optoelectronic Information, Chongqing University of Technology, Chongqing 400054 (China); Li, Biao; Xu, Dahai [College of Physical Science and Technology, Yangtze University, Jingzhou, Hubei 434023 (China)
2014-01-17
Using the first principles calculations associated with nonequilibrium Green's function, we have studied the electronic structures and quantum transport properties of defective armchair graphene nanoribbon (AGNR) in the presence of divacancy defects. The triple pentagon–triple heptagon (555–777) defect in the defective AGNR is energetically more favorable than the pentagon–octagon–pentagon (5–8–5) defect. Our calculated results reveal that both 5–8–5-like defect and 555–777-like defect in AGNR could improve the electron transport. It is anticipated that defective AGNRs can exhibit large range variations in transport behaviors, which are strongly dependent on the distributions of the divacancy defect.
International Nuclear Information System (INIS)
Jund, Philippe; Viennois, Romain; Tédenac, Jean-Claude; Colinet, Catherine; Hug, Gilles; Fèvre, Mathieu
2013-01-01
We report an ab initio study of the semiconducting Mg 2 X (with X = Si, Ge) compounds and in particular we analyze the formation energies of the different point defects with the aim of understanding the intrinsic doping mechanisms. We find that the formation energy of Mg 2 Ge is 50% larger than that of Mg 2 Si, in agreement with the experimental tendency. From a study of the stability and the electronic properties of the most stable defects, taking into account the growth conditions, we show that the main cause of the n doping in these materials comes from interstitial magnesium defects. Conversely, since other defects acting like acceptors such as Mg vacancies or multivacancies are more stable in Mg 2 Ge than in Mg 2 Si, this explains why Mg 2 Ge can be of n or p type, in contrast to Mg 2 Si. The finding that the most stable defects are different in Mg 2 Si and Mg 2 Ge and depend on the growth conditions is important and must be taken into account in the search for the optimal doping to improve the thermoelectric properties of these materials.
Directory of Open Access Journals (Sweden)
Kessler Julia
2017-01-01
Full Text Available This scientific survey is about periodic lattice structures which are made by Selective Laser Melting (SLM. Selective laser melting is based on Additive Manufacturing. The increased use and increasing demand of lattice structures in different fields of applications forms the necessity of a closer look on complex structures. Lattice structures can be found in different fields of applications for example in lightweight applications, filters and heat exchangers. Because of the expanding of application areas and thus arising requirements, the quality improvement is indispensable. Additive manufacturing and especially the SLM process enable the manufacturing of highly complex shapes and structures. Further it allows the integration of lightweight structures within to be manufactured applications. These high performance structures and applications need specific boundary and process conditions [1-3]. The main aim of this survey is an extraction of important parameters concerning the shape of lattices. A first focus will be on mechanical properties and the therefore necessary tensile tests.
Nucleon structure in lattice QCD with dynamical domain-wall fermions quarks
International Nuclear Information System (INIS)
Huey-Wen Lin; Shigemi Ohta
2006-01-01
We report RBC and RBC/UKQCD lattice QCD numerical calculations of nucleon electroweak matrix elements with dynamical domain-wall fermions (DWF) quarks. The first, RBC, set of dynamical DWF ensembles employs two degenerate flavors of DWF quarks and the DBW2 gauge action. Three sea quark mass values of 0.04, 0.03 and 0.02 in lattice units are used with about 200 gauge configurations each. The lattice cutoff is about 1.7 GeV and the spatial volume is about (1.9 fm) 3 . Despite the small volume, the ratio of the isovector vector and axial charges g A /g V and that of structure function moments u-d / Δ u-Δ d are in agreement with experiment, and show only very mild quark mass dependence. The second, RBC/UK, set of ensembles employs one strange and two degenerate (up and down) dynamical DWF quarks and Iwasaki gauge action. The strange quark mass is set at 0.04, and three up/down mass values of 0.03, 0.02 and 0.01 in lattice units are used. The lattice cutoff is about 1.6 GeV and the spatial volume is about (3.0 fm) 3 . Even with preliminary statistics of 25-30 gauge configurations, the ratios g A /g V and u-d / Δu - Δd are consistent with experiment and show only very mild quark mass dependence. Another structure function moment, d 1 , though yet to be renormalized, appears small in both sets
NUCLEON STRUCTURE IN LATTICE QCD WITH DYNAMICAL DOMAIN--WALL FERMIONS QUARKS
International Nuclear Information System (INIS)
LIN, H.W.; OHTA, S.
2006-01-01
We report RBC and RBC/UKQCD lattice QCD numerical calculations of nucleon electroweak matrix elements with dynamical domain-wall fermions (DWF) quarks. The first, RBC, set of dynamical DWF ensembles employs two degenerate flavors of DWF quarks and the DBW2 gauge action. Three sea quark mass values of 0.04, 0.03 and 0.02 in lattice units are used with 220 gauge configurations each. The lattice cutoff is a -1 ∼ 1.7GeV and the spatial volume is about (1.9fm) 3 . Despite the small volume, the ratio of the isovector vector and axial charges g A /g V and that of structure function moments u-d / Δu-Δd are in agreement with experiment, and show only very mild quark mass dependence. The second, RBC/UK, set of ensembles employs one strange and two degenerate (up and down) dynamical DWF quarks and Iwasaki gauge action. The strange quark mass is set at 0.04, and three up/down mass values of 0.03, 0.02 and 0.01 in lattice units are used. The lattice cutoff is a -1 ∼ 1.6GeV and the spatial volume is about (3.0fm) 3 . Even with preliminary statistics of 25-30 gauge configurations, the ratios g A /g V and u-d / Δu-Δd are consistent with experiment and show only very mild quark mass dependence. Another structure function moment, d 1 , though yet to be renormalized, appears small in both sets
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.
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.
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
A new crystal lattice structure of Helicobacter pylori neutrophil-activating protein (HP-NAP)
International Nuclear Information System (INIS)
Tsuruta, Osamu; Yokoyama, Hideshi; Fujii, Satoshi
2012-01-01
A new crystal lattice structure of H. pylori neutrophil-activating protein has been determined. Iron loading causes a series of conformational changes at the ferroxidase centre. A new crystal lattice structure of Helicobacter pylori neutrophil-activating protein (HP-NAP) has been determined in two forms: the native state (Apo) at 2.20 Å resolution and an iron-loaded form (Fe-load) at 2.50 Å resolution. The highly solvated packing of the dodecameric shell is suitable for crystallographic study of the metal ion-uptake pathway. Like other bacterioferritins, HP-NAP forms a spherical dodecamer with 23 symmetry including two kinds of channels. Iron loading causes a series of conformational changes of amino-acid residues (Trp26, Asp52 and Glu56) at the ferroxidase centre
Investigation of the vacuum structure of the Georgi-Glashow model on the lattice
International Nuclear Information System (INIS)
Bornyakov, V.G.; Ilgenfritz, E.M.; Mitrjushkin, V.K.; Zadorozhny, A.M.; Mueller-Preussker, M.
1988-08-01
Distributions and correlations of magnetic fluxes as well as correlations between magnetic fluxes and other local observables are calculated numerically in order to explain the phase structure of the 4D Georgi-Glashow model on the lattice. We use and compare different definitions of magnetic fluxes. The data suggest a simple picture characterizing typical magnetic fluctuations in different regions of the phase space. A relaxation procedure exposes Abelian monopole-loop configurations in one of the phases. (author). 21 refs, 12 figs
Traveling waves and spreading speed on a lattice model with age structure
Directory of Open Access Journals (Sweden)
Zongyi Wang
2012-09-01
Full Text Available In this article, we study a lattice differential model for a single species with distributed age-structure in an infinite patchy environment. Using method of approaches by Diekmann and Thieme, we develop a comparison principle and construct a suitable sub-solution to the given model, and show that there exists a spreading speed of the system which in fact coincides with the minimal wave speed.
Priyadarshini, Lakshmi
Frequently transported packaging goods are more prone to damage due to impact, jolting or vibration in transit. Fragile goods, for example, glass, ceramics, porcelain are susceptible to mechanical stresses. Hence ancillary materials like cushions play an important role when utilized within package. In this work, an analytical model of a 3D cellular structure is established based on Kelvin model and lattice structure. The research will provide a comparative study between the 3D printed Kelvin unit structure and 3D printed lattice structure. The comparative investigation is based on parameters defining cushion performance such as cushion creep, indentation, and cushion curve analysis. The applications of 3D printing is in rapid prototyping where the study will provide information of which model delivers better form of energy absorption. 3D printed foam will be shown as a cost-effective approach as prototype. The research also investigates about the selection of material for 3D printing process. As cushion development demands flexible material, three-dimensional printing with material having elastomeric properties is required. Further, the concept of cushion design is based on Kelvin model structure and lattice structure. The analytical solution provides the cushion curve analysis with respect to the results observed when load is applied over the cushion. The results are reported on basis of attenuation and amplification curves.
Fracture mechanical evaluation of high temperature structure and creep-fatigue defect assessment
Energy Technology Data Exchange (ETDEWEB)
Park, Chang Gyu; Kim, Jong Bum; Lee, Jae Han
2004-02-01
This study proposed the evaluation procedure of high temperature structures from the viewpoint of fracture mechanics on the cylindrical structure applicable to the KALIMER, which is developed by KAERI. For the evaluation of structural integrity, linear and non-linear fracture mechanics parameters were analyzed. Parameters used in creep defect growth applicable to high temperature structure of liquid metal reactor and the evaluation codes with these parameters were analyzed. The evaluation methods of defect initiation and defect growth which were established in R5/R6 code(UK), JNC method (Japan) and RCC-MR A16(France) code were analyzed respectively. The evaluation procedure of leak before break applicable to KALIMER was preliminarily developed and proposed. As an application example of defect growth, the creep-fatigue defect growth on circumferential throughwall defect in high temperature cylindrical structure was evaluated by RCC-MR A16 and this application technology was established.
Directory of Open Access Journals (Sweden)
Jens Götze
2017-10-01
Full Text Available Quartz samples of different origin from 10 localities in the Southern Ural region, Russia have been investigated to characterize their trace element compositions and defect structures. The analytical combination of cathodoluminescence (CL microscopy and spectroscopy, electron paramagnetic resonance (EPR spectroscopy, and trace-element analysis by inductively coupled plasma mass spectrometry (ICP-MS revealed that almost all investigated quartz samples showed very low concentrations of trace elements (cumulative concentrations of <50 ppm with <30 ppm Al and <10 ppm Ti and low abundances of paramagnetic defects, defining them economically as “high-purity” quartz (HPQ suitable for high-tech applications. EPR and CL data confirmed the low abundances of substitutional Ti and Fe, and showed Al to be the only significant trace element structurally bound in the investigated quartz samples. CL microscopy revealed a heterogeneous distribution of luminescence centres (i.e., luminescence active trace elements such as Al as well as features of deformation and recrystallization. It is suggested that healing of defects due to deformation-related recrystallization and reorganization processes of the quartz lattice during retrograde metamorphism resulted in low concentrations of CL activator and other trace elements or vacancies, and thus are the main driving processes for the formation of HPQ deposits in the investigated area.
Structural defects in monocrystalline silicon: from radiation ones to growing and technological
International Nuclear Information System (INIS)
Gerasimenko, N.N.; Pavlyuchenko, M.N.; Dzhamanbalin, K.K.
2001-01-01
The systematical review of properties and conditions of radiation structures in monocrystalline silicon including own defects (elementary and complex, disordered fields) as well as defect-impurity formations is presented. The most typical examples of principle effects influence of known defects on radiation-induced processes (phase transformations, diffusion and heteration and others are considered. Experimental facts and models of silicon radiation amorphization have been analyzed in comparison of state of the radiation amorphization radiation problem of metals and alloys. The up-to-date status of the problem of the radiation defects physics are discussed, including end-of-range -, n+-, rod-like- defects. The phenomenon self-organization in crystals with defects has been considered. The examples of directed using radiation defects merged in independent trend - defects engineering - are given
Subsurface defects structural evolution in nano-cutting of single crystal copper
International Nuclear Information System (INIS)
Wang, Quanlong; Bai, Qingshun; Chen, Jiaxuan; Sun, Yazhou; Guo, Yongbo; Liang, Yingchun
2015-01-01
Highlights: • An innovative analysis method is adopted to analyze nano-cutting process accurately. • A characteristic SFT and stair-rod dislocation are found in subsurface defect layer. • The formation mechanism of stair-rod dislocation is investigated. • The local atomic structure of subsurface defects is introduced. - Abstract: In this work, molecular dynamics simulation is performed to study the subsurface defects structural distribution and its evolution during nano-cutting process of single crystal copper. The formation mechanism of chip and machined surface is interviewed by analyzing the dislocation evolution and atomic migration. The centro-symmetry parameter and spherical harmonics method are adopted to characterize the distribution and evolution of the subsurface defect structures and local atomic structures. The results show that stacking faults, dislocation loops, “V-shaped” dislocation loops, and plenty of point defects are formed during the machined surface being formed in shear-slip zone. In subsurface damage layers, stair-rod dislocation, stacking fault tetrahedra, atomic cluster defect, and vacancy defect are formed. And the formation mechanism of stair-rod dislocation is investigated by atomic-scale structure evolution. The local atomic structures of subsurface defects are icosahedrons, hexagonal close packed, body-centered cubic, and defect face center cubic, and the variations of local atomic structures are investigated
Subsurface defects structural evolution in nano-cutting of single crystal copper
Energy Technology Data Exchange (ETDEWEB)
Wang, Quanlong [School of Mechatronics Engineering, Harbin Institute of Technology, Harbin 150001 (China); Center for Precision Engineering, Harbin Institute of Technology, Harbin 150001 (China); Bai, Qingshun [School of Mechatronics Engineering, Harbin Institute of Technology, Harbin 150001 (China); Chen, Jiaxuan, E-mail: wangquanlong0@hit.edu.cn [Center for Precision Engineering, Harbin Institute of Technology, Harbin 150001 (China); Sun, Yazhou [School of Mechatronics Engineering, Harbin Institute of Technology, Harbin 150001 (China); Guo, Yongbo [Center for Precision Engineering, Harbin Institute of Technology, Harbin 150001 (China); Liang, Yingchun [School of Mechatronics Engineering, Harbin Institute of Technology, Harbin 150001 (China)
2015-07-30
Highlights: • An innovative analysis method is adopted to analyze nano-cutting process accurately. • A characteristic SFT and stair-rod dislocation are found in subsurface defect layer. • The formation mechanism of stair-rod dislocation is investigated. • The local atomic structure of subsurface defects is introduced. - Abstract: In this work, molecular dynamics simulation is performed to study the subsurface defects structural distribution and its evolution during nano-cutting process of single crystal copper. The formation mechanism of chip and machined surface is interviewed by analyzing the dislocation evolution and atomic migration. The centro-symmetry parameter and spherical harmonics method are adopted to characterize the distribution and evolution of the subsurface defect structures and local atomic structures. The results show that stacking faults, dislocation loops, “V-shaped” dislocation loops, and plenty of point defects are formed during the machined surface being formed in shear-slip zone. In subsurface damage layers, stair-rod dislocation, stacking fault tetrahedra, atomic cluster defect, and vacancy defect are formed. And the formation mechanism of stair-rod dislocation is investigated by atomic-scale structure evolution. The local atomic structures of subsurface defects are icosahedrons, hexagonal close packed, body-centered cubic, and defect face center cubic, and the variations of local atomic structures are investigated.
A New Defected Ground Structure for Different Microstrip Circuit Applications
Directory of Open Access Journals (Sweden)
S. Das
2007-04-01
Full Text Available In this paper, a microstrip transmission line combined with a new U-headed dumb-bell defected ground structure (DGS is investigated. The proposed DGS of two U-shape slots connected by a thin transverse slot is placed in the ground plane of a microstrip line. A finite cutoff frequency and attenuation pole is observed and thus, the equivalent circuit of the DGS unit can be represented by a parallel LC resonant circuit in series with the transmission line. A two-cell DGS microstrip line yields a better lowpass filtering characteristics. The simulation is carried out by the MoM based IE3D software and in the experimental measurements a vector network analyzer is used. The effects of the transverse slot width and the distance between arms of the U-slot on the filter response curve are studied. This DGS is utilized for different microstrip circuit applications. The DGS is placed in the ground of a capacitive loaded microstrip line and a very low cutoff frequency is obtained. The DGS is adopted under the coupled lines of a parallel line coupler and an improvement in coupling coefficient is noticed. The proposed DGS is also incorporated in the ground plane under the feed lines and the coupled lines of a bandpass filter to improve separately the stopband and passband performances.
Polarized Raman study on the lattice structure of BiFeO3 films prepared by pulsed laser deposition
Yang, Yang; Yao, Yingbang; Zhang, Q.; Zhang, Xixiang
2014-01-01
Polarized Raman spectroscopy was used to study the lattice structure of BiFeO3 films on different substrates prepared by pulsed laser deposition. Interestingly, the Raman spectra of BiFeO3 films exhibit distinct polarization dependences
Related Structure Characters and Stability of Structural Defects in a Metallic Glass.
Niu, Xiaofeng; Feng, Shidong; Pan, Shaopeng
2018-03-22
Structural defects were investigated by a recently proposed structural parameter, quasi-nearest atom (QNA), in a modeled Zr 50 Cu 50 metallic glass through molecular dynamics simulations. More QNAs around an atom usually means that more defects are located near the atom. Structural analysis reveals that the spatial distribution of the numbers of QNAs displays to be clearly heterogeneous. Furthermore, QNA is closely correlated with cluster connections, especially four-atom cluster connections. Atoms with larger coordination numbers usually have less QNAs. When two atoms have the same coordination number, the atom with larger five-fold symmetry has less QNAs. The number of QNAs around an atom changes rather frequently and the change of QNAs might be correlated with the fast relaxation metallic glasses.
Related Structure Characters and Stability of Structural Defects in a Metallic Glass
Niu, Xiaofeng; Feng, Shidong; Pan, Shaopeng
2018-01-01
Structural defects were investigated by a recently proposed structural parameter, quasi-nearest atom (QNA), in a modeled Zr50Cu50 metallic glass through molecular dynamics simulations. More QNAs around an atom usually means that more defects are located near the atom. Structural analysis reveals that the spatial distribution of the numbers of QNAs displays to be clearly heterogeneous. Furthermore, QNA is closely correlated with cluster connections, especially four-atom cluster connections. Atoms with larger coordination numbers usually have less QNAs. When two atoms have the same coordination number, the atom with larger five-fold symmetry has less QNAs. The number of QNAs around an atom changes rather frequently and the change of QNAs might be correlated with the fast relaxation metallic glasses. PMID:29565298
Zhou, Yuan-Qi; Zhan, Li-Hua
2016-05-01
Composite stiffened-structure consists of the skin and stringer has been widely used in aircraft fuselage and wings. The main purpose of the article is to detect the composite material reinforced structure accurately and explore the relationship between defect formation and structural elements or curing process. Based on ultrasonic phased array inspection technology, the regularity of defects in the manufacture of composite materials are obtained, the correlation model between actual defects and nondestructive testing are established. The article find that the forming quality of deltoid area in T-stiffened structure is obviously improved by pre-curing, the defects of hat-stiffened structure are affected by the mandrel. The results show that the ultrasonic phased array inspection technology can be an effectively way for the detection of composite stiffened-structures, which become an important means to control the defects of composite and improve the quality of the product.
Growth, defect structure, and THz application of stoichiometric lithium niobate
Energy Technology Data Exchange (ETDEWEB)
Lengyel, K.; Péter, Á.; Kovács, L.; Corradi, G.; Dravecz, G.; Hajdara, I.; Szaller, Zs.; Polgár, K. [Wigner Research Centre for Physics, Hungarian Academy of Sciences, 1121 Budapest, Konkoly-Thege M. út 29-33 (Hungary); Pálfalvi, L.; Unferdorben, M. [Institute of Physics, University of Pécs, 7624 Pécs, Ifjúság útja 6 (Hungary); Hebling, J. [Institute of Physics, University of Pécs, 7624 Pécs, Ifjúság útja 6 (Hungary); MTA-PTE High Field Terahertz Research Group, 7624 Pécs (Hungary)
2015-12-15
preferred for most nonlinear optical applications apart holography and have the additional advantage to minimize the absorption even in the far-infrared (THz) range. The review also provides a discussion on the progress made in the characterization of non-stoichiometry related intrinsic and extrinsic defect structures in doped LN crystals, with emphasis on ODR-ion-doped and/or closely stoichiometric systems, based on both spectroscopic measurements and theoretical modelling, including the results of first principles quantum mechanical calculations on hydroxyl defects. It will also be shown that new perspective applications, e.g., the generation of high energy THz pulses with energies on the tens-of-mJ scale, are feasible with ODR-doped sLN crystals if optimal conditions, including the contact grating technique, are applied.
Gluon structure function of a color dipole in the light-cone limit of lattice QCD
International Nuclear Information System (INIS)
Gruenewald, D.; Ilgenfritz, E.-M.; Pirner, H. J.
2009-01-01
We calculate the gluon structure function of a color dipole in near-light-cone SU(2) lattice QCD as a function of x B . The quark and antiquark are external nondynamical degrees of freedom which act as sources of the gluon string configuration defining the dipole. We compute the color dipole matrix element of transversal chromo-electric and chromo-magnetic field operators separated along a direction close to the light cone, the Fourier transform of which is the gluon structure function. As vacuum state in the pure glue sector, we use a variational ground state of the near-light-cone Hamiltonian. We derive a recursion relation for the gluon structure function on the lattice similar to the perturbative Dokshitzer-Gribov-Lipatov-Altarelli-Parisi equation. It depends on the number of transversal links assembling the Schwinger string of the dipole. Fixing the mean momentum fraction of the gluons to the 'experimental value' in a proton, we compare our gluon structure function for a dipole state with four links with the next-to-leading-order MRST 2002 and the CTEQ AB-0 parametrizations at Q 2 =1.5 GeV 2 . Within the systematic uncertainty we find rather good agreement. We also discuss the low x B behavior of the gluon structure function in our model calculation.
International Nuclear Information System (INIS)
Minakawa, Nobuaki; Moriai, Atsushi; Morii, Yukio
2001-01-01
It is necessary to determine Δd/d in the internal stress measurement by the neutron diffraction method. Therefore, in case the non-strain spacing of lattice planes d 0 (hkl) is measured using bulk material, even though it does and attaches in a sample table length or every width and it is performing the diffraction measurement, it is difficult to determine for a true non-strain spacing of lattice planes by a processing strain, the grain-orientation, etc. It is available for the infinite thing spacing of lattice planes near non-strain condition to be measured by doing random rotation for bulk material in a beam center, and measuring an average spacing of lattice planes. Practical non-strain spacing of lattice planes measurement equipment was made, and the measurement was performed about much structure material. (author)
Tunable multi-wavelength polymer laser based on a triangular-lattice photonic crystal structure
International Nuclear Information System (INIS)
Huang, Wenbin; Pu, Donglin; Qiao, Wen; Wan, Wenqiang; Liu, Yanhua; Ye, Yan; Wu, Shaolong; Chen, Linsen
2016-01-01
A continuously tunable multi-wavelength polymer laser based on a triangular-lattice photonic crystal cavity is demonstrated. The triangular-lattice resonator was initially fabricated through multiple interference exposure and was then replicated into a low refractive index polymer via UV-nanoimprinting. The blend of a blue-emitting conjugated polymer and a red-emitting one was used as the gain medium. Three periods in the scalene triangular-lattice structure yield stable tri-wavelength laser emission (625.5 nm, 617.4 nm and 614.3 nm) in six different directions. A uniformly aligned liquid crystal (LC) layer was incorporated into the cavity as the top cladding layer. Upon heating, the orientation of LC molecules and thus the effective refractive index of the lasing mode changes which continuously shifts the lasing wavelength. A maximum tuning range of 12.2 nm was observed for the lasing mode at 625.5 nm. This tunable tri-wavelength polymer laser is simple constructed and cost-effective. It may find application in the fields of biosensors and photonic integrated circuits. (paper)
International Nuclear Information System (INIS)
Mourou, G.; Williamson, S.
1985-01-01
The authors have directly observed the laser-induced melt metamorphosis of thin aluminum films. The time required for the melt to evolve is dependent on the degree to which the Al specimen is superheated. The temperature of this superheated state can also be monitored on the picosecond time scale. The picosecond electron probe not only reveals information about the structure of a material but also about the lattice temperature. The change in lattice parameter that is observed as a shift in diffracted ring diameter is directly related to the thermal expansion coefficient. Also, based on the Debye-Waller effect, a reduction in the intensity of the diffraction rings can be observed due to increased lattice vibration. Presently, a 1-kHz-1-mJ/pulse Nd:YAG laser is being used to measure the temperature overshoot of laser-induced Al films. The high repetition rate permits signal averaging to be employed thereby increasing the sensitivity of the thermometric technique
Li, Z Y; Lam, W M; Yang, C; Xu, B; Ni, G X; Abbah, S A; Cheung, K M C; Luk, K D K; Lu, W W
2007-03-01
Recently, strontium (Sr) as ranelate compound has become increasingly popular in the treatment of osteoporosis. However, the lattice structure of bone crystal after Sr incorporation is yet to be extensively reported. In this study, we synthesized strontium-substituted hydroxyapatite (Sr-HA) with different Sr content (0.3%, 1.5% and 15% Sr-HA in mole ratio) to simulate bone crystals incorporated with Sr. The changes in chemical composition and lattice structure of apetite after synthetic incorporation of Sr were evaluated to gain insight into bone crystal changes after incorporation of Sr. X-ray diffraction (XRD) patterns revealed that 0.3% and 1.5% Sr-HA exhibited single phase spectrum, which was similar to that of HA. However, 15% Sr-HA induced the incorporation of HPO4(2-) and more CO3(2-), the crystallinity reduced dramatically. Transmission electron microscopy (TEM) images showed that the crystal length and width of 0.3% and 1.5% Sr-HA increased slightly. Meanwhile, the length and width distribution were broadened and the aspect ratio decreased from 10.68+/-4.00 to 7.28+/-2.80. The crystal size and crystallinity of 15% Sr-HA dropped rapidly, which may suggest that the fundamental crystal structure is changed. The findings from this work indicate that current clinical dosage which usually results in Sr incorporation of below 1.5% may not change chemical composition and lattice structure of bone, while it will broaden the bone crystal size distribution and strengthen the bone.
Acoustic method for investigation of the structural defects in metals
International Nuclear Information System (INIS)
Nicolaescu, I.I.; Curcaneanu, Nicoleta
1997-01-01
In this work an acoustic method is presented called, the resonant bar method, which is based on the interaction between ultrasound and the structural defects in high purity metals. By this method the internal dislocation friction (Q -1 ) and the propagation velocity (v) of the ultrasound in the bar is measured. Both quantities are shown to depend on the dislocation densities and the length of dislocation loop. The experimental setup is shown. It consists of the resonant bar, the excitation spool, a generator of variable frequency and amplitude, a receptor spool, a selective amplifier and the adjacent measuring and displaying apparatus. The two spools are located inside of a toroidal permanent magnet. The bar oscillations are produced by the variable electromagnetic force appearing between the whirl current induced in the sample by the generator and the field of toroidal magnet. This method is applied to nonmagnetic materials with high electric conductivity. If the bar under study consists of a insulating material then on its ends either a conducting thin layer or a metallic thin sheet is deposed. The installation allows measuring the acoustic parameters of materials (v and Q -1 ) by two procedures, the method of free damped oscillations and the method of forced oscillations. Also, the internal friction can be measured with this installation, either dependent on or independent of the generator amplitude. Measurements on aluminium samples resulted in the following values: Q -1 (3 ppm) = 10 -3 and Q -1 (150 ppm) = 10 -5 . By means of this installation internal friction can be studied in re-baked, annealed, mechanical deformed and irradiated samples or in materials submitted to other processes
Zhang, David Z.; Zhang, Peng; Zhao, Miao; Jafar, Salman
2018-01-01
Developments in selective laser melting (SLM) have enabled the fabrication of periodic cellular lattice structures characterized by suitable properties matching the bone tissue well and by fluid permeability from interconnected structures. These multifunctional performances are significantly affected by cell topology and constitutive properties of applied materials. In this respect, a diamond unit cell was designed in particular volume fractions corresponding to the host bone tissue and optimized with a smooth surface at nodes leading to fewer stress concentrations. There were 33 porous titanium samples with different volume fractions, from 1.28 to 18.6%, manufactured using SLM. All of them were performed under compressive load to determine the deformation and failure mechanisms, accompanied by an in-situ approach using digital image correlation (DIC) to reveal stress–strain evolution. The results showed that lattice structures manufactured by SLM exhibited comparable properties to those of trabecular bone, avoiding the effects of stress-shielding and increasing longevity of implants. The curvature of optimized surface can play a role in regulating the relationship between density and mechanical properties. Owing to the release of stress concentration from optimized surface, the failure mechanism of porous titanium has been changed from the pattern of bottom-up collapse by layer (or cell row) to that of the diagonal (45°) shear band, resulting in the significant enhancement of the structural strength. PMID:29510492
Liu, Fei; Zhang, David Z; Zhang, Peng; Zhao, Miao; Jafar, Salman
2018-03-03
Developments in selective laser melting (SLM) have enabled the fabrication of periodic cellular lattice structures characterized by suitable properties matching the bone tissue well and by fluid permeability from interconnected structures. These multifunctional performances are significantly affected by cell topology and constitutive properties of applied materials. In this respect, a diamond unit cell was designed in particular volume fractions corresponding to the host bone tissue and optimized with a smooth surface at nodes leading to fewer stress concentrations. There were 33 porous titanium samples with different volume fractions, from 1.28 to 18.6%, manufactured using SLM. All of them were performed under compressive load to determine the deformation and failure mechanisms, accompanied by an in-situ approach using digital image correlation (DIC) to reveal stress-strain evolution. The results showed that lattice structures manufactured by SLM exhibited comparable properties to those of trabecular bone, avoiding the effects of stress-shielding and increasing longevity of implants. The curvature of optimized surface can play a role in regulating the relationship between density and mechanical properties. Owing to the release of stress concentration from optimized surface, the failure mechanism of porous titanium has been changed from the pattern of bottom-up collapse by layer (or cell row) to that of the diagonal (45°) shear band, resulting in the significant enhancement of the structural strength.
Energy Technology Data Exchange (ETDEWEB)
Stein, W.D.R.
2007-04-23
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{sub 3}O{sub 6}). The structure of the tetraborates MB{sub 4}O{sub 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
De Novo generation of molecular structures using optimization to select graphs on a given lattice
DEFF Research Database (Denmark)
Bywater, R.P.; Poulsen, Thomas Agersten; Røgen, Peter
2004-01-01
A recurrent problem in organic chemistry is the generation of new molecular structures that conform to some predetermined set of structural constraints that are imposed in an endeavor to build certain required properties into the newly generated structure. An example of this is the pharmacophore...... model, used in medicinal chemistry to guide de novo design or selection of suitable structures from compound databases. We propose here a method that efficiently links up a selected number of required atom positions while at the same time directing the emergent molecular skeleton to avoid forbidden...... positions. The linkage process takes place on a lattice whose unit step length and overall geometry is designed to match typical architectures of organic molecules. We use an optimization method to select from the many different graphs possible. The approach is demonstrated in an example where crystal...
International Nuclear Information System (INIS)
Sasaki, T.; Arafune, K.; Lee, H.S.; Ekins-Daukes, N.J.; Tanaka, S.; Ohshita, Y.; Yamaguchi, M.
2006-01-01
Lattice-mismatched In 0.16 Ga 0.84 As solar cells were grown on GaAs substrates using graded In x Ga 1- x As buffer layers and homogenous In 0.16 Ga 0.84 As buffer layers. The indium composition x in the graded buffer changed from 0% to 16% continuously. Thermal cycle annealing (TCA) was performed after the growth of the graded buffer layers. The effects of TCA on the solar cell open-circuit voltage and quantum efficiency have been investigated. The minority carrier lifetime is observed to increase in the p-type In 0.16 Ga 0.84 As layer after applying the TCA process. Electron-beam-induced current microscopy also shows a related reduction in dislocation density in the p-type In 0.16 Ga 0.84 As layer after TCA processing. Cross-sectional transmission electron microscopy performed on the graded buffer layer suggests that the strain present in the cell layers is reduced after the TCA process, implying that the TCA treatment promotes strain relaxation in the graded buffer layers
International Nuclear Information System (INIS)
Verite, G.
2007-09-01
This research aims at determining, by means of DFT (density functional theory) electronic structure computations, the structure, the stability, and the mobility of isolated point defects, lack defects, auto-interstitial defects, or small aggregate defects in the compact hexagonal zirconium (hc Zr). After a literature survey on the studied materials and a review of computer simulation methods in material science, the author presents and comments the available results from experiments or simulations on point defects in hc Zr. He presents the growth phenomenon under radiation. Then, he briefly described the computing techniques used in this study, reports the determination of the network parameters and elastic constants of each material. He reports and comments the results obtained with the SIESTA code and with a Monte Carlo kinetic simulation. The different types of defects are investigated
Shallow nitrogen ion implantation: Evolution of chemical state and defect structure in titanium
Energy Technology Data Exchange (ETDEWEB)
Manojkumar, P.A., E-mail: manoj@igcar.gov.in [Indira Gandhi Centre for Atomic Research, Kalpakkam 603102 (India); Chirayath, V.A.; Balamurugan, A.K.; Krishna, Nanda Gopala; Ilango, S.; Kamruddin, M.; Amarendra, G.; Tyagi, A.K. [Indira Gandhi Centre for Atomic Research, Kalpakkam 603102 (India); Raj, Baldev [National Institute of Advanced Studies, Bangalore 560 012 (India)
2016-09-15
Highlights: • Low energy nitrogen ion implantation in titanium was studied. • Chemical and defect states were analyzed using SIMS, XPS and PAS. • SIMS and depth resolved XPS data showed good agreement. • Depth resolved defect and chemical states information were revealed. • Formation of 3 layers of defect states proposed to fit PAS results. - Abstract: Evolution of chemical states and defect structure in titanium during low energy nitrogen ion implantation by Plasma Immersion Ion Implantation (PIII) process is studied. The underlying process of chemical state evolution is investigated using secondary ion mass spectrometry and X-ray photoelectron spectroscopy. The implantation induced defect structure evolution as a function of dose is elucidated using variable energy positron annihilation Doppler broadening spectroscopy (PAS) and the results were corroborated with chemical state. Formation of 3 layers of defect state was modeled to fit PAS results.
International Nuclear Information System (INIS)
Zurba, Nadia Khaled; Ferreira, Jose Maria da Fonte
2012-01-01
This article reports the investigation of crystalline micro and nanoparticles codoped with lanthanide ions, aiming at correlate their host lattice structure and chemical composition to the luminescence features. For this purpose, five phosphors were characterized by X-ray diffraction (XRD), scanning electron microscopy coupled to energy dispersive X-ray (EDX) spectroscopy, and photoluminescence (PL) spectroscopy, namely performed by their chromatic coordinates, radiance, luminance and PL emission spectra. This type of investigation concerning the optical characterization of luminescent crystalline micro and nanoparticles doped with lanthanide ions might be useful for scientific and practical applications, such as in light-emitting devices, luminescent paintings, ceramics, sensors, in nanoscience and nanotechnology. (author)
Bose-Einstein condensates in optical lattices: Band-gap structure and solitons
International Nuclear Information System (INIS)
Louis, Pearl J. Y.; Kivshar, Yuri S.; Ostrovskaya, Elena A.; Savage, Craig M.
2003-01-01
We analyze the existence and stability of spatially extended (Bloch-type) and localized states of a Bose-Einstein condensate loaded into an optical lattice. In the framework of the Gross-Pitaevskii equation with a periodic potential, we study the band-gap structure of the matter-wave spectrum in both the linear and nonlinear regimes. We demonstrate the existence of families of spatially localized matter-wave gap solitons, and analyze their stability in different band gaps, for both repulsive and attractive atomic interactions
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
International Nuclear Information System (INIS)
Julien, C.M.; Camacho-Lopez, M.A.
2004-01-01
Lithiated spinel manganese oxides with various amounts of lithium have been prepared through solid-state reaction and electrochemical intercalation and deintercalation. Local structure of the samples are studied using Raman scattering and Fourier transform infrared spectroscopy. We report vibrational spectra of lithiated manganese oxides Li x Mn 2 O 4 as a function of lithium concentration in the range 0.1≤x≤2.0. Raman and Fourier transform infrared (FTIR) spectral results indicated multiple-phase reactions when the lithium content is modified in the spinel lattice. Lattice dynamics of lithiated spinel manganese oxides have been interpreted using either a classical factor-group analysis or a local environment model. The structural modifications have been studied on the basis of vibrations of LiO 4 tetrahedral and MnO 6 octahedral units when Li/Mn≤0.5, and LiO 4 , LiO 6 , and MnO 6 structural units when Li/Mn>0.5
Measurement of deforming mode of lattice truss structures under impact loading
Directory of Open Access Journals (Sweden)
Zhao H.
2012-08-01
Full Text Available Lattice truss structures, which are used as a core material in sandwich panels, were widely investigated experimentally and theoretically. However, explanation of the deforming mechanism using reliable experimental results is almost rarely reported, particularly for the dynamic deforming mechanism. The present work aimed at the measurement of the deforming mode of lattice truss structures. Indeed, quasi-static and Split Hopkinson Pressure Bar (SHPB tests have been performed on the tetrahedral truss cores structures made of Aluminum 3003-O. Global values such as crushing forces and displacements between the loading platens are obtained. However, in order to understand the deforming mechanism and to explain the observed impact strength enhancement observed in the experiments, images of the truss core element during the tests are recorded. A method based on the edge detection algorithm is developed and applied to these images. The deforming profiles of one beam are extracted and it allows for calculating the length of beam. It is found that these lengths diminish to a critical value (due to compression and remain constant afterwards (because of significant bending. The comparison between quasi-static and impact tests shows that the beam were much more compressed under impact loading, which could be understood as the lateral inertia effect in dynamic bucking. Therefore, the impact strength enhancement of tetrahedral truss core sandwich panel can be explained by the delayed buckling of beam under impact (more compression reached, together with the strain hardening of base material.
Quantum information processing using designed defect states in
DEFF Research Database (Denmark)
Pedersen, Jesper; Flindt, Christian; Mortensen, Niels Asger
2007-01-01
We propose a new physical implementation of spin qubits for quantum information processing, namely defect states in antidot lattices de¯ned in the two-dimensional electron gas at a semiconductor heterostructure. Calculations of the band structure of the periodic antidot lattice are presented...
Influence of irradiation on defects creation in pin diode structure
International Nuclear Information System (INIS)
Sopko, V.; Dammer, J.; Sopko, B.; Chren, D.
2012-01-01
In this paper the manufacture of type S1 PIN diodes and radiation defect induce by fast neutrons were studied. A shift from VV"- to VV (neutral) is observed in neutron irradiated diodes. From the results obtained, an explanation that clearly offers itself is that the nature of the defects produced by irradiation of material exhibiting N type conductivity is different from those for type P material. Given that the experiments were conducted with the same material, i.e., the dopant present in the material remained unchanged, it can be stated that simply by changing the type of conductivity with increasing dose, a different kind of defects is produced, having different activation energies in the forbidden band. All these results are consistent with the ongoing RD 50 experiments at CERN.
International Nuclear Information System (INIS)
Li Yingwai; Landau, David P; Wüst, Thomas
2012-01-01
Wang-Landau sampling has been applied to investigate the thermodynamics and structural properties of a lattice hydrophobic-polar heteropolymer (the HP protein model) interacting with an attractive substrate. For simplicity, we consider a short HP sequence consisting of only 36 monomers interacting with a substrate which attracts all monomers in the sequence. The conformational “phase transitions” have been identified by a canonical analysis of the specific heat and suitable structural observables. Three major “transitions”, namely, adsorption, hydrophobic core formation and “flattening” of adsorbed structures, are observed. Depending on the surface attractive strength relative to the intra-protein attraction among the H monomers, these processes take place in different sequences upon cooling.
SFM-FDTD analysis of triangular-lattice AAA structure: Parametric study of the TEM mode
Hamidi, M.; Chemrouk, C.; Belkhir, A.; Kebci, Z.; Ndao, A.; Lamrous, O.; Baida, F. I.
2014-05-01
This theoretical work reports a parametric study of enhanced transmission through annular aperture array (AAA) structure arranged in a triangular lattice. The effect of the incidence angle in addition to the inner and outer radii values on the evolution of the transmission spectra is carried out. To this end, a 3D Finite-Difference Time-Domain code based on the Split Field Method (SFM) is used to calculate the spectral response of the structure for any angle of incidence. In order to work through an orthogonal unit cell which presents the advantage to reduce time and space of computation, special periodic boundary conditions are implemented. This study provides a new modeling of AAA structures useful for producing tunable ultra-compact devices.
Pressure-induced structural change from hexagonal to fcc metal lattice in scandium trihydride
International Nuclear Information System (INIS)
Ohmura, A.; Machida, A.; Watanuki, T.; Aoki, K.; Nakano, S.; Takemura, K.
2007-01-01
We synthesized scandium hydrides by hydrogenation of a scandium foil with hydrogen fluid under high pressure at ambient temperature. Scandium dihydride (ScH 2 ) and trihydride (ScH 3 ) were prepared near 4 and 5 GPa, respectively. The hydrogenation process and pressure-induced structural changes in ScH 3 were investigated by synchrotron radiation X-ray diffraction measurements up to 54.7 GPa. A structural transition from hexagonal to the fcc lattice began at 30 GPa and was completed at 46 GPa via an intermediate state similar to those reported for other hexagonal trihydrides. The intermediate state was not interpreted in terms of a coexisting state for the low-pressure hexagonal and the high-pressure fcc structures. The onset transition pressure of ScH 3 supported the previously proposed relation that the hexagonal-fcc transition pressure is inversely proportional to the ionic radius of the trihydride
PZT microfibre defect structure studied by Raman spectroscopy
Czech Academy of Sciences Publication Activity Database
Kozielski, L.; Buixaderas, Elena; Clemens, F.
2010-01-01
Roč. 43, č. 41 (2010), 415401/1-415401/6 ISSN 0022-3727 R&D Projects: GA ČR GAP204/10/0616 Institutional research plan: CEZ:AV0Z10100520 Keywords : point defects * phase transitions * Raman spectroscopy Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 2.105, year: 2010
Investigation of electronic lattice structure by positron annihilation in some insulators
International Nuclear Information System (INIS)
Coussot, Gerard
1970-01-01
The angular distribution of gamma quanta resulting from positron annihilation in single insulator crystals was measured with long slit geometry apparatus for intense positron sources ( 64 Cu ≅ 1 Ci). Two new phenomena were observed in the angular correlation curves. In the f. c. c. MgO, UO 2 , CaF 2 crystals, modulations appeared at angles corresponding to the limit of the first Brillouin zone in relation to the crystallographic direction studied. In SiO 2 , F 2 Mg, F 2 Mn crystals, a narrow peak at 0 mrad and a fine structure superimposed on the broad distribution, were resolved. The fine structure which is correlated with the narrow component is characterized by modulations appearing at angles corresponding to the projection of reciprocal lattice vectors along the crystallographic direction investigated. The narrow peak at p ≅ 0 suggests the formation of a bound state (positron-electron). If this bound state is described by a Bloch wave, the modulations observed correspond to the Fourier components which contribute to every reciprocal lattice vector p = G ('Umklapp' process). This model predicts that the 'Umklapp' process in polycrystals must produce a change in slope which can be experimentally observed. A systematic research of optimal observation conditions shows that the intensity of the narrow component is closely correlated with the purity and the perfection of the crystal where p-Ps is presumably formed as suggested by magnetic experiments. (author) [fr
Ringel, S. A.; Chatterjee, B.
2004-01-01
Hydrogen passivation of heteroepitaxial InP solar cells is of recent interest for deactivation of dislocations and other defects caused by the cell/substrate lattice mismatch that currently limit the photovoltaic performance of these devices. In this paper we present strong evidence that, in addition to direct hydrogen-dislocation interactions, hydrogen forms complexes with the high concentration of interstitial Zn defects present within the p(+) Zn-doped emitter of MOCVD-grown heteroepitaxial InP devices, resulting in a dramatic increase of the forward bias turn-on voltage by as much as 280 mV, from 680 mV to 960 mV. This shift is reproducible and thermally reversible and no such effect is observed for either n(+)p structures or homoepitaxial p(+)n structures grown under identical conditions. A combination of photoluminescence (PL), electrochemical C-V dopant profiling, SIMS and I-V measurements were performed on a set of samples having undergone a matrix of hydrogenation and post-hydrogenation annealing conditions to investigate the source of this voltage enhancement and confirm the expected role of interstitial Zn and hydrogen. A precise correlation between all measurements is demonstrated which indicates that Zn interstitials within the p(+) emitter and their interaction with hydrogen are indeed responsible for this device behavior.
Ground state structure of U2Mo: static and lattice dynamics study
International Nuclear Information System (INIS)
Mukherjee, D.; Sahoo, B.D.; Joshi, K.D.; Kaushik, T.C.
2016-01-01
According to experimental reports, the ground state stable structure of U 2 Mo is tetragonal. However, various theoretical studies performed in past do not get tetragonal phase as the stable structure at ambient conditions. Therefore, the ground state structure of U 2 Mo is still unresolved. In an attempt to understand the ground state properties of this system, we have carried out first principle electronic band structure calculations. The structural stability analysis carried out using evolutionary structure search algorithm in conjunction with ab-inito method shows that a hexagonal structure (space group P6/mmm) is the lowest enthalpy structure at ambient condition and remains stable upto 200 GPa. The elastic and lattice dynamical stability further supports the stability of this phase at ambient condition. Further, using the 0 K calculations in conjunction with finite temperature corrections, we have derived the isotherm and shock adiabat (Hugoniot) of this material. Various equilibrium properties such as ambient pressure volume, bulk modulus, pressure derivative of bulk modulus etc. are derived from equation of state. (author)
Effect of grain boundary structures on the behavior of He defects in Ni: An atomistic study
Institute of Scientific and Technical Information of China (English)
H F Gong; Y Yan; X S Zhang; W Lv; T Liu; Q S Ren
2017-01-01
We investigated the effect of grain boundary structures on the trapping strength of HeN (N is the number of helium atoms) defects in the grain boundaries of nickel.The results suggest that the binding energy of an interstitial helium atom to the grain boundary plane is the strongest among all sites around the plane.The HeN defect is much more stable in nickel bulk than in the grain boundary plane.Besides,the binding energy of an interstitial helium atom to a vacancy is stronger than that to a grain boundary plane.The binding strength between the grain boundary and the HeN defect increases with the defect size.Moreover,the binding strength of the HeN defect to the Σ3 (1 12)[110] grain boundary becomes much weaker than that to other grain boundaries as the defect size increases.
Influence of point defects on the near edge structure of hexagonal boron nitride
McDougall, Nicholas L.; Partridge, Jim G.; Nicholls, Rebecca J.; Russo, Salvy P.; McCulloch, Dougal G.
2017-10-01
Hexagonal boron nitride (hBN) is a wide-band-gap semiconductor with applications including gate insulation layers in graphene transistors, far-ultraviolet light emitting devices and as hydrogen storage media. Due to its complex microstructure, defects in hBN are challenging to identify. Here, we combine x-ray absorption near edge structure (XANES) spectroscopy with ab initio theoretical modeling to identify energetically favorable defects. Following annealing of hBN samples in vacuum and oxygen, the B and N K edges exhibited angular-dependent peak modifications consistent with in-plane defects. Theoretical calculations showed that the energetically favorable defects all produce signature features in XANES. Comparing these calculations with experiments, the principle defects were attributed to substitutional oxygen at the nitrogen site, substitutional carbon at the boron site, and hydrogen passivated boron vacancies. Hydrogen passivation of defects was found to significantly affect the formation energies, electronic states, and XANES. In the B K edge, multiple peaks above the major 1 s to π* peak occur as a result of these defects and the hydrogen passivated boron vacancy produces the frequently observed doublet in the 1 s to σ* transition. While the N K edge is less sensitive to defects, features attributable to substitutional C at the B site were observed. This defect was also calculated to have mid-gap states in its band structure that may be responsible for the 4.1-eV ultraviolet emission frequently observed from this material.
Directory of Open Access Journals (Sweden)
Xun Zhang
2014-01-01
Full Text Available Optimal sensor placement is a key issue in the structural health monitoring of large-scale structures. However, some aspects in existing approaches require improvement, such as the empirical and unreliable selection of mode and sensor numbers and time-consuming computation. A novel improved particle swarm optimization (IPSO algorithm is proposed to address these problems. The approach firstly employs the cumulative effective modal mass participation ratio to select mode number. Three strategies are then adopted to improve the PSO algorithm. Finally, the IPSO algorithm is utilized to determine the optimal sensors number and configurations. A case study of a latticed shell model is implemented to verify the feasibility of the proposed algorithm and four different PSO algorithms. The effective independence method is also taken as a contrast experiment. The comparison results show that the optimal placement schemes obtained by the PSO algorithms are valid, and the proposed IPSO algorithm has better enhancement in convergence speed and precision.
A lattice calculation of the nucleon's spin-dependent structure function g2 revisited
International Nuclear Information System (INIS)
Goeckeler, M.; Rakow, P.E.L.; Schaefer, A.; Schierholz, G.
2000-11-01
Our previous calculation of the spin-dependent structure function g 2 is revisited. The interest in this structure function is to a great extent motivated by the fact that it receives contributions from twist-two as well as from twist-three operators already in leading order of 1/Q 2 thus offering the unique possibility of directly assessing higher-twist effects. In our former calculation the lattice operators were renormalized perturbatively and mixing with lower-dimensional operators was ignored. However, the twist-three operator which gives rise to the matrix element d 2 mixes non-perturbatively with an operator of lower dimension. Taking this effect into account leads to a considerably smaller value of d 2 , which is consistent with the experimental data. (orig.)
Directory of Open Access Journals (Sweden)
Yoshihisa Suzuki
2016-07-01
Full Text Available Good model systems are required in order to understand crystal growth processes because, in many cases, precise incorporation processes of atoms or molecules cannot be visualized easily at the atomic or molecular level. Using a transmission-type optical microscope, we have successfully observed in situ adsorption, desorption, surface diffusion, lattice defect formation, and kink incorporation of particles on growth interfaces of colloidal crystals of polystyrene particles in aqueous sodium polyacrylate solutions. Precise surface transportation and kink incorporation processes of the particles into the colloidal crystals with attractive interactions were observed in situ at the particle level. In particular, contrary to the conventional expectations, the diffusion of particles along steps around a two-dimensional island of the growth interface was not the main route for kink incorporation. This is probably due to the number of bonds between adsorbed particles and particles in a crystal; the number exceeds the limit at which a particle easily exchanges its position to the adjacent one along the step. We also found novel desorption processes of particles from steps to terraces, attributing them to the assistance of attractive forces from additionally adsorbing particles to the particles on the steps.
Selected topics in high temperature chemistry defect chemistry of solids
Johannesen, Ø
2013-01-01
The properties of materials at high temperature play a vital role in their processing and practical use. The real properties of materials at elevated temperatures are very often governed by defects in their structure. Lattice defects may consist of point defects like vacancies, interstitial atoms or substituted atoms. These classes are discussed in general and specifically for oxides, nitrides, carbides and sulfides. Defect aggregates, shear structures and adaptive structures are also described. Special attention is paid to hydrogen defects which seem to play an important role in several mater
International Nuclear Information System (INIS)
Pasternak, M.
1978-05-01
Moessbauer studies on 129 I, 57 Fe and 119 Sn were conducted in several disordered and microscopic systems in order to investigate properties of lattice dynamics, chemical bonding and phase transitions. The project included the following studies: (1) Granular crystals of Sn embedded in tin-oxide matrix; the nature of the superconductivity transition of very small grains of tin was investigated. (2) Lattice dynamics and characterization of amorphous tin oxide obtained by condensing atoms of Sn and O 2 gas on a 77 K substrate. The hyperfine interaction and the temperature dependence of the Debye-Waller factor were essential to determine the structure of the amorphous tin oxide. (3) The nature of the chemical bond of the alkaly halides ionic crystals and molecules; molecules of Li, Na, K, Rb and Cs iodides were trapped in agron matrices, and the isomer-shift values were obtained from absorption spectra. (4) Binding of single iron and tin atoms to CH 4 , NH 3 , H 2 and C 6 H 6 molecules, with samples at low temperatures between 2 and 77 K; conclusions were derived regarding the cryochemistry of these systems, as related to fundamental problems of catalysis, chemisorption and ''cracking'' of organic molecules
TCM Analysis of Defected Ground Structures for MIMO Antenna Designs in Mobile Terminals
Ghalib, Asim; Sharawi, Mohammad S.
2017-01-01
In this paper, the theory of characteristic modes (TCM) is used for the first time to analyze the behavior of defected ground structures (DGS) when added to antenna designs. A properly designed DGS introduces currents opposite in direction
Energy Technology Data Exchange (ETDEWEB)
BLUM, T.; BOER, D.; CREUTZ, M.; OHTA, S.; ORGINOS, K.
2002-03-18
The RIKEN BNL Research Center workshop on ''Hadron Structure from Lattice QCD'' was held at BNL during March 11-15, 2002. Hadron structure has been the subject of many theoretical and experimental investigations, with significant success in understanding the building blocks of matter. The nonperturbative nature of QCD, however, has always been an obstacle to deepening our understanding of hadronic physics. Lattice QCD provides the tool to overcome these difficulties and hence a link can be established between the fundamental theory of QCD and hadron phenomenology. Due to the steady progress in improving lattice calculations over the years, comparison with experimentally measured hadronic quantities has become important. In this respect the workshop was especially timely. By providing an opportunity for experts from the lattice and hadron structure communities to present their latest results, the workshop enhanced the exchange of knowledge and ideas. With a total of 32 registered participants and 26 talks, the interest of a growing community is clearly exemplified. At the workshop Schierholz and Negele presented the current status of lattice computations of hadron structure. Substantial progress has been made during recent years now that the quenched results are well under control and the first dynamical results have appeared. In both the dynamical and the quenched simulations the lattice results, extrapolated to lighter quark masses, seem to disagree with experiment. Melnitchouk presented a possible explanation (chiral logs) for this disagreement. It became clear from these discussions that lattice computations at significantly lighter quark masses need to be performed.
Directory of Open Access Journals (Sweden)
Gawdzińska K.
2017-09-01
Full Text Available Diagnostics of composite castings, due to their complex structure, requires that their characteristics are tested by an appropriate description method. Any deviation from the specific characteristic will be regarded as a material defect. The detection of defects in composite castings sometimes is not sufficient and the defects have to be identified. This study classifies defects found in the structures of saturated metallic composite castings and indicates those stages of the process where such defects are likely to be formed. Not only does the author determine the causes of structural defects, describe methods of their detection and identification, but also proposes a schematic procedure to be followed during detection and identification of structural defects of castings made from saturated reinforcement metallic composites. Alloys examination was conducted after technological process, while using destructive (macroscopic tests, light and scanning electron microscopy and non-destructive (ultrasonic and X-ray defectoscopy, tomography, gravimetric method methods. Research presented in this article are part of author’s work on castings quality.
Directory of Open Access Journals (Sweden)
K. Ben Messaoud
2014-01-01
Full Text Available This study concerns structural and optothermal properties of iron ditelluride layered structures which were fabricated via a low-cost protocol. The main precursors were FeCl3 · 6H2O and Fe2O3. After a heat treatment within a tellurium-rich medium at various temperatures (470°C, 500°C, and 530°C during 24 h, classical analyses have been applied to the iron ditelluride layered structures. A good crystalline state with a preferential orientation of the crystallites along (111 direction has been recorded. Moreover, additional opto-thermal investigation and analyses within the framework of the Lattice Compatibility Theory gave plausible explanation for prompt temperature-dependent incorporation of tellurium element inside hematite elaborated matrices.
International Nuclear Information System (INIS)
Petit, T.; CEA Centre d'Etudes de Grenoble, 38
1996-01-01
Uranium dioxide is the standard nuclear fuel used in French h power plants. During irradiation, fission products such as krypton and xenon are created inside fuel pellets. So, gas release could become, at very high burnup, a limiting factor in the reactor exploitation. To study this subject, we have realised calculations using the Density Functional Theory (DFT) into the Local Density Approximation (LDA) and the Atomic Sphere Approximation (ASA). First, we have validated our approach by calculating cohesive properties of thorium, protactinium and uranium metals. The good agreement between our results and experimental values implies that 5f electrons are itinerant. Calculated lattice parameter, cohesive energy and bulk modulus for uranium and thorium dioxides are in very good agreement with experiment. We show that binding between uranium and oxygen atoms is not completely ionic but partially covalent. The question of the electrical conductivity still remains an open problem. We have been able to calculate punctual defect formation energies in uranium dioxide. Accordingly to experimental observations, we find that it is easier to create a defect in the oxygen sublattice than in the uranium sublattice. Finally, we have been able to predict a probable site of krypton atoms in nuclear fuel: the Schottky trio. Experiences of Extended X-ray Absorption Fine structure Spectroscopy (EXAFS) and X-ray Photoelectron Spectroscopy (XPS) on uranium dioxide doped by ionic implantation will help us in the comprehension of the studied phenomena and the interpretation of our calculations. (author)
Solid state proton spin-lattice relaxation in four structurally related organic molecules
International Nuclear Information System (INIS)
Beckmann, Peter A.; Burbank, Kendra S.; Lau, Matty M.W.; Ree, Jessica N.; Weber, Tracy L.
2003-01-01
We report and interpret the temperature dependence of the proton spin-lattice relaxation rate at 8.50 and 22.5 MHz in four polycrystalline solids composed of structurally related molecules: 2-ethylanthracene, 2-t-butylanthracene, 2-ethylanthraquinone, and 2-t-butylanthraquinone. We have been unable to grow single crystals and therefore do not know the crystal structures. Hence, we use the NMR relaxometry data to make predictions about the solid state structures. As expected, we are able to conclude that the ethyl groups do not reorient in the solid state but that the t-butyl groups do. The anthraquinones have a ''simpler'' structure than the anthracenes. The best dynamical models suggest that there is a unique crystallographic site for the t-butyl groups in 2-t-butylanthraquinone and two sites, each with half the molecules, for the ethyl groups in 2-ethylanthraquinone. There are also two sites in 2-ethylanthracene, but with unequal weights, suggesting four sites in the unit cell with lower symmetry than the two anthraquinones. Finally, the observed relaxation rate data in 2-t-butylanthracene is very complex and its interpretation demonstrates the uniqueness problem that arises in interpreting relaxometry data without the knowledge of the crystal structure
International Nuclear Information System (INIS)
Burbery, N.J.; Das, R.; Ferguson, W.G.
2016-01-01
Grain boundaries (GBs) provide a source and/or a sink for crystal defects and store elastic energy due to the non-uniform atomic bonding structure of the GB core. GB structures are thermodynamically driven to transition to the lowest energy configuration possible; however to date there has been little evidence to explain why specific GB structures have a low energy state. Furthermore, there is little quantitative demonstration of the significance of physical and GB structure characteristics on the GB energy, thermal stability, and the effect of temporary local GB structure transformations on defect interactions. This paper evaluates the defect interactions and structure stability of multiple Σ5(310) GB structures in bi-crystals of pure aluminium, and systematically investigates the features at 0 K to characterise multiple metastable structures. Structure stability is evaluated by utilising unstable vacancy defects to initiate GB transformations, and using nudged elastic band simulations to quantify this with the activation energy. The emission of stable vacancy defects from the ‘stable’ and metastable grain boundaries is also evaluated in the same manner. A detailed analysis of dislocation nucleation at the atomistic scale demonstrates that local transformations of GB structure between stable and metastable intermediates can provide a mechanism to accommodate the generation of crystal defects. Kinetic (time-dependent) effects that compete with energetic driving forces for structural transformations of GBs are shown to cause a significant effect on the activation properties that may exceed the influence of GB potential energy. The results demonstrate that GB structural multiplicity can be associated with the generation and absorption of dislocations and vacancies. This paper demonstrates the suitability of atomistic simulations coupled with nudged elastic band simulations to evaluate fundamental thermodynamic properties of pure FCC metals. Overall, this paper
Energy Technology Data Exchange (ETDEWEB)
Burbery, N.J. [Department of Mechanical Engineering, University of Auckland, Auckland 1010 (New Zealand); Das, R., E-mail: r.das@auckland.ac.nz [Department of Mechanical Engineering, University of Auckland, Auckland 1010 (New Zealand); Ferguson, W.G. [Department of Chemical and Materials Engineering, University of Auckland, Auckland 1010 (New Zealand)
2016-08-15
Grain boundaries (GBs) provide a source and/or a sink for crystal defects and store elastic energy due to the non-uniform atomic bonding structure of the GB core. GB structures are thermodynamically driven to transition to the lowest energy configuration possible; however to date there has been little evidence to explain why specific GB structures have a low energy state. Furthermore, there is little quantitative demonstration of the significance of physical and GB structure characteristics on the GB energy, thermal stability, and the effect of temporary local GB structure transformations on defect interactions. This paper evaluates the defect interactions and structure stability of multiple Σ5(310) GB structures in bi-crystals of pure aluminium, and systematically investigates the features at 0 K to characterise multiple metastable structures. Structure stability is evaluated by utilising unstable vacancy defects to initiate GB transformations, and using nudged elastic band simulations to quantify this with the activation energy. The emission of stable vacancy defects from the ‘stable’ and metastable grain boundaries is also evaluated in the same manner. A detailed analysis of dislocation nucleation at the atomistic scale demonstrates that local transformations of GB structure between stable and metastable intermediates can provide a mechanism to accommodate the generation of crystal defects. Kinetic (time-dependent) effects that compete with energetic driving forces for structural transformations of GBs are shown to cause a significant effect on the activation properties that may exceed the influence of GB potential energy. The results demonstrate that GB structural multiplicity can be associated with the generation and absorption of dislocations and vacancies. This paper demonstrates the suitability of atomistic simulations coupled with nudged elastic band simulations to evaluate fundamental thermodynamic properties of pure FCC metals. Overall, this paper
International Nuclear Information System (INIS)
Mallick, Sougata; Mallik, Srijani; Bedanta, Subhankar
2015-01-01
Microdimensional triangular magnetic antidot lattice arrays were prepared by varying the speed of substrate rotation. The pre-deposition patterning has been performed using photolithography technique followed by a post-deposition lift-off. Surface morphology taken by atomic force microscopy depicted that the growth mechanism of the grains changes from chain like formation to island structures due to the substrate rotation. Study of magnetization reversal via magneto optic Kerr effect based microscopy revealed reduction of uniaxial anisotropy and increase in domain size with substrate rotation. The relaxation measured under constant magnetic field becomes faster with rotation of the substrate during deposition. The nature of relaxation for the non-rotating sample can be described by a double exponential decay. However, the relaxation for the sample with substrate rotation is well described either by a double exponential or a Fatuzzo-Labrune like single exponential decay, which increases in applied field
Stochastic inflation lattice simulations: Ultra-large scale structure of the universe
International Nuclear Information System (INIS)
Salopek, D.S.
1990-11-01
Non-Gaussian fluctuations for structure formation may arise in inflation from the nonlinear interaction of long wavelength gravitational and scalar fields. Long wavelength fields have spatial gradients α -1 triangledown small compared to the Hubble radius, and they are described in terms of classical random fields that are fed by short wavelength quantum noise. Lattice Langevin calculations are given for a ''toy model'' with a scalar field interacting with an exponential potential where one can obtain exact analytic solutions of the Fokker-Planck equation. For single scalar field models that are consistent with current microwave background fluctuations, the fluctuations are Gaussian. However, for scales much larger than our observable Universe, one expects large metric fluctuations that are non-Guassian. This example illuminates non-Gaussian models involving multiple scalar fields which are consistent with current microwave background limits. 21 refs., 3 figs
International Nuclear Information System (INIS)
Hernandez, Laura; Pinettes, Claire
2005-01-01
We have studied by Monte Carlo simulations the thermal behaviour of a small (N=13 particles) cluster described by a Heisenberg model, including nearest-neighbour ferromagnetic interactions and radial surface anisotropy, in an applied magnetic field. We have studied three different lattice structures: hexagonal close packed, face centered cubic and icosahedral. We show that the zero-field thermal behaviour depends not only on the value of the anisotropy constant but also on the lattice structure. The behaviour in an applied field, additionally depends, on the different orientations of the field with respect to the crystal axes. According to these relative orientations, hysteresis cycles show different step-like characteristics
Energy Technology Data Exchange (ETDEWEB)
Hernandez, Laura [Laboratoire de Physique Theorique et Modelisation, CNRS-UMR 8089, Universite de Cergy-Pontoise, 5 mail Gay Lussac, Neuville-sur-Oise, 95031 Cergy-Pontoise, Cedex (France)]. E-mail: Laura.Hernandez@ptm.u-cergy.fr; Pinettes, Claire [Laboratoire de Physique Theorique et Modelisation, CNRS-UMR 8089, Universite de Cergy-Pontoise, 5 mail Gay Lussac, Neuville-sur-Oise, 95031 Cergy-Pontoise, Cedex (France)
2005-08-15
We have studied by Monte Carlo simulations the thermal behaviour of a small (N=13 particles) cluster described by a Heisenberg model, including nearest-neighbour ferromagnetic interactions and radial surface anisotropy, in an applied magnetic field. We have studied three different lattice structures: hexagonal close packed, face centered cubic and icosahedral. We show that the zero-field thermal behaviour depends not only on the value of the anisotropy constant but also on the lattice structure. The behaviour in an applied field, additionally depends, on the different orientations of the field with respect to the crystal axes. According to these relative orientations, hysteresis cycles show different step-like characteristics.
Structure and flux pinning properties of irradiation defects in YBa2Cu3O7-x
International Nuclear Information System (INIS)
Kirk, M.A.
1992-06-01
We review our investigations of defects produced in YBa 2 Cu 3 O 7-x by various forms of irradiation. The defect microstructure has been studied by transmission electron microscopy (TEM). Irradiation enhancements of flux pinning have been studied by SQUID magnetometry on single crystals. In many cases the same single crystals were used in both TEM and SQUID investigations. The primary atom recoil spectra for all the irradiations studied have been carefully calculated and used to correlate the TEM and magnetization results for the different types of irradiation. Correlation of annealing experiments, employing both TEM and SQUID measurements, among several types of irradiation has also yielded information on the different defect structures present. Defect densities, sizes and strain field anisotropies have been determined by TEM. Defect flux pinning anisotropies have been determined for two field orientations in twinned single crystals. The temperature dependences of the flux pinning have been measured. The maximum field of irreversibility at 70 K is shown to change markedly upon both neutron and proton irradiations in some crystals and not others. The defect structure, chemistry and location in the unit cell has been determined in some cases. Some interaction with existing defect structure has been observed in proton and electron irradiations. The damage character and directionality has been determined in GeV ion irradiated crystals
Flavor structure of Λ baryons from lattice QCD: From strange to charm quarks
Gubler, Philipp; Takahashi, Toru T.; Oka, Makoto
2016-12-01
We study Λ baryons of spin-parity 1/2± with either a strange or charm valence quark in full 2 +1 flavor lattice QCD. Multiple S U (3 ) singlet and octet operators are employed to generate the desired single baryon states on the lattice. Via the variational method, the couplings of these states to the different operators provide information about the flavor structure of the Λ baryons. We make use of the gauge configurations of the PACS-CS Collaboration and chirally extrapolate the results for the masses and S U (3 ) flavor components to the physical point. We furthermore gradually change the hopping parameter of the heaviest quark from strange to charm to study how the properties of the Λ baryons evolve as a function of the heavy quark mass. It is found that the baryon energy levels increase almost linearly with the quark mass. Meanwhile, the flavor structure of most of the states remains stable, with the exception of the lowest 1/2- state, which changes from a flavor singlet Λ to a Λc state with singlet and octet components of comparable size. Finally, we discuss whether our findings can be interpreted with the help of a simple quark model and find that the negative-parity Λc states can be naturally explained as diquark excitations of the light u and d quarks. On the other hand, the quark-model picture does not appear to be adequate for the negative-parity Λ states, suggesting the importance of other degrees of freedom to describe them.
Electron beam generation and structure of defects in carbon and boron nitride nano-tubes
Energy Technology Data Exchange (ETDEWEB)
Zobelli, A
2007-10-15
The nature and role of defects is of primary importance to understand the physical properties of C and BN (boron nitride) single walled nano-tubes (SWNTs). Transmission electron microscopy (TEM) is a well known powerful tool to study the structure of defects in materials. However, in the case of SWNTs, the electron irradiation of the TEM may knock out atoms. This effect may alter the native structure of the tube, and has also been proposed as a potential tool for nano-engineering of nano-tubular structures. Here we develop a theoretical description of the irradiation mechanism. First, the anisotropy of the emission energy threshold is obtained via density functional based calculations. Then, we numerically derive the total Mott cross section for different emission sites of carbon and boron nitride nano-tubes with different chiralities. Using a dedicated STEM (Scanning Transmission Electron Microscope) microscope with experimental conditions optimised on the basis of derived cross-sections, we are able to control the generation of defects in nano-tubular systems. Either point or line defects can be obtained with a spatial resolution of a few nanometers. The structure, energetics and electronics of point and line defects in BN systems have been investigated. Stability of mono- and di- vacancy defects in hexagonal boron nitride layers is investigated, and their activation energies and reaction paths for diffusion have been derived using the nudged elastic band method (NEB) combined with density functional based techniques. We demonstrate that the appearance of extended linear defects under electron irradiation is more favorable than a random distribution of point defects and this is due to the existence of preferential sites for atom emission in the presence of pre-existing defects, rather than thermal vacancy nucleation and migration. (author)
Electron beam generation and structure of defects in carbon and boron nitride nano-tubes
International Nuclear Information System (INIS)
Zobelli, A.
2007-10-01
The nature and role of defects is of primary importance to understand the physical properties of C and BN (boron nitride) single walled nano-tubes (SWNTs). Transmission electron microscopy (TEM) is a well known powerful tool to study the structure of defects in materials. However, in the case of SWNTs, the electron irradiation of the TEM may knock out atoms. This effect may alter the native structure of the tube, and has also been proposed as a potential tool for nano-engineering of nano-tubular structures. Here we develop a theoretical description of the irradiation mechanism. First, the anisotropy of the emission energy threshold is obtained via density functional based calculations. Then, we numerically derive the total Mott cross section for different emission sites of carbon and boron nitride nano-tubes with different chiralities. Using a dedicated STEM (Scanning Transmission Electron Microscope) microscope with experimental conditions optimised on the basis of derived cross-sections, we are able to control the generation of defects in nano-tubular systems. Either point or line defects can be obtained with a spatial resolution of a few nanometers. The structure, energetics and electronics of point and line defects in BN systems have been investigated. Stability of mono- and di- vacancy defects in hexagonal boron nitride layers is investigated, and their activation energies and reaction paths for diffusion have been derived using the nudged elastic band method (NEB) combined with density functional based techniques. We demonstrate that the appearance of extended linear defects under electron irradiation is more favorable than a random distribution of point defects and this is due to the existence of preferential sites for atom emission in the presence of pre-existing defects, rather than thermal vacancy nucleation and migration. (author)
Structural and electronic properties of zigzag InP nanoribbons with Stone–Wales type defects
International Nuclear Information System (INIS)
Longo, R C; Carrete, J; Varela, L M; Gallego, L J
2016-01-01
By means of density-functional-theoretic calculations, we investigate the structural and electronic properties of a hexagonal InP sheet and of hydrogen-passivated zigzag InP nanoribbons (ZInPNRs) with Stone–Wales (SW)-type defects. Our results show that the influence of this kind of defect is not limited to the defected region but it leads to the formation of ripples that extend across the systems, in keeping with the results obtained recently for graphene and silicene sheets. The presence of SW defects in ZInPNRs causes an appreciable broadening of the band gap and transforms the indirect-bandgap perfect ZInPNR into a direct-bandgap semiconductor. An external transverse electric field, regardless of its direction, reduces the gap in both the perfect and defective ZInPNRs. (paper)
International Nuclear Information System (INIS)
Sakaki, Kouji; Akiba, Etsuo; Mizuno, Masataka; Araki, Hideki; Shirai, Yasuharu
2009-01-01
The formation of the vacancy and dislocation by the initial hydrogenation and dehydrogenation in LaNi 4.5 M 0.5 (M = Al, Co, and Ni) was observed by means of the positron lifetime technique. The concentrations of vacancy introduced by these processes were 0.25, 0.13 and 0.01 at.% for LaNi 5 , LaNi 4.5 Co 0.5 and LaNi 4.5 Al 0.5 , respectively. Al substitution into LaNi 5 significantly prevented from vacancy formation, compared with LaNi 5 and LaNi 4.5 Co 0.5 . In LaNi 4.5 Al 0.5 , the increase of the hardness and the enhancement of the pulverization, i.e. enhancement of the formation of micro cracks compared with LaNi 5 were observed while the Co substitution had little effect on pulverization and hardness as well as vacancy formation. These results show that the formation of micro cracks became more active process by Al substitution than the formation of the lattice defects to release the strain energy generated by the hydride formation because of the higher formation energy of the lattice defects in LaNi 4.5 Al 0.5 , although both the formation of micro cracks and lattice defects were still observed in all alloys we studied
Electronic transport on the spatial structure of the protein: Three-dimensional lattice model
International Nuclear Information System (INIS)
Sarmento, R.G.; Frazão, N.F.; Macedo-Filho, A.
2017-01-01
Highlights: • The electronic transport on the structure of the three-dimensional lattice model of the protein is studied. • The signing of the current–voltage is directly affected by permutations of the weak bonds in the structure. • Semiconductor behave of the proteins suggest a potential application in the development of novel biosensors. - Abstract: We report a numerical analysis of the electronic transport in protein chain consisting of thirty-six standard amino acids. The protein chains studied have three-dimensional structure, which can present itself in three distinct conformations and the difference consist in the presence or absence of thirteen hydrogen-bondings. Our theoretical method uses an electronic tight-binding Hamiltonian model, appropriate to describe the protein segments modeled by the amino acid chain. We note that the presence and the permutations between weak bonds in the structure of proteins are directly related to the signing of the current–voltage. Furthermore, the electronic transport depends on the effect of temperature. In addition, we have found a semiconductor behave in the models investigated and it suggest a potential application in the development of novel biosensors for molecular diagnostics.
HAIM OMLET: An Expert System For Research In Orthomodular Lattices And Related Structures
Dankel, D. D.; Rodriguez, R. V.; Anger, F. D.
1986-03-01
This paper describes research towards the construction of an expert system combining the brute force power of algorithmic computation and the inductive reasoning power of a rule-based inference engine in the mathematical area of discrete structures. Little research has been conducted on extending existing expert systems' technology to computationally complex areas. This research addresses the extension of expert systems into areas such as these, where the process of inference by itself will not produce the proper results. Additionally, the research will demonstrate the benefits of combining inference engines and mathematical algorithms to attack computationally complex problems. The specific aim is to produce an expert system which embodies expert level knowledge of orthomodular lattices, graphs, structure spaces, boolean algebras, incidence relations, and projective configurations. The resulting system, implemented on a micro-computer, will provide researchers a powerful and accessible tool for exploring these discrete structures. The system's "shell" will provide a structure for developing other expert systems with similar capabilities in such related areas as coding theory, categories, monoids, automata theory, and non-standard logics.
Front propagation in a regular vortex lattice: Dependence on the vortex structure.
Beauvier, E; Bodea, S; Pocheau, A
2017-11-01
We investigate the dependence on the vortex structure of the propagation of fronts in stirred flows. For this, we consider a regular set of vortices whose structure is changed by varying both their boundary conditions and their aspect ratios. These configurations are investigated experimentally in autocatalytic solutions stirred by electroconvective flows and numerically from kinematic simulations based on the determination of the dominant Fourier mode of the vortex stream function in each of them. For free lateral boundary conditions, i.e., in an extended vortex lattice, it is found that both the flow structure and the front propagation negligibly depend on vortex aspect ratios. For rigid lateral boundary conditions, i.e., in a vortex chain, vortices involve a slight dependence on their aspect ratios which surprisingly yields a noticeable decrease of the enhancement of front velocity by flow advection. These different behaviors reveal a sensitivity of the mean front velocity on the flow subscales. It emphasizes the intrinsic multiscale nature of front propagation in stirred flows and the need to take into account not only the intensity of vortex flows but also their inner structure to determine front propagation at a large scale. Differences between experiments and simulations suggest the occurrence of secondary flows in vortex chains at large velocity and large aspect ratios.
Electronic transport on the spatial structure of the protein: Three-dimensional lattice model
Energy Technology Data Exchange (ETDEWEB)
Sarmento, R.G. [Departamento de Ciências Biológicas, Universidade Federal do Piauí, 64800-000 Floriano, PI (Brazil); Frazão, N.F. [Centro de Educação e Saúde, Universidade Federal de Campina Grande, 581750-000 Cuité, PB (Brazil); Macedo-Filho, A., E-mail: amfilho@gmail.com [Campus Prof. Antonio Geovanne Alves de Sousa, Universidade Estadual do Piauí, 64260-000 Piripiri, PI (Brazil)
2017-01-30
Highlights: • The electronic transport on the structure of the three-dimensional lattice model of the protein is studied. • The signing of the current–voltage is directly affected by permutations of the weak bonds in the structure. • Semiconductor behave of the proteins suggest a potential application in the development of novel biosensors. - Abstract: We report a numerical analysis of the electronic transport in protein chain consisting of thirty-six standard amino acids. The protein chains studied have three-dimensional structure, which can present itself in three distinct conformations and the difference consist in the presence or absence of thirteen hydrogen-bondings. Our theoretical method uses an electronic tight-binding Hamiltonian model, appropriate to describe the protein segments modeled by the amino acid chain. We note that the presence and the permutations between weak bonds in the structure of proteins are directly related to the signing of the current–voltage. Furthermore, the electronic transport depends on the effect of temperature. In addition, we have found a semiconductor behave in the models investigated and it suggest a potential application in the development of novel biosensors for molecular diagnostics.
Electronic structure and lattice dynamics of rhombohedral BiAlO_3 from first-principles
International Nuclear Information System (INIS)
Kaczkowski, J.
2016-01-01
The structural, elastic, electronic, dynamical (zone-center phonon modes and Born effective charge tensors), and ferroelectric properties of the rhombohedral BiAlO_3 were calculated within various exchange-correlation functionals. The standard local-density (LDA) and generalized gradient (GGA) approximations, and nonlocal hybrid Heyd-Scuseria-Ernzerhof (HSE) were used. We have also performed the electronic structure calculations with meta-GGA Tran-Blaha functional. BiAlO_3 is indirect band gap semiconductor with the value of band gap: 2.87 eV (GGA), 4.14 eV (HSE), and 3.78 eV (TB-mBJ). The calculated spontaneous polarization is 81 μC/cm"2 (87 μC/cm"2) for GGA (HSE). The vibrational spectrum including LO-TO splitting was calculated within GGA. The zone-center phonon modes with LO-TO splitting for BiAlO_3 were compared with those in isostructural BiFeO_3. - Highlights: • Electronic structure of the rhombohedral phase of BiAlO_3 were calculated. • Structural, elastic, dynamical, and ferroelectric properties were investigated. • Calculations were done within GGA, hybrid HSE, and TB-mBJ functionals. • The lattice dynamics with LO-TO splitting were investigated within GGA functional.
Defect-impurity interactions in ion-implanted metals
International Nuclear Information System (INIS)
Turos, A.
1986-01-01
An overview of defect-impurity interactions in metals is presented. When point defects become mobile they migrate towards the sinks and on the way can be captured by impurity atoms forming stable associations so-called complexes. In some metallic systems complexes can also be formed athermally during ion implantation by trapping point defects already in the collision cascade. An association of a point defect with an impurity atom leads to its displacement from the lattice site. The structure and stability of complexes are strongly temperature dependent. With increasing temperature they dissociate or grow by multiple defect trapping. The appearance of freely migrating point defects at elevated temperatures, due to ion bombardment or thermal annealing, causes via coupling with defect fluxes, important impurity redistribution. Because of the sensitivity of many metal-in-metal implanted systems to radiation damage the understanding of this processes is essential for a proper interpretation of the lattice occupancy measurements and the optimization of implantation conditions. (author)
First Trimester Influenza Vaccination and Risks for Major Structural Birth Defects in Offspring.
Kharbanda, Elyse Olshen; Vazquez-Benitez, Gabriela; Romitti, Paul A; Naleway, Allison L; Cheetham, T Craig; Lipkind, Heather S; Klein, Nicola P; Lee, Grace; Jackson, Michael L; Hambidge, Simon J; McCarthy, Natalie; DeStefano, Frank; Nordin, James D
2017-08-01
To examine risks for major structural birth defects in infants after first trimester inactivated influenza vaccine (IIV) exposures. In this observational study, we used electronic health data from 7 Vaccine Safety Datalink sites to examine risks for selected major structural defects in infants after maternal IIV exposure. Vaccine exposures for women with continuous insurance enrollment through pregnancy who delivered singleton live births between 2004 and 2013 were identified from standardized files. Infants with continuous insurance enrollment were followed to 1 year of age. We excluded mother-infant pairs with other exposures that potentially increased their background risk for birth defects. Selected cardiac, orofacial or respiratory, neurologic, ophthalmologic or otologic, gastrointestinal, genitourinary and muscular or limb defects were identified from diagnostic codes in infant medical records using validated algorithms. Propensity score adjusted generalized estimating equations were used to estimate prevalence ratios (PRs). We identified 52 856 infants with maternal first trimester IIV exposure and 373 088 infants whose mothers were unexposed to IIV during first trimester. Prevalence (per 100 live births) for selected major structural birth defects was 1.6 among first trimester IIV exposed versus 1.5 among unexposed mothers. The adjusted PR was 1.02 (95% CI 0.94-1.10). Organ system-specific PRs were similar to the overall PR. First trimester maternal IIV exposure was not associated with an increased risk for selected major structural birth defects in this large cohort of singleton live births. Copyright © 2017 Elsevier Inc. All rights reserved.
Tuning optical properties of opal photonic crystals by structural defects engineering
di Stasio, F.; Cucini, M.; Berti, L.; Comoretto, D.; Abbotto, A.; Bellotto, L.; Manfredi, N.; Marinzi, C.
2009-06-01
We report on the preparation and optical characterization of three dimensional colloidal photonic crystal (PhC) containing an engineered planar defect embedding photoactive push-pull dyes. Free standing polystyrene films having thickness between 0.6 and 3 mm doped with different dipolar chromophores were prepared. These films were sandwiched between two artificial opals creating a PhC structure with planar defect. The system was characterized by reflectance at normal incidence angle (R), variable angle transmittance (T) and photoluminescence spectroscopy (PL) Evidence of defect states were observed in T and R spectra which allow the light to propagate for selected frequencies within the pseudogap (stop band).
Study of reticular defects in V3Si (A15 structure)
International Nuclear Information System (INIS)
Ben Lamine, Abdelmottaleb
1980-01-01
The A15 crystal structure is that of superconductive compounds with high critical temperature. This research thesis aims at studying its possible reticular defects. In a first part, the author presents this structure and more particularly its crystallographic properties, reports the indexing of electronic diffraction diagrams (point diagrams and line diagrams of Kikuchi) in the case of V 3 Si. Then, after having described the sample preparation technique, the author reports the study of reticular defects by high voltage electronic microscopy on a raw V 3 Si crystal. The existence of a specific defect is highlighted and the crystallographic study of this defect is reported. It has been performed by means of computer-based simulation of contrast (TWODIS software). Results are then discussed
International Nuclear Information System (INIS)
Kurozumi, Y.
2004-01-01
It is well known that ultrasonic waves are affected strongly by macro-structures in cast stainless steel, as in the primary pipe or other components in pressurized water reactors (PWRs). In this work, ultrasonic refractive angles and defect detection sensitivities are investigated at different incident angles to cast stainless steel. The aims of the investigation are to clarify the transmission of ultrasonic waves in cast stainless steel and to contribute to the transducer design. The results are that ultrasonic refractive angles in cast stainless steel shift towards the 45-degree direction with respect to the direction of dendritic structures by 11.8 degrees at the maximum and that the sensitivity of transducer for inner surface breaking cracks increases with decreasing incident angle. However, in an ultrasonic inspection of actual welds at smaller incident angles, a trade-off occurs between increased defect detection sensitivity and decreased defect discrimination capability due to intense false signals produced by non-defective features. (orig.)
Reversal of lattice, electronic structure, and magnetism in epitaxial SrCoOx thin films
Jeen, H.; Choi, W. S.; Lee, J. H.; Cooper, V. R.; Lee, H. N.; Seo, S. S. A.; Rabe, K. M.
2014-03-01
SrCoOx (x = 2.5 - 3.0, SCO) is an ideal material to study the role of oxygen content for electronic structure and magnetism, since SCO has two distinct topotactic phases: the antiferromagnetic insulating brownmillerite SrCoO2.5 and the ferromagnetic metallic perovskite SrCoO3. In this presentation, we report direct observation of a reversible lattice and electronic structure evolution in SrCoOx epitaxial thin films as well as different magnetic and electronic ground states between the topotactic phases.[2] By magnetization measurements, optical absorption, and transport measurements drastically different electronic and magnetic ground states are found in the epitaxially grown SrCoO2.5 and SrCoO3 thin films by pulsed laser epitaxy. First-principles calculations confirm substantial, which originate from the modification in the Co valence states and crystallographic structures. By real-time spectroscopic ellipsometry, the two electronically and magnetically different phases can be reversibly changed by changing the ambient pressure at greatly reduced temperatures. Our finding provides an important pathway to understanding the novel oxygen-content-dependent phase transition uniquely found in multivalent transition metal oxides. The work was supported by the U.S. Department of Energy, Basic Energy Sciences, Materials Sciences and Engineering Division.
Jenett, Benjamin; Calisch, Sam; Cellucci, Daniel; Cramer, Nick; Gershenfeld, Neil; Swei, Sean; Cheung, Kenneth C
2017-03-01
We describe an approach for the discrete and reversible assembly of tunable and actively deformable structures using modular building block parts for robotic applications. The primary technical challenge addressed by this work is the use of this method to design and fabricate low density, highly compliant robotic structures with spatially tuned stiffness. This approach offers a number of potential advantages over more conventional methods for constructing compliant robots. The discrete assembly reduces manufacturing complexity, as relatively simple parts can be batch-produced and joined to make complex structures. Global mechanical properties can be tuned based on sub-part ordering and geometry, because local stiffness and density can be independently set to a wide range of values and varied spatially. The structure's intrinsic modularity can significantly simplify analysis and simulation. Simple analytical models for the behavior of each building block type can be calibrated with empirical testing and synthesized into a highly accurate and computationally efficient model of the full compliant system. As a case study, we describe a modular and reversibly assembled wing that performs continuous span-wise twist deformation. It exhibits high performance aerodynamic characteristics, is lightweight and simple to fabricate and repair. The wing is constructed from discrete lattice elements, wherein the geometric and mechanical attributes of the building blocks determine the global mechanical properties of the wing. We describe the mechanical design and structural performance of the digital morphing wing, including their relationship to wind tunnel tests that suggest the ability to increase roll efficiency compared to a conventional rigid aileron system. We focus here on describing the approach to design, modeling, and construction as a generalizable approach for robotics that require very lightweight, tunable, and actively deformable structures.
International Nuclear Information System (INIS)
Stock, D. M.; Weber, B.; Gaertner, K.
2000-01-01
The relation between the bond defect, which is a topological defect, and structural transformations between crystalline and amorphous silicon, is studied by molecular-dynamics simulations. The investigation of 1-keV boron implantation into crystalline silicon proves that the bond defect can also be generated directly by collisional-induced bond switching in addition to its formation by incomplete recombination of primary defects. This supports the assumption that the bond defect may play an important role in the amorphization process of silicon by light ions. The analysis of the interface between (001) silicon and amorphous silicon shows that there are two typical defect configurations at the interface which result from two different orientations of the bond defect with respect to the interface. Thus the bond defect appears to be a characteristic structural feature of the interface. Moreover, annealing results indicate that the bond defect acts as a growth site for interface-mediated crystallization
Schliesser, Jacob M.
Low-temperature heat capacity data contain information on the physical properties of materials, and new models continue to be developed to aid in the analysis and interpretation of heat capacity data into physically meaningful properties. This work presents the development of two such models and their application to real material systems. Equations describing low-energy vibrational modes with a gap in the density of states (DOS) have been derived and tested on several material systems with known gaps in the DOS, and the origins of such gaps in the DOS are presented. Lattice vacancies have been shown to produce a two-level system that can be modeled with a sum of low-energy Schottky anomalies that produce an overall linear dependence on temperature in the low-temperature heat capacity data. These two models for gaps in the vibrational DOS and the relationship between a linear heat capacity and lattice vacancies and many well-known models have been applied to several systems of materials to test their validity and applicability as well as provide greater information on the systems themselves. A series of bulk and nanoscale Mn-Fe and Co-Fe spinel solid solutions were analyzed using the entropies derived from heat capacity data, and excess entropies of mixing were determined. These entropies show that changes in valence, cation distribution, bonding, and the microstructure between the mixing ions is non-ideal, especially in the nanoparticles. The heat capacity data of ten Al doped TiO2 anatase nanoparticle samples have also been analyzed to show that the Al3+ dopant ions form small regions of short-range order, similar to a glass, within the TiO2 particles, while the overall structure of TiO2 remains unchanged. This has been supported by X-ray diffraction (XRD) and electron energy-loss spectroscopy and provides new insights to the synthesis and characterization of doped materials. The final investigation examines nanocrystalline CuO using heat capacities, magnetization
Xifang, Chen; Wenxia, Zhang; Qianjin, Wang; Jiyang, Fan
Carbon quantum dots (CQDs) have attracted great attention in the past few years due to their low cytotoxicity, exploited various synthesis methods, unexampled abundance of raw materials on earth, and robust near-infrared to near-UV luminescence. Carbon nanoparticles have applications in biological labeling, delivery of drugs and biological molecules into cells, and light emitting diodes and lasing. CQDs generally exist as nanodiamonds or graphite quantum dots according to previous research reports. In this study, we report the first synthesis of the third-allotrope CQDs through carbonization of sucrose and study their luminescence properties. These CQDs have a body-centered cubic structure and each lattice point is composed of eight atoms which form a sub-cube (so called C8 crystal structure). High-resolution transmission electron microscopy and X-ray diffraction confirm the C8 structure of the synthesized carbon nanocrystallites with an average size of 2 nm. The C8 CQDs exhibit double-band luminescence with two peaks centered at around 432 and 520 nm. The study based on the photoluminescence, UV-Vis absorption, Fourier-transform infrared, and X-ray photoelectron spectroscopies reveals that the green emission originates from the C=O related surface defect.
DEFF Research Database (Denmark)
Laver, M.; Bowell, C.J.; Forgan, E.M.
2009-01-01
High-purity niobium exhibits a surprisingly rich assortment of vortex lattice (VL) structures for fields applied parallel to a fourfold symmetry axis, with all observed VL phases made up of degenerate domains that spontaneously break some crystal symmetry. Yet a single regular hexagonal VL domain...
Energy Technology Data Exchange (ETDEWEB)
Xu Xixiang [College of Science, Shandong University of Science and Technology, Qingdao 266510 (China)], E-mail: xixiang_xu@yahoo.com.cn
2009-10-02
Integrable couplings of relativistic Toda lattice systems in polynomial form and rational form, and their hierarchies, are derived from a four-by-four discrete matrix eigenvalue problem. The bi-Hamiltonian structure for every integrable coupling in the two hierarchies obtained is established by means of the discrete variational identity. Ultimately, Liouvolle integrability of the obtained integrable couplings is demonstrated.
Synthesis of spatially variant lattices.
Rumpf, Raymond C; Pazos, Javier
2012-07-02
It is often desired to functionally grade and/or spatially vary a periodic structure like a photonic crystal or metamaterial, yet no general method for doing this has been offered in the literature. A straightforward procedure is described here that allows many properties of the lattice to be spatially varied at the same time while producing a final lattice that is still smooth and continuous. Properties include unit cell orientation, lattice spacing, fill fraction, and more. This adds many degrees of freedom to a design such as spatially varying the orientation to exploit directional phenomena. The method is not a coordinate transformation technique so it can more easily produce complicated and arbitrary spatial variance. To demonstrate, the algorithm is used to synthesize a spatially variant self-collimating photonic crystal to flow a Gaussian beam around a 90° bend. The performance of the structure was confirmed through simulation and it showed virtually no scattering around the bend that would have arisen if the lattice had defects or discontinuities.
Random lattice structures. Modelling, manufacture and FEA of their mechanical response
Maliaris, G.; Sarafis, I. T.; Lazaridis, T.; Varoutoglou, A.; Tsakataras, G.
2016-11-01
The implementation of lightweight structures in various applications, especially in Aerospace/ Automotive industries and Orthopaedics, has become a necessity due to their exceptional mechanical properties with respect to reduced weight. In this work we present a Voronoi tessellation based algorithm, which has been developed for modelling stochastic lattice structures. With the proposed algorithm, is possible to generate CAD geometry with controllable structural parameters, such as porosity, cell number and strut thickness. The digital structures were transformed into physical objects through the combination of 3D printing technics and investment casting. This process was applied to check the mechanical behaviour of generated digital models. Until now, the only way to materialize such structures into physical objects, was feasible through 3D printing methods such as Selective Laser Sintering/ Melting (SLS/ SLM). Investment casting possesses numerous advantages against SLS or SLA, with the major one being the material variety. On the other hand, several trials are required in order to calibrate the process parameters to have successful castings, which is the major drawback of investment casting. The manufactured specimens were subjected to compression tests, where their mechanical response was registered in the form of compressive load - displacement curves. Also, a finite element model was developed, using the specimens’ CAD data and compression test parameters. The FE assisted calculation of specimen plastic deformation is identical with the one of the physical object, which validates the conclusions drawn from the simulation results. As it was observed, strut contact is initiated when specimen deformation is approximately 5mm. Although FE calculated compressive force follows the same trend for the first 3mm of compression, then diverges because of the elasto-plastic FE model type definition and the occurred remeshing steps.
Guo, Jianhui; Shi, Lei; Zhao, Jiyin; Wang, Yang; Yuan, Xueyou; Li, Yang; Wu, Liang
2018-04-01
The recent discovered compound SrFeO2 is an infinite-layer-structure iron oxide with unusual square-planar coordination of Fe2+ ions. In this study, SrFe1‑xMoxO2+δ (x parasitic ferromagnetism of the compound and its relationship to the defect structures are investigated. It is found that substitution of high-valent Mo6+ for Fe2+ results in excess oxygen anions O2‑ inserted at the interlayer sites for charge compensation, which further causes large atomic displacements along the c-axis. Due to the robust but flexible Fe-O-Fe framework, the samples are well crystallized within the ab-plane, but are significantly poorer crystallized along the c-axis. Defect structures including local lattice distortions and edge dislocations responsible for the lowered crystallinity are observed by high resolution transmission electron microscopy. Both the magnetic measurements and electron spin resonance spectra provide the evidence of a parasitic ferromagnetism (FM). The week FM interaction originated from the imperfect antiferromagnetic (AFM) ordering could be ascribed to the introduction of uncompensated magnetic moments due to substitution of Mo6+ (S = 0) for Fe2+ (S = 2) and the canted/frustrated spins resulted from defect structures.
A comparison of VRML and animation of rotation for teaching 3-dimensional crystal lattice structures
Sauls, Barbara Lynn
Chemistry students often have difficulty visualizing abstract concepts of molecules and atoms, which may lead to misconceptions. The three-dimensionality of these structures presents a challenge to educators. Typical methods of teaching include text with two-dimensional graphics and structural models. Improved methods to allow visualization of 3D structures may improve learning of these concepts. This research compared the use of Virtual Reality Modeling Language (VRML) and animation of rotation for teaching three-dimensional structures. VRML allows full control of objects by altering angle, size, rotation, and provides the ability to zoom into and through objects. Animations may only be stopped, restarted and replayed. A web-based lesson teaching basic concepts of crystals, which requires comprehension of their three-dimensional structure was given to 100 freshmen chemistry students. Students were stratified by gender then randomly to one of two lessons, which were identical except for the multimedia method used to show the lattices and unit cells. One method required exploration of the structures using VRML, the other provided animations of the same structures rotating. The students worked through an examination as the lesson progressed. A Welch t' test was used to compare differences between groups. No significant difference in mean achievement was found between the two methods, between genders, or within gender. There was no significant difference in mean total SAT in the animation and VRML group. Total time on task had no significant difference nor did enjoyment of the lesson. Students, however, spent 14% less time maneuvering VRML structures than viewing the animations of rotation. Neither method proved superior for presenting three-dimensional information. The students spent less time maneuvering the VRML structures with no difference in mean score so the use of VRML may be more efficient. The investigator noted some manipulation difficulties using VRML to
Effects of moiré lattice structure on electronic properties of graphene
Huang, Lunan; Wu, Yun; Hershberger, M. T.; Mou, Daixiang; Schrunk, Benjamin; Tringides, Michael C.; Hupalo, Myron; Kaminski, Adam
2017-07-01
We study structural and electronic properties of graphene grown on silicone carbide (SiC) substrate using a scanning tunneling microscope, spot-profile-analysis low-energy electron diffraction, and angle-resolved photoemission spectroscopy. We find several new replicas of Dirac cones in the Brillouin zone. Their locations can be understood in terms of a combination of basis vectors linked to SiC 6 × 6 and graphene 6 √{3 }×6 √{3 } reconstruction. Therefore, these new features originate from the moiré caused by the lattice mismatch between SiC and graphene. More specifically, Dirac cone replicas are caused by underlying weak modulation of the ionic potential by the substrate that is then experienced by the electrons in the graphene. We also demonstrate that this effect is equally strong in single- and trilayer graphene; therefore, the additional Dirac cones are intrinsic features rather than the result of photoelectron diffraction. These new features in the electronic structure are very important for the interpretation of recent transport measurements and can assist in tuning the properties of graphene for practical applications.
A lattice Boltzmann model for substrates with regularly structured surface roughness
Yagub, A.; Farhat, H.; Kondaraju, S.; Singh, T.
2015-11-01
Superhydrophobic surface characteristics are important in many industrial applications, ranging from the textile to the military. It was observed that surfaces fabricated with nano/micro roughness can manipulate the droplet contact angle, thus providing an opportunity to control the droplet wetting characteristics. The Shan and Chen (SC) lattice Boltzmann model (LBM) is a good numerical tool, which holds strong potentials to qualify for simulating droplets wettability. This is due to its realistic nature of droplet contact angle (CA) prediction on flat smooth surfaces. But SC-LBM was not able to replicate the CA on rough surfaces because it lacks a real representation of the physics at work under these conditions. By using a correction factor to influence the interfacial tension within the asperities, the physical forces acting on the droplet at its contact lines were mimicked. This approach allowed the model to replicate some experimentally confirmed Wenzel and Cassie wetting cases. Regular roughness structures with different spacing were used to validate the study using the classical Wenzel and Cassie equations. The present work highlights the strength and weakness of the SC model and attempts to qualitatively conform it to the fundamental physics, which causes a change in the droplet apparent contact angle, when placed on nano/micro structured surfaces.
Research Trends on Defect and Life Assessment of High Temperature Structure
International Nuclear Information System (INIS)
Lee, Hyeong Yeon; Lee Jae Han
2008-01-01
This report presents the analysis on the state-of-the-art research trends on defect assessment and life evaluation of high temperature structure based on the papers presented in the two international conferences of ASME PVP 2007 / CREEP 8 which was held in 2007 and ICFDSM VI(International Conference on Fatigue Damage of Structural Materials VI) which was held in 2006
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
Properties of Ti-6Al-4V non-stochastic lattice structures fabricated via electron beam melting
International Nuclear Information System (INIS)
Cansizoglu, O.; Harrysson, O.; Cormier, D.; West, H.; Mahale, T.
2008-01-01
This paper addresses foams which are known as non-stochastic foams, lattice structures, or repeating open cell structure foams. The paper reports on preliminary research involving the design and fabrication of non-stochastic Ti-6Al-4V alloy structures using the electron beam melting (EBM) process. Non-stochastic structures of different cell sizes and densities were investigated. The structures were tested in compression and bending, and the results were compared to results from finite element analysis simulations. It was shown that the build angle and the build orientation affect the properties of the lattice structures. The average compressive strength of the lattice structures with a 10% relative density was 10 MPa, the flexural modulus was 200 MPa and the strength to density ration was 17. All the specimens were fabricated on the EBM A2 machine using a melt speed of 180 mm/s and a beam current of 2 mA. Future applications and FEA modeling were discussed in the paper
Displacive stability of a void in a void lattice
International Nuclear Information System (INIS)
Brailsford, A.D.
1977-01-01
It has recently been suggested that the stability of the void-lattice structure in irradiated metals may be attributed to the effect of the overlapping of the point-defect diffusion fields associated with each void. It is shown here, however, that the effect is much too weak. When one void is displaced from its lattice site, the displacement is shown to relax to zero as proposed, but a conservative estimate indicates that the characteristic time is equivalent to an irradiation dose of the order of 300 displacements per atom which is generally much greater than the dose necessary for void-lattice formation
Energetics of intrinsic point defects in uranium dioxide from electronic-structure calculations
International Nuclear Information System (INIS)
Nerikar, Pankaj; Watanabe, Taku; Tulenko, James S.; Phillpot, Simon R.; Sinnott, Susan B.
2009-01-01
The stability range of intrinsic point defects in uranium dioxide is determined as a function of temperature, oxygen partial pressure, and non-stoichiometry. The computational approach integrates high accuracy ab initio electronic-structure calculations and thermodynamic analysis supported by experimental data. In particular, the density functional theory calculations are performed at the level of the spin polarized, generalized gradient approximation and includes the Hubbard U term; as a result they predict the correct anti-ferromagnetic insulating ground state of uranium oxide. The thermodynamic calculations enable the effects of system temperature and partial pressure of oxygen on defect formation energy to be determined. The predicted equilibrium properties and defect formation energies for neutral defect complexes match trends in the experimental literature quite well. In contrast, the predicted values for charged complexes are lower than the measured values. The calculations predict that the formation of oxygen interstitials becomes increasingly difficult as higher temperatures and reducing conditions are approached
The effect of defects on structural failure: A two-criteria approach
International Nuclear Information System (INIS)
Dowling, A.R.; Townley, C.H.A.
1976-01-01
The two-criteria approach to the study of defects in structures assumes that failure occurs when the applied load reaches the lower of either a load to cause brittle failure in accordance with the theories of linear elastic fracture mechanics or a collapse load dependent on the ultimate stress of the material and the structural geometry. This simple approach is described and compared with previously published experimental results for various geometries and materials. The simplicity of this method of defect analysis lies in the fact that each criterion is sufficiently well understood to permit scaling and geometry changes to be accommodated readily. It becomes apparent that a sizeable transition region exists between the two criteria but this can be described in an expression relating the criteria. This expression adequately predicts the behaviour of cracked structures of both simple and complex geometry. A design curve for defect assessment is proposed for which it is unnecessary to consider the transition region. (author)
Direct observation of the point-defect structure of depleted-zones in ion-irradiated metals
International Nuclear Information System (INIS)
Wei, C.
1978-01-01
The point-defect structure of individual depleted zones has been studied systematically. Four-pass zone-refined tungsten field-ion microscope (FIM) specimens were irradiated in-situ at 10 K with 30 keV Cr + , Mo + , or W + ions to a total dose of (2 to 10) x 10 12 ion cm -2 and examined by the pulse field-evaporation technique at 10 K. The experimental conditions were such that each depleted zone was created by a single incident-ion. The number of vacant lattice sites within a depleted zone was compared with a modified Kinchin--Pease model. The radial distribution function was determined for each depleted zone; it was found that the vacant lattice sites within the volume of each depleted zone tended to exist in a highly clustered state. It was found that the diameter D of each depleted zone was described by the equation D approximately equal to [y 2 ]/sup 1 / 2 / where [y 2 ]/sup 1 / 2 / is the second moment of the theoretical distribution curve, of the fraction of incident ion energy deposited in atom motion, transverse to the direction of the incident ion-beam. The spatial distribution of self-interstitial atoms (SIAs) in a specimen irradiated with 30 keV Cr + ions and in a specimen irradiated with 18 keV Au + ions, at 10 K, was determined. A low bound to the average range of replacement collision sequences (RCSs) was found to be 175 +- 85 A. A detailed FIM study was also made of the vacancy structure of a (220) platelet created by a single 30 keV W + ion in a platinum-4.0 at. % gold alloy; the specimen was irradiated at 40 K and then isochronally warmed to 100 K. The (220) platelet was found to consist of 31 vacant lattice sites, lying in four (220) planes, and clustered in a disc-shaped region which is approximately 20 A in diameter. It was suggested that prismatic dislocation loops lying on (220) type planes in ion or fast neutron irradiated platinum can form as a result of the direct collapse of (220) type vacancy platelets
International Nuclear Information System (INIS)
Simon, G H; König, T; Heinke, L; Lichtenstein, L; Heyde, M; Freund, H-J
2011-01-01
We present an extensive atomic resolution frequency modulation dynamic force microscopy study of ultrathin aluminium oxide on a single crystalline NiAl(110) surface. One-dimensional surface defects produced by domain boundaries have been resolved. Images are presented for reflection domain boundaries (RDBs), four different types of antiphase domain boundaries, a nucleation-related translation domain boundary and also domain boundary junctions. New structures and aspects of the boundaries and their network are revealed and merged into a comprehensive picture of the defect arrangements. The alumina film also covers the substrate completely at the boundaries and their junctions and follows the structural building principles found in its unit cell. This encompasses square and rectangular groups of surface oxygen sites. The observed structural elements can be related to the electronic signature of the boundaries and therefore to the electronic defects associated with the boundaries. A coincidence site lattice predicted for the RDBs is in good agreement with experimental data. With Σ = 19 it can be considered to be of low-sigma type, which frequently coincides with special boundary properties. Images of asymmetric RDBs show points of good contact alternating with regions of nearly amorphous disorder in the oxygen sublattice. (paper)
On the Advantages and Defects of the American Structuralism
Institute of Scientific and Technical Information of China (English)
徐晓莹
2004-01-01
During the years at the end of the nineteenth century and beginning of the twentieth century when Saussure was working out his ideas in Europe, synchronic linguistics was emerging independently, and in a very different style, in America, under the leadership of the anthropologist Franz Boas. Boas set a direction for American linguistics. The school founded by Boas was called structural linguistics. Beside Boas, the other two major representatives of this school during this period were: Sapir and Bloomfield.
Lattice Boltzmann study of slip flow over structured surface with transverse slots
Chen, Wei; Wang, Kai; Wang, Lei; Hou, Guoxiang; Leng, Wenjun
2018-04-01
Slip flow over structured superhydrophobic surface with transverse slots is investigated by the lattice Boltzmann method. The Shan-Chen multiphase model is employed to simulate the flow over gas bubbles in the slots. The Carnahan-Starling equation of state is applied to obtain large density ratio. The interface thickness of the multiphase model is discussed. We find that the Cahn number Cn should be smaller than 0.02 when the temperature T = 0.5T c to restrict the influence of interface thickness on slip length. Influences of slot fraction on slip length is then studied, and the result is compared with single LB simulation of which the interface is treated as free-slip boundary. The slip length obtained by the multiphase model is a little smaller. After that, the shape of the liquid-gas interface is considered, and simulations with different initial protrusion angles and capillary numbers are performed. Effective slip length as a function of initial protrusion angle is obtained. The result is in qualitative agreement with a previous study and main features are reproduced. Furthermore, the influence of Capillary number Ca is studied. Larger Ca causes larger interface deformation and smaller slip length. But when the interface is concaving into the slot, this influence is less obvious.
Zargarian, A; Esfahanian, M; Kadkhodapour, J; Ziaei-Rad, S
2016-03-01
In this paper, the effects of cell geometry and relative density on the high-cycle fatigue behavior of Titanium scaffolds produced by selective laser melting and electron beam melting techniques were numerically investigated by finite element analysis. The regular titanium lattice samples with three different unit cell geometries, namely, diamond, rhombic dodecahedron and truncated cuboctahedron, and the relative density range of 0.1-0.3 were analyzed under uniaxial cyclic compressive loading. A failure event based algorithm was employed to simulate fatigue failure in the cellular material. Stress-life approach was used to model fatigue failure of both bulk (struts) and cellular material. The predicted fatigue life and the damage pattern of all three structures were found to be in good agreement with the experimental fatigue investigations published in the literature. The results also showed that the relationship between fatigue strength and cycles to failure obeyed the power law. The coefficient of power function was shown to depend on relative density, geometry and fatigue properties of the bulk material while the exponent was only dependent on the fatigue behavior of the bulk material. The results also indicated the failure surface at an angle of 45° to the loading direction. Copyright © 2015 Elsevier B.V. All rights reserved.
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)
Thermographic inspection of bond defects in Fiber Reinforced Polymer applied to masonry structures
Masini, N.; Aiello, M. A.; Capozzoli, L.; Vasanelli, E.
2012-04-01
Nowadays, externally bonded Fiber Reinforced Polymers (FRP) are extensively used for strengthening and repairing masonry and reinforced concrete existing structures; they have had a rapid spread in the area of rehabilitation for their many advantages over other conventional repair systems, such as lightweight, excellent corrosion and fatigue resistance, high strength, etc. FRP systems applied to masonry or concrete structures are typically installed using a wet-layup technique.The method is susceptible to cause flaws or defects in the bond between the FRP system and the substrate, which may reduce the effectiveness of the reinforcing systems and the correct transfer of load from the structure to the composite. Thus it is of primary importance to detect the presence of defects and to quantify their extension in order to eventually provide correct repair measurements. The IR thermography has been cited by the several guidelines as a good mean to qualitatively evaluate the presence of installation defects and to monitor the reinforcing system with time.The method is non-destructive and does not require contact with the composite or other means except air to detect the reinforcement. Some works in the literature have been published on this topic. Most of the researches aim at using the IR thermography technique to characterize quantitatively the defects in terms of depth, extension and type in order to have an experimental database on defect typology to evaluate the long term performances of the reinforcing system. Nevertheless, most of the works in the literature concerns with FRP applied to concrete structures without considering the case of masonry structures. In the present research artificial bond defects between FRP and the masonry substrate have been reproduced in laboratory and the IR multi temporal thermography technique has been used to detect them. Thermographic analysis has been carried out on two wall samples having limited dimensions (100 x 70 cm) both
Polarized Raman study on the lattice structure of BiFeO3 films prepared by pulsed laser deposition
Yang, Yang
2014-11-01
Polarized Raman spectroscopy was used to study the lattice structure of BiFeO3 films on different substrates prepared by pulsed laser deposition. Interestingly, the Raman spectra of BiFeO3 films exhibit distinct polarization dependences. The symmetries of the fundamental Raman modes in 50-700 cm-1 were identified based on group theory. The symmetries of the high order Raman modes in 900-1500 cm-1 of BiFeO3 are determined for the first time, which can provide strong clarifications to the symmetry of the fundamental peaks in 400-700 cm-1 in return. Moreover, the lattice structures of BiFeO3 films are identified consequently on the basis of Raman spectroscopy. BiFeO3 films on SrRuO3 coated SrTiO3 (0 0 1) substrate, CaRuO3 coated SrTiO3 (0 0 1) substrate and tin-doped indium oxide substrate are found to be in the rhombohedral structure, while BiFeO3 film on SrRuO3 coated Nb: SrTiO3 (0 0 1) substrate is in the monoclinic structure. Our results suggest that polarized Raman spectroscopy would be a feasible tool to study the lattice structure of BiFeO3 films.
Wang, Qinghua; Ri, Shien; Tsuda, Hiroshi; Kodera, Masako; Suguro, Kyoichi; Miyashita, Naoto
2017-09-19
Quantitative detection of defects in atomic structures is of great significance to evaluating product quality and exploring quality improvement process. In this study, a Fourier transform filtered sampling Moire technique was proposed to visualize and detect defects in atomic arrays in a large field of view. Defect distributions, defect numbers and defect densities could be visually and quantitatively determined from a single atomic structure image at low cost. The effectiveness of the proposed technique was verified from numerical simulations. As an application, the dislocation distributions in a GaN/AlGaN atomic structure in two directions were magnified and displayed in Moire phase maps, and defect locations and densities were detected automatically. The proposed technique is able to provide valuable references to material scientists and engineers by checking the effect of various treatments for defect reduction. © 2017 IOP Publishing Ltd.
Energy Technology Data Exchange (ETDEWEB)
Zhang, Huai-Yong; Zhao, Ying-Qin; Lu, Qing [Sichuan Univ., Chengdu (China). Inst. of Atomic and Molecular Physics; Zeng, Zhao-Yi [Chongqing Normal Univ. (China). College of Physics and Electronic Engineering; Chinese Academy of Engineering Physics, Mianyang (China). National Key Laboratory for Shock Wave and Detonation Physics Research; Cheng, Yan [Sichuan Univ., Chengdu (China). Inst. of Atomic and Molecular Physics; Sichuan Univ., Chengdu (China). Key Laboratory of High Energy Density Physics and Technology of Ministry of Education
2016-11-01
Lattice dynamics, structural phase transition, and the thermodynamic properties of barium titanate (BaTiO{sub 3}) are investigated by using first-principles calculations within the density functional theory (DFT). It is found that the GGA-WC exchange-correlation functional can produce better results. The imaginary frequencies that indicate structural instability are observed for the cubic, tetragonal, and orthorhombic phases of BaTiO{sub 3} and no imaginary frequencies emerge in the rhombohedral phase. By examining the partial phonon density of states (PDOSs), we find that the main contribution to the imaginary frequencies is the distortions of the perovskite cage (Ti-O). On the basis of the site-symmetry consideration and group theory, we give the comparative phonon symmetry analysis in four phases, which is useful to analyze the role of different atomic displacements in the vibrational modes of different symmetry. The calculated optical phonon frequencies at Γ point for the four phases are in good agreement with other theoretical and experimental data. The pressure-induced phase transition of BaTiO{sub 3} among four phases and the thermodynamic properties of BaTiO{sub 3} in rhombohedral phase have been investigated within the quasi-harmonic approximation (QHA). The sequence of the pressure-induced phase transition is rhombohedral → orthorhombic → tetragonal → cubic, and the corresponding transition pressure is 5.17, 5.92, 6.65 GPa, respectively. At zero pressure, the thermal expansion coefficient α{sub V}, heat capacity C{sub V}, Grueneisen parameter γ, and bulk modulus B of the rhombohedral phase BaTiO{sub 3} are estimated from 0 K to 200 K.
Kumar, Dablu; Ranjan, Rakesh
2018-03-01
12-Core 5-LP mode homogeneous multicore fibers have been proposed for analysis of inter-core crosstalk and dispersion, with four different lattice structures (circular, 2-ring, square lattice, and triangular lattice) having cladding diameter of 200 μm and a fixed cladding thickness of 35 μm. The core-to-core crosstalk impact has been studied numerically with respect to bending radius, core pitch, transmission distance, wavelength, and core diameter for all 5-LP modes. In anticipation of further reduction in crosstalk levels, the trench-assisted cores have been incorporated for all respective designs. Ultra-low crosstalk (-138 dB/100 km) has been achieved through the triangular lattice arrangement, with trench depth Δ2 = -1.40% for fundamental (LP01) mode. It has been noted that the impact of mode polarization on crosstalk behavior is minor, with difference in crosstalk levels between two polarized spatial modes as ≤0.2 dB. Moreover, the optimized cladding diameter has been obtained for all 5-LP modes for a target value of crosstalk of -50 dB/100 km, with all the core arrangements. The dispersion characteristic has also been analyzed with respect to wavelength, which is nearly 2.5 ps/nm km at operating wavelength 1550 nm. The relative core multiplicity factor (RCMF) for the proposed design is obtained as 64.
Structural defect generation in indium antimonide single crystals during electro-erosion cutting
International Nuclear Information System (INIS)
Kravetskij, M.Yu.; Matsas, E.P.; Skorokhod, M.Ya.; Fomin, A.V.; Khromyak, K.Ya.
1990-01-01
Using X-ray topography structural defects generating during electro-erosion cutting of InSb single crystals are studied. It is shown that dislocations, are introduced into so cut dislocation-free ingot plates, nucleation centers being located on their surfaces. It is detected that foreign phase inclusions in InSb are efficient sources of dislocations during cutting
Effect of Hydrostatic Pressure on Defect Structure and Durability of Ultrafine-Grained Aluminum
Czech Academy of Sciences Publication Activity Database
Betekhtin, V.I.; Kadomtsev, A. G.; Sklenička, Václav; Narykova, M. V.
2011-01-01
Roč. 37, č. 10 (2011), s. 977-979 ISSN 1063-7850 Institutional research plan: CEZ:AV0Z20410507 Keywords : defect structure * ultrafine-grained aluminium * durability Subject RIV: JG - Metallurgy Impact factor: 0.565, year: 2011
Synthesis and structural characterization of defect spinels in the Lithium-Manganese-Oxide system
CSIR Research Space (South Africa)
Thackeray, MM
1993-10-01
Full Text Available Lithium-manganese-oxides prepared at moderate temperatures are under investigation as insertion electrodes for rechargeable lithium batteries. The structures of two defect-spinel compounds synthesised by the reaction of MnCO3 and Li2CO3 at 400...
Synthesis and structural characterization of defect spinels in the lithium-manganese-oxide system
CSIR Research Space (South Africa)
Thackeray, MM
1993-10-01
Full Text Available Lithium-manganese-oxides prepared at moderate temperatures are under investigation as insertion electrodes for rechargeable lithium batteries. The structures of two defect-spinel compounds synthesized by the reaction of MnCO3 and Li2CO3 at 400°C...
Radiation defect formation in two-barrier structures based on silicon
International Nuclear Information System (INIS)
Madatov, R.S.; Abbasov, F.P.; Mustafayev, Yu.M.
2013-01-01
It was developed a silicon-based photodetector with high integral sensitivity in low-wave spectrum. It was investigated the effect of gamma radiation on the mechanism of current transport in the structure of Schottky barrier type and in transitions. It is shown that the double-barrier structures can improve the photovoltaic parameters of conventional detectors. For the first time it was obtained and studied the characteristics of two-barrier structures created on the same plane. The advantages over conventional structures are shown. The annealing point is changing the structure of radiation defects and leads to their disappearance
On the effect of the lattice asymmetry parameter on the phase structure of SU(N) pure gauge theories
International Nuclear Information System (INIS)
Averchenkova, L.A.; Petrov, K.V.; Petrov, V.K.; Zinovjev, G.M.
1998-01-01
The role of the lattice asymmetry parameter ξ in the phase structure description of the SU(2) and SU(3) gluodynamics at finite temperature has been studied analytically in the SU(N)∼Z(N) approach. The properties of thermodynamic quantities have been investigated near the physical border. The effective action which includes the first non-trivial order from the space-like part allows estimates to be made of the phase structure not only close to the physical border but in the whole area of couplings. We find that thermodynamic quantities depend on ξ and this dependence may be strong enough, up to discontinuity over this parameter for some of them. The Hamiltonian formulation of the SU(2) gauge theory on the asymmetric lattice is presented. (orig.)
International Nuclear Information System (INIS)
Peng Juan; Li Shu-Shen
2012-01-01
We study the electronic spectrum of coupled quantum dots (QDs) arranged as a graphene hexagonal lattice in the presence of an external perpendicular magnetic field. In our tight-binding model, the effect of the magnetic field is included in both the Peierls phase of the Hamiltonian and the tight-binding basis Wannier function. The energy of the system is analyzed when the magnetic flux through the lattice unit cell is a rational fraction of the quantum flux. The calculated spectrum has recursive properties, similar to those of the classical Hofstadter butterfly. However, unlike the ideal Hofstadter butterfly structure, our result is asymmetric since the impacts of the specific material and the magnetic field on the wavefunctions are included, making the results more realistic. (condensed matter: electronic structure, electrical, magnetic, and optical properties)
Sim, Hasung; Lee, Seongsu; Hong, Kun-Pyo; Jeong, Jaehong; Zhang, J. R.; Kamiyama, T.; Adroja, D. T.; Murray, C. A.; Thompson, S. P.; Iga, F.; Ji, S.; Khomskii, D.; Park, Je-Geun
2016-11-01
Dy B4 has a two-dimensional Shastry-Sutherland (Sh-S) lattice with strong Ising character of the Dy ions. Despite the intrinsic frustrations, it undergoes two successive transitions: a magnetic ordering at TN=20 K and a quadrupole ordering at TQ=12.5 K . From high-resolution neutron and synchrotron x-ray powder diffraction studies, we have obtained full structural information on this material in all phases and demonstrate that structural modifications occurring at quadrupolar transition lead to the lifting of frustrations inherent in the Sh-S model. Our paper thus provides a complete experimental picture of how the intrinsic frustration of the Sh-S lattice can be lifted by the coupling to quadrupole moments. We show that two other factors, i.e., strong spin-orbit coupling and long-range Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction in metallic Dy B4 , play an important role in this behavior.
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
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.
Tailoring the strain in Si nano-structures for defect-free epitaxial Ge over growth.
Zaumseil, P; Yamamoto, Y; Schubert, M A; Capellini, G; Skibitzki, O; Zoellner, M H; Schroeder, T
2015-09-04
We investigate the structural properties and strain state of Ge nano-structures selectively grown on Si pillars of about 60 nm diameter with different SiGe buffer layers. A matrix of TEOS SiO2 surrounding the Si nano-pillars causes a tensile strain in the top part at the growth temperature of the buffer that reduces the misfit and supports defect-free initial growth. Elastic relaxation plays the dominant role in the further increase of the buffer thickness and subsequent Ge deposition. This method leads to Ge nanostructures on Si that are free from misfit dislocations and other structural defects, which is not the case for direct Ge deposition on these pillar structures. The Ge content of the SiGe buffer is thereby not a critical parameter; it may vary over a relatively wide range.
Defect study in ZnO related structures-A multi-spectroscopic approach
International Nuclear Information System (INIS)
Ling, C.C.; Cheung, C.K.; Gu, Q.L.; Dai, X.M.; Xu, S.J.; Zhu, C.Y.; Luo, J.M.; Zhu, C.Y.; Tam, K.H.; Djurisic, A.B.; Beling, C.D.; Fung, S.; Lu, L.W.; Brauer, G.; Anwand, W.; Skorupa, W.; Ong, H.C.
2008-01-01
ZnO has attracted a great deal of attention in recent years because of its potential applications for fabricating optoelectronic devices. Using a multi-spectroscopic approach including positron annihilation spectroscopy (PAS), deep level transient spectroscopy (DLTS), photoluminescence (PL) and X-ray photoelectron spectroscopy (XPS), we have studied the two observed phenomena from ZnO related structures. They namely included the H 2 O 2 pre-treatment induced ohmic to rectifying contact conversion on Au/n-ZnO contact and the p-type doping by nitrogen ion implantation. The aim of the studies was to offering comprehensive views as to how the defects influenced the structures electrical and optical properties of the structures. It was also shown that PAS measurement using the monoenergetic positron beam could offer valuable information of vacancy type defects in the vertical ZnO nanorod array structure
Defect study in ZnO related structures-A multi-spectroscopic approach
Energy Technology Data Exchange (ETDEWEB)
Ling, C.C. [Department of Physics, The University of Hong Kong, Pokfulam Road, Hong Kong (China)], E-mail: ccling@hku.hk; Cheung, C.K.; Gu, Q.L.; Dai, X.M.; Xu, S.J.; Zhu, C.Y.; Luo, J.M.; Zhu, C.Y.; Tam, K.H.; Djurisic, A.B.; Beling, C.D.; Fung, S.; Lu, L.W. [Department of Physics, The University of Hong Kong, Pokfulam Road, Hong Kong (China); Brauer, G.; Anwand, W.; Skorupa, W. [Institut fuer Ionenstrahlphysik und Materialforschung, Forschungszentrum Dresden-Rossendorf, Postfach 510119, D-01314 Dresden (Germany); Ong, H.C. [Department of Physics, Chinese University of Hong Kong, Shatin, Hong Kong (China)
2008-10-31
ZnO has attracted a great deal of attention in recent years because of its potential applications for fabricating optoelectronic devices. Using a multi-spectroscopic approach including positron annihilation spectroscopy (PAS), deep level transient spectroscopy (DLTS), photoluminescence (PL) and X-ray photoelectron spectroscopy (XPS), we have studied the two observed phenomena from ZnO related structures. They namely included the H{sub 2}O{sub 2} pre-treatment induced ohmic to rectifying contact conversion on Au/n-ZnO contact and the p-type doping by nitrogen ion implantation. The aim of the studies was to offering comprehensive views as to how the defects influenced the structures electrical and optical properties of the structures. It was also shown that PAS measurement using the monoenergetic positron beam could offer valuable information of vacancy type defects in the vertical ZnO nanorod array structure.
Energy Technology Data Exchange (ETDEWEB)
Zargarian, A.; Esfahanian, M. [Department of Mechanical Engineering, Isfahan University of Technology, Isfahan 84156-83111 (Iran, Islamic Republic of); Kadkhodapour, J., E-mail: j.kad@srttu.edu [Department of Mechanical Engineering, Shahid Rajaee Teacher Training University, Tehran (Iran, Islamic Republic of); Institute for Materials Testing, Materials Science and Strength of Materials (IMWF), University of Stuttgart, Stuttgart (Germany); Ziaei-Rad, S. [Department of Mechanical Engineering, Isfahan University of Technology, Isfahan 84156-83111 (Iran, Islamic Republic of)
2016-03-01
In this paper, the effects of cell geometry and relative density on the high-cycle fatigue behavior of Titanium scaffolds produced by selective laser melting and electron beam melting techniques were numerically investigated by finite element analysis. The regular titanium lattice samples with three different unit cell geometries, namely, diamond, rhombic dodecahedron and truncated cuboctahedron, and the relative density range of 0.1–0.3 were analyzed under uniaxial cyclic compressive loading. A failure event based algorithm was employed to simulate fatigue failure in the cellular material. Stress-life approach was used to model fatigue failure of both bulk (struts) and cellular material. The predicted fatigue life and the damage pattern of all three structures were found to be in good agreement with the experimental fatigue investigations published in the literature. The results also showed that the relationship between fatigue strength and cycles to failure obeyed the power law. The coefficient of power function was shown to depend on relative density, geometry and fatigue properties of the bulk material while the exponent was only dependent on the fatigue behavior of the bulk material. The results also indicated the failure surface at an angle of 45° to the loading direction. - Highlights: • Numerical simulation was used to predict fatigue behavior of titanium scaffolds. • Good agreement between numerical and experimental results • S–N curves obeyed the power law. • Fatigue strength of scaffolds was proportional to their Young's modulus. • Failure surface of scaffolds was inclined at an angle of 45° to loading.
International Nuclear Information System (INIS)
Galluzzi, F.; Scafe, E.; Beghi, M.; Fossati, S.; Tincani, M.; Pizzini, S.
1985-01-01
An extensive experimental study of minority carrier recombination in CZ grown polycrystalline silicon intentionally doped with metallic impurities (Ti, V, Fe, Cr, Zr) is reported. Experimental values of average diffusion lengths have been compared with values calculated by a simple model of carrier recombination, taking into account the effects of impurities, grain boundaries and intragrain crystal defects. The results are fairly consistent and allow the determination of threshold densities for structural defects and deep impurities. The author's analysis gives a simple quantitative description of recombination processes in solar-grade silicon, as far as the average behaviour is concerned
Positron lifetime calculation for defects and defect clusters in graphite
International Nuclear Information System (INIS)
Onitsuka, T.; Ohkubo, H.; Takenaka, M.; Tsukuda, N.; Kuramoto, E.
2000-01-01
Calculations of positron lifetime have been made for vacancy type defects in graphite and compared with experimental results. Defect structures were obtained in a model graphite lattice after including relaxation of whole lattice as determined by the molecular dynamics method, where the interatomic potential given by Pablo Andribet, Dominguez-Vazguez, Mari Carmen Perez-Martin, Alonso, Jimenez-Rodriguez [Nucl. Instrum. and Meth. 115 (1996) 501] was used. For the defect structures obtained via lattice relaxation positron lifetime was calculated under the so-called atomic superposition method. Positron lifetimes 204 and 222 ps were obtained for the graphite matrix and a single vacancy, respectively, which can be compared with the experimental results 208 and 233 ps. For planar vacancy clusters, e.g., vacancy loops, lifetime calculation was also made and indicated that lifetime increases with the number of vacancies in a cluster. This is consistent with the experimental result in the region of higher annealing temperature (above 1200 deg. C), where the increase of positron lifetime is seen, probably corresponding to the clustering of mobile vacancies
Defect structures in YBa2Cu3O/sub 7-x/ produced by electron irradiation
International Nuclear Information System (INIS)
Kirk, M.A.; Baker, M.C.; Liu, J.Z.; Lam, D.J.; Weber, H.W.
1987-12-01
Defect structures in YBa 2 Cu 3 O/sub 7-x/ produced by electron irradiation at 300 0 K were investigated by transmission electron microscopy. Threshold energies for the production of visible defects were determined to be 152 keV and 131 keV (+- 7 keV) in directions near the a and b (b > a) axes (both perpendicular to c, the long axis in the orthorhombic structure), respectively. During above threshold irradiations in an electron flux of 3 x 10 18 cm -2 s -1 , extended defects were observed to form and grow to sizes of 10 to 50 nm over 1000 s in material thicknesses 20 to 200 nm. Such low electron threshold energies suggest oxygen atom displacements with recoil energies near 20 eV. The observation of movement of twin boundaries during irradiation just above threshold suggests movement of the basal plane oxygen atoms by direct displacement or defect migration processes. Crystals irradiated above threshold were observed after about 24 hours to have transformed to a structure heavily faulted on planes perpendicular to the c axis. 3 refs., 3 figs
Wang, Qi Jie; Zhang, Ying; Soh, Yeng Chai
2005-12-01
This paper presents a novel lattice optical delay-line circuit using 3 × 3 directional couplers to implement three-port optical interleaving filters. It is shown that the proposed circuit can deliver three channels of 2pi/3 phase-shifted interleaving transmission spectra if the coupling ratios of the last two directional couplers are selected appropriately. The other performance requirements of an optical interleaver can be achieved by designing the remaining part of the lattice circuit. A recursive synthesis design algorithm is developed to calculate the design parameters of the lattice circuit that will yield the desired filter response. As illustrative examples, interleavers with maximally flat-top passband transmission and with given transmission performance on passband ripples and passband bandwidth, respectively, are designed to verify the effectiveness of the proposed design scheme.
Remote defect imaging for plate-like structures based on the scanning laser source technique
Hayashi, Takahiro; Maeda, Atsuya; Nakao, Shogo
2018-04-01
In defect imaging with a scanning laser source technique, the use of a fixed receiver realizes stable measurements of flexural waves generated by laser at multiple rastering points. This study discussed the defect imaging by remote measurements using a laser Doppler vibrometer as a receiver. Narrow-band burst waves were generated by modulating laser pulse trains of a fiber laser to enhance signal to noise ratio in frequency domain. Averaging three images obtained at three different frequencies suppressed spurious distributions due to resonance. The experimental system equipped with these newly-devised means enabled us to visualize defects and adhesive objects in plate-like structures such as a plate with complex geometries and a branch pipe.
Effects of graphene defect on electronic structures of its interface with organic semiconductor
Energy Technology Data Exchange (ETDEWEB)
Yang, Qing-Dan; Wang, Chundong; Mo, Hin-Wai; Lo, Ming-Fai; Yuen, Muk Fung; Ng, Tsz-Wai, E-mail: tszwaing@cityu.edu.hk, E-mail: apcslee@cityu.edu.hk; Zhang, Wen-Jun; Lee, Chun-Sing, E-mail: tszwaing@cityu.edu.hk, E-mail: apcslee@cityu.edu.hk [Department of Physics and Materials Science, Center of Super-Diamond and Advanced Films (COSDAF), City University of Hong Kong (Hong Kong); Dou, Wei-Dong [Department of Physics and Materials Science, Center of Super-Diamond and Advanced Films (COSDAF), City University of Hong Kong (Hong Kong); Physics Department, Shaoxing University, Shaoxing 312000 (China); Tsang, Sai-Wing [Department of Physics and Materials Science, City University of Hong Kong (Hong Kong)
2015-03-30
Electronic structures of copper hexadecafluorophthalocyanine (F{sub 16}CuPc)/graphene with different defect density were studied with ultra-violet photoelectron spectroscopy. We showed that the charge transfer interaction and charge flow direction can be interestingly tuned by controlling the defect density of graphene through time-controlled H{sub 2} plasma treatment. By increasing the treatment time of H{sub 2} plasma from 30 s to 5 min, both the interface surface dipole and the electron transporting barrier at F{sub 16}CuPc/graphene interface are significantly reduced from 0.86 to 0.56 eV and 0.71 to 0.29 eV, respectively. These results suggested that graphene's defect control is a simple approach for tuning electronic properties of organic/graphene interfaces.
Atomic structure of pyramidal defects in GaN:Mg: Influence of annealing
Energy Technology Data Exchange (ETDEWEB)
Liliental-Weber, Z.; Tomaszewicz, T.; Zakharov, D.; O' Keefe, M. [Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720 (United States); Hautakangas, S.; Saarinen, K. [Materials Science and Engineering, University of California, Berkeley, Berkeley, CA 94720 (United States); Freitas, J.A.; Henry, R.L. [ESTD-Electronic Materials Branch, Naval Research Laboratory, Washington, D.C. 20375 (United States)
2006-05-15
The atomic structure of the characteristic defects (Mg-rich hexagonal pyramids) in p-doped bulk and MOCVD GaN:Mg thin films grown with Ga polarity was determined at atomic resolution by direct reconstruction of the scattered electron wave in a transmission electron microscope. Small cavities were present inside the defects, confirmed also with positron annihilation. The inside walls of the cavities were covered by GaN of reverse polarity compared to the matrix. Annealing of the MOCVD layers lead to slight increase of the defect size and an increase of the room temperature photoluminescence intensity. Positron annihilation confirms presence of vacancy clusters of different sizes triggered by the Mg doping in as-grown samples and decrease of their concentration upon annealing at 900 and 1000 C. (copyright 2006 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)
Defects in ZnO, CdTe, and Si: Optical, structural, and electrical characterization
Deicher, M; Kronenberg, J; Johnston, K; Roder, J; Byrne, D J
Electronic and optical properties of semiconductors are extremely sensitive to defects and impurities that have localized electronic states with energy levels in the band gap of the semiconductor. Spectroscopic techniques like photo-luminescence (PL), deep level transient spectroscopy (DLTS), or Hall effect that are able to detect and characterize band gap states do not reveal direct information about their microscopic origin. To overcome this chemical "blindness" radioactive isotopes are used as a tracer. Moreover, the recoil energies involved in ${\\beta}$- and ${\\gamma}$-decays can be used to create intrinsic, isolated point defects (interstitials, vacancies) in a controlled way. A microscopic insight into the structure and the thermodynamic properties of complexes formed by interacting defects can be gained by detecting the hyperfine interaction between the nuclear moments of radioactive dopants and the electromagnetic fields present at the site of the radioactive nucleus. These techniques will be used to...
Comprehensive Study of Solar Cell Structure Defects by Means of Noise and Light Emission Analysis
Directory of Open Access Journals (Sweden)
Robert Macku
2012-01-01
Full Text Available This paper discusses the issue of silicon solar cells localized defects from metrological and physical points of view. Structure imperfections represent the real problem because of solar cells long-term degradation and conversion efficiency decreasing. To this aim we pay our attention to research relating to the defect light emission and correlation with rectangular microplasma fluctuation. A sensitive CCD camera has been used for mapping of surface photon emission. The operation point of the samples has been set to reverse bias mode, and different electric field intensity was applied. We managed to get interesting information using a combination of optical investigation and electrical noise measurement in time and spectral domain. It will be revealed that a direct correlation between noise and photon emission exists and the results related to several defect spots are presented in detail in this paper.
Modulation of the photonic band structure topology of a honeycomb lattice in an atomic vapor
Energy Technology Data Exchange (ETDEWEB)
Zhang, Yiqi, E-mail: zhangyiqi@mail.xjtu.edu.cn [Key Laboratory for Physical Electronics and Devices of the Ministry of Education & Shaanxi Key Lab of Information Photonic Technique, Xi’an Jiaotong University, Xi’an 710049 (China); Liu, Xing [Key Laboratory for Physical Electronics and Devices of the Ministry of Education & Shaanxi Key Lab of Information Photonic Technique, Xi’an Jiaotong University, Xi’an 710049 (China); Belić, Milivoj R., E-mail: milivoj.belic@qatar.tamu.edu [Science Program, Texas A& M University at Qatar, P.O. Box 23874 Doha (Qatar); Wu, Zhenkun [Key Laboratory for Physical Electronics and Devices of the Ministry of Education & Shaanxi Key Lab of Information Photonic Technique, Xi’an Jiaotong University, Xi’an 710049 (China); Zhang, Yanpeng, E-mail: ypzhang@mail.xjtu.edu.cn [Key Laboratory for Physical Electronics and Devices of the Ministry of Education & Shaanxi Key Lab of Information Photonic Technique, Xi’an Jiaotong University, Xi’an 710049 (China)
2015-12-15
In an atomic vapor, a honeycomb lattice can be constructed by utilizing the three-beam interference method. In the method, the interference of the three beams splits the dressed energy level periodically, forming a periodic refractive index modulation with the honeycomb profile. The energy band topology of the honeycomb lattice can be modulated by frequency detunings, thereby affecting the appearance (and disappearance) of Dirac points and cones in the momentum space. This effect can be usefully exploited for the generation and manipulation of topological insulators.
Energy Technology Data Exchange (ETDEWEB)
Pineda-Hernandez, G. [Facultad de Ingenieria Quimica, Benemerita Universidad Autonoma de Puebla, C.P. 72570 Puebla, Pue. (Mexico); Escobedo-Morales, A., E-mail: alejandroescobedo@hotmail.com [Facultad de Ingenieria Quimica, Benemerita Universidad Autonoma de Puebla, C.P. 72570 Puebla, Pue. (Mexico); Pal, U. [Instituto de Fisica, Benemerita Universidad Autonoma de Puebla, Apdo. Postal J-48, C.P. 72570 Puebla, Pue. (Mexico); Chigo-Anota, E. [Facultad de Ingenieria Quimica, Benemerita Universidad Autonoma de Puebla, C.P. 72570 Puebla, Pue. (Mexico)
2012-08-15
In the present article, the effect of gallium doping on the morphology, structural, and vibrational properties of hydrothermally grown ZnO nanostructures has been studied. It has been observed that incorporated gallium plays an important role on the growth kinetics and hence on the morphology evolution of the ZnO crystals. Ga doping in high concentration results in the contraction of ZnO unit cell, mainly along c-axis. Although Ga has high solubility in ZnO, heavy doping promotes the segregation of Ga atoms as a secondary phase. Incorporated Ga atoms strongly affect the vibrational characteristics of ZnO lattice and induce anomalous Raman modes. Possible mechanisms of morphology evolution and origin of anomalous Raman modes in Ga doped ZnO nanostructures are discussed. -- Highlights: Black-Right-Pointing-Pointer Ga doped ZnO nanostructures were successfully grown by hydrothermal chemical route. Black-Right-Pointing-Pointer Ga doping has strong effect on the resulting morphology of ZnO nanostructures. Black-Right-Pointing-Pointer Anomalous vibrational modes in wurtzite ZnO lattice are induced by Ga doping. Black-Right-Pointing-Pointer Incorporated Ga atoms accommodate at preferential lattice sites.
Transmission electron microscopy of defects and internal fields in GaN structures
Energy Technology Data Exchange (ETDEWEB)
Mokhtari, H
2001-07-01
The main aim of this study was to understand the microstructure of GaN and InGaN/GaN and to examine electric fields around the defects, and across the quantum wells by electron holography. For this reason different types of GaN and InGaN/GaN samples have been prepared and studied. Conventional transmission electron microscopy has been used for structural study of two MBE grown GaN/GaAs samples, grown at room temperature and at 340 deg C. The structure of the samples were found to be hexagonal polycrystalline in an amorphous GaN matrix, and textured hexagonal polycrystalline material respectively. The experimental results indicate that the higher growth temperature results in a more crystalline material with a higher density of bigger grain sizes. Different types of undoped and Si doped GaN/Sapphire samples were studied, with respect to the defect structure in GaN films. GaN was found to be a highly defective material with a dislocation density of 10{sup 9}/cm{sup 2}. The majority of the dislocations are edge dislocations. It has been found that nanopipes are open core screw dislocations, and the population and size of the nanopipes is proportional to the Si doping concentration. Dislocation structures were found to depend on the Si doping level in the material, with higher Si doping giving a lower density of dislocations with a more random distribution. In addition some EELS, EDX and HRTEM have been performed on the nanopipes and dislocations in order to investigate Si segregation in the defects. In MBE grown GaN/In{sub 0.1}Ga{sub 0.9}N/GaN SQWs and MQWs, V shaped defects were found to be present in the InGaN regions, which locally reduced the width of the InGaN layers. (author)
Transmission electron microscopy of defects and internal fields in GaN structures
International Nuclear Information System (INIS)
Mokhtari, H.
2001-07-01
The main aim of this study was to understand the microstructure of GaN and InGaN/GaN and to examine electric fields around the defects, and across the quantum wells by electron holography. For this reason different types of GaN and InGaN/GaN samples have been prepared and studied. Conventional transmission electron microscopy has been used for structural study of two MBE grown GaN/GaAs samples, grown at room temperature and at 340 deg C. The structure of the samples were found to be hexagonal polycrystalline in an amorphous GaN matrix, and textured hexagonal polycrystalline material respectively. The experimental results indicate that the higher growth temperature results in a more crystalline material with a higher density of bigger grain sizes. Different types of undoped and Si doped GaN/Sapphire samples were studied, with respect to the defect structure in GaN films. GaN was found to be a highly defective material with a dislocation density of 10 9 /cm 2 . The majority of the dislocations are edge dislocations. It has been found that nanopipes are open core screw dislocations, and the population and size of the nanopipes is proportional to the Si doping concentration. Dislocation structures were found to depend on the Si doping level in the material, with higher Si doping giving a lower density of dislocations with a more random distribution. In addition some EELS, EDX and HRTEM have been performed on the nanopipes and dislocations in order to investigate Si segregation in the defects. In MBE grown GaN/In 0.1 Ga 0.9 N/GaN SQWs and MQWs, V shaped defects were found to be present in the InGaN regions, which locally reduced the width of the InGaN layers. (author)
Montalto, L.; Natali, P. P.; Daví, F.; Mengucci., P.; Paone, N.; Rinaldi, D.
2017-12-01
Among scintillators, the PWO is one of the most widely used, for instance in CMS calorimeter at CERN and PANDA project. Crystallographic structure and chemical composition as well as residual stress condition, are indicators of homogeneity and good quality of the crystal. In this paper, structural characterization of a defective PbWO4 (PWO) crystal has been performed by X-ray Diffraction (XRD), Energy Dispersive Spectroscopy (EDS) and Photoelasticity in the unusual (a, c) crystallographic plane. XRD and EDS analysis have been used to investigate crystallographic orientation and chemical composition, while stress distribution, which indicates macroscopic inhomogeneities and defects, has been obtained by photoelastic approaches, in Conoscopic and Sphenoscopic configuration. Since the sample is cut along the (a, c) crystallographic plane, a new method is proposed for the interpretation of the fringe pattern. The structural analysis has detected odds from the nominal lattice dimension, which can be attributed to the strong presence of Pb and W. A strong inhomogeneity over the crystal sample has been revealed by the photoelastic inspection. The results give reliability to the proposed procedure which is exploitable in crystals with other structures.
Directory of Open Access Journals (Sweden)
M. AKBARI
2013-12-01
Full Text Available Energy group structure has a significant effect on the results of multigroup transport calculations. It is known that UO2–PUO2 (MOX is a recently developed fuel which consumes recycled plutonium. For such fuel which contains various resonant nuclides, the selection of energy group structure is more crucial comparing to the UO2 fuels. In this paper, in order to improve the accuracy of the integral results in MOX thermal lattices calculated by WIMSD-5B code, a swarm intelligence method is employed to optimize the energy group structure of WIMS library. In this process, the NJOY code system is used to generate the 69 group cross sections of WIMS code for the specified energy structure. In addition, the multiplication factor and spectral indices are compared against the results of continuous energy MCNP-4C code for evaluating the energy group structure. Calculations performed in four different types of H2O moderated UO2–PuO2 (MOX lattices show that the optimized energy structure obtains more accurate results in comparison with the WIMS original structure.
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.)
Atomic and electronic structures of lattice mismatched Cu{sub 2}O/TiO{sub 2} interfaces
Energy Technology Data Exchange (ETDEWEB)
Wang, Shuzhi [Materials Sciences Division, Lawrence Berkeley National Laboratory, One Cyclotron Road, Mail Stop 66, Berkeley, California 94720 (United States); Kavaipatti, Balasubramaniam; Ramesh, Ramamoorthy [Department of Materials Science and Engineering, University of California at Berkeley, Berkeley, California 94720 (United States); Kim, Sung-Joo; Pan, Xiaoqing [Department of Materials Science and Engineering, University of Michigan, Ann Arbor, Michigan 48109 (United States); Ager, Joel W.; Wang, Lin-Wang, E-mail: lwwang@lbl.gov [Materials Sciences Division, Lawrence Berkeley National Laboratory, One Cyclotron Road, Mail Stop 66, Berkeley, California 94720 (United States); Joint Center of Artificial Photosynthesis, Berkeley, California 94720 (United States)
2014-05-26
Heterojunction interfaces between metal oxides are often highly lattice mismatched. The atomic and electronic structures of such interfaces, however, are not well understood. We have synthesized Cu{sub 2}O/TiO{sub 2} heterojunction thin films with 13% lattice mismatch and studied the interface via experimental methods and large-scale density function theory calculations of supercells containing ∼1300 atoms. We find that an interface of epitaxial quality is formed via a coincidence site lattice of 8 Cu{sub 2}O unit cells matching 9 TiO{sub 2} unit cells. Calculations reveal the existence of a dislocation core of the O sublattices at the interface and a random arrangement of one layer of interfacial Cu atoms. The interfacial electronic structure is found to be mostly determined by the interfacial Cu distribution, rather than by the O dislocation core. The conduction band minimum and valence band maximum states are spatially separated, and there is no strongly localized state near the core.
International Nuclear Information System (INIS)
Piil, Rune; Moelmer, Klaus
2007-01-01
By adjusting the tunneling couplings over longer than nearest-neighbor distances, it is possible in discrete lattice models to reproduce the properties of the lowest energy band of a real, continuous periodic potential. We propose to include such terms in problems with interacting particles, and we show that they have significant consequences for scattering and bound states of atom pairs in periodic potentials
Slezak, H
1975-12-04
The clinical examination of the vitreous in the extreme fundus periphery is difficult; therefore only very little was known up to now about the relations of the posterior limiting membrane of the vitreous and the preretinal tract to retinal lattice degenerations arranged parallel to the ora serrata in several rows. There will be reports of new findings gained by depression biomicroscopy.
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
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.
Galashev, A. E.; Ivanichkina, K. A.; Vorob'ev, A. S.; Rakhmanova, O. R.
2017-06-01
The structure and stability of a two-layer defective silicene on Ag(001) and Ag(111) substrates have been investigated using the molecular dynamics method. The transformation of the radial distribution function of silicene due to the formation of monovacancies, divacancies, trivacancies, and hexavacancies is reduced primarily to a decrease in the intensity of the peaks and the disappearance of the "shoulder" in the second peak. With the passage of time, multivacancies can undergo coalescence with each other and the fragmentation into smaller vacancies, as well as form vacancy clusters. According to the geometric criterion, the Ag(001) substrate provides a higher stability of a perfect two-layer silicene. It has been found, however, that the defective silicene on this substrate has a lower energy only when it contains monovacancies and divacancies. A change in the size of defects leads to a change in the energy priority when choosing between the Ag(001) and Ag(111) substrates. The motion of a lithium ion inside an extended channel between two silicene sheets results in a further disordering of the defective structure of the silicene, during which the strongest stresses in the silicene are generated by forces directed perpendicular to the external electric field. These forces dominate in the silicene channel, the wall of which is supported by the Ag(001) or Ag(111) substrate.
Energy Technology Data Exchange (ETDEWEB)
Lambert, M
1958-06-19
A study was made of the behavior of atomic defects, vacancies and interstitials, generated from the Li{sup 6}(n,{alpha})H{sup 3} reaction in Lip crystals. Defects appear as cavities and platelets around ten angstrom in size and increase both with neutron dose and annealing temperature. For longer irradiations, metallic lithium precipitates out, in epitaxy with LiF lattice, and later, lithium salts appear due to the penetration of atmospheric gases through the cracks present in the damaged crystal. Various x-ray experiments followed the formation and evolution of these imperfections when their atomic concentration reached 10{sup -4}. (author)
Stringy models of modified gravity: space-time defects and structure formation
International Nuclear Information System (INIS)
Mavromatos, Nick E.; Sakellariadou, Mairi; Yusaf, Muhammad Furqaan
2013-01-01
Starting from microscopic models of space-time foam, based on brane universes propagating in bulk space-times populated by D0-brane defects (''D-particles''), we arrive at effective actions used by a low-energy observer on the brane world to describe his/her observations of the Universe. These actions include, apart from the metric tensor field, also scalar (dilaton) and vector fields, the latter describing the interactions of low-energy matter on the brane world with the recoiling point-like space-time defect (D-particle). The vector field is proportional to the recoil velocity of the D-particle and as such it satisfies a certain constraint. The vector breaks locally Lorentz invariance, which however is assumed to be conserved on average in a space-time foam situation, involving the interaction of matter with populations of D-particle defects. In this paper we clarify the role of fluctuations of the vector field on structure formation and galactic growth. In particular we demonstrate that, already at the end of the radiation era, the (constrained) vector field associated with the recoil of the defects provides the seeds for a growing mode in the evolution of the Universe. Such a growing mode survives during the matter dominated era, provided the variance of the D-particle recoil velocities on the brane is larger than a critical value. We note that in this model, as a result of specific properties of D-brane dynamics in the bulk, there is no issue of overclosing the brane Universe for large defect densities. Thus, in these models, the presence of defects may be associated with large-structure formation. Although our string inspired models do have (conventional, from a particle physics point of view) dark matter components, nevertheless it is interesting that the role of ''extra'' dark matter is also provided by the population of massive defects. This is consistent with the weakly interacting character of the D-particle defects, which predominantly interact only
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.
Localization of Stable and Chaotic Nonpropagating Structures in Nonlinear Mesoscopic Lattices.
Greenfield, Alan Barry
Recent developments in the study of non-linear localized states, especially non-propagating ones, are outlined. Theoretical models of linear and nonlinear states in a lattice of coupled pendulums and related systems are reviewed. Particular attention is paid to those states which can be described by the Nonlinear Schrodinger equation as well as states where two modes can coexist and states exhibiting chaos. Measurement of localized stable and chaotic states in a 35 site physical pendulum lattice is reported. Various measurement techniques that were used are explained. States that were measured include the tanh profile or kink soliton, and the corresponding uniform state in the wavelength 2 mode, a similar soliton and uniform state in the wavelength 4 mode, a domain wall between the wavelength 2 and 4 modes and a domain wall between a chaotic state and the wavelength 2 mode. Amplitude profiles were measured for the stable kink and domain wall states and smooth curves were obtained by dividing the kink states by the corresponding uniform states. Return maps were measured for two sites in the chaotic domain wall. Simulation of a chaotic domain wall in a 50 site numerical lattice is reported. This system has the advantage that its parameters can be modified much more easily than those of the physical lattice. An attempt is made at quantifying the level of chaos as a function of lattice site with fractal dimension calculations on return maps embedded in a three dimensional space. The drive plane of the chaotic domain wall is mapped out in the drive amplitude - drive frequency plane. Transitions to various stable and quasiperiodic domain walls are noted.
National Research Council Canada - National Science Library
Ko, Ray T; Steffes, Gary J
2007-01-01
Defect detection within thick multilayer structures containing steel fasteners is a challenging task in eddy current testing due to the magnetic permeability of the fasteners and overall thickness of the structure...
Jakes, Peter; Kungl, Hans; Schierholz, Roland; Eichel, Rüdiger-A
2014-09-01
The defect structure for copper-doped sodium potassium niobate (KNN) ferroelectrics has been analyzed with respect to its defect structure. In particular, the interplay between the mutually compensating dimeric (Cu(Nb)'''-V(O)··) and trimeric (V(O)··-Cu(Nb)'''-V(O)··)· defect complexes with 180° and non-180° domain walls has been analyzed and compared to the effects from (Cu'' - V(O)··)(x)× dipoles in CuO-doped lead zirconate titanate (PZT). Attempts are made to relate the rearrangement of defect complexes to macroscopic electromechanical properties.
Non-probabilistic defect assessment for structures with cracks based on interval model
International Nuclear Information System (INIS)
Dai, Qiao; Zhou, Changyu; Peng, Jian; Chen, Xiangwei; He, Xiaohua
2013-01-01
Highlights: • Non-probabilistic approach is introduced to defect assessment. • Definition and establishment of IFAC are put forward. • Determination of assessment rectangle is proposed. • Solution of non-probabilistic reliability index is presented. -- Abstract: Traditional defect assessment methods conservatively treat uncertainty of parameters as safety factors, while the probabilistic method is based on the clear understanding of detailed statistical information of parameters. In this paper, the non-probabilistic approach is introduced to the failure assessment diagram (FAD) to propose a non-probabilistic defect assessment method for structures with cracks. This novel defect assessment method contains three critical processes: establishment of the interval failure assessment curve (IFAC), determination of the assessment rectangle, and solution of the non-probabilistic reliability degree. Based on the interval theory, uncertain parameters such as crack sizes, material properties and loads are considered as interval variables. As a result, the failure assessment curve (FAC) will vary in a certain range, which is defined as IFAC. And the assessment point will vary within a rectangle zone which is defined as an assessment rectangle. Based on the interval model, the establishment of IFAC and the determination of the assessment rectangle are presented. Then according to the interval possibility degree method, the non-probabilistic reliability degree of IFAC can be determined. Meanwhile, in order to clearly introduce the non-probabilistic defect assessment method, a numerical example for the assessment of a pipe with crack is given. In addition, the assessment result of the proposed method is compared with that of the traditional probabilistic method, which confirms that this non-probabilistic defect assessment can reasonably resolve the practical problem with interval variables
Non-probabilistic defect assessment for structures with cracks based on interval model
Energy Technology Data Exchange (ETDEWEB)
Dai, Qiao; Zhou, Changyu, E-mail: changyu_zhou@163.com; Peng, Jian; Chen, Xiangwei; He, Xiaohua
2013-09-15
Highlights: • Non-probabilistic approach is introduced to defect assessment. • Definition and establishment of IFAC are put forward. • Determination of assessment rectangle is proposed. • Solution of non-probabilistic reliability index is presented. -- Abstract: Traditional defect assessment methods conservatively treat uncertainty of parameters as safety factors, while the probabilistic method is based on the clear understanding of detailed statistical information of parameters. In this paper, the non-probabilistic approach is introduced to the failure assessment diagram (FAD) to propose a non-probabilistic defect assessment method for structures with cracks. This novel defect assessment method contains three critical processes: establishment of the interval failure assessment curve (IFAC), determination of the assessment rectangle, and solution of the non-probabilistic reliability degree. Based on the interval theory, uncertain parameters such as crack sizes, material properties and loads are considered as interval variables. As a result, the failure assessment curve (FAC) will vary in a certain range, which is defined as IFAC. And the assessment point will vary within a rectangle zone which is defined as an assessment rectangle. Based on the interval model, the establishment of IFAC and the determination of the assessment rectangle are presented. Then according to the interval possibility degree method, the non-probabilistic reliability degree of IFAC can be determined. Meanwhile, in order to clearly introduce the non-probabilistic defect assessment method, a numerical example for the assessment of a pipe with crack is given. In addition, the assessment result of the proposed method is compared with that of the traditional probabilistic method, which confirms that this non-probabilistic defect assessment can reasonably resolve the practical problem with interval variables.
Structure and defect studies of In2O3:Zn,Zr for higher stability TCO
Herwadkar, Aditi; Kim, Kwiseon
2010-03-01
The defects structures among the transparent conducting oxides (TCO) plays a major role in determining stability of the oxide over a temperature range and in tuning electrical and optical properties for the different TCO applications In2O3 crystallizes in the cubic bixbyite structure. The structure can be derived from the related fluorite structure by removing one fourth of the anions and allowing for small shifts of the ionic positions. In2O3 has two non-equivalent six-fold coordinated cation sites. For one of the sites, the cation is bounded by two structural vacancy along the body diagonal and for the other non-equivalent site the vacancies lie along the face diagonal. These vacancies are actually empty oxygen vacancy positions. Indium is in +3 charge state. ZnO on the other hand crystallizes to form wurtzite structure with four-fold coordination for Zn and is in +2 charge state where as the crystal structure of ZrO is rulite with Zr in +4 charge state and is four fold coordinated. Co-doping of Zn and Zr with each substituting the In atom satisfies the octet rule and is lower in energy then the individual substitutions with overall neutrality. The formation enthalpy as a function of pair (Zn, Zr) shows a minimum at experimental composition of In2(Zn,Zr)3O24. We in this work present the electronic structure optimization and study the defect states in this material.
Directory of Open Access Journals (Sweden)
Patrick Terriault
2017-01-01
Full Text Available Emergent additive manufacturing processes allow the use of metallic porous structures in various industrial applications. Because these structures comprise a large number of ordered unit cells, their design using conventional modeling approaches, such as finite elements, becomes a real challenge. A homogenization technique, in which the lattice structure is simulated as a fully dense volume having equivalent material properties, can then be employed. To determine these equivalent material properties, numerical simulations can be performed on a single unit cell of the lattice structure. However, a critical aspect to consider is the boundary conditions applied to the external faces of the unit cell. In the literature, different types of boundary conditions are used, but a comparative study is definitely lacking. In this publication, a diamond-type unit cell is studied in compression by applying different boundary conditions. If the porous structure’s boundaries are free to deform, then the periodic boundary condition is found to be the most representative, but constraint equations must be introduced in the model. If, instead, the porous structure is inserted in a rigid enclosure, it is then better to use frictionless boundary conditions. These preliminary results remain to be validated for other types of unit cells loaded beyond the yield limit of the material.
DEFF Research Database (Denmark)
Cimoli, Bruno; Johansen, Tom Keinicke; Olmos, Juan Jose Vegas
2018-01-01
We report a high performance linear phase low pass filter (LPF) designed for partial response (PR) modulations. For the implementation, we adopted microstrip technology and a variant of the standard stepped‐impedance technique. Defected ground structures (DGS) are used for increasing the characte......We report a high performance linear phase low pass filter (LPF) designed for partial response (PR) modulations. For the implementation, we adopted microstrip technology and a variant of the standard stepped‐impedance technique. Defected ground structures (DGS) are used for increasing...... the characteristic impedance of transmission lines. Experimental results prove that the proposed filter can successfully modulate a non‐return‐to‐zero (NRZ) signal into a five levels PR one....
Jiang, Tao; Wang, Yanyan; Li, Yingsong
2017-07-01
In this paper, a triple stop-band filter with a ratioed periodical defected microstrip structure is proposed for wireless communication applications. The proposed ratioed periodical defected microstrip structures are spiral slots, which are embedded into a 50 Ω microstrip line to obtain multiple stop-bands. The performance of the proposed triple stop-band filter is investigated numerically and experimentally. Moreover, the equivalent circuit model of the proposed filter is also established and discussed. The results are given to verify that the proposed triple stop-band filter has three stop bands at 3.3 GHz, 5.2 GHz, 6.8 GHz to reject the unwanted signals, which is promising for integrating into UWB communication systems to efficiently prevent the potential interferences from unexpected narrowband signals such as WiMAX, WLAN and RFID communication systems.
Jung, Jae Hoon; Park, Ji-Hye; Yoo, Chungkwon; Kim, Yong Yeon
2018-03-01
The purpose of this article is to compare the locations of localized retinal nerve fiber layer (RNFL) defects in red-free fundus photographs and optical coherence tomography (OCT) en face images. We performed a retrospective, comparative study on 46 eyes from 46 glaucoma patients with localized RNFL defects observed in red-free fundus photographs. En face structural images were obtained in the superficial and whole retinal layers using OCT and were overlaid on the corresponding red-free fundus photographs. The proximal/distal angular locations and angular width of each RNFL defect in red-free photos (red-free defects) and in en face structural images (en face defects) were compared. In the superficial retinal layer, there were no significant differences between red-free and en face defects on the proximal/distal angular location and angular width. In the whole retinal layer, the degree of the distal angular location of the en face defects was significantly larger than that of the red-free defects (71.85±18.26 vs. 70.87±17.90 degrees, P=0.003). The correlations of clinical variables with the differences in angular parameters between red-free and en face defects were not significant in the superficial retinal layer. The average RNFL thickness was negatively correlated with the difference in the distal angular location in the whole retinal layer (Pearson correlation coefficient=-0.401, P=0.006). Localized RNFL defects detected in OCT en face structural images of the superficial retinal layer showed high topographic correlation with defects detected in red-free photographs. OCT en face structural images in the superficial layer may be an alternative to red-free fundus photography for the identification of localized RNFL defects in glaucomatous eyes.
2013-01-01
Original Articles Guided Bone Regeneration in Long-Bone Defects with a Structural Hydroxyapatite Graft and Collagen Membrane Teja Guda, PhD,1,2 John...Joint Surg Br 90-B, 1617, 2008. 6. Carlo Reis, E.C., Borges AaPB, Araujo, M.V.F., Mendes, V.C., Guan, L., and Davies, J.E. Periodontal regeneration...Regeneration of periodontal tissues: combinations of barrier membranes and grafting materials–biological foundation and preclinical evi- dence: a
Conference Analysis Report of Assessments on Defect and Damage for a High Temperature Structure
International Nuclear Information System (INIS)
Lee, Hyeong Yeon
2008-11-01
This report presents the analysis on the state-of-the-art research trends on creep-fatigue damage, defect assessment of high temperature structure, development of heat resistant materials and their behavior at high temperature based on the papers presented in the two international conferences of ASME PVP 2008 which was held in Chicago in July 2008 and CF-5(5th International Conference on Creep, Fatigue and Creep-Fatigue) which was held in Kalpakkam, India in September 2008
Conference Analysis Report of Assessments on Defect and Damage for a High Temperature Structure
Energy Technology Data Exchange (ETDEWEB)
Lee, Hyeong Yeon
2008-11-15
This report presents the analysis on the state-of-the-art research trends on creep-fatigue damage, defect assessment of high temperature structure, development of heat resistant materials and their behavior at high temperature based on the papers presented in the two international conferences of ASME PVP 2008 which was held in Chicago in July 2008 and CF-5(5th International Conference on Creep, Fatigue and Creep-Fatigue) which was held in Kalpakkam, India in September 2008.
Energy Technology Data Exchange (ETDEWEB)
Jonkman, Jason [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Damiani, Rick R [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Struve, Achim [University of Applied Sciences Flensburg; Faber, Torsten [University of Applied Sciences Flensburg; Ummenhofer, Thomas [Karlsruhe Institute of Technology
2017-11-07
The call for more cost-effective and environmentally friendly tower concepts is motivated by tower costs [1] and tower CO2-emission contributions [2], which are high relative to the whole wind turbine system. The proposed rotatable tower concept with yaw bearing at the bottom instead of the top of the tower will provide beneficial economic and environmental impacts to the turbine system. This wind alignment capability indicates a load-direction-derived tower design. By combining this approach with a lattice concept, large material and cost savings for the tower can be achieved. This paper presents a way to analyze and verify the proposed design through aero-servo-elastic simulations, which make future certifications of rotatable tower concepts viable. For this reason, the state-of-the-art, open-source lattice-tower finite-element-method (FEM) module SubDyn [10], developed by the National Renewable Energy Laboratory, has been modified to account for arbitrary member cross-sections. Required changes in the beam element stiffness and mass matrix formulation took place according to an energy method [13]. All validated adaptions will be usable within the aero-servo-elastic simulation framework FAST and are also beneficial for other nonrotatable lattice structures.
Structural Defects in Donor-Acceptor Blends: Influence on the Performance of Organic Solar Cells
Sergeeva, Natalia; Ullbrich, Sascha; Hofacker, Andreas; Koerner, Christian; Leo, Karl
2018-02-01
Defects play an important role in the performance of organic solar cells. The investigation of trap states and their origin can provide ways to further improve their performance. Here, we investigate defects in a system composed of the small-molecule oligothiophene derivative DCV5T-Me blended with C60 , which shows power conversion efficiencies above 8% when used in a solar cell. From a reconstruction of the density of trap states by impedance spectroscopy, we obtain a Gaussian distribution of trap states with Et=470 meV below the electron transport level, Nt=8 ×1014 cm-3 , and σt=41 meV . From Voc vs illumination intensity and open-circuit corrected charge carrier extraction measurements, we find that these defects lead to trap-assisted recombination. Moreover, drift-diffusion simulations show that the trap states decrease the fill factor by 10%. By conducting degradation measurements and varying the blend ratio, we find that the observed trap states are structural defects in the C60 phase due to the distortion of the natural morphology induced by the mixing.
Phase structure of the O(n) model on a random lattice for n > 2
DEFF Research Database (Denmark)
Durhuus, B.; Kristjansen, C.
1997-01-01
We show that coarse graining arguments invented for the analysis of multi-spin systems on a randomly triangulated surface apply also to the O(n) model on a random lattice. These arguments imply that if the model has a critical point with diverging string susceptibility, then either γ = +1....../2 or there exists a dual critical point with negative string susceptibility exponent, γ̃, related to γ by γ = γ̃/γ̃-1. Exploiting the exact solution of the O(n) model on a random lattice we show that both situations are realized for n > 2 and that the possible dual pairs of string susceptibility exponents are given...... by (γ̃, γ) = (-1/m, 1/m+1), m = 2, 3, . . . We also show that at the critical points with positive string susceptibility exponent the average number of loops on the surface diverges while the average length of a single loop stays finite....
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.)
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.)
International Nuclear Information System (INIS)
Wiktor, Julia
2015-01-01
During in-pile irradiation the fission of actinide nuclei causes the creation of large amounts of defects, which affect the physical and chemical properties of materials inside the reactor, in particular the fuel and structural materials. Positron annihilation spectroscopy (PAS) can be used to characterize irradiation induced defects, empty or containing fission products. This non-destructive experimental technique involves detecting the radiation generated during electron-positron annihilation in a sample and deducing the properties of the material studied. As positrons get trapped in open volume defects in solids, by measuring their lifetime and momentum distributions of the annihilation radiation, one can obtain information on the open and the chemical environments of the defects. In this work electronic structure calculations of positron annihilation characteristics were performed using two-component density functional theory (TCDFT). To calculate the momentum distributions of the annihilation radiation, we implemented the necessary methods in the open-source ABINIT program. The theoretical results have been used to contribute to the identification of the vacancy defects in two nuclear ceramics, silicon carbide (SiC) and uranium dioxide (UO 2 ). (author) [fr
Acousto-defect interaction in irradiated and non-irradiated silicon n+-p structures
Olikh, O. Ya.; Gorb, A. M.; Chupryna, R. G.; Pristay-Fenenkov, O. V.
2018-04-01
The influence of ultrasound on current-voltage characteristics of non-irradiated silicon n+-p structures as well as silicon structures exposed to reactor neutrons or 60Co gamma radiation has been investigated experimentally. It has been found that the ultrasound loading of the n+-p structure leads to the reversible change of shunt resistance, carrier lifetime, and ideality factor. Specifically, considerable acoustically induced alteration of the ideality factor and the space charge region lifetime was observed in the irradiated samples. The experimental results were described by using the models of coupled defect level recombination, Shockley-Read-Hall recombination, and dislocation-induced impedance. The experimentally observed phenomena are associated with the increase in the distance between coupled defects as well as the extension of the carrier capture coefficient of complex point defects and dislocations. It has been shown that divacancies and vacancy-interstitial oxygen pairs are effectively modified by ultrasound in contrast to interstitial carbon-interstitial oxygen complexes.
A Design of a Terahertz Microstrip Bandstop Filter with Defected Ground Structure
Directory of Open Access Journals (Sweden)
Arjun Kumar
2013-01-01
Full Text Available A planar microstrip terahertz (THz bandstop filter has been proposed with defected ground structure with high insertion loss (S21 in a stopband of −25.8 dB at 1.436 THz. The parameters of the circuit model have been extracted from the EM simulation results. A dielectric substrate of Benzocyclobutene (BCB is used to realize a compact bandstop filter using modified hexagonal dumbbell-shape defected ground structure (DB-DGS. In this paper, a defected ground structure topology is used in a λ/4, 50 Ω microstrip line at THz frequency range for compactness. No article has been reported on the microstrip line at terahertz frequency regime using DGS topology. The proposed filter can be used for sensing and detection in biomedical instruments in DNA testing. All the simulations/cosimulations are carried out using a full-wave EM simulator CST V.9 Microwave Studio, HFSS V.10, and Agilent Design Suite (ADS.
Energy Technology Data Exchange (ETDEWEB)
Erhart, P.
2006-07-01
The present dissertation deals with the modeling of zinc oxide on the atomic scale employing both quantum mechanical as well as atomistic methods. The first part describes quantum mechanical calculations based on density functional theory of intrinsic point defects in ZnO. To begin with, the geometric and electronic structure of vacancies and oxygen interstitials is explored. In equilibrium oxygen interstitials are found to adopt dumbbell and split interstitial configurations in positive and negative charge states, respectively. Semi-empirical self-interaction corrections allow to improve the agreement between the experimental and the calculated band structure significantly; errors due to the limited size of the supercells can be corrected by employing finite-size scaling. The effect of both band structure corrections and finite-size scaling on defect formation enthalpies and transition levels is explored. Finally, transition paths and barriers for the migration of zinc as well as oxygen vacancies and interstitials are determined. The results allow to interpret diffusion experiments and provide a consistent basis for developing models for device simulation. In the second part an interatomic potential for zinc oxide is derived. To this end, the Pontifix computer code is developed which allows to fit analytic bond-order potentials. The code is subsequently employed to obtain interatomic potentials for Zn-O, Zn-Zn, and O-O interactions. To demonstrate the applicability of the potentials, simulations on defect production by ion irradiation are carried out. (orig.)
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.)
Effect of pressure and doping on lattice structure of zinc oxide
Energy Technology Data Exchange (ETDEWEB)
Zolfaghari, Mahmoud, E-mail: mzolfaghari@phys.usb.ac.ir
2017-01-15
The semiconductor ZnO belongs to the IIb-VI binary compound. It has a high exciton binding energy of 60 meV. The bonding in these materials is covalent with some ionic character. Induced changes on the physical properties of Mn doped ZnO samples due to different dopant concentrations and pressure were evaluated. The results obtained showed higher solubility limit for Mn doped ZnO due to pressure. The trend of XRD results for higher Mn concentration (9 at%) as pressure increases, was towards doping improvement. The XRD, SEM and UV–vis study of the samples also revealed that there were variations in the lattice parameters, nanoparticle size and bandgap energy of the doped and pressurized doped samples. Further, the directions of variation of bandgap energy values and calculated particle size, as well as SEM values of the doped samples due to pressure variation were found to be the same i.e. all of them together either increase or decrease as pressure varies. However, these variations were found to be opposite to that of lattice constants (all a and most c values) variation for both Mn dopant concentrations (3 at% and 9 at%). These physical variations of unpressurized doped samples can be attributed to the change in the polar bonding of the elemental constitutions in the lattice. While for the pressurized doped samples, the variations attributed to repulsion of lone pairs as well as change in the electronegativity of the system.
International Nuclear Information System (INIS)
Kakinoki, J.
1974-01-01
Methods for obtaining the intensity of X-ray diffraction by one-dimensional by disordered lattices have been studied, and matrix method was developed. The method has been applied for structural analysis. Several problems concerning neutron diffraction were shown in the course of analysis. Large single crystals should be used for measurement. It is hard to grasp the local variation of structure. The technique of topography is still in development. Measurement of weak intensity diffraction is not sufficient. Technique of photography to observe overall feature is not good. General remarks concerning the one-dimensionally disordered lattices are as follows. A large number of parameters for analysis are not practical, and the disorder parameters are preferably two. In case of the disorder between two kinds of layers having same frequency and different structure, peak shift is not caused, and Laue term remains at the position. Reliability of the structural analysis of liquid and amorphous solid is discussed. The analysis is basically the analysis two atom molecule of same kind of atoms. The intensity of diffraction can be obtained from radial distribution function (RDF). Since practical observation is limited to a finite region, termination effect should be taken into consideration. Accuracy of analysis is not good in case of X-ray diffraction. The analysis by neutron diffraction is preferable. (Kato, T.)
Zou, You-Hao; Zhang, Jian-Bo; Xiong, Guang-Yi; Chen, Ying; Liu, Chuan; Liu, Yu-Bin; Ma, Jian-Ping
2017-10-01
The topological charge density and topological susceptibility are determined by a multi-probing approximation using overlap fermions in quenched SU(3) gauge theory. Then we investigate the topological structure of the quenched QCD vacuum, and compare it with results from the all-scale topological density. The results are consistent. Random permuted topological charge density is used to check whether these structures represent underlying ordered properties. The pseudoscalar glueball mass is extracted from the two-point correlation function of the topological charge density. We study 3 ensembles of different lattice spacing a with the same lattice volume 163×32. The results are compatible with the results of all-scale topological charge density, and the topological structures revealed by multi-probing are much closer to all-scale topological charge density than those from eigenmode expansion. Supported by National Natural Science Foundation of China (NSFC) (11335001, 11275169, 11075167), It is also supported in part by the DFG and the NSFC (11261130311) through funds provided to the Sino-German CRC 110 "Symmetries and the Emergence of Structure in QCD". This work was also funded in part by National Basic Research Program of China (973 Program) (2015CB856700)
Effect of vanadium doping on structural and magnetic properties of defective nano-nickel ferrite
Heiba, Zein K.; Mohamed, Mohamed Bakr; Wahba, Adel Maher; Almalowi, M. I.
2018-04-01
Nano-nickel ferrites defected by vanadium doping (NiV x Fe2-1.67 x O4, 0 ≤ x ≤ 0.25) were prepared using a simple sol gel method. Rietveld analysis revealed a nonmonotonic change in lattice parameter, oxygen parameter and magnetization upon doping with vanadium. Cation distributions suggested from either Rietveld analysis or from experimental magnetic moments were in a good agreement. For low doping values ( x = 0.05), vanadium was residing mainly in octahedral sites, while for samples with vanadium content ( x ≥ 0.1) a significant part of vanadium ions resided at tetrahedral sites; a result which has been confirmed by the analysis of Fourier-transform infrared (FTIR) spectrums obtained for the samples. The transmission electron microscope (TEM) image showed fine spherical particles with size of ˜ 11 nm. All samples showed a superparamagnetic nature with a nonmonotonic change of either magnetization ( M S) or coercivity (H C) with the content of nonmagnetic V5+. The cation occupancies indicated presence of an enormous number of vacancies through doping with high valence cation V5+, making present samples potential electrodes for Li- or Na-ion batteries.
International Nuclear Information System (INIS)
Shi, Lei
2016-01-01
Uranium dioxide (UO_2) is the most widely used nuclear fuel in existing nuclear reactors around the world. While in service for energy supply, UO_2 is submitted to the neutron flux and undergoes nuclear fission chain reactions, which create large number of fission products and point defects. The study of the behavior of the fission products and point defects is important to understand the fuel properties under irradiation. We conduct electronic structure calculations based on the density functional theory (DFT) to model this radiation damage at the atomic scale. The DFT+U method is used to describe the strong correlation of the 4f electrons of cerium and 5f electrons of uranium in the materials studied (UO_2, CeO_2 and (U, Ce)O_2). (U, Ce)O_2 is studied because it is considered as a low radioactive model material of mixed actinide oxides such as the MOX fuel (U, Pu)O_2 used in light water reactors and fast neutron reactors. Cerium dioxide (CeO_2) is studied to provide reference data of (U, Ce)O_2. We perform a DFT+U study of point defects and gaseous fission products (Xe and Kr) in CeO_2 and compare our results to the existing ones of UO_2. We study the bulk properties as well as the behavior of defects for (U, Ce)O_2, and compare our results to the ones of (U, Pu)O_2. Furthermore, for the study of defects in UO_2, methodological improvements are explored considering the spin-orbit coupling effect and the finite-size effect of the simulation supercell. (author) [fr
Identifying Structural Flow Defects in Disordered Solids Using Machine-Learning Methods
Cubuk, E. D.; Schoenholz, S. S.; Rieser, J. M.; Malone, B. D.; Rottler, J.; Durian, D. J.; Kaxiras, E.; Liu, A. J.
2015-03-01
We use machine-learning methods on local structure to identify flow defects—or particles susceptible to rearrangement—in jammed and glassy systems. We apply this method successfully to two very different systems: a two-dimensional experimental realization of a granular pillar under compression and a Lennard-Jones glass in both two and three dimensions above and below its glass transition temperature. We also identify characteristics of flow defects that differentiate them from the rest of the sample. Our results show it is possible to discern subtle structural features responsible for heterogeneous dynamics observed across a broad range of disordered materials.
Diffuse scattering and defect structure simulations a cook book using the program DISCUS
Neder, Reinhard B
2009-01-01
In recent years it has become apparent that knowing the average atomic structure of materials is insufficient to understand their properties. Diffuse scattering in addition to the Bragg scattering holds the key to learning about defects in materials, the topic of many recent books. What has been missing is a detailed step-by-step guide how to simulate disordered materials. The DISCUS cook book fills this need covering simple topics such as building a computer crystal to complextopic such as domain structures, stacking faults or using advanced refinement techniques to adjust parameters on a dis
International Nuclear Information System (INIS)
Yang, H.; Chi, Z. H.; Yao, L. D.; Zhang, W.; Li, F. Y.; Jin, C. Q.; Yu, R. C.
2006-01-01
The multiferroic material BiMnO 3 synthesized under high pressure has been systematically studied by transmission electron microscopy and electron energy-loss spectroscopy, and some important structural defects are revealed in this multiferroic material. The frequently observed defects are characterized to be Σ3(111) twin boundaries, Ruddlesden-Popper [Acta Crystallogr. 11, 54 (1958)] antiphase boundaries, and a p p superdislocations connected with a small segment of Ruddlesden-Popper defect. These defects are present initially in the as-synthesized sample. In addition, we find that ordered voids (oxygen vacancies) are easily introduced into the multiferroic BiMnO 3 by electron-beam irradiation
International Nuclear Information System (INIS)
Deus, P.; Schneider, H.A.; Voland, U.
1980-01-01
A general method of determination of the mean square amplitudes of lattice oscillations (MSA) for crystals with sphalerite structure is described and applied to InP. The linearity of suitable functions of the measured integral BRAGG intensities of sin 2 theta/lambda 2 is used for the verification of the parameters selected for the correction of extinction and DTS. In this way the accuracy of the results is increased. The MSAs of the InP-sublattices are evaluated. According to theoretical expectations the MSAs of the P-sublattice are larger because of the greater contributions of optical phonons. (author)
Energy Technology Data Exchange (ETDEWEB)
Zhang, Yanhui, E-mail: yanhui.z@hotmail.com [Karlsruhe Institute of Technology (KIT), Institute for Applied Materials-Applied Materials Physics (IAM-AWP), Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen (Germany); High-performance Ceramics Division, Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, 110016, Shenyang (China); Franke, Peter; Li, Dajian; Seifert, Hans Jürgen [Karlsruhe Institute of Technology (KIT), Institute for Applied Materials-Applied Materials Physics (IAM-AWP), Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen (Germany)
2016-12-01
Reliable lattice stability of cubic AlN with rock-salt structure (rs-AlN) is the prerequisite of accurate thermodynamic modeling of cubic (M, Al)N solid solutions (M = Ti, Zr, Cr etc.). In order to derive the Gibbs energy of metastable rs-AlN, and then its lattice stability, we did the pressure-temperature (P-T) assessment of AlN phases by equations-of-state modeling. Meanwhile, the molar volumes and the heat capacities of wurtzite and rock-salt AlN, as well as the wurtzite-to-rock-salt structural transition at high P&T were successfully incorporated in CALPHAD-type database by integrating thermodynamic data from experiments and ab-initio calculations. These results promise subsequent investigations on phase stabilities and transitions of solid solutions with AlN component and the development of novel multicomponent coatings. - Highlights: • Phase stability investigation for novel multi-component metastable coatings. • Structural transition at high temperature and high pressure. • Integrating thermodynamic data from ab-initio calculations and experiments. • Thermal expansion, isothermal compressibility and heat capacity of w-AlN and rs-AlN.
Defect structure, nonstoichiometry, and phase stability of Ca-doped YCrO3
International Nuclear Information System (INIS)
Carini, G.F. II; Anderson, H.U.; Nasrallah, M.M.; Sparlin, D.M.
1991-01-01
The dependence of the defect structure of Ca-doped YCrO 3 on oxygen activity and temperature was investigated by high temperature thermogravimetric measurements. Defect models developed from electrical conductivity data obtained in a previous study were used to interpret the thermogravimetric data. A correlation was found between the electrical conductivity and the thermogravimetric data which suggested that these data were concomitantly dependent on the acceptor dopant and oxygen vacancy dependence of the thermodynamic parameters. Kroeger-Vink type diagrams showing the regions of stability with respect to oxygen activity and temperature were constructed. The TGA data show that Ca-doped YCrO 3 is even more stable toward reduction than doped LaCrO 3
Directory of Open Access Journals (Sweden)
F. Panella
2018-05-01
Full Text Available This work presents the combination of Deep-Learning (DL and image processing to produce an automated cracks recognition and defect measurement tool for civil structures. The authors focus on tunnel civil structures and survey and have developed an end to end tool for asset management of underground structures. In order to maintain the serviceability of tunnels, regular inspection is needed to assess their structural status. The traditional method of carrying out the survey is the visual inspection: simple, but slow and relatively expensive and the quality of the output depends on the ability and experience of the engineer as well as on the total workload (stress and tiredness may influence the ability to observe and record information. As a result of these issues, in the last decade there is the desire to automate the monitoring using new methods of inspection. The present paper has the goal of combining DL with traditional image processing to create a tool able to detect, locate and measure the structural defect.
Phase structure, magnetic monopoles and vortices in the lattice Abelian Higgs model
International Nuclear Information System (INIS)
Ranft, J.; Kripfganz, J.; Ranft, G.
1982-04-01
We present Monte Carlo calculations of lattice Abelian Higgs models in 4 dimensions and with charges of the Higgs particles equal to q = 1, 2 and 6. The phase transitions are studied in the plane of the two coupling constants considering separately average plaquette and average link expectation values. The density of topological excitations is studied. In the confinement phase we find finite densities of magnetic monopole currents, electric currents and vortex currents. The magnetic monopole currents vanish exponentially in the Coulomb phase. The density of electric currents and vortex currents is finite in the Coulomb phase and vanishes exponentially in the Higgs phase. (author)
Finite-temperature phase structure of lattice QCD with Wilson quark action
International Nuclear Information System (INIS)
Aoki, S.; Ukawa, A.; Umemura, T.
1996-01-01
The long-standing issue of the nature of the critical line of lattice QCD with the Wilson quark action at finite temperatures, defined to be the line of vanishing pion screening mass, and its relation to the line of finite-temperature chiral transition is examined. Presented are both analytical and numerical evidence that the critical line forms a cusp at a finite gauge coupling, and that the line of chiral transition runs past the tip of the cusp without touching the critical line. Implications on the continuum limit and the flavor dependence of chiral transition are discussed. copyright 1996 The American Physical Society
Phase structure of 3DZ(N) lattice gauge theories at finite temperature
International Nuclear Information System (INIS)
Borisenko, O.; Chelnokov, V.; Cortese, G.; Gravina, M.; Papa, A.; Surzhikov, I.
2013-01-01
We perform a numerical study of the phase transitions in three-dimensional Z(N) lattice gauge theories at finite temperature for N>4. Using the dual formulation of the models and a cluster algorithm we locate the position of the critical points and study the critical behavior across both phase transitions in details. In particular, we determine various critical indices, compute the average action and the specific heat. Our results are consistent with the two transitions being of infinite order. Furthermore, they belong to the universality class of two-dimensional Z(N) vector spin models
Khoromskaia, Venera; Khoromskij, Boris N.
2014-12-01
Our recent method for low-rank tensor representation of sums of the arbitrarily positioned electrostatic potentials discretized on a 3D Cartesian grid reduces the 3D tensor summation to operations involving only 1D vectors however retaining the linear complexity scaling in the number of potentials. Here, we introduce and study a novel tensor approach for fast and accurate assembled summation of a large number of lattice-allocated potentials represented on 3D N × N × N grid with the computational requirements only weakly dependent on the number of summed potentials. It is based on the assembled low-rank canonical tensor representations of the collected potentials using pointwise sums of shifted canonical vectors representing the single generating function, say the Newton kernel. For a sum of electrostatic potentials over L × L × L lattice embedded in a box the required storage scales linearly in the 1D grid-size, O(N) , while the numerical cost is estimated by O(NL) . For periodic boundary conditions, the storage demand remains proportional to the 1D grid-size of a unit cell, n = N / L, while the numerical cost reduces to O(N) , that outperforms the FFT-based Ewald-type summation algorithms of complexity O(N3 log N) . The complexity in the grid parameter N can be reduced even to the logarithmic scale O(log N) by using data-sparse representation of canonical N-vectors via the quantics tensor approximation. For justification, we prove an upper bound on the quantics ranks for the canonical vectors in the overall lattice sum. The presented approach is beneficial in applications which require further functional calculus with the lattice potential, say, scalar product with a function, integration or differentiation, which can be performed easily in tensor arithmetics on large 3D grids with 1D cost. Numerical tests illustrate the performance of the tensor summation method and confirm the estimated bounds on the tensor ranks.
Defect properties from X-ray scattering experiments
International Nuclear Information System (INIS)
Peisl, H.
1976-01-01
Lattice distortions due to defects in crystals can be studied most directly by elastic X-ray or neutron scattering experiments. The 'size' of the defects can be determined from the shift of the Bragg reflections. Defect induced diffuse scattering intensity close to and between Bragg reflections gives information on the strength and symmetry of the distortion fields and yields the atomic structure of point defects (interstitials, vacancies, small aggregates). Diffuse scattering is a very sensitive method to decide whether defects are present as isolated point defects or have formed aggregates. X-ray scattering has been used to study defects produced in various ionic crystals by γ- and neutron irradiation. After an introduction to the principles of the method the experimental results will be reviewed and discussed in some detail. (orig.) [de
International Nuclear Information System (INIS)
Li Zhiwei; Ma Xiaoming; Pang Hua; Li Fashen
2011-01-01
In this paper we present a detailed Moessbauer spectroscopy study of the structural and magnetic properties of the undoped parent compound CaFe 2 As 2 single crystal. By fitting the temperature dependence of the hyperfine magnetic field we show that the magneto-structural phase transition is clearly first order in nature and we also deduce the compressibility of our sample to be 1.67 x 10 -2 GPa -1 . Within Landau's theory of phase transition, we further argue that the observed phase transition may stem from the strong magneto-structural coupling effect. The temperature dependence of the Lamb-Moessbauer factor shows that the paramagnetic phase and the antiferromagnetic phase exhibit similar lattice dynamics in high-frequency modes with very close Debye temperatures, Θ D ∼ 270 K.
International Nuclear Information System (INIS)
Fujishiro, Fumito; Mochizuki, Shosuke
2003-01-01
The electrical conductivity of (x)AgI-(1-x)ZnO (0≤x≤1) composites at room temperature increases with increasing AgI content and reaches a maximum at about 50% AgI. The results obtained by the scanning electron microscopy, X-ray diffractometry and photoluminescence spectroscopy have clarified high-ionic-conduction pathways related to mesoscopic defect structure at AgI/ZnO interfaces and mesoscopically disordered structure in AgI domain. We have observed also new optical phenomenon, which may arise from excitation energy transfer between AgI-exciton and photoinduced oxygen vacancy at the AgI/ZnO interface
Directory of Open Access Journals (Sweden)
Chávez Francisco P
2010-01-01
Full Text Available Abstract Background Inorganic polyphosphate (polyP, a polymer of tens or hundreds of phosphate residues linked by ATP-like bonds, is found in all organisms and performs a wide variety of functions. PolyP is synthesized in bacterial cells by the actions of polyphosphate kinases (PPK1 and PPK2 and degraded by exopolyphosphatase (PPX. Bacterial cells with polyP deficiencies due to knocking out the ppk1 gene are affected in many structural and important cellular functions such as motility, quorum sensing, biofilm formation and virulence among others. The cause of this pleiotropy is not entirely understood. Results The overexpression of exopolyphosphatase in bacteria mimicked some pleitropic defects found in ppk1 mutants. By using this approach we found new structural and functional defects in the polyP-accumulating bacteria Pseudomonas sp. B4, which are most likely due to differences in the polyP-removal strategy. Colony morphology phenotype, lipopolysaccharide (LPS structure changes and cellular division malfunction were observed. Finally, we used comparative proteomics in order to elucidate the cellular adjustments that occurred during polyP deficiency in this bacterium and found some clues that helped to understand the structural and functional defects observed. Conclusions The results obtained suggest that during polyP deficiency energy metabolism and particularly nucleoside triphosphate (NTP formation were affected and that bacterial cells overcame this problem by increasing the flux of energy-generating metabolic pathways such as tricarboxilic acid (TCA cycle, β-oxidation and oxidative phosphorylation and by reducing energy-consuming ones such as active transporters and amino acid biosynthesis. Furthermore, our results suggest that a general stress response also took place in the cell during polyP deficiency.
Structure optimization by heuristic algorithm in a coarse-grained off-lattice model
International Nuclear Information System (INIS)
Jing-Fa, Liu
2009-01-01
A heuristic algorithm is presented for a three-dimensional off-lattice AB model consisting of hydrophobic (A) and hydrophilic (B) residues in Fibonacci sequences. By incorporating extra energy contributions into the original potential function, we convert the constrained optimization problem of AB model into an unconstrained optimization problem which can be solved by the gradient method. After the gradient minimization leads to the basins of the local energy minima, the heuristic off-trap strategy and subsequent neighborhood search mechanism are then proposed to get out of local minima and search for the lower-energy configurations. Furthermore, in order to improve the efficiency of the proposed algorithm, we apply the improved version called the new PERM with importance sampling (nPERMis) of the chain-growth algorithm, pruned-enriched-Rosenbluth method (PERM), to face-centered-cubic (FCC)-lattice to produce the initial configurations. The numerical results show that the proposed methods are very promising for finding the ground states of proteins. In several cases, we found the ground state energies are lower than the best values reported in the present literature
Simplicial lattices in classical and quantum gravity: Mathematical structure and application
International Nuclear Information System (INIS)
LaFave, N.J.
1989-01-01
Geometrodynamics can be understood more clearly in the language of geometry than in the language of differential equations. This is the primary motivation for the development of calculational schemes based on Regge Calculus as an alternative to those schemes based on Ricci Calculus. The author develops the mathematics of simplicial lattices to the same level of sophistication as the mathematics of pseudo-Riemannian geometry for continuum manifolds. This involves the definition of the simplicial analogues of several concepts from differential topology and differential geometry-the concept of a point, tangent spaces, forms, tensors, parallel transport, covariant derivatives, connections, and curvature. These simplicial analogues are used to define the Einstein tensor and the extrinsic curvature on a simplicial geometry. He applies this mathematical formalism to the solution of several outstanding problems in the development of a Regge Calculus based computational scheme for general geometrodynamic problems. This scheme is based on a 3 + 1 splitting of spacetime within the Regge Calculus prescription known as Null-Strut Calculus (NSC). NSC, developed by Warner Miller, describes the foliation of spacetime into spacelike hypersurfaces built of tetrahedra. The outstanding problems discussed include (a) the rigidification of the 3-layered sandwich and the evolution problem; (b) the formulation of initial data; and (c) in inclusion of matter on the lattice. The resulting calculational scheme is applied to two test problems, the Friedmann model and the second-order Doppler effect. Finally, he describes avenues of investigation for NSC in quantum gravity
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
Di-interstitial defect in silicon revisited
International Nuclear Information System (INIS)
Londos, C. A.; Antonaras, G.; Chroneos, A.
2013-01-01
Infrared spectroscopy was used to study the defect spectrum of Cz-Si samples following fast neutron irradiation. We mainly focus on the band at 533 cm −1 , which disappears from the spectra at ∼170 °C, exhibiting similar thermal stability with the Si-P6 electron paramagnetic resonance (EPR) spectrum previously correlated with the di-interstitial defect. The suggested structural model of this defect comprises of two self-interstitial atoms located symmetrically around a lattice site Si atom. The band anneals out following a first-order kinetics with an activation energy of 0.88 ± 0.3 eV. This value does not deviate considerably from previously quoted experimental and theoretical values for the di-interstitial defect. The present results indicate that the 533 cm −1 IR band originates from the same structure as that of the Si-P6 EPR spectrum
Antisite Defects of the L12 Structure Determined by the Phase Field Microelasticity Model
International Nuclear Information System (INIS)
Jing, Zhang; Zheng, Chen; Yan-Li, Lu; Yong-Xin, Wang; Yan, Zhao
2009-01-01
A phase field microelasticity simulation is performed to examine the antisite defect of L1 2 -Ni 3 Al in Ni 75 Al 5.3 V 19.7 ternary alloy. Combinimg strain energy with the phase field model leads to an atom configuration change as time proceeds. For the Ni sublattice, the antisite defect Al Ni , the equilibrium occupancy probability (OP) of which declines, precedes Ni Ni and V Ni in reaching equilibrium; subsequently, Ni Ni and V Ni present a phenomenon of symmetrical rise and decline individually. Similarly, for the Al sublattice, the antisite defect Ni Al , the OP of which eventually rises, takes fewer time steps than Al Ai and V Al to attain equilibrium. Thereafter, Al Al rises while V Al declines symmetrically at the axes of the Ni Al MAI curve. Furthermore, the OP for the Al sublattice is much more sensitive to strain energy than that for the Ni sublattice. (condensed matter: structure, mechanical and thermal properties)
Analysis of structure and defects in thin silicon films deposited from hydrogen diluted silane
International Nuclear Information System (INIS)
Elzakker, G. van; Nadazdy, V.; Tichelaar, F.D.; Metselaar, J.W.; Zeman, M.
2006-01-01
Thin silicon layers have been deposited from silane diluted with hydrogen. The dilution ratio R (R = [H 2 ]/[SiH 4 ]) has been varied between R = 0 and R = 40. The structural properties of Si:H films have been studied using transmission electron microscopy imaging and Raman spectroscopy. The phase evolution from the amorphous phase into the mixed and eventually microcrystalline phase strongly depends on the hydrogen dilution. The initiation of the microcrystalline growth occurs between R = 20 and R = 25. The phase transition becomes more abrupt with increasing hydrogen dilution. Optoelectronic properties of the layers have been determined. Increasing hydrogen dilution results in films with increasing effective defect density and Urbach energy, which is related to inhomogeneous growth. The charge deep-level transient spectroscopy technique (Q-DLTS) was applied for the first time on hydrogen diluted thin silicon films in order to investigate the energy distribution of the defect states in these layers as a function of the dilution ratio R. The Q-DLTS spectra indicate a difference in defect-state distribution when the films evolve from the amorphous phase into the microcrystalline phase
Energy Technology Data Exchange (ETDEWEB)
Hu, Yonghong, E-mail: hchyh2001@tom.com [School of Nuclear Technology and Chemistry & Biology, Hubei University of Science and Technology, Xianning 437100 (China); Wu, Yunyi [Department of Energy Materials and Technology, General Research Institute for Nonferrous Metals, Beijing (China); Zhang, Shengli [Institute of Optoelectronics & Nanomaterials, Herbert Gleiter Institute of Nanoscience, College of Materials Science and Engineering, Nanjing University of Science and Technology, Nanjing 210094 (China)
2016-12-15
Defects are inevitably present in materials, and their existence strongly affects the fundamental physical properties of 2D materials. Here, we performed first-principles calculations to study the structural and electronic properties of antimonene with Stone–Wales defects, highlighting the differences in the structure and electronic properties. Our calculations show that the presence of a SW defect in antimonene changes the geometrical symmetry. And the band gap decreases in electronic band structure with the decrease of the SW defect concentration. The formation energy and cohesive energy of a SW defect in antimonene are studied, showing the possibility of its existence and its good stability, respectively. The difference charge density near the SW defect is explored, by which the structural deformations of antimonene are explained. At last, we calculated the STM images for the SW defective antimonene to provide more information and characters for possible experimental observation. These results may provide meaningful references to the development and design of novel nanodevices based on new 2D materials.
Defect structure of TiS{sub 3} single crystals of the A-ZrSe{sub 3} type
Energy Technology Data Exchange (ETDEWEB)
Bolotina, N. B., E-mail: nb-bolotina@mail.ru [Russian Academy of Sciences, Shubnikov Institute of Crystallography, Federal Scientific Research Centre “Crystallography and Photonics,” (Russian Federation); Gorlova, I. G. [Russian Academy of Sciences, Kotel’nikov Institute of Radioengineering and Electronics (Russian Federation); Verin, I. A. [Russian Academy of Sciences, Shubnikov Institute of Crystallography, Federal Scientific Research Centre “Crystallography and Photonics,” (Russian Federation); Titov, A. N. [Russian Academy of Sciences, Mikheev Institute of Metal Physics, Ural Branch (Russian Federation); Arakcheeva, A. V. [Phase Solutions, Co Ltd. (Switzerland)
2016-11-15
The defect structure of TiS{sub 3} single crystals of the A-ZrSe{sub 3} type has been determined based on X-ray diffraction data. Shear defects manifest themselves as displacements of ab layers (which can imitate a twin) by ∼0.5a. Regular shears facilitate the formation of a superstructure along the c axis. A model of defect in the layer structure is proposed to explain the atomic displacements at an angle to the layer plane.
Winget, Paul; Schirra, Laura K; Cornil, David; Li, Hong; Coropceanu, Veaceslav; Ndione, Paul F; Sigdel, Ajaya K; Ginley, David S; Berry, Joseph J; Shim, Jaewon; Kim, Hyungchui; Kippelen, Bernard; Brédas, Jean-Luc; Monti, Oliver L A
2014-07-16
The electronic structure of the hybrid interface between ZnO and the prototypical organic semiconductor PTCDI is investigated via a combination of ultraviolet and X-ray photoelectron spectroscopy (UPS/XPS) and density functional theory (DFT) calculations. The interfacial electronic interactions lead to a large interface dipole due to substantial charge transfer from ZnO to 3,4,9,10-perylenetetracarboxylicdiimide (PTCDI), which can be properly described only when accounting for surface defects that confer ZnO its n-type properties. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Morphology, deformation, and defect structures of TiCr2 in Ti-Cr alloys
International Nuclear Information System (INIS)
Chen, K.C.; Allen, S.M.; Livingston, J.D.
1992-01-01
The morphologies and defect structures of TiCr 2 in several Ti-Cr alloys have been examined by optical metallography, x-ray diffraction, and transmission electron microscopy (TEM), in order to explore the room-temperature deformability of the Laves phase TiCr 2 . The morphology of the Laves phase was found to be dependent upon alloy composition and annealing temperature. Samples deformed by compression have also been studied using TEM. Comparisons of microstructures before and after deformation suggest an increase in twin, stacking fault, and dislocation density within the Laves phase, indicating some but not extensive room-temperature deformability
Defect Structure of High-Temperature-Grown GaMnSb/GaSb
International Nuclear Information System (INIS)
Romanowski, P.; Bak-Misiuk, J.; Dynowska, E.; Domagala, J.Z.; Wojciechowski, T.; Jakiela, R.; Sadowski, J.; Barcz, A.; Caliebe, W.
2010-01-01
GaMnSb/GaSb(100) layers with embedded MnSb inclusions have been grown at 720 K using MBE technique. This paper presents the investigation of the defect structure of Ga1-xMnxSb layers with different content of manganese (up to x = 0.07). X-ray diffraction method using conventional and synchrotron radiation was applied. Dimensions and shapes of inclusions were detected by scanning electron microscopy. Depth profiles of elements were measured using secondary ion mass spectroscopy technique. (authors)
Evolution of MBE HgCdTe defect structure studied with ion milling method
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Pociask-Bialy Malgorzata
2017-01-01
Full Text Available In this paper, is shown how ion milling can assist in assessing the defect structure of MCT by revealing the residual doping, and establishing the minimum level of donor concentration Nmd, which is needed for obtaining n-regions with a reproducible n value. For this purpose, a study of the electrical properties of ion-milled LWIR n-type MCT films, un-doped and doped with indium with the concentration NIn = 5 × 1014–1017 cm−3 is proposed.
Role of masking oxide on silicon in processes of defect generation at formation of SIMOX structures
Askinazi, A Y; Miloglyadova, L V
2002-01-01
One investigated into Si-SiO sub 2 structures formed by implantation of oxygen ions into silicon (SIMOX-technology) by means of techniques based on measuring of high-frequency volt-farad characteristics and by means of electroluminescence. One determined existence of electrically active centres and of luminescence centres in the formed oxide layer near boundary with silicon. One clarified the role SiO sub 2 masking layer in silicon in defect generation under formation of the masked oxide layer. One established dependence of concentration of electrically active and luminescence centres on thickness of masking layer
Tuning the band structure of graphene nanoribbons through defect-interaction-driven edge patterning
Du, Lin; Nguyen, Tam N.; Gilman, Ari; Muniz, André R.; Maroudas, Dimitrios
2017-12-01
We report a systematic analysis of pore-edge interactions in graphene nanoribbons (GNRs) and their outcomes based on first-principles calculations and classical molecular-dynamics simulations. We find a strong attractive interaction between nanopores and GNR edges that drives the pores to migrate toward and coalesce with the GNR edges, which can be exploited to form GNR edge patterns that impact the GNR electronic band structure and tune the GNR band gap. Our analysis introduces a viable physical processing strategy for modifying GNR properties by combining defect engineering and thermal annealing.
Computer simulation and implementation of defected ground structure on a microstrip antenna
Adrian, H.; Rambe, A. H.; Suherman
2018-03-01
Defected Ground Structure (DGS) is a method reducing etching area on antenna ground to form desirable antenna’s ground field. This paper reports the method impact on microstrip antennas working on 1800 and 2400 MHz. These frequencies are important as many radio network applications such mobile phones and wireless devices working on these channels. The assessments were performed by simulating and fabricating the evaluated antennas. Both simulation data and implementation measurements show that DGS successfully improves antenna performances by increasing bandwidth up to 19%, reducing return loss up to 109% and increasing gain up to 33%.
International Nuclear Information System (INIS)
Piercy, G.R.
1960-01-01
An investigation was made of the mobility and types of point defect introduced in platinum by deformation in liquid nitrogen, quenching into water from 1600 o C, or reactor irradiation at 50 o C. In all cases the activation energy for motion of the defect was determined from measurements of electrical resistivity. Measurements of density, hardness, and x-ray line broadening were also made there applicable. These experiments indicated that the principal defects remaining in platinum after irradiation were single vacant lattice sites and after quenching were pairs of vacant lattice sites. Those present after deformation In liquid nitrogen were single vacant lattice sites and another type of defect, perhaps interstitial atoms. (author)
Thermal annealing of carbon nanotubes reveals a toxicological impact of the structural defects
Energy Technology Data Exchange (ETDEWEB)
Figarol, Agathe, E-mail: figarol@emse.fr [Ecole Nationale Supérieure des Mines, SPIN-EMSE, CNRS: UMR 5307, LGF (France); Pourchez, Jérémie, E-mail: pourchez@emse.fr [Ecole Nationale Supérieure des Mines, CIS-EMSE, EA 4624, SFR IFRESIS, LINA (France); Boudard, Delphine [Université Jean Monnet Saint-Etienne, EA 4624, SFR IFRESIS, LINA (France); Forest, Valérie [Ecole Nationale Supérieure des Mines, CIS-EMSE, EA 4624, SFR IFRESIS, LINA (France); Berhanu, Sarah [Armines - Mines ParisTech, Centre des Matériaux, CNRS UMR 7633 (France); Tulliani, Jean-Marc [Politecnico di Torino, Department of Applied Science and Technology (Italy); Lecompte, Jean-Pierre [Centre Européen de la céramique CNRS: UMR 7315, SPCTS (France); Cottier, Michèle [Université Jean Monnet Saint-Etienne, EA 4624, SFR IFRESIS, LINA (France); Bernache-Assollant, Didier [Ecole Nationale Supérieure des Mines, CIS-EMSE, EA 4624, SFR IFRESIS, LINA (France); Grosseau, Philippe [Ecole Nationale Supérieure des Mines, SPIN-EMSE, CNRS: UMR 5307, LGF (France)
2015-04-15
The biological response to pristine and annealed multi-walled carbon nanotubes (MWCNT) was assessed on murine macrophages (RAW 264.7). First, the physicochemical features of the as-produced MWCNT and annealed at 2125 °C for 1 h were fully characterized. A decrease in structural defects, hydrophobicity and catalytic impurities was detected after annealing. Thereafter, their impact on cytotoxicity, oxidative stress, and pro-inflammatory response was investigated at concentrations ranging from 15 to 120 µg mL{sup −1}. No effect of the 2125 °C treatment was detected on the cytotoxicity. In contrast, the annealed carbon nanotubes showed a significant increase of the pro-inflammatory response. We assumed that this behavior was due to the reduction in structural defects that may modify the layer of adsorbed biomolecules. Surprisingly, the purification of metallic catalysts did not have any significant impact on the oxidative stress. We suggested that the structural improvements from the 2125 °C treatment can decrease the carbon nanotube scavenging capacity and thus allow a higher free radical release which may counterbalance the decrease of oxidative stress due to a lower content of metallic impurities.
Lattice dynamics of alkali hydrides and deuterides with the NaCl type structure
International Nuclear Information System (INIS)
Dyck, W.; Jex, H.
1981-01-01
The deformation dipole model, the shell model, and also extended versions of these models have been investigated for the lattice dynamics of LiH and LiD. A deformation dipole model with 13 adjustable parameters gave the best fit to the phonon dispersion of LiD known from neutron and Raman experiments. The model has been used to compute elastic and dielectric constants, Szigeti effective charges, phonon densities of states, Debye temperatures and second-order Raman spectra of LiD and LiH. Good agreement with the experimental data was obtained. The contributions of short-range three- and four-body forces to the model force constants are discussed. First calculations of the phonon dispersion curves of the hydrides and deuterides of Na, K, Rb and Cs, which are based on shell models, are presented. (author)
Bykov, Igor; Zagorodniy, Yuriy; Yurchenko, Lesya; Korduban, Alexander; Nejezchleb, Karel; Trachevsky, Vladimir; Dimza, Vilnis; Jastrabik, Lubomir; Dejneka, Alexander
2014-08-01
The nature of intrinsic and impurity point defects in lead zirconate titanate (PZT) ceramics has been explored. Using electron paramagnetic resonance (EPR), nuclear magnetic resonance (NMR), and X-ray photoelectron spectroscopy (XPS) methods, several impurity sites have been identified in the materials, including the Fe(3+)-oxygen vacancy (VO) complex and Pb ions. Both of these centers are incorporated into the PZT lattice. The Fe(3+) –VО paramagnetic complex serves as a sensitive probe of the local crystal field in the ceramic; the symmetry of this defect roughly correlates with PZT phase diagram as the composition is varied from PbTiO3 to PbZrO3. NMR spectra (207)Pb in PbTiO3, PbZrO3, and PZT with iron content from 0 to 0.4 wt% showed that increasing the iron concentration leads to a distortion of the crystal structure and to improvement of the electrophysical parameters of the piezoceramics. This is due to the formation of a phase which has a higher symmetry, but at high concentrations of iron (>0.4 wt%), it leads to sharp degradation of electrophysical parameters.
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Danilo Sergi
2016-01-01
Full Text Available This study uses the lattice Boltzmann method (LBM to simulate in 2D the capillary infiltration into porous structures obtained from the packing of particles. The experimental problem motivating the work is the densification of carbon preforms by reactive melt infiltration. The aim is to determine the optimization principles for the manufacturing of high-performance ceramics. Simulations are performed for packings with varying structural properties. The results suggest that the observed slow infiltrations can be ascribed to interface dynamics. Pinning represents the primary factor retarding fluid penetration. The mechanism responsible for this phenomenon is analyzed in detail. When surface growth is allowed, it is found that the phenomenon of pinning becomes stronger. Systems trying to reproduce typical experimental conditions are also investigated. It turns out that the standard for accurate simulations is challenging. The primary obstacle to overcome for enhanced accuracy seems to be the over-occurrence of pinning.
Directory of Open Access Journals (Sweden)
Lana Damaj
2015-01-01
Full Text Available A wideband dual-polarized coplanar waveguide (CPW fed antenna integrating a wide stop-band filter is presented. The designed filter is based on a nonuniform defected ground structure (DGS in order to obtain a wide stop-band and a compact size. This filter is used to reject harmonics and spurious radiation arising from the RF front end. The complete structure (antenna and filter has been optimized to have a compact size of 0.6×0.6λ02 (λ0 being the free-space wavelength at the lowest operating frequency. The realized antenna operates in the frequency range between 2.7 GHz and 5.9 GHz (bandwidth of about 74%. The isolation between feeding ports is more than 18 dB. The complete structure has a wide stop-band characteristic (103% for harmonic rejection. The simulated numerical results have been confirmed with measurements.
Influence of Cast Iron Structure on the Glassmold Equipment Operational Defects
Directory of Open Access Journals (Sweden)
I. O. Leushin
2015-01-01
Full Text Available The growing demand for glass packaging contributes to the increase in production capacity of glass-container plants. Their equipment (cast iron glass-forming sets operates in continuous mode under complex cyclic thermal loads, which lead to the formation of operational defects on the working surfaces of details: graphite falling, cracks, oxidation, etc. Particular influence on the formation of these defects renders the microstructure of the material at the time of installation of details on the line.The article identifies the causes for formation of operational defects, formulates the ways to remedy them and prevent their occurrence.The authors studied details made from grey cast iron with flake and spherical forms of graphite. It is found that in the process of exploitation of the material is greatly reducing its hardness, strength, resistance to oxidation through of graphitization processes, chemical interaction of glass and iron, shock loads working edges. It is proved that the choice of initial microstructure of cast iron (the metal base, the graphite form, the presence of structural-free cementite exercises a determining influence on the durability of the mold tooling. The article proposes differential (layered arrangement of the graphite phase of cast iron in the alloy matrix (ferrite. This arrangement of high-carbon phase can simultaneously increase the thermal and oxidation resistance of the material. The formation of a layered structure of iron is produced by the intensification of the processes of alloying, modifying and directional freezing the melt.These data can be used to select the material of details by manufacturers glass-molds tooling.
Structural peculiarities and point defects of bulk-ZnO single crystals
International Nuclear Information System (INIS)
Kaurova, I.A.; Kuz’micheva, G.M.; Rybakov, V.B.; Cousson, A.; Gayvoronsky, V.Ya.
2014-01-01
Highlights: • ZnO single crystals of different color were grown by the hydrothermal method. • Point defects in ZnO have been firstly investigated by neutron diffraction. • Presence of additional reflections caused by kinetic growth effects was revealed. • The relationship between the color and zinc and oxygen vacancies was found. • Photoinduced variation of transmittance versus the CW laser intensity was analyzed. - Abstract: ZnO single crystals are related to promising direct wide band gap semiconductor materials belonging to the A II B VI type of compounds with wurtzite structure. “Unintentional” n-type conductivity in ZnO may be caused by zinc and oxygen vacancies, and interstitial zinc atoms. To date, the comprehensive structural investigation and analysis of point defects in ZnO is absent in literature. Green, light green and almost colorless ZnO single crystals grown by the hydrothermal method in concentrated alkali solutions 4M(KOH) + 1M(LiOH) + 0.1M(NH 4 OH) on monohedral seeds [0 0 0 1] at crystallization temperatures in the range of 330–350 °C and pressures in the range of 30–50 MPa have been firstly investigated by neutron diffraction. It was revealed the presence of additional reflections (∼12–∼16%) for all the crystals caused by kinetic growth effects that give grounds to assign them to the space group P3 rather than to P6 3 mc. Analysis of the refined compositions together with the color of ZnO crystals does not rule out the relationship between the color and vacancies in the zinc and oxygen positions whose concentration decreases with the discoloration of the samples. The analysis of the photoinduced variation of the total and on-axis transmittance versus the CW laser intensity showed that the colored samples have profound deep defects related to oxygen vacancies
Neutron scattering from a substitutional mass defect
International Nuclear Information System (INIS)
Williams, R.D.; Lovesey, S.W.
1985-06-01
The dynamic structure factor is calculated for a low concentration of light mass scatterers substituted in a cubic crystal matrix. A new numerical method for the exact calculation is demonstrated. A local density of states for the low momentum transfer limit, and the shifts and widths of the oscillator peaks in the high momentum transfer limit are derived. The limitations of an approximation which decouples the defect from the lattice is discussed. (author)
Defect and structural imperfection effects on the electronic properties of BiTeI surfaces
International Nuclear Information System (INIS)
Fiedler, Sebastian; Seibel, Christoph; Lutz, Peter; Bentmann, Hendrik; Reinert, Friedrich; El-Kareh, Lydia; Bode, Matthias; Eremeev, Sergey V; Tereshchenko, Oleg E; Kokh, Konstantin A; Chulkov, Evgueni V; Kuznetsova, Tatyana V; Grebennikov, Vladimir I
2014-01-01
The surface electronic structure of the narrow-gap seminconductor BiTeI exhibits a large Rashba-splitting which strongly depends on the surface termination. Here we report on a detailed investigation of the surface morphology and electronic properties of cleaved BiTeI single crystals by scanning tunneling microscopy, photoelectron spectroscopy (ARPES, XPS), electron diffraction (SPA-LEED) and density functional theory calculations. Our measurements confirm a previously reported coexistence of Te- and I-terminated surface areas originating from bulk stacking faults and find a characteristic length scale of ∼100 nm for these areas. We show that the two terminations exhibit distinct types of atomic defects in the surface and subsurface layers. For electronic states resided on the I terminations we observe an energy shift depending on the time after cleavage. This aging effect is successfully mimicked by depositon of Cs adatoms found to accumulate on top of the I terminations. As shown theoretically on a microscopic scale, this preferential adsorbing behaviour results from considerably different energetics and surface diffusion lengths at the two terminations. Our investigations provide insight into the importance of structural imperfections as well as intrinsic and extrinsic defects on the electronic properties of BiTeI surfaces and their temporal stability. (paper)
Local structure and defects in ion irradiated KTaO3
Zhang, F. X.; Xi, J.; Zhang, Y.; Tong, Yang; Xue, H.; Huang, R.; Trautmann, C.; Weber, W. J.
2018-04-01
The modification of the local structure in cubic perovskite KTaO3 irradiated with 3 MeV and 1.1 GeV Au ions is studied by Raman and x-ray absorption spectroscopy, complemented by density functional theory (DFT) calculations. In the case of irradiation with 3 MeV Au ions where displacement cascade processes are dominant, the Ta L3-edge x-ray absorption measurements suggest that a peak corresponding to the Ta-O bonds in the TaO6 octahedra splits, which is attributed to the formation of TaK antisite defects that are coupled with oxygen vacancies, V O. This finding is consistent with the DFT calculations. Under irradiation with 1.1 GeV ions, the intense ionization and electronic energy deposition lead to a blue shift and an intensity reduction of active Raman bands. In the case of sequential irradiations, extended x-ray absorption fine structure measurements reveal a decrease in concentration of coupled TaK-V O defects under subsequent irradiation with 1.1 GeV Au ions.
Integrable nonlinear Schrödinger system on a lattice with three structural elements in the unit cell
Vakhnenko, Oleksiy O.
2018-05-01
Developing the idea of increasing the number of structural elements in the unit cell of a quasi-one-dimensional lattice as applied to the semi-discrete integrable systems of nonlinear Schrödinger type, we construct the zero-curvature representation for the general integrable nonlinear system on a lattice with three structural elements in the unit cell. The integrability of the obtained general system permits to find explicitly a number of local conservation laws responsible for the main features of system dynamics and in particular for the so-called natural constraints separating the field variables into the basic and the concomitant ones. Thus, considering the reduction to the semi-discrete integrable system of nonlinear Schrödinger type, we revealed the essentially nontrivial impact of concomitant fields on the Poisson structure and on the whole Hamiltonian formulation of system dynamics caused by the nonzero background values of these fields. On the other hand, the zero-curvature representation of a general nonlinear system serves as an indispensable key to the dressing procedure of system integration based upon the Darboux transformation of the auxiliary linear problem and the implicit Bäcklund transformation of field variables. Due to the symmetries inherent to the six-component semi-discrete integrable nonlinear Schrödinger system with attractive-type nonlinearities, the Darboux-Bäcklund dressing scheme is shown to be simplified considerably, giving rise to the appropriately parameterized multi-component soliton solution consisting of six basic and four concomitant components.
International Nuclear Information System (INIS)
Kwak, D.W.; Lee, D.W.; Oh, J.S.; Lee, Y.H.; Cho, H.Y.
2012-01-01
SiGe-on-Insulator (SGOI) structures were created using the Ge condensation method, where an oxidation process is performed on the SiGe/Si structure. This method involves rapid thermal chemical vapor deposition and H + /He + ion-implantations. Deep level defects in these structures were investigated using deep level transient spectroscopy (DLTS) by varying the pulse injection time. According to the DLTS measurements, a deep level defect induced during the Ge condensation process was found at 0.28 eV above the valence band with a capture cross section of 2.67 × 10 −17 cm 2 , two extended deep levels were also found at 0.54 eV and 0.42 eV above the valence band with capture cross sections of 3.17 × 10 −14 cm 2 and 0.96 × 10 −15 cm 2 , respectively. In the SGOI samples with ion-implantation, the densities of the newly generated defects as well as the existing defects were decreased effectively. Furthermore, the Coulomb barrier heights of the extended deep level defects were drastically reduced. Thus, we suggest that the Ge condensation method with H + ion implantation could reduce deep level defects generated from the condensation and control the electrical properties of the condensed SiGe layers. - Highlights: ► We have fabricated low-defective SiGe-on-Insulator (SGOI) with implantation method. ► H + and He + -ions are used for ion-implantation method. ► We have investigated the deep level defects of SGOI layers. ► Ge condensation method using H + ion implantation could reduce extended defects. ► They could enhance electrical properties.
X-ray diffuse scattering effects from Coulomb-type defects in multilayered structures
International Nuclear Information System (INIS)
Olikhovskii, S.I.; Molodkin, V.B.; Skakunova, E.S.; Kislovskii, E.N.; Fodchuk, I.M.
2009-01-01
The theoretical X-ray diffraction model starting from Takagi-Taupin equation has been developed for the description of coherent and diffuse components of the rocking curve (RC) measured from the multilayered crystal structure with randomly distributed Coulomb-type defects in all the layers and substrate. The model describes both diffuse scattering (DS) intensity distribution and influence of DS on attenuation and angular redistribution of the coherent X-ray scattering intensity. By analyzing the total measured RC with using the proposed diffraction model, the chemical compositions, strains, and characteristics of dislocation loops in layers and substrate of the multilayered structure with InGaAsN/GaAs single quantum well have been determined. (Abstract Copyright [2009], Wiley Periodicals, Inc.)
Magnetite Fe3O4 (111) Surfaces: Impact of Defects on Structure, Stability, and Electronic Properties
Noh, Jung Hyun
2015-08-04
We present a comprehensive investigation, via first-principles density functional theory (DFT) calculations, of various surface terminations of magnetite, Fe3O4 (111), a major iron oxide which has also a number of applications in electronics and spintronics. We compare the thermodynamic stability and electronic structure among the different surfaces terminations. Interestingly, we find that surfaces modified with point defects and adatoms can be more stable than bulk-like terminations. These surfaces show different surface chemistry, electronic structures and distinctive spin polarization features near the Fermi level from those previously considered in the literature. Our studies provide an atomic level insight for magnetite surfaces, which is a necessary step to understanding their interfaces with organic layers in OLED and spintronic devices.
Multiband Bandstop Filter using an I-Stub-Loaded Meandered Defected Microstrip Structure
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G. R. Koirala
2016-04-01
Full Text Available This paper presents a compact multiband bandstop filter (BSF that utilizes an I-stub embedded within a meandered defected microstrip structure (MDMS. The proposed design for obtaining a single stopband is analyzed by using a transmission line network model. On the basis of the single stopband structure, we designed and fabricated a dual- and tri-band bandstop filters operating at 2.5/6.78 GHz and 1.98/5.60/7.78 GHz, respectively, thereby exploring the concept of generating as many stopbands by simply adding the same number of I-stubs. The proposed filter also features the possibility of tuning the resonant frequencies by varying the width of the I-stubs.
Harmonic Suppressed Slot Antennas Using Rectangular/Circular Defected Ground Structures
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Mohammad Saeid Ghaffarian
2012-01-01
Full Text Available Two wide rectangle-shaped microstrip-fed 2.6-GHz slot antennas using defected ground structures (DGSs with a low design complexity are proposed to achieve wideband harmonic suppression. To accomplish this, two rectangular DGSs (RDGSs in the first antenna and two circular DGSs (CDGSs in the second one with various dimensions are etched into the ground plane, which could have a wideband-stop characteristic. Simulated and measured reflection coefficients indicate that the two proposed structures effectively suppress the second and third harmonics up to 23 dB between 3.5 and 10.5 GHz with a maximum ripple of 2.4 dB. In addition, the radiation patterns and peak gains of the antennas can be suppressed at least 17 dB and 7.1 dBi, respectively, at the third harmonic frequency of 7.86 GHz.
Magnetite Fe3O4 (111) Surfaces: Impact of Defects on Structure, Stability, and Electronic Properties
Noh, Jung Hyun; Osman, Osman I; Aziz, Saadullah G.; Winget, Paul; Bredas, Jean-Luc
2015-01-01
We present a comprehensive investigation, via first-principles density functional theory (DFT) calculations, of various surface terminations of magnetite, Fe3O4 (111), a major iron oxide which has also a number of applications in electronics and spintronics. We compare the thermodynamic stability and electronic structure among the different surfaces terminations. Interestingly, we find that surfaces modified with point defects and adatoms can be more stable than bulk-like terminations. These surfaces show different surface chemistry, electronic structures and distinctive spin polarization features near the Fermi level from those previously considered in the literature. Our studies provide an atomic level insight for magnetite surfaces, which is a necessary step to understanding their interfaces with organic layers in OLED and spintronic devices.
Vectors of Defects in Reinforced Concrete Structures in Onshore Oil and Gas Process Plants
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Dabo Baba Hammad
2018-01-01
Full Text Available There is a global outcry over the speedy deterioration of structures in oil and gas facilities. While marine environment is considered the leading factor in the deterioration of offshore structures, there is no single factor considered as the main cause of the problem in onshore structures. Therefore, the aim of this paper is to present the result of global survey on the major factors causing the deterioration of concrete structures in onshore oil and gas facilities. To realize the objectives of the paper, an e-questionnaire was administered through two International LinkedIn groups with a membership mainly dominated by experts in onshore oil and gas facilities. 159 respondents completed the questionnaires, and the reliability of the responses was calculated to be 0.950 which is considered excellent. Relative importance index was used in ranking the factors, and it was observed that environmental factors ranked as the dominant factors causing the deterioration of concrete structures in onshore process plants. Another important finding in the study is the role that experience plays on the perception of experts on the causes of defects on concrete structures.
Lattice Location of Transition Metals in Semiconductors
2002-01-01
%IS366 %title\\\\ \\\\Transition metals (TMs) in semiconductors have been the subject of considerable research for nearly 40 years. This is due both to their role as important model impurities for deep centers in semiconductors, and to their technological impact as widespread contaminants in Si processing, where the miniaturization of devices requires to keep their sheet concentration below 10$^{10}$ cm$^{-2}$. As a consequence of the low TM solubility, conventional ion beam methods for direct lattice location have failed completely in identifying the lattice sites of isolated transition metals. Although electron paramagnetic resonance (EPR) has yielded valuable information on a variety of TM centers, it has been unable to detect certain defects considered by theory, e.g., isolated interstitial or substitutional Cu in Si. The proposed identity of other EPR centers such as substitutional Fe in Si, still needs confirmation by additional experimental methods. As a consequence, the knowledge on the structural propert...
Söngen, Hagen; Reischl, Bernhard; Miyata, Kazuki; Bechstein, Ralf; Raiteri, Paolo; Rohl, Andrew L.; Gale, Julian D.; Fukuma, Takeshi; Kühnle, Angelika
2018-03-01
It seems natural to assume that defects at mineral surfaces critically influence interfacial processes such as the dissolution and growth of minerals in water. The experimental verification of this claim, however, is challenging and requires real-space methods with utmost spatial resolution, such as atomic force microscopy (AFM). While defects at mineral-water interfaces have been resolved in 2D AFM images before, the perturbation of the surrounding hydration structure has not yet been analyzed experimentally. In this Letter, we demonstrate that point defects on the most stable and naturally abundant calcite (10.4) surface can be resolved using high-resolution 3D AFM—even within the fifth hydration layer. Our analysis of the hydration structure surrounding the point defect shows a perturbation of the hydration with a lateral extent of approximately one unit cell. These experimental results are corroborated by molecular dynamics simulations.
Electronic structure and lattice dynamics of CaPd3B studied by first-principles methods
International Nuclear Information System (INIS)
Music, Denis; Ahuja, Rajeev; Schneider, Jochen M.
2006-01-01
Using first-principles methods, we have studied the electronic structure and lattice dynamics of CaPd 3 B and compared them to isostructural MgNi 3 C. CaPd 3 B possesses less electronic states at the Fermi level, but more phonon modes at low frequencies, than MgNi 3 C. According to the phonon density of states, low frequency acoustic modes are dominated by Pd states, corresponding to Ni in MgNi 3 C. Furthermore, these Pd modes show soft phonons, which may be significant for second-order phase transitions. Based on the comparison to MgNi 3 C, we suggest that the properties of these two compounds may be similar
Directory of Open Access Journals (Sweden)
Zbisław Tabor
2011-05-01
Full Text Available In the study an algorithm based on a lattice gas model is proposed as a tool for enhancing quality of lowresolution images of binary structures. Analyzed low-resolution gray-level images are replaced with binary images, in which pixel size is decreased. The intensity in the pixels of these new images is determined by corresponding gray-level intensities in the original low-resolution images. Then the white phase pixels in the binary images are assumed to be particles interacting with one another, interacting with properly defined external field and allowed to diffuse. The evolution is driven towards a state with maximal energy by Metropolis algorithm. This state is used to estimate the imaged object. The performance of the proposed algorithm and local and global thresholding methods are compared.
Yumak, A.; Boubaker, K.; Petkova, P.; Yahsi, U.
2015-10-01
In is known that short-chain chlorinated paraffins (SCCPs) are highly complex technical mixtures of polychlorinated n-alkanes with single chlorine content. Due to their physical properties (viscosity, flame resistance) they are used in many different applications, such as lubricant additives, metal processing, leather fat-liquoring, plastics softening, PVC plasticizing and flame retardants in paints, adhesives and sealants. SCCPs are studied here in terms of processing-linked molecular structure stability, under Simha and Somcynsky-EOS theory calculations and elements from Simha-Somcynsky-related Lattice Compatibility Theory. Analyses were carried out on 1-chloropropane, 2-chloropropane, 1-chlorobutane, 2-chlorobutane, 1-chloro 2-methylane, and 2-chloro 2-methylane as (SCCPs) universal representatives. This paper gives evidence to this stability and reviews the current state of knowledge and highlights the need for further research in order to improve future (SCCPs) monitoring efforts.
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.)
International Nuclear Information System (INIS)
Ishikawa, K.; Schierholz, G.; Teper, M.; Schneider, H.
1982-12-01
We present some techniques for elucidating hadronic structure via lattice Monte Carlo calculations. Applying these techniques, we measure the fluctuations of colour magnetic and electric fields as well as the topological charge density inside and outside the lowest lying 0 + and 2 + glueballs in the SU(2) non-abelian lattice gauge theory. This gives us a detailed picture of the glueball structure. We also obtain, as a by-product, a reliable estimate of the gluon condensate sup(αs)/sub(π) and an estimate of the O - glueball mass which agrees with our previous estimates. (orig.)
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
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.
International Nuclear Information System (INIS)
Reed, D.J.
1977-01-01
Recent theoretical calculations of the properties of rare gases, and in particular helium, in the common f.c.c. and b.c.c. metals, are reviewed from the viewpoint of the investigator concerned with the behaviour of rare gas in such radiation damage processes as surface blistering and void swelling. Particular attention is paid to mechanisms by which helium may migrate in a damaged metal lattice during irradiation and to the properties of small gas and vacancy clusters which may represent bubble or void nuclei. Initially the proposed rapid migration of interstitial helium is discussed together with the substitutional de-trapping mechanism, whereby thermally activated helium jumps from a substitutional to an interstitial position. This enables a mechanism of substitutional helium diffusion to be proposed which may proceed at temperatures below those of self-diffusion. The formation, binding, migration and dissociation energies of gas-vacancy clusters have been reviewed. The relevance of the predicted trend towards the optimum stability of clusters composed of equal numbers of gas atoms and vacancies is discussed. The limited data available concerned with the binding of a helium atom to a pure dislocation line is presented together with comments on the possible nature of the interaction of helium with the dislocation jog. (author)
International Nuclear Information System (INIS)
Jo, Jong Chull; Roh, Kyung Wan; Jhung, Myung Jo
2006-12-01
During this work period, a preliminary research has been conducted in the three different and related areas as stated in the proposal: literature survey, preliminary feasibility study of LBM and FEM coupling for FSI problems, and benchmark problems. As far as the literature review was concerned, approximately one hundred articles were found for the LBM techniques and critical review has been performed. The reviewed articles were classified into several topics that are useful for a subsequent development of the proposed computer program. Those topics included immiscible multicomponent flows, flow with energy transport, coupled multi-physics applications, application of the boundary conditions, irregular lattices, and turbulence. Furthermore, some fundamental review of the LBM was also included in this report. Secondly, a description of the LBM and FEM coupling program, which has been developed so far, was described here along with some demonstration examples. The preliminary study showed a great potential of the proposed technique for FSI application. A sample computer program list is also attached as Appendix A. As a future benchmark study, a set of test cases were proposed so that experimental data would be obtained in the next phase of the study. These data would be beneficial to understand the fundamental physics of the FSI nature under different basic conditions, and also provide benchmark results against which the developed program at a later stage could be validated. Finally, the future research direction as the extension of the present work is provided with emphasis on its goal, as well as merits and benefits resulting from the proposed research for the regulatory evaluation activities of KINS and the associated technical activities of industries such as design, manufacturing, fabrication, operation and maintenance
Rout, Dipak; Kumar, Govind; Vijaya, R.
2018-01-01
A photonic crystal hetero-structure consisting of a passive planar defect of SiO2 thin film sandwiched between two identical opals grown by inward growing self-assembly method using Rhodamine-B dye-doped polystyrene microspheres is studied for the characteristics of dye emission. The optical properties and the defect mode characteristics of the hetero-structure are studied from the reflection and transmission measurements. Laser-induced fluorescence from the hetero-structure showed amplified and spectrally narrowed emission compared to the photonic crystal emphasizing the role of the defect mode and distributed feedback. The enhanced emission is also complemented by the reduction in fluorescence decay time in the case of the hetero-structure in comparison to the 3D photonic crystals.
Structural and defects induced phenomena in γ-rays irradiated 6H-SiC
International Nuclear Information System (INIS)
Sibuyi, P.; Ngom, B.D.; Kotsedi, L.
2016-01-01
Damages and/or defects induced by γ-rays irradiation on 6H-SiC single crystals in channeled configuration towards 〈006〉/〈0012〉 crystallographic directions are reported in the range of 0–1200 kGy. Atomic force microscopy, X-rays diffraction, Raman and photoluminescence investigations were used to obtain a comprehensive set of informations on the nature and population distribution of the induced defects. Primarily, there was no carbon clusterization upon γ-rays irradiation and hence no formation of others SiC polytypes. In contrast, the γ-rays irradiation has induced an increase of the surface roughness at higher doses, which indicates a structural degradation. Larger doses induced an emergence of deeper shallow traps at energies greater than 350 meV below the bandgap. - Highlights: • No formation of others SiC polytypes. • The gamma rays irradiation has induced a slight surface amorphization. • A re-crystallization at lower and higher doses is noticed. • Larger doses induced a substantial internal stress.
Reliability implications of defects in high temperature annealed Si/SiO2/Si structures
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Warren, W.L.; Fleetwood, D.M.; Shaneyfelt, M.R.; Winokur, P.S.; Devine, R.A.B.; Mathiot, D.; Wilson, I.H.; Xu, J.B.
1994-01-01
High-temperature post-oxidation annealing of poly-Si/SiO 2 /Si structures such as metal-oxide-semiconductor capacitors and metal-oxide-semiconductor field effect transistors is known to result in enhanced radiation sensitivity, increased 1/f noise, and low field breakdown. The authors have studied the origins of these effects from a spectroscopic standpoint using electron paramagnetic resonance (EPR) and atomic force microscopy. One result of high temperature annealing is the generation of three types of paramagnetic defect centers, two of which are associated with the oxide close to the Si/SiO 2 interface (oxygen-vacancy centers) and the third with the bulk Si substrate (oxygen-related donors). In all three cases, the origin of the defects may be attributed to out-diffusion of O from the SiO 2 network into the Si substrate with associated reduction of the oxide. The authors present a straightforward model for the interfacial region which assumes the driving force for O out-diffusion is the chemical potential difference of the O in the two phases (SiO 2 and the Si substrate). Experimental evidence is provided to show that enhanced hole trapping and interface-trap and border-trap generation in irradiated high-temperature annealed Si/SiO 2 /Si systems are all related either directly, or indirectly, to the presence of oxygen vacancies
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....
Ab-initio study of magnetism behavior in TiO{sub 2} semiconductor with structural defects
Energy Technology Data Exchange (ETDEWEB)
Zarhri, Z., E-mail: z.zarhri@gmail.com; Houmad, M.; Ziat, Y.; El Rhazouani, O.; Slassi, A.; Benyoussef, A.; El Kenz, A.
2016-05-15
Magnetic, electronic and structural properties of titanium dioxide material with different structural defects are studied using the first-principles ab-initio calculations and the Korringa–Kohn–Rostoker method (KKR) combined with the coherent potential approximation (CPA) method in connection with the local density approximation (LDA). We investigated all structural defects in rutile TiO{sub 2} such as Titanium interstitial (Ti{sub i}), Titanium anti-sites (Ti{sub o}), Titanium vacancies (V{sub Ti}), Oxygen interstitial (O{sub i}), Oxygen anti-sites (O{sub Ti}) and oxygen vacancies (V{sub o}). Mechanisms of hybridization and interaction between magnetic atoms are investigated. The transition temperature is computed using the Mean Field Approximation (MFA).Magnetic stability energy of ferromagnetic and disordered local moment states is calculated to determine the most stable state. Titanium anti-sites have a half-metallic aspect. We also studied the change type caused by structural defects in this material. - Highlights: • Green function technique is used to study disordered systems. • We used DFT to study electronic structure of TiO{sub 2} perturbed by defects. • TiO{sub 2} with titanium antisite defect posesses a magnetic behavior. • The transition temperature is computed using the Mean Field Approximation.
Dumoulin, Jean
2013-04-01
Infrared thermography for Non Destructive Testing (NDT) has encountered a wide spreading this last 2 decades, in particular thanks to emergence on the market of low cost uncooled infrared camera. So, infrared thermography is not anymore a measurement technique limited to laboratory application. It has been more and more involved in civil engineering and cultural heritage applications, but also in many other domains, as indicated by numerous papers in the literature. Nevertheless, laboratory, measurements are done as much as possible in quite ideal conditions (good atmosphere conditions, known properties of materials, etc.), while measurement on real site requires to consider the influence of not controlled environmental parameters and additional unknown thermal properties. So, dedicated protocol and additional sensors are required for measurement data correction. Furthermore, thermal excitation is required to enhance the signature of defects in materials. Post-processing of data requires to take into account the protocol used for the thermal excitation and sometimes its nature to avoid false detection. This analysis step is based on signal and image processing tool and allows to carry out the detection. Characterization of anomalies detected at the previous step can be done by additional signal processing in particular for manufactured objects. The use of thermal modelling and inverse method allows to determine properties of the defective area. The present paper will first address a review of some protocols currently in use for field measurement with passive and/or active infrared measurements. Illustrations in various experiments carried out on civil engineering structure will be shown and discussed. In a second part, different post-processing approaches will be presented and discussed. In particular, a review of the most standard processing methods like Fast Fourier Analysis, Principal Components Analysis, Polynomial Decomposition, defect characterization using
Atomic structure of defects in GaN:Mg grown with Ga polarity
International Nuclear Information System (INIS)
Liliental-Weber, Z.; Tomaszewicz, T.; Zakharov, D.; Jasinski, J.; O'Keefe, M.A.; Hautakangas, S.; Laakso, A.; Saarinen, K.
2003-01-01
Electron microscope phase images, produced by direct reconstruction of the scattered electron wave from a focal series of high-resolution images, were used to determine the nature of defects formed in GaN:Mg crystals. We studied bulk crystals grown from dilute solutions of atomic nitrogen in liquid gallium at high pressure and thin films grown by the MOCVD method. All the crystals were grown with Ga-polarity. In both types of samples the majority of defects were three dimensional Mg-rich hexagonal pyramids with bases on the (0001) plane and six walls on {11(und 2)3} planes seen in cross-section as triangulars. Some other defects appear in cross-section as trapezoidal (rectangular) defects as a result of presence of truncated pyramids. Both type of defects have hollow centers. They are decorated by Mg on all six side walls and a base. The GaN which grows inside on the defect walls shows polarity inversion. It is shown that change of polarity starts from the defect tip and propagates to the base, and that the stacking sequence changes from ab in the matrix to bc inside the defect. Exchange of the Ga sublattice with the N sublattice within the defect leads to 0.6 ± 0.2(angstrom) displacement between Ga sublattices outside and inside the defects. It is proposed that lateral overgrowth of the cavities formed within the defect takes place to restore matrix polarity on the defect base
Phase-structure of SU(3) lattice gauge-higgs model
International Nuclear Information System (INIS)
Gerdt, V.P.; Mitrjushkin, V.K.; Zadorozhny, A.M.
1985-01-01
Phase structure is investigated of SU(3) symmetric gauge-Higgs theory with a defrost radial mode. The Higgs fields are considered in the fundamental representation of SU(3) group. It is shown that the phase structures of SU(3) and SU(2) symmetric coincide qualitatively
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
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.
Numerical tools for the study of defect dynamics in quasiperiodic structures
International Nuclear Information System (INIS)
Barak, G.; Lifshitz, R.
2004-01-01
Full Text:We have developed a set of numerical tools for the quantitative study of defect dynamics in quasiperiodic structures, with the intention of addressing in the near future some of the open questions regarding the dynamics of dislocations in quasicrystals. IS'e intend to apply these tools to study dislocation motion in the dynamical equation of Lifshitz and Petrich [1] whose steady-state solutions are quasiperiodic, exhibiting dodecagonal (12-fold) rotational symmetry. Here we demonstrate our ability to inject an arbitrary set of dislocations-parametrized by the homotopy group of the D-torus (here D=4)-and quantitatively follow the positions of these dislocations as the equation evolves in time. We measure dislocation velocities as a function of applied stress and shear, as well as the phonon and phason strains that accompany this motion as the system evolves in time
Elimination of trench defects and V-pits from InGaN/GaN structures
International Nuclear Information System (INIS)
Smalc-Koziorowska, Julita; Grzanka, Ewa; Czernecki, Robert; Schiavon, Dario; Leszczyński, Mike
2015-01-01
The microstructural evolution of InGaN/GaN multiple quantum wells grown by metalorganic chemical vapor phase epitaxy was studied as a function of the growth temperature of the GaN quantum barriers (QBs). We observed the formation of basal stacking faults (BSFs) in GaN QBs grown at low temperature. The presence of BSFs terminated by stacking mismatch boundaries (SMBs) leads to the opening of the structure at the surface into a V-shaped trench loop. This trench may form above an SMB, thereby terminating the BSF, or above a junction between the SMB and a subsequent BSF. Fewer BSFs and thus fewer trench defects were observed in GaN QBs grown at temperatures higher than 830 °C. Further increase in the growth temperature of the GaN QBs led to the suppression of the threading dislocation opening into V-pits
Directory of Open Access Journals (Sweden)
S. S. Karthikeyan
2015-09-01
Full Text Available A compact (0.16 λg x 0.08 λg and wide stop¬band lowpass filter design using open complementary split ring resonator (OCSRR and defected ground structure (DGS is presented in this paper. Low pass filter is con-structed using two cascaded stages of OCSRR. Since the rejection bandwidth of the OCSRR is narrow, tapered dumbbell shaped DGS section is placed under the OCSRR to enhance the bandwidth. The cutoff frequency (fc of the proposed lowpass filter is 1.09 GHz. The rejection band¬width of the filter covers the entire ultra wideband spec¬trum. Hence the spurious passband suppression is achieved up to 10 fc. The designed filter has been fabri¬cated and validated by experimental results
The influence of melt purification and structure defects on mid-infrared light emitting diodes
Krier, A
2003-01-01
Mid-infrared light emitting diodes which exhibit more than 7 mW (pulsed) and 0.35 mW dc output power at 3.3 mu m and at room temperature have been fabricated by liquid phase epitaxy using Pb as a neutral solvent. Using Pb solution an increase in pulsed output power of between two and three times was obtained compared with InAs light emitting diodes (LEDs) made using rare-earth gettering. The performance improvements were attributed to a reduction in residual carrier concentration arising from the removal of un-intentional donors and structure defects in the InAs active region material. These LEDs are well matched to the CH sub 4 absorption spectrum and potentially could form the basis of a practical infrared CH sub 4 gas sensor.
A Compact Narrow-Band Bandstop Filter Using Spiral-Shaped Defected Microstrip Structure
Directory of Open Access Journals (Sweden)
J. Wang
2014-04-01
Full Text Available A novel compact narrow-band bandstop filter is implemented by using the proposed spiral-shaped defected microstrip structure (SDMS in this paper. Compared with other DMSs, the presented SDMS exhibits the advantage of compact size and narrow stopband. Meanwhile, an approximate design rule of the SDMS is achieved and the effects of the dimensions on the resonant frequency and 3 dB fractional bandwidth (FBW are analyzed in detail. Both the simulation and measurement results of the fabricated bandstop filter show that it has a 10 dB stopband from 3.4 GHz to 3.6 GHz with more than 45 dB rejection at the center frequency.
Crystal defect studies using x-ray diffuse scattering
International Nuclear Information System (INIS)
Larson, B.C.
1980-01-01
Microscopic lattice defects such as point (single atom) defects, dislocation loops, and solute precipitates are characterized by local electronic density changes at the defect sites and by distortions of the lattice structure surrounding the defects. The effect of these interruptions of the crystal lattice on the scattering of x-rays is considered in this paper, and examples are presented of the use of the diffuse scattering to study the defects. X-ray studies of self-interstitials in electron irradiated aluminum and copper are discussed in terms of the identification of the interstitial configuration. Methods for detecting the onset of point defect aggregation into dislocation loops are considered and new techniques for the determination of separate size distributions for vacancy loops and interstitial loops are presented. Direct comparisons of dislocation loop measurements by x-rays with existing electron microscopy studies of dislocation loops indicate agreement for larger size loops, but x-ray measurements report higher concentrations in the smaller loop range. Methods for distinguishing between loops and three-dimensional precipitates are discussed and possibilities for detailed studies considered. A comparison of dislocation loop size distributions obtained from integral diffuse scattering measurements with those from TEM show a discrepancy in the smaller sizes similar to that described above
Crystal defect studies using x-ray diffuse scattering
Energy Technology Data Exchange (ETDEWEB)
Larson, B.C.
1980-01-01
Microscopic lattice defects such as point (single atom) defects, dislocation loops, and solute precipitates are characterized by local electronic density changes at the defect sites and by distortions of the lattice structure surrounding the defects. The effect of these interruptions of the crystal lattice on the scattering of x-rays is considered in this paper, and examples are presented of the use of the diffuse scattering to study the defects. X-ray studies of self-interstitials in electron irradiated aluminum and copper are discussed in terms of the identification of the interstitial configuration. Methods for detecting the onset of point defect aggregation into dislocation loops are considered and new techniques for the determination of separate size distributions for vacancy loops and interstitial loops are presented. Direct comparisons of dislocation loop measurements by x-rays with existing electron microscopy studies of dislocation loops indicate agreement for larger size loops, but x-ray measurements report higher concentrations in the smaller loop range. Methods for distinguishing between loops and three-dimensional precipitates are discussed and possibilities for detailed studies considered. A comparison of dislocation loop size distributions obtained from integral diffuse scattering measurements with those from TEM show a discrepancy in the smaller sizes similar to that described above.
Ospina, D. A.; Cisternas, E.; Duque, C. A.; Correa, J. D.
2018-03-01
By first principles calculations which include van der Waals interactions, we studied the electronic structure of hexagonal boron-nitride/black-phosphorene heterostructures (hBN/BP). In particular the role of several kind of defects on the electronic properties of black-phosphorene monolayer and hBN/BP heterostructure was analyzed. The defects under consideration were single and double vacancies, as well Stone-Wale type defects, all of them present in the phosphorene layer. In this way, we found that the electronic structure of the hBN/BP is modified according the type of defect that is introduced. As a remarkable feature, our results show occupied states at the Fermi Level introduced by a single vacancy in the energy gap of the hBN/BP heterostructure. Additionally, we performed simulations of scanning tunneling microscopy images. These simulations show that is possible to discriminate the kind of defect even when the black-phosphorene monolayer is part of the heterostructure hBN/BP. Our results may help to discriminate among several kind of defects during experimental characterization of these novel materials.
Analysis of Side-Wall Structure of Grown-in Twin-Type Octahedral Defects in Czochralski Silicon
Ueki, Takemi; Itsumi, Manabu; Takeda, Tadao
1998-04-01
We analyzed the side-wall structure of grown-in octahedral defects in Czochralski silicon standard wafers for large-scale integrated circuits. There are two types of twin octahedral defects: an overlapping type and an adjacent type. In the twin octahedral defects of the overlapping type, a hole is formed in the connection part. The side-wall layer in the hole part is formed continually and is the same thickness as the side-wall layers of both octahedrons. In the twin octahedral defects of the adjacent type, a partition layer is formed in the connection part. Our electron energy-loss spectroscopy analyses identified that the side-wall layer includes SiO2.
International Nuclear Information System (INIS)
Maruno, Ken-ichi; Biondini, Gino
2004-01-01
We present a class of solutions of the two-dimensional Toda lattice equation, its fully discrete analogue and its ultra-discrete limit. These solutions demonstrate the existence of soliton resonance and web-like structure in discrete integrable systems such as differential-difference equations, difference equations and cellular automata (ultra-discrete equations)
Mixing Energy Models in Genetic Algorithms for On-Lattice Protein Structure Prediction
Directory of Open Access Journals (Sweden)
Mahmood A. Rashid
2013-01-01
Full Text Available Protein structure prediction (PSP is computationally a very challenging problem. The challenge largely comes from the fact that the energy function that needs to be minimised in order to obtain the native structure of a given protein is not clearly known. A high resolution 20×20 energy model could better capture the behaviour of the actual energy function than a low resolution energy model such as hydrophobic polar. However, the fine grained details of the high resolution interaction energy matrix are often not very informative for guiding the search. In contrast, a low resolution energy model could effectively bias the search towards certain promising directions. In this paper, we develop a genetic algorithm that mainly uses a high resolution energy model for protein structure evaluation but uses a low resolution HP energy model in focussing the search towards exploring structures that have hydrophobic cores. We experimentally show that this mixing of energy models leads to significant lower energy structures compared to the state-of-the-art results.
Response of Soft Continuous Structures and Topological Defects to a Temperature Gradient.
Kurita, Rei; Mitsui, Shun; Tanaka, Hajime
2017-09-08
Thermophoresis, which is mass transport induced by a temperature gradient, has recently attracted considerable attention as a new way to transport materials. So far the study has been focused on the transport of discrete structures such as colloidal particles, proteins, and polymers in solutions. However, the response of soft continuous structures such as membranes and gels to a temperature gradient has been largely unexplored. Here we study the behavior of a lamellar phase made of stacked surfactant bilayer membranes under a temperature gradient. We find the migration of membranes towards a low-temperature region, causing the increase in the degree of membrane undulation fluctuations towards that direction. This is contrary to our intuition that the fluctuations are weaker at a lower temperature. We show that this can be explained by temperature-gradient-induced migration of membranes under the topological constraint coming from the connectivity of each membrane. We also reveal that the pattern of an edge dislocation array formed in a wedge-shaped cell can be controlled by a temperature gradient. These findings suggest that application of a temperature gradient provides a novel way to control the organization of soft continuous structures such as membranes, gels, and foams, in a manner essentially different from the other types of fields, and to manipulate topological defects.
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