Tuning of magnetic property by lattice strain in lead substituted cobalt ferrite

Energy Technology Data Exchange (ETDEWEB)

Kumar, Rajnish [Department of Physics, Indian Institute of Technology Patna, Bihta, Patna 801103 (India); Singh, Rakesh Kr. [Aryabhatta Center for Nanoscience and Nanotechnology, Aryabhatta Knowledge University, Patna 800001 (India); Zope, Mukesh Kumar [Indira Gandhi Institute of Medical Sciences, Sheikhpura, Patna 800014 (India); Kar, Manoranjan, E-mail: mano@iitp.ac.in [Department of Physics, Indian Institute of Technology Patna, Bihta, Patna 801103 (India)

2017-06-15

Highlights: • Increase of lattice parameter due to Pb substitution in CFO. • Magnetism due to lattice strain in nonmagnetic (Pb) substituted CFO. • Saturation magnetization increases up to 2% Pb concentration. • Magnetocrystalline anisotropy constant increases up to 2% Pb concentration. • Existence of non-collinear spin structure which can be explained by three sublattice model of Yafet and Kittel. - Abstract: Co{sub 1−x}Pb{sub x}Fe{sub 2}O{sub 4} (x = 00–0.15) have been synthesized using citric acid modified sol-gel method. Samples for x ≤ 0.02 have been ball milled to reduce the particle size. Hence, all the materials under the study are in almost equal crystallite size (∼15 nm). The phase purity and structural study have been carried out using X-ray powder diffraction (XRD) technique. The Rietveld refinement of XRD patterns reveals the increasing lattice parameter with the lead (Pb) concentration. Detailed analysis of the Raman spectroscopy data supports the XRD pattern analysis results. Magnetic hysteresis loop measurements have been performed using Vibrating Sample Magnetometer (VSM) at room temperature over field range of ±20 kOe. Magnetocrystalline anisotropy constant was calculated using Law of Approach (LA) to saturation, which shows increasing behavior till 2% Pb concentration. The large difference in experimental and theoretical saturation magnetic moment per formula unit shows existence of three sublattice model suggested by Yafet-Kittel.

Estimation of lattice strain in nanocrystalline RuO2 by Williamson-Hall and size-strain plot methods.

Science.gov (United States)

Sivakami, R; Dhanuskodi, S; Karvembu, R

2016-01-05

RuO2 nanoparticles (RuO2 NPs) have been successfully synthesized by the hydrothermal method. Structure and the particle size have been determined by X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM) and transmission electron microscopy (TEM). UV-Vis spectra reveal that the optical band gap of RuO2 nanoparticles is red shifted from 3.95 to 3.55eV. BET measurements show a high specific surface area (SSA) of 118-133m(2)/g and pore diameter (10-25nm) has been estimated by Barret-Joyner-Halenda (BJH) method. The crystallite size and lattice strain in the samples have been investigated by Williamson-Hall (W-H) analysis assuming uniform deformation, deformation stress and deformation energy density, and the size-strain plot method. All other relevant physical parameters including stress, strain and energy density have been calculated. The average crystallite size and the lattice strain evaluated from XRD measurements are in good agreement with the results of TEM. Copyright © 2015 Elsevier B.V. All rights reserved.

Influence of strain gradients on lattice rotation in nano-indentation experiments: A numerical study

KAUST Repository

Demiral, Murat

2014-07-01

In this paper the texture evolution in nano-indentation experiments was investigated numerically. To achieve this, a three-dimensional implicit finite-element model incorporating a strain-gradient crystal-plasticity theory was developed to represent accurately the deformation of a body-centred cubic metallic material. A hardening model was implemented to account for strain hardening of the involved slip systems. The surface topography around indents in different crystallographic orientations was compared to corresponding lattice rotations. The influence of strain gradients on the prediction of lattice rotations in nano-indentation was critically assessed. © 2014 Elsevier B.V..

Influence of strain gradients on lattice rotation in nano-indentation experiments: A numerical study

KAUST Repository

Demiral, Murat; Roy, Anish; El Sayed, Tamer S.; Silberschmidt, Vadim V.

2014-01-01

In this paper the texture evolution in nano-indentation experiments was investigated numerically. To achieve this, a three-dimensional implicit finite-element model incorporating a strain-gradient crystal-plasticity theory was developed to represent accurately the deformation of a body-centred cubic metallic material. A hardening model was implemented to account for strain hardening of the involved slip systems. The surface topography around indents in different crystallographic orientations was compared to corresponding lattice rotations. The influence of strain gradients on the prediction of lattice rotations in nano-indentation was critically assessed. © 2014 Elsevier B.V..

Comment on 'Magic strains in face-centered and body-centered cubic lattices'

Energy Technology Data Exchange (ETDEWEB)

Waal, B.W. van de (Technische Hogeschool Twente, Enschede (Netherlands). Dept. of Physics)

1990-03-01

The six symmetry-related so-called magic strain tensors that transform a f.c.c. lattice (or a b.c.c. lattice) into itself, which have been reported recently by Boyer are not unique: An infinite number of displacement tensors can be constructed that transform one lattice into another, or into itself. There is no connection with fivefold symmetry, other than that in any f.c.c. crystal. (orig.).

Thickness dependent properties of CMR Manganite thin films on lattice mismatched substrates: Distinguishing Strain and Interface Effects

Science.gov (United States)

Davidson, Anthony, III; Kolagani, Rajeswari; Bacharova, Ellisaveta; Yong, Grace; Smolyaninova, Vera; Schaefer, David; Mundle, Rajeh

2007-03-01

Epitaxial thin films of CMR manganite materials have been known to show thickness dependent electrical and magnetic properties on lattice mismatched substrates. Below a critical thickness, insulator-metal transition is suppressed. These effects have been largely attributed to the role of bi-axial lattice mismatch strain. Our recent results of epitaxial thin films of La0.67Ca0.33MnO3 (LCMO) on two substrates with varying degrees of compressive lattice mismatch indicate that, in addition to the effect of lattice mismatch strain, the thickness dependence of the properties are influenced by other factors possibly related to the nature of the film substrate interface and defects such as twin boundaries. We have compared the properties of LCMO films on (100) oriented LaAlO3 and (001) oriented NdCaAlO4 both of which induce compressive bi-axial strain. Interestingly, the suppression of the insulator-metal transition is less in films on NCAO which has a larger lattice mismatch. We will present results correlating the electrical and magneto transport properties with the structure and morphology of the films.

Lattice strain accompanying the colossal magnetoresistance effect in EuB6.

Science.gov (United States)

Manna, Rudra Sekhar; Das, Pintu; de Souza, Mariano; Schnelle, Frank; Lang, Michael; Müller, Jens; von Molnár, Stephan; Fisk, Zachary

2014-08-08

The coupling of magnetic and electronic degrees of freedom to the crystal lattice in the ferromagnetic semimetal EuB(6), which exhibits a complex ferromagnetic order and a colossal magnetoresistance effect, is studied by high-resolution thermal expansion and magnetostriction experiments. EuB(6) may be viewed as a model system, where pure magnetism-tuned transport and the response of the crystal lattice can be studied in a comparatively simple environment, i.e., not influenced by strong crystal-electric field effects and Jahn-Teller distortions. We find a very large lattice response, quantified by (i) the magnetic Grüneisen parameter, (ii) the spontaneous strain when entering the ferromagnetic region, and (iii) the magnetostriction in the paramagnetic temperature regime. Our analysis reveals that a significant part of the lattice effects originates in the magnetically driven delocalization of charge carriers, consistent with the scenario of percolating magnetic polarons. A strong effect of the formation and dynamics of local magnetic clusters on the lattice parameters is suggested to be a general feature of colossal magnetoresistance materials.

Unique Piezoelectric Properties of the Monoclinic Phase in Pb (Zr ,Ti )O3 Ceramics: Large Lattice Strain and Negligible Domain Switching

Science.gov (United States)

Fan, Longlong; Chen, Jun; Ren, Yang; Pan, Zhao; Zhang, Linxing; Xing, Xianran

2016-01-01

The origin of the excellent piezoelectric properties at the morphotropic phase boundary is generally attributed to the existence of a monoclinic phase in various piezoelectric systems. However, there exist no experimental studies that reveal the role of the monoclinic phase in the piezoelectric behavior in phase-pure ceramics. In this work, a single monoclinic phase has been identified in Pb (Zr ,Ti )O3 ceramics at room temperature by in situ high-energy synchrotron x-ray diffraction, and its response to electric field has been characterized for the first time. Unique piezoelectric properties of the monoclinic phase in terms of large intrinsic lattice strain and negligible domain switching have been observed. The extensional strain constant d33 and the transverse strain constant d31 are calculated to be 520 and -200 pm /V , respectively. These large piezoelectric coefficients are mainly due to the large intrinsic lattice strain, with very little extrinsic contribution from domain switching. The unique properties of the monoclinic phase provide new insights into the mechanisms responsible for the piezoelectric properties at the morphotropic phase boundary.

Unique Piezoelectric Properties of the Monoclinic Phase in Pb(Zr,Ti)O_{3} Ceramics: Large Lattice Strain and Negligible Domain Switching.

Science.gov (United States)

Fan, Longlong; Chen, Jun; Ren, Yang; Pan, Zhao; Zhang, Linxing; Xing, Xianran

2016-01-15

The origin of the excellent piezoelectric properties at the morphotropic phase boundary is generally attributed to the existence of a monoclinic phase in various piezoelectric systems. However, there exist no experimental studies that reveal the role of the monoclinic phase in the piezoelectric behavior in phase-pure ceramics. In this work, a single monoclinic phase has been identified in Pb(Zr,Ti)O_{3} ceramics at room temperature by in situ high-energy synchrotron x-ray diffraction, and its response to electric field has been characterized for the first time. Unique piezoelectric properties of the monoclinic phase in terms of large intrinsic lattice strain and negligible domain switching have been observed. The extensional strain constant d_{33} and the transverse strain constant d_{31} are calculated to be 520 and -200  pm/V, respectively. These large piezoelectric coefficients are mainly due to the large intrinsic lattice strain, with very little extrinsic contribution from domain switching. The unique properties of the monoclinic phase provide new insights into the mechanisms responsible for the piezoelectric properties at the morphotropic phase boundary.

Lattice strain induced multiferroicity in PZT-CFO particulate composite

Science.gov (United States)

Pradhan, Lagen Kumar; Pandey, Rabichandra; Kumar, Rajnish; Kar, Manoranjan

2018-02-01

Lead Zirconate Titanate [Pb(Zr0.52Ti0.48)O3/PZT] and Cobalt Ferrite [CoFe2O4/CFO] based multiferroic composites [(1-x)PZT-(x)CFO] with (x = 0.10-0.40) have been prepared to study its magnetoelectric (ME) and multiferroic properties. X-ray diffraction method along with the Rietveld refinement technique reveals that the crystal symmetries corresponding to PZT and CFO exist independently in the composites. The effect of interfacial strain on lattice distortion in PZT has been observed. It is well correlated with the magnetoelectric coupling of the composites. Dispersion behavior of dielectric constant with frequency can be explained by the modified Debye model. Different relaxation phenomena have been observed in PZT-CFO particulate composites. The ferroelectric properties of composites decrease with the increase in percentage of CFO in the composite. Both saturation (Ms) and remanent (Mr) magnetization increase with the increase in CFO content in the composite. The maximum ME coupling was found to be 1.339 pC/cm2 Oe for the composition (0.80) PZT-(0.20) CFO at the application of maximum magnetic field of 50 Oe. The multiferroic properties in CFO-PZT can be explained by the lattice strain at the CFO-PZT interfaces.

Study of lattice strain evolution during biaxial deformation of stainless steel using a finite element and fast Fourier transform based multi-scale approach

International Nuclear Information System (INIS)

Upadhyay, M.V.; Van Petegem, S.; Panzner, T.; Lebensohn, R.A.; Van Swygenhoven, H.

2016-01-01

A multi-scale elastic-plastic finite element and fast Fourier transform based approach is proposed to study lattice strain evolution during uniaxial and biaxial loading of stainless steel cruciform shaped samples. At the macroscale, finite element simulations capture the complex coupling between applied forces in the arms and gauge stresses induced by the cruciform geometry. The predicted gauge stresses are used as macroscopic boundary conditions to drive a mesoscale elasto-viscoplastic fast Fourier transform model, from which lattice strains are calculated for particular grain families. The calculated lattice strain evolution matches well with experimental values from in-situ neutron diffraction measurements and demonstrates that the spread in lattice strain evolution between different grain families decreases with increasing biaxial stress ratio. During equibiaxial loading, the model reveals that the lattice strain evolution in all grain families, and not just the 311 grain family, is representative of the polycrystalline response. A detailed quantitative analysis of the 200 and 220 grain family reveals that the contribution of elastic and plastic anisotropy to the lattice strain evolution significantly depends on the applied stress ratio.

Determination of lattice parameters, strain state and composition in semipolar III-nitrides using high resolution X-ray diffraction

Energy Technology Data Exchange (ETDEWEB)

Frentrup, Martin, E-mail: frentrup@physik.tu-berlin.de; Wernicke, Tim; Stellmach, Joachim; Kneissl, Michael [Institute of Solid State Physics, Technische Universität Berlin, Hardenbergstr. 36, 10623 Berlin (Germany); Hatui, Nirupam; Bhattacharya, Arnab [Department of Condensed Matter Physics and Materials Science, Tata Institute of Fundamental Research, Homi Bhabha Road, Mumbai 400005 (India)

2013-12-07

In group-III-nitride heterostructures with semipolar or nonpolar crystal orientation, anisotropic lattice and thermal mismatch with the buffer or substrate lead to a complex distortion of the unit cells, e.g., by shearing of the lattice. This makes an accurate determination of lattice parameters, composition, and strain state under assumption of the hexagonal symmetry impossible. In this work, we present a procedure to accurately determine the lattice constants, strain state, and composition of semipolar heterostructures using high resolution X-ray diffraction. An analysis of the unit cell distortion shows that four independent lattice parameters are sufficient to describe this distortion. Assuming only small deviations from an ideal hexagonal structure, a linear expression for the interplanar distances d{sub hkl} is derived. It is used to determine the lattice parameters from high resolution X-ray diffraction 2ϑ-ω-scans of multiple on- and off-axis reflections via a weighted least-square fit. The strain and composition of ternary alloys are then evaluated by transforming the elastic parameters (using Hooke's law) from the natural crystal-fixed coordinate system to a layer-based system, given by the in-plane directions and the growth direction. We illustrate our procedure taking an example of (112{sup ¯}2) Al{sub κ}Ga{sub 1−κ}N epilayers with Al-contents over the entire composition range. We separately identify the in-plane and out-of-plane strains and discuss origins for the observed anisotropy.

An assessment of the lattice strain in the CrMnFeCoNi high-entropy alloy

International Nuclear Information System (INIS)

Owen, L.R.; Pickering, E.J.; Playford, H.Y.; Stone, H.J.; Tucker, M.G.; Jones, N.G.

2017-01-01

The formation of single phase solid solutions from combinations of multiple principal elements, with differing atomic radii, has led to the suggestion that the lattices of high-entropy alloys (HEAs) must be severely distorted. To assess this hypothesis, total scattering measurements using neutron radiation have been performed on the CrMnFeCoNi alloy and compared with similar data from five compositionally simpler materials within the same system. The Bragg diffraction patterns from all of the studied materials were similar, consistent with a face-centered cubic structure, and none showed the pronounced dampening that would be expected from a highly distorted lattice. A more detailed evaluation of the local lattice strain was made by considering the first six coordination shells in the pair distribution functions (PDF), obtained from the total scattering data. Across this range, the HEA exhibited the broadest PDF peaks but these widths were not disproportionately larger than those of the simpler alloys. In addition, of all the materials considered, the HEA was at the highest homologous temperature, and hence the thermal vibrations of the atoms would be greatest. Consequently, the level of local lattice strain required to rationalise a given PDF peak width would be reduced. As a result, the data presented in this study do not indicate that the local lattice strain in the equiatomic CrMnFeCoNi HEA is anomalously large.

Systematic design of 3D auxetic lattice materials with programmable Poisson's ratio for finite strains

Science.gov (United States)

Wang, Fengwen

2018-05-01

This paper presents a systematic approach for designing 3D auxetic lattice materials, which exhibit constant negative Poisson's ratios over large strain intervals. A unit cell model mimicking tensile tests is established and based on the proposed model, the secant Poisson's ratio is defined as the negative ratio between the lateral and the longitudinal engineering strains. The optimization problem for designing a material unit cell with a target Poisson's ratio is formulated to minimize the average lateral engineering stresses under the prescribed deformations. Numerical results demonstrate that 3D auxetic lattice materials with constant Poisson's ratios can be achieved by the proposed optimization formulation and that two sets of material architectures are obtained by imposing different symmetry on the unit cell. Moreover, inspired by the topology-optimized material architecture, a subsequent shape optimization is proposed by parametrizing material architectures using super-ellipsoids. By designing two geometrical parameters, simple optimized material microstructures with different target Poisson's ratios are obtained. By interpolating these two parameters as polynomial functions of Poisson's ratios, material architectures for any Poisson's ratio in the interval of ν ∈ [ - 0.78 , 0.00 ] are explicitly presented. Numerical evaluations show that interpolated auxetic lattice materials exhibit constant Poisson's ratios in the target strain interval of [0.00, 0.20] and that 3D auxetic lattice material architectures with programmable Poisson's ratio are achievable.

On the evolution and modelling of lattice strains during the cyclic loading of TWIP steel

International Nuclear Information System (INIS)

Saleh, Ahmed A.; Pereloma, Elena V.; Clausen, Bjørn; Brown, Donald W.; Tomé, Carlos N.; Gazder, Azdiar A.

2013-01-01

The evolution of lattice strains in fully annealed Fe–24Mn–3Al–2Si–1Ni–0.06C twinning-induced plasticity (TWIP) steel is investigated via in situ neutron diffraction during cyclic (tension–compression) loading between strain limits of ±1%. The pronounced Bauschinger effect observed upon load reversal is accounted for by a combination of the intergranular residual stresses and the intragranular sources of back stress, such as dislocation pile-ups at the intersection of stacking faults. The recently modified elasto-plastic self-consistent (EPSC) model which empirically accounts for both intergranular and intragranular back stresses has been successfully used to simulate the macroscopic stress–strain response and the evolution of the lattice strains. The EPSC model captures the experimentally observed tension–compression asymmetry as it accounts for the directionality of twinning as well as Schmid factor considerations. For the strain limits used in this study, the EPSC model also predicts that the lower flow stress on reverse shear loading reported in earlier Bauschinger-type experiments on TWIP steel is a geometrical or loading path effect

Strain-induced topological magnon phase transitions: applications to kagome-lattice ferromagnets

Science.gov (United States)

Owerre, S. A.

2018-06-01

A common feature of topological insulators is that they are characterized by topologically invariant quantity such as the Chern number and the index. This quantity distinguishes a nontrivial topological system from a trivial one. A topological phase transition may occur when there are two topologically distinct phases, and it is usually defined by a gap closing point where the topologically invariant quantity is ill-defined. In this paper, we show that the magnon bands in the strained (distorted) kagome-lattice ferromagnets realize an example of a topological magnon phase transition in the realistic parameter regime of the system. When spin–orbit coupling (SOC) is neglected (i.e. no Dzyaloshinskii–Moriya interaction), we show that all three magnon branches are dispersive with no flat band, and there exists a critical point where tilted Dirac and semi-Dirac point coexist in the magnon spectra. The critical point separates two gapless magnon phases as opposed to the usual phase transition. Upon the inclusion of SOC, we realize a topological magnon phase transition point at the critical strain , where D and J denote the perturbative SOC and the Heisenberg spin exchange interaction respectively. It separates two distinct topological magnon phases with different Chern numbers for and for . The associated anomalous thermal Hall conductivity develops an abrupt change at , due to the divergence of the Berry curvature in momentum space. The proposed topological magnon phase transition is experimentally feasible by applying external perturbations such as uniaxial strain or pressure.

New position of Dirac points in the strained graphene reciprocal lattice

Directory of Open Access Journals (Sweden)

Cui-Lian Li

2014-08-01

Full Text Available In the strained graphene, Fermi velocity shows space-dependent and it changes as the position of Dirac point shifts. In this paper, we apply the tight-binding approach within linear elasticity theory to investigate the shifting of Dirac points in the strained graphene reciprocal lattice space. Based on this, we derive the analytical expression on the new positions of the Dirac points as the strain parameter varies. Comparing the data from our analytical expression, ones from Eq. (20 in Phys. Rev. B 80, 045401 (2009, and those from numerical calculation, we find that our analytical expression raises the effective prediction range of the strain parameter from 3% to 15%. i.e., our analytical expression is practicable until the strain parameter is larger than 15%. This almost includes the whole range where the Dirac points present and the energy gap is zero. Moreover, we further calculate the energy gap by numerical method when the shear strain parameter varies from 0 to 20%, and find that the energy gap can not open until the strain parameter is larger than 16%. After this, the energy gap open and the Dirac points disappear.

Lattice distortion and strain relaxation in epitaxial thin films of multiferroic TbMnO3 probed by X-ray diffractometry and micro-Raman spectroscopy

Science.gov (United States)

Hu, Y.; Stender, D.; Medarde, M.; Lippert, T.; Wokaun, A.; Schneider, C. W.

2013-08-01

A detailed structural XRD analysis of (1 1 0)-oriented TbMnO3 thin films grown on (1 1 0)-YAlO3 substrates shows the co-existence of a strained and relaxed "sublayer" within the films due to strain relaxation during epitaxial growth by pulsed laser deposition. The substrate-film lattice mismatch yields a compressive strain anisotropy along the two in-plane directions, i.e. [1 -1 0] and [0 0 1] and a monoclinic distortion. A further manifestation of the growth-induced strain is the hardening of Raman active modes as a result of changed atomic motions along the [1 -1 0] and [0 0 1] directions.

Digital Image Correlation of 2D X-ray Powder Diffraction Data for Lattice Strain Evaluation

Science.gov (United States)

Zhang, Hongjia; Sui, Tan; Daisenberger, Dominik; Fong, Kai Soon

2018-01-01

High energy 2D X-ray powder diffraction experiments are widely used for lattice strain measurement. The 2D to 1D conversion of diffraction patterns is a necessary step used to prepare the data for full pattern refinement, but is inefficient when only peak centre position information is required for lattice strain evaluation. The multi-step conversion process is likely to lead to increased errors associated with the ‘caking’ (radial binning) or fitting procedures. A new method is proposed here that relies on direct Digital Image Correlation analysis of 2D X-ray powder diffraction patterns (XRD-DIC, for short). As an example of using XRD-DIC, residual strain values along the central line in a Mg AZ31B alloy bar after 3-point bending are calculated by using both XRD-DIC and the conventional ‘caking’ with fitting procedures. Comparison of the results for strain values in different azimuthal angles demonstrates excellent agreement between the two methods. The principal strains and directions are calculated using multiple direction strain data, leading to full in-plane strain evaluation. It is therefore concluded that XRD-DIC provides a reliable and robust method for strain evaluation from 2D powder diffraction data. The XRD-DIC approach simplifies the analysis process by skipping 2D to 1D conversion, and opens new possibilities for robust 2D powder diffraction data analysis for full in-plane strain evaluation. PMID:29543728

Digital Image Correlation of 2D X-ray Powder Diffraction Data for Lattice Strain Evaluation

Directory of Open Access Journals (Sweden)

Hongjia Zhang

2018-03-01

Full Text Available High energy 2D X-ray powder diffraction experiments are widely used for lattice strain measurement. The 2D to 1D conversion of diffraction patterns is a necessary step used to prepare the data for full pattern refinement, but is inefficient when only peak centre position information is required for lattice strain evaluation. The multi-step conversion process is likely to lead to increased errors associated with the ‘caking’ (radial binning or fitting procedures. A new method is proposed here that relies on direct Digital Image Correlation analysis of 2D X-ray powder diffraction patterns (XRD-DIC, for short. As an example of using XRD-DIC, residual strain values along the central line in a Mg AZ31B alloy bar after 3-point bending are calculated by using both XRD-DIC and the conventional ‘caking’ with fitting procedures. Comparison of the results for strain values in different azimuthal angles demonstrates excellent agreement between the two methods. The principal strains and directions are calculated using multiple direction strain data, leading to full in-plane strain evaluation. It is therefore concluded that XRD-DIC provides a reliable and robust method for strain evaluation from 2D powder diffraction data. The XRD-DIC approach simplifies the analysis process by skipping 2D to 1D conversion, and opens new possibilities for robust 2D powder diffraction data analysis for full in-plane strain evaluation.

submitter Digital Image Correlation of 2D X-ray Powder Diffraction Data for Lattice Strain Evaluation

CERN Document Server

Zhang, Hongjia; Salvati, Enrico; Daisenberger, Dominik; Lunt, Alexander J G; Fong, Kai Soon; Song, Xu; Korsunsky, Alexander M

2018-01-01

High energy 2D X-ray powder diffraction experiments are widely used for lattice strain measurement. The 2D to 1D conversion of diffraction patterns is a necessary step used to prepare the data for full pattern refinement, but is inefficient when only peak centre position information is required for lattice strain evaluation. The multi-step conversion process is likely to lead to increased errors associated with the ‘caking’ (radial binning) or fitting procedures. A new method is proposed here that relies on direct Digital Image Correlation analysis of 2D X-ray powder diffraction patterns (XRD-DIC, for short). As an example of using XRD-DIC, residual strain values along the central line in a Mg AZ31B alloy bar after 3-point bending are calculated by using both XRD-DIC and the conventional ‘caking’ with fitting procedures. Comparison of the results for strain values in different azimuthal angles demonstrates excellent agreement between the two methods. The principal strains and directions are calculated...

Applied strain dependence of critical current and internal lattice strain for BaHfO_3-doped GdBa_2Cu_3O_y coated conductors

International Nuclear Information System (INIS)

Usami, Takashi; Yoshida, Yutaka; Ichino, Yusuke; Sugano, Michinaka; Machiya, Shutaro; Ibi, Akira; Izumi, Teruo

2016-01-01

The strain effect of REBa_2Cu_3O_y (REBCO: RE = Y, Gd, Sm)-coated conductors (CCs) on critical current (I_c) is one of the most fundamental factors for superconducting coil applications. In this study, we aim to clarify the effect of artificial pinning center shapes on the strain effect in BHO-doped GdBCO CCs. To achieve this, we fabricated a Pure-GdBCO CC, a BHO nanorod-doped GdBCO CC and a multilayered-GdBCO (ML-GdBCO) CC, and carried out bending tests. As the result, the strain dependence of I_c for each CC showed an upward convex and the peak strain of the BHO-doped GdBCO CC shifts towards the compressive strain independent of the BHO shapes. In addition, the strain sensitivity of I_c in the GdBCO CCs including BHO becomes smaller. To clarify the difference between the strain sensitivity of I_c and the peak strain among the CCs, we evaluated the residual strain and the slopes of the internal lattice strains against the applied tensile strain (β). From this measurement, the residual strains for the Pure-GdBCO CC and the ML-GdBCO CC were almost the same. In addition, there was no change in the β value between the Pure-GdBCO and ML-GdBCO CCs. These results suggest that the changes in peak strain and strain sensitivity were not related to the internal lattice strain. (author)

Strain evolution in Si substrate due to implantation of MeV ion observed by extremely asymmetric x-ray diffraction

International Nuclear Information System (INIS)

Emoto, T.; Ghatak, J.; Satyam, P. V.; Akimoto, K.

2009-01-01

We studied the strain introduced in a Si(111) substrate due to MeV ion implantation using extremely asymmetric x-ray diffraction and measured the rocking curves of asymmetrical 113 diffraction for the Si substrates implanted with a 1.5 MeV Au 2+ ion at fluence values of 1x10 13 , 5x10 13 , and 1x10 14 /cm 2 . The measured curves consisted of a bulk peak and accompanying subpeak with an interference fringe. The positional relationship of the bulk peak to the subpeak and the intensity variation of those peaks with respect to the wavelengths of the x rays indicated that crystal lattices near the surface were strained; the lattice spacing of surface normal (111) planes near the surface was larger than that of the bulk. Detailed strain profiles along the depth direction were successfully estimated using a curve-fitting method based on Darwin's dynamical diffraction theory. Comparing the shapes of resultant strain profiles, we found that a strain evolution rapidly occurred within a depth of ∼300 nm at fluence values between 1x10 13 and 5x10 13 /cm 2 . This indicates that formation of the complex defects progressed near the surface when the fluence value went beyond a critical value between 1x10 13 and 5x10 13 /cm 2 and the defects brought a large strain to the substrate.

Change in lattice parameter of tantalum due to dissolved hydrogen

Directory of Open Access Journals (Sweden)

Gyanendra P. Tiwari

2012-06-01

Full Text Available The volume expansion of tantalum due to the dissolved hydrogen has been determined using Bragg equation. The hydrogen was dissolved in the pure tantalum metal at constant temperature (360 °C and constant pressure (132 mbar by varying the duration of hydrogen charging. The amount of dissolved hydrogen was within the solid solubility limit. The samples with different hydrogen concentration were analyzed by X-ray diffraction technique. Slight peak shifts as well as peak broadening were observed. The relative changes of lattice parameters plotted against the hydrogen concentration revealed that the lattice parameters varied linearly with the hydrogen concentration.

Effect of epitaxial strain and lattice mismatch on magnetic and transport behaviors in metamagnetic FeRh thin films

Science.gov (United States)

Xie, Yali; Zhan, Qingfeng; Shang, Tian; Yang, Huali; Wang, Baomin; Tang, Jin; Li, Run-Wei

2017-05-01

We grew 80 nm FeRh films on different single crystals with various lattice constants. FeRh films on SrTiO3 (STO) and MgO substrates exhibit an epitaxial growth of 45° in-plane structure rotation. In contrast, FeRh on LaAlO3 (LAO) displays a mixed epitaxial growth of both 45° in-plane structure rotation and cube-on-cube relationships. Due to the different epitaxial growth strains and lattice mismatch values, the critical temperature for the magnetic phase transition of FeRh can be changed between 405 and 360 K. In addition, the external magnetic field can shift this critical temperature to low temperature in different rates for FeRh films grown on different substrates. The magnetoresistance appears a maximum value at different temperatures between 320 and 380 K for FeRh films grown on different substrates.

Effect of epitaxial strain and lattice mismatch on magnetic and transport behaviors in metamagnetic FeRh thin films

Directory of Open Access Journals (Sweden)

Yali Xie

2017-05-01

Full Text Available We grew 80 nm FeRh films on different single crystals with various lattice constants. FeRh films on SrTiO3 (STO and MgO substrates exhibit an epitaxial growth of 45° in-plane structure rotation. In contrast, FeRh on LaAlO3 (LAO displays a mixed epitaxial growth of both 45° in-plane structure rotation and cube-on-cube relationships. Due to the different epitaxial growth strains and lattice mismatch values, the critical temperature for the magnetic phase transition of FeRh can be changed between 405 and 360 K. In addition, the external magnetic field can shift this critical temperature to low temperature in different rates for FeRh films grown on different substrates. The magnetoresistance appears a maximum value at different temperatures between 320 and 380 K for FeRh films grown on different substrates.

Lattice distortion and strain relaxation in epitaxial thin films of multiferroic TbMnO{sub 3} probed by X-ray diffractometry and micro-Raman spectroscopy

Energy Technology Data Exchange (ETDEWEB)

Hu, Y.; Stender, D. [Paul Scherrer Institute, General Energy Research Department, 5232 Villigen-PSI (Switzerland); Medarde, M. [Paul Scherrer Institute, Laboratory for Developments and Methods, 5232 Villigen-PSI (Switzerland); Lippert, T., E-mail: thomas.lippert@psi.ch [Paul Scherrer Institute, General Energy Research Department, 5232 Villigen-PSI (Switzerland); Wokaun, A.; Schneider, C.W. [Paul Scherrer Institute, General Energy Research Department, 5232 Villigen-PSI (Switzerland)

2013-08-01

A detailed structural XRD analysis of (1 1 0)-oriented TbMnO{sub 3} thin films grown on (1 1 0)-YAlO{sub 3} substrates shows the co-existence of a strained and relaxed “sublayer” within the films due to strain relaxation during epitaxial growth by pulsed laser deposition. The substrate-film lattice mismatch yields a compressive strain anisotropy along the two in-plane directions, i.e. [1 −1 0] and [0 0 1] and a monoclinic distortion. A further manifestation of the growth-induced strain is the hardening of Raman active modes as a result of changed atomic motions along the [1 −1 0] and [0 0 1] directions.

In Situ Investigation of the Evolution of Lattice Strain and Stresses in Austenite and Martensite During Quenching and Tempering of Steel

DEFF Research Database (Denmark)

Villa, M.; Niessen, F.; Somers, M. A. J.

2018-01-01

Energy dispersive synchrotron X-ray diffraction was applied to investigate in situ the evolution of lattice strains and stresses in austenite and martensite during quenching and tempering of a soft martensitic stainless steel. In one experiment, lattice strains in austenite and martensite were...... measured in situ in the direction perpendicular to the sample surface during an austenitization, quenching, and tempering cycle. In a second experiment, the sin2ψ method was applied in situ during the austenite-to-martensite transformation to distinguish between macro- and phase-specific micro......-stresses and to follow the evolution of these stresses during transformation. Martensite formation evokes compressive stress in austenite that is balanced by tensile stress in martensite. Tempering to 748 K (475 °C) leads to partial relaxation of these stresses. Additionally, data reveal that (elastic) lattice strain...

Great Disparity in Photoluminesence Quantum Yields of Colloidal CsPbBr3 Nanocrystals with Varied Shape: The Effect of Crystal Lattice Strain.

Science.gov (United States)

Zhao, Jiangtao; Liu, Mei; Fang, Li; Jiang, Shenlong; Zhou, Jingtian; Ding, Huaiyi; Huang, Hongwen; Wen, Wen; Luo, Zhenlin; Zhang, Qun; Wang, Xiaoping; Gao, Chen

2017-07-06

Understanding the big discrepancy in the photoluminesence quantum yields (PLQYs) of nanoscale colloidal materials with varied morphologies is of great significance to its property optimization and functional application. Using different shaped CsPbBr 3 nanocrystals with the same fabrication processes as model, quantitative synchrotron radiation X-ray diffraction analysis reveals the increasing trend in lattice strain values of the nanocrystals: nanocube, nanoplate, nanowire. Furthermore, transient spectroscopic measurements reveal the same trend in the defect quantities of these nanocrystals. These experimental results unambiguously point out that large lattice strain existing in CsPbBr 3 nanoparticles induces more crystal defects and thus decreases the PLQY, implying that lattice strain is a key factor other than the surface defect to dominate the PLQY of colloidal photoluminesence materials.

38 CFR 4.58 - Arthritis due to strain.

Science.gov (United States)

2010-07-01

... 38 Pensions, Bonuses, and Veterans' Relief 1 2010-07-01 2010-07-01 false Arthritis due to strain... FOR RATING DISABILITIES Disability Ratings The Musculoskeletal System § 4.58 Arthritis due to strain. With service incurred lower extremity amputation or shortening, a disabling arthritis, developing in...

Mechanically Strain-Induced Modification of Selenium Powders in the Amorphization Process

International Nuclear Information System (INIS)

Fuse, Makoto; Shirakawa, Yoshiyuki; Shimosaka, Atsuko; Hidaka, Jusuke

2003-01-01

For the fabrication of particles designed in the nanoscale structure, or the nanostructural modification of particles using mechanical grinding process, selenium powders ground by a planetary ball mill at various rotational speeds have been investigated. Structural analyses, such as particle size distributions, crystallite sizes, lattice strains and nearest neighbour distances were performed using X-ray diffraction, scanning electron microscopy and dynamical light scattering.By grinding powder particles became spherical composites consisting of nanocrystalline and amorphous phase, and had a distribution with the average size of 2.7 μm. Integral intensities of diffraction peaks of annealed crystal selenium decreased with increasing grinding time, and these peaks broadened due to lattice strains and reducing crystallite size during the grinding. The ground powder at 200 rpm did not have the lattice strain and showed amorphization for the present grinding periods. It indicates that the amorphization of Se by grinding accompanies the lattice strain, and the lattice strain arises from a larger energy concerning intermolecular interaction. In this process, the impact energy is spent on thermal and structural changes according to energy accumulation in macroscopic (the particle size distribution) and microscopic (the crystallite size and the lattice strain) range

The Role of Hydrogen-Enhanced Strain-Induced Lattice Defects on Hydrogen Embrittlement Susceptibility of X80 Pipeline Steel

Science.gov (United States)

Hattori, M.; Suzuki, H.; Seko, Y.; Takai, K.

2017-08-01

Studies to date have not completely determined the factors influencing hydrogen embrittlement of ferrite/bainite X80 pipeline steel. Hydrogen embrittlement susceptibility was evaluated based on fracture strain in tensile testing. We conducted a thermal desorption analysis to measure the amount of tracer hydrogen corresponding to that of lattice defects. Hydrogen embrittlement susceptibility and the amount of tracer hydrogen significantly increased with decreasing crosshead speed. Additionally, a significant increase in the formation of hydrogen-enhanced strain-induced lattice defects was observed immediately before the final fracture. In contrast to hydrogen-free specimens, the fracture surface of the hydrogen-charged specimens exhibited shallower dimples without nuclei, such as secondary phase particles. These findings indicate that the presence of hydrogen enhanced the formation of lattice defects, particularly just prior to the occurrence of final fracture. This in turn enhanced the formation of shallower dimples, thereby potentially causing premature fracture of X80 pipeline steel at lower crosshead speeds.

Growth, characterization and estimation of lattice strain and size in CdS nanoparticles: X-ray peak profile analysis

Science.gov (United States)

Solanki, Rekha Garg; Rajaram, Poolla; Bajpai, P. K.

2018-05-01

This work is based on the growth, characterization and estimation of lattice strain and crystallite size in CdS nanoparticles by X-ray peak profile analysis. The CdS nanoparticles were synthesized by a non-aqueous solvothermal method and were characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), Raman and UV-visible spectroscopy. XRD confirms that the CdS nanoparticles have the hexagonal structure. The Williamson-Hall (W-H) method was used to study the X-ray peak profile analysis. The strain-size plot (SSP) was used to study the individual contributions of crystallite size and lattice strain from the X-rays peaks. The physical parameters such as strain, stress and energy density values were calculated using various models namely, isotropic strain model, anisotropic strain model and uniform deformation energy density model. The particle size was estimated from the TEM images to be in the range of 20-40 nm. The Raman spectrum shows the characteristic optical 1LO and 2LO vibrational modes of CdS. UV-visible absorption studies show that the band gap of the CdS nanoparticles is 2.48 eV. The results show that the crystallite size estimated from Scherrer's formula, W-H plots, SSP and the particle size calculated by TEM images are approximately similar.

In Situ Investigation of the Evolution of Lattice Strain and Stresses in Austenite and Martensite During Quenching and Tempering of Steel

Science.gov (United States)

Villa, M.; Niessen, F.; Somers, M. A. J.

2018-01-01

Energy dispersive synchrotron X-ray diffraction was applied to investigate in situ the evolution of lattice strains and stresses in austenite and martensite during quenching and tempering of a soft martensitic stainless steel. In one experiment, lattice strains in austenite and martensite were measured in situ in the direction perpendicular to the sample surface during an austenitization, quenching, and tempering cycle. In a second experiment, the sin2 ψ method was applied in situ during the austenite-to-martensite transformation to distinguish between macro- and phase-specific micro-stresses and to follow the evolution of these stresses during transformation. Martensite formation evokes compressive stress in austenite that is balanced by tensile stress in martensite. Tempering to 748 K (475 °C) leads to partial relaxation of these stresses. Additionally, data reveal that (elastic) lattice strain in austenite is not hydrostatic but hkl dependent, which is ascribed to plastic deformation of this phase during martensite formation and is considered responsible for anomalous behavior of the 200 γ reflection.

Strain Engineering for Phosphorene: The Potential Application as a Photocatalyst

OpenAIRE

Sa, Baisheng; Li, Yan-Ling; Qi, Jingshan; Ahuja, Rajeev; Sun, Zhimei

2014-01-01

Phosphorene has been attracted intense interest due to its unexpected high carrier mobility and distinguished anisotropic optoelectronic and electronic properties. In this work, we unraveled strain engineered phosphorene as a photocatalyst in the application of water splitting hydrogen production based on density functional theory calculations. Lattice dynamic calculations demonstrated the stability for such kind of artificial materials under different strains. The phosphorene lattice is unst...

Evaluation of carbon incorporation and strain of doped MgB2 superconductor by Raman spectroscopy

International Nuclear Information System (INIS)

Yeoh, W.K.; Zheng, R.K.; Ringer, S.P.; Li, W.X.; Xu, X.; Dou, S.X.; Chen, S.K.; MacManus-Driscoll, J.L.

2011-01-01

Raman spectroscopy is employed to study both the strain and the carbon substitution level in SiC-doped MgB 2 bulk samples. Raman spectroscopy was demonstrated to be a better method to distinguish the individual influences of strain and carbon than standard X-ray diffraction. It is found that the lattice parameter correlation method for C content determination is invalid for highly strained samples. Our result also provides an alternative explanation for lattice variation in non-carbon-doped MgB 2 , which is basically due to lattice strain.

Defect luminescence and lattice strain in Mn{sup 2+} doped ZnGa{sub 2}O{sub 4}

Energy Technology Data Exchange (ETDEWEB)

Somasundaram, K.; Abhilash, K.P. [Department of Physics, Nallamuthu Gounder Mahalingam College, Pollachi, 642001 Coimbatore (India); Sudarsan, V., E-mail: vsudar@barc.gov.in [Chemistry Division, Bhabha Atomic Research Centre, Trombay, Mumbai 400085 (India); Christopher Selvin, P., E-mail: pcsphyngmc@rediffmail.com [Department of Physics, Nallamuthu Gounder Mahalingam College, Pollachi, 642001 Coimbatore (India); Kadam, R.M. [Radiochemistry Division, Bhabha Atomic Research Centre, Trombay, Mumbai 400085 (India)

2016-06-15

Undoped and Mn{sup 2+} doped ZnGa{sub 2}O{sub 4} phosphors were prepared by solution combustion method and characterized by XRD, SEM, luminescence and electron paramagnetic resonance (EPR) techniques. Based on XRD results, it is inferred that, strain in ZnGa{sub 2}O{sub 4} host lattice increases with incorporation of Mn{sup 2+} ions in the lattice. Mn{sup 2+} doping at concentration levels investigated, lead to significant reduction in the defect emission and this has been attributed to the formation of higher oxidation states of Mn ions in the lattice. Electron Paramagnetic Resonance studies confirmed that majority of Mn ions exist as Mn{sup 2+} species and they occupy tetrahedral Zn{sup 2+} site in ZnGa{sub 2}O{sub 4} lattice with an average hyperfine coupling constant, A{sub iso}∼82 G.

Transmission Electron Microscope Measures Lattice Parameters

Science.gov (United States)

Pike, William T.

1996-01-01

Convergent-beam microdiffraction (CBM) in thermionic-emission transmission electron microscope (TEM) is technique for measuring lattice parameters of nanometer-sized specimens of crystalline materials. Lattice parameters determined by use of CBM accurate to within few parts in thousand. Technique developed especially for use in quantifying lattice parameters, and thus strains, in epitaxial mismatched-crystal-lattice multilayer structures in multiple-quantum-well and other advanced semiconductor electronic devices. Ability to determine strains in indivdual layers contributes to understanding of novel electronic behaviors of devices.

Misfit Strain in Superlattices Controlling the Electron-Lattice Interaction via Micro strain in Active Layers

International Nuclear Information System (INIS)

Poccia, N.; Ricci, A.; Bianconi, N.

2010-01-01

High-temperature superconductivity (HTS) emerges in quite different electronic materials: cuprates, diborides, and iron-pnictide superconductors. Looking for unity in the diversity we find in all these materials a common lattice architecture: they are practical realizations of heterostructures at atomic limit made of superlattices of metallic active layers intercalated by spacers as predicted in 1993 by one of us. The multilayer architecture is the key feature for the presence of electronic topological transitions where the Fermi surface of one of the subbands changes dimensionality. The superlattice misfit strain η between the active and spacer layers is shown to be a key variable to drive the system to the highest critical temperature Tc that occurs at a particular point of the 3D phase diagram Tc(θ, η) where d is the charge transfer or doping. The plots of Tc as a function of misfit strain at constant charge transfer in cuprates show a first-order quantum critical phase transition where an itinerant striped magnetic phase competes with superconductivity in the proximity of a structural phase transition, that is, associated with an electronic topological transition. The shape resonances in these multi gap superconductors is associated with the maximum Tc.

Ag{sub 2}CdI{sub 4}: Synthesis, characterization and investigation the strain lattice and grain size

Energy Technology Data Exchange (ETDEWEB)

Ghanbari, Mojgan [Institute of Nano Science and Nano Technology, University of Kashan, Kashan, P.O. Box 87317-51167, I.R. (Iran, Islamic Republic of); Gholamrezaei, Sousan [Young Researchers Club, Arak Branch, Islamic Azad University, Arak (Iran, Islamic Republic of); Salavati-Niasari, Masoud, E-mail: salavati@kashanu.ac.ir [Institute of Nano Science and Nano Technology, University of Kashan, Kashan, P.O. Box 87317-51167, I.R. (Iran, Islamic Republic of)

2016-05-15

In this work the Ag{sub 2}CdI{sub 4} nanostructures have been synthesized via a solid state reaction from reaction of AgI and CdI{sub 2} as precursors. The effect of the mole ratio of precursors, time and temperature of reaction has been optimized to achieve the best product on morphology and purity. Nanostructures have been characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman (FT-IR) techniques, X-ray energy dispersive spectroscopy (EDS) and Ultraviolet spectroscopy (UVvis). The XRD patterns of nanostructures have been used to estimate the grain sizes and strain lattice. Grain size of nanostructures is in range of 5–17 nm and the strain of lattice is changed in range of 0.0024–0.014. The band gap of these nanostructures has been estimated by DRS spectrum about 5.4 eV. Raman spectroscopy has been confirmed the XRD results and show that the Ag{sub 2}CdI{sub 4} nanostructures have been synthesized. SEM and TEM images have been used for investigation of morphology of product. Results show that the best morphology and purity have been achieved in 12 h and 200 °C in 1:1 mol ratio of precursors. - Highlights: • Ag{sub 2}CdI{sub 4} nanostructures have been synthesized by low temperature solid state method. • The reaction has been optimized for purity, morphology, and grain size and strain lattice. • Effective parameters have been optimized such as time, temperature and mole ratio.

Triple and Quadruple Junctions Thermophotovoltaic Devices Lattice Matched to InP

Science.gov (United States)

Bhusal, L.; Freundlich, A.

2007-01-01

complications due to the creation of defects and short life of the device or to introduce high content of indium, which again is found problematic due to the difficulties in diluting nitrogen in the presence of high indium [9]. An availability of material of proper band gap and lattice matching on InP are important issues for the development of TPV devices to perform better. To address those issues, recently we have shown that by adjusting the thickness of individual sublayers and the nitrogen composition, strain balanced GaAs(1-x)N(x)/InAs(1-y)N(y) superlattice can be designed to be both lattice matched to InP and have an effective bandgap in the desirable 0.4- 0.7eV range [10,11]. Theoretically the already reduced band gap of GaAs(1-x)N(x), due to the nitrogen effects, can be further reduced by subjecting it to a biaxial tensile strain, for example, by fabricating pseudomorphically strained layers on commonly available InP substrates. While such an approach in principle could allow access to smaller band gap (longer wavelength), only a few atomic monolayers of the material can be grown due to the large lattice mismatch between GaAs(1-x)N(x) and InP (approx.3.8-4.8 % for x<0.05, 300K). This limitation can be avoided using the principle of strain balancing [12], by introducing the alternating layers of InAs(1-y)N(y) with opposite strain (approx.2.4-3.1% for x<0.05, 300K) in combination with GaAs(1-x)N(x). Therefore, even an infinite pseudomorphically strained superlattice thickness can be realized from a sequence of GaAs(1-x)N(x) and InAs(1-y)N(y) layers if the thickness of each layer is kept below the threshold for its lattice relaxation

Strain buildup in GaAs due to 100 MeV Ag ion irradiation

Energy Technology Data Exchange (ETDEWEB)

Mishra, Shramana; Bhaumik, Sudipta; Panda, Jaya Kumar [Department of Physics and Meteorology, Indian Institute of Technology, Kharagpur 721 302 (India); Ojha, Sunil [Inter-University Accelerator Center, Aruna Asaf Ali Marg, New Delhi 110 067 (India); Dhar, Achintya [Department of Physics and Meteorology, Indian Institute of Technology, Kharagpur 721 302 (India); Kabiraj, D. [Inter-University Accelerator Center, Aruna Asaf Ali Marg, New Delhi 110 067 (India); Roy, Anushree, E-mail: anushree@phy.iitkgp.ernet.in [Department of Physics and Meteorology, Indian Institute of Technology, Kharagpur 721 302 (India)

2013-12-01

The formation of strained layers and a non-monotonic evolution of strain in high energy (100 MeV) silver ion (Ag{sup 7+}) irradiated undoped semi-insulating GaAs are observed and analyzed using Raman scattering and high resolution X-ray diffraction (HRXRD) measurements. At low fluence, compressively strained layers are formed, whereas, with increase in fluence both compressive and tensile strains appear as observed from HRXRD measurements. Further, at low fluence, the change in compressive strain with increase in fluence is found to be sharper than what is observed at higher fluence, thereby suggesting a critical fluence value, beyond which there is a simultaneous generation and annihilation of vacancy type defects. The initial blue shift and subsequent relative red shift beyond above critical fluence in the Raman peak also qualitatively reveal non-monotonic evolution of strain in this case. Finally, we demonstrate the sensitivity of Raman spectroscopy in detecting the decrease in lattice ordering in the crystal in the low fluence regime, below the detection limit of Rutherford back-scattering channeling (c-RBS) measurements.

Electric field induced lattice strain in pseudocubic Bi(Mg{sub 1/2}Ti{sub 1/2})O{sub 3}-modified BaTiO{sub 3}-BiFeO{sub 3} piezoelectric ceramics

Energy Technology Data Exchange (ETDEWEB)

Fujii, Ichiro, E-mail: ifujii@rins.ryukoku.ac.jp [Department of Materials Chemistry, Ryukoku University, Otsu, Shiga 520-2194 (Japan); Iizuka, Ryo; Ueno, Shintaro; Nakashima, Kouichi; Wada, Satoshi [Interdisciplinary Graduate School of Medical and Engineering, University of Yamanashi, Kofu, Yamanashi 400-8510 (Japan); Nakahira, Yuki; Sunada, Yuya; Magome, Eisuke; Moriyoshi, Chikako; Kuroiwa, Yoshihiro [Department of Physical Science, Hiroshima University, Higashihiroshima, Hiroshima 739-8526 (Japan)

2016-04-25

Contributions to the piezoelectric response in pseudocubic 0.3BaTiO{sub 3}-0.1Bi(Mg{sub 1/2}Ti{sub 1/2})O{sub 3}-0.6BiFeO{sub 3} ceramics were investigated by synchrotron X-ray diffraction under electric fields. All of the lattice strain determined from the 110, 111, and 200 pseudocubic diffraction peaks showed similar lattice strain hysteresis that was comparable to the bulk butterfly-like strain curve. It was suggested that the hysteresis of the lattice strain and the lack of anisotropy were related to the complex domain structure and the phase boundary composition.

Dependence of hydrogen-induced lattice defects and hydrogen embrittlement of cold-drawn pearlitic steels on hydrogen trap state, temperature, strain rate and hydrogen content

International Nuclear Information System (INIS)

Doshida, Tomoki; Takai, Kenichi

2014-01-01

The effects of the hydrogen state, temperature, strain rate and hydrogen content on hydrogen embrittlement susceptibility and hydrogen-induced lattice defects were evaluated for cold-drawn pearlitic steel that absorbed hydrogen in two trapping states. Firstly, tensile tests were carried out under various conditions to evaluate hydrogen embrittlement susceptibility. The results showed that peak 2 hydrogen, desorbed at temperatures above 200 °C as determined by thermal desorption analysis (TDA), had no significant effect on hydrogen embrittlement susceptibility. In contrast, hydrogen embrittlement susceptibility increased in the presence of peak 1 hydrogen, desorbed from room temperature to 200 °C as determined by TDA, at temperatures higher than −30 °C, at lower strain rates and with higher hydrogen content. Next, the same effects on hydrogen-induced lattice defects were also evaluated by TDA using hydrogen as a probe. Peak 2 hydrogen showed no significant effect on either hydrogen-induced lattice defects or hydrogen embrittlement susceptibility. It was found that hydrogen-induced lattice defects formed under the conditions where hydrogen embrittlement susceptibility increased. This relationship indicates that hydrogen embrittlement susceptibility was higher under the conditions where the formation of hydrogen-induced lattice defects tended to be enhanced. Since hydrogen-induced lattice defects formed by the interaction between hydrogen and strain were annihilated by annealing at a temperature of 200 °C, they were presumably vacancies or vacancy clusters. One of the common atomic-level changes that occur in cold-drawn pearlitic steel showing higher hydrogen embrittlement susceptibility is the formation of vacancies and vacancy clusters

Final Report for Award DE-SC0005403. Improved Electrochemical Performance of Strained Lattice Electrolytes via Modulated Doping

Energy Technology Data Exchange (ETDEWEB)

Hertz, Joshua L. [Univ. of Delaware, Newark, DE (United States); Prasad, Ajay K. [Univ. of Delaware, Newark, DE (United States)

2015-09-06

The enclosed document provides a final report to document the research performed at the University of Delaware under Grant DE-SC0005403: Improved Electrochemical Performance of Strained Lattice Electrolytes via Modulated Doping. The ultimate goal of this project was to learn how to systematically strain the inter-atomic distance in thin ceramic films and how to use this newfound control to improve the ease by which oxygen ions can conduct through the films. Increasing the ionic conductivity of ceramics holds the promise of drastic improvements in the performance of solid oxide fuel cells, chemical sensors, gas permeation membranes, and related devices. Before this work, the experimental evidence advocating for strain-based techniques was often controversial and poorly characterized. Enabling much of this work was a new method to quickly create a very wide range of ceramic nanostructures that was established during the first phase of the project. Following this initial phase, we created a variety of promising nanostructured epitaxial films and multilayers with systematic variations in lattice mismatch and dopant content. Over the course of the work, a positive effect of tensile atomic strain on the oxygen conductivity was conclusively found using a few different forms of samples and experimental techniques. The samples were built by sputtering, an industrially scalable technique, and thus the technological implementation of these results may be economically feasible. Still, two other results consistently achieved over multiple efforts in this work give pause. The first of these results was that very specific, pristine surfaces upon which to build the nanostructures were strictly required in order to achieve measurable results. The second of these results was that compressively strained films with concomitant reductions in oxygen conductivity are much easier to obtain relative to tensile-strained films with increased conductivity.

Modeling Shock Induced Plasticity in Copper Single Crystal: Numerical and Strain Localization Issues

International Nuclear Information System (INIS)

Shehadeh, M

2011-01-01

Multiscale dislocation dynamics plasticity (MDDP) simulations are carried out to address the following issues in modeling shock-induced plasticity: 1- the effect of finite element (FE) boundary conditions on shock wave characteristics and wave-dislocation interaction, 2- the effect of the evolution of the dislocation microstructure on lattice rotation and strain localization. While uniaxial strain is achieved with high accuracy using confined boundary condition, periodic boundary condition yields a disturbed wave profile due the edge effect. Including lattice rotation in the analysis leads to higher dislocation density and more localized plastic strain. (author)

Pseudomagnetic fields and triaxial strain in graphene

DEFF Research Database (Denmark)

Settnes, Mikkel; Power, Stephen; Jauho, Antti-Pekka

2016-01-01

Pseudomagnetic fields, which can result from nonuniform strain distributions, have received much attention in graphene systems due to the possibility of mimicking real magnetic fields with magnitudes of greater than 100 T. We examine systems with such strains confined to finite regions ("pseudoma......Pseudomagnetic fields, which can result from nonuniform strain distributions, have received much attention in graphene systems due to the possibility of mimicking real magnetic fields with magnitudes of greater than 100 T. We examine systems with such strains confined to finite regions......-binding calculations of single pseudomagnetic dots in extended graphene sheets confirm these predictions, and are also used to study the effect of rotating the strain direction with respect to the underlying graphene lattice, and varying the size of the pseudomagnetic dot....

Neutron diffraction studies on lattice strain evolution around a crack-tip during tensile loading and unloading cycles

Energy Technology Data Exchange (ETDEWEB)

Sun Yinan [Department of Materials Science and Engineering, University of Tennessee, Knoxville, TN 37996 (United States)]. E-mail: ysun1@utk.edu; Choo, Hahn [Department of Materials Science and Engineering, University of Tennessee, Knoxville, TN 37996 (United States); Metals and Ceramics Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831 (United States); Liaw, Peter K. [Department of Materials Science and Engineering, University of Tennessee, Knoxville, TN 37996 (United States); Lu Yulin [Department of Materials Science and Engineering, University of Tennessee, Knoxville, TN 37996 (United States); Yang Bing [Department of Materials Science and Engineering, University of Tennessee, Knoxville, TN 37996 (United States); Brown, Donald W. [Materials Science and Technology Division, Los Alamos National Laboratory, Los Alamos, NM 87545 (United States); Bourke, Mark A.M. [Materials Science and Technology Division, Los Alamos National Laboratory, Los Alamos, NM 87545 (United States)

2005-10-15

Elastic lattice-strain profiles ahead of a fatigue-crack-tip were measured during tensile loading and unloading cycles using neutron diffraction. The crack-closure phenomenon after an overload was observed. Furthermore, the plastic-zone size in front of the crack-tip was estimated from the diffraction-peak broadening, which showed good agreement with the calculated result.

Lattice strain estimation for CoAl{sub 2}O{sub 4} nano particles using Williamson-Hall analysis

Energy Technology Data Exchange (ETDEWEB)

Aly, Kamal A., E-mail: kamalaly2001@gmail.com [Physics Department, Faculty of Science & Arts, Khulais, University of Jeddah, Jiddah (Saudi Arabia); Physics Department, Faculty of Science, Al-Azhar University, Assiut Branch, Assiut (Egypt); Khalil, N.M. [Chemistry Department, Faculty of Science & Arts, Khulais, University of Jeddah, Jiddah (Saudi Arabia); Refractories, Ceramics and Building Materials Department, National Research Centre, 12311 Cairo (Egypt); Algamal, Yousif [Chemistry Department, Faculty of Science & Arts, Khulais, University of Jeddah, Jiddah (Saudi Arabia); Saleem, Qaid M.A. [Chemistry Department, Faculty of Science & Arts, Khulais, University of Jeddah, Jiddah (Saudi Arabia); Chemistry Department, Faculty of Education, Aden University, Sabwa (Yemen)

2016-08-15

CoAl{sub 2}O{sub 4} nanoparticles were prepared via coprecipitation technique through mixing 1:1 M ratio of cobalt nitrate and aluminium nitrate solutions at pH 10. CoAl{sub 2}O{sub 4} crystalline phase was confirmed by X-ray diffraction. Scanning electron microscopy (SEM) result reveals that the particles of CoAl{sub 2}O{sub 4} fired at 900 °C were relatively small (21 nm) and uniform. Increased temperature to 1200 °C gives rise to blocky particles and changes in the powders shape, that because of agglomeration came from the calcination of CoAl{sub 2}O{sub 4}. Furthermore, the particle size increase with increasing the calcinated temperature. The crystalline sizes were evaluated by using X-ray peak broadening analysis suggested by Williamson-Hall (W-H) analysis. It was successfully applied for lattice strain and to calculate mechanical stress and energy density values using different three models namely uniform deformation model (UDM), uniform deformation stress model (UDSM) and uniform deformation energy density model (UDEDM). Also, the root mean square strain was determined. These models gave a different strain values which suggested an isotropic nature of the nanoparticles. Besides, the obtained results W-H analysis are in good agreement with that deduced from SEM analysis and Scherrer's formula. - Highlights: • CoAl{sub 2}O{sub 4} nanoparticles were prepared via coprecipitation technique. • CoAl{sub 2}O{sub 4} nanoparticles were characterized by SEM and XRD. • the lattice size and strain were investigated according to W-H analysis. • The latic size were investigated by W-H analysis, SEM and Sherrar's method. • The root mean square strain was determined.

Self-organized lattice of ordered quantum dot molecules

International Nuclear Information System (INIS)

Lippen, T. von; Noetzel, R.; Hamhuis, G.J.; Wolter, J.H.

2004-01-01

Ordered groups of InAs quantum dots (QDs), lateral QD molecules, are created by self-organized anisotropic strain engineering of a (In,Ga)As/GaAs superlattice (SL) template on GaAs (311)B in molecular-beam epitaxy. During stacking, the SL template self-organizes into a two-dimensionally ordered strain modulated network on a mesoscopic length scale. InAs QDs preferentially grow on top of the nodes of the network due to local strain recognition. The QDs form a lattice of separated groups of closely spaced ordered QDs whose number can be controlled by the GaAs separation layer thickness on top of the SL template. The QD groups exhibit excellent optical properties up to room temperature

Determination of Strain Rate Sensitivity of Micro-struts Manufactured Using the Selective Laser Melting Method

Science.gov (United States)

Gümrük, Recep; Mines, R. A. W.; Karadeniz, Sami

2018-03-01

Micro-lattice structures manufactured using the selective laser melting (SLM) process provides the opportunity to realize optimal cellular materials for impact energy absorption. In this paper, strain rate-dependent material properties are measured for stainless steel 316L SLM micro-lattice struts in the strain rate range of 10-3 to 6000 s-1. At high strain rates, a novel version of the split Hopkinson Bar has been developed. Strain rate-dependent materials data have been used in Cowper-Symonds material model, and the scope and limit of this model in the context of SLM struts have been discussed. Strain rate material data and the Cowper-Symonds model have been applied to the finite element analysis of a micro-lattice block subjected to drop weight impact loading. The model output has been compared to experimental results, and it has been shown that the increase in crush stress due to impact loading is mainly the result of strain rate material behavior. Hence, a systematic methodology has been developed to investigate the impact energy absorption of a micro-lattice structure manufactured using additive layer manufacture (SLM). This methodology can be extended to other micro-lattice materials and configurations, and to other impact conditions.

Lattice thermal transport in group II-alloyed PbTe

Science.gov (United States)

Xia, Yi; Hodges, James M.; Kanatzidis, Mercouri G.; Chan, Maria K. Y.

2018-04-01

PbTe, one of the most promising thermoelectric materials, has recently demonstrated a thermoelectric figure of merit (ZT) of above 2.0 when alloyed with group II elements. The improvements are due mainly to significant reduction of lattice thermal conductivity (κl), which was in turn attributed to nanoparticle precipitates. However, a fundamental understanding of various phonon scattering mechanisms within the bulk alloy is still lacking. In this work, we apply the newly-developed density-functional-theory-based compressive sensing lattice dynamics approach to model lattice heat transport in PbTe, MTe, and Pb0.94M0.06Te (M = Mg, Ca, Sr, and Ba) and compare our results with experimental measurements, with focus on the strain effect and mass disorder scattering. We find that (1) CaTe, SrTe, and BaTe in the rock-salt structure exhibit much higher κl than PbTe, while MgTe in the same structure shows anomalously low κl; (2) lattice heat transport of PbTe is extremely sensitive to static strain induced by alloying atoms in solid solution form; (3) mass disorder scattering plays a major role in reducing κl for Mg/Ca/Sr-alloyed PbTe through strongly suppressing the lifetimes of intermediate- and high-frequency phonons, while for Ba-alloyed PbTe, precipitated nanoparticles are also important.

Strain distributions and their influence on electronic structures of WSe2-MoS2 laterally strained heterojunctions

Science.gov (United States)

Zhang, Chendong; Li, Ming-Yang; Tersoff, Jerry; Han, Yimo; Su, Yushan; Li, Lain-Jong; Muller, David A.; Shih, Chih-Kang

2018-02-01

Monolayer transition metal dichalcogenide heterojunctions, including vertical and lateral p-n junctions, have attracted considerable attention due to their potential applications in electronics and optoelectronics. Lattice-misfit strain in atomically abrupt lateral heterojunctions, such as WSe2-MoS2, offers a new band-engineering strategy for tailoring their electronic properties. However, this approach requires an understanding of the strain distribution and its effect on band alignment. Here, we study a WSe2-MoS2 lateral heterojunction using scanning tunnelling microscopy and image its moiré pattern to map the full two-dimensional strain tensor with high spatial resolution. Using scanning tunnelling spectroscopy, we measure both the strain and the band alignment of the WSe2-MoS2 lateral heterojunction. We find that the misfit strain induces type II to type I band alignment transformation. Scanning transmission electron microscopy reveals the dislocations at the interface that partially relieve the strain. Finally, we observe a distinctive electronic structure at the interface due to hetero-bonding.

Stability of germanene under tensile strain

KAUST Repository

Kaloni, Thaneshwor P.

2013-09-01

The stability of germanene under biaxial tensile strain and the accompanying modifications of the electronic properties are studied by density functional theory. The phonon spectrum shows that up to 16% strain the germanene lattice is stable, where the Dirac cone shifts towards higher energy and hole-doped Dirac states are achieved. The latter is due to weakening of the Ge-Ge bonds and reduction of the s-p hybridization. Our calculated Grüneisen parameter shows a similar dependence on the strain as reported for silicene (which is different from that of graphene). © 2013 Elsevier B.V. All rights reserved.

Stability of germanene under tensile strain

KAUST Repository

Kaloni, Thaneshwor P.; Schwingenschlö gl, Udo

2013-01-01

The stability of germanene under biaxial tensile strain and the accompanying modifications of the electronic properties are studied by density functional theory. The phonon spectrum shows that up to 16% strain the germanene lattice is stable, where the Dirac cone shifts towards higher energy and hole-doped Dirac states are achieved. The latter is due to weakening of the Ge-Ge bonds and reduction of the s-p hybridization. Our calculated Grüneisen parameter shows a similar dependence on the strain as reported for silicene (which is different from that of graphene). © 2013 Elsevier B.V. All rights reserved.

Channeling techniques to study strains and defects in heterostructures and multi quantum wells

Science.gov (United States)

Pathak, A. P.; Dhamodaran, S.; Sathish, N.

2005-08-01

The importance and advantages of heterostructures and Quantum Wells (QWs) in device technology has made research challenging due to lack of direct techniques for their characterization. Particularly the characterization of strain and defects at the interfaces has become important due to their dominance in the electrical and optical properties of materials and devices. RBSiC has been used to study variety of defects in single crystalline materials, for nearly four decades now. Channeling based experiments play a crucial role in giving depth information of strain and defects. Ion beams are used for both material characterizations as well as for modifications. Hence it is also possible to monitor the modifications online, which are discussed in detail. In the present work, Swift Heavy Ion (SHI) modification of III-V semiconductor heterostnictures and MQWs and the results of subsequent strain measurements by RBSiC in initially strained as well as lattice matched systems are discussed. We find that the compressive strain decreases due to SHI irradiation and a tensile strain is induced in an initially lattice matched system. The incident ion fluence dependence of strain modifications in the heterostructures will also be discussed. The use of high energy channeling for better sensitivity of strain measurements in low mismatch materials will be discussed in detail. Wherever possible, a comparison of results with those obtained by other techniques like HRXRD is given.

Effect of naturally-occurring uranium and thorium on the level of crystal lattice damage of Malaysian Zircon

International Nuclear Information System (INIS)

Meor Yusoff Sulaiman; Khangoankar, P.R.; Kamarudin Husin

1999-01-01

Malaysian zircon is classified as a radioactive mineral due to its high uranium and thorium content. Recoil α, which is produce from the decay process of these radioactive elements, could results to the damage of the crystal. Metamictization or crystal lattice damage level of this mineral can be determined from their crystallise size and lattice strain values. Results for two local zircon samples with different uranium and thorium content seem to suggest that there is some relationship between the concentration of these elements and its metamictization level. Comparison of the lattice strain value with previous results conducted on zircon from different country shows that the value is still within the range obtained. Microstructure analysis was also done on the samples. Fractures and pores formed on the mineral surface support the lattice expansion phenomena obtained from the crystallographic analysis. Production of a clean, white non-radioactive zircon pigment is among the commercial potential that could be derived from this study. (Author)

Effect of fluence on the lattice site of implanted Er and implantation induced strain in GaN

CERN Document Server

Wahl, U; Decoster, S; Vantomme, A; Correi, J G

2009-01-01

A GaN thin film was implanted with 5 × 1014 cm−2 of 60 keV stable 166Er, followed by the implantation of 2 × 1013 cm−2 radioactive 167Tm (t1/2 = 9.3 d) and an annealing sequence up to 900 °C. The emission channeling (EC) technique was applied to assess the lattice location of Er following the Tm decay from the conversion electrons emitted by 167mEr, which showed that more than 50% of 167mEr occupies substitutional Ga sites. The results are briefly compared to a 167mEr lattice location experiment in a GaN sample not pre-implanted with 166Er. In addition, high-resolution X-ray diffraction (HRXRD) was used to characterize the perpendicular strain in the high-fluence implanted film. The HRXRD experiments showed that the Er implantation resulted in an increase of the c-axis lattice constant of the GaN film around 0.5–0.7%. The presence of significant disorder within the implanted region was corroborated by the fact that the EC patterns for off-normal directions exhibit a pronounced angular broadening of t...

Computer simulation of strain-induced ordering in interstitial solutions based on the b.c.c. Ta lattice

International Nuclear Information System (INIS)

Blanter, M.S.; Khachaturyan, A.G.

1980-01-01

A computer simulation is made of strain-induced ordering of interstitial atoms within octahedral interstices in the Ta host lattice. The calculation technique allows to take into account infinite-range strain-induced interaction. Computer simulation of ordering process enables to model the sequence of structure changes which occur during the ordering process and to find the equilibrium structure of the stable interstitial superstructures. The structures of high-temperature ordering phases obtained by the method of static concentration waves coincide with those obtained by means of computer simulation. However computer simulation enables to predict the structures of low-temperature ordered phases which cannot be obtained by the method of concentration waves. Comparison of computer simulation results and structures of observed ordered phases demonstrates good agreement. (author)

Strain distributions and their influence on electronic structures of WSe2–MoS2 laterally strained heterojunctions

KAUST Repository

Zhang, Chendong

2018-01-12

Monolayer transition metal dichalcogenide heterojunctions, including vertical and lateral p–n junctions, have attracted considerable attention due to their potential applications in electronics and optoelectronics. Lattice-misfit strain in atomically abrupt lateral heterojunctions, such as WSe2–MoS2, offers a new band-engineering strategy for tailoring their electronic properties. However, this approach requires an understanding of the strain distribution and its effect on band alignment. Here, we study a WSe2–MoS2 lateral heterojunction using scanning tunnelling microscopy and image its moiré pattern to map the full two-dimensional strain tensor with high spatial resolution. Using scanning tunnelling spectroscopy, we measure both the strain and the band alignment of the WSe2–MoS2 lateral heterojunction. We find that the misfit strain induces type II to type I band alignment transformation. Scanning transmission electron microscopy reveals the dislocations at the interface that partially relieve the strain. Finally, we observe a distinctive electronic structure at the interface due to hetero-bonding.

Strain distributions and their influence on electronic structures of WSe2–MoS2 laterally strained heterojunctions

KAUST Repository

Zhang, Chendong; Li, Ming-yang; Tersoff, Jerry; Han, Yimo; Su, Yushan; Li, Lain-Jong; Muller, David A.; Shih, Chih-Kang

2018-01-01

Monolayer transition metal dichalcogenide heterojunctions, including vertical and lateral p–n junctions, have attracted considerable attention due to their potential applications in electronics and optoelectronics. Lattice-misfit strain in atomically abrupt lateral heterojunctions, such as WSe2–MoS2, offers a new band-engineering strategy for tailoring their electronic properties. However, this approach requires an understanding of the strain distribution and its effect on band alignment. Here, we study a WSe2–MoS2 lateral heterojunction using scanning tunnelling microscopy and image its moiré pattern to map the full two-dimensional strain tensor with high spatial resolution. Using scanning tunnelling spectroscopy, we measure both the strain and the band alignment of the WSe2–MoS2 lateral heterojunction. We find that the misfit strain induces type II to type I band alignment transformation. Scanning transmission electron microscopy reveals the dislocations at the interface that partially relieve the strain. Finally, we observe a distinctive electronic structure at the interface due to hetero-bonding.

Strain quantification in epitaxial thin films

International Nuclear Information System (INIS)

Cushley, M

2008-01-01

Strain arising in epitaxial thin films can be beneficial in some cases but devastating in others. By altering the lattice parameters, strain may give a thin film properties hitherto unseen in the bulk material. On the other hand, heavily strained systems are prone to develop lattice defects in order to relieve the strain, which can cause device failure or, at least, a decrease in functionality. Using convergent beam electron diffraction (CBED) and high-resolution transmission electron microscopy (HRTEM), it is possible to determine local strains within a material. By comparing the results from CBED and HRTEM experiments, it is possible to gain a complete view of a material, including the strain and any lattice defects present. As well as looking at how the two experimental techniques differ from each other, I will also look at how results from different image analysis algorithms compare. Strain in Si/SiGe samples and BST/SRO/MgO capacitor structures will be discussed.

Lattice strains in gold and rhenium under nonhydrostatic compression to 37 GPa

International Nuclear Information System (INIS)

Duffy, Thomas S.; Shen, Guoyin; Heinz, Dion L.; Shu, Jinfu; Ma, Yanzhang; Mao, Ho-Kwang; Hemley, Russell J.; Singh, Anil K.

1999-01-01

Using energy-dispersive x-ray diffraction techniques together with the theory describing lattice strains under nonhydrostatic compression, the behavior of a layered sample of gold and rhenium has been studied at pressures of 14-37 GPa. For gold, the uniaxial stress component t is consistent with earlier studies and can be described by t=0.06+0.015P where P is the pressure in GPa. The estimated single-crystal elastic moduli are in reasonable agreement with trends based on extrapolated low-pressure data. The degree of elastic anisotropy increases as α, the parameter which characterizes stress-strain continuity across grain boundaries, is reduced from 1.0 to 0.5. For rhenium, the apparent equation of state has been shown to be strongly influenced by nonhydrostatic compression, as evidenced by its dependence on the angle ψ between the diffracting plane normal and the stress axis. The bulk modulus obtained by inversion of nonhydrostatic compression data can differ by nearly a factor of 2 at angles of 0 degree sign and 90 degree sign . On the other hand, by a proper choice of ψ, d spacings corresponding to quasihydrostatic compression can be obtained from data obtained under highly nonhydrostatic conditions. The uniaxial stress in rhenium over the pressure range from 14-37 GPa can be described by t=2.5+0.09P. The large discrepancy between x-ray elastic moduli and ultrasonic data and theoretical calculations indicates that additional factors such as texturing or orientation dependence of t need to be incorporated to more fully describe the strain distribution in hexagonal-close-packed metals. (c) 1999 The American Physical Society

The lattice correspondence and diffusional-displacive phase transformations

International Nuclear Information System (INIS)

Nie, J.F.; Muddle, B.C.

1999-01-01

When a coherent interface is maintained between parent and product phases in a solid state phase transformation, then it is always possible to define a lattice correspondence across this interface and describe the structural change by a homogeneous lattice deformation, S T . For certain transformations, this strain is an invariant plane strain, with the invariant plane defining the planar, coherent interface between parent and product. This group includes the familiar martensitic face-centred cubic to close-packed hexagonal transformation in, for example, cobalt-based alloys, but it is demonstrated here that it also contains transformations giving rise to a broad range of plate-shaped, diffusional precipitation products. For many such transformation products, the transformation strain has a significant shear component and the accommodation of shear strain energy is potentially an important, and often overlooked, factor in both the nucleation and growth of such products. More commonly S T is not an invariant plane strain and, if a planar interface is to be preserved between parent and product, it is necessary to combine S T with a lattice invariant strain to allow a partially-coherent interface that is macroscopically invariant. It is demonstrated that there are diffusional transformation products which also have the geometric and crystallographic features of both of the common forms of partially-coherent martensitic products

Engineering Strain for Improved III-Nitride Optoelectronic Device Performance

Science.gov (United States)

Van Den Broeck, Dennis Marnix

Due to growing environmental and economic concerns, renewable energy generation and high-efficiency lighting are becoming even more important in the scientific community. III-Nitride devices have been essential in production of high-brightness light-emitting diodes (LEDs) and are now entering the photovoltaic (PV) realm as the technology advances. InGaN/GaN multiple quantum well LEDs emitting in the blue/green region have emerged as promising candidates for next-generation lighting technologies. Due to the large lattice mismatch between InN and GaN, large electric fields exist within the quantum well layers and result in low rates of radiative recombination, especially for the green spectral region. This is commonly referred to as the "green gap" and results in poor external quantum efficiencies for light-emitting diodes and laser diodes. In order to mitigate the compressive stress of InGaN QWs, a novel growth technique is developed in order to grown thick, strain-relaxed In yGa1-yN templates for 0.08 structure, "semibulk" InGaN templates were achieved with vastly superior crystal and optical properties than bulk InGaN films. These semibulk InGaN templates were then utilized as new templates for multiple quantum well active layers, effectively reducing the compressive strain in the InGaN wells due to the larger lattice constant of the InGaN template with respect to a GaN template. A zero-stress balance method was used in order to realize a strain-balanced multiple quantum well structure, which again showed improved optical characteristics when compared to fully-strain active regions. The semibulk InGaN template was then implemented into "strain-compensated" LED structures, where light emission was achieved with very little leakage current. Discussion of these strain-compensated devices compared to conventional LEDs is detailed.

Strained superlattices and magnetic tunnel junctions based on doped manganites

International Nuclear Information System (INIS)

Yafeng Lu

2001-01-01

In the first part of this work the effect of biaxial strain on the structure and transport properties of doped manganites has been studied to explore the relevance of Jahn-Teller electron-lattice interaction for the CMR phenomenon in these materials. A series of high quality, coherently strained La 2/3 (Ca or Ba) 1/3 MnO 3 /SrTiO 3 superlattices with different modulation periods have been fabricated on (001) SrTiO 3 and NdGaO 3 substrates by laser molecular beam epitaxy. A detailed structural characterization was performed by high-angle X-ray diffraction (HAXRD) and low-angle X-ray reflectivity (LAXRR). The fabricated superlattices are very flat, show excellent structural coherence and very small mosaic spread (0.2 ∝0.03 ). The in-plane coherency strain could be varied by changing the thickness ratio of the constituent layers allowing for a systematic variation of the resulting lattice distortion of La 2/3 (Ca or Ba) 1/3 MnO 3 . By the in-plane coherency strain the out-of-plane lattice constant could be continuously adjusted by varying the relative thickness of the SrTiO 3 and La 2/3 (Ca or Ba) 1/3 MnO 3 layers: the c-axis lattice constant of La 2/3 Ba 1/3 MnO 3 was found to vary from 3.910 A to 3.975 A due to a compressive in-plane strain, whereas the c-axis constant of La 2/3 Ca 1/3 MnO 3 was found to change from 3.87 A to 3.79A due to tensile in-plane strain. The strain results in a biaxial distortion ε bi of La 2/3 (Ca or Ba) 1/3 MnO 3 that strongly affects the electrical transport properties and the magnetoresistance. Our measurements show that there is a clear correlation between ε bi and the temperature T p corresponding to the maximum in the resistivity versus temperature curves as well as the measured magnetoresistance in the two systems. In the second part of this work we have investigated the spin-dependent tunneling in trilayer structures of La 2/3 Ba 1/3 MnO 3 /SrTiO 3 /La 2/3 Ba 1/3 MnO 3 . (orig.)

Effects of radiation damage on the silicon lattice

Science.gov (United States)

Dumas, Katherine A.; Lowry, Lynn; Russo, O. Louis

1987-01-01

Silicon was irradiated with both proton and electron particle beams in order to investigate changes in the structural and optical properties of the lattice as a result of the radiation damage. Lattice expansions occurred when large strain fields (+0.34 percent) developed after 1- and 3-MeV proton bombardment. The strain was a factor of three less after 1-MeV electron irradiation. Average increases of approximately 22 meV in the 3.46-eV interband energy gap and 14 meV in the Lorentz broadening parameter were measured after the electron irradiation.

Strain-induced friction anisotropy between graphene and molecular liquids

Science.gov (United States)

Liao, Meng; To, Quy-Dong; Léonard, Céline; Monchiet, Vincent; Vo, Van-Hoang

2017-01-01

In this paper, we study the friction behavior of molecular liquids with anisotropically strained graphene. Due to the changes of lattice and the potential energy surface, the friction is orientation dependent and can be computed by tensorial Green-Kubo formula. Simple quantitative estimations are also proposed for the zero-time response and agree reasonably well with the molecular dynamics results. From simulations, we can obtain the information of structures, dynamics of the system, and study the influence of strain and molecular shapes on the anisotropy degree. It is found that unilateral strain can increase friction in all directions but the strain direction is privileged. Numerical evidences also show that nonspherical molecules are more sensitive to strain and give rise to more pronounced anisotropy effects.

Light-induced lattice expansion leads to high-efficiency perovskite solar cells

Energy Technology Data Exchange (ETDEWEB)

Tsai, Hsinhan; Asadpour, Reza; Blancon, Jean-Christophe; Stoumpos, Constantinos C.; Durand, Olivier; Strzalka, Joseph W.; Chen, Bo; Verduzco, Rafael; Ajayan, Pulickel M.; Tretiak, Sergei; Even, Jacky; Alam, Muhammad Ashraf; Kanatzidis, Mercouri G.; Nie, Wanyi; Mohite, Aditya D.

2018-04-05

Hybrid-perovskite based high-performance optoelectronic devices and clues from their operation has led to the realization that light-induced structural dynamics play a vital role on their physical properties, device performance and stability. Here, we report that continuous light illumination leads to a uniform lattice expansion in hybrid perovskite thin-films, which is critical for obtaining high-efficiency photovoltaic devices. Correlated, in-situ structural and device characterizations reveal that light-induced lattice expansion significantly benefits the performances of a mixed-cation pure-halide planar device, boosting the power conversion efficiency from 18.5% to 20.5%. This is a direct consequence of the relaxation of local lattice strains during lattice expansion, which results in the reduction of the energetic barriers at the perovskite/contact interfaces in devices, thus improving the open circuit voltage and fill factor. The light-induced lattice expansion stabilizes these high-efficiency photovoltaic devices under continuous operation of full-spectrum 1-Sun illumination for over 1500 hours. One Sentence Summary: Light-induced lattice expansion improves crystallinity, relaxes lattice strain, which enhances photovoltaic performance in hybrid perovskite device.

Enhanced Proton Conductivity in Y-Doped BaZrO3 via Strain Engineering.

Science.gov (United States)

Fluri, Aline; Marcolongo, Aris; Roddatis, Vladimir; Wokaun, Alexander; Pergolesi, Daniele; Marzari, Nicola; Lippert, Thomas

2017-12-01

The effects of stress-induced lattice distortions (strain) on the conductivity of Y-doped BaZrO 3 , a high-temperature proton conductor with key technological applications for sustainable electrochemical energy conversion, are studied. Highly ordered epitaxial thin films are grown in different strain states while monitoring the stress generation and evolution in situ. Enhanced proton conductivity due to lower activation energies is discovered under controlled conditions of tensile strain. In particular, a twofold increased conductivity is measured at 200 °C along a 0.7% tensile strained lattice. This is at variance with conclusions coming from force-field simulations or the static calculations of diffusion barriers. Here, extensive first-principles molecular dynamic simulations of proton diffusivity in the proton-trapping regime are therefore performed and found to agree with the experiments. The simulations highlight that compressive strain confines protons in planes parallel to the substrate, while tensile strain boosts diffusivity in the perpendicular direction, with the net result that the overall conductivity is enhanced. It is indeed the presence of the dopant and the proton-trapping effect that makes tensile strain favorable for proton conduction.

Conduction gap in graphene strain junctions: direction dependence

International Nuclear Information System (INIS)

Nguyen, M Chung; Nguyen, V Hung; Dollfus, P; Nguyen, Huy-Viet

2014-01-01

It has been shown in a recent study (Nguyen et al 2014 Nanotechnology 25 165201) that unstrained/strained graphene junctions are promising candidates to improve the performance of graphene transistors which is usually hindered by the gapless nature of graphene. Although the energy bandgap of strained graphene still remains zero, the shift of Dirac points in the k-space due to strain-induced deformation of graphene lattice can lead to the appearance of a finite conduction gap of several hundred meV in strained junctions with a strain of only a few per cent. However, since it depends essentially on the magnitude of the Dirac point shift, this conduction gap strongly depends on the direction of applied strain and the transport direction. In this work, a systematic study of conduction-gap properties with respect to these quantities is presented and the results are carefully analyzed. Our study provides useful information for further investigations to exploit graphene-strained junctions in electronic applications and strain sensors. (paper)

Engineering strain measurements using the NPD at LANSCE

International Nuclear Information System (INIS)

Bourke, M.A.M.; Goldstone, J.A.; Lovell, K.J.

1991-01-01

The presence of residual stress in engineering components can affect their mechanical properties and structural integrity. Neutron diffraction is the only measuring technique which can provide spatially resolved non-destructive strain measurements in the interior of a component. By recording the change in the interplanar spacings elastic strains can be measured for individual lattice reflections. Also on a pulsed source, where all lattice reflections are recorded, profile refinement is an option which allows the strain to be obtained from changes in the lattice parameter. Measurements made at LANSCE demonstrate the potential for stress measurements on a pulsed source and indicate the advantages and disadvantages over measurements made on a reactor. (author)

Band-gap tunability and dynamical instability in strained monolayer and bilayer phosphorenes

International Nuclear Information System (INIS)

Huang, G Q; Xing, Z W

2015-01-01

Very recently, field-effect transistors based on few-layer phosphorene crystals with a thickness of down to a few nanometres were successfully fabricated, triggering interest in this new functional two-dimensional material. In this work, we apply first-principles calculations to studying the evolution of electronic and phononic structures with out-of-plane strain for monolayer and bilayer phosphorenes. It is found that the vertical stress can be used to tune the band gap of a semiconducting phosphorene in a wide range. On the other hand, the vertical stress can make the phosphorene lattice become dynamically unstable and surface reconstruction or structural phase transition may occur. Due to the interlayer van der Waals coupling, the dynamically stable range of bilayer phosphorene under vertical stress is wider than that of monolayer phosphorene. It is proposed whether or not a semiconductor-semimetal transition occurring in a strained phosphorene is determined not only by its band gap closing, but also by its lattice stability against strain. This information is essential for the strain engineering of phosphorene and future device fabrication. (paper)

Engineering strain measurements using the NPD at LANSCE

International Nuclear Information System (INIS)

Bourke, M.A.M.; Goldstone, J.A.; Lovell, K.J.

1990-01-01

The presence of residual stress in engineering components can affect their mechanical properties and structural integrity. Neutron diffraction is the only measuring technique which can provide spatially resolved non-destructive strain measurements in the interior of a component. By recording the change in the interplanar spacings elastic strains can be measured for individual lattice reflections. Also on a pulsed source, where all lattice reflections are recorded, profile refinement is an option which alloys the strain to be obtained from changes in the lattice parameter. Measurements made at LANSCE demonstrate the potential for stress measurements on a pulsed source and indicate the advantages and disadvantages over measurements made on a reactor. 5 refs., 5 figs

Nanoscale measurements of phosphorous-induced lattice expansion in nanosecond laser annealed germanium

Science.gov (United States)

Boninelli, S.; Milazzo, R.; Carles, R.; Houdellier, F.; Duffy, R.; Huet, K.; La Magna, A.; Napolitani, E.; Cristiano, F.

2018-05-01

Laser Thermal Annealing (LTA) at various energy densities was used to recrystallize and activate amorphized germanium doped with phosphorous by ion implantation. The structural modifications induced during the recrystallization and the related dopant diffusion were first investigated. After LTA at low energy densities, the P electrical activation was poor while the dopant distribution was mainly localized in the polycrystalline Ge resulting from the anneal. Conversely, full dopant activation (up to 1 × 1020 cm-3) in a perfectly recrystallized material was observed after annealing at higher energy densities. Measurements of lattice parameters performed on the fully activated structures show that P doping results in a lattice expansion, with a perpendicular lattice strain per atom βPs = +0.7 ± 0.1 Å3. This clearly indicates that, despite the small atomic radius of P compared to Ge, the "electronic contribution" to the lattice parameter modification (due to the increased hydrostatic deformation potential in the conduction band of P doped Ge) is larger than the "size mismatch contribution" associated with the atomic radii. Such behavior, predicted by theory, is observed experimentally for the first time, thanks to the high sensitivity of the measurement techniques used in this work.

Short period strain balanced gallium arsenide nitride/indium arsenide nitride superlattice lattice matched to indium phosphide for mid-infrared photovoltaics

Science.gov (United States)

Bhusal, Lekhnath

Dilute nitrogen-containing III-V-N alloys have been intensively studied for their unusual electronic and optical behavior in the presence of a small amount of nitrogen. Those behaviors can further be manipulated, with a careful consideration of the strain and strain balancing, for example, in the context of a strain-balanced superlattice (SL) based on those alloys. In this work, the k.p approximation and the band anti-crossing model modified for the strain have been used to describe the electronic states of the strained bulk-like GaAs1-xNx and InAs 1-yNy ternaries in the vicinity of the center of the Brillouin zone (Gamma-point). Band-offsets between the conduction and valence bands of GaAs1-xNx and InAs1-yN y have also been evaluated, before implementing them into the SL structure. By minimizing the total mechanical energy of the stack of the alternating layers of GaAs1-xNx and InAs1-yNy in the SL, the ratio of the thicknesses of the epilayers is determined to make the structure lattice-matching on the InP(001), through the strain-balancing. Mini-band energies of the strain-balanced GaAs1-xNx/InAs 1-yNy short-period SL on InP(001) is then investigated using the transfer matrix formalism. This enabled identifying the evolution of the band edge transition energies of the superlattice structure for different nitrogen compositions. Results show the potential of the new proposed design to exceed the existing limits of bulk-like InGaAsN alloys and offer the applications for photon absorption/emission energies in the range of ~0.65-0.35eV at 300K for a typical nitrogen composition of ≤5%. The optical absorption coefficient of such a SL is then estimated under the anisotropic medium approximation, where the optical absorption of the bulk structure is modified according to the anisotropy imposed by the periodic potential in the growth direction. As an application, the developed SL structure is used to investigate the performance of double, triple and quadruple junction

Multiaxial Stress-Strain Modeling and Effect of Additional Hardening due to Nonproportional Loading

International Nuclear Information System (INIS)

Rashed, G.; Ghajar, R.; Farrahi, G.

2007-01-01

Most engineering components are subjected to multiaxial rather than uniaxial cyclic loading, which causes multiaxial fatigue. The pre-requisite to predict the fatigue life of such components is to determine the multiaxial stress strain relationship. In this paper the multiaxial cyclic stress-strain model under proportional loading is derived using the modified power law stress-strain relationship. The equivalent strain amplitude consisted of the normal strain excursion and maximum shear strain amplitude is used in the proportional model to include the additional hardening effect due to nonproportional loading. Therefore a new multiaxial cyclic stress-strain relationship is devised for out of phase nonproportional loading. The model is applied to the nonproportional loading case and the results are compared with the other researchers' experimental data published in the literature, which are in a reasonable agreement with the experimental data. The relationship presented here is convenient for the engineering applications

An in situ thermo-mechanical rig for lattice strain measurement during creep using neutron diffraction

Science.gov (United States)

Wang, Y. Q.; Kabra, S.; Zhang, S. Y.; Truman, C. E.; Smith, D. J.

2018-05-01

A long-term high-temperature testing stress rig has been designed and fabricated for performing in situ neutron diffraction tests at the ENGIN-X beamline, ISIS facility in the UK. It is capable of subjecting metals to high temperatures up to 800 °C and uniaxial loading under different boundary conditions including constant load, constant strain, and elastic follow-up, each with minimum of external control. Samples are held horizontally between grips and connected to a rigid rig frame, a soft aluminium bar, and a stepper motor with forces up to 20 kN. A new three zone split electrical resistance furnace which generates a stable and uniform heat atmosphere over 200 mm length was used to heat the samples. An 8 mm diameter port at 45° to the centre of the furnace was made in order to allow the neutron beam through the furnace to illuminate the sample. The entire instrument is mounted on the positioner at ENGIN-X and has the potential ability to operate continuously while being moved in and out of the neutron diffraction beam. The performance of the rig has been demonstrated by tracking the evolution of lattice strains in type 316H stainless steel under elastic follow-up control at 550 °C.

Growth of strained, ferroelectric NaNbO{sub 3} thin films by pulsed laser deposition

Energy Technology Data Exchange (ETDEWEB)

Sellmann, Jan; Schwarzkopf, Jutta; Duk, Andreas; Kwasniewski, Albert; Schmidbauer, Martin; Fornari, Roberto [IKZ, Berlin (Germany)

2012-07-01

Due to its promising ferro-/piezoelectric properties and high Curie temperature NaNbO{sub 3} has attracted much attention. In contrast to bulk crystals, thin epitaxial films may incorporate and maintain a certain compressive or tensile lattice strain, depending on the used substrate/film combination. This deformation of the crystal lattice is known to strongly influence the ferroelectric properties of perovskites. In the case of NaNbO{sub 3} compressive strain is achieved in films deposited on NdGaO{sub 3} and SrTiO{sub 3} substrates while deposition on DyScO{sub 3} and TbScO{sub 3} leads to tensile in-plane strain. In order to characterize and practically apply the ferroelectric films, it is necessary to embed them in a capacitor structure for which we use pseudomorphically grown SrRuO{sub 3} as bottom electrodes. We report on the deposition of SrRuO{sub 3} and NaNbO{sub 3} single layers on SrTiO{sub 3}, DyScO{sub 3}, TbScO{sub 3} and NbGaO{sub 3} substrates by means of pulsed laser deposition. By adjusting the substrate temperature, the oxygen partial pressure and the laser frequency we have successfully deposited smooth, strained, single phase NaNbO{sub 3} thin films. Investigations of the films by atomic force microscopy and high resolution X-ray diffraction reveal the dependence of the surface morphology and the incorporated lattice strain on the deposition parameters and the lattice mismatch, respectively. All films exhibit piezoelectric properties, as proven by piezoresponse force microscopy.

Enhanced Electron Mobility in Nonplanar Tensile Strained Si Epitaxially Grown on SixGe1-x Nanowires.

Science.gov (United States)

Wen, Feng; Tutuc, Emanuel

2018-01-10

We report the growth and characterization of epitaxial, coherently strained Si x Ge 1-x -Si core-shell nanowire heterostructure through vapor-liquid-solid growth mechanism for the Si x Ge 1-x core, followed by an in situ ultrahigh-vacuum chemical vapor deposition for the Si shell. Raman spectra acquired from individual nanowire reveal the Si-Si, Si-Ge, and Ge-Ge modes of the Si x Ge 1-x core and the Si-Si mode of the shell. Because of the compressive (tensile) strain induced by lattice mismatch, the core (shell) Raman modes are blue (red) shifted compared to those of unstrained bare Si x Ge 1-x (Si) nanowires, in good agreement with values calculated using continuum elasticity model coupled with lattice dynamic theory. A large tensile strain of up to 2.3% is achieved in the Si shell, which is expected to provide quantum confinement for electrons due to a positive core-to-shell conduction band offset. We demonstrate n-type metal-oxide-semiconductor field-effect transistors using Si x Ge 1-x -Si core-shell nanowires as channel and observe a 40% enhancement of the average electron mobility compared to control devices using Si nanowires due to an increased electron mobility in the tensile-strained Si shell.

Generalized hydrodynamic transport in lattice-gas automata

Science.gov (United States)

Luo, Li-Shi; Chen, Hudong; Chen, Shiyi; Doolen, Gary D.; Lee, Yee-Chun

1991-01-01

The generalized hydrodynamics of two-dimensional lattice-gas automata is solved analytically in the linearized Boltzmann approximation. The dependence of the transport coefficients (kinematic viscosity, bulk viscosity, and sound speed) upon wave number k is obtained analytically. Anisotropy of these coefficients due to the lattice symmetry is studied for the entire range of wave number, k. Boundary effects due to a finite mean free path (Knudsen layer) are analyzed, and accurate comparisons are made with lattice-gas simulations.

Intragranular twinning, detwinning, and twinning-like lattice reorientation in magnesium alloys

International Nuclear Information System (INIS)

Wu, Wei; Gao, Yanfei; Li, Nan; Parish, Chad M.; Liu, Wenjun; Liaw, Peter K.; An, Ke

2016-01-01

Deformation twinning plays a critical role on improving metals or alloys ductility, especially for hexagonal close-packed materials with low symmetry crystal structure. A rolled Mg alloy was selected as a model system to investigate the extension twinning behaviors and characteristics of parent-twin interactions by nondestructive in situ 3D synchrotron X-ray microbeam diffraction. Besides twinning-detwinning process, the “twinning-like” lattice reorientation process was captured within an individual grain inside a bulk material during the strain reversal. The distributions of parent, twin, and reorientated grains and sub-micron level strain variation across the twin boundary are revealed. A theoretical calculation of the lattice strain confirms that the internal strain distribution in parent and twinned grains correlates with the experimental setup, grain orientation of parent, twin, and surrounding grains, as well as the strain path changes. The study suggests a novel deformation mechanism within the hexagonal close-packed structure that cannot be determined from surface-based characterization methods.

Effect of strain on geometric and electronic structures of graphene on a Ru(0001) surface

Institute of Scientific and Technical Information of China (English)

Sun Jia-Tao; Du Shi-Xuan; Xiao Wen-De; Hu Hao; Zhang Yu-Yang; Li Guo; Gao Hong-Jun

2009-01-01

The atomic and electronic structures of a graphene monolayer on a Ru(0001) surface under compressive strain are investigated by using first-principles calculations. Three models of graphene monolayers with different carbon periodicities due to the lattice mismatch are proposed in the presence and the. absence of the Ru(0001) substrate separately. Considering the strain induced by the lattice mismatch, we optimize the atomic structures and investigate the electronic properties of the graphene. Our calculation results show that the graphene layers turn into periodic corrugations and there exist strong chemical bonds in the interface between the graphene N x N superlattice and the substrate. The strain does not induce significant changes in electronic structure. Furthermore, the results calculated in the local density approximation (LDA) are compared with those obtained in the generalized gradient approximation (GGA), showing that the LDA results are more reasonable than the GGA results when only two substrate layers are used in calculation.

EXPERIMENTAL TESTS OF VANADIUM STRENGTH MODELS AT HIGH PRESSURES AND STRAIN RATES

Energy Technology Data Exchange (ETDEWEB)

Park, H; Barton, N R; Becker, R C; Bernier, J V; Cavallo, R M; Lorenz, K T; Pollaine, S M; Remington, B A; Rudd, R E

2010-03-02

Experimental results showing significant reductions from classical in the Rayleigh-Taylor (RT) instability growth rate due to high pressure material strength or effective lattice viscosity in metal foils are presented. On the Omega Laser in the Laboratory for Laser Energetics, University of Rochester, target samples of polycrystalline vanadium are compressed and accelerated quasi-isentropically at {approx}1 Mbar pressures, while maintaining the samples in the solid-state. Comparison of the results with constitutive models for solid state strength under these conditions show that the measured RT growth is substantially lower than predictions using existing models that work well at low pressures and long time scales. High pressure, high strain rate data can be explained by the enhanced strength due to a phonon drag mechanism, creating a high effective lattice viscosity.

Shear deformation and relaxed lattice constant of (Ga,Mn)As layers on GaAs(113)A

Energy Technology Data Exchange (ETDEWEB)

Dreher, Lukas; Daeubler, Joachim; Glunk, Michael; Schoch, Wladimir; Limmer, Wolfgang; Sauer, Rolf [Institut fuer Halbleiterphysik, Universitaet Ulm, D-89069 Ulm (Germany)

2008-07-01

The shear deformation and the relaxed lattice constant of compressively strained (Ga,Mn)As layers with Mn concentrations of up to 5%, pseudomorphically grown on GaAs(113)A and GaAs(001) substrates by low-temperature molecular-beam epitaxy, have been studied by high resolution X-ray diffraction (HRXRD) measurements. Rocking curves reveal a triclinic distortion of the (113)A layers with a shear direction towards the [001] crystallographic axis, whereas the (001) layers are tetragonally distorted along [001]. The relaxed lattice constants were derived from {omega}-2{theta} scans for the symmetric (113) and (004) Bragg reflections, taking the elastic anisotropy of the cubic system into account. The increase of the lattice constant with Mn content has been found to be smaller for the (113)A layers than for the (001) layers, presumably due to the enhanced amount of excess As in the (113)A layers.

Intertwined Lattice Deformation and Magnetism in Monovacancy Graphene

OpenAIRE

Padmanabhan, Haricharan; Nanda, B. R. K.

2016-01-01

Using density functional calculations we have investigated the local spin moment formation and lattice deformation in graphene when an isolated vacancy is created. We predict two competing equilibrium structures: a ground state planar configuration with a saturated local moment of 1.5 $\\mu_B$, and a metastable non-planar configuration with a vanishing magnetic moment, at a modest energy expense of ~50 meV. Though non-planarity relieves the lattice of vacancy-induced strain, the planar state i...

Influence of the Strain History on TWIP Steel Deformation Mechanisms in the Deep-Drawing Process

Science.gov (United States)

Lapovok, R.; Timokhina, I.; Mester, A.-K.; Weiss, M.; Shekhter, A.

2018-06-01

A study of preferable deformation modes on strain path and strain level in a TWIP steel sheet was performed. Different strain paths were obtained by stretch forming of specimens with various shapes and tensile tests. TEM analysis was performed on samples cut from various locations in the deformed specimens, which had different strain paths and strain levels and the preferable deformation modes were identified. Stresses caused by various strain paths were considered and an analytical analysis performed to identify the preferable deformation modes for the case of single crystal. For a single crystal, in assumption of the absence of lattice rotation, the strain path and the level of accumulated equivalent strain define the preferable deformation mode. For a polycrystalline material, such analytical analysis is not possible due to the large number of grains and, therefore, numerical simulation was employed. For the polycrystalline material, the role of strain path diminishes due to the presence of a large number of grains with random orientations and the effect of accumulated strain becomes dominant. However, at small strains the strain path still defines the level of twinning activity. TEM analysis experimentally confirmed that various deformation modes lead to different deformation strengthening mechanisms.

Characterization of carrier transport properties in strained crystalline Si wall-like structures in the quasi-quantum regime

Energy Technology Data Exchange (ETDEWEB)

Mayberry, C. S.; Huang, Danhong, E-mail: danhong.huang@us.af.mil; Kouhestani, C. [Air Force Research Laboratory, Space Vehicles Directorate, Kirtland Air Force Base, New Mexico 87117 (United States); Balakrishnan, G. [Department of Electrical and Computer Engineering, University of New Mexico, Albuquerque, New Mexico 87106 (United States); Islam, N. [Department of Electrical and Computer Engineering, University of Missouri-Columbia, Columbia, Missouri 65211 (United States); Brueck, S. R. J. [Department of Electrical and Computer Engineering, University of New Mexico, Albuquerque, New Mexico 87106 (United States); Department of Physics and Astronomy, University of New Mexico, Albuquerque, New Mexico 87106 (United States); Sharma, A. K. [Air Force Research Laboratory, Space Vehicles Directorate, Kirtland Air Force Base, New Mexico 87117 (United States); Department of Electrical and Computer Engineering, University of New Mexico, Albuquerque, New Mexico 87106 (United States)

2015-10-07

We report the transport characteristics of both electrons and holes through narrow constricted crystalline Si “wall-like” long-channels that were surrounded by a thermally grown SiO{sub 2} layer. The strained buffering depth inside the Si region (due to Si/SiO{sub 2} interfacial lattice mismatch) is where scattering is seen to enhance some modes of the carrier-lattice interaction, while suppressing others, thereby changing the relative value of the effective masses of both electrons and holes, as compared to bulk Si. In the narrowest wall devices, a considerable increase in conductivity was observed as a result of higher carrier mobilities due to lateral constriction and strain. The strain effects, which include the reversal splitting of light- and heavy-hole bands as well as the decrease of conduction-band effective mass by reduced Si bandgap energy, are formulated in our microscopic model for explaining the experimentally observed enhancements in both conduction- and valence-band mobilities with reduced Si wall thickness. Also, the enhancements of the valence-band and conduction-band mobilities are found to be associated with different aspects of theoretical model.

Bidirectional Fano Algorithm for Lattice Coded MIMO Channels

KAUST Repository

Al-Quwaiee, Hessa

2013-01-01

channel model. Channel codes based on lattices are preferred due to three facts: lattice codes have simple structure, the code can achieve the limits of the channel, and they can be decoded efficiently using lattice decoders which can be considered

Heteroepitaxial growth of strained multilayer thin films of high-temperature superconductors

International Nuclear Information System (INIS)

Gross, R.; Gupta, A.; Olsson, E.; Segmueller, A.; Koren, G.

1991-01-01

Recently, the heteroepitaxial growth of multilayer structures of different copper oxide superconductors has been reported by several groups. In general, two different types of multilayer structures should be distinguished. The first kind of mulitlayer is formed by high-T c materials having the same crystal structure and almost the same lattice constants, as for example ReBa 2 Cu 3 O 7 (Re=rare earth) multilayers with alternating Re-elements. In these multilayers the two different rare earth copper oxides (Y/Dy, Y/Pr) have the same orthorhombic unit cell. Due to the very similar lattice constants, the misfit strain is easily accommodated without the formation of defects. The second kind of multilayer is formed by layers of materials having different crystal structure and lattice parameters. In these multilayers the misfit can be coherently accommodated below a critical modulation thickness as discussed below. This renders possible the heteroepitaxial growth of strained multilayer structures, both of two copper oxides of different crystal structure, as has been demonstrated recently for the system YBa 2 Cu 3 O 7-δ /Nd 1.83 Ce 0.17 CuO x , and of superconducting copper oxides and insulating materials. For multilayers of different copper oxides, a combination of almost all high-Tc materials should be possible, since the presence of the CuO 2 sheets in these materials results in similar lattice constants in their basal planes ('a' and 'b'). (orig./BHO)

High resolution electron back-scatter diffraction analysis of thermally and mechanically induced strains near carbide inclusions in a superalloy

Energy Technology Data Exchange (ETDEWEB)

Karamched, Phani S., E-mail: phani.karamched@materials.ox.ac.uk [Department of Materials, University of Oxford, Parks Road, Oxford OX1 3PH (United Kingdom); Wilkinson, Angus J. [Department of Materials, University of Oxford, Parks Road, Oxford OX1 3PH (United Kingdom)

2011-01-15

Cross-correlation-based analysis of electron back-scatter diffraction (EBSD) patterns has been used to obtain high angular resolution maps of lattice rotations and elastic strains near carbides in a directionally solidified superalloy MAR-M-002. Lattice curvatures were determined from the EBSD measurements and used to estimate the distribution of geometrically necessary dislocations (GNDs) induced by the deformation. Significant strains were induced by thermal treatment due to the lower thermal expansion coefficient of the carbide inclusions compared to that of the matrix. In addition to elastic strains the mismatch was sufficient to have induced localized plastic deformation in the matrix leading to a GND density of 3 x 10{sup 13} m{sup -2} in regions around the carbide. Three-point bending was then used to impose strain levels within the range {+-}12% across the height of the bend bar. EBSD lattice curvature measurements were then made at both carbide-containing and carbide-free regions at different heights across the bar. The average GND density increases with the magnitude of the imposed strain (both in tension and compression), and is markedly higher near the carbides particles. The higher GND densities near the carbides (order of 10{sup 14} m{sup -2}) are generated by the large strain gradients produced around the plastically rigid inclusion during mechanical deformation with some minor contribution from the pre-existing residual deformation caused by the thermal mismatch between carbide and nickel matrix.

Aliasing modes in the lattice Schwinger model

International Nuclear Information System (INIS)

Campos, Rafael G.; Tututi, Eduardo S.

2007-01-01

We study the Schwinger model on a lattice consisting of zeros of the Hermite polynomials that incorporates a lattice derivative and a discrete Fourier transform with many properties. Such a lattice produces a Klein-Gordon equation for the boson field and the exact value of the mass in the asymptotic limit if the boundaries are not taken into account. On the contrary, if the lattice is considered with boundaries new modes appear due to aliasing effects. In the continuum limit, however, this lattice yields also a Klein-Gordon equation with a reduced mass

Strain release in metastable CdSe/CdS quantum dots

Energy Technology Data Exchange (ETDEWEB)

Gong, Ke; Beane, Gary; Kelley, David F., E-mail: dfkelley@ucmerced.edu

2016-06-01

Highlights: • We have synthesized CdSe/CdS core/shell quantum dots in the “stable” and “metastable” regimes. • Annealing of metastable particles causes lattice strain release, producing hole-trapping defects. • Electron microscopy imaging is relatively insensitive to defects that result in rapid radiationless decay. - Abstract: It has recently been shown (J. Phys. Chem. Lett., 2015, 6, 1559) that high quantum yields (QYs) in zincblende CdSe/CdS quantum dots can be achieved when the lattice strain energy density is in the stable (0–0.59 eV/nm{sup 2}) or metastable (0.59–0.85 eV/nm{sup 2}) regime. Annealing of metastable particles causes a dramatic reduction in the observed QY and a red shift of the absorbance and photoluminescence. In this work we demonstrate that the decline in QY upon annealing is due to the formation of hole traps. These traps, while dramatically affecting the observed QY, produce no significant changes in either morphology or crystallinity as determined by high resolution transmission electron microscopy (HRTEM).

Dependence on the growth direction of the strain in AlGaSb alloys

Energy Technology Data Exchange (ETDEWEB)

Rojas-Lopez, M; Delgado-Macuil, R; Gayou, V L; Orduna-Diaz, A [CIBA-Tlaxcala, IPN, Tlaxcala, Tlax. (Mexico); Momox-Beristain, E [FC-BUAP, Puebla, Pue. (Mexico); Salazar-Hernandez, B [CIICAp-UAEM, Cuernavaca, Mor. (Mexico); Rodriguez, A G, E-mail: marlonrl@yahoo.com.m [IICO-UASLP, San Luis Potosi, S.L.P. (Mexico)

2009-05-01

High resolution x-ray diffraction profiles were obtained from Al{sub x}Ga{sub 1-x}Sb layers grown on (001) and (111) GaSb substrates. The out of plane lattice parameter, was estimated directly from the symmetrical diffractions for (001) and (111) alloys. These results show that all the layers are strained, and those grown on (001) GaSb are slightly more strained than the corresponding layers grown on (111) GaSb. This difference is explained by the dependence of the strain ratio on growth direction. The out of plane lattice parameter as a function of Al content is higher than the corresponding bulk lattice parameter of Al{sub x}Ga{sub 1-x}Sb layers obtained with Vegard's law. Also, the perpendicular and the in-plane lattice parameter expected for pseudomorphic alloys, was estimated from the strain ratios, assuming an elastic deformation and using the EDX alloy composition to interpolate the elastic constants C{sub ij}. This estimation also shows that almost all the layers are fully strained.

Dynamic scattering theory for dark-field electron holography of 3D strain fields.

Science.gov (United States)

Lubk, Axel; Javon, Elsa; Cherkashin, Nikolay; Reboh, Shay; Gatel, Christophe; Hÿtch, Martin

2014-01-01

Dark-field electron holography maps strain in crystal lattices into reconstructed phases over large fields of view. Here we investigate the details of the lattice strain-reconstructed phase relationship by applying dynamic scattering theory both analytically and numerically. We develop efficient analytic linear projection rules for 3D strain fields, facilitating a straight-forward calculation of reconstructed phases from 3D strained materials. They are used in the following to quantify the influence of various experimental parameters like strain magnitude, specimen thickness, excitation error and surface relaxation. © 2013 Elsevier B.V. All rights reserved.

Anomalous giant piezoresistance in AlAs 2D electron systems with antidot lattices.

Science.gov (United States)

Gunawan, O; Gokmen, T; Shkolnikov, Y P; De Poortere, E P; Shayegan, M

2008-01-25

An AlAs two-dimensional electron system patterned with an antidot lattice exhibits a giant piezoresistance effect at low temperatures, with a sign opposite to the piezoresistance observed in the unpatterned region. We suggest that the origin of this anomalous giant piezoresistance is the nonuniform strain in the antidot lattice and the exclusion of electrons occupying the two conduction-band valleys from different regions of the sample. This is analogous to the well-known giant magnetoresistance effect, with valley playing the role of spin and strain the role of magnetic field.

Lattice strain measurements on sandstones under load using neutron diffraction

Science.gov (United States)

Frischbutter, A.; Neov, D.; Scheffzük, Ch.; Vrána, M.; Walther, K.

2000-11-01

Neutron diffraction methods (both time-of-flight- and angle-dispersive diffraction) are applied to intracrystalline strain measurements on geological samples undergoing uniaxial increasing compressional load. The experiments were carried out on Cretaceous sandstones from the Elbezone (East Germany), consisting of >95% quartz which are bedded but without crystallographic preferred orientation of quartz. From the stress-strain relation the Young's modulus for our quartz sample was determined to be (72.2±2.9) GPa using results of the neutron time-of-flight method. The influence of different kinds of bedding in sandstones (laminated and convolute bedding) could be determined. We observed differences of factor 2 (convolute bedding) and 3 (laminated bedding) for the elastic stiffness, determined with angle dispersive neutron diffraction (crystallographic strain) and with strain gauges (mechanical strain). The data indicate which geological conditions may influence the stress-strain behaviour of geological materials. The influence of bedding on the stress-strain behaviour of a laminated bedded sandstone was indicated by direct residual stress measurements using neutron time-of-flight diffraction. The measurements were carried out six days after unloading the sample. Residual strain was measured for three positions from the centre to the periphery and within two radial directions of the cylinder. We observed that residual strain changes from extension to compression in a different manner for two perpendicular directions of the bedding plane.

Femtosecond visualization of lattice dynamics in shock-compressed matter.

Science.gov (United States)

Milathianaki, D; Boutet, S; Williams, G J; Higginbotham, A; Ratner, D; Gleason, A E; Messerschmidt, M; Seibert, M M; Swift, D C; Hering, P; Robinson, J; White, W E; Wark, J S

2013-10-11

The ultrafast evolution of microstructure is key to understanding high-pressure and strain-rate phenomena. However, the visualization of lattice dynamics at scales commensurate with those of atomistic simulations has been challenging. Here, we report femtosecond x-ray diffraction measurements unveiling the response of copper to laser shock-compression at peak normal elastic stresses of ~73 gigapascals (GPa) and strain rates of 10(9) per second. We capture the evolution of the lattice from a one-dimensional (1D) elastic to a 3D plastically relaxed state within a few tens of picoseconds, after reaching shear stresses of 18 GPa. Our in situ high-precision measurement of material strength at spatial (<1 micrometer) and temporal (<50 picoseconds) scales provides a direct comparison with multimillion-atom molecular dynamics simulations.

Phase volume fractions and strain measurements in an ultrafine-grained NiTi shape-memory alloy during tensile loading

International Nuclear Information System (INIS)

Young, M.L.; Wagner, M.F.-X.; Frenzel, J.; Schmahl, W.W.; Eggeler, G.

2010-01-01

An ultrafine-grained pseudoelastic NiTi shape-memory alloy wire with 50.9 at.% Ni was examined using synchrotron X-ray diffraction during in situ uniaxial tensile loading (up to 1 GPa) and unloading. Both macroscopic stress-strain measurements and volume-averaged lattice strains are reported and discussed. The loading behavior is described in terms of elasto-plastic deformation of austenite, emergence of R phase, stress-induced martensitic transformation, and elasto-plastic deformation, grain reorientation and detwinning of martensite. The unloading behavior is described in terms of stress relaxation and reverse plasticity of martensite, reverse transformation of martensite to austenite due to stress relaxation, and stress relaxation of austenite. Microscopically, lattice strains in various crystallographic directions in the austenitic B2, martensitic R, and martensitic B19' phases are examined during loading and unloading. It is shown that the phase transformation occurs in a localized manner along the gage length at the plateau stress. Phase volume fractions and lattice strains in various crystallographic reflections in the austenite and martensite phases are examined over two transition regions between austenite and martensite, which have a width on the order of the wire diameter. Anisotropic effects observed in various crystallographic reflections of the austenitic phase are also discussed. The results contribute to a better understanding of the tensile loading behavior, both macroscopically and microscopically, of NiTi shape-memory alloys.

Relationship between changes in the crystal lattice strain and thermal conductivity of high burnup UO{sub 2} pellets

Energy Technology Data Exchange (ETDEWEB)

Amaya, Masaki, E-mail: amaya.masaki@jaea.go.j [Fuel Safety Research Group, Nuclear Safety Research Center, Japan Atomic Energy Agency, Tokai-mura, Naka-gun, Ibaraki 319-1195 (Japan); Nakamura, Jinichi; Fuketa, Toyoshi [Fuel Safety Research Group, Nuclear Safety Research Center, Japan Atomic Energy Agency, Tokai-mura, Naka-gun, Ibaraki 319-1195 (Japan); Kosaka, Yuji [Nuclear Development Corporation, 622-12, Funaishikawa, Tokai-mura, Naka-gun, Ibaraki 319-1111 (Japan)

2010-01-01

Two kinds of disk-shaped UO{sub 2} samples (4 mm in diameter and 1 mm in thickness) were irradiated in a test reactor up to about 60 and 130 GWd/t, respectively. The microstructures of the samples were investigated by means of optical microscopy, scanning electron microscopy/ electron probe micro-analysis (SEM/EPMA) and micro-X-ray diffractometry. The measured lattice parameters tended to be considerably smaller than the reported values, and the typical cauliflower structure which is often observed in high burnup fuel pellet is hardly seen in these samples. Thermal diffusivities of the samples were also measured by using a laser flash method, and their thermal conductivities were evaluated by multiplying the heat capacity of unirradiated UO{sub 2} and sample densities. While the thermal conductivities of sample 2 showed recovery after being annealed at 1500 K, those of sample 4 were not clearly observed even after being annealed at 1500 K. These trends suggest that the amount of accumulated irradiation-induced defects depends on the irradiation condition of each sample. From the comparison of the changes in the lattice parameter and strain energy density before and after the thermal diffusivity measurements, it is likely that the thermal conductivity recovery in the temperature region from 1200 to 1500 K is related to the migration of dislocation.

Lattice-Based Revocable Certificateless Signature

Directory of Open Access Journals (Sweden)

Ying-Hao Hung

2017-10-01

Full Text Available Certificateless signatures (CLS are noticeable because they may resolve the key escrow problem in ID-based signatures and break away the management problem regarding certificate in conventional signatures. However, the security of the mostly previous CLS schemes relies on the difficulty of solving discrete logarithm or large integer factorization problems. These two problems would be solved by quantum computers in the future so that the signature schemes based on them will also become insecure. For post-quantum cryptography, lattice-based cryptography is significant due to its efficiency and security. However, no study on addressing the revocation problem in the existing lattice-based CLS schemes is presented. In this paper, we focus on the revocation issue and present the first revocable CLS (RCLS scheme over lattices. Based on the short integer solution (SIS assumption over lattices, the proposed lattice-based RCLS scheme is shown to be existential unforgeability against adaptive chosen message attacks. By performance analysis and comparisons, the proposed lattice-based RCLS scheme is better than the previously proposed lattice-based CLS scheme, in terms of private key size, signature length and the revocation mechanism.

Buried Porous Silicon-Germanium Layers in Monocrystalline Silicon Lattices

Science.gov (United States)

Fathauer, Robert W. (Inventor); George, Thomas (Inventor); Jones, Eric W. (Inventor)

1998-01-01

Monocrystalline semiconductor lattices with a buried porous semiconductor layer having different chemical composition is discussed and monocrystalline semiconductor superlattices with a buried porous semiconductor layers having different chemical composition than that of its monocrystalline semiconductor superlattice are discussed. Lattices of alternating layers of monocrystalline silicon and porous silicon-germanium have been produced. These single crystal lattices have been fabricated by epitaxial growth of Si and Si-Ge layers followed by patterning into mesa structures. The mesa structures are strain etched resulting in porosification of the Si-Ge layers with a minor amount of porosification of the monocrystalline Si layers. Thicker Si-Ge layers produced in a similar manner emitted visible light at room temperature.

Emergence of Clostridium difficile infection due to a new hypervirulent strain, polymerase chain reaction ribotype 078

NARCIS (Netherlands)

Goorhuis, Abraham; Bakker, Dennis; Corver, Jeroen; Debast, Sylvia B.; Harmanus, Celine; Notermans, Daan W.; Bergwerff, Aldert A.; Dekker, Frido W.; Kuijper, Ed J.

2008-01-01

Since 2005, an increase in the prevalence of Clostridium difficile infection (CDI) due to polymerase chain reaction ribotype 078 has been noticed in The Netherlands. This strain has also been identified as the predominant strain in pigs and calves. CDI caused by type 078 was studied in relation to

Advancements in simulations of lattice quantum chromodynamics

International Nuclear Information System (INIS)

Lippert, T.

2008-01-01

An introduction to lattice QCD with emphasis on advanced fermion formulations and their simulation is given. In particular, overlap fermions will be presented, a quite novel fermionic discretization scheme that is able to exactly preserve chiral symmetry on the lattice. I will discuss efficiencies of state-of-the-art algorithms on highly scalable supercomputers and I will show that, due to many algorithmic improvements, overlap simulations will soon become feasible for realistic physical lattice sizes. Finally I am going to sketch the status of some current large scale lattice QCD simulations. (author)

Annealing effect of H+ -implanted single crystal silicon on strain and crystal structure

International Nuclear Information System (INIS)

Duo Xinzhong; Liu Weili; Zhang Miao; Gao Jianxia; Fu Xiaorong; Lin Chenglu

2000-01-01

The work focuses on the rocking curves of H + -implanted single silicon crystal detected by Four-Crystal X-ray diffractometer. The samples were annealed under different temperatures. Lattice defect in H + -implanted silicon crystals was detected by Rutherford Backscattering Spectrometry. It appeared that H-related complex did not crush until annealing temperature reached about 400 degree C. At that temperature H 2 was formed, deflated in silicon lattice and strained the lattice. But defects did not come into being in large quantity. The lattice was undamaged. When annealing temperature reached 500 degree C, strain induced by H 2 deflation crashed the silicon lattice. A large number of defects were formed. At the same time bubbles in the crystal and blister/flaking on the surface could be observed

Stepwise transformation behavior of the strain-induced martensitic transformation in a metastable stainless steel

International Nuclear Information System (INIS)

Hedstroem, Peter; Lienert, Ulrich; Almer, Jon; Oden, Magnus

2007-01-01

In situ high-energy X-ray diffraction during tensile loading has been used to investigate the evolution of lattice strains and the accompanying strain-induced martensitic transformation in cold-rolled sheets of a metastable stainless steel. At high applied strains the transformation to α-martensite occurs in stepwise bursts. These stepwise transformation events are correlated with stepwise increased lattice strains and peak broadening in the austenite phase. The stepwise transformation arises from growth of α-martensite embryos by autocatalytic transformation

Initial Mechanical Testing of Superalloy Lattice Block Structures Conducted

Science.gov (United States)

Krause, David L.; Whittenberger, J. Daniel

2002-01-01

The first mechanical tests of superalloy lattice block structures produced promising results for this exciting new lightweight material system. The testing was performed in-house at NASA Glenn Research Center's Structural Benchmark Test Facility, where small subelement-sized compression and beam specimens were loaded to observe elastic and plastic behavior, component strength levels, and fatigue resistance for hundreds of thousands of load cycles. Current lattice block construction produces a flat panel composed of thin ligaments arranged in a three-dimensional triangulated trusslike structure. Investment casting of lattice block panels has been developed and greatly expands opportunities for using this unique architecture in today's high-performance structures. In addition, advances made in NASA's Ultra-Efficient Engine Technology Program have extended the lattice block concept to superalloy materials. After a series of casting iterations, the nickel-based superalloy Inconel 718 (IN 718, Inco Alloys International, Inc., Huntington, WV) was successfully cast into lattice block panels; this combination offers light weight combined with high strength, high stiffness, and elevated-temperature durability. For tests to evaluate casting quality and configuration merit, small structural compression and bend test specimens were machined from the 5- by 12- by 0.5-in. panels. Linear elastic finite element analyses were completed for several specimen layouts to predict material stresses and deflections under proposed test conditions. The structural specimens were then subjected to room-temperature static and cyclic loads in Glenn's Life Prediction Branch's material test machine. Surprisingly, the test results exceeded analytical predictions: plastic strains greater than 5 percent were obtained, and fatigue lives did not depreciate relative to the base material. These assets were due to the formation of plastic hinges and the redundancies inherent in lattice block construction

Strain amplitude-dependent anelasticity in Cu-Ni solid solution due to thermally activated and athermal dislocation-point obstacle interactions

Science.gov (United States)

Kustov, S.; Gremaud, G.; Benoit, W.; Golyandin, S.; Sapozhnikov, K.; Nishino, Y.; Asano, S.

1999-02-01

Experimental investigations of the internal friction and the Young's modulus defect in single crystals of Cu-(1.3-7.6) at. % Ni have been performed for 7-300 K over a wide range of oscillatory strain amplitudes. Extensive data have been obtained at a frequency of vibrations around 100 kHz and compared with the results obtained for the same crystals at a frequency of ˜1 kHz. The strain amplitude dependence of the anelastic strain amplitude and the average friction stress acting on a dislocation due to solute atoms are also analyzed. Several stages in the strain amplitude dependence of the internal friction and the Young's modulus defect are revealed for all of the alloy compositions, at different temperatures and in different frequency ranges. For the 100 kHz frequency, low temperatures and low strain amplitudes (˜10-7-10-5), the amplitude-dependent internal friction and the Young's modulus defect are essentially temperature independent, and are ascribed to a purely hysteretic internal friction component. At higher strain amplitudes, a transition stage and a steep strain amplitude dependence of the internal friction and the Young's modulus defect are observed, followed by saturation at the highest strain amplitudes employed. These stages are temperature and frequency dependent and are assumed to be due to thermally activated motion of dislocations. We suggest that the observed regularities in the entire strain amplitude, temperature and frequency ranges correspond to a motion of dislocations in a two-component system of obstacles: weak but long-range ones, due to the elastic interaction of dislocations with solute atoms distributed in the bulk of the crystal; and strong short-range ones, due to the interaction of dislocations with solute atoms distributed close to dislocation glide planes. Based on these assumptions, a qualitative explanation is given for the variety of experimental observations.

Collisional shifts in optical-lattice atom clocks

International Nuclear Information System (INIS)

Band, Y. B.; Vardi, A.

2006-01-01

We theoretically study the effects of elastic collisions on the determination of frequency standards via Ramsey-fringe spectroscopy in optical-lattice atom clocks. Interparticle interactions of bosonic atoms in multiply occupied lattice sites can cause a linear frequency shift, as well as generate asymmetric Ramsey-fringe patterns and reduce fringe visibility due to interparticle entanglement. We propose a method of reducing these collisional effects in an optical lattice by introducing a phase difference of π between the Ramsey driving fields in adjacent sites. This configuration suppresses site-to-site hopping due to interference of two tunneling pathways, without degrading fringe visibility. Consequently, the probability of double occupancy is reduced, leading to cancellation of collisional shifts

Mineral Replacement Reactions as a Precursor to Strain Localisation: an (HR-)EBSD approach

Science.gov (United States)

Gardner, J.; Wheeler, J.; Wallis, D.; Hansen, L. N.; Mariani, E.

2017-12-01

Much remains to be learned about the links between metamorphism and deformation. Our work investigates the behaviour of fluid-mediated mineral replacement reaction products when exposed to subsequent shear stresses. We focus on albite from a metagabbro that has experienced metamorphism and subsequent deformation at greenschist facies, resulting in a reduction in grain size and associated strain localisation. EBSD maps show that prior to grain size reduction, product grains are highly distorted, yet they formed, and subsequently deformed, at temperatures at which extensive dislocation creep is unlikely. The Weighted Burgers Vector can be used to quantitatively describe the types of Burgers vectors present in geometrically necessary dislocation (GND) populations derived from 2-D EBSD map data. Application of this technique to the distorted product grains reveals the prominence of, among others, dislocations with apparent [010] Burgers vectors. This supports (with some caveats) the idea that dislocation creep is not responsible for the observed lattice distortion, as there are no known slip systems in plagioclase with a [010] Burgers vector. Distortion in a replacement microstructure has also been attributed to the presence of nanoscale product grains, which share very similar, but not identical, orientations due to topotactic nucleation from adjacent sites on the same substrate. As a precipitate, the product grains should be expected to be largely free of elastic strain. However, high angular resolution EBSD results demonstrate that product grains contain both elastic strains (> 10-3) and residual stresses (several hundred MPa), as well as GND densities on the order of 1014-1015 m-2. Thus we suggest the observed distortion (elastic strain plus rotations) in the lattice is produced during the mineral replacement reaction by a lattice mismatch and volume change between parent and product. Stored strain energy then provides a driving force for recovery and

Optimizing structure in nanodiamonds using in-situ strain-sensitive Bragg coherent diffraction imaging.

Science.gov (United States)

Hruszkewycz, Stephan; Cha, Wonsuk; Ulvestad, Andrew; Fuoss, Paul; Heremans, F. Joseph; Harder, Ross; Andrich, Paolo; Anderson, Christopher; Awschalom, David

The nitrogen-vacancy center in diamond has attracted considerable attention for nanoscale sensing due to unique optical and spin properties. Many of these applications require diamond nanoparticles which contain large amounts of residual strain due to the detonation or milling process used in their fabrication. Here, we present experimental, in-situ observations of changes in morphology and internal strain state of commercial nanodiamonds during high-temperature annealing using Bragg coherent diffraction imaging to reconstruct a strain-sensitive 3D image of individual sub-micron-sized crystals. We find minimal structural changes to the nanodiamonds at temperatures less than 650 C, and that at higher temperatures up to 750 C, the diamond-structured volume fraction of nanocrystals tend to shrink. The degree of internal lattice distortions within nanodiamond particles also decreases during the anneal. Our findings potentially enable the design of efficient processing of commercial nanodiamonds into viable materials suitable for device design. We acknowledge support from U.S. DOE, Office of Science, BES, MSE.

Strain induced irreversible critical current degradation in highly dense Bi-2212 round wire

CERN Document Server

Bjoerstad, R; Rikel, M.O.; Ballarino, A; Bottura, L; Jiang, J; Matras, M; Sugano, M; Hudspeth, J; Di Michiel, M

2015-01-01

The strain induced critical current degradation of overpressure processed straight Bi 2212/Ag wires has been studied at 77 K in self-field. For the first time superconducting properties, lattice distortions, composite wire stress and strain have been measured simultaneously in a high energy synchrotron beamline. A permanent Ic degradation of 5% occurs when the wire strain exceeds 0.60%. At a wire strain of about 0.65% a drastic n value and Ic reduction occur, and the composite stress and the Bi-2212 lattice parameter reach a plateau, indicating Bi-2212 filament fracturing. The XRD measurements show that Bi-2212 exhibits linear elastic behaviour up to the irreversible strain limit.

First-principles studies on the pressure dependences of the stress-strain relationship and elastic stability of semiconductors

International Nuclear Information System (INIS)

Wang, S Q; Ye, H Q; Yip, S

2006-01-01

We investigate the stress-strain relationship and elastic stability of zinc-blende GaP, GaN, InP and BN lattices under hydrostatic pressure by first-principles calculation. A simple and direct ab initio implementation for studying the mechanical properties of cubic crystals is developed. The four phases' full-set stress-strain coefficients in wide pressure ranges are theoretically calculated. The fundamental mechanism of elastic stability and the origin of phase transformation under hydrostatic pressure are explored. We found that the abilities for most of these lattices are enhanced to sustain axial strain but weaken to shear strain under higher pressure. The conditions of lattice stability are analysed using both the thermodynamic work-energy criterion and the elastic-stiffness criteria. We show that the lattice collapse of the perfect crystals is caused by the disappearance of their bulk moduli under volume dilation. Lattice defects are considered to be the main reason causing phase transformation under pressure. The correlation between the phonon softening and the variation of elastic coefficients is studied. The pressure dependence of the Kleinman internal strain parameter and its relationship to elastic stability is also explored

Strain Imaging of Nanoscale Semiconductor Heterostructures with X-Ray Bragg Projection Ptychography

Science.gov (United States)

Holt, Martin V.; Hruszkewycz, Stephan O.; Murray, Conal E.; Holt, Judson R.; Paskiewicz, Deborah M.; Fuoss, Paul H.

2014-04-01

We report the imaging of nanoscale distributions of lattice strain and rotation in complementary components of lithographically engineered epitaxial thin film semiconductor heterostructures using synchrotron x-ray Bragg projection ptychography (BPP). We introduce a new analysis method that enables lattice rotation and out-of-plane strain to be determined independently from a single BPP phase reconstruction, and we apply it to two laterally adjacent, multiaxially stressed materials in a prototype channel device. These results quantitatively agree with mechanical modeling and demonstrate the ability of BPP to map out-of-plane lattice dilatation, a parameter critical to the performance of electronic materials.

Excitation-dependent local symmetry reversal in single host lattice Ba2A(BO3)2:Eu3+ [A = Mg and Ca] phosphors with tunable emission colours.

Science.gov (United States)

Jayakiruba, S; Chandrasekaran, S Selva; Murugan, P; Lakshminarasimhan, N

2017-07-05

Eu 3+ activated phosphors are widely used as red emitters in various display devices and light emitting diodes (LEDs). The emission characteristics of Eu 3+ depend on the local site symmetry. The present study demonstrates the role of excitation-dependent local symmetry changes due to the structural reorganization on the emission colour tuning of Eu 3+ from orange-red to orange in single host lattices, Ba 2 Mg(BO 3 ) 2 and Ba 2 Ca(BO 3 ) 2 . The choice of these lattices was based on the difference in the extent of strain experienced by the oxygen atoms. The samples with Eu 3+ at Ba or Mg (Ca) sites were synthesized using the conventional high-temperature solid-state reaction method. The samples were characterized using powder XRD, 11 B MAS-NMR, FT-IR, and diffuse reflectance UV-Vis spectroscopic techniques. The room temperature photoluminescence (PL) recorded using different excitation wavelengths revealed a clear difference in the PL emission features due to symmetry reversal from non-inversion to inversion symmetry around Eu 3+ . The reorganization of highly strained oxygen atoms leads to such symmetry reversal. First-principles calculations were used to deduce the optimized structures of the two borate host lattices, and local geometries and their distortions upon Eu 3+ substitution. The outcomes of these calculations support the experimental findings.

Light-induced lattice expansion leads to high-efficiency perovskite solar cells

Science.gov (United States)

Tsai, Hsinhan; Asadpour, Reza; Blancon, Jean-Christophe; Stoumpos, Constantinos C.; Durand, Olivier; Strzalka, Joseph W.; Chen, Bo; Verduzco, Rafael; Ajayan, Pulickel M.; Tretiak, Sergei; Even, Jacky; Alam, Muhammad Ashraf; Kanatzidis, Mercouri G.; Nie, Wanyi; Mohite, Aditya D.

2018-04-01

Light-induced structural dynamics plays a vital role in the physical properties, device performance, and stability of hybrid perovskite–based optoelectronic devices. We report that continuous light illumination leads to a uniform lattice expansion in hybrid perovskite thin films, which is critical for obtaining high-efficiency photovoltaic devices. Correlated, in situ structural and device characterizations reveal that light-induced lattice expansion benefits the performances of a mixed-cation pure-halide planar device, boosting the power conversion efficiency from 18.5 to 20.5%. The lattice expansion leads to the relaxation of local lattice strain, which lowers the energetic barriers at the perovskite-contact interfaces, thus improving the open circuit voltage and fill factor. The light-induced lattice expansion did not compromise the stability of these high-efficiency photovoltaic devices under continuous operation at full-spectrum 1-sun (100 milliwatts per square centimeter) illumination for more than 1500 hours.

Graphene antidot lattice waveguides

DEFF Research Database (Denmark)

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...

Strain-balanced InGaN/GaN multiple quantum wells

Energy Technology Data Exchange (ETDEWEB)

Van Den Broeck, D. M.; Hosalli, A. M.; Bedair, S. M. [Department of Electrical and Computer Engineering, North Carolina State University, Raleigh, North Carolina 27695 (United States); Bharrat, D.; El-Masry, N. A. [Department of Material Science and Engineering, North Carolina State University, Raleigh, North Carolina 27695 (United States)

2014-07-21

InGaN/GaN multiple quantum well (MQW) structures suffer from a high amount of compressive strain in the InGaN wells and the accompanied piezoelectric field resulting in both a blue shift in emission and a reduction of emission intensity. We report the growth of In{sub x}Ga{sub 1−x}N/GaN “strain-balanced” multiple quantum wells (SBMQWs) grown on thick In{sub y}Ga{sub 1−y}N templates for x > y by metal organic chemical vapor deposition. SBMQWs consist of alternating layers of In{sub x}Ga{sub 1−x}N wells and GaN barriers under compressive and tensile stress, respectively, which have been lattice matched to a thick In{sub y}Ga{sub 1−y}N template. Growth of the In{sub y}Ga{sub 1−y}N template is also detailed in order to achieve thick, relaxed In{sub y}Ga{sub 1−y}N grown on GaN without the presence of V-grooves. When compared to conventional In{sub x}Ga{sub 1−x}N/GaN MQWs grown on GaN, the SBMQW structures exhibit longer wavelength emission and higher emission intensity for the same InN mole fraction due to a reduction in the well strain and piezoelectric field. By matching the average lattice constant of the MQW active region to the lattice constant of the In{sub y}Ga{sub 1−y}N template, essentially an infinite number of periods can be grown using the SBMQW growth method without relaxation-related effects. SBMQWs can be utilized to achieve longer wavelength emission in light emitting diodes without the use of excess indium and can be advantageous in addressing the “green gap.”.

Lattice Boltzmann model capable of mesoscopic vorticity computation

Science.gov (United States)

Peng, Cheng; Guo, Zhaoli; Wang, Lian-Ping

2017-11-01

It is well known that standard lattice Boltzmann (LB) models allow the strain-rate components to be computed mesoscopically (i.e., through the local particle distributions) and as such possess a second-order accuracy in strain rate. This is one of the appealing features of the lattice Boltzmann method (LBM) which is of only second-order accuracy in hydrodynamic velocity itself. However, no known LB model can provide the same quality for vorticity and pressure gradients. In this paper, we design a multiple-relaxation time LB model on a three-dimensional 27-discrete-velocity (D3Q27) lattice. A detailed Chapman-Enskog analysis is presented to illustrate all the necessary constraints in reproducing the isothermal Navier-Stokes equations. The remaining degrees of freedom are carefully analyzed to derive a model that accommodates mesoscopic computation of all the velocity and pressure gradients from the nonequilibrium moments. This way of vorticity calculation naturally ensures a second-order accuracy, which is also proven through an asymptotic analysis. We thus show, with enough degrees of freedom and appropriate modifications, the mesoscopic vorticity computation can be achieved in LBM. The resulting model is then validated in simulations of a three-dimensional decaying Taylor-Green flow, a lid-driven cavity flow, and a uniform flow passing a fixed sphere. Furthermore, it is shown that the mesoscopic vorticity computation can be realized even with single relaxation parameter.

Strain relaxation and ambipolar electrical transport in GaAs/InSb core-shell nanowires.

Science.gov (United States)

Rieger, Torsten; Zellekens, Patrick; Demarina, Natalia; Hassan, Ali Al; Hackemüller, Franz Josef; Lüth, Hans; Pietsch, Ullrich; Schäpers, Thomas; Grützmacher, Detlev; Lepsa, Mihail Ion

2017-11-30

The growth, crystal structure, strain relaxation and room temperature transport characteristics of GaAs/InSb core-shell nanowires grown using molecular beam epitaxy are investigated. Due to the large lattice mismatch between GaAs and InSb of 14%, a transition from island-based to layer-like growth occurs during the formation of the shell. High resolution transmission electron microscopy in combination with geometric phase analyses as well as X-ray diffraction with synchrotron radiation are used to investigate the strain relaxation and prove the existence of different dislocations relaxing the strain on zinc blende and wurtzite core-shell nanowire segments. While on the wurtzite phase only Frank partial dislocations are found, the strain on the zinc blende phase is relaxed by dislocations with perfect, Shockley partial and Frank partial dislocations. Even for ultrathin shells of about 2 nm thickness, the strain caused by the high lattice mismatch between GaAs and InSb is relaxed almost completely. Transfer characteristics of the core-shell nanowires show an ambipolar conductance behavior whose strength strongly depends on the dimensions of the nanowires. The interpretation is given based on an electronic band profile which is calculated for completely relaxed core/shell structures. The peculiarities of the band alignment in this situation implies simultaneously occupied electron and hole channels in the InSb shell. The ambipolar behavior is then explained by the change of carrier concentration in both channels by the gate voltage.

Unusual strain in homoepitaxial CdTe(001) layers grown by molecular beam epitaxy

Energy Technology Data Exchange (ETDEWEB)

Heinke, H.; Waag, A.; Moeller, M.O.; Regnet, M.M.; Landwehr, G. [Physikalisches Institut, Univ. Wuerzburg (Germany)

1994-01-01

For homoepitaxial CdTe(001) films grown by molecular beam epitaxy onto CdTe(001) substrates, a difference between the lattice constants of the substrate and the layer was systematically observed using high resolution X-ray diffraction. Reciprocal space maps point out an unusual strain state of such layers which is indicated by the position of their reciprocal lattice points. They lie in a section of reciprocal space which is usually forbidden by elasticity theory. The strain is laterally anisotropic leading to a monoclinic symmetry of the thin films. The lateral strain is depth dependent. Possible reasons for the formation of the unusual strain are discussed, and a correlation of the unusual strain with the growth conditions is attempted

Quantitative strain analysis of surfaces and interfaces using extremely asymmetric x-ray diffraction

International Nuclear Information System (INIS)

Akimoto, Koichi; Emoto, Takashi

2010-01-01

Strain can reduce carrier mobility and the reliability of electronic devices and affect the growth mode of thin films and the stability of nanometer-scale crystals. To control lattice strain, a technique for measuring the minute lattice strain at surfaces and interfaces is needed. Recently, an extremely asymmetric x-ray diffraction method has been developed for this purpose. By employing Darwin's dynamical x-ray diffraction theory, quantitative evaluation of strain at surfaces and interfaces becomes possible. In this paper, we review our quantitative strain analysis studies on native SiO 2 /Si interfaces, reconstructed Si surfaces, Ni/Si(111)-H interfaces, sputtered III-V compound semiconductor surfaces, high-k/Si interfaces, and Au ion-implanted Si. (topical review)

Testing the holographic principle using lattice simulations

Directory of Open Access Journals (Sweden)

Jha Raghav G.

2018-01-01

Full Text Available The lattice studies of maximally supersymmetric Yang-Mills (MSYM theory at strong coupling and large N is important for verifying gauge/gravity duality. Due to the progress made in the last decade, based on ideas from topological twisting and orbifolding, it is now possible to study these theories on the lattice while preserving an exact supersymmetry on the lattice. We present some results from the lattice studies of two-dimensional MSYM which is related to Type II supergravity. Our results agree with the thermodynamics of different black hole phases on the gravity side and the phase transition (Gregory–Laflamme between them.

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

Science.gov (United States)

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

2018-03-01

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

APS-U LATTICE DESIGN FOR OFF-AXIS ACCUMULATION

Energy Technology Data Exchange (ETDEWEB)

Sun, Yipeng; Borland, M.; Lindberg, R.; Sajaev, V.

2017-06-25

A 67-pm hybrid-seven-bend achromat (H7BA) lattice is being proposed for a future Advanced Photon Source (APS) multi-bend-achromat (MBA) upgrade project. This lattice design pushes for smaller emittance and requires use of a swap-out (on-axis) injection scheme due to limited dynamic acceptance. Alternate lattice design work has also been performed for the APS upgrade to achieve better beam dynamics performance than the nominal APS MBA lattice, in order to allow off-axis accumulation. Two such alternate H7BA lattice designs, which target a still-low emittance of 90 pm, are discussed in detail in this paper. Although the single-particle-dynamics performance is good, simulations of collective effects indicate that surprising difficulty would be expected accumulating high single-bunch charge in this lattice. The brightness of the 90-pm lattice is also a factor of two lower than the 67-pm H7BA lattice.

Supersymmetry on a space-time lattice

International Nuclear Information System (INIS)

Kaestner, Tobias

2008-01-01

In this thesis the WZ model in one and two dimensions has been thoroughly investigated. With the help of the Nicolai map it was possible to construct supersymmetrically improved lattice actions that preserve one of several supersymmetries. For the WZ model in one dimension SLAC fermions were utilized for the first time leading to a near-perfect elimination of lattice artifacts. In addition the lattice superpotential does not get modified which in two dimensions becomes important when further (discrete) symmetries of the continuum action are considered. For Wilson fermions two new improvements have been suggested and were shown to yield far better results than standard Wilson fermions concerning lattice artifacts. In the one-dimensional theory Ward Identities were studied.However, supersymmetry violations due to broken supersymmetry could only be detected at coarse lattices and very strong couplings. For the two-dimensional models a detailed analysis of supersymmetric improvement terms was given, both for Wilson and SLAC fermions. (orig.)

Supersymmetry on a space-time lattice

Energy Technology Data Exchange (ETDEWEB)

Kaestner, Tobias

2008-10-28

In this thesis the WZ model in one and two dimensions has been thoroughly investigated. With the help of the Nicolai map it was possible to construct supersymmetrically improved lattice actions that preserve one of several supersymmetries. For the WZ model in one dimension SLAC fermions were utilized for the first time leading to a near-perfect elimination of lattice artifacts. In addition the lattice superpotential does not get modified which in two dimensions becomes important when further (discrete) symmetries of the continuum action are considered. For Wilson fermions two new improvements have been suggested and were shown to yield far better results than standard Wilson fermions concerning lattice artifacts. In the one-dimensional theory Ward Identities were studied.However, supersymmetry violations due to broken supersymmetry could only be detected at coarse lattices and very strong couplings. For the two-dimensional models a detailed analysis of supersymmetric improvement terms was given, both for Wilson and SLAC fermions. (orig.)

Superfluidity of bosons on a deformable lattice

International Nuclear Information System (INIS)

Jackeli, G.; Ranninger, J.

2001-01-01

We study the superfluid properties of a system of interacting bosons on a lattice, which, moreover, are coupled to the vibrational modes of this lattice, treated here in terms of Einstein phonon modes. The ground state corresponds to two correlated condensates: that of the bosons and that of the phonons. Two competing effects determine the common collective sound-wave-like mode with sound velocity v, arising from gauge symmetry breaking. (i) The sound velocity v 0 (corresponding to a weakly interacting Bose system on a rigid lattice) in the lowest-order approximation is reduced due to reduction of the repulsive boson-boson interaction, arising from the attractive part of the phonon-mediated interaction in the static limit. (ii) The second-order correction to the sound velocity is enhanced as compared to that of bosons on a rigid lattice when the boson-phonon interaction is switched on due to the retarded nature of the phonon-mediated interaction. The overall effect is that the sound velocity is essentially unaffected by the coupling with phonons, indicating the robustness of the superfluid state. The induction of a coherent state in the phonon system driven by the condensation of the bosons could be of experimental significance, permitting spectroscopic detection of superfluid properties of bosons. Our results are based on an extension of the Beliaev-Popov formalism for a weakly interacting Bose gas on a rigid lattice to one on a deformable lattice with which it interacts

Strain-enhanced tunneling magnetoresistance in MgO magnetic tunnel junctions

OpenAIRE

Loong, Li Ming; Qiu, Xuepeng; Neo, Zhi Peng; Deorani, Praveen; Wu, Yang; Bhatia, Charanjit S.; Saeys, Mark; Yang, Hyunsoo

2014-01-01

While the effects of lattice mismatch-induced strain, mechanical strain, as well as the intrinsic strain of thin films are sometimes detrimental, resulting in mechanical deformation and failure, strain can also be usefully harnessed for applications such as data storage, transistors, solar cells, and strain gauges, among other things. Here, we demonstrate that quantum transport across magnetic tunnel junctions (MTJs) can be significantly affected by the introduction of controllable mechanical...

Highly luminescent, high-indium-content InGaN film with uniform composition and full misfit-strain relaxation

Science.gov (United States)

Fischer, A. M.; Wei, Y. O.; Ponce, F. A.; Moseley, M.; Gunning, B.; Doolittle, W. A.

2013-09-01

We have studied the properties of thick InxGa1-xN films, with indium content ranging from x ˜ 0.22 to 0.67, grown by metal-modulated epitaxy. While the low indium-content films exhibit high density of stacking faults and dislocations, a significant improvement in the crystalline quality and optical properties has been observed starting at x ˜ 0.6. Surprisingly, the InxGa1-xN film with x ˜ 0.67 exhibits high luminescence intensity, low defect density, and uniform full lattice-mismatch strain relaxation. The efficient strain relaxation is shown to be due to a critical thickness close to the monolayer range. These films were grown at low temperatures (˜400 °C) to facilitate indium incorporation and with precursor modulation to enhance surface morphology and metal adlayer diffusion. These findings should contribute to the development of growth techniques for nitride semiconductors under high lattice misfit conditions.

On Traveling Waves in Lattices: The Case of Riccati Lattices

Science.gov (United States)

Dimitrova, Zlatinka

2012-09-01

The method of simplest equation is applied for analysis of a class of lattices described by differential-difference equations that admit traveling-wave solutions constructed on the basis of the solution of the Riccati equation. We denote such lattices as Riccati lattices. We search for Riccati lattices within two classes of lattices: generalized Lotka-Volterra lattices and generalized Holling lattices. We show that from the class of generalized Lotka-Volterra lattices only the Wadati lattice belongs to the class of Riccati lattices. Opposite to this many lattices from the Holling class are Riccati lattices. We construct exact traveling wave solutions on the basis of the solution of Riccati equation for three members of the class of generalized Holling lattices.

Residual stress relief due to fatigue in tetragonal lead zirconate titanate ceramics

International Nuclear Information System (INIS)

Hall, D. A.; Mori, T.; Comyn, T. P.; Ringgaard, E.; Wright, J. P.

2013-01-01

High energy synchrotron XRD was employed to determine the lattice strain ε{111}and diffraction peak intensity ratio R{200}in tetragonal PZT ceramics, both in the virgin poled state and after a bipolar fatigue experiment. It was shown that the occurrence of microstructural damage during fatigue was accompanied by a reduction in the gradient of the ε{111}–cos 2 ψ plot, indicating a reduction in the level of residual stress due to poling. In contrast, the fraction of oriented 90° ferroelectric domains, quantified in terms of R{200}, was not affected significantly by fatigue. The change in residual stress due to fatigue is interpreted in terms of a change in the average elastic stiffness of the polycrystalline matrix due to the presence of inter-granular microcracks

Residual stress relief due to fatigue in tetragonal lead zirconate titanate ceramics

Science.gov (United States)

Hall, D. A.; Mori, T.; Comyn, T. P.; Ringgaard, E.; Wright, J. P.

2013-07-01

High energy synchrotron XRD was employed to determine the lattice strain ɛ{111} and diffraction peak intensity ratio R{200} in tetragonal PZT ceramics, both in the virgin poled state and after a bipolar fatigue experiment. It was shown that the occurrence of microstructural damage during fatigue was accompanied by a reduction in the gradient of the ɛ{111}-cos2 ψ plot, indicating a reduction in the level of residual stress due to poling. In contrast, the fraction of oriented 90° ferroelectric domains, quantified in terms of R{200}, was not affected significantly by fatigue. The change in residual stress due to fatigue is interpreted in terms of a change in the average elastic stiffness of the polycrystalline matrix due to the presence of inter-granular microcracks.

LATTICE: an interactive lattice computer code

International Nuclear Information System (INIS)

Staples, J.

1976-10-01

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

Internal residual strain mapping in carburized chrome molybdenum steel after quenching by neutron strain scanning

International Nuclear Information System (INIS)

Sakaida, Yoshihisa; Serizawa, Takanobu; Manzanka, Michiya

2011-01-01

A hollow circular cylinder specimen with an annular U-notch of chrome molybdenum steel with 0.20 mass% C (SCM420) was carburized in carrier gas and quenched in oil bath. In order to determine the case depth, the specimen was cut off and carbon content and Vickers hardness gradients were measured experimentally near the carburized surface. The residual strain mapping in the interior of carburized cylinder was conducted nondestructively by neutron strain scanning. In this study, the neutron diffraction from Fe-211 plane was used for strain scanning. The neutron wavelength was tuned to 0.1654nm so that diffraction angle became about 90deg. Radial, hoop and axial residual strains were measured by scanning diffracting volume along the axial direction of cylinder specimen. Each residual strain was calculated from lattice spacing change. Unstressed lattice spacing was determined experimentally using reference coupon specimens that were cut from the interior of same carburized cylinder. As a result, the diffraction peak width at half height, FWHM, near the carburized surface was about 3.7 times wider than that of coupon specimens. On the other hand, the most peak widths in the interior equaled to that of coupon specimens. Peak width broadened slightly as the diffracting volume approached the carburized case layer. From the center to the quarter of cylinder specimen, the hoop and axial strains were tensile, and the radial one was compressive in the interior. From the quarter to the edge of the cylinder specimen, the hoop tensile strain increased, radial and axial strains changed to tensile and compressive, respectively. Therefore, the interior of the cylinder specimen was found to be deformed elastically to balance the existence of compressive residual stresses in the carburized case layer. (author)

Inexpensive chirality on the lattice

International Nuclear Information System (INIS)

Kamleh, W.; Williams, A.G.; Adams, D.

2000-01-01

Full text: Implementing lattice fermions that resemble as closely as possible continuum fermions is one of the main goals of the theoretical physics community. Aside from a lack of infinitely powerful computers, one of the main impediments to this is the Nielsen-Ninomiya No-Go theorem for chirality on the lattice. One of the consequences of this theorem is that exact chiral symmetry and a lack of fermion doublers cannot be simultaneously satisfied for fermions on the lattice. In the commonly used Wilson fermion formulation, chiral symmetry is explicitly sacrificed on the lattice to avoid fermion doubling. Recently, an alternative has come forward, namely, the Ginsparg-Wilson relation and one of its solutions, the Overlap fermion. The Ginsparg-Wilson relation is a statement of lattice-deformed chirality. The Overlap-Dirac operator is a member of the family of solutions of the Ginsparg-Wilson relation. In recent times, Overlap fermions have been of great interest to the community due to their excellent chiral properties. However, they are significantly more expensive to implement than Wilson fermions. This expense is primarily due to the fact that the Overlap implementation requires an evaluation of the sign function for the Wilson-Dirac operator. The sign function is approximated by a high order rational polynomial function, but this approximation is poor close to the origin. The less near-zero modes that the Wilson- Dirac operator possesses, the cheaper the Overlap operator will be to implement. A means of improving the eigenvalue properties of the Wilson-Dirac operator by the addition of a so-called 'Clover' term is put forward. Numerical results are given that demonstrate this improvement. The Nielsen-Ninomiya no-go theorem and chirality on the lattice are reviewed. The general form of solutions of the Ginsparg-Wilson relation are given, and the Overlap solution is discussed. Properties of the Overlap-Dirac operator are given, including locality and analytic

Compressive strain-dependent bending strength property of Al2O3-ZrO2 (1.5 mol% Y2O3) composites performance by HIP

International Nuclear Information System (INIS)

Reyes-Rojas, A.; Esparza-Ponce, H.; De la Torre, S.D.; Torres-Moye, E.

2009-01-01

Nanometric powders and sintered ceramics of Al 2 O 3 -ZrO 2 (1.5 mol% Y 2 O 3 ) prepared by hot isostatic pressing HIP have been studied. A detailed crystallographic study has been performed through X-ray diffraction, Williamson-Hall method, Rietveld method and high-resolution electron microscopy HREM analysis. The crystallographic structure data, such as domain size, lattice parameters, wt% phase, and micro-strain direction have been obtained using Rietveld refinement and Williamson-Hall methods. The results revealed that the compressive strain (ε) increased from 0.56 to 1.18 (10 -3 ) as the t-ZrO 2 content increased too. The HREM interface study conducted along the [0 0 0 1]Al 2 O 3 ||[0 0 1]ZrO 2 zone axis revealed a micro-strain lattice distortion accumulated at the grain boundary due to the ZrO 2 martensitic phase transformation on cooling, t-ZrO 2 grains coalescence and to the grain growth of α-Al 2 O 3 which cause elongated tetragonal crystals. Micro-strain lattice distortion is adjusted by the shear displacements of the planes (1 1 0) and (11-bar0) along [1-bar10] and [1-bar1-bar0] crystallographic directions, respectively; these planes are arrested by the (101-bar0) alumina plane. In this case, semi-coherent interfaces were observed along the grain boundary. It is verified that the bending strength increased in connection with the strain accumulation and amount of tetragonal structure

Extended Josephson Relation and Abrikosov lattice deformation

International Nuclear Information System (INIS)

Matlock, Peter

2012-01-01

From the point of view of time-dependent Ginzburg Landau (TDGL) theory, a Josephson-like relation is derived for an Abrikosov vortex lattice accelerated and deformed by applied fields. Beginning with a review of the Josephson Relation derived from the two ingredients of a lattice-kinematics assumption in TDGL theory and gauge invariance, we extend the construction to accommodate a time-dependent applied magnetic field, a Floating-Kernel formulation of normal current, and finally lattice deformation due to the electric field and inertial effects of vortex-lattice motion. The resulting Josephson-like relation, which we call an Extended Josephson Relation, applies to a much wider set of experimental conditions than the original Josephson Relation, and is explicitly compatible with the considerations of TDGL theory.

Estimation of lattice strain for zirconia nanoparticles based on Williamson- Hall analysis

Energy Technology Data Exchange (ETDEWEB)

Aly, Kamal A., E-mail: kamalaly2001@gmail.com [Physics Department, Faculty of Science & Arts, Khullais, University of Jeddah, Jeddah (Saudi Arabia); Physics Department, Faculty of Science, Al-Azhar University, Assiut Branch, Assiut (Egypt); Khalil, N.M. [Chemistry Department, Faculty of Science & Arts, Khullais, University of Jeddah, Jeddah (Saudi Arabia); Refractories, Ceramics and Building Materials Department, National Research Centre, 12311, Cairo (Egypt); Algamal, Yousif [Chemistry Department, Faculty of Science & Arts, Khullais, University of Jeddah, Jeddah (Saudi Arabia); Saleem, Qaid M.A. [Chemistry Department, Faculty of Science & Arts, Khullais, University of Jeddah, Jeddah (Saudi Arabia); Aden University, Shabwa (Yemen)

2017-06-01

Nanoparticles of Zirconia were prepared (ZrO{sub 2}) by the neutralization of zirconium oxychloride octahydrate (ZrOCl{sub 2}-8H{sub 2}O) (2M) and ammonia solution (2M) at pH 8. The ZrO{sub 2} crystalline state was revealed by X-ray diffraction (XRD). The analysis of Scanning electron microscopy (SEM) and Transmission Electron microscope (TEM) images reveals that the as-synthesized ZrO{sub 2} particles at firing temperature of 800 °C are uniform and of range of 30 nm. Increasing of the temperature up to 1100 °C leads to the increase in particle size and alters the powders shape due to agglomeration arose from zirconia calcination as well as the increase in particle size. The X-ray peak broadening analysis (XRDBA) was used in the estimation of the crystalline size. Williamson-Hall (W-H) analysis was applied successfully to determine the energy density, stress, and the strain values via uniform deformation model (UDM), uniform deformation stress model (UDSM) and uniform deformation energy density model (UDEDM). The mean of the strain root square was calculated. The different strain values obtained from these models predicting the zirconia isotropic behavior. In addition to that, the W-H analysis results were discussed in terms of that obtained by Scherrer’s relationship, SEM and TEM images. - Graphical abstract: XRD patterns for zirconia nano-particles at different calcined temperature. - Highlights: • Nanoparticles of Zirconia (ZrO{sub 2}) were synthesized. • The ZrO{sub 2} crystalline state was revealed by XRD, SEM and TEM. • SEM and TEM images reveals that the ZrO{sub 2} particles are uniform and relatively small. • Both blocky particles and the powders shape are affected by the firing temperature. • The crystalline sizes were estimated using X-ray peak broadening analysis (XRDBA).

[Lattice degeneration of the retina].

Science.gov (United States)

Boĭko, E V; Suetov, A A; Mal'tsev, D S

2014-01-01

Lattice degeneration of the retina is a clinically important type of peripheral retinal dystrophies due to its participation in the pathogenesis of rhegmatogenous retinal detachment. In spite of extensive epidemiological, morphological, and clinical data, the question on causes of this particular type of retinal dystrophies currently remains debatable. Existing hypotheses on pathogenesis of retinal structural changes in lattice degeneration explain it to a certain extent. In clinical ophthalmology it is necessary to pay close attention to this kind of degenerations and distinguish between cases requiring preventive treatment and those requiring monitoring.

Commensurability effects in holographic homogeneous lattices

International Nuclear Information System (INIS)

Andrade, Tomas; Krikun, Alexander

2016-01-01

An interesting application of the gauge/gravity duality to condensed matter physics is the description of a lattice via breaking translational invariance on the gravity side. By making use of global symmetries, it is possible to do so without scarifying homogeneity of the pertinent bulk solutions, which we thus term as “homogeneous holographic lattices.' Due to their technical simplicity, these configurations have received a great deal of attention in the last few years and have been shown to correctly describe momentum relaxation and hence (finite) DC conductivities. However, it is not clear whether they are able to capture other lattice effects which are of interest in condensed matter. In this paper we investigate this question focusing our attention on the phenomenon of commensurability, which arises when the lattice scale is tuned to be equal to (an integer multiple of) another momentum scale in the system. We do so by studying the formation of spatially modulated phases in various models of homogeneous holographic lattices. Our results indicate that the onset of the instability is controlled by the near horizon geometry, which for insulating solutions does carry information about the lattice. However, we observe no sharp connection between the characteristic momentum of the broken phase and the lattice pitch, which calls into question the applicability of these models to the physics of commensurability.

Calculating luminosity for a coupled Tevatron lattice

International Nuclear Information System (INIS)

Holt, J.A.; Martens, M.A.; Michelotti, L.; Goderre, G.

1995-05-01

The traditional formula for calculating luminosity assumes an uncoupled lattice and makes use of one-degree-of-freedom lattice functions, β H and β v , for relating transverse beam widths to emittances. Strong coupling requires changing this approach. It is simplest to employ directly the linear normal form coordinates of the one turn map. An equilibrium distribution in phase space is expressed as a function of the Jacobian's eigenvectors and beam size parameters or emittances. Using the equilibrium distributions an expression for the luminosity was derived and applied to the Tevatron lattice, which was coupled due to a quadrupole roll

Towards a physical interpretation of the entropic lattice Boltzmann method

Science.gov (United States)

Malaspinas, Orestis; Deville, Michel; Chopard, Bastien

2008-12-01

The entropic lattice Boltzmann method (ELBM) is one among several different versions of the lattice Boltzmann method for the simulation of hydrodynamics. The collision term of the ELBM is characterized by a nonincreasing H function, guaranteed by a variable relaxation time. We propose here an analysis of the ELBM using the Chapman-Enskog expansion. We show that it can be interpreted as some kind of subgrid model, where viscosity correction scales like the strain rate tensor. We confirm our analytical results by the numerical computations of the relaxation time modifications on the two-dimensional dipole-wall interaction benchmark.

Entropy-driven crystal formation on highly strained substrates

KAUST Repository

Savage, John R.

2013-05-20

In heteroepitaxy, lattice mismatch between the deposited material and the underlying surface strongly affects nucleation and growth processes. The effect of mismatch is well studied in atoms with growth kinetics typically dominated by bond formation with interaction lengths on the order of one lattice spacing. In contrast, less is understood about how mismatch affects crystallization of larger particles, such as globular proteins and nanoparticles, where interparticle interaction energies are often comparable to thermal fluctuations and are short ranged, extending only a fraction of the particle size. Here, using colloidal experiments and simulations, we find particles with short-range attractive interactions form crystals on isotropically strained lattices with spacings significantly larger than the interaction length scale. By measuring the free-energy cost of dimer formation on monolayers of increasing uniaxial strain, we show the underlying mismatched substrate mediates an entropy-driven attractive interaction extending well beyond the interaction length scale. Remarkably, because this interaction arises from thermal fluctuations, lowering temperature causes such substrate-mediated attractive crystals to dissolve. Such counterintuitive results underscore the crucial role of entropy in heteroepitaxy in this technologically important regime. Ultimately, this entropic component of lattice mismatched crystal growth could be used to develop unique methods for heterogeneous nucleation and growth of single crystals for applications ranging from protein crystallization to controlling the assembly of nanoparticles into ordered, functional superstructures. In particular, the construction of substrates with spatially modulated strain profiles would exploit this effect to direct self-assembly, whereby nucleation sites and resulting crystal morphology can be controlled directly through modifications of the substrate.

Demonstration of a chamber for strain mapping of steel specimens under mechanical load in a hydrogen environment by synchrotron radiation

Science.gov (United States)

Connolly, Matthew; Park, Jun-Sang; Bradley, Peter; Lauria, Damian; Slifka, Andrew; Drexler, Elizabeth

2018-06-01

We demonstrate a hydrogen gas chamber suitable for lattice strain measurements and capturing radiographs of a steel specimen under a mechanical load using high energy synchrotron x-rays. The chamber is suitable for static and cyclic mechanical loading. Experiments were conducted at the 1-ID-E end station of the Advanced Photon Source, Argonne National Laboratory. Diffraction patterns show a high signal-to-noise ratio suitable for lattice strain measurements for the specimen and with minimal scattering and overlap from the gas chamber manufactured from aluminum. In situ radiographs of a specimen in the hydrogen chamber show the ability to track a growing crack and to map the lattice strain around the crack with high spatial and strain resolution.

Strain mediated magnetoelectric coupling induced in (x) Bi{sub 0.5}Na{sub 0.5}TiO{sub 3}-(1−x) MgFe{sub 2}O{sub 4} composites

Energy Technology Data Exchange (ETDEWEB)

Manjusha [Smart Materials Research Laboratory, Department of Physics, Indian Institute of Technology Roorkee, Roorkee 247667 (India); Yadav, K.L., E-mail: klyadav35@yahoo.com [Smart Materials Research Laboratory, Department of Physics, Indian Institute of Technology Roorkee, Roorkee 247667 (India); Adhlakha, Nidhi [Elettra-Sincrotrone Trieste S.C.p.A, Area Science Park, I-34012 Trieste (Italy); Shah, Jyoti; Kotnala, R.K. [CSIR-National Physical Laboratory, New Delhi 110012 (India)

2017-06-01

Particulate composites of ferroelectric and ferrite phases having general formula (x)Bi{sub 0.5}Na{sub 0.5}TiO{sub 3}-(1−x)MgFe{sub 2}O{sub 4} (x=0, 0.5, 0.6, 0.7, 0.8 and 1.0), equivalently denoted as (x)BNT-(1−x)MgFO were synthesized by solid state reaction method. From X-ray diffraction analysis, the structural transformation from tetragonal to rhombohedral corresponding to BNT phase was observed in composites with x=0.5 to x=0.8. Shifting of (012) BNT peak towards left (x=0.5, 0.8) and right side (x=0.6, 0.7) observed due to occupation of Bi{sup 3+} ions at interstitial and substitutional sites into host MgFO lattice respectively. BNT produced strain in MgFO lattice. Scanning electron micrographs show closely packed microstructure with grain size variations from 0.62 to 2.90 µm. The value of magnetoelectric (ME) coupling coefficient increases from 2.42 (x=0.5) to 4.79 (x=0.8) mV/cm. Oe due to strain produced in MgFO and BNT lattices.

Improved models of dense anharmonic lattices

Energy Technology Data Exchange (ETDEWEB)

Rosenau, P., E-mail: rosenau@post.tau.ac.il; Zilburg, A.

2017-01-15

We present two improved quasi-continuous models of dense, strictly anharmonic chains. The direct expansion which includes the leading effect due to lattice dispersion, results in a Boussinesq-type PDE with a compacton as its basic solitary mode. Without increasing its complexity we improve the model by including additional terms in the expanded interparticle potential with the resulting compacton having a milder singularity at its edges. A particular care is applied to the Hertz potential due to its non-analyticity. Since, however, the PDEs of both the basic and the improved model are ill posed, they are unsuitable for a study of chains dynamics. Using the bond length as a state variable we manipulate its dispersion and derive a well posed fourth order PDE. - Highlights: • An improved PDE model of a Newtonian lattice renders compacton solutions. • Compactons are classical solutions of the improved model and hence amenable to standard analysis. • An alternative well posed model enables to study head on interactions of lattices' solitary waves. • Well posed modeling of Hertz potential.

DFT-Assisted Polymorph Identification from Lattice Raman Fingerprinting.

Science.gov (United States)

Bedoya-Martínez, Natalia; Schrode, Benedikt; Jones, Andrew O F; Salzillo, Tommaso; Ruzié, Christian; Demitri, Nicola; Geerts, Yves H; Venuti, Elisabetta; Della Valle, Raffaele Guido; Zojer, Egbert; Resel, Roland

2017-08-03

A combined experimental and theoretical approach, consisting of lattice phonon Raman spectroscopy and density functional theory (DFT) calculations, is proposed as a tool for lattice dynamics characterization and polymorph phase identification. To illustrate the reliability of the method, the lattice phonon Raman spectra of two polymorphs of the molecule 2,7-dioctyloxy[1]benzothieno[3,2-b]benzothiophene are investigated. We show that DFT calculations of the lattice vibrations based on the known crystal structures, including many-body dispersion van der Waals (MBD-vdW) corrections, predict experimental data within an accuracy of ≪5 cm -1 (≪0.6 meV). Due to the high accuracy of the simulations, they can be used to unambiguously identify different polymorphs and to characterize the nature of the lattice vibrations and their relationship to the structural properties. More generally, this work implies that DFT-MBD-vdW is a promising method to describe also other physical properties that depend on lattice dynamics like charge transport.

Nonpolar ZnO film growth and mechanism for anisotropic in-plane strain relaxation

International Nuclear Information System (INIS)

Pant, P.; Budai, J.D.; Narayan, J.

2010-01-01

Using high-resolution transmission electron microscopy (HRTEM) and X-ray diffraction, we investigated the strain relaxation mechanisms for nonpolar (1 1 -2 0) a-plane ZnO epitaxy on (1 -1 0 2) r-plane sapphire, where the in-plane misfit ranges from -1.5% for the [0 0 0 1]ZnO-parallel [1 -1 0 -1]sapphire to -18.3% for the [-1 1 0 0]ZnO-parallel [-1 -1 2 0]sapphire direction. For the large misfit [-1 1 0 0]ZnO direction the misfit strains are fully relaxed at the growth temperature, and only thermal misfit and defect strains, which cannot be relaxed fully by slip dislocations, remain on cooling. For the small misfit direction, lattice misfit is not fully relaxed at the growth temperature. As a result, additive unrelaxed lattice and thermal misfit and defect strains contribute to the measured strain. Our X-ray diffraction measurements of lattice parameters show that the anisotropic in-plane biaxial strain leads to a distortion of the hexagonal symmetry of the ZnO basal plane. Based on the anisotropic strain relaxation observed along the orthogonal in-plane [-1 1 0 0] and [0 0 0 1]ZnO stress directions and our HRTEM investigations of the interface, we show that the plastic relaxation occurring in the small misfit direction [0 0 0 1]ZnO by dislocation nucleation is incomplete. These results are consistent with the domain-matching paradigm of a complete strain relaxation for large misfits and a difficulty in relaxing the film strain for small misfits.

Ferromagnetic (Ga,Mn)As layers and nanostructures: control of magnetic anisotropy by strain engineering

Energy Technology Data Exchange (ETDEWEB)

Wenisch, Jan

2008-07-01

This work studies the fundamental connection between lattice strain and magnetic anisotropy in the ferromagnetic semiconductor (Ga,Mn)As. The first chapters provide a general introduction into the material system and a detailed description of the growth process by molecular beam epitaxy. A finite element simulation formalism is developed to model the strain distribution in (Ga,Mn)As nanostructures is introduced and its predictions verified by high-resolution X-ray diffraction methods. The influence of lattice strain on the magnetic anisotropy is explained by an magnetostatic model. A possible device application is described in the closing chapter. (orig.)

On d -Dimensional Lattice (co)sine n -Algebra

International Nuclear Information System (INIS)

Yao Shao-Kui; Zhang Chun-Hong; Zhao Wei-Zhong; Ding Lu; Liu Peng

2016-01-01

We present the (co)sine n-algebra which is indexed by the d-dimensional integer lattice. Due to the associative operators, this generalized (co)sine n-algebra is the higher order Lie algebra for the n even case. The particular cases are the d-dimensional lattice sine 3 and cosine 5-algebras with the special parameter values. We find that the corresponding d-dimensional lattice sine 3 and cosine 5-algebras are the Nambu 3-algebra and higher order Lie algebra, respectively. The limiting case of the d-dimensional lattice (co)sine n-algebra is also discussed. Moreover we construct the super sine n-algebra, which is the super higher order Lie algebra for the n even case. (paper)

The epitaxial growth and interfacial strain study of VO{sub 2}/MgF{sub 2} (001) films by synchrotron based grazing incidence X-ray diffraction

Energy Technology Data Exchange (ETDEWEB)

Fan, L.L. [Key Laboratory for Advanced Technology in Environmental Protection of Jiangsu Province, Yancheng Institute of Technology, Yancheng 224051 (China); National Synchrotron Radiation Laboratory, University of Science and Technology of China, Hefei 230029 (China); Chen, S. [National Synchrotron Radiation Laboratory, University of Science and Technology of China, Hefei 230029 (China); Liu, Q.H. [Science and Technology on Electro-optical Information Security Control Laboratory, Tianjin 300300 (China); Liao, G.M.; Chen, Y.L.; Ren, H. [National Synchrotron Radiation Laboratory, University of Science and Technology of China, Hefei 230029 (China); Zou, C.W., E-mail: czou@ustc.edu.cn [National Synchrotron Radiation Laboratory, University of Science and Technology of China, Hefei 230029 (China)

2016-09-05

High quality VO{sub 2} films with different thickness were epitaxially grown on MgF{sub 2} (001) substrates by oxide molecular beam epitaxy method. The evolution of interfacial strain was investigated by synchrotron based grazing incidence X-ray diffraction. By adjusting the incidence angles, the penetration depth of X-ray in VO{sub 2} film could be controlled and the thickness-depend lattice distortion in the epitaxial VO{sub 2} film was investigated. Due to the lattice mismatching, the pronounced tensile strain was observed in ultra-thin VO{sub 2} film. As the film thickness increasing, the interfacial strain relaxed gradually and became fully relaxed for thick VO{sub 2} films. Combined with the electric transport measurement, it was revealed that the phase transition temperature of ultra-thin VO{sub 2} film decreased greatly. The effect of interfacial strain induced phase transition modulation and the intrinsic mechanism was systematically discussed. - Highlights: • We prepared high quality VO{sub 2} epitaxial films on MgF{sub 2} (001) substrates by oxide molecular beam epitaxy method. • Synchrotron radiation grazing incidence X-ray diffraction was employed to detect evolution of strain along depth profile. • Based on a classic band structure model, the mechanism of strain controlled phase transition of VO{sub 2} was discussed.

Lattice QCD

International Nuclear Information System (INIS)

Hasenfratz, P.

1983-01-01

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

Intrinsic Dirac half-metal and quantum anomalous Hall phase in a hexagonal metal-oxide lattice

Science.gov (United States)

Zhang, Shou-juan; Zhang, Chang-wen; Zhang, Shu-feng; Ji, Wei-xiao; Li, Ping; Wang, Pei-ji; Li, Sheng-shi; Yan, Shi-shen

2017-11-01

The quantum anomalous Hall (QAH) effect has attracted extensive attention due to time-reversal symmetry broken by a staggered magnetic flux emerging from ferromagnetic ordering and spin-orbit coupling. However, the experimental observations of the QAH effect are still challenging due to its small nontrivial bulk gap. Here, based on density functional theory and Berry curvature calculations, we propose the realization of intrinsic QAH effect in two-dimensional hexagonal metal-oxide lattice, N b2O3 , which is characterized by the nonzero Chern number (C =1 ) and chiral edge states. Spin-polarized calculations indicate that it exhibits a Dirac half-metal feature with temperature as large as TC=392 K using spin-wave theory. When the spin-orbit coupling is switched on, N b2O3 becomes a QAH insulator. Notably, the nontrivial topology is robust against biaxial strain with its band gap reaching up to Eg=75 meV , which is far beyond room temperature. A tight-binding model is further constructed to understand the origin of nontrivially electronic properties. Our findings on the Dirac half-metal and room-temperature QAH effect in the N b2O3 lattice can serve as an ideal platform for developing future topotronics devices.

Dynamic scattering theory for dark-field electron holography of 3D strain fields

International Nuclear Information System (INIS)

Lubk, Axel; Javon, Elsa; Cherkashin, Nikolay; Reboh, Shay; Gatel, Christophe; Hÿtch, Martin

2014-01-01

Dark-field electron holography maps strain in crystal lattices into reconstructed phases over large fields of view. Here we investigate the details of the lattice strain–reconstructed phase relationship by applying dynamic scattering theory both analytically and numerically. We develop efficient analytic linear projection rules for 3D strain fields, facilitating a straight-forward calculation of reconstructed phases from 3D strained materials. They are used in the following to quantify the influence of various experimental parameters like strain magnitude, specimen thickness, excitation error and surface relaxation. - Author-Highlights: • We derive a simple dynamic scattering formalism for dark field electron holography based on a perturbative two-beam theory. • The formalism facilitates the projection of 3D strain fields by a simple weighting integral. • The weighted projection depends analytically on the diffraction order, the excitation error and the specimen thickness. • The weighting integral formalism represents an important prerequisite towards the development of tomographic strain reconstruction techniques

Steering the motion of rotary solitons in radial lattices

International Nuclear Information System (INIS)

He, Y. J.; Malomed, Boris A.; Wang, H. Z.

2007-01-01

We demonstrate that rotary motion of a two-dimensional soliton trapped in a Bessel lattice can be precisely controlled by application of a finite-time push to the lattice, due to the transfer of the lattice's linear momentum to the orbital momentum of the soliton. A simple analytical consideration treating the soliton as a particle provides for an accurate explanation of numerical findings. Some effects beyond the quasi-particle approximation are explored too, such as destruction of the soliton by a hard push

Hamiltonian approach to the lattice massive Schwinger model

International Nuclear Information System (INIS)

Sidorov, A.V.; Zastavenko, L.G.

1996-01-01

The authors consider the limit e 2 /m 2 much-lt 1 of the lattice massive Schwinger model, i.e., the lattice massive QED in two space-time dimensions, up to lowest order in the effective coupling constant e 2 /m 2 . Here, m is the fermion mass parameter and e is the electron charge. They compare their lattice QED model with the analogous continuous space and lattice space models, (CSM and LSM), which do not take account of the zero momentum mode, z.m.m., of the vector potential. The difference is that (due to extra z.m.m. degree of freedom) to every eigenstate of the CSM and LSM there corresponds a family of eigenstates of the authors lattice QED with the parameter λ. They restrict their consideration to small values of the parameter λ. Then, the energies of the particle states of their lattice QED and LSM do coincide (in their approximation). In the infinite periodicity length limit the Hamiltonian of the authors lattice QED (as well as the Hamiltonian of the LSM) possesses two different Hilbert spaces of eigenfunctions. Thus, in this limit the authors lattice QED model (as well as LSM) describes something like two connected, but different, worlds

Pseudo Landau levels and quantum oscillations in strained Weyl semimetals

Science.gov (United States)

Alisultanov, Z. Z.

2018-05-01

The crystal lattice deformation in Weyl materials where the two chiralities are separated in momentum space leads to the appearance of gauge pseudo-fields. We investigated the pseudo-magnetic field induced quantum oscillations in strained Weyl semimetal (WSM). In contrast to all previous works on this problem, we use here a more general tilted Hamiltonian. Such Hamiltonian, seems to be is more suitable for a strained WSMs. We have shown that a pseudo-magnetic field induced magnetization of strained WSM is nonzero due to the fact that electric field (gradient of the deformation potential) is induced simultaneously with the pseudo-magnetic field. This related with fact that the pseudo Landau levels (LLs) in strained WSM are differ in vicinities of different WPs due to the presence of tilt in spectrum. Such violation of the equivalence between Weyl points (WPs) leads to modulation of quantum oscillations. We also showed that magnetization magnitude can be changed by application of an external electric field. In particular, it can be reduced to zero. The possibility of controlling of the magnetization by an electric field is interesting both from a fundamental point of view (a new type of magneto-electric effect) and application point of view (additional possibility to control diamagnetism of deformed WSMs). Finally, a coexistence of type-I and type-II Weyl fermions is possible in the system under investigation. Such phase is absolutely new for physics of topological systems.

Internal strain measurement using pulsed neutron diffraction at LANSCE

International Nuclear Information System (INIS)

Goldstone, J.A.; Bourke, M.A.M.; Shi, N.

1994-01-01

The presence of residual stress in engineering components can effect their mechanical properties and structural integrity. Neutron diffraction in the only technique that can make nondestructive measurements in the interior of components. By recording the change in crystalline lattice spacings, elastic strains can be measured for individual lattice reflections. Using a pulsed neutron source, all lattice reflections are recorded in each measurement, which allows for easy examination of heterogeneous materials such as metal matrix composites. Measurements made at the Manuel Lujan Jr. Neutron Scattering Center (LANSCE) demonstrate the potential at pulsed sources for in-situ stress measurements at ambient and elevated temperatures

Nitrogen lattice location in MOVPE grown Ga1-xInxNyAs1-y films using ion beam channeling

International Nuclear Information System (INIS)

Nebiki, Takuya; Narusawa, Tadashi; Kumagai, Akiko; Doi, Hideyuki; Saito, Tadashi; Takagishi, Shigenori

2006-01-01

We have investigated the nitrogen lattice location in MOVPE grown Ga 1-x In x N y As 1-y with x=0.07 and y=0.025 by means of ion beam channeling technique. In this system, the lattice constant of the Ga 1-x In x N y As 1-y film is equal to GaAs lattice. Therefore, we can grow apparently no strain, high quality and very thick GaInNAs film on GaAs substrate. The quality of the films as well as the lattice location of In and N were characterized by channeling Rutherford backscattering spectrometry and nuclear reaction analysis using 3.95 MeV He 2+ beam. The fraction of substitutional nitrogen in the film was measured using the 14 N(α,p) 17 O endothermic nuclear reaction. Our results indicate that more than 90% of In and N atoms are located the substitutional site, however, N atoms are slightly displaced by ∼0.2 A from the lattice site. We suggest that the GaInNAs film has a local strain or point defects around the N atoms. (author)

Effects of strain on the Schwinger pair creation in graphene

International Nuclear Information System (INIS)

Fanbanrai, P.; Hutem, A.; Boonchui, S.

2015-01-01

The effects of strain on mechanically deformed graphene are determined by looking at how the strain affects the amplitude of the Schwinger two particle pair state. The influences of the lattice distortions, such as isotropic tensile strain ϵ is , shear strain ϵ ss , uniaxial armchair strain ϵ as , and zigzag strain ϵ zs , on the photon emission spectrum have been analyzed. We find that the intensities of the emission increases or decreases when compared to those of the unstrained graphene, depending on the type of strain applied. Thus the structure of energy band, the frequencies of the photons and the emission spectrum can be controlled by use of the different strains

Lattice-induced nonadiabatic frequency shifts in optical lattice clocks

International Nuclear Information System (INIS)

Beloy, K.

2010-01-01

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

Discussion on accuracy of weld residual stress measurement by neutron diffraction. Influence of strain free reference

International Nuclear Information System (INIS)

Suzuki, Hiroshi; Akita, Koichi

2012-01-01

It is required to evaluate a strain-free reference, α 0 , to perform accurate stress measurement using neutron diffraction. In this study, accuracy of neutron stress measurement was quantitatively discussed from α 0 evaluations on a dissimilar metal butt-weld between a type 304 austenitic stainless steel and an A533B low alloy ferritic steel. A strain-free standard specimen and a sliced specimen with 10 mm thickness taken from the dissimilar metal butt-weld were utilized. In the lattice constant evaluation using the standard specimen, average lattice constant derived from multiple hkl reflections was evaluated as the stress-free reference with cancelling out an intergranular strain. Comparing lattice constant distributions in each reflection with average lattice constant distribution in the standard specimen, αFe211 and γFe311 reflections were judged as a suitable reflection for neutron strain measurement to reduce intergranular strain effects. Residual stress distribution in the sliced specimen evaluated using α 0 measured here exhibited higher accuracy than that measured using strain gauges. On the other hand, α 0 distributions were evaluated using the sliced specimen under the plane-stress condition. Existence of slight longitudinal residual stresses near the weld center decreased accuracy of the α 0 evaluations, which means that it is required to optimize the thickness of the sliced specimen for accurate α 0 evaluation under plane strain condition. As a conclusion of this study, it was confirmed that procedures of accurate α 0 evaluation, optimization of the measurement condition, and multiple evaluations on the results play an important role to improve accuracy of the residual stress measurement using neutron diffraction. (author)

Strong coupling constant from Adler function in lattice QCD

Science.gov (United States)

Hudspith, Renwick J.; Lewis, Randy; Maltman, Kim; Shintani, Eigo

2016-09-01

We compute the QCD coupling constant, αs, from the Adler function with vector hadronic vacuum polarization (HVP) function. On the lattice, Adler function can be measured by the differential of HVP at two different momentum scales. HVP is measured from the conserved-local vector current correlator using nf = 2 + 1 flavor Domain Wall lattice data with three different lattice cutoffs, up to a-1 ≈ 3.14 GeV. To avoid the lattice artifact due to O(4) symmetry breaking, we set the cylinder cut on the lattice momentum with reflection projection onto vector current correlator, and it then provides smooth function of momentum scale for extracted HVP. We present a global fit of the lattice data at a justified momentum scale with three lattice cutoffs using continuum perturbation theory at 𝒪(αs4) to obtain the coupling in the continuum limit at arbitrary scale. We take the running to Z boson mass through the appropriate thresholds, and obtain αs(5)(MZ) = 0.1191(24)(37) where the first is statistical error and the second is systematic one.

Dynamics of surface solitons at the edge of chirped optical lattices

International Nuclear Information System (INIS)

Kartashov, Yaroslav V.; Torner, Lluis; Vysloukh, Victor A.

2007-01-01

We address soliton formation at the edge of chirped optical lattices imprinted in Kerr-type nonlinear media. We find families of power thresholdless surface waves that do not exist at other types of lattice interfaces. Such solitons form due to combined action of internal reflection at the interface, distributed Bragg-type reflection, and focusing nonlinearity. Remarkably, we discover that surfaces of chirped lattices are soliton attractors: Below an energy threshold, solitons launched well within the lattice self-bend toward the interface, and then stick to it

Multigrid for Staggered Lattice Fermions

Energy Technology Data Exchange (ETDEWEB)

Brower, Richard C. [Boston U.; Clark, M. A. [Unlisted, US; Strelchenko, Alexei [Fermilab; Weinberg, Evan [Boston U.

2018-01-23

Critical slowing down in Krylov methods for the Dirac operator presents a major obstacle to further advances in lattice field theory as it approaches the continuum solution. Here we formulate a multi-grid algorithm for the Kogut-Susskind (or staggered) fermion discretization which has proven difficult relative to Wilson multigrid due to its first-order anti-Hermitian structure. The solution is to introduce a novel spectral transformation by the K\\"ahler-Dirac spin structure prior to the Galerkin projection. We present numerical results for the two-dimensional, two-flavor Schwinger model, however, the general formalism is agnostic to dimension and is directly applicable to four-dimensional lattice QCD.

In-situ measurement of texture and elastic strains with HIPPO-CRATES

International Nuclear Information System (INIS)

Hartig, Ch.; Vogel, S.C.; Mecking, H.

2006-01-01

In this paper, the micromechanical interaction between constituents of a metallic material during elastic and plastic deformation are analyzed by comparing experimental results with modeling predictions. This comparison aims at determining the locally acting internal stresses, the spatial distribution of strains and the rules allowing deriving the macroscopic behavior of the material from the behavior of its microscopic constituents. We report the application of a new deformation apparatus CRATES, which allows measuring texture and crystal lattice spacings, and from these crystal lattice strains, using neutron diffraction. From the in-situ measured elastic lattice strains ε hkl the corresponding local stresses can be derived. The deformation apparatus allows uni-axial tensile or compressive deformation up to 100 kN and is specifically designed for use in the HIPPO neutron time-of-flight diffractometer. In this paper, we report initial results on an iron-copper model system (Fe100, Fe33Cu67, Fe67Cu33, vol.%) and commercial magnesium alloys (Mg-AZ31 and Mg-AZ80). Finite element calculations using a crystal-plastic constitutive law, allowing for shear and hardening of crystallographic slip-systems, were used for the interpretation of the measurements

Effects of anharmonic strain on the phase stability of epitaxial films and superlattices: Applications to noble metals

International Nuclear Information System (INIS)

Ozolins, V.; Wolverton, C.; Zunger, A.

1998-01-01

Epitaxial strain energies of epitaxial films and bulk superlattices are studied via first-principles total-energy calculations using the local-density approximation. Anharmonic effects due to large lattice mismatch, beyond the reach of the harmonic elasticity theory, are found to be very important in Cu/Au (lattice mismatch 12%), Cu/Ag (12%), and Ni/Au (15%). We find that left-angle 001 right-angle is the elastically soft direction for biaxial expansion of Cu and Ni, but it is left-angle 201 right-angle for large biaxial compression of Cu, Ag, and Au. The stability of superlattices is discussed in terms of the coherency strain and interfacial energies. We find that in phase separating systems such as Cu-Ag the superlattice formation energies decrease with superlattice period, and the interfacial energy is positive. Superlattices are formed easiest on (001) and hardest on (111) substrates. For ordering systems, such as Cu-Au and Ag-Au, the formation energy of superlattices increases with period, and interfacial energies are negative. These superlattices are formed easiest on (001) or (110) and hardest on (111) substrates. For Ni-Au we find a hybrid behavior: superlattices along left-angle 111 right-angle and left-angle 001 right-angle behave like phase separating systems, while for left-angle 110 right-angle they behave like ordering systems. Finally, recent experimental results on epitaxial stabilization of disordered Ni-Au and Cu-Ag alloys, immiscible in the bulk form, are explained in terms of destabilization of the phase separated state due to lattice mismatch between the substrate and constituents. copyright 1998 The American Physical Society

Strain and strain-release engineering at epitaxial SiGe islands on Si(0 0 1) for microelectronic applications

International Nuclear Information System (INIS)

Vastola, G.; Marzegalli, A.; Montalenti, F.; Miglio, Leo

2009-01-01

We report original finite element method simulations of the strain components at nanometric GeSi island on Si(0 0 1), for realistic shape, sizes and average composition, discussing the main mechanisms acting in the misfit strain relaxation. The tensile strain induced in a 30 nm Si capping layer and the one upon removing the island, after fixing the top part of the Si layer, is discussed in view of application as a field effect transistor channel, with high career mobility induced by the lattice deformation. The large shear components obtained for steeper island morphologies are predicted to be particularly performing, especially in comparison to one another strained-silicon configuration (totally top-down originated), recently developed by IBM corporation.

Electric-field-induced strain contributions in morphotropic phase boundary composition of (Bi{sub 1/2}Na{sub 1/2})TiO{sub 3}-BaTiO{sub 3} during poling

Energy Technology Data Exchange (ETDEWEB)

Khansur, Neamul H.; Daniels, John E. [School of Materials Science and Engineering, UNSW Australia, New South Wales 2052 (Australia); Hinterstein, Manuel [School of Materials Science and Engineering, UNSW Australia, New South Wales 2052 (Australia); Institute for Applied Materials, Karlsruhe Institute for Technology, P.O. Box 3640, 76021 Karlsruhe (Germany); Wang, Zhiyang [School of Materials Science and Engineering, UNSW Australia, New South Wales 2052 (Australia); The Australian Synchrotron, Clayton, Victoria 3168 (Australia); Groh, Claudia [Institute of Materials Science, Technische Universität Darmstadt, Alarich-Weiss-Straße 2, 64287 Darmstadt (Germany); Jo, Wook [School of Materials Science and Engineering, Ulsan National Institute of Science and Technology, Ulsan 44919 (Korea, Republic of)

2015-12-14

The microscopic contributions to the electric-field-induced macroscopic strain in a morphotropic 0.93(Bi{sub 1/2}Na{sub 1/2}TiO{sub 3})−0.07(BaTiO{sub 3}) with a mixed rhombohedral and tetragonal structure have been quantified using full pattern Rietveld refinement of in situ high-energy x-ray diffraction data. The analysis methodology allows a quantification of all strain mechanisms for each phase in a morphotropic composition and is applicable to use in a wide variety of piezoelectric compositions. It is shown that during the poling of this material 24%, 44%, and 32% of the total macroscopic strain is generated from lattice strain, domain switching, and phase transformation strains, respectively. The results also suggest that the tetragonal phase contributes the most to extrinsic domain switching strain, whereas the lattice strain primarily stems from the rhombohedral phase. The analysis also suggests that almost 32% of the total strain is lost or is a one-time effect due to the irreversible nature of the electric-field-induced phase transformation in the current composition. This information is relevant to on-going compositional development strategies to harness the electric-field-induced phase transformation strain of (Bi{sub 1/2}Na{sub 1/2})TiO{sub 3}-based lead-free piezoelectric materials for actuator applications.

Unquenched lattice upsilon spectroscopy

International Nuclear Information System (INIS)

Marcantonio, L.M.

2001-03-01

A non-relativistic effective theory of QCD (NRQCD) is used in calculations of the upsilon spectrum. Simultaneous multi-correlation fitting routines are used to yield lattice channel energies and amplitudes. The lattice configurations used were both dynamical, with two flavours of sea quarks included in the action; and quenched, with no sea quarks. These configurations were generated by the UKQCD collaboration. The dynamical configurations used were ''matched'', having the same lattice spacing, but differing in the sea quark mass. Thus, it was possible to analyse trends of observables with sea quark mass, in the certainty that the trend isn't partially due to varying lattice spacing. The lattice spacing used for spectroscopy was derived from the lattice 1 1 P 1 - 1 3 S 1 splitting. On each set of configurations two lattice bare b quark masses were used, giving kinetic masses bracketing the physical Υ mass. The only quantity showing a strong dependence on these masses was the hyperfine splitting, so it was interpolated to the real Υ mass. The radial and orbital splittings gave good agreement with experiment. The hyperfine splitting results showed a clear signal for unquenching and the dynamical hyperfine splitting results were extrapolated to a physical sea quark mass. This result, combined with the quenched result yielded a value for the hyperfine splitting at n f = 3, predicting an η b mass of 9.517(4) GeV. The NRQCD technique for obtaining a value of the strong coupling constant in the M-barS-bar scheme was followed. Using quenched and dynamical results a value was extrapolated to n f = 3. Employing a three loop beta function to run the coupling, with suitable matching conditions at heavy quark thresholds, the final result was obtained for n f = 5 at a scale equal to the Z boson mass. This result was α(5)/MS(Mz)=0.110(4). Two methods for finding the mass of the b quark in the MS scheme were employed. The results of both methods agree within error but the

Phase engineering of monolayer transition-metal dichalcogenide through coupled electron doping and lattice deformation

International Nuclear Information System (INIS)

Ouyang, Bin; Lan, Guoqiang; Song, Jun; Guo, Yinsheng; Mi, Zetian

2015-01-01

First-principles calculations were performed to investigate the phase stability and transition within four monolayer transition-metal dichalcogenide (TMD) systems, i.e., MX 2 (M = Mo or W and X = S or Se) under coupled electron doping and lattice deformation. With the lattice distortion and electron doping density treated as state variables, the energy surfaces of different phases were computed, and the diagrams of energetically preferred phases were constructed. These diagrams assess the competition between different phases and predict conditions of phase transitions for the TMDs considered. The interplay between lattice deformation and electron doping was identified as originating from the deformation induced band shifting and band bending. Based on our findings, a potential design strategy combining an efficient electrolytic gating and a lattice straining to achieve controllable phase engineering in TMD monolayers was demonstrated

Lattice strings

International Nuclear Information System (INIS)

Thorn, C.B.

1988-01-01

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

Observation of electron polarization above 80% in photoemission from strained III-V compounds

International Nuclear Information System (INIS)

Garwin, E.L.; Maruyama, T.; Prepost, R.; Zapalac, G.H.

1992-02-01

Spin-polarized electron photoemission has been investigated for strained III--V compounds; (1) strained In x Ga 1-x As epitaxially grown on a GaAs substrate, and (2) strained GaAs grown on a GaAs 1-x P x buffer layer. The lattice mismatched heterostructure results in a highly strained epitaxial layer, and electron spin polarization as high as 90% has been observed

Ba{sub y}Sr{sub 1−y}TiO{sub 3} buffer layers for strain tuning of infinite-layer Sr{sub 1−x}La{sub x}CuO{sub 2} thin films

Energy Technology Data Exchange (ETDEWEB)

Sakuma, Keita, E-mail: sakuma.keita@d.mbox.nagoya-u.ac.jp; Ito, Masataka; He, Yilun; Hajiri, Tetsuya; Ueda, Kenji; Asano, Hidefumi

2016-08-01

We report on the precise tuning of lattice strain in an infinite-layer electron-doped high temperature superconductor Sr{sub 1−x}La{sub x}CuO{sub 2} (SLCO; a{sub SLCO} = 0.3949 nm for x = 0.1), which is a perovskite-related oxide, using perovskite BaTiO{sub 3}–SrTiO{sub 3} (BSTO; Ba{sub y}Sr{sub 1−y}TiO{sub 3}) buffer layers. The BSTO buffer layers formed on (001) (La{sub 0.18}Sr{sub 0.82})(Al{sub 0.59}Ta{sub 0.41})O{sub 3} substrates by magnetron sputtering were fully relaxed with high crystalline quality due to high oxygen partial pressure deposition and post annealing at 950 °C. The lattice constants of the BSTO buffer layers could be controlled in the range of 0.3926–0.3973 nm by changing the Ba content (y = 0.2–0.7). These BSTO buffer layers allow coherent growth of SLCO thin films, and a clear dependence of the superconducting transition temperature on the lattice strain was observed. The fabrication of these BSTO/superconductor heterostructures may provide novel devices composed of functional perovskite thin films, in addition to a general approach for the precise control of lattice strain in functional perovskite thin films. - Highlights: • Ba{sub y}Sr{sub 1−y}TiO{sub 3} buffer layers were developed for the strain tuning of perovskite-related oxides. • Strain effect in Sr{sub 1−x}La{sub x}CuO{sub 2} was investigated by using Ba{sub y}Sr{sub 1−y}TiO{sub 3} buffer layers. • Ba{sub y}Sr{sub 1−y}TiO{sub 3} buffer layers can be used to tune the strain in other perovskite oxides.

Coupled matter-wave solitons in optical lattices

Science.gov (United States)

Golam Ali, Sk; Talukdar, B.

2009-06-01

We make use of a potential model to study the dynamics of two coupled matter-wave or Bose-Einstein condensate (BEC) solitons loaded in optical lattices. With separate attention to linear and nonlinear lattices we find some remarkable differences for response of the system to effects of these lattices. As opposed to the case of linear optical lattice (LOL), the nonlinear lattice (NOL) can be used to control the mutual interaction between the two solitons. For a given lattice wave number k, the effective potentials in which the two solitons move are such that the well (Veff(NOL)), resulting from the juxtaposition of soliton interaction and nonlinear lattice potential, is deeper than the corresponding well Veff(LOL). But these effective potentials have opposite k dependence in the sense that the depth of Veff(LOL) increases as k increases and that of Veff(NOL) decreases for higher k values. We verify that the effectiveness of optical lattices to regulate the motion of the coupled solitons depends sensitively on the initial locations of the motionless solitons as well as values of the lattice wave number. For both LOL and NOL the two solitons meet each other due to mutual interaction if their initial locations are taken within the potential wells with the difference that the solitons in the NOL approach each other rather rapidly and take roughly half the time to meet as compared with the time needed for such coalescence in the LOL. In the NOL, the soliton profiles can move freely and respond to the lattice periodicity when the separation between their initial locations are as twice as that needed for a similar free movement in the LOL. We observe that, in both cases, slow tuning of the optical lattices by varying k with respect to a time parameter τ drags the oscillatory solitons apart to take them to different locations. In our potential model the oscillatory solitons appear to propagate undistorted. But a fully numerical calculation indicates that during evolution

Coupled matter-wave solitons in optical lattices

International Nuclear Information System (INIS)

Golam Ali, Sk; Talukdar, B.

2009-01-01

We make use of a potential model to study the dynamics of two coupled matter-wave or Bose-Einstein condensate (BEC) solitons loaded in optical lattices. With separate attention to linear and nonlinear lattices we find some remarkable differences for response of the system to effects of these lattices. As opposed to the case of linear optical lattice (LOL), the nonlinear lattice (NOL) can be used to control the mutual interaction between the two solitons. For a given lattice wave number k, the effective potentials in which the two solitons move are such that the well (V eff (NOL)), resulting from the juxtaposition of soliton interaction and nonlinear lattice potential, is deeper than the corresponding well V eff (LOL). But these effective potentials have opposite k dependence in the sense that the depth of V eff (LOL) increases as k increases and that of V eff (NOL) decreases for higher k values. We verify that the effectiveness of optical lattices to regulate the motion of the coupled solitons depends sensitively on the initial locations of the motionless solitons as well as values of the lattice wave number. For both LOL and NOL the two solitons meet each other due to mutual interaction if their initial locations are taken within the potential wells with the difference that the solitons in the NOL approach each other rather rapidly and take roughly half the time to meet as compared with the time needed for such coalescence in the LOL. In the NOL, the soliton profiles can move freely and respond to the lattice periodicity when the separation between their initial locations are as twice as that needed for a similar free movement in the LOL. We observe that, in both cases, slow tuning of the optical lattices by varying k with respect to a time parameter τ drags the oscillatory solitons apart to take them to different locations. In our potential model the oscillatory solitons appear to propagate undistorted. But a fully numerical calculation indicates that during

Fluorescence imaging of lattice re-distribution on step-index direct laser written Nd:YAG waveguide lasers

Energy Technology Data Exchange (ETDEWEB)

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.

Lattice artifacts in the non-Abelian Debye screening mass in one-loop order

International Nuclear Information System (INIS)

Kaste, P.; Rothe, H.J.

1997-01-01

We compute the electric screening mass in lattice QCD with Wilson fermions at finite temperature and chemical potential to one-loop order, and show that lattice artifacts arising from a finite lattice spacing result in an enhancement of the screening mass as compared to the continuum. We discuss the magnitude of this enhancement as a function of the temperature and chemical potential for lattices with a different number of lattice sites in the temporal direction that can be implemented in lattice simulations. Most of the enhancement is found to be due to the fermion loop contribution. copyright 1997 The American Physical Society

Charge-lattice interplay in layered cobaltates RBaCo2O5+x

Science.gov (United States)

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

2017-10-01

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

Finite lattice extrapolation algorithms

International Nuclear Information System (INIS)

Henkel, M.; Schuetz, G.

1987-08-01

Two algorithms for sequence extrapolation, due to von den Broeck and Schwartz and Bulirsch and Stoer are reviewed and critically compared. Applications to three states and six states quantum chains and to the (2+1)D Ising model show that the algorithm of Bulirsch and Stoer is superior, in particular if only very few finite lattice data are available. (orig.)

Strain-Driven Stacking Faults in CdSe/CdS Core/Shell Nanorods.

Science.gov (United States)

Demortière, Arnaud; Leonard, Donovan N; Petkov, Valeri; Chapman, Karena; Chattopadhyay, Soma; She, Chunxing; Cullen, David A; Shibata, Tomohiro; Pelton, Matthew; Shevchenko, Elena V

2018-04-19

Colloidal semiconductor nanocrystals are commonly grown with a shell of a second semiconductor material to obtain desired physical properties, such as increased photoluminescence quantum yield. However, the growth of a lattice-mismatched shell results in strain within the nanocrystal, and this strain has the potential to produce crystalline defects. Here, we study CdSe/CdS core/shell nanorods as a model system to investigate the influence of core size and shape on the formation of stacking faults in the nanocrystal. Using a combination of high-angle annular dark-field scanning transmission electron microscopy and pair-distribution-function analysis of synchrotron X-ray scattering, we show that growth of the CdS shell on smaller, spherical CdSe cores results in relatively small strain and few stacking faults. By contrast, growth of the shell on larger, prolate spheroidal cores leads to significant strain in the CdS lattice, resulting in a high density of stacking faults.

OPTIMIZING THE DYNAMIC APERTURE FOR TRIPLE BEND ACHROMATIC LATTICES

International Nuclear Information System (INIS)

KRAMER, S.L.; BENGTSSON, J.

2006-01-01

The Triple Bend Achromatic (TBA) lattice has the potential for lower natural emittance per period than the Double Bend Achromatic (DBA) lattice for high brightness light sources. However, the DBA has been chosen for 3rd generation light sources more often due to the higher number of undulator straight section available for a comparable emittance. The TBA has considerable flexibility in linear optics tuning while maintaining this emittance advantage. We have used the tune and chromaticity flexibility of a TBA lattice to minimize the lowest order nonlinearities to implement a 3rd order achromatic tune, while maintaining a constant emittance. This frees the geometric sextupoles to counter the higher order nonlinearities. This procedure is being used to improve the nonlinear dynamics of the TBA as a proposed lattice for NSLS-II facility. The flexibility of the TBA lattice will also provide for future upgrade capabilities of the beam parameters

Nucleation and strain-stabilization during organic semiconductor thin film deposition.

Science.gov (United States)

Li, Yang; Wan, Jing; Smilgies, Detlef-M; Bouffard, Nicole; Sun, Richard; Headrick, Randall L

2016-09-07

The nucleation mechanisms during solution deposition of organic semiconductor thin films determine the grain morphology and may influence the crystalline packing in some cases. Here, in-situ optical spectromicroscopy in reflection mode is used to study the growth mechanisms and thermal stability of 6,13-bis(trisopropylsilylethynyl)-pentacene thin films. The results show that the films form in a supersaturated state before transforming to a solid film. Molecular aggregates corresponding to subcritical nuclei in the crystallization process are inferred from optical spectroscopy measurements of the supersaturated region. Strain-free solid films exhibit a temperature-dependent blue shift of optical absorption peaks due to a continuous thermally driven change of the crystalline packing. As crystalline films are cooled to ambient temperature they become strained although cracking of thicker films is observed, which allows the strain to partially relax. Below a critical thickness, cracking is not observed and grazing incidence X-ray diffraction measurements confirm that the thinnest films are constrained to the lattice constants corresponding to the temperature at which they were deposited. Optical spectroscopy results show that the transition temperature between Form I (room temperature phase) and Form II (high temperature phase) depends on the film thickness, and that Form I can also be strain-stabilized up to 135 °C.

Hole doped Dirac states in silicene by biaxial tensile strain

KAUST Repository

Kaloni, Thaneshwor P.

2013-03-11

The effects of biaxial tensile strain on the structure, electronic states, and mechanical properties of silicene are studied by ab-initio calculations. Our results show that up to 5% strain the Dirac cone remains essentially at the Fermi level, while higher strain induces hole doped Dirac states because of weakened Si–Si bonds. We demonstrate that the silicene lattice is stable up to 17% strain. It is noted that the buckling first decreases with the strain (up to 10%) and then increases again, which is accompanied by a band gap variation. We also calculate the Grüneisen parameter and demonstrate a strain dependence similar to that of graphene.

Hole doped Dirac states in silicene by biaxial tensile strain

KAUST Repository

Kaloni, Thaneshwor P.; Cheng, Yingchun; Schwingenschlö gl, Udo

2013-01-01

The effects of biaxial tensile strain on the structure, electronic states, and mechanical properties of silicene are studied by ab-initio calculations. Our results show that up to 5% strain the Dirac cone remains essentially at the Fermi level, while higher strain induces hole doped Dirac states because of weakened Si–Si bonds. We demonstrate that the silicene lattice is stable up to 17% strain. It is noted that the buckling first decreases with the strain (up to 10%) and then increases again, which is accompanied by a band gap variation. We also calculate the Grüneisen parameter and demonstrate a strain dependence similar to that of graphene.

A model for the formation of lattice defects at silicon oxide precipitates in silicon

International Nuclear Information System (INIS)

Vanhellemont, J.; Gryse, O. de; Clauws, P.

2003-01-01

The critical size of silicon oxide precipitates and the formation of lattice defects by the precipitates are discussed. An expression is derived allowing estimation of self-interstitial emission by spherical precipitates as well as strain build-up during precipitate growth. The predictions are compared with published experimental data. A model for stacking fault nucleation at oxide precipitates is developed based on strain and self-interstitial accumulation during the thermal history of the wafer. During a low-temperature treatment high levels of strain develop. During subsequent high-temperature treatment, excess strain energy in the precipitate is released by self-interstitial emission leading to favourable conditions for stacking fault nucleation

The use of pulsed neutron diffraction to measure strain in composites

International Nuclear Information System (INIS)

Bourke, M.A.M.; Goldstone, J.A.; Shi, N.; Gray, G.T. III; James, M.R.

1994-01-01

Neutron diffraction is a technique for measuring strain in crystalline materials. It is non destructive, phase discriminatory and more penetrating than X rays. Pulsed neutron sources (in contrast with steady state reactor sources) are particularly appropriate for examining heterogeneous materials or for recording the polycrystalline response of all lattice reflections. Several different aspects of composite behavior can be characterized and examples are given of residual strain measurements, strain relaxation during heating, applied loading, and determination of the strain distribution function

Application of local approach to quantitative prediction of degradation in fracture toughness of steels due to pre-straining and irradiation

International Nuclear Information System (INIS)

Miyata, T.; Tagawa, T.

1996-01-01

Degradation of cleavage fracture toughness for low carbon steels due to pre-straining and irradiation was investigated on the basis of the local fracture criterion approach. Formulation of cleavage fracture toughness through the statistical modelling proposed by BEREMIN has been simplified by the present authors to the expression involving yield stress and cleavage fracture stress of materials. A few percent pre-strain induced by cold rolling deteriorates significantly the cleavage fracture toughness. Ductile-brittle transition temperature is increased to more than 70 C higher by 8% straining in 500 MPa class high strength steel. Quantitative prediction of degradation has been successfully examined through the formulation of the cleavage fracture toughness. Analytical and experimental results indicate that degradation in toughness is caused by the increase of flow stress in pre-strained materials. Quantitative prediction of degradation of toughness due to irradiation has been also examined for the past experiments on the basis of the local fracture criterion approach. Analytical prediction from variance of yield stress by irradiation is well consistent with the experimental results. (orig.)

Resonant tunneling measurements of size-induced strain relaxation

Science.gov (United States)

Akyuz, Can Deniz

Lattice mismatch strain available in such semiconductor heterostructures as Si/SiGe or GaAs/AlGaAs can be employed to alter the electronic and optoelectronic properties of semiconductor structures and devices. When deep submicron structures are fabricated from strained material, strained layers relax by sidewall expansion giving rise to size- and geometry-dependent strain gradients throughout the structure. This thesis describes a novel experimental technique to probe the size-induced strain relaxation by studying the tunneling current characteristics of strained p-type Si/SiGe resonant tunneling diodes. Our current-voltage measurements on submicron strained p-Si/SiGe double- and triple-barrier resonant tunneling structures as a function of device diameter, D, provide experimental access to both the average strain relaxation (which leads to relative shifts in the tunneling current peak positions) and strain gradients (which give rise to a fine structure in the current peaks due to inhomogeneous strain-induced lateral quantization). We find that strain relaxation is significant, with a large fraction of the strain energy relaxed on average in D ≤ 0.25 m m devices. Further, the in-plane potentials that arise from inhomogeneous strain gradients are large. In the D ˜ 0.2 m m devices, the corresponding lateral potentials are approximately parabolic exceeding ˜ 25 meV near the perimeter. These potentials create discrete hole states in double-barrier structures (single well), and coupled hole states in triple-barrier structures (two wells). Our results are in excellent agreement with finite-element strain calculations in which the strained layers are permitted to relax to a state of minimum energy by sidewall expansion. Size-induced strain relaxation will undoubtedly become a serious technological issue once strained devices are scaled down to the deep submicron regime. Interestingly, our calculations predict and our measurements are consistent with the appearance of

Generalized isothermic lattices

International Nuclear Information System (INIS)

Doliwa, Adam

2007-01-01

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

Elimination of spurious lattice fermion solutions and noncompact lattice QCD

Energy Technology Data Exchange (ETDEWEB)

Lee, T.D.

1997-09-22

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

Compressive strain-dependent bending strength property of Al{sub 2}O{sub 3}-ZrO{sub 2} (1.5 mol% Y{sub 2}O{sub 3}) composites performance by HIP

Energy Technology Data Exchange (ETDEWEB)

Reyes-Rojas, A. [Centro de Investigacion en Materiales Avanzados S.C. (CIMAV), Miguel de Cervantes 120, Complejo Industrial Chihuahua, Cd. de Chihuahua, Chihuahua (Mexico)], E-mail: armando_reyesmx@yahoo.com.mx; Esparza-Ponce, H. [Centro de Investigacion en Materiales Avanzados S.C. (CIMAV), Miguel de Cervantes 120, Complejo Industrial Chihuahua, Cd. de Chihuahua, Chihuahua (Mexico); De la Torre, S.D. [Centro de Investigacion e Innovacion Tecnologica (CIITEC)-IPN, D.F. Mexico (Mexico); Torres-Moye, E. [Centro de Investigacion en Materiales Avanzados S.C. (CIMAV), Miguel de Cervantes 120, Complejo Industrial Chihuahua, Cd. de Chihuahua, Chihuahua (Mexico)

2009-04-15

Nanometric powders and sintered ceramics of Al{sub 2}O{sub 3}-ZrO{sub 2} (1.5 mol% Y{sub 2}O{sub 3}) prepared by hot isostatic pressing HIP have been studied. A detailed crystallographic study has been performed through X-ray diffraction, Williamson-Hall method, Rietveld method and high-resolution electron microscopy HREM analysis. The crystallographic structure data, such as domain size, lattice parameters, wt% phase, and micro-strain direction have been obtained using Rietveld refinement and Williamson-Hall methods. The results revealed that the compressive strain ({epsilon}) increased from 0.56 to 1.18 (10{sup -3}) as the t-ZrO{sub 2} content increased too. The HREM interface study conducted along the [0 0 0 1]Al{sub 2}O{sub 3}||[0 0 1]ZrO{sub 2} zone axis revealed a micro-strain lattice distortion accumulated at the grain boundary due to the ZrO{sub 2} martensitic phase transformation on cooling, t-ZrO{sub 2} grains coalescence and to the grain growth of {alpha}-Al{sub 2}O{sub 3} which cause elongated tetragonal crystals. Micro-strain lattice distortion is adjusted by the shear displacements of the planes (1 1 0) and (11-bar0) along [1-bar10] and [1-bar1-bar0] crystallographic directions, respectively; these planes are arrested by the (101-bar0) alumina plane. In this case, semi-coherent interfaces were observed along the grain boundary. It is verified that the bending strength increased in connection with the strain accumulation and amount of tetragonal structure.

Lattice fermions

Energy Technology Data Exchange (ETDEWEB)

Randjbar-Daemi, S

1995-12-01

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

Lattice fermions

International Nuclear Information System (INIS)

Randjbar-Daemi, S.

1995-12-01

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

Job strain and the risk of disability pension due to musculoskeletal disorders, depression or coronary heart disease: a prospective cohort study of 69,842 employees.

Science.gov (United States)

Mäntyniemi, Anne; Oksanen, Tuula; Salo, Paula; Virtanen, Marianna; Sjösten, Noora; Pentti, Jaana; Kivimäki, Mika; Vahtera, Jussi

2012-08-01

Observational studies suggest that high job strain is a risk factor for retirement on health grounds, but few studies have analysed specific diagnoses. We examined job strain's association with all-cause and cause-specific disability pensions. Survey responses to questions about job strain from 48,598 (response rate, 68%) public sector employees in Finland from 2000 to 2002 were used to determine work unit- and occupation-based scores. These job strain scores were assigned to all the 69,842 employees in the same work units or occupations. All participants were linked to the disability pension register of the Finnish Centre of Pensions with no loss to follow-up. Cox proportional hazard models were used to calculate HRs and their 95% CIs for disability pensions adjusted by demographic, work unit characteristics and baseline health in analyses stratified by sex and socioeconomic position. During a mean follow-up of 4.6 years, 2572 participants (4%) were granted a disability pension. A one-unit increase in job strain was associated with a 1.3- to 2.4-fold risk of requiring a disability pension due to musculoskeletal diseases in men, women and manual workers, depending on the measure of job strain (work unit or occupation based). The risk of disability pension due to cardiovascular diseases was increased in men with high job strain but not in women nor in any socioeconomic group. No consistent pattern was found for disability pension due to depression. High job strain is a risk factor for disability pension due to musculoskeletal diseases.

Effect of Strain on the Reactivity of Metal Surfaces

DEFF Research Database (Denmark)

Mavrikakis, Manos; Hammer, Bjørk; Nørskov, Jens Kehlet

1998-01-01

Self-consistent density functional calculations for the adsorption of O and CO, and the dissociation of CO on strained and unstrained Ru(0001) surfaces are used to show how strained metal surfaces have chemical properties that are significantly different from those of unstrained surfaces. Surface...... reactivity increases with lattice expansion, following a concurrent up-shift of the metal d states. Consequences for the catalytic activity of thin metal overlayers are discussed....

Impact of lattice strain on the tunnel magnetoresistance in Fe/insulator/Fe and Fe/insulator/La0.67Sr0.33MnO3 magnetic tunnel junctions

KAUST Repository

Useinov, Arthur

2013-08-19

The objective of this work is to describe the tunnel electron current in single-barrier magnetic tunnel junctions within an approach that goes beyond the single-band transport model. We propose a ballistic multichannel electron transport model that can explain the influence of in-plane lattice strain on the tunnel magnetoresistance as well as the asymmetric voltage behavior. We consider as an example single-crystal magnetic Fe(110) electrodes for Fe/insulator/Fe and Fe/insulator/La0.67Sr0.33MnO3 tunnel junctions, where the electronic band structures of Fe and La0.67Sr0.33MnO3 are derived by ab initio calculations.

Impact of lattice strain on the tunnel magnetoresistance in Fe/insulator/Fe and Fe/insulator/La0.67Sr0.33MnO3 magnetic tunnel junctions

KAUST Repository

Useinov, Arthur; Saeed, Yasir; Schwingenschlö gl, Udo; Singh, Nirpendra; Useinov, N.

2013-01-01

The objective of this work is to describe the tunnel electron current in single-barrier magnetic tunnel junctions within an approach that goes beyond the single-band transport model. We propose a ballistic multichannel electron transport model that can explain the influence of in-plane lattice strain on the tunnel magnetoresistance as well as the asymmetric voltage behavior. We consider as an example single-crystal magnetic Fe(110) electrodes for Fe/insulator/Fe and Fe/insulator/La0.67Sr0.33MnO3 tunnel junctions, where the electronic band structures of Fe and La0.67Sr0.33MnO3 are derived by ab initio calculations.

Axial strain in GaAs/InAs core-shell nanowires

Energy Technology Data Exchange (ETDEWEB)

Biermanns, Andreas; Pietsch, Ullrich [Universitaet Siegen, Festkoerperphysik, 57068 Siegen (Germany); Rieger, Torsten; Gruetzmacher, Detlev; Ion Lepsa, Mihail [Peter Gruenberg Institute (PGI-9), Forschungszentrum, 52425 Juelich (Germany); JARA-Fundamentals of Future Information Technology, 52425 Juelich (Germany); Bussone, Genziana [Universitaet Siegen, Festkoerperphysik, 57068 Siegen (Germany); ESRF, 6 rue Jules Horowitz, BP220, F-38043 Grenoble Cedex (France)

2013-01-28

We study the axial strain relaxation in GaAs/InAs core-shell nanowire heterostructures grown by molecular beam epitaxy. Besides a gradual strain relaxation of the shell material, we find a significant strain in the GaAs core, increasing with shell thickness. This strain is explained by a saturation of the dislocation density at the core-shell interface. Independent measurements of core and shell lattice parameters by x-ray diffraction reveal a relaxation of 93% in a 35 nm thick InAs shell surrounding cores of 80 nm diameter. The compressive strain of -0.5% compared to bulk InAs is accompanied by a tensile strain up to 0.9% in the GaAs core.

Substrate-dependent post-annealing effects on the strain state and electrical transport of epitaxial La5/8-yPryCa3/8MnO3 films

International Nuclear Information System (INIS)

Hu, Sixia; Wang, Haibo; Dong, Yongqi; Hong, Bing; He, Hao; Bao, Jun; Huang, Haoliang; Yang, Yuanjun; Luo, Zhenlin; Yang, Mengmeng; Gao, Chen

2014-01-01

Large scale electronic phase separation (EPS) between ferromagnetic metallic and charge-ordered insulating phases in La 5/8-y Pr y Ca 3/8 MnO 3 (y = 0.3) (LPCMO) is very sensitive to the structural changes. This work investigates the effects of post-annealing on the strain states and electrical transport properties of LPCMO films epitaxially grown on (001) pc SrTiO 3 (tensile strain), LaAlO 3 (compressive strain) and NdGaO 3 (near-zero strain) substrates. Before annealing, all the films are coherent-epitaxial and insulating through the measured temperature range. Obvious change of film lattice is observed during the post-annealing: the in-plane strain in LPCMO/LAO varies from −1.5% to −0.1% while that in LPCMO/STO changes from 1.6% to 1.3%, and the lattice of LPCMO/NGO keeps constant because of the good lattice-match between LPCMO and NGO. Consequently, the varied film strain leads to the emergence of metal-insulator transitions (MIT) and shift of the critical transition temperature in the electrical transport. These results demonstrate that lattice-mismatch combined with post-annealing is an effective approach to tune strain in epitaxial LPCMO films, and thus to control the EPS and MIT in the films

Entire solutions for bistable lattice differential equations with obstacles

CERN Document Server

Hoffman, Aaron; Vleck, E S Van

2018-01-01

The authors consider scalar lattice differential equations posed on square lattices in two space dimensions. Under certain natural conditions they show that wave-like solutions exist when obstacles (characterized by "holes") are present in the lattice. Their work generalizes to the discrete spatial setting the results obtained in Berestycki, Hamel, and Matuno (2009) for the propagation of waves around obstacles in continuous spatial domains. The analysis hinges upon the development of sub and super-solutions for a class of discrete bistable reaction-diffusion problems and on a generalization of a classical result due to Aronson and Weinberger that concerns the spreading of localized disturbances.

Effect of lattice mismatch on the magnetic properties of nanometer-thick La0.9Ba0.1MnO3 (LBM) films and LBM/BaTiO3/LBM heterostructures

Science.gov (United States)

Mirzadeh Vaghefi, P.; Baghizadeh, A.; Willinger, M.; Lourenço, A. A. C. S.; Amaral, V. S.

2017-12-01

Oxide multiferroic thin films and heterostructures offer a wide range of properties originated from intrinsic coupling between lattice strain and nanoscale magnetic/electronic ordering. La0.9Ba0.1MnO3 (LBM) thin-films and LBM/BaTiO3/LBM (LBMBT) heterostructures were grown on single crystalline [100] silicon and [0001] Al2O3 using RF magnetron sputtering to study the effect of crystallinity and induced lattice mismatch in the film on magnetic properties of deposited films and heterostructures. The thicknesses of the films on Al2O3 and Si are 70 and 145 nm, respectively, and for heterostructures are 40/30/40 nm on both substrates. The microstructure of the films, state of strain and growth orientations was studied by XRD and microscopy techniques. Interplay of microstructure, strain and magnetic properties is further investigated. It is known that the crystal structure of substrates and imposed tensile strain affect the physical properties; i.e. magnetic behavior of the film. The thin layer grown on Al2O3 substrate shows out-of-plane compressive strain, while Si substrate induces tensile strain on the deposited film. The magnetic transition temperatures (Tc) of the LBM film on the Si and Al2O3 substrates are found to be 195 K and 203 K, respectively, slightly higher than the bulk form, 185 K. The LBMBT heterostructure on Si substrate shows drastic decrease in magnetization due to produced defects created by diffusion of Ti ions into magnetic layer. Meanwhile, the Tc in LBMBTs increases in respect to other studied single layers and heterostructure, because of higher tensile strain induced at the interfaces.

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

CERN Document Server

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

2002-01-01

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

In-plane anisotropic strain of elastically and plastically deformed III-nitrides on lithium gallate

Energy Technology Data Exchange (ETDEWEB)

Namkoong, Gon, E-mail: gnamkoon@odu.ed [Old Dominion University, Electrical and Computer Engineering, Applied Research Center, 12050 Jefferson Avenue, Newport News, VA 23606 (United States); Huang, Sa; Moseley, Michael; Doolittle, W. Alan [Georgia Institute of Technology, School of Electrical and Computer Engineering, 777 Atlantic Dr., Atlanta, GA 30332 (United States)

2009-10-30

We have investigated both elastically and plastically deformed GaN films on lithium gallate, LiGaO{sub 2}, by molecular beam epitaxy. The in-plane lattice parameters were determined from high resolution X-ray diffraction and indicated two different groups of in-plane lattice parameters, influenced by the a- and b-axis of LiGaO{sub 2}. The measured in-plane lattice parameters indicate that there exist both compressive and tensile strains of in-plane GaN along the a- and b-axis of LiGaO{sub 2}, respectively. This anisotropic strain in GaN films forms a slight distortion of the basal-plane hexagonal structure of GaN films, leading to a different critical thickness of 4.0 {+-} 0.17 and 7.8 {+-} 0.7 nm along the a- and b-axis of LiGaO{sub 2}, respectively.

In-plane anisotropic strain of elastically and plastically deformed III-nitrides on lithium gallate

International Nuclear Information System (INIS)

Namkoong, Gon; Huang, Sa; Moseley, Michael; Doolittle, W. Alan

2009-01-01

We have investigated both elastically and plastically deformed GaN films on lithium gallate, LiGaO 2 , by molecular beam epitaxy. The in-plane lattice parameters were determined from high resolution X-ray diffraction and indicated two different groups of in-plane lattice parameters, influenced by the a- and b-axis of LiGaO 2 . The measured in-plane lattice parameters indicate that there exist both compressive and tensile strains of in-plane GaN along the a- and b-axis of LiGaO 2 , respectively. This anisotropic strain in GaN films forms a slight distortion of the basal-plane hexagonal structure of GaN films, leading to a different critical thickness of 4.0 ± 0.17 and 7.8 ± 0.7 nm along the a- and b-axis of LiGaO 2 , respectively.

The 2-D lattice theory of Flower Constellations

Science.gov (United States)

Avendaño, Martín E.; Davis, Jeremy J.; Mortari, Daniele

2013-08-01

The 2-D lattice theory of Flower Constellations, generalizing Harmonic Flower Constellations (the symmetric subset of Flower Constellations) as well as the Walker/ Mozhaev constellations, is presented here. This theory is a new general framework to design symmetric constellations using a 2× 2 lattice matrix of integers or by its minimal representation, the Hermite normal form. From a geometrical point of view, the phasing of satellites is represented by a regular pattern (lattice) on a two-Dimensional torus. The 2-D lattice theory of Flower Constellations does not require any compatibility condition and uses a minimum set of integer parameters whose meaning are explored throughout the paper. This general minimum-parametrization framework allows us to obtain all symmetric distribution of satellites. Due to the J_2 effect this design framework is meant for circular orbits and for elliptical orbits at critical inclination, or to design elliptical constellations for the unperturbed Keplerian case.

Investigations into the Surface Strain/Stress State in a Single-Crystal Superalloy via XRD Characterization

Directory of Open Access Journals (Sweden)

Haodong Duan

2018-05-01

Full Text Available The present study was aimed at determining the surface strain/stress state in an Ni-based single-crystal (SC superalloy that was subjected to two different cooling rates from solid solution temperature through using the X-ray diffraction (XRD method. The normal stresses σ 11 s and σ 22 s were determined, then the Von Mises stresses ( σ V M s were derived from them. Field emission gun scanning electron microscope (FEG-SEM and transmission electron microscope (TEM micrographs were taken to illustrate the strain/stress state change. The precipitation of the secondary γ′ phases in the γ phase and the formation of the dislocation in the interphase upon a slower cooling rate caused the γ phase lattice distortion to increase, so a larger σ V M s of the γ phase was realized in comparison to the faster cooling sample. For both of the two cooling modes, we found that the σ V M s of the γ′ phase increased due to the growth of the γ′ phase during the aging process. Also, the aging process led to pronouncedly anisotropic lattice mismatches in the {331} and {004} planes. In addition, the surface strain/stress states of a cylinder sample and a tetragonal sample were also studied using a faster cooling rate, and σ 11 s and σ 22 s were analyzed to explain the influence of the shape factor on the stress anisotropy in the [001] and [ 1 1 ¯ 0 ] orientations. The strain in the [001] orientation of the γ phase is more sensitive to the shape change.

Stranski-Krastanow islanding initiated on the stochastic rough surfaces of the epitaxially strained thin films

International Nuclear Information System (INIS)

Tarik Ogurtani, Omer; Celik, Aytac; Emre Oren, Ersin

2014-01-01

Quantum dots (QD) have discrete energy spectrum, which can be adjusted over a wide range by tuning composition, density, size, lattice strain, and morphology. These features make quantum dots attractive for the design and fabrication of novel electronic, magnetic and photonic devices and other functional materials used in cutting-edge applications. The formation of QD on epitaxially strained thin film surfaces, known as Stranski-Krastanow (SK) islands, has attracted great attention due to their unique electronic properties. Here, we present a systematic dynamical simulation study for the spontaneous evolution of the SK islands on the stochastically rough surfaces (nucleationless growth). During the development of SK islands through the mass accumulation at randomly selected regions of the film via surface drift-diffusion (induced by the capillary and mismatch stresses) with and/or without growth, one also observes the formation of an extremely thin wetting layer having a thickness of a few Angstroms. Above a certain threshold level of the mismatch strain and/or the size of the patch, the formation of multiple islands separated by shallow wetting layers is also observed as metastable states such as doublets even multiplets. These islands are converted into a distinct SK islands after long annealing times by coalescence through the long range surface diffusion. Extensive computer simulation studies demonstrated that after an initial transient regime, there is a strong quadratic relationship between the height of the SK singlet and the intensity of the lattice mismatch strain (in a wide range of stresses up to 8.5 GPa for germanium thin crystalline films), with the exception at those critical points where the morphological (shape change with necking) transition takes place.

Lattice gauge theory

International Nuclear Information System (INIS)

Mack, G.

1982-01-01

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

Persistence of metastable vortex lattice domains in MgB2 in the presence of vortex motion.

Science.gov (United States)

Rastovski, C; Schlesinger, K J; Gannon, W J; Dewhurst, C D; DeBeer-Schmitt, L; Zhigadlo, N D; Karpinski, J; Eskildsen, M R

2013-09-06

Recently, extensive vortex lattice metastability was reported in MgB2 in connection with a second-order rotational phase transition. However, the mechanism responsible for these well-ordered metastable vortex lattice phases is not well understood. Using small-angle neutron scattering, we studied the vortex lattice in MgB2 as it was driven from a metastable to the ground state through a series of small changes in the applied magnetic field. Our results show that metastable vortex lattice domains persist in the presence of substantial vortex motion and directly demonstrate that the metastability is not due to vortex pinning. Instead, we propose that it is due to the jamming of counterrotated vortex lattice domains which prevents a rotation to the ground state orientation.

Strain relaxation of CdTe on Ge studied by medium energy ion scattering

Energy Technology Data Exchange (ETDEWEB)

Pillet, J.C., E-mail: jean-christophe.pillet@cea.fr [Univ. Grenoble Alpes, CEA, LETI, MINATEC campus, F38000 Grenoble (France); CEA, LETI, Département Optique et Photonique, F38054 Grenoble (France); Pierre, F. [Univ. Grenoble Alpes, CEA, LETI, MINATEC campus, F38000 Grenoble (France); CEA, LETI, Service de Caractérisation des Matériaux et Composants, F38054 Grenoble (France); Jalabert, D. [Univ. Grenoble Alpes, CEA, LETI, MINATEC campus, F38000 Grenoble (France); CEA-INAC/UJF-Grenoble 1 UMR-E, SP2M, LEMMA, Minatec Grenoble F-38054 (France)

2016-10-01

We have used the medium energy ion scattering (MEIS) technique to assess the strain relaxation in molecular-beam epitaxial (MBE) grown CdTe (2 1 1)/Ge (2 1 1) system. A previous X-ray diffraction study, on 10 samples of the same heterostructure having thicknesses ranging from 25 nm to 10 μm has allowed the measurement of the strain relaxation on a large scale. However, the X-ray diffraction measurements cannot achieve a stress measurement in close proximity to the CdTe/Ge interface at the nanometer scale. Due to the huge lattice misfit between the CdTe and Ge, a high degree of disorder is expected at the interface. The MEIS in channeling mode is a good alternative in order to profile defects with a high depth resolution. For a 21 nm thick CdTe layer, we observed, at the interface, a high density of Cd and/or Te atoms moved from their expected crystallographic positions followed by a rapid recombination of defects. Strain relaxation mechanisms in the vicinity of the interface are discussed.

Differential phase-contrast dark-field electron holography for strain mapping

Energy Technology Data Exchange (ETDEWEB)

Denneulin, Thibaud, E-mail: thibaud.denneulin@cemes.fr; Houdellier, Florent, E-mail: florent.houdellier@cemes.fr; Hÿtch, Martin, E-mail: martin.hytch@cemes.fr

2016-01-15

Strain mapping is an active area of research in transmission electron microscopy. Here we introduce a dark-field electron holographic technique that shares several aspects in common with both off-axis and in-line holography. Two incident and convergent plane waves are produced in front of the specimen thanks to an electrostatic biprism in the condenser system of a transmission electron microscope. The interference of electron beams diffracted by the illuminated crystal is then recorded in a defocused plane. The differential phase recovered from the hologram is directly proportional to the strain in the sample. The strain can be quantified if the separation of the images due to the defocus is precisely determined. The present technique has the advantage that the derivative of the phase is measured directly which allows us to avoid numerical differentiation. The distribution of the noise in the reconstructed strain maps is isotropic and more homogeneous. This technique was used to investigate different samples: a Si/SiGe superlattice, transistors with SiGe source/drain and epitaxial PZT thin films. - Highlights: • DPC dark-field electron holography is set up with a condenser biprism. • The DPC phase is directly proportional to the lattice deformation. • The technique is illustrated with epitaxial SiGe and Pb(Zr,Ti)O{sub 3} samples. • The defocus allows us to control the strain sensitivity and the spatial resolution. • A solution is proposed to setup this technique with a post-specimen biprism.

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

International Nuclear Information System (INIS)

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

2005-01-01

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

Recursive evaluation of space-time lattice Green's functions

International Nuclear Information System (INIS)

De Hon, Bastiaan P; Arnold, John M

2012-01-01

Up to a multiplicative constant, the lattice Green's function (LGF) as defined in condensed matter physics and lattice statistical mechanics is equivalent to the Z-domain counterpart of the finite-difference time-domain Green's function (GF) on a lattice. Expansion of a well-known integral representation for the LGF on a ν-dimensional hyper-cubic lattice in powers of Z −1 and application of the Chu–Vandermonde identity results in ν − 1 nested finite-sum representations for discrete space-time GFs. Due to severe numerical cancellations, these nested finite sums are of little practical use. For ν = 2, the finite sum may be evaluated in closed form in terms of a generalized hypergeometric function. For special lattice points, that representation simplifies considerably, while on the other hand the finite-difference stencil may be used to derive single-lattice-point second-order recurrence schemes for generating 2D discrete space-time GF time sequences on the fly. For arbitrary symbolic lattice points, Zeilberger's algorithm produces a third-order recurrence operator with polynomial coefficients of the sixth degree. The corresponding recurrence scheme constitutes the most efficient numerical method for the majority of lattice points, in spite of the fact that for explicit numeric lattice points the associated third-order recurrence operator is not the minimum recurrence operator. As regards the asymptotic bounds for the possible solutions to the recurrence scheme, Perron's theorem precludes factorial or exponential growth. Along horizontal lattices directions, rapid initial growth does occur, but poses no problems in augmented dynamic-range fixed precision arithmetic. By analysing long-distance wave propagation along a horizontal lattice direction, we have concluded that the chirp-up oscillations of the discrete space-time GF are the root cause of grid dispersion anisotropy. With each factor of ten increase in the lattice distance, one would have to roughly

Nanoscale strain engineering of graphene and graphene-based devices

Institute of Scientific and Technical Information of China (English)

N-C Yeh; C-C Hsu; M L Teague; J-Q Wang; D A Boyd; C-C Chen

2016-01-01

Structural distortions in nano-materials can induce dramatic changes in their electronic properties. This situation is well manifested in graphene, a two-dimensional honeycomb structure of carbon atoms with only one atomic layer thickness. In particular, strained graphene can result in both charging effects and pseudo-magnetic fields, so that controlled strain on a perfect graphene lattice can be tailored to yield desirable electronic properties. Here, we describe the theoretical foundation for strain-engineering of the electronic properties of graphene, and then provide experimental evidence for strain-induced pseudo-magnetic fields and charging effects in monolayer graphene. We further demonstrate the feasibility of nano-scale strain engineering for graphene-based devices by means of theoretical simula-tions and nano-fabrication technology.

Area of Lattice Polygons

Science.gov (United States)

Scott, Paul

2006-01-01

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

Coupling effect of topological states and Chern insulators in two-dimensional triangular lattices

Science.gov (United States)

Zhang, Jiayong; Zhao, Bao; Xue, Yang; Zhou, Tong; Yang, Zhongqin

2018-03-01

We investigate topological states of two-dimensional (2D) triangular lattices with multiorbitals. Tight-binding model calculations of a 2D triangular lattice based on px and py orbitals exhibit very interesting doubly degenerate energy points at different positions (Γ and K /K' ) in momentum space, with quadratic non-Dirac and linear Dirac band dispersions, respectively. Counterintuitively, the system shows a global topologically trivial rather than nontrivial state with consideration of spin-orbit coupling due to the "destructive interference effect" between the topological states at the Γ and K /K' points. The topologically nontrivial state can emerge by introducing another set of triangular lattices to the system (bitriangular lattices) due to the breakdown of the interference effect. With first-principles calculations, we predict an intrinsic Chern insulating behavior (quantum anomalous Hall effect) in a family of the 2D triangular lattice metal-organic framework of Co(C21N3H15) (TPyB-Co) from this scheme. Our results provide a different path and theoretical guidance for the search for and design of new 2D topological quantum materials.

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

Energy Technology Data Exchange (ETDEWEB)

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

2017-07-15

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

Analysis of strain error sources in micro-beam Laue diffraction

International Nuclear Information System (INIS)

Hofmann, Felix; Eve, Sophie; Belnoue, Jonathan; Micha, Jean-Sébastien; Korsunsky, Alexander M.

2011-01-01

Micro-beam Laue diffraction is an experimental method that allows the measurement of local lattice orientation and elastic strain within individual grains of engineering alloys, ceramics, and other polycrystalline materials. Unlike other analytical techniques, e.g. based on electron microscopy, it is not limited to surface characterisation or thin sections, but rather allows non-destructive measurements in the material bulk. This is of particular importance for in situ loading experiments where the mechanical response of a material volume (rather than just surface) is studied and it is vital that no perturbation/disturbance is introduced by the measurement technique. Whilst the technique allows lattice orientation to be determined to a high level of precision, accurate measurement of elastic strains and estimating the errors involved is a significant challenge. We propose a simulation-based approach to assess the elastic strain errors that arise from geometrical perturbations of the experimental setup. Using an empirical combination rule, the contributions of different geometrical uncertainties to the overall experimental strain error are estimated. This approach was applied to the micro-beam Laue diffraction setup at beamline BM32 at the European Synchrotron Radiation Facility (ESRF). Using a highly perfect germanium single crystal, the mechanical stability of the instrument was determined and hence the expected strain errors predicted. Comparison with the actual strain errors found in a silicon four-point beam bending test showed good agreement. The simulation-based error analysis approach makes it possible to understand the origins of the experimental strain errors and thus allows a directed improvement of the experimental geometry to maximise the benefit in terms of strain accuracy.

Atomic displacements due to interstitial hydrogen in Cu and Pd

Indian Academy of Sciences (India)

2015-11-27

Nov 27, 2015 ... Atomic displacements; density functional theory; Kanzaki method. ... pseudopotentials for H, Cu and Pd are generated self-consistently. ... Both Cu and Pd lattices show lattice expansion due to the presence of hydrogen and ...

A theoretical model on surface electronic behavior: Strain effect

International Nuclear Information System (INIS)

Qin, W.G.; Shaw, D.

2009-01-01

Deformation from mechanical loading can affect surface electronic behavior. Surface deformation and electronic behavior can be quantitatively expressed using strain and work function, respectively, and their experimental relationship can be readily determined using the Kelvin probing technique. However, the theoretical correlation between work function and strain has been unclear. This study reports our theoretical exploration, for the first time, of the effect of strain on work function. We propose a simple electrostatic action model by considering the effect of a dislocation on work function of a one-dimensional lattice and further extend this model to the complex conditions for the effect of dislocation density. Based on this model, we established successfully a theoretical correlation between work function and strain.

Effects of nutritional supplementation with l-arginine on repair of injuries due to muscle strain: experimental study on rats

Directory of Open Access Journals (Sweden)

Lauren Izabel Medeiros Couto

2015-08-01

Full Text Available ABSTRACTOBJECTIVE: To evaluate the influence of oral supplementation with arginine on regeneration of injuries due to straining of the anterior tibial muscle of rats. METHODS: Twenty-four Wistar rats of weight 492.5 ± 50.45 g were used. Injuries were induced through straining the anterior tibial muscles. The rats were separated into three groups of eight rats each. In the untreated group (UTG, after induction of injuries, the rats were observed for 24 h. In the simulation group (SG and the arginine group (AG respectively, the rats received isotonic saline solution and arginine solution via direct gavage, over a seven-day period. At the end of the period, blood samples were collected for serum evaluations of creatine kinase (CK, lactic dehydrogenase (LDH, aspartate aminotransferase (AST and C-reactive protein (CRP. The right and left anterior tibial muscles were resected for histopathological evaluations on the muscle injuries, investigating edema, hemorrhage and disorganization or morphometric alteration of the muscle fibers. The tissue repair was investigated in terms of proliferation of adipose tissue, angiogenesis and collagen fibers. The ANOVA and Student's tmethods were used and p≤ 0.05 was taken to be statistically significant. RESULTS: In the serum evaluations, the AG showed lower CK assay values and higher AST values. In the histopathological evaluation, the UTG presented edema and hemorrhage compatible with injuries due to strain; the SG presented edema and hemorrhage with proliferation of adipose tissue and collagen fibers; and the AG presented not only the findings of the SG but also, especially, intense angiogenesis. CONCLUSION: Oral supplementation with arginine did not cause any significant metabolic alterations that would contraindicate its use and it induced angiogenesis during the repair of muscles injured due to strain.

Measurement of deforming mode of lattice truss structures under impact loading

Directory of Open Access Journals (Sweden)

Zhao H.

2012-08-01

Full Text Available Lattice truss structures, which are used as a core material in sandwich panels, were widely investigated experimentally and theoretically. However, explanation of the deforming mechanism using reliable experimental results is almost rarely reported, particularly for the dynamic deforming mechanism. The present work aimed at the measurement of the deforming mode of lattice truss structures. Indeed, quasi-static and Split Hopkinson Pressure Bar (SHPB tests have been performed on the tetrahedral truss cores structures made of Aluminum 3003-O. Global values such as crushing forces and displacements between the loading platens are obtained. However, in order to understand the deforming mechanism and to explain the observed impact strength enhancement observed in the experiments, images of the truss core element during the tests are recorded. A method based on the edge detection algorithm is developed and applied to these images. The deforming profiles of one beam are extracted and it allows for calculating the length of beam. It is found that these lengths diminish to a critical value (due to compression and remain constant afterwards (because of significant bending. The comparison between quasi-static and impact tests shows that the beam were much more compressed under impact loading, which could be understood as the lateral inertia effect in dynamic bucking. Therefore, the impact strength enhancement of tetrahedral truss core sandwich panel can be explained by the delayed buckling of beam under impact (more compression reached, together with the strain hardening of base material.

Quantitative Characterization of the Nanoscale Local Lattice Strain Induced by Sr Dopants in La1.92Sr0.08CuO4

Science.gov (United States)

Lin, J. Q.; Liu, X.; Blackburn, E.; Wakimoto, S.; Ding, H.; Islam, Z.; Sinha, S. K.

2018-05-01

The nanometer scale lattice deformation brought about by the dopants in the high temperature superconducting cuprate La2 -xSrx CuO4 (x =0.08 ) was investigated by measuring the associated x-ray diffuse scattering around multiple Bragg peaks. A characteristic diffuse scattering pattern was observed, which can be well described by continuum elastic theory. With the fitted dipole force parameters, the acoustic-type lattice deformation pattern was reconstructed and found to be of similar size to lattice thermal vibration at 7 K. Our results address the long-term concern of dopant introduced local lattice inhomogeneity, and show that the associated nanometer scale lattice deformation is marginal and cannot, alone, be responsible for the patched variation in the spectral gaps observed with scanning tunneling microscopy in the cuprates.

Large area strain analysis using scanning transmission electron microscopy across multiple images

International Nuclear Information System (INIS)

Oni, A. A.; Sang, X.; LeBeau, J. M.; Raju, S. V.; Saxena, S.; Dumpala, S.; Broderick, S.; Rajan, K.; Kumar, A.; Sinnott, S.

2015-01-01

Here, we apply revolving scanning transmission electron microscopy to measure lattice strain across a sample using a single reference area. To do so, we remove image distortion introduced by sample drift, which usually restricts strain analysis to a single image. Overcoming this challenge, we show that it is possible to use strain reference areas elsewhere in the sample, thereby enabling reliable strain mapping across large areas. As a prototypical example, we determine the strain present within the microstructure of a Ni-based superalloy directly from atom column positions as well as geometric phase analysis. While maintaining atomic resolution, we quantify strain within nanoscale regions and demonstrate that large, unit-cell level strain fluctuations are present within the intermetallic phase

New integrable lattice hierarchies

International Nuclear Information System (INIS)

Pickering, Andrew; Zhu Zuonong

2006-01-01

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

Lattice gauge theories

International Nuclear Information System (INIS)

Creutz, M.

1983-04-01

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

Strain-induced enhancement of thermoelectric performance of TiS2 monolayer based on first-principles phonon and electron band structures

Science.gov (United States)

Li, Guanpeng; Yao, Kailun; Gao, Guoying

2018-01-01

Using first-principle calculations combined with Boltzmann transport theory, we investigate the biaxial strain effect on the electronic and phonon thermal transport properties of a 1 T (CdI2-type) structural TiS2 monolayer, a recent experimental two-dimensional (2D) material. It is found that the electronic band structure can be effectively modulated and that the band gap experiences an indirect-direct-indirect transition with increasing tensile strain. The band convergence induced by the tensile strain increases the Seebeck coefficient and the power factor, while the lattice thermal conductivity is decreased under the tensile strain due to the decreasing group velocity and the increasing scattering chances between the acoustic phonon modes and the optical phonon modes, which together greatly increase the thermoelectric performance. The figure of merit can reach 0.95 (0.82) at an 8 percent tensile strain for the p-type (n-type) doping, which is much larger than that without strain. The present work suggests that the TiS2 monolayer is a good candidate for 2D thermoelectric materials, and that biaxial strain is a powerful tool with which to enhance thermoelectric performance.

Convection-diffusion lattice Boltzmann scheme for irregular lattices

NARCIS (Netherlands)

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

2000-01-01

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

Zero Modes and Global Antiferromagnetism in Strained Graphene

Directory of Open Access Journals (Sweden)

Bitan Roy

2014-05-01

Full Text Available A novel magnetic ground state is reported for the Hubbard Hamiltonian in strained graphene. When the chemical potential lies close to the Dirac point, the ground state exhibits locally both the Néel and ferromagnetic orders, even for weak Hubbard interaction. Whereas the Néel order parameter remains of the same sign in the entire system, the magnetization at the boundary takes the opposite sign from the bulk. The total magnetization vanishes this way, and the magnetic ground state is globally only an antiferromagnet. This peculiar ordering stems from the nature of the strain-induced single-particle zero-energy states, which have support on one sublattice of the honeycomb lattice in the bulk, and on the other sublattice near the boundary of a finite system. We support our claim with the self-consistent numerical calculation of the order parameters, as well as by the Monte Carlo simulations of the Hubbard model in both uniformly and nonuniformly strained honeycomb lattice. The present result is contrasted with the magnetic ground state of the same Hubbard model in the presence of a true magnetic field (and for vanishing Zeeman coupling, which is exclusively Néel ordered, with zero local magnetization everywhere in the system.

Tunable surface configuration of skyrmion lattices in cubic helimagnets

Science.gov (United States)

Wan, Xuejin; Hu, Yangfan; Wang, Biao

2018-06-01

In bulk helimagnets, the presence of magnetic skyrmion lattices is always accompanied by a periodic stress field due to the intrinsic magnetoelastic coupling. The release of this nontrivial stress field at the surface causes a periodic displacement field, which characterizes a novel particle-like property of skyrmion: its surface configuration. Here, we derive the analytical solution of this displacement field for semi-infinite cubic helimagnet with the skyrmion magnetization approximated by the triple-Q representation. For MnSi, we show that the skyrmion lattices have a bumpy surface configuration characterized by periodically arranged peaks with a characteristic height of about 10‑13 m. The pattern of the peaks can be controlled by varying the strength of the applied magnetic field. Moreover, we prove that the surface configuration varies together with the motion and deformation of the skyrmion lattices. As a result, the surface configuration can be tuned by application of electric current, mechanical loads, as well as any other effective external fields for skyrmion lattices.

Vacuum polarization and chiral lattice fermions

International Nuclear Information System (INIS)

Randjbar Daemi, S.; Strathdee, J.

1995-09-01

The vacuum polarization due to chiral fermions on a 4-dimensional Euclidean lattice is calculated according to the overlap prescription. The fermions are coupled to weak and slowly varying background gauge and Higgs fields, and the polarization tensor is given by second order perturbation theory. In this order the overlap constitutes a gauge invariant regularization of the fermion vacuum amplitude. Its low energy - long wavelength behaviour can be computed explicitly and we verify that it coincides with the Feynman graph result obtainable, for example, by dimensional regularization of continuum gauge theory. In particular, the Standard Model Callan-Symanzik, RG functions are recovered. Moreover, there are no residual lattice artefacts such as a dependence on Wilson-type mass parameters. (author). 16 refs

Lattices with unique complements

CERN Document Server

Saliĭ, V N

1988-01-01

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

EDITORIAL: Excelling under strain: band engineering in nanomaterials Excelling under strain: band engineering in nanomaterials

Science.gov (United States)

Demming, Anna

2013-08-01

interest in strain studies as well. Researchers in China investigated the effects of tensile strain on the thermal conductivity of graphene nanoribbons. Tuning the thermal conductivity of nanomaterials is highly desirable to optimize their functionality [5]. Wei and colleagues use computer simulations based on reverse nonequilibrium molecular dynamics (RNEMD) to demonstrate what they describe as 'a strain-induced magic flexibility of thermal engineering for carbon-based nanostructures', which may provide a new approach for tailoring nanomaterial functionality. Despite the attractions of more recently discovered carbon nanomaterials silicon remains the bedrock of the semiconductor device industry. Germanium nanostructures also hold significant interest, such as Ge nanowires, which have high mobility and a conveniently low synthesis temperature [6]. In fact the potential applications of germanium nanowires in field effect transistors and nanobridge devices prompted Jagadish and colleagues in Australia, Korea and the UK to investigate the growth of taper-free kinked Ge nanowires in silicon [7]. As they point out many recent reports have highlighted such kinked nanowires as valuable components for novel nanodevices. The work reported by Hrauda and colleagues in this issue looks at the growth of germanium islands on a silicon substrate rather than nanowires [2]. They grow islands on pre-patterned silicon with different levels of Ge deposition with the aim of better understanding how to manage the effects of strain due to lattice mismatch between the two metals. Their results show that considerably more Ge can be deposited without dislocations forming than previously thought and reveal a distinctive cycle of changing island morphologies as Ge is deposited. They add, 'Strain relaxation is revealed to be the main driving force of a rather complex evolution of island shape and Ge distribution'. In reference to his theory of atoms Bohr is once said to have told Werner Heisenberg

Pricing Employee Stock Options (ESOs) with Random Lattice

Science.gov (United States)

Chendra, E.; Chin, L.; Sukmana, A.

2018-04-01

Employee Stock Options (ESOs) are stock options granted by companies to their employees. Unlike standard options that can be traded by typical institutional or individual investors, employees cannot sell or transfer their ESOs to other investors. The sale restrictions may induce the ESO’s holder to exercise them earlier. In much cited paper, Hull and White propose a binomial lattice in valuing ESOs which assumes that employees will exercise voluntarily their ESOs if the stock price reaches a horizontal psychological barrier. Due to nonlinearity errors, the numerical pricing results oscillate significantly so they may lead to large pricing errors. In this paper, we use the random lattice method to price the Hull-White ESOs model. This method can reduce the nonlinearity error by aligning a layer of nodes of the random lattice with a psychological barrier.

Mechanical properties of regular hexahedral lattice structure formed by selective laser melting

International Nuclear Information System (INIS)

Sun, Jianfeng; Yang, Yongqiang; Wang, Di

2013-01-01

The Ti–6Al–4V lattice structure is widely used in the aerospace field. This research first designs a regular hexahedral unit, processes the lattice structure composed of the Ti–6Al–4V units by selective laser melting technology, obtains the experimental fracture load and the compression deformation of them through compression tests, then conducts a simulation of the unit and the lattice structure through ANSYS to analyze the failure point. Later, according to the force condition of the point, the model of maximum load is built, through which the analytical formula of the fracture load of the unit and the lattice structure are obtained. The results of groups of experiments demonstrate that there exists an exponential relationship between the practical fracture load and the porosity of the lattice structure. There also exists a trigonometric function relationship between the compression deformation and the porosity of the lattice structure. The fracture analysis indicates that fracture of the units and lattice structure is brittle fracture due to cleavage fracture. (paper)

Direct numerical simulation of turbulent pipe flow using the lattice Boltzmann method

Science.gov (United States)

Peng, Cheng; Geneva, Nicholas; Guo, Zhaoli; Wang, Lian-Ping

2018-03-01

In this paper, we present a first direct numerical simulation (DNS) of a turbulent pipe flow using the mesoscopic lattice Boltzmann method (LBM) on both a D3Q19 lattice grid and a D3Q27 lattice grid. DNS of turbulent pipe flows using LBM has never been reported previously, perhaps due to inaccuracy and numerical stability associated with the previous implementations of LBM in the presence of a curved solid surface. In fact, it was even speculated that the D3Q19 lattice might be inappropriate as a DNS tool for turbulent pipe flows. In this paper, we show, through careful implementation, accurate turbulent statistics can be obtained using both D3Q19 and D3Q27 lattice grids. In the simulation with D3Q19 lattice, a few problems related to the numerical stability of the simulation are exposed. Discussions and solutions for those problems are provided. The simulation with D3Q27 lattice, on the other hand, is found to be more stable than its D3Q19 counterpart. The resulting turbulent flow statistics at a friction Reynolds number of Reτ = 180 are compared systematically with both published experimental and other DNS results based on solving the Navier-Stokes equations. The comparisons cover the mean-flow profile, the r.m.s. velocity and vorticity profiles, the mean and r.m.s. pressure profiles, the velocity skewness and flatness, and spatial correlations and energy spectra of velocity and vorticity. Overall, we conclude that both D3Q19 and D3Q27 simulations yield accurate turbulent flow statistics. The use of the D3Q27 lattice is shown to suppress the weak secondary flow pattern in the mean flow due to numerical artifacts.

Coherently Strained Si-SixGe1-x Core-Shell Nanowire Heterostructures.

Science.gov (United States)

Dillen, David C; Wen, Feng; Kim, Kyounghwan; Tutuc, Emanuel

2016-01-13

Coherently strained Si-SixGe1-x core-shell nanowire heterostructures are expected to possess a positive shell-to-core conduction band offset, allowing for quantum confinement of electrons in the Si core. We report the growth of epitaxial, coherently strained Si-SixGe1-x core-shell heterostructures through the vapor-liquid-solid mechanism for the Si core, followed in situ by the epitaxial SixGe1-x shell growth using ultrahigh vacuum chemical vapor deposition. The Raman spectra of individual nanowires reveal peaks associated with the Si-Si optical phonon mode in the Si core and the Si-Si, Si-Ge, and Ge-Ge vibrational modes of the SixGe1-x shell. The core Si-Si mode displays a clear red-shift compared to unstrained, bare Si nanowires thanks to the lattice mismatch-induced tensile strain, in agreement with calculated values using a finite-element continuum elasticity model combined with lattice dynamic theory. N-type field-effect transistors using Si-SixGe1-x core-shell nanowires as channel are demonstrated.

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

Directory of Open Access Journals (Sweden)

Juan Tang

2014-01-01

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

Dynamical x-ray diffraction studies of interfacial strain in superlattices grown by molecular beam epitaxy

International Nuclear Information System (INIS)

Vandenberg, J.M.; Chu, S.N.G.; Hamm, R.A.; Panish, M.B.; Ritter, D.; Mancrander, A.T.

1992-01-01

This paper reports on dynamical X-ray diffraction studies that have been carried out for lattice-matched InGaAs/InP superlattices grown by modified molecular beam epitaxy (MBE) techniques. The (400) X-ray satellite pattern, which is predominantly affected by the strain modulation, was analyzed. The strain and thickness of the actual layers including the presence of strained interfacial regions were determined

Strain-enhanced tunneling magnetoresistance in MgO magnetic tunnel junctions.

Science.gov (United States)

Loong, Li Ming; Qiu, Xuepeng; Neo, Zhi Peng; Deorani, Praveen; Wu, Yang; Bhatia, Charanjit S; Saeys, Mark; Yang, Hyunsoo

2014-09-30

While the effects of lattice mismatch-induced strain, mechanical strain, as well as the intrinsic strain of thin films are sometimes detrimental, resulting in mechanical deformation and failure, strain can also be usefully harnessed for applications such as data storage, transistors, solar cells, and strain gauges, among other things. Here, we demonstrate that quantum transport across magnetic tunnel junctions (MTJs) can be significantly affected by the introduction of controllable mechanical strain, achieving an enhancement factor of ~2 in the experimental tunneling magnetoresistance (TMR) ratio. We further correlate this strain-enhanced TMR with coherent spin tunneling through the MgO barrier. Moreover, the strain-enhanced TMR is analyzed using non-equilibrium Green's function (NEGF) quantum transport calculations. Our results help elucidate the TMR mechanism at the atomic level and can provide a new way to enhance, as well as tune, the quantum properties in nanoscale materials and devices.

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

Science.gov (United States)

Jeevanesan, Bhilahari; Orth, Peter P.

2014-10-01

We investigate the classical Heisenberg and planar (X Y ) spin models on the windmill lattice. The windmill lattice is formed out of two widely occurring lattice geometries: a triangular lattice is coupled to its dual honeycomb lattice. Using a combination of iterative minimization, heat-bath Monte Carlo simulations, and analytical calculations, we determine the complete ground-state phase diagram of both models and find the exact energies of the phases. The phase diagram shows a rich phenomenology due to competing interactions and hosts, in addition to collinear and various coplanar phases, also intricate noncoplanar phases. We briefly outline different paths to an experimental realization of these spin models. Our extensive study provides a starting point for the investigation of quantum and thermal fluctuation effects.

Additive lattice kirigami.

Science.gov (United States)

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

2016-09-01

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

Detailed design of a lattice composite fuselage structure by a mixed optimization method

Science.gov (United States)

Liu, D.; Lohse-Busch, H.; Toropov, V.; Hühne, C.; Armani, U.

2016-10-01

In this article, a procedure for designing a lattice fuselage barrel is developed. It comprises three stages: first, topology optimization of an aircraft fuselage barrel is performed with respect to weight and structural performance to obtain the conceptual design. The interpretation of the optimal result is given to demonstrate the development of this new lattice airframe concept for the fuselage barrel. Subsequently, parametric optimization of the lattice aircraft fuselage barrel is carried out using genetic algorithms on metamodels generated with genetic programming from a 101-point optimal Latin hypercube design of experiments. The optimal design is achieved in terms of weight savings subject to stability, global stiffness and strain requirements, and then verified by the fine mesh finite element simulation of the lattice fuselage barrel. Finally, a practical design of the composite skin complying with the aircraft industry lay-up rules is presented. It is concluded that the mixed optimization method, combining topology optimization with the global metamodel-based approach, allows the problem to be solved with sufficient accuracy and provides the designers with a wealth of information on the structural behaviour of the novel anisogrid composite fuselage design.

Lattice QCD evaluation of baryon magnetic moment sum rules

International Nuclear Information System (INIS)

Leinweber, D.B.

1991-05-01

Magnetic moment combinations and sum rules are evaluated using recent results for the magnetic moments of octet baryons determined in a numerical simulation of quenched QCD. The model-independent and parameter-free results of the lattice calculations remove some of the confusion and contradiction surrounding past magnetic moment sum rule analyses. The lattice results reveal the underlying quark dynamics investigated by magnetic moment sum rules and indicate the origin of magnetic moment quenching for the non-strange quarks in Σ. In contrast to previous sum rule analyses, the magnetic moments of nonstrange quarks in Ξ are seen to be enhanced in the lattice results. In most cases, the spin-dependent dynamics and center-of-mass effects giving rise to baryon dependence of the quark moments are seen to be sufficient to violate the sum rules in agreement with experimental measurements. In turn, the sum rules are used to further examine the results of the lattice simulation. The Sachs sum rule suggests that quark loop contributions not included in present lattice calculations may play a key role in removing the discrepancies between lattice and experimental ratios of magnetic moments. This is supported by other sum rules sensitive to quark loop contributions. A measure of the isospin symmetry breaking in the effective quark moments due to quark loop contributions is in agreement with model expectations. (Author) 16 refs., 2 figs., 2 tabs

Tunable strain effect and ferroelectric field effect on the electronic transport properties of La0.5Sr0.5CoO3 thin films

Science.gov (United States)

Zhu, Q. X.; Wang, W.; Zhao, X. Q.; Li, X. M.; Wang, Y.; Luo, H. S.; Chan, H. L. W.; Zheng, R. K.

2012-05-01

Tensiled La0.5Sr0.5CoO3 (LSCO) thin films were epitaxially grown on piezoelectric 0.67Pb (Mg1/3Nb2/3)O3-0.33PbTiO3 (PMN-PT) single-crystal substrates. Due to the epitaxial nature of the interface, the lattice strain induced by ferroelectric poling or the converse piezoelectric effect in the PMN-PT substrate is effectively transferred to the LSCO film and thus reduces the tensile strain of the film, giving rise to a decrease in the resistivity of the LSCO film. We discuss these strain effects within the framework of the spin state transition of Co3+ ions and modification of the electronic bandwidth that is relevant to the induced strain. By simultaneously measuring the strain and the resistivity, quantitative relationship between the resistivity and the strain was established for the LSCO film. Both theoretical calculation and experimental results demonstrate that the ferroelectric field effect at room temperature in the LSCO/PMN-PT field-effect transistor is minor and could be neglected. Nevertheless, with decreasing temperature, the ferroelectric field effect competes with the strain effect and plays a more and more important role in influencing the electronic transport properties of the LSCO film, which we interpreted as due to the localization of charge carriers at low temperature.

Computer simulation of the interaction between an extended dislocation and radiation defects in the fcc lattice

International Nuclear Information System (INIS)

Kuramoto, E.; Nakamura, Y.; Tsutsumi, T.

1993-01-01

The interaction between an extended dislocation and a radiation-induced defect, especially, a self-interstitial atom (SIA), has been investigated in the model fcc lattice by computer simulation technique. An SIA was absorbed into the core of one of the two partial dislocations of the extended screw dislocation as a crowdion which extends along the dislocation line. Under the applied shear stress this crowdion acted as a pinning point, resulting in irradiation hardening. On the other hand, an SIA was absorbed at the jog site of the extended edge dislocation (at one of the two jog sites on two partial dislocations) and after some relaxation the total jog was shifted to one atomic distance through the spreading out of the strain due to an SIA from one partial side to the other side. (orig.)

Pressure drop characteristics in tight-lattice bundles for reduced-moderation water reactors

International Nuclear Information System (INIS)

Tamai, Hidesada; Kureta, Masatoshi; Yoshida, Hiroyuki; Akimoto, Hajime

2004-01-01

The reduced-moderation water reactor (RMWR) consists of several distinctive structures; a triangular tight-lattice configuration and a double-flat core. In order to design the RMWR core from the point of view of thermal-hydraulics, an evaluation method on pressure drop characteristics in the rod bundles at the tight-lattice configuration is required. In this study, calculated results by the Martinelli-Nelson's and Hancox's correlations were compared with experimental results in 4 x 5 rod bundles and seven-rod bundles. Consequently, the friction loss in two-phase flows becomes smaller at the tight-lattice configuration with the hydraulic diameter less than about 3 mm. This reason is due to the difference of the configuration between the multi-rod bundle and the circular tube and due to the effect of the small hydraulic diameter on the two-phase multiplier. (author)

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

International Nuclear Information System (INIS)

Roskies, R.; Wu, J.C.

1986-01-01

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

Large local lattice expansion in graphene adlayers grown on copper

Science.gov (United States)

Chen, Chaoyu; Avila, José; Arezki, Hakim; Nguyen, Van Luan; Shen, Jiahong; Mucha-Kruczyński, Marcin; Yao, Fei; Boutchich, Mohamed; Chen, Yue; Lee, Young Hee; Asensio, Maria C.

2018-05-01

Variations of the lattice parameter can significantly change the properties of a material, and, in particular, its electronic behaviour. In the case of graphene, however, variations of the lattice constant with respect to graphite have been limited to less than 2.5% due to its well-established high in-plane stiffness. Here, through systematic electronic and lattice structure studies, we report regions where the lattice constant of graphene monolayers grown on copper by chemical vapour deposition increases up to 7.5% of its relaxed value. Density functional theory calculations confirm that this expanded phase is energetically metastable and driven by the enhanced interaction between the substrate and the graphene adlayer. We also prove that this phase possesses distinctive chemical and electronic properties. The inherent phase complexity of graphene grown on copper foils revealed in this study may inspire the investigation of possible metastable phases in other seemingly simple heterostructure systems.

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

Directory of Open Access Journals (Sweden)

Maruszewski, Bogdan

2008-02-01

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

Strain effects on the spin polarized electron gas in ABO3/SrTiO3 (A = Pr, Nd and B = Al, Ga) heterostructures

KAUST Repository

Nazir, Safdar

2013-04-11

The spin polarized two dimensional electron gas in the correlated ABO3/SrTiO3 (A = Pr, Nd and B = Al, Ga) heterostructures is investigated by ab-initio calculations using density functional theory. Structural relaxation shows a strong buckling at and near the TiO2 terminated n-type interface (IFs) due to significant TiO6 octahedral distortions. We find in all cases, metallic states in a very narrow region of the SrTiO3, in agreement with experimental results. We demonstrate that the interface magnetism strongly reacts to the magnitude of the lattice strain. The orbital occupations and, hence, the charge carrier density change systematically as a function of the lattice mismatch between the component materials.

Strain effects on the spin polarized electron gas in ABO3/SrTiO3 (A = Pr, Nd and B = Al, Ga) heterostructures

KAUST Repository

Nazir, Safdar; Schwingenschlö gl, Udo

2013-01-01

The spin polarized two dimensional electron gas in the correlated ABO3/SrTiO3 (A = Pr, Nd and B = Al, Ga) heterostructures is investigated by ab-initio calculations using density functional theory. Structural relaxation shows a strong buckling at and near the TiO2 terminated n-type interface (IFs) due to significant TiO6 octahedral distortions. We find in all cases, metallic states in a very narrow region of the SrTiO3, in agreement with experimental results. We demonstrate that the interface magnetism strongly reacts to the magnitude of the lattice strain. The orbital occupations and, hence, the charge carrier density change systematically as a function of the lattice mismatch between the component materials.

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

International Nuclear Information System (INIS)

Callaway, D.J.E.

1985-01-01

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

Evolving Lattices for Analyzing Behavioral Dynamics of Characters in Literary Text

Directory of Open Access Journals (Sweden)

Eugene S Kitamura

2011-10-01

Full Text Available This paper is about an application of rough set derived lattices in order to analyze the dynamics of literary text. Due to the double approximation nature of rough set theory, a pseudo-closure obtained from two different equivalence relations allows us to form arbitrary lattices. Moreover, such double approximations with different equivalence relations permit us to obtain lattice fixed points based on two interpretations. The two interpretations used for literary text analysis are subjects and their attributes. The attributes chosen for this application are verbs. The progression of a story is defined by the sequence of verbs (or event occurrences. By fixing a window size and sliding the window down the story steps, we obtain a lattice representing the relationship between subjects and their attributes within that window frame. The resulting lattice provides information such as complementarity (lattice complement existence rate and distributivity (lattice complement possession rate. These measurements depend on the overlap and the lack of overlap among the attributes of characters. As the story develops and new character and attributes are provided as the source of lattices, one can observe its evolution. In fact, a dramatic change in the behavior dynamics in a scene is reflected in the particular shifts in the character-attribute relationship. This method lets us quantify the developments of character behavioral dynamics in a story.

Electroweak interactions on the lattice

International Nuclear Information System (INIS)

Kieu, T.D.

1994-07-01

It is shown that the lattice fermion doubling phenomenon is connected to the chiral anomaly which is unique to the electroweak interactions. The chiral anomaly is the breaking of chiral gauge symmetry at the quantum level due to the quantum fluctuations. Such breaking, however, is undesirable and to be avoided. The preservation of gauge symmetry imposes stringent constraints on acceptable chiral gauge theory. It is argued that the constraints are unnecessary because the conventional quantization of chiral gauge theory has missed out some crucial contributions of the chiral interactions. The corrected quantization yields consistent theory in which there is no gauge anomaly and in which various mass terms can be introduced with neither the loss of gauge invariance nor the need for the Higgs mechanism. The new quantization also provide a solution to the difficulty of how to model the electroweak interactions on the lattice. 9 refs. 1 fig

Lattice QCD on fine lattices

Energy Technology Data Exchange (ETDEWEB)

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

2016-11-01

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

Vortex Lattices in the Bose-Fermi Superfluid Mixture.

Science.gov (United States)

Jiang, Yuzhu; Qi, Ran; Shi, Zhe-Yu; Zhai, Hui

2017-02-24

In this Letter we show that the vortex lattice structure in the Bose-Fermi superfluid mixture can undergo a sequence of structure transitions when the Fermi superfluid is tuned from the BCS regime to the BEC regime. This is due to the difference in the vortex core structure of a Fermi superfluid in the BCS regime and in the BEC regime. In the BCS regime the vortex core is nearly filled, while the density at the vortex core gradually decreases until it empties out in the BEC regime. Therefore, with the density-density interaction between the Bose and the Fermi superfluids, interaction between the two sets of vortex lattices gets stronger in the BEC regime, which yields the structure transition of vortex lattices. In view of the recent realization of this superfluid mixture and vortices therein, our theoretical predication can be verified experimentally in the near future.

Energy loss in degenerate semiconductors due to inelastic interaction with acoustic and piezoelectric phonons at low lattice temperatures

International Nuclear Information System (INIS)

Midday, S; Bhattacharya, D P

2011-01-01

The energy loss rate of an electron in a degenerate semiconductor because of inelastic interaction with deformation potential and piezoelectric acoustic phonons is calculated in the case when the lattice temperature is low, so that the approximations of the well-known traditional theory are not valid. Compared to the traditional results and those for non-degenerate semiconductors, the theory here reveals a more complex and altogether different dependence of the loss rate on the carrier energy and the lattice temperature. The numerical results obtained here for Si and GaAs show how significantly the degeneracy level, the true phonon distribution or the inelasticity of the interaction affects the loss characteristics at low temperatures.

Strain field due to self-interstitial impurity in Ni

Indian Academy of Sciences (India)

The embedded-atom method have been applied to study the strain field ... coordinates which are essentially the Fourier inverses of the direct space ..... stiffness, low coefficient of thermal expansion and chemical compatibility in a variety of.

Ab-initio calculation of the valence-band offset at strained GaAs/InAs (001) heterojunction

International Nuclear Information System (INIS)

Tit, N.; Peressi, M.

1993-06-01

We present a self consistent pseudopotential calculation of the valence band offset (VBO) at GaAs/InAs (001) strained heterojunction, which is chose as an example of the isovalent polar with common-anion lattice mismatched heterojunctions. The effects of strain are studied by looking at the variation of the VBO versus the in plane lattice constant, which is imposed by the substrate. Our results show that the VBO can be tuned by about 0.17 eV going from GaAs to InAs substrates. Comparison of our work with the available experimental and theoretical results is also discussed. (author). 25 refs, 3 figs, 5 tabs

Hydrogen embrittlement of austenitic stainless steels revealed by deformation microstructures and strain-induced creation of vacancies

International Nuclear Information System (INIS)

Hatano, M.; Fujinami, M.; Arai, K.; Fujii, H.; Nagumo, M.

2014-01-01

Hydrogen embrittlement of austenitic stainless steels has been examined with respect to deformation microstructures and lattice defects created during plastic deformation. Two types of austenitic stainless steels, SUS 304 and SUS 316L, uniformly hydrogen-precharged to 30 mass ppm in a high-pressure hydrogen environment, are subjected to tensile straining at room temperature. A substantial reduction of tensile ductility appears in hydrogen-charged SUS 304 and the onset of fracture is likely due to plastic instability. Fractographic features show involvement of plasticity throughout the crack path, implying the degradation of the austenitic phase. Electron backscatter diffraction analyses revealed prominent strain localization enhanced by hydrogen in SUS 304. Deformation microstructures of hydrogen-charged SUS 304 were characterized by the formation of high densities of fine stacking faults and ε-martensite, while tangled dislocations prevailed in SUS 316L. Positron lifetime measurements have revealed for the first time hydrogen-enhanced creation of strain-induced vacancies rather than dislocations in the austenitic phase and more clustering of vacancies in SUS 304 than in SUS 316L. Embrittlement and its mechanism are ascribed to the decrease in stacking fault energies resulting in strain localization and hydrogen-enhanced creation of strain-induced vacancies, leading to premature fracture in a similar way to that proposed for ferritic steels

Interface strain coupling and its impact on the transport and magnetic properties of LaMnO3 thin films grown on ferroelectrically active substrates

International Nuclear Information System (INIS)

Zheng, R.K.; Wang, Y.; Habermeier, H.-U.; Chan, H.L.W.; Li, X.M.; Luo, H.S.

2012-01-01

Highlights: ► Strong interface strain coupling in LaMnO 3 /PMN-PT heterostructure. ► In situ dynamic turning of the strain and lattice distortion of LaMnO 3 films. ► Coupling of electrons to lattice strain is crucial to understand the strain effect. - Abstract: Thin films of LaMnO 3 have been epitaxially grown on 〈0 0 1〉 oriented ferroelectric 0.67Pb(Mg 1/3 Nb 2/3 )O 3 -0.33PbTiO 3 (PMN-PT) single-crystal substrates. The poling of the PMN-PT crystal causes a decrease in the resistance and an increase in the magnetization and magnetoresistance of the LaMnO 3 film. In situ X-ray diffraction measurements revealed that these changes arise from the poling-induced strain in the PMN-PT substrate, which reduces the in-plane tensile strain and the Jahn–Teller (JT) distortion of MnO 6 octahedra of the LaMnO 3 film. Moreover, it was found that the transport properties of LaMnO 3 films are much more sensitive to the poling-induced strain than that of CaMnO 3 films for which there is no JT distortion, implying that the electron–lattice coupling is one of the most important ingredients in understanding the strain effect in LaMnO 3 films.

On singularities of lattice varieties

OpenAIRE

Mukherjee, Himadri

2013-01-01

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

A study of graphite-epoxy laminate failures due to high transverse shear strains using the multi-span-beam shear test procedure

Science.gov (United States)

Jegley, Dawn C.

1989-01-01

The multi-span-beam shear test procedure is used to study failure mechanisms in graphite-epoxy laminates due to high transverse shear strains induced by severe local bending deformations in test specimens. Results of a series of tests on specimens with a variety of stacking sequences, including some with adhesive interleaving, are presented. These results indicate that laminates with stacking sequences with several + or - 45 and 90 deg plies next to each other are more susceptible to failures due to high transverse shear strains than laminates with + or - 45 and 0 deg plies next to each other or with + or - 45 deg plies next to layers of adhesive interleaving. Results of these tests are compared with analytical results based on finite elements.

Apiary B Factory lattice design

International Nuclear Information System (INIS)

Donald, M.H.R.; Garren, A.A.

1991-04-01

The Apiary B Factory is a proposed high-intensity electron-positron collider. This paper will present the lattice design for this facility, which envisions two rings with unequal energies in the PEP tunnel. The design has many interesting optical and geometrical features due to the needs to conform to the existing tunnel, and to achieve the necessary emittances, damping times and vacuum. Existing hardware is used to a maximum extent. 8 figs. 1 tab

Bidirectional Fano Algorithm for Lattice Coded MIMO Channels

KAUST Repository

Al-Quwaiee, Hessa

2013-05-08

Recently, lattices - a mathematical representation of infinite discrete points in the Euclidean space, have become an effective way to describe and analyze communication systems especially system those that can be modeled as linear Gaussian vector channel model. Channel codes based on lattices are preferred due to three facts: lattice codes have simple structure, the code can achieve the limits of the channel, and they can be decoded efficiently using lattice decoders which can be considered as the Closest Lattice Point Search (CLPS). Since the time lattice codes were introduced to Multiple Input Multiple Output (MIMO) channel, Sphere Decoder (SD) has been an efficient way to implement lattice decoders. Sphere decoder offers the optimal performance at the expense of high decoding complexity especially for low signal-to-noise ratios (SNR) and for high- dimensional systems. On the other hand, linear and non-linear receivers, Minimum Mean Square Error (MMSE), and MMSE Decision-Feedback Equalization (DFE), provide the lowest decoding complexity but unfortunately with poor performance. Several studies works have been conducted in the last years to address the problem of designing low complexity decoders for the MIMO channel that can achieve near optimal performance. It was found that sequential decoders using backward tree 
search can bridge the gap between SD and MMSE. The sequential decoder provides an interesting performance-complexity trade-off using a bias term. Yet, the sequential decoder still suffers from high complexity for mid-to-high SNR values. In this work, we propose a new algorithm for Bidirectional Fano sequential Decoder (BFD) in order to reduce the mid-to-high SNR complexity. Our algorithm consists of first constructing a unidirectional Sequential Decoder based on forward search using the QL decomposition. After that, BFD incorporates two searches, forward and backward, to work simultaneously till they merge and find the closest lattice point to the

Permanent magnetic lattices for ultracold atoms and quantum degenerate gases

International Nuclear Information System (INIS)

Ghanbari, Saeed; Kieu, Tien D; Sidorov, Andrei; Hannaford, Peter

2006-01-01

We propose the use of periodic arrays of permanent magnetic films for producing magnetic lattices of microtraps for confining, manipulating and controlling small clouds of ultracold atoms and quantum degenerate gases. Using analytical expressions and numerical calculations we show that periodic arrays of magnetic films can produce one-dimensional (1D) and two-dimensional (2D) magnetic lattices with non-zero potential minima, allowing ultracold atoms to be trapped without losses due to spin flips. In particular, we show that two crossed layers of periodic arrays of parallel rectangular magnets plus bias fields, or a single layer of periodic arrays of square-shaped magnets with three different thicknesses plus bias fields, can produce 2D magnetic lattices of microtraps having non-zero potential minima and controllable trap depth. For arrays with micron-scale periodicity, the magnetic microtraps can have very large trap depths (∼0.5 mK for the realistic parameters chosen for the 2D lattice) and very tight confinement

Spin-echo observation of radio frequency induced flux lattice annealing (RIFLA) in a type-II superconductor

International Nuclear Information System (INIS)

Clark, W.G.; Hanson, M.E.; Wong, W.H.

1999-01-01

We report the annealing of a strained flux line lattice (FLL) in 10 μm diameter type-II superconducting NbTi filaments by an RF magnetic field at 4.2 K in a magnetic field of 1 T. The strained FLL is prepared by slowly changing the direction of the applied magnetic field. When the RF magnetic field used to generate a 93 Nb NMR spin echo anneals the FLL, there is a corresponding reduction in the amplitude of the spin echo. Starting from an annealed condition, a rotation threshold of 3 mr is needed to produce enough FLL strain to be observed in these measurements. (orig.)

Reactor lattice codes

International Nuclear Information System (INIS)

Kulikowska, T.

2001-01-01

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

Critical thickness and strain relaxation in molecular beam epitaxy-grown SrTiO3 films

International Nuclear Information System (INIS)

Wang, Tianqi; Ganguly, Koustav; Marshall, Patrick; Xu, Peng; Jalan, Bharat

2013-01-01

We report on the study of the critical thickness and the strain relaxation in epitaxial SrTiO 3 film grown on (La 0.3 Sr 0.7 )(Al 0.65 Ta 0.35 )O 3 (001) (LSAT) substrate using the hybrid molecular beam epitaxy approach. No change in the film's lattice parameter (both the in-plane and the out-of-plane) was observed up to a film thickness of 180 nm, which is in sharp contrast to the theoretical critical thickness of ∼12 nm calculated using the equilibrium theory of strain relaxation. For film thicknesses greater than 180 nm, the out-of-plane lattice parameter was found to decrease hyperbolically in an excellent agreement with the relaxation via forming misfit dislocations. Possible mechanisms are discussed by which the elastic strain energy can be accommodated prior to forming misfit dislocations leading to such anomalously large critical thickness

Lattice topology dictates photon statistics.

Science.gov (United States)

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

2017-08-21

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

Substrate-dependent post-annealing effects on the strain state and electrical transport of epitaxial La{sub 5/8-y}Pr{sub y}Ca{sub 3/8}MnO{sub 3} films

Energy Technology Data Exchange (ETDEWEB)

Hu, Sixia; Wang, Haibo; Dong, Yongqi; Hong, Bing; He, Hao; Bao, Jun [National Synchrotron Radiation Laboratory and School of Nuclear Science and Technology, University of Science and Technology of China, Hefei, Anhui 230026 (China); Huang, Haoliang [CAS Key Laboratory of Materials for Energy Conversion and Collaborative Innovation Center of Chemistry for Energy Materials, University of Science and Technology of China, Hefei, Anhui 230026 (China); Yang, Yuanjun; Luo, Zhenlin, E-mail: zlluo@ustc.edu.cn; Yang, Mengmeng; Gao, Chen, E-mail: cgao@ustc.edu.cn [National Synchrotron Radiation Laboratory and School of Nuclear Science and Technology, University of Science and Technology of China, Hefei, Anhui 230026 (China); CAS Key Laboratory of Materials for Energy Conversion and Collaborative Innovation Center of Chemistry for Energy Materials, University of Science and Technology of China, Hefei, Anhui 230026 (China)

2014-06-15

Large scale electronic phase separation (EPS) between ferromagnetic metallic and charge-ordered insulating phases in La{sub 5/8-y}Pr{sub y}Ca{sub 3/8}MnO{sub 3} (y = 0.3) (LPCMO) is very sensitive to the structural changes. This work investigates the effects of post-annealing on the strain states and electrical transport properties of LPCMO films epitaxially grown on (001){sub pc} SrTiO{sub 3} (tensile strain), LaAlO{sub 3} (compressive strain) and NdGaO{sub 3} (near-zero strain) substrates. Before annealing, all the films are coherent-epitaxial and insulating through the measured temperature range. Obvious change of film lattice is observed during the post-annealing: the in-plane strain in LPCMO/LAO varies from −1.5% to −0.1% while that in LPCMO/STO changes from 1.6% to 1.3%, and the lattice of LPCMO/NGO keeps constant because of the good lattice-match between LPCMO and NGO. Consequently, the varied film strain leads to the emergence of metal-insulator transitions (MIT) and shift of the critical transition temperature in the electrical transport. These results demonstrate that lattice-mismatch combined with post-annealing is an effective approach to tune strain in epitaxial LPCMO films, and thus to control the EPS and MIT in the films.

Void lattices

International Nuclear Information System (INIS)

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

1976-01-01

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

Anisotropically biaxial strain in non-polar (112-0) plane In x Ga1-x N/GaN layers investigated by X-ray reciprocal space mapping.

Science.gov (United States)

Zhao, Guijuan; Li, Huijie; Wang, Lianshan; Meng, Yulin; Ji, Zesheng; Li, Fangzheng; Wei, Hongyuan; Yang, Shaoyan; Wang, Zhanguo

2017-07-03

In this study, the indium composition x as well as the anisotropically biaxial strain in non-polar a-plane In x Ga 1-x N on GaN is studied by X-ray diffraction (XRD) analysis. In accordance with XRD reciprocal lattice space mapping, with increasing indium composition, the maximum of the In x Ga 1-x N reciprocal lattice points progressively shifts from a fully compressive strained to a fully relaxed position, then to reversed tensile strained. To fully understand the strain in the ternary alloy layers, it is helpful to grow high-quality device structures using a-plane nitrides. As the layer thickness increases, the strain of In x Ga 1-x N layer releases through surface roughening and the 3D growth-mode.

Strain engineering of Dirac cones in graphyne

Energy Technology Data Exchange (ETDEWEB)

Wang, Gaoxue; Kumar, Ashok; Pandey, Ravindra, E-mail: pandey@mtu.edu [Department of Physics, Michigan Technological University, Houghton, Michigan 49931 (United States); Si, Mingsu [Key Laboratory for Magnetism and Magnetic Materials of the Ministry of Education, Lanzhou University, Lanzhou 730000 (China)

2014-05-26

6,6,12-graphyne, one of the two-dimensional carbon allotropes with the rectangular lattice structure, has two kinds of non-equivalent anisotropic Dirac cones in the first Brillouin zone. We show that Dirac cones can be tuned independently by the uniaxial compressive strain applied to graphyne, which induces n-type and p-type self-doping effect, by shifting the energy of the Dirac cones in the opposite directions. On the other hand, application of the tensile strain results into a transition from gapless to finite gap system for the monolayer. For the AB-stacked bilayer, the results predict tunability of Dirac-cones by in-plane strains as well as the strain applied perpendicular to the plane. The group velocities of the Dirac cones show enhancement in the resistance anisotropy for bilayer relative to the case of monolayer. Such tunable and direction-dependent electronic properties predicted for 6,6,12-graphyne make it to be competitive for the next-generation electronic devices at nanoscale.

Lattice theory for nonspecialists

International Nuclear Information System (INIS)

Hari Dass, N.D.

1984-01-01

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

Hamiltonian lattice field theory: Computer calculations using variational methods

International Nuclear Information System (INIS)

Zako, R.L.

1991-01-01

I develop a variational method for systematic numerical computation of physical quantities -- bound state energies and scattering amplitudes -- in quantum field theory. An infinite-volume, continuum theory is approximated by a theory on a finite spatial lattice, which is amenable to numerical computation. I present an algorithm for computing approximate energy eigenvalues and eigenstates in the lattice theory and for bounding the resulting errors. I also show how to select basis states and choose variational parameters in order to minimize errors. The algorithm is based on the Rayleigh-Ritz principle and Kato's generalizations of Temple's formula. The algorithm could be adapted to systems such as atoms and molecules. I show how to compute Green's functions from energy eigenvalues and eigenstates in the lattice theory, and relate these to physical (renormalized) coupling constants, bound state energies and Green's functions. Thus one can compute approximate physical quantities in a lattice theory that approximates a quantum field theory with specified physical coupling constants. I discuss the errors in both approximations. In principle, the errors can be made arbitrarily small by increasing the size of the lattice, decreasing the lattice spacing and computing sufficiently long. Unfortunately, I do not understand the infinite-volume and continuum limits well enough to quantify errors due to the lattice approximation. Thus the method is currently incomplete. I apply the method to real scalar field theories using a Fock basis of free particle states. All needed quantities can be calculated efficiently with this basis. The generalization to more complicated theories is straightforward. I describe a computer implementation of the method and present numerical results for simple quantum mechanical systems

Hamiltonian lattice field theory: Computer calculations using variational methods

International Nuclear Information System (INIS)

Zako, R.L.

1991-01-01

A variational method is developed for systematic numerical computation of physical quantities-bound state energies and scattering amplitudes-in quantum field theory. An infinite-volume, continuum theory is approximated by a theory on a finite spatial lattice, which is amenable to numerical computation. An algorithm is presented for computing approximate energy eigenvalues and eigenstates in the lattice theory and for bounding the resulting errors. It is shown how to select basis states and choose variational parameters in order to minimize errors. The algorithm is based on the Rayleigh-Ritz principle and Kato's generalizations of Temple's formula. The algorithm could be adapted to systems such as atoms and molecules. It is shown how to compute Green's functions from energy eigenvalues and eigenstates in the lattice theory, and relate these to physical (renormalized) coupling constants, bound state energies and Green's functions. Thus one can compute approximate physical quantities in a lattice theory that approximates a quantum field theory with specified physical coupling constants. The author discusses the errors in both approximations. In principle, the errors can be made arbitrarily small by increasing the size of the lattice, decreasing the lattice spacing and computing sufficiently long. Unfortunately, the author does not understand the infinite-volume and continuum limits well enough to quantify errors due to the lattice approximation. Thus the method is currently incomplete. The method is applied to real scalar field theories using a Fock basis of free particle states. All needed quantities can be calculated efficiently with this basis. The generalization to more complicated theories is straightforward. The author describes a computer implementation of the method and present numerical results for simple quantum mechanical systems

Microstructural changes and effect of variation of lattice strain on positron annihilation lifetime parameters of zinc ferrite nanocomposites prepared by high enegy ball-milling

Directory of Open Access Journals (Sweden)

Abhijit Banerjee

2012-12-01

Full Text Available Zn-ferrite nanoparticles were synthesized at room temperature by mechanical alloying the stoichiometric (1:1 mol% mixture of ZnO and α-Fe2O3 powder under open air. Formation of both normal and inverse spinel ferrite phases was noticed after 30 minutes and 2.5 hours ball milling respectively and the content of inverse spinel phase increased with increasing milling time. The phase transformation kinetics towards formation of ferrite phases and microstructure characterization of ball milled ZnFe2O4 phases was primarily investigated by X-ray powder diffraction pattern analysis. The relative phase abundances of different phases, crystallite size, r.m.s. strain, lattice parameter change etc. were estimated from the Rietveld powder structure refinement analysis of XRD data. Positron annihilation lifetime spectra of all ball milled samples were deconvoluted with three lifetime parameters and their variation with milling time duration was explained with microstructural changes and formation of different phases with increase of milling time duration.

Few quantum particles on one dimensional lattices

Energy Technology Data Exchange (ETDEWEB)

Valiente Cifuentes, Manuel

2010-06-18

There is currently a great interest in the physics of degenerate quantum gases and low-energy few-body scattering due to the recent experimental advances in manipulation of ultracold atoms by light. In particular, almost perfect periodic potentials, called optical lattices, can be generated. The lattice spacing is fixed by the wavelength of the laser field employed and the angle betwen the pair of laser beams; the lattice depth, defining the magnitude of the different band gaps, is tunable within a large interval of values. This flexibility permits the exploration of different regimes, ranging from the ''free-electron'' picture, modified by the effective mass for shallow optical lattices, to the tight-binding regime of a very deep periodic potential. In the latter case, effective single-band theories, widely used in condensed matter physics, can be implemented with unprecedent accuracy. The tunability of the lattice depth is nowadays complemented by the use of magnetic Feshbach resonances which, at very low temperatures, can vary the relevant atom-atom scattering properties at will. Moreover, optical lattices loaded with gases of effectively reduced dimensionality are experimentally accessible. This is especially important for one spatial dimension, since most of the exactly solvable models in many-body quantum mechanics deal with particles on a line; therefore, experiments with one-dimensional gases serve as a testing ground for many old and new theories which were regarded as purely academic not so long ago. The physics of few quantum particles on a one-dimensional lattice is the topic of this thesis. Most of the results are obtained in the tight-binding approximation, which is amenable to exact numerical or analytical treatment. For the two-body problem, theoretical methods for calculating the stationary scattering and bound states are developed. These are used to obtain, in closed form, the two-particle solutions of both the Hubbard and

Few quantum particles on one dimensional lattices

International Nuclear Information System (INIS)

Valiente Cifuentes, Manuel

2010-01-01

There is currently a great interest in the physics of degenerate quantum gases and low-energy few-body scattering due to the recent experimental advances in manipulation of ultracold atoms by light. In particular, almost perfect periodic potentials, called optical lattices, can be generated. The lattice spacing is fixed by the wavelength of the laser field employed and the angle betwen the pair of laser beams; the lattice depth, defining the magnitude of the different band gaps, is tunable within a large interval of values. This flexibility permits the exploration of different regimes, ranging from the ''free-electron'' picture, modified by the effective mass for shallow optical lattices, to the tight-binding regime of a very deep periodic potential. In the latter case, effective single-band theories, widely used in condensed matter physics, can be implemented with unprecedent accuracy. The tunability of the lattice depth is nowadays complemented by the use of magnetic Feshbach resonances which, at very low temperatures, can vary the relevant atom-atom scattering properties at will. Moreover, optical lattices loaded with gases of effectively reduced dimensionality are experimentally accessible. This is especially important for one spatial dimension, since most of the exactly solvable models in many-body quantum mechanics deal with particles on a line; therefore, experiments with one-dimensional gases serve as a testing ground for many old and new theories which were regarded as purely academic not so long ago. The physics of few quantum particles on a one-dimensional lattice is the topic of this thesis. Most of the results are obtained in the tight-binding approximation, which is amenable to exact numerical or analytical treatment. For the two-body problem, theoretical methods for calculating the stationary scattering and bound states are developed. These are used to obtain, in closed form, the two-particle solutions of both the Hubbard and extended Hubbard models

Phase transitions in cooperative coinfections: Simulation results for networks and lattices

Science.gov (United States)

Grassberger, Peter; Chen, Li; Ghanbarnejad, Fakhteh; Cai, Weiran

2016-04-01

We study the spreading of two mutually cooperative diseases on different network topologies, and with two microscopic realizations, both of which are stochastic versions of a susceptible-infected-removed type model studied by us recently in mean field approximation. There it had been found that cooperativity can lead to first order transitions from spreading to extinction. However, due to the rapid mixing implied by the mean field assumption, first order transitions required nonzero initial densities of sick individuals. For the stochastic model studied here the results depend strongly on the underlying network. First order transitions are found when there are few short but many long loops: (i) No first order transitions exist on trees and on 2-d lattices with local contacts. (ii) They do exist on Erdős-Rényi (ER) networks, on d -dimensional lattices with d ≥4 , and on 2-d lattices with sufficiently long-ranged contacts. (iii) On 3-d lattices with local contacts the results depend on the microscopic details of the implementation. (iv) While single infected seeds can always lead to infinite epidemics on regular lattices, on ER networks one sometimes needs finite initial densities of infected nodes. (v) In all cases the first order transitions are actually "hybrid"; i.e., they display also power law scaling usually associated with second order transitions. On regular lattices, our model can also be interpreted as the growth of an interface due to cooperative attachment of two species of particles. Critically pinned interfaces in this model seem to be in different universality classes than standard critically pinned interfaces in models with forbidden overhangs. Finally, the detailed results mentioned above hold only when both diseases propagate along the same network of links. If they use different links, results can be rather different in detail, but are similar overall.

Magnon Hall effect on the Lieb lattice.

Science.gov (United States)

Cao, Xiaodong; Chen, Kai; He, Dahai

2015-04-29

Ferromagnetic insulators without inversion symmetry may show magnon Hall effect (MHE) in the presence of a temperature gradient due to the existence of Dzyaloshinskii-Moriya interaction (DMI). In this theoretical study, we investigate MHE on a lattice with inversion symmetry, namely the Lieb lattice, where the DMI is introduced by adding an external electric field. We show the nontrivial topology of this model by examining the existence of edge states and computing the topological phase diagram characterized by the Chern numbers of different bands. Together with the topological phase diagram, we can further determine the sign and magnitude of the transverse thermal conductivity. The impact of the flat band possessed by this model on the thermal conductivity is discussed by computing the Berry curvature analytically.

Strain study of gold nanomaterials as HR-TEM calibration standard.

Science.gov (United States)

Peng, X Y; Zhou, L Q; Li, X; Tao, X F; Ren, L L; Cao, W H; Xu, G F

2015-12-01

This work presents the use of high resolution electron microscopy (HREM) and geometric phase analysis (GPA) to measure the interplanar spacing and strain distribution of three gold nanomaterials, respectively. The results showed that the {111} strain was smaller than the {002} strain for any kind of gold materials at the condition of same measuring method. The 0.65% of {111} strain in gold film measured by HREM (0.26% measured by GPA) was smaller than the {111} strains in two gold particles. The presence of lattice strain was interpreted according to the growth mechanism of metallic thin film. It is deduced that the {111} interplanar spacing of the gold thin film is suitable for high magnification calibration of transmission electron microscopy (TEM) and the gold film is potential to be a new calibration standard of TEM. Copyright © 2015 Elsevier Ltd. All rights reserved.

MEETING: Lattice 88

Energy Technology Data Exchange (ETDEWEB)

Mackenzie, Paul

1989-03-15

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

MEETING: Lattice 88

International Nuclear Information System (INIS)

Mackenzie, Paul

1989-01-01

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

Strain in GaAs / InAs core-shell nanowire heterostructures grown on GaAs

Energy Technology Data Exchange (ETDEWEB)

Biermanns, Andreas; Davydok, Anton; Pietsch, Ullrich [Universitaet Siegen, Festkoerperphysik (Germany); Rieger, Torsten; Lepsa, Mihail Ion [Peter Gruenberg Institut 9, Forschungszentrum Juelich (Germany); JARA - Fundamentals of Future Information Technology (Germany)

2012-07-01

The growth of semiconductor nanowires (NWs) has attracted significant interest in recent years due to the possible fabrication of novel semiconductor devices for future electronic and opto-electronic applications. Compared to planar heterostructures, the nanowire approach offers an advantage regarding the possibility to form heterostructures between highly lattice mismatched systems, because the free surface of the nanowires allows to relieve the strain more efficiently. One particular way to form heterostructures in the NW geometry, is the fabrication of core-shell devices, in which a NW core is surrounded by a shell of different material. The understanding of the mutual strain between core and shell, as well as the relaxation behavior of the system are crucial for the fabrication of functional devices. In this contribution we report on first X-ray diffraction measurements of GaAs-core/InAs-shell nanowires grown on GaAs(111) by molecular beam epitaxy. Using symmetric- and grazing-incidence X-ray diffraction, the relaxation state of the InAs shell as well as the strain in the GaAs core are measured as function of the InAs shell thickness, showing a gradual relaxation behavior of the shell.

Study of interfacial strain at the α-Al2O3/monolayer MoS2 interface by first principle calculations

Science.gov (United States)

Yu, Sheng; Ran, Shunjie; Zhu, Hao; Eshun, Kwesi; Shi, Chen; Jiang, Kai; Gu, Kunming; Seo, Felix Jaetae; Li, Qiliang

2018-01-01

With the advances in two-dimensional (2D) transition metal dichalcogenides (TMDCs) based metal-oxide-semiconductor field-effect transistor (MOSFET), the interface between the semiconductor channel and gate dielectrics has received considerable attention due to its significant impacts on the morphology and charge transport of the devices. In this study, first principle calculations were utilized to investigate the strain effect induced by the interface between crystalline α-Al2O3 (0001)/h-MoS2 monolayer. The results indicate that the 1.3 nm Al2O3 can induce a 0.3% tensile strain on the MoS2 monolayer. The strain monotonically increases with thicker dielectric layers, inducing more significant impact on the properties of MoS2. In addition, the study on temperature effect indicates that the increasing temperature induces monotonic lattice expansion. This study clearly indicates that the dielectric engineering can effectively tune the properties of 2D TMDCs, which is very attractive for nanoelectronics.

Slip systems, dislocation boundaries and lattice rotations in deformed metals

DEFF Research Database (Denmark)

Winther, Grethe

2009-01-01

Metals are polycrystals and consist of grains, which are subdivided on a finer scale upon plastic deformation due to formation of dislocation boundaries. The crystallographic alignment of planar dislocation boundaries in face centred cubic metals, like aluminium and copper, deformed to moderate...... of the mechanical anisotropy of rolled sheets. The rotation of the crystallographic lattice in each grain during deformation also exhibits grain orientation dependence, originating from the slip systems. A combined analysis of dislocation boundaries and lattice rotations concludes that the two phenomena are coupled...

Strain-Induced Pseudo--Magnetic Fields in Graphene: MegaGauss in Nanobubbles

Science.gov (United States)

Levy, Niv

2011-03-01

Recent theoretical proposals suggest that strain can be used to modify graphene electronic states through the creation of a pseudo--magnetic field. This effect is unique to graphene because of its massless Dirac fermion-like band structure and particular lattice symmetry (C3v). Scanning tunneling microscopy shows that graphene grown on a platinum (111) surface forms nanobubbles, which are highly strained due to thermal expansion mismatch between the film and the substrate. We find that scanning tunneling spectroscopy measurements of these nanobubbles exhibit Landau levels that form in the presence of strain-induced pseudo--magnetic fields greater than 300 Tesla. This demonstration of enormous pseudo--magnetic fields opens the door to both the study of charge carriers in previously inaccessible high magnetic field regimes and deliberate mechanical control over electronic structure in graphene or so-called ``strain engineering''. In collaboration with S. A. Burke ,2 , K. L. Meaker 2 , M. Panlasigui 2 , A. Zettl 2,3 , F. Guinea 4 , A. H. Castro Neto 5 and M. F. Crommie 2,3 . 1. Present address: Department of Physics and Astronomy and Department of Chemistry, University of British Columbia, Vancouver, BC V6T 121, Canada. 2. Department of Physics, University of California, Berkeley, CA 94720, USA. 3. Materials Science Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA. 4. Instituto de Ciencia de Materiales de Madrid (CSIC), Madrid 28049, Spain. 5. Department of Physics, Boston University, Boston, MA 02215, USA.

Search for the non-canonical Ising spin glass on rewired square lattices

Science.gov (United States)

Surungan, Tasrief

2018-03-01

A spin glass (SG) of non-canonical type is a purely antiferromagnetic (AF) system, exemplified by the AF Ising model on a scale free network (SFN), studied by Bartolozzi et al. [ Phys. Rev. B73, 224419 (2006)]. Frustration in this new type of SG is rendered by topological factor and its randomness is caused by random connectivity. As an SFN corresponds to a large dimensional lattice, finding non-canonical SG in lattice with physical dimension is desireable. However, a regular lattice can not have random connectivity. In order to obtain lattices with random connection and preserving the notion of finite dimension, we costructed rewired lattices. We added some extra bonds randomly connecting each site of a regular lattice to its next-nearest neighbors. Very recently, Surungan et al., studied AF Heisenberg system on rewired square lattice and found no SG behavior [AIP Conf. Proc. 1719, 030006 (2016)]. Due to the importance of discrete symmetry for phase transition, here we study similar structure for the Ising model (Z 2 symmetry). We used Monte Carlo simulation with Replica Exchange algorithm. Two types of structures were studied, firstly, the rewired square lattices with one extra bonds added to each site, and secondly, two bonds added to each site. We calculated the Edwards-Anderson paremeter, the commonly used parameter in searching for SG phase. The non-canonical SG is clearly observed in the rewired square lattice with two extra bonds added.

High-temperature atomic superfluidity in lattice Bose-Fermi mixtures.

Science.gov (United States)

Illuminati, Fabrizio; Albus, Alexander

2004-08-27

We consider atomic Bose-Fermi mixtures in optical lattices and study the superfluidity of fermionic atoms due to s-wave pairing induced by boson-fermion interactions. We prove that the induced fermion-fermion coupling is always attractive if the boson-boson on-site interaction is repulsive, and predict the existence of an enhanced BEC-BCS crossover as the strength of the lattice potential is varied. We show that for direct on-site fermion-fermion repulsion, the induced attraction can give rise to superfluidity via s-wave pairing at striking variance with the case of pure systems of fermionic atoms with direct repulsive interactions.

High-temperature atomic superfluidity in lattice Bose-Fermi mixtures

International Nuclear Information System (INIS)

Illuminati, Fabrizio; Albus, Alexander

2004-01-01

We consider atomic Bose-Fermi mixtures in optical lattices and study the superfluidity of fermionic atoms due to s-wave pairing induced by boson-fermion interactions. We prove that the induced fermion-fermion coupling is always attractive if the boson-boson on-site interaction is repulsive, and predict the existence of an enhanced BEC-BCS crossover as the strength of the lattice potential is varied. We show that for direct on-site fermion-fermion repulsion, the induced attraction can give rise to superfluidity via s-wave pairing at striking variance with the case of pure systems of fermionic atoms with direct repulsive interactions

Twisted mass lattice QCD

International Nuclear Information System (INIS)

Shindler, A.

2007-07-01

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

Twisted mass lattice QCD

Energy Technology Data Exchange (ETDEWEB)

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

2007-07-15

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

Lattice regularized chiral perturbation theory

International Nuclear Information System (INIS)

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

2004-01-01

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

Role of lattice inhomogeneities on the electronic properties of selenium deficient Bi2Se3

Science.gov (United States)

Tayal, Akhil; Kumar, Devendra; Lakhani, Archana

2017-11-01

Inter-layer coupling is widely considered to play a crucial role in tuning electronic properties of 3D topological insulators. The aim of this study is to evaluate the role of crystallographic defects on inter-layer coupling in the Se deficient Bi2Se3 (0 0 3) crystal using extended x-ray absorption fine structure spectroscopy (EXAFS) technique. EXAFS measurements at Se-K and Bi-L3 edges reveal distinct local geometry around these atomic sites. It has been observed that short inter-layer Bi-Se and Se-Se bonds emerge in the sample. This additional structural motif coexists with the conventional crystallographic arrangement. Within the quintuple layer Bi-Se bonds are preserved with slight compression in intra-planer Bi-Bi and Se-Se distance and overall reduction in c/a ratio. These findings suggest formation of deformed lattice region, localized and dispersed inhomogeneously within the sample. Such inhomogeneities have also resulted in interesting transport properties such as quantum Hall effect (QHE), large linear magnetoresistance and π-Berry phase in Shubnikov-de Haas (SdH) oscillations of bulk crystals. Detailed analyses of magnetotransport measurements suggest that tuning of inter-layer coupling by local lattice deformation is the key factor for unusual transport properties. Role of axial strain, and stacking faults generated due to defects and charged Se vacancies are discussed to understand the observed electronic properties.

Twins and strain relaxation in zinc-blende GaAs nanowires grown on silicon

Energy Technology Data Exchange (ETDEWEB)

Piñero, J.C., E-mail: josecarlos.pinero@uca.es [Dpto. Ciencias de los Materiales, Universidad de Cádiz, 11510, Puerto Real, Cádiz (Spain); Araújo, D.; Pastore, C.E.; Gutierrez, M. [Dpto. Ciencias de los Materiales, Universidad de Cádiz, 11510, Puerto Real, Cádiz (Spain); Frigeri, C. [Istituto CNR-IMEM Parco Area delle Scienze 37/A, Fontanini, 43010, Parma (Italy); Benali, A.; Lelièvre, J.F.; Gendry, M. [INL-Institut des Nanotechnologies de Lyon, UMR 5270 Ecole Centrale de Lyon 36, Avenue Guy de Collongue, 69134, Ecully Cedex (France)

2017-02-15

Highlights: • A TEM-HREM study of GaAs nanowires, growth over Si, is presented. • Misfit dislocations are detected in the Si/GaAs magma interface. • The study demonstrates strain relaxation through twin formation in some nanowires. - Abstract: To integrate materials with large lattice mismatch as GaAs on silicon (Si) substrate, one possible approach, to improve the GaAs crystalline quality, is to use nanowires (NWs) technology. In the present contribution, NWs are grown on <111> oriented Si substrates by molecular beam epitaxy (MBE) using vapor-liquid-solid (VLS) method. Transmission electron microscopy (TEM) analyses show that NWs are mainly grown alternating wurtzite and zinc blend (ZB) phases, and only few are purely ZB. On the latter, High Resolution Electron Microscopy (HREM) evidences the presence of twins near the surface of the NW showing limited concordance with the calculations of Yuan (2013) [1], where {111} twin planes in a <111>-oriented GaAs NW attain attractive interactions mediated by surface strain. In addition, such twins allow slight strain relaxation and are probably induced by the local huge elastic strain observed by HREM in the lattice between the twin and the surface. The latter is attributed to some slight bending of the NW as shown by the inversion of the strain from one side to the other side of the NW.

Strain-engineered growth of two-dimensional materials.

Science.gov (United States)

Ahn, Geun Ho; Amani, Matin; Rasool, Haider; Lien, Der-Hsien; Mastandrea, James P; Ager Iii, Joel W; Dubey, Madan; Chrzan, Daryl C; Minor, Andrew M; Javey, Ali

2017-09-20

The application of strain to semiconductors allows for controlled modification of their band structure. This principle is employed for the manufacturing of devices ranging from high-performance transistors to solid-state lasers. Traditionally, strain is typically achieved via growth on lattice-mismatched substrates. For two-dimensional (2D) semiconductors, this is not feasible as they typically do not interact epitaxially with the substrate. Here, we demonstrate controlled strain engineering of 2D semiconductors during synthesis by utilizing the thermal coefficient of expansion mismatch between the substrate and semiconductor. Using WSe 2 as a model system, we demonstrate stable built-in strains ranging from 1% tensile to 0.2% compressive on substrates with different thermal coefficient of expansion. Consequently, we observe a dramatic modulation of the band structure, manifested by a strain-driven indirect-to-direct bandgap transition and brightening of the dark exciton in bilayer and monolayer WSe 2 , respectively. The growth method developed here should enable flexibility in design of more sophisticated devices based on 2D materials.Strain engineering is an essential tool for modifying local electronic properties in silicon-based electronics. Here, Ahn et al. demonstrate control of biaxial strain in two-dimensional materials based on the growth substrate, enabling more complex low-dimensional electronics.

Efficiency of free-energy calculations of spin lattices by spectral quantum algorithms

International Nuclear Information System (INIS)

Master, Cyrus P.; Yamaguchi, Fumiko; Yamamoto, Yoshihisa

2003-01-01

Ensemble quantum algorithms are well suited to calculate estimates of the energy spectra for spin-lattice systems. Based on the phase estimation algorithm, these algorithms efficiently estimate discrete Fourier coefficients of the density of states. Their efficiency in calculating the free energy per spin of general spin lattices to bounded error is examined. We find that the number of Fourier components required to bound the error in the free energy due to the broadening of the density of states scales polynomially with the number of spins in the lattice. However, the precision with which the Fourier components must be calculated is found to be an exponential function of the system size

Supersymmetric lattices

International Nuclear Information System (INIS)

Catterall, Simon

2013-01-01

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

Spin Chern number and topological phase transition on the Lieb lattice with spin–orbit coupling

International Nuclear Information System (INIS)

Chen, Rui; Zhou, Bin

2017-01-01

We propose that quantum anomalous Hall effect may occur in the Lieb lattice, when Rashba spin–orbit coupling, spin-independent and spin-dependent staggered potentials are introduced into the lattice. It is found that spin Chern numbers of two degenerate flat bands change from 0 to ±2 due to Rashba spin–orbit coupling effect. The inclusion of Rashba spin–orbit coupling and two kinds of staggered potentials opens a gap between the two flat bands. The topological property of the gap is determined by the amplitudes of Rashba spin–orbit coupling and staggered potentials, and thus the topological phase transition from quantum anomalous Hall effect to normal insulator can occur. Finally, the topological phase transition from quantum spin Hall state to normal insulator is discussed when Rashba spin–orbit coupling and intrinsic spin–orbit coupling coexist in the Lieb lattice. - Highlights: • Spin Chern numbers of the bulk states on the Lieb lattice are calculated. • RSOC plays an important role on the topological phase transition on the Lieb lattice. • Quantum anomalous Hall effect can occur due to RSOC and staggered potentials. • Topological phase transition can occur when ISOC and RSOC coexist.

Understanding the effects of strain on morphological instabilities of a nanoscale island during heteroepitaxial growth

Energy Technology Data Exchange (ETDEWEB)

Feng, Lu; Wang, Jing; Wang, Shibin; Li, Linan; Shen, Min; Wang, Zhiyong; Chen, Zhenfei; Zhao, Yang [Tianjin Key Laboratory of Modern Engineering Mechanics, Tianjin 300072 (China); Department of Mechanics, Tianjin University, Tianjin 300072 (China)

2015-07-21

A comprehensive morphological stability analysis of a nanoscale circular island during heteroepitaxial growth is presented based on continuum elasticity theory. The interplay between kinetic and thermodynamic mechanisms is revealed by including strain-related kinetic processes. In the kinetic regime, the Burton-Cabrera-Frank model is adopted to describe the growth front of the island. Together with kinetic boundary conditions, various kinetic processes including deposition flow, adatom diffusion, attachment-detachment kinetics, and the Ehrlich-Schwoebel barrier can be taken into account at the same time. In the thermodynamic regime, line tension, surface energy, and elastic energy are considered. As the strain relief in the early stages of heteroepitaxy is more complicated than commonly suggested by simple consideration of lattice mismatch, we also investigate the effects of external applied strain and elastic response due to perturbations on the island shape evolution. The analytical expressions for elastic fields induced by mismatch strain, external applied strain, and relaxation strain are presented. A systematic approach is developed to solve the system via a perturbation analysis which yields the conditions of film morphological instabilities. Consistent with previous experimental and theoretical work, parametric studies show the kinetic evolution of elastic relaxation, island morphology, and film composition under various conditions. Our present work offers an effective theoretical approach to get a comprehensive understanding of the interplay between different growth mechanisms and how to tailor the growth mode by controlling the nature of the crucial factors.

Lattice Dynamical Properties of Ferroelectric Thin Films at the Nanoscale

Energy Technology Data Exchange (ETDEWEB)

Xi, Xiaoxing [Temple University

2014-01-13

In this project, we have successfully demonstrated atomic layer-by-layer growth by laser MBE from separate targets by depositing SrTiO3 films from SrO and TiO2 targets. The RHEED intensity oscillation was used to monitor and control the growth of each SrO and TiO2 layer. We have shown that by using separate oxide targets, laser MBE can achieve the same level of stoichiometry control as the reactive MBE. We have also studied strain relaxation in LaAlO3 films and its effect on the 2D electron gas at LaAlO3/SrTiO3 interface. We found that there are two layers of different in-plane lattice constants in the LaAlO3 films, one next to the SrTiO3 substrate nearly coherently strained, while the top part relaxed as the film thickness increases above 20 unit cells. This strain relaxation significantly affect the transport properties of the LaAlO3/SrTiO3 interface.

Role of scaffold network in controlling strain and functionalities of nanocomposite films.

Science.gov (United States)

Chen, Aiping; Hu, Jia-Mian; Lu, Ping; Yang, Tiannan; Zhang, Wenrui; Li, Leigang; Ahmed, Towfiq; Enriquez, Erik; Weigand, Marcus; Su, Qing; Wang, Haiyan; Zhu, Jian-Xin; MacManus-Driscoll, Judith L; Chen, Long-Qing; Yarotski, Dmitry; Jia, Quanxi

2016-06-01

Strain is a novel approach to manipulating functionalities in correlated complex oxides. However, significant epitaxial strain can only be achieved in ultrathin layers. We show that, under direct lattice matching framework, large and uniform vertical strain up to 2% can be achieved to significantly modify the magnetic anisotropy, magnetism, and magnetotransport properties in heteroepitaxial nanoscaffold films, over a few hundred nanometers in thickness. Comprehensive designing principles of large vertical strain have been proposed. Phase-field simulations not only reveal the strain distribution but also suggest that the ultimate strain is related to the vertical interfacial area and interfacial dislocation density. By changing the nanoscaffold density and dimension, the strain and the magnetic properties can be tuned. The established correlation among the vertical interface-strain-properties in nanoscaffold films can consequently be used to tune other functionalities in a broad range of complex oxide films far beyond critical thickness.

Measurement of strain in InGaN/GaN nanowires and nanopyramids

DEFF Research Database (Denmark)

Stankevic, Tomas; Mickevicius, Simas; Nielsen, Mikkel Schou

2015-01-01

The growth and optoelectronic properties of core-shell nanostructures are influenced by the strain induced by the lattice mismatch between core and shell. In contrast with planar films, nanostructures contain multiple facets that act as independent substrates for shell growth, which enables diffe...

High-order dynamic lattice method for seismic simulation in anisotropic media

Science.gov (United States)

Hu, Xiaolin; Jia, Xiaofeng

2018-03-01

The discrete particle-based dynamic lattice method (DLM) offers an approach to simulate elastic wave propagation in anisotropic media by calculating the anisotropic micromechanical interactions between these particles based on the directions of the bonds that connect them in the lattice. To build such a lattice, the media are discretized into particles. This discretization inevitably leads to numerical dispersion. The basic lattice unit used in the original DLM only includes interactions between the central particle and its nearest neighbours; therefore, it represents the first-order form of a particle lattice. The first-order lattice suffers from numerical dispersion compared with other numerical methods, such as high-order finite-difference methods, in terms of seismic wave simulation. Due to its unique way of discretizing the media, the particle-based DLM no longer solves elastic wave equations; this means that one cannot build a high-order DLM by simply creating a high-order discrete operator to better approximate a partial derivative operator. To build a high-order DLM, we carry out a thorough dispersion analysis of the method and discover that by adding more neighbouring particles into the lattice unit, the DLM will yield different spatial accuracy. According to the dispersion analysis, the high-order DLM presented here can adapt the requirement of spatial accuracy for seismic wave simulations. For any given spatial accuracy, we can design a corresponding high-order lattice unit to satisfy the accuracy requirement. Numerical tests show that the high-order DLM improves the accuracy of elastic wave simulation in anisotropic media.

Comparison of electromechanical properties and lattice distortions of different cuprate high temperature superconductors

CERN Document Server

Scheuerlein, C.; Grether, A; Rikel, M O; Hudspeth, J; Sugano, M; Ballarino, A; Bottura, L

2016-01-01

The electromechanical properties of different cuprate high-temperature superconductors, notably two ReBCO tapes, a reinforced and a nonreinforced Bi-2223 tape, and a Bi-2212 wire, have been studied. The axial tensile stress and strain, as well as the transverse compressive stress limits at which an irreversible critical current degradation occurs, are compared. The experimental setup has been integrated in a high-energy synchrotron beamline, and the self-field critical current and lattice parameter changes as a function of tensile stress and strain of a reinforced Bi-2223 tape have been measured simultaneously. Initially, the Bi-2223 filaments exhibit nearly linear elastic behavior up to the strain at which an irreversible degradation is observed. At 77 K, an axial Bi-2223 filament precompression of 0.09% in the composite tape and a Bi-2223 Poisson ratio ν = 0.21 have been determined.

Vortex lattices in layered superconductors

International Nuclear Information System (INIS)

Prokic, V.; Davidovic, D.; Dobrosavljevic-Grujic, L.

1995-01-01

We study vortex lattices in a superconductor--normal-metal superlattice in a parallel magnetic field. Distorted lattices, resulting from the shear deformations along the layers, are found to be unstable. Under field variation, nonequilibrium configurations undergo an infinite sequence of continuous transitions, typical for soft lattices. The equilibrium vortex arrangement is always a lattice of isocell triangles, without shear

Monte Carlo study of the double and super-exchange model with lattice distortion

Energy Technology Data Exchange (ETDEWEB)

Suarez, J R; Vallejo, E; Navarro, O [Instituto de Investigaciones en Materiales, Universidad Nacional Autonoma de Mexico, Apartado Postal 70-360, 04510 Mexico D. F. (Mexico); Avignon, M, E-mail: jrsuarez@iim.unam.m [Institut Neel, Centre National de la Recherche Scientifique (CNRS) and Universite Joseph Fourier, BP 166, 38042 Grenoble Cedex 9 (France)

2009-05-01

In this work a magneto-elastic phase transition was obtained in a linear chain due to the interplay between magnetism and lattice distortion in a double and super-exchange model. It is considered a linear chain consisting of localized classical spins interacting with itinerant electrons. Due to the double exchange interaction, localized spins tend to align ferromagnetically. This ferromagnetic tendency is expected to be frustrated by anti-ferromagnetic super-exchange interactions between neighbor localized spins. Additionally, lattice parameter is allowed to have small changes, which contributes harmonically to the energy of the system. Phase diagram is obtained as a function of the electron density and the super-exchange interaction using a Monte Carlo minimization. At low super-exchange interaction energy phase transition between electron-full ferromagnetic distorted and electron-empty anti-ferromagnetic undistorted phases occurs. In this case all electrons and lattice distortions were found within the ferromagnetic domain. For high super-exchange interaction energy, phase transition between two site distorted periodic arrangement of independent magnetic polarons ordered anti-ferromagnetically and the electron-empty anti-ferromagnetic undistorted phase was found. For this high interaction energy, Wigner crystallization, lattice distortion and charge distribution inside two-site polarons were obtained.

Effect of room temperature lattice vibration on the electron transport in graphene nanoribbons

Science.gov (United States)

Liu, Yue-Yang; Li, Bo-Lin; Chen, Shi-Zhang; Jiang, Xiangwei; Chen, Ke-Qiu

2017-09-01

We observe directly the lattice vibration and its multifold effect on electron transport in zigzag graphene nanoribbons in simulation by utilizing an efficient combined method. The results show that the electron transport fluctuates greatly due to the incessant lattice vibration of the nanoribbons. More interestingly, the lattice vibration behaves like a double-edged sword that it boosts the conductance of symmetric zigzag nanoribbons (containing an even number of zigzag chains along the width direction) while weakens the conductance of asymmetric nanoribbons. As a result, the reported large disparity between the conductances of the two kinds of nanoribbons at 0 K is in fact much smaller at room temperature (300 K). We also find that the spin filter effect that exists in perfect two-dimensional symmetric zigzag graphene nanoribbons is destroyed to some extent by lattice vibrations. Since lattice vibrations or phonons are usually inevitable in experiments, the research is very meaningful for revealing the important role of lattice vibrations play in the electron transport properties of two-dimensional materials and guiding the application of ZGNRs in reality.

Strain effects on the optical parameters of quantum dots nanocrystals employed in biomedical applications

International Nuclear Information System (INIS)

Liaparinos, P.F.

2014-01-01

The purpose of this study was to perform the influence of the strain (lattice and radius) effects on the optical parameters of nanocrystals for use in medical imaging instrumentation technology. The present manuscript involved (a) quantum dots (QD) based nanophosphors with particle size 3–5 nm in diameter, (b) dielectric constants (core) of nanophosphors in the range 2–4, and (c) the whole portion of the electromagnetic spectrum visible to the human eye, 400–700 nm. Lattice strain effects on the optical properties were evaluated by the modification of the bulk dielectric function using a Drude–Sommerfeld model for the free or conduction electrons, and a core term representing the bound electrons. The Mie scattering theory, was used to predict the shifted optical parameters. Results showed that (i) lattice stain reduces the real part (n) of refractive index, (ii) the reduction of n becomes higher with the increase of ε core (ω) and (iii) no significant variations on n were observed under the variability of incident light wavelength (400–700 nm). Light wavelength was found to affect significantly the imaginary part (k) of the complex refractive index. In addition, the radius strain (i) decreases the light extinction coefficient, m ext , (ii) increases the anisotropy factor, g and (iii) increases the light absorption probability, p. However, in cases of ε core (ω)=2, radius strain of 5% seems to present slightly higher p values than the cases of radius strain 10%. The present investigation found that the modification on the optical parameters enhances the utilization of quantom-dots luminescent nanomaterial in optical diffusion studies with requirements of high sensitivity (such as nuclear medical imaging modalities) rather than of high light spatial resolution (such as X-ray projection medical imaging systems). -- Highlights: • The strain effects on the optical parameters of quantum dots were examined. • Light wavelength affects significantly the

Reactor lattice codes

International Nuclear Information System (INIS)

Kulikowska, T.

1999-01-01

The present lecture has a main goal to show how the transport lattice calculations are realised in a standard computer code. This is illustrated on the example of the WIMSD code, belonging to the most popular tools for reactor calculations. Most of the approaches discussed here can be easily modified to any other lattice code. The description of the code assumes the basic knowledge of reactor lattice, on the level given in the lecture on 'Reactor lattice transport calculations'. For more advanced explanation of the WIMSD code the reader is directed to the detailed descriptions of the code cited in References. The discussion of the methods and models included in the code is followed by the generally used homogenisation procedure and several numerical examples of discrepancies in calculated multiplication factors based on different sources of library data. (author)

Parallel performance and accuracy of lattice Boltzmann and traditional finite difference methods for solving the unsteady two-dimensional Burger's equation

Science.gov (United States)

Velivelli, A. C.; Bryden, K. M.

2006-03-01

Lattice Boltzmann methods are gaining recognition in the field of computational fluid dynamics due to their computational efficiency. In order to quantify the computational efficiency and accuracy of the lattice Boltzmann method, it is compared with efficient traditional finite difference methods such as the alternating direction implicit scheme. The lattice Boltzmann algorithm implemented in previous studies does not approach peak performance for simulations where the data involved in computation per time step is more than the cache size. Due to this, data is obtained from the main memory and this access is much slower than access to cache memory. Using a cache-optimized lattice Boltzmann algorithm, this paper takes into account the full computational strength of the lattice Boltzmann method. The com parison is performed on both a single processor and multiple processors.

Infective Endocarditis Complicated by Intraventricular Abscesses, Pericarditis, and Mycotic Aneurysm Due to an Emerging Strain of Serotype VI Streptococcus agalactiae.

Science.gov (United States)

Hirai, Nobuyasu; Kasahara, Kei; Uno, Kenji; Ogawa, Yoshihiko; Ogawa, Taku; Yonekawa, Shinsuke; Nakano, Ryuichi; Yano, Hisakazu; Sakagami, Azusa; Uemura, Takayuki; Okura, Hiroyuki; Saito, Yoshihiko; Yoshikawa, Masahide; Mikasa, Keiichi

2017-11-22

An increasing number of invasive infections due to Streptococcus agalactiae in non-pregnant adults have been reported. We report a case of infective endocarditis complicated by intraventricular abscesses, pericarditis, and mycotic aneurysm due to S. agalactiae belonging to ST681 with a capsular serotype VI in a woman with diabetes. The patient also had a myocardial infarction and was treated with percutaneous coronary intervention, pericardiocentesis, and 6 weeks of antibiotic treatment. Invasive infections due to serotype VI S. agalactiae are common in Asian countries such as Taiwan and Japan, so continuous monitoring of invasive S. agalactiae strains is warranted.

Three-dimensional lattice Boltzmann model for compressible flows.

Science.gov (United States)

Sun, Chenghai; Hsu, Andrew T

2003-07-01

A three-dimensional compressible lattice Boltzmann model is formulated on a cubic lattice. A very large particle-velocity set is incorporated in order to enable a greater variation in the mean velocity. Meanwhile, the support set of the equilibrium distribution has only six directions. Therefore, this model can efficiently handle flows over a wide range of Mach numbers and capture shock waves. Due to the simple form of the equilibrium distribution, the fourth-order velocity tensors are not involved in the formulation. Unlike the standard lattice Boltzmann model, no special treatment is required for the homogeneity of fourth-order velocity tensors on square lattices. The Navier-Stokes equations were recovered, using the Chapman-Enskog method from the Bhatnagar-Gross-Krook (BGK) lattice Boltzmann equation. The second-order discretization error of the fluctuation velocity in the macroscopic conservation equation was eliminated by means of a modified collision invariant. The model is suitable for both viscous and inviscid compressible flows with or without shocks. Since the present scheme deals only with the equilibrium distribution that depends only on fluid density, velocity, and internal energy, boundary conditions on curved wall are easily implemented by an extrapolation of macroscopic variables. To verify the scheme for inviscid flows, we have successfully simulated a three-dimensional shock-wave propagation in a box and a normal shock of Mach number 10 over a wedge. As an application to viscous flows, we have simulated a flat plate boundary layer flow, flow over a cylinder, and a transonic flow over a NACA0012 airfoil cascade.

Dynamic stress relaxation due to cyclic variation of strain at elevated temperature

International Nuclear Information System (INIS)

Suzuki, F.

1975-01-01

The relaxation of stress which occurs when low amplitude alternating strains are superimposed on constant mean total strains is studied in this paper. Experiments were carried out on a 0.16 per cent carbon steel and an AISI 347 stainless steel at 450 0 C and 650 0 C respectively in which the decrease of axial mean stress was measured as a function of time. When even a low amplitude alternating strain was applied, the rate of stress relaxation was observed to increase. Analytical predictions based on creep and static relaxation data show fairly good agreement with experiments in the period corresponding to transient creep. (author)

Probing localized strain in solution-derived YB a2C u3O7 -δ nanocomposite thin films

Science.gov (United States)

Guzman, Roger; Gazquez, Jaume; Mundet, Bernat; Coll, Mariona; Obradors, Xavier; Puig, Teresa

2017-07-01

Enhanced pinning due to nanoscale strain is unique to the high-Tc cuprates, where pairing may be modified with lattice distortion. Therefore a comprehensive understanding of the defect landscape is required for a broad range of applications. However, determining the type and distribution of defects and their associated strain constitutes a critical task, and for this aim, real-space techniques for atomic resolution characterization are necessary. Here, we use scanning transmission electron microscopy (STEM) to study the atomic structure of individual defects of solution-derived YB a2C u3O7 (YBCO) nanocomposites, where the inclusion of incoherent secondary phase nanoparticles within the YBCO matrix dramatically increases the density of Y1B a2C u4O8 (Y124) intergrowths, the commonest defect in YBCO thin films. The formation of the Y124 is found to trigger a concatenation of strain-derived interactions with other defects and the concomitant nucleation of intrinsic defects, which weave a web of randomly distributed nanostrained regions that profoundly transform the vortex-pinning landscape of the YBCO nanocomposite thin films.

Toward lattice fractional vector calculus

International Nuclear Information System (INIS)

Tarasov, Vasily E

2014-01-01

An analog of fractional vector calculus for physical lattice models is suggested. We use an approach based on the models of three-dimensional lattices with long-range inter-particle interactions. The lattice analogs of fractional partial derivatives are represented by kernels of lattice long-range interactions, where the Fourier series transformations of these kernels have a power-law form with respect to wave vector components. In the continuum limit, these lattice partial derivatives give derivatives of non-integer order with respect to coordinates. In the three-dimensional description of the non-local continuum, the fractional differential operators have the form of fractional partial derivatives of the Riesz type. As examples of the applications of the suggested lattice fractional vector calculus, we give lattice models with long-range interactions for the fractional Maxwell equations of non-local continuous media and for the fractional generalization of the Mindlin and Aifantis continuum models of gradient elasticity. (papers)

Toward lattice fractional vector calculus

Science.gov (United States)

Tarasov, Vasily E.

2014-09-01

An analog of fractional vector calculus for physical lattice models is suggested. We use an approach based on the models of three-dimensional lattices with long-range inter-particle interactions. The lattice analogs of fractional partial derivatives are represented by kernels of lattice long-range interactions, where the Fourier series transformations of these kernels have a power-law form with respect to wave vector components. In the continuum limit, these lattice partial derivatives give derivatives of non-integer order with respect to coordinates. In the three-dimensional description of the non-local continuum, the fractional differential operators have the form of fractional partial derivatives of the Riesz type. As examples of the applications of the suggested lattice fractional vector calculus, we give lattice models with long-range interactions for the fractional Maxwell equations of non-local continuous media and for the fractional generalization of the Mindlin and Aifantis continuum models of gradient elasticity.

Lattice gas cellular automata and lattice Boltzmann models an introduction

CERN Document Server

Wolf-Gladrow, Dieter A

2000-01-01

Lattice-gas cellular automata (LGCA) and lattice Boltzmann models (LBM) are relatively new and promising methods for the numerical solution of nonlinear partial differential equations. The book provides an introduction for graduate students and researchers. Working knowledge of calculus is required and experience in PDEs and fluid dynamics is recommended. Some peculiarities of cellular automata are outlined in Chapter 2. The properties of various LGCA and special coding techniques are discussed in Chapter 3. Concepts from statistical mechanics (Chapter 4) provide the necessary theoretical background for LGCA and LBM. The properties of lattice Boltzmann models and a method for their construction are presented in Chapter 5.

NMR studies of interfaces, strain and anisotropy in Co/Cu multilayers

International Nuclear Information System (INIS)

Thomson, T.; Riedi, P.C.

1999-01-01

59 Co NMR studies of multilayers are able to give three direct pieces of information: (i) the crystal phase of Co, fcc (217.4 MHz), hcp (220-228 MHz) and in exotic cases bcc (198 MHz) for films measured at T= 4.2 K, (ii) the nature of the interfaces from low frequency satellite lines, and (iii) the strain state deduced from small changes in the line positions. Extensive studies of Co/Cu multilayer interfacial structures as a function of deposition technique, layer thickness, substrate/buffer layer structure and annealing temperature have been undertaken. This work has shed new light on the relationship between interfacial structure and magnetoresistance and in particular has demonstrated that flat, atomic scale, interfaces lead to greater magnetoresistance. The difference between the Co and Cu lattice constant results in an extensive, tensile in-plane strain developing in Co layers provided that some epitaxial registry is present. Information on strain effects can be obtained from the position and width of the NMR lines. The magnetic anisotropy field can be determined by measuring the field dependence of the enhancement effect due to electronic magnetisation. This provides unique insight into the distribution of magnetic anisotropy within the Co layers, as the enhancement can be investigated independently for each NMR line and, hence, provides environment specific information on magnetic anisotropy at the interfaces and in the interior of the layers

Strain mapping under spherical indentations using transmission Kikuchi diffraction

International Nuclear Information System (INIS)

Cackett, A.; Hardie, C.; Wilkinson, A.; Dicks, K.

2015-01-01

Due to restrictions on both the specimen volumes available and the activity levels research facilities can handle, testing techniques on the micron-scale are very attractive for the study of irradiated material. However, the results of such small tests are convoluted by plasticity size-effects. Spherical nano-indentation is increasingly used to probe irradiated material, but to characterise the area of plastic deformation surrounding indentations a method capable of providing crystallographic information at extremely high spatial resolution is required. Transmission Kikuchi Diffraction (TKD) is a novel diffraction technique that can be performed in a scanning electron microscope. Using this technique, spatial resolutions below 10 nm have been achieved. Initial results, shown here, demonstrate the use of TKD in mapping the lattice rotations caused by indentation produced with a spherical diamond tip. With the addition of strain mapping software the plastic zone size was also evaluated for the first time using diffraction patterns generated via TKD. For a tip of radius 15 μm, inserted into Fe to a strain of 0.07, the plastic zone was observed to extend 1.3 μm to either side of the incident location of indentation and the deformation depth was approximately 0.5 μm. (authors)

Nondestructive strain depth profiling with high energy X-ray diffraction: System capabilities and limitations

Science.gov (United States)

Zhang, Zhan; Wendt, Scott; Cosentino, Nicholas; Bond, Leonard J.

2018-04-01

Limited by photon energy, and penetration capability, traditional X-ray diffraction (XRD) strain measurements are only capable of achieving a few microns depth due to the use of copper (Cu Kα1) or molybdenum (Mo Kα1) characteristic radiation. For deeper strain depth profiling, destructive methods are commonly necessary to access layers of interest by removing material. To investigate deeper depth profiles nondestructively, a laboratory bench-top high-energy X-ray diffraction (HEXRD) system was previously developed. This HEXRD method uses an industrial 320 kVp X-Ray tube and the Kα1 characteristic peak of tungsten, to produces a higher intensity X-ray beam which enables depth profiling measurement of lattice strain. An aluminum sample was investigated with deformation/load provided using a bending rig. It was shown that the HEXRD method is capable of strain depth profiling to 2.5 mm. The method was validated using an aluminum sample where both the HEXRD method and the traditional X-ray diffraction method gave data compared with that obtained using destructive etching layer removal, performed by a commercial provider. The results demonstrate comparable accuracy up to 0.8 mm depth. Nevertheless, higher attenuation capabilities in heavier metals limit the applications in other materials. Simulations predict that HEXRD works for steel and nickel in material up to 200 µm, but experiment results indicate that the HEXRD strain profile is not practical for steel and nickel material, and the measured diffraction signals are undetectable when compared to the noise.

Renormalons on the lattice

CERN Document Server

Crisafulli, M.; Martinelli, G.; Sachrajda, Christopher T.; Crisafulli, M; Gimenez, V; Martinelli, G; Sachrajda, C T

1994-01-01

We present the first lattice calculation of the B-meson binding energy \\labar and of the kinetic energy \\lambda_1/2 m_Q of the heavy-quark inside the pseudoscalar B-meson. In order to cancel the ambiguities due to the ultraviolet renormalons present in the operator matrix elements, this calculation has required the non-perturbative subtraction of the power divergences present in the Lagrangian operator \\energy and in the kinetic energy operator \\kkinetic. The non-perturbative renormalization of the relevant operators has been implemented by imposing suitable renormalization conditions on quark matrix elements in the Landau gauge.

Lattice degeneracies of geometric fermions

International Nuclear Information System (INIS)

Raszillier, H.

1983-05-01

We give the minimal numbers of degrees of freedom carried by geometric fermions on all lattices of maximal symmetries in d = 2, 3, and 4 dimensions. These numbers are lattice dependent, but in the (free) continuum limit, part of the degrees of freedom have to escape to infinity by a Wilson mechanism built in, and 2sup(d) survive for any lattice. On self-reciprocal lattices we compare the minimal numbers of degrees of freedom of geometric fermions with the minimal numbers of naive fermions on these lattices and argue that these numbers are equal. (orig.)

Lattice gauge theory using parallel processors

International Nuclear Information System (INIS)

Lee, T.D.; Chou, K.C.; Zichichi, A.

1987-01-01

The book's contents include: Lattice Gauge Theory Lectures: Introduction and Current Fermion Simulations; Monte Carlo Algorithms for Lattice Gauge Theory; Specialized Computers for Lattice Gauge Theory; Lattice Gauge Theory at Finite Temperature: A Monte Carlo Study; Computational Method - An Elementary Introduction to the Langevin Equation, Present Status of Numerical Quantum Chromodynamics; Random Lattice Field Theory; The GF11 Processor and Compiler; and The APE Computer and First Physics Results; Columbia Supercomputer Project: Parallel Supercomputer for Lattice QCD; Statistical and Systematic Errors in Numerical Simulations; Monte Carlo Simulation for LGT and Programming Techniques on the Columbia Supercomputer; Food for Thought: Five Lectures on Lattice Gauge Theory

Application of Powder Diffraction Methods to the Analysis of the Atomic Structure of Nanocrystals: The Concept of the Apparent Lattice Parameter (ALP)

Science.gov (United States)

Palosz, B.; Grzanka, E.; Gierlotka, S.; Stelmakh, S.; Pielaszek, R.; Bismayer, U.; Weber, H.-P.; Palosz, W.; Curreri, Peter A. (Technical Monitor)

2002-01-01

The applicability of standard methods of elaboration of powder diffraction data for determination of the structure of nano-size crystallites is analysed. Based on our theoretical calculations of powder diffraction data we show, that the assumption of the infinite crystal lattice for nanocrystals smaller than 20 nm in size is not justified. Application of conventional tools developed for elaboration of powder diffraction data, like the Rietveld method, may lead to erroneous interpretation of the experimental results. An alternate evaluation of diffraction data of nanoparticles, based on the so-called 'apparent lattice parameter' (alp) is introduced. We assume a model of nanocrystal having a grain core with well-defined crystal structure, surrounded by a surface shell with the atomic structure similar to that of the core but being under a strain (compressive or tensile). The two structural components, the core and the shell, form essentially a composite crystal with interfering, inseparable diffraction properties. Because the structure of such a nanocrystal is not uniform, it defies the basic definitions of an unambiguous crystallographic phase. Consequently, a set of lattice parameters used for characterization of simple crystal phases is insufficient for a proper description of the complex structure of nanocrystals. We developed a method of evaluation of powder diffraction data of nanocrystals, which refers to a core-shell model and is based on the 'apparent lattice parameter' methodology. For a given diffraction pattem, the alp values are calculated for every individual Bragg reflection. For nanocrystals the alp values depend on the diffraction vector Q. By modeling different a0tomic structures of nanocrystals and calculating theoretically corresponding diffraction patterns using the Debye functions we showed, that alp-Q plots show characteristic shapes which can be used for evaluation of the atomic structure of the core-shell system. We show, that using a simple

Stress distribution and lattice distortions in Nb3Sn multifilament wires under uniaxial tensile loading at 4.2 K

International Nuclear Information System (INIS)

Scheuerlein, C; Flükiger, R; Kadar, J; Bordini, B; Ballarino, A; Bottura, L; Di Michiel, M; Buta, F; Seeber, B; Senatore, C; Siegrist, T; Besara, T

2014-01-01

The lattice parameter changes in three types of Nb 3 Sn 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 Nb 3 Sn 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 Nb 3 Sn and unreacted Nb. This is in contrast to the bronze route wire, where the matrix can carry substantial loads. In straight wires the axial Nb 3 Sn 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 Nb 3 Sn 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 influence on the Nb 3 Sn texture. (paper)

Nonsymmorphic symmetry-protected topological modes in plasmonic nanoribbon lattices

Science.gov (United States)

Zhang, Yong-Liang; Wu, Raymond P. H.; Kumar, Anshuman; Si, Tieyan; Fung, Kin Hung

2018-04-01

Using a dynamic eigenresponse theory, we study the topological edge plasmon modes in dispersive plasmonic lattices constructed by unit cells of multiple nanoribbons. In dipole approximation, the bulk-edge correspondence in the lattices made of dimerized unit cell and one of its square-root daughter with nonsymmorphic symmetry are demonstrated. Calculations with consideration of dynamic long-range effects and retardation are compared to those given by nearest-neighbor approximations. It is shown that nonsymmorphic symmetry opens up two symmetric gaps where versatile topological edge plasmon modes are found. Unprecedented spectral shifts of the edge states with respect to the zero modes due to long-range coupling are found. The proposed ribbon structure is favorable to electrical gating and thus could serve as an on-chip platform for electrically controllable subwavelength edge states at optical wavelengths. Our eigenresponse approach provides a powerful tool for the radiative topological mode analysis in strongly coupled plasmonic lattices.

Lattice degeneracies of fermions

International Nuclear Information System (INIS)

Raszillier, H.

1983-10-01

We present a detailed description of the minimal degeneracies of geometric (Kaehler) fermions on all the lattices of maximal symmetries in n = 1, ..., 4 dimensions. We also determine the isolated orbits of the maximal symmetry groups, which are related to the minimal numbers of ''naive'' fermions on the reciprocals of these lattices. It turns out that on the self-reciprocal lattices the minimal numbers of naive fermions are equal to the minimal numbers of degrees of freedom of geometric fermions. The description we give relies on the close connection of the maximal lattice symmetry groups with (affine) Weyl groups of root systems of (semi-) simple Lie algebras. (orig.)

Texture of poled tetragonal PZT detected by synchrotron X-ray diffraction and micromechanics analysis

International Nuclear Information System (INIS)

Hall, D.A.; Steuwer, A.; Cherdhirunkorn, B.; Withers, P.J.; Mori, T.

2005-01-01

The texture and lattice elastic strain due to electrical poling of tetragonal PZT (lead zirconate titanate) ceramics have been measured using high energy synchrotron X-ray diffraction. It is shown that XRD peak intensity ratios associated with crystal planes of the form {002}, {112} and {202} exhibit a linear dependence on cos-bar 2 Ψ, where Ψ represents the orientation angle between the plane normal and the macroscopic poling axis. The observed dependence of texture and lattice strain on the grain orientation can be understood on the basis that the macroscopic strain due to poling is the average of the poling strains of all the individual grains

Vortex lattices in superconducting niobium and skyrmion lattices in chiral MnSi. An investigation by neutron scattering

International Nuclear Information System (INIS)

Muehlbauer, Sebastian C.

2009-01-01

In this thesis, we present a comprehensive small angle neutron scattering study of the vortex lattice (VL) in an ultra-pure Nb single crystal sample, characterized by a residual resistivity ratio of ∝ 10 4 . We systematically investigate the morphology of vortex structures with the magnetic field applied along a four-fold left angle 100 right angle axis. We succeed to deconvolute the general morphology of the VL and its orientation to three dominant mechanisms: First, non-local contributions, second, the transition between open and closed Fermi surface sheets and, third, the intermediate mixed state (IMS) between the Meissner and the Shubnikov phase. We present first time microscopic measurements of the intrinsic bulk VL tilt modulus c 44 by means of time resolved stroboscopic small angle neutron scattering in combination with a tailored magnetic field setup. In our study we find that the VL in Nb responds to an external force - in the form of a changed magnetic field - with an exponential relaxation. As expected, the relaxation process shows increasing VL stiffness with increasing magnetic field and reduced damping with increasing temperature. Besides this general trend, we observe a dramatic changeover of the relaxation process associated with the non-trivial VL morphology in the IMS and the crossover from attractive to repulsive vortex-vortex interaction. Furthermore we use small angle neutron scattering to establish the existence of a skyrmion lattice in the A-phase of MnSi. Due to a parallel alignment of the magnetic field with respect to the neutron beam, we are able to resolve the complete magnetic structure of the A-phase: The structure in the A-phase, reminiscent of a vortex lattice, consists of topological knots of the magnetization with particle-like properties, arranged in a regular six-fold lattice. The orientation of this lattice is strictly driven by the orientation of the applied magnetic field, regardless of the underlying crystal symmetry. The

Vortex lattices in superconducting niobium and skyrmion lattices in chiral MnSi. An investigation by neutron scattering

Energy Technology Data Exchange (ETDEWEB)

Muehlbauer, Sebastian C

2009-12-10

In this thesis, we present a comprehensive small angle neutron scattering study of the vortex lattice (VL) in an ultra-pure Nb single crystal sample, characterized by a residual resistivity ratio of {proportional_to} 10{sup 4}. We systematically investigate the morphology of vortex structures with the magnetic field applied along a four-fold left angle 100 right angle axis. We succeed to deconvolute the general morphology of the VL and its orientation to three dominant mechanisms: First, non-local contributions, second, the transition between open and closed Fermi surface sheets and, third, the intermediate mixed state (IMS) between the Meissner and the Shubnikov phase. We present first time microscopic measurements of the intrinsic bulk VL tilt modulus c{sub 44} by means of time resolved stroboscopic small angle neutron scattering in combination with a tailored magnetic field setup. In our study we find that the VL in Nb responds to an external force - in the form of a changed magnetic field - with an exponential relaxation. As expected, the relaxation process shows increasing VL stiffness with increasing magnetic field and reduced damping with increasing temperature. Besides this general trend, we observe a dramatic changeover of the relaxation process associated with the non-trivial VL morphology in the IMS and the crossover from attractive to repulsive vortex-vortex interaction. Furthermore we use small angle neutron scattering to establish the existence of a skyrmion lattice in the A-phase of MnSi. Due to a parallel alignment of the magnetic field with respect to the neutron beam, we are able to resolve the complete magnetic structure of the A-phase: The structure in the A-phase, reminiscent of a vortex lattice, consists of topological knots of the magnetization with particle-like properties, arranged in a regular six-fold lattice. The orientation of this lattice is strictly driven by the orientation of the applied magnetic field, regardless of the underlying

Bloch oscillations and accelerated Bose–Einstein condensates in an optical lattice

Energy Technology Data Exchange (ETDEWEB)

Sacchetti, Andrea, E-mail: andrea.sacchetti@unimore.it

2017-01-30

Highlights: • Discrete nonlinear Schrödinger model for accelerated BECs in optical lattices. • Numerical computation of wavefunction BECs dynamics. • Correlation between nonlinearity and the oscillating period of the BEC's center of mass. • Discussion of the validity of the Bloch Theorem for accelerated BECs in an optical lattice. - Abstract: We discuss the method for the measurement of the gravity acceleration g by means of Bloch oscillations of an accelerated BEC in an optical lattice. This method has a theoretical critical point due to the fact that the period of the Bloch oscillations depends, in principle, on the initial shape of the BEC wavepacket. Here, by making use of the nearest-neighbor model for the numerical analysis of the BEC wavefunction, we show that in real experiments the period of the Bloch oscillations does not really depend on the shape of the initial wavepacket and that the relative uncertainty, due to the fact that the initial shape of the wavepacket may be asymmetrical, is smaller than the one due to experimental errors. Furthermore, we also show that the relation between the oscillation period and the scattering length of the BEC's atoms is linear; this fact suggests us a new experimental procedure for the measurement of the scattering length of atoms.

Analysis of YBCO high temperature superconductor doped with silver nanoparticles and carbon nanotubes using Williamson-Hall and size-strain plot

Science.gov (United States)

Dadras, Sedigheh; Davoudiniya, Masoumeh

2018-05-01

This paper sets out to investigate and compare the effects of Ag nanoparticles and carbon nanotubes (CNTs) doping on the mechanical properties of Y1Ba2Cu3O7-δ (YBCO) high temperature superconductor. For this purpose, the pure and doped YBCO samples were synthesized by sol-gel method. The microstructural analysis of the samples is performed using X-ray diffraction (XRD). The crystalline size, lattice strain and stress of the pure and doped YBCO samples were estimated by modified forms of Williamson-Hall analysis (W-H), namely, uniform deformation model (UDM), uniform deformation stress model (UDSM) and the size-strain plot method (SSP). These results show that the crystalline size, lattice strain and stress of the YBCO samples declined by Ag nanoparticles and CNTs doping.

A FeNiMnC alloy with strain glass transition

Directory of Open Access Journals (Sweden)

Hui Ma

2018-02-01

Full Text Available Recent experimental and theoretical investigations suggested that doping sufficient point defects into a normal ferroelastic/martensitic alloy systems could lead to a frozen disordered state of local lattice strains (nanomartensite domains, thereby suppressing the long-range strain-ordering martensitic transition. In this study, we attempt to explore the possibility of developing novel ferrous Elinvar alloys by replacing nickel with carbon and manganese as dopant species. A nominal Fe89Ni5Mn4.6C1.4 alloy was prepared by argon arc melting, and XRD, DSC, DMA and TEM techniques were employed to characterize the strain glass transition signatures, such as invariance in average structure, frequency dispersion in dynamic mechanical properties (storage modulus and internal friction and the formation of nanosized strain domains. It is indicated that doping of Ni, Mn and C suppresses γ→α long-range strain-ordering martensitic transformation in Fe89Ni5Mn4.6C1.4 alloy, generating randomly distributed nanosized domains by strain glass transition. Keywords: Strain glass transition, Elinvar alloys, Point defects, Nanosized domains

Exciton confinement in strain-engineered metamorphic InAs/I nxG a1 -xAs quantum dots

Science.gov (United States)

Khattak, S. A.; Hayne, M.; Huang, J.; Vanacken, J.; Moshchalkov, V. V.; Seravalli, L.; Trevisi, G.; Frigeri, P.

2017-11-01

We report a comprehensive study of exciton confinement in self-assembled InAs quantum dots (QDs) in strain-engineered metamorphic I nxG a1 -xAs confining layers on GaAs using low-temperature magnetophotoluminescence. As the lattice mismatch (strain) between QDs and confining layers (CLs) increases from 4.8% to 5.7% the reduced mass of the exciton increases, but saturates at higher mismatches. At low QD-CL mismatch there is clear evidence of spillover of the exciton wave function due to small localization energies. This is suppressed as the In content x in the CLs decreases (mismatch and localization energy increasing). The combined effects of low effective mass and wave-function spillover at high x result in a diamagnetic shift coefficient that is an order of magnitude larger than for samples where In content in the barrier is low (mismatch is high and localization energy is large). Finally, an anomalously small measured Bohr radius in samples with the highest x is attributed to a combination of thermalization due to low localization energy, and its enhancement with magnetic field, a mechanism which results in small dots in the ensemble dominating the measured Bohr radius.

Strain-induced alignment and phase behavior of blue phase liquid crystals confined to thin films.

Science.gov (United States)

Bukusoglu, Emre; Martinez-Gonzalez, Jose A; Wang, Xiaoguang; Zhou, Ye; de Pablo, Juan J; Abbott, Nicholas L

2017-12-06

We report on the influence of surface confinement on the phase behavior and strain-induced alignment of thin films of blue phase liquid crystals (BPs). Confining surfaces comprised of bare glass, dimethyloctadecyl [3-(trimethoxysilyl)propyl] ammonium chloride (DMOAP)-functionalized glass, or polyvinyl alcohol (PVA)-coated glass were used with or without mechanically rubbing to influence the azimuthal anchoring of the BPs. These experiments reveal that confinement can change the phase behavior of the BP films. For example, in experiments performed with rubbed-PVA surfaces, we measured the elastic strain of the BPs to change the isotropic-BPII phase boundary, suppressing formation of BPII for film thicknesses incommensurate with the BPII lattice. In addition, we observed strain-induced alignment of the BPs to exhibit a complex dependence on both the surface chemistry and azimuthal alignment of the BPs. For example, when using bare glass surfaces causing azimuthally degenerate and planar anchoring, BPI oriented with (110) planes of the unit cell parallel to the contacting surfaces for thicknesses below 3 μm but transitioned to an orientation with (200) planes aligned parallel to the contacting surfaces for thicknesses above 4 μm. In contrast, BPI aligned with (110) planes parallel to confining surfaces for all other thicknesses and surface treatments, including bare glass with uniform azimuthal alignment. Complementary simulations based on minimization of the total free energy (Landau-de Gennes formalism) confirmed a thickness-dependent reorientation due to strain of BPI unit cells within a window of surface anchoring energies and in the absence of uniform azimuthal alignment. In contrast to BPI, BPII did not exhibit thickness-dependent orientations but did exhibit orientations that were dependent on the surface chemistry, a result that was also captured in simulations by varying the anchoring energies. Overall, the results in this paper reveal that the orientations

Geometry of lattice field theory

International Nuclear Information System (INIS)

Honan, T.J.

1986-01-01

Using some tools of algebraic topology, a general formalism for lattice field theory is presented. The lattice is taken to be a simplicial complex that is also a manifold and is referred to as a simplicial manifold. The fields on this lattice are cochains, that are called lattice forms to emphasize the connections with differential forms in the continuum. This connection provides a new bridge between lattice and continuum field theory. A metric can be put onto this simplicial manifold by assigning lengths to every link or I-simplex of the lattice. Regge calculus is a way of defining general relativity on this lattice. A geometric discussion of Regge calculus is presented. The Regge action, which is a discrete form of the Hilbert action, is derived from the Hilbert action using distribution valued forms. This is a new derivation that emphasizes the underlying geometry. Kramers-Wannier duality in statistical mechanics is discussed in this general setting. Nonlinear field theories, which include gauge theories and nonlinear sigma models are discussed in the continuum and then are put onto a lattice. The main new result here is the generalization to curved spacetime, which consists of making the theory compatible with Regge calculus

Representation theory of lattice current algebras

International Nuclear Information System (INIS)

Alekseev, A.Yu.; Eidgenoessische Technische Hochschule, Zurich; Faddeev, L.D.; Froehlich, L.D.; Schomerus, V.; Kyoto Univ.

1996-04-01

Lattice current algebras were introduced as a regularization of the left-and right moving degrees of freedom in the WZNW model. They provide examples of lattice theories with a local quantum symmetry U q (G). Their representation theory is studied in detail. In particular, we construct all irreducible representations along with a lattice analogue of the fusion product for representations of the lattice current algebra. It is shown that for an arbitrary number of lattice sites, the representation categories of the lattice current algebras agree with their continuum counterparts. (orig.)

ISABELLE lattice

International Nuclear Information System (INIS)

Smith, L.

1975-01-01

An analysis is given of a number of variants of the basic lattice of the planned ISABELLE storage rings. The variants were formed by removing cells from the normal part of the lattice and juggling the lengths of magnets, cells, and insertions in order to maintain a rational relation of circumference to that of the AGS and approximately the same dispersion. Special insertions, correction windings, and the working line with nonlinear resonances are discussed

Soft network materials with isotropic negative Poisson's ratios over large strains.

Science.gov (United States)

Liu, Jianxing; Zhang, Yihui

2018-01-31

Auxetic materials with negative Poisson's ratios have important applications across a broad range of engineering areas, such as biomedical devices, aerospace engineering and automotive engineering. A variety of design strategies have been developed to achieve artificial auxetic materials with controllable responses in the Poisson's ratio. The development of designs that can offer isotropic negative Poisson's ratios over large strains can open up new opportunities in emerging biomedical applications, which, however, remains a challenge. Here, we introduce deterministic routes to soft architected materials that can be tailored precisely to yield the values of Poisson's ratio in the range from -1 to 1, in an isotropic manner, with a tunable strain range from 0% to ∼90%. The designs rely on a network construction in a periodic lattice topology, which incorporates zigzag microstructures as building blocks to connect lattice nodes. Combined experimental and theoretical studies on broad classes of network topologies illustrate the wide-ranging utility of these concepts. Quantitative mechanics modeling under both infinitesimal and finite deformations allows the development of a rigorous design algorithm that determines the necessary network geometries to yield target Poisson ratios over desired strain ranges. Demonstrative examples in artificial skin with both the negative Poisson's ratio and the nonlinear stress-strain curve precisely matching those of the cat's skin and in unusual cylindrical structures with engineered Poisson effect and shape memory effect suggest potential applications of these network materials.

Anisotropic chemical strain in cubic ceria due to oxygen-vacancy-induced elastic dipoles.

Science.gov (United States)

Das, Tridip; Nicholas, Jason D; Sheldon, Brian W; Qi, Yue

2018-06-06

Accurate characterization of chemical strain is required to study a broad range of chemical-mechanical coupling phenomena. One of the most studied mechano-chemically active oxides, nonstoichiometric ceria (CeO2-δ), has only been described by a scalar chemical strain assuming isotropic deformation. However, combined density functional theory (DFT) calculations and elastic dipole tensor theory reveal that both the short-range bond distortions surrounding an oxygen-vacancy and the long-range chemical strain are anisotropic in cubic CeO2-δ. The origin of this anisotropy is the charge disproportionation between the four cerium atoms around each oxygen-vacancy (two become Ce3+ and two become Ce4+) when a neutral oxygen-vacancy is formed. Around the oxygen-vacancy, six of the Ce3+-O bonds elongate, one of the Ce3+-O bond shorten, and all seven of the Ce4+-O bonds shorten. Further, the average and maximum chemical strain values obtained through tensor analysis successfully bound the various experimental data. Lastly, the anisotropic, oxygen-vacancy-elastic-dipole induced chemical strain is polarizable, which provides a physical model for the giant electrostriction recently discovered in doped and non-doped CeO2-δ. Together, this work highlights the need to consider anisotropic tensors when calculating the chemical strain induced by dilute point defects in all materials, regardless of their symmetry.

DNA-linked NanoParticle Lattices with Diamond Symmetry: Stability, Shape and Optical Properties

Science.gov (United States)

Emamy, Hamed; Tkachenko, Alexei; Gang, Oleg; Starr, Francis

The linking of nanoparticles (NP) by DNA has been proven to be an effective means to create NP lattices with specific order. Lattices with diamond symmetry are predicted to offer novel photonic properties, but self-assembly of such lattices has proven to be challenging due to the low packing fraction, sensitivity to bond orientation, and local heterogeneity. Recently, we reported an approach to create diamond NP lattices based on the association between anisotropic particles with well-defined tetravalent DNA binding topology and isotropically functionalized NP. Here, we use molecular dynamics simulations to evaluate the Gibbs free energy of these lattices, and thereby determine the stability of these lattices as a function of NP size and DNA stiffness. We also predict the equilibrium shape for the cubic diamond crystallite using the Wulff construction method. Specifically, we predict the equilibrium shape using the surface energy for different crystallographic planes. We evaluate surface energy directly form molecular dynamics simulation, which we correlate with theoretical estimates from the expected number of broken DNA bonds along a facet. Furthermore we study the optical properties of this structure, e.g optical bandgap.

Control of threading dislocations by strain engineering in GaInP buffers grown on GaAs substrates

Energy Technology Data Exchange (ETDEWEB)

Li, K.L., E-mail: klli2010@sinano.ac.cn [Key Laboratory of Nanodevices and Applications, Suzhou Institute of Nano-Tech and Nano-Bionics, CAS, Suzhou 215123 (China); University of Chinese Academy of Sciences, Beijing 100049 (China); Sun, Y.R. [Key Laboratory of Nanodevices and Applications, Suzhou Institute of Nano-Tech and Nano-Bionics, CAS, Suzhou 215123 (China); University of Chinese Academy of Sciences, Beijing 100049 (China); Dong, J.R. [Key Laboratory of Nanodevices and Applications, Suzhou Institute of Nano-Tech and Nano-Bionics, CAS, Suzhou 215123 (China); He, Y.; Zeng, X.L. [Key Laboratory of Nanodevices and Applications, Suzhou Institute of Nano-Tech and Nano-Bionics, CAS, Suzhou 215123 (China); University of Chinese Academy of Sciences, Beijing 100049 (China); Zhao, Y.M.; Yu, S.Z.; Zhao, C.Y. [Key Laboratory of Nanodevices and Applications, Suzhou Institute of Nano-Tech and Nano-Bionics, CAS, Suzhou 215123 (China)

2015-10-30

High quality strain-relaxed In0.3Ga0.7As layers with threading dislocation density about 2 × 10{sup 6} cm{sup −2} and root-mean-square surface roughness below 8.0 nm were obtained on GaAs substrates using compositionally undulating step-graded Ga{sub 1−x}In{sub x}P (x = 0.48–0.78) buffers. The transmission electron microscopy results reveal that the conventional step-graded GaInP buffers produce high density dislocation pile-ups, which are induced by the blocking effect of the nonuniform misfit dislocation strain field and crosshatched surface on the gliding of threading dislocations. In contrast, due to strain compensation, insertion of the tensile GaInP layers decreases the surface roughness and promotes dislocation annihilation in the interfaces, and eventually reduces the threading dislocation density. This provides a promising way to achieve a virtual substrate with the desired lattice parameter for metamorphic device applications. - Highlights: • Metamorphic GaInP buffers were grown by metal–organic chemical vapor deposition. • The compositionally undulating buffers effectively reduce the threading dislocation density. • High quality strain-relaxed In{sub 0.3}Ga{sub 0.7}As layers were obtained.

Chiral Extrapolations of the $\\boldsymbol{ρ(770)}$ Meson in $\\mathbf{N_f=2+1}$ Lattice QCD Simulations

Energy Technology Data Exchange (ETDEWEB)

Molina, Raquel [Univ. of Sao Paulo (Brazil); Hu, Bitao [George Washington Univ., Washington, DC (United States); Doering, Michael [Thomas Jefferson National Accelerator Facility (TJNAF), Newport News, VA (United States); George Washington Univ., Washington, DC (United States); Mai, Maxim [George Washington Univ., Washington, DC (United States); Alexandru, Andrei [George Washington Univ., Washington, DC (United States)

2018-04-01

Several lattice QCD simulations of meson-meson scattering in p-wave and Isospin = 1 in Nf = 2 + 1 flavours have been carried out recently. Unitarized Chiral Perturbation Theory is used to perform extrapolations to the physical point. In contrast to previous findings on the analyses of Nf = 2 lattice data, where most of the data seems to be in agreement, some discrepancies are detected in the Nf = 2 + 1 lattice data analyses, which could be due to different masses of the strange quark, meson decay constants, initial constraints in the simulation, or other lattice artifacts. In addition, the low-energy constants are compared to the ones from a recent analysis of Nf = 2 lattice data.

Strain distributions in nano-onions with uniform and non-uniform compositions

International Nuclear Information System (INIS)

Duan, H L; Karihaloo, B L; Wang, J; Yi, X

2006-01-01

Nano-onions are ellipsoidal or spherical particles consisting of a core surrounded by concentric shells of nanometre size. Nano-onions produced by self-assembly and colloidal techniques have different structures and compositions, and thus differ in the state of strains. The mismatch of the thermal expansion coefficients and lattice constants between neighbouring shells induces stress/strain fields in the core and shells, which in turn affect their physical/mechanical properties and/or the properties of the composites containing them. In this paper, the strains in embedded and free-standing nano-onions with uniform and non-uniform compositions are studied in detail. It is found that the strains in the nano-onions can be modified by adjusting their compositions and structures. The results are useful for the band structure engineering of semiconductor nano-onions

Thermomechanically induced residual strains in Al/SiCp metal-matrix composites

DEFF Research Database (Denmark)

Lorentzen, T.; Clarke, A.P.

1998-01-01

Residual lattice strains in the aluminium and SiC phases of F3S.20S extruded A359 20% SiC metal-matrix composite were measured by using neutron diffi action at room and elevated temperatures to monitor the effects of in situ uniaxial plastic deformations. The results are interpreted with referenc...

Introduction to lattice gauge theory

International Nuclear Information System (INIS)

Gupta, R.

1987-01-01

The lattice formulation of Quantum Field Theory (QFT) can be exploited in many ways. We can derive the lattice Feynman rules and carry out weak coupling perturbation expansions. The lattice then serves as a manifestly gauge invariant regularization scheme, albeit one that is more complicated than standard continuum schemes. Strong coupling expansions: these give us useful qualitative information, but unfortunately no hard numbers. The lattice theory is amenable to numerical simulations by which one calculates the long distance properties of a strongly interacting theory from first principles. The observables are measured as a function of the bare coupling g and a gauge invariant cut-off ≅ 1/α, where α is the lattice spacing. The continuum (physical) behavior is recovered in the limit α → 0, at which point the lattice artifacts go to zero. This is the more powerful use of lattice formulation, so in these lectures the author focuses on setting up the theory for the purpose of numerical simulations to get hard numbers. The numerical techniques used in Lattice Gauge Theories have their roots in statistical mechanics, so it is important to develop an intuition for the interconnection between quantum mechanics and statistical mechanics. This will be the emphasis of the first lecture. In the second lecture, the author reviews the essential ingredients of formulating QCD on the lattice and discusses scaling and the continuum limit. In the last lecture the author summarizes the status of some of the main results. He also mentions the bottlenecks and possible directions for research. 88 refs

Basis reduction for layered lattices

NARCIS (Netherlands)

Torreão Dassen, Erwin

2011-01-01

We develop the theory of layered Euclidean spaces and layered lattices. We present algorithms to compute both Gram-Schmidt and reduced bases in this generalized setting. A layered lattice can be seen as lattices where certain directions have infinite weight. It can also be

Basis reduction for layered lattices

NARCIS (Netherlands)

E.L. Torreão Dassen (Erwin)

2011-01-01

htmlabstractWe develop the theory of layered Euclidean spaces and layered lattices. With this new theory certain problems that usually are solved by using classical lattices with a "weighting" gain a new, more natural form. Using the layered lattice basis reduction algorithms introduced here these

Transmission-lattice based geometric phase analysis for evaluating the dynamic deformation of a liquid surface.

Science.gov (United States)

Shi, Wenxiong; Huang, Xianfu; Liu, Zhanwei

2014-05-05

Quantitatively measuring a dynamic liquid surface often presents a challenge due to high transparency, fluidity and specular reflection. Here, a novel Transmission-Lattice based Geometric Phase Analysis (TLGPA) method is introduced. In this method, a special lattice is placed underneath a liquid to be tested and, when viewed from above, the phase of the transmission-lattice image is modulated by the deformation of the liquid surface. Combining this with multi-directional Newton iteration algorithms, the dynamic deformation field of the liquid surface can be calculated from the phase variation of a series of transmission-lattice images captured at different moments. The developed method has the advantage of strong self-adaption ability to initial lattice rotational errors and this is discussed in detail. Dynamic 3D ripples formation and propagation was investigated and the results obtained demonstrated the feasibility of the method.

Strain-engineering of the topological insulator HgTe

International Nuclear Information System (INIS)

Leubner, Philipp

2017-01-01

The subject of this thesis is the control of strain in HgTe thin-film crystals. A major task was the experimental control of the strain in the HgTe films. This was achieved by a new epitaxial approach and confirmed by cristallographic analysis and magneto-transport measurements. In this work, strain was induced in thin films by means of coherent epitaxy on substrate crystals. In principle, compressive strain can be achieved by using an appropriate Cd 1-x Zn x Te substrate. This concept was modified and applied in this work. Epilayers have been fabricated by molecular-beam epitaxy (MBE). The growth of thick buffer layers of CdTe on GaAs:Si was established as an alternative to commercial CdTe and Cd 0.96 Zn 0.04 Te substrates. Residual strain was found in the buffer layers, and was attributed to a combination of finite layer thickness and mismatch of the thermal expansion coefficients of CdTe and GaAs. CdTe-Cd 0.5 Zn 0.5 Te strained-layer-superlattices have been grown by a combination of MBE and atomic-layer epitaxy (ALE), and have been analyzed by HRXRD. The crystal quality has been found to degrade with increasing Zn-fraction. HgTe quantum wells (QWs) sandwiched in between CdHgTe barriers have been fabricated in a similar fashion on superlattices and conventional CdTe and Cd 0.96 Zn 0.04 Te substrates. We have determined the QW thickness with an accuracy of ±0.5 nm by an analysis of the beating patterns in the thickness fringes of HRXRD measurements and X-ray reflectometry measurements. We have, for the first time, induced compressive strain in HgTe QWs by an epitaxial technique (i.e. the effective lattice constant of the superlattice is lower compared to the lattice constant of HgTe). The problem of the lattice mismatch between superlattice and barriers has been circumvented by using CdHgTe-ZnHgTe superlattices instead of CdHgTe as a barrier material. Furthermore, the growth of compressively strained HgTe bulk layers (with a thickness of at least 50 nm) was

Strain-engineering of the topological insulator HgTe

Energy Technology Data Exchange (ETDEWEB)

Leubner, Philipp

2017-07-24

The subject of this thesis is the control of strain in HgTe thin-film crystals. A major task was the experimental control of the strain in the HgTe films. This was achieved by a new epitaxial approach and confirmed by cristallographic analysis and magneto-transport measurements. In this work, strain was induced in thin films by means of coherent epitaxy on substrate crystals. In principle, compressive strain can be achieved by using an appropriate Cd{sub 1-x}Zn{sub x}Te substrate. This concept was modified and applied in this work. Epilayers have been fabricated by molecular-beam epitaxy (MBE). The growth of thick buffer layers of CdTe on GaAs:Si was established as an alternative to commercial CdTe and Cd{sub 0.96}Zn{sub 0.04}Te substrates. Residual strain was found in the buffer layers, and was attributed to a combination of finite layer thickness and mismatch of the thermal expansion coefficients of CdTe and GaAs. CdTe-Cd{sub 0.5}Zn{sub 0.5}Te strained-layer-superlattices have been grown by a combination of MBE and atomic-layer epitaxy (ALE), and have been analyzed by HRXRD. The crystal quality has been found to degrade with increasing Zn-fraction. HgTe quantum wells (QWs) sandwiched in between CdHgTe barriers have been fabricated in a similar fashion on superlattices and conventional CdTe and Cd{sub 0.96}Zn{sub 0.04}Te substrates. We have determined the QW thickness with an accuracy of ±0.5 nm by an analysis of the beating patterns in the thickness fringes of HRXRD measurements and X-ray reflectometry measurements. We have, for the first time, induced compressive strain in HgTe QWs by an epitaxial technique (i.e. the effective lattice constant of the superlattice is lower compared to the lattice constant of HgTe). The problem of the lattice mismatch between superlattice and barriers has been circumvented by using CdHgTe-ZnHgTe superlattices instead of CdHgTe as a barrier material. Furthermore, the growth of compressively strained HgTe bulk layers (with a

Is the effect of job strain on myocardial infarction risk due to interaction between high psychological demands and low decision latitude?

DEFF Research Database (Denmark)

Hallqvist, J; Diderichsen, Finn; Theorell, T

1998-01-01

The objectives are to examine if the excess risk of myocardial infarction from exposure to job strain is due to interaction between high demands and low control and to analyse what role such an interaction has regarding socioeconomic differences in risk of myocardial infarction. The material...

Strain and spin-orbit effects in self-assembled quantum dots

International Nuclear Information System (INIS)

Zielinski, M.; Jaskolski, W.; Aizpurua, J.; Bryant, G.W.

2005-01-01

The Effects of strain and spin-orbit interaction in self-assembled lien-shaped InAs/GaAs quantum dots are investigated. Calculations are performed with empirical tight-binding theory supplemented by the valence force field method to account for effects of strain caused by lattice mismatch at the InAs-GaAs interface. It is shown that both effects influence strongly the electron and hole energy structure: splitting of the energy levels, the number of bound states, density distributions, and transition rates. We show that piezoelectric effects are almost negligible in quantum dots of the size investigated. (author)

Lattice Higgs models

International Nuclear Information System (INIS)

Jersak, J.

1986-01-01

This year has brought a sudden interest in lattice Higgs models. After five years of only modest activity we now have many new results obtained both by analytic and Monte Carlo methods. This talk is a review of the present state of lattice Higgs models with particular emphasis on the recent development

Nuclear lattice simulations

Directory of Open Access Journals (Sweden)

Epelbaum E.

2010-04-01

Full Text Available We review recent progress on nuclear lattice simulations using chiral effective field theory. We discuss lattice results for dilute neutron matter at next-to-leading order, three-body forces at next-to-next-toleading order, isospin-breaking and Coulomb effects, and the binding energy of light nuclei.

Strain Relaxation and Vacancy Creation in Thin Platinum Films

International Nuclear Information System (INIS)

Gruber, W.; Chakravarty, S.; Schmidt, H.; Baehtz, C.; Leitenberger, W.; Bruns, M.; Kobler, A.; Kuebel, C.

2011-01-01

Synchrotron based combined in situ x-ray diffractometry and reflectometry is used to investigate the role of vacancies for the relaxation of residual stress in thin metallic Pt films. From the experimentally determined relative changes of the lattice parameter a and of the film thickness L the modification of vacancy concentration and residual strain was derived as a function of annealing time at 130 deg. C. The results indicate that relaxation of strain resulting from compressive stress is accompanied by the creation of vacancies at the free film surface. This proves experimentally the postulated dominant role of vacancies for stress relaxation in thin metal films close to room temperature.

Intersubband energies in strain-compensated InGaN/AlInN quantum well structures

Energy Technology Data Exchange (ETDEWEB)

Park, Seoung-Hwan, E-mail: shpark@cu.ac.kr [Department of Electronics Engineering, Catholic University of Daegu, Hayang, Kyeongsan, Kyeongbuk, 712-702 (Korea, Republic of); Ahn, Doyeol [Institute of Quantum Information Processing and Systems, University of Seoul, 90 Jeonnong, Tongdaimoon-Gu, Seoul, Korea 130-743 (Korea, Republic of)

2016-01-15

Intersubband transition energies in the conduction band for strain-compensated InGaN/AlInN quantum well (QW) structures were investigated as a function of strain based on an effective mass theory with the nonparabolicity taken into account. In the case of an InGaN/AlInN QW structure lattice-matched to GaN, the wavelength is shown to be longer than 1.55 μm. On the other hand, strain-compensated QW structures show that the wavelength of 1.55 μm can be reached even for the QW structure with a relatively small strain of 0.3 %. Hence, the strain-compensated QW structures can be used for telecommunication applications at 1.55 μm with a small strain, compared to conventional GaN/AlN QW structure.

Computing the writhe on lattices

International Nuclear Information System (INIS)

Laing, C; Sumners, D W

2006-01-01

Given a polygonal closed curve on a lattice or space group, we describe a method for computing the writhe of the curve as the average of weighted projected writhing numbers of the polygon in a few directions. These directions are determined by the lattice geometry, the weights are determined by areas of regions on the unit 2-sphere, and the regions are formed by the tangent indicatrix to the polygonal curve. We give a new formula for the writhe of polygons on the face centred cubic lattice and prove that the writhe of polygons on the body centred cubic lattice, the hexagonal simple lattice, and the diamond space group is always a rational number, and discuss applications to ring polymers

Tunable gaps and enhanced mobilities in strain-engineered silicane

International Nuclear Information System (INIS)

Restrepo, Oscar D.; Mishra, Rohan; Windl, Wolfgang; Goldberger, Joshua E.

2014-01-01

The recent demonstration of single-atom thick, sp 3 -hybridized group 14 analogues of graphene enables the creation of materials with electronic structures that are manipulated by the nature of the covalently bound substituents above and below the sheet. These analogues can be electronically derived from isolated (111) layers of the bulk diamond lattice. Here, we perform systematic Density Functional Theory calculations to understand how the band dispersions, effective masses, and band gaps change as the bulk silicon (111) layers are continuously separated from each other until they are electronically isolated, and then passivated with hydrogen. High-level calculations based on HSE06 hybrid functionals were performed on each endpoint to compare directly with experimental values. We find that the change in the electronic structure due to variations in the Si-H bond length, Si-Si-Si bond angle, and most significantly the Si-Si bond length can tune the nature of the band gap from indirect to direct with dramatic effects on the transport properties. First-principles calculations of the phonon-limited electron mobility predict a value of 464 cm 2 /Vs for relaxed indirect band gap Si-H monolayers at room temperature. However, for 1.6% tensile strain, the band gap becomes direct, which increases the mobility significantly (8 551 cm 2 /Vs at 4% tensile strain). In total, this analysis of Si-based monolayers suggests that strain can change the nature of the band gap from indirect to direct and increase the electron mobility more than 18-fold

Lattice defects in rutile, TiO2

International Nuclear Information System (INIS)

Nakagawa, M.; Itoh, H.; Nakanishi, S.; Kondo, K.; Okada, M.; Atobe, K.

1991-01-01

Rutile, TiO 2 , having a relatively high melting point exhibits strong optical absorption after neutron irradiation (8 x 10 16 n f /cm 2 ) at 15K. The band peak is located near 0.96 μ, having a FWHM of 0.87 eV (at liquid nitrogen temperature). After inverse recovery at 120K, lattice defects due probably to F centers are annealed out at about 220K. (author)

Estimation of Peaking Factor Uncertainty due to Manufacturing Tolerance using Statistical Sampling Method

Energy Technology Data Exchange (ETDEWEB)

Lee, Kyung Hoon; Park, Ho Jin; Lee, Chung Chan; Cho, Jin Young [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of)

2015-10-15

The purpose of this paper is to study the effect on output parameters in the lattice physics calculation due to the last input uncertainty such as manufacturing deviations from nominal value for material composition and geometric dimensions. In a nuclear design and analysis, the lattice physics calculations are usually employed to generate lattice parameters for the nodal core simulation and pin power reconstruction. These lattice parameters which consist of homogenized few-group cross-sections, assembly discontinuity factors, and form-functions can be affected by input uncertainties which arise from three different sources: 1) multi-group cross-section uncertainties, 2) the uncertainties associated with methods and modeling approximations utilized in lattice physics codes, and 3) fuel/assembly manufacturing uncertainties. In this paper, data provided by the light water reactor (LWR) uncertainty analysis in modeling (UAM) benchmark has been used as the manufacturing uncertainties. First, the effect of each input parameter has been investigated through sensitivity calculations at the fuel assembly level. Then, uncertainty in prediction of peaking factor due to the most sensitive input parameter has been estimated using the statistical sampling method, often called the brute force method. For our analysis, the two-dimensional transport lattice code DeCART2D and its ENDF/B-VII.1 based 47-group library were used to perform the lattice physics calculation. Sensitivity calculations have been performed in order to study the influence of manufacturing tolerances on the lattice parameters. The manufacturing tolerance that has the largest influence on the k-inf is the fuel density. The second most sensitive parameter is the outer clad diameter.

Hyper-lattice algebraic model for data warehousing

CERN Document Server

Sen, Soumya; Chaki, Nabendu

2016-01-01

This book presents Hyper-lattice, a new algebraic model for partially ordered sets, and an alternative to lattice. The authors analyze some of the shortcomings of conventional lattice structure and propose a novel algebraic structure in the form of Hyper-lattice to overcome problems with lattice. They establish how Hyper-lattice supports dynamic insertion of elements in a partial order set with a partial hierarchy between the set members. The authors present the characteristics and the different properties, showing how propositions and lemmas formalize Hyper-lattice as a new algebraic structure.

An overview of lattice QCD

International Nuclear Information System (INIS)

Woloshyn, R.M.

1988-03-01

The basic concepts of the Lagrangian formulation of lattice field theory are discussed. The Wilson and staggered schemes for dealing with fermions on the lattice are described. Some recent results for hadron masses and vector and axial vector current matrix elements in lattice QCD are reviewed. (Author) (118 refs., 16 figs.)

Critical thickness and strain relaxation in high-misfit heteroepitaxial systems: PbTe1-xSex on PbSe (001)

International Nuclear Information System (INIS)

Wiesauer, Karin; Springholz, G.

2004-01-01

Strain relaxation and misfit dislocation formation is investigated for the high-misfit PbTe 1-x Se x /PbSe (001) heteroepitaxial system in which the lattice mismatch varies from 0% to 5.5%. Because a two-dimensional (2D) layer growth prevails for all PbTe 1-x Se x ternary compositions, the lattice mismatch is relaxed purely by misfit dislocations. In addition, it is found that strain relaxation is not hindered by dislocation kinetics. Therefore, this material combination is an ideal model system for testing the equilibrium Frank-van der Merwe and Matthews-Blakeslee strain relaxation models. In our experiments, we find significantly lower values of the critical layer thickness as compared to the model predictions. This discrepancy is caused by the inappropriate description of the dislocation self-energies when the layer thickness becomes comparable to the dislocation core radius. To resolve this problem, a modified expression for the dislocation self-energy is proposed. The resulting theoretical critical thicknesses are in excellent agreement with the experimental data. In addition, a remarkable universal scaling behavior is found for the strain relaxation data. This underlines the breakdown of the current strain relaxation models

Hydrostatic-pressure and uniaxial-strain experiments for controlling the spin-Peierls transition

International Nuclear Information System (INIS)

Mito, Masaki; Deguchi, Hiroyuki; Fujita, Wataru; Kondo, Ryusuke; Kagoshima, Seiichi

2010-01-01

The spin-Peierls (SP) system is considered to be a quantum spin system strongly coupled with the lattice. We have succeeded in controlling SP transition by applying hydrostatic pressure and/or uniaxial strain. The observed phenomenon could be a typical example for understanding the SP transition based on the Hamiltonian. (author)

Hadron structure from lattice QCD

International Nuclear Information System (INIS)

Schaefer, Andreas

2008-01-01

Some elements and current developments of lattice QCD are reviewed, with special emphasis on hadron structure observables. In principle, high precision experimental and lattice data provide nowadays a very detailled picture of the internal structure of hadrons. However, to relate both, a very good controle of perturbative QCD is needed in many cases. Finally chiral perturbation theory is extremely helpful to boost the precision of lattice calculations. The mutual need and benefit of all four elements: experiment, lattice QCD, perturbative QCD and chiral perturbation theory is the main topic of this review

Lattice formulations of reggeon interactions

International Nuclear Information System (INIS)

Brower, R.C.; Ellis, J.; Savit, R.; Zinn-Justin, J.

1976-01-01

A class of lattice analogues to reggeon field theory is examined. First the transition from a continuum to a lattice field theory is discussed, emphasizing the necessity of a Wick rotation and the consideration of symmetry properties. Next the theory is transformed to a discrete system with two spins at each lattice site, and the problems of the triple-reggeon interaction and the reggeon energy gap are discussed. It is pointed out that transferring the theory from the continuum to a lattice necesarily introduces new relevant operators not normally present in reggeon field theory. (Auth.)

Effect of pressure and doping on lattice structure of zinc oxide

Energy Technology Data Exchange (ETDEWEB)

Zolfaghari, Mahmoud, E-mail: mzolfaghari@phys.usb.ac.ir

2017-01-15

The semiconductor ZnO belongs to the IIb-VI binary compound. It has a high exciton binding energy of 60 meV. The bonding in these materials is covalent with some ionic character. Induced changes on the physical properties of Mn doped ZnO samples due to different dopant concentrations and pressure were evaluated. The results obtained showed higher solubility limit for Mn doped ZnO due to pressure. The trend of XRD results for higher Mn concentration (9 at%) as pressure increases, was towards doping improvement. The XRD, SEM and UV–vis study of the samples also revealed that there were variations in the lattice parameters, nanoparticle size and bandgap energy of the doped and pressurized doped samples. Further, the directions of variation of bandgap energy values and calculated particle size, as well as SEM values of the doped samples due to pressure variation were found to be the same i.e. all of them together either increase or decrease as pressure varies. However, these variations were found to be opposite to that of lattice constants (all a and most c values) variation for both Mn dopant concentrations (3 at% and 9 at%). These physical variations of unpressurized doped samples can be attributed to the change in the polar bonding of the elemental constitutions in the lattice. While for the pressurized doped samples, the variations attributed to repulsion of lone pairs as well as change in the electronegativity of the system.

Ultrafast lattice dynamics in photoexcited nanostructures. Femtosecond X-ray diffraction with optimized evaluation schemes

International Nuclear Information System (INIS)

Schick, Daniel

2013-01-01

Within the course of this thesis, I have investigated the complex interplay between electron and lattice dynamics in nanostructures of perovskite oxides. Femtosecond hard X-ray pulses were utilized to probe the evolution of atomic rearrangement directly, which is driven by ultrafast optical excitation of electrons. The physics of complex materials with a large number of degrees of freedom can be interpreted once the exact fingerprint of ultrafast lattice dynamics in time-resolved X-ray diffraction experiments for a simple model system is well known. The motion of atoms in a crystal can be probed directly and in real-time by femtosecond pulses of hard X-ray radiation in a pump-probe scheme. In order to provide such ultrashort X-ray pulses, I have built up a laser-driven plasma X-ray source. The setup was extended by a stable goniometer, a two-dimensional X-ray detector and a cryogen-free cryostat. The data acquisition routines of the diffractometer for these ultrafast X-ray diffraction experiments were further improved in terms of signal-to-noise ratio and angular resolution. The implementation of a high-speed reciprocal-space mapping technique allowed for a two-dimensional structural analysis with femtosecond temporal resolution. I have studied the ultrafast lattice dynamics, namely the excitation and propagation of coherent phonons, in photoexcited thin films and superlattice structures of the metallic perovskite SrRuO 3 . Due to the quasi-instantaneous coupling of the lattice to the optically excited electrons in this material a spatially and temporally well-defined thermal stress profile is generated in SrRuO 3 . This enables understanding the effect of the resulting coherent lattice dynamics in time-resolved X-ray diffraction data in great detail, e.g. the appearance of a transient Bragg peak splitting in both thin films and superlattice structures of SrRuO 3 . In addition, a comprehensive simulation toolbox to calculate the ultrafast lattice dynamics and the

Scaling Laws for Dynamic Aperture due to Chromatic Sextupoles

CERN Document Server

Scandale, Walter

1997-01-01

Scaling laws for the dynamic aperture due to chromatic sextupoles are investigated. The problem is addressed in a simplified lattice model containing 4 N identical cells and one linear betatron phase shifter to break the overall cell-lattice symmetry. Two families of chromatic sextupoles are used to compensate the natural chromaticity. Analytical formulae for the dynamic apertur as a function of the number of cells and of the cell length are found and confirmed through computer tracking.

Irreversible stochastic processes on lattices

International Nuclear Information System (INIS)

Nord, R.S.

1986-01-01

Models for irreversible random or cooperative filling of lattices are required to describe many processes in chemistry and physics. Since the filling is assumed to be irreversible, even the stationary, saturation state is not in equilibrium. The kinetics and statistics of these processes are described by recasting the master equations in infinite hierarchical form. Solutions can be obtained by implementing various techniques: refinements in these solution techniques are presented. Programs considered include random dimer, trimer, and tetramer filling of 2D lattices, random dimer filling of a cubic lattice, competitive filling of two or more species, and the effect of a random distribution of inactive sites on the filling. Also considered is monomer filling of a linear lattice with nearest neighbor cooperative effects and solve for the exact cluster-size distribution for cluster sizes up to the asymptotic regime. Additionally, a technique is developed to directly determine the asymptotic properties of the cluster size distribution. Finally cluster growth is considered via irreversible aggregation involving random walkers. In particular, explicit results are provided for the large-lattice-size asymptotic behavior of trapping probabilities and average walk lengths for a single walker on a lattice with multiple traps. Procedures for exact calculation of these quantities on finite lattices are also developed

High Strain Rate and Shock-Induced Deformation in Metals

Science.gov (United States)

Ravelo, Ramon

2012-02-01

Large-scale non-equilibrium molecular Dynamics (MD) simulations are now commonly used to study material deformation at high strain rates (10^9-10^12 s-1). They can provide detailed information-- such as defect morphology, dislocation densities, and temperature and stress profiles, unavailable or hard to measure experimentally. Computational studies of shock-induced plasticity and melting in fcc and bcc single, mono-crystal metals, exhibit generic characteristics: high elastic limits, large directional anisotropies in the yield stress and pre-melting much below the equilibrium melt temperature for shock wave propagation along specific crystallographic directions. These generic features in the response of single crystals subjected to high strain rates of deformation can be explained from the changes in the energy landscape of the uniaxially compressed crystal lattice. For time scales relevant to dynamic shock loading, the directional-dependence of the yield strength in single crystals is shown to be due to the onset of instabilities in elastic-wave propagation velocities. The elastic-plastic transition threshold can accurately be predicted by a wave-propagation stability analysis. These strain-induced instabilities create incipient defect structures, which can be quite different from the ones, which characterize the long-time, asymptotic state of the compressed solid. With increase compression and strain rate, plastic deformation via extended defects gives way to amorphization associated with the loss in shear rigidity along specific deformation paths. The hot amorphous or (super-cooled liquid) metal re-crystallizes at rates, which depend on the temperature difference between the amorphous solid and the equilibrium melt line. This plastic-amorphous transition threshold can be computed from shear-waves stability analyses. Examples from selected fcc and bcc metals will be presented employing semi-empirical potentials of the embedded atom method (EAM) type as well as

Understanding Oxygen Vacancy Formation, Interaction, Transport, and Strain in SOFC Components via Combined Thermodynamics and First Principles Calculations

Science.gov (United States)

Das, Tridip

Understanding of the vacancy formation, interaction, increasing its concentration and diffusion, and controlling its chemical strain will advance the design of mixed ionic and electronic conductor (MIEC) materials via element doping and strain engineering. This is especially central to improve the performance of the solid oxide fuel cell (SOFC), an energy conversion device for sustainable future. The oxygen vacancy concentration grows exponentially with the temperature at dilute vacancy concentration but not at higher concentration, or even decreases due to oxygen vacancy interaction and vacancy ordered phase change. This limits the ionic conductivity. Using density functional theory (DFT), we provided fundamental understanding on how oxygen vacancy interaction originates in one of the typical MIEC, La1-xSrxFeO3-delta (LSF). The vacancy interaction is determined by the interplay of the charge state of multi-valence ion (Fe), aliovalent doping (La/Sr ratio), the crystal structure, and the oxygen vacancy concentration and/or nonstoichiometry (delta). It was found excess electrons left due to the formation of a neutral oxygen vacancy get distributed to Fe directly connected to the vacancy or to the second nearest neighboring Fe, based on crystal field splitting of Fe 3d orbital in different Fe-O polyhedral coordination. The progressively larger polaron size and anisotropic shape changes with increasing Sr-content resulted in increasing oxygen vacancy interactions, as indicated by an increase in the oxygen vacancy formation energy above a critical delta threshold. This was consistent with experimental results showing that Sr-rich LSF and highly oxygen deficient compositions are prone to oxygen-vacancy-ordering-induced phase transformations, while Sr-poor and oxygen-rich LSF compositions are not. Since oxygen vacancy induced phase transformations, cause a decrease in the mobile oxygen vacancy site fraction (X), both delta and X were predicted as a function of

Tensile Strain Effects on the Magneto-transport in Calcium Manganese Oxide Thin Films: Comparison with its Hole-doped Counterpart

Science.gov (United States)

Lawson, Bridget; Neubauer, Samuel; Chaudhry, Adeel; Hart, Cacie; Ferrone, Natalie; Houston, David; Yong, Grace; Kolagani, Rajeswari

Magnetoresistance properties of the epitaxial thin films of doped rare earth manganites are known to be influenced by the effect of bi-axial strain induced by lattice mismatch with the substrate. In hole-doped manganites, the effect of both compressive and tensile strain is qualitatively consistent with the expected changes in unit cell symmetry from cubic to tetragonal, leading to Jahn-Teller strain fields that affect the energy levels of Mn3 + energy levels. Recent work in our laboratory on CaMnO3 thin films has pointed out that tetragonal distortions introduced by tensile lattice mismatch strain may also have the effect of modulating the oxygen content of the films in agreement with theoretical models that propose such coupling between strain and oxygen content. Our research focuses on comparing the magneto-transport properties of hole-doped manganite LaCaMnO3 thin films with that of its electron doped counter parts, in an effort to delineate the effects of oxygen stoichiometry changes on magneto-transport from the effects of Jahn-Teller type strain. Towson University Office of Undergraduate Research, Fisher Endowment Grant and Undergraduate Research Grant from the Fisher College of Science and Mathematics, Seed Funding Grant from the School of Emerging technologies and the NSF Grant ECCS 112856.

Validation of WIMS-CANDU using Pin-Cell Lattices

International Nuclear Information System (INIS)

Kim, Won Young; Min, Byung Joo; Park, Joo Hwan

2006-01-01

The WIMS-CANDU is a lattice code which has a depletion capability for the analysis of reactor physics problems related to a design and safety. The WIMS-CANDU code has been developed from the WIMSD5B, a version of the WIMS code released from the OECD/NEA data bank in 1998. The lattice code POWDERPUFS-V (PPV) has been used for the physics design and analysis of a natural uranium fuel for the CANDU reactor. However since the application of PPV is limited to a fresh fuel due to its empirical correlations, the WIMS-AECL code has been developed by AECL to substitute the PPV. Also, the WIMS-CANDU code is being developed to perform the physics analysis of the present operating CANDU reactors as a replacement of PPV. As one of the developing work of WIMS-CANDU, the U 238 absorption cross-section in the nuclear data library of WIMS-CANDU was updated and WIMS-CANDU was validated using the benchmark problems for pin-cell lattices such as TRX-1, TRX-2, Bapl-1, Bapl-2 and Bapl-3. The results by the WIMS-CANDU and the WIMS-AECL were compared with the experimental data

Non-Abelian vortex lattices

Science.gov (United States)

Tallarita, Gianni; Peterson, Adam

2018-04-01

We perform a numerical study of the phase diagram of the model proposed in [M. Shifman, Phys. Rev. D 87, 025025 (2013)., 10.1103/PhysRevD.87.025025], which is a simple model containing non-Abelian vortices. As per the case of Abrikosov vortices, we map out a region of parameter space in which the system prefers the formation of vortices in ordered lattice structures. These are generalizations of Abrikosov vortex lattices with extra orientational moduli in the vortex cores. At sufficiently large lattice spacing the low energy theory is described by a sum of C P (1 ) theories, each located on a vortex site. As the lattice spacing becomes smaller, when the self-interaction of the orientational field becomes relevant, only an overall rotation in internal space survives.

Edge states in a ferromagnetic honeycomb lattice with armchair boundaries

Science.gov (United States)

Pantaleón, Pierre A.; Xian, Y.

2018-02-01

We investigate the properties of magnon edge states in a ferromagnetic honeycomb lattice with armchair boundaries. In contrast with fermionic graphene, we find novel edge states due to the missing bonds along the boundary sites. After introducing an external on-site potential at the outermost sites we find that the energy spectra of the edge states are tunable. Additionally, when a non-trivial gap is induced, we find that some of the edge states are topologically protected and also tunable. Our results may explain the origin of the novel edge states recently observed in photonic lattices. We also discuss the behavior of these edge states for further experimental confirmations.

Critical sizes of light-water moderated UO2 and PuO2-UO2 lattices

International Nuclear Information System (INIS)

Tsuruta, Harumichi; Kobayashi, Iwao; Suzuki, Takenori; Ohno, Akio; Murakami, Kiyonobu

1978-02-01

Experimental critical sizes are presented for a total of about 250 lattices with 2.6 w/o UO 2 and 3.0 w/o PuO 2 -natural UO 2 fuel rods. The moderator was H 2 O and water-to-fuel volume ratios in the lattice cells ranged from 1.50 to 3.00 in the UO 2 lattices and from 2.42 to 5.55 in the PuO 2 -UO 2 lattices. The critical sizes were determined with the number of the fuel rods and a water level which were required to make the lattice critical in the shape of a rectangular parallelepiped over the temperature range from room temperature to 80 0 C. Reactivity variations of the PuO 2 -UO 2 lattices due to decaying of 241 Pu to 241 Am were traced during 3 years. Some critical sizes of the UO 2 and PuO 2 -UO 2 lattices with a water gap and of the UO 2 lattices with liquid poison in the moderator are also reported. Some physics parameters, such as the temperature coefficient of reactivity, the water-level worth, the reflector saving, the ratio between a migration area and an infinite multiplication factor and the critical buckling, are shown in relation to the critical sizes of the unperturbed lattices without the water gap and liquid poison. (auth.)

Strain effect on the adsorption, diffusion, and molecular dissociation of hydrogen on Mg (0001) surface

Energy Technology Data Exchange (ETDEWEB)

Lei, Huaping; Wang, Caizhuang; Yao, Yongxin; Hupalo, Myron [Ames Laboratory, USDOE, Ames, Iowa 50011 (United States); Wang, Yangang [Ames Laboratory, USDOE, Ames, Iowa 50011 (United States); Supercomputing Center of Computer Network Information Center, CAS, Beijing 100190 (China); McDougall, Dan; Tringides, Michael; Ho, Kaiming [Ames Laboratory, USDOE, Ames, Iowa 50011 (United States); Department of Physics and Astronomy, Iowa State University, Ames, Iowa 50011 (United States)

2013-12-14

The adsorption, diffusion, and molecular dissociation of hydrogen on the biaxially strained Mg (0001) surface have been systematically investigated by the first principle calculations based on density functional theory. When the strain changes from the compressive to tensile state, the adsorption energy of H atom linearly increases while its diffusion barrier linearly decreases oppositely. The dissociation barrier of H{sub 2} molecule linearly reduces in the tensile strain region. Through the chemical bonding analysis including the charge density difference, the projected density of states and the Mulliken population, the mechanism of the strain effect on the adsorption of H atom and the dissociation of H{sub 2} molecule has been elucidated by an s-p charge transfer model. With the reduction of the orbital overlap between the surface Mg atoms upon the lattice expansion, the charge transfers from p to s states of Mg atoms, which enhances the hybridization of H s and Mg s orbitals. Therefore, the bonding interaction of H with Mg surface is strengthened and then the atomic diffusion and molecular dissociation barriers of hydrogen decrease accordingly. Our works will be helpful to understand and to estimate the influence of the lattice deformation on the performance of Mg-containing hydrogen storage materials.

EVALUATION OF DISTAL UPPER EXTREMITY (DUE MUSCULOSKELETAL DISORDERS BY STRAIN INDEX (SI IN AN IRONWORK INDUSTRY

Directory of Open Access Journals (Sweden)

Seyed-Ali Moussavi-Najarkola

2008-04-01

Full Text Available Background and aims:Work-related musculoskeletal disorders (WMSDS is one of the mostimportant problems in working populations of Iranian industries; so, in order to evaluate theintegrated roles and effects of various ergonomic risk factors inducing such disorders, the StrainIndex (SI methods was used.Methods: This was a cross-sectional study conducted on 448 male subjects including 63controls working in administrative jobs and 385 cases working in lathing, welding, melting andfoundry jobs using integrated procedure which includes observations, interview, NordicMusculoskeletal Questionnaire (NMQ methods and SI model. All workers were questioned.Data were analyzed using SPSS software v. 11 and Excel package.Results: The most prevalent MSDs in upper limbs were found in melting lathing, foundry andwelding respectively. There was a significant relationship between age and job groups (c2=7.33;df=16; p<0.001. One-way analysis of variance showed a significant differences among means ofcalculated Strain Indices of administrative (1.06, lathing (6.52, welding (3.68, melting (7.79and foundry (6.33 jobs (F=5.92; df=16; p=0.005. Also it was revealed that melting job wasattributed as "hazardous job" (4 risk level, lathing and foundry jobs were referred to "moderaterisk level" (3 risk level, welding job was allocated as "uncertain risk level" (2 risk level, andadministrative job was attributed as "safe risk level" (1 risk level. Moreover, there was asignificant relationship between DUE and job groups (c2=11.92; df=12; p=0.004.The paired ttestshowed significant difference with direct and relatively complete correlation between meansof Strain Indices in right (6.53 and left (4.29 hands (r=0.69; t=3.15; p<0.001.Conclusion: The Strain Index (SI model can be referred as an efficient and applicable methodfor the assessment of ergonomics risk factors inducing upper extremity musculoskeletal disorders(UEMSDs, classifying jobs, correcting and modifying work situations

Tunnelling effect enhanced by lattice screening as main cold fusion mechanism: An brief theoretical overview

International Nuclear Information System (INIS)

Frisone, F.

2007-01-01

In this paper are illustrated the main features of tunneling traveling between two deuterons within a lattice. Considering the screening effect due lattice electrons we compare the d-d fusion rate evaluated from different authors assuming different screening efficiency and different d-d potentials. Then, we propose a effective potential which describe very well the attractive contribute due to plasmon exchange between two deuterons and by means of it we will compute the d-d fusion rates for different energy values. Finally the good agreement between theoretical and experimental results proves the reality of cold fusion phenomena and the reliability of our model

Brittle superconducting magnets: an equivilent strain model

International Nuclear Information System (INIS)

Barzi, E.; Danuso, M.

2010-01-01

To exceed fields of 10 T in accelerator magnets, brittle superconductors like A15 Nb 3 Sn and Nb 3 Al or ceramic High Temperature Superconductors have to be used. For such brittle superconductors it is not their maximum tensile yield stress that limits their structural resistance as much as strain values that provoke deformations in their delicate lattice, which in turn affect their superconducting properties. Work on the sensitivity of Nb 3 Sn cables to strain has been conducted in a number of stress states, including uniaxial and multi-axial, producing usually different results. This has made the need of a constituent design criterion imperative for magnet builders. In conventional structural problems an equivalent stress model is typically used to verify mechanical soundness. In the superconducting community a simple scalar equivalent strain to be used in place of an equivalent stress would be an extremely useful tool. As is well known in fundamental mechanics, there is not one single way to reduce a multiaxial strain state as represented by a 2nd order tensor to a scalar. The conceptual experiment proposed here will help determine the best scalar representation to use in the identification of an equivalent strain model.

Lattice distortion and spontaneous {gamma}{sub 5g} ferro-quadrupole moment in phase IV of Ce{sub x}La{sub 1-x}B{sub 6}

Energy Technology Data Exchange (ETDEWEB)

Nemoto, Yuichi [Graduate School of Science and Technology, Niigata University, Niigata 950-2181 (Japan)]. E-mail: nemoto@phys.sc.niigata-u.ac.jp; Akatsu, Mitsuhiro [Graduate School of Science and Technology, Niigata University, Niigata 950-2181 (Japan); Goto, Terutaka [Graduate School of Science and Technology, Niigata University, Niigata 950-2181 (Japan); Suzuki, Osamu [National Institute for Materials Science, Tukuba 305-0003 (Japan); Nakamura, Shintaro [Center for Low Temperature Science, Tohoku University, Sendai 980-8577 (Japan); Kunii, Satoru [Department of Physics, Graduate School of Science, Tohoku University, Sendai 980-8578 (Japan)

2005-04-30

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

Characterisation of the residual strain profiles in aluminium titanate/alumina functionally graded materials using x-ray diffraction data

International Nuclear Information System (INIS)

Skala, R.D.

2002-01-01

Full text: In previous studies of the aluminium titanate/alumina functionally graded system, it was proposed that the mechanisms responsible for the observed flaw tolerance and quasi-ductile behaviour of the composite system were due to the generation of residual strain fields in the bulk of the composite. These residual strain fields are induced by a combination of the thermal expansion coefficient mismatch between the alumina and aluminium titanate phases and also the high degree of thermal anisotropy exhibited by the aluminium titanate phase. In the current study, both the macro-strain (linear) and micro-strain (non-linear) were extracted from x-ray diffraction data. The macro-strains were extracted from variations in the lattice parameters, whilst the micro-strains were extracted from line broadening of the diffraction peaks. Strain profiles were obtained by carefully removing layers of the composite till the centre region was reached. Analysis of the data showed that the macro-strain in the alumina phase was compressive and decreased from -0.149 ± 0.012 % at the surface to -0.086 ± 0.006 % at the centre of the composite system. The macro-strain in the aluminium titanate phase was observed to remain constant at a value of 0.181 ± 0.013 % and be tensile in nature. The micro-strains within the composite system were also seen to exhibit a similar profile with the micro-strain in the alumina phase ranging from 0.065 ± 0.003 % to 0.008 ± 0.005 % from the surface to the centre respectively and the aluminium titanate phase displaying a mean micro-strain value of 0.117 ± 0.033 %. These results were also seen to correlate well with the compositional profiles observed in previous studies of the system. Copyright (2002) Australian X-ray Analytical Association Inc

Superspace approach to lattice supersymmetry

International Nuclear Information System (INIS)

Kostelecky, V.A.; Rabin, J.M.

1984-01-01

We construct a cubic lattice of discrete points in superspace, as well as a discrete subgroup of the supersymmetry group which maps this ''superlattice'' into itself. We discuss the connection between this structure and previous versions of lattice supersymmetry. Our approach clarifies the mathematical problems of formulating supersymmetric lattice field theories and suggests new methods for attacking them

Dynamical lattice theory

International Nuclear Information System (INIS)

Chodos, A.

1978-01-01

A version of lattice gauge theory is presented in which the shape of the lattice is not assumed at the outset but is a consequence of the dynamics. Other related features which are not specified a priori include the internal and space-time symmetry groups and the dimensionality of space-time. The theory possesses a much larger invariance group than the usual gauge group on a lattice, and has associated with it an integer k 0 analogous to the topological quantum numer of quantum chromodynamics. Families of semiclassical solutions are found which are labeled by k 0 and a second integer x, but the analysis is not carried far enough to determine which space-time and internal symmetry groups characterize the lowest-lying states of the theory

The New Phases due to Symmetry Protected Piecewise Berry Phases; Enhanced Pumping and Non-reciprocity in Trimer Lattices.

Science.gov (United States)

Liu, Xuele; Agarwal, G S

2017-03-24

Finding new phase of matter is a fundamental task in physics. Generally, various phases or states of matter (for instance solid/liquid/gas phases) have different symmetries, the phase transitions among them can be explained by Landau's symmetry breaking theory. The topological phases discovered in recent years show that different phases may have the same symmetry. The different topological phases are characterized by different integer values of the Berry phases. By studying one dimensional (1D) trimer lattices we report new phases beyond topological phases. The new phases that we find are characterized by piecewise continuous Berry phases with the discontinuity occurring at the transition point. With time-dependent changes in trimer lattices, we can generate two dimensional (2D) phases, which are characterized by the Berry phase of half period. This half-period Berry phase changes smoothly within one state of the system while changes discontinuously at the transition point. We further demonstrate the existence of adiabatic pumping for each phase and gain assisted enhanced pumping. The non reciprocity of the pumping process makes the system a good optical diode.

A Worm Algorithm for the Lattice CP(N-1) Model arXiv

CERN Document Server

Rindlisbacher, Tobias

The CP(N-1) model in 2D is an interesting toy model for 4D QCD as it possesses confinement, asymptotic freedom and a non-trivial vacuum structure. Due to the lower dimensionality and the absence of fermions, the computational cost for simulating 2D CP(N-1) on the lattice is much lower than the one for simulating 4D QCD. However to our knowledge, no efficient algorithm for simulating the lattice CP(N-1) model has been tested so far, which also works at finite density. To this end we propose and test a new type of worm algorithm which is appropriate to simulate the lattice CP(N-1) model in a dual, flux-variables based representation, in which the introduction of a chemical potential does not give rise to any complications.

Micropatterning of bacteria on two-dimensional lattice protein surface observed by atomic force microscopy

International Nuclear Information System (INIS)

Oh, Y.J.; Jo, W.; Lim, J.; Park, S.; Kim, Y.S.; Kim, Y.

2008-01-01

In this study, we characterized the two-dimensional lattice of bovine serum albumin (BSA) as a chemical and physical barrier against bacterial adhesion, using fluorescence microscopy and atomic force microscopy (AFM). The lattice of BSA on glass surface was fabricated by micro-contact printing (μCP), which is a useful way to pattern a wide range of molecules into microscale features on different types of substrates. The contact-mode AFM measurements showed that the average height of the printed BSA monolayer was 5-6 nm. Escherichia coli adhered rapidly on bare glass slide, while the bacterial adhesion was minimized on the lattices in the range of 1-3 μm 2 . Especially, the bacterial adhesion was completely inhibited on a 1 μm 2 lattice. The results suggest that the anti-adhesion effects are due by the steric repulsion forces exerted by BSA

Computing nucleon EDM on a lattice

Science.gov (United States)

Abramczyk, Michael; Aoki, Sinya; Blum, Tom; Izubuchi, Taku; Ohki, Hiroshi; Syritsyn, Sergey

2018-03-01

I will discuss briefly recent changes in the methodology of computing the baryon EDM on a lattice. The associated correction substantially reduces presently existing lattice values for the proton and neutron theta-induced EDMs, so that even the most precise previous lattice results become consistent with zero. On one hand, this change removes previous disagreements between these lattice results and the phenomenological estimates of the nucleon EDM. On the other hand, the nucleon EDM becomes much harder to compute on a lattice. In addition, I will review the progress in computing quark chromo-EDM-induced nucleon EDM using chiral quark action.

Computing nucleon EDM on a lattice

Energy Technology Data Exchange (ETDEWEB)

Abramczyk, Michael; Izubuchi, Taku

2017-06-18

I will discuss briefly recent changes in the methodology of computing the baryon EDM on a lattice. The associated correction substantially reduces presently existing lattice values for the proton and neutron theta-induced EDMs, so that even the most precise previous lattice results become consistent with zero. On one hand, this change removes previous disagreements between these lattice results and the phenomenological estimates of the nucleon EDM. On the other hand, the nucleon EDM becomes much harder to compute on a lattice. In addition, I will review the progress in computing quark chromo-EDM-induced nucleon EDM using chiral quark action.

Cold collisions in dissipative optical lattices

International Nuclear Information System (INIS)

Piilo, J; Suominen, K-A

2005-01-01

The invention of laser cooling methods for neutral atoms allows optical and magnetic trapping of cold atomic clouds in the temperature regime below 1 mK. In the past, light-assisted cold collisions between laser cooled atoms have been widely studied in magneto-optical atom traps (MOTs). We describe here theoretical studies of dynamical interactions, specifically cold collisions, between atoms trapped in near-resonant, dissipative optical lattices. The extension of collision studies to the regime of optical lattices introduces several complicating factors. For the lattice studies, one has to account for the internal substates of atoms, position-dependent matter-light coupling, and position-dependent couplings between the atoms, in addition to the spontaneous decay of electronically excited atomic states. The developed one-dimensional quantum-mechanical model combines atomic cooling and collision dynamics in a single framework. The model is based on Monte Carlo wavefunction simulations and is applied when the lattice-creating lasers have frequencies both below (red-detuned lattice) and above (blue-detuned lattice) the atomic resonance frequency. It turns out that the radiative heating mechanism affects the dynamics of atomic cloud in a red-detuned lattice in a way that is not directly expected from the MOT studies. The optical lattice and position-dependent light-matter coupling introduces selectivity of collision partners. The atoms which are most mobile and energetic are strongly favoured to participate in collisions, and are more often ejected from the lattice, than the slow ones in the laser parameter region selected for study. Consequently, the atoms remaining in the lattice have a smaller average kinetic energy per atom than in the case of non-interacting atoms. For blue-detuned lattices, we study how optical shielding emerges as a natural part of the lattice and look for ways to optimize the effect. We find that the cooling and shielding dynamics do not mix

Dislocation, crystallite size distribution and lattice strain of magnesium oxide nanoparticles

Science.gov (United States)

Sutapa, I. W.; Wahid Wahab, Abdul; Taba, P.; Nafie, N. L.

2018-03-01

The oxide of magnesium nanoparticles synthesized using sol-gel method and analysis of the structural properties was conducted. The functional groups of nanoparticles has been analysed by Fourier Transform Infrared Spectroscopy (FT-IR). Dislocations, average size of crystal, strain, stress, the energy density of crystal, crystallite size distribution and morphologies of the crystals were determined based on X-ray diffraction profile analysis. The morphological of the crystal was analysed based on the image resulted from SEM analysis. The crystallite size distribution was calculated with the contention that the particle size has a normal logarithmic form. The most orientations of crystal were determined based on the textural crystal from diffraction data of X-ray diffraction profile analysis. FT-IR results showed the stretching vibration mode of the Mg-O-Mg in the range of 400.11-525 cm-1 as a broad band. The average size crystal of nanoparticles resulted is 9.21 mm with dislocation value of crystal is 0.012 nm-2. The strains, stress, the energy density of crystal are 1.5 x 10-4 37.31 MPa; 0.72 MPa respectively. The highest texture coefficient value of the crystal is 0.98. This result is supported by morphological analysis using SEM which shows most of the regular cubic-shaped crystals. The synthesis method is suitable for simple and cost-effective synthesis model of MgO nanoparticles.

Vortex lattice ordering in the flux flow state of Nb thin films

International Nuclear Information System (INIS)

Grimaldi, Gaia; Leo, Antonio; Nigro, Angela; Pace, Sandro

2010-01-01

We measure current-voltage characteristics at high driving currents for different magnetic fields and temperatures in Nb thin films of rather strong pinning. In a definite range of the B-T phase diagram we find that a current induced transition occurs in the flux flow motion of the vortex lattice, namely a dynamic ordering (DO). Contrary to the case of weaker pinning materials, DO is observed only at low fields, due to the stronger intrinsic disorder that can deform plastically the moving vortex lattice even for small applied fields.

Topological magnon bands in ferromagnetic star lattice

International Nuclear Information System (INIS)

Owerre, S A

2017-01-01

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

Topological magnon bands in ferromagnetic star lattice.

Science.gov (United States)

Owerre, S A

2017-05-10

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

Round atrophic holes in lattice degeneration--an important cause of phakic retinal detachment.

Science.gov (United States)

Tillery, W V; Lucier, A C

1976-01-01

Round atrophic holes in lattice degeneration are an important cause of phakic retinal detachment. Detachments due solely to round holes in lattice accounted for almost 2.8% of all retinal detachments treated at Wills Eye Hospital from January 1970 to August 1973. These detachments had the following important characteristics: 1. One of the patients were under the age of 30 years. 2. Over 75% of the patients had refractive errors more myopic than -3 D spherical equivalent. 3. Inferior detachments were slightly more common than superior detachments. When located inferiorly, there was a tendency for slow progression as indicated by the frequent presence of pigmented demarcation lines. 4. Surgical repair with standard scleral buckling techniques was successful in 98% of these detachments. Young, moderate to highly myopic patients with round holes in areas of lattice degeneration seem to have a greater risk of developing this type of detachment. Patients with the triad of youth, myopia, and round holes in lattice degeneration deserve close observation.

Influence of blocking effect and energetic disorder on diffusion in one-dimensional lattice

International Nuclear Information System (INIS)

Mai Thi Lan; Nguyen Van Hong; Nguyen Thu Nhan; Hoang Van Hue

2014-01-01

The diffusion in one-dimensional disordered lattice with Gaussian distribution of site and transition energies has been studied by mean of kinetic Monte-Carlo simulation. We focus on investigating the influence of energetic disorders and diffusive particle density on diffusivity. In single-particle case, we used both analytical method and kinetic Monte-Carlo simulation to calculate the quantities that relate to diffusive behavior in disordered systems such as the mean time between two consecutive jumps, correlation factor and diffusion coefficient. The calculation shows a good agreement between analytical and simulation results for all disordered lattice types. In many - particle case, the blocking effect results in decreasing correlation factor F and average time τ jump between two consecutive jumps. With increasing the number of particles, the diffusion coefficient D M decreases for site-energy and transition-energy disordered lattices due to the F-effect affect affects stronger than τ-effect. Furthermore, the blocking effect almost is temperature independent for both lattices. (author)

Understanding lattice defects to influence ferromagnetic order of ZnO nanoparticles by Ni, Cu, Ce ions

Energy Technology Data Exchange (ETDEWEB)

Verma, Kuldeep Chand, E-mail: dkuldeep.physics@gmail.com [Department of Physics, Panjab University, Chandigarh 160014 (India); Kotnala, R.K., E-mail: rkkotnala@gmail.com [CSIR-National Physical Laboratory, New Delhi 110012 (India)

2017-02-15

Future spintronics technologies based on diluted magnetic semiconductors (DMS) will rely heavily on a sound understanding of the microscopic origins of ferromagnetism in such materials. It remains unclear, however, whether the ferromagnetism in DMS is intrinsic - a precondition for spintronics - or due to dopant clustering. For this, we include a simultaneous doping from transition metal (Ni, Cu) and rare earth (Ce) ions in ZnO nanoparticles that increase the antiferromagnetic ordering to achieve high-T{sub c} ferromagnetism. Rietveld refinement of XRD patterns indicate that the dopant ions in ZnO had a wurtzite structure and the dopants, Ni{sup 2+}, Cu{sup 2+}, Ce{sup 3+} ions, are highly influenced the lattice constants to induce lattice defects. The Ni, Cu, Ce ions in ZnO have nanoparticles formation than nanorods was observed in pure sample. FTIR involve some organic groups to induce lattice defects and the metal-oxygen bonding of Zn, Ni, Cu, Ce and O atoms to confirm wurtzite structure. Raman analysis evaluates the crystalline quality, structural disorder and defects in ZnO lattice with doping. Photoluminescence spectra have strong near-band-edge emission and visible emission bands responsible for defects due to oxygen vacancies. The energy band gap is calculated using Tauc relation. Room temperature ferromagnetism has been described due to bound magnetic polarons formation with Ni{sup 2+}, Cu{sup 2+}, Ce{sup 3+} ions in ZnO via oxygen vacancies. The zero field and field cooling SQUID measurement confirm the strength of antiferromagnetism in ZnO. The field cooling magnetization is studied by Curie-Weiss law that include antiferromagnetic interactions up to low temperature. The XPS spectra have involve +3/+4 oxidation states of Ce ions to influence the observed ferromagnetism. - Graphical abstract: The lattice defects/vacancies attributed by Ni and Ce ions in the wurtzite ZnO structure are responsible in high T{sub c} -ferromagnetism due to long-range magnetic

Effects of gauge volume on pseudo-strain induced in strain measurement using time-of-flight neutron diffraction

International Nuclear Information System (INIS)

Suzuki, Hiroshi; Harjo, Stefanus; Abe, Jun; Xu, Pingguang; Aizawa, Kazuya; Akita, Koichi

2013-01-01

Spurious or pseudo-strains observed in time-of-flight (TOF) neutron diffraction due to neutron attenuation, surface-effects and a strain distribution within the gauge volume were investigated. Experiments were carried out on annealed and bent ferritic steel bars to test these effects. The most representative position in the gauge volume corresponds to the neutron-weighted center of gravity (ncog), which takes into account variations in intensity within the gauge volume due to neutron attenuation and/or absence of material in the gauge volume. The average strain in the gauge volume was observed to be weighted towards the ncog position but following an increase in the size of the gauge volume the weighted average strain was changed because of the change in the ncog position when a strain gradient appeared within the gauge volume. On the other hand, typical pseudo-strains, which are well known, did appear in through-surface strain measurements when the gauge volume was incompletely filled by the sample. Tensile pseudo-strains due to the surface-effect increased near the sample surface and exhibited a similar trend regardless of the size of the gauge volume, while the pseudo-strains increased faster for the smaller gauge volume. Furthermore, a pseudo-strain due to a change in the ncog position was observed even when the gauge volume was perfectly filled in the sample, and it increased with an increase in the size of the gauge volume. These pseudo-strains measured were much larger than those simulated by the conventional modeling, whereas they were simulated by taking into account an incident neutron beam divergence additionally in the model. Therefore, the incident divergence of the incident neutron beam must be carefully designed to avoid pseudo-strains in time-of-flight neutron diffractometry

Enhanced photovoltaic currents in strained Fe-doped LiNbO{sub 3} films

Energy Technology Data Exchange (ETDEWEB)

Inoue, Ryotaro [Division of Physics, Institute of Liberal Education, School of Medicine, Nihon University, 31-10, Ooyaguchi-kamicho, Itabashi-ku, Tokyo 173-8601 (Japan); Takahashi, Shusuke; Kitanaka, Yuuki; Oguchi, Takeshi; Noguchi, Yuji; Miyayama, Masaru [Department of Applied Chemistry, School of Engineering, The University of Tokyo, 7-3-1, Hongo, Bunkyo-ku, Tokyo 113-8654 (Japan)

2015-12-15

We investigate the impact of strain on photovoltaic current (J{sub z}) characteristics for iron-doped LiNbO{sub 3} (Fe-LN) under visible light illumination by thin-film experiments. The J{sub z} values are demonstrated to be dramatically enhanced for the film with a tensile strain along the P{sub s} direction, which is over 500 times as large as that of the bulk (strain-free) Fe-LN crystals. Density functional theory (DFT) calculations show that the tensile strain increases an off-center displacement of Fe{sup 2+} that is opposite to the P{sub s} direction. Our experimental and DFT study demonstrates that the control of the lattice strain is effective in enhancing the photovoltaic effect in the Fe-LN system. (copyright 2015 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

Introduction to lattice gauge theories

International Nuclear Information System (INIS)

La Cock, P.

1988-03-01

A general introduction to Lattice Gauge Theory (LGT) is given. The theory is discussed from first principles to facilitate an understanding of the techniques used in LGT. These include lattice formalism, gauge invariance, fermions on the lattice, group theory and integration, strong coupling methods and mean field techniques. A review of quantum chromodynamics on the lattice at finite temperature and density is also given. Monte Carlo results and analytical methods are discussed. An attempt has been made to include most relevant data up to the end of 1987, and to update some earlier reviews existing on the subject. 224 refs., 33 figs., 14 tabs

A 3D Lattice Modelling Study of Drying Shrinkage Damage in Concrete Repair Systems

Directory of Open Access Journals (Sweden)

Mladena Luković

2016-07-01

Full Text Available Differential shrinkage between repair material and concrete substrate is considered to be the main cause of premature failure of repair systems. The magnitude of induced stresses depends on many factors, for example the degree of restraint, moisture gradients caused by curing and drying conditions, type of repair material, etc. Numerical simulations combined with experimental observations can be of great use when determining the influence of these parameters on the performance of repair systems. In this work, a lattice type model was used to simulate first the moisture transport inside a repair system and then the resulting damage as a function of time. 3D simulations were performed, and damage patterns were qualitatively verified with experimental results and cracking tendencies in different brittle and ductile materials. The influence of substrate surface preparation, bond strength between the two materials, and thickness of the repair material were investigated. Benefits of using a specially tailored fibre reinforced material, namely strain hardening cementitious composite (SHCC, for controlling the damage development due to drying shrinkage in concrete repairs was also examined.

Angles in hyperbolic lattices

DEFF Research Database (Denmark)

Risager, Morten S.; Södergren, Carl Anders

2017-01-01

It is well known that the angles in a lattice acting on hyperbolic n -space become equidistributed. In this paper we determine a formula for the pair correlation density for angles in such hyperbolic lattices. Using this formula we determine, among other things, the asymptotic behavior of the den......It is well known that the angles in a lattice acting on hyperbolic n -space become equidistributed. In this paper we determine a formula for the pair correlation density for angles in such hyperbolic lattices. Using this formula we determine, among other things, the asymptotic behavior...... of the density function in both the small and large variable limits. This extends earlier results by Boca, Pasol, Popa and Zaharescu and Kelmer and Kontorovich in dimension 2 to general dimension n . Our proofs use the decay of matrix coefficients together with a number of careful estimates, and lead...

Lattice Location of Transition Metals in Semiconductors

CERN Multimedia

2002-01-01

%IS366 %title\\\\ \\\\Transition metals (TMs) in semiconductors have been the subject of considerable research for nearly 40 years. This is due both to their role as important model impurities for deep centers in semiconductors, and to their technological impact as widespread contaminants in Si processing, where the miniaturization of devices requires to keep their sheet concentration below 10$^{10}$ cm$^{-2}$. As a consequence of the low TM solubility, conventional ion beam methods for direct lattice location have failed completely in identifying the lattice sites of isolated transition metals. Although electron paramagnetic resonance (EPR) has yielded valuable information on a variety of TM centers, it has been unable to detect certain defects considered by theory, e.g., isolated interstitial or substitutional Cu in Si. The proposed identity of other EPR centers such as substitutional Fe in Si, still needs confirmation by additional experimental methods. As a consequence, the knowledge on the structural propert...

Working Group Report: Lattice Field Theory

Energy Technology Data Exchange (ETDEWEB)

Blum, T.; et al.,

2013-10-22

This is the report of the Computing Frontier working group on Lattice Field Theory prepared for the proceedings of the 2013 Community Summer Study ("Snowmass"). We present the future computing needs and plans of the U.S. lattice gauge theory community and argue that continued support of the U.S. (and worldwide) lattice-QCD effort is essential to fully capitalize on the enormous investment in the high-energy physics experimental program. We first summarize the dramatic progress of numerical lattice-QCD simulations in the past decade, with some emphasis on calculations carried out under the auspices of the U.S. Lattice-QCD Collaboration, and describe a broad program of lattice-QCD calculations that will be relevant for future experiments at the intensity and energy frontiers. We then present details of the computational hardware and software resources needed to undertake these calculations.