Koneva, N. A., E-mail: koneva@tsuab.ru; Kozlov, E. V. [Tomsk State University of Architecture and Building, 634003, Tomsk, Solyanaya Sq., 2 (Russian Federation)
2016-01-15
Generalization of the results of electron microscopy investigations of the crystal lattice bending-torsion (χ) and the internal stresses (IS) was conducted. The deformed polycrystalline alloys and steels were investigated. The sources of χ and IS origin were established. The regularities of their change with the distance from the sources and the evolution with deformation were revealed. The contribution of IS into the deformation resistance was determined. The nature of formation of two sequences of dislocation substructure transformations during deformation of alloys was established.
Lattice effects in YVO3 single crystal
Marquina, C; Sikora, M; Ibarra, MR; Nugroho, AA; Palstra, TTM
2005-01-01
In this paper we report on the lattice effects in the Mott insulator yttrium orthovanadate (YVO3). Linear thermal expansion and magnetostriction experiments have been performed on a single crystal, in the temperature range from 5 K to room temperature. The YVO3 orders antiferromagnetically at T-N =
Invariant patterns in crystal lattices: Implications for protein folding algorithms
HART,WILLIAM E.; ISTRAIL,SORIN
2000-06-01
Crystal lattices are infinite periodic graphs that occur naturally in a variety of geometries and which are of fundamental importance in polymer science. Discrete models of protein folding use crystal lattices to define the space of protein conformations. Because various crystal lattices provide discretizations of the same physical phenomenon, it is reasonable to expect that there will exist invariants across lattices related to fundamental properties of the protein folding process. This paper considers whether performance-guaranteed approximability is such an invariant for HP lattice models. The authors define a master approximation algorithm that has provable performance guarantees provided that a specific sublattice exists within a given lattice. They describe a broad class of crystal lattices that are approximable, which further suggests that approximability is a general property of HP lattice models.
Coulomb crystals in the harmonic lattice approximation
Baiko, D A; De Witt, H E; Slattery, W L
2000-01-01
The dynamic structure factor ${\\tilde S}({\\bf k},\\omega)$ and the two-particle distribution function $g({\\bf r},t)$ of ions in a Coulomb crystal are obtained in a closed analytic form using the harmonic lattice (HL) approximation which takes into account all processes of multi-phonon excitation and absorption. The static radial two-particle distribution function $g(r)$ is calculated for classical ($T \\gtrsim \\hbar \\omega_p$, where $\\omega_p$ is the ion plasma frequency) and quantum ($T \\ll \\hbar \\omega_p$) body-centered cubic (bcc) crystals. The results for the classical crystal are in a very good agreement with extensive Monte Carlo (MC) calculations at $1.5 \\lesssim r/a calculated for classical and quantum bcc and face-centered cubic crystals, and anharmonic corrections are discussed. The inelastic part of the HL static structure factor $S''(k)$, averaged over orientations of wave-vector {\\bf k}, is shown to contain pronounced singularities at Bragg diffraction positions. The type of the singularities is di...
Stress Wave Propagation in Two-dimensional Buckyball Lattice
Xu, Jun; Zheng, Bowen
2016-11-01
Orderly arrayed granular crystals exhibit extraordinary capability to tune stress wave propagation. Granular system of higher dimension renders many more stress wave patterns, showing its great potential for physical and engineering applications. At nanoscale, one-dimensionally arranged buckyball (C60) system has shown the ability to support solitary wave. In this paper, stress wave behaviors of two-dimensional buckyball (C60) lattice are investigated based on square close packing and hexagonal close packing. We show that the square close packed system supports highly directional Nesterenko solitary waves along initially excited chains and hexagonal close packed system tends to distribute the impulse and dissipates impact exponentially. Results of numerical calculations based on a two-dimensional nonlinear spring model are in a good agreement with the results of molecular dynamics simulations. This work enhances the understanding of wave properties and allows manipulations of nanoscale lattice and novel design of shock mitigation and nanoscale energy harvesting devices.
Photonic band gap of 2D complex lattice photonic crystal
GUAN Chun-ying; YUAN Li-bo
2009-01-01
It is of great significance to present a photonic crystal lattice structure with a wide photonic bandgap. A two-dimension complex lattice photonic crystal is proposed. The photonic crystal is composed of complex lattices with triangular structure, and each single cell is surrounded by six scatterers in an hexagon. The photonic band gaps are calculated based on the plane wave expansion (PWE) method. The results indicate that the photonic crystal has tunable large TM polarization band gap, and a gap-midgap ratio of up to 45.6%.
Shao, Yongliang; Zhang, Lei; Hao, Xiaopeng; Wu, Yongzhong; Dai, Yuanbin; Tian, Yuan; Huo, Qin
2014-08-05
We report a method to obtain the stress of crystalline materials directly from lattice deformation by Hooke's law. The lattice deformation was calculated using the crystallographic orientations obtained from electron backscatter diffraction (EBSD) technology. The stress distribution over a large area was obtained efficiently and accurately using this method. Wurtzite structure gallium nitride (GaN) crystal was used as the example of a hexagonal crystal system. With this method, the stress distribution of a GaN crystal was obtained. Raman spectroscopy was used to verify the stress distribution. The cause of the stress distribution found in the GaN crystal was discussed from theoretical analysis and EBSD data. Other properties related to lattice deformation, such as piezoelectricity, can also be analyzed by this novel approach based on EBSD data.
Enhancement of polymer dye lasers by multifunctional photonic crystal lattice
Christiansen, Mads Brøkner; Xiao, Sanshui; Mortensen, Asger
2009-01-01
The light output of dye doped hybrid polymer band-edge lasers is increased more than 100 times by using a rectangular lattice photonic crystal, which provides both feedback and couples more pump light into the laser.......The light output of dye doped hybrid polymer band-edge lasers is increased more than 100 times by using a rectangular lattice photonic crystal, which provides both feedback and couples more pump light into the laser....
Optical spectra and lattice dynamics of molecular crystals
Zhizhin, GN
1995-01-01
The current volume is a single topic volume on the optical spectra and lattice dynamics of molecular crystals. The book is divided into two parts. Part I covers both the theoretical and experimental investigations of organic crystals. Part II deals with the investigation of the structure, phase transitions and reorientational motion of molecules in organic crystals. In addition appendices are given which provide the parameters for the calculation of the lattice dynamics of molecular crystals, procedures for the calculation of frequency eigenvectors of utilizing computers, and the frequencies and eigenvectors of lattice modes for several organic crystals. Quite a large amount of Russian literature is cited, some of which has previously not been available to scientists in the West.
A novel lattice energy calculation technique for simple inorganic crystals
Kaya, Cemal [Department of Chemistry, Faculty of Science, Cumhuriyet University, 58140 Sivas (Turkey); Kaya, Savaş, E-mail: savaskaya@cumhuriyet.edu.tr [Department of Chemistry, Faculty of Science, Cumhuriyet University, 58140 Sivas (Turkey); Banerjee, Priyabrata [Surface Engineering and Tribology Group, CSIR-Central Mechanical Engineering Research Institute, Mahatma Gandhi Avenue, Durgapur 713209 (India)
2017-01-01
In this pure theoretical study, a hitherto unexplored equation based on Shannon radii of the ions forming that crystal and chemical hardness of any crystal to calculate the lattice energies of simple inorganic ionic crystals has been presented. To prove the credibility of this equation, the results of the equation have been compared with experimental outcome obtained from Born-Fajans-Haber- cycle which is fundamentally enthalpy-based thermochemical cycle and prevalent theoretical approaches proposed for the calculation of lattice energies of ionic compounds. The results obtained and the comparisons made have demonstrated that the new equation is more useful compared to other theoretical approaches and allows to exceptionally accurate calculation of lattice energies of inorganic ionic crystals without doing any complex calculations.
A novel lattice energy calculation technique for simple inorganic crystals
Kaya, Cemal; Kaya, Savaş; Banerjee, Priyabrata
2017-01-01
In this pure theoretical study, a hitherto unexplored equation based on Shannon radii of the ions forming that crystal and chemical hardness of any crystal to calculate the lattice energies of simple inorganic ionic crystals has been presented. To prove the credibility of this equation, the results of the equation have been compared with experimental outcome obtained from Born-Fajans-Haber- cycle which is fundamentally enthalpy-based thermochemical cycle and prevalent theoretical approaches proposed for the calculation of lattice energies of ionic compounds. The results obtained and the comparisons made have demonstrated that the new equation is more useful compared to other theoretical approaches and allows to exceptionally accurate calculation of lattice energies of inorganic ionic crystals without doing any complex calculations.
On the stress-free lattice expansion of porous cordierite
Bruno, Giovanni, E-mail: brunog@corning.com [Corning SAS, CS and S, CETC, F-77210 Avon (France); Efremov, Alexander M. [Corning Inc., Modeling and Simulation, CSC, St Petersburg, 194021 (Russian Federation); Clausen, Bjorn [Los Alamos National Laboratory, LANSCE, Los Alamos, NM 87545 (United States); Balagurov, Anatoly M.; Simkin, Valeriy N. [FLNP, JINR, Dubna, 141980 (Russian Federation); Wheaton, Bryan R.; Webb, James E. [Corning Inc., CS and S, SP, Corning, NY 14830 (United States); Brown, Donald W. [Los Alamos National Laboratory, LANSCE, Los Alamos, NM 87545 (United States)
2010-04-15
An extensive investigation of the lattice expansion (up to 1200 deg. C) of porous synthetic cordierite (obtained by firing a mixture of talc, clay, alumina and silica) was carried out using time-of-flight neutron diffraction at LANSCE, Los Alamos, NM, USA and FNLP, Dubna, Russia. An extruded rod and several powders, with different particle size (dispersity), were studied, with the aim of monitoring the variation of the (lattice) micro-strain as a function of temperature and its influence on the microscopic and macroscopic thermal expansion. Results show a different expansion of the a- and b-axes of the orthorhombic cell (in the rod above 800 deg. C). While the finest powder seems to contract more along the c-axis, thus hinting at the presence of smaller stress, the integral peak width increases as a function of temperature in the intermediate range (300-700 deg. C). This could be explained by the integrity factor modeling in terms of micro-cracking. In polycrystalline cordierite, the model implies tension along the a- and b-axes (positive thermal expansion) accompanied by compression along the c-axis (negative thermal expansion) and a stress release upon cooling, via a thermal micro-cracking mechanism. The calculations of the cordierite macroscopic thermal expansion having as input crystal axial expansions assumed to be stress-free allowed us to conclude that even a fine powder (5 {mu}m particle size) cannot be considered completely stress-free. This conclusion is supported by microstructural observations.
The lattice parameter of highly pure silicon single crystals
Becker, P.; Scyfried, P.; Siegert, H.
1982-08-01
From crystal to crystal comparison, the d 220 lattice spacing in PERFX and WASO silicon crystals used in the only two existing absolute measurements have been found to be equal within ±2×10-7 d 220. This demonstrates that generic variabilities of the two crystals account only for a small part of the 1.8×10-6 d 220 difference in the two absolute measurements. In a new series of 336 single measurements, our d 220 value reported recently has been confirmed within ±2×10-8 d 220. From these results we derive the following lattice parameter for highly pure silicon single crystals: a 0=(543 102.018±0.034) fm (at 22.5°C, in vacuum).
Photonic Crystal Waveguides in Triangular Lattice of Nanopillars
Chigrin, Dmitry N.; Lavrinenko, Andrei
2004-01-01
Photonic nanopillars waveguides have been analysed. Dielectric nanopillars are arranged in such way that they from a tringular lattice of 2D photonic crystal. Dispersion of the modes depends on the direction of the triangular lattice, Ã-J or Ã-X, in which nanopillars arrays are extended. Light....... Transmission spectra calculated by FDTD method completely reflect peculiarities of modes dispersion, showing up to 80% transmission for a realistic SOI nanopillar structure....
Photographic appraisal of crystal lattice growth technique
Kapoor D
2005-01-01
Full Text Available Concept of creating mechanical retention for bonding through crystal growth has been successfully achieved in the present study. By using polyacrylic acid, sulphated with sulphuric acid as etchant, abundant crystal growth was demonstrated. Keeping in view the obvious benefits of crystal growth technique, the present SEM study was aimed to observe and compare the changes brought about by different etching agents (phosphoric acid, polyacrylic acid and polyacrylic acid sulphated and to evaluate their advantages and disadvantages in an attempt to reduce iatrogenic trauma caused due to surface enamel alteration. Control and experimental groups were made of 24 and 30 premolars, respectively, for scanning electron microscopic appraisal of normal unetched and etched enamel surface and fracture site and finished surface evaluation. When compared with conventional phosphoric acid and weaker polyacrylic acid, investigations indicated that crystal growth treatment on enamel surface caused minimal iatrogenic trauma and surface alteration were restored to the original untreated condition to a large extent.
Thermal characterization of nanoscale phononic crystals using supercell lattice dynamics
Davis, Bruce L.; Hussein, Mahmoud I.
2011-12-01
The concept of a phononic crystal can in principle be realized at the nanoscale whenever the conditions for coherent phonon transport exist. Under such conditions, the dispersion characteristics of both the constitutive material lattice (defined by a primitive cell) and the phononic crystal lattice (defined by a supercell) contribute to the value of the thermal conductivity. It is therefore necessary in this emerging class of phononic materials to treat the lattice dynamics at both periodicity levels. Here we demonstrate the utility of using supercell lattice dynamics to investigate the thermal transport behavior of three-dimensional nanoscale phononic crystals formed from silicon and cubic voids of vacuum. The periodicity of the voids follows a simple cubic arrangement with a lattice constant that is around an order of magnitude larger than that of the bulk crystalline silicon primitive cell. We consider an atomic-scale supercell which incorporates all the details of the silicon atomic locations and the void geometry. For this supercell, we compute the phonon band structure and subsequently predict the thermal conductivity following the Callaway-Holland model. Our findings dictate that for an analysis based on supercell lattice dynamics to be representative of the properties of the underlying lattice model, a minimum supercell size is needed along with a minimum wave vector sampling resolution. Below these minimum values, a thermal conductivity prediction of a bulk material based on a supercell will not adequately recover the value obtained based on a primitive cell. Furthermore, our results show that for the relatively small voids and void spacings we consider (where boundary scattering is dominant), dispersion at the phononic crystal unit cell level plays a noticeable role in determining the thermal conductivity.
Thermal characterization of nanoscale phononic crystals using supercell lattice dynamics
Bruce L. Davis
2011-12-01
Full Text Available The concept of a phononic crystal can in principle be realized at the nanoscale whenever the conditions for coherent phonon transport exist. Under such conditions, the dispersion characteristics of both the constitutive material lattice (defined by a primitive cell and the phononic crystal lattice (defined by a supercell contribute to the value of the thermal conductivity. It is therefore necessary in this emerging class of phononic materials to treat the lattice dynamics at both periodicity levels. Here we demonstrate the utility of using supercell lattice dynamics to investigate the thermal transport behavior of three-dimensional nanoscale phononic crystals formed from silicon and cubic voids of vacuum. The periodicity of the voids follows a simple cubic arrangement with a lattice constant that is around an order of magnitude larger than that of the bulk crystalline silicon primitive cell. We consider an atomic-scale supercell which incorporates all the details of the silicon atomic locations and the void geometry. For this supercell, we compute the phonon band structure and subsequently predict the thermal conductivity following the Callaway-Holland model. Our findings dictate that for an analysis based on supercell lattice dynamics to be representative of the properties of the underlying lattice model, a minimum supercell size is needed along with a minimum wave vector sampling resolution. Below these minimum values, a thermal conductivity prediction of a bulk material based on a supercell will not adequately recover the value obtained based on a primitive cell. Furthermore, our results show that for the relatively small voids and void spacings we consider (where boundary scattering is dominant, dispersion at the phononic crystal unit cell level plays a noticeable role in determining the thermal conductivity.
Thermodynamic properties of the magnetized Coulomb crystal lattices
Kozhberov, A. A.
2016-08-01
It is thought that Coulomb crystals of ions with hexagonal close-packed lattice may form in the crust of strongly-magnetized neutron stars (magnetars). In this work we are trying to verify this prediction assuming that the direction of the magnetic field corresponds to the minimum of the zero-point energy. We also continue a detailed study of vibration modes and thermodynamic properties of magnetized Coulomb crystals in a wide range of temperatures and magnetic fields. It is demonstrated that the total Helmholtz free energy of the body-centered cubic Coulomb crystal is always lower than that of the Coulomb crystal with hexagonal close-packed or face-centered cubic lattice, which casts doubt on the hypothesis above.
Phonon-enhanced crystal growth and lattice healing
Buonassisi, Anthony; Bertoni, Mariana; Newman, Bonna
2013-05-28
A system for modifying dislocation distributions in semiconductor materials is provided. The system includes one or more vibrational sources for producing at least one excitation of vibrational mode having phonon frequencies so as to enhance dislocation motion through a crystal lattice.
Reversible Nanoparticle Cubic Lattices in Blue Phase Liquid Crystals.
Gharbi, Mohamed Amine; Manet, Sabine; Lhermitte, Julien; Brown, Sarah; Milette, Jonathan; Toader, Violeta; Sutton, Mark; Reven, Linda
2016-03-22
Blue phases (BPs), a distinct class of liquid crystals (LCs) with 3D periodic ordering of double twist cylinders involving orthogonal helical director twists, have been theoretically studied as potential templates for tunable colloidal crystals. Here, we report the spontaneous formation of thermally reversible, cubic crystal nanoparticle (NP) assemblies in BPs. Gold NPs, functionalized to be highly miscible in cyanobiphenyl-based LCs, were dispersed in BP mixtures and characterized by polarized optical microscopy and synchrotron small-angle X-ray scattering (SAXS). The NPs assemble by selectively migrating to periodic strong trapping sites in the BP disclination lines. The NP lattice, remarkably robust given the small particle size (4.5 nm diameter), is commensurate with that of the BP matrix. At the BP I to BP II phase transition, the NP lattice reversibly switches between two different cubic structures. The simultaneous presence of two different symmetries in a single material presents an interesting opportunity to develop novel dynamic optical materials.
Elcoro, Luis; Etxebarria, Jesus
2011-01-01
The requirement of rotational invariance for lattice potential energies is investigated. Starting from this condition, it is shown that the Cauchy relations for the elastic constants are fulfilled if the lattice potential is built from pair interactions or when the first-neighbour approximation is adopted. This is seldom recognized in widely used…
Cubic to tetragonal crystal lattice reconstruction during ordering or decomposition
Cheong, Byung-kl [Carnegie-Mellon Univ., Pittsburgh, PA (United States). Dept. of Materials Science and Engineering
1992-09-01
This thesis studied thermodynamic stability and morphology of product phases in diffusional phase transformations involving cubic-to-tetragonal crystal lattice reconstructions. Two different kinds of diffusional transformations were examined: L1{sub 0} ordering (fcc to fct lattice change) and decomposition of off-stoichiometric B2 ordering alloys accompanying bcc to fcc Bain transformation. In the first case, Fe-45 at.% Pd alloys were studied by TEM; in the second, the Bain strain relaxation during decomposition of hyper-eutectoid Cu-9.04 wt% Be alloy was studied. CuAu and InMg were also studied.
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.
Molecular dynamics simulation of triclinic lysozyme in a crystal lattice.
Janowski, Pawel A; Liu, Chunmei; Deckman, Jason; Case, David A
2016-01-01
Molecular dynamics simulations of crystals can enlighten interpretation of experimental X-ray crystallography data and elucidate structural dynamics and heterogeneity in biomolecular crystals. Furthermore, because of the direct comparison against experimental data, they can inform assessment of molecular dynamics methods and force fields. We present microsecond scale results for triclinic hen egg-white lysozyme in a supercell consisting of 12 independent unit cells using four contemporary force fields (Amber ff99SB, ff14ipq, ff14SB, and CHARMM 36) in crystalline and solvated states (for ff14SB only). We find the crystal simulations consistent across multiple runs of the same force field and robust to various solvent equilibration schemes. However, convergence is slow compared with solvent simulations. All the tested force fields reproduce experimental structural and dynamic properties well, but Amber ff14SB maintains structure and reproduces fluctuations closest to the experimental model: its average backbone structure differs from the deposited structure by 0.37Å; by contrast, the average backbone structure in solution differs from the deposited by 0.65Å. All the simulations are affected by a small progressive deterioration of the crystal lattice, presumably due to imperfect modeling of hydrogen bonding and other crystal contact interactions; this artifact is smallest in ff14SB, with average lattice positions deviating by 0.20Å from ideal. Side-chain disorder is surprisingly low with fewer than 30% of the nonglycine or alanine residues exhibiting significantly populated alternate rotamers. Our results provide helpful insight into the methodology of biomolecular crystal simulations and indicate directions for future work to obtain more accurate energy models for molecular dynamics.
Aqueous solubility prediction: do crystal lattice interactions help?
Salahinejad, Maryam; Le, Tu C; Winkler, David A
2013-07-01
Aqueous solubility is a very important physical property of small molecule drugs and drug candidates but also one of the most difficult to predict accurately. Aqueous solubility plays a major role in drug delivery and pharmacokinetics. It is believed that crystal lattice interactions are important in solubility and that including them in solubility models should improve the accuracy of the models. We used calculated values for lattice energy and sublimation enthalpy of organic molecules as descriptors to determine whether these would improve the accuracy of the aqueous solubility models. Multiple linear regression employing an expectation maximization algorithm and a sparse prior (MLREM) method and a nonlinear Bayesian regularized artificial neural network with a Laplacian prior (BRANNLP) were used to derive optimal predictive models of aqueous solubility of a large and highly diverse data set of 4558 organic compounds over a normal ambient temperature range of 20-30 °C (293-303 K). A randomly selected test set and compounds from a solubility challenge were used to estimate the predictive ability of the models. The BRANNLP method showed the best statistical results with squared correlation coefficients of 0.90 and standard errors of 0.645-0.665 log(S) for training and test sets. Surprisingly, including descriptors that captured crystal lattice interactions did not significantly improve the quality of these aqueous solubility models.
Perlovich, German L; Kurkov, Sergey V; Hansen, Lars Kr; Bauer-Brandl, Annette
2004-03-01
Thermodynamic differences between ibuprofen (IBP) racemate and the (+)-enantiomer were studied by X-ray diffraction, thermoanalysis, and crystal energy calculations. The thermodynamic functions of sublimation (as a measure of crystal lattice energy) were obtained by the transpiration method. The sublimation enthalpies (DeltaH(sub)) of (+/-)-IBP and (+)-IBP are 115.8 +/- 0.6 and 107.4 +/- 0.5 kJ. mol(-1), respectively. Using the temperature dependency of the saturated vapor pressure, the relative fractions of enthalpy and entropy of the sublimation process were calculated, and the sublimation process for both the racemate and the enantiomer was found to be enthalpy driven (62%). Two different force fields, Mayo et al. (M) and Gavezzotti (G), were used for comparative analysis of crystal lattice energies. Both force fields revealed that the van der Waals term contributes more to the packing energy in (+)-IBP than in (+/-)-IBP. The hydrogen bonding energy, however, contributes at 29.7 and 32.3% to the total crystal lattice energy in (+)-IBP and (+/-)-IBP (M), respectively. Furthermore, different structure fragments of the IBP molecule were analyzed with respect to their contribution to nonbonded van der Waals interactions. The effect of the C-H distance on the van der Waals term of the crystal lattice energy was also studied.
Large-lattice-parameter perovskite single-crystal substrates
Uecker, Reinhard; Bertram, Rainer; Brützam, Mario; Galazka, Zbigniew; Gesing, Thorsten M.; Guguschev, Christo; Klimm, Detlef; Klupsch, Michael; Kwasniewski, Albert; Schlom, Darrell G.
2017-01-01
The pseudobinary system LaLuO3-LaScO3 was explored in hopes of discovering new perovskite-type substrates with pseudocubic lattice parameters above 4 Å. A complete solid solution of the type (LaLuO3)1-x(LaScO3)x forms between the end members LaLuO3 and LaScO3, enabling large single crystals of (LaLuO3)1-x(LaScO3)x to be grown from the melt. A single crystal with x≈0.34 was demonstrated. Considering the maximum thermal load of the iridium crucibles appropriate for Czochralski growth of this solid solution, the theoretically maximum achievable x-value is 0.67. Based on the phase diagram determined, it is anticipated that single crystals with pseudocubic lattice constants between 4.09 and 4.18 Å can be grown in this system by the Czochralski method.
Molecular modeling study of chiral drug crystals: lattice energy calculations.
Li, Z J; Ojala, W H; Grant, D J
2001-10-01
The lattice energies of a number of chiral drugs with known crystal structures were calculated using Dreiding II force field. The lattice energies, including van der Waals, Coulombic, and hydrogen-bonding energies, of homochiral and racemic crystals of some ephedrine derivatives and of several other chiral drugs, are compared. The calculated energies are correlated with experimental data to probe the underlying intermolecular forces responsible for the formation of racemic species, racemic conglomerates, or racemic compounds, termed chiral discrimination. Comparison of the calculated energies among ephedrine derivatives reveals that a greater Coulombic energy corresponds to a higher melting temperature, while a greater van der Waals energy corresponds to a larger enthalpy of fusion. For seven pairs of homochiral and racemic compounds, correlation of the differences between the two forms in the calculated energies and experimental enthalpy of fusion suggests that the van der Waals interactions play a key role in the chiral discrimination in the crystalline state. For salts of the chiral drugs, the counter ions diminish chiral discrimination by increasing the Coulombic interactions. This result may explain why salt forms favor the formation of racemic conglomerates, thereby facilitating the resolution of racemates.
Chaotic phenomena of charged particles in crystal lattices.
Desalvo, Agostino; Giannerini, Simone; Rosa, Rodolfo
2006-06-01
In this article, we have applied the methods of chaos theory to channeling phenomena of positive charged particles in crystal lattices. In particular, we studied the transition between two ordered types of motion; i.e., motion parallel to a crystal axis (axial channeling) and to a crystal plane (planar channeling), respectively. The transition between these two regimes turns out to occur through an angular range in which the particle motion is highly disordered and the region of phase space spanned by the particle is much larger than the one swept in the two ordered motions. We have evaluated the maximum Lyapunov exponent with the method put forward by Rosenstein et al. [Physica D 65, 117 (1993)] and by Kantz [Phys. Lett. A 185, 77 (1994)]. Moreover, we estimated the correlation dimension by using the Grassberger-Procaccia method. We found that at the transition the system exhibits a very complex behavior showing an exponential divergence of the trajectories corresponding to a positive Lyapunov exponent and a noninteger value of the correlation dimension. These results turn out to be linked to a physical interpretation. The Lyapunov exponents are in agreement with the model by Akhiezer et al. [Phys. Rep. 203, 289 (1991)], based on the equivalence between the ion motion along the crystal plane described as a "string of strings" and the "kicked" rotator. The nonintegral value of the correlation dimension can be explained by the nonconservation of transverse energy at the transition.
Crystal lattice optimization and new forms of silicon
Stucke, David P.
In Chapter 1 a basic outline of the two main methods used in this thesis is given. A genetic algorithm optimization method based on the concept of natural selection is given. The important factors to consider in creating an effective genetic algorithm search are described. I then give a brief overview of Density Functional Theory (DFT) which is the technique most commonly used to do ab-inito calculations on solid-state systems. The basis for its formulation along with how it is applied to a practical system with some approximations is discussed. In Chapter 2 a description of a genetic search algorithm for optimizing the crystal structure of an infinite crystal is given. This method is applied to a system of colloidal spheres, where the packing density is the figure of merit for structure selection. Our examination of self-assembled multi-component crystals of nanoparticles predicts several new structures with stoichiometries of AB (fused spheres), ABC2, ABC 3, ABC4 and AB2 C2. These new structures have hierarchical layered or linear arrangements that could be useful for functional self-assembled systems. For example, the fused-sphere binary crystal assembles with zig-zag rows of parallel nanowires. The genetic search suceeds while a comparable stochastic algorithm fails to find any structures better than the well-known unary or binary phase-separated systems. Here we describe the algorithm and the results it produces: several new classes of binary and ternary crystals of spherical nanoparticles, including a family of layered perovskite-like systems and an unusual three-dimensional array of parallel zig-zag nanowires. In Chapter 3, We discuss the possibility of constructing new forms of silicon by building in multiple bonds consistent with molecules that have been produced experimentally. We find a dilated diamond crystal lattice containing a silicon-silicon triple bond that is metastable. This structure has very soft vibrational modes that are common in similar
Jie Zha; Zhi-Yong Zhong; Huai-Wu Zhang; Qi-Ye Wen; Yuan-Xun Li
2009-01-01
Band gap characteristics of the photonic crystals in terahertz range with square lattice and triangular lattice of GaAs cylinders are comparatively studied by means of plane wave method (PWM). The influence of the radius on the band gap width is analyzed and the critical values where the band gap appears are put forward. The results show that themaximum band gap width of photonic crystal with triangular lattice of GaAs cylinders is much wider than that of photonic crystal with square lattice. The research provides a theoretic basis for the development of terahertz (THz) devices.
Compact triplexer in two-dimensional hexagonal lattice photonic crystals
Hongliang Ren; Jianping Ma; Hao Wen; Yali Qin; Zhefu Wu; Weisheng Hu; Chun Jiang; Yaohui Jin
2011-01-01
We design a contpact triplexer based on two-dimensional (2D) hexagonal lattice photonic crystals (PCs). A folded directional coupler (FDC) is introduced in the triplexer beside the point-defect micro-cavities and line-defect waveguides. Because of the reflection feedback of the FDC, high channel drop efficiency can be realized and a compact size with the order of micrometers can be maintained. The proposed device is analyzed using the plane wave expansion method, and its transmission characteristics are calculated using the finites-difference time-domain method. The footprint of the triplexer is about 12× 9 μm, and its extinction ratios are less than -20 dB for 1310 nm, approximately -20 dB for 1490 nm, and under -4O dB for 1550 nm, making it a potentially essential device ii future fiber-to-the-home networks.%@@ We design a compact triplexer based on two-dimensional (2D) hexagonal lattice photonic crystals (PCs).A folded directional coupler (FDC) is introduced in the triplexer beside the point-defect micro-cavities and line-defect waveguides.Because of the reflection feedback of the FDC, high channel drop efficiency can be realized and a compact size with the order of micrometers can be maintained.The proposed device is analyzed using the plane wave expansion method, and its transmission characteristics are calculated using the finite-difference time-domain method.The footprint of the triplexer is about 12×9 μm, and its extinction ratios are less than -20 dB for 1310 nm, approximately -20 dB for 1490 nm, and under -40 dB for 1550 nm, making it a potentially essential device in future fiber-to-the-home networks.
Photonic band structures of two-dimensional photonic crystals with deformed lattices
Cai Xiang-Hua; Zheng Wan-Hua; Ma Xiao-Tao; Ren Gang; Xia Jian-Bai
2005-01-01
Using the plane-wave expansion method, we have calculated and analysed the changes of photonic band structures arising from two kinds of deformed lattices, including the stretching and shrinking of lattices. The square lattice with square air holes and the triangular lattice with circular air holes are both studied. Calculated results show that the change of lattice size in some special ranges can enlarge the band gap, which depends strongly on the filling factor of air holes in photonic crystals; and besides, the asymmetric band edges will appear with the broken symmetry of lattices.
Optical trapping via guided resonance modes in a Slot-Suzuki-phase photonic crystal lattice.
Ma, Jing; Martínez, Luis Javier; Povinelli, Michelle L
2012-03-12
A novel photonic crystal lattice is proposed for trapping a two-dimensional array of particles. The lattice is created by introducing a rectangular slot in each unit cell of the Suzuki-Phase lattice to enhance the light confinement of guided resonance modes. Large quality factors on the order of 10⁵ are predicted in the lattice. A significant decrease of the optical power required for optical trapping can be achieved compared to our previous design.
Three-sublattice skyrmion crystal in the antiferromagnetic triangular lattice
Rosales, H. D.; Cabra, D. C.; Pujol, Pierre
2015-12-01
The frustrated classical antiferromagnetic Heisenberg model with Dzyaloshinskii-Moriya (DM) interactions on the triangular lattice is studied under a magnetic field by means of semiclassical calculations and large-scale Monte Carlo simulations. We show that even a small DM interaction induces the formation of an antiferromagnetic skyrmion crystal (AF-SkX) state. Unlike what is observed in ferromagnetic materials, we show that the AF-SkX state consists of three interpenetrating skyrmion crystals (one by sublattice), and most importantly, the AF-SkX state seems to survive in the limit of zero temperature. To characterize the phase diagram we compute the average of the topological order parameter which can be associated with the number of topological charges or skyrmions. As the magnetic field increases this parameter presents a clear jump, indicating a discontinuous transition from a spiral phase into the AF-SkX phase, where multiple Bragg peaks coexist in the spin structure factor. For higher fields, a second (probably continuous) transition occurs into a featureless paramagnetic phase.
Levitas, Valery I.; Chen, Hao; Xiong, Liming
2017-08-01
A continuum/atomistic approach for predicting lattice instability during crystal-crystal phase transformations (PTs) is developed for the general loading with an arbitrary stress tensor and large strains. It is based on a synergistic combination of the generalized Landau-type theory for PTs and molecular dynamics (MD) simulations. The continuum approach describes the entire dissipative transformation process in terms of an order parameter, and the general form of the instability criterion is derived utilizing the second law of thermodynamics. The feedback from MD allowed us to present the instability criterion for both direct and reverse PTs in terms of the critical value of the modified transformation work, which is linear in components of the true stress tensor. It was calibrated by MD simulations for direct and reverse PTs between semiconducting silicon Si i and metallic Si ii phases under just two different stress states. Then, it describes hundreds of MD simulations under various combinations of three normal and three shear stresses. In particular, the atomistic simulations show that the effects of all three shear stresses along cubic axes on lattice instability of Si i are negligible, which is in agreement with our criterion.
Quadrupole lattice resonances in plasmonic crystal excited by cylindrical vector beams
Sakai, Kyosuke; Nomura, Kensuke; Yamamoto, Takeaki; Omura, Tatsuya; Sasaki, Keiji
2016-10-01
We report a scheme to exploit low radiative loss plasmonic resonance by combining a dark (subradiant) mode and a lattice resonance. We theoretically demonstrate that such dark-mode lattice resonances in periodic arrays of nanodisks or plasmonic crystals can be excited by vertically incident light beams. We investigate the excitation of lattice resonances in a finite sized, square-lattice plasmonic crystal by two types of cylindrical vector beams and a linearly polarized Gaussian beam. Quadrupole lattice resonances are excited by all three beams, and the largest peak intensity is obtained by using a specific type of cylindrical vector beam. Because of their lower radiative losses with many hotspots, the quadrupole lattice resonances in plasmonic crystal may pave the way for photonic research and applications that require strong light-matter interactions.
A new approach for modelling lattice energy in finite crystal domains
Bilotsky, Y.; Gasik, M.
2015-09-01
Evaluation of internal energy in a crystal lattice requires precise calculation of lattice sums. Such evaluation is a problem in the case of small (nano) particles because the traditional methods are usually effective only for infinite lattices and are adapted to certain specific potentials. In this work, a new method has been developed for calculation of lattice energy. The method is a generalisation of conventional geometric probability techniques for arbitrary fixed lattices in a finite crystal domain. In our model, the lattice energy for wide range of two- body central interaction potentials (including long-range Coulomb potential) has been constructed using absolutely convergent sums. No artificial cut-off potential or periodical extension of the domain (which usually involved for such calculations) have been made for calculation of the lattice energy under this approach. To exemplify the applications of these techniques, the energy of Coulomb potential has been plotted as the function of the domain size.
Highly cooperative stress relaxation in two-dimensional soft colloidal crystals
Van Der Meer, Berend; Qi, Weikai; Fokkink, Remco G.; Van Der Gucht, Jasper; Dijkstra, Marjolein; Sprakel, Joris
2014-01-01
Stress relaxation in crystalline solids is mediated by the formation and diffusion of defects. Although it iswell established how externally generated stresses relax, through the proliferation and motion of dislocations in the lattice, it remains relatively unknown how crystals cope with internal st
Highly cooperative stress relaxation in two-dimensional soft colloidal crystals
Meer, van der B.; Qi, Weikai; Fokkink, R.G.; Gucht, van der J.; Dijkstra, M.; Sprakel, J.H.B.
2014-01-01
Stress relaxation in crystalline solids is mediated by the formation and diffusion of defects. Although it is well established how externally generated stresses relax, through the proliferation and motion of dislocations in the lattice, it remains relatively unknown how crystals cope with internal s
Kalyoncu, Sibel; Hyun, Jeongmin; Pai, Jennifer C; Johnson, Jennifer L; Entzminger, Kevin; Jain, Avni; Heaner, David P; Morales, Ivan A; Truskett, Thomas M; Maynard, Jennifer A; Lieberman, Raquel L
2014-09-01
Protein crystallization is dependent upon, and sensitive to, the intermolecular contacts that assist in ordering proteins into a three-dimensional lattice. Here we used protein engineering and mutagenesis to affect the crystallization of single chain antibody fragments (scFvs) that recognize the EE epitope (EYMPME) with high affinity. These hypercrystallizable scFvs are under development to assist difficult proteins, such as membrane proteins, in forming crystals, by acting as crystallization chaperones. Guided by analyses of intermolecular crystal lattice contacts, two second-generation anti-EE scFvs were produced, which bind to proteins with installed EE tags. Surprisingly, although noncomplementarity determining region (CDR) lattice residues from the parent scFv framework remained unchanged through the processes of protein engineering and rational design, crystal lattices of the derivative scFvs differ. Comparison of energy calculations and the experimentally-determined lattice interactions for this basis set provides insight into the complexity of the forces driving crystal lattice choice and demonstrates the availability of multiple well-ordered surface features in our scFvs capable of forming versatile crystal contacts.
Beaucage, Timothy R [University of Maine; Beenfeldt, Eric P [University of Maine; Speakman, Scott A [ORNL; Porter, Wallace D [ORNL; Payzant, E Andrew [ORNL; Pereira da Cunha, Mauricio [University of Maine
2006-01-01
Among the langasite family of crystals (LGX), the three most popular materials are langasite (LGS, La3Ga5SiO14), langatate (LGT, La3Ga5.5Ta0.5O14) and langanite (LGN, La3Ga5.5Nb0.5O14). The LGX crystals have received significant attention for acoustic wave (AW) device applications due to several properties, which include: (1) piezoelectric constants about two and a half times those of quartz, thus allowing the design of larger bandwidth filters; (2) existence of temperature compensated orientations; (3) high density, with potential for reduced vibration and acceleration sensitivity; and (4) possibility of operation at high temperatures, since the LGX crystals do not present phase changes up to their melting point above 1400degC. The LGX crystals' capability to operate at elevated temperatures calls for an investigation on the growth quality and the consistency of these materials' properties at high temperature. One of the fundamental crystal properties is the thermal expansion coefficients in the entire temperature range where the material is operational. This work focuses on the measurement of the LGT thermal expansion coefficients from room temperature (25degC) to 1200degC. Two methods of extracting the thermal expansion coefficients have been used and compared: (a) dual push-rod dilatometry, which provides the bulk expansion; and (b) x-ray powder diffraction, which provides the lattice expansion. Both methods were performed over the entire temperature range and considered multiple samples taken from <001> Czochralski grown LGT material. The thermal coefficients of expansion were extracted by approximating each expansion data set to a third order polynomial fit over three temperature ranges reported in this work: 25degC to 400degC, 400degC to 900degC, 900degC to 1200degC. An accuracy of fit better than 35ppm for the bulk expansion and better than 10ppm for the lattice expansion have been obtained with the aforementioned polynomial fitting. The
Wall Orientation and Shear Stress in the Lattice Boltzmann Model
Matyka, Maciej; Mirosław, Łukasz
2013-01-01
The wall shear stress is a quantity of profound importance for clinical diagnosis of artery diseases. The lattice Boltzmann is an easily parallelizable numerical method of solving the flow problems, but it suffers from errors of the velocity field near the boundaries which leads to errors in the wall shear stress and normal vectors computed from the velocity. In this work we present a simple formula to calculate the wall shear stress in the lattice Boltzmann model and propose to compute wall normals, which are necessary to compute the wall shear stress, by taking the weighted mean over boundary facets lying in a vicinity of a wall element. We carry out several tests and observe an increase of accuracy of computed normal vectors over other methods in two and three dimensions. Using the scheme we compute the wall shear stress in an inclined and bent channel fluid flow and show a minor influence of the normal on the numerical error, implying that that the main error arises due to a corrupted velocity field near ...
Descriptors for predicting the lattice constant of body centered cubic crystal
Takahashi, Keisuke; Takahashi, Lauren; Baran, Jakub D.; Tanaka, Yuzuru
2017-05-01
The prediction of the lattice constant of binary body centered cubic crystals is performed in terms of first principle calculations and machine learning. In particular, 1541 binary body centered cubic crystals are calculated using density functional theory. Results from first principle calculations, corresponding information from periodic table, and mathematically tailored data are stored as a dataset. Data mining reveals seven descriptors which are key to determining the lattice constant where the contribution of descriptors is also discussed and visualized. Support vector regression (SVR) technique is implemented to train the data where the predicted lattice constants have the mean score of 83.6% accuracy via cross-validation and maximum error of 4% when compared to experimentally determined lattice constants. In addition, trained SVR is successful in predicting material combinations from a desired lattice constant. Thus, a set of descriptors for determining the lattice constant is identified and can be used as a base descriptor for lattice constants of further complex crystals. This would allow for the acceleration of the search for lattice constants of desired atomic compositions as well as the prediction of new materials based on a specified lattice constant.
Extremely Low Loss THz Guidance Using Kagome Lattice Porous Core Photonic Crystal Fiber
Hossain, Anwar; Hasanuzzaman, G.K.M.; Habib, Selim;
2015-01-01
A novel porous core Kagome lattice photonic crystal fiber is proposed for extremely low loss THz waves guiding. It has been reported that 82.5% of bulk effective material loss of Topas can be reduced......A novel porous core Kagome lattice photonic crystal fiber is proposed for extremely low loss THz waves guiding. It has been reported that 82.5% of bulk effective material loss of Topas can be reduced...
Orientation dependence of the stress rupture properties of Nickel-base superalloy single crystals
Mackay, R. A.
1981-01-01
The influence of orientation of the stress rupture behavior of Mar-M247 single crystals was studied. Stress rupture tests were performed at 724 MPa and 774 C where the effect of anisotropy is prominent. The mechanical behavior of the single crystals was rationalized on the basis of the Schmid factors for the operative slip systems and the lattice rotations which the crystals underwent during deformation. The stress rupture lives were found to be greatly influenced by the lattice rotations required to produce intersecting slip, because steady-state creep does not begin until after the onset of intersecting slip. Crystals which required large rotations to become oriented for intersecting slip exhibited a large primary creep strain, a large effective stress level at the onset of steady-state creep, and consequently a short stress rupture life. A unified analysis was attained for the stress rupture behavior of the Mar-M247 single crystals tested in this study at 774 C and that of the Mar-M200 single crystals tested in a prior study at 760 C. In this analysis, the standard 001-011-111 stereographic triangle was divided into several regions of crystallographic orientation which were rank ordered according to stress rupture life for this temperature regime. This plot indicates that those crystals having orientations within about 25 deg of the 001 exhibited significantly longer lives when their orientations were closer to the 001-011 boundary of the stereographic triangle than to the 001-111 boundary.
Orientation dependence of the stress rupture properties of Nickel-base superalloy single crystals
Mackay, R. A.
1981-05-01
The influence of orientation of the stress rupture behavior of Mar-M247 single crystals was studied. Stress rupture tests were performed at 724 MPa and 774 C where the effect of anisotropy is prominent. The mechanical behavior of the single crystals was rationalized on the basis of the Schmid factors for the operative slip systems and the lattice rotations which the crystals underwent during deformation. The stress rupture lives were found to be greatly influenced by the lattice rotations required to produce intersecting slip, because steady-state creep does not begin until after the onset of intersecting slip. Crystals which required large rotations to become oriented for intersecting slip exhibited a large primary creep strain, a large effective stress level at the onset of steady-state creep, and consequently a short stress rupture life. A unified analysis was attained for the stress rupture behavior of the Mar-M247 single crystals tested in this study at 774 C and that of the Mar-M200 single crystals tested in a prior study at 760 C. In this analysis, the standard 001-011-111 stereographic triangle was divided into several regions of crystallographic orientation which were rank ordered according to stress rupture life for this temperature regime. This plot indicates that those crystals having orientations within about 25 deg of the 001 exhibited significantly longer lives when their orientations were closer to the 001-011 boundary of the stereographic triangle than to the 001-111 boundary.
A stress field in the vortex lattice in the type-II superconductor
Maruszewski, Bogdan
2008-02-01
Full Text Available Magnetic flux can penetrate a type-II superconductor in the form of Abrikosov vortices (also called flux lines, flux tubes, or fluxons, each carrying a quantum of magnetic flux. These tiny vortices of supercurrent tend to arrange themselves in a triangular and/or quadratic flux-line lattice, which is more or less perturbed by material inhomogeneities that pin the flux lines. Pinning is caused by imperfections of the crystal lattice, such as dislocations, point defects, grain boundaries, etc. Hence, a honeycomb-like pattern of the vortex array presents some mechanical properties. If the Lorentz force of interactions between the vortices is much bigger than the pinning force, the vortex lattice behaves elastically. So we assume that the pinning force is negligible in the sequel and we deal with soft vortices. The vortex motion in the vortex lattice and/or creep of the vortices in the vortex fluid is accompanied by energy dissipation. Hence, except for the elastic properties, the vortex field is also of a viscous character. The main aim of the paper is a formulation of a thermoviscoelastic stress - strain constitutive law consisted of coexistence of the ordered and disordered states of the vortex field. Its form describes an auxetic-like thermomechanical (anomalous property of the vortex field.
Direct calculation of the lattice Green function with arbitrary interactions for general crystals.
Yasi, Joseph A; Trinkle, Dallas R
2012-06-01
Efficient computation of lattice defect geometries such as point defects, dislocations, disconnections, grain boundaries, interfaces, and free surfaces requires accurate coupling of displacements near the defect to the long-range elastic strain. Flexible boundary condition methods embed a defect in infinite harmonic bulk through the lattice Green function. We demonstrate an efficient and accurate calculation of the lattice Green function from the force-constant matrix for general crystals with an arbitrary basis by extending a method for Bravais lattices. New terms appear due to the presence of optical modes and the possible loss of inversion symmetry. By separately treating poles and discontinuities in reciprocal space, numerical accuracy is controlled at all distances. We compute the lattice Green function for a two-dimensional model with broken symmetry to elucidate the role of different coupling terms. The algorithm is generally applicable in two and three dimensions to crystals with arbitrary number of atoms in the unit cell, symmetry, and interactions.
Gao, Dingshan; Zhou, Zhiping; Citrin, David S
2008-03-01
The photonic crystal structure with parallelogram lattice, capable of bending a self-collimated wave with free angles and partial bandgap reflection, is presented. The equifrequency contours show that the direction of the collimation wave can be turned by tuning the angle between the two basic vectors of the lattice. Acute, right, and obtuse angles of collimating waveguide bends have been realized by arc lattices of parallelogram photonic crystals. Moreover, partial bandgap reflection of the parallelogram lattice photonic crystals is validated from the equifrequency contours and the projected band structures. A waveguide taper based on this partial bandgap reflection is also designed and proved to have above 85% transmittance over a very wide operating bandwidth of 180 nm.
Mackay, R. A.; Maier, R. D.
1982-01-01
Constant load creep rupture tests were performed on MAR-M247 single crystals at 724 MPa and 774 C where the effect of anisotropy is prominent. The initial orientations of the specimens as well as the final orientations of selected crystals after stress rupture testing were determined by the Laue back-reflection X-ray technique. The stress rupture lives of the MAR-M247 single crystals were found to be largely determined by the lattice rotations required to produce intersecting slip, because second-stage creep does not begin until after the onset of intersecting slip. Crystals which required large rotations to become oriented for intersecting slip exhibited the shortest stress rupture lives, whereas crystals requiring little or no rotations exhibited the lowest minimum creep rates, and consequently, the longest stress rupture lives.
Oxygen plasma etching-induced crystalline lattice transformation of colloidal photonic crystals.
Ding, Tao; Wang, Fei; Song, Kai; Yang, Guoqiang; Tung, Chen-Ho
2010-12-15
This communication describes the transformation of a colloidal crystalline lattice that was realized via oxygen plasma etching of colloidal crystals made of SiO2@PMMA core-shell microspheres. The plasma etching of the colloidal crystals proceeded nonuniformly from the top to the bottom of the colloidal crystals. The PMMA shell was etched away by the oxygen plasma in a layer-by-layer manner, and the silica core was drawn into the pit formed by the neighboring spheres in the layer below. Consequently, the crystalline lattice was transformed while the order was maintained. Scanning electron microscopy images and reflection spectra further confirmed the change in the crystalline structures. Colloidal crystals with sc and bcc lattices can be fabricated if the ratio of the polymer shell thickness to the silica core diameter is equal to certain values. More importantly, this approach may be applicable to the fabrication of various assembly structures with different inorganic particles.
Mackay, Rebecca A.; Maier, Ralph D.
1982-10-01
The influence of orientation on the stress rapture properties of MAR-M247 single crystals was studied. Stress rupture tests were performed at 724 MPa and 774 °C where the effect of anisotropy is prominent. The mechanical behavior of the single crystals was rationalized on the basis of the Schmid factors for the operative slip systems and the lattice rotations which the crystals underwent during deformation. The stress rupture lives at 774 °C were found to be greatly influenced by the lattice rotations required to produce intersecting slip, because second-stage creep does not begin until after the onset of intersecting slip. Crystals which required large rotations to become oriented for intersecting slip exhibited a large primary creep strain, a large effective stress level at the onset of steady-state creep, and consequently, a short stress rupture life. Those crystals having orientations within about 25° of the [001] exhibited significantly longer lives when their orientations were closer to the [001]-[011] boundary of the stereographic triangle than to the [001]-[1l 1] boundary, because they required smaller rotations to produce intersecting slip and the onset of second-stage creep. Thus, the direction off the [001], as well as the number of degrees off the [001], has a major influence on the stress rapture lives of single crystals in this temperature regime.
Two-Dimensional Anharmonic Crystal Lattices: Solitons, Solectrons, and Electric Conduction
Velarde, Manuel G.; Ebeling, Werner; Chetverikov, Alexander P.
2011-01-01
Reported here are salient features of soliton-mediated electron transport in anharmonic crystal lattices.After recalling how an electron-soliton bound state (solectron) can be formed we comment on consequences like electron surfing on a sound wave and balistic transport, possible percolation in 2d lattices, and a novel form of electron pairing with strongly correlated electrons both in real space and momentum space.
Tuning of band gaps for a two-dimensional piezoelectric phononic crystal with a rectangular lattice
Yize Wang; Fengming Li; Yuesheng Wang; Kikuo Kishimoto; Wenhu Huang
2009-01-01
In this paper, the elastic wave propagation in a two-dimensional piezoelectric phononic crystal is studied by considering the mechanic-electric coupling. The gener-alized eigenvalue equation is obtained by the relation of the mechanic and electric fields as well as the Bloch-Floquet the-orem. The band structures of both the in-plane and anti-plane modes are calculated for a rectangular lattice by the plane-wave expansion method. The effects of the lattice constant ratio and the piezoelectricity with different filling fractions are analyzed. The results show that the largest gap width is not always obtained for a square lattice. In some situations, a rectangular lattice may generate larger gaps. The band gap characteristics are influenced obviously by the piezoelectric-ity with the larger lattice constant ratios and the filling frac-tions.
Mao, Albert H; 10.1063/1.4742068
2012-01-01
Accurate models of alkali and halide ions in aqueous solution are necessary for computer simulations of a broad variety of systems. Previous efforts to develop ion force fields have generally focused on reproducing experimental measurements of aqueous solution properties such as hydration free energies and ion-water distribution functions. This dependency limits transferability of the resulting parameters because of the variety and known limitations of water models. We present a solvent-independent approach to calibrating ion parameters based exclusively on crystal lattice properties. Our procedure relies on minimization of lattice sums to calculate lattice energies and interionic distances instead of equilibrium ensemble simulations of dense fluids. The gain in computational efficiency enables simultaneous optimization of all parameters for Li+, Na+, K+, Rb+, Cs+, F-, Cl-, Br-, and I- subject to constraints that enforce consistency with periodic table trends. We demonstrate the method by presenting lattice-d...
V.M. Chernov
2016-12-01
Full Text Available The state of a low-temperature embrittlement (cold brittleness and dislocation mechanisms for formation of the temperature of a ductile-brittle transition and brittle fracture of metals (mono- and polycrystals with various crystal lattices (BCC, FCC, HCP are considered. The conditions for their formation connected with a stress-deformed state and strength (low temperature yield strength as well as the fracture breaking stress and mobility of dislocations in the top of a crack of the fractured metal are determined. These conditions can be met for BCC and some HCP metals in the initial state (without irradiation and after a low-temperature damaging (neutron irradiation. These conditions are not met for FCC and many HCP metals. In the process of the damaging (neutron irradiation such conditions are not met also and the state of low-temperature embrittlement of metals is absent (suppressed due to arising various radiation dynamic processes, which increase the mobility of dislocations and worsen the strength characteristics.
Prokoshkin, S. D.; Korotitskiy, A. V.; Brailovski, V.; Inaekyan, K. E.; Dubinskiy, S. M.
2011-08-01
X-ray diffraction has been used to study shape-memory alloys of composition Ti-(49.73-51.05 at %) Ni subjected to quenching and thermomechanical treatment (TMT) by the scheme "cold deformation ( e = 0.3-1.9) + postdeformation annealing (200-500°C) to provide different defectness of the parent B2 austenite. For the quenched alloys, the concentration dependences of the lattice parameters of the B19' martensite, maximum lattice strain upon martensitic transformation, the crystallographic orientation of the lattice in single crystals, and the reserve of recoverable strain in polycrystals have been determined. The lattice parameters of martensite formed from polygonized, i.e., nanosubgranular, or from nanocrystalline austenite differ from the corresponding parameters of quenched martensite formed from recrystallized austenite, and their difference increases with increasing defectness of the parent-austenite lattice. An increase in the defectness of the austenite lattice is accompanied by a decrease in the reserve of recoverable strain. The deformation of the existing martensite or the formation of stress-assisted martensite under the anisotropic action of external stresses changes the interplanar spacing and the thermal expansion coefficient in different crystallographic directions but does not affect the averaged lattice parameters near the M s- M f interval and the reserve of recoverable strain.
Landa, Michal; Novák, Václav; Sedlák, Petr; Sittner, Petr
2004-04-01
Measurements of elastic constants of the austenite phase when approaching the phase transformation either upon cooling or stressing is of the crucial interest for the shape memory alloy field. Acoustic properties (wave velocity and also attenuation changes) of the Cu-Al-Ni single crystal were investigated in situ during stress-induced martensitic transformation at constant (room) temperature. The parent austenite cubic lattice of the Cu-Al-Ni exhibits very high elastic anisotropy (anisotropy factor A approximately 12). The measurements were made using nine combinations of (i) applied uniaxial compression in a given crystal direction, (ii) the wave propagation and (iii) polarization vectors. The chosen configurations are sufficient for evaluation of all independent third order elastic constants (TOEC). The longitudinal modes were also measured by the immersion technique, using the transducer pair in a water tank installed on the testing machine. The device works as "a ultrasonic extensometer" measuring a transverse strain of the specimen. The dependencies of both natural and initial wave velocities on the applied stress may be evaluated. Three elastic constants of the stress-induced martensite were determined. The elastic properties were found to vary with the increasing stress above the Ms transformation temperature, which is interpreted as a precursor for the martensitic transformation. The onset of the transformation was additionally identified from the acoustic emission measurement.
FORMATION (DECOMPOSITION) ENTHALPY CALCULATIONS FOR CRYSTAL LATTICES OF ALKALINE-EARTH FLUORIDES
Gruba, O.; Germanyuk, N.; Ryabukhin, A.
2015-01-01
A series of calculations of structural and thermochemical properties has been carried out for the alkaline-earth fluorides. The calculations have been carried out using the modified model of effective ionic radii and the model of enthalpy calculation for the crystal lattice. The results of the calculations are in accordance with the known experimental data within confidence intervals.
Light source design using Kagome-lattice hollow core photonic crystal fibers
Hossain, Md. Anwar; Namihira, Yoshinori
2014-09-01
Supercontinuum (SC) light source is designed using high pressure Xe-filled hollow core Kagome-lattice photonic crystal fiber. Using finite element method with perfectly matched layer, SC spectra in normal chromatic dispersion region have been generated using picosecond optical pulses from relatively less expensive laser sources.
First principles computation of lattice energies of organic solids: the benzene crystal.
Ringer, Ashley L; Sherrill, C David
2008-01-01
We provide a first-principles methodology to obtain converged results for the lattice energy of crystals of small, neutral organic molecules. In particular, we determine the lattice energy of crystalline benzene using an additive system based on the individual interaction energies of benzene dimers. Enthalpy corrections are estimated so that the lattice energy can be directly compared to the experimentally determined sublimation energy. Our best estimate of the sublimation energy is 49.4 kJ mol(-1), just over the typical experimentally reported values of 43-47 kJ mol(-1). Our results underscore the necessity of using highly correlated electronic structure methods to determine thermodynamic properties within chemical accuracy. The first coordination sphere contributes about 90 % of the total lattice energy, and the second coordination sphere contributes the remaining 10 %. Three-body interactions are determined to be negligible.
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.
Lattice Dynamic of Ag8SnSe6 Crystal
I.V. Semkiv
2016-10-01
Full Text Available The synthesis and structure properties of Ag8SnSe6 argyrodite are described. Argyrodite belongs to the orthorhombic space group Pmn21 with 15 atoms per primitive cell. Classification of the main phonon modes of crystal carried out. First-principles phonon-dispersion curves for argyrodite Ag8SnSe6 are calculated. Peak position in Raman spectra and IR-spectra was clarified.
Numerical Research of Materials Crystal Lattice Parameters Based on Rare-Earth Metals
Obkhodsky Artem
2017-01-01
Full Text Available Geometrical parameters (coordinates and angles of CeO2 crystal lattice by molecular dynamics method are calculated. Calculated parameters of crystal lattice are applied for definition the energy band structure via Hartree-Fock method in an approximation to CO LCAO (crystal orbitals as linear combination of atomic orbitals and using the model of cyclic cluster. Calculated minimum energy band p-d is within the value range of experimental data. Valence band maximum is 4.2 while minimum energy band p-d width is 2.8 eV Quantum-chemical calculations are accelerated by Schwarz inequality and direct inversion method in iterative subspace. The obtained mathematical model is implemented into software package for calculating material properties.
Stress topology within silicon single-crystal cantilever beam
Alexander P. Kuzmenko
2015-06-01
Full Text Available Flexural elastic deformations of single-crystal silicon have been studied using microspectral Raman scattering. Results are reported on nano-scaled sign-changing shifts of the main peak of the microspectral Raman scattering within the single-crystal silicon cantilever beam during exposure to flexural stress. The maximum value of Raman shift characteristic of the 518 cm−1 silicon peak at which elasticity still remains has been found to be 8 cm−1 which corresponds to an applied deformation of 4 GPa. We report three-dimensional maps of the distribution of internal stresses at different levels of deformation up to irreversible changes and brittle fracture of the samples that clearly show compression and tension areas and an undeformed area. A qualitative explanation of the increase in the strength of the cantilever beam due to its small thickness (2 μm has been provided that agrees with the predictions of real-world physical parameters obtained in SolidWorks software environment with the SimulationXpress module. We have defined the relative strain of the beam surface which was 2% and received a confirmation of changes in the silicon lattice parameter from 0.54307 nm to 0.53195 nm by the BFGS algorithm.
Analysis of band gap of non-bravais lattice photonic crystal fiber
Yichao MA; Heming CHEN
2009-01-01
This article designs a novel type ofnon-bravais lattice photonic crystal fiber. To form the nesting complexperiod with positive and negative refractive index materials respectively, a cylinder with the same radius and negative refractive index is introduced into the center of each lattice unit cell in the traditional square lattice air-holes photonic crystal fiber. The photonic band-gap of the photonic crystal fiber is calculated numerically by the plane wave expansion method. The result shows that compared with the traditional square photonic band-gap fiber (PBGF),when R/A is 0.35, the refractive index of the substrate, airhole, and medium-column are 1.30, 1.0, and -1.0,respectively. This new PBGF can transmit signal by the photonic band-gap effect. When the lattice constant Λvaries from 1.5 μm to 3.0 μm, the range of the wavelength ranges from 880 nm to 2300 nm.
Theory of the lattice dynamics of model crystals containing screw dislocations
Glass, N. E.
1976-08-01
A theoretical study of the lattice dynamics of a simple cubic model-crystal is made. The perturbation matrix of a single screw dislocation is determined and is used with the perfect lattice Green function to find four secular equations for the frequencies altered by the dislocation. The solutions yield, depending on the model parameters, up to four separate bands of optic localized-modes across the Brillouin zone. No shifts in the perfect lattice acoustical bands are found. The frequencies of the dislocation-induced localized modes are well separated from the frequencies of the perfect lattice modes and should present no difficulty in being distinguished experimentally. The Green function of the lattice containing many parallel screw dislocations is determined by following the method in use for point defects. With this imperfect-lattice Green function, the neutron cross-section for coherent one-phonon inelastic scattering by the dislocation localized-modes is obtained. Using model parameters corresponding to simple metals, the numerical evaluation yields cross-sections on the borderline of present capabilities for experimental detection and indicates the desirability of an experimental test-search. The most important parameter is found to be the ratio of the longitudinal (lambda) to the transverse (..mu..) force constants. As lambda:..mu.. increases, the localized-mode branches separate, the many-dislocation effects become noticeable, and the cross-section for inelastic scattering by the localized-modes rises. Crystals undergoing transverse mode softening, in which lambda:..mu.. grows as ..mu.. tends toward zero, may be useful in the experimental detection of dislocation-induced lattice modes.
Schmidt, Martin U; Dinnebier, Robert E; Kalkhof, Holger
2007-08-23
Diaryl azo pigments play an important role as yellow pigments for printing inks, with an annual pigment production of more than 50,000 t. The crystal structures of Pigment Yellow 12 (PY12), Pigment Yellow 13 (PY13), Pigment Yellow 14 (PY14), and Pigment Yellow 83 (PY83) were determined from X-ray powder data using lattice energy minimizations and subsequent Rietveld refinements. Details of the lattice energy minimization procedure and of the development of a torsion potential for the biphenyl fragment are given. The Rietveld refinements were carried out using rigid bodies, or constraints. It was also possible to refine all atomic positions individually without any constraint or restraint, even for PY12 having 44 independent non-hydrogen atoms per asymmetric unit. For PY14 (23 independent non-hydrogen atoms), additionally all atomic isotropic temperature factors could be refined individually. PY12 crystallized in a herringbone arrangement with twisted biaryl fragments. PY13 and PY14 formed a layer structure of planar molecules. PY83 showed a herringbone structure with planar molecules. According to quantum mechanical calculations, the twisting of the biaryl fragment results in a lower color strength of the pigments, whereas changes in the substitution pattern have almost no influence on the color strength of a single molecule. Hence, the experimentally observed lower color strength of PY12 in comparison with that of PY13 and PY83 can be explained as a pure packing effect. Further lattice energy calculations explained that the four investigated pigments crystallize in three different structures because these structures are the energetically most favorable ones for each compound. For example, for PY13, PY14, or PY83, a PY12-analogous crystal structure would lead to considerably poorer lattice energies and lower densities. In contrast, lattice energy calculations revealed that PY12 could adopt a PY13-type structure with only slightly poorer energy. This structure was
Schmidt,M.; Dinnebier, R.; Kalkhof, H.
2007-01-01
Diaryl azo pigments play an important role as yellow pigments for printing inks, with an annual pigment production of more than 50,000 t. The crystal structures of Pigment Yellow 12 (PY12), Pigment Yellow 13 (PY13), Pigment Yellow 14 (PY14), and Pigment Yellow 83 (PY83) were determined from X-ray powder data using lattice energy minimizations and subsequent Rietveld refinements. Details of the lattice energy minimization procedure and of the development of a torsion potential for the biphenyl fragment are given. The Rietveld refinements were carried out using rigid bodies, or constraints. It was also possible to refine all atomic positions individually without any constraint or restraint, even for PY12 having 44 independent non-hydrogen atoms per asymmetric unit. For PY14 (23 independent non-hydrogen atoms), additionally all atomic isotropic temperature factors could be refined individually. PY12 crystallized in a herringbone arrangement with twisted biaryl fragments. PY13 and PY14 formed a layer structure of planar molecules. PY83 showed a herringbone structure with planar molecules. According to quantum mechanical calculations, the twisting of the biaryl fragment results in a lower color strength of the pigments, whereas changes in the substitution pattern have almost no influence on the color strength of a single molecule. Hence, the experimentally observed lower color strength of PY12 in comparison with that of PY13 and PY83 can be explained as a pure packing effect. Further lattice energy calculations explained that the four investigated pigments crystallize in three different structures because these structures are the energetically most favorable ones for each compound. For example, for PY13, PY14, or PY83, a PY12-analogous crystal structure would lead to considerably poorer lattice energies and lower densities. In contrast, lattice energy calculations revealed that PY12 could adopt a PY13-type structure with only slightly poorer energy. This structure was
Photonic Bandgap Properties of Atom-lattice Photonic Crystals in Polymer
REN Lin; WANG Dian; SUN Gui-ting; NIU Li-gang; YANG Han; SONG Jun-feng
2011-01-01
The present paper covers the various photonic crystals(PhCs) structures mimicking real atom-lattice structures in electronic crystals by using the femtosecond laser-induced two-photon photopolymerization of SU-8 resin. The bandgap properties were investigated by varying the crystal orientations in ＜111＞, ＜110＞ and ＜100＞ of diamond-lattice PhCs. lhe photonic stop gaps were present at λ=3.88 μm in ＜111＞ direction, λ=4.01 μtm in ＜110＞ direction and λ=5.30 μm in ＜100＞ direction, respectively. In addition, defects were introduced in graphite-lattice PhCs and the strong localization of photons in this structure with defects at λ=5 μm was achieved. All the above work shows the powerful capability of femtosecond laser fabrication in manufacturing various complicated threedimensional photonic crystals and of controlling photons by inducing defects in the PhCs samples.
Zhu, Xueyong [Department of Molecular Biology, The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, CA 92037 (United States); Xu, Xiaojin [Department of Molecular Biology, The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, CA 92037 (United States); Glycobiology Institute, Department of Biochemistry, University of Oxford, South Parks Road, Oxford OX1 3QU (United Kingdom); Wilson, Ian A., E-mail: wilson@scripps.edu [Department of Molecular Biology, The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, CA 92037 (United States); The Skaggs Institute for Chemical Biology, The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, CA 92037 (United States)
2008-08-01
The structure of the 1918 H1N1 neuraminidase was determined to 1.65 Å from crystals with a lattice-translocation defect using uncorrected, as well as corrected, diffraction data. Few examples of macromolecular crystals containing lattice-translocation defects have been published in the literature. Lattice translocation and twinning are believed to be two common but different crystal-growth anomalies. While the successful use of twinned data for structure determination has become relatively routine in recent years, structure determination of crystals with lattice-translocation defects has not often been reported. To date, only four protein crystal structures containing such a crystal defect have been determined, using corrected, but not uncorrected, intensity data. In this report, the crystallization, structure determination and refinement of N1 neuraminidase derived from the 1918 H1N1 influenza virus (18NA) at 1.65 Å resolution are described. The crystal was indexed in space group C222{sub 1}, with unit-cell parameters a = 117.7, b = 138.5, c = 117.9 Å, and the structure was solved by molecular replacement. The lattice-translocation vector in the 18NA crystal was (0, 1/2, 1/2) or its equivalent vector (1/2, 0, 1/2) owing to the C lattice symmetry. Owing to this special lattice-translocation vector in space group C222{sub 1}, structure refinement could be achieved in two different ways: using corrected or uncorrected diffraction data. In the refinement with uncorrected data, a composite model was built to represent the molecules in the translated and untranslated layers, respectively. This composite structure model provided a unique example to examine how the molecules were arranged in the two lattice domains resulting from lattice-translocation defects.
Lattice dynamics of KxRhO2 single crystals
Bin-Bin Zhang
2015-08-01
Full Text Available A series of crystals KxRhO2 (x = 0.72, 0.63, 0.55, 0.39, and 0.24 have been synthesized and their vibrational properties have been studied by first principles calculations, Raman spectroscopy, and inelastic neutron scattering. The measured vibrational spectra of KxRhO2 for x = 0.72 and 0.63 are consistent with the theoretical prediction for the stoichiometric KRhO2. For samples with x = 0.55, 0.39 and 0.24, extra vibrational modes have been observed and they are believed to be due to the symmetry reduction and the loss of translational symmetry induced by K disorder. The good agreement was found for the phonon density of states among the Raman spectroscopic observations, inelastic neutron scattering and the first principles calculations, as an evidence for the generation of structure disorder by K deficiency.
Adaptive bimaterial lattices to mitigate thermal expansion mismatch stresses in satellite structures
Toropova, Marina M.; Steeves, Craig A.
2015-08-01
Earth-orbiting satellites regularly pass from sunlight to shade and back; these transitions are typically accompanied by significant temperature changes. When adjoining parts of a satellite that are made of different materials are subjected to large temperature changes, thermal mismatch stresses arise that are a function of the temperature change and the difference in coefficients of thermal expansion (CTEs) between the two materials. These thermal stresses are linked to undesirable deformation and, through long-term cycling, fatigue and failure of the structure. This paper describes a type of anisotropic lattice that can serve as a stress-free adaptor between two materials, eliminating thermal mismatch stresses and their concomitant consequences. The lattices consist of planar nonidentical anisotropic bimaterial cells, each designed based on a virtual triangle. Physically the cells consist of a triangle made of material with higher CTE surrounded by a hexagon made of material with lower CTE. Different skew angles of the hexagon make a particular cell and the whole lattice anisotropic. The cells can be designed and combined in a lattice in such a way that one edge of the lattice has CTE that coincides with the CTE of the first part of the structure (substrate 1), while the other edge of the lattice has CTE equal to the CTE of the second part of the structure (substrate 2). If all joints between the parts of each cell, neighbouring cells, and the lattice and the substrates are pinned, the whole structure will be free of thermal stresses. This paper will discuss the fundamental principles governing such lattices, their refinement for special circumstances, and opportunities for improving the structural performance of the lattices. This will be presented coupled to a rational strategy for lattice design.
A novel optical beam splitter based on photonic crystal with hybrid lattices
Zhu Qing-Yi; Fu Yong-Qi; Hu De-Qing; Zhang Zhi-Min
2012-01-01
A novel optical beam splitter constructed on the basis of photonic crystal (PC) with hybrid lattices is proposed in this paper.The band gap of square-lattice PC is so designed that the incident light is divided into several branch beams.Triangular-lattice graded-index PCs are combined for focusing each branch.Computational calculations are carried out on the basis of finite-different time-domain algorithm to prove the feasibility of our design.The waveguide is unnecessary in the design.Thus the device has functions of both splitting and focusing beams.Size of the divided beam at site of full-width at half-maximum is of the order of λ/2.The designed splitter has the advantages that it has a small volume and can be integrated by conventional semiconductor manufacturing process.
Slow light with large group index - bandwidth product in lattice-shifted photonic crystal waveguides
Tang, Jian; Li, Wenhui; Wu, Jun; Xu, Zhonghui
2016-10-01
This study presents a systematic optimization procedure to generate slow light with large group index, wideband, and low dispersion in an lattice-shifted photonic crystal waveguide. The waveguide is based on triangular lattice photonic crystal imposed by selectively altering the locations of the holes adjacent to the line defect. Under a constant group index criterion of ± 10% variation, when group indices are nearly constants of 24, 33, 46, 57, and 66, their corresponding bandwidths of flat band reach 24.2, 17.6, 12.8, 10.1 and 8.6 nm around 1550 nm, respectively. A nearly constant large group index - bandwidth product (GBP) of 0.37 is achieved for all cases. Low dispersion slow light propagation is confirmed by studying the relative temporal pulse-width spreading with the 2-D finite-difference time-domain method.
Feng, Xi; Li, Hu; Yuxia, Tang
2016-07-01
Under total reflection conditions, it typically seems as though light waves will be reflected completely on the interface; in actuality, the waves can penetrate the medium as evanescent waves. In this paper, we present a twinned lattice photonic crystal with a unit cell composed of AB layers and their mirror. We assume that the refractive index n 0 of the input and output end is equal to n B and larger than n A . We first demonstrate the dependence of band structure on the incidence angle and normalized wavelength, in which the resonant tunneling bands are exposed. We then draw a comparison of bands between ABBA and AB. To conclude, we discuss the resonant tunneling effect in the twinned lattice photonic crystal under the total reflection conditions. As incidence angle increases, the resonant tunneling band ultimately vanishes completely.
Light confinement at a Dirac point in honeycomb-like lattice photonic crystal
Mao, Qiuping; Xie, Kang; Hu, Lei; Li, Qian; Zhang, Wei; Jiang, Haiming; Hu, Zhijia; Wang, Erlei
2017-02-01
Optical waveguides and cavities are important components among modern optical devices. Traditional optical cavities rely on total internal reflection or photonic bandgaps to achieve field confinement. Recently, a new type of trapped mode, the Dirac mode, has been reported to occur in triangular or honeycomb lattice photonic crystal. This novel localized mode is attribute to neither of the traditional light-guiding mechanisms and owns different characteristics. Here we report the discovery of the Dirac mode in honeycomb-like photonic crystal lattice. The Dirac mode occurs at a Dirac frequency, which is beyond the complete photonic bandgaps. It has a different algebraic-decay feature. Our discovery extends applicability of the Dirac mode in designing for optical devices.
Extraordinary lateral beaming of sound from a square-lattice phononic crystal
Bai, Xiaoxue; Qiu, Chunyin; He, Hailong; Peng, Shasha; Ke, Manzhu [Key Laboratory of Artificial Micro- and Nano-structures of Ministry of Education and School of Physics and Technology, Wuhan University, Wuhan 430072 (China); Liu, Zhengyou, E-mail: zyliu@whu.edu.cn [Key Laboratory of Artificial Micro- and Nano-structures of Ministry of Education and School of Physics and Technology, Wuhan University, Wuhan 430072 (China); Institute for Advanced Studies, Wuhan University, Wuhan 430072 (China)
2017-03-03
Highlights: • An extraordinary lateral beaming phenomenon is observed in a finite phononic crystal made of square lattice. • The phenomenon can be explained by the equivalence of the states located around the four corners of the first Brillouin zone. • The lateral beaming behavior enables a simple design of acoustic beam splitters. • In some sense, the phenomenon can be described by a near zero refractive index. - Abstract: This work revisits the sound transmission through a finite phononic crystal of square lattice. In addition to a direct, ordinary transmission through the sample, an extraordinary lateral beaming effect is also observed. The phenomenon stems from the equivalence of the states located around the four corners of the first Brillouin zone. The experimental result agrees well with the theoretical prediction. The lateral beaming behavior enables a simple design for realizing acoustic beam splitters.
F. Shen
2016-02-01
Full Text Available Negative refractive collimation beam at the low frequency region is achieved in a square lattice sonic crystal with the small magnitude of effective refractive index. A simple tuning approach for such acoustic beam is also proposed by attaching an additional concave surface of incidence to the crystal slab. This can increase the propagation distance of collimation beam, enhance or suppress the beam intensity. The proposed approach is rather general and applicable to other acoustic materials as long as their effective index can be retrieved. Moreover, the results can be applied to wavefront manipulation and transmission enhancement.
Colloidal nanoparticles trapped by liquid-crystal defect lines: A lattice Monte Carlo simulation
Jose, Regina; Skačej, Gregor; Sastry, V. S. S.; Žumer, Slobodan
2014-09-01
Lattice-based Monte Carlo simulations are performed to study a confined liquid crystal system with a topological disclination line entangling a colloidal nanoparticle. In our microscopic study the disclination line is stretched by moving the colloid, as in laser tweezing experiments, which results in a restoring force attempting to minimize the disclination length. From constant-force simulations we extract the corresponding disclination line tension, estimated as ˜50 pN, and observe its decrease with increasing temperature.
Square-lattice large-pitch hollow-core photonic crystal fiber
Couny, F.; Roberts, John; Birks, T.A.;
2008-01-01
We report on the design, fabrication and characterization of silica square-lattice hollow core photonic crystal fibers optimized for low loss guidance over an extended frequency range in the mid-IR region of the optical spectrum. The fiber's linear optical properties include an ultra-low group...... velocity dispersion and a polarization cross-coupling as low as -13.4dB over 10m of fiber....
Crystal structure of human CRMP-4: correction of intensities for lattice-translocation disorder
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.
Wavelets centered on a knot sequence: piecewise polynomial wavelets on a quasi-crystal lattice
Atkinson, Bruce W; Geronimo, Jeffrey S; Hardin, Douglas P
2011-01-01
We develop a general notion of orthogonal wavelets `centered' on an irregular knot sequence. We present two families of orthogonal wavelets that are continuous and piecewise polynomial. As an application, we construct continuous, piecewise quadratic, orthogonal wavelet bases on the quasi-crystal lattice consisting of the $\\tau$-integers where $\\tau$ is the golden-mean. The resulting spaces then generate a multiresolution analysis of $L^2(\\mathbf{R})$ with scaling factor $\\tau$.
Controlling the focusing properties of a triangular-lattice metallic photonic-crystal slab
Feng Shuai; Wang Yi-Quan; Li Zhi-Yuan; Cheng Bing-Ying; Zhang Dao-Zhong
2007-01-01
This paper studies the focusing properties of a two-dimensional photonic crystal (PC) slab consisting of a triangular lattice of metallic cylinders immersed in a dielectric background. Through the analysis of the equifrequency-surface contours and the field patterns of a point source placed in the vicinity of the PC slab, it finds that both the image distance and image quality can be controlled by simply adjusting the refractive index of the background material.
Formation of Bragg Band Gaps in Anisotropic Phononic Crystals Analyzed With the Empty Lattice Model
Yan-Feng Wang
2016-05-01
Full Text Available Bragg band gaps of phononic crystals generally, but not always, open at Brillouin zone boundaries. The commonly accepted explanation stems from the empty lattice model: assuming a small material contrast between the constituents of the unit cell, avoided crossings in the phononic band structure appear at frequencies and wavenumbers corresponding to band intersections; for scalar waves the lowest intersections coincide with boundaries of the first Brillouin zone. However, if a phononic crystal contains elastically anisotropic materials, its overall symmetry is not dictated solely by the lattice symmetry. We construct an empty lattice model for phononic crystals made of isotropic and anisotropic materials, based on their slowness curves. We find that, in the anisotropic case, avoided crossings generally do not appear at the boundaries of traditionally defined Brillouin zones. Furthermore, the Bragg “planes” which give rise to phononic band gaps, are generally not flat planes but curved surfaces. The same is found to be the case for avoided crossings between shear (transverse and longitudinal bands in the isotropic case.
Zhu, X.; Xu, X.; Wilson, I.A.
2009-05-28
Few examples of macromolecular crystals containing lattice-translocation defects have been published in the literature. Lattice translocation and twinning are believed to be two common but different crystal-growth anomalies. While the successful use of twinned data for structure determination has become relatively routine in recent years, structure determination of crystals with lattice-translocation defects has not often been reported. To date, only four protein crystal structures containing such a crystal defect have been determined, using corrected, but not uncorrected, intensity data. In this report, the crystallization, structure determination and refinement of N1 neuraminidase derived from the 1918 H1N1 influenza virus (18NA) at 1.65 {angstrom} resolution are described. The crystal was indexed in space group C222{sub 1}, with unit-cell parameters a = 117.7, b = 138.5, c = 117.9 {angstrom}, and the structure was solved by molecular replacement. The lattice-translocation vector in the 18NA crystal was (0, 1/2, 1/2) or its equivalent vector (1/2, 0, 1/2) owing to the C lattice symmetry. Owing to this special lattice-translocation vector in space group C222{sub 1}, structure refinement could be achieved in two different ways: using corrected or uncorrected diffraction data. In the refinement with uncorrected data, a composite model was built to represent the molecules in the translated and untranslated layers, respectively. This composite structure model provided a unique example to examine how the molecules were arranged in the two lattice domains resulting from lattice-translocation defects.
Blocks and residual stresses in shaped sapphire single crystals
Krymov, V. M.; Nosov, Yu. G.; Bakholdin, S. I.; Maslov, V. N.; Shul‧pina, I. L.; Nikolaev, V. I.
2017-01-01
The formation of blocks and residual stresses in shaped sapphire crystals grown from the melt by the Stepanov method (EFG) has been studied. The probability of block formation is higher for the growth along the c axis compared to that grown in the a-axis direction. The distribution of residual stress in sapphire crystals of tubular, rectangular and round cross section was measured by the conoscopy method. It was found that the magnitude of the residual stress increases from the center to the periphery of the crystal and reaches up to about 20 MPa. Residual stress tensor components for solid round rod and tubular single crystals were determined by numerical integration.
Structure and lattice dynamics of rare-earth ferroborate crystals: Ab initio calculation
Chernyshev, V. A.; Nikiforov, A. E.; Petrov, V. P.; Serdtsev, A. V.; Kashchenko, M. A.; Klimin, S. A.
2016-08-01
The ab initio calculation of the crystal structure and the phonon spectrum of crystals RFe3(BO3)4 ( R = Pr, Nd, Sm) has been performed in the framework of the density functional theory. The ion coordinates in the unit cell, the lattice parameters, the frequencies and the types of fundamental vibrations, and also the intensities of lines in the Raman spectrum and infrared reflection spectra have been found. The elastic constants of the crystals have been calculated. For low-frequency A 2 mode in PrFe3(BO3)4, a "seed" vibration frequency that strongly interacts with the electronic excitation on a praseodymium ion was found. The calculation results satisfactory agree with the experimental data.
Helium and neon diffusion in pure hematite (α-Fe2O3) crystal lattice
Balout, Hilal; Roques, Jérôme; Gautheron, Cécile; Tassan-Got, Laurent
2016-04-01
Hematite (α-Fe2O3) has the corundum-type structure and is relatively present on Earth and Mars surface associated to ore mineral precipitation or as a weathering phase. He and Ne retention in such mineral has been intensively investigated experimentally because of the potential use of (U-Th-Sm)/(He-Ne) chronometer and thermochronometer. Therefore, the He/Ne diffusion in hematite crystal is an important issue for the interpretation of (U-Th)/(He-Ne) thermochronometric ages. For this purpose an accurate investigation of helium and neon diffusion in hematite crystal lattice has been achieved by computational multi-scale approach. Different insertion sites and diffusion pathways are first characterized where the spin polarized density functional theory (sp-DFT) approach coupled to the nudged elastic band (NEB) method is used to determine the migration energies between the insertion sites. Then, a statistical method, based on transition state theory (TST), is used to compute the jump probability between sites. The previous results are used as input data in a 3D random walk simulation, which permits to determine the effective activation energy and diffusion coefficient. Using the He/Ne diffusion coefficients, the closure temperature Tc has been calculated. For typical grain size of 100 microns, Tc will be of 116° C and 297° C for He and Ne atoms, respectively. These results Show that He and Ne atoms are highly retained in the crystal lattice at surface temperature. The obtained diffusion coefficients confirm that He/Ne retentively power in hematite lattice is very important, allowing a large range of different geological applications such the measurement of hematite crystallization ages on Earth and Mars.
On anisotropy function in crystal growth simulations using Lattice Boltzmann equation
Younsi, Amina
2016-01-01
In this paper, we present the ability of the Lattice Boltzmann (LB) equation, usually applied to simulate fluid flows, to simulate various shapes of crystals. Crystal growth is modeled with a phase-field model for a pure substance, numerically solved with a LB method in 2D and 3D. This study focuses on the anisotropy function that is responsible for the anisotropic surface tension between the solid phase and the liquid phase. The anisotropy function involves the unit normal vectors of the interface, defined by gradients of phase-field. Those gradients have to be consistent with the underlying lattice of the LB method in order to avoid unwanted effects of numerical anisotropy. Isotropy of the solution is obtained when the directional derivatives method, specific for each lattice, is applied for computing the gradient terms. With the central finite differences method, the phase-field does not match with its rotation and the solution is not any more isotropic. Next, the method is applied to simulate simultaneous...
CCSD(T)/CBS fragment-based calculations of lattice energy of molecular crystals
Červinka, Ctirad; Fulem, Michal; Růžička, Květoslav
2016-02-01
A comparative study of the lattice energy calculations for a data set of 25 molecular crystals is performed using an additive scheme based on the individual energies of up to four-body interactions calculated using the coupled clusters with iterative treatment of single and double excitations and perturbative triples correction (CCSD(T)) with an estimated complete basis set (CBS) description. The CCSD(T)/CBS values on lattice energies are used to estimate sublimation enthalpies which are compared with critically assessed and thermodynamically consistent experimental values. The average absolute percentage deviation of calculated sublimation enthalpies from experimental values amounts to 13% (corresponding to 4.8 kJ mol-1 on absolute scale) with unbiased distribution of positive to negative deviations. As pair interaction energies present a dominant contribution to the lattice energy and CCSD(T)/CBS calculations still remain computationally costly, benchmark calculations of pair interaction energies defined by crystal parameters involving 17 levels of theory, including recently developed methods with local and explicit treatment of electronic correlation, such as LCC and LCC-F12, are also presented. Locally and explicitly correlated methods are found to be computationally effective and reliable methods enabling the application of fragment-based methods for larger systems.
Optical induction of Bessel-like lattices in methyl-red doped liquid crystal cells
Mantashyan, Paytsar; Drampyan, Rafael; Beeckman, Jeroen; Willekens, Oliver; Neyts, Kristiaan
2015-03-01
The optical induction of annular photonic lattices by a traveling Bessel beam has been investigated in Methyl-red (MR) doped nematic liquid crystal (LC). Non-diffracting Bessel beams were formed by an axicon. The induced Bessel-like lattice had a ~15 μm period in the radial direction. The lattice was tested by measuring the forward diffracted power of the recording Bessel beam. The dependency on the angle between the polarization of the laser beam and the director of the LC and on the axial position of the LC cell had been investigated. A diffraction efficiency of 14% had been obtained. Investigations have been performed for different MR dye doping concentrations. An erasure time of the lattice of 60 s has been determined by a 532 nm probe Gaussian beam of 2 mW in a LC cell with MR dye concentration of 1.15 wt%. The induced periodically varying refractive index in the LC medium is analogous to microstructured fibers and allows the study of light localization and soliton behavior in highly nonlinear waveguide arrays.
Compression Stress Effect on Dislocations Movement and Crack propagation in Cubic Crystal
Suprijadi,; Yusfi, Meiqorry
2012-01-01
Fracture material is seriously problem in daily life, and it has connection with mechanical properties itself. The mechanical properties is belief depend on dislocation movement and crack propagation in the crystal. Information about this is very important to characterize the material. In FCC crystal structure the competition between crack propagation and dislocation wake is very interesting, in a ductile material like copper (Cu) dislocation can be seen in room temperature, but in a brittle material like Si only cracks can be seen observed. Different techniques were applied to material to study the mechanical properties, in this study we did compression test in one direction. Combination of simulation and experimental on cubic material are reported in this paper. We found that the deflection of crack direction in Si caused by vacancy of lattice,while compression stress on Cu cause the atoms displacement in one direction. Some evidence of dislocation wake in Si crystal under compression stress at high tempera...
Salahinejad, Maryam; Le, Tu C; Winkler, David A
2013-01-28
Accurate computational prediction of melting points and aqueous solubilities of organic compounds would be very useful but is notoriously difficult. Predicting the lattice energies of compounds is key to understanding and predicting their melting behavior and ultimately their solubility behavior. We report robust, predictive, quantitative structure-property relationship (QSPR) models for enthalpies of sublimation, crystal lattice energies, and melting points for a very large and structurally diverse set of small organic compounds. Sparse Bayesian feature selection and machine learning methods were employed to select the most relevant molecular descriptors for the model and to generate parsimonious quantitative models. The final enthalpy of sublimation model is a four-parameter multilinear equation that has an r(2) value of 0.96 and an average absolute error of 7.9 ± 0.3 kJ.mol(-1). The melting point model can predict this property with a standard error of 45° ± 1 K and r(2) value of 0.79. Given the size and diversity of the training data, these conceptually transparent and accurate models can be used to predict sublimation enthalpy, lattice energy, and melting points of organic compounds in general.
Lattice Boltzmann Simulation of Kinetic Isotope Effect During Snow Crystal Formation
Lu, G.; Depaolo, D. J.; Kang, Q.; Zhang, D.
2007-12-01
The isotopic composition of precipitation, especially that of snow, plays a special role in the global hydrological cycle and in reconstruction of past climates using polar ice cores. The fractionation of the major water isotope species (HHO, HDO, HHO-18) during ice crystal formation is critical to understanding the global distribution of isotopes in precipitation. Ice crystal growth in clouds is traditionally treated with a spherically-symmetric steady state diffusion model, with semi-empirical modifications added to account for ventilation and for complex crystal morphology. Although it is known that crystal growth rate, which depends largely on the degree of vapor over- saturation, determines crystal morphology, there are no quantitative models that relate morphology to the vapor saturation factor. Since kinetic (vapor phase diffusion-controlled) isotopic fractionation also depends on growth rate, there should be direct relationships between vapor saturation, crystal morphology, and crystal isotopic composition. We use a 2D lattice Boltzmann model to simulate diffusion-controlled ice crystal growth from vapor- oversaturated air. In the model, crystals grow solely according to the diffusive fluxes just above the crystal surfaces, and hence crystal morphology arises from the initial and boundary conditions in the model and does not need to be specified a priori. Crystal growth patterns can be varied between random growth and deterministic growth (along the maximum concentration gradient for example). The input parameters needed are the isotope- dependent vapor deposition rate constant (k) and the water vapor diffusivity in air (D). The values of both k and D can be computed from kinetic theory, and there are also experimentally determined values of D. The deduced values of k are uncertain to the extent that the condensation coefficient for ice is uncertain. The ratio D/k is a length (order 1 micron) that determines the minimum scale of dendritic growth features
Surface plasmon resonance biosensor based on large size square-lattice photonic crystal fiber
Bing, Pibin; Li, Zhongyang; Yuan, Sheng; Yao, Jianquan; Lu, Ying
2016-04-01
A surface plasmon resonance biosensor based on large size square-lattice photonic crystal fiber has been designed and simulated by finite element method. The square-lattice airholes are first coated with a calcium fluoride layer to provide mode confinement, then a nanoscale gold layer is deposited to excite the plasmon mode, and finally, the sample is infiltrated into the holes. The numerical results reveal that the resonance properties are easily affected by many parameters. The refractive index resolution of corresponding sensor can reach 4.3 × 10-6 RIU when the optimum parameters are set as the radius of curvature of the airhole r = 2 μm, the thickness of the core struts c = 200 nm, the auxiliary dielectric layer s = 1 μm, and the gold film d = 40 nm. In addition, the effective area and nonlinear coefficient are calculated.
2D photonic crystals on the Archimedean lattices (tribute to Johannes Kepler (1571 1630))
Gajić, R.; class="cross-out">D. Jovanović,
2008-03-01
Results of our research on 2D Archemedean lattice photonic crystals are presented. This involves the calculations of the band structures, band-gap maps, equifrequency contours and FDTD simulations of electromagnetic propagation through the structures as well as an experimental verification of negative refraction at microwaves. The band-gap dependence on dielectric contrast is established both for dielectric rods in air and air-holes in dielectric materials. A special emphasis is placed on possibilities of negative refraction and left-handedness in these structures. Together with the familiar Archimedean lattices like square, triangular, honeycomb and Kagome' ones, we consider also, the less known, (3 2, 4, 3, 4) (ladybug) and (3, 4, 6, 4) (honeycomb-ring) structures.
An improvement of the lattice theory of dislocation for a two-dimensional triangular crystal
Wang Shao-Feng
2005-01-01
The structure of dislocation in a two-dimensional triangular crystal has been studied theoretically on the basis of atomic interaction and lattice statics. The theory presented in this paper is an improvement to that published previously.Within a reasonable interaction approximation, a new dislocation equation is obtained, which remedies a fault existing in the lattice theory of dislocation. A better simplification of non-diagonal terms of the kernel is given. The solution of the new dislocation equation asymptotically becomes the same as that obtained in the elastic theory, and agrees with experimental data. It is found that the solution is formally identical with that proposed phenomenologically by Foreman et al, where the parameter can be chosen freely, but cannot uniquely determined from theory. Indeed, if the parameter in the expression of the solution is selected suitably, the expression can be well applied to describe the fine structure of the dislocation.
Boatner, L.A.
2008-06-24
This effort addressed the technical problem of identifying and growing, on a commercial scale, suitable single-crystal substrates for the subsequent deposition of epitaxial thin films of high temperature semiconductors such as GaN/AlN. The lack of suitable lattice-matched substrate materials was one of the major problem areas in the development of semiconducting devices for use at elevated temperatures as well as practical opto-electronic devices based on Al- and GaN technology. Such lattice-matched substrates are necessary in order to reduce or eliminate high concentrations of defects and dislocations in GaN/AlN and related epitaxial thin films. This effort concentrated, in particular, on the growth of single crystals of ZnO for substrate applications and it built on previous ORNL experience in the chemical vapor transport growth of large single crystals of zinc oxide. This combined expertise in the substrate growth area was further complemented by the ability of G. Eres and his collaborators to deposit thin films of GaN on the subject substrates and the overall ORNL capability for characterizing the quality of such films. The research effort consisted of research on the growth of two candidate substrate materials in conjunction with concurrent research on the growth and characterization of GaN films, i.e. the effort combined bulk crystal growth capabilities in the area of substrate production at both ORNL and the industrial partner, Commercial Crystal Growth Laboratories (CCL), Naples, Florida, with the novel thin-film deposition techniques previously developed in the ORNL SSD.
Sitnikova, V. E.; Dunaev, A. A.; Mamalimov, R. I.; Pakhomov, P. M.; Khizhnyak, S. D.; Chmel, A. E.
2017-07-01
The Fourier IR reflection spectra of ZnSe ceramics prepared by hot pressing (HP), physical vapor deposition (PVD), and PVD combined with hot isostatic pressing (HIP) are presented. The optical constants of polished and dry-ground specimens were used for comparison. The grinding treatment simulated the erosion of the outer surface of optical elements made of zinc selenide under the influence of solid dust particles and deposits. In the polished specimens residual stresses showed up in the IR reflection spectra of the ZnSePVD and ZnSeHIP ceramics, which had well-defined orientation of grains, but were not present in the spectra of the ZnSeHIP ceramics as a result of mutual compensation of the stresses in the randomly oriented grains of the material. The stresses, which appeared as a shift of the absorption bands calculated by the Kramers-Kronig method, increased significantly after abrasive treatment of the specimens. For all the treated ceramics the intensity of the absorption bands resulting from the anharmonicity of the vibrations in the distorted crystal lattice increased by several times. The last effect also depends on the production prehistory of the ceramics.
T H Freeda; C Mahadevan
2001-10-01
Pure and impurity added (with NH4Cl, NH4NO3, NH4H2PO4, and (NH4)2SO4) KDP single crystals were grown by the gel method using silica gels. X-ray diffraction data were collected for powder samples and used for the estimation of lattice variation and thermal parameters like Debye–Waller factor, mean-square amplitude of vibration, Debye temperature and Debye frequency. The thermal parameters do not vary in a particular order with respect to impurity concentration. The results obtained are reported and discussed.
QSPR modeling mineral crystal lattice energy by optimal descriptors of the graph of atomic orbitals
Toropova, A. P.; Toropov, A. A.; Maksudov, S. Kh.
2006-09-01
Models of the crystal lattice of minerals of general formula of A mC n: m, n = 1,2: A = Li, K, Na, Mg, Ca, Mn, Cu, Zn, Sr, Cd, Ba, Hg, Pb, Cs, and Rb ; C = Be, O, F, S, Cl, Br, and I; as a mathematical function of their structure have been constructed. Two elucidations of molecular structure have been used: molecular graph (vertexes are atoms, i.e., Li, Na, K, etc.) and graph of atomic orbitals, GAO (vertexes are atomic orbitals, i.e., 1s 2, 2p 5, 3d 10, etc). Statistical characteristics of the GAO-based models are better.
[Lattice vibration of Sr3TaGa3Si2O14 single crystal].
Yang, Hong; Lu, Gui-Wu; Yu, Ying-Hui; Li, Ying-Feng; Wang, Zeng-Mei
2008-03-01
Based on the space group theory, the normal vibration modes of Sr3 TaGa3Si2O14 (STGS) single crystal were predicted, and the Raman scattering intensities of non-polar and polar modes were calculated. The Raman spectrum of STGS crystal was measured, and lattice vibration modes of STGS crystal were assigned. For symmetry species A1, six typical Raman-active optical modes have been recorded at 126, 245, 557, 604, 896 and 991 cm(-1), respectively. It is easy to assign the mode of 126 cm(-1) as the relative translation between SiO4, Sr and the TaO6. The mode 245 cm(-1) corresponds to the twisting vibration of SiO4 correlating with the Sr-TaO6-Sr stretching vibration. The mode 557 cm(-1) was assigned as the O-Ta-O stretching vibration, while the mode 604 cm(-1) as the O-Ga-O stretching vibration. The band at 896 cm(-1) in the Raman spectrum was assigned to be the O-Si-O stretching vibration of the two SiO4 tetrahedra in the primitive cell of STGS single crystal. Meanwhile, the band at 991 cm(-1) in the Raman spectrum was assigned to be the Si-O stretching vibration of the two SiO4 tetrahedra in the primitive cell of STGS single crystal. The layer structure of STGS crystal was identified by both theory study and Raman spectroscopy experiment results. The small anisotropy and piezoelectric modulus of STGS crystal were ascribed to the weak distortion of decahedral unit.
Peng, Y; Chew, Y T; Qiu, J
2003-01-01
An alternative new method called lattice Boltzmann method (LBM) is applied in this work to simulate the flows in Czochralski crystal growth, which is one of the widely used prototypical systems for melt-crystal growth. The standard LBM can only be used in Cartesian coordinate system and we extend it to be applicable to this axisymmetric thermal flow problem, avoiding the use of three-dimensional LBM on Cartesian coordinate system. The extension is based on the following idea. By inserting position and time dependent source terms into the evolution equation of standard LBM, the continuity and NS equations on the cylindrical coordinate system can be recovered. Our extension is validated by its application to the benchmark problem suggested by Wheeler .
Crystal field-phonon coupling in the Kondo lattice CeCu2
Witte, U.; Kramp, S.; Braden, M.; Svoboda, P.; Loewenhaupt, M.
CeCu2 is a Kondo lattice and shows antiferromagnetic order below 3.5K. In earlier neutron-scattering experiments on a polycrystalline sample an anomaly in the inelastic neutron spectra at about 14 meV and at temperatures between 100 and 150K was observed. This has led to the assumption of a coupling between a crystal field transition between two excited levels and phonons. Inelastic neutron measurements on a single crystal confirm this assumption. We find an unusual strong energy shift (up to 15%) of certain phonons with increasing temperature, depending on their symmetry. At the same time the magnetic response is strongly broadened due to the coupling to the phonons.
Crystal field-phonon coupling in the Kondo lattice CeCu{sub 2}
Witte, U. [TU Dresden, Institut fuer Angewandte Physik (IAPD), 01062 Dresden (Germany); HMI Berlin, Glienicker Str. 100, 14109 Berlin (Germany); Kramp, S. [HMI Berlin, Glienicker Str. 100, 14109 Berlin (Germany); Braden, M. [LLB Saclay, 91191 Gif-Sur-Yvette Cedex (France); Svoboda, P. [Charles University, 12116 Praha (Czech Republic); Loewenhaupt, M. [TU Dresden, Institut fuer Angewandte Physik (IAPD), 01062 Dresden (Germany)
2002-07-01
CeCu{sub 2} is a Kondo lattice and shows antiferromagnetic order below 3.5 K. In earlier neutron-scattering experiments on a polycrystalline sample an anomaly in the inelastic neutron spectra at about 14 meV and at temperatures between 100 and 150 K was observed. This has led to the assumption of a coupling between a crystal field transition between two excited levels and phonons. Inelastic neutron measurements on a single crystal confirm this assumption. We find an unusual strong energy shift (up to 15%) of certain phonons with increasing temperature, depending on their symmetry. At the same time the magnetic response is strongly broadened due to the coupling to the phonons. (orig.)
Measurement of the \\{220\\} lattice-plane spacing of a $^{28}$Si crystal
Massa, Enrico; Kuetgens, Ulrich; Ferroglio, Luca
2010-01-01
The spacing of the \\{220\\} lattice planes of a $^{28}$Si crystal was measured by combined x-ray and optical interferometry to a $3.5\\times 10^{-9}$ relative accuracy. The result is $d_{220}=(192014712.67 \\pm 0.67)$ am, at 20.0 $^\\circ$C and 0 Pa. This value is greater by $(1.9464 \\pm 0.0067)\\times 10^{-9} d_{220}$ than the spacing in natural Si, a difference which confirms quantum mechanics calculations. Subsequently, this crystal has been used to determine the Avogadro constant by counting the Si atoms, a key step towards a realization of the mass unit based on a conventional value of the Planck or the Avogadro constants.
Lattice strain of osmium diboride under high pressure and nonhydrostatic stress
Kavner, Abby; Weinberger, Michelle B.; Shahar, Anat; Cumberland, Robert W.; Levine, Jonathan B.; Kaner, Richard B.; Tolbert, Sarah H.
2012-01-01
The lattice strain behavior of osmium diboride—a member of a group of third-row transition metal borides associated with hard/superhard behavior—has been studied using radial diffraction in a diamond anvil cell under high pressure and non-hydrostatic stress. We interpret the average values of the measured lattice strains as a lower-bound to the lattice-plane dependent yield strengths using existing estimates for the elastic constants of OsB2, with a yield strength of 11 GPa at 27.5 GPa of hydrostaticpressure. The measured differential lattice strains show significant plane-dependent anisotropy, with the (101) lattice plane showing the largest differential strain and the (001) lattice plane showing the least strain. At the highest pressure, the a-axis develops a larger compressive strain and supports a larger differential strain than either the b or c axes. This causes an increase in the c/a ratio and a decrease in the a/b ratio especially in the maximum stress direction. The large strength anisotropy of this material points to possible ways to modulate directional mechanical properties by taking advantage of the interplay between aggregate polycrystalline texture with directional mechanical properties.
Lattice Boltzmann Simulation of Water Isotope Fractionation During Growth of Ice Crystals in Clouds
Lu, G.; Depaolo, D.; Kang, Q.; Zhang, D.
2006-12-01
The isotopic composition of precipitation, especially that of snow, plays a special role in the global hydrological cycle and in reconstruction of past climates using polar ice cores. The fractionation of the major water isotope species (HHO, HDO, HHO-18) during ice crystal formation is critical to understanding the global distribution of isotopes in precipitation. Ice crystal growth in clouds is traditionally treated with a spherically- symmetric steady state diffusion model, with semi-empirical modifications added to account for ventilation and for complex crystal morphology. Although it is known that crystal growth rate, which depends largely on the degree of vapor over-saturation, determines crystal morphology, there are no existing quantitative models that directly relate morphology to the vapor saturation factor. Since kinetic (vapor phase diffusion-controlled) isotopic fractionation also depends on growth rate, there should be a direct relationship between vapor saturation, crystal morphology, and crystal isotopic composition. We use a 2D Lattice-Boltzmann model to simulate diffusion-controlled ice crystal growth from vapor- oversaturated air. In the model, crystals grow solely according to the diffusive fluxes just above the crystal surfaces, and hence crystal morphology arises from the initial and boundary conditions in the model and does not need to be specified a priori. The input parameters needed are the isotope-dependent vapor deposition rate constant (k) and the water vapor diffusivity in air (D). The values of both k and D can be computed from kinetic theory, and there are also experimentally determined values of D. The deduced values of k are uncertain to the extent that the sticking coefficient (or accommodation coefficient) for ice is uncertain. The ratio D/k is a length that determines the minimum scale of dendritic growth features and allows us to scale the numerical calculations to atmospheric conditions using a dimensionless Damkohler number
Modelling of acoustic waves propagating in nesting Fibonacci super-lattice phononic crystal
Zhao, Min; Qi, Hai-Feng; Xu, Jia-Hui; Xie, Ya-Zhuo; Zhang, Xing-Gan; Gao, Jian
2014-07-01
Herein, we report construction of one kind of nesting-Fibonacci-super-lattice phononic crystal, in which the super-lattice cell is a well-defined Fibonacci generation sequence. We present a comparative study on band-gap structures of acoustic waves propagating in one-dimensional, nesting Fibonacci-periodic structure and simple-periodic structure. We find that there are more band gaps in nesting Fibonacci super-lattice models, and that they present behavior different from the split-up of band gaps with different generation numbers. With the increase of generation number, more band gaps split and occur. Additionally, when generation number becomes larger, Bragg scattering becomes more significant: the characteristic curves become flatter and band gaps become wider. Furthermore, we study the effect of various parameters such as density, thickness and defects on band-gap structures. Our work is significant both for understanding the intrinsic physical properties of nesting Fibonacci sequences and for providing flexible choices to meet real engineering requirements.
Coherent lattice dynamics in opaque crystals: Testing the adequacy of two-tensor model
Misochko, O. V.; Lebedev, M. V.
2016-11-01
We report the ultrafast pump-probe study of B i2T e3 , Sb, Bi, and Te aimed to check the two-tensor model predictions for the creation of lattice coherence. The dependence of coherent ultrafast response on phonon frequency was measured for topological insulator B i2T e3 , the spectrum of which possesses two fully symmetric phonons. The effect of the pump pulse duration and power on the magnitude of coherent amplitude was evaluated in the model opaque crystals, such as two semimetals, bismuth and antimony, and semiconducting tellurium. In our analysis of the pump-probe data, we separated the transient total reflectivity into the sum of two contributions: one due to the photogenerated carriers and the second due to the coherent phonons. All fully symmetric phonons exhibit a cosinelike dependence and grow linearly with increasing average pump power provided the pulse duration remains unchanged. Varying the pump pulse duration, we observed a monotonic decrease of coherent amplitude for longer pulses, whereas the electronic contribution was almost unchanged. This lack of the correlation between the carriers and the coherent amplitude was further supported by coherent control experiments on Te. Based on the comparison of theoretical predictions with experimental observations, we conjecture that the lattice coherence creation in opaque crystals can be linked to a Raman-like process.
Nucleation in a Potts lattice gas model of crystallization from solution
Duff, Nathan; Peters, Baron
2009-11-01
Nucleation from solution is important in many pharmaceutical crystallization, biomineralization, material synthesis, and self-assembly processes. Simulation methodology has progressed rapidly for studies of nucleation in pure component and implicit solvent systems; however little progress has been made in the simulation of explicit solvent systems. The impasse stems from the inability of rare events simulation methodology to be combined with simulation techniques which maintain a constant chemical potential driving force (supersaturation) for nucleation. We present a Potts lattice gas (PLG) to aid in the development of new simulation strategies for nucleation from solution. The PLG captures common crystallization phase diagram features such as a eutectic point and solute/solvent melting points. Simulations of the PLG below the bulk solute melting temperature reveal a competition between amorphous and crystalline nuclei. As the temperature is increased toward the bulk melting temperature, the nucleation pathway changes from a one step crystalline nucleation pathway to a two step pathway, where an amorphous nucleus forms and then crystallizes. We explain these results in terms of classical nucleation theory with different size-dependant chemical potentials for the amorphous and crystalline nucleation pathways. The two step pathway may be particularly important when crystallization is favored only at postcritical sizes.
Nucleation in a Potts lattice gas model of crystallization from solution.
Duff, Nathan; Peters, Baron
2009-11-14
Nucleation from solution is important in many pharmaceutical crystallization, biomineralization, material synthesis, and self-assembly processes. Simulation methodology has progressed rapidly for studies of nucleation in pure component and implicit solvent systems; however little progress has been made in the simulation of explicit solvent systems. The impasse stems from the inability of rare events simulation methodology to be combined with simulation techniques which maintain a constant chemical potential driving force (supersaturation) for nucleation. We present a Potts lattice gas (PLG) to aid in the development of new simulation strategies for nucleation from solution. The PLG captures common crystallization phase diagram features such as a eutectic point and solute/solvent melting points. Simulations of the PLG below the bulk solute melting temperature reveal a competition between amorphous and crystalline nuclei. As the temperature is increased toward the bulk melting temperature, the nucleation pathway changes from a one step crystalline nucleation pathway to a two step pathway, where an amorphous nucleus forms and then crystallizes. We explain these results in terms of classical nucleation theory with different size-dependant chemical potentials for the amorphous and crystalline nucleation pathways. The two step pathway may be particularly important when crystallization is favored only at postcritical sizes.
Kaya, Savaş; Kaya, Cemal
2015-09-08
This paper presents a new technique for estimation of lattice energies of inorganic ionic compounds using a simple formula. This new method demonstrates the relationship between chemical hardness and lattice energies of ionic compounds. Here chemical hardness values of ionic compounds are calculated via our molecular hardness equation. The results obtained using the present method and comparisons made by considering experimental data and the results from other theoretical methods in the literature showed that the new method allows easy evaluation of lattice energies of inorganic ionic crystals without the need for ab initio calculations and complex calculations.
无
2010-01-01
Absolute band gaps of a two-dimensional triangular-lattice photonic crystal are calculated with the finite-difference time-domain method in this paper.Through calculating the photonic band structures of the triangular-lattice photonic crystal consisting of Ge rods immersed in air with different shapes,it is found that a large absolute band gap of 0.098 (2c/a) can be obtained for the structures with hollow triangular Ge rods immersed in air,corresponding to 19.8% of the middle frequency.The influence of the different factors on the width of the absolute band gaps is also discussed.
Sedao, Xxx; Maurice, Claire; Garrelie, Florence; Colombier, Jean-Philippe; Reynaud, Stéphanie; Quey, Romain; Pigeon, Florent
2014-04-01
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.
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.
Slow light engineering in polyatomic photonic crystal waveguides based on square lattice
Wang, Daobin; Zhang, Jie; Yuan, Lihua; Lei, Jingli; Chen, Sai; Han, Jiawei; Hou, Shanglin
2011-12-01
In this paper, the slow light properties of the polyatomic Photonic Crystal (PhC) which has multiple different air holes in each primitive cell are investigated. A slow light waveguide with "U-type" group index-frequency curve, which results in nearly constant group index over large bandwidth, is achieved using this new photonic crystal geometry based on the square lattice. Also, the radius and position of the innermost rows of small air holes have been modified to investigate the feasibility of controlling the dispersion relation by subtle structural modification. Numerical results demonstrate that decreasing the group velocity effectively and meanwhile maintaining a large Normalized Delay-Bandwidth Product ( NDBP) can be achieved by only modifying the radius of the innermost rows of small air holes. Shifting the innermost rows of small air holes toward the waveguide core is highly beneficial to enlarge the slow light bandwidth, but it contributes nothing to the promotion of NDBP. Our results provide important theoretical basis for the potential application offered by the polyatomic photonic crystal in future optical networks.
TAILORING OF FLATTENED DISPERSION IN TRIANGULAR-LATTICE PHOTONIC CRYSTAL FIBER
Sandhir Kumar Singh
2011-12-01
Full Text Available The interest of researchers and engineers in several laboratories, since the1980s, has been attracted by the ability to structure materials on the scale of the optical wavelength, a fraction of micrometers or less, in order to develop new optical medium, known as photonic crystals . Photonic crystals rely on a regular morphological microstructure of air-holes, incorporated into the material, which radically alters its optical properties. In Photonic Crystal Fiber (PCF it is possible to realize flat dispersion over a wide wavelength range that cannot be realized with a conventional single-mode fiber. In PCFs, the dispersion can be controlled and tailored with unprecedented freedom. In fact, due to the high refractive index difference between silica and air, and to the flexibility of changing air-hole sizes and patterns, the waveguide contribution to the dispersion parameter can be significantly changed, thus obtaining unusual position of the zero dispersion wavelength, as well as particular values of the dispersion curve slope. In particular, by manipulating the air- hole radius or the lattice period of the micro structured cladding, it is possible to control the zero-dispersion wavelength, which can be tuned over a very wide range, or the dispersion curves, which can be engineered to be ultra flattened. In this paper the geometric parameters of triangular PCF have been properly changed to optimize the dispersion compensation over a wide wavelength range.
Staircase of crystal phases of hard-core bosons on the kagome lattice
Huerga, Daniel; Capponi, Sylvain; Dukelsky, Jorge; Ortiz, Gerardo
2016-10-01
We study the quantum phase diagram of a system of hard-core bosons on the kagome lattice with nearest-neighbor repulsive interactions, for arbitrary densities, by means of the hierarchical mean-field theory and exact diagonalization techniques. This system is isomorphic to the spin S =1 /2 XXZ model in presence of an external magnetic field, a paradigmatic example of frustrated quantum magnetism. In the nonfrustrated regime, we find two crystal phases at densities 1/3 and 2/3 that melt into a superfluid phase when increasing the hopping amplitude, in semiquantitative agreement with quantum Monte Carlo computations. In the frustrated regime and away from half-filling, we find a series of plateaux with densities commensurate with powers of 1/3. The broader density plateaux (at densities 1/3 and 2/3) are remnants of the classical degeneracy in the Ising limit. For densities near half-filling, this staircase of crystal phases melts into a superfluid, which displays finite chiral currents when computed with clusters having an odd number of sites. Both the staircase of crystal phases and the superfluid phase prevail in the noninteracting limit, suggesting that the lowest dispersionless single-particle band may be at the root of this phenomenon.
Yaqoob, Faisal; Huang, Mengbing
2016-09-01
Fundamental understanding of impurity diffusion in crystals remains a challenge due to lack of experimental capabilities for measuring the diffusion properties of atoms according to their substitutional and interstitial lattice locations. With examples of indium and silver in ZnO crystals, we demonstrate an ion beam based method to experimentally determine the energetics and entropy changes in diffusion of substitutional and interstitial impurity atoms. While the interstitial Ag diffuses much faster than the substitutional Ag, as normally expected, the interstitial In migrates slower than the substitutional In, which is attributed to a large negative entropy change (˜-10 kB), possibly caused by the large atomic size of In. The activation energy and the diffusivity pre-exponential factor for the interstitial Ag are significantly enhanced, being more than a factor of two and ˜13 orders of magnitude, respectively, relative to the case for the interstitial In. This implies two different diffusion mechanisms between these two types of interstitial atoms in ZnO crystals: the direct interstitial diffusion mechanism for the interstitial In and the kick-out diffusion mechanism for the interstitial Ag. In addition, the activation energies and the diffusivity prefactors follow the Meyer-Neldel relationship with an excitation energy of ˜92 meV.
Superconductivity in LiOHFeS single crystals with a shrunk c-axis lattice constant
Lin, Hai; Kang, RuiZhe; Kong, Lu; Zhu, XiYu; Wen, Hai-Hu
2017-02-01
By using a hydrothermal ion-exchange method, we have successfully grown superconducting crystals of LiOHFeS with T c of about 2.8 K. Being different from the sister sample (Li1- x Fe x )OHFeSe, the energy dispersion spectrum analysis on LiOHFeS shows that the Fe/S ratio is very close to 1:1, suggesting an almost charge neutrality and less electron doping in the FeS planes of the system. Comparing with the non superconducting LiOHFeS crystal, each peak of the X-ray diffraction pattern of the superconducting crystal splits into two, and the diffraction peaks locating at lower reflection angles are consistent with that of non-superconducting ones. The rest set of diffraction peaks with higher reflection angles is corresponding to the superconducting phase, suggesting that the superconducting phase may has a shrunk c-axis lattice constant. Magnetization measurements indicate that the magnetic shielding due to superconductivity can be quite high under a weak magnetic field. The resistivity measurements under various magnetic fields show that the upper critical field is quite low, which is similar to the tetragonal FeS superconductor.
Spin-3/2 Ising model AFM/AFM two-layer lattice with crystal field
Erhan Albayrak; Ali Yigit
2009-01-01
The spin-3/2 Ising model is investigated for the case of antiferromagnetic (AFM/AFM) interactions on the two-layer Bethe lattice by using the exact recursion relations in the pairwise approach for given coordination numbers q = 3, 4 and 6 when the layers are under the influences of equal external magnetic and equal crystal fields. The ground state, (GS) phase diagrams are obtained on the different planes in detail and then the temperature-dependent phase diagrams of the system are calculated accordingly. It is observed that the system presents both second- and first-order phase transitions for all q, therefore, tricritical points. It is also found that the system exhibits double-critical end points and isolated points. The model aiso presents two Néel temperatures, T_N, and the existence of which leads to the reentrant behaviour.
Haiyang Wang
2016-10-01
Full Text Available A refractive index sensor based on dual-core photonic crystal fiber (PCF with hexagonal lattice is proposed. The effects of geometrical parameters of the PCF on performances of the sensor are investigated by using the finite element method (FEM. Two fiber cores are separated by two air holes filled with the analyte whose refractive index is in the range of 1.33–1.41. Numerical simulation results show that the highest sensitivity can be up to 22,983 nm/RIU(refractive index unit when the analyte refractive index is 1.41. The lowest sensitivity can reach to 21,679 nm/RIU when the analyte refractive index is 1.33. The sensor we proposed has significant advantages in the field of biomolecule detection as it provides a wide-range of detection with high sensitivity.
Wang, Haiyang; Yan, Xin; Li, Shuguang; An, Guowen; Zhang, Xuenan
2016-10-08
A refractive index sensor based on dual-core photonic crystal fiber (PCF) with hexagonal lattice is proposed. The effects of geometrical parameters of the PCF on performances of the sensor are investigated by using the finite element method (FEM). Two fiber cores are separated by two air holes filled with the analyte whose refractive index is in the range of 1.33-1.41. Numerical simulation results show that the highest sensitivity can be up to 22,983 nm/RIU(refractive index unit) when the analyte refractive index is 1.41. The lowest sensitivity can reach to 21,679 nm/RIU when the analyte refractive index is 1.33. The sensor we proposed has significant advantages in the field of biomolecule detection as it provides a wide-range of detection with high sensitivity.
Cao, D.X. [Royal Melbourne Inst. of Tech., VIC (Australia); Sood, D.K. [Academia Sinica, Shanghai, SH (China). Shanghai Inst. of Nuclear Research; Brown, I.G. [Lawrence Berkeley Lab., CA (United States)
1993-12-31
Single crystal samples of (100) oriented cubic zirconia stabilised with 9.5 mol % yttria were implanted with platinum ions, using a metal vapour vacuum arc (MEVVA) high current ion implanter, to a nominal dose of 1x10{sup 17} ions/cm{sup 2}. The implanted samples were annealed isothermally in air ambient at 1200 deg C, from 1-24 hours. Rutherford Backscattering Spectrometry and Channeling (RBSC) of 2 MeV He ions are employed to determine depth distributions of ion damage, Pt ions and substitutionality of Pt ions before and after annealing. The damage behaviour, Pt migration and lattice location are discussed in terms of metastable phase formation and solid solubility considerations. 7 refs., 3 figs.
Yang Xuefeng; Cui Jian; Zhang Yuan [School of Mathematical Sciences, Dalian University of Technology, Dalian 116024 (China); Liu Yue [School of Physics and Optoelectronic Technology, Dalian University of Technology, Dalian 116024 (China)
2012-07-15
The dispersion relations of the externally and thermally (naturally) excited dust lattice modes (both longitudinal and transverse) in two-dimensional Debye-Yukawa complex plasma crystals are investigated. The dispersion relations are calculated numerically by taking the neutral gas damping effects into account and the numerical results are in agreement with the experimental data given by Nunomura et al.[Phys. Rev. E 65, 066402 (2002)]. It is found that for the mode excited by an external disturbance with a real frequency, the dispersion properties are changed at a critical frequency near where the group velocity of the mode goes to zero. Therefore, the high frequency branch with negative dispersion cannot be reached. In contrast, for the thermally excited mode, the dispersion curve can extend all the way to the negative dispersion region, while a 'cut-off' wave number exists at the long wavelength end of the dispersion in the transverse mode.
Local atomic arrangements and lattice distortions in layered Ge-Sb-Te crystal structures
Lotnyk, Andriy; Ross, Ulrich; Bernütz, Sabine; Thelander, Erik; Rauschenbach, Bernd
2016-05-01
Insights into the local atomic arrangements of layered Ge-Sb-Te compounds are of particular importance from a fundamental point of view and for data storage applications. In this view, a detailed knowledge of the atomic structure in such alloys is central to understanding the functional properties both in the more commonly utilized amorphous-crystalline transition and in recently proposed interfacial phase change memory based on the transition between two crystalline structures. Aberration-corrected scanning transmission electron microscopy allows direct imaging of local arrangement in the crystalline lattice with atomic resolution. However, due to the non-trivial influence of thermal diffuse scattering on the high-angle scattering signal, a detailed examination of the image contrast requires comparison with theoretical image simulations. This work reveals the local atomic structure of trigonal Ge-Sb-Te thin films by using a combination of direct imaging of the atomic columns and theoretical image simulation approaches. The results show that the thin films are prone to the formation of stacking disorder with individual building blocks of the Ge2Sb2Te5, Ge1Sb2Te4 and Ge3Sb2Te6 crystal structures intercalated within randomly oriented grains. The comparison with image simulations based on various theoretical models reveals intermixed cation layers with pronounced local lattice distortions, exceeding those reported in literature.
Vibrational states of a water molecule in a nano-cavity of beryl crystal lattice
Zhukova, Elena S., E-mail: zhukovaelenka@gmail.com; Gorshunov, Boris P. [Moscow Institute of Physics and Technology, 9 Institutskiy per., 141700 Dolgoprudny, Moscow Region (Russian Federation); 1. Physikalisches Institut, Universität Stuttgart, Pfaffenwaldring 57, 70550 Stuttgart (Germany); A.M. Prokhorov General Physics Institute, Russian Academy of Sciences, Vavilova Street 38, 119991 Moscow (Russian Federation); Torgashev, Victor I. [Faculty of Physics, Southern Federal University, 5 Zorge St., 344090 Rostov-on-Don (Russian Federation); Lebedev, Vladimir V. [Moscow Institute of Physics and Technology, 9 Institutskiy per., 141700 Dolgoprudny, Moscow Region (Russian Federation); Landau Institute for Theoretical Physics, Russian Academy of Sciences, Akademika Semenova av., 1-A, 142432 Chernogolovka, Moscow Region (Russian Federation); Shakurov, Gil' man S. [Kazan Physical-Technical Institute, Russian Academy of Sciences, 10/7 Sibirsky Trakt, 420029 Kazan (Russian Federation); Kremer, Reinhard K. [Max-Planck-Institut für Festkörperforschung, Heisenbergstrasse 1, 70569 Stuttgart (Germany); Pestrjakov, Efim V. [Institute of Laser Physics, Russian Academy of Sciences, 13/3 Ac. Lavrentyev' s Prosp., 630090 Novosibirsk (Russian Federation); Thomas, Victor G.; Fursenko, Dimitry A. [Institute of Geology and Mineralogy, Russian Academy of Sciences, 3 Ac. Koptyug' s Prosp., 630090 Novosibirsk (Russian Federation); Prokhorov, Anatoly S. [Moscow Institute of Physics and Technology, 9 Institutskiy per., 141700 Dolgoprudny, Moscow Region (Russian Federation); A.M. Prokhorov General Physics Institute, Russian Academy of Sciences, Vavilova Street 38, 119991 Moscow (Russian Federation); Dressel, Martin [1. Physikalisches Institut, Universität Stuttgart, Pfaffenwaldring 57, 70550 Stuttgart (Germany)
2014-06-14
Low-energy excitations of a single water molecule are studied when confined within a nano-size cavity formed by the ionic crystal lattice. Optical spectra are measured of manganese doped beryl single crystal Mn:Be{sub 3}Al{sub 2}Si{sub 6}O{sub 18}, that contains water molecules individually isolated in 0.51 nm diameter voids within the crystal lattice. Two types of orientation are distinguished: water-I molecules have their dipole moments aligned perpendicular to the c axis and dipole moments of water-II molecules are parallel to the c-axis. The optical conductivity σ(ν) and permittivity ε{sup ′}(ν) spectra are recorded in terahertz and infrared ranges, at frequencies from several wavenumbers up to ν = 7000 cm{sup −1}, at temperatures 5–300 K and for two polarizations, when the electric vector E of the radiation is parallel and perpendicular to the c-axis. Comparative experiments on as-grown and on dehydrated samples allow to identify the spectra of σ(ν) and ε{sup ′}(ν) caused exclusively by water molecules. In the infrared range, well-known internal modes ν{sub 1}, ν{sub 2}, and ν{sub 3} of the H{sub 2}O molecule are observed for both polarizations, indicating the presence of water-I and water-II molecules in the crystal. Spectra recorded below 1000 cm{sup −1} reveal a rich set of highly anisotropic features in the low-energy response of H{sub 2}O molecule in a crystalline nano-cavity. While for E∥c only two absorption peaks are detected, at ∼90 cm{sup −1} and ∼160 cm{sup −1}, several absorption bands are discovered for E⊥c, each consisting of narrower resonances. The bands are assigned to librational (400–500 cm{sup −1}) and translational (150–200 cm{sup −1}) vibrations of water-I molecule that is weakly coupled to the nano-cavity “walls.” A model is presented that explains the “fine structure” of the bands by a splitting of the energy levels due to quantum tunneling between the minima in a six-well potential
Vibrational states of a water molecule in a nano-cavity of beryl crystal lattice.
Zhukova, Elena S; Torgashev, Victor I; Gorshunov, Boris P; Lebedev, Vladimir V; Shakurov, Gil'man S; Kremer, Reinhard K; Pestrjakov, Efim V; Thomas, Victor G; Fursenko, Dimitry A; Prokhorov, Anatoly S; Dressel, Martin
2014-06-14
Low-energy excitations of a single water molecule are studied when confined within a nano-size cavity formed by the ionic crystal lattice. Optical spectra are measured of manganese doped beryl single crystal Mn:Be3Al2Si6O18, that contains water molecules individually isolated in 0.51 nm diameter voids within the crystal lattice. Two types of orientation are distinguished: water-I molecules have their dipole moments aligned perpendicular to the c axis and dipole moments of water-II molecules are parallel to the c-axis. The optical conductivity σ(ν) and permittivity ɛ'(ν) spectra are recorded in terahertz and infrared ranges, at frequencies from several wavenumbers up to ν = 7000 cm(-1), at temperatures 5-300 K and for two polarizations, when the electric vector E of the radiation is parallel and perpendicular to the c-axis. Comparative experiments on as-grown and on dehydrated samples allow to identify the spectra of σ(ν) and ɛ'(ν) caused exclusively by water molecules. In the infrared range, well-known internal modes ν1, ν2, and ν3 of the H2O molecule are observed for both polarizations, indicating the presence of water-I and water-II molecules in the crystal. Spectra recorded below 1000 cm(-1) reveal a rich set of highly anisotropic features in the low-energy response of H2O molecule in a crystalline nano-cavity. While for E∥c only two absorption peaks are detected, at ~90 cm(-1) and ~160 cm(-1), several absorption bands are discovered for E⊥c, each consisting of narrower resonances. The bands are assigned to librational (400-500 cm(-1)) and translational (150-200 cm(-1)) vibrations of water-I molecule that is weakly coupled to the nano-cavity "walls." A model is presented that explains the "fine structure" of the bands by a splitting of the energy levels due to quantum tunneling between the minima in a six-well potential relief felt by a molecule within the cavity.
Spin liquid in a single crystal of the frustrated diamond lattice antiferromagnet CoAl2O4
Zaharko, O.; Christensen, Niels Bech; Cervellino, A.
2011-01-01
We study the evidence for spin liquid in the frustrated diamond lattice antiferromagnet CoAl2O4 by means of single-crystal neutron scattering in zero and applied magnetic fields. The magnetically ordered phase appearing below T-N = 8 K remains nonconventional down to 1.5 K. The magnetic Bragg peaks...
Ohashi, Yuji; Kitahara, Masanori; Kudo, Tetsuo; Arakawa, Mototaka; Yokota, Yuui; Shoji, Yasuhiro; Yamaji, Akihiro; Kurosawa, Shunsuke; Kamada, Kei; Yoshikawa, Akira
2017-06-01
The relationship among lattice constant a, Al content, and acoustic properties were experimentally examined using a plate specimen perpendicular to Y-axis prepared from Ca3Ta(Ga0.75Al0.25)3Si2O14 [CTGAS(0.25)] single crystal grown by Czochralski method. As the acoustic properties, leaky surface acoustic wave (LSAW) velocities with different propagation directions, X- and Z-propagations, and longitudinal wave velocity propagating along Y-axis direction were measured by the line-focus-beam/plane-wave ultrasonic-material-characterization (LFB/PW-UMC) system. The measured results of LSAW velocity distributions revealed inhomogeneity in radial direction of the crystal ingot exhibiting lower velocity area at the center of the ingot. In addition, the distributions of lattice constant a and chemical composition (especially Al content) were measured along the radial direction. Abnormal changes suggesting existence of residual stresses concentrated on the central part of the crystal ingot other than the effect of chemical composition change were detected from the relationships among the measured parameters.
Y J Jeon; M Jamil; Hyo-Dong Lee; J T Rhee
2008-09-01
This article reports a comparative study of the phase separation process in a polymer-dispersed liquid crystal, based on a Metropolis Monte Carlo simulation study of three lattice systems. We propose a model for the different processes occurring in the formation of polymer-dispersed liquid crystals (PDLCs). The mechanism of PDLC is studied as a function of quench temperature, concentration and degree of polymerization of liquid crystals and polymers. The obtained resultant phase diagrams of the three systems are approximated and compared with the Flory–Huggins theory, and show a good agreement. It has been observed in the simulation results that among all the three systems, the 40 × 40 × 40 lattice showed the most accurate, reliable and stable results.
High-Pressure Crystal Structure, Lattice Vibrations, and Band Structure of BiSbO4.
Errandonea, Daniel; Muñoz, Alfonso; Rodríguez-Hernández, Placida; Gomis, Oscar; Achary, S Nagabhusan; Popescu, Catalin; Patwe, Sadeque J; Tyagi, Avesh K
2016-05-16
The high-pressure crystal structure, lattice-vibrations, and electronic band structure of BiSbO4 were studied by ab initio simulations. We also performed Raman spectroscopy, infrared spectroscopy, and diffuse-reflectance measurements, as well as synchrotron powder X-ray diffraction. High-pressure X-ray diffraction measurements show that the crystal structure of BiSbO4 remains stable up to at least 70 GPa, unlike other known MTO4-type ternary oxides. These experiments also give information on the pressure dependence of the unit-cell parameters. Calculations properly describe the crystal structure of BiSbO4 and the changes induced by pressure on it. They also predict a possible high-pressure phase. A room-temperature pressure-volume equation of state is determined, and the effect of pressure on the coordination polyhedron of Bi and Sb is discussed. Raman- and infrared-active phonons were measured and calculated. In particular, calculations provide assignments for all the vibrational modes as well as their pressure dependence. In addition, the band structure and electronic density of states under pressure were also calculated. The calculations combined with the optical measurements allow us to conclude that BiSbO4 is an indirect-gap semiconductor, with an electronic band gap of 2.9(1) eV. Finally, the isothermal compressibility tensor for BiSbO4 is given at 1.8 GPa. The experimental (theoretical) data revealed that the direction of maximum compressibility is in the (0 1 0) plane at ∼33° (38°) to the c-axis and 47° (42°) to the a-axis. The reliability of the reported results is supported by the consistency between experiments and calculations.
Regulski, Wojciech; Szumbarski, Jacek
2016-01-01
In this paper, the performance of two lattice Boltzmann method formulations for yield-stress (i.e. viscoplastic) fluids has been investigated. The first approach is based on the popular Papanastasiou regularisation of the fluid rheology in conjunction with explicit modification of the lattice Boltzmann relaxation rate. The second approach uses a locally-implicit formulation to simultaneously solve for the fluid stress and the underlying particle distribution functions. After investigating issues related to the lattice symmetry and non-hydrodynamic Burnett stresses, the two models were compared in terms of spatial convergence and their behaviour in transient and inertial flows. The choice of lattice and the presence of Burnett stresses was found to influence the results of both models, however the latter did not significantly degrade the velocity field. Using Bingham flows in ducts and synthetic porous media, it was found that the implicitly-regularised model was superior in capturing transient and inertial fl...
Lattice variation and thermal parameters of NiMg1–SO4 7H2O single crystals
M Theivanayagom; C Mahadevan
2001-10-01
NiMg1–SO4.7H2O single crystals were grown by the slow evaporation method from aqueous solutions. Density was measured by the floatation method. X-ray diffraction data were collected for powder samples and used for the estimation of lattice variation and thermal parameters like Debye–Waller factor, mean-square amplitude of vibration and Debye temperature. Lattice volumes approximately obey a relation similar to Retger’s rule. Values of thermal parameters do not follow any particular order with composition. The results obtained are reported.
Tensor tomography of stresses in cubic single crystals
Dmitry D. Karov
2015-03-01
Full Text Available The possibility of optical tomography applying to investigation of a two-dimensional and a three-dimensional stressed state in single cubic crystals has been studied. Stresses are determined within the framework of the Maxwell piezo-optic law (linear dependence of the permittivity tensor on stresses and weak optical anisotropy. It is shown that a complete reconstruction of stresses in a sample is impossible both by translucence it in the parallel planes system and by using of the elasticity theory equations. For overcoming these difficulties, it is offered to use a method of magnetophotoelasticity.
Zhang Bing-Zhi; Cui Hu; Li Xiang-Heng; She Wei-Long
2009-01-01
We theoretically study the beam dynamical hehaviour in a modulated optical lattice with a quadratic potential in a photovoltaic photorefractive crystal. We find that two different Bloch oscillation patterns appear for the excitation of both broad and narrow light beams. One kind of optical Landau-Zener tunnelling also appears upon the Bloch oscillation and can be controlled by adjusting the parameter of the optical lattice. Unlike the case of linear potential, the energy radiation due to Landau-Zener tunnelling can be confined in modulated lattices of this kind. For high input intensity levels, the Landau-Zener tunnelling is suppressed by the photovoltaic photorefractive nonlinearity and a symmetry breaking of beam propagation from the modulational instability appears.
Vairavel, Mathayan; Sundaravel, Balakrishnan; Panigrahi, Binaykumar
2016-09-01
There are contradictory theoretical predictions of lattice location of oxygen interstitial atom at tetrahedral and octahedral interstices in bcc Fe. For validating these predictions, 300 keV O18 ions with fluence of 5 × 1015 ions/cm2 are implanted into bcc Fe single crystals at room temperature and annealed at 400 °C. The Rutherford backscattering spectrometry (RBS) and nuclear reaction analysis (NRA)/channeling measurements are carried out with 850 keV protons. The lattice location of implanted O18 is analysed using the α-particles yield from O18(p,α)N15 nuclear reaction. The tilt angular scans of α-particle yield along and axial directions are performed at room temperature. Lattice location of O18 is found to be at tetrahedral interstitial site by comparing the experimental scan with simulated scans using FLUX7 software.
Vortex lattice mobility and effective pinning potentials in the peak effect region in YBCO crystals
G Pasquini; V Bekeris
2006-01-01
The peak effect (PE) in the critical current density in both low and high temperature superconductors has been the subject of a large amount of experimental and theoretical work in the last few/several years. In the case of YBCO, crucial discussions describing a dynamic or a static picture are not settled. In that region of field and temperature the mobility of the vortex lattice (VL) is found to be dependent on the dynamical history. Recently we reported evidence that the VL reorganizes and accesses to robust VL configurations (VLCs) with different effective pinning potential wells arising in response to different system histories. One of the keys to understand the nature of the PE is to investigate the VL behavior in the vicinity of the various VLCs in the region of the PE. The stability of these VLCs was investigated and it was found that they have distinct characteristic relaxation times, which may be related to elastic or plastic creep processes. In this paper we review some of these results and propose a scenario to describe the PE in YBCO crystals.
Lattice Boltzmann simulation of asymmetric flow in nematic liquid crystals with finite anchoring
Zhang, Rui; Roberts, Tyler; Aranson, Igor S.; de Pablo, Juan J.
2016-02-01
Liquid crystals (LCs) display many of the flow characteristics of liquids but exhibit long range orientational order. In the nematic phase, the coupling of structure and flow leads to complex hydrodynamic effects that remain to be fully elucidated. Here, we consider the hydrodynamics of a nematic LC in a hybrid cell, where opposite walls have conflicting anchoring boundary conditions, and we employ a 3D lattice Boltzmann method to simulate the time-dependent flow patterns that can arise. Due to the symmetry breaking of the director field within the hybrid cell, we observe that at low to moderate shear rates, the volumetric flow rate under Couette and Poiseuille flows is different for opposite flow directions. At high shear rates, the director field may undergo a topological transition which leads to symmetric flows. By applying an oscillatory pressure gradient to the channel, a net volumetric flow rate is found to depend on the magnitude and frequency of the oscillation, as well as the anchoring strength. Taken together, our findings suggest several intriguing new applications for LCs in microfluidic devices.
Stress-magnetization properties of a silicon iron single crystal under stress
Saito, Akihiko; Hashimoto, Masaaki; Kawaguchi, Eiji; Murashige, Shinichi
1996-07-01
The effects of tensile and compressive stress on magnetization changes in a Si-Fe single crystal with a (110) surface and longitudinal directions declined from the [001] direction were investigated. We found a peculiar magnetization change, namely a reversible magnetization change due to stress consisting of two peak values in a constant magnetic field. The double peak characteristic appears in samples with angle smaller than 55° for compressive stress and with angle larger than 60° for tensile stress.
Risteiu, M.; Dobra, R.; Andras, I.; Roventa, M.; Lorincz, A.
2017-06-01
The paper shows the results of a lab model for strain gauges based measuring system for multiple measuring heads of the mechanical stress in lattice structures of the bucket wheel excavator for open pit mines-harsh environment. The system is designed around a microcontroller system. Because of specific working conditions, the measuring system sends data to a processing system (a PC with Matlab software), we have implemented a secure communication solution based on ISM standard, by using NRF24L01 module. The transceiver contains a fully integrated frequency synthesizer based on crystal oscillator, and a Enhanced ShockBurst™ protocol engine. The proposed solution has a current consumption around 9.0 mA at an output power of -6dBm and 12.3mA in RX mode. Built-in Power Down and Standby modes makes power saving easily realizable for our solution battery powered. The stress from structures is taken by specific strain gauges adapted to low frequency vibrations. We are using a precision 24-bit analog-to-digital converter (ADC) designed for weigh scales and industrial control applications to interface directly with a bridge sensor-instrumentation device, with low drift voltage, low noise, common mode rejection signal, frequency and temperature stability. As backup implementation for measurements a high speed storage implementation is used.
Measurement of probability distributions for internal stresses in dislocated crystals
Wilkinson, Angus J.; Tarleton, Edmund; Vilalta-Clemente, Arantxa; Collins, David M. [Department of Materials, University of Oxford, Parks Road, Oxford OX1 3PH (United Kingdom); Jiang, Jun; Britton, T. Benjamin [Department of Materials, Imperial College London, Royal School of Mines, Exhibition Road, London SW7 2AZ (United Kingdom)
2014-11-03
Here, we analyse residual stress distributions obtained from various crystal systems using high resolution electron backscatter diffraction (EBSD) measurements. Histograms showing stress probability distributions exhibit tails extending to very high stress levels. We demonstrate that these extreme stress values are consistent with the functional form that should be expected for dislocated crystals. Analysis initially developed by Groma and co-workers for X-ray line profile analysis and based on the so-called “restricted second moment of the probability distribution” can be used to estimate the total dislocation density. The generality of the results are illustrated by application to three quite different systems, namely, face centred cubic Cu deformed in uniaxial tension, a body centred cubic steel deformed to larger strain by cold rolling, and hexagonal InAlN layers grown on misfitting sapphire and silicon carbide substrates.
Wu, Songtao; Zhu, Gaohua; Zhang, Jin S; Banerjee, Debasish; Bass, Jay D; Ling, Chen; Yano, Kazuhisa
2014-05-21
We report anisotropic expansion of self-assembled colloidal polystyrene-poly(dimethylsiloxane) crystals and its impact on the phonon band structure at hypersonic frequencies. The structural expansion was achieved by a multistep infiltration-polymerization process. Such a process expands the interplanar lattice distance 17% after 8 cycles whereas the in-plane distance remains unaffected. The variation of hypersonic phonon band structure induced by the anisotropic lattice expansion was recorded by Brillouin measurements. In the sample before expansion, a phononic band gap between 3.7 and 4.4 GHz is observed; after 17% structural expansion, the gap is shifted to a lower frequency between 3.5 and 4.0 GHz. This study offers a facile approach to control the macroscopic structure of colloidal crystals with great potential in designing tunable phononic devices.
F Bakhshi Garmi
2016-02-01
Full Text Available In this paper we studied the focusing effect of electromagnetic wave in the two-dimensional graded photonic crystal consisting of Silicon rods in the air background with gradually varying lattice constant. The results showed that graded photonic crystal can focus wide beams on a narrow area at frequencies near the lower edge of the band gap, where equal frequency contours are not concave. For calculation of photonic band structure and equal frequency contours, we have used plane wave expansion method and revised plane wave expansion method, respectively. The calculation of the electric and magnetic fields was performed by finite difference time domain method.
Deformed lattice states in a Zn{sub 0.9}V{sub 0.1}Se cubic crystal
Maksimov, V. I., E-mail: kokailo@rambler.ru; Dubinin, S. F.; Surkova, T. P.; Parkhomenko, V. D. [Russian Academy of Sciences, Institute of Metal Physics, Ural Branch (Russian Federation)
2016-01-15
Neutron scattering patterns have been recorded for a bulk Zn{sub 0.9}V{sub 0.1}Se cubic crystal at room temperature; they are indicative of macroscopic deformation in the material and its significant inhomogeneity. Specific features of the previously found state, preceding the fcc ↔ hcp structural transformation of the sphalerite lattice upon strong destabilization induced by vanadium ions in the doped ZnSe matrix, are discussed taking into account the data obtained.
Im, Song-Jin; Husakou, Anton; Herrmann, Joachim
2010-08-01
We study the delivery of few-cycle soliton-like pulses at 800 nm with gigawatt power or microjoule energy through a hollow-core kagome-lattice photonic crystal fiber over 1 m with preserved temporal and spectral shape. We show that with optimized pressure of the argon filling, 5 fs input pulses are compressed up to 2.5 fs after 20 cm and restore their shape after 1 m propagation.
Towards true 3-dimensional BCC colloidal crystals with controlled lattice orientation
Dziomkina, N.; Hempenius, Mark A.; Vancso, Gyula J.
2009-01-01
A fabrication method of colloidal crystals possessing the BCC crystal structure is described. BCC colloidal crystals with a thickness of up to seven colloidal layers were grown in the direction of the (100) crystal plane. Defect free colloidal crystals with a homogeneous surface coverage were
On pressure figures in single crystals, mechanical strength, and high stresses
Schloessin, H. H.; Secco, R. A.; Spal, R. D.
1994-07-01
A static or impulsive point force, applied to differently oriented faces of a single crystal, produces different characteristic pressure or percussion figures (p-figures). They characterize the various ways of compliance of different constitutions and structures of solid matter to surface and internal stresses beyond those within the elastic range of Hertz and Boussinesq stresses. The range of applied forces throughout which p-figures nucleate, grow and change, depends not only on substrate and structure but also on the crystal volume, shape, and boundary conditions at the load-free surfaces. P-figures may be seen as vignettes which sum up what we customarily describe as mechanical strength. Different states in the p-figure development with increasing load, reveal the tactics which a crystal of particular substance, structure, and orientation uses to redistribute the loading from the initial Hertzian surface contact area to internal, elastically, and plastically supported, load surfaces. They include mechanical twinning, plastic deformation and flow, fracture and, in many cases, localized electronic and polymorphic structure transformation. The theory of surface dislocations is most suitable to describe the features and interactions of the different forms of compliance and to determine their stress fields. In the past, p-figures have been most significant in crystallography and mineralogy based on optical microscopy. In ongoing experiments, we are using synchrotron x-ray diffraction microscopy of crystals set on a goniometer stage, fitted with an on-line controlled indentation device, to see the generation of p-figures in the form of time sequences of O- and H-beam diffraction images of their lattice strains.
Near-field imaging of a square-lattice metallic photonic-crystal slab at the second band
Feng Shuai; Feng Zhi-Fang; Ren Kun; Ren Cheng; Li Zhi-Yuan; Cheng Bing-Ying; Zhang Dao-Zhong
2006-01-01
Imaging properties of a two-dimensional photonic crystal slab lens are investigated through the finite-difference time-domain method. In this paper, we consider the photonic crystal slab consisting of a square lattice of square metallic rods immersed in a dielectric background. Through the analysis of the equifrequency-surface contours and the field patterns of a point source placed in the vicinity of the photonic crystal slab, we find that a good-quality image can form at the frequencies in the second TM-polarized photonic band. Comparing the images formed at different frequencies, we can clearly see that an excellent-quality image is formed by the mechanisms of simultaneous action of the self-collimation effect and the negative-refraction effect.
Liu, Rongqiang; Zhao, Haojiang; Zhang, Yingying; Guo, Honghwei; Deng, Zongquan
2015-12-01
The plane wave expansion (PWE) method is used to calculate the band gaps of two-dimensional (2D) phononic crystals (PCs) with a hybrid square-like (HSL) lattice. Band structures of both XY-mode and Z-mode are calculated. Numerical results show that the band gaps between any two bands could be maximized by altering the radius ratio of the inclusions at different positions. By comparing with square lattice and bathroom lattice, the HSL lattice is more efficient in creating larger gaps.
Stanislavchuk, T. N.; Litvinchuk, A. P.; Hu, Rongwei; Jeon, Young Hun; Ji, Sung Dae; Cheong, S.-W.; Sirenko, A. A.
2015-10-01
Optical properties and lattice dynamics of hexagonal 2 H -BaMn O3 single crystals are studied experimentally in a wide temperature range by means of rotating analyzer ellipsometry and Raman scattering. The magnitude of the direct electronic band gap is found to be Eg=3.2 eV . At room temperature the far-infrared (IR) ellipsometry spectra reveal six IR-active phonons; two of them are polarized along the c axis and four are polarized within the a-b plane. Seven phonon modes are identified in the Raman scattering experiments. Group theoretical mode analysis and complementary density functional theory lattice dynamics calculations are consistent with the 2 H -BaMn O3 structure belonging to the polar P 63m c space group at room temperature. All observed vibrational modes are assigned to specific eigenmodes of the lattice. The neutron diffraction measurements reveal a structural phase transition upon cooling below TC=130 ±5 K , which is accompanied by a lattice symmetry change from P 63m c to P 63c m . Simultaneously, at temperatures below TC several additional IR- and Raman-active modes are detected in experimental spectra. This confirms the occurrence of a structural transition, which is possibly associated with the appearance of electrical polarization along the c axis and a previously known tripling of the primitive cell volume at low temperatures.
无
2006-01-01
During the crystal growth of Nd, Cr∶GSGG by Czochralski method, in some cases eutectic reaction occurred in the nether region of the crystal, and the boule was divided into two obvious different parts, which is upper Nd,Cr∶GSGG crystal and the nether coexisting Nd,Cr∶GSGG and GdScO3. By X-ray powder diffraction, the structure change of NdCr∶GSGG crystal of Φ 27 mm×120 mm with eutectic along its grown direction was studied. By the least square method and extrapolation function f=sinθ-sinθ1-t(t is an adjustable parameter), the lattice parameters of Nd,Cr∶GSGG and additional GdScO3 phase were computed. The results indicate that the lattice parameters of Nd,Cr∶GSGG increase along its growth direction, which changes from a=(1.25650±0.00007) nm of the top to (1.25798±0.00010) nm of the bottom. In the process of Nd,Cr∶GSGG growth, Gd3+ in Nd,Cr∶GSGG is partly replaced by Nd3+ with larger ionic radii, and the volatilization of Ga component results in its composition variance, which cause the lattice parameters increase along growth direction. In the eutectic section, there are the Nd,Cr∶GSGG and the second phase orthorhombic GdScO3. The lattice parameters of GdScO3 are a=0.5443±0.0007, b=0.5699±0.0005 and c=(0.7865±0.0009) nm, and that of Nd,Cr∶GSGG is (1.25798±0.00010) nm. In the final growth stage, excessive volatilization of Ga composition during the crystal growth causes the growth melt deflect of the Nd,Cr∶GSGG solid solution range seriously, and results in the eutectic reaction, and the outgrowth of Nd,Cr∶GSGG and GdScO3. So it is necessary to decrease the effect of gallium volatilization during the growth in order to avoid eutectic growth and obtain a high-quality Nd,Cr∶GSGG.
Van Enter, A C D
2003-01-01
We consider various sufficiently nonlinear sigma models for nematic ordering of RP^{N-1} type and of lattice gauge type with continous symmetries. We rigorously show that they exhibit a first-order transition in the temperature. The result holds in dimension 2 or more for the RP{N-1} models and in dimension 3 or more for the lattice gauge models. In the two-dimensional case our results clarify and solve a recent controversy about the possibilty of such transitions. For lattice gauge models our methods provide the first prof of a first-order transition in a model with a continous gauge symmetry.
Zhou Yun Song; Wang Fu He
2003-01-01
We investigate the properties of guide modes localized at the interfaces of photonic crystal (PC) heterostructures which are composed of two semi-infinite two-dimensional PCs consisting of non-circular air cylinders with different rotating angles embedded in a homogeneous host dielectric. Photonic band gap structures are calculated with the use of the plane-wave expansion method in combination with a supercell technique. We consider various configurations, for instance, rectangular (square) lattice-rectangular (square) air cylinders, and different rotating angles of the cylinders in the lattices on either side of the interface of a heterostructure. We find that the absolute gap width and the number of guide modes strongly depend on geometric and physical parameters of the heterostructures. It is anticipated that the guide modes in such heterostructures can be engineered by adjusting parameters.
Calculations of the Spin-Lattice Coupling Coefficients Fij and Zij for MgO:Co2+Crystal
ZHENG Wen-Chen; WU Shao-Yi
2001-01-01
According to a uniform and simple method of calculating spin-lattice coupling coefficients and the pert1rbation formulas of gi factors and hyperfine structure constants Ai based on the cluster approach for 3d7 ions in cubic,tetragonal and trigonal octahedral crystal fields, the spin-lattice coupling coefficients Fij (F11, Fl2, F44), Zij (Z11, Z12,Z44) and also g factor and hyperfine constant A for MgO:Co2+ are calculated by using the parameters obtained from the optical spectra without adjustable parameters. The calculated results show good agreement with the observed values.The difiiculty in explaining the coeficients Fij and Zij is therefore removed.``
Charles M. Reinke
2011-12-01
Full Text Available Recent work has demonstrated that nanostructuring of a semiconductor material to form a phononic crystal (PnC can significantly reduce its thermal conductivity. In this paper, we present a classical method that combines atomic-level information with the application of Bloch theory at the continuum level for the prediction of the thermal conductivity of finite-thickness PnCs with unit cells sized in the micron scale. Lattice dynamics calculations are done at the bulk material level, and the plane-wave expansion method is implemented at the macrosale PnC unit cell level. The combination of the lattice dynamics-based and continuum mechanics-based dispersion information is then used in the Callaway-Holland model to calculate the thermal transport properties of the PnC. We demonstrate that this hybrid approach provides both accurate and efficient predictions of the thermal conductivity.
Reinke, Charles M.; Su, Mehmet F.; Davis, Bruce L.; Kim, Bongsang; Hussein, Mahmoud I.; Leseman, Zayd C.; Olsson-III, Roy H.; El-Kady, Ihab
2011-12-01
Recent work has demonstrated that nanostructuring of a semiconductor material to form a phononic crystal (PnC) can significantly reduce its thermal conductivity. In this paper, we present a classical method that combines atomic-level information with the application of Bloch theory at the continuum level for the prediction of the thermal conductivity of finite-thickness PnCs with unit cells sized in the micron scale. Lattice dynamics calculations are done at the bulk material level, and the plane-wave expansion method is implemented at the macrosale PnC unit cell level. The combination of the lattice dynamics-based and continuum mechanics-based dispersion information is then used in the Callaway-Holland model to calculate the thermal transport properties of the PnC. We demonstrate that this hybrid approach provides both accurate and efficient predictions of the thermal conductivity.
Analytical stress tensor and pressure calculations with the CRYSTAL code
Doll, K.
2010-02-01
The calculation of the stress tensor and related properties and its implementation in the CRYSTAL code are described. The stress tensor is obtained from the earlier implemented analytical gradients with respect to the cell parameters. Subsequently, the pressure and enthalpy are computed, and a test concerning the pressure-driven phase transition in KI is used as an illustration. Finally, the possibility of applying external pressure is implemented. The constant-pressure optimization offers an alternative optimization method in addition to the already implemented optimization at constant volume.
Raman electron spin-lattice relaxation with the Debye-type and with real phonon spectra in crystals.
Hoffmann, Stanislaw K; Lijewski, Stefan
2013-02-01
Electron spin-lattice relaxation temperature dependence was measured for Ti(2+) (S=1) and for Cu(2+) (S=1/2) ions in SrF(2) single crystal by electron spin echo method in temperature range 4-109K. The spin relaxation was governed by the two-phonon Raman processes. The relaxation theory is outlined and presented in a form suitable for applying with real phonon spectra. The experimental relaxation results were described using Debye-type phonon spectrum and the real phonon spectrum of SrF(2) crystal. The Debye approximation does not fit well the results for SrF(2) both at low and at high temperature. The relaxation rate is faster than that predicted by Debye-type phonon spectrum at low temperatures where excess of lattice vibrations over the Debye model exists but is slower at higher temperatures (above 50K) where density of phonon states continuously decreases when approaching to the maximal acoustic phonon frequency. The expected deviation from Debye approximation was analyzed also for Cu(2+) in NaCl and MgSiO(3) crystals for which phonon spectra are available. The fitting with the real phonon spectrum allowed us to calculate spin-phonon coupling parameter as 267 cm(-1) for Ti(2+) and 1285 cm(-1) for Cu(2+) in SrF(2).
Chetverikov, A. P.; Ebeling, W.; Velarde, M. G.
2016-09-01
We present computational evidence of the possibility of fast, supersonic or subsonic, nearly loss-free ballistic-like transport of electrons bound to lattice solitons (a form of electron surfing on acoustic waves) along crystallographic axes in two-dimensional anharmonic crystal lattices. First we study the structural changes a soliton creates in the lattice and the time lapse of recovery of the lattice. Then we study the behavior of one electron in the polarization field of one and two solitons with crossing pathways with suitably monitored delay. We show how an electron surfing on a lattice soliton may switch to surf on the second soliton and hence changing accordingly the direction of its path. Finally we discuss the possibility to control the way an excess electron proceeds from a source at a border of the lattice to a selected drain at another border by following appropriate straight pathways on crystallographic axes.
Structural evolution of amino acid crystals under stress from a non-empirical density functional
Sabatini, Riccardo; Küçükbenli, Emine; Kolb, Brian; Thonhauser, T.; de Gironcoli, Stefano
2012-10-01
Use of the non-local correlation functional vdW-DF (from ‘van der Waals density functional’ Dion M et al 2004 Phys. Rev. Lett. 92 246401) has become a popular approach for including van der Waals interactions within density functional theory. In this work, we extend the vdW-DF theory and derive the corresponding stress tensor in a fashion similar to the LDA and GGA approach, which allows for a straightforward implementation in any electronic structure code. We then apply our methodology to investigate the structural evolution of amino acid crystals of glycine and l-alanine under pressure up to 10 GPa—with and without van der Waals interactions—and find that for an accurate description of intermolecular interactions and phase transitions in these systems, the inclusion of van der Waals interactions is crucial. For glycine, calculations including the vdW-DF (vdW-DF-c09x) functional are found to systematically overestimate (underestimate) the crystal lattice parameters, yet the stability ordering of the different polymorphs is determined accurately, at variance with the GGA case. In the case of l-alanine, our vdW-DF results agree with recent experiments that question the phase transition reported for this crystal at 2.3 GPa, as the a and c cell parameters happen to become equal but no phase transition is observed.
Martínez, Luis Javier; Huang, Ningfeng; Ma, Jing; Lin, Chenxi; Jaquay, Eric; Povinelli, Michelle L
2013-12-16
A new photonic crystal structure is generated by using a regular graphite lattice as the base and adding a slot in the center of each unit cell to enhance field confinement. The theoretical Q factor in an ideal structure is over 4 × 10(5). The structure was fabricated on a silicon-on-insulator wafer and optically characterized by transmission spectroscopy. The resonance wavelength and quality factor were measured as a function of slot height. The measured trends show good agreement with simulation.
Xiaozhi Wu; Shaofeng Wang
2007-01-01
Applying the parametric derivation method, Peierls energy and Peierls stress are calculated with a non-sinusoidal force law in the lattice theory, while the results obtained by the power-series expansion according to sinusoidal law can be deduced as a limiting case of nonsinusoidal law. The simplified expressions of Peierls energy and Peierls stress are obtained for the limit of wide and narrow. Peierls energy and Peierls stress decrease monotonically with the factor of modification of force law. Present results can be used expediently for prediction of the correct order of magnitude of Peierls stress for materials.
Seabra, Luis; Sindzingre, Philippe; Momoi, Tsutomu; Shannon, Nic
2016-02-01
A large part of the interest in magnets with frustrated antiferromagnetic interactions comes from the many new phases found in applied magnetic field. In this article, we explore some of the new phases which arise in a model with frustrated ferromagnetic interactions, the J1-J2-J3 Heisenberg model on a square lattice. Using a combination of classical Monte Carlo simulation and spin-wave theory, we uncover behavior reminiscent of some widely studied frustrated antiferromagnets, but with a number of new twists. We first demonstrate that, for a suitable choice of parameters, the phase diagram as a function of magnetic field and temperature is nearly identical to that of the Heisenberg antiferromagnet on a triangular lattice, including the celebrated 1 /3 -magnetization plateau. We then examine how this phase diagram changes when the model is tuned to a point where the classical ground state is highly degenerate. In this case, two new phases emerge: a classical, finite-temperature spin liquid, characterized by a "ring" in the spin structure factor S (q ) ; and a vortex crystal, a multiple-Q state with finite magnetization, which can be viewed as an ordered lattice of magnetic vortices. All of these new phases persist for a wide range of magnetic fields. We discuss the relationship between these results and published studies of frustrated antiferromagnets, together with some of the materials where these new phases might be observed in experiment.
The cone phase of liquid crystals: Triangular lattice of double-tilt cylinders
Yashodhan Hatwalne; N V Madhusudana
2003-08-01
We predict the existence of a new defect-lattice phase near the nematic–smectic-C (NC) transition. This tilt-analogue of the blue phase is a lattice of double-tilt cylinders which are disclination lines in the smectic layer normal as well as the c-ﬁeld. We discuss the structure and stability of the cone phase. We suggest that many ‘nematics’ exhibiting short range layering and tilt order may in fact be in the molten cone phase, which is a line liquid.
Wei, Zhenyi; Tou, Shushi; Wu, Bo; Bai, Kewu
2016-12-01
ZnZrAl2 is a kind of heterogeneous nucleation to promote the refine of grain of ZA43 alloy. ZnZrAl2 intermetallic is also considered as a candidate for superalloys. The crystal lattice structure, alloy thermodynamics and mechanical properties of ZnZrAl2 intermetallic compound were investigated by ab initio calculations based on density functional theory (DFT). In particular, the site preference of atoms in different sublattices was predicted based on alloy thermodynamics. At ground state, the most stable structure is L12 structure with sublattice model (Zn)1a(Zr0.3333Al0.6667)3c or (Zr)1a(Zn0.3333Al0.6667)3c, and the occupying preferences of Zn, Zr and Al atoms are independent with the increasing temperature. The bulk, shear, Young's modulus and the Poisson's ratio of the L12 structure ZnZrAl2 were calculated based on the site occupying configurations. The results show that ZnZrAl2 is a brittle material in nature. Electronic structures analysis revealed that Al-Zr atoms possess a covalent bonding character, while the Zn-Zr atoms have a metallic bonding character. ZnZrAl2 has stable mechanical properties at high temperature. The grain refinement effect of ZnZrAl2 precipitates in Zn-Al alloys were discussed based on crystal lattice match theory.
Probing the sheath electric field with a crystal lattice by using thermophoresis in dusty plasma
Land, Victor; Matthews, Lorin; Hyde, Truell
2010-01-01
A two-dimensional dust crystal levitated in the sheath of a modified Gaseous Electronics Conference (GEC) reference cell is manipulated by heating or cooling the lower electrode. The dust charge is obtained by measuring global characteristics of the levitated crystal obtained from top-view pictures. From the force balance, the electric field in the sheath is reconstructed. From the Bohm criterion, we conclude that the dust crystal is levitated mainly above and just below the classical Bohm point.
Huang, Qing; Liu, Peng; Liu, Tao; Guo, Sha-Sha; Zhang, Lian; Wang, Xue-Lin
2012-09-01
A z-cut LiNbO3 crystal was immersed in a molten benzoic acid for 10 min and then was implanted with 6-MeV oxygen ions at a fluence of 6 × 1014 ions/cm2. Lattice damage in this crystal was measured by a Rutherford backscattering and channeling technique and was compared with lattice damage in a proton-exchanged LiNbO3 crystal and an oxygen-ion-implanted LiNbO3 crystal. A totally amorphous layer was formed at the crystal's surface after both proton exchange and oxygen-ion implantation processes were performed, even though either process alone never led to a relative disorder of the lattice up to 0.2. It indicates that the crystal lattice in the proton-exchanged layer is unstable and can be easily damaged by ion implantation subsequently. The waveguide structure formed by proton exchange was destroyed by oxygen-ion implantation. Oxygen-ion implantation induced an increase in extraordinary refractive index and formed another waveguide structure underneath the amorphous surface layer.
Energy Transport between Hole Gas and Crystal Lattice in Diluted Magnetic Semiconductor
Kivioja, J. M.; Prunnila, M.; Novikov, S.; Kuivalainen, P.; Ahopelto, J.
2006-01-01
The temperature dependent energy transfer rate between charge carriers and lattice has been experimentally investigated in ferromagnetic semiconductors. Studied 100 nm thick low-temperature MBE grown Mn_{x}Ga_{1-x}As samples had manganese concentrations x=3.7 % and 4.0 %. Curie temperatures estimated from temperatures of peak resistivities were 60 K and 62 K, respectively.
Wielewski, Euan J.; Boyce, Donald; Park, Jun-Sang; Miller, M P; Dawson, Paul
2017-03-01
Determining reliable single crystal material parameters for complex polycrystalline materials is a significant challenge for the materials community. In this work, a novel methodology for determining those parameters is outlined and successfully applied to the titanium alloy, Ti-6Al-4V. Utilizing the results from a lattice strain pole figure experiment conducted at the Cornell High Energy Synchrotron Source, an iterative approach is used to optimize the single crystal elastic moduli by comparing experimental and simulated lattice strain pole figures at discrete load steps during a uniaxial tensile test. Due to the large number of unique measurements taken during the experiments, comparisons were made by using the discrete spherical harmonic modes of both the experimental and simulated lattice strain pole figures, allowing the complete pole figures to be used to determine the single crystal elastic moduli. (C) 2016 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Lattice constant and hardness of InSb:Bi bulk crystals grown by vertical directional solidification
Maske, Dilip; Deshpande, Manisha; Choudhary, Rashmi; Gadkari, Dattatray
2016-05-01
Ingots of the Bi doped InSb (InSb1-xBix) bulk semiconductor crystals were grown by specially designed Vertical Directional Solidification (VDS) technique. Substrates of seven crystals grown with various composition values of x (0 ≤ x 0.05.
Yang Ping; Li Pei; Zhang Li-Qiang; Wang Xiao-Liang; Wang Huan; Song Xi-Fu; Xie Fang-Wei
2012-01-01
The lattice,the band gap and the optical properties of n-type ZnO under uniaxial stress are investigated by firstprinciples calculations.The results show that the lattice constants change linearly with stress.Band gaps are broadened linearly as the uniaxial compressive stress increases.The change of band gap for n-type ZnO comes mainly from the contribution of stress in the c-axis direction,and the reason for band gap of n-type ZnO changing with stress is also explained.The calculated results of optical properties reveal that the imaginary part of the dielectric function decreases with the increase of uniaxial compressive stress at low energy.However,when the energy is higher than 4.0 eV,the imaginary part of the dielectric function increases with the increase of stress and a blueshift appears.There are two peaks in the absorption spectrum in an energy range of 4.0-13.0 eV.The stress coefficient of the band gap of n-type ZnO is larger than that of pure ZnO,which supplies the theoretical reference value for the modulation of the band gap of doped ZnO.
Lattice Boltzmann Simulation of 3D Nematic Liquid Crystal near Phase Transition
ZHANG Jun; TAO Rui-Bao
2002-01-01
Phase transition between nematic and isotropic liquid crystal is a very weak first order phase transition.We avoid to use the normal Landau-de Gennes's free energy that reduces a strong first order transition, and set up adata base of free energy calculated by means of Tao-Sheng Lin's extended molecular field theory that can explain theexperiments of the equilibrium properties of nematic liquid crystal very well. Then we use the free energy method oflattice Boltzmann developed by Oxford group to study the phase decomposition, pattern formation in the flow of theliquid crystal near transition temperature.
Stress Wave Isolation by Purely Mechanical Topological Phononic Crystals
Chaunsali, Rajesh; Li, Feng; Yang, Jinkyu
2016-08-01
We present an active, purely mechanical stress wave isolator that consists of short cylindrical particles arranged in a helical architecture. This phononic structure allows us to change inter-particle stiffness dynamically by controlling the contact angles of the cylinders. We use torsional travelling waves to control the contact angles, thereby imposing a desired spatio-temporal stiffness variation to the phononic crystal along the longitudinal direction. Such torsional excitation is a form of parametric pumping in the system, which results in the breakage of the time-reversal symmetry. We report that, in quasi-static sense, the system shows topologically non-trivial band-gaps. However, in a dynamic regime where the pumping effect is significant, these band-gaps become asymmetric with respect to the frequency and wavenumber domains in the dispersion relationship. By using numerical simulations, we show that such asymmetry has a direct correspondence to the topological invariant, i.e., Chern number, of the system. We propose that this asymmetry, accompanied by selective inter-band transition, can be utilized for directional isolation of the stress wave propagating along the phononic crystal.
Janssen, Lukas; Andrade, Eric C.; Vojta, Matthias
2016-12-01
The Heisenberg-Kitaev model is a paradigmatic model to describe the magnetism in honeycomb-lattice Mott insulators with strong spin-orbit coupling, such as A2IrO3 (A =Na , Li ) and α -RuCl3 . Here, we study in detail the physics of the Heisenberg-Kitaev model in an external magnetic field. Using a combination of Monte Carlo simulations and spin-wave theory, we map out the classical phase diagram for different directions of the magnetic field. Broken SU(2) spin symmetry renders the magnetization process rather complex, with sequences of phases and metamagnetic transitions. In particular, we find various large-unit-cell and multi-Q phases including a vortex-crystal phase for a field in the [111 ] direction. We also discuss quantum corrections in the high-field phase.
Engineering the near-field imaging of a rectangular-lattice photonic-crystal slab in the second band
无
2009-01-01
Imaging properties of a two-dimensional rectangular-lattice photonic crystal (PC) slab consisting of air holes immersed in a dielectric are studied in this work. The field patterns of electromagnetic waves radiated from a point source through the PC slab are calculated with the finite-difference time-domain method. Comparing the field patterns with the corresponding equifrequency-surface contours simulated by the plane-wave expansion method, we find that an excellent-quality near-field image may be formed through the PC slab by the mechanisms of the simultaneous action of the self-collimation effect and the negative-refraction effect. Near-field imaging may be obtained within two different frequency regions in two vertical directions of the PC slab.
Nuclear Spin-Lattice Relaxation of Single Crystal Sr{sub 14}Cu{sub 24}O{sub 41}
Ohsugi, S., E-mail: ohsugi@cit.sangitan.ac.jp [College of Industrial Technology, Department of Electrical Engineering and Electronics (Japan); Matsumoto, S. [National Institute for Materials Science, Tsukuba Magnet Laboratory (Japan); Kitaoka, Y. [Osaka University, Department of Physical Science, Graduate School of Engineering Science (Japan); Matsuda, M. [Japan Atomic Energy Research Institute, Advanced Science Research Center (Japan); Uehara, M. [Aoyama-Gakuin University, Department of Physics (Japan); Nagata, T. [Ochanomizu University, Department of Physics (Japan); Akimitsu, J. [Aoyama-Gakuin University, Department of Physics (Japan)
2004-12-15
Nuclear spin-lattice relaxation rate T{sub 1}{sup -1} has been measured for the ladder sites of two single crystals Sr{sub 14}Cu{sub 24}O{sub 41} (Sr14-A,B) by {sup 63}Cu NMR/NQR. The hole localization around 100 K appears as a peak in the T variation of T{sub 1}{sup -1}(NQR). On the other hand, it is suppressed in the T{sub 1}{sup -1} (NMR) data under the magnetic field H {approx} 11 T, and a new peak appears around 20 K. T{sub 1}{sup -1}(NMR) around the peak is more enlarged for Sr14-B than for Sr14-A. Hence, holes on the ladders of Sr14-B tend to be more localized. This is considered to be an origin for the occurrence of the magnetic order in Sr14-B under H {approx} 11 T.
Engineering the near-field imaging of a rectangular-lattice photonic-crystal slab in the second band
FENG Shuai; AO Ling; WANG YiQuan
2009-01-01
Imaging properties of a two-dimensional rectangular-lattice photonic crystal (PC) slab consisting of air holes immersed in a dielectric are studied in this work. The field patterns of electromagnetic waves radiated from a point source through the PC slab are calculated with the finite-difference time-domain method. Comparing the field patterns with the corresponding equifrequency-surface contours simu-lated by the plane-wave expansion method, we find that an excellent-quality near-field image may be formed through the PC slab by the mechanisms of the simultaneous action of the self-collimation effect and the negative-refraction effect. Near-field imaging may be obtained within two different frequency regions in two vertical directions of the PC slab.
Polymer lattices as mechanically tunable 3-dimensional photonic crystals operating in the infrared
Chernow, V. F., E-mail: vchernow@caltech.edu [Division of Engineering and Applied Sciences, California Institute of Technology, Pasadena, California 91125 (United States); Alaeian, H. [Department of Electrical Engineering, Stanford University, Stanford, California 94305 (United States); Department of Materials Science and Engineering, Stanford University, Stanford, California 94305 (United States); Dionne, J. A. [Department of Materials Science and Engineering, Stanford University, Stanford, California 94305 (United States); Greer, J. R. [Division of Engineering and Applied Sciences, California Institute of Technology, Pasadena, California 91125 (United States); The Kavli Nanoscience Institute, California Institute of Technology, Pasadena, California 91125 (United States)
2015-09-07
Broadly tunable photonic crystals in the near- to mid-infrared region could find use in spectroscopy, non-invasive medical diagnosis, chemical and biological sensing, and military applications, but so far have not been widely realized. We report the fabrication and characterization of three-dimensional tunable photonic crystals composed of polymer nanolattices with an octahedron unit-cell geometry. These photonic crystals exhibit a strong peak in reflection in the mid-infrared that shifts substantially and reversibly with application of compressive uniaxial strain. A strain of ∼40% results in a 2.2 μm wavelength shift in the pseudo-stop band, from 7.3 μm for the as-fabricated nanolattice to 5.1 μm when strained. We found a linear relationship between the overall compressive strain in the photonic crystal and the resulting stopband shift, with a ∼50 nm blueshift in the reflection peak position per percent increase in strain. These results suggest that architected nanolattices can serve as efficient three-dimensional mechanically tunable photonic crystals, providing a foundation for new opto-mechanical components and devices across infrared and possibly visible frequencies.
Mapping residual stresses in PbWO$_{4}$ crystals using photo-elastic analysis
Lebeau, Michel; Majni, G; Paone, N; Pietroni, P; Rinaldi, D
2005-01-01
Large scintillating crystals are affected by internal stresses induced by the crystal growth temperature gradient remanence. Cutting boules (ingots) into finished crystal shapes allows for a partial tension relaxation but residual stresses remain the main cause of breaking. Quality control of residual stresses is essential in the application of Scintillating Crystals to high-energy physics calorimeters (e.g. CMS ECAL at CERN LHC). In this context the industrial process optimisation towards stress reduction is mandatory. We propose a fast technique for testing samples during the production process in order to evaluate the residual stress distribution after the first phases of mechanical processing. We mapped the stress distribution in PbWO/sub 4/slabs cut from the same production boule. The analysis technique is based on the stress intensity determination using the photo-elastic properties of the samples. The stress distribution is mapped in each sample. The analysis shows that there are regions of high residu...
Palani Natarajan; Paloth Venugopalan; Jarugu Narasimha Moorthy
2010-09-01
Tetrakis(2,6-dimethyl-4-acetoxyphenyl)pyrene H2 containing flexible acetate functionalities at the para positions of sterically-hindered and rigid aryl rings functions as an inclusion host system. Depending on the orientations of the acetate functionalities, a variety of conformers may indeed be expected. A limited number of the crystal structures of the inclusions compounds of H2 reveal that one indeed observes 2 different conformations for the host based on the orientations of the acetate functionalities. The inclusion compound of H2 with benzene guest molecules is particularly appealing in terms of how the latter are held in trough domains of the host by weak C−H$\\cdots$O and C−H$\\cdots$ hydrogen bonds. More experimentation and analyses of crystal structures of such systems is expected to lead to better insights toward realizing multicomponent molecular crystals in a rational manner.
Kyu; Hwan; Hwang; G.; Hugh; Song; Chanmook; Lim; Soan; Kim; Kyung-Won; Chun; Mahn; Yong; Park
2003-01-01
A channel-drop filter has been designed based on the two-dimensional triangular-lattice hole photonic-crystal structure, which consists of two line defects and two point defects, by a two-dimensional finite-difference time-domain simulation.
Analysis of the crystal lattice instability for cage–cluster systems using the superatom model
Serebrennikov, D. A., E-mail: dserebrennikov@innopark.kantiana.ru, E-mail: dimafania@mail.ru; Clementyev, E. S. [I. Kant Baltic Federal University, “Functional Nanomaterials” Scientific–Educational Center (Russian Federation); Alekseev, P. A. [“Kurchatov Institute” National Research Center (Russian Federation)
2016-09-15
We have investigated the lattice dynamics for a number of rare-earth hexaborides based on the superatom model within which the boron octahedron is substituted by one superatom with a mass equal to the mass of six boron atoms. Phenomenological models have been constructed for the acoustic and lowenergy optical phonon modes in RB{sub 6} (R = La, Gd, Tb, Dy) compounds. Using DyB{sub 6} as an example, we have studied the anomalous softening of longitudinal acoustic phonons in several crystallographic directions, an effect that is also typical of GdB{sub 6} and TbB{sub 6}. The softening of the acoustic branches is shown to be achieved through the introduction of negative interatomic force constants between rare-earth ions. We discuss the structural instability of hexaborides based on 4f elements, the role of valence instability in the lattice dynamics, and the influence of the number of f electrons on the degree of softening of phonon modes.
Montalto, L; Paone, N; Scalise, L; Rinaldi, D
2015-06-01
The assessment of the stress state of scintillating crystals is an important issue for producers as well as users of such materials, because residual stress may arise during growth process. In this paper, a measurement system, based on the use of a photoelastic, conoscopic optical setup, is proposed for the assessment of stress state in scintillating crystals. Local stress values can be measured on the crystal in order to observe their spatial distribution. With the proposed system, it is possible to vary the dimensions of the inspected measurement volume. It has been validated with reference to a known stress state induced in a birefringent crystal sample and it has been tested for the case of loaded and unloaded samples, showing sub-millimetric spatial resolution and stress uncertainty ≤0.25 MPa. The proposed measurement system is a valid method for the inspection of scintillating crystals required by producers and users of such materials.
Petrushin, N.V.; Ignatova, I.A.; Logunov, A.V.; Samojlov, A.I.; Razumovskij, I.M.
Effect of Cr, Co, Nb and W alloying elements on crystal lattice parameters of ..gamma.. ahd ..gamma..' phases in Ni-Cr-Co-W-Al-Ti- Nb-Hf alloys and on their dimensional misfit at 293 and 1173 K is studied. Alloying at which alloys have the parameter of ..gamma..-solid solution lattice less than that of ..gamma..'-phase results in low heat-resistant properties and in considerable difference of coefficients of thermal expansion of the phases. Definite positive misfit of ..gamma..- and ..gamma..'-phase lattices and a low temperature gradient are the conditions of high heat resistance of complex-alloyed nickel alloys. Possible mechanisms of lattice misfit effect on strength and coalescence kinetics of the second phase in heterogeneous alloys at high temperatures are discussed.
Marquardt, Katharina; Dohmen, Ralf; Wagner, Johannes
2014-05-01
Diffusion along interface and grain boundaries provides an efficient pathway and may control chemical transport in rocks as well as their mechanical strength. Besides the significant relevance of these diffusion processes for various geologic processes, experimental data are still very limited (e.g., Dohmen & Milke, 2010). Most of these data were measured using polycrystalline materials and the formalism of LeClaire (1951) to fit integrated concentration depth profiles. To correctly apply this formalism, certain boundary conditions of the diffusion problem need to be fulfilled, e.g., surface diffusion is ignored, and furthermore the lattice diffusion coefficient has to be known from other studies or is an additional fitting parameter, which produces some ambiguity in the derived grain boundary diffusion coefficients. We developed an experimental setup where we can measure the lattice and grain boundary diffusion coefficients simultaneously but independent and demonstrate the relevance of surface diffusion for typical grain boundary diffusion experiments. We performed Mg2SiO4 bicrystal diffusion experiments, where a single grain boundary is covered by a thin-film of pure Ni2SiO4 acting as diffusant source, produced by pulsed laser deposition. The investigated grain boundary is a 60° (011)/[100]. This specific grain boundary configuration was modeled using molecular dynamics for comparison with the experimental observations in the transmission electron microscope (TEM). Both, experiment and model are in good agreement regarding the misorientation, whereas there are still some disagreements regarding the strain fields along the grain boundary that are of outmost importance for the strengths of the material. The subsequent diffusion experiments were carried out in the temperature range between 800° and 1450° C. The inter diffusion profiles were measured using the TEMs energy dispersive x-ray spectrometer standardized using the Cliff-Lorimer equation and EMPA
Luealamai, Sutha; Panijpan, Bhinyo
2012-01-01
The authors have developed a computer-based learning module on the unit cell of various types of crystal. The module has two components: the virtual unit cell (VUC) part and the subsequent unit cell hunter part. The VUC is a virtual reality simulation for students to actively arrive at the unit cell from exploring, from a broad view, the crystal…
Luealamai, Sutha; Panijpan, Bhinyo
2012-01-01
The authors have developed a computer-based learning module on the unit cell of various types of crystal. The module has two components: the virtual unit cell (VUC) part and the subsequent unit cell hunter part. The VUC is a virtual reality simulation for students to actively arrive at the unit cell from exploring, from a broad view, the crystal…
Non-spherical voids and lattice reorientation patterning in a shock-loaded Al single crystal
Hong, Chuanshi; Fæster, Søren; Hansen, Niels
2017-01-01
An Al single crystal shock loaded in the direction and captured at incipient spallation was examined by combining X-ray tomography, electron backscatter diffraction on a scanning electron microscope, and transmission electron microscopy (TEM). Octahedral voids with {1 1 1} faces were...
Crystal lattice dependency of the free radicals found in irradiated glycine
Bie, M.J.A. de; Braams, R.
1969-01-01
The EPR spectra, and hence the stable free radicals, are different for the - or γ-irradiated α-, β- and γ-crystal forms of polycrystalline glycone. Therefore comparisons of the trideutero-glycine EPR spectrum with the EPR spectra of non-deuterated glycine are open to question
Chernov, Alexander A.
2005-01-01
Nucleation, growth and perfection of protein crystals will be overviewed along with crystal mechanical properties. The knowledge is based on experiments using optical and force crystals behave similar to inorganic crystals, though with a difference in orders of magnitude in growing parameters. For example, the low incorporation rate of large biomolecules requires up to 100 times larger supersaturation to grow protein, rather than inorganic crystals. Nucleation is often poorly reproducible, partly because of turbulence accompanying the mixing of precipitant with protein solution. Light scattering reveals fluctuations of molecular cluster size, its growth, surface energies and increased clustering as protein ages. Growth most often occurs layer-by-layer resulting in faceted crystals. New molecular layer on crystal face is terminated by a step where molecular incorporation occurs. Quantitative data on the incorporation rate will be discussed. Rounded crystals with molecularly disordered interfaces will be explained. Defects in crystals compromise the x-ray diffraction resolution crucially needed to find the 3D atomic structure of biomolecules. The defects are immobile so that birth defects stay forever. All lattice defects known for inorganics are revealed in protein crystals. Contribution of molecular conformations to lattice disorder is important, but not studied. This contribution may be enhanced by stress field from other defects. Homologous impurities (e.g., dimers, acetylated molecules) are trapped more willingly by a growing crystal than foreign protein impurities. The trapped impurities induce internal stress eliminated in crystals exceeding a critical size (part of mni for ferritin, lysozyme). Lesser impurities are trapped from stagnant, as compared to the flowing, solution. Freezing may induce much more defects unless quickly amorphysizing intracrystalline water.
Bagulya, A.V.; Goncharova, L.A. [Lebedev Physical Institute, Russian Academy of Sciences, Leninskii pr., 53, Moscow 119991 (Russian Federation); Ivliev, A.I., E-mail: cosmo@geokhi.r [Vernadsky Institute of Geochemistry and Analytical Chemistry, Russian Academy of Sciences, Kosygina str., 19, 119991 (Russian Federation); Kalinina, G.V., E-mail: ugeochem@geochem.home.chg.r [Vernadsky Institute of Geochemistry and Analytical Chemistry, Russian Academy of Sciences, Kosygina str., 19, 119991 (Russian Federation); Kashkarov, L.L. [Vernadsky Institute of Geochemistry and Analytical Chemistry, Russian Academy of Sciences, Kosygina str., 19, 119991 (Russian Federation); Konovalova, N.S.; Okat' eva, N.M. [Lebedev Physical Institute, Russian Academy of Sciences, Leninskii pr., 53, Moscow 119991 (Russian Federation); Polukhina, N.G., E-mail: poluhina@sci.lebedev.r [Lebedev Physical Institute, Russian Academy of Sciences, Leninskii pr., 53, Moscow 119991 (Russian Federation); Roussetski, A.S.; Starkov, N.I.; Tsarev, V.A. [Lebedev Physical Institute, Russian Academy of Sciences, Leninskii pr., 53, Moscow 119991 (Russian Federation); Vladymyrov, M.S., E-mail: neworld@itep.r [Lebedev Physical Institute, Russian Academy of Sciences, Leninskii pr., 53, Moscow 119991 (Russian Federation)
2009-10-15
The results of measurements of the major track parameters for tracks formed by the accelerated {sup 131}Xe (E = 1.5 GeV) nuclei in individual olivine grains from the Marjalahti pallasite are presented. For each of ten treated crystals, the structure and the main crystal lattice symmetry axis were determined by the X-ray diffraction analysis. The basic track parameters (etching rate V{sub TR} and etched length L) were shown to be independent of the angle between the monocrystal main symmetry axis for each examined crystal and the direction of the accelerated nucleus beam.
Short wavelength (UV + VIS) guidance in kagomé lattice hollow core photonic crystal fibre
Février, Sébastien; Beaudou, Benoît
2010-04-01
Hollow-core microstructured fibres are designed for the short wavelength domains, either visible or ultra-violet ones. The experimental results confirm that kagomé-lattice antiresonant fibres are good candidate for this purpose. Thorough numerical modelling is carried out in order to determine the physical causes responsible for the loss level observed. From these computations the following conclusions are drawn: (i) the sole antiresonant core surround dictates the location of the transmission windows and (ii) the cladding bridges are sources of extra leakage from the core to the surrounding solid cladding. A straightforward model is therefore devised to determine accurately the loss level in this kind of structure by quasi-analytical calculus.
Designing an ultra negative dispersion Photonic Crystal Fiber (PCFs) with square lattice geometry
Maji, Partha Sona
2015-01-01
In this article we have theoretically investigated the dispersion characteristics of dual-core PCF, based on square-lattice geometry by varying different parameters. The fiber exhibits a very large negative dispersion because of rapid slope change of the refractive indices at the coupling wavelength between the inner core and outer core. The dependence of different geometrical parameters namely hole-to-hole spacing (pitch) and different air-hole diameter (d) was investigated in detail. By proper adjustment of the available parameters, a high negative dispersion value of -47,500 ps/nm/km has been achieved around the wavelength of 1550nm. Our proposed fiber will be an excellent device for dispersion compensation in long-haul data transmission as being thousand times more than the available DCFs.
Molecular motions in thermotropic liquid crystals studied by NMR spin-lattice relaxation
Zamar, R.C.; Gonzalez, C.E.; Mensio, O. [Cordoba Univ. Nacional (Argentina). Facultad de Matematica, Astronomia y Fisica
1998-12-01
Nuclear magnetic resonance relaxation experiments with field cycling techniques proved to be a valuable tool for studying molecular motions in liquid crystals, allowing a very broad Larmor frequency variation, sufficient to separate the cooperative motions from the liquid like molecular diffusion. In new experiments combining NMR field cycling with the Jeener-Broekaert order-transfer pulse sequence, it is possible to measure the dipolar order relaxation time (T{sub 1D}), in addition to the conventional Zeeman relaxation time (T{sub 1Z}) in a frequency range of several decades. When applying this technique to nematic thermotropic liquid crystals, T{sub 1D} showed to depend almost exclusively on the order fluctuation of the director mechanism in the whole frequency range. This unique characteristic of T{sub 1D} makes dipolar order relaxation experiments specially useful for studying the frequency and temperature dependence of the spectral properties of the collective motions. (author)
Acoustic band gaps of the woodpile sonic crystal with the simple cubic lattice
Wu, Liang-Yu; Chen, Lien-Wen, E-mail: chenlw@mail.ncku.edu.t [Department of Mechanical Engineering, National Cheng Kung University, Tainan 70101, Taiwan (China)
2011-02-02
This study theoretically and experimentally investigates the acoustic band gap of a three-dimensional woodpile sonic crystal. Such crystals are built by blocks or rods that are orthogonally stacked together. The adjacent layers are perpendicular to each other. The woodpile structure is embedded in air background. Their band structures and transmission spectra are calculated using the finite element method with a periodic boundary condition. The dependence of the band gap on the width of the stacked rods is discussed. The deaf bands in the band structure are observed by comparing with the calculated transmission spectra. The experimental transmission spectra for the {Gamma}-X and {Gamma}-X' directions are also presented. The calculated results are compared with the experimental results.
Lattice and Molecular Vibrations in Single Crystal I2 at 77 K by Inelastic Neutron Scattering
Smith, H. G.; Nielsen, Mourits; Clark, C. B.
1975-01-01
Phonon dispersion curves of single crystal iodine at 77 K have been measured by one-phonon coherent inelastic neutron scattering techniques. The data are analysed in terms of two Buckingham-six intermolecular potentials; one to represent the shortest intermolecular interaction (3.5 Å) and the oth...... to represent the more distant interactions. Moderate agreement is obtained between the observed and calculated frequencies, but it also oappears necessary to treat the second-nearest-neighbor interaction (3.97 Å) separately from the van der Waals interactions (distances ⩾ 4.2 Å).......Phonon dispersion curves of single crystal iodine at 77 K have been measured by one-phonon coherent inelastic neutron scattering techniques. The data are analysed in terms of two Buckingham-six intermolecular potentials; one to represent the shortest intermolecular interaction (3.5 Å) and the other...
Thermoelastic stresses in SiC single crystals grown by the physical vapor transport method
Zibing Zhang; Jing Lu; Qisheng Chen; V.Prasad
2006-01-01
A finite element-based thermoelastic anisotropic stress model for hexagonal silicon carbide polytype is developed for the calculation of thermal stresses in SiC crystals grown by the physical vapor transport method.The composite structure of the growing SiC crystal and graphite lid is considered in the model.The thermal expansion match between the crucible lid and SiC crystal is studied for the first time.The influence of thermal stress on the dislocation density and crystal quality iS discussed.
Ma, Wencheng; Zhao, Wenhan; Wu, Ming; Ding, Guoqiang; Liu, Lijun
2017-09-01
Transient numerical calculations were carried out to predict the evolutions of temperature and thermal stress in sapphire single crystal during the cooling process by heat exchanger method (HEM). Internal radiation in the semitransparent sapphire crystal was taken into account using the finite volume method (FVM) in the global heat transfer model. The numerical results seem to indicate that the narrow bottom region of the sapphire crystal is subjected to high thermal stress during the cooling process, which could be responsible for the seed cracking of the as-grown crystal, while the thermal stress is relatively small in the central main body of the crystal, and is less than 10 MPa during the whole cooling process. The fast decrease of the thermal stress in the bottom region of the crystal during the initial stage of cooling process is dominated by the reduction of the cooling helium gas in the heat exchanger shaft, and is not significantly affected by the heating power reduction rate.
Banavoth, Murali
2016-12-14
Hybrid organic-inorganic perovskite crystals have recently become one of the most important classes of photoactive materials in the solar cell and optoelectronic communities. Albeit improvements have focused on state-of-the-art technology including various fabrication methods, device architectures, and surface passivation, progress is yet to be made in understanding the actual operational temperature on the electronic properties and the device performances. Therefore, the substantial effect of temperature on the optoelectronic properties, charge separation, charge recombination dynamics, and photoconversion efficiency are explored. The results clearly demonstrated a significant enhancement in the carrier mobility, photocurrent, charge carrier lifetime, and solar cell performance in the 60 ± 5 °C temperature range. In this temperature range, perovskite crystal exhibits a highly symmetrical relaxed cubic structure with well-aligned domains that are perpendicular to a principal axis, thereby remarkably improving the device operation. This finding provides a new key variable component and paves the way toward using perovskite crystals in highly efficient photovoltaic cells.
Liu, Y.; Crespillo, M. L.; Huang, Q.; Wang, T. J.; Liu, P.; Wang, X. L.
2017-02-01
As one of the representative ABO3 perovskite-structured oxides, lanthanum aluminate (LaAlO3) crystal has emerged as one of the most valuable functional-materials, and has attracted plenty of fundamental research and promising applications in recent years. Electronic, magnetic, optical and other properties of LaAlO3 strongly depend on its crystal structure, which could be strongly modified owing to the nuclear or electronic energy loss deposited in an ion irradiation environment and, therefore, significantly affecting the performance of LaAlO3-based devices. In this work, utilizing swift (tens of MeV) Si-ion irradiation, the damage behavior of LaAlO3 crystal induced by nuclear or electronic energy loss has been studied in detail utilizing complementary characterization techniques. Differing from other perovskite-structured crystals in which the electronic energy loss could lead to the formation of an amorphous region based on the thermal spike mechanism, in this case, intense electronic energy loss in LaAlO3 will not induce any obvious structural damage. The effects of ion irradiation on the mechanical properties, including hardness increase and elastic modulus decrease, have been confirmed. On the other hand, considering the potential applications of LaAlO3 in the field of integrated optoelectronics, the optical-waveguide properties of the irradiation region have been studied. The significant correspondence (symmetrical inversion) between the iWKB-reconstructed refractive-index profile and SRIM-simulated dpa profile further proves the effects (irradiation-damage production and refractive-index decrease) of nuclear energy loss during the swift-ion penetration process in LaAlO3 crystal. In the case of the rather-thick damage layer produced by swift-ion irradiation, obtaining a damage profile will be constrained owing to the analysis-depth limitation of the characterization techniques (RBS/channeling), and our analysis process (optical guided-mode measurement and
Effect of lattice disorder on the thermal conductivity of ZnBeSe, ZnMgSe and ZnBeMgSe crystals
Strzałkowski, K., E-mail: skaroll@fizyka.umk.pl
2015-08-01
Zn{sub 1−x−y}Be{sub x}Mg{sub y}Se mixed crystals investigated in this work were grown from the melt by the high pressure high temperature modified Bridgman method in the range of composition 0 < x,y < 0.33. Photopyroelectric (PPE) calorimetry in the back (BPPE) and front (FPPE) configuration was applied for thermal investigation of solid samples. The thermal diffusivity and effusivity of investigated crystals were derived from the experimental data. Since dynamic thermal parameters are connected with each other, thermal conductivity of the specimens was calculated from theoretical dependencies between them. The influence of the beryllium (x) and magnesium (y) content on thermal properties of these crystals have been presented and discussed. Order-disorder effects observed for these materials previously have been also taken into account. Finally, thermal diagrams, i.e. thermal conductivity versus composition were presented and discussed applying model given by Sadao Adachi. - Highlights: • Investigated II–VI crystals were obtained by a high pressure modified Bridgman method. • A complete thermal characterization of Zn{sub 1−x−y}Be{sub x}Mg{sub y}Se semiconductors was carried out. • The effect of lattice disorder on thermal properties was presented and discussed. • Obtained data were analyzed applying lattice thermal conductivity model. • Contribution to thermal resistivity arising from lattice disorder was calculated.
Properties of localization in silicon-based lattice periodicity breaking photonic crystal waveguides
Wu, Yuquan; Wang, Xiaofei; Wang, Yufang; Zhang, Guoquan; Fan, Wande; Cao, Xuewei, E-mail: xwcao@nankai.edu.cn [School of Physics, Nankai University, Tianjin, 300071 (China); Wu, Yuanbin [School of Physics, Nankai University, Tianjin, 300071 (China); Dip. di Fisica, Università di Roma “La Sapienza”, Piazzale Aldo Moro 5, I-00185 Roma (Italy); EDSFA, Université de Nice Sophia Antipolis, 06103 Nice (France)
2013-11-15
The light localization effects in silicon photonic crystal cavities at different disorder degrees have been studied using the finite difference time domain (FDTD) method in this paper. Numerical results showed that localization occurs and enhancement can be gained in the region of the cavity under certain conditions. The stabilities of the localization effects due to the structural perturbations have been investigated too. Detailed studies showed that when the degree of structural disorder is small(about 10%), the localization effects are stable, the maximum enhancement factor can reach 16.5 for incident wavelength of 785 nm and 23 for 850 nm in the cavity, with the degree of disorder about 8%. The equivalent diameter of the localized spot is almost constant at different disorder degrees, approximating to λ/7, which turned out to be independent on the structural perturbation.
On the interplay between heavy-fermion and soft crystal field excitations in Kondo lattices
Kagan, Yu.; Kikoin, K.A.; Mishchenko, A.S. [Rossijskij Nauchnyj Tsentr ``Kurchatovskij Inst.``, Moscow (Russian Federation)
1997-06-13
On the grounds of the microscopic theory of heavy-fermion spin-liquids a novel description of low-energy excitation spectra in CeNiSn and related compounds is offered. The anomalous properties of orthorhombic CeNiSn and related materials are explained by the interplay between the fermi-type spinon excitations with the energy scale T{sup *}{approx}T{sub K} and the one-site crystal field excitations with the energy {Delta}{sub CF}
Quantum computation in a one-dimensional crystal lattice with NMR force microscopy
Ladd, T D; Dana, A; Yamaguchi, F; Yamamoto, Y
2000-01-01
A proposal for a scalable, solid-state implementation of a quantum computer is presented. Qubits are fluorine nuclear spins in a solid crystal of fluorapatite [Ca_5 F(PO_4)_3] with resonant frequencies separated by a large field gradient. Quantum logic is accomplished using nuclear-nuclear dipolar couplings with decoupling and selective recoupling RF pulse sequences. Magnetic resonance force microscopy is used for readout. This proposal takes advantage of many of the successful aspects of solution NMR quantum computation, including ensemble measurement and long T_1, but it allows for more qubits and the potential for initialization. As many as 300 qubits can be implemented in the realistic laboratory extremes of T=10 mK and B_0=20 T with the existing sensitivity of force microscopy.
Jiang, Wenchun; Wei, Zhiquan; Luo, Yun; Zhang, Weiya; Woo, Wanchuck
2016-06-01
This paper uses finite element method and neutron diffraction measurement to study the residual stress in lattice truss sandwich structure. A comparison of residual stress and thermal deformation between X-type and pyramidal lattice truss sandwich structure has been carried out. The residual stresses are concentrated in the middle joint and then decreases gradually to both the ends. The residual stresses in the X-type lattice truss sandwich structure are smaller than those in pyramidal structure. The maximum longitudinal and transverse stresses of pyramidal structure are 220 and 202 MPa, respectively, but they decrease to 190 and 145 MPa for X-type lattice truss sandwich structure, respectively. The thermal deformation for lattice truss sandwich panel structure is of wave shape. The X-type has a better resistance to thermal deformation than pyramidal lattice truss sandwich structure. The maximum wave deformation of pyramidal structure (0.02 mm) is about twice as that of X-type (0.01 mm) at the same brazing condition.
Qiao, Mei; Wang, Tie-Jun; Song, Hong-Lian; Zhang, Jing; Liu, Yong; Liu, Peng; Zhang, Huai-Jin; Wang, Xue-Lin
2017-01-01
To investigate irradiation effects of LaAlO3 crystals, planar waveguides were fabricated via the medium- and high-energy C3+ ions irradiation. The characterizations of waveguides showed that irradiation at different conditions induced diverse variations of the number of guiding modes, refractive index profiles and lattice damage. Rutherford backscattering/channeling spectra in combination with X-ray diffraction and micro-Raman spectra was used to probe the lattice damage distributions in the near surface of irradiated areas, where the electronic energy loss is predominant. The annealing process with the restoring of the lattice damage to some extent was investigated at temperatures ranging from 533 to 773 K. Meanwhile, as a crucial element of integrated optics and optoelectronics, the light propagation properties of optical waveguide were also investigated. These enable a feasible application of LaAlO3 in integrated optical system.
A novel two-dimensional MgB6 crystal: metal-layer stabilized boron kagome lattice.
Xie, Sheng-Yi; Li, Xian-Bin; Tian, Wei Quan; Chen, Nian-Ke; Wang, Yeliang; Zhang, Shengbai; Sun, Hong-Bo
2015-01-14
Based on first-principles calculations, we designed for the first time a boron-kagome-based two-dimensional MgB6 crystal, in which two boron kagome layers sandwich a triangular magnesium layer. The two-dimensional lattice is metallic with several bands across the Fermi level, and among them a Dirac point appears at the K point of the first Brillouin zone. This metal-stabilized boron kagome system displays electron-phonon coupling, with a superconductivity critical transition temperature of 4.7 K, and thus it is another possible superconducting Mg-B compound besides MgB2. Furthermore, the proposed 2D MgB6 can also be used for hydrogen storage after decoration with Ca. Up to five H2 molecules can be attracted by one Ca with an average binding energy of 0.225 eV. The unique properties of 2D MgB6 will spur broad interest in nanoscience and technology.
Jin, Lin; Auerbach, Scott M; Monson, Peter A
2012-03-15
The potential of tailored nanopores to transform technologies such as drug delivery, biofuel production, and optical-electronic devices depends on fundamental knowledge of the self-assembly of ordered nanoporous solids. Atomic-level geometries of critical nuclei that lead to such solids have remained hidden in the nanoscale blind spot between local (5 nm) probes of structure. Heroic efforts at molecular simulation of nanopore formation have provided massive libraries of hypothetical structures; (1-5) however, to date no statistical simulation has generated a crystallization pathway from random initial condition to ordered nanoporous solid, until now. In this work, we show that a recently developed atomic lattice model of silica and related materials can form ordered nanoporous solids with a rich variety of structures including known chalcogenides, zeolite analogs, and layered materials. We find that whereas canonical Monte Carlo simulations of the model consistently produce the amorphous solids studied in our previous work, parallel tempering Monte Carlo gives rise to ordered nanoporous solids. The utility of parallel tempering highlights the existence of barriers between amorphous and crystalline phases of our model. Moreover, the self-assembly or nanoporous crystalline phases in the model open the door to detailed understanding of nanopore nucleation.
Li, Chao-Ying; Liu, Shi-Fei; Fu, Jin-Xian [Shangrao Normal University, Jiangxi (China). School of Physics and Electronic Information
2016-07-01
The electron paramagnetic resonance (EPR) parameters [i.e. g factors g{sub i} (i=x, y, z) and hyperfine structure constants A{sub i}] and the local lattice structure for the Cu{sup 2+} centre in Tl{sub 2}Zn(SO{sub 4}){sub 2}.6H{sub 2}O (TZSH) crystal were theoretically investigated by utilising the perturbation formulae of these parameters for a 3d{sup 9} ion under rhombically elongated octahedra. In the calculations, the admixture of d orbitals in the ground state and the ligand orbital and spin-orbit coupling interactions are taken into account based on the cluster approach. The theoretical EPR parameters show good agreement with the observed values, and the Cu{sup 2+}-H{sub 2}O bond lengths are obtained as follows: R{sub x}∼1.98 Aa, R{sub y}∼2.09 Aa, R{sub z}∼2.32 Aa. The results are discussed.
Souza, A.L.R.; Cassimiro, D.L.; Almeida, A.E.; Ribeiro, C.A.; Gremiao, M.P.D. [UNESP, Araraquara, SP (Brazil); Sarmento, V.H.V. [Universidade Federal de Sergipe (UFS), Itabaiana, SE (Brazil); Andreani, T.; Silva, A.M.; Souto, E.B. [Universidade de Tras-os-Montes e Alto Douro, Vila Real (Portugal)
2012-07-01
Full text: Praziquantel (PZQ) is the drug of choice for oral treatment of schistosomiasis and other fluke infections that affect humans. Its low oral bioavailability demands the development of innovative strategies to overcome the first pass metabolism. In this work, solid lipid nanoparticles loaded with PZQ (PZQ-SLN) were prepared by a modified oil-in-water microemulsion method selecting stearic acid as lipid phase after solubility screening studies. The mean particle size (Z-Ave) and zeta potential (ZP) were 500 nm and -34.0 mV, respectively. Morphology and shape of PZQ-SLN were analysed by scanning electron microscopy revealing the presence of spherical particles with smooth surface. Differential scanning calorimetry suggested that SLN comprised a less ordered arrangement of crystals and the drug was molecularly dispersed in the lipid matrix. No supercooled melts were detected. The entrapment efficiency (EE) and loading capacity of PZQ, determined by high performance liquid chromatography, were 99.0 and 17.5, respectively. Effective incorporation of PZQ into the particles was confirmed by small angle X-ray scattering revealing the presence of a lipid lamellar structure. Stability parameters of PZQ-SLN stored at room temperature (25 deg C) and at 4 deg C were checked by analysing Z-Ave, ZP and the EE for a period of 60 days Results showed a relatively long-term physical stability after storage at 4 deg C, without drug expulsion. (author)
Analysis of optomechanical coupling in two-dimensional square lattice phoxonic crystal slab cavities
El-Jallal, Said; Oudich, Mourad; Pennec, Yan; Djafari-Rouhani, Bahram; Laude, Vincent; Beugnot, Jean-Charles; Martínez, Alejandro; Escalante, José María; Makhoute, Abdelkader
2013-11-01
We theoretically investigate phonon-photon interaction in cavities created in a phoxonic crystal slab constituted by a two-dimensional (2D) square array of holes in a silicon membrane. The structure without defects provides 2D band gaps for both electromagnetic and elastic waves. We consider two types of cavities, namely, an L3 cavity (a row of three holes is removed) and a cross-shape cavity, which both possess highly confined phononic and photonic localized modes suitable for enhancing their interaction. In our theoretical study, we take into account two mechanisms that contribute to optomechanical interaction, namely, the photoelastic and the interface motion effects. We show that, depending on the considered pair of photonic and phononic modes, the two mechanisms can have similar or very different magnitudes, and their contributions can be either in or out of phase. We find out that only acoustic modes with a specific symmetry are allowed to couple with photonic cavity modes. The coupling strength is quantified by two different methods. In the first method, we compute a direct estimation of coupling rates by overlap integrals, while in the second one, we analyze the temporal modulation of the resonant photonic frequency by the phonon-induced acoustic vibrational motion during one acoustic period. Interestingly, we obtain high optomechanical interaction, with the coupling rate reaching more than 2.4 MHz for some specific phonon-photon pairs.
Lattice dynamics of K{sub x}RhO{sub 2} single crystals
Zhang, Bin-Bin; Dong, Song-Tao; Lv, Yangyang; Yao, Shuhua, E-mail: shyao@nju.edu.cn; Zhang, Shan-Tao; Gu, Zheng-Bin; Zhou, Jian, E-mail: zhoujian@nju.edu.cn; Chen, Yan-Feng [National Laboratory of Solid State Microstructures and Department of Materials Science and Engineering, Nanjing University, Nanjing 210093 (China); Zhang, NaNa [College of Chemistry & Chemical and Environmental Engineering, Weifang University, Weifang, 261061 (China); Chen, Y. B. [National Laboratory of Solid State Microstructure and Department of Physics, Nanjing University, Nanjing 210093 (China); Guedes, Ilde [Departamento de Física, Universidade Federal do Ceará, Campus do Pici, CP 6030, Fortaleza CE 60455-760 (Brazil); Yu, Dehong [Bragg Institute, Australian Nuclear Science and Technology Organisation, Lucas Heights, NSW 2234 (Australia)
2015-08-15
A series of crystals K{sub x}RhO{sub 2} (x = 0.72, 0.63, 0.55, 0.39, and 0.24) have been synthesized and their vibrational properties have been studied by first principles calculations, Raman spectroscopy, and inelastic neutron scattering. The measured vibrational spectra of K{sub x}RhO{sub 2} for x = 0.72 and 0.63 are consistent with the theoretical prediction for the stoichiometric KRhO{sub 2}. For samples with x = 0.55, 0.39 and 0.24, extra vibrational modes have been observed and they are believed to be due to the symmetry reduction and the loss of translational symmetry induced by K disorder. The good agreement was found for the phonon density of states among the Raman spectroscopic observations, inelastic neutron scattering and the first principles calculations, as an evidence for the generation of structure disorder by K deficiency.
Lattice dynamics of diamond-like crystals from a tight-binding calculation of valence bands
Roman, R.; Pascual, J.
1988-11-01
We report on the results of calculations of the TA(X) phonon energy in the series of C, Si, Ge, Sn homopolar crystals. The starting point is the tight-binding model for the electronic Hamiltonian where Es and Ep are taken to be the free atomic energies while the interatomic matrix elements are described by a universal d-2 Harrison's scaling law. The change of the total energy with the atomic distortion is given in terms of changes in the valence band energy and changes in the overlap energy. The numerical calculations for Si gives U1 = -21.77eV and U2 = 60.44eV, close to the values predicted by Harrison U1 = -17.76eV and U2 = 53.28eV. The calculations of the TA(X) phonon energy gives (in the case the interatomic distances are held constant): 26.09 THz (C), 6.46 THz (Si), 3.37THz (Ge) and 1.91 THz (Sn), in reasonably good agreement with the experimental results 24.1 THz (C), 4.49 THz (Si), 2.39 THz (Ge) and 1.26 THz (Sn).
X.P. Tan; J.L. Liu; X P Song; T. Jin; X.F. Sun; Z.Q. Hu
2011-01-01
A conventional X-ray difFractometer has been used to determine the -y/y＇ lattice misfit and γ＇ volume fraction for a Ru-containing nickel-based single crystal superalloy at room temperature. The rocking curve was used to characterize the distribution of subgrains. The diffraction peaks obtained by w-20 scan were used to determine the γ/γ＇ lattice misfit and γ＇ volume fraction. A three peaks fitting model was proposed. The peak fitting results are in good agreement with the model. The X-ray diffraction results indicate that the nickel-based single crystal superalloy was not a perfect monocrystalline material, which is comprised of many subgrains; and each subgrain also consists of large numbers of mosaic structures. In addition, two anomalous reflection phenomena were found during the experiment and discussed with respect to their occurrence and impact on the measurement. The experimental results show that the γ/γ＇ lattice misfit and ~/r volume fraction will be various at the different regions of its dendritic microstructure. The average γ/γ＇ lattice misfit and γ＇ volume fraction of the experimental alloy are approximately-0.2% and 70%, respectively. Furthermore, the γ＇ volume fraction calculated by atom microprobe （AP） data is also basically consistent with the experimental results.
Moon, Myung-Kook [Korea Atomic Energy Research Institute, Neutron Beam Application, 150 Duckjin-Dong, Yusung, Daejon 305-600 (Korea, Republic of)]. E-mail: moonmk@kaeri.re.kr; Lee, Chang-Hee [Korea Atomic Energy Research Institute, Neutron Beam Application, 150 Duckjin-Dong, Yusung, Daejon 305-600 (Korea, Republic of); Em, Vyacheslav T. [Korea Atomic Energy Research Institute, Neutron Beam Application, 150 Duckjin-Dong, Yusung, Daejon 305-600 (Korea, Republic of); Mikula, Pavol [Nuclear Physics Institute and Research Centre Rez, Ltd., 250 68 Rez (Czech Republic); Hong, Kwang-Pyo [Korea Atomic Energy Research Institute, Neutron Beam Application, 150 Duckjin-Dong, Yusung, Daejon 305-600 (Korea, Republic of); Choi, Young-Hyun [Korea Atomic Energy Research Institute, Neutron Beam Application, 150 Duckjin-Dong, Yusung, Daejon 305-600 (Korea, Republic of); Cheon, Jong-Kyu [Korea Atomic Energy Research Institute, Neutron Beam Application, 150 Duckjin-Dong, Yusung, Daejon 305-600 (Korea, Republic of); Choi, Young-Nam [Korea Atomic Energy Research Institute, Neutron Beam Application, 150 Duckjin-Dong, Yusung, Daejon 305-600 (Korea, Republic of); Kim, Shin-Ae [Korea Atomic Energy Research Institute, Neutron Beam Application, 150 Duckjin-Dong, Yusung, Daejon 305-600 (Korea, Republic of); Kim, Sung-Kyu [Korea Atomic Energy Research Institute, Neutron Beam Application, 150 Duckjin-Dong, Yusung, Daejon 305-600 (Korea, Republic of); Jin, Kyung-Chan [Korea Institute of Industrial Technology 35-3 Hongchon-Ri, Ipchang-Myun, Chonan-Si, Chungnam 330-825 (Korea, Republic of)
2005-12-01
Reflectivity and resolution properties of a variety of optimized focusing monochromator performances based on cylindrically bent perfect Si-crystals were tested with the aim of evaluating their possible use in a strain/stress diffractometer. It has been found that the optimized monochromator performances of the curved Si(311) crystals (for the take-off angle 2{theta}{sub M}=60 deg.) provide a good luminosity and a sufficiently high resolution (full width at half maximum (FWHM) of the instrumental {delta}d/d-profile can be about 2x10{sup -3} in the vicinity of the lattice spacing d=0.117nm for 2{theta}{sub S}{approx}90 deg.) of the strain/stress diffractometer with the figure of merit more than one order of magnitude larger than that related to the conventional flat mosaic Ge(220) monochromator of {eta}=15{sup '}.
Tae Ho Yeom
2016-04-01
Full Text Available In this study, to understand the effects of paramagnetic impurities, we investigated the temperature dependent of the spin-lattice relaxation times of pure LiNbO3, LiNbO3:Mg, LiNbO3:Mg/Ti, LiNbO3:Mg/Fe, and LiNbO3:Mg/Fe (thermally treated at 500°C single crystals. The results for the LiNbO3:Mg single crystals doped with Fe3+ or Ti3+ are discussed with respect to the site distribution and atomic mobility of Li and Nb. In addition, the effects of a thermal treatment on LiNbO3:Mg/Fe single crystals were examined based on the T1 analysis of 7Li and 93Nb. It was found that the presence of impurities in the crystals induced systematic changes of activation energies concerning atomic mobility.
Stress-induced stabilization of crystals in shape memory natural rubber.
Heuwers, Benjamin; Quitmann, Dominik; Hoeher, Robin; Reinders, Frauke M; Tiemeyer, Sebastian; Sternemann, Christian; Tolan, Metin; Katzenberg, Frank; Tiller, Joerg C
2013-01-25
In contrast to all known shape memory polymers, the melting temperature of crystals in shape memory natural rubber (SMNR) can be greatly manipulated by the application of external mechanical stress. As shown previously, stress perpendicular to the prior programming direction decreases the melting temperature by up to 40 K. In this study, we investigated the influence of mechanical stress parallel to prior stretching direction during programming on the stability of the elongation-stabilizing crystals. It was found that parallel stress stabilizes the crystals, which is indicated by linear increase of the trigger temperature by up to 17 K. The crystal melting temperature can be increased up to 126.5 °C under constrained conditions as shown by X-ray diffraction measurements.
Scheuerlein, C; Buta, F; Seeber, B; Senatore, C; Flükiger, R; Siegrist, T; Besara, T; Kadar, J; Bordini, B; Ballarino, A; Bottura, L
2014-01-01
The lattice parameter changes in three types of Nb3Sn superconducting wires during uniaxial stress-strain measurements at 4.2 K have been measured by high-energy synchrotron x-ray diffraction. The nearly-stress-free Nb3Sn lattice parameter has been determined using extracted filaments, and the elastic strain in the axial and transverse wire directions in the different wire phases has been calculated. The mechanical properties of the PIT and RRP wire are mainly determined by the properties of Nb3Sn and unreacted Nb. This is in contrast to the bronze route wire, where the matrix can carry substantial loads. In straight wires the axial Nb3Sn pre-strain is strongest in the bronze route wire, its value being smaller in the PIT and RRP wires. A strong reduction of the non-Cu elastic modulus of about 30\\% is observed during cool-down from ambient temperature to 4.2 K. The Nb3Sn Poisson ratio at 4.2 K measured in the untwisted bronze route wire is 0.35. The present study also shows that the process route has a strong...
Phase Transitions in a Non-Uniformly Stressed Iron Borate Single Crystal
Dzhuraev, D. R.; Niyazov, L. N.; Sokolov, B. Yu.
2016-05-01
Based on the Landau thermodynamic theory, phase transformations observed in a FeBO3 single crystal subject to spatially non-uniform mechanical stresses are analyzed. It is demonstrated that the main results of theoretical consideration of structural and magnetic phase transitions in the examined crystal do not contradict with the available experimental data.
Dynamic transition in current-driven disordered flux-line lattice in single-crystal of Bi-2212
Ammor, L.; Ruyter, A.
2014-11-15
We have measured the current–voltage characteristics for both as-grown and irradiated Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+δ} single crystals at T = 5 K in a magnetic field applied parallel to c axis. The results show a variety of dynamical behavior above the depinning threshold, depending on the vortex–vortex interaction (λ{sub ab}/a{sub 0}) strength and the nature of the quenched disorder (point-like or columnar defects). When the flux lattice is soft, our experimental measurements in both samples have been attributed to plastic flow, including strong metastability and history dependence of the depinning process. The vortex motion in this regime is thought of relatively weakly pinned vortices past more strongly pinned neighbors. A power-law scaling, fit between voltage and applied current can be obtained for the onset of motion in both samples, with different apparent critical exponent depending on defect nature and the strength of interactions. In the plastic regime, the usual scaling ansatz associated with dynamic critical phenomena V scales as (I − I{sub c}){sup β}, where β ∼ 2.2 ± 0.1 and 1.22 ± 0.021 for as-grown and β ≈ 1.49 ± 0.07 for irradiated samples, respectively. Finally, in both cases of defects, with increasing the strength of vortex–vortex interaction a dynamical transition is observed as confirmed by the discontinuity in the vortex–vortex interactions dependence of the critical exponent β. More, our results confirm the important role of the system dimensionnality on vortex dynamics.
Panwisawas, Chinnapat; D'Souza, Neil; Collins, David M; Bhowmik, Ayan
2017-09-11
Time dependent plastic deformation in a single crystal nickel-base superalloy during cooling from casting relevant temperatures has been studied using a combination of in-situ neutron diffraction, transmission electron microscopy and modelling. Visco-plastic deformation during cooling was found to be dependent on the stress and constraints imposed to component contraction during cooling, which mechanistically comprises creep and stress relaxation. Creep results in progressive work hardening with dislocations shearing the γ' precipitates, a high dislocation density in the γ channels and near the γ/γ' interface and precipitate shearing. When macroscopic contraction is restricted, relaxation dominates. This leads to work softening from a decreased dislocation density and the presence of long segment stacking faults in γ phase. Changes in lattice strains occur to a similar magnitude in both the γ and γ' phases during stress relaxation, while in creep there is no clear monotonic trend in lattice strain in the γ phase, but only a marginal increase in the γ' precipitates. Using a visco-plastic law derived from in-situ experiments, the experimentally measured and calculated stresses during cooling show a good agreement when creep predominates. However, when stress relaxation dominates accounting for the decrease in dislocation density during cooling is essential.
Honda, Zentaro; Kodama, Takafumi; Hagiwara, Masayuki; Kida, Takanori; Okutani, Akira; Sakai, Masamichi; Fukuda, Takeshi; Kamata, Norihiko
2016-09-01
We report on the syntheses, crystal structures, and magnetic properties of a series of transition metal coordination polymers M2(pymca)3(ClO4), (pymca = pyrimidine-2-carboxylic acid, M = Fe (1), Co (2), and Ni (3)). These compounds are found to crystallize in a trigonal crystal system, space group P31m, with the lattice constants a = 9.727 Å and c = 5.996 Å for 1, a = 9.608 Å and c = 5.996 Å for 2, and a = 9.477 Å and c = 5.958 Å for 3 at room temperature. In these compounds, each pymca ligand connects to two M2+ ions, forming a honeycomb network in the ab plane. The temperature dependences of magnetic susceptibilities in these compounds show broad maxima, indicating antiferromagnetic interactions within two-dimensional honeycomb layers. We also observed an antiferromagnetic phase transition at low temperatures by magnetic susceptibility and heat capacity measurements. From the crystal structures and magnetic properties, we conclude that the compounds 1, 2, and 3 are good realizations of honeycomb-lattice antiferromagnets.
Effect of thermal shield and gas flow on thermal elastic stresses in 300 mm silicon crystal
GAO Yu; XIAO Qinghua; ZHOU Qigang; DAI Xiaolin; TU Hailing
2006-01-01
The thermal elastic stresses induced in 300 mm Si crystal may be great troubles because it can incur the generation of dislocations and undesirable excessive residual stresses.A special thermal modeling tool, CrysVUn, was used for numerical analysis of thermal elastic stresses and stress distribution of 300 mm Si crystal under the consideration of different thermal shields and gas flow conditions.The adopted governing partial equations for stress calculation are Cauchy's first and second laws of motion.It is demonstrated that the presence and shape of thermal shield, the gas pressure and velocity can strongly affect von Mises stress distribution in Si crystal.With steep-wall shield, however, the maximal stress and ratio of high stress area are relatively low.With slope-wall shield or without shield, both maximal stress and ratio of high stress area are increased in evidence.Whether thermal shields are used or not, the increase of gas flow velocity could raise the stress level.In contrast, the increase of gas pressure cannot result in so significant effect.The influence of thermal shield and gas flow should be attributed to the modification of heat conduction and heat radiation by them.
Drikis, Ivars; Plate, Matiss; Sennikovs, Juris; Virbulis, Janis
2017-09-01
Simulations of 3D anisotropic stress are carried out in and oriented Si crystals grown by FZ and CZ processes for different diameters, growth rates and process stages. Temperature dependent elastic constants and thermal expansion coefficients are used in the FE simulations. The von Mises stress at the triple point line is 5-11% higher in crystals compared to crystals. The process parameters have a larger effect on the von Mises stress than the crystal orientation. Generally, the crystal has a higher azimuthal variation of stress along the triple point line ( 8%) than the crystal ( 2%). The presence of a crystal ridge increases the stress beside the ridge and decreases it on the ridge compared with the round crystal.
Li, Youyong; Lin, Shiang-Tai; Goddard, William A
2004-02-18
Self-assembled supramolecular organic liquid crystal structures at nanoscale have potential applications in molecular electronics, photonics, and porous nanomaterials. Most of these structures are formed by aggregation of soft spherical supramolecules, which have soft coronas and overlap each other in the packing process. Our main focus here is to study the possible packing mechanisms via molecular dynamics simulations at the atomistic level. We consider the relative stability of various lattices packed by the soft dendrimer balls, first synthesized and characterized by Percec et al. (J. Am. Chem. Soc. 1997, 119, 1539) with different packing methods. The dendrons, which form the soft dendrimer balls, have the character of a hard aromatic region from the point of the cone to the edge with C(12) alkane "hair". After the dendrons pack into a sphere, the core of the sphere has the hard aromatic groups, while the surface is covered with the C(12) alkane "hair". In our studies, we propose three ways to organize the hair on the balls, Smooth/Valentino balls, Sticky/Einstein balls, and Asymmetric/Punk balls, which lead to three different packing mechanisms, Slippery, Sticky, and Anisotropic, respectively. We carry out a series of molecular dynamics (MD) studies on three plausible crystal structures (A15, FCC, and BCC) as a function of density and analyze the MD based on the vibrational density of state (DoS) method to extract the enthalpy, entropy, and free energies of these systems. We find that anisotropic packed A15 is favored over FCC, BCC lattices. Our predicted X-ray intensities of the best structures are in excellent agreement with experiment. "Anisotropic ball packing" proposed here plays an intermediate role between the enthalpy-favored "disk packing" and entropy-favored "isotropic ball packing", which explains the phase transitions at different temperatures. Free energies of various lattices at different densities are essentially the same, indicating that the
Hachi Younes El
2015-01-01
Full Text Available To better understand the properties of polycrystals at a microscopic scale during cyclic mechanical loading we have measured the relationship between grain orientations, their positions inside the sample and their internal stresses. In this work, in-situ 3DXRD technique was performed on over hundred grains during the stress-induced martensitic transformation in a Cu-Al-Be shape memory alloy. Information about the position, orientation, and stress field was obtained for each austenitic grain. These results have been used to develop a procedure that allows automatic processing for a large number of grains, matching them during loading and leads to a quantitative stress field. A strong heterogeneity of stress state between the grains at the surface and in the volume is evident.
Sanchez-Bajo, F. [Universidad de Extremadura, Departamento de Fisica Aplicada, Badajoz (Spain); Ortiz, A.L. [Universidad de Extremadura, Departamento de Ingenieria Mecanica, Energetica y de los Materiales, Badajoz (Spain); Cumbrera, F.L. [Universidad de Extremadura, Departamento de Fisica, Badajoz (Spain)
2009-01-15
An analytical model for the determination of crystallite size and crystal lattice microstrain distributions in nanocrystalline (nc) materials by X-ray diffractometry (XRD) is presented. It entails generalizing the variance method to establish analytically the connection between the variance coefficients of the physically broadened XRD peaks and the characteristic parameters of explicit distributions of crystallite sizes and crystal lattice microstrains, which results in a more detailed characterization of the nc-materials. The proposed model is generic in nature and has the potential to be used under the assumption of different mathematical functions for the two distributions, which suggests that it may have an important role to play in the characterization of nc-materials. Nevertheless, the specialization to the case of nc-materials with log-normal crystallite size distribution and three typical types of lattice microstrains is used as an illustration and to formulate explicit analytical expressions of interest. Finally, the usefulness of the proposed model is demonstrated on standard XRD profiles. (orig.)
Simple Derivation of the Maxwell Stress Tensor and Electrostrictive Effects in Crystals
Juretschke, H. J.
1977-01-01
Shows that local equilibrium and energy considerations in an elastic dielectric crystal lead to a simple derivation of the Maxwell stress tensor in anisotropic dielectric solids. The resulting equilibrium stress-strain relations are applied to determine the deformations of a charged parallel plate capacitor. (MLH)
Realignment of Nanocrystal Aggregates into Single Crystals as a Result of Inherent Surface Stress
Liu, Zhaoming [Department of Chemistry, Zhejiang University, Hangzhou Zhejiang 310027 China; Pan, Haihua [Qiushi Academy for Advanced Studies, Zhejiang University, Hangzhou Zhejiang 310027 China; Zhu, Genxing [Department of Chemistry, Zhejiang University, Hangzhou Zhejiang 310027 China; Li, Yaling [Department of Chemistry, Zhejiang University, Hangzhou Zhejiang 310027 China; Tao, Jinhui [Physical Sciences Division, Pacific Northwest National Laboratory, Richland WA 99354 USA; Jin, Biao [Department of Chemistry, Zhejiang University, Hangzhou Zhejiang 310027 China; Tang, Ruikang [Department of Chemistry, Zhejiang University, Hangzhou Zhejiang 310027 China; Qiushi Academy for Advanced Studies, Zhejiang University, Hangzhou Zhejiang 310027 China
2016-07-19
Assembly of nanoparticles building blocks during single crystal growth is widely observed in both natural and synthetic environments. Although this form of non-classical crystallization is generally described by oriented attachment, random aggregation of building blocks leading to single crystal products is also observed, but the mechanism of crystallographic realignment is unknown. We herein reveal that random attachment during aggregation-based growth initially produces a non-oriented growth front. Subsequent evolution of the orientation is driven by the inherent surface stress applied by the disordered surface layer and results in single crystal formation via grain boundary migration. This mechanism is corroborated by measurements of orientation rate vs external stress, demonstrating a predictive relationship between the two. These findings advance our understanding of aggregation-based growth of natural minerals by nanocrystals, and suggest an approach to material synthesis that takes advantage of stress induced co-alignment.
Zhang, Hai-Feng, E-mail: hanlor@163.com, E-mail: lsb@nuaa.edu.cn [Key Laboratory of Radar Imaging and Microwave Photonics (Nanjing Univ. Aeronaut. Astronaut.), Ministry of Education, Nanjing University of Aeronautics and Astronautics, Nanjing 210016 (China); Nanjing Artillery Academy, Nanjing 211132 (China); Liu, Shao-Bin, E-mail: hanlor@163.com, E-mail: lsb@nuaa.edu.cn; Jiang, Yu-Chi [Key Laboratory of Radar Imaging and Microwave Photonics (Nanjing Univ. Aeronaut. Astronaut.), Ministry of Education, Nanjing University of Aeronautics and Astronautics, Nanjing 210016 (China)
2014-09-15
In this paper, the tunable all-angle negative refraction and photonic band gaps (PBGs) in two types of two-dimensional (2D) plasma photonic crystals (PPCs) composed of homogeneous plasma and dielectric (GaAs) with square-like Archimedean lattices (ladybug and bathroom lattices) for TM wave are theoretically investigated based on a modified plane wave expansion method. The type-1 structure is dielectric rods immersed in the plasma background, and the complementary structure is named as type-2 PPCs. Theoretical simulations demonstrate that the both types of PPCs with square-like Archimedean lattices have some advantages in obtaining the higher cut-off frequency, the larger PBGs, more number of PBGs, and the relative bandwidths compared to the conventional square lattices as the filling factor or radius of inserted rods is same. The influences of plasma frequency and radius of inserted rod on the properties of PBGs for both types of PPCs also are discussed in detail. The calculated results show that PBGs can be manipulated by the parameters as mentioned above. The possibilities of all-angle negative refraction in such two types of PPCs at low bands also are discussed. Our calculations reveal that the all-angle negative phenomena can be observed in the first two TM bands, and the frequency range of all-angle negative refraction can be tuned by changing plasma frequency. Those properties can be used to design the optical switching and sensor.
Zhang, Hai-Feng; Liu, Shao-Bin; Jiang, Yu-Chi
2014-09-01
In this paper, the tunable all-angle negative refraction and photonic band gaps (PBGs) in two types of two-dimensional (2D) plasma photonic crystals (PPCs) composed of homogeneous plasma and dielectric (GaAs) with square-like Archimedean lattices (ladybug and bathroom lattices) for TM wave are theoretically investigated based on a modified plane wave expansion method. The type-1 structure is dielectric rods immersed in the plasma background, and the complementary structure is named as type-2 PPCs. Theoretical simulations demonstrate that the both types of PPCs with square-like Archimedean lattices have some advantages in obtaining the higher cut-off frequency, the larger PBGs, more number of PBGs, and the relative bandwidths compared to the conventional square lattices as the filling factor or radius of inserted rods is same. The influences of plasma frequency and radius of inserted rod on the properties of PBGs for both types of PPCs also are discussed in detail. The calculated results show that PBGs can be manipulated by the parameters as mentioned above. The possibilities of all-angle negative refraction in such two types of PPCs at low bands also are discussed. Our calculations reveal that the all-angle negative phenomena can be observed in the first two TM bands, and the frequency range of all-angle negative refraction can be tuned by changing plasma frequency. Those properties can be used to design the optical switching and sensor.
Nakano, S.; Gao, B.; Kakimoto, K.
2017-06-01
In this study, we investigate the influence of thermal stress on the dislocation density and residual stress in GaN single crystals by numerical analysis. The results show that the dislocation density increases, but the thermal stress does not decrease, and the residual stress increases throughout the cooling process. The reason for this phenomenon is that the dislocation density is higher at the periphery of the crystal and distribution of dislocation density in the crystal is inhomogeneous. Then, the increase of dislocation does not allow the thermal stress on the entire crystal to relax.
The model of solid phase crystallization of amorphous silicon under elastic stress
2000-01-01
Solid phase crystallization of an amorphous silicon (a-Si) film stressed by a Si3N4 cap was studied by laser Raman spectroscopy. The a-Si films were deposited on Si3N4 (50 nm)/Si(100) substrate by rf sputtering. The stress in an a-Si film was controlled by thickness of a Si3N4 cap layer. The Si3N4 films were also deposited by rf sputtering. It was observed that the crystallization was affected by the stress in a-Si films introduced by the Si3N4 cap layer. The study suggests that the elastic s...
Usov, I. O.; Valdez, J. A.; Sickafus, K. E.
2011-02-01
To better appreciate dynamic annealing processes in ion irradiated MgO single crystals of three low-index crystallographic orientations, lattice damage variation with irradiation temperature was investigated. Irradiations were performed with 100 keV Ar ions to a fluence of 1 × 10 15 Ar/cm 2 in a temperature interval from -150 to 1100 °C. Rutherford backscattering spectroscopy combined with ion channeling was used to analyze lattice damage. Damage recovery with increasing irradiation temperature proceeded via two characteristic stages separated by 200 °C. Strong radiation damage anisotropy was observed at temperatures below 200 °C, with (1 1 0) MgO being the most radiation damage tolerant. Above 200 °C damage recovery was isotropic and almost complete recovery was reached at 1100 °C. We attributed this orientation dependence to a variation of dynamic annealing mechanisms with irradiation temperature.
Mirković, J; Savel'ev, S E; Sugahara, E; Kadowaki, K
2001-01-29
The vortex-lattice melting transition in Bi(2)Sr(2)CaCu(2)O(8 + delta) single crystals was studied using in-plane resistivity measurements in magnetic fields tilted away from the c axis to the ab plane. In order to avoid the surface barrier effect which hinders the melting transition in the conventional transport measurements, we used the Corbino geometry of electric contacts. The complete H(c) - H(ab) phase diagram of the melting transition in Bi(2)Sr(2)CaCu(2)O(8 + delta) is obtained for the first time. The c-axis melting field component H(c)(melt) exhibits the novel, stepwise dependence on the in-plane magnetic fields H(ab) which is discussed on the basis of the crossing vortex-lattice structure. The peculiar resistance behavior observed near the ab plane suggests the change of phase transition character from first to second order.
夏志国; 孙家跃; 杜海燕
2004-01-01
According to the Van Uitert experimental equation, crystal-lattice environment of Eu2+ in the Sr4Si3O8Cl4 crystal was discussed. By adding Mg2+ to the host lattice, Sr4-xMgxSi3O8Cl4∶Eu2+ was synthesized and the emission peak shifted from blue-green (488 nm) to blue-violet (411 nm) with the increase of amount of the magnesium which replaced the strontium. By analyzing the spectra of Sr4-xMgxSi3O8Cl4∶Eu2+ the two Eu2+ emission centers were found because of the change of crystal-lattice environment in the host and the crystal structure was obtained by X-ray diffraction data.
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.
Han, Tianheng; Chu, Shaoyan; Lee, Young S
2012-04-13
We report thermodynamic measurements of the S=1/2 kagome lattice antiferromagnet ZnCu3(OH)6Cl2, a promising candidate system with a spin-liquid ground state. Using single crystal samples, the magnetic susceptibility both perpendicular and parallel to the kagome plane has been measured. A small, temperature-dependent anisotropy has been observed, where χ(z)/χ(p)>1 at high temperatures and χ(z)/χ(p)kagome Heisenberg antiferromagnet model to the experiments on ZnCu3(OH)6Cl2.
Zehnder, Ralph A; Wilson, Christopher S; Christy, Hunter T; Harris, Kenneth S; Chauhan, Varun; Schutz, Victor; Sullivan, Matthew; Zeller, Matthias; Fronczek, Frank R; Myers, Jacob A; Dammann, Kyle; Duck, James; Smith, Peter M; Okuma, Antony; Johnson, Kristin; Sovesky, Robert; Stroudt, Cameron; Renn, Robert A
2011-02-07
A series of trivalent lanthanide hydroxysulfates, Ln(OH)SO(4), (Ln = Pr through Yb, except radioactive Pm) has been synthesized via hydrothermal methods from Ln(2)(SO(4))(3)·8H(2)O by reaction with aqueous NaOH at 170 °C in Teflon lined Parr steel autoclaves, and were characterized by single crystal X-ray diffraction and FT-IR spectroscopy. Two types of arrangements were found in the solid state. The lighter (Ln = Pr-Nd, Sm-Gd) and heavier lanthanide(III) hydroxysulfates (Tb-Yb) are each isostructural. Both structure types exhibit the monoclinic space group P2(1)/n, but the unit cell content is doubled with two crystallographically distinct LnO(8) polyhedra for the heavier lanthanide compounds. The lighter complexes maintain the coordination number 9, forming a three-dimensional extended lattice. The heavier counterparts exhibit the coordination number 8, and arrange as infinite columns of two crystallographically different LnO(8) polyhedra, while extending along the "c" axis. These columns of LnO(8) polyhedra are surrounded and separated by six columns of sulfate ions, also elongating in the "c" direction. The rigid sulfate entities seem to obstruct the closing in of the lighter LnO(9) polyhedra, and show an inclining degree of torsion into the "ac" layers. The crystal lattice of the lighter 4f complexes can sufficiently withstand the tension buildup, caused by the decreasing Ln(3+) radius, up to Gd(OH)SO(4). The energy profile of this structural arrangement then seems to exceed levels at which this structure type is favorable. The lattice arrangement of the heavier Ln-analogues seems to offer a lower energy profile. This appears to be the preferred arrangement for the heavier lanthanide hydroxysulfates, whose crystal lattice exhibits more flexibility, as the coordination sphere of these analogues is less crowded. The IR absorbance frequencies of the hydroxide ligands correlate as a function of the Ln(3+) ionic radius. This corresponds well with the X-ray single
Maasa Nakano
2013-04-01
Full Text Available Micrometer order magnetophotonic crystals with periodic arranged metallic glass and oxide glass composite materials were fabricated by stereolithographic method to reflect electromagnetic waves in terahertz frequency ranges through Bragg diffraction. In the fabrication process, the photo sensitive acrylic resin paste mixed with micrometer sized metallic glass of Fe72B14.4Si9.6Nb4 and oxide glass of B2O3·Bi2O3 particles was spread on a metal substrate, and cross sectional images of ultra violet ray were exposed. Through the layer by layer stacking, micro lattice structures with a diamond type periodic arrangement were successfully formed. The composite structures could be obtained through the dewaxing and sintering process with the lower temperature under the transition point of metallic glass. Transmission spectra of the terahertz waves through the magnetophotonic crystals were measured by using a terahertz time domain spectroscopy.
Measuring nonlinear stresses generated by defects in 3D colloidal crystals
Lin, Neil Y C; Schall, Peter; Sethna, James P; Cohen, Itai
2016-01-01
The mechanical, structural and functional properties of crystals are determined by their defects and the distribution of stresses surrounding these defects has broad implications for the understanding of transport phenomena. When the defect density rises to levels routinely found in real-world materials, transport is governed by local stresses that are predominantly nonlinear. Such stress fields however, cannot be measured using conventional bulk and local measurement techniques. Here, we report direct and spatially resolved experimental measurements of the nonlinear stresses surrounding colloidal crystalline defect cores, and show that the stresses at vacancy cores generate attractive interactions between them. We also directly visualize the softening of crystalline regions surrounding dislocation cores, and find that stress fluctuations in quiescent polycrystals are uniformly distributed rather than localized at grain boundaries, as is the case in strained atomic polycrystals. Nonlinear stress measurements ...
He, Xiaolin; Sun, Zhongqin; He, Kanglai; Guo, Shuyuan
2017-04-01
Parasporal crystals synthesized by Bacillus thuringiensis (Bt) have been widely used as microbial pesticides because of their toxicity to the larval stages of specific insects. However, parasporal crystals can be damaged by environmental stresses, such as high temperature, ultraviolet radiation, and desiccation. To reduce environmental susceptibility of parasporal crystals and extend the duration of their activity, we developed a new type of protection by making microcapsules of crystals (MCs). The microcapsules were self-assembled by alternate deposition (layer by layer) of low-cost chitosan and sodium alginate (or sodium carboxymethyl cellulose) on the crystal surface. Crystal toxins (Cry1Ac) were released from microcapsules at pH values above 9.0. Bioassay results demonstrated that microencapsulated preparations had larvicidal toxicity equivalent to the non-encapsulated form. Microencapsuled crystals were protected from environmental stresses such as high temperature and desiccation. The results indicate that microcapsule protection can enhance the efficacy of Bt in pest control, especially to Lepidoptera larvae that have a alkaline midgut.
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.
Cubic Single Crystal Representations in Classical and Size-dependent Couple Stress Elasticity
Bansal, Dipanshu; Aref, Amjad J; Hadjesfandiari, Ali R
2015-01-01
Beginning with Cosserat theory in the early 20th century, there have been several different formulations for size-dependent elastic response. In this paper, we concentrate on the application of classical Cauchy theory and the recent parsimonious consistent couple stress theory to model a homogeneous linear elastic solid, exemplified by a pure single crystal with cubic structure. The focus is on an examination of elastodynamic response based upon wave velocities from ultrasonic excitation and phonon dispersion curves, along with adiabatic bulk moduli measurements. In particular, we consider in detail elastic parameter estimation within classical elasticity and consistent couple stress theory for four different cubic single crystals (NaCl, KCl, Cu, CuZn). The classical theory requires the estimation of three independent material parameters, while only one additional parameter relating skew-symmetric mean curvature to skew-symmetric couple-stress is needed for the size-dependent consistent couple stress theory. ...
Direct observation of lattice strain in Si1-xGex/Si crystals using planar channeling patterns
Breese, MBH; deKerckhove, DG; King, PJC; Smulders, PJM
1997-01-01
This paper describes the direct observation of lattice strain in channeling patterns produced by 3 MeV protons transmitted through strained Si1-xGex/Si bilayers close to planar channeling directions. Blocking lines arising from each layer can be separately resolved at certain alignments, whereas onl
REFINEMENT OF THE CRYSTAL STRUCTURE OF GUANIDINIUM ALUMINUM SULFATE HEXAHYDRATE.
FERROELECTRIC CRYSTALS, * CRYSTAL STRUCTURE ), (*GUANIDINES, CRYSTAL STRUCTURE ), (*ALUMINUM COMPOUNDS, CRYSTAL STRUCTURE ), SULFATES, HYDRATES, X RAY DIFFRACTION, CHROMIUM COMPOUNDS, CRYSTAL LATTICES, CHEMICAL BONDS
Trasi, Niraj S; Purohit, Hitesh S; Taylor, Lynne S
2017-07-07
Tacrolimus, an immunosuppressant, is a poorly water soluble compound whereby the commercially available capsule formulations contain the drug in amorphous form. The goal of this study was to evaluate the robustness of the innovator product and five generic formulations to crystallization following storage at stress conditions. Products were purchased from a pharmacy and stored at 40°C/75% relative humidity (RH), open dish conditions. Crystallinity was determined using X-ray diffraction. The quantity of the ingredients in the formulations were determined using different approaches and the various factors that might cause instability in the formulations were studied. After 4 weeks of open dish storage at 40°C/75% RH, one of the generic formulations showed evidence of tacrolimus crystallization. Further investigations revealed batch-to-batch variations in crystallization tendency with the extent of crystallinity varying between 50 and 100% for different batches. Crystallization was also observed at lower storage temperatures (30°C) when the RH was maintained at 75%. It was found that crystallization could be induced in a model formulation by wet granulating an ethanolic solution of the drug with lactose and drying at 60-70°C followed by exposure to stress conditions. It seems probable that the generic that was susceptible to crystallization contains amorphous drug physically mixed with polymeric excipients, rather than as an amorphous solid dispersion. This study highlights the importance of considering the manufacturing process on the stability of the resultant amorphous product.
Stress induced birefringence in hybrid TIR/PBG guiding solid photonic crystal fibers
Lyngsøe, Jens Kristian; Mangan, Brian Joseph; Olausson, Christina Bjarnal Thulin
2010-01-01
We report on two types of polarization maintaining solid photonic crystal fibers that guide light by a combination of a photonic bandgap and total internal reflection. Group and phase birefringence are studied experimentally and numerically for stress-applying parts made from B-doped and F......-doped silica. The stress field originating from Ge-doped cladding rods is shown to interfere with the stress field from the B-doped and F-doped rods. Since the differential expansion coefficients of B-doped and F-doped silica have opposite signs this interference is either destructive or constructive...
On the role of crystal and stress anisotropy in magnetic Barkhausen noise
Sheikh Amiri, Meisam, E-mail: Meisam.SheikhAmiri@izfp-extern.fraunhofer.de [Saarland University, Chair in Nondestructive Testing and Quality Assurance, Campus E3 1, 66123 Saarbrücken (Germany); Thielen, Matthias [Saarland University, MWW, Campus E3 1, 66123 Saarbrücken (Germany); Rabung, Madalina [Fraunhofer Institute for Nondestructive Testing (IZFP), Campus E3 1, 66123 Saarbrücken (Germany); Marx, Michael [Saarland University, MWW, Campus E3 1, 66123 Saarbrücken (Germany); Szielasko, Klaus [Fraunhofer Institute for Nondestructive Testing (IZFP), Campus E3 1, 66123 Saarbrücken (Germany); Boller, Christian [Saarland University, Chair in Nondestructive Testing and Quality Assurance, Campus E3 1, 66123 Saarbrücken (Germany); Fraunhofer Institute for Nondestructive Testing (IZFP), Campus E3 1, 66123 Saarbrücken (Germany)
2014-12-15
The article describes the micromagnetic behavior of non- and pre-plastically deformed high strength steel samples under applied stress using different magnetic nondestructive methods such as magnetic Barkhausen noise analysis and hysteresis measurements. It was found that the maximum amplitude of Barkhausen noise (M{sub MAX}) increases with applied stress up to a certain point and then decreases again (so-called M{sub MAX}(σ)-curve). Changes of magnetostriction, hysteresis curves and magnetic domain structures have been measured and have been further investigated to find out the reasons with respect to macro- and microscopic material behavior. The results obtained are mainly discussed on the basis of the Villari effect and the relation between applied stress and the Barkhausen noise parameters is described. It is concluded that the interaction between crystal and stress anisotropy is the main reason of the specific M{sub MAX}(σ)-curve observed. - Highlights: • The effect of applied and residual stresses on MBN has been deeply investigated. • The maximum amplitude of MBN rises with applied stress and then falls again. • Magnetostriction, B–H and MFM measurements have been done to find out the reason. • Interaction between crystal and stress anisotropy is the reason of MBN behavior.
Berréhar, J.; Caroli, C.; Lapersonne-Meyer, C.; Schott, M.
1992-11-01
We study the stress relaxation in single-crystal films of polymerized polydiacetylene, in epitaxy with their monomer substrate. Polymerization induces a uniaxial stress. Two types of surface patterns are observed and studied by atomic force microscopy: films thicker than 175 nm exhibit quasiperiodic cracks perpendicular to the polymer chains; thinner ones exhibit regular wrinkles with the same orientation. The wrinkle surface deformation is stress relaxing and plastic. We show that all experimental results, in particular, the order of magnitude of the pattern spacings, are compatible with the following interpretation: as polymerization proceeds, the uniaxial stress generates a Grinfeld instability (Dok. Akad. Nauk SSSR 290, 1358 (1986) [Sov. Phys. Dokl. 31, 831 (1986)]) fed by surface diffusion. The crack pattern is a secondary instability, initiated at the sites of stress concentration provided by the wrinkles.
Gonzalez Cezar Henrique
2004-01-01
Full Text Available Recently, electrical resistivity (ER measurements have been done during some thermomechanical tests in copper based shape memory alloys (SMA's. In this work, single crystals of Cu-based SMA's have been studied at different temperatures to analyse the relationship between stress (s and ER changes as a function of the strain (e. A good consistency between ER change values is observed in different experiments: thermal martensitic transformation, stress induced martensitic transformation and stress induced reorientation of martensite variants. During stress induced martensitic transformation (superelastic behaviour and stress induced reorientation of martensite variants, a linear relationship is obtained between ER and strain as well as the absence of hys teresis. In conclusion, the present results show a direct evidence of martensite electrical resistivity anisotropy.
Guo, Xiaobin; Zhang, Yong; Zhang, Jin; Deng, Yunlai; Zhang, Xinming
2017-10-01
We investigate the relationship between inhomogeneously distributed S precipitates and hardness of stress-aged single-crystal Al-Cu-Mg. First, the effect of crystallographic anisotropy is considered and modeled from the results of free-stress aged single-crystal Al-1.2Cu-0.5Mg with ( 1\\bar{1}8 ), ( \\bar{1}\\bar{2}5 ), (356), and (319) plane orientations. Effect of crystallographic anisotropy depends on the angle between the plane orientation of the single crystal and {012} habit planes of the S precipitates. Second, the effects of the magnitude of the applied stress and direction on the S-laths' size and distribution are considered. As the applied stress-induced S-laths inhomogeneously distribute during aging, the effect of the single-crystal's orientation on the distribution of S-laths is modeled. The results show that a single crystal near (111) plane orientation has the lowest stress-orienting effect. Finally, at higher applied stresses, such as 50 MPa, the S precipitates disperse more homogeneously due to the influence of the dislocations. Inhibiting the effect of dislocation depends on the angle between the plane orientation of the single crystal and the {111} dislocation slide planes. A precipitate-strengthening model of the stress-aged Al-Cu-Mg alloys is established based on crystallographic anisotropy, stress-orienting precipitates, and inhibiting the effect of dislocations.
Lu, Ying; Wang, Yaotao; Fu, Lianlian; Jiang, Zhiyong; Men, Yongfeng
2014-11-13
Crystalline lamellar thickness in syndiotactic polypropylene (sPP) during crystallization from either isothermal molten or stretching induced localized melt states and during subsequent heating was investigated by means of temperature dependent small-angle X-ray scattering techniques. Well-defined crystallization lines where the reciprocal lamellar thickness is linearly dependent on crystallization temperature were observed. Unlike in the case of polybutene-1 where stretching crystallization line was shifted to direction of much smaller lamellar thickness (Macromolecules 2013, 46, 7874), the stretching induced crystallization line for sPP deviates from its corresponding isothermal crystallization line only slightly. Such phenomenon could be attributed to the fact that both crystallization processes from quiescent melt and stress induced localized melt are mediated in a mesomorphic phase in sPP. Subsequent heating of sPP after crystallization revealed the same melting behavior in both systems for the two kinds of crystallites obtained from either quiescent melt or stretching induced localized melt. Both of them underwent melting and recrystallization when the lamellar thickness was smaller than a critical value and melting directly without changing in thickness when the lamellar thickness was larger than the critical value. The melting behavior in sPP systems can be understood by considering the chain relaxation ability within crystalline phase and also can be used as evidence that the crystallization from molten state and stress-induced crystallization passed through the intermediate phase before forming crystallites.
Lijewski, S; Goslar, J; Hoffmann, S K
2006-07-05
The electron spin-lattice relaxation of Cu(2+) has been studied by the electron spin echo technique in the temperature range 4.2-115 K in triglycine sulfate (TGS) family crystals. Assuming that the relaxation is due to Raman relaxation processes the Debye temperature Θ(D) was determined as 190 K for TGS, 168 K for triglycine selenate (TGSe) and 179 K for triglycine fluoroberyllate (TGFB). We also calculated the Θ(D) values from the sound velocities derived from available elastic constants. The elastic Debye temperatures were found as 348 K for TGS, 288 K for TGSe and 372 K for TGFB. The results shown good agreement with specific heat data for TGS. The elastic Θ(D) are considerably larger than those determined from the Raman spin-lattice relaxation. The possible reasons for this discrepancy are discussed. We propose to use a modified expression describing two-phonon Raman relaxation with a single variable only (Θ(D)) after elimination of the sound velocity. Moreover, we show that the relaxation data can be fitted using the elastic Debye temperature value as a constant with an additional relaxation process contributing at low temperatures. This mechanism can be related to a local mode of the Cu(2+) defect in the host lattice. Electron paramagnetic resonance g-factors and hyperfine splitting were analysed in terms of the molecular orbital theory and the d-orbital energies and covalency factors of the Cu(gly)(2) complexes were found. Using the structural data and calculated orbital energies the spin-phonon coupling matrix element of the second-order Raman process was calculated as 553 cm(-1) for TGS, 742 cm(-1) for TGSe and 569 cm(-1) for TGFB.
Hoffmann, Stanislaw K.; Lijewski, Stefan
2015-03-01
Electron spin-lattice relaxation rate is determined by electron spin echo method in temperature range 4-60 K. The Raman relaxation processes dominate and its theory is outlined in a form suitable for calculations of relaxation rate using real phonon spectrum. A few approximations have been considered: when phonon spectrum and Debye temperature are not available; when Debye temperature is available but phonon spectrum is not; and when spin-phonon coupling is known. All these approximations use the Debye model of phonons and give a non-satisfactory description the temperature dependence of the relaxation rate. A perfect description of experimental results is obtained when real phonon spectrum is considered. The value of the spin-phonon coupling parameter was determined as G = = 1362cm-1 . This value is discussed by a comparison with G-values published for various ions and crystals.
Kim, K. M.; Smetana, P.
1990-03-01
Growth of large diameter Czochralski (CZ) silicon crystals require complete elimination of dislocations by means of Dash technique, where the seed diameter is reduced to a small size typically 3 mm in conjunction with increase in the pull rate. The maximum length of the large CZ silicon is estimated at the fracture stress limit of the seed neck diameter ( d). The maximum lengths for 200 and 300 mm CZ crystals amount to 197 and 87 cm, respectively, with d = 0.3 cm; the estimated maximum weight is 144 kg.
Iwaki, T.; Kobayashi, N.
1987-03-01
The resolved shear stresses (RSSs) in a Czochralski grown fcc single crystal during and after pulling are calculated numerically for various growth directions. The fcc crystal has twelve RSSs of which only five are independent. The total of twelve RSSs, the total of five larger RSSs, and the maximum RSS are obtained to evaluate the contribution of each RSS to dislocation generation or dislocation density. From their cross-sectional patterns, it is found that the <111> growth direction is the most advantageous for the reduction of RSS. Finally, the relation between the cross-sectional patterns of the three RSS measures and some etch-patterns is discussed.
Waskowska, A.; Gerward, Leif; Olsen, J.S.
2008-01-01
to occur at the same temperature as the magnetic transition, T-c = 130 K, which also is the same T-c as for the parent crystal CdCr2Se4. The low temperature phase has been described in orthorhombic space group Fddd. For In admixture, a structural transition occurs in the paramagnetic state at about T...
Hui Zhang
2014-05-01
Full Text Available In this paper, we have investigated the dependence of both the electromechanical effect and the electrostriction on the compressive stress in PMN-30%PT single crystal on the basis of single domain polarization rotation model. In the model, the electroelastic energy induced by the compressive stress is taken into account. The results have demonstrated that the compressive stress can lead to a significant change in the initial polarization state in the crystal. The reason lies in the stress induced anisotropy which is the coupling between the compressive stress and the electrostrictive coefficients. Thus, the initial polarization state in single crystal is determined by the combination of both electrocrystalline anisotropy and the stress induced anisotropy. The compressive stress along the [100] axis can make the polarization in the crystal be perpendicular to the stress direction, and make it difficult to be polarized to the saturation. This model is useful for better understanding both the polarization rotation and electromechanical effect in ferroelectric crystals with the compressive stress present.
Mechanisms of High Temperature/Low Stress Creep of Ni-Based Superalloy Single Crystals
Michael J. Mills
2009-03-05
Cast nickel-based superalloys are used for blades in land-based, energy conversion and powerplant applications, as well as in aircraft gas turbines operating at temperatures up to 1100 C, where creep is one of the life-limiting factors. Creep of superalloy single crystals has been extensively studied over the last several decades. Surprisingly, only recently has work focused specifically on the dislocation mechanisms that govern high temperature and low stress creep. Nevertheless, the perpetual goal of better engine efficiency demands that the creep mechanisms operative in this regime be fully understood in order to develop alloys and microstructures with improved high temperature capability. At present, the micro-mechanisms controlling creep before and after rafting (the microstructure evolution typical of high temperature creep) has occurred have yet to be identified and modeled, particularly for [001] oriented single crystals. This crystal orientation is most interesting technologically since it exhibits the highest creep strength. The major goal of the program entitled ''Mechanisms of High Temperature/Low Stress Creep of Ni-Based Superalloy Single Crystals'' (DOE Grant DE-FG02-04ER46137) has been to elucidate these creep mechanisms in cast nickel-based superalloys. We have utilized a combination of detailed microstructure and dislocation substructure analysis combined with the development of a novel phase-field model for microstructure evolution.
Maji, Partha Sona
2014-01-01
In this article, silica based triangular lattice PCF has been investigated towards both narrowband and broadband dispersion compensation for application in the communication wavelength. A dual core structure is obtained by introducing two different air-hole diameters in the cladding of the PCF. Dependence of individual structural parameters towards high negative dispersion (both narrowband and broadband) has been investigated in details with multipole mode based solver. The numerical investigation exhibits narrowband of very large negative dispersion of -37,300 ps/nm/km around the wavelength of 1550 nm. Present investigation also reports broadband dispersion values varying from -800 ps/nm/km to -2600 ps/nm/km over a 200 nm wavelength (1400 nm to 1600 nm) range, and kappa values near 300 nm, which matches well with standard single mode fiber. Using the principle of power transfer from the inner core to the outer core after the coupling wavelength, we have investigated possible design of ASE suppressed amplifie...
Wang, Qi; Sun, Shanshan; Zhang, Xiao; Pang, Fei; Lei, Hechang
2016-08-01
The anomalous Hall effect (AHE) is investigated for a ferromagnetic Fe3Sn2 single crystal with a geometrically frustrated kagome bilayer of Fe. The scaling behavior between anomalous Hall resistivity ρxy A and longitudinal resistivity ρx x is quadratic and further analysis implies that the AHE in the Fe3Sn2 single crystal should be dominated by the intrinsic Karplus-Luttinger mechanism rather than extrinsic skew-scattering or side-jump mechanisms. Moreover, there is a sudden jump of anomalous Hall conductivity σxy A appearing at about 100 K where the spin-reorientation transition from the c axis to the a b plane is completed. This change of σxy A might be related to the evolution of the Fermi surface induced by the spin-reorientation transition.
Low-temperature change of lattice parameters in LiKB{sub 4}O{sub 7} single crystals
Adamiv, Volodymyr; Burak, Yaroslav; Teslyuk, Ihor [Institute of Physical Optics, Lviv (Ukraine)
2009-02-15
Structural investigations of LiKB{sub 4}O{sub 7} crystals in the 13-290 K temperature range have been carried out by means of the high-resolution powder diffraction technique applying synchrotron radiation. It is shown that the structural phase transitions are absent and all the linear thermal expansion coefficients {alpha}{sub ij} are positive in the investigated temperature range. (copyright 2009 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)
Makthal, Nishanth; Rastegari, Sheila; Sanson, Misu; Ma, Zhen; Olsen, Randall J; Helmann, John D; Musser, James M; Kumaraswami, Muthiah
2013-06-21
Regulation of oxidative stress responses by the peroxide stress regulator (PerR) is critical for the in vivo fitness and virulence of group A Streptococcus. To elucidate the molecular mechanism of DNA binding, peroxide sensing, and gene regulation by PerR, we performed biochemical and structural characterization of PerR. Sequence-specific DNA binding by PerR does not require regulatory metal occupancy. However, metal binding promotes higher affinity PerR-DNA interactions. PerR metallated with iron directly senses peroxide stress and dissociates from operator sequences. The crystal structure revealed that PerR exists as a homodimer with two metal-binding sites per subunit as follows: a structural zinc site and a regulatory metal site that is occupied in the crystals by nickel. The regulatory metal-binding site in PerR involves a previously unobserved HXH motif located in its unique N-terminal extension. Mutational analysis of the regulatory site showed that the PerR metal ligands are involved in regulatory metal binding, and integrity of this site is critical for group A Streptococcus virulence. Interestingly, the metal-binding HXH motif is not present in the structurally characterized members of ferric uptake regulator (Fur) family but is fully conserved among PerR from the genus Streptococcus. Thus, it is likely that the PerR orthologs from streptococci share a common mechanism of metal binding, peroxide sensing, and gene regulation that is different from that of well characterized PerR from Bacillus subtilis. Together, our findings provide key insights into the peroxide sensing and regulation of the oxidative stress-adaptive responses by the streptococcal subfamily of PerR.
Dubinskiy, S. [École de technologie supérieure, 1100, Notre-Dame Street West, Montreal, Quebec H3C 1K3 (Canada); National University of Science and Technology “MISIS”, 4, Leninskiy prosp., Moscow 119049 (Russian Federation); Prokoshkin, S. [National University of Science and Technology “MISIS”, 4, Leninskiy prosp., Moscow 119049 (Russian Federation); Brailovski, V., E-mail: vladimir.brailovski@etsmtl.ca [École de technologie supérieure, 1100, Notre-Dame Street West, Montreal, Quebec H3C 1K3 (Canada); Inaekyan, K. [École de technologie supérieure, 1100, Notre-Dame Street West, Montreal, Quebec H3C 1K3 (Canada); Korotitskiy, A. [National University of Science and Technology “MISIS”, 4, Leninskiy prosp., Moscow 119049 (Russian Federation)
2014-02-15
Phase and structure transformations in biomedical Ti–21.8Nb–6.0Zr (TNZ) and Ti–19.7Nb–5.8Ta (TNT) shape memory alloys (at.%) under and without load in the − 150 to 100 °S temperature range are studied in situ using an original tensile module for a low-temperature chamber of an X-ray diffractometer. Alpha″- and beta-phase lattice parameters, the crystallographic resource of recovery strain, phase and structure transformation sequences, and microstress appearance and disappearance are examined, compared and discussed. For both alloys, the crystallographic resource of recovery strain decreases with temperature increase to become 4.5% for TNZ and 2.5% for TNT alloy (at RT). Loading at low temperatures leads to additional α″-phase formation and reorientation. Heating under load, as compared to strain-free heating, affects the reverse transformation sequence of both alloys in different ways. For TNZ alloy, strain-free heating results in simultaneous ω→β and α″→β transformations, whereas during heating under stress, they are sequential: β + ω→α″ precedes α″→β. For TNT alloy, strain-free heating results in reverse α″→β transformation, whereas during heating under stress, α″→β transformation is preceded by α″-phase reorientation. - Highlights: • Comparative in situ XRD analysis of Ti–Nb–Zr(Ta) shape memory alloys is realized. • Lattice parameters of β- and α″-phases are calculated in the − 150 to + 100 °C range. • The higher the temperature, the lower the α″→β transformation strain. • Loading at low temperatures results in α″-phase formation and reorientation. • Transformation sequences upon heating with and without loading are different.
Diagnostics of boundary layer transition by shear stress sensitive liquid crystals
Shapoval, E. S.
2016-10-01
Previous research indicates that the problem of boundary layer transition visualization on metal models in wind tunnels (WT) which is a fundamental question in experimental aerodynamics is not solved yet. In TsAGI together with Khristianovich Institute of Theoretical and Applied Mechanics (ITAM) a method of shear stress sensitive liquid crystals (LC) which allows flow visualization was proposed. This method allows testing several flow conditions in one wind tunnel run and does not need covering the investigated model with any special heat-insulating coating which spoils the model geometry. This coating is easily applied on the model surface by spray or even by brush. Its' thickness is about 40 micrometers and it does not spoil the surface quality. At first the coating obtains some definite color. Under shear stress the LC coating changes color and this change is proportional to shear stress. The whole process can be visually observed and during the tests it is recorded by camera. The findings of the research showed that it is possible to visualize boundary layer transition, flow separation, shock waves and the flow image on the whole. It is possible to predict that the proposed method of shear stress sensitive liquid crystals is a promise for future research.
The stress statistics of the first pop-in or discrete plastic event in crystal plasticity
Derlet, P. M.; Maaß, R.
2016-12-01
The stress at which the first discrete plastic event occurs is investigated using extreme value statistics. It is found that the average of this critical stress is inversely related to the deforming volume, via an exponentially truncated power-law. This is demonstrated for the first pop-in event observed in experimental nano-indentation data as a function of the indenter volume, and for the first discrete plastic event seen in a dislocation dynamics simulation. When the underlying master distribution of critical stresses is assumed to be a power-law, it becomes possible to extract the density of discrete plastic events available to the crystal, and to understand the exponential truncation as a break-down of the asymptotic Weibull limit.
Competing magnetic ground states and their coupling to the crystal lattice in CuFe2Ge2
May, Andrew F.; Calder, Stuart; Parker, David S.; Sales, Brian C.; McGuire, Michael A.
2016-01-01
Identifying and characterizing systems with coupled and competing interactions is central to the development of physical models that can accurately describe and predict emergent behavior in condensed matter systems. This work demonstrates that the metallic compound CuFe2Ge2 has competing magnetic ground states, which are shown to be strongly coupled to the lattice and easily manipulated using temperature and applied magnetic fields. Temperature-dependent magnetization M measurements reveal a ferromagnetic-like onset at 228 (1) K and a broad maximum in M near 180 K. Powder neutron diffraction confirms antiferromagnetic ordering below TN ≈ 175 K, and an incommensurate spin density wave is observed below ≈125 K. Coupled with the small refined moments (0.5–1 μB/Fe), this provides a picture of itinerant magnetism in CuFe2Ge2. The neutron diffraction data also reveal a coexistence of two magnetic phases that further highlights the near-degeneracy of various magnetic states. These results demonstrate that the ground state in CuFe2Ge2 can be easily manipulated by external forces, making it of particular interest for doping, pressure, and further theoretical studies. PMID:27739477
庄飞; 吴良; 等
2002-01-01
The plane-wave expansion method is used to calculate the band structure of a two-dimensional photonic crystal formed by a hexagonal structure of anisotropic cylinders.Two cylindrical inclusions in the unit cell have two different radii,R1 and R2(R1
Chatterjee, Sulagna; Chattopadhyay, Sanatan
2017-01-01
In the current work, an analytical model has been developed to estimate the amount of induced stress in nanowires which are horizontally embedded with different fractions within an Insulator-on-Silicon substrate. For estimating such stress, different crystallographic orientations of substrates and embedded nanowires have been considered. The induced stress for both the difference in thermo-elastic constants and lattice-mismatch is included and accuracy of the analytical model has been verified with the similar results obtained from ANSYS Multiphysics. Induced stress is observed to be insensitive of the nanowire size, however, depends significantly on the fractional insertion of the nanowires. A tensile stress of 1.95 GPa and a compressive stress of -1.0719 GPa have been obtained for the oriented Si-nanowires. Hole mobility of 850 cm2/Vs can be achieved for the 3/4th insertion of the nanowires which is comparable to electron mobility and therefore can be utilized for the design of symmetric nano-electronic devices.
Perlovich, German L; Volkova, Tatyana V; Bauer-Brandl, Annette
2006-07-01
Temperature dependencies of saturated vapor pressure and heat capacities for the 2-, 3-, and 4-hydroxybenzoic acids were measured and thermodynamic functions of sublimation calculated (2-hydroxybenzoic acid: DeltaG(sub) (298) = 38.5 kJ/mol; DeltaH(sub) (298) = 96.6 +/- 0.8 kJ/mol; DeltaS(sub) (298) = 191 +/- 3 J/mol . K; 3-hydroxybenzoic acid: DeltaG(sub) (298) = 50.6 kJ/mol; DeltaH(sub) (298) = 105.2 +/- 0.8 kJ/mol; DeltaS(sub) (298) = 180 +/- 2 J/mol . K; 4-hydroxybenzoic acid: DeltaG(sub) (298) = 55.0 kJ/mol; DeltaH(sub) (298) = 113.3 +/- 0.7 kJ/mol; DeltaS(sub) (298) = 193 +/- 2 J/mol . K). Analysis of crystal lattice packing energies based on geometry optimization of the molecules in the crystal using diffraction data and the program Dmol(3) was carried out. The energetic contributions of van der Waals, Coulombic, and hydrogen bond terms to the total packing energy were analyzed. The fraction of hydrogen bond energy in the packing energy increases as: 3-hydroxybenzoic (29.7%) Enthalpies of evaporation were estimated from enthalpies of sublimation and fusion. Temperature dependencies of the solubility in n-octanol and n-hexane were measured. The thermodynamic functions of solubility and solvation processes were deduced. Specific and nonspecific solvation terms were distinguished using the transfer from the "inert" n-hexane to the other solvents. The transfer of the molecules from water to n-octanol is enthalpy driven process.
Magnetic field induced strain assisted by stress in Ni-Fe-GaCo single crystals
Chumlyakov Y.
2010-06-01
Full Text Available Ferromagnetic shape memory alloys (FSMA have the possibility to induced a strain by applying a magnetic field. The main advantage of the FSMA is that the strain cycling frequency is two orders of magnitude higher than coventional shape memory alloys. The best alloy showing this effect is the Ni-Mn-Ga system, with a high mobility of its martensite variants and high magnetocrystalline anisotropy constant. Nevertheless, due to the high brittleness of this alloy, other systems (Ni-Fe-Ga, Co-Ni-Al, Co-Ni-Ga, ... are being investigated as an alternative to Ni-Mn-Ga. In the current work, Ni-Fe-Ga-Co single crystals have been studied. In spite of the formation of L10 martensite (low mobility of the variants, the [001] crystals exhibited magnetic-field-induced strains (in tension larger than 2%, under an assisting tensile stress around 16 MPa and fields below 15 kOe. In martensitic samples previously compressed, application of a constant tensile stress along the same axis together with a perpendicular magnetic field produces the elongation of the sample by variant reorientation, as one of the variants rotates its c axis from the field direction to the stress-axis direction. An estimated magnetostress of ~0.8 MPa is in good agreement with the theoretical value given by the ratio of magnetocrystalline anisotropy constant and twinning shear.
Chakrabarti, J; Bagchi, B; Chakrabarti, Jayprokas; Basu, Asis; Bagchi, Bijon
2000-01-01
Fermions on the lattice have bosonic excitations generated from the underlying periodic background. These, the lattice bosons, arise near the empty band or when the bands are nearly full. They do not depend on the nature of the interactions and exist for any fermion-fermion coupling. We discuss these lattice boson solutions for the Dirac Hamiltonian.
Elimination of spurious lattice fermion solutions and noncompact lattice QCD
Lee, T.D.
1997-09-22
It is well known that the Dirac equation on a discrete hyper-cubic lattice in D dimension has 2{sup D} degenerate solutions. The usual method of removing these spurious solutions encounters difficulties with chiral symmetry when the lattice spacing l {ne} 0, as exemplified by the persistent problem of the pion mass. On the other hand, we recall that in any crystal in nature, all the electrons do move in a lattice and satisfy the Dirac equation; yet there is not a single physical result that has ever been entangled with a spurious fermion solution. Therefore it should not be difficult to eliminate these unphysical elements. On a discrete lattice, particle hop from point to point, whereas in a real crystal the lattice structure in embedded in a continuum and electrons move continuously from lattice cell to lattice cell. In a discrete system, the lattice functions are defined only on individual points (or links as in the case of gauge fields). However, in a crystal the electron state vector is represented by the Bloch wave functions which are continuous functions in {rvec {gamma}}, and herein lies one of the essential differences.
Crystal Structure of Oxidative Stress Sensor Keap1 in Complex with Selective Autophagy Substrate p62
Kurokawa, Hirofumi
Keap1, an adaptor protein of cullin-RING ubiquitin ligase complex, represses cytoprotective transcription factor Nrf2 in an oxidative stress-dependent manner. The accumulation of selective autophagy substrate p62 also activates Nrf2 target genes, but the detailed mechanism has not been elucidated. Crystal structure of Keap1-p62 complex revealed the structural basis for the Nrf2 activation in which Keap1 is inactivated by p62. The accumulation of p62 is observed in hepatocellular carcinoma. The activation of Nrf2 target genes, including detoxifying enzymes and efflux transporters, by p62 may protect the cancer cells from anti-cancer drugs.
Silva, F.T. da; Nunes, M.A.M. [Universidade Federal do Rio Grande do Norte (PPGCEM/UFRN), Natal (Brazil). Programa de Pos-Graduacao em Ciencia e Engenharia de Materiais; Oliveira, R.M.V. de; Silva, G.G. da [Instituto Federal do Rio Grande do Norte (IFRN), Natal (Brazil); Souza, C.P. de; Gomes, U.U. [Universidade Federal do Rio Grande do Norte (UFRN), Natal (Brazil)
2010-07-01
The tungsten carbide (WC) has wide application due to its properties like high melting point, high hardness, wear resistance, oxidation resistance and good electrical conductivity. The microstructural characteristics of the starting powders influences the final properties of the carbide. In this context, the use of nanoparticle powders is an efficient way to improve the final properties of the WC. The high energy milling stands out from other processes to obtain nanometric powders due to constant microstructural changes caused by this process. Therefore, the objective is to undertake an analysis of microstructural characteristics on the crystallite size and microdeformations of the crystal lattice using the technique of X-ray diffraction (XRD) using the Rietveld refinement. The results show an efficiency of the milling process to reduce the crystallite size, leading to a significant deformation in the crystal lattice of WC from 5h milling. (author)
Theory of Lattice Strain for Materials Undergoing Plastic Deformation
Karato, S.
2008-12-01
Radial x-ray diffraction is used to probe physical properties of materials including elastic and plastic properties. The theory used behind such an practice is the one developed by Singh (1993) in which the relation between lattice strain and elastic constants and macroscopic stress is derived. In this theory, the variation of inferred stress with the crystallographic planes, (hkl), is due to the elastic anisotropy. However, recent experimental studies showed that in many cases, the variation of stress with (hkl) far exceeds the value expected from this theory. I have developed a modified theory to rectify this problem with Singh's theory. In Singh's theory, the stress distribution in a polycrystalline material is treated only either unrelaxed or relaxed state. The role of plastic deformation is included only to the extent that plastic flow influences this stress state. Such an assumption corresponds to a Voigt model behavior, which is not an appropriate model at high temperatures where continuing plastic flow occurs with concurrent microscopic equilibrium, elastic deformation. This is a Maxwell model type behavior, and my model provides a stress analysis in a Maxwell material with anisotropic and non-linear power-law rheology. In this theory, the lattice strain corresponding to an imposed macroscopic strain-rate is calculated by three steps: (i) conversion of macroscopic strain-rate to macroscopic stress, (ii) conversion of macroscopic stress to microscopic stress at individual grains, and (iii) calculation of microscopic strain due to microscopic stress. The first step involves anisotropy in macroscopic viscosity that depends on anisotropy in crystal plasticity and lattice-preferred orientation. The second step involves anisotropic crystal plasticity and finally the third step involves elastic crystal anisotropy. In most cases, the influence of LPO is weak and in such a case, the lattice strain depends on (hkl) due to the anisotropy in both elastic and plastic
Shape Memory Behavior of [111]-Oriented NiTi Single Crystals After Stress-Assisted Aging
Irfan Kaya; Hirobumi Tobe; Haluk Ersin Karaca; Emre Acar; Yuriy Chumlyakov
2016-01-01
The shape memory behavior of [111]-oriented NistTi49 (at.％) single crystals was investigated after stressassisted aging at 500 ℃ for 1.5 h under a compressive stress of-150 MPa.It was found that a single family of Ni4Ti3 precipitates with two crystallographically equivalent variants was formed after aging under compressive stress.Stressassisted aging resulted in tensile two-way shape memory effect strain of 1.56％ under-5 MPa.Thermal cycling under -600 MPa resulted in a transformation strain of-2.15％,while the subsequent thermal cycling under-5 MPa resulted in a tensile two-way shape memory effect strain of 2.2％.
The effect of diffusion induced lattice stress on the open-circuit voltage in silicon solar cells
Weizer, V. G.; Godlewski, M. P.
1984-01-01
It is demonstrated that diffusion induced stresses in low resistivity silicon solar cells can significantly reduce both the open-circuit voltage and collection efficiency. The degradation mechanism involves stress induced changes in both the minority carrier mobility and the diffusion length. Thermal recovery characteristics indicate that the stresses are relieved at higher temperatures by divacancy flow (silicon self diffusion). The level of residual stress in as-fabricated cells was found to be negligible in the cells tested.
Young's Modulus, Residual Stress, and Crystal Orientation of Doubly Clamped Silicon Nanowire Beams.
Calahorra, Y; Shtempluck, O; Kotchetkov, V; Yaish, Y E
2015-05-13
Initial or residual stress plays an important role in nanoelectronics. Valley degeneracy in silicon nanowires (SiNWs) is partially lifted due to built-in stresses, and consequently, electron-phonon scattering rate is reduced and device mobility and performance are improved. In this study we use a nonlinear model describing the force-deflection relationship to extract the Young's modulus, the residual stress, and the crystallographic growth orientation of SiNW beams. Measurements were performed on suspended doubly clamped SiNWs subjected to atomic force microscopy (AFM) three-point bending constraints. The nanowires comprised different growth directions and two SiO2 sheath thicknesses, and underwent different rapid thermal annealing processes. Analysis showed that rapid thermal annealing introduces compressive strains into the SiNWs and may result in buckling of the SiNWs. Furthermore, the core-shell model together with the residual stress analysis accurately describe the Young's modulus of oxide covered SiNWs and the crystal orientation of the measured nanowires.
无
2006-01-01
A two-dimensional model was established in the rectangular co-ordinate to study the thermal stress in the sapphire single crystal grown by the improved Kyropoulos. In the simulation, the distribution, the maximum and minimum values of the thermal stress were calculated. In addition, the relationship between the thermal stress and the shouldering angles was obtained that for lower shouldering angles, the maximum of the thermal stress value is lower and the minimum value is higher. It indicates that the distribution of the thermal stress can be improved by decreasing the shouldering angles of the crystal during the growth process. To evaluate the model, the experiment was carried out and the results are in good agreement with the calculation.
Effect of impurities and stress on the damage distributions of rapidly grown KDP crystals
Runkel, M.; Tan, M.; De Yoreo, J.; Zaitseva, N.
1997-12-20
Development of high damage threshold, 50 cm, rapidly grown KF*P frequency triplers for operation of the National Ignition Facility (NIF) in the 14 J/cm2, 351 nm, 3 ns regime requires a thorough understanding of how the crystal growth parameters and technologies affect laser induced damage. Of particular importance is determining the effect of ionic impurities (e.g. Cr3+, Fe3+, Al3+) which may be introduced in widely varying concentrations via starting salts. In addition, organic particulates can contaminate the solution as leachants from growth platforms or via mechanical ablation. Mechanical stresses in the crystals may also play a strong role in the laser-induced damage distribution (LIDD), particularly in the cases of large boules where hydrodynamic forces in the growth tank may be quite high. WE have developed a dedicated, automated damage test system with diagnostic capabilities specifically designed for measured time resolved bulk damage onset and evolution. The data obtained make it possible to construct characteristic damage threshold distributions for each sample. Test results obtained for a variety of KDP samples grown from high purity starting salts and individually doped with Lucite and Teflon, iron, chromium, and aluminium show that the LIDD drops with increasing contamination content. The results also show that solution filtration leads to increased damage performance for undoped crystals but is not solely responsibility for producing the high LIDDs required by the NIF. The highest LIDD measured on a rapidly grown sample indicate that it is possible to produce high damage threshold material using ultrahigh purity, recrystallized starting salts, continuous filtration and a platform designed to minimize internal stress during growth.
Sun, Fujun; Zhou, Jian; Huang, Lijun; Fu, Zhongyuan; Tian, Huiping
2017-09-01
In this paper, we present a novel optical sensor based on photonic crystal slot nanobeam cavity (PCSNC) with rectangular air holes. By introducing a continuous slot and quadratically modulated hole spacing (lattice constant a) structure, the majority of the optical field is localized in the slot region, which enhances the light-matter interaction. With applying the three dimensional finite-difference time-domain (3D-FDTD) simulations, three key geometric parameters (hole width wx, slot width ws and the number of the holes N) are optimized to achieve a high sensitivity (S) while keeping a high quality (Q) factor. The highest S over 1000 nm/RIU (refractive index unit) is achieved when the slot width equals to 200 nm. The highest Q-factor of 2.15×107 is obtained when 30 holes are placed on both sides of the host waveguide with the slot width of 80 nm. Considering the transmission efficiency and the trade-off between S and Q-factor, the slot width and the number of the tapered region are chosen as 80 nm and 20, respectively. A high S approximately 835 nm/RIU and a Q-factor about 5.50×105 with small effective mode volume of 0.03(λ/nair)3 are achieved simultaneously, resulting in an ultra-high figure-of-merit (FOM) above 2.92×105. Furthermore, the active sensing region of the optimized structure occupies only about 12 μm×0.08 μm, which makes the device attractive for realizing on-chip integrated sensor arrays.
Perlovich, German L; Volkova, Tatyana V; Bauer-Brandl, Annette
2006-10-01
Temperature dependencies of saturated vapor pressure for the monoclinic modification of paracetamol (acetaminophen), acetanilide, and phenacetin (acetophenetidin) were measured and thermodynamic functions of sublimation calculated (paracetamol: DeltaGsub298=60.0 kJ/mol; DeltaHsub298=117.9+/-0.7 kJ/mol; DeltaSsub298=190+/-2 J/mol.K; acetanilide: DeltaGsub298=40.5 kJ/mol; DeltaHsub298=99.8+/-0.8 kJ/mol; DeltaSsub298=197+/-2 J/mol.K; phenacetin: DeltaGsub298=52.3 kJ/mol; DeltaHsub298=121.8+/-0.7 kJ/mol; DeltaSsub298=226+/-2 J/mol.K). Analysis of packing energies based on geometry optimization of molecules in the crystal lattices using diffraction data and the program Dmol3 was carried out. Parameters analyzed were: (a) energetic contribution of van der Waals forces and hydrogen bonding to the total packing energy; (b) contributions of fragments of the molecules to the packing energy. The fraction of hydrogen bond energy in the packing energy increases as: phenacetin (17.5%)Enthalpies of evaporation were estimated from enthalpies of sublimation and fusion. Activity coefficients of the drugs in n-octanol were calculated from cryoscopic data and by estimation of dilution enthalpy obtained from solubility and calorimetric experiments (for infinite dissolution). Solubility temperature dependencies in n-octanol and n-hexane were measured. The thermodynamic functions of solubility and solvation processes were deduced. Specific and nonspecific solvation terms were distinguished using the transfer from the "inert" n-hexane to the other solvents. The transfer of the molecules from water to n-octanol is enthalpy driven for paracetamol; for acetanilide and phenacetin, entropy driven.
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); Guo, Yongbo [Center for Precision Engineering, Harbin Institute of Technology, Harbin 150001 (China); Xie, Wenkun [School of Mechatronics Engineering, Harbin Institute of Technology, Harbin 150001 (China); Center for Precision Engineering, Harbin Institute of Technology, Harbin 150001 (China)
2015-11-15
Graphical abstract: In this paper, molecular dynamics simulation is performed to study the distribution of dislocation defects and local atomic crystal structure of single crystal copper. The stress distribution is investigated which is calculated by virial stress and analyzed by static pressure. The results are shown in (a)–(d). It is indicated that the compressive stress mainly spreads over the shear-slip zone, and the tensile stress is consisted in flank friction zone, shown in (a). The high tensile stress in subsurface is the source of stress, shown in (b). By the driven action of the stress source, the initial stair-rod dislocation nucleates. Then the dislocation climbs along four {1 1 1} planes under the stress driven action, shown in (d). Finally, the SFT is formed by the interaction of the compressive stress and the tensile stress which come from the shear-slip zone and friction zone, respectively. Besides, stair-rod dislocation, stacking faults and dislocation loop are also nucleated in the subsurface, shown in (c). Dislocation distribution, local atomic crystal structure state and stress-induced formation process of SFT by atomic. - Highlights: • A novel defect structure “stress-induced stacking fault tetrahedra” is revealed. • Atomic structural evolution and stress state distribution of the SFT are studied. • The stress-induced formation mechanism of the SFT is proposed. - Abstract: Stacking fault tetrahedra commonly existed in subsurface of deformed face center cubic metals, has great influence on machining precision and surface roughness in nano-cutting. Here we report, a stacking fault tetrahedra is formed in subsurface of workpiece during nano-cutting. The variation of cutting force and subsurface defects distribution are studied by using molecular dynamics simulation. The stress distribution is investigated which is calculated by virial stress and analyzed by static compression. The result shows that the cutting force has a rapidly
Mousavi, Seyedeh Laleh; Sabaeian, Mohammad
2016-10-01
We report on the modeling of the depolarization loss in the conventional and panda-shaped photonic crystal fiber lasers (PCFLs) due to the self-heating of the fiber, which we call it thermal stress-induced depolarization loss (TSIDL). We first calculated the temperature distribution over the fiber cross sections and then calculated the thermal stresses/strains as a function of heat load per meter. Thermal stress-induced birefringence (TSIB), which is defined as | n x - n y |, in the core and cladding regions was calculated. Finally, TSIDL was calculated for the conventional and panda-shaped PCFLs as a function of fiber length and, respectively, saturated values of 22 and 25 % were obtained which were independent of heat load per meter. For panda-shaped PCFLs, prior to being saturated, an oscillating and damping behavior against the fiber length was seen where in some lengths reached 35 %. The results are close to an experimental value of 30 % reported for a pulsed PCFL (Limpert et al., Opt Express 12:1313-1319, 2004) where the authors reported a degree of polarization of 70 % (i.e., a depolarization of 30 %). The most important result of this work is a saturation behavior of TSIDL at long-enough lengths of the fiber laser which is independent of heat load per meter. To our knowledge, this the first report of TSIBL for PCFLs.
Stress and mixed boundary conditions for two-dimensional dodecagonal quasi-crystal plates
Yan Gao; Si-Peng Xu; Bao-Sheng Zhao
2007-05-01
For plate bending and stretching problems in two-dimensional (2D) dodecagonal quasi-crystal (QC) media, the reciprocal theorem and the general solution for QCs are applied in a novel way to obtain the appropriate stress and mixed boundary conditions accurate to all order. The method developed by Gregory and Wan is used to generate necessary conditions which the prescribed data on the edge of the plate must satisfy in order that it should generate a decaying state within the plate; these decaying state conditions are obtained explicitly for axisymmetric bending and stretching of a circular plate when stress or mixed conditions are imposed on the plate edge. They are then used for the correct formulation of boundary conditions for the interior solution. For the stress data, our boundary conditions coincide with those obtained in conventional forms of plate theories. More importantly, appropriate boundary conditions with a set of mixed edge-data are obtained for the ﬁrst time. Furthermore, the corresponding necessary conditions for transversely isotropic elastic plate are obtained directly, and their isotropic elastic counterparts are also obtained.
Hattori, Ken; Oi, Hideo; Tanaka, Kota; Kumagai, Tomohiro; Daimon, Hiroshi
2012-05-01
We have applied a three-dimensional (3D) reciprocal-lattice analysis method using a typical reflection high-energy electron diffraction (RHEED) system - all RHEED patterns in scanning sample-surface azimuth are converted into 3D reciprocal-lattice space. This analysis method can determine complex crystal orientations of nanoclusters, islands, and grains with multiple domains, which are difficult to obtain from a small number of non-converted two-dimensional RHEED patterns. For an Al-deposited Si(111) surface followed by annealing, we successfully determined new crystal orientations of Al grains: Al(001), Al(012) and Al(011) ∥ Si(111) with Al[100] ∥ Si. The typical acquisition time of 3D RHEED patterns is 10-20 min, which is shorter than that by a standard X-ray diffraction system with φ and ω scans for 3D reciprocal-lattice mapping. This is one of the advantages of this analysis method, in addition to the convenient observation of in situ vacuum-fabricated nanocrystals on substrate surfaces with high sensitivity.
Wang, Da-Wei; Zhu, Shi-Yao; Scully, Marlan O
2014-01-01
We show that the timed Dicke states of a collection of three-level atoms can form a tight-binding lattice in the momentum space. This lattice, coined the superradiance lattice (SL), can be constructed based on an electromagnetically induced transparency (EIT) system. For a one-dimensional SL, we need the coupling field of the EIT system to be a standing wave. The detuning between the two components of the standing wave introduces an effective electric field. The quantum behaviours of electrons in lattices, such as Bloch oscillations, Wannier-Stark ladders, Bloch band collapsing and dynamic localization can be observed in the SL. The SL can be extended to two, three and even higher dimensions where no analogous real space lattices exist and new physics are waiting to be explored.
Stress-relaxation tests in the work-hardening regime of tungsten single crystals below 300 K
Brunner, D. [Max-Planck-Institut fuer Metallforschung, Heisenbergstrasse 3, 70569 Stuttgart (Germany)], E-mail: d.brunner@mf.mpg.de
2008-06-15
The influence of work hardening on the results of stress-relaxation tests was studied for highly pure tungsten single crystals isothermally deformed at four temperatures of 274, 241, 131, and 78 K. A method accounting for strong work hardening on the determination of the strain-rate sensitivity from stress-relaxation tests is introduced by establishing special diagrams of SR tests denoted as YX diagrams.
Vetter, Ulrich; Nijjar, Anmol S; Zandi, Bahram; Öhl, Gregor; Wahl, Ulrich; De Vries, Bart; Hofsäss, Hans; Dietrich, Marc
2006-01-01
We report a detailed crystal field analysis of Pm3+ and Sm3+ as well as lattice location studies of 147Pm and 147Nd in 2H-aluminum nitride (w-AlN). The isotopes of mass 147 were produced by nuclear fission and implanted at an energy of 60 keV. The decay chain of interest in this work is 147Nd→147Pm→147Sm (stable). Lattice location studies applying the emission channeling technique were carried out using the β− particles and conversion electrons emitted in the radioactive decay of 147Nd→147Pm. The samples were investigated as implanted, and also they were investigated after annealing to temperatures of 873 K as well as 1373 K. The main fraction of about 60% of both 147Pm as well as 147Nd atoms was located on substitutional Al sites in the AlN lattice; the remainder of the ions were located randomly within the AlN lattice. Following radioactive decay of 147Nd, the cathodoluminescence spectra of Pm3+ and Sm3+ were obtained between 500 nm and 1050 nm at sample temperatures between 12 K and 300 K. High-re...
2011-11-01
tendency for a saturation stress value, most likely because the experimental size-effect data does not include small enough sizes of micron-sized crystals...D, Gumbsch P, Kraft O, Scripta Mater 2008; 58:587. 7) Tang H, Schwarz KW, Espinosa HD, Acta Mater 2007; 55:1607. 8) Zhou C, Biner S, Lesar R
The influence of the excitation pulse shape on the stress wave propagation in a bcc iron crystal
Červená O.
2008-12-01
Full Text Available This article presents a large-scale molecular dynamic simulations of wave propagation in a cracked bcc (body centered cubic iron crystal based on an N-body potential model which gives a good description of an anisotropic elasticity. The crystal is loaded by a stress pulse on its front face and the response is detected on its opposite face. The various shapes, amplitudes, and widths of stress pulse are considered. The simulations are performed also for a central pre-existing Griffith crack. The crack is embedded in a bcc iron crystal having a basic cubic orientation. The acquired results bring important information for further analysis oriented to new NDT nanoscale methods.
THE CRYSTAL STRUCTURE OF ANTIMONY (III) SULFOBROMIDE, SBSBR,
ANTIMONY COMPOUNDS, *SULFUR COMPOUNDS, CRYSTAL STRUCTURE , CRYSTAL STRUCTURE , BROMIDES, SYMMETRY(CRYSTALLOGRAPHY), FOURIER ANALYSIS, MOLECULAR STRUCTURE, CRYSTAL LATTICES, CHEMICAL BONDS, X RAY DIFFRACTION.
Molnar, P.; Sittner, P.; Lukas, P.; Hannula, S.-P.; Heczko, O.
2008-06-01
Stress-induced martensite variant reorientation in magnetic shape memory Ni-Mn-Ga single crystal was studied in situ by the neutron diffraction technique. Principles of determination of individual tetragonal martensitic variants in shape memory alloys are explained. Using neutron diffraction we show that the macroscopic strain originates solely from the martensite structure reorientation or variant redistribution. Neutron diffraction also reveals that the reorientation of martensite is not fully completed even at a stress value of 25 MPa, which is about 20 times larger than the mean stress needed for reorientation. Only one twinning system is active during the reorientation process.
Coincident site lattice-matched growth of semiconductors on substrates using compliant buffer layers
Norman, Andrew
2016-08-23
A method of producing semiconductor materials and devices that incorporate the semiconductor materials are provided. In particular, a method is provided of producing a semiconductor material, such as a III-V semiconductor, on a silicon substrate using a compliant buffer layer, and devices such as photovoltaic cells that incorporate the semiconductor materials. The compliant buffer material and semiconductor materials may be deposited using coincident site lattice-matching epitaxy, resulting in a close degree of lattice matching between the substrate material and deposited material for a wide variety of material compositions. The coincident site lattice matching epitaxial process, as well as the use of a ductile buffer material, reduce the internal stresses and associated crystal defects within the deposited semiconductor materials fabricated using the disclosed method. As a result, the semiconductor devices provided herein possess enhanced performance characteristics due to a relatively low density of crystal defects.
Cooperative dynamics in ultrasoft 2D crystals
Sprakel, Joris; van der Meer, Berend; Dijkstra, Marjolein; van der Gucht, Jasper
2015-03-01
The creation, annihilation, and diffusion of defects in crystal lattices play an important role during crystal melting and deformation. Although it is well understood how defects form and react when crystals are subjected to external stresses, it remains unclear how crystals cope with internal stresses. We report a study in which we create a highly localized internal stress, by means of optical tweezing, in a crystal formed from micrometer-sized colloidal spheres and directly observe how the solid reacts using microscopy. We find that, even though the excitation is highly localized, a collective dance of colloidal particles results; these collective modes take the form of closed rings or open-ended strings, depending on the sequence of events which nucleate the rearrangements. Surprisingly, we find from Brownian Dynamics simulations that these cooperative dynamics are thermally-activated modes inherent to the crystal, and can even occur through a single, sufficiently large thermal fluctuation, resulting in the irreversible displacement of 100s of particles from their lattice sites.
Localized structures in Kagome lattices
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.
Borwein, J M; McPhedran, R C
2013-01-01
The study of lattice sums began when early investigators wanted to go from mechanical properties of crystals to the properties of the atoms and ions from which they were built (the literature of Madelung's constant). A parallel literature was built around the optical properties of regular lattices of atoms (initiated by Lord Rayleigh, Lorentz and Lorenz). For over a century many famous scientists and mathematicians have delved into the properties of lattices, sometimes unwittingly duplicating the work of their predecessors. Here, at last, is a comprehensive overview of the substantial body of
Falin, M L; Latypov, V A; Leushin, A M
2003-01-01
SrF sub 2 and BaF sub 2 crystals, doped with the Yb sup 3 sup + ions, have been investigated by electron paramagnetic resonance and optical spectroscopy. As-grown crystals of SrF sub 2 and BaF sub 2 show the two paramagnetic centres for the cubic (T sub c) and trigonal (T sub 4) symmetries of the Yb sup 3 sup + ions. Empirical diagrams of the energy levels were established and the potentials of the crystal field were determined. Information was obtained on the SrF sub 2 and BaF sub 2 phonon spectra from the electron-vibrational structure of the optical spectra. The crystal field parameters were used to analyse the crystal lattice distortions in the vicinity of the impurity ion and the F sup - ion compensating for the excess positive charge in T sub 4. Within the frames of a superposition model, it is shown that three F sup - ions from the nearest surrounding cube, located symmetrically with respect to the C sub 3 axis from the side of the ion-compensator, approach the impurity ion and cling to the axis of the...
Samojlov, A.I.; Ignatova, I.A.; Krivko, A.I.; Kozlova, V.S.; Dodonova, L.P.
1983-01-01
A method is outlined that enables with the use of Fourier-analysis of summary unresolved X-ray diffraction profile of the matrix ..gamma.. and intermetallic ..gamma..' phases of nickel heat resisting alloys of the Ni-Cr-Co-Al-Ti-Nb-W-Mo-V -Hf system, to calculate the location of reflexes of each phase, that is, to determine the periods of their crystal lattices in the alloy (in monolith) directly without electrolytic separation of ..gamma..'-phase. The limits of the method applicability were determined.
Kuzel, R., E-mail: kuzel@karlov.mff.cuni.c [Department of Condensed Matter Physics, Faculty of Mathematics and Physics, Charles University in Prague, 121 16 Praha 2 (Czech Republic); Nichtova, L.; Matej, Z. [Department of Condensed Matter Physics, Faculty of Mathematics and Physics, Charles University in Prague, 121 16 Praha 2 (Czech Republic); Musil, J. [Department of Physics, Faculty of Applied Sciences, University of West Bohemia in Pilsen, Pilsen (Czech Republic)
2010-12-30
Remarkable properties of titanium dioxide films such as hydrophilicity or photocatalytic activity depend largely on their phase composition, microstructure and in particular on the crystallinity. By in-situ X-ray diffraction studies of isochronal and isothermal annealing of amorphous films with different thickness at different temperatures it was found that the crystallization process can be quite well described by the Johnson-Mehl-Avrami-Kolmogorov formula modified by the introduction of crystallization onset. This and other parameters of the formula strongly depend on the film thickness. For thickness below about 500 nm the crystallization is very slow. Simultaneously, the appearance and increase of tensile stresses with the annealing time were observed and these stresses were confirmed by detailed studies by both total pattern fitting and sin{sup 2{psi}} method on post-annealed samples. The stresses rapidly increase with decreasing thickness of the films. It seems that there is a strong correlation between the stresses and crystallization onset and/or crystallization rate. Tensile stresses that are generated during crystallization further inhibit crystallization and cause significant thickness dependence of the crystallization. The temperature and time dependence of microstructure of crystallized amorphous films differ significantly from those obtained for as-deposited nanocrystalline films or nanocrystalline powders. During annealing, quite large crystallites are formed quickly with the preferred orientation (001) that is suppressed with the proceeding time.
Kamiyama, E.; Vanhellemont, J.; Sueoka, K.; Araki, K.; Izunome, K.
2013-02-01
When pulling large diameter Si crystals from a melt close to the Voronkov criterion, small changes in pulling speed and thermal gradient can lead to the formation of voids leading to detrimental pits on the polished wafer surface. The creation of voids is mainly due to the lowering of the vacancy formation energy due to increased thermal compressive stress. The small size and low density of the formed voids when pulling crystals close to the Voronkov criterion conditions are a challenge for wafer surface inspection tools and possible solutions are discussed.
Obtaining local reciprocal lattice vectors from finite-element analysis.
Sutter, John P; Connolley, Thomas; Hill, Tim P; Huang, Houcheng; Sharp, Doug W; Drakopoulos, Michael
2008-11-01
Finite-element analysis is frequently used by engineers at synchrotron beamlines to calculate the elastic deformation of a single crystal undergoing mechanical bending or thermal load. ANSYS Workbench software is widely used for such simulations. However, although ANSYS Workbench software provides useful information on the displacements, strains and stresses within the crystal, it does not yield the local reciprocal lattice vectors that would be required for X-ray diffraction calculations. To bridge this gap, a method based on the shape functions and interpolation procedures of the software itself has been developed. An application to the double-crystal bent Laue monochromator being designed for the I12 (JEEP) wiggler beamline at the Diamond Light Source is presented.
李未; 陈小玲
2011-01-01
利用二维三角晶格介质柱光子晶体TE偏振的禁带与介质柱半径的变化关系,分析了二维光子晶体的带隙分布及斜边耦合特性.结果表明,光子禁带的大小受到构成光子晶体的介电材料的空间排列分布以及介质柱半径大小的影响;束缚在光子晶体中的光波可以在波导和谐振腔中进行传输,达到选择输出光波的目的.%The paper study the relation between two dimensional triangular lattice photonic crystal band gap for TE polarizationand dielectric cylinder radius, and study distribution of two dimensional photonic crystal defect state. Results show, the photonic crystal band gaps were distributed by dielectric material space distribution and medium size of the radius; Tied in the photon crystals of light waves can transmission in waveguides and resonator cavity to select the output of light waves.
Flakus, Henryk T; Hachuła, Barbara; Garbacz, Aleksandra
2012-11-29
Polarized IR spectra of hydrogen-bonded acetone oxime and 3,5-dimethylpyrazole crystals were measured at 293 and 77 K in the ν(X-H) and ν(X-D) band frequency ranges. These crystals contain molecular trimers in their lattices. The individual crystal spectral properties remain in a close relation with the electronic structure of the two different molecular systems. We show that a vibronic coupling mechanism involving the hydrogen-bond protons and the electrons on the π-electronic systems in the molecules determines the way in which the vibrational exciton coupling between the hydrogen bonds in the trimers occurs. A strong coupling in 3,5-dimethylpyrazole trimers prefers a "tail-to-head"-type Davydov coupling widespread via the π-electrons. A weak through-space exciton coupling in acetone oxime trimers involves three adjacent hydrogen bonds in each cycle. The relative contribution of each exciton coupling mechanism in the trimer spectra generation is temperature and the molecular electronic structure-dependent. This explains the observed difference in the temperature-induced evolution of the compared spectra. The mechanism of the H/D isotopic "self-organization" processes in the crystal hydrogen bonds was also analyzed. The two types of the hydrogen-bond trimers exhibit the same way, in which the H/D isotopic recognition mechanism occurs. In acetone oxime and 3,5-dimethylpyrazole trimers, identical hydrogen isotope atoms exist in these entire hydrogen-bond systems.
Donnellan, Thomas; Maxwell, E A; Plumpton, C
1968-01-01
Lattice Theory presents an elementary account of a significant branch of contemporary mathematics concerning lattice theory. This book discusses the unusual features, which include the presentation and exploitation of partitions of a finite set. Organized into six chapters, this book begins with an overview of the concept of several topics, including sets in general, the relations and operations, the relation of equivalence, and the relation of congruence. This text then defines the relation of partial order and then partially ordered sets, including chains. Other chapters examine the properti
THE CRYSTAL STRUCTURE OF 2-(4’-AMINO-5’AMINO PYRIMIDY) -2-PENTENE-4-ONE.
NITROGEN HETEROCYCLIC COMPOUNDS, CRYSTAL STRUCTURE ), (*AMINES, CRYSTAL STRUCTURE ), (*KETONES, CRYSTAL STRUCTURE ), CRYSTAL LATTICES, FOURIER ANALYSIS, LEAST SQUARES METHOD, MOLECULAR STRUCTURE, PYRIMIDINES, CHEMICAL BONDS
Solitons in nonlinear lattices
Kartashov, Yaroslav V; Torner, Lluis
2010-01-01
This article offers a comprehensive survey of results obtained for solitons and complex nonlinear wave patterns supported by purely nonlinear lattices (NLs), which represent a spatially periodic modulation of the local strength and sign of the nonlinearity, and their combinations with linear lattices. A majority of the results obtained, thus far, in this field and reviewed in this article are theoretical. Nevertheless, relevant experimental settings are surveyed too, with emphasis on perspectives for implementation of the theoretical predictions in the experiment. Physical systems discussed in the review belong to the realms of nonlinear optics (including artificial optical media, such as photonic crystals, and plasmonics) and Bose-Einstein condensation (BEC). The solitons are considered in one, two, and three dimensions (1D, 2D, and 3D). Basic properties of the solitons presented in the review are their existence, stability, and mobility. Although the field is still far from completion, general conclusions c...
Hamiltonian monodromy as lattice defect
Zhilinskii, B.
2003-01-01
The analogy between monodromy in dynamical (Hamiltonian) systems and defects in crystal lattices is used in order to formulate some general conjectures about possible types of qualitative features of quantum systems which can be interpreted as a manifestation of classical monodromy in quantum finite particle (molecular) problems.
Yamamoto, Shigeki; Miyada, Mai; Sato, Harumi; Hoshina, Hiromichi; Ozaki, Yukihiro
2017-02-09
Low-frequency vibrational modes of lamellar crystalline poly(glycolic acid) (PGA) were measured on Raman and far-infrared (FIR) spectra. Among the observed bands, an FIR band at ∼70 cm(-1) and a Raman band at 125 cm(-1) showed a gradual lower-frequency shift with increasing temperature from 20 °C to the melting point at ∼230 °C. Their polarization direction was perpendicular to the chain axis of PGA. Both spectra were quantum-mechanically simulated with the aid of a fragment method, the Cartesian-coordinate tensor transfer, which enabled an explicit consideration of molecular interactions between two adjacent polymer chains. Good agreement was achieved between the experiment and theory in both spectra. The temperature-sensitive bands at ∼70 cm(-1) in FIR and at 125 cm(-1) in Raman comprise the out-of-plane C═O bending motion. The temperature-dependent shifts of the low-frequency bands were successfully simulated by the DFT-spectral calculation, exploring that the main origin of the shifts is the thermal expansion of the crystal lattice. This result indicates that the thermally shifted bands may be used as an indicator of the lattice expansion of PGA. Possible changes in intermolecular interactions of PGA under temperature rising were ascribed on the basis of natural bond orbital theory. The steric repulsion between the carbonyl O atom in one chain and the H-C bond in the adjacent chain will be a dominant interaction in the lattice-expanding process, which would cause the observed thermal shifts of the bending modes. Comparisons of the spectral assignment for PGA obtained in this study and that for poly-(R)-3-hydroxybutyrate (PHB) reported by us suggest that crystalline polyesters give vibrational modes composed of out-of-plane bending motion of C═O groups between ∼70 and ∼125 cm(-1), the modes of which are sensitive to the thermal expansion of crystal lattice and its concomitant changes in their intermolecular interactions.
EFFECT OF PAN-MILLING STRESS ON CRYSTAL STRUCTURES OF HIGH DENSITY POLYETHYLENE
Hua Huang
2000-01-01
A detailed study was performed on the crystal structures of pan-milled high-density polyethylene (HDPE) using differential scanning calorimetry (DSC) and X-ray diffraction. The crystallinity of HDPE first decreased slightly, followed by a gradual increase with increasing milling times. Monoclinic crystals appeared after 4 cycles of milling. With increasing times of milling, the proportion of monoclinic crystals increased significantly while the proportion of orthorhombic crystals decreased gradually. With increasing times of milling, the crystallite size of orthorhombic form decreased greatly, while the size of monoclinic crystallites kept almost constant during milling.
Liu, Hai; Zhu, Chenghao; Wang, Yan; Tan, Ce; Li, Hongwei; Cheng, Deqiang
2017-05-01
A transverse-stress sensor with polarization filtering function based on a specially designed photonic crystal fiber (PCF) is proposed. Four ultralarge side-holes are introduced into the cladding layer, and two of them are gold-coated to enhance the stress sensitivity. The finite element method is applied to study the polarization-dependent wavelength-selective sensing characteristics at the optical communication wavelength. Results reveal that the sensor can achieve a high sensitivity in either direction that can be divided into an x-direction component and a y-direction component. Combining the advantages of side-hole structure and surface plasmon resonance technology, the proposed sensor is believed to be an excellent candidate for the transverse-stress measurement.
On the lattice rotations accompanying slip
Wronski, M.; Wierzbanowski, K.; Leffers, Torben
2013-01-01
of the crystal lattices, and this texture may have a strong effect on the properties of the materials. The texture is introduced by lattice rotations in the individual grains during processing. The present critical assessment deals with the lattice rotations during rolling of face centred cubic (fcc) metals...... and alloys. Sixteen years ago, a modification of the traditional procedure for the calculation of these lattice rotations was suggested, a modification that would permit a realistic modelling of the development of the brass type texture, one of the two types of texture developed during rolling of fcc...
Transmission Electron Microscope Measures Lattice Parameters
Pike, William T.
1996-01-01
Convergent-beam microdiffraction (CBM) in thermionic-emission transmission electron microscope (TEM) is technique for measuring lattice parameters of nanometer-sized specimens of crystalline materials. Lattice parameters determined by use of CBM accurate to within few parts in thousand. Technique developed especially for use in quantifying lattice parameters, and thus strains, in epitaxial mismatched-crystal-lattice multilayer structures in multiple-quantum-well and other advanced semiconductor electronic devices. Ability to determine strains in indivdual layers contributes to understanding of novel electronic behaviors of devices.
Martínez de Mendívil, Jon; Pérez Delgado, Alberto; Lifante, Ginés; Jaque, Daniel [Departamento de Física de Materiales, Facultad de Ciencias, Universidad Autónoma de Madrid, Madrid 28049 (Spain); Ródenas, Airán [Departament de Química Física i Inorgànica, Universitat Rovira i Virgili, Tarragona 43007 (Spain); Institute of Photonics and Quantum Sciences, Heriot-Watt University, Edinburgh EH14 4AS (United Kingdom); Benayas, Antonio, E-mail: antonio.benayas@emt.inrs.ca [Departamento de Física de Materiales, Facultad de Ciencias, Universidad Autónoma de Madrid, Madrid 28049 (Spain); Institut National de la Recherche Scientifique, Centre – Énergie Matériaux et Télécommunications, 1650, Boul. Lionel Boulet Varennes, Quebec J3X 1S2 (Canada); Aguiló, Magdalena; Diaz, Francesc [Departament de Química Física i Inorgànica, Universitat Rovira i Virgili, Tarragona 43007 (Spain); Kar, Ajoy K. [Institute of Photonics and Quantum Sciences, Heriot-Watt University, Edinburgh EH14 4AS (United Kingdom)
2015-01-14
The laser performance and crystalline micro-structural properties of near-infrared step-index channel waveguides fabricated inside Neodymium doped YAG laser ceramics by means of three-dimensional sub-picosecond pulse laser direct writing are reported. Fluorescence micro-mapping of the waveguide cross-sections reveals that an essential crystal lattice re-distribution has been induced after short pulse irradiation. Such lattice re-distribution is evidenced at the waveguide core corresponding to the laser written refractive index increased volume. The waveguides core surroundings also present diverse changes including slight lattice disorder and bi-axial strain fields. The step-index waveguide laser performance is compared with previous laser fabricated waveguides with a stress-optic guiding mechanism in absence of laser induced lattice re-distribution.
Martínez de Mendívil, Jon; Ródenas, Airán; Benayas, Antonio; Aguiló, Magdalena; Diaz, Francesc; Pérez Delgado, Alberto; Lifante, Ginés; Jaque, Daniel; Kar, Ajoy K.
2015-01-01
The laser performance and crystalline micro-structural properties of near-infrared step-index channel waveguides fabricated inside Neodymium doped YAG laser ceramics by means of three-dimensional sub-picosecond pulse laser direct writing are reported. Fluorescence micro-mapping of the waveguide cross-sections reveals that an essential crystal lattice re-distribution has been induced after short pulse irradiation. Such lattice re-distribution is evidenced at the waveguide core corresponding to the laser written refractive index increased volume. The waveguides core surroundings also present diverse changes including slight lattice disorder and bi-axial strain fields. The step-index waveguide laser performance is compared with previous laser fabricated waveguides with a stress-optic guiding mechanism in absence of laser induced lattice re-distribution.
Ivanchin, Alexander
2010-01-01
It has been shown that to calculate the parameters of the electrostatic field of the ion crystal lattice it sufficient to take into account ions located at a distance of 1-2 lattice spacings. More distant ions make insignificant contribution. As a result, the electrostatic energy of the ion lattice in the alkaline halide crystal produced by both positive and negative ions is in good agreement with experiment when the melting temperature and the shear modulus are calculated. For fcc and bcc metals the ion lattice electrostatic energy is not sufficient to obtain the observed values of these parameters. It is possible to resolve the contradiction if one assumes that the electron density is strongly localized and has a crystal structure described by the lattice delta - function. As a result, positive charges alternate with negative ones as in the alkaline halide crystal. Such delta-like localization of the electron density is known as a model of nearly free electrons.
High Precision Calculations of the Lennard-Jones Lattice Constants for Five Lattices
Stein, Matthew
2017-01-01
The total potential energy of a crystal as described by the Lennard-Jones (L-J) potential depends in part upon the calculation of lattice constants. Knowing these constants to high precision is useful for prediction of the lattice type and simulation of crystals such as rare-gas solids or germanium detectors, but reaching higher precision is computationally costly and challenging. Presented here is the extension of the precision of the lattice constants, Lp, up to 32 decimal digits, and in some cases corrections from previous publication. The Lp terms are given for 4 cubic, face-centered cubic, body-centered cubic, hexagonal-close-pack, and diamond lattices. This precision was obtained through the use of careful parallelization technique, exploitation of the symmetries of each lattice, and the ``onionization'' of the simulated crystal. The results of this computation, along with the tools and algorithm strategies to make this computation possible, are explained in detail graphically.
Reda, Daniel C.; Muratore, Joseph J., Jr.; Heineck, James T.
1993-01-01
Time and flow-direction responses of shearstress-sensitive liquid crystal coatings were explored experimentally. For the time-response experiments, coatings were exposed to transient, compressible flows created during the startup and off-design operation of an injector-driven supersonic wind tunnel. Flow transients were visualized with a focusing Schlieren system and recorded with a 1000 frame/sec color video camera. Liquid crystal responses to these changing-shear environments were then recorded with the same video system, documenting color-play response times equal to, or faster than, the time interval between sequential frames (i.e., 1 millisecond). For the flow-direction experiments, a planar test surface was exposed to equal-magnitude and known-direction surface shear stresses generated by both normal and tangential subsonic jet-impingement flows. Under shear, the sense of the angular displacement of the liquid crystal dispersed (reflected) spectrum was found to be a function of the instantaneous direction of the applied shear. This technique thus renders dynamic flow reversals or flow divergences visible over entire test surfaces at image recording rates up to 1 KHz. Extensions of the technique to visualize relatively small changes in surface shear stress direction appear feasible.
Reda, Daniel C.; Muratore, Joseph J., Jr.; Heineck, James T.
1993-01-01
Time and flow-direction responses of shearstress-sensitive liquid crystal coatings were explored experimentally. For the time-response experiments, coatings were exposed to transient, compressible flows created during the startup and off-design operation of an injector-driven supersonic wind tunnel. Flow transients were visualized with a focusing Schlieren system and recorded with a 1000 frame/sec color video camera. Liquid crystal responses to these changing-shear environments were then recorded with the same video system, documenting color-play response times equal to, or faster than, the time interval between sequential frames (i.e., 1 millisecond). For the flow-direction experiments, a planar test surface was exposed to equal-magnitude and known-direction surface shear stresses generated by both normal and tangential subsonic jet-impingement flows. Under shear, the sense of the angular displacement of the liquid crystal dispersed (reflected) spectrum was found to be a function of the instantaneous direction of the applied shear. This technique thus renders dynamic flow reversals or flow divergences visible over entire test surfaces at image recording rates up to 1 KHz. Extensions of the technique to visualize relatively small changes in surface shear stress direction appear feasible.
Yoshida, Hiroyuki; Noguchi, Naoya; Matsushita, Yoshitaka; Ishii, Yuto; Ihara, Yoshihiko; Oda, Migaku; Okabe, Hirotaka; Yamashita, Satoshi; Nakazawa, Yasuhiro; Takata, Atsushi; Kida, Takanori; Narumi, Yasuo; Hagiwara, Masayuki
2017-03-01
We have succeeded in preparing single crystals of CaCu3(OH)6Cl2 • 0.6H2O, a candidate for the S = 1/2 Kagome lattice antiferromagnet. Magnetic properties of the compound are dominated by the nearest neighbor antiferromagnetic interaction J1, and the next nearest neighbor ferromagnetic J2 and an antiferromagnetic Jd across a hexagon, which is different from related compounds Kapellasite and Haydeeite with ferromagnetic J1. Magnetic susceptibility exhibits a sudden increase below 13 K and a cusp anomaly at T* = 7.2 K in the ab-plane, whereas only a moderate enhancement is observed below T* along the c-axis. A tiny peak detected in heat capacity at T* indicates the occurrence of a magnetic phase transition. The low temperature magnetic heat capacity was reproduced by assuming a two-dimensional spin-wave component and a temperature-linear term. The spin-wave contribution suggests a magnon excitation in a short-range ordered region, whereas the relatively large T-linear term 5.9 mJ/(Cu-mol·K2) at H = 0 T of this insulating compound suggests the existence of an unusual quasi-particle excitation below T*. They apparently reveal the unconventionality of the ground state of this S = 1/2 Kagome lattice antiferromagnet.
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.
Zhang, Shunzu; Shi, Yang [Key Laboratory of Mechanics on Disaster and Environment in Western China attached to the Ministry of Education of China, Lanzhou University, Lanzhou, Gansu 730000 (China); Department of Mechanics and Engineering Sciences, College of Civil Engineering and Mechanics, Lanzhou University, Lanzhou, Gansu 730000 (China); Gao, Yuanwen, E-mail: ywgao@lzu.edu.cn [Key Laboratory of Mechanics on Disaster and Environment in Western China attached to the Ministry of Education of China, Lanzhou University, Lanzhou, Gansu 730000 (China); Department of Mechanics and Engineering Sciences, College of Civil Engineering and Mechanics, Lanzhou University, Lanzhou, Gansu 730000 (China)
2017-03-26
Considering the magneto-mechanical coupling of magnetostrictive material, the tunability of in-plane wave propagation in two-dimensional Terfenol-D/epoxy phononic crystal (PC) plate is investigated theoretically by the plane wave expansion method. Two Schemes, i.e. magnetic field is rotated in x–y plane and x–z plane, are studied, respectively. The effects of amplitude and direction of magnetic field, pre-stress and geometric parameters are discussed. For Scheme-I, band gap reaches the maximum at an optimal angle 45° of magnetic field. However, the optimal angle is 0° for Scheme-II, because band gap decreases monotonically until disappears with the increasing angle. For both cases, higher-order band gaps generate and become stronger as magnetic field amplitude increases, while increasing compressive pre-stress has the opposite effect. Meanwhile, filling fraction plays a key role in controlling band gaps. These results provide possibility for intelligent regulation and optimal design of PC plates. - Highlights: • The in-plane wave propagation in phononic crystal thin plate is tuned theoretically. • Magnetostrictive material is introduced in the study. • The effects of magnetic field and pre-stress are considered. • The variations of band gaps with external stimuli are discussed.
Heuwers, Benjamin; Quitmann, Dominik; Katzenberg, Frank; Tiller, Joerg C
2012-09-26
Lightly cross-linked natural rubber (NR, cis-1,4-polyisoprene) was found to be an exceptional cold programmable shape memory polymer (SMP) with strain storage of up to 1000%. These networks are stabilized by strain-induced crystals. Here, we explore the influence of mechanical stress applied perpendicular to the elongation direction of the network on the stability of these crystals. We found that the material recovers its original shape at a critical transverse stress. It could be shown that this is due to a disruption of the strain-stabilizing crystals, which represents a completely new trigger for SMPs. The variation of transverse stress allows tuning of the trigger temperature T(trig) (σ) in a range of 45 to 0 °C, which is the first example of manipulating the transition of a crystal-stabilized SMP after programming.
Chotiyarnwong, Pojchong; Stewart-Jones, Guillaume B; Tarry, Michael J; Dejnirattisai, Wanwisa; Siebold, Christian; Koch, Michael; Stuart, David I; Harlos, Karl; Malasit, Prida; Screaton, Gavin; Mongkolsapaya, Juthathip; Jones, E Yvonne
2007-05-01
T-cell recognition of the antigenic peptides presented by MHC class I molecules normally triggers protective immune responses, but can result in immune enhancement of disease. Cross-reactive T-cell responses may underlie immunopathology in dengue haemorrhagic fever. To analyze these effects at the molecular level, the functional MHC class I molecule HLA-A*1101 was crystallized bound to six naturally occurring peptide variants from the dengue virus NS3 protein. The crystals contained high levels of solvent and required optimization of the cryoprotectant and dehydration protocols for each complex to yield well ordered diffraction, a process that was facilitated by the use of a free-mounting system.
Cartalade, Alain; Plapp, Mathis
2016-01-01
A lattice-Boltzmann (LB) scheme, based on the Bhatnagar-Gross-Krook (BGK) collision rules is developed for a phase-field model of alloy solidification in order to simulate the growth of dendrites. The solidification of a binary alloy is considered, taking into account diffusive transport of heat and solute, as well as the anisotropy of the solid-liquid interfacial free energy. The anisotropic terms in the phase-field evolution equation, the phenomenological anti-trapping current (introduced in the solute evolution equation to avoid spurious solute trapping), and the variation of the solute diffusion coefficient between phases, make it necessary to modify the equilibrium distribution functions of the LB scheme with respect to the one used in the standard method for the solution of advection-diffusion equations. The effects of grid anisotropy are removed by using the lattices D3Q15 and D3Q19 instead of D3Q7. The method is validated by direct comparison of the simulation results with a numerical code that uses t...
Sueoka, K.; Nakamura, K.; Vanhellemont, J.
2017-09-01
For the development of crystal pulling processes for 450 mm-diameter defect-free Si crystals, it is important to evaluate the impact of thermal stress on intrinsic point defect behavior during crystal growth. In a crystal growing from a melt, the melt/solid interface can be considered as being stress-free. Due to that the thermal stress in the growing substrate near the interface is internal plane stress. Previously, we evaluated the impact of (001) planar-isotropic stress on the formation enthalpy (Hf) of the vacancy (V) and the self-interstitial (I) using density functional theory (DFT) calculations, and explained quantitatively the published experimental values of the so-called ;Voronkov criterion;. The thermal stress in a growing crystal is indeed planar but is not isotropic in the plane except for the central region of the crystal. The purpose of the present study is to estimate the impact of planar-anisotropic stress on the formation enthalpy Hf of V and I. It is found that the three stress dependencies of σx: σy=1: 1 (planar-isotropic), 2: 1, 5: 1 (planar-anisotropic) are close to each other, independent of the assumption of isotropic or anisotropic planar stress. This is the reason why the experimental results obtained over the whole radial direction of the crystal are well reproduced by the calculated results assuming planar-isotropic stress. A uniaxial stress dependence which is a good assumption for the crystal peripheral region, leads also to results that are close to those for the planar stress dependence. Also the mechanisms behind the experimentally observed impact of interstitial oxygen (Oi), introduced during Czochralski Si growth, on V and I concentrations are clarified. DFT calculations are performed to obtain the formation energies (Ef) of V and I at all sites within a sphere with 5 Å radius around the Oi atom. Formation (vibration) entropy (Sf) calculations for V and I are also performed. It is found that both EfV and SfV of V in the zigzag
Su, Ruifeng; Liu, Haitao; Liang, Yingchun; Yu, Fuli
2017-01-01
Thermal problems are huge challenges for solid state lasers that are interested in high output power, cooling of the nonlinear optics is insufficient to completely solve the problem of thermally induced stress, as residual thermal stress remains after cooling, which is first proposed, to the best of our knowledge. In this paper a comprehensive model incorporating principles of thermodynamics, mechanics and optics is proposed, and it is used to study the residual thermal stress of a mounted KDP crystal after cooling process from mechanical perspective, along with the effects of the residual thermal stress on the second harmonic generation (SHG) efficiency of a high-average-power laser. Effects of the structural parameters of the mounting configuration of the KDP crystal on the residual thermal stress are characterized, as well as the SHG efficiency. The numerical results demonstrate the feasibility of solving the problems of residual thermal stress from the perspective on structural design of mounting configuration.
Study on transmission properties of 2-D super-lattice photonic crystals%2维超晶格结构光子晶体传输特性研究
闫明宝; 傅振堂; 王伟宇
2012-01-01
The finite difference time domain method was used to calculate the transmission characteristics of 2-D super-lattice photonic crystal formed by cylinders and elliptic rods or cylinders and composite medium rods. It is shown that the width of the band gap becomes lager and the central frequency becomes higher with increase of the sectional area of elliptical rods for the cylinder-elliptical rods super-lattice. As to the case of composite medium rods super-lattice, the thicker the nested elliptical rod, the narrower the band gap is and the lower the central frequency is when the long axis is along the direction of incident wave. However, the wider band gap appeared in the range of high frequency band and in the low frequency band the band gap vanished when the long axis direction is perpendicular to the incident wave. The study provides the theory of the manufacture of photonic crystals.%为了研究超晶格结构对光子晶体禁带的影响,应用时域有限差分法对圆/椭圆、圆/复合柱超晶格结构光子晶体的传输特性进行了计算,得到了相应的透射谱.结果表明,对圆/椭圆超晶格,禁带宽度随椭圆柱截面积的增大而变宽,中心频率变大;对于圆/复合柱超晶格结构,椭圆柱内接于圆孔时,禁带宽度随截面积的增大而变窄,中心频率变小;当长轴垂直入射波方向时,高频段出现较宽禁带,低频禁带完全消失;而椭圆孔中内嵌圆柱时,禁带宽度变化与前者相反.该研究为光子晶体器件的制作提供了理论依据.
Huang, X.; Borrego, A.; Pantleon, W.
2001-01-01
of microstructures have been identified. A correlation is found between microstructure and grain orientation, which agrees well with earlier observations in tensile deformed aluminum polycrystals and copper single crystals. The stress–strain curve of the copper polycrystal is calculated with good accuracy from...... single crystal data, which are weighted according to the volume fractions of the three different types based on a quantitative texture measurement of the polycrystal....
Compression Stress Effect on Dislocations Movement and Crack propagation in Cubic Crystal
Suprijadi; Ely, Aprilia; Meiqorry, Yusfi
2011-01-01
Fracture material is seriously problem in daily life, and it has connection with mechanical properties itself. The mechanical properties is belief depend on dislocation movement and crack propagation in the crystal. Information about this is very important to characterize the material. In FCC crystal structure the competition between crack propagation and dislocation wake is very interesting, in a ductile material like copper (Cu) dislocation can be seen in room temperature, but in a brittle ...
Yunfei Liang
2016-02-01
Full Text Available The additional 1.5 wt% Mo was added in a Ni-base single crystal (SC alloy with the composition of Ni–6.5Al–8.0Mo–2.4Cr–6.2Ta–4.9Co–1.5Re–(0.01–0.05Y (wt% to study the effect of Mo content on the microstructure and stress-rupture properties. The creep and stress-rupture tests under the conditions of 850 °C/500 MPa and 1100 °C/130 MPa were conducted, and the microstructure of as-cast, heat treated and stress ruptured specimens were analyzed. It was found that the 1.5 wt% Mo addition enhanced the stress-rupture lives at both intermediate (850 °C and high (1100 °C temperatures. The microstructure analysis showed that adding 1.5 wt% Mo in the basic alloy affected the microstructure dramatically, i.e., the Mo-rich phases formed in the specimens of as-cast and stress-ruptured specimens. It is considered that the improvement of the stress-rupture lives is duo to the strengthening effect of Mo to both γ and γ′ phases and the decrease of stacking fault energy, diffusion constant and dislocation spacing. The Mo-rich phases precipitated under condition of 1100 °C/130 MPa did not affect the creep and stress-rupture properties obviously in the present study.
LI Jinquan; SU Xiaoping; NA Mujilatu; YANG Hai; LI Jianmin; YU Yunqi; MI Jianjun
2006-01-01
The professional modeling software package CrysVUn was employed to study the process of a large sapphire single crystal growth using Kyropoulos method.The influence of gas pressure on thermal field, solid-liquid interface shape, gas velocity field and von Mises stress were studied for the first time.It is found that the root of the seed melt when gas pressure equals to one atmosphere or more than one atmosphere, especially during the seeding period, this result is consistent with the experimental observation, and this paper presents three ways to solve this problem.The temperature gradient and stress decreases significantly as the gas pressure increases.The convexity of the solid-liquid interface slightly increases when the gas pressure increases.Numerical analysis was used to optimize the hot zone design.
Stress-induced deformation at Ap～Mp and thermal cycling behavior of Cu-Al-Ni single crystals
陈庆福; 蔡伟; 赵连城
2001-01-01
Stress-induced deformation in Ap～Mp and concomitant shape recovery behavior of Cu-13.4Al-4.0Ni single crystals were studied. Abnormal high stress-induced deformation exists in Ap～Mp under the conditions of either heating with load or cooling with load. The recovered deformation is successively composed of four parts, the recoveries from superelasticity, normal reverse transformation, thermally activated reverse transformation of partially stabilized martensite and reverse transformation of stabilized martensite by over-heating. With increasing cycling number, the recovery part from normal reverse transformation decreases, while that from reverse transformation of stabilized martensite by over-heating increases, which shows a typical stabilization of martensite.
Zhang, Limin; Jiang, Weilin; Dissanayake, Amila; Peng, Jinxin; Ai, Wensi; Zhang, Jiandong; Zhu, Zihua; Wang, Tieshan; Shutthanandan, Vaithiyalingam
2016-06-01
Lattice disorder and compositional changes in InxGa1-xN (x = 0.32, 0.47, 0.7, 0.8, and 1.0) films on GaN/Al2O3 substrates, induced by room-temperature irradiation of 5 MeV Xe ions, have been investigated using both Rutherford backscattering spectrometry under ion-channeling conditions and time-of-flight secondary ion mass spectrometry. The results show that for a fluence of 3 × 1013 cm-2, the relative level of lattice disorder in InxGa1-xN increases monotonically from 59% to 90% with increasing indium concentration x from 0.32 to 0.7; a further increase in x up to 1.0 leads to little increase in the disorder level. In contrast to Ga-rich InxGa1-xN (x = 0.32 and 0.47), significant volume swelling of up to ˜25% accompanied with oxidation in In-rich InxGa1-xN (x = 0.7, 0.8, and 1.0) is observed. In addition, irradiation-induced atomic mixing occurs at the interface of In-rich InxGa1-xN and GaN. The results from this study indicate an extreme susceptibility of the high In-content InxGa1-xN to heavy-ion irradiation, and suggest that cautions must be exercised in applying ion-implantation techniques to these materials at room temperature. Further studies of the irradiation behavior at elevated temperatures are warranted.
Zhang, Limin; Jiang, Weilin; Dissanayake, Amila C.; Peng, Jinxin; Ai, Wensi; Zhang, Jiandong; Zhu, Zihua; Wang, Tieshan; Shutthanandan, V.
2016-06-27
Lattice disorder and compositional changes in InxGa1-xN (x=0.32, 0.47, 0.7, 0.8 and 1.0) films on GaN/Al2O3 substrates, induced by room-temperature irradiation of 5 MeV Xe ions, have been investigated using both Rutherford backscattering spectrometry under ion-channeling conditions and time-of-flight secondary ion mass spectrometry. The results show that for a fluence of 3E13 cm-2, the relative level of lattice disorder in InxGa1-xN increases monotonically from 59% to 90% with increasing indium concentration x from 0.32 to 0.7; a further increase in x up to 1.0 leads to little increase in the disorder level. In contrast to Ga-rich InxGa1-xN (x=0.32 and 0.47), significant volume swelling of up to ~25% accompanied with oxidation in In-rich InxGa1-xN (x=0.7, 0.8 and 1.0) is observed. In addition, irradiation-induced atomic mixing occurs at the interface of In-rich InxGa1-xN and GaN. The results from this study indicate an extreme susceptibility of the high In-content InxGa1-xN to heavy-ion irradiation, and suggest that cautions must be exercised in applying ion-implantation techniques to these materials at room temperature. Further studies of the irradiation behavior at elevated temperatures are warranted.
Bingtao Tian
2016-04-01
Full Text Available Lithium triborate (LiB3O5, LBO crystal is now one of the most useful nonlinear optical materials for frequency conversion of high power lasers. The use of the crystal, however, has been hampered by the unavailability of antireflective (AR coatings with high laser damage resistance. In this work, a “point contact” dip-coating method is developed to prepare sol–gel SiO2 AR coatings on small-size LBO crystals. Using this approach, we obtain a homogenous coating surface on an 8 mm×8 mm×3 mm LBO crystal. The stress measurements show that the stresses in sol–gel SiO2 coatings vary with the time of natural drying, which is beyond our expectation. The anisotropic Young’s modulus of the LBO crystal and the different evolution tendency of the stress in the different SiO2 coating layers are found to be responsible for the crack of the double-layer AR coatings on anisotropic LBO crystal. Meanwhile, the resulting coatings on LBO crystal achieve a LIDT of over 15 J/cm2 (532 nm, 3ns and the coated LBO is expected to have a transmittance of over 99% at 800 nm.
Tian, Bingtao; Wang, Xiaodong, E-mail: xiaodong-wang@tongji.edu.cn; Niu, Yanyan; Zhang, Zhihua; Wu, Guangming; Zhou, Bin; Shen, Jun [Shanghai Key Laboratory of Special Artificial Microstructure Materials and Technology, Tongji University, Shanghai 200092 (China); School of Physics Science and Engineering, Tongji University, Shanghai, 200092 (China); Zhang, Jinlong [School of Physics Science and Engineering, Tongji University, Shanghai, 200092 (China); Key Laboratory of Advanced Micro-Structure Materials, Ministry of Education, Shanghai, 200092 (China); Institute of Precision Optical Engineering, Tongji University, Shanghai, 200092 (China); Zhang, Qinghua [Chengdu Fine Optical Engineering Research Center, Chengdu, 610041 (China)
2016-04-15
Lithium triborate (LiB{sub 3}O{sub 5}, LBO) crystal is now one of the most useful nonlinear optical materials for frequency conversion of high power lasers. The use of the crystal, however, has been hampered by the unavailability of antireflective (AR) coatings with high laser damage resistance. In this work, a “point contact” dip-coating method is developed to prepare sol–gel SiO{sub 2} AR coatings on small-size LBO crystals. Using this approach, we obtain a homogenous coating surface on an 8 mm×8 mm×3 mm LBO crystal. The stress measurements show that the stresses in sol–gel SiO{sub 2} coatings vary with the time of natural drying, which is beyond our expectation. The anisotropic Young’s modulus of the LBO crystal and the different evolution tendency of the stress in the different SiO{sub 2} coating layers are found to be responsible for the crack of the double-layer AR coatings on anisotropic LBO crystal. Meanwhile, the resulting coatings on LBO crystal achieve a LIDT of over 15 J/cm{sup 2} (532 nm, 3ns) and the coated LBO is expected to have a transmittance of over 99% at 800 nm.
Effects of external stress on defect complexes in semiconductors
Tessema, Genene [Department of Physics, Addis Ababa University, PO Box 1176, Addis Ababa (Ethiopia); Helmholtz-Institut fuer Strahlen und Kernphysik, Nussalle 14-16, 53115 Bonn (Germany)
2007-07-04
Crystal field gradients that exist at lattice sites in solids depend on the symmetry of charge distribution around atomic sites. The charge symmetry could be broken either by the presence of impurity complexes in the host matrix or by external stress on the samples, which leads to an observable magnitude of electric field gradients (EFGs). The perturbed {gamma}-{gamma} angular correlation (PAC) method is employed here to investigate the effect of uniaxial stress on {sup 111}Cd sites in crystalline doped semiconductors.
Dual Lattice of ℤ-module Lattice
Futa Yuichi
2017-07-01
Full Text Available In this article, we formalize in Mizar [5] the definition of dual lattice and their properties. We formally prove that a set of all dual vectors in a rational lattice has the construction of a lattice. We show that a dual basis can be calculated by elements of an inverse of the Gram Matrix. We also formalize a summation of inner products and their properties. Lattice of ℤ-module is necessary for lattice problems, LLL(Lenstra, Lenstra and Lovász base reduction algorithm and cryptographic systems with lattice [20], [10] and [19].
Chotiyarnwong, Pojchong [Department of Immunology, Division of Medicine, Hammersmith Hospital, Imperial College, London (United Kingdom); Medical Molecular Biology Unit, Faculty of Medicine, Siriraj Hospital, Mahidol University (Thailand); Stewart-Jones, Guillaume B.; Tarry, Michael J. [Division of Structural Biology and Oxford Protein Production Facility (OPPF), The Henry Wellcome Building for Genomic Medicine, Roosevelt Drive, Headington, Oxford OX3 7BN (United Kingdom); Dejnirattisai, Wanwisa [Department of Immunology, Division of Medicine, Hammersmith Hospital, Imperial College, London (United Kingdom); Medical Molecular Biology Unit, Faculty of Medicine, Siriraj Hospital, Mahidol University (Thailand); Siebold, Christian; Koch, Michael; Stuart, David I.; Harlos, Karl [Division of Structural Biology and Oxford Protein Production Facility (OPPF), The Henry Wellcome Building for Genomic Medicine, Roosevelt Drive, Headington, Oxford OX3 7BN (United Kingdom); Malasit, Prida [Medical Molecular Biology Unit, Faculty of Medicine, Siriraj Hospital, Mahidol University (Thailand); Medical Biotechnology Unit, National Center for Genetic Engineering and Biotechnology (BIOTEC), National Science and Technology Development Agency, Pathumthani, Bangkok (Thailand); Screaton, Gavin [Department of Immunology, Division of Medicine, Hammersmith Hospital, Imperial College, London (United Kingdom); Mongkolsapaya, Juthathip, E-mail: j.mongkolsapaya@imperial.ac.uk [Department of Immunology, Division of Medicine, Hammersmith Hospital, Imperial College, London (United Kingdom); Medical Molecular Biology Unit, Faculty of Medicine, Siriraj Hospital, Mahidol University (Thailand); Jones, E. Yvonne, E-mail: j.mongkolsapaya@imperial.ac.uk [Division of Structural Biology and Oxford Protein Production Facility (OPPF), The Henry Wellcome Building for Genomic Medicine, Roosevelt Drive, Headington, Oxford OX3 7BN (United Kingdom); Department of Immunology, Division of Medicine, Hammersmith Hospital, Imperial College, London (United Kingdom)
2007-05-01
Crystals of an MHC class I molecule bound to naturally occurring peptide variants from the dengue virus NS3 protein contained high levels of solvent and required optimization of cryoprotectant and dehydration protocols for each complex to yield well ordered diffraction, a process facilitated by the use of a free-mounting system. T-cell recognition of the antigenic peptides presented by MHC class I molecules normally triggers protective immune responses, but can result in immune enhancement of disease. Cross-reactive T-cell responses may underlie immunopathology in dengue haemorrhagic fever. To analyze these effects at the molecular level, the functional MHC class I molecule HLA-A*1101 was crystallized bound to six naturally occurring peptide variants from the dengue virus NS3 protein. The crystals contained high levels of solvent and required optimization of the cryoprotectant and dehydration protocols for each complex to yield well ordered diffraction, a process that was facilitated by the use of a free-mounting system.
Boggon, T. J.; Helliwell, J. R.; Judge, Russell A.; Siddons, D. P.; Snell, Edward H.; Stojanoff, V.
2000-01-01
A comprehensive study of microgravity and ground grown chicken egg white lysozyme crystals is presented using synchrotron X-ray reciprocal space mapping, topography techniques and diffraction resolution. Microgravity crystals displayed, on average, reduced intrinsic mosaicities but no differences in terms of stress over their earth grown counterparts. Topographic analysis revealed that in the microgravity case the majority of the crystal was contributing to the peak of the reflection at the appropriate Bragg angle. In the earth case at the diffraction peak only a small volume of the crystal contributed to the intensity. The techniques prove to be highly complementary with the reciprocal space mapping providing a quantitative measure of the crystal mosaicity and stress (or variation in lattice spacing) and topography providing a qualitative overall assessment of the crystal in terms of its X-ray diffraction properties. Structural data collection was also carried out both at the synchrotron and in the laboratory.
Okutani, Satoshi; Iwai, Takayoshi; Iwatani, Shintaro; Matsuno, Kiyoshi; Takahashi, Yasuhiro; Hase, Toshiharu
2015-09-01
During amino-acid crystal fermentation, mechanical stress on bacterial cells caused by crystal collision often impacts negatively on bacterial growth and amino-acid production. When Escherichia coli cells were cultivated under mechanical stress of polyvinyl chloride particles as a model of the crystal fermentation, activities of iron-sulfur (Fe-S) cluster-containing enzymes were apparently decreased. Based on an assumption that function of Fe-S cluster assembly machinery would be elevated to recover the enzyme activities in such stressed cells, we analyzed levels of various components of Fe-S cluster assembly machinery by western blotting. It was found that the expression of HscA, a chaperon component of the machinery, was up-regulated and that shorter forms of HscA with the N-terminal region truncated were accumulated, suggesting an important role of HscA against the mechanical stress. An overexpression of HscA gene in E. coli cells gave a positive effect on rescue of the stress-induced decrease of the activity of Fe-S cluster-containing enzyme. These results may provide a new strategy to alleviate the mechanical stress during the amino-acid crystal fermentation.
Hamiltonian tomography of photonic lattices
Ma, Ruichao; Owens, Clai; LaChapelle, Aman; Schuster, David I.; Simon, Jonathan
2017-06-01
In this paper we introduce an approach to Hamiltonian tomography of noninteracting tight-binding photonic lattices. To begin with, we prove that the matrix element of the low-energy effective Hamiltonian between sites α and β may be obtained directly from Sα β(ω ) , the (suitably normalized) two-port measurement between sites α and β at frequency ω . This general result enables complete characterization of both on-site energies and tunneling matrix elements in arbitrary lattice networks by spectroscopy, and suggests that coupling between lattice sites is a topological property of the two-port spectrum. We further provide extensions of this technique for measurement of band projectors in finite, disordered systems with good band flatness ratios, and apply the tool to direct real-space measurement of the Chern number. Our approach demonstrates the extraordinary potential of microwave quantum circuits for exploration of exotic synthetic materials, providing a clear path to characterization and control of single-particle properties of Jaynes-Cummings-Hubbard lattices. More broadly, we provide a robust, unified method of spectroscopic characterization of linear networks from photonic crystals to microwave lattices and everything in between.
Senyshyn, A.; Oganov, A. R.; Vasylechko, L.; Ehrenberg, H.; Bismayer, U.; Berkowski, M.; Matkovskii, A.
2004-01-01
The structure of Nd0.75Sm0.25GaO3 was studied by high-resolution powder diffraction methods using conventional x-ray and synchrotron radiation in the temperature range 85-1173 K. The GdFeO3 structure type was confirmed for Nd0.75Sm0.25GaO3 in the temperature region investigated and no structural transitions were observed. The cell parameters show a monotonic and anisotropic increase with temperature. The interatomic potential was fitted using the GULP code. Using this potential, a self-consistent approximation following the Debye model was constructed from the elastic constants of the crystals. The total phonon DOS, its projections onto atomic species, heat capacity Cv, Grüneisen parameter ggr and thermal expansion coefficient agr were considered in the framework of quasiharmonic lattice dynamics and the Debye model. The shape of the phonon DOS calculated from lattice dynamics differs significantly from the respected Debye DOS. The rare earth, gallium and oxygen atoms dominate in different frequency regions of the phonon spectrum. The heat capacity is well reproduced by the Debye model below 100 K, where acoustic phonons play an important role and above 800 K when the classical limit is reached. Predicted values of Grüneisen parameter and thermal expansion coefficients in the frame of the Debye model are {\\sim } 35% too low. Therefore, the thermal properties of Nd0.75Sm0.25GaO3 cannot be explained by acoustic phonons only and hence, Nd0.75Sm0.25GaO3 cannot be described perfectly as a Debye-like solid with respect to its thermodynamic properties.
Senyshyn, A [Lviv Polytechnic National University, Bandera Street 12, 79013 Lviv (Ukraine); Oganov, A R [Laboratory of Crystallography, Department of Materials, ETH Zurich, CH-8092 Zurich (Switzerland); Vasylechko, L [Lviv Polytechnic National University, Bandera Street 12, 79013 Lviv (Ukraine); Ehrenberg, H [Darmstadt University of Technology, Institute for Materials Science, Petersenstrasse 23, D-64287 Darmstadt (Germany); Bismayer, U [Mineralogisch-Petrographisches Institut, Universitat Hamburg, Grindelallee 48, D-20146 Hamburg (Germany); Berkowski, M [Institute of Physics Polish Academy of Sciences, Al. Lotnikow 32/46, 02-668 Warsaw (Poland); Matkovskii, A [Lviv Polytechnic National University, Bandera Street 12, 79013 Lviv (Ukraine)
2004-01-28
The structure of Nd{sub 0.75}Sm{sub 0.25}GaO{sub 3} was studied by high-resolution powder diffraction methods using conventional x-ray and synchrotron radiation in the temperature range 85 - 1173 K. The GdFeO{sub 3} structure type was confirmed for Nd{sub 0.75}Sm{sub 0.25}GaO{sub 3} in the temperature region investigated and no structural transitions were observed. The cell parameters show a monotonic and anisotropic increase with temperature. The interatomic potential was fitted using the GULP code. Using this potential, a self-consistent approximation following the Debye model was constructed from the elastic constants of the crystals. The total phonon DOS, its projections onto atomic species, heat capacity C{sub v}, Grueneisen parameter {gamma} and thermal expansion coefficient {alpha} were considered in the framework of quasiharmonic lattice dynamics and the Debye model. The shape of the phonon DOS calculated from lattice dynamics differs significantly from the respected Debye DOS. The rare earth, gallium and oxygen atoms dominate in different frequency regions of the phonon spectrum. The heat capacity is well reproduced by the Debye model below 100 K, where acoustic phonons play an important role and above 800 K when the classical limit is reached. Predicted values of Grueneisen parameter and thermal expansion coefficients in the frame of the Debye model are {approx} 35% too low. Therefore, the thermal properties of Nd{sub 0.75}Sm{sub 0.25}GaO{sub 3} cannot be explained by acoustic phonons only and hence, Nd{sub 0.75}Sm{sub 0.25}GaO{sub 3} cannot be described perfectly as a Debye-like solid with respect to its thermodynamic properties.
Rahnamaye Aliabad, H.A. [Department of Physics, Hakim Sabzevari University, Sabzevar (Iran, Islamic Republic of); Vaezi, Hamide [Department of Physics, Khayyam Institute of Higher Education, Mashhad (Iran, Islamic Republic of); Basirat, Shiva [Department of Physics, Payame Noor University of Mashhad, Mashhad (Iran, Islamic Republic of); Ahmad, Iftikhar [Center for Computational Materials Science, University of Malakand, Chakdara (Pakistan); Abbottabad University of Science and Technology, Havelian (Pakistan)
2017-07-17
The electronical and optical properties of CdGa{sub 2}S{sub 4} under high pressures were studied using the full potential linearized augmented plane wave (FP-LAPW) method within the GGA and mBJ exchange correlation potentials from 0.0 to 16.92 GPa. The obtained results show that the lattice constants, bandgap values, and optoelectronic properties are sensitive to applied external pressures. The mBJ results indicate that the bandgap increases and the static dielectric constants decrease with increasing the pressure. The two none zero dielectric tensor components show considerable anisotropy between the perpendicular and parallel components. The maximum absorption for x direction in all pressures takes place in vacuum UV region. Also, the plasma frequency shifts to the higher energies with increasing the pressure for application in optical devices. The calculated results by mBJ are in close agreement with the experimental values. (copyright 2017 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)
Wright, A.F.
1999-02-01
Charge-state calculations based on density-functional theory are used to study the formation energy of hydrogen in wurtzite and zinc-blende GaN as a function of Fermi level Comparison of these results reveals notable differences including a 0.56 eV lower formation energy for H2 in wurtzite, and different configurations for H2 and H- in the two crystal structures. Furthermore, H+ is found to be equally stable at bond-centered and anti-bonding sites in wurtzite, whereas it is unstable at a bond-centered site in zinc blende. These differences are due to distinct features of the two crystal structures including: the lower symmetry of wurtzite which provides a wider selection of bonding sites for H+, and the existence of extended three-fold symmetric channels oriented along the c-axis in wurtzite which provide more favorable bonding configurations for H2 and H-.N-H+ stretch-mode vibration frequencies, clustering of ?3+ in p-type material, and diffusion barriers for H" are also investigated in wurtzite GaN. A diffusion barrier of 1.6 eV is found for H- in wurtzite GaN, significantly lower than a previous estimate, and a tendency for H+ clustering in p-type material is found.
无
2001-01-01
Various training methods for two way memory effect (TWME) and stressed two way memory effect (STWME) were tried on Cu-13.4Al-4.0Ni (mass fraction, %) single crystals by applying tensile stress along 〈001〉 direction of β phase. The training method of cooling with load can induce a lot of martensite prone to stabilize, thus cause large residual deformation, wide hysteresis and small TWME. Training with constant load can produce STWME larger than 8% with the least residual deformation. By training procedure of martensite reorientation below Mf followed by thermal cycling, the TWME is relatively large with very small residual deformation and with comparatively narrow hysteresis of two-way memory. The obtained two-way memory curve after such training is not a closed loop, and the obtained TWME is not stable. However, these can be improved by thermal cycling. Training with martensite reorientation below Mf and thermal cycling under relatively low constant stress throughout the whole training procedure is the optimum way of obtaining TWME, and more than 1.7% TWME can be obtained. The thermomechanical history of the sample has a pronounced effect on the training result. Thermomechanical cycling has a softening effect on martensite.
各向异性金刚石结构的光子晶体%Anisotropic Photonic Crystals with Diamond Lattice
詹仪; 郑义; 李效增; 李秀霞
2009-01-01
基于平面波展开法,理论分析了填充率、介质各向异性的程度对单轴金刚石结构三维光子晶体禁带的影响.结果表明,当填充率和介质各向异性取合适的值,单轴各向异性金刚石结构光子晶体存在着完全带隙.介质各向异性的引入使该晶体的带隙变窄甚至完全关闭.在各个布里渊区域里,带隙率和带隙宽度随介质各向异性程度的变化而变化.各向异性的引入为调整光子禁带提供了一种方法.%With the plane-wave expansion method, the photonic-band-gap structure for a diamond lattice consisting of a uniaxial anisotropic-dielectric sphere in air was studied through tuning three inequivalent 1/3 Brillouin zone. The results show that choosing the suitable range of filling fraction and anisotropy, a full band gap opens in the whole Brillouin zone for this anisotropic PBG structure. The gap to midgap ratio and bandgap width is tunable as a result of the changing extraordinary axis orientation of the uniaxial sphere. Anisotropy in sphere dielectric function is found to narrow or even close band gaps. The band gap width and close rate are affected by the extraordinary axis directions and anisotropy. The results in turn suggest a potential approach to obtain some degree of tunability of the photonic band structures.
胡晓颖; 郭晓霞; 胡文弢; 呼和满都拉; 郑晓霞; 荆丽丽
2015-01-01
=0.6 we calculated the first normalized gap width ∆Ω/Ωg. when f =0.6 andθ=0◦, the first gap width∆Ω=0.812(µ0ω/g) and the normalized gap width∆Ω/Ωg=0.9187. The results show that from the first normalized gap widths the largest one can be found when f = 0.6 and θ = 5◦, the first gap width∆Ω = 0.937 ( µ0ω/g) and the normalized gap width ∆Ω/Ωg = 0.9591. The results show that the numerical, rotating square rods can make the low frequency band gap widen in the triangular lattice of two-dimensional magnonic crystal.
Kagan, Yu.; Kikoin, K.A.; Mishchenko, A.S. [RRC Kurchatov Inst., Moscow (Russian Federation). Super Conductivity and Solid State
1997-02-01
On the grounds of the microscopic theory of heavy-fermion spin liquids a novel description of low-energy excitation spectra in CeNiSn and related compounds is offered. The anomalous properties of orthorhombic CeNiSn and related materials are explained by the interplay between the fermi-type spinon excitations with the energy scale T{sup *} {approx} T{sub K} and the one-site crystal field excitations with the energy {Delta}{sub CF} < T{sup *}. The theory gives both quantitative and qualitative description of inelastic neutron scattering spectra and low-temperature thermodynamics. It resolves also the apparent contradiction between metallic conductivity and gap-wise behavior of thermodynamic properties and spin response at low temperatures. (orig.). 8 refs.
Errandonea, Daniel; Muñoz, Alfonso; Rodríguez-Hernández, Placida; Proctor, John E; Sapiña, Fernando; Bettinelli, Marco
2015-08-03
The crystal structures, lattice vibrations, and electronic band structures of PbCrO4, PbSeO4, SrCrO4, and SrSeO4 were studied by ab initio calculations, Raman spectroscopy, X-ray diffraction, and optical-absorption measurements. Calculations properly describe the crystal structures of the four compounds, which are isomorphic to the monazite structure and were confirmed by X-ray diffraction. Information is also obtained on the Raman- and IR-active phonons, with all of the vibrational modes assigned. In addition, the band structures and electronic densities of states of the four compounds were determined. All are indirect-gap semiconductors. In particular, chromates are found to have band gaps smaller than 2.5 eV and selenates higher than 4.3 eV. In the chromates (selenates), the upper part of the valence band is dominated by O 2p states and the lower part of the conduction band is composed primarily of electronic states associated with the Cr 3d and O 2p (Se 4s and O 2p) states. Calculations also show that the band gap of PbCrO4 (PbSeO4) is smaller than the band gap of SrCrO4 (SrSeO4). This phenomenon is caused by Pb states, which, to some extent, also contribute to the top of the valence band and the bottom of the conduction band. The agreement between experiments and calculations is quite good; however, the band gaps are underestimated by calculations, with the exception of the bang gap of SrCrO4, for which theory and calculations agree. Calculations also provide predictions of the bulk modulus of the studied compounds.
Santocanale, Luigi
2002-01-01
A μ-lattice is a lattice with the property that every unary polynomial has both a least and a greatest fix-point. In this paper we define the quasivariety of μ-lattices and, for a given partially ordered set P, we construct a μ-lattice JP whose elements are equivalence classes of games in a preor...
Jacobi photonic lattices and their SUSY partners.
Zúñiga-Segundo, A; Rodríguez-Lara, B M; Fernández C, David J; Moya-Cessa, H M
2014-01-13
We present a classical analog of quantum optical deformed oscillators in arrays of waveguides. The normal modes of these one-dimensional photonic crystals are given in terms of Jacobi polynomials. We show that it is possible to attack the problem via factorization by exploiting the corresponding quantum optical model. This allows us to provide an unbroken supersymmetric partner of the proposed Jacobi lattices. Thanks to the underlying SU(1, 1) group symmetry of the lattices, we present the analytic propagators and impulse functions for these one-dimensional photonic crystals.
Effects of crystal defects on stress-corrosion susceptibility in aluminum alloy 7075
Bentle, G. G.; Jacobs, A. J.
1970-01-01
Point defects were introduced into specimens of three heat-treated tempers of alloy 7075 by neutron irradiation. Continuous ultrasonic monitoring allowed crack growth to be observed. Effects on stress-corrosion susceptibility, elongation, hardness, and yield strength are noted and compared for the three tempers.
Debord, B; Chafer, M; Baz, A; Maurel, M; Blondy, J M; Hugonnot, E; Scol, F; Vincetti, L; Gerome, F; Benabid, F
2016-01-01
The advent of photonic bandgap (PBG) guiding hollow- core photonic crystal fiber (HC-PCF) sparked the hope of guiding light with attenuation below the fundamental silica Rayleigh scattering limit (SRSL) of conventional step-index fibers. Unfortunately, the combination of the strong core-cladding optical-overlap, the surface roughness at the silica cladding struts and the presence of interface-modes limited the lowest reported transmission-loss to 1.2 dB/km at 1550 nm. This hope is recently revived by the introduction of hypocycloid core- contour (i.e. negative curvature) in inhibited-coupling (IC) guiding HC-PCF, and the reduction of their confinement loss to a level that makes them serious contenders for light transmission below the SRSL in UV- VIS-NIR spectral range. Here, we report on several IC guiding HC-PCFs with a hypocycloid core-contour and a cladding structure made of a single ring from a tubular lattice. The fibers guide in the UV-VIS and NIR, and among which we list one with a record transmission ...
Bimaterial lattices as thermal adapters and actuators
Toropova, Marina M.; Steeves, Craig A.
2016-11-01
The goal of this paper is to demonstrate how anisotropic biomaterial lattices can be used in thermal actuation. Compared to other lattices with tailored thermal expansion, the anisotropy of these bimaterial lattices makes them uniquely suitable for use as thermal actuators. Each individual cell, and hence lattices consisting of such cells, can be designed with widely different predetermined coefficients of thermal expansion (CTE) in different directions, enabling complex shape changes appropriate for actuation with either passive or active control. The lattices are composed of planar non-identical cells that each consist of a skewed hexagon surrounding an irregular triangle. The cells and all members of any cell are connected to each other by pins so that they have no rotational constraints and are able to expand or contract freely. In this case, the skew angles of the hexagon and the ratio of the CTEs of the two component materials determine the overall performance of the lattice. At its boundaries, the lattice is connected to substrates by pins and configured such that the CTE between two neighboring lattice vertices coincides with the CTE of the adjacent substrate. Provided the boundary behavior of the lattice is matched to the thermal properties of the substrates, temperature changes in the structure produce thermal strains without producing any corresponding stresses. Such lattices can be used in three different ways: as adaptive elements for stress-free connection of components with different CTEs; for fine tuning of structures; and as thermally driven actuators. In this paper, we demonstrate some concepts for lattice configurations that produce thermally-driven displacements that enable several actuators: a switch, a valve and tweezers.
Anisotropic dissipation in lattice metamaterials
Dimitri Krattiger
2016-12-01
Full Text Available Plane wave propagation in an elastic lattice material follows regular patterns as dictated by the nature of the lattice symmetry and the mechanical configuration of the unit cell. A unique feature pertains to the loss of elastodynamic isotropy at frequencies where the wavelength is on the order of the lattice spacing or shorter. Anisotropy may also be realized at lower frequencies with the inclusion of local resonators, especially when designed to exhibit directionally non-uniform connectivity and/or cross-sectional geometry. In this paper, we consider free and driven waves within a plate-like lattice−with and without local resonators−and examine the effects of damping on the isofrequency dispersion curves. We also examine, for free waves, the effects of damping on the frequency-dependent anisotropy of dissipation. Furthermore, we investigate the possibility of engineering the dissipation anisotropy by tuning the directional properties of the prescribed damping. The results demonstrate that uniformly applied damping tends to reduce the intensity of anisotropy in the isofrequency dispersion curves. On the other hand, lattice crystals and metamaterials are shown to provide an excellent platform for direction-dependent dissipation engineering which may be realized by simple changes in the spatial distribution of the damping elements.
Direct shear of olivine single crystals
Tielke, Jacob A.; Zimmerman, Mark E.; Kohlstedt, David L.
2016-12-01
Knowledge of the strengths of the individual dislocation slip systems in olivine is fundamental to understanding the flow behavior and the development of lattice-preferred orientation in olivine-rich rocks. The most direct measurements of the strengths of individual slip systems are from triaxial compression experiments on olivine single crystals. However, such experiments only allow for determination of flow laws for two of the four dominant slip systems in olivine. In order to measure the strengths of the (001)[100] and (100)[001] slip systems independently, we performed deformation experiments on single crystals of San Carlos olivine in a direct shear geometry. Experiments were carried out at temperatures of 1000 ° to 1300 °C, a confining pressure of 300 MPa, shear stresses of 60 to 334 MPa, and resultant shear strain rates of 7.4 × 10-6 to 2.1 × 10-3 s-1. At high-temperature (≥1200 °C) and low-stress (≤200 MPa) conditions, the strain rate of crystals oriented for direct shear on either the (001)[100] or the (100)[001] slip system follows a power law relationship with stress, whereas at lower temperatures and higher stresses, strain rate depends exponentially on stress. The flow laws derived from the mechanical data in this study are consistent with a transition from the operation of a climb-controlled dislocation mechanism during power-law creep to the operation of a glide-controlled dislocation mechanism during exponential creep. In the climb-controlled regime, crystals oriented for shear on the (001)[100] slip system are weaker than crystals orientated for shear on the (100)[001] slip system. In contrast, in the glide-controlled regime the opposite is observed. Extrapolation of flow laws determined for crystals sheared in orientations favorable for slip on these two slip systems to upper mantle conditions reveals that the (001)[100] slip system is weaker at temperatures and stresses that are typical of the asthenospheric mantle, whereas the (100
Lee, R. G.; Idesman, A.; Nyakiti, L.; Chaudhuri, J.
2009-02-01
A three-dimensional numerical finite element modeling method is applied to compare interfacial residual thermal stress distribution in AlN single crystals grown by using different substrates such as silicon carbide, boron nitride, tungsten, tantalum carbide, and niobium carbide. A dimensionless coordinate system is used which reduces the numbers of computations and hence simplifies the stress analysis. All components of the stress distribution, both in the film and in the substrate, including the normal stress along the growth direction as well as in-plane normal stresses and shear stresses are fully investigated. This information about the stress distribution provides insight into understanding and controlling the AlN single crystal growth by the sublimation technique. The normal stress in the film at the interface along the growth direction and the shear stresses are zero except at the edges, whereas in-plane stresses are nonzero. The in-plane stresses are compressive when TaC and NbC substrates are used. A small compressive stress might be beneficial in prohibiting crack growth in the film. The compressive stress in the AlN is lower for the TaC substrate than that for the NbC. Tensile in-plane stresses are formed in the AlN for 6H-SiC, BN, and W substrates. This tensile stress in the film is detrimental as it will assist in the crack growth. The stress concentration at the edges of the AlN film at the interface is compressive in nature when TaC and NbC are used as a substrate. This causes the film to bend downward (i.e., convex shape) and assist it to adhere to the substrate. The AlN film curves upward or in a concave shape when SiC, BN, and W substrates are used since the stress concentration at the edges of the AlN film is tensile at the interface and this may cause detachment of the film from the substrate.
Observation of resonant lattice modes by inelastic neutron scattering
Bjerrum Møller, Hans; Mackintosh, A.R.
1965-01-01
Observation by inelastic neutron scattering of resonant lattice modes due to small concentration of W atoms in Cr host crystal; frequencies and lifetimes of phonons with frequencies near that of resonant mode are considerably affected by presence of defects....
Lattice dynamics of strontium tungstate
Prabhatasree Goel; R Mittal; S L Chaplot; A K Tyagi
2008-11-01
We report here measurements of the phonon density of states and the lattice dynamics calculations of strontium tungstate (SrWO4). At ambient conditions this compound crystallizes to a body-centred tetragonal unit cell (space group I41/a) called scheelite structure. We have developed transferable interatomic potentials to study the lattice dynamics of this class of compounds. The model parameters have been fitted with respect to the experimentally available Raman and infra-red frequencies and the equilibrium unit cell parameters. Inelastic neutron scattering measurements have been carried out in the triple-axis spectrometer at Dhruva reactor. The measured phonon density of states is in good agreement with the theoretical calculations, thus validating the inter-atomic potential developed.
Abdolvand, Hamidreza; Majkut, Marta; Oddershede, Jette
2015-01-01
-of-mass positions and volumes as measured by three-dimensional X-ray diffraction (3DXRD) microscopy. The constructed microstructure is meshed with different element densities and for different numbers of grains. Then a selected group of twin and parent pairs are studied. It is shown that the measured average stress...... each grain, stresses in the parent and twin are quite different if they are plotted in the global coordinate system. However, if the stress tensor is rotated into the local coordinate system of the twin habit plane, all the stress components averaged over the presented population are close, except......Stress heterogeneity within each individual grain of polycrystalline Zircaloy-2 is studied using a crystal plasticity finite element (CPFE) model. For this purpose, the weighted Voronoi tessellation method is used to construct 3D geometries of more than 2600 grains based on their center...
Directed self-assembly of spheres into a two-dimensional colloidal crystal by viscoelastic stresses.
Pasquino, Rossana; Snijkers, Frank; Grizzuti, Nino; Vermant, Jan
2010-03-02
Ordering induced by shear flow can be used to direct the assembly of particles in suspensions. Flow-induced ordering is determined by the balance between a range of forces, such as direct interparticle, Brownian, and hydrodynamic forces. The latter are modified when dealing with viscoelastic rather than Newtonian matrices. In particular, 1D stringlike structures of spherical particles have been observed to form along the flow direction in shear thinning viscoelastic fluids, a phenomenon not observed in Newtonian fluids at similar particle volume fractions. Here we report on the formation of freestanding crystalline patches in planes parallel to the shearing surfaces. The novel microstructure is formed when particles are suspended in viscoelastic, wormlike micellar solutions and only when the applied shear rate exceeds a critical value. In spite of the very low volume fraction (less than 0.01), particles arrange themselves in 2D crystalline patches along the flow direction. This is a bulk phenomenon because 2D crystals form throughout the whole gap between plates, with the gap thickness being much larger than the particle size. Shear flow may hence be an easy method to drive particles into crystalline order in suspensions with viscoelastic properties. The crystalline structure reported here could be used to design new materials with special mechanical, optical, thermal, or electric properties.
Geometry and dynamics in Hamiltonian lattices
Rink, B.W.
2003-01-01
E. Fermi, J. Pasta and S. Ulam introduced the Fermi-Pasta-Ulam lattice in the 1950s as a classical mechanical model for a mono-atomic crystal or a one-dimensional continuum. The model consisted of a discrete number of equal point masses that interact with their nearest neighbours only. On the basis
Introduction to Louis Michel's lattice geometry through group action
Zhilinskii, Boris
2015-01-01
Group action analysis developed and applied mainly by Louis Michel to the study of N-dimensional periodic lattices is the central subject of the book. Different basic mathematical tools currently used for the description of lattice geometry are introduced and illustrated through applications to crystal structures in two- and three-dimensional space, to abstract multi-dimensional lattices and to lattices associated with integrable dynamical systems. Starting from general Delone sets the authors turn to different symmetry and topological classifications including explicit construction of orbifolds for two- and three-dimensional point and space groups. Voronoï and Delone cells together with positive quadratic forms and lattice description by root systems are introduced to demonstrate alternative approaches to lattice geometry study. Zonotopes and zonohedral families of 2-, 3-, 4-, 5-dimensional lattices are explicitly visualized using graph theory approach. Along with crystallographic applications, qualitative ...
Optical vortex array in spatially varying lattice
Kapoor, Amit; Senthilkumaran, P; Joseph, Joby
2015-01-01
We present an experimental method based on a modified multiple beam interference approach to generate an optical vortex array arranged in a spatially varying lattice. This method involves two steps which are: numerical synthesis of a consistent phase mask by using two-dimensional integrated phase gradient calculations and experimental implementation of produced phase mask by utilizing a phase only spatial light modulator in an optical 4f Fourier filtering setup. This method enables an independent variation of the orientation and period of the vortex lattice. As working examples, we provide the experimental demonstration of various spatially variant optical vortex lattices. We further confirm the existence of optical vortices by formation of fork fringes. Such lattices may find applications in size dependent trapping, sorting, manipulation and photonic crystals.
Fractional Bloch oscillations in photonic lattices
Corrielli, Giacomo; Della Valle, Giuseppe; Longhi, Stefano; Osellame, Roberto; 10.1038/ncomms2578
2013-01-01
Bloch oscillations, the oscillatory motion of a quantum particle in a periodic potential, are one of the most fascinating effects of coherent quantum transport. Originally studied in the context of electrons in crystals, Bloch oscillations manifest the wave nature of matter and are found in a wide variety of different physical systems. Here we report on the first experimental observation of fractional Bloch oscillations, using a photonic lattice as a model system of a two-particle extended Bose-Hubbard Hamiltonian. In our photonic simulator, the dynamics of two correlated particles hopping on a one-dimensional lattice is mapped into the motion of a single particle in a two-dimensional lattice with engineered defects and mimicked by light transport in a square waveguide lattice with a bent axis.
Fractional Bloch oscillations in photonic lattices.
Corrielli, Giacomo; Crespi, Andrea; Della Valle, Giuseppe; Longhi, Stefano; Osellame, Roberto
2013-01-01
Bloch oscillations, the oscillatory motion of a quantum particle in a periodic potential, are one of the most fascinating effects of coherent quantum transport. Originally studied in the context of electrons in crystals, Bloch oscillations manifest the wave nature of matter and are found in a wide variety of different physical systems. Here we report on the first experimental observation of fractional Bloch oscillations, using a photonic lattice as a model system of a two-particle extended Bose-Hubbard Hamiltonian. In our photonic simulator, the dynamics of two correlated particles hopping on a one-dimensional lattice is mapped into the motion of a single particle in a two-dimensional lattice with engineered defects and mimicked by light transport in a square waveguide lattice with a bent axis.
Campos, R G; Campos, Rafael G.; Tututi, Eduardo S.
2002-01-01
It is shown that the nonlocal Dirac operator yielded by a lattice model that preserves chiral symmetry and uniqueness of fields, approaches to an ultralocal and invariant under translations operator when the size of the lattice tends to zero.
New integrable lattice hierarchies
Pickering, Andrew [Area de Matematica Aplicada, ESCET, Universidad Rey Juan Carlos, c/ Tulipan s/n, 28933 Mostoles, Madrid (Spain); Zhu Zuonong [Departamento de Matematicas, Universidad de Salamanca, Plaza de la Merced 1, 37008 Salamanca (Spain) and Department of Mathematics, Shanghai Jiao Tong University, Shanghai 200030 (China)]. E-mail: znzhu2@yahoo.com.cn
2006-01-23
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.
Louis-Achille, V
1999-07-01
Studies of natural and synthetic apatites allow to propose such crystals as matrix for nuclear waste storage. The neodymium substituted britholite, Ca{sub 9}Nd(PO{sub 4}){sub 5}(SiO{sub 4})F{sub 2}. is a model for the trivalent actinide storage Neodymium can be substituted in two types of sites. The aim of this thesis is to compare the chemical nature of this two sites in fluoro-apatite Ca{sub 9}(PO{sub 4}){sub 6}F{sub 2} and then in britholite, using ab initio atomistic modeling. Two approaches are used: one considers the infinite crystals and the second considers clusters. The calculations of the electronic structure for both were performed using Kohn and Sham density functional theory in the local approximation. For solids, pseudopotentials were used, and wave functions are expanded in plane waves. For clusters, a frozen core approximation was used, and the wave functions are expanded in a linear combination of Slater type atomic orbitals. The pseudopotential is semi-relativistic for neodymium, and the Hamiltonian is scalar relativistic for the clusters. The validation of the solid approach is performed using two test cases: YPO{sub 4} and ScPO{sub 4}. Two numerical tools were developed to compute electronic deformation density map, and calculate partial density of stases. A full optimisation of the lattice parameters with a relaxation of the atomic coordinates leads to correct structural and thermodynamic properties for the fluoro-apatite, compared to experience. The electronic deformation density maps do not show any significant differences. between the two calcium sites. but Mulliken analysis on the solid and on the clusters point out the more ionic behavior of the calcium in site 2. A neodymium substituted britholite is then studied. Neodymium location only induces local modifications in; the crystalline structure and few changes in the formation enthalpy. The electronic study points out an increase of the covalent character the bonding involving neodymium
Liu, Yupu; Di, Youying; He, Donghua; Zhou, Qian; Dou, Jianmin
2011-11-01
As part of our ongoing project involving the study of (1-C(n)H(2n+1)NH(3))(2)MCl(4)(s) (where M is a divalent metal ion and n = 8-18), we have synthesized the compounds (1-C(n)H(2n+1)NH(3))(2)ZnCl(4)(s) (n = 8, 10, 12, and 13), and the details of the structures are reported herein. All of the compounds were crystallized in the monoclinic form with the space group P2(1)/n for (1-C(8)H(17)NH(3))(2)ZnCl(4)(s), P21/c for (1-C(10)H(21)NH(3))(2)ZnCl(4)(s), P2(1)/c for (1-C(12)H(25)NH(3))(2)ZnCl(4)(s), and P2(1)/m for (1-C(13)H(27)NH(3))(2)ZnCl(4)(s). The lattice potential energies and ionic volumes of the cations and the common anion of the title compounds were obtained from crystallographic data. Molar enthalpies of dissolution of the four compounds at various molalities were measured at 298.15 K in the double-distilled water. According to Pitzer's theory, molar enthalpies of dissolution of the title compounds at infinite dilution were obtained. Finally, using the values of molar enthalpies of dissolution at infinite dilution (Δ(s)H(m)(∞)) and other auxiliary thermodynamic data, the enthalpy change of the dissociation of [ZnCl(4)](2-)(g) for the reaction [ZnCl(4)](2-)(g)→ Zn(2+)(g) + 4Cl(-)(g) was obtained, and then the hydration enthalpies of cations were calculated by designing a thermochemical cycle.
Sober Topological Molecular Lattices
张德学; 李永明
2003-01-01
A topological molecular lattice (TML) is a pair (L, T), where L is a completely distributive lattice and r is a subframe of L. There is an obvious forgetful functor from the category TML of TML's to the category Loc of locales. In this note,it is showed that this forgetful functor has a right adjoint. Then, by this adjunction,a special kind of topological molecular lattices called sober topological molecular lattices is introduced and investigated.
Nie, Weijie; He, Ruiyun; Cheng, Chen; Rocha, Uéslen; Rodríguez Vázquez de Aldana, Javier; Jaque, Daniel; Chen, Feng
2016-05-15
We report on the fabrication of optical lattice-like waveguide structures in an Nd:YAP laser crystal by using direct femtosecond laser writing. With periodically arrayed laser-induced tracks, the waveguiding cores can be located in either the regions between the neighbored tracks or the central zone surrounded by a number of tracks as outer cladding. The polarization of the femtosecond laser pulses for the inscription has been found to play a critical role in the anisotropic guiding behaviors of the structures. The confocal photoluminescence investigations reveal different stress-induced modifications of the structures inscribed by different polarization of the femtosecond laser beam, which are considered to be responsible for the refractive index changes of the structures. Under optical pump at 808 nm, efficient waveguide lasing at ∼1 μm wavelength has been realized from the optical lattice-like structure, which exhibits potential applications as novel miniature light sources.
Atkinson, D; van Steenwijk, F.J.
The resistance between two arbitrary nodes in an infinite square lattice of:identical resistors is calculated, The method is generalized to infinite triangular and hexagonal lattices in two dimensions, and also to infinite cubic and hypercubic lattices in three and more dimensions. (C) 1999 American
Lattice Regularization and Symmetries
Hasenfratz, Peter; Von Allmen, R; Allmen, Reto von; Hasenfratz, Peter; Niedermayer, Ferenc
2006-01-01
Finding the relation between the symmetry transformations in the continuum and on the lattice might be a nontrivial task as illustrated by the history of chiral symmetry. Lattice actions induced by a renormalization group procedure inherit all symmetries of the continuum theory. We give a general procedure which gives the corresponding symmetry transformations on the lattice.
S. Schleef
2014-10-01
Full Text Available Laboratory-based, experimental data for the microstructural evolution of new snow are scarce, though applications would benefit from a quantitative characterization of the main influences. To this end, we have analyzed the metamorphism and concurrent densification of new snow under isothermal conditions by means of X-ray microtomography and compiled a comprehensive data set of 45 time series. In contrast to previous measurements on isothermal metamorphism on time scales of weeks to months, we analyzed the initial 24–48 h of snow evolution at a high temporal resolution of 3 hours. The data set comprised natural and laboratory-grown snow, and experimental conditions included systematic variations of overburden stress, temperature and crystal habit to address the main influences on specific surface area (SSA decrease rate and densification rate in a snowpack. For all conditions, we found a linear relation between density and SSA, indicating that metamorphism has an immediate influence for the densification of new snow. The slope of the linear relation, however, depends on the other parameters which were analyzed individually to derive a best-fit parameterization for the SSA decrease rate and densification rate. In the investigated parameter range, we found that the initial value of the SSA constituted the main morphological influence on the SSA decrease rate. In turn, the SSA decrease rate constituted the main influence on the densification rate.
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INTERFACE DEVICE FOR NONDESTRUCTIVE TESTING OF RESIDUAL SURFACE STRESSES
Gennady A. Perepelkin
2016-01-01
Full Text Available The paper considers the organization of connection of a personal computer with a device for nondestructive testing of residual surface stresses. The device works is based on the phenomenon of diffraction of ionizing radiation from the crystal lattice near the surface of the crystallites. Proposed software interface to the organization for each type of user: the device developers, administrators, users. Some aspects of the organization of communication microcontroller to a PC via USB-port
Giant crystals inside mitochondria of equine chondrocytes.
Nürnberger, S; Rentenberger, C; Thiel, K; Schädl, B; Grunwald, I; Ponomarev, I; Marlovits, St; Meyer, Ch; Barnewitz, D
2017-05-01
The present study reports for the first time the presence of giant crystals in mitochondria of equine chondrocytes. These structures show dark contrast in TEM images as well as a granular substructure of regularly aligned 1-2 nm small units. Different zone axes of the crystalline structure were analysed by means of Fourier transformation of lattice-resolution TEM images proving the crystalline nature of the structure. Elemental analysis reveals a high content of nitrogen referring to protein. The outer shape of the crystals is geometrical with an up to hexagonal profile in cross sections. It is elongated, spanning a length of several micrometres through the whole cell. In some chondrocytes, several crystals were found, sometimes combined in a single mitochondrion. Crystals were preferentially aligned along the long axis of the cells, thus appearing in the same orientation as the chondrocytes in the tissue. Although no similar structures have been found in the cartilage of any other species investigated, they have been found in cartilage repair tissue formed within a mechanically stimulated equine chondrocyte construct. Crystals were mainly located in superficial regions of cartilage, especially in joint regions of well-developed superficial layers, more often in yearlings than in adult horses. These results indicate that intramitochondrial crystals are related to the high mechanical stress in the horse joint and potentially also to the increased metabolic activity of immature individuals.
Stabilizing internal stress as the thermodynamic factor of martensite aging effects
Kosogor, Anna [Department of Radiophysics, Taras Shevchenko University, 03022 Kyiv (Ukraine); L' vov, Victor A., E-mail: victorlvov@univ.kiev.ua [Department of Radiophysics, Taras Shevchenko University, 03022 Kyiv (Ukraine); Institute of Magnetism, Vernadsky Str. 36-b, 03142 Kyiv (Ukraine); Soederberg, Outi; Hannula, Simo-Pekka [Department of Materials Science and Engineering, Aalto University School of Chemical Technology, PO Box 16200, Espoo FI-00076 Aalto (Finland)
2011-05-15
Highlights: > A martensite aging is accompanied by reconfiguration of the crystal defects system. > The reconfiguration causes an internal stressing of crystal lattice. > The internal stressing elevates the martensitic transformation temperature. > A theory that accounts for the internal stress adequately describes aging effects. > A quantitative description of aging effects observed in Au-Cd alloys is presented. - Abstract: The symmetry-conforming Landau theory has been developed for the description of interplay between the symmetry of the deformable crystal lattice and the configuration of crystallographic defects in martensitic alloys. For this purpose, the multi-component non-scalar order parameter describing the slow reconfiguration of defects after the deformation of crystal lattice has been introduced within the framework of the Landau theory of martensitic transformations (MTs). Due to the transformational equivalence of the configurational order parameter and strain/stress tensor components, the conception of stabilizing internal stress (SIS), which is linearly related to this parameter, has been formulated. The complete agreement between the developed theory and the symmetry-conforming short-range-order principle formulated by Ren and Otsuka has been established. The effect of stabilizing the product (martensitic) phase after aging has been described by considering the stress-temperature phase diagram, which was constructed by taking into account the time dependence of SIS. The applicability of the theory to the aging effects in the Au-Cd shape memory alloy has been demonstrated. The time dependencies of the experimentally observed slow changes in the MT temperatures, lattice parameters and yield stress values have been derived from the SIS conception.
无
2001-01-01
By applying tensile stress along 〈100〉 of β phase, the superelastic behavior and stabilization of stress-induced martensite (SIM) of Cu-13.4Al-4.0Ni(mass fraction, %) single crystals were studied. The results show that the pseudo-yield stress decreases with the increase of cycling number, and keeping load isothermally has an effect on stabilization of SIM. Previous thermal cycling between (Ms-20 ℃) and (Af+20 ℃) promotes the superelasticity and the stabilization of SIM as well; the pre-thermal cycling also reduces the pseudo-yield stress. However, once the stabilization of SIM is produced, it can be destabilized by either the afterwards thermal cooling-heating cycling or load and immediately unload cycling in (Af～Md). Isothermal treatment in (Af～Md) brings restabilization of SIM. The maximum superelastic value from β→β′1(18 R) is 9% for the studied single crystal. When test temperature is in Af～(Af+50 ℃) and stress is in 0～350 MPa, the superelastic behavior exist.
Volgmann, Kai Tristan
2016-07-29
Low-dimensional diffusion was investigated to improve the understanding of the fundamentals of ion movement in condensed matter. Different model systems with different dimensionality of cation migration pathways were investigated using solidstate nuclear magnetic resonance (NMR) spectroscopy and impedance spectroscopy. Both experimental methods made it possible to complementarily study both Li and Na mobility over a wide range of jump rates. Metallic lithium as a well-known model system for isotropic diffusion was investigated using {sup 7}Li field-cycling NMR. The spin-lattice relaxation (SLR) rates were separated into an electronic contribution and a diffusion-induced contribution. The Korringa product was calculated from the actual measurements. The main focus was the comparison of different theoretical models describing the Li motion in metallic lithium. The well-known model by Bloembergen, Purcell and Pound already reproduced the data well, but two models by Sholl improved the results taking into account the type of crystal lattice and jump correlation effects. A single-vacancy diffusion mechanism was observed, but a double-vacancy mechanism was not excluded as elevated temperatures near the melting point of lithium were not available. Li{sub 0.7}Nb{sub 3}S{sub 4} is isostructural to Li{sub 0.7}Nb{sub 3}Se{sub 4} which was reported as possible 1D Li ion conductor due to its channel structure. Thus, Li{sub 0.7}Nb{sub 3}S{sub 4} was investigated as 1D model system using solid-state NMR spectroscopy. Multinuclear NMR spectroscopy gave insights into structural properties. Li dynamics was observed by several NMR methods over a wide temperature range. {sup 7}Li NMR motional narrowing led to an estimate of the activation energy for local Li hopping. {sup 7}Li NMR spin-alignment echo (SAE) was used for the determination of Li jump rates on a macroscopic scale. Possible dimensionality effects were investigated by {sup 7}Li NMR SLR. Out of the phase system Li{sub 2}O
Analysis of gamma prime shape changes in a single crystal Ni-base superalloy
Gayda, J.; Mackay, R. A.
1989-01-01
The microstructural evolution of a commercial single crystal superalloy, NASAIR 100, is analyzed using the existing high-temperature lattice mismatch data and high-temperature moduli obtained from tests on single crystals of gamma and gamma prime. A multiparticle analysis of the microstructural evolution is performed using a novel microstructural lattice simulation technique, MCFET. Under a uniaxial stress, a regular array of gamma prime particles in the simulated microstructure is predicted to coalesce and form a plate morphology, with the broad faces of the plates and stress axis perpendicular in tension but parallel in compression. These results are consistent with changes in gamma prime shape observed in NASAIR 100 following creep testing at 1000 C.
Choe, Jung-Yoon; Park, Ki-Yeun; Kim, Seong-Kyu
2015-01-01
The aim of this study is to clarify the effect of oxidative stress on monosodium urate (MSU)-mediated apoptosis of renal cells. Quantitative real-time polymerase chain reaction and immunoblotting for Bcl-2, caspase-9, caspase-3, iNOS, cyclooxygenase-2 (COX-2), interleukin-1β (IL-1β), IL-18, TNF receptor-associated factor-6 (TRAF-6), and mitogen-activated protein kinases were performed on human embryonic kidney 293 (HEK293) cells, which were stimulated by MSU crystals. Fluorescence-activated cell sorting was performed using annexin V for assessment of apoptosis. Reactive oxygen species (ROS) were measured. IL-1β siRNA was used for blocking IL-1β expression. MSU crystals promoted ROS, iNOS, and COX-2 expression and also increased TRAF-6 and IL-1β expression in HEK293 cells, which was inhibited by an antioxidant ascorbic acid. Caspase-dependent renal cell apoptosis was induced through attenuation of Bcl-2 and enhanced caspase-3 and caspase-9 expression by MSU crystals, which was significantly reversed by ascorbic acid and transfection of IL-1β siRNA to HEK293 cells. Ascorbic acid inhibited phosphorylation of extracellular signal-regulated kinase and Jun N-terminal protein kinase stimulated by MSU crystals. ROS accumulation and iNOS and COX-2 mRNA expression by MSU crystals was also suppressed by transfection with IL-1β siRNA. Oxidative stress generated by MSU crystals promotes renal apoptosis through the mitochondrial caspase-dependent apoptosis pathway.
Contribution of molecular flexibility to the elastic-plastic properties of molecular crystal α-RDX
Pal, Anirban; Picu, Catalin R.
2017-01-01
We show in this work that the mechanical properties of molecular crystals are strongly affected by the flexibility of the constituent molecules. To this end, we explore several kinematically restrained models of the molecular crystal cyclotrimethylene trinitramine in the α phase. We evaluate the effect of gradually removing the flexibility of the molecule on various crystal-scale parameters such as the elastic constants, the lattice parameters, the thermal expansion coefficients, the stacking fault energy and the critical stress for the motion of a dislocation (the Peierls-Nabarro stress). The values of these parameters evaluated with the fully refined, fully flexible atomistic model of the crystal are taken as reference. It is observed that the elastic constants, the lattice parameters and their dependence on pressure, and the thermal expansion coefficient can be accurately predicted with models that consider the NO2 and CH2 groups rigid, and the N-N bonds and the bonds of the triazine ring inextensible. Eliminating the dihedral flexibility of the ring leads to larger errors. The model in which the entire molecule is considered rigid or is mapped to a blob leads to even larger errors. Only the fully flexible, reference model provides accurate values for the stacking fault energy and the Peierls-Nabarro critical stress. Removing any component of the molecular flexibility leads to large errors in these parameters. These results also provide guidance for the development of coarse grained models of molecular crystals.
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.
Cheng, Szu-Cheng; Jheng, Shih-Da
2016-08-01
This paper reports a novel type of vortex lattice, referred to as a bubble crystal, which was discovered in rapidly rotating Bose gases with long-range interactions. Bubble crystals differ from vortex lattices which possess a single quantum flux per unit cell, while atoms in bubble crystals are clustered periodically and surrounded by vortices. No existing model is able to describe the vortex structure of bubble crystals; however, we identified a mathematical lattice, which is a subset of coherent states and exists periodically in the physical space. This lattice is called a von Neumann lattice, and when it possesses a single vortex per unit cell, it presents the same geometrical structure as an Abrikosov lattice. In this report, we extend the von Neumann lattice to one with an integral number of flux quanta per unit cell and demonstrate that von Neumann lattices well reproduce the translational properties of bubble crystals. Numerical simulations confirm that, as a generalized vortex, a von Neumann lattice can be physically realized using vortex lattices in rapidly rotating Bose gases with dipole interatomic interactions.
Jammed lattice sphere packings
Kallus, Yoav; Marcotte, Étienne; Torquato, Salvatore
2013-01-01
We generate and study an ensemble of isostatic jammed hard-sphere lattices. These lattices are obtained by compression of a periodic system with an adaptive unit cell containing a single sphere until the point of mechanical stability. We present detailed numerical data about the densities, pair correlations, force distributions, and structure factors of such lattices. We show that this model retains many of the crucial structural features of the classical hard-sphere model and propose it as a...
On Traveling Waves in Lattices: The Case of Riccati Lattices
Dimitrova, Zlatinka
2012-09-01
The method of simplest equation is applied for analysis of a class of lattices described by differential-difference equations that admit traveling-wave solutions constructed on the basis of the solution of the Riccati equation. We denote such lattices as Riccati lattices. We search for Riccati lattices within two classes of lattices: generalized Lotka-Volterra lattices and generalized Holling lattices. We show that from the class of generalized Lotka-Volterra lattices only the Wadati lattice belongs to the class of Riccati lattices. Opposite to this many lattices from the Holling class are Riccati lattices. We construct exact traveling wave solutions on the basis of the solution of Riccati equation for three members of the class of generalized Holling lattices.
Lattice Entertain You: Paper Modeling of the 14 Bravais Lattices on Youtube
Sein, Lawrence T., Jr.; Sein, Sarajane E.
2015-01-01
A system for the construction of double-sided paper models of the 14 Bravais lattices, and important crystal structures derived from them, is described. The system allows the combination of multiple unit cells, so as to better represent the overall three-dimensional structure. Students and instructors can view the models in use on the popular…
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.)
Ma, Changdong; Lu, Fei; Xu, Bo; Fan, Ranran
2016-05-01
We investigated lattice modification and its physical mechanism in H and He co-implanted, z-cut potassium titanyl phosphate (KTiOPO4). The samples were implanted with 110 keV H and 190 keV He, both to a fluence of 4 × 1016 cm-2, at room temperature. Rutherford backscattering/channeling, high-resolution x-ray diffraction, and transmission electron microscopy were used to examine the implantation-induced structural changes and strain. Experimental and simulated x-ray diffraction results show that the strain in the implanted KTiOPO4 crystal is caused by interstitial atoms. The strain and stress are anisotropic and depend on the crystal's orientation. Transmission electron microscopy studies indicate that ion implantation produces many dislocations in the as-implanted samples. Annealing can induce ion aggregation to form nanobubbles, but plastic deformation and ion out-diffusion prevent the KTiOPO4 surface from blistering.
New methods for indexing multi-lattice diffraction data
Gildea, Richard J. [Diamond Light Source Ltd, Harwell Science and Innovation Campus, Didcot OX11 0DE (United Kingdom); Waterman, David G. [STFC Rutherford Appleton Laboratory, Didcot OX11 0QX (United Kingdom); CCP4, Research Complex at Harwell, Rutherford Appleton Laboratory, Didcot OX11 0FA (United Kingdom); Parkhurst, James M.; Axford, Danny [Diamond Light Source Ltd, Harwell Science and Innovation Campus, Didcot OX11 0DE (United Kingdom); Sutton, Geoff [University of Oxford, Oxford OX3 7BN (United Kingdom); Stuart, David I. [Diamond Light Source Ltd, Harwell Science and Innovation Campus, Didcot OX11 0DE (United Kingdom); University of Oxford, Oxford OX3 7BN (United Kingdom); Sauter, Nicholas K. [Lawrence Berkeley National Laboratory, Berkeley, CA 94720 (United States); Evans, Gwyndaf; Winter, Graeme, E-mail: graeme.winter@diamond.ac.uk [Diamond Light Source Ltd, Harwell Science and Innovation Campus, Didcot OX11 0DE (United Kingdom)
2014-10-01
A new indexing method is presented which is capable of indexing multiple crystal lattices from narrow wedges of data. The efficacy of this method is demonstrated with both semi-synthetic multi-lattice data and real multi-lattice data recorded from microcrystals of ∼1 µm in size. A new indexing method is presented which is capable of indexing multiple crystal lattices from narrow wedges of diffraction data. The method takes advantage of a simplification of Fourier transform-based methods that is applicable when the unit-cell dimensions are known a priori. The efficacy of this method is demonstrated with both semi-synthetic multi-lattice data and real multi-lattice data recorded from crystals of ∼1 µm in size, where it is shown that up to six lattices can be successfully indexed and subsequently integrated from a 1° wedge of data. Analysis is presented which shows that improvements in data-quality indicators can be obtained through accurate identification and rejection of overlapping reflections prior to scaling.
Kim, Do Jin; Bitto, Eduard; Bingman, Craig A; Kim, Hyun-Jung; Han, Byung Woo; Phillips, George N
2015-07-01
Members of the universal stress protein (USP) family are conserved in a phylogenetically diverse range of prokaryotes, fungi, protists, and plants and confer abilities to respond to a wide range of environmental stresses. Arabidopsis thaliana contains 44 USP domain-containing proteins, and USP domain is found either in a small protein with unknown physiological function or in an N-terminal portion of a multi-domain protein, usually a protein kinase. Here, we report the first crystal structure of a eukaryotic USP-like protein encoded from the gene At3g01520. The crystal structure of the protein At3g01520 was determined by the single-wavelength anomalous dispersion method and refined to an R factor of 21.8% (Rfree = 26.1%) at 2.5 Å resolution. The crystal structure includes three At3g01520 protein dimers with one AMP molecule bound to each protomer, comprising a Rossmann-like α/β overall fold. The bound AMP and conservation of residues in the ATP-binding loop suggest that the protein At3g01520 also belongs to the ATP-binding USP subfamily members.
Experimental Realization of a Quantum Pentagonal Lattice
Yamaguchi, Hironori; Okubo, Tsuyoshi; Kittaka, Shunichiro; Sakakibara, Toshiro; Araki, Koji; Iwase, Kenji; Amaya, Naoki; Ono, Toshio; Hosokoshi, Yuko
2015-01-01
Geometric frustration, in which competing interactions give rise to degenerate ground states, potentially induces various exotic quantum phenomena in magnetic materials. Minimal models comprising triangular units, such as triangular and Kagome lattices, have been investigated for decades to realize novel quantum phases, such as quantum spin liquid. A pentagon is the second-minimal elementary unit for geometric frustration. The realization of such systems is expected to provide a distinct platform for studying frustrated magnetism. Here, we present a spin-1/2 quantum pentagonal lattice in the new organic radical crystal α-2,6-Cl2-V [=α-3-(2,6-dichlorophenyl)-1,5-diphenylverdazyl]. Its unique molecular arrangement allows the formation of a partially corner-shared pentagonal lattice (PCPL). We find a clear 1/3 magnetization plateau and an anomalous change in magnetization in the vicinity of the saturation field, which originate from frustrated interactions in the PCPL. PMID:26468930
Epelbaum E.
2010-04-01
Full Text Available We review recent progress on nuclear lattice simulations using chiral eﬀective ﬁeld theory. We discuss lattice results for dilute neutron matter at next-to-leading order, three-body forces at next-to-next-toleading order, isospin-breaking and Coulomb eﬀects, and the binding energy of light nuclei.
Equation of state for charge-doping-induced deformation and hardening in cubic crystals
Li, Yao; Liu, Xiaofei; Guo, Wanlin
2017-08-01
Charge doping would inevitably induce strain, which can significantly influence device performance but cannot be directly predicted by classical mechanical laws. Here we present a set of equations of states for deformable cubic crystals subjected to charge doping by introducing the quantum electronic stress at fixed lattice as equivalent mechanical pressure into the classical hydrostatic pressure-vs-deformation equations. The equations are proved to be efficient for all the cubic crystals considered in this work (diamond, Si, Ge, GaAs, Al, and ZrO2) by first-principles calculations. The proposed method and presented equations should pave a convenient way to predict doping effects on device performance.
Keller, Hanne Dauer
2015-01-01
Kapitlet handler om stress som følelse, og det trækker primært på de få kvalitative undersøgelser, der er lavet af stressforløb.......Kapitlet handler om stress som følelse, og det trækker primært på de få kvalitative undersøgelser, der er lavet af stressforløb....
Keller, Hanne Dauer
2015-01-01
Kapitlet handler om stress som følelse, og det trækker primært på de få kvalitative undersøgelser, der er lavet af stressforløb.......Kapitlet handler om stress som følelse, og det trækker primært på de få kvalitative undersøgelser, der er lavet af stressforløb....
Load Relaxation of Olivine Single Crystals
Cooper, R. F.; Stone, D. S.; Plookphol, T.
2016-12-01
Single crystals of ferromagnesian olivine (San Carlos, AZ, peridot; Fo90-92) have been deformed in both uniaxial creep and load relaxation under conditions of ambient pressure, T = 1500ºC and pO2 = 10-10 atm; creep stresses were in the range 40 ≤ σ1 (MPa) ≤ 220. The crystals were oriented such that the applied stress was parallel to [011]c, which promotes single slip on the slowest slip system in olivine, (010)[001]. The creep rates at steady state match well the results of earlier investigators, as does the stress sensitivity (a power-law exponent of n = 3.6). Dislocation microstructures, including spatial distribution of low-angle (subgrain) boundaries, additionally confirm previous investigations. Inverted primary creep (an accelerating strain rate with an increase in stress) was observed. Load-relaxation, however, produced a singular response—a single hardness curve—regardless of the magnitude of creep stress or total accumulated strain preceding relaxation. The log-stress v. log-strain rate data from load-relaxation and creep experiments overlap to within experimental error. The load-relaxation behavior is distinctly different that that described for other crystalline solids, where the flow stress is affected strongly by work hardening such that a family of distinct hardness curves is generated, which are related by a scaling function. The response of olivine for the conditions studied, thus, indicates flow that is rate-limited by dislocation glide, reflecting specifically a high intrinsic lattice resistance (Peierls stress).
Nathal, M. V.; Ebert, L. J.
1984-01-01
The effects of cobalt, tantaium, and tungsten contents on the microstructure and mechanical properties of single crystal Mar-M247 were investigated. Elevated temperature tensile and creep-rupture properties of 001 oriented single crystals were related to microstructural features of the alloys. Substitution of Ni for Co in the high refractory metal alloys increased the lattice mismatch, which was considered to be the cause of the increases in tensile and creep strength. Substitution of Ni for Ta caused large decreases in tensile strength and creep life, consistent with decreases in gamma prime volume fraction, lattice mismatch, and solid solution hardening. Substitution of W for Ta resulted in decreased life at high stresses, which was related to small decreases in mismatch and volume fraction. However, the W substitution resulted in improved life at low stresses, which was related to solid solution strengthening by W.
Lattice effects in the light actinides
Lawson, A.C.; Cort, B.; Roberts, J.A.; Bennett, B.I.; Brun, T.O.; Dreele, R.B. von [Los Alamos National Lab., NM (United States); Richardson, J.W. Jr. [Argonne National Lab., IL (United States)
1998-12-31
The light actinides show a variety of lattice effects that do not normally appear in other regions of the periodic table. The article will cover the crystal structures of the light actinides, their atomic volumes, their thermal expansion behavior, and their elastic behavior as reflected in recent thermal vibration measurements made by neutron diffraction. A discussion of the melting points will be given in terms of the thermal vibration measurements. Pressure effects will be only briefly indicated.
Vanhellemont, Jan; Kamiyama, Eiji; Nakamura, Kozo; Śpiewak, Piotr; Sueoka, Koji
2017-09-01
This paper reviews recent considerable progress made in the last few years in understanding the behavior and properties of intrinsic point defects close to moving melt/solid Si interfaces during single crystal Si growth from a melt. The so called Voronkov criterion allows to determine whether the grown Si crystal is interstitial I- or vacancy V-rich. This criterion is written as the ratio Γ of the pulling rate v over the thermal gradient G at the interface. Crystals pulled with Γ above a critical value Γcrit are vacancy-rich while below Γcrit, they are interstitial-rich. Various expressions based on the intrinsic point defect thermal equilibrium concentration and diffusivity have been proposed to calculate Γcrit and are briefly discussed in this paper. Recently it was shown that the thermal stress at the interface and heavy doping with neutral and/or electrically active impurities, have a considerable impact on the intrinsic point defect balance and thus also on Γcrit. Furthermore, high energy barriers of formation energies of I and V around three or four atom layers from (001) free surface support a model in which the boundary conditions of the point defect concentrations at the surface in simulations can be set at fixed values. The situation is quite different for Ge single crystal pulling where the vacancy is always the dominant intrinsic point defect so that the Voronkov criterion cannot be applied. Prediction of vacancy cluster concentration/size distributions as a function of the pulling conditions is however still possible. The possibility of reaching Voronkov criterion conditions for Ge by doping with specific impurities is also discussed. Finally, impacts of stress and doping on self-diffusion in Si and Ge are evaluated with comparing the previous experimental results.
New methods for indexing multi-lattice diffraction data.
Gildea, Richard J; Waterman, David G; Parkhurst, James M; Axford, Danny; Sutton, Geoff; Stuart, David I; Sauter, Nicholas K; Evans, Gwyndaf; Winter, Graeme
2014-10-01
A new indexing method is presented which is capable of indexing multiple crystal lattices from narrow wedges of diffraction data. The method takes advantage of a simplification of Fourier transform-based methods that is applicable when the unit-cell dimensions are known a priori. The efficacy of this method is demonstrated with both semi-synthetic multi-lattice data and real multi-lattice data recorded from crystals of ∼1 µm in size, where it is shown that up to six lattices can be successfully indexed and subsequently integrated from a 1° wedge of data. Analysis is presented which shows that improvements in data-quality indicators can be obtained through accurate identification and rejection of overlapping reflections prior to scaling.
Crystal plasticity and grain crushing in high-porosity rocks
Rahmani, H.; Tjioe, M.; Borja, R. I.
2012-12-01
Previous studies show the significance of considering microstructure of individual crystals in modeling the inelastic behavior of high-porosity rocks. Plastic deformation of high-porosity crystalline rocks, exemplified by limestone, is mainly attributed to crystal plasticity and cataclastic flow. Crystal plasticity is defined as the plastic deformation along potential slip systems within the crystal lattice. In the context of continuum mechanics this micro-mechanism is modeled by a nonlinear relationship between stresses and strains. Two types of nonlinearity characterize the inelastic behavior of the crystal grains: material nonlinearity and geometric nonlinearity. Material nonlinearity defines the changes in stiffness matrix due to plastic slip along slip systems. Geometric nonlinearity contributes to the changes in stiffness matrix due to changes in the geometry of the crystal grains. Geometric nonlinearity is modeled using theory of finite deformation, which assumes the geometry of slip systems to be a function of crystal deformation. This type of nonlinearity is very important in modeling crystal deformation mainly because of plastic spin induced by anisotropy in the crystal structure. However, considering the geometry of slip systems as a function of crystal slip makes the equations highly nonlinear. As a result, many studies either ignore geometric nonlinearity or make other assumptions to simplify the equations. Cataclastic flow, on the other hand, is characterized by pervasive grain crushing in which larger grains are converted into smaller ones. We model cataclastic flow as strong discontinuity in the grain scale via an assumed enhanced strain method formulated within the context of nonlinear finite elements. The method allows the individual finite elements, identified to be in critical condition, to break into two pieces along a plane identified by theory of bifurcation. We show that modeling cataclastic flow combined with finite deformation crystal
Von Smekal, L; Sternbeck, A; Williams, A G
2007-01-01
We propose a modified lattice Landau gauge based on stereographically projecting the link variables on the circle S^1 -> R for compact U(1) or the 3-sphere S^3 -> R^3 for SU(2) before imposing the Landau gauge condition. This can reduce the number of Gribov copies exponentially and solves the Gribov problem in compact U(1) where it is a lattice artifact. Applied to the maximal Abelian subgroup this might be just enough to avoid the perfect cancellation amongst the Gribov copies in a lattice BRST formulation for SU(N), and thus to avoid the Neuberger 0/0 problem. The continuum limit of the Landau gauge remains unchanged.
Jammed lattice sphere packings.
Kallus, Yoav; Marcotte, Étienne; Torquato, Salvatore
2013-12-01
We generate and study an ensemble of isostatic jammed hard-sphere lattices. These lattices are obtained by compression of a periodic system with an adaptive unit cell containing a single sphere until the point of mechanical stability. We present detailed numerical data about the densities, pair correlations, force distributions, and structure factors of such lattices. We show that this model retains many of the crucial structural features of the classical hard-sphere model and propose it as a model for the jamming and glass transitions that enables exploration of much higher dimensions than are usually accessible.
Jammed lattice sphere packings
Kallus, Yoav; Marcotte, Étienne; Torquato, Salvatore
2013-12-01
We generate and study an ensemble of isostatic jammed hard-sphere lattices. These lattices are obtained by compression of a periodic system with an adaptive unit cell containing a single sphere until the point of mechanical stability. We present detailed numerical data about the densities, pair correlations, force distributions, and structure factors of such lattices. We show that this model retains many of the crucial structural features of the classical hard-sphere model and propose it as a model for the jamming and glass transitions that enables exploration of much higher dimensions than are usually accessible.
Physics of higher orbital bands in optical lattices: a review
Li, Xiaopeng; Liu, W. Vincent
2015-01-01
Orbital degree of freedom plays a fundamental role in understanding the unconventional properties in solid state materials. Experimental progress in quantum atomic gases has demonstrated that high orbitals in optical lattices can be used to construct quantum emulators of exotic models beyond natural crystals, where novel many-body states such as complex Bose-Einstein condensation and topological semimetals emerge. A brief introduction of orbital degree of freedom in optical lattices is given ...
Jensen, Line Skov; Lova, Lotte; Hansen, Zandra Kulikovsky; Schønemann, Emilie; Larsen, Line Lyngby; Colberg Olsen, Maria Sophia; Juhl, Nadja; Magnussen, Bogi Roin
2012-01-01
Stress er en tilstand som er meget omdiskuteret i samfundet, og dette besværliggør i en vis grad konkretiseringen af mulige løsningsforslag i bestræbelsen på at forebygge den såkaldte folkesygdom. Hovedkonklusionen er, at selv om der bliver gjort meget for at forebygge, er der ikke meget der aktivt kan sættes i værk for at reducere antallet af stressramte, før en fælles forståelse af stressårsager og effektiv stresshåndtering er fremlagt. Problemformuleringen er besvaret gennem en undersø...
Lattice parameters guide superconductivity in iron-arsenides
Konzen, Lance M. N.; Sefat, Athena S.
2017-03-01
The discovery of superconducting materials has led to their use in technological marvels such as magnetic-field sensors in MRI machines, powerful research magnets, short transmission cables, and high-speed trains. Despite such applications, the uses of superconductors are not widespread because they function much below room-temperature, hence the costly cooling. Since the discovery of Cu- and Fe-based high-temperature superconductors (HTS), much intense effort has tried to explain and understand the superconducting phenomenon. While no exact explanations are given, several trends are reported in relation to the materials basis in magnetism and spin excitations. In fact, most HTS have antiferromagnetic undoped ‘parent’ materials that undergo a superconducting transition upon small chemical substitutions in them. As it is currently unclear which ‘dopants’ can favor superconductivity, this manuscript investigates crystal structure changes upon chemical substitutions, to find clues in lattice parameters for the superconducting occurrence. We review the chemical substitution effects on the crystal lattice of iron-arsenide-based crystals (2008 to present). We note that (a) HTS compounds have nearly tetragonal structures with a-lattice parameter close to 4 Å, and (b) superconductivity can depend strongly on the c-lattice parameter changes with chemical substitution. For example, a decrease in c-lattice parameter is required to induce ‘in-plane’ superconductivity. The review of lattice parameter trends in iron-arsenides presented here should guide synthesis of new materials and provoke theoretical input, giving clues for HTS.
Ludwig, A.; Vakhrushev, A.; Holzmann, T.; Wu, M.; Kharicha, A.
2015-06-01
During many industrial solidification processes equiaxed crystals form, grow and move. When those crystals are small they are carried by the melt, whereas when getting larger they sediment. As long as the volume fraction of crystals is below the packing limit, they are able to move relatively free. Crystals being backed in a so called packed bed form a semi-solid slurry, which may behave like a visco-plastic material. In addition, cooling-induced density increase of both, liquid and solid phases might lead to shrinkage of the whole casting domain. So deformation happens and gaps between casting and mold occur. In the present work, a two-phase Eulerian-Eulerian volume averaging model for describing the motion of equiaxed crystals in the melt is combined with a similar two-phase model for describing the dynamic of the packed bed. As constitutive equation for the solid skeleton in the packed bed Norton-Hoff law is applied. Shrinkage induced by density changes in the liquid or the solid phase is explicitly taken into account and handled by remeshing the calculation domain accordantly.
Lipstein, Arthur E
2014-01-01
We formulate the theory of a 2-form gauge field on a Euclidean spacetime lattice. In this approach, the fundamental degrees of freedom live on the faces of the lattice, and the action can be constructed from the sum over Wilson surfaces associated with each fundamental cube of the lattice. If we take the gauge group to be $U(1)$, the theory reduces to the well-known abelian gerbe theory in the continuum limit. We also propose a very simple and natural non-abelian generalization with gauge group $U(N) \\times U(N)$, which gives rise to $U(N)$ Yang-Mills theory upon dimensional reduction. Formulating the theory on a lattice has several other advantages. In particular, it is possible to compute many observables, such as the expectation value of Wilson surfaces, analytically at strong coupling and numerically for any value of the coupling.
Root lattices and quasicrystals
Baake, M.; Joseph, D.; Kramer, P.; Schlottmann, M.
1990-10-01
It is shown that root lattices and their reciprocals might serve as the right pool for the construction of quasicrystalline structure models. All noncrystallographic symmetries observed so far are covered in minimal embedding with maximal symmetry.
ORGINOS,K.
2003-01-07
I review the current status of hadronic structure computations on the lattice. I describe the basic lattice techniques and difficulties and present some of the latest lattice results; in particular recent results of the RBC group using domain wall fermions are also discussed. In conclusion, lattice computations can play an important role in understanding the hadronic structure and the fundamental properties of Quantum Chromodynamics (QCD). Although some difficulties still exist, several significant steps have been made. Advances in computer technology are expected to play a significant role in pushing these computations closer to the chiral limit and in including dynamical fermions. RBC has already begun preliminary dynamical domain wall fermion computations [49] which we expect to be pushed forward with the arrival of QCD0C. In the near future, we also expect to complete the non-perturbative renormalization of the relevant derivative operators in quenched QCD.
Superalloy Lattice Block Structures
Nathal, M. V.; Whittenberger, J. D.; Hebsur, M. G.; Kantzos, P. T.; Krause, D. L.
2004-01-01
Initial investigations of investment cast superalloy lattice block suggest that this technology will yield a low cost approach to utilize the high temperature strength and environmental resistance of superalloys in lightweight, damage tolerant structural configurations. Work to date has demonstrated that relatively large superalloy lattice block panels can be successfully investment cast from both IN-718 and Mar-M247. These castings exhibited mechanical properties consistent with the strength of the same superalloys measured from more conventional castings. The lattice block structure also accommodates significant deformation without failure, and is defect tolerant in fatigue. The potential of lattice block structures opens new opportunities for the use of superalloys in future generations of aircraft applications that demand strength and environmental resistance at elevated temperatures along with low weight.
无
2010-01-01
The effect of dendrite arm spacing and the size of γ’ phase on stress rupture properties of as-cast Ni3Al-based single crystal superalloy IC6SX was studied.It has been found that the stress rupture properties were affected by dendrite arm spacing and the size of γ’ phase significantly,i.e.,the stress rupture lives of as-cast specimens under the test condition of 1100°C/120 MPa were significantly increased from about 10 h to 31 h with decreasing dendrite arm spacing and the size of γ’ phase from 3.0 μm and 1.6 μm to 1.3 μm and 0.8 μm,respectively.The creep cracks generated easily in the brittle Y-NiMo phase.Then the cracks gradually mergered and grew up during creep,and finally led to specimens fracture.The orientated coarsening of γ’ phase has been found in the stress ruptured specimens,due to the elements diffusion.However,the γ’ phase did not form the integrated structure during the short periods of 10-31 h as the creep tests lasted.
Vector Lattice Vortex Solitons
WANG Jian-Dong; YE Fang-Wei; DONG Liang-Wei; LI Yong-Ping
2005-01-01
@@ Two-dimensional vector vortex solitons in harmonic optical lattices are investigated. The stability properties of such solitons are closely connected to the lattice depth Vo. For small Vo, vector vortex solitons with the total zero-angular momentum are more stable than those with the total nonzero-angular momentum, while for large Vo, this case is inversed. If Vo is large enough, both the types of such solitons are stable.
Pica, C; Lucini, B; Patella, A; Rago, A
2009-01-01
Technicolor theories provide an elegant mechanism for dynamical electroweak symmetry breaking. We will discuss the use of lattice simulations to study the strongly-interacting dynamics of some of the candidate theories, with matter fields in representations other than the fundamental. To be viable candidates for phenomenology, such theories need to be different from a scaled-up version of QCD, which were ruled out by LEP precision measurements, and represent a challenge for modern lattice computations.
Automated Lattice Perturbation Theory
Monahan, Christopher
2014-11-01
I review recent developments in automated lattice perturbation theory. Starting with an overview of lattice perturbation theory, I focus on the three automation packages currently "on the market": HiPPy/HPsrc, Pastor and PhySyCAl. I highlight some recent applications of these methods, particularly in B physics. In the final section I briefly discuss the related, but distinct, approach of numerical stochastic perturbation theory.
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....
Rinaldi, D., E-mail: d.rinaldi@univpm.i [Dipartimento di Fisica e Ingegneria dei Materiali e del Territorio, Universita Politecnica delle Marche, via Brecce Bianche, 60131 Ancona (Italy); INFN section of Perugia (Italy); Ciriaco, A. [Dipartimento di Fisica e Ingegneria dei Materiali e del Territorio, Universita' Politecnica delle Marche, via Brecce Bianche, 60131 Ancona (Italy); Lebeau, M. [CERN PH department, 1211 Geneva 23 (Switzerland); Paone, N. [Dipartimento di Meccanica, Universita' Politecnica delle Marche, via Brecce Bianche, 60131 Ancona (Italy)
2010-04-11
Residual internal stresses in PbWO{sub 4} (PWO) scintillating crystals grown by Bridgman method have been systematically studied. Residual stresses induced during growth play an important role in production yield. Cracking probability during mechanical processing as well as stable mechanical properties in finished crystal are closely related to internal stress levels. A regular production of good-quality crystals requires a fast and easy feed-back on growth parameters. Samples from a pre-serial production were analyzed in order to give the producer a quality feed-back for process optimization. By means of photoelasticity, we measured residual stress distribution in several sections along the growth axis and for typical positions in every section. The stress analysis revealed defects occurring during the crystallization process, attributed to dislocations, lattice disorientation and poly-crystallinity. This work had been prompted by the need for quality monitoring of a pre-serial production of PWO for the CMS experiment at CERN's LHC. Mapping stress levels inside the ingot volume and proposing a synthetic parameter to be used as a quality indicator, the resulting analysis should contribute to parameter optimization and improve the growth performance. The proposed method may be useful in conventional crystal production.
2012-07-09
controls the yield stress [20]. However, the experimental data [4] do not show any such tendency for a saturation stress value, most likely because the...D M, Parthasarathy T A, Uchic M D, Tang M and Woodward C 2008 Acta Mater. 56 3245 [6] Senger J, Weygand D, Gumbsch P and Kraft O 2008 Scr. Mater. 58
Solitons in spiraling Vogel lattices
Kartashov, Yaroslav V; Torner, Lluis
2012-01-01
We address light propagation in Vogel optical lattices and show that such lattices support a variety of stable soliton solutions in both self-focusing and self-defocusing media, whose propagation constants belong to domains resembling gaps in the spectrum of a truly periodic lattice. The azimuthally-rich structure of Vogel lattices allows generation of spiraling soliton motion.
Ultrastrong steel via minimal lattice misfit and high-density nanoprecipitation
Jiang, Suihe; Wang, Hui; Wu, Yuan; Liu, Xiongjun; Chen, Honghong; Yao, Mengji; Gault, Baptiste; Ponge, Dirk; Raabe, Dierk; Hirata, Akihiko; Chen, Mingwei; Wang, Yandong; Lu, Zhaoping
2017-04-01
Next-generation high-performance structural materials are required for lightweight design strategies and advanced energy applications. Maraging steels, combining a martensite matrix with nanoprecipitates, are a class of high-strength materials with the potential for matching these demands. Their outstanding strength originates from semi-coherent precipitates, which unavoidably exhibit a heterogeneous distribution that creates large coherency strains, which in turn may promote crack initiation under load. Here we report a counterintuitive strategy for the design of ultrastrong steel alloys by high-density nanoprecipitation with minimal lattice misfit. We found that these highly dispersed, fully coherent precipitates (that is, the crystal lattice of the precipitates is almost the same as that of the surrounding matrix), showing very low lattice misfit with the matrix and high anti-phase boundary energy, strengthen alloys without sacrificing ductility. Such low lattice misfit (0.03 ± 0.04 per cent) decreases the nucleation barrier for precipitation, thus enabling and stabilizing nanoprecipitates with an extremely high number density (more than 1024 per cubic metre) and small size (about 2.7 ± 0.2 nanometres). The minimized elastic misfit strain around the particles does not contribute much to the dislocation interaction, which is typically needed for strength increase. Instead, our strengthening mechanism exploits the chemical ordering effect that creates backstresses (the forces opposing deformation) when precipitates are cut by dislocations. We create a class of steels, strengthened by Ni(Al,Fe) precipitates, with a strength of up to 2.2 gigapascals and good ductility (about 8.2 per cent). The chemical composition of the precipitates enables a substantial reduction in cost compared to conventional maraging steels owing to the replacement of the essential but high-cost alloying elements cobalt and titanium with inexpensive and lightweight aluminium
Effects of Microstructural Parameters on Creep of Nickel-Base Superalloy Single Crystals
MacKay, Rebecca A.; Gabb, Timothy P.; Nathal, Michael V.
2013-01-01
Microstructure-sensitive creep models have been developed for Ni-base superalloy single crystals. Creep rupture testing was conducted on fourteen single crystal alloys at two applied stress levels at each of two temperatures, 982 and 1093 C. The variation in creep lives among the different alloys could be explained with regression models containing relatively few microstructural parameters. At 982 C, gamma-gamma prime lattice mismatch, gamma prime volume fraction, and initial gamma prime size were statistically significant in explaining the creep rupture lives. At 1093 C, only lattice mismatch and gamma prime volume fraction were significant. These models could explain from 84 to 94 percent of the variation in creep lives, depending on test condition. Longer creep lives were associated with alloys having more negative lattice mismatch, lower gamma prime volume fractions, and finer gamma prime sizes. The gamma-gamma prime lattice mismatch exhibited the strongest influence of all the microstructural parameters at both temperatures. Although a majority of the alloys in this study were stable with respect to topologically close packed (TCP) phases, it appeared that up to approximately 2 vol% TCP phase did not affect the 1093 C creep lives under applied stresses that produced lives of approximately 200 to 300 h. In contrast, TCP phase contents of approximately 2 vol% were detrimental at lower applied stresses where creep lives were longer. A regression model was also developed for the as-heat treated initial gamma prime size; this model showed that gamma prime solvus temperature, gamma-gamma prime lattice mismatch, and bulk Re content were all statistically significant.
Huang, W
2007-03-15
A new methodology for strain and stress analysis by X ray diffraction (XRD) in single crystal was developed. It can be applied to determine the second order stress (in grain scale) in single and multi-crystal material with non-cubic lattice. This method is based on the method Ortner I. It has introduced the metric tensor G which is deduced from the lattice space measured by XRD. In the developed method, when the crystal reference is non-orthonormal, an orthonormal reference associated with the crystal basis is defined, so all calculation could be done with usual calculation laws. The use of the least square method allows the acquisition of many more measurements than the six absolute necessary. Then a better metric tensor G is calculated and the statistical error is obtained. This developed method was applied in a bi crystal copper. The experimental results have shown that this method is also effective. The second order residuals stresses for coarse Zn grains in a galvanized coating were determined after annealing. The four coarse grains with different orientations were also characterized and demonstrated the elastic and plastic deformation mechanism in a grain or between the grains during in situ tensile loading. So this method is well able to determine the strains and stresses in grain scale in a mono crystal or multi crystal with any crystalline structure. (author)
Huang, W
2007-03-15
A new methodology for strain and stress analysis by X ray diffraction (XRD) in single crystal was developed. It can be applied to determine the second order stress (in grain scale) in single and multi-crystal material with non-cubic lattice. This method is based on the method Ortner I. It has introduced the metric tensor G which is deduced from the lattice space measured by XRD. In the developed method, when the crystal reference is non-orthonormal, an orthonormal reference associated with the crystal basis is defined, so all calculation could be done with usual calculation laws. The use of the least square method allows the acquisition of many more measurements than the six absolute necessary. Then a better metric tensor G is calculated and the statistical error is obtained. This developed method was applied in a bi crystal copper. The experimental results have shown that this method is also effective. The second order residuals stresses for coarse Zn grains in a galvanized coating were determined after annealing. The four coarse grains with different orientations were also characterized and demonstrated the elastic and plastic deformation mechanism in a grain or between the grains during in situ tensile loading. So this method is well able to determine the strains and stresses in grain scale in a mono crystal or multi crystal with any crystalline structure. (author)
Mechanical properties of lattice grid composites
Hualin Fan; Daining Fang; Fengnian Jin
2008-01-01
An equivalent continuum method only considering the stretching deformation of struts was used to study the in-plane stiffness and strength of planar lattice grid composite materials. The initial yield equations of lattices were deduced. Initial yield surfaces were depicted separately in different 3D and 2D stress spaces. The failure envelope is a polyhedron in 3D spaces and a polygon in 2D spaces. Each plane or line of the failure envelope is corresponding to the yield or buckling of a typical bar row. For lattices with more than three bar rows, subsequent yield of the other bar rowafter initial yield made the lattice achieve greater limit strength. The importance of the buckling strength of the grids was strengthened while the grids were relative sparse. The integration model of the method was used to study the nonlinear mechanical properties of strain hardening grids. It was shown that the integration equation could accurately model the complete stress-strain curves of the grids within small deformations.
Coupling Bright and Dark Plasmonic Lattice Resonances
Rodriguez, S R K; Maes, B; Janssen, O T A; Vecchi, G; Rivas, J Gomez
2011-01-01
We demonstrate the coupling of bright and dark Surface Lattice Resonances (SLRs), which are collective Fano resonances in 2D plasmonic crystals. As a result of this coupling, a frequency stop-gap in the dispersion relation of SLRs is observed. The different field symmetries of the low and high frequency SLR bands lead to pronounced differences in their coupling to free space radiation. Standing waves of very narrow spectral width compared to localized surface plasmon resonances are formed at the high frequency band edge, while subradiant damping onsets at the low frequency band edge leading the resonance into darkness. We introduce a coupled oscillator analog to the plasmonic crystal, which serves to elucidate the physics of the coupled plasmonic resonances and to estimate very high quality factors (Q>700) for SLRs, which are the highest known for any 2D plasmonic crystal.
A Bijection between Lattice-Valued Filters and Lattice-Valued Congruences in Residuated Lattices
Wei Wei
2013-01-01
Full Text Available The aim of this paper is to study relations between lattice-valued filters and lattice-valued congruences in residuated lattices. We introduce a new definition of congruences which just depends on the meet ∧ and the residuum →. Then it is shown that each of these congruences is automatically a universal-algebra-congruence. Also, lattice-valued filters and lattice-valued congruences are studied, and it is shown that there is a one-to-one correspondence between the set of all (lattice-valued filters and the set of all (lattice-valued congruences.
Knuth, Kevin H.
2009-12-01
Previous derivations of the sum and product rules of probability theory relied on the algebraic properties of Boolean logic. Here they are derived within a more general framework based on lattice theory. The result is a new foundation of probability theory that encompasses and generalizes both the Cox and Kolmogorov formulations. In this picture probability is a bi-valuation defined on a lattice of statements that quantifies the degree to which one statement implies another. The sum rule is a constraint equation that ensures that valuations are assigned so as to not violate associativity of the lattice join and meet. The product rule is much more interesting in that there are actually two product rules: one is a constraint equation arises from associativity of the direct products of lattices, and the other a constraint equation derived from associativity of changes of context. The generality of this formalism enables one to derive the traditionally assumed condition of additivity in measure theory, as well introduce a general notion of product. To illustrate the generic utility of this novel lattice-theoretic foundation of measure, the sum and product rules are applied to number theory. Further application of these concepts to understand the foundation of quantum mechanics is described in a joint paper in this proceedings.
Kinematics of continuously distributed defects in crystals
Glanville, M J
2001-01-01
Crystals are formed by atoms arranged in perfectly symmetrical crystal lattices. However in reality these lattices are never perfect, and deviations, or defects occur. These defects can have an important effect on the physical properties of a crystal and scientists have developed a range of ways to measure this defectiveness, one such being the Burger's Vector. By describing a crystal lattice as a collection of lattice vectors, and then smoothing and extrapolating it is possible to define a crystalline material by a crystal state SIGMA = left brace 1 sub a (x), B:a = 1,2,...right brace where B is the region over which the crystal is defined, x is a point of B and 1 sub a (x) are the lattice vector fields at the point x. Parry and others have demonstrated that using this definition it is possible to generate a set of functions that encompass all possible mathematical measures of defectiveness for crystals with three lattice vectors. In this thesis I, extend this to show that such a basis of measures of defecti...
无
2010-01-01
Large scale molecular dynamics simulations of nanomachining and stretching of single crystal copper are performed to analyze the machining process’ influence on the material’s mechanical properties. The simulation results show that the machining process will introduce interfacial defects inside the specimen and enhance the compressive stress beneath the surface. Gener- ally speaking, interfacial defects lead to the decrease of the strength limit, while residue compressive stress can enhance the elastic limit and even the strength limit. Various machining parameters are adopted to investigate their influence on the me- chanical behavior of machined specimen. Lower cutting speed and smaller cutting depth lead to less defects and greater residue compressive stress, which brings about better mechanical properties. The elastic limit increases by 36.8% under the cutting depth of 0.73 nm and decreases by 21.1% under the cutting depth of 1.46 nm. The strength limit increases by 7.7% under the cutting speed of 100 m/s and decreases by 28.2% under the cutting speed of 300 m/s.
Youssef, G; Crum, R; Prikhodko, S V; Seif, D; Po, G; Ghoniem, N; Kodambaka, S; Gupta, V
2013-02-28
An apparatus and test procedure for fabrication and loading of single crystal metal nanopillars under extremely high pressures (>1 GPa) and strain rates (>10(7) s(-1)), using laser-generated stress waves, are presented. Single-crystalline Cu pillars (∼1.20 μm in tall and ∼0.45 μm in diameter) prepared via focused ion beam milling of Cu(001) substrates are shock-loaded using this approach with the dilatational stress waves propagating along the [001] axis of the pillars. Transmission electron microscopy observations of shock-loaded pillars show that dislocation density decreases and that their orientation changes with increasing stress wave amplitude, indicative of dislocation motion. The shock-loaded pillars exhibit enhanced chemical reactivity when submerged in oil and isopropyl alcohol solutions, due likely to the exposure of clean surfaces via surface spallation and formation of surface steps and nanoscale facets through dislocation motion to the surface of the pillars, resulting in growth of thin oxide films on the surfaces of the pillars.
2D InP photonic crystal fabrication process development
Rong, B.; Van der Drift, E.; Van der Heijden, R.W.; Salemink, H.W.M.
2006-01-01
We have developed a reliable process to fabricate high quality 2D air-hole and dielectric column InP photonic crystals with a high aspect ratio on a STS production tool using ICP N2+Cl2 plasma. The photonic crystals have a triangular lattice with lattice constant of 400 nm and air-hole and dielectri
Lattice Boltzmann Stokesian dynamics.
Ding, E J
2015-11-01
Lattice Boltzmann Stokesian dynamics (LBSD) is presented for simulation of particle suspension in Stokes flows. This method is developed from Stokesian dynamics (SD) with resistance and mobility matrices calculated using the time-independent lattice Boltzmann algorithm (TILBA). TILBA is distinguished from the traditional lattice Boltzmann method (LBM) in that a background matrix is generated prior to the calculation. The background matrix, once generated, can be reused for calculations for different scenarios, thus the computational cost for each such subsequent calculation is significantly reduced. The LBSD inherits the merits of the SD where both near- and far-field interactions are considered. It also inherits the merits of the LBM that the computational cost is almost independent of the particle shape.
Weisz, Peter; Majumdar, Pushan
2012-03-01
Lattice gauge theory is a formulation of quantum field theory with gauge symmetries on a space-time lattice. This formulation is particularly suitable for describing hadronic phenomena. In this article we review the present status of lattice QCD. We outline some of the computational methods, discuss some phenomenological applications and a variety of non-perturbative topics. The list of references is severely incomplete, the ones we have included are text books or reviews and a few subjectively selected papers. Kronfeld and Quigg (2010) supply a reasonably comprehensive set of QCD references. We apologize for the fact that have not covered many important topics such as QCD at finite density and heavy quark effective theory adequately, and mention some of them only in the last section "In Brief". These topics should be considered in further Scholarpedia articles.
Improved Lattice Radial Quantization
Brower, Richard C; Fleming, George T
2014-01-01
Lattice radial quantization was proposed in a recent paper by Brower, Fleming and Neuberger[1] as a nonperturbative method especially suited to numerically solve Euclidean conformal field theories. The lessons learned from the lattice radial quantization of the 3D Ising model on a longitudinal cylinder with 2D Icosahedral cross-section suggested the need for an improved discretization. We consider here the use of the Finite Element Methods(FEM) to descretize the universally-equivalent $\\phi^4$ Lagrangian on $\\mathbb R \\times \\mathbb S^2$. It is argued that this lattice regularization will approach the exact conformal theory at the Wilson-Fisher fixed point in the continuum. Numerical tests are underway to support this conjecture.
Graphene antidot lattice waveguides
Pedersen, Jesper Goor; Gunst, Tue; Markussen, Troels
2012-01-01
We introduce graphene antidot lattice waveguides: nanostructured graphene where a region of pristine graphene is sandwiched between regions of graphene antidot lattices. The band gaps in the surrounding antidot lattices enable localized states to emerge in the central waveguide region. We model...... the waveguides via a position-dependent mass term in the Dirac approximation of graphene and arrive at analytical results for the dispersion relation and spinor eigenstates of the localized waveguide modes. To include atomistic details we also use a tight-binding model, which is in excellent agreement...... with the analytical results. The waveguides resemble graphene nanoribbons, but without the particular properties of ribbons that emerge due to the details of the edge. We show that electrons can be guided through kinks without additional resistance and that transport through the waveguides is robust against...
Digital lattice gauge theories
Zohar, Erez; Reznik, Benni; Cirac, J Ignacio
2016-01-01
We propose a general scheme for a digital construction of lattice gauge theories with dynamical fermions. In this method, the four-body interactions arising in models with $2+1$ dimensions and higher, are obtained stroboscopically, through a sequence of two-body interactions with ancillary degrees of freedom. This yields stronger interactions than the ones obtained through pertubative methods, as typically done in previous proposals, and removes an important bottleneck in the road towards experimental realizations. The scheme applies to generic gauge theories with Lie or finite symmetry groups, both Abelian and non-Abelian. As a concrete example, we present the construction of a digital quantum simulator for a $\\mathbb{Z}_{3}$ lattice gauge theory with dynamical fermionic matter in $2+1$ dimensions, using ultracold atoms in optical lattices, involving three atomic species, representing the matter, gauge and auxiliary degrees of freedom, that are separated in three different layers. By moving the ancilla atoms...
Oates, Chris
2012-06-01
Since they were first proposed in 2003 [1], optical lattice clocks have become one of the leading technologies for the next generation of atomic clocks, which will be used for advanced timing applications and in tests of fundamental physics [2]. These clocks are based on stabilized lasers whose frequency is ultimately referenced to an ultra-narrow neutral atom transition (natural linewidths magic'' value so as to yield a vanishing net AC Stark shift for the clock transition. As a result lattice clocks have demonstrated the capability of generating high stability clock signals with small absolute uncertainties (˜ 1 part in 10^16). In this presentation I will first give an overview of the field, which now includes three different atomic species. I will then use experiments with Yb performed in our laboratory to illustrate the key features of a lattice clock. Our research has included the development of state-of-the-art optical cavities enabling ultra-high-resolution optical spectroscopy (1 Hz linewidth). Together with the large atom number in the optical lattice, we are able to achieve very low clock instability (< 0.3 Hz in 1 s) [3]. Furthermore, I will show results from some of our recent investigations of key shifts for the Yb lattice clock, including high precision measurements of ultracold atom-atom interactions in the lattice and the dc Stark effect for the Yb clock transition (necessary for the evaluation of blackbody radiation shifts). [4pt] [1] H. Katori, M. Takamoto, V. G. Pal'chikov, and V. D. Ovsiannikov, Phys. Rev. Lett. 91, 173005 (2003). [0pt] [2] Andrei Derevianko and Hidetoshi Katori, Rev. Mod. Phys. 83, 331 (2011). [0pt] [3] Y. Y. Jiang, A. D. Ludlow, N. D. Lemke, R. W. Fox, J. A. Sherman, L.-S. Ma, and C. W. Oates, Nature Photonics 5, 158 (2011).
Catterall, Simon; Kaplan, David B.; Unsal, Mithat
2009-03-31
We provide an introduction to recent lattice formulations of supersymmetric theories which are invariant under one or more real supersymmetries at nonzero lattice spacing. These include the especially interesting case of N = 4 SYM in four dimensions. We discuss approaches based both on twisted supersymmetry and orbifold-deconstruction techniques and show their equivalence in the case of gauge theories. The presence of an exact supersymmetry reduces and in some cases eliminates the need for fine tuning to achieve a continuum limit invariant under the full supersymmetry of the target theory. We discuss open problems.
Grabisch, Michel
2008-01-01
We extend the notion of belief function to the case where the underlying structure is no more the Boolean lattice of subsets of some universal set, but any lattice, which we will endow with a minimal set of properties according to our needs. We show that all classical constructions and definitions (e.g., mass allocation, commonality function, plausibility functions, necessity measures with nested focal elements, possibility distributions, Dempster rule of combination, decomposition w.r.t. simple support functions, etc.) remain valid in this general setting. Moreover, our proof of decomposition of belief functions into simple support functions is much simpler and general than the original one by Shafer.
Luo, Hui [Department of Materials Science, Sichuan University, 610064 Chengdu (China); Southwest Institute of Technical Physics, Chengdu 610041 (China); Guan, Zhouguo [Southwest Institute of Technical Physics, Chengdu 610041 (China); He, Zhiyu, E-mail: hzyscu@163.com [Department of Materials Science, Sichuan University, 610064 Chengdu (China); Huang, Wei [Department of Materials Science, Sichuan University, 610064 Chengdu (China); Zhang, Wei; Niu, Ruihua; Yao, Chao; Yang, Yongqiang; Zhang, Huirong; Zhang, Zhibin [Southwest Institute of Technical Physics, Chengdu 610041 (China)
2015-11-05
Large and heavily Ho{sup 3+}-doped BaY{sub 2}F{sub 8} single crystals were grown by the Czochralski method. X-ray powder diffraction was applied to analyze the phase of the crystal samples. Simultaneously, metallographic microscope, scanning electron microscopy and energy dispersive spectrometer were employed to observe and investigate defects in the as grown crystals. Two significant kinds of defects, namely cracking and impurities were discovered in the samples of Ho{sup 3+}:BaY{sub 2}F{sub 8} single crystals. Theoretical analyses suggested that mechanisms concerning the formation of the impurities such as bubbles and inclusions were considered to be closely related to the growth temperature and atmosphere while the former defect was primarily brought by the lattice distortion relating to the thermal stress and the impurities. Based on the results of experiments and theoretical analyses, the parameters of growth process were optimized and a crack free 20 mol% Ho{sup 3+}:BaY{sub 2}F{sub 8}single crystal has been successfully obtained. Furthermore, the UV–Vis-IR (0.2–10 μm) absorption spectra of BaY{sub 2}F{sub 8} single crystal and the crystal heavily doped with Ho{sup 3+} ions (20 mol%) have been investigated at room temperature. - Highlights: • Main reason of cleavages is the crystal lattice distortion caused by the impurities. • Lattice distortion was caused by carbon phases derived from the graphite crucible. • High quality crystal can be obtained by using CF{sub 4} and high purity graphite crucibles. • The crystal exhibits the broader absorption band and larger absorption cross section.
Levitas, Valery I.; Chen, Hao; Xiong, Liming
2017-01-01
Starting with thermodynamic predictions and following with molecular dynamics simulations, special triaxial compression-tension states were found for which the stresses for the instability of the crystal lattice of silicon (Si) are the same for direct and reverse phase transformations (PTs) between semiconducting Si I and metallic Si II phases. This leads to unique homogeneous and hysteresis-free first-order PTs, for which each intermediate crystal lattice along the transformation path is in indifferent thermodynamic equilibrium and can be arrested and studied by fixing the strain in one direction. By approaching these stress states, a traditional two-phase system continuously transforms to homogenous intermediate phases. Zero hysteresis and homogeneous transformations are the optimal property for various PT applications, which drastically reduce damage and energy dissipation.
Futa Yuichi
2016-03-01
Full Text Available In this article, we formalize the definition of lattice of ℤ-module and its properties in the Mizar system [5].We formally prove that scalar products in lattices are bilinear forms over the field of real numbers ℝ. We also formalize the definitions of positive definite and integral lattices and their properties. Lattice of ℤ-module is necessary for lattice problems, LLL (Lenstra, Lenstra and Lovász base reduction algorithm [14], and cryptographic systems with lattices [15] and coding theory [9].
An Algorithm on Generating Lattice Based on Layered Concept Lattice
Zhang Chang-sheng
2013-08-01
Full Text Available Concept lattice is an effective tool for data analysis and rule extraction, a bottleneck factor on impacting the applications of concept lattice is how to generate lattice efficiently. In this paper, an algorithm LCLG on generating lattice in batch processing based on layered concept lattice is developed, this algorithm is based on layered concept lattice, the lattice is generated downward layer by layer through concept nodes and provisional nodes in current layer; the concept nodes are found parent-child relationships upward layer by layer, then the Hasse diagram of inter-layer connection is generated; in the generated process of the lattice nodes in each layer, we do the pruning operations dynamically according to relevant properties, and delete some unnecessary nodes, such that the generating speed is improved greatly; the experimental results demonstrate that the proposed algorithm has good performance.
Muthu, K. [Department of Chemistry, Annamalai University, Annamalainagar-608 002 (India); Bhagavannarayana, G. [Crystal Growth and X-ray Analysis Activity, Council of Scientific and Industrial Research, National Physical Laboratory, New Delhi-110 012 (India); Meenakshisundaram, S.P., E-mail: aumats2009@gmail.com [Department of Chemistry, Annamalai University, Annamalainagar-608 002 (India)
2013-01-25
Highlights: Black-Right-Pointing-Pointer A small quantity incorporation of Mg(II)- enhances the SHG efficiency of ZTS. Black-Right-Pointing-Pointer Crystal stress is observed. Black-Right-Pointing-Pointer Structure of Mg(II)-incorporated ZTS is elucidated. Black-Right-Pointing-Pointer Crystalline perfection is evaluated by HRXRD. - Abstract: Single crystals of Mg(II)-incorporated tris(thiourea)Zn(II) sulfate (MZTS) have been grown from aqueous solution at room temperature by slow evaporation solution growth technique. The incorporation of Mg(II)- into the crystalline lattice was well confirmed by energy dispersive X-ray spectroscopy (EDS) and by single crystal X-ray diffraction technique. The reduction in the intensities observed in powder X-ray diffraction patterns of doped specimen and slight shifts in vibrational frequencies in FT-IR indicate the lattice stress as a result of doping. Thermal studies reveal the purity of the material and no decomposition is observed up to the melting point. High transmittance is observed in the visible region and the band gap energy is estimated by Kubelka-Munk algorithm. Surface morphology of doped material was observed by scanning electron microscopy (SEM). Decreased crystalline perfection by doping observed by high-resolution X-ray diffraction (HRXRD) analysis is justified by the crystal stress. Even a small quantity incorporation of Mg(II)- enhances the SHG efficiency significantly. The as-grown crystal is further characterized by microhardness and dielectric studies.
Plastic deformation of tubular crystals by dislocation glide
Beller, Daniel A.; Nelson, David R.
2016-09-01
Tubular crystals, two-dimensional lattices wrapped into cylindrical topologies, arise in many contexts, including botany and biofilaments, and in physical systems such as carbon nanotubes. The geometrical principles of botanical phyllotaxis, describing the spiral packings on cylinders commonly found in nature, have found application in all these systems. Several recent studies have examined defects in tubular crystals associated with crystalline packings that must accommodate a fixed tube radius. Here we study the mechanics of tubular crystals with variable tube radius, with dislocations interposed between regions of different phyllotactic packings. Unbinding and separation of dislocation pairs with equal and opposite Burgers vectors allow the growth of one phyllotactic domain at the expense of another. In particular, glide separation of dislocations offers a low-energy mode for plastic deformations of solid tubes in response to external stresses, reconfiguring the lattice step by step. Through theory and simulation, we examine how the tube's radius and helicity affects, and is in turn altered by, the mechanics of dislocation glide. We also discuss how a sufficiently strong bending rigidity can alter or arrest the deformations of tubes with small radii.
Plastic deformation of tubular crystals by dislocation glide.
Beller, Daniel A; Nelson, David R
2016-09-01
Tubular crystals, two-dimensional lattices wrapped into cylindrical topologies, arise in many contexts, including botany and biofilaments, and in physical systems such as carbon nanotubes. The geometrical principles of botanical phyllotaxis, describing the spiral packings on cylinders commonly found in nature, have found application in all these systems. Several recent studies have examined defects in tubular crystals associated with crystalline packings that must accommodate a fixed tube radius. Here we study the mechanics of tubular crystals with variable tube radius, with dislocations interposed between regions of different phyllotactic packings. Unbinding and separation of dislocation pairs with equal and opposite Burgers vectors allow the growth of one phyllotactic domain at the expense of another. In particular, glide separation of dislocations offers a low-energy mode for plastic deformations of solid tubes in response to external stresses, reconfiguring the lattice step by step. Through theory and simulation, we examine how the tube's radius and helicity affects, and is in turn altered by, the mechanics of dislocation glide. We also discuss how a sufficiently strong bending rigidity can alter or arrest the deformations of tubes with small radii.
Ke, Shaoying; Lin, Shaoming; Ye, Yujie; Mao, Danfeng; Huang, Wei; Xu, Jianfang; Li, Cheng; Chen, Songyan
2017-10-01
The dependence of the morphology and crystallinity of an amorphous Ge (a-Ge) interlayer between two Si wafers on the annealing temperature is identified to understand the bubble evolution mechanism. The effect of a-Ge layer thickness on the bubble density and size at different annealing temperatures is also clearly clarified. It suggests that the bubble density is significantly affected by the crystallinity and thickness of the a-Ge layer. With the increase of the crystallinity and thickness of the a-Ge layer, the bubble density decreases. It is important that a near-bubble-free Ge interface, which is also an oxide-free interface, is achieved when the bonded Si wafers (a-Ge layer thickness ⩾ 20 nm) are annealed at 400 °C. Furthermore, the crystallization temperature of the a-Ge between the bonded Si wafers is lower than that on a Si substrate alone and the Ge grains firstly form at the Ge/Ge bonded interface, rather than the Ge/Si interface. We believe that the stress-induced crystallization of a-Ge film and the intermixing of Ge atoms at the Ge/Ge interface can be responsible for this feature.
Shigaki, Kenta; Noda, Fumiaki; Yamamoto, Kazami; Machida, Shinji; Molodojentsev, Alexander; Ishi, Yoshihiro
2002-12-01
The JKJ high-intensity proton accelerator facility consists of a 400-MeV linac, a 3-GeV 1-MW rapid-cycling synchrotron and a 50-GeV 0.75-MW synchrotron. The lattice and beam dynamics design of the two synchrotrons are reported.
de Raedt, Hans; von der Linden, W.; Binder, K
1995-01-01
In this chapter we review methods currently used to perform Monte Carlo calculations for quantum lattice models. A detailed exposition is given of the formalism underlying the construction of the simulation algorithms. We discuss the fundamental and technical difficulties that are encountered and gi
Knuth, Kevin H
2009-01-01
Previous derivations of the sum and product rules of probability theory relied on the algebraic properties of Boolean logic. Here they are derived within a more general framework based on lattice theory. The result is a new foundation of probability theory that encompasses and generalizes both the Cox and Kolmogorov formulations. In this picture probability is a bi-valuation defined on a lattice of statements that quantifies the degree to which one statement implies another. The sum rule is a constraint equation that ensures that valuations are assigned so as to not violate associativity of the lattice join and meet. The product rule is much more interesting in that there are actually two product rules: one is a constraint equation arises from associativity of the direct products of lattices, and the other a constraint equation derived from associativity of changes of context. The generality of this formalism enables one to derive the traditionally assumed condition of additivity in measure theory, as well in...
Williamson, S. Gill
2010-01-01
Will the cosmological multiverse, when described mathematically, have easily stated properties that are impossible to prove or disprove using mathematical physics? We explore this question by constructing lattice multiverses which exhibit such behavior even though they are much simpler mathematically than any likely cosmological multiverse.
Phenomenology from lattice QCD
Lellouch, L P
2003-01-01
After a short presentation of lattice QCD and some of its current practical limitations, I review recent progress in applications to phenomenology. Emphasis is placed on heavy-quark masses and on hadronic weak matrix elements relevant for constraining the CKM unitarity triangle. The main numerical results are highlighted in boxes.
Noetherian and Artinian Lattices
Derya Keskin Tütüncü
2012-01-01
Full Text Available It is proved that if L is a complete modular lattice which is compactly generated, then Rad(L/0 is Artinian if, and only if for every small element a of L, the sublattice a/0 is Artinian if, and only if L satisfies DCC on small elements.
Magnetic properties of checkerboard lattice: a Monte Carlo study
Jabar, A.; Masrour, R.; Hamedoun, M.; Benyoussef, A.
2017-06-01
The magnetic properties of ferrimagnetic mixed-spin Ising model in the checkerboard lattice are studied using Monte Carlo simulations. The variation of total magnetization and magnetic susceptibility with the crystal field has been established. We have obtained a transition from an order to a disordered phase in some critical value of the physical variables. The reduced transition temperature is obtained for different exchange interactions. The magnetic hysteresis cycles have been established. The multiples hysteresis cycle in checkerboard lattice are obtained. The multiples hysteresis cycle have been established. The ferrimagnetic mixed-spin Ising model in checkerboard lattice is very interesting from the experimental point of view. The mixed spins system have many technological applications such as in domain opto-electronics, memory, nanomedicine and nano-biological systems. The obtained results show that that crystal field induce long-range spin-spin correlations even bellow the reduced transition temperature.
HAFNIUM IMPLANTED IN IRON .1. LATTICE LOCATION AND ANNEALING BEHAVIOR
DEBAKKER, JMGJ; PLEITER, F; SMULDERS, PJM
1993-01-01
Perturbed angular correlation, Rutherford backscattering and channelling experiments were conducted to study the lattice location and annealing behaviour of 110 keV hafnium ions implanted into iron single crystals. It was found that a fraction of 11-25% of the implanted hafnium atoms are located at
Hafnium implanted in iron 1. Lattice location and annealing behavior
de Bakker, J.M.G.J.; Pleiter, F; Smulders, P.J M
1993-01-01
Perturbed angular correlation, Rutherford backscattering and channelling experiments were conducted to study the lattice location and annealing behaviour of 110 keV hafnium ions implanted into iron single crystals. It was found that a fraction of 11-25% of the implanted hafnium atoms are located at
Hafnium implanted in iron 1. Lattice location and annealing behavior
de Bakker, J.M.G.J.; Pleiter, F; Smulders, P.J M
1993-01-01
Perturbed angular correlation, Rutherford backscattering and channelling experiments were conducted to study the lattice location and annealing behaviour of 110 keV hafnium ions implanted into iron single crystals. It was found that a fraction of 11-25% of the implanted hafnium atoms are located at
Restle, M; BharuthRam, K; Quintel, H; Ronning, C; Hofsass, H; Wahl, U; Jahn, SG
1996-01-01
The lattice site occupation of Li in CdTe at temperatures between 40 and 500 K was investigated with the emission channeling method. Radioactive Li-8 ions were implanted at low doses into CdTe single crystals. Emission channeling patterns of alpha-particles emitted in the nuclear decay of Li-8 (t(1/
Growth of coincident site lattice matched semiconductor layers and devices on crystalline substrates
Norman, Andrew G; Ptak, Aaron J
2013-08-13
Methods of fabricating a semiconductor layer or device and said devices are disclosed. The methods include but are not limited to providing a substrate having a crystalline surface with a known lattice parameter (a). The method further includes growing a crystalline semiconductor layer on the crystalline substrate surface by coincident site lattice matched epitaxy, without any buffer layer between the crystalline semiconductor layer and the crystalline surface of the substrate. The crystalline semiconductor layer will be prepared to have a lattice parameter (a') that is related to the substrate lattice parameter (a). The lattice parameter (a') maybe related to the lattice parameter (a) by a scaling factor derived from a geometric relationship between the respective crystal lattices.
Stein, W.D.R.
2007-04-23
directions the dispersion was investigated to a maximum energy of 10 THz. For experimental phonon dispersion several lattice dynamical models are discussed. A shell model with angular forces and additional force constants could describe the phonon dispersion with an averaged deviation of 0.234 THz. The crystal structure of the tetraborates was investigated at room temperature and in addition for the barium and lead compound at 100 K. The comparison of the structure of the isostructural compounds SrB{sub 4}O{sub 7} and PbB{sub 4}O{sub 7} shows a noticeable shift of the lead against the strontium position, which as a result of the similar ion radii of the two ions could be assigned to the lone electron pair at the lead atom. The comparison of the crystal structure at low temperature shows similar to bismuth triborate an increase of the influence of the lone electron pair at lower temperatures. In barium tetraborate two different bond valence sums of the two crystallographic different barium positions are observed. As its origin the strong internal stresses are discussed. (orig.)
Light propagation and localization in modulated photonic lattices and waveguides
Garanovich, Ivan L; Sukhorukov, Andrey A; Kivshar, Yuri S
2011-01-01
We review both theoretical and experimental advances in the recently emerged physics of modulated photonic lattices. Artificial periodic dielectric media, such as photonic crystals and photonic lattices, provide a powerful tool for the control of the fundamental properties of light propagation in photonic structures. Photonic lattices are arrays of coupled optical waveguides, where the light propagation becomes effectively discretized. Such photonic structures allow one to study many useful optical analogies with other fields, such as the physics of solid state and electron theory. In particular, the light propagation in periodic photonic structures resembles the motion of electrons in a crystalline lattice of semiconductor materials. The discretized nature of light propagation gives rise to many new phenomena which are not possible in homogeneous bulk media, such as discrete diffraction and diffraction management, discrete and gap solitons, and discrete surface waves. Recently, it was discovered that applyin...
Li, J.; Oudriss, A.; Metsue, A.; Bouhattate, J.; Feaugas, X.
2017-03-01
Hydrogen diffusion has an important role in solute-dependent hydrogen embrittlement in metals and metallic alloys. In spite of extensive studies, the complexity of hydrogen diffusion in solids remains a phenomenon that needs to be clarified. In this paper, we investigate the anisotropy of hydrogen diffusion in pure nickel single crystals using both an experimental approach and a thermodynamic development. As a first approximation, experimental data from electrochemical permeation and thermal desorption spectroscopy are described using the classical Fick’s laws and an apparent diffusion tensor. Within a thermodynamic framework, the diffusion equation can be derived from Fick’s laws with an apparent diffusion coefficient which contains an added solute content dependent term β. This term is due to the elastic strain field associated with the insertion of solute atoms. For nickel crystals, the dependence of β on the crystallographic orientation arises from the elastic anisotropy. Additionally, our results elucidate the discrepancies between the thermodynamic model and experimental observations of the effect of the solute concentration on the diffusion process. Moreover, this highlights the importance of the impact of hydrogen on vacancy formation and the subsequent consequences on the anisotropy of the apparent diffusion coefficient.
Li, J.; Oudriss, A.; Metsue, A.; Bouhattate, J.; Feaugas, X.
2017-01-01
Hydrogen diffusion has an important role in solute-dependent hydrogen embrittlement in metals and metallic alloys. In spite of extensive studies, the complexity of hydrogen diffusion in solids remains a phenomenon that needs to be clarified. In this paper, we investigate the anisotropy of hydrogen diffusion in pure nickel single crystals using both an experimental approach and a thermodynamic development. As a first approximation, experimental data from electrochemical permeation and thermal desorption spectroscopy are described using the classical Fick’s laws and an apparent diffusion tensor. Within a thermodynamic framework, the diffusion equation can be derived from Fick’s laws with an apparent diffusion coefficient which contains an added solute content dependent term β. This term is due to the elastic strain field associated with the insertion of solute atoms. For nickel crystals, the dependence of β on the crystallographic orientation arises from the elastic anisotropy. Additionally, our results elucidate the discrepancies between the thermodynamic model and experimental observations of the effect of the solute concentration on the diffusion process. Moreover, this highlights the importance of the impact of hydrogen on vacancy formation and the subsequent consequences on the anisotropy of the apparent diffusion coefficient. PMID:28327592
Interfacial dislocation motion and interactions in single-crystal superalloys
Liu, B. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Raabe, D. [Max Planck Inst. fur Eisenforshung. Dusseldorf (Germany); Roters, F. [Max Planck Inst. fur Eisenforshung. Dusseldorf (Germany); Arsenlis, A. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
2014-10-01
The early stage of high-temperature low-stress creep in single-crystal superalloys is characterized by the rapid development of interfacial dislocation networks. Although interfacial motion and dynamic recovery of these dislocation networks have long been expected to control the subsequent creep behavior, direct observation and hence in-depth understanding of such processes has not been achieved. Incorporating recent developments of discrete dislocation dynamics models, we simulate interfacial dislocation motion in the channel structures of single-crystal superalloys, and investigate how interfacial dislocation motion and dynamic recovery are affected by interfacial dislocation interactions and lattice misfit. Different types of dislocation interactions are considered: self, collinear, coplanar, Lomer junction, glissile junction, and Hirth junction. The simulation results show that strong dynamic recovery occurs due to the short-range reactions of collinear annihilation and Lomer junction formation. The misfit stress is found to induce and accelerate dynamic recovery of interfacial dislocation networks involving self-interaction and Hirth junction formation, but slow down the steady interfacial motion of coplanar and glissile junction forming dislocation networks. The insights gained from these simulations on high-temperature low-stress creep of single-crystal superalloys are also discussed.
Equivalence classes of Fibonacci lattices and their similarity properties
Lo Gullo, N.; Vittadello, L.; Bazzan, M.; Dell'Anna, L.
2016-08-01
We investigate, theoretically and experimentally, the properties of Fibonacci lattices with arbitrary spacings. Different from periodic structures, the reciprocal lattice and the dynamical properties of Fibonacci lattices depend strongly on the lengths of their lattice parameters, even if the sequence of long and short segment, the Fibonacci string, is the same. In this work we show that by exploiting a self-similarity property of Fibonacci strings under a suitable composition rule, it is possible to define equivalence classes of Fibonacci lattices. We show that the diffraction patterns generated by Fibonacci lattices belonging to the same equivalence class can be rescaled to a common pattern of strong diffraction peaks thus giving to this classification a precise meaning. Furthermore we show that, through the gap labeling theorem, gaps in the energy spectra of Fibonacci crystals belonging to the same class can be labeled by the same momenta (up to a proper rescaling) and that the larger gaps correspond to the strong peaks of the diffraction spectra. This observation makes the definition of equivalence classes meaningful also for the spectral and therefore dynamical and thermodynamical properties of quasicrystals. Our results apply to the more general class of quasiperiodic lattices for which similarity under a suitable deflation rule is in order.
Shaping Crystals using Electrophoresis
Palacci, Jeremie; Mackiewicz, Kristian
2016-11-01
Electrophoresis is size and shape independent as stressed by Morrison in his seminal paper. Here we present an original approach to reshape colloidal crystals using an electric field as a carving tool.
Basis reduction for layered lattices
Torreão Dassen, Erwin
2011-01-01
We develop the theory of layered Euclidean spaces and layered lattices. We present algorithms to compute both Gram-Schmidt and reduced bases in this generalized setting. A layered lattice can be seen as lattices where certain directions have infinite weight. It can also be interpre
Spin qubits in antidot lattices
Pedersen, Jesper Goor; Flindt, Christian; Mortensen, Niels Asger;
2008-01-01
and density of states for a periodic potential modulation, referred to as an antidot lattice, and find that localized states appear, when designed defects are introduced in the lattice. Such defect states may form the building blocks for quantum computing in a large antidot lattice, allowing for coherent...
Prediction of molecular crystal structures
Beyer, Theresa
2001-07-01
The ab initio prediction of molecular crystal structures is a scientific challenge. Reliability of first-principle prediction calculations would show a fundamental understanding of crystallisation. Crystal structure prediction is also of considerable practical importance as different crystalline arrangements of the same molecule in the solid state (polymorphs)are likely to have different physical properties. A method of crystal structure prediction based on lattice energy minimisation has been developed in this work. The choice of the intermolecular potential and of the molecular model is crucial for the results of such studies and both of these criteria have been investigated. An empirical atom-atom repulsion-dispersion potential for carboxylic acids has been derived and applied in a crystal structure prediction study of formic, benzoic and the polymorphic system of tetrolic acid. As many experimental crystal structure determinations at different temperatures are available for the polymorphic system of paracetamol (acetaminophen), the influence of the variations of the molecular model on the crystal structure lattice energy minima, has also been studied. The general problem of prediction methods based on the assumption that the experimental thermodynamically stable polymorph corresponds to the global lattice energy minimum, is that more hypothetical low lattice energy structures are found within a few kJ mol{sup -1} of the global minimum than are likely to be experimentally observed polymorphs. This is illustrated by the results for molecule I, 3-oxabicyclo(3.2.0)hepta-1,4-diene, studied for the first international blindtest for small organic crystal structures organised by the Cambridge Crystallographic Data Centre (CCDC) in May 1999. To reduce the number of predicted polymorphs, additional factors to thermodynamic criteria have to be considered. Therefore the elastic constants and vapour growth morphologies have been calculated for the lowest lattice energy
Moon, Myung-Kook [Neutron Beam Application, Korea Atomic Energy Research Institute, 150 Duckjin-Dong, Yusung, Daejon 305-600 (Korea, Republic of)]. E-mail: moonmk@kaeri.re.kr; Em, Vyacheslav T. [Neutron Beam Application, Korea Atomic Energy Research Institute, 150 Duckjin-Dong, Yusung, Daejon 305-600 (Korea, Republic of); Lee, Chang-Hee [Neutron Beam Application, Korea Atomic Energy Research Institute, 150 Duckjin-Dong, Yusung, Daejon 305-600 (Korea, Republic of); Mikula, Pavol [Nuclear Physics Institute and Research Centre Rez Ltd., 250 68 Rez (Czech Republic); Hong, Kwang-Pyo [Neutron Beam Application, Korea Atomic Energy Research Institute, 150 Duckjin-Dong, Yusung, Daejon 305-600 (Korea, Republic of); Choi, Young-Hyun [Neutron Beam Application, Korea Atomic Energy Research Institute, 150 Duckjin-Dong, Yusung, Daejon 305-600 (Korea, Republic of); Cheon, Jong-Kyu [Neutron Beam Application, Korea Atomic Energy Research Institute, 150 Duckjin-Dong, Yusung, Daejon 305-600 (Korea, Republic of); Nam, Uk-Won [Nuclear Physics Institute and Research Centre Rez Ltd., 250 68 Rez (Czech Republic); Kong, Kyung-Nam [Nuclear Physics Institute and Research Centre Rez Ltd., 250 68 Rez (Czech Republic); Korea Astronomy Observatory, Yusung, Daejeon 305-348 (Korea, Republic of); Jin, Kyung-Chan [Korea Institute of Industrial Technology, 35-3 Hongchon-Ri, Ipchang-Myun, Chonan-Si, Chungnam, 330-825 (Korea, Republic of)
2005-11-01
Optimized diffractometer arrangements for residual strain measurements employing curved crystal monochromators provide good luminosity and a high {delta}d/d resolution in the vicinity of usually used scattering angle 2{theta}{sub S}{approx}+/-90{sup o}. Due to a variety of designs of the diffractometers which could be installed at a constant or different take-off angles, except a few attempts, there is a lack of experimental evidence providing a help in a choice of parameters for an optimum performance. In addition to our earlier investigations with curved Si(311) monochromator employed in different diffraction geometries (see paper I [M.K. Moon et al., Physica B, submitted [1
Grunert, C Matthias; Schweifer, Johannes; Weinberger, Peter; Linert, Wolfgang; Mereiter, Kurt; Hilscher, Gerfried; Müller, Martin; Wiesinger, Günter; van Koningsbruggen, Petra J
2004-01-12
[micro-Tris(1,4-bis(tetrazol-1-yl)butane-N4,N4')iron(II)] bis(hexafluorophosphate), [Fe(btzb)(3)](PF(6))(2), crystallizes in a three-dimensional 3-fold interlocked structure featuring a sharp two-step spin-crossover behavior. The spin conversion takes place between 164 and 182 K showing a discontinuity at about T(1/2) = 174 K and a hysteresis of about 4 K between T(1/2) and the low-spin state. The spin transition has been independently followed by magnetic susceptibility measurements, (57)Fe-Mössbauer spectroscopy, and variable temperature far and midrange FTIR spectroscopy. The title compound crystallizes in the trigonal space group P3 (No. 147) with a unit cell content of one formula unit plus a small amount of disordered solvent. The lattice parameters were determined by X-ray diffraction at several temperatures between 100 and 300 K. Complete crystal structures were resolved for 9 of these temperatures between 100 (only low spin, LS) and 300 K (only high spin, HS), Z = 1 [Fe(btzb)(3)](PF(6))(2): 300 K (HS), a = 11.258(6) A, c = 8.948(6) A, V = 982.2(10) A(3); 100 K (LS), a = 10.989(3) A, c = 8.702(2) A, V = 910.1(4) A(3). The molecular structure consists of octahedral coordinated iron(II) centers bridged by six N4,N4' coordinating bis(tetrazole) ligands to form three 3-dimensional networks. Each of these three networks is symmetry related and interpenetrates each other within a unit cell to form the interlocked structure. The Fe-N bond lengths change between 1.993(1) A at 100 K in the LS state and 2.193(2) A at 300 K in the HS state. The nearest Fe separation is along the c-axis and identical with the lattice parameter c.
Lattice-Matched Semiconductor Layers on Single Crystalline Sapphire Substrate
Choi, Sang; King, Glen; Park, Yeonjoon
2009-01-01
SiGe is an important semiconductor alloy for high-speed field effect transistors (FETs), high-temperature thermoelectric devices, photovoltaic solar cells, and photon detectors. The growth of SiGe layer is difficult because SiGe alloys have different lattice constants from those of the common Si wafers, which leads to a high density of defects, including dislocations, micro-twins, cracks, and delaminations. This innovation utilizes newly developed rhombohedral epitaxy of cubic semiconductors on trigonal substrates in order to solve the lattice mismatch problem of SiGe by using trigonal single crystals like sapphire (Al2O3) as substrate to give a unique growth-orientation to the SiGe layer, which is automatically controlled at the interface upon sapphire (0001). This technology is different from previous silicon on insulator (SOI) or SGOI (SiGe on insulator) technologies that use amorphous SiO2 as the growth plane. A cubic semiconductor crystal is a special case of a rhombohedron with the inter-planar angle, alpha = 90 deg. With a mathematical transformation, all rhombohedrons can be described by trigonal crystal lattice structures. Therefore, all cubic lattice constants and crystal planes (hkl) s can be transformed into those of trigonal crystal parameters. These unique alignments enable a new opportunity of perfect lattice matching conditions, which can eliminate misfit dislocations. Previously, these atomic alignments were thought to be impossible or very difficult. With the invention of a new x-ray diffraction measurement method here, growth of cubic semiconductors on trigonal crystals became possible. This epitaxy and lattice-matching condition can be applied not only to SiGe (111)/sapphire (0001) substrate relations, but also to other crystal structures and other materials, including similar crystal structures which have pointgroup rotational symmetries by 120 because the cubic (111) direction has 120 rotational symmetry. The use of slightly miscut (less than
Crystal growth and crystallography
Chernov, A. A.
1998-01-01
Selected topics that may be of interest for both crystal-structure and crystal-growth communities are overviewed. The growth of protein crystals, along with that of some other compounds, is one of the topics, and recent insights into related phenomena are considered as examples of applications of general principles. The relationship between crystal growth shape and structure is reviewed and an attempt to introduce semiquantitative characterization of binding for proteins is made. The concept of kinks for complex structures is briefly discussed. Even at sufficiently low supersaturations, the fluctuation of steps may not be sufficient to implement the Gibbs-Thomson law if the kink density is low enough. Subsurface ordering of liquids and growth of rough interfaces from melts is discussed. Crystals growing in microgravity from solution should be more perfect if they preferentially trap stress-inducing impurities, thus creating an impurity-depleted zone around themselves. Evidently, such a zone is developed only around the crystals growing in the absence of convection. Under terrestrial conditions, the self-purified depleted zone is destroyed by convection, the crystal traps more impurity and grows stressed. The stress relief causes mosaicity. In systems containing stress-inducing but poorly trapped impurities, the crystals grown in the absence of convection should be worse than those of their terrestrial counterparts.
Microstructure Evolution of a Single Crystal Nickel-Base Superalloy During Heat Treatment and Creep
YANG Da-yun,JIN Tao; ZHAO Nai-ren; WANG ZHi-hui; SUN Xiao-feng; GUAN Heng-rong; HU Zhuang-qi
2004-01-01
Microstructure evolution of a single crystal nickel-base superalloy during heat treatment and tensile creep at1010℃ and 248 MPa for 30h was observed and analyzed. Internal stresses because of lattice mismatch between γ and γphase provided the driving force for γ shape evolution during heat treatment. More than 65 vol. % distorted cubic γ phase keeping coherency with the γ matrix precipitated after solution at 1295 ℃ for 32h. The shape of γ phase was perfectly cubic with increasing precipitate size during the two-step aging treatment. Due to the applied stress and internal stress field the continuous γ-γ lamellar structure perpendicular to the applied stress was formed after 30h tensile creep.
Crystal growth and structural analysis of zirconium sulphoselenide single crystals
K R Patel; R D Vaidya; M S Dave; S G Patel
2008-08-01
A series of zirconium sulphoselenide (ZrSSe3–, where = 0, 0.5, 1, 1.5, 2, 2.5, 3) single crystals have been grown by chemical vapour transport technique using iodine as a transporting agent. The optimum condition for the growth of these crystals is given. The stoichiometry of the grown crystals were confirmed on the basis of energy dispersive analysis by X-ray (EDAX) and the structural characterization was accomplished by X-ray diffraction (XRD) studies. The crystals are found to possess monoclinic structure. The lattice parameters, volume, particle size and X-ray density have been carried out for these crystals. The effect of sulphur proportion on the lattice parameter, unit cell volume and X-ray density in the series of ZrSSe3– single crystals have been studied and found to decrease in all these parameters with rise in sulphur proportion. The grown crystals were examined under optical zoom microscope for their surface topography study. Hall effect measurements were carried out on grown crystals at room temperature. The negative value of Hall coefficient implies that these crystals are -type in nature. The conductivity is found to decrease with increase of sulphur content in the ZrSSe3– series. The electrical resistivity parallel to c-axis as well as perpendicular to -axis have been carried out in the temperature range 303–423 K. The results obtained are discussed in detail.
Stassis, C.; Zaretsky, J.; Misemer, D. K.;;
1983-01-01
to the propagation of elastic waves. The frequencies of the T1[ξξ0] branch for ξ between approximately 0.5 and 0.8 are slightly above the velocity-of-sound line determined from the low-frequency measurements. Since a similar effect has been observed in FCC Yb, it is natural to assume that the anomalous dispersion......A large single crystal of FCC Ca was grown and was used to study the lattice dynamics of this divalent metal by coherent inelastic neutron scattering. The phonon dispersion curves were measured, at room temperature, along the [ξ00], [ξξ0], [ξξξ], and [0ξ1] symmetry directions. The dispersion curves...... bear a striking resemblance to those of FCC Yb, which is also a divalent metal with an electronic band structure similar to that of Ca. In particular, the shear moduli c44 and (c11-c 12)/2 differ by a factor of 3.4, which implies that FCC Ca (like FCC Yb) is very anisotropic with regard...
Gupta, R.
1998-12-31
The goal of the lectures on lattice QCD (LQCD) is to provide an overview of both the technical issues and the progress made so far in obtaining phenomenologically useful numbers. The lectures consist of three parts. The author`s charter is to provide an introduction to LQCD and outline the scope of LQCD calculations. In the second set of lectures, Guido Martinelli will discuss the progress they have made so far in obtaining results, and their impact on Standard Model phenomenology. Finally, Martin Luescher will discuss the topical subjects of chiral symmetry, improved formulation of lattice QCD, and the impact these improvements will have on the quality of results expected from the next generation of simulations.
Lattice Quantum Chromodynamics
Sachrajda, C. T.
2016-10-01
I review the the application of the lattice formulation of QCD and large-scale numerical simulations to the evaluation of non-perturbative hadronic effects in Standard Model Phenomenology. I present an introduction to the elements of the calculations and discuss the limitations both in the range of quantities which can be studied and in the precision of the results. I focus particularly on the extraction of the QCD parameters, i.e. the quark masses and the strong coupling constant, and on important quantities in flavour physics. Lattice QCD is playing a central role in quantifying the hadronic effects necessary for the development of precision flavour physics and its use in exploring the limits of the Standard Model and in searches for inconsistencies which would signal the presence of new physics.
Lattices of dielectric resonators
Trubin, Alexander
2016-01-01
This book provides the analytical theory of complex systems composed of a large number of high-Q dielectric resonators. Spherical and cylindrical dielectric resonators with inferior and also whispering gallery oscillations allocated in various lattices are considered. A new approach to S-matrix parameter calculations based on perturbation theory of Maxwell equations, developed for a number of high-Q dielectric bodies, is introduced. All physical relationships are obtained in analytical form and are suitable for further computations. Essential attention is given to a new unified formalism of the description of scattering processes. The general scattering task for coupled eigen oscillations of the whole system of dielectric resonators is described. The equations for the expansion coefficients are explained in an applicable way. The temporal Green functions for the dielectric resonator are presented. The scattering process of short pulses in dielectric filter structures, dielectric antennas and lattices of d...
Fractional lattice charge transport
Flach, Sergej; Khomeriki, Ramaz
2017-01-01
We consider the dynamics of noninteracting quantum particles on a square lattice in the presence of a magnetic flux α and a dc electric field E oriented along the lattice diagonal. In general, the adiabatic dynamics will be characterized by Bloch oscillations in the electrical field direction and dispersive ballistic transport in the perpendicular direction. For rational values of α and a corresponding discrete set of values of E(α) vanishing gaps in the spectrum induce a fractionalization of the charge in the perpendicular direction - while left movers are still performing dispersive ballistic transport, the complementary fraction of right movers is propagating in a dispersionless relativistic manner in the opposite direction. Generalizations and the possible probing of the effect with atomic Bose-Einstein condensates and photonic networks are discussed. Zak phase of respective band associated with gap closing regime has been computed and it is found converging to π/2 value. PMID:28102302
Borsanyi, Sz; Kampert, K H; Katz, S D; Kawanai, T; Kovacs, T G; Mages, S W; Pasztor, A; Pittler, F; Redondo, J; Ringwald, A; Szabo, K K
2016-01-01
We present a full result for the equation of state (EoS) in 2+1+1 (up/down, strange and charm quarks are present) flavour lattice QCD. We extend this analysis and give the equation of state in 2+1+1+1 flavour QCD. In order to describe the evolution of the universe from temperatures several hundreds of GeV to several tens of MeV we also include the known effects of the electroweak theory and give the effective degree of freedoms. As another application of lattice QCD we calculate the topological susceptibility (chi) up to the few GeV temperature region. These two results, EoS and chi, can be used to predict the dark matter axion's mass in the post-inflation scenario and/or give the relationship between the axion's mass and the universal axionic angle, which acts as a initial condition of our universe.
Parametric lattice Boltzmann method
Shim, Jae Wan
2017-06-01
The discretized equilibrium distributions of the lattice Boltzmann method are presented by using the coefficients of the Lagrange interpolating polynomials that pass through the points related to discrete velocities and using moments of the Maxwell-Boltzmann distribution. The ranges of flow velocity and temperature providing positive valued distributions vary with regulating discrete velocities as parameters. New isothermal and thermal compressible models are proposed for flows of the level of the isothermal and thermal compressible Navier-Stokes equations. Thermal compressible shock tube flows are simulated by only five on-lattice discrete velocities. Two-dimensional isothermal and thermal vortices provoked by the Kelvin-Helmholtz instability are simulated by the parametric models.
Jipsen, Peter
1992-01-01
The study of lattice varieties is a field that has experienced rapid growth in the last 30 years, but many of the interesting and deep results discovered in that period have so far only appeared in research papers. The aim of this monograph is to present the main results about modular and nonmodular varieties, equational bases and the amalgamation property in a uniform way. The first chapter covers preliminaries that make the material accessible to anyone who has had an introductory course in universal algebra. Each subsequent chapter begins with a short historical introduction which sites the original references and then presents the results with complete proofs (in nearly all cases). Numerous diagrams illustrate the beauty of lattice theory and aid in the visualization of many proofs. An extensive index and bibliography also make the monograph a useful reference work.
Lattice Quantum Chromodynamics
Sachrajda, C T
2016-01-01
I review the the application of the lattice formulation of QCD and large-scale numerical simulations to the evaluation of non-perturbative hadronic effects in Standard Model Phenomenology. I present an introduction to the elements of the calculations and discuss the limitations both in the range of quantities which can be studied and in the precision of the results. I focus particularly on the extraction of the QCD parameters, i.e. the quark masses and the strong coupling constant, and on important quantities in flavour physics. Lattice QCD is playing a central role in quantifying the hadronic effects necessary for the development of precision flavour physics and its use in exploring the limits of the Standard Model and in searches for inconsistencies which would signal the presence of new physics.
Analysis of two-dimensional photonic band gap structure with a rhombus lattice
Limei Qi; Ziqiang Yang; Xi Gao; Zheng Liang
2008-01-01
@@ The relative band gap for a rhombus lattice photonic crystal is studied by plane wave expansion method and high frequency structure simulator (HFSS) simulation. General wave vectors in the first Briliouin zone are derived. The relative band gap as a function of air-filling factor and background material is investigated, respectively, and the nature of photonic band gap for different lattice angles is analyzed by the distribution of electric energy. These results would provide theoretical instruction for designing optical integrated devices using photonic crystal with a rhombus lattice.
International Lattice Data Grid
Davies, C T H; Kenway, R D; Maynard, C M
2002-01-01
We propose the co-ordination of lattice QCD grid developments in different countries to allow transparent exchange of gauge configurations in future, should participants wish to do so. We describe briefly UKQCD's XML schema for labelling and cataloguing the data. A meeting to further develop these ideas will be held in Edinburgh on 19/20 December 2002, and will be available over AccessGrid.